Biomass and coal fly ash in concrete: Strength, durability, microstructure, quantitative kinetics of pozzolanic reaction and alkali silica reaction investigations.

摘要

Biomass represents an important sustainable energy resource, with biomass-coal cofiring representing among the most effective and cost efficient CO 2 reduction strategies. Fly ash generated during coal combustion represents a technically advantageous, inexpensive, and environmentally beneficial admixture in concrete production, partially replacing cement. However, strict interpretation of American Society of Testing and Materials (ASTM) and American Concrete Institute (ACI) standards prohibits use of fly ashes from any source other than coal in concrete production; therefore, fly ash from biomass coal cofiring is excluded from use in concrete.; This dissertation discusses biomass impacts on concrete properties through experiments conducted on several combinations of blended and pure biomass fly ash in concrete mixtures to determine the effects on freshly mixed concrete, strength and durability of hardened concrete, and implication for long-term material properties. The results show that the performance of biomass and blended biomass-coal fly ash is comparable to that of traditional (neat) coal fly ash. Pozzolanic reactions occur simultaneously but not necessarily proportionally to strength development. Mixtures of biomass and coal fly ash in all proportions mitigate alkali-silica-reaction-based (ASR-based) expansion in concrete. Biomass-specific results indicate that biomass-containing fly ash samples can generate 3-6 times the strength of some neat coal fly ash samples in terms of pozzolanic reactions and that biomass-containing fly ash samples have better or comparable ASR mitigation performance relative to neat coal fly ash. Biomass fly ash applications in concrete production involve pozzolanic, cementitious, and ASR reactions in combination with mixture compositions and preparation techniques to dictate ultimate properties. In these practical applications, biomass fly ash demonstrates no consistent improvement or deprecation of concrete properties relative to coal fly ash. Quantitative pozzolanic reaction mechanism and kinetic analyses indicate biomass and coal fly ashes exhibit comparable reaction rates and react by similar mechanisms.; The general conclusion from the experiments is that biomass-containing fly ash, when used in concrete, performs comparable to or better than similar neat coal fly ash preparations in most respects; Substantial efforts were made to ensure samples represent typical commercial samples. Therefore, there exists no reason to exclude biomass from cofiring applications on the basis of fly ash performance in concrete and the related standards should be revised.