What is durability of concrete?
The durability of concrete is defined as the ability to resist weathering action (Chemical or physical), chemical attack, abrasion, or any other process of deterioration.
- Durability is the capacity to withstand significant wear and tear for an extended period of time.
- It is an ability to perform satisfactorily in any exposure condition to which it is subjected over a long period of time.
- Factors such as concrete ingredients, proportioning of concrete mix, and placing &curing methods, all affect the ultimate durability and life span of concrete structure
The more the structure durable, the more it will be long-lasting. So, Everybody loves their property and wants to stay as long as possible. In the case of building it must be safe as well as economical considering the durability of the building.
Factors affecting durability of concrete
- Homogeneous mix
- Water Cement Ratio
- Mix Proportion
- Use of fresh water
- Size of aggregate
- Quality of Cement
1) Homogeneous mix
The concrete should be mixed thoroughly to form a homogeneous mixture. If it is not mixed thoroughly then all the ingredients of the mixture like cement, sand, and aggregate could not touch each other and can not get the required strength.
It can be done with the help of a mixture of about 15 to 25 rotation of mixture with the limiting capacity of mixture pots. If concrete is mixing with hand manually then it should be mixed by stirring all gradient up and down for more than 10 times.
Compacting of concrete is very necessary to prevent it from segregation. Segregation is the process of separating the ingredient of concrete from each other.
It should be kept in mind that concrete should be compacted with the help of compacting machine or vibrator layer by layer according to design.
Over compaction of concrete may cause the ingredient like aggregate to settle down living the sand and cement at the upper portion of the structure. This makes concrete weak in different regions.
So, Concrete should be compacted properly to prevent it from being porous and weak.
The most important factor for concrete to be durable is the proper curing of the concrete structure. The process of spreading water on the structure after a few hours and during the hydration period is known as curing.
During the hydration period, concrete gets its strength. Without curing, there is no chance that concrete will get its full strength.
Cement curing has a different time period. OPC needs at least 7 days for curing whereas PPC needs about 10 days for curing.
It also depends on the hot weather. If the weather is hot, then curing time may increase than the actual requirement of concrete for curing. So, Sufficient curing of concrete is required for developing its full strength.
4) Water Cement Ratio
The water-cement ratio is the ratio of water to be added in cement while preparing a concrete structure.
It should be maintained very wisely because more water causes bleeding in concrete and less water may cause segregation. And both of them reduce the strength of concrete.
So, The water-cement ratio should be appropriate, considering the strength and workability criteria.
5) Mix Proportion
The mix proportion is to provide the ingredient of concrete-like cement, sand, and aggregate in fixed proportion according to design criteria. Any disturbance of the proportion of ingredients may reduce the required durability of the concrete structure.
So, The concrete mix should be designed properly and should have all the ingredients in the right proportions.
6) Use of fresh water
The water used for mixing should be free from all harmful organic substances.
The presence of organic substances may react with concrete internally and damage the ingredient like steel, quality of cement, etc.
7) Size of aggregate
Aggregate contains more than 50% part of the concrete structure. It doesn’t mean that for higher strength concrete, we should provide a larger size of aggregate.
To get proper strength and better durability the aggregate should be hard, durable, and properly graded. For most R.C.C. works, a 20 mm size of aggregate is suitable to make concrete.
8) Quality of Cement
The most important ingredient is cement. Cement is the binding material of structure so, No structure is possible to construct without cement.
The cement used for R.C.C. work should be of good quality and measured by weight only, and not by volume.
External Factors affecting durability of concrete
- Concrete Facing a very hot or cold climate may reduce the durability of concrete.
- Concrete facing several impacts or sudden loads may affect the durability of the structure.
- Concrete facing continuous and periodic loads like a bridge, or a culvert may reduce durability.
- Structure near water resources may reduce their durability.
Internal factors affecting durability of concrete
- Quality of steel rod used in it.
- Quality of ingredients used in the concrete structure.
- The shape of the concrete structure.
- The concrete cover is provided in the concrete structure.
How to improve the durability of concrete structure?
- Concrete should be mixed homogeneously while preparing.
- Good quality concrete ingredients like cement, sand, and aggregate should be used to prepare concrete.
- Concrete should be compacted after placing concrete in formwork.
- Curing should be done for at least 14 days to get strong and durable concrete.
- Water should be added according to design. i.e water cement ratio should be maintained in the right proportion.
- The size of the aggregate should not be greater or smaller enough to create void or segregation.
Durability testing methods
- Rapid Chloride Penetration Test (RCPT)
- Water Permeability of Concrete (WP)
- Initial Surface Absorption Test (ISAT)
- Water Absorption test for concrete (WA)
1) Rapid Chloride Penetration Test (RCPT)
It is also known as a Rapid Chloride permeability tester. This RCPT test instrument is designed to carry out testing as per ASTM C1202 standard.
ASTM C1202 is a standard method for electrical indication of concrete’s ability to resist chloride ion penetration.
This instrument is supplied complete with 4 sets of cells connecting cables, temperature sensors, a desiccator, a vacuum pump, and software. The Rapid Chloride permeability tester has four channels and at a time four concrete samples can be tested.
2) Water Permeability of Concrete(WP)
This method is suited for concrete with high permeability, the test is carried out using a disc of concrete and involves water flowing out through the disc at a steady rate.
It should be borne in mind that (a) the disc cannot be made too thin, (b) the permeability of concrete being essentially low, the experiments could take a lot of time.
A modification of the above test is carried out using larger specimens, and water is applied under pressure at one end. After a fixed time interval, the specimens are split open and the depth of water penetration is observed. This depth of penetration is taken as a measure of the permeability of concrete.
3) Initial surface Absorption Test (ISAT)
The permeability of concrete is important when dealing with the durability of concrete used for water-retaining structures or watertight sub-structures. Structures exposed to harsh environmental conditions also require low porosity as well as permeability.
Such adverse elements can result in the degradation of reinforced concrete, for example, corrosion of steel leading to an increase in the volume of the steel, cracking and eventual spalling of the concrete. In situ tests are available for assessing the ease with which water, gas, and deleterious matter such as chloride ions can penetrate into the concrete.
4) Water Absorption Test for Concrete (WATC)
The water absorption test, also known as the saturation coefficient test, is used to measure the durability of concrete. The test involves immersing a sample of concrete in water for a specified period of time, typically 24 hours, and then measuring the weight of the sample before and after immersion.
The saturation coefficient is then calculated as the ratio of the weight of the absorbed water to the dry weight of the sample.
A lower saturation coefficient indicates greater durability, as the concrete is less porous and less likely to absorb water. This test helps to determine the quality of the concrete and how long it will last.
So, friends, I hope this article on “durability of concrete structure” remains helpful for you. Please share and comment if you have any questions.