Soil stabilization is essential for the development of resilient infrastructure on soft and collapsible ground. Conventional stabilization relies heavily on ordinary Portland cement (OPC), a material with a high carbon footprint and limited durability in aggressive environments. This study investigates the feasibility of a cementless geopolymer binder—derived from industrial by-products such as fly ash, ground granulated blast furnace slag (GGBS), and alkaline activators to stabilize sandy soils. This study examined how varying levels of cementless geopolymer addition influence the soil's mechanical characteristics. A sandy-clayey soil, locally available in Korea, was utilized in this study with a 0%, 10%, 20%, 30%, and 40% replacement with cementless geopolymer binder. Water content was fixed at 30% for this testing. After 5-days of curing, specimens were checked for Unconfined Compressive Strength (UCS) to check the impact of cementless geopolymer on soil stabilization. Optimal mix designs, with 30~40% replacement with cementless geopolymer, achieved considerably higher UCS values after 5-days of curing at ambient temperatures, surpassing the performance of OPC stabilized specimens while reducing CO₂ emissions. The results demonstrate that cement less geopolymer binders can serve as sustainable, high performance alternatives for soil stabilization, offering both environmental benefits and enhanced durability in chemically aggressive settings.