Evaluating Support Conditions for Precast Concrete Inlay Panels using Finite Element Analysis

Precast concrete inlay panels (PCIPs) are a unique application of precast concrete pavement used for overnight rehabilitations of high-traffic volume asphalt highways exhibiting structural rutting issues. The pavement is rehabilitated by partially milling the existing asphalt, preparing the panel support layer, placing the panels, and grouting. Proper panel support is essential for successful, long-lasting performance of the PCIPs. For this reason, three different types of support conditions (referred to as asphalt-supported, grade-supported, and grout-supported) were constructed in a trial installation of the PCIPs to compare performance of the three alternatives. The panels rest directly on top of the asphalt in the asphalt-supported condition, and the panels are supported by a cement-treated bedding material or by a rapid-setting grout in the grade-supported and grout-supported conditions, respectively. Earth Pressure Cells (EPCs) and thermistors were installed in the PCIP trial construction at the top of the base layer to measure pressure and temperature in this location. The hypothesis of this research is that the performance of the PCIPs will be affected by the type of support condition, the properties of the support layer and the existing asphalt. The performance of the PCIPs was evaluated by analysis of the field data and by finite element analysis (FEA). The field data was analyzed to identify seasonal trends, trends over time, and to compare the three types of support conditions. The pavement base layer is subjected to larger magnitude compressive pressures in the winter and smaller magnitude upwards pressures in the summer. Furthermore, in the second winter, the average pressure increased by 0.9 kPa and the average temperature was 1°C cooler relative to the first winter; a t-test indicated that these differences were statistically significant. These changes could potentially be a result of some deterioration in the pavement, but this is not conclusive. Statistical analyses were also performed to compare the pressures collected from two different EPC pairs that corresponded to the same support condition. Results of the t-test indicated that there were statistically significant differences in the average pressure for the same support condition, and this was the case for all three types of support conditions. This indicated that the pressure differences were not a result of the type of support condition, but were caused by other factors. Therefore, conclusions about the relative performance of the support conditions cannot be drawn from the data at this time. It is recommended to continue monitoring and evaluating the field data. A finite element model of the PCIPs was developed using Abaqus software. The model consisted of three panels on a base and subbase, all modelled as continuum elements, on a dense-liquid foundation. Dowel bars for load transfer were modelled as embedded beam elements, and frictional contact properties were defined at the pavement layer interfaces. Two variations of the model were developed: one model did not have a support layer (the “AS” model) and one model included a support layer (the “GR” model). The AS model represents the asphalt-supported condition, and the GR model represents the grade- and grout-supported conditions. The model was verified with theoretical solutions and the mesh, number of panels, and extents of the base/subbase were chosen through verification tests. The model was calibrated and validated using field test data. Parametric studies were completed to evaluate the performance of the pavement for a range of conditions. The parameters considered were low and high interface friction between the panel and underlying layer, a support modulus of 4,000, 12,000, or 20,000 MPa, a support thickness of 12, 18, or 24 mm, and a base modulus of 1,000, 8,000, and 15,000 MPa. The maximum tensile stress in the panel and the base layers were evaluated as measures of the pavement performance. The loading combinations evaluated were a +10°C temperature gradient, a -10°C temperature gradient, a +10°C gradient with axle loading, and a -10°C gradient with axle loading. For each combination of parameters, the minimum tensile stresses in the panel and base was obtained from the finite element analysis (FEA). The trends in the stresses were analyzed and synthesized to produce practical recommendations for the optimal support condition, support modulus and thickness that would minimize panel and base stresses for the parameters and loading studied. It is recommended to reduce the bonding at the interface and to use the grade-supported condition for the most optimal performance. The presence of a thin support layer in between the panel and base was beneficial in reducing stresses in the base layer. Furthermore, two flow charts were developed as decision-making tools for selecting the most optimal conditions for PCIP, given information about the existing base stiffness or for a pre-selected support condition. In conclusion, the FEA demonstrated that the research hypothesis was correct; the properties of the support, base, and type of support condition had an impact on the pavement performance. The recommendations of this research can be used to make choices in the design or construction of the PCIP that will minimize stresses and make this pavement more durable and long-lasting