This study investigates the high-temperature and freeze-thaw resistance mechanisms of magnesium potassium phosphate cement (MKPC) blended with coal-based synthetic natural gas slag (CBSNGS). Mechanical tests demonstrated that a 45-min ball-milling treatment and 15 wt% CBSNGS provide the optimal enhancement. This optimal CBSNGS-MKPC mixture exhibited rapid early strength development, with compressive strength increasing from 28.3 MPa at 3 h to 61.3 MPa at 28 d, and the flexural strength increasing from 5.6 MPa at 3 h to 9.5 MPa at 28 d, respectively. As the calcination temperature increased, the compressive strength of CBSNGS-MKPC decreased sharply from 61.3 MPa at room temperature to 30.8 MPa at 300 degrees C, followed by a gradual decline to 29.9 MPa at 600 degrees C and a minimum of 28.6 MPa at 900 degrees C, before slightly recovering at 1200 degrees C. Under thermal exposure up to 1200 degrees C, CBSNGS-MKPC exhibited significantly improved strength retention relative to plain MKPC, attributed to reduced dehydration-induced damage and enhanced high-temperature densification. Multi-technique characterization (XRD, TG-DTG, DSC, Raman, SEM/EDS) revealed a sequential transformation from K-struvite dehydration (<300 degrees C) to phosphate polycondensation and formation of anhydrous Mg-P phases (300-600 degrees C), followed by crystallization of Mg2P2O7 and Mg-3(PO4)(2) and the emergence of Mg-Si phases above 900 degrees C. CBSNGS promoted solid-state reactions and generated thermally stable ceramic networks that accounted for the superior high-temperature stability. Freeze-thaw tests showed that CBSNGS improves durability by refining pore structure and reducing capillary continuity. The 15 wt% mixture exhibited the lowest mass loss (0.42 % after 200 cycles) and high residual strength. Despite progressive freeze-thaw cycling, the compressive strength of CBSNGS-MKPC remained above 47.3 MPa after 200 cycles, while the flexural strength decreased modestly from 8.1 MPa to 7.2 MPa. CBSNGS acts both as a microstructural densifier, enabling MKPC to achieve enhanced thermal resistance and freeze-thaw durability while providing a sustainable utilization pathway for industrial residue.

Deep saline sandstone reservoirs represent a promising medium for underground compressed air energy storage (CAES); however, their characteristically low porosity and permeability, combined with poorly constrained mechanical stability, have impeded practical engineering deployment. In this study, deep saline sandstone cores from Well Ma-29 were subjected to static CO₂–brine immersion experiments conducted at 10 MPa and 80 °C for a duration of up to four months. A comprehensive multi-technique characterization framework was employed, integrating triaxial compression, Brazilian splitting, nanoindentation, porosity–permeability and wave velocity measurements, alongside XRD, ICP, pH monitoring, NMR, SEM/EDS, and CT analyses. This approach enabled a systematic investigation of the coupled evolutionary behavior of mechanical properties, transport characteristics, geochemical conditions, and pore structure in the sandstone. The results indicate that triaxial compressive strength underwent its most pronounced reduction at two months (by 20.3%–31.2%), with residual decreases of 2.1%–18.9% relative to the initial values persisting at four months; cohesion decreased significantly while the internal friction angle exhibited limited variation. Permeability increased by 50% at two months, with a net gain of 8% retained at four months. The pH declined from an initial value of 8.25 to a minimum of 6.64 before stabilizing, while calcite content dropped sharply by 90.7% within the first month, with the system approaching a chemically self-limiting equilibrium between months three and four. NMR, SEM/EDS, and CT characterization provided microscale validation of a cyclic “carbonate dissolution–reprecipitation–re-dissolution” mechanism, elucidating the structural origin of the non-monotonic, inversely coupled evolution observed in mechanical and transport properties. An integrated assessment concludes that CO₂–brine-altered sandstone satisfies the fundamental petrophysical requirements for CAES reservoir application; nevertheless, the reduced mechanical safety margin and periodic oscillations in pore-throat plugging impose constraints on the permissible injection–withdrawal pressure differential. Accordingly, these static baseline findings imply that developing adaptive injection-withdrawal protocols guided by real-time geochemical monitoring should be prioritized as a critical future research direction toward the safe and sustainable operation of saline aquifer-based CAES systems.

Alkali-activated materials (AAMs) are promising low-carbon alternatives to Portland cement, however, their widespread application is hindered by inherent brittleness and pronounced drying shrinkage. This study investigates the use of natural, cost-effective halloysite nanotubes (HNTs) as an additive to enhance the strength and mitigate drying shrinkage in AAMs. The key innovation lies in the dual-regulation mechanism involving the inherent tubular nanostructure of HNTs and their calcination-induced reactivity. The effects of HNTs content (0.5 similar to 3 wt%) and calcination temperature (0 similar to 900 degrees C) on the performance and underlying mechanisms of AAMs were systematically evaluated. The results show that 2 wt% HNTs yielded optimal performance, with 28-day compressive and flexural strengths of 106.8 MPa and 9.2 MPa, representing increases of 9.27% and 26.08%, respectively, compared to the control, and an 11.3% reduction in 84-day drying shrinkage. Thermal activation further enhanced HNTs reactivity, with higher calcination temperatures promoting dihydroxylation and increasing Si/Al dissolution in alkaline media. Notably, HNTs calcined at 750 degrees C accelerated the reaction kinetics, inducing an additional exothermic peak and reducing setting time by approximately 45%, while simultaneously enhancing compressive strength and reducing drying shrinkage. Microstructural analysis revealed that the performance enhancement was due to matrix densification driven by reduced capillary porosity and gel-structure rearrangement. Compared to commercial carbon nanofibers, HNTs offer a more cost-effective, eco-friendly, and efficient alternative. This research clarifies the microstructural mechanisms of HNTs modified AAMs, offering novel insights for the design of high-performance, sustainable composite building materials.

Underwater casting alkali-activated mortar (UCAAM) combines sustainability and corrosion resistance, exhibiting significant application potential in the underwater repair of ordinary Portland cement (OPC) concrete structures. However, the underwater environment significantly exacerbates the complexity of the bonding interface between UCAAM and OPC, and systematic research on the relevant interface regulation mechanisms and reinforcement mechanisms remains insufficient. At first, this study interrogates the quasi-static and dynamic bond performance of the UCAAM-OPC interface, complemented by nanoindentation and backscattered electron-energy dispersive spectroscopy (BSE-EDS) analyses to characterize the micromechanical properties and microstructural evolution of the interfacial transition zone (ITZ). Experimental results verify the efficacy of UCAAM for OPC repair: polyacrylamide (PAM) incorporation increases 28d bond strength by 73%, with further gains achieved through interfacial roughening. PAM-modified specimens demonstrate markedly enhanced dynamic splitting tensile peak strength and impact energy absorption capacity. Nanoindentation data confirm that PAM increases the ITZ elastic modulus and hardness. At the same time, BSE-EDS characterisation reveals that PAM facilitates directional Ca enrichment at the ITZ, providing nucleation sites for cross-linking polymerisation of the C-(A)-S-H gel. This microstructural optimisation increases the average ITZ Ca/Si ratio by 59% relative to the reference group, thereby enhancing interfacial bond strength. Finally, a multiple linear regression model was developed and validated to predict the variation in the dynamic splitting tensile strength of the interface under the coupled effects of quasi-static splitting tensile strength, strain rate, and ITZ microscopic parameters. Collectively, these findings provide critical theoretical underpinnings for advancing alkali-activated repair materials in underwater infrastructure remediation.

The evolution of surface morphology, mechanical properties, and microscopic characteristics in spontaneously combusted coal gangue (SCG) geopolymers activated with K2OnSiO(2)+KOH or Na2OnSiO(2)+NaOH was examined under varying silicate moduli (M = 1.0-2.0) and alkali contents (R2O = 6-14 %) over a two-year period. In particular, we conducted in depth analysis using FTIR Si-O-T deconvolution, TG-MS gel quantification, and SEM-EDS. The results indicate that the differences in ionic radius, hydration radius, and diffusion rate between K+ and Na+ significantly influence the reaction pathways, product phases, and hydration kinetics. Moderate parameters (M = 1.6, R2O = 10 %) optimize the depolymerization-polycondensation balance, whereas higher values (M = 2.0, R2O = 14 %) drive long-term secondary polymerization after 720 days, reorganizing low-polymerized aluminosilicates into highly crosslinked K/N-A-S-H phases, with blue shifts of Q(3) and Q(4). In sodium-based systems, NaFeSi2O6 initially formed and subsequently transformed into F-A-S-H, eventually yielding N-A-S-H, F-A-S-H, and C-(N)-A-S-H, accompanied by efflorescence, cracking, and strength degradation. In contrast, in potassium-based systems, F-A-S-H evolved into lamellar or blocky forms and synergized with K-A-S-H and C-(K)-A-S-H to form a three-dimensional cross-linked network that later developed semi-crystalline features. A high Al content yields polyhedral or layered morphologies, whereas high Si/Al ratios (>2) result in bulk/honeycomb structures. The gel phase composition typically maintains a Na/K:Al:Si = 1:1:3. This study systematically addresses the knowledge gap in the long-term evolution mechanisms of geopolymers. SEM first reveals the depolymerization-repolymerization process in K+/Na+ based geopolymer and induced crystal morphology evolution under varying Si/Al/K(Na) stoichiometries, enabling novel utilization of SCG.

Municipal Solid Waste Incineration fly ash (MSWI FA), as a typical high-risk solid waste, presents significant challenges in its safe disposal and resource utilization. In this study, MSWI FA and spontaneous combustion coal gangue (SCG) were synergistically used to synthesize composite geopolymers by leveraging their complementary high-calcium and aluminosilicate characteristics. The geopolymerization mechanism, phase evolution, chemical bonding states, and the speciation of Pb2+, Zn2+, and Cd2+ were systematically investigated over a one-year period, with their spatial association with the gel matrix examined by SEM-EDS. Under alkaline activation, reactive [SiO4]4-and [AlO4]5-species released from SCG interact with Ca2+ from MSWI FA, forming a highly polymerized C-(K)-A-S-H gel, and K+ further promotes structural densification. Optimal mechanical performance and heavy metal immobilization are achieved at 40% SCG content. Based on ionic potential theory, Pb2+ reacts with [SiO4] tetrahedra to form stable Pb-O-Si covalent bonds, whereas Zn2+ and Cd2+ are mainly immobilized through ion exchange and isomorphous substitution. Fractal analysis shows that the pore structure exhibits multi-fractal characteristics, and the pore volume fractal dimension (D) is negatively correlated with heavy metal leaching concentration. Higher D values indicate a more tortuous pore network, which effectively restricts longterm metal migration. This study provides a promising strategy for avoiding the high-energy calcination carbon footprint typically required for raw coal gangue activation, while offering important technical support for the long-term environmental risk assessment of hazardous waste stabilization.

Magnesium potassium phosphate cement (MKPC) exhibits rapid setting and high early strength, but its long-term performance is limited by microstructural heterogeneity and pore structure defects. These microstructural defects can increase pore connectivity and facilitate the ingress of aggressive agents, thereby limiting the long-term durability and service reliability of MKPC-based repair and protective materials. Nanomaterials have been applied to improve MKPC performance; however, the differences between conventional nano-SiO2 (NS) and nano-Fe2O3 (NF), particularly their effects on hydration regulation and microstructure evolution, remain insufficiently understood. In this study, the effects of NF and NS incorporation on the hydration behavior, phase evolution, pore structure, and mechanical properties of MKPC were comparatively investigated. Orthogonal experiments, mechanical testing, calorimetry, XRD, FTIR, Raman mapping, SEM/EDS, MIP, and nanoindentation were employed to establish the relationship between nano-modification, microstructural evolution, and mechanical performance. The results provide a basis for selecting suitable nanomodifiers for MKPC-based materials used in rapid repair, protective applications, and other construction scenarios requiring rapid strength development and improved microstructural compactness. Compared with pure MKPC and previously reported NS-MKPC results, NF-MKPC showed higher strength development, refined pore structure, and improved micromechanical uniformity. The observed performance enhancement of NF-MKPC is consistent with accelerated early hydration, possible heterogeneous nucleation, pore refinement, and matrix densification. In comparison, NS-MKPC exhibited a different hydration and pore-evolution behavior under the investigated conditions. These findings indicate that NF and NS may regulate hydration and microstructure development differently in MKPC and provide guidance for selecting suitable nano-modifiers for high-performance phosphate cement materials. Under the investigated conditions, NF modification shows potential for MKPC applications requiring rapid strength development and improved microstructural compactness, such as rapid pavement repair, concrete surface repair, and protective coating applications.

Alkali-activated materials (AAMs), as a green and sustainable cementitious material, hold broad application prospects in the treatment of heavy metal-containing waste. This study investigated the effects of AAMs with different CaO contents and SiO2/Al2O3 molar ratio on the leaching of Zn2+ and Cd2+. The immobilization mechanisms of Zn2+ and Cd2+ was revealed by analyzing the physical encapsulation, adsorption capacity and gel microstructure of AAMs. The immobilization of Cd2+ was greatly affected by the CaO content, and the high-calcium system dominated by C-A-S-H gel was more conducive to the immobilization of Cd2+. The immobilization of Zn2+ was synergistically governed by the CaO content and the SiO2/Al2O3 molar ratio. And Zn2+ severely inhibited the alkali-activation reaction in systems with low calcium content and high SiO2/Al2O3 molar ratio. The immobilization of Zn2+ and Cd2+ in the low-calcium system was dominated by adsorption and ion exchange and the leaching concentrations of Zn2+ and Cd2+ were both higher than those in the pore solution. In the high-calcium system, Cd2+ was observed to replace the Ca2+ in skeleton and interlayer of C-A-S-H gel, and Cd(OH)2 precipitation was formed. The presence of Zn2+ prompted the reorganization of negatively charged [AlO4] tetrahedral units around it, which disrupted the local network structure of the gel. AAMs with relatively high aluminum content were more favorable for the immobilization of Zn2+. The results provide guidance for the mix design of AAMs for the immobilization of Zn2+ and Cd2+.

Severe electrochemical corrosion and leaching degradation of underground structures are induced by coupled stray current and groundwater in rail transit systems like subways. The microstructural evolution of fly ash geopolymer (FAG) during accelerated leaching was systematically investigated by simulating a coupled direct current (DC) stray current and soft water environment. Pore solution alkalinity and electrolytic cell OH- concentration were utilized as evaluation indicators, combined with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP). Results indicate that substantial OH- leaching occurs under the coupled stray-current and soft-water exposure, leading to reduced pore-solution alkalinity and changes consistent with the degradation of the N-A-S-H binding network. Consequently, porosity, most probable pore diameter, and the quantity of harmful pores are increased. However, no obvious changes in the major diffraction peaks associated with quartz and mullite were detected within the resolution of the qualitative XRD analysis. Furthermore, a linearly decreasing trend over time is observed for the coupled leaching rate. Mix proportion analysis demonstrates that FAG leaching resistance is improved by reducing the water-to-binder ratio; specifically, superior gel phase content and pore structure are maintained at a ratio of 0.30. Additionally, cumulative OH- leaching is effectively reduced by decreasing the sodium silicate modulus, with optimal resistance exhibited between 1.0 and 1.2. Concurrently, pore solution alkalinity before and after leaching is significantly elevated by increasing the alkali dosage. This exerts a pronounced inhibitory effect on OH- leaching, thereby substantially enhancing the overall leaching resistance.

Carbon nanotubes (CNTs) has shown great potential as reinforcements for alkali-activated slag/fly ash (SFA), yet their effectiveness is often limited by weak interfacial bonding, leading to poor load transfer and premature crack propagation. To address this issue, SiO2-coated CNTs (SiO2-CNTs) with a nano-silica shell were synthesized and systematically compared with pristine and functionalized CNTs (p-CNTs, f-CNTs). Three-point bending tests demonstrated that at an optimal dosage of 0.075 %, SiO2-CNTs increased initiation toughness, peak toughness, and fracture energy of SFA composites by 91.1 %, 155.7 %, and 362.1 %, respectively. Digital image correlation confirmed that incorporation of SiO2-CNTs extended the fracture process zone by up to 81.8 %, slowed crack propagation, and enhanced crack tortuosity. Microstructural analyses and molecular dynamics simulations revealed that the SiO2 shell not only improved CNT dispersion and interfacial adhesion but also formed robust Si-O-C bonds, resulting in stronger anchoring. Consequently, the pull-out energy of SiO2-CNTs was enhanced by factors of 11.5 and 2.57 compared to p-CNTs and f-CNTs. These findings demonstrate that nano-SiO2 coating effectively increases pull-out resistance and bridging capacity of CNTs, thereby delaying crack initiation, slowing propagation, and markedly improving the fracture toughness of SFA composites.

Carbon nanotubes (CNTs) and their modified derivatives show considerable potential for enhancing the impact resistance of alkali-activated materials (AAMs) under extreme loading conditions. In this study, three SiO2-coated CNTs with different coating thicknesses (5Si-C, 10Si-C and 20Si-C) were synthesised, and their effects on the dynamic mechanical behaviour of alkali-activated slag-fly ash (SFA) composites were investigated using split Hopkinson pressure bar (SHPB) tests. The results demonstrate that SiO2-CNTs provide a more pronounced strengthening and toughening effect than pristine CNTs (p-CNTs) and functionalised CNTs (f-CNTs). In particular, 10Si-C/SFA exhibits increases of 29.65 % and 34.19 % in static compressive and flexural strength, respectively; within the investigated strain-rate range, its dynamic compressive strength is enhanced by 33.97-57.59 %, while the peak and total impact toughness reach up to 6.63 and 3.37 times those of the control, respectively. The post-impact fragment size distributions display typical fractal characteristics, with SiO2CNTs-especially 10Si-C-significantly reducing the fragmentation fractal dimension and thus enabling a favourable "high SEA-low fragmentation" response. X-CT analysis shows that 10Si-C/SFA develops the densest and least-connected pore network among all mixtures, while SEM observations further indicate that the reactive SiO2 coating chemically interacts with the matrix, promoting the formation of C(N)-A-S-H gels and enhancing interfacial bonding. Overall, the SiO2-CNT interface-engineering strategy achieves synergistic toughening and densification of AAMs under high strain-rate loading, providing important experimental evidence and mechanistic insight for the design and optimisation of impact-resistant, low-carbon cementitious materials.

The cement industry, contributing 8 % of global CO2 emissions primarily through Ordinary Portland Cement (OPC) production (similar to 0.8-1.0 t CO2/t), urgently requires low-carbon alternatives. This study elucidates atomic-scale dissolution mechanisms in alkali-activated ground granulated blast furnace slag (AAS) via integrated experimental-computational analysis. First-principles simulations of 412-atom GGBS models reveal Ca2+/Mg2+ leaching initiates through non-bridging oxygen bond cleavage (ICOHP = -0.18-0.58 eV), while Al3+/Si4+ release follows oligomer-mediated pathways. Quantum mechanics/molecular mechanics (QM/MM) calculations quantify bond-breaking energy barriers (Al-O-Al: 5.26 < Si-O-Al: 15.51 < Si-O-Si: 38.93 kcal/mol), governed by frontier orbital energy gaps (Delta E = 1.53-2.03 eV). Reactive molecular dynamics (MD) simulations identify three dissolution stages: Na+-assisted ion leaching (0-1 ns, D = 3.40 x 10(-7) m(2)/s), Al-O/Si-O network depolymerization (1-7 ns), and Ca-mediated calcium aluminosilicate hydrate (C-A-S-H) nucleation (7-30 ns). By modulating electronic structures to target these mechanisms, we achieve a 63 % carbon reduction compared to OPC. These findings establish design principles for next-generation GGBS-based cementitious materials, enabling scalable, low-carbon construction solutions with performance parity to conventional cement.

The co-treatment of municipal solid waste incineration fly ash (MSWIFA) and coal fly ash (CFA) by alkali activation offers economic and environmental benefits. However, understanding of MSWIFA/CFA composite alkali-activated cementitious system mechanistic understanding is still relatively limited. This study investigated performance parameters, including compressive strength, heavy metals (HMs) leaching characteristics, and pore solution of MSWIFA/CFA alkali-activated solidified bodies (MCFAs) under various mix ratios. Multiscale characterization was employed to explore hydration heat evolution, mineralogy, molecular structure, microstructure, and pore structure evolution. Results demonstrated that with 30 wt% CFA content, sodium silicate modulus of 1.72, and alkali equivalent of 0.1, the MCFAs achieved a 60-day compressive strength of 19.4 MPa and exhibited the lowest HMs leaching. In alkaline environments, reactive silico-aluminous components in raw materials dissociated into [Al(OH)4]− and [SiO(OH)3]− units. These units subsequently formed gel phases with Ca2+ and Na+. Excess aluminate generated ettringite (AFt) and Friedel's salt. Hydration products grew over time and gradually filled pores. Crystals bridged hydration products and crack structures. These findings provide valuable theoretical basis for management and solidification/stabilization technical promotion of MSWIFA.

Surface modification is a critical strategy for CNT-reinforced alkali-activated materials, as it enhances CNT/matrix interfacial compatibility and overall performance. However, existing studies on the role of CNTs during early hydration remain largely qualitative, lacking quantitative evidence and systematic comparisons among CNTs with different surface states. In this study, pristine CNTs (p-CNTs), functionalized CNTs (f-CNTs), and SiO₂-coated CNTs (SiO₂-CNTs) were incorporated into alkali-activated slag/fly ash (SFA) binders. By integrating experimental characterization with molecular simulations, this study established a systematic mechanistic framework and elucidated how CNT surface modification regulated the early reaction process and micromechanical properties of alkali-activated binders. The results demonstrate that CNTs primarily accelerate early-age hydration, particularly from the induction period to the early deceleration stage, with limited influence on the ultimate reaction extent. The incorporation of CNTs promotes the formation of early aluminosilicate products and C(N)-A-S-H gel, accelerates precursor dissolution, and facilitates the development of a denser and more continuous gel network. Meanwhile, the Ca/Si ratio and micromechanical load-bearing capacity of the hydration products are significantly enhanced. Among all mixtures, 10Si-C/SFA exhibits the most pronounced improvement, with elastic modulus and hardness increasing by 29.5% and 49.1%, respectively. Molecular dynamics simulations further reveal that SiO₂-CNTs possess the strongest interfacial affinity, precursor enrichment capability, and nucleation-inducing effect. These findings identify SiO₂ coating as an effective approach for optimizing the CNT/matrix interface and regulating the hydration process of alkali-activated materials.

Understanding the time-dependent evolution of the interfacial micromechanical properties between magnesium potassium phosphate cement (MPC) and ordinary Portland cement concrete (PCC) pavement is crucial for improving the structural performance after rapid repair. This study investigates the hydration time-dependent evolution of the interfacial mechanical behavior, chemical reactivity, and microstructural development between MPC and PCC interface by a multi-scale characterization approach, including nanoscratch testing, scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS), and Raman spectroscopy. Results demonstrated a rapid increase in scratch hardness and fracture toughness within the early hydration time of 6 h, indicating prompt strength development. At 3 d, scratch hardness and fracture toughness further increased, with ITZ-4 consistently exhibiting superior performance. Raman spectroscopy quantification revealed chemical stratification and progressive phosphate penetration, notably identifying v1 and v3 PO4 3- vibrational peaks and amorphous phosphate species bridging the MPC and PCC phases. Phosphate penetration into the aggregate surface was observed as early as 6 h, while delayed and weaker interaction occurred at the OPC interface. SEM/ EDS analysis confirmed phosphorus diffusion and dense hydration product formation across the interface. The development of interfacial strength was attributed to a synergistic mechanism combining chemical bonding via ion exchange, formation of magnesium phosphate hydrates, physical densification through crystallization, and microvoid filling by amorphous gels. I provide fundamental insight into the interfacial reinforcement mechanisms in MPC-based repair material, offering valuable guidance for optimizing rapid repair strategies in concrete infrastructure.

A detailed investigation of tricalcium aluminate (C(3)A) under CO2 exposure is essential for developing Al-rich materials via carbonation. In this study, the carbonation properties of C(3)A were investigated, including the carbonation kinetics, the contribution of mineral evolution to strength development, the effects of dissolution properties, and the influence of temperature and prehydration treatment. The results indicate that compared to other Portland cement clinkers, C(3)A exhibited the highest early carbonation rate (k(1) = 59.96 min(-1)) due to its high dissolution rate but the lowest degree of carbonation (22.9%) due to its low Ca2+ leaching concentration (<= 388.3 mg/L). Hydration took precedence over carbonation in C(3)A, forming hydrogarnet (C(3)AH(6)), which exhibited lower carbonation activity and was unfavorable for subsequent carbonation. The elastic modulus of C(3)A decreased from 4.89 +/- 0.34 to 4.14 +/- 0.42 GPa after 2 h of prehydration followed by 72 h of carbonation at 25 degrees C, as determined by three-dimensional digital image correlation. Increasing the temperature from 25 to 60 degrees C effectively promoted the carbonation of hydration products, primarily C(3)AH(6) and Al-monocarbonate (C(4)ACH(11)), facilitating the formation of aragonite fibers and gibbsite. Aragonite fibers, with an average length of 1.914 mu m, increased in content from 9.5 to 18.5 wt %, interlacing with each other to form an urchin-like structure that provided a fibrous effect, increasing the flexural strength from 5.85 +/- 0.19 to 9.07 +/- 0.34 MPa. Gibbsite increased in content from 7.0 to 13.4 wt % and tightly wrapped around the surfaces of unreacted C(3)A grains, working synergistically with CaCO3 crystals with an average elastic modulus of 59.2 GPa (determined by nanoindentation) to serve as cementing agents, increasing the compressive strength from 28.71 +/- 2.45 to 45.14 +/- 3.94 MPa and the elastic modulus from 4.89 +/- 0.34 to 11.77 +/- 0.99 GPa. In comparison, at 25 degrees C, C(3)A powder primarily produced nanospherical vaterite with a crystallite size of approximately 27 nm and only trace amounts of gibbsite (0.8-4.0 wt %).

Leveraging alkali-activated materials (AAMs) prepared from industrial wastes offers significant potential for sustainable construction, yet their widespread application is hindered by inherent limitations in tensile strength and shrinkage. Incorporating carbon nanotubes (CNTs) presents a promising strategy to enhance the performance of these waste-derived binders. This work critically reviews the macro-properties and nano-/micro-structural mechanisms of CNT-reinforced AAM nanocomposites, evaluating their viability for sustainable infrastructure applications. Following an analysis of CNT dispersion behavior in alkaline media, the impacts of CNTs on mechanical strength, drying shrinkage, durability, hydration products, pore structure, microcracking, and interfacial bonding are systematically examined. Results demonstrate that CNTs significantly enhance mechanical strength, toughness, and durability while mitigating drying shrinkage. Microstructural analysis reveals that CNTs act as nucleation sites, promoting gel phase formation, increasing Al–Si substitution, and extending aluminosilicate chain length. Simultaneously, CNTs refine pore structure and bridge microcracks, impeding crack initiation and propagation. Discrepancies in reported fluidity, mechanical strength, and microstructural results are attributed to the variations in AAM precursor composition (waste source) and liquid-phase environments affecting CNT dispersion. This review not only advances the understanding of CNT–AAM interactions but also identifies critical research gaps in CNT dispersion stability, long-term durability mechanisms under environmental stress, and nanoscale interfacial characterization, which are essential for optimizing waste-derived AAM nanocomposites for sustainable construction.

With the increasing frequency of river and lake dredging, large amounts of sediment are continuously produced, posing significant challenges in resource-efficient, low-carbon disposal. Solidification technology, known for its economic viability, adaptability, and environmental friendliness, has become a key research direction for sediment treatment. Based on publications from the Web of Science, this study combines bibliometric analysis and machine learning trend prediction to explore the development trajectory, research hotspots, and future trends in sediment solidification. Publication volume has steadily increased since 2000, with a notable surge in the past five years. Academic influence has shifted from a few core works to a diversified and mature research system. International collaboration and interdisciplinary integration are growing, with China taking a central role in both publication output and academic influence. Research has evolved from focusing on pollutant migration and environmental safety to addressing mechanical properties and engineering applicability, and more recently, expanding to high-performance solidification materials, micro-mechanism analysis, and intelligent methods. Machine learning models, such as ridge regression and Huber regression, are effective in long-term trend modeling, while ensemble methods capture abrupt changes in trends. Predictions suggest that future research will focus on micro-mechanism analysis, low-carbon material adaptability, multi-pollutant co-solidification, and intelligent formulation optimization. This study provides data-driven insights and methodological guidance for future scientific planning and engineering applications.

The sustainable development of construction materials requires both performance improvement and effective utilization of industrial solid wastes. This study investigates the effect of coal-based synthetic natural gas slag (CBSNGS) on the hydration behavior, phase characteristics, and microstructure of magnesium potassium phosphate cement (MKPC). A combination of XRD, FTIR, TG/DTG, DSC, isothermal calorimetry, SEM/EDS, and nitrogen adsorption techniques was employed to elucidate the role of CBSNGS in the MKPC. Results show that CBSNGS incorporation does not alter the fundamental hydration pathway of MKPC, with struvite-K remaining the dominant crystalline phase. However, ball-milled CBSNGS primarily affects hydration kinetics and microstructural evolution through heterogeneous nucleation and modification of the water balance in the MKPC. The increased specific surface area and water absorption capacity of CBSNGS reduce the effective water-to-binder ratio, leading to changes in setting behavior, pore-scale redistribution within the mesopore range, and delayed but enhanced strength development at later curing ages. SEM/EDS observations reveal that CBSNGS particles are spatially associated with Si- and Al-rich domains, contributing to improved packing and microstructural continuity of MKPC matrix. CBSNGS serves as a functional modifier that regulates hydration kinetics and microstructure in MKPC, demonstrating its potential for value-added utilization and solid-waste recycling of industrial solid waste in phosphate-based cementitious systems.