Mohamed Elkashef, Ph.D, representing the University of California, Davis Pavement Research Center (UCPRC) delivers a presentation on UCPRC's research related to the use of RAP in asphalt mixes. Presentation delivered on Nov. 7, 2019 at the California Asphalt Pavement Association Fall Asphalt Pavement Conference in Sacramento, Calif.

1. Research Results and
Recommendations for
High RAP mixes in California
Mohamed Elkashef, UC Pavement Research Center
CalAPA conference, November 2019

2. High RAP defined as > 25% binder replacement.
Why RAP binder replacement ?
Use of Rejuvenators
 Type of rejuvenators.
 Rejuvenators Vs softening agents.
 How to account for the rejuvenator ?
2

3. RAP increases mix stiffness and reduces cracking/fatigue
resistance.
Partial to full blending occurs between RAP/Virgin binder.
Full blending is difficult to attain with increasing RAP
content and RAP stiffness.
Rejuvenators can mitigate the effect of using high RAP.
Effect of rejuvenators on durability and moisture sensitivity.
3

4.  Mixes between 30-50% RAP
 Proposed AASHTO standard of practice
 Pre-selection of materials
• RAP binder (PGH > 100 is not recommended to use in high RAP mixes)
• Virgin binder (limit on ΔTc )
• Intermediate temperature for binder evaluation
• Glover-Rowe parameter
• Crossover temperature (@ phase angle = 45oC)
• Intermediate temperature for mixes
• SCB: FI >= 7 after STOA
• High temp. blending charts can be used to estimate rejuvenator dose
• RAP binder availability factor dependent on mixing temperature and
PGH of RAP
4

5. NCAT
 Test sections containing 15-35% RAP
 1.5” surface lifts
 Different AC content, compaction density, binder types to yield
different expected cracking resistance.
 FI and IDEAL-CT ranked mixes similarly
 IDEAL-CT faster and easier to perform
MnROAD
 30-40% RAP mixes with different types of rejuvenators.
 10 different test sections.
 Assess long-term performance
5

6. Industry:
- Maximize binder replacement, aggregate replacement less important
- Limit use of extraction and recovery (except for greater than 25% binder
replacement)
Caltrans:
 Manage risks of effect of RAP binder on cracking resistance
 Have tests and specifications to assess and manage that risk
 Tests should balance providing actionable information with time, cost,
simplicity; variability needs to be appropriate for use in specifications
 Tests need to provide information/indicators about the property being
investigated of interest in California: stiffness and fatigue cracking
6

7. Routine mix design, QC/QA
Getting started on field use and spec development as
soon as possible
7

8. Blending charts
 High temperature PG restricts use of RAP compared to low and
intermediate temperatures
 RAP1 (Sacramento) PG 107-2
 RAP2 (SF Bay Area) PG 89-8
8
Based on
HT
Based on
IT
RAP1 18% 27%
RAP2 25% 32%
Based on
HT
Based on
IT
RAP1 6% 8%
RAP2 8% 10%
No change in virgin
binder
Using softer virgin
binder

9.  Not consistent.Varies based on RAP stiffness, test frequency (rate of
loading), and test temperature.
 R1 (Sacramento RAP)
 Continuous PG107-2
 R2 (Bay Area RAP)
 Continuous PG89-8
9
RAP binder blends using a PG64-16

10.  Effect measured by binder testing
does not truly represent mix
testing, mainly due to blending.
 Softer RAP2 (Bay Area region)
produced stiffer mixes because
RAP binder did not completely
blend with virgin binder
10
FAM mixes

11. 11
 Dependent on time, temperature, RAP stiffness, and RAP binder
replacement.
 Higher RAP binder replacement and stiffer RAP require longer time
at high temperatures to get blending/diffusion.
 Sufficient time and temperature needed, but results in more aging.
 AC content – Overall binder properties.
 RAS does not blend effectively (tear offs)
 Predictive models (correlating binder and mix testing) need to
account for blending.

12. 12
 Wafer composite binder specimens made of 1-mm thick virgin binder
placed on top of a 1-mm thick aged RAP binder
 Control wafer specimens made of 2-mm thick fully blended
RAP/virgin binder.
Wafer DSR specimen Change in modulus with time

13. 13
RAP in RHMA Mixes
 Amount of RAP limited to 10
percent to maintain gap-gradation
and pass Superpave volumetric
requirements
 Reduced cracking resistance
negating benefit of RHMA-G as an
overlay to resist reflection
cracking.
Ongoing study
 Using Coarse RAP to limit binder
replacement

14. 14
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0 1 2 3 4 5
Load(kN)
Deformation (mm)
Peak load
Slope(Spp)
P1= peak load
P2= peak load
Work of
fracture (Wf)
Slope(Sasc)
 Uses a notched semi-circular
specimen.
 Parameters calculated from
SCB test results.
• FI = Fracture Energy/Spp
• Front slope (Sasc)
• Stress-Intensity factor (KIC)

15.  Mixes containing different RAP percentages and binder types
tested using SCB and Beam Fatigue.
 Flexibility index was found not to correlate well with fatigue results.
15
R
2
= 0.32
200
400
600
800
0.0 2.5 5.0 7.5 10.0 12.5
FI
StrainlevelwhenNf=1M
MIX
0% RAP with AR binder
12%RAP with PM binder
15%RAP with neat binder
15%RAP with PG+X binder
15%RAP with PM binder
25%RAP with neat binder
25%RAP with PM binder

16. SCB fracture toughness & beam fatigue
16
R
2
= 0.61
2500
5000
7500
10000
12500
5 10
Sasc
E50
MIX
0% RAP with AR binder
12%RAP with PMbinder
15%RAP with neat binder
15%RAP with PG+Xbinder
15%RAP with PMbinder
25%RAP with neat binder
25%RAP with PMbinder
R
2
= 0.72
-5
-4
-3
-2
-1
0
-1.0 -0.5 0.0
ln(KIC)
ln(StrainlevelwhenNf=1M/E50)
MIX
0% RAP
12%RAP
15%RAP
15%RAP
15%RAP
25%RAP
25%RAP
SCB stiffness & beam stiffness

17. 17
 Both bio-based and petroleum-based rejuvenators were added at 10%
dose of RAP binder.
 Effect of rejuvenator can be assessed using critical temperatures and
ΔTc
RAP RAP+PetR RAP+BioR
High Temp. (oC) 95.1 82.1 70.5
Intermediate Temp. (oC) 49.7 42.2 28.1
Low Temp. (oC) -4.2 -9.4 -21.5
ΔTc -1.2 0.8 2

18. 18
 Colloidal Instability Index (CII):
Saturates+Asphaltenes /Aromatics+ Resins
CII = 0.67
CII = 0.58
CII = 0.52

19.  Rejuvenation enhance low temperature properties of the RAP binder.
 Rejuvenation improves stress relaxation properties of the RAP binder.
19

20. RAP
20
Rejuvenated RAP

21.  Work with industry to test and evaluate plant mixes and raw
materials for HMA with more than 25% RAP.
 Objectives:
 Evaluate ability of simple mix testing to flag high RAP mixes.
 Evaluate effect of time/temperature on blending, aging and overall mix
properties.
 Assess suitability of blending charts to produce well-performing mixes.
 Approach:
 Document the approach and assumptions, analyze performance-
related test results; binder extraction/blending results if available
 Combine results with lab study underway
Deliverables
 Initial specification limits for mix tests, effectiveness of blending
charts and parameters to limit risk for cracking
21

22.  4 plant mixes from different plants.
 Mixes collected at 2 aging conditions:
 a) No silo time, b) >= 6 hours silo time
 Mixes compacted at UCPRC and tested for:
 Stiffness using beam bending frequency sweeps.
 Fatigue using beam bending fatigue.
 Repeated load triaxial test using AMPT
 Simple tests include SCB and IDEAL-CT to assess stiffness/fatigue.
 Raw materials collected and tested:
 Binder Testing.
 Fine Aggregate Matrix (FAM) testing.
22

23.  Performance-related tests include SCB , IDEAL-CT, Beam fatigue and
flexural stiffness, Hamburg, and FAM
23
Mix RAP RAS Virgin
Binder
AC
Content
Rejuvenator Silo Times (hrs)
A 50% - PG64-10 5.1% Aromatic
10%
0, 6
B 40% - PG58-28 5.3% - 0, 16
C 20% 3% PG58-22 5% - 0, 5
D 35% - PG64-10 5.8% Bio-derived 0,6

24.  Flexibility index dropped
significantly with silo time.
 More silo time promotes
blending and induce aging.
 Mix B not containing rejuvenator
also exhibited same effect.
 High FI at 0 hours despite high
RAP content (possible indication
of poor blending).
24

25.  Fine portion of the asphalt mix passing
#8.
 Tested in a DSR under oscillatory
sinusoidal loading.
 Sample dimensions 12.5 mm x 50 mm
 FAM mixes provided a good alternative
to testing full-graded mixes to get
complete stiffness curves and fatigue;
only research use at this point
25

26.  Increase in stiffness with silo time
evident at all test frequencies
(i.e. temperatures)
26

27.  Linear amplitude sweep: Modulus is measured with increasing strain
amplitudes.
 Aged mix start at a higher stiffness but fails at a lower strain level
27
Fatigue Life Modulus vs strain level

28.  Effect of rejuvenators on properties of binders and mixes with aging
 Assess rejuvenators’ effectiveness without extraction and recovery
 Understand blending/diffusion between RAP and virgin binders with
and without rejuvenators.
 Effect of silo time and temperature on blending and aging
 Assess suitability of current tests; SCB and IDEAL-CT, to get strong
indicators of stiffness and fatigue performance
 Review panel: A. Epps Martin, E. Arambula
28

29.  Testing include FAM and full-graded mixes
 Long term aging of mixes to study durability of rejuvenated mixes.
 Stiffness (Frequency sweeps)
 Cracking (Beam fatigue, SCB, IDEAL-CT)
29
Factor Number Variables
RAP sources
RAP content (%)
Virgin binders
Rejuvenators
Rejuvenator dosages
3
3
2
3
2
Central Valley, Bay Area, Southern California
0, 25, 50
PG58-22, PG64-16
Aromatic extract, bio-based, tall oil
Dependent on product

30.  Selection of projects for pilots using draft specifications
 Build pilots, collect plant mix, cores and beams, and raw materials, perform
full set of binder and mix tests
 Run CalME using properties of tested mixes assuming different conditions
(climates, traffic, etc.) to look at effects of specification and whether higher
stiffnesses in some structures are appropriate
 Provide recommendations on suitability of high RAP mixes for different
applications, including different specs for thicker layers, and updated
specifications
 Establish long-term monitoring, periodic review for pilot sections
 Deliverables: updated specifications for different structures and climates
30

31. Any Questions ?
melkashef@ucdavis.edu
http://www.ucprc.ucdavis.edu/
Director: Prof. John Harvey
Associate Director: Dr. David Jones
31