Abstract
In this study, the use of nano-silica (nano-SiO2) and bentonite as mortar additives for combating reinforcement corrosion is reported. More specifically, these materials were used as additives in ordinary Portland cement (OPC)/fly ash blended mortars in different amounts. The effects of nano-silica and bentonite addition on compressive strength of mortars at different ages was tested. Accelerated corrosion testing was used to assess the corrosion resistance of reinforced mortar specimens containing different amounts of nano-silica and bentonite. It was found that the specimens containing nano-SiO2 not only had higher compressive strength, but also showed lower steel mass loss due to corrosion compared to reference specimens. However, this was accompanied by a small reduction in workability (for a constant water to binder ratio). Mortar mixtures with 4% of nano-silica were found to have optimal performance in terms of compressive strength and corrosion resistance. Control specimens (OPC/fly ash mortars without any additives) showed low early age strength and low corrosion resistance compared to specimens containing nano-SiO2 and bentonite. In addition, samples from selected mixtures were analyzed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Finally, the influence of Ca/Si ratio of the calcium silicate hydrate (C-S-H) in different specimens on the compressive strength is discussed. In general, the study showed that the addition of nano-silica (and to a lesser extent bentonite) can result in higher strength and corrosion resistance compared to control specimens. Furthermore, the addition of nano-SiO2 can be used to offset the negative effect of fly ash on early age strength development.
Highlights
Reinforced concrete (RC) is the most widely used construction material in the world
Steel reinforcement inside the concrete is protected from active corrosion by a passive layer which spontaneously forms on its surface in the alkaline environment [1,2,3]
It can be seen that the maximum slump flow was found in the control mix with an average value of 177.5 mm while the minimum slump flow was observed in the mix containing 6% nano-SiO2 with an average slump flow of 150 mm
Summary
Reinforced concrete (RC) is the most widely used construction material in the world. It is cheap, widely available, and durable. Steel reinforcement inside the concrete is protected from active corrosion by a passive layer which spontaneously forms on its surface in the alkaline environment [1,2,3]. The passive layer may breakdown either due to chloride ingress, when a sufficient amount of chloride ionsreaches the reinforcement [4]; or due to carbonation of the concrete cover [5], when the alkalinity of the concrete pore solution is lost [6]. Once the passivity is lost, active corrosion of the reinforcement starts. Corrosion of reinforcement causes more problems than cover cracking alone: it causes
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