GB833071A - Hydraulic cement and method of preparation thereof - Google Patents

Abstract

An hydraulic cement is prepared without clinkering in a process comprising grinding in the dry state a mixture of from 5 to 73,7% by weight of calcium oxide, from 1 to 94% by weight of silicon dioxide, from 1 to 94% by weight of aluminium oxide, and from 0 to 25% by weight of iron oxide, and continuing the grinding until sufficient calcium oxide has reacted with the other oxides to cause a rise in temperature of less than 20 DEG F. at three minutes after 200 grams of the ground mixture have been hydrated by mixing with 200 c.c. of water in an insulated container, the ground mixture and water being at ambient temperature when mixed, and the grinding being conducted at a temperature below the point of incipient fusion of the components of the mixture. The reaction is continued until at least 85% of the calcium oxide has reacted. The rate and extent of the reaction can be enhanced by heating the mixture during or after grinding at a temperature below that of incipient fusion. The calcium oxide may be that available commercially as quick lime or it may be obtained from limestone. Sources of silicon dioxide are sand and pozzolanic materials e.g. pumicite and fly ash, these materials, providing also a source of the other specified oxides. The aluminium oxide can be in the form of clays and shales, while sources of iron oxide are Mill scale and iron ore. The current may also contain minor amounts of other metallic oxides, e.g. manganese oxide and magnesium oxide, derived from the raw materials employed. Raw materials are selected such that at least 90% of the mixture before grinding consists of calcium oxide, silicon dioxide, aluminium oxide and iron oxide. Gypsum can be added to the mixture, before or after grinding, as a retarding agent. The cement can be mixed with water or additionally with sand and coarse aggregates in proportions of from 2 to 6 parts aggregate to one of cement. In three examples the preparation of cements from mixtures of calcium oxide with pumicite, with fly ash, and with sand and clay, is described.