Is concrete durable?

Durability is not a default feature of concrete.

Concrete durability refers to the ability of concrete to withstand the conditions for which it is designed without deterioration for a long period of time. It refers to its ability to resist weathering action, chemical attack, and abrasion while maintaining its desired engineering properties.

Durability can be against physical or chemical attacks.

Physical Durability       

This refers to its ability to resist freezing and thawing action, permeability of water and temperature stresses. Also the following:

Ultraviolet Resistance

The ultraviolet portion of solar radiation does not harm concrete. Using colored pigments in  concrete retains the color in aesthetic elements (walls or floors, for  example) long after paints have faded due to the sun’s effects.

Abrasion

Examples of severe abrasion and erosion are particles in rapidly moving  water, floating ice, or areas where steel studs are allowed on tires.

Chemical Durability       

Chemical durability refers to its ability to resist the following:

1. Alkali Aggregate Reaction

2. Sulphate Attack

3. Chloride Ingress

4. Delayed Ettringite Formation

5. Corrosion of reinforcement

Factors Affecting Durability of Concrete            Durability of Concrete depends upon the following factors:        

Mix Design       The exposure of the concrete has to be considered when designing a mix. Care has to be exercised for harsh and severe environments. A structure exposed to seawater or seawater spray is most vulnerable in the tidal or splash zone where there are repeated cycles of wetting and drying and/or freezing and thawing. Sulfates and chlorides in seawater require the use of low permeability concrete to minimize steel corrosion and sulfate attack. A cement resistant to sulfate exposure is helpful.        

Compaction       Concrete may contain voids caused by inadequate compaction. And the degree of compaction is affected by the workmanship, type of compacting tools used, condition of the formwork and how congested the reinforcement bars are.

Curing       Curing of concrete plays a major role in developing the microstructure and pore structure of concrete. Curing of concrete means maintaining moisture inside the body of concrete during the early ages and beyond in order to develop the desired properties in terms of strength and durability. A good curing practice involves keeping the concrete damp until the concrete is strong enough to do its job. However, good curing practices are not always religiously followed in most of the cases, leading to a weak concrete.

Cover       Cover refers to the distance between the outside of a concrete structure and the reinforcement. This distance has to be a minimum distance – as specified by the structural engineer. There needs to be a minimal distance between the reinforcement bar and the outside of the panel to reduce corrosion.

Permeability       This is probably the most important contributing factor for concrete durability. High permeability means high porosity.

Solution: Concrete  will remain durable if:

• The degree of exposure is taken into consideration in the mix design

• The ingredients in the mix contain minimum impurities.

• Curing is carried out properly.

• It is properly compacted.

• Sufficient cover is provided to protect the steel reinforcement.