Characteristic analysis of air bubbles on the rheological properties of cement mortar

Abstract This research studies the influence of bubble properties on rheological properties of freshly mixed cement mortar. Cement mortar with various fluidity and air content are prepared by changing the dosage of surfactant and superplasticizer. The tests on surface tension, adsorption, air content, bubble size distribution, and rheological measurements are employed to reveal the influence mechanism of bubble properties on the fluidity. The results show that the increase in the proportion of air bubbles in the range of 100 to 500 μm significantly reduces the fluidity of the cement mortar. When the air content is constant, the yield stress of cement mortar has an exponential relationship with fluidity. When the cement mortar shows the same fluidity, the yield stress gradually decreases after the air content exceeds 13%, until it reaches the theoretical yield stress. This is due to the increase in the dosage of surfactants, the decrease in the surface tension of the bubbles, and the increase in the number of large-size deformed bubbles. This article quotes the Bingham capillary number (Cay) for evaluation.