Title: Evaluating the Performance and Feasibility of Using Recovered Fly Ash and Fluidized Bed Combustion (FBC) Fly Ash as Concrete Pozzolan
Author(s): Farshad Rajabipour; Mona Zahedi; Gopakumar Kaladharan
Appears on pages(s):
Keywords: fly ash, FBC, fluidized bed combustion, SCM, supplementary cementitious materials, durability, pozzolan
Supplementary cementitious materials (SCM) are a key ingredient of today’s concrete and can vastly improve the durability (e.g., ASR mitigation) and sustainability of concrete mixtures. While the demand for fly ash (the highest used SCM) and other suitable pozzolans continues to grow, the supply of high-quality and specification-compliant fly ash has been shrinking. To maintain and expand the market share and ensure the durability of concrete products and structures, it is critical that a stable supply of high-duality and economical fly ash and other SCMs is available for foreseeable future. This study evaluates the feasibility, performance, and beneficiation of two alternative and abundant sources of fly ash: recovered landfilled fly ash and fluidized bed combustion (FBC) fly ash. Samples of both fly ashes were collected from an ash landfill in
Pennsylvania and two FBC power utilities in Pennsylvania. These fly ashes were characterized against the composition, physical properties, and performance requirements of ASTM C618. A statistical sampling plan was also developed for characterizing the heterogeneity of fly ash in landfills. The results show that the ash from the Pennsylvania landfill can be classified as ASTM C618 Class F ash and used in concrete after drying and particle size reduction (e.g., via sieving). Other ash landfilled should be evaluated on a case-by-case basis to determine (a) their heterogeneity, (b) their viability for use as concrete pozzolan, and (c) beneficiation measures that may be needed such as carbon reduction and separation of deleterious substances where possible. The results also show that FBC fly ashes from the two Pennsylvania powder plants generally meet the chemical and physical requirements of ASTM C618, with exception of elevated SO3 in one fly ash. Regardless, paving-grade concrete with good fresh and hardened performance could be prepared incorporation 20% of these fly ashes as a cement replacement. Further research 4 is recommended to evaluate other coal-based FBC fly ashes in the United States in terms of their properties, uniformity in time, and performance in concrete mixtures. Overall, it is determined that some FBC fly ashes have a very good potential for use as pozzolan. Specifications (prescriptive
or performance) need to be developed to identify good quality FBC fly ashes and enable their use as concrete pozzolan.