Vol.22, No.2, 2022, pp. 159–168
UDC:

Ultrasonic pulse velocity (UPV) and Rebound Hammer (RH) are NDT techniques used routinely to evaluate the health of concrete elements. Concrete elements can be evaluated using UPV in three different methods i.e., direct, in-direct, semi-direct methods based on the direction of waves passing through concrete. In this paper, work is divided into three phases: in phase 1, a correlation between direct and in-direct velocities (Vd and Vs) for ON and OFF of reinforcement is developed for quality assessment of concrete through UPV. Much work has not been done in previous literature on the correlation between direct, in-direct, and semi-direct methods for assessing uniformity, homogeneity, and quality of concrete. Beams, columns and slabs are measured using two different methods, i.e. direct and in-direct. The best fit correlation between Vd and Vs is obtained using regression computational technique. In phase 2, the compressive strength of concrete is predicted using methods RH, UPV, and SONREB, and inter comparison is established. In phase 3, a series of reinforced concrete beam specimens are cast with different reinforcement percentages (1, 1.5, and 2), and the difference in velocity at stress conditions is obtained. The velocity is 10 to 20 % less in the in-direct method compared to direct method, and the best fit correlation is obtained between Vd and Vs. The effect of stress results in a decrease in UPV direct measurements for stressed beams. The reliability of predicting strength using SONREB method is enhanced as compared with the UPV and RH methods.

Keywords: non-destructive testing (NDT), ultrasonic pulse velocity (UPV), rebound hammer (RH), concrete strength, quality assessment, velocity correlations