Theoretical analysis of carbonation mechanism of cement and application to the effects of the addition of fly ash

Abstract

An equation was derived to analyze carbonation phenomena in cement based on the Tomosawa theory, and it was applied to examine the difference between the cement content and degree of charcoal oxidation. Two types of fly ash cement based on ordinary Portland cement (OPC), high-alite cement (HAC), low-heat Portland cement (LHC), and moderate-heat Portland cement (MPC) were prepared, and the degree of carbonation was measured by acceleration examination. With these measurements, long-term carbonation was simulated using the new equation. Under the accelerated condition (CO₂ 5 %), when 18 % fly ash was added to Portland cement (OPC+FA18) and 18 % fly ash to HAC (HAC+FA18), the degree of carbonation in one month was examined relative to unmodified cement, and the carbonation rate increased by approximately 1.8 and 1.6 times, respectively. The degree of carbonation of MPC was approximately the same as that of OPC, but the carbonation of LHC was about three times greater. Therefore, fly ash cement (OPC+FA18, HAC+FA18) and LHC are more useful in the environment because these cements have a superior ability to prevent carbon dioxide release compared with that of OPC.