In reinforced concrete (RC) structures, new-to-old concrete interfaces are widely present due to precast splices, repairs, and construction joints. In this paper, both monolithic and segmental specimens were fabricated with five kinds of water–cement ratios, including ordinary and high-strength concrete. The impressed current-accelerated corrosion test was used, and the degree of reinforcement corrosion was controlled by Faraday’s Law. In the accelerated corrosion process, the concrete surface cracking, steel corrosion, and mechanical properties of the corroded steels in the segmental specimens were investigated and compared with monolithic specimens considering the pouring method, concrete strength, and the strength difference between new and old concrete. The prediction of concrete cracking time was also discussed. The results indicated that, for the monolithic specimens, longitudinal cracks could be observed on the ordinary concrete surface, while no cracks were produced on a high-strength concrete surface; only the rust leaked out at the ends. For the segmental specimens, both longitudinal and transverse cracks were produced on an ordinary concrete surface, while only transverse cracks were produced at the high-strength new-to-old concrete interfaces. The steel embedded in the segmental specimens suffered more sectional loss at the new-to-old concrete interfaces. An influence coefficient based on the section loss of the rebar was proposed to evaluate the influence of interfaces on the rust uniformity of rebars. When there were differences in strength between new and old concrete, the influence of the interface on the uniformity of steel bar cross-section loss slightly increased. Based on available theoretical analysis for uniform corrosion, the concrete cracking time of the monolithic specimens was predicted, which was basically consistent with experimental phenomena. However, further research is needed to predict the service life of segmental specimens with new-to-old concrete interfaces. Zhang et al. [Steel corrosion in concrete has become the most significant cause of structural deterioration, especially for marine structures. Chloride ions in the marine environment can penetrate the concrete cover and make the steel depassivate and lose the protective oxide film. Once corrosion initiates, corrosion products will continuously accumulate around the reinforcement, leading to the cracking and spalling of the surrounding concrete and causing the degradation of RC structures ,2,3. Theg et al.  studied In practical engineering, new-to-old concrete structures are widely present due to precast splices, repairs, and construction joints. If reinforcement corrosion occurs at the new-to-old concrete interface, it inevitably leads to a serious impact on the bond strength of the interface and further endangers structural safety. Zhao et al.  found thHowever, existing research has rarely considered the surface crack propagation and steel corrosion behavior caused by the presence of new-to-old concrete interfaces. Thus, in this study, the differences in surface cracking and reinforcement corrosion between monolithic and segmental specimens were comprehensively compared, revealing the morphology and generation mechanism of concrete surface cracking. The effect of concrete strength on the durability of RC structures with new-to-old concrete interfaces was also investigated. Additionally, the prediction of the concrete cracking time was also discussed to provide practical recommendations for engineering practice.In this study, both monolithic and segmental specimens with new-to-old concrete interfaces were fabricated, as shown in After curing, a ZBL-F800 crack comprehensive tester was introduced to observe whether there were obvious cracks at the adhesive interface for segmental specimens. Any specimens with initially visible interface cracks were discarded and re-prepared to prevent any impact on the test results.3, water demand ratio ≤ 95%; S95 ground-granulated blast-furnace slag: specific surface area ≥ 400 m2/kg, mobility ratio ≥ 95%, 28d activity index ≥ 95%).The influence of the casting method, concrete strength, and strength difference between new and old concrete on the corrosion of steel bars was considered in the specimen design, as shown in fy of 300 MPa), with a uniform diameter of 16 mm and a net concrete cover thickness of 25 mm. Two bars (HPB300) were randomly selected and tested for tensile strength (averaged) with a mechanical universal machine in accordance with the requirements of specification GB/T 228.1-2021 [The casting methods included integral and segmental casting. As shown in 8.1-2021 . It was 2, according to the research of Gan et al. [Since the accelerated corrosion test could shorten the time significantly and the process of steel corrosion in both the accelerated corrosion and normal corrosion tests was similar , the impn et al. , and themL is the mass loss of iron (g); M is the molar mass of iron (56 g/mol for Fe); Z is the valency of the iron element ; F is the Faraday constant ; t is the duration of electrochemical corrosion (s); I is the magnitude of the electric current (A), which can be obtained by i is the current density (A/m2) and taken as 2.5 mA/cm2 in this study, and S is the surface area of reinforcement (m2).Faraday’s law was used to obtain the designed amount of reinforcement corrosion, in terms of mass loss of reinforcement:ηt = 4%, ηt = 6%, and ηt = 8% were calculated to be 60 h, 90 h, and 120 h, respectively. Existing research has found that the measured corrosion levels are generally lower than the theoretical ones derived from Faraday’s law [The duration needed to reach a designed amount of mass loss can be calculated based on Faraday’s law. Therefore, the theoretical corrosion duration times of specimens with theoretical corrosion rates of ay’s law ,31. The The development of cracks and corrosion products accumulated on the concrete surfaces was observed during the whole accelerated-corrosion process. The crack widths on the concrete surface were measured using a ZBL-F800 crack comprehensive tester. A total of sixteen points along the longitudinal crack were selected, with a point spacing of 30 mm. The first measuring point was located at the leftmost end of the specimen where the steel bar was bonded to the concrete. Similar procedures were conducted for transverse cracks that appeared at the new-to-old concrete interface, where six points were measured with the same spacing of 30 mm, as shown in mo and mc, respectively), as shown in Equation (2):After finishing the accelerated corrosion test, the covering concrete was completely removed from the reinforcement and the corroded steel bars were obtained. Then, rust was cleaned from the steel bars following the treatment method provided in ASTM G1-03 , and theSl is the uncorroded cross-sectional area of reinforcement (m2); S2 is the corroded cross-sectional area of reinforcement (m2); dl is the uncorroded rebar diameter (m2); and d2 is the corroded rebar diameter (m2).Meanwhile, the diameters of all cleaned bars were also measured with a digital display caliper with a precision of 0.01 mm. The measuring points were also selected every 30 mm along the length of the steel bar and started from the end section, where the steel bar and concrete were bonded together with a total of 16 points. These measuring points corresponded one-to-one with those along the longitudinal crack on the concrete surface. Each point on the rebar was measured twice. The two measuring positions at the same point were kept perpendicular to each other, and the average value of the two data was taken as the diameter of the point. After obtaining the diameter of the corroded steel bar, the sectional loss After evaluating the corrosion levels, the corroded bars were subjected to strain-rate-controlled tensile testing according to the standard code GB/T 288.1-2021  using anηt) predicted by Faraday’s Law reached 2%, local micro-cracks (with a width of about 0.08 mm) were generated on the surface of Specimen 1-b (w/c = 0.60), while there were no cracks on the surface of Specimen 5-b (w/c = 0.53).In the accelerated corrosion process, as corrosion products gradually accumulated, longitudinal cracks were observed to be generated on exposed concrete surface for the monolithic Specimens 1-b and 5-b, which were made of ordinary concrete with w/c = 0.60 and 0.53, respectively. It was observed that, when the theoretical corrosion rate of the steel bar  being higher than that of the old concrete , it was observed that, in the segments outside the interfaces, the cross-sectional loss of steel bars in part A was generally higher than that in part B. Compared with Specimens 24-a and 23-a, Specimen 25-a exhibited the lowest values in both average and maximum cross-sectional losses.kj) of construction joints on the local weight loss to reflect the influence of joints on the rust uniformity of rebars, which was defined as follows:m2 is the rust amount of the rebar in joint section (g); m1 is the rust amount of the rebar in the non-joint new concrete section (g); and m3 is the rust amount of the rebar in non-joint old concrete section (g). The values of kj were in the range of 1.15–3.33, with an average of 1.76.Huang et al.  found thks based on the section loss of steel bars was proposed to evaluate the influence of joints on the rust uniformity of rebars, as defined below:Si is the section loss of the rebar at the new-to-old concrete interface; in this study, there were two interfaces; thus, it was the sum of the two, i.e., Si = Si1 + Si2; Sn and So were the average section losses of the rebar at each measuring point in the new and old concrete sections, respectively.Considering that the cross-sectional loss measurement of steel bars in this study was more detailed than mass loss measurement, an influence coefficient ks of all segmental specimens under the theoretical corrosion rate of 6% are listed in ks were in the range of 1.180–1.401, with an average value of 1.286. The maximum value of ks was 1.401 for Specimen 3-b and the minimum was 1.180 for Specimen 14-a. The results show that, when the new and old concrete sections had the same mix proportion, the values of ks decreased almost linearly with the decrease in the water–cement ratio, which means that increasing the concrete strength could reduce the non-uniformity of steel corrosion due to the presence of the joint. But when there were differences in strength between the new and old concrete, the influence of the interface on the uniformity of steel bar cross-section loss slightly increased. For example, compared with Specimens 13-a and 14-a, the ks value of Specimen 23-a increased by 4.00% and 10.08%, respectively. A similar trend was found in Specimens 25-a and 24-a.The influence coefficients ηw), the average cross-section loss (ηs-ave), and maximum cross-section loss (ηs-max) of the corroded steel. The relationship between these three parameters and the theoretical corrosion rate (ηt) predicted from Faraday’s Law was analyzed in detail.In this section, more attention was paid to three parameters obtained in the experiments to measure the corrosion level of steel, namely the mass loss (ηt = 6%). It is also important to note that the maximum sectional loss of steel for each segmental specimen was larger than the theoretical corrosion rate predicted from Faraday’s Law (ηt = 6%). The ratios between the measured maximum cross-section losses of steel to the theoretical corrosion rates from Faraday’s Law ranged from 1.05 to 1.6. Thus, for the segmental specimens, sectional loss of steel is suggested to represent the corrosion level of steel.And an exponential relationship could be established between the maximum reinforcement cross-sectional loss Tensile tests were performed on corroded reinforcements. The results indicated that rebars in monolithic specimens fractured at the middle section due to uniform cross-section losses, while rebars in segmental specimens fractured at the minimum cross-sections, i.e., at the new-to-old concrete interfaces. fyc, and nominal ultimate strength, fuc, of corroded steel bars are listed in Until now, different methods have been used to assess the strength properties, such as nominal (apparent) strength and residual (or true) strength ; that isCorroded steels in segmental specimens showed a larger decrease in nominal ultimate strength than those in monolithic specimens. Concrete strength significantly affected the nominal ultimate strength of corroded steels in both monolithic and segmental specimens. The reduction in ultimate strength decreased with rising concrete strength, but the trend was less evident for yield strength, which could be influenced by various factors besides the minimum cross-sectional area.It is also worth mentioning that, when using ordinary concrete with a water–cement ratio of 0.60 and 0.53 for all specimens under the theoretical corrosion rate of 6%, both the yield and ultimate stresses of corroded steels decreased greatly by 12.10–16.56%. However, when high-performance concrete with water–cement ratios of 0.44, 0.33, and 0.24 was used for all specimens under the theoretical corrosion rate of 6%, both the yield and ultimate stresses of the rusted steel only slightly decreased by 2.37–7.01%. This implies that the use of high-strength concrete can effectively reduce the strength loss of corroded steels, because the water-cement ratio affects the permeability of concrete. For segmental specimens, the tensile behavior of corroded steels largely depended on the steel corrosion at the new-to-old concrete interface, and the concrete type was an important factor affecting the bonding performance at the new-to-old concrete interface.fyc  of the corroded steel. It was more appropriate to use cross-section loss to evaluate steel corrosion in segmental specimens with the new-to-old concrete interfaces.Furthermore, for the segmental specimens, it was found that the correlation between the maximum sectional loss and the tensile behavior of corroded steel was the strongest, as shown in q in smooth steel bars when concrete cracking was initiated based on the theory of elastic mechanics:c is the net concrete cover thickness (in this study c = 25 mm), d is the rebar diameter (d = 16 mm), and ftk is the standard value of axial tensile strength. Thus, the uniform corrosion-induced stresses when concrete cracking was initiated for the monolithic Specimen 1-b (ftk = 2.01 MPa) with w/c = 0.60 and Specimen 5-b (ftk =2.40 MPa) with w/c = 0.53 were 2.49 MPa and 2.97 MPa, respectively.This paper refers to the expression proposed by Jin et al.  for unifq in rebars prior to concrete expansion cracking, which was expressed as a function of the steel corrosion rate ρ:δ is the thickness of the rust layer; n is the volume expansion ratio of the corroded rebar, typically ranging between 2 and 4; ρ is the corrosion rate of the rebar, evaluated using the cross-sectional loss percentages; and R is the rebar radius.Jin et al.  also pro3O4. Referring to the volume expansion ratio of the corrosion products given by Ji et al. [n was set to be 2.0.The experimental results in i et al. , n was sCombining Equations (8) and (9), the predicted cross-sectional losses for the monolithic Specimens 1-b and 5-b when concrete cracking was initiated were 1.78% and 2.13%, respectively, consistent with the experimental observation in According to Faraday’s law in Equation (1), the time for concrete cracking initiation can be predicted as follows:By substituting the cross-sectional losses obtained for the monolithic Specimens 1-b and 5-b when concrete cracking initiated into Equation (10), the predicted concrete cracking times for the monolithic Specimens 1-b and 5-b were 26.8 h and 32.0 h, respectively.Through theoretical calculation, it was found that the cross-sectional loss predicted for concrete cracking initiation in monolithic specimens was basically consistent with experimental phenomena. However, because the focus of this study was on concrete surface cracking and the subsequent mechanical properties of corroded rebars, the initial cracking time was not monitored, so a comparison between the predicted initial cracking time and the actual one was not possible.As for the segmental specimens, non-uniform corrosion-induced rust expansion should be considered. It is necessary to combine experiments and numerical simulation to obtain relevant data, such as the time for concrete cracking, the corresponding cross-sectional loss of steel bars, and the non-uniform rust expansion pressure at concrete cracking. It is also possible to combine existing theoretical non-uniform corrosion models for analysis, and thus to achieve the prediction of concrete cracking time for segmental specimens. This needs further research in the future.Monolithic and segmental specimens with new-to-old concrete interfaces were tested to investigate their concrete surface cracking based on the impressed current-accelerated corrosion method. Moreover, the steel corrosion and mechanical properties of the corroded steels were observed and examined for their differences in the two kinds of specimens. Important conclusions are summarized as follows:In the accelerated corrosion process, for the monolithic specimens, longitudinal cracks were generated on the ordinary concrete surface, whereas no cracks were produced on the high-strength concrete surface; only the rust products leaked out at the ends. For the segmental specimens, both longitudinal and transverse cracks were generated on the ordinary concrete surface, whereas only transverse cracks appeared on the high-strength new-to-old concrete interfaces.(1)The steels embedded in segmental specimens suffered higher cross-sectional loss at the new-to-old concrete interfaces, with the maximum sectional loss of the steel sharply decreasing as the concrete strength increased. An influence coefficient based on the section loss of the rebar was proposed to evaluate the influence of interfaces on the rust uniformity of rebars. When there were differences in strength between new and old concrete, the influence of the interface on the uniformity of the steel bar cross-section loss slightly increased.(2)Both the mass loss and sectional loss could be used to describe the steel uniform corrosion in the monolithic specimens, but for the segmental specimens, it was more appropriate to use cross-sectional loss to evaluate steel corrosion, due to the steel at the new-to-old concrete interface suffering worse sectional loss.(3)The corroded steels embedded in the monolithic specimens fractured at the middle section, while those embedded in the segmental specimens fractured at the new-to-old concrete interface. The corroded steel bars in the segmental specimens showed worse tensile behavior compared with those in the monolithic specimens.(4)Based on available theoretical analysis for uniform corrosion, the concrete cracking time of the monolithic specimens was predicted, which was basically consistent with experimental phenomena. However, further research is needed to predict the service life of segmental specimens.Since accelerated corrosion only lasts for a few tens of hours, corrosion products do not have enough time to invade the concrete pores. In future studies, wet–dry cycling tests can be carried out to simulate the real environment to study the cracking behavior of the concrete protective layer in new and old concrete structures. The cracking of new-to-old concrete under the coupling of carbonation and other factors can also be studied in depth to better understand the reaction kinetics, diffusion mechanisms, and influencing factors. Secondly, this experiment only considered the effects of the pouring method, concrete strength, and strength difference between new and old concrete. Other design parameters such as the concrete cover thickness, the type and quantity of steel bars, and the interface treatment, can be considered in the future to reveal the rust cracking process caused by the presence of new-to-old concrete interfaces. Furthermore, some microscopic detection methods, such as slicing and optical scanning, should be introduced to study the rust expansion behavior and achieve service life prediction for RC structures with new-to-old concrete interfaces.


Through the phases of this article, a refined trigonometric shear deformation theory (RTSDT), taking into account transverse shear deformation effects, is presented for the thermoelastic bending analysis of concrete slabs reinforced with ferric oxide (Fe2O3) nanoparticles. Thermoelastic properties are generated using Eshelby’s model in order to determine the equivalent Young’s modulus and thermal expansion of the nano-reinforced concrete slab. For an extended use of this study, the concrete plate is subjected to various mechanical and thermal loads. The governing equations of equilibrium are obtained using the principle of virtual work and solved using Navier’s technique for simply supported plates. Numerical results are presented considering the effect of different variations such as volume percent of Fe2O3 nanoparticles, mechanical loads, thermal loads, and geometrical parameters on the thermoelastic bending of the plate. According to the results, the transverse displacement of concrete slabs subjected to mechanical loading and containing 30% nano-Fe2O3 was almost 45% lower than that of a slab without reinforcement, while the transverse displacement under thermal loadings increased by 10%.Nanoparticles, by virtue of their amorphous nature and high specific surface area, exhibit ideal pozzolanic activity which leads to the formation of additional C-S-H gel by reacting with calcium hydroxide, resulting in a denser matrix. The proportions of ferric oxide (Fe Nanotechnology has become one of the most important and exciting areas of many fields such as physics, chemistry, biology, and, very recently, civil engineering. It has also attracted a great deal of attention in the field of material science and technology. To contribute in the development of concrete physical and mechanical conventional properties, researchers intent to replace long-used pozzolanic powder additives in concrete composition, such as micro silica fume (MS), blast furnace slag, and fly ash, with new materials to achieve a more efficient and durable concrete while considering the economy aspects ,2.Intrinsically, the specific objective of researchers lately was to find the preference for how to use nanoparticles with amorphous form to add even more capabilities to a concrete matrix. The required improvement of concrete properties reinforced with nanoparticles is mostly to be achieved due to the unique properties of those nano-sized elements, such as their high strength, elevated modulus of elasticity, high specific surface area, exorbitant electrical conductivity, enhancement of calcium silicate gel (C-S-H), and specific chemical activities   are as follows:The components of the elastic stiffness matrix [f} = {f1, f2, f3, f4}T are given byThe components of the generalized thermal force vector {To analyze the static behavior of simply supported nano-iron-reinforced concrete slabs, various numerical examples are presented and discussed to predict the mechanical and thermoelastic bending of the slab by using the refined trigonometric shear deformation theory (RTSDT).mE = 20 GPa and thermal expansion mα = 13.5 (10−6/K). The concrete matrix is incorporated with iron nanoparticles for Young’s modulus of rE = 200 GPa and thermal expansion rα = 12 (10−6/K). Poisson’s ratios are mυ = 0.3 and rυ = 0.291 for concrete and iron nanoparticles, respectively. Dimensionless displacements and stresses generated by the mechanical external loads are presented according to the following definitions:Herein is presented a concrete slab with Young’s modulus of Dimensionless displacements and stresses generated by the temperature loadings are expressed by the following definitions:T = zT2, non-linearly varying (across the thickness) temperature distribution T = ψ(z)T3, and a combination of both T = zT2 + ψ(z)T3 are treated, where the reference values are 0E = 1 GPa and α0 = 10−6/K. Note that in most of the literature, the thermal stress problems are considered under a steady state temperature distribution that is linear with respect to the thickness direction.To demonstrate the preceding thermal–structural analysis, different sample problems are considered. For the sake of brevity, only linearly varying (across the thickness) temperature distribution P’ are embraced for comparison with the present refined trigonometric shear deformation theory as presented in First, it is decisive to verify the adequacy of the present adopted (RTSDT) mathematical model since analytical results for the mechanical bending analysis of concrete slabs reinforced with iron nanoparticles are not available in the literature. Considering the material and geometric parameters similar to Thai and Choi , the resAs shown in 2O3) nanoparticles, and in the absence of studies in the literature dealing with a similar analytical model, a comparison was made between the elastic stiffnesses (ijC) obtained from a concrete slab reinforced with iron nanoparticles (using the Eshelby homogenization model) and the elastic stiffnesses (ijC) obtained from a concrete slab reinforced with silica nanoparticles using the Voigt homogenization model without taking into account the agglomeration effect of (SiO2) nanoparticles in the concrete matrix.In order to validate the elastic properties estimated by the Eshelby analytical model of a concrete matrix reinforced with ferric oxide (Fe2O3 and SiO2) have the same effect on the concrete, in which the reduced elastic stiffnesses (ijC) of a concrete slab increase with the concentration of reinforcements (rV). Yet, it is especially noticeable in 2O3) reinforcements, the stiffnesses are further more improved compared to nano-silica (SiO2) reinforcements, particularly in the case of (C12) which denotes the elastic stiffness of the plate in  plan. This improvement is mainly due to the nanoparticle’s high mechanical properties such as Young’s modulus.ω) of a concrete slab reinforced with iron nanoparticles Fe2O3. These material properties are determined by Eshelby’s homogenization model, and the other one expresses the variation of (ω) as well but this time of a concrete slab reinforced by silica nanoparticles, on which these elastic properties are determined by the Voigt homogenization law without considering the agglomeration effect of the SiO2 nanoparticles  is shown in l., 2021 ).It is clear from 2. It is also worth noting that the higher the percentage of particles is, the lower the deflection is.Thus, we should retain from rV) of iron nanoparticles. Several theories are used to determine the accuracy of the theory used in our analysis (the refined trigonometric shear deformation theory) in predicting the mechanical behaviors of concrete nano-composite.From a = b), concrete slab reinforced with different concentrations of iron nanoparticles (Fe2O3) are shown in Different subjected loading patterns on a rectangular (The slab is considered simply supported . As it w(x/a) of the plate by varying the reinforcement volume from 0% (non-reinforced concrete plate) to rV = 30%. The plate is supposed to be subjected to sinusoidal loading.2O3 concentrations. It also confirms the stiffening effect caused by iron nanoparticles by decreasing the deflection of the nano-composite plate, knowing that the deflection of a reinforced plate (rV = 30%) is way lower  than the non-reinforced concrete plate (rV = 0%).U) of a non-reinforced concrete plate (Vr = 30% (U) of the composite.te plate a and of Vr = 30% b. The pla = b) concrete slab under sinusoidal loading. The concrete slab is reinforced with different volumes of ferric oxide nanoparticles , while varying the geometric ratio (a/h). The constraints became nearly unchangeable when a/h exceeded 30.r). interestingly decreases the normal stress  must be verified analytically for predicting the thermoelastic bending of slabs. Since there are no models of concrete slabs reinforced with iron nanoparticles in the literature, it is quite appropriate to check the accuracy of the present mathematical model (RTSDT) using the functionally graded (FG) sandwich-structured plate of Zenkour (2008) .P = 0’ and considering the material and geometrical parameters similar to those of Zenkour (2008) [By setting ‘r (2008) , the resAs observed, the different plate theories are very consistent in predicting thermoelastic bending. Similar displacement, normal, and shear stresses results can be obtained using different shear deformation theories or shape functions.(Vr) in concrete matrix. The concrete slab is assumed to be simply supported and subjected to a thermal load that varies linearly through the plate thickness (2O3) has a weakening effect on the slab behavior when considering the thermal load. It can be clearly seen that by increasing the volume of nano-iron (rV), the deflection increases, and this is due to the thermoelastic properties of the nano-iron reinforcements .In contrast to the case of the mechanical bending, here the reinforcement by nano-iron (Fea/h and a/b) on the non-dimensional transverse displacement (2O3) nanoparticles is illustrated in The effect of geometric ratios (a/h) ratio of a plate subjected to a linearly varying thermal load is shown with regard to the different nanometric ferric oxide incorporation volumes (rV), whereas a/b) ratio of a concrete plate subjected to a combination of linear and non-linear thermal field  of the nano-iron incorporated in the concrete matrix. Therefore, the higher the percentage of particles present in the concrete matrix, the higher the deflection became, regardless of the geometric ratios.x/a) of an unreinforced concrete slab and a concrete slab incorporated with iron nanoparticles of volume rV = 30% is shown in Vr is 30%, the plate deflects even more in comparison to the non-reinforced concrete plate.A comparison between the thermoelastic deflection (rV = 30%) subjected to different thermal loads, as a function of different geometric ratios.a/h) ratio has an increasing effect on the deflection of the plate. However, when the ratio (a/h) exceeds 10, the deflection starts to be stable. On the other hand, the length-to-width ratio (a/b) has a sliding effect on the thermoelastic deflection of the plate. It can be noticed also from In z/h) of an unreinforced concrete slab (rV = 0%) and a ferric oxide Fe2O3 reinforced concrete slab (rV = 30%). It is evident that the stresses are tensile below the mid-plane (z/h = 0) and compressive above the mid-plane for both plates  was used to simulate the plate, which is assumed simply supported and subjected to different thermal and mechanical loads. The Eshelby homogenization model was used to determine the thermoelastic properties of the nano-composite and virtual work principle to determine the governing equations.The use of iron nanoparticles as reinforcement in a concrete matrix can improve its performance against external mechanical loads.2O3 was almost 45% lower than that of non-reinforced ones.The deflection of iron nanoparticles-reinforced slabs when subjected to different mechanical loads is further decreased by increasing the volume of the nano-iron particles and thickness to length ratios, since the transverse displacement of slabs containing 30% nano-FeIron nanoparticles have a greater impact than silica nanoparticles when it comes to strengthening concrete against mechanical loads.On the other hand, incorporating iron nanoparticles in a concrete matrix will weaken the nano-composite structure when exposed to thermal loads, where the transverse displacement increases by almost 10%.Based on this study, the findings are the following:Eventually, the authors hope that the outcomes of this investigation will contribute to the mathematical modeling of nanoparticles-reinforced concretes.


The vast majority of acute diarrheal diseases are self-limiting and do not require treatment on a regular basis. Empirical antibiotics should only be used to treat dysenteric and invasive bacterial diarrhea. Antibiotic misuse in the treatment of acute diarrhea is widespread in clinical practice worldwide. Hence, the purpose of this study was to examine the pattern of antibiotic use for the acute diarrheal diseases at Hiwot Fana Specialized University Hospital, Harar, Ethiopia.A retrospective, institution-based cross-sectional study was conducted to investigate the antibiotic utilization pattern for the treatment of acute diarrheal diseases from September 1 to September 30, 2022. Data were obtained retrospectively from patient cards treated for diarrheal disorders from August 1, 2021 to August 31, 2022, using standardized questionnaires, and the analysis was performed using IBM SPSS Statistics version 27.Among 332 patients in present study, 271 (81.63%) of them received nine different types of antibiotics, with the most commonly prescribed drugs were Cotrimoxazole (30.26%), Ciprofloxacin (19.19%), and Azithromycin (17.71%). Based on the presence of blood in the stools, 14.76% of the cases were invasive bacterial in nature. Antibiotics were prescribed about 2.55 times more frequently to patients under the age of 12 than to subjects 65 and older . Patients who received three or more medications were 2.77 times more likely to be prescribed antibiotics . For every unit increase in the number of drugs prescribed, the odds of prescribing antibiotics increased by 2.44 units .The current study found that antibiotics were overused in both adults and children with acute diarrheal diseases at Hiwot Fana Specialized University Hospital. The number of antibiotics prescribed was significantly associated with the patient’s age and the number of medications prescribed. To reduce antibiotic overuse, health professionals have to follow the national standard treatment guidelines. Antibiotics are medicines that are currently used worldwide to treat bacterial infections in both humans and animals , 2. TheyAntibiotics agent misuse raises therapy costs, adverse drug reactions (ADRs), and patient mortality . InapproDiarrhea is regarded the passing of three or more loose or liquid stools per day. The passing of formed stools on a regular basis is not diarrhea, nor is the passing of loose, “pasty” stools by breastfed babies . There aSince pathogens cannot be identified in more than 90% of diarrhea cases, empirical antibiotic therapy is advised. The clinical value of empiric antibiotic therapy should, however, be evaluated against the risk of side effects and the possibility of removing healthy bacteria . ResistaAntibiotic use is estimated to be inappropriate in 20–50% of cases, according to estimates . This leOnly in cases of serious bloody diarrhea or dysentery are antibiotics advised. Unfortunately, reports from several parts of the world indicated that improper use of antibiotics in the management of diarrhea is widespread . To suppThis study was carried out at Hiwot Fana Specialized University Hospital, a comprehensive teaching hospital for Haramaya University located in Harar town, 526 km to the east of Ethiopia’s capital, Addis Ababa. It is now the primary teaching and referral hospital in the country’s eastern region. Internal medicine, gynecology, obstetrics, surgery, dentistry, antenatal care, ophthalmology, hospital pharmacy, dermatology, and an antiretroviral therapy clinic are among the services provided by the hospital. From September 1 to September 30, 2022, a cross-sectional study design was used to assess the antibiotics utilization pattern for the management of acute diarrheal diseases in this hospital.An institution-based cross-sectional study was conducted retrospectively, using quantitative approach to assess antibiotic utilization pattern for the treatment of acute diarrheal disease.The source was all diarrheal patient records at Hiwot Fana Specialized University Hospital.The study included patient charts used for the diagnosis and treatment of acute diarrheal disease at Hiwot Fana Specialized University Hospital from August 1, 2021 to August 31, 2022.n = sample size, Zα/21− = standard normal variable at (1 − α) % confidence level and α (level of significance) was taken to be 5% (95% confidence level is used = 1.96), P = prevalence rate estimate for the population (50%), d = margin of the tolerated sampling error (0.5)To obtain the largest possible minimum sample size for this study, it was calculated using the single population proportion formula, assuming a 95% confidence interval, a 5% margin of error, and a prevalence of 50% and calculated with following formula:N) of patients who were treated for acute diarrheal disease within study period was 3752. Since the population size was less than 10,000 (N = 3752), a reduction formula was utilized using STAT CALC of Epi Info software and the actual sample size was found to be about 332. A systematic sampling technique was used to identify the patient charts. The sampling interval was determined by dividing the total number of patient charts by the sample size, yielding the interval (k = 11), and every 11th chart was selected. The first patient chart was chosen by lottery from the first to the eleventh patient chart, based on the time order of the records.As a result, the n value was calculated and found to be around 384. The number of medical cards . A total of 332 patient records were included in the study. Among 332 patients, 183 (55.12%) were males and 149 (44.88%) were females. Children under 5 years of age were 48.80% and patients > 65 years were 6.63%  patients had experienced the illness for 2–3 days  patients had a stool examination ordered and 119 (50.21%) stool specimens were recorded positive as 81 (34.18%) were with unspecified bacteria and 57 (24.05%) contain amoeba, giardia, and ascariasis. Majority, 85.24% of stools were non-bloody and 14.76% have blood in stools , Ciprofloxacin (19.19%), Azithromycin (17.71%), Ceftriaxone (7.01%) and Amoxicillin (6.27%) were the most frequently prescribed antibiotics. In the same manner, of 162 under five children, 136 83.95%) were prescribed with at least one antibiotic (Table % were prThe adherence to Standard Treatment Guideline (STG) was routinely assessed to show the appropriateness of antibiotics prescribing pattern. The result shows that 116 34.94%) cases were treated in line with STG, while 216 (65.06%) cases were not treated according to National Standard Treatment Guideline recommendations , General Practitioners, 61 (18.37%) and Nurses, 61 (18.37%). About 44 (13.25%) of patient records had no name of prescribers. The better proportion of antibiotic prescription in line with STG was among Senior Physicians (64.71%) and General Practitioners (55.74%), while Nurses (75.41%) and Medical Interns (65.77%) prescriptions were not in line with National Standard Treatment Guideline recommendations (Table P = 0.013) and number of medicines prescribed (P < 0.006), were significantly associated with antibiotic prescribing. Antibiotic drugs were 2.46 times more likely to be given to patients under the age of 12 than to patients 65 and older . When compared to those who received one or two antibiotics per prescription, those who received three or more drugs per prescription were more likely to receive an antibiotic. Hence, patient taking four drugs have more than three times probability of antibiotic prescribed for them   = 76.95, P < 0.001, indicated that the model was able to distinguish between the respondents who had been prescribed antibiotics and those who had not. Hosmer and Lemeshow test also supported the model fitness . The model as a whole also explained between 58.4% (Cox and Snell R square) and 78.1% (Nagelkerke R square) of the variance in antibiotic prescription and correctly classified 64.33% of those who had one. According to the model’s sensitivity, it correctly identified 59.6% of the group with antibiotic prescribed. Furthermore, the specificity was 67.4%. Age (P = 0.011) and number of medicines prescribed (P < 0.002) significantly associated with antibiotic prescribing after adjusting for potential confounders using multivariate logistic regression (Table P < 0.002). The odds of prescribing antibiotics increased by 2.44 units for every unit increase in the number of medicines prescribed .The full analysis model fitness test was performed to confirm the suitability and found analysis model containing all predictors was statistically significant, This institution-based cross sectional study has investigated the pattern of antibiotic use for acute diarrheal diseases in Hiwot Fana Specialized University Hospital, Harar, Ethiopia. In the present study, 81.63% of patients have received at least one antibiotic drug. This result is slightly lower than study done at Bishoftu General Hospital, Ethiopia which was 86.8%  and far Antibiotic self-medication was reported to be common and about 44–45.1% in Ethiopia and Eritrea, according to several studies and a comprehensive review –41. ThisFor the 332 patients treated for acute diarrhea that were included in the current study, a total of 737 medications were prescribed, resulting in an average of 2.72 drugs per prescription, which is similar to study done in south India with 2.7 , but mucThe percentage of encounters in this study when at least one antibiotic was prescribed was 41.52%, which is much higher than the WHO standard value of 20–26.2%. This result is comparable with study done in Bahawalpur, Pakistan which was 48.6% . SimilarIn present study, 83.95% of children under 5 years with acute diarrhea have received at least one antibiotic drug which is lower than study done in Bishoftu General Hospital, Ethiopia with 92.6% . HoweverThis study discovered a significant correlation between patient age and number of medications for antibiotics prescribed. Antibiotic prescriptions were found to be associated with being under the age of 12 as they got the highest proportion of antibiotics when compared to the other patient categories which is similar to research from Eritrea , BangladP < 0.001; OR 2.02; 95% CI 1.62–2.52) [P < 0.001; OR 2.68, 95% CI 2.20–3.25) [Antibiotics were about 2.55 times more likely to be prescribed to patients under the age of 12 than to subjects of 65 years and older . When compared to subjects who received one or two drugs per prescription, those who received more than two drugs were 2.77 times more likely to receive an antibiotic . The odds of prescribing antibiotics were increased by 2.44 units for every one unit increase in the number of medicines prescribed . It is consistent with study done in Asmara, which found that probabilities increased by 2.02 for every one-unit increase (62–2.52)  and Zamb20–3.25) .The current study limitation is that, it was conducted in only one hospital and so cannot be generalized to other facilities. However, because Hiwot Fana Specialized University Hospital is the only tertiary hospital in the research area, the current study can provide a picture of how antibiotics are used in East Ethiopia. This study discovered a significant incidence of incorrect antibiotic use, which may fuel rising antimicrobial resistance and associated costs on a national and worldwide scale. In general, the study determined the prevalence of antibiotic use, identified the types of antibiotics used in the treatment of acute diarrheal illness, and rated prescribers’ adherence to standard treatment guidelines.The present study revealed that there was high overuse of antibiotics for both adults and children with acute diarrheal disease in Hiwot Fana Specialized University Hospital. The most common antibiotics prescribed were Cotrimoxazole, Ciprofloxacin and Azithromycin. The proportion of prescriptions containing an antibiotic was 41.52%, which is much higher than WHO-recommended standard (20–26.2%). The average number of prescriptions per encounter fell just short of WHO recommendations, and adherence to the Standard Treatment Guideline (STG) was also inadequate. Antibiotic prescribing revealed a strong correlation with patient age and the number of medications per prescription. Thus, to reduce antibiotics overuse, health professionals have to follow the national standard treatment guidelines.


Bloodstream infections are a growing public health concern due to emerging pathogens and increasing antimicrobial resistance. Rapid antibiotic susceptibility testing (AST) is urgently needed for timely and optimized choice of antibiotics, but current methods require days to obtain results. Here, we present a general AST protocol based on surface-enhanced Raman scattering (SERS-AST) for bacteremia caused by eight clinically relevant Gram-positive and Gram-negative pathogens treated with seven commonly administered antibiotics. Our results show that the SERS-AST protocol achieves a high level of agreement (96% for Gram-positive and 97% for Gram-negative bacteria) with the widely deployed VITEK 2 diagnostic system. The protocol requires only five hours to complete per blood-culture sample, making it a rapid and effective alternative to conventional methods. Our findings provide a solid foundation for the SERS-AST protocol as a promising approach to optimize the choice of antibiotics for specific bacteremia patients. This novel protocol has the potential to improve patient outcomes and reduce the spread of antibiotic resistance.The online version contains supplementary material available at 10.1007/s11274-023-03717-x. Bloodstream infections (BSI) are a leading infectious syndrome and can lead to sepsis that is a medical emergency with a high mortality rate, resulting in rising costs of its management , being an optical technique, works based on the light field that is resonantly excited by an incident light field in proximity of a metal nanostructure. Upon such resonant excitation, the free electrons inside the metal nanostructure undergo collective motion and build up coherently accumulated field on the surface. The strong local field thus enhances Raman scattering of molecules residing within. Its up-to-date developments and applications have been reviewed , xanthine (25%), adenine (14%), and guanine (12%). Moreover, Chiu et al. -cm−1 peak is attributed to hypoxanthine (xanthine) secreted by Gram-negative bacteria  and cefotaxime (CTX), respectively. The consistency of our SERS-AST results of S. aureus-OXA and E. coli-CTX combinations was 93% compared with those of conventional AST methods. This success was made possible with the development of a sample preparation procedure—lysis with ACK buffer and sonication followed by repetitive dilution plus centrifugation—that effectively remove the interference from other concurrently present constituents in blood-culture samples. Can the SERS-AST method, acting on the basis of the prompt variation in bacterial metabolism in response to antibiotic treatment , Escherichia coli (20.5%), Klebsiella pneumoniae (7.7%), Pseudomonas aeruginosa (5.3%), Enterococcus faecalis (5.2%), Staphylococcus epidermidis (3.8%), Enterobacter cloacae (2.9%), Streptococcus pneumoniae (2.8%), Enterococcus faecium (2.8%), and Acinetobacter baumannii (2.0%). Second, in 2017, WHO published its first ever list of antibiotic-resistant “priority pathogens” of 12 families of bacteria. According to this list, A. baumannii, P. aeruginosa, and Enterobacteriaceae are of most critical priority, followed by E. faecium, S. aureus, Helicobacter pylori, Campylobacter spp., Salmonellae, and Neisseria gonorrhoeae  and four Gram-negative species  to be the targets of this study. Seven frequently administrated antibiotics  analysis. The SERS biomarker signals of the blood-culture samples of totally 20 bacterium-antibiotic combinations at different antibiotic concentrations illustrate the distinctive responses of the susceptible and resistant strains of each bacterium species after the antibiotic treatment of two or three hours. The efficacy of the SERS-AST protocol is demonstrated by its rates of agreement with those obtained from VITEK 2 (a widely deployed AST diagnostic system) for each bacterium-antibiotic combination. Four issues are then discussed. First, the slower antibiotic mode of action causes the lower agreement rates of the samples treated with of levofloxacin (a quinolone antibiotic). Second, the optical density concurrently measured after the antibiotic treatment shows inconsistent phenotypical response of bacteria. Third, the relatively poor agreement of S. aureus, S. epidermidis, E. faecalis and E. faecium) were treated with four antibiotics—oxacillin (OXA), levofloxacin (LVX), vancomycin (VAN) and ampicillin (AMP), while the four chosen Gram-negative bacteria  were treated with four antibiotics—cefotaxime (CTX), ceftazidime (CAZ), levofloxacin (LVX) and imipenem (IPM). The eight bacterial species are most frequently isolated bacterial species from the blood culture of patients  that is widely employed in many clinical microbiology laboratories around the world owing to its high AST accuracy.The goal of this study is to obtain the AST outcomes of different bacterium-antibiotic combinations with the SERS-AST protocol and to reveal the possible complications involved owing to the potentially differing metabolic responses upon antibiotic treatment. The four chosen Gram-positive bacteria , and the AST might have been performed or completed using VITEK 2. Since hemoglobin dominates the SERS signal of blood-culture samples  of the control sample was checked at the end of incubation with the target larger than 1 to ensure enough bacterial amount. The incubation time might be prolonged to 3 h if the growth rate of some bacteria is comparatively lower, such as some samples of E. faecium, E. faecalis, S. epidermidis and A. baumannii. The antibiotic-cultured samples underwent centrifugation followed by the wash procedure three times to remove the drug and the culture medium. The concentrations of all the bacterial samples were adjusted to 3 × 109 CFU/ml for SERS measurements. An additional step of 30-minute water bath at 37℃ was adopted specifically for A. baumannii to boost its SERS signal.The bacterial pellet was diluted with Mueller Hinton broth (MHB) to 2.5 × 10LSI CLSI  (Table S9 CFU/ml) onto the slide with its pipet tip being protruded through and fixed on the hole, resulting in a circular droplet on the AgNP/AAO slide. In this way, the constant separation between the pipet tip apex and the slide surface ensured a constant diameter (~ 1.5 mm) for each sample droplet. The droplets on the central SERS-active region of the AgNP/AAO slide were arranged so that there was always a control-sample droplet adjacent to any sample droplet . The SERS signal obtained on any sample droplet could be compared with that obtained on an adjacent control-sample droplet. The slide with the sample droplets was then removed from the trough and placed on a hot plate to dry the droplets at 55 °C for 15 min before SERS measurements. As a result, the bacteria in the sample droplet lost their viability (confirmed with agar-plate culture) and the secreted molecules from the bacteria were firmly attached on the surface of the AgNP/AAO slide. As shown in Figure S1, there is still large unused area of the SERS-active region, allowing for more sample droplets treated with other antibiotics.The substrates for SERS were silver nanoparticles embedded in nanochannels of anodic aluminum oxide (AgNP/AAO) and were fabricated by anodization-etching-electroplating on glass slides , a spectrometer, and a thermoelectric-cooled charge-coupled camera. The typical laser irradiation power density at the substrate surface was about 1 × 10−1, respectively, were considered as their corresponding biomarkers. Their signal variations were used to determine the respective bacterial responses to antibiotic treatment. Different from the commonly secreted adenine and hypoxanthine by Gram-positive and Gram-negative bacteria, respectively, the dominant secretion of A. baumannii is xanthine  of the AgNP/AAO slide showed that the average standard deviation across the SERS-active area was 15%  generalizes the one reported in our previous work , S. epidermidis (n = 21), E. faecalis (n = 20), E. faecium (n = 21), E. coli (n = 20), E. cloacae (n = 20), K. pneumoniae (n = 21), and A. baumannii (n = 21). Three samples failed to generate analyzable SERS signals, including one S. epidermidis and one E. faecium sample with insufficient growth and one A. baumannii sample that generated unrecognizable SERS signals. Results of three K. pneumoniae-IPM tests were also excluded because of improper antibiotic preparation. There were six bacterium-antibiotic combinations  excluded from the ROC analysis due to insufficient numbers (< 3) of antibiotic-resistant samples. A total of 401 SERS spectra underwent the ROC analysis.From March 2016 to June 2019, a total of 164 bacterial isolates from blood samples were analyzed, including A. baumannii by heating in water is demonstrated. In the end, the dependence of the SERS signal of susceptible bacterial isolates on the treatment time of LVX is presented to illustrate how its slower mechanism of action affects the AST outcome.The SERS-AST results of blood-culture Gram-positive isolates are presented first, followed by those of blood-culture Gram-negative isolates. The signal-ratio distributions of their respective biomarkers under different designated antibiotics at their corresponding four drug concentrations show the distinctive antibiotic responses of the susceptible and resistant species. The SERS-AST results obtained from the ROC analysis based on the collected blood-culture isolates are summarized in the corresponding tables. Besides, boosting the SERS signal of −1, the ratio of its signal strength of the antibiotic-treated sample to that of the untreated control sample . As shown in Table S. aureus-OXA and S. aureus-LVX combinations  at their respective break-point drug concentrations  is expectantly about 0.5 while that for the S. aureus-LVX combination (0.83) is higher than 0.7. That is, the change of S. aureus isolates under the treatment of LVX is comparatively smaller than that under the treatment of OXA for a reason discussed later.As the SERS spectra of the chosen Gram-positive bacteria  consistently exhibit a prominent peak at 730 cmentclass1pt{minimaentclass1pt{minimaS. aureus samples, there was no VAN-resistant S. epidermidis sample. For E. faecalis, OXA- and VAN-resistant sample were both absent, too. On the other hand, AMP-, VAN- and LVX-resistant E. faecium samples were obtained. The corresponding distributions of S. aureus, except the E. faecium-LVX combination. The ROC analysis was thus performed on all these combinations. All the analysis results  and the lower agreement rate is correlated with the smaller decrease in E. faecium-LVX combination: its AUC is 0.67 and its E. faecium-LVX combination, its E. faecium isolates susceptible and resistant to LVX  to achieve a high E. faecium-LVX combination will be further discussed later.Similar to the entclass1pt{minimaentclass1pt{minimaentclass1pt{minimaE. coli, E. cloacae and K. pneumoniae is at 724 cm−1 while that of A. baumannii is at 654 cm−1. As a consequence, the ratio of the signal strength of the biomarker at 724 cm−1 . Since there was no IPM-resistant E. coli isolate collected, no ROC analysis was performed in the E. coli-IPM combination. The distributions of E. coli isolates under the treatment of CTX, CAZ and LVX at their respective concentrations show a common behavior , the prominent peak of ior Fig. . The obtE. coli isolates, there was no LVX- and IPM-resistant E. cloacae isolate. The corresponding E. cloacae and K. pneumoniae isolates under the treatment of CTX and CAZ also exhibit the common behavior  exhibits a prominent spectral peak at 654 cm−1, as its dominant secreted purine derivative is xanthine ; similarly, K. pneumoniae samples treated with LVX is also higher than that treated with CAZ (0.68 vs. 0.13). Such behavior is reflected by the fact that in both cases the signal ratio of the bacterial isolates susceptible to the treated antibiotic at its break-point concentration does not decrease significantly , the antibiotic treatment time has to be at least 3 h. to show significant cell death probably because the bacterial response to the antibiotic may be slow. On the other hand, the bacterial response to the antibiotic is expectantly prompt in the S. epidermidis- and A. baumannii-LVX combinations, because their LVX is a quinolone antibiotic that binds to gyrase- or topoisomerase IV-DNA cleavage complex to form permanent chromosomal breaks Mitscher . The nonS. aureus-OXA and E. coli-CTX combinations  and 3 Gram-negative species  and the extra five antibiotics . The resultant mean agreement rates for Gram-positive and Gram-negative species are 96% and 97%, respectively, indicating that the SERS-AST protocol can be successfully applied to these bacterium-antibiotic combinations and is expected to be equally applicable to other untested combinations. Two slight modifications are however needed to incorporate the differences in bacterial species and in antibiotics. First, additional 30-min incubation of the A. baumannii sample in water at 37 °C was needed to boost its secreted xanthine to account for the lower permeation efficiency of its outer membrane. Second, extended antibiotic treatment of LVX to compensate its slower mechanism of action effect is recommended to engender a prominent change of the SERS biomarker signal with respective to the antibiotic concentration and thus can produce more consistent AST outcomes. In sum, these results suggest that this simple general SERS-AST protocol can be implemented easily in hospital to shortening the waiting time to obtain highly accurate antibiotic-resistance reports. Nevertheless, there are still several issues that are worthy of further investigation.Based on the demonstration of the SERS-AST protocol—including (1) sample preparation, (2) antibiotic treatment, (3) SERS measurement, and (4) ROC analysis—for blood-culture isolates developed in our previous work on the 600 readings. In this study, most of the tested cases show that the behavior of the optical density ratios—the ratio between the bacterial number after overnight incubation with and without mixing with a designated antibiotic—is consistent with that of the SERS signal ratios, as exemplified in the S. epidermidis-OXA combination . We found that approximately 30% of the AST results measured by OD600 values were inconsistent with those determined by SERS-AST or VITEK 2. Most of the disagreement cases were Gram-negative bacteria treated with β-lactam antibiotics, such as the ones in the E. cloacae-CTX combination. It has been shown that the initial response of E. cloacae to the treatment of a ꞵ-lactam antibiotic is cell elongation, instead of decreased number of live cells . Such morphological change is postulated to be a repair process for survival   and can degrade third-generation cephalosporin antibiotics at different rates . The Advanced Expert System (AES) of VITEK 2 can identify bacteria with ESBL by special software and modify the primary laboratory results accordingly  Table . K. pneuP. aeruginosa is another pathogen that shows high occurrence rate (5.3%) and critical antibiotic-resistant priority (by WHO) but was not studied here. The permeation efficiency of its cell envelope is as poor as A. baumannii and moreover the strong fluorescence emitted by its intracellular pigment (pyoverdine) . A new sample preparation procedure would be needed to tackle the different biological characteristics and behaviors of these two pathogens. Third, polyclonal infection (PI) did occur in a few clinical cases in this study and thus raises the questions about the interpretation of the obtained SERS-AST result. Can the SERS spectrum be used to identify the responsible species in the PI case? Can the SERS spectrum after the antibiotic treatment be used to determine the respective resistograms of the co-present pathogens? More development of the current SERS-AST protocol to tackle the PI cases is needed. Fourth, in the whole SERS-AST protocol, 2 h are needed for sample washing and concentration adjustment in the pretreatment of blood-culture samples and the post-treatment of incubated samples with antibiotics, and about an hour is needed to adjust bacterial concentration for SERS measurement. The automation of these steps would certainly shorten the total operation time of the protocol.Given the successful outcomes of SERS-AST in expediting the AST process without overnight incubation, there are still several issues for further investigation. First, can the treatment time of antibiotics be shortened? Adopting new culture media and condition may increase growth rate, adding cations and adjusting pH condition may boost the release of purines and derivative, and new SERS substrates and new optical detection schemes may help distinguish smaller difference between the SERS biomarker signals of susceptible and resistant strains. These three research directions are expected to yield a shorter incubation time in the SERS-AST protocol. Second, S. aureus and E. coli isolates treated with oxacillin and cefotaxime, respectively, we in this work have further extended the application of this protocol to 18 other bacterium-antibiotic combinations, including three new Gram-positive species , three new Gram-negative species , and five new antibiotics . From the total 401 tests of blood-culture isolates, overall 96% agreement was achieved between the results of the SERS-AST protocol, obtained within five hours, and the VITEK 2 based on overnight incubation. This outcome proves that the SERS-AST protocol is a simple general AST method that can provide opportune and accurate AST information. This study also shows the developed and proposed strategies to accommodate unique biological characteristics and activities of bacterial species (low permeability of A. baumannii envelope) and distinctive mechanisms of action of antibiotics (elongated action of levofloxacin). These strategies can be easily incorporated to the protocol and are not expected to significantly influence the AST performance of all other bacterium-antibiotic combinations. The success of this study implies that this new AST paradigm based on prompt bacterial metabolism could potentially revolutionize the AST process.The emergency of new pathogens and antimicrobial resistance worldwide has stimulated the development of new antibiotics and fast diagnostic methods for precise and timely antimicrobial administration. Based on our previous successful demonstrations of the antimicrobial susceptibility testing with surface-enhanced Raman scattering (SERS-AST protocol) on blood-culture Supplementary material 1 (DOCX 887.0 kb)Below is the link to the electronic supplementary material.