A Few Words About Asphalt Quality Modified Asphalt in a RAP World Asphalt Pavement Association of New Mexico and Asphalt Institute June 16, 2016 Albuquerque, NM
Workshop Goals Asphalt Quality a civil engineering perspective on asphalt quality very basic introduction to polymer modification set the stage for Mike RAP Issues grade dumping and bumping characterization of RAP binders blending charts effect of RAP on binder properties effect of RAP on mix properties modified asphalt in a RAP world
Quality = Consistency Asphalt Quality (Two Definitions) same results: day after day after day Quality = How good is it? good stuff better stuff best stuff
Asphalt Quality (PG 64-22) 1.60 0.400 Original DSR, kpa 1.50 1.40 1.30 1.20 1.10 1.00 0.90 DSR m-value 0.80 1/9/2012 1/23/2012 2/6/2012 2/20/2012 3/5/2012 3/19/2012 4/2/2012 4/16/2012 4/30/2012 5/14/2012 5/28/2012 6/11/2012 6/25/2012 7/9/2012 7/23/2012 8/6/2012 8/20/2012 9/3/2012 9/17/2012 10/1/2012 10/15/2012 0.390 0.380 0.370 0.360 0.350 0.340 0.330 0.320 0.310 0.300 m-value 0.290 Avg DSR = 1.29 kpa Std Dev = 0.08 kpa
Asphalt Quality Good Best! Let s discuss asphalt quality in these terms Better
Performance Graded Asphalt Binders PG spec involves running binder tests at anticipated pavement temperatures PG 64-22 high temp grade (deg C) low temp grade (deg C)
Another Way to Look at It Test asphalt binder at temps this layer feels (high, intermediate, low) Testing binder to get good performance for this layer at expected pavement temps.
PG Physical Property Tests Dynamic Shear Rheometer (high temp grade) Bending Beam Rheometer (low temp grade)
Concept of Temperature Spread Numerical difference between high and low temperature grade e.g., PG 64-22 = 64-(-22) = 86 deg spread sometimes called Useful Temperature Interval (UTI) Supply versus Demand roadway environmental conditions demand an 86 degree spread binder PG 64-22 supplies at least 86 degrees Temperature spread is gross indicator of binder quality
Nominal versus Theoretical Temperature Spread Nominal: PG 64-22 = 86 deg Theoretical: PG 65.6-23.7 = 89.3 deg DSR Value m-value 1.00 spec 0.300 spec 65.6 64 70 13.7-12 -18
Effect of Test Precision on Asphalt Quality Laboratory Acceptable Test Parameter HAC Glendale HAC Albuquerque Range 1 Original Binder G*/sin δ @ 58º C, kpa 1.15 1.14 0.96-1.34 Absolute Viscosity @ 60º C, P 847 851 764-934 RTFO Binder G*/sin δ @ 58º C, kpa 3.14 2.62 2.25-3.51 Mass Loss, % 0.012 0.089 0.027-0.075 PAV Binder (100º C) G*sin δ @ 19º C, kpa 3902 4083 2388-4558 Creep Stiffness @ -18º C, MPa Creep Slope (m) @ -18º C 192 0.296 214 0.300 167-239 0.278-0.318 1. Based on AASHTO multilab precision statements
Asphalt Quality PG 64-22 Good PG 70-22- Better PG 76-28 Best! Main takeaway asphalt binder quality is indicated by PG temperature spread
How Do We Increase the Temp Spread to Improve Asphalt Quality? Modify the asphalt! Use soft asphalt to provide better low temp properties (cracking) Use modifier to maintain high temperature properties (rutting)
So you want to use modified asphalt binders Will it have the intended performance effect? effect as stand along modifier effect as co-modifier How can it be specified? recipe vs performance vs both How much does it cost? price volatility, availability How must it be handled and incorporated? Does it stay homogeneous? Is it heat stable? Does it affect constructability? Are there testing considerations? Compatibility concerns with other additives? for example, RAP, RAS, etc.
Types of Modifiers Inorganic acids (e.g., PPA) Polymers and attendant stuff Construction Enhancers (e.g., WMA additives) Waste Post Consumer Products (e.g., crumb rubber) Fillers and Fibers Antistripping agents Hydrocarbons Antioxidants Extenders Rejuvenators
Log Log Stiffness, Viscosity, etc. Modification via polymer polymer modified Unmodified Log Temperature
Types of Polymers Elastic Type - SB diblock (Dynasol 1205) - SBS (LCY 3501, Kraton D1118) - SBR latex (Ultrapave 1156) - Waste rubber (CRM WRF-14) Plastic Type - EVA (Exxon Polybilt 103) - polyethylene (Novaphalt)
How to Test Polymer Modified Binders PG tests Elastic Recovery Force Ductility MSCR % Recovery
Polymer Modified Asphalt (Elastic) Advantages Significant performance history Elastic effect Improved cohesion τ = σ tan (φ) + c Many specs designed around stretchy polymers (no mysteries) Favorable co-modifier with others (e.g., PPA) Disadvangates Can be challenging to manufacture Compatibility can be a problem Tougher to handle Not heat stable Challenge to emulsify Sometimes supply/price not stable Relatively expensive
Engineering Management Question How is modified asphalt strategy affected by incorporation of Reclaimed Asphalt Pavement?
Take it Away Mike!