Thermal Decomposition of Tricalcium Silicate Hydrate

Abstract

C,SH,, can be prepared in stirred suspensions using lime and silicic acid with CdSi = 3.0 for 14 days at 270°C under saturated steam pressure. The C,SH,,5 which forms consists of long, fibrous or prismatic aggregates having a specific surface area of 14.0 m'/g. The specimen gives an average CdSi ratio of 2.98 (29 crystals) and lattice parameters of a = 1.00291(8) nm and c = 0.74842(11) nm by ATEM and XRD examinations, respectively. NMR examination confirms the existence of dimer silicate anions in C,SH,,s, suggesting the possible composition Ca,(Si,O,)(OH),. Upon being heated, C,SH,,5 dehydrates at 520-550°C with a sharp endothermy and decomposes to CaO plus a calciochondrodite-like phase, which on further heating dissociates, with a gradual weight loss, to a;-C,S with CaO at 800°C. The intermediate calciochondrodite-like phase has low crystallinity, but zgSi MAS NMR and infrared spectra identical for highly crystalline calciochondrodite. CPMAS measurements indicate the possibility that the calciochondrodite-like phase contains both protonated and unprotonated monosilicate anions. The amount of CaO which forms through the two-step process agrees with the calculated values from the stoichiometry of decomposition: [Ca,(Si,O,)(OH),] + [Ca,(SiO,),(OH),] + CaO + 2H,O + a;-(Ca,(SiO,) + 2Ca0 + H,O.

Preparation of a Novel Cementitious Material from Hydrothermally Synthesized C–S–H Phases

“…The hydrogen‐bonding system interconnects the isolated SiO 4 tetrahedra in a chain‐like pattern along the b ‐axis of α‐C 2 SH . In addition, weak bands typical for ν 1 ‐OH of Ca(OH) 2 and jaffeite could be resolved at 3643 cm −1 and 3624–3607 cm −1 , respectively . In the ground samples (ESMRT‐ESM500), there were additional bands at 694, 778, 798, 1096, and 1172 cm −1 assigned to quartz.…”

“…The sample HP showed the typical bands for α‐C 2 SH [and references therein] at 675, 709 (OH–(Ca) librations), 757 (ν 1 ‐Si–O(H)), 863, 943, 984 (Si–O stretching in SiO 4 tetrahedra), and 1281 cm −1 (δ‐OH). In addition, there were bands at 830 cm −1 and 1054 cm −1 belonging to jaffeite . The OH range was characterized by the sharp band at 3537 cm −1 (ν 1 ‐OH, α‐C 2 SH) and the broad bands centered at 2450 cm −1 and 2850 cm −1 , typical for OH stretching of hydroxyl involved in strong H‐bonding.…”