The effect of loading duration on damage initiation in high-strength concrete

Abstract

The rate sensitivity of the failure strength of concrete and other brittle materials is well documented. However, the underlying mechanism(s) that gives rise to this phenomenon remains a topic of debate. Experimental results suggest that the time-dependent failure process plays a significant role in the observed strength increase. This study investigates the failure process in high-strength concrete (HSC) specimens under uniaxial compression loading. This is accomplished through the use of a modified Kolsky compression bar to apply controlled and repeatable mechanical loading in combination with the non-destructive observation capability of high-resolution X-ray computed-microtomography (micro-CT). The evolution of specimen damage morphology is observed as a result of intermittent short-duration uniaxial stress loadings. Experimental results show that HSC specimens are capable of supporting the applied stress above their quasi-static failure strength for short durations. This duration is found to be a function of the overload stress level. Additionally, micro-CT results reveal that specimens undergo a brief period of void compaction followed by the coalescence and propagation of cracks before completely losing load bearing capability.