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

Abstract

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 (DCO2). Additionally, the water vapour diffusion coefficients (DH2O) were analysed. DCO2 and DH2O 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 DCO2 and DH2O and increase compressive strength. DCO2 and DH2O show a linear correlation for samples with w/c ≥ 0.6 but a non-linear relationship for dense concrete (w/c ≤ 0.5). DCO2 ranges from 2.6−9 m2/s to 1.9−7 m2/s for w/c of 0.5 and 1.25, respectively. DH2O were between 2.8−8 m2/s and 4.5−7 m2/s. A model for estimating DCO2 in concrete with high limestone contents was derived based on the experimental analysis of the correlations between mix design, compressive strength, and CO2 diffusion.