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

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.