Effect of rubber polymeric materials on moisture susceptibility of asphalt mixtures: Optimization and evaluation study

Pavements made with plain asphalt mixtures are subjected to premature failures due to the exposure to moisture. Polymers are one of the promising additives that are commonly used to extend the service life of asphalt mixtures. This paper evaluates the moisture sensitivity of asphalt mixtures using rubber polymeric materials such as crumb rubber and centrifuged latex. The crumb rubber material is collected from scrap tires (powder form), while the centrifuged latex material is extracted from hevea brasiliensis rubber tree (liquid form). Both crumb rubber and centrifuged latex polymeric materials are incorporated through the wet process at different percentages i.e., 2%, 4%, 6%, 8%, and 10% by the weight of the binder. The optimum crumb rubber and centrifuged latex contents are 8% and 6%, respectively, as per the storage stability test. Then moisture sensitivity of unmodified and rubber modified mixes is analyzed through different laboratory tests: marshal stability ratio, tensile strength ratio, and resilient modulus ratio. The tests clearly show that asphalt mixes exhibit higher moisture resistance with crumb rubber and centrifuged latex polymeric materials. In terms of marshal stability ratio and tensile strength ratio tests, crumb rubber material gives better moisture damage resistance than centrifuged latex material. The cost analysis reveals that rubber-modified mixes show slightly higher costs than unmodified mixes; however, this cost variation is insignificant. As a whole, pavements made with rubber-modified asphalt mixes have longer durability due to its higher moisture damage resistance.