Institute for Transportation

About the research

Iowa has three classes of public roads: state primary highways, county (secondary) roads, and city streets. Among these, Iowa county roads serve rural Iowa transport needs by assuring a public road connection (i.e., to local access roads) for serving as conduits that channel the flow of people and commodities to and from towns and terminals (i.e., farm-to-market roads). Many Iowa county pavement systems are multilayered structures that have experienced multiple cycles of construction and renewal that make it more complex to estimate pavement structures’ current structural capacities.

This study developed a Microsoft Excel macro and Visual Basic for Applications (VBA)-based automated Pavement Structural Analysis Tool (PSAT) with three analyzing options—asphalt concrete (AC) pavement systems with 1 to 10 layers on a (1) stabilized base, (2) granular base, and (3) stabilized base and granular base—to estimate the current structural capacities of in-service pavement systems by following consecutive sections within the user-friendly platform. To address this aim, a systematic approach to develop a highly realistic annotated synthetic database was created for use in artificial neural network (ANN)-based pavement response prediction models that required inputs of pavement materials and structural features and outputs of pavement responses, deflections, and strains at critical locations within the pavement structure. In addition, the equivalent layer theory (ELT) concept was integrated into the PSAT to simplify multilayered pavement systems into three-layered systems—an asphalt layer, a base layer, and a subgrade layer. Thus, it could make it easier for an Iowa county engineer to understand the current structural capacities of in-service county pavements. Mechanistic- and empirical-based approaches were also integrated into the tool to estimate the remaining service life (RSL) associated with two types of major failures for flexible pavements, namely fatigue and rutting failures, by relating pavement responses predicted by the ANN models through transfer functions. The PSAT is expected to be used as part of routine pavement analysis, design, and asset management practices for better prioritization and allocation of resources, as well as to support effective communication related to pavement needs both with the public and with elected officials.

About the research

Improving the accuracy of work zone data is a multi-layered problem of which a number of agencies have been working to address over the last several years. Connected temporary traffic control devices (cTTCDs) such as smart arrow boards and other connected devices have the capabilities to improve the accuracy of work zone data without a contractor or agency employee having to manually enter the information. As the number and types of devices have increased, little guidance has been developed on how to use information from these devices within an agency. This project will document and evaluate how cTTCDs can be used by an agency for both historical and real-time applications. The approach starts with an agency state-of-the-practice review to summarize how the data are currently being utilized. A number of integration methods will be evaluated with the goal of highlighting noteworthy practices and documenting agency considerations when integrating the data into their systems.

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.