Evidence of a Fractal Percolating Network During Geopolymerization

Abstract

This study focuses on the transition from the paste state to the solid state which occurs during the hardening of metakaolin‐based Na‐geopolymers. The occurrence of primary interactions and the structural properties were investigated using classical oscillatory rheology (OR) methods. A time‐frequency‐resolved rheology (TF2R) method was used in order to obtain more detailed information about the percolation and aggregation mechanisms. The results obtained show the occurrence of the following process: (i) Elastic behavior predominates initially over the viscous behavior at low frequency. (ii) A percolating process then takes place when the viscoelastic parameters become parallel over more than two frequency decades. At the gel point, a mass‐fractal dimension of approximately 2 was determined. (iii) During the formation of the porous network, the viscous behavior predominates over the elastic one due to the occurrence of polycondensation reactions. (iv) Lastly, a solid state is reached, where the elastic modulus shows a plateau and the viscous modulus decreases. These macroscopic mechanical results are compared using the small angle x‐ray scattering technique. Scattering experiments were in complete agreement with the rheological measurements and showed the presence of aggregated oligomers and a mass fractal dimension equal to 2.1 at the gel point, increasing up to a surface fractal dimension reflecting the formation of the mesoporous network.