Effects of CO2 surface treatment on strength and permeability of one-day-aged cement mortar

Many of the degradation problems of concrete can be attributed to the weak surface layer. Surface treatment of concrete has been proven a simple and effective method to enhance the durability of concrete. In the present study, two series of portland cement mortar specimens with w/c ratios of 0.4 and 0.3 were prepared. CO2 treatment was applied to he mortars 24 h after casting. The results indicated that CO2 treatment resulted a carbonated a layer of less than 1.6 mm in thickness, slightly increased compressive strength, but significantly reduced the water permeability, water-vapor transmission and chloride migration of the mortars. Environmental Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FT-IR) Spectroscopy and thermogravimetric analysis (TGA) results indicated that calcium silicate hydrate with low Ca/Si ratio and CaCO3 were the products in the carbonated surface layer.