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Illinois Highway Materials Sustainability Efforts

Posted by Content Coordinator on Wednesday, September 10th, 2014



The Illinois Department of Transportation (IDOT) has many years of experience using a variety of
reclaimed and recycled materials in highway construction. Major material use in highway
construction is in the form of aggregates, concrete, and hot-mix asphalt (HMA). It should be no
surprise that reclaimed and recycled material use is aligned with usage of these basic construction
materials. This report presents the quantity of materials used in 2013, along with specific reporting
as required in Illinois Public Act 097-0314. Specific reporting on use of shingles, along with efforts
to reduce the carbon footprint and to achieve cost savings through the use of recycled and
reclaimed materials, in asphalt paving projects is presented.

In 2013, reclaimed and recycled materials totaling 1,713,296 t were used in Illinois highways. On a
tons per mile basis, the amount of recycled materials used 2013 was nearly a fourfold increase
over the amount in 2009. These materials were valued at more than $58 million, which is a
reduction from the 2012 value because of a revised approach in determining reclaimed material
values in this report.

The materials used by IDOT in highway construction can be summarized in four major groups,
which are items that relate to uses of aggregate, HMA, concrete, and other. The latter category is
made up of by-product lime used for soil modification, glass beads used for pavement-marking
retroreflectivity, and steel used for reinforcement. The HMA category includes slags used as
aggregate, crumb rubber, reclaimed asphalt pavement (RAP), and reclaimed asphalt shingles
(RAS). Concrete-related materials include fly ash, ground granulated blast furnace slag (GGBFS),
and microsilica used to replace cement or provide specific properties to the final concrete product.
Aggregate use consists of recycled concrete material (RCM) and RAP used as an aggregate in lieu
of natural aggregates.

The use of RAS has grown to 39,791 t in 2013, which is a 221% increase over 2012 quantities.
This increase is the result of a combination of reasons: six additional RAS processing facilities,
HMA plant modifications by contractors, specifications that increased asphalt binder replacement
(ABR) from both RAP and RAS, marketing efforts of the RAS producers, and under-reporting of
usage for 2012. The number of districts to which the contractors supplied RAS in HMA projects
increased to seven in 2013 from four in 2012.

Warm-mix asphalt (WMA) technologies can provide environmental benefits through the use of less
fuel for heating HMA. After being criticized for having an overly burdensome process for adoption of
WMA technologies, IDOT developed a reciprocity procedure with other states and as of April 15,
2013, accepts 15 WMA technologies. Even with this policy change, which removed a main barrier,
use of WMA in 2013 was 124,599 t, or approximately 3% of the HMA placed in 2013. When
contractors responded to a questionnaire on WMA use, many cited the lack of a clear economic
benefit as a reason for not using this technology.

Contractors with HMA projects in 2013 were provided a questionnaire about HMA, RAS, RAP, and
recycling in general. The responses indicated that HMA plant upgrades with the addition of bins,
tanks, and controls were a major factor in being able to take advantage of high recycling values
allowed in current specifications. The contractors were generally pleased with RAS specifications
and the RAS material being supplied. Once a plant was set up to use RAS, the contractor expected
continued use of mixes containing this material. Local agency projects likely utilize as many or
more tons of RAS annually than state projects do, although exact amounts are not known. process and transport excess material rather than dispose of it; however, transportation logistics can be difficult to overcome.

In 2012, IDOT initiated an effort to develop a total recycle asphalt (TRA) mix that could be supplied with approximately 97% recycled material. The TRA does not use any newly mined material and relies on slag and RCM for aggregate, along with RAP and RAS. Approximately 3% new soft paving asphalt binder is added to the mix to obtain the required properties for pavement use.

In 2013, IDOT let and constructed three TRA projects. Construction bid savings from these projects ranged from 4% to 26% over the cost of a nearby conventional HMA project. Pre- and postconstruction surveys were conducted in Fall 2013 and Spring 2014 and the performance data recorded. Out of the three TRA projects, one experienced high-severity distress along 82% of the length of the pavement centerline. Other performance differences will require additional monitoring over time. For TRA and other high-recycle mixes, it is essential that the performance be the same as traditional HMA mixes; otherwise, any savings in construction will be spent to repair or replace the pavement sooner than expected.

Current limits on ABR are controlled by specification and have been increased over time. Owing to the lengthy time of adoption of high ABR mixes, construction, and performance feedback, it is not known whether these changes result in performance equivalent to traditional HMA. Fracture energy and modulus testing on various high ABR mixes indicated that it is possible to differentiate among various mixes using those test methods. Research work is underway to establish fracture energy testing protocols and specifications, with the goal of adopting testing procedures to ensure adequate performance properties in high ABR mixes.

An environmental evaluation of these and other mixes was conducted. This evaluation showed that increased ABR was a prime factor in reducing greenhouse gases and reducing overall energy consumption caused by the high-energy content of asphalt binder. The use of steel slag, although a recycled material, caused an increase in greenhouse gases because of the material’s high specific gravity. The increase was primarily from transportation of additional material to produce the volume of mix needed and the extra heating required on the increased mass.

Finally, IDOT has taken steps to increase sustainability efforts by modifying the cooperative research agreement with the Illinois Center for Transportation at the University of Illinois at Urbana- Champaign to focus more on sustainability issues and chartering a sustainability committee.

Figure 1. Reclaimed material use, 2013.

Download full version (PDF): Illinois Highway Materials Sustainability Efforts

About the Illinois Center for Transportation
The Illinois Center for Transportation (ICT) is a premier transportation research center that builds on the experience of renowned experts in transportation and related fields at the University of Illinois, the Illinois Department of Transportation (IDOT), and other universities in Illinois and across the country by providing the appropriate tools and support required for objective research. 

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