Potential Use of Sewage Sludge Ash in Lime-Based Materials

Recycling of wastes and their by-products is attracting increasing interest worldwide because of the high environmental impact in the cement, concrete and other industries. This work deals with the study of the physico-chemical characteristics of binders based on sewage sludge ashes and lime. In a first step, we used X-ray fluorescence to determine the chemical composition of ash, lime and binders. This allowed us to see that the chemical composition of sewage sludge ash is similar to that of cement. We then used X-ray diffraction to identify the main mineralogical phases in the samples. Compressive strengths of mortars containing 20%, 40%, 60% and 80% of SSA showed that SSA has a long-term positive effect which might be related to a slight pozzolanic activity. The L4 binder consisting of 80% fine ash and 20% lime has a higher compressive strength than the others. The binder setting start time is greater than that of cement but shorter than that of lime. The study of the thermophysical properties of the L4 binder shows that it has a higher thermal resistance than cement and clay mortars. Moreover, it heats up less quickly because of its low effusivity compared to the latter two. This analysis highlighted the principal characteristics that must be taken into account to use SSA correctly in lime-based materials.