Institute for Transportation

About the research

Recent federal legislation requires state highway agencies (SHA) and local road agencies to utilize performance-based approaches in their pavement management decision-making processes. The use of a remaining service life (RSL) model would be one such performance-based approach that could facilitate the pavement management decision-making process.

This study developed a Microsoft Excel macro and Visual Basic for Applications (VBA)-based Iowa Pavement Analysis Techniques (IPAT) automation tool that Iowa county engineers can use to estimate the project- and network-level pavement performance and RSL. To address this aim, statistics and artificial neural network (ANN)-based pavement performance and RSL models were developed using pavement structural features, traffic, construction history, and pavement performance records obtained from the Iowa Department of Transportation (DOT) Pavement Management Information System (PMIS) and the Iowa county agencies’ database. The accuracy of models was evaluated using real database representing Iowa county pavement systems.

The IPAT tool provides a series of options for four pavement types representing Iowa county pavement systems—jointed plain concrete pavement (JPCP), asphalt concrete (AC) pavement, AC over JPCP, and portland cement concrete (PCC) overlay—to estimate RSL through different approaches based on various conditions and distress data availability from an individual county. As part of data processing, the concept of developing an Iowa historical performance databank (HPD) was introduced and demonstrated by using raw data collected from county pavements. In addition, the feasibility of integrating preservation and rehabilitation techniques for RSL predictions using ANN models was investigated to evaluate the effects of treatments on RSL of pavements.

The IPAT tool is expected to be used as part of performance-based pavement management strategies and to significantly help decision-makers facilitating maintenance and rehabilitation decisions for better prioritization and allocation of resources.

About the research

Lateral slide-in bridge construction, also referred to as slide-in bridge construction (SIBC), has gained increasing attention as a viable accelerated bridge construction (ABC) approach. The use of SIBC is one of several ABC methods being promoted through the Federal Highway Administration (FHWA) Every Day Counts (EDC) program. The Iowa Department of Transportation (DOT) completed its first lateral slide-in bridge project in the fall of 2013 during the replacement of a single-span bridge on IA 92 over a small stream just west of Massena in southwest Iowa.

After that, the Iowa DOT planned to construct a multi-span bridge using slide-in construction techniques, which raised many questions. As such, it was vitally important that Iowa DOT design engineers have the best information regarding the performance of various critical details. The addition of more spans creates a more complex system that requires connections (and other details) that were previously not needed in a single-span slide. Furthermore, the fact that the multi-span bridge would need to slide on abutments plus piers (as opposed to just abutments in a single-span case) created possible uplift and overturning scenarios.

The objective of this project was to develop economical and durable design details to be used with the lateral slide concept with a focus on pier connection details. The ultimate goals with this research and the design/construction of the multi-span bridge were to end up with a bridge that is a strong, durable, economical bridge that can be constructed utilizing the lateral slide method and provide modifications to the Iowa DOT’s three-span standards.

The general finding from the field monitoring work was that the current slide-in practice works well with the multi-span steel girder superstructure and the wall pier. No significant response from the substructure was visually observed during the slide-in, and no cracking occurred on the concrete deck or piers. This indicated that the superstructure with steel girders and concrete diaphragms can be built with the lateral slide-in method.

Significant strain was measured from the pile strain gauges. The piles were functionally adequate to carry the vertical load, and the moment carried by each pile was minimal. An uplifting action was captured on Pier 1. However, this effect was minimal on Pier 2.

Based on the results from the work conducted in the four tasks, further research, including laboratory tests and analytical simulation, is proposed as additional Phase II work

About the research

Iowa has a long history of converting two-lane and four-lane roadways to a three-lane cross section consisting of a through lane in each direction of travel and a center two-way left turn lane (TWLTL) for safety purposes. Several notable studies were conducted in Iowa in the early 2000s demonstrating the safety effectiveness of such conversions as well as offering guidance for conversion. These studies also suggested possible greater safety impacts compared to other contemporary studies.

Several different roadway and roadside characteristics may impact the possible effectiveness of three-lane cross sections. Some of these characteristics are collected and maintained by the Iowa Department of Transportation (DOT) through the Roadway Asset Management System (RAMS) (and formerly Geographic Information Management System [GIMS]). However, accuracy issues have been found to exist with some of these characteristics, including the presence of a TWLTL, due to the frequency of update and reliance on agency reporting. Additionally, several other characteristics that may potentially impact safety and/or operations have not been traditionally inventoried.

The primary objectives of this project are to identify three-lane roadways throughout the State of Iowa and collect (or update) pertinent roadway and roadside characteristics. Emphasis will be on current characteristics but may extend to historic characteristics, where available. Furthermore, relevant crash experience along the identified three-lane roadways will be captured for future safety analysis. Documenting the history and characteristics of three-lane sections will facilitate evaluation of the safety and/or operational-related impacts of these roadways. It will also allow for identification of common characteristics of well-performing, existing sites and similarities between them and potential three-lane conversion sites.

About the research

Iowa State University’s Center for Industrial Research and Service (CIRAS) will provide support services to DBE businesses in Iowa with the goal of increasing their overall participation in Iowa Department of Transportation (DOT) let projects. CIRAS will leverage existing partnerships and programs to increase awareness of the DBE/SS program and leverage other federal programs such as the Procurement Technical Assistance Program (PTAP) and Small Business Development Center (SBDC) to provide needed services to DBEs.

About the research

The Iowa Crash Analysis Tool (ICAT) provides a platform for users to access, query, and summarize crash data for the State of Iowa. ICAT provides considerable resources to query and download crash data but is somewhat limited in its’ ability to visually display person-level attributes and the interaction of different attributes. Through this project, InTrans will support the Iowa Department of Transportation (DOT) in the development of interactive dashboards that can be used within ICAT, allowing users to visualize selected summary statistics of crashes. This project will require significant coordination with the Iowa DOT, along with the vendor supporting ICAT (Great Arc), particularly in the areas of connecting to the data used within ICAT to provide an interactive experience with end users. InTrans researchers will use their experience in developing other crash dashboards and coordinate with the Iowa DOT’s Traffic and Safety Bureau on the dashboard layout, style, and integration within ICAT. The dashboards will connect to an Iowa DOT crash database format that is currently under development within the DOT; therefore, initial dashboard creation may require establishing a database similar to the anticipated format and structure. Ultimately, this project will yield an integrated dashboard interface within ICAT, expanding ICAT’s existing functionality, application, and user experience.

About the research

This is a continuation of a previous project, RB11-015: Investigation of the Effect of Speed on Dynamic ImpactFactor for Bridges with Different Entrance Conditions, which determined that the roughness at the entrance to bridges is a primary influence on general dynamic impact factors. This new project will take the information found in that project and attempt to correlate the International Roughness Index (IRI) data collected by the Iowa Department of Transportation (DOT) with the dynamic impact factor (DIF) used when analyzing bridges for heavy load permits. The goal of this project is to develop a method to estimate the DIF value for a large number of bridges that can be used by load rating engineers.

About the research

The aim of the work described in this report was to investigate the impacts of internally cured (IC) concrete paving on warping in test pavements built in Iowa. The study involved both laboratory investigations and field implementation of internally cured concrete for Iowa pavement systems.

The primary objective of this research was to perform a full-scale field demonstration using IC technology and to investigate its performance in rural roadways. Two overlay construction projects were identified for the field demonstration. Samples of the mixtures were taken at the time of placement and sent to the laboratory for parallel testing with laboratory prepared mixtures.

A number of sensors were embedded in the concrete slabs to monitor moisture and temperature over time. Periodic measurements were taken throughout the year to observe and evaluate the dimensional stability of the slabs.

To assess the value proposition of using internal curing in concrete overlays, life-cycle cost analyses were conducted using reported costs from the projects. Because little structural benefit is expected from the IC mixtures, the assessment was based on a predicted reduction in maintenance costs of the sections due to improved permeability determined in the laboratory tests. Both the net present value (NPV) and equivalent annual annuity (EAA) calculation results indicate a net savings over time with the use of IC technology.

Based on the field and laboratory results, using lightweight fine aggregate (LWFA) improved the concrete hydration for about one month after placing. The biggest challenge appears to be related to obtaining and preconditioning the LWFA.

In summary, the technique does appear to be of benefit for reducing the potential for early-age cracking, improving ride and increasing the longevity of relatively thin overlays. Assuming that the challenges of transportation and storage can be overcome, this is a viable technique to help improve the performance of such pavements.

About the research

It is common practice to put additional longitudinal reinforcement (b2 bars) over intermediate supports to resist any negative moment induced by the superimposed dead loads and live loads on bridges. However, little research has been conducted on the performance of the additional negative reinforcing steel. Requirements for the termination of the additional negative moment reinforcing steel have largely been based on engineering judgement, previous performance, and existing practice.

The main objective of this research was to evaluate the effect of different amounts of b2 bar on resisting the negative moment over the pier on a continuous prestressed concrete girder bridge when it is subject to the live load-generated moment and secondary moment. To achieve this objective, a live load field test was performed on a bridge designed with different amounts of b2 bars to allow for comparison of the varying levels of negative moment reinforcement present.

A full-scale finite element model was developed and validated against the field-collected data to study b2 bar performance subjected to live loads. An evaluation was performed utilizing an analytical approach by calculating the time-dependent secondary moment using mRESTRAINT and loading the beam-line finite element model with the maximum negative moment.

It was found that the negative moment induced by the live load and secondary moment does appear through the service life of the bridge. The high differential shrinkage rate between the fresh deck concrete and the girder concrete is the main source of the negative moment over the supports. The magnitude of the secondary moment was found to be highly influenced by the time when the continuity is established.

The results also indicated that the additional longitudinal reinforcing steel provides minimal effect on resistance to the negative moment prior to the formation of deck cracking, regardless of whether the negative moment was induced by live loads or by the secondary moment. The current design approach determines the b2 bar requirement for the strength level based on the live load, while it may be necessary to include the secondary moment in the design.

About the research

The opportunity to produce a high-value material derived from vegetable oil from the Midwest creates a tremendous economic opportunity to replace a dangerous and carcinogenic material in butadiene, which is derived from crude oil petroleum. The majority of butadiene is imported to use for subsequent production of polymers or is contained in polymers imported to the US. Development of the biopolymer technology for asphalt paving was sponsored by the Iowa Highway Research Board (IHRB) under a special funding mechanism for high-risk/high-potential-pay-off research. The biopolymers developed by Iowa State University were found to be an excellent alternative to the polymers currently used.

Since the conclusion of the first phase of this study in April 2014, a ton-per-day pilot plant was designed and built at Iowa State University’s BioCentury Research Farm, west of Ames, at a cost of more than $6 million. The pilot plant was installed in late 2015, winterized for the 2015–2016 winter, and reopened in Spring 2016.

The research team worked since the completion of the Phase I IHRB project in getting the pilot plant working and correctly calibrated. The Bio-Polymer Processing Facility underwent rigorous troubleshooting and upgrades during 2016 and became capable of producing biopolymers in sufficient quantities to conduct field demonstration paving projects. Research done during this work led to optimized formulations of biopolymer and furthered the march toward the implementation of biopolymer for field demonstration projects.

Due to the high number of mix designs that include reclaimed or recycled asphalt pavement (RAP), the biopolymer was transformed with a rejuvenator into a liquefied state to perform easier and more efficient blending with neat binders. From this new biopolymer/rejuvenator combination, called BioMAG, one test section and two demonstration projects were paved at the National Center for Asphalt Technology (NCAT) Test Track at Auburn University in Alabama and two sites in Iowa. The section at the NCAT Test Track is performing well against rutting and cracking.

Currently, additional data are being collected about other distresses. For the two demonstration projects in Iowa, mix and binder were collected from the Altoona, Iowa site. Full mix and binder characterization have shown that BioMAG performs well in RAP mix designs and improves resistance against low temperature cracking and rutting.

About the research

While for decades horizontally curved steel girder bridges have been a solution for constructing interchanges between state and Interstate highways, concerns remain regarding their design and construction. The cross-frames in these bridges are especially critical because, unlike in straight bridges, they are major load carrying elements.

The design and analysis of cross-frames in curved bridges is complex due to complexities in how loads are transmitted throughout these types of bridges. However, a unique opportunity exists to improve the design of these components using modern computer software and short- and long-term monitoring.

This project investigated a horizontally curved bridge located in Story County near Ames, Iowa, to understand the behavior of cross-frames during construction and over the service life of the bridge. The project involved a numerical investigation using finite element modeling and short-term and long-term monitoring in the field to (1) identify sections of the bridge to instrument under dead, live, and temperature loading; (2) evaluate the performance of cross-frames through long-term monitoring; (3) evaluate the performance of cross-frames using live load tests; and (4) provide recommendations for practice.

The research results suggest that the cross-frames close to supports may experience high stress levels, and therefore special attention is required for their design compared to the other cross-frames. The cross-frames within the interior bays were also found to carry higher forces than those in the outer bays. This situation requires additional analysis during design to ensure the safety and performance of curved girder bridges.