Over the course of its development, each of the models in HIPERPAV have been individually calibrated.
In fact, the FHWA recently completed an extensive validation of HIPERPAV for a range of design, materials and climatic conditions for several sites in the United States. The validation process included the instrumentation of pavements under construction with the objective to study how those pavements behave at early-ages and verify the accuracy of HIPERPAV in predicting the stresses, concrete strength development, and crack susceptibility of concrete pavements during the first 72 hours after placement.
The validation results demonstrated an excellent predictive capability of HIPEPRAV for the overall early age behavior. In general, it was observed that the numerous models in HIPERPAV predict well the early-age behavior of pavements under different design, material, construction and climatic conditions. The overall system was found to predict crack formation with an accuracy of approximately 5 hours. This is considered a reasonable approximation and is easily accounted for by the variability in each of the factors affecting stresses and strength.
The states in which full-scale validation was performed included Minnesota, Nebraska, Arizona, Texas, and North Carolina. The highway departments in each of these states have been cooperative and instrumental in the success of this phase.
Field Data Collection, Instrumentation, and Testing
The input data needed for the HIPERPAV software was carefully collected, namely, the pavement design, concrete materials, environmental conditions and construction methods. In addition, slabs were instrumented with gages to measure the strains and deflections of the pavement during the first 72 hours after placement.
A list of the devices and field tests used to collect data in these field sites are:
- Horizontal strain gages
- Vertical deflection gages (LVDT’s)
- Measurements of crack and joint movements using Demec points
- Push-off test to measure friction force between the concrete slab and the subbase, and
- Pulse velocity measurements to estimate concrete’s elastic modulus.
Data was also gathered in the laboratory to obtain the concrete’s material properties:
- Tensile strength
- Modulus of elasticity
- Coefficient of thermal expansion (CTE)
- Drying shrinkage
- Oxide analysis
- Heat of hydration
Then, the experimentally measured stresses generated in the concrete pavement could be compared to the predicted ones generated by the HIPERPAV software. This validation was performed to increase user confidence in the accuracy of the HIPERPAV program.