Pure Al2O3·2SiO2 synthesized via a sol-gel technique as a raw material to replace metakaolin: Chemical and structural characterization and thermal behavior

The performance of alkali activated cements is strongly influenced by mineralogical composition and the impurity content of metakaolin, their aluminosilicate precursor. In this study, pure aluminosilicates were synthesized via the sol-gel technique and the possibility of using them to replace metakaolin was explored. The study of their thermal behavior by simultaneous Thermogravimetry/Differential Thermal Analysis allowed the best temperature for inducing their complete dehydroxylation to be determined. X-ray diffraction, Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy showed that, after calcination, the materials were amorphous, homogeneous, and had a higher content of reactive Al(V) than metakaolin. The reactivity of the materials was ascertained by a leaching test carried out in strong alkaline solution. The quantification of the released aluminate and silicate species, carried out by inductively coupled plasma atomic emission spectroscopy, provided results which encouraged the use of the synthesized materials in the preparation of alkali activated cements and geopolymers