Standard Materials Library

Each of the material models included in CalME has a set of model parameters that need to be determined. In order to use a material as part of a pavement design in CalME, one first needs to characterize the material by providing parameters for the models that predict different damages under different traffic and environmental loadings.

A Standard Materials Library (SML) has been introduced into CalME to provide a list of predefined materials for use in pavement design. The SML is essentially a database of materials that have been characterized through previous studies that sampled and tested materials from across the state. Specifically, model parameters and the associated uncertainties when applicable have been determined for these materials.

The CalME SML continues to grow. Additional materials are being added to the SML as more data become available.

Each material in the library has been classified in one of three groups: asphaltic material, non-asphaltic bound material, and unbound material-based on the models applicable for that material.

In terms of material characterization, most of the current effort has focused on asphaltic materials, which are defined as materials bounded by asphalt binder and that are typically used in surface layers. These materials must be strong enough to allow production of viable laboratory specimens for a series of lab tests to determine the stiffness characteristics, and the fatigue and permanent deformation resistances of each material.

On the other hand, most of the models for non-asphaltic materials (both bound and unbound) use default model parameters and require no additional laboratory testing for them to be characterized. The only exception is the stiffness of a pavement layer. Typically, layer stiffnesses are estimated with falling weight deflectometer (FWD) tests and the resulting data are used to back-calculate layer stiffness and to provide an estimate of the within-project variability of the stiffnesses for Monte Carlo simulation.

Types of Material Models

The models needed for each material in CalME can be divided into the following three functional groups:

1.Environmental models: models that affect pavement response to environmental conditions, e.g., a heat transfer model that is used to determine pavement temperature

2.Stiffness models: models for layer stiffness given all of the potential relevant factors such as loading duration, material temperature, loading stress, time of the year, age, fatigue damage, etc.

3.Physical evolution models: models for changing the physical conditions of a material. These are the models needed for updating primary distresses/damage given all potential critical primary responses (stress, strain, deflection), the corresponding number of traffic load applications, and the current damage. Examples of physical evolution models include an asphalt mix fatigue damage model and a cement-treated material curing model. Note that physical evolution can include both damage causing stiffness decreases and stiffnesses increases from mechanisms such as aging and curing.

As one can see, CalME requires more than just damage models to work.

Material Characterization

Material characterization is the process of selecting the appropriate set of material models and identifying the corresponding model parameters through laboratory and/or field testing for a given material. Different types of materials require different materials characterization process for each of the above three functional groups of models. The material models selected for CalME for each of the functional groups are presented next along with the material classification.