Ultrasonic Pulse Velocity Test Procedure on Concrete, IS 516 Part-5 Sec-1

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This article covers the definition, apparatus list, IS code and test procedure for ultrasonic pulse velocity test on concrete, IS 516 Part-5 Sec-1. In addition, some general guidance on the interpretation of the test results are also covered here.
Additional procedure for indirect transmission of transducers, estimation of the depth of a surface crack and determination of dynamic Yang’s Modulus of elasticity are also covered here.

Before that take a look at why the test ultrasonic pulse velocity is performed on concrete.

Why ultrasonic pulse velocity test is performed?

Ultrasonic pulse velocity test is performed on concrete to check their quality and homogeneity and also cracks, voids, cavities and defects in the concrete by passing electronic wave through the concrete. The apparatus used in the test is called ultrasonic pulse velocity meter.


Ultrasonic Pulse Velocity Test Procedure on Concrete, IS 516 Part-5 Sec-1 2018

 
Ultrasonic Pulse Velocity Test on Concrete | Concrete UPV Test

Table of Contents  (toc)


Read here the test procedure of ultrasonic pulse velocity test on concrete and the list of apparatus which are used in this test as per IS 516 Part-5 Sec-1 : 2018.


Apparatus List for Ultrasonic Pulse Velocity Test on Concrete

The apparatus used in UPV test is called Ultrasonic Pulse Velocity Meter ( or Tester). This consists the following:
  • Electrical Pulse Generator,
  • A pair of Transducer (a transmitter and a receiver),
  • Standard Calibration Bar
  • An Amplifier and
  • Electronic Timing Device.


IS Code for Ultrasonic Pulse Velocity Test on Concrete

The Indian standard code i. e. IS code for ultrasonic pulse velocity test for concrete is IS 516 (Part-5 Sec-1) : 2018. The old IS code for the UPV test is IS 13311 Part-1.


Test Procedure for Ultrasonic Pulse Velocity Test on Concrete

The test method is explained here in 9 parts.
  1. Preparation of Specimen: Concrete Surface Preparation,
  2. Ultrasonic Measurement: Placement of the Two Transducers on Concrete Surface,
  3. Procedure of Ultrasonic Pulse Velocity Test for Different Transducer Arrangements
  4. Ultrasonic Pulse Velocity Test: Results
  5. Interpretation of UPV Test Result
  6. Important Things to Keep in Mind While Performing the Test
  7. Additional Procedure for Indirect/Surface Transmission of Transducers,
  8. Estimation of the Depth of a Surface Crack Using UPV Measurement, and
  9. Determination of Dynamic Yang’s Modulus of Elasticity Using UPV Measurement.


Preparation of Specimen : Concrete Surface Preparation

  1. At the observation site, locate dry location in the concrete structure.
  2. Use a grinding wheel or carborundum stones to remove any plaster or other coating from the concrete surface.
  3. Use adequate acoustical couplants like grease, petroleum jelly, liquid soap, kaolin glycerol between the concrete structure and the face of each transducer to improve the contact between them.
  4. If the concrete surface is very rough, then smooth and level an area of the surface where the transducer is to be placed.
  5. Take care to avoid any damage to the concrete surface or concrete structure.
  6. Divide the entire structure in suitable grid markings of 300 mm x 300 mm or even smaller. Each junction point of the grid becomes a point of observation.


Ultrasonic Measurement : Placement of the Two Transducers on Concrete Surface

The two transducers are placed on the concrete surface by three methods.
(A) Direct transmission method : Both transducers are placed opposite faces of concrete surface (see Fig. A).
(B) Semi-direct transmission method : Both transducers are placed adjacent faces of concrete surface (see Fig. B).
(C) Indirect or surface transmission method : Both transducers are placed same face of concrete surface (see Fig. C).

Three methods to Place the Transducers on Concrete Surface
  • Direct transmission (cross probing) method is the most efficient method to measure ultrasonic pulse velocity. So if possible it will be adopted as first choice.
  • Sometimes, it may be necessary to place the transducers on opposite faces but not directly opposite to each other but adjacent faces. Such arrangement also regarded as semi-direct transmission method.
  • The indirect transmission arrangement is the least sensitive and shall be used when only one face of the concrete member is accessible, or when the quality of the surface concrete relative to the overall quality is of interest.
Indirect transmission (surface probing) method is not so efficient as cross probing method, because the signal produced at the receiving transducer has an amplitude of only 2 % to 3 % of that produced by cross probing and the test results are greatly affected by the surface layers of concrete which may have different properties from that of concrete inside the structural member. The indirect velocity is invariably lower than the direct velocity on the same concrete element. This difference may vary from 5 % to 20 % depending largely on the quality of the concrete under test. For good quality concrete, a difference of about 0.5 km/s may generally be encountered. For the procedure and for calculating the exact value of ultrasonic pulse velocity by surface probing (see part 6th of the procedure).


Procedure for Ultrasonic Pulse Velocity Test for Different Transducer Arrangements

  1. Major the distance (L) between the grid points where the transmitting and receiving transducers are to be placed. It is the path length (L) between the transducers.
  2. Apply typical acoustical couplants like petroleum jelly, grease, liquid soap or kaolin glycerol paste between the concrete surface and the face of each transducer. This helps to smooth and ensure good acoustical contact between the transducers and the concrete surface.
  3. Press the transmitter and receiver transducers on the predetermined grid points of the concrete surface.
  4. Transmitter transducer produce the the ultrasonic pulse and after traversing, the pulse of vibrations is converted into an electrical signal by the second transducer.
  5. Switch on the ultrasonic pulse velocity meter.
  6. Record the traverse time (T) that displayed on the ultrasonic pulse velocity meter. It is the time required to traverse the ultrasonic pulse from transmitter to receiver probes.
  7. Compute the apparent pulse velocity by the formula:
V = L/T

Surface probing (indirect transmission) in general gives lower pulse velocity than in case of cross probing and depending on number of parameters, the difference could be of the order of about 0.5 km/s. In view of this, it is recommended that, in surface probing method the pulse velocity may be increased by 0.5 km/s, for values ≥ 3.0 km/s.
(The additional procedure for this method is explained in part 6 of procedure.)


Ultrasonic Pulse Velocity Test : Results

The quality grade of concrete in terms of uniformity, incidence or absence of internal flaws, cracks and segregation, etc is related to apparent pulse velocity as given in the below table.

Table: Velocity Criterion for Concrete Quality Grading

Sl No.

Average Value of Pulse Velocity by Cross Probing (km/s)

Concrete Quality Grading

(i)

Above 4.40

Excellent

(ii)

3.75 to 4.40

Good

(ii)

3.00 to 3.75

Doubtful

(iv)

Below 3.00

Poor

In Case of 'doubtful' quality it may be necessary to carry out further tests.

If the difference between maximum and minimum value of apparent pulse velocity is less than 0.5 km/s then the concrete is considered as uniform quality and if the difference is greater than 0.5 km/s then the concrete is considered as doubtful.

Interpretation of UPV Test Result

The ultrasonic pulse velocity of concrete is mainly related to its density and modulus of elasticity. This in turn, depends upon the materials and mix proportions used in making concrete as well as the method of placing, compaction and curing of concrete. For example, if the concrete is not compacted as thoroughly as possible, or if there is segregation of concrete during placing or there are internal cracks or flaws, the pulse velocity will be lower, although the same materials and mix proportions are used.

Since actual values of the pulse velocity obtained, depend on a number of parameters, any criterion for assessing the quality of concrete on the basis of pulse velocity as given in above Table can be held as satisfactory only to a general extent. However, when the comparison is made amongst different parts of a structure, which have been built at the same time with supposedly similar materials, construction practices and supervision, the assessment of quality becomes more meaningful and reliable. Whenever the UPV values are lesser by more than 10 percent of average value of the member/part of structure, the location shall be considered as having internal flaws or segregation caused by poor workmanship or there could be micro-cracks.


Important Things to Keep in Mind While Performing the Test

  1. If the concrete is firm then the pulse traverses through direct path. So high pulse velocity is obtained.
  2. If a flaw or damage is present in the traverse path then the pulse traverses around the damage and takes more time than direct traverse. So the pulse velocity obtained in such conditions is lower than the direct traverse.
  3. If it is necessary to work on concrete surfaces formed by other means, for example trowelling, it is desirable to measure pulse velocity over a longer path length than would normally be used. The recommended minimum path length of one unmoulded concrete surface is 150 mm for the direct transmission method and 400 mm for the indirect transmission method.
  4. The preferred natural frequency of transducers is within the range of 20 kHz to 150 kHz. Generally, low frequency transducers are preferable for long path lengths and high frequency transducers for short path lengths. Transducers with a frequency of 50 kHz to 60 kHz are useful for most all-round applications. 
  5. Since size of aggregates affects the pulse velocity measurement. So the minimum path length of 100 mm is recommended for concrete, in which the nominal maximum size of aggregate is less than or equal to 20 mm and the minimum path length of 150 mm is recommended for concrete, in which the nominal maximum size of aggregate is between 20 mm and 40 mm.
  6. Larger grid spacing up to maximum 500 mm x 500 mm may be adopted for general overall assessment of larger structures having uniform cross-section showing no signs of distress. The number of individual test points or grid spacing depends upon the size of the structure, the accuracy required and the variability of the concrete.


Additional Procedure for Indirect (or Surface) Transmission of Transducers

Why this Additional Procedures are Required ?

With indirect transmission, there is some uncertainty regarding the exact length of the transmission path because of the significant size of the areas of contact between the transducers and the concrete. It is therefore preferable to make a series of measurements with the transducers at different distances apart to eliminate this uncertainty.

The Additional Procedures

  1. Place the transmitting transducer in contact with the concrete surface at a fixed point x and the receiving transducer at fixed increments x along a chosen line on the surface (see Fig. 1).
  2. Draw a graph (best straight line) between the recorded transmission time the distance separating the transducers (see Fig. 2).
  3. Measure the slope (tan ф) of the straight line. Where ф is the angle between the straight line and distance axis.
  4. Find the inverse value of the slope. This gives the mean pulse velocity along the chosen line on the concrete surface.
Transducer Setup
Fig. 1 Transducer Setup

Ultrasonic Pulse Velocity Determination by Indirect Transmission
Fig. 2 Ultrasonic Pulse Velocity Determination by Indirect Transmission

Where the points measured and recorded in this way indicate a discontinuity, it is likely that a surface crack or surface layer of inferior quality is present and a velocity measured in such an instance is unreliable.


Estimation of the Depth of a Surface Crack Using UPV Measurement

Measurement of Depth or Crack by UPV Method
Fig, 3 Measurement of Depth or Crack by UPV Method

Longitudinal pulse velocity = α
Distance travelled in uncracked concrete = 2x
Distance travelled in cracked concrete = 2√(x² + h²)
Tc² (in cracked concrete) = (4x² + 4h²)/α²
Ts² (in uncracked concrete) = 4x²/α²
Therefore,
Where,
Tc = travel time around the crack,
Ts = travel time along the surface of the same type of concrete without any crack, and
h = depth of crack.


Determination of Dynamic Yang’s Modulus of Elasticity Using UPV Measurement

The dynamic Young's modulus of elasticity (E) of the concrete may be determined from the pulse velocity and the dynamic Poisson's ratio (μ), using the following relationship:
Where,
E = dynamic Young Modulus of elasticity in MPa;
ρ = density in kg/m³; and
V = pulse velocity in mm.
The above relationship may be expressed as:

The value of the dynamic Poisson's ratio varies from 0.20 to 0.35, with 0.24 as average. However, it is desirable to have an independent measure of it for the particular type of concrete under test. The dynamic Poisson's ratio may be obtained from measurements on concrete test-beams of the pulse velocity (V) along with length (l) of the beam and the fundamental resonant frequency (n) of the beam in longitudinal mode of vibration. From these measurements, the factor f(μ) is calculated by the relation:
where,
n = fundamental resonant frequency in cycles per second; and
l = length of specimen, in meter.

The explanation of apparatus list, IS code, procedure, some guidance and additional procedure for ultrasonic pulse velocity test on concrete has been completed. Thanks for reading full article.

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