The Incremental Recursive Procedure

CalME uses an incremental-recursive performance prediction process. Figure 1 below shows a flowchart of this process and it illustrates both the “incremental” and the “recursive” parts of the module. Specifically, “incremental” refers to the part of the process where pavement performance is predicted for each time increment and “recursive” refers to the part where the pavement condition is updated using the damage and distress states (or levels) predicted for the preceding time increment before the incremental pavement distresses are predicted for the next time increment.

Figure 1 - flowchart of the incremental-recursive performance prediction used in CalME

The incremental recursive procedure works in increments of time and uses the output from one increment, recursively, as input to the next increment. The procedure predicts the pavement conditions, in terms of layer moduli, crack propagation, permanent deformation, as a function of time.

Although currently disabled, CalME will also allow the user to include one or more Maintenance & Rehabilitation actions, either at fixed points in time or triggered based on the predicted pavement condition.

The duration of each increment is 30 days for pavement design. The program will select the day in the middle of each increment as the representative day for the climatic conditions during that increment. The representative day is divided into periods. The default division is into 5 periods of 4, 4, 5, 5, and 6 hours, starting at 13 hours (1 pm). Both the time increment and the time periods can be customized for research and calibration. It is possible to use time increments form one hour and upwards. For calibration using HVS (heavy vehicle simulator) or track tests an increment of one hour is used.

At the beginning of the simulation, the program predicts the pavement temperature profile for every hour over the whole analysis period. These temperatures are then looked up as needed during the simulation.

For the first period of the first time increment the program applies the load spectrum, read from the WIM data table, one load at a time. If the calculation considers wheel wander, the load is applied at the first lateral position. The temperature at one third depth of each asphalt layer is determined. The master curve for each asphalt material is used with this temperature and the loading time (depending on the vehicle speed and the depth in the structure) to determine the modulus of each asphalt layer. The modulus may also be influenced by existing damage to the layer and by aging/hardening. The moduli of the unbound materials may also be influenced by the stiffness of the pavement layers above the material and by the load level.

For each load, at each load position, the critical stresses and strains in the materials are calculated at a reference line. As the default the reference line is assumed to be at the center line of the single wheel and of one wheel in the dual wheel, but the wheels may be offset with respect to the reference line. For each layer the increase in damage and in permanent deformation is calculated using the time hardening procedure. For the next load or load position the new conditions of the pavement layers are used for determining the moduli and the increase in damage and permanent deformation.

When all load positions for all loads during the first period have been completed, the temperatures and moduli for next period are calculated and the loads of the period are applied, and so on until all periods of all increments in the desired analysis period have been completed.

Note that this incremental recursive procedure