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Task 6 – Monitor the Performance of the Stress Relief Course (SRC): Evaluation of Experimental SRC Interlayer on US95, Las Vegas
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Reflective cracking is one of the major type of distresses associated with the use of asphalt concrete (AC) overlay for rehabilitating deteriorated asphalt pavements. This report describes the research efforts completed in Nevada to identify the best promising techniques to mitigate reflective cracking in AC overlays under Nevada’s climatic and materials conditions. The main outcome of the study was the development of a preliminary performancebased mix design specification for an experimental stress relief course (referred to as ESRC) to be placed between the AC overlay and the milled AC surface. Consequently, in summer of 2015, the Nevada Department of Transportation (NDOT) implemented the developed specification on a demonstration project on US 95 in southern Nevada. The project included test sections with three different strategies: (1) AC overlay on top of the ESRC mixture, (2) AC overlay on top of the NDOT fine-graded Type 3 mixture (SRC-T3), and (3) AC overlay without any stress relief layer. An extensive laboratory evaluation was conducted on all three mixtures using both laboratory-mixed laboratory-compacted (LL) and field-mixed laboratory-compacted (FL) mixtures. Core samples were also collected after construction and were evaluated for in-place thickness and air voids as well as resistance to reflective cracking. The data showed promising results for the ESRC mixture in terms of its resistance to fatigue and reflective cracking while maintaining an acceptable level of stability and resistance to rutting. A windshield survey conducted approximately 13 months after construction showed no distresses in any of the surveyed sections. A distress survey conducted 26 months after construction showed few medium and low severity cracks on T2C and T3-SRC sections while only few low severity cracks were observed on the ESRC section. A simple life cycle cost analysis (LCCA) showed that even though the ESRC mixture has a higher initial construction cost, its agency and user life cycle costs per lane mile are lower and resulting in an average savings of 23%. In summary, the study showed a very good performance for the ESRC mixture thus far, making it a promising technique for reflective cracking mitigation in Nevada.