Evaluation of Damage and Nonlinearity of Cold Recycled Materials Mixtures Using a New Strain Sweep Testing Procedure

This article describes a new strain sweep testing method to identify the effects of damage and reversible nonlinearity. Indirect tensile stiffness modulus tests were performed at increasing strain (up to 322 μϵ) to evaluate the stiffness behavior with increasing damage; parallel tests at small strain (43 μϵ) were performed to evaluate the linear behavior. Tests were carried out on two cement-bitumen-treated material (CBTM) mixtures produced in Italy and Poland. Two asphalt concrete (AC) specimens extracted from a Polish road were also tested for comparison. Results were analyzed separately for the steps of increasing strain, and the steps at small-strain. Two approaches were used in the analysis: one was based on the resilient stiffness modulus; the other was based on the dissipated energy. The results showed that both approaches allowed for separation of the effects due to nonlinearity from those due to damage in both CBTM and AC mixtures. Moreover, the damage evolution on CBTM mixtures was not affected by the testing temperature and the mixture composition.