Effects of Fe 2 O 3 /SiO 2 Molar Ratios in the Fe-Silica on the Compressive Strengths and Microstructural Properties of Geopolymer Materials Derived from Waste Fired Clay Brick and Metakaolin

Ferrisilicate was considered a crystalline zeolite containing iron (III) and silicon in the zeolite lattice positions. The aim of this work is to study the influence of Fe 2 O 3 /SiO 2 molar ratios contained in the Fe-silica on the properties of geopolymer materials derived from waste fired clay brick and metakaolin. Fe-silica with various Fe 2 O 3 /SiO 2 molar ratios of 0.2, 0.4, 0.6, 0.8 and 1.0 were synthesised using rice husk ash and hematite. 0 and 10 wt. % of each type of aluminosilicate is added to each type of Fe-silica. A commercial sodium silicate solution with a SiO 2 /Na 2 O molar ratio of 1.6 is used as a hardener. X-ray diffractometry and Fourier Transform Infrared spectroscopy are used for the characterisation of the Fe-silica and the geopolymers. In addition to these analyses, the compressive strengths of the geopolymer materials have been measured and the fragments obtained have been examined using a scanning electron microscope. The results show that the compressive strengths of metakaolin-based geopolymers increase from 53.34 to 69.08 MPa when the Fe 2 O 3 /SiO 2 molar ratios contained in the Fe-silica are incremented from 0 to 0.8. When the Fe 2 O 3 /SiO 2 molar ratio is increased from 0.8 to 1.0, they are reduced from 69.08 to 63.22 MPa. In contrast, those of geopolymer materials derived from waste fired clay brick decrease from 45.42 to 21.15 MPa when their Fe 2 O 3 /SiO 2 molar ratios rise from 0 to 0.6 increases from 21.15 to 24.11 MPa beyond 0.6. The micrograph of the geopolymer material from the mixture of metakaolin and Fe-silica with a molar ratio of Fe 2 O 3 /SiO 2 equal to 0.8 is more compact, homogeneous and partially smooth compared to other geopolymers. The presence of hematite and cristobalite, which act as fillers, is evident from the X-ray patterns of geopolymer materials after the addition of Fe-silica. This work shows that the addition of metakaolin to multi-molar of Fe-silica significantly improves the compressive strength of geopolymer materials. On the other hand, this addition leads to a reduction in the compressive strength when waste fired clay brick is used.