Pore structure analysis of hardened cement mortars containing silica fume and different nano-powders

Abstract

In this article, the 56-day pore structures of the cement mortars produced by the addition of silica fume and nano-SiO2 (NS), nano-Al2O3 (NA) and nano-Fe2O3 (NF) powders in singular, binary or ternary combinations at 3 different proportions (0.5%, 1.25% and 2.5%) of the binder content were investigated through MIP and BET analyses. The compressive strengths and capillary water absorptions of produced mortars were also determined in order to investigate the effects of changes in pore structure on these properties.As a result, it was found that pore structures of the mortars determined by MIP and BET were influenced by the choice of singular, binary or ternary uses as well as the content of nano-powder(s) added into the mortar. The highest reductions in porosity of mortars and the total volume of mercury intruded were obtained by the use of NA powder at 1.25% for singular, NS+NA powders at 0.5% for binary, and all three powders at 1.25% for the ternary combination. On the other hand, the specific surface area of the mortars were increased the most by the addition of 1.25% of NA, 0.5% of NS+NA and 0.5% of NS+NA+NF. Among the 22 mortar groups produced within the scope of this study, NA content of 1.25% yielded the best results on the properties measured by MIP and BET (total volume of mercury intruded, porosity and specific surface area) as well as the pore-size distributions. The reduction in pore volume, the pore-size distribution becoming finer and the improvement in physico-mechanical properties of the mortars after the addition of nano-powders could be explained by the filler effect or amount of hydration products of cement. However, the addition of the powders at proportions in excess of 1.25% resulted in an increase in the pore volume of some mortars because of agglomeration.