Institute for Transportation

About the research

The overall objectives of this research project are to:

• Evaluate the accuracy and efficacy of existing tests (e.g. microwave oven, Phoenix test, Cementometer) to measure w/cm as an acceptance parameter for Wisconsin Department of Transportation (WisDOT) projects.
• Analyze, correlate, and validate the w/cm ratio against performance-based tests for freshly mixed concrete at the batch plant (including strength, SAM, and surface resistivity) and freshly placed concrete in the field (focusing on strength and surface resistivity) for WisDOT projects.
• Assess the effects of variations in the w/cm ratio on concrete performance-based tests to provide specific guidance and recommendations regarding acceptable fluctuations in the w/cm ratio for WisDOT projects.
• Develop proposed specification parameters to accept the w/cm ratio to align with current WisDOT strength requirements and/or recommend alternative acceptance criteria.

About the research

High-traffic (HT) asphalt mixtures in Wisconsin are designed using 100 gyrations, however concerns have been raised regarding the ability to achieve balanced performance and adequate field compaction using such a high gyration level. This research aims to propose modification to WisDOT’s HT mix design specifications to improve constructability while maintaining or enhancing performance.

The study began with a synthesis of HT mix design requirements in several states. A benchmarking study was then conducted using eight HT mixes, sampled from different projects in Wisconsin, using the Indirect Tensile Asphalt Cracking Test (IDEAL-CT) and Hamburg Wheel Tracking Test (HWTT) to assess cracking and rutting resistance, respectively. The mixes underwent extraction and recovery, and the recovered binders were evaluated for Performance Grade (PG) and Multiple Stress Creep Recovery (MSCR). The virgin binders and recycled asphalt materials (RAM) used in the mixes were also collected and evaluated to determine their PG and MSCR. Mix results were benchmarked against WisDOT HT mixes, leading to the selection of three mixes for redesign and further testing. The mixes were reproduced as lab-mixed lab-compacted (LMLC) specimens, redesigned using the Bailey Method and Asphalt Film Thickness (AFT), and compacted at 75 gyrations to 4.0% air voids without air-void regression.

Overall, it was noted that the cracking resistance was significantly influenced by the stiffness of the recovered binder’s PG, and the recycled binder ratio. Performance testing showed that the redesigned mixes achieved similar or improved cracking resistance, rutting resistance, and compactability compared to baseline HT mixes designed at 100 gyrations with air-void regression. To evaluate the impact of air-void regressed design accompanied with reduced gyration level, a fourth mix was selected for redesign using 3.0% regressed air voids and 75 gyrations, resulting in improved cracking and rutting resistance.

The findings of this study support using 75 gyrations at 4.0% air voids for HT mixes in Wisconsin with air-void regression. The study also highlighted the impact of the recovered binder’s PG on the mixture cracking resistance. Additionally, the Bailey Method and AFT can be used to guide the selection of aggregate gradation, and asphalt binder content. A special provision is proposed for initial implementation.

About the research

Underwater concrete placement in bridge substructures often raises concerns regarding concrete quality, primarily due to the potential for aggregate segregation, especially in deep drilled shafts. Recognizing these challenges, the goal of this research project was to critically evaluate and recommend enhancements to existing Wisconsin Department of Transportation (WisDOT) policies, standards, and specifications regarding underwater concrete placement for bridge substructures and the prevention of aggregate segregation in deep drilled shafts. Relevant research studies and the practices of other departments of transportation (DOTs) and the construction industry, especially agencies and companies operating in marine settings, were explored. Additionally, a nationwide survey was distributed to key personnel in 50 state DOTs to better understand current practices, trends, and common difficulties. This research synthesis report collates and presents a detailed assessment of concrete placement techniques, challenges in the construction of pile-encased piers, strategies to achieve non-segregating concrete in foundations, and the influence of materials- and construction-related variables. Based on the insights obtained, the report sets forth refinements to available guidelines, particularly those regarding the construction of concrete piers and abutments in aquatic environments.

About the research

Cantilevered traffic sign support structures are subject to wind and truck-induced gusts, which generate torsional and flexural forces that are transferred to their foundations. To standardize the design and construction of these foundations, the Wisconsin Department of Transportation (WisDOT) has developed pre-designed foundation plans.

Focusing on the transmission of moment and torsional forces, this study examined the loads transferred to the foundations of cantilevered traffic sign structures under wind loading conditions. The primary objective was to evaluate whether the current foundation designs are adequate or potentially over-designed.

Two test structures with drilled shaft foundations were subjected to both static and dynamic loading. The investigation analyzed load transfer from the superstructure to the foundations, assessed foundation behavior, and explored opportunities for optimized design. This was accomplished through a combination of geotechnical testing, instrumentation-based data collection, finite element modeling (FEM), and structural health monitoring (SHM).

Model validation was achieved by comparing results from free-vibration and static pull tests with EM outputs. A parametric study further informed the optimization of foundation designs. The results suggest that the current foundation designs, while structurally effective, may include conservative assumptions, particularly in terms of foundation depth, relative to the actual service-level demands observed in testing and modeling. The analysis indicates that it may be possible to reduce foundation depth while still maintaining acceptable performance limits, thereby supporting opportunities for more efficient foundation designs in future practice.

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.