Infrastructure Technology Institute
The quality of the natural environment and, in the long term, global warming, are serious concerns for our society. The International Panel on Climate Change predicts a likely increase in the average global temperature of at least 2° C over the next 100 years, and for high-emission scenarios, 2.5 to 6.5° C1. The consequences of this temperature rise may be severe and widespread, including changing weather patterns and a substantial rise in sea level – on the order of a meter or more. Transportation plays a central role in this process: one-third of US CO2 emissions come from oil-based transportation fuel use; transportation emissions are projected to grow about 10% over next two decades.
Can transportation infrastructure research save the environment? Surely not alone – but it can make some important contributions. Some of the work done by ITI offers good examples.
Structural Health Monitoring
Structural health monitoring (SHM) contributes to better-informed decisions about investment in transportation infrastructure repair and rehabilitation. Continuous monitoring techniques – for bridge scour, foundation movement, and stresses and strains in steel and concrete structures – can give early warnings of the need for restorative action, and in some cases, for emergency shutdown and repair.
The value of early warning is time: time to set priorities that fit resource constraints, to plan the most efficient restoration actions, and to develop and implement traffic management plans that minimize temporary congestion. With sufficient advanced information, infrastructure managers may be able to coordinate multiple rehabilitation projects to avoid amplifying traffic disruptions. In the case of emergent problems, remote automated SHM may provide sufficient warning of incipient failure to allow better-planned closure and traffic rerouting.
We have demonstrated the value of early warning with such applications as SHM of scour-endangered bridges using tilt meters, crack monitoring in a steel box girder bridge with acoustic emission testing, and autonomous strain measurements on a variety of steel bridges and bridge bearings. Most of these applications involve semi-permanent instrumentation, autonomous remote monitoring, and wireless communication to permit low cost continuous tracking of many facilities simultaneously.
SHM can also identify non-threatening structural damage – isolating benign damage that can be ignored, thus avoiding unnecessary expenditures and disruptions. In statistical terms, this means avoiding Type II errors, where the conservative null hypothesis is that the infrastructure element is at serious risk, and the error is in accepting this hypothesis when it is not true. Such errors waste money and time that could be spent on other infrastructure projects.
The ITI team has assessed a major bridge displaying a crack in a fracture critical top chord using acoustic emission testing to determine that the crack was inactive under load and thus there was no need for corrective action. The bridge has remained in service with the benign crack.
Congestion Consequences of Infrastructure Projects
Reductions in traffic delays resulting from better infrastructure management, more focused rehabilitation projects, and avoidance of unnecessary work can produce substantial savings in fuel consumption and associated greenhouse gas emissions, as well as valuable time savings for travelers. The Texas Transportation Institute mobility study for 2007 estimated that congestion cost US urban travelers 4.2 billion extra hours and 2.9 billion gallons of fuel for a total cost of $78 billion2. The Federal Highway Administration reports that about 10% of this congestion is due to work zones3. This is likely to be an under-estimate, because work zones – especially large ones – lead to significant traffic diversions, which serve to reallocate congestion across the network. The impact on neighboring communities, in terms of localized d elays and crash risks, amplifies the cost of maintenance and rehabilitation.
ITI faculty and students are studying the total cost of work zone congestion, particularly for smaller projects that do not always get the the most advanced traffic management technologies (Intelligent Transportation Systems – ITS). Traffic management focuses on the critical issue of worker safety, but sometimes overlooks traffic operations and associated environmental consequences. This work is attempting to account for the impacts of transportation infrastructure projects on the full set of stakeholders to provide a basis for managing these impacts.
Advanced Materials for Infrastructure
Advanced infrastructure materials and materials processing techniques can provide important environmental advantages. Concretes with higher strengths can mean reduced material quantities for infrastructure projects. Cements that make greater use of recycled materials release less CO2 in the manufacturing process. New weathering steels eliminate the need for painting and repainting, not only reducing costs, but also preventing environmental hazards associated with field painting.
ITI researchers are advancing the frontiers of both concrete and steel as infrastructure materials. Weldable, weathering, high strength steel developed at Northwestern with ITI support has been built into two highway bridges, and a third is in the planning stage. Our steel researchers are also proposing a version of this steel for guard rails that eliminates the need for galvanizing and/or painting. Through fundamental studies of cement chemistry, we are defining new manufacturing techniques and developing a better understanding of the long-term design strength of concrete.
Infrastructure preservation and rehabilitation programs and projects can be designed to reduce environmental impacts – pollution emissions, spills, and energy consumption – and, with the right choices can contribute to environmental benefits through anticipation of infrastructure problems, thoughtful project selection and scheduling, choice of the “greenest” materials, and sensitive project management.
Driving infrastructure management and reinvestment decisions with objective data, and using the right materials for the job, can help ensure that we have the transportation capacity and quality that we need to remain economically competitive while protecting and enhancing the quality of our environment. This is the work of ITI.
1. Climate Change 2007, Synthesis Report: http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf
2. David Schrank and Tim Lomax, The 2007 Urban Mobility Report: http://tti.tamu.edu/documents/mobility_report_2007.pdf
3. Federal Highway Administration, Focus on Congestion Relief: http://www.fhwa.dot.gov/congestion/describing_problem.htm