Research, Development, and Technology

Turner-Fairbank Highway Research Center

6300 Georgetown Pike

McLean, VA 22101-2296

PUBLICATION NO. FHWA-HRT-21-055 OCTOBER 2021

FlexMATTM Asphalt Pavement Analysis 

Tools Summary and FlexMAT 

Specified Data Structure for 

Cyclic Fatigue Test 
Introduction - 1 - October 2021 

FLEXMAT ASPHALT PAVEMENT 

ANALYSIS TOOLS SUMMARY

FLEXMAT ASPHALT PAVEMENT ANALYSIS TOOLS

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 mastercurve 

coefficients and time-temperature shift factors. It analyzes the AMPT cyclic fatigue test results 

(AASHTO TP133) to provide inputs to FlexPAVETM 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 Sapp 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; 

https://www.fhwa.dot.gov/pavement/pubs/hif19091.pdf.) 

1. "FlexMAT Cracking v2.1.xlsm" (file): Actual FlexMAT v2.1 file, cracking analysis 

version, ready for testing using the new universal data structure format requirement. 

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, published in 2021. (FHWA-HRT-21-044; 

https://www.fhwa.dot.gov/publications/research/infrastructure/pavements/21044/index.cfm) 

2. "FlexMAT Rutting v2.1.xlsm" (file): Actual FlexMAT v2.1 file, rutting analysis version, 

ready for testing using the new universal data structure format requirement. 

CLIMATIC DATA FILES

Use .csv files with the FlexMAT Rutting v2.1 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 yr (1996–2015) of temperature 

information. 

3. "Rutting Climate Files.zip" (files): Contains the updated temperature database required 

for RSI calculations in FlexMAT v2.1 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 v2.1 file, it will be automatically identified. If not, the user will 

be prompted to identify the folder’s location.
Introduction - 2 - October 2021 

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: 

4. "AMPT-DM v1.0_final.docx" (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.

5. "AMPT-Fatigue v1.0_final.docx" (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.

6. "AMPT-Rutting v1.0_final.docx" (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.

7. "Input Examples" (folder): Contains dummy examples of Dynamic Modulus, Cyclic 

Fatigue, and SSR tests in new (universal) formats (compatible with FlexMAT v2.1).

CONTACT

Comments and questions can be forwarded to: 

Matthew Corrigan, Research Engineer 

Federal Highway Administration

matthew.corrigan@dot.gov
AMPT Cyclic Fatigue Data Requirements v1.0 - 3 - October 2021 

FLEXMAT SPECIFIED DATA STRUCTURE FOR CYCLIC FATIGUE TEST

GENERAL DATA STRUCTURE ITEMS

• The data files must be in ASCII text format. No specific file extension or file naming convention is required. FlexMAT will browse all the 

files in selected folder to identify relevant file(s).

• The informational items (those that are not used by FlexMAT) and data (FlexMAT required) are separated by sections. Sections have unique 

and defined key words enclosed in square brackets ([ ]). 

• The comment character is an exclamation point (!).

• Any comments or nondata items within required sections must be preceded by the comment character (!) as the first character in the line. 

Blank lines are acceptable within any of the sections and will be skipped when reading. 

• Section headers are not case-sensitive, but it is recommended to use upper-case letters for ease of readability and consistency. 

• The decimal point or period (“.”) must be the decimal separator symbol in numeric data fields.

• Within the test data, a comma, space, or tab must be used as field separator. Consecutive field separators (comma and space, for example) will 

be treated as a single-field separator.

• The positive (+) and negative (–) signs must apply to all loads, actuator displacements, and linear variable differential transformer

displacements, and must be shown as: 

o Loads: Compression positive (+), Tension negative (–). 

o Displacements: Extension positive (+), Retraction negative (–). 

o Pressures positive (+), Vacuum negative (–). 

• The current version of FlexMAT can accept input of both SI and U.S. units; however, the fatigue analysis and output are based on SI units. SI 

units should be considered for all data items and units indicated in Section G [UNIT].

FATIGUE TEST FILE LOCATION

The program input requires a separate folder for each specimen. Within that folder, the program looks for the file with keyword “AMPT-FT” in the 

first line. 

Note of Caution: If the folder contains any redundant or surplus files in the specified data format, the program uses data from the first read file in the 

calculation. Therefore, the folder must have only one file in the specified data format. However, there can be any number of files in other data 

formats or file types within the folder.
AMPT Cyclic Fatigue Data Requirements v1.0 - 4 - October 2021 

DATA STRUCTURE—FATIGUE TEST DATA

ITEM DATA DESCRIPTION

A AMPT-FT A - Required. First line in the file must have this 

key word for this data file. FlexMAT browses the 

files in the folder to identify files to read.

B [VERSION] 

1.0

B - Required. Must have this section completed 

and only data item is the version number, 

currently 1.0, of the file format. Used to track 

version of file when data format is updated in the 

future. Not to be confused with FlexMAT 

version. Any informational item in this section 

must start with comment character (!).

C [SUPPLEMENTARY INFORMATION]

Project name, device name, device software version, operator, target temperature, or 

any other test related information

C - Optional. Optional section to document 

supplementary information. Not required but 

recommended to include project name, device 

name, device software version, and operator as a 

minimum. Can contain any information and not 

used in the analysis. If available, FlexMAT will

read and include it in the report section for 

reference.

D [SPECIMEN INFORMATION]

Dimensions, conditioning time, properties, or any other specimen-related information

D - Optional. Optional section to document 

specimen information. Can be included or 

excluded and can contain any information. 

FlexMAT does not read and skips this section.

E [SPECIMEN IDENTIFICATION] E - Required. Must have this section completed. 

Only data item is the specimen ID. Any 
AMPT Cyclic Fatigue Data Requirements v1.0 - 5 - October 2021 

! Specimen identification number (maximum 80 characters)

ABCDEFG

informational item in this section must start with 

comment character (!).

F [FIELD SEPARATOR]

! 0=comma (“,”), 1=space (“ ”), 2=tab

! If comma and space are used together, please select 0 (comma) 

! If tab and space are used together, please select 2 (tab) 

0

F - Required. Must have this section completed. 

Only data item is the character type used as the 

field separator (delimiter) to separate fields 

(numeric data values) in each input record (line). 

Any informational item in this section must start 

with comment character (!).

G [UNIT]

! 0 = U.S. Units, 1 = SI Units

! U.S.: Modulus in ksi, Temperature in F, Pressure in psi, Axial Stress in psi, Load in 

kips, Displacement in mils

! SI: Modulus in MPa, Temperature in C, Pressure in kPa, Axial Stress in kPa, Load in 

kN, Displacement in mm

1

G - Required. Must have this section completed. 

Only data item is the unit type used. Must be 0 

(U.S. Units - Modulus in ksi, Temperature in F, 

Pressure in psi, Axial Stress in psi, Load in kips, 

Displacement in mils), or 1 (SI Units - Modulus 

in MPa, Temperature in C, Pressure in kPa, Axial 

Stress in kPa, Load in kN, Displacement in mm). 

For the selected unit type, the parameters should 

be reported in the stated magnitude. For example, 

if SI units is selected, Modulus should be reported 

in MPa not kPa. Any informational item in this 

section must start with comment character (!).

H [TEST PARAMETERS]

Frequency, Target Temperature, Axial Gauge Length, Dynamic Modulus Fingerprint 

Test Parameters, Target On-Specimen Peak-To-Peak Microstrain, or any other test 

parameters.

H - Optional. Optional section to document test 

parameters. Can be included or excluded and can 

contain any information. FlexMAT does not read 

and skips this section.
AMPT Cyclic Fatigue Data Requirements v1.0 - 6 - October 2021 

I [TEST DATA]

Supplemental test data such as complete Dynamic Modulus Fingerprint Test including 

parameters like Modulus, Cycle Count, Phase Angle, Stress, Microstrain, 

Temperature, or any other test data.

I - Optional. Optional section to document 

supplemental test data. Can be included or 

excluded and can contain any information. 

FlexMAT does not read and skips this section. 

J [PID TUNING QUALITY PARAMETER]

! Machine Compliance Factor, Target on Specimen Peak to Peak Strain

1.833, 420

J - Required. Must have this section completed. 

Only two data items are included, separated by 

comma, space, or tab with the following 

sequence: Machine Compliance Factor (MCF) 

and the Target On-Specimen Peak-to-Peak strain 

(microstrain). Any informational item in this 

section must start with comment character (!).

K [FINGERPRINT TEST DATA] 

! Time, Axial Stress, Actuator Strain, Axial Strain #1, Axial Strain #2 ... 

5.000, 32.29, 8.323, 9.046, 6.989, 9.864, 18.05, 0.036621, 0.000916 

5.001, 17.76, 4.161, 7.302, 5.463, 9.210, 18.05, 0.020142, 0.000458 

5.002, 4.305, 8.323, 5.777, 5.245, 4.632, 18.05, 0.004883, 0.000916 

.... 

K - Required. Must have this section completed. 

Test data from the fingerprint dynamic modulus 

test in the units specified in the [UNIT] section, 

one line per time increment, data items separated 

by comma, space, or tab, with the following 

sequence per line: Time (sec), Axial Stress (kPa 

or psi), Peak to Peak Actuator Strain (microstrain), LVDT Axial Strain #1 (microstrain), 

LVDT Axial Strain #2 (microstrain), LVDT 

Axial Strain #3 (microstrain), Temperature (C or 

F), Load (kN or kips), Actuator Displacement 

(mm or mils), LVDT Displacement #1 (mm or 

mils), LVDT Displacement #2 (mm or mils), 

LVDT Displacement #3 (mm or mils). Any 

informational item in this section must start with 

comment character (!).

L [FINAL FINGERPRINT DYNAMIC MODULUS]

! Units should be based on the selection made in [UNIT] header. 

L - Required. Must have this section completed. 

Only data item is the Final Fingerprint Dynamic 

Modulus reported in the units specified in the 
AMPT Cyclic Fatigue Data Requirements v1.0 - 7 - October 2021 

5042 [UNIT] section. Any informational item in this 

section must start with comment character (!).

M [FATIGUE INITIAL CYCLES TEST DATA]

! Time, Axial Stress, Actuator Strain, Axial Strain #1, Axial Strain #2 ... 

0.0000, -0.29, 6.93, 0.41, 0.62, 0.27, 15.04, -0.02, 0.001, 0.009, 0.0044, 0.0019 

0.0010, 0.18, 000, 0.19, -0.02, -0.16, 15.04, 0.0916, 0.00,0.013, -0.002, -0.0011 

0.0020, 0.413, 3.46, 0.19, 0.19, 0.49, 15.05, 0.003, 0.0004, 0.0013, 0.0013, 0.0034 

....

M - Required. Must have this section. Test data 

from fatigue initial cycles in the units specified in 

the [UNIT] section, one line per time increment, 

data items separated by comma, space, or tab, 

with the following sequence per line: Time (sec), 

Axial Stress (kPa or psi), Peak to Peak Actuator 

Strain (microstrain), LVDT Axial Strain #1 

(microstrain), LVDT Axial Strain #2 

(microstrain), LVDT Axial Strain #3 (microstrain), Temperature (C or F), Load (kN or kips), 

Actuator Displacement (mm or mils), LVDT 

Displacement #1 (mm or mils), LVDT 

Displacement #2 (mm or mils), LVDT 

Displacement #3 (mm or mils). Any 

informational item in this section must start with 

comment character (!).

N [FATIGUE TEST DATA]

! Cycle, Dynamic Modulus, Phase Angle, Peak to Peak Stress, Maximum Stress .... 

10, 4708.6, 28.052, 1139.1, 272.4, -875.4, 1594.8, 241.9, 263.5 .... 

20, 4646.4, 28.108, 1194.5, 374.9, -818.2, 1603.0, 257.1, 283.2 .... 

....

N - Required. Must have this section completed. 

Test data from fatigue test in the units specified in 

the [UNIT] section, one line per reported load 

cycle (every 10th cycle), data items separated by 

comma, space, or tab, with the following 

sequence per line: Cycle, Dynamic Modulus 

(MPa or ksi), Phase Angle (Degrees), Peak to 

Peak Stress (kPa or psi), Maximum Stress (kPa or 

psi), Minimum Stress (kPa or psi), Peak to Peak 

Actuator Strain (microstrain), Peak to Peak 

Average Strain (microstrain), LVDT Peak to Peak 

Strain #1 (microstrain), LVDT Peak to Peak 

Strain #2 (microstrain), LVDT Peak to Peak 

Strain #3 (microstrain), Maximum Actuator 

Strain (microstrain), Minimum Actuator Strain 
AMPT Cyclic Fatigue Data Requirements v1.0 - 8 - October 2021 

(microstrain), LVDT Maximum Strain #1 

(microstrain), LVDT Minimum Strain #1 

(microstrain), LVDT Maximum Strain #2 

(microstrain), LVDT Minimum Strain #2 

(microstrain), LVDT Maximum Strain #3 

(microstrain), LVDT Minimum Strain #3 (microstrain), Temperature (C or F), Peak to Peak Load 

(kN or kips), Maximum Load (kN or kips), 

Minimum Load (kN or kips), Peak to Peak 

Actuator Displacement (mm or mils), LVDT 

Peak to Peak Displacement #1 (mm or mils), 

LVDT Peak to Peak Displacement #2 (mm or 

mils), LVDT Peak to Peak Displacement #3 (mm 

or mils), Maximum Actuator Displacement (mm 

or mils), Minimum Actuator Displacement (mm 

or mils), LVDT Maximum Displacement #1 (mm 

or mils), LVDT Minimum Displacement #1 (mm 

or mils), LDVT Maximum Displacement #2 (mm 

or mils), LVDT Minimum Displacement #2 (mm 

or mils), LVDT Maximum Displacement #3 (mm 

or mils), LVDT Minimum Displacement #3 (mm 

or mils). Any informational item in this section 

must start with comment character (!).
HRDI-20/10-21(WEB)E Recycled

Recyclable