In order to investigate the effect of pre-loading damage on the structural performance of Carbon Fiber Reinforced Polymer (CFRP) strengthened Reinforced Concrete (R.C.) beams, experimental and Finite Element Modelling (FEM) investigation was carried out on six R.C. beams. Five of the R.C. beams were damaged up to different levels of strain in the main steel bars before Flexure CFRP strengthening. One of the R.C. beams loaded up to failure and was kept as a control beam for comparison. The experimental results showed that the failure mode of the CFRP strengthened specimen was controlled by CFRP debonding followed by concrete crushing; however, the control beam failed in concrete crushing after yielding the steel bars, which is a ductile failure. The CFRP sheet increases the strength and initial stiffness of the R.C. beams and reduces ductility and toughness. Also, CFRP application increases the first crack and yielding steel bars load by 87.4% and 34.4%, respectively. Furthermore, the pre-damage level does not influence the strength and ductility of the strengthened R.C. beams except for the highest damage levels, which experienced a slight decrease in load capacity and ductility. However, the initial stiffness decreases with increasing pre-damage levels by 40%.Design guideline ACI 440.2R (2004) predicts the ultimate load capacity marvelously for externally bonded Fiber-Reinforced Polymer (FRP) beams compared to the experimental maximum load capacity. The excellent agreement between experimental and FEM results indicates that the constitutive models used for concrete and reinforcement and the cohesive interface model can well capture fracture behavior. However, The FEM analysis predicts the beam to be slightly stiffer and more robust, probably because of the assumed perfect bond between concrete and reinforcement. The developed FEM can be used for further parametric study. Many R.C. structures are damaged. Most of them are suffering from various deteriorations such as cracks and concrete spalling. Many factors are at the origin of these deteriorations, such as aging, corrosion of steel, earthquake, environmental effects, and accidental impacts on the structure , 2.Nowadays, it is necessary to find repair techniques suitable for low costs and fast processing time. Externally bonded FRP has emerged as a new structural strengthening technology in response to the increasing need for repair and strengthening of reinforced concrete structures because of their high tensile strength, lightweight, resistance to corrosion, high durability, and ease of installation , 3.The FRP is characterized by high-strength fibers embedded in polymer resin. The most common type of FRP in the industry is made with carbon, aramid, or glass fibers. Repairing beam structures by externally bonded FRP composites consists of adhering FRP laminates at the tensile face of the beam. Among these types of FRP, the application of CFRP to strengthen and repair the concrete beams has received the most attention from the research community –3. reviewed carried  also car have con developeThe performance of Externally Bonded (EB) FRP to concrete is heavily impacted by the environmental conditions to which it is subjected while in service. The two most prevalent environmental conditions that affect the bond behavior of EB-FRP are temperature and humidity . 9] rev rev9] re carried The most published work on damaged R.C. beams repaired by FRP dealt with repairing these structures damaged by the corrosion effect. However, several studies have been carried out on the retrofitting of the pre-damage R.C. beams due to overloading –13. carried  carried  has repo investigThe failure mode of the control beam was by steel yielding, giving a large deflection of the beam providing sufficient ductility; however, for all repaired beams, the authors observed two failure modes: peeling off and interfacial debonding, which are a brittle and sudden failure. The authors concluded that all the repaired R.C. beams had a mechanical behavior in load capacity and rigidity higher than that of the control beam. In addition, it was determined that, for any damage degree, the CFRP laminates provide the repaired R.C. beam higher mechanical performances. The load capacity increases by 87% and 44% for damage degree 0% and 100%, respectively. The beam RB4 was completely damaged (pre-cracked to failure and large deflection: 10 mm), the contribution of CFRP laminate on the load capacity was very significant (144%). Furthermore, 80% and the 0% damage degree beams behaved likely, and they gave a higher performance in terms of load capacity and rigidity due to the additional contribution of the reinforced concrete. Finally, there was no rupture of the CFRP laminates for all repaired beams due to the lack of end anchorage. assessedFurthermore, results showed that enhancing the flexural stiffness and load capacity would be smaller with the increase in the pre-repair damage level. The CFRP repair technique increases the load capacity regardless of the pre-repair damage level, where it increases the load capacity by 83%, 56%, and 48% for the pre-repair damage levels of 35%, 66%, and 100%, respectively. It has been noted that the CFRP repair technique recovers the stiffness and increases it further than the undamaged stiffness, whereby it increases the stiffness by 17%, 10%, and 4.6% for the pre-repair damage levels of 35%, 66%, and 100% respectively. Finally, they concluded that failure modes are governed by the pre-repair flexural cracks, which induce an intermediate crack at the adhesive layer, thus causing CFRP debonding. investig establisBy contrast, the mid-span deflection of retrofitted beams significantly decreased compared to the control beams, which had the highest deflections. Moreover, the effects of retrofitting at different damage levels were nearly the same. carried  developeThe behavior of CFRP strengthened R.C. beams, and CFRP debonding mechanism is still an outgoing topic of research. Most of the research deal with the strengthening of R.C. beams without pre-damage. Therefore, more research is needed to investigate the behavior of repaired R.C. beams that experienced pre-repair flexure cracks.This research aims to examine the flexural behavior and structural performance of pre-damaged reinforced concrete beams due to overloading, rehabilitated with externally bonded CFRP. The effect of pre-repair flexural cracks is examined on the bond between concrete substrates and CFRP sheets. The failure mode, load-deflection response, CFRP strain, and ductility of the bare and CFRP strengthened beams are discussed.Six reinforced concrete beams with the same cross-section and span are cast and tested under four-point bending. The R.C. specimens are pre-loaded to certain strain levels in the main tensile reinforcement bars and then strengthened by a CFRP sheet. The materials used to cast R.C. beams are sand, gravel, water, cement, and reinforcement bars. Moreover, CFRP and epoxy resin were used to strengthen the R.C. damage beam externally. The properties of the materials obtained from testing in the lab based on ASTM and from Manufacture suppliers are presented in the following sections.3, 1.31%, and 12.5mm, respectively. Ordinary Portland Cement (OPC) obtained from the Tasluja factory is used. Normal tap water was used for the mix proportions and curing of the specimens. The prepared materials  were used to obtain trial mixes. The trial mixes for normal strength concrete were executed according to [River sand from Derbandi Ranya with 2.64 specific gravity and 2.91 fineness modulus was used for the trail mix. In addition, the percentage of absorption is 1.432%. River gravel obtained from Peramagrun is used for the mixed proportions. The specific gravity, dry rodded unit weight, percentage of absorption, and nominal maximum aggregate size are 2.63, 1647 kg/mrding to  based onSamples of deformed steel bars used for main tensile reinforcement and stirrups in the R.C. beams were prepared and tested according to . The steASOFABRIC-C300 carbon fiber fabric with ASODUR-1330 two components (A and B) epoxy adhesive products of AB-SCHOMBURG was used to strengthen the pre-damage R.C. beams. The carbon fiber fabric has 50cm width and 100m length rolled, as shown in All the R.C. beams have identical cross-sections and spans (150mm x 250mm x 1800mm). R.C. beams were designed according to , intentiSix plywood molds and reinforcement cages were constructed and prepared for casting the R.C. beams, and 25mm plastic covers were used for the bottom and side cover of the reinforcement bars. The plywood molds were oiled before concrete casting to protect the molds and remove the molds easily after concrete hardening. A laboratory rotary mixer was used for mixing the materials. An electrical vibrator was used to vibrate and compact the fresh concrete in the molds to minimize air voids and segregations.After the concrete was cast, the top surface of the fresh concrete was leveled and smoothed. The R.C. beams were left for 24 hours in the molds covered with wet gunny sacks. The hardened R.C. beams were removed from the molds and water cured for seven days and left for 28 days before the pre-loading process to gain full concrete strength. The R.C. beams were painted using white color water emulsion painting and labeled using the marker. The reason for the painting is to notice the crack when it occurred.All the R.C. beams except for B1 and B2 were loaded and damaged before strengthening. The damage levels were based on the strain in the main tensile bars of the R.C. beams. Four different damage levels were conducted depending on the specific strain in the tensile bars. B3 was damaged up to 1800microstrain; however, B4 was damaged up to yield strain (2400microstrain) of the main bar. Moreover, B5 was loaded up to 3000microstrain, and B6 was loaded up to 4000microstrain. Before applying CFRP and epoxy resin on the concrete tension face, dust, piece of extra concrete, water emulsion paint, and moisture should be removed using a mechanical grinder and brush. Therefore, the R.C. beams were overturned on the bottom surface. The surface was washed using water and dried using an air blower before CFRP application.The pre- damaged R.C. beams were strengthened with 150mm width of one layer of CFRP in the tension face. The two-component resin A and B were mixed and applied on concrete surfaces and CFRP sheets, and then the saturated CFRP sheet was applied on the concrete surface. A wooden roller was slowly used to press out air and extra resin. Based on the manufacturer’s technical report, the strengthened beams were left for 28 days in the laboratory to harden the epoxy resin.Three different gauge lengths of strain gauges were installed, 3mm strain gauges installed on the main tensile bars at mid-span and on the fourth stirrup from the support to read the tensile strain of the bars. 10mm strain gauges were installed on the CFRP sheets at mid-span and near the supports to measure the tensile strain of the CFRP sheet. Furthermore, 80mm strain gauges were installed on the top, top face, and bottom of the concrete section at mid-span to measure the concrete’s top compressive strain and bottom tensile strain.Five Linear Variable Differential Transformers (LVDT) were used to measure the deflection at mid-span, under the point load, and mid-way between the point load and the right support and to measure top concrete compressive strain and bottom tensile strain.Windmill MicroLink, 851 data logger with 594 box , were used to collect and read the load cells, LVDTs, and strain gauges.Five R.C. beams (B2-B6) with different pre-loading levels were tested to investigate the effect of different pre-damage levels on the failure mode, crack pattern, load-deflection curve, strain contribution of CFRP, and ductility of the CFRP strengthened R.C. beams. The specimen B2 is strengthened without pre-loading; B3, B4, B5, and B6 were pre-loaded up to 53.7%, 81.2%, 84.5%, and 97.4% of the ultimate load capacity of the control beam before FRP strengthening.The control beam experienced a flexure crack mostly under and between the point loads (constant moment region) and propagated towards the support, as shown in Furthermore, the strengthened R.C. beams (B2-B6) suffered from more flexure cracks than B1 before failure; as shown in All the strengthened R.C. failed in CFRP debonding; CFRP debonding was initiated near the supports and propagated toward mid-span. Before CFRP debonding, the epoxy resin fractured because of reaching its tensile capacity.The beams B2-B4 failed in CFRP end peeling off, as shown in All the strengthened R.C. beams, B2-B6, have higher ultimate load capacity and lower mid-span deflection than specimen B1, as shown in Figs The post debonding behavior of the strengthened R.C. beams was similar to the behavior of the control beam. The yielding strain of the steel bar is 2400 microstrain, so the steel bars yielded before failure in all the R.C. beams. The strain result is not presented because some of the strain gauges were damaged or did not read the value properly. Since the concrete crushing for B1 occurred near the right point load, the top concrete strain gauge did not reach the strain failure of concrete at mid-span. Similarly, for B3, the steel strain gauge provided a higher value because the wider flexure crack occurred at mid-span.fu) provided by the manufacture datasheet is 21000 microstrain. In all the CFRP strengthened beams, CFRP strain at debonding was between 41.2%-33% of the FRP rupture strain. B2 gives the highest CFRP strain before debonding; however, B6 gives the lowest CFRP strain. The strain contribution of CFRP decreases with increasing the damage level because the concrete substrate is weakened, and the pre-repair flexural cracks induce intermediate cracks at the adhesive layer and cause early debonding before reaching the CFRP sheet to its yielding strain. For B2 with zero damage level, the CFRP strain reached 41.2% of the CFRP rupture strain. The ratio of CFRP strain to the strain of rupture for B3, B4, and B5 were approximately the same 36.4%, 38.2%, and 38.7%, respectively. Beam B6, with a higher damage level, gives the lowest ratio, 33%.The rupture tensile strain of CFRP  to B2. The initial stiffness of B2, B3, B4, B5, and B6 are increased by 196%, 180%, 128%, 90%, and 78% compared to the initial stiffness of B1, respectively.Increasing the damage level reduces the initial stiffness of the strengthened R.C. beams, as shown in The performance factor is the product of the ductility factor and strength factor. All the R.C. beams have approximately similar performance factors greater than one except for B6, which has the lowest performance factor, less than one.FRP strengthening systems should be designed to resist tensile forces while maintaining strain compatibility between the FRP and the concrete substrate. Design recommendations presented in ACI committee 440  are baseThe constituent materials, fibers, and resins of an FRP system affect its durability and resistance to environmental exposure. Eqs Because FRP materials are linear elastic until failure, Hooke’s law can determine the design modulus of elasticity for unidirectional FRP. The expression for the modulus of elasticity, given in 3, recognizes that the modulus of elasticity is typically unaffected by environmental conditions.Other design guides such as  is requiThe Concrete Society Technical Report 55  does notf*fu and ε*fu are ultimate tensile strength and rupture strain of CFRP from the manufacture datasheet, respectively. ffu and εfu, are ultimate tensile strength and strain of CFRP after environmental reduction, respectively.Where; fd, as defined in Most of the externally bonded FRP system fails in FRP debonding or cover delamination. To prevent such debonding failure mode, the effective strain in FRP reinforcement should be limited to the strain level at which debonding may occur, εf′c is concrete compressive strength, εfd is designed strain, Ef is modulus of elasticity, tf is thickness, and n is number of plies of CFRP.Where; The calculation procedure described in  illustrabi is the initial substrate strain, equal to zero in our case because the R.C. beams were unloaded and upturned before applying the CFRP sheets. If the left term of the equation controls, concrete crushing controls flexural failure of the section. However, if the right term of the equation controls, FRP failure (rupture or debonding) controls flexural failure of the section.Eqs ffe, εfe and df are effective strength, strain, and depth of CFRP, respectively, C is the depth of neutral axis, εcu is ultimate strain of concrete, and εbi is initial substrate strain.Where; The strain and stress in the tensile steel bars are calculated using Eqs The procedure is repeated until the equilibrium of the internal forces and strain compatibility are satisfied.εs, fs, Es, and fy are strain, stress, and modulus of elasticity, and yield strength of steel reinforcement, respectively. d is effective depth of the section, As and Af are area of steel and CFRP reinforcement, respectively. b is the width of the cross-section and α1 and β1 are the values associated with the Whitney stress block (α1 = 0.85 and β1 from ACI 318–05).Where; The nominal bending strength of the section with FRP external reinforcement is computed from A reduction factor for FRP, ψf, is applied to the flexural strength contribution of the FRP reinforcement. Proposed value of ψf is 0.85. The strength reduction factor, ψf, is used to improve the reliability of strength prediction and accounts for the different failure modes observed for FRP-strengthened members (delamination of FRP reinforcement).The R.C. beams were modeled for finite element analysis using ABAQUS CAE, and the results are calibrated based on the experimental results. Four solid plates with (60mm x 20mm x 200mm) dimensions were used to model the loading plates and the supports. The plates were modeled as pure elastic behavior using (E = 200GPa).The material properties presented in section 2.2 and 2.3 were used to model the concrete and the steel reinforcement, respectively. The concrete Poisson’s ratio was taken as 0.2 for all the R.C. beams. Because CFRP is orientated in a uniaxial direction only, the CFRP sheet was modeled as linear elastic isotropic up to failure with the same data obtained from the manufacture datasheet presented in section 2.4. and assumed Poisson’s ratio (0.3). Furthermore, the stress-strain curve of the steel reinforcement obtained from the experimental test, as presented in section 2.3, was used to model the steel reinforcement properties with Poisson’s ratio equal to 0.3.The concrete constitutive models implemented in ABAQUS include the Concrete Smeared Cracking model and the Concrete Damaged Plasticity (CDP) model. Since CDP is a powerful tool to model the plastic behavior of concrete, in this study only CDP is utilized to model the concrete behavior. CDP includes plasticity, compressive behavior, and tensile behavior.Because the descending part of the compressive stress-strain curve could not be achieved experimentally, Chin and Mansur  model isWhere;ε0 and Eit are initial strain and modulus of elasticity of concrete, respectively. fc and ε strength and strain of concrete, respectively.Furthermore, Sneed  model isft and εt tensile strength and strain of concrete, respectively. σ and ε tensile stress and strain of concrete, respectively. Ec modulus of elasticity of concrete.Where; The R.C. beams had been optimized using mesh sensitivity and chosen meshing size of 20mm was found to best approximate the overall structural response of the examined beams and be less time-consuming.An 8-node linear brick, reduced integration, hourglass control (C3D8R) element type is assigned to the concrete and loading plates. Furthermore, a 2-node linear beam in space (B31) element type is set to the reinforcement cage. Finally, a 4-node doubly curved thin or thick shell, reduced integration, hourglass control, finite membrane strains (S4R) are assigned to the CFRP sheet.The interaction between the concrete and steel reinforcement and the R.C. beam and the loading plates should be defined in ABAQUS. A perfect bond between the concrete and steel reinforcement was assumed using the embedded region. In the embedded region, the concrete is the host, and the steel reinforcement is the embedded region. The perfect bond assumption may lead to higher stiffness of the model in the load-deflection curve response than the experimental. Furthermore, a perfect bond between the loading plates and the R.C. beam is assumed using Tie contact. The R.C. beam is the master surface; however, the loading plates are the slave surface.The model for the interface between FRP and concrete is of essential importance. A perfect bond model and cohesive models were evaluated for describing the concrete-FRP interface. The ultimate load and stiffness were overestimated with a perfect bond between the FRP and concrete compared to experimental results. The reason for this is that degradation in the bond cannot be captured in this type of model, and it implies that a perfect bond model is not suitable in a study focusing on debonding.The cohesive model available in ABAQUS is a better choice for representing the interface behavior. The cohesive model defines surfaces of separation and describes their interaction by defining a relative displacement at each contact point. The definition of the model is characterized by the parameters, initial stiffness, shear strength, fracture energy that equals the area under the traction–displacement curve, and the curve shape of the bond-slip model. The following relations 15 through 17 for initial stiffness, shear strength, and fracture energy, as a function of the adhesive and concrete properties, were recommended by :Knn=1tnn is normal stiffness from peeling off test, tc is the concrete thickness = 5 mm, tepoxy is the epoxy or adhesive thickness = 1 mm, Ec = Young’s modulus of concrete, and Eepoxy = Young’s modulus of adhesive. The approximate value of Knn = 1700MPa.Where; Kss = Ktt = shear stiffness from lap joint test, Gc is Shear modulus of concrete = 10800 MPa, Gepoxy is Shear modulus of epoxy or adhesive = 665MPa.Where; Kct = Tensile strength of concrete, MPa, bf = FRP plate width, mm, bc = Concrete width, mm.Where; fThe damage initiation was assumed to occur when a quadratic traction function involving the nominal stress ratios reached value one.Interface damage evolution has been expressed in terms of energy release. The description of this model is available in the ABAQUS material library . The depIn order to find the values of initial stiffness, shear strength, and fracture energy that gave the best fit, simulations were performed, and the results were compared with experimental results. The shear strength has more effect on the debonding failure load and load-deflection curve than the other parameters. The pre-loading scheme distinguished in the laboratory test was also considered in the numerical calculations by creating a pre-defined field. Loading and unloading simulations, as the experiment, are conducted on the R.C. beam models before CFRP strengthening to obtain pre-loading scheme. Then the pre-loading is added to the CFRP strengthened R.C. beams through the pre-defined field by importing and assigning the stress from the output file of the loading and unloading simulation to the steel reinforcement and concrete beam elements separately at the initial stage of the analysis.An incremental iterative procedure was employed to obtain a solution for the analyzed structures and loading programs. Two static point loads were applied at the loading plates corresponding to the experimental location using displacement control. The displacement increments were implemented as a smooth step in the loading amplitude.The boundary condition of the supporting plates was specified at the appropriate nodes as a simply supported beam. One plate has restrained the displacement in the X and Y direction representing pin support, and the other plate has restrained the displacement only in the Y direction representing roller support.When performing a nonlinear analysis, convergence difficulties may occur, especially when cracks start to initiate. To prevent convergence issues, dynamic explicit integration was used to perform nonlinear analysis.Furthermore, Figs The load-deflection curves of the control beams and retrofitted R.C. beams obtained from the experiment and FEM analysis are illustrated in The experimental and numerical investigations were carried out on six R.C. beams to study the influence of pre-damage loading on the load capacity and structural performance of CFRP strengthened R.C. beams. One beam is left as control beam, the other five beams were strengthened in flexure. Four R.C. beams are pre-damaged to different levels of strain in the steel bar before CFRP strengthening. The experimental results compared to the design guideline. Also, the FEM calibrated based on the experimental load-deflection response. The following conclusions can be drawn:The failure mode of the CFRP strengthened specimen was controlled by CFRP debonding followed by concrete crushing; however, the control beam failed in concrete crushing after yielding the steel bars, which is typical tension control failure according to ACI-318.The epoxy resin properties significantly influence the debonding failure because the epoxy resin ruptured in tension before CFRP debonding. So, improving the epoxy properties, predominantly tensile and flexure strength, enhances the bond strength and postpones the CFRP debonding.CFRP sheet restores and upgrades the strength and stiffness of the damaged R.C. beams; however, it reduces ductility and toughness. Also, CFRP application increases the first crack and yielding steel bars load by 87.4% and 34.4%, respectively.The pre-damage level does not influence the strength and ductility of the strengthened R.C. beams except for the highest damage levels, which experienced a slight decrease in load capacity and ductility. However, the initial stiffness decreases with increasing pre-damage levels by 40%.ACI 440.2R predicts the ultimate load capacity marvelously for externally bonded FRP beams compared to the experimental ultimate load capacity.It can be concluded that there is a good agreement between FEM and experimental results for the control beams and strengthened R.C. beams. The good agreement indicates that the constitutive models used for concrete and reinforcement and the cohesive interface model can well capture fracture behavior. However, The FEM analysis predicts the beam to be slightly stiffer and stronger, probably because of the assumed perfect bond between concrete and reinforcement. The developed FEM can be used for further parametric studies.S1 Data(XLSX)Click here for additional data file.


Bacteroidetes and increasing bacteria in the phylum Proteobacteria, thus altering the normal pattern of colonization that infants experience. Delivery by cesarean section and formula feeding magnify and prolong this effect. Our mini review shows that the impact of intravenous antibiotic administration during gestation has on early colonization, growth, or immune programming in the developing offspring has not been well studied in human or animal models.Infants are born into a world filled with microbes and must adapt without undue immune response while exploiting the microbiota's ability to produce otherwise unavailable nutrients. The process by which humans and microbes establish this relationship has only recently begun to be studied with the aid of genomic methods. Nearly half of all pregnant women receive antibiotics during gestation to prevent maternal and neonatal infection. Though this has been largely successful in reducing early-onset sepsis, we have yet to understand the long-term consequences of antibiotic administration during gestation to developing infants. Studies involving antibiotic use in infants suggest that dysbiosis during this period is associated with increased obesity, allergy, autoimmunity, and chronic diseases in adulthood, however, research around the limited doses of intravenous antibiotics used for intrapartum prophylaxis is limited. In this mini review, we focused on the state of the science regarding the effects of intrapartum antibiotic prophylaxis on the newborn microbial colonization process. Although, the literature indicates that there is wide variety in the specific bacteria that colonize infants from birth, limited parenteral antibiotic administration prior to delivery consistently affects the microbiota of infants by decreasing bacteria in the phylum  Most living organisms have formed either a symbiotic or competitive relationships with them in order to survive. Often these relationships change depending on the micro and macro-environments in which each individual species inhabits. Most evidence indicates that a human infant is born nearly, if not entirely, sterile and no convincing evidence has been presented yet that bacteria are present in utero  remains the leading cause of infectious morbidity and mortality in newborns. Intrapartum antibiotic prophylaxis (IAP) administered to all GBS positive women has resulted in an 80% reduction in early onset neonatal sepsis  , 73, 74.fter IAP . Moreovefter IAP  also foufter IAP . Stokholfter IAP  conductefter IAP .The gastrointestinal microbiota has been consistently shown to exert major influences on obesity and immune system development and function , 77. Antst generation cephalosporin commonly used for cesarean prophylaxis, and then exposed them to dextran sulfate sodium (DSS) at 7 weeks of age. Offspring of dams exposed to antepartum antibiotics developed earlier and more severe colitis supporting the theory that injected antenatal antibiotics can exert long-term effects on offspring GI tract immunity , GT: 1ZIABC011153-09, CD: F31NR017821, and WH: 1ZIANR000018.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


Geopolymer concrete possesses superior fire resistance compared to ordinary Portland cement (OPC)-based concrete; however, there are concerns regarding its vulnerability when exposed to real fire events. In the present study, the fire resistance of fly-ash-based geopolymer concrete was evaluated relative to that of OPC-based concrete. Concrete specimens of standard strength grades of 20, 40, and 60 MPa were exposed to fire at 500 and 1200 °C for 2 h to simulate real fire events. Visual observation was performed, mass loss and residual compressive strength were measured, and scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) analyses were conducted. OPC-based concrete suffered major cracks accompanied with spalling for the high-strength specimen, while geopolymer concrete experienced minor cracks with no spalling. Mass losses of the geopolymer concrete—of 1.69% and 4%, after the exposure to fire at 500 and 1200 °C, respectively—were lower than those of the OPC-based concrete. More than 50% of the residual compressive strength for low- and medium-strength geopolymer concrete, after the exposure to fire at 1200 °C, was maintained. After the exposure to fire at 500 °C, the residual compressive strength of the geopolymer concrete increased from 13 to 45%, while the OPC-based concrete was not able to sustain its compressive strength. SEM images showed that the matrix of the geopolymer concrete, after the exposure to fire, was denser than that of the OPC-based concrete, while the FTIR spectra of the geopolymer concrete showed a minor shift in wavelength. Hence, our findings indicate that fly-ash-based geopolymer concrete has an excellent fire resistance as compared to OPC-based concrete. At present, fire events that are caused by the ignition or explosion of hydrocarbon-based fuels in the built environment are common. These events induce a rapid rise in temperature from the flashover state to more than 1100 °C within a few minutes . In lighAs the most utilized material in the construction industry, concrete is generally known to have good fire resistance. Most studies involving ordinary Portland cement (OPC)-based concrete emphasize thermal properties and the addition of reinforcement to improve fire resistance; however, the concrete still cannot withstand high temperatures. The properties of concrete at the physical and chemical levels are adversely affected by fire. In the case of destructive fires, even high-quality designed concrete structures are severely affected, and eventually collapse. In 2017, the 24-storey Grenfell Tower in London, England caught fire, which was started by a malfunctioning fridge–freezer on the fourth floor; the event caused 72 deaths and severe structural damage [Geopolymer concrete has been advocated as an eco-friendly alternative to OPC-based concrete. Davidovits  propoundEven though geopolymer concrete possesses superior fire resistance compared to OPC-based concrete, there are still concerns regarding its vulnerability when exposed to real fire events; its fire resistance has not been comprehensively tested in previous studies, which have predominantly adopted exposure to fire in controlled environments that differ to real fire events. Therefore, the present study evaluates the fire resistance of fly-ash-based geopolymer concrete that was exposed to fire at 500 and 1200 °C for 2 h to simulate real fire events; its fire resistance was then compared with that of OPC-based concrete.Trial mixes were produced to examine the fire resistance of fly-ash-based geopolymer concrete with different grades of strength when exposed to fire at 500 and 1200 °C. The mixes were produced to meet the requirements of standard strength grades of 20, 40, and 60 MPa. OPC-based concrete specimens were employed as control specimens in order to comparatively evaluate the fire resistance of the geopolymer concrete. In total, 12 cube specimens of geopolymer and OPC-based concrete of a standard size of 100 mm × 100 mm × 100 mm were prepared based on the optimal mix design. The specimens were exposed to fire at 500 and 1200 °C for 2 h. The transfer of heat within the specimens was recorded using K-type thermocouples. Visual observation of the physical appearance of the concrete, after cooling, was performed in order to detect cracking and spalling during exposure to the fire. Mass losses were determined by weighing the specimens before and after exposure to the fire. Compression tests were conducted to determine their residual compressive strength. Scanning electron microscopy (SEM), with gold coating and an accelerating voltage of 5 kV, at working distance ranges from 4 to 10 mm, was conducted in order to analyze the morphology of the specimens. The SEM was conducted using a field emission scanning electron microscope of model SUPRA™ 66VP, which was manufactured by ZEISS International . Fourier-transform infrared (FTIR) spectroscopy was performed to analyze the changes in microstructural properties as a result of the exposure to the fire. The FTIR was conducted using an FTIR spectrometer of model Frontier™ 01, which was manufactured by PerkinElmer .Commercially available Class F fly ash that meets the requirements of ASTM C618-19 [3 Powder, which was manufactured by Malvern Panalytical B.V. . As per the diffraction peaks for the phases in the 28.5° 2-θ to 30° 2-θ range, the OPC exhibited comparatively high crystallization phases consisting of alite and calcium carbonate content. Broad diffraction corresponding to portlandite was also detected in the 22° 2-θ to 25° 2-θ range, indicating that the fly ash was mostly glassy, with high crystallization for phases of quartz, cristobalite, and stishovite. The quartz phase showed high crystallinity in the 20° 2-θ, 26° to 27° 2-θ, and 50° 2-θ ranges. The cristobalite and stishovite showed a high peak of crystallization phase in the 24° 2-θ range. The identified phases belong to the silica group, which is the key component of pozzolanic characteristics, and can generate cementitious compounds in the presence of an alkaline solution.2/Na2O weight ratio of 2.5, a density of 1.39 g/mL, and a temperature of 25 °C. For the sodium hydroxide, a 10 M concentration was adopted. The sodium hydroxide solution was prepared by dissolving sodium hydroxide pellets in distilled water for ~24 h prior to preparing the specimens; 40 g of the sodium hydroxide was dissolved in 1 L of water to produce 1 M concentration of sodium hydroxide. Hence, in order to produce 10 M concentration of sodium hydroxide, 400 g of sodium hydroxide pellets was dissolved in 1 L of water.Sodium hydroxide and sodium silicate were employed as the alkaline activators. The sodium silicate solution was of a standard grade, with a SiOFor preparation of the OPC-based concrete mix, sand and coarse aggregates were mixed for 30 s, before adding half of the water, and then mixing again for a minute. Mixing was then stopped for 8 min to allow the sand and coarse aggregates to absorb some water prior to adding OPC. After eight minutes, OPC was added, and mixing was continued for one minute. The remaining half of the water was then added, and mixing was continued again for one more minute. For preparation of the geopolymer concrete mixes, sand and coarse aggregates were mixed for 30 s prior to adding fly ash, and then mixed for a further minute, ensuring that the constituents were uniformly mixed. Subsequently, sodium hydroxide and sodium silicate were stirred into the mixture for three minutes, ensuring that they were uniformly mixed without segregation.The fresh mixtures were then poured into the mold in two layers, with each layer tamped using a rod to remove trapped air. Cast specimens were cured at ambient temperature for 24 h to allow them to harden. OPC-based concrete specimens were taken out of the mold and cured in water for 28 days . On the A setup using natural gas was established to conduct flame tests in order to evaluate the fire resistance of the specimens when subjected to fire at 500 and 1200 °C for 2 h. For OPC-based concrete, the specimens were taken out of the curing tank and dried for 1 h, or until the surface of the concrete has dried, prior to the test. The distance between the fire torch and the specimen was kept constant at 200 mm, ensuring that the flame did not damage the thermocouple. Prior to commencing the test, the specimens were weighed to ensure that their density was consistent. The apparatus for the flame test was set up as shown in The physical appearance of the specimens, for all standard grades of strength, before and after the exposure to fire, is shown in Subsequent to the exposure to fire at 1200 °C, apparent changes in color were detected for all specimens. For the OPC-based concrete specimens, the color of burnt specimens changed to whitish yellow, owing to the complete loss of moisture in the concrete. For the geopolymer concrete specimens, the color changed to reddish brown for the low-strength concrete and black for the medium- and high-strength concretes, owing to the high content of iron oxide in fly ash. Similar changes in color were also observed by Kong and Sanjayan [Surface cracking was prominent due to the high temperature differential between the surface and core of the specimens. Cracks were more evident on the OPC specimens than on the geopolymer concrete specimens, due to the complete loss of moisture within the concrete. Subsequent to the exposure to fire at 1200 °C, no spalling was observed on OPC20, as shown in Conversely, the geopolymer concrete specimens showed no spalling. Even though the structure of geopolymer concrete is denser than that of OPC-based concrete, the differential thermal stress did not cause spalling. Cracks on the surface of the specimens were evident subsequent to the exposure to fire at 1200 °C, but they were not predominant as compared to those on the OPC-based concrete specimens, as displayed in Mass loss refers to the mass of the burnt specimens that is expressed as a percentage of their original mass at ambient temperature. Mass losses of the specimens were determined by measuring the masses of the specimens before and after the exposure to fire. The mass loss increased after the exposure to fire at 1200 °C. The mass losses were higher for OPC-based concrete than for geopolymer concrete, owing to breakdown of the hydration product and total loss of free water. When the concrete was exposed to fire at a high temperature, the free water evaporated. Volume of the evaporation rose as the heating temperature increased. Moreover, the OPC-based concrete suffered major cracks and spalling. OPC20 and OPC40 suffered high mass losses of 6.795% and 8.756%, respectively. As for OPC60, due to the significant loss in cross-sectional area from the spalling, its mass loss could not be determined, and is displayed as 0%. For the geopolymer concrete specimens, their mass losses were significantly lower than those of the OPC-based concrete specimens. GEO20 and GEO40 endured mass losses of 2.855% and 2.722%, respectively. The highest mass loss was that of GEO60 after the exposure to fire at 1200 °C, which was 4.001%. According to Kong and Sanjayan  and SarkThe development of compressive strength was monitored for 28 days. Under the exposure to fire, the concrete gradually lost strength as the temperature increased. Most of the geopolymer specimens also suffered a reduction in strength, albeit at a slower rate than that of OPC-based concrete specimens. Conversely, GEO20 and GEO40 gained strength after the exposure to fire at 500 °C, with residual compressive strengths of 145.33% for GEO20 and 113.21% for GEO40. In addition, GEO60 lost strength by a small amount after the exposure to fire at 500 °C, with a residual compressive strength of 93.02%. For OPC-based concrete specimens exposed to fire at 500 °C, OPC40 obtained the highest residual compressive strength of 58.66%, while those of OPC20 and OPC60 were 50.6% and 46.93%, respectively. The increase in strength of geopolymer concrete after the exposure to fire demonstrated that, during the exposure to fire, further geopolymerization reactions took place in the concrete matrix. A similar increase in the strength of geopolymer concrete was also found by Kodur and Phan  and SarkThe residual compressive strengths of all specimens decreased considerably after the exposure to fire at 1200 °C in comparison to those at 500 °C. GEO20 obtained a residual compressive strength of 98.4%, which was higher than those of GEO40 and GEO60, which obtained residual compressive strengths of 67.36% and 36%, respectively, indicating that low-strength geopolymer concrete possesses a high level of fire resistance. Moreover, after the exposure to fire, GEO40 was able to preserve more than 60% of the initial strength. Conversely, OPC-based concrete specimens suffered major losses in strength after the exposure to fire at 1200 °C; the residual compressive strengths were 34.9% for OPC20, 24.4% for OPC40, and 0% for OPC60.The severe loss in strength of OPC-based concrete was facilitated by the total loss of water from evaporation, followed by the formation of major cracks and the occurrence of spalling due to the thermal stresses within the concrete. The high thermal strain within the concrete also contributed to the loss in strength. The higher reduction in strength of the OPC-based concrete relative to that of the geopolymer concrete is consistent with the findings of Ali , Sarker SEM analysis was performed on medium-strength specimens, namely, OPC40 and GEO40. SEM images of the specimens are presented in Differences in the matrix structures of OPC40 and GEO40, due to the exposure to fire, are evident. The matrix of OPC40 suffered heavy damage, with visible breaking of the bonds between the cement paste and aggregates. In contrast, the matrix of GEO40 appeared to be stable, homogeneous, and dense, at a high magnification level, after the exposure to fire, due to sintering and further geopolymerization of fly ash with the alkaline solution within the matrix, which is consistent with the findings of Kong and Sanjayan ,12. Loss−1 band indicates that formation of geopolymers was taking place, where the transition of SiO2 and Al2O3 occurred due to the chemical reaction between fly ash and an alkaline solution. When the concrete was exposed to fire, there was a reduction in the intensity of the spectra. The wavelength number remained the same for the peak showing the corresponding T-O-T  group, due to the asymmetric stretching vibration. The low frequency also indicates that geopolymerization took place when the specimen was exposed to fire. Bands at 3500 and 1100 cm−1 decreased in intensity with increasing burning temperature, signifying the dehydration of geopolymers due to bending vibrations of the H-O-H and hydroxyl functional groups. The changes occurred due to the loss of bound water within the geopolymer concrete matrix [−1 represent the silicates in cement [−1. The lower intensity indicates that the decomposition of C-S-H showed apparent changes in the OPC-based specimens. Comparable shifts for geopolymer and OPC-based concrete have been reported by Luhar et al. [FTIR analysis was conducted to characterize the specimens and indicate the pattern of chemical reaction changes. FTIR spectra of the specimens after the exposure to fire at 500 and 1200 °C are shown in e matrix . Meanwhin cement , and temr et al. , indicat(a)OPC-based concrete suffered major cracks accompanied with spalling for the high-strength specimen, while geopolymer concrete experienced minor cracks with no spalling. Physical damage endured by the geopolymer concrete was minor compared to that endured by the OPC-based concrete. Therefore, the structural integrity of the geopolymer concrete was maintained after the exposure to fire;(b)Mass losses of the OPC-based concrete were 5.33% and 8.75%, while those of the geopolymer concrete were 1.69% and 4%, after the exposure to fire at 500 and 1200 °C, respectively, due to dehydration of free water within the concrete. Therefore, the geopolymer concrete demonstrated a higher level of fire resistance in comparison to the OPC-based concrete;(c)Measurements of residual compressive strength revealed that the geopolymer concrete displayed excellent stability and fire resistance. More than 50% of the residual compressive strength for low- and medium-strength geopolymer concrete was maintained after the exposure to fire at 1200 °C. Subsequent to the exposure to fire at 500 °C, the residual compressive strength of the geopolymer concrete increased from 13% to 45%, while the OPC-based concrete was not able to sustain its compressive strength, due to complete dehydration of the concrete;(d)SEM images showed that the matrix of the geopolymer concrete, at the microstructural level, is denser than that of the OPC-based concrete after the exposure to fire, owing to further geopolymerization reaction during the exposure to fire. The OPC-based concrete endured heavy damage due to the decomposition of cement paste and disintegration of cement–aggregate bonding;(e)The FTIR spectra of the geopolymer concrete showed a minor shift in wavelength due to the loss of water, and low intensity owing to chemical reactions that occurred during the exposure to fire, indicating that the geopolymer concrete has excellent thermal stability after the exposure to fire.The fire resistance of fly-ash-based geopolymer concrete was evaluated relative to that of OPC-based concrete. Specimens were exposed to fire at 500 and 1200 °C for 2 h to simulate real fire events. Visual observation was performed on the physical appearance of the specimens before and after the exposure to fire in order to detect the formation of cracks and the occurrence of spalling. Mass loss and residual compressive strength of the specimens were measured before and after the exposure to fire. Microstructural analyses, comprising SEM and FTIR analyses, were also conducted. Based on the results obtained, the following conclusions can be drawn:The findings of this study confirm that fly-ash-based geopolymer concrete has excellent fire resistance in comparison to OPC-based concrete. Analyses of the heat transfer and thermal distribution of geopolymer concrete with the exposure to fire, as well as investigations that consider the influence of the distance between the flame and the specimen, are recommended for future research.


The high efficiency of the application of bimodal clinker component and granulated blast-furnace slag is shown. It is established that the optimal content of nanoscale additives, including microsilica, should be insignificant and determined experimentally.The subject of this study is the dispersed composition of multicomponent cement systems. This study aims to reduce interparticle voids, increasing the strength and concentration of the solid phase. The investigated concrete mixture contained two fine aggregate fractions, granite-gabbro crushed stone of 5–10 mm fraction, Portland cement of CEM I 42.5N class, finely dispersed granular blast furnace slag, microsilica, highly dispersed cement fraction, superplasticizer Glenium 430, and high-valence hardening accelerator. A laser analyzer determined the shape and size of dispersed particles of the components. The structure of the cement stone was studied by scanning microscopy, thermographic, and X-ray phase analysis methods. The strength of concrete with an optimized dispersed composition at the age of 2 days was 52, 63, and 74 MPa, while that at the age of 28 days was 128, 137, and 163 MPa. For this concrete, the consumption of multicomponent cement was 650, 700, and 750 kg/m The disadvantages of high-performance concrete (HPC) and ultrahigh-performance concrete (UHPC) are the binder’s high absolute and specific consumption per strength unit. HPC and UHPC have achieved the maximum compressive strength in their existing components’ structure. However, with a further increase in the load, the coarse aggregate becomes the weakest part of the concrete. The only solution is to remove the coarse aggregate to increase the compressive strength of concrete even further. The next step in increasing the compressive strength of the concrete is to remove the coarse aggregate. Coarse aggregate is absent in reactive powder concrete . CompariThe use of steel and polypropylene fibers improves the strength characteristics of all types of concrete and dispersed reinforcement. Therefore, the hack-characteristics of concrete can be further analyzed without taking into account the reinforcement ,3,4.A promising direction for reactive powder concrete production is the use of self-compacting concrete (SCC) ,6,7. TheFor low yield stress, the self-compacting concrete mixture includes an increase of up to 0.5 quota of sand in a concrete mixture, a decrease of up to 3–10 mm in the maximum size of a coarse aggregate, and a low water content. High fluidity and self-compacting of the concrete mixture are achieved by reducing contact interactions between aggregate grains, as well as a high content of cement paste ,8,9,10.Concretes with a high cement content have an increased heat release . For thiIt is possible to obtain concrete mixtures with a high cement paste content at lower consumption of clinker cement with its partial replacement by highly dispersed mineral additives  . HoweverConsidering the spatial and geometric parameters of clinker and mineral additives makes it possible to increase the strength of concrete and other structural properties of concrete. When replacing part of the cement with mineral additives, it is necessary to take into account the ratio of sizes (dispersion) of clinker particles and particles of mineral additives. The key factor is using different dispersed mineral additives in one concrete mix. Pozzolanic activity and the energy state of mineral additives also significantly affect the solid phase concentration per unit volume of the concrete mixture .Mineral additive particles of each subsequent more finely dispersed fraction should be placed in between larger particles or grains, providing the maximum possible filling of voids. Small mineral particles with a tessellated distribution on the exterior of clinker particles, large mineral additives, and Coulomb reciprocal action between particles lead to their spontaneous orientation in the space between larger particles. They are hooked with high binding energy in the interparticle voids of a multicomponent system at their hierarchical dispersed granulometric levels of the mix structure. The binding energy increases with decreasing particle size; hence, dispersity can be used to increase the cement paste density. The self-organization of the concrete mixture’s structure decreases the disarrangement of the system’s component, increasing the particles’ potential energy and viscosity. All of this ensures high homogeneity and non-delamination of self-compacting concrete. The volume of the remaining voids in such a system will be minimal ,21.Thus, obtaining self-compacting concrete of high strength classes can be ensured only by synthesizing a homogeneous optimized discrete–continuous dispersed-particle size distribution of particles and grains of the solid phase in each hierarchical structural level of the material. The scanning electron microscopy, thermographic, and X-ray phase analysis methods were used to study the structure of the cement paste . It was The sufficient amount of empirical data on reactive powder concrete microstructure gives possibilities to suggest four commonly used mixture design methods for UHPC . These mIt follows from the above review that there are a sufficient amount of empirical data on the microstructure of reactive powder concrete. However, these data did not lead to creating a unified theory and design model of the concrete mix. This article aims to suggest a simple model to optimize the ratio of finely dispersed clinker particles and mineral additives. The objectives are the experimental study of multicomponent cement paste and optimizing the dispersed composition of concrete modified with mineral additives to reduce interparticle voids with a significant increase in the solid phase concentration per unit of volume and strength.2/kg, finely dispersed granular blast furnace slag with a specific surface area of 423 m2/kg, microsilica, and fine fraction of cement. Cement consumption, including multicomponent, depending on the research task, varied in the range of 450–750 kg/m3 of concrete. As a superplasticizer, Glenium 430  was used in the amount of 0.45–0.56% of the cement mass, and a high-valence hardening accelerator AC was used in the amount of 0.07% following the Schulze–Hardy rule [The properties and structure of concrete were studied using two fractions of fine aggregate 0.315 and 0.16 mm in size, respectively, in the amounts of 80% and 20%, granite-gabbro crushed stone of 5–10 mm size, Portland cement of the CEM I class 42.5 N with a specific surface area of 253 mrdy rule ,38.The structure of the cement stone was studied with an ARL X’TRA X-ray Diffractometer, Termo Fceser Scientifie Ins. Waltham, Massachusetts, USA. Differential thermal analysis was achieved with a DTG–60 thermal analyzer, Shimadzu Co, Kyoto, Japan. Structure microanalysis was completed with a Quanta 200 FEG scanning electron microscope, Thermo Fisher Scientific, Waltham, MA, USA.Multiple research methods were used. The shape and size of dispersed particles of the components were determined by the sedimentation method according to Russian State Standard GOST 8269.0–97 “Mountainous rock road-metal and gravel, industrial waste products for construction works methods of physical and mechanical tests”  and by aThe study of the structure using scanning microscopy with microanalysis showed that finely ground granulated blast furnace slag with an optimal amount and fineness has a uniform distribution (coefficient of variation less than 0.5%) of its particles in the matrix of a multicomponent cement paste.2/kg dispersion. Particles with a size of 1–5 microns and less constituted up to 50%, and particles up to 10 microns constituted up to 76%. This fine fraction content and the used clinker component were 2.5 times higher than their content in industrial Portland cement . Their simultaneous inclusion as an impurity phase reduces the strength of new hydrosilicate phases of cement stone. Thus, the contribution of calcium hydrosulfoaluminates to the strength of the cement stone structure is dual. Therefore, it is advisable to use cement with a low tricalcium aluminate content for high-strength concretes.Calcium hydroxide is released from the hydration of calcium silicate minerals of clinker. Calcium hydroxide reacts with silica fume as an amorphous polymorph of silicon dioxide and other silicious components, mainly in an amorphous form, composing strong low-basicity secondary calcium hydrosilicates. In this case, the hydration processes of the clinker minerals C3S and C2S are accelerated. Later, the product of the pozzolanic reaction of the lower-kinetic-energy particles of the hydrate phases has significantly less deficiency, a higher degree of structure ordering, and high density and strength due to close coagulation of these particles.With a low degree of disorder, their compressive strength can reach 1000 MPa. This product’s chemically bound water content is 1.5–2 times lower than in primary neoplasms of hydrosilicate phases . Later, Thus, for a significant increase in the strength of reactive powder concrete, a multilevel particle packing of a multicomponent concrete mixture with a regularity of the particle size distribution is required. Complete hydration of the clinker particles’ minerals is not required to ensure the high strength of such a structure. The SCC mixture with a cone flow diameter of 88 cm, prepared following the previously stated provisions, has low yield stress, high deformability, the absence of water gain, gravity segregation, and separation stability. There are uniformly distributed grains of coarse aggregate on the surface of the concrete mixture, confirming the properties mentioned above .Experimental studies of the authors showed the optimal amount of highly dispersed cement at 6% and microsilica at 3%. It was also found that the optimal content of the superplasticizer GleniumACE 430 is 0.45–0.56% of the cement mass, and that of the high-valence hardening accelerator AC is 0.07%. The optimum content of the hardening accelerator AC was determined, taking into account the Schulze–Hardy rule . The use3 consumption of multicomponent cement, respectively.Studies have also shown that the decrease in the optimized and self-organized interparticle void content at four dispersed levels of concrete modified with mineral additives due to the optimal spatial, geometric, and quantitative parameters of mineral additives, as well as the almost mosaic energy state of the surface of the original powder components, is 12–14% or more, with a more than twofold increase in the strength of concrete. The contribution to reducing the interparticle void content of real concrete modified with mineral additives only due to finely dispersed slag, depending on its content, is more than 9%, which is in good agreement with the theoretical value (8.09%). In particular, the compressive strength of concrete at the age of 2 days after hardening under normal conditions was 52, 63, and 74 MPa, while that at 28 days was 128, 137, and 163 MPa, with 650, 700, and 750 kg/mStudies were carried out using scanning electron microscopy to assess the quality of the concrete structure .The use of mineral additives with parameters , determined according to the results of this and previously published research  significThe structure of concrete with mineral chemical modifiers, which have optimal parameters, is distinguished by a significantly lower content of portlandite, and the degree of hydration of Portland cement is 83–85%, exceeding the same indicator for the control composition by 20–27%, confirming its higher strength.The close parking method of the UHPC mixture design based on packing density refers to the proportion of solid volume to the cement and additive system’s total volume ,23,24. TThe unit cell of the particles of the clinker component is presented in the form of a simple pseudo-cubic packing of particles of the same diameter , Image 1(1)The dispersion of mineral additives is optimum in the sense that the mineral additive particles fill the voids between the clinker particles , Image 2(2)The dispersion of clinker particles and mineral additive particles is the same. The density of the original cement paste does not change if the mineral additive is added ((3)2/kg. In this case, the increase in the cement paste density could be more than without mineral additives. However, increased mineral additive content could also lead to the formation of large stable aggregates of small microsilica particles with a high binding energy between particles. These large aggregates of mineral additives can lead to the decompaction of clinker particles  to obtain high-strength self-compacting concrete. Their content should be insignificant. The increased content of nanosized mineral additives can decrease the positive effect of their use due to the aggregation of nanosized particles.The above-proposed physical model of concrete microstructure and particle packing is confirmed by the presented and previous ,16 exper2/kg or less dispersion. This coarse cement fraction ensures the long-term preservation of strong relics of clinker particles with a high modulus of elasticity in concrete. The finely dispersed granulated blast furnace slag should be in an amount of 20–25% of the cement mass with the dispersion of 380–450 m2/kg to fill the first level of interparticle voids of Portland cement.The total volume of a multicomponent binder could be determined using the absolute volume method. The dispersion of a multicomponent binder has three levels. For example, the first level could be Portland cement with 220–250 m2/kg. This dispersion ensures a uniform course of the pozzolanic reaction in all micro volumes containing mineral modifiers particles and prevents aggregates of particles of mineral modifiers.For the second level, finely dispersed Portland cement could be used in an amount of 4–12% with the dispersion of 900–1100 m2/kg. Microsilica percolates between larger particles. The fixation of particles of neoplasms of hydration phases occurs due to molecular selection by strong flocculation [−9 m between the particles. The strong flocculation significantly increases the density and strength of concrete modified with mineral additives. In addition, due to the pozzolanic reaction, strong dendrite-like secondary low-basicity hydrosilicate phases are formed. This is because highly dispersed amorphous silicon dioxide, interacting with calcium hydroxide, forms fibrous and tubular nanosized calcium hydrosilicates almost during the preparation of the concrete mixture. These hydrosilicates of calcium create agglomerations that facilitate the clustering of particles of neoplasms of hydrate phases in high-density packing. The amount of microsilica, in this case, is small and is determined experimentally. Using a multicomponent highly dispersed binder requires the mandatory use of polycarboxylate-type superplasticizers and, preferably, high-valence hardening accelerators.For the third level, microsilica could be used in the amount of 2–6% with the dispersion of 18,000–21,000 mculation ,13 at a 3. High alkali content requires aggregates containing reactive silica to provide alkaline corrosion of the aggregates. Consequently, using limestone and dolomite flour in concrete modified with mineral additives is less effective than mineral additives containing reactive silica.In addition, with a high cement content, the total alkali content in various components of the concrete composition could exceed the critical value of 3 kg/mThis study shows that the determining factor in obtaining a homogeneous, highly filled, dense structure of a cement stone with low defectiveness is the use of heterogeneous mineral additives only with a specific surface area and content that are functionally related to the spatial geometric and energy state of the parameters of the particles that form the interparticle voids of the matrix component. With optimal values of geometric and quantitative parameters using mineral additives, the initial interparticle void content of concrete modified with mineral additives is reduced by 12–14% or more, and the strength of concrete is more than doubled. The volume of interparticle voids decreases by 9% or more due to the use of finely dispersed slag.It is advisable to use particles of the clinker phase of several geometrical sizes, providing an increase in the concentration of the solid phase in a unit volume, a homogeneous course of pozzolanic, and hydration reactions of clinker minerals in all microvolumes of concrete modified with mineral additives. In addition, there is also a significant increase in the density of the cement stone, and the presence of large, strong relics of the particles of the clinker component at a later date, significantly contributing to the integral strength and durability of concrete.The high efficiency of the complex application of polycarboxylate-type superplasticizers and high-valence hardening accelerator AC has also been established. The optimum content of the hardening accelerator AC is 0.07% of the cement mass as determined taking into account the Schulze–Hardi rule. Using a high-valence hardening accelerator provides a synergistic effect of using the superplasticizer Glenium 430. This makes it possible to additionally reduce water-containing concrete mixtures up to 20%. The introduction of the hardening accelerator into the concrete mixer must be carried out after the plasticizer, 8–10 s before the end of the preparation of the concrete mixture.


Staphylococcus aureus was the most common infection-causing pathogen (37.4% vs. 27.9% for PJI). Overall, there was no statistical difference in pathogen distribution (p = 0.254). For FRIs, combinations of gentamicin + vancomycin (93.2%), co-amoxiclav + glycopeptide and meropenem + vancomycin (91.9% each) would have been effective for empiric therapy, similar to PJIs. Difficult to treat pathogens were more frequently detectable in PJIs (11.6% vs. 2.3%). Empiric therapy combinations such as gentamicin + vancomycin, co-amoxiclav + glycopeptide or meropenem + vancomycin, are effective antibiotic strategies for both FRI and PJI patients. More DTT pathogens were detectable in PJIs compared to FRIs.This study aims to investigate (1) microbial patterns in fracture-related infections (FRIs) in comparison to microbiological patterns of periprosthetic joint infections (PJIs), (2) the identification of effective empiric antibiotic therapy for FRIs and PJIs and (3) analysis of difficult-to-treat (DTT) pathogens. Patients treated for FRIs or PJIs from 2017 to 2020 were evaluated for pathogens detected during treatment. Antibiotic susceptibility profiles were examined with respect to broadly used antibiotics and antibiotic combinations. Resistance rates to rifampicin or fluoroquinolone were determined. A total of 81 patients with PJI and 86 with FRI were included in the study. For FRIs  Staphylococcus aureus and gram-negative bacteria [Implant-associated infections, such as periprosthetic joint infection (PJI) and fracture-related infection (FRI), represent a major complication in orthopedic and trauma surgery with a significant socioeconomic burden ,2. Steadbacteria ,7. For Fbacteria . Whether2. Most patients had comorbidities with a mean CCI of 2 (range 0–6) and a mean ASA score of 3 (range 0–4). PJI mainly occurred at the knee  and the hip . In 19 cases (23.5%), PJI involved a revision prosthesis. The mean delay from prosthesis implantation to revision surgery due to PJI was 3.95 years (range: 9 days–29 years). The FRI cohort comprised 86 patients. Out of these, 62 (71.1%) were male and 24 (28.9%) female. The mean age was 55.9 ± 16.7 years and the mean BMI 27.5 ± 5.5 kg/m2. The mean CCI was 1 (range 0–6) and the mean ASA score was 2 (range 1–4). FRI mainly occurred at the tibia (43.0%), followed by infections of ankle and foot fractures (16.3% each). Initially, 19 patients (22.1%) received fracture treatment due to an open injury. The mean delay from initial fracture care to onset of infection symptoms was 0.39 years (range 3 days–9.6 years) (p = 0.085). However, PJI patients were older than FRI patients (p < 0.001), showed a higher BMI (p = 0.002) and had statistically significant more comorbidities as indexed by the CCI (p < 0.001), although not according to the ASA score (p = 0.085).In total, 81 patients were diagnosed with PJI. Overall, 48 (59.3%) of the patients were male and 35 (40.7%) female. Mean age was 70.6 ± 10.3 years. The mean BMI was 31.2 ± 8.2 kg/m6 years) . In compStaphylococcus aureus was the most frequently detected pathogen in both cohorts (27.9% PJI vs 37.4% FRI). One Staphylococcus aureus was methicillin-resistant in the FRI cohort (1.2%). The second most evident pathogen in the PJI cohort was Staphylococcus epidermidis (23.3%), followed by other Staphylococcus species (15.1%), Streptococcus species and gram-negative bacteria (10.5% each). In the FRI cohort, the second most prevalent bacteria were gram-negative bacteria (20.5%), followed by Staphylococcus epidermidis (16.9%). A chi-square test was used to compare pathogen distribution between the two cohorts, resulting in no statistically significant difference (χ²(6) = 7.784, p = 0.254, φ = 0.214).In 11 cases (13.6%) of the PJI patients and in 12 cases (14.0%) of the FRI patients, the infection was culture-negative. A polymicrobial infection was present in 14 cases (17.3%) of the PJI cohort and in 9 cases (10.5%) of the FRI cohort . IsolateTo assess the best possible empirical antibiotic coverage, combinations of antibiotics have been hypothesized as a potential empirical antibiotic therapy against later evidenced pathogens. In the PJI cohort, a combination of piperacillin/tazobactam and ciprofloxacin achieved a 93.0% antibiotic coverage of later evidenced pathogens. The combination gentamicin and vancomycin would have covered 90.1% of all patients who suffered from PJI. High resistance rates were found for empirical monotherapy with ceftriaxone (33.8%), co-amoxiclav (29.6%) and piperacillin/tazobactam alone (25.4%) .p = 0.001).In the FRI cohort, the hypothetical combination of gentamicin with vancomycin resulted in the broadest antibiotic coverage , followed by co-amoxiclav in combination with glycopeptide antibiotics and meropenem combined with vancomycin (91.9% each). Furthermore, ciprofloxacin and piperacillin/tazobactam in combination with a glycopeptide reached an antibiotic coverage of 90.5%. For ceftriaxone (31.1%) monotherapy antibiotic coverage would have been achieved in only 31.1%, which could be improved to 10.8% by an additional combination with a glycopeptide . CompariThe present cohort study compares for the first-time microbiologic epidemiology of PJI with FRI at a center specialized in bone and joint infection treatment. Based on antibiotic susceptibility testing of the evidenced germs, common treatment regimens for empirical antibiotic treatment have been investigated and best practice options have been evaluated based upon the present results. For both PJI and FRI, antibiotic combinations of either meropenem + vancomycin, co-amoxiclav + glycopeptide or piperacillin/tazobactam + glycopeptide and vancomycin + gentamicin seem reasonable combinations to achieve an approximate 90% safe susceptibility to empirical antibiotic therapy.Staphylococcus aureus followed by Staphylococcus epidermidis were the most common evidenced pathogens causing FRI and PJI in the present study. This is in line with several studies investigating infection-causing agents [Enterococcus species and gram-negative bacteria in FRI might be due to a higher rate of previous antibiotic treatment against mainly gram-positive germs. However, this hypothesis cannot be proven due to the retrospective study design.For both PJI and FRI the number of culture-negative infections and polymicrobial infections was relatively low but comparable to each other. In the literature, higher rates of polymicrobial have been reported for PJI 16–46.6%) ,10. In i–46.6% ,1g agents ,17,19. APseudomonas spp. and a glycopeptide to cover gram-positive germs [There are limited data on the usefulness and adequate administration of empiric antibiotic therapy for bone and joint infections. For FRI, the inferiority of late-onset targeted antibiotic therapy has been demonstrated compared to early empiric antibiotic therapy using vancomycin combined with rifampicin . Howeverve germs . Targeteve germs . Anotherve germs ,25. The ve germs ,27.The reported numbers of DTT pathogens in PJI in this study (11.6%) is similar to previously reported rates in PJI (18.4%) . For FRIThis study has some limitations. Data analysis of one orthopedic center may lead to a local epidemiological bias. In addition, the retrospective design restricts analysis to already existing resistograms. In some cases, antibiotic testing for certain antibiotics was not performed, which leads to “unknown” listed antibiotic susceptibility. This is mainly due to different panels of antibiotics available for automated and manual susceptibility testing according to the interpretative criteria released by the European Committee on Antimicrobial Susceptibility Testing (EUCAST).In addition, the retrospective file analysis did not consistently allow identification of antibiotic pretreatment and its effect on the detection of infection-causing pathogens. The analysis of PJI and FRI patients from 2017 to 2020 ensures consistent diagnosis and inclusion of patients according to well-established diagnostic criteria. However, subgroup analysis to answer questions concerning the relevance of anatomic location or durability of infection was not possible due to the low volume in numbers.n = 4). Difficult-to-treat FRI or PJI were present when at least one of the causing microorganisms was resistant to biofilm-active antibiotics including rifampicin-resistant staphylococci, enterococci, fluoroquinolone-resistant gram-negative bacteria and fungi [A retrospective cohort study of patients treated for FRI or PJI was conducted in a level 1 trauma center in Germany. Prior of beginning the study, a positive ethics committee votum was obtained from the ethics committee of the University Hospital Regensburg (file number 20-1680-101). The inclusion period was defined from 1 January 2017 to 31 December 2020. Eligible patients being 18 years or older were screened by international classification of disease (ICD)-10 diagnosis codes . Afterwards, patients’ medical charts, surgery protocols, laboratory findings as well as microbiological and histopathological reports were screened for inclusion criteria of PJI and FRI. PJI was considered confirmed if at least one of the following criteria was met according to the EBJIS consensus for the diagnosis of PJI . FRI wasnd fungi .Patient characteristics  and details of orthopedic implant-associated infections  were assessed retrospectively by reviewing electronic medical records. Comorbidities were assessed by obtaining the ASA score as well as the Charlson Comorbidity Index (CCI). The microbiological database was searched for the pathogens detected and for antimicrobial susceptibility testing. Detection was either based on preoperatively or intraoperatively deep tissue sampling or aspiration of the affected joint. Routinely, at least five deep tissue samples have been taken for microbiological analysis.2. Liquid culture media were incubated for 14 days in ambient air. All culture media were incubated at 37 °C and inspected every day for bacterial growth. Bacteria were identified by matrix-assisted laser desorption ionization time of flight mass spectrometry (MALDI TOF MS) using a Microflex LT mass spectrometer and BioTyper software . Antibiotic susceptibility testing followed guidelines from the European Committee on Antimicrobial Susceptibility Testing (EUCAST) and was performed using a BD Pheonix M50 nephelometer or manually by disc diffusion. In case of removal of orthopedic devices, sonication of the orthopedic implants has been performed, as mentioned before [All tissue samples collected were homogenized and seeded on solid and liquid culture media. Agar plates were incubated for 48 h in the absence and presence of COd before .t-test. Chi-square test was used for comparison of categorical variables. Mann–Whitney-U-test was calculated to determine if there were differences in the antimicrobial regimes between PJI and FRI patients. For all tests, p values < 0.05 were considered statistically significant.Descriptive and statistical data analysis was performed using the IBM SPSS Statistics software . Frequencies were expressed as numbers and percentages. Continuous parameters were presented as means ± standard deviation (SD) and compared by Student’s Despite the undoubted differences between PJIs and FRIs, which range from etiopathogenesis to possible therapeutic strategies, the pathogens that cause infection in both diseases are comparable. The hypothetical analysis of possible antibiotic regimes reveals that for an empirical antibiotic therapy, a combination of vancomycin + meropenem, glycopeptide + co-amoxiclav or piperacillin/tazobactam + glycopeptide are the best therapy options for both FRIs and PJIs. For local antibiotics, the well-established combination of vancomycin with gentamicin is the best treatment option. Difficult-to-treat bacteria are more often evidenced in PJI than FRI. Standardized microbial testing against biofilm active antibiotics such as rifampicin and fluoroquinolones should be implemented in routine microbiological testing for implant associated infections.


In vivo pig skin was treated with AFL and topical BLM or NI with BLM, alone or with additional EP, and followed for 1, 2 and 4 h and eventually up to 9 d. BLM biodistribution was assessed by spatiotemporal mass spectrometry imaging. Cutaneous pharmacokinetics were assessed by mass spectrometry quantification and temporal imaging. Tolerability was evaluated by local skin reactions (LSRs) and skin integrity measurements. AFL and NI resulted in distinct BLM biodistributions: AFL resulted in a horizontal belt-shaped BLM distribution along the skin surface, and NI resulted in BLM radiating from the injection site. Cutaneous pharmacokinetic analyses and temporal imaging showed a substantial reduction in BLM concentration within the first few hours following administration. LSRs were tolerable overall, and all interventions permitted almost complete recovery of skin integrity within 9 d. In conclusion, AFL and NI result in distinct cutaneous biodistribution patterns and pharmacokinetic profiles for BLM applied to in vivo skin. Evaluation of LSRs showed that both methods were similarly tolerable, and each method has potential for individualized approaches in a clinical setting.Bleomycin (BLM) is being repositioned in dermato-oncology for intralesional and intra-tumoural use. Although conventionally administered by local needle injections (NIs), ablative fractional lasers (AFLs) can facilitate topical BLM delivery. Adding local electroporation (EP) can augment intracellular uptake in the target tissue. Here, we characterize and compare BLM biodistribution patterns, cutaneous pharmacokinetic profiles, and tolerability in an  P, −7.5) and has a molar mass of 1415 Da, it can neither penetrate the stratum corneum unassisted nor can it easily cross the cell membrane. A drug delivery system is required for topical administration  is a cytotoxic antitumor agent used for a variety of approved and off-label dermatologic indications including hypertrophic and keloid scars, warts, and non-melanoma skin cancer  to overcome the skin barrier. Several alternative drug delivery systems that may be used to treat BCCs have been tested, including hollow micro-needles  and conducted in accordance with the Federation of European Laboratory Animal Science Associations guidelines. The study included four female gilt pigs (62–75 kg) situated in single confinement with snout access to companion pigs. The pigs acclimatized for two weeks prior to inclusion. General anesthesia was induced using intramuscular benzodiazepine and inhalation of 2% isoflurane and was maintained using isoflurane supported by a bolus of intravenous propofol when required. The pigs were anesthetized up to 4 times . The treatment areas on the back along the spine and down the flanks were carefully shaved to preserve intact skin and 2 × 2-cm sample areas were demarcated with indelible ink, as shown in All BLM used was from the same batch (7K062C) and source  and was prepared in 0.9% saline (SAL) as a 15,000 IU/mL solution  at 250 Hz with 80 mJ/microbeam energies with a 5% density  , using Tegaderm  as a perforable lid . The skin was penetrated from a 15-degree angle, depositing 0.1 mL BLM intradermally and resulting in an immediate papule, which indicated successful delivery .EP was performed with high-frequency pulse  delivering 1300 V/cm at 250 kHz using a probe interface featuring eight needles in a 2 × 4 grid formation . EP was 2/h) .The skin tolerability of the applied interventions was assessed by scoring LSRs for erythema and edema on a visual and descriptive categorial scale used in similar studies  were excised for liquid chromatography-mass spectrometry (LC-MS) quantification and matrix-assisted laser desorption/ionization (MALDI) imaging, snap-frozen on COFull-skin biopsy samples for LC-MS were dissected into 32 pieces using a scalpel and suspended in 1 mL phosphate-buffered saline. The tissue suspensions were lysed for 30 min . Next, the homogenates were extracted for 2 h in rotating vials. Samples were centrifuged at 400 RCF for 15 min at 4 °C. Fluid was extracted for LC-MS analyses. Samples for MALDI imaging were vertically cryosectioned at full width (8 mm) in carboxymethylcellulose and fixed on glass slides for analyses.4, 25% MeOH) to 250 µL skin homogenate, followed by 10 min centrifugation at 20,000 RCF. Calibration curves were created based on a 0.5 mg/mL BLM stock . The stock was diluted to 2000 ng/mL and then diluted 1:1 seven times, to a minimum concentration of 15.625 ng/mL. The eight-point calibration curve was applied at the beginning and end of every sample list. The limit of quantification (LOQ) was 14.49 ng/mL. Samples were analyzed by LC-MS on a Thermo TSQ Vantage triple-quadrupole mass spectrometer equipped with a Thermo Accela high-performance liquid chromatography system . A 100 × 2.1 mm Kinetex 2.6 µ XB-C18 100 A column was used with isocratic elution . The transition pairs used for quantitation were m/z 713.5 to 530.0 for BLM B2 and m/z 708.0 to 493.5 for BLM A2.The skin homogenates were precipitated by adding 500 µL precipitation solution (2% ZnSO2O) was applied using an iMatrix sprayer and the following settings: height, 80 mm; width, 40 mm; depth, 40 mm; line distance, 1 mm; speed, 90 mm/s; density, 3 µL/cm3; and 12 cycles. Mass spectrometry imaging was performed on SMALDI5 and SMALDI10  Q-Exactive systems, using either line or pixel mode. The images were acquired at a mass resolution of 140,000 at 200 m/z and a scan range of 225–1750 m/z. The acquired Thermo RAW files were converted to imzML format using RawToIMZML, and the images were generated in MSiReader . The phospholipid PC signal (36:4) detected as its H+ adduct at m/z 782.56939 was used as a tissue biomarker for the skin, and BLM B2 was detected at m/z 1425.51881.The skin samples were dried in a vacuum desiccator for 30 min prior to coating with the matrix. The matrix  and plotted using Prism 8 software .Descriptive statistics are presented as medians and IQR. Non-parametric Mann–Whitney tests were used throughout a 5% alpha level and corrected with Holm–Bonferroni Imaging revealed that both laser-assisted (AFL + BLM) and needle-injection (NI + BLM) delivery methods resulted in detectable intradermal concentrations of BLM. The spatial resolution showed that AFL + BLM led to BLM accumulating in the coagulation zones, dispersing into the surrounding tissue, and forming a horizontal belt-like shape that was limited in depth by the laser-channel dimensions , 1–4 h. Supporting information, Figure S2).Images of EP and non-EP samples were similar. For example, there were no differences between AFL + BLM + EP and AFL + BLM images. The BLM + EP control intervention resulted in negligible traces of BLM on the skin surface. All BLM-negative control images were negative for BLM (3 (IQR: 210.9–357.7) of BLM, which was the maximum BLM load observed in this study and saturated a full-skin biopsy. In comparison, after 1 h, AFL + BLM resulted in 15.4 µg/cm3 and NI + BLM in 133.6 µg/cm3 of BLM, equivalent to 5.5% and 48.3% of the maximum load, respectively , as shown in Punch biopsies taken immediately after BLM injection  had 276.1 µg/cmectively . Low conp = .003) but the laser-exposed skin gradually recovered over 9 d, as shown by the clinical photographs in p = .029). EP alone resulted in mild erythema, but also aggravated erythema when combined as AFL + BLM + EP or NI + BLM + EP treatments. Moderately intense LSRs following NI + BLM + EP appeared concurrently with a substantial loss of skin integrity, and this was the only intervention in which skin integrity did not completely recover within 9 d  are expressed as a proportion of applied concentrations (µg/mL). NI + BLM results in most of the BLM applied being deposited in the skin, whereas AFL + BLM only deposit a fraction of the applied volume, rendering direct comparisons very difficult. Regardless, both delivery methods deposited high concentrations of BLM. A recent study that used mass spectrometry to quantify BLM in human tumor tissue following intravenous administration found that approximately 0.1 µg/g of BLM was present 8 min after infusion .In our study, BLM was present in samples for the entire study duration of 9 d, regardless of the administration route. However, intradermal BLM was washed out within 4 h after AFL + BLM, whereas an insignificant quantity of BLM remained 4 h after NI + BLM. Intradermal drug residence time is essential when supplementing treatments with EP: the current consensus on BCC treatment is that EP should follow within minutes of BLM administration . We applied 80 mJ/mb and reached a median depth of 1253 µm. This fits well with a previous study using in vivo pig skin where 80 mJ/mb created laser channels of ∼1300 µm depth (Olesen et al., ex vivo study has shown that laser-channel dimensions alter BLM penetration depth (Hendel et al., in vivo.Distinct biodistribution patterns were visualized by mass spectrometry imaging  and are in vivo skin. Evaluation of LSRs showed that both methods were well tolerated, and each method has potential for different indications and individualized approaches in a clinical setting.In conclusion, AFL and NI result in distinct but effective cutaneous biodistribution patterns and pharmacokinetic profiles for BLM applied to Click here for additional data file.


SLC27A1, ACOX3, NR4A1, VEGFA, JUN, EGR1, CACNB1, GADD45A and DUSP1, were co-enriched in the peroxisome proliferator-activated receptor (PPAR) signaling pathway, p53 signaling pathway and mitogen-activated protein kinases (MAPK) signaling pathway, etc. Transcriptome results of the Jingxing Yellow chicken population showed that the SLC27A1 gene was significantly associated with hexanal and enriched in the PPAR pathway. Our study provides a comprehensive insight into the key genes related to hexanal content, and can be further explored by functional and molecular studies.The role of hexanal in flavor as an indicator of the degree of oxidation of meat products is undeniable. However, the genes and pathways of hexanal formation have not been characterized in detail. In this study, we performed differential gene expression analysis and weighted gene co-expression network analysis (WGCNA) on groups of Tiannong partridge chickens with different relative hexanal content in order to find the genes involved in the formation of hexanal and the specific pathways of hexanal formation. Then we confirmed the relationship of these candidate genes with hexanal using Jingxing Yellow chicken and Wenchang chicken. In this study, WGCNA revealed a module of co-expressed genes that were highly associated with the volatile organic compound hexanal. We also compared transcriptome gene expression data of samples from chicken groups with high and low relative contents of hexanal and identified a total of 651 differentially expressed genes (DEGs). Among them, 356 genes were up regulated, and 295 genes were downregulated. The different biological functions associated with the DEGs, hub genes and hexanal were identified by functional analysis using the Kyoto Encyclopedia of Genes and Genomes (KEGG) annotations. Among all the hub genes in the significant module identified by WGCNA, more were enriched in the PPAR signaling pathway, the proteasome pathway, etc. Additionally, we found that DEGs and hub genes, including  Volatile organic compounds (VOCs) are the key constituents of meat aroma and flavor and advance the cognition of meat quality . TherefoVvLOXA may be a crucial gene in the regulation of C6 volatiles synthesis [Some studies have identified genes whose proteins take part in the regulation of hexanal content. For instance, after treating bananas to increase their storage time, the relative content of the compound hexanal, which contributes to their aroma, was reduced, and the activities of LOX and AAT were inhibited. Among the metabolic pathways identified, besides amino acid metabolism pathways involved in fruit ripening, lipid metabolism pathways were also affected . By compynthesis . During ynthesis . The gasynthesis . As far In this study, 398 125-day-old Tiannong partridge hens were used as experimental subjects. WGCNA was performed on relative contents of hexanal, and then 10 samples from each group with high and low relative contents of hexanal were subjected to differential gene expression analysis to identify candidate genes associated with the VOC hexanal. Further, transcriptome data from 18 samples in population of Jingxing Yellow chicken were analyzed to identify candidate genes in relation to hexanal.This study and all experimental protocols were approved by the Laboratory Animal Welfare and Animal Experimental Ethical Inspection board of Foshan University (No. 18091801). In total, 398 female Tiannong partridge chickens were obtained from Guangdong Tinoo’s Foods Group Co., Ltd. . The birds were raised in an environmentally controlled room, using commercial standard feeding. At the age of 125 days, after a 12-h overnight fast, the chickens were electrically stunned and killed by exsanguination. After slaughtering, the pectoral muscle samples were dissected from the same area of each chicken and stored at −80 °C for subsequent RNA isolation. The rest of pectoral muscle samples were stored at −80 °C for the determination of hexanal content.®-Spectrophotometer  and RNA integrity and concentration were measured using the RNA Nano 6000 Assay Kit for the Bioanalyzer 2100 system . RNA-sequencing was performed on an Illumina NovaSeq 6000 S2  and 150-bp paired-end reads were generated [Total RNA was extracted from 398 chicken pectoral muscle tissue samples using TRIzol reagent  and certain total RNA samples were selected for subsequent RNA sequencing. The RNA quality was assessed as previously described by Resnyk et al. . The RNAenerated . We thenenerated . Softwarhttp://bigd.big.ac.cn/gsa (accessed on 8 March 2021). The procedure for the determination of hexanal by GC-MS analysis and the relative content of hexanal of 18 samples of Jingxing yellow chickens are shown in the literature [Transcriptome data from 18 breast muscle tissue samples of Jingxing yellow chickens  were uplterature .All Tiannong partridge samples were clustered to exclude any obvious outliers . We then performed network construction and module detection using a step-by-step procedure. We constructed a weighted co-expression network using the thresholding power β (β = 1 to 30) to calculate adjacency between genes. Additionally, we chose the soft thresholding power (β = 8) to construct a network based on the criterion of approximate scale-free topology, using mergeCutHeight = 0.25 and minModule-Size = 30. We calculated the gene significance (GS), the correlation of the module and the gene expression profile (MM).p value of less than 0.05 and absolute log2 fold change (FC) values of at least 0.585 were DEGs [From the 398 breast muscle tissues, 10 samples with high (H) and low (L) hexanal relative contents were selected to perform this analysis. The analysis of differentially expressed transcripts was performed with the edgeR package (v 4.0.2). Genes with a ere DEGs . Hierarc−(ΔΔCt) formula was used to quantify the relative gene expression with GAPDH as a reference gene [The primers for qRT-PCR were designed by Primer premier software . The forward (F) and reverse (R) primer of each gene were derived from different exons, and the size of each PCR product was about 150~250 bp. qRT-PCR was carried out in a Bio-rad CFX96 Real-Time Detection system  employing KAPA SYBR FAST q-PCR Kit  according to the manufacturer’s instructions. The 2nce gene .t-test) to calculate the statistical significance . p values of less than 0.05 were considered statistically significant. The biological pathways were established using the Kyoto Encyclopedia of Genes and Genomes (KEGG) database (https://www.kegg.jp/kegg/pathway.html accessed on 8 March 2021). The significance level for KEGG pathways was set to p < 0.05. The correlation analysis between candidate gene expression and hexanal content was performed in R statistical software (version 3.6.1) in Jingxing yellow chickens.The mean and standard deviation of the relative contents of hexanal were analyzed using Microsoft Excel 2016 . The results obtained in this study were expressed as the mean ± standard deviation (SD). We used univariate analysis , dark green module , salmon module  were selected from the Jingxing Yellow chicken we published [To verify the ublished . The genSLC27A1, ACOX3, and JUN) that are significantly associated with hexanal content. KEGG enrichment analysis revealed the relevant module enriched in the regulation of the PPAR signaling pathway, indicating a close relationship between fatty acids and hexanal content. In addition, many studies concerning the oxidation of hexanal by fatty acid, e.g., linoleic acid, have been performed [SLC27A1, which may be a promising novel candidate gene for hexanal (which will be discussed below). Thus, our findings not only confirmed that the PPAR pathway is very important to produce hexanal but also identified novel potential candidate genes for hexanal formation. Our study provides some valuable evidence to gain a better understanding of hexanal genetics and thus provide potential molecular intervention targets for hexanal.In this study, we first performed a system network analysis by transcriptome data summary statistics with hexanal content. We successfully identified four modules  containing 50 interconnected genes and several core genes  in Berkshire pigs, and all four SNPs were significantly associated with meat quality traits, such as IMF and meat color . Signifirocesses . NR4A1 wf cattle . VEGFA wrian pig . Accordiipocytes . CACNB1  chicken . The JUNtor HSF1 . Fewer sSLC27A1, ACOX3, JUN, ROR1, GADD45A and DUSP1. In Jingxing Yellow chickens, SLC27A1 gene expression was also significantly correlated with hexanal content. These findings have revealed promising candidate genes for improvement of hexanal in further molecular studies.To understand the differences in gene expression patterns between the high hexanal group and low hexanal group in Tiannong partridge chicken, the hexanal-related genes were identified. In this study, we performed RNA-seq and characterized nearly 400 samples. Co-expression network analysis identified four modules that were associated with hexanal. The hub genes obtained using the GS value were enriched in the proteasome pathway. Moreover, besides identifying DEGs using the R software, we also identified genes related to hexanal content. Additionally, we found that DEGs and hub genes were co-enriched in the PPAR signaling pathway, Tight junction, Wnt signaling pathway, p53 signaling and MAPK signaling pathway, which included