The push for sustainability in the construction sector has demanded the use of increasingly renewable resources. These natural fibers are biodegradable and non-toxic, and their mechanical capabilities are superior to those of synthetic fibers in terms of strength and durability. A lot of research recommends coconut fibers as an alternative to synthetic fibers. However, the knowledge is scattered, and no one can easily judge the suitability of coconut fibers in concrete. This paper presents a summary of research progress on coconut fiber  reinforced concrete. The effects of coconut fibers on the properties of concrete are reviewed. Factors affecting the fresh, hardened, and durability properties of concrete reinforced with coconut fiber are discussed. Results indicate that coconut fiber improved the mechanical performance of concrete due to crack prevention, similar to the synthetic fibers but decreased the flowability of concrete. However, coconut fibers improved flexure strength more effectively than compressive strength. Furthermore, improvement in some durability performance was also observed, but less information is available in this regard. Moreover, the optimum dose is an important parameter for high-strength concrete. The majority of researchers indicate that 3.0% coconut fiber is the optimum dose. The overall study demonstrates that coconut fibers have the creditability to be used in concrete instead of synthetic fibers. Conventional concrete (CC) is generally robust in compression but not in tension. Steel bars are often employed when tensile stresses are created or tension zones are discovered to overcome this deficit in traditional concrete, which is commonly referred to as reinforced cement concrete (RCC). Fibers are added to concrete to increase its inherent tensile strength, resulting in a specific form of concrete known as fiber reinforced concrete (FRC) ,2,3,4. I2 emissions into the surrounding environment as well. Biocomposites are becoming more popular as appealing products in a variety of industries, including automotive, aviation, packaging, construction, architectural, and biomedical [Besides secondary cementitious materials, which help in ecofriendly concrete ,7,8, natomedical . Furtheromedical . Coir isomedical . Due to omedical . Numerouomedical ,15,16,17omedical .A growing number of academics and scientists have been interested in using natural fibers as an alternative to conventional glass and carbon fibers as a reinforcement in polymer composites in the last several decades . Among tNatura fibers have extremely good compatibility with a variety of thermoplastics, thermosetting polymers, and cementitious materials due to their lower density, better thermal insulation properties, mechanical properties, lower prices, unlimited availability, nontoxic approaches, and problem-free disposals, among other characteristics. Despite the fact that natural fibers have been extensively investigated in terms of their thermal, mechanical, and morphological characteristics, little is known about their compressive qualities. As a result, this study discusses the chemical, physical, workability, mechanical, and durability properties of coconut fiber reinforced concrete, as well as their application. Coconut fiber is classified into the following four types: bristle coil, buffering coil, brown fibers, and white fibers. Bristle coil is the most common form of coconut fiber. The brown fiber is generated from mature coconut, and it is typically highly strong, thick, and has great abrasion resistance, making it the most favored and most widely used fiber on the planet . Unlike Many variables may impact the performance of natural fiber-reinforced composites, including the fiber type used and the amount of fiber used. Aside from the hydrophilic nature of the fiber, the characteristics of natural fiber-reinforced composites may be altered by the quantity of fiber used in the composite and the amount of filler used. In general, substantial fiber content is essential for composites to function well in order to obtain high performance. The optimum is also important for the better performance of concrete. The effect of fiber content on the properties of natural fiber-reinforced composites is particularly significant. A lot of researchers focus on coconut fiber instead of steel fibers. As the steel fiber is costly as well as thermal expansion and corrosion problems. However, the knowledge of coconut fiber in concrete is scattered, and no one can easily judge the importance of coconut fiber in concrete. Therefore, this review focuses on the physical properties of coconut fibers, fresh properties, and mechanical and durability aspects of concrete reinforced with coconut fiber. A successful project will also give the idea to a new researcher to choose and apply coconut fiber in concrete. Coconut fiber, also known as coir, is derived from the fibrous husk of the coconut plant and is used in the production of coir. This is the thick fibrous middle layer of the coconut, which is shown in Coconut fibers are mostly brown in color with varying lengths and diameters. Moreover, other properties such as tensile strength and modulus of elasticity vary depending on the source and usage. A different researcher reported different physical properties of coconut fiber. The details of the various physical properties of fibers as per past researchers are given in Concrete workability is a term that relates to how easily mixed concrete can be placed, compacted, and finished while retaining its homogeneity to the greatest extent possible. Unworkable concrete is one that cannot be easily worked. In unworkable, the cement paste is not sufficiently lubricated and it does not adhere to the aggregates correctly, resulting in significant aggregate segregation. Maintaining the homogeneity of an unworkable concrete mix is very difficult, and compaction of concrete requires a significant amount of work, which has a negative impact on the mechanical and durability performance of concrete.According to one study, the value of slump flow decreased when the dose of coconut fibers was raised. The maximum slump flow was reached at zero percent addition (control concrete) while the lowest slump flow was recorded at three percent addition of coconut fibers, as indicated in As illustrated in 2 > 90%).Density is an important factor that influences the flowability of concrete. A lack of workability leads to voids in occupied space and reduced density. To investigate the durability of coconut fiber, several treatments were carried out on the material. For the first minute, each coconut fiber was soaked in an adherent solution  to ensure that it adhered to the other fibers. During this process, the adherent solution surrounds the coconut fiber, forming bonding layers between the two materials. A coating agent was then applied, which consisted of pozzolanic materials (silica fume or metakaolin). Pozzolans are attracted to the coconut fiber by the adhering solution in which they are dissolved. The production of “chicken fingers” is comparable to the process used in the development of this novel medicine . Table 2Using a latex polymer film and a pozzolan layer, the coconut fiber treatment was created to increase the flexural strength and durability of cement-based composites. The performance of the sample treated with silica fume and natural latex was 42.2 percent better than the performance of the sample without any treatment. When fiber samples were subjected to degradation tests, the mass conservation rate increased as a consequence of this treatment . This treatment resulted in an enhancement in the retention of the fiber structure against the degradation process, according to the microstructural examinations of the treated fibers isolated from CF. This treatment  has the potential to be a viable alternative to the use of coconut fibers in the creation of novel cementitious composite materials that have appropriate performance and long-term durability. The compressive and flexural strengths of the structures increased by up to 13 percent and 9 percent, respectively, according to the testing data. However, in terms of durability, the chloride penetration, intrinsic permeability, and carbonation depth increased with CF. The authors propose that the coconut fiber could be treated prior to being used in concrete to ensure that it is protected against deterioration . Two appCompressive strength is a material’s or structure’s capacity to bear loads without cracking or deflection. Compression shrinks a material’s size. Concrete’s compressive strength gives an indication of the concrete’s properties. This single test determines whether or not concrete was correctly performed. In commercial and industrial construction, concrete’s compressive strength ranges from 15 MPa (2200 psi) to 30 MPa (4400 psi). Compressive strength is tested on a cube or a cylinder. The American Society for Testing Materials established ASTM C39/C39M  for compResearch also found that fibers boosted concrete’s compressive strength up to a certain point before decreasing owing to a lack of workability . Even atSplitting tensile strength refers to the stresses generated when compressive loads are applied using compressive testing equipment in such a manner that a concrete cylindrical specimen splits vertically in half. It is referred to as the indirect approach for determining the tensile strength of concrete. The direct technique is not practicable due to insufficient grip on the cylindrical sample and the eccentric force. As a result, the direct tensile test is not the standard procedure. At the stipulated duration of curing, concrete tensile strength was discovered according to ASTM C496-71  for a tyAccording to the results of the research, the split tensile strength is 40 percent greater than the reference mix when just 2.0 percent of the fibers are added. The fact that fibers enhance tensile strength more than compressive strength is also mentioned . When coIn the relative analysis of concrete shown in 2 of approximately equal to 90%.As previously stated, the split tensile strength follows the same pattern as the compressive strength. Split tensile strength is 10–15% of concrete’s compressive strength. As a consequence, compressive and split strength correlated significantly. The following equation has been developed with different doses of coconut fibers:However, different codes recommended different equation to predict split tensile strength from compressive strength, which are listed below. ACI-318.11  EquationA comparison among split tensile strength from Equation (1), different codes, and past studies is given in The tensile capacity of concrete may be determined in many ways, one of which is a flexural test. Flexure strength is the capability of an unreinforced concrete beam or reinforced concrete beam to withstand bending failure. According to ASTM standards, it is determined by loading 6 × 6-inch (150 × 150-mm) concrete beams with a span length that is at least three times the depth .A regression model between compressive and flexural strength is shown in The water absorption test analyses the rate of water absorption of the outer and inner concrete surfaces. The test includes measuring the increase in mass of concrete samples caused by water absorption as a function of the time when the specimen is exposed to water. Higher water absorption results in less durability since water contains various hazardous compounds that seep into the concrete, causing concrete breakdown and resulting in reduced durability.2 to diffuse through the concrete. The addition of coconut fibers (CF) limits the CO2 diffusion channel, resulting in an increase in the resistance to CO2 penetration into the concrete. As a consequence, the rate of carbonation depth has decreased significantly [2 to penetrate the concrete, resulting in enhanced carbonation speed in the concrete structure [The carbonation of concrete is a crucial characteristic connected with steel reinforcement corrosion. Carbonation depth entirely depends on permeability. By contrast, other influencing variables such as temperature, carbon dioxide concentration, water/binder ratio, and relative humidity are consistent throughout all specimens. The findings show that carbonation depth rises with fiber concentration, implying that carbonation happens faster on a more porous material. The 2.4 percent CF carbonation depth was 74.3 percent greater than the reference concrete at 546 days, while the 0.6 percent CF result was equivalent to the reference concrete with a 4.3 percent difference as shown in ficantly . In conttructure .The water absorption by immersion provides an estimate of the total (reachable) pore volume of the concrete, but it provides no information on the permeability of the concrete, which is more essential in terms of long-term performance.The permeability of concrete after the addition of coconut fiber is seen in 2 to form CSH. Ca(OH)2 may also have an unfavorable influence on the interfacial and microstructure characteristics of a material owing to the orientation and crystallinity of the material. A study also reported that Ca(OH)2 is chemically active, which causes a decrease in the durability of concrete by reacting with other chemicals, forming harmful compounds [The use of scanning electron microscopy (SEM) improves the capacity to evaluate the microstructure of cement and concrete. It will also assist in analyzing the impacts of supplemental cementing ingredients or fibers, as well as evaluating concrete durability issues. The microstructure of the coconut fiber reinforced concrete was investigated using SEM . The samompounds . The incompounds . A studyompounds . The incThe flowability of concrete decreased with the addition of coconut fiber due to the larger surface area of the fiber, which enhanced the internal friction among concrete ingredients, leading to less workability. Furthermore, an increase in fresh density is observed up to 2% addition of coconut fibers.Mechanical characteristics such as compressive, split tensile, and flexure strength were improved up to a certain dose of coconut fiber, which depends on physical properties of fibers such as length, diameter, and aspect ratio. Furthermore, it can also be observed that coconut fibers improved flexure capacity (47%) more efficiently than compressive capacity (12%).Increased durability properties were also observed with the addition of coconut fibers. However, less information is available in this regard.The optimum dose of coconut fibers is the most important parameter for better performance of concrete, as a higher dose results in more voids in hardened concrete due to lack of workability, leading to lower mechanical and durability performance of concrete. The optimum dose of concrete varies depending on fiber length, diameter, and aspect ratio. However, the majority of researchers recommended the optimum dose of coconut fiber is from 2 to 3% by volume of cement.This paper presents a summary of research progress on natural fibers (coconut fibers). Coconut fibers are an inexpensive, recyclable, low-density, and environmentally acceptable building material. These fibers have excellent tensile qualities, and they may be utilized instead of traditional fibers such as glass and carbon steel fibers. Based on a detailed review, the following conclusions have been made:It can be concluded that coconut fibers enhanced flexure capacity more efficiently than compressive capacity. Therefore, further research was recommended to add some pozzolanic materials such as fly ash and silica fume to the improved compressive capacity of fiber reinforced concrete for high strength concrete. It is necessary to conduct detailed research investigations into the influence of coconut fibers on crack abridgment, cement matrix pore structure, water, and chloride permeability properties of concrete. It is also necessary to investigate a novel strategy that makes use of the water retention capacity of coconut fibers in order to generate high-performance cement composites using internal curing technology.


The structural design process is iterative and involves many design parameters. Thus, this paper presents a controlled framework for selecting the adequate structural floor system for reinforced concrete buildings and efficiently utilizing the corresponding construction materials. Optimization was performed using an evolutionary algorithm to minimize the total construction cost, considering the costs of concrete, steel reinforcement, formwork, and labor. In the problem formulation, the characteristic compressive strength of concrete was treated as a design variable because it affects the mechanical performance of concrete. The design variables included the column spacings, concrete dimensions, and steel reinforcement of different structural components. The constraints reflected the Egyptian code of practice provisions. Because the choice of the structural floor system affects the design details, three systems were considered: solid slabs, flat slabs with drop panels, and flat slabs without drop panels. Two benchmark examples were presented, and the optimal design results of the structural floor systems were compared. The solid slab system had the lowest construction cost among the three structural floor systems. Comparative diagrams were developed to investigate the distribution of construction costs of each floor system. The results revealed that an adequate choice of design variables could save up to 17% of the building’s total construction cost. Reinforced concrete (RC) has been extensively used in building construction for its versatility and ease of construction . The firThe majority of previous studies focused on the optimization of individual RC structural elements, such as slabs ,23,24, bDespite the intensive efforts of the researchers to minimize the costs of RC buildings, little attention was paid to considering different structural floor systems. Thus, the main aim of the current study was to determine the most economical structural floor system. To this end, three different structural floor systems were considered: solid slabs (SS), flat slabs with drop panels (FSDP), and flat slabs without drop panels (FS). The design variables in most studies were limited to the concrete dimensions and steel reinforcement, neglecting the concrete characteristic compressive strength The structural design started with calculating the applied loads. These loads were calculated as per the Egyptian code for calculating loads and forces in structural and building works (ECL) . Then, sIn the current study, the structural analysis of solid slabs and flat slabs was performed using the empirical methods provided by ECP 203-18 . In the Step 1. Checking the rectangularity of the slabs as per Equation (1).Step 2. For flat slabs, calculation of the column strip width Step 3. Determining the preliminary slab thickness Step 4. For flat slabs with drop panels, determining the preliminary drop panel thickness Step 5. Determining the preliminary width cl represents the column under consideration and Step 6. Calculation of the uniform load g and the live load p. The dead load g is calculated using Equation (10), while the live load p is provided using ECL based on the function of the building [building .(9)wsl=Step 7. Calculation of the applied bending moments s represents the critical cross-section under consideration; Step 8. Calculation of the maximum permissible bending moment Step 9. Checking that Step 10. Calculation of the required steel reinforcement area Step 11. Calculation of the minimum and maximum permitted areas of steel reinforcement Step 12. Selecting the bar diameter Step 13. Calculation of the chosen steel reinforcement area Step 14. Checking that Step 15. Determining the shrinkage steel reinforcement area Step 16. Calculation of the tensile strength of concrete Step 17. Calculation of the cracking bending moment Step 18. Calculation of the unfactored applied bending moments Step 19. Calculation of the elastic modulus of concrete Step 20. Determining the distance n is the modular ratio of concrete to steel, and Step 21. Calculation of the moment of inertia Step 22. Calculation of the effective moment of inertia Step 23. Calculation of the short-term deflections Step 24. Calculation of the total long-term deflection Step 25. Checking that Step 26. Check the punching shear stresses, where this shall be applied for flat slabs only because the presence of beams eliminates the risk of punching shear failure. The check starts with determining the effective depth Step 27. For each slab–column connection, calculation of the critical shear perimeter Step 28. Calculation of the applied punching shear load Step 29. Calculation of the applied punching shear stress Step 30. Calculation of the nominal concrete punching shear strength Step 31. Checking that In the current study, the beams existed only in the solid slab structural floor system, and these were classified into four groups: interior beams in the long direction, interior beams in the short direction, edge beams in the long direction, and edge beams in the short direction. Using a conservative approach, all cross-sections of beams were designed as rectangular sections. Step 1. Determining the preliminary beam height b represents the beam under consideration and Step 2. Determining the preliminary beam width Step 3. Checking that the span-to-depth ratio Step 4. Checking the side buckling for each beam. This can be achieved when the span is less than or equal to the two values Step 5. Calculation of the uniform load applied on each beam Step 6. Calculation of the applied bending moment Step 7. Calculation of the maximum permissible bending moment Step 8. Checking that Step 9. Calculation of the required steel reinforcement area Step 10. Calculation of the minimum and maximum permitted areas of steel reinforcement Step 11. Determining the beam bar diameter Step 12. Calculation of the chosen steel reinforcement area Step 13. Checking that Step14. Determining the shrinkage steel reinforcement area Step15. Determining the top steel reinforcement area Step 16. Calculation of the cracking bending moment Step 17. Calculation of the unfactored applied bending moments Step 18. Determining the distance Step 19. Calculation of the cracked moment of inertia Step 20. Calculation of the effective moment of inertia Step 21. Calculation of the short-term deflections Step 22. Calculation of the long-term deflection Step 23. Checking that Step 24. Calculation of the applied shear load Step 25. Calculation of the applied shear stress Step 26. Calculation of the maximum shear strength Step 27. Checking that Step 28. Calculation of the concrete nominal shear strengths Step 29. Determining the shear stress Step 30. Determining the number of branches Step 31. Determining the spacing Step 32. Checking that According to ECP 203-18, the columns should be designed to resist the axial loads and bending moments. In the current study, the columns were classified into four groups based on their locations: interior columns, edge columns in the x-direction, edge columns in the y-direction, and corner columns. For simplification, each group had a square cross-section. Three steel reinforcement arrangements were utilized to satisfy the design provisions . Each arStep 1. Calculation of the concrete cross-sectional area Step 2. Calculation of the axial design load N is the number of stories, H is the typical story height.Step 3. Determining the steel arrangement of each column. The spacing Step 4. Determining the bar diameter Step 5. Calculation of the chosen vertical steel reinforcement area Step 6. Checking that Step 7. Determining the number of lateral ties Step 8. Calculation of the volume of steel lateral ties Step 9. Checking that Step 10. Calculation of the maximum axial load Step 11. Checking that the axial design load Step 12. For flat slabs only, calculation of the design bending moment Step 13. For flat slabs only, constructing an interaction diagram for each column to check its safety. In this diagram, five points  were used to represent the failure envelope, i.e., the boundaries of the diagram . The axial load Point 4 represents the pure bending failure mode. The bending moment Point 5 represents the pure axial tension failure. The axial load Step 14. For flat slabs only, checking the adequacy of each column. This step can be achieved by ensuring that the axial load The total cost of a construction project consists of a set of direct costs and indirect costs. The direct costs include materials and labor costs, while the indirect costs include accounting services, administration, and site overhead. The indirect costs are often independent of the design parameters. Thus, the current study considers the direct costs of the skeleton structure of the RC building. Here, the costs of concrete, steel reinforcement, formwork, and labor of floors and columns are considered.3) for 17 months before increasing to 46 USD/m3 in December 2021. The unit price In practice, the concrete cost is calculated by multiplying the concrete volume The design variables of the optimization problem are defined in x is the vector of design variables; I, J, and K are the number of strength constraints regarding slabs, beams, and columns, respectively; L, M, and O are the number of serviceability constraints regarding slabs, beams, and columns, respectively; x; and Z is the number of design variables. The strength and serviceability criteria were illustrated in The general formulation of the design optimization problem can be expressed asThe mathematical model was built using Microsoft Excel 2016 spreadsheets. The model was fully programmed using Visual Basic for Applications (VBA) embedded within Microsoft Excel. Repetitive tasks, such as running the solver tool and constructing tables, were also programmed using VBA. In the current study, each structural floor system had its spreadsheet comprising all the data. This data included the calculations regarding structural analysis; design steps of structural elements; and the construction costs of concrete, steel reinforcement, and formwork and labor.The evolutionary method was utilized by the solver tool available in Microsoft Excel to perform the optimization for two reasons. First, it uses a variety of algorithms, along with local search methods. It relies on controlled sampling combined with deterministic methods to explore the search space efficiently. Second, it can handle non-smooth and discontinuous functions . The evoTwo benchmark examples with rectangular layouts were optimized . In the A four-story building with a rectangular layout and a 3.3 m typical story height was considered. The total lengths of the building in the x- and y-directions were 30 m and 25 m, respectively. In case 1, the concrete grade and column spacing in the long and short directions were constant  and deflections of structural elements. Accordingly, smaller In both cases, SS was the cheapest and FSDP was the most expensive structural floor system. The slabs of FSDP and FS utilized more steel reinforcement than those of SS slabs to satisfy the shrinkage provisions imposed, as Enhancing the slabs with drop panels reduced the punching stresses at the slab–column connections. Despite the reduction in punching stresses in FSDP compared to FS, In case 1, SS was 9.7% and 5.5% cheaper than FSDP and FS, respectively, and FS was 4.5% cheaper than FSDP. In case 2, SS was 5.9% cheaper than FSDP and 2.5% cheaper than FSDP, and FS was 3.5% cheaper than FSDP.b et al.  reportedb et al.  used difb et al.  and Harrb et al.  in LondoA ten-story building with a rectangular layout and a 3 m typical story height was considered. The total lengths of the building in the x- and y-directions were 35 m and 40 m, respectively. The design variables were all the parameters defined in n et al. .The design variables of the best run of each structural floor system are presented in The concrete dimensions of SS columns were smaller than those of FSDP and FS. This can be explained in terms of the lower axial loads and lack of punching shear stresses and bending moments at the slab–column connections of SS. At lower story levels, the concrete dimensions of the FSDP columns were larger than those of FS because the chosen For all structural floor systems, the optimal concrete dimensions of columns decreased at higher story levels in proportion to the reduced axial loads. However, although the axial loads applied on columns decrease at higher story levels, it can be observed that the concrete dimensions of FS columns did not decrease at stories 9–10. The lower concrete dimensions of FS columns could not resist the punching stresses.2, 26.52 USD/m2, and 25.57 USD/m2, respectively. Hence, SS was 4.9% and 1.6% cheaper than FSDP and FS, respectively, and FS was 3.4% cheaper than FSDP.In this study, a design optimization model was developed to minimize the construction costs of materials and labor in RC buildings. The optimization model was built using the evolutionary algorithm provided by the Microsoft Excel solver tool. Three structural floor systems were considered: SS, FSDP, and FS. The design constraints were based on the design provisions of ECP 203-18 to ensure the safety of each floor system. Discrete values of design variables were utilized per construction industry requirements to account for the practical considerations.Two benchmark examples were considered to investigate the effects of the design variables on the optimal results of each structural floor system. The results revealed that solid slab buildings produced the most cost savings among the three systems.The construction costs could be significantly reduced by considering the concrete compressive strength and the column spacings as design variables. The optimizer tended to reduce the column spacings to minimize the straining actions of the structural elements and, consequently, achieve economical concrete dimensions and steel reinforcement.Low concrete grades are sufficient for low-rise residential buildings with small column spacings to resist the low stresses applied on floors and columns. As the number of stories increases, the tendency toward selecting a higher concrete grade increases to reduce the concrete dimensions of columns. The cost of columns decreased significantly with reducing the concrete dimensions in the higher story levels. In the case of FS, the cost of columns was less likely to decrease in higher story levels to resist the punching shear stresses. The cost of floors constituted the major part of the construction cost concerning the structural elements.The optimal distribution of construction materials can vary based on the considered unit prices. In the current study, steel reinforcement constituted about 50% of the construction cost due to the high unit price of steel reinforcement in Egypt.The current study revealed the possibilities of determining an economical structural floor system, concrete grade, concrete dimensions, and steel reinforcement of RC buildings by considering the integration of structural components. The contribution of the concrete grade and column spacing in reducing the construction costs was discussed. The presented optimization method could be applied to RC buildings subjected to seismic and wind loads in future work by considering the additional load cases provided by the design code. Thus, the effects of the additional design constraints on the optimal construction costs could be examined. The input data, design calculations, and unit costs of materials and labor could be adjusted to fulfill the restrictions of any design code or consider different structural floor systems.


This study investigates the strength and permeability properties of pervious concrete-containing coal bottom ash (CBA) aggregates. Two pervious concrete mixtures were fabricated with different aggregate size distributions. One mixture contained CBA aggregates with a single-type distribution and the other mixture contained CBA aggregates with a hybrid-type distribution. The test parameters of the CBA pervious concrete included the water/cement (W/C) ratio and compaction level to investigate their effects on the properties. W/C ratios of 0.25, 0.30, and 0.35 were considered for the mixture, and compaction levels of 0.5, 1.5, and 3.0 MPa were applied to fabricate the pervious specimen. The increase in the W/C ratio reduced the strength by approximately 20% to 30% of the CBA pervious concrete. The increase in the compaction level reduced the permeability by approximately four to five times but significantly increased the strength of the CBA pervious concrete. The test results indicate that the use of single-type CBA or hybrid CBA aggregates with different size distributions affected the properties of the pervious concrete. The strength of specimens, including hybrid CBA aggregates, was 30% to 45% greater than that of the specimens containing single-type CBA aggregates. Meanwhile, the use of hybrid CBA aggregates reduced the permeability of the CBA pervious concrete by approximately 20% to 35%. Finally, relationships between the strength properties, permeability characteristics and total void ratios of the CBA pervious concrete specimens are suggested based on the test results. The demand for electricity has been increasing over time, which is motivating the development of thermal power plants. According to a study by Abbas et al. , the amoFor pervious concrete, coarse aggregates and cement paste act as the skeleton; thus, in the usage of coarse aggregates, the type and size might directly affect the properties of the concrete. In a study by Ćosić et al. , it was Kováč and Sičáková  investigThe workability of pervious concrete is lower than that of normal concrete due to the concrete mixture containing coarse aggregate and cement paste. The lack of fine aggregates reduces the workability of pervious concrete, potentially decreasing the adhesion between the coarse aggregates and the cement paste. Therefore, precompaction is necessary when casting pervious concrete. It has been reported that pervious concrete mixtures under different compaction levels show different properties .However, most previous studies have focused on analyzing the strength and permeability of pervious concrete containing only natural aggregates. There are few studies on the strength and permeability of pervious concrete-containing CBA aggregates.Therefore, this study investigates the permeability and strength properties of CBA pervious concrete, including the compressive, splitting, and flexural tensile strengths. The effects of the size distributions of CBA aggregates, W/C ratios, and compaction levels on the properties of CBA pervious concrete are evaluated. Finally, the relationships between the strength, permeability, and total void ratio are presented to obtain prediction equations for the strength and permeability of CBA pervious concrete.The single and hybrid CBAs used in the mixtures were provided by a thermal power plant company in Yeongheung, Korea. According to KS F 2504 , density3 and 3670 cm2/g, respectively.Ordinary Portland cement (OPC) type I, achieving 51 MPa in compressive strength after 28 days, was used for the mixtures. The cement was supplied by the Ssangyong C & E Company . The OPC had a density and specific surface area of 3.13 g/cmTwo series of mixtures, as shown in The CBA aggregates were prepared under SSD conditions before they were mixed in concrete because of their high-water absorption capacities. Finally, to improve the adhesion between CBA aggregates, a cohesive agent was used in the mixtures. The cohesive agent was a viscosity-modifying admixture, including water-soluble polymers that improved the viscosity of the mixing water. In addition, these water-soluble polymers in cohesive agents retain cement constituents in suspension, so the adhesion between CBA aggregates was increased.Since the concrete had not yet hardened in the fresh stage after mixing, the cohesive strength between the cement paste and the aggregates was weak. This cohesive strength could be improved by applying a precompaction load. However, excessive compaction could result in segregated CBA aggregates in fresh concrete. Hence, the compaction load was limited, and three levels of compaction  were considered. The compacted CBA pervious specimens are shown in The material properties, including the total void ratio, permeability, and strength, of the CBA pervious concrete were examined after the concrete specimens were cured in water at 24 ± 2 °C for 28 days.T (%) is the total void ratio, dW (g) is the mass of the CBA pervious concrete in the dry state, wW (g) is the mass of the CBA pervious concrete weighed in water, wρ (g/cm3) is the density of water, and cV (cm3) is the cylindrical concrete specimen volume.The total void ratio of the CBA pervious specimens was calculated as follows:Tcoef (mm/s) is the coefficient of water permeability, L (mm) is the height of specimen, h (mm) is the difference in water head between the steel cylinder and steel box, Q (mm3) is the volume of water in the measuring cylinder, A (mm2) is the cross-section area of the specimen, and t1 and t2 (s) are the initial and final times of the flowing water from the side arm outlet of the steel box. The height of the water pressure through the sample or the constant water head difference between the steel cylinder and steel box (h) was estimated from the water head of the bottom of the side arm outlet in the water box to the water head of the bottom of the side arm outlet in the water cylinder.The compressive strength of the CBA pervious concrete was estimated according to the European standard EN 12390-3:2019 . For theThe test results of the total void ratio of CBA pervious concrete at various W/C ratios are shown in The test results reveal that the total void ratios of both the single-type and hybrid CBA aggregate mixture series increased as the W/C ratio increased. For the mixture series containing single-type CBA aggregates (S mixture series), an increase in the total void ratio was observed with increasing W/C ratios. Specifically, for the S-C0.5 mixture specimens, the total void ratio increased by 3.99% and 7.65% as the W/C ratio increased from 0.25 to 0.30 and 0.35, respectively. Similarly, the total void ratios of the S-W25-C1.5, S-W30-C1.5, and S-W35-C1.5 specimens were 27.6%, 29.5%, and 33.4%, respectively, at each W/C ratio. For the S-C3.0 mixture series, the total void ratio of the S-W35-C3.0 specimen reached its greatest value of 27.3%, while those of the S-W25-C3.0 and S-W30-C3.0 specimens were 23.8% and 25.3%, respectively.For the mixture series containing hybrid CBA aggregates (H mixture series), the value of the total void ratio of the H-C0.5 series specimens was slightly increased by increasing the W/C ratio from 0.25 to 0.35. An increasing tendency in the total void ratio was observed in the H-C1.5 series specimens. The total void ratio of the H-W25-C1.5 specimen was 25.0%, while those of the H-W30-C1.5 and H-W35-C1.5 specimens were 26.8% and 29.0%, respectively. W/C ratios of 0.30 and 0.35 led to increases in the total void ratios of the H-C3.0 series specimens by 8.88% and 20.62%, respectively.According to previous studies ,26,27,28This figure also presents the effects of the compaction levels on the total void ratios of CBA pervious concrete specimens. The total void ratio of the S-W25-C3.0 specimen with a 0.25 W/C ratio was 29.79% and 13.77% lower than that of the S-W25-C0.5 and S-W25-C1.5 specimens, respectively. The S-W30-C3.0 specimen exhibited the lowest total void ratio of 25.3%, while those of the S-W30-C0.5 and S-W30-C1.5 specimens were 35.2% and 29.5%, respectively. Similarly, the total void ratio of the S-W35 mixture series decreased from 36.5% to 27.3% as the compaction levels increased from 0.5 to 3.0 MPa.For the concrete specimens containing hybrid CBA aggregates, the total void ratio of the H-W25 series was reduced by 18.28% and 37.05% at compaction levels of 1.5 and 3.0 MPa, respectively. Similarly, the H-W35-C3.0 specimen showed the lowest total void ratio of 23.2%, while those of the H-W35-C0.5 and H-W35-C1.5 specimens were 31.9% and 29.0%, respectively.Applying compaction to CBA pervious concrete caused the concrete to become denser since the distances between aggregates decreased, and thus the cement paste was thicker  in the hMoreover, the total void ratio of the pervious concrete with single-type CBA aggregates was higher than that of the pervious concrete with hybrid CBA aggregates. To prove this claim, a scanning electron microscopy (SEM) analysis was conducted. Two cylindrical specimens of each mixture with single-type and hybrid CBA aggregates were cut into halves. Then, as presented in In addition, the SEM results implied that the compaction had a different influence on the voids at each position in the pervious concrete specimen. This finding shows that the voids in CBA pervious concrete or the distances between the aggregate particles decreased from the top to the middle position of the specimens in both series. This phenomenon implied that the cohesive strength between the CBA aggregates was enhanced by compacting the aggregates. Nevertheless, when the compaction energy was released, the compacted particles expanded to obtain the initial stage. Therefore, the microstructure at the middle position was denser than that at the top position.A slight increasing tendency in permeability was observed in the H mixture series. For the H-C0.5 mixture series, the permeability coefficient increased by 11.63% and 16.33% as the W/C ratio increased from 0.25 to 0.30 and 0.35, respectively. For the H-C1.5 mixture series, the H-W25-C1.5, H-W30-C1.5, and H-W35-C1.5 specimens were 0.80, 1.16, and 1.29 mm/s at each W/C ratio, respectively. As in the case of the S-C3.0 series, the permeability of the H-C3.0 mixture series was constant at various W/C ratios.The test results in this study show that the permeability of the CBA pervious concrete slightly increased with increasing W/C ratio. In particular, when the compaction level was 3.0 MPa, the permeability of the concrete was not affected by W/C ratio. Cui et al.  reportedAs shown in For the H mixture series, a similar decreasing tendency in the permeability affected by the compaction level was recognized. The permeability of the S mixture series significantly decreased by approximately 95% at various W/C ratios with increasing compaction level. In particular, when a compaction level of 3.0 MPa was applied to the specimens, the H mixture series almost lost its permeability. Therefore, low permeability coefficients of nearly 0 mm/s of the H mixture series were obtained at various W/C ratios.In addition, the test results indicate that the permeability coefficients of the S mixture series were greater than those of the H mixture series at various W/C ratios. As shown in The compressive strength of CBA pervious concrete is shown in The strength at the interfacial transition zone (ITZ) between CBA aggregates and cement paste played an important role in the strength of the concrete. An increase in the W/C ratio could generate micropores around the ITZ and finally reduce the strength of the CBA pervious concrete. In addition, according to previous studies ,28,32, tThe effect of the compaction level on the compressive strength of CBA pervious concrete can be found in this figure. The test results show that the compaction level improved the compressive strengths of both mixture series.For the pervious concrete specimens with hybrid types of CBA aggregates, the influence of the compaction level on the compressive strength of the pervious concrete specimens was considerable. As an example, the compressive strengths of concrete specimens with compactions of 1.5 (H-W25-C1.5) and 3.0 MPa (H-W25-C3.0) were 34.39% and 65.61% greater than those of the concrete specimens with a compaction of 0.5 MPa (H-W25-C0.5) at a W/C ratio of 0.25.It was assumed that the cement paste thickness of the CBA pervious concrete was improved by increasing the compaction level. Moreover, the porosity of the CBA pervious concrete decreased, which improved its compressive strength. Sahdeo et al.  recognizThe compressive strength of the pervious concrete with hybrid CBA aggregates was greater than that of the pervious concrete with single-type CBA aggregates at various W/C ratios. The denser microstructure of pervious concrete with hybrid CBA aggregates resulted in a higher compressive strength than that of pervious concrete with a single type of CBA aggregate. The same tendency was reported in a study by Yang et al. . This stThe splitting tensile strength of CBA pervious concrete is shown in The test results show that the splitting tensile strength of the CBA pervious concrete was improved by applying compaction to pervious CBA concrete. Specifically, for concrete specimens with hybrid CBA aggregates at a W/C ratio of 0.25, the splitting tensile strengths of the H-W25-C0.5, H-W25-C1.5, and H-W25-C3.0 specimens were 0.86, 0.94, and 1.05 MPa, respectively. The splitting tensile strength of concrete specimens with hybrid CBA aggregates at a W/C ratio of 0.30 increased from 0.75 to 1.01 MPa with increasing the compaction level from 0.5 to 3.0 MPa.A similar tendency of splitting tensile strength in compacted pervious concrete according to the compaction levels was observed in the study by Bonicelli et al. . This stOverall, the flexural tensile strength of CBA pervious concrete decreased as the W/C ratio increased. For the pervious concrete with single-type CBA aggregates at a compaction level of 0.5 MPa (S-C0.5 series), the flexural tensile strength decreased slightly with increasing W/C ratio. Specifically, the flexural tensile strength of the concrete specimen with a single type of CBA aggregate at a compaction level of 0.5 MPa slightly decreased from 0.94 to 0.82 MPa as the W/C ratio increased from 0.25 to 0.35. Costa et al.  investigHowever, the concrete specimen with a single type of CBA aggregate at compaction levels of 1.5 and 3.0 MPa (S-C1.5 and S-C3.0 series) represented a significant reduction in the flexural tensile strength. Specifically, the flexural tensile strength of the concrete specimen with a single type of CBA aggregate at a compaction level of 1.5 MPa decreased by 20.11% and 41.53% as the W/C ratio increased from 0.25 to 0.30 and 0.35, respectively. Therefore, the test results in this study imply that the compaction level of the CBA pervious concrete could be considered when the extent of the effect of the W/C ratio on the flexural tensile strength in the concrete was evaluated.Regarding the compaction effect, the increase in compaction significantly improved the flexural tensile strength in both mixture series. As shown in this figure, a significant improvement in the flexural tensile strength was observed in pervious concrete with hybrid CBA aggregates due to the compaction levels. The flexural tensile strength of the H-W25-C3.0 specimen was 2.2 times and 1.2 times greater than that of the H-W25-C0.5 and H-W25-C1.5 specimens, respectively. At a W/C ratio of 0.30, the H-W30-C3.0 specimen presented the greatest flexural tensile strength of 2.01 MPa, while those of the H-W30-C0.5 and H-W30-C1.5 specimens were 1.10 and 1.96 MPa, respectively. Similarly, the flexural tensile strengths of the H-W35-C0.5, H-W35-C1.5, and H-W35-C3.0 specimens were 1.02, 1.70, 1.79 MPa, respectively.Finally, the test results demonstrate that the flexural tensile strength of the CBA pervious concrete was improved by using the hybrid CBA type. This phenomenon was reported in a study by Ćosić et al. . AccordiThe total void ratio of CBA pervious concrete is an important parameter used to characterize the property of the concrete. Therefore, relationships used to predict the compressive and splitting tensile strength and permeability coefficient of the CBA pervious concrete based on the total void ratio were analyzed.cf′ is the compressive strength (MPa) and ν is the total void ratio (%).The relationship between the compressive strength and the total void ratio of CBA pervious concrete is illustrated in sf is the splitting tensile strength (MPa) and ν is the total void ratio (%).coefP is the permeability coefficient (mm/s) and v is the total void ratio (%).Finally, the relationship between the permeability and total void ratio is illustrated in R2) of the three equations in Equation (3) through (5) were greater than 0.7, which implied that the equations could be used to reasonably predict the compressive and splitting tensile strength and the permeability coefficient of the CBA pervious concrete by using the measurement of the total void ratio.The coefficients of determination (This study investigated the strength and permeability properties in CBA pervious concrete. In addition, the relationships between the strength properties and total void ratio were presented. The following key findings and conclusions can be drawn from the extensive test results and discussion:1. By increasing the W/C ratio, the permeability of the CBA pervious concrete slightly increased. In terms of the effect of the compaction level on the total void ratio, the compaction level significantly reduced the permeability of the CBA pervious concrete. At a compaction level of 3.0 MPa, the CBA pervious concrete almost lost its permeability properties. In addition, the use of the hybrid CBA type slightly reduced the permeability of the CBA pervious concrete.2. The compressive strength of CBA pervious concrete tended to decrease as the W/C ratio increased. The test results revealed that compaction levels had a great effect on the compressive strength of the CBA pervious concrete. In particular, the compaction of the pervious concrete affected the compressive strength of the pervious concrete with the hybrid type of CBA aggregate to a greater degree than that of the pervious concrete with single-type CBA aggregate.3. An increase in the W/C ratio reduced the splitting tensile strength of the CBA pervious concrete. The compaction levels had a significant effect on the splitting tensile strength of CBA pervious concrete. Specifically, the splitting tensile strength of the pervious concrete with hybrid CBA aggregates improved by 22~33%. Finally, the use of hybrid CBA aggregates was more favorable for improving the splitting tensile strength of CBA pervious concrete.4. The flexural tensile strength of the pervious concrete with hybrid CBA aggregates decreased by 26~31% as the W/C ratio increased from 0.25 to 0.35. In addition, the flexural tensile strength of the pervious concrete with single-type CBA aggregates increased by 2.0~2.5 times and that of the pervious concrete with hybrid CBA aggregates increased by 1.7~2.0 times as the compaction of the pervious concrete increased from 0.5 to 3.0 MPa.5. The relationships between the strengths, permeabilities and total void ratios were investigated by regression analyses. Equations from the regression analyses could be reasonably used to predict the strengths and permeabilities of the CBA pervious concrete specimens because the coefficients of determination of the equations were greater than 0.7.


A drug–drug multicomponent crystal consisting of metformin (MET) and dobesilate (DBS) was prospectively connected by solvent cooling and evaporating co-crystallization using the multicomponent crystal strategy, not only to optimize the physicochemical properties of single drugs, but also to play a role in the cooperative effect of DBS with the potential vascular protective effects of MET against diabetic retinopathy (DR). The crystal structure analysis demonstrated that MET and DBS were coupled in a 3D supramolecular structure connected by hydrogen-bonding interactions with a molar ratio of 1:1. Almost all hydrogen bond donors and receptors of MET and DBS participated in the bonding, which hindered the combination of remaining potential hydrogen bond sites and water molecules, resulting in a lower hygroscopicity property than MET alone. The latest tenth edition of the Diabetes Atlas of the International Diabetes Federation showed, that in 2021, the global diabetes adult patients reached 537 million; every 5 s, one person died of diabetes or related complications .Diabetic retinopathy (DR), a leading cause of irreversible blindness in working-aged people, is an exclusive microvascular complication of diabetes . EpidemiThe golden time against the microcirculatory dysfunction is to ameliorate diabetic microcirculation as early as possible in the process of disease, and many trials approve the calcium salt, Dobesilate DBS, a, as a pMetformin MET, b, the moExcept for the improvement of visual acuity and fundus symptoms, the reduced incidence of severity progression of DR, such as macular edema, is reflected in clinical research of treatment metformin with calcium dobesilate , which iThe drug–drug multicomponent crystal is a definition of multicomponent crystals, particularly multicomponent crystals containing combined drugs, which show great potential in pharmaceutical preparations ,17, and Good properties may result from the establishment of intermolecular interactions between components, the drug–drug multicomponent crystal that is different from single drug crystals carries out molecular recognition and assembly through noncovalent bonds including hydrogen bonds, van der Waals forces, pi–pi stacking, and electrostatic forces without destroying covalent bonds . Among t1H NMR spectroscopy analysis further clarified the molecular composition. Single crystal X-ray diffraction (SCXRD) systematically defined the internal bonding law and the structural difference between the new compound and previously determined structures of MET and DBS salts, the experimental powder X-ray diffraction (PXRD) matched the simulated pattern from single crystal, and the relationship between hydrogen-bonding interactions and hygroscopicity property was conducted by Hirshfeld surface and Dynamic vapor sorption (DVS).The drug–drug multicomponent crystal of MET–DBS was prospectively yielded for the first time based on the above two ideas of drug combinations and multicomponent crystal technology. The participation of hydrogen bonds was preliminarily surveyed by Fourier-transform infrared spectroscopy (FT-IR), and According to the characteristic and fingerprint region of the FI-IR spectrum, we identified and distinguished the characteristic functional groups of the drug–drug multicomponent crystal of MET–DBS and two single drugs, and the differences in absorption peaks between them were found and analyzed, indicating the generation of a new compound, as shown in −1) was shifted from 1625 cm−1 in MET·HCl to 1640 cm−1 in MET–DBS, which moved slightly to a higher frequency. At the same time, the stretching vibration frequency of N-H in MET·HCl was transferred from 3371, 3294, 3173 cm−1 to 3443, 3350, 3203 cm−1 in MET–DBS, which may be due to the influence of the charge assisted hydrogen bond in MET·HCl, resulting in its vibration frequency being lower than that in MET–DBS.The frequency range of the C=N stretching vibration , 9.80 , and 8.80 , respectively, representing six hydrogen atoms of methyl groups in MET·HCl, and two hydrogen atoms of hydroxyl groups in DBS·K.2 groups in the guanidine group of MET·HCl, two hydrogen atoms in the benzene ring of DBS·K, and another hydrogen atom in the benzene ring which was located at 6.87 . The other two hydrogen atoms of the amino group with relatively high chemical shifts in MET·HCl were transferred to 7.18  in the drug–drug multicomponent crystal.The six hydrogen atoms in the 6.64–6.50 multiple absorption peaks  were attributed to two NH1H NMR Spectroscopy Analysis in Materials and Methods.Therefore, they were all hydrogen atoms in the two single drug molecular structures in MET–DBS, the deviation of the chemical shift was not obvious compared with the single drugs, and it was proven that the molar ratio between MET and DBS in the drug–drug multicomponent crystal was 1:1, as shown in 3, which was suitable for SCXRD analysis. The detailed crystallographic data and structural refinement were given in 1H NMR spectra. The hydrogen atom in the sulfonic acid group of DBS was transferred to the imino group of MET, which further proved that it was a salt-type multicomponent crystal. The pKa difference between bases and acids, if ΔpKa > 3, is usually used as an indicator of salt formation [The salts of MET and DBS were used as crystalline materials, and the anion exchange method was expected to prepare phase-pure MET–DBS drug–drug multicomponent crystals. After cooling and evaporating crystallization, the yellow block-shaped crystals appeared after about 2 weeks, and the crystal size chosen for the diffraction test was 0.17 × 0.12 × 0.1 mmormation . The pKaormation  and −2.8ormation , respectFrom the RXRD patterns in As shown in In the one-dimensional chain along the c-axis drawn in Based on the one-dimensional chain structure, O1 in the sulfonyl group of one DBS anion and N4 in the phenolic hydroxyl group of one MET cation interacted with another DBS anion, respectively, to form O4-H4···O1 and N4-H4A···O4 hydrogen bonds with O4···O1 and N4···O4 angles of 172.3° and 140(3)° in The two-dimensional surface formed a further three-dimensional stacking architecture structure through the 2)2 groups of MET in the two crystal forms were almost in the opposite direction due to the different dihedral angles, but the single crystal of MET–DBS existed in the same conformation as other drug–drug multicomponent crystals containing MET cations as reported in CCDC [To better compare the differences in the crystal structures of the multicomponent and single drug molecules, the single crystal of MET·HCl (CCDC no. 2170425) was obtained experimentally, and the diethylammonium salt of DBS  was foun in CCDC . AdditioTo further explore the molecular internal environment and intermolecular interaction of the drug–drug multicomponent crystal, both qualitatively and quantitatively, the Hirshfeld surface analysis and calculation of MET–DBS were carried out by using crystal Explorer 17.5 software . Taking In the Hirshfeld surface map, the dark red spots signified the strongest intermolecular interactions, and the MET established a relationship with DBS via N-H···O as the main hydrogen bond force, including O-H···O bonds between MET. The relatively weak interactions on the surface, represented by white and blue areas, were gradually weaker than van der Waals forces. By analyzing the unique 2D fingerprint spectrum, we could see that the main intermolecular interactions in the formation of MET–DBS were H···O and H···H interactions. The proportion of H···H, C···H, and H···N in the whole was 48.5%, 10.7%, and 8.1%; H···H accounted for a half of the whole, suggesting that the molecular surface was mainly composed of a series of H atoms.A large number of H atoms on the molecular surface promoted the contribution of the strong H···O bond, which was nearly 1/3, which made it the main noncovalent driving force for drug–drug supramolecular structure formation, presented as one spike in The hydrogen-bonding interactions also existed in MET·HCl, and the main hydrogen bond donors and acceptors of MET in the structure of MET·HCl, or MET–DBS, all came from the N atoms, so the related interactions were counted, such as the N···H and Cl···H interactions in MET·HCl, and the N···H and O···H interactions in MET–DBS. In DVS was a dynamic analysis used to study the weight change of drugs caused by water absorption with an increase in humidity. In Potassium 2,5-dihydroxybenzenesulfonate (DBS·K) was purchased from Bide Pharmatech Ltd. . Metformin hydrochloride (MET·HCl) was received from Adamas Reagent Company . The solvent water was accessed from Milli-Q Advantage A10 Water Purifier and all chemicals were used without further purification.MET·HCl  and DBS·K  were weighed into a 50 mL single mouth eggplant flask, adding 10 mL of pure water, drop by drop, and stirring until dissolved. Under the conditions of an ambient temperature, we continued stirring for 3 h, vacuum filtration occurred to remove insoluble impurities, the filtrate was transferred to a 10 mL round bottom centrifuge tube uncovered and placed in a 4 °C refrigerator undisturbed, cooling and evaporating occurred slowly for crystallization, then yellow block-shaped crystals appeared after about 2 weeks, which were suitable for SCXRD analysis and further characterization studies.−1 with 10 accumulative scans under ambient temperature.Each 1–2 mg of powder sample was ground with dried KBr powder and pressed into a tablet. The measurements were carried out using a Nicolet FT-IR spectrometer  in a scanning range of 4000–500 cm1H NMR spectra were measured with a Bruker AVANCE III NMR spectrometer  at 600 MHz with DMSO-d6 as the NMR solvent. The 1H NMR data for the drug–drug multicomponent crystal of MET–DBS, MET·HCl, and DBS·K respectively was:The 1H NMR  δ 9.80 , 8.80 , 7.18 , 6.87 , 6.64–6.50 , 2.92 .1H NMR  δ 7.21 , 6.78 , 2.92 .1H NMR  δ 9.80 , 8.80 , 6.89 , 6.60 .SCXRD data were measured on a Bruker SMART CCD diffractometer  with Cu-Kα radiation (λ = 1.54184 Å) at 293 K. The structure was analyzed by the Olex2  1.2 progA Bruker D8 advanced X-ray diffractometer  was utilized to collect powder X-ray diffraction data with Cu-Kα radiation (λ = 1.5406 Å). 40 kV and 40 mA were the voltage and current, respectively. At an ambient temperature and a scan speed of 5°/min, data for each sample were captured in the 2θ range of 5–50° (step size 0.01°).e and di were defined, respectively: de, the distance from the point of crystal surface to the nearest atomic nucleus outside the surface; di, the distance from the point of crystal surface to the nearest nucleus inside the surface. Each point on the 2D fingerprint plots was formed by the discrete intervals composed of di and de (0.01 × 0.01 Å), with colors ranging from blue to green and red.The 3D Hirshfeld surface of molecules and 2D fingerprint plots were calculated and produced by using the program Crystal Explorer 17.5 software. The parameter of dThe vapor sorption and desorption profiles of the materials were determined at 25 °C using an Aquadyne DVS analyzer . Each sample was dried under dry nitrogen purge until a consistent weight was received. Then, the samples of MET·HCl (81.46 mg) and MET–DBS (82.81 mg) were investigated simultaneously at each step size of 5% RH, following the sorption and desorption cycle of 2%–95%–2%. The relative humanity (RH) was shifted to the next step if the weight change within 10 min was less than 0.02%, with an 8 hour maximum equilibrium time.The drug–drug multicomponent crystal consisting of MET and DBS with 1:1 stoichiometry was the first generated in this paper. There was a complex hydrogen-bonding network between MET and DBS, which was mainly connected by N-H···O bonds, nearly 1/3 of the driving force was contributed by the H···O bond, as visualized by Hirshfeld surface analysis. The hydrogen-bonding interactions were not only formed between MET and DBS in the Almost all hydrogen bond donors and receptors in MET and DBS were involved in bonding, which significantly reduced the number of sites in contact with water molecules in the air, thus reducing the hygroscopicity of MET. This structural change resulted in a transformation in its property, showing the great potential of drug–drug multicomponent crystals in the pharmaceutical field. It was worthy of in-depth research to contribute to the development of optimal new medications for diabetic complications.


During the last 20 years, France has taken important steps to tackle antibiotic resistance. These include national awareness campaigns for the general public, and supporting changes in terms of antibiotic prescription for healthcare practitioners. To prepare the upcoming 2022/2023 campaign, we conducted two surveys to assess (1) the general public’s knowledge, attitudes and behaviours regarding antibiotics and (2) the perceptions and practices of general practitioners (GPs).Two quantitative telephone surveys were conducted using the same methodology as that used in 2010 by the National Health Insurance Authority. The first was conducted in 2019 in a national representative quota sample of 1204 persons aged over 15 years living in metropolitan France, including an over-sample of 332 parents of children aged six years or under. The second was conducted in 2020 in a national representative sample of 388 GPs.Twenty-seven percent of respondents reported taking antibiotics during the previous year. Sixty-five percent of GPs declared prescribing fewer antibiotics during the previous five years. However, 33% of GPs reported they often had patients who put high pressure to get antibiotics. The pressure from elderly patients, especially those with comorbidities was notable. Three percent of respondent patients reported putting often pressure on their GP. All respondents expressed total trust in their GP irrespective of whether s/he had prescribed them antibiotics. Half knew that antibiotics act only on bacteria, and 38% said they understood precisely what antibiotic resistance is.Although antibiotic use is decreasing in France, patient pressure on GPs to prescribe antibiotics is very high. GPs are key ambassadors in reducing antibiotic use. Awareness campaigns must target elderly patients in particular.The online version contains supplementary material available at 10.1186/s13756-022-01162-3. Despite an 18% drop in the number of antibiotic prescriptions for non-hospitalised patients between 2009 and 2019 –5. The tLes antibiotiques, c’est pas automatique” (“antibiotics are not automatic”), ran from 2002 to 2005, and was associated with a 26.5% decrease in total antibiotic use [With regard to public awareness, campaigns to date have been organised by the Ministry of Health and the National Health Insurance Authority. The first such campaign, called “otic use . The twoFrench health authorities have supported changes for antibiotic prescription by healthcare professionals via: (1) regular awareness raising for general practitioners (GPs) through visits from Health Insurance representatives , (2) perSanté publique France, the French national public health agency, is responsible for monitoring antibiotic use and resistance in the country. It will organise future nationwide awareness campaigns. To establish the upcoming campaign, we needed to assess the knowledge and practices of the French population and their GPs regarding antibiotics.We organized two quantitative surveys in 2019 and 2020, using the same methodology as that used in 2010 when the National Health Insurance ran related surveys. The same Institute, BVA group, collected data.The first survey was conducted in October 2019 and comprised a telephone survey of a representative sample of the general public aged over 15 years, residing in metropolitan France. Samples were constructed using quotas based on the following variables: gender, age, social category of the household reference person, region and urban area type. Quotas came from the 2015 general population census data. A total of 1,204 persons were interviewed, including an over-sample of 332 parents of children aged six years or under , applications, websites), and their perception of previous antibiotic awareness campaigns.The questions in the general public and GP surveys were identical to those in the 2010 surveys. However, the 2019 and 2020 surveys also contained extra items on new tools and sources, such as the use of non-prescription pads and smartphone applications. Questions were a yes or no answers or with possible answers being: ‘Yes, often’/‘Yes, sometimes’/’Yes, rarely’/’No, never’/’Don’t know’ or ‘Totally agree’/’Mostly agree’/‘Mostly disagree’/’Totally disagree’.A descriptive analysis using Student’s t-test was performed for surveys using socio-demographic variables. As we did not have the 2010 surveys database, statistical comparisons were not systematically done and we only mentioned in the discussion those provided by BVA or those we were able to calculate.Twenty-seven percent of the study population reported receiving antibiotics for themselves during the previous twelve months. Just over half (54%) of those who had a child aged six years or under reported a prescription for antibiotics for their child(ren) during the previous year.With regard to the GP survey, 65% declared they had reduced their prescriptions for antibiotics over the previous five years. According to the disease, it varied from 51% reduction for angina to 34% for acute otitis. Only 2% reported an increase in antibiotic prescription , and because they had already had a consultation for the illness (50%) Fig. .Fig. 4PaIn 2020, GPs reported that people in employment were the category most frequently requesting antibiotics (32%), followed by the elderly with multiple pathologies (24%) Fig. .Fig. 5PaWhen a patient insisted, only 2% GPs reported giving in and prescribing antibiotics directly even though the antibiotics were not useful.The majority of GPs (64%) declared they did not automatically prescribe antibiotics but advised the patient to contact them again in two or three days if symptoms persisted. Thirty-two percent of participants in the general public survey reported they had experienced this situation.Thirty-four percent of GPs declared using different strategies to delay prescribing antibiotic . Twenty-four percent of participants in the general public survey reported having be faced to this practice.The public expressed a high level of trust in their GP’s diagnosis irrespective of whether s/he prescribed antibiotics (89%) or not 91%). Only 14% of patients thought that non-prescription meant the doctor took their illness lightly  and webDuring the previous 12 months, 9 percent of GPs reported had often come across cases of antibiotic resistance.In 2020, 59% of GPs believed that their patients were well informed about the ineffectiveness of antibiotics against viruses. This proportion dropped to 24% regarding their knowledge about the ineffectiveness of antibiotics for acute bronchitis Fig. .Fig. 7GIn the general public survey, 88% participants felt well informed about the need to strictly comply with medical prescriptions. More specifically, 96% knew that they should not take a double dose of antibiotics if a dose is missed, 88% were aware that leftover antibiotics from a previous treatment should not be reused, and 82% that antibiotic treatment should not be interrupted even when one feels better. Sixty percent had already heard about antibiotic resistance. However, only 38% of all participants and 38% of parents with a child aged six years or under indicated that they knew exactly what it was. Low social economic status workers and the elderly were the least informed.Only half the participants in the general public survey knew that antibiotics only target bacteria Fig. .Fig. 8GeEven if parents of young children have globally a better knowledge, less than half of the respondents in the general public survey could not individuate for which diseases antibiotics are or are not effective Table .Table 2GHalf believed that antibiotics always helped a person to get well quickly and saved time, and 44% believed that antibiotics helped workers to become fit enough to return to work quickly.In most cases, young people aged 15 to 24 years old, people older than 64 years old, and the lowest socio-professional categories were the least well informed. Older people were the sub-population with the most inaccurate beliefs about antibiotics.Eighty-nine percent of GPs thought that public awareness campaigns helped to support their explanations to patients regarding antibiotics, and 87% believed these campaigns increased patient acceptance of their decision not to prescribe them. Seventy-seven percent reported that campaigns helped to reduce the pressure patients put on them to obtain a prescription. Most of the GPs (60%) felt campaigns helped save time during consultations.One in two GPs (55%) reported changing the way they prescribed antibiotics as a result of awareness campaigns. Physicians aged over 60 were particularly likely to feel that campaigns supported their practice (85%), and had changed the way they prescribed (62%).The two surveys we conducted in 2019 and 2020 aimed to assess the general public’s and GPs perceptions about antibiotic use, antibiotic resistance, and the perceived effectiveness of awareness-raising campaigns.Even if it was almost stable for the public (27% versus 31% in 2010), our findings show a decrease over time in the children’s use of antibiotics during the last twelve months: 54% of parents said their child(ren) aged 6 years or under had received an antibiotic, compared to 65% from 2010. During the last five years, 65% of GPs declared having reduced their prescriptions for antibiotics in general. Only 2% stated they prescribe more.This is in line with sources that find a reduction of the use of antibiotics in France , 10, 11.In line with previous findings in the US , the UK Compared to the 2010 survey, where the "often" and "sometimes" responses were mixed, GPs felt greater pressure from patients insisting on a prescription (69% in 2010 vs. 77% in 2020). According to GPs, the percentage of elderly with comorbidities increased among the patients most in demand of antibiotic (13% in 2010 vs 24% in 2020). Among the public, 17% reported they had put some «pressure» on their GP often or sometimes (13% in 2010).However, nearly all the participants in the general public survey (90%) declared that they trusted their GP’s decision irrespective of whether s/he prescribed them antibiotics or not. This finding is very important to reassure GP, and highlights that they are important ambassadors for antibiotic stewardship , 18, 19.Only 2% of physicians report prescribing antibiotics when patients insist. This proportion may be underestimated. Nevertheless, many physicians are adopting strategies to avoid systematic prescribing. Two thirds advised their patients to wait several days without a prescription of antibiotics in case of a suspected viral infection, and a third used delayed prescribing strategies. Less than half (42%) use the non-prescription pad that explains to the patient why he or she will not receive antibiotics. Only 12% of patients seemed to be aware of this tool. Beyond the reporting bias and the perception discrepancy mentioned above, these results show that its use should be developed.The majority of GPs used RST, CRP and digital decision support tools, such as smartphone applications and dedicated websites, were used to a lesser extent. GPs reported that these digital tools facilitated consultations and their communication with patients, especially those requesting explanations and/or insisting that antibiotics be prescribed .Finally, GPs were very favourable of national public awareness campaigns and considered the could help them to reduce antibiotic prescription demands. A high percentage of participants in the general public survey felt they were well informed about antibiotic use and compliance with prescriptions. But despite an improvement, the proportion of people saying they know what is antibioresistance is only 38% in 2019 (29% in 2010) and only 50% of the participant’s knew that antibiotics are only effective against bacteria (40% in 2010).In line with Eurobarometer findings  and receThe two quantitative studies described here complement qualitative studies also conducted in France , 15. TheSelf-report surveys may not reflect real behavior or practices. However (i) panels from which the study samples were drawn are regularly renewed; (ii) recall and social desirability biases were the same for the 2010 and 2019/2020 surveys; (iii) results were in line with antibiotic prescription data and other similar studies. Moreover, GPs perceptions cannot be generalized to all healthcare professionals who prescribe antibiotics.The GPs survey started 2 weeks after the first Covid-19 lockdown. Since the questions were related to the past 12 months, we do not believe that Covid-19 may have had a major impact on the results.Although antibiotic use is decreasing in France, patient pressure on GPs to prescribe antibiotics is very high. The French population still only has partial knowledge of antibiotic resistance and needs to be better informed especially elderly people. GPs are key ambassadors in reducing antibiotic use. A new public information campaign will take in account results of our survey in 2022–2023. It will be preceded by support and information for health professionals.Additional file 1. Fig. S1 General Public Sample Structure. (% Adjusted) and Fig. S2 General Practitioners’ Sample structure


To manage pandemics, like COVID-19, leadership can enable health services to weather the storm. Yet there is limited clarity on how leadership manifested and was discussed in the literature during COVID-19. This can have considerable public health implications given the importance of leadership in the health sector. This article addresses this missed opportunity by examining the literature on leadership during a pandemic. Following a systematic search of nine academic databases in May 2021, 1,747 publications were screened. Following this, a lexical analysis of the results section was conducted, sourced from a corpus of publications across myriad journals. The results found a prevalence of references to “leader” as a sole actor, risking the perpetuation of a view that critical decisions emanate from a singular source. Moreover, “leadership” was a concept disconnected from the fray of frontline workers, patients, and teams. This suggests a strong need for more diverse vocabularies and conceptions that reflect the “messiness” of leadership as it takes shape in relation to the challenges and uncertainties of COVID-19. There is a considerable opportunity to advance scholarship on leadership via further empirical studies that help to clarify different approaches to lead teams and organizations during a pandemic. When the World Health Organization (WHO) declared a public health emergency of global concern on March 11, 2020  within the title and/or abstract of the publication to optimize the relevance of each publication. Alternative terms that potentially denote leadership were purposely absent from the search strategy to optimize coherence—for instance, although the terms, management, administration, supervision, and authority, might be relevant, they are not synonymous with leadership—as such, they did not form part of the search strategy to optimize comparability among the publications that were identified. Publications were included in this review if they: pertained to COVID-19; were published in English; represented an empirical study , rather than a literature review , a conceptual study, a discursive article, a study protocol, an editorial, a commentary, or a book review; were authored; and represented a refereed journal publication. This study purposely focused on empirical studies, irrespective of research design, to clarify patterns in academic discourse on how leadership was portrayed – as such, gray literature and policies were not included in this lexical analysis.A search strategy was deployed in nine academic databases in May 2021 to identify all publications on leadership during COVID-19. Given their relevance and comprehensiveness, the following academic databases were included: APA PsycArticles; APA PsycInfo; Business Source Complete; CINAHL Plus with Full Text; Health Business Elite; Health Source: Nursing/Academic Edition; Medline; Psychology and Behavioral Sciences Collection; and SocINDEX with Full Text. The search strategy encompassed leaden = 1,692) and conferred about those that warranted discussion. Of the 40 publications deemed to be eligible, 4 were inaccessible and were omitted from the analysis—thus, 36 publications were included in this review. The results section from each publication was then sourced and prepared for a lexical analysis—this involved copying and pasting the text (excluding tables and figures) into a single Word file. Focusing solely on the results section of each publication helped to ensure the lexical analysis was not diluted by potentially redundant text .Of the 2,377 publications identified via the aforesaid academic databases, 40 met the aforesaid criteria see . To optiOf the 36 publications, most were published in 2021 (61.1%), rather than 2020 (38.9%), and most presented a study conducted on one continent (86.1%)—chiefly, North America (47.2%). Other continents represented included: Europe (19.4%); Asia (13.9%); Oceania (2.8%); and Africa (2.8%). Several publications reported on a study that was conducted in more than one nation (13.9%). The publications were published in journals pertaining to several different disciplines, including: management (41.7%); healthcare (38.9%); psychology (16.7%); and, to a lesser extent, education (2.8%).To optimize the likelihood of a systematic approach , the lexleadership and COVID—were examined.Leximancer was used in three steps. First, after uploading the Word file into Leximancer, the “discovery” mode was used to, “see what concepts were automatically generated by Leximancer without intervention” . Second,COVID, significant, work, and countries , they were inclined to refer to significant, work, and countries (and the concepts therein):The concept map at 70% theme visibility and the accompanying thematic summary reveal four themes—namely: ries see . These hCOVID-19 efforts. Nursing leaders augmented their work schedules to increase visibility and support .Furthermore, these authors argued that continued references to leadership can unhelpfully reinforce an unsophisticated assumption that it is the panacea for organizational woes:We also, in contrast to most writings on leadership, deliberately use alternative vocabulary to leadership… to address various options… this helps managers and others break away from being trapped in narrow-minded, leadership-infused language and thinking. We strongly warn against the over-use of the term “leadership”… If we look at virtually all leadership and management literatures and listen to the large majority of managers and management educators there is a strong and often naïve belief… that “leaders rule and lead followers.” We need to support alternative vocabularies and mind-sets… Our suggestion [is] to see leadership as just one option and to emphasize both a range of alternatives, and the need to include subordinates in the active work of finding a good combination of alternatives… leadership recipes are attractive and seductive, but [are] seldom… helpful… We have studied many managers creating problems for themselves through a naïve and uncritical belief in seductive leadership ideals .Given the findings from the lexical analysis, the emerging literature on leadership during COVID-19 would benefit from more varied vocabularies and conceptions that reflect the “messiness” of leadership . WithoutDespite the value of the findings presented in this article, four methodological limitations warrant mention. First, the search strategy is unlikely to have identified all relevant articles, given the many potential ways to refer to the key terms . Second, given the sole use of a lexical analysis, a thematic or critical analysis of the publications is likely to yield different findings. Third, given the study period, the lexical analysis was unlikely to include studies that serve to identify the longer-term effects associated with particular leadership approaches. And fourth, the geographical scope of the publications represented in this study directed attention to better-resourced nations. There is therefore no assumption that the findings have relevance to all nations or continents.Notwithstanding the aforesaid limitations, a key strength of this study is the use of a lexical analysis to ascertain patterns in academic discourse on leadership during COVID-19. For three key reasons, using Leximancer can be particularly useful during a global pandemic. First, it can simultaneously make sense of “voluminous and disparate bodies of texts” —this benThe findings from this article have clear implications for scholars. Beyond the oft-cited call for more research, what is particularly needed is research that is empirical. This is because, of the 1,707 publications that were excluded from this study, many were: commentaries; conceptual and rhetorical analyses of the performance of political leaders; personal accounts of COVID-19 experiences; or reflections on the leadership of those on the frontline , 48–53. AD conceived the study design, deployed the search strategy, and developed the Sections titled, Methods and Results. AD and AM designed the study as well as developed and tested the search strategy, reviewed the identified publications, identified those that met the inclusion criteria, as well as extracted and analyzed content from the relevant publications. AM developed the Sections titled, Introduction and Discussion. All authors have agreed to be personally accountable for their contributions and ensure that questions related to the accuracy or integrity of any part of the work, even ones they were not personally involved, are appropriately investigated, resolved, and the resolution documented in the literature, and reviewed and approved the final manuscript.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.