Institute for Transportation

About the research

Real-time smoothness (RTS) technology is arguably one of the most impactful technologies for concrete pavement construction quality control resulting from the Second Strategic Highway Research (SHRP2) Program. Contractors participating in equipment loans through the SHRP2 Solutions Implementation Assistance Program have quickly realized the benefits of RTS for improving smoothness for as-constructed concrete pavement in order to achieve smoothness specification requirements while maximizing incentives and minimizing disincentives and corrective actions.

Over the course of implementing this technology through equipment loans and workshops, it has become apparent that additional guidance for specifying and achieving concrete pavement smoothness is needed. Many agencies struggle to understand what a reasonable specification looks like with respect to smoothness limits and incentive/disincentive levels. And frequently they do not fully understand the impacts of design factors (curvature, grade and super-elevation changes, leave-outs, etc.) and prescriptive requirements for materials, mixtures, and construction equipment, on the contractor’s ability to achieve the smoothness requirements. Likewise, many contractors do not fully understand the impacts various construction factors such as the concrete mixture, paving equipment, and paving crew, have on smoothness. They often do not understand the importance of continually checking smoothness to adjust operations to ensure the smoothness requirements for the final product are achieved.

The purpose of this project is to continue implementing RTS technology through field trials, while also using what has been learned to-date to generate guide specifications and develop best practices for concrete pavement smoothness.  In short, the objective is to provide guidelines on how to specify and build smooth concrete pavements. RTS equipment demonstrations should provide contractors and agencies with a working knowledge of RTS technologies as well as an improved understanding of how material non-uniformity and paving processes impact the initial smoothness and long-term performance of portland cement concrete pavements.

About the research

The main objective of this synthesis was to identify and summarize how agencies collect, analyze, and report different work-zone traffic-performance measures, which include exposure, mobility, and safety measures. The researchers also examined communicating performance to the public. This toolbox provides knowledge to help state departments of transportation (DOTs), as well as counties and cities, to better address reporting of work-zone performance.

About the research

The objective of this project is to evaluate the performance of a second-generation accelerated bridge construction (ABC) bridge that utilizes two types of continuity connections: the transverse joint at pier diaphragms and the longitudinal joint between precast superstructure/deck units.

The bridge replacement project located on IA 92 over Little Silver Creek in Pottawattamie County, Iowa was used to demonstrate a second-generation ABC technique that had been previously used in Iowa. As a part of the holistic evaluation, the performance of an ultra-high performance concrete (UHPC) longitudinal joint detail and a high-performance material (HPM) transverse joint detail were studied through laboratory testing and numerical simulations. Additionally, field testing was conducted to evaluate the in-place integrity of the bridge.

The goals of this project are to demonstrate the performance and benefits of the ABC techniques using prefabricated bridge elements and systems (PBES) and HPMs and to contribute toward increased adoption of the technologies by Iowa and other states.

Through this project, the Iowa DOT gained valuable insights into the innovative ABC techniques used. The following were some of the lessons learned:

• UHPC is an excellent material for longitudinal closure pour connections.
• There may not be a need to use a compression block for the beam-to-beam transverse closure pours on a similar ABC project in the future.
• The UHPC longitudinal joints and the HPC transverse joints at the pier location are sufficient for the modular bridge systems of ABC projects.

About the research

The goal of this project was to establish the Iowa Department of Transportation (DOT) open traffic data service, which will allow vendors and agencies to provide near real-time, proactive alerts to commercial drivers regarding traffic conditions along their routes. This open data service provides operations-related data to any commercial, public or private entity to develop their own applications or integrate these data into their existing hardware, software, and logistics systems.

The open data service makes transportation related data accessible to both internal DOT and external third-party users. A combination of high-performance computing (HPC) on premise and on the cloud was used to create data feeds which provide clean data streams, alerts for traffic congestion using machine learning, performance reporting, and data analytics.

About the research

A large number of bridges in the nation are rated as structurally deficient and require immediate retrofits or replacements that will impose a significant financial burden on bridge owners. A fast, cost-efficient, and reliable retrofit solution is needed to tackle this problem. Typical bridge deck deterioration starts with shrinkage cracks, and additional cracks may occur due to traffic loads and time-dependent effects, which are worsened by freeze-thaw cycles over time. These cracks then lead to water and chloride penetration into the concrete deck, causing rebar corrosion and further damage to the superstructure.

A potential solution, suggested in a previous study, is to apply a thin layer of ultra-high-performance concrete (UHPC) on top of normal concrete (NC) bridge decks. Because UHPC has a higher tensile strength and low permeability, cracking as well as water and chloride ingression can be minimized, which in turn will extend the lifespan of the bridge. Moreover, UHPC is also deemed to have a higher fatigue resistance than NC.

In this study, a new UHPC mix to accommodate surface crowning was developed by a material supplier and tested in the laboratory. Using this new mix, the thin UHPC overlay concept was successfully implemented on a county bridge in Iowa. The implementation involved state and county engineers, a local contractor, and a material supplier. The bridge overlay was periodically monitored, and thus far there have been no concerns regarding the performance of the UHPC overlay or the bond at the interface between the UHPC and NC layers. In addition to the field implementation, three concrete slabs with and without a UHPC overlay were tested in the laboratory.

The results showed that a UHPC overlay in the positive moment region increased the strength by 18% while showing a more ductile response. In the negative moment region, although wire mesh was used, its effectiveness was not significant due to its small steel area. The effectiveness of the wire mesh could be improved by increasing the amount of steel area within the overlay, but its impact on the UHPC-NC interface bond needs to be evaluated.

About the research

This report summarizes the findings from a study that evaluated consumer acceptance of different blends of ethanol at fueling stations in Iowa. This project expanded on an earlier evaluation of two stations that participated in the Fueling Our Future pilot program, which was administered by the Iowa Renewable Fuel Infrastructure Program (RFIP) of the Iowa Department of Agriculture and Land Stewardship (IDALS) and the Iowa Department of Transportation (Iowa DOT).

Because the two stations initially surveyed were typical of rural cooperatives, offered significantly different fuel options than Iowa’s conventional gas stations, and yielded a small sample size, a second phase of the research was initiated that conducted additional surveys at 16 stations. In addition, the air quality impacts of several different implementation scenarios for Fueling Our Future and similar programs were evaluated. Because most stations where surveys were conducted did not offer a range of biodiesels, biodiesel was not included in this study.

Findings are presented for all respondents together and for drivers of flexible fuel and non-flexible fuel vehicles separately. Among other key findings, the survey showed that cost was the primary factor in fuel selection for purchasers of E-0, E-10, and E-85 ethanol blends, and compatibility of the fuel with the respondent’s vehicle was a major factor for all respondents. Concerns about compatibility, followed by cost, were the top reasons why respondents did not select a higher ethanol blend. More than 80% of respondents selected the particular station due to location.

The results of the air quality analysis showed that statewide adoption of ethanol options and subsequent changes in purchasing behavior (based on the percentage difference between the statewide sales information and the customer survey information) could result in a 20% reduction in nitrogen oxides (NO_x), a reduction in particulate matter (PM) emissions much greater than 100%, a 3% reduction in carbon monoxide (CO), and a 20% reduction in hydrocarbon (HC) emissions.

About the research

In work-zone configurations where lane drops are present, merging of traffic at the taper presents an operational concern. In addition, as flow through the work zone is reduced, the relative traffic safety of the work zone is also reduced. Improving work-zone flow-through merge points depends on the behavior of individual drivers. By better understanding driver behavior, traffic control plans, work zone policies, and countermeasures can be better targeted to reinforce desirable lane closure merging behavior, leading to both improved safety and work-zone capacity.

The researchers collected data for two work-zone scenarios that included lane drops: one on the Interstate and the other on an urban roadway. Then, these scenarios were modeled and calibrated in Vissim using real-world speeds, travel times, queue lengths, and merging behaviors (percentage of vehicles merging upstream and near the merge point).

Once built and calibrated, strategies for the various countermeasures were modeled in the work zones. The models were then used to test and evaluate how various merging strategies affect safety and operations at the merge areas in these work zones.

About the research

The overall objective of the Second Strategic Highway Research Program (SHRP2) project R06E Real-Time Smoothness Measurements on Portland Cement Concrete (PCC) Pavements during Construction was to enable real-time control of concrete pavement smoothness during construction by evaluating and demonstrating promising technologies, and the development of both model specifications and construction guidance that are capable of working with the identified technology in such a way as to further the objective of rapid implementation by state highway agencies.

Seven potential real-time smoothness measurement devices were identified and studied as part of the project. Two of the devices were found to warrant subsequent evaluation and demonstration as part of Phase Ill of the project: These included the GOMACO Smoothness Indicator (GSI) and the Ames Engineering Real-Time Profiler (RTP). The GOMACO device was piloted and evaluated during concrete paving projects in Arkansas and Michigan, and the Ames device was piloted in Michigan, New York, and Texas.

During the project, it was noted that there was consensus among contractors that the real-time smoothness measuring technology represents a valuable process control tool in that the ability to have real-time feedback from intentional process changes has the greatest potential to make lasting improvements in the smoothness of concrete pavements. While the current state of the practice is to cautiously make an equipment/process change and wait approximately 24 hours for feedback when the hardened pavement can be profiled, real-time smoothness measuring devices allow the contractors to make adjustments to their concrete equipment and/or process while the concrete is still wet, minimizing more costly corrections later.

The objectives of this Task Order are to provide technology deployment support as follows: (1) equipment loan program; (2) conduct showcases; (3) conduct workshops; (4) documentation of results/case studies; (5) specification refinement; and (6) marketing and outreach. These objectives seek to ensure routine use of the R06E product technology by agencies and contractors that routinely construct PCC projects.

For more information, read the “Proven technologies to identify surface irregularities that can impact concrete pavement smoothness, and provide opportunity for corrections in real time,” article on FHWA’s website.

Related Resources

Below is a playlist of all CP Tech Center videos on real-time smoothness (RTS):

About the research

This project will provide guidance, provide sensitivity analyses, and use one to two recommended current concrete overlay design methods to create a guide that engineers will be able to use in order to conduct concrete overlay designs.

About the research

The initial phase of this project was conducted to determine whether adding slag cement to concrete mixtures increases the surface scaling caused by the routine application of deicer salt. A total of 28 field sites that included portland cement concrete pavements and bridge decks containing slag cement were evaluated. Laboratory testing was conducted on 6 in. diameter core samples extracted from 12 field sites and 3 subsites, including 6 pavement sites and 6 bridge decks. The laboratory testing program consisted of scaling tests, rapid chloride permeability tests, surface chloride profile tests, and petrographic examination. The results of this study suggest that construction-related issues played a bigger role in the observed scaling performance than did the amount of slag in the concrete mixture.