Analysis on microstructure of calcium silicate hydrate by XAFS

Tobermorite is an important crystal phase of autoclaved aerated light-weight concrete (ALC) and amorphous calcium silicate hydrate (C-S-H) is a main hydration production in concrete. These microstructures were investigated by XAFS (X-ray Absorption Fine Structure), particularly XANES (X-ray Absorption Near Edge Structure) spectra. It was found that the absorption energy of main peak for the XANES spectra of α-quartz and phyllosilicate minerals changes with SiO₄ binding mode and that it is nearly linearly related to the Si ls binding energy in XPSs. In the XANES spectra of α-quartz and natural tobermorite, the main absorbance energy decreased in the order of α-quartz, 1.1 nm tobermorite, and 1.4 nm tobermorite, corresponding to changes in the binding mode of SiO₄ tetrahedron with Q₄, mixed Q₃-Q₂, and Q₂. Moreover, the width of the main peak was increased in the above order, which was considered to correspond to the structural regularity (crystallinity). In the XANES spectra of C-S-H as a low crystalline calcium silicate hydrate, it was found that the absorbed energy of the main peak decreased, and the peak width increased with increase of Ca/Si molar ratio. It is attributed to the decrease in the degree of polymerization of SiO₄ tetrahedron with increase of Ca/Si molar ratios. (author)