Manufacturing of fired bricks derived from wastes: utilization of water treatment sludge and concrete demolition waste

Abstract

The treatment of wastewater certainly contributes to reduce water pollution on environment, but it also generates large amounts of water treatment sludge (WTS) which must be further treated to reduce potential health risks and environmental impacts. However, from a circular economy approach, WTS should be considered as a byproduct which can replace natural raw materials for construction industry. Moreover, this sector is urged to reduce its CO2 footprint which is mainly produced by the embodied impact of construction materials during the initial and final phase, in a life cycle assessment perspective. For these reasons, this paper assesses WTS for replacing natural clay in brick industry and it also evaluates the impact of adding concrete waste (CW) to the blend for improving technological properties of the so-made bricks. Thus, bricks containing sludge and CW (i.e. from 0 to 20%) have been successfully manufactured by firing at 1000 °C and tested. It was observed that water absorption and apparent porosity values increase while bulk density, compressive strength and thermal conductivity values decrease by depending on the increment in CW content. The bulk density of the fired bricks having 5–20 wt% CW content ranged from 1.72 to 2.10 g/cm3, compressive strength ranged from 8.9 to 20.2 MPa, water absorption from 7.9 to 17.5% and thermal conductivity from 0.889 to 0.659 W/m K. Because of these reasons, it is concluded that this novel brick made by WTS and CW can be properly manufactured at industrial scale, shows good performance and reduces environmental issues of both brick industry and water treatment plants.