Nonlinear Ultrasonic Characterization of Performance Variation of Basalt Fiber-Reinforced Concrete Subjected to Thermal Treatment and Water Curing

In this paper, the performance of basalt fiber-reinforced concrete (BFRC) during the thermal treatment and the subsequent recovery in water are investigated by adopting the ultrasonic second harmonic generation (SHG) technique. The nonlinear parameter is calculated by the noncontact SHG technique as the evaluation indicator to characterize the microstructural variation of concrete. Meanwhile, the longitudinal wave velocity and the resonance frequency are also measured as a comparison. Results show that the participation of chopped basalt fiber has a significant improvement on the concrete performance of resistance to thermal damage and recoverability after the water curing, but an appropriate mixing ratio is required to ensure the best performance. Furthermore, for a better understanding of the performance difference of concretes with different mixing ratios, the X-ray computed tomography (CT) technique and scanning electron microscopy (SEM) are employed to reconstruct the microstructural images, and the underlying reason of the change in the nonlinear parameter is analyzed from the perspective of microstructure.