Experimental Study on the Mechanical Behavior of Frozen Soil Reinforced with Disposable Face Masks

A vast amount of waste disposable face masks (FM) has threatened the ecosystem since COVID-19 became a pandemic. Given the urgency of the situation, this study innovatively assessed the potential utilization of the waste FM fibers to reinforce the subgrade in the permafrost regions. The effect of FM contents (0.5%, 1%, and 1.5%) and length-width (LW) ratios (1, 2, and 3) of the frozen silty clay specimens (-10 degrees C) with different initial moisture contents (w = 15%, 20%, and 25%) on the mechanical behavior, including the peak deviatoric stress (q), the increment of peak deviatoric stress (lambda), and the initial elastic modulus (E0), was analyzed. The pore structure change mechanism under the influence of FM and w was further revealed via nuclear magnetic resonance (NMR). The results indicated that the incorporation of FM improved the soil strength at a certain w, while the FM content and LW ratio were found to have different effects on the q values. The most effective reinforcement can be identified at w = 20%, according to the relatively large lambda values (29.2%-79.1%). Moreover, the E0 values of specimens with higher initial moisture content and FM content were smaller, which can be explained by the cracks generated due to the water-ice phase change and uneven distribution of FM. NMR results revealed that the FM had less effect on the pore-water relaxation characteristics, and the change in soil structure was more remarkable in the frozen specimens with higher w. This study pointed out that the tension of FM and its bonding soil particles played the leading role in soil stress-strain behavior. The results of this study recommend that waste face masks (FM) be added to the soil in the subgrade to improve its strength in permafrost regions. The mechanical properties (including the peak deviatoric stress and initial elastic modulus) of soils reinforced by various FM contents and different FM sizes were determined via experiments. The reinforcing mechanism is discussed by observing the surface of frozen soils and detecting the change in pore structure before and after freeze-thaw to explain the complex mechanical behavior of reinforced soils. The moisture content of soils is a significant factor influencing the reinforcement effect. According to the test results, different reinforcement parameters, for example, the content of additive FM and the FM size, should be selected in the specimens with different moisture contents for the best reinforcement effect. This paper provides novel and valuable guidance for waste FM utilization and subgrade strengthening in permafrost areas.