α-C2SH synthesis in the mixtures with CaO/SiO2 = 1.5 and application as a precursor for binder material

Abstract

The parameters of-C2SH hydrothermal synthesis (4-72 h; 200 C) from a non-stoichiometric composition (CaO/SiO 2 = 1.5) of CaO and SiO 2 .nH 2 O mixture were determined, and a sequence of intermediary compound formation was examined and explained. It was estimated that in the synthesis products,-C 2 SH dominates at 200 C after 8 to 24 h. When duration of hydrothermal treatment was shorter-C-S-H(I) and C-S-H(II), as longer-kilchoanite, prevail in the products. Also, the hydration and strength properties of the binder material created on-C 2 SH basis were determined. The binder material was prepared by mixing-C2SH and quartz sand (1:1 by mass). Later on, sample was ground at 950 rpm for 4 min and burned at 450 C for 30 min under air atmosphere. It was determined that calorimetric curve of created binder material di ers from the one of ordinary cements as it involves only the three exothermic reactions and the amount of total cumulative heat grows with the increasing hydration time. As expected, the tendency of strength increment was observed after 7-28 days of hardening: Compressive strength increased to 15.5 and 24.0 MPa, respectively. The products of synthesis and hardening were characterized by XRD, FT-IR, and STA analyses.

Influence of Cr3+, Co2+ and Cu2+ on the formation of calcium silicates hydrates under hydrothermal conditions at 200 °C

“…The previous results were confirmed by a Simultaneous Thermal Analysis: a broad endothermic effect at 84°C temperature can be assigned to the removal of chemically bound water in semicrystalline or amorphous CSH [45][46][47] (Figure 3). Since the results of XRD do not showed the formation of crystalline compounds in CaO-SiO 2 -Al 2 O 3 -Cr(NO 3 ) 3 -H 2 O system (except calcium carbonate), the effect at 272°C temperature can be attributed to the decomposition of low crystallinity compounds (CAH, CASH or compounds containing nitrate anion) [46,48] as well as to Cr 3+ oxidation to Cr 6+ (chromates formation) [49].…”