05-07-2013, 04:57 PM
PLASTIC SHRINKAGE CRACKING IN CONCRETE
PLASTIC SHRINKAGE.pptx (Size: 3.21 MB / Downloads: 87)
INTRODUCTION
Plastic shrinkage cracking occurs when the concrete is in the plastic state, which is within the first 24 hours. Plastic shrinkage cracks are usually spaced 1 to 3 feet apart, are generally parallel to one another.
PLASIC SHRINKAGE CRACKING :
THE AMERICAN CONCRETE INSTITUTE
defines plastic shrinkage cracking as the “ cracking that occurs on the surface of fresh concrete soon after it is placed and still it is in plastic’’.
HOW IT OCCURS
PLASTIC SHRINKAGE CRACKS are caused by the rapid loss of water from the surface of concrete before it has set.
The critical condition exist when the rate of evaporation of surface moisture exceeds the rate at which bleed water can replace it .
NOMOGRAPH :
Nomo graph is a graph that relates air temperature , relative humidity and wind velocity to predict the evaporation rates for a concrete surface with bleed water.
COMPUTER PROGRAM
Computer program makes the Nomograph and the equations easy to use.
The user simply enters the air temperature, concrete temperature , relative humidity , and wind velocity .