Investigating Merits of Introducing Nano-Silica on the Formation of Calcium Silicate Hydrate and on the Compressive Strength of the Hardened Cement Paste

The influence of adding Nano particles of silicon dioxide replacing cement on cement pastes was studied, summarized and evaluated for both water and vacuum cured. The effect of (5-20 nm) Nano-Silica on the mechanical properties and strength development of Nano-cement materials were documented using Material Tests System (MTS). The continuous hydration process, formation of C-S-H and the residual quantity of calcium hydroxide (CH) was monitored using Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). The experimental results show the effect of Nano-Silica addition on the compressive strength and the signature phase of (C-S-H) during the hydration process of a cement paste, Percentage 5% and 10% Nano-Silica by volume of Nano-Silica were used in this study and compared with 0% Nano-Silica which represents control paste. The rate of water to cementations material for all admixtures was kept constant (w/c) 0.40. The experimental results show that the compressive strengths of cement paste with 5% Nano-Silica particles were all higher than those of controlled paste (0% Nano-Silica) for water and vacuum cured specimens. This is attributed to the reaction between Nano-Silica and calcium hydroxide (CH) to develop more calcium silicate hydrate (C-S-H) resulting in higher strength of the cement pastes. On the contrary, the adding of 10% Nano-Silica yields lower compressive strength than the reference paste (0% Nano-Silica). The result also show that the vacuum cured specimens yield higher strength compared to water cured specimens up to 28 days. Nevertheless, the final strength for water cured specimens was higher than for vacuum cured specimens.