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SWUTC Research Project Description

Fatigue Modeling of Hot Mix Asphalt using Field Samples to Ensure a State of Good Repair

University:  Texas A&M University

Principal Investigator:
Amy Epps Martin
Texas Transportation Institute
(979) 862-7150

Project Monitor:
Dr. M. Emin Kutay
428 S. Shaw Lane, Room 3554
Engineering Building
Department of Civil and Environmental Engineering
Michigan State University
East Lansing, MI 48824

Funding Source:  USDOT and State of Texas General Revenue Funds

Total Project Cost: $59,880

Project Number:  600451-00012

Date Started: 4/1/12

Estimated Completion Date:  3/31/13

Project Summary

Project Abstract:
In order to better predict fatigue failure in hot mix asphalt (HMA), new and efficient test
methods and models are needed. The Simplified Viscoelastic Continuum Damage (S‐VECD)
model and the Modified Calibrated Mechanistic with Surface Energy (CMSE*) model were
recently developed for this purpose. The objectives of this project are to explore the
advantages of merging the two approaches by: (1) applying the S‐VECD model to field and
laboratory specimens, (2) comparing the S‐VECD model results with those determined from the CMSE* model results for field and laboratory specimens, and (3) exploring the application of field sample test data acquired with the CMSE* laboratory test protocols to the S‐VECD model. A symbiotic model that merges the two approaches would allow agencies to further maximize the net economic benefit of their HMA pavements and sustain the aging infrastructure.

Project Objectives:
The objectives of this project are:

  • To apply the S-VECD model to field samples and laboratory specimens,
  • To compare the S-VECD model results with those determined from the CMSE* model results for field samples and laboratory specimens, and
  • To explore the application of field sample test data acquired with the CMSE* laboratory test protocols to the S-VECD model.

Task Descriptions:
Task 1. Experiment Design
To fulfill the objectives of the project, several field samples and laboratory specimens will be tested in the laboratory. As part of TxDOT Project 0-6009, several field sections have been identified and the performance of corresponding field samples have been evaluated using the CMSE* method during four consecutive years. The characteristics of the different field sections will be assessed, and one or two sections will be selected for use in this project. In
addition, the necessary raw materials to prepare laboratory specimens will be estimated and obtained from the respective sources.

Task 2. Laboratory Testing
The test procedures that have been developed at TTI/Texas A&M University and recently modified and successfully applied to field samples as part of TxDOT Project 0-6009 to calculate the number of loads to fatigue failure (Nf) using the CMSE* model will be used in this project. The two direct tension test protocols are the Viscoelastic Characterization (VEC) test and the Modified Repeated Direct Tension (RDT*) test.

For the S-VECD model, the required laboratory test parameters are obtained with the Dynamic Modulus (E*) test at various temperatures and frequencies and a repeated uniaxial tension-compresion protocol, called the push-pull test, at different temperatures and strain levels. The PP-VECD Modeling and Analysis Software, which is available to the public in beta version, will be used to estimate Nf of the field samples and laboratory specimens.

Task 3. Analysis and Comparison of Results
The estimated Nf obtained from the CMSE* and the S-VECD models will be compared for both field samples and laboratory specimens and any differences will be explained. In addition, other fatigue parameters such as the Damage Density Growth will also be obtained using the CMSE* laboratory test data.

In addition, because of the similar nature of the laboratory test, the RDT* test results will be used in lieu of the push-pull test data in the S-VECD software analysis tool to compare the results obtained using both laboratory tests.

Task 4. Documentation
A paper documenting the findings of the study will be prepared and submitted to the ASTM Journal of Testing and Evaluation (JTE) in order to disseminate the information to the research community. This paper would also serve as a final report to SWUTC.

Implementation of Research Outcomes:
Fatigue cracking is a primary form of distress in hot-mix asphalt. The long-term nature of fatigue due to repeated loading and aging and its required tie to pavement structure present challenges in terms of evaluating mixture resistance. This project focused on comparing stiffness and fatigue life output from two recently developed approaches that use repeated direct tension tests:  the Modified Calibrated Mechanistic with Surface Energy (CMSE*) approach and the Push-Pull Viscoelastic Continuum Damage (PP-VECD) approach.

Products developed by this research:

Slide Presentation:  Uniaxial Fatigue Testing, for incorporation into CVEN 417/653 Bituminous Materials course at Texas A&M University.

Slide Presentation: Uniaxial Fatigue Testing, sent to Texas Department of Transportation (TxDOT).

Technical Note:  Final report to be submitted as a Technical Note to ASCE Journal of Materials in Civil Engineering.

Impacts/Benefits of Implementation:
Through the comparison of two recently developed approaches to evaluate fatigue resistance of hot mix asphalt, this study provides insight to their similarities and shortcoming in terms of both testing and analysis. By providing a better understanding of mixture resistance to fatigue cracking, this study will enable state departments of transportation and other transportation agencies to better plan and use the most economical methods for extending the life of the pavement to provide a safer, efficient, and sustainable transportation system.

Web Links:
Final Technical Report