During the global coronavirus (COVID-19) pandemic, a huge amount of personal precautionary equipment, such as disposable face masks, was used, but further usage of these face mask leads to adverse environmental effects. Here, we evaluated the feasibility of using mask chips to reinforce clayey soil, testing this with static and impact loading, including uniaxial compression, diametral point load, and drop-weight impact loading tests. The concurrent influences of shape, size, and percentage of waste material were considered. Generally, the contribution of shredded face mask (SFM) was majorly attributable to its tensile reinforcement. As a consequence, the strength of the mixture, measured by the static tests, was increased. This property was enhanced by the addition of rectangular mask chips. We determined the optimum percentage of SFM, beyond which the uniaxial compression strength and the point load strength index decreased. An increase in the percentage of SFM in the soil produced a higher damping coefficient and lower stiffness coefficient, causing greater flexibility. This trend increased beyond 1.2% of SFM (by volume of clay soil). Generally, based on our results, 1-1.5% of SFM was the optimum content.

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.

The widespread usage of disposable face masks (DFM) during the COVID-19 pandemic has exacerbated waste management challenges, prompting an investigation into their potential reuse as a soil reinforcement material. Previous researchers have investigated the effect of mask fibres on pavement subbases and the environmental problems caused by these fibres. This study examines the mechanical properties of sandy soil enhanced with shredded and layered DFM under triaxial testing conditions, focusing on key parameters like shear resistance, elastic modulus, stress-strain characteristics, axial resistance, failure envelope, and brittleness index. Results show that adding DFM significantly improves soil cohesion, friction angle, shear strength, and peak deviatoric stress, especially at higher fibre contents and relative densities. However, increased DFM fibre content was associated with reduced elastic modulus, which stabilised in specimens with layered DFM, suggesting complex interactions between DFM content and soil mechanics. Concerns include potential void formation leading to asymmetric settlement and environmental issues on non-biodegradable fibre integration in soil. These findings highlight the need for meticulous mixture preparation, large-scale studies, and environmental assessments to evaluate the impact of using DFM in soil reinforcement, particularly for road construction and slope stabilisation. This research provides crucial insights into the potential of DFM for soil reinforcement.

Discarded disposable face masks can easily cause environmental pollution, and microbial-induced calcium carbonate precipitation (MICP) technology can lead to soil brittleness. This article attempted to combine discarded disposable face masks with MICP technology by adding the shredded face mask (SFM) with six different percentages (0%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% by weight) to ISO standard sand. The test results showed that the optimal content of SFM was 0.2%. Compared with the sand samples without SFM, the water absorption rate decreased by 26.99%, the dry and saturated unconfined compressive strengths (UCS) increased by 145.11% and 252.38%, respectively, and the failure strain increased by 127%, and the calcium carbonate content increased by 20.1%. Meanwhile, 0.2% SFM fiber can form a three-dimensional network structure, which restricts the displacement and deformation of sand particles, improves the brittleness of the sand samples, and enhances the strength of the sand samples. This study provides an effective method for recycling discarded disposable face masks while promoting the application of fiber-reinforced MICP-treated sand in geotechnical engineering.

The paper explores challenges arising from the existence of expansive clay soils, renowned for causing structural damage and exhibiting detrimental environmental effects. Implementing a novel approach, this study introduces the use of fly ash (Class F) and shredded face masks (FMs) to enhance soil properties. Fly ash (FA), known for its pozzolanic properties, is combined with shredded waste FMs to reinforce the soil. Remolded specimens underwent comprehensive laboratory testing, including Unconfined Compressive Strength (UCS), California Bearing Ratio (CBR), Swell Test, Consolidation Test, and Triaxial Test. The optimal blend identified as 0.9% FMs + 20% FA achieves an optimal equilibrium of strength, stability, and reduction in swelling. The UCS exhibited an increase with the addition of FA, and this improvement was further enhanced with the inclusion of 0.9% FMs, surpassing the specified subgrade CBR values. The percentage of swell exhibited a notable decrease from 5.9% to 1.8% with the incorporation of FA + FMs. This sustainable approach aims to conserve valuable resources and mitigate challenges associated with waste disposal along with the economic benefits to contribute to achieve UN SDGs 2030.

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.

This study rigorously examined the enhancement of the mechanical properties of clay through the application of disposable face mask fibers (DFMF). By subjecting the reinforced specimens to a comprehensive series of unconfined strength tests, it was found that adding DFMF to the base soil decreased the maximum dry unit weight (MDUW) and increased the optimum moisture content (OMC). The study examined the effects of DFMF content on the compounds, revealing that a maximum increase of 0.2 in DFMF content improves their unconfined compressive strength (UCS); Therefore, 0.2% mask DFMF content was noticed to be the optimum DFMF content, which constituted maximum strength.

The introduction of face masks as a precautionary method to slow down the infectious rate of Coronavirus (Covid-19) has resulted in environmental challenges in the last two years. Since most of these masks are made up of polymeric materials, their extensive usage has produced millions of tons of waste materials in a short period of time, leading to the disposal load increase on the waste management systems around the globe. Hence, the present investigation aimed to evaluate the possibility of randomly distributing the shredded surgical face mask (SFM) fiber in the soil as a reinforcement element and its influence on the mechanical properties of sandy soil stabilized with cement from macro and microstructural aspects. To that end, a series of laboratory investigations, including unconfined compression test, and scanning electron microscopy (SEM), were conducted on soil specimens with five different amounts of cement (2, 4, 6, 8, and 10% soil dry weight) and four percent of SFM (0, 0.25, 0.5, and 0.75%). Additionally, the influence of four various relative densities (D-r = 35%, 50%, 70%, and 85% sand) on specimens' mechanical properties after 7 days of curing time has been investigated. The experimental results indicated that adding cement to the soil specimens caused an increase in unconfined compressive strength (UCS), secant modulus (E-50), and absorbed energy (AE) of blended specimens. The mentioned parameters of the cemented specimens reinforced with 0.25% SFM fibers remarkably improved the strength 26%-59% for 2%-10% cemented samples. Moreover, up to 0.25%-SFM fiber addition to the mixture eventuated in a more ductile specimen. Through the SEM pictures, the proper inter-lock of the fibers, sand and the cementitious materials were demonstrated. In the end, a novel key parameter was defined, and several relationships were suggested to estimate the mechanical properties of the improved sand.

Due to their extensive use during and after the COVID-19 pandemic, many disposable face masks are irresponsibly deposited into the water environment, threatening the health of people living nearby. However, the effects of water conditions on the degradation and potential hazards of these masks are generally unclear. This paper entailed the release and cellular toxicity of micro/nano plastics from disposable face masks once discarded in different waters, including soil water, river water, and tap water, with deionized (DI) water as control. At first, polypropylene (PP) was confirmed to be the major component of disposable face masks with Raman and Fourier transform infrared (FTIR) techniques. To monitor the release rate of PP from masks, a silver nanoparticle (AgNP)-based surface-enhanced Raman scattering (SERS) method was established by employing the unique Raman fingerprint of PP at 2882 cm(-1). During 30-d incubation in different waters, the release rates of PP, sizes of PP aggregates, length of fibers, and proportions of plastics smaller than 100 nm were in the order of soil water > river water > tap water > DI water. All the obtained PP exhibited significant toxicity in human lung cancer (A549) cells at concentrations of 70 mg/L for 48 h, and the ones obtained in soil water exhibited the most severe damage. Overall, this paper revealed that environmental waters themselves would worsen the adverse effects of disposable face masks, and the key compounds affecting the degradation of masks remain to be clarified. Such information, along with the established methods, could be beneficial in assessing the health risks of disposable face masks in different waters.