Capillary absorption of concrete after mechanical loading

Microcracks, which are always present in concrete, play a critical role in the durability of concrete because they provide additional pathways for aggressive agents such as chlorides to penetrate into the material. A thorough understanding of the transport properties of cracked/damaged concrete is thus essential for predicting its long-term durability. In addition, for concrete in an unsaturated state, water acts as the main medium for the ingress of chloride ions into concrete. This paper presents an experimental investigation into the capillary absorption of concrete after being subjected to compressive or tensile loading. Sorptivity is chosen as a parameter to describe the rate of water penetrating into concrete since it can characterise the tendency of cementitious materials to absorb and transmit water by the capillary mechanism. A series of water absorption experiments were conducted on concrete samples after being subjected to uniaxial compressive or tensile loading. Three load levels were considered - 70%, 80% and 90% of the corresponding compression and tension loading capacity. An improved gravimetrical test device was used to measure the cumulative water absorbed by concrete at the given time of exposure. The results show that mechanical loading, compression or tension, has an important influence on the water absorption of concrete. The rate of capillary absorption of load-damaged concrete can be up to double that of sound concrete samples for the ranges of load level studied.