Effect of Dispersed Polypropylene Fibers on the Strength and Stiffness of Cement-Stabilized Clayey Sand

Soil stabilization with hydraulic binders like cement is widely used in road construction but significantly contributes to CO 2 emissions. This study investigates a more sustainable alternative involving the use of dispersed polypropylene fiber reinforcement to improve the mechanical properties of stabilized soils while reducing cement consumption. Nine clay sand mixtures with varying cement (2–6%) and fiber (0–0.5%) contents were tested using unconfined compressive strength (UCS) and ultrasonic pulse velocity (UPV) methods. Fiber addition improved UCS by 5.59% in a mix with 2% cement and 0.25% fibers and by 25.45% in one with 4% cement and 0.25% fibers. This shows that fibers can improve strength at different cement levels. A novel reinforcement index ( R i ) was introduced to predict UCS empirically. The model showed that using 0.5% fibers ( R i = 1.0 % ) enabled a 25.12% reduction in cement without compromising strength. However, this improvement came at the cost of stiffness: deformation modulus E 50 decreased by up to 67.51% at 0.5% fiber content. Statistical validation using MAE, RMSE, and MAPE confirmed the model’s accuracy. Although the results were based on a single soil type, they showed that polypropylene fibers can support decarbonization efforts by reducing cement demand and represent a technically feasible approach to more sustainable geotechnical engineering applications.