Meaning
Vertical movement of a slab corner or edge relative to its subgrade occurs due to moisture and temperature differentials between the top and bottom of the concrete. The edge lift displacement measures this physical separation, which creates an unsupported gap beneath the slab perimeter. This displacement reaches its peak during dry periods when the top surface shrinks significantly more than the bottom.
Joint Stress
Concentrated loads applied to unsupported slab edges cause high bending stresses. When heavy forklifts travel across a joint suffering from edge lift displacement, the slab undergoes rapid cyclic bending. This action leads to joint spalling and eventual subgrade failure.
Boundary Resistance
Stiffness of the subgrade and the weight of the slab itself resist the tendency of the concrete to curl upward. Calculating the expected edge lift displacement involves analyzing the slab thickness, the subgrade reaction modulus, and the concrete shrinkage properties. Dowel bars placed across joints limit this relative movement by transferring loads to the adjacent slab panel.
Without these steel connectors, the edges would lift freely, resulting in a stepped joint profile that disrupts vehicle traffic. Heavy aggregate interlock also helps maintain alignment, though it becomes less effective as the joint opens.
Control Measure
Optimizing the concrete mixture limits the total shrinkage that drives edge deformation. Reducing the cement paste content and maximizing the aggregate size lowers the resulting edge lift displacement. Wet curing of the slab surface for an extended period ensures uniform moisture distribution during early hydration.
