Thermal stability of one-part metakaolin geopolymer composites containing high volume of spodumene tailings and glass wool

This paper deals with the synthesis and thermal stability of one-part metakaolin geopolymer composites containing high volume of spodumene tailings (Quartz Feldspar Sand; QFS) and glass wool (GW). One of the objectives of the study was to prepare materials encompassing a maximum amount of waste streams with some potential thermal stability. Several compositions were prepared with sodium metasilicate anhydrous (Na2SiO3) wt.% of 0.5, 2.5, 5, 10 and 12,5. The one-part metakaolin geopolymer composites were cured at 60 degrees C for 24 h and the mechanical properties were assessed at 7 days and after post-heat treatment at 500, 750, 1000, 1100 or 1200 degrees C. X-ray diffraction, dilatometry, scanning electron microscopy and thermogravimetry analyses were used to study the stability of the prepared geopolymer composites until 1100-1200 degrees C. The results showed that more than 20 MPa compressive strength could be achieved with metakaolin geopolymer composites containing only 20 wt% of metakaolin. Metakaolin-GW geopolymer composites were stable up to 500 degrees C. Meanwhile, their counterparts containing QFS were stable up to 1100-1200 degrees C; samples prepared with higher dosage of sodium (Na2SiO3 > 5 wt%) retained more than 50% of their initial strength after thermal treatment at 1100 degrees C. Interestingly, for dosages of Na2SiO3 <= 5 wt%, more than 300% increase of strength was observed after thermal treatment at 1100-1200 degrees C. The use of QFS limited the thermal shrinkage at mild temperatures (<1000 degrees C), but favoured densification and strength development at 1100-1200 degrees C.