Compressive Strengths and Microstructural Properties of Geopolymeric Materials Arising from the Addition of Semi-crystalline Alumina to Silica-rich Aluminosilicate Sources

This work aims to investigate the behaviour of the semi-crystalline alumina added to the aluminosilicates rich in amorphous and crystalline silica during the geopolymerization. Waste fired brick and metakaolin used in this work are rich in amorphous silica and quartz, respectively. Bauxite calcined at 600 °C was used as a semi-crystalline alumina source. The calcined product was added to each aluminosilicate with mass ratios calcined bauxite/metakaolin or calcined bauxite/waste fired brick equals 0, 0.1, 0.2, 0.3 and 0.4. Geopolymer pastes were obtained by adding sodium waterglass to each composition. The hardened pastes were cured at room temperature for 28 days before characterization. The compressive strengths of the geopolymer materials when the mass ratios of calcined bauxite/metakaolin are ranging from 0 to 0.3 increase from 36.33 to 55.09 MPa and drop from 55.09 to 43.19 MPa when that mass ratios increase from 0.3 to 0.4. Whereas those from waste fired brick decrease from 47.81 to 19.91 MPa with increasing the mass ratios. The spectra of the energy dispersive X-ray analysis of geopolymer materials from metakaolin and the one from waste fired brick without addition indicate the formation of Si-rich geopolymer networks. Whereas the one from waste fired brick after the addition of semi-crystalline alumina are mainly composed of Al-rich geopolymer structures. It can be concluded that the semi-crystalline alumina added to the metakaolin spread in the network of the final products while this alumina does not react with amorphous silica contained in the structure of waste fired brick during the geopolymerization.