Use of Commercial Starch, Starches Derived from Cassava, Potato, and Yam as Additives for Synthesising Metakaolin-Based Geopolymer Composites

Abstract

The main objective of this work is to investigate the use of different starch sources (yam, sweet potato, cassava, and commercial starch) as additives for the production of metakaolin-based geopolymer composites. Geopolymer composites were prepared by replacing metakaolin with 0 and 15 wt% of each type of starch. The different powders obtained were separately mixed with a hardener containing a molar ratio of SiO₂/Na₂O of 1.6. X-ray diffraction and Fourier transform infrared spectroscopy analysis were used to determine the structural properties. The compressive strength and morphology of the prepared geopolymer composites were investigated. Results show that the reference geopolymer compressive strength is 36.25 MPa. These are 64.66, 48.49, 46.03, and 44.71 MPa when commercial starch, yam starch, cassava starch, and sweet potato starch, respectively have been used as additives. It can be seen that the compressive strength values of the geopolymers containing starches are higher than those of the reference geopolymer. The compressive strength of the geopolymer composite made by replacing metakaolin with commercial starch is higher than those made with yam starch, cassava starch, and sweet potato starch. The X-ray patterns of all the geopolymers show the same mineral and the infrared spectra show the same absorption bands, except for the one at 2,935 cm^-1 which appears on the spectra of the geopolymers containing starch. The geopolymer composite containing commercial starch has a more compact and dense microstructure. Those containing starches from yam, cassava, sweet potato, and the reference geopolymer material have a coarser microstructure. Compressive strength is consistent with the more compact and dense microstructure of geopolymer composite containing commercial starch. The incorporation of 15 wt% of starches derived from yam, cassava, sweet potato, and commercial starch was found to increase compressive strength. It was found that starches from various crops could be used as additives in the synthesis of geopolymer composites.