A polymer of calcium aluminate and water glass as cement substitute

Abstract Calcium aluminate cement (CAC) is a suitable source of tetrahedral aluminum, which reacts with tetrahedral silicon from water glass (aqueous sodium or potassium silicate solution) in an exothermic reaction, forming inorganic polymer structures that are stable at high temperatures. All tetrahedrally configurated aluminum atoms of the various calcium aluminates tested, react with tetrahedral silicon groups to form –O–Si–O–Al–O– chains with an average Si/Al ratio near of 1. Octahedrally configurated aluminum, as in γ-Al2O3, does not react at room temperature. The sodium-to-silicate ratio of the silicate solution was measured to be 1:1, so most water glasses require activation with NaOH. The number of positive charges in the activated water glass (Na+ or K+ ions) corresponds to the negatively charged AlIV centers of the CACs, suggesting a sodium-to-aluminum ratio of 1:1. The polymer hardens at temperatures between 4 and 65 °C. The workability is identical to that of ordinary Portland cement (OPC) and enables concrete structures to be cast at room temperature without additional energy supply. The new polymer has the potential to completely replace OPC in all its applications, but can reduce annual CO2 emissions from OPC production worldwide from the current 8% to less than 2%.