Influence of micromechanical property on the rate-dependent flexural strength of ultra-high performance concrete containing coarse aggregates (UHPC-CA)

The flexural strength of ultra-high performance concrete with basalt aggregates (UHPC-CA) strongly depends on the micromechanical property of CA, interfacial transition zone (ITZ) and matrix. However, the influence of micromechanical property on the rate-dependent flexural strength of UHPC-CA has not been well understood. Here, different initial micromechanical property distributions are produced by controlling the hydration development, and its influences on the rate-dependent flexural strength of UHPC-CA are investigated by a multi-scale analysis method. The results show that a more homogeneous micromechanical property of UHPC-CA results in a higher flexural strength, but a lower dynamic increase factor (DIF) of flexural strength. The lower DIF can mainly be attributed to the lower increasing rate of mesoscale fracture of CA. Moreover, based on a meso-mechanical model, it is revealed that higher fracture toughness ratios of ITZ/CA and ITZ/Matrix result in lower critical angles (βcr) of fractures of CA and matrix, consequently, higher mechanical contribution from CA and matrix.