Numerical modelling of moisture transfers with hysteresis within cementitious materials: Verification and investigation of the effects of repeated wetting–drying boundary conditions

Abstract

a b s t r a c tIn natural environment, the cover layer of reinforced concrete structures is affected by periodic variations of external relative humidity (RH). However, most moisture transport models in the literature only focus on drying of materials. In this study, a method coupling a moisture transport model with any kind of hysteresis modelling is presented. Two hysteresis models (conceptual and empirical) have been implemented and compared. The scope of the study is limited to cyclic variations of RH with no direct contact with liquid water during the wetting steps. Experimental data verifications show that the conceptual approach yields better results than the empirical one. Comparisons of non-hysteresis and hysteresis modellings have been carried out for different cycle durations, RH amplitudes and initial moisture states. All comparisons and investigations enhance the necessity of considering hysteresis to quantify moisture transport under repeated drying-wetting boundary conditions.

Investigation of moisture transport properties of cementitious materials

“…Qualitatively, we found that K l plays the main role for the calculation of mass loss curves while x D has very limited influence. This is in agreement with results in previous studies where the mass loss curves were generally used to inversely determine K l [32,33,34,51,18,36,20]. Adjusting the value of x D can however improve the shape of saturation profiles determined by gamma-ray attenuation (see Fig.…”

“…Consequently, the following fitting procedure has been adopted here. First, we let x D = 2.74 (commonly-used value in previous studies [27,34,51,18,36,20]) to fit the measured drying kinetics by adjusting K l . Second, we change the value of x D to optimize the fitting of gamma-ray saturation profile at a given time of drying.…”

“…The numerical implementation of Eq. (5) was done by the finite difference method in spacial discretization and backward Euler method in time step (see details in [20]). The mass loss was calculated by integrating the mass transfer through the boundary (Eq.…”

“…As it has been pointed out in the literature, microstructure of the material is altered whatever the selected method of drying pre-treatment (oven-drying, vacuum drying, freezing drying or solvent exchange) [19]. Supercritical drying can be considered as a better drying method to preserve the microstructure [19,20]. Halamickova et al [21] pointed out other arguments.…”

“…(5), another important transport coefficient is the relative permeability k rl . Following previous studies [33,20], the van Genuchten-Mualem equation (denoted by VGMa in the present paper) [40] in a simple analytical form is employed here, as follows.…”