Structural Cracks: Causes and their identification

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The various causes are:
• Structural cracks 

1) Due to incorrect design
2) Faulty construction 
3) Overloading

• Non Structural cracks

1) Moisture changes: Shrinkage effect,depending on the water content, cement concrete and aggregates.
2) Thermal movement: Concrete made in hot weather needs more water for same work-ability and hence results in more shrinkage.
3) Elastic deformation
4) Creep: Building items such as concrete and brick work when subjected to a sustained load not only undergo elastic strain but also develop gradual and slow time dependent deformation known as creep or plastic strain.
5) Chemical reaction: Certain chemical reaction in building materials result is appreciable change in volume of resulting products and internal stresses are set up which may result in outward thrust and formation of cracks.
6) Foundation movement and settlement of soil: Buildings on expansion clays are extremely crack prone. 
7) Vegetation: Large trees growing in the vicinity of buildings cause damage in all type of soil conditions. If the soil is a shrinkable clay, the cracking is severe.

Structural cracks due to shrinkage can be identified as: 
  1. Corrosion of the reinforcement: If the reinforcement is placed too near the surface, it has chances to corrode. The iron expands due to oxidation and conversion to Iron oxide, which in turn results in cracks. So if the reinforcement is visible from the concrete surface, there are chances of cracks present and upcoming.

  1. Vertical cracks: These cracks mostly occur when the foundation has settled or disturbed unequally along its surface.

  2. Linear cracks: These cracks gradually grow and though they appear to be linear, there are interruptions in the crack-line which implies the crack is towards spreading itself.
  3. Network of cracks: These are due to the reaction of aggregate with some alkali hydroxide present in the concrete and can be easily seen by a network of cracks roughly growing as a circle in a group. 

1 comment :

  1. Structural cracks are not dangerous if crack widths are limited to some extent. Deflections and crack widths of beams can be calculated by using some of the free online spreadsheets like this: . You only need to sign up to unlock the input fields.