Title : DURABILITY PROVISIONS IN CODES FOR CONCRETE RAIL AND ROAD BRIDGES IN INDIA
Authors : Ajoy K.Mullick
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Price : 250
Abstract : Indian Roads Congress (IRC) Codes of Practice for reinforced and prestressed concrete bridges (IRC: 18 and IRC: 21) have recently been revised, with greater emphasis on durability and service life. The approach to durability design and provisions for 100 years’ service life in the revised Code (IRC: 112 – 2011) are described in the paper. Relevant provisions in Indian Railways Code for Concrete Rail Bridges (IRS Concrete Bridge Code) are also discussed. Although various mechanisms of deterioration of concrete are taken note of in both the Codes, primacy of corrosion of steel due to carbonation and chloride ingress are recognized. The exposure conditions are classified, depending upon the chances of carbonation taking place and availability of chloride ions. All mechanisms of chemical attack are dependent upon fluid transport into concrete. Defence against corrosion is sought in terms of appropriate combination of cover thickness and effective chloride diffusion coefficient dependant on water/binder ratio and type of binders, following Fick’s second law of diffusion. The use of the concept is elucidated by examples of bridge pier in chloride-environment, which also helps in calibration of the provisions of cover and w/b ratio in the Code for different exposure conditions. New provisions of use of stainless steel reinforcement or controlled permeability formwork are described. For other mechanisms of attack, requirements are in terms of cement types (e.g. sulphate attack) and aggregates (e.g. ASR) or chemical admixtures (e.g. AEA for freeze thaw), which are briefly explained.