Self-healing cold mix asphalt containing steel slag: A sustainable approach to cleaner production

Cold-mix asphalt, produced at ambient temperatures, generates significantly lower CO2 emissions compared to hot-mix asphalt, which requires high-temperature mixing and compaction. However, concerns have arisen regarding the lower durability of cold-mix asphalt when exposed to various environmental stressors, leading to the formation of cracks. This paper explores the benefits of a hybrid application of coarse and powdered slag to enhance crack healing in cold-mix asphalt through the use of microwave radiation. To do so, we quantified extent of microwave-induced healing in dry, wet and freeze-thaw conditioned cold mix asphalt containing steel slags. Latter healing is facilitated by heat generated via absorption of electromagnetic waves. Heat distribution within the specimens and crack zone found to be more uniform when the coarse slag (>4.75 mm) was supplemented with slag powder (∼0.075 mm) as evidenced by thermography analysis. It was further found that freeze-thaw conditioned specimens significantly benefited from microwave-induced healing as evidenced by a 74% recovery in semi-circular bending strength. This enhancement is attributed to the increased diffusion and contact area at heated crack surfaces. Overall, microwave treatment of cold mix asphalt specimens showed an increase in binder wettability and aggregate coating, resulting in improved performance. Notably, the most significant improvements were observed in the stiffness modulus, with increases of 23%, 46%, and 70% for dry, wet, and freeze-thaw conditioned specimens, respectively. Study outcomes support the vision toward the NetZero carbon emission pavements by promoting the durability of cold-mix asphalt to be a viable alternative to hot-mix asphalt.