No abstract

The changes in hydrated cement composition were measured as a means of quantifying the impact of nano silica size and surface area on cementitious properties. Nano silica dispersions were dosed to have an equal amount of exposed and reactive silica surface area, which contribute to pozzolanic reaction. The amount of calcium hydroxide was measured through thermogravimetric analysis to identify hydrate growth. The chemical shrinkage and compressive strength were also evaluated as a means to understand the impact that nano silica had on the early stages of hydration. Cement composites receiving the higher dosages of the larger nano silica particles exhibited higher levels of enhancement, showing decreased calcium hydroxide, decreased chemical shrinkage and increased compressive strength. The smaller nano silica particles exhibited enhancements at lower dosages, but at higher dosages an increase in calcium hydroxide, an increase in chemical shrinkage, and a decrease in compressive strength was recognized.

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.