Investigating the Sensitivity of Aggregate Size within Sand Mastic by Modeling the Microstructure of an Asphalt Mixture

Abstract

The objective of this study is to investigate the sensitivity of aggregate size within sand mastic by modeling the microstructure of an asphalt mixture. The sensitivity of the maximum aggregate size on the sand mastic phase is investigated through discrete-element simulations. A three-dimensional (3D) discrete-element model of asphalt mixture was prepared from X-ray computed tomography (X-ray CT) images. In the discrete-element model, an asphalt mixture is divided into aggregate, sand mastic, and air void phases. In this study, the sand mastic is defined as fines and fine aggregates mixed with asphalt binder. Three different nominal maximum aggregate sizes (NMASs) of sand mastic, namely, 1.18 mm, 0.6 mm, and 0.3 mm, were used in the 3D model to investigate the best gradation of sand mastic. The dynamic moduli of three different NMASs of sand mastic were measured for use in the 3D discrete-element modeling simulation. Laboratory-measured dynamic moduli of asphalt mixtures were compared with prediction results. The sand mastics with NMASs of 1.18 mm and 0.6 mm could be used to predict the asphalt mixture modulus across a range of temperatures and loading frequencies with good accuracy. The sand mastic with a NMAS of 0.3 mm overpredicted at high and low temperatures. The overprediction resulted from the difficulty of proper visualization of the smaller aggregate size in the model.