Crazing – Causes & Prevention
CRAZING

A network of fine cracks across the surface of concrete.

  • Causes: Crazing is caused by minor surface shrinkage in rapid drying conditions. (i.e. Low humidity and hot temperatures, or alternate wetting and drying.)
    Prevention: Finish and cure concrete correctly.
 
Honeycombing & avoiding honey combing
Honeycombing & avoiding honey combing

  • When too much coarse aggregate appears on the surface.
  • Causes: Poor compaction, segregation during placing or paste leakage from forms. A poor concrete mix with not enough fine aggregate causing a rocky mix.


  • Prevention: Use a better mix design. Take care during placing concrete to avoid segregation. Compact concrete properly. Good watertight formwork.
  • Repair: If honeycombing happens only on the surface it can be rendered. If honeycombing happens throughout the concrete it may need to be removed and replaced. The surface may require rendering. Rendering means to cover the surface with a layer of mortar.
 
Types of cracks


  • Cracks could be either structural or non structural in nature . Cracks may also occur when concrete is in fresh state or in hardened state .


  • Good construction practices like timely curing , correct mix proportions usage of blended cement etc helps in avoiding cracks.
 
Plastic Shrinkage Cracks and avoiding them


  • Cracking is more common in summer (on very hot days or in low humidity and moderate winds), but may also occur during winter.
  • Plastic shrinkage cracks appear in lines, roughly parallel or in a crazed haphazard way. They are usually 300–600 mm long but may be between 25 mm and 2m in length.


  • Prevention
  • Dampen the subgrade and forms and protect concrete from the wind.
  • Dampen the subgrade and forms and protect concrete from the wind.
  • Keep all materials cool on hot days.
 
Cracks after hardening of concrete


  • Cracks after hardening may be caused by drying shrinkage, movement or settling of the ground, or placing higher loads on the concrete than it was designed to carry.


  • Little can be done with cracks after hardening. Careful and correct placement helps prevent serious cracking after hardening.
 
Reinforcement & Necessity of reinforcement in concrete


  • The steel found in many concrete structures is called REINFORCEMENT.


  • Reinforcement helps concrete resist TENSILE and SHEAR forces, and helps control CRACKING in concrete.
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