Abstract
Mechanical activation of the calcium-rich fly ash formed in circulating fluidized bed combustion (CFBC) boilers was investigated to enhance the compressive strength performance of the pastes. We studied the effect of the activation on the physical, chemical, and mineral characteristics of fly ash and its pastes. Our study shows that already a short mechanical activation yields a 10-fold improvement in the compressive strength of the pastes, reaching 60 MPa after 90 days of curing without any chemical activation or blending. Mechanical activation caused fragmentation of large porous aggregates in the raw ash enhancing the physical properties and reactivity of fly ash particles. Similarly to calcium sulfoaluminate cements, the mechanical strength was provided by the formation of abundant ettringite and possibly C-(A)-S-H gel-like phase that created a highly compact microstructure. Our findings suggest that mechanically activated Ca-rich CFBC fly ash can be successfully used as an alternative binder.
Highlights
Notwithstanding the increasing pressure to reduce cement clinker production, the second largest industrial CO2 emitter [1], the demand for cement and concrete remains high in general construction practices and is predicted to grow by more than 20% in the coming decades [2]
Marjanovic et al [47] has shown more than 10fold increase in the compressive strengths of geopolymers made of mechanically activated thermal power plant fly ash, when compared to geopolymer made of raw ash precursor
Cement-free activation of Ca-rich fly ash, combining mechanical activation and blending with silica fume and flue gas desulfurization gypsum as a grinding aid, and/or polycarboxilate ether based plasticizer additive and NaOH alkali activation, was reported to yield ca. 35% increase in compressive strength, topping at 46 MPa in 28 days, compared to blends without mechanical activation [48]
Summary
Notwithstanding the increasing pressure to reduce cement clinker production, the second largest industrial CO2 emitter [1], the demand for cement and concrete remains high in general construction practices and is predicted to grow by more than 20% in the coming decades [2]. To overcome these issues, research and innovation in the cement and concrete field has been aimed at making radical changes towards sustainable concrete use and to find suitable less greenhouse gas-intensive replacements [3]. Class C ashes have a highly variable chemical and phase composition [11], that impedes their usability in the construction field
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