Testing Protocols to Ensure Mix Performance w/ High RAP and RAS

I. L. Al-Qadi, H. Ozer, J. Lambros, & D. L. LippertA. Elkhatib, T. Khan, and P. Sighn

Illinois Center for Transportation University of Illinois at Urbana-Champaign

February 3, 2015

Challenges with RAP/RAS SuperPave was developed for neat materials More recycled materials are used in HMA moving

away from specifying virgin components especially asphalt PG grades in final mix

Currently recycle usage is allowed by method specifications intended to limit risk of cracking by ABR limits and grade bumping, not actual mix performance

Fatigue cracking issue: stiffer mixes with high ABR may exhibit early fatigue cracking

Thermal/Block cracking issue: Stiffer mixes have reduced relaxation potential

Challenges (RAB/RAS Binder) Shingle asphalt is air blown to harden asphalt

(PG 112+02) then additional aging on the roofs RAP AC can be hard or soft depends on

project(s) milled Counteracting binder selection of virgin binder

becomes arbitrary Neat asphalt blending with RAP and RAS for

final mix is not well understood

A D

A : RAP-bitumen D : Virgin bitumen

C

C : Transition zone

Measurement Scheme at a Glance

Scan size: 30m

B : Blended zone

B

Alex Schmets4

RAS and Virgin Binder Interface

TT- RAS binder

Virgin binder

Mixing zone

Topography Phase 50m5Alex Schmets

5

Comparing RAP & RAS Rejuvenation

B: RAP-binder/ Virgin-bitumen A: RAS-binder/ Virgin-bitumen

OR

B

Mixing Blending

A

TRAS >180 C TRAP ~130 CAlex Schmets

Mixture Tests Available

DCT (ASTM D7313) SCB (AASHTO TP105)

Beam Fatigue Test

Texas Overlay Test

Push-pull Fatigue

Test Method Selection Criteria Significant and meaningful spread in test

output Correlation to independent tests and

engineering intuition Correlation to field performance Applicability and seamless

implementation

Semi-Circular Bending Test Relies on simple

three point bending

Easy specimen preparation

Can use AASHTO T283 equipment

Repeatability

Research ApproachParameter Variables

Material Source Plant Mixes, Lab-Mixes, Field CoresN-Design N30, N50, N70, N80, N90

Nominal Maximum Aggregate Size

4.75 mm, 9.5 mm, 12.5 mm, 19.0 mm

Asphalt BinderPG52-28, PG58-22, PG58-28, PG64-22, PG70-22, PG70-28, PG76-22

Recycled Materials RAP, RAS, Recycled Concrete, and Steel SlagAsphalt Binder Ratio 0 to 60

RAP Content (%) 0 to 53RAS Content (%) 0 to 8.5

Assessment of variety of plant mixes, lab design mixes, and field cores

Correlation to other tests (modulus and fatigue) Theoretical and numerical evaluation

Overall Framework

FEM Results FEM

simulations of N80-25 mix

0

500

1000

1500

2000

2500

3000

3500

4000

0 1 2 3 4

Load

CMOD (mm)

Experimental - 6.25mm/minNumerical - 6.25mm/minExperimental - 50mm/minNumerical - 50mm/min

Fracture Process Zone

Fracture Process Zone

25C @ 50mm/min

-12C @ 0.7 mm/minN90 Control (0% RAS)

-12C @ 0.7 mm/min

25C @ 50mm/min

N90 30% ABR (7% RAS)

SCB Fracture Results

Establishment of Test Temperature and Loading Rate

SCB fracture test results at -12C Limited data spread

Establishment of Test Temperature and Load Rate

SCB fracture energy results for the same mixes at 25 C using displacement control at 50 mm/min

Significant spread in fracture energy

0

600

1,200

1,800

2,400

3,000

N5050%(P8)

N5060%(P9)

N7025%(P10)

N7050%(P11)

N8025%(P12)

N8050%(P13)

N5034%(P14)

N5060%(P15)

N5060%(P1)

N5029%(P2)

N7029%(P3)

N3037%(P4)

N706%(P5)

N906%(P6)

N500%(P7)

Frac

ture

Ene

rgy

(J/m

2 )

Max fracture energy = 2148 J/m2

Min fracture energy = 877 J/m2

Data Spread 1271 J/m2

Establishment of Test Temperature and Load Rate

A comparison of low temperature and intermediate temperature (25oC ) SCB test results indicate the suitability test to discriminate mixes

25 oC and 50 mm/min loading rate were selected

SCB Fracture Results Flexibility Index calculated for two lab design

(N90) mixes w/ and w/o ABR (30% ~ 7% RAS):

Flexibility Index (FI) = A /m

SCB Fracture Results Flexibility Index calculated for two lab design

(N90) mixes w/ and w/o ABR (30% ~ 7% RAS):

Development of Flexibility Index A theoretically-supported flexibility index (FI)

Flexibility Index (FI) = A /m

Development of Flexibility Index A theoretically-supported flexibility index (FI)

2

Development of Flexibility Index A theoretically-supported flexibility index (FI)

FI Results Flexibility index calculated for selected plant

mixes

4.4 4.83.0 3.2

0.6

5.0

12.2

0

4

8

12

N5060% ABR

(P1)

N5029% ABR

(P2)

N7029% ABR

(P3)

N3037% ABR

(P4)

N706% ABR

(P5)

N906% ABR

(P6)

N500% ABR

(P7)

Flex

ibili

ty In

dex

FI - Plant MixesP5

P8P9P3

P4P13P11

P1P2P6

P12P7

P10

0 2 4 6 8 10Flexibility Index (FI) - Plant Mixes

Increasing cracking potential

Mix ID PG RAP(%) RAS(%)

ABR(%)

AC(%)

VMA(%)

(P5) N70-6 64-22 10 - 6 6.1 15.8(P9) N50-60 52-28 42 6 59 5.6 13.0(P11) N70-50 58-28 30 5 48 6.0 14.5(P12) N80-25 70-28 8 5 26 6.1 16.1(P10) N70-25 58-28 29 - 25 6.0 14.5(P7) N50-0 64-22 - - - 5.9 16.7

Type IType IIIType II

FI (with SF): Field Cores

F18F5

F19F9

F4F24

F2F17

F3F1

F22F21

F26F25

F20F23

0.0 2.0 4.0 6.0 8.0 10.0Flexibility Index (FI) - Field Cores

Increasing cracking potential

Type IType II Type III

FI Categorization & Implementation

Mix Category Mix Type Based on

Flexibility Index (FI)

Potential Actions and Remedies

Unacceptable Mix Type III( 10 is considered high performance mix.

-40C -20C 20C 40C

Low Temperature Cracking

Fatigue Cracking/ Service Temperature

Permanent Deformation

Low in-service temperatures

Intermediate in-service temperatures

High Temperatures

Low Temperature + Fatigue Cracking

Final Remarks We need to engineer our asphalt

concrete mixes Wheel Track, Tensile, and SCB A simple, reliable, and scientifically

sound test is introduced Flexibility Index can discriminate between

mixes More Validation is underway

Acknowledgment IDOT FHWA ICT Engineers: Aaron Coenen, Greg

Renshaw, and Jim Meister ICT Students and Staff

THANK YOU

Main Quad University of Illinois at Urbana-Champaign31

Testing Protocols to Ensure Mix Performance w/ High RAP and RASChallenges with RAP/RAS Challenges (RAB/RAS Binder)Slide Number 4Slide Number 5Comparing RAP & RAS RejuvenationMixture Tests Available Test Method Selection Criteria Semi-Circular Bending TestResearch ApproachOverall FrameworkFEM ResultsFracture Process ZoneFracture Process ZoneSCB Fracture ResultsEstablishment of Test Temperature and Loading RateEstablishment of Test Temperature and Load RateEstablishment of Test Temperature and Load RateSCB Fracture ResultsSCB Fracture ResultsDevelopment of Flexibility IndexDevelopment of Flexibility IndexDevelopment of Flexibility IndexFI ResultsFI - Plant MixesFI (with SF): Field CoresFI Categorization & ImplementationSlide Number 28Final RemarksAcknowledgmentTHANK YOU