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<p>Geopolymers, prepared from metakaolin activated by potassium-based activators with corundum filler, were subjected to the temperatures up to 1200&#xa0;°C. The Si/Al molar ratio of individual mixtures ranged between 1.0 and 1.9. The increasing Si/Al ratio caused higher strengths; material activated by KOH only (without added potassium silicate) achieved compressive strength 9.2&#xa0;MPa and flexural strength 1&#xa0;MPa, while the highest compressive strength had material with Si/Al ratio 1.8 (86.5&#xa0;MPa) and highest flexural strength had material with Si/Al ratio 1.4 (3.6&#xa0;MPa). The research on the impact of thermal loading (200 to 1200&#xa0;°C) on the geopolymers was realized by thermogravimetry, thermodilatometry and by determination of residual mechanical properties, phase composition and pore size distribution. The compressive strength of all materials after heating increased significantly and reached its maximum between 800&#xa0;°C and 1000&#xa0;°C. The increase was more than 280% in the material with lowest added Si/Al ratio and it was between 90 and 136% in the materials with higher Al/Si ratios. The flexural strength of most materials decreased after heating to 200&#xa0;°C with maximal decrease to 50–90% of original strength and after that flexural strength increased with residual flexural strength more than 1&#xa0;MPa at 1200&#xa0;°C in all materials. The thermal load up to 1200&#xa0;°C promoted crystallization of new phases (leucite and mullite) which contributed to the increase of compressive strength. The porosity of geopolymers, determined by mercury porosimetry, gradually decreased upon the thermal loading, the smallest pores (with diameter 0.001–0.01&#xa0;μm) disappeared completely and sparse larger pores appeared between the newly formatted crystal phases. The tested materials proved excellent heat resistance and therefore they are very promising in the field of fire safety of buildings and also as a refractory material.</p>

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Thermally-induced chemical and physical transformations in metakaolin-based geopolymers

  • 期刊论文

  • 发表日期：

    2025年8月19日

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  • Alena Vimmrová,
  • Dana Koňáková,
  • Eva Vejmelková,
  • Vojtěch Pommer,
  • Jitka Krejsová,
  • Klára Kulhavá,
  • Robert Černý,
  • Martin Keppert

摘要

Geopolymers, prepared from metakaolin activated by potassium-based activators with corundum filler, were subjected to the temperatures up to 1200 °C. The Si/Al molar ratio of individual mixtures ranged between 1.0 and 1.9. The increasing Si/Al ratio caused higher strengths; material activated by KOH only (without added potassium silicate) achieved compressive strength 9.2 MPa and flexural strength 1 MPa, while the highest compressive strength had material with Si/Al ratio 1.8 (86.5 MPa) and highest flexural strength had material with Si/Al ratio 1.4 (3.6 MPa). The research on the impact of thermal loading (200 to 1200 °C) on the geopolymers was realized by thermogravimetry, thermodilatometry and by determination of residual mechanical properties, phase composition and pore size distribution. The compressive strength of all materials after heating increased significantly and reached its maximum between 800 °C and 1000 °C. The increase was more than 280% in the material with lowest added Si/Al ratio and it was between 90 and 136% in the materials with higher Al/Si ratios. The flexural strength of most materials decreased after heating to 200 °C with maximal decrease to 50–90% of original strength and after that flexural strength increased with residual flexural strength more than 1 MPa at 1200 °C in all materials. The thermal load up to 1200 °C promoted crystallization of new phases (leucite and mullite) which contributed to the increase of compressive strength. The porosity of geopolymers, determined by mercury porosimetry, gradually decreased upon the thermal loading, the smallest pores (with diameter 0.001–0.01 μm) disappeared completely and sparse larger pores appeared between the newly formatted crystal phases. The tested materials proved excellent heat resistance and therefore they are very promising in the field of fire safety of buildings and also as a refractory material.