1. Rethinking PP Timing Strategies
Tiered Superpave Specifications to Reduce Age-Induced Surface Damage
Emulsion Task Force
Indianapolis
June 13, 2019
Gayle King

2. Outline Tiered Cracking Specifications
Background
PP Roadmap
PG & Superpave Implementation
Increasing demand for high RAP mixes (9-58)
Evolving PG specifications for cracking (9-59;-60)
G* max; Minimum ΔTc (or equivalent); G-R
Impact on asphalt supply and use of RAP
Questions:
Can seals limit age-induced surface damage?
Should seals be part of a tiered approach that pavement designers use to limit surface damage?

3. PP Roadmap Research Needs: Materials
Materials Research Need Statement
Optimize PP timing strategies based upon in-place material properties
Estimated cost: $10 million
Can early seals reduce aging rates near the pavement surface? Probably yes!
Pooled Fund Study: AI: M. Anderson, Blankenship, King
Supported by: MN, MD, OH, WI, TX, FHWA, MLRRB
CTAA 2016: Early seals slow evolution of aging: G-R, LAS
AAPT 2016: DC(T) testing, including early seal effectiveness
Agencies now chip seal new rural AC pavements. SD,MN

4. PG Grade Bumping Tiered Quality Standards for Rutting
Premise: Mixes require stiffer binders at high summertime temperatures when subjected to heavy, slow moving traffic.
Tiers: G*/sin δ MSCR
Standard: Th; M332: Jnr ≤ 4.0
Heavy: Th+6C; M332: Jnr ≤ 2.0
Very Heavy: Th+12C; M332: Jnr ≤ 1.0
Extreme: Th+18C; M332: Jnr ≤ 0.5
To Meet Spec: add more polymer/additive

5. Recycling/Rejuvenators High RAP/RAS
Problem: RAP mixtures prone to early surface damage. NCHRP 9-58
TX A&M High RAP/RAS study for TXDOT
Softer virgin AC with PAV20 ΔTc of -4.5
RAP had much lower ΔTc
Sections with various recycling agents
Surface damage: < 1 year
Loving County, TX
20% RAP; ΔTc < -10 after construction
Remove and replace in 4 months

6. New surface damage failure parameters
Evolving PG Specifications for Cracking Failure Parameters and Early Implementation
New surface damage failure parameters
Black Space parameters: ΔTc, G-R, R-value
Failure stress and strain: ABCD, Dent, S-Dent
Fatigue: LAS
Physical Hardening: Hesp approach, ΔTc
Agencies implement stopgap specs (REOB)
BBR: max G* and min ΔTc
UT, FL, NV, Northeast
DENT, Isothermal Hardening
Ontario

7. Evolving PG Specifications for Cracking Impact on asphalt supply and use of RAP
Black Space parameters (ΔTc, R-value) are inherent crude quality parameters related to molecular motion at low pavement temperatures.
Poor AC quality (low ΔTc) is difficult to restore, even with the best rejuvenators.
Aging, REOB & wax negatively impact ΔTc.
RAP quality matters!
Polymers and other anti-rutting additives may reduce ΔTc, but rarely increase it.

8. A tiered quality specification for cracking Making Preservation Part of the Solution
Where to set threshold values for ΔTc?
Strict limits eliminate some asphalt sources and greatly restrict RAP use
Less stringent limits shorten pavement surface life.
Solution: Tiered quality standards for ΔTc
Impose strict limits for high volume surface mixes
Adopt intermediate limits for binder/base course and low volume surfaces
Pavement Preservation option: Accept a third lower PG quality standard for base mixes, or for rural surface mixes (mill & fill) only if an air-impermeable seal is placed on the surface

9. Tiered Cracking Specifications What’s missing?
Research Needs:
Establish appropriate ΔTc threshold values for traffic, climate, and pavement layer
Modify LTPPBind grade selection
Field research and models which tie effectiveness of early pavement seals to limit aging and/or moisture related damage
Implementation/supply issues:
Ease grade proliferation by tying tiered rutting grades to tiered cracking specs??

10. Tiered Cracking Specifications Where to start?
Organize invited workshop, to include:
Researchers for cracking specifications
FAA & AASHTO Pooled-Fund Studies: AI
NCHRP 9-58: TTI, UNH, UNR
NCHRP 9-59: AAT, NCAT
NCHRP 9-60: WRI, AAT, NCAT
TRB/NCHRP: Ed Harrigan
Stakeholder representation
ETF
Binder & Mix ETGs ??
Agencies/Universities implementing ΔTc: UT, FL, NV