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SUSTAINABILITY Reinventing Civil Structures With Stainless Steel Reinforcement Bars

October 20, 2018

India has over 7500 km of vast coast line surrounded by Indian Ocean in the southern edge, facing Arabian Sea in the west side, and Bay of Bengal in the east. Concrete structures in the Indian peninsula are unceasingly exposed to marine environment, enhancing the risk of corrosion in the reinforcing bars used in reinforced cement concrete (RCC) structures. This becomes a cause of great concern, as these structures are vulnerable to encounter high maintenance costs, and sometimes, inevitable accidents.

The prime reason for such quick deterioration of reinforced concrete is corrosion of the carbon steel reinforcing bars. Though, initially when steel bars are reinforced, they do not corrode. This is because the concrete aggregate consists of oxides of calcium with alkaline condition (pH between 10-12.5). The steel forms a passive layer under oxide film and hence does not corrode. However, with the passage of time, moisture (from rain or high humid conditions) and pollutants, such as chlorides (from coastal environment), and carbon dioxide and sulphur dioxide (from urban environment), penetrate through the concrete cover and reduce pH below 10, leading to initiation of corrosion process in the bars. This leads to stress generation, which in-turn forms a pin-hole, followed by small cracks, and finally to plaster spallation exposing the rebars, as shown below.

Untimely wear and tear of concrete infrastructure due to corrosion, especially along the coastline, is a major economical and technical challenge for civil engineers across the world. Stainless steel reinforcing bars have proven to be the best solution under such an extreme environment. They provide structural strength, defy corrosion, and offer a long-term solution for infrastructure and construction segment. The stainless steel reinforcement bars can be used for highway bridge decks, overpasses, tunnels, marine structures and restoration work where corrosive conditions can cause premature failure of structures made with carbon steel reinforced bars. Stainless steel rebars have several advantages over traditional methods as these are corrosion resistant, easy to install, fire resistant, and allow thinner concrete cover. Analysis by International Stainless Steel Forum shows, stainless steel rebars can sustain with the design life of structures up to 125 years. When LCC (life cycle cost) is calculated using stainless steel rebar, it is very cost effective as repair work becomes necessary for carbon steel reinforced structures earlier in the cycle.

An example to emphasize the choice of stainless steel for improving the life cycle of RCC structures is that of Progreso Pier in Mexico. It is the first concrete structure in the world built with nickel-containing stainless steel reinforcement. Despite the relatively poor grade of concrete used, the pier has withstood the harsh marine environment and has been in continuous service for over 70 years without any major repair or routine maintenance activities. On the contrary, a neighbouring pier located just 200 meters to the west of the Progreso Pier has now deteriorated columns and the superstructure almost entirely vanished, despite being twenty years younger. The newer pier was built with carbon steel rebar.

About ISSDA

Established in 1989 by leading stainless steel producers, Indian Stainless Steel Development Association (ISSDA) was formed with the explicit objective of diversifying the applications of stainless steel in India and increasing usage volumes in the country. At the point of formation of ISSDA, the main visible application in daily life was essentially household kitchenware which has now diversified significantly. Through the focused efforts of ISSDA and its member companies, the widespread and visible use of stainless steel in different walks of life is all too evident, especially in the Architecture, Building & Construction (ABC) and the Automotive, Railway and Transportation (ART) sectors. The technical strength of ISSDA is derived from its close association with the NICKEL INSTITUTE, the International Stainless Steel Forum and close collaboration with more than 20 national stainless steel development associations (SSDAs) around the world.

 

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