Institute for Transportation

About the research

Base stabilization additives are used to increase the strength and stiffness of road foundations in weak and susceptible soils. Numerous additives exist for improving performance of aggregate base layers, however, most independent studies have focused on non-proprietary additives. Additives are being used to stabilize base/subbase/subgrade layers, but engineering methods for pavement thickness design need to be better defined. In particular, determining granular equivalency (GE) factors for various proprietary geomaterial stabilizers will benefit the Minnesota Department of Transportation (MnDOT) and county engineers by establishing design parameter values and a means for comparing additive effectiveness and cost.

The research has three main goals: (1) evaluate the performance of selected proprietary additives by conducting laboratory and field tests; (2) prepare pavement designs and construction specifications based on the test results; and (3) analyze the benefits of additives in terms of pavement construction cost savings and long-term service life. The laboratory study will be based on ASTM/AASHTO/MnDOT test standards and designed to determine the relationships between strength, stiffness, moisture content, gradation, freeze-thaw durability, and leaching. The field testing will involve full-scale testbed construction using the most promising mix designs. Field testing will incorporate accelerated loading testing to evaluate performance of each test bed. The primary goals of this project will be to determine reliable GE factors for a variety of conditions and document performance, cost benefits, and life-cycle cost analysis. The outcome of this research will provide guidance for the selection of proprietary additives and optimized design for base stabilization of roads.

About the research

Geogrids have been widely used in roadway construction as reinforcement in pavement foundations. Geogrids have been effective in practice for reducing rutting damage, distributing traffic loads within the pavement foundation layers, increasing the resilient modulus of the base course, and stabilizing the subgrade layer. For this project, an integrated mobile accelerated test system (IMAS), an automated plate load test (APLT) device, and finite element simulation approaches were used to evaluate the effects of geogrid reinforcement. Test configurations were constructed by varying geogrid types (i.e., light-duty biaxial, heavy-duty biaxial, light-duty triaxial, and heavy-duty triaxial), geogrid locations in the base course (i.e., at the interface between the base and the subgrade or in the base course), and base aggregate thicknesses (6, 10, and 16 in) in the laboratory and in experimental field tests.

The finite element method (FEM) models were calibrated based on the results from the experimental test sections. Then, the calibrated FEM models were used to determine granular equivalent (GE) values for the remaining sections. Testing results included resilient modulus, deflection, and permanent deformation of the pavement foundation to evaluate the structural benefits of geogrids as a function of the GE. The results of this research revealed that improvement in pavement performance using geosynthetic reinforcement depended on various factors and variables. A new formulation was proposed to predict the GE factor of geogrid reinforcement of flexible pavements. The products produced by this research include this report, which improves geogrid understanding, and a well-developed method to apply GE factors during pavement design. It is expected that one or more of the following benefits will be achieved during implementation: increased service life, reduced gravel and/or asphalt thickness, and reduced maintenance costs.

About the research

The goal of this research project was to determine the environmental impact of potassium acetate (KAc) as a deicer, including its effects on water quality and the resulting toxicity to biota. The motivation for the research was the Minnesota Department of Transportation’s (MnDOT’s) exploratory use of KAc to significantly reduce the use of chloride-based deicers in controlling snow and ice on roads and the potential benefits, including reduced environmental effects.

This study evaluated the environmental impact of KAc as a deicer through field measurements, laboratory experiments, and modeling. Field sites, including bridges and tunnels, were selected to investigate a range of conditions, and sampling characterized KAc concentrations in soil and water as well as measured dissolved oxygen, biochemical oxygen demand, pH, and other water-quality parameters. Laboratory experiments investigated the persistence of KAc and its microbial toxicity at higher resolution than possible in field sampling.

To predict the spatial and temporal extent of KAc’s environmental effects, models of the fate and transport of KAc in runoff to streams and lakes were constructed and evaluated. A detailed user’s manual for the models is provided as an appendix in this report.

The researchers recommend that the two models, KAcStream and KAcLake, be used by MnDOT to guide its choice of sites and concentrations of KAc deicer applications. These models also allow for initial estimates of the environmental impact of KAc applications.

About the research

White-Nose Syndrome and increased disturbance of habitats used by bats for roosting and foraging has led to a growing concern about the U.S. bat population over the last decade. Bridge repair and replacement projects are required to follow additional regulatory requirements to avoid and minimize impacts to bats, when protected bat species are present on bridges. Some of these requirements (e.g., timing restrictions) are challenging to implement given Minnesota’s short construction season.

The objective of this project was to evaluate the feasibility and efficacy of deploying non-lethal ultrasonic acoustic devices in the field to temporarily deter bats from roosting on bridges ahead of construction or maintenance activities, while minimizing harm to bats and non-target species. The technology was evaluated at two test sites in Minnesota, one short-term and one long-term, during the summer of 2019. Considering the findings from both the acoustic monitoring data and the field inspections, acoustic deterrents appeared to effectively work to temporarily deter bats from select abutments.

This report presents the field study design, findings from the field implementation, research benefits, and implementation steps for the Minnesota Department of Transportation (MnDOT).

About the research

Throughout the US, many state departments of transportation (DOTs) are experiencing issues with the loosening of anchor bolt nuts on overhead sign, luminaire, and traffic signal (SLTS) structures. Retightening loose nuts imposes a significant drain on state DOT resources. In addition, loosening of these nuts increases fatigue stresses on the anchor bolts, possibly increasing the risk of failure.

Loose anchor bolt nuts were recorded on both old and new structures, some immediately after installation. Even after retightening by Minnesota Department of Transportation (MnDOT) maintenance workers, anchor bolt nuts were found to come loose within two years. In a previous project, new retightening specifications were developed based on laboratory testing, field monitoring, surveys of current practices, and finite element modeling.

This project focused on implementation and evaluation of the proposed specifications from the previous project. Structural monitoring also continued on a previously instrumented overhead sign structure. Difficulties were discovered with the proposed procedures during implementation, including structure clearance, instruction clarity, and retightening timing. Overall, though, the proposed procedures were found to be effective in preventing loosening. Revisions to the specifications were suggested along with recommendations for further review to simplify the procedures through a future laboratory study.

About the research

Concrete grinding residue (CGR) is a slurry waste consisting of water and concrete fines generated from diamond grinding operations that is used to smooth a concrete pavement surface. During this process, CGRs are mostly disposed along the roadside, which can influence soils and plant communities along the roadways. To understand the effects of CGR on soil physical and chemical properties and plant growth, a controlled field site at the Kelly Farm in Iowa was used with CGR application rates of 0, 10, 20, and 40 dry ton/acre to test properties of soils and plants before the application and one month, six months and one year after the CGR application. Two roadsides along Interstate 90 in Minnesota where CGR material was applied in the past were investigated as well. Laboratory and field experiments were conducted to measure plant biomass, bulk density, hydraulic conductivity, infiltration, pH, electrical conductivity (EC), alkalinity, metals, cation exchange capacity (CEC), exchangeable sodium percentage (ESP), and percentage base saturation (PBS) of soil samples collected from the test sites. Statistical analyses were conducted to correlate the CGR additions to the properties of soils and plants. The results of statistical analyses from the Kelly Farm indicated that CGR material did not significantly affect soil physical properties and plant biomass but impacted the chemical properties of soil. Changes in some soil properties such as pH and percent base saturation (PBS) due to CGR did not persist after one year. The results from two Minnesota roadsides indicated that the areas receiving CGR applications in the past did not negatively affect soil quality and plant growth.

About the research

Mixture proportioning generally uses a recipe based on a previously produced concrete, rather than adjusting the proportions based on the needs of the mixture and the locally available materials. As budgets grow tighter and environmental regulations increase, an emphasis on lowering the carbon footprint, is focusing attention on making mixtures that are more efficient in their usage of materials yet do not compromise engineering performance. A means of reducing environmental impact is to reduce the amount of binder in the mixture.

MnROAD is planning to construct several cells using reduced cementitious content mixtures, with the aim of monitoring the constructability and longevity of the concrete. The proposed work has been designed to identify the behavior and performance of concrete paving mixes with low cementitious content, i.e., between 475 to 500 lb/CY, and lower cementitious content, i.e., 430 to 470 lb/CY.

The objectives of this study included:

• Investigate the early-age characteristics (i.e., placement issues, slow strength gain) of concrete paving mixes containing low and lower cementitious content
• Assess causes of, or potential for, durability issues with very low cementitious content
• Identify effect of reduced cementitious content on long term serviceability and economics of concrete pavements (i.e., benefits of reduced shrinkage)
• Develop recommended specifications, mixing, and placement practices for the use of very low cementitious content concrete paving mixes

About the research

Connected vehicle technologies hold the potential to produce a number of safety, mobility and environmental benefits. The benefits of connected vehicle technologies are expected to be wide ranging and include reduced crashes, improved mobility and reduced emissions. Local transportation agencies, such as counties and cities can be expected to be affected by the transition to connected vehicle technologies. These agencies can also expect to benefit from connected vehicle technologies, through aspects such as a reduced need to construct roadway infrastructure (fostered by mobility improvements), increased fleet safety (e.g., maintenance vehicles in plowing operations), and other benefits.

However, transitioning highway infrastructure to be ready for connected and autonomous vehicles (CAVs) will ultimately require a significant investment in infrastructure upgrades, new technologies, and power and connectivity. Agencies are already grappling with how and where to invest scarce resources to meet existing needs and addressing CAVs adds an additional burden. As a result, there is a need for local agencies to not only understand what the potential benefits of connected vehicle technologies are, but also how they should be preparing for the transition to such technologies for the infrastructure and fleets that they manage.

This toolbox was developed to provide a summary of information that local agencies should be aware of to prepare for CAVs. The main goal of this toolbox is to assist local agencies in preparing for CAVs in the short term—5 to 10 years. Since local agencies are not generally expected to have the resources to become test beds, this report provides information so that local agencies can leverage ongoing activities and resources to prepare for CAVs.

About the research

The Minnesota Department of Transportation (MnDOT) constructed its first glass fiber polymer (GFRP) reinforced bridge deck on MN 42 over Dry Creek just north of Elgin, Minnesota. Successful implementation of the GFRP reinforced bridge decks would eliminate the steel corrosion problems that often shorten the life of the deck. Although there has been wide use of GFRP reinforcement in bridge decks in some parts of Canada, there have been relatively few GFRP reinforced bridge decks built in the United States. The Canadian decks were primarily designed using the empirical design method in the Canadian Highway Bridge Design Code. This method differs significantly from the design guidelines produced by AASHTO and ACI Committee 440 on fiber-reinforced polymer (FRP) reinforcement. To maximize the knowledge and experience gained in constructing this type of bridge decks, this research project investigates the performance of a case-study bridge deck focusing on key issues such as cracking, deck stiffness, load distribution factors, and GFRP rebar strains. The main goals of this project are:

• Collect behavior information and response characteristics of the bridge deck under service loads
• Identify the load distribution characteristics, especially for the bridge girders supporting the deck
• Examine the short-and long-term durability of the bridge deck in terms of formation and propagation of cracks
• Assess the impact of using non-conventional, corrosion-resistant deck reinforcement on maintenance needs and life-cycle cost with a specific interest in including service-life design philosophies

The outcome of this project will directly contribute to the development of guidance and details for the construction of corrosion-resistant bridges with service lives beyond 100 years.

About the research

Air void content, specifically at longitudinal joints, is a crucial factor affecting pavement life. Compaction affects the Air void content achieved, which directly impacts the performance of pavement, and thus has been identified as one of the most critical factors associated with the performance of flexible pavements. This study examines pavement historical data, constructs an air void performance database, and performs a statistical analysis on factors affecting air void content and then analyzes the effect of air void content on performance. Microsoft Access is used to create a database. JMP, a statistical software program, is used for the analysis of the data from the database created for 43 projects. Air void distribution is determined across and within the projects. An analysis of variance (ANOVA) analysis shows that binder content (%), aggregate size, voids in the mineral aggregate (VMA)%, film thickness, and the amount of reclaimed asphalt pavement (RAP) (%) significantly affect the air void content achieved. The air void contents achieved for most lots of the projects are found to be within the acceptable ranges of 4-8% immediately after construction. The correlation between air void content and the distresses observed for the pavement sections used in this work have R-square values below 0.20, which does not meet the recommended value of being equal to or greater than an R-square value of 0.70. However, from previous literature, National Center for Asphalt Technology (NCAT) researchers suggest that with a 1% decrease in air voids, pavement service life would increase by 10%. Based on these increases in pavement service life, it is estimated that by increasing the density/reducing air voids by 1%, net present value cost savings could be $88,000 out of a $1,000,000 project.