Effect of Partial Replacement of Cement by Waste Sludge from Water Supply Plant on Compressive Strength and Water Absorption of Hardened Concrete

Abstract

AbstractIn this study, effect of partial replacement of cement by waste sludge from water supply plant on compressive strength and water absorption of hardened concrete was investigated to evaluate potential use of such waste for concrete production. After drying at 110 °C in a laboratory oven, the sludge was grounded and sieved to have a particle size of less than 0.14 mm to partially replace cement at levels of 0, 10, 20, and 30% by mass. Mixture proportion of reference concrete with 0% sludge replacement in which a desired slump and compressive strength at 28 days were 6 ± 2 cm and 45 MPa, respectively was designed according to Bolomey-Skramtaev method. All concretes with a water-to-binder ratio of 0.53 were prepared. The results showed that the waste sludge decreased slump of fresh concrete when the mixing water amount of all concrete mixture proportions was kept constant. The higher the waste sludge replacement, the lower the slump of fresh concrete. The partial replacement of cement by waste sludge in a range of 10–30% decreased the compressive strength of hardened concrete by 15.10–47.17% when compared with the reference concrete at the age of 28 days. The sludge replacements at 10 and 20% by mass increased the water absorption by 3.82 and 93.51%, respectively. Consequently, replacing 10% of cement with the sludge for concrete production was beneficial in terms of not only ensuring designed slump, compressive strength, and water absorption at the age of 28 days but also decreasing carbon dioxide emission from cement production and utilizing the waste sludge from the water supply plants towards sustainable development.KeywordsCement replacementCompressive strengthHardened concreteWaste sludgeWater absorption