Foamed fly ash geopolymer was synthesized in this work to produce geopolymeric lightweight concrete (GLWC). Fly ash was activated by sodium silicate solution, and aluminum powder was employed as an in situ chemical foaming agent. The synthesized pastes were cured at 40 °C for 28 days, with bulk densities of resultant GLWCs ranging from 600 to 1600 kg/m³. The resulting mechanical properties, thermal conductivity, microstructure, and reaction product were fully characterized. Results show that GLWC had higher mechanical strength than commercial aerated concrete and developed 80–90% of its corresponding 28 days strength after curing for 7 days. For densities from 1200 to 600 kg/m³, the thermal conductivity diminished from 0.70 to 0.22 W/mK, which is much better than that of its counterpart, ordinary Portland cement (OPC). Scanning electron microscopy (SEM) images revealed decent matrices comprising geopolymeric gel and unreacted fly ash.

The development of sustainable cementitious materials is essential and urgent for the construction industry. Benefiting from excellent engineering properties and a reduced greenhouse gas footprint, alkali-activated materials (AAM) are among the robust alternatives to Portland cement for civil infrastructure. Meanwhile, concrete production also accounts for around 20% of all industrial water consumption, and the global freshwater shortage is increasing. This review discusses recent investigations on seawater-mixed AAMs, including the effects of seawater on workability, reaction mechanism, shrinkage, short and long-term strength, binding of chloride and corrosion of steel reinforcement. Attention is also paid to the utilization of sea sand as aggregate, as well as discussions on the challenges and further research perspectives on the field application of AAMs with seawater and sea sand.

The production of municipal solid waste incineration fly ash (MSWI-FA) and municipal sludge (MS) has been increasing annually, raising concerns about proper disposal. In this study, a thermal treatment method with attributes of energy efficiency and complete detoxification was applied to synergistically convert MSWI-FA and MS into precursors for the synthesis of high-strength alkali-activated materials (AAMs). The impact of mass ratios of MSWI-FA and MS on the mineralogy, microstructure, and reactivity of obtained precursors were investigated. The mechanism of alkali activation was deeply studied by characterizing the evolution of reaction products. The strength development of synthesized AAMs was characterized in a one-year time scale, as well as the environmental compatibility. The results revealed that strength, with values ranging from 12.8–33.0 MPa at 3 d, 29.5–44.1 MPa at 28 d and 39.3–54.8 MPa at 365 d. Furthermore, after one year of curing, the release of Ni, Cr, Cu, Pb, Zn, Mn, and Ba from synthesized AAMs into both deionized water and acetic acid were far below the regulatory limits in China. All these contribute to promoting the safe disposal and effective valorization of MSWI-FA and MS.

Geopolymer is a sustainable low-carbon cementitious material that is able to incorporate large amounts of solid waste as precursors or activators. As the proportion of municipal solid waste incineration continues to rise in China, the large-scale generation of municipal solid waste incineration fly ash (MSWI FA) has emerged as a significant challenge. The production of geopolymers represents a potential pathway for the comprehensive utilization of MSWI FA. However, most studies have reported that geopolymers containing MSWI FA exhibit low strength, which diminishes their economic value. Furthermore, the unclear environmental risks associated with MSWI FA-based geopolymers have impeded their broader application. This study explores the use of MSWI FA as a substitute for ground granulated blast furnace slag (GGBS) or coal fly ash (CFA) in the production of high-performance geopolymers, achieving compressive strengths exceeding 60 MPa, even when the MSWI FA content reaches 50%. A synergistic effect is observed between MSWI FA and CFA, which enhances the reactivity of CFA. With reasonable formulation, the environmental risks of geopolymers containing MSWI FA are manageable in normal rainfall scenarios. However, there remains a potential risk of soil and groundwater contamination under extreme conditions, such as acid rain.

Iron ore sintering is a simple and sustainable way to treat zinc-bearing secondary resources. In this paper, the reaction behavior of zinc was studied by combining thermodynamic calculation and simulation tests under sintering temperature and atmosphere. The evolution law of Zn-containing phases during the heating process was also revealed. The results showed that Zn-containing substances were mainly converted to ZnO when the temperature reached 700 °C in the pre-drying zone, and ZnO started to combine with Fe₂O₃ to form ZnFe₂O₄ when the temperature reached 800 °C in the combustion zone. ZnFe₂O₄ remained stable at 1300 °C, and did not change in the atmosphere with low CO concentration. In conventional sintering conditions, the removal rate of zinc was about 5 wt%, zinc was mainly converted to ZnFe₂O₄ and stuck in the sinter. Therefore, to meet the zinc amount of the blast furnace load, pretreatment of raw materials or ore matching to control zinc content is necessary.