Institute for Transportation

About the research

Recent advances in data collection technologies have made it increasingly possible to monitor traffic conditions with increasing levels of detail, facilitating the task of providing advance warning of work zone conditions to the traveling public. Today, a variety of such technologies exist, including automated vehicle identification (e.g., Bluetooth), automatic vehicle location (AVL) (e.g., average segment speeds), and trajectory data from connected vehicles. Different data sources provide different types of information, have different latency, varying spatial and temporal resolutions, and different requirements for use. There is a need to gather and synthesize available information about the effectiveness and limitations of alternative data sources for the application of real-time work zone monitoring and communicating information to the public. The possibility of integrating multiple data sources for monitoring and public information uses also needs to be investigated.

About the research

Bridge decks are often the first bridge component requiring major repair or complete replacement. Since the early 2000’s, a new class of cement–based materials, known as ultra-high performance concrete (UHPC), has become available. UHPC is nearly impenetrable and has many other high–quality attributes. A bridge will soon be constructed that has a deck comprised of traditional concrete plus a UHPC overlay course. The objective of this study is to monitor and evaluate the construction of the two–course deck as well as the performance of the deck for 2 years post–construction. The study will consist of a literature review of two–course decks and UHPC overlay construction to determine best practices; field monitoring during construction to document construction quality; a laboratory investigation of the two–course deck system to assess its durability; load tests and field monitoring for 2 years; and service life and life–cycle cost analyses to compare the performance of the two–course deck system with that of more typical deck systems. The final deliverables will communicate the lessons learned from the project and provide guidance for future design, construction, and QA/QC practices regarding bridge deck construction using a UHPC top course.

About the research

The purpose of this project is to aid the Iowa Department of Transportation (DOT) in the implementation of a new access management program. This program incorporates modern access management strategies for highways and is supportive of DOT goals to support the economic vitality of the State, preserve the functional integrity of the public’s capital investment in the highway system, and help ensure that the traveling public are provided with safe roads.

In prior years, both the new access control rules and a new access management manual were drafted. The Rules, “Primary Highway Access Control”, Iowa Administrative Code (IAC) 761–112 required a legislative review. That was completed in October 2022. The Iowa DOT is now proceeding with implementation of the new access management program.

About the research

The objective of this project was to demonstrate the field implementation of an innovative longitudinal joint design developed during a previous phase of research. To achieve this objective, a yet-to-be-constructed box girder bridge in Washington County, Iowa, was selected to demonstrate the construction and performance of the joint.

In order to evaluate the joint’s performance, a seven-day period of field monitoring was conducted shortly after construction was completed. In addition, long-term evaluation of the joint was performed through the completion of live load field tests and deck concrete crack inspections. The live load tests were performed every 12 months, and crack inspections of the bridge deck were performed every six months. During the field tests and monitoring, temperature, strain, and displacement data were collected at critical locations and analyzed to evaluate joint performance with respect to cracking resistance and load distribution.

The results indicate that the innovative joint is sufficient to resist early-age longitudinal joint cracking. Joint cracks that were seen on another box girder bridge with traditional narrow joints were not observed in this case. The innovative joint performed well with respect to load distribution. The whole bridge superstructure behaved as an integrated structure regardless of the transverse location of a passing truck. In addition, the box girder bridge was constructed using integral abutments, which added transverse restraint and positively affected the strain distribution at the joint ends.

About the research

Shrinkage and temperature forces are known to have short- and long-term effects on both the superstructures and substructures of bridges. In the substructure, such effects are more pronounced if frame piers are used, given their volumetric change is often restrained.

The main objective of this research was to investigate the forces developed in frame piers and their supporting foundations due to volumetric changes caused by thermal and shrinkage effects. For this purpose, a set of finite element (FE) models capable of simulating shrinkage strain, creep strain, thermal strain, strength development of concrete, and nonlinear behavior of concrete were developed and calibrated using experimental test results. Field data were then collected from bridges instrumented with vibrating wire strain gauges embedded in the frame piers at the time of construction. Further to obtaining firsthand information from the field, the FE models were validated using collected field data. Various frame pier geometries were then analyzed using the validated model to identify the most susceptible geometries.

The results of the study indicated that frame piers cast in Iowa on warm summer days, particularly in June and July, experience the most demand from temperature and shrinkage effects compared to frame piers cast at other times of the year. The most critical factors affecting frame pier susceptibility were found to be column stiffness, length of the cap beam, and flexural stiffness of the cap beam. Column stiffness was observed to be the most impactful factor on the susceptibility of frame piers to these effects. Basic susceptibility metrics, such as the length of the frame and the length-to-height ratio of the frame, were found to be not accurate enough to predict susceptibility, as accurate susceptibility metrics must account for column stiffness and column restraint factors. These results led to the development of two-dimensional linear elastic models that simplified the assessment process without losing accuracy. Overall, the requirements set by the Iowa DOT’s Bridge Design Manual were found to be adequate in capturing the performance of frame piers subjected to temperature and shrinkage forces.

About the research

Concrete diamond grinding on pavement projects generates a nonhazardous waste byproduct called concrete grinding residue (CGR). CGR has known cementitious characteristics that suggest a latent use as a soil-stabilizing amendment, especially for poor and problematic soils.

In this study, Western Iowa loess soil was amended with CGR and subjected to rainfall simulations and wind erosion tests to measure the erodibility of several soil mixtures. The results of the rainfall simulations showed that CGR-amended silty soil (loess) had only slightly different optimum moisture contents and maximum dry densities compared to untreated loess, while rainwater runoff samples of CGR-amended loess exhibited dramatically higher turbidity and total suspended solids. The results of the wind erosion tests showed that erosion was lower in more granular shoulder material and higher in shoulder material containing more organics. Wind erosion tests performed on CGR-amended Western Iowa loess showed modest improvement in this highly friable silty soil compared to untreated loess.

A field study conducted in Washington and Clinton Counties in Iowa compared CGR-stabilized and untreated sections to determine the effectiveness of CGR as a stabilizer for shoulder material. The CGR-stabilized sections in Washington County did not show significant improvement in strength, while the CGR-stabilized sections in Clinton County exhibited a 20% to 40% improvement in the composite elastic modulus and California bearing ratio values.

About the research

The objective of this project is to conduct an independent evaluation of the impact of biodiesel on fuel economy and carbon reduction in the Iowa Department of Transportation (DOT) snowplow fleet. This includes an evaluation of fuel economy, maintenance, and driver/maintenance personnel concerns.

The team will coordinate with the Iowa DOT and monitor snowplow operations. Fuel use and snowplow maintenance using varying levels of both biodiesel and regular diesel will be monitored.

About the research

A project recently completed for the Iowa Department of Transportation investigated the contributions of concrete encasements of steel H-piles used for bridges, which have historically not been considered in the design process. The initial reason for the project was to determine the remaining capacity of a pile when subjected to scour, leaving bare the uncased portion of a pile. A tool was developed to calculate capacity and a subsequent laboratory investigation was completed to validate the pile capacity assessment tool. The study concluded the pile capacity is greater than what has been otherwise calculated. As a secondary result, consideration has been given to revising the capacity calculations of new piles especially in fully-encased pile bents. This project aims to identify the unbraced height limits of steel H-piles when fully-encased.

About the research

Fiber-reinforced concrete (FRC) has become more widely used in thin concrete overlays in recent years. It is well known that synthetic macro-fibers increase the fracture toughness and residual strength of concrete, which mitigates cracking and improves the fatigue life of concrete overlays. Some of the other benefits of fiber-reinforcement could further benefit the performance and service life of concrete overlays by improving joint behavior, load transfer, and pavement smoothness. However, the performance benefits of these mechanisms are not well-quantified and are not considered in current concrete overlay design procedures. This study will take comprehensive performance measurements at a number of FRC overlay test sections that have been built in Iowa in recent years. The analysis will provide more insight into the full benefits of fiber-reinforcement and how they impact design choices and overlay service life. With a more complete understanding of the performance benefits of using fibers in concrete overlays, agencies would be able to optimize their FRC overlay designs, better predict long-term performance, and use resources more efficiently for maintaining Iowa’s roadway network.

About the research

With slide-in bridge construction (SIBC), the bridge superstructure is constructed off the final alignment and then slid laterally from the temporary worksite onto the in-place substructure. Once the sliding is complete, closure joints between the bridge super- and sub-structure are cast to establish continuity. The cementitious materials and reinforcement design used to complete the closure joints affect when the bridge can be opened to traffic or construction loading.

The goal of this research was to investigate the performance of closure joints using ultra-high performance concrete (UHPC) and noncontact lap-spliced reinforcing steel bar, with a specific focus on determining when a noncontact lap-splice has sufficient strength to either open a bridge or expose it to additional construction loading.

The research was also conducted to explore an alternative material to UHPC—hybrid composite synthetic concrete (HCSC)—which may be able to provide sufficient early-age capacity when used in the same way.

A series of laboratory tests were performed on 96 samples including four noncontact lap-splice connection designs with different rebar development lengths and joint filling materials. A time-dependent pull-out test was performed on each design with a focus on the performance at the material early age. Each sample was loaded with a pull-out force until failure. The ultimate capacity of each sample was captured and analyzed.

Based on the test results, recommendations for the selection of UHPC/HCSC closure joints reinforced with lap-spliced rebars were developed.