Tests on concrete pipes

To evaluate the properties of the concrete pipes (pressure type, non pressure type and prestressed concrete pipes) the following tests are done as per IS 3597:1998 .

  1. Absorption test
  2. Hydro static test
  3. Permeability test
  4. Three-edge bearing test

General precautions

Before we move on to the testing part lets go through a few general precautions that one has to follow in order to get more accurate results.

  1. The test specimens should not have been exposed to a temperature below 4°C for 24 hours immediately preceding the test and should be free from all visible moisture.
  2. The specimens should be inspected and any specimen with visible flaws should be discarded.
  3. If any test specimen fails because of mechanical reasons, such as failure of testing equipment or improper specimen preparation, it should be discarded and another specimen should be taken.

ABSORPTION TEST

TEST SPECIMEN REQUIREMENT:

Each specimen selected at random should have a square area of 100cm² ± 10 % of the length of the pipe as measured on the surface of the pipe and a thickness equal to the full depth of the pipe thickness and should be free from visible cracks.

Procedure:

  1. Specimens shall be dried in a mechanical convection oven at a temperature of 105°C to 115°C until two successive weighings at intervals of not less than 8 hrs show an increment of loss not more than 0.1 % of the mass of the specimen. The drying time should be not less than 36 hours.
  2. The dry mass of the specimen should be the mass after the final drying, determined at ambient temperature(A).
  3. After drying and weighing, the specimens should be immersed in clean water at room temperature for the specified period.
  4. The specimens should then be removed from the water and allowed to drain for not more than one minute.
  5. The superficial water should then be removed by absorbent cloth or paper and the specimens are weighed immediately and noted down (B).

NOTE: The least count/accuracy of the weighing balance should be 0.1 g in which the test specimen is weighed.

Result:

Percentage Absorption = (B-A)/A  × 100.

NOTE: The percentage absorption is expressed in terms of the dry mass of the specimen and results should be reported separately for each specimen.

HYDROSTATIC TEST

TEST SPECIMEN REQUIREMENT:

The specimens for determination of leakage under internal hydrostatic pressure should be sound and full-size pipe. If the pipes are tested after storing in adverse weather condition pre-soaking shall be permitted. For pre-soaking, the pipes are submerged in water or sprayed with water for a period not less than 6 hours prior to testing and excess water removed.

Procedure:

  1. The pipe should be supported in such a way that the longitudinal axis is approximately horizontal and the exterior surface excepting the supports can be examined readily.
  2. The equipment for making the test should be such that the specimen under test can be filled with water for the exclusion of air and subjected to the required hydrostatic pressure. Apply hydrostatic pressure to the whole pipe including the portion of the socket and rebated joints, that is, subjected to pressure in “as laid” condition.
  3. The specimen should be filled with water and expel the air. Pressure should be applied at a gradual rate until the specified test pressure is reached, or until beads of water on the pipe surface is seen, whichever occurs first.
  4. Pressure should be maintained for 1 min + 30 s for each 10 mm of wall thickness, or for twice that entire period if the application of pressure resulted in the formation of beads of water on the pipe surface.
  5. At the end of the holding period, the pressure should be released immediately if the test pressure has been maintained. If the beads of the water have not grown, the run the pressure should be increased slowly until the test pressure is reached or the beads of water grow or run (whichever occurs first).
  6. If the test pressure has been reached without the beads of water growing or running, the test pressure should be maintained constant for 1 min + 30s for each 10 mm of wall thickness. At the end of the holding period, the pressure should be released immediately.
  7. After releasing the pressure, the test pipe should be drained completely.

PERMEABILITY TEST

Procedure:

  1. The dry surface of the pipe should be scrapped off by wire brush and loose particles, if any, removed.
  2. Sealant should then be applied to the lower portion of the cup and should be pressed on the pipe.
  3. The water should then be filled in the cup with wash bottle after hardening of the sealant. The glass tube with cork shall then be fixed in the cup as shown in the figure.
  4. Water in the tube should then be filled using wash bottle and air shall be allowed to escape during filling.
  5. Precaution should be taken so that water does not leak either from cup ends or from rubber stopper.
  6. Water should be filled up to zero mark and reading should be taken at every half-hour interval up to 2 hours.
  7. On each pipe, simultaneously three tests should be done immediately after the curing of the coating as shown in the figure.
  8. The drop of water level in the stand pipe at the end of 2 hrs is initial absorption. The difference in any two readings shall not be more than 0.8 cm³.
  9. Fill the water in the stand pipe again up to the mark and take readings at half-hour interval up to 4 hours.

Result:

Absorption in the fourth hour, that is, the difference between fourth and third reading is the final permeability.

NOTE: The average reading of three tests conducted on a pipe shall be expressed in cm³ and this shall not exceed 0.3 cm³.

THREE-EDGE BEARING TEST

TESTING MACHINE:

Any mechanical or hand-powered device may be used in which the head that applies the load moves at such a speed as to increase the load at a uniform rate of approximately 20 percent of the expected crushing load per linear metre per minute. The loading device shall be calibrated within an accuracy of ±2 percent.

TESTING SETUP:

CRACK MEASURING GAUGE:

The crack measuring gauge should be made from 0.25 mm thick strip and should be of a shape as shown in Fig.2 below.

Procedure:

  1. The specimen should be placed on the two bottom bearing strips in such a manner that the pipe fits firmly and with the most uniform possible bearing on each strip for the full length of the pipes less than the socket portion if any.
  2. If mutually agreed upon by the manufacturer and the purchaser prior to the test, a fillet of plaster of Paris not exceeding 25 mm in thickness may be cast on the surface of the upper and lower bearing before the pipe is placed. The width of the fillet cap,top or bottom, should be no more than 25 mm per 300 mm diameter. but in no case less than 25mm.
  3. Each end of the pipe at a point mid-way between the lower bearing strips should be marked and then diametrically opposite points thereof should be established.
  4. The top bearing block should be so placed that it contacts the two ends of the pipe at these marks. After placing the specimen in the machine on the bottom strips, the top bearing should be symmetrically aligned in the testing machine.
  5. Load should be applied until either the formation of a 0.25 mm wide crack or ultimate strength load, as may be specified.
  6. The 0.25 mm crack load is the maximum load applied to the pipe before a crack having a width of 0.25 mm measured at close intervals, occurs throughout a length of 300mm or more.
  7. The crack should be considered 0.25 mm in width when the point of the measuring gauge penetrates 1.5 mm at close intervals throughout the specified distance of 300 mm. The ultimate load will be reached when the pipe will sustain no greater load.

Result:

Crushing strength (in Newton per linear metre of the pipe) = (Total load/Nominal laying length)

NOTE: In case of spigot and socket ended pipes, the effective length should be equal to the overall length minus the depth of socket and in case of the collar and flush jointed pipes, the effective length should be equal to the overall length.