New Approach to Determining Concrete Slab Lift-Off by Use of Interfacial Fracture Mechanics Concepts
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Negative temperature gradient and the moisture gradient through the thickness of a concrete slab result in curling and warping of the slab edges to a concave configuration. The tendency of the slab pavement to separate from the subbase layer, called lift-off, is mainly controlled by such environmental effects and the weight of the slab itself. Because of such effects, cracks may propagate at the interface of the concrete slab and the subgrade. The induced stress and displacement fields around the interface crack tip are characterized by the stress intensity factors. The stress intensity factors can then be used in assessment of the cracked bond strength by employing any fracture criteria; therefore, it is necessary that the stress intensity factors be obtained. This paper proposes a new approach for determination of slab lift-off that uses concepts from interfacial fracture mechanics. A two-dimensional finite element analysis was performed to simulate lift-off in concrete slab pavements, and the effect of interface cracking on the mechanism of the lift-off was investigated. The relative stress intensity factors as well as the relative slab lift-off were determined for different crack lengths, loading conditions, and material properties of the slab and the subgrade. The presented model was validated with experiments. This paper discusses the remarkable effects of the material properties and the induced contraction stress on the slab lift-off. The findings presented provide researchers with some insight as to the effect of curing conditions and relative stiffness on slab lift-off and answer some of the primary questions regarding the mechanism of interfacial fracture in concrete slabsubgrade structures caused by the lift-off.
