Existing models do not agreement on the coordination and symmetry of calcium in calcium (alumino)silicate hydrate (C-(A-)S-H) with various compositions and under different synthesis conditions. The order and symmetry of Ca contribute to the stacking sequence of layers and the inclusion of aluminum at elevated temperature forms cross-linked sites in aluminosilicate chains, which further improves the microstructure and physical properties of the hardened cement paste. The present work presents a detailed atomic and nano-scale characterization of the Al uptake in C-(A-)S-H with various Ca/Si ratios and equilibrium temperatures.<br/>The results from the Near Edge X-ray Absorption Fine Structure at Ca L3,2 edge showed that Ca in C-(A-)S-H is not octahedrally coordinated, regardless of Ca/Si, Al content, or equilibrium temperature. The crystallinity of Ca systematically increases as temperature rises. Al K edge of 4-fold coordinated Al systematically shifts to higher energy with increasing degree of polymerization. The ordering of Al in aluminosilicate chains increases with increasing quantity of 4-fold Al. The nanostructure of C-(A-)S-H was imagined by synchrotron soft x-ray ptychography with spatial resolution of ~6nm. C-(A-)S-Hs at 20°C consist of foil-fiber networks with minor changes accompanying with varying Ca/Si ratios and Al inclusion. C-(A-)S-H fibers are coarser at 80 °C and are thicker in higher Al concentration. C-S-H synthesized at 80°C contains two phases with two distinct basal spacings and orders of crystallinity.

Effect of temperature and calcium to silicon ratio on structure of calcium (alumino)silicate hydrate at atomic scale and nano scale

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.