The objective of this project is to determine the long term durability and the possible economic benefits of using 100 percent fly ash concrete in construction applications. The binder material in traditional concretes for construction applications is Portland cement. While this binder material offers excellent performance in these applications, its production is an energy intensive process. A material that resembles Portland cement both chemically and physically is Class C fly ash, which is already being manufactured as a by-product of the combustion of coal to generate electricity at coal-fired power plants. The cementitious nature of this material is well documented, and it routinely has been used for years to replace some of the Portland cement in conventional concrete mixtures. Some fly ashs, such as the fly ash produced at the Corette power plant in Billings, Montana, however, are sufficiently cementitious to totally replace the Portland cement as the binder in concrete, and thus this ash, as well as other similar ashes, are currently being underutilized relative to the full benefit that they have to offer to the concrete industry. Furthermore, recent research on fly ash activation indicates that it may be possible to stimulate the cementitious behavior of many fly ashes to point where they can be used as the primary binders in concrete, they have become more motivated to explore extensive use of supplementary and alternate binders, such as fly ash, as a result of recent domestic shortages of Portland cement as well as increases in its cost.
Over the past several years, Montana State University (MSU) has been researching the role that Corette Class C fly ashes might have in concrete construction materials, principally with a view toward minimizing the myriad of environmental impacts associated with using traditional Portland cement concrete. In work done at MSU with concrete made with only Corette ash as the binder, it was quickly discovered that if offered exceptional performance with respect to short term strength gain (e.g., 2,900 psi at one day), long term ultimate strength (e.g., in excess of 4,500 psi at 28 days), and workability. Mix design procedures were subsequently developed for this 100 percent fly ash concrete in a series of ongoing projects at MSU. Additional work was also done to validate the engineering performance of this material in reinforced concrete elements, so that engineers could confidently design structural members using it. In order for this new concrete to be used in commercial applications, however, its durability and the potential cost benefits that it offers need to be further investigated.
The objective of this project is to evaluate these remaining performance and cost issues related to using 100 percent fly ash concrete in commercial construction applications, and to subsequently manufacture prototype item(s) using this material. Important durability issues include freeze-thaw, sulfate, and hydrogen sulfide resistance, and its performance with alkalisilica reactive aggregates. Tests will be done to experimentally assess the performance of this concrete in these environments. Relative to the commercialization, initial work will be done in the precast concrete arena. Precast concrete building products (e.g. septic tanks, manholes, curbstones, pipe, etc.) are manufactured at a plant rather than in the field, which offers the opportunity to more closely control and monitor the concrete manufacturing and placing process than is available in many field applications. Furthermore, this material may offer additional advantages over Portland cement concrete in this application than just reduced material costs. While work to-date has focused on ash available from a single source, the potential of other ashes available in the western and Midwestern regions to serve as the sole binder in concrete will also be investigated. Promising ash concretes (activated as necessary by water or by alkali solutions) from a workability and strength perspective will also be subjected to durability tests.
Jerry Stephens
Department of Civil Engineering, Montana State University
CE Department/MSU
Bozeman, MT 59717
(406) 994-6113 Telephone
(406) 994-6105 Fax
jerrys@ce.montana.edu