Carbonation Progress Mechanism of Cement Containing Different Amounts of Powder Admixtures

The cement industry is also reducing carbon dioxide emissions to prevent the global warming. As one of the methods, the use of many powder admixtures are considered. While the use of admixtures is highly advantageous in various terms of durability, it is known that carbonation resistance is inferior when compared to ordinary Portland cement. In this study, we investigated the progress mechanism of carbonation using cement with high content of powder admixtures. First, we compared the progress of carbonation in the real environment and accelerated environment. As a result, it was confirmed that, although carbonation is delayed in a real environment, the progress of carbonation is quicker than when not using large amount of admixtures. The effect is more remarkable as the curing period decrease, and it is found that it has correlation with the compressive strength. Next, the progress of carbonation was considered to be influenced by the pH and the hydrate products of the sample. The pH and hydrate and carbonate products were evaluated quantitatively at depth positions from the surface before and after carbonation. As a result, it was confirmed that the carbonation depth increased as the pH was lowered by the high content of the admixture, and the calcium hydroxide is converted to calcium carbonate. It was also confirmed that the type of calcium carbonate produced was different. Furthermore, with the change of the pore structure, the tendency of carbonation to accelerate was also recognized. On the other hand, it was also confirmed that the carbonation depth identified by the phenolphthalein solution was different from the actual formation position of calcium carbonate.