Acid-based geopolymers using waste fired brick and different metakaolins as raw materials

Three metakaolins and waste fired brick were used to explore the effects of iron oxide, amorphous silica and quartz in the raw materials on the compressive strength and the microstructural properties of acid-based geopolymers cured at room temperature and 60 °C. Quartz content in the metakaolin from Dibamba is about 22.0 wt% and each other samples contain around 8.0 wt%. Waste fired brick and metakaolin from Bangoua contain nanocrystalline hematite and have higher amorphous silica content. The higher quartz content in the metakaolin from Dibamba could prevent the incorporation of PO4 units in the networks. The compressive strengths of the acid-based geopolymers cured at room temperature are higher (35.3–56.4 MPa) compared to those cured at 60 °C (17.8–32.9 MPa). The higher amorphous silica and nanocrystalline hematite content in the starting materials could accelerate the hardening process. It can be concluded that iron oxide, amorphous silica and quartz in the starting material could affect the compressive strengths of acid-based geopolymers. •The compressive strengths of the specimens cured at room temperature are higher.•The compressive strengths of the acid-based geopolymer cured at 60 °C are lower.•The higher quartz content in the sample could prevent the incorporation of PO4 units in the networks.•The higher quartz content could affect the properties of the geopolymer cements cured at 60 °C.•The higher amorphous silica and FeIV content in the sample could accelerate the hardening process.