FHWA’s activity in pavement structural design advances understanding and improvement of pavement life-cycle cost procedures and improves design methods for pavement preservation, maintenance, and rehabilitation.

Spotlight Project: Mixture Performance Test Comparison Study

In the asphalt materials field, the premier topic of focus in mixture design and characterization relates to performance tests, especially those which can be conducted at intermediate (less than about 30 ℃) temperatures and are capable of assessing fatigue resistance. A study is underway to compare six index-based cracking tests to field performance. This study features collaboration with industry, academic, and agency partners to advance the community’s knowledge of test variability, feasibility in a State quality assurance program, and ability to accurately align with known field performance.

Image source: Copyright  Dennis Hill, 2011

FHWA’s work in pavement materials seeks to enhance and optimize mixture design, testing, and specifications that improve pavement performance for mixtures. Research includes use of both virgin and alternative materials, such as recycled/reclaimed materials or industrial byproducts.

Spotlight Project: T-FAST – Test  for Assessing Alkali-Silica Reactivity (ASR) of Aggregates

ASR is a very serious distress mechanism for concrete. The cement reacts with silica in the aggregate and can form an expansive gel which cracks the concrete. Not all aggregates are reactive in this way. Most aggregate tests rely on the measurement of physical expansion of mortar or concrete samples and do not always screen aggregates very well.

The Turner-Fairbank Highway Research Center's Chemistry Laboratory has developed a simple test method which uses pure chemistry to predict expansion rather than the need to measure it. To date, 100-percent agreement has been achieved with historical block farm data. Research is continuing to expand the method to mix designs and advance mitigation strategies.

Image source: FHWA, 2006

FHWA researches new and innovative materials and practices that minimize the environmental impacts of pavement.

Spotlight Project: Epoxy-Modified Asphalt (EMA) Research for Durable Open-Graded Friction Course (OGFC)

The use of EMA has proven to be a way to increase asphalt durability and resistance to deformation, failure, and long-term oxidative aging. The predominant failure in OGFC is raveling (aggregate loss) related to long-term oxidative aging and binder loss of adhesion with aggregates. Several State highway agencies (SHAs) are interested in utilizing OGFC as a paving surface mix for various safety and environmental benefits. Thus, EMA may become a solution to enhance the durability of OGFC and allow SHAs to achieve safety, performance, and environmental goals.

The international experience with field sections constructed with EMA in  New Zealand and the Netherlands has been promising. In cooperation with the New Zealand Transport Agency (NZTA) at Waka Kotahi, Delft University of Technology (TU Delft), and the National Center for Asphalt Technology (NCAT), FHWA is advancing an understanding of epoxy-modified asphalts’ reactivity and dosage selection, and the workability window of epoxy systems in OGFC mixtures to advance the knowledge and state of the practice of EMA mixtures and technologies. These studies open the door for successful field trials of Epoxy-modified asphalt in the United States.

Image source: FHWA, 2014