Composite geopolymers of metakaolin and geothermal nanosilica waste: Fid-Bau Portal

Composite geopolymers of metakaolin and geothermal nanosilica waste

Gomez-Zamorano, L.Y. / Vega-Cordero, E. / Struble, L.

Highlights•Geothermal nanosilica was used to produce metakaolin-geopolymers.•The addition of the nanosilica reduced the demand of the sodium silicate.•High contents of nanosilica increased the porosity and reduced the strength.•Crystallization of nepheline and albite was observed at high temperatures.•The XRD amorphous halo shifted to higher angles due to geopolymerization.

AbstractThis paper investigated the effect of a nanometric silica from a geothermal waste on the compressive strength, microstructure, and reaction products formed on geopolymers cured at room temperature; the thermal stability was evaluated after exposure up to 800°C. The geothermal silica waste replaced 0–20% of the metakaolin and was suspended in the alkaline solution, to avoid agglomeration. Sodium silicate and sodium hydroxide were used as alkaline solutions and added to adjust the molar ratios of SiO2/Al2O3 at 2.8, 3.0 and 3.2, Na2O/SiO2=0.32 and H2O/Na2O=10. The compressive strength of the geopolymers was evaluated up to 60days of curing. The pastes were characterized by X-ray diffraction, Fourier transformed infrared spectroscopy, and scanning electron microscopy. X-ray diffraction showed the formation of amorphous reaction products, with a shifting in the amorphous halo related to the raw materials; on the other hand, a shift in the characteristic band of aluminosilicates in the infrared spectra also evidenced the geopolymerization process. While the addition of the geothermal silica waste reduced slightly the strength at room and high temperature due to the formation of porosity, its use diminished the demand of waterglass and therefore obtaining low-cost and more sustainable binders.