Mechanical and chemical properties of metakaolin-based geopolymer exposed to elevated temperature

A method is presented to fabricate metakaolin-based geopolymers that are structurally and mechanically stable up to 600 degrees C. The chemical environment of the geopolymers is characterized using thermogravimetric analysis and Fourier-transform infrared spectroscopy. Residual free water turned into steam and caused damage to the geopolymer when exposed to elevated temperatures. The curing temperature was increased from 80 to 120 degrees C to remove water during the curing process. A correlation was drawn between the amount of Si-O-Al linkage formed and the position of fingerprint peaks in infrared spectra, providing a tool to evaluate the level of geopolymerization. Flexural and tensile properties of geopolymers fabricated using the optimized method were measured for no heat treatment and for exposure to elevated temperatures of 200, 400, and 600 degrees C. The flexural strength was measured to be 10.80 +/- 2.99 MPa at room temperature, 10.36 +/- 0.64 MPa at 400 degrees C, and 8.04 +/- 1.60 MPa at 600 degrees C. The flexural modulus is reported to be 13.09 +/- 3.40 GPa at room temperature and 11.03 +/- 0.53 GPa at 600 degrees C. The flexural toughness decreased with increasing temperature. The tensile properties of the geopolymer were measured with direct tensile tests paired with an extensometer. The tensile strength decreased from 4.16 +/- 2.08 MPa at room temperature to 3.13 +/- 0.97 MPa at 400 degrees C, and 2.75 +/- 0.86 MPa at 600 degrees C. The Young's modulus decreased from 45.38 +/- 30.30 GPa at room temperature to 26.88 +/- 6.65 GPa at 600 degrees C. Both flexural and tensile tests have shown that the metakaolin-based geopolymers cured at 120 degrees C is mechanically stable at temperatures up to 600 degrees C.

Automated summary

This study presents a method for fabricating metakaolin-based geopolymers that can maintain their structural and mechanical stability up to 600 degrees C. The chemical composition of the geopolymers was analyzed using thermogravimetric analysis and Fourier-transform infrared spectroscopy. The presence of residual free water led to damage when exposed to high temperatures, so the curing temperature was increased to remove water during the curing process. A correlation was found between the formation of Si-O-Al linkage and the position of fingerprint peaks in infrared spectra, providing a means to evaluate the extent of geopolymerization. The flexural and tensile properties of the geopolymers were measured at different temperatures, and it was found that the metakaolin-based geopolymers cured at 120 degrees C remained mechanically stable up to 600 degrees C.