Using simple soil water content sensors to measure water availability in fresh concrete

University of Pretoria, Department of Civil Engineering, Lynnwood Road, Hatfield, Pretoria, South Africa

^* Corresponding author: phia.smit@up.ac.za

Abstract

Preventing plastic shrinkage cracks improves the durability of concrete. This is because plastic shrinkage cracks serve as pathways by which corroding agents can penetrate concrete. Freshly cast concrete is a saturated mixture of reactive and non-reactive materials. As water moves out of the concrete mass and as water is used in the hydration process, the free water in the mixture reduces. Eventually, the mixture can be considered to be unsaturated. In this research project, the viability of using soil water content sensors to measure the change in water availability in concrete from fresh state to early-age was explored. The soil water content sensors measured dielectric permittivity. The dielectric permittivity, cumulative evaporation and setting time of mortars with varying water/cement ratios were tested. It was found that the dielectric constant was influenced by changes in fresh mortar and that the sensors have the potential to qualitatively monitor cement content, bleeding, hydration and evaporation. Further work is required in this field.