Complete Testing Suite for HMA Performance...

“Where Excellence and Transportation Meet”

Illinois Center for TransportationUniversity of Illinois at Urbana Champaign

Complete Testing Suite for HMA Performance

Prediction

Presenter: Imad L. Al-Qadi, PhD, PE, Dist.M.ASCE

H. Ozer, P. Singhvi, J. Rivera, A. El Khatib, M. Mueller,

and J. Trepanier,



Loaded Flexible Pavement

Aggregate Base Deflection

Free Water

Wedge

Hydrostatic

Pressure

Subgrade Deflection

Direction of Travel

2



Source: Nunn and Ferne (2001)

Pavement DistressesHeavy traffic

Segregation due to

paver operation

Aging and thermal loads

3



Rutting/ Cracking in HMA

4



Flexible Pavement System

Long-Lasting

Pavement

5

Materials

Pavement

StructureSustainability

Material Characterization

Asphalt concreteGranular Materials

Recycled Material

RAP, RAS, REOB

Rolling ResistanceRoughness, Texture, Def.,

Heat Exchange



Contribution of Asphalt Binder• An analysis of over 1000 mixes shows

increased energy with increased binder %

Binder (40-91%)

Other Materials

Transportation



Contribution of Asphalt Binder• An analysis of over 1000 mixes shows

increased energy with increased binder %

Binder (40-91%)

Other Materials

Transportation

Recycled Asphalt Shingles

Recycled Asphalt Pavement

Asphalt Binder Replacement (ABR)



0.7

0.8

0.9

1.0

1.1

1.2

1.3

0 10 20 30 40 50 60

Rela

tive E

nerg

y &

GW

P

%ABR

Energy

GHG

Environmental Savings from ABR

20% Energy

Savings

22% CO2

Savings

60% ABR

MIX:

SMA

mix

SMA

mix

Virgin

mix

Yang et al. (2014). Environmental impacts from producing asphalt mixtures with varying degrees of recycled asphalt materials.



Challenges with RAP/RAS (ABR)

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

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

• 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



Superpave™

-40°C -20°C 20°C 40°C

Low Temperature

CrackingFatigue/Block/Other

Forms of Cracking

Permanent

Deformation

Volumetrics Rut Test Cracking Test



Pavement Cracking

• Traffic loading, temperature, AC material properties all play a role VERY COMPLEX

• We can’t afford running a battery of tests to simulate these conditions SUCH TESTS DO NOT EVEN EXIST

• We need a simple, affordable (money AND time), and meaningful test as a best approximate to overall cracking related damage THERMAL, FATIGUE, BLOCK,…



IL-SCB Test• Modified SCB fracture test

conducted at 25˚C

• LVDT control load rate @ 50 mm/min

• Parameters calculated:• Fracture energy (Gf)

• Peak load (Pmax) & corresponding displacement (uo)

• Critical displacement (u1)

• Slope at inflection point (m)



SCB Simulations

• Perform numerical simulations of SCB test with bulk characteristic from complex modulus tests

10

100

1000

10000

1.E-06 1.E-04 1.E-02 1.E+00 1.E+02 1.E+04

E*,

ksi

Loading Frequency, Hz

54 38 21 4 -10 Master Curve

Duplicate Nodes

CZ Element

Bulk Properties from

Complex Modulus Test

Fracture Properties

Using Cohesive Zone

Model



FEM Results

• FEM simulations of SMA with 25% ABR

0

500

1000

1500

2000

2500

3000

3500

4000

0 1 2 3 4

Load

CMOD (mm)

N80 - 25 T = 25 C

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



DIC: Full Field Measurements



FPZ (Temperature Effect)eyy

25°C

-12°C

0%RAS (64-22)

7%RAS (64-22)

5mm



Fracture Energy Ambiguities



Development of Flexibility Index

Flexibility Index (FI) = 𝑮𝑭 ×𝟏

𝒂𝒃𝒔(𝒎)



Applicability and Seamless Implementation



Applicability and Implementation

• Can use AASHTO T-283 (TSR) equipment

• Two low-costprototypes were already manufactured (9-18K)



Conditioning Method

• Water bath conditioning allows the use of AASHTO T-283 (TSR) set up



IL-SCB Tool

• A software tool was developed to process IL-SCB results



Provide a Significant and Meaningful Spread in Test Output



Case Study: High ABR Mixes

• Goal: Identify a difference in the performance of:

Mix ABR Binder Constant

Properties

Expected

Behavior

L4 0% 64-22 AC (%): 6

VMA (%):

15.3

Increment

in ABR

Decreases

Toughness

L7 20% 58-28

L9 30% 58-28

L10 60% 52-34



Low Temperature SCB (-12ºC):

0

0.01

0.02

200 400 600 800 1000

Pro

babili

ty D

ensity

Fracture Energy (J/m2)

L4

L7

SCB (-12ºC, 1 mm/min, CMOD Control)

ABR

0% vs 20%

Overlap:

43%

μ = 742 σ = 57

μ = 795 σ = 22




0

0.01

0.02

200 400 600 800 1000

Pro

ba

bili

ty D

en

sity


L7

L9


ABR

20% vs 30%

Overlap:

11%

μ = 795 σ = 22μ = 677

σ = 55




0

0.01

0.02

200 400 600 800 1000

Pro

babili

ty D

ensity


L4

L7

L9

L10


ABR

30% vs 60%

Overlap:

58%

μ = 677 σ = 55

μ = 635 σ = 130



Low Temperature SCB:

• High Repeatability:

• ~ 9% COV

• Low

Discrimination:

• 40% Overlap

30 %

40%

Normal Distribution Overlap:



0

0.002

0.004

0.006

0.008

0.01

700 1200 1700 2200

Pro

ba

bili

ty D

en

sity


L4

L7

SCB (25ºC, 50 mm/min)

Intermediate Temperature SCB (25 ºC):

ABR

0% vs 20%

Overlap:

3%

μ = 1622 σ = 51

μ = 1895σ = 73



0

0.002

0.004

0.006

0.008

0.01

700 1200 1700 2200

Pro

ba

bili

ty D

en

sity


L7

L9



ABR

20% vs 30%

Overlap:

37%

μ = 1622 σ = 51

μ = 1703 σ = 174



0

0.002

0.004

0.006

0.008

0.01

700 1200 1700 2200

Pro

ba

bili

ty D

en

sity


L4

L7

L9

L10



ABR

30% vs 60%

Overlap:

21%

μ = 1280 σ = 164

μ = 1703 σ = 174



30 %

40%

Intermediate Temperature SCB:

• Intermediate

Repeatability:

• ~ 10% COV

• Intermediate

Discrimination:

• ~ 25%

Overlap




Flexibility Index SCB (25 ºC):

0

0.3

0.6

0.9

1.2

1.5

0 5 10 15 20

Pro

babili

ty D

istr

ibution

Flexibility Index

L4

L7

L9

L10


Overlaps:

< 3%

Increase in ABR = Reduction in FI

60% 30% 20% 0%



30 %

40%

Flexibility Index SCB (25 ºC):

• Reduced

Repeatability:

• ~ 15% COV

• High

Discrimination:

• ~ 3% Overlap




Correlation to FieldPerformance



Accelerated Loading Facility• Simulates truck traffic with controlled loading and pavement

temperatures.

• Up to 35,000 cycles can be applied per week.

• Wheel load can be varied from 33 kN (7,500 lb) representing a light

truck to 84 kN (19,000 lb) simulating a heavy axle.



Lane Properties

ABR Group Lane WMA Binder Grade

Control 1 - PG64-22

20%

(w/ RAP)

9 Water PG64-22

4 Chemical PG64-22

40% (RAP)

8 - PG58-28

11 Chemical PG58-28

5 - PG64-22

20%

(w/ RAS)

7 - PG58-28

3 - PG64-22



IL-SCB vs. Fatigue Cracking



Field Cores

• Field cores were obtained from nine IDOT districts

• Flexibility index values were compared to field performance data obtained from districts



Field Correlation (D1)District 1

Section #Field Perf. FI

Thickness

(mm)

5 Bad 1.3 40

10 Bad 1.4 41

4 Bad 1.8 41

7 Good 2.3 38

6 Bad 2.9 38

2 Bad 3.1 38

11 Good 3.4 26

12 Bad 3.9 38

3 Good 4.9 41

1 Good 5.0 37

8 Good 6.0 25

13 Bad 10.4 41

9 Good 10.9 26

Increasing

FI



Effect of Construction Year



Balanced Mix

0 5 10 15 20 25

Fle

xib

ility

In

de

x

Rut Depth (mm) @ Maximum Allowable Passes

SOFT & FLEXIBLE

UnstableStiff & Brittle

Stiff & FLEXIBLE



Balanced Mix

0 5 10 15 20 25

Fle

xib

ility

In

de

x

Rut Depth (mm) @ Maximum Allowable Passes

SOFT & FLEXIBLE

UnstableStiff & Brittle

Stiff & FLEXIBLE

High

Performance



Final Remarks• Asphalt mixture brittleness can result from

mixture volumetrics as well as adding recycled materials (RAP and RAS)

• Low temperature fracture tests could not distinguish between AC mixes

• IL-SCB test is a practical, affordable, and reliable test to distinguish between mixes’ cracking resistance

• The method is supported by extensive lab and field testing, theoretical, and numerical methods, and DIC technique



Findings and Remarks

• IL-SCB test method and the proposed Flexibility Index have successfully screened hundreds of AC mixes for changes in brittleness

• Implementation of a balanced mix design and field performance validation is underway• Simple interaction plots combining Hamburg and IL-

SCB tests

• A life-cycle approach is needed to assess sustainability impact of recycled materials• Pavement performance and traffic volumes are critical



Acknowledgements

• ICT R27-128 Project Technical Review Panel

• Undergrad and graduate students involved

• ICT research engineers

ICT.illinois.edu



HMA Testing “Book Ends”

HMA

HARD SOFT

Courtesy of David Lippert

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