The U.S. National Highway System (NHS) – the federally managed bridge and road network that moves American people and goods – has suffered from decades of insufficient maintenance and heavy use. Lack of funds, increasing traffic loads, and environmental exposure have encouraged rapid bridge deterioration in an already aging system. In 2016, nearly 40% of the nation’s bridges were over 50 years old and 9.1% were rated “structurally deficient.” To properly prioritize maintenance, repairs, and reconstruction, the Federal Highway Administration (FHWA) has implemented the National Highway Performance Plan (NHPP), which requires states to design and implement management strategies for their NHS assets.
To fulfill Montana’s NHPP requirements, two WTI employees, Senior Research Engineer Damon Fick and Researcher Matt Bell, have developed a bridge assessment program for the Montana Department of Transportation (MDT) using three decades of inspection and deterioration data. By performing a time-based statistical analysis on these data Bell and Fick were able to create graphical deterioration projections – or Deterioration Curves – for bridges across the state. These were then adjusted to better reflect the deterioration observed in MDT’s real-world observations. “These bridge deterioration curves guide maintenance planning and decision-making at both the project and network level,” noted Bell. “By reflecting what we see in the real world, MDT can use the curves to appropriately allocate money for future work and make sure maintenance is happening at the right time.
While the deterioration curves indicate the general deterioration rate of bridges across Montana, Bell and Fick will identify specific deterioration variables (deicers, precipitation, traffic volume, etc.) in their next MDT project. “Faster or slower deterioration rates in different Montana districts may be related to maintenance practices, as much as, or in combination with, environmental conditions,” said Bell. “For example, bridges that permit heavy truck loads may experience faster deterioration. If we understand the specific impact, MDT can improve truck permitting and preemptively identify maintenance activities and building specifications. Continually improving the accuracy of the deterioration curves will support the decision-making process for our colleagues at MDT.”
Road salt, most often sodium chloride (NaCl) melts ice and is a crucial tool for winter maintenance crews around the world. However, the constant application of road salt is resulting in long-term environmental and economic impacts. To slow the negative effects of sodium chloride deicers by optimizing salt use, researchers from WTI and Washington State University completed Understanding the Salt Phase Diagram, a project sponsored by Clear Roads, a Federal Highway Administration (FHWA) pooled fund. Led by Laura Fay, WTI’s Cold Climate Operations and Systems Program Manager, the team completed a literature review and laboratory investigation of the NaCl phase diagram, a graphical representation of the physical states (liquids or solid salt/ice) of salt brine depending on concentration and temperature. They distilled the information into training materials to help winter maintenance practitioners better understand the salt phase diagram and to support efficient and effective roadway deicing.
To provide visual aids for the training materials, the researchers needed to demonstrate the behavior of salt solutions in a laboratory setting. They collected video and photographic evidence of ice formation in salt brine at a range of concentrations and temperatures, verifying the familiar process of lowering ice’s freezing point with the addition of salt. They also clarified the effects of high salt concentrations on ice formation.
By synthesizing their laboratory data, the researchers created an updated NaCl phase diagram, fact sheet, and accompanying video. WTI’s Visual Communications Manager, Neil Hetherington, ensured that the phase diagram was associated with easily recognizable design elements (e.g., green = good = ice prevention). Fay noted, “Neil [Hetherington] took subject matter that was science and engineering heavy and converted it into useful, digestible information that is easily transferable. He also took time to collect quality photographs which effectively conveyed the information.”
The research has been well received. Fay has presented the training materials and findings to multiple organizations. “These materials serve as powerful education tools,” noted Fay, “and they are being used across the country.”
Concrete can be susceptible to expansive reactions between alkalis in the Portland cement and reactive forms of silica in the aggregates, which can ultimately reduce the lifespan of the concrete used in pavements and other structures. When this occurs, it can result in costly repairs or even replacement of infrastructure. While alkali-silica reactivity (ASR) has been documented as an issue in many states, little work has been conducted to determine the presence/potential of ASR in Montana. The primary objectives of the proposed research are to evaluate the potential for ASR in the state of Montana, and to develop a testing protocol for identifying potential reactive aggregates. This research will also identify/document existing ASR damage in the state and investigate the potential underlying geological features that may contribute to the presence of reactive aggregates. Finally, this research will evaluate potential techniques used to mitigate the damaging effects of ASR.
Sponsored by the Montana Department of Transportation (MDT), this research project will provide a better understanding of reactive aggregates (including severity) and a better understanding of potential ASR issues in the state of Montana. This information will be helpful in promoting sustainability and extending the service life of Montana concrete pavements and structures. Principal Investigator Mike Berry is conducting this research in partnership with MDT and the Montana Contractors Association.
Ultra-high performance concrete (UHPC) has mechanical and durability properties that far exceed those of conventional concrete. However, using UHPC in conventional concrete applications has been cost prohibitive, with commercially available/proprietary mixes costing approximately 30 times more than conventional concrete. Previous WTI research resulted in nonproprietary UHPC mixes made with materials readily available in Montana. These mixes are significantly less expensive than commercially available UHPC mixes, thus opening the door for their use in construction projects in the state. The Montana Department of Transportation (MDT) Bridge Bureau is interested in using UHPC in field-cast joints between precast concrete deck panels. The use of UHPC in this application will reduce development lengths, and subsequently reduce the requisite spacing between the decks and improve the overall performance of the bridge. Through this project, P.I. Michael Berry will build on the non-proprietary Phase I UHPC research he recently completed for MDT and focus on ensuring the successful application of this material in these field-cast joints.
If these mixes are viable for this application, Montana could take advantage of the cost savings of the non-proprietary mixes and ultimately improve the performance and durability of bridges. More information on this Phase II project is available here.
Geosynthetic materials are routinely used in transportation applications to facilitate construction, improve stability, and enhance longevity. Departments of transportation have generally had good experience with these products, although a robust and non-proprietary design process for geosynthetic reinforced paved roads is still lacking. The Montana Department of Transportation (MDT) believes that geosynthetics can be used responsibly to provide cost-savings on a number of upcoming highway construction projects in the state, based on their in-house experience as well as previous research and evaluation by WTI. MDT desires experimental evidence of performance for these typical projects in order to proceed with future designs.
Principal Investigator Steve Perkins is leading a new study to conduct full-scale indoor testing of reinforced pavement test sections using a traffic simulator to provide performance data and to evaluate a spreadsheet-based design tool that can be used to augment current design procedures. The results from this study can be directly implemented into future MDT highway construction designs having similar conditions to the test sections. These recommendations will pertain most directly to operational conditions where a stable construction platform is established over relatively weak subgrade when it is advantageous to reduce base course thickness in order to save both time and money.
To follow this project, visit its webpage on the WTI website.
WTI research is prominently featured in the new issue of Solutions, the research newsletter of the Montana Department of Transportation. Three recently completed projects are profiled in feature articles:
“Prefabricated Steel Truss/Bridge Deck Systems.” This study was a WTI and MSU Civil Engineering project led by Damon Fick, Tyler Kuehl, Michael Berry, and Jerry Stephens. It evaluated a prototype of a welded steel truss constructed with an integral concrete deck, which has been proposed as a potential alternative for accelerated bridge construction (ABC) projects in Montana. Steel truss bridges are relatively light weight compared with plate girder systems, which makes them a desirable alternative for both material savings and constructability. See the WTI website for more information.
“Evaluation of Effectiveness and Cost-Benefits of Woolen Roadside Reclamation Products.” This research project developed three types of products for study: woolen erosion control blankets (ECBs), wool incorporated into wood fiber compost, and wool incorporated into silt fence. The project, supported by Montana Department of Transportation (MDT) and the Center for Environmentally Sustainable Transportation in Cold Climates, compared the wool products’ performance to roadside reclamation products commonly used for revegetating cut slopes. Rob Ament (P.I.) and Eli Cuelho served on the research team. Additional information is available on the WTI website.
“Feasibility of Non-Proprietary Ultra-High Performance Concrete (UHPC) for Use in Highway Bridges in Montana.” Ultra-high performance concrete (UHPC) has mechanical and durability properties that far exceed those of conventional concrete. However, using UHPC in conventional concrete applications has been cost prohibitive, costing 20 times that of conventional concrete. The overall objective of the Phase I research was to develop and characterize economical non-proprietary UHPC mixes made with materials readily available in Montana. The research was led by Michael Berry. Additional project information is available on the WTI website.
The MDT Solutions newsletter is available on the MDT website.
WTI Research Scientist Laura Fay was interviewed last week by MINNPOST.com on the topic of local road agencies that choose to unpave roads. The discussion focused on Laura’s research sponsored by the Transportation Research Board, in which she surveyed local, state, or federal agencies on how they manage low-volume roads. The survey identified nearly 70 road projects in 27 states in which the road agency chose to convert a road to an unpaved, gravel road instead of re-paving it. The project will also result in a guidebook to help local officials decide if unpaving a road is safe and cost-effective. Read the full article here or go to the WTI website for more information about the research project.