Mesoscale Cracking of Cement-treated Composites with Initial Defects

To investigate the effect of initial microscopic defects on the mesoscopic fracture of cement-treated base (CTB) materials, a mesoscale heterogeneous numerical model was established using the discrete element method (DEM) and randomization method. Experiments were conducted to obtain the model parameters through an inverse analysis. A discrete fracture network (DFN) was then used to characterize the initial microscopic defects in cement mortar during hardening. Based on the established mesoscale DEM model with initial defects, virtual semicircular bending tests were conducted, the results of which show good agreement with the experimental results. In addition, the mesoscale cracking process was simulated, and the influence of the density and width of the DFN on microstructure cracking was analyzed; the proposed model could better characterize the mesoscopic random cracking behavior. The failure of CTB could most likely be due to the accumulation of damages at mesoscopic level. The simulated crack was formed by the aggregation, connection, and expansion of microfractures. Tension is the driving force of crack evolution, and cracks usually extend along weak areas such as the interfaces between mortar and aggregate. The results also show that the initial microscopic defects negatively affect the structural strength but increase the failure allowable deformation. Furthermore, the fracture density of 20-40 m•m-2 and fracture width of 0.3 - 0.45 mm have the most significant influence on the material strength. The reasonable control of the initial defect density and width in the construction process is beneficial for improving the anticrack ability of the material. This paper provides a new numerical method for investigating the progressive failure process and failure mechanism of cement-treated composites. © 2020, Editorial Department of China Journal of Highway and Transport. All right reserved.