This study aims to evaluate the effect of curing and drying conditions on the strength properties of concrete containing coal bottom ash (CBA) and fly ash as substitutes for fine aggregates and cement, respectively. The strength properties of the concrete including CBA and fly ash were evaluated under two different curing and drying conditions: saturated surface-dry (SSD) conditions and oven-dried conditions at curing ages of 28 and 91 days. The natural fine aggregates of the mixtures were replaced by CBA fine aggregates at 25%, 50%, 75%, and 100% by volume. In addition, the cement in the mixtures was partly replaced with fly ash at 20% and 40%. The experimental program included the measurement of the unit weight, compressive strength, splitting tensile strength, flexural strength, and ultrasonic pulse velocity of the concrete. The test results showed that the compressive strength, splitting tensile strength, and flexural strength decreased as the CBA content increased under both SSD and oven-dried conditions. The curing and drying conditions of the concrete with CBA and fly ash considerably influenced the reduction in the compressive, splitting, and flexural tensile strengths of the concrete. Additionally, the experimental results showed that fly ash insignificantly contributed to the reduction in the strength properties under both SSD and oven-dried conditions. Finally, the relationships between ultrasonic pulse velocity and the splitting tensile strength, flexural tensile strength, and compressive strength were investigated. Sustainable development in the construction industry is pursued by many nations worldwide, so the utilization of waste from the industry has become more essential. Moreover, the utilization of waste as a binder in concrete can reduce the amount of cement used, which ultimately reduces the price of the concrete and the carbon dioxide emissions from the cement industry . TherefoThe utilization of CBA as a fine aggregate for fabricating concrete has been reported by several studies ,14,15,16Fly ash has been applied in concrete as a cementitious material or filler material. It is known that the use of fly ash in concrete has many benefits, such as reducing the hydration heat, increasing the workability of fresh concrete, reducing the shrinkage, and especially improving the strength of concrete at long-term curing ages ,21,22,23Although CBA and fly ash have been widely applied in the concrete industry, few studies ,31 have Therefore, this study aimed to investigate the effect of curing and drying conditions on the strength properties of concrete containing CBA and fly ash. The mechanical properties of concrete were evaluated under two different drying conditions: saturated surface-dry (SSD) conditions and oven-dried conditions. In addition, the effects of the CBA and fly ash contents on the mechanical properties of the concrete were analyzed. The strength properties of the concrete with CBA and fly ash at each drying condition were measured at curing ages of 28 and 91 days. Finally, the relationships between the splitting tensile strength, flexural tensile strength, compressive strength, and ultrasonic pulse velocity were provided based on the test results.3, respectively. The natural fine and coarse aggregates had maximum sizes of 5 and 20 mm, respectively. The particle size distributions of the natural coarse and fine aggregates are shown in The natural coarse and fine aggregates used in this study were crushed. Both natural coarse and fine aggregates were tested to determine their physical properties, including their density, water-absorption capacity, and particle size distribution. The density of aggregates was measured under SSD conditions. The SSD condition was considered the state in which the aggregate had a dry surface but the particle pores in aggregates were saturated with water. Thus, the water absorption from the aggregate could be disregarded. The physical properties of the natural coarse and fine aggregates are presented in 3, was lower than that of the natural fine aggregate. The water absorption rate of fine CBA aggregate is the rate of the increase in mass due to water in the pores of the fine aggregate. The water absorption of aggregate would increase with the internal pore structures of aggregate. Generally, the number of pores in fine CBA aggregates is greater than that in fine and coarse natural aggregates. Therefore, the water absorption of the CBA fine aggregate used in this study was much greater than that of the natural fine and coarse aggregates. Specifically, the water absorption of CBA, at 3.88%, was approximately six times greater than that of the natural fine aggregate, at 0.64%.The CBA and fly ash used in this study were collected from a thermal power plant company . CBA was used as a substitute for natural fine aggregates in the mixtures. The test results in To make the maximum size of the CBA similar to that of the fine aggregate, the original CBA obtained from a thermal power plant was ground with a ball mill. Then, CBA with particle sizes in the range of 0.15~5.0 mm was chosen to replace the fine aggregates by the sieve test. The sieve analysis results of the combinations of CBA and natural fine aggregate at different replacement ratios are shown in 2) occupying more than 50% of the total amounts of components. The other main components of the CBA aggregate were Al2O3, Fe2O3, and CaO.By using an X-ray fluorescence (XRF) spectrometer, the chemical compositions of CBA and fine aggregates were obtained, as shown in 3 and 2800 cm2/g, respectively. Additionally, fly ash had a density and fineness modulus of 2.23 g/cm3 and 3650 cm2/g, respectively. The chemical compositions of OPC and fly ash are shown in 2 and Al2O3.The binder used in this study included ordinary Portland cement (OPC) and fly ash. OPC was supplied by Ssangyong C&E Company . The OPC used in the mixtures was type I with an initial setting time of 45 min and a final setting time of 360 min. The density and fineness modulus of the OPC were 3.15 g/cmTo investigate the effects of fly ash and CBA on the properties of the concrete, two series of mixing proportions in terms of fly ash contents were prepared. The mixing proportions of this study are presented in detail in For the first series of mixing proportions, the cement was replaced by fly ash at a replacement ratio of 20% by volume, and the natural fine aggregates were replaced by CBA at four different replacement ratios by volume: 25%, 50%, 75%, and 100%. For the second series of mixing proportions, the volume of cement was replaced by fly ash at a replacement ratio of 40%, and the volume of natural fine aggregates was replaced by CBA at two different replacement ratios: 50% and 100%. The last two digits in the mixture identifications represented the curing age of the concrete specimens.The water to binder ratios of the first and second mixing series were 0.32 and 0.34, respectively.The water-absorption capacity of CBA was much greater than that of natural fine aggregates. Thus, in particular, the aggregates and CBA were prepared under SSD conditions to ensure that they did not absorb the mixing water. The ratio of fine aggregate content to total aggregate content remained constant at 0.43 by volume. A high-range water-reducing agent (HWRA) and air-entraining (AE) admixture were added to the mixture to improve the workability of the concrete mixtures. The HWRA and AE were supplied by Silkroad C&T Company . The amount of HWRA was equivalent to 1.2% binder by weight, while that of the AE admixture was equal to 2.8% HWRA by weight.Cylindrical specimens with dimensions of 100 mm (diameter) × 200 mm (length) were cast to measure the mechanical properties of CBA concrete, including the unit weight, compressive strength, and splitting tensile strength. Prism specimens with dimensions of 100 mm × 100 mm × 400 mm were cast to measure the flexural tensile strength. To investigate the effects of curing and drying conditions on the mechanical properties, two different curing and drying conditions for concrete specimens were considered: SSD conditions and oven-dried conditions.For the SSD condition, the specimens were demolded after 24 h of concrete casting and then cured in a water tank at 24 ± 2 °C until the testing date. Thereafter, the moisture on the concrete specimen surface was removed with towels before testing. Additionally, for the oven-dried conditions, the specimens were demolded after 24 h of concrete casting and then cured in a water tank at 24 ± 2 °C for 7 days. After that, they were cured at room temperature in the laboratory until 1 day before testing. Finally, the concrete specimens were dried in an oven at 105 ± 5 °C for 24 h before the measurement.CBA is a high water-absorption material, and thus, moisture content or drying conditions can strongly affect the properties of concrete, including CBA. Typical curing of concrete at room temperature is an actual condition for concrete structures in construction sites. However, the moisture content of concrete specimens under typical conditions depends on the room temperature and humidity. The room temperature and humidity also vary with the environmental conditions under which the test is performed. Consequently, the test results at room temperature may vary depending on the temperature and humidity to which the concrete specimen is subjected. Therefore, the method of concrete curing at room temperature is not considered in this study.Meanwhile, the SSD condition is an ideal condition under which the concrete specimen is fully saturated with moisture. Oven-drying conditions are another ideal condition under which concrete specimens are assumed to be dried completely. In terms of moisture contents and drying conditions, the SSD conditions and oven-dried conditions selected in this study are two extreme conditions because actual drying conditions of concrete specimens probably exist on the spectrum between SSD conditions and oven-dried conditions. Therefore, test results obtained under the SSD and oven-dried conditions might be meaningful in academic research, although they do not reflect the actual drying conditions in practice.For the fresh concrete, the workability of each mixture was examined by implementing a slump test according to Korean standard KS F 2402 . For harThe material properties of the F20 series specimens in To investigate the material properties, the unit weight, compressive strength, and splitting tensile strength of the CBA concrete were measured by using cylindrical specimens in accordance with Korean standards KS F 2405 and KS F 2423 ,38. AccoFinally, the ultrasonic pulse velocity was measured by using transducers and a pulse generation circuit with a frequency of 54 kHz in accordance with ASTM C597-02 . Before The slump test results of the F20 and F40 series specimens are shown in The slump of the F40 mixture series was greater than that of the F20 mixture series. At the different CBA contents, an increase of approximately 15% in slump was observed in the F40 mixture series. This meant that the fly ash contents improved the workability of the CBA concrete mixture. The increase in slump of the F40 mixtures was due to the characteristics of the fly ash particles. According to scanning electron microscopy (SEM) results, the fly ash particles had a smooth surface, a spherical shape, and a small size compared to OPC particles. These characteristics effectively reduced interparticle friction and created a ball-bearing effect in the particle matrix of the mixture.The unit weight test results of the F20 and F40 series under the SSD conditions and oven-dried conditions are presented in These results were obtained at a curing age of 28 days. The results indicated that higher CBA contents in the concrete specimens led to a reduction in the unit weight. For the SSD condition, the unit weight of the F20 and F40 series decreased by 4.5% and 4.7%, respectively, when the CBA contents increased from 0% to 100%. It was assumed that compared to the density of fine natural aggregate, the low density of the CBA fine aggregate was the main reason for the decrease in the unit weight in the CBA concrete .For the oven-dried conditions, a reduction in the unit weight was also observed in both the F20 and F40 series. The unit weight of the F20 series decreased by 5.1% and that of the F40 series decreased by 4.5%. The decrease in the unit weight in the CBA concrete was due to the porosity of the CBA fine aggregate being higher than that of the natural fine aggregate.The test results also indicated that the drying condition affected the unit weight of the CBA concrete. The unit weights of specimens in the oven-dried conditions were lower than those of specimens under the SSD conditions. For the F20 series, specifically, the unit weight of the specimens under the oven-dried conditions at the various CBA contents was 3.4~4.2% lower than that under the SSD conditions. For the F40 series, the unit weight of the specimens under the oven-dried conditions at the various CBA contents was 3.4~3.8% lower than that under the SSD conditions.In addition, the fly ash contents affected the unit weight of the CBA concrete. For both SSD and oven-dried conditions, the unit weight of the CBA concrete with a high fly ash content was lower than that of the CBA concrete with a low fly ash content. The density of the fly ash was lower than that of OPC; therefore, replacement of the OPC by fly ash contributed to the reduction in the unit weight of the CBA concrete.The typical failure pattern of the specimen under the compressive strength test is presented in The compressive strength test results of the CBA concrete under the two different drying conditions are presented in A slight decrease in the compressive strength was also reported by Rafieizonooz et al. . MoreoveThe effect of the drying conditions of the specimen on the compressive strength was significant. After the CBA concrete specimens were oven-dried, the compressive strength of the concrete specimens was 15.1~16.7% lower for the F20 series and 14.7~15.2% lower for the F40 series at various CBA contents. According to the study by Hager , hydrateThe replacement of cement with fly ash tended to decrease the compressive strength of the CBA concrete. As an example, the compressive strength of the F40-B050–28(S) specimen was 4.3% lower than that of the F20-B025–28(S) specimen under SSD conditions. The difference between the compressive strengths of the F20 and F40 series in oven-dried conditions was not significant. As an example, the compressive strength of the F20-B050–28(D) specimen was 53.0 MPa while that of the F40-B050–28(D) was 51.9 MPa.2 and Al2O3. These compositions played an important role in the pozzolanic reaction. Therefore, the development of the pozzolanic reaction with curing age produced calcium silicates and aluminates, which filled the voids in the concrete matrix and improved the strength of the concrete.The effect of the curing age on the compressive strength of the F20 series is shown in In addition, the curing-time extension motivates the complete hydration of the cementitious materials, which contributes to improving the strengths of concrete at long curing ages. Thus, a greater compressive strength was observed at 91 days of curing due to the combined effects of the curing age and pozzolanic reaction of the substituted materials. This phenomenon was also reported in previous studies ,29.The elastic modulus of the concrete mixture is provided in The splitting tensile test results of the CBA concrete are provided in The drying condition also had a significant influence on the splitting tensile strength of the CBA concrete. The splitting tensile strength under the oven-dried conditions was lower than that under the SSD conditions. The reduction rate in the splitting tensile strength of the F20 series ranged from 11.2% to 16.2%, while that in the splitting tensile strength of the F40 series ranged from 8.2% to 11.8%. The evaporation of free water in cement paste and water in the C-S-H gel also contributed to the reduction in the splitting tensile strength of the CBA concrete.The influence of the fly ash content on the splitting tensile strength can also be observed in The influence of the curing age on the splitting tensile strength of the F20 series is shown in The tensile strength of concrete can be determined by either a direct tensile test or an indirect tensile test. In the direct tensile test method, there is difficulty gripping both ends of a concrete specimen, and eccentricity at both ends of a specimen can cause variability in the experimental tensile strength results. Therefore, the indirect tensile test method is preferred. The indirect tensile test methods include splitting and flexural tensile tests, which were used in this study. In particular, the flexural tensile strength, or modulus of rupture of concrete, can be used to control tensile cracks in concrete members.According to ACI 363R-10 , the dirThe direct tensile strength of concrete can also be estimated by using the flexural tensile strength, as expressed in the following equation:To determine the precise coefficient of the equation, it is necessary to perform the direct tensile test and analysis of the test results. Estimating the coefficient of the equations will be conducted in future studies.The flexural tensile strength results of the CBA concrete under the SSD conditions are shown in The flexural tensile strength of the F20 series specimens at a curing age of 91 days is shown in t,fOD and t,fSSD are the splitting tensile strength (MPa) under the oven-dried and SSD conditions, respectively. c,f′OD and c,f′SSD are the compressive strengths (MPa) under oven-dried and SSD conditions, respectively. The coefficients of determination (R2) of this equation were close to 1, which indicates that these equations could be used to precisely predict the values of the splitting tensile strength by using the compressive strength of CBA concrete.The relationship between the splitting tensile strength and compressive strength under the SSD and oven-dried conditions is shown in t,fSSD is the splitting tensile strength (MPa) and c,f′SSD is the compressive strength (MPa) under the SSD conditions.In addition, based on the test results in this study and in another study , the relOverall, the prediction is in good agreement with the test results. Specifically, the equation could more precisely predict the splitting tensile strength of the CBA concrete with low fly ash (F20 series), while it overestimated the splitting tensile strength of the CBA concrete with high fly ash (F40 series). In addition, the coefficient of determination for this equation is high, at a value of 0.8365. This implies that the splitting tensile strength could be predicted practically by using the proposed equation.r,fSSD is the flexural tensile strength (MPa) and c,f′SSD is the compressive strength (MPa).The relationship between the flexural tensile strength and compressive strength of the CBA concrete under the SSD conditions is presented in The measurements were scattered because they were measured at curing ages of 28 and 91 days. Therefore, the coefficient of determination of this equation was slightly low.r,fSSD is the flexural tensile strength (MPa) and c,f′SSD is the compressive strength (MPa) under the SSD conditions. This equation showed a low coefficient of determination with a value of 0.5759 because most test results deviated from the prediction line. It was assumed that the accuracy of prediction would be enhanced if more test results were included.In addition, based on the test results in this study and previous studies ,31, the t,fSSD is the splitting tensile strength (MPa) and r,fSSD is the flexural tensile strength (MPa).t,fSSD is the splitting tensile strength (MPa) and r,fSSD is the flexural tensile strength (MPa) under the SSD conditions. This equation presents a high coefficient of determination of 0.9238. This finding indicates that the proposed equation could be practically used to predict the splitting tensile strength of CBA concrete based on the flexural tensile strength.In addition, the relationship between the splitting tensile strength and flexural tensile strength of the CBA concrete, based on the test results in this study and a previous study , is presThe strength of the CBA concrete might be decreased by CBA as a partial or full replacement of aggregate. In particular, the use of concrete containing CBA as a replacement for coarse aggregate is hardly used in structural members due to high strength reduction but is usually used in nonstructural members of concrete structures.Meanwhile, the strength test results in this study showed that concrete containing CBA as a replacement of fine aggregate and fly ash as a partial replacement of cement obtained remarkable strength of the concrete. Moreover, due to the pozzolanic reaction of fly ash, the replacement of fine aggregate with fly ash could overcome the reduction of strength in the CBA concrete in the long term. Finally, the overall strength test results in this study implied that concrete containing CBA as a partial replacement of fine aggregate could be used in structural members if the strength reduction due to CBA fine aggregate was acceptable in terms of the design of reinforced concrete structures.However, the investigation of this study was restricted to selected mechanical properties, such as compressive, splitting tensile, and flexural tensile strength. To extend the use of the concrete analyzed in this study, more characteristics of concrete, for example, durability and bonding of the concrete, should be analyzed, but they were out of the scope of this study.The test results of the ultrasonic pulse velocity of CBA concrete are shown in The relationships between the ultrasonic velocity and compressive and splitting tensile strengths of concrete containing CBA aggregate were suggested in some studies ,17,31, bc,f′OD and c,f′SSD are the compressive strengths (MPa) under oven-dried and SSD conditions, respectively. VOD and VSSD are the ultrasonic velocity (m/s) under oven-dried and SSD conditions, respectively. Regression analysis indicated that the coefficient of determination of the equation was close to 1, which indicates that this equation could be effectively used to predict the compressive strength.The relationship between the compressive strength and ultrasonic velocity under the SSD and oven-dried conditions is presented in Meanwhile, Rafieizonooz et al.  suggesteThe test results obtained from this study and previous studies are shown in Therefore, based on the test results in this study and previous studies, an additional exponential equation for predicting the compressive strength of the CBA concrete was proposed as follows:2 is the sum of the squared errors, iy is the measurement, and y′i is the prediction.Moreover, to estimate the level of prediction accuracy, the sum of squared errors for the prediction equation was calculated as follows:2) for Equations (11)–(13) were 8432, 9628, and 4319, respectively. This comparison showed that the sum of the squared errors in Equation (13) was the lowest among the three equations. Therefore, compared with Equations (11) and (12), Equation (13) more accurately predicted the compressive strength of the CBA concrete by using the ultrasonic velocity.The sums of the squared errors  under oven-dried and SSD conditions, respectively. VOD and VSSD are the ultrasonic velocity (m/s) under oven-dried and SSD conditions, respectively. These equations predicted the splitting tensile strength of the CBA concrete well.The relationships between the splitting tensile strength and ultrasonic velocity of the CBA concrete are presented in As described in the regression equation to predict compressive strength, the coefficient of determination of the proposed equation for the flexural tensile strength was close to 1.In addition, the relationship between the ultrasonic velocity and flexural strength of the CBA concrete, based on the test results in this study and a previous study , is showThe predictions in The unit weight of the CBA concrete containing fly ash was sensitive to oven-drying. Specifically, the unit weight of the CBA concrete was reduced by approximately 5% when the drying method was changed from the SSD conditions to oven-dried conditions. The reduction in the unit weight resulted from the evaporation of the absorbed water and free water in the CBA concrete specimens. In addition, the substitution of natural aggregates and cement with CBA and fly ash tended to reduce the unit weight of the CBA concrete by approximately 4.8~5.7%.The compressive and splitting tensile strengths of the CBA concrete decreased significantly under oven-dried conditions. The compressive and splitting tensile strengths under oven-dried conditions were approximately 15% lower than those under SSD conditions. This implied that they depended on the drying condition of the concrete specimen. However, the CBA and fly ash contents slightly contributed to the reduction in the compressive and splitting tensile strengths of the CBA concrete.The flexural tensile strength of the CBA concrete was also slightly influenced by the replacement of fine aggregate with CBA. However, the flexural tensile strength of the CBA concrete was considerably enhanced at a long-term curing age by approximately 22%. The test results revealed that the flexural strength of the CBA concrete was increased by the pozzolanic reaction of the CBA and fly ash materials.Strength test results implied that the replacement of fine aggregate with fly ash could overcome the reduction of strength in the CBA concrete in the long term due to the pozzolanic reaction of fly ash. Therefore, in terms of strength, concrete containing CBA as a replacement of fine aggregate and fly ash as a partial replacement of cement could be used in structural members.The drying conditions caused a significant decrease in the ultrasonic velocity in the CBA concrete. For the F20 series concrete, the ultrasonic velocities under oven-dried conditions were 5.8~6.2% lower than those under SSD conditions with various CBA contents. For the F40 series concrete, the ultrasonic velocities under oven-dried conditions were 5.8~6.6% lower than those under SSD conditions with various CBA contents.The relationships between the ultrasonic velocity and compressive, splitting tensile, and flexural tensile strengths under the SSD and oven-dried conditions were presented. The relationships highly varied depending on the drying and curing conditions. Therefore, when the strength of the CBA concrete is predicted by using ultrasonic velocity measurements, the drying and curing conditions should be considered.The effects of the curing and drying conditions on the strength properties of CBA concrete at various CBA contents were investigated in this study. Given the extensive experimental results, the following conclusions could be drawn:


This study experimentally investigated various axial compressive parameters of a new type of confined concrete, which is termed bamboo sheet twining tube-confined concrete (BSTCC). This new composite structure was composed of an outer bamboo composite tube (BCT) jacket and a concrete core. Under axial compression, the parameters of thirty-six specimens include concrete strength  and BCT thickness . The mechanical properties of the BSTCC specimens from the perspective of the failure mode, stress-strain relationship, effect of BCT thickness and dilation behavior were analyzed. The results showed that, in compression, with an increase in BCT thickness in the range of 18-layers of bamboo sheets, the strength increased remarkably. When the strength of the concrete core was high, the confinement effect of the BCT was reduced. In addition, the BCT thickness relieved the dilation of the BSTCC specimens. Finally, the experimental results were compared with predictions obtained from 7 existing FRP-confined concrete models. All the predictions had good agreement with the test results, which further confirmed that the models developed for FRP-confined concrete can provide an acceptable approximation of the ultimate strength of the BSTCC specimens. It is well known that steel tubes and fiber reinforced polymer (FRP) material as external confinement of concrete enhances concrete axial compressive strength and ductility significantly ,2,3. TheIn recent years, natural fiber reinforcements, as alternatives to carbon or aramid fibers, have been widely applied in aerospace, automobile, infrastructure, and other industrial fields ,9. The aAccording to previous studies, bamboo is a very attractive material due to its renewable short natural growth cycle and abundance of bamboo resources ,17,18,19If the bamboo is wound to form a tube and the core is filled with concrete, the excellent tensile performance of bamboo will be expected to develop to confine the concrete core. Therefore, to verify the feasibility of using bamboo composite tubes as external confining materials for a concrete core, Kou et al.  proposedOn the base of the structure of bamboo composite tube confined concrete, the mechanical behavior of bamboo sheet twining tube-confined concrete (BSTCC) under axial compression was investigated. The bamboo was wound to form different thick composite tubes, and concrete filled its core. The influence of the wall thickness of bamboo composite tube and different concrete strength on the confinement of the concrete core were fully analyzed. Parameters of the specimens in this paper vary over wide ranges, with unconfined concrete strength from 39.15–70.59 MPa and bamboo sheet layers (6–30). In addition, the new tests significantly widened the range of confinement ratios (the ratio of the ultimate confining pressure to the unconfined concrete strength) of 0.04–0.34 for the 36 tests considered in this paper. Utilizing the good tensile strength of bamboo, the results presented in the study are expected to provide a new structure for confining concrete with bamboo composite tubes.Thirty-six specimens (thirty bamboo sheet twining tube-confined concrete columns (BSTCC) and six unconfined concrete columns) with inner diameters of 150 mm and heights of 300 mm were designed and prepared for the monotonic axial compression test. The main variation parameters included the number of bamboo sheet layers , which is the thickness of the bamboo composite tube (BCT), and the grade of the concrete (C30 or C50). The specific parameters of the specimens are shown in The cement used in the test was Portland 42.5 . The specimens were cast in two batches with two different concrete mix ratios. To determine the concrete strength, three concrete cubes with dimensions of 150 × 150 × 150 mm were prepared in the same batch for each mix ratio. The specimens were cured under the same conditions for 28 days. It can be seen from Bamboo sheets provided by Haofeng Decoration Material Co., Ltd.  were used to manufacture composite tubes as the confined material in the test. The bamboo sheets were prepared by slicing softened moso bamboo stem along the bamboo fiber, and the nominal thickness of each bamboo sheet was 0.5 mm. Five coupons of bamboo sheets from the same batch were made to obtain the tensile properties of the bamboo sheets parallel to the bamboo grain . The tenThe epoxy resin adhesives (L-500AS/L-500BS) used in this test were provided by Sanyu Resin Co., Ltd. . The average tensile strength, elastic modulus, and ultimate tensile strain values were 67.7 MPa, 2.9 GPa, and 0.029, respectively.The detailed production steps of BCT and BSTCC are shown in The compression tests were conducted on a high-stiffness testing machine with a capacity of 3000 kN provided by Popwil Electromechanical Control Engineering Co., Ltd.  a. Prior The measurement of strain distribution along specimen height and perimeter may be enabled by the digital image correlation (DIC) measurement technique. However, the data processing of DIC is complex. Installing strain gauges around the mid-height section and laser displacement sensors were adopted in this test, which have been also verified in most previous studies on FRP-confined concrete ,3,4,5,6.maxP is the maximum axial load, ccf and ccε are the peak stress and the peak strain, respectively, and cuf and cuε denote the ultimate strength and the corresponding ultimate strain, respectively. Similar to conventional FRP-confined concrete, the confinement action of BCTs in concrete cores is passive and develops through the restraint of the lateral expansion of the concrete under uniaxial compressive loading. It is commonly assumed that the BCT ruptures when the hoop stress in the BCT reaches its tensile strength. Based on the deformation compatibility between the confining wrap and the concrete surface and assumption of a uniform confining pressure distribution, the confining pressure can be calculated using the following equation [lf is the lateral confining pressure provided by the BCT. fE, ft, and fε are the elastic modulus, thickness, and ultimate rupture strain of the BCT, respectively. D is the diameter of the concrete core in mm.equation :(1)fl=2EThe typical failure mode of the BSTCC specimens with different parameters is shown in The axial stress versus axial/lateral strain curves of the unconfined concrete and the BSTCC specimens are shown in As shown in The dilation behavior of the confined concrete can be effectively characterized by the lateral-to-axial strain relationship because the lateral dilation driven by the axial shortening of concrete is the cause of the confining pressure supplied by the BCT jacket, which in turn counteracts the lateral dilation. The lateral-to-axial strain curves of those specimens with the same concrete grade are shown together in cε and lε are the axial strain and lateral strain, respectively; cof and coε are the compressive strength of unconfined concrete in MPa and the corresponding axial strain, respectively; lf is the corresponding continuous confinement pressure for a given lateral strain; iv is the initial Poisson ratio of the concrete obtained from the unconfined concrete; and n is the curve shape parameter to adjust the initial transition radius of the predicted lateral-to-axial strain relationship curve.The lateral-to-axial strain relationship is an important index in the passively confined model of confined concrete, which provides the response of interaction between the concrete core and the external jackets. Several lateral-to-axial strain models have been proposed by Lim and Ozbakkaloglu , Jiang aAs shown in For FRP-confined concrete, the ultimate compressive strength is one of the critical parameters. To date, many models have been developed to predict the ultimate stress for FRP-confined concrete. In this study, a total of seven strength models for circular FRP-confined concrete collected from the literature are listed in α, β, and η of some models are listed in The axial behavior of confined concrete was first proposed by Richart et al. . The difAV), the standard deviation (SD), and coefficient of variation (COV), as given by Equations (7)–(9), respectively.Theo. and Expe. represent the predicted and experimental values, respectively. n represents the total amount of data.To evaluate the effectiveness of these existing FRP-confined concrete models for the BSTCC specimens, three statistical indices that were adapted to quantitatively assess the possible differences. These are the average value , the prediction values of these two ultimate strength models are larger than the experimental values. Similarly, the same phenomenon is observed in the Fahmy and Wu model, although the dispersion is low. The Samaan et al. model overestimates the ultimate strength of most BSTCC specimens owing to the overly large coefficient for the confinement effects, and the AV is 1.15. Because these models do not consider the effect of concrete strength, when the concrete strength is high, the prediction results are even larger. Therefore, the results indicate that the existing models developed for FRP-confined concrete can provide an acceptable approximation of the ultimate strength of the BSTCC specimens.As indicated in (1)The failure mode of the BSTCC specimens is a serrated crack that initiates at the middle of the specimen, and then the crack propagates towards the two ends of the specimen along its longitudinal direction. The BCT provides strong lateral confinement, and the ability to bear axial loads as the BCT thickness increases, which limits the failure of the specimens and resists lateral expansion deformation.(2)The complete stress-strain curves can be divided into three stages for the BSTCC specimens under compression: the first linear elastic stage, the second nonlinear transition region, and the third nonlinear stage. Furthermore, the initial stiffness of the BSTCC specimens is independent of the BCT thickness.(3)Compared with the unconfined concrete, the effect of the BCT thickness on the ultimate stress and strain is significant. The compressive strength of the BSTCC specimens increases with increasing BCT thickness. However, the increase ratio of the ultimate stress does not always increase with an increase in the number of bamboo sheet layers; only when the layer number is in a certain range does the increase ratio of the ultimate stress increase as the number of bamboo sheet layers increases. In addition, when the strength of the concrete core is high, the confinement effect also decreases.(4)After evaluating the existing lateral-to-axial strain models, the results show that the model of Lim and Ozbakkaloglu has better performance. Based on the lateral-to-axial strain model proposed by Lim and Ozbakkaloglu, the authors modified the calculation formulas. The proposed model of the lateral-to-axial strain model shows good agreement with the experimental results.(5)The experimental results are compared with predictions of some existing FRP-confined concrete models. For the BSTCC specimens, the models proposed by Wu and Wei and Wei and Wu are superior to the other existing models because they are capable of predicting the ultimate stress with good accuracy and generality.This study investigated the compressive behavior of bamboo sheet twining tube-confined concrete specimens (BSTCCs) through a series of tests, whose major parameters were the concrete strength and the bamboo composite tube (BCT) thickness. The test results are also compared with seven existing strength models for FRP-confined concrete to examine the applicability of such models to BSTCC. Based on the test results and analysis, the following conclusions can be drawn:


There was a 5.5–13.5% increase in the flexural tensile strength depending on the mixture type. Moreover, in the case of fiber-reinforced concretes, the ductility was enhanced and the samples were characterized by significant residual flexural tensile strengths. Additionally, from the workability tests it was concluded that after the incorporation of fibers, the consistency class decreased by one, two or three. Nevertheless, the compressive strengths of concrete with and without fibers were very similar to each other, and varied from 58.05 to 61.31 MPa. Moreover, it was concluded that results obtained from three-point bending tests significantly differed from empirical formulas for the calculation of the flexural tensile strength of fiber-reinforced concretes with dispersed steel fibers present in the literature. As a result, the new formula determined by the authors was proposed for concrete with polymer fibers with a nominal fiber content ≤1.0% and slenderness of up to 200. It must be mentioned that the formula gave a very good agreement with studies presented in different literature positions. In addition, an attempt was made to evaluate the strengths of tested mixes in accordance with the Model Code 2010. However, it occurred that the proposed fiber-reinforced concrete mixtures would not be able to replace traditional reinforcement in a form of steel bars. Furthermore, in uniaxial tensile tests, it was not possible to determine the σ–w graphs, and received results for maximum tensile strength did not show the clear influence of fibers incorporation on concrete. Then, the fracture energy enhancement (from about 16 to 22 times) and dependencies: crack mouth opening displacement–deflection; crack mouth opening displacement–crack tip opening displacement; and crack tip opening displacement–deflection were analyzed. Finally, the results from flexural tensile tests were compared with measurements of the surface displacement field obtained through the Digital Image Correlation technique. It was concluded that this technique can be successfully used to determine the crack mouth and crack tip opening displacements with very high accuracy.Fiber reinforcement is currently most often used in floors, railway sleepers, prefabricated structural elements such as slabs, beams and tanks, and in small architecture elements. Designing elements or structures made of fiber-reinforced concrete requires knowledge of its basic mechanical parameters. In the case of concretes with metallic fibers, the literature can find many tests and standard guidelines regarding compressive, flexural, tensile strength and fracture energy. The properties of concretes with non-metallic fibers are slightly less recognized, especially concretes with new types of polymer fibers. Additionally, the lack of standardized methods of testing concrete with polymer fibers make their application much more difficult. In the article, the possibility of using the EN 14651 standard to assess the flexural tensile strength of concrete with the addition of 2.0 and 3.0 kg/m Fiber-reinforced concrete (FRC) is obtained by adding steel or non-metallic, e.g., synthetic fibers to the concrete mix. Metallic fibers are often used to significantly improve the mechanical properties of concrete, and when protection against cracks is very crucial. Therefore, steel fibers are used in the production of, among others, industrial floors ,2, prefaf-fiber length; df-fiber diameter), type and nominal volume content (Vf) of fibers in the concrete. In addition, the bonding mechanism between the fiber and concrete also has an impact, i.e., whether the fibers are monofilament or fibrillated. Synthetic fibers can be divided into micro-and macrofibers. They are distinguished by their diameter: the microfibers have df < 30 mm and the macrofibers have df > 30 mm ;j or δ = δj  [N/mm2];j or δ = δj  [N];Thanks to the obtained graphs F-CMOD and F-δ, it was possible to determine the flexural tensile strength in the range of limit of proportionality standard . It mustThe uniaxial tensile test was performed on larger samples than those usually used in the tests ,63,64. IThe Digital Image Correlation technique is based on the idea of comparing the random speckle pattern, which was sprayed on the studied surface, of a reference image with the speckles in deformed images during the test. Thanks to this, it is possible to track the deformations and create the local strain map which allows to characterize both the fracture process zone and the crack. The aim to use the DIC technique was to compare the values of CMOD and CTOD measured in the DIC system with the ones from the clip gauges, and to visualize the crack propagation and to analyze the strain. The set-up of the DIC system is presented in 3 were tested for compressive strength (fc) in accordance with EN 206 ;fc—standard deviation of compressive strength [MPa];sn-1,α—with a confidence level of α = 0.05, for six samples (n − 1 = 5) − t5;0.05 = 1.67, for five samples (n − 1 = 4) − t4;0.05 = 1.46 [-].tThe addition of fibers to the concrete mix increased the fh the PC . Moreoves, e.g., ,66,67. IL) and to CMOD = 0.5 (F1); 1.5 (F2); 2.5 (F3), and 3.5 mm (F4) were determined for the tested concrete mixes  performed better, in particular where fewer fibers (2 kg/m3) have been used. However, the best results were obtained for a hybrid blend with Vf = 2 kg/m3. This may be because of the fact that the combination of two types of fibers more effectively bridged the cracks that appear in the initial stage of cracking, and the lower fiber content allowed for more even distribution of all fibers in the concrete. Furthermore, when comparing the results with the ones obtained in the other literature positions, it occurred that the level of enhancement in the flexural tensile strength (ffl) is in agreement with many of them. For example in ,2],R,jk—characteristic residual flexural tensile strength corresponding to CMOD = CMODj or δ = δj  [N/mm2],fR,jm—mean residual flexural tensile strength corresponding to CMOD = CMODj or δ = δj  [N/mm2],f2] calculated from Equation (11);R,j—standard deviation of fR,j from fR,jm [N/mm2] calculated from Equation (12)n—number of samples [-],k—factor depending on the number of samples given in sModel Code 2010  proposesR,1k were smaller than 1.0. Additionally, only for the mixtures PM_3 and PD_2 the ratio fR,3k/fR,1k was greater than 0.5, so it is possible to assign them to letters c and a of Parameter 2, respectively. It is also not possible to completely or partially replace the traditional reinforcement with the fibers, as none of the concrete met the two above-mentioned requirements simultaneously: fR,1k/R,3k/fR,1k > 0.5. It is also worth mentioning that the characteristic values of the residual strengths were significantly reduced as a result of the large standard deviation  between samples in a given series. In future tests, it is advisable to increase the number of samples within each mixture. Furthermore, concrete mixes with different amounts of cement, coarse and fine aggregate, water and superplasticizer should be tested to verify made conclusions.F-CMOD). In the article, this area is counted up to CMOD = 3.5 mm. F-CMOD=3.5) calculated for all three specimens within each mixture. It can be concluded that specimens with more fibers performed best. The calculated toughness index Ti, which is equal to the ratio of GF-CMOD=3.5 for FRC to GF-CMOD=3.5 for PC samples, indicates that the fracture energy for PM_3 and PD_3 increased 22 and 19.6 times, respectively  and the coefficient of variation (VGF-CMOD=3.5) of the fracture energy. All the mixtures were characterized by quite high sGF-CMOD=3.5 and VGF-CMOD=3.5, which is also visible in GF-CMOD=3.5. In the case of the PM_3 mix, it was noticeable that some of the twisted fibers did not disintegrate, which influenced the distribution of the fibers in the crack cross-section and make it uneven. In order to avoid this situation in the future, the fibers should be added at the initial stage along with aggregates so that they have the possibility of breaking the bundles of fibers. A similar situation occurred in the case of PM_2. On the other hand, in the PD_3 mixture, there was no tendency to create bundles of fibers and the PD_2 mixture was characterized by the lowest VGF-CMOD=3.5. Thus, the reason for such large differences in GF-CMOD=3.5 in PD_3 may be connected with a significantly different number of fibers in the crack cross-section. It is noteworthy that the F-CMOD plot for the sample PD_3_3 clearly differed from F-CMOD plots for PD_3_1 and PD_3_2 and took much larger force values for the same values of CMOD. Additionally, by comparing A significant increase in the level of fracture energy absorption indicates the positive effect of synthetic fibers on the ductility of concrete, which makes it possible to avoid sudden, brittle failure of the FRC element. In addition, the greater the fiber content, the greater the toughness. t obtained during the UTT are presented in t. Despite PM_3 and FF_2, the samples had lower strength by around 11.5%. On the other hand, the small effect of Vf is visible, since mixes with 3 kg/m3 behaved better than the ones with 2 kg/m3 of the same fibers. Additionally, the hybrid mixture had ft 2.6% higher than the mix with no fibers. As was seen before, FF_2 performed usually better than other concrete mixtures with 2 kg/m3 of fibers. In future research, a higher number of tested samples should be used to limit the influence of different amounts of fibers in the cracked cross-section within one mixture.The results of the maximum tensile strength fIn the case of plain concrete, it was not expected to obtain σ-w curve since brittle failure was predicted. On the other hand, studied FRC were supposed to behave in a more ductile way. However, for none of them σ-w curve was received because the failure was really sudden. In 2 = 0.999). 2 = 0.998) was determined (Equation (14)). For the CTOD-δ relationship  were subjected to the DIC post-processing analyzes in the GOM Correlate 2020 software. Then, the CMOD and CTOD values were read from the program and together with the results from clip gauges plotted in the relevant figures together with corresponding F. 3 of synthetic fibers of different geometry and form. The following conclusions were drawn from the conducted research:As a result of adding synthetic fibers to concrete, the workability of the mixes deteriorated significantly. The consistency class decreased by three for FF_2, two for PM_3, PD_3 and PD_2, and one for PM_2, compared to plain concrete. Nevertheless, the type and fiber content did not significantly affect the compressive strength, which ranged from 58.06 to 61.31 MPa, depending on the mixture, while for concrete without fibers it was equal to 58.05 MPa.f = 48 mm) performed better, and in particular the one where a smaller amount of fibers (2 kg/m3) has been used. However, the best results were obtained with a hybrid blend with Vf = 2 kg/m3. This may be due to the fact that the combination of two types of fibers more effectively bridged the microcracks, and the lower fiber content allowed fibers for their more even distribution in the concrete.The fibers contributed to an increase in the flexural tensile strength of approximately 5.5% for PM_3, PM_2, and PD_3; 11.5% for PD_2 and 13.5% for FF_2. The mixtures with slightly shorter fibers (lf = 54 mm) performed best. It was because longer fibers more efficiently bridged the macrocracks. It is also worth noting that among the mixtures with 2 kg/m3, the highest values for almost all residual strengths were achieved for the hybrid blend, which may indicate the positive effect of combining two different types of fibers.The damage of beams without fibers was brittle and sudden, unlike for the fiber-reinforced concrete samples, which were still able to transfer a significant load with increasing crack mouth opening displacement, and possessed some ductility. The residual flexural tensile strengths of concrete with synthetic fibers usually reached higher values, when the fiber content was higher. Additionally, the mixture with the incorporation of the larger amount of fibers which were longer  resulting from the used test method-according to EN 14651. Additionally, in the case of some mixtures, it was noticeable that some of the twisted fibers did not disintegrate, which resulted in the uneven distribution of fibers. The reason for large deviations in the results of individual samples may be connected with a different number of fibers in the cross-section of the crack.The formula proposed by the authors for calculating the flexural tensile strength for concrete with polymer fibers with a nominal fiber content of ≤ 1.0% and slenderness up to 200 correlates very well with the results of the presented studies, as well as with those contained in various literature positions. Regarding the formula proposed in the EN 14651 standard to determine the relationship between the deflection and the crack mouth opening displacement, it was concluded that it differs from the relationship recorded during the presented tests of beams with synthetic fibers. As a result, a new formula was proposed by the authors, together with equations describing crack mouth opening displacement–crack tip opening displacement and crack tip opening displacement–deflection dependencies.3 of tested fibers in the concrete mix would not partially or fully replace traditional reinforcement in a form of steel bars. Furthermore, it was not possible to obtain σ-w curves from uniaxial tensile tests, and received results for maximum tensile strength did not show the clear influence of fibers’ incorporation on concrete.According to Model Code 2010, the use of 2 and 3 kg/mThe DIC technique can be successfully used to determine the crack mouth and crack tip opening displacements with very high accuracy.The article presents the possibility of using the EN 14651 standard to determine the flexural tensile strength of concrete with the addition of 2 and 3 kg/m


Extracorporeal membrane oxygenation (ECMO) is an emerging treatment modality associated with a high frequency of antibiotic use. However, several covariables emerge during ECMO implementation, potentially jeopardizing the success of antimicrobial therapy. These variables include but are not limited to: the increased volume of distribution, altered clearance, and adsorption into circuit components, in addition to complex interactions of antibiotics in critical care illness. Furthermore, ECMO complicates the assessment of antibiotic effectiveness as fever, or other signs may not be easily detected, the immunogenicity of the circuit affects procalcitonin levels and other inflammatory markers while disrupting the immune system. We provided a review of pharmacokinetics and pharmacodynamics during ECMO, emphasizing practical application and review of patient-, illness-, and ECMO hardware-related factors. Extracorporeal membrane oxygenation (ECMO) has been increasingly employed in critical care, showing a reduction in 90-day mortality in ARDS vs. conventional care in mixed metanalysis . HoweverThe primary advantage of ECMO is to provide ventilatory or hemodynamic support in severely critically ill patients as a bridge to recovery in otherwise irrecoverable patients. The presumption is that stress related to ECMO implementation is less deleterious than mechanical ventilation or classical circulatory system support via implanted devices or medical therapy ,10. In tA common indication for ECMO is acute respiratory distress syndrome (ARDS), most commonly from infectious etiopathogenesis ,7,8. In ECMO introduces several variables into antibiotic pharmacokinetics and pharmacodynamics, which must be considered to maximize therapeutic benefit and minimize risks. Moreover, the effect of ECMO on said parameters may be further complicated by patient characteristics and concomitant illnesses or organ failure ,19,20,212-removal device, Impella, intra-aortic balloon counterpulsation, and cytokine scavengers add other variables to understanding distribution, activity and metabolism of antibiotics in these situations [The need for understanding how to optimize antibiotics effectiveness in ECMO-related situations is critical as the implementation and indications of the ECMO continues to progress, while the emergence of ECMO-derivative techniques such as a COtuations ,23,24,25ECMO is a relatively young modality that evolved from cardiopulmonary bypass . In esseCannulas provide an access port to the patient’s vascular system. They are single lumen and dual lumen ,28. To pThe ECMO system comprises several items in the circuit, with a pump and a membrane allowing for gas exchange as main components, connected via relatively high bore tubing  Figure . The tubThe pump allows for high throughput, from the high bore intake cannula, through the oxygenator into the return cannula. There are two main types of pumps: roller and centrifugal . The latThe membrane oxygenator’s function is to provide a large surface area allowing for efficient gas exchange . The effFinally, a heat exchanger allows for precise and dynamic thermoregulation, and several in-line monitors and couplings allow for drug administration or system sampling ,29. TherIn general, the evolution of the ECMO circuitry is reflected in a decreased form factor and lower immunogenicity of the hardware . The forInfection is the main driver for ECMO initiation, with meta-analysis of the CESAR and EOLIA trials finding ARDS to be the main indication for initiation of said therapy, with >60% being precipitated by pneumonia ,8,13,23.Candida sp. may have superseded other organisms [Enterococcus (4%) are common pathogens [Given the implantation of multiple invasive devices, ECMO itself confers risk for development of infections, including bloodstream infection at risk linearly related to the duration of therapy . The prerganisms . Coagulaathogens . Each hoCurrently, there is no recommendation for routine infection prophylaxis in ECMO patients , althougAntibiotic mechanisms of action can be classically divided into bacteriostatic, which inhibit bacterial replication while relying on the host’s immune system to clear the infection, and bactericidal, which lyse bacteria. These effects are highly dependent on free drug plasma concentrations and hence not only antibiotic selection. Dosing is also paramount to effective therapy. As bacteriostatic antibiotics rely on host mechanisms, immunosuppression or existence of a nidus or niche allowing unimpeded bacterial replication results in resumption of bacterial growth once the bacteriostatic compound reaches subtherapeutic levels. Thus, the application of said antibiotics in critical care is somewhat limited. However, many bactericidal antibiotics exercise bacteriostatic effects below their bactericidal concentration. Considering that ECMO and routine dosing of antibiotics depresses the concentration of antibiotics to bacteriostatic levels, thus maintaining the adequate function of the immune system, may be the next step in assessing the effectiveness of the antibiotic.Antibiotic efficacy depends on several factors . Most imThe concentration of antibiotics is determined by the dose and the medium volume where the antibiotics are being diluted. Thus, the volume of distribution (Vd) is critical for determining antibiotic concentration . The amoAntibiotic concentrations can exert several actions depending on specific drug properties. The minimal bacteriostatic concentration (MBsC) relates to the minimum concentration that will inhibit bacterial replication in vitro and is utilized as a surrogate determinant of a specific antibiotic’s potency. Furthermore, bacteriostatic concentrations need to be sustained over time, as replication is impeded only under therapeutic concentrations. Consequently, antibiotic dosing must be frequent enough to prevent levels from dropping below MBC to maintain effectiveness. Conversely, increasing antibiotic concentrations diminishes returns despite bacteriostatic antibiotics exhibiting bactericidal activity at higher concentrations. However, the concentrations necessary for this effect to occur for these types of antibiotics are not feasible in this clinical setting. However, what is critical is the immune system’s performance to eradicate the bacteria. Bacteriostatic antibiotics retard bacteria growth, but eliminating the pathogens relies on immune system function.The bactericidal effect refers to the direct killing of the pathogen. However, this effect depends on several factors. Minimal bactericidal concentration (MBC) is the level at which bacterial lysis begins to occur and is the determinant of a specific drug’s potency against the pathogen. As drug levels vary, a fall in concentration results in a predominant inhibitory, or bacteriostatic, action of the antibiotics, finally reaching a minimal inhibitory concentration (MIC)  Figure . At thisBelow MIC, drug actions do not necessarily cease. Several other antibacterial effects emerge, and the minimal concentration at which this effect occurs is called minimal antibacterial concentration (MAC). The post-antibiotic effect (PAE) refers to suppression of bacterial growth after a short pulse dose and has been previously described with several antibiotics and different bacterial strains ,51,52 F. Althoug5 of CFU during overnight exposure. These conditions diverge from physiological conditions in vivo. Notably, a plasma pH of 7.2 would signify severe acidosis and be considered an emergency. Catabolic processes during inflammation affect the circulating protein concentrations, while constant alterations in pH affect the electrostatic charge. Proteins abound in plasma, interacting with antibiotics in several ways, are highly variable in level and type, resulting from the ICU illness. Said factors are critical in dictating the amount of free antibiotic molecules that are critical for the antibacterial action as well as its potency.However, one must realize that antibiotic potency is measured in vitro under artificial conditions. The killing or bacteriostatic activity assessment is performed at pH of 7.2, in a protein-free, aerobic medium. Antibiotic activity is measured against 10The testing condition diverges substantially from the clinical reality of antibiotic dosing. A single dose of antibiotics is exceedingly rare in critical care situations. The bacterial load may be several-fold higher, and penicillin bactericidal properties are particularly sensitive to bacterial load. Most importantly, the in vitro test measures bacteria in the exponential growth phase, which is not necessarily the host’s phase. Measurement of antibiotic success is a change in physical properties of the growth medium, which may not be the best measurements of drug action or concentration translatable to the bedside. Conversely, measurements of antibiotics in serum in relation to antimicrobial activity may also be subjected to several biases. Poor penetration into bacterial nidus or sanctuary sites may necessitate increased dosages to achieve therapeutic concentrations within the target area. The ECMO circuit itself may offer a sanctuary for a pathogen to grow . FurtherSeveral factors specific to ECMO further complicate the understanding of pharmacokinetics and pharmacodynamics of antibiotics in this setting. Some are related to critical care illness, while others are specific to the ECMO circuit itself.Fluid resuscitation affects the volume of distribution, especially in the case of septic shock, where a large amount of fluid needs to be given to defend perfusion pressure despite venodilation and increase in vascular capacitance ,74. EndoThe interaction of the antibiotics during ECMO is complex and most likely results in a suboptimal level of the antibiotics . In addiNotably, since ECMO is an emergent treatment, large, randomized trials or even case series testing for pharmacodynamic or pharmacokinetic alterations concerning antibiotic microbial effectiveness in this population are lacking. Most of the data reported arise from observational trials.Patients on ECMO may exhibit various and wide-ranging alterations in pharmacokinetics, some attributable to said treatment and others related to the critical illness itself ,80. AlteAntibiotic strategies not accounting for these changes carry an increased chance of treatment failure, both instances of underdosing and supratherapeutic levels causing side effects, which have been reported . In addiThe critical illness itself may incur fluid status dysregulation, thus an increase in the volume of distribution . It has Activation of the immune system may be altered in a way that is difficult to characterize at the current state of knowledge. This may significantly affect antibiotics’ MIC and MAB levels. In addition, some of the medications administered during ECMO may have additional antibacterial effects. For example, non-inflammatory nonsteroidal drugs alter the activity of Gram(+) bacteria and may enhance the antibiotic’s effect and modulate immune system activity ,85,86. IVarious circuit parameters may alter pharmacokinetics . These pVarious properties of specific antibiotics directly influence ECMO effects on their pharmacodynamics. These include whether the antibiotic itself is lipophilic or hydrophilic, the tendency for protein binding, and the site of metabolic breakdown  82,102,,102,103.Vancomycin is a hydrophilic glycopeptide antibiotic with bactericidal properties and low protein binding ,47. As cAmikacin is a hydrophilic aminoglycoside with bactericidal and post-antibiotic inhibition effects , with a Meropenem is a carbapenem antibiotic, with effects similar to that of beta-lactams, exhibiting both bactericidal and post-antibiotic inhibitory effects ,60. ProtImipenem, also within the carbapenem classification, has also been studied. One study including 247 ECMO patients found lower plasma levels and higher dosing recommendable . Others Cefazolin was reported as being sequestered in the ECMO circuit, although the physical properties of the circuit were critical ,109. Up Ceftazidime demonstrated to be unaffected in serum dynamics in 30 ECMO patients compared to 75 non-ECMO ICU patients (from a mean age of ECMO 47.7 vs. 61.2 for non-ECMO in a prospective study). Consequently, adult dosing recommendations are to use a loading dose of 2 g intravenously and to adjust the dosing based on GFR  .For teicoplanin, 89% of the drug can be sequestered, according to an in vitro study of the primed circuit . Two in Ciprofloxacin belongs to the fluoroquinolone family. These drugs are lipophilic bactericidal, exhibiting a volume of distribution mostly unaffected by critical illness  and low Piperacillin should be used with caution in ECMO patients, wherein they tend not to achieve the desired therapeutic targets in these patients. One single-center study showcased this phenomenon, wherein piperacillin–tazobactam-treated patients were less likely to achieve a prespecified ×4 MIC (48% vs. 13% in non-ECMO patients) . A loadiLinezolid patients receiving linezolid may also show a tendency to not achieve desired plasma levels (35% vs. 15%) . NeverthCaspofungin falls under the echinocandin classification as a lipophilic antifungal. However, reports regarding circuit sequestration are conflicting. For example, circuit loss secondary to sequestration may be as high as 43%, while others have deemed this drug as unaffected by ECMO ,82. One Micafungin, another echinocandin, exhibited similar results, with sequestration gauged around 45–99% . HoweverAspergillus sp. infection. While it was previously assumed that high circuit losses could be expected due to the drug being highly lipophilic, one large retrospective study found no significant pharmacokinetic changes during ECMO. The in vitro study showed significant absorption by circuit [Voriconazole is a triazole antifungal commonly employed in  circuit ,110. Som circuit . The med circuit .In addition, a member of the triazole family, fluconazole, has exhibited minimal sequestration. However, data sufficient for dosing recommendations remain lacking .Standard precautions regarding drug interactions apply, as patients on ECMO are bound to receive diverse agents during their course. More importantly, nearly 50% of all ECMO patients may necessitate renal replacement therapy (RRT) during their illness, further confounding antibiotic dosing ,83. The Further compounding this issue in patients receiving concurrent ECMO and RRT, commonly utilized formulae employed for dosing calculations such as EGFR and Cockcroft-Gault may lose accuracy in this setting . In addiVarious drug properties, including molecular size, protein binding, distribution volume, and metabolism, affect dialysis-mediated removal. In general, highly protein-bound drugs possess large molecular weight or volume of distribution, and/or non-renally cleared medications are least likely to be impacted by RRT . Both thWhile there is a paucity of data regarding pharmacodynamics in patients receiving concurrent ECMO and RRT, it is safe to suggest that the importance of therapeutic monitoring is further enhanced in these patients. A sieving coefficient can be determined for a drug if both plasma and ultrafiltrate concentrations are known (ultrafiltrate/plasma) . This coImpala and other devices are not present in the data pertinent to the concomitant application of ECMO and cytokine absorption technique. Several reports demonstrated that ECMO did not interfere with successful treatment of bacterial infections. However, given that these are mostly case reports, there is a lack of randomized controlled studies comparing success rates between patients treated with a similar regimen of antibiotics on ECMO vs. patients treated with mechanical ventilation. The CEASAR study was the only one designed in a way that demonstrated the superiority of transferring the patient to the specialized center vs. regional care . There wThe definite answer may be difficult to study as comparing study design in the CEASAR format may be unfeasible due to the ethical constraint. However, it is also interesting that since the study’s conclusion, no similar study design was followed, while ECMO proponents relied on case reports.Antibiotic therapy success may be difficult to achieve in the ECMO patient. The emergence of critical care illness creates a difficult condition at the baseline. The variability introduced by the circuit further complicates clinical decision making. Although we suggest utilizing good stewardship in antibiotic dosing combined with drug level monitoring, one must realize that these methods are likely to be insufficient to predict the appropriate regimen in the ECMO situation . Utilizi


Morbidity and Mortality Weekly Report (MMWR) about distinctive diseases appearing in “active homosexuals” in Los Angeles associated with immunosuppression [MMWR announcement of more cases appearing in San Francisco and New York City [In the summer of 1980, I began an Infectious Disease fellowship in Boston because of an increasing interest in understanding how microbes affected society. My laboratory projects focused on developing skills to track the molecular epidemiology of antibiotic resistance [pression . This waork City . Other rThe pandemic worsened quickly as more cases were identified, and in the absence of an identified aetiological agent, societal responses bifurcated. Because of the initial lack of US and global commitment to supporting an accelerated research programme or services for those in need, and as those most heavily impacted belonged to highly stigmatized populations, the responsibility for caring for the increasing number of desperately ill people was addressed by front‐line clinicians and newly constituted community‐based organizations that sprung up to provide meals, home care and other much needed assistance.MMWR to the identification of HIV, the aetiological agent of AIDS, and another year before a commercially available diagnostic test became available. It took another 11 years before a meaningful treatment paradigm emerged, based on virological detection with newly developed nucleic amplification testing (NAAT) and the use of combination highly active antiretroviral therapy that targeted multiple steps in the virus life cycle. The timeline would invariably have been longer if community‐based activism had not arisen to address the neglect of global leaders and normative bodies. As more sexually and gender minority people felt increasingly vulnerable to an escalating pandemic, they repurposed lessons from the US Civil Rights and Women’s movements, as well as Gay Liberation to challenge researchers and public health officials to rethink traditional ways of conducting clinical trials and engaging at risk stakeholders [It took more than three years from that first report in the eholders .The infusion of enhanced accountability in an era of increasingly instant communication led by community‐based groups like ACT‐UP influenced the conduct of subsequent research, including testing of vaccines against SARS‐CoV‐2. Moreover, activism that was initially US‐centric morphed into a multicentric international movement with indigenous leadership, like the Treatment Action Campaign. In an era of U = U and PrEP, the inevitability of powerful and successful tools may seem obvious, but decades of suffering, advocacy and careful clinical investigation led to these outcomes. And despite these advances, we remain without a safe and effective vaccine or cure, so the AIDS pandemic is far from over.The 40th anniversary of the first report of AIDS, is an appropriate time to reflect on what we learned that can inform our efforts to stem to the global spread of SARS‐CoV‐2. The global HIV response has demonstrated that supporting basic and clinical research yields multiple dividends, including the ability to jumpstart responses to future health crisis. Tools and templates created to address HIV have been leveraged to respond to SARS‐CoV‐2 . For exaHistory repeats itself, first as tragedy, second as farce,” [As someone whose personal and professional identity was forged in the crucible of AIDS in the 1980s, I have thought about Karl Marx’s aphorism that “ farce,”  when musThere are also longer view lessons from the AIDS epidemic that need to be considered when addressing future pandemics. As humans diminish centres of biodiversity by heavy deforestation, contact with new species and therefore new pathogens, is inevitable . Global The authors have declared no conflict of interest.KHM conceptualized and wrote the editorial.None declared.


Clostridioides difficile and antibiotic-resistant infections and related deaths . This study analyzed data from the Centers for Medicare & Medicaid Services (CMS) Part D Prescriber Public Use Files (PUFs)Antibiotic prescribing can lead to adverse drug events and antibiotic resistance, which pose ongoing urgent public health threats  and provider characteristics, including names, National Provider Identifier, specialty (including prescriber type), and zip code. There is a 2-year lag in data availability, during which prescription drug claims are finalized. Because beneficiary and antibiotic claim counts fewer than 11 are suppressed, the 2019 Medicare Part D Prescribers by Provider data set was used to assess prescriber-level antibiotic prescriptions among health care providers in the United States who distributed 11 or more antibiotic prescriptions.Higher-volume prescribers were defined as those in the highest 10th percentile of prescriber-level antibiotic volume (number of antibiotic prescriptions filled) across all Medicare providers nationwide. The cumulative percentage of antibiotic volume prescribed by higher-volume prescribers was assessed overall, and the percentage of higher-volume prescribers in each U.S. Census Bureau regionDuring 2019, the Medicare Part D Prescribers by Provider data set included 1.2 million prescribers. After excluding prescribers with fewer than 11 antibiotic prescriptions and those in U.S. territories or overseas military bases, 697,065 (56%) prescribers were included in the analysis. A total of 59.4 million antibiotic prescriptions were filled by Part D beneficiaries, with a median of 47 (IQR = 23–100) antibiotic prescriptions per prescriber. Among all antibiotic prescriptions, 41% (24.4 million) were written by the top 10%  of antibiotic prescribers by number of prescriptions written (antibiotic volume) ; these pApproximately one half (48%) of higher-volume prescribers practiced in the South and prescribed 49% (12.3 million) of the total antibiotic prescriptions in this region . Higher-The goal of antibiotic stewardship is to improve the way health care providers prescribe antibiotics to optimize patient outcomes and reduce emergence of antibiotic resistance. During 2019, 41% of all Medicare Part D antibiotic prescriptions were prescribed by 10% of antibiotic prescribers, indicating that a small proportion of prescribers accounted for a disproportionately large number of antibiotic prescriptions. A similar 2016 study using claims data in Tennessee found that 50% of the state’s antibiotic volume was attributed to 9% of prescribers (This study demonstrates a way to identify antibiotic prescribers who account for a large proportion of prescribing and could provide a basis for additional assessment of appropriateness and outreach. For example, public health organizations could use Medicare Part D data to identify individual higher-volume antibiotic prescribers by specialty for focused stewardship interventions. The higher-volume prescribers in primary care specialties prescribed one-quarter of the total Medicare Part D antibiotic volume during 2019. Studies indicate that primary care providers have varying prescribing rates, suggesting opportunities for improvement in settings in which most antibiotics are prescribed (The publicly available CMS Part D Prescribers by Provider data set might enable public health organizations and health care systems to efficiently identify prescribers for stewardship outreach in their jurisdictions without the need for complex analytic methods or need to acquire prescription claims data or diagnosis data.The findings in this report are subject to at least four limitations. First, the CMS Part D Prescribers by Provider data set captured prescription claims submitted to Medicare Part D and is thus not representative of the entire older adult population. Second, these data might not reflect health care providers’ prescribing behavior for their entire patient population and might overrepresent health care providers with a larger share of Medicare beneficiaries, patients with complex medical conditions, or visits for conditions for which antibiotics are prescribed. Third, this data only describes volume of prescribing and does not report diagnosis and underlying conditions; therefore, the data cannot be used to assess appropriateness of prescribing. Finally, the 2-year lag in data availability affects timeliness, which would be important for real-time audit and feedback. Nonetheless, these data are useful for characterizing provider prescribing behaviors and supporting public health stewardship outreach.This report demonstrates how publicly available data might be leveraged to monitor antibiotic use and identify higher-volume prescribers. CMS Part D Prescribers by Provider data can be used by public health organizations and health care systems to guide antibiotic stewardship interventions and optimize antibiotic prescribing to limit the emergence of antibiotic resistance and improve patient outcomes.Health care providers vary in their propensity to prescribe antibiotics. Peer comparison audit and feedback is an effective antibiotic stewardship intervention to improve antibiotic prescribing.The highest 10% of antibiotic prescribers prescribed 41% of total antibiotic prescriptions for Medicare Part D beneficiaries in 2019. The antibiotic prescribing rate of these higher-volume prescribers was 60% higher than that of lower-volume prescribers.Publicly available Medicare Part D data can be used by public health organizations and health care systems to guide antibiotic stewardship interventions and optimize antibiotic prescribing to limit the emergence of antibiotic resistance and improve patient outcomes.


Between 45% and 70% antibiotics prescribed correspond to AWaRe's access group and up to 25% to AWaRe's watch group. Over 70% of antibiotics dispensed in veterinary consultations for any species correspond to the OIE's veterinary critically important antimicrobial agents. Overall, the study demonstrated positive features of veterinary antimicrobial stewardship in Bhutan, given the conservative proportion of consultation that results in this type of prescription and the type of antibiotic prescribed. Although the veterinary service closely follows the Bhutanese Standard Treatment Guidelines, the prescription of antibiotics to key species should be closely monitored. Our study suggests that further improvements of antibiotic stewardship can be achieved through standardisation of antibiotic prescription to some species, a revision of the guidelines toward reducing the prescription of antibiotics of high relevance for human medicine, and by including details of clinical investigation, use of tests, and treatment outcomes in veterinary consultation records.The veterinary prescription of antibiotics in low- and middle-income countries (LMIC) remains largely undocumented. In Bhutan, however, the national veterinary service keeps records of their activities and prescriptions, which offer an opportunity to establish a benchmark to assess the use of these agents in this and other LMIC. A cross-sectional retrospective study was designed and 2,266 handwritten veterinary records from 2017 were sampled from 23 animal health premises (AHPs) to estimate individual and an overall proportion of consultations that resulted in an antibiotic prescription. The frequency of antibiotic prescription per species, type of AHP, and according to WHO's AWaRe index and OIE list of priority antimicrobials were also explored. It was estimated that 31%  of the veterinary consultations resulted in an antibiotic prescription. The incidence of antibiotic prescription was highest in consultations of poultry across AHP. Across species,  Antimicrobial resistance (AMR) occurs when microorganisms such as bacteria, viruses, parasites, or fungi change in ways that make the drugs used to treat them ineffective. Although most One Health research emphasizes on zoonotic threats , AMR is The monitoring of veterinary antibiotic usage is context specific. In high-income countries, intense control and regulation have resulted in a reduction of antibiotic prescription and improved stewardship. In low- and middle-income countries (LMIC), antibiotics are less regulated, and there is limited reporting on the extent of their use , 5. AccoBhutan, a landlocked nation in the Himalayas, has unique features of livestock management and veterinary health care delivery among the LMICs. According to Bhutanese principles, animals are rarely slaughtered and instead are cared for until they die of natural causes. In Bhutan, the veterinary service is public and free of charge; veterinarians and para-veterinarians follow the Standard Treatment Guidelines of Bhutan  compiledAWaRe index for antibiotic stewardship . The study is reported according to the STROBE-Vet statement .Dzongkhags (districts) which are further divided into 205 geogs (groups of villages). In Bhutan, the veterinary service has a hierarchical structure. Livestock and companion animals in each geog receive health care from personnel employed in two types of animal health premises (AHP): para-veterinarians in local Livestock Extension Centers (LEC) or veterinarians employed by the Dzongkhag Veterinary Hospital (DVH). In geogs where a DVH exists, the LEC is incorporated into the DVH. Beyond their local dispensing of health care, the veterinarians and laboratory personnel of the DVH oversee and provide technical support to all LEC under their Dzonghkag jurisdiction. DVHs, in turn, receive technical support from one of four Regional Livestock Development Centers (RLDC), and these from the National Center for Animal Health (NCAH).The Kingdom of Bhutan is administratively divided into 20 To estimate the proportion of veterinary consultations that resulted in an antibiotic prescription, we designed a retrospective cross-sectional study of veterinary consultation records (the unit of interest) performed in the West Regional Livestock Development Center jurisdiction of Bhutan in 2017 . We focused on this year because this was the last year for which both consultation records and an official livestock census  were avaWe estimated the sample of veterinary records necessary to answer the research question using a combination of expert opinion, preliminary analysis, and a cluster-sample design. Based on preliminary analysis of veterinary records from two LEC and local expert opinion, we estimated that the number of consultations per LEC in 2017 was between 300 and 400, and that about one-third resulted in the prescription of antibiotics. To ensure adequate representation of syndromes and treatments throughout 2017 , it was determined that 120 records (10 random records per month) would be collected from each AHP. To estimate the number of AHP sourcing veterinary records, an intraclass correlation estimate for the antibiotic prescription proportion was needed; however, this estimate is unknown in Bhutan. We assumed a conservative design effect of 5.5 [assumed intraclass correlation (ICC) (5.5–1)/(120–1) = 0.04] to ensure appropriate study power. Thus, if 33.3% of the veterinary consultations in 2017 resulted in an antibiotic prescription and 120 veterinary records were collected from each AHP, then we estimated that 17 AHP and 2,040 veterinary records in total were needed to be 95% confident that our estimate of the proportion of veterinary consultations that result in an antibiotic prescription was within 5% of the true population value  suggests that the proportion of veterinary consultations that resulted in antibiotic prescription in 2017 was 27% . This proportion ranged between 19% (11–29%) and 43% (33–53%) across AHP. The estimate based on set 2  varies minimally , while the estimate based on set 3  suggests that 31%  veterinary consultations resulted in an antibiotic prescription in 2017.The estimate based on set 1 [consultation records Characteristic of the veterinary records scrutinised are shown in The overall proportion of consultations that resulted in antibiotic prescription oscillated around 30% for both DVH and LEC throughout the year 2017. This is explained by a consistent antibiotic prescription incidence in bovine and canine consultations, which represent 84% of all records scrutinised. Among the top 3 species, the incidence of antibiotic prescription in avian consultations is particularly high in LEC with an estimated 75%. The incidence of antibiotic prescription is also high for equine in DVHs, but the limited number of records for this and other species results in significant variability of these estimates.access or watch, with some exceptions: oxytetracycline is classified as a watch antibiotic and not access as the rest of the tetracyclines  and 75% (avian) corresponded to access agents, between 5% and up to 25% to watch agents, and up to 20% of the antibiotics prescribed had “undefined” classification. As per the OIE guidelines, over 70% of the prescriptions for any species corresponded to VCIA; the prescription of VHIA was limited across species, and about 25% prescriptions had no classification in the list .Our estimate of the proportion of veterinary consultations that resulted in a prescription of antibiotics is possibly the first for Bhutan, and one of few estimates for LMIC, where the use of antibiotics remains largely undocumented . We estiThe proportion estimates reported in this study were derived from a fixed-effect model. Because there is a unique set of Standard Treatment Guidelines  used by i2 = 73%). A priori, it was hypothesized that the mix of species presented to each AHP could explain the variability, as some species were found to be frequently treated with antibiotics (avian and equine). Detailed quantification of the type of consultation per AHP  to treat diarrhea, which is not a pathognomonic sign of bacterial disease as it can be caused by bacterial  or viral  infection, parasitic infestation , climate (heat stress), or normal physiological processes that could be misdiagnosed  (Pasteurella multocida) and fowl typhoid  on a dose of 1 g/L of drinking water for 7 days (As part of our oppings) . While tr 7 days . Understr 7 days , and ther 7 days . Given tAWaRe index. Although the preferred prescription usually corresponds to an access agent, the ample use of watch antibiotics to treat common health issues in bovine, particularly mastitis and teat cracks, requires close surveillance for three reasons: (a) the importance of these antibiotics for human health; (b) the importance of milk from a nutritional and economic perspective in this country; and (c) because farmers may not be familiar with the concept of withdrawal periods. The intramammary formulations and injectable oxytetracycline used to treat ruminants have withdrawal periods of at least 96 h in large ruminants and 72 h in small ones  which boosted the number of clusters needed to estimate the underlying proportion investigated. The results produced by the study seem robust: the prescribing proportion estimates derived from the three sets of data were consistent, the ICC for the most extensive dataset (set 3) was smaller than initially estimated (~0.03), and more clusters than needed were available for inclusion in the study (23 instead of 17).We envision three uses for the results in this study. First, the study provides a benchmark to compare the progress made around antibiotic stewardship in Bhutan. Second, the study provides a methodology to investigate the proportion of veterinary consultations that result in an antibiotic prescription across Bhutan and other nations with a similar veterinary service structure. Third, the study highlights areas that can be enhanced toward improved antibiotic stewardship. These areas include the revision of antibiotic recommendations for certain species, close monitoring of watch antibiotics prescribed to key livestock species and ascertainment of withdrawal periods, and improved consultation records, including clinical investigation, diagnostic test, and treatment outcome. Considering the limitations previously described, our results suggest that the Bhutanese veterinary service practices a conservative prescription of antibiotics in terms of frequency and type as per the AWaRe index, which is a positive feature of antimicrobial stewardship. The Bhutanese approach to antibiotic prescription, which is managed by a hierarchical veterinary service and harmonised through standard treatment guidelines, may serve as an example, and could help in guiding veterinary antimicrobial stewardship processes in other low- and middle-income countries.jp.villanueva@unimelb.edu.au.The datasets presented in this article are not readily available because the datasets contain identifiable data of people. Requests to access the datasets should be directed to JV-C, MS, and JM conceptualized the study design, sample size, and fieldwork with input from KR, SD, UN, PT, and PS. JV-C carried out the fieldwork with collaboration from KR, SD, UN, PT, and PS. JV-C undertook all analyses with input from MS and JM. JV-C wrote the main manuscript text. All authors were involved in the design of the study, reviewed and commented on the manuscript.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.