The influence of water/cement ratio and air entrainment on the electric resistivity of ionically conductive mortar

Abstract

Ionically-conductive mortar can be used for indoor radiant heating partition walls. In these applications, mortar blocks are soaked in electrolyte solutions of CuSO4. The surfaces of the block are coated with sealant and epoxy resin afterwards to prevent evaporation. The mortar block becomes a heating element due to ionic conduction if a voltage is applied to the electrodes in the block. Its electrical conductivity depends on the dispersion of the electrolyte, and hence on the porosity of the mortar. The test specimens in this study were divided into four groups according to the different air entrainment agents, including aluminum powder and hydrogen peroxide as well as two air-entraining agents, SJ-2 and K12. Each group was manufactured with water/cement ratios in the range of 0.5 to 0.9. The test results showed that the conductivity of the mortar was strongly influenced by the air-entrainment and the water cement ratios. The volumetric electric resistivity and the associated microstructures of the mortar were investigated. The test results showed that the specimens made with aluminum powder and a water-cement ratio of 0.65-0.75 had high porosity. The porosity of those specimens was further increased by adding two different air-entraining agents. The specimens with aluminum powder and SJ-2, along with a water-cement ratio of 0.7 appeared to be the optimum mixture. Its resistivity was 19.37 ω.m at 28 days under 25.31% porosity. The experimental results indicate that an ionically-conductive mortar can be produced by combining different air-entrainment agents with variable water-cement ratios to meet a specified electrical heating requirement.