CDW-Based Geopolymers: Pro and Cons of Using Unselected Waste

Geopolymer technology is considered a strategic alternative for recycling construction and demolition waste (CDW) and to produce new construction products which meet the requirements of environmental and energy sustainability. The separation and management of CDW fractions is still a technological complex process and, even if large-scale separation technology is quite common, the necessity to perform this treatment may reduce the environmental and economic benefits of CDW reuse. So, a very promising option is represented by the manufacturing of geopolymers using unseparated CDW. In this aim, waste deriving from cement-based mortars, bricks and natural stones have been selected and widely characterized from a mineralogical, chemical and morphological point of view. Then, geopolymer mortars were produced using several amounts of either a single fraction or a mixture of the selected waste. The chemical, physical, mechanical, and microstructural characterization of the geopolymer-produced mortars was carried out to assess how the combination and different quantities of the mixed CDW affected the final properties. In particular, geopolymeric mortars produced from the unselected CDW showed higher mechanical properties, despite the lower apparent density, when compared to geopolymeric mortars produced from single fractions of CDW. The improvement of mechanical features seems to be not affected by the waste amount used, providing encouraging findings to promote the actual use of unseparated CDW with the resulting enhancement of environmental and economic benefits.