CO₂ uptake of slag-blended concrete

CO₂ uptake due to carbonation is an important issue for sustainability in the concrete industry. This study presents an analysis model of CO₂ uptake of slag-blended concrete considering the service stage and the recycling stage. First, a slag-blended cement hydration model is used to evaluate the content of carbonatable substances, porosity, and diffusivity. Regarding the service stage, a one-dimensional carbonation model is proposed to evaluate carbonation depth. For the recycling stage, an unreacted core model is proposed to evaluate the carbonation fraction of crushed, spherical concrete. Second, CO₂ uptake in the service stage and recycling stage is determined based on the carbonated fraction, shape of the concrete element, concrete component, and exposure conditions. The total CO₂ uptake ratio is determined based on the content of CO₂ uptake and CO₂ emissions. Third, the analysis results show that for concrete with a water-to-binder ratio of 0.3, as the slag replacement ratio increases from 0 to 50%, the total CO₂ uptake ratio increases from 21.43 to 28.87%. For concrete with 50% slag as the binder, as the water-to-binder ratio increases from 0.30 to 0.35, the total CO₂ uptake ratio increases from 28.87 to 30.59%. The sizes and types of the structural elements and the diameter of the crushed concrete can impact the rate of CO₂ uptake, but do not modify the total CO₂ uptake ratio.