Utilizing Nano Silica to Reduce Calcium Oxychloride Formation in Cementitious Materials

Abstract

This paper examines the use of two nano silica (NS) materials as an additive that can reduce the susceptibility of concrete to deicing salt damage. The motivation for this research is to evaluate whether NS can be used to improve resistance to calcium oxychloride formation because of deicing salts. Deicing salts, like calcium chloride and magnesium chloride, can react with water and calcium hydroxide in concrete to form an expansive product called calcium oxychloride. This work builds on previous observations that supplementary cementitious materials (SCMs), such as Class F fly ash, slag, and silica fumes, can reduce calcium oxychloride formation through dilution of the cement, which results in a reduction in calcium hydroxide and the pozzolanic reaction, which further reduces calcium hydroxide through chemical reaction. This paper investigates whether NS additions during the mixing process can provide similar results to other SCMs. Both NSs had the same particle size distribution and specific surface area, but NS2 had alumina on the surface while NS1 did not. Toward this end, the calcium hydroxide content and calcium oxychloride were measured using thermal gravimetric analysis and low-temperature differential scanning calorimetry, respectively. The addition of NS to a mixture was found to reduce the calcium oxychloride at lower dosages as compared to Class F fly ash.