Wet carbonation of cementitious materials offers a pathway for carbon dioxide utilisation and the production of value-added carbonate phases, but its reaction mechanisms are difficult to follow using conventional laboratory X-ray diffraction. High water content, X-ray absorption, sample sedimentation, gas bubbling, and rapidly changing phase assemblages complicate time-resolved measurement and quantitative analysis. We developed a low-cost flat-plate solid-gas-aqueous reaction cell for in-situ transmission synchrotron powder X-ray diffraction. The cell enables carbon dioxide to be bubbled through a cementitious suspension while diffraction patterns are collected, allowing phase evolution to be monitored under active reaction conditions.
The method combines careful beam and sample-position alignment, direct-beam and cell-background measurements, transmission and geometric corrections, and sequential Rietveld refinement in TOPAS. Crystalline and non-crystalline components were modelled, with molecular-scattering-power and direct-derivation approaches explored for quantitative phase analysis. A wet carbonation experiment using dicalcium silicate in water demonstrated progressive consumption of the starting silicate and formation of calcite, together with lower levels of vaterite, aragonite, and amorphous calcium carbonate. Measurements with sarcosine also showed that additives can alter carbonate-phase development. The experiment identified continuing analytical challenges arising from bubbling-induced inhomogeneity, cell-thickness variation, beam-intensity variation, background determination, and quantification of amorphous phases. The prototype provides a practical platform for resolving solid-gas-aqueous reaction pathways and can guide future laboratory and synchrotron studies of cement carbonation and related carbon-mineralisation processes.