August 2011 Guide to Cement-Based Integrated Pavement ... · specific engineering pavement...

Guide to Cement-Based Integrated Pavement Solutions

August 2011

Cement-Based Integrated Pavement Solutions

Heavy Industrial Airports Highways Country RoadsArterials CommercialInterstatesLight Industrial

Residential

1 41 4 1 4

1 2 4

1 4 6

1 2 41 4 6

** The use of 7 & 8 applies to all uses depending on quality of soil and need for stabiliaztion

1 2 31 2 4 7

Heavy Industrial Light Industrial Airports Commercial Residential Recreation

LAND USE

CEMENT-BASED INTEGRATED PAVEMENT SOLUTIONS

1 2 3 4 5 6 7 8

Conventional Overlays CRCP

VIBRATORY COMPACTION

Pervious Concrete

Full-Depth Reclamation

Cement- Treat-ed Base

Cement- Modified

Soils

Roller- Com-pacted Con-

crete

EXTERNAL COMPACTION

Concrete Recycling Full-Depth Repair Partial-Depth Repair Dowel Bar Retrofit Slab Stabilization Diamond Grinding

SUSTAINABLE PRACTICE - PRESERVATION OF THE SYSTEM’S EQUITY

This page illustrates the land-use applications for the cement-based integrated pavement solutions described in this guide.

For more information on these applications, please see the table of contents to locate page numbers for each application.

Technical Report Documentation Page

1. Report No. 2. Government Accession No. 3. Recipient’s Catalog No.

4. Title and Subtitle 5. Report Date

Guide to Cement-Based Integrated Pavement Solutions August 2011

6. Performing Organization Code

7. Author(s) 8. Performing Organization Report No.

Sabrina Garber, Robert Otto Rasmussen, and Dale Harrington

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS)

Institute for Transportation

Iowa State University

2711 South Loop Drive, Suite 4700

Ames, IA 50010-8664

11. Contract or Grant No.

12. Sponsoring Organization Name and Address 13. Type of Report and Period Covered

Portland Cement Association

5420 Old Orchard Road

Skokie, IL 60077

14. Sponsoring Agency Code

15. Supplementary Notes

16. Abstract

This guide provides a clear, concise, and cohesive presentation of cement-bound materials options for 10 specific engineering pavement applications: new concrete pavements, concrete overlays, pervious concrete, precast pavements, roller-compacted concrete, cement-treated base, full-depth reclamation with cement, cement-modified soils, recycled concrete aggregates, and repair and restoration. Each application is presented as a method for meeting specific design and construction objectives that today’s pavement practitioners must accomplish. The benefits, considerations, brief description, and summary of materials, design, and construction requirements, as well as a list of sustainable attributes, are provided for every solution. This guide is intended to be short, simple, and easy to understand. It was designed so that the most up-to-date and relevant information is easily extractable. It is not intended to be used as a design guide for any of the applications identified herein. Recommendations for additional information that can provide such details are given at the end of each solution discussion. The intended audience is practitioners, including engineers and managers who face decisions regarding what materials to specify in the pavement systems they design or manage. The audience also includes city and county engineers, along with the A/E firms that often represent them, and state DOT engineers at all levels who are seeking alternatives in this era of changing markets.

17. Key Words 18. Distribution Statement

pavement solutions, portland cement concrete, overlays, pervious pavement, roller-compacted concrete, full-depth reclamation, cement-treated base, cement-modified soils, pavement repair, pavement restoration

No restrictions.

19. Security Classification (of this report)

20. Security Classification (of this page)

21. No. of Pages 22. Price

Unclassified. Unclassified. 92

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized

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Guide to Cement-Based Integrated Pavement Solutions

AuthorsSabrina Garber, The Transtec Group, Inc.

Robert Otto Rasmussen, The Transtec Group, Inc.

Contributing AuthorDale Harrington, Snyder and Associates

Editorial StaffSabrina Shields-Cook, Managing Editor

Carol Gostele, Copyeditor

Mina Shin, Graphic Designer

Technical Advisory CommitteeWayne Adaska, Portland Cement Association

Tom Cackler, National Concrete Pavement Technology Center

Greg Dean, American Concrete Pavement Association, Southeast Chapter

Gary Fick, Trinity Construction Management Services

Jerry Reece, North Carolina Concrete Pavement Association

Matt Singel, Cement Council of Texas

Gordon Smith, Iowa Concrete Paving Association

Leif Wathne, American Concrete Pavement Association

August 2011

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About This GuideThis Guide to Cement-Based Integrated Pavement Solu-tions is a product of the National Concrete Pavement Technology Center (National CP Tech Center) at Iowa State University’s Institute for Transportation, with funding from the Portland Cement Association. It provides a clear, concise, and cohesive presentation of cement-bound materials options for specific engineer-ing pavement applications. Each application identified in this guide is presented as a method for meeting specific design and construction objectives that today’s pavement practitioners must accomplish.

AcknowledgmentsThe authors and co-authors, the National CP Tech Center, and the Portland Cement Association are grateful to the knowledgeable and experienced profes-sionals, public and private, who contributed to the development of this guide. While the authors gener-ated the overall content, it was the technical advisory committee’s and technical reviewers’ careful reviews of drafts, thoughtful discussions, and suggestions for revisions and refinements that make this guide a com-prehensive resource for practitioners. The National CP Tech Center and the Portland Cement Association appreciate the committee’s and reviewers’ invaluable assistance.

Photo CreditsThe photographs on the cover and throughout this guide were provided by the following individuals and organizations:

•American Concrete Pavement Association

•American Concrete Pavement Association, Southeast Chapter

•California Nevada Cement Association

•Cement Council of Texas

•Charger Enterprises

•Chicago Department of Transportation

•Illinois Tollway

•Iowa Concrete Paving Association

•John Kevern, University of Missouri-Kansas City

•National Concrete Pavement Technology Center

•Portland Cement Association

•The Transtec Group, Inc.

For More InformationFor technical assistance regarding cement-based concrete paving, contact the Portland Cement Association or the National CP Tech Center:

Wayne Adaska, Director, PavementsPortland Cement Association5420 Old Orchard Rd.Skokie, IL 60077847-966-6200, [email protected], www.cement.org/

Tom Cackler, DirectorSabrina Shields-Cook, Managing EditorNational CP Tech CenterInstitute for Transportation, Iowa State University2711 S. Loop Drive, Suite 4700Ames, IA 50010-8664515-294-7124, [email protected], www.cptechcenter.org/

DisclaimersNeither Iowa State University nor this document’s authors, editors, designers, illustrators, distributors, or technical advisors make any representations or warranties, expressed or implied, as to the accuracy of information herein and disclaim liability for any inaccuracies.

Iowa State University does not discriminate on the basis of race, color, age, religion, national origin, sexual orientation, gender identity, sex, marital status, disability, genetic testing, or status as a U.S. veteran. Inquiries can be directed to the Director of Equal Opportunity and Diversity, Iowa State University, 3680 Beardshear Hall, 515-294-7612.

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Contents

About This Guide ............................................................................iv

Acknowledgments .........................................................................iv

Photo Credits ...................................................................................iv

Contents .............................................................................................v

List of Figures ................................................................................. vii

List of Tables ......................................................................................x

Preface ................................................................................................xi

Important Defi nitions ..................................................................xii

Table of Solutions ........................................................................ xiv

1. New Concrete Pavements ....................................................1-1Objectives ......................................................... 1-1Solution ............................................................ 1-1Benefi ts ............................................................. 1-1Considerations .................................................. 1-1Typical Applications .......................................... 1-1Description ....................................................... 1-1Materials ........................................................... 1-3Design .............................................................. 1-4Construction ..................................................... 1-5Sustainability .................................................... 1-7For More Information ....................................... 1-7

2. Concrete Overlays ...................................................................2-1Objectives ......................................................... 2-1Solution ............................................................ 2-1Benefi ts ............................................................. 2-1Considerations .................................................. 2-1Typical Applications .......................................... 2-1Description ....................................................... 2-1Materials ........................................................... 2-2Design .............................................................. 2-3Construction ..................................................... 2-5Sustainability .................................................... 2-6For More Information ....................................... 2-7

3. Pervious Concrete ...................................................................3-1Objectives ......................................................... 3-1Solution ............................................................ 3-1Benefi ts ............................................................. 3-1Considerations .................................................. 3-1Typical Applications .......................................... 3-1Description ....................................................... 3-2Materials ........................................................... 3-3Design .............................................................. 3-4Construction ..................................................... 3-5Sustainability .................................................... 3-6For More Information ....................................... 3-6

4. Precast Pavements..................................................................4-1Objectives ......................................................... 4-1Solution ............................................................ 4-1Benefi ts ............................................................. 4-1Considerations .................................................. 4-1Typical Applications .......................................... 4-1Description ....................................................... 4-1Materials ........................................................... 4-2Design .............................................................. 4-3Construction ..................................................... 4-3Sustainability .................................................... 4-5For More Information ....................................... 4-5

5. Roller-Compacted Concrete ...............................................5-1Objectives .......................................................... 5-1Solution ............................................................. 5-1Benefi ts .............................................................. 5-1Considerations .................................................. 5-1Typical Applications ........................................... 5-1Description ........................................................ 5-2Materials ............................................................ 5-3Design ............................................................... 5-3Construction ..................................................... 5-5Sustainability ..................................................... 5-6For More Information ........................................ 5-7

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6. Cement-Treated Base ............................................................6-1Objectives ......................................................... 6-1Solution ............................................................ 6-1Benefi ts ............................................................. 6-1Considerations .................................................. 6-1Typical Applications .......................................... 6-1Description ....................................................... 6-1Materials ........................................................... 6-2Design .............................................................. 6-3Construction ..................................................... 6-3Sustainability .................................................... 6-5For More Information ....................................... 6-5

7. Full-Depth Reclamation with Cement (FDR) .................7-1Objectives ......................................................... 7-1Solution ............................................................ 7-1Benefi ts ............................................................. 7-1Considerations .................................................. 7-1Typical Applications .......................................... 7-1Description ....................................................... 7-1Materials ........................................................... 7-2Design .............................................................. 7-2Construction ..................................................... 7-2Sustainability .................................................... 7-3For More Information ....................................... 7-3

8. Cement-Modifi ed Soils (CMS) .............................................8-1Objectives ......................................................... 8-1Solution ............................................................ 8-1Benefi ts ............................................................. 8-1Considerations .................................................. 8-1Typical Applications .......................................... 8-1

Description ....................................................... 8-1Materials ........................................................... 8-2Design .............................................................. 8-2Construction ..................................................... 8-2Sustainability .................................................... 8-3For More Information ....................................... 8-3

9. Recycled Concrete Aggregates ..........................................9-1Objectives ......................................................... 9-1Solution ............................................................ 9-1Benefi ts ............................................................. 9-1Considerations .................................................. 9-1Typical Applications .......................................... 9-1Description ....................................................... 9-1Materials ........................................................... 9-2Design ............................................................... 9-2Construction ..................................................... 9-3Sustainability ..................................................... 9-4For More Information ....................................... 9-4

10. Repair and Restoration .................................................... 10-1Description .................................................... 10-1Full-Depth Repairs ........................................ 10-1Partial-Depth Repairs ..................................... 10-2Stitching ........................................................ 10-2Slab Stabilization ........................................... 10-2Slab Jacking ................................................... 10-3Joint Resealing ............................................... 10-3Dowel Bar Retrofi t ......................................... 10-3Diamond Grooving and Grinding .................. 10-4For More Information .................................... 10-5

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List of Figures

Figure 1-1. Schematic of typical concrete pavement cross-section ..................................................................... 1-1

Figure 1-2. Schematic of the various types of new concrete pavements ............................................................. 1-2

Figure 1-3. Concrete mixture constituents ......................................................................................................... 1-3

Figure 1-4. Sawcutting JPCP.............................................................................................................................. 1-5

Figure 1-5. Concrete placed over dowel baskets ................................................................................................ 1-6

Figure 1-6. Dowel-bar inserter .......................................................................................................................... 1-6

Figure 1-7. JRCP reinforcement in place before paving ...................................................................................... 1-6

Figure 1-8. CRCP reinforcement placed before paving....................................................................................... 1-6

Figure 1-9. Burlap drag on fresh concrete .......................................................................................................... 1-7

Figure 1-10. Curing compound applied by spray nozzles on a cure cart ........................................................... 1-7

Figure 2-1. Unbonded overlay ........................................................................................................................... 2-2

Figure 2-2 Overlay applications ......................................................................................................................... 2-2

Figure 2-3. Typical cross-section of unbonded overlay ....................................................................................... 2-3

Figure 2-4. Unbonded concrete overlay construction over a nonwoven geotextile interlayer ............................. 2-5

Figure 2-5. Bonded overlay construction ........................................................................................................... 2-6

Figure 3-1. Miller Park in Fair Oaks, California ................................................................................................. 3-1

Figure 3-2. Imperial Beach Sports Park, California ............................................................................................ 3-1

Figure 3-3. Pervious concrete for alley in Chicago, Illinois ................................................................................ 3-2

Figure 3-4. Pervious concrete ............................................................................................................................ 3-2

Figure 3-5. Pervious concrete pavement parking lot .......................................................................................... 3-2

Figure 3-6. Fresh pervious concrete .................................................................................................................. 3-3

Figure 3-7. Pervious concrete pavement in the rain ........................................................................................... 3-4

Figure 3-8. Schematic of pervious full exfiltration pavement design .................................................................. 3-5

Figure 3-9. Schematic of pervious partial exfiltration pavement design ............................................................. 3-5

Figure 3-10. Schematic of pervious no exfiltration pavement design ................................................................. 3-5

Figure 3-11. Compacting the placed pervious concrete ..................................................................................... 3-5

Figure 3-12. Curing pervious concrete with plastic sheeting ............................................................................. 3-6

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Figure 4-1. Precast pavement system cross-section ............................................................................................ 4-1

Figure 4-2. Nighttime placement of precast panels in Virginia ........................................................................... 4-2

Figure 4-3. Precast pavement system in Indonesia ............................................................................................. 4-2

Figure 4-4. Concrete poured into form for precast panel ................................................................................... 4-4

Figure 4-5. Vibrators for consolidation of concrete around reinforcement in precast prestressed panel .............. 4-4

Figure 4-6. Placement of precast panel for precast JCP system ........................................................................... 4-4

Figure 4-7. Placement of a prestressed precast panel ......................................................................................... 4-4

Figure 5-1. Typical RCC versus PCC surface ...................................................................................................... 5-2

Figure 5-2. Pavement cross-section with RCC surface ....................................................................................... 5-2

Figure 5-3. Pavement cross-section with RCC base ............................................................................................ 5-2

Figure 5-4. RCC construction for commercial and heavy industrial applications ............................................... 5-2

Figure 5-5. Typical mix design constituents ....................................................................................................... 5-3

Figure 5-6. RCC material looks drier than conventional concrete ...................................................................... 5-3

Figure 5-7. Flexural beam testing ...................................................................................................................... 5-4

Figure 5-8. Typical RCC design relies on aggregate interlock at cracks ............................................................... 5-4

Figure 5-9. RCC delivered to jobsite .................................................................................................................. 5-5

Figure 5-10. Tilt-drum mixer ............................................................................................................................ 5-5

Figure 5-11. Ready-mix transit trucks dumping into haul trucks ....................................................................... 5-5

Figure 5-12. Mobile RCC pugmill mixing plant and mixing chamber ................................................................ 5-6

Figure 5-13. RCC placement ............................................................................................................................. 5-6

Figure 5-14. Compacting RCC using both vibratory and pneumatic-tired rollers .............................................. 5-6

Figure 5-15. RCC in-place density measurement ............................................................................................... 5-7

Figure 5-16. Curing RCC .................................................................................................................................. 5-7

Figure 6-1. Load distribution of CTB compared to unstabilized granular base ................................................... 6-2

Figure 6-2. Typical pavement cross-sections showing CTB layers....................................................................... 6-2

Figure 6-3. Completed CTB for new pavement construction in Oklahoma ........................................................ 6-2

Figure 6-4. Spreading dry cement on grade prior to mixing .............................................................................. 6-4

Figure 6-5. Applying cement slurry on grade prior to mixing (cement slurry is applied the same way for FDR and CMS applications) ......................................... 6-4

Figure 6-6. Constructing CTB using mixed-in-place method ............................................................................. 6-4

Figure 6-7. Placement of plant-mixed CTB on prepared subgrade ..................................................................... 6-4

Figure 7-1. Schematic of the mixing chamber of a reclaimer machine ............................................................... 7-2

Figure 7-2. Reclaimer pulverizing existing asphalt pavement and base material ................................................. 7-2

Figure 7-3. Dry cement placed on pulverized material ...................................................................................... 7-3

Figure 7-4. Applying cement slurry on grade prior to mixing (cement slurry is applied the same way for CTB applications) ......................................................... 7-3

Figure 7-5. Mixing the cement into the pulverized material ............................................................................... 7-3

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Figure 7-6. Equipment for compaction and finishing ........................................................................................ 7-3

Figure 8-1. Typical cross-section with CMS ....................................................................................................... 8-2

Figure 8-2. Cement slurry added to subgrade material (cement slurry is applied the same way for CTB and FDR applications) ......................................... 8-2

Figure 8-3. Pulvermizer used for in-place mixing of CMS ................................................................................. 8-3

Figure 8-4. Sheepsfoot roller used for compaction ............................................................................................. 8-3

Figure 9-1. Recycled concrete aggregates ........................................................................................................... 9-2

Figure 9-2. Example of equipment used to break existing concrete ................................................................... 9-3

Figure 9-3. Broken concrete pavement is removed for recycling ........................................................................ 9-3

Figure 9-4. Existing concrete recycled in-place and reused for base material on the Tri-State Tollway in Illinois ........................................................................ 9-3

Figure 10-1. Full-depth repair of a concrete pavement slab ............................................................................. 10-1

Figure 10-2. Partial-depth repair process at joint ............................................................................................. 10-2

Figure 10-3. Cross-section of concrete pavement showing stitching. ............................................................... 10-2

Figure 10-4. Drilling operation as part of slab stabilization .............................................................................. 10-3

Figure 10-5. Application of joint sealant .......................................................................................................... 10-4

Figure 10-6. Contiguous concrete slabs prepared for dowel bar retrofitting ..................................................... 10-4

Figure 10-7. Diamond grinding concrete pavement for surface restoration ...................................................... 10-4

Figure 10-8. Longitudinal grooving of a concrete pavement to restore macrotexture ....................................... 10-5

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List of Tables

Table 1. Table of solutions ...................................................................................................................................xv

Table 2-1. Current state-of-the-practice overlay design methodologies .............................................................. 2-3

Table 2-2. Joint pattern for bonded concrete overlays ........................................................................................ 2-4

Table 2-3. Joint pattern for unbonded concrete overlays of concrete pavements ................................................ 2-5

Table 2-4. Joint pattern for unbonded concrete overlays of HMA and composite pavements ............................. 2-5

Table 3-1. Typical values for material properties ................................................................................................ 3-3

Table 5-1. List of design methodologies ............................................................................................................. 5-4

Table 6-1. Typical CTB properties ...................................................................................................................... 6-3

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How is this guide unique?Portland cement is the fundamental ingredient in con-crete. When you think of cement, it may be automatic to think of concrete; when you think of cement and pavements, you probably think of cement in conven-tional concrete used for pavement surface layers. But did you know that cement can be used in other pave-ment layers and for other applications? In fact, cement can be used in many other applications for pavement systems.

Pavement systems containing cement-bound layers have been used worldwide for over a century, with great success. Portland cement can be used in virtually every layer in a pavement system. Typical applica-tions include improving the quality of subgrade soils and stabilizing base materials. Integrating multiple cement-based layers into a pavement design may pro-vide a cost-effective method for achieving a stronger, more durable, sustainable pavement. For instance, using a cement-modified soil and cement-treated base as opposed to an unbound granular base placed on an unprepared subgrade can reduce the required thickness of the base material. In addition, a cement-treated base may decrease the thickness needed for the concrete or asphalt surface, resulting in less materials and overall reduced cost.

In addition to being the key constituent of new con-crete pavement and concrete overlay surfaces, other unique surface applications of cement include roller-compacted concrete (RCC), precast pavements, and pervious concrete pavements. Cement is also used in numerous pavement repair techniques, as well as an array of pavement recycling and reclamation applications.

A great deal of research and effort by many sources has gone into developing literature about the indi-vidual pavement applications using cement. With so

many applications, engineers and other practitioners could benefit from one publication that integrates and summarizes all cement-based pavement applications and helps them select and apply appropriate solutions for specific needs. This publication fills that need.

The Guide to Cement-Based Integrated Pavement Solutions provides a clear, concise, and cohesive discussion of 10 cement-bound material options for specific engineering pavement applications, or solutions: new concrete pave-ments, concrete overlays, pervious concrete, precast pavements, roller-compacted concrete, cement-treated base, full-depth reclamation with cement, cement- modified soils, recycled concrete aggregates, and repair and restoration. Each application is presented as a method for meeting specific design and construction objectives that today’s pavement practitioners must accomplish. The benefits, considerations, brief descrip-tion, and summary of materials, design, and construc-tion requirements, as well as a list of sustainable attri-butes, are provided for every solution.

This guide is intended to be short, simple, and easy to understand. It was designed so that the most up-to-date and relevant information is easily extractable. It is not intended to be used as a design guide for any of the applications identified herein. Recommendations for additional information that can provide such details are given at the end of each solution discussion.

Who is this guide for?It was developed for practitioners, including engineers and managers who face decisions regarding what mate-rials to specify in the pavement systems they design or manage. The audience also includes city and county engineers, along with the A/E firms that often represent them, and state DOT engineers at all levels who are seeking alternatives in this era of changing markets.

Preface

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Important Definitions

This symbol represents applications of highly traf-ficked roadways that experience high volumes of heavy truck traffic such as major highways and interstates.

This symbol represents applications for city streets and local roads that experience moderate levels of passenger vehicle traffic and maybe some heavy truck traffic.

This symbol represents roadway shoulder applications.

This symbol represents applications including com-mercial parking lots, driveways, and residential roadways.

This symbol represents applications for general-pur-pose aviation and/or commercial or military airfield facilities.

This symbol represents applications for facilities that experience high volumes of heavy truck traffic and/or storage facilities, such as shipping yards, where heavy containers are stored for long periods of time.

Highways Commercial / Lightweight

Airfields

Heavy Industrial

Streets & Local Roads

Shoulders

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ASTM

ASTM International, originally known as the Ameri-can Society for Testing and Materials, is an interna-tional standards setting organization.

Base

The pavement layer constructed immediately beneath a hot-mix asphalt (HMA) surface and sometimes beneath a concrete surface. Material requirements for this layer are more stringent than those for most sub-base and subgrade layers.

Concrete

An initially plastic (slumpable) mixture created by the combination of cement, coarse and fine aggregates, water, and various chemical admixtures that hardens to a solid material over time.

Concrete pavement

A pavement system in which the surface layer is concrete. Typical concrete pavement systems include a concrete surface over a subbase and subgrade layers.

Fine aggregate

Defined by ASTM C33 as sand with 95–100 percent of the total material passing a No. 4 (4.75 mm) sieve.

Fines

Portion of the soil finer than a No. 200 (75 µm) sieve.

Flexible pavement

A pavement system in which the surface layer is hot-mix asphalt (HMA). Typical flexible pavement systems include an HMA surface over a base, subbase, and subgrade layers.

Pavement system

The combination of surface, base/subbase, and improved subgrade layers constructed for the purpose of supporting traffic.

Portland cement

A commercial product that, when combined with water, forms a paste that over time becomes a hard-ened solid. It is typically combined with fine aggre-gates to form mortar or a combination of fine and coarse aggregates to form concrete.

Subbase

The pavement layer constructed between the base and subgrade in a flexible pavement system, or the layer often found beneath a concrete surface in a concrete pavement system.

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Table of Solutions

Within an integrated pavement solutions system, numerous alternative paving materials and techniques are available. While their common link is the use of portland cement, there remain notable differences that must be recognized. To assist in the selection of the most appropriate solutions for a given project, Table 1 should be referenced.

Within this table, the various solutions are shown in the left column, along with a brief description of each. To assist in the selection of the most appropriate solutions, the challenges that a user might be facing are in the adjacent columns. This cross-referencing is intended to help narrow the selection of the available solutions. Complementing the table are both the ben-efits and typical applications. These too are intended to refine the selection of possible solutions.

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Table 1. Table of solutions

Solution / Definition Objectives BenefitsTypicalApplications

New Concrete Pavements

New concrete pavements include both jointed and continuously reinforced concrete pavements. Thicknesses can range from 6 to 15 inches, depending on traffic, environment, and soils.

• Provide long life and reduced maintenance.

• Improve the surface.

• Provide high load-carrying capacity.

• Expedite construction/renewal.

• Reduce urban heat island effect.

• Increase light reflectance.

• Provide a sustainable option.

• Concrete pavements can withstand many environments.

• Concrete pavements typically last much longer than their original design life.

• Concrete pavement surfaces reflect light and reduce the urban heat island effect.

• Vehicle fuel consumption for the driving public is reduced on concrete surfaces.

• Highways

• Streets and Local Roads

• Shoulders

• Commercial/ Lightweight

• Airfields

• Heavy Industrial

Concrete Overlays

Overlays are a method of rehabilitating and/or increasing the structural capacity of existing pavements. Bonded overlays are thin (2- to 6-in.) layers of concrete bonded directly to a sound underlying pavement in order to increase structural capacity. Unbonded overlays are used principally when the underlying pavement is in fair to poor condition and are thick (4 to 11 in.) enough to support the traffic loads but recognizing the structural capacity of the underlying pavement.

• Extend pavement life.


• Increase load-carrying capacity.


• Reduce urban heat island effect.

• Increase light reflectance.


• Reconstruction costs are avoided.

• Construction of an overlay is much faster than reconstruction.

• Concrete pavement surfaces reflect light and reduce the urban heat island effect.

• Highways


• Shoulders


• Airfields


Pervious Concrete

Pervious concrete is a paving material consisting of almost exclusively coarse aggregate, but with sufficient cement paste to bind the mixture into a strong but open (porous) material with exceptional drainage properties.

• Satisfy EPA Storm Water Phase II regulations.

• Earn LEED credits.

• Improve safety.

• Reduce tire-pavement noise.


• Pervious concrete is an EPA Best Management Practice.

• Stormwater runoff and flash flooding is minimized.

• Hydroplaning and splash and spray are minimized.

• Noise from the tire-pavement interaction is reduced.

• Pervious concrete surfaces reflect light and help reduce the urban heat island effect.


• Shoulders


Precast Pavements

Precast pavements are a technique for constructing or repairing a concrete pavement surface where casting and curing of panels are done in advance. Precast pavements are a highly durable finished pavement and not just a temporary fix. They are a repair option for jointed concrete pavements (JCP) or reconstruction option for both JCP and HMA pavements. Rapid placement of the hardened panels can then be conducted within short traffic closure windows.

• Provide long life.





• Construction can be completed during short (overnight or weekend) closures.

• Lane closures and associated user delays during construction are minimized.

• Precast pavements are a highly durable finished pavement and not just a temporary fix.

• Precast pavement surfaces reflect light and help reduce the urban heat island effect.

• Highways

• Airfields


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Table 1. Table of solutions (Continued)


Roller-Compacted Concrete

Roller-compacted concrete (RCC) is a stiff and strong concrete mixture that is typically placed with asphalt pavers as either a surface or a support layer. Roller-compacted concrete surfaces can be used for low-speed or industrial applications. Roller-compacted concrete layers can also serve as a support layer to a thin (1.5- to 2-in.) HMA (or occasionally concrete) surface.

• Provide low-cost option.


• Expedite construction.

• Allow early opening to traffic.


• Roller-compacted concrete provides a strong, dense, and durable material that can be quickly constructed.

• Construction is fast with no forms or finishing.

• No steel reinforcement and minimum labor make RCC economical.

• For many applications, joint sawing is optional for aesthetic purposes resulting in additional cost savings.

• Roller-compacted concrete pavement surfaces reflect light and help reduce the urban heat island effect.

• Highways


• Shoulders

• Airfields



Cement-Treated Base

Cement-treated base (CTB) is a mixture of aggregate material and/or granular soils combined with engineered amounts of portland cement and water that hardens after compaction and curing to form a stronger, stiffer, and more durable paving material. Cement-treated base is used as a pavement base for flexible pavements or a subbase for concrete pavements.

• Provide a strong, uniform base/subbase for current and future loading conditions using in-place or locally available marginal soils and granular material.

• Reduce stresses on the subgrade.

• Stabilize a variety of soils with a single stabilizer.

• Reduce rutting and deflections in a flexible pavement surface.

• Improve the structural capacity of the existing soil.


• A stiffer base reduces deflections due to traffic loads, thereby extending pavement life.

• Subgrade failures, pumping, rutting, joint faulting, and road roughness are reduced.

• Base thickness is reduced compared to unbound granular base thicknesses.

• Marginal aggregates, including recycled materials, can be used, thus reducing the need for virgin, high-quality aggregates.

• Highways


• Shoulders

• Airfields



Full-Depth Reclamation

Full-depth reclamation (FDR) is a technique in which hot-mixed asphalt (HMA) material from the existing pavement is removed, combined with portland cement, and used to create a new and improved base. The FDR base is then topped with a new HMA or concrete surface layer.

• Provide a strong, uniform base/subbase for current and future loading conditions using existing failed asphalt surface and base material.

• Maintain existing grade with minimum material removal or addition.

• Reduce or totally eliminate the need for virgin aggregates.

• Reduce stresses on the subgrade.

• Reduce rutting and deflections in a flexible pavement surface.

• Improve the structural capacity of stabilized base over unstabilized base material.

• Provide pavement reconstruction method that is fast and minimizes traffic disruption.


• The performance of the base layer is improved over an unbound granular base.

• Little, if any, material is hauled off or onto the site, resulting in less truck traffic, lower emissions, and less damage to local roads. Work can be completed quickly compared to removal and replacement techniques.

• Full-depth reclamation process is economical compared to removal and replacement and thick overlays.

• Highways


• Airfields



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Cement-Modified Soils

Cement-modified soils (CMS) are soils and/or manufactured aggregates mixed with a small proportion of portland cement. Cement-modified soils exhibit reduced plasticity, minimized volumetric changes due to moisture changes, increased bearing strength, and improved stability.

• Reduce the plasticity and high-volume change characteristics of clay soils due to moisture variations.

• Improve stability of a poorly graded sandy soil. Improve the properties of a sandy soil containing a high-plasticity clay.

• Provide a method to dry out a wet subgrade.

• Provide a firm construction platform to work on.


• Cement-modified soils provide a weather-resistant work platform for construction operations.

• Fatigue failures caused by repeated high deflections are controlled.

• There is a reduction in moisture sensitivity and subgrade seasonal load restrictions.

• No mellowing period is needed as required by other stabilizing agents.

• Highways


• Shoulders

• Airfields



Recycled Concrete Aggregates

Recycled concrete aggregates (RCA) are aggregates produced from the recycling of existing concrete. Existing concrete is removed, processed into appropriate aggregate sizes, and reused in various pavement applications.

• Recycle excavated concrete pavement.

• Minimize construction cost.

• Reduce dependence on good quality virgin aggregates, which may be hard to find or expensive to bring in.


• Recycled concrete aggregates are versatile because they can be used in any pavement layer.

• Material costs are reduced.

• Construction time can be expedited with on-site recycling plants.

• Pavement suffering from ASR or D-cracking can be recycled instead of discarded.

• The need for old concrete disposal is reduced.

• Highways


• Shoulders

• Airfields



Repair and Restoration

Repair and restoration is a series of techniques including diamond grinding, dowel bar retrofit, full and partial depth repairs, joint sealing, patching, and slab stabilization that extend the life of a concrete pavement. These techniques can often be used in lieu of resurfacing or reconstructing.

• Extend life.



• Repair and restoration fixes distressed concrete pavement (Comment—areas may not be isolated, i.e., diamond grinding an entire roadway).

• These are options for low-cost concrete pavement life extensions.

• Highways

• Airfield


Table 1. Table of solutions (Continued)

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New Concrete Pavements

Objectives•Providelonglifeandreducedmaintenance.

•Improvethesurface.

•Providehighload-carryingcapacity.

•Expediteconstruction/renewal.

•Reduceurbanheatislandeffect.

•Increaselightreflectance.

•Provideasustainableoption.

Solution•Constructanewconcretepavement.

Benefits•Concretepavementscanwithstandmanyenvironments.

•Concretepavementstypicallylastmuchlongerthantheiroriginaldesignlife.

•Concretepavementsurfacesreflectlightandreducetheurbanheatislandeffect.

•Vehiclefuelconsumptionforthedrivingpublicisreducedonconcretesurfaces.

Considerations•Theconcretemixturemustbedesignedproperlyfortheenvironment.

•Properconstructionpracticesareessentialtolong-termperformance.

Typical ApplicationsConcretepavementapplicationsincludehighways(mainline,shoulders,frontageroads),streetsandlocal

roads,aswellasheavyindustrialapplications,airfields(runways,taxiways,roadways,aprons,parkingfacili-ties),andcommercial/lightweightindustrialapplica-tionssuchasdrivewaysandparkinglots.

Highways

Commercial / Lightweight

Airfields

Heavy Industrial


Shoulders

DescriptionApavementstructureisacombinationofasurfacecourseandbase/subbasecoursesplacedonapreparedsubgrade.Anewconcretepavementisonewherethesurfacecourseismadeofconcrete(Figure1-1).

Prepared Subgrade

Concrete Surface

Subbase

Prepared Subgrade

Concrete Surface

Subbase

Figure 1-1. Schematic of typical concrete pavement cross-section

1 Guide to Cement-Based Integrated Pavement Solutions

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ConcretepavementshavebeenbuiltintheUnitedStatessincethefirstconcretestreetwasbuiltinBelle-fontaine,Ohio,in1891.Thispavementisstillinser-vicetoday.Concretepavementscanbeveryversatile;theycanbedesignedtohandlethefreezingwintersofMichigan’sUpperPeninsulaorthescorchingheatofNewMexicointheSouthwest.Concretepavementscanbeadurable,economical,andsustainablesolutionformanyapplicationsifpropermaterialmixturesareusedandthepavementstructureisbothdesignedandconstructedproperly.

TherearedifferenttypesofconcretepavementsbuiltintheUnitedStates;however,thetwomostcom-mononesarejointedconcretepavements(JCP)andcontinuouslyreinforcedconcretepavements(CRCP).Eachtypeissuitablefornewconstruction,reconstruc-tion,andoverlaysofexistingroads.

Jointedconcretepavementcanbeeitherplain(JPCP)orreinforced(JRCP).Bothhaveregularlyspacedtransversecontractionjointswithdowelsforloadtransferandlongitudinalconstructionjointsheldtogetherwithtiebars.Concretewillcrack;jointsaredesignedtocontrolwherethesecracksoccur.Theideaistodesignajointspacingthatensuresthatcracksoccurunderthejointsinsteadofrandomlyacrossthepavement.Jointedreinforcedconcretepavementincludeswiremeshand/ordeformedsteelbarrein-forcementthroughouteachslab(theareaboundedbytransverseandlongitudinaljoints).Thereinforcementisintendedtoholdtightanycracksthatmayformwithintheslab.

Continuouslyreinforcedconcretepavementsdonotrequiretransversecontractionjoints,butdoincludetransverseandlongitudinalconstructionjoints.Continuouslyreinforcedconcretepavementscontaincontinuouslongitudinalandtransversereinforcementthroughtheentirepavement(morethanJRCP).Rein-forcementinCRCPisdesignedtocontroltransversecrackwidths;reinforcementkeepscracksheldtightlytogetherandisnotdesignedtohelpcarrytrafficloads.StandardCRCPdesignsareoftenchosenbystates(likeTexas,Virginia,andIllinois)toaccommodatehightrafficandheavyloads.

Figure1-2illustratestypicaljointingandreinforce-mentforJPCP,JRCP,andCRCPdesigns.

Concretepavementsareoftendesignedspecificallyforagivenproject;however,someagencieshaveadoptedstandardvaluesforthegeometriccharacteristicsof

Figure 1-2. Schematic of the various types of new concrete pavements (from IMCP manual, Iowa State University, 2006)

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pavementsaswellasforthematerials’specificationssothatdesignsbecomemorepractical.

Theexcellentperformanceofconcretepavementsreliesontheuseofsuitablematerials,anadequatedesign,andsoundconstructionpractices.Bothstruc-turalandfunctionalperformanceisenhancedwhenalloftheseaspectsarecarefullyidentifiedandaccountedfor.Themostinfluentialdesign-relatedvariablesforstructuralperformance(atagivenleveloftraffic)areslabthickness,jointspacing,reinforcement,concretestrength,andsupportconditions.Functionalperfor-manceofthepavementisoftenrelatedtofeatureslikesmoothness,texture,andnoise.Theseareaffected—inpart—bytheconcretepavementtexturealongwiththeconcretematerialusedand,inparticular,itsdurability.

MaterialsMixturesforconcretepavementstypicallyincorporatethefollowingconstituents:ablendofcoarseandfineaggregates,portlandcement,water,andsometimesothercementitiousmaterialssuchasflyashandslagcement,and/orchemicaladmixtures(seeFigure1-3).Thecompatibilityofmaterialsinconcretepavementsisimportantbecauseitwillaffectlong-termpavementperformance.

Ablendofcoarseandfineaggregatesistypicallyusedinconcretepavingmixtures.Theaggregatesareoftennaturalbutcanalsobemanufactured.Coarseaggregatesmayevenincludeapercentageofrecycledaggregates.AfineaggregateisdefinedbyASTMC33ashaving95percentormorematerialparticlespassingthe#4(4.75mm)sieve.ASTMC33alsoprovidesguidelinesontypicalaggregategradationsforconcrete.Moststateshavestandardsandspecifica-tionsthatidentifycertaingradationlimitsforspecificapplicationsandfurtheridentifyalimitforrecycledaggregatecontent.Aggregatesstronglyinfluencecon-crete’sfreshproperties(particularlyworkability)andlong-termdurability.Awell-gradedblendofaggre-gateswillfurtherensurelong-termpavementperfor-mance.Achievingawell-gradedaggregatesupplycanoftenbeattainedbyaddinganintermediate(#8to3/8in.[2.36to9.5mm])aggregate.

Portlandcementgivesthematerialitsstrengthandbindstheaggregatestogether.Therearedifferenttypesofcement,butthemostcommonforpavingincludeTypesI,II,I/II,andIII.TypeIiscommonlyusedinnormalconcretemixtures.TypeIIissimilartoTypeIbutgivesofflessheatandismoderatelysulfateresis-tant.ItiscommontouseaTypeI/IIcementinpavingapplications,whichmeetstherequirementsasbothaTypeIandaTypeII.TypeIIIcementsgainstrength

Figure 1-3. Concrete mixture constituents (from IMCP Manual, Iowa State University, 2006)

9–15% Cement

15–16% Water

25–35% Fine aggregate

30–45% Coarse aggregate

Paste (cement + water)

Mortar (paste + fine aggregate)

Concrete (mortar + coarse aggregate)

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quicklyandareoftenusedinfast-trackpavingorrepair.BlendedcementssuchasTypeIP(portland-pozzolancement)orTypeIS(portlandblast-furnaceslag)cementsincludeothercementitiousmaterialsandareoptionsforuseinpavingmixtures.

Itiscommonforpavingmixturestoincludesupple-mentarycementitiousmaterials(SCMs)thatareaddedtothemixturebyreplacingapercentage(eithermassorvolumetric)oftheportlandcementcontent.Thesemayincludeindustrialbyproductslikeflyashorslagcement.Theproportionsinwhichthematerialsareusedusuallyvaryineverydesignandaretypicallyselectedtobalancecost,strengthrequirements,work-ability,anddurability.

Waterforconcreteshouldbepotable(fitforhumanconsumption).Somewaterrecycledfromreturnedconcreteandplantwashingcanbeacceptable.Speci-ficationsformixingwaterinconcretemixturescanbefoundinASTMC1602.Typicalwater-to-cementitiousmaterials(w/cm)ratiosfornormalconcretepav-ingmixturesrangefrom0.40to0.45.Higherw/cmratioswillresultinincreasedworkabilitybutalsolowerstrengthanddecreasedlong-termpavementperformance.

Admixturescommonlyusedinconcretemixturesincludeair-entrainingadmixtures,water-reducingadmixtures,retarders,andaccelerators.Air-entrainingadmixturesareusedtodevelopanairvoidsystemthatisnecessaryforconcretedurability,particularlyinfreeze-thawenvironments.Water-reducingadmixturesareusedtoreducew/cmratioswhileimprovingwork-ability.Retardersdecreasesettimeandaregenerallyusedinhotweatherplacements.Acceleratorsincreasesettimesforcoldweatherconcreting.Theamountofadmixturerequiredforeachdependsontheamountandtypeofcementitiousmaterialused.Itisagoodpracticetofollowthemanufacturer’srecommenda-tionsfordosage.Severaladmixturescanbeusedinonemixture,buttrialbatchesmustberuninordertoensurecompatibility.

Ifdesignedproperlyfortheenvironmentinwhichtheywillbeplaced,concretepavementswilllastalongtime.VariousAmericanConcreteInstitute(ACI)internationaldocuments,theNationalConcretePave-mentTechnologyCenter’s(CPTechCenter)Integrated

Materials and Construction Practices for Concrete Pave-ment (IMCP) Manual,andthePortlandCementAsso-ciation’s(PCA)Design and Control of Concrete Mixturesprovidedetailedrecommendationsofhowtopropor-tionamixtureandensuregoodperformanceinavari-etyofenvironments.Ingeneral,compatiblematerialscoupledwithlowpermeability(i.e.,loww/cmratiosandtheuseofSCMs)andaproperairvoidsystemwillresultingoodlong-termconcreteperformance.

DesignAconcretepavementdesignincludescalculatingarequiredpavementthickness,determiningajointlayout,andidentifyingtherequiredsteelcontent(ifapplicable).ThemostnationallyacceptedmethodforconcretepavementdesignistheAmerican Association of State Highway and Transportation Officials (AASHTO) Design Guide(1993).Amajoreffortiscurrentlyunder-waytoregionallycalibrateandshifttothenewAASHTOMechanistic-EmpiricalPavementDesignGuide(M-EPDG).

OtherdesigntoolssuchastablesfromtheACICom-mittee330reportGuide for the Design and Construction of Concrete Parking Lots, the Continuously Reinforced Concrete Pavement Design and Construction Guidelines(Rasmussen,Rogers,andFerragut2009),andtheAmericanConcretePavementAssociation’sStreetPavesoftwareprogramcanbeusedtoprovidesatisfactoryresults.

Aconcretepavementneedstobethickenoughtowithstandthestressandfatiguecausedbytheenvi-ronmentinwhichitisconstructedandtheloadsunderwhichitmustperformoverananticipatedlifetime.Somecriticaldesigninputsforcalculatingthicknessincludetheestimatedtrafficloadingduringthedesignlife,failurecriteria,concretestrength,andstiffnessanddrainagecharacterizationofsupportinglayers.

ForJCP,thespacingofcontractionjointsisdesignedatintervalssuchthatpotentialvolumetricchangesoftheconcretedonotresultinunintendeddamagetothepavement(i.e.,uncontrolledcracking).TheFederalHighwayAdministration’sHighPerformanceConcretePaving(HIPERPAV)softwarecanbeusedasaneffectivetoolfordesigningproperjointspacing.

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Jointedplainconcretepavementtransversecontrac-tionjointsaretypicallyspacedat15to20ft(5to6.1m)inordertocontrolcracking.TransversecontractionjointsinJRCPcanbespacedfartherapart(typicallyabout30to40ft[9to12m])becauseofthesteelcontent.ContractionjointsarenotrequiredinCRCP.Continuouslyreinforcedconcretepavementisdesignedtohaverandomtransversecracksthatareheldtightlytogetherbythereinforcingsteel.Inallconcretepavements,longitudinalconstructionjointsareplacedbetweenlanesandtransverseconstructionjointsareconstructedattheendofeachday’spaving.

Reinforcementusedinconcretepavementsincludesdowels,tiebars,andcontinuoussteelbarsthroughouttheslab.Dowelsprovideloadtransferandverticalsupportforjointedpavementsatthetransversejoints.Tiebarspromoteaggregateinterlockandaremostoftenusedalonglongitudinaljoints.WireordeformedsteelbarreinforcementinJRCPkeepsrandomcracksheldtightlytogether.Designingthereinforcementincludesidentifyingthetype,size,andspacing.Moststatesalreadyhavestandardsandspecificationsforthedesignofpavementreinforcement.Thecriticaldesignfactorsforreinforcementincludepavementthickness,concretematerialproperties,andtypeofsupport.

Asubbaseisusuallyadvisableforheaviertraffickedpavements.Asubbaseinlightdutypavements(e.g.,residentialandcollectorstreetsandparkinglots)isnotalwaysnecessaryanddependsonunderlyingsoils,drainageneeds,andloads.

ConstructionTheconstructionofaconcretepavementinvolvesobtainingthematerials,batchingandmixing,placing,texturing,andcuring.

Batchingistheprocessofmeasuringtheconstituentsbymassorvolumeaccordingtoamixturedesignandintroducingthemintoamixer.Thesizeofthebatchdependsonthecapacityofthemixer.Inmostcases,eitherastationaryoraready-mixplantisusedformixingpavingconcrete,whichisthentypicallytrans-portedtothejobindumptrucksforslipformpaving.Truckmixerscanalsotransportpavingconcretebutareusedmoreoftenforfixed-formplacements.Whenplanningforequipment,itisimportanttoconsider

theproductioncapacityandtypicalhaultimes.Proj-ectsincongestedareas,whichdonotallowforon-siteproduction,mayrequireamixdesignthatpermitsextendedhaulingandplacementtimes.

Concreteisplacedusingslipformorfixed-formpav-ingmethods,dependinguponthenatureoftheproj-ect.Theconcretemixturesrequiredbyeitherplace-mentmethodcanvarysignificantly.Slipformpavingoperationsrequirealow-slumpmixturethatwillnotsloughafterextrusionbythepavingmachine,whilefixed-formpavingoperationsrelyonahigherslumpmixturethatwillfloweasilytofilltheforms.Slipformpavingisgenerallyforplacementsthatrequirehighproductionrates,suchasmainlinepaving.Fixed-formpavingisadaptabletonearlyanyplacementcircum-stance,butbecauseitrequiressettingupsideformstoholdtheconcrete,itisgenerallyusedinirregularsectionswhereslipformpavingisnotpractical.

Contractionjointsshouldbeformedorsawcutassoonaspossibleandaretypicallysawedtoadepthofone-thirdthatofthepavementthickness.Figure1-4depictsthisprocess.ContractorexperienceandtoolssuchastheFederalHighwayAdministrationHIPER-PAVcomputersoftwareprogramcanhelpidentifypropersawcuttimesbasedonmaterials,design,andconstructionmethods.Jointsshouldbesealedwithanappropriatematerial,althoughsomestatesare

Figure 1-4. Sawcutting JPCP

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experimentingwithunsealedcontractionjoints.Localpracticeshouldgovernaccordingly.

Whenused,dowelscanbeplacedinprefabricateddowelbasketsandsecuredinplacepriortopaving.Figure1-5showsfreshconcreteplacedoverdowelbarssecuredindowelbarbaskets.Alternatively,dowelscanbeinsertedintothefreshconcreteduringplacementusingadowel-barinserter(seeFigure1-6).

Thereareseveraloptionsforplacingtiebarsaswell.Atie-barinserteriscommonlyusedtoplacetiebarsbetweenlaneswhentwolanesareconstructedatthesametime.Forlaneadditions,single-piecetiebarscanbedrilledandinsertedintotheexistinghardenedconcreteandepoxiedintoplace.Benttiebarscanalsobeinsertedduringpavingandpulledstraightafterthepavementhashardened.Finally,two-piecetiebars

canbeused,whereone-halfofthetiebarisinsertedduringplacementandlaterthesecondhalfisscrewedintothefirsthalf.

ReinforcingsteelforJRCPandCRCPisplacedbeforepavingbeginsasseeninFigure1-7andFigure1-8.

Textureisappliedtothesurfaceoftheconcreteafterplacementandbeforecuring.Thepurposeistoincreasefrictionandimprovewetweatherdrivingconditions.Twocommonlyusedwettexturetech-

Figure 1-5. Concrete placed over dowel baskets

Figure 1-6. Dowel-bar inserter

Figure 1-7. JRCP reinforcement in place before paving

Figure 1-8. CRCP reinforcement placed before paving

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niquesincludetininganddrag.Tinedsurfacesareappliedusingasteelrakeandcanbeappliedlongitu-dinallyorinthetransversedirection.Dragtexturesareappliedbydraggingapieceofartificialturforheavyburlaponthesurface(seeFigure1-9).Additionaltexturesincludediamondgrindingandgrooving.Ifused,grindingandgroovingaredoneaftercuringandoncethepavementisabletowithstandtheweightofthemachinethatmustbeused.

Propercuringmeasurespreventrapidwaterlossfromthemixtureandallowmorethoroughcementhydra-tion.Itisessentialtoapplycuringasearlyaspossibleafterplacingconcreteandtocontinueuntilenoughhydrationhastakenplaceandtherequiredhardenedpropertieshavebeenachieved.Avarietyofcuringmethodsandmaterialsisavailableforconcretepave-ment,includingwatersprayorfog,wetburlapsheets,plasticsheets,andinsulatingblankets.Mostcom-monlyused,however,istheapplicationofaliquidmembrane-formingcompound(seeFigure1-10).

Sustainability•Concretepavementshavelongevity.

•Industrialby-products(e.g.,flyash,slagcement,silicafume)canbeusedinmixturedesign.

•Concretepavementsurfacesarehighlyreflective,makingthemmorevisibleatnight.Bettervisibilityimprovessafety.Brighterstreetsrequirelesslighting;therefore,energyrequirementsarereduced.

Figure 1-9. Burlap drag on fresh concreteFigure 1-10. Curing compound applied by spray nozzles on a cure cart

•Concrete’slightsurfacereducestheurbanheatislandeffect.

•Studiessuggestconcretesurfacesreducevehiclefuelconsumptionforthedrivingpublic.

For More InformationAmericanAssociationofStateHighwayandTrans-portationOfficials.1993.American Association of State Highway and Transportation Officials (AASHTO) Design Guide.

AmericanConcreteInstitute.2008.Guide for the Design and Construction of Concrete Parking Lots.ACIReport330R-08.

AmericanConcretePavementAssociation.2002.Concrete Pavement for General-Aviation, Business and Commuter Aircraft.ConcreteInformation,IS202.

AmericanConcretePavementAssociation.2005.StreetPave Computer Program.SW03.

AmericanConcretePavementAssociation.2006.Design of Concrete Pavement for Streets and Roads. Con-creteInformation,EB237.

FederalHighwayAdministration.1990.Concrete Pave-ment Joints.TechnicalAdvisory,T5040.30.

FederalHighwayAdministration.2007.HIPERPAVsoftware,www.HIPERPAV.com,www.fhwa.dot.gov/pavement/pub_details.cfm?id=660.

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Novak,L.andD.Bilow.2009.A Sustainable Approach to Outdoor Lighting Utilizing Concrete Pavement. SP393.

PortlandCementAssociation.2011.Design and Con-trol of Concrete Mixtures.15thedition.

PortlandCementAssociation.2010.Integrated Paving Solutions—Concrete Pavements.http://www.integrated-pavingsolutions.org/concretepavements.html.

Rasmussen,R.O.,S.I.Garber,G.Fick,T.R.Ferragut,andP.D.Wiegand.2008. How to Reduce Tire-Pavement Noise: Interim Better Practices for Constructing and Texturing Concrete Pavement Surfaces.PooledFundTPF-5(139).

Rasmussen,Rogers,andFerragut.2009.Continuously Reinforced Concrete Pavement Design and Construction Guidelines.Draft,FederalHighwayAdministrationandContinuouslyReinforcedConcreteInstitute,May.

Taylor,G.andJ.Patten.2006.Effects of Pavement Structure on Vehicle Fuel Consumption—Phase III.Proj-ect54-HV775,TechnicalReportCSTT-HVC-TR-068,NRC-CNRC,January27.

Taylor,P.,S.Kosmatka,G.Voigt,etal.2006.Integrated Materials and Construction Practices for Concrete Pave-ment: A State-of-the-Practice Manual.NationalConcretePavementTechnologyCenter/CenterforTransporta-tionResearchandEducation,IowaStateUniversity,December.

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Concrete Overlays

Objectives•Extendpavementlife.


•Increaseload-carryingcapacity.


•Reduceurbanheatislandeffect.

•Increaselightreflectance.


Solution•Constructaconcreteoverlay.

Benefits•Reconstructioncostsareavoided.

•Constructionofanoverlayismuchfasterthanreconstruction.

•Concretepavementsurfacesreflectlightandreducetheurbanheatislandeffect.

Considerations•Properassessmentofexistingpavementconditionsisnecessarytodeterminefeasibility.

•Anylossofsubgradesupportordrainageproblemsmustbecorrected.

Typical ApplicationsConcreteoverlayscanbeusedfortherehabilitationofavarietyofsurfaces.However,variousfactorsneedtobetakenintoaccountbeforeselectingtheappropri-ateoverlaysystemincludingtheexistingpavement

condition,overlaydesigndetails,pre-overlaywork,constructionmaterials,andfuturemaintenanceandrehabilitation.

Highways


Airfields

Heavy Industrial


Shoulders

DescriptionConcreteoverlaysareadurableandcost-effectivemaintenanceandrehabilitationalternativewhenproperlydesignedandconstructed.Rehabilitationoftheexistingpavementissimplifiedbythefactthatitdoesnotneedtoberemoved,andquiteoften,fewpre-overlayrepairsneedtobecarriedout.Overlayspreservepavementserviceabilityforseveraldecadesbeyondtheoriginaldesignlife.

Overlaysareconstructedusingconventionalconcretepavingprocedures.Jointspacing,loadtransferdesign,andreinforcementmethodsaresimilartonewpave-ments.Inaddition,typicalconcretemixturesareused,whichcanbeadjustedtoallowforhigherstrengthsoranexpeditedconstructionprocess.


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Concreteoverlaysareabletorestorethefunctionofafacilityveryeffectively.Theconstructionofanewsurfaceresultsinsubstantiallyimprovedsurfacechar-acteristicsincludingrideability,improvednoiselevels,andincreasedfriction.Beforeplacementofanoverlaycanoccur,theexistingpavementmustbesufficientlyevaluatedinordertoensureitisagoodcandidateforoverlayconstruction.Therearetwomaintypesofcon-creteoverlays:bondedandunbonded(seeFigure2-1).

Bothoverlaytypescanbeconstructedoverconcrete,flexible,andcompositepavements(seeFigure2-2).

Bondedoverlaysarerelativelythinandconstructeddirectlyontopofexistingpavements.Bondedover-laysrestorethesurfaceandaddsomestructuralcapacitytoroadwaysthataresomewhattomoderatelydistressed.

Unbondedconcreteoverlaysaretypicallythickerthanbondedoverlaysandrequireaseparationlayer(i.e.,bondbreaker).Unbondedoverlaysrestorethestruc-turalcapacityofexistingpavementsthataremoder-atelytosignificantlydeteriorated.

MaterialsThetypeofprojectandtheconstructionscheduledictatetheconcretemixturematerials.Conventionalmixturesshouldbecarefullyselectedtoallowtheresultingmixturetobedense,relativelyimpermeable,andresistanttoenvironmentaleffectsoverthelengthofitsservicelife.Mostagenciesspecifya28-dayunconfinedcompressivestrengthrequirementof4,000psi(28MPa)fortheirpavements.OntheotherFigure 2-1. Unbonded overlay

Figure 2-2. Overlay applications

Bonded Overlay Systems Unbonded Overlay Systems

Bonded Concrete Overlays of Concrete Pavements–previously called bonded overlays–

Bonded Concrete Overlays of Asphalt Pavements–previously called ultra-thin whitetopping–

Bonded Concrete Overlays of Composite Pavements

Unbonded Concrete Overlays of Concrete Pavements–previously called unbonded overlays–

Unbonded Concrete Overlays of Asphalt Pavements–previously called conventional whitetopping–

Unbonded Concrete Overlays of Composite Pavements

In general, bonded overlays are used to add structural capacity and/or eliminate surface distress when the existing pavement is in good structural condition.

Bonding is essential, so thorough surface preparation is necessary before resurfacing.

In general, unbonded overlays are used to rehabilitate pavement with some structural deterioration.

They are basically new pavements constructed on an existing, stable platform (the existing pavement).

(Resurfacing/Minor Rehabilitation) (Minor/Major Rehabilitation)

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hand,somestatesuserapid-strengthconcretemix-turesthathaveahighcementitiousmaterialcontent,alowwater-to-cementitiousmaterials(w/cm)ratio,andsmallertopsizeaggregate.Thesetypesofmixturescanbeusedwithacceleratingadmixturestoallowforfasteropeningtimes.

TypeIandTypeIIcementsarenormallyusedincon-cretemixturesforconcreteoverlays.TypeIIIcementcanbeusedwhenhighearlystrengthisdesired.Vari-ousadmixturesarecommonlyintroducedaswellandincludewaterreducers,airentrainment,andSCMs.Supplementarycementingmaterialssuchasflyashandslagcementimprovetheworkabilityofthecon-crete,increasedurabilityandlong-termstrength,andextendplacementtimeduringhotweather.Amaxi-mumw/cmratioof0.45iscommonforpavementsinamoistenvironmentwithmanyfreeze-thawcycles,althoughlowervaluesareusedtominimizedryingshrinkage.

Aggregatesusedinoverlaysrangefromcrushedstonesandrivergravelstorecycledconcreteaggregateandshouldpossessadequatestrengthandbephysicallyandchemicallystablewithintheconcretemixture.Themaximumcoarseaggregatesizeshouldbeusedinordertominimizepasterequirements,reduceshrink-age,minimizecosts,andimprovemechanicalinter-lockpropertiesatjointsandcracks.

Theseparationlayerinunbondedoverlaysiscriticaltotheirlong-termperformance(seeFigure2-3).A1-in.(25mm)thickconventionalHMAsurfacemix-tureismostcommonlyused.However,theuseofanonwovengeotextileinterlayerhasbeenshowntobeapromisingalternative.Researchandprojectexperi-encehasshownthatnonwovengeotextilesprovide

Figure 2-3. Typical cross-section of unbonded overlay

Separation Layer

Prepared/Untreated Subgrade

Overlay

Base/Subbase

Existing Pavement

Prepared/Untreated Subgrade

Overlay

Base/Subbase

Existing Pavement

uniform,elasticsupportoftheconcreteslab,reducepumpingprocesses,andpreventreflectivecracking.

Concreteoverlayshavebeenshowntoadd15to30yearsofservicelifetoaroadway.Long-termdurabilitywillresultfrompropermaterialsselection,sufficientpre-overlaywork,effectivedesignmethods,andsuc-cessfulconstructionpractices.Pavementmanagementandpreservationactivitiessuchasroutineandpre-ventivemaintenanceandminorrehabilitationshouldbecarefullyconsideredaswellinordertofurtherincreasetheservicelifeofaconcreteoverlay.

DesignThedesignofanoverlayincludescalculatingathick-ness,establishingajointlayout,anddeterminingreinforcementcontent.Thereareseveralstate-of-the-practicedesignmethodsthatarelistedinTable2-1.Inthecaseofanunbondedoverlay,theoverlaydesignmustincludeaninterlayer.

Bonded OverlaysThedesignofabondedconcreteoverlaydependsontheassumptionthattheoverlayandexistingpavementwillbeonemonolithicstructure.

Forbondedoverlays,typicalthicknessesrangefrom2to5in.(50to125mm).Forhigh-trafficroads,a6in.(150mm)bondedoverlayorgreatercanbeconstructed.

Table 2-1. Current state-of-the-practice overlay design methodologies

State-of-the-Practice Concrete Overlay

Design Methods

Bonded concrete overlay of concrete pavements

• 1993 AASHTO Guide

• M-E PDG

Bonded concrete overlay of HMA and composite pavements


• M-E PDG

• Modified ACPA method

Unbonded concrete overlay of all types


• M-E PDG

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TypicaljointdesignpatternsarelistedinTable2-2.Recommendationsforjointdepthdependonthetypeofjointandexistingpavement,aswellastheequip-mentusedforconstruction.

Overlayjointwidthsforbondedconcretepavementsareequaltoexistingpavementjoints.Forconven-tionalsaws,transversejointsinbondedoverlaysofconcretepavementsshouldbefulldepthplus0.50in.(13mm).Similarly,longitudinaljointsarecuteitherfulldepthornolessthanhalfofthepavementthick-ness.TransversejointsinbondedoverlaysofHMAandcompositepavementsconstructedusingacon-ventionalsawshouldbecuttoadepthofone-fourthofthepavementthickness(T/4);longitudinaljointsshouldbesawcuttoadepthofone-thirdofthepave-mentthickness(T/3).

Reinforcementsuchastiebars,dowelbars,andotherembeddedsteelproductsaretypicallynotusedforoverlayslessthan6in.(150mm)thick.

Continuouslyreinforcedbondedoverlayshavebeenconstructedbysomeagencies,andinthesecasessteelisplacedatsufficientdepthtoprovideaminimumof3in.(75mm)ofconcretecover.Thesteelcanbeposi-tioneddirectlyontopoftheoldpavement,whichhastheaddedbenefitofeffectivelyrestrainingconcretevolumechangesattheinterface.

Table 2-2. Joint pattern for bonded concrete overlays

Joint Pattern for Bonded Overlays

Bonded Overlay of JPCP Match joints with existing pavement joints.

Bonded Overlay of CRCPMatch longitudinal joints with existing pavement joints.

Bonded Overlay of HMA and Composites

Use small square patterns in the range of 3 to 8 ft. (0.9 to 2.4 m).

Maximum dimensions of the square panels should be no greater than 1.5 times the thickness of the overlay.

Avoid longitudinal joints in the wheel paths.

Unbonded OverlaysThedesignofanunbondedoverlayissimilartodesigninganewconcretepavementoverastabilizedsubbase.Anunbondedoverlaydesignassumesthereisnobondbetweenthebottomsurfaceoftheoverlayandthetopsurfaceoftheexistingpavement.

Thedesignthicknessofanunbondedoverlaytypicallyrangesfrom6to11in.(150to280mm)butcanbeasthinas4in.(100mm)forlower-volumeroadsorwhenoverheadclearanceisanissueandloadingislight.

Unbondedoverlaysofconcretepavementsrequireaninterlayerasaseparationlayer.Thedesignofthesepa-rationlayeriscriticaltothelong-termperformanceoftheoverlaybecauseithelpspreventreflectivecrackingandallowstheoverlayandexistingpavementstruc-turetomoveindependentlyofoneanother.Drainagemustbeconsideredduringdesignofthisinterlayer.

Themostcommonseparationlayerisa1-in.(25-mm)HMAsurfacemixture;however,anonwovengeotex-tilespecificallymanufacturedforuseasaninterlayerbetweencementitiouslayershasalsobeenusedasanalternative.ThethicknessoftheHMAinterlayerissometimesincreasedslightlyforunbondedoverlaysofCRCP.Anincreaseininterlayerthicknessmayalsoberequirediftheexistingpavementexperienceslargerdegreesoffaulting.Ageotextileisnotagoodalterna-tiveinsuchcases.

ItshouldbenotedthatwhileunbondedoverlaysofHMAorcompositepavementsdonotrequireaninterlayer,ifafull-depthconcretepatchhasbeencon-structedintheexistingpavementitmustbeisolated.Onetechniqueforisolatingthepatchistoapplyadebondingagentormaterial(e.g.,asphaltemulsioncoating)tothesurfaceofthepatchbeforethecon-structionoftheoverlay.

Foranunbondedoverlayofconcrete,manystatestrytomatchthetransversejointsintheoverlaywiththoseintheexistingpavement.However,somestatesintentionallydesigntransversejointsintheoverlayatanoffsetfromthoseintheexistingpavement.Jointspacingsaredesignedbasedonthethicknessoftheoverlay.TypicaljointpatternsforunbondedoverlaysarelistedinTable2-3andTable2-4.Jointdepthsdependonthetypeofsawusedforconstruction.

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Unbondedoverlaysofconcrete,HMA,orcompositepavementsshouldincludetransversejointsthat,whencutwithconventionalsaws,areconstructedatdepthsofT/4toT/3.LongitudinaljointsshouldbeatdepthsofT/3.

Dowelsareusedinjointswhentheoverlay’sdesignthicknessisgreaterthan8in.(200mm)andexpectedtocarryheavytrucktraffic.Tiebarsmaybeappropri-ateinopen-ditch(orshoulder)sectionsifthedesignthicknessisgreaterthan5in.(125mm).Tiedshoul-dersaretheapprovedmethodforprovidingoverlayedgesupport.Tiebarsatconfinedcurb-and-guttersectionsshouldbeconsiderediftheoverlaydesignthicknessisgreaterthan6in.(150mm).

ConstructionTheconstructionofanoverlay(seeFigure2-4)isaprocesssimilartoconventionalconcretepavement

Unbonded Overlays of Concrete Pavements

Design Thickness Joint Pattern

<5 in. (125 mm) Use square panels measuring 6 x 6 ft (1.8 x 1.8 m) panels

5 – 7 in. (125 – 175 mm)

Maximum joint spacing in feet = 2 times thickness in inches

> 7 in. (175 mm) Maximum joint spacing =15 ft. (4.6 m)

Table 2-3. Joint pattern for unbonded concrete overlays of concrete pavements

Unbonded Overlays of Concrete Pavements

Design Thickness Joint Pattern

<6 in. (150 mm) Maximum joint spacing in feet = 1.5 times thickness in inches

6 – 15 in. (150 – 380 mm)

Maximum joint spacing in feet = 2 times thickness in inches

> 15 in. (380 mm) Maximum joint spacing =15 ft. (4.6 m)

Table 2-4. Joint pattern for unbonded concrete overlays of HMA and composite pavements

andincludesconcreteproduction,preparationoftheexistingsurface,andtheplacement,curing,andsaw-cuttingofnewconcrete.

Whilemixingandplacingarethesameforbothbondedandunbondedoverlays,therearesubtledif-ferencesintheotherstepsoftheprocessbasedonthetypeofoverlaytobeconstructedandthetypeofexistingpavement.

Bonded Overlays Forbondedoverlaysofanykind,repairsneedtobemadetoplacetheexistingpavementingoodcondi-tionoratleastinfaircondition.Forexistingconcretepavement,thatwouldincluderepairingwidecracksandsubsurfacevoids.ForexistingHMAandcompos-itepavements,repairsincludeaddressingpotholes,moderatetoseverealligatorcracking,andlossofsubgradesupport.Methodsforaddressingtheverti-calmovementofconcreteincompositepavementsareexplainedintheNationalConcretePavementTech-nologyCenter’sGuide to Concrete Overlays.

Afterrepair,thesurfaceofanexistingpavementispreparedandcleanedofanyloosedebris.Surfacepreparationandcleaningpromotesabondbetweentheoverlayandexistingpavement.Themostcom-monmethodusedtoprepareaconcretesurfaceisshotblasting.Thesurfaceisthencleanedbysweepingand/orusingcompressedair.MillingHMAand/orcompositesurfacescanalsobeanappropriatemethodofrepair;however,toomuchmilling(foreitherrepairorpreparation)willreducestructuralcapacity.The

Figure 2-4. Unbonded concrete overlay construction over a nonwoven geotextile interlayer

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minimumremainingHMAneedstobeatleast3in.(75mm),preferably4in.(100mm)MillingneedstobedonetothetopofthenearestHMAliftlinetopreventfracturingoftheHMA.Hot-mixasphaltandcompositepavementsarethensweptcleanorblownwithcompressedair.

Placementofconcreteoverexistingpavementsshouldfollowstandardconventionalconcretepavingprac-tices(seeFigure2-5).PlacementoverHMAorcom-positepavementscanbeaccomplishedusingfixed-formorslipformconstructiontechniques.WhenHMAsurfacetemperaturesaregreaterthan120°F(49°C),thesurfaceshouldbecooledbyapplyingwaterinfrontofthepaver;however,nostandingwatershouldbeallowedatthetimeofpaving.Ifthesurfacecan-notbecooledsufficiently,placementmayneedtoberescheduledforanotherpartoftheday.

Curingabondedoverlayandproperlytimedsawcutsarecriticalfactorsnomatterwhattypeofexistingpavementliesbeneathit.Thenewconcretelayerhasahighsurface-to-volumeratiothatmakesitvulnerabletorapidmoistureloss.Curingcompoundsshouldbeappliedattwicetheratetypicalforconventionalcon-cretepracticesandshouldcoatthesurfaceandedgesevenly.Jointsmustbecutassoonaspossibleandcanbeconstructedwithconventionalorearly-entrysaws.Itmaybenecessarytohavemultiplesawsonhandinordertosawcutjointsfastenoughtopreventuncon-trolledcracking.Jointsealantsmaynotberequired.

Unbonded Overlays Beforeanunbondedoverlayisconstructedoveranyexistingpavementtype(i.e.,concrete,HMA,orcom-posite),distressesthatcauseamajorlossofstructuralintegritywillrequirerepair.Hot-mixasphaltandcompositepavementsmaybemilledtocorrectsurfacedefectsthatare2in.(50mm)ordeeper.Aminimumof3to4in.(75to100mm)ofHMAmustremaininplaceaftermillingiftheoverlaydesignthicknessis6in.(150mm)orgreater.Iflessthan6in.(150mm),anoverlayofatleast6in.(150mm)ofremainingHMAisrecommended;otherwise,abondedoverlayshouldbedesigned.

Afterrepair,ifanyarenecessary,thesurfaceissweptorairblown.Iftheexistingpavementisconcrete,thesurfacemustbevoidofanyloosedebrisbeforethebond-breakerinterlayerisconstructed.Hot-mixasphaltandcompositesurfacescanbesimplysweptclean;smallremainingdebrisisnotanissue.

Likebondedoverlays,placementofunbondedover-laysoverexistingconcreteshouldfollowstandardconventionalconcretepavingpractices.PlacementoverHMAorcompositepavementscanbeaccom-plishedusingfixed-formorslipformconstructiontechniques.Thepavementneedstobecooledpriortopaving,whensurfacetemperaturesaregreaterthan120°F(49°C).Dowelbasketsmustbesecuredproperlytotheexistingpavementunlessadowelbarinserterisused.

Curingandsawcuttingfollowsthesamelogicasthatforbondedoverlays:quick,thorough,evenapplica-tionofcuringandproperlytimedsawcutsarecriticaltolong-termperformance.

Sustainability•Concreteoverlaysmakeuseoftheexistingpave-ment,eliminatingtheneedforremovalanddisposal.

•Concreteoverlayscanbeconstructedandopenedtotrafficwithinaday,reducingusercostsanddriverfrustration.

•Concreteoverlayspossessalowlife-cyclecost,withlonglivesandminimalmaintenancecosts.

Figure 2-5. Bonded overlay construction

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•Industrialby-products(e.g.,flyash,slagcement,silicafume)canbeusedinmixturedesign.

•Concretepavementsurfacesarehighlyreflective,makingthemmorevisibleatnight.Bettervisibilityimprovessafety.

•Concrete’slightsurfacereducestheurbanheatislandeffect.

For More InformationAmericanConcreteInstitute.2006.Concrete Overlays for Pavement Rehabilitation.ReportNo.ACI325.13R-06.

Harrington,D.,etal.2008.Guide to Concrete Overlays—Sustainable Solutions for Resurfacing and Rehabilitating Existing Pavements.SecondEdition.NationalConcretePavementTechnologyCenter.September.

NationalConcretePavementTechnologyCenter.2010.Guide for the Design of Concrete Overlays Using Existing Methodologies (Draft).Fall.

PortlandCementAssociation.2010.Integrated Paving Solutions—Concrete Overlays.http://www.integrated-pavingsolutions.org/ConcreteOverlays.html.

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Pervious Concrete

Objectives•SatisfyEPAStormWaterPhaseIIregulations.

•EarnLEEDcredits.

•Improvesafety.

•Reducetire-pavementnoise.


Solution•Useperviousconcrete.

Benefits•PerviousconcreteisanEPABestManagementPractice.

•Stormwaterrunoffandflashfloodingisminimized.

•Hydroplaningandsplashandsprayareminimized.

•Noisefromthetire-pavementinteractionisreduced.

•Perviousconcretesurfacesreflectlightandhelpreducetheurbanheatislandeffect.

Considerations•Perviousconcretemayrequireperiodicmaintenancetopreventclogging.

•Perviousconcretemaycauseravelingandabrasionproblemsonhigher-speedroadways.

Typical Applications



Shoulders

OrganizationssuchastheGreenHighwaysPartner-shipareactivelyfacilitatingtheredevelopmentofmanyinner-citylandscapesinanefforttomakethemmoresustainable.Perviousconcretepavementsarebecomingmoreattractivealternativesforavarietyofnewconstructionandurbanretrofitapplications.Figure3-1showsperviousconcreteinstalledataparktomeetAmericanswithDisabilitiesAct(ADA)accessibilityrequirements.Figure3-2showsperviousconcreteinstalledataparktominimizeimpervious

Figure 3-1. Miller Park in Fair Oaks, California

Figure 3-2. Imperial Beach Sports Park, California


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surfacerunoff.Figure3-3showsaChicago,Illinois,neighborhoodalleyconstructedofperviousconcretetominimizerunoff.Theabilitytomanagestormwaterrunoffmakesperviousconcreteacommonchoiceforapplications,includingcitystreetsandlocalroads,shoulders,pedestrianwalkways,alleys,andparkinglots.

Perviouspavementcanalsobeusedasasubbaseforconventionalconcrete,atlow-watercrossings,andforrecreationalareassuchastenniscourtsandgreenhouses.

Figure 3-3. Pervious concrete for alley in Chicago, Illinois

storageandretentiontimeforegressandpercolationofwaterintothesubgrade.Themixdesigniscom-posedofnarrowspeciallygradedcoarseaggregate,cement,water,andasmallamountoffineaggregate.Theresultisamaterialwithinterconnectedairvoidsofbetween15to25percent,dependingonthemixdesign.Whencomparedtoconventionalconcretepavements,theexposedaggregatesurfaceofpervi-ousconcretecanprovideenhancedtractionforbothpedestriansandvehicles.Thepotentialforvehicleshydroplaningduringwetweatherconditionsisalsoreduced.Ifnotcuredproperly,surfaceparticlesmaybecomelooseorravel.Withpropercompactionandcuring,ravelingcanbeprevented.

Figure 3-4. Pervious concrete

Figure 3-5. Pervious concrete pavement parking lot

DescriptionPerviousconcrete(seeFigure3-4)isusedinahighlypermeablepavementthatcapturesrainwaterandallowsittopassthroughthesurfaceandpercolateintotheunderlyinglayer.Perviousconcretepavementsminimizestormwaterrunoff,flashflooding,andstandingwater;theycanreduceoreveneliminatetheneedforon-siteholdingpondsorburiedstormwaterretentionstructures.Figure3-5showsaparkinglotmadeofperviousconcrete.

Perviousconcretecanbeplaceddirectlyonadrain-ableaggregatebase,abovesand,oronsoilswithsuf-ficientdrainageproperties.Perviousconcretemayalsobeplacedoverimpermeablesoilssuchasclay;how-ever,provisionsneedtobemadeforadequatewater

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Perviousconcretepavementscanlastformorethan20yearswithnominalmaintenance.Toensureadequatedrainage,routinemaintenanceistypicallyrequired.Theamountofroutinemaintenancedependsontherateofsoilloading.Sweeping,vacuuming,orpowersprayingcanbeusedtomitigatecloggingandrestorepermeability.Thesepavementshavebeensuccessfulinfreeze-thawandsulfateenvironmentswhendesignedandconstructedproperly.Theabilityforperviousconcretepavementstodrainwaterquicklyminimizesthesaturationwithinthevoidsthatcouldotherwisefreezeandcausedamage.Perviousconcreteismoresusceptibletosulfateenvironments;however,ifkeptisolatedfromsulfaterichsoilsorproducedwithSCMs,perviouspavementscanperformsatisfactorily.

MaterialsSeeTable3-1fortypicalvaluesofmaterialpropertiesforperviousconcrete.

Perviousconcreteusesbasicallythesamematerialsasconventionalconcrete.Oneexceptionisthatthefineaggregatecontentislimitedandthecoarseaggregateiskepttoanarrowgradation(seeFigure3-6).Com-monlyusedgradationsofcoarseaggregateincludeASTMC33No.67,No.8,orNo.89.Number89istypicallyusedinmixturesforparkinglotsandpedes-trianwalkways.Roundedorangular(i.e.,crushed)aggregatescanbeusedforperviousconcretemixtures.Maximumaggregatesizeandthetypeofaggregatewillaffectthefinalsurfacetexture.

Figure 3-6. Fresh pervious concrete

Table 3-1. Typical values for material properties

Property Typical Values

Unit Weight 70-80% of conventional concrete mixtures

Density100-125 lb/ft3 (1600-2000 kg/m3) – this is dependent on mix design and construction procedures

Percent Voids 15-25%

Permeability 100 in./hr – over 2000 in/hr (2.5-50 m/hr)

Compressive Strength

2500 psi (17 MPa) but this can range from 500 – 4000 psi (3.5 – 28 MPa)

Perviousconcretemixescontainminimalamountsofwater,withwater-to-cementitiousmaterials(w/cm)ratiosaround0.30;however,ratiosashighas0.34to0.40havebeenusedsuccessfullywiththeproperinclusionofchemicaladmixtures,suchasretarders.

Portlandcementsandblendedcementsmaybeusedinperviousconcreteapplications.Inaddition,SCMssuchasflyash,pozzolans,andslagcementcanbeusedtoimprovematerialpropertiessuchasworkabil-ityandstrength.Infreeze-thawenvironments,air-entrainingadmixturesarerecommended.

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DesignAperviouspavementisdesignedaseitheranactiveorapassivesystem.Anactivesystemisdesignedtohandlemuchmorerainfallthanisexpectedtofallonjustthepavementitself.Apassivesystemisapervi-ousconcretepavementthathandlesrainfallthatfallsdirectlyonthepavementsurface.Apassivemitiga-tionsystemcancapturemuch,ifnotall,ofthe“firstflush,”butitisnotintendedtooffsetexcessrunofffromadjacentimpervioussurfaces.Anactivemitiga-tionsystemisdesignedtomaintainrunoffatasiteatspecificlevels.Foreithersystem(activeorpassive),aproperthicknessmustbedesigned.Perviouspave-mentthicknessisdesignedbasedonthecalculationofhydrologicandmechanicalpropertiesincludingtheamountofexpectedrainfall,pavementcharacter-istics,andunderlyingsoilproperties.StandarddesignproceduresincludeACI522R,ACI325.9R,orACI330R.SeeFigure3-7forperviousconcretesubjectedtorainfall.

Designsforperviousconcretepavementsurfacesmustconsiderpermeabilityandstoragecapacity.

Figure 3-7. Pervious concrete pavement in the rain

Designersshouldensurethatpermeabilityissufficienttoaccommodateallrainfallingonthesurfaceoforrunningontoperviousconcrete.Whilethepermeabil-ityofperviousconcretesisafactorindesign,theflowratethroughthesubbaseandsubgrademaybemorerestrictiveandcontroltheamountofwaterleavingthesystem.Thetotalstoragecapacityoftheperviousconcretesystemincludesthecapacityoftheperviousconcretepavement,thecapacityofanysubbaseused,andtheamountofwaterthatleavesthesystembyinfiltrationintotheunderlyingsoil.

Infreeze-thawclimates,perviousconcretesystemsshouldnotbedesignedtostorewaterintheconcreteitselfbecauseoftheexpansivenatureofwaterwhenitfreezes.Fortypicaldesigns,thestoragecapacityandinfiltrationrateofthesubbaseandsubgradesaresignificant.

Typicaldesignthicknessesinclude5-to6-in.(125-to150-mm)thickperviousconcretewithadrainableaggregatebasegenerally6-to12-in.(150-to300-mm)thick.Thebaselayershouldallowapercolationrateof0.5in./hr(13mm/hr)ifnooverflowpipingis

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installed.Infreeze-thawenvironments,aminimumof12in.(300mm)ofadrainableaggregatebase,suchas1-in.(25-mm)crushedstone,istypicallyconstructed.Athickerpavementsystemmayneedtobeusedifheavierloadsandhighertrafficareanticipated,orifthepercolationrateofthebaselayerisinadequate.

Figure3-8,Figure3-9,andFigure3-10showtypicalschematicsofperviouspavementdesigns.Fullexfil-trationdesignsareonlyusedwherethenaturalsoilhasahighinfiltrationrateorgoodlateralpermeability.Partialexfiltrationdesignsarethemostcommonandtypicallyusedtocontrolthewaterqualityvolume.Noexfiltrationdesignsareusedwhereproblemsoilsareaconcernorwhereitisnotdesirabletointroducewaterintoadjacentlocations.

Figure 3-8. Schematic of pervious full exfiltration pavement design

Precast Pavement

Drainable Base

Untreated Subgrade

Pervious Pavement

Drainable Base

Untreated Subgrade

Friction Reducing Medium

Figure 3-9. Schematic of pervious partial exfiltration pavement design

Figure 3-10. Schematic of pervious no exfiltration pavement design

Precast Pavement

Drainable Base

Untreated Subgrade

Pervious Pavement

Drainable Base

Untreated Subgrade

Tile Drain w/ Up-Turned ElbowFriction Reducing Medium

Precast Pavement

Drainable Base

Untreated Subgrade

Pervious Pavement

Drainable Base

Untreated Subgrade


Tile Drain

ConstructionTheconstructionofperviousconcretepavementincludesproductionofconcrete,placement,compac-tion,andcuring.

Perviousconcreteproductionrequirestightercon-trolofmixtureproportioning.Itisalsoimportanttomaintainaggregatemoistureatsaturatedsurfacedrymoisturecontentduringproduction.Waterabsorbedbythemixturefromaggregatesthataretoodrywillresultinamixthatistoodryforplacementandcom-paction.Toomuchwaterinaggregateswillincreasew/cmanddecreasestrengthanddurability.

Alowslumpandstifferconsistencymaydischargeslowerfromtransitmixersthanconventionalconcrete.Waterreducersandviscosity-modifiedadmixturescanbeusedtoincreaseflowabilityandmaintainstabilityoftheconcreteduringdischargeandplacement.Unitweightorbulkdensitytestsprovidethebestroutinetesttomonitorquality,aswellasseven-daycorestoevaluatethicknessandstrength.

Conventionalformworkistypicallyusedtoplaceperviousconcrete,andplacementshouldbecontinu-ouswithspreadingandstrikeoffactivitiesperformedinarapidmanner.Compactionandfinishingisgenerallyaccomplishedbyaweightedroller-screedthatspinsasitispulledacrossthefreshconcrete.Thespinningtubeprovidessomesurfacecompactionandcreatesasmoothuniformsurface(Figure3-11).Recommendedjointspacingsof20ft(6m)havebeensuggested,althoughsomeinstallationshavehadjointspacingsof45ft(13.5m)ormorewithout

Figure 3-11. Compacting the placed pervious concrete

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uncontrolledcracking.Becausesettingtimeandshrinkageareacceleratedinperviousconcretecon-struction,jointsareusuallytooledintotheconcretesoonafterconsolidationwitharollingjointtool.

Theopenstructureandrelativelyroughsurfaceofperviousconcreteexposemoresurfaceareaofthecementpastetoevaporation,makingcuringextremelyimportant.Curingforperviousslabsandpavementsbeginsbeforetheconcreteisplaced—thesubgrademustbemoistenedtopreventitfromabsorbingmoisturefromtheconcrete.Afterplacement,fogmist-ingfollowedbyplasticsheetingistherecommendedcuringprocedure,andsheetingshouldremaininplaceuntiltheconcreteachievesadequatestrengthtosupportthetrafficloadwithoutdamagingthesurface(seeFigure3-12).Curingshouldbestartedassoonaspracticallypossibleafterplacing,compacting,andjointing.

Sustainability•Heatandlightisreflectedduetoitslightercolorandlowerdensity,decreasingtheimpactofheatislandeffects.

Figure 3-12. Curing pervious concrete with plastic sheeting

•Perviousconcretereducesrunoffandthushelpspreventpollutionofnaturalbodiesofwater.

•Theneedforon-siteholdingpondsorexpensiveirrigationsystemsisreducedoreliminated,resultingindecreasedcostsandmoreuseablelandspace.

•Safetyisimprovedbecausethepotentialforhydro-planingisreducedsincewaterisabletoescapefromthesurface.

•Noiseisreduced,improvingtravelingexperience.

For More InformationAmericanConcretePavementAssociation.2006.Stormwater Management with Pervious Concrete Pave-ment.ConcreteInformation,IS334P.

AmericanConcretePavementAssociation.2007.Green Highways.ConcretePavementResearchandTechnologySpecialReport,SR385P.

AmericanConcreteInstitute.2010.Pervious Concrete.ACICommittee522,522R.

GreenHighwaysPartnership.www.greenhighway-spartnership.org.

NationalReadyMixedConcreteAssociation.Pervious Concrete.www.perviouspavement.org.

Obla,K.2007.Perviousconcreteforsustainabledevelopment.InRecent Advances in Concrete Technol-ogy.Washington,D.C.

PortlandCementAssociation.2010.Integrated Paving Solutions—Pervious Concrete.http://www.integrated-pavingsolutions.org/perviousconcrete.html.

Tennis,P.D.,M.Leming,andD.J.Akers.2004.Pervi-ous Concrete Pavements.EB302.02.Skokie,Illinois:PortlandCementAssociation;SilverSpring,Maryland:NationalReadyMixedConcreteAssociation.

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Precast Pavements

Objectives•Providelonglife.


•Providehighload-carryingcapacity.



Solution•Useprecastconcretepavementsystems.

Benefits•Constructioncanbecompletedduringshort(over-nightorweekend)closures.

•Laneclosuresandassociateduserdelaysduringconstructionareminimized.

•Precastpavementsareahighlydurablefinishedpavementandnotjustatemporaryfix.

•Precastpavementsurfacesreflectlightandhelpreducetheurbanheatislandeffect.

Considerations•InitialcostsaregenerallyhigherthanconventionalPCCpavement.

•Thelearningcurveforproduction,placement,andtestingcanbesteep.

Typical ApplicationsPrecastconcretepavementsaretypicallyusedforhighway,airfield,andheavyindustrialapplications.

Highways

Airfields

Heavy Industrial

DescriptionPrecastpavementsareconstructedusingprefabricatedconcreteslabsinstalledoverapreparedsubbaseorexistingpavement(seeFigure4-1).Precastpanelsarefabricatedoffsiteatestablishedprecastconcretefacilitiespriortoconstruction,transportedtothejobsite,andtheninstalledonsiteandopenedtotraf-fic.PrecastpavementshavebeenusedprimarilyforreconstructionandrepairofJCP—buthavealsobeenusedfornewconstruction—andhavethepotentialtobeusedforreconstructionofHMApavements.Precastpavementsystemscanalsobeusedasanunbondedoverlay,acost-effectivesolutiontoaddstructuralcapacityandextendthelifeofanexistingroadway.

Thebenefitsofprecastpavementareprimarilyrealizedthroughreconstructionofexistingfacilities

Prepared Subgrade

Precast Pavement

Subbase

Prepared Subgrade

Precast Pavement

Subbase

Prepared Subgrade

Precast Pavement

Subbase


Figure 4-1. Precast pavement system cross-section


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duringshortclosures,asshowninFigure4-2dur-ingthenighttimereconstructionofInterstate66inVirginia.Precastpavementhasalsobeenusedsuc-cessfullyfornewconstructionofhighways,likethatshowninFigure4-3inIndonesia.Forthisproject,upto0.6miles(1.0km)ofprecastpavementwasplaceddaily.

RepairorreconstructionofJCPandHMApavementsusingprecastpavementsystemscanbeaccomplishedquickly,duringshortovernightorweekendclosures,thusreducinguserdelayandassociatedcosts.Precastpanelscanbeusedforisolatedfull-depthrepairs,suchasjointreplacements,forsingleormultipleconsecu-tiveslabreplacements,orfortotalreconstructionofanentiresection.

TherearetwoprimarytypesofprecastpavementsystemsusedintheUnitedStatestodate.Thefirst

Figure 4-2. Nighttime placement of precast panels in Virginia

Figure 4-3. Precast pavement system in Indonesia

typeofsystemusesprestressedconcretepanelsthatarepretensionedinonedirectionduringfabricationandposttensionedtogetherintheotherdirectionafterplacementonsite.Theothertypeofsystemisajointedsystem,whichreplicatesconventionalJCPusingprecastpanels.Fortheprestressedsystem,loadtransferbetweenpanelsisprovidedbyposttension-ing;dowelsareusedforthejointedsystem.Decidingonwhichsystemtousewilldependprimarilyonthetypeofapplicationbutalsoonissuessuchascostandcontractorexpertise.

Unlesstheyaretobeusedasatemporarypatch,precastpavementsaredesignedtoperformequaltoorbetterthannewconcretepavement.Whiletheridequalityofthesurfaceasinstalledisacceptableforopeningtotraffic,diamondgrindingcanbeusedtoensurethefinalridingsurfacemeetsthestringentrequirementsforhigh-speedroadways.

MaterialsPrecastconcretehasbeenprovenadurablehigh-performanceproductforbridgeandcommercialbuildingconstruction.Theconcretemixturesusedaresimilartothoseutilizedforotherprecastelementsandarenotrestrictedto“paving”mixtures.However,considerationmustbegiventopavement-specificrequirements,suchasrequirementsforskidresistanceanddurabilityinpotentiallyaggressiveenvironments.Highstrength,lowpermeabilityconcretemixtureswithaloww/cmratioanduniformaggregategrada-tionareusedroutinelybyprecastfabricationplantsandwillgenerallybesuitableforpavementpanelsaswell.

Strengthrequirementsaretypicallynotdifficulttoachieveduetotheneedforrapidproductionofprecastpanelsbyturningoverthecastingbedseverydayoreveryotherday.Typicalprecastpavementmixturesaredesignedforaverage28-daycompres-sivestrengthsbetween4,000and6,000psi(28–41MPa),andhigherstrengthsusuallyachieved.Forprestressedprecastpanels,strengthsof3,000to4,000psi(21–28MPa)aretypicallyrequiredforreleaseofpretensioning.Lowpermeabilitypreventschloridesandothercorrosiveagentsfrompenetratingthecon-creteandreachingthereinforcementandprestressing

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steelinthepanels.Aggregatesmustmeetspecifiedskid-andabrasion-resistancerequirementstypicalforpavements.

DesignForprestressedprecastpavementsystems,thepremisefordesignistofirstcalculatethethicknessthatwouldberequiredforconventionalconcretepavement,thentoreducethatthickness,asmuchaspractical,byadjustingtheprestresslevelssuchthatstressesintheprecastpavementwillbeequivalenttotheconven-tionalconcretepavement.Additionalprestresscanbeaddedtofurtherincreasethedesignlifeofthepave-ment.Precastpanelsaretypicallyaminimumof8in.(200mm)thick,buttheycanbeadjustedasnecessarytomatchthethicknessandcross-sectionoftheexist-ingpavement.

JointedprecastpavementsystemsaretypicallydesignedtoreplicateconventionalJCP.Forrepairorreconstructionprojects,theprecastpanelsaredesignedtomatchthethicknessoftheslabbeingremovedminus1/4–1/2in.(6–13mm)toaccommo-dateirregularitiesinthebasebeneaththepavementslabbeingremoved.Fornewconstruction,thepanelsaredesignedtomatchthethicknessthatwouldbespecifiedforaconventionalconcretepavementdesignbasedonprojectconditions.

Forprestressedsystems,therearetwotypesofjoints:(1)theintermediatejointsbetweentheindividualpanels,and(2)theexpansionjointsattheendsofeachposttensionedsectionofprecastpanels.Theintermediatejointsare“nonworking”jointsthatareposttensionedtogetherandsealedwithepoxyappliedtotheabuttingfacesoftheprecastpanelsduringconstruction.Theexpansionjointsaredesignedtoaccommodateor“absorb”movementduetoexpan-sionandcontractionoftheposttensionedslabs.

Forjointedsystems,doweledjointsareusedsimilartoconventionalJCP.However,itshouldbenotedthatthereisnotanysignificantcontributiontoloadtransferfromaggregateinterlock,asisthecaseforconventionalJCP.Groutormortaristypicallyusedtoensurefullbeddingofthedowelbarsintheprecastpanelsafterinstallationandtofillthejointbetweenthepanels.

Prestressedpanelsaretypicallydesignedwithminimalnonprestressedreinforcement.Thisisbecausepre-stressinghelpstominimizeoreveneliminatecrack-ingthroughso-called“elasto-plastic”behavior,whichhelpskeepanycracksthatdoformtightlyclosed.Jointedprecastpanelsaretypicallyheavilyreinforcedwithtwomatsofmildsteelreinforcementtopreventanycracksthatmayformduringhandlingorfromwideningoverthelifeofthepavement.

Subbaselayers,ifincludedintheprecastpavementdesign,shouldbedesignedtoprovideuniformsup-port.TypicalbasematerialsincludeHMA,crushedstone,stonedust,andleanconcrete.

ConstructionPrecastpavementconstructionencompassesprefabri-cationoftheconcretepanelsandsubsequentplace-mentatthejobsite.

Theprefabricationprocessincludessettinguptheformstoverystricttolerances,securingreinforcement,prestressing,andaddingotherembedmentswithintheforms.Nextintheprefabricationprocessisplac-ingconcreteintotheforms(Figure4-4andFigure4-5),screeding,texturing,andcuringtheconcrete.Finally,removingthepanelsfromtheforms,complet-inganyadditionalstepsrequiredbeforeplacement,andstockpilingthepanelsforshipmenttotheprojectconcludestheprocess.

Aprimarybenefitofprefabricationisthehighdegreeofqualitycontrolthatexistsinprecastconcretefacili-tiesalongwiththecontrolledenvironmentunderwhichthepanelscanbeproduced.Thishelpstoensureuniformityofmaterials,workmanship,andadequatecuringfortheprecastpanels.Goodcon-structionpracticesrecommendthatanestablishedprefabricationfacilitybeused,asopposedtoatempo-raryplantsetupnearthejobsite.

Deliveryoftheprecastpanelstothesiteisacriti-calaspectoftheinstallationprocess,andcaremustbetakentoensurethatthepanelsarenotdamagedinanywayduringhandlingorshipping.Figure4-6andFigure4-7showtypicalplacementmethodsforprecastpavementsystems.Providingaflat,uniform,andstableplatformfortheprecastpanelstoreston

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Figure 4-4. Concrete poured into form for precast panel

Figure 4-5. Vibrators for consolidation of concrete around reinforcement in precast prestressed panel

isimportant,regardlessofthesubbasematerialused.Forprestressedprecastsystems,someformoffriction-reducingmaterialisneededbetweentheprecastpavementandunderlyingsubbasematerialtoreducefrictionalrestraintstressesthatcanaccumulateduringposttensioninganddailyexpansionandcontractioncycles.Tohelpensurefullsupportbeneaththepanels,groutorurethanefoamistypicallyinjectedbeneaththeslabsafterinstallationtofillanyvoidsthatmayexist.

Theconstructionprocessvarieswitheachjob,butbasedonthetypeofprecastpavementsystemused,commonstepsincludethefollowing:

•Sawcuttingandremovingexistingpavement(repair/reconstruction)orensuringthesubbaseisproperlyprepared(newconstruction)

Figure 4-6. Placement of precast panel for precast JCP system

Figure 4-7. Placement of a prestressed precast panel

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•Sawcuttingandjackhammeringdowelslotsordrill-ingandepoxyingdowels(jointedsystems)

•Finallevelingandgradeadjustmentofthesubbase

•Installationoftheprecastpanel(s)

•Applyingtemporaryposttensioningtopulladjacentpanelstogether(prestressedsystem)

•Applyingfinalposttensioningafterafullsectionofpanelshavebeeninstalled(prestressedsystem)

•Backfillingofthedowelslots(jointedsystems)andposttensioningblockouts(prestressedsystem)

•Groutingofposttensioningtendons(prestressedsystem)

•Groutingorfoaminjectionbeneaththepanels

•Fillingjointsaroundtheperimeterofthepanels(jointedsystems)

•Sealingjoints

•Diamondgrindingforsmoothness(asnecessary)

Sustainability•Materialusageisoptimizedthroughminimizingthethicknessoftheprecastpanels.

•Constructionwasteisreducedbecausetheexactamountofnecessarycomponentsisdeliveredtothesite—thereisnoadditional“incidental”thicknesstotheslab.

•Thereissignificantusercostsavingsinclud-ingfuelconsumptionandlostworktimeduetodelays.

•Anysparecomponents/panelscanberecycled,andtheirmaterialsusedagaininanotherproduct.

•MixturesforprecastsystemsuselocallyderivedmaterialsandcanincorporaterecycledSCMslikeflyashandslagcement.

For More InformationBuch,N.2007.Precast Concrete Panel Systems for Full-Depth Pavement Repairs: Field Trials.ReportNo.

FHWA-IF-07-019,FederalHighwayAdministration,February.

FederalHighwayAdministration.2009.Precast Prestressed Concrete Pavement for Reconstruction and Rehabilitation of Existing Pavements.TechBrief,FHWA-IF-09-008,www.fhwa.dot.gov/pavement/pub_details.cfm?id=632.

Merritt,D.K.,B.F.McCullough,N.H.Burns,andA.K.Schindler.2000.The Feasibility of Using Precast Concrete Panels to Expedite Highway Pavement Construc-tion.ReportNo.FHWA/TX-01/1517-1,CenterforTransportationResearch,February.

Merritt,D.K.,B.F.McCullough,andN.H.Burns.2002.Construction and Preliminary Monitoring of the Georgetown, Texas Precast Prestressed Concrete Pave-ment.ResearchReport1517-01-IMP,CenterforTransportationResearch,UniversityofTexasatAustin,December.

Merritt,D.K.,A.J.Miron,R.B.Rogers,andR.O.Rasmussen.2007.ConstructionoftheIowaHighway60PrecastPrestressedConcretePavementBridgeApproachSlabDemonstrationProject.IowaHighwayResearchBoard(IHRB)ProjectHR-1085,TheTranstecGroup,July.

Nantung,T.,J.Firmansjah,E.Suwarto,andA.Karya.2010.DesignandconstructionofprecastprestressedconcretepavementinIndonesia.InProceedings,2010 fib International Congress and PCI Annual Convention/Bridge Conference,21May–2June,Washington,D.C.

PortlandCementAssociation.2010.Precast/Prestressed Concrete.www.cement.org/buildings/precast_splash,(15June2010).

Tayabji,S.andK.Hall,K.2010.Precast Concrete Panels for Repair and Rehabilitation of Jointed Concrete Pavements.ReportNo.FHWA-IF-09-003,FederalHighwayAdministration,April.

TheTranstecGroup.2010.PrecastPavement.TheTranstecGroup,www.precastpavement.com(15June2010).

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Roller-Compacted Concrete

Objectives•Providealow-costpavementoption.

•Provideastrong,durablepavementthatwillsup-portheavyloads.

•Minimizetrafficdisruptionandprovideforrequiredearly-openingtotraffic.

•Widenalaneoraddashoulderinacost-effectivemanner.


Solution•Constructwithroller-compactedconcrete(RCC).

Benefits•Roller-compactedconcreteprovidesastrong,dense,anddurablematerialthatcanbequicklyconstructed.

•Constructionisfast,withnoformsorfinishing.

•NosteelreinforcementandminimumlabormakeRCCeconomical.

•Formanyapplications,jointsawingisoptionalforaestheticpurposesresultinginadditionalcostsavings.

•Roller-compactedconcretepavementsurfacesreflectlightandhelpreducetheurbanheatislandeffect.

Considerations•AmixerwithadequateenergyisrequiredtomixRCC.

•Typically,anasphalt-typepaverisusedforplacement.

•Surfacetypicallyisnotassmoothorconsistentinappearanceasconventionalconcrete.

•Forhighertrafficspeeds,thesurfacemayneedtobediamondgroundortoppedwithaconcreteorHMAoverlay.

Typical ApplicationsRoller-compactedconcretepavementapplicationsincludestreetsandlocalroads,highwaysandshoul-ders,airfields,heavyindustrial,andcommercial/lightindustrial.Roller-compactedconcreteisanidealcandidateinsituationswheresurfacesmoothnessandappearancearesecondarytohighdurability,lowmaintenance,earlytrafficking,andlowinitialcost.

Roller-compactedconcretewithasurfacetreatmentsuchasdiamondgrindingoranoverlaycanbeusedforpavementsthatexperiencehigh-speedtraffic,includinghighways.Insuchapplications,RCCactsasabaseorsubbase.

Highways


Airfields

Heavy Industrial


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E DescriptionRoller-compactedconcretehasasimilarstrengthtoconventionalconcrete,yetitcanbemoreeconomi-cal.PavementswithRCCcanresistruttingandspansoftlocalizedsubgrades.Theywillnotdeformunderheavy,concentratedwheelloads,willresistdeteriora-tionfromfuelorhydraulicfuelspills,andwillremainrigidunderhightemperatures.ThecompressivestrengthofRCCiscomparabletothatofconventionalconcrete,rangingfrom4,000to6,000psi(28to41MPa),withflexuralstrengthranginginvaluesfrom500to1,000psi(3.4to6.9MPa).Thestrengthmakesitabletowithstandhighconcentratedloadsandimpactsfromheavyindustrial,military,andminingapplications,aswellassupportlightvehicletrafficshortlyafterplacement.

Roller-compactedconcretecanbeusedasapavementsurfacelayerforlow-speedroadsandindustrialfacili-tieswheresurfacesmoothnessandappearancearenotamajorconcernascomparedtohighdurability,lowmaintenance,andlowinitialcost(seeFigure5-1).Diamond-groundRCChadbeenusedsuccessfullyonurbanarterialswithoutanyadditionalsurfacetreat-ment.Roller-compactedconcretecanalsobeabaseorsubbaseforhighwaysandotherhigh-speedtrafficroadways(seeFigure5-2andFigure5-3).

Roller-compactedconcretecombinesvariousaspectsofconventionalconcretepavementmaterialspracticeswithsomeconstructionpracticestypicalofflex-iblepavements.Ithasthesamebasicingredientsasconventionalconcrete:cement,water,andaggregates(suchasgravelorcrushedstone),butitistypically

Figure 5-1. Typical RCC versus PCC surface

Figure 5-2. Pavement cross-section with RCC surface

Prepared Subgrade

Subbase

RCC

Prepared Subgrade

Subbase

RCC

Figure 5-3. Pavement cross-section with RCC base

Prepared Subgrade

RCC

Pavement Surface

Prepared Subgrade

RCC

Pavement Surface

placedwithasphalt-typepavingequipmentandcompactedbyvibratorysteeldrumrollerstoaspecificdensity(seeFigure5-4).

Unlikeconventionalconcrete,RCCisa“drier”mixandstiffenoughtobecompactedbyvibratoryrollers.SincethepastecontentinRCCislower,lessconcreteshrinkageandreducedcrackingfromshrinkage-relatedstressesresult.Inaddition,non-air-entrainedRCCpavementscanprovidereliableanddurableper-formanceinfreeze-thawenvironmentsaslongasthemixisproperlyproportionedwithadequatecementcontentandsoundaggregates.Theconcretemustalsobethoroughlymixed,adequatelycompacted,andproperlycured.

Figure 5-4. RCC construction for commercial and heavy industrial applications

RCC Pavement

PCC Pavement

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ROLLER-COMPACTED CONCRETE

MaterialsThegoalinselectingtheappropriatequantityofmate-rialsforRCCistoproportionthemixsothatthereisenoughpastetocovertheaggregatesandfillthevoids(seeFigure5-5).PrimarydifferencesinproportionsbetweenRCCpavementmixturesandconventionalconcretepavementmixturesarethefollowing:

•Roller-compactedconcreteisgenerallynotairentrained.

•Roller-compactedconcretetypicallyhasalowerwatercontent.

•Roller-compactedconcretetypicallyhasalowerpastecontent.

•Roller-compactedconcretegenerallyrequiresalargerfineaggregatecontentinordertoproduceacombinedaggregatethatiswellgradedandstableundertheactionofavibratoryroller.

•Roller-compactedconcreteusuallyhasanominalmaximumsizeofaggregatenotgreaterthan3/4in.(19mm)inordertominimizesegregationandpro-ducearelativelysmoothsurfacetexture.

Aggregateselectionisveryimportant.Naturalorman-ufacturedaggregatescanbeused.Mineralaggregatesconstituteupto85percentofthevolumeofRCCandplayaninfluentialroleinachievingtherequiredworkability,specifieddensityinthefieldundervibra-torycompaction,compressiveandflexuralstrengths,thermalproperties,long-termperformance,anddurability.Aggregatefinesaretypicallyintherangeof2–8percent,passingthe#200(75μm)sieve.Siltsandclays,however,shouldbeavoided.

CementitiousmaterialsusedinRCCpavementmix-turesincludeportlandcementorblendedhydrauliccementandmayincludepozzolanssuchasflyashandslagcement.TypesIandIIcementsarecommonlyusedinRCCpavements.TypeIIIcanbeusedwhenearlystrengthgainisrequired,andTypeVcanbeusedinareasthathavespecificsoilconditionscallingforthistypeofcement.

Theuseofablendedcement,pozzolans,orslagcementmayhelpimproveworkability,reducethepotentialforalkali-aggregatereaction,extendthecom-pactiontime,andhelpinfreeze-thawconditions.TheuseofflyashinRCCisaneffectivemeansofprovid-ingadditionalfinematerialneededtoensureadequatecompaction,particularlyinthoseRCCmixturesthatcontainstandardgradedconcretefineaggregate.

Watercontentshouldbejustenoughtoensureevendistributionofthepastebutdryenoughtosupportthevibratoryroller(seeFigure5-6).Chemicaladmix-turescanbeused.Higherdosagesofchemicaladmix-turesthaninconventionalconcretemayberequired,andmaterialcompatibilityshouldbeestablishedthroughtrialbatches.

DesignRoller-compactedconcretepavementsfallintotwomaincategories:(1)heavy-dutyindustrialpavements(e.g.,portsandmultimodalterminals),and

Figure 5-6. RCC material looks drier than conventional concreteFigure 5-5. Typical mix design constituents

RCC

50

45

40

35

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Cement + Fly Ash

Coarse Aggregate

Fine Aggregate

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Conventionalconcrete

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E (2)pavementscarryingmixed-vehicletraffic(e.g.,trucksandpassengervehicles).Table7showsalistofdesignmethodologies.ThicknessdesignforRCCpavementsemploysthesamebasicstrategyasforcon-ventionalconcretepavements;however,therearenodowelsorsteelreinforcementinRCCtoaccommodateloadtransfer.Thepavementshouldbethickenoughtoallowforflexuralstressesandfatiguedamagecausedbywheelloadswithinallowablelimits.Fatigueduetoflexuralstressisusedtocalculatetherequiredpavementthickness.TheminimumthicknessofanRCCpavementistypically4in.(100mm).Asingleliftshouldbenothickerthan10in.(250mm).

Baseandsubbaselayerrequirementsaresimilartothoserequiredforconventionalconcrete;however,RCCcanbemoresensitivetothemoisturecontentofgranularsubbases.

Historically,RCCisconstructedwithoutjoints.WhenRCCisallowedtocracknaturally,aggregateinterlockusuallyprovidesadequateloadtransferacrossthecracks.Crackstypicallyoccurat20-to60-ft(6.1-to18.3-m)intervals,dependingontheRCC’spropertiesandpavementthickness.TheprimaryreasonjointsareusedinRCCpavementsistoinitiatecrackloca-tionsortoimproveaestheticsinparkinglots,accessroads,orareasofchannelizedtrafficatspeedsgreaterthan30mph.Figure5-7showsflexuralbeamtesting.

WhenjointsareconstructedinRCC,theyarefewerinnumberandspacedfartherapartthaninconventionalconcretepavements.DowelsortiebarsarenotusedinRCCpavementsforloadtransferthewaytheyareusedinconventionalconcrete;therefore,thedesignerneedstoconsidertheabsenceofloadtransferdevicesinthedesign.Figure5-8showsatypicalRCCdesigncrack.

Whereconcentratedlanetrafficisnotcommon,jointscanbesawedinsquarepatternsusingthetransversespacingof15-to20-ft(4.6-to6.1-m)intervalsforpavementslessthan8in.(200mm)thickand3to4times(infeet)thepavementthickness(ininches)for

Figure 5-7. Flexural beam testing

Figure 5-8. Typical RCC design relies on aggregate interlock at cracks

Subbase

RCC

Subbase

Crack

Aggregate interlock

RCC

Table 5-1. List of design methodologies

PropertyHeavy Industrial Applications

Conventional Roadway Applications

RCC-Pave Computer Software (PCA) U.S. Army Corps of Engineers (USACE) StreetPave (ACPA) Guide for Design of Jointed Concrete Pavements for Streets and Local Roads (ACI 325.12R-02)

Guide for the Design and Construction of Concrete Parking Lots (ACI 330R-08)

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pavements8in.(200mm)thickorgreater.Inareaswithconcentratedlaneloading,thelongitudinalspac-ingshouldbe20ft(6.1m)forpavementslessthan8in.(200mm)thickand2.5times(infeet)thepave-mentthickness(ininches)forpavements8in.(200mm)thickorgreater.

ConstructionAcontinuoussupplyoffreshRCCmaterialtothepavementplacementmachineryisnecessaryforproducingaqualityproduct.Therefore,therateofRCCproductionandtransportationcapabilityshouldmatchthespeedofconstructionatthesite(seeFigure5-9).AnRCCmixingfacilitymusthavetheefficiencytoevenlydispersetherelativelysmallamountofwaterpresentinthestiff,drymix.Consequently,therela-tivelydryRCCrequiresrigorousmixingenergiesandbatchingtimestoprovideauniformmixture,whichcanreducetheplant’smixingcapacitywhencomparedtoconventionalconcrete.

Therightmixingequipmentisvitaltoensuringacontinuousandconsistentqualitysupplytothepaver.TherearetwotypesofmixersforRCC:batchtypeandcontinuousmixers.Mostconcretebatch-typemix-ersconsistofatilt(Figure5-10)orfixeddrumandtransitmixers(drybatchready-mixtrucks)(Figure5-11).Thesemixersaretypicallyusedforsmallerprojectsbecauseofthereducedmixingcapacityandlongermixingtime.ContinuousmixersaretypicallyusedforlargerprojectsbecausetheycanproduceRCCatafasterratethanbatchmixers.Typically,RCCisblendedincontinuoushorizontalshaftmixerssuchaspugmills.High-outputpugmillshavethemixingefficiencyneededtoevenlydispersethecementandrelativelysmallamountofwaterusedinthisdriermix(seeFigure5-12).Roller-compactedconcreteistypi-callydeliveredindumptrucks,buttransitmixerscansometimesbeusedforsmallprojects.

Duringplacement,itisimportantthatthesubbaseand/orsubgradebeuniformlymoist.Ingeneral,RCCpavementsareconstructedusingbothasphaltandconventionalconcretepavementconstructiontech-niques.Roller-compactedconcreteistypicallyplacedwithanasphalt-typepaver.Whenconfiguredwithahigh-densityscreed,rollingcompactionisreduced,thusminimizingvariationsinsurfacetoleranceand

Figure 5-9. RCC delivered to jobsite

Figure 5-11 Ready-mix transit trucks dumping into haul trucks

Figure 5-10. Tilt-drum mixer

improvingsurfacesmoothness.Ahigh-densitypaverisoftenusedtoaccommodatetherelativelylargeamountofmaterialmovingthroughthepaver.Forpavementthicknessesgreaterthan10in.(250mm),multipleliftsareused.

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E Compactionisthemostimportantstageofconstruc-tion,asitplaysalargeroleindensity,strength,dura-bility,smoothness,andsurfacetexture.SinceRCCmixturesarerelativelydryandstiff(zeroslump),a10-ton(10.2-t)vibratorysteeldrumandrubber-tiredrollersaregenerallyusedduringplacementoperations(seeFigures5-13through5-16fortheRCCplace-mentthroughcuringprocess).Whenusinghigh-densitypavers,highercompactionisaccomplishedprimarilybythepaverandpavingscreeds.Rollingbeginssoonafterplacementandcontinuesuntilthedensityofthepavementmeetsaminimumof98per-centofthemodifiedProctordensity.Finalcompactionisgenerallyachievedwithinonehourofmixing.

PropercuringandhydrationoftheRCCmixtureiscriticaltothelong-termdurabilityofthepavement.BecauseRCChasalowwatercontentandexhibitsnobleedwater,propercuringtechniquesareimportant

Figure 5-12. Mobile RCC pugmill mixing plant and mixing chamber

topreventevaporationandprematuredryingofthesurface.Lackofadequatemoistureforcuringcanresultinscaling,dusting,andravelingofthehardenedsurface.

Formostprojects,awhiteconcretecuringcompoundconformingtoASTMC309(SpecificationforLiquidMembrane-FormingCompoundsforCuringCon-crete)isused.Awatercurecanalsobeimplemented,wherethepavementissprayedorirrigatedtokeepitmoist.However,moisturecuringofRCCrequiresacontinuousapplicationofwaterfortheentirecuringperiod.

Sustainability•Longservicelifewithminimalmaintenance,lowinitialcosts,incorporationofby-productmateri-als,andimprovedsafetymakeRCCasustainableoption.

Figure 5-13. RCC placement

Figure 5-14. Compacting RCC using both vibratory and pneumatic-tired rollers

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Figure 5-15. RCC in-place density measurement

•Roller-compactedconcretesurfacesreflectheat,whichreducestheheatislandeffect.

•Roller-compactedconcretehasahighalbedo,mak-ingforbetternightvisibilityandimprovedsafety.

For More InformationAdaska,W.2006.Roller-Compacted Concrete (RCC).ReportNo.SN2975,PortlandCementAssociation.

Adaska,W.2008.Applications and Design of RCC Pave-ments.PortlandCementAssociationSlidepresenta-tion,http://www.secement.org/rcc.htm.

AmericanConcreteInstitute.1999.State-of-the-Art Report on Roller-Compacted Concrete Pavements. ReportNo.ACI325.10R-99,FarmingtonHills,Michigan.

Gauthier,P.andJ.Marchand.2005.Design and Construction of Roller Compacted Concrete Pavements in Quebec.CementAssociationofCanada,Ottawa,Canada.

Harrington,D.,F.Abdo,W.Adaska,andC.Hazaree.2010.Guide for Roller-Compacted Concrete Pavements.SN298,PortlandCementAssociationandNationalConcretePavementTechnologyCenter,August.

Piggott,R.1999.Roller-Compacted Concrete Pave-ments—A Study of the Long Term Performance.RP366.Skokie,Illinois:PortlandCementAssociation.

PortlandCementAssociation.2010.Integrated Pav-ing Solutions—Roller-Compacted Concrete.http://www.integratedpavingsolutions.org/RCC.html.Figure 5-16. Curing RCC

•TheabilitytousesomefinesallowsRCCtoincorpo-ratematerialthatwouldotherwisenotbeacceptableforconventionalconcrete.

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Cement-Treated Base

Objectives•Provideastrong,uniformbase/subbaseforcur-rentandfutureloadingconditionsusingin-placeorlocallyavailablemarginalsoilsandgranularmaterial.

•Reducestressesonthesubgrade.

•Stabilizeavarietyofsoilswithasinglestabilizer.

•Reduceruttinganddeflectionsinaflexiblepave-mentsurface.

•Improvethestructuralcapacityoftheexistingsoil.


Solution•Acement-treatedbase(CTB)usingexistingsoilsorlocallyavailableborrowmaterial.

Benefits•Astifferbasereducesdeflectionsduetotrafficloads,therebyextendingpavementlife.

•Subgradefailures,pumping,rutting,jointfaulting,androadroughnessarereduced.

•Basethicknessisreducedcomparedtounboundgranularbasethicknesses.

•Marginalaggregates,includingrecycledmaterials,canbeused,thusreducingtheneedforvirgin,high-qualityaggregates.

Considerations•ThepotentialforreflectivecrackingandincreasedfrictionbetweentheCTBandsurfaceneedtobeconsidered.

Typical ApplicationsCement-treatedbaseprovidesadurable,long-lastingbaseinalltypesofclimates.Itisoftenusedinhigh-way,streetandlocalroad,shoulder,commercial,andheavyindustrialapplications.Cement-treatedbaseisalsocommoninairfieldapplications,particularlylargeairportrunwayapplications.TheFederalAviationAdministrationrequiresCTBforrunwaysthatexperi-encehighvolumesofheavyaircrafttraffic.

Highways


Airfields

Heavy Industrial


Shoulders

DescriptionCement-treatedbaseconsistsofnativesoils,gravels,ormanufacturedaggregatesblendedwithmeasuredamountsofportlandcementandwaterthathardensaftercuringtoformadurablepavingmaterial.Theversatilityofcementiscriticaltothesuccessofthestabilizationoperation,becausesiteconditionscaneasilychangeduringaprojectandthestabilizerneeds


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toadapttothechangingconditions.Cementisknownasa“universalstabilizer”becauseitworkswelloverawiderangeofdifferentsoiltypes.

PavementswithCTBwillbemuchstrongerthananunstabilized,granularbase.ThicknessesforCTBarelessthanthoserequiredforunstabilizedgranularbasescarryingthesametraffic.Cement-treatedbasecandistributeloadsoverawiderarea(seeFigure6-1),reducingthestressesonthesubgrade.Ithasahighload-carryingcapacity,doesnotconsolidatefurtherunderload,reducesruttinginHMApavements,andisresistanttofreeze-thawdeterioration.

Inapavementsystem,CTBisgenerallyconstructedoverthesubgrade(seeFigure6-2).AnHMAorcon-cretewearingsurfaceisplacedontheCTBtocom-pletethepavementstructure.Thedesignofaconcretesurfacelayermusttakeintoaccountincreasedfric-tionvaluesbetweenthelayers.Insomeinstances,aninterlayerisusedtoreducerestraintstressesandthepotentialforreflectivecracking.SeeFigure6-3foracompletedCTBsectionofroadway.

MaterialsCement-treatedbaseisamixtureofaggregatemate-rial,portlandcement,andwater.Themixtureshouldbedesignedbasedonstrengthandresistancetofreeze-thawandwetenvironments.

TheaggregatematerialusedinaCTBmixturecanbeavarietyofmaterialsorcombinationsthereof.Thesematerialsincludeexistingorborrowedstone,gravel,sand,silt,andcaliche.Recycledconcreteaggregates(RCA)andrecycledasphaltpavementcanalsobeincorporated.Awell-gradedsandyandgravellyaggre-gatematerialblendtypicallyrequirestheleastamountofcementforadequatehardening,whereasanaggre-gatematerialthatisclassifiedaseitherapoorlygradedsandymaterialdeficientinfinesorasiltyand/orclayeymaterialbothrequiremorecementforharden-ing.ManystatespecificationsrequirethataggregatesusedinCTBmeettypicalgradationandAtterberglimitrequirements.

Anyportlandcementtypecanbeused,butTypesIandIIarethemostcommon.Cementcontentdependsonthetypeofaggregatematerialused;

Figure 6-1. Load distribution of CTB compared to unstabilized granular base

Figure 6-2. Typical pavement cross-sections showing CTB layers

Prepared Subgrade

Concrete Surface

CTB Subbase

Prepared Subgrade

Concrete Surface

CTB Subbase

Prepared Subgrade

Concrete Surface

CTB Subbase

Prepared Subgrade

HMA Surface

CTB Subbase

Prepared Subgrade

HMA Surface

CTB Base


Figure 6-3. Completed CTB for new pavement construction in Oklahoma

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however,itusuallyrangesfrom3to8percentformostapplications.Ingeneral,acementcontentthatwillprovideaseven-dayunconfinedcompressivestrengthofbetween300and400psi(2.1and2.8MPa)issatisfactoryformostCTBapplications.

TheengineeringpropertiesoftheCTBmixturearedependentonindividualconstituentmaterialsthatmakeupthemixture(i.e.,aggregatematerialandcementtype),curingconditions,andage.Agemakesadifferencebecausecementwillcontinuetohydrateovertime,whichwillincreasestrength.Generalrangesforcompressivestrength,modulusofrupture,modulusofelasticity,andPoisson’sratioarelistedinTable6-1.

DesignACTBservesasanintegralcomponentofthepave-mentsystem.Itneedstobestrongenoughtowith-standthestressandfatiguecausedbytheenviron-mentinwhichitisconstructedandtheloadsunderwhichitmustperformoverananticipatedlifetime.SomecriticaldesigninputsforcalculatingCTBthick-nessincludetheestimatedtrafficloadingduringthedesignlife,subgradestrength,andCTBstrength.

ThemostcommonapproachfordeterminingCTBthicknessistofollowtheAmericanAssociationofStateHighwayandTransportationOfficials(AASHTO)DesignGuide(1993)procedureforpavementdesign,whichusesastructurallayercoefficienttomodelbasematerial.AmajoreffortiscurrentlyunderwaytoregionallycalibrateandshifttothenewAAS-HTOMechanistic-EmpiricalPavementDesignGuide(M-EPDG).AnotherapproachistousethePortlandCementAssociationproceduregiveninthePCApub-lication“Thickness Design for Soil-Cement Pavements.”

Theabilityofapavementbasetocarryloadsdependsonthestrengthofthebasematerialandthethicknessofthebaselayer.Althoughathin,strongbasecantheoreticallycarrythesameloadasathick,weakerbase,thethicker,weakerbaseisusuallypreferred.Thisisbecausethethin,strongerbaseismorebrittleandmorelikelytocrack,resultinginpotentialreflec-tivecrackinginthesurfacepavement.Onmajorhighways,typicalthicknessesrangefrom6to12in.(150to300mm).

ConstructionConstructionincludesinitialpreparation,process-ing,compaction,finishing,andcuring.ThefollowingparagraphsgiveabriefsummaryofCTBconstruction.

Initialpreparationincludesthefollowingsteps:(1)Shapeareatocrownandgrade;(2)Correctunstablesubgradeareas;(3)Ifnecessary,scarify,pulverize,andprewetthesoil(ingeneral,notmuchpulverizationisrequiredforCTB);and(4)Reshapecrownandgrade.

Processingiscontinuousandaccomplishedinoneday.TherearetwomethodsforprocessingCTB:mixed-in-placeorcentral-plant-mixed.

ForCTBmixed-in-place,cementisplaceddryontothesurfaceofthein-placeaggregateusingamechani-calspreaderattachedtoadumptruckorbulkcementtruck.Thecementmayalsobeplacedonthesurfaceinslurryform.Thein-placeaggregatecanbeeithertheexistingmaterialorborrowedmaterial.Asingle-shaftpulvermixercombinestheaggregateandcement.Ifnecessary,waterisappliedonthesurfaceordirectlyintothemixingchamber.Thesingle-shaftmixerthenmixesthecement,water,andaggregateuntilauniform,thoroughlymixedmaterialisachieved(seeFigure6-4,Figure6-5,andFigure6-6).

Thecentral-plant-mixedmethodrequiresmixingcement,aggregatematerial,andwaterinastationaryplant.Mixingatacentralplantisgenerallydonebypugmillsorrotary-drummixers.Rotary-drummix-ersworkwellformixingcoarse,nonplasticaggregatematerial.High-speedrotaryshaftpugmillsworkwellforcoarseaggregatematerialandnonplasticfine-grainedmateriallikesandsandsilts.Forplantswithrotary-drumorbatch-typepugmills,materialis

Table 6-1. Typical CTB properties

Property 7-Day Value

Compressive Strength300 – 800 psi (2.1 – 5.5 MPa)

Modulus of Rupture (Flexural Strength)

100 – 200 psi (0.7 – 1.4 MPa)

Modulus of Elasticity600,000 – 1,000.000 psi (4,100 – 6,900 MPa)

Poisson’s Ratio 0.15

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batchedbyweight,mixed,dumpedintohaultrucks,anddeliveredtothesite.Atplantswithcontinuous-flow-typepugmills,themostcommontypeofcentralplant,materialsareindividuallymeteredbyweightorvolumeandfedintothemixerbyanaugerscrew,belt,orrotary-vanefeeder.Aftermixingattheplant,theCTBmaterialisdumpedintotrucks,hauledtothesite,andspreadevenlyoverthearea(seeFigure6-7).AnaggregatespreaderiscommonlyusedtoplacetheCTBmixtureoverthesubgrade.

TheCTBmixtureshouldbecompactedatoptimummoisturetomaximumdrydensityasdeterminedbypreliminarylaboratorytestingperAASHTOT134orASTMD558,orasdefinedbyprojectspecifications.Vibratory-steelrollers,sheepsfootrollers,orpneu-matic-tirerollersaretypicallyused,dependingonthetypeofaggregatematerialusedintheCTBmixture.

Thefinishingoperationsfollowimmediatelyafteradequatecompactionisobtained.Thegoalofthefin-ishingprocessistoproduceahigh-qualitysurfacethathasadequatecompactionandisvoidofanysoftareasorsurfacecompactionplanes.ThestepsforfinishingCTBalsodependonthetypeofaggregatematerialusedintheCTBmixture.Ingeneral,finishingaCTBmixtureincludesacombinationofshaping,scratchingthesurface,applyingabroomdrag,lightlyapplyingwater,androllingwithapneumaticsteelroller.

Afterfinishing,theCTBmustbeadequatelycured,allowingcementtohydrateandthecement-aggregate

Figure 6-4. Spreading dry cement on grade prior to mixing

Figure 6-5. Applying cement slurry on grade prior to mixing (cement slurry is applied the same way for FDR and CMS applications)

Figure 6-6. Constructing CTB using mixed-in-place method

Figure 6-7. Placement of plant-mixed CTB on prepared subgrade

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mixturetoharden.Thenewlyconstructedbaseshouldbekeptcontinuouslymoist(bylightlywateringormisting)fora3-to7-dayperiod,oramoisture-retain-ingcoverorcuringcompoundcanbeplacedovertheCTBsoonaftercompletion.

Sustainability•In-situorlocalmarginalaggregatescanbeusedinCTB.Thiswillminimizetheneedtohaulincostlyselectgranularaggregates.

•Cement-treatedbasemayrequiretheuseofindus-trialby-productssuchasflyash.

•RecycledasphaltpavementmixedwithcementmakesanexcellentCTB.

•Cement-treatedbaseprovidesastrongerbasethanunboundgranularmaterial;therefore,forthesameload-carryingcapacity,lessmaterialisrequired.

•Haulinglessmaterialreducesthenumberoftrucksandpossibledamagetosurroundingroads,result-inginfuelsavings,loweremissions,andprematurefutureroadwaymaintenance.

For More InformationAmericanAssociationofStateHighwayandTranspor-tationOfficials(AASHTO).1993.American Association

of State Highway and Transportation Officials Design Guide.

AmericanConcreteInstitute.2009.State-of-the-Art Report on Soil CementReportNo.ACI-230.1R,Farm-ington,Hills,Michigan:AmericanConcreteInstitute.

AmericanConcretePavementAssociation.2007.Sub-grades and Subbases for Concrete Pavements.EB204P.

George,K.P.2002.Minimizing Cracking in Cement-Treated Materials for Improved PerformanceRD123.01.Skokie,Illinois:PortlandCementAssociation.

Guthrie,W.S.,S.Sebesta,andT.Scullion.2002.Selecting Optimum Cement Contents for Stabilizing Aggre-gate Base Material.TechnicalReport7-4920-2,TexasTransportationInstitute.

HalstedG.E.,D.R.Luhr,andW.S.Adaska.2006.Guide to Cement-Treated Base.EB236.Skokie,Illinois:PortlandCementAssociation.

PortlandCementAssociation.2001.Thickness Design of Soil-Cement Pavements.EB068.Skokie,Illinois:PortlandCementAssociation.

PortlandCementAssociation.2010.Integrated Paving Solutions—Cement-Treated Base.http://www.integrated-pavingsolutions.org/cement-treatedbase.html.

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Full-Depth Reclamation with Cement (FDR)

Objectives•Provideastrong,uniformbase/subbaseforcurrentandfutureloadingconditionsusingexistingfailedasphaltsurfaceandbasematerial.

•Maintainexistinggradewithminimummaterialremovaloraddition.

•Reduceortotallyeliminatetheneedforvirginaggregates.

•Reducestressesonthesubgrade.

•Reduceruttinganddeflectionsinaflexiblepave-mentsurface.

•Improvethestructuralcapacityofstabilizedbaseoverunstabilizedbasematerial.

•Providepavementreconstructionmethodthatisfastandminimizestrafficdisruption.


Solution•Full-depthreclamationwithcementtorecycleandreusetheexistingpavementmaterialecycleandreusetheexistingpavementmaterial.

Benefits•Theperformanceofthebaselayerisimprovedoveranunboundgranularbase.

•Little,ifany,materialishauledofforontothesite,resultinginlesstrucktraffic,loweremissions,andlessdamagetolocalroads.Workcanbecompletedquicklycomparedtoremovalandreplacementtechniques.

•Full-depthreclamationprocessiseconomicalcomparedtoremovalandreplacementandthickoverlays.

Considerations•ThepotentialforreflectivecrackingandincreasedfrictionbetweentheFDRandsurfacepavementneedstobeconsidered.

•Undergroundutilitiesneedtobeconsideredduringthedesignandconstructionphase.

Typical ApplicationsRecycledmaterialsandrecyclingtechniquesareusedinhighway,streetandlocalroad,commercial/lightweightindustrial,airfield,andheavyindustrialapplications.

Description

Highways


Airfields

Heavy Industrial


Full-depthreclamationwithcementisatechniqueinwhichanexistingHMApavementandbasematerialisreclaimed(pulverizedasnecessary),combinedwithportlandcement,andthenrecompactedtocreateanewandimprovedbase.TheFDRbaseisthentoppedwithanewHMAorconcretesurfacelayer.


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Full-depthreclamationisappropriateunderthefol-lowingconditions:

•Thepavementisdamagedandcannotberehabili-tatedwithsimpleresurfacingmethods.

•Theexistingpavementdistressindicatesthataproblemlikelyexistsinthesurface,base,and/orsubgrade.

•Theexistingpavementdistresswouldotherwiserequirefull-depthpatchingovermorethan15–20percentofthesurfacearea.

•Thepavementstructureisinadequateforthecur-rentorfuturetraffic.

MaterialsMaterialsusedforFDRincludetheexistingHMAsurfacethathasbeenpulverizedandblendedwiththeunderlyingbase,subbase,and/orsubgrade,cement,andwater.Laboratorytestingandtrialmixesallowselectingthebestproportionsofcementforthejob.Theamountofwaterandcementrequiredinthemixwilldependupontheproject-specifiedstrengthandgradationofthefinalblendobtainedfrompulverizingtheHMAduringconstructionandmixingitwiththebasematerial.Typicalspecificationsforpulverizingcallforaminimumof100percentpassingthe3-in.(75-mm)sieve,95percentpassingthe2-in.(50-mm)sieve,and55percentpassingtheNo.4(4.75-mm)sieve.Ingeneral,acementcontentthatprovidesaseven-dayunconfinedcompressivestrengthbetween300to400psi(2.1to2.8MPa)issatisfactoryformostFDRapplications.

DesignFull-depthreclamationdesignisaprocessthatinvolves(1)determiningthetypeofexistingpavementlayersandtheirrespectivethicknesses,and(2)identi-fyingwhichmaterialwillbecombinedwithcementinordertocreateastablebaseforanewpavementstruc-ture.ThethicknessdesignissimilartoaCTBandiscalculatedbasedonstrengthofthematerial,strengthandstiffnesscharacterizationsofadditionallayers,anticipatedloads,andperformancerequirements(i.e.,life,serviceability,reliability).TheAASHTOprocedureforpavementdesignorPCAthicknessdesignproce-

durecanbeused.TypicalthicknessvaluesforFDRrangefrom6to12in.(150to300mm).

ConstructionFull-depthreclamationrequiresareclaimermixer,grader,cementspreader,watertruck,androller.Areclaimermachinetypicallymakesaninitialpassovertheexistingflexiblepavement,pulverizingtheHMAsurfaceandblendingitwiththebaseand/orsubgradematerial(seeFigure7-1andFigure7-2).Watermaybeaddedduringthismixingstagetobringthemate-rialuptooptimummoisturecontent.Thematerialisthengradedaccordingly.Next,cementisspreadeitherdryorinslurryforminacontrolledmannerontothesurface(seeFigure7-3andFigure7-4).Thereclaimerthenmixesthecementintothepulverizedmaterial.

Figure 7-1. Schematic of the mixing chamber of a reclaimer machine

Figure 7-2 Reclaimer pulverizing existing asphalt pavement and base material

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Figure 7-6. Equipment for compaction and finishing

Figure 7-3. Dry cement placed on pulverized material

Figure 7-4. Applying cement slurry on grade prior to mixing (cement slurry is applied the same way for CTB applications)

Figure 7-5. Mixing the cement into the pulverized material

Mixingcontinuesuntilthematerialisthoroughlymixed.Thisisfollowedbycompaction,finalgrading,curing,andsurfacing.Smooth-wheeledrollersareusedforcompaction.TheFDRshouldbecuredforfromthreetosevendays.Surfacetreatmentsincludechipseals,HMA,orconcrete.Thewholeprocesscanbeperformedundertraffic(seeFigure7-5).Figure7-6showstheequipmentusedforcompactionandfinishing.

Sustainability•Existingmaterialsarereused,reducingtheexploita-tionofvirginmaterial.

•Damageisreducedtosurroundingroadsfromhaul-ingexistingbasematerialsoutandbringingvirginmaterialsin.

•Costsrelatedtotheprocessing,purchasing,andtransportationofvirginaggregatesareminimized.

•Trucktrafficisreduced,resultinginfuelsavingsandloweremissions.

For More InformationAsphaltRecycling&ReclaimingAssociation.2001.Basic Asphalt Recycling Manual.Annapolis,Maryland:AsphaltRecycling&ReclaimingAssociation.

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Brown,Ashley,andVannoy.2006.Cementstabiliza-tionofaggregatebasematerialblendedwithreclaimedasphaltpavement.Master’sthesis,DepartmentofCivilandEnvironmentalEngineering,BrighamYoungUni-versity,August.

EuropeanConcretePavementAssociation.2010.EUPAVE—In Situ Pavement Recycling.www.eupave.eu/documents/activity-areas/in-situ-pavement-recycling.xml?lang=en.

Luhr,D.R.,W.S.Adaska,andG.E.Halsted.2005.Guide to Full-Depth Reclamation (FDR) with Cement. EB234,PortlandCementAssociation.

PortlandCementAssociation.2001.Thickness Design for Soil-Cement Pavements.EB068.Skokie,Illinois:PortlandCementAssociation.

PortlandCementAssociation.2010.Integrated Paving Solutions—Full-Depth Reclamation with Cement.http://www.integratedpavingsolutions.org/FDR.html.

Syed,I.M.2007.Full-Depth Reclamation with Portland Cement: A Study of Long-Term Performance. SR016.Skokie,Illinois:PortlandCementAssociation.

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Cement-Modified Soils (CMS)

Objectives•Reducetheplasticityandhigh-volumechangechar-acteristicsofclaysoilsduetomoisturevariations.

•Improvestabilityofapoorlygradedsandysoil.Improvethepropertiesofasandysoilcontainingahigh-plasticityclay.

•Provideamethodtodryoutawetsubgrade.

•Provideafirmconstructionplatformtoworkon.


Solution•Addasmallamountofcementtothesoiltocreateacement-modifiedsoil.

Benefits•Cement-modifiedsoilsprovideaweather-resistantworkplatformforconstructionoperations.

•Fatiguefailurescausedbyrepeatedhighdeflectionsarecontrolled.

•Thereisareductioninmoisturesensitivityandsub-gradeseasonalloadrestrictions.

•Nomellowingperiodisneededasrequiredbyotherstabilizingagents.

Considerations•Cement-modifiedsoilsarenotintendedtowith-standthesameCTBdurabilityandcompressivestrengthrequirements.

Typical ApplicationsCement-modifiedgranularsoilscanbeusedasatreatedsubgradeandworkingplatformbeneathabaseorsubbase.

Highways


Airfields

Heavy Industrial


Shoulders

DescriptionCement-modifiedsoilsaresoilsand/ormanufacturedaggregatesmixedwithasmallproportionofportlandcement.Bycombiningsmallamountsofcementwithsoils,plasticityisreduced,volumetricchangesduetomoisturecontentareminimized,bearingstrengthisincreased,andstabilityisimproved.Asaresult,aweather-resistantworkplatformforconstructionoper-ationsandastronger,permanentpavementlayerforenhancedsupportandcapacitycanbeconstructed.


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Cement-modifiedsoilsarenormallyusedtoimprovematerialpropertiesinthesubgrade.Theycanelimi-natetheneedforextensiveremovalandreplacementofexistingsoils,savingconsiderabletimeandmoney.ThemostcommonapplicationofCMSisasanoptionforsubgradematerialwhenexistingoravailablesoilsareofpoorquality(seeFigure8-1).

TheprimarydifferencebetweenCMSandCTBisthatCTBtypicallycontainsmorecementandisrequiredtomeetcertainstrengthvaluesperspecificationsandtoserveasadurable,freeze-thawresistantmaterial.Cement-modifiedsoilstypicallydonothavetomeetthesamerequirementsforstrengthanddurabil-ity;instead,smallamountsofcementareaddedtomitigateexpansionduetomoisturevariationsandimprovecohesioncausedbypoorsoils.Anadditionalbenefitisanimprovementinstrengthandstiffness.

Figure 8-1. Typical cross-section with CMS

DesignThedesignofaCMSlayerfocusesoncreatingawork-ingplatformfortheconstructionofbase/subbaseand,subsequently,thesurfacelayer.TheCMSlayer,however,doesnotcontributeappreciablytothestruc-turalcapacityofthepavement.Accordingtomoststateand/orjob-specificspecifications,aCMSlayerisdesignedtomeetcertainAtterberglimitrequirementsasdeterminedbyproperlaboratorytestingmethods.Cement-modifiedsoilsaretypicallynotdesignedtomeetacompressivestrengthrequirement,butratherdesignedtomeetreducedplasticityrequirementsandincreasedCBRvalues.Thedesignwillvary,dependingonexistingsoilproperties.Acommonthicknessof6in.(150mm)hasbeenshowntoprovideanadequateworkingplatformforconstructionofbaseorsubbaselayers.

ConstructionCement-modifiedsoilsareproducedinplaceusingexistingsoils.Cement-modifiedsoilsconstructionconsistsofmixingthecementintothesoilusingmixed-in-placemethods.However,becauseofthecohesivenessofthesoilsomeadditionaleffortmayberequiredforthepulverizationandmixingopera-tions.Wetsoilsmayrequiremultiplemixingpasses.Ifthesoilisdry,pre-wettingandallowingthewatertosoakinmayfacilitatepulverization(seeFigure8-2).IncontrasttonormalCTBconstruction,thetimelimitbetweenmixingandcompactingisnotasstringent,Materials

Cement-modifiedsoilsareprincipallyusedtomodifyfine-grainedsoilssuchassiltsandclaysandgranu-larsoilshavingahighplasticityand/orfinecontent.Cementcontentforeachistypicallybasedoniden-tifyingtheappropriateamountnecessarytomeetspecifications.

MostCMSinvolveshighplasticitysoilssuchasclays.Specificationswilloftenrequireenoughcementcontenttoreducetheplasticityindex(PI)towithinarangeof12to15.Typically,acementcontentof3to4percentwillreducethePIsufficientlyandincreasetheCaliforniabearingratio(CBR)andresistanceval-ues.Thecement-modifiedsoilshouldprovideafirmfoundationforcompactionofthebase/subbaselayeraboveit.

Figure 8-2. Cement slurry added to subgrade material (cement slurry is applied the same way for CTB and FDR applications)

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althoughalloperations,includingcompaction,shouldbecompletedinthesameday.

Ingeneral,in-placemixingandconstructionsequencefollowsthesesteps:

•Forinitialpreparation,shapetheareatocrownandgradeandcorrectanysoftorunsuitableareas.

•Ifnecessary,prewetdrysoilstoaidpulverizationordrybackwetsoilsbyaerationwithdischarroworrotarymixerwithitshoodopen.

•Distributecementindryformwithmechanicalspreaderorinslurryformfromdistributortruck.

•Mixwithpulvermixer,addingwaterifnecessary,untilahomogeneous,friablemixtureisobtainedthatwillmeetthespecifiedpulverizationrequire-ments(seeFigure8-3).

•Compactwithtamping(sheepsfoot)roller(seeFigure8-4).

•Completesurfacecompactionwithasteeldrum,pneumatictire,orotherappropriatetypeofroller.

•Withgrader,shapeareatofinalcrownandgrade.

•Sealsurfacewithpneumatic-tireroller.

Unlikecement-treatedbases,CMSisoftennotcured.However,curingwithalightwatersprayorbitumi-nouscoatingwillprovidethemaximumbenefitfromthecement.

Sustainability•CMSreduceswastebyallowingtheuseofexistingmaterial.

•In-situmarginalsubgradesoilscanbeimproved,minimizingtheneedtohaulincostlyselectgranularaggregates.

•CMSprovidesastrongermorestablesubgrade,whichmayreducethequantityofbasematerialneeded.

For More InformationBhattacharja,S.andJ.Bhatty.2003.Comparative Performance of Portland Cement and Lime Stabilization of Moderate to High Plasticity Clay Soils.RD125.Skokie,Illinois:PortlandCementAssociation.

Halsted,G.E.,W.S.Adaska,andW.T.McConnell.2008.Guide to Cement-Modified Soil (CMS).EB242.SkokieIllinois:PortlandCementAssociation.

PortlandCementAssociation.2010.Integrated Paving Solutions—Cement-Modified Soil.http://www.integrat-edpavingsolutions.org/CMS.html.

Scullion,T.,S.Sebesta,J.Harris,andI.Syed.2005.Evaluating the Performance of Soil-Cement and Cement-Modified Soil for Pavements: A Laboratory Investigation.RD120.Skokie,Illinois:PortlandCementAssociation.

Figure 8-3. Pulvermizer used for in-place mixing of CMS

Figure 8-4. Sheepsfoot roller used for compaction

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Recycled Concrete Aggregates

Objectives•Recycleexcavatedconcretepavement.

•Minimizeconstructioncost.

•Reducedependenceongoodqualityvirginaggre-gates,whichmaybehardtofindorexpensivetobringin.


Solution•Useoldconcreteasaggregatesinnewpavementlayers.

Benefits•Recycledconcreteaggregates(RCA)areversatilebecausetheycanbeusedinanypavementlayer.

•Materialcostsarereduced.

•Constructiontimecanbeexpeditedwithon-siterecyclingplants.

•PavementsufferingfromASRorD-crackingcanberecycledinsteadofdiscarded.

•Theneedforoldconcretedisposalisreduced.

Considerations•IfASRorD-crackingexistsinrecycledpavementmaterial,specialattentionmustbegiventomixturedesign.

•RecycledconcreteaggregatesinHMAmayincreasebindercontentrequirements.

•Concretemixturedesignswillhavetobeadjustedforstrength.

•Additionalqualitycontrolmeasuresmaybeneces-sarytoensureconcreteworkability.

Typical ApplicationsRecycledconcreteaggregatesareusedinhighway,streetandlocalroad,shoulder,airfield,commer-cial/lightweightindustrial,andheavyindustrialapplications.

Highways


Airfields

Heavy Industrial


Shoulders

DescriptionRecycledconcreteaggregatesareaggregatesproducedfromtherecyclingofexistingconcrete.Existingcon-creteisremoved,processedintoappropriateaggregatesizes,andreusedinvariouspavementapplications.ThebenefitsofusingRCAinpavementsincludereducedmaterialcosts,minimizeduseofdeplet-ingvirginaggregatesources,anddecreasedlandfillcontent.

Recycledconcreteaggregatesareprimarilyusedinbasesandsubbases.Accordingtoa2008FederalHighwayAdministrationnationalreview,84percentofstatesarerecyclingconcreteaggregate.Whilemost


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statesuseRCAasabasematerial,22percentuseRCAasaggregatefornewconcretepavements.

Recycledconcreteaggregatesareidealforthebottomliftofatwo-liftpavingmixturedesign.Two-liftpav-ingisaconstructiontechniquethatinvolvesplac-ingaconcretesurfacelayerintwoconsecutivelifts.Theprocessissometimesreferredtoas“wet-on-wet”becausethetoplayerisplacedimmediatelyafterthebottomlayer,beforethebottomlayerhardens.Theadvantagetothiskindofconstructionisthatgoodqualityaggregatesareonlyrequiredinthetoplift,whereasaggregatessuchasRCAcanthenbeusedforthelowerlift.

ThequalityofRCAisverydependentonthequal-ityofthematerialfromwhichitwasprocessed.Oldconcretepavementisbrokendownin-place,removed,andcrushedtoproduceRCA.Recycledconcreteaggregatesproducedfromallbutthepoorestqualityoriginalconcretecanbeexpectedtopassthesametestsrequiredofvirginconventionalaggregates.

MaterialsRecycledconcreteaggregates(seeFigure9-1)pro-ducedfromconcretepavementrecyclingcontainsboththeoriginalaggregatesandhydratedcementpaste.Recycledconcreteaggregatescanbeprocessedtoexhibitpropertiesthatmeetthesamegradationrequirementsasvirginaggregatesusedforsimi-larapplications.Recycledconcreteaggregatesmayimproveearlystrengthpropertiesinsomeapplica-tionsbecauseofthecontinuedhydrationofexposed

cementparticlesintheRCA.TherearesomematerialcharacteristicsspecifictoRCAinsomeapplicationsthatshouldbeunderstoodandaccountedforineitherdesignorconstruction.

ConcretepavementscontainingRCAcanresultinincreasedporosityandabsorption,highercoefficientofthermalexpansionandshrinkage,lowerstrengths,andreducedspecificgravitywhencomparedtotheuseofonlyvirginaggregates.Thechloridecontentofrecycledaggregatesshouldbeinvestigatedifthemate-rialwillbeusedinreinforcedconcrete.Toachievethesameworkability,slump,andw/cmratioasinconven-tionalconcrete,mixturesincorporatingRCAtypicallyrequirehigherpastecontentand/orgreateramountsofwaterreducer.InanHMAsurfaceandasphalt-stabilizedbaseand/orsubbaselayers,RCAcanhelptoimprovestabilityandfrictionbuttypicallyrequiresanincreaseinbindercontent.

AsanaggregateinCTBlayers,RCArequiresnospecialconsiderationandperformssimilartovirginaggregate.Recycledconcreteaggregatescanbemoresusceptibletoabrasion.Therefore,whenusedasanaggregateinunboundbaseand/orsubbaselayers,theconstructionprocessshouldbeadjustedasneededforproperhandling.

PavementssufferingfromASRorD-crackingcanberecycled,butspecialattentionmustbegiventoconcretemixturedesign.SupplementarycementitiousmaterialsthatmitigateASRmustbeincorporatedintoconcretemixturedesignswhenASR-distressedRCAisused.D-crackedRCAmustbeprocessedtoproperaggregatesizesforthepreventionoffurtherD-crack-ingdistress.

Whendesignedandconstructedappropriately,pave-mentsbuiltwithrecycledmaterialscanbedurable.Thekeyistodesignamixturewithpropermaterialproportionsfortheintendedapplication.

DesignItiscommontocombineRCAwithvirginaggregateinmixturesfornewconcreteorHMAsurfacelayers.Inconcretesurfaceapplications,upto30percentofnaturalcrushedcoarseaggregatecanbereplacedwithcoarseRCAwithoutsignificantlyaffectinganyoftheFigure 9-1. Recycled concrete aggregates

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mechanicalpropertiesoftheconcrete.Asreplacementamountsincrease,dryingshrinkageandcreepwillincreaseandtensilestrengthandmodulusofelastic-itywilldecrease;however,compressivestrengthandfreeze-thawresistancearenotsignificantlyaffected.SpecialcareisnecessarywhenusingfineRCAinconcretemixtures.Onlyamaximumof10to20percentfineRCAhasbeenshowntobebeneficial.RecycledconcreteaggregatescontentinHMAsurfacelayersisnotlimitedifthemixturedesignpropertiesadheretoallspecifiedperformancerequirements(e.g.,abrasion).

Recycledconcreteaggregatescontentforbaseandsubbaseapplicationsisnotasstrict.Ingeneral,awell-gradedRCAcanresultinaverystablesubbase,andRCAcontentinCTBshouldbesuchthatitstillmeetsallperformancerequirements.

ConstructionThestepsrequiredfortheRCAproductionprocessarecrushingandremovingexistingpavementmaterial,removinganyreinforcementand/orothercontami-nants,andprocessingthereclaimedmaterialdowntoappropriateaggregatesizes.Ingeneral,equipmentusedforRCAproductionincludesthefollowing:

•Hand-operatedorvehicle-mountedcrushingdevices(e.g.,hand-heldtools,drophammers/blades,impactbreakers/hammers,etc.)(seeFigure9-2)

•Abackhoeorbulldozerwitharhinohornattach-mentforlooseningthecrushedmaterialfromthelayerbeneathitandanyreinforcement

•Front-endloadersordumptrucksfortransporting(seeFigure9-3)

•Arecyclingplantthatcanbestationary,portable,ormobile

Figure9-4showsexistingconcreterecycledin-placeandreusedforbasematerial.

Whenusedinnewconcrete,itisrecommendedthatRCAbeprewettedandclosetoasaturatedsurfacedry

Figure 9-2. Example of equipment used to break existing concrete

Figure 9-3. Broken concrete pavement is removed for recycling

Figure 9-4. Existing concrete recycled in-place and reused for base material on the Tri-State Tollway in Illinois

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conditionbeforebatching.Additionalqualitycontrolmeasuresmaybenecessarytoensuregoodmoisturecontrol.ConcreteandHMAmixturescontainingRCAcanbetransported,placed,andcompactedinthesamemannerasconventionalmixtures.

TheconstructionofCTBandunboundbase/subbaselayersfollowstypicalstandardprocedures.IfRCAisusedinwhatisintendedtobeadrainablebaseorsubbaselayer,itisadvisedthathandling(i.e.,shap-ing)thematerialiskepttoaminimum;thetendencyforfineparticulatestobreakofffromthesurfaceoftheRCAisincreased,otherwise.

Inadrainablelayer,increasedfinesdecreasetheabil-ityforwatertoescapeoutofthelayer.Itisalsorec-ommendedthatRCAbaseandsubbasedrainagelayersaredaylightedforthisreason.

Recycledconcreteaggregatesusedinunboundbaseand/orsubbaselayerscancontainverysmallpercent-agesofcontaminants(suchasHMAbinder)withoutadverselyaffectingperformance.

Sustainability•Existingmaterialsarereused,reducingtheexploi-tationofvirginmaterialandminimizinglandfillmaterial.

•Costsrelatedtotheprocessing,purchasing,andtransportationofvirginaggregatesareminimized.

•In-placerecyclingreducestrucktrafficandfuelconsumption,andalsoreduceslocalroaddamagefromhaultrucks.

•UsingRCA,particularlyinapplicationsthatexposeittotheatmosphere(e.g.,embankmentfill,gravelroads,andrailroadballast),resultsinaprocesscalledcarbonsequestering.TheprocessessentiallyrecapturesCO2fromtheatmosphere.

For More InformationAmericanConcreteInstituteCommittee555.2001.Removal and Reuse of Hardened Concrete. ACI-555R-01.

AmericanConcretePavementAssociation.2009.Recy-cling Concrete Pavements.EB043P.

AmericanConcretePavementAssociation.2010.Recy-cled Concrete Aggregates Can Be Used in Any Application in Which Virgin Aggregate Can Be Used, and Even Some It Typically Is Not.TS043.4P.

ConstructionMaterialsRecyclingAssociation.2006–2010.Economical Good Sense.www.concreterecycling.org.

FederalHighwayAdministration.2008.Recycled Con-crete Aggregate.NationalReview,http://www.fhwa.dot.gov/pavement/recycling/rca.cfm.

FederalHighwayAdministration.2010.Use of Recycled Concrete Pavement as Aggregate in Hydrau-lic-Cement Concrete PavementTechnicalAdvisory,T5040.37,http://www.fhwa.dot.gov/pavement/t504037.cfm.

NationalConcretePavementTechnologyCenter.Resources on Two-Lift Concrete Paving.http://www.cptechcenter.org/projects/two-lift-paving(accessedJuly2010).

PortlandCementAssociation.2010.Integrated Paving Solutions—Recycled Concrete.http://www.integrated-pavingsolutions.org/RecycledConcrete.html

PortlandCementAssociation.Concrete Technology—Materials: Aggregates,www.cement.org/tech/cct_aggre-gates_recycled.asp

Taylor,P.,S.Kosmatka,G.Voigtetal.2006.Integrated Materials and Construction Practices for Concrete Pave-ment.NationalConcretePavementTechnologyCenter,IowaStateUniversity.

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Repair and Restoration

DescriptionTherepairandrestorationofconcretepavementsaretasksconductedtoimproveadistressedpavementbyrestoringbothfunctionandstructuralcapacity.Thevarioustechniquesthatfallintothiscategorycanbeconductedoneormoretimesduringthelifeofthepavement.Thetypeofrepairdependsontheconditionofthepavementatthetime.Quiteoften,promptrepairsaremoreeffectiveandlessexpensivethandelayedrepairsorrehabilitation.Thefollowingsummarizessomeofthemorecommonrepairsandrehabilitationtechniquesusedonconcretepavementsinordertoextendperformance.

Full-Depth RepairsFull-depthrepairsareusedtoaddressanareaofmajordistressinapavement.Thiscouldbealocalizedeventorextendedthroughoutthepavementsection.

Afull-depthrepaircanprovidegoodlong-termper-formance(morethan10to15years)ifthequalityoftherepairisgoodandtherightmaterialsareused.

Inconcretepavements,full-depthrepairsmostoftenconsistofcast-in-placeconcretethatreplacesthefulldepthoftheexistingslab.Figure10-1showstheprocessforfull-depthrepairofaJPCPpanel(fromtoptobottom):identifycandidateslabs,removeexistingpavement,andreplacewithnewconcrete.

Asimilartechniqueisusedforjointedpavements,wherepartorallofaslabpanelcanbereplacedwiththejointreinforcementbeingreplacedatthesametime.

Figure10-1. Full-depth repair of a concrete pavement slab


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Partial-Depth RepairsApartial-depthrepairconsistsoftheremovalandreplacementofsmall,shallowareasofdeterioratedconcretepavementatspalledordistressedjoints.Forapartial-depthrepairtobepractical,thedistresstypi-callyhadnotextendeddeeperthanone-thirdofthedepthoftheslab.However,duetotherecentavail-abilityofjointmillingmachinesasa“U”mill,partialdepthrepairshaveextendedtoT/2.Theloadtransferdevices,ifpresent,shouldbefullyfunctional.Figure10-2showsapavementshowingspalling.Spallingcancauserideandnoiseproblemsforthetravelingpublic,

andthuspartial-depthrepairscanremedyfunctionalperformance.Apartial-depthrepairbeginswiththeremovalofdistressedconcretebysawing,chip-ping,and/ormillinguntilsoundconcreteisexposed.Repairmaterialisthenappliedandthesurfacetexturerestored.Finally,curingshouldbeconductedpertherecommendationsspecificforthepatchmaterialused.

StitchingStitchingisarepairmethodforrestoringloadtransferatlongitudinalcracks(seeFigure10-3).Thistypeofrepairisanoptionwhenslabsarenotseverelydis-tressed.Holesaredrilledatadiagonalfromonesideofthecracktotheother.Theangleofthediagonalshouldbeconsistentandmeasurebetween35and45degrees.Epoxyfollowedbyatiebarfillthehole.Thetiebarshouldpassthroughthecrackatmid-depth.Itisimportantnottodamagethesurfaceoftheconcretewhileperformingthistypeofrepair.Surfacedam-agecanbeavoidedbychoosingappropriatedrillingequipmentsuchasahydraulic-powereddrillandabitthatis0.375in.(10mm)greaterthanthediameterofthetiebarthatwillbeinserted.Thesizeofthetiebardependsonslabthickness,angleofhole,andhole’sdistancefromthecrack.

Figure10-2. Partial-depth repair process at joint

Figure 10-3. Cross-section of concrete pavement showing stitching

Slab StabilizationSlabstabilizationisarepairtechniqueforconcretepavementinwhichaflowablematerialisinsertedbeneaththepavementslabsinordertorestoretheirsupport.Duringtheprocess,voidsarefilledthatliebetweentheslabandthesupportinglayer.Theseareoftencausedbywaterinfiltrationandsubsequent

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pumpingoffinestothesurface.Voidsweakenthestructureandwithoutrepaircanleadtobreakingupoftheslabsduetotrafficloads.Thematerialthatisinsertedshouldfillthevoidsbutshouldnotlifttheslab.

Slabstabilizationrestoresslabsupport,reducespave-mentdeflections,andminimizestheprogressionoffurtherdistress.Thesuccessoftherepairdepends,inpart,onidentifyingtheareaswithlossofsupport.Furthermore,theinjectionofmaterialundertheslabmustbeperformedinsuchawaythatthevoidisadequatelyfilled,whichencouragestheuseofanexperiencedcontractor.Figure10-4showstypicaltasksduringaslabstabilizationrepair,whereholesaredrilledintotheconcreteslab,whichisthenfilledwithgroutmaterial.

Slab JackingSlabjackingisarepairprocedureinwhichaconcretepavementslabisraisedbyapplyingpressurizedgroutbeneaththeslab.Slabjackingisusedtofixlocalizedspotsofsettlementoftenfoundnearfillareas,culverts,andbridgeapproaches.Whendoneproperly,thistechniquecanrestoretheridequalityofapavement,althoughitdoesnotcorrectfaultedjoints.Thegroutmixtureorpolyurethaneusedintherepairshouldbecertifiedforthispurpose.Theprocedureissimilartoslabstabilizationinthatthelocationsshouldfirstbecarefullyidentified.Holesaredrilled,andapumpingsequenceisidentifiedtoachievethedesiredeffect.Materialistheninjected—insequence—sothatthe

Figure 10-4. Drilling operation as part of slab stabilization

slabisraisednomorethan0.25in.(6mm).Thispro-cesscontinuesuntiltheslabreachesthedesiredgrade.Successinslabjackingismorelikelywhenperformedonstructurallysoundpavementwithlocalizeddepres-sions.Aprovenprocessanddurablematerialsshouldbeused.

Joint ResealingJointresealingconsistsofplacingasealingmaterialinanexistingjointorcracktoreducemoistureinfiltra-tionandminimizeintrusionofincompressibles.Whencracksandjointsarenotproperlysealed,watercansometimesinfiltrateandsaturatethelowerlayersofthepavement.This,inturn,cancausevariouspave-mentdistresses.Sealingmaterialistypicallyaliquid(hotorcold)butcanalsobeanexpansionjointfiller(preformed).Thejointdesigntypicallydictatesthetypeofsealanttobeused.Thedesiredpropertiesofthesealantaredurabilitytotrafficandenvironment,extensibilitythatallowsjoint/crackmovementwithoutrupture,andadhesivenessthatpermitsadherencetothecrackorjointwalls.Ajointresealingprocedurefollowsfivebasicsteps:oldsealantremoval,jointrefacing,jointreservoircleaning,backerrodinstal-lation,andnewsealantinstallation.Thekeyfactorsforthesuccessofthisrepairaretheproperselectionofjoints/cracks,selectionofsealingmaterial,restora-tionofthejointreservoirandshapefactor,reservoirpreparation,andpropersealantapplication.Figure10-5showstheapplicationofjointsealant.

Dowel Bar RetrofitLoadtransferacrosstransversejointshasalwaysbeenafactorcontributingtothelifeofaconcretepave-ment.Steeldowelsareoftenusedtoensureloadtransfer.However,problemscansometimesariseovertime,includingcorrosionandhighbearingstressesthatcanerodethesurroundingconcrete.Onolderconcretepavements,orthosethatweredesignedforlowertraffic,loadtransfermaybeprovidedbyaggre-gateinterlockonly.Overtime,thelossofloadtransfercanmanifestitselfintojointfaultingandslabcrackingandthusshouldberemedied.

Loadtransferrestorationisdefinedastheinstallationofmechanicaldevicesinanexistingpavement.Along

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transversejoints,theloadtransferisusuallyaccom-plishedbyinstallingdowelbars.Todefinewhetherornotloadtransferisadequate,afallingweightdeflec-tometercanbeusedtoassesstheloadtransfereffi-ciency.Agoodcandidateforrepairisapavementingoodstructuralconditionbutwithpoorloadtransfer(lessthan50to60percent).Pavementswithfaultingbetween0.12and0.5in.(3and13mm)arealsogoodcandidates,asarethosewithlessthan10percentofslabswithmultiplecracks.

Dowelbarretrofitbeginswithslotting,typicallybysawingandchipping.Thejointispreparedandthedowelbaraffixedtoajointinsert.Therepairmaterialisthenplacedandcuredasneeded.Quiteoften,dia-mondgrindingcanbeconductedafteralldowelbarretrofitsarecomplete.Figure10-6displaysaconcretepavementwhereslotshavebeencutandcleanedto

retrofitdowelbars.Notethatretrofittingisoftendoneinthewheelpathsonly.

Diamond Grooving and GrindingDiamondgroovingandgrindingaresurfacetreat-mentsperformedtoimprovethefunctionalcharac-teristicsofapavement.Diamondgrindingconsistsofremovingaverythinlayerofthesurfaceusingasetofcloselyspaceddiamondsawblades.Theresultofthistechniqueincludesimprovementstosmoothness,fric-tion,andnoise.Grindingisrecommendedwhenthepavementisstructurallysound,andbeforeconduct-ingthisrepairthehardnessoftheconcreteaggregateshouldbedeterminedsothatthediamondbladesareselected,sized,andspacedaccordingly.Theneedfor

Figure 10-5. Application of joint sealant

Figure 10-6. Contiguous concrete slabs prepared for dowel bar retrofitting

Figure 10-7 Diamond grinding concrete pavement for surface restoration

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associatedtreatments(e.g.,loadtransferrestoration)shouldalsobeconsideredpriortothistreatment.Fig-ure10-7displaysthetypicalappearanceofaconcretepavementthathasbeendiamondground.

Diamondgroovingisusuallydonetominimizethehydroplaningeffectinapavement.Channelsaregroovedontothesurfacetoaccomplishthisgoal.Dia-mondsawbladesareusedtocuttheseparallelgroovesineitherlongitudinal(morecommon)ortransversepatterns.Otherbenefitsofthisrepairareimprovedwetweatherfrictionandthereductioninsplashandspraywhenthepavementiswet.

Candidatepavementsfordiamondgroovingareoftenbasedonhistoricalcrashrates.Thissurfacetreat-mentisgenerallyperformedatlocalizedareasandonpavementsthatarestructurallysound.Thesuc-cessofthisrepairdependsontheselectionofpropercandidateprojectsandtheproperselectionofgroovedimensions.

Figure10-8illustratesaconcretepavementwherediamondgroovingisbeingperformed.Inthiscase,thegroovingpatternislongitudinal.

For More InformationAmericanConcretePavementAssociation.2008.Con-crete Pavement Field Reference: Preservation and Repair.EB239P.Skokie,Illinois:AmericanConcretePavementAssociation.

Fanous,F.S.,J.K.Cable.etal.2006.Laboratory Study of Structural Behavior of Alternative Dowel Bars (Proj. 7).Researchproject,NationalConcretePavementTech-nologyCenter,IowaStateUniversity,April.

FederalHighwayAdministration.2008.Concrete Pave-ment Preservation Workshop.Draftinstructorguide.

Taylor,P.C.,S.H.Kosmatka,G.F.Voigt,etal.2007.Integrated Materials and Construction Practices for Con-crete Pavement: A State-of-the-Practice Manual.NationalConcretePavementTechnologyCenter,IowaStateUniversity,October.

TexasDepartmentofTransportation.2008.Pave-ment Design Guide.TxDOTConstructionDivision.November.

Figure 10-8. Longitudinal grooving of a concrete pavement to restore macrotexture

National Concrete Pavement Technology CenterInstitute for Transportation

Iowa State University

2711 South Loop Drive, Suite 4700Ames, IA 50010-8664

515-294-5798www.cptechcenter.org SR035

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