Retrieval of the saturated hydraulic conductivity of cement-based materials using electrical capacitance tomography

Abstract

Moisture transport properties have an important part in the durability of cement-based materials, because water plays a major role in the majority of degradation mechanisms and can carry other agents that are detrimental. One of the key transport properties is the permeability, or saturated hydraulic conductivity (SHC), which is a function of porosity, pore size distribution, and pore connectivity. Therefore, information on the SHC is very useful in predicting the durability; however measuring SHC is often difficult due to required experimental setup and the low SHC of cement-based materials. In this paper, we propose an electrical capacitance tomography (ECT) -based approach to estimate the SHC of cement-based materials. The proposed technique is applied to capillary absorption experiments, where specimens are imaged with ECT during water absorption, and the time-series of ECT reconstructions are used for tracing the water front propagation. The water front data, in turn, is used for estimating the SHC of the material. Here, we make a simplifying approximation for the moisture ingress and use (a 1D) sharp front model for estimating the SHC from the ECT-based data. The proposed SHC estimation scheme is tested both numerically and experimentally. The results of the numerical studies support the feasibility of the SHC retrieval both in ideal cases of 1D moisture flow and also in more realistic cases where the flows are not 1D. In the experimental part, the ECT-based estimates for the SHCs of mortars are in good agreement with the values determined using the falling-head method measured independently.