Study of the hydraulic conductivity of a highly compressible clayey soil stabilized with kraft black liquor and composite cement

This This study investigated the hydraulic conductivity of a compacted high plasticity clayey soil (CH) and its mixtures with kraft black liquor (KBL) and cement for use in sanitary landfill bottom liners. Black liquor dosages of 3 and 5% were used in relation to the dry mass of the soil, and two types of cement were tested: composed of granulated blast furnace slag (CP II˗E˗32) and of carbonate material (CP II˗F˗32). The addition of black liquor reduced the hydraulic conductivity of the soil by up to 10 times. Mixtures with 3% black liquor and 5% liquor-cement CP II˗F˗32 showed the best performance, with hydraulic conductivity values in the range of 2.4 to 3.4 x 10-10 m/s. Mixtures with CP II˗E˗32 cement had higher and more variable hydraulic conductivity. Black liquor additions increased the pH of the mixtures and the concentration of adsorbed Na+ in the leachate. The combined addition of black liquor and cement increased the effective cation exchange capacity (CEC), particularly with CP II˗F˗32 cement. The higher concentration of Ca2+ in the leachate of mixtures with CP II˗E˗32 cement contributed to the poorer hydraulic performance. However, the higher concentration of Al3+ in the leachate of mixtures with CP II˗F˗32 cement did not impact hydraulic conductivity. It was concluded that the dispersion of clay particles induced by black liquor was the primary mechanism for reducing hydraulic conductivity. Mixtures with 3% black liquor and 5% liquor-cement CP II˗F˗32 showed the lowest hydraulic conductivity values, indicating their potential as a suitable stabilizer for landfill liners.