Salient parameters affecting the performance of foamed geopolymers as sustainable insulating materials

The carbon footprint of buildings is mainly attributed to the embodied carbon of building materials and their hygrothermal performance. In recent years, the search for materials with low gray energy and better hygrothermal performance has increased. Foamed geopolymers are among the materials that are attracting a lot of attention. Their high hygrothermal performance and the fact that they can be synthesized from abundant earth elements at ambient hygrothermal conditions are the main reasons for their growing popularity. Foamed geopolymers can also be produced from commonly available industrial wastes providing new opportunities for a circular economy. Many studies have been done to engineer these materials for specific applications in water purification, catalysis, thermal insulation, hazardous waste encapsulation, and acoustic isolation. Several recent papers have been discussing the mechanical features of geopolymers. Recent reviews also focus on the processing, applications, and properties of foamed geopolymers. However, a review about the impact of manufacturing parameters on porosity, pore nucleation, and pore parameters is still missing. These parameters determine the intrinsic and extrinsic thermal isolation properties of foamed geopolymers. This article aims to address this research gap. The effects of pore-forming agents, molar ratios of oxides, water, curing temperature, and pH on the microstructure of foamed geopolymers are discussed in this paper. The influences of these factors on intrinsic and extrinsic pore parameters are presented.