This paper systematically presented the trend of mechanical properties and micro-characteristics of fly ash-based geopolymer pastes up to 730 days (d) and analyzed the reason causing the divergent tendencies among the geopolymers synthesized with five Class F fly ashes (FFA). The test results showed that the geopolymer specimens had continuously increased compressive strength due to the sustained geopolymerization, although the rate of rise experienced three stages, including rapid growth, gentle consolidation, and slight increase. The microscopic detections revealed that the decrease in the Si/Al molar ratio, Na/Al molar ratio, and porosity of geopolymers were linearly related to the enhancement of compressive strength in 730 d, while increased amorphous phase content (APC) of geopolymers only contributed to that in 28 d. Besides, the differentiation of five FFA caused the divergence of compressive strength in the early stage, but the convergence was observed starting from 210 d, which was explained well by the corresponding divergence and convergence of micro-characteristics. This research proposed that, under dry ambient environments, the mechanism of medium and long-term FFA-based geopolymerization reaction for enhancing the compressive strength did not seem to be on the newly generated geopolymer gel with low Si/Al molar ratio but possibly on the recombination and optimization of Si–Al molecular structure between the existing geopolymer gel and newly formed Al-rich gel that released from residual FFA particles.

中文翻译：

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不同粉煤灰地质聚合物微观和宏观性能的长期发展


本文系统地展示了粉煤灰基地聚合物浆体在 730 天 (d) 内的力学性能和微观特性的变化趋势，并分析了用五种 F 级粉煤灰 (FFA) 合成的地聚合物之间出现不同趋势的原因。测试结果表明，由于持续的地聚合作用，地聚合物试件的抗压强度不断增加，但上升速率经历了快速增长、平缓固结和小幅增长三个阶段。显微检测表明，730 d内，地聚合物Si/Al摩尔比、Na/Al摩尔比和孔隙率的降低与抗压强度的提高呈线性相关，而地聚合物非晶相含量（APC）的增加仅贡献到28天。此外，5个FFA的分化导致早期抗压强度出现分歧，但从210 d开始出现收敛，这可以通过相应的微观特征的分歧和收敛得到很好的解释。本研究提出，在干燥的环境下，中长期基于FFA的地质聚合反应提高抗压强度的机制似乎并不在于新生成的低Si/Al摩尔比的地质聚合物凝胶，而可能在于现有地质聚合物凝胶和残留 FFA 颗粒释放的新形成的富铝凝胶之间的 Si-Al 分子结构的重组和优化。