Effects of the simultaneous use of post-industrial polypropylene waste plastic and soybean oil recycling additive on the performance of high-RAP recycled mixtures

Abstract

Using reclaimed asphalt pavement (RAP) in asphalt concrete (AC) reduces the need for nonrenewable resources. However, excessive RAP can cause premature cracking in pavements due to its stiff and aged nature. To address this issue, studies propose the incorporation of recycling agents (RA) in RAP recycled mixtures. Nevertheless, incorporating RA may reduce mixture's rutting and moisture resistance. Alternatively, incorporating waste plastic in AC can positively balance the RA negative effects. Therefore, this study explores the simultaneous use of polypropylene (PP) waste plastics and soybean oil RA to improve the overall performance of high-RAP mixtures. Due to its high melting point, PP can have different roles in the asphalt mixture depending on the mixing temperature used. To explore that, three different methods of incorporating PP into a high-RAP mixture were attempted. Five different mixtures were developed varying the binder (virgin and modified with RA), and the PP mixing procedure. Then, the mixtures were subjected to performance-based testing procedures (SCB IFIT and HWTT) as well as to boiling test to verify binder-aggregate adhesion. It was confirmed that the use of soybean oil enhances the cracking performance of the high-RAP mixtures, but the rutting and moisture performances were compromised. However, incorporating PP made the mixture more resistant to moisture and rutting in different instances. It was found that pre-heating the aggregates at higher than PP melting point allows a better coating of aggregates by PP, and results in improved binder-aggregate adhesion, leading to better cracking, rutting, and moisture performance of high-RAP mixtures.