Cracking resistance of crumb rubber modified green asphalt mixtures, using calcium carbonate nanoparticles and two by-product wax-based warm mix additives

Common procedures to incorporate the recycled crumb rubber (CR) in asphalt binders take a long time and use a high-temperature heating process, which makes these rubberized mixtures even more expensive and environment-unfriendly than conventional mixtures. In trying to make a cheaper and greener asphalt mixture, in this paper, the CR incorporation heating process and its duration were lowered (140-150 degrees C in 15 minutes), and the effect of these changes was studied on the pavement's tensile/shear cracking resistance. Because the main disadvantage of using CR is the increase of viscosity, two by-products, slack wax (SW) and polypropylene wax (PPW) were used to correct the viscosity; also their effect on fracture toughness (Keff) and fracture energy (Gf) was assessed. As results showed that the following process decreases the cracking resistance, calcium carbonate nanoparticles (CCN) in different contents were added. Results show that adding 15% CR reduces Keff and Gf by about 18 and 16%, respectively. Adding the SW and PPW further reduces them by about 8 and 16%, respectively. In this condition, adding CCN in optimal content (about 5%) compensates for these reductions. Although these greener asphalts have the same cracking resistance as the control mixture, the environmental and costeffectiveness analysis shows the developed materials are greener and cheaper.