Geotechnical property development and micro characteristic evolution of solidified sludge using a novel mixed agent

Low-strength sludge takes up a lot of space in landfills, creating an environmental concern and a resource waste that needs to be treated right away. A novel mixed solidifying agent in this work is introduced to the geotechnical characteristics’ improvement of sludge for the first time. The role of each component in the mixed agent is explored by a series of different additive dosages in solidification. According to water content tests, shear wave velocity tests, unconfined compression strength tests, direct shear strength tests, X-ray diffraction, and scanning electron microscopy, the strength development of solidified sludge is comprehensively analyzed under different dosages and curing ages. The micro-analysis result shows that the geotechnical characteristics improved mostly due to hydration products such as ettringite, calcium silicate hydrate gel, aluminum gel, and hydrogarnet. Besides, the generation of hydration products consumes the water in sludge, fills soil particle pores, and connects the soil particles, which makes the structure of solidified sludge compacted, hence, improving the strength of the solidified sludge. Furthermore, the relationship between the shear wave velocity and undrained shear strength parameters follows the power function and indicates that the shear wave velocity can characterize the strength level of the solidified sludge.