Consider the following statements related to non-destructive testing of concrete: 1. Indentation test is used to assess the quality of concrete. 2. Resonant Frequency method is based on a laboratory test. 3. Compressive strength of concrete is estimated through Pulse Velocity Measurement 4. Dynamic Modulus of Elasticity is determined by a Sonometer Test. 5. Thickness of concrete can be estimated by in-situ Rebound Hammer Test. Which of the above statements are correct? Correct Answer 1, 2, 3 and 4 only Concept: Indentation test: It is a quick in situ test to measure the hardness of concrete. The hardness of concrete is very closely related with the tensile strength of concrete, so the measure of hardness can give a qualitative assessment of the concrete characteristics. Thus, the indentation test of concrete can provide a rough assessment of the quality of the concrete. ∴ Statement 1 is correct. Resonant Frequency method: This method is comparatively new in non-destructive testing techniques where resonance frequencies of an object is measured. This is a laboratory-based method where waves produced by a short stress pulse interfering in the specimen are analyzed. The resonance method is applied to structures that are not easy to access for testing, like concrete slabs and floors. ∴ Statement 2 is correct. Ultrasonic Pulse Velocity (UPV) Method: An ultrasonic pulse velocity (UPV) test is an in-situ, non-destructive test to check the quality of concrete. In this test, the strength and quality of concrete is assessed by measuring the velocity of an ultrasonic pulse passing through a concrete structure. Higher velocities indicate good quality and continuity of the material. With the help of this method, the compressive strength of concrete and depth of crack in the concrete can be measured. ∴ Statement 3 is correct. Sonometer Test: This non-destructive test is also based on the resonance frequency principle where the fundamental resonant frequency of vibration of a specimen is measured. This method is predominantly used to calculate the dynamic Young’s Modulus of elasticity of concrete and to study the deterioration effects of concrete subjected to repeated cycles of freezing and thawing. ∴ Statement 4 is correct. Rebound Hammer Test: Rebound hammer test is a non-destructive testing method of concrete that provide a convenient and rapid indication of the compressive strength of the concrete. The rebound hammer is also called as Schmidt hammer. This method is used to determine the compressive strength of the concrete by relating the rebound index and the compressive strength and also to assess the uniformity of the concrete. But the thickness of concrete cannot be estimated by this method. ∴ Statement 5 is incorrect.