Thermal stability of C-S-H phases and applicability of Richardson and Groves' and Richardson C-(A)-S-H(I) models to synthetic C-S-H

• Published in: Cement and concrete research Vol. 93; pp. 45 - 56
• Main Authors: Tajuelo Rodriguez, Elena, Garbev, Krassimir, Merz, Daniela, Black, Leon, Richardson, Ian G.
• Format: Journal Article
• Language: English
• Published: Elmsford Elsevier Ltd 01-03-2017; Elsevier BV
• Subjects: A. Calorimetry; B. Calcium silicate hydrate (C-S-H); B. Spectroscopy; B. Thermal analysis; B. X-ray diffraction; Bulk sampling; Dicalcium silicate; Heating; Thermal stability; Transformations; Weight loss; Wollastonite; B. X-ray diffraction; B. Spectroscopy; A. Calorimetry; B. Calcium silicate hydrate (C-S-H); B. Thermal analysis
• ISSN: 0008-8846; 1873-3948
• DOI: 10.1016/j.cemconres.2016.12.005

Synthetic C-S-H samples prepared with bulk C/S ratios from 0.75 to 1.5 were analyzed by coupled TG/DSC/FTIR and in-situ XRD while heating, in order to correlate observed weight loss curves with the kinetics of evolved gases, and to investigate the transformations C-S-H→β-wollastonite→α-wollastonite. The temperature of the transformation to β-wollastonite increased with increasing C/S. The temperature for the transformation from β- to α-wollastonite meanwhile decreased with increasing C/S; indicating that excess CaO stabilized the α-polymorph. The transformation C-S-H→β-wollastonite was accompanied by the formation of α′LC2S for C/S>1. In the case of C-S-H with C/S=1.5, both β-C2S and rankinite were formed and then decomposed before the transformation to β-wollastonite and α′LC2S. C-S-H with low C/S was found to be more stable upon heating. The chemical structural models of Richardson and Groves' and Richardson C-A-S-H(I) were used to obtain the structural-chemical formulae.