Use of Performance Based Testing for High RAP Mix Design and Production Monitoring

Abstract

In 2014 the Wisconsin Department of Transportation (WisDOT) and industry developed a pilot program for hot mix asphalt (HMA) with higher recycled asphalt content that required use of performance tests during mix design and production. Following the balanced mix design concept mixture tests were selected to address rutting resistance after short-term aging and durability after long-term aging. The test selected were the Hamburg Wheel Tracking (HWT) test, the semi-circular bend (SCB) test at intermediate temperature and the disc-shaped compact tension (DC(T)) test at low pavement temperatures. Asphalt binder extraction and grading from aged mix was also required. The focus of this paper is to summarize the mixture performance test and recovered binder data gathered during the pilot project on STH 77 in Ashland County, Wisconsin; suggest modifications to the SCB test procedure; and present accelerated aging protocols for continued use of performance testing in practice. Semi-circular bend test results collected during the project at 25°C did not relate well to values published in the literature or show adequate sensitivity to changes in mix properties. The effects of test temperature and an alternative analysis method are presented. Based on the results recommendations include use of a climate based approach for test temperature selection and inclusion of post peak analysis to better discriminate between mix composition and aging conditions. Accelerated long-term aging protocols involving loose mix aging at 135°C for 12 and 24 hours are compared to AASHTO R 30 compacted mix aging using recovered binder and mixture fracture properties. Results found that 12 hour loose mix aging produced similar recovered binder grading to AASHTO R 30, whereas the effect of aging on mixture fracture tests was inconclusive. The relationship between laboratory and field aging is investigated through comparison of field cores to laboratory aged plant produced mix from a project constructed in southeast Minnesota in 2006. Lastly, the laboratory performance of the high recycled and conventional mix designs are compared on the basis of mixture cracking resistance and recovered asphalt binder properties after extended aging. The high recycle mix exhibited equal or better performance relative to the conventional mix across all selected performance tests. This comparative analysis also provides an example of how the inclusion of performance testing can influence the materials selection process and produce test results indicative of improved overall performance of the mix.