Spatial and temporal moisture movement within surface-zone concrete under simulated hot climatic conditions

Abstract

The ambient environment has a significant influence on the permeation properties of the surface and near-surface zone of concrete (i.e. the cover zone). Monitoring the water transport properties within this region is crucial in evaluating the long-term concrete performance for a particular exposure condition. This research presents an experimental study of water and moisture transport within the surface region of concrete samples with and without supplementary cementitious materials. The samples were conditioned under two regimes representing poor and good curing; the samples were then exposed to a simulated hot environment with a diurnal temperature fluctuation of 20–40°C and 60% ambient relative humidity, which was represented by ambient conditions of North Africa. Water diffusivity (D𝜣) is a fundamental hydraulic property that is important to characterise water transport of unsaturated concrete. However, its evaluation is complicated, time-consuming and involves expensive equipment. Therefore, in addition to monitoring the water movement into concrete, this study also presents initial developments in application of discretized electrical conductivity measurements as a relatively simple and low-cost technique to evaluate the water diffusivity of concrete (D𝜣). Moisture movement within the surface region was monitored using discretised electrical conductivity measurements, which, together with gravimetric measurements, allowed evaluation of the volumetric uptake and sorptivity of the concrete and the rate and depth of water penetration into the concrete cover zone; it is shown that when these are combined, the degree of saturation, effective porosity and total porosity of the surface region could be estimated. Electrical measurement, taken at discrete depths from the exposed concrete surface, showed that, during absorption, the penetration of water into concrete could be modelled by a sigmoidal function. The results also showed that the convective zone could be estimated by evaluating the electrical conductivity profile through the surface zone prior to and after water absorption.