Model synthetic pastes for low pH cements

• Published in: Cement and concrete research 2020-10, Vol.136, p.106168, Article 106168
• Main Authors: Kangni-Foli, E., Poyet, S., Le Bescop, P., Charpentier, T., Bernachy-Barbé, F., Dauzères, A., L'Hôpital, E., Neji, M., d'Espinose de Lacaillerie, J.-B.
• Format: Article
• Language: English
• Subjects: Calcium; Calcium-silicate-hydrate (C-S-H); Chemical Sciences; Material chemistry; Microstructure; Mineralogy; Model pastes; Pastes; Portland cements; Ratios; Silicon dioxide; Superplasticizers; Tricalcium silicate; Workability
• ISSN: 0008-8846; 1873-3948
• DOI: 10.1016/j.cemconres.2020.106168

Model synthetic pastes were designed to obtain a simplified silica system that could be used in durability studies on materials with low calcium-to-silica ratios. The synthetic pastes made use of the well-known pozzolanic reaction between tricalcium silicate (C3S) and nanosilica, covering calcium-to-silica ratios (C/S) from 0.8 to 3.0. The pure C3S paste (C/S = 3.0) contained C-S-H and portlandite, while pastes with C/S < 1.4 only included C-S-H. The pore solution pH directly correlated with the C/S ratio. The synthetic pastes demonstrated a mineralogy, a C-S-H structure, a mean chain length and pore network features that were similar to ordinary Portland cement (OPC) and low-pH materials, depending on their C/S ratios. The main shortcomings were: (1) high water-to-binder ratio and high superplasticizer dosage to maintain the workability of the synthetic pastes of low C/S ratios and (2) significant cracking of the pastes of low C/S ratios.