How RAP Content and Anti-stripping Additives Affect the Moisture Susceptibility of Recycled Asphalt Mixtures

Reclaimed asphalt pavement (RAP) materials are among the recycled materials that can be used in the construction industry. Although they have been used in many projects, there are still concerns about the impact of different percentages of RAP materials on the quality, performance, and durability of hot mix asphalt (HMA). Therefore, this chapter tries to evaluate the moisture susceptibility of asphalt mixtures containing various amounts of RAP. For this purpose, HMA mixtures containing 0%, 20%, 40%, and 60% RAP were prepared. On the other hand, the impact of an anti-stripping agent on these mixtures was evaluated by adding 0%, 0.5%, 1%, and 1.5%. Therefore, the mixtures were subjected to the modified Lotman test (indirect tensile strength (ITS)) and the boiling water test to simultaneously assess the impact of the anti-stripping agent and RAP materials on the moisture susceptibility of recycled mixtures. The K-means clustering method was used as an image processing tool to evaluate the stripping potential of the asphalt mixtures. Findings show that replacing up to 60% of the virgin aggregate with RAP improved ITS values for both conditioned and unconditioned specimens. The anti-stripping agent only improved the conditioned samples due to the increased bonding between the virgin aggregates and binder. Linear regression was used to test the relationship between the proposed stripping index and the results of the modified Lottman test (ITS), and the R2 of linear regression was 0.91, which indicates that the model is highly predictive.