Mechanical Strength Analysis of Ternary Cement Pastes Containing Nanosilica and Metakaolin

Abstract

Supplementary cementitious materials’ (SCM) usage in cement based composites is increasing in construction, aiming to improve performance, sustainability and cost of those materials. Among those SCM’s, Metakaolin (MK) and Nanosilica (NS) have been studied by many authors with interesting results, usually an increase in mechanical strength and microstructure refinement. However, the combined use of those two in a ternary mixture with Portland cement was studied by few authors. The present work aims to evaluate this type of mixture through an analysis of compressive strength of 6 different mix proportions. The mix proportions used were a reference paste with 100% Portland cement, two pastes with 1 and 2.5% replacement of clinker by Colloidal Nanosilica and three pastes with 15% replacement of clinker for complementary contents of NS and MK (0 + 15%, 1 + 14% and 2.5 + 12.5%). The compressive strength tests were performed at 1, 3, 7 and 28 days of hydration. The results were analyzed by statistical methods, such as ANOVA test and Duncan Test. At early ages, the use of nanosilica increased the compressive strength. The ternary mixtures presented the highest strength values at 7 and 28 days, and a synergistic effect between these SCM’s was observed at 7 and 28 days, for the 12.5MK2.5NS paste.