Novel method to evaluate 3-D printed concrete quality using ultrasonic scatter energy techniques

This study investigates the feasibility and effectiveness of a non-destructive ultrasonic testing method to evaluate the quality of 3-D printed concrete (3DPC) under varying printing conditions. To simulate different types of layer completions of 3DPC under real-world conditions, three printing schemes with different open times were adopted: no time gap, a 2-minute time gap, and a 5-minute time gap between printing subsequent layers. An air-coupled ultrasonic scanning system was used to measure multiple ultrasonic signals collected from three different 3DPC specimens. The signals were analysed in the frequency-wavenumber (f-k) domain to decompose forward propagating and scattered wave fields. The experimental results demonstrate that ultrasonic scatter energy increases with longer time gaps between subsequent layers in 3DPC. Additionally, the scatter energy was found to correlate well with defect density of 3DPC, assessed by digital image processing using image binarization methods. The findings of this study suggest that the ultrasonic scatter energy approach shows potential more thoroughly assess the quality of 3DPC structures because it interrogates the full volume of the materials and it provides superior damage sensitivity than ultrasonic velocity measurements do.