Introduction. Pavement Layer Bonding. SEAUPG Jacksonville, Florida November 14-16, Acknowledgements. Importance of Bonding

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1 Acknowledgements Pavement Layer Bonding Bryan Wilson, P.E. (Texas A&M Transportation Institute) TxDOT Evaluation of Design and Construction Issues of Thin HMA Overlays Performance Evaluation and Specification of Trackless Tack Comparative Analysis of Tack Coat, Underseal Membrane, and Underseal Technologies. Ohio DOT Tack Coat Performance and Materials Study Arif Chowdhury Ah Young Seo Maryam Sakhaeifar Sheng Hu Amin Banihashemrad SEAUPG November 16, 2017 Ohio University Akron University Importance of Bonding HMA overlay life largely dependent on bond quality Poor bonding can lead to: Slippage cracking Delamination Fatigue cracking Introduction Simplified physics of bonding Tack Coat Improves load transfer Decreases pavement deflection ers stress concentrations Non-bonded layers Bonded layers Shot Rate: gal/sy Emulsion (traditional/trackless) or binder 1

2 Trackless Tack Underseal Membrane VS HMA Screed Spray bar Shot Rate: gal/sy Polymer-modified emulsion Requires spray-paver Underseal (traditional) Research Questions How is overlay performance influenced by bonding? Which material and construction parameters influence bonding? Aggregate Shot Rate: >0.3 gal/sy Polymer-modified emulsion or binder (Fournier, 2009) Models Reflection Cracking Fatigue and Rutting Overlay Performance vs Bonding Crack tip Layer Thickness (mm) Modulus (MPa) Poisson Ratio Surface AC 30 5, Intermediate AC 40 7, Existing AC 50 4, Existing PCC , Subbase Subgrade Bottom of layers under load 2

3 Reflective Cracking Prediction Rutting Prediction Reflection Cracking (%) Years * Assumption that both layers had the same bond condition. Years * Assumption that both layers had the same bond condition. Fatigue Prediction Fatigue Life (Years) 10 No Bond Partial Bond Full Bond Which Parameters Influence Bonding? Shear Index * Assumption that both layers had the same bond condition. Detailed physics of bonding US 183 Cedar Park Surface Energy energy substrate Mechanical Interlock 3 emulsion trackless tacks 0, 0.04, 0.07, 0.1 gal/sy Existing, New, Milled Thin overlay energy substrate Failure modes Adhesive Cohesive Cohesive (substrate) 3

4 Bond Testing Results (US 183) Bond Strength Bond Energy Shear Strength (psi) New inch/min (Texas) 2-inch/min (Ohio) 0 Existing New Milled Existing New Milled Existing New Milled Trackless Calumet Tack E E Trackless Tack etacb B Trackless Tack FastSet C C * 0.5-inch/min test rate Results (US 183) Tack Rate FRA 270 Columbus, OH SS-1H, Trackless, Rubberized gal/sy New HMA, Milled HMA Distributor, Spray paver * 0.5-inch/min test rate Section Layout Section Layout Intermediate Course (Milled surface) Surface Course (New surface) Rubberized Tack (Spray Paver) SS 1H (Spray Paver) SS 1H (Distributor) V. V. ~500 ft US 40 Rubberized Tack (Spray Paver) V. ~700 ft SS 1H (Distributor) w/tracking Livingston Ave. w/tracking w/tracking Bridge Project Start Right lane divides Surface Course (continued) SS 1H (Distributor) Trackless Tack (Distributor) ~500 ft Livingston Ave. Bridge SB Mainline 4

5 Tack Type and Application Method Tack Rate Bond Strength (psi) Trackless SS 1H None Rubber SS 1H Distributor Distributor Spray paver Spray paver * 2-inch/min test rate Tack Type and Application Method Initial 8 Months 95% Confidence bond bond Surface Type US 79 Oakwood Bond Strength Tack coat CSS-1H Trackless emulsion Trackless hot-applied Underseal Membrane Polymer-modified emulsion Underseal (seal coat) AC-15P gal/sy Existing seal coat Distributor, Spray paver Section Layout Delayed Reflection Cracking Testing 5

6 US 79 Results US 79 Crack Propagation * 0.5-inch/min test rate No Tack CSS-1H Trackless Tack (Emulsion) Trackless Tack (Hot applied) Spray paver (PM Emulsion) Underseal How is overlay performance influenced by bonding? Conclusion Better bonding reduces reflection cracking and fatigue cracking. Better bonding reduces rutting. In certain cases, the optimal bond is lower than a % bond condition. What Influences Bonding? Tack type Stiffer tack > softer tack No tack can work too (new HMA). Tack rate Not clearly significant Very high rates may reduce strength Application method Distributor (uncontaminated) > spray paver Tracking and contamination can potentially reduce bond (but not always) What Influences Bonding? Bond age Strength 2x higher after 8-months spray paver Strength 2-3x higher after 1-year for trackless tack emulsion Surface type New HMA > Old HMA Milling, sound layer = Good Milling, degraded layer = Bad Temperature Average of Mix + Surface er temp > er temp 6

7 Questions? Bryan Wilson, PE 7