Investigation of Bonding Condition in Concrete Overlay by Laboratory Testing, Finite Element Modeling, and Field Evaluation

To evaluate the effect of bonded versus unbonded condition in concrete overlay structure, a field evaluation, laboratory experiment, and 3-D finite element analysis (FEA) model were carried out. First, a field evaluation of bonded and unbonded pavement test sections in Iowa was performed. Cores were extracted from existing pavements and tested for their bond strengths with shear testing equipment. The bond strength between an overlay and the existing pavement gradually increased over time, regardless of the initial bond strength. In some cases, an insufficient bond shear strength at the interface between the concrete overlay and the existing pavement seemed to have contributed to increased distress on the overlay surface.

Second, a laboratory experiment was conducted to investigate an effect of bonding in pavement structure. Concrete cylinder specimens that were one-half regular concrete and one-half polymer concrete were fabricated, and their indirect tensile strength was measured at the bonding interface. The experiment results indicated that polymer concrete samples exhibited higher indirect tensile strength than regular concrete samples at the interface. Finally, a 3-D FEA model using eight-node solid elements and a spring element was developed to quantify the bonding level.

This model can simulate various bond levels from fully bonded to unbonded by a change of the stiffness of the spring element. The most appropriate spring stiffness was identified for different bonding conditions of overlaid pavements. A parametric study was conducted with spring stiffness changed to develop a matrix that can be used to quantify different levels of bonding. This matrix can help pavement engineers select the most appropriate spring stiffness for a given bonding condition and overlay thickness.