Mechanical Strength, Water Seepage and Microstructure of a Novel Landfill Solidified Sludge Liner Material

In order to prepare a novel landfill liner material, we used industrial calcium-containing waste (slag, fly ash, and desulfurized gypsum) to solidify municipal sludge. The mechanical and permeability properties of the solidified sludge material (SSM) were evaluated using straight shear, uniaxial compression, and permeability tests. The hydration products, microscopic morphology, and elemental composition of the SSM after the wet and dry cycles were analyzed using a combination of scanning electron microscopy (SEM + EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). The SSM has high strength and low hydraulic conductivity. The values of cohesion c and internal friction angle φ reached 0.45–3.31 MPa and 6.52–36.28°. The SSM exhibited a compressive strength of 0.93–11.67 MPa and hydraulic conductivity of 4.80 × 10−9–1.34 × 10−7 cm/s. Analysis shows that SiO2, Al2O3, and CaO in industrial calcium-containing solid wastes and sludges produce dense bulk and agglomerated C-S-H and C-A-S-H gels under alkali excitation. The optimum ratio of sludge, desulfurized gypsum, fly ash, and slag in the solidified sludge was 1:0.61:0.62:0.54, whereas the optimum exciter was Ca(OH)2. The SSM may be used as a good barrier material to prevent water seepage in landfills.