The document explains concrete non-destructive testing (NDT) methods to assess the integrity and quality of concrete structures without causing damage. It details various tests, such as penetration resistance, rebound hammer, and ultrasonic pulse velocity, each serving different purposes like evaluating strength and detecting defects. Additionally, it introduces a training course by Techshore Inspection Services that covers NDT techniques and offers placement assistance for aspiring professionals in the civil construction field.

1. What is concrete non-destructive testing (NDT)?
It is very important to ensure that the structure is suitable for its intended use after the concrete has
hardened. For this purpose, we can perform non-destructive testing that does not damage the
concrete. Non-destructive testing can be applied to both old and new structures. For new structures,
they are mainly used for quality control or to clarify doubts about the quality of materials or
construction.
Non-destructive testing can be useful in the following cases:
• Quality control of precast elements or structures
• Elimination of ambiguities about the acceptability of the material supplied
• Monitoring of strength development in connection with removal of formwork, completion of
curing, prestressing, application of loads, or similar purposes
• Determination of the location, quantity, or condition of reinforcement
Different NDT methods for concrete:
1.Penetration Resistance Test
This test is performed using a Winsor probe testing machine. A steel probe is fired at the surface of
the concrete by a sudden explosion. The depth of penetration is inversely proportional to the strength
of the concrete. The purpose of this test is to determine the uniformity of the concrete, to indicate the
zones of poor quality or damaged concrete, and to evaluate the strength of the concrete in place. It is
also useful to evaluate the strength of the concrete on site for early removal. The hardened concrete
penetration resistance test can be performed based on the procedures and specifications of the
standard hardened concrete penetration resistance test method
2.Rebound Hammer Test
This test is a quick indicator of the compressive strength of the concrete. The rebound hammer, also
called a Schmidt hammer, consists of a spring-loaded mass that slides on a plunger in a tubular housing.
When the ram of the rebound hammer is pressed against the concrete surface, a spring-controlled
mass strikes the concrete surface with constant energy and rebounds. The amount of rebound, which
is a measure of surface hardness, is measured on a scale. This measured value is called the rebound
number. A concrete with low strength and low stiffness absorbs more energy and thus gives a lower

2. rebound value. The purpose of this test is to determine the compressive strength of the concrete by
relating the rebound number, to assess the uniformity of the concrete, to evaluate the quality of the
concrete based on the standard specifications, to relate one concrete element to another in terms of
quality
3. The Half Cell Potential Test
The Half Cell Potential Testing method is suggested for diagnosing the probability of reinforcement
corrosion in turn which is used for assessment of the durability of reinforced concrete. Non-destructive
technique such as half-cell potential measurement (HCP) is a well-known technique for investigation
of corrosion in steel. Corrosion of steel can be assessed by Half-Cell Potential (HCP) measurement by
an electrochemical process as per ASTM C87. The electrical potential difference between the upper
steel rebars and a standard portable reference electrode in contact with the concrete surface is
measured. The half-cell is made by a Copper/ Copper Sulphate or Silver/ Silver Chloride cell but other
combinations are also used. The concrete acts as an electrolyte and the risk of corrosion of steel
reinforcement in immediate region of the test location may be related empirically to the measured
potential difference.
4. Ultrasonic Pulse Velocity (UPV)
This test determines the integrity and quality of structural concrete (up to 6 feet thick) by measuring
the velocity and attenuation of an ultrasonic wave passing through the element being tested. Areas
with lower velocities typically have lower density and strength than areas with high velocities. Data
collected along multiple inspection paths can be used to create tomographic images of defects. The

3. purpose of the inspection is to detect voids, honeycombs, cracks, and other defects; identify areas of
substandard concrete; define the size and shape of a defect by using multiple inspection paths; provide
two-sided access required for direct path inspection; inspect around corners when complex geometry
precludes direct path inspection, such as at beam intersections; and inspect across a surface to
measure the depth of cracks opening at the surface.
5. Permeability Test
This test is very important as reinforcement is prone to corrosion when it reacts with the water, which
in turn forms a layer around the reinforcement and causes an increase in the volume of concrete which
ultimately leads to surface cracking. To resist the reinforcement to corrode, the concrete is set to be
permeable and permeability test of concrete tests the same. Not only the water or moisture there are
other atmospheric deleterious materials which ingress with reinforced concrete leads to corrosion of
steel.
There are different methods to measure the Concrete Permeability out of them below mentioned tests
are most commonly used
• Rapid Chloride Permeability Test- This test is used to determine the concrete’s ability to resist
the penetration of chloride ions in it. Chloride ions are passed through the sample of concrete
electrically. The readings are taken as the current passes through the concrete sample. On
average 2 to 3 samples are taken from each batch of concrete and the average reading is taken
as the final value.

4. • Water Permeability test by pressure-- Water permeability test (water penetration test), is
generally performed to measure the permeability of concrete, having high permeability. In this
test, water with pressure is continuously passed through a disc-shaped concrete sample for a
fixed time interval. The amount of water passing through the concrete disc determines the
permeability of concrete.
6. Radiographic test
This test is used to determine the location of reinforcing steel, voids in concrete, and the position of
prestressing wires and channels. Radiographic testing relies on the ability of X-rays or gamma rays to
penetrate the material being tested. When radiation penetrates a concrete element, different parts of
the reinforced concrete element, such as steel bars, concrete, and voids, absorb a different number of
X-rays. A radiation-sensitive X-ray film is used to capture images of voids and steel bars. This allows the
viewer to accurately identify and determine the location of steel bars, voids and cracks.

5. 7. Covermeter Test
This test is used to specify the location of reinforcement bars in concrete and determine the
exact concrete cover needed. The magnetic rebar locator test plays a significant role in construction
works because the information about the location of steel bars, concrete cover, and bar sizes is
essential, directly or indirectly, in many field applications. A covermeter is a device that gives
information about concrete covers and steel reinforcement in concrete using magnetic fields. Magnetic
instruments for locating reinforcement steel (present within the concrete) work on the principle that
the steel affects the alternating magnetic field.
8. Carbonation depth measurement Test
Carbonation is a process in which carbon dioxide from the atmosphere diffuses through the porous
cover concrete and can lower the pH to 8 or 9, at which point the passivation/oxide film is no longer
stable. The carbonation process involves the following two stages: First, atmospheric carbon dioxide
(CO2) reacts with water in the concrete pores to form carbonic acid (H2CO3). Then, the carbonic acid
reacts with calcium hydroxide [Ca(OH)2] to form calcium carbonate (CaCO3). This process leads to a
reduction in the pH of the pore solution from 12.5 to 13.5 to about 8 to 9, which results in
depassivation of the protective layer of the reinforcing bars and initiates their corrosion.
9. Infrared Thermography
Thermal radiation from a component is detected by infrared thermography, which uses the thermal
signal to create a 2D image of the object. Thermal conduction and thermal radiation are the two basic
principles of heat transfer on which it is built. Low density or delaminated concrete is less thermally
conductive than sound concrete, which has no voids, gaps or cracks, resulting in low temperature

6. variations at the concrete surface. Sensitive infrared thermography technology can detect and record
these temperature variations. This enables fast, area-wide mapping of interior conditions.
10. Pile Integrity Test
The procedure for measuring and analysing the velocity (required) and force (optional) of the
pile caused by an impact device (a hand-held hammer or similar type) acting generally axially
and perpendicularly on the surface of the pile head is called the pile integrity test. It is also
known as the low strain impact integrity test. Pile integrity tests can be used for quality control
of new construction or for forensic analysis of existing piles. A motion transducer (e.g., an
accelerometer) attached to the pile head is typically used to record the pile response during a
pile integrity test (PIT) in which the pile head is struck lightly with a hand-held hammer. The
compressive stress wave generated by the hammer blows travels through the pile. On its way
back to the pile head, this wave is reflected by the pile tip or other anomalies inside the pile.
Any change in impedance within the pile (caused by variations in pile cross-section, concrete
density, or shaft and soil properties) can affect the reflected signal.

7. Techshore Inspection Services offers a comprehensive 2.5-month duration course in QA/QC Civil-
Concrete NDT and Quantity Surveying & Cost Estimation. With an inclusive curriculum and eligibility
open to +2/ITI/Diploma/Degree/B-Tech holders, this program is designed to equip you with the skills
and knowledge necessary for a thriving career in this field.
Course curriculum highlights:
• Ultrasonic Pulse Velocity Testing
• Rebound Hammer Testing
• Rebar Locator
• Carbonation And Chloride Testing
• Coating Thickness Measurements On Concrete
• Half-Cell Potential Testing
• Infrared Thermography
• Radiography
• Pile Integrity Testing, etc.
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