Study on the Improvement Performance of Different Clay Components with Desulfurization Gypsum-Containing Cementitious Material

The use of cementitious materials to improve clay is a common technique in engineering. However, the effectiveness of these materials, particularly desulfurized gypsum, on clays with different mineral compositions remains unclear, resulting in a lack of theoretical basis for their application in engineering. This study investigated the synergistic effects of clinker–metakaolin–desulfurized gypsum on clays with various mineral compositions through a series of macroscopic and microscopic laboratory tests. The results revealed that the stress–strain relationships of all clay samples exhibited softening characteristics. The softening was most pronounced in kaolinite samples, followed by illite and bentonite samples. For single-phase clays, the unconfined compressive strength followed the order of kaolinite > illite > bentonite. For multiphase clays, the order was illite + kaolinite > bentonite + illite + kaolinite > bentonite + kaolinite > bentonite + illite. The strength enhancement in the improved soils was primarily due to kaolinite and illite. As the content of desulfurized gypsum increased, the ettringite crystals in the improved soils transformed from cluster-like to framework-like structures. When the gypsum content exceeded 10%, the macroscopic performance of the improved soils decreased. These findings provide valuable insights for related engineering applications.