Papers by Keyword: Class C Fly Ash

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Authors: Lucie Vodová, Radomír Sokolař
Abstract: Fluidized fly ash (class C according to ASTM) from thermal power plants Hodonin and Ledvice and stoneware clay B1 were used in the experimental work dealing with SO2 emissions during the firing at 1200°C. The aim of the work was to define the temperature at which sulphur dioxide begins to leak, and the leakage rate of SO2. It was found that temperature of decomposition of anhydrite depends on particle size. For milled fly ash is this temperature 150°C lower than for unmilled ashes. The addition of clay also decreases the temperature of decomposition. Sulphur dioxide begins to leak at 975 °C for samples with 40% addition of fly ash.
Authors: Chandani Tennakoon, Kwesi Sagoe-Crentsil, Jay G. Sanjayan, Ahmad Shayan
Abstract: The present study evaluates potential re-use options for two different types of brown coal fly ash (class C) sourced from Australia as feedstock for geopolymer binder systems. The study covers analysis of fundamental material and mix-design requirements for geopolymer binders as a basis to achieve durable brown coal ash geopolymer matrices. The study established that reference unblended 100% brown coal ash geopolymer mortar samples yielded low strength, typically below 5MPa and poor durability. However, appropriate blends of brown coal ash with selected black coal fly ash (class F) and blast furnace slag to achieve target Si/Al ratios significantly enhanced both setting characteristics, as well as early age compressive strength development (25-35MPa) while improving overall durability performance compared to reference mixes. Moreover, lagoon fly ash blended geopolymer shows better durability while dry precipitator fails to perform well. The discussion also focuses on key source material parameters and reaction processes that influence compressive strength and durability behaviour of marginal brown coal ash sources during geopolymerisation reactions.
Authors: Patthamaporn Timakul, Kanyarat Thanaphatwetphisit, Pavadee Aungkavattana
Abstract: This study investigated the effect of silica to alumina ratio on the compressive strength of geopolymer. The high calcium fly ash (Class C, ASTM 618) wastes from Mae Moh Thailand power plant, which is SiO2 (30.97%) and Al2O3 (17.16%)-rich materials was employed as the main solid part to prepare geopolymers, apart from kaolinite. The combination of sodium hydroxide (NaOH), sodium silicate (Na2SiO3) solution, and distilled water as 1:1:4 mass ratios were used as the liquid activator. The curing temperature in the oven was fixed at 75oC and varied curing time for 24, 48, 72 and 96 hours. Further curing was done at room temperature for 28 days before characterizations. XRD study of synthesized geopolymers showed a hump of not well-defined peaks and some major peaks of quartz, and unreacted kaolinite indicating the incomplete geopolymerization reaction. Infrared study showed the Al-O-Si and Si-O-Si bonds in all geopolymers samples. The compressive strength of geopolymer increased from 32 to 40 MPa when the ratio of SiO2 : Al2O3 was increased from 2.60 to 2.65. However, the compressive strength was decreased after increasing the SiO2 : Al2O3 ratio from 2.65 to 3.0. The highest compressive strength was found when the SiO2 : Al2O3 ratio was 2.65 with the curing condition at 75oC for 96 h which the samples also possessed high density.
Authors: Xiao Lu Guo, Hui Sheng Shi, Mao Song Lin, Wen Jing Dong
Abstract: Geopolymers with calcium contents were prepared from class C fly ash, metakaolin, and Ca(OH)2. Geopolymer products and ordinary cement hydration products were divided with gradient acid dissolution test. The effects of calcium in class C fly ash geopolymer were investigated through the calcium concentration of acid solution. In an appropriate alkali situation, most of the calcium will be dissolved from class C fly ash. Part of the calcium will react with silicate and aluminum to form geopolymeric gels as the presence of gismondine (zeolite). Part of calcium was hydrated to form calcium silicate hydrate(C-S-H), and the rest of calcium may be adsorbed within the geopolymeric binding structure to balance charge anion. The class C fly ash geopolymer is a composite system with the coexistence of geopolymeric and C-S-H gels.
Authors: Xue Ying Li, En Zu Zheng, Chun Long Ma
Abstract: The compressive strength of geopolymer prepared from a class C fly ash (CFA) at different curing conditions and mass ratio of water to fly ash were investigated. The geopolymer was activated with a mixed solution of sodium hydroxide (NaOH) and sodium silicate. The results revealed that the obtained compressive strength was in the range of 11.7~61.9MPa and the compressive strength decreased with the increment of the mass ratio of water to CFA (W/F). The geopolymer samples with the highest strength were obtained when W/F was 0.30 with proper delay time 1d before being demoulded and then followed by curing at 60°C for 24h. For geopolymer with lower W/F (0.30), its optimum curing temperature was better not higher than 60°C, however, for the higher W/F, the curing temperature was suit to more than 70°C.
Authors: Xiao Lu Guo, Hui Sheng Shi
Abstract: In this paper, leaching behavior of heavy metals from the class C fly ash (CFA)-based geopolymers were studied. The CFA-based geopolymers were prepared from CFA, flue gas desulfurization gypsum (FGDG), and water treatment residual (WTR). The extraction-leaching concentrations of heavy metals from CFA-based geopolymers were lower than their maximum concentration limits according to the U.S. environmental protection law. And the encapsulated and fixed ratios of heavy metals by the CFA-based geopolymers were 96.02~99.88 %. The dynamic real-time leaching concentration of Pb (II) were less than 1.1 µg / L, Cr (VI) less than 3.25 mg / L while Hg (II) less than 4.0 µg / L. Additionally, dynamic accumulated leaching concentrations were increased at the beginning of leaching process then kept stable. The leaching results indicated that the security of heavy metals in CFA-based geopolymer was safe.
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