Carbonation process in cement with mineral additions of natural zeolite and silica fume – Early hydration period (minutes) up to 24 hours

Abstract The carbonation of cement with additions of clinoptilolite and silica fume during the first minutes up to the 24th h of hydration is studied. The crystallization of calcite on the surface proceeds directly between the calcium ions from the solution and CO 2 from air without formation of portlandite and ettringite. The crystallite size of calcite up to 120 min is about 50–60 nm and then to 480 min it lowers (20–30 nm). The mixture with clinoptilolite displays slowed process of gypsum dissolution. The thermal reactions in the range 480–700 °C are related to dehydration–decarbonation of the unstable, imperfectly crystallized Ca-carbonates. In the range 700–850 °C the main event is decomposition of stable carbonate phases.