Application of Sewage Dry Sludge in Concrete Mixtures

In recent decades, disposal of dry sludge have been an important problem of sewagetreatment plants due to environmental restrictions. The material is not usually permitted to be buried in soil or used as agricultural fertilizer because of high heavy metal contents.Some investigations performed on application of these materials in construction materialsespecially concrete mix designs. In this research, application of dry sludge produced in theAlborz (Qazvin) industrial/domestic sewage treatment plant in mass concrete at water tocement (w/c) ratios of 0.55 and 0.45 was investigated. The dry sludge was characterized for chemical composition (XRF analysis), crystalline phases (XRD analysis) and pozzolanicactivity (Thermal gravimetery). Thereafter, it was used at 0, 5, 10, 20 and 30% of cement content in concretes. Effect of the dry sludge on compressive strength at different ages of curing 3, 7, 28 and 90 days was investigated. Besides, flexural strength, water absorption and porosity of concretes containing 20% dry sludge were measured after 28 and 90 days of curing. It was found that using dry sludge at 5, 10 and 20% caused decrease in compressive strength about 9, 14.5 and 29% in 28 days cured and 3.5, 8 and 20% in 90 days cured specimens in comparison to control specimens, respectively.