Concretes with the same strength can have various deformability that influences span structures deflection. In addition, a significant factor is the non-linear deformation of concrete dependence on the load. The main deformability parameter of concrete is the instantaneous modulus of elasticity. This research aims to evaluate the relation of concrete compressive and tensile elastic properties testing. The beam samples at 80 × 140 × 1400 cm with one rod Ø8 composite or Ø10 steel reinforcement were experimentally tested. It was shown that instantaneous elastic deformations under compression are much lower than tensile. Prolonged elastic deformations under compression are close to tensile. It results in compressive elasticity modulus exceeding the tensile. The relation between these moduli is proposed. The relation provides operative elasticity modulus testing by the bending tensile method. The elasticity modulus’s evaluation for the reinforced span structures could be based only on the bending testing results. A 10% elasticity modulus increase, which seems not significant, increases at 30–40% the stress of the reinforced span structures under load and 30% increases the cracking point stress. Elastic modulus is an important mechanical parameter for measuring the stiffness of concrete members and structural design ,2. The b4.axial compression deformation test;5.calculated by the multi-scale model and homogeneity theory based on the micro-elastic properties by the nanoindentation test;6.evaluated by the relationship between the compressive strength or the dynamic elastic modulus and the static elastic modulus;7.use of ultrasonic waves.The main concrete elasticity parameter is elasticity modulus or Young’s modulus. It can be obtained by the following methods ,5,6:4.axThe standard compression test considers only instant elastic deformations, so this elasticity modulus is instantaneous ,8. Many In , the effThe three-phase model is proposed for the random concrete microstructure using the Voronoï tessellation to evaluate the interfacial transition zone volume fraction in concrete analytically . The intThe review  summarisA homogenisation scheme of concrete was developed to estimate the effective elastic moduli of a hydrating cement paste . The homStatic and dynamic modulus of elasticity significantly depends on the component composition of the concrete. An example is research  that preIn , differeThe mechanical properties of concrete are highly dependent on the properties and proportions of binders and aggregates. More than 3000 components of experimental data on the relationship between concrete compressive strengths and modulus of elasticity were collected in  and analThe  reviews Static and dynamic methods have tested the elasticity modulus of concrete samples of different compositions . The invIn , the infThe use of local materials for developing ultra-high performance concrete (UHPC) possibly decreases the elasticity modulus of ultra-high performance concrete. In , the equHowever, in practice, there is no material operatively in-controlled or out-controlled by elasticity parameters. At first, it is related to the testing method’s hardness and long-term sensor and centre installation. Due to that, the three-point bending method of elasticity testing by the only deflection definition appeared simple, available, and accurate. There are few recent studies ,26 on thThe continuous damage mechanics theory proposes an elastic bimodulus creep damage constitutive model is proposed in  based onThe main imperative of the isotropic theory of elasticity about equality of concretes’ compressive and tensile elasticity demands modern retesting. The observed differences between concrete’ compressive and tensile deformative properties and design and control consequences determine the novelty of this study.Thus, this research aims to evaluate the relation of concrete compressive and tensile elastic properties testing, taking into account non-linear deformability and effectiveness of elasticity modulus increasing in reducing bending concrete elements deflections.Research tasks were concluded in empirical research of concrete elastic properties and its data testing in design:Research the concrete deformability on standard beam samples with the equal strength of concrete and different elastic properties under compression and bending tensile;Research the deformations of concrete beams, reinforced by steel and composite, under bending load;Modelling and deflection calculation of the same beams under the same load conditions;Estimation of elasticity modulus increasing effectiveness in bending reinforced concrete elements exploitation.Standard methods of Russian State Standards GOST 24452-80 “Concretes. Methods of prismatic, compressive strength, modulus of elasticity and Poisson’s ratio determination”  and RussThere is no standard testing method of bending tensile elasticity modulus of concrete. This testing was carried out on the base of small cement beams (5 × 5 × 15 cm) by Russian State Standard GOST 310.4-81* “Cements. Мethods of bending and compression strength determination” . MechanibtE was determined by the famous based on Mor integral theory of elasticity’s equation [F is the load, l is the two-point size, b is the sample width, h is the sample height, f is the deflection.Bending tensile elasticity modulus equation ,33:(1)EbThe elasticity modulus of cement hydrated paste was determined on the polymer plate samples testing device. Cement hydrated paste samples 70 × 5 × 5 mm were used.According to the producer’s data for the Tinius Olsen h100ku machine, the load accuracy was ± 0.5% in the range from 0.2–100% of the installed load sensor (100 kN). The resolution of measuring the crosshead’s movement is 0.1 mm with an error of up to 0.01 mm. The centre point displacement of the subjected load’s sample was monitored by a mechanical dial gauge mounted on the small test chamber’s bottom. This monitoring was aimed to exclude the machine compliance influence. The difference between the displacements’ readings along the traverse and the dial gauge did not exceed 2% .In research of concrete elasticity increasing effectiveness, the beam samples 80 × 140 × 1400 cm with one rod Ø8 composite or Ø10 steel reinforcement were made. The beam testing scheme and photo are shown in All bending tensile tests were made using each classes series of 3 samples.Reinforced concrete beams were modelled in the FEM software LIRA-SAPR. This software provides linear and non-linear calculations. Non-linear schemes were used for calculations of concrete structures deflection. The non-linear three-line concrete deformation code is used .the HWC B25 with normal elasticity modulus E = 30,000 MPa (concrete 1);the HWC B25 with increased elasticity modulus E = 33,000 MPa due to fractioned coarse aggregate 10–20 mm (concrete 2);the LWC B15 D1600 with E = 15,000 MPa on the base of expanded clay gravel and quartz sand (concrete 3);the LWC B7.5 D1000 with E = 5000 MPa on the base of expanded clay gravel and perlite sand (concrete 4).The hydrated cement paste samples were made from cement paste of normal density.The industrial concrete mixes with regulated elasticity modulus for samples were made on automatic mixing plant PK SCM Ltd.  from local producers materials. Granite coarse aggregate 5–20, 10–20 mm fractions, quartz sand and Portland cement B42.5 CEM I were used for heavyweight concrete (HWC). Expanded clay gravel, quartz sand, perlite sand, and Portland cement B42.5 CEM I for lightweight concrete (LWC). Materials proportions were received based on authors’ previous works :the HWC The average deformability parameters of sample beams 400 × 100 × 100 mm under compression and bending are presented in Curves’ analysis clears specifies of different concrete types deformation under compression and bending tensilePlastic deformations under compression on the load stages delay begin to develop already after reaching 20% of breaking load, and with the load increasing plastic deformations’ part grows, and total modulus of deformation degrades in arithmetical progression keeping instantaneous elasticity modulus;Plastic deformations under tensile bending are minimal and do not develop until concrete destruction;Plastic deformations of concrete on porous aggregates are much less compared to heavyweight concretes.These facts prove the difference between deformation and destruction mechanisms under compression and tensile. In addition, it points to the solving significance of hydrated cement paste and aggregates contact zone (ITZ) in deformation under compression process ,12,13.Deformation’s process under compression developing up to 20% breaking load is the process of developing micro-cracking with stress relaxation by the contact zone and, as a result, delayed macro-cracking until total destruction. The micro-cracking and macro-cracking process under tensile is developing very quickly right before the destruction until that structure resists elastically. These ideas are presented in destruction under compression and tensile models in The test results showed that bending tensile elasticity modulus is several times less than compression elasticity modulus for concrete as the hydrated cement paste. Thus, the difference between compressive and tensile deformations concludes in hydrated cement paste properties ,25.The important feature is that increasing the elasticity modulus of equal-strength concretes’ results in proportional and not significant deflection decreasing, but non-proportional cracking point stress increasing. 10% elasticity modulus growth accords to 30% cracking point stress growth. Finally, the cracking point stress of high-modulus concrete with low-modulus reinforcement is close to the cracking point stress of normal concrete with high-modulus steel reinforcement. Cracking point stress of lightweight concretes decreases accordingly to elasticity modulus decreasing but not to strength.Beam stress-reinforcement stress curves are presented in Reinforcement stress demonstrates that elasticity modulus increasing results in reinforcement’s involvement level in total resistance growth. On cracking point, steel stress/normal concrete stress ratio is 18.6, steel stress/high-modulus concrete stress ratio is 28.2, composite stress/normal concrete stress ratio is 6.6, composite stress /high modulus concrete stress ratio is 14.4. Reinforcement involving resistance is 1.5…2 times higher in high-modulus concrete, and the effect grows using low-modulus reinforcement.By design LIRA-SAPR software, the non-linear deflection calculation was made based on the three-line deformation diagram and equality of compressive and tensile deformations principal. The deflection was calculated with cracking point loads for each variant. Calculation results are presented in As it can be seen, calculated deflections are much more depressive than fact. It proves that the three-line deformation diagram in tensile results in deflections’ calculation mistakes. The two-line elastic scheme is much more accurate.The empirical results of this research point to the concrete’s bimodularity properties. These results could be used to develop the elastic bimodulus creep damage constitutive model proposed in . ClassicMany investigations included bimodular materials’ properties modelling on the base, in first, the models of Ambartsumyan . HoweverBased on the elastic theory for different elastic modulus at tension and compression, the analytical solution was deduced for the bending-compression column subject to combined loads . As a reThe analytical and empirical results proved that all kinds of concretes under tensile deform elastically until destruction. Concrete deformation under compression has a classic visco-elastic character beginning to 20% of breaking stress. Plastic deformation’s part is much less in lightweight concretes on porous aggregates than heavyweight concretes. Thus, the main plasticity factor is the porous hydrated cement paste’s aggregate contact zone, which in lightweight concrete is much denser. Under tensile, the porous contact zone cannot be the reserve for plastic deformations, so the deformation character becomes definitely elastic.Bending tensile tests showed that the tensile modulus of elasticity is several times lower than compressive; the same is for hydrated cement paste. It proves that hydrated cement paste structure under compression is more resistant than tensile because of inner friction between particles and layers.The simple Equation (2) of compressive/bending tensile modulus of elasticity relation can be suggestedIt could be the base of the simple operative elasticity modulus test method of three-point bending tensile by the deflections under load.It is empirically proved that increasing equal-strength concrete’ elasticity modulus significantly influences the cracking point stress of reinforced structure but not on the deflection. Modulus of elasticity 10% increasing results in 30% cracking point stress growth due to lower plastic deformation of concrete with higher elasticity in contact adhesive zone to reinforcement and higher involving level of reinforcements in concrete tensile resistance. In practice, these effects could be achieved only in the case of regulation, coding and operative control of industrial concrete elasticity modulus.This study determined the difference between concrete’s compressive and bending tensile deformative properties so as consequences of this difference in elastic properties evaluation and considering in reinforced span structures design. Based on the results obtained, it is possible to draw the following conclusions.Concrete tensile deformations’ character is elastic, not depending on the load level in contrast with the viscoelastic character of deformations under compression. The concrete deformations’ models under compression and tensile are proposed.The three-line deformation model of span structures is ineffective. This model exceeds calculated deflections and over reinforcement in span structures design. The elastic two-line model is more applicable than the three-line deformation model.Instantaneous elastic deformations under compression are much lower than tensile. Prolonged elastic deformations under compression are close to tensile. It results in compressive elasticity modulus exceeding the tensile. The relation between these moduli is proposed. The relation provides operative elasticity modulus testing by the bending tensile method.The elasticity modulus’s evaluation for the reinforced span structures could be based only on the bending testing results. A 10% elasticity modulus increase, which seems not significant, increases at 30–40% the stress of the reinforced span structures under load and 30% increases the cracking point stress.


Concrete-filled composite columns are widely used in the construction industry, exploiting the benefits of combining steel and concrete, providing, for instance, high load-bearing capacities and enhanced fire resistance. These solutions are extensively used in high-rise buildings and/or when high fire resistance performance requirements are imposed. In this exploratory research, a new type of concrete-filled composite column is investigated using fire resistance tests. Promoting the use of cold-formed steel products and developing innovative solutions for low-rise buildings with lower passive fire protection requirements led to the solutions presented in this research. Hence, a set of fire-resistance tests were undertaken on concrete-filled closed built-up cold-formed steel columns, where single cold-formed steel shapes are combined and fastened to create a box-shaped cross-section. The experimental results were then compared with the corresponding bare steel solutions to assess, in detail, the observed enhancements. Additionally, the effect of restraint on thermal elongation was assessed. Concrete-filled composite columns are well known for their high load-bearing capacity, increased stiffness, high ductility, energy absorption, and enhanced structural fire performance ,2. TheseConcrete-filled tubular solutions are predominantly being used in high-rise buildings where high load-bearing capacity and fire resistance is required. However, for low- and mid-rise buildings, the use of composite concrete-filled members is less common. This is mainly due to the lack of versatility of existing solutions and the consideration of prefabrication and modularity as specific requirements to tackle. There is an urge in the construction sector to develop and promote prefabricated solutions with a higher level of versatility. Cold-formed steel (CFS) products present themselves as highly versatile solutions that may be widely used in low- to medium-rise buildings, with significant environmental benefits. Moreover, optimal solutions can be specified for a wider range of scenarios when compared with the more traditional concrete-filled solutions using standard hollow steel sections. Despite the advantages of cold-formed products, such as versatility, lightness, high strength-to-weight ratio, ease of erection and transportation ,15, one Additionally, the fabricated closed built-up CFS sections can be easily filled with concrete to address existing shortcomings related to the low load-bearing capacity of individual members, low fire resistance, and plate stability due to the reduced thickness of the individual members. The concrete infill will substantially increase the load-bearing capacity of CFS columns and their fire resistance while mitigating local buckling phenomena due to the confinement provided by the concrete which prevents inward deformation of the plate elements . This phThe number of hybrid or multi-material structural solutions in use will increase significantly, targeting enhanced structural performance . The comIn this exploratory research, this synergy between CFS and concrete is investigated under fire conditions with restrained thermal elongation (considering indirect fire actions), assessing in detail the behavior of this new type of concrete-filled closed built-up CFS composite columns.This research investigated the behavior of concrete-filled closed built-up cold-formed steel composite columns using experimental tests. Two basic configurations were selected, comprising two commercially available cold-formed steel sections, namely, lipped channels . According to EN 10147, the yield strength is 280 MPa, and the ultimate strength is 360 MPa.The closed built-up cold-formed steel columns were filled with C20/25 normal-weight concrete, aiming to accurately assess the impact of the concrete infill on the overall closed built-up CFS columns in terms of structural fire performance mitigating local buckling phenomena. In this investigation, eight fire-resistance tests were conducted, considering the influence of restraint on thermal elongation, hence assessing in detail the influence of indirect fire actions. Additionally, both pinned and fixed boundary conditions were considered. There were two repetitions per tested configuration and boundary condition.Design buckling resistance of a compression memberReduction factor for relevant buckling modeEffective are of a cross-sectionYield strengthPartial safety factor for resistance of membersPlate thicknessEffective height of a cross-sectionEffective width of a cross-section, effective plate widthEffective lip length of a cross-sectionReduction factor for the distortional buckling resistanceReduction factor for plate bucklingWidth of a cross-section, plate widthElastic critical plate buckling stressBuckling factor depending on the stress distribution and boundary conditions of the plateModulus of elasticityPoisson’s ratio Elastic critical buckling stress for an edge stiffenerSpring stiffness per unit length of a stiffenerEffective second moment of area of the stiffenerEffective area of a stiffenerRelative slenderness of a memberImperfection factorElastic flexural buckling forceElastic torsional buckling forceElastic torsional-flexural buckling forceEffective length of a memberRadius of hydration of a cross-sectionIn the fire resistance tests of the concrete-filled composite columns, the concrete infill was considered as a fire protection material ; hence, the adopted service load in the experimental tests was based on design buckling load of the bare steel built-up CFS columns determined according to the EN 1993-1-1  and EN 11993-1-3  adopts tIn The fire resistance tests were conducted considering the influence of indirect fire actions, hence considering the influence of restraint on thermal elongation. As previously mentioned, the service load applied to the columns corresponded to 50% of the design buckling load. Consequently, the columns initially loaded up the desired service load, using force control, which was kept constant during the fire resistance test. In The device depicted in To fix the columns, a special device was also developed to simulate adequately the desired boundary conditions b. The deAll specimens were instrumented with thermocouples in different positions at the cross-section level and in different locations along the length of the column. Additionally, the service load generated axial forces, and vertical and lateral displacements were monitored during the tests. In The fire resistance test with restrained thermal elongation consisted of several steps:Applying the service load . The combination of additional axial forces and degradation of mechanical properties of steel and concrete led to the collapse of the composite columns. When the axial forces started to decrease and once again reached the initial service load, the composite column was no longer able to withstand the initially applied service load. This time instant defines the fire resistance of the column in terms of load-bearing capacity.In the scope of this investigation, the mechanical properties of CFS were also determined at ambient temperature. In a previous study, the mechanical properties of the S280GD+Z steel were assessed . Aiming Additionally, it was observed that at 200 °C the ultimate strength  was assessed in terms of time and temperature. From the experimental results, it was possible to extract the most relevant results in terms of critical temperature (temperature from which the column was no longer able to withstand the applied service load), the critical time, the maximum axial load (The temperature evolution at the cross-section level was assessed for both configurations tested and the temperature in the chamber of the furnace. For both R and 2R composite sections, the monitored temperature at every location specified in As expected, the highest critical temperature was obtained for the doubly symmetric concrete-filled closed built-up 2R CFS columns of around 527 ºC. In terms of the Since restraint to thermal elongation was a specific parameter investigated in the experimental tests, additional axial forces generated during the fire test were monitored. In Analyzing the experimental results, it was observed that the ratio It is worth mentioning that considering the influence of restraint on thermal elongation, the failure time and temperature will be lower than for the scenarios where axial restraint to thermal elongation is not considered. According to the EN 1993-1-2 , conductTo assess the proposed solution’s validity and efficiency, the observed results were compared with results for similar solutions but without the concrete infill ,44, and This solution will open new market opportunities for CFS products, allowing the development of new structural systems or strengthening solutions for existing ones. Such a type of composite solution considering steel as the main material also presents the potential for prefabrication and modularity, and moving construction operations to the workshop, creating, for instance, new market opportunities for prefabricated steel-concrete composite solutions. Future research should consider the use of lightweight materials as infill, such as lightweight or ultralightweight concrete.The benefits of the synergies created between CFS and concrete are clear from the experimental tests, where these new solutions presented an improved structural fire performance, with an increase of 153% in terms of fire resistance for some of the established comparisons. Additionlly, the impact of restraint on thermal elongation was assessed. During heating and due to the imposed restraint, additional axial forces are generated, hence reducing the fire resistance and, consequently, the critical temperature. It is also worth noting the advantages of using such a composite solution to mitigate the local buckling phenomena of the thin-walled steel plate elements.Finally, the observed results show that composite CFS-concrete solutions should be further explored and investigated, taking advantage of the versatility of CFS products. Such versatility enables the adoption of optimal solutions contributing to the reduce the consumption of raw materials in the construction sector. Moreover, it is envisaged that such solutions have the potential to create a new structural solution for low- to mid-rise buildings, targeting prefabrication, industrialization, and modularity, with reuse in mind.


The modern types of concrete are a mixture of aggregates, cement, water and optional additives and admixtures. In particular, polymer additives seem to be a promising type of component that can significantly change concrete and mortar properties. Currently, the most popular polymer additives include superplasticizers, latexes and redispersible powders. Moreover, in order to improve the properties of concrete-based composite admixtures, which enhance the resistance to cracking, polymer fibres and recycled polymers have been researched. All the types of polymeric materials mentioned above are broadly used in the construction industry. This work summarizes the current knowledge on the different types of popular polymeric additives. Moreover, it describes the correlation between the chemical structure of additives and the macro-behaviour of the obtained concrete. The lower weight results from the inner voids in their structure. Generally, inner voids can occur when applying cement paste or lightweight aggregates, which have a porous structure. The other approach to obtain inner voids involves the application of coarse aggregate particles [The cement industry, as it provides building materials for the construction industry, counts among the most significant manufacturers in terms of produce volume. Cement is not a stand-alone building material, although it is the main ingredient of the standard building material called concrete. The latter is the most extensively used building material in the construction industry, has various applications and is mainly used to form structural elements. The widespread use of concrete results from several reasons, such as the abundance of substrate resources, low cost and high compressive strength . Concretarticles . Accordiarticles . The cor2 (C3S), 2CaO·SiO2 (C2S), 3CaO·Al2O3 (C3A) and 4CaO·Al2O3·Fe2O2 (C4AF), calcium aluminate cement (CAC), in which the main active constituent is monocalcium aluminate CaO Al2O3 (CA), and calcium sulphate.. It should be stressed that they can achieve great early strength, rapid setting and shrinkage compensation better than the standard OPC-based materials. In the case of such systems, CAC fulfils a composite superposition effect on the creation of ettringite, whereas gypsum promotes the formation of ettringite [Currently, the new and most commonly used generation of cement-based composites is ternary and quaternary binder systems, with the addition of different cementitious materials. The ternary binder systems are based on Portland cement (OPC), composed mainly of 3CaO·SiOtringite . The inttringite ,8,9. Thetringite . Their itringite , settingtringite , freezintringite , mechanitringite  and antitringite ,15. Usintringite ,17,18. Ttringite . Moreovetringite .Apart from the addition of polymers to the cementitious matrix, scientists are looking for other solutions aimed at eliminating concrete weaknesses, such as its brittleness and its low load capacity. In response to the demand for improved concrete, researchers made an effort to overcome the toughness limitations of plain concrete. In the course of this study, fibres have been examined as an additive incorporated into the cementitious matrix. In recent years, most publications in this field suggest the application of polymer fibres in order to improve the ability to enhance tensile ,21,22 anThis paper is devoted to the overview of recent developments and research concerning polymer additives used in concrete-based composites. Introducing different polymers in the cementitious matrix can improve the parameters of mortar and concrete. The selection of works discussed in our study focuses mainly on the changes caused in concrete-based materials by the incorporation of various polymer additives .The review specifically concerns superplasticizers, latexes, redispersible powders, admixtures to enhance crack resistance, fibres and recycled polymers that can play the role of the additives in concrete-based composites. Particular focus has been placed on the relationship between the chemical structure of the described additives and the macro-behaviour of concrete.The rapid development in the concrete industry in the 1990s was accomplished by the introduction of a new type of chemical admixture referred to as plasticizers. The first generation was based on lignosulphonate compounds, which decreased the water/cement ratio by around 5–10% . It is wA group of compounds providing further reduction in the water/cement ratio of around 25% is called superplasticizers ,39,40. T2+ cations with different bonding strengths. According to the published data, the strength of these bonds decreases in the following order: phosphate > carboxylate > sulfonate > sulphate > alkoxide and water [− groups shows improved effectiveness in dispersing cement particles, compared to, for example, plasticizers containing -SO3− groups. Moreover, attempts were made to research the efficiency of polymers admixtures containing the most effective groups chelating calcium ions, i.e., phosphonates and phosphate groups [There are a variety of types of superplasticizers differing in chemical structure. They can be classified into groups, such as lignosulphonates, sulfonates, naphthenates, melamine sulfonates and polycarboxylates . The colnd water . Therefoe groups ,45,46.The phosphated comb polymer superplasticizer was synthesized by J. Stecher and J. Plank  and its Both plasticizers and superplasticizers are such necessary admixtures in concrete that they are listed in the European standard PN-EN 206, where they are mentioned as a possible solution to achieve the right consistency by reducing the amount of water, or reducing the cement content, or to modify consistency without changing the amount of water and cement .In order to reduce the water volume and achieve higher solid content while maintaining proper consistency, superplasticizers, called high-range water reducers, are often used in the formulation of concrete. Scientists and engineers have determined the basic properties of superplasticizers and confirmed that their use allows manufacturers to improving the workability of fresh concrete , chloridN. Roussel et al.  have indMany studies have shown that the fluidity of fresh cement paste depends on the amount of superplasticizer adsorbed by a square meter of solid particles ,58,59. TIn the case of Portland cement hydration, the main composition of solid surfaces is a result of the hydration of calcium silicate and aluminate phases. Among them, certain interfaces can be specified separating the ettringite, gypsum, CSH and anhydrous phases. According to previous studies, ettringite shows the highest adsorption capacity for superplasticizers. The CSH phase adsorbs superplasticizers at least 3–10 times less than ettringite. Consequently, ettringite is considered to be the crucial phase to understand the fresh concrete rheology . Marchon4, CaSO4·2H2O and CaSO4·0,5H2O, responsible for faster hydration of SAC as compared to OPC. In the article by H. Tian et al. [The other recently analysed super plasticizer is Welan gum . In the n et al. , the effThe adsorption of the superplasticizer on the solid surface depends on the chemical structure of the polymer. The added superplasticizer is adsorbed onto the surface as a consequence of electrostatic or specific interaction with the interface .It is a well-known fact that the type of functional group of superplasticizer is characterised by a different adsorption affinity toward a given surface. This phenomenon was discussed by J. Stecher and J. Plank . The aut2 (C3S), inhibiting its dissolution and delaying the hydration process [It has also been noted that superplasticizers impact the setting time of fresh concrete and the mechanical properties of concrete. Polycarboxylate superplasticizers display the property of slowing down ettringite formation but increase its total surface area . It was  process . Shen et process . Further process ,68,73. M process  have preIt is well known that superplasticizers act as dispersants in colloidal particle suspensions that prevent undesired agglomeration and reduce overall viscosity. In order to allow the cement paste flow, the yield stress associated with the network of rigid particles has to be exceeded. The yield stress of cement paste is connected with colloidal and contact interactions among the particles and it depends on the nature of solid particles and their volume fraction . SuperplThe mechanism based on electrochemical forces was first developed to explain the properties of plasticizers such as lignosulphonate. Lignosulphonate compounds have a bipolar structure and display properties typical of polyelectrolytes. The mechanism of their interaction is based on the physical repulsion of negatively charged cement particles, leading to the disintegration of cement lumps into smaller particles, which decreases the surface tension on the surface of the grains wetted by mixing water. Consequently, fine cement grains move more quickly . ElectroIn contrast to linear polycondensates, which disperse cement particles via electrostatic repulsion, PCE molecules, having comb-shaped structures, achieve the dispersing effect mainly via steric hindrance ,65. In gA different approach to superplasticizers and their interactions with cement has been presented in the works by Flatt and Hust  and FlatThe rapid development of the construction industry induced the pursuit to improve the basic properties of concrete and to overcome its limitations, such as brittleness, low durability and insufficient strain capacity, through modifications of the microstructure of hydrated cement. In recent years, the innovations in building construction have progressed considerably and the research on high-performance cement-based materials has been furthered to cope with the requirements of the industry. One of the possibilities to improve concrete performance, including strength and durability, is to introduce polymers into the cement matrix. Cement–polymer composites are created by substituting all or a part of the cement hydrate binder with polymers. Polymer-modified concrete was first introduced in the 1990s and is commonly being used as one of the typical construction materials .Nowadays, various types and forms of polymers are used as chemical admixtures . Among tInitially, polymer-modified mortar and concrete were produced by the addition of a polymer dispersion in latex or emulsion form to the plain cement-based composition during the mixing process. The main advantages of polymer latexes are their ability to create flexible polymer films after dehydration, as well as providing proper adhesion and cohesion in cementitious materials . As mentRedispersible polymer powders (RDP) are a modern type of substances produced by spray-drying polymer dispersions and often used for the same purpose as polymer latexes. They are spray-dried to receive polymer powders . It is iThe properties of cement–polymer concrete and mortars obtained using RDP powders are comparable to those formed in the process of polymer dispersion . The majThe incorporation of polymer into the cementitious matrix changes the microstructure of concrete . The impPolymer film formation is a multistep phenomenon in which four stages have been distinguished .g) of the polymer [In the first stage, the polymer particles are dispersed in water (solvent). The evaporation of water leads to the agglomeration of polymer particles and the formation of the second stage, consisting of a close-packed array with entrapped water in the interstices. The next stage is a consequence of water expulsion from interstices by hydration and evaporation processes and is characterized by a dense array of hexagonal, deformed polymer particles. Some researchers point to an additional, intermediary stage (Stage III*) occurring between stage III and stage IV, formed of a randomly packed array of deformed particles surrounded by water-filled interspaces. Finally, stage IV is formed as a result of the coalescence of polymer particles into a homogeneous polymer film. The transition from stage III to IV is possible only if the ambient temperature is above the glass transition temperature  fibres, polyamide (PA) fibres, polyethylene (PE) fibres and polyvinyl alcohol (PVA) fibres. In In the last decades, researchers investigated the influence of synthetic fibres on the rheology and mechanical properties of cement-based materials. Scientists have studied the effect of various types of fibres, differing in chemical structure, volume in the cementitious matrix, size (macro- and micro-) and geometry ,108. MorThe addition of fibres to the cementitious matrix influences both the fresh and the hardened state of concrete. It is well known that polymer fibres reduce the workability of fresh mortar . This phAs mentioned earlier, the fibres’ effect on the mechanical strength of concrete depends on their size and chemical structure and on the quantity of fibres in the cementitious matrix . The resFurthermore, the improvement of compressive strength of self-compacting concrete due to the incorporation of PP macro-fibres has been confirmed by Gencel et al. . RamezanIn recent years, researchers have focused on hybrid fibres because of their superior effects on composite performance compared to mono fibre blends. Chen and Liu  tested s3 whiskers, PVA and steel fibres. CaCO3 whiskers are a novel type of micro-fibres that are able to significantly improve the mechanical properties of cementitious materials. The previous tests proved that cement-based composites reinforced with multiscale hybrid fibres could improve the flexural strength, energy absorption capacity and reduce the plastic shrinkage of concrete.Cao et al.  have creThe microstructural analysis is an appropriate method that allows us to understand the physical and mechanical properties of fibre-reinforced cementitious materials. Therefore, scientists pay considerable attention to the microstructural characterization of concrete. The literature review has revealed many articles focused on the study of microstructures present in fibre-reinforced concrete by means of several techniques, such as scanning electron microscopy (SEM) ,121,122,Generally, the hydrophobic nature of polymer plastic fibres causes their poor bonding in hydrophilic cementitious materials. The SEM analysis shows the presence of entrapped air voids around polyolefine fibres . In orde2+ and Na+ cations from the cement paste. The improved bonding enhances the post-cracking behaviour of concrete reinforced with the modified fibre compared to concrete reinforced with non-modified PP fibre. C. Signorini et al. [Another experimentally tested method of surface modification of fibres is thin layer coating. Hernandez-Cruz et al.  have invi et al.  have invRecently, the possibilities of using recycled plastic waste fibres in concrete have attracted the attention of many researchers. Literature reviews indicate numerous experimental studies devoted to reinforcing concrete with recycled plastic fibres ,134,135.B.S. Al-Tulaian et al.  have invOchi et al.  examinedThe influence of recycled PET fibres on the reinforced concrete’s early-age performance and mechanical characteristics has also been investigated. Borg et al.  used fibM. Horgnies et al.  studied In summary, concrete strengthening by introducing polymer-based additives into the cement matrix has been studied. For this reason, the effects of the addition of superplasticizers, latexes and redispersible powders, admixtures, fibres and recycled polymers into concrete have been described. The examination of the literature allowed us to establish the following conclusions.The addition of a plasticizer or superplasticizer allows the appropriate consistency to be achieved mainly by reducing the amount of water or the cement content.The most important factors influencing the parameters of obtained concrete-based composites include the type, the number and the density of the adsorbing groups, length of the side-chain and its grafting density. Moreover, it should be stressed that the dosage and quantity of the superplasticizer used in the procedure has a significant impact on the adsorption efficiency of the superplasticizer onto cement particles. Redispersible powders and polymer dispersions affect the cement hydration process. In various forms, such as redispersible powders, latexes, liquid resins and water-soluble homo- or copolymers, they are able to form flexible polymer films after dehydration. Furthermore, they provide proper adhesion and cohesion in cementitious materials.Polymeric fibres are known as materials characterized by elasticity, chemical resistance, high strength and excellent wear resistance. For this reason, cement-based materials containing fibres are characterized by improved mechanical properties, toughness, ductility and post-cracking resistance. In addition, it should be emphasized that the low melting temperature of polymeric fibres leads to the formation of concrete-based composites with reduced spalling at higher temperatures.2 and NOx.Based on the literature review, it was proved that polymer-based additives constitute valuable components of concrete that allow its limitations to be overcome. Prospectively, it is likely that further studies will focus on self-repairing concrete-based composites. Moreover, the most recent technological advances have been made in order to receive concrete without reinforcement, in the self-compacting technology, without scratches and cracks, with high aesthetic values and the highest quality. Most importantly, in the future, concrete will be lighter, safer, more flexible and durable, as well as environmentally friendly. The concrete of the future will also have the potential to use solar and wind energy, as well as capture and consume CO


The treatment of extended-spectrum beta-lactamase (ESBL)-producing urinary tract infections (UTI) may include either intravenous (IV) or oral (PO) antibiotics, according to the Infectious Diseases Society of America guidelines for resistant gram negative infections. The purpose of this study is to evaluate if PO step-down antibiotics, the switch group, compared to continued IV therapy in these UTIs affects clinical outcomes.This multicenter retrospective cohort study was conducted in hospitalized patients with an ESBL-producing UTI between July 2016 and March 2020. The control group received a complete antibiotic course with a carbapenem. The switch group was transitioned to an oral agent within five days from initiation of a carbapenem. The primary endpoint was a composite all-cause clinical failure, which was defined as readmission or hospital mortality within 30 days of hospital discharge or a change in antibiotic during hospital admission. The secondary endpoints included individual components of the primary outcome, readmission indication, inpatient length of stay, direct antibiotic costs, and adverse events. The study included 153 patients: 95 and 58 patients in the control and switch groups, respectively. Demographics between the two groups were similar (Table 1). The mean ± SD duration of therapy was 8.7 ± 3.1 and 7.1 ± 3.3 days, respectively. Four oral agents were used for step-down therapy . The primary outcome occurred in 28% in both groups . The individual components of the primary outcome and readmission indication were also similar: readmission , readmission due to a recurrent UTI , hospital mortality , and change in antibiotic . The median (IQR) length of stay and direct antibiotic cost in the control and switch groups were 8 (6) vs 5 (2) days (p< 0.01) and &278 (&244) vs &180 (&104) (p< 0.01), respectively. Adverse events were similar in both groups except for diarrhea .Table 1. Baseline Demographics. SD: standard deviation, ICU: intensive care unit, qSOFA: quick Sequential Organ Failure Assessment, ESBL: extended spectrum beta-lactamase, UTI: urinary tract infectionFigure 1. Oral Antibiotics. QD: once daily, BID: twice daily, Q2D: every 2 days, Q3D: every 3 days, DS tab: double strength tabletThere was no difference in clinical failure, readmission rate, mortality rate, or change in antibiotic between the control and switch groups; however, the switch group was associated with reduced hospital length of stay and direct antibiotic cost. All Authors: No reported disclosures


There is increased interest in applying electromagnetic (EM) shielding to prevent EM interference, which destroys electronic circuits. The EM shielding’s performance is closely related to the electrical conductivity and can be improved by incorporating conductive materials. The weight of a structure can be reduced by incorporating lightweight aggregates and replacing the steel rebars with CFRP rebars. In this study, the effects of lightweight coarse aggregate and CFRP rebars on the mechanical and electrical characteristics of concrete were investigated, considering the steel fibers’ incorporation. The lightweight coarse aggregates decreased the density and strength of concrete and increased the electrical conductivity of the concrete, owing to its metallic contents. The steel fibers further increased the electrical conductivity of the lightweight aggregate concrete. These components improved the EM shielding performance, and the steel fibers showed the best performance by increasing shielding effectiveness by at least 23 dB. The CFRP rebars behaved similarly to steel rebars because of their carbon fiber content. When no steel fiber was mixed, the shielding effectiveness increased by approximately 2.8 times with reduced spacing of CFRP rebars. This study demonstrates that lightweight aggregate concrete reinforced with steel fibers exhibits superior mechanical and electrical characteristics for concrete and construction industries. With the development of information and communication technology, the use of electronic devices and interest in electromagnetic interference (EMI) shielding have increased in recent years. EMI causes electromagnetic (EM) waves to explode an electric circuit, resulting in its destruction. When EM waves are generated from outside a building and penetrate it, electronic devices inside the building may malfunction or break down because of EMI ,2. EMI sThree phenomena occur when an EM wave is incident on concrete: absorption, reflection, and multiple reflections. Absorption is caused by conduction, dielectric, and magnetic losses. EM waves react with the electric charge when they are incident on concrete, and the microcurrent flows instantaneously. This reaction induces electrical resistance loss, and the concrete eventually absorbs the EM waves ,6,7,8. SOrdinary concrete has high electrical resistance and low electrical conductivity, and the electrical conductivity of concrete can be improved by incorporating conductive materials. Conductive materials range from the macroscale to the nanoscale, and conductive fibers include carbon nanotubes (CNTs), carbon fibers, and steel fibers . Jung etThe interest in lightweight characteristics for structures is growing of late in the concrete and construction industries. A representative method for reducing the weight of structures is to utilize lightweight aggregates, and many studies on lightweight aggregate concrete have been conducted ,19,20,21In this study, the research items largely focused on the density and mechanical and electrical characteristics of concrete. First, the variation in the density of concrete according to the incorporation of lightweight coarse aggregates was analyzed. Next, steel fibers were added to lightweight aggregate concrete, which is vulnerable to external forces, to evaluate the strength characteristics. Subsequently, the effects of the lightweight coarse aggregate and steel fiber on the electrical resistivity and shielding effectiveness were evaluated in terms of electrical characteristics. Furthermore, the effects of the reinforcement type and spacing on shielding effectiveness were analyzed.The mix proportions of the concrete used in this study are listed in 2/g. The steel slag powder had a Blaine of approximately 4893 cm2/g, and it was obtained by pulverizing steel slag aggregate using ball mill equipment  [3 and an air-entraining agent were used. In contrast, lightweight aggregates exhibit a significant moisture-absorbing property and have many pores inside. This property results in fluidity loss during concrete mixing, and it increases the amount of superplasticizer added to the mixture [, Korea) ,34. Rive, Korea)  and ASTM, Korea) . The fin mixture ,38. Howe mixture  to minimIn this study, three categories  were applied to evaluate the effects of steel slag, lightweight coarse aggregate, and steel fiber on concrete. The density of the concrete was determined according to ASTM C567 . The molCylinder test specimens were prepared and cured under standard conditions for seven days to evaluate the equilibrium density. Next, each specimen was immersed in water at 23 ± 2 °C for one day. The specimen was then exposed to 23 ± 2 °C and a relative humidity of 50% ± 5% for 28 days after casting. Similar to oven-dry density, the equilibrium density was averaged using three specimens. The equilibrium density was calculated using Equation (2).The compressive strength of the concrete was determined according to ASTM C39 . A univeThe electrical conductivity and shielding effectiveness were evaluated for the electrical properties of concrete. In Equations (3) and (4), A panel with a cross-section of 300 mm × 300 mm and a thickness of 140 mm was manufactured to simulate the wall structure  and ACI 3, and the equilibrium density increased to 2323 kg/m3 when steel slag was substituted by 15%. LC-SS15 had the lowest equilibrium density of 2029 kg/m3. If the amount of the unit binder is increased, the concrete weight can be reduced using bottom-ash-based lightweight coarse aggregate, whose density is approximately 30% lower than that of conventional coarse aggregate [3, which was approximately 3.6% lower than that of NC-NN despite the increase in density caused by the steel fibers. ACI 318-19 [3. In this study, the equilibrium densities of LC-SS15 and LC-SS15F, which were mixed by 100% substitution of coarse aggregate with lightweight coarse aggregate, were 2029 and 2119 kg/m3, respectively. These lightweight aggregate concrete specimens satisfied the limit stated above.I 318-19  limits t3, respectively, compared to the equilibrium density. In addition, the dry densities of LC-SS15 and LC-SS15F mixed with lightweight coarse aggregate decreased by 62 and 84 kg/m3, respectively. LC-SS15 showed a decrease in dry density by approximately 12% compared to that of NC-SS15. Kim et al. [The dry density showed similar trends to the equilibrium density, but the dry density values were generally lower than the equilibrium density values for all concrete mixes. The dry densities of NC-NN, NC-SS15, and NC-SS15F decreased by 93, 90, and 72 kg/mm et al.  also obs2) production [oduction ,46. Manyoduction ,33,34,35LC-SS15, considered for weight reduction of concrete, exhibited the lowest compressive strength despite the low water-to-binder ratio. This is because lightweight coarse aggregates have a lower density than coarse aggregates, contain numerous pores, and exhibit low strength resistance ,47. HongBrittle failure did not occur in either NC-SS15F or LC-SS15F, steel-fiber-reinforced concrete (SFRC), even after attaining the peak load. The SFRC showed a constant increase in load up to the first peak load and exhibited hardening behavior after reaching the first peak load. Hardening behavior continued until the peak load was reached, and beyond the peak load, softening and ductile behaviors were observed. As shown in 2+, Mg2+, Al3+, Fe2+, K+, and Na+; negative ions: OH− and SO42−) in the pore water, and electronic conduction occurs according to the movement of electrons in a conductive material [material . The amo2O3). Fe2O3 in steel slag can make concrete electrically conductive, and many researchers have reported changes in electrical properties caused by steel slag incorporated into concrete or mortar [Steel slag is a by-product generated during the manufacture of high-strength rebars, and it contains high amount of iron, particularly hematite  [2O3 in the steel slag absorbed the EM waves, and steel slag slightly improved EM shielding [ (Al2O3) . Wang et (Al2O3)  observedhielding .2O3 and Al2O3 in the lightweight coarse aggregate. Metallic contents prevent wave propagation [2O3 content similar to that of the coarse aggregate but contained approximately 1.12 times more Fe2O3. The lightweight coarse aggregate slightly improved the shielding effectiveness of LC-SS15, owing to the difference in the metallic contents. In addition, the pore characteristics of the lightweight coarse aggregate also influenced the shielding effectiveness. The lightweight coarse aggregate had a porous interior, so its EM-wave absorbing characteristics were superior to those of the coarse aggregate. This property tended to improve the shielding effectiveness of LC-SS15 [The effect of the lightweight coarse aggregate on the shielding effectiveness was analyzed by comparing NC-SS15 and LC-SS15. Compared to NC-SS15, LC-SS15 exhibited improved shielding effectiveness by approximately 1.7 dB on average, increasing by up to 4.5 dB at 1.0 GHz. The lightweight coarse aggregate slightly improved the shielding effectiveness, similar to the steel slag; this was attributed to the effects of Fepagation . The lig LC-SS15 .When steel fibers were incorporated into the concrete, the shielding effectiveness of SFRC increased by at least 23.0 dB for all frequency ranges. NC-SS15F had an increased value by approximately 31.9 dB on average compared to NC-SS15, and LC-SS15F showed an increased value by approximately 38.5 dB on average compared to LC-SS15. As a metallic material, the steel fiber attenuated EM waves by inducing electronic and ionic polarization . NC-SS153, satisfying the density requirement for lightweight aggregate concrete.The density of concrete decreased when all coarse aggregates were replaced with lightweight coarse aggregates. Despite the addition of steel fibers, LC-SS15F had an equilibrium density of 2119 kg/mThe compressive and flexural strengths decreased when the lightweight coarse aggregate was incorporated. However, the strength and ductile performance improved with the incorporation of steel fibers.2O3 and Al2O3, which improved the electrical conductivity of the concrete. In addition, steel fibers formed the best electrically conductive path by entangling inside the concrete.The lightweight coarse aggregate contained metallic FeWhen 0.75% steel fiber content was used, the shielding effectiveness of the concrete increased by at least 23.0 dB. In addition, the CFRP rebars exhibited improved conductivity, and shielding effectiveness similar to those of the steel rebars. However, reducing the CFRP rebar spacing of SFRC from 100 to 50 mm had an insignificant influence on the shielding effectiveness.In this study, the effects of lightweight coarse aggregate and steel fiber on the mechanical and electrical characteristics of concrete were investigated. The main conclusions of this study are as follows:


Although basalt fiber-reinforced polymers (BFRPs) have been known for a few decades, new trends such as sustainability and environmental care have provoked intensified research on its structural applications. In construction, BFRPs, as internal reinforcement, have to compete with traditional steel reinforcement products. Because of their high resistance to aggressive environments, BFRPs have emerged as an attractive solution for the infrastructure in coastal zones. In this article, we discuss some aspects of BFRP applications such as flexural reinforcement of concrete beams. The mechanical performances of a BFRP-reinforced beam are illustrated by using a widely accepted model based on the classical beam theory. The elasticity modulus of the BFRP reinforcement is lower than that of structural steel. Therefore, to meet serviceability requirements , BFRP could be pre-tensioned. The positive effect of pre-tensioning is outlined by finite element analysis. An original numerical procedure involves a constitutive relation for concrete based on damage mechanics. Experimental results previously reported in the literature provide the background for the numerical model procedures. The numerical procedure predicts the mechanical response of the concrete beam with BFRP reinforcement subjected to four-point bending in terms of load-deflection relationship and dominant failure mode. As compared with steel, fiber-reinforced polymers (FRPs) are approximately three times lighter and have five times higher tensile strength ,2,3,4. ABFRP reinforcement has emerged as a potential replacement for traditional internal steel reinforcement, specifically for concrete structures in coastal zones. The replacement of steel with BFRP will possibly reduce structural deterioration due to corrosion ,14. PiloDespite all the above advantages, when applying BFRPs in their current form, designers have to circumvent some issues inherent in this type of reinforcement: (i) The elasticity modulus of BFRP is considerably lower than that of steel. Therefore, BFRP-reinforced beams provide lower flexural rigidity as compared with reinforced concrete beams. To satisfy serviceability requirements , the load-bearing capacity of a BFRP-reinforced beam should be limited as compared with that of a steel-reinforced concrete beam . The pre-tensioning of the tensile reinforcement is a viable option to address this issue, even though it implies mounting dedicated anchorage devices in BFRP-reinforced beams, thus, complicating their fabrication. (ii) Generally, the shear strength of beams with flexural FRP reinforcement is lower than that of beams with flexural steel reinforcement in the absence of shear reinforcement. The lower shear resistance of FRP-reinforced beams, mainly attributed to the much lower dowel action, implies more rigorous requirements for transverse reinforcement. (iii) In their current form, BFRP bars require a sand coating to improve bond strength (of the BFRP-concrete interface). Overall, bond behavior for various loading conditions, including cycling and sustained load, requires additional research to mitigate computational uncertainty in design.BFRP reinforcement is gaining positions in FRP structures. However, without being embraced by design guidelines in some countries , reportedly, the use of BFRPs still lags behind other FRP materials . Since bIn this study, we investigate the mechanical response of a reinforced concrete beam strengthened to flexure with internal BFRP reinforcement. The scope of the study is limited to the analytical and numerical aspects of the structure response description. However, the performed simulations use an input  and benchmark empirical data from sources in the literature. An investigation of beam behavior implies taking into consideration multiple resisting and failure mechanisms. For this reason, a numerical algorithm allows for the implementation of customized constitutive relations, and failure criteria is used for the prediction of the beam response. This study also includes an analytical approach based on the classical beam theory . The beam behavior is assessed quantitatively by obtaining the load-deflection relationship.Quantitative algorithms available in the design codes are based on a model initially developed to predict the moment-deflection relationship of a reinforced concrete beam loaded to flexure . Based oA widely accepted analytical approach is used along with an original numerical procedure based on the FEM to assess the mechanical response of BFRP-reinforced beams. The numerical procedure takes into consideration the interaction of many interacting mechanisms . The numerical algorithm uses a constitutive relation for concrete defined in the framework of continuum damage mechanics. A damage variable is plugged into the stress-strain relationship. In this context, reaching the pre-established critical value of the damage variable at a specified location corresponds to macroscopic crack initiation. Thus, the employed algorithm can also predict the crack pattern at the structural element failure. In recent publications reporting advanced FEM simulations, damage mechanics has been applied as part of a complex numerical analysis ,19. At tAccording to recent trends, in addition to the need to satisfy purely structural provisions, structures and constituent materials are expected to meet a broader range of requirements. In this context, a discussion on the environmental impact of the BFRP material, as compared with that of traditional steel reinforcement, is proposed to readers.This study reported herein is a continuation of previous experimental investigations of the mechanical response of concrete beams reinforced with tensile BFRP reinforcement and subjected to a four-point bending test, as shown in The failure of the beam shown in The modeled beam has a length of 2400 mm and a rectangular cross-section of 125 mm in width and 200 mm in height. The simply supported span and the constant moment region are 2000 mm and 600 mm, respectively. The internal tensile flexural reinforcement consists of two 10 mm diameter BFRP bars at the tension face. At the compression face, two 6 mm diameter mild steel bars are placed in order to support the steel stirrups. Between the beam end and the loading points, the stirrups are spaced at 100 mm, and between the loading points, no stirrups are placed. The concrete cover of 25 mm provides an effective depth of 170 mm. The pre-tensioned BFRP rods enhance the performances of the beam .A model based on the classical beam theory is employed to outline the effect of the type of internal flexural reinforcement (BFRP or mild steel) on beam response (in terms of the load–deflection relationship). This model, referred to further in the text as the “analytical model”, is currently available in some design code provisions. It has strong theoretical and experimental bases. Considerable research work has been carried out . The numerical algorithm takes into consideration the pre-tensioning of the BFRP reinforcement. It accounts for many interacting mechanisms  which depend on multiple factors. The following sections provide a discussion of the beam mechanical behavior considered in the context of each model. The discussion is supported by numerical results, some of which are compared with experimental data.Equation (1) provides an assessment of the deflection ( bending  as folloIn Equation (1), =4.73fc′ , where fon point . The effthe beam a, , yt is Recently, the accurate assessment of the effective moment of inertia of concrete beams with internal BFRP has drawn significant research interest ,21,26. IIn Equation (5), the coefficient The meaning of a and L is the same as in Equation (2).n) of a BFRP-reinforced beam [Equation (8) provides an estimate for the nominal flexural capacity (Mced beam : (8)Mn={In Equation (8), concrete ; ρf=Af/by = 0). The pre-tensioning of the BFRP tensile reinforcement is also modeled.A detailed finite element model of the BFRP-reinforced beam is built using ANSYS mechanical APDL 19 . Pre-tenThe load in the four-point bending test is incrementally applied. Stress and strain distributions in concrete are obtained by nonlinear static analysis for each increment of the applied load. The components of the stress and the strain tensors provide the input needed for the constitutive relation. Then, the damage variable is evaluated for each finite element, and the material properties of finite elements affected by damage are modified according to the pre-established constitutive relation. Finite elements of a critical level of damage  are deactivated.Constitutive relations are defined for all constituent materials  and a failure criterion for concrete.Constitutive relations are defined for all constituent materials , and a failure criterion for concrete. The response of concrete is simulated by assuming a coupling between elasticity and damage, according to Equation (10) :(10)σij=The damage variable is assumed to depend on a set of model constants that should be identified through a comparison with experimental data. Within the model employed, the evolution of the damage variable depends on the equivalent strain  as:(11)εWhen the damage variable reaches a specified, predefined value, a macroscopic crack is initiated in the corresponding location. The critical value of the damage variable is another model constant that should be identified against experimental data. In the identification process, the initial data contain the elasticity modulus of the undamaged material and the geometry of the test specimens. Then, strength requirements for the given concrete grade (in terms of compressive and tensile strength) are met based on tuning of the model constants. BFRP = 54 GPa and the Poisson’s ratio νBFRP = 0.23 [For the material model of the BFRP bar, an approximation is used by assuming material isotropy. This assumption is motivated by the choice of the finite element employed to mesh the BFRP reinforcement. The finite element LINK180 supports only axial tension/compression. The relevant material properties of BFRP are the elasticity modulus EP = 0.23 ,32,33,34A predefined model for steel is used defining an initial elastic behavior followed by a hardening phase when yielding occurs ,36. Howeirements .The analytical model is comprehensive and a well-motivated model from a theoretical point of view. Validation through a comparison with empirical data has shown that the model accurately reproduces the experimental evidence, despite the slight overestimation of deflections for the lower moment level . It should be pointed out that analytical models do not capture the kinetics of the process of crack propagation. Crack propagation is considered to be an instantaneous process. The model contains only two states of the tension face of the beam, uncracked p,1 = 16 kN or 20% of the BFRP rods load-carrying capacity, and Fp,2 = 24 kN or 30% of the BFRP rods load-carrying capacity [The positive effect of pre-tensioning on the overall behavior of the FRP-reinforced beam is apparent in capacity . Figure Thus, pre-tensioning can compensate for the lower flexural rigidity of beams reinforced by flexural BFRP reinforcement as compared with traditional reinforced concrete beams. This conclusion agrees with previous results obtained by finite element simulation  and expe2,eq) is an indicator defined to assess possible climate-change emissions during the material production process. This indicator evaluates the carbon dioxide emitted during the whole production process and the in-use period. The monitored period might include the extraction of raw materials, their transport, refining, processing, assembly, and finally, their use, for example, as constituents of a structural element. The marker employed to assess effects resulting in ozone depletion is referred to as the relative level of CFC-11  emitted during the material production. Currently, it is widely accepted that ozone depletion due to man activities is mainly provoked by chlorofluorocarbons. Reportedly, the total amount of effective halogens (chlorine and bromine) in the atmosphere can be calculated [2). The marker used to quantify the influence of the production of a given material on freshwater eutrophication is the equivalent quantity of phosphorus (kg Peq). Eutrophication, most commonly driven by nitrogen and phosphorus, includes the growth of plants and algae and may result in oxygen depletion of the water. The comparison between steel and BFRP in terms of the above-mentioned environmental markers highlights the better performance of the latter material from an ecological perspective.lculated . In thislculated ,43,44. TThe comparison between the load-deflection responses of two geometrically identical beams, i.e., one with flexural steel reinforcement and the other with flexural BFRP reinforcement, outlines the lower flexural rigidity of the BFRP-reinforced beam. The numerical framework for this comparison is widely accepted, and reportedly, experimentally verified.The finite element analysis has illustrated the positive effect of pre-tensioning on BFRP reinforcement, not taken into consideration the aforementioned model. The finite element analysis results show that the load-carrying capacity increases with an increase in the pre-tensioning force, confirming the experimental data found in the literature. Moreover, the finite element method-based algorithm allows for the modeling of a gradual propagation of damage and cracking in concrete. In addition to material models for BFRP and steel, the numerical FEM algorithm employs an original procedure defining a constitutive relation for concrete based on the continuum damage mechanics. A damage variable is plugged into the stress-strain relationship for concrete to account for damage accumulation. The deactivation of the finite elements in which the damage variable reaches a pre-established critical value simulates macroscopic cracking. Therefore, the model can predict the crack pattern at failure. As shown by the comparison between the environmental markers, the production and the implementation of BFRPs in construction, as a replacement for traditional steel reinforcement, reduces the negative impact on the environment. BFRP appears as an eco-friendly material that is in line with the concept of structural sustainability.To summarize, BFRP appears as an attractive, eco-friendly material that, in some cases, will possibly enhance the sustainability of the civil engineering infrastructure, specifically in aggressive environments. On the one hand, reportedly, BFRPs possess many advantages: they are non-corrosive and non-toxic, of good magnetic insulation properties, are resistant to high temperature and high moisture conditions, are chemically stable, and support weathering tests well. On the other hand, some researchers report insufficient resistance to alkali in concrete. Regarding structural applications , BFRPs possess high tensile strength, but relatively low elasticity modulus, thus, providing a lower flexural rigidity to structural elements subjected to bending. Other critical aspects in the design and construction of concrete elements with internal BFRP reinforcement are the lower dowel action, the need for improvement of the bond behavior by implementing various types of coating, the need for complicated anchorage devices (for the pre-tensioned applications), and some difficulties in the fabrication of bent bars. In some countries, the lack of standards also impedes the application of BFRPs as a structural material, which is a situation requiring more intensive research in this field. Solutions to some issues inherent to currently available BFRP technology for construction have been discussed with respect to the background of design and analysis procedures for BFRP-reinforced structural elements. Further research should include simulation of benchmark experimental studies to validate the numerical procedure for various loading conditions. A possible implementation of the proposed algorithm requires checking the reproducibility of numerical results. A detailed finite element analysis would also provide an additional estimate of design code provisions.


The purpose of this study was to evaluate the mechanism of action and the inhibiting effects of two types of desensitizers against dentin demineralization using pre-demineralized hypersensitivity tooth model in vitro. In this study, we confirmed that a hypersensitivity tooth model from our preliminary experiment could be prepared by immersing dentin discs in an acetic acid-based solution with pH 5.0 for three days. Dentin discs with three days of demineralization were prepared and applied by one of the desensitizers containing calcium fluoro-alumino-silicate glass  or fluoro-zinc-silicate glass , followed by an additional three days of demineralization. Dentin discs for three days of demineralization (de3) and six days of demineralization (de6) without the desensitizers were also prepared. The dentin discs after the experimental protocol were scanned using swept-source optical coherence tomography (SS-OCT) to image the cross-sectional (2D) view of the samples and evaluate the SS-OCT signal. The signal intensity profiles of SS-OCT from the region of interest of 300, 500, and 700 µm in depth were obtained to calculate the integrated signal intensity and signal attenuation coefficient. The morphological differences and remaining chemical elements of the dentin discs were also analyzed using scanning electron microscopy and energy-dispersive X-ray spectroscopy. SS-OCT images of CS and NS groups showed no obvious differences between the groups. However, SS-OCT signal profiles for both the CS and NS groups showed smaller attenuation coefficients and larger integrated signal intensities than those of the de6 group. Reactional deposits of the desensitizers even after the additional three days of demineralization were observed on the dentin surface in NS group, whereas remnants containing Zn were detected within the dentinal tubules in CS group. Consequently, both CS and NS groups showed inhibition effects against the additional three days of demineralization in this study. Our findings demonstrate that SS-OCT signal analysis can be used to monitor the dentin demineralization and inhibition effects of desensitizers against dentin demineralization in vitro. Dentin hypersensitivity (DH) is a dental condition characterized by localized sharp pain arising in response to external stimuli, typically thermal, tactile, evaporative, osmotic, or chemical stress, without any other dental defects or disease ,3,4,5,6.Several desensitizers have been introduced for treatment of DH to occlude dentinal tubules and reduce dentin permeability. The dentin desensitizer Nanoseal  is composed of a liquid (A), formed by dispersing fine calcium fluoro-alumino-silicate glass particles, and phosphoric acid aqueous liquid (B). The chemical composition of Nanoseal is similar to that of silicate cement, setting with initial acid–base reaction to form a less soluble phosphate salt. It also interacts with the inorganic components of dentin to form nano-sized deposits on the surface. DH can be suppressed by sealing the dentinal tubules with a nanoparticle-deposited layer, which provides resistance to demineralization ,14,15,16Caredyne Shield  is a tooth surface-coating material containing fluoro-zinc-silicate glass, which provides antibacterial properties , preventRestorative resin composites can be used to seal the hypersensitivity tooth surface if it is accompanied with tooth loss. The properties of restorative composites are influenced by resin matrix, reinforced fillers, silane coupling agents, initiator-activator systems, and inhibitors . The mecOptical coherence tomography (OCT) is an interferometric technique that can create cross-sectional images of biological structures . OCT imaThe purpose of this study was to evaluate the mechanism of actions and the inhibiting effects of two types of desensitizers against dentin demineralization using pre-demineralized hypersensitivity tooth model in vitro. Swept-source optical coherence tomography (SS-OCT) imaging and signal analysis of the pre-demineralized dentin surface were performed with the application of desensitizers. For the confirmation study, demineralized specimens with the application of desensitizers were observed morphologically using SEM, and the remaining chemical elements were analyzed using energy-dispersive X-ray spectroscopy (EDX).Two commercially available desensitizers , CaredynGroup 1: sound dentin without any treatment as a control (sound).Group 2: demineralized dentin for three days (de3).Group 3: demineralized dentin for six days (de6).Group 4: demineralized dentin for six days with Caredyne Shield. Caredyne Shield was applied to the demineralized dentin after three days of demineralization, and the surface was further demineralized for three days (CS).Group 5: demineralized dentin for six days with Nanoseal. Nanoseal was applied to the demineralized dentin after three days of demineralization, and the surface was further demineralized for three days (NS).Twenty-five dentin discs were selected from the 30 discs for SS-OCT analysis and the remaining five dentin discs were used for SEM analysis. The 25 discs were further divided into five groups of five samples each to allocate the following experimental protocol:2, 2.2 mM Na2HPO4, and 50 mM CH3COOH (adjusted to pH 5.0 with 1 M KOH) at 37 °C for the experimental periods [The pulp side of all the dentin surfaces of Groups 2, 3, 4, and 5 were covered with nail varnish, and the occlusal dentin surfaces were exposed to create artificial demineralization. The specimen discs were then immersed in the demineralization solution containing 2.2 mM CaCl periods . In this periods ,32. The In Groups 4 and 5, one of the desensitizing materials of Caredyne Shield or Nanoseal was applied to the dentin window after the three days of demineralization. The samples were again immersed in the demineralization solution for three days . The demFollowing each treatment protocol for the experimental groups, the dentin surfaces were subjected to SS-OCT scanning to obtain a cross-sectional (2D) image of the dentin and SS-OCT signal. The SS-OCT system used in this study was a frequency-domain OCT system . The central wavelength was 1310 nm, with sweeping in the wavelength range from 1260 to 1360 nm at a 20 kHz sweep rate. The scanning light was projected onto the observation sites across the area of interest using a handheld probe. The axial resolution of the device was 12 µm in air and 8 µm in dentin, assuming a refractive index of approximately 1.63 . The latFive locations were randomly selected from each of the samples as the observation sites, where SS-OCT scanning was performed. As a result, 25 images in total were observed for each group. A signal intensity profile in dB unit for each SS-OCT image was obtained to calculate the values of maximum signal intensity, integrated signal intensity, and signal attenuation coefficient.For the maximum signal intensity, the signal intensity profile up to the depth for 800 µm was employed from the SS-OCT image and averaged, where the value was calculated.I is the reflectivity signal intensity in (dB), c is a constant, and z is the depth variable, which has a factor of 2. The µt was calculated using linear least-squares regression to fit the natural log of the average OCT profiles obtained from the ROI.For the integrated signal intensity and signal attenuation coefficient, a region of interest (ROI) with a width of 1000 µm and optical depth of 300, 500, or 700 µm from the surface of the specimen discs was set on the obtained SS-OCT images, avoiding the high Fresnel reflection of the outermost surface layer. Six areas of ROI were selected from one image n = 150, . A signaThe remaining five dentin discs of the 30 discs were used for SEM study. A deep slit on the pulp side was initially prepared with a diamond bur to facilitate subsequent fracture of the dentin surface. The area other than the occlusal dentin surface was protected with a nail varnish to prevent the artificial demineralization solution from penetrating through the pulpal side. The dentin surfaces were allocated to one of the five groups and treated in the same manner as the SS-OCT specimens. After careful removal of nail varnish, the specimens were rinsed with deionized water for 10 s and dehydrated using ascending grades of ethanol up to 100%. The specimens were then immersed in t-butyl alcohol, critical point dried, and were gently split with a scalpel blade to provide a sagittal view of the treated dentin. The specimens were fixed on stubs with double-sided adhesive carbon tape and were coated with gold in a vacuum-metalizing machine. Both the part of the treated surfaces as well as the sagittally fractured surface of each tooth were examined using SEM  operating at 5.0 kV ,38. To cp < 0.05 were considered significant.The integrated signal intensities and µt values were statistically analyzed using one-way ANOVA with Tukey’s post hoc between the groups. All of the statistical analyses were performed at a 95% level of confidence using JMP 12 software . Values of The SS-OCT images obtained from each group are presented in The SS-OCT signal profile and maximum values of signal intensity in dB unit obtained from the dentin surfaces are shown in The results of integrated signal intensity obtained from the ROI of 300, 500, and 700 µm in depth are presented in The results of attenuation coefficient obtained from each ROI are presented in Representative SEM images and EDX spectra obtained from the sagittally fractured dentin surfaces are shown in The three days of demineralization in this study (de3 group) removed the smear and opened the dentinal tubules, with slight demineralization of superficial intertubular dentin. However, the morphological structure of peritubular dentin appeared to remain  and six days (de6) in a demineralization solution adjusted to pH 5.0. Erosion has been considered the main etiological factor for DH ,32,39. Tp > 0.05). However, integrated OCT signals after three days of demineralization were significantly higher than those of the sound dentin for all the ROI depths (p < 0.05). Because backscattered OCT signal from the structure was obtained between the media with different refractive indices, the intensified signal after the three days of demineralization most likely arose from the mineral loss, forming dentin porosity, producing micro-interfaces, and resulting in higher reflectivity and increased brightness [In this study, OCT signal after three days of demineralization presented a similar profile as that of sound dentin. No significant differences of attenuation coefficient or maximum value of the signal intensity were observed between the values of sound dentin and three days demineralization (ightness .p < 0.05). Moreover, the values of the integrated signal intensity after six days of demineralization were significantly lower than those of sound dentin and after three days demineralization for the ROIs of 500 and 700 µm (p < 0.05) [The OCT signal profile after six days of demineralization revealed clear reduction of signal intensity toward deeper dentin, resulting in a higher attenuation coefficient than after three days of demineralization for all the ROI depths ( < 0.05) . The hig < 0.05) ,43. Consp < 0.05). NS forms a nanoparticle-sized layer as the reactional product comprising CaF2, Ca3(PO4), phosphate silicate, and fluoro-alumino-silicate glass, with a thickness of approximately 1 µm on the dentin surface [In this study, the maximum signal intensity of SS-OCT obtained from NS group was significantly higher than those of the other groups ( surface ,44. Alth surface . The res2+ and Ca2+ from CS was accelerated under the acidic conditions of pH 4.5 and 5.0 [MMPs are involved in collagen degradation of caries’ process . When th and 5.0 . In the  and 5.0 . Zinc re and 5.0 . The int and 5.0 . ConsequOCT signal of CS group sample showed significantly higher integrated values and lower attenuation coefficients from the ROIs of 300, 500, and 700 µm than those of the NS group samples. The CS group showed less discrepancy of this optical value compared with the sound dentin because both the CS and NS groups showed intermediate values of the attenuation coefficient between the sound dentin and six-days demineralized dentin, suggesting the preventive effect against further demineralization.Some deposits remained under the surface rather than on the surface of the dentinal tubules in the CS group, as observed in the SEM images. For the sagittally fractured surface, deposits were observed on the inner wall of the dentine tubules . This reThe current in vitro study highlights the ability of dentin desensitizers to withstand the challenges of demineralization. Because of the limitations of reactional products of dentin desensitizers against chemical and mechanical challenges, the results emphasize that the effects of the desensitizers on the dentin surface to protect against the acidic challenges were limited and could be observed within the additional three days of demineralization. Clinically, the oral cavity is a dynamic environment because of the presence of occlusions, mastication, and tooth-brushing abrasion. Although long-lasting desensitizing effect or anti-demineralization effect of the desensitizers appears difficult to achieve, dentin desensitizers represent a less invasive treatment and their application can be repeated. Further studies should be conducted to confirm the long-term effects of these products against the high frequency of acidic beverage consumption and tooth brushing.Under the conditions and limitations of this in vitro study, both dentin desensitizers for Caredyne Shield and Nanoseal showed inhibition effects against demineralization from different mechanisms of action. Our findings demonstrate that SS-OCT signal analysis can be used for monitoring dentin demineralization after the application of these materials in vitro.


In China, there were few studies to estimate antibiotic use for children with upper respiratory infections at the national level. The aim of this study was to describe the antibiotic prescribing practice for children aged < 5 years old with upper respiratory infections (URIs) using a nationwide claims database.This was a retrospective cross-sectional study using a sampled database from the China Health Insurance Research Association (CHIRA). Study subjects included children younger than 5 years with outpatient visits in 2015 that resulted in a diagnosis of a upper respiratory infection. We calculated the percentage of visits who received antibiotics, the proportion of injection formulations, the percentage of combined antibiotics and the proportion of each antibiotic class. The patterns of antibiotic prescription were also described by medical institution type, city level and geographical region.P < 0.001), with the lowest (16.0%) in infants and the highest in patients at age 3 to < 4 years (29.9%) and age 4 to < 5 years (32.5%). The Midwestern region, underdeveloped cities and low-level hospitals represented relatively higher rates of prescribing antibiotics (P < 0.001) and higher proportions of injection dosage forms (P < 0.001). The most 3 common antibiotic classes prescribed of all visits with antibiotic prescriptions were the third-generation cephalosporins (34.9%), macrolides (24.3%), and the second-generation cephalosporins (23.3%).Among the 92,821 visits, 27.1% were prescribed antibiotics, of which 27.0% received injection formulations. The rate of antibiotic prescribing varied by age group (In mainland China, the overall rate of antibacterial prescribing and the proportion of injection formulations prescribed in children under 5 years with URIs were at a low level, but still higher in underdeveloped regions and cities. Moreover, the overuse of the second and third generation cephalosporins, macrolides, remains a serious issue. Further efforts should be focused on reducing those non-first-line antibiotic prescribing and narrowing the gaps among regions and cities. Antibiotics are one of the most common medications prescribed for outpatients –3, and UEscherichia coli and Klebsiella pneumoniae during 2014–2017 [Over and inappropriate use of antibiotics, especially the broad-spectrum antibiotics, not only contributes to the financial burden on health services but also exposes patients to adverse events. More importantly, it is a major contributor to emerging antimicrobial resistance , which pThe surveillance of antibiotic use is necessary to formulate targeted strategies for prevention and containment of antimicrobial resistance. To date, in mainland China, there are mainly 2 nationwide network systems to monitor antibiotic use and antimicrobial resistance, such as China Antimicrobial Surveillance Network (CHINET) and China Antimicrobial Resistance Surveillance System (CARSS). However, the available national surveillance data samples are largely from adult patients, which might not truly reflect the situation in the pediatric settings. In addition, previous studies on pediatric antibiotic use for URIs were limited to selected health facilities or certain areas in China , 19, whiThis was a retrospective, cross-sectional study using a sample from a national insurance reimbursement claims database managed by the China Health Insurance Research Association (CHIRA). The CHIRA database was established in 2007 and is managed by the Ministry of Human Resources and Social Security of the People’s Republic of China. As an administrative database, the CHIRA retrospectively and continuously collects reimbursement records of outpatient, emergency, and hospitalization of insured patients in that year since 2013. Those patients were covered by the public health insurance of China, including the Urban Employee Basic Health Insurance, the Urban Resident Basic Medical Insurance, and the New Cooperative Medical Scheme. In 2013, 95.1% of the population in mainland China covered by public medical insurance [Anonymized information on patients , clinical diagnoses, medical institutions , medical procedures, prescribed drugs  were extracted. All information generated during the same visit could be linked by a unique identifier consisting of the hospital code, patient identification number and the date of visit. This study was performed in strict accordance with the human subject protection guidance of Ministry of Science and Technology of China, and was approved by the Ethics Committee of Beijing Children’s Hospital, Capital Medical University. Informed consent was not required for the use of encrypted retrospective information.Study subjects included children younger than 5 years with outpatient visits between 1 January and 31 December 2015 that resulted in a diagnosis of a URI. Diagnoses of URIs were identified according to the diagnosis description in the Chinese version of International Classification of Diseases, Tenth Revision (ICD-10), codes J00–J06   classification system (version 2020) . AntibioDemographic data including sex, age, and geographical location were collected. We divided the enrolled children into five age groups: 0 to < 1 year; 1 to < 2 years; 2 to < 3 years; 3 to < 4 years; and 4 to < 5 years. Based on the geographical location, medical institutions were separated into the eastern, central, and western regions . Cities In this study, the antibiotic prescriptions were analyzed using every outpatient visit as the unit. The multiple prescriptions and diagnoses for the same patient at the same time in the same hospital were considered as one visit. Evaluation indicators were as follows: (1) the proportion of visits with an antibiotic prescribed; (2) the proportion of injectable antibiotics prescribed; (3) the proportion of combined antibiotics prescribed;(4) the proportion of antibiotics prescribed in each ATC category. To investigate the antibiotic use in detail, we performed a comprehensive analysis according to the geographic regions, the level of the cities and the level of medical care institutions.P-values less than 0.05 were considered statistically significant. All data were exported into an Excel spreadsheet (Microsoft). Descriptive analyses were conducted using Excel (Microsoft). SPSS25.0 and GraphPad Prism 8 were used for statistical analysis and plotting, respectively.Prescription rates, the proportions of injectable antibiotics and combined antibiotics were compared across subgroups using the Chi-Square test. Table p < 0.001), and the rate of prescribing antibiotics and the proportion of injection formulations were highest in central region, at 36.9 and 64.5%, respectively, followed by the west  and east  of China. Compared with other cities, visits from the fourth-tier cities received more antibiotics and injections . Among medical institutions, healthcare providers in primary care facilities tended to prescribe more antibiotics and injection dosage for URIs than those in tertiary hospitals (P < 0.001).Table Figure As early as 2000, the Respiratory Group of Pediatrics Society, Chinese Medical Association have published the guideline for rational use of antibiotics for acute respiratory infections . FurtherCurrently, the percentage of visits with an antibiotic prescribed is a main indicator for assessing and supervising antibiotic use . In 2011In other countries, there also showed high antibiotic prescription rates for URIs. In the United States, Fleming-Dutra. et al.  reportedIn our study, approximately one-third of the prescribed antibiotics were in injection formulations. According the Guiding Principles of China , most paIn our study, the most common antibiotics prescribed (79%) were third generation cephalosporins, macrolides and second generation cephalosporins, which is consistent with prior studies in China , 19, 37 Compared with the top 10 antibacterial agents in pediatrics worldwide , the proOur analysis also showed that pediatric visits in midwestern China and underdeveloped cities received more antibiotics and injection dosage forms. To some extent, such differences were related to the imbalanced economic development and discrepancies in healthcare education resources. Also, studies in Japan  and KoreTo our knowledge, in mainland China, this study is the first to describe antibiotic prescriptions for children with URIs using a claim database covering almost all provinces of China. However, there were also some limitations. First, data from rural areas were not available in the 2015 CHIRA database, therefore, it was not representative of rural China. Second, in this study, each visit for an infection was the unit of analysis and not each infection episode. Thus, antibiotic prescriptions within the same infection episode were captured multiple times. Third, the diagnosis of URIs identified was failed to eliminate other co-infections. Therefore, we could not verify that all antibiotic prescriptions in the dataset were for URIs. Fourth, it is not possible to determine how many patients were bacterial infected in our study because testing for respiratory pathogens is not routinely performed in outpatient settings. Therefore, it is urgent to promote the development of rapid pathogen tests to guide the rational use of antibiotics. Another limitation is that the CHIRA database does not collect information on vital signs, physical exam findings, drug allergy and previous medication failure of patients, which could affect physician’s treatment decisions on antibiotic selection.In mainland China, the overall rate of antimicrobial prescribing and the proportion of injection formulations prescribed in children under 5 years with upper respiratory infections were at a low level, but still higher in underdeveloped regions and cities. Moreover, the overuse of the third generation cephalosporins, macrolides, and the second generation cephalosporins remains a serious issue. Further efforts should be focused on reducing those non-first-line antibiotic prescribing and narrowing the gaps among regions and cities.