Effect of limestone fillers on CO2 and water vapour diffusion in carbonated concrete

Replacing Portland cement clinker partially with limestone powder offers economic and ecological benefits but may decrease the resistance against carbonation. The diffusivity of carbon dioxide and the moisture conditions in concrete significantly influence the carbonation rate. Thus a test method was developed to determine the effective CO₂ diffusion coefficient (D_CO2). Additionally, the water vapour diffusion coefficients (D_H2O) were analysed. D_CO2 and D_H2O increase with increasing water-to-cement ratios (w/c, related to the CEM I content in the binder). At the same w/c ratio, higher amounts of limestone decrease D_CO2 and D_H2O and increase compressive strength. D_CO2 and D_H2O show a linear correlation for samples with w/c ≥ 0.6 but a non-linear relationship for dense concrete (w/c ≤ 0.5). D_CO2 ranges from 2.6⁻⁹ m²/s to 1.9⁻⁷ m²/s for w/c of 0.5 and 1.25, respectively. D_H2O were between 2.8⁻⁸ m²/s and 4.5⁻⁷ m²/s. A model for estimating D_CO2 in concrete with high limestone contents was derived based on the experimental analysis of the correlations between mix design, compressive strength, and CO₂ diffusion.