1. Critical Factors Affecting Asphalt Concrete Durability
WHRP Project
Ramon Bonaquist
Chief Operating Officer Advanced Asphalt Technologies, LLC
May 16, 2017 1

2. Outline Objective What is Asphalt Concrete Durability? Approach
Major Findings
Application 2

3. Project Development and Oversight
Need Clear Objective!
“The objective of this study is to apply the findings from an investigation of critical factors determining asphalt durability to support revisions to specifications and associated guidance documents.” (WHRP RFP)
“The researchers should note that the intent of this work is to evaluate material properties as opposed to construction practices. “(WHRP RFP)

4. What is Asphalt Concrete Durability?
Definition From TRL Road Note 42
Ability of compacted asphalt concrete to maintain its structural integrity throughout its expected service life when exposed to the damaging effects of the environment and traffic loading

5. Durability Distresses
Considered in This Project
Raveling
Cracking
Stripping

6. Approach Synthesis of Current Research Laboratory Experiment
Mix composition
Resistance to cracking and aging
Analysis of WisDOT Specifications

7. Synthesis of Current Research
General Category
Specific Factors
Environment
Temperature
Moisture
Drainage
Surface
Subsurface
Construction
Weather Conditions
Segregation
Compaction
Joints
Layer Bond
Mixture Composition
Aggregate Properties
Binder Properties
Gradation
Volumetric Properties

8. Changes in Mix Composition to Improve Durability
Increase Effective Volume of Binder
Use Polymer Modification
Use Softer Grade of Binder
Place Limits on Recycled Binder Effectiveness

9. Laboratory Experiment
Factor
Low
Middle
High
Effective Binder Volume (Nominal Maximum Aggregate Size, mm)
19.0
12.5
9.5
Recycle Binder Content
Virgin
RAP
RAP+RAS
Low Temperature Grade
-22
-28
-34
Polymer Modification
Neat V E
Conditioning
Short-term
4 hours at 135 °C
Long-term
Short-term hours at 85 °C

10. Experimental Design Full Factorial Partial Factorial
34 x 2 = 162 Tests
Partial Factorial
Efficient Designs in Process Improvement Literature
Nonlinear Effects
Interaction
27 x 2 = 54 Tests

11. Partial Factorial
9 binders
9 aggregates

12. Resistance to cracking increases with increasing FI
Modified Illinois SCB
15 °C, 0.5 mm/min vs
25 °C, 50 mm/min
FI = Energy/Post Peak Slope
Resistance to cracking increases with increasing FI
PPS SI
SI = Stiffness Index
50% of Peak Load
AI=Aging Index
=SILTOA/SISTOA

13. FI Correlation to Cracking Performance
Imad L. Al-Qadi
I-FIT (Illinois Flexibility Index Test) Protocol – Contractor Perspectives

14. Virgin Binders Binder Modification M 320 Cont. Grade Jnr, 1/kPa %R, %H I L
64 C
58 C
64S-22
None
66.1
23.7
-25.6
3.05 NA
64V-22
Medium
77.6
22.8
-25.1
0.34
49.4
64E-22
High
80.6
21.9
-25.3
0.10
79.1
58S-28
58.2
20.2
-29.0
3.64
58V-28
68.5
19.1
-28.9
0.57
34.6
58E-28
74.4
15.8
-31.8
0.07
86.0
52S-34
54.2
11.9
-34.0
6.42
58V-34
62.9
13.1
-36.4
59.6
58E-34
68.7
10.5
-36.2
0.24
75.1

15. Mixtures Type Mix ID Nom Max Size, mm Gradation Binder Content, wt %
VBE,
vol. %
RAP Binder ratio
RAS Binder ratio
Virgin 8
19.0
Fine
4.8
9.9 2
12.5
5.7
11.6 9
9.5
6.3
11.7
RAP 5
4.9
8.8
0.255 6
5.4
10.5
0.186 1
6.1
12.0
0.246 +
RAS 3
5.1
9.2
0.208
0.162 7
5.8
12.3
0.119
0.158 4
0.121
0.180

16. Effect of VBE

17. Effect of Virgin Binder Grade

18. Effect of Recycled Binder

19. Effect of Polymer Modification

20. Flexibility Index Regression Equation
Where:
FISTOA = short-term oven conditioned flexibility index
VBE = effective volume of binder, vol %
(TVirgin)Low = continuous low temperature grade of the virgin binder, °C
RBREFF = effective RAP binder ratio
F = ratio of intermediate grade change for RAS to RAP
R% = percent recovery from AASHTO M332

21. Analysis of Coefficients
Variable
Partial Regression Coefficient
t- Statistic
p-value
Standardized Partial Regression Coefficient
Intercept
-18.76
-6.051 NA
VBE
1.37
6.325
0.52
Virgin Binder Low PG
-0.39
-5.773
-0.49
Effective RAP Binder Ratio
-10.18
-4.736
% Recovery
3.10
2.893
0.25

22. Predicted vs Measured
r2 = 83 %
se = 1.33

23. Long Term Flexibility Index
Improving STOA FI
also
Improves LTOA FI

24. Application 1 Factor Effects
Solve for FI for selected
VBE
Virgin Binder Low Temperature Grade
Recycle Content
Modification

25. Effect of Recycled Binder
No Grade Change
AASHTO M 323 Change
VBE
Low Grade
RBR FI
% of Control Life
10.5
-28
0.00
6.5
100
0.05
6.0 92
0.10
5.5 84
0.15
5.0 77
0.20
4.5 69
0.25
4.0 61
0.30
3.5 53
VBE
Low Grade
ABR FI
% of Control Life
10.5
-28
0.00
6.5
100
0.05
6.0 92
0.10
5.5 84
0.15
5.0 77
-34
0.20
6.9
105
0.25
6.3 97
0.30
5.8 89

26. Application 2 Specification
Select FI (e.g. virgin mix at minimum VBE) then solve for combinations of factors giving equal FI
Yields a specification with selected cracking resistance

27. Example Design Specification

28. Major Conclusions
Resistance to aging was not significantly affected by mixture composition
Cracking resistance as measured by the flexibility index was significantly affected by:
VBE: Improves with increasing VBE
Low Temperature Grade: Improves with decreasing low temperature grade
Recycled Binder: Improves with decreasing recycled amounts of recycled binder
Modification: Improves with increasing percent recovery

29. Major Conclusions
Improving resistance to cracking for short-term aging also improved resistance to cracking for long-term aging
Binder with normal aging characteristics
Statistical design and analysis used for process improvement yielded useful regression equation
Agencies to set specification requirements
Producers to design mixtures to meet a performance test requirement

30. Ramon Bonaquist
Advanced Asphalt Technologies, LLC
40 Commerce Circle
Kearneysville, WV 25430