Effect of Short-Term Sustained Uniaxial Loadings on Water Absorption of Concrete

The synergetic effects of the environmental and loading actions on mass transport process in concrete play an important role for the deterioration of mechanical properties and durability problems of reinforced concrete (RC) structures. Water is either the main agent responsible for the deterioration of concrete or the principal transport medium carrying aggressive species to ingress into concrete. This paper presents the results of an experimental investigation on the effect of short-term sustained uniaxial compressive or tensile loadings on water absorption by hollow cylindrical concrete specimens. An improved test apparatus aimed for the coupled effect of sustained loading on water absorption was designed to measure in real time the amount of water absorbed by the concrete specimen. The cumulative water content and axial/lateral strain of specimens under various stress levels (approximately 0–50%) were recorded. It was noted that under the short-term sustained tensile loading, the cumulative water content at a given exposed time generally increases with an increase of the stress level, while for the compressive case it initially decreases and then increases. The initial and secondary sorptivities, which are defined for characterizing the tendency of concrete to absorb water by the capillarity versus the compressive stress level, conformed to the polynomial function, except for the tensile loading case. which exhibited a linear relation. The ratio between initial and secondary sorptivity, as well as the quantitative correlations between the two sorptivities and stress level were proposed to account for the sustained loading effect on water absorption of concrete. Based on the unsaturated flow theory (UFT) model and experimental data, two forms of diffusivity, i.e., the exponential law and power functions, were both adopted to predict water distribution within a concrete sample under compressive/tensile stress states after 32-h absorption. The results indicated that the predicted water penetration depths by means of both exponential law and power functions in the UFT model increases with the increase of sustained compressive/tensile stress levels. The validation of the proposed model shows good correlation between the predicted water zpenetration depth and the test data.