Physical, mechanical and thermal behaviour of adobe stabilized with the sludge of wastewater treatment plants

Abstract

The need for treated water is essential for life. With the constant increase in population, the most common way to purify surface water is through conventional water treatment plants (WTPs). The high volume of residue (sludge) generated in this process is most often returned to the catchment site, negatively affecting the ecosystem. The sludge of WTPs is similar to soil because it is composed of inorganic solids. Adobe is a construction material made from water and soil without the burning process, so it is considered sustainable, recyclable, and energy-efficient and can be stabilized with various materials. Therefore, the objective of this work is to develop adobes using the sludge of WTPs and to analyse their physical, mechanical and thermal properties. Adobes were produced with five concentrations of sludge by mass: 0, 1, 3, 5 and 7%. It was observed that with the increase in the sludge concentration, there was an increase in the capillarity and a decrease in mass, the water absorption was limited to 3% of sludge, and there was an increase in the bulk density. The linear shrinkage, thermal conductivity and compressive strength were not influenced. The addition of WTP sludge altered some properties of adobe. The use of WTP sludge in adobe is limited to 3%; above that, the adobe becomes unstable in relation to water. Therefore, the use of WTP sludge in the manufacture of adobe is feasible in controlled concentrations and is a sustainable use of the residue.