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Evaluation of Recycled Base Aggregates

Thursday, September 19, 2019 - 15:45

This study intended to provide quantitative evaluation of the use of RAP and RCA as base layers in HMA pavements. The study used field and laboratory testing programs and data from WisDOT PIF database quantify the performance of base materials and test sections on pavements with CA, RCA, and RAP base layers. Analysis of the particle size distributions for the investigated CA, RCA, and RAP base materials indicated high sand size fractions in both RCA and RAP base materials compared with CA base materials. The RCA base materials exhibited the highest absorption and high percentages of mass loss in Micro-Deval test. The predicted CBR and resilient modulus values for all investigated base layer types are comparable. Difficulties were noted in retrieving RCA base materials from STH 78, STH 32, and STH50 leading the research team to believe this is due self-cementing effects. The results of the FWD analyses pertaining to D0 and SNeff demonstrate that, in general, the investigated HMA pavement sections with RCA base layers exhibited the lowest deflections and the highest structural capacity (SNeff) compared with those pavement sections with CA and RAP base layers. The pavement sections with CA base layers exhibited the highest deflection and the lowest structural capacity. In general, the back-calculated base layer moduli (EBase) for all investigated pavement tests indicate the highest average values for RCA base layers followed by the RAP base layers, while the CA base layers possessed the lowest average values. The most commonly observed pavement surface distress in the investigated pavement test sections included: transverse cracking, longitudinal cracking, alligator (fatigue) cracking, rutting, bleeding, edge cracking, pavement edge heave, and block cracking. Based on the visual distress survey of the investigated pavement sections, fatigue cracking is the most commonly observed surface distress associated with CA and RAP base layers. Transverse and longitudinal cracks were commonly observed on pavement sections with RCA base layers. The general ranking of the investigated pavements was based on the overall average and does not account for the pavement age. An attempt to correlate the calculated PCI average values with pavement age did not lead to a reliable trend. The pavement surface profile measurements results indicated relatively high IRI values and high variability exhibited by the pavement sections on RCA base layer materials. The average IRI value for all pavement sections indicates the pavement test sections with RAP base layers exhibited the smoothest ride quality. Based on the results of this study, the research team believes that the performance of the HMA pavements with RCA (with the exception of STH 78) and RAP is satisfactory/adequate and comparable with the performance of the HMA pavements with CA base course layers. The research team recommends that WisDOT continues the practice of using the RCA and RAP in base course layers of HMA pavements with implementing control measures listed in Chapter 7 of this report.  This report is available online at https://wisconsindot.gov/documents2/research/0092-17-01-final-report.pdf