Assessment of Strength of Concrete by Non-Destructive Testing Techniques

In this paper an attempt was made to establish Non Destructive Evaluation (NDE) technique for assessment of compressive strength of in-situ concretes of various types by conducting Ultrasonic Pulse Velocity (UPV) and Rebound Hammer tests. A combined method of Pulse Velocity and Rebound Number as a NDE technique was developed by conducting UPV, Rebound Hammer and destructive tests on concrete cubes of various mixes. It can be used for integrity assessment of concrete structures and also for evaluation of strength of concrete up to 75 MPa. The various concretes like Plain concrete, Recycled aggregate concrete, concrete with replacement of fly ash with10%, 20%, 30%, of M15, M20, M25, M30, M35 and M40 mixes were designed as per Sp23-1982. Concrete cubes of size 150x150x150mm were cast and tested for compressive strength at 7days, 14 days, 28 days, 56 days and 90 days for all the mixes. Just before conducting destructive test, UPV and Rebound Hammer tests were conducted on the same cubes as per IS 13311 (Part1&2). A comparative study was made among the compressive strength, Pulse Velocity, and Rebound Number for all types of concrete of various mixes and curves were drawn. Regression analysis was also made for the tests being conducted and kept them ready for assessment of compressive strength of in-situ concrete structures. It is observed that the Pulse velocity and Rebound Number increases with the age of concrete increases. As there are no standard curves for evaluating the compressive strength of in-situ concretes of various types from UPV and Rebound Hammer tests, NDE technique developed here can be used for further course of study. It is concluded that the curves obtained for assessment of compressive strength of concretes from the values of Pulse Velocity and Rebound Number can be incorporated in the IS codes for future reference.