Experimental investigation of fracture behavior of cementitious materials subjected to ultrasonic vibration

Developing more efficient concrete demolition and recycling technologies is essential for advancing the circular economy in the construction sector. This study experimentally investigates the fracture process of cementitious materials subjected to ultrasonic vibration at 15 kHz frequency and 32 μm amplitude, using cement paste, mortar, and concrete specimens (Φ50 mm × 100 mm). The results demonstrate that ultrasonic vibration induces and propagates cracking preferentially at the aggregate-matrix interface, generating sufficient fracture energy within seconds at the laboratory scale. Although concrete specimens containing larger aggregates demand greater energy input, the required mechanical load remains substantially lower than the theoretical fatigue load at equivalent cycles, suggesting that ultrasonic secondary effects (e.g., cavitation, thermal conversion) may contribute to the fracture process beyond the applied load alone. Furthermore, wave propagation analysis suggests that energy accumulation in specific zones may influence fracture location, and the resulting fragment size distribution of concrete specimens exhibits lower variability compared to cement paste and mortar, owing to crack propagation along aggregate interfaces. These findings suggest, at the laboratory scale level, that ultrasonic vibration technology may offer an alternative approach to concrete demolition and recycling, with the capacity to produce more uniform demolished fragments potentially suitable for recycled aggregate production.