Supercritical carbonation of Portland cement binders was studied to analyse the influence of the type of cement on carbonation at high CO2 pressures (CO2 at 20 MPa and 318 K) and to improve the understanding of the effects on the microstructure and physicochemical properties of binders. The results were compared with those obtained in a natural exposure. Microstructural properties of supercritically and atmospherically carbonated Portland cement binders were examined using the complementary analytical techniques of FTIR, TG-DTA, and BSEM-EDX. Supercritically carbonated binders showed a microstructure based on a more polymerized and lower Ca form of CSH gel, formed by decalcification of high-Ca form of CSH gel. Results suggested that during the treatment at artificially intensified conditions, the crystallized calcium carbonate came mainly from the carbonation of the CSH gel, and at atmospheric conditions, from the carbonation of the portlandite phase.