It is often necessary to test concrete structure after the concrete has hardened to determine whether the structure is suitable for its designed use. Ideally, such testing should be done without damaging the structure.
The non-destructive test is used for testing concrete range from completely non-destructive where there is no damage to the concrete. Through those where the concrete surface is slight damage, to partially destructive test such as core test, pull out and pull off test, where the surface has to be repaired after the test. The non-destructive test is applied to both old and new structures. For new structure, the Principle of application of the non-destructive test is likely to be for quality control or the resolution of doubts above the quality of materials for construction.
Non-destructive testing of concrete is the best method to obtain the compressive strength and other properties of concrete from the existing structure. The method for calculating the good quality of concrete in building or structure is evaluated by testing specimen cast simultaneously for compressive, flexural and tensile strength.
1.2: Purpose of Non-destructive test
1)Estimating the in-situ compressive strength.
2)Estimating the uniformity and homogeneity.
3)Estimating the quality in relation to the standard requirement.
4)Measurement of elastic modulus.
5)Identifying an area of lower integrity to comparison to other parts.
6)Detection of the presence of cracks, voids, and other imperfection.
7)Monitoring change in the structure of the concrete which may occur with time.
8)Identification of reinforcement profile and measurement of cover, bar, diameter, etc.
9)Chloride, sulphate, alkali contents or degree of carbonation.
10)Condition of pre-stressing reinforcement steel with respect to corrosion.
1.3: Types of Non-destructive test
Following are the non-destructive test on concrete
1)Ultrasonic testing (UT)
It is a type of non-destructive testing technique, that promote high frequency of the sound wave to determine imperfection in metal materials as well as the change in their properties within the material, that would cause problem or failure of the components being tested. It measures the time of travel of ultrasonic pulse passing through the concrete. The time taken for the pulse to pass through the concrete is measured by the help of the electronic measuring circuit.
It is a non-destructive testing technique that utilizes x-rays or radioactive isotopes to test metal materials much the same way that doctor analyze x-rays image taken of their patient. This method of testing concrete can be used to determine the location of reinforcement, measure density. May be established whether honeycombing has occurred in structural concrete units.
3)Liquid penetrate testing(LT)
It is a non-destructive testing technique where the material being tested is coated with a liquid dye solution (sometimes fluorescent dye is used).
The dye is then removed and a developer is applied which acts to draw a dye out of any defect present allowing the defect to be seen easily.
4)Magnetic particles testing (MT)
It is a non-destructive testing technique utilized to detects (such as cracks) at or near the surface in metals. These techniques utilize a magnetic field combined with the application of fine magnetic particles to reveal defects.
5)Rebound hammer method
The rebound hammer is a surface hardness test for which an empirical co-relation has been stabilized between strength and rebound number. The known instrument to make the use of the rebound principle for concrete testing is the Schmidt hammer. which weight about 1.8 kg and is suitable for both laboratory and fieldwork. It consists of a spring control hammer mass that slides on a plunger within a tubular housing. The hammer is forced against the surface of the concrete by the spring and the distance of the rebound is measured on a scale.