In any concrete structure that is exposed to atmosphere, the surface of concrete comes in contact with Carbon-di- oxide present in the atmosphere. The calcium present in the cement concrete will react with Carbon-di-oxide forming calcium
carbonate resulting in reduction of alkalinity in concrete. Whenever, the concrete is dense and impervious to atmo- spheric agents, the carbonation will be restricted to surface only. However, if the concrete is pervious, the carbonation reaction continues inwards and reaches the concrete sur- rounding the