Influence of Loading Pressure and Sample Preparation on Ionic Concentration and Resistivity of Pore Solution Expressed from Concrete Samples

Pore solution expression is an established method to obtain samples of the liquid phase from cementitious systems. This experimental method applies pressure to a cementitious sample, forcing its liquid phase out of the pores. By collecting and studying the liquid phase in cementitious systems, it is possible to obtain information on its ionic concentrations. The ionic concentrations can be used for modeling calibrations and to estimate the resistivity of the pore solution. When the bulk resistivity of concrete is normalized by the pore solution resistivity, it is possible to determine the formation factor. The formation factor is related to the transport properties of the concrete and, as such, it can be used to estimate the rates of transport of ionic species within a concrete structure. The formation factor is currently being included in AASHTO PP84, Standard Practice for Developing Performance Engineered Concrete Pavement Mixtures, as an indicator of transport properties for quality control operations. Pore solution expression is included as one of the available procedures of AASHTO PP84-19 to determine the pore solution electrical resistivity. Previous studies on paste and mortar samples have demonstrated that increased loading pressure during the pore solution expression might impact the final ionic concentrations of the expressed solution. This study aims to verify if the pore solutions of concrete specimens are also influenced by the selected loading pressure and whether the potential consequent change in the measured ionic concentrations of the solution also has an impact on its resistivity. No appreciable trend in increased solubility was observed for the range of applied normal pressures between 600 and 985 MPa. Cyclic loading regimes increased the variability of alkali solubility. Sample preparation, in some cases, influenced the water content of the sample and induced unwanted alteration on the ionic concentrations of the mixtures under study.