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

Abstract

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.

Durability of concretes exposed to high concentrations of CaCl2 and MgCl2

“…Pore solution expression was performed on concrete cylinders following the procedure described in Montanari et al [ 25 ]. The concrete cylinders were crushed with an electrical hammer equipped with a flat head.…”

“…The concrete cylinders were crushed with an electrical hammer equipped with a flat head. The crushed concrete was sieved using a 9.5-mm sieve and then introduced inside an apparatus similar to the one designed by Longuet and then modified and improved by Barneyback and Diamond [ 25 – 27 ]. The apparatus is constituted of three interlocking gigs.…”

“…Pore solution electrical resistivity was measured by means of a cylindrical plastic cell, whose ends were in contact with two stainless steel electrodes [ 25 , 28 ]. The pore solution was introduced inside the plastic cell through a syringe.…”

Estimating Na+ and K+ concentrations of the pore solution based on ex-situ leaching tests and thermodynamic modeling

“…High-pressure pore solution extraction (PSE) performed on a hardened cement paste, mortar, or concrete sample is a widely-used technique for pore solution analysis as it expresses the liquid directly from the crushed sample [10][11][12][13][14][15]. However, the feasibility of PSE is affected by the binder type, water-to-binder ratio (w/b), and aggregates -when presentsince sufficient available pore water is required for expression.…”

“…3. Several studies have shown that the alkali concentrations obtained from PSE are independent of the amount of pressure applied [14,15]. This suggests a In prior studies, V , and V , have been calculated following equations 2 and 3 with the same free water measurement used for both.…”