Expansive soils are known as problematic due to their significant volume change during seasonal moisture fluctuation. The present study reports the suitability of alkali-activated fly ash as an alternate binder, to conventional stabilizers like cement, used to mitigate the volumetric shrinkage of expansive soil. Alkali-activated fly ash is an alternative binder in which liquid alkali activator (LAA) is added to FA, which consists of 50:50 sodium silicates (Na2SiO3) and sodium hydroxide (NaOH) solution by weight. Laboratory investigation includes the determination of volumetric shrinkage strain through image analysis and scanning electron microscopy (SEM) images at 7-, 14-, and 28-days curing period. Results indicate a significant reduction in volumetric shrinkage strains from 56 to 15, 11, and 5%, respectively, with a treatment of expansive soil with LAA/FA = 1, 1.25, and 1.5 at a curing period of 28 days. The SEM images captured to observe the microstructural changes at a 28-days curing period reveal that the right amount of dense crystalline products is formed at an LAA/FA = 1.5. From the analysis, an LAA/FA ratio of 1.25 may be considered as an optimum dosage to control the volumetric shrinkage strain. © 2022, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.