Effect of sea salt on carbonation and CO2 uptake in cement mortar

Previous studies mainly focused on the effects of concrete carbonation on chloride ion penetration due to the resulting reinforcement corrosion. However, the influence of sea salt, common in coastal areas, on the carbonation of cement-based building materials is still being determined. Thus, cement mortar samples were immersed in simulated seawater and then submitted to an accelerated carbonation test at a CO2 concentration of 5% and a relative humidity of 58%. For the samples that underwent different carbonation cycles, weight changes and carbonation depth were measured, and the associated mechanisms were demonstrated by combined thermogravimetry and differential thermal analysis (TG-DTA), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). The results showed that salt crystals do not significantly change cement mortar's pore size distribution and composition but effectively influence the carbonation rate. The carbonation rate of the cement mortar sample containing sea salt was 36 mm/year, 36.8 % lower than that of the control sample. Carbonate crystals efficiently occupy the pore volume in the size range of 0.02–0.15 0.5 μ m, significantly reducing the carbonation rate. The results can provide a research basis for estimating the carbonation rate and measuring the CO2 regions.