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This report focuses on the first extensive forensic excavation of a paved test cell at the Minnesota Road Research Project (Mn/ROAD). A trench was dug in Cell 28 of the Low Volume Loop at Mn/ROAD to investigate a localized failure of the roadway. This report documents the trenching process and serves as a historical record of the in situ conditions of Cell 28 in the early summer of 1997. Data collected during this forensic excavation has contributed to the conclusion that mechanistic pavement design methods should include a maximum allowable stress criteria for aggregate base and subgrade. In addition, minimum hot-mix asphalt pavement thicknesses are required to prevent failures of aggregate base and subgrade. The tests performed during the investigation, as well as the analysis of available data, are discussed. The conclusions of the forensic research team as to the historical performance and subsequent deterioration of Cell 28 also are included.

In this project, researchers examined the current practices that local agencies use and evaluated the thickness design procedures by comparing predicted lives for the current designs with those obtained from the mechanistic-empirical design procedure ROADENT. Researchers determined current practices by sending a questionnaire to all cities and counties and visiting two counties and one city. In general, the questionnaire responses show that cities and counties use a variety of practices for the design, construction, and management of low volume pavements in Minnesota. Relative to the current designs, ROADENT predictions of fatigue behavior require a thicker design for medium and high-traffic roads than the Soil Factor design, and a thicker design for high-traffic roads than the R-Value procedure. The required thicknesses based on development of rut depth are not consistent with the current designs. To develop consistent procedures for the design, construction, and management of low volume roads in Minnesota, the report recommends converting the differences in performance predictions to thicknesses through the use of existing procedures and the mechanistic-empirical procedure; developing a best practices manual; and implementing the design procedure and manual.

This report documents the research that incorporated reliability analysis into the existing mechanistic-empirical (M-E) flexible pavement design method for Minnesota. Reliability in pavement design increases the probability that a pavement structure will perform as intended for the duration of its design life. The report includes a comprehensive literature review of the state-of-the-art research. The Minnesota Road Research Project (Mn/ROAD) served as the primary source of data, in addition to the literature review. This research quantified the variability of each pavement design input and developed a rational method of incorporating reliability analysis into the M-E procedure through Monte Carlo simulation. Researchers adapted the existing computer program, ROADENT, to allow the designer to perform reliability analysis for fatigue and rutting. A sensitivity analysis, using ROADENT, identified the input parameters with the greatest influence on design reliability. Comparison designs were performed to check ROADENT against the 1993 AASHTO guide and the existing Minnesota granular equivalency methods. Those comparisons showed that ROADENT produced very similar design values for rutting. However, data suggests that the fatigue performance equation will require further modification to accurately predict fatigue reliability.

This Technical Summary pertains to Report 2023-19, “Cost Estimate of B vs. C Grade Asphalt Binders,” published May 2023.

This report presents results from a laboratory study and field implementation of acoustic emission monitoring of fatigue cracks in cover-plated steel bridge girders. The acoustic monitoring successfully detected growing fatigue cracks in the lab when using both source location and a state of stress criteria. Application of this methodology on three field bridges also proved successful by detecting a propagating crack in two of the bridges and an extinguished crack in a third bridge. Researchers tested a double angle retrofit, designed by the Minnesota Department of Transportation, both in the lab and in the field of girder with fatigue cracks in the top flange. This retrofit does not require removal of concrete deck, and only involves bolting the retrofit to the bridge girder web. The double angle retrofit applied to laboratory test girder resulted in a reduction of flange stresses by 42 percent. Field implementation of the retrofit had mixed success. On one bridge, stress ranges in the cracked flange was reduced by 43 percent. However, on a second test bridge, the reduction was only 8 percent, likely due to the inadequate space for proper installation of the retrofit.

This report presents information about requiring warranties on roadway .construction. Nationwide, several states have implemented short-term pavement warranty projects, and several models are outlined that have successful warranty programs. Both the Wisconsin and Michigan Departments of Transportation have instituted very successful warranty programs. Lessons learned from their experiences could be used to initiate programs in Minnesota, both at a state and local level. Advantages and disadvantages of requiring warranties on highway construction are presented. Design/build contracts are different from warranties, and information about them are presented as well. Recommendations are given for steps and considerations in implementing a warranty program for local agencies.

This report presents the results of a four-year study on techniques for revegetation of native sedges in created basins. Although often the dominant genus in shallow wetlands, sedges (Carex spp.) do not readily recolonize after restoration or creation of the water table. It is unlikely that sedges will naturally establish in created wetlands. The results of seed germination studies on five Carex species suggest the highest germination rates in fresh seeds - with one exception. Wet/cold storage also can prolong seed viability for at least two-and-a-half years. Dry storage is not recommended for wetland sedge seeds. Short-term wet/cold treatment after prolonged dry storage does not improve germination rates. Sensitive to deep water, rising water levels, and competition during the establishment year, seedlings grew well across a wide range of water depths in subsequent growing seasons. Both species outcompeted annual weeds within two to three growing seasons, but not Phalaris arundinacea (reed canary grass). The study recommends weed control during the establishment year to prevent the invasion of P. arundinacea. Wetland soil promotes seedling growth relative to other soils, but does not affect germination rates. Because of the potential for the introduction of undesirable weeds, the study does not recommend the use of donor wetland soil. Instead, study results suggest the potential for the use of organic top-dressings.

This report describes the results of a project to develop an on-board emissions and performance measurement system (OEPMS) for the quantification of carbon monoxide (CO) emissions. Researchers measured emissions from a 1990, 2.5 liter TBI engine passenger automobile over a typical suburb-to-city commute in the Minneapolis/St. Paul metropolitan area. As a test of the OEPMS, researchers measured CO emissions during cold weather cold starts and commutes at temperatures characteristic of the area's winter weather. Open-loop and closed-loop emissions of CO were measured and compared. Additionally, the effectiveness of magnetic-type block heaters was examined. Tests with the OEPMS provided a wide range of results. The OEPMS proved very durable and easily adaptable for a wide variety of testing. The OEPMS holds promise for future research into fuels, emissions reducing technologies, regulations, and commute habits in real world situations.

This research developed an online procedure to estimate the weaving capacity through time for a simple ramp-weave section, the most common type of weaving areas in the Twin Cities' freeway network. The field observations and the analysis of the traffic data collected from a sample weaving section indicate that the freeway-to-ramp and ramp-to-freeway vehicles first merge and travel together at the beginning portion of the auxiliary lane before they split to the mainline or exit ramp. The length of the shared portion of the auxiliary lane, called an "effective weaving zone," varied depending on the length of an auxiliary lane and the amount of weaving volume. The above merge-split behavior and the resulting mixed flow on the auxiliary lane for a short time period explains the fact that the maximum possible weaving volume in a simple ramp-weave section equals the maximum through volume that the auxiliary lane can handle. Researchers used a Kalman Filter to obtain estimated weaving volume data from three weaving, which supported this observation. Based on the above findings, an online procedure was developed to estimate the maximum possible weaving volume for a given ramp-weave area through time using the volume and occupancy measurements from the loop detectors. The proposed procedure assumes that the maximum possible weaving volume for a given time interval is a function of downstream traffic conditions that can be quantified by estimating the time-variant merging and diverging capacities of a given weaving section. Test results with the five-minute data from a ramp-weave site indicate that the maximum possible weaving volume can be estimated with reasonable accuracy during congested peak periods.

This report was created at the request of the Bureau of Public Roads to forecast the construction and maintenance costs for Minnesota roads from 1965-1985. After 1972, costs were expected to increase.