The identification of geopolymer affinity in specific cases of clay materials

The article describes a synthesis of a geopolymer matrix based on a specific raw material –thermally treated shale – a waste material from mining activity. The intensity of the thermal treatment has been studied by solid-state 27Al nuclear magnetic resonance. The amount of 38–54 wt.% of aluminum ions in tetra-coordination, according to the sampling point, signals the possibility of converting the waste material into a solid geopolymer matrix. A mineralogical analysis has specified that this value corresponds to the aluminum ions involved in two different shale components: the amorphous clayed residues and a mullite phase. In spite of the high content of mullite and quartz, the amorphous clay residues in the shale react with an aqueous alkaline solution and create stabile solids which have shown excellent mechanical properties. The character of the geopolymer bonds has been investigated by infrared spectroscopy, which has proven the presence of geopolymer chaining and distinguished them from mullite wavenumbers. The obtained results have confirmed that the shale could be used as a new raw material for geopolymer synthesis.