Application of geopolymers with different binding materials for the stabilization of sulfate-rich soils

Sulfate-rich soils (SRS) exhibit poor engineering properties, and studies focusing on the stabilization of these soils remain limited in the existing literature. Previous research has shown that the use of calcium-based stabilization agents, such as cement and lime, during the treatment of SRS can lead to adverse effects such as efflorescence, swelling, and associated deformation issues. Therefore, selecting an appropriate stabilization technique is critical to ensuring the safety and long-term performance of engineering structures built on such soils. In recent years, geopolymer-based soil stabilization has garnered increasing attention as a sustainable alternative to traditional cement-based methods due to its lower carbon footprint. In this study, an environmentally friendly and innovative geopolymer stabilization approach was applied for soils with extremely high sulfate content (284,400 ppm), taking into account potential issues such as swelling and settlement associated with calcium-based additives. The proposed method aims to improve the resistance of sulfate-rich soils (SRS) to deformation by increasing their bearing capacity and compressive strength. Ground granulated blast furnace slag (GGBS), metakaolin (MK), Class F fly ash (FA), sodium hydroxide (NaOH), and sodium silicate (Na 2 SiO 3 ) were used in the production of geopolymers. During sample preparation, the deep soil mixing (DSM) method was considered, and unconfined compressive strength (UCS) tests were conducted to evaluate the strength performance of sulfate-rich soils (SRS) stabilized with geopolymer. Additionally, samples cured for 28 days were subjected to durability tests. The experimental results showed that when GGBS, MK, and FA were used separately, GGBS and FA contributed more effectively to early-age strength development, while MK had a greater effect on long-term strength increase. Considering the strength values obtained after 7 and 28 days of curing, the maximum strength increase of 64.13% was achieved in the MK100 specimen. While the combined use of GGBS and MK resulted in an average 38% increase in specimen strength, the combined addition of GGBS and FA caused an average 22% decrease in strength. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) analyses were performed to investigate the microstructural changes, chemical composition, and elemental distributions of the stabilized SRS. Additionally, Fourier-transform infrared spectroscopy (FT-IR) analysis was performed to identify the chemical properties and functional groups present in the samples, and the findings were comprehensively evaluated.