Carbon sequestration via CO2 curing of cement compacts: Optimizing flue gas inherent heat and water vapor

Abstract

Globally, the rising concern over the concentration of atmospheric carbon dioxide (CO2) has pushed the academic and industry parties to alleviate such emissions. One of the most promising means is to directly mineralize the CO2 from flue gas via fixing carbon in cement/waste-based construction products. Industrial flue gas (∼20 % CO2) emitted with inherent heat and water vapor can be utilized to optimize the efficiency of CO2 sequestration. For this purpose, this study investigated the carbonation behavior of cement compacts subjected to CO2 temperatures from 80 to 140 °C with a relative humidity (RH) range of 2–90 %. The experimental test results demonstrated that mechanical strength was enhanced with increasing curing temperature and RH up to 120 °C and 60 % RH, owing to a dense matrix with refined pore structure by the highest reaction products. Phase assemblage transitions and microstructural evolution were further studied via examining the BSE images at different depths. A reaction annulus that evolved from hydrates (inner layer) towards stable carbonates (outer layer) was found in samples exposed to temperatures ≤ 120 °C. At 140 °C, a direct carbonation of calcium silicate was observed. These findings lay a basis for optimizing the carbonation temperature and RH for a further in-situ application strategy.