Corrosion Protection of Reinforced Steel in Concrete by Using Paints Based on Different Clays

Abstract

Premature failure of reinforced concrete structures occurs primarily due to early corrosion of steel reinforcement. These reinforcements are prevented from corrosion by the formation of a passive oxide film in the high pH environment of concrete. However, pH decreases in actual conditions due to the ingress of harmful ions like chloride, etc., leading to localized corrosion. Chloride ions are considered as the most harmful, which comes from the deliberate additions of calcium chloride in the cement as accelerator or from the environment (marine/coastal regions, de-icing salts). The corrosion products thus formed, being more voluminous, resulting in expanded pressure in the surrounding concrete, leading to cracking of the concrete. The formation of such cracks accelerates further corrosion. In view of the intensity of the problem, serious efforts have been done to prevent corrosion of reinforcement. These have led to the development of varying types of prevention techniques/measures including coatings, control of concrete mix and reinforcement with superior corrosion resistance. These preventive techniques have inherent advantages and disadvantages with respect to the type of structure and the surrounding environment. It is generally agreed that good concrete in terms of quality of ingredients, mix proportion, water-cement ratio, etc., has no substitute for the prevention of reinforcement corrosion. However, corrosion takes place due to the presence of fine cracks in the concrete assisting in the ingress of harmful ions. This necessitates an alternative preventive technique/measure which can be selected based on the type of structure to be protected, life expectancy, nature of environment, and cost of application. This work provides a detailed study on the corrosion of the process of reinforced concrete, its mechanism and protection techniques. These techniques include; 1. Using pozzolanic materials or supplementary cementitious materials as replacement of cement to enhance concrete properties to obtain good concrete mix design. 2. Preparing and applying two paint formulations in presence and absence of talc to provide extra anti-corrosion protection on reinforced concrete.