Mechanical response and micro-mechanism of humus soil solidified by industrial solid waste-cement

To advance the resource utilization of humus soil within the realm of geotechnical engineering, the industrial solid waste materials (including biomass fly ash, carbide slag and phosphogypsum) cooperated with cement are used to solidify the humus soil. The humus soil mined from an obsolete simple landfill in Guangdong Province, China is solidified by the industrial solid waste-cement. Then the mechanical properties, durability and the underlying microscopic mechanisms are investigated by using the conventional triaxial tests, wet-dry and freeze-thaw cycling tests, scanning electron microscopy (SEM), X-ray diffraction (XRD), fourier-transform infrared spectroscopy (FTIR) and mercury intrusion porosimetry (MIP) tests. The results show that with the increase of P_o-b (i.e., the replacement ratio of cement by industrial solid waste), the relationship between deviatoric stress and axial strain of the samples gradually transits from strain softening to strain hardening. The appropriate incorporation of the ternary industrial solid waste materials (ranging from 25 % to 50 % for P_o-b) is beneficial in slowing down the deterioration rate of the industrial solid waste-cement solidified humus soil samples under the action of wetting-drying cycles. Furthermore, the cement-solidified humus soil samples exhibit excellent ultimate deviatoric stress and frost resistance. The microstructural analyses show that a large number of reaction products such as ettringite crystal and C―(A)―S―H gel enhance the bonding between humus soil particles and also fill in the microscopic pores. The research results provide a theoretical foundation for the restoration and reuse of humus soil mined from landfill sites.