Study of recycled polyethylene materials as asphalt modifiers

There has been interest in modifying asphalt with polyethylene materials, which are a major plastic waste substance, especially low-density polyethylene (LDPE). In this study, combinations of three low molecular weight polyethylene (PE) wax materials and three recycled LDPE materials were used as asphalt modifiers. The modified asphalts were studied using the SuperpaveTM MP1 and MP1a specifications, 1% direct tension test (DTT) failure strain criteria, phase separation, and microscopy. When the molecular weight distribution of the polyethylene modifiers was widened, the bending beam rheometer thermal stress curve of the modified asphalt shifted to the low-temperature end, giving a better critical cracking temperature. Not all recycled LDPE are the same. When using recycled LDPE in asphalt modification, we have to consider the LDPE properties, such as molecular weight and molecular weight distribution, which have been found to play important roles in asphalt's low-temperature properties, hot storage stability, and polymer phase distribution. This study showed that LDPE with lower molecular weight and wider molecular weight distribution are more suitable materials for asphalt modification, compared with high molecular weight LDPE with very narrow molecular weight distribution.Key words: superpave, low-density polyethylene (LDPE), polyethylene, asphalt, recycled, bending beam rheometer (BBR), direct tension tests (DTT), molecular weight distribution, low-temperature grading.