A prospective approach for enhancing the performance of carbon-mixed concrete via retarder incorporation

The concrete that absorbs carbon dioxide during the mixing process, termed as carbon-mixed concrete, has become a hot research topic under the background of dual carbon goals. However, the workability of concrete significantly decreases even with the absorption of a minimal amount of carbon dioxide, indicating a potential challenge in its practical application. Therefore, this study investigated the effects of incorporating 0.5%, 1.0%, and 2.0% carbon dioxide (relative to the mass of cementitious materials) and retarder on the mechanical properties and microstructure of concrete through mercury intrusion, X-ray diffraction, and scanning electron microscopy, revealing the mechanism of retarder improving carbon-mixed concrete. The results indicated that the flowability and 28-day compressive strength of concrete mixed with 0.5% carbon dioxide decreased by 68.75% and 10.77%, respectively. However, after adding 0.25% retarder, these values for the carbon-mixed concrete only decreased by 18.75% and 3.52%. Meanwhile, the introduction of carbon dioxide can form carbonates and carboaluminates and refine the internal pores of the concrete matrix. This study proposes an effective method to improve the performance of carbon-mixed concrete, which can promote the efficient absorption of carbon dioxide in the concrete industry.