Balanced Mix Design: High Recycled Mixes · 2021. 2. 2. · •The need for a Balanced Mix Design...

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Balanced Mix Design:

High Recycled MixesMinnesota Asphalt Conference

Khaled Hasiba, P.E.

© 2021 Cargill, Incorporated. All rights reserved.

Current Pavement Condition

Truck Freight Volume in the U.S.

9.96

10.49

10.42

10.77

11.49

11.84

9.00 9.50 10.00 10.50 11.00 11.50 12.00

2014

2015

2016

2017

2018

2019

Volume in Billion Tons

ACSE Report Card (2017)

2

Source: Freight volume moved by trucks in the U.S. 2014-2019 (Statista)


Need for Balanced Mix Design

• Some DOTs indicate that cracking and raveling have become

the primary factor controlling service life of asphalt pavement

• Superpave volumetric design is better at addressing rutting than

cracking

• Volumetric design cannot account for binder compositional

changes:

– Binder quality has changed due to evolution of production processes.

– Effect of additives (WMA, Rejuvenators, REOB, polymers, fibers, etc.)

– Impact of recycled materials (RAP and RAS)

Source: pavementinteractive.org

2

3

7

11

18

20

21

28

Rutting

Moisture Damage

Slippage

Raveling

Longitudinal Cracking

Fatigue Cracking

Thermal Cracking

Reflection Cracking

Source: Development of Framework for Balanced Mix Design, R. West

3


What is Balanced Mix Design (BMD)?

• Mix design approach that addresses multiple modes of

distresses

• BMD incorporates two or more performance tests to assess

how well the mix resists cracking (durability) and rutting

(stability)

• Takes into consideration mix aging, traffic, climate and

location within the pavement structure

• Design property could be binder content, RAP and RAS

content, rejuvenator dosage rate or binder rheology.

Source: Innovation in Asphalt Mix Design Procedures

4


Performance Testing: Cracking

• Evaluates mix durability and resistance to fatigue and thermal cracking

• Involves modes of distresses and aging conditions

DCT IDEAL-CT I-FIT / SCB Overlay Beam Fatigue

Low Temp PG +10 25⁰C or room 25⁰C or room 25⁰C Varies 4-25⁰C

Cut and notched Compacted to height Cut and notched Cut sample Slab compacted, cut

5


Performance Testing: Permanent Deformation

• Evaluates mix stability and rut resistance

• Function of traffic level and/or mix type and application

Hamburg APA Flow Number

Wheel Tracking Asphalt Paving Analyzer AMPT

45-65⁰C 45-65⁰C 45-65⁰C

Dry or submerged Dry or submerged Dry

6


Current Use of Rutting Tests

7

Source: Development of Framework for Balanced Mix Design, R. West

7


Case Studies

8

8


NCAT Test Track

45% RAP + Rejuvenator

In partnership with VDOT

• Balanced Mix Design

- AC% optimized by IDEAL-CT and APA

- Air voids allowed to vary (higher density)

9

Description HT

PG

LTm

PG

ΔTc IFIT

FI

DCT

-12⁰C

IDEAL

-CT

Overlay

NJDOT

APA at

64⁰ C

30%RAP Control 76.7 -14.6 -9.2 6.1 520 124 296 2.51mm

45%RAP Rejuvenator 75.9 -22.0 -2.0 8.0 565 100 325 2.55mm

No Rutting

Smooth Ride

0 Cracking


MnDOT Approved Mix for I-94 Freeway

Balanced Mix Design for Minnesota

Approval Process

1. Lab Samples were prepared based on rejuvenator

supplier dosage recommendations and HMA producer’s

mix design.

2. Lab performance tests were conducted to determine

reasonable equivalence to control.

3. Binder extraction tests were conducted on lab samples

to determine reasonable equivalence to control.

10

Description Extract AC% HT PG LT S PG LT m PG ΔTc DCT -20⁰C HWT at 50⁰C n=5k

25%RAP Control 5.19% 65.1 -29.6 -24.3 -5.2 502.8 7.95mm

45%RAP Rejuvenator 4.51% 66.5 -28.7 -27.2 -1.5 495.0 2.35mm

45% RAP + Anova™ Rejuvenator vs. Control: 25% RAP

“Performance-modified” Volumetric Mix Design:

– AC% optimized by VMD, standard densities

– Performance checked with DCT and Hamburg


50% RAP Millings, Wearing Course

Project Highlights: Minnesota

11

Project Property Value / Description

Date May 2017

Tonnage 1000 Tons

Mix Type MNDOT Wear Course Dense Graded

Production Temp. 270-310⁰F

Compaction Temp. 260-280⁰F

Field Density 92.2-93.3% (Nuclear Density Gauge)

Performance Flexibility Index of 9.0±1.5

11


45% RAP 12.5mm Wearing Course

Project Highlights: Minnesota


Date July 2018

Tonnage 3000 Tons

Mix Type Hennepin County Wear Course

Performance DCT at -20⁰C 350 J/m2

HWT at 50⁰C <12.5mm

12


37% FRAP, 4% RAS, Surface Course

Project Highlights: Wisconsin

13


Date August 2017

Tonnage 1050 Tons

Mix Type HMA – Municipal Surface Mix

Production Temp. 295-300⁰F

Compaction Temp. 270-275⁰F

Field Density 93.4% (Nuclear Density Gauge)

Performance 620 > 375 J/m2 DCT at -18⁰C

22 > 12 I-FIT Flexibility Index at 19⁰C

4.0 < 12.5mm HWT at 45⁰C

# of Gyrations % AC % Binder Replacement % Voids VMA Gmm

75 6.2% 44.0% 3.0% 14.8% 2.476

Gmb VFA Gse Gsb Dust/AC TSR

2.401 79.7% 2.729 2.644 1.04 96.2%

13


55% FRAP, 5% RAS, Surface Course

Project Highlights: Illinois

14


Date March 2018

Tonnage 700 Tons

Mix Type Surface Mix – Municipal Spec

Field Density > 350 J/m2 DCT at -12⁰C

< 12.5mm rutting HWT 50⁰C

14


Summary

• The need for a Balanced Mix Design derives from the change in binder quality and the

introduction of recycled materials.

• Balanced Mix Design uses performance-related tests to optimize and select design parameters

• BMD is an effective way to introduce higher recycled content and rejuvenators into the mix

without jeopardizing quality.

• Many agencies are looking into implementing performance related specifications or have

already done so.

• Rejuvenation has been used for several years as a practical solution to produce reliable high

recycled mixes for commercial and agency applications.

15


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Balanced Mix Design: High Recycled Mixes · 2021. 2. 2. · •The need for a Balanced Mix Design...

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