Combined Effect Of Low Density Polyethylene (LDPE) and Steel Slag (SS) on the Properties and Service Life of Asphalt Mixes / Pavements

Abstract

The use of waste, recycled, and modified materials is a growing trend, particularly in the construction of roadways, as it not only seeks to be sustainable but also increases the lifespan of pavements. This can be done by mixing steel slag (SS) with a certain kind of plastic polymer, known in the industry as low-density polyethylene (LDPE). Pallets made of LDPE, which is not biodegradable, are used to make plastic bags, and steel slag (SS) is a byproduct of the steel manufacturing process. Both of these pollutants are harmful to the environment, though using them to make pavement helps lessen environmental pollution. The use of LDPE as a binder modifier in two bitumen grades, namely 60-70 and 80-100, is investigated in this study with 3%, 5%, and 7% by weight of bitumen in both grades, and SS was used as a replacement for coarse aggregate. Prior to creating and testing HMA samples for the modified and unmodified samples for dynamic modulus and martial mix design, physical characteristics of modified and unmodified bitumen grades as well as steel slag were studied. The dynamic modulus was measured at temperatures of 4.4 °C, 21.1 °C, 37.8 °C, and 54.4 °C with frequencies of 0.1 Hz, 0.5 Hz, 1 Hz, 5 Hz, 10 Hz, and 25 Hz. In addition to creating master curves for both bitumen grades, the dynamic modulus dataset also underwent design of experiment (DOE) and computational intelligence (CI) analyses. Lastly, damage analysis was performed using KENPAVE, a mechanistic-empirical tool that calculated design life in terms of percentage improvement and reduction in damage ratio for each grade and each modifier. Research result indicates that adding LDPE improves the softening point and penetration grade but reduces the ductility value because of the stiffness of bitumen, which leads to premature fatigue failure at higher LDPE contents. In addition, 3% LDPE by weight of bitumen and 3% SS-modified LDPE show improvements in Marshall Stability and dynamic modulus at all temperature and frequency ranges; they improve the stability by 13 to 16% in the case of 3% LDPE and by 30 to 32% in the case of 3% SS-LDPE. Moreover, the KENPAVE result of 3% LDPE indicates the improvement in design life is up to 19% to 25% and reduction in damage ratio up to 15 to 18%, while in the case of 3% SS-LDPE, the improvement in design life is up to 50% to 60% and reduction in damage ratio up to 25 to 35%. Overall, 3% LDPE and 3% SS-LDPE modified HMA in both bitumen grades 60-70 and 80-100 shows best results.