Institute for Transportation

About the research

This project summarized findings from a National Cooperative Highway Research Program (NCHRP) Innovations Deserving Exploratory Analysis (IDEA) study to develop and demonstrate the application of bio-renewable polymers for use in asphalt pavements by utilizing soybean oil through chemical synthesis. Triglyceride molecules from vegetable oils have been considered as important renewable resources, which can be used as biomonomers and be polymerized into biopolymers with properties similar to petroleum-derived monomers and polymers. In this research, non-food soybean oil was selected as a starting point to produce biopolymers. The modification effects and the effectiveness of the biopolymers were evaluated through a comprehensive asphalt binder investigation to optimize formulation of the biopolymers. Meanwhile, evaluation of the actual field performance of the biopolymer modified asphalt mixture is ongoing via the construction at the National Center for Asphalt Technology (NCAT) Test Track section.

Visit the Transportation Research Board’s project website

About the research

The objective of this project is to facilitate rapid highway renewal. This project is intended to identify existing alternative materials and systems for constructing embankments and roadways over unfavorable ground conditions; to develop or compile design guidelines, procedures, and QA/QC test procedures for construction of ground improvements; to develop performance-based construction specifications for selected soil improvement technologies; and to determine which existing and emerging technologies offer promise for treating areas of unfavorable subsurface conditions.

Visit the GeoTechTools website

About the research

The Iowa Department of Transportation (DOT) is responsible for approximately 4,100 bridges and structures that are a part of the state’s primary highway system, which includes the Interstate, US, and Iowa highway routes. A pilot study was conducted for six bridges in two Iowa river basins—the Cedar River Basin and the South Skunk River Basin—to develop a methodology to evaluate their vulnerability to climate change and extreme weather. The six bridges had been either closed or severely stressed by record streamflow within the past seven years.

An innovative methodology was developed to generate streamflow scenarios given climate change projections. The methodology selected appropriate rainfall projection data to feed into a streamflow model that generated continuous peak annual streamflow series for 1960 through 2100, which were used as input to PeakFQ to estimate return intervals for floods.

The methodology evaluated the plausibility of rainfall projections and credibility of streamflow simulation while remaining consistent with U.S. Geological Survey (USGS) protocol for estimating the return interval for floods. The results were conveyed in an innovative graph that combined historical and scenario-based design metrics for use in bridge vulnerability analysis and engineering design.

The pilot results determined the annual peak streamflow response to climate change will likely be basin-size dependent, four of the six pilot study bridges would be exposed to increased frequency of extreme streamflow and would have higher frequency of overtopping, the proposed design for replacing the Interstate 35 bridges over the South Skunk River south of Ames, Iowa is resilient to climate change, and some Iowa DOT bridge design policies could be reviewed to consider incorporating climate change information.

About the research

This analysis performed focused activities under the Concrete Pavement Road Map (CP Road map) Track 1, Mix Design and Analysis. These activities included verification tests for materials and mixtures, relationships and models that predict mixture performance, guides and specifications that can help users make good decisions, and communication and education tools that help practitioners stay abreast of innovations being developed.

About the research

The current National Bridge Inventory database lists the concrete bridge deck deterioration, in the form of reinforcement corrosion or concrete distress, as one of the leading causes of structural deficiency. The combination of aging infrastructure, growing number of structurally deficient or obsolete bridges, and continuous increase in traffic volume in the United States demands rapid improvements to the nation’s bridge infrastructure with an emphasis on increasing bridge longevity. A recent Highways for LIFE project sponsored by the Federal Highway Administration (FHWA) entitled Full Depth UHPC Waffle Bridge Deck Panels confirmed the significant benefits of ultra-high performance concrete (UHPC) deck systems in terms of excellent structural performance, durability, and ease of construction. However, the initial capital cost of this deck system is comparatively higher than the traditional, normal strength concrete decks, which may hinder the wider usage of UHPC waffle decks in bridges. In order to overcome this challenge and to improve longevity of bridge decks, this project explores the possibility of using a thin layer of UHPC overlaying a normal strength concrete (NC) deck.

The behavior of the interface connection will have a significant impact on the overall structural and durability performance of the UHPC-NC composite deck system. Consequently, an integrated experimental and analytical study was conducted at Iowa State University to understand the influence of several variables, such as normal concrete strength, interface roughness, and curing condition on the shear transfer behavior across the interface between UHPC and NC. The laboratory testing was performed in two phases, including slant shear testing in Phase I and flexural testing of composite deck specimens in Phase II. A total of sixty test units with five different surface textures and three different concrete strengths were loaded to failure. Then, five 8 in. thick, 2 ft wide, and 8ft long deck specimens with 1.5 in. thick UHPC overlays were tested to failure. With the interface texture being the main variable, the composite deck sections were subjected to a combined monotonically increasing flexure and shear loading. The slant shear test results demonstrated that the shear transfer across the interface for all five different textures is adequate for overlay applications, which was later confirmed by the composite deck sections tests. Based on the experimental results, the researchers found that the current AASHTO 2010 guidelines provide a conservative estimate for the UHPC-NC interface shear strength.

About the research

Large Dynamic Message Signs (DMSs) have been increasingly used on freeways, expressways and major arterials to better manage the traffic flow by providing accurate and timely information to drivers. Overhead truss structures are typically employed to support those DMSs allowing them to provide wider display to more lanes. In recent years, there is increasing evidence that the truss structures supporting these large and heavy signs are subjected to much more complex loadings than are typically accounted for in the codified design procedures. Consequently, some of these structures have required frequent inspections, retrofitting, and even premature replacement. Two manufacturing processes are primarily utilized on truss structures -welding and bolting. Recently, cracks at welding toes were reported for the structures employed in some states.

Extremely large loads (e.g., due to high winds) could cause brittle fractures, and cyclic vibration (e.g., due to diurnal variation in temperature or due to oscillations in the wind force induced by vortex shedding behind the DMS) may lead to fatigue damage, as these are two major failures for the metallic material. Wind and strain resulting from temperature changes are the main loads that affect the structures during their lifetime. The American Association of State Highway and Transportation Officials (AASHTO) Specification defines the limit loads in dead load, wind load, ice load, and fatigue design for natural wind gust and truck-induced gust.

The objectives of this study are to investigate wind and thermal effects in the bridge type overhead DMS truss structures and improve the current design specifications (e.g., for thermal design). In order to accomplish the objective, it is necessary to study structural behavior and detailed strain-stress of the truss structures caused by wind load on the DMS cabinet and thermal load on the truss supporting the DMS cabinet.

The study is divided into two parts. The Computational Fluid Dynamics (CFD) component and part of the structural analysis component of the study were conducted at the University of Iowa while the field study and related structural analysis computations were conducted at the Iowa State University. The CFD simulations were used to determine the air-induced forces (wind loads) on the DMS cabinets and the finite element analysis was used to determine the response of the supporting trusses to these pressure forces. The field observation portion consisted of short-term monitoring of several DMS Cabinet/Trusses and long-term monitoring of one DMS Cabinet/Truss. The short-term monitoring was a single (or two) day event in which several message sign panel/trusses were tested. The long-term monitoring field study extended over several months. Analysis of the data focused on trying to identify important behaviors under both ambient and truck induced winds and the effect of daily temperature changes.

Results of the CFD investigation, field experiments and structural analysis of the wind induced forces on the DMS cabinets and their effect on the supporting trusses showed that the passage of trucks cannot be responsible for the problems observed to develop at trusses supporting DMS cabinets. Rather the data pointed toward the important effect of the thermal load induced by cyclic (diurnal) variations of the temperature. Thermal influence is not discussed in the specification, either in limit load or fatigue design. Although the frequency of the thermal load is low, results showed that when temperature range is large the restress range would be significant to the structure, especially near welding areaswhere stress concentrations may occur. Moreover stress amplitude and range are the primary parameters for brittle fracture and fatigue life estimation. Long-term field monitoring of one of the overhead truss structures in Iowa was used as the research baseline to estimate the effects of diurnal temperature changes to fatigue damage. The evaluation of the collected data is an important approach for understanding the structural behavior and for the advancement of future code provisions. Finite element modeling was developed to estimate the strain and stress magnitudes, which were compared with the field monitoring data. Fatigue life of the truss structures was also estimated based on AASHTO specifications and the numerical modeling. The main conclusion of thestudy is that thermal induced fatigue damage of the truss structures supporting DMS cabinets is likely a significant contributing cause for the cracks observed to develop at such structures. Other probable causes for fatigue damage not investigated in this study are the cyclic oscillations of the total wind load associated with the vortex shedding behind the DMS cabinet at high wind conditions and fabrication tolerances and induced stresses due to fitting of tube to tube connections.

About the research

Due to quality control issues or soft toe conditions, the end bearing capacity of drilled shafts is often not mobilized before service load displacement limits are realized. Shaft capacity is therefore limited as it is developed primarily through mobilization of side-frictional resistance at relatively small displacements. It has been estimated that the end bearing component in-cohesionless soils can be as great as 20 times the resistance available due to side friction. To take advantage of such potential high end bearing capacities in soft-toe conditions, post-grouting of shaft tips is increasing in popularity. In the existing Broadway viaduct replacement project, initial load-testing has been completed on post-grouted drilled shafts that were constructed using the tube-sleeve (tube-a-manchette) approach. However, the increase in shaft capacity did not meet expectations, and questions remain as to the size and integrity of the grout bulb, and therefore the size of the contact area that should be used in analysis and design. It is our understanding that it has been suggested that the tube-a-manchette grouting technique be replaced with a flat-jacking approach, for which the distribution and contact area of the grout will be known. To date, there remain questions regarding the effectiveness of this technique. Current plans for replacing the Broadway viaduct also involve the replacement of the existing cellular abutments with slabs on LFCF material contained within mechanically stabilized earth (MSE) walls. Because this is the first such use of LFCF in a bridge project in Iowa, it will be highly beneficial to assess and document the performance and interaction of the fill with the surrounding walls and underlying foundation soils. The performance of the LFCF-MSE wall system will be studied by instrumenting the wall facade with tilt meters and the straps with strain gages. At each abutment, two soil settlement plates will be used to monitor the soil response at the base of the fill material and two will be installed immediately outside the MSE walls, for a total of eight settlement plates (to be installed by the DOT). Additionally, the pressure under the foamed concrete fill will be monitored using two soil pressure cells. The LFCF offers potential savings over the use of select fills, while post grouting of drilled shaft tips will likely provide savings in construction costs by decreasing the required shaft lengths for a given design load. Documentation and evaluation of the construction and performance of these materials and techniques will benefit future projects in which these technologies may be used.

About the research

In 2004, the Federal Highway Administration, Iowa State University, American Concrete Pavement Association, and the International Grooving and Grinding Association initiated a five-year Concrete Pavement Surface Characteristics Program (CPSCP). This program was administered through the National Concrete Pavement Technology Center located at Iowa State University. The purpose was to determine the interrelationship among noise, friction, smoothness, and texture properties of concrete pavements. It was envisioned at that time to consist of the following parts:

• Part 1: Portland Cement Concrete Pavement Surface Characteristics (referred to as Project 15 of FHWA/ISU Cooperative Agreement No. DTFH61-01X-0042)
• Part 2: 2005-2006 Field Data Collection of Current Surface Characteristics Practices
• Part 3: 2006-2012 Data Analysis and Innovative Surface Characteristics Solutions, Transportation Pooled Fund TPF-5(139)

Part 1 included the development of a long-term Strategic Plan as well as documentation on all concrete pavement noise reduction trials with a specific focus on European and U.S. methods. The report compiled information on design, bidding, construction, quality control, maintenance, and field evaluations. Part 2 consisted of the collection, measurement, presentation, and preliminary analysis of noise, skid, texture, and smoothness data for conventional texturing variations and grinding techniques on pavements. Part 3 investigated innovative texturing techniques with potential to reduce noise, while not degrading the other surface characteristics (smoothness, friction, drainage, etc.) of the pavement. Part 3 concluded with an extensive outreach effort including the development of guide specifications, a how-to guide for constructing concrete pavement textures, several technical briefs, and a day-long training workshop.

The CPSCP has led to better practices for designing and constructing quieter concrete pavements. The implementation of these guidelines has begun, and several early adopters have already been reported.

About the research

Lane departure crashes are a significant safety concern. The majority of lane departure crashes occur on rural two-lane roadways, with a disproportionate number of these crashes on horizontal curves. Curve-related crashes involve a number of roadway and driver causative factors. A primary driver factor is speeding.

Dynamic speed feedback sign (DSFS) systems are one method to reduce vehicle speeds and, consequently, crashes on curves. These systems show promise but they have not been fully evaluated on curves. The Center for Transportation Research and Education at Iowa State University conducted a national demonstration project to evaluate the effectiveness of two different DSFSs in reducing speed and crashes on curves at 22 total sites on rural two-lane roadways in seven States. The goal is to provide traffic safety engineers and other professionals with additional tools to manage speeds and crashes on rural horizontal curves more effectively.

Data were collected before and at 1, 12, and 24 months after installation of the DSFS. On average, most sites had decreases in mean speeds, with decreases up to 10.9 miles per hour (mph) noted for both the point of curvature (PC) and center of curve (CC). Most sites experienced changes in 85th percentile speed of 3 mph or more at the PC, with the majority of sites having a decrease of 2 mph at the CC. The numbers of vehicles traveling 5, 10, 15, or 20 mph over the posted or advisory speed limit were also compared. Large reductions in the number of vehicles traveling over the posted or advisory speed occurred for all of the after periods at the PC and CC, indicating that the signs were effective in reducing high-end speeds, as well as average and 85th percentile speeds.

A before-and-after crash analysis was also conducted, and crash modification factors (CMF) were developed. CMFs ranged from 0.93 to 0.95 depending on the crash type and direction of the crash.

Funding Sources:
Federal Highway Administration ($300,000.00)
Iowa Department of Transportation ($30,000.00)
Iowa Highway Research Board ($80,000.00)
Midwest Transportation Consortium ($71,769.00)
Texas Department of Transportation ($120,000.00)
Total: $601,769.00

About the research

Highway construction is among the most dangerous industries in the US. Internal traffic control design, along with how construction equipment and vehicles interact with the traveling public, have a significant effect on how safe a highway construction work zone can be.

An integrated approach was taken to research work-zone safety issues and mobility, including input from many personnel, ranging from roadway designers to construction laborers and equipment operators. The research team analyzed crash data from Iowa work-zone incident reports and Occupational Safety and Health Administration data for the industry in conjunction with the results of personal interviews, a targeted work-zone ingress and egress survey, and a work-zone pilot project.