Evaluation of CO₂ emission–absorption of fly-ash-blended concrete structures using cement-hydration-based carbonation model

Abstract

Concrete contains cement, which is known to emit large amounts of CO₂ in production, absorbs a certain amount of CO₂ by triggering a carbonation reaction with atmospheric CO₂. However, this CO₂ absorption is generally neglected when evaluating the CO₂ emission from concrete. Thus, it is necessary to discover and consider ways to quantitatively evaluate the CO₂ absorbed by concrete. To this end, a carbonation model that can accurately predict the carbonation depth of concrete is necessary. However, the existing carbonation prediction equation is a simple regression equation that merely considers factors such as water–cement ratio and CO₂ concentration, and has a drawback as the results vary considerably form one researcher to another. Meanwhile, currently the use of fly ash, which is effective in reducing both of hydration heat and CO₂ emission and enhancement of long-age strength, is increasing. Thus, in the present study, a method for measuring CO₂ absorption by fly-ash-blended concrete structures using a carbonation model based on fly-ash-blended hydration was developed and evaluated. An apartment complex in which fly-ash-blended concrete was used is evaluated for its CO₂ absorption by using the developed method in this study. As a result, carbonation depth, amounts of CO₂ emission and absorption of fly-ash-blended concrete structure by design strength was obtained. The CO₂ absorbed by service life is approximately 3.79–8.47 % of the CO₂ emitted during the manufacturing of the concrete structure.