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.