Study on the Mechanical Characteristics of Urban Sludge Solidified by Industrial Waste

Urban sludge is an extensive volume with a prominent environmental impact. The research explored an application technology for converting urban sludge into a usable improved soil resource by using industrial waste, providing a new reference for the reuse of industrial waste. In this study, three industrial wastes, namely ground granulated blast slag, calcium carbide residue, and desulfurized gypsum, were used as curing agents to solidify the urban sludge. Based on the unconfined compressive strength (UCS) test and chamber analysis, the effects of curing agent dosing and maintenance age of sludge-cured soil on the UCS and stress- strain were studied. The results showed that with the increase of curing agent, the UCS of cured soil first increased and then decreased, and the breaking strain showed a decreasing trend. The optimum ratio of materials was sludge: calcium carbide residue: ground granulated blast slag: desulfurization gypsum = 100:15:15:5, record this material ratio as C15G15D5. Moreover, trials showed that C15G15D5 cured the sludge soil better than the cement alone, which achieved the purpose of reusing the three industrial wastes and urban sludge. It was analyzed that the hydrated calcium silicate (C-S-H), calcium aluminate (C-A-H) and ettringite (AFt) in the hydration products were produced to make the soil skeleton stronger and enhance the strength of the sludge-cured soil.