为了研究碱激发低钙粉煤灰对弱膨胀土改良的作用效果，通过膨胀性试验、无侧限抗压强度试验、环境扫描电镜试验及X射线衍射分析仪（X-ray diffraction, XRD）物相分析试验研究不同掺量的碱性激发剂NaOH对低钙粉煤灰膨胀土力学性能的影响，对土体微观结构及孔隙形成特征进行分析量化，并基于XRD试验分析土体中矿物成分变化特征，揭示碱激发粉煤灰与土体之间的作用机理。结果表明：碱性激发剂可以提升粉煤灰的活性，加快水化反应，可以加快早期强度发展和提高后期强度；随着碱激发剂的增加，粉煤灰改良膨胀土的无侧限抗压强度先增后降，10%掺量的NaOH为最佳掺量；土体中孔隙类型复杂，碱激发改良土微观发现产生的凝胶可以填充孔隙，且和土体相互黏结，减少孔隙。NaOH作为激发剂，可以有效改善粉煤灰的活性，并提高膨胀土的基本特性。

In order to study the effect of alkali-excited low-calcium fly ash on the improvement of weak expansive soil, the effects of different amounts of alkaline excitation agent NaOH on the mechanical properties of low-calcium fly ash expansive soil were studied through expansion test, unconfined compressive strength test, environmental scanning electron microscope test and X-ray diffraction (XRD) phase analysis tests, and the soil microstructure and pore formation characteristics were analyzed and quantified. Based on XRD test, the change characteristics of mineral composition in soil were analyzed, and the mechanism of action between alkali excited fly ash and soil was revealed. The results show that alkaline activator can enhance the activity of fly ash, accelerate the hydration reaction, accelerate the development of early strength and improve the later strength. With the increase of alkali activator, the unconfined compressive strength of fly ash improved expansive soil first increases and then decreases, and 10% NaOH is the best content. The types of pores in the soil are complex, and the gel produced by the microscopic discovery of alkali-stimulated modified soil can fill the pores, and bond with the soil to reduce the pores. As an activator, NaOH can effectively improve the activity of fly ash and improve the basic properties of expansive soil.