Utilization of corn cob ash (CCA) to prepare geopolymer grout: reaction mechanism, crack repair effectiveness and life cycle assessment

Abstract

Corn cob ash (CCA) is a kind of agricultural solid waste produced by the burning of corn cob after removal of the corn kernels, which requires sustainable disposal routes. In order to utilize CCA and understand its role in geopolymer, CCA-amended geopolymer grout was prepared and effects of CCA on geopolymerization process and products were investigated in this study. With CCA included, there was less C-S-H/C-A-S-H gel and more calcite, also portlandite generated. Two extra weak exothermic peaks were observed for CCA-amended geopolymer with optimal mix proportion (CCA20A6), probably due to additional reactions induced by CCA, also verified by the disappearance of syngenite. Following application of CCA20A6 to repair cracks, compressive strength and ultrasonic pulse velocity (UPV) of the repaired composites were improved, and no cracking was observed at the bonding interface, verifying successful repair. Based on life cycle assessment in cradle-to-site boundary, the total embodied energy (EE) and global warming potential (GWP) of CCA20A6 were decreased by 7.8% and 15.5%, respectively, compared to non-CCA geopolymer. Considering performance of samples, the addition of CCA would lead to an about 30% decrease in economic index. In conclusion, CCA could play a role as a precursor due to soluble Si, Al, and Ca components, and also as an activator due to its intrinsic alkalinity, which makes CCA-amended geopolymer to be an eco-friendly grouting material with better performance as well as lower costs.

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