Cementitious Spray Dryer Ash-Tire Fiber Material for Maximizing Waste Diversion

Spray dryer absorber (SDA) material, also known as spray dryer ash, is a byproduct of coal combustion and flue gas scrubbing processes that has self-cementing properties similar to those of class C fly ash. SDA material does not usually meet the existing standards for use as a pozzolan in Portland cement concrete due to its characteristically high sulfur content, and thus unlike fly ash, it is rarely put to beneficial use. This paper presents the results of a study with the objective of developing beneficial uses for SDA material in building materials when combined with tire fiber reinforcement originating from a recycling process. Specifically, spray dryer ash was investigated for use as the primary or even the sole binding component in a mortar or concrete. This study differs from previous research in that it focuses on very high contents of spray dryer ash (80 to 100 percent) in a hardened product. The overarching objective is to divert products that are normally sent to landfills and provide benefit to society in beneficial applications. 1. Introduction Portland cement concretes and mortars are used extensively in construction of buildings, bridges, and other infrastructure ranging from low-strength sidewalks to high-performance airport runways. Despite recent advances in manufacture, Portland cement remains an energy-intensive product that requires mining of raw materials as well as significant energy input and processing. Incorporation of coal fly ash into concrete mixtures is now widely accepted given its capacity to produce an equivalent or even improved hardened concrete product with less Portland cement and, therefore, reduced raw materials extraction and carbon emissions [1]. However, a substantial portion of fly ash produced each year goes unused, and a significant portion of the country’s ash material is deemed useless because it is involved in the flue gas desulfurization process within the spray dryer absorbers utilized at many of the United States coal power plants [2]. It is the material from this subset of plants, alternatively called spray dryer absorber material, SDA material, or spray dryer ash, that is the subject of this research. Spray dryer ash is produced in far smaller quantities than fly ash in the US. The American Coal Ash Association, ACCA, estimates 1.4？million？tons for all dry flue gas desulfurization products, of which spray dryer ash makes up a large portion [3]. While nearly 42 percent of all fly ash produced in the United States (approximately 72？million？tons annually [3]) is used beneficially, only about 25 percent