GB711143A - Expanded constructional cements and plasters - Google Patents

Abstract

In a process for the production of a set, expanded constructional cement or plaster by the reaction, in situ, of aluminium powder and aqueous mild alkali, the expansion is effected in the presence of less than 1 per cent. by weight of a water-soluble lower aliphatic alcohol, preferably methanol or ethanol. Ferric oxide and powdered chalk may also be added to promote and enhance the expansion. When considerable expansion is desired additional lime may be incorporated if the free lime content of Portland cement is insufficient for reaction with the large amount, e.g. 4-8 per cent. of aluminium used. For preformed reinforced structural building units 1/4 to 1/2 per cent. of aluminium based on Portland cement is used and a mixing time of about 2 minutes with the mixing water at 75-80 DEG C. is employed. Alternatively substantial quantities, e.g. 4-6 per cent. of aluminium powder together with ferric oxide and alkali catalyst may be incorporated with Portland cement and the mixing continued for a sufficient time, e.g. 5-8 minutes to degasify the mixture thereby producing a material of density similar to that obtained with only 1/4 to 1/2 per cent. of aluminium but with greatly reduced free lime content and correspondingly improved quality. Known additives such as do not interfere chemically with the expansion process, e.g. bentonite, pigments, fillers such as cork, asbestos, woodwool, stone, sand, aggregate, sawdust, pumice and crushed concrete, and reinforcements such as steel wire or aluminium or aluminium alloy strip together with gypsum and other plasters and aluminous cements may also be incorporated. The cement mix may be used in situ or prefabricated and in cases where the lime content is very low may be formed into heat-radiating or surface combustion elements, thus it may be cast about an electric filament. In an example 20 ozs. of Chinnor cement 0.5 oz. of powdered aluminium and 0.05 oz. of ferric oxide powder are mixed with 350 ml. of water at 75 DEG C. to which has been added to 5 ml. of diluted aqueous mixture formed by adding 6.4 ml. of a 4 per cent. by weight aqueous solution of barium hydroxide or borax through 1 ml. of methanol or ethanol diluted with 20 times its volume of water, and the mixture is worked for 4 minutes. An expanded concrete of large cell size and a heat regeneration of 2 DEG C. after 5 hours is obtained.