The role of shear interlock effect of CA on the pre-peak cracking of UHPC-CA

Coarse aggregate (CA) can mitigate the shrinkage of Ultra-High Performance Concrete (UHPC), however, the pre-peak cracking process of UHPC containing CA (UHPC-CA) under mixed tensile-shear loading remains unclear. Herein, microcracking, mesoscale fracture and macroscale cracking resistance are quantified with the aim to clarify the role of CA on the pre-peak cracking mechanism of UHPC-CA. The results show that, as shear stress proportion increases, a localized strain concentration appears along CA, exhibiting a shear interlock effect of CA. Based on the integrated machine learning based acoustic emission mode classification, more shear microcracking events are detected. Moreover, higher shear proportion results in a higher fracture across CA at the mesoscale and a mineral crystal fracture mode transformation, from intergranular fracture to transgranular fracture, at the microscale. As a result, CA leads to a delayed initiation of full-developed fracture process zone and larger fracture energy, consequently, higher cracking resistance of UHPC-CA under mixed tensile-shear loading.