Water Permeability
When concrete is permeable, it allows water, air, and other harmful substances to penetrate into the concrete and reach the steel reinforcement. This can cause corrosion of the steel reinforcement and ultimately lead to spalling of the concrete.
Corrosion occurs when the steel reinforcement comes into contact with water and oxygen. The presence of CO2, SO3-, and Cl- can also accelerate the corrosion process. As the steel corrodes, it expands and creates pressure on the surrounding concrete, causing it to crack and eventually spall.
Making concrete impermeable can help prevent the penetration of water, air, and harmful substances, which in turn can prevent corrosion of the steel reinforcement and spalling of the concrete. This can be achieved by using a variety of techniques, such as adding waterproofing admixtures, using low water-to-cement ratios, and applying sealers and coatings to the surface of the concrete.
It's important to note that preventing spalling requires a combination of proper design, construction, and maintenance. In addition to making the concrete impermeable, it's also important to ensure that the concrete is properly reinforced, cured, and maintained over its lifetime to prevent the development of cracks and other defects that can lead to spalling.
Test Procedure for Concrete Permeability
Equipment Required:
Concrete mixer
Moulds of size 200mm dia and 120mm height
Trowel and finishing tools
Compression machine
Water pressure apparatus
Materials Required:
Concrete mix
Cement paste
Test Procedure:
Prepare the concrete mix as per the design mix and cast three specimens of size 200mm dia and 120mm height using the moulds.
After 24 hours, roughen the middle portion of each specimen to a diameter of 100mm using a trowel or any suitable tool. The remaining portion of each specimen should be sealed with cement paste.
Cure the specimens for 28 days in a water tank, ensuring that the temperature and humidity are maintained as per the standard curing conditions.
After 28 days, connect the water pressure apparatus to the roughened surface of each specimen and apply water pressure as follows:
1 bar (1kg/cm2) for 48 hours
3 bars for the next 24 hours
7 bars for the next 24 hours
After applying the water pressure, remove the specimens from the water tank and allow them to dry for 24 hours.
Place each specimen on the compression machine and apply a concentrated load at two diagonally opposite points slightly away from the central axis. The load should be increased gradually until the specimen cracks and the depth of penetration of water is measured.
Repeat the test for all three specimens and calculate the average of the three maximum values of penetration.
If the depth of penetration of water is less than or equal to 25mm, the specimen passes the permeability test. If the depth of penetration of water is more than 25mm, the specimen is considered to have failed the permeability test.
Record the test results in a tabular form, indicating the depth of penetration of water for each specimen and the average value.
Draw conclusions based on the test results and make recommendations for improvements in the concrete mix or construction practices, if necessary.