The following suite of tools help with characterization of cracking and rutting of asphalt pavements.

FlexPAVE^TM

FlexPAVE is a Microsoft^® Excel-based analysis tool for characterizing asphalt pavement structures. It uses the Fourier-Finite Element method to analyze three-dimensional viscoelastic pavement response, fatigue cracking, and rutting distress evolution under repeated moving traffic loads and temperature fluctuations. FlexPAVE uses the material models calibrated in FlexMAT, accounts for climatic characteristics, and ties the material models to the pavement structure analysis. Additional information can be found in the FlexPAVE v2.2 user manual. (Publication is pending.)

The FlexPAVE package contains the following folders and files.

FlexPAVE Source.zip: the overarching FlexPAVE folder, containing the database subfolders and required libraries and files for the operation of FlexPAVE. This folder is also referred to as FlexPAVE’s master folder.

There are four subfolders within the FlexPAVE master folder; Applications, ClimateData, MaterialData, and ProjectFiles. These four folders and their contents compose the database, libraries, and engine background of FlexPAVE. Each folder has a specific purpose and should not be tampered with, edited, or modified.

The contents of these folders:

Applications: executable and engine-related libraries needed for the simulation.

ClimateData: database of files required for EICM’s proper execution and the database of MERRA2 cells locally stored in the ‘HcdFiles’ subfolder.

Material Data: local database of materials separated into two subfolders. ‘Aggregate’ for the unbound materials (regardless of being ‘Unbound Base/Subbase’ or ‘Subgrade’ materials) and ‘Asphalt’ for the asphalt mixes.

ProjectFiles: subfolders for each project that has been created using the GUI.

In the case of the ProjectFiles folder, each subfolder contains several files required for their respective project simulation, including project specific climatic information, materials used, project-related inputs, project file (filename ending with .ptb), and, once the simulation is complete, the simulation results (Distress.csv file).

Note: the content of some of the folders previously described depend on the materials and projects that are stored locally by individual users, (i.e., individual local databases). Local databases can exist for materials, climatic stations, and projects.

FlexPAVE v2.2.xlsm: Actual FlexPAVE v2.2 file, pavement analysis. Recommended to be used only with Microsoft Excel 2016 or newer versions. Maintain the .xlsm in the same master folder as the ‘FlexPAVE Source’ subfolder to ensure the connection between the .xlsm and the required libraries and files contained in the ‘FlexPAVE Source’ folder.

FlexMAT^TM for Cracking

FlexMAT for Cracking is a Microsoft® Excel-based analysis tool for characterizing dynamic modulus and cracking of asphalt pavement mixtures from Asphalt Mixture Performance Tester (AMPT) test results. This includes determining the 2S2P1D dynamic modulus master curve coefficients and time-temperature shift factors. It analyzes the AMPT cyclic fatigue test results (AASHTO* TP133) to provide inputs to FlexPAVE™ cracking evaluation. These inputs include damage characteristic curve coefficients, failure criteria coefficients, ageing parameters, and the coefficient of thermal contraction. The analysis also supports balanced mix design and production evaluation by calculating the S_app  index cracking parameter from the test data.

Additional information can be found in the TechBrief, Cyclic Fatigue Index Parameter (Sapp) for Asphalt Performance Engineered Mixture Design, 2019. (FHWA-HIF-19-091).

FlexMAT Cracking v2.2.xlsm (file): Actual FlexMAT v2.2 file, cracking analysis version, using the universal data structure format v2 requirements.

FlexMAT^TM for Rutting

FlexMAT for Rutting is an Excel-based analysis tool for characterizing rutting of asphalt pavement mixtures from AMPT test results. This includes analyzing the AMPT stress sweep rutting (SSR) test results (AASHTO TP134) to provide shift permanent deformation model coefficients to FlexPAVE rutting evaluation. The analysis also supports balanced mix design and production evaluation by calculating the Rutting Strain Index (RSI) parameter from the test data.

Additional information can be found in the TechBrief, Rutting Strain Index (RSI) Parameter for Asphalt Balanced Mixture Design, 2021. (FHWA-HRT-21-044).

FlexMAT Rutting v2.2.xlsm (file): Actual FlexMAT v2.2 file, rutting analysis version, using the universal data structure format v2 requirement.

Weather (Climate) Data Files

Use .csv files with the FlexMAT Rutting v2.2 analysis tool to successfully perform the asphalt pavement rutting analysis. This set of files includes an expanded MERRA2 temperature database from 2,798 locations across the United States, and 20 years (1996–2015) of temperature information.

Rutting Climate Files.zip (files): Contains the updated temperature database required for RSI calculations in FlexMAT v2.2 for Rutting.

Extract the .csv files within the .zip file into a folder. If the folder is inside the same overarching folder as the FlexMAT Rutting v2.2 file, it will be automatically identified. If not, the user will be prompted to identify the folder’s location.

Data Structure Requirement Documents

Use these three documents to understand the AMPT test data and universal format required for FlexMAT to successfully import the test data and conduct the analysis. Each document will show the required data format the equipment manufacturers must use and report from their test equipment. These universal requirements allow the test data to be directly imported into FlexMAT from the equipment. If your equipment is not reporting data in the specified format, use these documents to verify requirements with the manufacturer:

FHWA-HRT-21-054 FlexMAT™ Asphalt Dynamic Modulus.pdf (file): Contains the FlexMAT-specified data structure for the dynamic modulus test using the AMPT. The test data output must follow the data structure for import to FlexMAT.

FHWA-HRT-21-055 FlexMAT™ Asphalt Cyclic Fatigue.pdf (file): Contains the FlexMAT-specified data structure for the cyclic fatigue test using the AMPT. The test data output must follow the data structure for import to FlexMAT.

FHWA-HRT-21-056 FlexMAT™ Asphalt Stress Sweep Rutting.pdf (file): Contains the FlexMAT-specified data structure for the stress sweep rutting test using the AMPT. The test data output must follow the data structure for import to FlexMAT.

Upon exporting files from the equipment, users should not open or modify the files using text editors or Microsoft® Excel because such operations may corrupt the files and make them unreadable in FlexMAT.

Example Test Data Report Files

Use these files as examples of test data output files from the equipment that adhere to the universal data structure requirements to successfully use and analyze the data in FlexMAT.

Input Examples (folder): Contains dummy examples of Dynamic Modulus, Cyclic Fatigue, and SSR tests in new (universal) formats (compatible with FlexMAT v2.2).

Related References and Research

Hot-Mix Asphalt Performance Related Specification Based on Viscoelastoplastic Continuum Damage (VEPCD) Models (FHWA-HRT-21-093)

Ruggedness and Interlaboratory Studies for Asphalt Mixture Performance Tester (AMPT) Cyclic Fatigue Test: Phase I Report (FHWA-HRT-21-057)

Ruggedness and Interlaboratory Studies for Asphalt Mixture Performance Tester (AMPT) Cyclic Fatigue Test: Phase II Report (FHWA-HRT-21-057)

Webinar: Seasonal Effects Due to Moisture Variation and Investigation of Cyclic Fatigue Test Temperature and Specimen End Failure on Pavement Performance (ZoomGov)     Passcode: r^5yZ5ka

TechBrief: Development of Balanced Mixture Design Index Parameters and the Flex Suite of Performance Analysis Tools for Asphalt Pavements (FHWA-HRT-24-113)

Development of Balanced Mixture Design Index Parameters and the Flex Suite of Performance Analysis Tools for Asphalt Pavements—Volume I (FHWA-HRT-24-112)

Development of Balanced Mixture Design Index Parameters and the Flex Suite of Performance Analysis Tools for Asphalt Pavements—Volume II (FHWA-HRT-24-111)

Ruggedness and Interlaboratory Studies for Asphalt Mixture Performance Tester (AMPT) Small Scale Dynamic Modulus: Phase I Report  (Publication pending)

Webinar: Phase 1-Ruggedness Study (ZoomGov)     Passcode: ^zuKC2op (Presentation begins at 00:06:35)

Ruggedness and Interlaboratory Studies for Asphalt Mixture Performance Tester (AMPT) Small Scale Dynamic Modulus: Phase II Report (Publication pending)

Webinar: Phase II-Interlaboratory Study (ZoomGov)     Passcode: 9@9^5PVb

NCHRP Project TFRS-01

FHWA Performance Related Specifications Whiteboard Video (YouTube)

FHWA Quality Assurance Specifications Whiteboard Video (YouTube)

FHWA Types and Uses of Construction Specifications Whiteboard Video (YouTube)