Cement Materials

THE hydraulic properties exhibited by the calcination products of certain limestones were recognized at an early datemore than 2000 years ago. It was known that calcined limestone with the addition of other minerals would react with water and produce an insoluble and stable product. This material could be cast in desired forms or could be used as a cement for the unification of other materials in large masses or for bonding brick or masonry structures. Cements are essentially mineral glues and it is their ability to unify other materials plus their fluidity when first mixed with water, enabling the mass to assume any desired shape, that has made them so extraordinarily useful to modern industry. Like other glues, cements do not exhibit their maximum strength when used alone and only when mixed with proper aggregates do their optimum properties appear. The resulting concrete, a mixture of cement, mineral aggregates and frequently of reinforcing steel, exhibits the most desirable properties of the individual constituents with regard to tensile strength, stability and permanence. The speed with which such mixtures can be -prepared and installed in place with mechanical equipment has facilitated their adoption by the engineering profession concerned with the construction industries. The development and application of improved methods of manufacture have resulted in such economies that the finished product can be sold at a remarkably low price. In addition, the necessary raw materials are of such common occurrence and wide geographic distribution that the manufacture of cement was established in 34 of the 48 states by 1946. Plants under construction will add to this number. In recent years the industry has been characterized by the development of a number of new cements designed to possess special properties essential for use in unusual environments. These have introduced the use of some new raw materials and also have complicated the processes of manufacture. In the following pages, the major varieties of cement of commercial importance are treated in the chronological order of their appearance on the market.