15. Cement and related products
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 example, hydrated calcium silicate (see Text Box 15.1) in hardened Portland cement has a layered structure which is analogous, at the nanometre scale, to that of phyllosilicate clays. Perhaps this is not surprising, because for economic and practical reasons the most commonly available minerals (i.e. those containing oxides of calcium, aluminium, iron and silicon) have been quarried as raw materials to make cement in the first place. We can view cement technology as a method of treating natural rock, so that it can be broken down, moulded into any desired shape, and then re-hardened to give useful artefacts.
Figures & Tables
Clay Materials Used in Construction
Concluding the trilogy on geological materials in construction by specially convened Geological Society working parties, this authoritative volume reviews many uses of clays, ranginf from simple fills to manufactured products. Comprehensive and international coverage is achieved by an expert team, including geologists, engineers and architects, who met over six years to produce the book. Packed with information prepared for a wide readership, this unique handbook is also copiously illustrated. The volume is dedicated to the memory of Professor Sir Alec Skempton.
Various definitions of ‘clay’ are explored. Clay mineralogy is described, plust the geological formation of clay deposits and their fundamental materials properties. World and British clay deposits are reviewed. New compositional data are provided for clay informations throughout the British stratigraphic column. Investigate techniques and interpretation are considered, ranging from site exploration to laboratory asessment of composition and engineering performance.
Major civil engineering applications are addressed, including earthworks, earthmoving and specialized roles utilizing clays. Traditional earthen building is included and shown to dominate construction in places. Clay-based construction materials are detailed, including bricks, ceramics and cements. The volume also includes a comprehensive glossary.