Cement Raw Materials, Natural

rocks that contain the proper proportions of CaO, SiO₂, Al₂O₃, and FeO, which are responsible for the basic properties of cement. Marls that contain 40–44 percent CaO meet these conditions most fully; the composition of marls with a higher or lower CaO content must be modified. Deposits of high-quality marls are fairly scarce in the USSR, and most Soviet plants therefore use a mixture of calcareous and argillaceous rocks. Limestones, chalk, and occasionally marbles, marls, travertine, and similar rocks are used as the basic calcareous component. The argillaceous component is usually in the form of easily melted clays and loams, or occasionally argillaceous schists, argillites, loess, and similar materials. When necessary, supplements are added to the raw material mixture. They fall into three categories: siliceous (quartz sands, opoka, and di-atomite), aluminous (bauxites, low-iron high-alumina clays), and iron-bearing (rich iron ores).

In the USSR, major deposits of cement marls are worked near the city of Novorossiisk and in Donetsk and Voronezh oblasts. Limestone deposits are worked in the Urals and the Soviet Far East; chalk is mined in the Volga Region and in Briansk, Belgorod, Kharkov, and Donetsk oblasts; and marble is quarried in Irkutsk Oblast.

Quality requirements for cement raw materials are regulated by the 1969 document “Technical Specifications for the Quality of the Primary Types of Raw Materials for the Production of Portland Cement Clinker.” In order to improve the properties of the cement, up to 5–7 percent gypsum (following All-Union State Standard 4013–61) and up to 15 percent natural active mineral admixtures are added during grinding. The latter include sedimentary rocks, such as diatomites, tripoli, and opokas (with deposits in the central regions of the European part of the RSFSR and in the Ukraine, the Urals, and western Kazakhstan), and volcanic rocks, such as tuffs, tuff lavas, volcanic ash, and pumice (with deposits in the Soviet Far East, Kazakhstan, Transcaucasia, and Transcarpathia). Gliezhi—naturally burned clay rocks found in deposits in Middle Asia and Western and Eastern Siberia—may also be used. Quality requirements for active mineral admixtures are specified by OST 21–9–74 Sectorial Standard of the All-Union Committee on Standardization of the Ministry of Building Materials of the USSR.

Abroad the largest deposits of cement raw materials are found in the USA, Canada, France, the Federal Republic of Germany, the German Democratic Republic, Poland, Czechoslovakia, and the People’s Republic of China.