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Purpose The purpose of this paper is to address the use of sludge from water treatment plant (WTP sludge), in its natural form (wet), in the construction industry, especially in the production of concrete, evaluating the effects of replacing natural sand with different WTP sludge levels in the concrete properties. Design/methodology/approach The dosage study evaluated mixtures with replacement levels of 0, 5, 7 and 10 percent of wet sludge in relation to the mass of natural sand, analyzing their effects on mechanical properties and water absorption in concrete with water/cement (w/c) ratios of 0.45, 0.55 and 0.65. Findings From the results obtained, it is possible to note that the addition of WTP sludge in its natural form (wet) reduces the strength of concrete. However, from a technical point of view, a level of replacement of up to 5 percent for applications in concrete is suitable, provided that it is not structural concrete. Practical implications Further studies should be conducted to verify the influence of the replacement of sand for heat-treated sludge in concrete properties, also analyzing the environmental viability linked to the calcination process. Originality/value Few studies are conclusive in relation to the use of WTP sludge in concrete production. This study shows statistically the negative effect of the addition of wet sludge in the mechanical properties and in the water absorption of concretes from different w/c ratios.

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The water treatment process generates a residue called water treatment plant (WTP) sludge, which needs to be correctly characterized to ensure appropriate disposal or reuse. This study aimed to characterize the centrifuged sludge produced at the Tamanduá WTP, Iguaçu Falls City, Brazil, and considered opportunities for its reuse in the production of concrete for the civil construction industry. Wet sludge (sludge in its natural form) analysis included the determination of total solids, moisture content, density, pH, and inorganic parameters (As, Al, Ba, Cd, Pb, Cr, F, Hg, Ag, and Se) through thermogravimetric analysis, X-ray diffraction, and chemical analysis by X-ray fluorescence and loss ignition. For calcined WTP sludge, chemical and mineralogical composition and laser granulometry were evaluated. The results indicated that calcined sludge had the potential to be used in the production of cement materials; conversely wet sludge did not reach the appropriate safety standards due to the high quantity of organic matter.