Gradation optimization and evaluation of AC-20 mixtures based on interlock-dense theory

Abstract

• The interlock-coarse gradation of AC-20 mixtures using the discrete element method was investigated. • The effects of rational ranges of key sieve pores on the performance of the AC-20 mixtures were studied. • The optimal composition of the interlock-dense gradation for the AC-20 mixture was proposed. Aggregate gradation is fundamental to the performance of asphalt mixtures, particularly to ensure high-temperature rutting resistance. Most studies have focused on gradation optimisation indices; however, these indices do not directly reflect the influence law of gradation on the interlock force of aggregate skeleton structures. The objective of the present study is to obtain the interlock-coarse gradation of AC-20 mixtures using the discrete element method. The effects of the rational ranges of key sieve pores on the performance of the mixtures were studied. Then, based on their optimal performance, the interlock-dense gradation of AC-20 mixtures was determined. The simulation results of the interlock force of the coarse aggregates represent the indoor test results of the shear strength and optimal composition of these aggregates. Based on the interlock force numerical tests, the composition of aggregates with size ranges 16–19, 13.2–16, 9.5–13.2, and 4.75–9.5 mm is 37:16:23:24. The recommended fine aggregate gradation is that with a gradation-decreasing coefficient of 0.75. Optimum mechanical properties are achieved when the AC-20 mixture contains 38–47 % fine aggregates, 4–8% 2.36–4.75-mm aggregates, and 4–6% mineral powder. The Marshall stability, dynamic stability, shear strength, and splitting strength of the AC-20 mixture with interlock-dense gradation improved by 25 %, 23 %, 15 %, and 7 %, respectively, compared with those of the mixtures with specific gradation.