Exploring the potential of siloxane surface modified nano-SiO2 to improve the Portland cement pastes hydration properties

This paper investigates the potential of siloxane surface modified nano-SiO2 as an admixture capable of modifying heat development and microstructure densification of Portland cement pastes. Two different types of siloxanes were grafted on nano-SiO2 (nS) particles. Calorimetric measurements of Portland cement pastes with 0.3 w/b ratio show that the siloxane functional group clearly interferes on the early age reactions of cement pastes with 0.1 or 0.5 by weight of functionalized nS. In situ soft X-ray transmission microscope images of nS/Ca(OH)2 solutions demonstrate that siloxane cover the nS surface and that the treatment allowed nS particles to last longer on a calcium hydroxide saturated solution before forming C–S–H. The possible reasons of this behavior are discussed, including the matrix densification and C–S–H nano-structure filling. The results indicate a potential use of this hybrid to improve the nanostructure of the cement paste matrix.