Effect of CO2-mixing dose and prolonged mixing time on fresh and hardened properties of cement pastes

• Published in: Journal of Zhejiang University. A. Science Vol. 24; no. 10; pp. 886 - 897
• Main Authors: Wang, Minlu, Luo, Shuang, Pham, Ba Tung, Ling, Tung-Chai
• Format: Journal Article
• Language: English
• Published: Hangzhou Zhejiang University Press 01.10.2023; Springer Nature B.V; College of Civil Engineering,Hunan University,Changsha 410082,China
• Subjects: Calcium carbonate; Carbon dioxide; Carbonates; Cement; Cement hydration; Cement paste; Civil Engineering; Classical and Continuum Physics; Coagulants; Compressive strength; Engineering; Flocculation; Industrial Chemistry/Chemical Engineering; Mechanical Engineering; Mechanical properties; Mixtures; Research Article; Workability; 水泥早期水化; Early cement hydration; Flowability; 碳酸钙; 流动性; mixing; 微观结构; Calcium carbonate; 搅拌; CO; Microstructure; CO2-mixing
• ISSN: 1673-565X; 1862-1775
• DOI: 10.1631/jzus.A2200571

This study aims to investigate the influence of CO 2 -mixing dose (mass fractions of 0.3%, 0.6%, and 0.9%) and prolonged mixing time on the fresh and hardened properties of cement pastes. The CO 2 -mixing can act as coagulant in fresh cement mixtures, resulting in a significant reduction in workability associated with the formation of a rich calcium carbonate network on the surface of cement particles. The CO 2 -mixing cement pastes were found to be much stiffer and more difficult to handle, place, and compact than the control mixture, which had a negative effect on the mechanical strength performance of the hardened pastes. However, prolonging the mixing time for 1 min (immediately after CO 2 -mixing) can effectively improve the workability (by ∼53%–85%) by breaking up the flocculation network of deposited calcium carbonates. As a result, the presence of detached calcium carbonate accelerated early cement hydration and densified the microstructure; this improved early-age compressive strength by ∼6%–32%, depending on the CO 2 -mixing dose used. Therefore, it seems that the CO 2 -mixing dose should be controlled at ⩽0.6% with the mixing time prolonged in order to attain satisfactory workability and mechanical strength.