Institute for Transportation

About the research

The objectives of the current research are as follows:

• Summarize existing mix design requirements for high traffic (HT) hot-mix asphalt (HMA) mixtures in regions with similar climates (“Wet-Freeze”) and aggregate resources to Wisconsin. Identify potential areas of concern and/or improvement.
• Benchmark existing Wisconsin Department of Transportation (WisDOT) HT mixture designs using volumetric and performance testing; proposed testing must include consideration of prior and ongoing HMA performance testing research.
• Propose modifications to existing HT mixture designs based on available data, benchmarking, and testing, and determine whether improvements to constructability and performance can be achieved using the proposed mix design procedure changes.

About the research

Placing concrete under water has been a necessity for several bridges built over water streams. Based on the current practice, there are two main approaches to construct underwater reinforced concrete (RC) structural elements: (1) drying the site first by using cofferdams and pumps and then pouring concrete as usual and (2) placing concrete in the presence of water. The former approach has been employed with a relative success from a technical perspective. However, it can cause a range of safety and environmental concerns, especially if the required equipment experiences any failure. Furthermore, the former approach costs notably more than the latter one (i.e., up to twofold). The outlined issues have encouraged transportation agencies to consider the latter approach, in which concrete is directly placed underwater, thus eliminating significant (and costly) site preparation requirements. Despite advantages, however, construction of RC structural elements, such as piers and abutments, without cofferdams can be challenging in aquatic environments. In particular, the quality of the concrete placed under water can be adversely affected because of the issues with segregation of the concrete and loss of the cement paste. Consequently, strength and durability of the RC structural elements placed in water can be compromised, requiring significant maintenance and repair.

To address the outlined issues and identify best practices for the placement of concrete underwater and deep drilled shafts, WisDOT has expressed interest in a comprehensive research on the subject of underwater concrete for bridge substructures. The goal of this research is to assess WisDOT current policy, standards, and specifications, the policy and practices of other DOTs, and current industry practices (including other marine environment construction industries), and then provide guidance to be used in improving WisDOT policy, standards, and specifications related to underwater concrete placement.

About the research

The new revision of the American Association of State Highway Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals (SLTS) has changed the wind loading of the SLTS in such a way that can create confusion to both structural and geotechnical designers.The Wisconsin Department of Transportation (WisDOT) uses the 2013 version of the specifications, which defines wind loads in terms of 3-s gust wind speeds instead of the formerly used fastest-mile wind speeds. The wind importance factor was adjusted to represent the wind pressure associated with 10-, 25-, or 100-year mean recurrence intervals and has been addressed in different wind maps consistent with American Society of Civil Engineers (ASCE) 7-2010 (and now 2016) standards.The maps include essential Extreme I load combinations, and wind loads from those maps are not factored (in other words the traditional load factor is already included in developing these maps).

Both of the 2013 and 2015 AASHTO LRFD SLTS design specifications have the same specifications for foundation design of SLTS. Once the design wind load is developed, the total moment and shear load at the ground line or the top of the foundation can be determined. A safety factor is then used to determine the factored moment, shear, torsion, and axial load effects. However, the issue lies in the fact that the two documents handle the design wind speeds differently and this results in potential confusing assumptions when the foundation is designed.

To address this issue, WisDOT has expressed interest in determining the type of loads and deformations experienced at the foundation of two types of wind-loaded structures (such as sign bridges, cantilevers, butterflies, overhead sign supports and high mast lightings). Following WisDOT’s suggestion, this will take place through the monitoring of (at least) two selected structures for a period of one year, capturing the effects of wind loads and member loads and deflections with a special focus on lateral movements, as well as the axial and torsional resistance required of the foundation. Furthermore, predictive models of the two structures and their foundations, validated with field monitoring data, will be developed. This will pave the way for potential modifications to design practice.

The ultimate goal of this research project is to advance the state-of-the-practice by monitoring, validating, and guiding the use of AASHTO LRFD SLTS design specifications for WisDOT.

About the research

The Wisconsin Department of Transportation recognizes the importance of accurately assessing the timber deck slab bridge inventory within the state. Of the 571 timber bridges in Wisconsin, 450 bridges are timber slab bridges. Current methods of load rating employ equations first developed in the later 1980s and early 1990s for determining the equivalent strip width. These equations often produce results that unnecessarily penalize the bridge by requiring a posted weight limit.

Through a program of bridge live load tests and analytical modeling, the researchers in this study have both measured and modeled the bridge behavior with more accuracy and have shown the current equivalent strip width calculation methodologies to be conservative, as was originally speculated. Ten unique bridges were tested a part of this study. Three of them were tested twice; once before and once after bridge strengthening measures were employed. An equation to calculate the equivalent strip width was developed with numerous variables in mind.

About the research

The main objective of this research project was to develop a cost-effective life-cycle treatment plan for the preservation of Wisconsin bridge decks. The research team identified a comprehensive list of strategies through a review of current practice and department of transportation (DOT) policies and provided data-driven estimates of the performance and ideal timing of treatments with respect to condition by analyzing historic bridge condition data from the Wisconsin DOT (WisDOT) and other state DOTs and by considering engineering economics principles.

The scope of work included, in part,a literature review and a survey of Midwest states on the selection, implementation, and performance of deck preservation treatments. Initial email surveys were followed up by phone interviews. Detailed findings from these efforts are presented in Appendix A of this report and earlier intermediary reports to WisDOT. The major task for this project was to gather an archive of deck overlay and sealant history for Wisconsin decks and analyze these data in conjunction with historic deck conditions. Similar but limited data sets from South Dakota and Minnesota were also analyzed for the same purpose. The most common deck treatment plans that were observed in the data set were contrasted both for performance and cost-effectiveness in order to identify the most cost-effective treatment options for different deck conditions and at different points throughout a deck’s life cycle. To the authors’ knowledge, the work presented is the most comprehensive data analysis on deck preservation treatment performance by a state agency.

Regardless of the treatment, treated decks have consistently lower life-cycle costs than untreated decks. Sealing and overlaying decks as early as possible in the life cycle lead to lower life-cycle costs. Multiple applications of deck seals are cost-effective, particularly on high-traffic corridors. The treatment plans with simulated life-cycle costs can be considered by state agencies as they develop deck preservation plans.

About the research

Since the early 2000s, several federal programs have existed to provide bridge owners with funding to cover “delta” costs associated with implementing new, emerging, and innovative bridge technologies. While these programs have generally included an evaluation component, there generally has not been a concerted effort to track the performance of these innovative bridges following the completion of the initial project.

The goal of this work was to conduct field reviews of the condition and performance of several innovative bridge concepts constructed in Wisconsin. The completion of this work was to provide a much needed review of the performance of these bridge as they had been in service for several years.

This report documents the condition of 11 innovative bridges or innovative bridge features in Wisconsin. The bridges have innovative technologies consisting of the following: inverted T-beams, exodermic deck, geosynthetic-reinforced soil (GRS) abutments, fiber-reinforced polymer (FRP) components, steel free deck, bi-directional post-tensioning, stainless steel reinforcement, and precast substructure components. Collectively, these innovations represent departures from conventional bridge design and construction—but aren’t so radical that further adoption would be impossible.

The results of the 11 bridge evaluations, each of which followed a protocol specific to the bridge, are contained in a mini-report as part of this final report. Each mini-report documents general bridge information, briefly describes the innovation used, and provides the result of the evaluation.

About the research

In bridge abutment design, the Wisconsin Department of Transportation (WisDOT) assumes the granular backfill material used behind bridge abutments as free-draining and no hydrostatic pressures are applied on the wall. This research investigated whether backfill materials meet the assumption of a freely-drained condition through a detailed laboratory and field study. In addition, the researchers investigated the viability of using recycled-asphalt pavement (RAP) and shingles (RAS) for granular backfill.

Laboratory testing involved characterizing the materials in terms of gradation/classification, erodibility, permeability, shear strength, and volume change (i.e., water-induced collapse). Laboratory tests revealed bulking moisture content for natural materials and collapse upon wetting. RAP and RAS materials exhibited collapse upon wetting and creep under constant loading.

The researchers performed scaled abutment model testing to assess pore pressure dissipation rates for the different materials and calibrate input parameters to predict drainage using fine element analysis (FEA). Abutment model testing indicated that addition of geocomposite vertical drain can substantially increase pore pressure dissipation rates and avoid material erosion.

Field testing involved in situ permeability, shear strength, and moisture content testing, and monitoring lateral earth pressures and pore pressures behind abutment walls at four bridges.

Results indicated that field conditions are more complex than the simple linear stress distribution typically assumed in the design for lateral earth pressures. Lateral earth pressures were greater than assumed in design over a majority of the monitoring period of this study.

Pore pressures behind an abutment wall were observed at one site following flooding. Predicted pore pressure dissipations using numerical analysis matched well with the measured values.

The researchers provided recommendations specific to the current WisDOT practice for abutment granular backfill design and construction as part of this project.

About the research

Within the recent past, the Wisconsin DOT changed the bridge approach slab design from a system using only one expansion joint to a system using three expansion joints (SDD 13B2). This change was due primarily to the need to accommodate differential expansion and contraction between the approach pavement and the bridge. Since implementing the new design detail, the Wisconsin DOT has become aware of the detail’s difficulty of constructability. As such, a more easily constructed, new standard design with one expansion joint and a sleeper slab was created (Bridge Standard 12) and has been used more recently. A review and analysis of Wisconsin approach slab performance was completed and other states’ practices were reviewed. As a result of this work, several conclusions and recommendations were made. Several are listed below.

The expansion and contraction requirement does not warrant the use of multiple expansion and contraction joints as seen in SDD 13B2. SDD 13B2 is more highly susceptible to inadequacies within the approach supporting materials. It is critical that the materials are prepared well and methods of preservation are built into the system for long-term performance.

For Bridge Standard 12, it is recommended that the slab design is revisited to ensure it is properly sized and reinforced to act as a bridge between the sleeper slab and abutment paving notch in the event that settlement of the backfill and subbase occurs. The continued use of a sleeper slab at the joint between the mainline pavement and approach slab is recommended. The continued use of polyethylene sheeting between the approach slab and supporting materials/sleeper slab interface is recommended

Attention should paid to the abutment backfill and approach support materials to mitigate potential differential settlement through improved compaction, reduced erosion, and/or use of alternative materials. Consideration should be given to flooding the structural backfill assuming the use of the current materials is maintained to eliminate post-construction collapse of the backfill material. Consideration should be given to alternative backfill materials such as geocomposite drains and/or recycled tire chips.

WisDOT project page

About the research

Nationally, there is concern regarding the design, fabrication, and erection of horizontally-curved steel girder bridges due to unpredicted girder displacements, fit-up, and locked-in stresses. One reason for the concerns is that up to one-quarter of steel girder bridges are being designed with horizontal curvature. The concerns are significant enough that a National Cooperative Highway Research Program (NCHRP) research problem statement was developed and given high priority for funding.

It is also noted that an urgent need exists to reduce bridge maintenance costs by eliminating or reducing deck joints. This can be achieved by expanding the use of integral abutments to include curved girder bridges.

The long-term objective of this effort is to establish guidelines for the use of integral abutments with curved girder bridges. The primary objective of this work was to monitor and evaluate the behavior of six in-service, horizontally-curved, steel-girder bridges with integral and semi-integral abutments. In addition, the influence and behavior of fixed and expansion piers were considered.

About the research

State highway agencies are increasingly intersted in using recycled asphalt shingles (RAS) in hot mix asphalt (HMA) applications, yet many agencies share common questions about the effect of RAS on the performance of HMA. Previous research has allowed for only limited laboratory testing and field surveys. The complexity of RAS materials and lack of past experiences led to the creation of Transportation Pooled Fund (TPF) Program TPF-5(213). The primary goal of this study is to address research needs of state DOT and environmental officials to determine the best practices for the use of recycled asphalt shingles in hot-mix asphalt applications.Agencies participating in the study include Missouri (lead state), California, Colorado, Illinois, Indiana, Iowa, Minnesota, Wisconsin, and the Federal Highway Administration. The agencies conducted demonstration projects that focused on evaluating different aspects (factors) of RAS that include RAS grind size, RAS percentage, RAS source (post-consumer versus post-manufactured), RAS in combination with warm mix asphalt technology, RAS as a fiber replacement for stone matrix asphalt, and RAS in combination with ground tire rubber. Field mixes from each demonstration project were sampled for conducting the following tests: dynamic modulus, flow number, four-point beam fatigue, semi-circular bending, and binder extraction and recovery with subsequent binder characterization. Pavement condition surveys were then conducted for each project after completion.

The demonstration projects showed that pavements using RAS alone or in combination with other cost saving technologies (e.g., WMA, RAP, GTR, SMA) can be successfully produced and meet state agency quality assurance requirements. The RAS mixes have very promising prospects since laboratory test results indicate good rutting and fatigue cracking resistance with low temperature cracking resistance similar to the mixes without RAS. The pavement condition of the mixes in the field after two years corroborated the laboratory test results. No signs of rutting, wheel path fatigue cracking, or thermal cracking were exhibited in the pavements. However, transverse reflective cracking from the underlying jointed concrete pavement was measured in the Missouri, Colorado, Iowa, Indiana, and Minnesota projects.