Past Research Cycle Highlights
The seventh cycle of accelerated performance testing began in 2018, providing unique opportunities to determine the field performance of breakthrough materials and concepts without the risk of failure that local and state agencies are unwilling to accept. Research during this cycle is primarily focused on pavement preservation, balanced mix design, cracking tests and rejuvenators.
Pavement Preservation
The pavement preservation group study is quantifying the life-extending and condition-improving benefits of different pavement preservation treatments and treatment combinations on low-volume and high-volume roadways in both northern and southern climates. By determining the field performance of treatments applied at various stages of pavement life and decay, historically broad performance expectations for various preservation options will be discretely quantified to allow agencies to make objective decisions regarding treatment selection. A second focus of the study is to develop specifications and recommended guidelines for quality assurance testing and inspection of pavement preservation treatments. Find out more about our pavement preservation study here.
Many of the same pavement preservation treatments installed in Alabama are being investigated in Minnesota using MnDOT materials and construction methods. The northern pavement preservation experiment sections are located on U.S. Route 169, a high-volume road, and County State Aid Highway (CSAH) 8 in Mille Lacs County, a low-volume road. This study includes treatment selection, test site selection and layout, scheduling, construction, performance monitoring, and data activities to quantify the life-extending benefits of pavement preservation treatments.
Balanced Mix Design
Four test sections on the Test Track focus on the balanced mix design of asphalt mixtures. These sections are sponsored by the Oklahoma and Texas Departments of Transportation. Oklahoma’s balanced mix design approach requires the use of the Hamburg wheel tracking test to evaluate rutting resistance and the Illinois flexibility index to evaluate cracking resistance. The overall objective of Oklahoma’s experiments is to implement performance testing and criteria for balanced mix design. Texas recently developed a special specification for balanced mix design that requires using the Hamburg wheel tracking test to evaluate rutting and moisture damage resistance and the overlay test for assessment of cracking resistance. Their objective is to compare the field performance of asphalt mixes designed using the proposed balanced mix design approach versus the Superpave volumetric approach under accelerated loading conditions.
Cracking Group
The aim of the cracking group experiment is to develop and implement asphalt performance tests to predict cracking for common pavement distresses found in North America. There are several lab tests that claim to relate to one or more modes of cracking. However, most of these tests lack robust validation outside of the state where the method was developed.
Both MnROAD and NCAT have developed test sections to validate laboratory cracking tests by establishing correlations between test results and measured cracking performance in real pavement test sections within a very short timeframe. This research will provide much needed data on where to set criteria for specifications.
Test sections with differing asphalt mixtures that have a range of expected cracking susceptibilities have been constructed at MnROAD. A suite of laboratory cracking tests conducted on the mixes will identify which test results best correlate with field cracking as well as consider their variability, utility and practicality of implementation for both mix design approval and quality control testing. A crucial component of the study is regular performance monitoring of the pavement test sections for ride quality, distresses, strength and response. Read more about the study at MnROAD here.
Rejuvenators
Cargill is sponsoring parallel testing at the NCAT Test Track and the Minnesota Department of Transportation’s MnROAD test highway to determine how to best implement balanced mix design procedures in asphalt mixes containing rejuvenators and high levels of reclaimed asphalt pavement. As part of the project, test sections made with Cargill’s Anova rejuvenator and a 45 percent reclaimed asphalt mix will be compared to control sections with lower recycled contents, measuring factors such as pavement ride quality, cracking and rutting. By conducting experiments at both the Test Track and MnROAD, researchers will be able to monitor results in both northern and southern climate extremes.
As part of the current research cycle, the Mississippi and Tennessee Departments of Transportation have both sponsored rejuvenating seal experiments. NCAT conducted a preliminary screening study to evaluate seven rejuvenating seals to determine which products would be used on the Test Track sections. The products were ranked based on their rheological properties and friction test results. The Mississippi DOT selected ReGenX TM (Blacklidge Emulsions) and Delta Mist TM (Collaborative Aggregates LLC) to be evaluated on its S3 Test Track section. The Tennessee DOT selected Reclamite ® (Ergon) and an experimental product, e-Fog S (Ergon), to be evaluated on its S4 Test Track section. The field performance of these four rejuvenating fog seals will be evaluated for the entire two-year Test Track cycle. More information about the preliminary study can be found here.
While not new construction, Section N7 with Delta S ®, sponsored by Collaborative Aggregates LLC, continues to be monitored by NCAT following completion of the 2015-2017 research cycle.