Properties and microstructure of CO2 surface treated cement mortars with subsequent lime-saturated water curing

Previous study has shown that CO2 surface treatment can provide significant protective effects on cement mortar at early ages. This study examines the compressive strength, water permeability, water-vapor transmission and chloride migration of mortars after CO2 surface treatment with subsequent lime water curing. Thermogravimetric analysis (TGA), Fourier Transform Infrared Spectroscopy (FTIR), and Environmental Scanning Electron Microscope (ESEM) combined with Energy Dispersive X-ray Spectroscopy (EDS) analysis were also employed to investigate the underlying microstructure and mechanisms. Results showed that combined effect of CO2 surface treatment and subsequent lime-water curing showed a slight effect on compressive strength, but a significant effect on the impermeability of the mortar. The effect on impermeability increased and calcium carbonate formed during the CO2 surface treatment transformed from amorphous to crystallized form as subsequent the lime water curing period was prolonged. Furthermore, the formation of more C-S-H was observed owing to the hydration of uncarbonated calcium silicates in cement clinker and the reactions of the silica gel from CO2 surface treatment and Ca(OH)(2) from the hydration of uncarbonated calcium silicates.