Model synthetic pastes for low pH cements

Abstract : 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.