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Factors Affecting the Strength and Density of Light Weight Concrete

Factors Affecting the Strength and Density of Concrete






The strength and durability of the LWA concrete is influenced by the following parameters:
  • ·         Grade and Granularity of the Aggregates
  • ·         Grade and the proportion of the cement
  • ·         Mixing water and consistency
  • ·         Method of mixing
  • ·         Compaction
  • ·         Curing



Grade and Granularity of the Aggregates
For increased strength, density and improved weather resistance, the fine grains of lightweight aggregate are substituted with sand. This will, in turn, increase the cement requirement.


Grade and the proportion of the cement
Lower cement content of 150 to 300kg/m3 might result in the lowering of the density and a higher strength is gained for higher cement content of a range 350 to 450kg/m3 for a properly compacted concrete. Rich concrete if not compacted may result in the same strength as that of the well compacted weak concrete.


Mixing Water and Consistency
The concrete must have a good consistency which can be checked using the slump. The plastic consistency can be induced by the addition of 2 to 4% of the vinsol resin (by weight of cement), an entraining agent without any loss in the strength of the cement.

Method of Mixing
Gravity type mixers are adequate for the concretes having low content of fine aggregates (10 to 15%). Positive type mixers are most effective if the fine aggregates proportion is 30 to 50%. They lead to a strength increase of 30 to 100% as compared to the gravity type mixers.

Compaction
Strength and the density are closely related to the degree of compaction. The strength varied with the vibrating frequency and amplitude as well as with the type of vibrator used. The compaction efficiency can be improved by applying pressure during vibration.

Curing
The fresh concretes are extremely sensitive to the intensive sunshine and wind. Hence, they must be protected by using damp sheets and covers. Also, methods of spraying have to carried out. Cool weather concreting will slow down the hardening procedures. The steam cured LWAC concrete must not be exposed to the temperatures which is lesser than 15 degree Celsius.


Applications of Lightweight Concrete

  • 1.    Used in Oil exploration Concrete Structures
  • 2.    Bridge Deck Construction
  • 3.    Floating Bridge Construction
  • 4.    Post-tensioned box girder Concrete Bridges
  • 5.    Offshore Construction

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