The corrosion behavior of steel under large temperature variation in high-altitude regions is a critical factor affecting its engineering applications. In this study, a freeze-thaw cycling apparatus was used to simulate the large temperature-difference environment characteristic of high-altitude regions, and 0.05 mol L-1 NaHSO3 was employed to simulate the corrosive effect of sulfur dioxide in typical industrial atmospheres. The corrosion degradation behavior of low-carbon steels (Q345, Q370) and weathering steel (Q500qENH) under freeze-thaw cycling conditions was systematically investigated. The gravimetric analysis, static tensile testing, scanning electron microscopy (SEM), laser confocal scanning microscopy, X-ray diffraction (XRD), and electrochemical techniques were employed to elucidate the corrosion kinetics, microstructural evolution of rust layers, and changes in mechanical properties of the three steels during freeze-thaw exposure. The results indicated that, under freeze-thaw cycling between-10 and 15 degrees C, the corrosion mass loss of all three steels followed a power-law relationship. Among them, the characteristic corrosion parameter n of Q345 and Q370 steels was greater than 1, indicating that both steels were in an accelerated corrosion stage. By contrast, the n value of Q500qENH weathering steel was approximately 0.9874, indicating that the rust layer formed on its surface could effectively retard the corrosion process. After 450 freeze-thaw cycles, the Q345 steel exhibited the most pronounced degradation in elastic modulus, with a reduction of 13.35%. The Q370 steel showed the largest decrease in elongation, reaching 9.23%. The Q500qENH steel experienced the greatest reduction in yield strength as 7.2%. The electrochemical analysis revealed that, among the three steels, Q500qENH steel exhibited a 5% increase in corrosion potential and a 2% decrease in corrosion current density, indicating that the rust layer formed on its surface was protective and could effectively suppress the corrosion process. The contents of Fe3O4/gamma-Fe2O3 and alpha-FeOOH in the corrosion products of all three steels increased progressively with the number of freeze-thaw cycles. The addition of alloying elements further enhanced the stability and corrosion resistance of the rust layer, thereby reducing the overall corrosion rate of the steels. This study is of important engineering significance for the corrosion protection design and material selection of steel structures under large temperature-difference conditions in high-altitude regions.

In this paper, natural brucite was used to replace the traditional heavy-burned MgO to prepare the magnesium phosphate cement (NBMAPC) in an innovative way. The influence of the change of phosphate/magnesium hydroxide in the brucite (P/M) molar ratio on the workability, mechanical properties, phase compositions, and microstructure of the NBMAPC was mainly investigated. The findings indicated a progressive decline in fluidity and setting time of the NBMAPC paste as the P/M molar ratio diminished. The compressive strength increased first and then decreased. The maximum hydration heat release rate increased, the total hydration heat decreased, and the hydration degree decreased. The microscopic test results revealed that the main hydration product of NBMAPC was MgNH4PO46H2O, exhibiting coexisting crystal and amorphous phases. A lower P/M molar ratio resulted in enhanced structural compactness of the hardened NBMAPC matrix and a corresponding reduction in total porosity.

Traditional magnesium oxysulfate cement (MOSC) is prepared from light-burned magnesia, magnesium sulfate heptahydrate with a large amount of energy consumption and CO2 release. This study used brucite and dilute sulfuric acid to prepare magnesium sulfate (MgSO4) solution where the temperature exceeded 70 degrees C; light-burned magnesia was added to create a new type of sustainable low carbon MOSC, of which the performances were evaluated. Additionally, the effects of MgSO4 solution temperatures on sustainable low carbon MOSC were investigated. The results showed that as the temperature of the MgSO4 solution increased, the setting time and the fluidity of the sustainable low carbon MOSC decreased. The compressive strength of this material showed that the samples prepared with 20 degrees C MgSO4 solution exhibited increasing compressive strength, reaching 34 MPa at 3 d age. However, the samples prepared with 40 degrees C and 60 degrees C MgSO4 solution showed compressive strength reduction as 23 and 18.2 MPa at 3 d age. Microscopic analysis revealed that the type of hydration products was not altered by the MgSO4 solution temperatures. Under 60 degrees C of the MgSO4 solution, the content of 318 crystalline phase in the material increased to 18.5%, while the 517 crystalline phase decreased to 13.1%. The porosity of the material increased to 26.55%.

To enhance the anti-washout performance of magnesium phosphate cement-based grouting materials (), this study investigates the incorporation of anionic polyacrylamide () as a functional additive. The effects of the water-to-binder ratio (0.20-0.30) and dosage (0-1.5 wt% of the combined mass of magnesia and phosphate) on the workability (fluidity, setting time and bleeding rate), mechanical properties (compressive strength, flexural strength and tensile bond strength) and microstructural characteristics of were systematically investigated. The results indicate that significantly reduces the bleeding rate of the slurry while extending the setting time. It also greatly enhances resistance to water-induced dispersion, with acceptable workability retained. When the content was 0.5 wt% and the water-to-binder ratio was 0.25, the suspension turbidity decreased by 66.3% compared to the control, while the fluidity remained at 250 mm and the setting time was 14 min. At this composition, the 3-day compressive strength, flexural strength, and tensile bond strength reached 21.25 MPa, 5.41 MPa and 2.71 MPa, respectively. Microstructural analysis revealed that retarded the hydration process, altered the crystal morphology and pore structure and facilitated the formation of K-struvite as a hydration product.

Nitrogen oxides (NOx) emitted from anthropogenic sources pose severe threats to urban environments. While incorporating nano-TiO2 into cementitious materials offers a promising photocatalytic remediation strategy, the coupled effects of pore-structure modification and curing age on the degradation efficiency remain underexplored. This study systematically investigated the NO gas degradation performance of nano-TiO2-modified cement paste by controlling the TiO2 content (3-12%), air-entraining agent content, water-cement ratio, and curing age. The results indicate that an optimal nano-TiO2 content of 6% yields the highest compressive strength. Meanwhile, higher nano-TiO2 content (up to 12%) significantly enhances NO removal (reaching 9.73%), but excessive air-entraining agents trap the photocatalyst, thereby reducing efficiency. Furthermore, increasing the water-cement ratio promotes gas diffusion, whereas prolonged curing densifies the matrix and obstructs UV-catalyst contact, decreasing the removal ratio by 20.3% at 28 days. Microstructural analyses elucidate that NO is photocatalytically oxidized into nitrate ions (NO3-) without degrading the essential C-S-H gel. This study provides critical insights into the microstructural optimization of photocatalytic cements, offering a practical design framework for photocatalytic cements with potential for long-term environmental application, pending durability validation.

Polyurethane (PU) foam material plays an important role in building energy conservation due to its low thermal conductivity. However, its flammability and toxic smoke emission pose fire hazards. Traditional additive flame retardants disrupt the closed-cell structure, increasing thermal conductivity and creating a trade-off between insulation and flame retardancy. This trade-off arises because solid additives compromise closed-cell integrity during foaming, opening paths for gas and solid heat transfer. This paper reviews recent progress in synergistic modification of PU foam material for both thermal insulation and flame retardancy. First, the key mechanisms affecting thermal conductivity are outlined, and approaches to enhance insulation via waste recycling, bio-based fillers, and aerogels are summarized. Incorporating aerogels can reduce the thermal conductivity to 0.01579 W/(m & sdot;K). Second, the mechanisms of catalytic charring, smoke suppression, and toxicity reduction of novel flame retardants (e.g., phosphorus/nitrogen and biobased) are analyzed. The phosphorus-nitrogen synergy raises the limiting oxygen index up to 58%. Unlike existing reviews limited to single modifications, this work systematically investigates synergistic strategies for balancing high flame retardancy and low thermal conductivity from a microstructure-macrofunction coupling perspective. By comparing reactive blending, surface coating, heterogeneous nucleation-driven pore optimization, and multi-element hybridization, it is demonstrated that surface coating technology concentrates flame-retardant elements on the foam skeleton surface without disrupting closed cells. For instance, a Cu2+-assisted nanosheet coating yields a V0 rating and a limiting oxygen index (LOI) of 36.0% while maintaining a thermal conductivity of 0.0281 W/(m & sdot;K). Similarly, in-situ aerogel growth constructs hierarchical porous networks and PVA-ATP organic aerogel-modified PU foam material achieves a thermal conductivity of 0.020 W/(m & sdot;K) and an LOI of 36.5%. These strategies ensure an LOI above 30% and V0 rating at a thermal conductivity baseline below 0.030 W/(m & sdot;K). However, surface coating still faces adhesion and weathering challenges, whereas heterogeneous nucleation-driven pore optimization combined with multi-element hybridization enables in-situ dense carbonization and increases closed-cell fraction to suppress vapor convection, offering an optimal route to break the performance trade-off. Finally, the future directions are discussed, including developing intrinsic nucleation-flame-retardant dual monomers, constructing in-situ aerogel/polyurethane micronano networks, and employing machine learning for high-throughput formulation design. This review aims to provide theoretical basis and reference for structurally and functionally integrated insulation materials combining low energy consumption with high fire safety.

In this study, brucite powder was used to prepare magnesium phosphate cement (BMPC) by replacing traditional dead-burned MgO. The effects of temperature (20 degrees C, 0 degrees C, -10 degrees C, -20 degrees C) and M/P (mass ratio of brucite to ammonium dihydrogen phosphate, 1.75, 2.00, 2.25) on the fluidity, setting time, and mechanical properties of the BMPC were investigated, and the related mechanisms were elucidated. The results showed that at a constant M/P, as the temperature decreased, the fluidity of the fresh BMPC decreased, while the setting time prolonged. Under the same temperature, a higher M/P led to reducing the fluidity and shortening the setting time. Compared with room temperature (20 degrees C), the BMPC prepared and cured in low-temperature environments exhibited higher compressive strengths. As the temperature increased, the amount of NH4MgPO4.6 H2O as the crucial hydration product decreased. The temperature had little impact on the porosity of the BMPC but altered the pore size distribution. In addition, the temperature influenced the microscopic morphology of NH4MgPO4.6 H2O.

This article investigated the factors and mechanisms that affected the workability and mechanical properties of cement paste incorporating nano-TiO2.The findings indicated that,for nano-TiO2 aqueous solution concentrations of 3％,6％,9％,and 12％,the optimal dispersion effect was achieved with an ultrasonic dispersion time of 20 minutes.Specifically,at a 6％nano-TiO2 content,both the workability and mechanical performance of the cement paste were enhanced.Furthermore,while nano-TiO2 did not alter the types of hydration products present in the cement paste,it did increase the amount of C-S-H gels.This enhancement was attributed to a higher number of nucleation sites for hydration products,which promoted hydration and reduced the porosity of the cement paste.

Magnesium phosphate cement offers high strength, excellent temperature resistance, alongside superior bonding properties; but its high density, substantial carbon emissions, and instability in foaming processes restrict its applications in thermal insulation and fire protection. This study employed natural brucite and ammonium dihydrogen phosphate as the base materials for magnesium phosphate cement, while magnesium carbonate, sodium bicarbonate, or sodium dodecyl sulfate (SDS) were used as foaming agents to prepare porous brucitebased magnesium phosphate cement (BMPC). The study focused on investigating the physical and mechanical properties, thermal conductivity, and microstructure of the BMPC. The results indicate that, within the same density range, magnesium carbonate-modified BMPC has the least impact on mechanical properties, while the thermal conductivity can be reduced by 46.6 % and the thermal diffusivity by 110.4 %. The results indicate that, within the same density range, magnesium carbonate-modified BMPC has the least impact on mechanical properties, the proportion of small and medium pores increases, and the fractal dimension is the lowest. BMPC offers advantages such as lightweight, thermal insulation, and low carbon emissions.

Magnesium phosphate cement (MPC) is an inorganic cementitious material formed by the reaction of magnesium raw materials with phosphates, characterized by high early strength and excellent durability. However, conventional MPC relies on dead-burned MgO, which is calcined above 1500 degrees C, resulting in high carbon emissions (exceeding 1500 kg/t). To reduce the carbon footprint of MPC, the dead-burned MgO was replaced by Mg(OH)2, the main component of natural brucite, to prepare low-carbon MPC and the reaction mechanisms of Mg(OH)2 ammonium dihydrogen phosphate (ADP) and potassium dihydrogen phosphate (KDP) solutions was investigated. The results indicated that low-carbon MPC exhibited faster setting and solidification than traditional MPC. The contact efficiency of Mg(OH)2 with ADP solution was significantly higher than with KDP solution, leading to primarily surface reaction in ADP solution. Compared to the KDP solution, ADP solution exhibited a lower kinetic parameter N and a higher K in the early stage of the reaction, resulting in the rapid formation of reaction products such as MgNH4PO4.6H2O and MgHPO4.3H2O that coated the Mg(OH)2 surface and hindered further reaction, leaving substantial residual Mg(OH)2 and ADP. In contrast, Mg(OH)2 in KDP solution underwent both surface and solution reactions, where lamellar products, Mg2KH(PO4)2.15H2O and MgHPO4.7H2O, gradually transformed into prismatic MgKPO4.6H2O as the reaction progressed, leading to near-complete consumption KDP and a higher reaction extent of Mg(OH)2 compared to ADP solution. This study provided new insights into the synthesis of low-carbon MPC and established a theoretical foundation for optimizing reaction conditions.

In this study, a viscosity-reducing polycarboxylic acid superplasticizer (VRPCE) was synthesized using methylallyl polyoxyethylene ether (HPEG), acrylic acid (AA), and maltodextrin maleic acid monoester (MDMA) as the main raw materials. The influences of the VRPCE on the microscopic properties of cement paste were studied by gel permeation chromatography (GPC), total organic carbon test (TOC), zeta potential, laser particle size analysis, XRD, MIP, TG, and SEM. Finally, the effects of the VRPCE on the macroscopic properties of cement mortar were evaluated through flow time, slump flow, compressive strength, shrinkage, and creep. The results showed that the VRPCE can improve the hydration degree of the cement, optimize the pore structure, increase the porosity, improve the fluidity, compressive strength, and creep, and decrease the shrinkage resistance of the cement mortar.

This study prepared a sulfoaluminate cement with high electromagnetic wave transmission performance by adding air entraining agent and glass powder and revealed the related mechanism. The test results showed the air-entraining agents and glass powder cannot affect the type of hydration products of the sulfoaluminate cement. The addition of the air-entraining agents and glass powder reduced the dielectric constant of the SAC while increasing the magnetic permeability. The air-entraining agents and glass powder increased the transmittance with a maximum value of 60.2%, illustrating the electromagnetic wave transmission performance of the sulfoaluminate cement could be improved. The electrical resistivity of the sulfoaluminate cement with the air-entraining agents and glass powder did not change significantly because the air-entraining agents increased the electrical resistivity and the effect of the glass powder was the opposite. The strengths of the sulfoaluminate cement with the air-entraining agents and glass powder decreased.

Magnesium Phosphate Cement (MPC) exhibits high strength, exceptional high-temperature resistance, and outstanding adhesion properties at the steel interface, rendering it an ideal material for fire resistive coatings on steel structures. In this study, natural brucite powder was employed as the magnesium source, while hollow glass microspheres (HGM) were utilized as functional modifiers to formulate brucite-based MPC fire resistive coatings for steel structures. This research explored the influence of the mass ratio of brucite powder to ammonium dihydrogen phosphate (M/P), the brucite particle size, and the addition of HGM on the physical, mechanical, and fire-retardant properties of the coatings. The microstructure of the brucite-based MPC before and after fire testing was examined using SEM, XRD, TG-DTG, and X-CT. The results indicated that with an M/P ratio of 2.5:1 and a brucite particle size of 75-150 mu m, the material exhibited optimal overall performance and was suitable as a matrix material for MPC. The incorporation of an appropriate amount of HGM increased the compressive strength of brucite-based MPC by 33.4 %, reduced the dry density by 20.5 %, extended the fire resistance of the structure, and decreased the thermal conductivity by 48.2 %. This can be attributed to: (i) HGM filling the pores in brucite-based MPC, creating a denser microstructure; (ii) HGM forming a closed porous structure with the MPC matrix, reducing thermal conductivity and increasing thermal resistance; (iii) The low thermal diffusivity of HGM/MPC impeded heat transfer, thereby decelerating thermal decomposition and flame propagation.

Traditional magnesium phosphate cement (MPC) has problems such as high carbon emissions and uncoordinated development of setting time and strength. For the purpose of reducing the carbon emission of MPC, improve its strength and promote the comprehensive utilization of brucite resources, magnesium phosphate cement (NBMPC) was prepared by using natural brucite (NB) as magnesia material, and modified by ultrafine metakaolin (UMK). The results showed that the initial setting time of NBMPC without UMK was 30 min, the compressive strength of 3 h and 28 d was 5.17 MPa and 46.57 MPa, respectively. When UMK content was 10 %, the maximum initial setting time of NBMPC was 51 min. When UMK content was 30 %, the highest compressive strength of NBMPC at 3 h and 28 d was 35.56 MPa and 70.74 MPa, respectively. The products of NBMPC were MgNH4PO4.6 H2O, hydrated MgHPO4 and a small amount of calcium phosphate compounds. The modification mechanism of UMK on NBMPC was chemical modification and physical filling. On the one hand, the chemical environment of Si and Al in UMK changed in NBMPC, resulting in the formation of aluminosilicate phosphate, MgNH4PO4.6 H2O containing Al and Si, and calcium phosphate compounds containing Al and Si. Amorphous AlPO4 was formed in NBMPC with higher UMK content. UMK promoted the early crystallization of MgNH4PO4.6 H2O, reduced the production of MgHPO4.7 H2O and inhibited its transformation. Moreover, UMK improved the pore size distribution of NBMPC and reduced its porosity. When preparing NBMPC, the content of UMK can be optimized according to the engineering type and construction environment.

The effects of graphene oxide (GO) with different contents on hydration process of tricalcium silicate (C3S) were investigated in this article. The scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, nitrogen desorption, nuclear magnetic resonance, Fourier transform infrared spectroscopy and Raman spectroscopy were used to analyze the micro-evolution of the GO/C3S hardened pastes, and the compressive strength of the GO/C3S was tested. The findings revealed that the addition of the GO increased the compressive strength of the GO/C3S because the GO can provide a large number of nucleation sites for hydration products, thereby accelerating the C3S hydration process. The GO also reduced the total pore volume of the C3S, leading to an increase in the proportion of gel pores and refinement in pore structure. Furthermore, the abundant oxygen-containing functional groups present on the GO surface can form hydrogen bonds with free water or interlayer water, thereby increasing the number of hydrogen bonds in the system.

Basalt fiber (BF) was mixed with sulphoaluminate cement (SAC) to test the mechanical properties and the electromagnetic properties. Additionally, the variation mechanism of macroscopic properties of the SAC-BF was analyzed by scanning electron microscope, X-ray diffraction and mercury intrusion porosimetry. It was found that the BF can promote the strength of the SAC. Moreover, the BF was capable to boost the electrical resistivity, the imaginary part of the dielectric constant and the electrical loss angle tangent of the SAC. The real part of the dielectric constant of the SAC was decreased. Furthermore, the BF could increase the fluctuation of magnetic conductivity and magnetic loss tangent, reduce the reflectivity and increase the transmittance and absorption of the SAC. Finally, the BF did not affect the hydration product type and can refine the internal pore structure of the SAC.

This article investigated the effect of the individual phases on the creep properties of cement paste. First of all, the contact creep modulus of the paste was obtained by the microindentation test, and the contact creep moduli of the individual phases in the paste were obtained by the nanoindentation test. Secondly, the volume fractions of individual phases were determined by micro test and statistical processing. Then, the contact creep modulus of the paste was calculated with the homogenization method of multiple scales and compared with the creep modulus of the paste measured by microindentation. Finally, the effect of pores, C-S-H, and unhydrated clinker (UC) on the creep modulus of the paste was quantitatively analyzed. The results showed that when the contact creep modulus of the pore was regarded as 0 GPa, the contact creep modulus of the paste was significantly underestimated. The effective contact creep modulus of the pore should be used for the homogenization calculation. The C-S-H gel with low density (LD) and C-S-H gel with high density (HD) had opposite effects on the modulus of creep of the paste so that those two gels needed to be treated separately during the homogenization process. The variation range of the contact creep modulus of UC was relatively large with slight effect on the homogenized contact creep modulus of the paste. Consequently, it can be treated as single-phase in the homogenization calculation.

The Euler method of computational fluid dynamics (CFD), the Bingham constitutive relationship and the measured concrete performance indexes were combined as the basis, the horizontal coil test and super high-rise building pumping test of concrete were simulated by software FLUENT. The data of maximum pump pressure, pressure loss of horizontal pipe, pressure loss per horizontal bend, pressure loss of vertical pipe and pressure loss per vertical bend from the test and numerical model were analyzed comparatively. The results showed that the simulation models can promisingly describe the flow behavior of concrete during pumping. In addition, it was found that the thickness of the lubricating layer forming during the concrete flow in the pump pipe was about 2 mm. Finally, the velocity vector analysis of concrete flow in the pump pipe was elucidated. The velocity gradient of the lubrication layer decreased with the increase of the distance from the pump pipe inlet. The velocity gradient of the concrete in the yield layer raised continuously. The flow velocity of concrete in the plug layer boosted with the thickness of the plug layer abated gradually. The concrete tended to be stable after flowing about 6 m in the horizontal pipe.

In this paper, the mesocalibration test was used to measure the contact parameters (restitution coefficient, rolling friction coefficient, static friction coefficient, and surface energy) between coarse aggregate particles and mortar particles in Discrete Element Method (DEM) model of concrete. Then, the DEM model of concrete slump was established according to the coarse aggregate gradation to study the flow behavior of coarse aggregate in fresh concrete. The slump test result was compared with the output of the slump DEM model with high consistent, indicating the promising reliability of the mesocalibration test. Finally, based on the mesocalibration test results, the DEM model of pumping concrete was established. It was obtained that the pumping pressure calculated by the numerical model was similar to that of the pumping test with satisfactory accuracy better than the concrete pumping pressure calculated according to the rheological test results of concrete and lubricating layer. On this basis, the movement trajectory of coarse aggregate in the pump pipe was analyzed and the influence of coarse aggregate on the pumping performance of concrete was revealed.

In this paper, the rheological mechanism of fresh concrete material was investigated and the method of evaluating its rheological property was optimized by combining the slump test of five groups of fresh concrete and lattice Boltzmann method (LBM). The rheological parameters of fresh concrete samples based on HerschelBulkley (H-B) model and Bingham model were obtained by rheometer and equation derivation with nonlinear and linear fitting approaches. The comparison of Bingham and H-B models in the simulation results of the slump test demonstrated that the H-B model was more accurate in expressing the rheological characteristics of the fresh concrete. In the Bingham model, the errors of slump s, spread sf and the time of spread reaching 500 mm T500 ranged from 2.00% to 39.29%. The errors of s and sf in the H-B model were less than 2%, and the error of T500 was about 5%. Afterwards, the results of the slump test were predicted based on the H-B model. The effects of rheological parameters (power-law index consistency index and yield stress) on velocity, viscosity, shear strain rate, flow rate and external contour were revealed.