The influence of aluminum additive on the α-C2S hydrate formation process

The influence of aluminum additive on the formation of alpha-C2SH and on kinetics of cementitious binder material at early stages of hydration was determined. alpha-C2SH was synthesized in the primary mixtures with CaO/(SiO2 + Al2O3) = 1.5 and Al2O3/(SiO2 + Al2O3) = 0; 0.025 and 0.05. The hydrothermal synthesis has been carried out in unstirred suspensions under saturated steam pressure in argon atmosphere at 175 A degrees C temperature for 4, 8;,16, 24, 48 and 72 h by applying extra argon gas (10 bar). It was determined that in CaO-SiO2 center dot nH(2)O-H2O suspensions within 4 h dicalcium silicate hydrates-alpha-C2S hydrate, C-S-H(II) and a low base semi-crystalline C-S-H(I) type calcium silicate hydrate-were formed. Meanwhile, Al2O3 additive changes the formation mechanism of synthesis products as well as their stability during the isothermal curing. It was observed that hydrogarnets formed after 4 h of hydrothermal treatment remained stable under all experimental conditions. It was determined that the addition of alpha-C2SH-Al in BM sample changed both the heat flow and the total quantity of heat released during early-stage hydration. It was determined that only 5 % of quartz reacts during the first 4.5 h of hydration in both BM samples, and the further reduction of its quantity depends on duration of process. The products of synthesis and hardening were characterized by simultaneous thermal analysis, microcalorimetry and X-ray diffraction analysis.