What is Permeability of Concrete?
Permeability is the ability of concrete to allow liquids or gases to pass through it. It measures the amount of water, air, and other substances that can penetrate the concrete through its pores. Concrete inherently contains pores that provide a pathway for these substances to enter.
One of the primary causes of concrete deterioration is the corrosion of reinforcement steel due to permeability. When water or moisture reaches the reinforcement steel, corrosion occurs, causing the steel to expand. This expansion leads to cracking and spalling of the concrete, reducing its durability and structural integrity.
To prevent such issues, concrete should be designed to be impermeable. However, in some cases, permeable concrete is intentionally used to facilitate water drainage, such as in pavements, parking areas, residential streets, and walkways.
To assess the permeability of concrete, several tests are conducted. This article explores the various permeability tests in detail.
Permeability Test of Concrete
Permeability tests are crucial, particularly for Reinforced Cement Concrete (RCC), as reinforcement bars are susceptible to corrosion upon exposure to water. Corrosion causes an increase in volume, leading to cracks in the concrete element. To evaluate the permeability of concrete, the following common tests are used:
1. Rapid Chloride Permeability Test (RCPT)
This test determines the ability of concrete to resist chloride ion penetration by measuring the passage of electric current through a concrete sample.
Apparatus Required:
- RCPT equipment with two reservoirs containing solutions:
- 3% Sodium Chloride (NaCl)
- 0.3M Sodium Hydroxide (NaOH)
- Concrete samples of 50mm and 100mm thickness
Procedure:
- Concrete samples of 50mm and 100mm thickness are cast and cured.
- The sample is placed between the two reservoirs.
- A 60V electric current is applied for 6 hours.
- The amount of current passing through the concrete sample is measured using an LCD display on the equipment.
- Typically, 2 to 3 samples from the same batch are tested to improve accuracy.
- The final permeability value is determined by averaging the results.
Formula for RCPT:
Q = 900 × ( I0 + 2×I30 + 2×I60 + 2×I120…….. + I360 )
Where:
- Q = Total charge passed (in coulombs)
- I0 = Initial current reading (in amperes)
- It = Current reading at time t after applying voltage
Interpretation of Test Results:
| Charge Passed (Coulombs) | Chloride Permeability |
| > 4000 | High |
| 2000 – 4000 | Moderate |
| 1000 – 2000 | Low |
| 100 – 1000 | Very Low |
| < 100 | Negligible |
- Water Permeability Test (Water Penetration Test)
This test determines the permeability of concrete by measuring the water passing through a sample under pressure.
Apparatus Required:
- Disc-shaped concrete sample (thickness > 20mm)
- Permeameter
- Water collection jar
Procedure:
- Place the concrete sample inside the permeameter.
- Fill the permeameter with water.
- Apply a specific pressure and allow water to pass through the concrete sample.
- Collect the water that penetrates the sample in a jar.
Formula for Water Permeability Test:
k = QL / tAh
Where:
- k = Coefficient of permeability
- Q = Discharge of water into the collection unit
- t = Elapsed time (in seconds)
- L = Length of the concrete specimen
- A = Cross-sectional area of the specimen
- h = Applied pressure head (in metres)
Effects of Permeability of Concrete
Permeability in concrete significantly impacts the durability and longevity of structures. If concrete is highly permeable, it allows the penetration of water, chemicals, and gases, leading to several adverse effects, including:
1. Corrosion of Reinforcement
Water and oxygen enter through pores and reach the steel reinforcement.
This causes rust formation, leading to expansion and cracking.
Over time, corrosion weakens the structural integrity of the concrete.
2. Reduced Strength and Durability
Excess moisture reduces the bonding between cement and aggregates.
Weak bonding decreases the compressive strength of concrete.
Concrete structures may deteriorate faster under load.
3. Chemical Attack and Efflorescence
Permeable concrete allows harmful chemicals (chlorides, sulfates, and acids) to penetrate.
Chemical reactions lead to degradation of concrete and loss of strength.
Efflorescence (white salt deposits) appears on concrete surfaces due to water-soluble salts.
4. Freeze-Thaw Damage
In cold climates, water enters the concrete and freezes.
Ice expansion creates internal pressure, causing cracks and scaling.
Continuous freeze-thaw cycles accelerate surface deterioration.
5. Increased Water Absorption
High permeability leads to water absorption, which results in dampness and leakage.
This affects indoor environments, causing mold growth and reducing comfort.
6. Alkali-Silica Reaction (ASR)
Moisture penetration triggers ASR, a chemical reaction between silica in aggregates and alkalis in cement.
ASR results in expansive gel formation, leading to cracks and structural damage.
7. Decreased Fire Resistance
High permeability allows moisture to escape as steam under high temperatures.
This creates internal pressure, leading to spalling and reducing fire resistance.
How to Reduce Permeability in Concrete
Use Low Water-Cement Ratio: Reduces pore formation.
Proper Curing: Enhances hydration and strength.
Admixtures & Pozzolanic Materials: Fly ash, silica fume, and slag improve density.
Good Compaction & Finishing: Eliminates voids and enhances surface quality.
Waterproofing Coatings & Sealants: Provides additional protection.
By controlling permeability, engineers can enhance the durability and service life of concrete structures, ensuring better performance under various environmental conditions.
IS Codes for Permeability Test of Concrete
In India, various IS codes provide guidelines for testing the permeability of concrete:
- IS 3085: 1965 – Method for Testing Permeability of Cement Mortar and Concrete
- IS 456: 2000 – Code of Practice for Plain and Reinforced Concrete
- IS 516: 1959 – Method of Test for Strength of Concrete
- IS 1199: 1959 – Methods of Sampling and Analysis of Concrete
Download our IS code App for all kinds of Is codes in Civil engineering.
These codes ensure standardised procedures and accurate assessment of concrete permeability.
Conclusion🎯
Permeability is a key factor in determining the durability and longevity of concrete structures. Excessive permeability leads to water ingress, which can cause reinforcement corrosion and structural deterioration. Conducting permeability tests such as the Rapid Chloride Permeability Test (RCPT) and Water Permeability Test helps engineers ensure high-quality, long-lasting concrete. Adhering to Indian standards (IS codes) further ensures reliability and consistency in construction projects.