Investigating the effect of using modified recycled concrete aggregate on the volumetric and mechanical properties of hot asphalt mixes

Coarse recycled concrete aggregates have weaker mechanical and physical properties than natural aggregate because of the porous and flimsy cement mortar.Hence, using coarse recycled concrete aggregate in the asphalt mixtures decreases their resistance to different failures. Therefore, in this research, in order to reduce the permeability and increase the resistance of adhered cement mortar, coarse recycled concrete aggregate was modified by two chemical (coating their surfaces using styrene butadiene rubber polymer) and physical (separation of cement mortar using heating) methods. The results of the dynamic creep test also show that employing coarse recycled concrete aggregate increases permanent deformation in the specimens under test because the asphalt mixture stiffness is decreased. But asphalt mixtures containing treated coarse recycled concrete aggregate have less permanent deformation because the styrene butadiene rubber polymer with the penetration into the void of coarse recycled concrete aggregate and reinforcing cement mortar, as well as removing the cement mortar by heat, increases their stability. Also, asphalt mixtures containing coarse recycled concrete aggregate have a lower fatigue life compared to the control mixture, and chemical modification of aggregates has been more effective in increasing the fatigue life of the mixtures containing them compared to the physical method. In addition, the results show that the presence of moisture reduces the resistance of controlled and modified asphalt mixtures against moisture damage, and this reduction is greater in mixtures containing coarse recycled concrete aggregate due to their high absorption.