Synchrotron X-ray Raman scattering shows the changes of the Ca environment in C-S-H exposed to high pressure

Abstract X-ray Raman Scattering (XRS) is a new probe to analyze the local chemical environment of elements of interest. In this communication, XRS is, for the first time, used in the field of cement study. In situ high-pressure XRS (HP-XRS) at Ca L2,3-edge was used to examine the pressure-induced change of Ca environment of C-S-H under a loading/unloading cycle of combined deviatoric stress and hydrostatic pressure up to 20 GPa. The peak positions of the Ca L2,3-edge systematically shifted to lower energies upon loading, suggesting a shortening of the Ca O bonds. The peak positions of the Ca L2,3-edge shifted to higher energies upon unloading, but permanent shifts in edge positions were observed after unloading to 0 GPa, suggesting a permanent deformation mainly due to a distortion in the interlayer Ca and a sliding at interlayer region. For the first time, the pressure-induced structural change of C-S-H is evidenced at the atomic scale.