Reduction of moisture susceptibility of cold asphalt mixture with Portland cement and bentonite nanoclay additives

This laboratory study investigated the effect of reducing moisture susceptibility of cutback asphalt mixture by adding Portland cement and bentonite, a nanoclay capable of absorbing water and sealing cracks through swelling. The initial strength, moisture susceptibility involving both soaking and freeze-thaw cycling, and cracking resistance at low temperature, were investigated. Test results showed that adding cement and nanoclay significantly improved the initial strength and cracking resistance, and reduced moisture susceptibility. The 20% cement content group generally had the best overall performance. The Marshall stability and indirect tensile strength were improved even after 24 h soaking or freeze-thaw cycling for the 20% cement content group, indicating the potential hydration of cement. For longer soaking time, higher cement content is associated with higher strength, which also indicated the hydration of added cement. Excessive cement caused thinner asphalt film and therefore the improvement of strength was relatively lower and the cracking resistance at low temperature was compromised. The scanning electron microscope (SEM) images showed after freeze-thaw cycling, the mixture surface changed from a smooth surface with a few wrinkles on edge of small particles to a rougher surface with gel structure. When the asphalt film was damaged during the freeze-thaw cycling, the infiltrated water reacted with encountered cement and bentonite cluster and the CSH cement hydration product was formed, sealing cracks or air voids and compensating the strength loss.