Confocal Raman microscopy as a non-destructive tool to study microstructure of hydrating cementitious materials

Non-destructive investigation of hydrated cement microstructure is still a big challenge. In this study, we present non-destructive image and structural analysis of hydrated monoclinic C3S clinker by means of confocal Raman microscopy (CRM), which to the best of our knowledge is used for studying hydrating cementitious systems for the first time. In detail, CRM enabled structural and spatial characterization of calcium-silicate-hydrate phases (C-S-H), portlandite (CH) and reactants on the micrometer scale without the need for extensive sample preparation. Two complementary data analysis tools (cluster analysis and graph basis analysis) revealed that m-C3S can be fully or partly hydrated to C-S-H as the ubiquitous phase. Furthermore, CH could be identified as macroscopic flakes of different size as well as intimately mixed with the C-S-H phase on a sub-micrometer scale. In addition, good quality Raman spectra of non-synthetic C-S-H, containing rarely reported lattice vibrations at ~ 130 cm− 1 and other characteristic Raman bands, are reported over a broad spectral range from around 100 up to 3700 cm− 1. Hence, this study introduces CRM as a promising novel technique for microstructural characterization of hydrating cementitious pastes.Cement chemistry notation: C: CaO, S: SiO2, H: H2O