ICT researchers, lead by Director Imad Al-Qadi, and the Illinois Tollway have teamed up on a project involving the performance of warm mix asphalt (WMA), which has several environmental benefits compared to the performance of traditional hot-mix asphalt.
In recent years, WMA techniques have been developed to reduce hot-mix asphalt (HMA) production temperatures. WMA is mixed and placed on the road at lower temperatures (as much as 50 to 100 degrees Fahrenheit lower than HMA). Compared to traditional asphalt construction, this reduction in production temperature uses less fossil fuel and produces fewer emissions, therefore, benefiting the environment. WMA may also perform better – a question which Al-Qadi and his team intend to answer. The research team also plans to determine how long WMA needs to cure to develop its ultimate performance strength. Knowing this ideal timeframe will help the agencies decide how soon it can open traffic on their roadways following construction. A past concern was that their roadways were being opened to traffic too soon after construction, and consequently the pavements were being prematurely distressed.
There are two unique aspects about this research being conducted by Al-Qadi and his team. The first is that this research is on Stone Mastic Asphalt (SMA), a specially designed mix that contains fibers and/or additives that enhance its performance for heavy traffic interstate/expressway placement. Several SMA mixes are being analyzed, containing a specific warm-mix technology, recycled pavement materials, rubber, and/or recycled roofing shingles. The second unique aspect is that performance tests are being conducted on field-compacted samples, rather than laboratory samples. This was done to better simulate the actual curing of WMA and to avoid any effects that re-heating the WMA may cause.
A testing program of this level has never been attempted before: samples were tested from compaction time until seven days (and some tests up to three weeks) over specific periods and in accordance with the detailed testing program that includes analyzing material susceptibility to rutting and cracking. To achieve this, the team mobilized sixgyratory compactors to the asphalt production facility for each mix investigation. Two of the facilities, located in Aurora and Naperville, Illinois, were approximately 30 minutes from the construction location on I-355 near I-88. The third facility, located in Janesville, Wisconsin was approximately 45 minutes from the construction location on I-90 near Belvidere, Illinois. With the samples being compacted anywhere from 130 to 200 miles from the University of Illinois’ Advanced Transportation Research and Engineering Laboratory (ATREL) in Rantoul, Illinois, some samples needed to be flown immediately from a nearby airport to meet the strict performance testing schedule.
Back at ATREL, comprehensive laboratory tests were conducted on the samples upon arrival and over the course of seven days (and some over three weeks). Those tests include complex modulus, flow number, wheel tracking, indirect tensile (IDT) creep and strength, and semi-circular bending (SCB) fracture.Additionally, this research project aims to verify the early age rutting potential of the innovative warm-mix SMA, usinga lightweight deflectometer (LWD) forin-situperformance testing.
The anticipated results of this research are to have a performance evaluation of warm mix SMA at early age, which will allow pavement engineers and/or contractors to determine the minimum traffic opening time; especially for high traffic volume interstates or expressways. The early age performance will be based on stiffness, rut resistance, and life-cycle assessment (LCA). As a result of this study, the Illinois Tollway will have the information they need to select the best asphalt mix and maximize its performance for future projects, which will save them time and money while also providing environmental benefits when compared to traditional HMA.