A comparative study of the compressive strengths and microstructural properties of geopolymer cements from metakaolin and waste fired brick as aluminosilicate sources

The main target of this work is to compare the compressive strengths and the microstructural properties geopolymer cements from waste fired brick as low-value aluminosilicate-rich waste and metakaolin. The chemical reagent used in this investigation is a sodium waterglass from rice husk ash. The obtained results show that waste fired brick contains a higher amount of SiO2 (60.98 wt%). The quartz content in the waste fired brick, standard and local metakaolins was estimated at approximately 8, 2 and 8 wt%, respectively. The X-ray patterns of these aluminosilicates indicate the broad hump structure between 15 and 35° (2θ) corresponding to the amorphous aluminosilicate phase. Besides this amorphous phase, waste fired brick shows the broad bands of hematite at 33.29 and 35.87° (2θ) indicating that some Al is replaced by Fe in IV-fold coordination. The micrographs of metakaolins show the platy-shaped with coarse-grain particles and the one of waste fired bricks indicates the platy- and spherical-shaped with smaller particle sizes. The compressive strength values of geopolymer cements from local and standard metakaolins are 40.32 and 44.46 MPa, respectively. Whereas the one from waste fired brick is 47.82 MPa. It was found that waste fired brick could be used as an alternative low-value aluminosilicate-rich waste for producing geopolymer cements with high compressive strength.