Determination of water permeability of concrete cover

1. Scope

   This standard specifies a method for the determination of the water permeability of concrete cover as a durability performance indicator. It covers concrete of grades ranging from 20 to 80 MPa.

2. Referenced documents

   The following documents contain provisions which constitute some of the provisions of this draft standard.

   • BS 6089: 1981, "Guide to Assessment of Concrete Strength in Existing Structures", British Standard Institution, London, 1981.
   • ISO/DIS 7031 Concrete hardened - Determination of the depth of penetration of water under pressure.
   • MS 26: Part 1:1991 Section Eight: Method for making test cubes from fresh concrete

3. Apparatus

   The apparatus comprises a pressure chamber with provisions for the accurate measurement of pressure, temperature and the volume of water permeating into the concrete cover to be tested for water permeability.

   A computerised data acquisition system is preferred for the real-time display of the value of water permeability against time. A permanent record of the ambient air temperature, humidity and the water temperature is to be kept while the test is in progress.

4. Test specimens

   The test should preferably be performed on a 150 mm concrete cube. Cored or sawn specimens from existing concrete structures should be taken from locations determined by a professional civil or structural engineer together with the relevant authorities. The principle of sampling, accuracy and tolerance shall be in accordance with information contained in the referenced documents. It is recommended that at least three test specimens be used in each test.

5. Conditioning of test specimens

   The test specimens should be placed on a raised wire gauze and conditioned at between 65 - 80% RH and around 26 - 33 ^oC and tested at 28 days. The duration of moist curing after the specimens are demoulded should be similar to the actual curing conditions of the concrete products or structures.

6. Test procedure
   • The test should preferably be conducted on test specimens of age 28 days. Specimens of other ages may be chosen according to special conditions or requirements.
   • The density of the test specimens should be determined before the test.
   • Careful setting up of the apparatus is necessary to prevent any seepage of water from the concrete cover in contact with the pressure chamber. If water leakage occurs, the test shall be stopped.
   • The water pressure is recommended to be between 1.5 bar and 4 bar depending on the quality of concrete specimens to be tested.
   • The apparatus should be calibrated with a mature concrete test cube of known value of water permeability and conditioned for the calibration.
   • The duration of calibration test is preferably not less than 1 hour. However, the duration may be reduced if the calibration test results indicate that a steady flow condition has occurred.

7. Test report

   The test report should contain the following mandatory and optional data:

   Mandatory data:

   • Apparent density
   • Conditions of curing and storage
   • Shape and dimensions of the test specimens
   • Age of concrete at the time of test
   • Type of water used for the test
   • Temperature and relative humidity in the test chamber
   • Direction of application of water pressure in relation with the direction of casting or mould filling.
   • Any deviation from the procedure specified.

   Optional data:

   • Computer printout from data acquisition system.
   • Sketches or photograph of the test specimen and while the test is in progress.