Effect of Strength Enhancer Admixtures on Carbonation Resistance of Concrete

Abstract

Supplementary Cementitious Materials (SCMs) have been used when mixing concrete to minimize the amount of Portland cement. This may lead to a decreased carbonation resistance, which in turn leads to risk for corrosion in reinforcement and poor mechanical performance and durability. In recent years, Strength Enhancing Admixtures (SEAs) have been used to enhance both the early and later age strength of concrete. It is however a new field of how they impact the carbonation resistance of concrete using SCMs. This study analyzed the effect of using strength enhancing admixtures on carbonation when using volcanic pozzolans and iron silicates as SCMs in concrete. For this, accelerated carbonation testing was performed according to the standard SS-EN 12390-12:2020 with a carbon dioxide concentration of 3%. Compressive strength testing (according to standard SS-EN 196-1:2016) and capillary absorption testing (according to standard NT Build 368,1991) was also carried out to study how the carbonation affects the mechanical performance and durability when using SEAs. The SEAs used were Master X-Seed STE53 and Master X-Seed 100. To be able to assess the effect of the SEAs, concrete mixes with varying dosages of SEA were prepared alongside mixes containing no SEA to compare the results to. The results show that the studied SEAs have a positive impact on the carbonation resistance in concrete utilizing pozzolans and iron silicates as SCMs. The effects were especially pronounced in the case of iron silicates. Compressive strength and capillary absorption were also affected positively, with the SEAs generally yielding an increase in 28 days and 56 days compressive strength, and an increased resistance to capillary water ingress. When comparing the two different SEAs, it was shown that Master X-Seed STE53 had a greater impact on reducing the carbonation rates.