Development of the Illinois Flexibility Index Test

The Illinois Flexible Index Test (I-FIT) Protocol was introduced in 2015 and the test protocol was accepted as AASHTO provisional specification TP 124. The I-FIT protocol offers various advantages to the industry due to its simplicity and affordability while providing meaningful results to discriminate between asphalt concrete (AC )mixes. The results obtained from various Illinois Center for Transportation projects by testing numerous lab-produced and plant-produced AC mixes indicate consistent trends with changes in AC mix constituents and I-FIT results. The results from two multiple projects to correlate FI values to field performance validate the ability of I-FIT to predict potential cracking. In one of the projects, consistency was demonstrated between the FI and transverse cracking for the AC mixes used in 12 overlay projects. In another experiment, there was a very good correlation between fatigue cracking at a full-scale accelerated loading facility (ALF) and FI values obtained by testing the plant-produced AC mixes collected during the production. Currently, Illinois DOT has been following a roadmap to implement I-FIT as part of performance specifications in Illinois. Pilot projects are underway allowing data collection from contractors and testing in the districts. Development of a mixture long-term aging protocol is subject of an ongoing study. Once the aging protocol is developed, according to the roadmap, I-FIT will be part of performance specifications in 2020.


  • English

Media Info

  • Media Type: Digital/other
  • Features: Figures; Photos; References; Tables;
  • Pagination: pp 31-59
  • Monograph Title: Relationship Between Laboratory Cracking Tests and Field Performance of Asphalt Mixtures
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 01722468
  • Record Type: Publication
  • Files: TRIS, TRB, ATRI
  • Created Date: Nov 15 2019 11:35AM