Evaluation of Material Composition on the Shear Performance of Asphalt Mixtures under Different Test Conditions

Although shear strength plays an important role in the performance of asphalt mixtures, it is still not adopted as a control index in traditional asphalt pavement structure design. Among most shear strength tests, the shape of specimen damage in the uniaxial penetration test and circle shear test proved to be more accurate in reflecting the practical asphalt pavement damage shape. To explore the impact of material composition on the shear performance of asphalt mixtures under different test conditions, uniaxial penetration tests, circle shear tests, and unconfined compressive strength tests were conducted to evaluate shear strength with considerations of asphalt mixture composition (asphalt binders, aggregate, and mineral powder). Experimental results demonstrate that the SBS-modified asphalt mixtures have a higher shear strength than conventional 70# asphalt mixtures, and the shear performance of mixtures is positively correlated with softening point of asphalt binder. For the same gradation, the shear strength of asphalt mixtures increases with the asphalt-aggregate ratio first, then decreases with the ratio increases. The shear performance of mixtures can be increased by properly increasing the maximum nominal aggregate size and reasonably adjusting the aggregate gradation. Mineral powder replaced by 20% cement or 10% PSP (phosphorus slag powder) can also satisfy the requirement. Both coarse aggregate and fine aggregate containing silt impact the shear performance of mixtures; it is recommended that the silt content of coarse aggregates is controlled within 3%, and that of fine aggregate should be within 1%.