development and implementation of performance grade ... · ‐ 425,000km2, 632,000 lane kms,...
TRANSCRIPT
Development and Implementation of Performance Grade Specifications for Asphalt Rubber Binder
David Jones
UC Pavement Research Center
DON’T ADD TO THE PILE!
OUTLINE
• Introduction
• DSR geometry
• Short- and long-term aging
• Conclusion
INTRODUCTION
• California‐ 425,000km2, 632,000 lane kms, 80,000km
managed by California Department of Transportation (Caltrans)
‐ Population of ~40 million‐ Produce ~40 million waste tyres/yr‐ Very diverse climate, topography, and geology
• Highest/lowest points in USA• Often hottest/coldest locations in USA on a
single day
• We like to think we are “green”
INTRODUCTION
• Rubberized asphalt concrete (RAC) initiative started in 1975 to:‐ Limit number of tyres in landfills‐ Improve AC performance, primarily reflective
cracking in overlays
• AB338 (2005) requires Caltrans to use asphalt rubber in at least 35% of all AC placed‐ Caltrans 2015 mandate requires that all surface
courses placed below 1,000m are AR mixes
• SB1 funding
INTRODUCTION
• Research‐ Mix design‐ Crack and rut resistance
• Mechanistic behavior/properties‐ Noise reduction‐ Warm-mix applications
• Emissions‐ Performance-grade specifications‐ Recycling and use of RAP in AR mixes
INTRODUCTION
• Two primary approaches‐ Terminal blend
• Particles <250µm, fully digested• ± 7-10% rubber by weight of binder• Similar to polymer in dense-graded mixes• PG-M specification (similar to South Africa)
‐ Wet process• Particles <2.36mm, incompletely digested• 18-22% rubber by weight of binder• Used in gap-graded and open-graded mixes• PG-AR specification
TESTING PROGRAM
• PG specification development‐ Phase 1
• Comparison of concentric cylinder and parallel plate on laboratory-produced AR binders
‐ Phase 2• Short- and long-term aging• Intermediate temperature• Multiple stress creep recovery• Low temperature• Preliminary testing on plant-produced binders• Draft specification and test methods
‐ Phase 3• Pilot study to verify test procedure and define performance grades
OUTLINE
• Introduction
• DSR geometry
• Short- and long-term aging
• Conclusion
PARALLEL PLATE VS. CONCENTRIC CYCLINDER
1 mm 2 mm
Critical factor Parallel Plate (PP) Concentric Cylinder (CC)Standard test method AASHTO T 315 Not available
Required material Small volume Large volumeTesting duration Short Long Sample trimming Yes No
Testing temperature High and intermediate High and intermediate
PARALLEL PLATE VS. CONCENTRIC CYCLINDER
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
UM-A UM-B UM-C TR-A TR-B PM-A PM-B
G*/s
in δ
at 6
4°C
(kPa
)
PP1 CC6
PARALLEL PLATE VS. CONCENTRIC CYCLINDER
All bindersy = 0.9526x + 0.0085
R² = 0.9508
425-850µmy = 0.8851x + 0.0734
R² = 0.949
250-425µmy = 1.0544x - 0.1735
R² = 0.9497
180-250µmy = 0.9552x + 0.0679
R² = 0.9963
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
G*/s
inδ
-Con
cent
ric C
ylind
er
G*/sinδ - Parallel Plate
Caltrans spec allows particles up to
2,300µm (<2.36mm)
OUTLINE
• Introduction
• DSR geometry
• Short- and long-term aging
• Conclusion
RTFO AGING CONSIDERATIONS
• AR binder and mix production temperatures‐ 190°C to 225°C vs. 143°C to 163°C
• Current RTFO testing temperature (163°C) is based on short-term aging of unmodified binders with no particulates
• Sample size based on required bitumen to coat bottle (35g)• Problems
‐ Poor coating, questionable aging, insufficient bitumen to test
PAV AGING CONSIDERATIONS
• Field temperatures are irrelevant
• Sample size based on required bitumen to coat pan (50g)
• Problems‐ Poor coating, separation of bitumen and rubber,
questionable aging, insufficient bitumen to test
PROPOSED CHANGES TO TEST METHODS
Test Parameter Current ProposedRTFO
Sample size (g) 35 45Temperature (°C) 163 190Duration (minutes) 85 85Oven tilt (°) zero zero
PAVSample size (g) 50 63Temperature (°C) 100 100Duration (hours) 20 20Pressure (Pa) 300 300
MODIFIED RTFO PROCEDURE
a) 35g at 163°C b) 45g at 163°C
c) 35g at 190°C d) 45g at 190°C
MODIFIED PAV PROCEDURE
OUTLINE
• Introduction
• DSR geometry
• Short- and long-term aging
• Conclusion
CONCLUSIONS
• Increased tonnage of AR mixes in recent years
• PG specification required in line with move towards performance-based/related specifications
• PG procedures for conventional binders are not appropriate for AR binders
• Revised procedures developed‐ Satisfactory results obtained to date‐ Incompletely digested particles still influence test results
• Provisional test method developed
• Pilot study testing is in progress‐ Shift factor will likely be required to compensate for incompletely digested
particles and to represent actual likely performance
