Recycling of red mud and flue gas residues in geopolymer aggregates (GPA) for sustainable concrete

This study proposed simultaneous utilization of red mud (RM) and flue gas residues (FGR) as a partial replacement of traditional precursors and energy-intensive activators. Reaction mechanisms of geopolymer pastes were investigated through isothermal calorimetry, X-ray diffraction, thermogravimetry and infrared spectroscopy, by varying the dosage of RM (40%) and FGR (24%, 32%). Results showed that use of RM and FGR as a replacement of FA and commercial activator had a limited influence on the compressive strength. RM and FGR participated in reaction at a slower rate. After optimization, heat-cured FGR0.32 mix was selected to manufacture geopolymer aggregates (GPA). Engineering properties, cost analysis and environmental impact of GPA were evaluated. Natural aggregates (NA) were replaced by GPA at replacement levels of 25%, 50%, 75% and 100% by volume to prepare concrete. GPA concrete with 25% and 100% replacement level could achieve the 94.6% and 86.6% of NA concrete strength respectively at 28 days age.

Automated summary

This study investigates the reaction mechanisms of geopolymer pastes using red mud and flue gas residues as partial replacements for traditional precursors and activators. The results show that the use of red mud and flue gas residues has a limited influence on compressive strength and participates in the reaction at a slower rate. After optimization, geopolymer aggregates were manufactured using heat-cured flue gas residue at a certain dosage. The engineering properties, cost analysis, and environmental impact of the geopolymer aggregates were evaluated.