Assessing rapid strength achievement in geopolymers from mixed construction and demolition waste

For Turkiye and other earthquake-prone countries, facing the challenge of downcycling and the accumulation of massive quantities of mixed construction and demolition waste (CDW), the rapid upcycling of CDW is essential for the very sake of affected communities. This is particularly important for nations that are major cement manufacturers and seek to transition to alternative and greener binders, as part of their commitment to Net-Zero targets. Accordingly, we aim to develop alkali (NaOH)-activated binders (i.e., geopolymers) based on mixed CDW fractions, constituting the majority of CDW compositions, (i.e., different masonry elements [red clay brick-RCB, hollow brick-HB, roof tile-RT], concrete [C], and glass [G]). These geopolymers are designed to achieve structural-strength grades (>50 MPa) within short timeframes using hightemperature curing, enabling rapid production of temporary prefabricated housing units and emergency shelters. The effects of curing temperature (105-125 degrees C) and Na concentration (8-15 %) on compressive strength were systematically evaluated. Optimal performance occurred at 12 % Na and 115 degrees C, where individual CDW-based precursors reached 2-day strengths up to 68.1 MPa, and mixed precursors yielded 56.5 MPa. The microstructure of mixed CDW-based geopolymers is significantly improved with increasing masonry content, enhancing compressive strength and altering geopolymerization products (forming a mixture of NASH and CASH structures). Compared to ordinary Portland cement (OPC) pastes, the developed CDW-based geopolymers demonstrated similar to 63 % lower embodied energy and similar to 68 % lower carbon footprint. The most efficient mixture required only 54 MJ/m(3) per MPa, compared to 108 MJ/m(3) per MPa for OPC, offering a twofold eco-efficiency advantage. These findings suggest that different CDW elements can be efficiently reintegrated rapidly into applications such as prefabrication, rapid housing, and emergency shelters, offering a sustainable and practical solution for post-disaster reconstruction.