Optimization of Hybrid Cement Composite with Carbon Nanotubes and Nano Silica using Response Surface Design

Abstract

The most common choice for fitting a second order model in response surface methodology is the central composite design. The central composite response surface methodology had been selected in order to investigate the performance of the cement-based design mixtures incorporating Nano silica particles (NS) in combination with multi walled carbon Nano tubes (CNTs). The proposed evaluation of the utilized hybrid NS particles - Multi walled CNTs within the cement matrix via the response surface method, showed that the combination of NS with relatively high amount of Multi walled CNTs (0.04%) had a positive effect on the hydration reaction. The presence of individual Multi walled CNTs worked as extra nucleation sites for the hydrates and enhanced the activity of the NS. While the combination of a lower amount of Multi walled CNTs in the presence of NS had a negative effect on the hydration reaction. NS agglomerations suck water between its particles and negatively affect the production of hydrates of the cement due to its re-agglomeration. The generated re-agglomeration of CNTs decreased the availability of Ca (OH)2 for the NS particles to react with and produce more Calcium Silicate Hydrate (C-S-H). Finally, as for the statistical analysis, the response surface model showed that the combination of the CNTs and NS interacted effectively for enhancing the mechanical properties of the cement matrix.