Title:

Developing Best Practices for Rehabilitation of Concrete with Hot Mix Asphalt Overlays Related to Density and Reflective Cracking

A common rehabilitation technique for deteriorated PCC pavements is an asphalt overlay. Due to joints and cracks in the underlying pavement structure, mechanically and thermally-driven movements lead to the development of reflective cracks in the asphalt overlay. Reflective cracking in an asphalt overlay is of concern due to increased moisture infiltration and roughness in the pavement structure leading to shorter overlay service life. Majority of current state of the practice for asphalt overlay design is policy-based and lacking an engineered design approach. The objective of the overall study is to develop a decision tree based tool for selecting suitable asphalt mixtures and overlay designs to extend the overlay lives by lowering reflective cracking and improving in-situ density. This research is one of the long-term research projects for the National Road Research Alliance (NRRA) that has already undertaken construction, instrumentation and monitoring 12 MnROAD test sections. While there are several tasks involved in the development of a decision tree tool for practitioners, the first task was to complete a comprehensive literature review on the current state of art practices for approaches to select an asphalt concrete overlays mixture and pavement structure. The next major task was to conduct laboratory testing on 8 varying mixtures used in field test sections and perform statistical analysis of asphalt mixture characteristics to develop a greater understand of key factors effecting reflective cracking performance. Varying mixture characteristics include design air void level from 3 to 5 percent, gradations, Nominal Maximum Aggregate Size (NMAS) from 9.5 mm to 19 mm and Reclaimed Asphalt Pavement (RAP) from 0 to 25 percent. Comparison of lab performance tests such as the Disk-Shaped Compact Tension (DCT), Semi-Circular Bend (SCB), Dynamic Modulus, Texas Overlay Tester, IDEAL CT, Hamburg and Simplified Viscoelastic Continuum Damage (S-VECD) cyclic fatigue test with field performance from MnROAD test sections was performed. At present, additional comparisons are being made between laboratory performance, field performance and simulated models of test sections in PavementME design software and commercial finite element software ABAQUS. Simulated models will be calibrated using initial reflective cracking performance data from field test sections and used for parametric evaluations in the development of a decision tree in future tasks. Results are focus on field evaluation of pavement performance through available dielectric profiling system (DPS) measurement data, field cores, distress surveys and field performance indices that take into account structure and time in service to evaluate asphalt density evolution over time. The effectiveness of different construction and mixture design techniques to achieve enhanced density in the various field sections at the time of construction (2017) will be evaluated along with how density changes for the various mixtures.

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