The use of Opuntia ficus-indica as a corrosion inhibitor in steel reinforced concrete

Abstract

Over the past several decades, engineers have sought various methods to improve durability of reinforced concrete and address degradation mechanisms which amongst many, include the corrosion of steel. Corrosion of steel remains one of the biggest challenges in engineering, which leaves a significant economic impact on the construction industry. Additives in fresh concrete have become an important component, contributing to an improved microstructure to enhance its properties with different additions intended for different applications. Several corrosion inhibitor additives are available commercially, but they are being scrutinized as in various instances, they present a bio-hazard (T. Acosta, 2007). The purpose of this study was to consider the use of a natural product, Opuntia ficus-indica (OFI) as a corrosion inhibitor in steel reinforced concrete. Finding a way to use such a natural additive to enhance concrete properties is ideal since this plant is readily available around the Maltese Islands and can be harvested locally. The aim of this study was to assess the influence of additives extracted from OFI, following different methods of preparation and mix design, with respect to mechanical and chemical properties of the concrete. Opuntia ficus-indica was incorporated in mortar mixes at different percentage replacements by; replacing the mix water with fresh liquid mucilage, or by replacing the cement with dry powdered mucilage from the inner part of the plant's clad ode. Both steel reinforced and unreinforced samples were cast to analyze performance characteristics. Results were then compared to performance results of control samples, inclusive of a control with no additive, and a control with an inorganic commercial inhibitor, in order to find the optimum amount of OFI additive corresponding to respective improved properties. Strength and durability were assessed with particular reference to durability indicators including porosity, permeability and most importantly for this study, corrosion potential. Before testing for corrosion potential of reinforced concrete samples, electrochemical characterisation tests using a potentiostat were carried out on solely steel samples. This was carried out as a pilot study to get a better understanding of how steel corrodes when exposed to different solutions and to see whether OFI inhibits corrosion when directly in contact with the steel. This study also helped to get a better understanding of corrosion tests. Findings confirmed that due to the presence of carbohydrates in OFI, additives beyond a certain percentage replacement reduce workability and retard cement hydration. Mortar samples showed good strength and reduced porosity, permeability and water absorption values in several instances. It was further noted that with respect to corrosion inhibition, all samples were greatly influenced by their respective exposure environment. Despite being in its early stages, this study showed that Opuntia ficus-indica additives can potentially be useful to enhance the durability of mortar samples in certain percentage replacements and can reduce the corrosion potential of steel in reinforced concrete.