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Publication Number: FHWA-HRT-12-031
Date: August 2012

 

User’s Guide: Estimation of Key PCC, Base, Subbase, and Pavement Engineering Properties From Routine Tests and Physical Characteristics

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CHAPTER 2. MODEL DEVELOPMENT

The LTPP study database, Long-Term Pavement Performance Standard Data Release Version 23.0, was used to develop the models.(10) Material properties and pavement engineering properties for which develop predictive models were developed were selected based on the following:

Predictive models were developed for PCC compressive strength, PCC flexural strength, PCC elastic modulus, PCC tensile strength, lean concrete base (LCB) modulus, and unbound materials resilient modulus. In addition, rigid pavement design feature inputs properties were developed using the MEPDG calibration data. These include the JPCP and CRCP deltaT parameters. For all PCC material properties, multiple models were developed for use in different project situations and to provide user prediction model alternatives depending on the extent of mix design information available.

In developing the models, a uniform set of statistical criteria were used to select independent parameters to define a relationship as well as to mathematically formulate prediction functions. The analyses examined several statistical parameters in choosing the optimal model and in determining the predictive ability of the model. In general, the optimal set of independent variables (Mallows coefficient, Cp), the interaction effects (variance inflation factor (VIF)), the significance of the variable (p-value), and the goodness of fit (R2) were verified. Additionally, the study validated or refined existing models and developed new relationships. In the analyses, the following general observations were made:

List of Models

The following models have been developed under this study.

PCC compressive strength models include the following:

PCC flexural strength models include the following:

PCC elastic modulus models include the following:

The PCC indirect tensile strength model is as follows:

PCC CTE models include the following:

The JPCP design deltaT model is as follows:

The CRCP design deltaT model is as follows:

The LCB elastic modulus model is as follows:

The unbound materials resilient modulus is as follows:

Practical Guide and Software Program

The models described in this user’s guide have been incorporated into a user friendly software program, Correlations, which was developed under this study and can be used independently from the MEPDG. The software was developed on the Microsoft.NET platform to be compatible with the latest versions of the Microsoft Windows® operating systems. It uses a modern user interface library to provide a familiar look and feel. It features multiple windows on the user interface that are initially docked inside the main window. These windows can be moved separately from the main window for better viewing of the inputs or results.

The program interface features tabs for PCC, design features, stabilized materials, and unbound materials. Models that belong to each of these categories are made available through a series of radio button selections placed in an accordion control. This placement not only provides the ability to make multiple selections, but it also conserves screen space so that the results of the calculations can be placed for easy viewing. Once a model is selected, the entry area adds controls for the available inputs of the model. Figure 2 shows a screenshot of the program and displays the various tabs and general layout of the user interface.

This figure shows a screenshot of the software program Correlations. It shows the general layout and displays the various tabs on the user interface. The four tabs represent Portland cement concrete (PCC), Design Features, Stabilized Materials, and Unbound Material categories of the predictive model. The screenshot 
in this figure displays the PCC screen and lists the five compressive strength model options.

Figure 2. Screenshot. View of Correlations user interface.

On all screens of the software, tooltips are provided for feedback on input range. Calculations occur after all necessary values have been input. Information about each model is available in an information window initially located at the bottom of the screen. This information is context-sensitive to the specific selections that the software user has made. Results of each calculation are displayed prominently in the results area window initially placed on the right side of the main window.

 


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The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT). Provide leadership and technology for the delivery of long life pavements that meet our customers needs and are safe, cost effective, and can be effectively maintained. Federal Highway Administration's (FHWA) R&T Web site portal, which provides access to or information about the Agency’s R&T program, projects, partnerships, publications, and results.
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