Institute for Transportation

About the research

Many transportation agencies across the United States currently use the traditional design-bid-build project delivery method as well as other alternative methods, including design-build and construction manager/general contractor (CMGC) to delivery infrastructure to the traveling public. These alternative methods often allow for faster completion of projects. However, there are some challenges associated with these delivery methods as well, including change of roles for transportation agency personnel, differences in procurement processes, and changes in specifications. The Iowa Department of Transportation is interested in learning from the successes and challenges of other transportation agencies to allow for more informed decisions regarding the use of alternative delivery in Iowa. Included in this work is facilitating a peer exchange, documentation of the peer exchange, and cataloging processes and specifications used by other agencies related to alternative delivery methods.

About the research

The objective of this research is to develop field-tested methods of integrating vehicle trajectory data into actuated signal control that can be directly implemented in traffic signal controllers. This research will identify the practical requirements and limitations of establishing trajectory-assisted actuated signal control, including requirements for acquisition, storage, and communication of vehicle trajectory data. The findings will be developed into a resource toolkit that will permit implementation and further development of the methods conceived during the course of the research.

About the research

Prolonged road/lane closures associated with the rehabilitation or replacement of bridges lead to congested traffic conditions, which, among other consequences, pose an increased risk of safety for both construction workers and the traveling public. In an attempt to minimize these concerns, sophisticated procedures, combining the use of prefabricated bridge components, high performance characteristics of unconventional construction materials, and careful planning, are being developed to expedite bridge projects from conception to delivery. These novel techniques can drastically reduce abridge on-site construction time while enhancing both the quality and durability of the completed structure, and have promoted accelerated bridge construction (ABC) among the bridge design community.

Effective ABC methods require easy-to-fabricate and lightweight modules that can be transported to the site and assembled relatively quickly with commonly used equipment. Moreover, the connections of the system must be properly designed and detailed to facilitate assembly and enable the overall structure to achieve a performance that is comparable, if not superior, to that of a similarly cast-in-place (CIP) system. The Iowa DOT has invested in the development of abutment connection details to facilitate implementation of ABC techniques in its practice.

Building on previous research, this project will advance the accelerated bridge construction method for integral bridge abutments supported on steel piles and constructed using prefabricated and in-situ concrete along with other advanced construction techniques (3D printing) and materials as appropriate.

About the research

Prestressed concrete structures have become a popular choice for transportation infrastructure applications. According to the National Bridge Inventory, the percentage of bridges built with prestressed concrete technology has been rapidly increased from 15.0% to 23.5% over the past two decades. Specifically, precast prestressed concrete beams (PPCBs) are extensively used for bridge superstructures, owing to a number of favorable attributes, including great quality control on material and workmanship from one side, and fast, economic, and energy-efficient construction from the other side. The bridge superstructures are, however, known to be vulnerable to continuous deterioration. As a consequence, a problem commonly observed in the PPCB that supports the bridge superstructure is that the beam ends experience a faster (and more severe) deterioration compared to the rest of the beam. This is not surprising considering the fact that the beam end regions are subjected to a harsher exposure condition. To minimize serviceability issues and avoid catastrophic failures, effective maintenance and repair efforts are essential. The ultimate goal of this research project is, therefore, to develop feasible and cost-effective preservation strategies to extend the service life of the PPCB used in bridges in service.

About the research

While single span lateral slides have been adopted by many states and are a common accelerated bridge construction (ABC) method for the construction of bridges when short closure durations are needed, multi-span lateral slides are far less common. A multi-span lateral slide incorporates additional construction complexities that must be considered by the designer, agency, and contractor. This project will involve the second phase of study for the currently ongoing project, which included planning and beginning phases of laboratory efforts. This second phase will be conducted to investigate the performance of the ultra-high performance concrete (UHPC) closure joint reinforced with non-contact, lap-spliced rebar, with a specific focus on determining when a non-contact lap splice has sufficient strength to either open a bridge or to expose it to additional construction loadings.

About the research

Building on previous research, the proposed project will advance the accelerated bridge construction method for bridge substructures using steel piles and precast pile caps and columns. The weight of the precast members will be reduced using hollow sections, which in turn will improve both construction tolerances and constructability. The hollow sections will be filled with in-situ concrete. The piles will be designed with temporary collars, which will eliminate the need to wait for the concrete to cure before continuing with the superstructure construction.

The research will include a large-scale test unit that will incorporate both vertical and battered steel piles. The testing of the system will incorporate service level and extreme loads and ensure dependable performance of the new system and its components. As part of the testing program, the performance of the column and pile foundations will be examined systematically. Analytical models will be developed to realize the observed performance of the test unit and the components. Using previously discovered analytical and experimental observations and findings, appropriate design recommendations will be developed for improving bridge construction.

About the research

The Iowa Department of Transportation (DOT) Office of Bridges and Structures continues to provide safe travel conditions on bridges in the state while maintaining critical infrastructure assets. Over the last 20 years, the Iowa DOT has funded numerous research projects with the goal of developing and evolving an autonomous structural health monitoring (SHM) system to assess the safety and remaining life of bridge structures. Many of these projects have been completed in cooperation with the Bridge Engineering Center (BEC) at Iowa State University (ISU); in fact, more than 15 bridges in Iowa and other states have been monitored over the last 20 years using various generations of SHM. As a result of these research projects, many objectives regarding the development and implementation of an autonomous SHM system were identified, including the target of a fast and meaningful evaluation of highway bridge structures. Given the maturity and proven effectiveness of the developed SHM system, the timing is favorable for the Iowa DOT to implement a long-term, statewide bridge SHM program.

This project will ultimately identify the key stakeholders and beneficiaries to SHM deployment in the State of Iowa, evaluate the return on investment, develop a SHM deployment guide, and demonstrate the deployment on two bridge projects in Iowa.

About the research

Recent advancement in bridge construction technologies, especially with respect to bridge decks and superstructures, have become commonplace in new bridge projects. Substructure construction has not made the same advancements, however. There are existing technologies that have potential for simplifying and expediting the construction of bridge substructures at the same or reduced cost using equipment that is more readily available. In this project, helical pile foundation implementation for bridges will be investigated and a design guide will be produced. This tool will give engineers direction for alternative deep foundation options on bridge structures. This is an advantage for any bridge project, but particularly for low-volume roads where budgetary considerations tend to be of specific priority.

About the research

Recent legislation in the State of Iowa has increased the allowable axle weight of certain implements of husbandry to 25 kips. This change poses a particular concern to those who oversee and manage the construction and preservation of bridge structures. Based upon initial estimates, it is expected that the resulting structural response of bridges will exceed that which would be otherwise seen from current legal loads. This project aims to identify the load response of Iowa bridges to the increased live load limit and develop recommendations for load factors, live load distribution factors, and impact factors for Iowa bridges. Additionally, an Iowa-specific notional vehicle to be used for load rating bridges for recently legislated 25 kip axle vehicles will be developed and proposed.

About the research

While asphalt pavement is one of the most common transportation infrastructures in the United States, it requires proper maintenance. Exposure of asphalt binders to air can result in an oxidation process that can result in brittle behavior and distress in an asphalt pavement surface. To mitigate asphalt road deterioration and extend pavement service lives, various preservation strategies can be employed.

Fog seals are a light application of conventional asphalt emulsion on an asphalt-surfaced road to prevent oxidation and reduce water infiltration. In recent years, bio-based products for pavement preservation have attracted considerable attention due to their relatively low cost and environmentally-friendly properties. A proprietary bio-based sealant, RePLAY, has been commercialized and successfully used in many states.

To evaluate RePLAY performance as an alternative fog sealant for preserving asphalt-surfaced roads in Iowa, a 3.3-mile pilot testing section was selected in Clinton County in June 2016 for investigation of both short- and long-term performance by spraying sections with three different applications of RePLAY. A control section without RePLAY application was also set up for comparison purposes.

The set of performance investigations,conducted for five consecutive years (summer 2016 through summer 2021) included visual distress surveys of surface friction, pavement-marking retroreflectivity, laboratory water absorption, air permeability, and depth of penetration. The field results showed that, while a RePLAY application could reduce surface friction and retroreflectivity at early stages, restoration occured after several weeks. A RePLAY-treated section also exhibited a lower growth rate for cracking.

The laboratory results showed that RePLAY is effective in reducing water absorption and air permeability. A life-cycle cost analysis was also conducted, and the findings suggest that RePLAY can be an effective alternative for Iowa asphalt pavement preservation with savings in maintenance costs.