Meaning
Structural movements measure the vertical displacement of a concrete slab’s edge when a wheel load passes across a joint. High slab edge deflection indicates a loss of support from either the subgrade or the joint’s shear transfer system, such as loose dowel bars. This displacement must be limited to prevent joint spalling and damage to the wheels of material handling equipment.
Deflection Measurement
Deflection is measured using dial gauges or heavy deflectometers placed on the edge of the slab during a loaded pass. This test records the maximum downward movement as the wheel approaches the joint. The difference in deflection between adjacent slabs is also recorded to assess joint efficiency.
Repeated passes during the test help establish the dynamic behavior of the joint system.
Soil Interaction
Excessive edge movement acts as a pump, forcing water and fine soil particles out from beneath the slab. This process creates voids along the joint, which further increases the deflection under subsequent loads. It eventually leads to a complete loss of subgrade support.
Repair Method
Stabilizing the joint requires injecting expanding polyurethane foam into the voids or installing retrofit dowels across the joint. This repair reduces the deflection to acceptable levels. This protects the floor from further damage.
