High ferrite Portland cement (HFPC) is a promising low-carbon alternative to ordinary Portland cement due to its lower clinkering temperature of 1330 degrees C and reduced CO2 emissions. However, the poor early strength development of clinker remains a key challenge and may be related to the hydration retardation between C3S and ferrite. This study comparatively investigates the hydration of C3S in the presence of C3A and ferrite phases sintered at 1330 degrees C (Ferrite(L)) and 1450 degrees C (Ferrite(H)). The results demonstrate that both Ferrite(L) and Ferrite(H) systems exert a more pronounced retardation effect on C3S hydration than C3A, indicating an intrinsic effect of the ferrite phase. Ferrite(H) shows an even stronger retardation effect, which is attributed to the combined contribution of the intrinsic ferrite effect and the additional Al release from its CAcontaining phase assemblage. This is supported by the higher dissolved Al concentration at 10 h in Ferrite(H) (0.113 mmol/L), about four times that in C3A (0.026 mmol/L). Furthermore, the incorporation of Al and Fe into the C-S-H structure prolongs mean chain length and enhances the hardness of C-(A/F-)S-H-rich hydration products. These results deepen the understanding of phase interactions in ferrite-rich cement systems and provide a basis for the design of low-carbon HFPC.

Manufacturing active belite polymorph (α’-C2S) is key to achieving low-carbon cement production, and its stabilization is highly dependent on the ion doping scheme. The BO33--Na⁺ co-doping scheme most effectively stabilizes the active α’-C₂S phase. However, how BO33- influences the hydration of B-Na-doped α’-C₂S under its combined retarding and polymorph-stabilizing effects remains unclear. Belite hydration is triggered by the breakage of Ca-O bonds, thus Ca dissolution was examined to clarify its hydration in this study. Compared with undoped α’-C₂S, charge redistribution and local coordination environment variation together enhance water affinity of B-Na-stabilized α’-C2S, but raise its Ca dissolution barrier. Compared with β-C₂S, Ca dissolution is accelerated in a boron-concentration-dependent manner. Metadynamics revealed that the initial coordination environment determines its Ca dissolution pathways, energy barrier, and enthalpy change; the breakage of Ca-O(-B) bond is a low-energy-barrier process. Metastable states—such as proton transfer, water dissociation, and oxygen translocation—help lower the activation energy for Ca-O bond breakage/formation, and steric hindrance plays a role in direct water adsorption. This finding thus marks a landmark in understanding the hydration mechanism of B-Na-stabilized α’-C2S.

The cement industry accounts for approximately 7-8 % of global anthropogenic CO2 emissions, necessitating the urgent development of low-carbon cementitious alternatives that incorporate industrial solid wastes. In this study, high-ferrite Portland cement (HFPC) clinkers were synthesized by co-calcining steel slag (SS) and limestone powder (LSP) at varying mass ratios (LSP: 30-55 wt%). The effects of LSP dosage and calcination temperature on mineral phase formation, microstructural evolution, hydration behavior, and mechanical performance were systematically investigated using X-ray diffraction (XRD), quantitative Rietveld refinement (QXRD), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), backscattered electron imaging (BSE), thermogravimetric analysis (TG-DTG), Fourier-transform infrared spectroscopy (FT-IR), mercury intrusion porosimetry (MIP), and isothermal calorimetry. Results demonstrate that increasing LSP content progressively drove mineral phase reconstruction from a C2S-C4AFC3MS2 assemblage toward a C3S-dominant system. HFPC-40 (40 wt% LSP, calcined at 1300 degrees C) achieved the highest C4AF content (25.19 wt%) and exhibited a unique two-stage hydration mechanism: rapid early-age C4AF hydration generating ettringite (AFt) and alumino-ferrite hydrate (A(F)H3) gel, followed by progressive C2S hydration producing C-S-H and Ca(OH)2 at later ages. HFPC-50 attained the highest 28-day compressive strength of 75.40 MPa, while excessive free CaO in HFPC-55 induced early cracking. MIP analysis confirmed that later-stage silicate hydration densified the microstructure, reducing porosity from 34 to 50 % at 3 days to approximately 19-21 % at 90 days across the HFPC-40, -45, and -50 compositions. This work provides mechanistic insights into waste-derived high-ferrite clinker systems and offers a technically viable, environmentally favorable pathway for large-scale steel slag valorization.

Urban air pollution and the high carbon footprint of construction materials pose significant environmental challenges. To address these issues, this study evaluates a novel TiO2-SiO2-based photocatalytic material that integrates CO2 capture via carbonation curing with advanced environmental purification. Distinct from conventional cementitious carriers where natural carbonation often induces pore blockage and activity loss, TSC utilizes controlled carbonation curing to permanently sequester CO2. This process constructively generates a stable, porous carbonate-silica matrix that ensures sustained reactant accessibility and efficient photocatalysis. Its NOx degradation performance was systematically optimized under varying gas flow rates, light intensities, and humidity levels. Model-based simulations for Hong Kong indicated a theoretical kinetic potential for NOx removal reaching 100% under peak UV conditions. While demonstrating robust climate adaptability, these results reflect a kinetic overcapacity relative to pollutant flux rather than absolute environmental clearance. Furthermore, TSC exhibited superior antimicrobial activity against Escherichia coli and Chlorella, attributed to enhanced reactive oxygen species (ROS) generation. By integrating carbon sequestration, air purification, and biofouling resistance, TSC emerges as a holistic, sustainable solution for resilient urban infrastructure.

Introduction Cement is a fundamental material for global infrastructure.Global cement production is projected to exceed 4.5 billion tons by 2030.The cement industry contributes about 7.5%of global anthropogenic carbon dioxide(CO2)emissions.These emissions mainly come from fossil fuel combustion and limestone decomposition during the calcination process.Replacing fossil fuels with concentrated solar energy(CSE)for clinker calcination is a key pathway to achieve carbon neutrality in this sector.The CSE technology can concentrate solar radiation up to 7000 times and generate ultra-high temperatures of above 3000 K.These conditions can meet the thermal requirements for cement clinker production. The spectral mismatch between cement materials and solar radiation as a critical bottleneck limits the efficiency of solar calcination..The solar spectrum concentrates its energy in the visible(400-700 nm)and near-infrared(NIR,700-2500 nm)bands.Most cement raw materials,such as calcium carbonate(CaCO3),silicon dioxide(SiO2),and aluminum oxide(Al2O3),are wide-bandgap materials.These materials absorb mainly in the ultraviolet region and are nearly transparent to visible and NIR light.This transparency leads to a low solar-to-thermal conversion efficiency.Iron oxide(Fe2O3)and iron-bearing ferrite minerals have narrower bandgaps of 2.0-2.2 eV.These minerals offer a stronger light absorption in the solar spectrum.This study was to investigate high-ferrite cement(HFC)clinkers to use the high absorption of the iron phase for better photothermal conversion.The calcination performance in electric furnace and solar furnace was compared and the first-principles calculations were performed.The goal was to reveal the photothermal coupling mechanism that could enable low-temperature and rapid clinker formation. Methods Three high-ferrite cement raw meals were prepared with analytical-grade reagents.These samples,named HFC-16,HFC-18,and HFC-20,were designed with different mass fractions of tetracalcium aluminoferrite(C4AF,16%,18%,and 20%),respectively.All raw materials were ground and passed through a 200-mesh sieve.The sintering was carried out in a conventional electric elevator furnace and a high-flux solar simulator,respectively.The solar simulator used a xenon lamp array to mimic the solar spectrum(AM1.5).This simulator generated a peak heat flux of>1800 kW/m2 at the focal plane. For the experiments in the electric furnace,the samples were heated to 800℃and held for 30 min.The samples were then heated at 1000,1200℃,or 1375℃and held for 2 h,respectively.For the experiments in the solar furnace,the samples were rapidly heated to 800℃and held for 1 min.They were then heated to the target temperature and held for 5 min.All the samples were rapidly cooled after firing.The phase composition of each sample was analyzed by X-ray diffraction(XRD).The Rietveld refinement was used for quantitative phase analysis.The optical properties were measured by ultraviolet-visible(UV-Vis)spectrophotometry in the range of 200-2500 nm.The total solar absorptance was calculated by the AM1.5 solar irradiance distribution.The electronic structures were simulated by a software named Vienna Ab initio Simulation Package(VASP).The simulations were based on the Density Functional Theory(DFT)with the GGA-PBE functional and a Hubbard U correction for Fe 3d orbitals. Results and Discussion The UV-Vis spectra of the raw materials show that wide-bandgap oxides(i.e.,CaO,SiO2,Al2O3)have a weak absorption in the solar spectrum region.Their absorptance values are all below 20%.Fe2O3 is a main absorber among all the raw materials.Its solar absorptance reaches 71.1%.As a result,increasing the Fe2O3 content in the raw meal improves the overall light absorption.The solar absorptance of the raw meal increases from 56.6%for HFC-16 to 60.5%for HFC-20.The light absorption of the clinker minerals depends on the calcination temperature.At 1000℃,the absorptance decreases slightly.This decrease is due to the decomposition of CaCO3 into weakly absorbing CaO and the low crystallinity of intermediate phases.At 1200℃,the absorptance increases sharply.The iron phase mineral formed at 1200℃shows a solar absorptance of 83.9%.This value is greater than that of the raw Fe2O3.For the clinker sample HFC-20,the total light absorptance is 75.6%at 1375℃. The results by the First-principles calculations explain the mechanism behind this enhancement.In the high-temperature ferrite solid solution(C4AF),Fe3+ions occupy both tetrahedral and octahedral sites.This mixed coordination induces a crystal field splitting and creates diverse intermediate energy levels.The substitution of Al3+for Fe3+also introduces lattice defects.These defects create dense defect states within the bandgap.The density of states(DOS)analysis indicates that Fe 3d orbitals dominate the conduction band minimum.O 2p orbitals dominate the valence band maximum.The strong O 2p → Fe 3d transitions are responsible for the intense broadband absorption in the visible and NIR regions. The comparison between the two heat sources shows a clear photothermal coupling effect in the solar furnace.The XRD patterns indicate that the solar-calcined samples processed at a thermocouple-measured temperature of only 800℃already contain distinct silicate mineral phases(i.e.,tricalcium silicate,C3S,and dicalcium silicate,C2S).In the conventional electric furnace,these phases only form at 1200℃.This result indicates that the iron phase absorbs a high-intensity photon energy locally and lowers the formation temperature of clinker minerals by approxiamtely 400℃.The electric furnace transfers heat slowly through conduction from the surface to the interior.The solar furnace delivers energy directly to the reactive iron-bearing sites.This direct energy delivery greatly accelerates the solid-state reaction kinetics. At the final sintering temperature of 1375℃,the two methods both produce clinkers with the target mineral phases(i.e.,C3S,C2S,tricalcium aluminate C3A,and C4AF).No free CaO appears in either case.This result confirms that the solar furnace can fully sinter cement clinker.The Rietveld refinement of the XRD patterns shows that the solar-calcined clinker exhibits broader diffraction peaks than the electric furnace clinker.The rapid heating rate and the unique photothermal environment in the solar furnace likely caused this broadening.Smaller crystallite sizes or higher lattice defect concentrations are the probable reasons.These findings indicate that solar calcination saves energy and changes the microstructural evolution of the cement minerals. Conclusions Based on the UV-Vis absorption testing and XRD analysis of raw materials,raw meals,and samples calcined at different temperatures,the overall light absorption intensity of the raw meal increased significantly as the Fe2O3 content in the raw meal increased.Furthermore,the light absorption intensity of the iron phase in the clinker minerals increased with increasing the calcination temperature.At 1200℃,its light absorption rate reached 83%.The light absorption intensity of the clinker also increased with the calcination temperature,reaching 75.6%at 1375℃.More importantly,the iron phase could trigger a photothermal coupling effect when calcined in a simulated high-concentration solar furnace,significantly lowering the formation temperature of clinker minerals.The results by the XRD Rietveld refinement and hydration calorimetry indicated that,compared with the electric furnace clinker,the simulated concentrated solar calcined clinker(SF-HFC)exhibited diffraction peak broadening characteristics.This could demonstrate that the photothermal effect of the iron phase significantly reduced the calcination temperature of cement clinker and lowered the production energy consumption,providing a material design strategy for high-efficiency and low-carbon cement manufacturing.

Abstract Low-carbon cement requires clinker designs with lower CaO demand and more effective utilization of industrial wastes. In this study, a steel slag-based Belite−Ferrite (BF) clinker dominated by dicalcium silicate (C2S) and tetracalcium aluminoferrite (C4AF) was developed and evaluated. The results indicate that the steel slag-based BF clinker highly promoted the formation of active α-C2S, which formed ∼23.2% active α-C2S in the total C2S phase, as well as reduced about 22−38% CO2 emissions compared with ordinary Portland cement (OPC) clinker. As an alternative material for OPC clinker, the produced BF clinker exhibited low early reactivity but presented a continuing hydration and strength growth in 28 d, which enhanced 5−19% compressive strength at 28 d with 10−40% replacement of OPC clinker in OPC-BF cement system. The estimated CO2 emissions of the OPC-BF cement system were 3−16% lower than those of the pure OPC system, indicating that steel slag-based BF clinker is a promising low-carbon component for OPC.

The growing iron content in modern low-clinker cements and solid waste-integrated binders introduces uncertainties to the structural stability and performance reliability of calcium silicate hydrate (C-S-H), yet the role of Fe within its fundamental structure has long remained unclear. This study addresses this key knowledge gap by elucidating how Fe participates in and influences the C-S-H structural framework. Through the synthesis of calcium ferrite silicate hydrate (C-F-S-H) and multi-scale structural characterization, including X-ray absorption fine structure spectroscopy, it is demonstrated that Fe does not merely exist as an external impurity, but directly incorporates into the C-S-H structure. Results show polycarboxylate ether (PCE) enables Fe incorporation via dual complexation with Ca/Fe ions, inhibiting rapid C-S-H precipitation and the formation of secondary Fe-rich phases. More importantly, Fe forms tetrahedral Fe-O units, occupying the bridging sites, and forming stable Fe-O-Si linkages that extend the chain connectivity of C-S-H. These molecular-level findings provide a foundation for optimizing Fe-rich, low-clinker, and low-carbon cementitious systems.

Ferrite-rich cement, a type of low-carbon cement, exhibits good durability and strength development. However, its strengthening mechanism is not fully understood, primarily due to the challenges of quantitative evaluation. By mixing synthetic ferrite with ordinary Portland cement, this study quantitatively illustrated the role of ferrite in cement hydration and performance, and proposed the fate of Fe. The results showed that ferrite improved the degree of hydration of silicate phases at later ages through synergistic hydration effect, and ferrite hydration consumed portlandite in the absence of AFt, forming Fe-bearing gel and low-Fe h-AFm. Fe atoms were primarily distributed around ferrite relics for its poor diffusivity, and the hydrates around ferrite relics mainly consisted of C-(A, F-)S-H, low-Fe h-AFm, and Fe(OH)3 gel at later ages. The pozzolanic-like reaction of ferrite consumed CH and lowered the elastic modulus of hydration products around ferrite, and the formation of Fe(OH)3 gel and C-(A, F)S-H with longer MCL enhanced its hardness. Based on these findings, the role of ferrite on cement hydration and performance was further elucidated.

This paper investigated the inhibition effects and mechanisms of organic phosphonic acids (OPAs) with distinct functional groups on triclinic tricalcium silicate (C3S) clinker hydration. In particular, the effects of three representative OPAs, namely ATMP, HEDP, and PBTC on adsorption/complexation behavior, hydration products, and microstructure characteristics of C3S clinker were studied. OPAs retardation of the C3S clinker hydration was governed by synergistic interactions of electrostatic adsorption, and cationic complexation, potentially involving intermolecular self-polycondensation. ATMP primarily relied on Ca2+ complexation through its [-C-PO(OH)2] groups, forming low-solubility precipitates that inhibited hydration. HEDP combined strong complexation with intermolecular self-polycondensation, driven by its [-C-PO(OH)(2)] and (-OH) groups, generating dense three-dimensional polymers that enhanced steric hindrance, while PBTC operated through surface adsorption and self-polycondensation. The revealed retardation efficiency hierarchy (HEDP > PBTC > ATMP) arose from functional group synergy: the maximal inhibition was provided by synergy of [-C-PO(OH)(2)] and (-OH) groups, a weaker one-by that of [-C-PO(OH)2] and (-COOH) groups, while isolated [-C-PO(OH)(2)] groups had the minimal retarding capacity.

γ-Dicalcium silicate (γ-C2S), a highly carbonation-reactive mineral, is conventionally applied in coatings through post-application carbonation curing, which may complicate practical application. In this study, the in situ carbonated waterborne coatings were proposed by using γ-C2S as a filler reacting with CO2 in the coating preparation process. The rheological evolution of γ-C2S slurry and its correlation with microstructure and macroscopic properties were investigated. The results show that in situ carbonation formed a three-dimensional network, composed of calcium carbonate and amorphous silica gel, thereby transforming the γ-C2S slurry from shear-thickening to shear-thinning behavior, and markedly increasing the yield stress and viscosity. The dispersant promoted the formation of high-aspect-ratio aragonite, strengthening the three-dimensional network and increasing the viscosity of the carbonated slurry, whereas the acrylic emulsion suppressed aragonite formation and mitigated carbonation-induced thickening. Carbonation and higher solids content improved the sedimentation resistance, sag resistance, and adhesion strength of the coating by promoting a denser three-dimensional structure. Based on these findings, a four-stage mechanism for the in situ carbonation of γ-C2S filler is proposed, involving γ-C2S dissolution, CO2 dissolution, formation of CaCO3 and amorphous silicagel, and continuous network development. This work provides a theoretical basis for the design of high-performance waterborne carbonated coatings.

High ferrite Portland cement (HFPC), a low-carbon alternative to ordinary Portland cement with reduced C3S and C3A alongside elevated C4AF and C2S, exhibits insufficient early- and mid-term strength development due to sluggish hydration kinetics. To address this limitation, the synergistic effects of Q phase (Ca20Al26Mg3Si3O68) clinker (0-12 wt%) and gypsum (0-8 wt%) on the hydration regulation, mechanical properties and microstructure evolution of HFPC were systematically investigated. Results demonstrate that a hybrid formulation containing 6 wt% Q phase clinker and 4 wt% gypsum achieves a 1-day compressive strength comparable to pure HFPC while significantly enhancing the 28-day strength to over 90 MPa. Gypsum addition was found to mitigate the early-stage hydration retardation induced by Q phase, primarily by promoting the nucleation and stabilization of ettringite. This synergy elongates C-(A-)S-H chains and enhances chloride binding than HFPC, with concurrent porosity reduction and pore size distribution homogenization collectively boosting mechanical and durability performance.

CO2-curing, CO2-mixing and single-component carbonation offer promising strategies for reducing the carbon footprint of concrete; their current sequestration efficiencies remain insufficient to achieve carbon neutrality. This study proposes an innovative pathway towards carbon-neutral concrete by developing Total Component CO2-sequestration Concrete (TC3). The key innovation involves that total components are incorporated into the overall decarbonization framework, either through direct pre-carbonation treatment of carbonatable raw materials, inherent carbon sequestration potential during the in-service stage and indirect carbon benefits from cement usage reduction. CO2 reduction evaluation shows that TC3 achieves a CO2 reduction around 160 kg/m3, equating to an approximately 42% reduction per unit volume compared to ordinary concrete. This reduction is almost 2 times that of CO2-curing and 8 times that of CO2-mixing compared to typical literature-reported values. The synergistic hydration effect of carbonated supplementary cementitious materials and CO2-rich mixing water reached a 28-d compressive strength of over 60 MPa. Furthermore, the compressive strength carbon emission index of TC3 is over 40% and 30% lower than that of CO2-mixing and CO2-curing, respectively. By overcoming the limitations of diffusion (CO2-curing) and dissolution (CO2-mixing), TC3 establishes a better and more comprehensive carbon management strategy. This paradigm transforms concrete from a carbon source into a CO2-storing unit, providing a robust pathway to reconcile growing global concrete demand with stringent carbon neutrality commitments.

With the rapidly growing demand for sustainable energy solutions, there has been increasing interest in harnessing ambient energy sources for power generation. In this work, we developed a dual-mode radiative cooling power generation (DRCPG) system for building-integrated energy harvesting. This system coupled the radiative cooling of engineered marble coating with the thermoelectric effect, further enhanced by a low-emission highabsorption coating applied to a concrete substrate. With the inclusion of a greenhouse effect, the daytime voltage increased to 305 mV, while the maximum power output reached 391 mW/m2. Importantly, the system maintains operation around the clock and demonstrates long-term stability in energy generation. Finite element simulations predicted an annual power density of 926 Wh/m2 for the DRCPG system, indicating that it could power 50-700 smart building microsensors per square meter. The system holds significant potential for energy harvesting applications, contributing to the advancement of sustainable smart buildings.

This study presents a novel sustainable cementitious material by synthesizing High Ferrite Belite-rich (HFBR) clinker from Bayer process red mud (BRM) waste and limestone. Through systematic optimization, the optimal red mud-to-limestone ratio of 52.5:47.5 was identified, producing clinker with C2S-C4AF-C12A7 mineral assemblage (61.2 %, 28.6 %, and 10.2 %, respectively) at 1200 degrees C. Unlike conventional Portland cement, HFBR clinker exhibits a unique two-stage hydration mechanism without calcium hydroxide formation. During early hydration (1-7 days), highly reactive C4AF and C12A7 rapidly form calcium aluminate hydrates (C3AH6) and aluminum hydroxide gel (AH3), achieving 14.9 MPa compressive strength at 1 day. Subsequently, C2S reacts with early hydration products to form silicon-containing calcium aluminate hydrate (C3ASH4) with a three-dimensional network structure, reaching 41.7 MPa at 90 days. Advanced characterization using XRD, 29Si NMR, nanoindentation, and mercury intrusion porosimetry confirmed the formation of an isolated silicate tetrahedra (Q0) structure and progressive pore refinement from 248 nm to 83 nm average diameter. This research demonstrates a viable pathway for red mud valorization while developing alternative low-carbon cementitious materials with distinct hydration chemistry and performance characteristics.

The global temperature rising and building cooling energy consumption increasing have caused a serious concern. This study proposed a novel carbonated inorganic radiative cooling material, called as gamma-dicalcium silicate carbonated radiative cooling coatings (CRCC), expected to be used for building cooling through spectral emission from buildings to space. In terms of CRCC, high reflectivity to the solar spectrum and high emissivity to the atmospheric window (8-13 mu m wavelength) can be achieved by simply optimizing the preparation solid/ water ratio. This is attributed to the reaction products actions between CO2 and gamma-dicalcium silicate. The predominantly consisting of CaCO3, the vibrational characteristics of C-O and Si-O bonds, and along with a surface porous structure offer the excellent and distinctive spectrum and scattering characteristics. The addition of nano Al2O3 could further enhance the spectral performance of CRCC, which present an exceeding 95 % reflectivity to solar spectrum, and over 97 % emissivity to the atmospheric window, resulting in a cooling effect of ca 7 degrees C for the modified CRCC surface. The numerical calculation and finite element analysis further validated the superior radiative cooling performance of CRCC, demonstrating their capability to maintain lower temperatures. We believe that the CRCC not only serves as a low-carbon construction material but also facilitates radiative cooling, contributing to energy savings in buildings, and achieving low-carbon environmental protection.

Ground granulated blast furnace slag (GGBS), calcium carbide slag (CS), and phosphogypsum (PG) were combined in a mass ratio of 60:30:10 (abbreviated as GCP) to solidify dredged sludge (DS) with high water content. The long-term strength characteristics of solidified DS under varying curing agent dosage and initial water contents, as well as its durability under complex environmental conditions, were investigated via a series of mechanical and microstructural tests. The superior performance of GCP-solidified DS (SDS-G) in terms of strength and durability was demonstrated in comparison to solidified DS using ordinary Portland cement (SDS-O). The results indicated that the unconfined compressive strength (UCS) of SDS-G was approximately 3.0-4.5 times greater than that of SDS-O at the same dosage and curing ages, exhibiting a consistent increase in strength even beyond 28 days of curing. Additionally, the strength and deformation modulus (E50) of SDS-G increased initially and then decreased during wet-dry cycles, with reductions in mass, volume, and strength significantly were smaller than those observed in SDS-O. Furthermore, the reductions in UCS and E50 induced by freeze-thaw cycles were considerably smaller for SDS-G than for SDS-O, with strength losses of 50.7% and 88.3%, respectively, after 13 freeze-thaw cycles. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses revealed that the enhancements observed in SDS-G were attributed to the formation of ettringite (AFt), which effectively fills larger pores between agglomerated soil particles, thereby creating a denser and more stable microstructure in conjunction with hydrated calcium aluminosilicate (C-(A)-S-H) gels.

Microscopic structural control offers a promising solution to the performance bottlenecks faced by most commercial microwave absorbers, often limited by their intrinsic electromagnetic properties. In this study, we have developed lightweight unidirectional aerogels with tunable electromagnetic properties using unidirectional freezing and freeze-drying techniques without high temperature calcination. Cellulose nanofibre (CNF) forms the structural framework, while multi-walled carbon nanotube (MWCNT) enhances electrical conductivity and mechanical stability. The incorporation of Fe3O4 nanoparticles further prevents the aerogels from collapsing under ambient conditions. By adjusting the MWCNT to Fe3O4 ratio, tunable microwave absorption across the entire frequency band is achieved, with optimal absorption intensity of -45.0 dB and an effective absorption bandwidth (EAB) of 6.1 GHz. The unique micron-level unidirectional pore structures also modulate the complex permittivity in response to different electromagnetic wave (EMW) incident directions, paving a feasible method for regulating microstructures with electromagnetic response characteristics. Radar cross section (RCS) and electromagnetic response simulations confirm the aerogels’ excellent EMW absorbing properties and sensitivity to incident direction, illustrating that microstructure regulation offers new insights for designing lightweight and high-performance EMW absorbing materials.

This study explored the high-ferrite Portland cement (HFC) abrasion resistance mechanism by analyzing the microstructure of its hydration products and the interfacial transition zone (ITZ). Two HFCs with different clinker composites (HFC1:C(4)AF=17.75 %, C3S=45.45 %; HFC2:C(4)AF=15.75 %, C3S=33.80 %) were subjected to thermogravimetric analysis, mercury intrusion porosimetry, and Si-29 nuclear magnetic resonance combined with thermodynamic modeling, yielding the hydration product characteristics. Their ITZ's micromechanical properties and thickness were determined via nanoindentation, microhardness, and SEM-EDS. HFC1 presented 26.2 % greater abrasion resistance and 21.2 % greater impact resistance energy compared to HFC2, in addition to better ITZ micromechanical properties. Nanoindentation and SEM-EDS measurements proved that HFC1 outperformed HFC2 in ITZ thickness, which was narrower by 64-89 % than that of HFC2. Moreover, at 28 days, the ITZ nanoindentation modulus and hardness of HFC1 exceeded those of HFC2 by 43.0 % and 39.0 %, respectively. The synergistic hydration at higher contents of C(4)AF and C3S was beneficial for C-S-H gel formation with a higher polymerization degree and a longer mean chain length. In HFC1, the latter exceeded that in HFC2 by 7 % on average. The total porosity and share of large pores (50 nm < d < 1000 nm) in HFC1 were lower than in HFC2 by 1.2 % and 8.0 %, respectively. Overall, the synergistic hydration between C3S and C(4)AF improved the polymerization of C-S-H gel. The C-S-H gel with a high degree of polymerization was more closely combined with the aggregate, improving its ITZ characteristics and enhancing the abrasion resistance.

The addition of supplementary cementitious materials (SCMs) to cement is an effective approach to reduce carbon emissions. However, achieving a balance between the SCMs content and the properties of cement remains a challenge. In this study, a low-clinker composite cement was developed by substituting clinker with fly ash, blast furnace slag, tuff, and limestone. Response surface methodology (RSM) and Box-Behnken design (BBD) were employed for experimental design, model construction. The BBD established a regression model to predict the relationship between SCM content and the compressive strength of cement through 29 sample points, and effectively reducing experimental costs. Through regression modeling, the optimal composition of cement was determined with the RMSE and MAE less than 0.5 MPa. Furthermore, comparative experiments were designed based on model predictions, and the phase composition and pore structure of the composite cement were analyzed. The RSM model successfully captured the effects of SCMs on cement compressive strength and provided accurate predictions.