Plastic shrinkage cracks are common in slabs.
Shrinkage cracks in concrete slab.
Shrinkage cracks in concrete occur due to change in moisture of concrete.
While the concrete is shrinking many things such as reinforcement or the subgrade restrain the concrete.
This restraint creates tensile stresses in the concrete slab which in turn may produce drying shrinkage cracking.
They expand when they absorb the moisture and shrink when they dry.
While shrinkage in poured concrete walls or floor slabs is a normal property of curing concrete shrinkage cracks can be controlled or where they have occurred in some cases repairs are needed.
In addition to reading about repairing concrete shrinkage cracks if crack repair is needed at all.
Most of this excess water begins to exit the concrete during placement curing and causes the concrete to shrink.
Concrete and mortar are porous in their structure in the form of inter molecular space.
When concrete is mixed more water than is needed for hydration is mixed with the dry components such as sand cement and an aggregate.
Shrinkage cracking can be managed by the use of control joints placed in the slab.
As the concrete slab dries after placement it shrinks.
Shrinkage cracks in a slab photo above are unlikely to be of any structural concern but can be a source of water entry or radon entry in buildings and may form a tripping hazard.
When the evaporation of the moisture at the surface of concrete is more than the availability of the rising bleed to fill the surface moisture if this process happens before concrete attaining its tensile strength the volume change may cause cracks.
Contraction joints or control joints when cracked are really just straight shrinkage cracks.
Plastic shrinkage concrete cracks when concrete is still in its plastic state before hardening it is full of water.
Most of the water will eventually evaporate causing shrinkage of the concrete slab.
When that water eventually leaves the slab it leaves behind large voids between the solid particles.
Some contractors cut or form a grid of small grooves in the slab to keep the shrinkage cracks in an orderly grid which looks better than random cracks but functions the same way.
This is the main cause of concrete shrinkage cracks on drying.
These cracks are comparatively short cracks.
