Development and Testing of Synthetic Riprap Constructed from Coal Combustion Products (CCPs)

摘要

Since the 1930's, fly ash - a pozzolanic material - has been used as a partial replacement of portland cement in concrete to improve the material's strength and durability, while also limiting the amount of early heat generation. From an environmental perspective, replacing cement with fly ash reduces concrete's overall carbon footprint and diverts an industrial by-product from the solid waste stream. Unfortunately, only about 40% of fly ash is reclaimed for beneficial reuse, with the remaining 60% disposed of in landfills. In some instances, the reason for only a 40% use rate is the lack of a viable market, but in other instances, it is because the fly ash does not meet the required specification for use in concrete or as soil stabilization. For instance, current specifications limit the carbon content of fly ashes used as partial replacement of cement in concrete to less than 6%. However, Ameren Corporation's (Ameren) Sioux Power Plant and other plants containing cyclone-fired boilers produce ash with very high levels of unburned carbon, often in the 20 to 50% range. Furthermore, activated carbon injection for mercury control will usually increase the carbon content of fly ashes from conventional boilers, reducing potential sales of ashes from these plants as well. In general, higher carbon contents reduce the reactivity of the ash and the efficacy of air-entraining admixtures. There are several ranges of potential products depending on the specific applications, such as armoring shorelines, streambeds, bridge abutments, and pilings against scour and ice damage. Scour is particularly critical for bridge abutments and pilings, as it is the number one cause of bridge failures. The proposed project will include evaluation of coal combustion products (CCPs) from several Ameren power plants, product development, mix design development, and small-scale specimen construction and testing. This research project will serve as a proof-of-concept for synthetic riprap constructed from 90% CCPs.