Reports

A bridge that spans the Mississippi River on U.S. Interstate 35W in Minneapolis, Minnesota has been fitted with a computerized system that sprays potassium acetate, the anti-icing chemical selected, on the bridge deck when data from sensors and a Road Weather Information System determine that hazardous winter driving conditions are imminent. The I-35W bridge (9340) was a candidate for this high-tech treatment due to the high incidence of winter traffic crashes on the bridge. The bridge is more susceptible to "black ice" and slippery conditions because of moisture from the Mississippi River's St. Anthony Falls, nearby power plants and industrial facilities, and of the high volume of traffic on the bridge. (Year 2000 average daily traffic is approximately 139,000 vehicles.) The formation of "black ice" is due to the combination of extreme cold and heavy vehicle exhaust from congestion on the bridge. In addition to traffic safety, the anti-icing system also contributes to sustainability, because the chemical used is environmentally less toxic and corrosive than sodium chloride, which traditionally has been used. This paper describes the anti-icing system and its operational test results.

Asphalt mixture variations that result from moisture fluctuations in aggregate stockpiles pose a serious problem at dryer-drum plants. The moisture content of a stockpile is infrequently measured, if at all. If the proportion of aggregate is not adjusted to account for its moisture content, an improper mix will result. This project looked at identifying a practical and accurate field method or probe for measuring the moisture content of aggregates, testing the probe in a hot-mix plant, and developing a control strategy for asphalt oil addition to the mix. Researchers identified a suitable commercial probe by reviewing past research and conducting laboratory studies. Testing in the plant showed that this probe could rapidly measure aggregate moisture in plant conditions at the same level of accuracy as gravimetric measurements. Researchers also developed a control strategy for the asphalt oil addition. Testing showed the effectiveness of this control, in conjunction with commercial probe moisture measurements in the feed bin. A problem with probe operations robustness was identified.

This project involved the development of a fault diagnostic system for Safetruck, an intelligent vehicle prototype. The fault diagnostic system continuously monitors the health of vehicle sensors, detects a failure when it happens, and identifies the source of the failure. The fault diagnostic system monitors several key components: the Global Positioning System, lateral accelerometer, and yaw-rate gyroscope, which constitute the set of lateral dynamic sensors, as well as the forward-looking radar that measures distance relative velocity, and azimuth angle to other vehicles and objects on the highway. To design the project's lateral fault diagnostic system, researchers exploited the model-based dynamic relationships that exist between the three lateral sensors. They verified the system's performance through extensive experiments on the Safetruck. This project also explored a number of new approaches to creating a reliable fault detection system for radar. Monitoring the radar's health poses a special challenge because the radar measures the distance to another independent vehicle on the highway. In the absence of inter-vehicle communications, the fault diagnostic system has no way of knowing the other vehicle's motion, which means that model-based approaches cannot be used. Experimental results indicate that an inexpensive redundant sensor combined with a specially designed nonlinear filter would provide the most reliable method for radar health monitoring.

This report presents the results of a cooperative study on the field use of a permeameter, built by researchers at the Minnesota Department of Transportation (Mn/DOT) and the University of Minnesota, to estimate the saturated hydraulic conductivity of pavement base materials. Field measurements using the permeameter were taken on various highway construction projects, and researchers measured the saturated hydraulic conductivity of samples in the laboratory. Researchers also reviewed theories for converting a field-measured flow rate into a saturated hydraulic conductivity estimate. By numerical simulation and analysis of the field data, researchers determined an appropriate method for converting the Mn/DOT permeameter flow measurements into estimates of hydraulic conductivity. Variations between the field estimated and laboratory measured hydraulic conductivity are within one order of magnitude. Variations between the field estimate and numerical simulation, however, are much closer. The study found the Mn/DOT permeameter can be used to obtain a reliable estimate of the base hydraulic conductivity provided that the base layer is at least 15 cm (6 in.) deep. When the base is too thin, permeameter readings are restricted to early infiltration times.

This report presents the results of a research project to evaluate the performance of six full-depth silica fume bridge decks, constructed between 1997 and 1999. The Minnesota Department of Transportation (Mn/DOT) constructed these decks to compare their performance and constructability in Minnesota, which involves the use of a seven-inch structural slab followed by a two-inch low slump overlay. Researchers conducted air content and slump field testing, visual inspections, and laboratory testing on chloride permeability, compressive strength, and hardened air system properties. In addition, they compared initial costs between the current deck system and the full-depth silica fume decks. The overall performance of the silica fume bridge decks has been good; however, two of the bridge decks did have problems related to the development of silica fume balls. Laboratory testing has shown that silica fume concrete performs better in terms of chloride permeability and compressive strength. Field tests have shown that placement of the silica fume concrete is comparable to a conventional concrete mix. Finally, cost comparisons have shown the placement of a full-depth silica fume deck to be slightly lower than the current deck system.

Previous research conducted by the Design Center for American Urban Landscape at the University of Minnesota suggests a need to develop a hierarchical network of arterials that would accommodate contemporary and future activity and movement patterns in suburban areas. This research project investigated the interaction between road section design and adjacent site design by applying livable community principles and developing a set of design criteria that would guide coordination of land use and transportation planning. The research hypothesized a need for a minimum of three roadway prototypes, district planning capabilities, and an integrated land use and transportation planning approach. Research findings indicate that a hierarchical network is feasible under the following circumstances: The district network assumes arterial segments designed at different speeds; Urban design performance criteria are used at the beginning of the planning process to establish quantitative measures; Spacing of controlled intersections corresponds to road speed design; Urban design templates, keyed to road design speed, are used to guide design of areas adjacent to the intersections; The existing development context becomes the basis for balancing activity and moment and for phasing change in the built environment.

This research project assesses the nature and extent of premature deterioration of segmental concrete block retaining walls (SCBRWs) along roadways in the Minneapolis-St. Paul area. Researchers conducted a two-stage condition survey on 104 SCBRWs. The first stage, a general distress survey, focused on determining the type, severity, and extent of distresses present. The second stage, a peak winter survey, assessed the extent of snow/ice cover and exposure to winter sun. According to research results, only 7% of the SCBRWs surveyed were in poor or very poor condition. But researchers observed many distress types in 50% or more of the walls surveyed, including freeze-thaw damage, scaling, manufacturing flaws, and efflorescence. Freeze-thaw damage and scaling were most highly associated with decreases in overall wall condition. Efflorescence and freeze-thaw damage were found to be at least partly dependent upon SCBRW age and block manufacturer. Durability problems appear to be directly related to the lack of durability of the block units, which suggests problems with the use of inadequate mix designs, non-durable aggregate, and/or inadequate curing procedures. The report includes recommendations to address possible deficiencies in manufacturing processes and quality.

This report presents the results of a study that investigated the reinforcement function of geosynthetics for typical Minnesota low volume roadways. Researchers conducted a series of numerical simulations using the finite difference program FLAC. The numerical tests consisted of a static, circular nine kip loading over a variety of typical surfaced and unsurfaced road cross sections that were reinforced with geotextiles and geogrids. Researchers used elastic and elasto-plastic models with frictional interfaces to simulate the layered roadway system. The results of the study indicate that the addition of a geosynthetic does provide reinforcement to the roadway as long as the geosynthetic is stiffer than the subgrade material. However, for most of the cases studied, the benefit in terms of deflection reduction, was very small. Only for the poorest subgrades was the reinforcement benefit substantial.

This project researched image compression methods for storage and transmission of digital images at the Minnesota Department of Transportation (Mn/DOT). Researchers compared the performance of several commercial and research methods for image compression based on the "typical" image provided by the Mn/DOT Office of Land Management. They also surveyed some new image compression methods based on wavelet thresholding. The report details the analyses and comparisons and includes recommendations. Researchers chose MrSID, a commercial software package for image compression, as a suitable method for the needs of MnDOT's Office of Land Management. MrSID uses a wavelet transform-based algorithm to achieve both the efficient storage and retrieval of large digital images. Its main practical advantages include improved utilization of storage and transmission resources and a multi-resolution browsing capability. MrSID can selectively decompress a portion of an image by zooming at different levels of detail.

Failures of the adjusting rings of manholes cost Minnesota cities about $7 million a year in damages in manholes, sewers, and paved surfaces. This study looks at the experience of Minnesota cities and other past research in evaluating the many available methods to repair rings and in recommending construction and repair methods that minimize the risk of damage. Poor construction of manholes and damage from frost heaving cause most failures. When repairs are necessary, survey results suggest three methods with the best cost/value ratios: The Cretex Internal Chimney Seal (Trademark), Flex-Seal Utility Sealant (Trademark), and Infi-Shield (Trademark) seal. One method still under evaluation, rings made of High-Density Polyethylene (HDPE), shows some initial indication of success. While lower in initial cost, other methods are less lasting, resulting in a poor cost/value ratio. Methods also must accommodate the tensile stresses and elongation strains associated with frost heaving through ice lenses. Materials must be elastic enough at sub-freezing temperatures to stretch without breaking when frost heaving opens a joint.