By Juan Pava, Amy Schutzbach, and Megan Swanson
Each year, the American Association of State Highway and Transportation Officials (AASHTO) Research Advisory Committee (RAC) solicits department of transportation research programs for the best research projects from across the country. These high value research projects are shared regionally, with each state’s RAC members voting to select the four most outstanding projects submitted for their region. These projects are then nationally recognized as AASHTO’s Sweet 16 High Value Research Projects for that year.
Since the inception of the Sweet 16 in 2010, IDOT’s research with ICT has been recognized as a Sweet 16 project in four consecutive years:
On March 31, 2015, IDOT submitted the following IDOT/ICT High Value Research projects for consideration as AASHTO Sweet 16 High Value Research Projects:
Mechanistic–Empirical Design, Implementation, and Monitoring for Flexible Pavements (14 Years, $1,327,504)
The objective of this series of projects (ICT R28-1, R28-2, R39, and R27-060) was to update Illinois’ mechanistic–empirical (M–E) full-depth hot-mix asphalt (HMA) pavement design procedures to reflect current Illinois materials and mixture design practices. These projects also supported a variety of M–E flexible pavement analysis, design, implementation, and monitoring activities. Additionally, the philosophy of an extended-life HMA pavement design procedure—one in which the tensile strain at the bottom of the asphalt layers was limited to 70 microstrain in order to eliminate the development of fatigue cracking—was established. Extensive lab testing was undertaken, full-scale pavement sections were constructed, accelerated loading was conducted, and responses under loading were measured to evaluate performance.
These projects developed implementable products in multiple areas. They provided assistance in the incorporation of IDOT-specific HMA modulus–temperature relationships, fatigue algorithms, design reliability/traffic multiplier factors, and maximum HMA thickness concepts into IDOT’s pavement design manuals for both state and local agencies. They also investigated the limiting strain theory and developed maximum thickness values for full-depth HMA and HMA overlays on rubblized concrete pavements, and provided guidance in the study of cold in-place recycling and full-depth recycling with asphalt products.
The real impact of this research occurred with its implementation. The Pavement Design chapter of IDOT’s Bureau of Design and Environment Manual was updated between April 2011 and March 2013 to reflect the new asphalt fatigue algorithm for both full-depth HMA and rubblizing design procedures, which reduced pavement thickness approximately 1.5 to 2.5 inches for the average pavement design statewide.
An analysis was conducted to determine the value of that one aspect of the research. Costs for all of these research projects (R28-1, R28-2, R39-1, and R27-60), which provided the technical background for the design updates, totaled $1,327,504—translating into an average annual cost of $93,685 per year over the life of the research and implementation efforts.
HMA pavement projects awarded between 2008 and 2014 were reviewed to determine pavement thickness savings using the new pavement design procedures. Benefits were estimated to be a savings of 63,180 tons of HMA binder annually, valued at $5.1 million. Additional benefits to the environment in the form of reduced CO2 emissions were estimated to be approximately 2,529 tons annually, with a value of approximately $96,000. Together, the total benefit realized from the HMA pavement design procedure refinement efforts totaled $5.2 million per year. This translated into an annualized benefit/cost ratio of 55.
These findings have helped shape Illinois’ pavement design policy and guidance, and provide longer lasting, cost-effective, and sustainable pavements for the people of Illinois. Additional reports for project R39 can be found at http://ict.illinois.edu/research/publications/.
Testing of Portland Cement (Current ASTM C150) with Limestone and Process Addition (ASTM C465) (33 months, $399,987)
The objective of this project was to study the performance of concrete mixes batched with cement containing different percentages of limestone and inorganic processing additions. Twenty-four concrete mixes with different cementitious combinations and aggregates were developed for this study. Each cement source was batched in a concrete mixture by replacing 30% of the total cement content with supplementary cementitious materials (SCMs), fly ash, or slag. Also, each cementitious combination was batched with fine aggregates (either natural or combined sand) and coarse aggregate (crushed limestone).
The study included measuring fresh properties such as the slump, air content, unit weight, and setting time. The hardened properties included measuring the strength and durability for each concrete mix combination. The strength results were measured in terms of compressive and flexural strength, and the durability results were measured in terms of rapid chloride penetration resistance (coulombs), water permeability (DIN 1048), chloride ion penetration, and freeze/thaw tests of the concrete mixes. The study found similar performance in terms of strength and durability of concrete between the conventional and modified cements and demonstrated the performance of the 24 concrete mixes with the SCMs and fine aggregate types.
Recommendations were made regarding the level of cementitious material content used in the concrete mix in order to maintain adequate strength at an early age (three- and seven-day) and to secure minimum, hardened entrained air content to resist the freeze/thaw attack.
With the demand for cement increasing, IDOT realized that this growing demand would have to be met by increased domestic production or by overseas supplements. IDOT wished to explore the feasibility of increasing cement production by exceeding the established ASTM C150 and C465 limits for limestone additions, while adhering to requirements to reduce CO2 emissions. It was also hoped that Portland cement manufactured under the new ASTM C150/AASHTO M85 specifications would produce a “greener,” more environmentally friendly product.
Mohsen Issa, professor in the Department of Civil and Materials Engineering, University of Illinois at Chicago, served as lead investigator of the study. He says the results showed that increasing the amount of limestone and inorganic process additions in cement in quantities exceeding 5% by weight and an increase of insoluble residue to 1.5% had negligible effects on the strength and durability properties of the concrete. Similar performance was observed in the concrete mixes with modified and conventional cement.
John Huang, chair of the IDOT Technical Review Panel for the project, adds that “although the cements with higher amounts of limestone had lower early-age strength, they still exceeded IDOT’s 14-day requirement for minimum compressive and flexural strengths.” On the basis of these findings, IDOT revised its specifications for the maximum limits of limestone addition to cement and created a new label, Type 1L, for that cement.
Development of a Traffic Incident Management Operational and Training Guide, Phase II (34 months, $374,669)
Crashes on the interstate can result in property damage, traffic delays, and sometimes loss of life. Unfortunately, these events can sometimes be compounded when secondary crashes occur if incident responders unknowingly create additional traffic conflicts for the motoring public. The overall goal of both phases of this project was to reduce responder fatalities and injuries, as well as to prevent secondary crashes, especially those involving incident responders. The phases of this project worked toward this goal by creating training materials to help incident responders work more safely and effectively.
To address the need for promptly training all traffic incident responders in the State of Illinois, Phase II of this project created online modules to supplement the in-class training developed as Phase I. Based on the recommendations of the project’s Technical Review Panel, responder feedback, and suggestions from the Federal Highway Administration, researchers identified material that could be presented online as a prerequisite to the in-class training. Additionally, this project modified the existing in-class training to obtain endorsement by the Strategic Highway Research Program II (SHRP-II) as equivalent to their national program. The researchers created 11 online training modules, each lasting between 15 and 30 minutes, allowing responders to view the training modules in multiple sessions as necessary. The researchers also created an online video game and an in-class trivia game. The online video game allows responders to refine their traffic control and vehicle-positioning skills.
To date, more than 3,000 responders from law enforcement, fire and rescue, transportation, and the towing and recovery sectors have been trained. Attendees have consistently ranked this training highly (4.5+ on a 5-point scale) and have ranked the instructors as highly knowledgeable (4.7+ on a 5-point scale). The impact is expected to be a clear and direct correlation to a decrease in responder injuries and fatalities, the number of secondary incidents, and a reduction in travel time related to congestion caused by these incidents. As more personnel are trained, Illinois expects to continue to witness an increase in safety and mobility with respect to incidents.
Principal investigator Ryan Fries, associate professor in the Department of Civil Engineering at Southern Illinois University Edwardsville says that developing online training was critical. “Some first responders can’t attend in-class training sessions, so the online modules provide an opportunity for them to learn important safety practices for managing traffic incidents on our roads. The training will be available online from anywhere at any time, without the recurring costs of trainers and facilities.”
According to IDOT’s Technical Review Panel chair, Geno Koehler, the benefits of the training are clear: “Improved practices increase safety along Illinois roadways—creating quicker responses to crashes and other incidents, cutting down on lane restrictions, and reducing secondary crashes.” In addition to improving safety, the training is expected to improve communication, coordination, and cooperation among emergency responders throughout the State of Illinois.
Impact of HPMS Sample Counting for 24 Hours Versus 48 Hours (13 months, $25,400)
The objective of this project was to evaluate the differences of average annual daily traffic computed from 24-hour and 48-hour traffic counts.
IDOT had conducted research in the 1980s comparing the two count durations and had been following the conclusions from that study in conducting 24-hour counts on state routes with an approved waiver from FHWA in 1992. Because traffic patterns have changed over the years, IDOT wanted to review the relative differences between the two count durations. IDOT’s concern was that the collection of 24-hour counts, as opposed to 48-hour counts, would enable more efficient use of agency resources, yet still maintain the statistical integrity of the annual average daily traffic (AADT) estimation process for Highway Performance Monitoring System (HPMS) reporting.
IDOT’s automated traffic recorder (ATR) continuous-count traffic data, collected from 103 statewide ATR locations, was used to perform a statistical analysis comparing the relative differences between 24-hour count periods and 48-hour count periods that are factored to compute the AADT. Statistical analyses were performed for statewide ATR data across various roadway functional classification categories and also split by District 1 (Chicago) and Districts 2–9 (downstate). In general, the analyses found that, with the application of appropriate daily traffic-count adjustment factors, the 24-hour counts were statistically comparable to 48-hour traffic counts.
This project allowed IDOT to secure an FHWA waiver on the HPMS sections to conduct 24-hour counts instead of the recommended 48-hour counts. This time savings on the counts allowed IDOT to better integrate the counts into the annual IDOT counting program and allow for additional counts to be conducted with the same resources by bringing the HPMS sections into alignment with the other locations. IDOT is able to conduct around 20,000 annual traffic counts with this waiver.
IDOT is proud to join with AASHTO RAC in promoting quality and excellence in research and in the application of research findings to improve state transportation systems.
Juan Pava is Work Zone Safety Engineer at IDOT’s Bureau of Safety Engineering;Amy Schutzbach and Megan Swanson are Engineer of Physical Research and Technical Research Coordinator at IDOT’s Bureau of Materials and Physical Research, respectively.