What is Shrinkage of Concrete || Plastic Shrinkage

What is Shrinkage?

Everyone is friendlier with the deformations due to loads on structural elements, a concrete member has two other types of deforestation known as shrinkage and creep

While the hydration process of cement concrete takes place, the volume of cement paste decreased due to water/moisture loss in concrete which is known as shrinkage

Change in concrete volume is one of the most detrimental properties of concrete mortar, which highly affect the long term strength and durability of concrete structure building

Microcracks are developed in the concrete due to shrinkage

Shrinkage is responsible for the development of a crack in wall, floor, pavement etc

Shrinkage is an inherent property of concrete. It can’t be prevented but it’s magnitude definitely can be reduced

The following four types of shrinkage strains are recognised

  1. Plastic Shrinkage
  2. Drying Shrinkage
  3. Autogenous Shrinkage
  4. Carbonation Shrinkage

What is Plastic Shrinkage?

Cement undergoes a volumetric contraction whose quantity is nearly one per cent of the absolute volume of dry cement. This kind of shrinkage is known as plastic shrinkage

Water loss from any factors like absorption by aggregate or evaporation from the concrete surface or subgrade is believed to be the reasons for plastic shrinkage and loss of water results in the reduction of volume

In the case of pavements and floors, where the large surface is come in direct contact to warm sun or drying wind, the surface of concrete dries extremely fast resulting in plastic shrinkage

In the case of a high water/cement ratio of concrete, a large quantity of water accumulate and bleeds at the surface. Which this surface water dries out, shrinkage cracks develop on the surface of the concrete

Causes of Plastic Shrinkage

Richer concrete also undergoes greater plastic shrinkage. 

The list of main causes of plastic shrinkage is as following:

  • High w/c ratio
  • Wrong concrete mix design
  • Rapid drying
  • Unintended vibration
  • Yielding of formwork
  • Greater bleeding

Prevention of plastic shrinkage

  • Plastic Shrinkage can be reduced by decreasing water loss from concrete. This can be obtained by covering the concrete surface with help of polyethene sheets immediately after finishing the operation or by working at night
  • A small quantity of aluminium powder also may be added to offset the effect of plastic shrinkage
  • Revibrate the concrete in a controlled manner
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