An experimental study on the effect of disposable COVID-19 face masks on the mechanical properties of cement-stabilized sand

The application of disposable face mask fibers in the enhancement of the mechanical properties of cement-stabilized soils is rigorously examined in this study through performing several triaxial tests on fiber-reinforced sand-cement mixtures with varying contents of additives under different confining pressures. To this end, sand samples stabilized with different percentages of cement (4% and 8%) are reinforced with various contents of face mask fibers (0%, 0.25%, 0.5% and 0.75%). After seven days of curing, the fiber-reinforced stabilized specimens are subjected to a comprehensive series of consolidated drained (CD) triaxial tests with all-round pressures of 50, 100 and 200 kPa. The results generally show that the addition of mask fibers to sand-cement mixtures up to 0.25% increases their ultimate strengths; whereas further increase of fiber content is observed to have an adverse impact on the strength parameters of the composite. Therefore, 0.25% mask fiber inclusion is reported to be the optimum content, which constitutes maximum strength characteristics of the samples. The contribution of mask fiber addition to the variation of ultimate strength of stabilized mixtures is noticed to be more pronounced in the samples with higher cement contents under greater isotropic confining pressures. Moreover, with increasing the percentage of mask fibers, the failure strain of all stabilized samples increases, thus exhibiting more ductile behavior. Unlike for the samples containing relatively low cement contents (4% herein) where brittleness index is barely affected by the mask fiber content, this parameter significantly decreases with the fiber inclusion for the specimens stabilized with relatively high cement contents (8% herein). Secant modulus is also observed to experience a decreasing trend with the addition of mask fibers to the mixture; the trend which is more pronounced for samples containing higher cement contents. Finally, the internal friction angle and cohesion of cement-stabilized samples generally show increasing trends with the addition of mask fibers up to 0.25% and then reveal decrement. Overall, the combination of cementation and fiber reinforcement demonstrates a significant synergistic effect, resulting in notable improvements in the mechanical properties of fine sands.