Germanium-based anode materials have achieved significant progress in lithium-ion batteries, primarily in cost reduction, structural optimization, and interface engineering. High material costs restrict large-scale application, thus prompting the development of diverse Ge sources (e.g., GeO₂, organic precursors), Ge/metal and Ge/metalloid composites, and Ge-based high-entropy alloys. Ge combined with conductive metals like Cu or Ni improves electrical conductivity and structural stability, while pairing with active elements like Si or Sn mitigates volume expansion. In high-entropy systems, Ge can regulate lithiation behavior, effectively controlling volume change.

To address severe volume expansion during cycling that leads to material pulverization and capacity decay, various nanostructural materials including Ge nanoparticles, nanowires, and porous frameworks are designed. Nanoparticles have low expansion and fast kinetics, requiring artificial SEI layers and conductive matrices for stability. Ge nanowires exhibit radial resilience and axial flexibility, especially when directly grown on current collectors, offering a practical potential. Porous Ge integrates nanoscale activity with a high tap density, improving energy density, while avoiding particle agglomeration.

Interface instability and poor conductivity at a high current are also challenges for Ge-based anodes. The reactive surface of Ge can form unstable SEI layers, limiting performance. To address this, some engineered artificial SEI coatings such as N-doped carbon, heterojunction-carbon, and TiO₂ are developed to enhance ion/electron transport and mechanical integrity. In addition, a uniform dispersion of nanoscale Ge within conductive networks also improves fast-charging capabilities and cycling stability. Integrating structure and composition design through high-throughput element screening, one-step synthesis, and precise structural tuning is a key to reducing Ge dependency and enhancing performance. Further advancement requires in-situ characterization and multiscale simulations to uncover lithiation-induced phase transitions and stress evolution, facilitating the transition of Ge-based anodes from lab-scale research to industrial application.

The market adoption of germanium-based anodes is expected to follow a trajectory starting from high-end applications and gradually expanding to broader markets. In the short term, their use focuses on niche sectors with extreme requirements for energy density and fast charging but low sensitivity to cost, such as aerospace, military equipment, advanced medical devices, and long endurance drones. In the medium to long term, as manufacturing costs decrease and processing techniques become mature, germanium is expected to serve as a dopant or an alloying modifier for mainstream anode materials like silicon and tin, enhancing their kinetics and structural stability, and thereby indirectly improving the range and fast-charging performance of electric vehicle batteries. China has a unique strategic advantage in the global germanium supply chain. China develops a complete technological system covering refining, purification, and deep processing, enabling efficient production of high-purity precursors such as GeO₂ and GeCl₄. In parallel, the extensive recycling of germanium-containing by-products from industries like optical fibers, infrared optics, and solar cells creates a sustainable "resource-product-recycling" loop. These advantages significantly lower the marginal cost of use and ensure resource security, offering a practical and competitive environment to overcome cost barriers and scale up applications.

In summary, with the increasing service temperature of aero-engines, the abradable/environmental barrier coatings (A/EBCs) that match SiC_f/SiC ceramic matrix composites (CMCs) become a key research direction. This review represents the research progress of A/EBCs in material design, microstructural regulation and performance evaluation, and points out that the current challenges mainly include thermal expansion mismatch between conventional coating materials and CMC substrate, poor high-temperature stability of lubricants, difficult balance between multi-scale pore structure and multi-performance, and lack of standardized evaluation systems and test standards suitable for multi-field coupling service environment. In the future, the research and development of A/EBCs should focus on the multi-objective synergistic design of material composition, multi-scale microstructure and performance evaluation system. It is necessary to strengthen the analysis of failure mechanism under multi-physical field coupling environment, develop new high-temperature stable matrix and lubricant materials, realize the precise regulation of multi-scale pore and interface structure, and establish a standardized preparation and performance evaluation system. Through the breakthrough of the above key technologies, the comprehensive performance and service durability of A/EBCs will be effectively improved, so as to promote the leapfrog development of high-temperature sealing technology and provide an important support for the performance improvement of next-generation aero-engines.

Although composite titanium salt coagulants demonstrate excellent performance, there are still some issues and challenges that need to be addressed. Future research can focus on the following aspects: (a) Enhancing Adaptability to Real Water Bodies. Currently, the complex composition of various actual water bodies imposes higher demands on the application of composite titanium salt coagulants. To ensure stable and efficient coagulation performance under complex water quality conditions, future efforts should focus on developing novel composite titanium salt coagulants with stronger specificity and broader applicability, thereby meeting the needs of more complex and demanding application scenarios. (b) Lower- Cost Preparation of Composite Titanium Salt Coagulants. At present, the preparation of composite titanium salt coagulants largely relies on complex processes such as SAT, ED, and sol-gel methods, which hinders their large-scale application. Future research should aim to develop simpler, greener, and more economically viable preparation pathways—for instance, utilizing industrial by-products or waste materials as raw materials—while optimizing the preparation process to reduce energy consumption and production costs. (c) Ensuring Ecological and Health Safety. Current research on the toxicity assessment of titanium-based coagulants has predominantly focused on TiCl₄ and Ti(SO₄)₂. Future studies should strengthen investigations into titanium residue and its ecotoxicological effects during the use of composite titanium salt coagulants. Meanwhile, it is essential to employ a wider range of aquatic organisms (e.g., fish, shellfish, and aquatic plants) for ecotoxicity studies, and to further explore the migration, transformation, and long-term accumulation of residual titanium in water bodies and organisms. This will provide a scientific basis for comprehensively safeguarding water environments and human health.

In transition towards a decarbonized energy system globally, hydrogen plays a crucial role as a zero carbon energy carrier. In this context, solid oxide electrolysis cell (SOEC) technology with its advantages in high-temperature operation significantly reduces material costs and improves overall system energy efficiency, compared to low-temperature solutions such as alkaline and proton exchange membrane electrolysis. SOEC system adopts a non-precious metal ceramic structure. When operating at 650-1000 ℃, electrochemical kinetics acceleration mechanism achieves a conversion efficiency of > 80%, providing a feasible approach to reduce cost of green hydrogen leveling. The existing domestic demonstration projects are limited to a scale of tens to hundreds of kilowatts, and the commercial implementation needs to break through bottleneck of "three highs and one low", thus increasing power density of fuel cell stack, extending its service life, and optimizing system integration, while reducing assets and operation and maintenance costs. Solving these obstacles requires collaborative efforts in three major fields, and innovation in materials and structures must break through conventional design framework of electrodes, electrolytes, and sealing glass. With precise microstructure design and interface stress control, system can maintain a high current density of 2 A·cm^-2, while controlling degradation rate at 1 mV per thousand hours, significantly extending lifespan of battery pack. Multi-energy coupling optimization is crucial, which requires integrating the SOEC with industrial waste heat and renewable resources, thus utilizing low-grade thermal energy (i.e., 200-300 ℃), efficiently offsetting internal heating demand, reducing external electricity consumption by approximately 30%, and comprehensively improving energy utilization efficiency. For those localized supply chains, establishing a complete domestic production capacity from precursor powder to single cell manufacturing, stacking and assembly to system integration is particularly crucial. The goal is to control stacking cost at RMB 2500 per kW and achieve an operating life of 5×10⁴ h, laying a foundation for large-scale applications. At present, although the SOEC has significant energy efficiency advantages, its promotion and application still face multiple constraints, i.e., gradual decay of oxygen electrodes under high temperature and high vapor partial pressure, mechanical and electrochemical damage caused by power fluctuations, and daunting initial capital investment. Subsequent exploration should focus on preparing new electrode materials with a higher stability, establishing flexible thermoelectric synergistic regulation mechanisms to adapt to fluctuating renewable energy, and promoting standardization and cost reduction and efficiency improvement throughout entire industry chain. The cost of photovoltaic and wind power continues to decrease, coupled with increasing demand for green hydrogen in chemical and metallurgical fields. Solid oxide electrolysis cell technology is expected to be widely applied in "electricity hydrogen ammonia/methanol" integrated system, distributed energy system, and sustainable refining scenarios. This technology will undoubtedly become a key pillar technology supporting the dual carbon goals in China.

The introduction of carbon peaking and carbon neutrality targets has made a green, low-carbon transition the prevailing trend in the cement manufacturing industry. Solid-waste valorisation, which involves substituting natural minerals and fossil fuels with suitable solid waste, can effectively reduce emissions from carbonate decomposition and fuel combustion. It is therefore regarded as a key technological pathway for achieving the carbon reduction goals. The existing studies on single dimensions such as energy or material saving, or carbon mitigation in clinker production using solid waste are relatively well-developed. However, valorisation can generate both environmental benefits and drawbacks, there is a clear need for a comprehensive assessment framework based on multiple indicators that can capture trade-offs across impact categories, rather than drawing conclusions from a single metric.

A multidimensional assessment framework was developed based on standard product carbon footprint and life-cycle assessment models. This framework could comprise three primary indicators, i.e., carbon, resources and environment and twelve secondary indicators, enabling the structured and transparent evaluation of benefits as well as potential burden shifting. A consistent system boundary was defined to cover the entire clinker production value chain, including solid waste inputs, raw material production, waste pre-treatment, transportation, clinker production and credits for avoiding conventional disposal methods (landfilling or incineration). Within this boundary, five substitution scenarios involving the use of solid waste were constructed and benchmarked against a mineral-only baseline, i.e., carbide slag (S1), manganese slag (S2), coal gangue (S3), fly ash (S4) and sewage sludge (S5). We then systematically quantified the potential benefits and burdens of solid waste utilisation in terms of carbon emissions, resource consumption and environmental impacts. This could provide a decision-relevant evidence to support the cement industry's transition to a low-carbon economy.

In terms of carbon emissions, all scenarios achieve net reductions, albeit with significant variation in magnitude. Scenario 1 demonstrates the most significant mitigation, reducing emissions by 35.2%, compared to the baseline, resulting in a total reduction of 351.3 kg CO₂eq. By contrast, Scenario 2 involves pre-treatment requiring additional Ca(OH)₂ and anhydrous Na₂SO₄, which increases raw-material production emissions by 9.8 kg CO₂eq relative to the baseline. Scenario 5 results in an increase of 4% in fuel-combustion emissions due to the high moisture content of the waste, leading to the weakest overall mitigation with a net reduction of only 38.9 kg CO₂eq. Overall, these results indicate that although carbon benefits are generally achievable across different types of waste, their magnitude depends on waste composition and the intensity of the pre-treatment. In terms of resources, overall consumption decreases across all scenarios, but there is a trade-off between "material savin" and "energy saving". Scenario 1 achieves the greatest overall saving of resources, with a reduction of 19.4% relative to the baseline. This is primarily due to its high substitution rate and avoidance of waste landfilling. However, its energy-intensive pre-treatment increases fossil resource consumption by 27.2%, offsetting the net energy benefit. Scenario 3 exhibits the most pronounced energy-saving effect, reducing fossil resource consumption by 18.9% via substituting approximately 20% of coal with coal gangue. However, although the substitution rate in Scenario 5 is 20%, a need to add bauxite to satisfy mineralogical requirements offset some of its material-saving potential. These findings highlight that the outcomes of resource use depend on substitution ratios and on the additional inputs required to meet clinker quality constraints. In terms of the environmental impact, the avoided disposal process has a significant effect on the results. When this process is included in the assessment, Scenario 1 demonstrates the most significant reduction in overall environmental impact at 84.7%, compared to the baseline. This is primarily due to the prevention of heavy metal emissions (i.e., Cd, Se and As) linked to landfill. Scenario 2 shows a similar pattern, but improvements in human toxicity indicators are limited because mercury (Hg) emissions associated with producing anhydrous sodium sulphate (i.e., anhydrous Na₂SO₄) offset part of the benefits. If avoided disposal is excluded, Scenario 3 exhibits the optimum overall environmental performance. In the comprehensive evaluation, Scenario 1 consistently ranks first under equal weighting and across all three dual-priority schemes, establishing itself as a core pathway with optimal overall benefits. Scenario 3 is suitable as a priority enhancement option under both "carbon emissions-resource priority" and "resource-environment priority" orientations. Scenario 2 can serve as an alternative under the objective of "carbon emissions-environment priority".

The five solid waste valorisation scenarios for clinker production had different advantages and constraints with regard to carbon mitigation, material conservation and environmental improvement. Scenario 1 delivered the optimum overall performance, but its high energy demand and associated pollutant emissions during pre-treatment could be limiting factors. Scenario 2 achieved considerable carbon reduction and environmental benefits, but it was limited by heavy metal emissions and energy consumption during pre-treatment. Scenario 3 could be characterised as "low risk, steady benefit", offering significant savings in fossil energy without apparent adverse environmental impact. Scenario 4 yielded the modest gains across the board without any negative effects, making it suitable for routine implementation. Scenario 5 showed the greatest advantage in terms of photochemical smog control, but it had the weakest overall performance. To advance the valorisation of solid waste in the cement sector, we could recommend optimising the pre-treatment of high-substitution waste (i.e., carbide and manganese slag) to reduce energy use and air pollutant emissions arising from energy-intensive steps. Large-scale substitution could be encouraged for wastes with a substantial valorisation potential (such as carbide and manganese slag) to further enhance integrated environmental benefits.

A cathode with mixed hole, oxygen vacancy, and proton conductivity extends the reactive zone for the oxygen reduction to water beyond the triple phase boundary, making the whole cathode surface an active electrocatalyst. The defect chemistry (i.e., concentrations and mobilities of point defects) of such materials with three charge carriers is complex, and some of the desired properties for a PCFC cathode material are in mutual conflict (i.e., proton uptake, electronic conductivity, catalytic activity, and long-term chemical stability). And the promising protonic cathode material needs a high catalytic activity for the oxygen reduction reaction to water to improve its performance. Nevertheless, the reactions both require the dissociation of the strong oxygen-oxygen bond.

The mechanism for this reaction is not exactly identical to that in oxide-ion-conducting cells (where the resulting oxide ions are incorporated into the cathode material, while on PCFC cathode, they are desorbed in the form of steam). The dependence of proton uptake on cation composition in cathode perovskites in order to extract the parameters that are most important for a high proton concentration. Regarding the optimization of PCFC cathode materials, refraining from striving for very high electronic conductivities is anticorrelated with proton uptake. It is prospected that the role plays due to oversized dopants in barium ferrate for enhancing the hydration properties. The beneficial effect on protonation is attributed to a higher degree of disorder in the local structure of doped samples, which translates in B-O-B bonds buckling. The B-O-B buckling reduces the Fe-O bond covalency (i.e., less Fe 3d-O 2p orbital overlap), thus decreasing the hole transfer from iron to oxygen. This leaves more negative charge density on the oxide ions, which increases their basicity and propensity for protonation.

In addition, although the existing thermogravimetric and electrical conductivity relaxation methods still have certain limitations in measuring proton concentration in mixed ionic conductors. The in-situ characterization techniques (such as in-situ transmission electron microscopy, in-situ spectroscopy, neutron diffraction, etc.) can be used to analyze the process of proton absorption and transport in mixed ionic conductors. Also, combining multi-scale simulations with experiments can further analyze numerical values such as the binding energy of proton absorption and the activation energy of diffusion. For instance, in-situ transmission electron microscopy is used to directly observe water entering Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ via introducing a small amount of water vapor into the TEM chamber. Electron energy loss spectroscopy is also used to determine the formation of oxygen bubbles on the material surface, while the protons ultimately remain within the material. This result provides the most direct evidence for studying the reactions of water and protons in mixed ionic conductors.

In summary, SOCs thin film preparation technologies can form a diversified system, but some common challenges remain. Although vapor-phase technologies have excellent performance, they generally face high equipment costs and great difficulty in scaling up. Liquid-phase technologies are prone to film cracks or pores due to drying and sintering stress. Future research should focus on three core directions, i.e., 1) promoting intermediate and low-temperature operation, further expanding the low-temperature application range of batteries through interface regulation and film formation process optimization; 2) pursuing high performance, developing three-dimensional structured films to expand reaction interfaces and improve mass transfer and catalytic efficiency; and 3) accelerating commercialization, optimizing low-cost preparation processes combined with intelligent manufacturing technologies, and breaking through the key technical bottlenecks of new film formation technologies. Thin film preparation technology will continue to be a core breakthrough to solve the high-temperature dependence and performance attenuation of SOCs, promoting their transition from laboratory research to commercial application.

The carbon mineralization of solid wastes enables the simultaneous achievement of efficient CO₂ capture and the activation enhancement of basic oxygen furnace (BOF) steel slag. However, the relatively low CO₂ concentration in industrial flue gas, the direct mineralization reaction between CO₂ on reaction of steel slag and the issue of low conversion efficiency should be concerned. This study was to employ a potassium glycinate (KG) solution to absorb and enrich CO₂ from flue gas. The CO₂-loaded KG solution was subsequently utilized to indirectly mineralize and modify BOF steel slag, thereby achieving both mineralization modification of steel slag powder and regeneration-recycling of the KG solution. The kinetic characteristics of the mineralization reaction between the CO₂-loaded KG solution and steel slag were investigated. The phase composition of mineralization products, the carbon sequestration capacity of steel slag, and the evolution of its reactivity were analyzed. Furthermore, a synergistic carbon capture approach integrating steel slag mineralization modification with carbonation curing of cement paste was explored, and its influence on the mechanical strength of cement was evaluated. This study could provide a technical support for CO₂ capture using steel slag and its high-value utilization in cement-based materials.

BOF steel slag with a CaO content of 37% was selected as a raw material. A 1 mol/L potassium glycinate (KG) solution was first carbonated to obtain a CO₂-loaded solution, which was subsequently used to mineralize the steel slag for different durations. The residual CO₂ loading in the mineralization filtrate was determined by acid-base titration. Combined with the measurements of pH value in the filtrate, the kinetic characteristics of steel slag mineralization at different reaction stages were elucidated, thereby identifying the optimal mineralization duration. X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were employed to quantify the carbon sequestration capacity and characterize the crystalline phases of both mineralized steel slag and carbonation-cured cement paste at different mineralization durations. Furthermore, the pozzolanic activity after mineralization was evaluated by a strength activity index method, based on a 30% replacement ratio and 28-d compressive strength. In addition, the mineralized steel slag was incorporated as a supplementary cementitious material into cement-based systems and subjected to synergistic carbonation curing in CO₂ atmosphere. The carbon sequestration efficiency and mechanical performance enhancement of mineralized steel slag under dual carbonation conditions were systematically assessed via compressive strength testing and microstructural phase analysis.

This study proposes and validates a complete collaborative process route, confirming that the mineral carbonation modification of steel slag with carbon-rich KG solution enhances its activity. The mineralized steel slag as an admixture can effectively improve the compressive strength of cement-based specimens. Compared with conventional organic amine solutions, the KG solution exhibits a faster CO₂ adsorption rate and a better adsorption efficiency. Also, the mineralization of steel slag with carbon-rich KG solution re-releases the CO₂ adsorption capacity of the KG solution, which, can effectively reduce the cost of indirect carbon mineralization of steel slag with respect to the CO₂ absorption effect in the first stage. The carbon mineralization product of steel slag contains calcite with an aragonite-like structure. The porous morphology of the product enhances its carbon sequestration capacity during the carbonation curing process of cement paste specimens. Furthermore, the metastable aragonite undergoes a dissolution-recrystallization effect during the curing process, effectively improving the early strength of cement-based materials.

This work evaluated the CO₂ capture and steel slag mineralization kinetics using KG solution, as well as the resource utilization effects. The results showed that the reaction rate between steel slag and carbon-rich KG solution could be rapid within the first 120 min, with the CO₂ reaction rate in KG reaching 92.8%. The calcium carbonate produced during the reaction encapsulated the steel slag particles, hindering the mineralization process, leading to a gradual slowdown of the reaction rate and stabilization in subsequent stages. After mineralization, the early activity of the steel slag was significantly enhanced, with a maximum 16.7% increase in 7-d compressive strength at a 10% dosage. Carbonation curing could effectively improve the early compressive strength of the steel slag cement paste. After 12 h of carbonation curing with 30% mineralized steel slag, the 7-d compressive strength was increased by 11.3%. The mineralization of steel slag with carbon-rich KG solution resulted in the formation of calcium carbonate with an aragonite crystal structure. The encapsulated calcium carbonate mineralization product on the steel slag provided nucleation sites for C-S-H gel in the cement hydration process, thereby accelerating the hydration process. Furthermore, the transformation of metastable aragonite into calcite during carbonation curing could enhance the cement matrix, leading to a cementitious strengthening effect. This method could have significant application prospects for the resource utilization of steel slag.

Magnesium silicate hydrate (M-S-H) cementitious material is regarded as a potential alternative to conventional Portland cement due to its excellent sulfate erosion resistance, heavy metal ion solidification performance, and low pH value during hydration. However, the industrialization process of M-S-H cementitious materials is currently restricted due to the high cost and unstable supply of traditional silicon sources that rely on industrial by-products (such as silica fume, fly ash, and slag). Natural layered silicates such as montmorillonite and kaolin have a similar tetrahedral-octahedral stacking unit structure to M-S-H, and can exhibit a good pozzolanic activity after mechanical or thermal activation. Exploring the use of calcined montmorillonite and kaolin as alternative silicon sources to partially or completely replace silica fume broadens the source of raw materials for M-S-H cementitious materials and reduces production costs. This work was to investigate the effects of partial or complete replacement of silica fume by calcined montmorillonite (MT) and calcined kaolin (KL) on the structure and strength of M-S-H cementitious materials, clarifying the action mechanism of aluminum in the two clay minerals on the M-S-H hydration process and layered structure.

Light-burned magnesia (LM) was used as a magnesium source and silica fume (SF) as a reference silicon source. Montmorillonite and kaolin were calcined in a muffle furnace at 750 ℃ for 1 h at a heating rate of 10 ℃/min to obtain calcined montmorillonite and calcined kaolin. The reference sample was prepared via mixing MgO and silica fume at a mass ratio of 4 : 6. On this basis, different mass fractions (i.e., 10%, 30%, 50%, 70%, and 100%) of calcined montmorillonite and kaolin were used to replace silica fume, and the samples were named as MT-10~MT-100 and KL-10~KL-100, respectively according to the replacement ratio. The mortar strength specimens were prepared with the samples above, superplasticizer, tap water, and standard sand, and the compressive strength was tested according to the standard GB/T 17671—1999 "Methods of testing cement- Determination of strength". The paste was prepared at a water-to-solid ratio of 0.5 and 0.7% superplasticizer based on the total mass of solids, cured in sealed glass tubes with liquid paraffin, and terminated hydration with isopropanol at a certain age, then dried in a vacuum oven at 40 ℃ for 48 h. The mineral phase, thermal behavior, functional groups, microstructure, and element distribution of the samples were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and solid-state ²⁹Si and ²⁷Al magic-angle spinning nuclear magnetic resonance (MAS NMR).

Calcined kaolin exhibits a great early strength enhancement effect, and its compressive strengths at 3 d and 7 d have a positive correlation with the dosage (i.e., correlation coefficients are 0.996 and 0.905, respectively). At the dosage of calcined kaolin of 70%, the strength at 3 d reaches 39.37 MPa and the strength at 7 d reaches 49.58 MPa, which are 464.0% and 400.3% higher than those of the reference sample, respectively. In contrast, the strength enhancement effect of calcined montmorillonite is weak. The strengths at 3 d and 7 d increase slowly with the increase of montmorillonite dosage. At the montmorillonite dosage of 70%, the strength at 3 d is only 8.94 MPa and the strength at 7 d is 14.28 MPa, which are 36.5% and 53.7% higher than those of the reference sample, respectively. The strength increases slowly in the montmorillonite dosage range of 10%-50%.

The microscopic analysis shows that calcination at 750 ℃ causes more thorough damage to the crystal structure of kaolin than that of montmorillonite. The XRD diffraction peaks of kaolin disappear completely after calcination, and the layered structure collapses completely, resulting in a higher pozzolanic activity. After calcination, the interlayer spacing of montmorillonite decreases, and some characteristic diffraction peaks are still retained, indicating that its crystal order is not completely destroyed and the pozzolanic activity is lower than that of calcined kaolin. The FTIR and NMR analysis further confirms that the structural hydroxyl groups of calcined kaolin are completely removed, and a large number of active Al and Si sites are exposed. Although montmorillonite also undergoes dehydroxylation and structural damage after calcination, the degree of disorder is lower than that of kaolin.

Aluminum in both calcined montmorillonite and kaolin can enter the M-S-H phase in the early stage of hydration, and form magnesium aluminosilicate hydrate (M-S-A-H) gel via substituting Si⁴⁺ in the silicate tetrahedron or Mg²⁺ in the magnesium-oxygen octahedron, which significantly improves the polymerization degree of the product. The formed M-S-A-H is external hydration products, mainly formed through element diffusion between particles. The analysis by the XRD, FTIR, and DTG shows that Mg-Al layered double hydroxide (Mg-Al LDH) is generated within the first 28 d of hydration in both raw material systems. The enhancement of cementitious material strength by calcined kaolin and montmorillonite is related to the formation of M-S-A-H. The strength improvement effect of calcined kaolin is higher than that of calcined montmorillonite due to the more thorough destruction of the crystal structure, higher degree of network disorder, more active Al and Si sites, and higher content of Al(V).

Calcined kaolin and montmorillonite could be used as alternative silicon sources for M-S-H cementitious materials. Calcined kaolin had a great early strength enhancement effect, and its compressive strength had a positive correlation with the dosage. At the dosage of 70%, the compressive strength at 7 d was increased by more than 400%, compared with the sample prepared with pure SF. The strength enhancement effect of calcined montmorillonite could be weak, and the strength was only increased by 53.7% at the same dosage and age. The difference in strength enhancement effect between calcined kaolin and montmorillonite could be due to the fact that the calcination at 750 ℃ caused more thorough damage to the crystal structure of kaolin than that of montmorillonite, resulting in a higher pozzolanic activity. Aluminum in both calcined montmorillonite and kaolin could enter the M-S-H phase in the early stage to form M-S-A-H gel, significantly improving the polymerization degree of the product. The formed M-S-A-H were external hydration products, and Mg-Al LDH was generated within the first 28 d of hydration.