1. Recycled Asphalt Pavement
Trevor Distin

2. ‘Trade in your old pavement for a new one’
Use of RAP in the USA
USA produces +-100Mtpa of RAP
ave of 17% RAP is recycled in HMA
23 States have experience with >25% RAP
aim is to increase RAP in all mixes >25%
still some perceptions that asphalt with RAP is inferior to all virgin material
Main driver for using RAP is economics & sustainability has become the new driver
NAPA reported that 25% RAP usage neutralise carbon foot print of HMA plant
‘Trade in your old pavement for a new one’

4. Obstacles to using > 20% RAP
Concern over comingled binder properties
Stiffening of binder could lead to early cracking
Use of high % RAP may negate the benefit of using PMBs
Durability of surface layers could lead to raveling
Variability/consistency of RAP
Lack of QC by contractor
Meeting skid resistance requirements
Two biggest obstacles in mix design:
Binder characteristics
0.075mm fines

5. Benefits of using RAP RAP reduces potential of mix to rut
Adding RAP stiffens the binder to a higher performance grade
Substituting RAP for PMB was found to render same rutting performance
Monitoring on 18 test sections up to 17 years with RAP showed pavements using >30% RAP are performing well
Up to 40% RAP does not increase CV of HMA
In some cases contractors found less variability in RAP than virgin aggregates

6. Summary of t-Test Analysis
Distress
Parameter
Virgin Performed Better than RAP
RAP Performed Better than Virgin
Insignificant Difference Between RAP and Virgin
RAP Performed Equal or Better Than Virgin
IRI 42 39 19 58
Rutting 33 29 38 67
Fatigue Cracking 10 61 71
Longtnl. Cracking 15 75 85
Transverse Cracking 32 53 68
Block Cracking 3 1 96 97
Raveling 7 78 93

7. MS CA AB AL AZ TX MB NJ MN MD FL NM OK CO MT MO GA ME
Did not use softer binder in RAP mixes

8. Variability: RAP vs. Aggregate
Based on 74 RAP stockpiles in 14 states, and 60 Aggregate stockpiles in 6 states

9. Benefits of RAP to contractors
Reduction in energy requirements to heat virgin agg & binders
Hedge against rising bitumen prices & global uncertainty which can effect supply
Reduces amount of virgin aggs & bitumen which reduces material costs

10. Differences by State Caltrans VDoT South Carolina North Carolina
Can use up to 15% in WC without additional testing otherwise can increase to 30%
No RAP allowed in OGA & BRA
VDoT
< 30% allowed in WC except SMA <20%
< 35% in base
South Carolina
non fractionated RAP: <20% in WC & <30% in base
Fractionated RAP: <25% in WC
North Carolina
<50% base
<30% in WC if RAP screened through 25 mm sieve

11. New Approach
Base max % RAP on net effect that RAP binder has on the properties of new mix
Limiting factor will be determined by:
recovered aged binder properties
% binder in RAP i.e. 4 vs 7% depending on grading
This means that you use double amount of coarse RAP vs fine RAP for same aged binder properties
Typically 70% of binder must be virgin

12. Virgin binder class to use
FHWA recommendations:
<15% RAP: no change in binder grade
<15 < 25%: bump to a the next softest grade
>25%: use blending charts
However studies have shown that:
20% RAP can be used without changing binder grade
NCAT test sections show that up to 45% RAP there is no evidence to bump down a grade

13. Determining blended binder grade

14. Rutting performance @ 10 M ESALs

15. Keep millings from different projects in separate stockpiles
Milled RAP
Keep millings from different projects in separate stockpiles
Milled RAP can typically be used “as is” in HMA without further crushing to save costs

16. Multi-Source RAP Stockpiles
Avoid contamination from the beginning
Mix it up while feeding the screen or crusher
Don’t over crush
Fractionation helps for design of high RAP mixes
Watch the weather when processing
Blend again when moving stockpiles 16

17. Fractionated RAP Screening RAP into two or more sizes
19 – 4.75mm RAP
-4.75mm RAP
+19mm RAP
Screening RAP into two or more sizes
Allows RAP to be used in practically any mix type
Do not crush RAP to avoid producing fines. Only crush oversize RAP 17 17

18. Fractionating vs. non fractionating

19. Stockpiling RAP
Building steep sided stockpiles will create segregation
helps meet binder content & air voids in mix

20. Minimise moisture Cover stockpiles Sloped pavement underneath
Free moisture in the RAP can cause caking of RAP in crushers and blinding of screens

21. Effect of moisture on heating

22. Testing of RAP Take samples daily from RAP stockpile
1 set of samples for 1000 tonnes of RAP
Binder Content: ignition method is preferred
Faster and more accurate
For dolomitic aggregates use solvent extraction
Grading especially % passing:
0.075mm sieve
Median sieve
Bulk SG
Potential errors when calculating BSG 22 22

23. Effect of RAP Gsb on VMA Gsb Virgin = 2.6700 12.4 12.6 12.8 13.0 13.2
13.4
13.6 10 20 30 40 50 60 70
RAP Aggregate %
VMA%
2.644
2.624

24. Other issues
Where skid resistance is a concern use small sized RAP < 7mm
Reduced mix temperature allows more RAP to be used
Using higher % RAP in WMA helped increase temperature of bag house
Aged binder on RAP works as an antistripping agent & improves TSR values

25. Other issues cont…
Consensus was that you could increase upper limits for RAP for WMA before changing binder grade:
< 25%: no change
>25 < 35%: bump to softer grade
> 35%: use blending charts
Lower mixing temperature resulted in less oxidation & light oil remaining in virgin bitumen
Steam produced from drying RAP creates inert atmosphere
Recovered binder from WMA with 25% RAP has same rheological properties as recovered binder from HMA with virgin bitumen

26. Recommendations
Optimise the use of RAP in asphalt mixes without compromising mix performance
Valuable resource
Engineered product
Reduce cost of asphalt
Reduce demand for non-renewable raw materials

27. Recommendations
Develop guidelines for the inclusion of various % RAP into different application i.e. mixes and layers
Procedures for processing & stock piling RAP
Developed simplified procedures for evaluating RAP and binder properties for >30% RAP
Determine effect of the properties of the aged binder and binder content of RAP on performance of mix specs

28. Proposal Dense graded wearing courses < 15% RAP >15%<30%
Must fractionate RAP <NMAS
>15%<30%
Only if aged binder content <30% of new mix
> 30%
Only if binder viscosity of new mix < max RTFOT
Subject to stringent process control & monitoring

29. Proposal Intermediate & base courses < 15% RAP >15%<30%
Must screened but not necessary to fractionate into different sizes
>15%<30%
Must fractionate into different sizes
> 30%
Aged binder must be < 30% of new mix
Subject to stringent process control & monitoring

30. Thank you