Owing to the energy consumption reduction and the CO<sub>2</sub> emission mitigation via using solid waste as raw materials, foam geopolymers with high porous structure have been emerged as one of the most interesting heat-preservation materials in recent years. Meanwhile, good long-term service and durability performance are highly desired for the heat-preservation materials with intrinsic pores. Herein, we reported a simple and facile foaming strategy for foam geopolymers synthesis from coal fly ash, involving the novel polymethylhydrosiloxane (PMHS) as the foaming agent, to increase its durability property. The macroscopic scale pore diameter of synthesized foam geopolymers could range in 0.27–6.82 mm. When 0.8%wt PMHS and 1.0%wt calcium stearate (CS) were applied to synthesize the sample “FGP-PMHS-0.8”, the pore structure achieved the optimal parameters, with the dry density of 460.2 kg/m<sup>3</sup> and the compressive strength of 0.77 Mpa. The synthesized “FGP-PMHS-0.8” possessed the thermal conductivity of 0.2279 W/(m K), which conforms to the general range for inorganic heat-preservation materials. Benefiting from the PMHS as foaming agent, the synthesized foam geopolymers showed the super hydrophobic property, with the contact angles of as high as 168°–170°; the water absorption rate of “FGP-PMHS-0.8” was 63.3%, which was far lower than the traditional foam geopolymers of 146.2%. Due to the effect of PMHS, part of the hydroxyl groups on foam geopolymers was replaced by the hydrophobic methyl groups, so the surface energy of foam geopolymers decreased, which increased its hydrophobicity. Overall, the development of foaming strategy via PMHS paves the way for developing durability performance of foam geopolymers, promoting the long-term service of inorganic heat-preservation materials.

Novel foaming strategy for the synthesis and performance of geopolymer foams

ACS Spring 2022

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