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Balanced Mix Design:
High Recycled MixesMinnesota Asphalt Conference
Khaled Hasiba, P.E.
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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)
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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
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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
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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
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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
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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
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Current Use of Rutting Tests
7
Source: Development of Framework for Balanced Mix Design, R. West
7
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Case Studies
8
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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)
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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
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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.
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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
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50% RAP Millings, Wearing Course
Project Highlights: Minnesota
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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
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45% RAP 12.5mm Wearing Course
Project Highlights: Minnesota
Project Property Value / Description
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
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37% FRAP, 4% RAS, Surface Course
Project Highlights: Wisconsin
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Project Property Value / Description
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%
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55% FRAP, 5% RAS, Surface Course
Project Highlights: Illinois
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Project Property Value / Description
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
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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.
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