Enhanced mechanical properties of cement pastes with CO2-bubbled alkanolamines: A study on hydration, carbonation, and mineralization behavior

This study investigates the use of two amines—N-methyldiethanolamine (MDEA) and 1-(2-Hydroxyethyl) Piperazine (HEPZ)—to enhance CO 2 mineralization in cement paste. A pre-treatment technique, which involved bubbling CO 2 into the amine solution, was implemented to mitigate the potential adverse effects of amine addition on mechanical properties. This approach improves the balance between strength development and CO 2 sequestration. Results demonstrate that MDEA significantly increases the early-age compressive strength of cement paste under sealed curing conditions; however, it reduces the strength development at later ages and significantly impedes carbonation during the accelerated carbonation stage. Conversely, while the addition of HEPZ has an adverse impact on the mid-to-late compressive strength of cement paste, this strength reduction can be effectively eliminated by CO 2 bubbling pre-treatment. Furthermore, HEPZ promotes a higher degree of carbonation at equivalent depths within the carbonation zone. Its strong CO 2 -capturing ability also helps mitigate the negative impact of the plugging effect caused by high CO 2 concentrations, which would otherwise hinder the carbonation process of the cement paste. • MDEA promoted C 4 AF and C 3 S hydration, enhancing early strength of cement paste. • HEPZ increased carbonation at the same depth in the carbonation zone of cement paste. • HEPZ weakened the plugging effect that hindered CO 2 diffusion in cement paste. • CO 2 bubbling eliminated the adverse effect of HEPZ on cement paste strength.