Author(s)

A Yagüe, S Valls & E Vàzquez

Abstract

Our society generates a large quantity of waste which we should re-use, as is the case with dry sludge from sewage treatment plants. This sludge has been subjected to anaerobic digestion and then to a drying process that partially stabilises the organic matter, eliminates pathogenic micro-organisms and reduces the total volume of sludge to be handled. A DRX study of its crystalline fraction detects the presence of calcite and silica, and the absence of clays. In this paper we study the influence of the presence of this sludge, used as an additive in Portland cement mortar, on the physical and mechanical properties of this mortar. The addition of sludge reduces the mechanical strength of the mortar, increases its porosity, reduces its density, and also retards the hydration process of the cement. The use of sludge in mortar is beneficial in that, when it reacts with the cement and comes to form part of the binding matrix, the sludge stabilises and the quantity of leachable heavy ions is reduced in comparison with that of free dry sludge. 1 Introduction This paper describes the preparation of a construction material containing waste added to a matrix with Portland cement. The waste in question is the dry sludge resulting from waste water treatment, which contains potentially toxic contaminants such as heavy metals. The sludge used is a dry sludge from Sabadell (Barcelona) produced by anaerobic biological digestion. In the final phase of the waste treatment process, it undergoes a thermal drying process which substantially reduces its volume, thus facilitating handling and eliminating any pathogenic microorganisms that could be present.

Keywords