Permeability of Concrete
1. objective
Permeability of cement mortar or concrete is of particular significance in structures which are intended to retain water or which come into contact with water. Besides functional considerations, permeability is also intimately related to the durability of concrete, specially its resistance, against progressive deterioration under exposure to severe climate, and leaching due to prolonged seepage of water, particularly when it contains aggressive gases or minerals in solution. The determination of the permeability characteristics of mortar and concrete, therefore, assumes considerable importance.
2. Apparatus required
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Fig. 1: Concrete Permeability ApparatusThe permeability cell shall consist of a metal cylinder for holding the specimen. A rubber or neoprene O-ring or other suitable gasket, seated in matching grooves shall be used between the cell and the cover plate to render the joint water-tight. |
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Fig. 2: Water Reservoir in Permeability ApparatusA suitable reservoir may consist of a length of metal pipe, 50 to 100 mm in diameter and about 500 mm long. The reservoir shall be fitted with a graduated side arm gauge-glass, and the necessary fittings and valves for admitting water and compressed air and for draining, bleeding and connection to the permeability cell. |
3. Reference
IRS Concrete Bridge Code : 1997.
4. Procedure
(a) Preparation of Test Specimen
Test specimen of 200 mm diameter and 120 mm thich shall be used. After 24 hrs of casting of specimen, central circular area of 100 mm diameter shall be roughened with a wire brush on the side on which the water pressure is to be applied. The unroughened part of the side of the test specimen which is subjected to water pressure is to be sealed with two coats of cement water paste (W/C = 0.4).
(b) Test Procedure
After 28 days curing, test specimen is fitted into a test apparatus where the
water pressure acts on the required face and remaining faces can be observed.
At first, a pressure of 1 Bar is applied for 48 hours, then 3 Bar for 24 hours and
7 Bar for 24 hours.
After the test, the specimen is split in the middle by the compression applied
on two round steel bars lying on opposite sides, above and below. The side after the
test specimen exposed to the water pressure should face downwards.
5. Observation
The greatest water penetration depth, is taken as the average value of the greatest penetration depths on three test specimen.