Thermal behavior of construction and demolition waste-based geopolymer

Unsorted Construction and Demolition Waste (CDW) from residential building was tested as solid precursor for obtaining eco-sustainable alkali activated materials with potential applications in the building industry. Suitable reactive systems for material consolidation were tested, including alkaline solutions of sodium hydroxides and/or silicates at different concentrations. Metakaolin (MK) was also tested as an additional precursor together with CDW in different ratios to optimize geopolymerization. An MK/CDW weight ratio of 40/60 and sodium silicate as alkaline activator allowed the production of a well-reacted and cohesive material, with a bulk density of 1.35 g/cm3, a monomodal mesoporosity with a modal pore size of 0.0214 µm (open porosity ∼42 vol%), and a compressive strength of 25 MPa, thus showing similar features to those of pure metakaolin based-geopolymers. Thermal characterization was performed up to 1000°C showing that the material can exhibit thermal stability up to 650°C. Above that temperature a shrinkage due to viscous flow occurred, followed by an expansion over 750°C with the formation of macropores and dense struts. Based on these results, the developed CDW-based geopolymer has the potential for use in green building applications, with adequate thermal stability up to medium-high temperatures.