Influences of CO2 Absorption under Ultrasonic Vibration and Water-Reducer Addition on the Rheological Properties of Cement Paste

Abstract

Research shows that ultrasonic vibratory stirring can effectively increase CO2 absorption by cement slurry. However, with the increase in CO2 absorption, the fluidity of slurry begins to decrease. Adding water reducer to fresh cement paste can improve its fluidity. In order to reveal the influences of ultrasonic vibration and water-reducer addition on the rheological properties of cement pastes after absorbing various amounts of CO2, changes in the rheological properties of yield stress and plastic viscosity (PV) were analysed. The results show that ultrasonic vibration can effectively increase the shear stress and PV of cement paste. Moreover, shear stress and PV are positively related to the CO2 absorption amount. Meanwhile, a new rheological model of cement paste carbonated under ultrasonic vibration was established based on the basic principles of rheology. Microstructural changes in cement paste before and after water-reducer addition were observed by scanning electron microscopy (SEM). A microrheological model of cement paste carbonated under ultrasonic vibration and with water reducer added was constructed. It describes the influencing mechanisms of ultrasonic vibration and water-reducer addition on the rheological properties of carbonated cement paste. Next, a molecular model was constructed in which CO2 was added into a C-S-H gel. Changes in intermolecular repulsion in the CO2+ C-S-H gel structure and in the CO2− water-reducer molecular structure were analysed. Finally, the rheological mechanism was further analysed in terms of the dispersion effect of the C-S-H gel. The results will play a major role in improving the fluidity of cement paste.