Antioxidant depletion was evaluated in high-density polyethylene (HDPE) geomembrane (GM) coupons immersed in radioactive synthetic leachate (RSL) representative of leachate in low-level radioactive waste (LLW) disposal facilities operated by the U.S. Department of Energy’s environmental restoration programs. Depletion was assessed at four temperatures (25, 50, 70, and 90°C). Comparative tests were conducted with nonradioactive synthetic leachate (NSL) having the same chemistry as RSL, except radionuclides were excluded. Control tests were conducted with deionized (DI) water. One-sided exposure tests were also conducted with the HDPE GM in RSL at 70 and 90°C. Specimens were removed periodically and tested to determine antioxidant depletion, melt flow index (MFI), crystallinity, and stress crack resistance. Standard and high-pressure oxidative induction time (OIT) tests were conducted to measure antioxidant depletion. Antioxidant depletion rates in RSL were only slightly greater than those in NSL, indicating that radionuclides in the LLW leachate had only minor effect on antioxidant depletion. Antioxidant depletion in RSL and NSL occurred 1.1–1.9 times faster than in DI water. Antioxidant depletion in HDPE GMs exposed to RSL and NSL at 90°C was complete after 12 months. MFI decreased systematically after 15 months of immersion, which is indicative of crosslinking due to oxidation. Crystallinity also decreased slightly after 12 months, whereas stress crack resistance (SCR) showed no trend over the immersion period. Arrhenius modeling was used to extrapolate the laboratory data at elevated temperatures to a typical LLW liner at 15°C. Predicted time for antioxidant depletion for a 2-mm-thick HDPE GM in a composite liner in contact with LLW leachate is estimated to be 730 years. The total service life of HDPE GMs in contact with LLW leachate is estimated to be at least 1975 years.

The most common recycled construction materials used as unbound base course in pavement construction are recycled concrete aggregate (RCA) and recycled asphalt pavement (RAP). This study investigated the mechanical properties of RCA and RAP as unbound base, including the relationships between resilient modulus (Mr) and composition (e.g., particle shape, binder type, aggregate mineralogy, and contamination). The recycled materials were collected from a wide geographical area, covering eight states in the U.S. The Mr tests were conducted following National Cooperative Highway Research Program (NCHRP) protocol, which measures specimen deflections externally and internally. Power function and NCHRP models were applied to estimate Mr. The NCHRP model was more reliable in capturing Mr dependency on stress state in RCA and RAP. A multiple linear regression model was developed to predict the Mr of RCA (R2=0.96) and RAP (R2=0.97). There was a high degree of correlation between the predicted Mr and the physical properties of RCA (R2=0.89) and RAP (R2=0.99).