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Evaluation and beneficiation of high sulfur and high alkali fly ashes for use as supplementary cementitious materials in concrete
Highlights High sulfur and high alkali off-specification fly ash were evaluated as SCMs. Possible contaminants are calcium sulfate, calcium sulfite, or sodium sulfate. Flow, pore solution pH, setting, strength, and expansion potential were evaluated. Performance was mostly acceptable and beneficiation is possible in other cases. Current SO3 specification limits might be too conservative.
Abstract Coal-fuel power plants with semi-dry or dry flue gas desulfurization (FGD) systems produce high sulfur and/or high alkali fly ashes due to comingling of fly ash with FGD products. Such fly ashes do not meet the SO3 content limit (5.0% max.) of ASTM C618 or are unable to mitigate the alkali-silica reaction. The mineralogy of the sulfur present in these ashes can vary significantly (e.g., CaSO4, CaSO3, Na2SO4) based on the FGD technology used and this affects the performance of these fly ashes in concrete. Thus, the single SO3% limit of ASTM C618 is unable to capture the complexity and performance of fly ash, and this results in elimination of potentially viable pozzolans for concrete. This study performs a systematic investigation of the effect of SO3 type and content in fly ash on various performance parameters of cement-fly ash pastes and mortars, including workability (flow and flow retention), pore fluid pH, setting time, strength development, and potential for deleterious expansion. To better quantify and understand these effects, the study considers both real and doped fly ashes (i.e., a blend of specification-compliant fly ash with target sulfur compounds). The poor performance observed in the case of setting time and pore fluid pH was successfully mitigated using chemical admixtures.
Evaluation and beneficiation of high sulfur and high alkali fly ashes for use as supplementary cementitious materials in concrete
Highlights High sulfur and high alkali off-specification fly ash were evaluated as SCMs. Possible contaminants are calcium sulfate, calcium sulfite, or sodium sulfate. Flow, pore solution pH, setting, strength, and expansion potential were evaluated. Performance was mostly acceptable and beneficiation is possible in other cases. Current SO3 specification limits might be too conservative.
Abstract Coal-fuel power plants with semi-dry or dry flue gas desulfurization (FGD) systems produce high sulfur and/or high alkali fly ashes due to comingling of fly ash with FGD products. Such fly ashes do not meet the SO3 content limit (5.0% max.) of ASTM C618 or are unable to mitigate the alkali-silica reaction. The mineralogy of the sulfur present in these ashes can vary significantly (e.g., CaSO4, CaSO3, Na2SO4) based on the FGD technology used and this affects the performance of these fly ashes in concrete. Thus, the single SO3% limit of ASTM C618 is unable to capture the complexity and performance of fly ash, and this results in elimination of potentially viable pozzolans for concrete. This study performs a systematic investigation of the effect of SO3 type and content in fly ash on various performance parameters of cement-fly ash pastes and mortars, including workability (flow and flow retention), pore fluid pH, setting time, strength development, and potential for deleterious expansion. To better quantify and understand these effects, the study considers both real and doped fly ashes (i.e., a blend of specification-compliant fly ash with target sulfur compounds). The poor performance observed in the case of setting time and pore fluid pH was successfully mitigated using chemical admixtures.
Evaluation and beneficiation of high sulfur and high alkali fly ashes for use as supplementary cementitious materials in concrete
Kaladharan, Gopakumar (author) / Rajabipour, Farshad (author)
2022-04-26
Article (Journal)
Electronic Resource
English
CAc , Calcium acetate monohydrate , CBr , Calcium bromide , CFA , Control fly ash , DFA , Doped fly ash , FBC , Fluidized bed combustion , FGD , Flue gas desulfurization , HSAFA , High sulfur and alkali fly ash , HSFA , High sulfur fly ash , Mac , Magnesium acetate tetrahydrate , PC-I , Type I portland cement , PC-I/II , Type I/II portland cement , TFA , Trona-impacted fly ash , Fly ash , Setting time , Pore solution pH , Expansion
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