In recent years, there has been an increased focus on making asphalt mixes more affordable, and this has led to the increased use of recycled materials and binder modifications. Consequently, premature cracking of the asphalt mixes becomes a national problem. There is an urgent need for a practical and reliable cracking test for routine use in the process of mix design, quality control (QC), and quality assurance (QA) testing. Various cracking tests have been developed in the past but none of them is simple enough for routine uses, especially for QC testing in contractors’ field labs. To address this problem, the researchers in the NCHRP 20-30/IDEA 195 Project developed an asphalt cracking test (IDEAL-CT) integrated with the folowing features:
1. Simplicity: no instrumentation, cutting, gluing, drilling, or notching;
2. Practicality: minimum training needed for routine operation;
3. Efficiency: test completion within 1 min.;
4. Test equipment: existing or low cost equipment (< $10,000);
5. Repeatability: coefficient of variation less than 20%;
6. Sensitivity: sensitive to mix factors (recycled materials, aggregates, binder, aging); and
7. Good correlation with field cracking performance: validated with field test sections in Texas, LTPP-SPS10 at Oklahoma, and Federal Highway Administration-Accelerated Loading Facility.
The researchers established and partially validated cracking criteria for different types of asphalt mixtures. They also developed an ASTM standard test procedure for determining the cracking tolerance index for any asphalt mixtures using the IDEAL-CT test. Furthermore, they collaborated with several equipment manufactures to make low cost stand-alone ITC test equipment or test fixtures which can be incorporated into existing commonly used load frames.
The objective of this research was to facilitate the implementation of the IDEAL-CT test by the state DOTs in their asphalt mix design and QA/QC activities.
The research objective was successfully achieved through the following tasks:
1. Task 1 ($55,000.00): Demonstration of the use of the IDEAL-CT for mix design and QC/QA testing: The IDEAL-CT test demonstration was carried out at the Texas Transportation Institute’s (TTI’s) Center for Infrastructure Renewal in College Station, Texas. One representative from each participating DOT was invited. Travel costs and other meeting-related expenses were covered by the implementation project. The demonstration included specimen preparation, conditioning, testing, data interpretation, and application for both mix design and QC/QA. Each participating DOT was asked to send two plant mixes (one good mix and one mix with poor cracking resistance) in advance, and these mixes were then used for the demonstration. Each attendee at the demonstration was asked to critique the test procedures and provide recommendations and guidance on what would assist its implementation in their state.
2. Task 2 ($9,000.00): Demonstration technical memorandum: A technical memo was written to document all the demonstration activities and the mixes tested for each participating DOT.
3. Task 3 ($20,000.00): Development of training videos and detailed successful case studies: The demonstration carried out in Task 1 was professionally videotaped and edited for developing training videos, including all aspects of specimen preparation, conditioning, testing, data interpretation, and application for mix design and QC/QA. As with all implementation efforts, it was important to provide successful case studies on how DOT’s had implemented this technology, from shadow testing to full implementation. The cost/benefit of test implementation to local contractors was also highlighted.
4. Task 4 ($25,000.00): Implementation group Webinars/conference calls and TRB Webinars: The research team and the participating DOTs held bi-monthly Webinars or conference call to update and exchange implementation progress, issues encountered, and lessons learned.
5. Task 5 ($10,645.00): Flyers and Video Development: Two one-page flyers along with videos were developed. One flyer was for DOT senior management that described the benefits, consequences of not adopting a cracking test, and the cost implications. A second flyer was developed for DOT bituminous engineers and hot mix specialists with more technical information on test set up, proposed criteria, and step by step implementation recommendations. Short high-definition professionally produced videos were also provided to accompany the flyers.
The contractor’s final report is available