EB043P Recycling Concrete Pavements · ENGINEERING BULLETIN Recycling Concrete Pavements ... ACI...

AMERICAN CONCRETEPAVEMENT ASSOCIATION

RecyclingConcrete Pavements

ENGINEERING BULLETIN

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This publication is intended SOLELY for use by PROFESSIONAL PERSONNEL who are competent to evaluate the significance and limitations of the information provided herein, and who will accept total responsibility for the application of this information. The American Concrete Pavement Asso-ciation DISCLAIMS any and all RESPONSIBILITY and LIABILITY for the accuracy of and the application of the information contained in this publication to the full extent permitted by law.

American Concrete Pavement Association5420 Old Orchard Rd., Suite A100Skokie, IL 60077-1059www.pavement.com

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Recycling ConcretePavements

ACPA is the premier national association representing concretepavement contractors, cement companies, equipment and materials manufacturers and suppliers. We are organized toaddress common needs, solve other problems, and accomplishgoals related to research, promotion, and advancing best practices for design and construction of concrete pavements.

American Concrete Pavement Association5420 Old Orchard Rd., Suite A100Skokie, IL 60077-1059(847) 966-ACPAwww.pavement.com

Recycling Concrete Pavements

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Keywords: AASHTO, ASTM, aggregate, alkali-aggregate reactivity (AAR), alkali-carbonate reactivity (ACR), alkali-silica reactivity(ASR), asphalt-treated subbase (ATB), base, beneficiation, carbonation, cement-treated subbase (CTB), cement-stabilized, coarseaggregate, cone crusher, crushed, daylighted, dense-graded, drainable, econocrete, edge drainage, fine aggregate, free-draining,gap-graded, geosynthetic, gradation, grading, granular, gravel, greenhouse gas, horizontal shaft impact crusher, impact crusher, jawcrusher, lean concrete subbase (LCB), materials-related, natural, open-graded, permeable, proportioning, recycled concrete aggre-gate (RCA), recycling, sieve, stabilized, subbase, sulfate resistance, sustainable, sustainability, unstabilized, vertical shaft impactcrusher, virgin aggregate, well-graded, workability, yield.

Abstract: This engineering bulletin provides background information on recycling concrete pavements into recycled concrete aggre-gate (RCA) for use in bases, subbases, new concrete mixtures, granular fill, etc. It details the economic and environmental (sustain-able) reasons to recycle concrete pavements, the methods and steps of producing RCA, the properties and characteristics of RCA,the various uses of RCA, the properties of concrete containing RCA, and the performance of concrete pavements constructed usingRCA. Recommendations and guidelines for using RCA in various applications also are provided.

EB043P

© 2009 American Concrete Pavement Association

All rights reserved. No part of this book may be reproduced in any form without permission inwriting from the publisher, except by a reviewerwho wishes to quote brief passages in a reviewwritten for inclusion in a magazine or newspaper.

ISBN 978-0-9800251-1-8

This publication is intended SOLELY for use by PROFES-SIONAL PERSONNEL who are competent to evaluate thesignificance and limitations of the information providedherein, and who will accept total responsibility for the appli-cation of this information. The American Concrete PavementAssociation DISCLAIMS any and all RESPONSIBILITY andLIABILITY for the accuracy of and the application of theinformation contained in this publication to the full extent permitted by law.

AAR alkali-aggregate reactivity

AASHTO American Association of State Highway andTransportation Officials

ACI American Concrete Institute

ACPA American Concrete Pavement Association

ACR alkali-carbonate reactivity

ASR alkali-silica reactivity

ASTM American Society for Testing and Materials

ATB asphalt-treated subbase

AVA air void analyzer

Ca(OH)2 calcium hydroxide

CO2 carbon dioxide

CRCP continuously reinforced concrete pavement

CTB cement-treated subbase

CTE coefficient of thermal expansion and contraction

DOT Department of Transportation

EPA Environmental Protection Agency

FHWA Federal Highway Administration

GHG greenhouse gas

JPCP jointed plain concrete pavement

JRCP jointed reinforced concrete pavement

LCB lean concrete subbase

NaCl sodium chloride (e.g., salt)

RCA recycled concrete aggregate

w/cm water-cementitious materials ratio

Acronyms Commonly Used in this Bulletin:

iii

Executive Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix

Executive Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi

Chapter 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

What is Concrete Recycling? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Why Concrete Pavement Recycling? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Economics of Concrete Pavement Recycling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Sustainability Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Conservation of Virgin Aggregate Resources. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Landfill Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Energy Savings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Reduced Emission of Greenhouse Gasses (GHGs) and Other Pollutants . . . . . . . . . . . . . 3

Carbon Sequestration Through RCA Carbonation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Pavement Performance Improvements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Foundation Stability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Concrete Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Recycled Concrete Pavements: A Proven Technology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Chapter 2. Production of Recycled Concrete Aggregate (RCA) . . . . . . . . . . . . . . . . . . 7

Evaluation of Source Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Pavement Preparation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Pavement Breaking and Removal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Removal of Embedded Steel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Crushing and Sizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Beneficiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Stockpiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

In-Place Concrete Recycling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Table of Contents

Recycling of Returned Ready Mixed Concrete. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Chapter 3. Properties and Characteristics of RCA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Physical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Particle Composition, Shape and Texture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Gradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Absorption Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Specific Gravity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Mechanical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Los Angeles Abrasion Mass Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Freeze-Thaw Durability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Chemical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Alkali-Silica Reactivity (ASR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Sulfate Soundness Mass Loss. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Chloride Content. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Precipitate Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Concerns with Surface Dust and Contaminants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Chapter 4. Uses of RCA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Unstabilized (Granular) Subbase and Backfill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Unstabilized Dense-graded Subbase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Unstabilized Free-draining Subbase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Cement-Stabilized Subbase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Concrete Mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Asphalt Pavement and Asphalt-Stabilized Subbase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Other Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Granular Fill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Erosion Control (Rip-rap) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Innovative Applications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Chapter 5. Properties of Concrete Containing RCA . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Properties of Fresh (Plastic) RCA Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

iv


Workability, Finishability and Water Bleeding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

Water Demand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Air Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Physical and Mechanical Properties of Hardened RCA Concrete . . . . . . . . . . . . . . . . . . . . . . . . 29

Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Modulus of Elasticity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Coefficient of Thermal Expansion and Contraction (CTE). . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Drying Shrinkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Creep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Permeability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Specific Gravity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Durability. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Freeze-Thaw Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Alkali-Silica Reactivity (ASR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Carbonation and Corrosion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Chapter 6. Performance of Concrete Pavements Constructed Using RCA . . . . . . . 33

Select Case Studies of Pavements with RCA Concrete Mixtures . . . . . . . . . . . . . . . . . . . . . . . . 33

I-80 near Pine Bluff, Wyoming – Recycling an ASR-Damaged Pavement . . . . . . . . . . . . . . . 34

U.S. 59 near Worthington, Minnesota – Recycling a D-cracked Pavement . . . . . . . . . . . . . . 36

I-94 near Paw Paw, Michigan – Learning from Failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

I-10 near Houston, Texas – Using 100 Percent RCA in Concrete . . . . . . . . . . . . . . . . . . . . . 38

Performance of Concrete Pavement Structures with RCA in

Subbase Layers and Fill Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Urban Recycling: Eden’s Expressway, Chicago, Illinois . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Chapter 7. Recommendations for Using Recycled Concrete . . . . . . . . . . . . . . . . . . . . 41

RCA Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Source Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Production Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Stockpiling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

v

Use in Pavement Subbase Layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Quality Requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Gradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Structural Design Considerations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Preventing Clogging of Edge Drainage Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Environmental Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Construction Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Use of RCA in Concrete Mixtures for Concrete Pavement Structures . . . . . . . . . . . . . . . . . . . . . 44

Quality Requirements and Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Materials-Related Distress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Contaminants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Gradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Mixture Proportioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Pavement Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Pavement Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Preparing the Foundation and Subbase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Concrete Production and Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Paving Operations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Ride Quality. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Two-Course Pavement Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Chapter 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Appendix A. Guidelines for Removing and Crushing Existing Concrete Pavement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Processing Salvaged Concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Quality Control (QC). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Measurement and Payment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

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Appendix B. Guidelines for Using RCA inUnstabilized (Granular) Subbases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Use of RCA in Unstabilized (Granular) Subbases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Ordering Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Grading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Physical Properties. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Deleterious Substances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59


Appendix C. Guidelines for Using RCA inConcrete Paving Mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

Ordering Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

Grading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

Physical Properties. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

Deleterious Substances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63


Appendix D. AASHTO Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

Appendix E. ASTM Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

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Executive Summary

The cost of virgin aggregate (e.g., aggregate minedfrom natural sources, such as crushed stone, naturalsand, crushed gravel, etc.) is increasing rapidly asavailable sources are depleted while policies andregulations restrict access to new sources. Concretepavement recycling is a proven technology thatoffers an alternative aggregate resource that is botheconomical and sustainable.

Concrete pavement recycling is a relatively simpleprocess that involves breaking, removing and crush -ing hardened concrete from an acceptable source toproduce recycled concrete aggregate (RCA), a gran -ular material that can be produced for any applicationfor which virgin aggregate might be used. Concretepavements are 100 percent recyclable (ACPA 2006).

Concrete recycling has been used extensively inEurope since the 1940’s and in the U.S. since the1970’s (NHI 1998). Concrete recycling for pavingapplications is now performed in at least 41 states(FHWA 2004). Production of RCA in the U.S. cur-rently averages about 100 million tons (91 millionmetric tons) per year (USGS 2000). The primaryapplication of RCA has been subbase materials, butit also has been used in concrete and asphalt con-crete paving layers, high-value rip-rap, general filland embankment, and other applications.

One major incentive for concrete pavement recyclingis economics. Aggregate costs (for fill, foundationand surface layers) constitute one of the greatestcosts of highway construction, comprising between20 and 30 percent of the cost of materials and sup-plies (Halm 1980). Concrete pavement recycling

saves much of these costs. The cost of producingRCA can be considered to be limited to the costs ofcrushing the demolished concrete and screeningand backhauling the RCA (along with quality controlcosts). The costs of concrete demolition, removaland hauling are required whether the pavement isrecycled or simply discarded. RCA production costsmay be offset by savings in hauling and disposalcosts, especially if the RCA is produced on site. Costsavings from concrete pavement recycling vary buthave been reported to be as high as $5 million on asingle project (CMRA 2008).

In addition, concrete pavement recycling is a smartand environmentally sustainable choice that con-serves aggregate and other resources, reducesunnecessary consumption of limited landfill space,saves energy, reduces greenhouse gas emissionsand captures carbon dioxide (CO2) from the atmos-phere. Concrete recycling can eliminate the need formining or extracting new virgin aggregates, and canreduce haul distances and fuel consumption associ-ated with both aggregate supply and concrete slabdisposal.

RCA particles tend to be highly angular and arecomprised of reclaimed virgin aggregate, reclaimedmortar or both. Reclaimed mortar generally hashigher absorption, lower strength and lower abrasionresistance than for most virgin aggregates. As aresult, RCA generally has lower specific gravity andhigher absorption than virgin aggregate. The proper-ties of a specific recycled concrete aggregatedepend upon many factors, including the properties

Summ

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8 ReferencesAppendices


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Appendices8 References

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4 Uses3 Properties

2 Production RCA:

1 IntroductionSum

mary/Overview

of the original concrete and the processes usedto produce the RCA, particularly the crushingprocesses. With proper care and process control,RCA can be produced to meet quality and gradingrequirements for almost any application for whichvirgin aggregate would be used. RCA should be considered to be an engineered material for whichthe properties must be determined prior to use sothat appropriate mixture design or constructionadjustments can be made, as required.

When RCA is used in the production of new con-crete mixtures, its effect on the properties of thosemixtures can range from minimal to significant, de -pending upon the nature, composition and gradationof the RCA. For example, when little reclaimedmortar is present in coarse RCA and virgin fineaggregate is used, the handling characteristics andengineering properties of the new concrete propertieswill be practically the same as if all virgin ag gregatehad been used; if the new mixture contains onlycoarse and fine RCA, these characteristics andproperties will probably be quite different from thoseof traditional concrete mixtures when all other mix-ture design factors remain constant. Changes in mixture design and admixture usage can reduce(and sometimes eliminate) many differences in theproperties of RCA concrete mixtures.

Fresh concrete mixtures containing RCA generallyexhibit higher water demand and shrinkage, althoughthese effects can be offset with good constructionpractices and mixture design modifications. When allother factors are held constant (i.e., no compen-sating mixture adjustments are made), hardenedRCA concrete can be expected to have somewhatlower (but still acceptable) strength and elastic mod-ulus values, significantly more permeability, drying

shrinkage and creep potential, slightly lower specificgravity, somewhat higher coefficient of thermalexpansion and contraction (CTE) and also maybe more difficult to finish. Mixture design modifica-tions can partially offset or eliminate many of thesedifferences.

Recycled concrete aggregate has been used in theconstruction of hundreds of highway constructionprojects in the U.S. (and around the world) sincethe 1970’s. These projects have included the useof RCA in pavement fill, foundation, subbase andsurface courses (both asphalt and concrete). Pro-jects have included relatively low-volume roads andsome of the most heavily traveled roadway in theworld (e.g., the Eden’s Expressway in Chicago).They also have included the recycling of pavementsthat were severely damaged by D-cracking or alkali-silica reactivity (ASR) damage back into new con-crete pavements.

Most of these projects have performed very well, frequently exceeding all expectations. Some pro-jects, however, have failed prematurely in ways thatwere noteworthy. Some of these failures providedlessons in the design and construction of pavementdetails while others have led to mixture design modi-fications to produce concrete properties and pave-ment performances similar to (and, in some cases,superior to) those of conventional concrete materialsand pavements.

This publication provides numerous recommenda-tions concerning RCA production and use (includingboth foundation applications and use in new con-crete mixtures), as well as guide specifications toassist users in developing successful RCA construc-tion projects.

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Executive Overview

For quick reference, key concepts for each chapter are listed as follows and indexed to the tabs on the pageedges of this publication.

Key Point Page

● The primary incentives for concrete pavement recycling are economic and environ-mental. Pavement recycling also may offer the opportunity to improve the potentialperformance of the pavement (through material modifications) while addressingother roadway deficiencies (e.g., geometrics, foundation corrections, etc.) duringreconstruction.

1

● The overall economic benefits of concrete recycling vary with many factors,including the availability and cost of virgin aggregate, processing and quality controlcosts for producing RCA of the required gradation and quality, hauling and tippingfees for disposing of old pavement, and project-specific environmental issues.

2

● Concrete recycling is a smart and environmentally conscious choice that conservesaggregate and other resources, reduces unnecessary consumption of limited landfillspace, saves energy and reduces greenhouse gas emissions, and actually removesCO2 from the air.

2

● Reconstruction using RCA can provide additional performance benefits through im -proved foundation strength and stability and comparable or increased concrete strength.

4

● Concrete recycling for paving applications is now performed in at least 41 states andhas the support of the FHWA, which states that “reusing the material used to buildthe original highway system…makes sound economic, environmental, and engi-neering sense.” The Environmental Protection Agency (EPA) has identified“increasing the recycling and beneficial use of industrial materials” as one of the fournational priorities of the Resource Conservation Challenge, an organized nationaleffort to reduce greenhouse gas (GHG) emissions and to conserve naturalresources; the use of RCA in new concrete mixtures certainly satisfies theserequirements.

4

Chapter 1. Introduction – Page 1

Key Point Page

● RCA must generally meet the same requirements as virgin aggregate for the targetapplication (e.g., concrete mixture, subbase layer, etc.). There are some clear differ-ences in the physical, mechanical and chemical properties of typical virgin aggregateand RCA, but most of these differences, however, require little (if any) considerationor procedural adjustment for use in typical applications.

17

● With appropriate adjustments, concrete crushing plants can be set up to producealmost any desired gradation, although there often is an excess of material passingthe No. 4 (4.75 mm) sieve.

18

● Absorption capacities of RCA are generally higher than those of conventional aggre-gates. The primary factor affecting RCA absorption is the amount of reclaimedmortar that is present because the reclaimed mortar is usually more porous andabsorbent and has a greater surface area than most types of virgin aggregate.

18

● L.A. abrasion mass loss values typically are higher for RCA than for the virgin aggre-gates contained in the RCA; they are, however, usually within specified limits.

19

● D-cracked concrete pavements commonly have been recycled into unstabilizedsubbase layers and fill without any problems relating to the durability of theaggregate. Such pavements also have been successfully recycled into new concrete layers since at least the early 1980’s.

19

Chapter 3. Properties and Characteristics of RCA – Page 17

Key Point Page

● The major steps in concrete pavement recycling are: evaluation of the sourceconcrete; preparation of the slab; breaking and removing the concrete; removalof any steel mesh, rebar or dowels; crushing the concrete and sizing the RCA;treating the RCA to remove any additional contaminants (a process commonlyknown as beneficiation), if necessary, and stockpiling the RCA.

7

● The same basic equipment used to processes virgin aggregates also can be usedto crush, size and stockpile RCA.

12

● The runoff from RCA stockpiles is initially highly alkaline due to the leaching of cal-cium hydroxide from the freshly crushed material. Runoff alkalinity usually decreasesrapidly within a few weeks as the exposed calcium hydroxide is depleted. In addition,runoff alkalinity is usually mitigated quickly through contact with and dilution by rela-tively low pH rainwater and other mechanisms, such as the reaction of dissolved cal-cium hydroxide with CO2 from the atmosphere to form a stable limestone-likematerial. The bottom line is that there appear to be no negative environmental effectsfrom using RCA that would significantly offset the positive environmental effect ofreduced use of virgin aggregate and landfills.

14

Chapter 2. Production of Recycled Concrete Aggregate (RCA) – Page 7

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Executive Overview

Key Point Page

● Unstabilized (granular) subbase applications are common for RCA produced fromconcrete pavements because of the potential for superior performance, economicsavings, conservation of resources and environmental considerations.

23

● RCA is an effective and economical material for dense-graded, unstabilized subbaseapplications. When properly graded, the angular nature of the product providesexcellent stability. In addition, fine RCA often experiences a degree of secondarycementing, which further strengthens and stiffens the subbase layer.

23

● RCA typically makes excellent free-draining subbase material when the productionyields relatively angular, rough-textured particles that can be graded to applicablespecification requirements. When these conditions are met, RCA can be placed toprovide a subbase layer that is both permeable and is highly stable.

24

● RCA has been used in concrete mixtures in the U.S. since the 1940’s for roadwaysurfaces, shoulders, median barriers, sidewalks, curbs and gutters, building andbridge foundations and even structural concrete.

25

● Most states allow the use of recycled concrete for erosion control (“rip-rap”) or slopestabilization.

26

Chapter 4. Uses of RCA – Page 23

Key Point Page

● The potential for ASR in new concrete containing RCA is affected by the originalalkali level of the old concrete, the remaining potential reactivity of the recycledaggregate, and the alkali content of new concrete. However, several tests exist toprovide mitigation methods (e.g., substitution of Class F fly ash and/or slagcement, the use admixtures, such as lithium nitrate, etc.) to greatly reduce thepotential of ASR expansion in new concrete.

20

● High levels of NaCl have been found in RCA produced from sources with long-termexposure to this deicing chemical. No serious problems caused entirely by highchloride contents have been reported; however, some testing might be necessarywhen using RCA with high levels of NaCl in concrete mixtures for jointed reinforcedconcrete pavements (JRCP) or continuously reinforced concrete pavements(CRCP) to ensure that the NaCl levels are not high enough to be of concern.

20

● Crushing concrete reveals previously unexposed surfaces that usually containsome calcium hydroxide and some previously-unhydrated or partially-hydratedcement grains. These materials can be dissolved and then recombined withatmospheric CO2 to form calcium carbonate precipitate, which can fill pavementdrain pipes and clog filter fabrics. Suggestions for avoiding this problem are pre-sented in Chapter 7. Precipitate and crusher fines do not pose a problem for concrete mixture and undrained subbase layer applications.

21

Chapter 3. Properties and Characteristics of RCA – Page 17 (Continued)


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Key Point Page

● When RCA is used in the production of new concrete mixtures, its effect onthe properties of those mixtures can range from minimal to significant,depending upon the nature, composition and gradation of the RCA.

27

● RCA particles tend to be angular and rough-textured, which can increasethe harshness of fresh concrete mixtures. The irregular shape and texture ofcoarse RCA particles generally does not cause significant workability prob-lems. The use of fine RCA, however, can greatly increase the harshness ofthe mixture. It is common to control workability by limiting the use of fineRCA in concrete mixtures to 30 percent or less replacement of natural sand.

28

● The higher absorption capacities of RCA (especially fine RCA) can lead to arapid loss of workability. Absorption problems have been addressed suc-cessfully by washing or wetting the aggregate and maintaining it in a moist(saturated, surface-dry) condition until batching.

28

● Concrete containing coarse and/or fine RCA can be produced with adequatelevels of compressive and flexural strength for paving and other applications,even when virgin aggregates are completely replaced by RCA products.

29

● The CTE of RCA concrete is typically about 10 percent higher than for con-ventional concrete.

30

● Studies have found 20 to 50 percent higher shrinkage in concrete containingcoarse RCA and natural sand, and 70 to 100 higher shrinkage in concretecontaining both coarse and fine RCA. Higher shrinkage can cause higherconcrete pavement moisture warping stresses, which can usually be offsetby reducing the panel dimensions.

30

● RCA concrete mixtures have been shown to have permeabilities up to fivetimes higher than that of concrete made using conventional aggregate. Thisincreased permeability can be offset by reducing the w/cm ratio by 0.05to 0.10 and/or by the substitution of fly ash and/or slag cement for a portionof the cement.

31

● RCA concrete can be highly durable, even when the RCA is produced fromconcrete with durability problems, provided that the mixture proportioning(including the use of chemical and mineral admixtures) is done properly andthe construction (including concrete curing) is of good quality.

31

Chapter 5. Properties of Concrete Containing RCA – Page 27

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Key Point Page

● “Closed system” aggregate processing plants are preferred because theyallow greater control over the aggregate particle size distribution and providea more uniform finished material.

41

● Moisture control of stockpiles is essential in ensuring the production of uniform RCA concrete.

42

● The pavement design process should consider the possibility of significantstiffening of unstabilized RCA subbase materials caused by continued hydra-tion of the cementitious materials (especially for dense-graded RCA basematerials containing fine RCA particles).

43

● Unbound RCA subbase layers that can pass water to pavement drainagesystems or are designed to be drainable daylighted subbases should be freeof fine materials to minimize the movement of dust and formation of calciumcarbonate precipitate that can clog filter fabrics and reduce drain capacity.Fine unstabilized RCA may be suitable for placement in any layer below thepavement drainage system.

44

● In general, RCA products intended for use in new concrete pavementsshould meet the same quality requirements as virgin aggregate.

45

● Techniques that may be effective in preventing recurrent ASR include: theuse of Class F fly ash and/or slag cement in place of a portion of thecement; limiting the content of fine RCA; reducing concrete permeabilitythrough lower water content; the use of admixtures such as lithium nitrate;and reducing slab exposure to moisture.

45

● Recurrent D-cracking may be prevented by reducing coarse RCA top size to3⁄4 in. (19 mm) or less and by reducing slab exposure to moisture throughthe same techniques described above.

45

Chapter 7. Recommendations for Using Recycled Concrete – Page 41

Key Point Page

● A 1994 literature review identified nearly 100 RCA concrete paving projectsin the U.S., including several where D-cracked or ASR-damaged pavementswere recycled; many more projects have utilized RCA in pavement founda-tions, subbase layers and other applications. Most of these projects haveperformed well and are considered successes. Some projects, however,have not been successful and have offered lessons in the use of RCA inpavement construction.

33

Chapter 6. Performance of Concrete Pavements Constructed Using RCA – Page 33

Chapter 7 continued on next page


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Executive Overview

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Key Point Page

● RCA intended for use in high-quality concrete should be free of potentiallyharmful components. More than 90 percent of the material should be cementpaste and aggregate. Small amounts of joint sealant material, motor oil andother pavement surface contaminants have not been found to cause prob-lems in RCA used in concrete mixtures.

45

● The basic proportioning of concrete containing RCA can be accomplishedusing the same procedures recommended for proportioning concrete con-taining only virgin aggregate.

45

● The physical and mechanical properties of RCA concrete must be determinedand considered in the development of RCA concrete pavement designdetails. For example, increased shrinkage and thermal response of concretecontaining RCA can cause larger joint movements, requiring different sealantmaterials or reduced panel dimensions.

46

Chapter 7. Recommendations for Using Recycled Concrete – Page 41 (Continued)

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1

Chapter 1.

Introduction

WHAT IS CONCRETE RECYCLING?Concrete recycling is a relatively simple process. Itinvolves breaking, removing and crushing hardenedconcrete from an acceptable source to produceRCA, a granular material that can be produced foruse as a substitute for virgin aggregate in almostany application.

Old concrete pavements (including parking lots,sidewalks, curb and gutter, etc.) that are to beremoved often are excellent sources of material forproducing RCA because they are generally of goodquality and are free of the contaminating materialsthat often must be removed from concrete buildingdemolition debris. Concrete pavements are 100 percent recyclable (ACPA 2006).

WHY CONCRETE PAVEMENTRECYCLING?Virgin aggregate production in the U.S. increasedfrom 58 million tons (53 million metric tons) in 1900(or 0.5 tons [450 kg]/person) to 2.3 billion tons (2.1billion metric tons) (9.6 tons [8.7 metric tons]/person)in 1996, as shown in Figure 1 (USGS 1997). Thedemand for aggregate for the construction of pave-ments and buildings continues to increase rapidly.

Virgin aggregate resources are vast, but finite; manyhigh-quality, conveniently located virgin aggregateresources are being depleted rapidly. In addition,environmental regulations, land use policies andurban/suburban construction and settlement are fur-ther limiting access to known aggregate resources.Virgin aggregate costs can be expected to rise with

scarcity and increasing haul distances. Concretepavement recycling is a proven technology thatoffers an economical and sustainable solution tothese problems.

The primary incentives for concrete pavement recycling are economic and environmental. Pave -ment recycling also may offer the opportunity toimprove the potential performance of the pavement(through material modifications) while addressingother roadway deficiencies (e.g., geometrics, foundation corrections, etc.) during reconstruction.These three categories of benefits (economics, environmental stewardship or sustainability, andimproved or corrected pavement performance) arediscussed below.

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1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020

3,300 (3,000)

2,750 (2,500)

2,200 (2,000)

1,650 (1,500)

1,100 (1,000)

550 (500)

0 (0)

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, in

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ns (m

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Sand and gravel Crushed stone

National aggregates production in the United Stateswith projections to 2020, based on growth rate of 1.0%

for stone and 0.5% for sand and gravel.

Figure 1. National aggregates production in the United Stateswith projections to 2020 (USGS 1997).


2

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Economics of Concrete PavementRecyclingAggregate costs (for fill, base/subbase and surfacelayers) constitute one of the greatest costs of high -way construction, comprising between 20 and 30percent of the cost of materials and supplies, and10 to 15 percent of total construction costs (exclud -ing engineering and right-of-way acquisition)(Halm 1980).

Virgin aggregate costs are increasing rapidly in manyareas as sources of high-quality virgin aggregatematerial are depleted and new sources cannot beextracted due to urban development, environmentalconcerns and governmental regulation (e.g., zoning).As available sources become increasingly scarce,haul distances increase, resulting in additional supplycosts. In some urban areas, conventional aggregatesmust be hauled from sources that are up to 70 miles(113 km) from the project site, and haul distancesgreater than 200 miles (320 km) are not uncommon(ECCO 1999). These haul distances and associatedcosts can be expected to continue to increase assources become more scarce.

The cost of producing RCA can be considered to belimited to the costs of crushing the demolished con-crete and screening and backhauling the RCA (alongwith quality control (QC) costs). The costs of con-crete demo lition, removal and hauling are requiredwhether the pavement is recycled or simply dis-carded. RCA production costs may be offset by savings in hauling and disposal costs, especially ifthe RCA is produced on site.

In a recent survey, prices for various RCA productsranged from less than $1 to more than $16 per ton($1 to $18 per 1,000 kg) (USGS 2000). Some stateshave estimated savings of up to 60 percent fromusing recycled concrete aggregates in lieu of virginaggregates (ECCO 1997a). When the RCA is usedas aggregate for new concrete paving, this can meana savings of about $4.00 per yd2 ($4.80 per m2).

More recently, it was reported that California’sDepartment of Transportation (CalTrans) saved5 million dollars by utilizing 800,000 tons of RCA

(700,000 tons were produced from the existingroadway and 100,000 tons were imported from othersources) in the reconstruction and widening of a portion of I-5 near Anaheim (CMRA 2008).

It is clear that concrete pavement recycling offersseveral potential sources of cost savings. The overalleconomic benefits of concrete recycling vary withmany factors, including the availability and cost ofvirgin aggregate, processing and quality controlcosts for producing RCA of the required gradationand quality, hauling and tipping fees for disposingof old pavement, and project-specific environ-mental issues.

Sustainability IssuesEvery pavement construction or rehabilitation effortdraws on a finite reserve of virgin aggregate re -sources. Concrete recycling is a smart and environ-mentally conscious choice that conserves aggregateand other resources, reduces unnecessary con-sumption of limited landfill space, saves energy andreduces greenhouse gas emissions, and actuallyremoves CO2 from the air.

The Environmental Protection Agency (EPA) hasidentified “increasing the recycling and beneficial useof industrial materials” as one of the four national priorities of the Resource Conservation Challenge,an organized national effort to reduce greenhousegas (GHG) emissions and to conserve naturalresources; the use of RCA in new concrete mixturescertainly satisfies these requirements (EPA 2009).

Conservation of Virgin Aggregate ResourcesReplacing the slabs in one lane-mile (1.61 lane-km)of a 10-in. (250-mm) thick concrete pavementrequires almost 2,000 yd3 (1,500 m3) of concrete,including about 3,000 tons (2,700 metric tons) ofcoarse and fine aggregate. In areas where accept-able aggregate supplies are limited, a single largehighway project can rapidly deplete the locally avail-able supply of virgin aggregate.

Because concrete is 100 percent recyclable, thissame lane-mile of paving slabs can be recycled toproduce about 4,000 tons (3,600 metric tons) of

3

coarse and fine RCA – enough to supply the ag -gregate required to replace all of the slabs with additional material left for other applications. It alsois worth noting that it can take significantly fewertons of RCA to replace an equivalent volume of conventional aggregate in almost any applicationbecause RCA generally has a lower specific gravitythan virgin aggregate.

Clearly, concrete recycling conserves valuableexisting aggregate supplies and mitigates the needfor new quarries.

Landfill ReductionPlacing demolished concrete slabs in landfills isbecoming increasingly expensive as available landfillspace becomes more scarce and more restricted(e.g., many urban landfill operators will not acceptconstruction and demolition debris). Concrete pave-ment recycling eliminates the need to dispose ofconcrete in landfills, resulting in both cost savingsand an extension of landfill usefulness for materialsnot as easily recycled as concrete.

Energy SavingsThe production and use of virgin aggregate involvesthe consumption of a great deal of energy (as motorfuel and/or electrical power) at each step, including:the mining or extraction of the aggregate; thecrushing, screening and washing; the stockpilingand/or transport to the job site; and the removal anddisposal of the material (if it is not recycled) at theend of its period of use. Concrete recycling cangreatly reduce the need for mining or extraction, andcan reduce haul distances and fuel consumptionassociated with both supply and disposal.

An example of documented fuel savings is providedby Yrjanson (1989), who describes a 16-mile (26-km)concrete recycling project in Minnesota in 1981. Atwo-lane concrete pavement was recycled intocoarse RCA for a new concrete pavement surfaceand fine RCA for a 1-in. (25-mm) lift on top of thesubbase. The Minnesota Department of Transporta-tion (DOT) estimated that recycling the concreteresulted in a 27 percent savings in the total cost ofthe project, including a savings of 151,000 gallons(572,000 liters) of fuel.

Reduced Emission of Greenhouse Gasses(GHGs) and Other PollutantsEach step that consumes fuel or requires electricalpower in the production and use of virgin aggregatedescribed above also is responsible for the genera-tion of GHGs and other pollutants. Water resourcesalso are consumed and solid wastes produced eitherdirectly or indirectly in many production and trans-port activities. Concrete recycling helps to reducethe environmental impact of pavement reconstruc-tion activities while helping to ensure the mainte-nance of our transportation infrastructure.

Carbon Sequestration Through RCACarbonationResearch at the University of New Hampshire hasshown that RCA has significant value as a sink forcarbon dioxide (CO2), a primary “greenhouse gas”,through the mechanism of spontaneous carbonation,in which atmospheric CO2 reacts with calciumhydroxide (Ca(OH)2), a by-product of the cementhydration, in the concrete mortar to produce calciumcarbonate (RMRC 2006). The potential for carbondioxide sequestration is equal to all of the CO2 thatwas originally evolved in from the raw materials (butnot the fossil fuels) used in producing the includedportland cement.

Rates of carbonation in RCA products increase withincreasing humidity, increasing CO2 concentration,increasing temperature and increasing surface areaof the RCA. Figure 2 shows an example of labora-tory test results documenting CO2 removal over time

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0 1 2 3 4 5

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Figure 2. Illustration of carbon sequestration by fine RCA inlaboratory column studies (after RMRC 2006).


4

for three levels of test moisture content. This studysuggests that the use of RCA in unstabilized applica-tions (e.g., unstabilized subbases, embankment sta-bilization, etc.) has the potential to “scrub” the localatmosphere of significant quantities of CO2, furthercementing the position of concrete as a “green” con-struction material.

Pavement Performance ImprovementsPavement reconstruction with either new or recycledaggregates offers the opportunity to correct pave-ment subgrade or subbase deficiencies to betterensure the performance of the new concrete pave-ment structure. Such corrections are not possiblewith typical rehabilitation and overlay options. Reconstruction also allows an opportunity for anyexisting concerns with pavement geometry,drainage and roadway safety to be addressed.Reconstruction using RCA can provide additionalperformance benefits through improved foundationstrength and stability and increased concretestrength.

Foundation StabilityThe angular, rough-textured nature of RCA results inexcellent particle interlock, resulting in highly stablelayers for pavement foundation, pipe bedding, andbackfill applications. The use of fine RCA in pave-ment layers or soil stabilization applications offersthe additional potential benefit of the development ofadditional strength and stiffness over time as the un-and partially-hydrated cement in the RCA continuesto hydrate.

This secondary cementing effect can be significant,turning an “unbound” layer of dense-graded or fineRCA into a layer that behaves more like a cement-stabilized subbase. The benefits of this stiffeningshould be considered in predicting pavement perfor-mance, and pavement structural designs (e.g., jointspacing, slab thickness, etc.) should be engineeredaccordingly.

Concrete StrengthSeveral studies have shown that the strength andelastic modulus of concrete produced using coarseRCA may be lower than those of concrete containing

all virgin aggregate if the RCA contains significantamounts of reclaimed mortar. However, researchhas shown that the replacement of up to 80 percentof the virgin fine aggregate with fine RCA can poten-tially increase the strength of the resulting concrete,with the peak strength increase occurring at areplacement rate of about 25 percent (Fergus 1981).Possible reasons for this are that the fine RCA ismore coarse than natural sand, resulting in a betteroverall gradation to the aggregate blend, and thatthe supplemental cementing action also may con-tribute to the increased strength.

These effects are discussed further in Chapter 3 andChapter 7, of this publication.

Recycled Concrete Pavements: A ProvenTechnologyConcrete recycling has been used extensively inEurope since the 1940’s and in the U.S. since the1970’s (NHI 1998), with one of the first U.S. applica-tions of RCA in pavement construction taking placein the 1940’s on U.S. Route 66 (Epps et al 1980). Production of RCA in the U.S. currently averagesabout 100 million tons/year (91 million metric tons/year) (USGS 2000). The primary applications ofRCA have been base and subbase materials, but italso has been used in concrete and asphalt pavinglayers, high-value rip-rap, general fill and embank-ment, and other applications.

Concrete recycling for paving applications is nowperformed in at least 41 states (Figure 3) and hasthe support of the Federal Highway Administration(FHWA), which states that “reusing the material usedto build the original highway system …makes soundeconomic, environmental, and engineering sense.”(FHWA 2007b, FHWA 2002). FHWA further statesthat “The engineering feasibility of using recycledmaterials has been demonstrated in research, fieldstudies, experimental projects and long-term perfor-mance testing and analysis… When appropriatelyused, recycled materials can effectively and safelyreduce cost, save time, offer equal or, in somecases, significant improvement to performance quali-ties, and provide long-term environmental benefits”(FHWA 2002).

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Allow RCA use (41)

Do not allowRCA use (9)

Figure 3. States that currently allow the use of recycled con-crete aggregate (RCA) in pavement and other applications(FHWA 2004).


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producing RCA for use in structural concrete or pave-ment surface layers. Lower quality materials may bebest suited for subbases, fill or other applications.

PAVEMENT PREPARATIONIf the RCA being produced is to be considered foruse in a new concrete mixture, efforts must be madeto minimize the potential for introducing contami-nants throughout the production process. Contami-nants are generally of much less concern for RCAintended for use in subbase aggregate and fill applications. Potential contaminants in concretepavement recycling typically include joint sealants,asphalt concrete shoulders and patching materials,reinforcing steel and dowel bars, and soils and foundation materials (NHI 1998).

Joint sealant removal typically is accomplishedusing a cutting tooth sealant plow or other sealantremoval tool mounted on an end loader or otherpiece of equipment. Some agencies elect to leavejoint sealants in place prior to demolition, relying onother means of removal in the production process(especially if the RCA is intended for subbase orfill applications).

Concrete pavements with asphalt concrete patchesand overlays can be processed to produce RCA foruse in new concrete mixtures or other applications,but it generally is recommended that the two mate-rials be recycled separately. Lab and field studies inthe U.S. have concluded that when recycled asphaltpavement (RAP) is used as an aggregate in a con-crete mixture, the asphalt cement inhibits air entrain-

RCA production processes should be selected andconducted to maximize the production of usableRCA in terms of both quality and quantity. CoarseRCA (material retained on the No. 4 [4.75mm] sieve)is typically more valuable and usable than fine RCA(material that passes the No. 4 [4.75mm] sieve), soefforts often are made to maximize the quantity ofcoarse RCA produced. RCA quality depends uponmany factors, including the quality of the originalconcrete, the presence of contaminants, and theprocesses used in RCA production.

The major steps in concrete pavement recycling are:evaluation of the source concrete; preparation of theslab; breaking and removing the concrete; removalof any steel mesh, rebar or dowels; crushing theconcrete and sizing the RCA; treating the RCA toremove any additional contaminants (a processcommonly known as beneficiation), if necessary; andstockpiling the RCA. The following sections discussthe impact of each of these steps on RCA quantityand quality.

EVALUATION OF SOURCECONCRETEThe first step in producing RCA from a concretepavement is to determine the quality and overallproperties of the source concrete. Records of theoriginal concrete components (aggregate sourcesand quality, cement type, admixtures, and reinforcingtype (including fibers) and quantity), concretestrength and durability can be useful in determiningthe potential applications for the RCA produced.High-quality, durable concrete may be suitable for

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ment in the concrete mixture (Bergren and Britson1977). However, it has been reported that Austriaroutinely recycles concrete with up to 30 percentcoarse RAP into new concrete paving mixtureswithout any apparent detrimental effects (FHWA2007a). Austrian specifications also allow up to 20percent RAP particles in RCA used in the lowercourse of two-layer concrete pavement construction.

The most efficient way to remove large asphaltrepairs and overlays from the concrete pavementoften is through cold milling (Figure 4), althoughheavy pavement scrapers and bulldozers also havebeen used successfully (Figure 5). Front-end loadersor brooms may then be used to pick up or removeany remaining loose material.

Deteriorated asphalt shoulders should be removedbefore slab breaking operations on reconstructionprojects (FHWA 1990a). This reduces lateral slab support and facilitates concrete pavement breakingand removal. Shoulders that are in good conditionmay remain in place for concrete inlay construction(ACPA 1993a).

PAVEMENT BREAKINGAND REMOVALAfter the pavement slabs have been prepared forprocessing, the recycling process continues withon-site demolition. The main purpose of pavementbreaking is to size the material for ease of handlingand transport to the crushing plant. Breaking alsoshould impart enough energy to maximize debondingof concrete to reinforcing steel (Yrjanson 1989, FHWA1990a). The slabs are broken into pieces small enough(typically 18 to 24 in. [45 to 60 cm]) to be lifted andtransported easily (the “pin and lift” technique, analternative means to quickly remove full individualjointed plain concrete pavement (JPCP) slabs, mayalso be used but it typically requires some additionalmeans to further break the individual slabs beforethey can be processed by the crushing equipment).

The most readily available equipment for this opera-tion is the “impact breaker”, which breaks the pave-ment by dropping or hurling a heavy mass onto thepavement (or, alternatively, onto an impact shoe sitting on the pavement surface). Examples includegravity drop hammers (Figure 6), hydraulic or pneu -matic hammers (Figure 7), trailer-mounted dieselhammers (the most common option) (Figure 8),spring-arm whiphammers and drop balls (not recom -mended because they tend to produce a greateramount of excessively small fragments that are lesseasily salvaged). Production rates of 1,100 to 1,300yd2/hr (900 to 1,100 m2/hr) for 8-in. (200-mm) thickconcrete pavements have been achieved with dieselhammers (NHI 1998, Dykins and Epps 1987).

“Vibrating beam breakers” (also called “resonantbreakers”) use a large forged steel beam with a12-in. (300-mm) square breaker plate attached at theend to break up the concrete pavement (Figure 9).

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Figure 4. Asphalt pavement surface removal using coldmilling machine (Photo credit: National Highway Institute).

Figure 5. Asphalt pavement surface removal using heavyscraper and end loader (Photo credit: National Highway Institute).

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The beam is excited to deliver a high-frequency, low-amplitude impact to the pavement surface, producing a smaller-sized slab fragments (generallyless than 8 in. [200 mm] in diameter). This equipmentis relatively quiet and does not disturb undergroundutilities, which makes it particularly well-suited for usein urban areas. Production rates of up to 800 yd2/hr(670 m2/hr) for 9-in. (225-mm) thick concrete pave-ments have been achieved (NHI 1998).

Several external factors affect the production ratesof breaking equipment, including slab thickness, concrete strength, and amount and type of slab rein-forcement. More impact energy is needed to break

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Figure 6. Examples of gravity drop hammer equipment forpavement breaking.

Figure 7. Multi-head hydraulic hammer pavement breakingequipment.

Figure 8. Trailer-mounted diesel hammer.

Figure 9. Vibrating beam pavement breaker.


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an existing concrete pavement as each of these fac-tors increases. Increases in subbase support reduceimpact energy requirements. Impact energy alsomust be controlled to minimize damage to the sub-base and subgrade layers and to underlying pave-ment drainage facilities, utilities, and culverts. Impactenergy can be varied by changing the drop height,the number of passes or the forward speed of theequipment.

Pavement breaking equipment and slab crackingpatterns (Figure 10) should be selected after consid-ering the intended crushing operation and desiredproduct yield and gradation. For example, impactcrushers typically can handle larger broken concretepieces than compression (jaw or cone) crushers,allowing the use of a larger crack pattern and oftenresulting in higher breaking production rates. How-ever, impact crushers generally yield slightly lesscoarse RCA and more fine RCA and minus No. 200(75 µm) fines than do compression crushers. Maxi-mizing coarse RCA yield may require the use ofcompression crushers and impact breaking equip-ment with an appropriate breaking pattern.

The first step in the removal process is to loosen theconcrete pieces and separate any debonded rein-forcing steel. Where steel mesh reinforcing or rebarare present and have not been broken or separatedfrom the concrete by the breaking operation, a backhoe or bulldozer with a “rhino horn” attachment

(a 30-in. [76-cm], curved and pointed steel pick, asshown in Figure 11) often serves as an excellentloosening tool. This tool can hook and pull the steelfree from the concrete rubble. Some hand work(e.g., workers with torches or hydraulic shears) maystill be required to cut the reinforcing steel and pro-duce slab fragments with manageable sizes. Rela-tively small pieces of embedded steel will usually notcause problems in the crushing operations and willbe removed after crushing. Dowel bars and tie barsgenerally also are removed during the crushingoperation, but may become loose and fall out duringdemolition (NHI 1998).

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Figure 10. Typical crack pattern for broken concrete pave-ment prior to removal.

Figure 11. “Rhino horn” for use in loosening broken pavement fragments.

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Front-end loaders and dump trucks can easilyhandle removal and transport of the broken pave-ment fragments to the crushing site (Figure 12).However, removal procedures vary with the intendeduse of the RCA.

Extra care must be taken to avoid contaminationwhen the RCA is to be used in a new concrete mixture(s). If the concrete is situated directly oncohesive soil, this material can adhere to the brokenconcrete during wet weather. Soil and clay balls canbe particularly troublesome, sometimes resulting inincreased water demand, reduced concrete strength,and surface flaws. In such situations, it is sometimesnecessary to limit removal operations to dry weather(Yrjanson 1989) or to use a 1-in. (25-mm) scalpingscreen ahead of the primary crusher.

Loader operators must avoid picking up subbasematerial with the broken concrete. The use ofbuckets and blades with digging teeth often helps inthis regard, and small concrete fragments (diametersmaller than 6 in. [150 mm]) often are left behind inan effort to reduce the amount of dirt and other con -taminants introduced to the recycling stream (NHI1998). Also, it has been reported that rubber-tiredloaders cause less subbase disturbance and pick upthan do tracked loaders (ACPA 1993b).

Recommendations for maximum allowable limits oncontaminants are presented in Chapter 3 of this publication.

Contaminants are usually of little or no concern inproducing RCA intended for subbase and fill appli -cations; thus, pavement removal operations can beconducted with less concern for contamination.

REMOVAL OF EMBEDDED STEELThe removal of reinforcing steel, tie bars and dowelscan occur during several phases of the recyclingprocess, but typically is accomplished during thebreaking and removal operation (particularly for con-tinuous reinforcing steel) or following the primaryand secondary crushing operations, where electro-magnets often are used to pick steel from the con-veyor belts (Figure 13). Manual labor may be usedto supplement magnetic steel removal operations.


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Figure 12. Removal and transport of broken pavement frag-ments using end loader and dump truck.

Figure 13. Removal ofreinforcing steel on thejob site or after crushing.


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Salvaged steel generally becomes the property ofthe contractor, who can typically sell it as scrapmetal. Wire mesh steel with large quantities ofbonded concrete often is wasted.

CRUSHING AND SIZINGThe same basic equipment used to processes virginaggregates also can be used to crush, size andstockpile the RCA (ECCO 1999), although equip-ment modifications (e.g., the use of more wear-resis-tant components and the addition of electromagnets)permit more efficient processing of most salvagedconcrete pavements.

Most concrete recycling plants have both primaryand secondary crushers. The primary crusher typi-cally reduces the material size down to about 3-4 in.(8-10 cm). The crushed material is then screenedand material larger than 3⁄8 in. (9 mm) is fed into a secondary crusher, which breaks the material to thedesired maximum coarse RCA size.

The three main types of crushers used in concreterecycling feature “jaw”, “cone” and “impact” designs,which differ in how they crush the concrete. Figure14 illustrates the differences between these typesof crushers.

Brokenconcrete feed

Jaw breakplate

Stationaryjaw

Discharge

Jaw breakplate

Swingjaw

Jaw Crusher

Rotor/impellors

Vertical Shaft Impact Crusher

Impactbreak plate

Rotation

Crushed concrete discharge

Broken concrete feed

Broken concrete feed

Eccentric rotation

Cone Crusher

Breakingplates Cone

DischargeDischarge

Horizontal Shaft Impact Crusher

Primarybreak plate

Secondarybreak plate

DischargeRotor/blow bars

Brokenconcrete feed

Figure 14. Schematic illustrations of various types of typical aggregate crushing equipment.

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Jaw crushers use a large steel plate to compressconcrete fragments against a stationary plate withinthe crusher housing. Aggregate top size is controlledby varying the amount of jaw closure. Jaw-typedesigns commonly are used in primary crusherapplications because they can handle larger slabfragments than cone crushers.

Cone crushers use an eccentric rotating cone to trapand crush concrete fragments against the innercrusher housing walls. When the material becomessmall enough, it escapes through the bottom of thecrusher housing. Most cone crushers can handleslab fragments no larger than 8 in. (20 cm) in diam-eter. For this reason, they are used most often asthe secondary crushing unit in concrete recyclingoperations.

lmpact crushers use heavy steel “blow bars” mountedon a horizontal or vertical rotor to repeatedly impactconcrete fragments and hurl them against steelanvils or “break plates” in the crusher housing. Therotor continues to hurl particles that are larger thanthe desired top size. Impact crushers tend to removemore mortar from crushed concrete particles, result -ing in more fine RCA and minus No. 200 (75 µm)fines and lower coarse RCA yield. They must be fab-ricated to withstand the impact of any steel reinforce-ment that enters the crusher.

While most concrete crushing plants are designedfor high-production use by large contractors, “miniconcrete crushers” (capable of being towed behinda pick-up truck) also are available for small, local projects (Figure 15).

Concrete recycling conveyor systems are generallythe same as for virgin aggregate crushing, exceptthat the crushing of concrete fragments with embed -ded steel requires that the belt below the primarycrusher be lowered to allow long pieces of steel toexit the crusher without jamming and ripping the belt.

The yield of coarse RCA from the recycling operationdepends upon many factors, including the type, size,quality and quantity of virgin coarse aggregate usedin the concrete, the quality and hardness of the con-

crete mortar, the breaking and removal operationsand the crushing processes used. Loss of materialthrough removal operations can be as high as 10percent (for recycling of jointed reinforced concretepavement (JRCP) with field removal of the wiremesh) and may approach zero for jointed plain con-crete pavements (JPCP). Crushing for larger top-size aggregate generally produces higher coarseRCA yields because less crushing is necessary. Forexample, 55 to 60 percent coarse RCA yield iscommon when crushing to ¾ in. (19 mm) top size,while 80 percent yield is not uncommon whencrushing to 1.5 in. (28 mm) top size (NHI 1998).

BENEFICIATIONBeneficiation can be described as the treatment ofany raw material to improve its physical or chemicalproperties prior to further processing or use. Thiscan be a necessary step in some aggregate pro-cessing operations (including concrete crushing toproduce RCA) to eliminate accidentally includedorganic material, excessive dust, and other con -taminants that would cause problems in theintended application of the aggregate. Aggregatebeneficiation takes advantage of the distinguishingproperties of the materials to be separated (e.g.,particle size, particle density, etc.) to concentrate thedesirable components.


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Figure 15. Mini concrete crushing plant.


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There are many established techniques for theremoval of residual soil, loose cement mortar, unde -sirable minerals (e.g., chert) and other con taminants,including special crushing processes, washing, wetor dry screening, and hydraulic or heavy media sep-aration (FHWA 2007b). Promising new technologies,such as air blowing and water floating techniques,also have been documented as being highly effec-tive (Park and Sim 2006).

The degree of beneficiation required depends uponthe condition and composition of the crushed con-crete, as well as the intended use of the RCA. Whileoften not required, washing has been shown to bebeneficial in removing dust that might otherwiseweaken the bond of coarse RCA particles withmortar in new concrete mixtures; such washing iscomparable to the washing process that might beemployed with dirty virgin aggregates. The removalof deleterious materials to levels that meet specifiedlimits is essential for RCA intended for use in newconcrete mixtures.

STOCKPILINGCoarse RCA can be stockpiled using the same tech-niques and equipment as are used with virgin coarseaggregate materials (Figure 16). Fine RCA stock-piles generally need to be protected from precipita-tion to reduce the potential for secondary cementingdue to hydration of exposed and previously unhy-drated (or partially hydrated) cement grains. As withvirgin fine and coarse aggregates, more than two

separate stockpiles may be necessary to allow theproduction of aggregate blends that meet projectspecifications.

The runoff from RCA stockpiles is initially highlyalkaline (e.g., one study found median pH values of9.3 and 9.8 for fine and coarse RCA stockpiles,respectively, and this was found to not be signifi-cantly greater than the runoff from a bituminousmilling stockpile, with a measured runoff pH of 8.1[Sadecki et al 1996]) due to the leaching of calciumhydroxide from the freshly crushed material. In addi-tion, studies have shown the presence of traceamounts of heavy metals and other naturally occur-ring contaminants in RCA stockpile runoff, althoughgenerally not to levels considered hazardous(Sadecki et al 1996). Runoff alkalinity usuallydecreases rapidly within a few weeks as theexposed calcium hy droxide is depleted through neu-tralization, dissolution and/or reaction with carbondioxide in the air, etc.; similarly, the concentrations ofother contaminants can be expected to decreaserapidly with time as well (Snyder 1995). In addition,runoff alkalinity is partially neutralized by rainwaterpH (which is in the range of 5.2 to 5.4), dilution asrainwater concentrates, the effects of soil bufferingand equilibration with atmospheric CO2 during trans-port from the RCA source to local surface waters.The bottom line is that there appear to be no nega-tive environmental effects from using RCA thatwould significantly offset the positive environmentaleffect of reduced use of virgin aggregate and land-fills (Reiner 2008).

IN-PLACE CONCRETE RECYCLINGWhen RCA is to be used in a subbase layer of theroadway and/or shoulders, production can beaccomplished using an in-place concrete recyclingtrain. Such systems typically utilize primary and sec-ondary crushers that have been specially adaptedfor in-place recycling and are mounted on crawlertracks. Figure 17 illustrates how the coarse RCA andfine RCA can be separated during recycling opera-tions, making it easy to use only the coarse RCA inthe subbase and/or shoulders.

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Figure 16. RCA crusher, conveyor and stockpiling operation.

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This in-place concrete pavement recycling techniquewas first used on I-80 near Des Moines, IA in 1994and has been used on several projects since then.Production rates vary with the material beingprocessed and the amount of reinforcing steelinvolved, but rates exceeding 2,000 lane-ft/day(610 lane-m/day) have been achieved (ECCO 1997).

In-place recycling saves the cost of fuel and laborinvolved in hauling raw and processed materials toand from the job site (in addition to the material andfuel savings associated with using recycled materialsinstead of mining virgin aggregates).

RECYCLING OF RETURNEDREADY MIXED CONCRETEApproximately 5% of the 445 million cubic yards ofready mixed concrete produced in the U.S. eachyear is returned to the concrete plant. Research hasshown that recycling of this material, as with re -cycling of any existing concrete material, presentssignificant sustainable benefits, including a reductionof landfill use and a reduction in virgin aggregatesuse (Obla 2009).


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Figure 17. In-place recycling of an existing concrete pave-ment with the coarse and fine RCA being separated as part ofthe process (Photo credit: Iowa DOT).


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Property Virgin aggregate RCA

Shape and Texture Well-rounded, smooth (gravel) toangular and rough (crushed rock)

Angular withrough surface

Absorption Capacity 0.8 – 3.7 percent 3.7 – 8.7 percent

Specific Gravity 2.4 – 2.9 2.1 – 2.4

L.A. Abrasion Test Mass Loss 15 – 30 percent 20 – 45 percent

Sodium Sulfate Soundness Test Mass Loss 7 – 21 percent 18 – 59 percent

Magnesium Sulfate Soundness Mass Loss 4 – 7 percent 1 – 9 percent

Chloride Content 0 – 2 lb/yd3

(0 - 1.2 kg/m3)1 – 12 lb/yd3

(0.6 – 7.1 kg/m3)

Table 1. Comparisons of Typical Virgin Aggregate and RCA Properties (Snyder et al 1994)


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PHYSICAL PROPERTIESParticle Composition, Shape andTextureRCA particles are comprised of reclaimed virginaggregate, reclaimed mortar or both. The relativeproportions of these components varies with theoriginal concrete mixture design, the properties ofthe virgin coarse aggregate particles (i.e., the angularity and surface texture, strength and elas-ticity), the bond between the virgin aggregate particles and the mortar, and the type and extentof crushing used in production.

Particle composition also varies with particle size.Larger particles tend to contain greater proportionsof reclaimed virgin aggregate while particles pass ingthe No. 4 (4.75 mm) sieve often are mainly crushedmortar (Fergus 1980).

RCA must generally meet the same requirements asvirgin aggregate for the target application (e.g., con-crete mixture, subbase layer, etc.). A summary andcomparison of the typical properties of virgin andrecycled concrete aggregates is presented in Table 1.There are some clear differences in the physical,mechanical and chemical properties of typical virginaggregate and RCA, mainly because of the inclusionof reclaimed mortar in the RCA. Most of these differ-ences, however, require little (if any) consideration orprocedural adjustment for use in typical applications.

The following sections summarize the properties andcharacteristics of RCA that may affect the propertiesof concrete and foundation layers constructed usingthe material.

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RCA particles tend to be highly angular and haverough surfaces (similar to crushed rock), althoughthese characteristics vary with the nature of theincluded virgin aggregate and the type and extentof crushing used in production. Some crushingprocesses remove most of the mortar from smooth-surfaced virgin coarse aggregates, producing acoarse RCA that closely resembles the original virgincoarse aggregate in all respects.

GradationWith appropriate adjustments, concrete crushingplants can be set up to produce almost any desiredgradation, although there often is an excess of fineRCA produced.

Proper screen selection will enable a crushing plantto meet the gradation limits for concrete aggregates

set forth in ASTM C33 (or AASHTO M43 gradations57 and 67).

Table 2 shows a variety of RCA gradations that havebeen produced on various concrete pavement recycling projects.

Absorption CapacityAbsorption capacities of RCA are generally muchhigher than those of conventional aggregates(Table 1). The primary factor affecting RCA absorp-tion is the amount of reclaimed mortar that is presentbecause the reclaimed mortar is usually moreporous and absorbent and has a greater surfacearea than most types of virgin aggregate. As RCAparticle size decreases, mortar content and absorp-tion tend to increase, as shown in Table 3 (Fergus1980, Swedeen 1990, Yrjanson 1989).

Sieve size

Iowa** Oklahoma*** Michigan**** Korea*****

Coarse Fine Coarse Fine Coarse Fine Coarse Fine

11⁄2 in. (38 mm) 100 — — — 100 — — —

1 in. (25 mm) 72 — 100 — 98 — 100 —

0.8 in. (20 mm) — — — — — — 96 —3⁄4 in. (19 mm) 39 — 98.5 — 76 — — —

0.6 in. (15 mm) — — — — — — 33 —1⁄2 in. (12.5 mm) 21 — 46.5 100 43 — — —3⁄8 in. (9.7 mm) 9.3 100 11.2 99.2 25 100 32 100

No. 4 (4.75 mm) 2.9 76 1.5 78.8 20 99 0 100

No. 8 (2.36 mm) 2 51 — — — 61 — 82

No. 10 (2.00 mm) — — — 48.5 — — — —

No. 16 (1.18 mm) — 30 — — — 40 — 54

No. 30 (600 µm) — 16 — — — 28 — 30

No. 40 (450 µm) — — — 19.4 — — — —

No. 50 (300 µm) — 8 — — — 19 — 10

No. 80 (180 µm) — — — 9.2 — — — —

No. 100 (150 µm) — 3.5 — — — 12 — 2

No. 200 (75 µm) 0.7 2 — 4.5 — — — —

* Gradations shown are production examples and are not necessarily recommended.** Produced 65% coarse RCA, 35% fine RCA - Yrjanson 1989

*** Produced 60% coarse RCA, 40% fine RCA - Yrjanson 1989**** Jaw crusher used - Yrjanson 1989

***** Advanced recycling techniques applied - Park and Sim 2006

Table 2. Typical RCA Gradations from Crushing Operations (percent passing)*

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The section titled Water Demand in Chapter 5 of thispublication describes techniques for addressing theeffects of increased absorption capacity in concretemixture design, including pre wetting of RCA, limitingthe inclusion of fine RCA, and the use of mineral andchemical admixtures.

Specific GravityConcrete mortar (comprising sand, cement, waterand air) generally has a much lower specific gravity(2.1 to 2.4) than most virgin aggregate types (2.4 to2.9). Therefore, RCA specific gravity mainly dependsupon the relative proportions of reclaimed mortarand reclaimed virgin aggregate, and tends to de -crease with particle size (generally increasing mortarcontent), as shown in Table 3.

MECHANICAL PROPERTIESLos Angeles Abrasion Mass LossThe Los Angeles (L.A.) abrasion test (ASTM C131or AASHTO T96) measures the amount of particledegradation (in terms of percent mass loss) thattakes place under standard aggressive handlingconditions. L.A. abrasion mass loss values typicallyare higher for RCA than for the virgin aggregatescontained in the RCA, as indicated in Table 1. Thisis usually attributed to the presence of the softercement mortar and the presence of particles thatwere only partially fractured during the crushingprocess (Snyder and Vandenbossche 1993).

L.A. abrasion test values for RCA usually are withinspecified limits. For example, ASTM recommends alimit of 50 percent mass loss for aggregates

intended for use in concrete, and 40 percent forcrushed stones intended for use in roadbed con-struction. Most states specify the same L.A. abrasiontest result limits for both virgin aggregates and RCA.Specifications may waive L.A. abrasion testing foreither RCA or virgin aggregate if the material has agood performance record.

Freeze-Thaw DurabilityConcrete pavements that have developed freeze-thaw durability cracking (“D-cracking”) due to the useof frost-susceptible coarse aggregate in the concretecommonly have been recycled into unstabilized sub-base layers and fill without any problems relating tothe durability of the aggregate. Such pavements alsohave been successfully recycled into new concretelayers since at least the early 1980’s.

When used as coarse aggregate in new concrete,the RCA has commonly been crushed to a ¾-in.(19-mm) top size. This approach has been suc-cessful in preventing recurrent D-cracking, but oftenhas resulted in reduced aggregate interlock loadtransfer capacity on undoweled pavements. How-ever, because most jointed concrete pavements(e.g., JPCP and JRCP) constructed today featureshort panel lengths and dowel load transfer systems,aggregate interlock load transfer capacity is not ofconcern for these pavements.

Two projects containing RCA from D-cracked pave-ments are described in Chapter 6 of this publication.

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Sieve size Percent retained Bulk specific gravity Percent Absorption

1.0 in. (25 mm)3⁄4 in. (19 mm)

1⁄2 in. (12.5 mm)3⁄8 in. (9.5 mm)

No. 4 (4.75 mm)

222331825

2.522.362.342.292.23

2.543.984.505.346.50

Weighted average 100 2.31 5.00

Table 3. Properties of One Coarse RCA (Fergus 1980)


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CHEMICAL PROPERTIESAlkali-Silica Reactivity (ASR)The potential for ASR in new concrete containingRCA is affected by the original alkali level of the oldconcrete, the remaining potential reactivity of therecycled aggregate, and the alkali content of newconcrete (Stark 1996). The use of low-lime Class Ffly ash and slag cement has greatly reduced ASRexpansion in new concrete. If fly ash and/or slagcement are being used to mitigate ASR in concreteutilizing RCA from an ASR-damaged concrete, theappropriate dosage levels should be determined byusing ASTM C1567. Other mitigating techniquesinclude limiting the content of RCA fines, reducingconcrete permeability through a lower water content,using admixtures such as lithium nitrate, andreducing slab exposure to moisture. Chapter 6 ofthis publication describes a project in Wyoming thatused fly ash and slag cement to reduce the potentialfor recurrent ASR in a concrete pavement con-structed using RCA from an ASR-affected source.

Research and construction projects have demon-strated that, with appropriate selection of cementi-tious materials, RCA containing reactive (and evenhighly reactive) aggregate can be used safely.

Sulfate Soundness Mass LossSulfate soundness tests are performed to provide anindication of aggregate resistance to weathering andother environmental effects. The two most widelyused tests are the sodium sulfate soundness testand the magnesium sulfate soundness test, whichare described in ASTM C88 and AASHTO T104.

RCA commonly fails the sodium sulfate soundnesstest while passing the magnesium sulfate soundnesstest with results that are better than those of the orig-inal aggregate (Snyder and Vandenbossche 1993).For example, sodium sulfate soundness mass lossestypically range from 18 to 59 percent for RCA mate-rials (Hansen 1992); ASTM recommends a limit of12 percent. Hansen also reported magnesium sulfatetest losses of 0.9 to 2.0 percent for coarse RCA while

the virgin coarse aggregates used had a loss of 3.9percent; ASTM recommends a limit of 18 percent.This contradiction between the two test methods suggests that either or both of these tests may beinadequate for predicting the durability of recycledaggregates. As a result, these tests often are waivedfor recycled concrete products.

Chloride ContentHigh chloride levels have been found in RCA pro-duced from sources with long-term exposure todeicing chemicals. Significant amounts of chloridesoften raise concerns about the potential for prob-lems with concrete durability, set times (e.g.,sodium chloride [NaCl] acts as a set accelerator)and corrosion of embed ded steel. No serious prob-lems caused entirely by high chloride contents havebeen reported; however, some testing might be nec-essary when using RCA with high chloride levels inJRCP or continuously reinforced concrete pave-ments (CRCP) to ensure that the chloride levels arenot of concern.

Much of the chloride content in RCA has been foundto be concentrated in fine particles produced fromconcrete at the pavement surface. For example, thetotal chloride content of RCA from I-84 near Water-bury, CT was found to be 12, 0.96 and 0.27 lb/yd3

(7.1, 0.57 and 0.16 kg/m3) at depths of 1.5, 4.0 and6.5 in. (38, 102 and 165 mm) below the surface(Lane 1980). The RCA from this project was used toproduce fresh paving concrete containing 1.93 lb/yd3

(1.14 kg/m3) total chloride. A typical NaCl limit forhighly reinforced concrete (e.g., bridge decks) isapproximately 4 lbs/yd3 (2.4 kg/m3) (Yrjanson 1989,Forster 1986). No critical level of chloride concentra-tion has been clearly defined for pavements (Forster1986).

It is best to check the chloride content of any recy-cled material that may contain excessive salt, andthen estimate the corresponding chloride content ofthe resulting mixture (Forster 1986). If chloride levelsare found (or believed) to be problematic, possiblesolutions include the use of epoxy-coated reinforcing

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steel and washing the fine RCA to reduce theamount of material passing the No. 200 (75 µm)sieve and the chloride content (Forster 1986,Van Matre and Schutzbach 1989).

Precipitate PotentialCrushing concrete reveals previously unexposed surfaces that usually contain some calcium hydrox ide(a by-product of the cement hydration reaction) aswell as some unhydrated or partially hydrated cementgrains. Calcium hydroxide is highly soluble and iseasily leached from the RCA particles in stockpilesand drainable subbase layers, resulting in highlyalkaline runoff and effluent. The dissolved calciumhydroxide can combine with CO2 (absorbed into thesolution from the atmosphere) to form calcium car-bonate, which precipitates out of solution to form aheavy, creamy substance that can fill pavement drainpipes and clog filter fabrics. Dust and other fine parti-cles from the crushing, screening and handling oper-ations also can settle on filter fabrics and in drainpipes, further exacerbating the problem (as describedin the next section of this publication). Over time,these materials can clog drain pipes and blind filterfabrics.

Suggestions for avoiding this problem are presentedin Chapter 7 of this publication and in ACPA’sEB204P (ACPA 2007). These suggestions includeusing only coarse, washed RCA in drainable sub-base layers, using daylighted subbase drainage de -signs, or modifying the filter fabric design to ensurethat it does not completely surround the edge drainpipe trench.

Precipitate and crusher fines do not pose a problemfor concrete mixture and undrained subbase layerapplications where the presence of partially hydratedcement grains can actually aid in stabilizing andstrengthening the layer.

CONCERNS WITH SURFACE DUSTAND CONTAMINANTSSmall quantities of fine particles (“crusher dust”)often remain on RCA particles after production. Thisdust may increase water demand and decreaseaggregate-mortar bond quality in new concrete mix-ture applications and may migrate into drainage sys-tems and filter fabric in drainable subbase layerapplications. Aggregate washing, as is often per-formed in processing dirty virgin aggregates, is notuniversally required in either of these applications,but may be helpful or desirable in some cases.

Contaminants are usually a concern only for RCAthat will be used in new concrete mixtures and notfor unstabilized subbase and fill applications.

Contamination usually is not a problem for ruralhighway or airport recycling that use materialsremoved from the project site. Initial preparation(including removal of asphalt, if required) and carefulremoval by loader operators (to avoid inclusion ofsubbase and soil materials) usually provides ade-quate contaminant control. However, when RCA ismanufactured from sources other than concretepavements, as is common in urban recycling opera-tions, it should be noted that contaminants such asplaster, soil, wood, gypsum, asphalt, plastic, vinyland rubber can be present in sufficient quantities towarrant concern.

For new concrete mixture applications, RCA con taminants generally should be limited to thesame values required for virgin coarse aggregate. Sug gested limits are presented in Chapter 7 of thispublication.

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Figure 18. Photo of RCA aggregate subbase stockpile (con-taining both concrete and asphalt material) in Minnesota(FHWA 2004).


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Through process control and blending, contractorscan produce RCA subbase material with almost anygradation.

Unstabilized Dense-graded SubbaseRCA is an effective and economical material forunstabilized dense-graded subbase applications.When properly graded, the angular nature of theproduct provides excellent stability. In addition, fineRCA often experiences a degree of secondarycementing, which further strengthens and stiffens thesubbase layer.

RCA should not be used in unstabilized dense-graded subbase layers that will provide any signifi-

RCA can be produced to be a substitute for almostany conventional virgin aggregate and, because ofthe chemical and residual cementitious properties ofthe reclaimed mortar, RCA also is useful in someadditional applications. Some of the most commonand interesting applications (and limitations) aredescribed below.

UNSTABILIZED (GRANULAR)SUBBASE AND BACKFILLUnstabilized (granular) subbase applications arecommon for RCA produced from concrete pavementsbecause of the potential for superior performance,economic savings, conservation of resources andenvironmental considerations (see ACPA’s EB204P(ACPA 2007) for additional details). Of the 41 statesindicating their production of RCA in 2004, 38 statedthat they use the material for aggregate subbaseapplications (FHWA 2004). In fact, some statesbelieve that RCA outperforms virgin aggregate inunstabilized subbase applications (FHWA 2004).

An important benefit to using RCA as unstabilizedsubbase material is that the presence of contami-nants (e.g., asphalt concrete, joint sealant materials,etc.) is of relatively little concern. For example, Min-nesota allows up to 3 percent asphalt binder byweight of aggregate, and California has no limit onthe relative proportions of RAP and RCA in their sub-base materials. This provides maximum contractorflexibility in production and construction. Figure 18shows the presence of both RAP and RCA in a Min-nesota RCA stockpile (FHWA 2004).

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cant flow or runoff to pavement edge drainage sys-tems because the contribution of crusher dust anddissolved calcium hydroxide can form deposits infilter fabrics and pipe drains.

Additional recommendations concerning the use ofRCA in unstabilized dense-graded subbases arepresented in Chapter 7 of this publication.

Unstabilized Free-draining SubbaseRCA typically makes excellent unstabilized free-draining subbase material when the production yieldsrelatively angular, rough-textured particles that can begraded to applicable specification requirements. Whenthese conditions are met, RCA can be placed to pro-vide a subbase layer that meets typical free-drainingsubbase permeability requirements and is highlystable.

The use of RCA in unstabilized free-draining subbaselayers has been associated with the deposit of crushedconcrete dust and leachate (calcium carbonate precipi-tate) in drainage pipes and on filter fabric. These prod-ucts can clog the fabrics and pipes, reducing thecapacity of the drainage system. The potential forthese problems can be greatly reduced by washing theRCA (to remove crusher dust) and by eliminating fineRCA (passing the No. 4 [4.75 mm] sieve) from thesubbase (Bruinsma 1995). Subbase layer stabilizationwith cement or asphalt also is effective in practicallyeliminating dust and leachate concerns.

Drainage systems also can be designed to allowresidual crusher dust to settle in a granular filter layerwhile only partially wrapping the longitudinal draintrench with filter fabric, as shown in Figure 19. Notethat the filter fabric (geotextile) does not completelysurround the trench, which prevents the fabric frombeing clogged by leachates or other fine particlescarried by water flowing through the subbase, andthe drain is offset at least 3 ft (1 m) from the edge ofpaving whenever possible, which protects it fromconstruction traffic.

Even still, such edge drainage systems have had aproblematic history in the field, even when the sub-base consisted of 100% virgin aggregates. Problems

range from crushing of the drainage pipe during con-struction, yielding it ineffective, to clogging of the pipedue to a lack of maintenance, mouse nests, etc.(Baumgardner 2002). In fact, inadequate mainte-nance has been sited as an universal problem(FHWA 1990b), prompting FHWA to recommend that“if a state highway association [SHA] is unwilling tomake the necessary maintenance commitment, sub-surface drainage systems should not be provided”(Baumgardner 2002).

Though often disregarded in the past due to themindset that they were less effective at removingwater from the pavement, daylighted subbases haveproven to be as effective as edge drainage structures(FHWA 2009). In a daylighted subbase, water and anyfree material that finds its way into the free-drainingsubbase will have many paths to follow that couldpotentially lead out of the pavement structure (Roddenand Voigt 2008). The magnitude of potential paths outof a daylighted subbase greatly reduces the probabilityof clogging of the subbase when using a RCA.

Additional recommendations concerning the use ofRCA in unstabilized free-draining subbases are pre-sented in Chapter 7 of this publication.

CEMENT-STABILIZED SUBBASECement-stabilized subbase layers (e.g., cement-treated subbase (CTB) and lean concrete subbase(LCB)), also can be constructed using RCA. Coatingor embedding the RCA in fresh cement paste ormortar prevents the migration of crusher fines and

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Subgrade

Geotextile

CollectorPipe

Concrete ShoulderFree-draining Subbase

Concrete Pavement

Minimum offset distance of 3 ft (1 m)

Separator Layer (Geotextile)

Figure 19. Typical drainage system detail for use of free-draining RCA subbase.

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the dissolution and transport of significant amountsof calcium hydroxide, which can otherwise form cal-cium carbonate precipitate in drain pipes (for moreon this topic, see the section titled Precipitate Poten-tial in Chapter 3 of this publication).

The physical and mechanical properties of RCA(particularly the absorption characteristics) must beconsidered in the design and production of CTB andLCB, similar to their consideration in concrete pro-duction using RCA, as described below.

CONCRETE MIXTURESRCA can be (and has been) incorporated as the pri-mary or sole aggregate source in new concretepavements. For example, RCA has been used inconcrete mixtures in the U.S. since the 1940’s forroadway surfaces, shoulders, median barriers, side-walks, curbs and gutters, building and bridge foun-dations and even structural concrete (NHI 1998,ECCO 1999). The design and performance of sev-eral RCA concrete pavements in the U.S. is dis-cussed in Chapter 6 of this publication. The use ofRCA also is common in the lower lift of two-lift con-crete pavements in Europe (FHWA 2007a).

RCA also can be used in paving surfaces con-structed using econocrete, which is a lower strength,more inexpensive concrete mixture that is identicalin concept to LCB but is used in pavement surfacing.

The basic techniques for batching, mixing, delivery,placement and finishing need not be significantly dif-ferent than those used for concrete mixtures con-taining virgin aggregate.

Two concerns when utilizing RCA in concrete mix-tures are increased water demand and prematurestiffening of the mixture caused by the presence offine particles and the more absorptive nature ofreclaimed mortar. Some agencies address theseproblems by limiting or eliminating the inclusion offine RCA in concrete mixture applications. Pre-soaking RCA and maintaining it in a proper moisturestate prior to use also can reduce these problems.These and other approaches are discussed inChapter 5 and Chapter 7 of this publication.

Air entrainment can be difficult to achieve if certaincontaminants are present in the RCA in sufficientquantities, and the measurement of air content in thefresh mixture can be complicated by the presence ofentrained and entrapped air in the reclaimed con-crete mortar (Wade et al 1997).

It also should be considered that the physical andmechanical properties of concrete products con-taining RCA may vary from those containing virginaggregate. For example, the strength and modulusof elasticity of RCA concrete may be lower and theCTE higher than for concrete prepared using virginaggregate when all other factors remain constant.Another example is that the potential for aggregateinterlock load transfer often is reduced when usingRCA coarse aggregate because the mortar com-prising a portion of the particles is less resistant toabrasion effects than most virgin aggregates. Differ-ences in strength and other physical properties oftencan be offset by modifying other aspects of the mix-ture design (e.g., reducing water-cementitous mate-rial ratio and/or including certain mineral admixtures)or the structure (e.g., increased concrete pavementthickness). Structural matters, such as load transfer,can usually be addressed with structural designmodifications (e.g., required use of dowel bars attransverse joints) (Wade et al 1997).

There also have been concerns about recycling oldconcrete with freeze-thaw durability or ASR prob-lems. However, modifications to traditional crushingand mixture design procedures have proven suc-cessful in preventing the reoccurrence of durabilityand reactivity problems in pavements containingRCA, as described in Chapter 6 of this publication.

Additional recommendations concerning the use ofRCA in concrete mixtures are presented in Chapter7 of this publication.

ASPHALT PAVEMENT ANDASPHALT-STABILIZED SUBBASERCA has been used successfully in new asphaltpavement and asphalt-stabilized subbase applica-tions. Typical RCA particle angularity and rough

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texture provide excellent potential for stability andsurface friction, and the use of asphalt to encapsu-late RCA particles effectively eliminates the poten-tial for clogging of drainage structures in subbaseapplications.

Unfortunately, the more absorptive nature of typicalRCA particles significantly increases asphalt binderdemand, which often increases costs prohibitively.

OTHER APPLICATIONSGranular FillCrushed concrete is an economical and highly stablematerial that is well-suited for granular fill applica-tions. This is a particularly good application for fineRCA products, which may be produced in quantitiesthat are excessive for subbase, concrete mixtureand other applications.

Erosion Control (Rip-rap)Most states allow the use of recycled concrete forerosion control (“rip-rap”) or slope stabilization(FHWA 2004). In this application, the concrete pave-ment is broken into pieces that are 6 in. (150 mm) orlarger. Maximum size often is dictated by aestheticconsideration and original pavement thickness (toavoid using large flat pieces). Protruding steel usu-ally is removed prior to use. An example RCA rip-rapinstallation is shown in Figure 20.

Innovative ApplicationsNumerous other applications for RCA products havebeen implemented, researched or suggested,including: soil stabilization, pipe bedding, landscapematerials, railroad ballast, agricultural soil treatments(similar to soil modification using lime), treatment ofacidic lake waters, trickling filters and effluent treat-ment, components of SO2 scrubbers, ingredients inmasonry block production, and formation of artificialreefs for establishing oyster beds. Additional detailsconcerning these applications can be found in Van-denbossche and Snyder (1993), FHWA (2004) andCMRA (2008).

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Property

Range of expected changes from similar mixtures using virgin aggregates

Coarse RCA only Coarse and Fine RCA

Workability Similar to slightly lower Slightly to significantly lower

Finishability Similar to more difficult More difficult

Water bleeding Slightly less Less

Water demand Greater Much greater

Air content Slightly higher Slightly higher

Table 4. Effects of RCA on Fresh Concrete Properties and Behavior (after FHWA 2007b, ACI 2001)


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PROPERTIES OF FRESH (PLASTIC)RCA CONCRETEThe use of RCA in concrete mixtures can alter theproperties and behavior of the fresh concrete (alsoknown as “plastic concrete”), mainly because of themore porous, rough-textured nature of the reclaimedmortar that comprises a portion of the RCA. Themagnitude of the effects varies with the nature andquantity of reclaimed mortar that is present. A sum-mary of the possible ranges of these effects on freshconcrete is presented in Table 4 and a brief discus-sion of each property effect is presented in the following sections. Appropriate techniques for suc-cessfully addressing any adverse effects also arediscussed in this section and in Chapter 7 of thispublication.

Workability, Finishability and WaterBleedingWell-rounded, compact aggregate particles withsmooth surface texture are most effective in pro-

When RCA is used in the production of new con-crete mixtures, its effect on the properties of thosemixtures can range from minimal to significant,depending upon the nature, composition and grada-tion of the RCA. For example, when little reclaimedmortar is present in coarse RCA and virgin fineaggregate is used, the handling characteristics andengineering properties of the resulting concrete willbe practically the same as if all virgin aggregate hadbeen used; if the new mixture contains only coarseand fine RCA, these characteristics and propertiesprobably will be quite different from those of tradi-tional concrete mixtures when all other mixturedesign factors remain constant. Changes in mixturedesign and admixture usage can reduce (and some-times eliminate) many differences in the propertiesof RCA concrete mixtures.

This chapter describes the impact of using RCA onthe properties of fresh (plastic) and hardened con-crete and describes measures that can be taken tomitigate any potentially negative effects.

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moting concrete workability. Many natural sands andgravels have these characteristics, but RCA particlestend to be angular and rough-textured, which canincrease the harshness of fresh concrete mixtures.The irregular shape and texture of coarse RCA parti-cles have generally not caused significant workabilityproblems. The use of fine RCA however, can greatlyincrease the harshness of the mixture as the angularRCA particles replace the more spherical conven-tional sands that often act as tiny ball bearings,decreasing the workability of the mixture and makingit more difficult to finish properly (Yrjanson 1989).Water bleeding from RCA concrete is generallyslightly less than that from mixtures prepared usingvirgin aggregates (Mukai et al 1979, Narud 1983).

To produce the same workability as a conventionalconcrete mixture, about 5 percent more water isrequired for a mixture containing coarse RCA (Mukaiet al 1979), and about 15 percent more water isneeded for a mixture containing both coarse and fineRCA (Buck 1976). This additional water demandincreases the water-cementitious materials (w/cm)ratio, resulting in corresponding decreases instrength.

For this reason, it is common to control workabilityby limiting the use of fine RCA in concrete mixturesto 30 percent or less replacement of natural sand.When greater amounts of fine RCA are used, chemical admixtures (such as water reducers andsuperplasticizers) and/or fly ash (which consists ofvery fine spherical particles) are useful in improvingconcrete workability. The Illinois DOT, for example,successfully used fly ash and small amounts of natural sand to utilize both coarse and fine RCA inthe concrete mixture for a new concrete inlay (VanMatre and Schutzbach 1989).

Water DemandThe higher absorption capacities of RCA (especiallyfine RCA) can lead to a rapid loss of workability,which can severely limit the time available forplacing and finishing the concrete. This may temptcontractors to add water at the jobsite, potentiallyresulting in concrete strength reductions and dur -

ability issues. Therefore, it is recommended that contractors not be allowed to add water in excess ofthe approved mixture design at the jobsite. Problemsassociated with the rapid loss of workability shouldbe addressed by altering and controlling the mois-ture content of the RCA before mixing.

Absorption problems have been addressed success-fully by washing or wetting the aggregate and main-taining it in a moist (e.g., saturated, surface-dry(SSD)) con dition until batching. On very small pro-jects it may be possible to modify mixing andbatching procedures to avoid absorption problems(e.g., adjusting batch water for RCA absorption, then combining RCA and water and allowing 15 minutesof soak time before combining with other batchingredients).

Air ContentAir contents of fresh concrete containing RCA oftenare up to 0.6 percent higher and are slightly morevariable than the air contents of fresh concretesusing conventional aggregates (Snyder and Van -denbossche 1993). This is generally assumed to becaused by the air that is entrained and entrapped inthe re claimed concrete mortar (Wade et al 1997).Because of this, it may be necessary to either in -crease total target air contents for RCA concretemixtures or to use air measurement systems thatmeasure only the air in the fresh paste (e.g., volu-metric air content measurement (ASTM C173/AASHTO T196) or the air void analyzer (AVA), asdescribed in Fick 2008 and Taylor et al 2006). Analternate approach is to use an aggregate correctionfactor to correct for air voids in the reclaimed mortar,as has been done in Wisconsin (Yrjanson 1989).

The use of RCA in new concrete mixtures shouldhave no impact on the effectiveness of air-entrainingadmixtures unless certain contaminants (e.g., asphaltor other petroleum-based materials) are present insufficient quantities. For example, the recycling ofasphalt and concrete together into a new concretesurface was considered the source of air entrain-ment problems on a project in Iowa (Bergren andBritson 1977).

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PHYSICAL AND MECHANICALPROPERTIES OF HARDENED RCACONCRETEThe effects of RCA on the physical and mechanicalproperties of hardened concrete (e.g., strength,elastic modulus, etc.) have been the subject of manystudies. The magnitudes of these effects can rangefrom non existent to significant, depending upon thenature, composition and gradation of the RCA. Asummary of the possible ranges of these effects onfresh concrete is presented in Table 5 and a briefdis cussion of each property effect is presented in thefollowing sections.

Changes in mixture design (e.g., reduced w/cmratio) and admixture usage (both chemical admix-tures and the use of supplemental cementitiousmaterials) can reduce (and sometimes eliminate)many of these effects; in other cases, it is simpler toconsider the expected RCA concrete properties inthe structural and geometric design of the pavementand develop the design accordingly. Appropriateapproaches to mixture proportioning modificationsand other structural or geometric adjustments arediscussed in some portions of this section and inChapter 7 of this publication.

StrengthConcrete containing coarse and/or fine RCA can beproduced with adequate levels of compressive andflexural strength for paving and other applications,

sometimes even with 100% replacement of virginaggregate with RCA (Yrjanson 1989, ACI 2001). Laband field tests also show adequate rates of strengthdevelopment for concrete mixtures using RCA.

When all other mixture design and curing parametersare held constant, RCA concrete strength generallyvaries directly with the strength of the source con-crete and varies inversely with the reclaimed mortarcontent (both coarse and fine RCA) and water-to-cement ratio for the new concrete mixture (Hansenand Narud 1983). Hansen (1986) found that strengthreductions range from approximately 0 to 24 percentwhen only coarse RCA is used, and can reach about40 percent when both coarse and fine RCA is used.The majority of the strength loss was attributed toparticles passing the No. 10 (2 mm) sieve. Largestrength reductions have not been observed on RCApaving projects in the U.S., as is documented inChapter 6 of this publication. Figure 21 presents asummary of compressive strength test data showingthe relatively minor strength reduction for concretecontaining only coarse RCA.

Strength reductions in RCA have been attributedto the inherently weaker composition of the RCA(caused by the reclaimed mortar component) andthe greater number of bonded interfaces in RCAconcrete (i.e., more potential failure surfaces,including virgin aggregate-old mortar, virgin ag -gregate-new mortar, and old mortar-new mortar)(Snyder 1994).

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Compressive strength 0% to 24% less 15% to 40% less

Tensile strength 0% to 10% less 10% to 20% less

Strength variation Slightly greater Slightly greater

Modulus of elasticity 10% to 33% less 25% to 40% less

CTE 0% to 30% greater 0% to 30% greater

Drying shrinkage 20% to 50% more 70% to 100% more

Creep 30% to 60% greater 30% to 60% greater

Permeability 0% to 500% greater 0% to 500% greater

Specific gravity 0% to 10% lower 5% to 15% lower

Table 5. Effect of RCA on Physical and Mechanical Properties of Hardened Concrete (after FHWA 2007b, ACI 2001, Hansen 1986)


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Blends of virgin and recycled fine aggregates (up toabout 30 percent replacement) can be used in con-crete mixtures to produce concrete with higherstrength than can be obtained from using eithervirgin or re cycled aggregates alone (Fergus 1981).This increase in strength has been attributed to im -provements in the gradation of the blended fineaggregate, par ticu larly over the No. 30 and No. 60(600- and 300-µm) sieves, where RCA fines tend tobe deficient (Fergus 1981).

Strength reductions from the use of RCA in concretemixtures can be offset (or eliminated) by modifyingthe concrete mixture design to reduce the w/cm ratio(often in combination with the use of water-reducingadmixtures) and/or the use of mineral admixturessuch as fly ash or slag cement.

Modulus of ElasticityThe static modulus of elasticity of RCA concrete, likestrength, is affected mainly by reclaimed mortar con-tent and the w/cm ratio. When other mixture designparameters are held constant, the elastic modulus ofconcrete containing only coarse RCA is typically 10 to33 percent lower than that of conventional concrete.When both coarse and fine RCA are used, the differ-ence increases to 25 to 40 percent (ACI 2001). Thesereductions are attributed to the increased overallmortar content (new and reclaimed), which has alower elastic modulus than most virgin aggregate.

Coefficient of Thermal Expansion andContraction (CTE)Tests of cores retrieved from several test sitesaround the U.S. suggest that the CTE of RCA concrete is typically about 10 percent higher thanfor conventional concrete (the observed range wasapproximately up to 30 percent higher) (Wade et al1997). The CTE is primarily a function of virginaggregate type and content.

Increased CTE values cause higher concrete pave -ment curling stresses when other factors remainconstant. In jointed concrete pavements (e.g., JPCPand JRCP), these in creases in curling stresses canusually be offset by reducing the panel dimensions.

Drying ShrinkageDrying shrinkage is primarily a function of paste con-tent and w/cm ratio and is restrained by virgin aggre-gate particles. Because concrete manufacturedusing RCA generally presents a higher paste content(con sidering both new and reclaimed paste), it is no surprise that studies have found 20 to 50 percenthigher shrinkage in concrete containing coarse RCAand natural sand, and 70 to 100 higher shrinkage inconcrete containing both coarse and fine RCA(ACI 2001 after BCSJ 1978).

Increased drying shrinkage values cause higher con-crete pavement moisture warping stresses whenother factors remain constant. In jointed concretepavements (e.g., JPCP and JRCP), these increasesin warping stresses can usually be offset by reducingthe panel dimensions.

CreepThe creep of RCA concrete typically is 30 to 60 per-cent higher than that of comparable concrete pro-duced using virgin aggregate. This is because creepis proportional to paste content, which can be up to50 percent higher in RCA concrete (ACI 2001).

The increased potential for creep in RCA concrete isactually beneficial because it can reduce long-termcurling and warping effects (caused by temperatureand drying shrinkage gradients) through a relaxationeffect, thereby reducing (after a time) slab stressescaused by these gradients.

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Figure 21. Compressive strengths of concretes containing dif-ferent combinations of coarse and fine aggregates from virginand recycled sources (Won 2007).

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PermeabilityThe rates of deterioration of many types of concretedistress (particularly materials-related distresses,such as freeze-thaw damage, D-cracking and ASR)are strongly affected by the ability of the hardenedconcrete to absorb water. The overall permeabilityand absorption characteristics of the concretedepend upon both the absorption capacity of theincluded aggregate and the permeability of the con-crete matrix (which is strongly correlated with w/c).

A study by Rasheeduzzafar and Khan (1984) indi-cated that there is no significant difference in perme-ability of concrete produced using RCA (whencompared to concrete produced using conventionalaggregate) when the w/c of the new concrete isgreater than or equal to the w/c of the concrete usedto produce the RCA. However, when the w/c of thenew concrete is less than that of the concrete usedto produce the RCA, the water absorption (and, it isassumed, the permeability) of the RCA concrete maybe up to three times greater than that of similar con-crete made using virgin aggregate. This same studyfound that reducing the w/c of the RCA concrete by0.05 to 0.10 was effective in compensating for theuse of RCA in terms of concrete absorption and per-meability.

Specific GravityThe density of RCA concrete is typically 5 to 15 per-cent lower than that of concrete manufactured usingvirgin aggregate (Hansen 1986). This is becausereclaimed mortar has a much lower specific gravitythan most virgin aggregates and can easily comprise

50 percent of the RCA volume, which reduces theoverall specific gravity of the concrete mixture. As aresult, a given volume of RCA may have significantlyless weight or mass than an equal volume of virginaggregate. For this reason, RCA must be substitutedfor virgin aggregate on a volumetric (rather thanweight) basis.

DurabilityThe effects of RCA on various aspects of concretedurability (e.g., freeze-thaw durability, ASR, etc.)also have been studied by many researchers. Thesestudies suggest that RCA concrete can be highlydurable, even when the RCA is produced from con-crete with durability problems, provided that the mix-ture proportioning (including the use of chemical andmineral admixtures) is done properly and the con-struction (including concrete curing) is of goodquality.

A summary of the impact of using RCA in concretemixtures on the durability of those mixtures is pre-sented in Table 6 and a brief discussion of eachproperty effect is presented in the following sections.Appropriate approaches to mixture proportioningmodifications and other adjustments are discussedin some portions of this section and in Chapter 7 ofthis publication.

Freeze-Thaw ResistanceMost studies of RCA concrete freeze-thaw resis-tance show no significant difference in the durabilityof RCA concrete and conventional concrete when

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Freeze-thaw durability Depends upon air void system Depends upon air void system

Sulfate resistance Depends upon mixture Depends upon mixture

ASR Less susceptible* Less susceptible*

Carbonization Up to 65% greater Up to 65% greater

Corrosion rate May be faster May be faster

Table 6. Effect of RCA on Concrete Durability (after FHWA 2007b)

* For new concrete mixtures utilizing coarse or coarse and fine RCA to be less susceptible to ASR, the distress mechanism must be identified andproper mitigation techniques should be implemented during the mixture design procedure.


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tend to be less susceptible to ASR than those con-taining conventional silicate aggregates.

Severely ASR-damaged concrete has been success-fully recycled into new concrete with little evidence ofrecurrent ASR damage. This usually is accomplishedby using a low-alkali cement (e.g., Type II or TypeV), a class F fly ash (either as an addition or partialreplacement of cement), slag cement and/or a loww/cm ratio (PCA 2007). If fly ash and/or slag cementare being used as a means to mitigate ASR in con-crete utilizing RCA from an ASR-damaged concrete,the appropriate dosage levels should be determinedby using ASTM C1567. Other mitigating techniquesinclude limiting the content of RCA fines, usingadmixtures such as lithium nitrate, and reducing slabexposure to moisture.

For example, the Wyoming DOT successfully recy-cled several sections of ASR-damaged Interstatehighway pavement into new concrete pavement inthe 1980’s; one of these projects is described as acase study in Chapter 6 of this publication. Whilemicroscopic examinations of cores retrieved fromthese pavements shows evidence of minor ASRactivity, these pavements have been in service formore than 20 years and show little, if any, evidenceof recurrent ASR damage.

Carbonation and CorrosionResearch indicates that rates of carbonation of con-crete containing RCA derived from carbonated con-crete is up to 65 percent higher than that of concretecontaining only conventional aggregate. These rates(and depths of carbonation) are significantly de -creased with decreases in the mixture w/cm ratio.

Increased surface carbonation can cause more rapidcorrosion of embedded steel reinforcing, particularly inlocations where chloride concentrations are high(caused by deicing chemicals or a marine environ-ment). This accelerated corrosion can be offset bylowering the w/cm ratio of the RCA concrete (ACI2001 after BCSJ 1978 and Rasheeduzzafar and Khan1984). Additional depth of concrete cover over thereinforcing also will effectively reduce corrosion rates.

the concrete from which the RCA is manufactured isdurable. Studies conducted in Japan using relativelylow quality concrete indicated lower resistance forfreezing and thawing if the RCA concrete includedboth coarse and fine RCA; when only coarse RCAwas used, the RCA concrete durability was similarto that of the source concrete (ACI 2001 afterBCSJ 1978).

There also have been successes in recycling con-crete with known freeze-thaw durability deficiencies(e.g., D-cracking) into coarse RCA for new concretemixtures. In such cases, the maximum particle sizeusually is limited to ¾ in. (19 mm) because it is thelargest aggregate particles that expand the most anddo the most damage during freeze-thaw cycles.Other steps commonly taken when recycling D-cracked concrete include the use of fly ash and areduced w/cm ratio (to create a stronger, less perme-able matrix that will pass less water to the aggregate)and the use of joint seals and pavement drainagesystems (to prevent critical saturation of the aggre-gate particles). When these steps are taken, the RCAconcrete generally has much better freeze-thaw dura-bility than did the source concrete. Two of the casestudies described in Chapter 6 of this publicationinvolved recycling D-cracked pavement.

Alkali-Silica Reactivity (ASR)ASR occurs when aggregates containing reactive sil-icates react with alkalis contained in the cement toform a highly expansive gel that surrounds and pen-etrates the aggregate particles. The disruptiveexpansive forces cause the aggregate particles andsurrounding mortar to crack and deteriorate (Farnyand Kerkhoff 2007).

RCA generally includes significant amounts ofreclaimed mortar, which is not inherently reactive;therefore, the concentration of reactive silicates inRCA is generally reduced. In addition, significantquantities of reactive fine aggregate particles arecontained in fine RCA, which can be processed intoapplications other than new concrete mixtures. As aresult, new concrete mixtures containing properlyprocessed RCA from an ASR-damaged concrete

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This section describes several RCA pavement con-struction projects and studies and discusses whatwas learned from them.

SELECT CASE STUDIES OFPAVEMENTS WITH RCACONCRETE MIXTURESIn 1993, the FHWA sponsored a study (Wade et al1997) that included a comprehensive evaluation ofthe properties and performances of 9 pavement pro-jects that featured the use of RCA in new concretepaving. At the time of evaluation, these pavementsections ranged in age from 6 to 15 years andincluded a broad range of pavement designs, trafficloads, and environmental conditions. The studyincluded pavements that had performed acceptably,as well as those that had not performed acceptably.Many of the selected sites included “control sec-tions” (similar pavement sections constructed withconventional concrete rather than RCA concrete),while others featured alternate designs or other fea-tures. Data collected included field condition (dis-tress) information, falling weight deflectometer testresults, results of strength and mechanical propertytests on cores, etc.

In 2006, the University of New Hampshire’s Recy-cled Materials Resource Center (RMRC) conductedfollow-up visits to all of the sites evaluated in theFHWA 1993 study (these sections were aged 18 to27 years in 2006), and also evaluated additionalRCA concrete pavement sites in Iowa and Illinois.This study included the collection of pavement

Using existing concrete pavements as a source ofaggregate for new pavement construction is not new.As mentioned, a portion of U.S. 66 was constructedusing RCA concrete shortly after World War II, andmany European countries utilized build ing rubble innew concrete pavement construction just after WorldWar II (Yrjanson 1989).

After those early recycling efforts, little work wasdone in the U.S. in the area of concrete recyclinguntil the mid-1970’s, when interest and activity incon crete pavement recycling increased. By the early1980’s, many concrete pavements were being recy-cled into new concrete pavement systems. A 1994literature review (Snyder et al 1994) identified nearly100 RCA concrete paving projects in the U.S.,including several where D-cracked or ASR-damagedpavements were recycled; many more projects haveutilized RCA in pavement foundations, subbaselayers and other applications. Most of these projectshave performed well and are considered successes.

Some projects, however, have not been successfuland have offered lessons in the use of RCA in pave-ment construction. For example, some early con-crete recycling projects indicated the need to includeat least some natural sand in RCA concrete mixturesto improve workability (Yrjanson 1989). There alsohave been cases where some JRCP constructedusing RCA concrete quickly developed transversecracks that deteriorated, indicating the need toadjust certain pavement design elements whenusing RCA concrete (mainly joint spacing, but alsoreinforcing steel content in JRCP) (Raja and Snyder1991).

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condition (distress) data and tests of cores from the midpanel and joint areas (strength tests, joint facetexture measurements, petrographic and micro-scopic examinations, etc.). The full details of thisstudy are described by Sturtevant (2007).

Some of the key findings of these studies include thefollowing (Wade et al 1997, Sturtevant 2007):

• The measurement of air content in fresh RCAconcrete may be accurately obtained using volumetric techniques (e.g., the “Roll-O-Meter”)rather than pressure techniques (e.g., the“Press-R-Meter”) because of the air contentand more porous nature of reclaimed mortar.

• Measures of the CTE were generally higher forRCA concrete than for conventional concretewhen other mixture design parameters wereheld constant.

• Modulus of elasticity test values for the agedcores were generally 1 to 18 percent lower forRCA concrete than for conventional concrete.Most literature reports a greater difference (15to 50 percent) for younger concrete specimens.The reduced differences were attributed to modi-fied mixture designs for the RCA concrete in thisstudy (e.g., lower w/cm ratio, etc.) and the bene-fits of extended curing.

• Tests of cores showed that the RCA concrete onthese projects had compressive strengths similarto or higher than those of their companion con-trol sections. This was, again, caused by areduced w/cm ratio and other modifications tothe RCA concrete mixture designs.

• Reducing coarse RCA top size may be effectivein preventing the recurrence of D-cracking, but italso reduces the texture available for aggregateinterlock load transfer at crack and joint faces.The use of dowel load transfer devices and properly designed longitudinal reinforcing (forCRCP and JRCP applications) often are essential to good performance.

• D-cracked or ASR-damaged pavement can besuccessfully recycled into coarse and fine RCAfor use in new concrete pavement with appro-

priate adjustments to the concrete mixturedesign and structural design of the pavement(e.g., panel lengths, load transfer design, etc.).

• Recycled concrete aggregate should be con -sidered an “engineered material” and concrete mixture designs and pavement structural designsshould be adjusted according to the specificproperties of the material being used to ensuregood performance.

Specific details on two of the more interesting projects evaluated under these national studies(I-80 in Wyoming and U.S. 59 in Minnesota) are presented below.

I-80 near Pine Bluff, Wyoming –Recycling an ASR-Damaged PavementDuring the early 1980’s, a section of I-80 west ofPine Bluffs, Wyoming was suffering from extensivealkali-aggregate damage (Figure 22), includingextensive map cracking, potholes and joint spalling.Asphalt concrete had been used to repair some pot-holes and for placing localized overlays to improveride quality, but these soon failed due to reflectioncracking and delamination. Further restoration andoverlay options were considered unfeasible becauseof the extent of the deterioration. Reconstruction withvirgin aggregate also was ruled out because therewas no suitable aggregate source near the site and

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Figure 22. Photo of I-80 in Wyoming prior to recycling. NoteASR damage throughout (Photo credit: Wyoming DOT).

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disposal and hauling costs would be high. Re cyclingthe existing concrete pavement into a new concretepavement surface was selected as the most feasibleand economical rehabilitation alter native for this section.

In 1985, the original concrete pavement (an 8-in.[200-mm] thick JPCP) was removed, along with 2 in.(50 mm) of the underlying crushed stone subbaseand the asphalt shoulders. The new pavement sec-tion consisted of a 10-in. (250-mm) JPCP on theremaining 4-in. (100-mm) crushed stone subbase.The transverse joints were skewed and placed at“random” intervals of 14, 16, 13, and 12 ft (4.3, 4.9,4.0, and 3.7 m). No load transfer devices wereinstalled at the transverse joints.

To ensure the feasibility of the RCA concrete mixture,several ASTM tests were conducted (i.e., C227,C289 and C441) to determine combinations of materials that would avoid recurrence of the ASRproblems in the original pavement. These tests indi-cated that further problems with the reactive aggre-gate in the existing pavement could be controlled by:1) using a low-alkali (less than 0.60 percent Na2O)Type II cement, 2) blending the recycled concreteaggregate with a quality virgin aggregate, and 3)using a Class F fly ash meeting the requirements ofTable 2A of ASTM C618 for reduction of expansion(Swedeen 1990).

The selected RCA concrete mixture design includeda 60:40 ratio of coarse to fine aggregate, a 65:35ratio of recycled to virgin coarse aggregates (1-in.[25-mm] top size), and a 22:78 ratio of recycled tovirgin fine aggregates. Class F fly ash comprisedapproximately 30 percent of the volume of thecementitious material, and a w/cm ratio of 0.38 wasused. An air-entraining admixture was used to pro-duce average total air contents of 5.5 percent.A control section was constructed in the eastboundlanes using all virgin aggregate, no fly ash, and aw/cm ratio of 0.44.

Construction was accomplished using typical con-struction equipment and procedures. Flexural beamtest results averaged 700 psi (4.8 MPa) for the

recycled concrete at 28 days. Cores obtained fromthe pavement in 1994 and 2006 indicated higherstrength for the RCA concrete than for the controlsection, probably due to the use of fly ash and amuch lower w/cm ratio in the recycled mixture(Wade et al 1995, Sturtevant 2007).

The control and RCA concrete sections were bothopened to traffic in late 1985 and have sustainedapproximately the same traffic loadings and ESALapplications. The two-way ADT has increased fromabout 4,400 (35 percent trucks) in 1985 to more than8,000 (45 percent trucks) in 2006. Although the areais relatively dry, modest levels of faulting began todevelop at the joints (which were undoweled) underthe heavy traffic loadings. After almost 20 years ofservice, the Wyoming DOT rehabilitated both therecycled and control sections in 2002 through dowelbar retrofit, diamond grinding and resealing the joints(Figure 23). Since that time, both sections have performed very well, providing excellent ride qualityand developing very little distress.

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Figure 23. Photos ofWyoming I-80 concrete recycling project near PineBluff in 2006 (Photo credit:University of New HampshireRecycled Materials ResearchCenter).


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The success of this project led to the reconstructionof a total of 28 centerline miles of ASR-affectedpavement on I-80 using RCA concrete between1985 and 1991. Wyoming DOT pavement manage-ment data from 2006 indicated a Pavement Condi-tion Index (PCI) of 99 to 100 (almost perfect) overthe entire 28-mile length of concrete pavement(Sharpe 2006).

There is evidence of some ASR activity in coresrecently obtained from the RCA concrete portion ofthe project (Sturtevant 2007) but progression is slowand only a few localized signs of ASR are visibleon the pavement surface. The sections are ex -pected to easily achieve their 30-year design lives(Sharpe 2006).

U.S. 59 near Worthington, Minnesota –Recycling a D-cracked PavementThe Minnesota DOT selected a 16-mile (26-km)D-cracked segment of U.S. 59 near Worthington fortheir first concrete recycling project. This project,which was completed in 1980, was the first majorconcrete recycling project in the United States inwhich a D-cracked concrete pavement was usedto furnish coarse RCA for new concrete pavement.

The original concrete surfacing was constructed in1955 and consisted of a “thickened edge” concretepavement (9 – 7 – 9 in. [230 – 180 – 230 mm])placed over a minimum of 3 in. (75 mm) of unstabi-lized subbase, which was placed on a pre-existingasphalt surface. At the time of recycling, the existingconcrete pavement was showing signs of extensiveD-cracking. This concrete was recycled to providecoarse RCA for a new 8-in. (200-mm) JPCP. Thefine RCA was placed in a construction platform layer1 in. (25 mm) thick atop the remaining unstabilizedsubbase.

The mixture design featured 100 percent coarseRCA, 100 percent natural sand fine aggregate,replacement of 15 percent (by weight) of cementwith 20 percent (by weight) of Class C fly ash, and aw/cm ratio of 0.44. The maximum particle size forthe coarse RCA was limited to 3⁄4 in. (19 mm) to

reduce the potential for recurrent D-cracking in thenew concrete pavement. The average slump and aircontent at the job site were 1.5 in. (38 mm) and 5.5percent, respectively. Compressive strengths aver-aged 4,580 psi (31.6 MPa) after 60 days.

Paving was performed using a traditional slipformpaving machine and standard paving techniques.The new transverse joints were skewed, undoweled,and spaced at 13-16-14-19-ft (4.0-4.9-4.3-5.8-m)intervals. Longitudinal edge drains also were pro-vided throughout the project.

The pavement was opened to traffic in late 1980, atwhich time the two-way ADT was about 2,150 vehi-cles per day. By 2006, the ADT had increased to anaverage of about 3,225, including 230 heavy com-mercial vehicles per day.

Significant faulting developed quickly after construc-tion. A 1994 survey reported average faulting ofnearly ¼ in. (6.1 mm) in the outer wheelpaths andload transfer efficiencies averaging 32 percent(Wade et al 1997). The development of faulting wasnot surprising given the lack of dowels at the trans-verse joints. Many panels could be observed rockingunder heavy traffic loads, and the longest panelshad begun to develop transverse cracks. Low-severity joint spalling had developed at 70 percentof the transverse joints by 1994, probably due tojoint sealant problems and excessive slab move-ments under heavy traffic loads (Wade et al 1997).

Cores obtained in 1994 (and at later times) weretested for strength, freeze-thaw durability, CTE andother properties. While most of the concrete proper-ties were comparable to those of good conventionalconcrete, freeze-thaw testing (ASTM C666 orAASHTO T161 Procedure B, modified) indicated thatthe concrete was not durable. Microscopic examina-tion of polished concrete specimens from the coresindicated a marginal air void system and somemicrocracking in the reclaimed mortar, but no evi-dence of recurrent D-cracking. Examination of failedfreeze-thaw specimens showed deterioration initi-ating at large entrapped air voids.

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The Minnesota DOT considered retrofitting dowelson this project to address faulting and slab move-ment problems as early as 1994, but was concernedthat D-cracking or other freeze-thaw durability prob-lems might re develop at any time. They continued tomonitor the pavement durability (and the develop-ment of additional faulting and slab cracking) andnoted no additional freeze-thaw-related deteriorationover the years. One possible explanation for the lackof freeze-thaw damage is that the field saturation conditions do not approach those of the ASTM test(caused by the presence of pavement drains andother factors).

In 2004, a major rehabilitation project was finallyundertaken, with activities including replacement ofsome long panels that had cracked, retrofit dowels(outer wheelpaths only), diamond grinding (toremove the accumulated faulting) and joint sealing(Figure 24). Since that time, the pavement has pro-vided a smooth, quiet ride. A 2006 condition surveyindicated very little additional cracking or deteriora-tion. This suggested that, after 26 years of service,this pavement still had a good deal of remaining ser-vice life and the concrete material itself was sounddespite being constructed using RCA from a badlyD-cracked pavement.

It appears that the RCA concrete generally has performed well on this project and that the primaryperformance-related problems have been related todeficiencies in the structural design. Had dowel barsbeen included in the 1980 pavement reconstruction,it seems likely that very little maintenance or reha -bilitation would have been required, although thelongest panels (19 ft [5.8 m]) may still have devel-oped cracking because they were significantly longerthan the suggested maximum joint spacing of 15 ft(4.6 m) for this pavement thickness/subbase com -bination.

There was no evidence of recurrent D-cracking onthis project, indicating that at least some pavementswith a history of durability problems can be success-fully recycled into new concrete paving mixtures.

I-94 near Paw Paw, Michigan –Learning from FailureDuring the mid-1980’s, the Michigan DOT con-structed several RCA concrete pavements on I-94with a thickness of 9 in. (230 mm) and 41-ft [(2.5-m)steel mesh-reinforced panels. These pavementsdeveloped intermediate transverse cracks thatrapidly faulted and spalled. It should be noted thatintermediate cracking is expected to occur on JRCP,but the reinforcing steel is expected to hold thecracks tight so that aggregate interlock can be maintained, thereby preventing the cracks from deteriorating.

On these projects, the coarse RCA was crushed to amaximum size of ¾ in. (19 mm) to prevent the recur-rence of D-cracking, which had been present in theoriginal concrete. The small top size of the coarseRCA (which included reclaimed mortar) re sulted inthe formation of cracks that were very straight bothacross and through the slab (Darter 1988), offeringvery little texture for aggregate interlock load transfer


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Figure 24. Trunk Highway 59 near Worthington, MN in 2006,after 15 years of service and 2004 rehab.


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(Snyder and Vandenbossche 1993). In addition, thereclaimed mortar is believed to have been less resis-tant to abrasion than virgin aggregate, resulting inrapid loss of aggregate interlock load transfer acrossthe reinforced cracks (Yrjanson 1989). No significantproblems were observed at the doweled joints.

The RCA was not solely responsible for the prob-lems that these projects suffered, however. In theinvestigation of one of these projects, Darter (1988)noted a series of design and construction flaws that,in combination with the use of the RCA, resulted inthe rapid deterioration of the pavements. Theseflaws included insufficient slab thickness, incompat-ible joint spacing between the reinforced mainlinepavement and the nonreinforced concrete shoulder,and the absence of a separation layer beneath thepermeable (open-graded) subbase, which allowedsignificant foundation settlement (Darter 1988). Inaddition, subsequent studies by Raja and Snyder(1991) indicated that the amount of longitudinal rein-forcement (0.16 percent by area of concrete) wasinadequate, particularly when considering the higherCTE of RCA concrete and the reduced potential foraggregate interlock at the transverse cracks.

These factors and the performance of these pave-ment sections illustrate the need for ensuring com-patibility between the pavement structural designdetails and the concrete mixture components andproportions. Specific recommendations are providedin Chapter 7 of this publication.

I-10 near Houston, Texas – Using 100Percent RCA in ConcreteIn 1995, the Texas DOT began a project to replace adistressed portion of I-10 near Houston using RCA

produced from the existing concrete pave ment,which was a CRCP that had carried heavy traffic foralmost 30 years (Won 2007). The concrete for thenew CRCP was manufactured using 100 percentcoarse and fine RCA.

The Texas DOT required that the RCA meet thesame specification requirements as virgin aggregateintended for use in concrete paving mixtures. Testsof the RCA (which contained siliceous river gravel[SRG] from the original concrete) generally produced specific gravity, mortar content, absorption and L.A.abrasion values in the ranges described previouslyin this publication.

Several cores were retrieved from representativelocations along the project and were used to deter-mine the in-situ properties of the concrete (i.e.,strength, elastic modulus, CTE, permeability, etc.).These tests indicated relatively low, but acceptable,strength and elastic modulus values for this 100 per-cent RCA concrete, as shown in Table 7.

Table 7 also shows unusually low CTE and perme-ability values for the RCA concrete – similar to orbetter than would be expected from conventionaland high-performance concrete. Higher values wereexpected because of the high reclaimed mortar con-tent of the RCA concrete. The low permeability mayindicate an absence of microcracking due to themore elastic nature of the RCA concrete. Won(2007) offered no explanation for the low expansionand contraction CTE and permeability values, butdid observe that they probably contributed to theexcellent performance of the constructed pavement.

The contractor initially had some difficulty in pro-ducing RCA concrete with consistent workability.

Property I-10 RCA concrete

28-Day compressive strength 4,615 psi (31.8 MPa )

28-Day elastic modulus 2.58 x 106 psi (17.8 MPa)

Coefficient of thermal expansion and contraction (CTE) 4.7 to 5.3 µε/°F (8.5 to 9.5 µε/°C)

Permeability (ASTM C1202/AASHTO T277) 466 coulombs (very low permeability)

Table 7. Selected Average in-situ RCA Concrete Properties for I-10 (after Won 2007)

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These problems were found to be caused by inade-quate moisture control of the recycled aggregatestockpiles. The situation was remedied with theinstallation of improved stockpile sprinkler systems.

There also were some problems with consistency ofconcrete strength as the averages of 10 flexural testresults often failed to meet the specified minimumvalue. These failures were generally the result ofone or two exceedingly low test results, probablydue to mixture variability and/or specimen handling.At the time, the contractor was required to modifythe mixture design to develop higher averagestrength. Since that time, the Texas DOT has recog-nized the sensitive nature (with regard to strengthand work ability) of concrete mixtures containing highcontents of fine RCA. In 1999, the Texas DOTdeveloped a special provision to limit the fine RCAcontent in concrete mixtures to 20 percent of allfine aggregate.

No significant adjustments in paving operations wererequired by the use of 100 percent coarse and fineRCA in the concrete (Won 2007).

After 12 years of service, the performance of the RCACRCP (Figure 25) has been described as excellent,with narrow crack widths, few minor spalls, no pun-chouts and none of the meandering cracks andspalls that have typically been associated with theuse of SRG in Texas CRCP (Won 2007). The trans-verse crack spacing distributions in this CRCP havebeen similar to those of CRCP containing virgin lime-stone aggregate (Won 2007). The relatively lowelastic modulus of the RCA concrete and the goodbond between the old and new mortar are consid-ered key factors in the excellent performance of thispavement to date.

PERFORMANCE OF CONCRETEPAVEMENT STRUCTURES WITHRCA IN SUBBASE LAYERS ANDFILL APPLICATIONSRCA is widely used in concrete pavement subbaselayers and fill applications with great success. Thereappear to be no documented pavement performance

problems that are related to structural deficiencies inany properly designed and constructed foundationplacement using RCA. There have been concernswith the impact and efficacy of concrete recycling inurban areas, as well as some problems with the useof RCA materials in drainable foundation layers. Thefollowing section address these aspects of usingRCA in pavement foundation layers.

Urban Recycling: Eden’s Expressway,Chicago, Illinois

Recycled concrete was used in the 1978 recon -struction of the Eden’s Expressway (I-94 through thenorthern suburbs of Chicago). This very high-profileproject was notable for several reasons (Dierkes1981, Krueger 1981):

• It was the first major urban freeway in the U.S.to be completely reconstructed.

• It was the largest highway project on which con-crete recycling had been used.

• It was the largest single highway contract everawarded in the U.S. at that time, with a total project cost of $113.5 million (1978 dollars).

• It was the first major recycling effort in the U.S.involving a mesh-reinforced concrete pavement.

At that time, the Illinois DOT did not allow the use ofRCA in new concrete surface layers, but did permitits use in subbase layers and fill applications, which


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Figure 25. Photo of I-10 RCA CRCP near Houston, Texas.

Figure 26. Concrete recycling operation set up inside of cloverleaf interchange.


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remaining 15 percent was used as a 3-in. (75-mm)unstabilized subbase over the chemically modified/stabilized subgrade. An asphalt-treated subbase and10-in. (250-mm) CRCP were placed over the RCAsubbase (NHI 1998).

This pavement has provided excellent service fornearly 30 years under extremely heavy traffic (upto 170,000 vehicles per day in 2007). This 1978recycling project demonstrated the feasibility (andeconomy) of completely recycling and reconstructinga high-volume urban concrete expressway. Just onemeasure of the savings realized was the estimated200,000 gallons (757,000 liters) of fuel that wouldhave been consumed in disposing of demolishedconcrete and hauling virgin aggregate (NHI 1998).

was an option on this project. Although there was anadequate supply of good quality aggregate in theChicago area, the 18-mile (29-km) haul distancefrom the stockpile to the job site would have requireda 3-hour round trip during daytime traffic conditions,so the recycling option was exercised (NHI 1998).

The crushing plant was set up in an interchangecloverleaf area (Figure 26). This area was heavilypopulated, so noise was a serious concern. Crush -ing operations were suspended from midnight until6 a.m. every day, and some modifications to typicaloperational procedures were instituted (e.g., truckdrivers were not allowed to bang their tailgates tohelp discharge materials from the truck beds).

About 350,000 tons (318,000 metric tons) of the oldpavement was crushed at this site. About 85 percentof the RCA produced was used in fill areas, while the

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Sieve opening Percent finer (mass)

>1.5 in. (38 mm) 97

1.5 in. (38 mm) 68

1.0 in. (25 mm) 53

3⁄4 in. (19 mm) 34

1/2 in. (13 mm) 26

3⁄8 in. (9.5 mm) 13

No. 4 (4.75 mm) 0

Table 8. Typical Grading of RCA Produced using a Jaw Crusher set to an Opening of 1 in. (25 mm) (after ACI 2001)


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Production ProcessesJaw crushers are most useful for the first stage ofcrushing operations because they usually can handleremaining embedded steel (if any is present). Sec-ondary crushers should be selected with considera-tion of the type of product desired. Jaw crusherstend to produce fewer fines than impact or conecrushers, resulting in higher yields of coarse RCA,which often is more useful than fine RCA, particu-larly in new concrete mixtures. Table 8 presents atypical gradation for concrete crushed using a jawcrusher set to an opening of 1 in. (25 mm). Impactand cone crushers often are more effective in re -moving most of the reclaimed mortar, producingcoarse RCA that looks and behaves similarly to theoriginal virgin aggregate in the source concrete.Impact crushers also can supply particle size distrib-utions that are well-suited for constructing unboundfoundation layers (ACI 2001).

“Closed system” aggregate processing plants arepreferred because they allow greater control over

RCA PRODUCTIONGuidelines for the production of RCA are available inAppendix A. Guidelines for Removing and CrushingExisting Concrete Pavement near the end of thispublication.

Source MaterialsDetermine the quality and properties of any candi-date source materials. If the pavement to be recy-cled is still in place, a materials engineer should visitthe site to observe the type and extent of any dis-tresses present, and to retrieve samples for visualinspection and laboratory evaluation (FHWA 2007b).With proper care in demolition and processing,existing concrete pavement usually can be recycledto produce aggregate for new paving applications;building demolition materials may contain consider-able amounts of contaminants and should be eval -uated carefully prior to selection for use in newpaving applications.

Chapter 7. Recommendations for UsingRecycled Concrete

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the aggregate particle size distribution and providea more uniform finished material (ACI 2001,Hansen 1986).

Fine impurities (e.g., dirt from pavement foundationsor plaster and gypsum from building demolition) usu-ally can be reduced to tolerable levels by screening.Wet screening is useful in eliminating lightweightcontaminants.

StockpilingCoarse RCA can be stockpiled using the same tech-niques and equipment as traditional coarse aggre-gate materials. Fine RCA stockpiles generally needto be protected from precipitation to reduce thepotential for secondary cementing due to hydrationof exposed and previously unhydrated (or partiallyhydrated) cement grains. As with virgin fine andcoarse aggregates, more than two separate stock-piles may be necessary to allow the production ofaggregate blends that meet project specifications.

Moisture control of stockpiles is essential in ensuringthe production of uniform RCA concrete. CoarseRCA stockpile sprinkler systems may be useful incontrolling absorption of mixture water and theresulting rapid loss of workability.

USE IN PAVEMENT SUBBASELAYERSThe following sections provide recommendationsand rationale concerning various aspects of usingRCA in pavement subbase layers. A detailed speci -fication concerning the use of RCA for unstabilizedsubbases can be found in AASHTO M319 and gen-eral guidelines are available in Appendix B. Guide-lines for Using RCA in Unstabilized (Granular)Subbases near the end of this publication.

Quality RequirementsThe final report for NCHRP Project 4-31 (Saeed2008) identifies several properties of recycled aggre -gate subbase materials that influence the perfor -mance of the overlying pavement. These propertiesinclude aggregate toughness, frost susceptibility,shear strength and stiffness. The following tests arerecommended for evaluating these properties: Micro-Deval (AASHTO T327), Tube Suction*, Static Triaxial(AASHTO T234) and Repeated Load Tests*, andResilient Modulus* (* indicates test proceduredescribed in Saeed et al 2001).

Saeed and Hammons (2008) also have provided amatrix (Table 9) that summarizes recommendations

Tests and Test Parameters

Traffic High Med. High Low Med. Low

Moisture High Low High Low High Low High Low

Climate Freeze Nonfreeze Freeze Nonfreeze

Micro-Deval Test (percent loss) < 5 percent < 15 percent < 30 percent < 45 percent

Tube Suction Test (dielectric constant) ≤ 7 ≤ 10 ≤ 15 ≤ 20

Static Triaxial Test(Max. Deviator

Stress)

OMC, σc = 5 psi(35 kPA)

> 100 psi(0.7 MPa)

> 60 psi(0.4 MPa)

> 25 psi(170 kPa) Not required

Sat., σc = 15 psi(103 kPA)

≥ 180 psi(1.2 MPa)

≥ 135 psi(0.9 MPa)

≥ 60 psi(410 kPa) Not required

Repeated LoadTest (Failure

Deviator Stress)

OMC, σc = 15 psi(103 kPA)

≥ 180 psi(1.2 MPa)

≥ 160 psi(1.1 MPa)


Sat., σc = 15 psi(103 kPA)

≥ 180 psi(1.2 MPa)

≥ 160 psi(1.1 MPa)


Stiffness Test (Resilient Modulus) ≥ 60 ksi(0.4 MPa)

≥ 40 ksi(275 kPa)

≥ 25 ksi(170 MPa) Not required

Table 9. Recommended RCA Subbase Quality Tests and Values for Various Applications (after Saeed and Hammons 2008)

Note: Low traffic: < 100,000 ESALs/year; Medium traffic: 100,000 to 1,000,000 ESALs/year; High traffic: 1,000,000 ESALs/year.

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for critical test values for each of these tests to en -sure good RCA subbase performance in specifictraffic, moisture and temperature conditions.

GradationIt is common to produce two sizes of RCA for pave-ment subbase applications. While almost any sizescan be produced, two of the most common anduseful sizes are 1.5 to 3 in. (38 to 76 mm) and 1.5 in.(38 mm) maximum size. Regardless of the size(s)produced, the grading bands should be adjustedto provide suitable gradations for the intended ap -plication (e.g., free-draining vs. dense-graded) and tominimize production of materials that cannot be used.

Guidance on specific gradations to achieve unstabi-lized subbase materials that provide good stabilitywith varying degrees of permeability (free drainagecapacity) can be found in ACPA’s EB204P (ACPA2007).

Structural Design ConsiderationsThe pavement design process should consider thepossibility of significant stiffening of unstabilizedRCA subbase materials caused by continued hydra-tion of the cementitious materials (especially fordense-graded RCA base materials containing fineRCA particles). After time, such unstabilized sub-bases can behave as stabilized subbases, resultingin excellent strength and erosion resistance, but alsoin higher curling and warping stresses in overlyingconcrete slabs. See ACPA’s EB204P (ACPA 2007)for more on this topic and means to mitigate potentialproblems.

Preventing Clogging of Edge DrainageStructuresThe formation of calcium carbonate precipitate inedge drainage structures and on associated filterfabrics as a result of using RCA in drainable founda-tions (Figure 27) has long been a concern. Themechanism of precipitate formation is presentedcompletely by Bruinsma et al (1997), who describethe dissolution of calcium hydroxide (a by-product ofcement hydration) into water from freshly exposedcrushed concrete surfaces and the subsequent pre-

cipitation of calcium carbonate as the dissolved cal-cium hydroxide reacts with atmospheric CO2. Theavailability of calcium hydroxide increases withincreasing surface area of crushed concrete (i.e.,with increasing content of fine RCA) and decreasesover time as the available calcium hydroxide isdepleted.

Bruinsma (1995) and Tamarisa (1993) also deter-mined that as much as 50 percent of the materialdeposited in drainage structures and on associatedfilter fabrics may be dust and insoluble residue pro-duced by the crushing operation. Bruinsma (1995)found that washing the product prior to use minimized the presence of this material.

There have been many lab and field studies to characterize and identify solutions to this potentialproblem. Some of the most important of thesestudies were summarized by Snyder (1995) andSnyder and Bruinsma (1996). The following con -clusions, drawn from these reports, are useful in preventing problems with pavement drainage systems when using RCA subbase materials:

• All recycled concrete aggregates, regardlessof gradation, may produce various amounts ofprecipitate, with the precipitate potential beingdirectly related to the amount of freshly exposed

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Figure 27. Photo of extreme (atypical) case of calcium car-bonate precipitate in a drainage outlet (Photo credit: RichardProszek, City of Seattle Materials Laboratory).


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cement paste surface (i.e., increased quantitiesof cement paste fines).

• Selective grading (i.e., elimination of fine RCAparticles) and blending with virgin aggregate willreduce, but not completely eliminate, precipitate potential.

• Washing the RCA prior to placement in the sub-base minimizes the contribution of “crusher dust”to drainage system problems, but does not significantly reduce precipitate potential.

• Accumulations of precipitate and insolubleresidue can significantly reduce the permittivityof filter fabrics. However, there are fabrics withinitial permittivities high enough to withstand typ-ical accumulations of precipitate and insolubleresidue and still have sufficient remaining permit-tivity to function adequately.

• Accumulations of precipitate and residue indrainage pipes can be significant and canreduce discharge capacity, but are rarely (if ever)observed to significantly impede drainage flow.

The following recommendations are presented forthe use of RCA in drainable, unstabilized subbaselayers:

• Unbound RCA subbase layers that can passwater to pavement edge drainage systems orare designed to be drainable daylighted sub-bases should be free of fine materials to mini-mize the movement of dust and formation ofcalcium carbonate precipitate that can clog filterfabrics and reduce drain capacity. Unstabilizedfine RCA may be suitable for placement in anylayer below the pavement drainage system.

• Washing the RCA prior to placement, while notabsolutely necessary, is effective in reducing pre-cipitate and dust deposits in drainage structures.

• For filter fabrics used in conjunction with drainable RCA subbase layers, consider usingmaterials with initial permittivity values that areat least double the minimum required so that adequate flow will be maintained even if someclogging takes place (Snyder 1995).

• When filter fabrics are used in conjunction withpipe drain trenches, leave the top of the trenchunwrapped (Figure 19) to reduce deposits ofresidue on the fabric.

• Consider using daylighted subbase designs thatprovide broad paths for drainage (rather thanconcentrating all residue in outlet structures),as described in ACPA’s EB204P (ACPA 2007).

RCA intended for use in cement-stabilized subbaselayers require none of the special treatment or handling described above for unstabilized RCA subbases. The considerations described below forRCA in concrete mixtures are generally applicable.

Environmental ConsiderationsThe effluent from RCA foundation layers is initiallyhighly alkaline (an effect that diminishes with time inservice), but is generally not considered to be anenvironmental hazard because it is effectively dilutedat a very short distance from the drain outlet withmuch greater quantities of surface runoff (Sadecki etal 1996, Reiner 2008). It is not uncommon, however,to see very small regions of vegetation kill in theimmediate area of the drain outlet. The gradationand washing recommendations provided above toprevent precipitate formation also are generallyeffective in reducing initial pH levels in RCA subbasedrainage effluent (Snyder and Bruinsma 1996).

Construction ConsiderationsRCA subbases can be placed using standard equipment and techniques. Efforts should be madeto avoid excessive handling and movement of theRCA during placement and compaction becausethese activities can produce additional fine materialthrough abrasion.

USE OF RCA IN CONCRETEMIXTURES FOR CONCRETEPAVEMENT STRUCTURESThe following sections provide recommendationsand rationale concerning various aspects of usingRCA in new concrete paving mixtures. A detailedspecification concerning the use of RCA in hydraulic

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cement concrete can be found in AASHTO MP16and general guidelines are available in Appendix C.Guidelines for Using RCA in Concrete Paving Mix-tures near the end of this publication.

Quality Requirements and PropertiesIn general, RCA products intended for use in newconcrete pavements should meet the same qualityrequirements as virgin aggregate (FHWA 2007b).Exceptions are the magnesium and sodium sulfatesoundness tests, which are sometimes waived forRCA because they may be unreliable in predictingRCA durability.

Materials-Related DistressIf any materials-related distresses (e.g., D-crackingor alkali-aggregate reactivity [AAR]) were observedin the source concrete, evaluations and tests shouldbe conducted to ensure that mitigation measureswill be effective in preventing recurrence of thesedistresses.

Techniques that may be effective in preventingrecurrent AAR (including ASR) include: the use oflithium-based admixtures; the use of Class F flyash and/or slag cement in place of a portion of thecement; limiting the content of fine RCA; reducingconcrete permeability through lower water content(reduced water-cementitious materials ratio); andreducing slab exposure to moisture through im -proved pavement drainage, joint sealing, increasingthe distance to water sources, and other techniques.

Recurrent D-cracking may be prevented by reducingthe coarse RCA top size to ¾ in. (19 mm) or lessand by reducing slab exposure to moisture throughthe same techniques described above.

ContaminantsRCA intended for use in high-quality concrete shouldbe free of potentially harmful components. More than90 percent of the material should be cement pasteand aggregate (FHWA 2007b). Typical suggestedlimits for various contaminants include: asphalt –1 percent by volume; gypsum – 0.5 percent byweight; organic substances – 0.15 percent by weight;soil – in accordance with ASTM C33; and glass –

not allowed because it can cause ASR problems,along with popouts and cracking.

If the RCA is suspected to contain excessiveamounts of salt, the chloride content of the RCAshould be measured and used to determine thechloride content of the corresponding mixture. Highlevels may cause problems with concrete durability,set times and corrosion of embedded steel. Theseproblems should be addressed by ensuring that anysteel reinforcing is epoxy-coated and/or by washing(or removing) the fine RCA to reduce the amount ofmaterial passing the No. 200 (75 µm) sieve, whichtends to have the highest chloride content. FHWA(2007b) recommends not using RCA derived fromconcrete containing more than 0.06 lb of chloride ionper cubic yard (0.04 kg of chloride ion per cubicmeter) in JRCP or CRCP. Dowel bars and rein-forcing steel in such installations should, as a min-imum, be epoxy-coated, with consideration given tousing more corrosion-resistant materials, such asstainless steel (solid, sleeved or clad) products, zinc-sleeved or clad steel products or other suitablematerials.

Small amounts of joint sealant material, motor oiland other pavement surface contaminants have notbeen found to cause problems in RCA used in concrete mixtures (NHI 1998).

GradationCoarse RCA should be graded as required for concrete durability and workability requirements, andto meet the appropriate grading requirements. Thecoarse, angular nature of fine RCA can reduce con-crete workability and make finishing more difficult. Toavoid these problems, limit fine RCA content to nomore than 30 percent replacement. Higher replace-ment rates can be used, but added water andcement may be required to achieve good workability,as described in the recommendations for mixtureproportioning below.

Mixture ProportioningThe basic proportioning of concrete containing RCAcan be accomplished using the same procedures


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recommended for proportioning concrete containingonly virgin aggregate. The following mixture propor-tioning recommendations and guidelines are gener-ally adopted from ACI 555R-01 (ACI 2001), exceptas noted:

• RCA specific gravity, unit weight and absorptionmust be determined before determining mixtureproportions. In particular, the lower specificgravity of RCA should be considered in deter-mining aggregate batch weights on the basis ofabsolute volumes of components.

• When developing a target average strength forthe mixture based on the minimum requiredstrength, use a higher standard deviation ofstrength (e.g., 700 psi [4.8 MPa]) if the RCAquality is variable. When the RCA quality is - uniform, use the same standard deviation ofstrength as for virgin aggregate (e.g., 500 psi[3.2 MPa]).

• Selection of the w/cm ratio is the most criticalpart of controlling the strength of the RCA con-crete. If a valid relationship between the w/cmratio and the RCA concrete strength is not avail-able during the preliminary mixture designphase, designers can use (for mixtures con-taining coarse RCA and virgin fine aggregate)the same relationship used for conventional con-crete mixtures. If trial mixtures show a lowerstrength than was assumed, reduce the w/cmratio accordingly.

• To obtain the same slump as a conventional con-crete mixture, the free water content of a mixturecontaining coarse RCA and natural sand shouldbe increased about 5 percent. If the mixture willcontain both coarse and fine RCA, up to 15 per-cent additional water may be required to main-tain workability. These increases in water contentcan be reduced or eliminated through the use ofchemical and/or mineral admixtures (e.g., flyash, water reducers, superplasticizers, etc.).

• The ratio of coarse aggregate to fine aggregateshould be approximately the same as for con-ventional concrete made using virgin aggre-gates.

• Reclaimed mortar included in RCA often con-tains both entrapped and entrained air, but nei-ther are effective in protecting the new concretepaste from freeze-thaw damage. Volumetric airmeters may more accurately indicate the effec-tive air content of fresh concrete than pressure-based air meters, which may reflect the air in thereclaimed mortar (Wade et al 1997). Freeze-thaw testing (ASTM C666/AASHTO T161) is thebest way to qualify concrete mixtures containingRCA for use in areas where freeze-thaw damageis a possibility (FHWA 2007b).

• Some states have found it difficult to entrain airin concrete containing both coarse and fine RCA(FHWA 2007b). The presence of contaminantsmay impact required chemical admixturedosages.

• Trial mixtures are essential. As a minimum, labo-ratory trials should be conducted to ensure thatthe properties of the RCA mixture meet jobrequirements. Field trials should be conductedwhen feasible.

Table 10 presents example RCA concrete mixturedesigns from several recent highway paving projects.

Pavement DesignThe physical and mechanical properties of RCA con-crete must be determined and considered in thedevelopment of RCA concrete pavement designdetails. For example, increased shrinkage andthermal response of concrete containing RCA cancause larger joint movements, requiring differentsealant materials or reduced panel dimensions. Theyalso may increase slab curling and warping deforma-tion. Strength and elastic modulus reductions canimpact stress distributions and fatigue damage andmay cause increases in required pavement thick-ness. RCA also tends to have lower potential foraggregate interlock load transfer, especially whenthe maximum particle size is reduced to addressfreeze-thaw durability concerns.

Table 11 summarizes some of the most commonpavement design modifications that should be con-sidered when using RCA concrete in new pavementconstruction.

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ComponentsMinnesota DOTlb/yd3 (kg/m3)

Wisconsin DOTlb/yd3 (kg/m3)

Grand Forks, NDIntʼl Airport

lb/yd3 (kg/m3)Wyoming DOTlb/yd3 (kg/m3)

Cement (Type I)Fly ash (Type C)WaterCoarse RCAVirgin coarse aggregateFine RCAVirgin fine aggregateAdmixtures:

Air entrainerWater Reducer

472 (280)83 (49)

255 (151)1,630 (967)

1,200 (712)

yesno

480 (285)110 (65)265 (157)

1,815 (1077)

1,315 (780)

yesno

400 (237)130 (77)230 (136)

1,650 (979)

1,260 (748)

yesyes

488 (290)133 (79)258 (153)

1,349 (800)601 (357)253 (150)882 (523)

yesyes

Table 10. Example RCA Concrete Mixture Proportions*

*Proportions shown are representative examples and are not necessarily recommended.

Concrete pavementdesign element Design recommendations

Pavement type

Use JPCP with panel length of 15 ft (4.6 m) or less to minimize potential for mid-panel cracking.

JRCP and CRCP may be considered if aggregate interlock is enhanced with largeraggregate top size and/or blending virgin and recycled coarse aggregate. Addi-tional reinforcement may be desirable to ensure that cracks are held tight.

Slab thickness

Generally the same as for conventional concrete pavement design provided thatthe RCA concrete mixture design provides adequate strength.

For two-course construction using RCA concrete, the overall slab thickness mightneed to be greater than what is required for a conventional concrete pavementdesign, depending on the materials and mixture proportions used in each lift.

Joint spacing Panel length should be selected to minimize the incidence of midpanel cracks inJPCP or to keep crack width to a minimum in JRCP.

Load transferThe criteria for using dowels in RCA concrete pavements should be identical tothose used for pavements constructed using virgin aggregate. Reinforcing steelrecommendations for crack load transfer are presented below.

Joint sealant reservoir designDimensions must consider both the selected sealant material and expected jointmovements caused by temperature and shrinkage effects, which may be higherfor RCA concrete.

Subbase type

Subbase material should be selected in consideration of the structural require-ments of the pavement type selected (as for conventional concrete pavementdesigns). Free-draining subbase layers should be considered for RCA concretepavements produced from D-cracked or ASR-damaged concrete.

ReinforcementHigher amounts of longitudinal steel reinforcing may be required in JRCP andCRCP to hold cracks tight so that aggregate interlock load transfer can be maintained.

Shoulder type Same as for conventional concrete pavement.

Table 11. RCA Concrete Pavement Structural Design Guidelines and Recommendations

Pavement ConstructionPreparing the Foundation and SubbaseProper preparation of the pavement foundationlayers is just as important for RCA concrete pave-ments as for conventional pavement construction.Weak support areas should be located and cor-rected prior to pavement construction. Subbaselayers should be properly placed and consolidated orcompacted, as appropriate.

Concrete Production and TestingThe high absorption capacity of RCA can causeproblems with mixture uniformity and premature stiff-ening. It is strongly recommended that contractorsuse a stockpile sprinkling system to keep coarseRCA stockpiles uniformly moist during concrete production.

Air content tests should be performed using volu-metric devices (e.g., the Roll-O-Meter) to developmore accurate estimates of total useful air content inthe fresh concrete.

Paving OperationsProperly developed and manufactured RCA concretemixtures can be placed using standard concretepaving, finishing and curing equipment and tech-niques. No special training or other requirements arenecessary. As larger percentages of fine RCA areused, finishing may become more difficult.

Ride QualityProjects constructed using RCA concrete shouldbe held to the same standards of ride quality andsmoothness as those built using conventional pavingconcrete.

Two-Course Pavement ConstructionTwo-course (or two-lift) construction using RCA con-crete usually involves the wet-on-wet placement of alower layer comprising concrete containing RCA anda relatively thin (1.5 to 3 in. [4 to 8 cm]) layer ofhigh-quality concrete wearing surface that is manu-factured using highly durable virgin aggregate (Fig-ures 28 and 29).

Two-course construction is popular in Europe, wherethe lower concrete layer can contain RCA containingsignificant amounts of recycled asphalt material fromsources such as adjacent asphalt shoulders, anATB, etc. (FHWA 2007a). The first two-course con-crete pavement in the U.S. was constructed in 1909.Although the typical two-course concrete pavementconstructed in the U.S. included the characteristichigh-quality concrete wearing surface, virgin aggre-gate, and not RCA, typically was used in the bottomlift. Because of this, many pavement engineers inthe U.S. have felt that the benefit of building animproved top lift was not justified by the increasedcost of two-course construction (Cable et al 2004).

Now that many high-quality, conveniently locatedvirgin aggregate resources are being depletedrapidly, because advances in RCA processing tech-nologies can now produce RCA aggregates that per-form comparably to virgin aggregates in newconcrete mixtures, and because the use of RCA inthe bottom lift of a two-course concrete pavementhas been proven a viable option in Europe (FHWA2007a), RCA is now being considered as a sustain-able and less costly bottom lift for two-course con-crete pavement applications in the U.S.

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Figure 28. Two-course concrete pavement construc-tion; this photo was taken after the first lift was spreadand consolidated and the second lift was spread, butbefore the second lift was slipformed, showing thesecond slipform paving machine and top lift (Photocredit: Missouri/Kansas Chapter, ACPA).

Figure 29. Two lift construction of a portion of I-70 in Salina, KS in 2008; note that in the paving train there are two combinationsof placers and slipform pavers, one for each lift, followed by texturing and curing machines (Photo credit: Missouri/KansasChapter, ACPA).


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Bruinsma , J. E. 1995. Formation and Mitigation ofCalcium Carbonate Precipitate and InsolubleResidue from Recycled Concrete Aggregate Bases.M.S. Thesis. University of Minnesota Department ofCivil Engineering.

Bruinsma, J. E., Peterson, K. R., and Snyder, M. B.1997. “A Chemical Approach to the Formation ofCalcite Precipitate from Recycled Concrete Aggre-gate Base Layers.” Transportation Research Record1577. Transportation Research Board. Washington,D.C. pp 10-17.

Buck, A. D. 1973. “Recycled Concrete.” HighwayResearch Record 430. Highway Research Board.Washington, D.C. pp 1-8.

Cable, J.K., Frentress, D.P., and Williams, J.A. 2004.Two Lift Portland Cement Concrete Pavements toMeet Public Needs. DTF61-01-X-00042 (Project 8).Center for Portland Cement Concrete PavementTechnology. Ames, IA.

CMRA 2008. “Case Histories.” http://www.concreterecycling.org/histories.html. Construction MaterialsRecycling Association. Last accessed 2/26/2009.

Darter, M. I. 1988. Initial Evaluation of MichiganJRCP Crack Deterioration. Michigan ConcretePaving Association. Lansing, MI.

Dierkes, J. H., Jr. 1981. “Urban Recycling of Port-land Cement Concrete Pavement—EdensExpressway, Chicago, Illinois.” Proceedings of theNational Seminar on PCC Pavement Recycling andRehabilitation, FHWA-TS-82-208. Federal HighwayAdministration. Washington, D.C. pp. 172-175.

ACI 2001. “Removal and Reuse of Hardened Con-crete.” ACI 555R-01. American Concrete Institute.Farmington Hills, MI.

ACPA 1993a. “Reconstruction Optimization ThroughConcrete Inlays.” TB013P. American Concrete Pave-ment Association. Skokie, IL.

ACPA 1993b. “Recycling Concrete Pavement.”TB014P. American Concrete Pavement Association.Skokie, IL.

ACPA 2006. “Natural Advantage.” QD016P. Amer-ican Concrete Pavement Association. Skokie, IL.http://www.pavement.com/Downloads/QDs/QD016P%20-%20Natural%20Advantage.pdf. Last accessed2/26/2009.

ACPA 2007. “Subgrades and Subbases for ConcretePavements.” EB204P. American Concrete PavementAssociation. Skokie, IL.

Baumgardner, R.H. 2002. “Maintenance of HighwayEdgedrains.” Federal Highway Administration. Wash-ington, D.C.

BCSJ (Building Contractor's Society of Japan) 1978.“Study on Recycled Aggregate and Recycled Aggre-gate Concrete.” Concrete Journal, v. 16, No. 7 (inJapanese). pp. 18-31.

Bergren, J. V. and Britson, R. A. 1977. “PortlandCement Concrete Utilizing Recycled Pavements.”Proceedings of the International Conference on Concrete Pavement Design. Purdue University. WestLafayette, IN. pp. 469-485.

Chapter 8. References

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Dykins, S. E. and Epps, J. A. 1987. “PortlandCement Concrete Pavement Pulverizing Equipment.”Transportation Research Record 1126. Transporta-tion Research Board. Washington, D.C. pp.136-144.

ECCO 1997. “Case History—In-Place ConcretePavement Recycling Makes a Green Statement.”EV14. Environmental Council of Concrete Organiza-tions. Skokie, IL.

ECCO 1997a. “Recycling Concrete Saves Re -sources, Eliminates Dumping.” EV15. EnvironmentalCouncil of Concrete Organizations. Skokie, IL.

ECCO 1999. “Recycling Concrete and Masonry.”EV22. Environmental Council of Concrete Organiza-tions. Skokie, IL. 1999.

EPA 2009. Industrial Materials Recycling Tools &Resources. Environmental Protection Agency.Washington, D.C. http://www.epa.gov/osw/conserve/rrr/imr/pdfs/tools1-09.pdf. Last accessed 6/19/2009.

Epps, J. A., Little, D. N., Holmgren, R. J., and Terrell,R. L. 1980. “Guidelines for Recycling PavementMaterials,” NCHRP Report 224, TransportationResearch Board, Washington, DC.

Farny, J. A. and Kerkhoff, B. 2007. “Diagnosis andControl of Alkali-Aggregate Reactions in Concrete.”IS413.02. Portland Cement Association. Skokie, IL.

FHWA 1990a. “Portland Cement Concrete PavementRecycling.” Pavement Rehabilitation Manual.Chapter 1, Federal Highway Administration. Wash-ington, D.C.

FHWA 1990b. “Pavement Subsurface Drainage.”Technical Guide Paper 90-01. Federal HighwayAdministration. Washington, D.C.

FHWA 2002. “Formal Policy on the Use of RecycledMaterials.” February 7, 2002.

FHWA 2004. “Recycled Concrete Aggregate – Fed-eral Highway Administration National Review.” Fed-eral Highway Administration. Washington, D.C.www.fhwa.dot.gov/pavement/recycling/rca.cfm. Lastaccessed 2/26/2009.

FHWA 2007a. Long-Life Concrete Pavements inEurope and Canada. FHWA-PL-07-027. FederalHighway Administration. Washington, D.C.

FHWA 2007b. “Use of Recycled Concrete Pavementas Aggregate in Hydraulic-Cement Concrete Pave-ment.” Technical Advisory T 5040.37. FederalHighway Administration. Washington, D.C.

FHWA 2009. “Daylighted Permeable Bases.” FHWA-HIF-09-009. Federal Highway Administration. Wash-ington, D.C.

Fick, G. J. 2008. Testing Guide for ImplementingConcrete Paving Quality Control Procedures.National Concrete Pavement Technology Center(CP Tech Center). http://www.cptechcenter.org/publications/mco/testing_guide.pdf. Last accessed2/29/2009.

Forster, S. W. 1986. “Recycled Concrete as Aggre-gate.” Concrete International. American ConcreteInstitute. Farmington Hills, MI. pp. 34-40.

Halm, H. J. 1980. “Concrete Recycling.” Transpor -tation Research News, Volume 89. TransportationResearch Board. Washington , D.C. pp. 6-10.

Hansen, T. C. 1986. “Recycled Aggregates andRecycled Aggregate Concrete Second State-of-the-Art Report Developments 1945-1985.” Materials andStructures, V. 1, no. 111. Springer Netherlands. May-June. pp. 201-246.

Hansen, T. C. and Narud, H. 1983. “Strength ofRecycled Concrete Made from Crushed ConcreteCoarse Aggregate.” Concrete International, v.5, No.1. American Concrete Institute. January 1983.pp 79-83.

Krueger, O. 1981. “Edens Expressway PavementRecycling-Urban Pavement Breakup. Removal andProcessing,” Proceedings of the National Seminaron PCC Pavement Recycling and Rehabilitation,FHWA-TS-82-208. Federal Highway Administration.Washington, D.C. pp. 165-169.

Lane, K. R. 1980. Construction of a Recycled Port-land Cement Concrete Pavement. Report No.FHWA/CT-80-12. Connecticut Department of Trans-portation, Federal Highway Administration. Wash-ington, DC.

Mukai et al 1979. “Study on Reuse of Waste Con-crete for Aggregate of Concrete.” Proceedings of theSeminar on Energy and Resources Conservation inConcrete Technology. Japan-U.S. Cooperative Sci-ence Program. Washington, D.C.

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NHI 1998. “Techniques for Pavement Rehabilitation:a Training Course – Participant’s Manual.” FHWA-HI-99-006. National Highway Institute, Federal HighwayAdministration. Washington, D.C.

Olba, K. 2009. “Sustainable Concrete ThroughReuse of Crushed Returned Concrete.” Paper No.09-0358. TRB 88th Annual Meeting Compendium ofPapers DVD. Transportation Research Board. Wash-ington, DC.

Park, C. and Sim, J. 2006. “Fundamental Propertiesof Concrete using Recycled Concrete Aggregateproduced through Advanced Recycling Process.”CD-ROM Preprint of the 85th Annual Meeting of theTransportation Research Board. TransportationResearch Board. Washington, DC.

PCA 2007. “Guide Specifications for Concrete Sub-ject to Alkali-Silica Reactions.” IS415.07. PortlandCement Association. Skokie, IL.

Raja, Z. I. and Snyder, M. B. 1991. “FactorsAffecting Deterioration of Transverse Cracks inJointed Reinforced Concrete Pavements.” Trans-portation Research Record No. 1307. TransportationResearch Board, National Research Council. Wash-ington, D.C. pp. 162-168.

Rasheeduzzafar, and Khan, A. 1984. “RecycledConcrete – A Source of New Aggregate.” Cement,Concrete, and Aggregates, v. 6, No. 1. AmericanSociety for Testing and Materials. Conshohocken,PA. July 1984. pp. 17-27.

Reiner, M. 2008. “Evaluation of Potential pH Envi-ronmental Hazards and Mitigation Measures whenUtilizing Recycled Concrete Aggregate in the Field.”Symbiotic Engineering Green Paper Number Six.Symbiotic Engineering. Boulder, CO. January 28,2008.

RILEM 1992. Recycling of Demolished Concrete andMasonry: Report of Technical Committee 37-DRC,Demolition and Reuse of Concrete (T.C. Hansen,ed.). RILEM (lnternational Union of Testing andResearch Laboratories for Materials and Structures).E & FN Spon. New York, NY.

Rodden, R.A., and Voigt, G.V. 2008. “Problems withand Alternatives to Permeable Subbases for Use inConcrete Pavement Structures.” Proceedings for the9th International Conference on Concrete Pave-ments. San Francisco, CA.

RMRC 2006. Final Report for Project 12. RecycledMaterials Resource Center at the University of newHampshire. Durham, NH. http://www.recycledmaterials.org/Research/past/P12/P12Final.pdf. LastAccessed 6/17/2009.

Sadecki, R. W., Busacker, G. P., Moxness, K. L.,Faruq, K. C., and Allen, L. G. 1996. An Investigationof Water Quality in Runoff from Stockpiles of Sal-vaged Concrete and Bituminous Paving. Report No.MN/PR – 96/31. Minnesota Department of Trans-portation. St. Paul, MN.

Saeed, A. 2008. “Performance-Related Tests ofRecycled Aggregates for Use in Unbound PavementLayers.” NCHRP Report 598. National CooperativeHighway Research Program. Washington, D.C.

Saeed, A., Hall, J. W., and Barker, W. 2001. “Per -formance-Related Tests of Aggregates for Use inUnbounded Pavement Layers.” NCHRP Report 453.National Cooperative Highway Research Program.Washington, D.C.

Saeed, A., and Hammons, M. I. 2008. “MinimumStandards for Using Recycled Materials in UnboundHighway Pavement Layers.” Airfield and HighwayPavements: Efficient Pavements Supporting Trans-portation's Future. 978-0-7844-1005-9. AmericanSociety of Civil Engineers. Reston, Virginia. pp.452-463.

Sharpe, J. 2006. “ASR-Affected Recycled PortlandCement Concrete Pavement.” Internal Report.Wyoming Department of Transportation. Cheyenne,WY. April 14, 2006.

Snyder, M. B. 1994, “Effect of Reinforcement Designand Foundation Stiffness on the Deterioration ofTransverse Cracks in Jointed Concrete Pavements.”Proceedings of the Third International Workshop onthe Design and Evaluation of Concrete Roads.C.R.O.W. The Netherlands.

Snyder, M. B. 1995. “Use of Crushed ConcreteProducts in Minnesota Pavement Foundations.”Report No. 96-12. Minnesota Department of Trans-portation. St. Paul, MN.

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Van Matre, F. R., and Schutzbach, A. M. 1989. “Illi-nois' Experience with a Recycled Concrete Inlay.”Proceedings of the Fourth International Conferenceon Concrete Pavement Design and Rehabilitation.Purdue University. West Lafayette, IN. pp. 625-639.

Vandenbossche, J. M. and Snyder, M. B. 1993.“Uses of Recycled Concrete – Final Report, VolumeI: Summary of Past and Current Practices.” MichiganConcrete Paving Association. Lansing, Michigan.

Wade, M. J., Cuttell, G.D., Vandenbossche, J. M.,Yu, H. T. Smith, K. D., and Snyder, M. B. 1997.“Performance of Concrete Pavements ContainingRecycled Concrete Aggregate.” FHWA-RD-96-164.Federal Highway Administration. U.S. DOT. Wash-ington, D.C.

Won, M. 2007. “Use of Crushed Concrete as CoarseAggregates in Concrete Pavement.” Proceedings ofthe International Workshop on Best Practices forConcrete Pavements, held in Recife, Brazil.IBRACON. São Paolo, Brazil.

Yrjanson, W. 1989. “Recycling of Portland CementConcrete Pavements.” Synthesis of Highway Prac-tice 154. National Cooperative Highway ResearchProgram, Transportation Research Board, NationalResearch Council. Washington, D.C.

Snyder, M. B. and J. E. Bruinsma 1996. “A Reviewof Studies Concerning the Effects of UnboundCrushed Concrete Bases on PCC PavementDrainage.” Transportation Research Record 1519.Transportation Research Board. Washington, D.C.pp. 51-58.

Snyder, M. B. and Vandenbossche, J. M. 1993.“New Research and Practice in the Recycling ofConcrete.” The Evolving World of Concrete, Con-crete Technology Seminars – 7. Michigan State Uni-versity. East Lansing, MI.

Snyder, M. B., Vandenbossche, J. M. Smith, K. D.,Wade, M. 1994. Synthesis on Recycled ConcreteAggregate. Interim Report—Task A, DTFH61-93-C00133. Federal Highway Administration. Wash-ington, D.C.

Stark, D. 1996. “The Use of Recycled-ConcreteAggregate from Concrete Exhibiting Alkali-SilicaReactivity.” RD114.01T. Portland Cement Associa-tion. Skokie, IL.

Sturtevant, J. 2007. Performance of Rigid PavementsContaining Recycled Concrete Aggregates. M.S.Thesis. University of New Hampshire. Durham, NH.

Swedeen, K. J. 1990. Use of Fly Ash in RecycledConcrete Pavement for Control of Alkali-Silica Reac-tion. Presentation at the Transportation ResearchBoard’s 69th Annual Meeting.

Tamirisa, R. 1993. “Study of Highway Base/SubbaseAggregates That Cause Depositions of CalcareousTufa in Drains.” Master’s Thesis. Department of CivilEngineering, University of Toledo. Toledo, Ohio.

Taylor, P. C., Kosmatka, S. H., and Voigt, G. F. et al2006. Integrated Materials and Construction Prac-tices for Concrete Pavement: A State-of-the PracticeManual. FHWA Publication HIF-07-004. FederalHighway Administration. Washington, D.C.

USGS 1997. “Natural Aggregates – Foundation ofAmerica’s Future.” USGS Fact Sheet FS 144-97.United States Geological Survey, U.S. Department ofthe Interior. Washington, D.C. (reprinted February1999).

USGS 2000. “Recycled Aggregates – ProfitableResource Conservation.” USGS Fact Sheet FS-181-99. United States Geological Survey, U.S. Depart-ment of the Interior. Washington, D.C.

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DESCRIPTIONThese guidelines are for breaking, removing,crushing, screening, and stockpiling existing con-crete pavement. All concrete pavement designatedon the plans for removal and salvage may be han-dled and processed as described herein.

REMOVALWhere asphalt resurfacing or patching material ispresent, remove the asphalt before removing theconcrete pavement unless otherwise directed on theproject plans and specifications or by the engineer.Remove all joint sealing materials before removingthe concrete pavement. Asphalt and sealing mate-rials removed from the project usually becomes theproperty of the contractor, who will dispose of themin an environmentally acceptable manner.

Fracture the existing concrete pavement in placeusing pavement breaking equipment with the capa -city to break the pavement into appropriately sizedpieces for removal from the site (the maximum frac-tured slab size for processing in the crushing opera-tion might also be considered at this point). Breakingand removal equipment or methods that damageculverts under the roadbed are not be permitted.

Remove and transport the broken material to thepavement fragment stockpile site. Remove concreteusing equipment and methods that avoid the inclu-sion of subgrade and subbase materials.

Remove all reinforcing steel (including dowels andtie bars) from the salvaged pavement either prior toor during the crushing operation. All reinforcing steel

GUIDELINES FOR REMOVING ANDCRUSHING EXISTING CONCRETEPAVEMENT(Note: These guidelines were derived mainly fromthe 1993 version of ACPA’s TB014P, “RecyclingConcrete Pavements,” from AASHTO M319,“Reclaimed Concrete Aggregate for Unbound Soil-Aggregate Base Course,” and from AASHTO MP16,“Reclaimed Concrete Aggregate for Use as CoarseAggregate in Hydraulic Cement Concrete.” Usersare referred to these documents, as well as existingState and Local construction specifications, for addi-tional details concerning the production of reclaimedconcrete aggregate products.)

SCOPEThese guidelines are intended to provide users witha framework for use in developing a suitable specifi-cation for removing and crushing existing concretepavement to produce reclaimed concrete aggregates(RCA) suitable for use in typical nonstructuralhighway construction applications (e.g., concretepavements, subbases, sidewalks, median barriers,curbing, etc.).

State and local regulations, laws and specificationsmay be applicable to specific projects and maysupersede these guidelines; users of these guide-lines are cautioned to contact appropriate state andlocal authorities to identify any additional or super-seding requirements/specifications.

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removed from the pavement usually becomes theproperty of the contractor, who will dispose of it in anenvironmentally acceptable manner.

PROCESSING SALVAGED CONCRETECrush and size the salvaged concrete to meet thespecified requirements for the intended use of therecycled material. Adjust the crushing operations tomaximize the production (yield) of recycled materialsthat meet the quality and grading requirements forthe intended use of the material. Any surplus sal-vaged concrete or unusable crushed material usuallybecomes the property of the contractor, who will dis-pose of it in an environmentally acceptable manner.

Remove any remaining reinforcing steel, dowel bars,dowel bar assemblies, joint filler, bituminous mate-rials (in excess of allowable limits) and other foreignmaterial from the crushed concrete and dispose ofsuch materials in an environmentally acceptablemanner.

QUALITY CONTROL (QC)Develop and implement a quality control (QC) planfor aggregate production. The QC plan shoulddescribe the production procedures, test methodsand frequency of testing to ensure consistent pro-duction of RCA meeting the requirements of theintended application. The QC plan also shoulddescribe methods to be used to ensure thatreclaimed concrete source materials are not contam-inated with unacceptable amounts of deleteriousmaterials. Establish methods and criteria for exam-ining RCA prior to its use.

Stockpile RCA products to assist in qualitative andquantitative identification of the presence of delete-rious materials. (Stockpiling can also be used as ameans to qualitatively assess the uniformity of thematerial.) Stockpiles may represent all or part of thematerial to be used on a specific project. Thus, con-struct stockpiles in a manner that will minimize seg-regation and permit visual examination andrepresentative sampling of the material.

Test RCA intended for use in concrete mixturesshould be tested according to AASHTO T85 (“Spe-cific Gravity and Absorption of Coarse Aggregate”) todetermine the specific gravity and absorption of thematerial. For specific gravity, the total variability oftests (from minimum value to maximum value)should not exceed 0.100. For absorption, the totalvariability of tests (from minimum value to maximumvalue) should not exceed 0.8 percent. Stockpile RCAhaving specific gravity and absorption variabilityvalues that fall outside of these limits separatelywhere they might be used included in a project withless stringent specific gravity and absorption values.

Note 1 − Coarse RCA may contain varyingamounts of reclaimed concrete mortar, which generally has a lower specific gravity and is moreabsorptive than virgin aggregate. Therefore, RCAcan be highly absorptive and can exhibit low spe-cific gravity values, and the absorption and specificgravity values can be highly variable, especiallybetween RCA obtained from different sources orproduced at different facilities. The use of aggre-gates with variable specific gravity and absorptioncharacteristics in concrete mixtures can adverselyaffect the weighing and batching processes in concrete production and can result in concretework ability and finishing problems and variability.Control of stockpile moisture conditions will helpalleviate absorption problems.

MEASUREMENT AND PAYMENTPayment for removal and crushing of existing con-crete pavement typically is based on the squareyards (square meters) of concrete pavementremoved (i.e., $/yd2 [$/m2]). Payment for this itemtypically constitutes full payment for breaking,removing, hauling, crushing, screening, and stock-piling the old concrete, and for removing and dis-posing of waste steel, foreign material andincidentals necessary to completing the work.


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GUIDELINES FOR USING RCA INUNSTABILIZED (GRANULAR)SUBBASES(Note: These guidelines were derived mainly fromthe 1993 version of ACPA’s TB014P, “RecyclingConcrete Pavements,” and from AASHTO M319,“Reclaimed Concrete Aggregate for Unbound Soil-Aggregate Base Course.” Users are referred tothese documents, as well as existing State andLocal construction specifications, for additionaldetails concerning the production of RCA products.)

SCOPEThese guidelines are intended to provide users witha framework for use in developing a suitable specifi-cation for using aggregate materials derived fromrecycled concrete aggregate (RCA) in constructingunstabilized subbases for typical road or highwayconstruction applications.

Note 1 – When properly processed, hauled,spread and compacted on a prepared subgrade toappropriate density standards, RCA used alone orblended with natural or crushed aggregate can beexpected to provide adequate stability and loadsupport for use as road or highway subbasecourses.

State and local regulations, laws and specificationsmay be applicable to specific projects and maysupersede these guidelines; users of these guide-lines are cautioned to contact appropriate state andlocal authorities to identify any additional or super-seding requirements/specifications.

These guidelines are not intended for use in the con-struction of unstabilized base/subbase courses inlocations where concrete or asphalt surfacing will notbe placed over the subbase.

Note 2 – The engineer is cautioned to provideappropriate construction specifications to ensurecompaction is achieved to such an extent that fur-ther densification of the compacted subbase mate-rial due to traffic loadings will be insignificant.

USE OF RCA IN UNSTABILIZED(GRANULAR) SUBBASESRCA may be used without restriction in unstabilized(granular) subbases where drainage layers or perfo-rated drainage pipes will not be installed, providedthat the crushed concrete material meets all otherrequirements of this specification.

Approval should be granted by the engineer beforeusing RCA in proximity to perforated drains for alluses not specifically addressed in the contract. Theengineer may approve the following uses of RCA asa granular material in embankment or backfill whereperforated pipe is installed, or is to be installed, orwhere water moving through these materials mayenter the perforated pipe:

• All RCA material will be placed below the invertelevation of any perforated subsurface drainagepipe.

• All RCA material products used are larger than(will not pass) the No. 4 (4.75 mm) sieve.

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Note 3 – The engineer should be aware of thehighly alkaline nature of RCA, the relatively highdegree of solubility of the hydroxide-bearing com-ponents of the material, and the potential increasein pH that could occur in waters percolatingthrough an RCA subbase. Depending on the sen-sitivity of local soils, surface waters and ground-water to the presence of alkaline material, theengineer should set appropriate limits on the prox-imity of placement of RCA relative to groundwaterand surface waters. Unstabilized RCA materialsshould not be used in the vicinity of metal culvertsthat are sensitive to highly alkaline environments.

Note 4 – The engineer is cautioned to minimize(or prevent, when possible) the use of unstabilizedRCA in locations where waters that pass throughthe aggregate would also flow through or overgeotextile drainage layers, geotextile-wrapped pipedrains, drain field or pavement drainage piping,or any other pavement drainage system. Soluble minerals and dust can be transported hydraulicallyfrom the RCA material and be precipitated out ordeposited in the drainage structures, therebyreducing the permeability and/or capacity of thedrainage system. Further discussion on this topiccan be found elsewhere in this publication, inAASHTO M319 and in numerous research reports.

Note 5 – The engineer should be aware that RCAsubbase layers can gain strength and lose per -meability over time due to recementing of mortarportion of the RCA. The structural design andgeometry of the overlying pavement surfacingshould be developed with consideration of thispossibility.

ORDERING INFORMATIONThe following information typically is included in thepurchase order or contract documents:

• grading to be furnished,

• soundness testing requirements,

• exceptions or additions to this specification, and

• additional testing requirements (if any).

GRADINGRCA or blends of RCA with other approved virginaggregate materials should comply with the grada-tion requirements of AASHTO M147, ASTM D2940,or the requirements of the specifying agency.

Note 6 − There is usually no reason that the gra-dation requirements for RCA to differ significantlyfrom those for virgin aggregate materials used forthe same application.

Note 7 − Depending upon the source of the concrete and the processes used in removing,crushing and processing the material, it may benecessary to produce RCA material of at leasttwo separate sizes that can be blended together(and/or with virgin aggregate) to meet the grada-tion requirements.

PHYSICAL PROPERTIESRCA consists of crushed concrete material andvirgin aggregate particles derived from the crushingof concrete pavement fragments.

Typical maximum Los Angeles abrasion loss valuesfor the coarse RCA are 50%, measured in accor-dance with AASHTO T96 (“Resistance to Degrada-tion of Small-Size Coarse Aggregate by Abrasionand Impact in the Los Angeles Machine”).

Note 8 − AASHTO T327 (“Standard Test Methodfor Resistance of Coarse Aggregate to Degrada-tion by Abrasion in the Micro-Deval Apparatus”)may be required in lieu of AASHTO T96 if thespecifying agency has experience with the proce-dure and has established appropriate testing limits.

RCA soundness testing may be required at the dis-cretion of the engineer.

Note 9 − RCA can be susceptible to sulfate attackwhen tested for soundness using sodium sulfate ormagnesium sulfate solutions, leading to unreason-ably high loss values. Sulfate soundness testmethods (AASHTO T104) may be applied if localexperience has found these methods to producesatisfactory results with RCA. Alternative test


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approaches include AASHTO T103, New YorkState DOT Test Method NY 703-08, Ontario Ministry of Transportation Test method LS-614,and the “No-Test” Alternative (acceptance or rejection based on other quality measures).

DELETERIOUS SUBSTANCESRCA containing more than five percent bituminousconcrete materials by mass may be validated foracceptance using one or more of the following criteria:

• validation by use of California Bearing Ratio(AASHTO T193) testing

• validation by use of Resilient Modulus (AASHTOT307) testing

• validation by field application

Details concerning these three validation approachesare presented in Appendix D of AASHTO M319(“Reclaimed Concrete Aggregate for Unbound Soil-Aggregate Base Construction”).

RCA material intended for use in unstabilized sub-base layers should be free of all materials that areconsidered to be solid waste or hazardous materials,as defined by the State or local highway agency.

QUALITY CONTROL (QC)If RCA or combinations of RCA and other approvedvirgin aggregate materials are to be used in a sub-base, approval should be granted by the engineer.The proposed percentages of combined materialsshould be established as part of the request. At theengineer’s discretion, revised density acceptancetesting may be required when percentages orsources of materials change.

Note 10 − Revised density acceptance testing isrecommended when percentages or sources ofmaterials change because RCA will have a dif-ferent specific gravity and absorption characteris-tics than virgin aggregate and may varysignificantly between sources.

The quality control (QC) plan for the RCA shoulddetail the production procedures, test methods and

frequency of testing to ensure consistent productionof RCA meeting the requirements of the intendedapplication. The QC plan will also describe methodsto be used to ensure that RCA materials are not con-taminated with unacceptable amounts of deleteriousmaterials. Methods and criteria for examining RCAmaterials prior to use should be established.

Note 11 − Density control is typically accomplishedusing the “Proctor test” to compare in-place den-sity values with the maximum dry density. Pro -cedural methods (e.g., specifying a designatednumber of compaction passes based on the expe-rience of the specifying agency) have also beenused successfully in the placement of RCA mate-rials in subbase applications. Density control problems may result, however, when RCA from different sources is used on a single job, or whenthe RCA is blended with other virgin aggregates.Alternate compaction control methods for such situations are described in Appendix A of AASHTOM319. Revised density acceptance testing is recommended when percentages or sourcesof materials change because RCA will have a different specific gravity and absorption charac -teristics than virgin aggregate and may vary sig -nificantly between sources.

Note 12 – Stockpiling may be required to assist inqualitatively identifying the presence of deleteriousmaterials and assessing the uniformity of thematerial. When this approach is used, the stock-pile may represent all or part of the material to beused on a project, and should be constructed in amanner that will minimize segregation and permitvisual examination and representative sampling ofthe material.

If RCA is blended with other approved aggregates,blending should be accomplished using a methodthat ensures uniform blending and prevents segre-gation.


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GUIDELINES FOR USING RCA INCONCRETE PAVING MIXTURES(Note: These guidelines were derived mainly from the1993 version of ACPA’s TB014P, “Recycling ConcretePavements,” and from AASHTO MP16, “ReclaimedConcrete Aggregate for Use as Coarse Aggregate inHydraulic Cement Concrete.” Users are referred tothese documents, as well as existing State and Localconstruction specifications, for additional details con-cerning the production of RCA products.)

SCOPEThese guidelines are intended to provide users witha framework for use in developing a suitable specifi-cation for using recycled concrete aggregate (RCA)in typical concrete paving mixtures.

Note 1 – Concrete pavement structures of accept-able strength and durability can be produced usingRCA materials that is properly processed and man-ufactured to meet the typical aggregate require-ments when those materials are incorporated in aconcrete mixture that is proportioned and mixed inaccordance with appropriate requirements and pro-cedures, and is placed, consolidated and curedproperly. However, using RCA in new concrete mix-tures requires the use of suitable quality control(QC) and quality assurance (QA) procedures toensure that deleterious materials that might be present in the RCA will not adversely impact thequality of the concrete pavement structure.

State and local regulations, laws and specificationsmay be applicable to specific projects and may

supersede this guide specification. Users of thisguide specification are cautioned to contact appro-priate state and local authorities to identify any addi-tional or superseding requirements/specifications.

ORDERING INFORMATIONThe following information typically is included in thepurchase order or contract documents:

• grading to be furnished,

• soundness testing requirements,

• designated aggregate class,

• whether any restrictions on reactive materialsapplies,

• exceptions or additions to this specification, and

• additional testing requirements (if any).

GRADINGRCA or RCA/virgin aggregate blends should conformto the aggregate gradation requirements prescribedfor the specific intended concrete application.

Note 2 − There is usually no reason that the gra-dation requirements for RCA to differ significantlyfrom those for virgin aggregate materials used forthe same application.

Note 3 − Depending upon the source of the concrete and the processes used in removing,crushing and processing the material, it may benecessary to produce RCA material of at leasttwo separate sizes that can be blended together(and/or with virgin aggregate) to meet the grada-tion requirements.

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PHYSICAL PROPERTIESRCA consists of crushed concrete material andvirgin aggregate particles derived from the crushingof concrete pavement fragments.

Typical maximum Los Angeles abrasion loss valuesfor the coarse RCA are 50%, measured in accor-dance with AASHTO T96 (“Resistance to Degrada-tion of Small-Size Coarse Aggregate by Abrasionand Impact in the Los Angeles Machine”).

Note 4 − AASHTO T327 (“Standard Test Methodfor Resistance of Coarse Aggregate to Degrada-tion by Abrasion in the Micro-Deval Apparatus”)may be required in lieu of AASHTO T96 if thespecifying agency has experience with the proce-dure and has established appropriate testing limits.

RCA used in concrete that will be subject to in -service wetting, extended exposure to humid at -mosphere, or contact with moist ground should notcontain any materials that are reactive with alkalicomponents in the cement in an amount sufficient tocause excessive expansion of mortar or concreteunless materials that will prevent harmful alkali-aggregate reactions (e.g., Class F fly ash, slagcement, etc.) will be added in appropriate quantities.If necessary, test RCA for Alkali-aggregate reactivity(AAR) in accordance with AASHTO T303 (“Acceler-ated Detection of Potentially Deleterious Expansionof Mortar Bars due to Alkali-Silica Reaction”) and/orASTM C1567 (“Standard Test Method for Deter-mining the Potential Alkali-Silica Reactivity of Combi-nations of Cementitious Materials and Aggregate(Accelerated Mortar-Bar Method)”) when alkali-silicareaction (ASR) is suspected, and in accordance withASTM C586 (“Standard Test Method for PotentialAlkali Reactivity of Carbonate Rocks for ConcreteAggregates (Rock Cylinder Method)”) when alkali-carbonate reaction (ACR) is suspected.

Note 5 − If the source and history of the RCA areknown and no reactive failures were present in thesource concrete, testing for reactive expansionmay not be necessary. However, unless a precisehistory is known, the source concrete may havenot been exposed to all elements required tocause reactive expansion and the RCA may beunknowingly reactive.

RCA used in concrete that will be subjected tofreeze-thaw action should not contain aggregatecomponents that will result in D-cracking of the concrete. When potential D-cracking is suspected,test RCA in accordance with AASHTO T161 (“Resis-tance of Concrete to Rapid Freezing and Thawing”)or equivalent local methods. Acceptance criteria forAASHTO T161 and equivalent methods should bebased on local criteria that have been developed toaddress the issue of D-cracking.

RCA should meet the flat and elongated particlerequirements of the specifying agency if the agencyhas such requirements.

Test RCA intended for use in concrete mixturesshould be tested according to AASHTO T85 (“Spe-cific Gravity and Absorption of Coarse Aggregate”) todetermine the specific gravity and absorption of thematerial. For specific gravity, the total variability oftests (from minimum value to maximum value)should not exceed 0.100. For absorption, the totalvariability of tests (from minimum value to maximumvalue) should not exceed 0.8 percent. Stockpile RCAhaving specific gravity and absorption variabilityvalues that fall outside of these limits separatelywhere they might be used included in a project withless stringent specific gravity and absorption values.

Note 6 − Coarse RCA may contain varyingamounts of reclaimed concrete mortar, which gen-erally has a lower specific gravity and is moreabsorptive than virgin aggregate. Therefore, RCAcan be highly absorptive and can exhibit low spe-cific gravity values, and the absorption and specificgravity values can be highly variable, especiallybetween RCA obtained from different sources orproduced at different facilities. The use of aggre-gates with variable specific gravity and absorptioncharacteristics in concrete mixtures can adverselyaffect the weighing and batching processes in con-crete production and can result in concrete worka-bility and finishing problems and variability. Controlof stockpile moisture conditions will help alleviateabsorption problems.


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DELETERIOUS SUBSTANCESRCA should not contain clay lumps and friable parti-cles, chert, and coal and lignite or other deleterioussubstances that exceed the maximum allowableamounts listed in Table 12.

Note 7 − The presence of deleterious materials inaggregates used in the production of concrete mix-tures can adversely affect concrete setting timeand/or strength, and can also induce expansivereactions that could result in premature deteriora-tion of the concrete structure. As a result, strictquality control (QC) and quality assurance (QA)procedures are required to ensure that RCA mate-rial used as coarse aggregate in the production ofconcrete mixtures will not adversely affect thequality of the concrete product.

QUALITY CONTROL (QC)If RCA or combinations of RCA and other approvedvirgin aggregate materials are to be used in a newconcrete mixture, approval from the engineer mightbe necessary. The proposed percentages of com-bined materials should be established as part of therequest. At the engineer’s discretion, revised con-crete mixture designs may be required when per-centages or sources of materials change.

Note 8 − A revised concrete mixture design is rec-ommended when percentages or sources of RCAmaterials change. It is likely that the RCA will havedifferent specific gravity and absorption character-istics than the virgin aggregate.

Develop and implement a quality control (QC) planfor aggregate production. The QC plan should de -scribe the production procedures, test methods andfrequency of testing to ensure consistent productionof RCA meeting the requirements of the intended

Table 12. Typical Limits for Deleterious Substances and Physical Property Requirements of RCA for Use in New Concrete Mixtures(after AASHTO MP16)

Classdesignationb

Clay lumpsand friable particles

Chert (sp grSSD < 2.40)c

Sum of clay lumps, friable particles and chert(sp gr SSD < 2.40)c

Other deleterioussubstancesd

Coal andlignite

Maximum allowable, percenta

A 2.0 3.0 2.3 0.3 0.2

B 3.0 5.0 5.0 0.3 0.2

C 3.0 8.0 8.0 0.3 0.2a The engineer may supplement the requirements of this table by placing limits on the amount of deleterious sub-

stances or physical properties in accordance with local experience and practice.b RCA conforming to the requirements for the various classes designated in this table should generally be suitable

for the following uses:

Typical suggested uses Weathering exposure Class of aggregate

Concrete pavements, cement-treated subbases,sidewalks, median barriers, curbing and other non-structural applications

Severe A

Moderate B

Negligible Cc These limitations in this table apply only to RCA in which chert appears as an impurity. They are not applicable to

gravels that are predominantly chert. Limitations on the soundness of such aggregate should be based on servicerecords in the environment in which the material is used.

d Other deleterious substances include adherent fines, vegetable matter, plastics, plaster, paper, gypsum board,metals, fabrics, wood, brick, tile, glass, and asphalt (bituminous) materials. The percentages of these materialsshould be determined in accordance with ASTM C295 or other equivalent methods approved by the specifyingagency.

application. The QC plan also should describemethods to be used to ensure that RCA sourcematerials are not contaminated with unacceptableamounts of deleterious materials. Methods and criteria for examining RCA should be establishedprior to its use.

Stockpile RCA products to assist in qualitative andquantitative identification of the presence of delete-rious materials. (Stockpiling can also be used as ameans to qualitatively assess the uniformity of thematerial.) Stockpiles may represent all or part of thematerial to be used on a specific project. Thus, con-struct stockpiles in a manner that will minimize seg-regation and permit visual examination andrepresentative sampling of the material.

If RCA is blended with other approved aggregates,blending should be accomplished using a methodthat ensures blending and prevents segregation.

RCA should be brought to and maintained at a mois-ture condition that approaches a saturated surface-dry (SSD) condition prior to batching. This may beaccomplished by using a water sprinkling system oranother approved method. Appropriate batch wateradjustments should be made if the RCA is not pre-cisely in a SSD condition at the time of batching.

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M6 Standard Specification for Fine Aggregate forHydraulic Cement Concrete

M43 Standard Specification for Sizes ofAggregate for Road and Bridge Construction

M80 Standard Specification for Coarse Aggregatefor Hydraulic Cement Concrete

M92 Standard Specification for Wire-Cloth Sievesfor Testing Purposes

M146 Standard Specification for Terms Relating toSubgrade, Soil-Aggregate, and Fill Materials

M147 Standard Specification for Materials forAggregate and Soil-Aggregate Subbase,Base and Surface Courses

M319 Standard Specification for ReclaimedConcrete Aggregate for Unbound Soil-Aggregate Base Course

MP16 Standard Specification for ReclaimedConcrete Aggregate for Use as CoarseAggregate in Hydraulic Cement Concrete

T2 Standard Method of Test for Sampling ofAggregates

T11 Standard Method of Test for Materials FinerThan 75-µm (No. 200) Sieve in MineralAggregates by Washing

T19 Standard Method of Test for Bulk Density(“Unit Weight”) and Voids in Aggregate

T27 Standard Method of Test for Sieve Analysis ofFine and Coarse Aggregates

T85 Standard Method of Test for Specific Gravityand Absorption of Coarse Aggregate

T87 Standard Method of Test for Dry Preparationof Disturbed Soil and Soil-Aggregate Samplesfor Test

T88 Standard Method of Test for Particle SizeAnalysis of Soils

T89 Standard Method of Test for Determining theLiquid Limit of Soils

T90 Standard Method of Test for Determining thePlastic Limit and Plasticity Index of Soils

AASHTO STANDARDS

All American Association of State Highway and Transportation Officials (AASHTO) documents references inthe text of this publications are listed as follows and can be obtained at https://bookstore.transportation.org/;please consult the AASHTO website to ensure that you have obtained the most recent version of anyAASHTO standard before using it.

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T96 Standard Method of Test for Resistance toDegradation of Small-Size Coarse Aggregateby Abrasion and Impact in the Los AngelesMachine

T99 Standard Method of Test for Moisture-DensityRelations of Soils Using a 2.5-kg (5.5-lb)Rammer and a 305-mm (12-in.) Drop

T103 Standard Method of Test for Soundness ofAggregates by Freezing and Thawing

T104 Standard Method of Test for Soundness ofAggregate by Use of Sodium Sulfate orMagnesium Sulfate

T112 Standard Method of Test for Clay Lumps andFriable Particles in Aggregate

T113 Standard Method of Test for LightweightPieces in Aggregate

T161 Standard Method of Test for Resistance ofConcrete to Rapid Freezing and Thawing

T176 Standard Method of Test for Plastic Fines inGraded Aggregates and Soils by Use of theSand Equivalent Test

T180 Standard Method of Test for Moisture-DensityRelations of Soils Using a 4.54-kg (10-lb)Rammer and a 457-mm (18-in.) Drop

T193 Standard Method of Test for The CaliforniaBearing Ratio

T196 Standard Method of Test for Air Content ofFreshly Mixed Concrete by the VolumetricMethod

T234 Standard Method of Test for StrengthParameter of Soils by Triaxial Compression

T260 Standard Method of Test for Sampling andTesting for Chloride Ion in Concrete andConcrete Raw Materials

T277 Standard Method of Test for ElectricalIndication of Concrete's Ability to ResistChloride Ion Penetration

T299 Standard Method of Test for RapidIdentification of Alkali-Silica Reaction Productin Concrete

T303 Standard Method of Test for AcceleratedDetection of Potentially DeleteriousExpansion of Mortar Bars due to Alkali-SilicaReaction

T307 Standard Method of Test for Determining theResilient Modulus of Soils and AggregateMaterials

T327 Standard Method of Test for Resistance ofCoarse Aggregate to Degradation byAbrasion in the Micro-Deval Apparatus


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C33 Standard Specification for ConcreteAggregates

C88 Standard Test Method for Soundness ofAggregates by Use of Sodium Sulfate orMagnesium Sulfate

C125 Standard Terminology Relating to Concreteand Concrete Aggregates

C131 Standard Test Method for Resistance toDegradation of Small-Size Coarse Aggregateby Abrasion and Impact in the Los AngelesMachine

C173 Standard Test Method for Air Content ofFreshly Mixed Concrete by the VolumetricMethod

C227 Standard Test method for Potential AlkaliReactivity of Cement-AggregateCombinations (Mortar-Bar Method)

C289 Standard Test method for Potential Alkali-Silica Reactivity of Aggregates (ChemicalMethod)

C295 Standard Guide for Petrographic Examinationof Aggregates for Concrete

C342 Standard Test Method for Potential VolumeChange of Cement-Aggregate Combinations(Withdrawn 2001)

C441 Standard Test Method for Effectiveness ofPozzolans or Ground Blast-Furnace Slag inPreventing Excessive Expansion of ConcreteDue to the Alkali-Silica Reaction

C586 Standard Test Method for Potential AlkaliReactivity of Carbonate Rocks for ConcreteAggregates (Rock Cylinder Method)

C618 Standard Specification for Coal Fly Ash andRaw or Calcined Natural Pozzolan for Use inConcrete

C666 Standard Test Method for Resistance ofConcrete to Rapid Freezing and Thawing

C856 Standard Practice for PetrographicExamination of Hardened Concrete

ASTM STANDARDS

All American Association of State Highway and Transportation Officials (AASHTO) documents references inAllAmerican Society for Testing and Materials (ASTM) documents references in the text of this publication arelisted as follows and can be obtained at www.astm.org; please consult the ASTM website to ensure that youhave obtained the most recent version of any ASTM standard procedure before using it.

Appendix E.

C1202 Standard Test Method for Electrical Indicationof Concretes Ability to Resist Chloride IonPenetration

C1293 Standard Test Method for Determination ofLength Change of Concrete Due to Alkali-Silica Reaction

C1567 Standard Test Method for Determining thePotential Alkali-Silica Reactivity of Combin -ations of Cementitious Materials andAggregate (Accelerated Mortar-Bar Method)

D2940 Standard Specification for Graded AggregateMaterial for Bases or Subbases for Highwaysor Airports

D5101 Standard Test Method for Measuring the Soil-Geotextile System Clogging Potential by theGradient Ratio

D6928 Standard Test Method for Resistance ofCoarse Aggregate to Degradation byAbrasion in the Micro-Deval Apparatus

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A

AAR – See Alkali-Aggregate Reactivity.

Absolute Volume – The displacement volume of aningredient of concrete or mortar; in the case ofsolids, the volume of the particles themselves,including their permeable or impermeable voids butexcluding space between particles; in the case offluids, the volume which they occupy.

Absorbed Moisture – The moisture held in a mate-rial and having physical properties not substantiallydifferent from those of ordinary water at the sametemperature and pressure.

Absorption – The amount of water absorbed underspecific conditions, usually expressed as a per-centage of the dry weight of the material; theprocess by which the water is absorbed.

Accelerator – An admixture which, when added toconcrete, mortar, or grout, increases the rate ofhydration of hydraulic cement, shortens the time ofset, or increases the rate of hardening or strengthdevelopment.

Admixture – A material other than water, aggre-gates, and cementitious material (including cement,slag cement, fly ash, and silica fume) that is used asan ingredient of concrete and is added to the bathbefore and during the mixing operation.

Aggregate – Granular material, such as sand,gravel, crushed stone, recycled concrete, or ironblast furnace slag.

Aggregate, Angular – See Angular Aggregate.

Aggregate Blending – The process of intermixingtwo or more aggregates to produce a different set ofproperties, generally, but not exclusively, to improvegrading or include a RCA.

Aggregate, Coarse – See Coarse Aggregate.

Aggregate, Crusher-Run – See Crusher-RunAggregate.

Aggregate, Dense-Graded – See Dense-GradedAggregate.

Aggregate, Fine – See Fine Aggregate.

Aggregate, Gap-Graded – See Gap-Graded Aggre-gate.

Aggregate Gradation – See Grading.

Aggregate Interlock – The projection of aggregateparticles or portion of aggregate particles from oneside of a joint or crack in concrete into recesses inthe other side of the joint or crack so as to affectload transfer in compression and shear and maintainmutual alignment.

Aggregate, Maximum Size – See Nominal Max-imum Size.

Aggregate, Natural – See Natural Aggregate.

Aggregate, Open-Graded – See Open-GradedAggregate.

Aggregate, Virgin – See Virgin Aggregate.

Aggregate, Well-Graded – See Well-Graded Aggre-gate.

Air Content – The amount of air in mortar or con-crete, exclusive of pore space in the aggregate parti-cles, usually expressed as a percentage of totalvolume of mortar or concrete.

Air-Entraining – The capabilities of a material orprocess to develop a system of minute bubbles of airin cement paste, mortar, or concrete during mixing.

GlossaryThis Glossary is not intended to cover all terms used in the vernacular of recycling concrete pavements andseveral other extensive sources of terms are readily available, such as ACI Committee 116 andAASHTO/ASTM standards.


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Air-Entraining Agent – An addition for hydrauliccement or an admixture for concrete or mortar whichcauses air, usually in small quantity, to be incorpo-rated in the form of minute bubbles in the concreteor mortar during mixing, usually to increase its work-ability and frost resistance.

Air-Meter – A device for measuring the air content ofconcrete and mortar.

Alkali-Aggregate Reactivity (AAR) – A chemicalreaction in mortar or concrete between alkalis(sodium and potassium) released from portlandcement or from other sources, and certain com-pounds present in the aggregates; under certainconditions, harmful expansion of the concrete ormortar may be produced.

Alkali-Carbonate Reactivity – The reactionbetween the alkalies (sodium and potassium) in port-land cement binder and certain carbonate rocks,particularly calcite dolomite and dolomitic lime-stones, present in some aggregates; the products ofthe reaction may cause abnormal expansion andcracking of concrete in service.

Alkali-Silica Reactivity (ASR) – The reactionbetween the alkalies (sodium and potassium) in port-land cement binder and certain siliceous rocks orminerals, such as opaline chert, strained quartz, andacidic volcanic glass, present in some aggregates;the products of the reaction may cause abnormalexpansion and cracking of concrete in service.

Angular Aggregate – Aggregate particles that pos-sess well-defined edges formed at the intersection ofroughly planar faces.

Asphalt-Treated Subbase (ATB) – A stabilized sub-base that is bound by asphalt binder.

ASR – See Alkali-Silica Reactivity.

ATB – See Asphalt-Treated Subbase.

B

Base – A layer within an asphalt pavement structure;usually a granular or stabilized material, either previ-ously placed and hardened or freshly placed, onwhich the pavement surface is placed in a lateroperation.

Beneficiation – The treatment of any raw materialto improve its physical or chemical properties prior tofurther processing or use.

Bulk Density – The mass of a material (includingsolid particles and any contained water) per unitvolume, including voids.

Bulk Specific Gravity – See Specific Gravity.

C

Calcium Hydroxide – A by-product of the cementhydration reaction that is highly soluble and is easilyleached from RCA particles in stockpiles and drain-able subbase layers.

Carbonation – Reaction between carbon dioxideand the products of portland cement hydration toproduce calcium carbonate.

Cement – A hydraulic cement consisting essentiallyof an intimate and uniform blend of portland cementor slag cement and fine pozzolan produced by inter-grinding portland-cement clinker and pozzolan withinspecified limits.

Cement-Treated Subbase (CTB) – A stabilized sub-base that is bound by portland cement with a gen-eral dosage of about 4 or 5 percent cement byweight. CTB are best controlled using compactionand/or density requirements, but typical targetstrengths for a CTB layer are between 300 and 800psi (2.1 and 5.5 MPa) compression at 7 days.

Cement-Stabilized Subbase – A class of stabilizedsubbases that includes cement-treated subbases(CTB) and lean concrete.

Cementitious – Having cementing properties.

Cementitious Materials – Substances that alonehave hydraulic cementing properties (set and hardenin the presence of water); includes slag cement, nat-ural cement, hydraulic hydrated lime, and combina-tions of these and other materials.

Chloride Content – Level of sodium chloride (NaCl)in the to-be-recycled concrete pavement due toexposure to deicing chemicals.



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Appendix – Glossary

CTE – See Coefficient of Thermal Expansion andContraction.

Curing – The maintenance of a satisfactory mois-ture content and temperature in concrete during itsearly stages so that desired properties may develop.

Curling – Deformation of concrete pavement slabsdue to thermal gradients.

D

D-cracking – (also known as Durability Cracking) –Cracking of the concrete that results from freeze-thaw deterioration of the coarse aggregate within theconcrete.

Daylighted Subbase – (also known as Daylighting)– An edge drainage system in which a subbase isextended through the edge of the pavement systemto a point where it is capable of freely carrying waterto side ditches, hence being daylighted.

Daylighting – See Daylighted Subbase.

Dense-Graded Aggregate – Aggregates graded toproduce low void content and maximum weightwhen compacted.

Dense-Graded Subbase – A subbase (typicallyunstabilized) that is composed of dense-gradedaggregate.

Density – Mass per unit volume; by common usagein relation to concrete, weight per unit volume, alsoreferred to as unit weight.

Dowel – 1) A load transfer device, commonly a plainround steel bar, which extends into two adjoiningportions of a concrete construction, as at a joint in apavement slab, so as to transfer shear loads; 2) adeformed reinforcing bar intended to transmit ten-sion, compression, or shear through a constructionjoint.

Drainable Subbase – See Permeable Subbase.

Drainage – The interception and removal of waterfrom, on, or under an area or roadway; the processof removing surplus ground or surface water artifi-cially; a general term for gravity flow of liquids inconduits.

Drying Shrinkage – Contraction caused by drying.

Coarse Aggregate – Aggregate predominatelyretained on the No. 4 (4.75 mm) sieve; may beeither virgin or recycled materials.

Coefficient of Thermal Expansion and Contrac-tion (CTE) – Change in linear dimension per unitlength or change in volume per unit volume perdegree of temperature change.

Combined Aggregate Grading – Particle size distri-bution of a mixture of fine and coarse aggregate.

Cone Crusher – A crusher that uses an eccentricrotating cone to trap and crush concrete fragmentsagainst the inner crusher housing walls; commonlyused in secondary crusher applications becausethey can handle slab fragments no larger than 8 in.(20 cm) in diameter.

Contaminant – In the context of recycled concrete,refers to materials such as joint sealants, asphaltconcrete shoulders, patching materials, etc. thatmight be included in the final RCA product.

Continuously Reinforced Concrete Pavement(CRCP) - A pavement with continuous longitudinalsteel reinforcement and no intermediate transverseexpansion or contraction joints.

CRCP – See Continuously Reinforced ConcretePavement.

Crushed Gravel – The product resulting from theartificial crushing of gravel with a specified minimumpercentage of fragments having one or more facesresulting from fracture; a type of virgin aggregate.

Crushed Stone – The product resulting from theartificial crushing of rocks, boulders, or large cobble-stones, substantially all faces of which possess well-defined edges and have resulted from the crushingoperation; a type of virgin aggregate.

Crusher, Cone – See Cone Crusher.

Crusher, Impact – See Impact Crusher.

Crusher, Jaw – See Jaw Crusher.

Crusher-Run Aggregate – Aggregate that has beenbroken in a mechanical crusher and has not beensubjected to any subsequent screening process; atype of virgin aggregate.

CTB – See Cement-Treated Subbase.

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Gap-Graded Aggregate – Aggregate so graded thatcertain intermediate sizes are substantially absent.

Geosynthetics – Thin pliable sheets of textile mate-rial of varying permeability. The varieties of geosyn-thetics include geotextiles, geogrids, geonets,geocells and geomembranes. The usefulness andeffectiveness of geosynthetics directly depends onthe type of geosynthetic, the intended function (filtra-tion, separation and/or reinforcement), in-situ soilconditions and installation techniques.

Geotextile – See Geosynthetics.

GHG – See Greenhouse Gas.

Gradation – See Grading.

Grading – The distribution of particles of granularmaterial among various sizes, usually expressed interms of cumulative percentages larger or smallerthan each of a series of sizes (sieve openings) orthe percentages between certain ranges of sizes(sieve openings).

Granular Subbase – See Unstabilized Subbase.

Gravel – Granular material predominantly retainedon the No. 4 (4.75 mm) sieve and resulting from nat-ural disintegration and abrasion of rock or pro-cessing of weakly bound conglomerate; a type ofvirgin aggregate.

Greenhouse Gas (GHG) – Any of the atmosphericgasses that contribute to the greenhouse effect.

H

Harsh Mixture – A concrete mixture that lacksdesired workability and consistency due to a defi-ciency of mortar.

Harshness – Deficient workability and cohesivenesscaused by insufficient sand or cement, or by improp-erly graded aggregate.

High Range Water-Reducing Admixture – SeeWater-Reducing Admixture.

Horizontal Shaft Impact Crusher – See ImpactCrusher.

Durability Cracking – See D-cracking.

E

Econocrete – Although sometimes known as leanconcrete subbase, this material is a lower strength,more inexpensive concrete mixture that is identicalin concept to lean concrete subbase material butused as a paving surface.

Edge Drainage System – A system designed tocarry water that has infiltrated the pavement surfaceto a side ditch. The two most common types of edgedrainage systems are collector pipes with redundantoutlets and daylighted subbases.

F

Fine Aggregate – Aggregate passing the 3/8-in.(9.5 mm) sieve and almost entirely passing the No. 4(4.75-mm) sieve and predominantly retained on theNo. 200 (75 mm) sieve; may be either virgin or recy-cled materials.

Fly Ash – The finely divided residue resulting fromthe combustion of ground or powdered coal andwhich is transported from the fire box through theboiler by flu gasses; Used as mineral admixture inconcrete mixtures.

Free-draining Subbase – A subbase with a targetpermeability between 50 and 150 ft/day (15 and46 m/day) in laboratory tests; the maximum perme-ability for a free-draining subbase is approximately350 ft/day (107 m/day) in laboratory tests and anymaterials that provide higher permeability ratesshould be considered permeable subbases.

Freeze-Thaw Durability – The ability of the con-crete material to resist repeated freezing andthawing cycled.

Fresh Concrete – (also known as Plastic Con-crete) – A condition of freshly mixed concrete suchthat it is readily remoldable and workable, cohesive,and has an ample content of cement and fines, butis not over-wet.

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L

Lean Concrete Subbase – A subbase that is boundby portland cement and with higher cement andwater contents than cement-treated subbases, butthey less cement than conventional concrete and anaverage 7-day compressive strength between 750and 1,200 psi (5.2 and 8.3 MPa). The aggregatesused in lean concrete subbases do not necessarilymeet conventional quality standards for aggregatesused in pavements.

Load Transfer Device – See Dowel.

Load Transfer Efficiency (LTE) – The ability of ajoint or crack to transfer a portion of a load appliedon side of the joint or crack to the other side of thejoint or crack.

Los Angeles Abrasion Mass Loss (L.A. AbrasionTest) – Measures the amount of particle degradation(in terms of mass loss) that takes place under stan-dard aggressive handling conditions.

LTE – See Load Transfer Efficiency.

M

Materials-Related Distress – Distresses (e.g.,D-cracking, ASR, etc.) that are related to the mate-rials that make up a concrete pavement structure.

Maximum Size of Aggregate – See Nominal Max-imum Size.

Mix – See Mixture.

Mixture – The assembled, blended, commingledingredients of mortar, concrete, or the like, or theproportions for their assembly.

Mixture Design – See Proportioning.

Moisture Content of Aggregate – The ratio,expressed as a percentage, of the weight of water ina given granular mass to the dry weight of the mass.

Mortar – Concrete with essentially no aggregatelarger than about 3⁄16 in. (4.8 mm).

Hydration – The chemical reaction between cementand water which causes concrete to harden.

I

Impact Crusher – A crusher that uses heavy steel“blow bars” mounted on a horizontal or vertical rotorto repeatedly impact concrete fragments and hurlthem against steel anvils or “break plates” in thecrusher housing; commonly used as in secondarycrusher applications and the crushing processesyields more fine aggregate and less coarse aggre-gate.

J

Jaw Crusher – A crusher that uses a large steelplate to compress concrete fragments against a sta-tionary plate within the crusher housing; commonlyused in primary crusher applications because theycan handle larger slab fragments.

Jointed Plain Concrete Pavement (JPCP) – Pave-ment containing enough joints to control all naturalcracks expected in the concrete; steel tie bars aregenerally used at longitudinal joints to prevent jointopening, and dowel bars may be used to enhanceload transfer at transverse contraction jointsdepending upon the expected traffic.

Jointed Reinforced Concrete Pavement (JRCP) –Pavement containing some joints and embeddedsteel mesh reinforcement (sometimes called distrib-uted steel) to control expected cracks; steel mesh isdiscontinued at transverse joint locations.

JPCP – See Jointed Plain Concrete Pavement.

JRCP – See Jointed Reinforced Concrete Pavement.

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Permeability – A soil’s ability to transmit waterthrough its voids. The permeability of any material isheavily dependent on the connectivity of its pore net-work; the more connected and the larger the porenetwork is, the greater the permeability.

Permeable Subbase – Unstabilized layer consistingof crushed aggregates with a reduced amount offines to promote drainage and increase the perme-ability of the subbase above 350 ft/day (107 m/day)in laboratory tests, although typical levels range from500 to 20,000 ft/day (152 to 6,100 m/day) in labora-tory tests. Despite their intuitive advantage to quicklybe able to remove excess water, permeable sub-bases are no longer considered a cost effectivedesign element for concrete pavements due to theirvery problematic history.

Plain Concrete – Concrete without reinforcement.

Plastic Concrete – See Fresh Concrete.

Proportioning – Selection of proportions of ingredi-ents for mortar or concrete to make the most eco-nomical use of available materials to produce mortaror concrete of the required properties.

Process Control – See Quality Control.

Q

QA – See Quality Assurance.

QC – See Quality Control.

Quality Assurance (QA) – All those planned andsystematic actions necessary to provide confidencethat a product or facility will perform satisfactorily inservice.

Quality Control (QC) – (also known as ProcessControl) – Actions and considerations taken by aproducer and/or contractor to assess, document,and adjust production and construction processes soas to control the level of quality being produced inthe end product. QC is not the same as qualityassurance (QA); in fact, QC is a component of QA.

N

Natural Aggregate – Aggregate resulting from thenatural disintegration and abrasion of rock; a type ofvirgin aggregate.

Natural Sand – Sand resulting from natural disinte-gration and abrasion of rock; a type of virgin aggre-gate.

Nominal Maximum Size – In specifications for anddescriptions of aggregate, the smallest sieveopening through which the entire amount of theaggregate is permitted to pass; sometimes referredto as maximum size (of aggregate).

O

Open-Graded Aggregate – Aggregate so gradedthat most intermediate and fine sizes are substan-tially absent; typically used in a permeable subbaseas a means to promote drainage.

Open-Graded Subbase – See Permeable Subbase.

P

Particle-Size Distribution – The division of particlesof a graded material among various sizes; for con-crete materials, usually expressed in terms of cumu-lative percentages larger or smaller than each of aseries of diameters or the percentages within certainranges of diameter, as determined by sieving.

Paste – Constituent of concrete consisting ofcement and water.

Pavement Structure – The combination ofasphalt/concrete surface course(s) and base/sub-base course(s) placed on a prepared subgrade tosupport the traffic load.

Percent Fines – Amount, expressed as a per-centage, of material in aggregate finer than a givensieve, usually the No. 200 (75 µm) sieve; also, theamount of fine aggregate in a concrete mixtureexpressed as a percent by absolute volume of thetotal amount of aggregate.

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Sand – The fine granular material (usually less than3⁄16 in. (4.75 mm) in diameter) resulting from the nat-ural disintegration of rock, or from the crushing of fri-able sandstone; a type of virgin aggregate.

Saturated Surface-Dry (SSD) – Condition of anaggregate particle or other porous solid when thepermeable voids are filled with water but there is nowater on the exposed surface.

Saturated Surface-Dry (SSD) Particle Density –The mass of the saturated-surface-dry aggregatedivided by its displaced volume in water or in con-crete. (Also called Bulk Specific Gravity).

Saturation – 1) In general, the condition of thecoexistence in stable equilibrium of either a vaporand a liquid or a vapor and solid phase of the samesubstance at the same temperature. 2) As applied toaggregate or concrete, the condition such that nomore liquid can be held or placed within it.

SCM – See Supplementary Cementitious Material.

Secondary Cementing – Also known as Rece-menting. The result of hydration of exposed and pre-viously unhydrated or partially-hydrated cementgrains of the mortar portion of RCA when the RCA isused in a new unstabilized mixture; can be signifi-cant enough to effectively cause an unstabilizedlayer of dense-graded RCA (often found in founda-tions, pipe beds, backfill applications, etc.) to behavelike a cement-treated material.

Set-Accelerating Admixture – See Accelerator.

Set-Retarding Admixture – See Retarder.

Sieve – A metallic plate or sheet, a woven-wirecloth, or other similar device, with regularly spacedapertures of uniform size, mounted in a suitableframe or holder for use in separating granular mate-rial according to size.

Sieve Analysis – The classification of particles, par-ticularly of aggregates, according to sizes as deter-mined with a series of sieves of different openings.

Slag Cement – The non-metallic by-product, con-sisting essentially of silicates and aluminosilicates oflime and other bases, which is produced in a moltencondition simultaneously with iron in a blast furnace.

R

Reactive-Aggregate – Aggregate containing certainsilica or carbonate compounds that are capable ofreacting with alkalis in portland cement, in somecases producing damaging expansion of concrete.

Recementing – See Secondary Cementing.

Reclaimed Asphalt Pavement (RAP) – Previouslyexisting asphalt pavement that has been processedfor reuse, typically as aggregate in a subbase layer.

Recycled Concrete – Previously existing, hardenedconcrete that has been crushed and sorted forreuse, such as aggregate in a subbase layer or anew concrete pavement. Recycled concrete cancome from any number of sources, not just concretepavements, and sorting processes can be adjustedto remove contaminants such as reinforcing steel.

Recycled Concrete Aggregate (RCA) – A granularmaterial that can be produced by recycling existingconcrete for use as a substitute for natural (virgin)aggregate in almost any application.

Recycling – The act of processing existing pave-ment material into usable material for a layer withina new pavement structure.

Reinforced Concrete – Concrete containing ade-quate reinforcement (prestressed or not prestressed)and designed on the assumption that the two mate-rials act together in resisting forces; see Continu-ously Reinforced Concrete Pavement and JointedReinforced Concrete Pavement.

Reinforcement – Bars, wires, strands, and otherslender members embedded in concrete in such amanner that the reinforcement and the concrete acttogether in resisting forces.

Retardation – Reduction in the rate of hardening orstrength development of fresh concrete, mortar, orgrout; i.e., an increase in the time required to reachinitial and final set.

Retarder – An admixture that delays the setting ofcement and hence of mixtures such as mortar orconcrete containing cement.

Rubblizing – A destructive procedure to breakexisting concrete pavement in place to fragmentsthat range in size from 4 to 8 in. (100 to 200 mm).

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Sulfate Attack – Chemical or physical reactionbetween certain constituents in cement and sulfatesin the soil or groundwater; sufficient attack may dis-rupt concrete that is susceptible to it.

Sulfate Resistance – The ability of aggregate,cement paste, or mixtures thereof to withstandchemical attack by sulfate ion in solution.

Sulfate Soundess Mass Loss – Provides an indica-tion of aggregate resistance to weathering and otherenvironmental effects.

Superplasticizer – See Water-Reducing Admixture.

Supplemental Cementing – The result of hydrationof exposed and previously unhydrated or partially-hydrated cement grains of the mortar portion of RCAwhen the RCA is used in a new cement-based mix-ture (e.g., concrete paving mixture, cement-treatedsubbase mixture, lean concrete mixture, etc.); can,especially with the inclusion of fine RCA, potentiallycause new concrete mixtures to have higherstrengths than comparable mixtures made with100% virgin aggregates.

Supplementary Cementitious Material (SCM) –Mineral admixtures consisting of powdered or pulver-ized materials which are added to concrete before orduring mixing to improve or change some of thefresh (plastic) or hardened properties of Portlandcement concrete. Materials are generally natural orby-products of other manufacturing processes.

T

Thermal Expansion – Expansion caused byincrease in temperature.

Thermal Movement – Change of dimension of con-crete or masonry resulting from change of tempera-tures. See also Contraction and Expansion.

U

Unit Water Content – The quantity of water per unitvolume of freshly mixed concrete, often expressedas pounds or gallons per cubic yard. It is the quantityof water on which the water-cement ratio is basedand does not include water absorbed by the aggregate.

Slump – A measure of consistency of freshly mixedconcrete, equal to the subsidence measured to thenearest 1⁄4-inch (6-mm) of the molded specimenimmediately after removal of the slump cone.

Specific Gravity – The ratio of the weight in air of agiven volume of material at a stated temperature tothe weight in air of an equal volume of distilled waterat the same temperature.

Stabilized Subbase – A subbase layer that is boundby either portland cement or asphalt binders. Stabi-lized subbases fall into three general categories:cement-treated, lean concrete and asphalt-treated.The primary benefit of stabilized bases is that theyprovide relatively strong, uniform support and areresistant to erosion (pumping).

Subbase – The layer(s) of select or engineeredmaterial of planned thickness placed between thesubgrade and a concrete pavement that serve oneor more functions such as preventing pumping, dis-tributing loads, providing drainage, minimizing frostaction, or facilitating pavement construction.

Subbase, Asphalt-Treated – See Asphalt-TreatedSubbase.

Subbase, Cement-Stabilized – See Cement-Stabi-lized Subbase.

Subbase, Cement-Treated – See Cement-TreatedSubbase.

Subbase, Daylighted – See Daylighted Subbase.

Subbase, Dense-Graded – See Dense-GradedSubbase.

Subbase, Free-Draining – See Free-Draining Sub-base.

Subbase, Lean Concrete – See Lean ConcreteSubbase.

Subbase, Permeable – See Permeable Subbase.

Subbase, Stabilized – See Stabilized Subbase.

Subbase, Unstabilized – See Unstabilized Sub-base.

Subgrade – The natural ground, graded and com-pacted, on which a pavement structure is built. Alsocalled grade.

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Water-Cement Ratio – The ratio of the amount ofwater, exclusive only of that absorbed by the aggre-gates, to the amount of portland cement in a con-crete or mortar mixture; preferably stated as adecimal by weight.

Water-Cementitious Materials Ratio – The ratio ofthe amount of water, exclusive only of that absorbedby the aggregates, to the amount of portland cementand other cementitious material (fly ash, pozzolan,etc.) in a concrete or mortar mixture; preferablystated as a decimal by weight.

Water-Reducing Admixture – A material that eitherincreases slump of freshly mixed mortar or concretewithout increasing water content or maintains aworkability with a reduced amount of water, theeffect being due to factors other than air entrain-ment; also known as water reducer.

Water-Reducing Admixture (High Range) – Awater-reducing admixture capable of producing largewater reduction or great flowability without causingundue set retardation or entrainment of air in mortaror concrete.

Weight Batching – Measuring the constituent mate-rials for mortar or concrete by weight.

Well-Graded Aggregate – Aggregate having a par-ticle size distribution that will produce maximum den-sity; i.e., minimum void space.

Workability – That property of freshly mixed con-crete or mortar which determines the ease andhomogeneity with which it can be mixed, placed,compacted, and finished.

X

Y

Yield – The volume of fresh concrete produced froma known quantity of ingredients; the total weight ofingredients divided by the unit weight of the freshlymixed concrete.

Z

Unit Weight – See Bulk Density and SpecificGravity.

Unreinforced Concrete – See Plain Concrete.

Unstabilized Subbase – A subbase layer composedof crushed stone, bank run sand-gravels, sands,soil-stabilized gravels, bottom ash, crushed or granu-lated slag, recycled concrete aggregate, or localmaterials such as crushed wine waste and sand-shell mixtures and not including any stabilizing agent(i.e., cement or asphalt binders). These are the mostcommon type of subbase for applications such asstreets, roadways and highways. The principal crite-rion for creating a good unstabilized subbase is tolimit the amount of fines passing the No. 200 sieve(75 µm) to 15%; if there are too many fines, theunstabilized subbase may hold water more readilyand will be prone to erosion, pumping and frostaction.

Untreated Subbase – See Unstabilized Subbase.

V

Vertical Shaft Impact Crusher – See ImpactCrusher.

Virgin Aggregate – Aggregate that is mined fromnatural sources; includes materials such as sand(either natural or crushed), gravel (either natural orcrushed), crushed stone, etc.

Virgin Material – Material that has not been previ-ously used or consumed, or subjected to processingother than for its production.

Volume Batching – The measuring of the con-stituent materials for mortar or concrete by volume.

W

w/c – See Water-Cement Ratio.

w/cm – See Water-Cementitious Materials Ratio.

Warping – Deformation of concrete pavement slabsdue to hygrothermal (relative humidity/dryingshrinkage) gradients.


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AAAR, see Reactivity, Alkali-aggregateAbrasion resistance, 25, 38Absorption, 17-19, 25, 28, 31, 38, 42, 46, 48, 56, 59,

62, 63, 65, 69Capacity, 17-19, 31, 48

ACR, see Reactivity, Alkali-carbonateAdmixture, 27, 29, 35, 46, 69, 70, 72, 75-77

Air-entraining, 28, 35, 47, 49, 69, 70Chemical, 13, 17, 19, 20, 23, 28, 29, 31, 46, 51,

67, 70, 73, 76Mineral, 19, 25, 30, 31, 46, 65, 72, 76Superplasticizer, 76Water reducer, 28, 46, 47

Adverse effects, see Effects, AdverseAggregate

Blending, 23, 35, 44, 47, 59, 64, 69Coarse, 13, 14, 17, 19-21, 25, 35, 42, 46, 47Coarse recycled concrete, 13, 14, 17-21, 25, 27-

32, 34, 36, 37, 41, 42, 45-48, 52, 55, 56, 58,61-63, 65-69, 71, 73

Costs, 1, 2Fine, 2, 4, 27, 30, 32, 35, 36, 39, 46, 47, 65, 69,

72-74Fine recycled concrete, 18, 19, 21, 23-32, 34, 36,

38, 39, 41-48, 76Gravel, 17, 38, 69, 71, 72, 77Interlock, 19, 25, 34, 37, 38, 46, 47, 69Natural sand, 4, 28, 30, 33, 36, 46, 74Reactive, 20, 32, 35, 61, 62, 75Recycled concrete, 1-5, 7-9, 10-15, 17-21, 23-26,

27-32, 33-40, 41-49, 51-54, 55-59, 61-64, 69-71, 75, 77

Resources, see Resources, AggregateToughness, 42Virgin, 1-4, 13, 14, 17-19, 23, 25, 27, 29-31, 34,

35, 38, 40, 41, 44-48, 56, 58, 59, 61-63, 69,71, 72, 74, 75, 77

Virgin coarse, 13, 14, 17, 18, 21, 47Virgin fine, 4, 27, 46, 47

AirContent, 25, 27, 28, 34-36, 46, 48, 66Entrained, 7, 25, 28, 46, 77Entrapped, 25, 28, 36, 46

Air-entrainment, 7, 25, 28, 35, 77Air-entraining admixture, see Admixture, Air-

entrainingAlkali-aggregate reactivity, see Reactivity, Alkali-

aggregateAlkali-carbonate reactivity, see Reactivity, Alkali-

carbonateAlkali-silica reactivity, see Reactivity, Alkali-silicaAlkalis, 32, 70, 75Asphalt concrete, see Concrete, AsphaltAsphalt-treated subbase, see Subbase, Asphalt-

treatedASR, see Reactivity, Alkali-silicaATB, see Subbase, Asphalt-treated

BBackfill, 4, 23, 57, 75Base, see SubbaseBatch, 28, 46, 64Batching, 25, 28, 56, 62, 64, 77Bedding, 4, 26Beneficiation, 7, 13, 14, 70Bleeding, 27, 28Blender of Aggregate, see Aggregate, BlendingBreaker

Impact, 3, 7-10, 12, 13, 27, 28, 31, 39, 41, 46,58, 61, 62

Resonant, 8Vibrating beam, 8, 9

Breaking equipment, 9, 10, 55Bulk density, 65, 70, 77

CCalcium carbonate precipitate, see LeachateCalcium hydroxide, 3, 14, 21, 24, 25, 43, 70Carbon dioxide, 2, 3, 14, 21, 70

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Carbon sequestration, 3Carbonation, 3, 32, 70Cement

Grains, 14, 21, 42, 75, 76Hydration, 3, 14, 21, 42, 43, 69, 70, 73, 75, 76Mortar, 3, 4, 13, 14, 17-19, 21, 23-25, 27-34, 36-

39, 41, 56, 58, 62Paste, 24, 28, 30, 44-46, 69, 74, 76Type, 7Low-alkali, 32, 35Partially-hydrated, 4, 8, 75, 76Portland, 3, 51-54, 70, 73, 75-77Slag, 20, 30, 32, 45, 62, 69, 70, 75

Cement-stabilized subbase, see Subbase, Cement-stabilized

Cement-treated subbase, see Subbase, Cement-treated

Chemical admixture, see Admixture, ChemicalChloride content, 17, 20, 21, 45, 70CO2, see Carbon dioxideCoarse

Aggregate, see Aggregate, CoarseRCA, see Aggregate, Coarse recycled concrete

Coefficient of thermal expansion and contraction, 25,30, 34, 36, 38, 71

Compatibility, 38Compressive strength, see Strength, CompressiveConcrete

Asphalt, 7, 23, 34, 71Crushed, 13, 14, 24, 26, 43, 52-54, 56-58, 62Hardened, 1, 27, 29, 31, 51, 67, 70, 75, 76Mixture, see Mixture, ConcretePavement structure, 4, 61, 73Pavement, Continuously reinforced, 20, 34, 38-

40, 45, 47, 71, 75Pavement, Jointed plain, 8, 13, 19, 30, 35, 36,

47, 73Pavement, Jointed reinforced, 13, 19, 20, 30, 33,

34, 37, 45, 47, 51, 53Plastic, 27-29, 46, 48, 72, 74, 75, 77Ready mixed, 15Recycling, see Recycling, ConcreteStrength, see Strength, Concrete

Cone crusher, see Crusher, ConeConservation, 2, 23, 52, 54

Construction, 1-4, 8, 19, 20, 23, 24, 26, 31, 33, 35,36, 38, 44, 46-49, 51, 52, 54, 55, 57, 59, 61,65, 71, 74, 76

Two-course, 25, 47, 48Contaminant, 7, 11, 13, 14, 21, 23, 25, 28, 41, 42,

45, 46, 75Continuously reinforced concrete pavement, see

Concrete pavement, Continuously reinforcedContractor, 12, 23, 38, 39, 51, 55, 56, 74Corrosion, 20, 31, 32, 45Cost savings, see Savings, CostCracking, 10, 19, 31, 32, 34, 36, 37, 45, 47, 62, 70-

73Durability, 19, 31, 32, 34, 36, 37, 45, 62, 71Intermediate, 37Map, 34Reflection, 34Slab, 10, 37

CRCP, see Concrete pavement, Continuouslyreinforced

Creep, 29, 30Crush, 1-3, 7, 8, 10-14, 17-19, 21, 24-26, 35, 37, 40,

41, 43, 52-58, 61, 62, 69, 71, 73-75, 77Crushed, see CrushCrushed concrete, see Concrete, CrushedCrushed stone, 19, 35Crusher, 11-14, 18, 21, 24, 41, 44, 69, 71-73, 77

Cone, 13, 41, 71Horizontal shaft impact, 72Jaw, 13, 18, 41, 71Mini concrete, 13Primary, 11-14, 18, 73Secondary, 4, 11-14, 23, 41, 71Vertical shaft impact, 13, 73

Crushing, see CrushCrushing plant, 8, 13, 18, 40CTB, see Subbase, Cement-treatedCTE, see Coefficient of thermal expansion and

contractionCuring, 29, 31, 34, 48, 49, 71Curling, 30, 43, 46, 71

DDaylighted subbase, see Subbase, DaylightedD-cracking, see Cracking, Durability


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Demolition, 1-3, 7, 8, 10, 41, 42, 53Dense-graded subbase, see Subbase, Dense-

gradedDensity, 13, 31, 57, 59, 65, 66, 70, 71, 75, 77Design

Mixture, 17, 19, 25, 27-31, 34-36, 39, 46, 47, 63,73

Structural, 25, 34, 37, 38, 43, 47, 58Detrimental effects, see Effects, DetrimentalDiamond grinding, 35, 37Disposal, 2, 3, 35, 71Dowel, 7, 10, 19, 25, 34, 35, 37, 45, 56, 71, 73Dowel load transfer, 19, 34Drainable subbase, see Subbase, DrainableDrainage, 4, 10, 21, 24, 26, 32, 43-45, 52, 54, 57,

58, 71, 72, 74, 76Drying shrinkage, see Shrinkage, DryingDurability, 7, 19, 20, 25, 28, 31, 32, 36, 37, 45, 46,

61, 71, 72Cracking, see Cracking, DurabilityFreeze-thaw, 19, 25, 31, 32, 36, 37, 46, 62, 71

Dust, 13, 14, 21, 24, 43, 44, 58

EE, see Modulus of elasticityEconocrete, see Subbase, Lean concreteEdge drainage, 21, 24, 36, 43, 44Effects

Adverse, 27, 56, 61-63Detrimental, 8Environmental, 14, 20, 76Negative, 14, 27

Elastic modulus, see Modulus of elasticityElectromagnet, 11, 12Embedded steel, see Steel, EmbeddedEnergy savings, see Savings, EnergyEntrained air, see Air, EntrainedEntrapped air, see Air, EntrappedEnvironmental

Effects, see Effects, EnvironmentalRegulations, see Regulations, Environmental

Epoxy-coated, see Reinforcement, Epoxy-coatedErosion control, 4, 26Evaluation, 7, 33, 41, 51, 53

Expansion, 20, 30, 35, 38, 62, 66, 67, 70, 71, 75, 76Extraction, 3

FFill

Applications, 7, 11, 21, 26, 39Granular, 26

FineAggregate, see Aggregate, FineRCA, see Aggregate, Fine recycled concrete

Finishability, 27Flexural strength, see Strength, FlexuralFly ash, 20, 28, 30, 32, 35, 36, 45-47, 54, 62, 67, 69,

72, 77Foundation, 1, 4, 7, 17, 38, 39, 41, 44, 48, 53, 54Free-draining subbase, see Subbase, Free-drainingFreeze-thaw durability, see Durability, Freeze-thawFresh concrete, see Concrete, PlasticFront-end loader, 8, 11Frost-susceptible, 19Fuel savings, see Savings, Fuel

GGeotextile, 24, 58, 68, 72GHG, see Greenhouse gasGradation, 2, 4, 10, 18, 23, 27, 29, 30, 41, 43-45,

58, 61, 69Granular, 1, 23, 24, 26, 42, 57, 69, 70, 72, 73, 75

Fill, see Fill, GranularSubbase, see Subbase, Unstabilized

Gravel, see Aggregate, GravelGreenhouse gas, 2, 3, 72

HHammer, 8, 9Hardened Concrete, see Concrete, HardenedHaul distance, 40Hauling, 2, 15, 35, 40, 56Heavy metals, see Metals, HeavyHorizontal shaft impact crusher, see Crusher,

Horizontal shaft impactHydration, see Cement hydration

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IImpact breaker, see Breaker, ImpactIn-place recycling, see Recycling, In-placeIntermediate cracking, see Cracking, Intermediate

JJaw crusher, see Crusher, JawJoint sealant removal, see Removal, Joint sealantJoint spalling, see SpallingJointed plain concrete pavement, see Concrete

pavement, Jointed plainJointed reinforced concrete pavement, see Concrete

pavement, Jointed reinforcedJPCP, see Concrete pavement, Jointed plainJRCP, see Concrete pavement, Jointed reinforced

LL.A. Abrasion, see Los Angeles abrasion testLandfill, 2, 3, 15LCB, see Subbase, Lean concreteLeachate, 24, 25, 43, 44, 51Lean concrete subbase, see Subbase, Lean

concreteLime, 20, 26, 70, 75Load transfer, 19, 25, 34-38, 46, 47, 69, 71Loader operator, 11, 21Local regulations, see Regulations, State and localLongitudinal reinforcement, see Reinforcement,

LongitudinalLos Angeles abrasion test, 17, 19, 38, 58, 62, 73Low-alkali cement, see Cement, Low-alkali

MMap cracking, see Cracking, MapMass Loss, 17, 19, 20, 73, 76Mechanical properties, see Properties, MechanicalMetals, Heavy, 14Microcracking, 36, 38Micro-deval test, 42, 58, 62, 66Milling, 8, 14Mineral admixture, see Admixture, MineralMini concrete crusher, see Crusher, Mini ConcreteMining, 3, 15

MixtureConcrete, 2, 7, 8, 11, 14, 17, 19, 21, 25, 27-35,

38, 39, 41, 44-48, 56, 61-63, 72Design, see Design, MixtureProportioning, 29, 31, 45, 46, 73, 74

Modulus of elasticity, 4, 25, 29, 30, 34, 38, 39, 46Modulus, Resilient, 42, 59, 66Moisture content, 4, 28, 71, 73Movement, 37, 44, 76

NNaCl, see Sodium chlorideNatural resources, see Resources, NaturalNatural sand, see Aggregate, Natural sandNegative effects, see Effects, Negative

OOpen graded subbase, see Subbase, PermeableOverlay, 4, 34

PPartially-hydrated cement, see Cement, Partially-

hydratedParticle size, 13, 17-19, 32, 36, 41, 42, 46, 65, 71,

77Paste, 24, 28, 30, 44, 45, 46, 69Patching materials, 7, 71Pavement condition index, 36PCI, see Pavement condition indexPerformance, 1, 4, 8, 13, 18, 19, 23, 25, 33-35, 37-

40, 42, 43, 53, 54Permeability, 20, 24, 29, 31, 38, 43, 45, 58, 72, 74Permeable subbase, see Subbase, PermeablePetrographic, 34, 67Physical properties, see Properties, PhysicalPin and lift, 8Pipe bedding, see BeddingPlastic concrete, see Concrete, PlasticPopout, 45Portland cement, see Cement, PortlandPrecipitate, 21, 24, 25, 43, 44, 51Preparation, 7, 21, 48, 65Primary crusher, see Crusher, PrimaryProcessing, 2, 8, 12, 13, 21, 41, 48, 52, 55, 56, 58,

61, 70, 72, 75, 77


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Production, 1-4, 7-11, 13-15, 17, 18, 21, 23-27, 41-43, 48, 55-57, 59, 61-63, 74, 77

PropertiesMechanical, 17, 19, 25, 29, 33, 46, 71Physical, 3, 17, 25, 29, 46, 58, 62, 63, 69, 70, 76

Proportioning, see Mixture, Proportioning

QQC, see Quality controlQuality control, 2, 52, 56, 59, 61, 63, 64, 74

RRCA, see Aggregate, Recycled ConcreteReactive aggregate, see Aggregate, ReactiveReactivity

Alkali-aggregate, 45, 62, 70Alkali-carbonate, 62, 70Alkali-silica, 20, 25, 31-36, 45, 47, 53, 62, 70, 73

Ready mixed concrete, see Concrete, Ready mixedRebar, see ReinforcementRecementing, 58, 75Reconstruction, 1-4, 8, 34, 36, 37, 39, 51Recycled, 2-5, 7, 9, 11, 13, 15, 17, 19, 20, 21, 26,

30, 32-37, 39, 41-43, 45, 47-49, 51-54, 56, 57,61, 69-72, 75, 77

Aggregate, see Aggregate, Recycled concreteRecycling

Concrete, 1-4, 7, 8, 11-15, 18, 21, 25, 28, 33-35,39, 40, 44, 51

In-place, 14, 15, 52, 59Reflection cracking, see Cracking, ReflectionRegulation

Environmental, 1, 55, 57, 61State and local, 1, 55, 57, 61

Rehabilitation, 2, 4, 35, 37, 51-54Reinforcement, 7, 9, 10, 13, 38, 47, 53, 71-75

Epoxy-coated, 7, 8, 10, 11, 15, 20, 32-34, 37, 45,47, 55, 56, 71, 75

Longitudinal, 24, 34, 36, 38, 47, 71, 73Tie bar, 10, 11, 55, 73

Reinforcing steel, 7, 8, 10, 11, 15, 20, 33, 37, 45, 47,55, 56, 75

Removal, 1-3, 7, 8, 10, 11, 13, 14, 21, 24, 41, 45,51, 52, 55, 56, 58, 61, 71, 76

Joint sealant, 7, 23, 36, 45, 47, 71

Removing, see RemovalResilient modulus, see Modulus, ResilientResonant breaker, see Breaker, ResonantResources

Aggregate, 1, 2, 48Natural, 2

Restoration, 34Rhino horn, 10Ride quality, 34, 35, 48Rip-rap, see Erosion controlRoll-O-Meter, 34, 48

SSalvaged Steel, see Steel, SalvagedSaturated surface dry, 28, 63, 64, 75Savings

Cost, 2, 3Energy, 3, 15, 23, 40Fuel, 3, 15, 40

SCM, see Supplemental cementitious materialsScreening, 2, 3, 14, 21, 42, 55, 56, 71Sealant removal, see Removal, Joint sealantSecondary crusher, see Crusher, SecondarySettlement, 1, 38Shrinkage, Drying, 29, 30, 71, 77Sieve, 7, 17-19, 21, 24, 29, 41, 45, 57, 65, 71, 72,

74, 75, 77Slab cracking, see Cracking, SlabSlag cement, see Cement, SlagSlope stabilization, see Stabilization, SlopeSlump, 36, 46, 76, 77Sodium chloride, 20, 70Soil stabilization, see Stabilization, SoilSpalling, 34, 36Specific gravity, 3, 17, 19, 29, 31, 38, 46, 56, 59, 62,

63, 65, 70, 75-77SSD, see Saturated surface dryStabilization

Slope, 26Soil, 4, 7, 11, 14, 21, 26, 45, 55, 57-59, 65

Stabilized subgrade, see Subgrade, StabilizedState regulations, see Regulations, State and localStatic triaxial test, 42

Index

Summ


RCA:2 Production

3 Properties4 Uses



ance7 Recom

mendations



84

SteelEmbedded, 10, 11, 13, 20, 32, 41, 45, 73Salvaged, 7, 8, 10-13, 15, 20, 21, 26, 32, 33, 37,

41, 45, 47, 53, 55, 56, 71, 73, 75Stiffening, 4, 25, 43, 48Stockpile, 3, 7, 12, 14, 23, 39, 40, 42, 48, 55, 56, 59,

62, 64Strength, 4, 7, 9, 11, 17, 25, 28-30, 33-36, 38, 39,

42, 43, 46, 47, 52, 58, 61, 63, 66, 69, 72, 73,75

Compressive, 29, 30, 34, 36, 38, 71Concrete, 4, 7, 9, 11, 28, 29, 39, 46Flexural, 29, 39

Structural design, see Design, StructuralSubbase, 2-4, 7, 10, 11, 14, 17, 19, 21, 23-26, 33,

35-40, 42-44, 47, 48, 54, 55, 57-59, 65, 70-77Asphalt-treated, 40, 48, 70, 76Cement-stabilized, 4, 24, 44, 70, 76Cement-treated, 24, 63, 70, 71, 73, 75, 76Daylighted, 21, 24, 44, 52, 71, 72, 76Dense-graded, 4, 23, 24, 43, 69, 71, 75, 76Drainable, 21, 39, 43, 44, 70, 71Free-draining, 24, 43, 47, 72, 76Lean concrete, 24, 25, 70, 72, 73, 76Permeable, 32, 38, 52, 53, 69, 71, 72, 74-76Unstabilized, 19, 21, 23, 36, 40, 43, 44, 59, 72,

76, 77Subgrade, 4, 10, 40, 55, 57, 65, 74, 76

Stabilized, 40Sulfate, 17, 20, 31, 45, 58, 66, 67, 76Superplasticizer, see Admixture, SuperplasticizerSupplemental cementitious materials, 29, 75, 76Surface Dust, see Dust

TTie bar, see Reinforcement, Tie barTwo-course construction, see Construction, Two-

courseTwo-lift construction, see Construction, Two-course

UUnstabilized subbase, see Subbase, Unstabilized

VVertical shaft impact crusher, see Crusher, Vertical

shaft impactVibrating beam breaker, see Breaker, Vibrating

beamVirgin

Aggregate, see Aggregate, VirginCoarse aggregate, see Aggregate, Virgin coarseFine aggregate, see Aggregate, Virgin fine

Volumetric, 28, 31, 34, 46, 48, 66, 67

Ww/c, see Water-cement ratiow/cm, see Water-cementitious materials ratioWarping, 30, 43, 46, 77Washing, 3, 14, 21, 24, 28, 43-45, 65Water

Demand, 11, 19, 21, 25, 27, 28Reducer, see Admixture, Water reducer

Water-cement ratio, 76, 77Water-cementitious materials ratio, 28-30, 32, 34-36,

45, 46, 77Workability, 27, 28, 33, 38, 39, 42, 45, 46, 56, 62,

70, 72, 77

YYield, 10, 13, 56, 77


7 Recomm

endations6 Perform

ance5 Properties


4 Uses3 Properties

2 Production RCA:

1 IntroductionSum

mary/Overview


RecyclingConcrete Pavements

ENGINEERING BULLETIN

Recyclin

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This publication is intended SOLELY for use by PROFESSIONAL PERSONNEL who are competent to evaluate the significance and limitations of the information provided herein, and who will accept total responsibility for the application of this information. The American Concrete Pavement Asso-ciation DISCLAIMS any and all RESPONSIBILITY and LIABILITY for the accuracy of and the application of the information contained in this publication to the full extent permitted by law.

American Concrete Pavement Association5420 Old Orchard Rd., Suite A100Skokie, IL 60077-1059www.pavement.com

EB

043PA

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PAVEMEN

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CIATION EB043PEB043P

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