• Calabria-Holley, Juliana
• Shakil, Muzzamil
• Ansell, Martin
• Paine, Kevin A.

Abstract

The effects of sol-gel silicates on Portland cement hydration were investigated. Silica sols were realized by tetraethylorthosilicate, triethoxymethylsilane, ethanol, water and nitric acid or ammonia. Solvent-free sols were also synthesised. The prepared sols were mixed with cement pastes at a w/c of 0.4 or 0.5 at varying doses of 0.5–10% by mass of dry cement. The solvent-free synthesised sol appeared to be a more suitable candidate. This is because observation of the hydration kinetics revealed a shortening of the dormant phase of cement hydration and exhibited a higher power output during this stage, representative of additional nucleation sites created in the system. However, the main peak power output that occurs at the end of acceleratory stage was decreased, further pronounced at higher sol dosages. This can be attributed to the ethoxy-based precursor, which produces ethanol as a by-product of hydrolysis reactions. It is therefore of great interest to investigate possible routes to optimise the sols to limit the alcohol content. SEM analyses on fractured surfaces of 28 day old pastes revealed a distinctive morphology, particularly at higher sol dosages. The development of C-S-H on portlandite was observed, which further suggests that the sol-gel silicates could be providing additional nucleation sites therefore acting as a seeding agent.

Topics

• impedance spectroscopy
• microstructure
• morphology
• surface
• phase
• scanning electron microscopy
• cement
• alcohol