Effect of Recycled Low-Density Polyethylene (LDPE) Cup Fibers on the Mechanical Performance and Crack Behavior of Cement Mortar

This study evaluated the effect of incorporating recycled low-density polyethylene (LDPE) fibers obtained from disposable plastic cups on the mechanical performance and crack propagation behavior of cement mortar. Four mortar mixtures were produced, including a control mixture without fibers and three mixtures containing 0.25%, 0.50%, and 1.00% LDPE fibers by volume. The mixtures were prepared using a local Type IP cement, river sand, and a water-to-cement ratio of 0.55. Digital Image Correlation (DIC) was employed to analyze crack initiation and propagation during loading. The experimental results were statistically evaluated using one-way analysis of variance (ANOVA) followed by Tukey's post hoc test. At 28 days, the specimens were tested for compressive strength, splitting tensile strength, flexural strength, and ultrasonic pulse velocity (UPV). The results revealed that the incorporation of LDPE fibers produced different effects depending on the evaluated property. Compressive strength decreased from 43.19 MPa for the control mixture to 33.08 MPa for the mixture containing 1.00% fibers. In contrast, the highest splitting tensile strength (2.35 MPa) was achieved with 0.50% fiber addition, while the maximum flexural strength (4.34 MPa) was obtained with 1.00% fibers. Furthermore, all fiber-reinforced mixtures exhibited higher ultrasonic pulse velocity than the control, reaching a maximum value of 3957.28 m/s at 0.25% fiber content. DIC observations indicated that the recycled LDPE fibers contributed to improved crack control by delaying crack propagation after crack initiation. Overall, although high fiber contents reduced compressive strength, the incorporation of recycled LDPE fibers enhanced the tensile and flexural performance of cement mortar, demonstrating their potential as a sustainable reinforcement for cement-based materials.