Tadas Dambrauskas

The Synthesis of α-C2S Hydrate Substituted with Al3+ Ions in Mixture with CaO/SiO2 = 1.75

The parameters of α-C2SH substituted with Al3+ ions hydrothermal synthesis was determined. α-C2SH was synthesized in the primary mixtures with CaO/(SiO2+Al2O3) = 1.75 and Al2O3/(SiO2+Al2O3) = 0; and 0.025. The hydrothermal synthesis has been carried out in unstirred suspensions under saturated steam pressure in argon atmosphere at 175 °C temperature for 4; 8; 16; 24; 48; 72 hours by applying extra argon gas (10 bar). It was determined that in unstirred CaO–SiO2·nH2O–H2O suspensions, the additive of Al2O3 changes the formation mechanism of synthesis products as well as their stability during the isothermal curing. It should be noted that in the mixtures with Al2O3, within 4 hours of isothermal curing at 175 °C all Al3+ ions were incorporated in the synthesis products structure. However, Al2O3 additive has negative influence on the formation of calcium silicate hydrates because even after 24 h of isothermal curing quite intensive diffraction peaks of unreacted portlandite were identified. When hydrothermal synthesis is extended to 48 hours, Ca (OH)2 fully reacted and dibasic calcium silicate hydrates start dominate in the products.