Concrete aggregates made from sludge-marine clay mixes

The large amounts of industrial sludge generated from the wastewater treatment of a copper slag recycling plant and the marine clay dredged out from excavation and tunneling works create problems of disposal. In this study, the potential use of the industrial sludge mixed with marine clay as concrete aggregate material was examined. Properties of the sintered aggregates, their performances in concrete, and their leaching characteristics were discussed. The results indicate that the incorporation of marine clay reduces the specific gravity and strength of the aggregates. The aggregates containing up to 50% by weight of clay demonstrated better aggregate impact resistance, with values ranging from 2 to 8% over the regular granite aggregates. The concrete test specimens with sludge-clay pellets as coarse aggregates yield 28-day compressive strengths ranging between 31.0 and 38.5 N/mm(2), which is comparable to concrete cast with regular granite aggregates. The contaminants leached from the sludge-clay aggregates were found to be below World Health Organization drinking water limits after 109 days, indicating no long-term adverse impact of leaching of the contaminants on the environment.