Cement prods. from calcium sulphate hemi:hydrate waste prods. - by mixing with sodium- or potassium hydroxide and sintering the mixt.

摘要

Plaster waste CaSO4.1/2H2O (I) is mixed with NaOH or KOH and sintered to give a prod. useful as an aggregate. The prod. may also be milled to a fine powder and opt. mixed with fly ash, cement, milled blast furnace slag etc. to give a prod. suitable as a substitute for cement. The milled prod. may also be mixed with additional (I) to give a granular aggregate useful in concrete and road making. Process utilises waste prod. (I) produced e.g. as a by-prod. in the prodn. of phosphoric acid or in the removal of SO2 and SO3 from flue gas. The finely milled prod. (less than 25 micron) reacts with water to give a hardened prod. similar to cement and plaster, or it may be mixed with +/- 25% milled fly ash (25 micron) and +/- 15% Portland cement to give a prod. similar to conventional cement. The portland cement may be replaced by portland clinker or milled blast furnace slag in the form of granules, cubes or fragments and heated to give a prod. suitable as an aggregate for addn. to concrete, asphalt, etc. as a replacement for gravel. The (I) may also be mixed with the cement prod. e.g. in a ratio of 1:3 and cast into small spheres or blocks and allowed to harden.