2025 Volume 78 Issue 1 Pages 416-424
Various CO2 fixation technologies for waste have been developed to achieve carbon neutrality worldwide. Ready-mixed concrete plants generate large amounts of sludge water from the washing of mixers and agitator trucks. As sludge water is rich in CaO, a compound in cement that reacts with CO2 to form stable minerals, research on using sludge water to sequester CO2 is underway. In this study, a method of blowing CO2 gas in the form of microbubbles ranging in size from 1μm to 100μm into sludge water was investigated to establish a more efficient CO2 fixation method for sludge. Simulated sludge water with a sludge concentration of 2.5wt.％ or 5.0wt.％ was used in the experiments. The investigated method was found to be able to fix CO2 in sludge water more efficiently than blowing CO2 bubbles of 14mm diameter. The factors affecting CO2 fixation are the temperature of the sludge water and its age（sludge water storage period）. Changes in the amount of minerals and hydration products in the sludge water due to CO2 fixation were also evaluated by Rietveld analysis. Based on the results obtained, the CO2 fixation efficiency relative to the amount of CaO in the real and simulated sludge water is inferred to be similar under the same conditions of sludge water temperature and sludge age.
