Institute for Transportation

About the research

Internal curing (IC) is a practical way of supplying additional curing water throughout the concrete mixture. This water can improve the hydration of cement, reduce autogenous shrinkage, and improve durability. The purpose of this document is to provide guidance for the development of project specifications for internally cured concrete projects. The guidance in this document is designed to supplement the agency’s standard specifications for concrete pavement. If the standard specifications are outdated, modifications other than those provided in this document may be necessary to produce a high-quality, long-lasting concrete. This document contains IC specification language, references to IC resources, references to IC instructional videos, and references to tools that can be used for IC of concrete or providing quality control.

About the research

The objectives of this study were to develop guidance for engineers on how implements of husbandry loads are resisted by traditional bridges, with a specific focus on bridges commonly found on the secondary road system; provide recommendations for accurately analyzing bridges for these loading effects; and make suggestions for the rating and posting of these bridges.

To achieve the objectives, the distribution of live load and dynamic impact effects for different types of farm vehicles on three general bridge types—steel-concrete, steel-timber, and timber-timber—were investigated through load testing and analytical modeling. The types of vehicles studied included, but were not limited to, grain wagons/grain carts, manure tank wagons, agriculture fertilizer applicators, and tractors.

Once the effects of these vehicles had been determined, a parametric study was carried out to develop live load distribution factor (LLDF) equations that account for the effect of husbandry vehicle loads. Similarly, recommendations for dynamic effects were also developed.

Finally, suggestions on the analysis, rating, and posting of bridges for husbandry implements were developed.

The third volume of the report contains six appendices that include the 19 mini-reports for field tested and analytically modeled steel-concrete, steel-timber, and timber-timber bridges, the farm implement and bridge inventories for the project, and survey responses.

About the research

Winter highway maintenance is an annual multi-billion dollar operation aimed at improving the safety and mobility of the highway system. To help the winter highway maintenance agencies optimize the usage of resources, it is important to develop a performance measurement system that can evaluate how well maintenance activities have been performed. In Iowa Highway Research Board Project TR-491, researchers developed a performance measure based on average vehicle speed, which takes into account severity of the storm. The model uses six categorical variables to define a storm and compute the acceptable traffic speed drop.

A previous Iowa Department of Transportation (DOT) agreement developed a sequential Bayesian dynamic model based on the model in TR-491, which is capable of predicting the acceptable drops during the storm, and allow uncertainty in input variables (sensor measurements) to propagate into uncertainty in speed reduction. One limitation of the sequential Bayesian model is that its uncertainty measure does not account for model uncertainty and the uncertainty in human-weather interaction. The model in TR-491 is based on survey of expert opinion, and its uncertainty is not considered in the original development and our follow up work. The uncertainty in human behavior under different weather conditions is also not considered due to lack of time.

The Iowa DOT is interested in refining this sequential Bayesian model to produce more accurate real-time prediction of traffic speed drops with better uncertainty measures so that it can be used to evaluate the performance of snow/ice removal efforts and the effectiveness of different snow removal methods. Ultimately, the DOT is interested in using this model to help managers reallocate resources to optimize objective functions such as minimizing the total costs or the speed drops. The DOT is interested in developing a dynamic model capable of predicting in real-time acceptable drops in traffic speed on highways during major weather events with realistic uncertainty measures. The primary usage of such model is to evaluate the performance of highway winter maintenance operations and optimize resource allocation.

The researchers developed a model to relate weather variables to traffic flow changes at a local level. Weather station data and maintenance crew reports were used to develop an empirical adaptive stochastic model using a Bayesian formulation. Data from early time segments provide a prior quantification of the expected effects of weather variables on traffic speed over subsequent time segments. Data in the next time segment are then used to adjust these quantifications to reflect observed traffic speeds during that period. Thus, rather than explicitly determining numerous temporally dependent interactions, the main effects associated with key factors are allowed to undergo small shifts over time to fit the data. The model incorporates an autoregressive error structure to reflect temporal dependencies in observations that occur at reasonably high frequencies.

About the research

About the research

The work to be covered by this project is the development of a Manual of Practice that will educate practicing engineers about when and how to use concrete mixtures containing ternary cementitious systems.

The information to be provided will be based on the findings of research recently completed through the ternary pooled fund and through a federal cooperative agreement with the National Concrete Pavement Technology Center. The manual will serve as a textbook to accompany a training program being developed by ACT (American Concrete Institute) for FHWA.

The research work has shown that ternary mixtures can be successful in a number of applications and provide enhanced performance while improving sustainability. Such mixtures do perform differently from conventional concrete, and the manual will document the benefits that may be expected as well as provide guidance for the precautions that need to be taken to ensure successful implementation.

About the research

Pavement design techniques have advanced to incorporate modern technology and scientific-based models to improve pavement construction, performance, maintenance, and rehabilitation. The reliability of these models depends upon input data gathered in the field via pavement instrumentation. There is a demonstrated lack of rigid pavement instrumentation and experimental field data nationally, leading to a shortage of pavement field data required to examine, model, and simulate the interaction of pavement components in the field (such as pavement base material, slab, tie bar, etc.). In order to rely upon more scientific-based models to improve pavement systems (and ultimately reduce pavement life-cycle costs), more data is required to refine existing and new pavement performance models. Perhaps the most commonly used and popularly accepted model-based, modern approach to highway design is embodied in the Mechanistic-Empirical Pavement Design Guide (MEPDG), which incorporates models embedded in dedicated software (such as AASHTOWare Pavement ME Design) to predict pavement performance in greater detail than prior predictive models. Such dedicated software incorporates scientific data such as material mechanics, climate data, axle-load spectra, and other factors. Full implementation of the Mechanistic-Empirical Pavement Design by state departments of transportation (DOTs) requires customization or calibration/validation of the software for variables and pavement conditions at state and local levels. This in turn requires the collection of region-specific field data on climate, material properties, load response, and pavement performance for use in calibration and implementation of the software. Mechanistic-Empirical Pavement Design software uses these data inputs to more accurately simulate the load response of pavements and long-term pavement performance. Local calibration of the software involves comparing long-term performance simulation results to actual performance data at local sites (if possible) or from matching pavements in the Federal Highway Administration Long-Term Pavement Performance (LTPP) database. Several numerical models are available to predict pavement performance, and these models are an effective tool to predict the likelihood of pavement damage and longevity. These numerical models also enable improvements in road design methods, whether for new or rehabilitated pavements, that will help mitigate the problems of load-induced damage. However, most of these models have not been calibrated against actual field data obtained under realistic conditions. To enhance the effectiveness of these models and to assist in their application, instrumented test sections of pavement can be monitored and data gathered to monitor performance factors (such as soil pressure, pavement temperature, strains and deflections caused by daily changes in temperature within the pavement, along with air temperature, wind speed, relative humidity, solar radiation, and precipitation). The pavement construction process can also be monitored, and the materials used in the pavement can be tested in the laboratory or in the field (using non-destructive testing) to ascertain material property information. As pavement systems are highly nonlinear in their responses to loads and load related strains, field data collected via instrumentation helps indicate which parameters need to be emphasized in the models to describe pavement performance and response to conditions. Data from the laboratory tests (or from non-destructive field testing) is input to the model to predict the road response. The predicted response is then compared to the measured response. A sensitivity analysis also helps determine which parameters should be adjusted to best fit actual conditions. Also the LTPP database can be used for calibration in addition to data related to material properties, traffic data, and pavement performance data provided by other DOTs. In the long term, the calibrated model is used in conjunction with existing Mechanistic-Empirical design models and Mechanistic-Empirical Pavement Design software to improve the design method. The data can be put into a format directly useful to designers and engineers. Since 2001, the New York State Department of Transportation (NYSDOT) has significantly invested in instrumenting test pavement sections to acquire local data to improve calibration of Mechanistic-Empirical Pavement Design software. The instrumented field pavements in New York include Interstate 490, Interstate 90, and Interstate 86. The installed sensors are still functioning to an extent that permits data collection of additional useful scientific information, and I-490 is providing high-quality data that will positively impact future design, construction, and maintenance of roads. As NYSDOT progresses in its adoption of the Mechanistic-Empirical Pavement Design approach, the test sections it has invested in over the past decade will play a key role in the validation of that approach. In addition to collecting load response data, it will be possible to assess the long-term performance of these pavements. (Mechanistic-Empirical Pavement Design requires both.) An extended study will verify that the performance benefit is maintained in the long term and that these designs will save money in the long run. Additionally, on I-86, three different concrete pavement rehabilitation techniques were tested previously, with some differences in the performance. Extended study will provide a definitive conclusion of which method provides the best performance and is the most economical. Several states previously have conducted projects using instrumentation in pavement test sections to collect pavement performance data. In addition to the three I-86 sections instrumented to measure deflection, strain, and temperature in order to study different techniques of portland cement concrete (PCC) pavement rehabilitation, additional sections on I-490 and two sections on I-90 are being used to measure the effects of varying base types. Other states such as Ohio, Minnesota, and Delaware, among others, have instrumented concrete sections to collect data which can be used for analysis. The sharing of data from multiple DOTs and geographic regions (via resources such as the LTPP database) adds significant value to pavement performance modeling tools and to the body of scientific knowledge; this pooled approach among multiple sources/DOTs also offers a more efficient and economical manner than on an individual basis. The objectives of this study include: (1) Collecting load response and performance data and environmental monitoring at selected test pavements for four years. (2) Installing new instrumented sections as needed for a better understanding of rigid pavement response, including monitoring for the duration of the project. (3) Determining the impact of a base and other components (such as dowel bars, tie bars, etc.) on long-term performance of rigid pavement utilizing the data acquired and other nationally available data on the topic. (4) Documentation of the processes, procedures, and findings. (5) Finalization of the rigid pavement design catalog with local validation and calibration of mechanistic-empirical models.

About the research

Concern has been expressed about the deicer scaling resistance of concrete containing slag, especially when the dosage of slag exceeds 50% of the total cementitious material in the mixture. Much of the concern appears to be based on the results of laboratory scaling tests based on ASTM C 672, despite indications that such mixtures often perform well in the field.

The initial phase of this study showed that construction-related issues played a bigger role in the observed scaling performance than did the amount of slag in the concrete mixture. The work also indicated that the test method (ASTM C 672) may be more severe than most environments. A second phase developed an alternative laboratory test method to ASTM C 672 that would better represent the field performance of concretes, based on a method from the Canadian Quebec Ministry of Transportation.

The work described in this report was to repeat some tests using similar materials in a second laboratory to evaluate repeatability of the test methods.

About the research

Nationally, there is concern regarding the design, fabrication, and erection of horizontally-curved steel girder bridges due to unpredicted girder displacements, fit-up, and locked-in stresses. One reason for the concerns is that up to one-quarter of steel girder bridges are being designed with horizontal curvature. The concerns are significant enough that a National Cooperative Highway Research Program (NCHRP) research problem statement was developed and given high priority for funding.

It is also noted that an urgent need exists to reduce bridge maintenance costs by eliminating or reducing deck joints. This can be achieved by expanding the use of integral abutments to include curved girder bridges.

The long-term objective of this effort is to establish guidelines for the use of integral abutments with curved girder bridges. The primary objective of this work was to monitor and evaluate the behavior of six in-service, horizontally-curved, steel-girder bridges with integral and semi-integral abutments. In addition, the influence and behavior of fixed and expansion piers were considered.

About the research

State highway agencies are increasingly intersted in using recycled asphalt shingles (RAS) in hot mix asphalt (HMA) applications, yet many agencies share common questions about the effect of RAS on the performance of HMA. Previous research has allowed for only limited laboratory testing and field surveys. The complexity of RAS materials and lack of past experiences led to the creation of Transportation Pooled Fund (TPF) Program TPF-5(213). The primary goal of this study is to address research needs of state DOT and environmental officials to determine the best practices for the use of recycled asphalt shingles in hot-mix asphalt applications.Agencies participating in the study include Missouri (lead state), California, Colorado, Illinois, Indiana, Iowa, Minnesota, Wisconsin, and the Federal Highway Administration. The agencies conducted demonstration projects that focused on evaluating different aspects (factors) of RAS that include RAS grind size, RAS percentage, RAS source (post-consumer versus post-manufactured), RAS in combination with warm mix asphalt technology, RAS as a fiber replacement for stone matrix asphalt, and RAS in combination with ground tire rubber. Field mixes from each demonstration project were sampled for conducting the following tests: dynamic modulus, flow number, four-point beam fatigue, semi-circular bending, and binder extraction and recovery with subsequent binder characterization. Pavement condition surveys were then conducted for each project after completion.

The demonstration projects showed that pavements using RAS alone or in combination with other cost saving technologies (e.g., WMA, RAP, GTR, SMA) can be successfully produced and meet state agency quality assurance requirements. The RAS mixes have very promising prospects since laboratory test results indicate good rutting and fatigue cracking resistance with low temperature cracking resistance similar to the mixes without RAS. The pavement condition of the mixes in the field after two years corroborated the laboratory test results. No signs of rutting, wheel path fatigue cracking, or thermal cracking were exhibited in the pavements. However, transverse reflective cracking from the underlying jointed concrete pavement was measured in the Missouri, Colorado, Iowa, Indiana, and Minnesota projects.

About the research

The Institute for Transportation (InTrans) at Iowa State University was a subcontractor to the Minnesota Department of Transportation on this transportation pooled fund study (TPF-5(132)). InTrans researchers made signifinant contributions on this project and links to the project pages are provided here.