U.S. Department of Transportation
Federal Highway Administration
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Washington, DC 20590
Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
This magazine is an archived publication and may contain dated technical, contact, and link information.
|Publication Number: FHWA-HRT-13-003 Date: March/April 2013|
Publication Number: FHWA-HRT-13-003
Issue No: Vol. 76 No. 5
Date: March/April 2013
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:
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
For more information on R&T communications products available from FHWA, visit FHWA's Web site at www.fhwa.dot.gov/research/library (or email email@example.com), or the National Transportation Library at ntl.bts.gov (or email firstname.lastname@example.org).
Publication Number: FHWA-HIF-12-037
Sulfur is expected to be in ample supply in the future, which makes it an appealing alternative to asphalt as a binder extender. This TechBrief provides an overview of the implications of using sulfur as a modifier, or extender, for asphalt concrete mixtures and the relationship to the performance of asphalt pavement.
Highway agencies use sulfur-extended asphalt in dense-graded mixtures with sulfur/asphalt binder mass ratios from 20/80 to 40/60, and at times up to 50/50. The emulsified portion of sulfur performs as an asphalt extender, while any excess sulfur performs as a mix filler or stabilizer. Allowable sulfur concentration in the binder depends on asphalt properties. On a long-term basis, approximately 20 percent of the sulfur remains dissolved or dispersed as part of the binder. Free sulfur, above approximately 20 percent by weight, solidifies to a crystalline state.
Previous research has shown that sulfur-extended asphalt pavement mixtures can provide performance equal to conventional asphalt concrete mixtures. Although laboratory testing of tensile strength ratios on some mixtures has indicated the potential for moisture susceptibility, field projects have not revealed evidence of stripping -- the loss of bonding between the aggregate and the binder -- as a concern under real pavement conditions. However, the report recommends evaluating stripping potential as part of the normal mix design process.
Although cracking is a concern in thin, high-strain pavement applications, in properly designed pavements, cracking is no more challenging than with conventional asphalt concrete. Because of the expected advantages of modulus and rutting resistance, the researchers conclude that sulfur-extended asphalt mixtures can be designed with softer performance-grade asphalts and higher binder contents to enhance durability. Although these mixtures smell differently and may cause eye irritation during the paving operation, potential savings in asphalt binder costs make sulfur-extended asphalt an alternative worth considering.
The TechBrief includes information about sulfur-extended asphalt’s background, properties, safety, and use. It is available to download at www.fhwa.dot.gov/pavement/pub_details.cfm?id=794. Printed copies are available from the PDC.
Publication Number: FHWA-HRT-12-051
This report provides guidelines for constructing geosynthetic reinforced soil (GRS)–integrated bridge systems (IBS) and serves as a template upon which highway agencies can develop their own standard specifications. The document is based on FHWA’s design and construction guidelines for GRS–IBS, Geosynthetic Reinforced Soil Integrated Bridge System Interim Implementation Guide (FHWA-HRT-11-026), and supports FHWA’s Every Day Counts initiative to accelerate deployment of proven, market-ready technologies.
Included in the report is information about material requirements, backfill, geosynthetics, construction, labor and equipment, site layout, excavation, superstructure placement, approach integration, site drainage, acceptance, measurement, and payment. The specifications cover construction of reinforced soil foundations, GRS abutments, and integrated approaches. Although this guide applies specifically to abutments built with concrete masonry blocks as the facing element, the recommendations can be adapted to other GRS structures built with different facing systems, such as timber, metal, or gabion baskets. Special design considerations may apply if facing elements other than concrete masonry blocks are used.
The report is available to download at www.fhwa.dot.gov/publications/research/infrastructure/structures/12051. Printed copies are available from the PDC.
Publication Number: FHWA-HRT-12-064
Ultra-high performance concrete (UHPC) has garnered interest from the highway community for its ability to create strong field-cast connections between prefabricated structural components. This TechBrief discusses research on the compressive mechanical response of a rapid-strengthening UHPC formulation exposed to a range of curing conditions.
As a field-cast grout, UHPC facilitates simplified construction practices and enhanced long-term performance. After mixing and prior to hardening, UHPC-class materials have a tendency to exhibit a dormant period. Quicker achievement of hardened properties could foster broader use of UHPC-class materials in accelerated bridge construction projects.
Researchers found that the early-age compressive strength gain of rapid-strengthening UHPC formulation is directly proportional to the curing temperature to which UHPC is subjected. Using specimens at room temperature as a baseline, cool-cure specimens required significantly longer curing time to reach comparable strength levels. Specimens subjected to elevated curing temperatures achieved higher strengths more quickly.
Further, the researchers found that the rate at which samples attained their compressive mechanical properties was not significantly affected by premix age at the time of mix initiation. Researchers also determined that a chemical accelerator used to promote rapid strength gain did not accelerate desired mechanical properties at early ages. The report recommends investigating the use of accelerating admixtures prior to deployment to ensure appropriate performance.
The TechBrief is available to download at www.fhwa.dot.gov/publications/research/infrastructure/structures/hpc/12064/index.cfm. Printed copies are available from the PDC.