Effect of CO2-mixing dose and prolonged mixing time on fresh and hardened properties of cement pastes
Minlu Wang, Shuang Luo, Ba Tung Pham, Tung‐Chai Ling
Abstract
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.