The objective of this work is to present the research progress and applications of fly ash-based geopolymer, and summarize the future research hotpots. Since 1998, scholars have made important contributions to the study of fly ash-based geopolymer, and a large number of research studies have been published. Therefore, a bibliometric analysis for the determination of the research status, trend, and history of fly ash-based geopolymer was conducted in the present study. A total of 4352 publications on fly ash-based geopolymer were collected between 1998 and 2022, with an increasing trend year by year. China and Australia are the largest contributors to the field, and the research institutions in each country cooperate closely. In addition, the most contributing research areas are MATERIALS SCIENCE, ENGINEERING, and CONSTRUCTION & BUILDING TECHNOLOGY. The keywords including fly ash, compressive strength, and mechanical property are the most frequently appearing words. On the whole, the development of fly ash-based geopolymer could be divided into three stages including the replacement of ordinary Portland cement, the development of multifunctional materials, and the reduction of environmental impact by the conversion of solid waste. This overview could provide an important guidance for the development of fly ash-based geopolymer.

Waste three-way catalysts (TWCs) and waste LiCoO ₂ batteries represent critical environmental challenges due to hazardous components yet contain high-value resources, and their recycling has garnered widespread attention. We propose a novel ‘waste-to-waste’ synergistic recycling where spent LiCoO ₂ batteries reconstruct mineral phases of waste TWCs, enabling co-recovery of platinum group metals and Li/Co without traditional oxidants. However, the environmental performance of this process still requires further analysis. A comprehensive life cycle assessment using the CML2001 framework evaluated seven impact categories across three core phases: carbothermal reduction, oxidation calcination and HCl leaching. The process achieves net-negative environmental impact with significant benefits in abiotic depletion potential elements (−0.062 kg Sb eq.), acidification potential (−120 g SO ₂ eq.) and eutrophication potential (−1.09 g phosphate eq.). Compared to the individual recycling of lithium-ion batteries, this synergistic recycling process can reduce CO ₂ emissions by approximately 75% or more. Oxidation calcination and HCl leaching are the main phases contributing to environmental burdens. Specifically, electricity consumption, the input of HCl and silicate cement are key factors generating environmental load. Therefore, exploring methods to improve heating efficiency in the oxidation calcination and HCl leaching phases, increasing the proportion of renewable energy in power generation, reducing the use of HCl and seeking environmentally friendly alternatives to silicate cement are crucial to mitigating the environmental impact of this process. Overall, the synergistic recycling process proposed in this study is environmentally friendly and aligns with the goals of a circular economy.

One-part geopolymer has emerged as a promising alternative to ordinary Portland cement. In this study, the effect of CaO dosage on the compressive strength of one-part geopolymers was systematically investigated, and its underlying modification mechanism was revealed via multi-scale characterizations including XRD, FTIR, TG, NMR and nitrogen adsorption–desorption. The results show that the compressive strength of the samples at all curing ages exhibits a trend of sharp initial decrease, followed by a slight rebound, and then a secondary decline with the increase in CaO dosage. All CaO-containing specimens exhibit significantly lower strengths than the CaO-free reference. Specifically, the reference sample achieves the highest 28-day compressive strength of 56.6 MPa. The strength of the sample at each curing age drops to the minimum at 5% CaO dosage, with a 28-day strength of only 17.9 MPa. Partial strength recovery of the sample is achieved at 7.5% CaO dosage. The strength deterioration is mainly attributed to the rapid hydration of CaO, which consumes free water and reactive silicon and hinders the generation of N-A-S-H gel rather than directly disrupting the aluminosilicate network. Meanwhile, the hydration products are continuously carbonated to form calcium carbonate, and the carbonation-induced volume expansion at excessive dosage may induce microcracks in the matrix that impair the structural integrity. Only at a moderate dosage of 7.5% CaO can a slight strength rebound be realized through the possible formation of C-S-H-type phases and the pore-filling effect. This study provides a theoretical basis for the material design and performance regulation of one-part geopolymers.