Magnesium oxychloride cement (MOC) is innovatively introduced into sludge solidification. The influence of initial water content

molar ratio of MgO/MgCl2

curing age and MgO activity on sludge solidification efficiency and the corresponding driving mechanisms are systematically studied by unconfined compressive strength

water content of solidified matrix

scanning electron microscopy (SEM) and energy dispersive spectrum (EDS). The results show that the higher the initial water content

the lower the strength of solidified samples

and the needle-rod shaped crystals (phase 3 or phase 5) can be clearly observed in MOC solidified sludge with medium water content. The increase in molar ratio of MgO/MgCl2 leads to an improvement in the compressive strength of samples

accompanied by the transformation of hydration products from amorphous gel to phase 3

phase 5 and Mg(OH)2 crystals. The strength of solidified sludge shows a increase trend with the prolongation of curing age

and the strength prior to 28 d increases relatively faster

followed by a stable trend after 28 d. Especially

the surface of specimens with high molar ratio of MgO/MgCl2 is prone to have frost at a longer curing stage. An enhancement in MgO activity produces more reactive components and leads to higher compressive strength of MOC solidified sludge

whereas the activity degree of MgO has no significant effect on the evolution of hydration products. The obtained results can provide a theoretical support for the development of green and low-carbon MOC-based cementitious material and its application in soil reinforcement fields such as sludge solidification.