Institute for Transportation

About the research

This study assessed the long-term performance of four aggressively rehabilitated gravel road test sections whose roadway cross-sectional profiles were rebuilt by recovering material from the ditches to restore the proper widths, elevations, and slopes of the roadways and the proper profiles of the drainage ditches. Two of the rehabilitated test sections were constructed with an enzymatic chemical soil stabilizer, while the other two were not. For each pair of test sections, one was constructed using smooth-tired compaction, while the other was constructed using sheepsfoot compaction. A fifth control section was also studied to establish a baseline that was representative of the surrounding roads in the project area.

Overall, this study demonstrated the effectiveness of aggressively rehabilitating gravel roads that had been lowered, widened, and flattened by decades of heavy traffic. Rebuilding the roadway cross sections improved the drainage capacity of the test sections relative to the much flatter control section. The enzymatic soil stabilizer showed measurable benefits in terms of strength, stiffness, and surface distresses. The benefits were greatest in the first year after construction but then decreased somewhat by the end of the second year. With additional field testing and observation, it could be determined whether the latter decrease was a temporary trend or whether the rehabilitation and stabilization will produce continued benefits over time.

About the research

Inclusion of randomly-oriented, discrete fibers in cementitious materials is proven to enhance many of the desired engineering properties, such as fracture toughness, flexural strength, and resistance to the formation and propagation of micro/macro cracks under extreme loads, in addition to reducing the risk of early-age cracks in concrete. The concrete fibers can be broadly categorized to metallic and non-metallic fibers. Among their differences, non-metallic fibers offer high corrosion resistance, in contrast to metallic fibers, which are vulnerable to corrosion, despite offering superior mechanical properties.

This project aims to conduct a holistic investigation of a hybrid of metallic and non-metallic fibers to introduce expected functionalities to fiber-reinforced cementitious materials, especially ultra-high performance concrete (UHPC). Use of alternative fibers for non-structural UHPC applications will particularly reduce costs and eliminate the need for Buy America as required with steel fibers. Considering the latest fiber products available in the market, this project will investigate the promise of a new generation of UHPC mixtures engineered by appropriate choices and dosages of fibers. Based on a suite of laboratory investigations, the ultimate goal of this project will be to develop practical guidelines to select a hybrid of metallic and non-metallic fibers for non-structural UHPC. The fiber selection criteria will be consistent with target applications, providing the desired mechanical and durability properties, paired with high corrosion resistance and adequate bond with the cementitious matrix.

About the research

In 1999, the Center for Transportation Research and Education (CTRE) at Iowa State University’s (Iowa State’s) Institute for Transportation (InTrans) developed the book Iowa Highway Research Board: 1949–1999. The book summarized the history of highway research in Iowa, the germination of the Iowa Highway Research Board (IHRB), and highlights of the board’s research program in its first 50 years.

Given the technological, computational, and theoretical advances in transportation engineering over the past 25 years, along with a desire to highlight the board’s historical and current impacts, the IHRB was interested in continuing the narrative begun in Iowa Highway Research Board: 1949–1999 to cover the board’s history since 1999.

The objective of this project was to create a book that encompasses the IHRB’s history and funded projects from 2000 to 2024.

About the research

An increasing number of concrete overlay projects in Iowa and around the United States have used fiber-reinforced concrete (FRC) mixtures. Fibers provide residual strength to concrete mixtures, and concrete overlay design procedures currently assume that fiber reinforcement enhances fatigue life. A number of studies have suggested that fibers may offer a number of additional performance benefits to concrete overlays. This study conducted a field investigation of six different concrete overlay sites in Iowa. Three of these sites contained test sections with varying thickness and joint spacing designs, and with and without fiber reinforcement. The field investigation performed a variety of tests to measure properties such as joint activation behavior, load transfer, structural response, pavement smoothness, and curling and warping behavior. This test regime allowed for a broad characterization of many aspects of the behavior and performance of concrete overlays, both with and without fiber reinforcement. The results indicated that, to date, fiber reinforcement did not appear to have a significant impact on load transfer, smoothness, or curling and warping at these concrete overlay sties. However, the comprehensive testing regime provided a number of insights into other aspects of concrete overlay design and performance, both with and without fiber reinforcement. The bond between concrete and asphalt was particularly important, even when the overlays were not intentionally designed to bond to the underlying asphalt layer. Finally, the report for this project also contains an appendix detailing a separate investigation of the behavior of FRC pavements placed without transverse joints.

About the research

This research will develop a guide to assist Iowa municipalities, transportation agencies, and others in conducting studies on one-way to two-way street conversions. This guide will compile resources from previous conversion projects in Iowa and other Midwestern states, incorporating data and results from those studies. These will be augmented with the use of other data sets, such as crash data or probe vehicle speed data, for past conversion projects in Iowa for which such data is available. The guide will provide information on several aspects of conversions, including traffic operations, design and implementation, and stakeholder impacts. The guide will also include information to support benefit/cost analyses.

About the research

The main objective of this research was to explore the optimized selection of superabsorbent polymer (SAP) products as internal curing materials in concrete and to examine the effects of the use of eight selected SAPs on properties that affect concrete performance, including shrinkage, hydration, permeability, and strength. Experimental results demonstrated that the use of SAPs improved the shrinkage and hydration of concrete while reducing strength and permeability, although the latter were still within acceptable bounds.

About the research

The project described in the report was developed in response to a documented need for more readily available guidance related to decision-making about roadway cross section reconfigurations. More specifically, there was a need for information that might help during the decision-making process involved in converting four-lane undivided roadway cross sections to three lanes (four- to three-lane conversion) with one through lane in each direction and a two-way left-turn lane.

In response to this need, this project, through consultation with practitioners, identified and developed summary responses to 14 commonly asked questions related to the planning, design, operation, and/or implementation of four- to three-lane conversions. Some of the responses to these questions may also be relevant to the process implemented for other types of conversions and roadway improvements. The summary responses to the questions identified were purposefully kept short and are contained in Appendix A of the report as well as separate standalone documents. References for each summary response, if needed by the user of this guidance, are provided in Appendix B of the report.

Conclusions and recommendations are summarized in the report based on the tasks completed as part of this project. The conclusions are related to the amount and relevancy of material available on four- to three-lane conversions and how the approach to roadway design and operational analysis is changing overall. Recommendations are made about the potential to answer more questions as they are identified, the development of materials specifically for elected officials, and a possible update of the Iowa guidelines for four- to three-lane conversions as an addendum to the national guidelines.

About the research

Live load field tests of bridges were carried out using certain implements of husbandry (IoH) to observe the transverse load distribution and the dynamic impacts. A finite element (FE) analysis of the field-tested bridges was performed. The strain data from the FE analysis were validated with the field test data to establish an FE analysis method for a parametric study. This parametric study was performed to observe the influence of various bridge parameters on the load distribution factors. Observation of the load distribution factors from the parametric study shows that the load distribution factor equations prescribed in the AASHTO LRFD (2020) capture the distribution for these IoH loads. Live load factors for this load type for prestressed concrete (PC) bridges and steel girder bridges were found through a calibration process using reliability theory, which involves the selection of a target safety index. The live load factor for each bridge type was calculated for the Strength I and II limit states. An Iowa-specific legally loaded vehicle (Terragator Max) was established using a conservative axle configuration and axle loads of 25 kips. Calibration of the live load factors yielded the following key findings:

• An update to the AASHTO load and resistance factors (LRFs) is not needed for existing terragator loads as long as the axle loads comply with the legal load limit of 25 kips.
• When a target safety index of 3.5 is considered, the current live load factor of 1.75 for Strength I should be increased to 1.90 if husbandry vehicles of a configuration similar to that of Terragator Max are manufactured.
• When a target safety index of 2.0 is considered, the same case does not suggest an update to the AASHTO live load factor.
• An update to the AASHTO Strength II LRFs is not required.
• The dead load factors were found to be lower than the current AASHTO-prescribed values. Therefore an update to the AASHTO LRFs is not required.

About the research

The design of drilled shafts in Iowa currently relies on the American Association of State Highway and Transportation Officials (AASHTO) LRFD Bridge Design Specifications. To improve design efficiency at the state level, a series of research projects was conducted to develop the Drilled SHAft Foundation Testing (DSHAFT) database, a regional database facilitating the collection, storage, and efficient access of load test data from Iowa and other states, and to utilize the collected data to establish regional resistance factors that are reflective of the uncertainties associated with predicting drilled shaft capacity under Iowa’s specific geological conditions and construction practices. Resistance factors established in a 2019 study for various resistance prediction methods generally showed improvements over those recommended by AASHTO.

The present research aimed to validate the proposed resistance factors and formulate design recommendations for implementation. To this end, the DSHAFT database was further expanded with additional test data. Additionally, regression analyses were conducted on test data from Iowa to develop local resistance predictions that may provide more accurate estimates of drilled shaft capacity locally. Results from the analysis indicated that a linear correlation between soil parameters and measured unit side resistance was the best fit for most soil types. Moreover, settlement data were collected at several production shafts that were part of a few Iowa DOT bridge replacement projects to evaluate the field performance of drilled shafts designed under the current Iowa DOT guidelines. Various challenges were encountered during the data collection process. Some of the data indicated unexpected negative settlements, and further investigation is needed to develop appropriate conclusions. Design recommendations were formulated based on all findings, and design examples were developed to illustrate the application of the design recommendations.

About the research

The goal of this project is to study the effectiveness of stabilization of granular-surfaced (“gravel”) roads using wicking and non-wicking geosynthetics. The project will continue a newly established cooperative partnership with the Iowa Army National Guard that enables long-term research on granular-surfaced roads at the Camp Dodge base in Johnston, Iowa. The Camp Dodge facility contains several miles of granular-surfaced roads that routinely exhibit various types of damage and distress including rutting, potholes, washboarding, frost boils, insufficient drainage, and other moisture related damage.