Synthesis and foaming of a novel type of porous geopolymer material via salt activation

The construction industry's dependency on Portland cement and its poor recycling of construction and demolition waste (CDW) significantly contribute to global CO₂ emissions and environmental degradation. This study presents the synthesis and characterization of an innovative, foamed geopolymer material derived from ceramic waste (waste bricks), activated with sodium dihydrogen phosphate and foamed using calcium carbonate and citric acid. The research aims to develop sustainable thermal insulation materials through salt activation, an underexplored alternative to traditional alkali activation. The effects of varying foaming agent content and foaming activator concentration on density, porosity, thermal conductivity, and mechanical strength were systematically investigated. The most suitable parameters yielded a bulk density as low as 525 kg m⁻³ and thermal conductivity of 0.00998 W (m K)⁻¹, placing the material among the most efficient thermal insulators. True porosity reached up to 68.3%, while compressive strength ranged from 0.4 to 9.37 MPa. Microstructural analysis confirmed a hybrid aluminosilicate-phosphate network with tunable pore morphology. These results demonstrate that salt-activated geopolymers can serve as eco-friendly, low-carbon materials or have use in insulation applications, offering a viable approach to both waste valorization and CO₂ mitigation in construction.