BASIC METHODS FOR NDT OF CONCRETE & REINFORCEMENT IN STRUCTURES
It becomes sometimes necessary to examine the hardened concrete structure for their suitability for its intended use. But the examination of such existing or new structures should be such that the structure is not damaged during the process. In such cases, the Nondestructive Test Methods are used for testing of concrete structures.
There are various NDT tests available for
concrete structures, but based on its suitability and applications they are selected. These tests can be completely nondestructive, or partially destructive tests which may not have much effect on the strength and durability of concrete structure. The following methods are commonly used for NDT of concrete structures. The typical applications of these methods are given in brief below :-
1. Visual inspection of concrete structure is carried out before any intended nondestructive test. Visual inspections provides information on type of concrete damage, their possible causes and type of NDT test suitable for further investigation. Visual inspection is carried out by experienced civil engineers who can interpret information from the damages in the concrete structure.
2. Schmidt NDT Test or Rebound Hammer Test, is carried out for the evaluation of surface hardness of concrete structures. The surface hardness of concrete is the indication of strength of concrete.
3. Carbonation Depth Measurement Test – This NDT is used to determine the penetration of moisture inside concrete. This helps in identifying the moisture reaching the reinforcement which may cause corrosion.
4. Halfcell Electrical Potential Method :This NDT test is used to detect the corrosion potential of reinforcing bars in concrete.
5. Ultrasonic Pulse Velocity Testing is used for the finding the compressive strength of concrete.
6. Crack Meter Test: this test gives an indication of the depth the crack has reached and the width of the crack. This is indicative of the failure in the structure where the crack is present.
7. Ferro Scanning : state of the art facility called FERRO SCANNING is done using latest models like HILTI PS200. The scanner by developing a magnetic field, produces pictures on the monitor’s screen and thus the grid is fully exposed. This is ideal for the formation of rebar grids in old structures where the information is required to assess the Dia, Depth and Spacing of rebar and its cover in concrete. The data is stored in memory of the scanner and can be downloaded on computer, which can be used for Reverse Engineering & for extensions to existing concrete members. It is used for quality control Inspection during and after the construction of RCC structures. The data obtained from time to time scanning is also very useful in preventive maintenance of structures