From the perspective of effective utilization of resources and environmental preservation, carbonation of waste hydrated cement paste (abbr.whcp) is a promising and environmentally beneficial application.Greenhouse gas CO2 can be captured, whcp can be reused, and building materials with excellent performance can be produced.In order to explore the accelerated carbonation mechanism of whcp, calcium silicate hydrate(C-S-H), the most dominant phase, with calcium to silicate ratio of 1.50 was synthesized and were exposed to CO2 for accelerated carbonation.A certain amount of water was mixed with dry powder homogeneously.The wet mixture was casted into a cylindrical stainless steel mold and compacted at 8.0 MPa and then the compacts were cured in a sealed chamber to initiate the carbonation reaction,where CO2 of 99.9% mass purity was injected into the chamber and the CO2 partial pressure was regulated at a constant of 0.2 MPa for different time in case of CO2 starvation.The carbonation degree was calculated by TG/DSC and the microstructure changes of C-S-H before and after accelerated carbonation were investigated with SEM, XRD, FT-IR and Nitrogen physisorption analysis.The results show that calcium silicate hydrate with a formula of C1.36SH1.35 was obtained.Carbonation degree reached more than 70% after carbonated for 2h.In the carbonation process the layer structure of C-S-H was destroyed, silica gel with more polymerization formed and calcium carbonate stacked together.Calcite, vaterite and aragonite exist in the carbonation products.The more polymerized silica gel makes the specific surface area and pore structure showed significant changes.