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.

Permeability and Equivalent Circuit Model of Ionically Conductive Mortar Using Electrochemical Workstation

“…In order to explore the rule of penetration of specimens with different porosity, four specimens made in the same period but different porosity were selected. The porosity of specimens, which was controlled by the mix ratio of air entraining agent [6], was 18.72%, 21.65%, 23.71%, and 25.87%, potential reflects the unstable to stable process of potential between the two electrodes.…”

“…Different from traditional conductive concrete, ionically conductive mortar is a new type of construction material. Ionically conductive mortar can be manufactured by immersing the porous cement mortar (porosity 17%~35%) into the electrolyte solution for a certain period of time [6][7][8]. The conductive circuit of the traditional conductive concrete consists of conductive materials inside the concrete such as steel fiber or graphite [1][2][3][4].…”

“…Meanwhile, the conductive mechanism of ionically conductive mortar is the movement of internal free ions under external electric load. Ionically conductive mortar has excellent conductivity and electric-heating performance [6][7][8], and can be used as the internal partition wall of the building for indoor heating [9]. The mobility of ionically conductive mortar is based on the amount of moisture and free ions inside mortar, references [7,9] provide the effective method to maintain the mobility of ionically conductive mortar by supplying the electrolyte solution.…”

“…The mobility of ionically conductive mortar is based on the amount of moisture and free ions inside mortar, references [7,9] provide the effective method to maintain the mobility of ionically conductive mortar by supplying the electrolyte solution. Previous experimental results have shown that the conductivity of ionically conductive mortar is determined by its porosity, the concentration, and type of electrolyte solution penetrated inside the cement [6][7][8]. However, it is very difficult to establish the mathematical relationships between the resistivity of ionically conductive mortar and these parameters by using traditional methods.…”

Experimental Study on Freezing and Thawing Cycles of Shrinkage-Compensating Concrete with Double Expansive Agents

“…Many cold regions, including northern Europe, North America, and the former Soviet Union, have attached great importance to frost resistance starting as early as the 1940s. Conventional methods for improving the frost resistance of concrete include the reduction of the water-cement ratio [4], special curing, [5] and the addition of additives [6]. The additive method, which is preferred by many researchers, includes the use of porous lightweight aggregate [7], supplementary cementitious materials (e.g., alkali, fly ash, lime powder) [8,9], fibers [10], expansive agents [11], etc.…”