NDT on concrete determines how secure a particular structure is and whether future repairs or rebuilds are necessary.



Introduction

Testing of concrete serves a variety of purposes that pertain to the strength, durability, and estimated viability of the structure over time. These test results can be used to determine whether repairs should be made to a structure or if the integrity of the structure is sufficient as is. The following is a list of 5 non-destructive testing methods for concrete and a short description as to how each works.



1. Rebound Hammer Testing



This test measures the surface hardness of an area of concrete and requires a tool called a Schmidt Hammer. The hammer features a hammer head that is spring controlled that slides on a plunger device. When testing, the hammer head is forced into the concrete via the spring mechanism and then rebounds once it contacts the concrete surface. This rebound is measured to help determine concrete surface hardness. Again, this method is performed multiple times to determine and average which will be used to signify the surface hardness of the concrete area tested.



2. Penetration Testing



While not technically a destructive testing method, penetration testing does involve a small probe being shot directly into the concrete via a loaded charge. Once the probe has been shot into the concrete, the depth the probe reaches is then measured, and this measurement is used to determine the compression strength of the structure. Care must be taken to ensure that the tool itself is properly calibrated, and several probes are often shot to achieve a solid average of depth to arrive at a final compression strength measurement.



3. Pull Out Testing



The pull-out test can be considered a “semi-destructive test” as it involves a steel ram that is shot into the concrete a distance of 3 inches. Once it has been lodged inside, a winch device is employed to pull the rod back out and while doing so, measurements are made to determine the relative compression strength of the concrete structure being tested. Such rests result in the need for minor repairs to the structure at the testing site.



4. Ultrasonic Pulse Velocity



Ultrasonic pulse velocity testing requires a pulse generator and a pulse receiver. The test is performed by shooting ultrasonic pulses through an area of concrete and the time is takes for the pulse to be received is then measured. Such tests can determine if there are irregularities of the concrete (such as areas that have not cured yet, or cracked or crumbling, or if other materials are present inside that can impede the signal. This is a quality test to determine if a section of concrete is “TRUE” and solid, of if repairs are imminent. It must be noted that because temperatures are a factor, they must be considered when performing such reading to determine accurate results.



5. Radiographic Testing



Shooting gamma rays inside concrete is yet another non-destructive method of testing concrete. The equipment is initially expensive, but the testing cost of each test is quite small in comparison. These tests can be used to determine internal location of reinforcements, overall concrete density, and whether any honeycombing has occurred. (Honeycombing is a process by which concrete has begun scaling or crumbling caused by incorrect material grading or poorly mixing before pouring.)

Conclusion

All these NDT methods, when used in conjunction, can be extremely vital in determining how secure a particular structure is and whether future repairs or rebuilds are necessary. Such tests, while sometimes cumbersome and somewhat expensive are incredibly useful when it comes to helping save lives and property due to failing concrete structures.



Citations

Posted in How To Guide, N.-D. T. (2019, April 14). Non-Destructive Tests on Concrete - Methods, Uses. Retrieved February 12, 2020, from https://theconstructor.org/practical-guide/non-destructive-testing-of-concrete/5553/