The durability of concrete is defined as the power to withstand weathering, chemical attack, friction or other technique of degradation.
Different concrete requires totally different levels of durability depending on the exposure environment and properties.
Features of Durable Concrete:
- A durable concrete is one which performs satisfactorily within the work environment throughout its anticipated exposure situations during service.
- Durable concrete will preserve its unique form, high quality and serviceability when exposed to its environment.
- It shouldn’t show signs of damage in disintegrated or unfavourable situations.
Importance of Durability of concrete:
- When designing a concrete mix or structure, the exposure situation at which the concrete is meant to withstand is to be assessed.
- It is reported that developed countries over 40 % of the overall sources of the building industries are spent on repairs and maintenance.
- Sometimes raw materials like limestone incorporate excess of chloride.
- Portland cement allowed a maximum chloride content of 0.05%.
Factors affecting the durability of concrete:
The durability of concrete depends on the following factors as follows:
Higher water/cement ratios are the reason for larger permeability, so for durable concrete using a lower W / C ratio is helpful.
Instead for using high W / C ratios to protect strong steel towards corrosion, use low W / C and sufficient cover.
The mixture should be designed to make sure cohesion and prevent isolation and bleeding.
If cement is decreased, the work capability might be decreased as a result of insufficient condensation at a fixed W / C ratio.
However, if the water is added to improve workability, the water/cement ratio will increase leads to extremely permeable materials.
Concrete as an entire will be caused by insufficient condensation.
Usually, this is being managed by means of compaction tools, type of formwork, and density of steelwork.
Concrete has resistant to the abrasive as a results of ordinary climate, abrasion resistance is directly related to the strength of concrete.
Examples of extreme abrasion and erosion are rapidly rising water, floating ice, or particular areas where steel studs happen and for areas with extreme friction, the study shows that grades M80 and above concrete work effectively.
Mosses and lichens of a better order, cause considerable damage the durability of concrete.
These crops produce weak acids within the hair roots, the acids which can be produced attack the cement paste causes the concrete to decompose and scale.
Freezing and Thawing:
The most potentially destructive weathering issue is freezing and thawing whereas the concrete is wet.
The degradation is because of the freezing of water and subsequent growth of the paste, combination particles, or both.
With an air inlet penetration, the concrete is immune to excessive chilly and thawing.
The microscopic air bubbles within the paste present a chamber for water, thus relieved of the hydraulic stress generated.
Air-entrance concrete, with a low water-to-cement ratio and an air content material of 5 to 8%, will withstand a lot of cycles of freezing and thawing.
It is extremely important to permit proper strength development, assist moisture retention and ensure complete hydration process
The thickness of the concrete cover should follow the boundaries laid down within the code.
It is an important issue for durability. It may be seen that high permeability is usually due to excessive porosity.
Subsequently, correct curing, adequate cement, correct condensation and appropriate concrete cover can provide a low permeability concrete.
Types of Durability of concrete:
There are several types but the main ones are:
Physical durability of concrete:
Physical stability are effective against the following actions:
- Freezing and Thawing Action.
- Temperature stress i.e. high heat of hydration.
- Percolation/permeability of water.
Chemical durability of concrete:
Chemical durability are effective against the following actions:
- Alkali aggregate reaction.
- Chloride injection.
- Delay Etringite Formation.
- Attack of sulfate.
- Corrosion of reinforcement.
Due to lack of durability in concrete:
1. External causes:
- Extreme weather conditions.
- Bulk temperature.
- Extreme humidity.
- Electrolytic action.
- Attack by natural or industrial liquid or gases.
2. Internal causes:
- Changes in volume due to differences in aggregates and thermal properties of cement paste.
- Frost action.
c)Alkali aggregate reactions:
- Alkali-silica reaction.
- Alkali silicate reaction.
- Alkali carbonate reaction.
- Corrosion of Steel.
As the harsh environment reduces the durability and the life of the concrete, some provision of extra depth or additional enhancements is made to concrete structures to help achieve this durability.