Meaning
Physical deformations occur in concrete slabs when temperature or moisture gradients cause the top and bottom of the slab to shrink at different rates. This slab corner curling raises the corners and edges of the slab off the subgrade, leaving them unsupported and highly vulnerable to cracking under wheel loads. This phenomenon is common in warehouse floors where the top surface dries faster than the bottom.
Deformation Mechanism
When the top of the slab dries out, it shrinks, while the bottom remains moist and maintains its volume. This difference in shrinkage creates an upward curling force at the joints and corners of the slab. Temperature differences between day and night can also cause similar temporary curling effects.
Continuous exposure to dry air currents accelerates this physical deformation.
Structural Risk
A curled slab corner has no contact with the subgrade and acts as a cantilever beam. When a heavy forklift drives over this curled corner, the concrete is subjected to high tensile stresses. This often results in a diagonal crack across the corner, which ruins the joint.
Mitigation Strategy
Reducing the water content in the concrete mix and using proper curing compounds can minimize the shrinkage gradient. Steel fiber reinforcement also helps resist the curling forces. These steps keep the slab flat and in contact with the subgrade.
