Effect of mineral admixture on CO₂ emissions and absorption in relation to service life and varying CO₂ concentrations

Abstract

Carbonation is a critical deterioration phenomenon, particularly for underground reinforced concrete (RC) structures due to the surrounding environment having a high CO₂ concentration. This paper presents an evaluation of CO₂ emissions and absorption with varying intended service life periods based on actual geometry and mix ratios of concrete for RC underground structures. Four mix ratios of concrete and CO₂ diffusion coefficient based micro modelling are considered, and the CO₂ emission and storage are evaluated for each step with material production and conveyance. Simulations for the CO₂ amount are also performed for varying intended service life periods and CO₂ concentrations. As the intended service life increases, the CO₂ emission rapidly increases due to the repeated repairs. In order to reduce CO₂ emissions, reducing ordinary Portland cement (OPC) by replacing it with a mineral admixture like fly ash (FA) is a crucial point in the initial construction stage, since CO₂ storage in use is limited to only over concrete. The effect of absorption increases with an increasing service life and a higher exterior CO₂ concentration. In the given period, the total CO₂ emissions and the absorbed CO₂ amount are evaluated to be increased linearly, regardless of the frequency of repairs.

Keywords:

• CO₂ emission
• concrete
• fly ash
• CO₂ storage
• carbonation