Constructive Sludge Management - Reutilization of Municipal Sewage-Sludge in Portland-Cement Mortars

Abstract

Sludges produced by the treatment of municipal sewage wastes are becoming increasingly difficult to dispose of because the quantity of sludge is increasing due to an increase in population and sewered areas. Many sludge disposal alternatives such as agricultural use, landfilling, marine disposal and incineration, etc, have adverse environmental impacts. There is a resulting increase of interest in reuse of sludge by incorporation into construction materials. In the present study, properties of digested, dewatered, dried and pulverized sludge blended Portland cement mortars are investigated. Sludge was used as replacement for 1, 2, 5, 10, 20, 30 and 40 percent by weight of the cement. The results indicate that initial and final setting times are longer with an increase of sludge. The mortar samples cast in standard moulds were cured for periods of 3, 7, 14 and 28 days before testing for compressive and tensile strength. The addition of 40 percent sludge caused the initial and final setting times of mortar to increase about 19 fold and 35 fold compared to control mortar with a water to cement ratio of 0.5. The effects of pulverized sludge on the Le Chatelier expansion and specific surface area of mortar are not significant. The addition of sludge adversely affected the compressive and tensile strength development. For 5 percent replacement of cement by pulverized sludge, the compressive and tensile strengths reduced by 32 and 38 percent, respectively.