Effects of Water-Binder Ratio and Aggregate Shape on Crack Evolution in Cement-Based Materials: Inclined Shear Test and DEM Simulation

Abstract

In this study, inclined shear tests (ISTs) coupled with acoustic emission (AE) monitoring and discrete element method (DEM) numerical simulations were employed to investigate the influence of the water/binder (w/b) ratio (w/b=0.35 and 0.23) and aggregate shape (rounded and angular) on the macro- and microfracture behavior of cement-based materials subjected to shear stress. The experimental results show that macrofracture parameters such as shear strength and stiffness increase as the w/b ratio decreases; however, they are not affected by aggregate shape, in agreement with simulations. The aggregate shape is related to the microcrack behavior. The microcrack distribution in the cement-angular aggregate mixture is confined to the area of the central shear zone, with much lower scatter than that in the cement-rounded aggregate mixture, in which microcracks are scattered around the central shear zone, in line with the macrocrack behavior. This finding is consistent with the numerical simulation results. The DEM simulation results show that the w/b ratio affects macroparameters, namely, Young’s modulus (E) and Poisson’s ratio (v). The value of E increases as the w/b ratio is reduced and vice versa. The aggregate shape affects only the microparameters (bond properties), which are higher for angular aggregates than rounded aggregates. A method of determination of the DEM input parameters (both micro- and macroparameters) considering different w/b ratios and aggregate shapes was proposed as well. This work provides insights into both the macro and microfracture behavior of cement mortar from the viewpoint of both tests and the relatively new DEM modeling technique. Verified with the IST data, which is rarely found in existing literature, there is generally good agreement between the simulations and tests. Moreover, a unique way of modeling, especially angular aggregate shape has been demonstrated. Further, some reference bond properties and a way to estimate them have been provided for similar simulations. The application of the model presented in this study may be extended to evaluate the strength of rock and assess its suitability as a potentially effective nuclear waste repository site or even evaluate the strength of confined concrete columns (structures) in future studies. These interesting ideas have been presented, for example, because due to the interlocking nature of angular aggregates, the bond properties of cement-based materials made of angular aggregates were found to be higher than those of their rounded aggregate counterparts.