Repurposing quarry waste while improving road base

Researchers are working to reduce waste in quarries across Illinois by repurposing the leftover material to improve the lifespan of roads.

Nearly two billion tons of aggregates are produced every year in the United States. Over the years, aggregate production has resulted in four billion tons of Quarry By-Product (QB) aggregates accumulating in 3,000 operating quarries across the U.S. The by-products associated with aggregate production are often considered waste.

Illinois Center for Transportation researchers and Illinois Department of Transportation staff are leading research efforts, which aim to improve pavement sustainability and longevity in Illinois by using QB aggregates. The research project, R27-168, “Field Performance Evaluation of Sustainable Aggregate By-product Applications,” is directed by Professors Erol Tutumluer and Hasan Ozer of ICT at the University of Illinois at Urbana-Champaign, and Ph.D. Civil Engineering candidate Issam Qamhia.

The researchers investigated the use of QB aggregates as unbound or chemically stabilized pavement layers. To accomplish that, 12 full-scale Hot-Mix Asphalt (HMA) roadway and four construction platform test sections were constructed at the Advanced Transportation Research and Engineering Laboratory (ATREL) of ICT, and were subjected to real-life traffic and environmental conditions. The test section’s performance was evaluated for surface deformation (rutting) and fatigue performance, which are indicators of pavement serviceability, using the Advanced Transportation Loading Assembly (ATLAS).

In addition to a conventional pavement section, two test sections were built as inverted pavements; and five utilized chemically-stabilized QB aggregates blended with recycled aggregates as a base layer. Inverted pavements have a conventional aggregate base constructed on top of a relatively strong chemically-stabilized subbase. To improve the service life of the pavement, stabilizers (cement and Class ‘C’ fly ash), various recycled materials, and QB aggregates were used.

The study concluded that all five sections with chemically-stabilized QB aggregate base, and the two inverted pavement sections, particularly the inverted pavement section with cement-stabilized QB aggregates, performed well. This could be a direct result of reduced stresses on weak supporting subgrade soil. The pressure on top of the subgrade soil was measured at three to five times lower than pavements constructed using conventional aggregate base materials.

Following the completion of ATLAS loading, several tests were conducted to verify the outcome of the loading tests, including Falling Weight Deflectometer (FWD) and Dynamic Cone Penetration (DCP). In addition, sections were flooded with water to verify their susceptibility to water and then trenched to observe any physical changes.

“Through test section construction and accelerated pavement testing, this research has successfully demonstrated in the field the effective uses of QB aggregates and QB aggregates mixed with 6-inch stones for building more sustainable, longer-lasting, and resilient road infrastructure,” project Principal Investigator Erol Tutumluer said. “These beneficial applications of QB aggregates will no doubt improve the efficiency of aggregate production and provide state and local agencies with economical road construction alternatives and environmental benefits.”

IDOT Engineer of HMA, Aggregate and Chemical Tests and project Technical Review Panel Chair Jim Trepanier said, “This research has shown that QB aggregates blended with cement can improve the performance of base, subbase, and subgrade layers. The key to successful widespread usage of the QB aggregates will be to identify cost effective means to apply the blended QB aggregate products in these applications.”

Overall, the results obtained from the study showed that QB aggregates can be successfully incorporated in standard pavement construction to enhance stability and lower permanent deformation of subgrade soils, while reducing environmental and economic impacts caused by QB aggregates accumulation at quarries.