Fiber-reinforced foamed geopolymer with enhanced strength: Synergistic roles of H2O2 and fly ash cenosphere

Although conventional foamed geopolymers offer attractive characteristics such as a low carbon footprint, light weight, and thermal insulation, their typically low mechanical strength restricts their application as lightweight structural materials. Moreover, their inherent brittleness results in poor crack-control. Once cracks form, both the thermal insulation functionality and the durability are significantly impaired. In this study, an innovative synergistic pore‑forming strategy, combining H 2 O 2 chemical foaming with fly ash cenosphere (FAC) templating, is proposed for the preparation of foamed geopolymers. The rigid skeleton of FAC is fully exploited to optimize strength, while polyethylene (PE) fibers are simultaneously introduced for cooperative toughening, thereby enhancing the deformation capacity and crack‑control ability of the resulting composite. The effects of H 2 O 2 dosage, precursor ratio, fiber length, and fiber content were systematically investigated from the perspectives of macroscopic tensile and compressive behavior, cracking patterns, thermal conductivity, and microstructures. The produced foamed geopolymer achieves a compressive strength of nearly 20 MPa at a density of 800 kg/m 3 , exceeding that of existing H 2 O 2 ‑foamed geopolymers of comparable density by more than 70%. It also attains a high tensile strain capacity of up to 6% while limiting the crack width to as low as 180 μm. Its thermal conductivity stays at approximately 0.2 W/(m·K), thereby retaining favorable thermal insulation performance. These findings offer valuable guidance and support for promoting the application of foamed geopolymers in integrated thermal-structural contexts.