ABSTRACT
Durability can be defined as the ability of a material to remain serviceable for at least the required lifetime of the structure of which it forms a part. Degradation can result from either the environment to which the concrete is exposed, for example, frost damage, or from internal causes within the concrete, as in alkali–aggregate reaction (AAR). The rate of most of the degradation processes is controlled by the rate at which moisture, air or other aggressive agents can penetrate the concrete. Hardened cement paste (hcp) and concrete contain pores of varying types and sizes, and therefore the transport of materials through concrete can be considered as a particular case of the more general phenomenon of flow through a porous medium. Different mechanisms will apply in different exposure conditions. A controlled amount of calcium sulphate, in the form of gypsum, is added to Portland cement during its manufacture to control the setting process.
