Hydration and synergistic features of nanosilica-blended high alkaline white cement pastes composites

M A Abdelzaher,Nabila Shehata

doi:10.1007/s13204-022-02399-5

Abstract

Nanosilica (NS) behavior on hydration and synergistic characteristics of highly alkaline (HA) white cement pastes composites containing 5–25 mass % of NS (as substitution) was studied. The hydration kinetics behavior from 1 to 100 days was examined for all the blends e.g.: whiteness reflection (Ry), setting, compressive mechanical strength (CS), bulk density (BD), combined water content (Wn), total porosity (TP), and free lime (FL) have all been checked. The substitution of 5 wt.% NS has improved the compression mechanical strength and physico-chemical features of HA-white cement pastes composite, especially the compressive mechanical strength, free lime content and bulk density. X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) techniques have been implemented to investigate the microstructure and features of NS pastes composites. NS (5%) improved the synergistic and hydration properties of the evaluated composite materials. NS has a substantial impact on the performance of HA-white cement composite pastes, reducing whiteness reflection (Ry), total porosity and setting times while enhancing mechanical strength, bulk density and gel-to-space ratio. SEM showed a thicker fiber microstructure and more calcium silicate hydrate products lead to a sharp decrease in porosity of all NS composites so it enhances the mechanical and physical properties, as well as the original morphology of calcium mono-carboaluminate hydrate. Highly recommended NS cement composite containing 95 percent + 5 percent NS has better performance and synergy than ordinary white cement. It showed a compact, high-density microstructure consisting of a large proportion of the microcrystalline fibrous group leading to reduced porosity of the blend.

Highlights

There is a growing dependence on the building and construction materials industry on the reused/recycled supplemental cementitious materials (SCMs), solid wastes and industrial by-products for the production of eco-cements which are recently preferred in green and sustainable synthesis of construction/building materials (Antwi-Afari et al 2021; Tayeh et al 2020; El-Kattan et al 2020; Juenger et al 2019)
The 5% NS mix is characteristic with very high specific surface area and unsaturated bonds, forming numerous active nucleation sites resulting in acceleration in the hydration process of the cement with special focus in early ages of hydration for specimens hydrated at 3 (30%), 7 (9%), 28 (7%) and 100 (3) days while the pozzolanic interaction with the CH and free lime content releasing along blends hydration to compose additional calcium hydrates, sodium silicate hydrate and calcium aluminate products is sluggish at late hydration ages (Heikal et al 2013)
The results demonstrate that partially replacing white cement with nano-silica filler leads to decrease in the whiteness of dry blends, retarding the setting times and total porosity (TP) of blends

Summary

Introduction

There is a growing dependence on the building and construction materials industry on the reused/recycled supplemental cementitious materials (SCMs), solid wastes and industrial by-products for the production of eco-cements which are recently preferred in green and sustainable synthesis of construction/building materials (Antwi-Afari et al 2021; Tayeh et al 2020; El-Kattan et al 2020; Juenger et al 2019). Numerous researches shown that adding white sand to cement reduces water demand (Tantawy et al 2013; AlJabri et al 2013), setting times, and porosity (Abbas et al 2021), while increasing combined water content (Abbas et al 2021; Janotka et al 2010) and compressive mechanical strength up to 15% of cement composites (Tantawy et al 2013; Damidot et al 2011).

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