Ultrasonic assessment of compressive strength of underwater concrete considering various mix parameters

Assessment of compressive strength is crucial for ensuring the safety of concrete structures. However, existing works mainly focus on wet concrete rather than fully saturated concrete underwater and neglect the influences of mix parameters. To this end, this study develops a testing system to measure ultrasonic waves underwater and investigates the influence of water-cement (W/C) ratio (ranging from 0.35 to 0.54), sand-aggregate (S/A) ratio (ranging from 0.57 to 0.87), and average diameter (Da) of coarse aggregate (ranging from 7.5 to 17.44) on the relationships between compressive strength and the velocities of pressure (P) and Rayleigh (R) waves. Ultrasonic and destructive experiments are performed on 96 concrete blocks with 32 mix parameters. The W/C and S/A ratios have a more significant influence on the relationship than the Da. Therefore, a set of formulas is developed to assess compressive strength based on the velocity of P and R waves considering the influence of W/C and S/A ratios. The developed formulas improve the accuracy by 32% to 57% compared to existing formulas, guiding the assessment of underwater infrastructures.