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Publication Number: FHWA-HRT-12-030
Date: August 2012

 

Estimation of Key PCC, Base, Subbase, and Pavement Engineering Properties From Routine Tests and Physical Characteristics

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CHAPTER 5. MODEL DEVELOPMENT

This chapter discusses the statistical analyses performed to develop the predictive models and the sensitivity analyses used to validate the models. All statistical analyses were performed using the SAS® software program.

Statistical Analyses Methods Adopted

After data assembly was completed, predictive relationships for the parameters identified in table 6 through table 8 were considered for statistical analyses. The following approaches/ options were considered for developing the various models:

Formulating Data for Statistical Models

Data were formulated in three distinct types depending on the nature and extent of data available for each parameter and the intended use of the predicted variable. Within each type, different model forms can be adopted depending on the relationship the dependent parameter holds with the independent variables. The three primary data formulation types adopted are data formulation types 1 through 3 and are discussed in the following sections.

Data Formulation Type 1

Data Formulation Type 2

Data Formulation Type 3

Table 13 to table 15 provide summaries of the model types evaluated for developing predictive relationships for PCC, stabilized, and unbound materials, respectively.

 

Table 13. Model types used to derive predictive relationships for PCC material properties or design features
for rigid pavements.

Material Property

Primary Model

Secondary Model

Model Variables

Model Type

Model Variables

Model Type

Compressive strength

Aggregate type, cement content, air content, w/c ratio, unit weight, admixtures, and SCMs

1

N/A

N/A

Elastic modulus

Aggregate type, cement content, air content, w/c ratio, unit weight, admixtures, and SCMs

1

Compressive strength/ flexural strength

1

Flexural strength

Aggregate type, cement content, air content, w/c ratio, unit weight, admixtures, and SCMs

1

Compressive strength

1

Indirect tensile strength (CRCP only)

Compressive strength/flexural strength

1

N/A

N/A

CTE

Aggregate type, aggregate volume, cement type, paste volume, and w/c ratio

1

Aggregate type

2

Erosion in CRCP design

Base type, index properties and strength of base, and climate (precipitation)

3

N/A

N/A

EI—JPCP

Base type, base properties, and climate (precipitation)

3

N/A

N/A

deltaT

Base type, construction time, PCC index properties, and climatic variables

3

N/A

N/A

N/A = Not applicable.

Table 14. Model types used to derive predictive relationships for stabilized materials.

Material Type*

Material Property

Constant or Time Dependent

Independent Variables

Model Type Evaluated

Lean concrete and cement-treated aggregate

Elastic modulus

Constant

Compressive strength

1

*All other material types have been excluded from this table, as the database provides data for LCB elastic modulus only.

 

Table 15. Model types used to derive predictive relationships for unbound materials.

Material Property

Independent Variables

Model Type

Resilient modulus determined using the following two options:

·   Regression coefficients k1, k2, and k3 for the generalized constitutive model that defines resilient modulus as a function of stress state and regressed from lab resilient modulus tests

·   Determine the average design resilient modulus for the expected in-place stress state from laboratory resilient modulus tests

Soil type, Atterberg limits, maximum dry density, optimum moisture content, gradation, and P200

1; after grouping data for coarse-grained and fine-grained soils

 


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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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