Mechanical Characteristics and Failure Mode of Wasted Polyester Fiber-reinforced and Cement-stabilized Sand

Using a low-cost and environmentally benign method to reinforce cement-stabilized sand is a key issue in geotechnical engineering. Polyester fiber from waste clothes was used to reinforce cement-stabilized sand in this study. The effects of the fiber content and fiber length on the unconfined compressive strength of cement-stabilized sand were examined. The failure modes of the cement-stabilized sand before and after reinforcement were qualitatively analyzed according to the macroscopic damage morphology of a test sample. The impacts of the fiber content and fiber length on changes in the failure mode of the cement-stabilized sand were analyzed according to the brittleness index. The degree of transformation from brittle failure to ductile failure of the cement-stabilized sand was evaluated. The results showed that the optimum reinforcement performance with waste polyester was obtained at a fiber content of 1.0% and fiber length of 9 mm. These conditions realized improvements in the unconfined compressive strength, peak strain, residual strength, and residual strain of the cement-stabilized sand of 43.3%, 18.2%, 276.9%, and 190.9%, respectively. After polyester reinforcement, the failure mode of the cement-stabilized sand gradually transformed from brittle failure to semi-ductile and ductile failure, as reflected by changes in the macroscopic damage morphology. Before reinforcement, the damage morphology consisted of individual cracks extending through the sample in the longitudinal direction, which is typical of brittle failure. After reinforcement, the damage morphology of the sample transformed into unilateral or sparse conjugate cracks representative of semi-ductile failure and dense network-type conjugate cracks representative of ductile failure. Using the optimum fiber content and fiber length yielded the most conjugated cracks on the sample surface, lowest brittleness index, and highest degree of transition from brittle failure to ductile failure. These research results provide a scientific basis for enhancing cement soil with an environmentally benign approach and for analyzing the failure mode of fiber soil.