Non-Destructive Testing and Evaluation of concrete structures using Rebound Hammer and UPV testing
The following Non Destructive Tests are the important tests that can be used for assessing the concrete integrity, strength and corrosion level etc.
- Rebound Hammer test
- Ultrasonic test
- Extraction of Concrete Core Samples
Rebound Hammer Test
This is a surface hardness test and consists essentially of impacting the concrete surface in a standard manner. This is achieved by activating a mass by a given energy and measuring the indentation or rebound. The most commonly and widely used instrument is a “Rebound Hammer”
Rebound Hammer Equipment
Ultrasonic Pulse Velocity (UPV) Test
Ultrasonic Pulse Velocity test is basically a wave propagation test and consists of transmitting ultrasonic pulses of 50 – 60 kHz frequency through a concrete medium and measuring the travel time of ultrasonic pulses for known or measured length. The length divided by time gives the velocity which can be suitably interpreted to assess qualitatively the condition of concrete with regard to homogeneity, uniformity, integrity, etc.
Equipment for Testing Ultrasonic Pulse Velocity for Concrete
Large Capacity Carbonation Chamber
Concrete specimens in the carbonation chamber
Cover Meter Survey for Thickness of Cover and Rebar Identification in Concrete Structures
All cover meters are electromagnetic in operation. Cover meter (also known as profometer) serves as an effective instrument for the measurement of cover thickness and location of rebars. By making certain assumptions about bar, the instrument can be calibrated to convert signal strength to distance and hence to indicate the depth of cover.
Evaluation of Durability Parameters of Concrete Structures
RAPID CHLORIDE PERMEABILITY TEST (RCPT)
The rapid chloride permeability test (RCPT) is conducted on concrete discs as per ASTM C 1202. Cylinders of 100 mm diameter and 200 mm height are cut into discs of 50 mm thickness. The specimens are submerged in water for 24 hours. Then, the specimens are subjected to the RCPT by impressing a 60 V current. From the results, using current and time, charge passed is calculated in terms of coulombs at the end of 6 hours.
RCPT SET UP
CONCRETE RESISTIVITY MEASUREMENT
Corrosion of reinforcement in the concrete structures takes place due to ingress of carbon dioxide/carbon monoxide or chloride from the environment. It is an electrochemical process that can be electrolytically minimised by a dry or impermeable material. Concrete resistivity therefore influences the corrosion rate of embedded steel once corrosive conditions exist. The Wenner four-probe system is a commonly used device to measure resistivity and consists of four equally spaced probes, which make contact with the concrete surface. In this method, a low frequency alternating current is passed between the two outermost probes and the resulting potential difference between the inner two probes is measured.
Wenner four-probe resistivity meter
Ultrasonic Pulse Echo/Ultrasonic Imaging for Thickness, Defect/Damage Identification in Concrete Structure
Ultrasonic Pulse Echo (UPE)
Ultrasonic pulse echo needs only one side access with transmitter and receiver at one side. Low frequencies from 25 kHz allow thickness measurement from more than 1 m but with limited resolution of objects, e.g. single rebars. Higher frequencies from about 150 KHz allow high resolution of objects but limited penetration. Thickness measurement with higher frequencies can be limited with less than 50 cm.
Ultrasonic Pulse Echo Instrument/
The transmitter and receiver are housed in the same unit which consists of A 24 element (6 x 4) matrix antenna array. The antenna array elements construction allows to test without using any contact liquid, i.e. with dry-point-contact. All of the elements have an independent spring load, which allows to test on uneven surfaces.
ULTRASONIC TOMOGRAPH MIRA SYSTEM
The low-frequency linear ultrasonic tomograph MIRA is a multifunctional focusing array system using shear waves and tomographic methods of signal processing. It is used to determine the flaws, cracks, honeycombs, positioning of ducts etc., and also to assess the state of reinforcement bars to some extent in concrete. The measuring block contains a matrix antenna of 48 (12 blocks with 4 elements in each) low-frequency broadband shear wave transducers with dry contact and ceramic wear-resistant tips.
Ultrasonic Tomograph MIRA System with a C-Scan
View of various dry point contact (DPC) transducers
Ground Penetrating Radar Equipment
Impact-Echo Scanner Equipment
Impact-echo method is a very potential method for non-destructive evaluation. The advantage of using a mechanical impact source and simple physics to evaluate the concrete medium makes it an attractive method. The development of the Impact-echo scanner for Impact-echo method has made it possible to solve larger field problems using the Impact-echo method. Efforts are directed towards improving the post-processing capabilities such that non-destructive evaluation is possible with improved clarity. Through recent research at CSIR-SERC, Impact-echo has been used for rebar identification for the first time. CSIR-SERC has developed expertise for identifying the smallest object using Impact-echo method, believed to be undetectable according to the literature.