Corrosion Preventive Methods Adopted for Concrete Bridges During Construction

Dr. V.V.L. Kanta Rao, Principal Scientist, Bridges and Structures Division, CSIR-Central Road Research Institute, New Delhi

Deformed carbon steel reinforcement bar is most vulnerable to corrosion. Corrosion of reinforcement results in cracking of concrete and loss of structural capacity. The corrosion of steel reinforcement in concrete structures, including bridges, is caused due to chlorides and atmospheric carbon dioxide. The concretes with high permeability allow easy passage of the chlorides and carbon dioxide into it to reach steel reinforcement. Various methods are available to prevent/delay the on-set of corrosion of reinforcement. This paper discusses the common methods adopted for prevention of corrosion during construction.

Introduction
Cement concrete is a versatile building material and is the second most consumed material in the world, after water. It is made using porland cement, coarse, and fine aggregates, water and one or more admixtures. Concrete is well known for the ease with which it is made, for its ability to be moulded in any form, and its high strength. The microstructure of concrete is such that it has capillary pores to the extent of 28%, which depends upon quality of concrete and the presence of water at the time of mixing of concrete. Concrete made with low w/c ratio is dense with lower amount of pores. These pores are created due to evaporation of excess free water during strengthening of concrete mass, and a concrete made with high w/c ratio will have pores inter connected and extend deep inside the mass of concrete from its surface. More are the inter connected pores, greater is the ease with which water can flow through the concrete (i.e. high permeability).