In this paper, the mesoscale damage properties of concrete and mortar were studied experimentally under Brazilian disc splitting tensile tests combining X-ray computed tomography (CT) and digital image correlation (DIC) technology. Considering the factors of water/cement ratios and loading rates, the influence of meso components on the macro tensile properties and failure modes of concrete were studied. The experimental results and analysis indicate that the following: (1) the existence of coarse aggregate makes the tensile strength of concrete lower than that of mortar and reduces the sensitivity of tensile strength to the loading rates; (2) the failure modes of mortar and concrete Brazilian discs differ in the crack initiation positions and localization phenomena. Under high loading rates, the local failure plays a critical role in the strength improvement of concrete; (3) for concrete, interface failure and mortar failure are the main failure modes under low loading rates, whereas aggregate failure gradually becomes the main failure mode with increasing loading rates. The decrease in water/cement ratios improves the strength of the mortar matrix and interfacial bonding performance, leading to more serious aggregate damage and higher strength. Concrete, with a complex heterogeneous structure, is considered as a three-phase composition of cement mortar, aggregates, and interfacial transition zones at the mesoscale ,2. UnlikOn the macroscopic scale, splitting tensile tests (Brazilian disc tests) are the most popular methods to determine the uniaxial tensile strength of concrete due to simple preparation and easy operation ,5. In thHowever, with the increase in loading rates, the macro tensile behavior of concrete specimens usually changes significantly . As geneOn the mesoscopic scale, the distribution and change in internal stress are closely associated with the volume fraction, distribution, and interaction of the three phases  of concrete ,20. CurrDIC technology can establish the displacement field and strain field of the specimen surface by using a camera and receiving surface images of the specimen. Numerous experiments on specimens of other shapes have demonstrated the capacity of DIC for the study of the deformation characteristics and the stress variation ,28. For The aim of this paper is to investigate the influence of mesoscopic damage characteristics on the macro splitting tensile properties of concrete. For this purpose, splitting tensile tests of concrete and mortar Brazilian disc specimens under different loading rates were carried out to compare the different effects of mesoscopic materials. Then, on the basis of the tensile strength and failure modes obtained from the macroscale experiments, DIC and X-CT technology were employed for the subsequent analysis. The distribution characteristics of each phase of concrete, their roles in the failure process, and their effects on the macrocrack morphology were discussed. Lastly, a three-dimensional model of crack distribution was established for statistical research on the volume proportion of each phase and the analysis of the three-dimensional morphology of cracks.The specimens were categorized into a concrete group and a mortar control group for comparative study. The mix proportions for concrete strength are summarized in Φ 74 mm × H 37 mm.In the design of the size of specimens, it is necessary to consider the obvious size effect of concrete materials due to the nonuniformity of the meso composition in concrete ,36.When The Brazilian disc test was based on the Chinese standard GB/T 50081-2002  and was carried out on an Instron 8802 servo-hydraulic testing machine, as shown in Six groups of specimens were tested under four different loading rates. The naming rules of the specimens were as follows: type of specimens-loading rates. For the convenience of recording, 02 m, 002 s, 02 s, and 2 s were used as loading rates corresponding to loading rates of 0.2 mm/min, 0.02 mm/s, 0.20 mm/s, and 2.00 mm/s, respectively. There were five specimens under each working condition. Moreover, two 10 mm wide and 2 mm thick wood cushions were glued to both ends of the specimen as loading strips.M is half the side length of the reference subarea, X-direction, and Y-direction.According to the literature, the DIC test system can obtain the deformation information by matching the corresponding subregions of the image before and after deformation. A square reference subregion is taken out from the image before deformation, and then the differences between the deformed and reference images are measured by the standard covariance cross-correlation function Equation (1). The coordinates of one point in the reference subregion are denoted as . In the CT scanning system, the X-ray from the radiation source reaches the detector after scanning the sample. After data processing, slice files in all directions are received, and the three-dimensional shape of the sample is reconstructed. There are two main factors affecting the accuracy of industrial CT systems . One is X-axis and Y-axis was 901 × 901 pixels, and the Z-axis resolution was approximately 450 pixels. The pixel size was calibrated to 0.0812 mm/pixels. In addition, the scanning time of each projection was 2.5 s, and approximately 450 layers were sliced along the thickness direction of each specimen.Herein, the YXLON microfocus X-ray computed tomography system was used in the CT scanning test. In the CT scanning system shown in As depicted in At the initial stage of loading, the load increased slowly with increasing displacement due to the deformation of the gasket. After the gasket was compacted, the stress increased sharply and declined soon after reaching the peak. Comparing the curves under different loading rates, it can be seen that the specimens presented obvious brittle failure under low loading rates, while the specimens presented ductile facture at a high loading rate of 2 mm/s. Additionally, it can be found that the failure displacements of mortar had an obvious increasing trend when the loading rate increased, gradually increasing from 2.38 mm (loading rate = 0.2 mm/min) to 2.77 mm (loading rate = 2 mm/s), which indicated that the failure displacement of mortar was sensitive to the loading rates. However, concrete has no obvious trend of the displacements at failure, and it varied with an average value of 2.72 mm. The aggregate may play a critical role in reducing the sensitivity of concrete.D is the diameter of the Brazilian disc, and H is the height of the Brazilian disc.According to ASTM D3967-16, the theoretical formula of tensile strength obtained from Brazilian disc splitting test is shown in Equation (2).After calculation, In this paper, CA  and MA specimens  under the loading rate of 0.2 mm/min were selected for a comparative study of DIC images.The characteristic points were marked on the test piece, as shown in In general, the strain level of the concrete characteristic points was higher than that of the mortar, which indicated that the aggregates improved the deformation ability of concrete. After reaching the peak load, the strain–time curves of the points in the vertical loading direction fluctuated slightly while the strain of the characteristic points in the load direction increased with time, which indicated the nonuniformity of strain at the characteristic points of the specimens. In the horizontal direction, the strain of point V3 nearest to the center was relatively large compared with the points at the edge of the specimens (V1 and V5). Thus, the strain level decreased from the center to the end, and the center of the specimen was the first to fail. However, along the loading direction, the strain levels at the edge of the mortar specimen were always higher than those at the center, which meant that macro cracks first occurred at the end of the specimens. For the concrete specimens, the strains at the center of the specimens were always at the highest level, indicating that the cracks first appeared at the center of the concrete specimens, and the crack propagated to the end of the specimen along the radial direction.ERF, as shown in Equation (3). Then, the error function evaluated at x is the measured distance, s is the fitting function parameter, and Before the macro cracks occurred, the size of the local stress concentration area also affected the failure process of specimens. In DIC images, the uniform width of a localized zone of concrete could be described following Equations (3) and (4). The particle displacements were fitted by the error function ge value .(3)ERFxLastly, the width of the localized zone in concrete was 3.78 mm at the peak load, which was little larger than that of mortar 3.45 mm). The localized zone of mortar appeared earlier, but did not spread significantly before failure. The existence of aggregate made the high strain region distribute around the aggregate in the strain map of concrete, and the different elastic moduli of aggregate and mortar led to uneven deformation, which gradually expanded the localization zone from center to both ends. The width of the localized zone in concrete was also little larger than the width recorded in other studies such as 3.41 mm  mm. The . This isCA specimens , CC specimens , and MA specimens (mortar) under loading rates of 2 mm/s and 0.2 mm/min were selected for the comparative study of CT slice images. Approximately 450 slice images were derived from each specimen along the thickness direction, and the typical slice images from the 250 images of the middle layer were extracted for analysis. Specifically, the 100th, 170th, 240th, and 310th slices of each specimen are presented in According to the crack distribution of the MA specimens shown in According to the typical section images of the group CA specimens in As illustrated in On a whole, aggregates affected the distribution of cracks along the radial and thickness directions, making the crack morphology complex. The strength of concrete improved with decreasing water/cement ratios and aggregate volume as the strength of hardening cement mortar increased, which made crack expansion more difficult. Meanwhile, the bonding performance of the interface between aggregate and mortar was also improved, making the interface strength higher. In terms of the loading rates, the tensile strength increased, and more secondary cracks appeared when the loading rates increased. The failure modes also turned to local impact failure instead of a single main crack. It could be inferred that multiple points of one specimen could reach the peak tensile strain at the same time under high loading rates; thus, several local failures appeared simultaneously.In addition, local failure became more obvious under high loading rates, especially for the concrete specimens, as the stress increased rapidly at the loading end. When the stress diffused to the center of the specimen, cracks at the weak interface developed with the main crack penetrating, forming band or block crushing zones, including aggregate fracture and mortar cracks. However, the main crack still grew slowly when the load level increased sharply. It can be inferred that local failure was the main reason for the enhanced strength. The cracks at the loading end expanded and penetrated rapidly under high-level confining pressure, causing damage to the aggregates, mortar, and interface, finally leading to an increase in strength. Therefore, the distribution of cracks and the failure modes of specimens also had a certain influence on the splitting tensile strength.A histogram can display the data frequency of each group in a graphical form, which represents the distribution probability of the CT number of materials with different densities and expresses the change in the content of each phase through the change in CT numbers . As diffIn general, the mortar had a relatively simple microstructure, presenting a single peak shape with a peak, while the concrete histogram had an obvious bimodal shape. It can be roughly inferred that a CT number in the range of 0–50 grayscale represented the pores and cracks, in the range of 50–100 represented the mortar matrix in the concrete, and in the range of 100–125 represented the aggregate by quantitative statistical analysis of CT numbers.As shown in The gray histograms of the type CA specimens in As shown in As mentioned before, appropriate threshold segmentation is crucial to obtain clear and accurate mesoscale structures. Since the bimodal feature of the histogram was not obvious, the Otsu algorithm was adopted. However, the Otsu method applied to the global specimen made the inner aggregate nebulous. Thus, a block multi-threshold segmentation method was purposed to explore a more accurate threshold segmentation method, as shown in Thus, multiple threshold segmentation was conducted to form a trivalued image Finally, the threshold segmentation image was obtained by the combination calculation shown in Equation (6).The segmented operation realized the decoupling of the gray value of each phase material and was used to segment and derive mortar matrix, aggregate, cracks, and holes in the image at one time. It can be seen from The three-dimensional internal damage of concrete was reconstructed according to the segmentation method mentioned above. Then, the volume proportion of each phase of specimens under different working conditions was arranged, as presented in For concrete specimens, the volume ratio of aggregate was approximately 50%, which was slightly larger than that of mortar. Under a high water/cement ratio, there were more pores and cracks in the concrete specimens, and the volume of mortar decreased. With increasing loading rates, the proportion of mortar and aggregate decreased while the volume proportion of pores and cracks increased. When the loading rate increased from 0.2 mm/min to 2 mm/s, the crack volume ratio of CA specimens increased from 1.36% to 7.69%, and that of CC specimens increased from 1.51% to 12.17%. This indicated that specimens with higher strength cracked more seriously under the influence of the loading rates. However, the proportion of pores was always less than 0.5%, and it was actually smaller than the actual value, considering that the micropores along the crack propagation path were included in the crack volume ratio by mistake. Furthermore, CT images also missed some smaller pores. The pore proportion of the mortar specimen was larger than that of the concrete specimen, but the crack volume was approximately 2% less than that of the concrete, which also shows that the existence of aggregates could make the crack develop more maturely.The single porosity parameter could not completely reflect the relationship between the tensile strength and the pore structure, as the distribution of pore size also had a critical influence on strength properties . Herein,For specimen MA-02 m, after removing the largest volume elements (cracks), the pores were numbered from large to small to draw the distribution curves of pore volume and cumulative volume, as shown in 3. According to The pore volume curve was overall smooth, as presented in 3 mm3 for CC specimens under a loading rate of 2 mm/s. Therefore, data extraction was required before analyzing particle size distribution statistics. After calculation, data points with slopes of less than 1 per tangent were eliminated. Then, the equivalent particle sizes of the aggregates were calculated, and the interval was divided according to the 2 mm resolution, as illustrated in For specimen CC-02 m, the aggregate volume curve and cumulative volume distribution curve are shown in A change in the stress–strain state of the specimens at the macro level leads to a change in the deformation in the local material region . To furtCompared with mortar, the secondary cracks of concrete specimens appeared more frequently. At low loading rates, there were many concavities on the crack surface due to the aggregates on the crack propagation path, for which the shape was the same as the aggregate shape at the corresponding position. When the cracks extended to the surface of the larger aggregates, they cracked along the surface of the aggregates, dividing the cracks into two parts. This meant that the cracks in concrete were mainly distributed around the aggregates at low loading rates, and that aggregates were an important factor influencing the crack surface distribution. At high loading rates, the crack surfaces became relatively smooth but were still affected by aggregates with larger inner concave shapes. In addition, specimens with higher strength also had smoother crack surfaces. With the decrease in water/cement ratios and the increase in loading rates, fragmentation zones appeared near small aggregates, forcing small aggregates to break away from the matrix, and this process also improved the strength of the concrete. On a whole, the aggregate distribution influenced the distribution of cracks, and aggregate failure was an important factor to enhance the strength of concrete.For the splitting tensile tests, the tensile strength of concrete was 11–30% lower than that of mortar under different loading rates. Compared with concrete, the failure displacement of mortar was more sensitive to the loading rates and increased by 16.38% when the loading rate increased from 0.2 mm/min to 2 mm/s.The stress field obtained by the DIC test showed that the cracking modes of the mortar and concrete specimens were different. Concrete specimens cracked from the center, and mortar specimens cracked from the edge, which could affect the reliability of the tensile strength calculation of mortar specimens. Macro cracks gradually formed when the tensile strain of mortar and concrete reached 0.0237 and 0.0836, respectively.According to the images obtained from the CT test, the failure mode of the concrete and mortar specimens changed from a single main crack to local punching failure at the loading end with the increase in the loading rates and the decrease in the water/cement ratio. For concrete, interface failure and mortar failure were the main failures under low loading rates, whereas aggregate failure became the main failure mode under a loading rate of 2 mm/s.According to the three-dimensional reconstruction results, the internal pores of mortar were small and dense. The size and distribution of aggregates affected the morphology of cracks and made the cracks concave. With the decrease in the water/cement ratios and the increase in the loading rates, the crack surfaces became relatively smooth, as the small aggregates were forced to break away from the matrix.In this paper, Brazilian disc splitting tensile tests were carried out, and X-ray CT technology and DIC technology were introduced to study the mesoscale damage characteristics and failure process of the concrete and mortar specimens. The main conclusions could be drawn as follows:


Antibiotics are a key part of modern healthcare, but their use has downsides, including selecting for antibiotic resistance, both in the individuals treated with antibiotics and in the community at large. When evaluating the benefits and costs of mass administration of azithromycin to reduce childhood mortality, effects of antibiotic use on antibiotic resistance are important but difficult to measure, especially when evaluating resistance that “spills over” from antibiotic-treated individuals to other members of their community. The aim of this scoping review was to identify how the existing literature on antibiotic resistance modeling could be better leveraged to understand the effect of mass drug administration (MDA) on antibiotic resistance.Mathematical models of antibiotic use and resistance may be useful for estimating the expected effects of different MDA implementations on different populations, as well as aiding interpretation of existing data and guiding future experimental design. Here, strengths and limitations of models of antibiotic resistance are reviewed, and possible applications of those models in the context of mass drug administration with azithromycin are discussed.Statistical models of antibiotic use and resistance may provide robust and relevant estimates of the possible effects of MDA on resistance. Mechanistic models of resistance, while able to more precisely estimate the effects of different implementations of MDA on resistance, may require more data from MDA trials to be accurately parameterized. Chlamydia trachomatis ”. The second search used “mass drug administration” and “antibiotic.” This search provided an initial set of studies relevant to the topic. References from the initially identified studies were also reviewed and included in this review if relevant. Only articles published in English were included. This review did not limit the included articles based on year of publication.Streptococcus, Staphylococcus, or enteric bacteria like Escherichia coli. However, despite this substantial body of research, we still lack a definitive understanding of the relationship between an individual’s antibiotic use and the rates of antibiotic resistance in the wider population [Hundreds of empirical studies have measured the association between antibiotic use and resistance. In a 2014 meta-analysis , 67% of S. pneumoniae, the pathogen and antibiotic class most studied in population-level studies of antibiotic use and resistance [S. pneumoniae that cause pneumonia in older adults [First, population-level resistance is not just the aggregate of individual-level resistance selected for by those individuals’ use of antibiotics. Instead, there is a complex interplay between individual-level antibiotic use and the transmission of susceptible and resistant bacteria , 19. Ressistance , 21. Ther adults . Howeverr adults , 23. BetSecond, antibiotic resistance is not itself a pathogen; it is a feature of some members of a bacterial species. In some cases, when an antibiotic-resistant pathogen has minimal competition from the antibiotic-susceptible strains of the same species, conceptualizing “resistance” as a standalone pathogen is effective. For example, Donker et al.  evaluateS. pneumoniae and E. coli carried by recipients of MDA-azithromycin increase substantially after treatment [Competition can occur within the human host, and recent models of resistance have demonstrated how this within-host competition can help explain a key feature of antibiotic resistance epidemiology, namely, the durable co-existence of antibiotic-resistance and -susceptible strains of the same bacterial species . Competireatment , 27, 28 reatment , 30. Altreatment , 31.Third, use of one antibiotic can select for resistance to other antibiotics, because the same resistance mechanism provides resistance to those other antibiotics  or because one genetic element can include multiple genes that provide resistance against multiple antibiotics  , 32. MorFinally, all the foregoing phenomena —spillover, competition between susceptible and resistant strains, and co-selection—are likely highly contextual, depending on patterns of between-host transmission, heterogeneous patterns of background antibiotic use , and theThe saying goes: all models are wrong, but some are useful. A clearly “wrong” but parsimonious and potentially useful approach to modeling the complex relationship between antibiotic use and resistance is to infer the likely effects of a change in antibiotic use, such as MDA-azithromycin, using cross-sectional patterns of population-level antibiotic use and resistance Fig. . In otheTo illustrate this approach, compare MDA-azithromycin with outpatient azithromycin use in the US. Azithromycin use among American children aged 0‒2 years amounts to approximately 1 dose per year.A conceptually similar but more quantitatively rigorous approach would be to fit a linear or quasibinomial regression to cross-sectional data about antibiotic use and resistance across US states or European countries. The regression model could then be used to estimate how a change in the input antibiotic use rate would affect the output antibiotic resistance rate  Fig. 1)1). StatiStatistical modeling has at least three fundamental limitations. First, it assumes that the processes that relate inter-country or inter-state differences in antibiotic use to differences in resistance are the same processes that govern how a perturbation in antibiotic use, such as MDA-azithromycin, would affect antibiotic rates . In otheC. trachomatis carriage across clinical trials [Second, statistical models can only attribute differences in resistance to differences in use or to other population-level covariates such as socioeconomic factors . Statistl trials , 29. At l trials –43. SmalS. pneumoniae and E. coli are fairly well studied [Finally, a statistical model can only be built for antibiotics and pathogens for which there are pre-existing data. While the effects of azithromycin use on macrolide resistance among  studied , 27, 28, studied . Compari studied , 23, 45 The illustration above, comparing MDA-azithromycin with US azithromycin use, has many other weaknesses that could likely be ameliorated with more sophisticated statistical models. As one example, the crude model above only considers a single pathogen and antibiotic. A more careful approach would account for, or at least evaluate, the effect of the use of multiple antibiotics , 46, 47.Statistical models are likely useful for roughly estimating the absolute quantitative effect that MDA-azithromycin would have on population-level antibiotic resistance, but they cannot evaluate mechanistic questions or counterfactuals. Mechanistic models, on the other hand, make assumptions about the underlying dynamics that relate use and resistance. For example, a model might assume that a host can be colonized by only one strain of a bacterial species, either susceptible or resistant, while another model might assume that a host can be colonized by multiple strains at the same time. In either case, the model must specify factors like how the host immune system or antibiotic treatment will affect the colonizing bacteria.The most familiar mechanistic model of infectious disease is the classic susceptible-infected-recovered (SIR) model. A simple mechanistic model of antibiotic use and resistance is a susceptible-infected model, with two different infected compartments, one representing infection with the susceptible bacterial strain and the other representing the resistance strain Fig. . ConceptMechanistic models could be adapted to evaluate the effect of antibiotic use in one population on resistance in another population  and thenE. coli, it may be important to model environmental compartments, such as water sources [Mechanistic models of MDA-azithromycin would likely include three classes of hosts: first, the children treated with MDA; second, those children’s close contacts, such as family members and untreated children; and third, one or more further removed populations, such as other members of a settlement or the population of a larger administrative region Fig. . Dependi sources . While aS. pneumoniae serotypes [Contemporary models differ in their representation of the modeled bacteria Fig. . Some moerotypes , 56, 57.erotypes , 25. Morerotypes .Mechanistic models of disease transmission are typically agent-based , 58 or cS. pneumoniae [Every process in a mechanistic model must be accompanied by a quantitative parameter, and models of antibiotic use and resistance for MDA will have many classes of parameters Table . In manyeumoniae –65. In peumoniae , 57.TablTo help quantify population-level effects of MDA, future MDA studies would measure rates of pathogen carriage and resistance to relevant antibiotics among individuals who are in the treated community but who are not treated themselves . IdeallyMechanistic modeling has important limitations. Population-level dynamics of resistance are complex, and models of resistance are not reliably predictive . For MDAIt is worth noting that even in well-resourced settings like the US or Europe, the costs and benefits of antibiotic use have not been rigorously quantified. In general, antibiotic use is considered inappropriate when less intensive antibiotic therapy —a lower dose of antibiotics, a shorter regimen, a more narrow-spectrum antibiotic, an antibiotic less likely to select for problematic antibiotic resistance, or even no antibiotic at all— is expected to have the same clinical benefit –72. If aThere are many unknowns about the degree to which MDA selects for resistance, in whom, and at what cost. Future clinical studies can address some of these knowledge gaps. However, MDA studies cannot feasibly address the risk of resistance for every subgroup of patients , 12. Mat


In order to explore the influence law and action mechanism of carbon nanofibers on the basic mechanical properties of concrete, the author proposes the mechanical properties and microscopic mechanism of carbon nanofiber-modified concrete. Concrete was prepared with different dosages of carbon nanofibers, and the compressive strength, flexural strength, and splitting strength of carbon nanofiber-modified concrete were tested, and the modification mechanism was explored. Experimental results show that an appropriate amount of carbon nanofibers can improve the mechanical properties of concrete. When the dosage is 0.3%, the mechanical properties of carbon nanofiber-modified concrete are the best, and its compressive strength, flexural strength, and split tensile strength are increased by 9.2%, 13.2%, and 17.5%, respectively, compared with plain concrete. Carbon nanofibers can form a three-dimensional network structure inside the concrete, which can improve the microscopic morphology of the concrete, enhance the toughness and integrity of the concrete, fill the pore defects inside the concrete, refine the pore size distribution, and consume part of the fracture failure energy when the concrete is damaged. As we all know, the three major building materials widely used in civil engineering are cement, steel, and wood . ConcretCarbon fiber is a high-strength, high-modulus, corrosion-resistant, electrically and thermally conductive fibrous carbon material developed in the 1960s . Carbon Also, the dispersibility and electrical stability of carbon fiber in cement matrix are still outstanding issues, which directly affect the mechanical properties and pressure sensitivity of carbon fiber cement-based composites. Due to the difficulty in dispersing carbon fiber, the mechanical and electrical properties of its cement base and concrete are not stable enough. Regarding the dispersion of carbon fiber, relevant scholars have done in-depth research, but the problem has not been fundamentally solved. It is still difficult to apply a large number of projects in engineering, and the high price of carbon fiber also limits its wide application. Therefore, we need to seek conductive materials that have good compatibility with cement-based materials, do not affect their mechanical properties, and have good pressure sensitivity. The emergence of nanomaterials makes us see the light of day. Nanocarbon black is one of the cheaper nanomaterials; it has excellent electrical conductivity and high diffusivity, small size, large specific surface area, and excellent interface properties. It can be spread evenly in the cement matrix without dispersant, which not only reduces the artificial strength and high sensitivity of the cementitious and rock pressure-sensitive materials but also improves their stability and makes them less expensive. The sensitivity of nanocarbon black stone materials is good. It is a good business and shows a promising future of use.Among the carbon nanofiber-reinforced composite materials, the most studied matrix materials are mainly metal-based, polymer-based, and so on. There are few studies on composite materials with cement-based materials as the matrix, and they are still in their infancy. The research focus mainly includes the dispersion of carbon nanofibers in the matrix and the mechanical properties and durability of carbon nanofiber cement-based composites. Due to the high ratio of carbon nanofibers and strong van der Waals force, carbon nanofibers are prone to agglomeration and entanglement, so it is difficult to achieve a uniform dispersion state in cementitious materials, paper, which cannot improve the effect. In addition, agglomerated carbon nanofibers, like impurities in cement materials, inhibit the hydration of the cement and ultimately affect its microscopic morphology. Foreign researchers have carried out detailed research on the dispersion of carbon nanofibers and carbon nanofiber cement-based composites and often use a combination of ultrasonic treatment and dispersion to uniformly disperse carbon nanofibers in cementitious materials.Setiawan et al. used a polycarboxylic acid superplasticizer as a dispersant, and with the ultrasonic process, the carbon nanofibers were uniformly dispersed in the aqueous solution. The dosages of 0.1% and 0.2%, respectively, were applied to the cement-based materials, and the water-cement ratio was 0.4. The mechanical properties of carbon nanofiber cement-based composites were studied at 7 days, 14 days, and 28 days, respectively, including flexural strength, fracture deformation, ultimate strain, and toughness. The dispersion of carbon nanofibers in the matrix is also discussed. The results of the study showed that at 7 and 14 days of age, carbon nanofibers had no obvious enhancement effect on cement-based materials, but at 28 days, the mechanical properties  of carbon nanofiber cement-based composites were all higher than those of blank samples . The resThe author intends to prepare nanocarbon fiber reinforced cement concrete specimens, starting from the strength indicators such as compressive strength, flexural strength, and splitting strength, and explore the influence law and mechanism of carbon nanofibers on the basic mechanical properties of concrete; the modification effect of carbon nanofibers on concrete is explored from the microscopic level in order to provide a theoretical basis and application basis for the research and application of high-durability protective materials and to make up for the deficiencies in the existing research on carbon nanofiber modified concrete.3, and a mud content of 1.1%; limestone crushed stone: large crushed stone (apparent density 2730 kg/m3) and small crushed stone (apparent density 2644 kg/m3) are mixed in a mass ratio of 7 : 3; water reducing agent: polycarboxylate high-performance water reducing agent ; Fmax is the maximum load (N); and A is the cross-sectional area of specimen under compression (mm2).In the formula, There are a lot of holes in ordinary concrete, the hydration products are in a loose state, and the integrity is poor. When the dosage is 0.1%, the carbon nanofibers are sparsely distributed in the concrete, and only a few sporadically interspersed in the gel material can be seen under the scanning electron microscope, so the modification of concrete is of little significance. Continuing to increase the dosage, the carbon nanofibers are distributed more and more widely in the concrete, and the hydration products are interwoven vertically and horizontally, overlapping each other into a three-dimensional network structure, and the material integrity is gradually strengthened. The crystal form of the hydration product is smaller than that of ordinary concrete, and when the dosage is 0.3%, the distribution and modification effect of carbon nanofibers in concrete are better . Carbon Carbon nanofiber monofilaments are wrapped by C-S-H gel particles, which connect the gel particles together like molecular chains, thereby enhancing the toughness and integrity of the gel.Carbon nanofibers are very small in size and can have a small size effect when mixed into concrete, filling part of the pore defects of the concrete, effectively reducing the content of macropores in concrete and improving the particle gradation of cementitious materials. The fine pores are filled in the structure, the pore structure is refined inside the concrete, and the strength, compactness, and impermeability of the concrete are improved .The fibrous structure of carbon nanofibers bridges the micropores and microcracks inside the concrete structure, effectively preventing the further development of microcracks. At the same time, the molecular chain effect of carbon nanofibers strengthens the connection between the components, enhances the integrity of the concrete, and then improves the strength of the concrete. With the continuous destruction of concrete under the external action, the microcracks gradually expand, and the tensile stress received by the carbon nanofibers in the process of crack development gradually increases and finally pulls out of the cement slurry or directly breaks . In the Adding an appropriate amount of carbon nanofibers can improve the mechanical properties of concrete. When the dosage is 0.3%, the basic mechanical strength indicators of the material are the best, and the compressive strength, flexural strength, and split tensile strength are better than those of plain concrete; they are improved by 9.2%, 13.2%, and 17.5%, respectively.An appropriate amount of carbon nanofibers is well dispersed in concrete, which can form a three-dimensional network structure and reduce the crystal form of hydration products.The carbon nanofibers in the modified concrete connect the gel particles together like molecular chains, which enhances the toughness and integrity of the gel.The size of carbon nanofibers is extremely small, which can fill the pore defects in concrete to a certain extent.The carbon nanofibers are bridged between the microcracks of the modified concrete, which can consume part of the fracture failure energy when the concrete is damaged.


Background: The Centers for Disease Control and Prevention (CDC) estimates that outpatient settings account for 85%–90% of antibiotic prescriptions in the United States, and ~30% of those prescriptions are unnecessary. One of the most common examples of inappropriate prescribing is for viral upper respiratory infections (URIs). Up to 50% of prescriptions written for URIs are deemed inappropriate, making it an important focus for Antibiotic Stewardship programs. In this study, we evaluated the effect of a behaviorally enhanced quality improvement intervention in reducing inappropriate antibiotic prescribing for viral URIs. Methods: A quasi-experimental study assessed the effects of an Antibiotic Stewardship intervention on antibiotic prescribing for viral URIs. The outcome of interest was a change in the number of antibiotics prescribed at each participating clinic over a 1-year preimplementation period and a 2-year postimplementation period. Time trends were analyzed using segmented regression analysis, and a stepped wedge design was used to account for intervention roll-out across clinics. Results: From 2017 to 2020, there were 63,028 patient visits in 21 clinic locations. Antibiotics were prescribed an average of 11.5% and 5.8% of visits during the pre- and postimplementation periods, respectively. The most frequently prescribed antibiotic over the study period was azithromycin , followed by amoxicillin (n = 924). Overall, the intervention was associated with a 46% reduction in antibiotic prescriptions or 0.54 times (P = .001) as many inappropriate antibiotics prescribed as before the intervention. There was no significant change in the month-to-month trend in inappropriate prescriptions after the intervention was implemented (P = .87). Conclusions: Our study demonstrates that a behaviorally enhanced quality improvement intervention to reduce inappropriate prescribing for URI in ambulatory care encounters was successful in reducing potentially inappropriate prescriptions for presumed viral respiratory infections.Funding: NoDisclosures: None


The aim of this study is to evaluate how much the changes in the concrete mix design, which enable carbon footprint reduction, are impacting mechanical properties and predicted service life of concrete structure. The starting point of this study was concrete mix used in a recent reinforced concrete Pelješac Bridge in the Adriatic. In the first round of experiments the amount of cement in this initial mix was significantly lowered, without jeopardising workability of the mix. In the second round, the main part of the cement was substituted with the combination of fly ash and limestone or calcined clay and limestone. All supplementary cementitious materials used were sourced in the region of the structure. The calcined clays used in this study were collected locally and found to have a low kaolin content. On all mixes fresh and mechanical properties were tested to ensure that the requested equal or better workability and mechanical stability were reached. Furthermore, on each mix chloride migration was tested to evaluate the resistance of mix to chloride penetration. All mixtures were evaluated based on the overall performance considering mechanical, durability, and carbon footprints. The results indicate that the total cement content had a significant effect on durability and thus service life. The bridge mix design was determined to be ‘over designed,’ as all alternative mixes achieved a similar or higher sustainability index with lower amount of cement.The online version contains supplementary material available at 10.1617/s11527-022-02090-9. Concrete is known to be the most sought-after building material in the world. Among all other industries, the cement industry has a significant carbon footprint of about 8% . ConsequPerformance-based concrete design is one of the most straightforward and effective methods for enhancing clinker efficiency. In accordance with the 2016 united nations environment program standards (UNEP-SBCI) , clinkerw/c). The extent of cement hydration is limited due to the lack of water in these systems, and the unhydrated cement particles end up acting as fillers [Other obstacles include concerns about long-term durability due to lower binder content, loss of workability due to insufficient cement paste volume, and problems with the bond between the steel and cement matrix . Because fillers ––which c fillers , 21.2 cements. Low-CO2 cements containing SCM have shown improved mechanical strength, durability, and sustainability, resulting in blended cements being the most produced cements worldwide [The second most applied strategy of increasing clinker efficiency is introducing supplementary cementitious materials (SCMs), such as fly ash (FA) and blast furnace slag (BFS), for low COorldwide –24 Howevorldwide –27. HoweThe objective of this work was to determine if reducing cement content and substituting it with locally available SCMs would affect the overall performance of the concrete structure in a marine environment. The effect of changes at the material level on the overall performance of structures is of paramount importance for wider acceptance and application of these solutions in practice. Numerous published studies attempt to comprehend the material properties resulting from variations in concrete formulation, which is undeniably essential and frequently leads to significant advances in cement research. The intent of this manuscript, on the other hand, is to demonstrate the impact of these changes in material properties on the overall performance of structures. The manuscript is based on a case study that takes the actual mix design for a built bridge, attempts to produce alternative mixes using locally available materials, and evaluates their overall performance in the structure. Therefore, the idea of this study is to analyse the limit to which it is possible to reduce the environmental impact of materials without compromising the performance of the structure.The performance criteria were taken from a real concrete structure of Peljesac Bridge, a recently completed monumental structure designed for a 100-year service life in an aggressive Adriatic marine environment . BeginniThe bridge mix was designed using blended cement with slag addition, CEM II B–S in accordance with EN 196-1. The primary material in all alternative binder systems was Portland cement (CEM I 425R) according to EN 196-1. The physical and chemical composition, as well as the mean particle size of all cementitious materials were determined using X-ray fluorescence method and laser diffraction technique , whereas in BD340, the binder content was reduced while maintaining the same water/binder ratio. All other mixes in the study followed equivalent mix design method. Initially, the cement type in the bridge mix was replaced with CEM I, to optimize the binder content and achieve the desired strength and workability. At this stage, mixtures with varying binder contents ranging from 350 to 200 kg/mon curve . With thon curve . In the All the mixes were prepared and tested in fresh state according to EN 12350. Specimens were demoulded 24 h after casting and then cubes were transferred to the humidity chamber (relative humidity maintained more than 95% and temperature of 20 ± 1 °C) until testing day. In designing the experimental plan, an engineering approach was used, employing standardized methods, methods normally used in practice. Since the basic idea of the work was to show the effects of cement reduction on a real case in a real environment, the methods and concrete age at which the tests were performed were the same for all mixes and conformed to standards. Although further environmental savings would be possible if the performance of the materials were considered at a later age (for example 56 or 90 days), this rigorous and conservative approach was nevertheless used to clearly demonstrate potential savings from changes in concrete formulations.Three concrete specimen of 15 cm × 15 cm × 15 cm were prepared to measure the compressive strength after 7 and 28 days of curing as per EN 12390-3 standard. Cylindrical specimen of 20 cm height and 10 cm diameter were prepared to test the chloride penetration resistance of the mixtures. After the 28 days of curing, the cylindrical specimens were split diametrically into three slices with thickness of 5 cm for the experiment.xd, was visible as whitish colour. Then the non-steady state migration coefficients (Dnssm) were determined based on the Nernst–Plank equation.The chloride ingress resistance was expressed in terms of chloride migration coefficient, which was determined by nord test build 492 . After td) and initiate the corrosion of reinforcement [s), chloride diffusion coefficients (Dcl) and the ageing coefficients (m). Therefore, service life of structure is written as a function of each above-mentioned parameter.In this study, the calculation of service life of the reinforced structure included the corrosion initiation and propagation time. The initiation time was calculated based on the Fick’s 2nd law of diffusion , 36 as aorcement . Therefoi et al.  reportedi et al. . Howeverk’ determined experimentally from several previous studies by the authors was taken as 1.69 [Previous investigations on these and related systems found that chloride migration produces higher values than bulk diffusion. Since chloride migration was measured for all systems, a correlation factor was used to compare the two approaches. as 1.69 .Atotal) were calculated for one cubic meter of concrete, which were total sum of each individual values of materials multiplied (xi) by corresponding quantity (qi) in one cubic meter of concrete.The environmental impact and materials costs (2) to the atmosphere. Each material was analyzed up to the point of manufacturing, excluding the sources of raw materials. The conversion parameters for each material used to calculate the total embodied carbon/energy are given in additional documents . GWP is a measure of the total emission of greenhouse gases  per kilogram, and data were gathered from local suppliers. Fly ash and calcined clay are still not commercially available, and as a result, a similar price was assumed for fly ash-limestone and LC2 blends. The prices of each material used in the study are given in additional documents (see Table 4 in Supporting Information).β) proposed by Muller et al. [IP5) based on the study by Yu et al. [Reducing the binder content or using alternative binders in concrete without considering the impact on durability would be a failure in terms of sustainability. Moreover, in today’s world, economic advantages will be to the detriment of a more environmentally friendly concrete. Therefore, the sustainability of any concrete mix is a function of these parameters. To allow comparison of the mixes, the values of all parameters were converted into a single value indicating the sustainability of each mix. The overall performance of each mix was expressed using two different approaches: (1) sustainability factor u et al. .fck is 28-day compressive strength of the mixture, tSL is the service life of the structure and embodied carbon is expressed as global warming potential.Muller et al. proposed a sustainability factor to evaluate the concrete mixture in terms of durability and environmental impact. The factor is determined by following relationship :5\documeThis approach considers five distinct factors and weights them differently. For example, a global sustainability of concrete is determined more by its life span, embodied energy, and cost than by its strength. The concept is derived from a study , and is IP5) is calculated based on the following relationship:Ii are the five different indices and wi is the weight of each index presented in Table After determining each index, the overall performance indicator called the five-performance index . This coefficient was then transferred into chloride diffusion coefficient shown in Fig. The durability performance of each mixture was evaluated by measuring non-stead state chloride migration coefficient  are illustrated in Fig. 3 concrete. As a result, reducing the binder content and substituting with alternative binders can create a significant reduction of the overall environmental impact of concrete. Additionally, the FALS mixture demonstrated the greatest reduction in carbon footprint in this case. In the case of calcined clay, the GWP was found to be reduced by between 30 and 40%, but the embodied energy was just 15–25%. Although the embodied energy of calcined clay is primarily due to the calcination process, some studies indicate that it could be further reduced. The primary issue is a lack of sufficient or accurate data for calcined clay. However, all alternative mixtures demonstrated a reduction in environmental impact compared to mix BD435.The figure demonstrated that the clinker component accounted for more than 70% of the carbon and energy embodied in 1 mThe material cost for the unit-volume of concrete calculated and given in Table The contribution from the clinker phase to the overall cost was found to be significant and hence it is clear that blended mixtures were more economical than 100% Portland cement mixtures.Several parameters were discussed in the preceding sections, along with their individual contributions to each mixture. However, the overall performance of each mixture in terms of mechanical properties, environmental impact, and material cost must be discussed collectively. Therefore, each mixture should be ranked according to its sustainability. As mentioned in Sect. 3, while the lowest values were obtained for C300 and C340. Considering overall performance, the higher binder content with alternative binders were better than BD435.The sustainability factor for each mixture is depicted in Fig. IP5 values determined with BD435 as reference mixture are shown in the Fig. In this technique, all sustainability parameters were weighted equally. In a concrete construction, for instance, service life is more significant than strength, particularly if the same desired compressive strength is achieved. On the other hand, a stronger concrete does not always imply more durable concrete across all environments. Simultaneously, not all concrete with superior durability must be high strength. Strength should be specified in terms of the structure’s ability to withstand applied loads, not as a performance metric for durability. As a result, the sustainability approach should be weighted differently and include additional parameters such as material cost. As a result, the second approach would provide a more precise picture of sustainability. Section 3  are impaired. However, since all indices were considered with the same significance, all mixture performed significantly better than BD435, with the exception of the control mixtures in Fig. In the Fig. 3 Fig. b, the siIn comparison to the first method, the calcined clay mixture with both binder content levels showed good performance when compared to the bridge mixture. Even though the LC mixture demonstrated poor performance in terms of service life, they were still successful in achieving good sustainability in terms of environmental impact and materials cost. In the case of fly ash mixture, both mixes were significantly better than BD435.Comparison of overall performance indicators shows how by decreasing the amount of cement used alone cannot result in an overall better performance, as was demonstrated by mixes C340 and C300. But reducing the amount of cement in the mixture and supplementing it with other cementitious materials that are locally available could produce mixtures with competitive sustainability performance indicators. Therefore, all alternative systems with reduced total binder have exhibited very good potential in the practical application. Additional to this, this study proved that good quality concrete can be produced with very low kaolin clay, producing concrete with comparable performance in terms of strength and durability compared to cement with slag or fly ash. Therefore, the performance-based design by optimisation of binder content and usage of alternative binder would be a good strategy for a more sustainable approach in concrete industry.3 and 300 kg/m3. Next, the Portland cement was replaced by 30% and 45% with fly ash/calcined clay and limestone. The compressive strength and non-steady state chloride migration coefficients were evaluated for all the mixtures. From these results, the service life, environmental impact, and materials cost were evaluated. The overall sustainability of each mixture was evaluated and discussed using two different approaches.In this experimental study, a real-structure concrete mix design was compared to different approaches of lowering carbon footprint of concrete. The concrete was prepared with reduced binder contents of 340 kg/mResults presented in the study demonstrated on a real case scenario that the total binder content of concrete could be significantly reduced without compromising the mechanical and durability performance of concrete used in this specific structure exposed to harsh marine environment. Additionally, the usage of alternative binders along with reduction in the total binder content, provides an extra pull towards sustainability. The fly ash used, which was collected as waste stream, showed good results compared to the bridge mixture even with low binder content. The calcined clays used in this study was technically low-grade clay, and still it provided satisfying results in the overall sustainability performance. Unlike the fly ash and limestone mixture, in the case of calcined clay and limestone mixture, the kaolinite content and total binder significantly influenced the individual parameters. However, the five-performance sustainability approach demonstrated that low grade clay could also be a viable alternative to the original bridge design.The study demonstrates unequivocally that optimizing total binder content and utilizing alternative binders  are critical factors in ensuring the overall sustainability of concrete. The study also experimentally proves that a significant savings in carbon footprint can be achieved without compromising mechanical stability or service life of concrete in structures even when exposed to aggressive marine environment.Supplementary file1 (DOCX 30 kb)Below is the link to the electronic supplementary material.


Antibiotic consumption (ABC) surveillance is a critical component of the strategic priority response to the increasing antibiotic resistance threat. Levels of ABC at the national and provincial levels in South Africa are unknown because of inadequate ABC surveillance systems and literature. Antibiotic consumption in the public sector of Limpopo province, South Africa, 2014-2018This retrospective study used sales data retrieved from a pharmaceutical warehouse distribution database to quantify ABC. Antibiotic consumption was measured by the defined daily dose (DDD) per 1000 inhabitants per day (DID) and 75% drug utilisation index (DU75%). Change in consumption was measured by the compound annual growth rate (CAGR).Between 2014 and 2018, the mean ABC was 4.6 ± 1.0 DID, with an overall decrease of 1.6% in the CAGR. Penicillins , sulphonamide and trimethoprim combinations  were the most consumed antibiotics. Macrolides had the highest relative increase in consumption during the study period, with a CAGR of 18.5%. In contrast, tetracyclines had the highest relative decrease in consumption, with a CAGR of 100.0%. The CAGR ratio for broad- to narrow-spectrum increased by 39.3%, from 0.4 in 2014 to 2.1 in 2018. The DU75% comprised amoxicillin (28.4%), sulphamethoxazole and trimethoprim (SMX-TMP) (27.2%), doxycycline (12.3%) and azithromycin (9.2%).While ABC remained relatively stable throughout the study, there was an increase in broad-spectrum ABC that requires further investigation.This study contributes ABC surveillance data in Southern Africa, described by ATC classification, which is essential for monitoring and evaluating antibiotic stewardship programmes. The PDoH provides healthcare services throughout the province through its 30 district hospitals, five regional hospitals, four specialised hospitals, two tertiary hospitals, 481 community health centres and fixed clinics and 42 mobile clinics.18 The LPPD is responsible for the direct and indirect distribution of pharmaceuticals, including antibiotics, to all district and specialised hospitals and fixed and mobile primary healthcare institutions. Furthermore, tertiary and regional hospitals utilise a direct procurement approach, supplemented by the LPPD on an emergency basis.18The study was conducted in the Limpopo province in South Africa. The province is located in the northern region of South Africa, sharing a border with three SSA countries .19 Therefore, topical antibiotics, antimycotics and antifungals (J02), antivirals (J05), antimycobacterial (J04), antimalarials (P01B), antiprotozoals used as antibiotic agents (P01AB), antibiotics used as intestinal anti-infectives (A07AA) and antiseptic agents were excluded.19 Moreover, the authors focused on ABC for human consumption only; nonhuman use  was therefore excluded.This study focused on the J01 (antibiotic for systemic use) antimicrobial group of the Anatomical Therapeutic Chemical (ATC) classification system.This study used sales data from the public sector central depot’s pharmaceutical distribution database data to quantify and describe antibiotic distribution trends retrospectively over five years (2014 to 2018).7; that is, the ATC classification system and the DDD were used as units of measurement.19 The ATC classification system divides drugs into distinct groups  based on their mode of action and therapeutic and chemical characteristics.7 The active substances in the ATC system are classified according to the organ or system on which they act, as well as their therapeutic, pharmacological and chemical properties. Medications are categorised into five distinct levels. The DDD is the ‘assumed average daily maintenance dose for a drug used for its primary indications in adults’.7 The ATC and DDD are available as a downloadable computer software tool known as the WHO antimicrobial consumption tool.20 Data  were manually entered into the software to calculate the ABC.The GLASS methodology was adopted for this study19 The estimated total annual human population  of the Limpopo province available from Statistics South Africa was utilised for DID adjustments to account for population size variations and to enable comparison across time and population groups, because it was not probable to estimate the population of the public sector only.13 The relative consumption by the antibiotic subgroup is presented as a percentage of the total consumption of antibiotics for systemic use. To show changes in consumption over time, the total antibiotic or pharmacological subgroups or antibiotic agents at ATC level five, compound annual growth rate (CAGR) was determined.21 The broad- to narrow-spectrum ratio was calculated through the consumption of broad-spectrum penicillins, cephalosporins, macrolides (except erythromycin) and fluoroquinolones  to the consumption of narrow-spectrum penicillins, cephalosporins and macrolides (narrow-spectrum penicillins [J01CE] + narrow-spectrum [J01DB] + erythromycin [FA01]).21 Arithmetic means were calculated to determine the central tendency of the ABC data. The total mean consumption of different antibiotic agents at ATC level five was ranked from highest to lowest, and the most commonly consumed antibiotic agents accounting for 75% of total mean consumption (DU75%) were established.22The results for this study are provided following selected ABC quality indicators. The total ABC and consumption by different antibiotic subgroups are reported in DID.Ethical approval of the study was obtained from the North-West University Health Research Ethics Committee (reference number NWU-00312-20-A1). Data sources access permission was granted by the Head of the Limpopo Department of Health (LDoH) (reference number LP-202003-012) and a letter of goodwill was obtained from the manager of the Limpopo Province Pharmaceutical Depot (LPPD) before conducting the study.The overall mean for antibiotic for systemic use (J01) consumption during the study period (from 2014 to 2018) was 4.6 ± 1.0 DID . BetweenOrally administered antibiotics contributed 98.9%, compared with 1.1% for parenteral administered antibiotics . The CAGThe penicillins (J01C) were the most consumed antibiotic subgroup, increasing from 35.8% of the relative consumption in 2014 to 45.0% in both 2015 and 2016 to more than half (58.4% and 57.3%) of relative consumption in 2017 and 2018, respectively . SulphonAt ATC level 4 , the relAt ATC level 3, the consumption of macrolides and lincosamides (J01F) increased by 18.5% . QuinoloThe consumption of broad-spectrum antibiotics increased with a CAGR of 28.5%, while the consumption of narrow-spectrum antibiotics decreased with a CAGR of 12.9% . There wFour antibiotic agents  comprised the overall DU75% during the entire study period (2014–2018) . Amoxici4 It should, however, be taken into account that the total annual population13 for the Limpopo province was utilised as the denominator in this investigation because it was not possible to determine the population for the public sector alone, whereas the sales data represented only the public sector. The ABC sales data furthermore excluded antibiotics procured directly from five regional and two tertiary hospitals and health facilities under other governmental departments, such as Correctional Services and Military Health. This study’s estimates may, consequently, be an underestimate of the ABC in the province. Nevertheless, these findings can serve as a baseline for future ABC quantification and monitoring in the Limpopo province.This study quantified and described ABC from sales data obtained from a pharmaceutical warehouse distribution’s database using the ATC and DDD index and tracked ABC change using CAGR, broad-to-narrow spectrum index and DU75%. At 4.6 ±1.0 DID between 2014 and 2018, the overall mean consumption rate was stable and low compared with global (14.1 DID) and SSA regional (8.2 DID) rates.23 and a national shortage of injectable cephalosporins such as ceftriaxone during the study period.24During the study period, oral and parenteral formulations accounted for 98.9% and 1.1%, respectively, with parenteral formulations decreasing by 14.0% compared with a 1.4% decrease in oral formulations. The rationale for a notable decrease in parenteral formulations could be linked to a global shortage of injectable penicillin, such as ampicillin and benzylpenicillin4 Amoxicillin, in particular, is the most consumed agent globally.12 The findings of this study showed that similar to global trends, penicillins were the most consumed antibiotics subgroup, with amoxicillin as the most consumed agent. Penicillins are indicated as first-choice agents for common respiratory infections in the South African Standard Treatment Guidelines (STGs) and Essential Medicines List, which is the reference for selecting and procuring medicines for the public health sector in South Africa.25 Moreover, in 2018, penicillins (amoxicillin with enzyme inhibitor and ampicillin) were the most commonly prescribed antibiotics for hospitalised patients in South Africa for skin and soft tissue infections, pneumonia and sepsis.27 Furthermore, the increase in relative consumption of broad-spectrum penicillins , macrolides and quinolones, corresponding with a decreased consumption of narrow-spectrum penicillins, resulted in 39.3% CAGR increase in the broad-to-narrow spectrum ratio  in this study, the increased broad-to-narrow spectrum ratio suggests that consumption of antibiotics from one subgroup was effectively replaced by the consumption of antibiotics from another subgroup.29Globally, penicillins are the most consumed antibiotics subgroup, accounting for 39.0% of all antibiotics consumed, followed by cephalosporins and quinolones.um ratio . These f30 in accordance with international guidelines’ recommendations in September 2016.31 Sulphamethoxazole and trimethoprim prophylaxis was recommended in 2014 international guidelines for patients with severe or advanced HIV infection (WHO stages 3 or 4)32 and a CD4+ cell level of fewer than 200 cells/mm, according to the latest (2020) Southern African antiretroviral therapy guidelines for adults.33 Moreover, adults with HIV infection who are clinically stable on antiretroviral therapy and show immunological recovery and viral suppression may discontinue SMX-TMP prophylaxis.33 The number of clinically deteriorating patients who met the early criteria for SMX-TMP prophylaxis may have been reduced by the implementation of the UTT programme.30 The UTT programme encourages antiretroviral therapy initiation regardless of CD4+ cell count or WHO clinical staging towards achieving a 90% viral suppression (enabling discontinuation of SMX-TMP).31Although the sulphonamide and trimethoprim subgroup was the second-most consumed antibiotic subgroup, the CAGR declined by 7.7% from 2014 to 2018. This decline could be attributed to the South African Health Ministry’s implementation of the HIV Universal Test and Treat (UTT) programme,24 Antibiotic shortages do not only result in limited accessibility but also contribute to inappropriate use, which perpetuates the development and spread of ABR.34 Given the STG’s extensive list of indications for cephalosporins, its unavailability may result in serious adverse patient outcomes.25 Tetracyclines’ decrease to zero distribution by 2018 can be ascribed to changes in South African sexually transmitted infection management guidelines, which now mostly recommend using macrolides and cephalosporins such as azithromycin and ceftriaxone, respectively, over tetracyclines such as doxycycline.36 Furthermore, malaria is endemic in the Limpopo province,37 South Africa. Since 2017, the new malaria treatment guidelines recommended artemether–lumefantrine and artesunate over quinine and doxycycline.38 This could have decreased tetracycline use in the present study.In this study, cephalosporins’ fluctuating consumption can be attributed to possible stock shortages. A 2018 survey of South African public sector pharmacists revealed cephalosporins as the second-most frequently out-of-stock antibiotic, after macrolides.Chlamydia trachomatis, Haemophilus ducreyi and Neisseria gonorrhoea) because of high quinolone resistance, respiratory infections , gastrointestinal tract (i.e. cholera) and enteric fever (i.e. typhoid fever)36 may have driven the macrolides’ highest CAGR (18.5%) during the study period (2014–2018) compared with the other antibiotic subgroups. However, there was intramacrolide subgroup variability, with long-acting broad-spectrum azithromycin consumption increasing at a CAGR of 53.4% at the detriment of intermediate-acting broad-spectrum macrolide  becausde of its pharmacokinetics , tolerability , high intracellular concentrations and potency against enteric bacteria such as Salmonella species and the absence of drug–drug interactions via the cytochrome P450 drug metabolism complex.40Azithromycin, a long-acting broad-spectrum macrolide, was introduced in the South African STG for the treatment of sexually transmitted infections  and hospital sector and seasonality. Finally, because of unavailability of sales data beyond 2018 as a result of database changes and access restrictions, only data from 2014 to 2018 were used; more recent data may show a different ABC pattern.14Despite these limitations, the study’s strength is that it is, to authors’ knowledge, the first study to describe ABC and therefore establishes a benchmark  for monitoring and evaluating future ASP policies and actions in the public sector of the Limpopo province. Public sector health facilities are the most convenient and first point of contact for healthcare to the general population of South Africa, covering health services for more than 90% of the province’s population.Recommendations on policy, practice and research include the following: firstly, the Limpopo Provincial Health Authority should consider implementing routine ABC surveillance reports using an internationally accepted methodology. Secondly, future research needs to ensure that ABC central warehouse data are integrated with data from direct procurement by specific healthcare facilities and data from private sector institutions and community pharmacies. Thirdly, future ABC analysis should consider determining seasonality and consumption variation between community and hospital healthcare sectors. Fourthly, the ABC surveillance data describe ABC at an ecological level and only serve as a proxy for actual antibiotic use; therefore, patient-level surveillance data are required to assess the quality of antibiotic prescribing and use. Antibiotic prescribing point prevalence surveys can be used to do this. Finally, community surveys are important to acquire a more comprehensive status of patients’ antibiotic knowledge, attitudes and practices.In conclusion, the study quantified and described ABC in the Limpopo province’s public sector using comparable international methodologies. Antibiotic consumption has remained stable from 2014 to 2018, while broad-spectrum ABC has increased, which is associated with the development and spread of antimicrobial resistance and requires further investigation.