The Effect of Nanosilica on the Early Strength of Alkali-Activated Portland Composite Cements

摘要

Significant reduction of carbon footprint of the construction industry is achieved through the use of composite Portland cements. However, substitution levels of additives in the composite cements are limited due to slow strength development arising from low reactivity of the pozzolana compared to clinker phases especially at the early age. The aim of the study was to evaluate effect of nanosilica on formation of strength properties and structure at the early age. The Portland composite cement containing clinker, granulated blast furnace slag, zeolite tuff as natural pozzolana and limestone with additives of nanosilica, Na_2SO_4 and polycarboxylate ether was investigated. The results obtained with the help of PSD, XRD, DTA, TG and SEM techniques showed that addition into the cement paste of the nanosilica particles with high surface reactivity improved the composite cement microstructure and leaching of calcium became significantly lower, because nanosilica particles react with calcium hydroxide with the formation of a denser C-S-H gel at the early age of hardening.