15.1 Introduction 15.1.1. What is cement? This review discusses the important role played by clay minerals in the manufacture and use of cement. The word ‘cement’ is generic and has a very broad meaning, but we are concerned here with those inorganic cements which find large-scale use in the construction industry. All types of cement as defined above share certain similarities in the ways they are utilized. Thus, to prepare it for use the dry cement powder is mixed with water and other chemicals(admixtures),converting it into a pourable liquid, a soft gel, a plastic mass, or a damp granular solid. It is important that the soft mixture can easily be moulded, and that it subsequently sets in a reasonable time. Final curing normally occurs over a longer timescale, to give a product with the required degree of hardness and durability. The mechanism of setting and curing involves hydrolysis and hydration reactions, in which the cement reacts with some of the mixing water to give new chemical compounds which take the form of interlocking crystals. The structure becomes mechanically rigid and strong, due to the interlocking. Cured cement can be used as a construction material in its own right, or as an adhesive which bind aggregate particles together to form concrete or mortar. This is illustrated by two examples, one a simple compound, the other a complex mixture of compounds of variable composition (see the Text Box below) The chemical structure of cured cement can be compared to that of certain aluminosilicate rocks which occur naturally. For