Relaxation modulus prediction of asphalt-rubber concrete based on micromechanics

Crumb rubber modified asphalt concrete (CRMAC) has been found to be an effective material comparing to the common asphalt concrete for its favorable engineering performance. Relaxation modulus of asphalt concretes is one of the fundamental engineering properties. Although laboratory tests provide the way to obtain the value of modulus of CRMAC, a predictive model based on the microstructure of CRMAC is more desirable considering saving of energy source. A modified Mori-Tanaka's theory for the effective moduli of composite materials is used to establish the effective relaxation modulus of CRMAC. "Four-unit, five-parameter" and Burgers models are employed to express the viscoelastic properties of asphalt concrete and crumb rubber in the model, respectively. The relaxation modulus of CRMAC is then predicted with the newly developed viscoelastic micromechanics model. Laboratory test results show that a discrepancy exists between the predicted and measured relaxation modulus. The reasons for the discrepancy between the measured and predicted results may be attributed to interface bonding, interaction of inclusions and matrix. Thus the studies on mechanical properties of crumb rubber and microstructure characteristics of CRMAC are essential to be carried out to obtain the satisfactory viscoelastic micromechanics model.