Nature of C-S-H in 20 year old neat ordinary Portland cement and 10 percent Portland cement-90 percent ground granulated blast furnace slag pastes

摘要

The purpose of this study was to investigate the effects of age on calcium silicate hydrate (C-S-H) present in two cement pastes: one in which the C-S-H at a younger age had a high Ca/Si ratio and another that had a low ratio. The study involved characterising a 20 year old neat ordinary Portland cement (OPC) paste (high Ca/Si) and a blend of the OPC with 90 percent ground granulated blast furnace slag (GGBS; low Ca/Si); the results are compared with data on the same mixes at 14 months old. The morphology of the outer product (Op) C-S-H in the blend was essentially the same as at 14 months, whereas that in the neat OPC paste appeared to be finer. The mean aluminosilicate chain length of the C-S-H was considerably longer in both pastes than in similar systems at younger ages. The chemical composition of the C-S-H in both pastes was significantly different than at 14 months: in the neat OPC paste, the Ca/Si ratio of the outer product C-S-H had increased with age, whereas that of the inner product C-S-H had decreased; the Ca/Si ratio of Op C-S-H in the blended paste had decreased with age. An entirely tobermorite based nanostructural model can account for the data for the C-S-H in the blend, whereas the data for the neat paste require some jennite or calcium hydroxide based structure; the distribution of the TEM-EDX analyses favours the T/CH model.