NCAT released eight technical reports in 2019 covering a wide range of topics. A brief summary of each follows, and full versions are available for download free of charge.
NCAT Report 19-01: Preliminary Evaluation of Recycled Asphalt Shingles in Warm Mix Asphalt in Wilson, North Carolina Download Full Report
NCAT documented the production and construction of a demonstration project using post-consumer recycled asphalt shingles (RAS) and manufacturer waste RAS in warm mix (WMA) and hot mix asphalt (HMA) and evaluated their properties using a range of laboratory tests.
In the Hamburg test, the WMA mixes had statistically higher rut depths than the HMA mixes; however, all of the mixes had relatively low results. The Overlay Tester and the I-FIT results indicated that the mix containing post-consumer RAS and WMA had better cracking resistance than the mix containing manufacturer waste RAS produced at HMA temperatures. All mixes had similar results for thermal cracking susceptibility. At the time of the 14-month project inspection, all four mixes exhibited similar field performance with no differences evident due to the type of RAS or the use of WMA.
NCAT Report 19-02: FHWA Demonstration Project for Enhanced Durability of Asphalt Pavements Through Increased In-Place Pavement Density, Phase 2 Download Full Report
A recent FHWA initiative focused on how to achieve higher in-place densities through improved compaction methods. The Phase 2 report includes best practices and provides specification examples.
The study documented field demonstration projects intended to help state highway agencies evaluate their current density requirements. Of the eight documented projects, six improved in-place density by at least 0.5 percent and all projects had at least one test section with an average in-place density greater than or equal to 94.0 percent. Methods used to obtain higher in-place densities generally fell into one of six categories: (1) including or increasing incentives and raising the minimum percent in-place density requirements; (2) better use of compaction equipment; (3) adjusting the asphalt mixture design to increase the asphalt content; (4) reducing variability; (5) following best practices; and (6) using new technologies.
NCAT Report 19-03: Best Practices for Determining Life Cycle Costs of Asphalt Pavements Download Full Report
State highway agencies continually face important financial decisions when planning a new or reconstructed highway. For example, what initial investment should be made? How much will be needed for maintenance? What construction materials should be used? The answers to these questions may surface in a life-cycle cost analysis, which estimates how much it will cost to build and maintain an asset over time. This report provides best practices to help highway agencies properly determine inputs for use in their life cycle cost analysis procedures and to calculate the life cycle costs of asphalt pavements.
NCAT Report 19-04: A Synthesis of Technical Needs of Asphalt Pavements for Local Roads Download Full Report
This synthesis of pavement engineering for low volume roads included a review of asphalt mix design guides, pavement design guides, and research reports, as well as a state of the practice survey to summarize current practices for designing low volume roads. The synthesis also identified common issues and knowledge gaps typically encountered when building and maintaining low volume roads.
Rural roads are often built with less-than-conventional design standards, resulting in road designs that are not optimally engineered. A proposed actions segment encourages agencies and industry to follow examples presented in the document in order to establish best practices for mixture design protocols and acceptance criteria.
NCAT Report 19-05: Three Wheel Polishing Device and Dynamic Friction Tester Accelerated Laboratory Friction Testing Repeatability and Reproducibility Study Download Full Report
This study examined the repeatability and reproducibility for a Three Wheel Polishing Device (TWPD) and dynamic friction tester (DFT) testing protocol for a proposed AASHTO standard to assist in implementing accelerated friction testing. The study evaluated slab compaction methods, TWPD polishing, and friction measurements with the DFT. Two laboratories used the same model of DFT but different models of the TWPD. Researchers found that the DFT did not influence the average of replicate friction measurements and different analysis methods provided comparable results. However, there was a significant difference between the friction coefficients measured by the two labs. Results also indicated that the compaction methods used in the labs did not create consistent slabs.
NCAT Report 19-06: Determining Initial Service Life for LCCA Using Comparable IRI as One of the Criteria Download Full Report
Since pavement smoothness is important to the traveling public, it should be a key factor in determining the timing for pavement rehabilitation. NCAT researchers evaluated data from the Long-Term Pavement Performance (LTPP) program to explore this issue.
LTPP data indicates that most asphalt pavements in the LTPP program were maintained or rehabilitated before reaching the mean international roughness index (MRI) threshold of 170 inches/mile currently suggested as the point where pavements are in poor condition by the FHWA Highway Performance Monitoring System guidelines. An MRI threshold of 120 in/mile is found to be more representative of the pavement roughness at the time of first intervention in the LTPP database. The ages of AC and PCC pavements at which their smoothness reaches 120 in/mile are similar for AC and PCC pavements.
NCAT Report 19-08: Mix Design Strategies for Improving Asphalt Mixture Performance Download Full Report
This report summarizes the findings from a literature review and a survey of State Asphalt Pavement Associations regarding adjustments to volumetric mix designs to improve asphalt mix durability. Three adjustments were identified as likely to provide the greatest improvement in pavement performance: (1) use more polymer modified asphalt binder; (2) increase the amount of new binder in a mixture by lowering the design air voids or increasing the minimum VMA requirement; and (3) increase in-place density by methods such as lowering Ndesign requirements. The report also briefly discusses how the Superpave5 mix design method, designed to improve in-place density, and the Bailey method, which can be used to better control the volumetric properties of asphalt mixtures, can have positive impacts on mixture performance when combined with the recommended adjustments.
NCAT Report 19-09: Quantifying Pavement Albedo Download Full Report
This report documents a study that measured albedo and other thermal properties of asphalt and concrete pavements at seven locations in the United States with a range of aggregate types, pavement surface ages, and climates. Results show that the albedo of all pavements change over time in an asymptotic fashion toward unique values for each site. An AC pavement albedo model was developed that reasonably predicted albedo over time based on pavement age and coarse aggregate color. The PCC albedo model, which included pavement age, coarse aggregate color, and surface texture, was unable to accurately predict albedo. Additional models reasonably predicted pavement thermal responses in warm, dry climates but did not adequately account for the influence of moisture and freezing climates. Pavement thermal properties were shown to affect pavement designs by as much as 15% based on AASHTOWare Pavement ME design results. Current highway sustainability rating systems have recognized the complexity of pavement albedo. Some systems only address qualitative cool pavement goals while others do not address albedo-related metrics or outcomes.