Self-consolidating concrete tested in prestressed girders

A team of University of Minnesota researchers recently completed a multi-year study of prestressed bridge girders made from self-consolidating concrete (SCC), a highly workable material that flows through congested reinforcement layouts without forming voids in the absence of vibration. Self consolidating concrete offers a number of advantages over conventional concrete including improved appearance (no need to patch “bug holes” that develop on the concrete surface), reduced manpower and noise during construction by eliminating the need for external consolidation through mechanical vibration, and the ability to be placed in highly congested forms.

Civil engineering professors Carol Shield and Catherine French worked with graduate student Bulent Erkmen on the project. The results of this study are a significant addition to engineers’ knowledge of SCC performance in bridge component applications. The research was sponsored by the Minnesota Department of Transportation.

Self-consolidating concrete contains chemical admixtures to make it less viscous, so it pours easily. Developed in Japan in the 1980s, it has been extensively used there in tunnels, walls, and bridges. SCC later gained a foothold in several European countries, where an international consortium was formed to develop SCC applications. Although still considered a new technology in the United States, SCC has been used in large construction projects and by several State Departments of Transportation.

The researchers worked with the Minnesota Department of Transportation and local fabricators to develop SCC mixes based on locally available materials, then used these mixes to fabricate prestressed bridge girders and cylinders. The mixes used a variety of cementitious materials, aggregates, and admixtures. The properties of the SCC mixes were evaluated in a fresh state using a variety of tests that the researchers evaluated and developed to determine flowability, passing ability, and resistance to segregation.

The girders were instrumented to monitor transfer length, camber, and prestress losses, and test cylinders were used to measure compressive strength and modulus of elasticity, as well as to monitor creep and shrinkage over time.

The overall performance of SCC girders in these tests was comparable to the performance of conventional concrete girders, with measured prestress losses generally agreeing with predictions. Further, the researchers determined that models of creep and shrinkage based on data from the test cylinders can give reasonable predictions of prestress losses for both conventional and SCC girders.

Self-Compacting Concrete (SCC) for Prestressed Bridge Girders (Mn/DOT 2008-51) is available from the CTS Web site.

Intelligent Transportation Systems

Transportation Data Research Laboratory plants seeds of diverse research

The wide variety of research carried out by the University of Minnesota – Duluth’s Transportation Data Research Laboratory (TDRL) is demonstrated by a research report describing three recently completed “seed” projects. The TDRL, led by Taek Kwon, is funded by the Northland Advanced Transportation Systems Research Laboratories, part of the Intelligent Transportation Systems Institute.

Gathering traffic data is difficult in rural areas where the electrical power needed to run sensor stations is not readily available. The need for on-site power prompted the development of a solar/wind power unit suitable for powering rural ITS applications. To demonstrate the potential of a remote power generator, TDRL researchers built a powered light pole using only commercial off-the-shelf components and tracked its performance over time. The power use data revealed that solar power alone was not sufficient to power the unit in the area where it was set up, but wind power could make up for the shortfall—particularly on stormy days, which often had weak sun but strong winds.

Collecting vehicle counts on gravel roads is another rural data collection challenge tackled by the TDRL. Vehicle detectors based on pneumatic tubes frequently fail due to punctures caused by sharp gravel; the accuracy of these detectors is also impaired by material buildup around the tubes. Instead of tubes, the prototype TDRL system uses a magnetic field detector based on a coil-wound fluxgate, similar to the technology used in the pavement-embedded inductive loop vehicle detectors installed in many urban highways. Unlike loop detectors, however, the fluxgate is not affected by vehicles stopped nearby.

Back in the lab, TDRL researchers developed a software development kit (SDK) that will enable researchers to work with the large volume of traffic and road/weather data that the TDRL gathers and archives on behalf of the Minnesota Department of Transportation (Mn/DOT). Because it was developed as a dynamically linked library (DLL), the kit can be integrated directly into a variety of software applications. Researchers from many institutions have already made use of the TDRL’s extensive data, and the new SDK will make it easier for them to turn data into new knowledge.

TDRL Projects: Solar/Wind Hybrid Renewable Light Pole, Gravel-Road Traffic Counter, DLL-Based Traffic Software Development Kit (CTS 08-21) is available from the ITS Institute Web site.

Transportation and the Environment

Making native prairie plants at home in revegetation areas

The findings from a recent study at the University of Minnesota Sandplain Research Farm may help the Minnesota Department of Transportation and other transportation agencies re-introduce native prairie plant species along roadways. Professor Peter Graham, graduate student Elena Beyhaut, and scientist Becki Tlusty investigated techniques of rhizobial inoculation to support the growth of legumes and improve soil nitrogen levels.

Nitrogen is an essential plant nutrient, but many soils do not contain enough of it to support the growth of desirable plants. Legumes can fix nitrogen in the soil through their symbiotic relationship with certain types of bacteria. In areas where the soil does not naturally contain suitable bacteria, they must be added to the soil by inoculation; successful inoculation enables legumes to flourish, adding nitrogen to the soil and ultimately supporting the growth of non-legume plant species such as native prairie grasses.

The researchers tested several soil inoculation techniques, monitoring plots to determine which techniques produced the best nitrogen levels and the most legume growth. Inoculation with granular peat inoculant emerged as the recommended technique, and the findings suggested that it should be applied more heavily than it is currently in Minnesota.

Improved Methodologies for the Inoculation of Prairie Legumes in Roadside/Revegetation Settings (Mn/DOT 2008-48) is available from the CTS Web site.

Transit, Bicyling, and Walking

TCRP research publications available online

The federal Transit Cooperative Research Program (TCRP), administered by the Transportation Research Board, provides practical transit research to address technical and operational issues. TCRP emphasizes putting research results into the hands of organizations and individuals that can use them to solve problems.
Recent TCRP publications include:

• Transit Systems in College and University Communities (TCRP Synthesis Report 78)
• Integration of Paratransit and Fixed-Route Transit Services (TCRP Synthesis Report 76)
• Uses of Fees or Alternatives to Fund Transit (TCRP Synthesis Report 28)

Safety

Human factors researchers probe perspectives of rural and urban teens and seniors

When planning crash reduction programs, one size does not fit all, according to a team of researchers investigating how differences in attitudes between rural and urban residents affect crash risk. Michael Manser, director of the ITS Institute’s HumanFIRST Program, and colleague Michael Rakauskas worked with researchers from the Minnesota Center for Survey Research and former HumanFIRST director Nic Ward, now at Montana State University, on the study of attitudes toward driving safety among different age groups of rural and urban residents in Minnesota.

Expanding on earlier work that investigated broad differences between the attitudes of urban and rural drivers, the researchers’ recent work focused on differences between older and younger drivers’ attitudes toward safety. The study included focus groups to explore issues that drivers consider important in regards to safety, and a survey to obtain detailed data on driving practices, perceptions, and safety interventions.

Teen drivers in the study demonstrated significant differences from parents and seniors in regards to driving safety. The results of the study suggest that young drivers and senior drivers are affected by different risk factors, and that important differences exist between drivers in rural and urban environments.

The young drivers offered a variety of perspectives on safety interventions such as graduated driver licensing (GDL), driver education programs, and smart technologies for teen driver assistance. For seniors, the question of if and when older drivers should be required to take driving tests to maintain their licenses was a topic of concern, as drivers noted that driving ability does not correlate neatly with age.

Generational Perspectives on Teen and Older Drivers on Traffic Safety in Rural and Urban Communities (Mn/DOT 2008-36) is available from the ITS Institute Web site.

TZD program launches redesigned Web site

 

The Minnesota Toward Zero Deaths program launched a redesigned Web site, minnesotatzd.org, at the Annual TZD Conference.

The new site features year-to-date tracking of traffic fatalities, a gateway to safety statistics, more user-friendly navigation, and expanded coverage of topics included in the Minnesota Strategic Highway Safety Plan. The site also offers tips for how groups can organize to identify and help find solutions to the traffic safety problems in their communities.

The minnesotatzd.org site is managed by CTS. For more information, contact Stephanie Malinoff at malinoff@cts.umn.edu, 612-624-8398.

Recent Research Reports

August through November 2008 updated list available

CTS periodically announces transportation-related research reports by University of Minnesota researchers, published by CTS, Mn/DOT, the Minnesota Local Road Research Board, and other sponsors. The complete list of reports released from August through November 2008, including abstracts, is now available. These reports are available in PDF format on the Research Reports Web page.

More Upcoming Events

February 5
Transportation Career Expo, Minneapolis. Contact Shawn Haag, 612-625-5608 haag0025@cts.umn.edu.

February 11
CTS Winter Luncheon, AI Johnson Room at the McNamara Alumni Center, Minneapolis. Contact Sara Van Essendelft, 612-624-3708, cceconf5@umn.edu. Sponsored by the ITS Institute.

February 11, 18, 25; March 4, 11, 25
Structural Engineering Series, Continuing Education and Conference Center, University of Minnesota, St. Paul campus.

February 12
Minnesota Pavement Conference, St. Paul, MN

April 25–29
American Planning Association National Planning Conference, Minneapolis.

May 19
CTS Spring Luncheon featuring Tom Vanderbilt, author of “Traffic: Why We Drive the Way We Do (and What It Says About Us),” Sheraton Hotel, Bloomington. Contact Sara Van Essendelft, 612-624-3708, cceconf5@umn.edu.

May 19–20
20th Annual CTS Transportation Research Conference, NEW LOCATION: Sheraton Hotel, Bloomington.