Ten decades ago, the usage of concrete was very few in construction. The old method of construction manners has followed to build a structure. But the conventional way does not give stability & longer life for the structure.
So the usage of concrete increases gradually in construction fields. Since 1830 concrete has come a long way of development and become a vital material in modern construction.
In simple words, the life span of the concrete is called durability.
In technical terms, the resistance capacity of concrete against the chemical attack, weathering action & environmental changes is called durability of concrete—generally, a concrete structure designed at a minimum lifespan of 100 years.
Durability is one of the most important properties of concrete. It depends on the compressive strength & tensile strength of the concrete.
Why is concrete durability important?
Everyone wants to build a long-lasting structure which does not require frequency maintenance work
Already the construction materials are in short supply & scientists researching replaceable material. By increasing the lifespan of the structure, we could avoid the over usage of natural materials.
Factors affecting the durability of concrete
The strength of the concrete depends on many factors, as described below.
The quality of coarse aggregates is significant for the durability of concrete. The coarse aggregate, which occupies 70-80% of the concrete volume, is responsible for its compressive strength.
So choosing the right classification & grading of aggregates plays a vital role. If the shape of the aggregates is flaky or elongated, then it is easily broken due to sudden impact.
The irregular shape of aggregates makes more voids in concrete.
The angular aggregates make bonding with each other, and it helps develop the strength of the concrete.
Quality of Fine Aggregate
The river sand is used as filler material in concrete. It should be free from silt & other marine impurities. The silt content test for sand has to be performed to measure the silt particles in sand. The allowable silt in the sand in the ranges between 6 to 8%.
Or we could use M Sand, which is free from silt and other impurities.
If the cement content is exceeded, it leads to shrinkage happening in concrete.
The lower cement content decreases the bondage between the concrete materials, reducing concrete strength.
So using the proper amount of cement content is essential.
Mix Ratio
The proper recommended mix ratio should be used for any construction work. Improper mix ratio directly affects the compressive strength of the structure. Eventually, it led to structural failure.
Water cement Ratio
A high amount of water increases the porosity in concrete then the water molecules easily penetrate the concrete and rust the steel bar.
In the case of low water content in concrete, it affects the workability of concrete. The recommended water-cement is 0.45 to 0.65 as per IS standards.
Concrete Cover
The steel embedded in concrete to increase its tensile strength. The exposure of the steel rod must be avoided else; it can be easily corroded by the atmospheric moisture.
The recommended clear cover steel has been given below based on concrete exposure.
Exposure
Nominal Concrete Cover
Mild
20
Moderate
30
Severe
45
Very Severe
50
Extreme
75
Compaction of Concrete
Improper compaction severely impacts the durability of concrete. There is a chance for voids formation on the concrete surface due to the improper compaction, which induces crack on concrete and, finally, will disintegrate quickly.
The concrete should be placed in the formwork without bleeding & segregation.
Workmanship
Even if you carefully selected the materials and cautiously implemented the standards, if the workmanship is poor, then the structure’s strength & durability will be affected severely. So keep on eye on proper workmanship while concrete pouring.
Curing Period
Curing of concrete increases the durability of the concrete. Improper or delayed curing induce shrinkage cracks. Proper curing helps to reduce the permeability of the concrete.
The recommended curing period for concrete, as per IS code 456.
Sometimes you may see white patches on concrete surfaces called Efflorescence.
The moisture content present in surroundings forms white patches on the surface. If the concrete surface does not resist permeability, it penetrates the surface and reacts with the steel to corrode.
Sulphate Attack
Sulphate Attack is the most damaging cause of concrete deterioration and affects the durability severely. It causes the concrete to expand and deformation.
When the structure comes in contact with water, it will undergo sulphate attack.
Also, cement & other aggregates contain some limited volume of sulphate content. If it exceeds the limitation, it may lead to crack formation on concrete. To avoid this, the sulphate content in concrete should not be exceeded by 4% by the mass of cement in concrete.
Chloride Attack
Same as sulphate attack, the concrete surface may be contaminated by external environment chloride. It causes corrosion, primarily in reinforcement. By using epoxy coated rebar, we can prevent reinforcement from chloride attack.
So the volume of chloride content must be controlled in construction materials.
Environmental Conditions
Environmental conditions play a crucial role in the structure’s durability.
Sometimes the concrete structure may be built near the seashore area, or the structure may be built-in cold weathering conditions. It may result in chemical attacks or freeze-thaw. It affects concrete durability because of steel corrosion.
How to test the durability of concrete?
IS code 516 has described the tests conducted to determine the strength & durability of concrete.
Water absorption Test – By immersingthe concrete sample into the water for a certain period, the resistance against water penetration will be derived. The concrete has excellent durability when its absorption value is low.
Rapid Chloride Permeability Test – This test is conducted to determine the concrete resistance against chloride ion penetration in concrete. The electric charge passed in the concrete for a certain period to find the resistance of concrete. The electrical charges passed a benchmark level indicating the strength of concrete.
Water Penetration Test – Using hydrostatic pressure after completion of 28 days curing period, the concrete will be tested for its water permeability. The specimen will be cut in half vertically after three days & measured.
How can you increase the durability of concrete?
Ensure to use proper mix ratio & workmanship.
Admixture can be used in concrete to reduce the quantity of water in the concrete.
Ensure the quality of material used in concrete and do some field tests to check the material quality.
