Soft X-ray Spectromicroscopic Investigation of Synthetic C-S-H and C3S Hydration Products

Abstract

Calcium silicate hydrates (C-S-H), the primary binding phase in concrete, is the most prominent physiochemical factor controlling the mechanical and chemical properties in the production of concrete. This paper reports the local-binding structure and morphological details of C-S-H as determined by high-resolution X-ray spectromicroscopy. Hydrated tricalcium silicate (C3S) was used to determine the properties and role of the outer products (Op) of C3S. C-S-H with different molar ratios of Ca/Si, were synthesized (Syn-CSH) to quantitatively evaluate the effect of silicate polymerization on Ca L and Si K edge of C-S-H. Near edge X-ray absorption fine structure (NEXAFS) spectroscopy of Syn-CSH showed no variation in peak positions and energy separation for CaLIII, II edge for the Ca/Si ratios investigated. Compared to Syn-CSH, C3S, when hydrated for 17d, had a similar local structure around Ca. Si K edge NEXAFS analysis on Syn-CSH showed a tendency for the peak positions of both the Si K edge and the peak induced by multiple scattering to shift to higher energy levels. The results also indicated that the distance between the two peaks increased with a decrease of the Ca/Si ratio in Syn-CSH. Silicate polymerization influenced the multiple scattering of distant shell atoms more than the binding energy of the core atoms. Op of C3S had a uniform and higher degree of silicate polymerization compared to the core area. The results imply that Op reduces the hydration process of C3S into the core area thereby playing a key role on the properties of concrete upon formation.