Measurement and characterization of aging-induced gradient properties inside asphalt mixture by composite specimen method

Abstract

Measurement and quantitative characterization of aging-induced gradient properties for the asphalt mixture is an important theoretical basis for the accurate mechanical behavior analysis and design of asphalt pavement. In this research, the composite specimen method is proposed to obtain asphalt binders at different depths inside the asphalt mixture. Aging-induced gradient properties have been measured by dynamic shear rheometer (DSR) tests to reveal the internal mechanism. G* master curves for asphalt binders in different depths have been constructed by a generalized logistic sigmoidal model (GLSM) to investigate the gradient aging effects in a wide range. It is found that the composite specimen method can restore the boundary conditions of asphalt binders through the process of specimen preparation, core drilling, core shifting, asphalt injecting, gradient aging test, and layered cutting. It is feasible to study gradient aging characteristics inside the asphalt mixture. Asphalt binder samples obtained from the surface of the composite specimen with the most serious aging degree have the maximum G* value and the minimum δ value. Under the same aging condition, the variation of G* of the asphalt binder along the depth is more pronounced than that of δ. The change behavior of G* and δ are generally the same, and there are only differences in G* and δ values and the depth range of gradient aging effects for different aging levels. At the same temperature and loading frequency, values for G* under the Aging-L3 condition are the largest, and values for δ are the smallest in this aging state. The aging influence depth range inside the composite specimens is about 3 cm, 4.5 cm, and 5.5 cm after oven aging at 85 °C for 5 days, 10 days, and 15 days, respectively. GLSM is well suited for constructing G* master curves of asphalt binders. The distinction between G* master curves is most obvious in the depth of 0 ∼ 1 cm and changes the most from the depth of 0 ∼ 1 cm to 1 ∼ 2 cm. Under the condition of Aging-L3, G* master curves are most differentiated at different depths, indicating the most significant gradient aging state inside the asphalt mixture composite specimen.