Tag Archives: Ultrasonic pulse velocity test

CONCRETE, quality tests on concrete

Ultrasonic pulse velocity test || UPV Test – Types and Methodology

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The ultrasonic pulse velocity test, or UPV test, is an example of a non-destructive concrete test. Generally, hardened concrete is subjected to non-destructive testing (NDT) and destructive tests (DT). Concrete is the world’s oldest and most significant construction material. Therefore, concrete testing is crucial for assessing the stability, strength, durability, and condition of structures.

Non-destructive testing of concrete is a way of analysing concrete structures without causing damage. This aids in ensuring the structural quality and condition. The strength of the concrete is also influenced by various characteristics, including hardness, density, curing circumstances, ingredient quality, workability and water-to-cement ratio, etc.

This article discusses the UPV test, which is one of the most well-liked and reliable non-destructive tests carried out on concrete structures.

  1. Ultra sonic Pulse Velocity test (UPV Test)
  2. Relevant IS code for Ultrasonic Pulse Velocity Test (UPV Test)
  3. Ultrasonic Pulse Velocity tester
  4. Principles of Ultrasonic Pulse Velocity test
  5. Objective of UPV tests
  6. Factors affecting Ultrasonic pulse velocity test
  7. Methodology of Ultrasonic Pulse velocity tests
    1. Direct method
    2. Indirect method
  8. Result interpretation of UPV testing
  9. Conclusion

Also read : Bitumen tests – 9 tests for flexible pavements

Ultra sonic Pulse Velocity test (UPV Test)

The most efficient and fast method of testing concrete is through ultrasonic pulse velocity tests, or UPV tests. The quality of concrete is assessed using the results of UPV tests, which evaluate the period of travel of ultrasonic pulse waves. A 50–55 kHz range must be maintained for the ultrasonic pulse wave’s frequency. The pulses are generated by the UPV tester’s pulse generator and are allowed to travel through the concrete. By monitoring the traversing distance and the duration, the pulse velocity can be determined. Higher velocity indicates that the density and elastic modulus of the concrete are higher.

Cracks and defects in the structure are detected using UPV tests. Significant variations in pulse velocity values are indicative of broken and degraded concrete. The concrete’s density and wave velocity are related. Therefore, this test has a tremendous potential for evaluating the quality of concrete.

Relevant IS code for Ultrasonic Pulse Velocity Test (UPV Test)

IS-13311 (Part 1):1992 (Reaffirmed- May 2013) “Non-Destructive Testing of Concrete- Methods of Test (Ultrasonic Pulse Velocity)”

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Ultrasonic Pulse Velocity tester

The UPV tester is the name of the type of equipment used to measure ultrasonic pulse velocity. The following accessories are included in ultrasonic pulse velocity tester.

  • Electrical Pulse generator
  • Pair of Transducers (probes)
  • Amplifier
  • Electronic timing device
Ultrasonic Pulse Velocity Tester
Ultrasonic Pulse Velocity Tester

Principles of Ultrasonic Pulse Velocity test

The electrical pulse generator generates pulses that are sent through the UPV tester’s transducer. Through the concrete surfaces, the pulse generates many reflections. Using the formula shown below, the pulse velocity is calculated.

Pulse velocity, V = L/T

where L is the traverse distance, T is the time for the receiver to receive the pulse

The geometry of the material is unrelated to the UPV test. Better concrete strength is associated with higher velocity and vice versa. One of the dynamic tests for concrete is the ultrasonic pulse velocity test.

Objective of UPV tests

The main objectives of the ultrasonic pulse velocity test or UPV tests are

  • To learn the homogeneity of the concrete.
  • Determines the presence of cracks, voids and imperfections. 
  • To calculate the elastic modulus of concrete. 
  • Finds the quality of concrete relative to the standard requirements. 
  • To determine the age of concrete. 

Factors affecting Ultrasonic pulse velocity test

The UPV test detects cracks and assists in structure development. However, a number of factors influence how pulse velocity is measured. As a result, compressive strength cannot generally be approximated from the pulse velocity. The following are the elements that impact the UPV test.

  • Presence of reinforcement
  • Water content
  • Mix proportion
  • Temperature of concrete
  • Concrete age
  • Stress level of concrete

Methodology of Ultrasonic Pulse velocity tests

Piezoelectric and magneto strictive types of transducers are suitable for use with the UPV test. Additionally, its frequency range should be between 20 and 150 kHz. The electronic timing device monitors time with an accuracy of 0.1 microseconds.

The transducer transmits the waves that travel through the concrete surface. The receiver transducer detects the electric signals that are generated once the pulse waves are transformed to them. The traversal length will be displayed as ( L). The electronic timing device calculates how long it takes for signals to arrive. Time is shown as (T).


The Electronic timing device measures the receiving time of the signals. The time is denoted as (T).

Pulse velocity (v) = L/T

There are three common methods for doing UPV tests. They are direct method and indirect method.

  • Direct Method of UPV Testing
  • Indirect Method of UPV Testing
Methodology of UPV test
Methodology of UPV test

Direct method

The maximum energy is transmitted at right angles to the face of the transmitter. As a result, to achieve the greatest results, the receiving transducer must be placed on the side of the transmitting transducer. This is referred to as the direct approach or cross probing.

Ultrasonic pulse velocity test
Ultrasonic Pulse velocity test -Types

Indirect method

In some circumstances, the opposite side of the structure may be inaccessible. The receiving and transmitting transducers are installed on the same face of the concrete members in this scenario. This is known as the indirect method or surface probing. This approach is less effective than the direct approach. The test findings are mostly influenced by the surface concrete, which has different properties from the structural components’ core concrete.

Result interpretation of UPV testing

The density and elastic modulus of concrete are correlated with the ultrasonic pulse velocity. This in turn depends on the components, mixing processes, placement techniques, concrete compaction and curing, casting temperature, etc.

The main causes of internal cracks and pockets in concrete are lack of compaction and concrete segregation. Lower pulse velocity values are a result of these concrete defects. However, the laboratory tests might have confirmed a well-designed concrete.

The range of pulse velocity in the direct method is as shown below.

  1. Above 4.5 Excellent
  2. 3.5 to 4.5 Good
  3. 3.0 to 3.5 Medium
  4. Below 3.0 Doubtful

Conclusion

The final assessment of compressive strength from UPV is not the sole criterion used to determine concrete strength. The strength is confirmed by comparing it to a compressive strength estimate derived from the same ingredient mix and conditions. The results of the UPV test and site tests conducted using similar ingredients may be correlated. When compared to actual UPV intensities, the numbers may change by about 20%.

CONCRETE, quality tests on concrete

Non Destructive test (NDT)- Hardened Concrete

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Non-destructive test (NDT) and destructive tests (DT) are the the tests done one hardened concrete. Concrete is the oldest and most important construction material in the world. Testing of the concrete plays and important role to know about the strength, durability and condition of the structure. This article is about the types of Destructive and non destructive tests done on concrete.

Also read : Flow table test for workability of concrete

Also read : Concrete mixing objective and types

Types of concrete tests

Tests on hardened concrete are classified into two types.

  • Non destructive tests (NDT)
  • Destructive test (DT)

Non destructive tests and Destructive tests are done to determine the important properties of concrete like compressive strength, flexural strength, tensile strength etc.

Non- Destructive tests

The standard method of testing hardened concrete is by testing the concrete specimens cast simultaneously with structural concrete. These tests can determine the compressive, flexural, and tensile strengths. The major disadvantage of these tests is the non availability of immediate results. Moreover, the properties of the concrete specimen may differ from what it is in the actual structure. This difference is due to pouring conditions, curing factor, compaction and concrete density, etc. These tests come under the category of destructive tests (DT). Destructive testing destroys or changes the part in some way such that even if it passes the test it is no longer fit for service.

Non Destructive test is for determining compressive strength and other properties of concrete from existing structures or buildings. NDT does not destroy or change the part such that it is still fit for service if it passes the test. The non-destructive test determines the properties of concrete or structures without their destruction. Moreover, we can study its changes over time, The measurements are repeated many times and validate in detail, and gets immediate results.

Objectives of Non destructive test

  • Quality check of the existing structure.
  • For determining the homogeneity, internal and external characteristics of the concrete. 
  • To detect the cracks and voids of the concrete structures. 
  • Assess the quality of concrete with the standard requirement. 
  • To study the ageing of concrete. 
  • For finding the compressive strength of structures.
  • Evaluation of elastic modulus

Classification of Non-Destructive test

Non destructive tests are the following types.

Penetration Resistance Test

The penetration resistance test is an NDT that determines the relative strength of the concrete structures. The Windsor probe is the equipment for conducting this test. This equipment includes of powder-actuates driver or gun, probes, loaded cartridges and a gauge that measures the penetration.

The penetration depth indicates the compressive strength of the concrete. However, this depends on the aggregate type and size. This test evaluates the poor quality and deterioration of concrete

The major disadvantage of this test is getting variable results. Several probes are often shot to achieve a solid average depth for arriving a final conclusion. So we cannot determine the exact strength. But it is a quick method to evaluate the quality and maturity of concrete. Care should be taken to calibrate the instrument before taking readings.

Rebound Hammer Test

The rebound hammer is also known as Schmidt’s Hammer test. It determines the strength of concrete based on the hardness of the concrete surface. It is a surface hardness tester. The equipment consists of a spring-controlled plunger, a hammer that weighs 1.8 kg, and a graduated scale. By pressing the hammer on the concrete surface, the graduate scale measures the rebound number. A low rebound number means the concrete has low compressive strength and stiffness.

Non destructive test - Rebound hammer test
Rebound hammer test

An accuracy of 15 to 20% is possible through this test. It is a simple and quick method. Also, the result relies on the surface smoothness, water content, type and size of aggregate and carbonation of the surface.

Ultrasonic Pulse Velocity Test

Ultrasonic pulse velocity test is another type of Non-destructive test. This test measures the time of travel of ultrasonic pulse waves for evaluating the concrete quality. The UPV test units consists of a pulse generator and pulse receiver. The frequency of the wave is 50-55 kHz. The pulse generator produces the pulses and is allowed to pass through the concrete. Then we calculate the velocity, by measuring the traversing distance and the time. Higher velocity means the concrete has a higher elastic modulus and density. It also determines the cracks and flaws in the structure. Large differences in pulse velocity values indicates a defective and deteriorated concrete.

For more details : Ultrasonic pulse velocity test || UPV Test – Methods and procedure

Non destructive test - pulse velocity test
Ultra sonic pulse velocity test

Pullout Test and Pull-off Test

The pullout test in concrete is done using the LOK test and CAPO test. It defines the strength of concrete by measuring the force to pull the embedded disc from the structure. This can be done for both fresh and hardened concrete. The pullout test equipment induces a pullout force toward the concrete. This pullout force is related to the concrete strength. The dimension of the ring, the orientation of the embedded insert, type of aggregate are some factors that influence this test. In addition, this test terminates the curing of concrete and measures the time for form removal. 

Non destructive test-Pull out test
Pull out test

Concrete Core Testing

The Concrete core testing is a non-destructive test of concrete. Concrete cores cut using a rotary cutting tool as shown in the fig. We get an uneven cylindrical core specimen. By testing this specimen in the compression testing machine in a moist condition, we get the strength. This sample also determines the density, depth of concrete carbonation, permeability, chemical analysis, etc. 

Concrete core cutting
Concrete core cutting

Thus through Non-destructive test, it is possible to investigate the variation in concrete quality with time and external factors. When compared to other destructive test, there is no wastage of materials. Therefore, NDT is quick and most effective test of concrete.