Understanding the cavitation effect of power ultrasound in cement paste

Abstract

While power ultrasound (PUS) has been proven to accelerate cement hydration, it remains unclear whether cavitation occurs during this process. This study aimed to test the cavitation effect of a single bubble in cement paste through a KI oxidation experiment. An ultrasonic pressure field model was established using the linear Helmholtz equation, and the cavitation effect of a single bubble in cement paste was simulated based on the modified Keller–Miksis model. The results indicate that the conventional water-cement ratio (w/c ratio ≤1.0) does not produce transient cavitation but can produce stable cavitation. The efficiency of stable cavitation initially increases and then decreases as the bubble diameter increases. An optimum stable cavitation efficiency is achieved with a 50 μm bubble, but the bubble expansion rate remains consistently less than 40 %. Increasing the acoustic pressure to 5 atm or higher can cause the bubbles in cement paste with a water-to-cement ratio of 1.0 to expand more than tenfold. However, even when the acoustic pressure was further increased to 10 atm, no noticeable bubble expansion was observed in the cement paste with a w/c ratio of 0.30. The high viscosity of cement paste is the primary cause of the high transient cavitation threshold of bubbles.