Preparation and characterization of ultra-lightweight fly ash-based cement foams incorporating ethylene-vinyl acetate emulsion and waste-derived C-S-H seeds

•Large stockpile of fly ash was recycled to produceULFC.•Effects of technological parameters on properties of ULFC were studied.•Foam stability andstrength of ULFC were improved by adding EVA and C-S-H seeds.•The amount of potential energy conservation of ULFC-insulated facades was calculated. Recycling of accumulated fly ash (FA) from the coal-burning power plant positively avoids the severe environment problems. Also, to achieve the energy-savings in building facades, the excellent fire-resistant and heat-insulating high-porosity fly ash-based foamed cement (ULFC) with dry density less than 160 kg/m3, was formulated in this work. Ethylene-vinyl acetate (EVA) emulsion was introduced into ULFC slurry, and a lab-made hardening accelerator named A-3 and waste-derived calcium silicate hydrate (C-S-H) seeds from the discarded cement foams were also developed and mixed to regulate the early hydration rate of this green FA-based binder incorporating FA up to 50 wt%. Results revealed that under the optimum preparation parameters, the dry density, compressive strength and heat conductivity of ULFC at 28 days can approach to 154.7 kg/m3, 0.47 MPa and 0.0514 W/(m·K), respectively. Morphological analysis elucidated that the polymeric EVA film solidified at the gas–solid interface and well-interwined with hardened cement stone to improve the compressive strength when the specimens was cured at a relative humility of 60–65%. Moreover, the foam stability of ULFC was promoted by the increased bubble confinement force with an incremental content of EVA. Also, an optimized air-void structure was observed in the sample containing synthetic C-S-H from X-CT due to its nucleation effect on the hydration of cement particles. From the energy consumption analysis in practical application, more than 50% energy consumed for heat supply was conserved in ULFC-embedded exterior wall.