Relationship Between Voids Beneath Slab And The Load Transfer Efficiency

Voids beneath slab of Portland Cement Concrete (PCC) pavement, one of the common defects of concrete pavement, may lead to other deteriorations, including cracks, pump and faulting, which together degrade the serviceability and life span of PCC pavement. To detect voids, the Variable Corner Deflection Analysis Procedure (the Load and Deflection Method) is hitherto the method most commonly used. Unfortunately, it is difficult to discriminate voids from the Load Transfer Efficiency (LTE), because of the complicated relationship between them. As the main objective of this thesis, some topics of this relationship are discussed.To begin with, available methods for detecting voids are reviewed and discussed systematically.Secondly, based on the mechanic characteristics of interface between concrete slab and aggregate base, the voids beneath slab is simulated, in which contact is taken into consideration. It is concluded that the tensile stress between surface and base, which can be modeled in ABAQUS, should be regarded. It is also testified that only voids along joint, not voids underneath the corners, can be detected out, if the deflections were gathered at the centerline of slab. Therefore, the correct place to detect voids should be the top of them.To simulate the behavior of joints, the mechanic characteristics of joints are discussed, followed by three tactics of modeling: virtual material, spring and beam.Finally, models of voids beneath slab, with different LTE and voids area, regarding contact, are established and analyzed. It is revealed that the relationship between voids and LTE is not a simple increasing or decreasing function. In general, LTE weakens down firstly and then strengthens up, when voids deteriorate, and LTE has been enhanced if the modulus of joints had been magnified.Fortunately, a new parameter can differentiate voids and LTE: LTE/|D2|, which has clear relationships with voids and LTE. This parameter can also represent various working conditions of true pavement, the combination of voids area and joints states. Accordingly, a new criterion for voids detection is concluded: voids exist at the place where LTE/|D2|