Nearly two billion tons of aggregate are produced every year in the United States. Although this production contributes significantly to the economy, the by-products associated with the process are often considered waste. According to the International Center for Aggregates, the stockpiling and disposal of aggregate by-products is a major problem facing the aggregate industry.
In a research project completed in June 2015, “Sustainable Aggregates Production: Green Applications for Aggregate By-Products” (R27-125), ICT researchers investigated methods for using aggregate by-products to help lower construction costs for the Illinois Department of Transportation (IDOT) and extend the use of natural aggregate resources. That study addressed quarry production techniques and properties of selected samples of quarry fines and contains recommendations about potential sustainable uses of fines.
In September 2015, a second-phase study was initiated. The main objective of this follow-up research project, “Field Performance Evaluations of Sustainable Aggregate By-product Applications” (R27-168), is to determine the most successful sustainable/green applications for using large quantities of quarry by-products (QB) in road construction. The project is slated to end in early 2018 with publication of a final report that includes field test results and characterizations for QB samples. The report will also contain recommendations for revisions to IDOT’s Standard Specifications for Road and Bridge Construction, as well as suggested modifications to IDOT’s Subgrade Stability Manual. In addition, typical field scenarios will be prepared as example designs for successful green QB applications.
Erol Tutumluer, professor in the Department of Civil and Environmental Engineering at the University of Illinois at Urbana-Champaign, is the principal investigator (PI); Hasan Ozer, research assistant professor, is the co-PI. Issam Qamhia, a third-year PhD student in civil engineering, serves as research assistant on the project.
“This project focuses on national and state priorities for research in the area of sustainable pavement construction with aggregates,” Tutumluer says. “According to a recent state survey, the excessive QB produced each year in Illinois can be up to 950,000 tons—or even greater. Through test section construction and accelerated pavement testing, we are evaluating in the field the use of QB and their blends for optimizing pavement thickness requirements.”
He adds, “One of the most promising areas for utilizing bulk amounts of QB is to blend them into the voids of large-sized virgin (primary crusher run) or recycled aggregate subgrade materials. Another very promising application is the chemical admixture stabilized subbase/base uses of QB. What we learn from this field study will not only help us build more sustainable, longer-lasting, and resilient road infrastructure—it will also provide the beneficial application of QB for improving efficiency of aggregate production and economic and environmental benefits.”
In the project, full-scale test sections were constructed at the Advanced Transportation Research and Engineering Laboratory (ATREL) in Rantoul, Illinois, to demonstrate innovative and sustainable uses of QB applications. Construction of the field pavement test sections at ATREL occurred over a three-week period in August 2016.
The test sections were constructed using the most promising applications for QB materials:
- Replacing embankment and/or subgrade/subbase
- Filling gaps/voids between large stones as aggregate subgrade on soft subgrades
- Blending with coarse aggregate fractions of virgin/recycled materials and other additives (such as fibers) for use as a subbase/base
- Increased fines content in dense-graded subgrade replacement and subbase
- Using as a cement or fly-ash-treated subbase (i.e., in inverted pavements)
- Using as a cement or fly-ash-treated subbase for use as a base
The constructed sections are being tested to failure using the Accelerated Transportation Loading System (ATLAS). ATLAS is used to evaluate full-scale transportation systems by subjecting them to real-life traffic and environmental conditions.
A full suite of strength, modulus, and deformation characteristics are being investigated in the laboratory to fully characterize the engineering behavior of QB. The pavement test sections will then be checked against current mechanistic pavement design requirements and adequacies from the field testing.
The project is expected to be completed in February 2018. The research findings will be used to develop performance evaluation criteria and create appropriate specifications for the use of aggregate by-products in sustainable pavement applications. This is expected to have an immediate impact on sustainable road construction practices in the State of Illinois by reducing total energy consumption and greenhouse gas emissions per ton of aggregate production—and bring significant savings to IDOT construction projects.
Sheila Beshears, Aggregate Technology Coordinator for IDOT’s Bureau of Materials and Physical Research, is the chair of the project’s Technical Review Panel. She explains in further detail: “Although IDOT already has a comprehensive sustainability program in place, there is always room for improvement. The one area that has been neglected is the increased amount of fines produced at the aggregate plants as a result of HMA mixes requiring finer coarse aggregates. The goal of this research is to find new uses for these products within the current IDOT pavement structure.”