Damage due to freeze-thaw
Water held in the pores of cement paste will freeze at low temperatures. Ice occupies a bigger volume than water so expansive forces can be generated if the pores are nearly full of water at the time of freezing, i.e. if the concrete is saturated. Damage occurs when the expansive pressure generated by freezing is greater than the local strength of the concrete.
A random pattern of cracks is formed on the surface of the concrete. The expansive pressure can result in surface scaling or disintegration to the depth to which freezing conditions have penetrated. Cycles of freezing and thawing result in progressively deeper damage.
Freezing of water in coarse aggregate particles can also disrupt the concrete. If the particle is close to the surface, the thin layer of paste between the aggregate and the surface is pushed off and the result is a ‘pop-out’. This type of deterioration will occur only if the aggregate is almost fully saturated.