Below are brief descriptions of communications products recently developed by the Federal Highway Administration’s (FHWA) Office of Research, Development, and Technology. All of the reports are or will soon be available from the National Technical Information Service (NTIS). In some cases, limited copies of the communications products are available from FHWA’s Research and Technology (R&T) Product Distribution Center (PDC).

When ordering from NTIS, include the NTIS publication number (PB number) and the publication title. You also may visit the NTIS Web site at www.ntis.gov to order publications online. Call NTIS for current prices. For customers outside the United States, Canada, and Mexico, the cost is usually double the listed price. Address requests to:

National Technical Information Service
5301 Shawnee Road
Alexandria, VA 22312
Telephone: 703–605–6000
Toll-free number: 1–888–584–8332
Web site: www.ntis.gov
Email: customerservice@ntis.gov

Requests for items available from the R&T Product Distribution Center should be addressed to:

R&T Product Distribution Center
Szanca Solutions/FHWA PDC
13710 Dunnings Highway
Claysburg, PA 16625
Telephone: 814–239–1160
Fax: 814–239–2156
Email: report.center@dot.gov

For more information on R&T communications products available from FHWA, visit FHWA’s Web site at www.fhwa.dot.gov, the FHWA Research Library at www.fhwa.dot.gov/research/library (or email fhwalibrary@dot.gov), or the National Transportation Library at ntl.bts.gov (or email library@dot.gov).

The Use of Recycled Tire Rubber to Modify Asphalt Binder and Mixtures (TechBrief)

Publication Number: FHWA-HIF-14-015

The paving industry has used recycled rubber from waste tires in asphalt since the 1960s. Recycled rubber can be used as an asphalt binder modifier and asphalt mixture additive in gap-graded and open-graded asphalt mixtures and surface treatments.

This technical brief provides an overview of the processes for tire rubber used as a modifier for asphalt binders and as an additive for asphalt mixtures. It includes considerations for laboratory and field testing as well as performance. As some aspects of the technology are still evolving, it covers best practices and areas of caution. The document also includes information on how to incorporate recycled tire rubber into the Superpave (SUperior PERforming Asphalt PAVEment) design system.

Until recently, the routine use of recycled tire rubber in pavements was limited to a few States. While performance is generally good, the cost of recycled tire rubber is generally higher than conventional practices. However, asphalt binder costs have increased over recent years because of the rising cost of crude oil. Polymers also have seen an increase in cost due to other market demands and fluctuations in availability. In contrast, over this same time period, recycled rubber from car and truck tires has experienced a relatively stable market price.

Local, State, and Federal regulations, such as FHWA’s 2006 recycled materials policy, have increased the availability of recycled tire rubber, driving a renewed interest in the material as an asphalt binder modifier and mixture additive to provide a long-lasting, cost-competitive, and environmentally responsible pavement system.

This technical brief includes information about mix design challenges, tires and tire processing, various processes for creating binders and mixtures using tire rubber, performance challenges, and industry resources on tire rubber.

The document is available to download at www.fhwa.dot.gov/pavement/pubs/hif14015.pdf.

Fatigue Testing of Galvanized and Ungalvanized Socket Connections (Report)

Publication Number: FHWA-HRT-14-066

Fatigue of structural supports for overhead signs, traffic signals, and high mast light poles has received focused attention from researchers in the last 25 years because of failures reported in welded details. These lightweight, flexible structures are often susceptible to vibration from wind, which may lead to fatigue cracking at welded details in the structure.

Researchers hypothesized that cracking in the zinc metal bath during galvanizing caused some premature failures. This report describes how researchers tested specimens from two pole manufacturers and presents the results showing the difference in fatigue life between galvanized and ungalvanized structures. Generally, the galvanized specimens showed a one-category reduction in fatigue life, meaning they would have a shorter expected life compared to identical specimens that were not galvanized.

The report assists stakeholders, including State transportation departments, researchers, consultants, and industry representatives, with the design and review of ancillary sign structures. It is available to download at www.fhwa.dot.gov/publications/research/infrastructure/bridge/14066/index.cfm. Printed copies are available from the PDC.

Wind Tunnel Investigations of an Inclined Stay Cable with a Helical Fillet (Report)

Publication Number: FHWA-HRT-14-070

In recent decades, engineers have recognized cable-stayed bridges as the most efficient and cost-effective structural form for medium- to long-span bridges. Though widely used, some of these bridges have experienced serviceability problems associated with large-amplitude vibration of the stay cables. This report discusses a study to supplement the existing knowledge base on some of the outstanding issues of stay cable vibrations and to develop technical recommendations that may be incorporated into design guidelines.

Because stay cables are laterally flexible with very low inherent damping, they are highly susceptible to environmental conditions such as wind and combinations of rain and wind. To counter this susceptibility, engineers use various mitigation measures on many cable-stayed bridges around the world. These measures include surface modifications, cable crossties, and external dampers.

This study examined wind and cable interaction, with particular focus on airflow close to the cable as well as forces on the cable surface. Researchers attached a helical fillet, a commonly used surface modification, to an existing cable model to evaluate the influence of this mitigation feature. To represent field orientations, they varied the cable inclination angle during testing. They conducted tests at various levels of damping, with and without the fillet, and in turbulent as well as smooth flow conditions.

The researchers found that a stay cable with a representative surface roughness, cross-sectional shape, and helical fillet inclined at 60 degrees can experience wind-induced vibrations with large amplitudes in smooth or turbulent flow. For a stay cable inclined at 45 degrees with a helical fillet, researchers did not observe large vibrations for the range of wind speed they investigated.

This report assists bridge engineers, wind engineers, and consultants involved in the design of cable-stayed bridges. It is available to download at www.fhwa.dot.gov/publications/research/infrastructure/structures/bridge/14070/index.cfm.

Slip and Creep of Thermal Spray Coatings (TechBrief)

Publication Number: FHWA-HRT-14-083

When used in high-strength bolted connections, coating systems to protect steel bridge systems and components from corrosion must meet required levels of slip and creep performance. The American Association of State Highway and Transportation Officials’ specifications for load and resistance factor design of bridges require bolted connections to be designed as slip critical under certain circumstances, including heavy impact loads or severe vibration. Slip-critical connections rely on the clamping force from bolts to develop frictional shear stresses to transfer force from one bridge element to the next.

In severe environments, thermal spray coatings offer better long-term corrosion protection for steel bridge systems and their components than zinc-bearing paint systems. Yet these coatings have not been mainstreamed into practice, in part because of the unknown frictional resistance they provide for slip resistance within high-strength bolted connections. This technical brief discusses research aimed at understanding key variables that influence the slip and creep performance of thermal spray coatings in high-strength bolted connections. It introduces limited data on slip coefficients developed by sealed and unsealed coatings.

Researchers found that because of rough textures, unsealed zinc and zinc/aluminum alloy thermal spray coatings had no problems passing slip performance requirements. However, once the surface was sealed, neither coating system could meet slip performance criteria. Until further research can demonstrate slip-critical performance of sealed thermal spray coatings, the researchers recommend that slip-critical surfaces be either masked off during manufacturing to prevent sealing or assembled before coating sealers are applied.

This document is available to download at www.fhwa.dot.gov/publications/research/infrastructure/structures/bridge/14083/index.cfm. Printed copies are available from the PDC.