12-12-2012, 06:34 PM
CRACKS IN CONCRETE
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INTRODUCTION
Concrete is a durable material. However, it has characteristics and properties that may result in distress manifestations. These manifestation may be caused in the fresh, unhardened state or in hardened state.
Whenever tensile stress in concrete, caused by various effects, exceeds the tensile strength in concrete, concrete will crack.
In the early stage of concrete formation, concrete strength is relatively weak and this makes it vulnerable to cracking.
Sources of tension in concrete:
External or Structural Sources
Gravity load; Dead & Live load
Lateral load; Wind & Seismic load
Loads from sub grade settlement or swelling
“Internal” Mechanism
Volume change restraint due to temperature
changes or drying shrinkage
Expansion due to corrosion of reinforcing steel or deleterious
CAUSES OF CRACKING IN PLASTIC CONCRETE
Very Rapid Loss of Moisture
Factors are:
Concrete and air temperature
Relative humidity
Wind velocity
Results in differential volume
change in top layer