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15 Factors Affecting Durability of Concrete

A durable concrete is one that performs satisfactorily under expected exposure conditions for specified life of the structure. Various factors affecting the concrete durability are discussed below.

Factors Affecting Durability of Concrete

Following are the factors affecting durability of concrete.

  1. Cement Content
  2. Aggregate Quality
  3. Water Quality
  4. Concrete Compaction
  5. Curing Period
  6. Permeability
  7. Moisture
  8. Temperature
  9. Abrasion
  10. Carbonation
  11. Wetting and Drying Cycles
  12. Freezing and Thawing
  13. Alkali-Aggregate Reaction
  14. Sulfate Attack
  15. Organic Acids

1. Cement Content

  • Quantity of cement used in concrete mix will also be a factor affecting durability of concrete.
  • If cement content used is lower than the required, then water cement ratio becomes reduced and workability also reduced.
  • Adding more water to this mix results in formation capillary voids which will make concrete as permeable material.
  • If excess cement content is used, problems like drying shrinkage, alkali-silica reaction may occur which finally effects the durability of concrete.
Cement Content
Fig 1: Cement Content

2. Aggregate Quality

  • Use of good quality aggregates in concrete mix will surely increase the durability of hardened concrete.
  • The shape of aggregate particles should be smooth and round. Flaky and elongated aggregates effects the workability of fresh concrete.
  • For better bond development between ingredients rough textured angular aggregates are recommended but they require more cement content.
  • Aggregate should be well graded to achieve dense concrete mix.
  • Aggregates should be tested for its moisture content before using. Excess moisture in aggregate may lead to highly workable mix.
Aggregates
Fig 2: Aggregates

3. Water Quality

  • Quality of water used in concrete mixing also effects the durability of concrete. In general, potable water is recommended for making concrete.
  • pH of water used shall be in the range of 6 to 8.
  • Water should be clean and free from oils, acids, alkalies, salts, sugar, organic materials etc.
  • Presence of these impurities will lead to corrosion of steel or deterioration of concrete by different chemical reactions
Adding Water to Concrete Mix
Fig 3: Adding Water to Concrete Mix

4. Concrete Compaction

  • While placing concrete, it is important to compact the placed concrete without segregation.
  • Improperly compacted concrete contain number of air voids in it which reduces the concrete strength and durability.
Fig 4: Compacting Fresh Concrete

5. Curing Period

  • Proper curing in initial stages of concrete hardening result in good durability of concrete.
  • Improper curing leads to formation of cracks due to plastic shrinkage, drying shrinkage, thermal effects etc. thereby durability decreases.
Drying Shrinkage due to Poor Curing
Fig 5: Drying Shrinkage due to Poor Curing

6. Permeability

  • Concrete durability gets affected when there is a chance of penetrability of water into it.
  • Permeability of water into concrete expand its volume and lead to formation of cracks and finally disintegration of concrete occurs.
  • Generally concrete contains small gel pores and capillary cavities. However, gel pores do not allow penetration of water through them since they are of very small size.
  • But, capillary cavities in concrete are responsible for permeability, which are formed due to high water cement ratio.
  • To prevent permeability, lowest possible water cement ratio must be recommended.
  • Use of pozzolanic materials also helps to reduce permeability by filling capillary cavities.
Capillary Absorption in Concrete Block
Fig 6: Capillary Absorption in Concrete Block

7. Moisture

  • Moisture present in the atmosphere will also affects durability of concrete structures.
  • Efflorescence in concrete occurs due to moisture, which will converts salts into soluble solutions and when it evaporates salts become crystallized on the concrete surface.
  • This will definitely damages the concrete structure and durability will be reduced.
Efflorescence
Fig 7: Efflorescence in Concrete

8. Temperature effects

  • Concrete is heterogeneous material, when fresh concrete is subjected to high temperature rate of hydration gets affected and strength and durability becomes reduced.
  • Concrete ingredients have different thermal coefficients, so at higher temperatures, spalling and deterioration of concrete happens.
Thermal Cracks in Concrete
Fig 8: Thermal Cracks in Concrete

9. Abrasion

  • Deterioration of concrete also occurs due to severe abrasion.
  • When concrete is subjected to rapidly moving water, steel tires, floating ice continuously wearing of surface occurs and durability gets affected.
  • Higher the compressive strength higher will be the abrasion resistance.
Abrasion of Concrete
Fig 9: Abrasion of Concrete

10. Carbonation

  • When moist concrete is exposed to atmosphere, carbon dioxide present in atmosphere reacts with concrete and reduces pH of concrete.
  • When pH of concrete reaches below 10, reinforcement present in the concrete starts corroding.
  • Corrosion of reinforcement causes cracks in concrete and deterioration takes place.
Carbonated Concrete
Fig 10: Carbonated Concrete

11. Wetting and Drying Cycles

  • When concrete is exposed to alternate wetting and drying conditions such as tidal waves from sea etc. secondary stresses are developed in concrete.
  • Due to these stresses cracks will form and reinforcement is exposed to atmosphere.
  • When chlorides or sulfates from sea water meets reinforcement corrosion occurs and durability of concrete is reduced.
  • Use of low-permeable concrete, proper cover for reinforcement can prevent this type of problems.
Concrete affected by alternate Wetting and Drying
fig 11: Concrete affected by alternate Wetting and Drying

12. Freezing and Thawing

  • When fully saturated concrete is exposed to repeat cycles of freezing of thawing, it is deteriorated by the action of freezing and softening of water in it.
  • It causes cracking on concrete surface in the form of maps which is called map cracking and effects durability of concrete.
  • The coarse aggregate present the concrete also effected by freeze and thaw cycles, spalling of concrete may occurs.
  • In this case, durability of concrete can be achieved by adding air-entraining admixtures to the mix and also reduce the maximum size of coarse aggregate.
Concrete affected by Freezing and Thawing
Fig 12: Concrete affected by Freezing and Thawing

13. Alkali Aggregate Reaction

  • Alkali-aggregate reaction or alkali-silica reaction, takes place between alkali content of cement and silica content of aggregates is also a major factor effecting durability of concrete.
  • Due to this reaction, Concrete expansion occurs which finally lead to severe cracking and concrete gets deteriorated.
  • Use of cement with less alkali content, Non-reactive aggregates, pozzolanic materials like fly ash or slag cement, Lithium-based admixture in concrete will help to overcome this problem.
Alkali-Aggregate Reaction
Fig 13: Alkali-Aggregate Reaction

14. Sulfate Attack

  • When concrete structures are attacked by sulfates like sodium sulfate, magnesium sulfate etc. concrete disintegration happens.
  • This reaction is due to the chemical reaction between hydrated cement products and sulfate solutions.
  • Sulfate attack generally happens when water used for concrete mix contains high sulfate content, Due to unwashed aggregates, when soil around the concrete structure contains sulfates in it etc.
  • This can be prevented by using sulfate resisting cement, by adding slag cement, by decreasing permeability etc.
Spalling of Concrete due to Sulfate Attack
Fig 14: Spalling of Concrete due to Sulfate Attack

15. Organic acids

  • When concrete surface is subjected to organic acids like acetic acid, lactic acid, butyric acid etc., concrete durability gets affected severely.
  • Formic acid on concrete surfaces can lead to corrosion of concrete.
Acid attack on Concrete Floor
Fig 15: Acid Attack on Concrete Floor

Quiz

Which of the following acids affects concrete durability?

Recommended pH value of water used for making concrete

Permeability in concrete is reduced when

Factors effecting concrete durability are

About Sadanandam Anupoju

Sadananda is a Civil Engineer and is an Author, Editor and Partner of The Constructor since 2016.

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  1. Various problem affecting the material ratio in concrete work

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