Corrosion of steel reinforcement bars in concrete Apr07

Corrosion of steel reinforcement bars in concrete...

Corrosion of steel reinforcement bars in concrete Reinforced concrete is a composite material comprising steel reinforcement bars embedded in a concrete mass.  Reinforcement bars carries the bulk of the tensile load and imparts a degree of cracking resistance to the concrete which itself is compressively loaded. The corrosion of steel reinforcement bars in concrete is a big universal problem. The damage which happens from corrosion may due to a large extent reduce the serviceability and structural integrity of reinforced concrete. Concrete provides stable long term corrosion protection to steel reinforcement bars because of passivation of the surface of steel by the highly alkaline property of the concrete. As long as this passivity is maintained, the corrosion of the reinforcement bars will not take place. For this the concrete should be sufficiently dense and impermeable so as not to allow transport of chlorides, carbon di oxide and oxygen. The passivation of steel reinforcement bars is deteriorates greatly due to chlorides even at high pH values. The carbon oxide in solution neutralizes the calcium hydro oxide saturated pore water (carbonation process) and lowers the pH value below the pH value at which the steel can remain passivated. Oxygen also plays a vital role in the passivation process. Whenever the reinforcement bar embedded in steel corrodes, the corrosion products increase its volume. All forms of iron oxide and hydro oxide have specific volumes greater than that of steel. The volume of the corrosion products vary by a factor which can be even more than 5 as indicated in Fig. 1. The expansive forces generated by the steel corrosion leads to tensile cracking and rust staining of the concrete. This in turn causes reduction in the serviceability and structural integrity of concrete besides affecting its aesthetics. Once the...