Reinforcement of steel in concrete enhances its tensile strength and helps sustain it against seismic activity. The most common material choice for reinforcement has been found to be steel. There are millions of buildings, structures and bridges that have been made using the combination of steel reinforcement in concrete.

In the 1990s, there was a sudden increase in the deterioration of RCC buildings, especially in coastal zones or cities with high humidity and pollution. This was immediately countered by using modified steels such as CRS steel with small additions of chromium (Cr), copper (Cu), vanadium (V) and titanium (Ti) as well as using coated steel bars. One of the most accepted technologies in the 1990s was the use of fusion bond epoxy coating on rebar because of its large tonnage production with high quality control. However, damage during handling and lower bond with concrete made has proved questionable in many sites, though none of the over 900 structures made have showed any distress to date.

Alternative technologies of TMT bars and stainless steel bars were adopted. Simultaneously, there was a demand for the enhancement of the life of structures to grow from 60 years to 120 years, and even 300 years. It became a dilemma to find out how a RCC structure would sustain for 120 years, or even 200-300 years, when present technologies assured only 30 to 60 years. In such a process, even after taking into account all concrete design possibilities of high-density concrete and longer cover thickness, the problem was how to remedy distress owing to corrosion. We then created a model of the life of a concrete structure based upon a fixed concrete design but varying reinforcing material, with and without coating, using inhibitors in admixture or using ultimate stainless steels as reinforcing bars.

About the author:
Professor AS Khanna, Chairman, SSPC India, retired as a professor from IIT-Bombay after 27 years of teaching and research, guiding 27 PhDs, 125 master’s and creating research expertise in high-temperature corrosion, coatings, surface engineering and corrosion of concrete structures. He has won several international awards such as the Humboldt Fellowship from Germany, the Royal Norwegian Fellowship and Fellowship of the Japan Key Centre, and has also worked as visiting professor in Germany and France. He is a coating expert and is associated with Hindustan Zinc for several assignments related to galvanization and its applications.

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