Experimental study on strength and water stability of concentrated solution sludge solidified with alkali-activated GGBS geopolymer

The concentrated solution sludge (CSS) produced by submerged combustion process on leachate has the characteristic of high soluble salt content. The sulfoaluminate cement (SAC) and alkali-activated GGBS geopolymer are used to solidify the CSS, respectively. A series of unconfined compressive strength (UCS) tests, water stability tests and microscopic observation tests are carried out on the solidified samples to investigate the curing effects and curing mechanisms of the SAC and alkali-activated GGBS geopolymer on the CSS. The results show that the UCS of the solidified sample with the SAC of 40% is 1.95 MPa at 28 d-curing age, and decreases to zero after 28 d-water immersion. The UCS of the solidified sample with the GGBS of 30% is 14.8 MPa at 28 d-curing age, and remains 3.6 MPa after 28 d-water immersion, which is much higher than the strength requirement of landfills. The three-dimensional geopolymeric gels and ettringite crystals produced by the GGBS geopolymerization are capable of effectively encapsulating and cementing the CSS particles, which is the curing mechanism of the alkali-activated GGBS-solidified CSS.