The impact of nano SiO₂ and superplasticizers on hydration and physical mechanical properties of cement

The aim of work is to determine the lowest and effective amount of nano SiO₂ (NS) for cementitious paste and identify the complex impact of NS and chemical admixtures on cement hydration and physical-mechanical properties. In order to achieve the aim, cementitious specimens with different types and amounts of NS were formed. Further, after the selection of NS and its amount, specimens were formed with various superplasticizers. The work analysis the following properties of cementitious mixtures and hardened cement stone: flow diameter, exothermal temperature, density, ultrasound pulse velocity, compressive strength, microstructure and mineralogical composition. It was determined that the greatest strength of cementitious specimens was obtained when 0.02 wt.% of NS was used, and, compared to control specimens, it increased by ∼15%. Additionally, the greatest increment in strength was observed for specimens with melamine-based superplasticizer. Compared to control specimens, the strength increased up to 23% and the obtained density and ultrasound pulse velocity were the greatest. XRD analysis showed that all specimens had analogue crystal hydrates formed but their amounts are different. SEM analysis showed that structure of the specimens with NS is denser. (paper)