Idaho Transportation Department Research Articles

Field Performance of High-Early-Strength Concrete with Polypropylene Fibers as a Cost-Effective Alternative for Longitudinal Connection between Bridge Deck Bulb-T Girders

High-early-strength (HES) concrete with polypropylene fibers has been used in several parts of bridges with precast concrete girders by the Idaho Transportation Department (ITD). This material is only slightly more expensive than conventional concrete, but speeds up the construction. ITD is interested in the suitability of HES concrete in the longitudinal closure pour connections between bridge deck bulb-T girders. In the laboratory phase of this project, an optimum HES concrete mix was identified through a series of laboratory experiments. The field performance of the HES concrete mix was examined by placing the material in the closure pour joints between deck bulb-T girders in a bridge in Idaho. The main focus of this paper is to report on the 20-month field performance of the bridge closure pour concrete. Tasks included six visits to the bridge site every 4 months to (1) measure strain data under ITD’s Under the Bridge Inspection Truck (UBIT), (2) measure strain data under commercial truck traffic, and (3) inspect the closure pour concrete. Based on the results, it was concluded that there were no changes in the closure pour concrete in the last 20 months.

Finite Element Modeling of Longitudinal Field-Cast Connections Between Precast Deck Bulb-T Bridge Girders

An alternative mix design using polypropylene fiber-reinforced high early strength concrete was proposed by the Idaho Transportation Department for the longitudinal connections between deck bulb-T precast bridge girders in accelerated bridge construction. In this paper, finite element models of the pullout behavior of headed reinforcing bars in the closure pour and bending tests of beams representing a 30 cm strip of the bridge deck were developed. The smeared crack model was used for concrete, while cohesive zone modeling showed good results in representing the interface between the closure pour and precast concrete. Steel–concrete bond-slip behavior was observed to be one of the most significant factors affecting the results. A scheme to simulate this behavior using zero-length nonlinear spring elements was designed. The finite element models were able to produce results similar to the experimental findings.

Accuracy Comparison of Aerial Lidar, Mobile-Terrestrial Lidar, and UAV Photogrammetric Capture Data Elevations over Different Terrain Types

Lidar and other remotely sensed data such as UAV photogrammetric data capture are being collected and utilized for roadway design on an increasing basis. These methods are desirable over conventional survey due to their efficiency and cost-effectiveness over large areas. A high degree of relative accuracy is achievable through the establishment of survey control. In this case study, elevations (z-values) derived from mobile-terrestrial lidar, aerial lidar, and UAV photogrammetric capture collected with survey control were statistically compared to conventionally surveyed elevations. A cost comparison of the methods is also included. Each set of z-values corresponds to a discrete horizontal point originally part of the conventional survey, collected as cross-sections. These cross-sections were surveyed at three approximate tenth-mile sample locations along US-30 near Georgetown, Idaho. The cross-sections were collected as elevational accuracy verification, and each sample location was selected as an area where the mobile-terrestrial lidar in particular was expected to have more difficulty achieving accuracy off the road surface. Processing and analysis were performed in Esri ArcMap 10.6, and all data were obtained from the Idaho Transportation Department, District 5. Overall, the aerial lidar elevations were found to be closest to conventionally surveyed elevations; on road surface and level terrain, mobile-terrestrial and UAV photogrammetric capture elevations were closer to the conventionally measured elevations.

Laboratory characterization of fine-grained soils for Pavement ME Design implementation in Idaho

The subgrade layer often represents the weakest component of a pavement system, and can significantly affect pavement response and performance under loading. Adequate characterization of subgrade properties is critical to the design and construction of long-lasting, economical pavement systems. The Mechanistic-Empirical (M-E) pavement design protocol implemented through AASHTOWare Pavement ME Design requires resilient modulus of the subgrade soil as one of the primary input parameters. However, performing repeated load triaxial tests to establish the resilient modulus properties of soils is a cumbersome task, and is rarely undertaken by state transportation agencies on a regular basis. The Idaho Transportation Department (ITD) has recently invested significant amount of time and resources to facilitate state-wide implementation of M-E pavement design practices. This study was recently undertaken to characterize typical subgrade soils in Idaho. Extensive laboratory characterization of the soils was carried out including repeated load triaxial testing for determining the resilient modulus values. Several different pavement sections were analyzed by using currently used default values and laboratory-established soil properties as subgrade layer inputs during M-E design. Default soil modulus values that are currently used, were found to be significantly higher than laboratory-established values, and therefore, resulted in the design of pavement sections that would fail considerably early into their service lives. The effect of moisture content on subgrade soil properties was also studied, and the importance of restricting soil moisture contents to the dry side of optimum was highlighted.

Integration of Traffic Speed Deflectometer and Ground-Penetrating Radar for Network-Level Roadway Structure Evaluation

The project has focused on the East Idaho Loop Corridor (EILC), representing 518 mi of primary roadways covering a wide range of geographic conditions. The Idaho Transportation Department (TD) has pursued this effort to support future project planning and design efforts and advance the management of its assets into a more efficient, best-first set of priorities. The EILC was surveyed with a traffic speed deflectometer (TSD) and with ground-penetrating radar (GPR). After preliminary review of the TSD data, segments were selected for falling weight deflectometer (FWD) testing to confirm patterns observed in the TSD data and to adapt FWD analysis methods to the TSD data. Ninety-nine borings were taken to confirm the pavement layer structure and verify thickness calculations. The Idaho TD data were analyzed at a 10-m interval with the GPR layer thickness data to determine subgrade modulus, pavement modulus, and structural number. These values were then used to estimate overlay requirements and, given traffic projections, to calculate the remaining life as a continuous function of roadway position. The data were incorporated into a spatial geodatabase that provides the Idaho TD with a convenient means to visualize and evaluate the overall condition of the network down to the detail of its individual segments. The segments were subdivided into homogenous subsections on the basis of remaining life, and these subsegments were used for identifying and programming rehabilitation projects. The level of condition detail available at the subsegment level allows for pavement design and for scoping restoration projects.

Safety Evaluations for Skewed Intersections on Low-Volume Roads

Safety on low-volume roads is a major concern. It has been reported that the traffic fatality rate is more than three times higher on rural roads than on other roads. Some of these fatalities occur at inter sections, and the safety risks increase when the intersections are skewed or have an elevation difference. In Idaho, some skewed intersections (e.g., those on SH-39 and US-91 in eastern Idaho) are the result of highways having been built parallel to rivers or railroad lines and local roads having been built later on a grid with a north–south or east–west orientation. In an attempt to improve the safety of existing intersections, the Idaho Transportation Department's District 5 performed a systematic and comprehensive evaluation of all of the intersections on the state highway system in southeastern Idaho. In total, 125 intersections along US-91 and 194 intersections along SH-39 were evaluated, and safety improvements were made. These improvements resulted in a reduction in the overall number of crashes along these two highways. This paper presents the results of these evaluations and the recommendations that followed.

Evaluating Snow and Ice Control Chemicals for Environmentally Sustainable Highway Maintenance Operations

AbstractThe use of chemicals and abrasives for highway winter maintenance operations is an essential strategy for ensuring a reasonably high level of service, yet the performance of such materials has to be balanced with their potential negative impacts on motor vehicles, transportation infrastructure, and the natural environment. In this context, this work presents a comprehensive and quantitative evaluation of snow and ice control chemicals currently used by various Idaho Transportation Department districts for highway maintenance operations, including rock salts (mainly solid sodium chloride), IceSlicer products (solid sodium chloride with trace amounts of other chlorides), and salt brines. The analysis has been enabled by the utilization of existing lab and field test data along with reasonable assumptions, in the effort to identify environmentally sustainable materials for winter highway operations. Despite its caveats, this case study is the first attempt to incorporate the most up-to-date informati...

Traffic Characteristics and Their Impact on Pavement Performance for the Implementation of the Mechanistic-Empirical Pavement Design Guide in Idaho

This study addresses the development of traffic characteristics to facilitate the implementation of the Mechanistic-Empirical Pavement Design Guide (MEPDG) in Idaho. Classification and weight data collected at 25 weigh-in-motion (WIM) sites were procured from Idaho Transportation Department (ITD). Among these 25 sites, only 12 sites were found to have complete and accurate data. Site-specific axle load spectra (ALS), monthly adjustment factors (MAF), vehicle class distribution factors (VCD), and number of axles per truck type were developed. Predicted distresses and International Roughness Index (IRI) based on a typical pavement section and traffic data obtained at the investigated WIM sites (level 1) were compared to predicted distresses/IRI using statewide/national (level 3) default traffic inputs. This comparison revealed that ALS, VCD, and MAF input level have significant impact on longitudinal cracking. Statewide ALS yielded high differences in alligator cracking predictions while MAF and VCD yielded only moderate differences compared to site-specific ALS. Very low prediction differences occurred in rutting when statewide/national default ALS, MAF, and VCD were used as opposed to site-specific data. The level of input of the investigated traffic parameters did not affect IRI. Finally, it was found that statewide/national number of axles per truck can be used instead of site-specific values without sacrificing accuracy of pavement performance predictions.

Visualizing Long-Range Health of Rural Recreational and Agricultural Corridors

This paper describes a system developed by the Idaho Transportation Department (ITD) and DKS Associates to produce visual displays of how growth in the key rural corridors in eastern Idaho will affect the health of state facilities and how investments can reduce the long-term impacts of that growth. The system includes a geographic information system (GIS) as the base platform where a variety of data on roadway characteristics, land use, population and employment forecasts, and traffic counts are stored and organized. The system also includes a module for producing travel forecasts from population and employment growth forecasts and from historical trends in growth in traffic volumes to reflect growth in the corridor and growth in recreational travel to the region. For a future scenario, the GIS program generates a graphic display of the level of service for different times of the day, days of the week, and seasons of the year. It also can generate a graphic display of the health of the corridor where “health” is defined by a set of factors and criteria that describe how the corridor would be perceived by travelers who use it and how the roadway facility affects the economic health of the corridor. The visualization tool has been successfully used by ITD to help the counties in eastern Idaho develop plans that anticipate and acknowledge the growth and other changes in the critical state route corridors.

Impact of Lime and Liquid Antistrip Agents on Properties of Idaho Hot-Mix Asphalt Mixture

In 2005, the Idaho Transportation Department constructed a field project on State Highway 67 (SH-67) to evaluate the impact of hydrated lime and a liquid antistrip agent on the mechanical properties of an Idaho hot-mix asphalt (HMA) mixture. This paper documents the results of a laboratory evaluation on field-produced HMA mixtures sampled from lime and liquid antistrip test sections on SH-67. As the two mixtures were subjected to multiple freeze-thaw (F-T) cycles, the mixture treated with hydrated lime (lime mixture) maintained good resilient-modulus properties over the entire 21 F-T cycles. The mixture treated with the liquid antistrip agent (liquid mixture) fully disintegrated after 22 F-T cycles. The results of a mechanistic analysis showed that, as a result of multiple F-T cycling, the liquid mixture will incur a 220% increase in potential rutting compared with the lime mixture, which will incur only a 65% potential increase in rutting. The dynamic moduli in compression demonstrated that both dry and moisture-conditioned lime mixtures can be considered less susceptible to rutting compared with liquid mixtures. Furthermore, the lime mixtures demonstrated better resistance to moisture damage than the liquid mixtures on the basis of the ratio of dynamic modulus in tension of moisture-conditioned to dry mixtures. The additional stiffness of the lime mixtures did not contribute to premature fatigue cracking when mixtures were subjected to dynamic creep testing in the tensile mode of loading.