Valorization of water treatment sludge waste by application as supplementary cementitious material

Abstract

This paper investigates the potential of using calcined water treatment sludge to the development of supplementary cementitious material. Sludge samples have been collected in the drying beds of a water treatment plant located in Southern Brazil and calcined in the laboratory. Chemical and mineralogical characterization has been performed through energy dispersive X-ray spectrometry, thermogravimetric analysis, and X-ray diffraction with crystalline phases quantified by Rietveld refinement. Morphological analysis has been supported by scanning electron microscope images. Physical characterization has been carried out through specific surface area, particle size distribution, and pozzolanic activity performance with Portland cement. Results have shown that the water treatment sludge is a non-hazardous and non-inert waste without environmental restrictions for use in construction. Considering technical, environmental and economic aspects related to energy consumption, sludge samples calcined at 600 °C for 1 h present the most promising results regarding the production of supplementary cementitious material equivalent to a normal pozzolan, while highly active pozzolan requires 750 °C for 1 h. Calcined water treatment sludge showed great technical and environmental potential to be used as an alternative source of supplementary cementitious material in the near future.