Use of performance-based testing for high RAP mix design and production monitoring

Abstract

In 2014 the Wisconsin Department of Transportation and industry developed a pilot programme for hot mix asphalt 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 ageing and durability after long-term ageing. The tests selected were the Hamburg Wheel Tracking test, the Semi-Circular Bend (SCB) test at intermediate temperature, and the Disc-Shaped Compact Tension test at low pavement temperatures. Asphalt binder extraction and grading from aged mix was also required. The focus of this paper is to summarise the mixture performance test and recovered binder data gathered during the pilot project on State Highway 77 in Ashland County, WI, suggest modifications to the SCB test procedure, and to present accelerated ageing protocols for continued use of performance testing in practice. SCB 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 ageing conditions. Accelerated long-term-ageing protocols involving loose mix ageing at 135°C for 12 and 24 h are compared to American Association of State Highway and Transportation Officials (AASHTO) R30 compacted mix ageing using recovered binder and mixture fracture properties. Results found that 12 h loose mix ageing produced similar recovered binder grading to AASHTO R30, whereas the effect of ageing on mixture fracture tests was inconclusive. The relationship between laboratory and field ageing is investigated through comparison of field cores to laboratory-aged plant-produced mix from a project constructed in SE 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 ageing. 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 material selection process and produce test results indicative of improved overall performance of the mix.