The Effects of Temperature Curing on the Strength Development, Transport Properties, and Freeze-Thaw Resistance of Blast Furnace Slag Cement Mortars Modified with Nanosilica.

Karol Federowicz,Pawel Sikora,Hussein Al-Kroom,Hamdy Abdel-Gawwad,Vitoria Figueiredo,Mohamed Abd Elrahman

doi:10.3390/ma13245800

Abstract

This investigation studies the effects of hot water and hot air curing on the strength development, transport properties, and freeze-thaw resistance of mortars incorporating low-heat blast furnace slag cement and nanosilica (NS). Mortar samples were prepared and stored in ambient conditions for 24 h. After demolding, mortar samples were subjected to two different hot curing methods: Hot water and hot air curing (40 °C and 60 °C) for 24 h. For comparison purposes, mortar reference mixes were prepared and cured in water and air at ambient conditions. Strength development (from 1 to 180 days), capillary water porosity, water sorptivity, and freeze-thaw resistance were tested after 180 days of curing. The experimental results showed that both curing regimes accelerate the strength development of mortars, especially in the first seven days of hydration. The highest early strengths were reported for mortars subjected to a temperature of 60 °C, followed by those cured at 40 °C. The hot water curing regime was found to be more suitable, as a result of more stable strength development. Similar findings were observed in regard to durability-related properties. It is worth noting that thermal curing can more efficiently increase strength in the presence of nanosilica, suggesting that NS is more effective in enhancing strength under thermal curing.

Highlights

Dynamic developments in industry at a worldwide level poses new challenges for the construction industry
This study aims to fill the gap in the existing knowledge and to shed light on the effects of temperature curing on the strength development, transport properties, and freeze-thaw resistance of low-heat blast-furnace slag cement mortars modified with nanosilica
From two days of curing on, a difference between the compressive strengths was observed, in favor of the N series. This effect can be attributed to the pozzolanic activity of nanosilica, which results in consumption of Ca(OH)2 and the production of additional calcium-silicate-hydrate seeds (C-S-H) phase [40,50]

Summary

Introduction

Dynamic developments in industry at a worldwide level poses new challenges for the construction industry. Despite the many advantages of concrete structures and their overall durability, exposure to harsh environments containing chloride ions, carbon dioxide, or sulphate can reduce their durability and performance over the years [9,10,11,12]. A common process of destruction involves sulphate penetration through the surface, which reacts with hydrates and produces ettringite or gypsum, leading to volume expansion [15,16]. This creates tensile stresses in the concrete, which result in subsequent cracks. It is very important to produce composites with dense and compacted microstructures and satisfactory early mechanical performance

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