Comparison of curing methods for bulk electrical conductivity testing of cement pastes

Abstract

Predicting the service life of concrete is one of the main problems faced by civil engineers. Measuring its electrical conductivity is a promising method to quickly find a qualitative indication of the ionic diffusion behaviour of a cementitious mix and, therefore, of its durability. However, one limitation on the ability to quantitatively measure bulk conductivity is the effect of the curing method on the measurement. The main phenomenon that occurs during curing and affects the conductivity is the leaching of alkalis from the pore solution into the curing solution driven by the alkali concentration gradient between these two solutions. The pore solution is therefore depleted in alkalis, reducing both pore solution and bulk conductivity. However, previous work has shown that leaching is not the only effect that the curing solution can have on the bulk conductivity. To avoid these effects, the curing solution must simulate the pore solution at each moment of hydration and for each cementitious mix. For this purpose, different curing solutions based on a sacrificial powder, a reduced volume of curing solution, and a simulated pore solution are proposed and investigated experimentally. The results show that a small volume of curing solution is the most promising method to prevent leaching without affecting the hydration rate.