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<p>Geopolymers possess very good compressive strength, but their low toughness and flexural strength inhibit them from various structural and non-structural applications. The geopolymers with better flexural strength would perform better in coating applications. The synthesis parameters of geopolymers and curing conditions play an important role in enhancing the flexural strength of geopolymers. Few studies have been reported on the optimization of the flexural strength of fly ash geopolymers; however, no study has been reported on the optimization of the flexural strength of fly ash geopolymers by varying mixing speed, mixing time, sodium hydroxide concentration, and curing temperature and time. This paper investigates the flexural strength optimization of fly ash-based geopolymer through response surface methodology (RSM) using a central composite design (CCD). The parameters of mixing speed and mixing time (250–600 rotations per minute (rpm) and 5–15&#xa0;min), sodium hydroxide (NaOH) concentration (8–12&#xa0;M), and curing temperature and curing time (40–80 ℃ and 1–28 days) were varied. Two separate optimizations of mixing conditions and synthesis and curing conditions were conducted. The Analysis of Variance (ANOVA) results of both optimizations showed the coefficient of determination (R<sup>2</sup>) and <i>F</i>-values of 0.9601 and 0.9887 and 33.72 and 97.17, respectively, and <i>p</i>-values of less than 0.05, and a non-significant lack of fit were obtained which showed well-fitting of the data to the quadratic model with a confidence level of 95%. The mixing speed and mixing time of 492&#xa0;rpm and 10&#xa0;min were found optimum in the first optimization, which resulted in the flexural strength of 10.45&#xa0;MPa and the NaOH concentration, curing temperature, and curing time of 12&#xa0;M, 80 ˚C, and 24&#xa0;h respectively were found optimum in the second optimization which resulted in the optimum flexural strength of 15.23&#xa0;MPa. The multi-parameter optimization through RSM enhanced the flexural strength of fly ash-based geopolymer, which shows that mixing conditions, synthesis parameters, and curing conditions play a significant role in flexural strength development of geopolymer. An enhanced flexural strength of fly ash geopolymers would improve their application in structural and non-structural applications.</p>

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Optimization of flexural strength in fly ash-based geopolymers through response surface methodology

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年9月23日

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  • Ahmer Ali Siyal,
  • Rashidah Mohamed Hamidi,
  • Rashid M. Shamsuddin,
  • Radin Maya Saphira Radin Mohamed,
  • Suhaib Umer Ilyas

摘要

Geopolymers possess very good compressive strength, but their low toughness and flexural strength inhibit them from various structural and non-structural applications. The geopolymers with better flexural strength would perform better in coating applications. The synthesis parameters of geopolymers and curing conditions play an important role in enhancing the flexural strength of geopolymers. Few studies have been reported on the optimization of the flexural strength of fly ash geopolymers; however, no study has been reported on the optimization of the flexural strength of fly ash geopolymers by varying mixing speed, mixing time, sodium hydroxide concentration, and curing temperature and time. This paper investigates the flexural strength optimization of fly ash-based geopolymer through response surface methodology (RSM) using a central composite design (CCD). The parameters of mixing speed and mixing time (250–600 rotations per minute (rpm) and 5–15 min), sodium hydroxide (NaOH) concentration (8–12 M), and curing temperature and curing time (40–80 ℃ and 1–28 days) were varied. Two separate optimizations of mixing conditions and synthesis and curing conditions were conducted. The Analysis of Variance (ANOVA) results of both optimizations showed the coefficient of determination (R2) and F-values of 0.9601 and 0.9887 and 33.72 and 97.17, respectively, and p-values of less than 0.05, and a non-significant lack of fit were obtained which showed well-fitting of the data to the quadratic model with a confidence level of 95%. The mixing speed and mixing time of 492 rpm and 10 min were found optimum in the first optimization, which resulted in the flexural strength of 10.45 MPa and the NaOH concentration, curing temperature, and curing time of 12 M, 80 ˚C, and 24 h respectively were found optimum in the second optimization which resulted in the optimum flexural strength of 15.23 MPa. The multi-parameter optimization through RSM enhanced the flexural strength of fly ash-based geopolymer, which shows that mixing conditions, synthesis parameters, and curing conditions play a significant role in flexural strength development of geopolymer. An enhanced flexural strength of fly ash geopolymers would improve their application in structural and non-structural applications.