Preparation and properties of metakaolin-fumed-silica geopolymer modified with sodium silicate and potassium silicate activators

Geopolymers, which are environmentally friendly materials with aluminosilicates as raw materials, are expected to replace cement in construction materials. Here, the effect of fumed silica (FS) on the properties of metakaolin (MK)-based geopolymer materials was investigated with MK, sodium silicate, and potassium silicate as the main raw materials; their microstructures were characterized, and their performance was tested. The geopolymer's compressive strength, particle size, and curing characteristics were measured with X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy for microstructural analysis. The total dissolved solids (TDS) method was employed to study the geopolymer and evaluate the effect of the resulting gel products on TDS. The results revealed that the strength of 4% FS could reach 56.3MPa after 7 days of incorporation, and the strength increased by 20% and 12% compared with the 0% and 2% groups, respectively. Meanwhile, studying the microstructure of kaolin revealed that the best mechanical and physical properties were obtained when kaolin was calcined at 700°C. In addition, the mixture of alkaline activators increased the reactivity of MK, and the mixed alkaline-excited geopolymer from sodium silicate and potassium silicate exhibited enhanced matrix strength properties compared to the single alkaline activators. Overall, the inclusion of the FS material resulted in the optimization of the mechanical properties, confirming the improvement in the mechanical properties.