Comparative reliability of ultrasonic pulse velocity and rebound hammer test methods in assessing compressive strength

This is an evaluation of the efficacy of the two most popular Non Destructive Testing (NDT) methods – Ultrasonic Pulse Velocity (UPV) and Rebound Hammer (RH) in assessing compressive strength of concrete. 150mmx150mmx150mm concrete cube samples were prepared, cured and subjected to UPV and RH tests at the end of : 1, 3, 7, 14, 21, 28, 56 and 90 days. The same samples were, then subjected to destructive (compressive strength) test. Correlation test, multiple regression analysis, graphs and visual inspection were used to analyze the data obtained. Results indicated increase in rebound hammer from 24 rebounds on the first day to 43 rebounds on the 90th day; while the result of UPV decreases from 43.10 Micro-Sec. on the first day, to 35.90 Micro-Sec. on the 90th day of curing. Regression Model which combines UPV with RH gave the following results: 10.93 N/mm2, 13.99 N/mm2, 25.23 N/mm2 29.72 N/mm2, 33.45 N/mm2, 33.32 N/mm2, 35.45 N/mm2 and 36.75N/mm2 for 1, 3, 14, 21, 28, 56 and 90 curing days, respectively. The conclusion drawn from the analysis, is that combination of rebound hammer and UPV methods is effective in assessing compressive strength of concrete. Hence it is recommended that for more accurate result, rebound hammer should be combined with UPV testing concrete, and that the following formula should be used = 45.80 + 0.88 X -1.31 X . 1 2Keywords: Concrete, Comparative study, compressive strength, rebound hammer, ultrasonic pulse velocit