ABSTRACT
The areas around aggregate in cement paste, which are looser and greater in pore numbers and sizes, are called "transition zone" or "interfacial transition zone (ITZ)". It is assumed that the ITZ has such a structure as described below [1]: plates of calcium hydroxide, Ca(OH)2, are crystallized like "card house", and the spaces between them are not completely filled with hydrates, thus making larger and greater volume of capillary pores than the bulk region. It is regarded that the existence of the ITZ around aggregate is the cause of the weaker strength of mortar and concrete than cement paste, and that aggressive agents, which influence durability of these cementitious materials, penetrate toward the inside of these materials through the porous ITZ.
