The primary goal of this project is to develop an environmentally friendly (i.e., green) concrete to reduce the significant environmental impacts associated with the use of traditional concrete. Typical concrete consists of sand/gravel bound together by Portland cement. In the concretes studied in this project, the sand/gravel will be replaced with recycled glass, and all of the Portland cement will be replaced with fly ash, which is a fine ash produced when coal is burned to generate electricity. This project will identify fly ashes from sources around the country that can be used in this new concrete. Concrete elements made with these ashes and recycled glass will then be tested to determine their engineering properties and durability. The project will conclude with a large-scale demonstration project. The benefits to society as a result of this research are at least twofold. The environmental impacts of using traditional concrete as a construction material are significant. Production of Portland cement is an energy intensive process, and is reportedly responsible for up to 7% of greenhouse gas emissions worldwide. Additionally, both the production of Portland cement and sand/gravel disturb virgin land. Conversely, the fly ash and recycled glass to be used in the proposed concrete represent two common waste streams. Thus, this new concrete minimizes energy use and environmental disturbance, while reusing waste materials. Additionally, the project will encourage interest and diversity in science and engineering by supporting students throughout its duration, including a Native American internship.
The primary goal of this project was to develop an environmentally friendly, sustainable concrete to reduce the myriad of environmental impacts associated with the production of traditional concrete, as well as reduce the volume of solid waste disposed in landfills. This study was focused on replacing 100 percent of the Portland cement in a given concrete mixture with fly ash (a byproduct of coal-fired power plants), and replacing the aggregate with recycled pulverized glass. The study included characterizing the engineering properties of this new concrete, as well as investigating appropriate design procedures for incorporating this new material in reinforced structural elements, such as beams and columns. A database with information on the 491 coal-fired power plants in the United States was screened based on macro-scale criteria to identify fly ashes that potentially offer sufficient self-cementitious behavior to serve as the sole binder in concrete. A total of 95 fly ashes were identified, and samples were obtained and tested for 15 of these ashes. Concretes subsequently made with these ashes and recycled glass aggregate were found to be viable for real-world applications, exhibiting controllable set times, adequate workability, and high early strength with significant strength gain over time. Concretes made with two of these fly ashes (i.e., from the Jefferies Energy Center in Kansas and Laramie River Station in Wyoming) and recycled glass aggregate were then evaluated further with a suite of mechanical and durability tests. Overall, these fly ash/glass concretes performed well. They exhibited 28-day unconfined compression strengths in excess of 4,000 psi (the standard for conventional structural concrete), although their corresponding tensile strengths were somewhat lower than would be expected for conventional concretes. Relative to durability, the concretes performed as well as conventional concrete specimens; however, further research is needed to better understand and improve their freeze-thaw resistance. The structural performance of these concretes was then evaluated with a series of beam tests. Duplicate specimens of three beam designs were tested for each of the fly ash/glass concretes. Results from these beam tests were compared to conventional concrete control specimens and building code capacity predictions. For two of the beam designs, the conventional concrete beams slightly outperformed the fly ash/glass concretes. The better performance of the conventional concrete in these two cases was attributed to its more robust compressive stress-strain response and increased tension strength relative to the fly ash/glass concrete. With respect to the applicability of building code capacity equations to fly ash/glass aggregate concretes, observed beam capacities for all beam designs either closely approached or exceeded predicted capacities. Indicating the suitability of using these concretes in structural elements. This research culminated in a field demonstration project in which several 10-foot by 10-foot by 10-inch thick concrete slabs were placed on a roadway in Lewistown, MT. All work was done with conventional construction equipment; i.e., the concrete was mixed and transported in ready mix trucks, and finished via roller screed, steel trowel, and broom. The road slabs are performing well, and will provide valuable information regarding this concrete’s field performance under environmental and vehicle loads. This research demonstrated that self-cementitious fly ash based concretes with glass aggregate can be suitable for use in nonstructural and structural applications. Although this research only had resources to thoroughly analyzed two fly ashes, this research identified and tested an additional 15 ashes that showed promise for use as the sole binder in concrete. Furthermore, these 15 ashes were only a subset of the 95 ashes identified as having the potential to serve as the sole binder in concrete.
