Assessing the upcycling potential of construction and demolition waste derived silt: Activation, physicochemical and mineralogical characterisation

The increase in infrastructure requirements of modern urban societies has led to repair, retrofitting or demolition of existing buildings producing enormous amounts of construction and demolition waste (CDW). Processing and recycling of fine fractions from CDW is an area of research with growing interest, primarily due to the mineralogy of such waste fines that make them potential candidates to be utilised within binder systems (cement-based or alkali-activated). The utilization of fine waste from CDW recycling in cementitious binders necessitates a deeper understanding of its physical, mineralogical, and chemical composition in order to enhance confidence in its application. Therefore, this study focuses on characterisation and developing a suitable treatment for CDW derived silt for its use as a binder precursor. To achieve this, the physical, chemical, mineralogical and pozzolanic properties of CDW derived silt were studied and mechanochemical activation (high energy milling) and thermal activation (calcination) were adopted to enhance its reactivity. The findings from XRD, FTIR, elemental composition, and examination of microstructure of treated and untreated samples collectively revealed alterations in the mineral phases and morphology resulting from the treatment processes. The reactivity of the activated samples was evaluated by examining their solubility in an alkaline environment using ICP-OES and measuring their heat of hydration using adapted R3 tests. It was determined that the samples calcined at 750°C exhibited a higher heat of hydration and a greater concentration of soluble silicon (Si) and aluminium (Al) in sodium hydroxide solution.