HYDRAULIC BINDERS FOR CEMENTS, COMPRISING AT LEAST SEVENTY PERCENT ETTRINGITE

摘要

A process is disclosed for the formation of hydraulic binders and building elements comprising from 70% ettringite and up to 30% calcium silicate hydrates. Ettringite is a very strong mineral and the product may be at least the equal in terms of mechanical properties of Portland cement while suffering shrinkage and expansion problems. The process comprises mixing powdered source materials of reactive CaSO4, CaO and Al2O3 with or without SiO2 and hydrating the intimate mixture at a ratio in the range of l part powdered source materials to 0.35-l part water. Most conveniently, impure source materials such as industrial by-products are used as they have been found to catalyse the hydration reaction. Further if gypsum is a powdered source material, in a natural, pure or chemical form, it is preferably calcined since such material sets quickly and gives early mechanical strength. A clinker of calcium sulphoaluminate may be produced for use as a powdered source material.