Effect of nano-silica on Portland cement matrix

T M Mendes,W L Repette

doi:10.1590/s1983-41952019000600009

Abstract

Abstract The use of nano-particles is a current trend that may play an important role for improving the mechanical performance of Portland cement. The aim of this study is to evaluate the effect of nano-silica on Portland cement matrix. The particle size distribution of Portland cement matrix was modified by the incorporation of 11, 6.2, 3.1, 1.7, 0.85 and 0.42 wt.% of nano-silica. The water demand and the consumption of dispersant were adjusted, and the rheological properties of suspensions were analyzed through rotational rheometry. The mechanical performance of studied mixtures was evaluated by the compressive strength. The pore size distribution was measured by mercury intrusion porosimetry (MIP), and the hydration was analyzed through X-ray diffractometry. The rheological behavior presented a considerable changed, as a consequence of high specific surface area of nano-particles. The optimum content of nano-silica, or the smaller quantity of nano-particles, that leads to the maximum strength gain, varied according to the water to solids ratio. An increasing on the hydration and a pore refinement were obtained due to the use of silica nanoparticles. The particle’s packing and the pozzolanic reaction were the two main effects of nano-silica on the microstructure of Portland cement matrix.

Highlights

The Portland cement is widely used as a building material, with a production of more than 4.3 billions of tons in 2014 [1], albeit with the increasing environmental impacts, mainly by the emission of CO2 and the consumption of non-removable raw materials
Flatt and Bowen [18] restricted to Van der Walls the forces for modeling the yield stress of ceramic suspensions, which is inversely proportional to the inter particle separation (1/IPS2)
The peak of calcium hydroxide (CH) at 2θ = 18.1o [14], presented a considerable intensity when compared to the initial diffractogram of Portland cement CPV-ARI Votorantim (CPV), without Portlandite [14]

Summary

Introduction

The Portland cement is widely used as a building material, with a production of more than 4.3 billions of tons in 2014 [1], albeit with the increasing environmental impacts, mainly by the emission of CO2 and the consumption of non-removable raw materials. Yu et al [7] evaluated the pozzolanic reaction of nanosilica, considering the higher mass loss from hydrated products (CSH/CAH), and the consumption of calcium hydroxide Ca(OH). Yu et al [7] evaluated the pozzolanic reaction of nanosilica, considering the higher mass loss from hydrated products (CSH/CAH), and the consumption of calcium hydroxide Ca(OH)2 These hydration products were measured by thermo-gravimetry. Rong et al [8] reported similar results, investigating the reduction of calcium hydroxide peak, measured by X-ray diffraction. A consequence of the increasing in the apparent yield stress and viscosity [11,12], was the higher water demand of mixtures containing nano-silica, as demonstrated by Quercia et al [13]. The aim of this research is to evaluate the effect of nano-silica on Portland cement matrix

Objectives

Results

Conclusion