Concrete NDT

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 anincrease in the volume of concretewhich ultimately leads tosurface 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 Permeabilityout 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 thelocation of reinforcement barsin concrete and determine the exactconcrete coverneeded. 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. Assured Placement Assistance: At Techshore, we don't just educate; we also empower you to secure a successful career. We understand the importance of gainful employment after your training. Our placement assistance program is designed to connect you with reputable employers in the industry. With our network and industry recognition, you'll have a competitive edge in your job search. Well-Experienced Faculties: Our faculty members are the cornerstone of our program's success. With years of practical experience in the civil-concrete quality control industry, they bring a wealth of knowledge to the classroom. Their guidance and mentorship will not only prepare you for the challenges you may encounter but also inspire you to excel in this field. At Techshore Inspection Services, we are committed to nurturing your potential, equipping you with the skills needed to thrive in the QA/QC Civil-Concrete NDT and Quantity Surveying & Cost Estimation field. Join us on this educational journey and pave the way for a successful and fulfilling career. Your future in the construction industry starts here.