Textile-reinforced concrete (TRC) is highly anticipated as an alternative to reinforced concrete due to its ability to enable lightweight design, free formability, and improved ductility. In this study, TRC panel test specimens were fabricated and four-point loading flexural tests were performed to examine the flexural characteristics of TRC panels reinforced with carbon fabric, and to investigate the effect of the fabric reinforcement ratio, anchorage length, and surface treatment of fabric. Furthermore, the flexural behavior of the test specimens was numerically analyzed using the general section analysis concept of reinforced concrete and compared with the experimental results. Due to bond failure between the carbon fabric and the concrete matrix, the TRC panel showed a large decrease in flexural performance in terms of flexural stiffness, flexural strength, cracking behavior, and deflection. This low performance was improved by increasing the fabric reinforcement ratio, anchoring length, and sand–epoxy surface treatment of the anchorage. Comparing the numerical calculation results with the experimental results, the deflection of the experimental results was approximately 50% larger than the numerical calculation results. This is because the perfect bond between the carbon fabric and the concrete matrix failed, and slip occurred. Reinforced concrete is a globally used construction material that consists of homogeneous reinforcing bars and heterogeneous concrete. It is a composite material that offers various advantages in terms of material and structure by complementing different mechanical properties through the interaction of compression and tension. Based on these advantages, reinforced concrete plays a significant role in building modern society. With the recent developments of technology, there is a trend towards constructing larger and ultra-high reinforced concrete structures. However, this trend also leads to an increase in load due to the weight of the structure and external force, which can cause cracks on the surface of the reinforced concrete, leading to corrosion of the reinforcement and concrete. Corrosion of reinforcing bars and concrete can result in a deterioration of durability and stability, leading to significant repair and reinforcement costs. Therefore, there is a need for a replacement material for reinforced concrete to prevent a reduction in the durability and stability of structures, and to promote sustainable development in the construction industry; further, the interest in alternative materials is also increasing ,2.Textile-reinforced concrete is being explored as an alternative material for reinforced concrete. It is a composite material composed of a high-performance cement-based matrix, usually with a small aggregate maximum size, and a bundle of high-toughness continuous multifilaments composed of glass, carbon, polymer, or other materials . TextileTextile-reinforced concrete has numerous advantages and efficient application targets, but clear design criteria and guidelines have not yet been established, resulting in experiments being conducted based on the experience of researchers. As it is a composite material composed of two different materials, there are difficulties in understanding the material properties compared to conventional construction materials. Furthermore, because the adhesion behavior between the two materials, textile and concrete, has not been clearly identified, there are many limitations in analyzing the composite behavior and applying it to actual structures ,9.According to the literature, the main failure of TRC is caused by the slippage of the textile and the separation of the matrix and the textile, and this failure mode is related to the incomplete bonding of the textile and the matrix ,11,12. AIn this study, to examine the difference in flexural behavior according to the textile reinforcement ratio, anchorage length, and surface treatment of concrete composite panels reinforced with carbon fabric, textile-reinforced concrete was fabricated and a flexural test performed. Differences in ultimate load, center deflection, and crack distribution ac-cording to each variable were compared and evaluated. In addition, the bending behavior was numerically calculated according to the nominal flexural strength calculation method of general reinforced concrete members and the deflection calculation method using the effective second moment of inertia, and the results were compared with the experimental results.The experiments were divided into two parts: Group I and Group II. A total of 15 variables were set, with 5 variables in the Group I experiment and 10 variables in the Group II experiment. Three specimens were produced for each variable, resulting in a total of 45 TRC panel specimens that were manufactured and tested. Details of the TRC panel specimens are presented in There were three parameters: the number of carbon-fiber textile layers, the anchorage length of the textile, and the presence or absence of sand–epoxy surface treatment on the textile. The number of carbon-fiber textile layer parameters was set to 0 (NF), 1 (C1)∼4 (C4) to examine the effect of the textile reinforcement ratio on the flexural behavior of the TRC panel. Section details according to the number of textile layers are shown in h) was based on 40 mm, but its height slightly varied depending on the number of textile layers. The actual measured height of the specimen and the location of each textile layer are presented in detail in The width of the TRC panel specimens was fixed at 100 mm, and the height Sections perpendicular to the axis of bending that are plane before bending remain plane after bending.(2)The concrete matrix and textile are fully bonded, so the strain in the textile is equal to the strain in the concrete matrix at the same level.(3)The stress–strain relationship of carbon-fiber textile is perfectly linear.(4)The tensile strength of concrete and compressive strength of carbon-fiber textile are neglected in flexural strength calculations.(5)Stress induced by flexural load acts only on the warp of the textile reinforcement.For the numerical calculation, the Hognestad  model waAccording to the assumption that the plane section remains plane, the strain of each textile layer and the compressive strain of concrete are proportional to the distance away from the neutral axis, as shown in Equation (4) can be derived using the force equilibrium condition, and When the compressive strain of the matrix reaches the ultimate compressive strain, the TRC panel fails and the resistance moment at that time corresponds to the nominal moment, The deflection of the carbon-fiber textile-reinforced concrete panel was calculated using the elastic deflection equation. As for the moment of inertia applied to the elastic deflection equation, the effective moment of inertia, ttee 440  as a metIn order to predict the deflection of reinforced concrete flexural members, ACI Committee 318  uses thethe span ,31. In tThe load–deflection curves were illustrated for the three TRC panel specimens for each variable resulting from the flexural test. The load–deflection relationships for the three specimens were averaged and are presented as one graph for each variable. For instance, in the case of the A4SE series test specimens, The NF-I and NF-II test specimens, which did not have fabric reinforcement, showed a linear increase in vertical deflection as the load increased and failed as soon as a flexural crack occurred between the two-point loading parts, with an average ultimate load of 3.68 kN and 3.01 kN, respectively. The difference in flexural strength between the NF-I and NF-II test specimens appears to be due to the difference in the compressive strength of the concrete matrix .The carbon fabric-reinforced TRC panel specimens exhibited the same initial behavior as the NF specimens, then developed flexural cracks and continued to behave without failure. The first flexural cracking load did not show any variation across the variables. All of the TRC specimens showed a sudden drop in load immediately after the first flexural crack occurred, a phenomenon resulting from the brittle stress redistribution from the concrete matrix to the carbon fabric . This phThe average load–deflection relationship between the A0 series, which had the shortest anchorage length, and the A4SE series treated with sand–epoxy, is shown in The maximum load was the highest for the C4L1A0 test specimen in the A0 series, with an average of 13.51 kN, and for the C4L1A4SE specimen in the A4SE series, with 27.45 kN. Both the A0 series and the A4SE series demonstrated higher maximum loads as the number of carbon fabric reinforcing layers increased . The C4LThe crack patterns observed after completing the flexural test on the TRC panel specimens are presented in The load–deflection curve according to the difference in anchorage length is shown in The number of cracks in the C2L1A0, C2L1A1, C2L1A2, C2L1A3, and C2L1A4 specimens were 2.3, 2.3, 2.7, 3.7, and 3.7, respectively, indicating an increase in the number of cracks with longer anchorage lengths. For the C2L1A0 specimen, large crack widths were observed, and carbon fabric slip between the cracks was visible. However, as anchorage length increased, crack widths decreased.The C1L1A4SE and C2L1A4SE specimens experienced flexural failure, while the C3L1A4SE and C4L1A4SE specimens developed flexural shear cracks that subsequently led to flexural shear failure. Flexural cracks occur due to tensile stress that arises in the vertical direction at the bottom of the specimen. The reduction in cross-sectional area resulting from the occurrence of flexural cracks causes an increase in inclined stress and shear stress at the tip of the flexural crack, which expands and leads to a flexural shear crack. The C1L1A4SE and C2L1A4SE specimens had a low carbon fabric reinforcement ratio, resulting in long flexural cracks towards the compression fiber, which made it difficult for them to expand into inclined cracks. In contrast, the C3L1A4SE and C4L1A4SE specimens could easily expand into inclined cracks due to the controlled expansion of flexural cracks, as the carbon fabric received the tensile stress adequately due to the increased carbon fabric reinforcement ratio. Upon examining the crack patterns of the SE series, the number of cracks increased, while the crack width decreased due to the sand–epoxy surface treatment.The load–deflection relationship curves of the TRC panel specimens were plotted using the two equations proposed by Branson and Bischoff. The flexural moment corresponding to the assumed The initial behavior of the numerical calculation and the experimental results was very similar in all specimens. The behavior before the first flexural crack occurred showed identical results, but the time of occurrence of the first flexural crack was slightly different. This was because the load at which the first flexural crack occurred in the TRC panel test specimen was mostly higher than the flexural strength of the concrete matrix itself .The behavior of all test specimens after the first flexural crack was closer to the experimental results when the Bischoff formula was applied than when the Branson formula was used. As the carbon fabric reinforcement ratio increased, the difference between the application results of the Branson formula and the Bischoff formula decreased . The behIn the case of maximum load, the experimental results were 8% to 22% higher when compared to the nominal strength by numerical calculation, except for the C2L1A4SE specimen. This difference can be attributed to the variation in ultimate compressive strain assumed in the numerical calculation and the difference in the first cracking load.To investigate the effect of the fabric reinforcement ratio, anchorage length, and surface treatment on concrete composite panels reinforced with carbon fabric, textile-reinforced concrete specimens were fabricated and flexural tests conducted. In addition, the flexural behavior of the TRC panel specimens was numerically calculated and compared with the experimental results, and the following conclusions were drawn.(1)All TRC specimens exhibited a sudden drop in load immediately after the first flexural crack occurred. This is due to the brittle stress redistribution from the concrete matrix to the carbon fabric, and it can be reduced by improving the bond between the matrix and the carbon fabric and increasing the fabric reinforcement ratio.(2)With an increase in the carbon fabric reinforcement ratio, from one layer to four layers, the degree of load reduction and reduction in flexural stiffness at the time of flexural cracks decreased, and the maximum load and number of cracks increased. This is because the carbon fabric rapidly contributes to the tensile stress acting on the bottom of the concrete matrix.(3)As the anchorage length increased from 50 mm to 275 mm, the flexural stiffness after the first cracking of the TRC panel increased, and the number of cracks increased.(4)Sand–epoxy surface treatment and an increase in anchorage length simultaneously contributed to the improvement of the load-carrying capacity of the TRC panel up to 110%. However, the effect of increasing the anchorage length was limited, and additional load-bearing capacity could be improved through sand–epoxy surface treatment.(5)Comparing the numerical calculation results with the experimental results, it was found that the deflection of the experimental results was approximately 50% larger than the numerical calculation results. This is because the bond between the carbon fabric and the concrete matrix failed, and slip occurred.To prevent slip of the fabric, it is necessary to secure a reliable bond between the carbon fabric and concrete using methods such as surface improvement through sand–epoxy surface treatment, sufficient anchorage length, and sufficient concrete thickness. In addition, it is necessary to accurately identify the bond behavior and set limitations for TRC material performance to design structures applying TRC.


The paper presents the results of the joining tests of the EN AW-6082 T6 alloy. The materials were joined using the EBW high-energy (electron beam welding) and friction stir welding (FSW) methods. In the case of FSW welding, the following parameters were used: the linear speed was 355 mm/min, and the rotational speed of the welding tool was 710. In the case of EBW welding, the following parameters were used: accelerating voltage U = 120 kV, beam intensity I = 18.7 mA, welding speed v = 1600 mm/min and, in the case of a smoothing weld, U = 80 kV, beam intensity I = 17 mA, and welding speed v = 700 mm/min. Comprehensive microstructural tests of all welded joints  and mechanical property tests (tensile and hardness tests) were carried out. The topographies of the fractures after the tensile test were also examined. Based on the results, it was found that the strength properties of the EBW joint were reduced by 23% and the FSW joint by 38% compared to the base material. A decrease in elongation was also noted, with an FSW elongation of 7.2% and an elongation of 2.7% for EBW. In the case of the EBW joint, magnesium evaporation was found in the weld during welding, while in the FSW joint, the dissolution of the Mg2Si particles responsible for strengthening the material during heat treatment to the T6 state was observed. The production of semi-finished products or products from aluminum-based materials is most often carried out by plastic consolidation or casting. Aluminum alloys have unique properties such as a high tensile strength to density ratio, susceptibility to plastic consolidation, good corrosion resistance, etc. ,2,3. ForMost of the problems associated with welding aluminum alloys result from its physical properties, such as high thermal conductivity, high chemical affinity for oxygen, a tendency to absorb hydrogen in the liquid state, high casting shrinkage and a linear expansion twice as high as in the case of steel . These pOne of the most promising methods of joining aluminum alloys is the friction stir welding method. Friction stir welding (FSW) was patented in 1991 at the Welding Institute in Cambridge, UK . This te12 W/mm2. By adjusting both the electron beam and the operating mode of the electron gun (oscillating or stationary beam), we can regulate the amount of heat introduced to the connected elements in a wide range [The second, constantly developing method of joining metals and their alloys is electron beam welding. Despite the fact that this technology has been known for over 60 years, in the last decade there has been a continuous increase in interest from both scientific units and industry. The electron beam welding (EBW) process consists of using the kinetic energy of electrons moving in a vacuum at a high speed up to 200 km/s) ,19,20,210 km/s ,1de range ,23,24.This article focuses on determining the quality of joints made of 6082 aluminum alloy, heat treated to the T651 condition. When selecting the alloy, its susceptibility to plastic processing was taken into account, and thus its common uses in industries such as the automotive  or shipbuilding industries was taken into account. At the same time, the limited weldability of the 6xxx series alloys, resulting from their tendency to hot cracking, and low fatigue strength force the search for new, more effective methods of joining them. In the global literature, one can find a large number of references to the subject of welding aluminum alloys of the 6xxx FSW and LBW series, often in comparison with traditional welding methods, such as MIG and TIG ,27,28,29The material used for the tests was aluminum alloy 6082-T651 in the form of a sheet with dimensions of 6.35 mm × 1000 mm × 2000 mm. Solution heat treatment was carried out at a temperature of 540 °C, artificial aging at a temperature of 170 °C for 8 h and annealing by a controlled value (permanent deformation of 0.5% to 3%). The chemical composition of the 6082 alloy is shown in The friction welding process was carried out using the Triflute type tool. The welding linear speed was 355 mm/min, the rotational speed of the welding tool was 710 rpm, while the direction of rotation of the tool was clockwise. Electron beam welding was performed on a welding machine that was manufactured by Cambridge Vacuum Engineering. The following parameters were used: accelerating voltage U = 120 kV, beam intensity I = 18.7 mA, and welding speed v = 1600 mm/min. In addition, the smoothing joint was obtained with the following parameters: accelerating voltage U = 80 kV, beam intensity I = 17 mA, and welding speed v = 700 mm/min.The tensile and bending tests of the obtained joints were carried out on the ZWICK ROEL Z050 testing machine. The width, thickness and length of the measurement base for the tensile test samples were 25 mm × 6.35 mm × 60 mm. The dimensions of the samples for testing the mechanical properties were selected on the basis of the PN-EN ISO 4136:2022-12 standard . The Shi2O using a voltage of 25 V for 30 s. The observation of the microstructure of the joints in scanning electron microscopy (SEM) and transmission electron microscopy (TEM) modes was performed on the HITACHI SU-70 electron microscope  equipped with a Thermo Scientific EDS system . Chemical composition is given in weight %. Thin films for TEM observation were prepared by mechanical thinning on abrasive papers and the electrolytic polishing of mechanically cut samples in the Struers A2 reagent.The studies of the microstructure of the joints in the light microscopy (MO) mode were carried out on the Olympus GX51 light microscope . Test specimens were excised and cold mounted in Struers EpoFix epoxy resin. The samples prepared in this way were ground on abrasive papers with a grain size of 240–2000. Diamond suspensions were used for polishing, with a DP-Suspension P of 9 μm, 3 μm, and 1 μm, and the specimens were made on a RotoPol-11 grinding and polishing machine with a RotoForce-1 Struers head. Finishing polishing was carried out using the OP-S suspension from Struers . The last stage in the case of observing the samples in polarized light was anodizing in a solution of 1.8 mL HBF4 and 100 mL H2Si phase, the presence of which can also be confirmed in various scientific and research articles [articles ,36.The microstructure of the FSW welded joint made of aluminum alloy grade 6082 (FSW 6082) visualized by light microscopy is shown in 2Si phase from the {100} family, formed during precipitation strengthening, and dispersoids of the Al(FeSi)Mn phases. The microstructure of the TMAZ zone is shown in 2 as well as a smaller average width of the heat affected zone—about 1 mm. Microstructural observations indicate the heterogeneity of the structure in individual areas of the weld caused by significant differences in the amount of heat input between different welds. In the smoothing joint, where the amount of linear energy was greater than in the area of the root of a weld, a dendritic structure with an average grain diameter of 151 μm is visible. A large temperature gradient caused the nucleation and growth of columnar grains. In the weld Mn phases was presented. In the area of the weld, there were no occurrences of Mg2Si lamellar precipitates; however, fine dispersoids of the Al(FeSi)Mn phases could be observed. Compared to the microstructure obtained in the FSW joint, a smaller amount of these particles can be seen, which are evenly distributed over the entire analyzed surface. In the case of the EBW joint, the average diameter of these particles was 110 nm, while in the FSW junction, it was 138 nm.The analysis of the chemical composition presented in Due to the fact that phases rich in magnesium were not detected in the EDS analysis of the weld presented in The results of mechanical property tests for the base material, FSW and EBW joints are shown in The hardness distribution map for the FSW joint is shown in The test results of various welding methods of aluminum alloy 6082 presented in the paper indicate a significant impact of the joining method on the properties of the joint. The main factor causing structural differences, and thus changes in the properties of joints, is the effectiveness of the impact of heat generated as a result of the energy supplied in the welding method used, causing structural changes. The FSW-welded joint studied in this paper is of great interest due to the possibility of joining metals and alloys that are difficult to weld using other methods ,57. The The applied joining technologies of the 6082 aluminum alloy allowed us to obtain homogeneous joints without inconsistencies and with comparable mechanical properties. The joint obtained by the EBW method obtained a tensile strength of 76% in relation to the starting material, while the FSW joint was 61%.The low plasticity in the EBW joint and the fracture of the brittle fracture type are caused by the unfavorable arrangement of the precipitates at the grain boundary. However, in the case of the fracture of the FSW joint and the base material, the fractures were plastic, which translated into a higher elongation obtained in the tensile test.The microstructural analysis of the FSW joint showed that structure-renewal processes dominated in the weld area. There is a change in the morphology and dissolution of the particles due to high temperature and the influence of the tool.In the joint obtained by the EBW method, magnesium loss was observed in the weld, which contributed to a decrease in hardness in this area. The largest loss of magnesium took place in the upper part of the weld, where an additional smoothing joint was made.


Due to its excellent mechanical properties and high aspect ratio, graphene can significantly improve the water and chloride ion permeability resistance of cementitious materials. However, few studies have investigated the effect of graphene size on the water and chloride ion permeability resistance of cementitious materials. The main issues are as follows: How do different sizes of graphene affect the water and chloride ion permeability resistance of cement-based materials, and by what means do they affect these properties? To address these issues, in this paper, two different sizes of graphene were used to prepare graphene dispersion, which was then mixed with cement to make graphene-reinforced cement-based materials. The permeability and microstructure of samples were investigated. Results show that the addition of graphene effectively improved both the water and chloride ion permeability resistance of cement-based materials significantly. The SEM (scanning electron microscope) images and XRD (X-ray diffraction) analysis show that the introduction of either type of graphene could effectively regulate the crystal size and morphology of hydration products and reduce the crystal size and the number of needle-like and rod-like hydration products. The main types of hydrated products are calcium hydroxide, ettringite, etc. The template effect of large-size graphene was more obvious, and a large number of regular flower-like cluster hydration products were formed, which made the structure of cement paste more compact and thus significantly improved the resistance to the penetration of water and chloride ions into the matrix of the concrete. Cement-based materials are the most widely used materials for construction projects. With the rapid development of the economy and the vigorous progression of urbanization, higher requirements are presented for cement-based materials, such as their mechanical performance and durability ,2,3,4,5.Graphene, as the thinnest two-dimensional nanomaterial known in the world, boasts a two-dimensional network lattice structure formed by single-layer carbon atoms with a sp2 hybridized orbital. It has excellent mechanical, thermal, electrical, and barrier properties and a large specific surface area ,15,16,17Existing studies have shown that there are generally two methods for using graphene or graphene oxide to improve the durability of cement-based materials. One is to add graphene or graphene oxide to cement-based materials as an admixture, and the other is to combine it with other substances to prepare nanocomposite materials as coatings on the surface of cement-based materials. So far, research has been focused on the preparation methods of graphene and the effects of the oxygen content of graphene on improving the durability of cement-based materials. Very few researchers have explored the influence of graphene on the durability of cement-based materials from the perspective of its size. The existing research generally believes that graphene can regulate the growth form of cement hydration products and has a template effect ,29. For Based on previous research, the effects of graphene with different sizes on the water and chloride ion permeabilities of cement-based materials were studied in this research by the water permeability height method and the rapid chloride ion migration method, respectively. Combined with XRD, SEM, EDS (energy-dispersive X-ray spectroscopy) and other characterisation methods, the changes in hydration product morphology and hydration rate in cement-based materials with graphene and graphene oxide were analyzed. To observe the interaction between graphene and cement-based materials more intuitively, cement paste/graphene/cement particle samples were prepared by a new method. The sample prepared by the new method allows cement to directly adhere to the surface of graphene instead of simply mixing graphene with cement. Therefore, the growth morphology and aggregation mode of cement hydration products on the graphene surface can be clearly observed by SEM, and the mechanism of graphene improving both water and chloride ion permeability resistance was studied. Cement: P.II42.5 Portland cement produced by Guangxi Yufeng Group Co., Ltd. , conforming to Chinese Standard GB175-2007, was used for preparing the samples. The main properties of the cement used are shown in Polycarboxylic acid water reducers (PCs), produced by Fuclear Technology Suzhou Co., Ltd. , with a water reduction efficiency of 30%, were used as a superplasticizer for preparing cement samples.Graphene dispersion: Two types of peeling graphene (PG1 and PG2) slurry prepared by Guangxi Qinglu Technology Company  were used for preparing graphene-reinforced cement composites in this study. The solid contents of the two types of graphene dispersion were 5% and 4% by weight, respectively. The graphene in the dispersion was in the agglomeration state as it was supplied. After treatment, a graphene slurry was prepared.Standard sand: the standard sand used for making cement mortars in this study was the ISO standard sand produced by Xiamen ISO Standard Sand Co., Ltd. Water: distilled water was used for all cement samples.According to previous findings , the besTo observe the dispersion effect, UV-vis spectrophotometry tests were carried out on the two groups of PG dispersion before and after mechanical stirring and ultrasonic dispersion treatment. The mechanical stirring and ultrasonic dispersion processes together lasted 15 min and the test wavelength was 187~700 nm. To eliminate the influence of PCs in the dispersion on the absorbance of graphene dispersion, the spectrophotometry test was carried out on PC solutions with the same concentration. Results show that the absorbance of the PC solution tended to approach zero after 600 nm (as shown in According to (1)−1, and the number of graphene layers was calculated. The results are shown in Two types of graphene were characterized with the XploRA plus Raman spectrometer with a scanning range of 500~3500 cmThe average number of layers of the two types of graphene can be calculated by the empirical Formula (1) based on their Raman spectrum shown in GI represents graphene peak G;Of which: ID2 represents graphene peak 2D, andGI/ID2 indicates the structural and crystalline integrity of graphene, the higher the value of GI/ID2, the more defects the graphene will have; otherwise, the more complete the structure of graphene, the better the crystallinity. In GI/ID2 values of PG1 and PG2 are 0.13 and 0.57, respectively, indicating that PG1 has fewer defects and higher crystallinity than PG2.The sheet diameter of graphene was measured by an LA-960 particle size analyzer . Figure (2)The chemical bonds and types of functional groups were measured with a PerkinElmer Frontier FTIR spectrometer. The results are shown in −1 corresponded to the -OH vibration absorption peak, 2928 cm−1 to the C-H vibration absorption peak, 1647 cm−1 to the C=C absorption peak, 1388 cm−1 to the HBrinterference peak, and 1065 cm−1 to the C-O-C stretching vibration absorption peak.It can be seen that the two types of graphene had similar absorption peaks, in which 3430 cmThe XRD curves of the two types of graphene were measured by D8AA25 XRD. Since the XRD curves of the two types of graphene were almost identical, only one curve is presented, as shown in It can be seen that an obvious characteristic carbon peak appeared at 26.2° (2θ). According to the Bragg Equation (2), the layer spacing of the two types of graphene can be obtained.d represents the crystal spacing;Of which n represents the reflection series, taking 1 in this study; andAccording to Equation (2), the layer spacing of the two types of graphene can be obtained at 0.314 nm.(3)The micromorphology of graphene was observed by the Phenom XL G2 scanning electron microscope. From (1)A water permeability test was conducted according to the water permeability height method recommended by Chinese Standard GB/T 50082-2009 Standard Test Method for Long-term Performance and Durability of Ordinary Concrete.(2)The chloride ion permeability test was carried out following the RCM method recommended by Chinese Standard GB/T 50082-2009 Standard Test Method for Long-term Performance and Durability of Ordinary Concrete.According to the authors’ previous research results, the content of graphene in the cement paste is 0.02% by weight of cement, while the content of PCs is 0.1% by weight of cement. The mix proportion of cement samples for the water permeability test is shown in The mix proportion of cement samples for the chloride ion permeability test is shown in The sample for the permeability test is in a round platform shape with an upper diameter of 175 mm, a lower diameter of 185 mm, and a height of 150 mm. After the samples were removed from their molds after 24 h of initial curing, the excessive cement slurry was brushed away from both ends and tops of the samples with a steel wire brush, and then the samples were cured in the standard maintenance room for 28 d. The samples were sealed in the permeability test mold before the test. The sealing process was as follows: First, the sealing material made of paraffin and rosin at a 5:1 ratio by weight was put into the oven to melt, followed by being daubed with a layer of 1–2 mm thick on the side of the samples with a brush. Afterwards, the samples were pressed into the preheated test molds at a slow speed until the sample reached the bottom of the test mold. The temperature of the test mold was determined just to be able to melt the sealing material slowly but not cause it to flow.Six samples were installed on a concrete water permeability instrument, as shown in After the water permeability test was completed, the samples were split into two parts along the longitudinal direction by a press machine. Then the water mark of the samples after splitting was traced with a waterproof pen, and a sample was divided into 10 equal parts along the water mark with a steel ruler. The water permeability height was then measured, and the average of the 10 measured values was taken as the water permeability height. The reading was accurate to 0.1 mm. The calculation process is shown in Equation (3) . The aveOf which The water permeability height of the three samples  subjected to water permeability after splitting is shown in It can be seen from −12 m2/s);The depth of chloride permeability of cement paste samples and related RCM test data are presented in U represents the absolute value of voltage used (V);T represents the average of the initial temperature and end temperature of the anode solution (°C);L represents the thickness of the sample (mm) (as accurate down to 0.1 mm);Xd represents the average chloride ion permeability depth (mm) (as accurate as 0.1 mm); andt represents test duration (h).−12 and 4.4 × 10−12 m2/s, respectively, representing a decrease of 33.9% and 21.4%, respectively, compared to that of the control sample.The chloride migration coefficients of the three groups of cement paste samples are shown in 3 solution after the permeability test, and the silver-white area that developed at the lower part of the samples was the part where chloride ions penetrated. It can be clearly seen that in the control sample, a large silvery-white area developed. However, the boundary was uneven, indicating that the internal structure of the control sample was uneven. While the silvery white area developed in the cement paste samples with PG1 and PG2 was slightly reduced compared with that in the control sample, the boundary was almost in a straight line, representing that the addition of graphene made the structure of the matrix more compact and uniform.After adding graphene to cement samples, the water permeability resistance and chloride ion permeability resistance of cement paste samples increased significantly, which is because the two-dimensional sheet structure and the impermeable property of graphene played a bridging role in the cement matrix, thus preventing the connection of internal cracks to deflect the interconnected pores in the cement paste and prolonging the migration channel of chloride ions . Due to In addition, graphene with a nanoflake structure produced a spatial crack prevention effect in the cement matrix, which can reduce and delay the generation of internal cracks in the cement matrix and thus improve the compactness of cement stones. The larger the size of graphene in a certain range, the more obvious the spatial crack prevention effect. The large-size PG1 graphene had fewer defects on the surface and more nucleation sites, whose template and bridging effects are more obvious than those with PG2. The large-size graphene is easy to curl and form a “semi-enclosed” structure. When water molecules and chloride ions penetrate the structure, they are difficult to penetrate into other parts of the cement matrix. Therefore, the hydration product structure inside the PG1 cement paste samples was denser, and both its water and chloride ion permeability resistances were higher.3S and C2S diffraction for PG1 and PG2 cement paste samples are also lower than those of the control sample, indicating that the addition of PG1 and PG2 accelerates cement hydration reactions.It can be seen that adding graphene did not change the position of the crystal diffraction peak in hydration products, suggesting that the addition of graphene did not change the type of cement hydration products but had an impact on the content and crystallinity of hydration products. Through peak intensity analysis, it is found that whether it was 3 d or 28 d, the diffraction peak of CH crystal near 18° (2θ) of the PG1 cement paste sample was significantly improved, indicating that the addition of PG1 can effectively improve the crystallization degree of CH crystal and accelerate the formation of CH crystal. This is because there are a large number of oxygen-containing functional groups on the surface and edge of PG1, providing reaction sites for the formation of CH crystals to accelerate their hydration reactions and regulate their size. This phenomenon can be explained by the classical heterogeneous nucleation theory . The pea(1)Graphene-reinforced cement-based material samples prepared by a conventional methodTo observe the microstructure of the cement slurry sample after the incorporation of graphene, the graphene-reinforced samples and control samples without graphene were examined by SEM. The mix proportion of the samples was the same as that of the samples for the chloride ion permeability test see , with 3 According to the types and data of elements in points 4 to 8 in One of the reasons for these phenomena is that graphene plays a bridging role  in the c(2)Cement paste/graphene/ cement particle samples prepared by a new methodIn the above tests, graphene was distributed in a cement paste sample in a three-dimensional disordered form. It was not easy to accurately observe the interaction between cement hydration products and graphene. To further observe the hydration of cement on the surface of graphene and analyze the regulation effect of PG1 and PG2 on cement hydration products, a new method was adopted in this paper: first, two cement paste samples with a diameter of 10 mm and a thickness of about 2–3 mm were made, and after their initial setting, several drops of PG1 and PG2 graphene dispersion made by mechanical stirring and ultrasonic were respectively absorbed with a rubber head dropper and evenly coated on the surface of cement paste. The amount of graphene dispersion should just cover the surface of the cement paste samples without overflowing to make graphene nanosheets distributed on the surface of the cement paste sample. Finally, a small number of cement particles (3~5 g) were evenly sprinkled by a cement sieve with an aperture of 80 um to prepare samples of cement paste/graphene/cement particles, which were moved to an environment chamber for standard curing. The cement paste/graphene/cement particle samples prepared by this new method ensured that graphene and cement hydration products on the surface of graphene could be observed on the surface of cement paste. Its structural diagram is exhibited in The SEM images of cement paste/graphene/cement particle specimens prepared by the above new method are shown in As shown in From 2, and a small amount of AFt were mainly at measurement points 9, 11, 13, and 15. At the same time, the content of C at those measurement points was higher than that of general cement hydration products, indicating that the cement hydration product was attached to the surface of graphene.According to the EDS element composition analysis results presented in (1)Due to the unique nano two-dimensional sheet-like structure of graphene, which plays a bridging role and template effect in the cement matrix, it prevents the connection of internal cracks, refines the size of hydration products, improves the density of cement-based materials, and makes graphene cement-based materials more resistant to water permeability and chloride ion penetration than the blank group.(2)XRD analysis shows that the addition of graphene does not change the type of cement hydration products but can improve the rate of the hydration reaction and accelerate the formation of CH crystals.(3)Through scanning electron microscopy observations of graphene cement mortar specimens, it is found that during the early stage of hydration, a large number of small granular hydration products are formed on the surface of graphene, and later, regular reef-like hydration products are generated, and the structure of the cement becomes denser.(4)By observing the newly prepared cement mortar-graphene-cement particle specimens through scanning electron microscopy, it can be directly observed that a large number of regular and dense flower clusters and needle clusters of hydration products are formed on the graphene surface. This indicates that graphene has a template effect, and its oxygen-containing groups on the surface provide reaction sites for cement hydration, regulating the morphology and size of the hydration products. As the hydration reaction proceeds, the hydration products increase, which makes the cement matrix more compact, thus improving the water permeability resistance and chloride ion permeability resistance of cement-based materials. Due to the larger average area diameter and fewer defects of PG1 than PG2, and the more complete structure, its template effect is more pronounced.(5)2, and a small amount of AFt, among others.Analysis of EDS elemental composition shows that the flaky substance inside the cement specimen is graphene, and the hydration products grow and cover the surface of graphene; the flower-cluster-shaped hydration products are mainly composed of C-S-H, Ca(OH)Studying the water and chloride ion permeability of cement-based materials is of great significance to assess the durability of concrete and propose measures to reduce building maintenance costs and improve building service life associated with concrete durability. Different from other studies, this paper investigated the influence of graphene on the water and chloride ion permeability of cement-based materials from the perspective of graphene size. Based on the results, the addition of either of the two types of graphene can reduce both the water and chloride ion permeability of cement-based materials. When graphene was well dispersed, large-size graphene had fewer defects and more oxygen-containing groups. Both the water and chloride ion permeability resistances of cement-based materials were improved more obviously. In this study, the cement slurry-graphene cement particle sample was prepared by a new method for the first time, and the growth law and morphology of the hydration products on the surface of graphene were observed by SEM, which further revealed the mechanism of graphene in improving the water and chloride ion permeability of cement-based materials. The specific conclusions are drawn as follows:Because the production technology of large-diameter graphene was simpler and the cost became lower, the research methods and results proposed in this study can not only enrich the existing research on graphene cement-based materials but also provide a theoretical basis and application reference for graphene to improve the durability of cement-based materials. However, there are still some limitations. There is a lack of research on the water permeability and chloride ion permeability of graphene for cement concrete materials because, compared with cement paste, the internal structure of concrete is more complex, and the effects of different sizes of graphene on the water and chloride ion permeabilities of concrete may be different. Therefore, further research is needed in this area.


Energy storage of passive muscles plays an important part in frequent activities of honey bee abdomens due to the muscle distribution and open circulatory system. However, the elastic energy and mechanical properties of structure in passive muscles remain unclear. In this article, stress relaxation tests on passive muscles from the terga of the honey bee abdomens were performed under different concentrations of blebbistatin and motion parameters. In stress relaxation, the load drop with the rapid and slow stages depending on stretching velocity and stretching length reflects the features of myosin–titin series structure and cross-bridge–actin cyclic connections in muscles. Then a model with 2 parallel modules based on the 2 feature structures in muscles was thus developed. The model described the stress relaxation and stretching of passive muscles from honey bee abdomen well for a good fitting in stress relaxation and verification in loading process. In addition, the stiffness change of cross-bridge under different concentrations of blebbistatin is obtained from the model. We derived the elastic deformation of cross-bridge and the partial derivatives of energy expressions on motion parameters from this model, which accorded the experimental results. This model reveals the mechanism of passive muscles from honey bee abdomens suggesting that the temporary energy storage of cross-bridge in terga muscles under abdomen bending provides potential energy for springback during the periodic abdomen bending of honey bee or other arthropod insects. The finding also provides an experimental and theoretical basis for the novel microstructure and material design of bionic muscle. Frequent movements of the honey bee abdomen, such as pumping in feeding , bendingSufficient researches on muscle structure have distinguished that myosin, actin  and titiThere is an intricate conversion  among chIn laser trap experiments, asynchronous motion  of diffeIn the present study, we applied stress relaxation tests with different motion parameters on muscles from the honey bee abdominal terga by applying blebbistatin  to partiApis mellifera Linnaeus), raised in the intelligent biomechanical laboratory of Tsinghua University in Beijing, China . Honey bees were fed with honey and water regularly and kept in a cage consisting of a 120 × 40 × 60 cm transparent glass cover and a 50 × 40 × 26 cm hive at room temperature. This experiment neither involved endangered or protected species nor required special permission.The species involved in this study were adult foraging worker bees  at 4 °C to remove viscera and get the selected terga area of the abdomen in 2 0.11 mmol/l, MgCl2 4 mmol/l, glucose 25 mmol/l, Na2HPO4 10 mmol/l, sucrose 125 mmol/l, 0.1% Janus green, pH 6.7) for 10 min to dye muscles and observed under a stereoscope to ensure the presence of fresh muscles on the sample in Honey bee abdomens were dissected in buffer solution A  in 2 5 mmol/l, MgCl2 4 mmol/l, glucose 25 mmol/l, Na2HPO4 10 mmol/l, sucrose 120 mmol/l, pH 6.7) and buffer solution C  for 30 min at 4 °C to make the solution fully permeate the muscle. Adding blebbistatin to the sample in the experimental group was to make cross-bridge combine with blebbistatin specifically and to change the mechanical properties of cross-bridge. After installing the sample and snipping the lateral connection aside crevice, muscles should be prestretched. In prestretching, muscles were stretched with a stretching velocity of 0.01 mm/s and ended stretching with continuous load growth for 10 s to ensure the separation of the 2 honey bee abdominal terga. Prestretching aimed to make a certain tension on muscles at the beginning of tests. Two or 3 stress relaxation tests were performed on each sample with various stretching velocities of 0.01–0.25 mm/s and stretching lengths of 0.01–0.4 mm. The range of stretching velocity and length was below the limit of muscle bearing and above the minimum of no obvious result. Besides, muscles were kept fresh in the experiment by spraying corresponding buffer solution on muscles between 2 tests. We conducted 21 tests of 9 samples in the control group and 13 tests of 5 samples in the experimental group. The 3 characters of test number represented group , muscle number in the group, and test number of the muscle, respectively. For example, c11 and c12 were the first and second tests of the first sample in the control group. Motion parameters of each test were shown in Before installing the sample, control group and experimental group were soaked separately in buffer solution B  composed of myosin and titin in series to represent the main structure of muscles. Another module was active elastic module (AEM) referring to the cyclical movement and nonlinear elasticity of cross-bridge.j can be expressed as E1 is the elastic coefficient), j is the stain in direction j). Using a Prony series expansion, In PVM, we used quasi-linear viscoelastic SYS  to descrS and the main load of PVM on muscles was N = 2. Besides, we considered that the load in measurement was along the main stress direction. Finally, the load fitting equation of PVM on relaxation stress can be expressed as:where C is a constant term coefficient) and i = 1,2) are fitting parameters.where i ≤ n), where Δli is the elastic deformation of cross-bridge in the direction of filament axis, E2 is the stiffness of cross-bridge, and n is the amount of connected cross-bridge. Considering the constant stretching velocity (v) in loading process and the time for stretching on one of the connected cross-bridges (Δti), the elastic deformation is expressed as ti (1 ≤ i ≤ n) was uniformly distributed on interval range of  for the asynchronous motion of different cross-bridge . Besides, the slope decreases with the increase of stretching velocity. However, the stretching length showed a low correlation to the ratio in P > 0.05). The result suggests that the influence of stretching velocity on the load drop in the 2 stages is different while the stretching length shows the influence on the 2 stages in the same degree.The normalized stress relaxation curve in x.5 s was solved through the 10 values from x s to (x+1) s, where x is the integer time in slow stress relaxation stage. It was distinct that slopes of load drop in the same muscles, but with different stretching velocities were basically in coincidence in the slow stress relaxation stage. The difference between the 2 slopes was less than 15% of the maximum when the time of stress relaxation came up to 1 s and the end of stress relaxation. Therefore, stretching velocity has little effect on the slow relaxation stage of muscles.To reveal the influence of stretching velocity on stress relaxation, we discussed the change trend of the load drop ratio in the 2 stress relaxation stages with different stretching velocities. The result showed that the ratio raised with the increase of stretching velocity in both groups, but the rate of raising became lower with high stretching velocity. It suggested that stretching velocity had an effect on the load drop in the rapid or slow stress relaxation stage and there was an upper limit on this effect. To identify the range of the effect, the stress relaxation curves of the same muscles with the same stretching length and different stretching velocities were performed in Stress relaxation curves of the same sample under the experimental condition of the same stretching velocity and different stretching lengths were shown in The stress relaxation curve is associated with the structure of muscles . The preR2) was above 0.9978 at all stretching parameters and solution conditions.As the model fitting, both PVM and AEM determined the load drop in the rapid stress relaxation stage, while only PVM determined the process of the slow stress relaxation stage. The data on slow stress relaxation in The load fitting equation of PVM determined by slow stress relaxation in Unexpectedly, R2) above 0.9950.The fitting equation in AEM fitted to the difference value between experimental data and the fitting equation in PVM was shown in P < 0.05).To identify the elastic deformation of cross-bridge, we compared fitting parameters in AEM of the experimental group with the parameters of the control group in v) and stretching length S, n) were various in different muscles. Due to the diversity of fitting parameters in different tests, using the model to calculate the theoretical value out of stress relaxation could be a way to verify the model  could be expressed as:To calculate the theoretical load in the loading process, the load was divided into 2 parallel parts for PVM and AEM of the model. The first part of the load depending on PVM in the loading process could be calculated through Boltzmann superposition principle for quasi-linear viscoelastic and ramp loading process . The relY(t) is stress relaxation coefficients. To get Y(t), applying step deformation to muscles was a direct method. However, the loading process in this study was a ramp loading process l0 is the maximum stretching length. Besides, it has been found that when l(t) and t leads Y(t):where )≈Y(t)l0 . AccordiN ≥ 10 and t < t0) to Equation (5) leads the theoretical approximate value of where The second part of the theoretical load in the loading process depended on AEM. As mentioned in AEM, s-bridge  and unifs-bridge , the avewhich could be expressed with the parameters of AEM as:where The contrast between the theoretical and experimental value of load in the loading process was shown in t0 in the test with a short stretching time. Therefore, the effect of the duration of decrease should be considered. First, experimental data on stress relaxation The main reason for the relative error in the loading process was the Backlash Error of Micro-nano Tensile System. The value of stretching length would decrease a little when the motor stopped rinciple . TherefoAs the correctness of the model with PVM and AEM verified, the energy storage and release of passive muscle could be expressed through this model by integration of force and deformation . Since tv1 for duration of t1 and then recovered with a constant velocity of v2. The expression of stretching length on the muscle is expressed as To obtain the analytical solution of energy and analyze the effect of motion parameters on energy storage and release, movement conditions of muscle were given. The passive muscle was stretched to maximum length with a constant velocity of The first part of the potential energy was determined by the work  (le(t)) . As the Besides, the released potential energy in PVM during recovery To discover the influence of motion parameters t, the value of Due to The second part of the elastic potential energy was s-bridge . Since Es-bridge , the defIn the recovery process After simplifying Equations (11) and (12), energy storage of AEM showed a positive correlation with stretching velocity for P < 0.05). Mechanical work on muscles converts into stored energy The above analysis on energy of PVM and AEM showed the same trend for velocity on energy storage and release. It demonstrated that the higher stretching velocity set the more energy stored in muscle during stretching, while the released energy raised with the increase of recovery velocity y (Heat) . The incThis relationship between energy storage/release and motion parameters on muscle suggests that the stretching velocity and length should be larger to get more energy stored in PVM, while just stretching velocity needs to be larger to store more energy in AEM. Besides, the released energy raised with the increase of recovery velocity at a low-number range. This relationship was confirmed with the experimental data in the loading process and other species like frogs  and rabbAccording to this model, the load drop in rapid stress relaxation stages corresponds with the release of elastic force from cross-bridge in AEM and viscoelastic force from titin–myosin in PVM, while the load drop in slow stage corresponds with the latter only. Besides, according to Expressions (2) and (4) of force from AEM and PVM in stress relaxation in the Statistics and Data Processing section, the 2 forces are linear correlation with the stretching velocity. As E2) or amount (n) of connecting cross-bridge could decline. The change of E2 indicates that after adding blebbistatin, the stiffness of cross-bridge decreases for the combination of cross-bridge and blebbistatin, which is in accord with the effect of blebbistatin  was improved to fit the data in stress relaxation tests. This model considered the mechanical properties and behavioral characteristics of different structural proteins in honey bee muscles to distinguish the different effects on muscle energy storage. The model fitted well with the experimental data in the stress relaxation stage and loading process. Changes in the fitting parameter in AEM with different concentrations of blebbistatin proved the stiffness or connecting number of cross-bridge would decrease with a combination of blebbistatin. Besides, expressions of energy storage and release on passive muscle were deduced, and consistent with the experimental data. The result suggests that with a larger velocity of cycle movement on the honey bee abdomen, the more energy would be stored and released for the elastic deformation of cross-bridge.iead026_suppl_Supplementary_TableClick here for additional data file.