Face mask chips-reinforced sands under monotonic and cyclic torsional shearing

In an effort to enhance engineering infrastructure and reduce environmental waste, the use of COVID-19 face-mask chips (FMC) in sand reinforcement is experimentally explored through drained hollow cylinder torsional shear tests, including monotonic stress paths with different fixed orientation of the principal stress axes and cyclic tests with traffic load and pure principal stress rotation. Fujian sand and Hong Kong CDG sand were used. The monotonic test results indicate that both sands exhibit a strong strength anisotropy, however, although the addition of FMC increases the peak stress ratio to failure of the composites for all tests, the strength anisotropy trends with alpha(sigma) are not changed. Results from x-Ray CT scanning analyses conducted on FMC-reinforced and unreinforced cylinder sand specimens supported the interpretation of experimental data. Furthermore, the inclusion of FMC induces increased plastic deformation under cyclic loads in all tests, however, the level of these plastic strains is sand-type and stress-level dependent. It was also observed that both sands exhibit non-coaxial characteristics, but the presence of FMC inclusions do not change the non-coaxial trends observed for the pure sands.