Optimization design and verification of SMA-13 mixture gradation using mortar theory

Abstract

The stone mastic asphalt (SMA) mixture is formed by asphalt mastic (including asphalt, mineral filler, fiber stabilizer, and fine aggregates) inlaid into gap-graded coarse aggregates. Mortar theory assumes that the SMA is a dispersed system (coarse, fine, and micro disperse systems) of multilevel interspace reticulate structures. Thus, this study investigates the effects of the composition of various dispersed systems on the performance of the SMA mixture with the nominal maximum particle size of 13.2 mm (SMA-13 mixture) based on mortar theory. The influence of coarse aggregate gradation on the shear strength of coarse aggregate–asphalt mortar based on a uniaxial penetration test was studied, and the optimal gradation composition of the coarse aggregate was proposed. The effects of the reserved air void (V0) and primary control sieve passing rate on the physical and mechanical properties of the SMA-13 mixture were studied. A dense skeleton gradation of the SMA-13 mixture was proposed and its performance was verified. The study showed that the importance of the mineral filler-to-asphalt ratio and fine aggregate-to-asphalt mortar ratio in the performance of asphalt mastic is exceeded that of the gradation-decreasing coefficient. The recommended values of the mineral filler-to-asphalt ratio, fine aggregate-to-asphalt mortar ratio, and gradation decreasing coefficient of the asphalt mastic were 1.6, 70:30, and 0.7, respectively. A parabolic correlation existed between the shear strength of coarse aggregate–asphalt mortar and 4.75–9.5 mm aggregate content. The performance of the SMA-13 mixture was positively correlated with V0 and the primary control sieve passing rate. The SMA-13 mixture that contained mineral materials of 9.5–16 mm and 4.75–9.5 mm in the range of 50:50–60:40, gradation decreasing coefficient of fine aggregate of 0.7, 4.75 mm sieve passage percentage of 22%–28%, and 0.075 mm sieve passage percentage of 7%–11%, possessed good shear and splitting strength. In addition, the performance of the SMA-13 mixture with the suggested gradation improved by more than 10%.