Mechanical characteristics of CSA-treated sand reinforced with fiber under freeze-thaw cycles

Earth structures like roads and railways in cold regions face recurring freeze-thaw (F-T) cycles, leading to issues often overlooked by design guidelines that focus primarily on strength, neglecting long-term stability and durability. To improve soil properties, soil stabilization with ordinary Portland cement (OPC) is common, but it has a high carbon footprint. This study explores the use of calcium sulfoaluminate (CSA) cement as a lower-carbon alternative. Samples were created with varying CSA cement (3 %, 5 %, 7 %) and polypropylene fiber (PPF) (0–1 %), then subjected to multiple F-T cycles. Tests like unconfined compressive strength (UCS) and ultrasonic pulse velocity (UPV) revealed that optimal fiber content varies with cement ratios, with excess fiber reducing strength. As the PPF content increases, the UPV value increases until it reaches the optimal value. By utilizing 5 % and 7 % CC, the UCS strength initially increases until 0.25 % PPF, then declines. In contrast, for samples reinforced with 3 % CC, the UCS value increases with PPF content up to 1 %. A similar trend was observed in the UCS test, where adding fiber dosage beyond the optimum limit caused strength reduction. Additionally, the study found that F-T cycles weaken soil by creating voids and pores, with excess fiber leading to overlapping that weakens cement-soil bonds. Stress-strain curves indicated improved ductility and durability with PPF, but resilience modulus and durability index declined with more F-T cycles. Scanning electron microscopy (SEM) confirmed these findings, highlighting the impact of voids, pores, and fiber on soil structure. The study aims to develop more durable and eco-friendly construction methods for cold environments. • Earth structure design in cold regions should prioritize long-term stability and durability. • The study analyzes freeze-thaw effects on soil treated with CSA cement and polypropylene fibers. • Proper fiber content improves soil strength, while excess fiber weakens the composite material. • Voids, pores, and fiber overlap reduce soil-cement bond strength, requiring better cold-weather construction methods.