Addressing workability issue and performance of CO2-mixed cement pastes.

This study proposes to premixing CO 2 with 10 % of cement and water before blending it with the remaining 90 % of cement powder, aiming to address the substantial workability loss caused by CO 2 -mixing at the fresh stage and promote a higher amount of CO 2 uptake. Four different CO 2 dosages (0.06, 0.6, 6, and 12 % by weight of 10 % cement) were systematically examined. The results reveal that the carbonated 10 % cement slurry exhibits a remarkable 4.78 % CaCO 3 content, accompanied by the formation of needle-like and flocculent reaction products on the surface of carbonated particles. This led to an increase in the particles' specific surface area and interparticle frictional force, subsequently resulting in a reduced sedimentation rate and a minor decrease in pH. However, no workability loss was noticed. In the early curing stages (1–7 days), all CO 2 -mixed samples manifest a noteworthy 7–18 % increase in compressive strength. However, this increment shows a slight reduction with extended curing times up to 28 days. This trend may be attributed to the formation of numerous microcracks in the matrix, particularly evident in samples with higher CO 2 concentrations (0.6 % and 1.2 %). [Display omitted] • Surface of carbonated cement particles is covered by numerous reaction products. • CO 2 -mixed cement pastes possessed comparable workability to control sample. • Higher strength compared to control sample is obtained with high CO 2 dosage. • The hydration of cement pastes is promoted at low CO 2 dosages. • Excessive CO 2 induces micro cracks on the surface of samples at later stages. [ABSTRACT FROM AUTHOR]