This work aims to investigate the feasibility that alkali-based geopolymer foams produced from metakaolin and Na₂O₂ are applied for fire protection. Dry bulk density, porosity, mechanical strength, thermal conductivity, and fire resistance of the geopolymer foams are discussed as a function of the Na₂O₂ amounts. As Na₂O₂ content varies from 1% to 4%, dry bulk density, mechanical strength and thermal conductivity of the geopolymer foams approximately exhibit opposite trends with that of the porosity. At the later stage of the 3 h fire-resistance tests, the reverse-side temperatures of all tested samples were always maintained at 220–250 °C. Meanwhile, the amorphous skeleton structures have been converted to smooth ceramics during the high temperature processes, which is the main reason that the geopolymer foams possess a stable porous structure and excellent fire resistance. Therefore, we could conclude that alkali-activated geopolymer foams with extraordinary fire resistance have great potential for fire protection applications.

This paper aims to investigate the influence of coal fly ash (CFA) addition on the fireproof properties of the metakaolin-based geopolymer foams. The physical properties, thermal conductivity and fire resistance of the CFA-metakaolin-based geopolymer foams are discussed. The CFA-metakaolin-based geopolymer foams achieve a dry density between 259.43 kg/m³ and 349.73 kg/m³, a porosity between 71.78% and 72.98%, a thermal conductivity between 0.0871 W/(m·K) and 0.0944 W/(m·K) and a compressive strength between 0.38 MPa and 0.56 MPa, exhibiting better physical properties than that of the porous blocks without CFA addition. It is also found that the CFA addition could decrease the viscous sintering temperature and change the phase compositions of sintering products, resulting in the porous structure deterioration in a certain extent and obvious rise of the final reverse-side temperature during the fire-resistance tests. Fortunately, the conversion of the amorphous geopolymer gel to ceramics has helped to maintain the main skeleton structure stability. The CFA-metakaolin-based geopolymer foams still exhibit excellent fire resistance, and the reverse-side temperatures are always within 250 °C after 3 h fire-resistance tests.

Safety treatment of the nuclear wastes is an important and challenging task troubled scholars for years. In this work, geopolymer was prepared to solidify simulated radionuclide strontium by 4A zeolite and metakaolinite. The effect of radionuclide strontium with different solidification conditions on electrical conductivity and final setting time were investigated and the variation tendency of electrical conductivity has well been in accord with the “three stage” during the whole geopolymerization process. Meanwhile, the mineral phases and chemical bonds of the geopolymer were analyzed by XRD and FTIR respectively. Results show that: (I)the electrical conductivity during the geopolymerization process has the same variation tendency as the final setting time, (II)strontium caused hysteresis effect on geopolymerization process, (III)strontium takes part in the polymerization reaction according to the XRD of geopolymer, and there's little chemical bond vibration effect with the addition of strontium according to the IR result. The results indicated that zeolite-like minerals are synthesized during the geopolymerization process. The immobilization of simulated radionuclide strontium is mainly attributed to absorption, ion exchange, and physical encapsulation.