The alkaline nature of cementitious materials has high potential of carbon sequestration. Research has shown that carbonation curing to cementitious materials at early age can improve their strength and densify their microstructure. Consequently, it is expected that carbonation curing can enhance the durability of concrete structure. However, carbonation can naturalize the alkaline environment of concrete, raising risks of steel corrosion. The debate between the carbonation-induced microstructure improvement and the neutralization-raised corrosion risks has not been resolved yet. Therefore, it provides great incentives to understand if carbonation of cementitious materials at early age accelerates corrosion of steel bar or not.

A hybrid calcium-sulphoaluminate and Portland cement (CSA-PC) mortar was prepared to coat steel bars of 0.7 mm. Three carbonation durations of 4, 24 h and 72 h were designed to treat the CSA-PC mortar. The alkalinity of the composite mortar after carbonation was characterized by phenolphthalein chromatography, and the water sorptivity of non-carbonated and carbonated mortar specimens was measured by using a contrast-enhancing X-ray computed tomography (XCT). The corrosion process of the steel bars was measured by open-circuit potential and corrosion current density up to 40 chlorine-salt drying-wetting (CSDW) cycles. The microstructure of the mortar and the corrosion rust distribution of the steel bars after the CSDW action were characterized by BSE-EDS and image analysis.

Early-age carbonation significantly reduced the alkalinity of the mortar matrix, which recovered after standard curing up to 28 d but remained below the alkalinity threshold for the formation of passivation of steel (pH=11.5). Carbonation densified the pore structure of the hybrid cement mortar and reduced the capillary water absorption. The water sorptivity of the carbonated mortar specimens was significantly lower than that of the uncarbonated specimens as observed by XCT, indicating an improvement in the impermeability of the mortar matrix. After 10 CSDW cycles, the open circuit potential of the carbonated specimens decreased significantly and the corrosion current density increased by nearly one order of magnitude. The early-age carbonation significantly increased the probability and rate of corrosion of the steel bars in the mortar under cyclic CSDW actions. BSE-EDS analysis further showed that after carbonation, the rebars were severely corroded with corrosion pits up to 200 µm in depth and 20% in area; corrosion products migrated and filled the mortar matrix around the rebars, generating cracks.

The alkalinity of the mortar matrix decreased after early age carbonation, following recovery to a certain value after standard curing, which remained below the alkalinity threshold for steel passivation. Carbonation was able to improve the compactness of the mortar matrix and enhance the material's impermeability. The open circuit potential of the carbonated material was lower and the corrosion current density was one order of magnitude higher after 10 CSDW cycles. Serious corrosion of the rebar occurred in the mortar after carbonation, the corrosion products migrated to the surrounding mortar matrix, and the volumetric expansion led to cracking of the matrix. The findings suggest that although early age carbonation may help to improve the performance of cementitious material matrix, it may be detrimental to the durability of reinforced concrete.

In recent years, China's tunnel engineering has developed rapidly, and concrete lining support technology has been widely used in tunnels, underground engineering projects and deep foundation pits. However, with increasing buried depth and ground stress, ordinary concrete lining support technology often has certain limitations. It is easy to crack during service and shows obvious brittleness when destroyed, which poses a threat to the safety of tunnel engineering. Therefore, in order to prevent cracking, steel fibers with random distribution are usually mixed into concrete to achieve, and in the engineering practice of tunnel lining detection, engineers urgently seek to use high-precision non-destructive testing methods to detect the health status of concrete lining. Therefore, two non-destructive testing methods, Digital image correlation technology (DIC) and Ultrasonic technology (UT), are used to characterize the cracking damage process of concrete, and the strong correlation and complementarity of DIC and UT are verified based on the law of energy evolution.

The specimens were designed with steel fiber and silica fume content as the control variables, and a total of 9 groups of orthogonal mix specimens were designed for splitting mechanical tests, with a water-glue ratio of 0.43, a mass steel fiber content of 40, 45 kg/m³, and 50 kg/m³, and the mineral admixture silica fume replaced cement with the same amount according to different volume parameters (3%, 6%, 9%), and the dimensions of the 10 groups of specimens in this experiment were: 100 mm × 100 mm ×100 mm.

In accordance with CECS13-2009 Fiber Concrete Test Method Standard, the electro-hydraulic servo pressure testing machine (WAW-1000) is used in the splitting test, the maximum test load is 1000 kN for the control parameters, the stress control loading speed is 0.04 MPa/s, and the failure standard is set to 30% of the peak load. Place the steel gasket up and down at the centerline position of the specimen, and the size of the gasket is 200 mm × 5 mm × 5 mm.

In this paper, by using DIC and UT, based on the energy evolution law, the crack propagation process of SFRC lining under different mix ratios is verified, and the strong correlation and complementarity between DIC and UT test results are verified. The influence of steel fiber and silica fume on fracture mechanical properties is revealed. The main conclusions are as follows:

The peak stress at 40, 45 kg/m³ and 50 kg/m³ was increased by 52.73%, 81.82% and 73.03% respectively compared with DZ, respectively, that is, the cleavage strength increased significantly when the steel fiber content was 45 kg/m³, and StF45-SF6% showed good safety reserve and ductility, and the increase of silica fume volume content at 50 kg/m³ led to a significant increase in the slope behind the peak of the stress-strain curve, which was negatively correlated with the cleavage strength.

According to the cloud map analysis of DIC, it is found that the cracking resistance of steel fiber on the main crack begins to increase after the stress reaches the 90%P_Max, and the crack mainly extends longitudinally. When the stress drops below 70%P_Max, the main fracture begins to expand laterally, and the inhibition effect of steel fiber across the fracture path gradually decreases to form macroscopic cracks. Under the same steel fiber content, the silica fume volume content was inversely proportional to the CTOD_c, that is, silica fume could provide additional viscosity and had a good hindrance effect on the expansion of CTOD.

According to the acoustic characteristics such as waveform, first wave amplitude and wave velocity, it can be divided into: no damage period, microcrack propagation period, macroscopic crack propagation period, and damage stability period. Based on the principle of energy evolution, it is verified that DIC and UT have strong correlation and complementarity, and the energy storage level of SFRC K_d increased by 12.5%~52.5% compared with DZ, and steel fiber significantly reduced the release rate of elastic strain energy.

The main summary of this paper is as follows: SFRC has a strong post-cracking bearing capacity, with steel fiber content of 45 kg/m³ and silica fume content of 6%, the highest energy storage level and the splitting strength can be increased by 81.82%; Based on the cloud map analysis of DIC, the bridging effect of silica fume is mainly manifested before the 90% peak stress. After 90% peak stress, the crack resistance of steel fibers is gradually enhanced, and the cracks are mainly propagated by longitudinal microcracks. After the stress drops to 70% of the peak stress, the steel fiber crack resistance is gradually weakened, and the fracture begins to expand horizontally rapidly. In addition, the ultrasonic velocity of SFRC showed a trapezoidal hierarchical attenuation trend during splitting damage. Analysis based on the energy evolution law, UT and DIC have strong correlation and complementarity in characterizing the crack propagation process.

Research and development of alternative technologies to conventional reinforcement and exploration of printable building materials with excellent properties ECC prepared from polymer fibers has high ductility, excellent toughness, and superior strain-hardening energy dissipation properties. The effects of polyethylene (PE) fiber dosage (1.0%, 1.5%, and 2.0%, in volume) and length (6, 9 mm, and 12 mm) on the pre-strain-hardening early properties, post-strain-hardening mechanical properties, and microstructure of 3D-printed HS-ECC were investigated. This study provides new ideas for the design and performance optimization of 3D-printed HS-ECC, which further promotes the application of 3D-printed technology in construction.

In this study, we experimentally investigated the effect patterns of polyethylene (PE) fiber doping (1.0%, 1.5%, 2.0%) and length (6, 9, 12 mm) on the pre-hardening early properties, post-hardening mechanical properties, and microstructure of 3D-printed HS-ECC. The rheological properties and early mechanical properties were correlated by actual printing tests. The influence mechanism of mechanical virtual was explored by utilizing microscopic testing means SEM, NMR methods combined with experimental results.

The static and dynamic yield stresses of HS-ECC increased with increasing fiber doping and length, and the effect of fiber doping was more pronounced. With the increase in vertical strain, the stress of the specimens increased approximately linearly before yielding, and the increase in stress slowed down after yielding. Specifically, increasing fiber doping and fiber length increased the early strength of 33D-printed HS-ECC, and the bridging effect of fibers increased with increasing doping and length. The pattern of printable properties was consistent with the rheological properties and early mechanical strength by actual printing tests.

The post-hardening mechanical properties of the 3D-printed HS-ECC with 2.0% 12 mm PE fibers yielded a tensile strain capacity of more than 4%, an average crack width of 89.72 μm, and a compressive strength of more than 80 MPa. The degree of destruction of the PE fibers after detachment from the substrate increased with fiber doping and length. The 6 mm PE fibers were easier to pull out than 12 mm, and thus the ductility of the material increased with the increase in fiber doping and length. to pull out and thus the ductility of the material decreases. In addition, nozzle extrusion-based 3D-printed HS-ECC allows for effective directional fiber orientation, resulting in increased ductility of the 3D-printed HS-ECC.

The pore size distributions peaked in the range of 0.001 µm to 0.010 µm. Cast samples contained and the proportion of small pores in the casting samples is less than 90%, while the 3D-printed samples are 60% to 70%, which indicates that the 3D printed samples contain a higher number of large pores. The primary and secondary peaks of samples V1, V2, L1, and L2 are lower compared to those of samples V3 and L3, and the trend suggests that the increase of fibers raises the number of pores, which results in the decrease of compressive strength. Although the variation of the primary peaks of the 3D printed samples is consistent with the pouring trend, the pattern of the secondary peaks is complex, which may be related to the time between the printed layers and the pressure on the upper layer of the material, resulting in an irregular distribution of pores. The total porosity increases by about 21.75% and 11.75% with increasing fiber doping and fiber length, while the mechanical properties of 3D-printed HS-ECC specimens decrease at the same time. The comparative results show that the porosity of cast HS-ECC is 1.24 to 1.67 times higher than that of 3D-printed HS-ECC, but the harmful porosity of 3D-printed HS-ECC accounts for about 30%, which may lead to the decrease in the mechanical properties of large-scale components.

With the increase of fiber doping and fiber length, its dynamic and static yield stress increases. In addition, the early mechanical strength of 3D-printed HS-ECC increases. Through the actual printing test, the pattern of its printable properties is consistent with the rheological properties and early mechanical strength. The post-hardening mechanical property test results yielded that the 3D-printed HS-ECC containing 2.0% 12 mm PE fibers possessed a tensile strain capacity of more than 4%, an average crack width of 89.72 μm, and a compressive strength of more than 80 MPa. The degree of damage of PE fibers after separation from the matrix increased with fiber doping and length. 6 mm PE fibers were easier to pull out compared to 12 mm, resulting in a decrease in the ductility of the material. In addition, nozzle extrusion-based 3D-printed HS-ECC allows for effective directional fiber orientation, resulting in an increase in the ductility of 3D-printed HS-ECC. The increase in fiber doping and length increased the total porosity by 21.75% and 11.75%, respectively, which led to a decrease in the mechanical properties of 3D-printed HS-ECC specimens. 3D-printed HS-ECC showed a decrease in the intra-strip porosity compared to casting, and an increase in the interlayer and inter-strip porosity resulted in a decrease in strength.

The brick-carved cultural relics is a precious cultural resource. The uniqueness of brick carving causes a high requirement for the technique and materials of in-situ repair. The difficulty is to preserve the original features of brick carving while restoring its microstructure. The inorganic reinforcing agents are beneficial for maintaining the physical properties of the historical material and have been considered the optimal choice for restoring the cohesive strength of the historical material in recent years. The restoration material prepared by basic magnesium sulfate cement (BMSC) has the advantages of high tensile strength, high resistance to weather, high viscosity, early strength, and low cost. It has a good effect in reinforcing the weathered sandstone of the cultural relics. The hydraulic lime is widely used due to its waterproof and breathable properties. But it is very expensive. The Silicon-based repair material has good permeability. But it has poor stability in the environment with the changing humidity. Three types of strengthening agents are selected as the alternative options for the restoration of brick carving based on the need for the brick repair and in-situ protection of the ancient mortar during the process of the restoration of brick carving.

Three strengthening agents are Ca-based hydraulic lime, Si-based silica sol, and Mg-based BMSC. Three steps are implemented in order to select the most effective strengthening agent in the restoration of the cultural relics of brick carving. That is the preparation and research of performances of three kinds of imitation bricks, infiltration reinforcement of the ancient material, and the verification of practical engineering. The powder of green bricks is used as the main material for replica bricks. The hydraulic lime, silica sol, and BMSC-based reinforcing agent are firstly mixed with the powder of green brick to form replica bricks, which are the Ca-bricks, Si-bricks and Mg-bricks. The multiple experiments were conducted to investigate the compatibility of replica bricks. The studied properties include the composition of crystal phase, compressive strength, porosity characteristics, and the hydraulic performance of the replica bricks, and so on. WW/T 0065—2015 "Code for Investigation of Stone Cultural Relics Protection Engineering" is referenced. Secondly, the adhesive properties and infiltration reinforcement of the strengthening agents were taken into consideration to evaluate the feasibility of application of these material to the restoration of the brick-carving cultural relics. Finally, the verification of the referred BMSC-based strengthening agent used in actual engineering was conducted because the laboratory environment is different from the complex environment where the cultural relics are located.

Ca-based and Si-based reinforcing agents only serve to adhere the powder of green brick. The BMSC-based reinforcement agent continues to hydrate after being added to the powder of green brick to form the replica bricks. The main hydration product is the 5·1·7 strength phase. So the BMSC-based reinforcing agent has the strongest adhesion among three types of reinforcing agents. The Mg-brick has the best performance among three kinds of replica bricks, which is similar to the green brick. But Mg-brick has the slight hydrophobicity. The properties of Ca-bricks and Si-bricks are close to the ancient bricks. The bending strength of the masonry of bonded Mg-bricks is 10 times that of the Si-bricks. Only the BMSC-based strengthening agent has no carbonization and has good aging resistance. The infiltration solution with a content of 30% BMSC-based reinforcement agent and a moisture content of 44%-50% has the best effect of reinforcement, maintaining the original physical properties of brick-carved cultural relics while restoring the original cohesion. The referred BMSC - based reinforcing agent can penetrate and bond the slag of brick carving of 9.5 times the mass of agent.

The BMSC-based reinforcing agent demonstrates higher penetration enhancement ability than reinforcing agents based on hydraulic lime or silica sol. The volume stability of the referred BMSC-based strengthening agent meets the requirements. It also can be found that the repair effect of the referred BMSC-based strengthening agent is good after two years. In summary, the optimal ratio of BMSC - based reinforcing agent shows good repair effect at low cost. The Mg-brick and BMSC - based reinforcing agent can be used for the restoration of brick carving.

In-situ polymerized cementitious materials (iPMCM) exhibit exceptional fluidity, interfacial adhesion, and toughness, making them promising candidates for rapid repair engineering and 3D printing applications. However, the delayed cement hydration caused by polymer significantly impedes early strength development, limiting their practical applications. Nano-silica (NS) has been proven to considerably enhance the early-age mechanical properties of cementitious materials due to its filler effect, nucleation effect, and pozzolanic effect, offering a solution for improving the strength development of iPMCM at the early age. However, the synergistic effects of NS and in-situ polymerization on the mechanical development remain unclear. This study systematically investigates the interaction of NS and in-situ polymerization on the hydration kinetics, microstructure, and mechanical properties of iPMCM. And the enhancement mechanism of NS on both the cement microstructure and the polymer network was in-depth discussed. The findings from this study provide an effective strategy for improving the early-age mechanical properties of iPMCM, broadening their real-world applications.

Orthogonal experiments L₂₅ (5⁶) were designed to optimize acrylamide (AM) monomer (1%-5% of cement mass), potassium persulfate (KPS) initiator (1%-5% of monomer mass), and NS (0-0.4% of cement mass) dosages based on 6 h compressive strength. P.I 42.5 cement, AM, KPS, and 15 nm NS were used with a fixed water-to-cement ratio of 0.4. NS was pre-dried at 60 ℃ for 24 h before dispersing in water with AM and KPS, and then the resulting solution was mixed with cement to prepare pastes. Samples were cast into 40 mm × 40 mm × 40 mm molds. After demolding curing for 1 d, the samples were cured at 20 ℃ and 95% RH for specific curing ages prior to mechanical property measurement. The hydration kinetic of cement pastes was monitored by a TAM Air calorimeter. The hydration products of hardened cement pastes were characterized by XRD and TGA. SEM and MIP were employed to observe the microstructure and to analyze the pore structure of iPMCM at different ages, respectively

The orthogonal experiment identified 4% AM, 0.3% NS, and 4% KPS as the optimal formulation, achieving a 284% increase in 6 h compressive strength (from 1.38 MPa to 5.3 MPa) and 381% increase in 6 h flexural strength (form 0.36 MPa to 1.73 MPa) compared to the control group. In addition, the optimal group exhibited varying degrees of improvement in compressive and flexural strengths than the control and in-situ polymerization groups after curing for 7 d and 28 d. The evolution of heat flow analyses during the cement hydration indicates that NS reduced the nucleation barrier for C-S-H formation and thus advancing silicate hydration. It resulted in an increase of CH content by 17.8%. Concurrently, NS promoted the earlier AM polymerization releasing a more significant heat, which contributed to accelerating cement hydration, and thereby improving the early-age compressive strength. MIP results suggest that the incorporation of NS into iPMCM reduced harmful pore (>50 nm) volume by 71.1% and increased less-harmful pore (20-50 nm) content, compared to the control group, significantly refining the pore structure of the hardened cement pastes. SEM observations demonstrate a denser organic-inorganic network in NS modified PAM hydrogel where NS is likely to act as a physical crosslinker via hydrogen bonding with polyacrylamide strengthening the polymer network.

This study demonstrates that modification using nano-silica effectively enhances the early strength of iPMCM with the optimal formulation of 4% AM, 0.3% NS, 4% KPS, which achieved a 284% improvement in 6 h compressive strength while maintaining superior 28 d flexural strength. The comprehensive experiment analyses conclude that the roles of NS in the early-age mechanical development of iPMCM includes: (i) Improving cement hydration and microstructure. Owing to its nucleation effect, NS accelerates the silicate hydration compensating for the delaying effect of in-situ polymerization on cement hydration. And the presence of NS refines the pore structure of iPMCM by reducing the amount of harmful pores, thus further improving the early strength of iPMCM. (ii) Strengthening the polymerization network. NS advances the occurrence of polymerization with a significant heat released. In iPMCM, NS may interact with polyacrylamide via hydrogen bonding, as a physical crosslinker strengthening the polymer network. These further contribute to the early-age strength development of iPMCM. The findings from this study provide a scientific foundation for the applications of iPMCM in rapid repair engineering, 3D printing structures, etc. The long-term durability and scalability for industrial applications will be further explored in future studies.

Lightweight Ultra High Performance Concrete (LUHPC) exhibits attributes such as reduced weight, high strength, and minimal shrinkage. As a substrate for paving layers, the surface roughness of LUHPC is a critical determinant of interlayer shear resistance, tensile pullout resistance, and the prevention of early slippage and delamination. Notably, the lower surface hardness of gangue porous aggregates contributes significantly to the textural enhancement of LUHPC surfaces. The incorporation of steel fibers not only strengthens the internal bonding within the concrete but also influences the surface texture of LUHPC after roughening treatments. Despite existing research on the textural properties of pavement surfaces, there remains a gap in understanding the preparation of roughened interfaces for efficient application and the quantitative characterization of macro-micro texture characteristics and roughness influenced by steel fibers, which correlates with interlayer shear performance. While existing research has investigated the texture characteristics of pavement surfaces, there remains a critical need for further exploration into the development of roughened interfaces that facilitate effective implementation, a more detailed quantitative characterization of macro-micro texture and roughness, particularly under the influence of steel fibers, is necessary. Such investigations are crucial for establishing a robust correlation with the interlayer shear performance of heterogeneous paving materials. Additionally, Lightweight UHPC-high viscosity high elasticity binder-SMA specimens were fabricated to assess shear strength across different shot blasting intensities and temperatures. Linear regression analyses were conducted to model the relationships between macro-micro texture parameters and shear strength.

The surface roughness of gangue aggregate LUHPC was achieved through a shot blasting process, with three-dimensional texture data acquired via a handheld laser scanner. The point cloud data was processed using Gaussian filtering in MATLAB software to reconstruct the specimen's surface topography. Subsequently, both macroscopic and microscopic texture profiles of LUHPC were extracted utilizing a band-pass filter. The influence of steel fibers on the surface roughness of the specimen was assessed. An enhanced evaluation index, the Extended Tectonic Depth (ETD), was proposed, drawing upon the sand laying method's measurement principles. The correlations between macro-texture parameters (R_a, R_q, EMTD, EMPD) and micro-texture parameters (C_MT, RMS) with ETD were analyzed. Furthermore, the relationship between shear strengths of the LUHPC-stress absorbing layer-SMA composite specimen and both macro- and micro-texture parameters was examined.

As the degree of shot blasting increased, the surface of LUHPC became rougher, the ETD grew larger, and the shear performance of LUHPC-high viscosity high elasticity binder-SMA improved at different temperatures. Under the influence of steel fiber, increasing the degree of shot blasting effectively enhanced the overall shear strength. With more shot blasting, the coverage of steel shot on the specimen's surface gradually increased, the depth of sanding continued to grow, the height of the steel fiber protrusions increased, and the peak of the specimen profile became larger, while the surface depth of the non-steel fiber portion tended to be homogeneous. The correlation of the ETD with R_a, R_q, EMPD, and RMS was better, and the correlation with EMTD and C_MT was average. The damage in LUHPC-SMA composite specimens primarily occurred in different surface layers of the bond layer, with no damage to the mixture. he correlation of the shear strength at 25 ℃ with R_q and RMS was good, with an R² greater than 0.85. The multivariate analysis of shear strength and macro-micro texture parameters showed that for bivariate macro texture parameters ETD, EMPD, EMTD, R_a, R_q, the R² was greater than 0.85 at 25 ℃, and ranged from 0.6 to 0.85 at -10 ℃. When the bivariate consisted of micro texture parameters RMS and C_MT, the correlation for both 25 ℃ and -10 ℃ was better, with an R² greater than 0.85. The correlation between shear strength and macro-micro texture parameters improved as the number of variables increased.

In view of the influence of steel fibres on the surface texture of the specimens after shot blasting, EMTD and EMPD were used to replace MTD and MPD to characterize the macroscopic texture properties of the materials more effectively; Based on the measurement principle of the sand laying method, the extended tectonic depth (ETD) was proposed as a new evaluation index. Multivariate linear regression analyses of ETD with macro texture parameters (R_a, R_q, EMTD, EMPD) and micro texture parameters (C_MT, RMS) were carried out, and the results showed that the correlation between ETD and macro-micro texture parameters was strong. According to the comprehensive consideration of each index parameter under different degrees of shot blasting, it was stipulated that the ETD of the extended construction depth of the lightweight UHPC surface in the interval of 0.60-0.70 mm was considered as a light shot blasting effect, the interval of 0.70-0.85 mm was considered as a moderate shot blasting effect, and the interval of 0.85-1.15 mm was considered as a heavy shot blasting effect. The correlation analysis of the shear strength of the composite specimens at -10℃ and 25 ℃ with the macroscopic texture parameters (ETD, EMPD, EMTD, R_a, R_q) and the microscopic texture parameters (C_MT and RMS) showed that: The larger the depth of the extended structure, the better the shear performance at the same temperature; The correlation with the shear strength was gradually strengthened with the increase of the number of variables; and the correlation of the all-variable indexes and shear strength was the best at 0.999. The correlation between all variables and shear strength reached 0.999. Comparing the experimental results under different levels of shot blasting, it was concluded that the extended structural depth of lightweight UHPC surfaces had a positive correlation with the shear strength, and therefore the extended structural depth of ETD was recommended to be 0.85-1.15 mm in this paper.

Solid oxide fuel cells (SOFC) is a device that converts chemical energy into electrical energy. Compared with traditional power generation equipment, SOFC has the advantages of flexible fuel use, no noise, low emission and high conversion efficiency. SOFC operates at high temperatures (600-1000 ℃) for a long time, due to the mismatch of Coefficient of Thermal Expansion between anode-electrolyte-cathode electrode, metal connector and sealing material and the combined effect of temperature gradient. Even if the stress caused by mismatching is not enough to cause structural failure in a short time, the battery running under such stress for a long time at high temperature will cause large creep damage to each component, and the initiation of cracks will cause SOFC leakage.

The porosity of porous electrode is closely related to its thermal expansion coefficient, elastic modulus, Poisson ratio, material diffusion, electrochemical reaction, effective conductivity, and other parameters, which is the main factor determining the performance of key SOFC components. When hydrogen is first supplied to the battery, the anode material will change, as well as the porosity of the anode layer, leading to variation on its physical and mechanical properties, which can affect its structural integrity and reliability under long-term high-temperature service conditions. Therefore, it is of great significance to study the effect of porous electrode porosity on the creep damage of SOFC at high temperature.

Based on the previous modeling and research of SOFC multi-physical field, the SOFC model of gradient pore anode under multi-field coupling is established. Then, according to the Wen-Tu creep damage model, the effect of anode porosity on SOFC creep damage was analyzed.

Considering that COMSOL Multiphysics has good multi-physics coupling ability and ABAQUS has strong nonlinear analysis and module development ability, the research method of COMSOL-ABAQUS is adopted. Firstly, the non-uniform temperature field calculated by COMSOL was applied to the node of the ABAQUS finite element model as a thermal load. Based on the creep model of ductile exhaustion theory and the damage mechanics model of continuum, the ABAQUS creep damage subroutine was written, and the USDFLD subroutine was embedded to simulate the creep damage and crack propagation law of single-channel SOFC. When ω=0.99 is defined, the crack initiation unit of the sample is regarded as the failure unit. According to the method proposed by Saanouni et al., the elastic modulus of the Gaussian point of the failure element is reduced to 1/10⁶ of the initial elastic modulus, so that the subsequent stress of the point is approximately zero, indicating that the bearing capacity is lost here. By combining the high efficiency of COMSOL and the strong nonlinear convergence of ABAQUS, SOFC finite element model is established to analyze the creep damage and crack propagation law of a single planar SOFC element.

Compared with the assumed uniform temperature field, the maximum equivalent stress of the upper connector, anode support, anode functional layer 2, anode functional layer 1, electrolyte, cathode and lower connector is 95%, 88%, 95%, 91%, 48%, 65% and 96% higher than that of the uniform temperature field, respectively. Therefore, the assumption of uniform temperature field is not accurate enough, and the real temperature distribution obtained under the coupling of multiple physical fields is needed to analyze the creep damage evolution of SOFC.

The critical damage lifetime of SOFC connectors with gradient pore anodes is 31.4%, 26.4% and 17.9% longer than that of SOFC connectors with anode uniform porosity of 0.2, 0.3 and 0.4, respectively.

Gradient pore anode design the upper connector of flat SOFC reaches the critical loss value at 64 kh, and the crack initiation, belonging to the surface crack, is located on the outer side of the 40 mm rib at the fuel outlet of the upper connector, and gradually expands to both sides. However, with the increase of time, the crack propagation rate gradually decreases, and the crack propagation almost stops at 80 kh. At this time, the crack length reaches a maximum of 32 mm, although it is a non-penetrating crack witch will not cause leakage, it is still a problem that cannot be ignored.

The main conclusions of this paper are summarized as follows: Compared with the assumed uniform temperature field, the maximum equivalent stress of each part of the flat plate SOFC under the coupling of multiple physical fields is higher than the predicted result under the uniform temperature field. The assumption that the uniform temperature field is not accurate enough requires the real temperature distribution obtained under the coupling of multiple physical fields to analyze the creep damage evolution of SOFC. At the same time, the critical damage life of SOFC connectors with gradient pore anodes is significantly longer than that of SOFC connectors with uniform anodes with different porosity. When the upper connector reaches the critical loss value, surface cracks are generated on the outer side of the fuel outlet rib of the upper connector and spread to both sides gradually, but with the increase of time, the crack propagation rate decreases gradually. Although it is a non-penetrating crack witch will not cause leakage, it is still a problem that cannot be ignored. This study shows that the gradient pore anode has potential advantages in long-term high temperature service and provides theoretical basis and data support for the structural integrity and reliability optimization design of SOFC structures.

In marine environments, the conventional steel reinforcement is prone to corrosion, leading to severe damage to concrete. Additionally, the deficiencies of ordinary concrete in terms of resistance to marine corrosion and impermeability significantly shorten the service life of marine concrete structures, which has attracted widespread attention. To enhance the durability of marine concrete, researchers are actively exploring new solutions. Among these, the use of FRP (Fiber Reinforced Polymer) reinforcement to replace traditional steel bars effectively addresses the issue of steel corrosion. Calcium sulfoaluminate (CSA) cement concrete, with its characteristics of early strength, high strength, corrosion resistance, and excellent impermeability, is particularly suitable for marine concrete structures that require high early-strength and durability. Based on this, the present study investigates the specific impact of different bond lengths of GFRP (Glass Fiber Reinforced Polymer) and BFRP (Basalt Fiber Reinforced Polymer) reinforcement on the bonding performance of the FRP-CSA full-coral aggregate concrete system.

This study investigated the influence of different bond lengths of FRP bars in full coral aggregate seawater sea-sand sulphoaluminate cement concrete (FCASS-CSAC) on the bond properties. This study used two different types of bars (GFRP and BFRP) and three different bond lengths (5 d, 7.5 d, 10 d, where d represents the diameter of the bars) to cross combine into 6 different types of specimens. All specimens were demolded after 24 h treatment and cured for 28 d in a standard curing chamber (temperature of (20±2) ℃, relative humidity of 95%). Subsequently, compressive strength tests and central pull-out tests were conducted to investigate the bond performance between FCASS-CSAC and FRP bars.

When the bond length of BFRP and GFRP reinforcement bars is 5 d, the bond stress is generally higher than when the bond length is 7.5 d or 10 d. Specifically, for BFRP bars, the bond strength at a bond length of 5 d is approximately 30% and 60% higher than that at bond lengths of 7.5 d and 10 d, respectively. The bonding performance of BFRP and GFRP reinforcement bars was compared, and the results show that, in the absence of ribbed features, BFRP reinforcement typically exhibits superior bonding performance, with the bond strength generally about 40% higher than that of GFRP bars. This suggests that BFRP reinforcement has a potential advantage in providing stronger bond strength, which may be related to its material properties and the way it interacts with the matrix.

The main conclusions of this study are summarized as follows. The bonding performance of BFRP reinforcement with FCASS-CSAC is generally superior to that of GFRP reinforcement, with an overall bond strength about 40% higher. The bond strength of both types of reinforcement decreases as the bond length increases, with BFRP reinforcement showing a significantly higher bond strength at a bond length of 5 d compared to 7.5 d and 10 d. Based on the experimental results, an empirical formula for predicting bond strength was proposed. Furthermore, finite element simulation analysis was conducted, and the analysis results showed good agreement with the experimental findings.

Fluorinated silane coupling agent was generated by reacting 2-(perfluorohexyl) ethyl methacrylate with trimethoxysilane, and then mechanically mixed with organic polysilazane (OPSZ) to obtain fluorinated modified OPSZ coating material. Finally, it was doped with micro nano SiO₂ particles and a durable superhydrophobic coating was prepared using a spray coating method that is widely applicable to various substrates. The prepared superhydrophobic coating still has a water contact angle of over 150° after undergoing 360 cm (load of 50 g) sandpaper friction or 12 tape peeling tests (adhesion of 1.75 N/cm), and water droplets can roll freely like lotus leaf surfaces. This work provides a simple method for preparing hydrophobic/superhydrophobic coatings with excellent durability, and has potential applications in anti fouling, anti-corrosion, and other aspects.

According to the National Standard of China GB/T 9286—1998 "Cross cut test for film of paint and varnish", the adhesion of the coating to the substrate was determined by cross-cutting the film. According to the National Standard of China GB/T 6739—2006 "Determination of film hardness by pencil method for paint and varnish", the pencil hardness of the prepared coating was determined using a QHQ-A pencil hardness meter. According to the National Standard of China GB/T 23989—2009 "Determination of solvent resistance wiping resistance of coatings", the resistance to MEK wiping off the prepared coating was determined. Tape peeling and sandpaper abrasion were used to test the mechanical stability of the coating. The 3M tape (adhesive, 1.75 N/m) was pressed onto the coated surface for 30 s with a 100 g loading before being entirely peeled off. In this experiment, we designated the press-peeling procedure as one testing cycle. Every two press-peeling cycles, the WCAs and SAs of the coating were monitored to evaluate the coating/substrate interfacial adhesive strength between the coating and the substrate. A 25 mm × 25 mm coating loaded with 50 g weights was placed face-to-face with sandpaper (1500 grit) and pulled horizontally at a uniform speed for the sandpaper abrasion test. The WCAs and SAs of the coatings were measured to demonstrate mechanical stability after each 40 cm abrasion distance.

Aqueous solutions of pH = 1, 4, 7, 10, 13 were configured using H₂SO₄ and NaOH, in which the coatings were placed for 24 h and 3.5% NaCl solution for 72 h to measure the WCA and SA values and to assess their resistance to acid and alkali corrosion and salt. The samples were exposed to UV light for 48 hours to assess weathering resistance.

The self-cleaning properties of the coatings were tested by contaminant removal experiments on the coated surfaces using carbon black nanoparticles as contaminants. In addition, it was evaluated how well the coatings cleaned themselves after exposure to red wine, cola, fruit juice, tea, milk, and coffee.

A durable high-hydrophobic coating based on Fluorinated silane coupling agent-modified OPSZ was designed and realized through a one-step synthesis method and spraying process, with a water contact angle of up to 115° and the coating hardness of up to 4H and excellent adhesion By adding micro-nano SiO₂ particles, a superhydrophobic coating with a water contact angle of 156.3° and a rolling angle of 5.6° was successfully prepared. The superhydrophobic coating still had excellent hydrophobic properties after undergoing 12 cycles of tape stripping or 360 cm sandpaper rubbing test. This was due to the excellent anchoring characteristics of polysilazane and the excellent low surface energy of modified OPSZ, which resulted in good coating durability. After being doped with micro-nano SiO₂ particles, a durable superhydrophobic coating was prepared using a spraying method commonly applicable to various substrates

This coating has the advantages of low process cost and convenient operation and can be used to develop large-scale, durable superhydrophobic coatings with broad application prospects and practical value. In conclusion, this study provides a new solution for developing new superhydrophobic coatings.