Ceramics-Silikáty

Drinking water treatment sludge (DWTS) is a by-product generated during the purification of groundwater used for the drinking water supply in the municipality of Vilnius, Lithuania. A scientific work on the replacement of the binder (Portland cement CEM I 42.5R), with drinking water treatment sludge (DWTS) in the mortar is presented in this research. DWTS was calcined at 850 °C for 4 hours and milled in a drum mill for 24 hours, before its incorporation into the mortar. The DWTS used in this study contains a high amount of Fe₂O₃ (seeking up to 68.2%). The calcined DWTS was incorporated into the mortar by replacing up to 10% of the binder by its weight (at increments of 2.5%). The following mortar properties were tested: hydration time and temperature, density, ultrasonic pulse velocity, water absorption, porosity, compressive and flexural strengths. The predicted frost resistance was calculated according to the obtained research results. The results of the tests revealed that the calcined DWTS has a positive effect on the mortar properties. The closed porosity increased from 7.4% to 8.4%. The density of the concrete modified with 10% DWTS decreased by 1.2%. In all the cases, the replacement of Portland cement with DWTS resulted in a lower flexural strength, compared to the control com-position. However, the results of the compressive strength tests indicate that up to 5% of the Portland cement can be replaced with DWTS without a loss of mechanical performance. In this study, the results of the compressive and flexural strengths were normalised and expressed in MPa/kg to evaluate the strength achieved per unit weight of Portland cement. With the incorporation of DWTS into the mortar, the number of predicted freeze-thaw cycles increases thus extending the durability of the mortar.