An assessment on parameters affecting the carbonation of alkali-activated slag concrete

This study investigated the factors affecting the carbonation of alkali-activated slag concrete (AASC). Concrete durability plays an important role in the longevity of concrete structures, but aggressive chemical agents can leave major undesirable impacts on the durability of concrete. One of such chemical agents is CO2 gas, whose penetration into concrete leads to a carbonation process which facilitates the electrochemical corrosion of steel reinforcements. One of the weaknesses of alkali-activated slag concrete in comparison with Portland cement concrete is its lower resistance against carbonation. Thus, in this paper, we studied the effect of such parameters as alkaline solution to slag ratio, partial replacement of slag with microsilica, compressive strength, and curing method on the carbonation of alkali-activated slag concrete. The samples were subjected to accelerated carbonation by being placed in a CO2 gas chamber for two cycles of 14 and 28 days, and then the resulting depth of carbonation was measured and analyzed. A sample of ordinary Portland cement concrete was used as the control sample. The SEM images taken from the samples were studied to determine the changes in the structure of the cement paste. The results showed that the replacement of 15% of slag with microsilica has a significant positive effect on the carbonation depth of alkali-activated slag concrete. Compared with the exponential relationships offered for ordinary concrete in the literature, the relationship between compressive strength and carbonation depth of AAS concrete was linear. The results showed that carbonation depth decreases with increase in compressive strength and decrease in AAS concrete permeability.