Alkali-activation of recycled construction and demolition waste aggregate with no added binder

Abstract

The alkaline-activation of aluminosilicate compounds present in fine particles of unselected construction and demolition waste (UCDW) aggregates is investigated here. The aim is to stabilize UCDW aggregates by adding an alkali-activating solution (AAS) composed of sodium hydroxide and sodium silicate and then assess their potential employment in stabilized base/subbase road pavement layers. Contrary to the practice in other studies, no industrial–waste by-products (i.e., fly ash, slag precursor) or other components containing silica-aluminates were added to the material. Workability, strength, and stiffness values were evaluated at laboratory temperature (around 25 °C) for 7, 28 and 60 days. The resulting mixtures were compared with those containing pure water and a diluted AAS (50% of pure AAS and 50% of water). The resilient modulus of UCDW aggregates compacted with pure AAS was considerably higher than those containing both diluted AAS and water only. Similar conclusions were drawn for the unconfined compressive strength and indirect tensile strength parameters, which for UCDW with pure AAS were comparable to those for ordinary cement-stabilized granular materials. These results demonstrate the potential offered by the alkali-activation of aluminosilicate compounds present in fine particles of UCDW. The microstructural observation, carried out by Field Emission Scanning Electron Microscopy, coupled with an elemental analysis performed by Energy Dispersive Spectroscopy, supported the successful alkali-activation of UCDW fines.