Philippe Michaud

Synthesis of consolidated materials from alkaline solutions and metakaolin: Existence of domains in the Al-Si-K/O ternary diagram

The activation of metakaolin using an alkaline solution is a method for producing high quality consolidated materials. Si, Al and K are the main factors that influence the nature of the consolidated materials. This study focuses on the effects of the composites on the final network formation. Two types of alkaline solutions, one (Sc) based on a commercial potassium silicate solution and the other (Sl) synthesized by mixing KOH and amorphous silica, were studied, and their effects on the network formation of consolidated materials were compared and discussed. Four types of materials were observed and identified based on different Si, Al and K contents, including a geopolymer, gel, sedimented materials and hardening materials. These behaviors are manifested in the various polycondensation mechanisms and microstructures, which were characterized using FTIR spectroscopy, thermal analysis, X-ray diffraction measurements and Scanning electron microscope observations. The influence of Si, Al and K is discussed according to network formation.

Geomaterial foams: role assignment of raw materials in the network formation

The geomaterial foams studied is based on geopolymerization reactions, which is a type of geosynthesis that involves silico-aluminates. Its study during formation has however revealed a different behavior than geopolymer, suggesting the formation of various networks. This work investigates the interaction between initial compounds (metakaolin, silica fume, potassium-based solution) by a kind of mixture decomposition to ultimately understand the formation mechanism of foam. The structural evolution was determined using thermal analysis, FTIR spectroscopy and 27Al and 29Si MAS-NMR measurements. The use of different raw materials in combination with various solutions demonstrates the formation of various species in solution. The reactivity of the solution will then evolve in different ways. The Si/K ratio controlled the type of species created and, particularly, the reactivity in the mixture. From the various reactions of dissolution and polycondensation that were deduced, we could identify the composition of the four networks (K0.5SiAl0.75O6.8H8.6; K2Si2O5; KAlSi2O4,1.5H2O; and amorphous silica) constituting the foam.

Role of Alkaline Cations on Geomaterial Foams

The synthesis of geopolymers based on alkaline polysialate, was achieved at slightly elevated temperature, by alkaline activation of raw minerals and industrial waste. The materials were prepared from a solution containing dehydroxylated kaolinite and alkaline hydroxide pellets dissolved in potassium or sodium silicate. Then the mixture was transferred to a polyethylene mould sealed with a top and placed in an oven at 70°C during 24 hours. The addition of an industrial waste, silica fume, leads to the formation of an in-situ inorganic foam. Whatever the alkaline cation, foam formation occurs. The properties depend on the viscosity of silicate precursors due to the amount of water and to the size of alkaline.