Geotechnical property development and micro-characteristic evolution of solidified sludge

Abstract

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 is introduced in this work to improve the geotechnical characteristics of sludge. The role of each component in the mixed agent is explored by using 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 analysed under different dosages and curing ages. The microanalysis results show that the geotechnical characteristics improved mostly due to hydration products such as ettringite, calcium silicate hydrate gel, aluminium gel and hydrogarnet. Moreover, the generation of hydration products consumes the water in sludge, fills soil particle pores and connects 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 characterise the strength level of the solidified sludge.