摘   要:碱是混凝土发生碱-硅酸反应（ASR）的重要因素之一。K⁺、Na⁺离子在水化产物和孔溶液中的分配直接影响碱与活性集料发生ASR的潜能。许多学者研究发现，水泥的主要水化产物C-S-H凝胶对K⁺、Na⁺有很强的结合力，且随其n(Ca)/n(Si)比降低，结合能力增强。本文采用HRTEM（高分辨率透射电镜）/EDS（能量散射谱仪）、FT-IR（付立叶变换红外光谱）以及29Si MAS NMR（带魔角旋转的核磁共振）测定不同粉煤灰掺量的水泥石样品中C-S-H凝胶的化学组成和结构变化，讨论其对C-S-H凝胶持碱能力的影响。结果表明：随粉煤灰掺量增加，二次火山灰反应生成大量低n(Ca)/n(Si)比的C-S-H凝胶。且随n(Ca)/n(Si)比降低，C-S-H凝胶的持碱能力增强。低n(Ca)/n(Si)比的C-S-H凝胶中硅氧四面体的平均链长较大，Si-OH数目增多，从而导致碱在C-S-H凝胶中的结合位置增多，因此碱离子更容易进入低n(Ca)/n(Si)比的C-S-H凝胶中。

Abstract: Alkali is one of the most important factors that can cause ASR. The binding of sodium and potassium into cement paste will influence the performance of concrete: for example, the alkali balances between solid and pore solution will affect the potential for reaction with alkali-susceptible aggregates. Many researchers found that low Ca/Si molar ratio hydrates combind more alkali than the high Ca/Si ratio hydrates. The chemical composition and microstructure of C-S-H phase for hydrated pastes with different content of fly ash are studied experimentally by HRTEM/EDS, FT-IR and 29Si MAS NMR. The results show that secondary pozzolanic reaction produced more C-S-H with low Ca/Si molar ratio. Therefor, more Na+ and K+ ions binded in C-S-H phases of low Ca/Si molar ratio was also found. And with the decreasing of Ca/Si molar ratio, the average length of chain of [SiO4]4- tetrahedral and the sum of Si-OH in C-S-H are increased. So there were more position in which the alkali can be conbinded.