Research Reports

The Minnesota Department of Transportation has typically used epoxy-coated, straight-legged stirrups anchored in the tension zone as transverse reinforcement in prestressed concrete bridge girders. This configuration is readily placed after stressing the prestressing strands. American Concrete Institute (ACI) and American Association of State Highway and Transportation Officials (AASHTO) specifications require stirrups with bent legs that encompass the longitudinal reinforcement to properly anchor the stirrups. Such a configuration is specified to provide mechanical anchorage to the stirrup, ensuring that it will be able to develop its yield strength with a short anchorage length to resist shear within the web of the girder. AASHTO specifications for anchoring transverse reinforcement are the same for reinforced and prestressed concrete; however, in the case of prestressed concrete bridge girders, there are a number of differences that serve to enhance the anchorage of the transverse reinforcement, thereby enabling the straight bar detail. These include the precompression in the bottom flange of the girder in regions of web-shear cracking. In addition, the stirrup legs are usually embedded within a bottom flange that contains longitudinal strands outside the stirrups. The increased concrete cover over the stirrups provided by the bottom flange and the resistance to vertical splitting cracks along the legs of the stirrups provided by the longitudinal prestressing reinforcement outside the stirrups help to enhance the straight-legged anchorage in both regions of web-shear cracking and flexure-shear cracking. A two-phase experimental program was conducted to investigate the anchorage of straight-legged, epoxy-coated stirrups, which included bar pullout tests performed on 13 subassemblage specimens that represented the bottom flanges of prestressed concrete girders, to determine the effectiveness of straight-legged stirrup anchorage in developing yield strains. Additionally, four girder ends were cast with straight-legged stirrup anchorage details and tested in flexure-shear and web-shear. The straight leg stirrup anchorage detail was determined to be acceptable for Minnesota Department of Transportation (MnDOT) M and MN shaped girders as nominal shear capacities were exceeded and yield strains were measured in the stirrups prior to failure during each of the tests.

In June and July 2013, MnDOT constructed three new concrete pavement test sections or cells at the MnROAD facility. On MnROAD's Interstate 94 mainline, a 7.5 inch thick sustainable concrete pavement was constructed using a 75% recycled concrete aggregate (RCA) mix, to study the performance of recycled aggregates in new concrete. Geocomposite transverse joint drains and preformed neoprene joint seals were also incorporated into this test section. Also on the MnROAD mainline, new bonded concrete overlays of distressed asphalt pavement (BCOA) test sections were built. These BCOA or whitetopping test cells were built with 4 and 5 inch thick fiber reinforced concrete slabs. On MnROAD's Low Volume Road loop, a 3 inch thick ultra-thin unbonded concrete overlay was constructed over two different thicknesses of geotextile fabric interlayer. The concrete overlay also contained structural fibers in the mix. This report documents the design, construction, field testing, sampling and testing, and sensor instrumentation associated with these new test sections. Additionally, a thin 5 inch concrete pavement (cell 32) on the low volume road was repaired and retrofitted with unique load transfer devices; post-repair diamond grinding was performed. The pervious concrete overlay test cell (Cell 39) was ground to ascertain 1) whether slurry from grinding operations significantly impair the permeability. Details about the cells: Mainline sustainable concrete pavement and whitetopping: Cells 613, 140 & 240, and 160-163 (SP 8680-169); Low-volume thin unbonded concrete overlay with geosynthetic interlayer and pervious pavement rehab: Cells 32, 39 (SP 8680-170).

A total of 12 sealant products were applied on the Smith Avenue High Bridge in St. Paul and evaluated over a three-year period. Details, such as surface preparation and application methods, were documented for each product and are conditions specific to each product. Sealant performance was evaluated through field permeability testing, visual observations, and petrographic examination. Visual observations provided evidence that approximately 67 percent of test sections were performing effectively after one winter but only 4 percent after two winters. After three winters, 58 percent of the test locations were visually characterized as ineffective and 42 percent as partially effective. Product performance significantly reduced over the third winter, primarily due to major loss of sealant and surface sand materials. Coring was performed after the second winter, and the cores were photographed and subjected to a petrographic evaluation. The observed depth of sealant penetration was highly variable and likely is dependent on the presence of debris within the crack, original crack width, and the deck temperatures during application. The predominant failure mode observed under magnification was detachment from the crack face and not within the sealant materials. Based on numerous factors, four epoxy and three methacrylate products were recommended for consideration on MnDOT's Approved Products List. Each product recommendation contains the surface preparation and application method conditions under which they were applied. It is also recommended that MnDOT look into increasing the frequency of its routine crack sealing maintenance program from the current five-year cycle.

This report presents a summary of pavement preservation activities and recommended uses, expected longevity, and expected pavement life extension. It also includes some basic information intended to be used by those less familiar with pavement preservation, pavement management, life cycle cost analysis, cost estimating, contracting methods and others to help inform and educate in this important aspect of pavement engineering. Tools and techniques are presented to assist local agency engineers in evaluating costs, benefits, timing, longevity, and the decision-making process for developing an effective pavement preservation program on an individual pavement segment or over an entire network. The report includes examples using real pavement engineering data from several cities and counties in Minnesota to demonstrate topics such as activity timing and the benefits of a preventive maintenance plan rather than a reactive one. A set of guidelines was developed as part of the associated project intended to serve as reference material and as a training program.

This report documents the development of an analysis procedure and an associated computation tool to estimate the impact of heavy vehicles on local agency pavements. The heavy vehicles of interest are those which were not anticipated at the time the pavement structure was designed, but which cause additional damage and thus create the need for rehabilitation or reconstruction sooner than expected. These unexpected heavy vehicles could be generated by new industrial facilities, mining activities, changes in urban waste collection patterns, temporary heavy construction in a limited geographical area, or for other reasons. The tool described in this report implements the procedure, and provides users with the ability to analyze a single roadway segment (for detailed impacts estimates) or an agency's entire network (for summary statistics over the system). The tool provides estimates of the percent of originally intended life that may be used by the unanticipated vehicles, the additional pavement structure that would have been required at construction to accommodate the additional vehicles, and the additional damage that they cause. The tool is contained in a macro-enabled Microsoft Excel spreadsheet and does not need additional files or external functionality to conduct an analysis.

This study developed a generic IDIQ contractive framework upon which MnDOT can produce its IDIQ contracting procedures based on this agency's policies, preferences, and applicable regulations. This report covers several aspects of this alternative contracting method, including successful contracting techniques and procedures, terminology in use by public transportation agencies, contract advertising and award practices, pricing methods, risk management issues, and effective contract administration practices. Besides benchmarking the state-of-practice of IDIQ contracting in federal and state transportation agencies, the report addresses three key aspects identified by the authors: mobilization cost payment, escalation of construction pricing on multi-year IDIQ contracts, and impact of IDIQ contracting on surety bonds. The study found that IDIQ contracting creates a capacity to expedite project delivery through an on-call contractor that can be mobilized and working in a much shorter period than traditional project delivery methods. It also found a number of distinct advantages for repetitive construction and maintenance projects including the ability to obligate unused fiscal year funding, incentivizing construction quality and economy of scale reductions in unit pricing. It also finds that once the IDIQ contract is awarded, the agency is able to utilize the contractor to furnish a number of preconstruction services in much the same manner as Construction Manager/General Contractor projects, which results in better pricing due to more constructable designs.

Roadside swales are drainage ditches that also treat runoff to improve water quality, including infiltration of water to reduce pollutant load. In the infiltration study, a quick and simple device, the Modified Philip Dunne (MPD) infiltrometer, was utilized to measure an important infiltration parameter (saturated hydraulic conductivity, Ksat) at multiple locations in a number of swales. The study showed that the spatial variability in the swale infiltration rate was substantial, requiring 20 or more measurements along the highway to get a good estimate of the mean swale infiltration rate. This study also developed a ditch check filtration system that can be installed in swales to provide significant treatment of dissolved heavy metals and dissolved phosphorous in stormwater runoff. The results were utilized to develop design guidelines and recommendations, including sizing and treatment criteria for optimal performance of the full-scale design of these filters. Finally, the best available knowledge on swale maintenance was combined with information obtained from new surveys conducted to develop recommendations for swale maintenance schedules and effort. The recommendations aim toward optimizing the cost-effectiveness of roadside swales and thus provide useful information to managers and practitioners of roadways. The research results and information obtained from this study can thus be used to design swale systems for use along linear roadway projects that will receive pollution prevention credits for infiltration. This will enable the utilization of drainage ditches to their full pollution prevention potential, before building other more expensive stormwater treatment practices throughout Minnesota and the United States.

The Minnesota Department of Transportation and Minnesota State University, Mankato, contracted with the Technical University of Gdansk, in Poland, for a second time to conduct rolling resistance at the MnROAD facility near Albertville, Minnesota. Rolling resistance testing was conducted on most of the cells of the MnROAD mainline and the low-volume road. A relative ranking of rolling resistance among the difference surfaces at MnROAD was developed. The research team from Poland conducted the testing for a week in early May 2014. The rolling resistance data collected were analyzed and are presented in this report. Additional analyses that were conducted include a relative comparison of fuel consumption predicted with the different rolling resistance coefficients measured at MnROAD, with standard concrete and asphalt pavements as references.

This report presents results of the research that examined various asphalt pavement surfaces in the MnROAD facility. It covers the fundamentals of surface profilometry, describes the construction of the textures and elucidates the performance trends of the various surface parameters. The variables examined include friction, measured with the lock wheel skid truck, smoothness, measured with the light weight profiler, mean profile depth measured by the circular track meter, sound absorption measured by the acoustic impedance tube and Tire- Pavement-Interaction-Noise measured by the on board sound intensity device. Traffic difference was found to be a significant variable in the friction trend of the asphalt surfaces when the low-volume road inside lane of the cells were compared to the corresponding outside lane and when the mainline driving and passing lanes were compared. Based on the Wilcoxon Rank sum, Wilcoxon Sign Rank, and the T-test, traffic levels affected skid resistance. Additionally, the frictional-time series appeared to follow the half-life equation typical of disintegrating materials. A similar test on tire-pavement-noise difference found traffic to be insignificant within the five years of monitored performance of the same test tracks. This study found that certain surface characteristics change with time regardless of traffic while others change with time and traffic. As the study found friction to be related to traffic, periodic measurements of friction can be performed when practicable, otherwise the half-life model developed in this study may be a rough predictor. In the deduced model, friction degradation appeared to be a function of the initial friction number and traffic-induced decay factor. In the low-volume road, there was hardly any evidence of effect of traffic on friction from a comparison of the traffic and environmental lanes. However, at higher traffic levels, (mainline driving versus passing lanes) traffic appeared to affect noise and friction. The study also proposes a temperature-based correction algorithm for Tire-Pavement-Interaction-Noise. From distress mapping, IRI, and permeability measurements, there were no noticeable trends within the five years of study. Additionally, this research performed advanced data analysis, identified significant variables and accentuated intrinsic relationships between them. Additionally, the "on board sound intensity" (OBSI)-Temperature correlation exhibited a negative polynomial relationship indicating the higher importance of temperature to OBSI relationship in asphalt than published characteristics of concrete pavements. It ascertained that texture mean profile depth was not as significant as texture skewness in predicting surface properties. Smoothness measurements indicated that most asphalt surfaces are not associated with laser-induced anomalous IRI reading errors. The major properties affecting ride in most asphalt surfaces were evidently extraneous to the surface texture features..

The project "Simplified Design Table for Minnesota Concrete Pavements" led to the creation of MnPCC-ME, a standalone 32-bit Windows executable program to replace the preexisting RigidPave. Whereas RigidPave was based upon the outdated AASHTO 1993 design procedure for rigid pavements, MnPCC-ME is based on MEPDG version 1.1, a mechanistic-empirical design procedure that accounts for the effects of traffic loading and environment. Furthermore, MnPCC-ME was localized for Minnesota pavements through: 1) the use of local climate data and weigh-in-motion traffic data; 2) the incorporation of previously conducted calibrations of the MEPDG for Minnesota pavements; and 3) the inclusion of advanced analysis features included in MnPCC-ME's flexible design counterpart, MnPAVE. The development and source code of MnPCC-ME is detailed in this final report.