Study on Green Corrosion Inhibitors from Natural Materials Extracts for RC Structures

Abstract

Concrete is used as a construction material extensively from times immemorial and it is congenially a durable material. Concrete has some durability issues in which corrosion of reinforcement is the major issue faced by construction industry when concrete used with reinforcement to build reinforced concrete (RC) structures. To monitor and control the corrosion of reinforcement in concrete, various techniques have been developed and are being used over various structures. Still, most of these require high cost and technical understanding. Utilization of corrosion inhibitors for RC structure is also one of the cost effective and easily employed method among all other methods. Corrosion inhibitors are added to concrete to delay the initiation of corrosion and to slow down the corrosion rate of reinforcement. Conventional corrosion inhibitors are primarily developed from inorganic substances in which most of them contain heavy metals viz. arsenic, cadmium, chromium, cobalt, lead and zinc. Therefore the use of conventional corrosion inhibitors is deleterious to human health as well as to the concrete which affect the hydration process, setting time and strength. As a result, some countries have started to restrict the use of such corrosion inhibitors. Recent research has been focused on the development of organic green corrosion inhibitors from agro-forestry material i.e. flowers, leaves, bark and stems. The efficiency of these corrosion inhibitors is relatively higher than conventional inhibitors as well as they are safe for human health. Green corrosion inhibitors can possibly a viable and economical solution for the corrosion issues of reinforcement in concrete. The present study is part of on-going research project of CSIR-CBRI which was performed in CBRI, roorkee and Nirma University, Ahmedabad. The aim of this study was to explore the possibility to use the extract of Phyllanthus emblica (Indian Gooseberry) leaves and Cynodon dactylon (Bermuda Grass) as a corrosion inhibitor for RC structures. In CBRI, the performance of selected elements' extracts was evaluated in saline medium of simulated concrete pore solution (SPS). Extracts were generated by maceration process and they were mixed with SPS for corrosion inhibition study. Corrosion was monitored by corrosion monitoring techniques i.e. half-cell potential, linear polarization resistance and corrosion inhibition efficiency. In Nirma University, Extract was generated by hot-reflux ix method It was mixed in concrete during mixing as an admixture and RC specimen was made for the corrosion study. Corrosion was monitored by half-cell potential. The corrosion resistance was increased by the addition of extracts. Phytochemicals of extract had played a vital role to inhibit the corrosion. By adsorption, phytochemicals formed a protective layer over the reinforcement and protect it from chloride. In SPS medium, the optimum efficiency was achieved by dry gooseberry extracts which were η = 43.98% and η = 84.57% for 1% and 2% contained dosage, respectively; this followed by fresh gooseberry and Bermuda grass. In RC medium, lowest corrosion probability was achieved in Bermuda grass extract; this followed by control and salt contaminated specimens.