Abstract This paper investigates the mechanisms of microstructure evolution of interfacial transition zone (ITZ) in alkali-activated fly ash-slag (AAFS) concrete using scanning electron microscope. Results indicate that the formation of original ITZ depends on the so-called “wall effect”, leading to a deficit of large grains and a higher effective alkaline activator/precursor ratio compared to paste matrix. The alkaline reaction process is correspondingly accelerated, which promotes the formation of low Ca C-(N)-A-S-H gels and reduces the porosity in the ITZ. Afterwards, the high Ca C-(N)-A-S-H gels are generated due to the release of more Ca from slag, resulting in the continuous refinement of pores. The C-(N)-A-S-H gels with rich Si and Al are then produced at 7 d, attributing to the species diffusion from paste matrix to ITZ. Consequently, a compact and dense microstructure is formed in the ITZ at 28 d, which would be beneficial to the long-term performance of concrete.

中文翻译：

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碱活化粉煤灰-矿渣混凝土界面过渡带的演化

摘要 本文采用扫描电子显微镜研究了碱活化粉煤灰渣（AAFS）混凝土界面过渡区（ITZ）的微观结构演化机制。结果表明，原始 ITZ 的形成取决于所谓的“壁效应”，与糊状基质相比，导致大晶粒缺陷和更高的有效碱性活化剂/前驱体比率。碱性反应过程相应加快，促进了低Ca C-(N)-ASH凝胶的形成，降低了ITZ的孔隙率。之后，由于从炉渣中释放出更多的 Ca，从而产生高 Ca C-(N)-ASH 凝胶，导致孔隙不断细化。然后在第 7 天产生富含 Si 和 Al 的 C-(N)-ASH 凝胶，这归因于从糊状基质到 ITZ 的物质扩散。最后，