Flue gas carbonation of cement-based building products

Flue gas carbonation of three commonly used cement-based building products, concrete masonry blocks, cement-bond fiberboards and cement-bond bead boards, was studied to investigate the feasibility of using as-captured cement kiln flue gas to accelerate hydration and store carbon dioxide for emission reduction. Compared to pure gas carbonation, the use of flue gas does not require chemical separation which is energy-intensive. However, the reaction efficiency was low because of low CO2 concentration in flue gas. It could take up to two weeks to achieve required strength. This paper presents an innovative process in which flue gas carbonation was carried out in 5 h with 7 cycles of injection and release. Cement-based building products could achieve 5-6% CO2 uptake independent from types of products. Compared to pure gas carbonation, degree of carbonation was low in flue gas but strength gain was in the same order of magnitude. Reaction product was typical calcium silicate carbo-hydrates, a carbonate modified hydrate. The size of carbonate crystal was much smaller by flue gas carbonation. However, their contribution to strength gain was comparable to larger crystals in pure gas carbonation. The successful capture and utilization of cement kiln flue gas made it feasible to establish a network to link cement plants (CO2 sources) to concrete plants (CO2 sinks) for emission reduction through utilization.