A doctor may recommend that a patient stop an antibiotic course before its scheduled completion time if further treatment may cause more harm than benefit.This study explores general practitioners’ (GP) opinions about the use of antibiotic deprescribing (AD) in general practice.n = 6,083) affiliated with the largest Spanish scientific society of primary care were invited to participate. The survey included two statements related to use and fourteen views about AD rated by GPs using a 5-item Likert scale.A cross-sectional, questionnaire-based study answered from February to March 2022. GPs (p < 0.005).Eleven hundred and seven doctors completed the surveys (18.2%), of whom 92.5%  reported having used the AD strategy in their practice at least once. GPs felt very confident in using a deprescribing strategy in patients with common cold and influenza  but less with acute bronchitis (45.5%); 12.1%  considered this practice harmful to patients. Respondents reported using AD more frequently when they initiated the antibiotic course  than when the treatment was initiated by another doctor . However, doctors aged >60 years were more prone to use AD compared with younger colleagues (64.5% vs. 50%; The GPs in this study employ the strategy of AD. Nonetheless, essential differences lie in their views of the way the strategy is used. Further studies are warranted to explore the beliefs behind these perceptions and promote wider use of AD by GPs. KEY MESSAGESAntibiotic deprescribing is used frequently by GPs in Spain.GPs do not perceive deprescribing antibiotics as a strategy that can harm patients.GPs are more likely to deprescribe an antibiotic course initiated by the patient than one prescribed by a physician.Dogmas are taken for granted until new evidence poses questions about their validity. A clear example in medicine is the long-standing belief that a course of antibiotics should always last for a defined number of days, irrespective disease’s course and the potential relief of symptoms after fewer days. For several years, patients have always been instructed to complete an antibiotic course once initiated. This was considered appropriate for reducing the development of antimicrobial resistance (AMR) , a dogmaDifferent strategies have been used to reduce inappropriate consumption of antibiotics in primary care. Most interventions have targeted prescribers and focused on initiatives to reduce the initiation of inappropriate antibiotic treatments. However, few initiatives have been taken to terminate inappropriate treatments already initiated. Most antibiotic prescriptions for respiratory tract infections (RTI) in primary care are inappropriate and fulfilling a course of inappropriate antibiotics may cause more harm than benefit.Deprescribing is often used in polypharmacy and describes the withdrawal process of an inappropriate medication to improve the overall outcome because continued treatment may cause more harm than benefit . We intrWe recently carried out a randomised clinical trial with patients with uncomplicated RTIs who had already taken a dose of an antibiotic course . Among tWe conducted a cross-sectional survey among a sample of the Spanish GPs from February to March 2022, using a survey distributed by email. We followed the STROBE guidelines for reporting observational cross-sectional studies . We framSupplementary Material Appendix 1) included several domains of two questions regarding AD use, and fourteen questions about views on AD, including the clinical conditions for which respondents feel confident in deprescribing an antibiotic when no longer necessary and the extent of confidence in stopping an antibiotic course initiated by themselves or other prescribers. Three sociodemographic data and information about their workplace were also collected.A panel of GPs designed the questionnaires. The survey .The survey was sent a single time, giving GPs one chance to respond to the questionnaire. Spain’s largest family medicine society is the Descriptive and bivariate analyses were carried out. The responses ‘strongly disagree’ and ‘disagree’ were aggregated for simplicity, as were the ‘strongly agree’ and ‘agree’ responses. A chi-square test was used to compare the agreement results on several statements and the diagnoses for which GPs claimed to use AD with age and gender. Data were analysed using SPSS (version 26.0).This study was granted an exemption from the Ethical Committee Board Jordi Gol i Gurina , as ethical approval for questionnaire-based surveys is not required in Spain. All the GPs who received this survey had previously consented to receive surveys.A total of 2,929 out of 6,083 contacts read or opened the email sent about the study and 1,107 (18.2%) responded and returned the questionnaire. More female than male doctors answered the questionnaire (68%). Most respondents (58%) stated they work as GPs in urban centres. A total of 1,024  respondents stated having recommended that patients cease an antibiotic course that they deemed inappropriate . A totalThe clinical conditions for which GPs felt comfortable deprescribing are detailed in Regarding attitudes towards AD, only a minority of GPs  considered the practice harmful to patients; the majority view was that AD would not generate an increase in complications and hospital admissions. Thus, the majority  agreed that this strategy should be included in clinical guidelines. In fact, using the AD strategy received greater favour than the practice of delayed antibiotic prescribing .p < 0.005). Notwithstanding this, only 14.9%  of the respondents considered it unethical to stop an antibiotic course prescribed by a colleague (p < 0.001).Nearly 97% of the respondents endorsed the AD strategy if they deemed that antibiotic treatment was no longer necessary. Respondents recommended AD equally to patients who had initiated treatment themselves and to patients that purchased the antibiotic from a pharmacy without a prescription . However, only 52.3%  of the respondents agreed to deprescribe an antibiotic regimen, despite deeming it no longer necessary, in instances when another doctor prescribed the antibiotic course. As shown in olleague , with thIn our study, more than 90% of the doctors reported having used the AD strategy at least once in their practice. In addition, 75% of the respondents declared that at least once a month, they see patients whose antibiotic courses are initiated unnecessarily. This strategy is generally performed in viral infections such as common cold and influenza but not in others, such as acute bronchitis. Only 45% of GPs agreed to perform AD in patients with acute bronchitis who had already commenced an antibiotic course. Most GPs felt comfortable ceasing an antibiotic course initiated from leftovers in the household or obtained at the pharmacy without a prescription. However, only about half of GPs considered AD appropriate if a colleague had started the antibiotic course.To our knowledge, this is the first time this topic has been studied in primary care. Its novelty and the large sample of responses are the major strengths of this study. Conducting online surveys with health professionals has several advantages in comparison to mailed questionnaires, as it is easier to implement large-scale surveys at a low cost . AnotherAnother weakness of these types of studies is the gap between opinion and actual practice. As in other opinion studies, the results obtained do not accurately reflect actual primary care practices. Rather, they correspond to hypothetical scenarios in which GPs were asked to give their opinion about each situation. Despite these weaknesses, this manuscript provides valuable insights into how GPs perceive the use of AD as a treatment strategy and serves as a point of departure for future qualitative studies.The term ‘deprescribing’ is mainly linked to chronic diseases, as it is increasingly recognised that many adults and older people take a large number of medications, often including unnecessary or potentially inappropriate ones . HoweverWhen it comes to antimicrobials, this inertia can even be more harmful than with chronic medications, as the emergence and spread of AMR can make the treatment of infectious diseases challenging in the future. Even short courses of antibiotics can have long‐term effects, causing the persistence of resistant organisms lasting years and altering the normal gut microbiome and might be detrimental . Beyond Many GPs would consider that discontinuing antibiotics in these circumstances should be the standard of care. However, the decision to discontinue an antibiotic recently started is not easy, particularly if initiated by a colleague. In fact, as suggested by qualitative research, GPs do not feel comfortable discontinuing treatments in general, and guidelines are not as authoritative for discontinuation as they are for starting drugs . DoctorsAnother factor to highlight is that many GPs do not wish to contradict the decision made by other doctors because it might be viewed as unfair . This phThe inappropriate use of antibiotics for uncomplicated RTIs is very high . Many stThe results of this questionnaire-based study show that healthcare professionals are reluctant to question the prescribing habits of their peers. In the case of antimicrobials, prescribing etiquette and its role as a key determinant of prescribing behaviours is highly significant, recognising the autonomous decision-making process of prescribing. These findings have clear implications for quality improvement interventions in antimicrobial prescribing. Therefore, understanding and addressing the determinants of antimicrobial prescribing behaviours hold the key to successful quality improvement intervention. Further qualitative research is needed to understand how to tackle ‘prescribing etiquette’ as part of the cultural and organisational factors that shape the GPs’ decision to prescribe.This paper shows that AD for acute conditions is used by GPs and highlights an array of beliefs about AD. Despite being deemed as a novel strategy to reduce antibiotic consumption, this practice is often used in our consultations, but probably not as much as could be warranted. We, therefore, have an ethical demand to stop this course when the clinician judges that it is no longer needed.Click here for additional data file.


This study evaluates dentists' antibiotic prescribing habits and the frequency of facing patient pressure for prescriptions.  An online anonymous survey was used to collect data on antibiotic prescribing practices, including prescribing unnecessary antibiotics if requested by patients. P < 0.001) in reporting that patients pressured them to prescribe antibiotics when antibiotics were not necessary for treatment or prophylactic purposes and in prescribing unnecessary antibiotics sometimes if requested by a patient (P=0.008). In addition, there was a statistical difference in dentists' confidence in their knowledge and practice in the area of antibiotic prescribing (P < 0.001).  The study population included 345 dentists; 227 (65.8%) were females and 118 (34.2%) were males. 54 (15.7%) reported that they prescribed unnecessary antibiotics more than once per week, 47 (13.6%) once per month, 135 (39.1%) rarely, and 109 (31.6%) never prescribed unnecessary antibiotics. 117 (33.9%) reported being pressured by patients to prescribe unnecessary antibiotics more than once per week. 110 (31.9%) reported being pressured by patients to do so at least once per month. There was a statistical difference between the two genders ( The results show that unnecessary antibiotic prescribing by dentists can be influenced by patient pressure. Antibiotics are frequently prescribed in the dental office, either as a treatment or as a prophylactic measure. Lack of knowledge regarding the choice of antibiotics or the indication for prescribing antibiotics is likely to lead to abuse, misuse, and unnecessary antibiotic prescribing. Inappropriate antibiotic prescribing practices have contributed to the problem of antibiotic resistance . In 2021Dealing with the global threat of antibiotic resistance , 4 cannoAlthough recent trends in inappropriate and unnecessary prescribing of antibiotics by dentists have been documented by researchers from other countries –9, littlA previous study of therapeutic adult antibiotic prescriptions by Jordanian dentists showed that dental practitioners had the tendency to prescribe antibiotics and to prescribe longer courses of antibiotics, and amoxicillin and metronidazole were the most commonly prescribed antibiotics . AuthorsThe objectives of this study were to evaluate dentists' antibiotic prescribing practices, the frequency of facing patient pressure for unnecessary prescriptions that could lead to unnecessary antibiotic prescribing, and the perceived reasons why patients may ask dentists to prescribe unnecessary antibiotics.This is a questionnaire-based cross-sectional observational study in which consenting practicing dentists completed an anonymised self-administered online questionnaire. The questionnaires were collected between January 2020 and June 2021.An anonymous online questionnaire was created by the authors and used to evaluate antibiotic prescribing habits, reasons that contribute to unnecessary antibiotic prescribing, and dentists' opinions on the frequency of facing requests for antibiotic prescriptions by patients when antibiotics are not indicated.The questionnaire was divided into five sections. The first section was a description of the purpose of the study and an informed consent where invited dentists indicated if they would consent to participate. The second section included questions about demographic characteristics of participants: sex, age, highest degree, practice area, years practicing dentistry, and type of employment. The third section included questions about antibiotic prescribing practices: frequency of prescribing if pressured by patients and perceived reasons why some patients request antibiotic prescriptions. The fourth section included questions about antibiotic prescribing habits, indications, the antibiotic of choice that dentists used in the treatment of patients with dental infections, the rationale for drug selection, and the duration of treatment. The fifth section's questions were about dentists' use of antibiotic prescribing guidelines, the resources dentists use to inform their decisions, and their confidence in their knowledge about antibiotic prescribing.Before distributing the questionnaire to practicing dentists, questions were tested for face and content validity by asking qualified experts to review the items of the English questionnaire, these experts were asked for suggestions to improve the questions, and ambiguous or confusing questions were deleted or revised and amended. Then, the questionnaire was pilot tested for comprehensibility, and to determine the time required to fill out the questionnaire, pilot testing was achieved by administering the questionnaire to a sample of 20 dentists who were excluded from the study. Testing and retesting of the questionnaire were undertaken; revisions and corrections were made when needed before drafting and distributing the final version.A Google Form was prepared to distribute the final version of the questionnaire to participating dentists. The questionnaire's link was posted on Facebook  and sent via dentists' WhatsApp groups. Potential respondents were asked to share the questionnaire's link with other dentists.The study was approved by the Institutional Review Board (IRB) of King Abdullah University Hospital (KAUH), Irbid, Jordan (Ref.: 114/118/2018).P < 0.05. For the purpose of this study, the analysis included responses to questions on the respondents' characteristics, the number of years each respondent had been practicing dentistry, the frequency of prescribing unnecessary antibiotics, exposure to patients' pressure to prescribe antibiotics, dentists' confidence in knowledge in the area of antibiotic prescribing, and dentists' prescribing practices.The collected anonymised data were analysed by Microsoft Office Excel 2013  and by the Statistical Program for Social Sciences IBM SPSS Statistics version 22 . The association between variables was determined by the chi-squared test or Fisher's exact test. The statistical significance level was set at The study population included 345 dentists; 227 (65.8%) were females and 118 (34.2%) were males with a mean age of 29.7 years . 69.3% were general dentists. 68.1% had been practicing dentistry for less than 5 years .54 (15.7%) of the respondents reported they prescribed unnecessary antibiotics more than once per week, 47 (13.6%) once per month, 135 (39.1%) rarely, and 109 (31.6%) never prescribed unnecessary antibiotics.P < 0.001) in reporting pressure by patients to prescribe antibiotics when they were sure that antibiotics were not necessary for treatment purposes (P=0.008). 117 (33.9%) reported being pressured by patients to prescribe unnecessary antibiotics more than once per week. 110 (31.9%) reported being pressured by patients to do so at least once per month. There was a statistical difference between the two genders (purposes  and proppurposes . In addiP < 0.001) felt confident about their knowledge and practice in the area of antibiotic prescribing. 53.6% of the study population  reported that they would always refuse patients' requests to prescribe unnecessary antibiotics. The relatively high percentage of patients demanding antibiotic prescriptions when it is not indicated should raise an alarm against antibiotic abuse by patients, should ring a bell for public health stakeholders, and serve as a call for more focus on implementing education programs aimed at raising awareness about the harm of patients self-administering antibiotics. An interesting finding was that cash payers (patients without insurance) were less likely to ask or pressure their dentists to prescribe antibiotics when antibiotics were not necessary, and this finding highlights the potential role of insurance companies in controlling the problem of unnecessary antibiotic prescribing.Analyzing the current guidelines in terms of antibiotic prophylactic prescription for the prevention of infective endocarditis reveals differences but indicates that there are currently relatively few patient subpopulations for which antibiotic prophylaxis may be indicated prior to certain dental procedures –24.In this study, a history of infective endocarditis was reported to be the most common cause for prophylactic antibiotic prescriptions by 74.8.% of the respondents, followed by the presence of a prosthetic heart valve for which 73.3% of the surveyed dentists prescribed antibiotic prophylaxis. These findings are similar to results reported in other populations. For example, in the US, 70% of dentists reported having had patients who took antibiotics before a dental procedure for the prevention of infective endocarditis , and in Regarding antibiotic prophylaxis for patients with prosthetic joints, the American Dental Association's (ADA) 2015 guidelines state: “In general, for patients with prosthetic joint implants, prophylactic antibiotics should not be given prior to dental procedures to prevent prosthetic joint infection,” and patient's preferences should be considered. In 2013, the ADA and the American Academy of Orthopaedic Surgeons (AAOS) codeveloped an evidence-based clinical practice guideline that limited the use of antibiotic prophylaxis to high-risk patients , 32. NevFindings from this study showed that amoxicillin was the most commonly prescribed antibiotic as reported by 72.5%) of dentists, followed by metronidazole, clindamycin, and amoxicillin/clavulanic acid. This finding confirms previous findings by many studies that have reported amoxicillin as one of the most common antibiotics used in dental practice and primary care settings –36. In B2.5% of dDentists should be cognizant that long courses of antibiotics result in the emergence of antibiotic resistance and may complicate the treatment . In thisThe topic of antibiotic prescribing is complex and wide, and dentists' knowledge of antibiotic prescribing cannot be evaluated objectively. The current study was a survey-type investigation that used social media platforms to distribute the questionnaire's link, and it has some limitations including its limitation in determining the response rate and selection bias because it is fairly difficult to know how many dentists received the questionnaire and how many dentists accurately reported their prescribing habits.The frequency of antibiotic prescribing by dentists in comparison to the prescribing habits of other healthcare providers was not carried out and is worthy of investigation.This study indicates that antibiotic prescribing by dentists is not consistent with the current guidelines. A significant number of respondents reported prescribing clindamycin for treatment purposes, and a minority reported that they routinely prescribe unnecessary antibiotics for common dental procedures. In addition, findings show that unnecessary antibiotic prescribing by dentists can be influenced by patients' pressure. Findings from this study provide a heuristic approach to identifying some of the factors and solutions to the problem of misuse and abuse of antibiotics in dental practice. Some solutions include updating and clarifying the guidelines, restricting antibiotic use to cases where the benefit outweighs the risk of harm, prohibiting over-the-counter antibiotic availability, educating dentists on how to respond to patients' requests for antibiotic prescriptions in order to minimize the use of antibiotics when they are not necessary, which is an important intervention strategy for addressing the challenge of bacterial resistance, and implementing antibiotic stewardship practices and programs.


This paper describes a study on finite element modeling (FEM) carried out on the ABAQUS platform for the prediction of flexural strength of corrosion-damaged reinforced concrete (RC) beams strengthened using layers of ultra-high-performance concrete (UHPC). Considering different combinations of the degree of reinforcement corrosion and thickness and configuration of UHPC layers, a total of twenty-two corroded, un-strengthened, and strengthened RC beam specimens were tested to record their flexural behavior. Following the flexural testing, the FEM was carried out considering the degradation in the diameter and the yielding strength of the corroded reinforcing bars. The cohesive surface bonding approach was used to simulate the interfacial bond stress slip between the corroded bars and surrounding concrete. The results of the FEM were validated using the experimental test results of the respective beam specimens. The FEM results  were found to be in close agreement with the corresponding experimental test results. This indicates that the proposed FEMs can capture the flexural behavior of the corroded RC beams strengthened using layers of UHPC with high accuracy. Furthermore, a parametric study was carried out using the validated FEMs to investigate the effects of varying the compressive strength and thickness of UHPC layers on the flexural strength of the corroded strengthened RC beams. Reinforcement corrosion in concrete structures is one of the main reasons behind the loss of load-carrying capacities sabotaging the service life of reinforced concrete (RC) elements. Reinforcement corrosion produces a variety of issues, including cracking and spalling of the concrete cover, loss of rebar diameter and strength, and loss of bond strength between rebars and surrounding concrete, which degrades structural integrity and serviceability, resulting in sudden collapse ,2,3. TheA review of several studies pertaining to the corrosion of RC beams and various strengthening materials and methods is reported in the literature. Research works in the past have demonstrated the efficacy of fiber-reinforced polymers (FRP) as a trustworthy material for the strengthening of RC buildings ,12,13. CThe numerical analysis using FEM makes it possible to anticipate the exact response of the same structural elements with alternative UHPC configurations and thicknesses without conducting additional experimental testing. Modeling the RC beams with corroded longitudinal reinforcing bars requires an appropriate approach for the degradation of bond-slip behavior. Several researchers have adopted finite element modelling to evaluate the structural behaviour of strengthened RC beams, including predicting failure loads and cracking patterns. However, a big challenge in numerical simulation is the modelling of concrete cracking. Bažant and Oh  and Tao The first one involves using a spring element to transfer tension between rebar and concrete. This approach is useful in 2D modeling, where only two nodes represent steel bars as truss elements. The nonlinearity of spring elements can be specified by inserting the experimental load against the displacement relationship. Li et al.  employedThe second approach to simulate the loss of bond strength between steel bars and concrete consists of modifying the properties of concrete and steel. To demonstrate the bond interaction between steel bars and concrete, Ziari and Kianoush  adjustedThe third approach simulates the connection as an interaction between three-dimensional surfaces of concrete and steel, as proposed by Amleh and Ghosh  for finiThree alternative methodologies to simulate the rebars-concrete bond for modeling steel reinforcing bars in the RC beams using finite element (FE) analysis have been reported in the literature, as described below:Although some previous studies on the application of UHPC in strengthening undamaged RC beams are reported in the literature, as briefly described above, there is a lack of data on the performance of UHPC strengthening of corroded RC beams. Furthermore, there is not enough information available on the numerical modelling of corroded RC beams after strengthening with different configurations and thicknesses of UHPC layers. Therefore, the work presented in this paper was aimed mainly at bridging this gap. The present study consisted of experimental investigation  and finite element modelling of the respective RC beams using ABAQUS to capture their structural behavior. The experimental investigation included strengthening the corroded RC beams with three different UHPC thicknesses and two various configurations. The FE simulation of the corroded strengthened and un-strengthened beam specimens was carried out using the fundamental knowledge of structural behavior and properties of the RC beams and UHPC strengthening layers. The commercial finite element analysis (FEA) software, ABAQUS/CAE 2017, was used to model the RC beam specimens using its sophisticated numerical capabilities and extensive choice of concrete material models. The load versus mid-span deflection curves were obtained from the results of numerical modelling and validated against the experimental test results. Furthermore, the FEM was used for parametric study to evaluate the effect of varying the compressive strength and thicknesses of the UHPC layers on the ultimate load-carrying capacities of the corroded strengthened RC beams.UU), was used as the control specimen, while the remaining twenty-one RC beam specimens were divided into three groups  and exposed to accelerated reinforcement corrosion using the impressed current technique to obtain theoretical mass losses of 10, 20, and 30%, respectively, in their longitudinal tensile steel bars. The RC beam specimens were connected in series to the accelerated corrosion setup, and a constant current density of 200 µA/cm2 was applied for the entire period of the corrosion process as recommended by El Maaddawy and Soudki  that define the contact in normal, shear, and tangential directions, respectively. The relationship between the bond stress and the slip of corroded steel bars can be used to simulate the post-elastic behavior, which is indicated by the initiation and evolution of bond deterioration. The bond damage criterion is activated when the associated stresses exceed a maximum allowable value, which can be used to approximate this relationship. To simulate the bond behavior between corroded steel bars and concrete in ABAQUS using the cohesive surface bonding approach, parameters that define the interaction behavior of the 3D surfaces were determined to capture the exact response of the bond-slip relationship between the two surfaces. Several models were reported in the literature to model the concrete-steel interaction for the RC elements. The following equations can be used to estimate the shear and normal stiffness elements that were used in ABAQUS.Unlike the case of finite element modeling of RC beams without corrosion, the assumption of the perfect bond cannot be used for modeling the RC beams with corroded steel bars since the bond of the corroded bars is significantly affected by the reinforcement corrosion. Therefore, the corroded bars were simulated using 3D surface interaction modeling methods available in ABAQUS to simulate the bond behavior between the corroded bars and surrounding concrete in a better way. In order to simulate the bonded surfaces between corroded steel reinforcement bars and surrounding concrete using a cohesive surface bonding approach, the surface-based cohesive behavior can be used to express the linear elastic relationship between two different surfaces due to its effectiveness and convenience . The iniy et al. . EquatioThe slip at maximum bond stress (nd Rafiq :(7)Smax=To simulate the bond degradation of the corroded bars based on the cohesive surface bonding approach, a reduction in the ion (6)) ,62. The The Equations (4)–(8) were used to calculate the values of stiffnesses, CRC-60) using different mesh sizes ranging from 15 to 75 mm. The mesh size of 15 × 15 mm showed the best results in terms of stiffness, ultimate load, and overall flexural behavior, as evidenced by the close matching of the load-deflection curves obtained using FEM, considering a mesh size of 15 mm, and the experimental test results.In order to model normal concrete, UHPC, and main steel bars, 3D stress eight-nodded linear brick elements (C3D8R) were used (solid continuum). This element type is suitable for linear as well as composite nonlinear analyses involving contact, deformations, and plasticity. Furthermore, this element was recommended in the ABAQUS Analysis user’s manual to avoid the shear-locking effect. In addition, steel plates were modeled at the loading points and supports to avoid the stress concentration of the eccentric loads and ensure uniform load distribution to the surface of the steel plates. The same FEM elements (C3D8R) were used to model the steel plates, and a perfect bonding behavior was assumed between the steel plated and normal concrete and/or UHPC. The support plates were restrained from movement in the transverse and vertical directions. In addition, two-nodded linear 3D truss elements (T3D2) were used to model the top steel reinforcement bars and stirrups. Typically, this structural element is long and slender and only transmits the axial loads. It allows the cross-section area of the truss elements to be defined, and the steel reinforcement can be shaped accordingly. As mentioned earlier, the degradation of the corroded steel bars due to reinforcement corrosion can be represented by a reduction in the yield strength and modulus of elasticity of the corroded bars, including the reduction in the cross-sectional area of the corroded steel bars. This reduction approach allows the utilization of the same rebar 3D element for various degrees of reinforcement corrosion. The reduction in the yield stress and elastic modulus of the corroded steel bars due to reinforcement corrosion was reported by Al-Osta et al. . The acta et al. .(9)fyc=In order to model the RC beam specimens in ABAQUS, a number of constraints were applied. These constraints determined the interactions between various parts of the FEM and the analysis of the degree of freedom (DOF) between different regions of the model. The following subsections illustrate the constraints used in the modeling in the present study.The bond between normal concrete and UHPC was considered perfect since no debonding was observed during the flexural testing. The usage of tie constraint enabled the combination of the normal concrete beam and UHPC jacketing. However, the meshes created on the normal concrete regions and the UHPC layers differed. As the UHPC surfaces are harder, they were considered the master surfaces, whereas the normal concrete beam surfaces were slave surfaces. Because of the tie constraint, the translation, rotation, and other degrees of freedom were considered equal for a normal concrete-UHPC composite. In addition, the bond between steel plates and concrete surfaces was modeled using tie-bond constraint.In order to model the interaction between top reinforcement steel bars (hangers) and stirrups with the concrete beams, the constraint of embedded regions was used, assuming a perfect bond. Considering the embedded region constraint, the stirrups and top steel bars are referred to as embedded regions in the concrete . Constraints were imposed based on the geometric relations between embedded and host elements. The translational DOF of the embedded nodes were controlled by the interposed values of their host elements corresponding to the DOF. In order to model the embedded elements in host elements , a truss-in-solid model has been used.The explicit dynamic analysis was implemented in the numerical modeling. This type of analysis was chosen because it can effectively address static issues, such as complex contact problems in quasi-static process modeling . This isThe FE models used a loading technique and support steel plates comparable to those used in the experimental testing. The beams in the FE models were loaded using specified displacements located at the middle of the top surface of the steel loading plate, with a 0.1 mm increment. Line supports were placed at the center line of the bottom surface of the steel plates to prevent any relative movements in the vertical and transverse directions . The load was measured at the middle of the plate’s top surface, where the specified displacements were applied. Another point on the bottom surface of the concrete or composite structure at the mid-span of the beam was used to record the beam deflections. A strain monitoring point was used to measure the concrete compressive strains at the mid-span of the tested beams, similar to the location of the concrete strain gauges placed during the experimental tests. In contrast, strain in the tensile steel bars was monitored at a point placed at the mid-span of the RC beam specimen.The experimental and numerical results pertaining to crack patterns, load-deflection behavior, and flexural strength are presented and discussed in this section. The FEMs were validated by comparing the numerical analysis results with the corresponding experimental test results.UU) compared to that obtained from the experimental test. It was observed that there is a high resemblance between the experimental and numerical crack patterns. Both experimental and numerical investigations indicated that the uncorroded control beam (UU) failed due to the yielding of the steel reinforcement bars, followed by concrete crushing.CUB (corroded un-strengthened), CRA-20 (corroded one-sided strengthened), and CSB-20 (corroded three-sided strengthened), respectively. It can be observed from UU), both experimental and numerical results indicated that the corroded un-strengthened beams  also failed due to steel yielding followed by concrete crushing. This finding implies that the damage of the main tensile steel bars due to reinforcement corrosion with actual mass loss of up to 21% did not change the ductile mode of failure of the RC beams. In addition, the flexural behavior of the UHPC-strengthened RC beams in the numerical simulation is similar to that observed during the experimental tests. Although only one major crack formed at the bottom and side surfaces of the UHPC layers in the three-sided strengthened RC beams due to the high tensile strength of the UHPC preventing any further cracks, several flexural cracks were observed in the one-sided strengthened RC beams. For the corroded strengthened beams also, a close matching of the crack patterns obtained from experimental tests and numerical modeling was observed, as shown in The crack patterns at failure load, predicted using the FEMs, were compared to that obtained from the experiments, as typically shown in UU), obtained experimentally and numerically, are shown in UU), including stiffness, yielding, cracking loads, and ultimate strength.The load versus mid-span deflection curves of the un-corroded un-strengthened control RC beam  and the thickness of UHPC layers on the flexural behavior of corroded strengthened RC beams.The compressive strength of UHPC used for strengthening the corroded RC beams was 170 MPa. In order to examine the effect of varying the compressive strength of UHPC, two values of a compressive strength less than 170 MPa  and two values of compressive strength more than 170 MPa  were considered to predict the flexural behavior of corroded strengthened RC beams using FEMs. In order to examine the effect of the thickness of UHPC strengthening layers, the parametric study using the validated FEMs was carried out considering six different thicknesses of the UHPC layers: 10, 20, 30, 40, 50, and 60 mm for one-sided UHPC-strengthening configuration and 15, 20, 25, 30, 35, and 40 mm for three-sided UHPC-strengthening configuration. The compressive strength of the UHPC was typically taken as 170 MPa in the calculation of the flexural strength of the strengthened RC beams for all the considered layer thicknesses. (1)The adoption of CDPM for simulating the normal concrete (used to cast the RC beams) and UHPC (for strengthening the corroded RC beams) and the selection of a cohesive surface bonding approach to simulate the bond between the corroded reinforcing bars and surrounding concrete were found to be appropriate in developing the FEMs, as evidenced by the high accuracy of the FEMs in simulating the flexural behavior of the corroded strengthened RC beams.(2)The FEMs developed in the present study can capture the flexural behavior of the corroded RC beams strengthened using layers of UHPC with a high degree of accuracy, including crack pattern, ultimate strength, and failure mode. The accuracy of the developed FEMs was confirmed through the comparison of the results obtained experimentally with the corresponding results predicted using the FEMs.(3)Parametric studies were carried out using the validated FEMs by varying the compressive strength and thickness of UHPC layers. The results of the parametric studies indicated that the flexural strength of corroded strengthened RC beams increases significantly with the increase in the compressive strength and thickness of UHPC layers and decreased significantly with the increase in the degree of reinforcement corrosion.(4)The proposed FEMs can be utilized to select the optimum thickness of the UHPC layers to achieve the desired ultimate load-carrying capacity of the corroded RC beam for given degrees of reinforcement corrosion, UHPC layer configurations, and the compressive strength of UHPC.In this paper, the finite element modeling (FEM) using the concrete-damaged plasticity model (CDPM) was carried out to simulate the flexural behavior of corrosion-damaged RC beams strengthened with UHPC layers having different configurations and thicknesses. The numerical modeling results were calibrated and validated utilizing the experimental data developed in the present work by testing the corroded strengthened RC beams. The calibrated FEMs were used for parametric studies to examine the effects of varying the compressive strengths and thicknesses of the UHPC layers on the flexural behavior of corroded strengthened RC beams. The following conclusions were drawn based on the outcomes of the present work:


Objectives: To determine the risk factors associated with a prolonged antibiotic course for community-acquired bacterial meningitis (BM) in children.Methods: This retrospective cohort study included children aged 1 month to 18 years with community-acquired BM due to a confirmed causative pathogen from 2011 to 2021. Patients were divided into an antibiotic prolongation group and a nonprolongation group according to whether the antibiotic course exceeded 2 weeks of the recommended course for the causative pathogen. Associations of important clinical characteristics and laboratory and other parameters with antibiotic prolongation were assessed using univariate and multivariable regression logistic analyses.Results: In total, 107 patients were included in this study. Augmented renal clearance (ARC)  was associated with a prolonged antibiotic course; however, septic shock, causative pathogen, preadmission antibiotic use, peripheral white blood cell (WBC) count, initial cerebrospinal fluid (CSF) WBC count, CSF glucose, CSF protein, and surgical intervention were not associated with the prolonged antibiotic course. Patients with ARC had more total fever days (median time: 14 vs. 7.5 days), longer hospitalization (median time: 39 vs. 24 days), higher rates of complications (72.34% vs. 50.00%) and antibiotic adjustments (78.723% vs. 56.667%) than patients with normal renal function.Conclusion: ARC is an independent risk factor for prolonged antibiotic use in children with community-acquired BM. ARC may be associated with longer fever and hospitalization durations, higher rates of complications and antibiotic adjustments. Bacterial meningitis (BM) is a life-threatening infectious disease of the central nervous system in childhood. The mortality rate varies from 5% to 30%, and approximately 30–54% of survivors develop neurological sequelae . AntibioThe adequate concentration of antibiotics in the cerebrospinal fluid (CSF) is essential to BM treatment. The fact that augmented renal clearance (ARC) can decrease the concentration of the drug in the body is widely recognized, especially for drugs that are primarily eliminated by renal excretion . AntibioPatients aged 1 month to 18 years with confirmed community-acquired BM admitted to the Department of Neurology, Children’s Hospital of Chongqing Medical University (CHCMU), from January 2011 to August 2021 were included in this study.The inclusion criteria were as follows: 1) community-acquired BM with a confirmed causative pathogen ; 2) aged between 1 month and 18 years; 3) liver and renal function testing performed within 72 h prior to the use of antimicrobial drugs; and 4) sensitive antimicrobial drugs based on pathogenic and drug sensitivity results.The exclusion criteria were as follows: 1) hospital-acquired BM; 2) renal insufficiency or renal impairment that occurred during treatment; 3) hemodialysis; 4) various bacteria cultured from blood and CSF, with mixed bacterial infection unable to be ruled out clinically; 5) lack of use of sensitive antimicrobial drugs according to drug susceptibility testing; 6) an antibiotic therapeutic dose different from that recommended for pediatric community-acquired BM; 7) discharged from the hospital after giving up treatment, thus not allowing the clinical prognosis to be assessed; or 8) combined with primary immunodeficiency or anatomical abnormalities, such as CSF leak during the course of the disease.Data from medical records was collected. The medical records of each patient included in the study were reviewed by two independent reviewers using a standardized data collection form. Discrepancies in the collected data were reconciled by a third reviewer. This study was approved by the Ethics Professional Committee of CHCMU .To determine the risk factors associated with a prolonged antibiotic course for community-acquired BM in children, 23 potentially relevant variables were chosen for analysis. There were no missing data for the 23 variables extracted from each patient’s medical record, including age; sex; height; weight; premature status; maximum body temperature; neck stiffness; initial peripheral white blood cell (WBC) count and neutrophil percentage; CSF WBC count; CSF glucose concentration; CSF protein concentration; C-reactive protein (CRP), blood and CSF culture results (causative pathogens); estimated glomerular filtration rate (eGFR); creatinine, urea, albumin, alanine aminotransferase (ALT), and aspartate aminotransferase (AST) levels; preadmission antibiotic use; antibiotic adjustments during the course of the disease; and septic shock. To assess the efficacy of treatment, the efficacy evaluation indicators used in this study were duration of fever, length of hospitalization, presence of complications , surgical intervention, antibiotic adjustment, and Glasgow Outcome Scale (GOS) at discharge.The modified Schwartz formula (eGFR = k×height/Scr) was used to estimate the eGFR in patients younger than 17 years old, where k is 0.45 for infants aged <1 year, 0.55 for children aged <13 years and adolescent females, and 0.7 for adolescent males; and Scr is the serum creatinine concentration (mg/dl). Height is expressed in centimeters (cm).Staphylococcus aureus, or rifampicin 10 mg/kg q12 h up to 600 mg/day, especially for Streptococcus pneumoniae. Chloramphenicol was considered when conventional antibiotic therapy was not effective.Patients were divided into an antibiotic nonprolongation group (ANPG) and an antibiotic prolongation group (APG). APG was the course of antibiotics 2 weeks longer than the recommended guideline, and ANPG was not exceed 2 weeks. The standard duration of antibiotic treatment for BM in this study was based on the European Society of Clinical Microbiology and Infectious Diseases guideline . The spe1. Confirmed BM  was defi2. The GOS  was used≥160 ml/min/1.73 m2. Since ARC was defined as eGFR ≥160 ml/min/1.73 m2 in children . Logistic regression analysis was performed to analyze the association of the influencing factors and the outcome. The receiver operating curve (ROC)-derived optimal cutoff was determined at the maximal Youden Index. p values <0.05 were considered statistically significant.Statistical analyses were conducted using SPSS version 26.0 . Summary statistics for normally distributed quantitative variables are expressed as the means ± SDs, and nonnormally distributed variables are expressed as medians and interquartile ranges (IQRs). Categorical data are summarized by ratios and percentages. Differences in proportions were tested by the xEscherichia coli; 37 Streptococcus pneumoniae; 8 Listeria monocytogenes; 12 GBS; 8 Haemophilus influenzae and 12 other bacteria ; more information on the characteristics are detailed in p < 0.001), eGFR (p < 0.001), peripheral WBC (p < 0.028), and surgical intervention (p < 0.046), the differences in the other characteristics were not statistically significant.We identified 107 patients with community-acquired BM due to a confirmed causative pathogen at CHCMU during the study period, of whom 60 (56.07%) were males and 47 (43.93%) were females. The median age was 0.49 years, with an IQR of 0.20–2.41 years. Confirmed bacterial etiologies were as follows: 30 p < 0.001), creatinine <14 μmol/L , CFS glucose   and surgical intervention  were significantly different between the two groups.The univariate analysis without any correction showed that the rates of elevated eGFR  was a potential risk factor for prolonged antibiotic use. On this basis, stepwise regression analysis was also performed, and the results showed that only one influencing factor, elevated eGFR, was significant . All results in this section are detailed in To explore potential independent factors, further analysis was performed using multivariable analysis. In an analytical model incorporating all factors simultaneously, it was suggested that only elevated eGFR  and a normal renal clearance (NRC) group (eGFR<160 ml/min/1.73 m2). The analysis suggested that the group with an elevated eGFR had more total fever days (median time: 14 vs. 7.5 days), a longer total hospitalization stay (median time: 39 vs. 24 days) and higher rates of complications (72.34% vs. 50.00) and antibiotic adjustments (78.723% vs. 56.667%) than the NRC group. However, ARC cannot yet be considered to affect the prognosis of patients (p = 0.097).The clinical efficacy indicators in the different eGFR subgroups were analyzed and are detailed in We studied for the first time the risk factors for prolonged antibiotic treatment in pediatric patients with BM and found that ARC was an independent risk factor. Prolonged antibiotic therapy not only indicates longer hospital stays and higher treatment expenses but also serves as an indicator of an unsatisfactory treatment process for patients with BM . Currentp = 0.04) than in the non-ARC group. There were few studies on the correlation between ARC and clinical efficacy. 2. However, the definition of ARC in children remains controversial  served as the ARC diagnostic value, corresponding to a sensitivity of 0.803 and a specificity of 0.829. These results confirm the reliability of an eGFR ≥160 ml/min/1.73 m2 as the criterion for determining ARC in children and provide a reference for ARC criteria in children, which is helpful for us to effectively identify ARC in patients in the clinic.The ARC phenomenon, in which renal function is significantly enhanced, usually occurs in critically ill patients . Some stoversial . Hirai eEscherichia coli meningitis but did not elaborate on the correlation between long-term antimicrobial use and complications. Based on the above findings, we speculated that ARC not only led to a prolonged course of antibiotics but was also correlated with other clinical outcomes of BM. We then divided our study into ARC and non-ARC groups and found a significantly longer duration of fever, a longer length of the hospital stays, a larger number of antimicrobial adjustments, and a higher rate of complications in the ARC group than in the non-ARC group. Poor treatment outcomes were reflected not only by poor temperature control but also by higher complication rates due to uncontrolled infections.Many studies have confirmed that ARC is clearly associated with subtherapeutic antimicrobial concentrations of renally eliminated drugs . BecauseAs the existing recommended antimicrobial regimens could not achieve the desired pharmacokinetics-pharmacodynamics targets in critically ill patients with ARC, incremental dosing adjustment of antibiotics was frequently needed . Specialin vivo were the most direct indicators of the effect of ARC on drug metabolism in patients, however, it was not available in the study.Because the study was a retrospective chart review, there were a few limitations. The definition of the prolonged antibiotic course criteria is not universally acknowledged. BM caused by multiple pathogens was included in this study, and the treatment regimen was different for each pathogen. Due to the limited samples for each pathogen, it was impossible to statistically analyze the effect of different treatment regimens for the same pathogen on antibiotic regimens. In future studies, we will increase the sample size for each pathogen and analyze the antibiotic regimen for each pathogen to further clarify whether it may lead to prolonged antibiotic therapy. The concentrations of antibiotic 2 was an appropriate cutoff for the definition of ARC. ARC may be associated with a prolonged duration of fever, a prolonged length of stay, and increased rates of complications and antibiotic adjustments. This further clarifies the impact of ARC on the clinical efficacy of antibiotics against BM in children. Clinicians should optimize antibiotic regimens early in the treatment of childhood BM in patients with ARC to achieve a good outcome.This study first identified risk factors for prolonged antibiotic treatment of community-acquired BM in children. We found that ARC was an independent risk factor for prolonged antibiotic treatment of BM in children and determined that an eGFR ≥160 ml/min/1.73 m


Based on the experiments, the fitting equation to determine the EPS-concrete strength–EPS-concrete density–cementitious material strength is z = 69.00087 + 0.0244x − 0.1746y − 0.00189x2 + 0.0000504706y2 + 0.00028401xy. Additionally, a strength-increasing design method for EPS concrete with different densities prepared by conventional Portland cement is clarified. This study can guide the preparation of EPS concrete.Concrete in which EPS (expanded polystyrene) particles partially or completely replace concrete aggregates is called EPS concrete. Compared to traditional concrete, EPS concrete has a controllable low density and good thermal-insulation performance, which make it promising for prospective applications. At present, research on EPS concrete mostly focuses on increasing its strength and EPS surface modifications. Few researchers have studied the influence of cementitious material strength and EPS-concrete density on the strength of EPS concrete. In this research, cement was used as the main material, and fly ash, silica fumes, and blast furnace slag were selected as admixtures. By changing the mixing proportions of the admixtures, the basic properties, such as the paste strength, change. Based on the mix proportions of the above different raw materials, EPS concrete with different density levels was prepared to explore the influence of the density of EPS concrete and the strength of cementitious materials on the strength of EPS concrete. The influence of the slurry strength on EPS-concrete strength was weaker than that of the density of EPS concrete. When the strength range of the cementitious materials is 35.7~70.5 MPa, the compressive strength range of 1000 kg/m According to data from the International Energy Agency, about 30% of global final energy consumption belongs to the construction industry, and energy consumption has increased by 21% since 2000 . Concrete is the most widely used material in building, but ordinary concrete has a large self-weight, low specific strength, and poor thermal-insulation performance ,6. In paResearch on EPS concrete is mainly carried out from two aspects ,14. The In this paper, the compressive strength of pastes is changed by changing the type and amount of the mineral admixtures ,39. By p3, and an apparent density of 33 kg/m3. The fly ash came from Sanmenxia thermal power station in Henan Province , S105 blast furnace slag and silica fumes were purchased from Hebei Yousheng refractory Co., Ltd., . Their chemical composition is shown in The cement used in the experiment was PO (ordinary Portland cement) 42.5 produced by Conch Cement . EPS pellets were provided by Yiwu mianer Crafts Co., Ltd.  with particle size of 0.5~1 mm, a bulk density of 18~21 kg/m3, 1200 kg/m3, and 1400 kg/m3 were configured. After changing the mineral admixtures, the changes in the paste test block and the corresponding EPS-concrete strength were tested.The experimental method is shown in 3, 1200 kg/m3, and 1400 kg/m3, respectively.In total, 15 groups of pastes with different strengths were used in the experiments. The mix proportions of the pastes are shown in During the experiment, the pastes were weighed according to the mix proportions and poured into the horizontal mixer for mixing; then, the pastes were pre-mixed for 2 min to ensure that the dry powder was evenly mixed; this was followed by adding 2/3 of the water and all of the EPS particles. After stirring for 3 min, the other 1/3 of the water was added, and the mixture was stirred for another 3 min. Finally, the samples were poured into 1000 × 1000 × 1000 mm molds. The curing and the tests were performed according to Standard JC/T 2458-2018 (polystyrene granule foamed concrete) .The compressive strengths and dry densities of the test blocks were tested according to the national standard JC/T 2458-2018 (polystyrene crosslinked polystyrene concrete) . A test 3. The steps for creating the concrete were as follows: first, the EPS-concrete test blocks were destroyed, and a certain number of samples from the middle were obtained. All of these samples were broken by being pushed through an 80 μm standard sieve. Finally, the samples were dried at 60 °C, and the Nicolet IS5 Fourier transform infrared spectrometer produced by the US company Thermo Fisher Scientific was used. The parameters were as follows: resolution 4 cm−1, scanning frequency 16 times per minute, and scanning range 400~4000 cm−1FTIR was used to determine whether the chemical bonds in the test blocks had changed. This was because, in addition to the EPS content, each group had the same proportions, so 28 d was selected as the aging period for the EPS-concrete samples with a density of 1000 k/mThe XRD patterns of fly ash, mineral powder, and silica fume are shown in 3, 1200 kg/m3, and 1400 kg/m3, the compressive strength increases from 8.8 MPa to 17.6 MPa, from 11.4 MPa to 18.0 MPa, and from 15.7 MPa to 26.6 MPa, respectively. The growth trend for strength is also different at different densities. Compared to the 1000 kg/m3 EPS concrete, the increasing trend of the 1200 kg/m3 and 1400 kg/m3 concrete sample with the increase in the paste strength is more obvious. Therefore, the lower the density of EPS concrete, the more difficult it is to improve its compressive strength.The influence of the paste strength on the strength of EPS concrete under different EPS-concrete densities is shown in 3, 1200 kg/m3, and 1400 kg/m3 of EPS concrete was fitted with the power function for the strength of EPS concrete. The fitting curves with different densities are shown in 3 and 1200 kg/m3 EPS concrete is smoother than that of the 1400 kg/m3 concrete. Therefore, when the density of EPS concrete is lower than 1000 kg/m3, the extreme value of the curve will continue to decrease and will become smooth earlier. When the density of EPS concrete is higher than 1400 kg/m3, the extreme value of the curve will be higher, and it will become gentler when the strength of paste is greater than 70 MPa. In addition, it can be seen that, with an increase in the density of EPS concrete, the fitting correlation also increases because, as the paste amount increases, the strength of the EPS concrete is more similar to that of the paste strength. When only the compressive strength data after 7 d is used, the range of the fitting formula is 35–60 MPa, and the range of the fitting formula is extended to 35–70 MPa after adding 28 d age data. This is because the more data points there are at each density, the higher the accuracy of the fitting formula is. At the same time, the data of compressive strength of 7 d age and 28 d age can make the fitting formula closer to the actual situation. The fitting formula is listed in The paste strength of the 1000 kg/m3 and 1200 kg/m3. As for increases in density, the 1400 kg/m3 EPS concrete still shows an increasing trend because the smallest amount of EPS particles was added, and the defects are relatively small. Some scholars have shown that the stress distribution of cement-based materials depends on the particle size, paste, and the relative elastic modulus of the particles. When the elastic modulus of the aggregate is higher than that of the paste, then the stress is concentrated near the aggregate ,42. Howe3. When the wave number is 3643 cm−1, it represents the stretching vibration peak of free hydroxyl, indicating the difference in water content. The peak value of the wave number is in the range of 3200~3500 cm−1 and represents hydroxyl, indicating the Ca(OH)2 content in the test block. The wave number of 1633 cm−1 represents the active carbon–carbon double bond, and this peak represents the EPS particles in the sample [−1 represents the C-O bond. According to the literature, this peak represents the degree of erosion in cement hydration products by CO2 [−1 and 463 cm−1, respectively, represent the stretching vibration deformation of the Si-O bond and Si-O. The number of Si-O bonds represented by the wave number at 983 cm−1 indicates the C-S-H content in hydrates, and there is little difference between each peak. This shows that there is little difference in the hydration products generated by each group of mixture ratios, and the changes in the strength of EPS concrete are mainly due to the effects of volcanic ash and micro-aggregates in various solid-waste products.e sample . Due to s by CO2 . The peac = 10.3 × γ1.918 × 10−6 . In the formula, the strength of the EPS concrete increases as the density increases, but the changes in the strength of the EPS concrete under different densities are not considered. In order to comprehensively consider the influence of the compressive strength of paste and the EPS-concrete density on the compressive strength of EPS concrete [Researchers Daneti  integratconcrete , Figure 3 and the strength of the paste is 70 MPa. The lowest point of EPS-concrete strength is in the opposite direction to the highest point and can be observed when the density of the EPS concrete is 1000 kg/m3 and the strength of the paste is 30 MPa. This is also consistent with experimental results. The surface fitting formula in As seen from 3 is used has a compressive strength 15 MPa. Moreover, if EPS concrete were prepared using PO 32.5 cement and a density of 1300 kg/m3, its strength would be 10 MPa.The surface fitting formula is depicted as a contour line in In addition, it can also be seen from the figure that, when preparing EPS concrete at a given density, it is difficult to achieve the goal of only using cement as paste. By adding a highly active mineral admixture, the density can be reduced, and the strength can be improved. At the same time, according to the surface fitting formula, the density of EPS concrete and the paste strength need to be considered at the same time when determining the strength of EPS concrete. It is difficult to improve the strength of EPS concrete by simply increasing the paste strength. It is simpler to improve the strength of EPS concrete by increasing the density. The formula that was fitted in this study can calculate the strength of EPS concrete according to the paste strength and the density of EPS concrete. It provides a basic method for the economical and reasonable preparation of EPS concrete. In this study, EPS concrete with three different densities were prepared using pastes with different properties. The relationship between the strength of EPS concrete and paste strength was explored, and the following conclusions were drawn:(1) According to the fitting, the relationship between the paste and the strength of EPS concrete is a power function with an index less than 0 and in the range of 30 MPa to 70 MPa, and the increase in the strength of EPS concrete gradually slows down as the paste strength increases.(2) The binary fitting formula for the EPS concrete density and paste relative to EPS concrete strength is:The formula can calculate the target EPS-concrete strength according to the raw materials and density used for preparation.(3) When preparing EPS concrete, the use of a mineral admixture can reduce the density of EPS concrete and improve its compressive strength. When using higher grade cement with a lower density, the strength of EPS concrete cannot be improved significantly.3 to 1800 kg/m3 is prepared, in future practice or scientific research, the strength of EPS concrete with a given density can be inferred by knowing the paste strength, facilitating construction practices. The workload in mix design will be greatly reduced, and the applicable scene of EPS concrete will also be improved.In terms of future research, it still is necessary to prepare EPS-concrete samples with other densities to modify this formula and to increase the scope of its application. In addition, the smaller the density interval of EPS concrete is, the more data is used, and the more accurate the fitting formula is. This will be a big challenge. At the same time, it is also necessary to increase the fitting formula of EPS concrete under other paste strengths. If EPS concrete with a density from 200 kg/m


Various studies have been recently conducted aiming at developing more sustainable cementitious systems so that concrete structures may not have a negative effect on the environment and are decomposed. It has been attempted to build sustainable binders by substituting silica fume, cement with fly ash, nano-silica, nano-alumina, and rice husk ash. In this paper, a series of experiments on concrete with different contents of rice husk ash , nano Consequently, the population is expected to increase to 9.8 billion by 20502. It is needed to annually build 10–30 million new residences for accommodating the growing population. Besides, other infrastructural advances are required3. As a result of the growing demand for building, cement concrete construction is also increased, and it is estimated that the worldwide cement production rise by 2.1% annually by 2030, and it would reach a total of 1.7 times the amount that is currently produced1. The cement industry is an energy-intensive industry5 with a considerable carbon mark that threatens environmental sustainability6. The annual emissions of concrete industry is up to 2.8 Gt 7, and it is estimated that concrete production accounts for 9% of overall greenhouse emissions8, and it is predicted that 9% of overall greenhouse emissions is originated from concrete production, and cement plants account for 7–8% of carbon dioxide emissions worldwide9. The two approaches for addressing the impact of the greenhouse gas from the cement industry are as follows: improving the cement production process efficiency, and partial replacement of normal cement with supplementary cementitious materials (SCMs). There are different SCMs for decreasing carbon dioxide release and improving the durability and mechanical characteristics of concrete, which include as follows: ground-granulated blast furnace slag10, silica fume11, calcined clays12, nano clay13, natural pozzolans14, carbon nanotubes15, graphene oxide16, nano17, nano18, nano19, nano20, fly ash22, nano24, nano25, and rice husk ash27.The annual growth rate of the current world population is 1%, and it is estimated to reach 8.5 billion by 203028, and above 75% of its weight is silica29. RHA can be potentially used as partial replacement for Portland cement for its non-crystalline silica content30. There are significant pozzolanic characteristics in RHA because of amorphous silica, contributing to its specific surface area and fineness31. The rice husk ash should have a particle size below 8 32. Using RHA, the concrete cost can be minimized33, the concrete’s mechanical properties35 and durability can be improved28. Besides, resistance to chemical attacks36 and corrosion of reinforced concrete can be enhanced by using RHA in concrete37.Rice husk is produced as a byproduct in areas where rice grows. For producing rice husk ash, rice husk burns at temperatures between 300 and 450 °C. 1000 kg of rice grain provides almost 200 kg rice husk. After burning, about 40 kg RHA are obtained, which indicates that almost 20% of ash is made from rice husk39. The concrete mixture can have an excellent performance because of the high-density continuous packing of binder constituents. Fluidity can be increased by the use of nano-additives in mixed design40. Among nano-additive for concrete, NA and NS have shown high efficacy to improve flexibility, durability, and strength42.In addition to waste concrete additives like RHA, nanomaterials are highly important in enhancing the durability and mechanical properties of concrete40. Since the hydrophilic NS is highly dispersed in water, NS that is used in concrete is chiefly hydrophilic43. NS can serve as a nano-filler and fill the empty spaces between calcium-silicate-hydrate (C-S-H) gel particles. Besides, NS is a pozzolan that has a high rate of pozzolanic reaction for its high surface area to volume ratio, which implies considerable chemical activities. When an optimal amount of NS is incorporated into the concrete, it can increase the compressive strength and refine the pores. Consequently, the concrete water permeability is reduced44. Although any dose above the optimal level causes enhancing compressive strength relative to the control mixture, it does not rise it by more than the optimal replacement level45. With addition of 1 and 2% NS, it is possible to improve the concrete’s tensile strength by up to 17 and 24% compared to the control mixture46. Using the filler and pozzolanic features of NS, concrete microstructure quality can be improved by declining porosity and improving pore structure40. Hydraulic permeability of porous concrete is declined by a 5% replacement of cement with NS47. As demonstrated by Rapid Chloride Penetration Test, substitution of 3 and 6% of NS can considerably improve permeability reduction in concrete5. As revealed by the measurements of viscosity, amount of water needed for maintaining the same workability was increased by the addition of NS40. NS concentrations beyond a specific threshold resulted in higher autogenous shrinkage due to self-desiccation, leading to a higher breaking potential48.NS is a fluffy white powder that includes amorphous silica powder. NS has strong surface adsorption, a large specific surface area, great chemical purity, acceptable dispersion, and big surface energy for its small particle size49. NA is an amphoteric oxide powder with acid-base characteristics, a large specific area, and thermal and mechanical stability. C-A-S  gel in concrete is improved using NA as a partial replacement by cement. There is an interaction between calcium hydroxide made by the hydration of calcium aluminates and nano-alumina. With the addition of NA, the water absorption, microstructure, and resistivity of cement-based materials can be enhanced50. With the addition of 0.2% by weight of NA, the concrete’s strength and deformation performance can be significantly improved51. It has been revealed that NA significantly elevates the elasticity modules (up to 143% at a dose of 5%). However, it modestly affects compressive strength52. Additionally, the overall porosity of NA can be reduced with the addition of NA25. The addition of NA reduced the concrete workability53. The frost resistance of concrete with NA is significantly enhanced because of a more compacted microstructure54.Apart from NS, the NA impact on durability and mechanical characteristics of concrete were investigated55. Despite the large number of studies investigating the role of NS, NA, and RHA in changing the durability and mechanical properties of concrete, only a few number of comparative studies have investigated the effects of all of them on concrete properties. Moreover, most works have just focused on studying normal curing conditions. Moisture and minerals cause significant concrete corrosion on beaches, which destroys inner bars56. Thus, the lifespan of concrete constructions in coastal environments is much shorter than elsewhere57. The impact of seawater on concrete is notable for many considerations. First, coastal and offshore constructions are subjected to both physical and chemical deterioration at the same time58, and second, oceans cover 80% of the earth’s surface57. The widespread use of concrete piers, breakwater decks, and retaining walls in the building of ports and docks. Consequently, it is important to investigate the mechanical properties and durability of concrete buildings cured in seawater. Since a few studies investigated concrete properties under the curing condition of Caspian seawater, in order to address this knowledge gap, the present work examined the comparative effects of NA, RHA, and NS on durability and mechanical properties of the concrete under Caspian seawater curing conditions. In addition, the Iranian national building code has several restrictions for construction in the Persian Gulf curing environment in the south of Iran. However, there is a lack of government information and guidelines for building in Caspian Seawater curing conditions. As far as we know, it is the first work studying the impact of these SCMs under the Caspian seawater curing condition. For a comparative assessment of the effect of various SCMs on different properties of concrete, we considered 16 groups of mix designs. With these samples, the effect of different SCMs can be compared because the only feature varying across mix designs with different SCMs that belong to the same category is the kind of SCMs.The matrix of concrete constructions should be taken into account to increase their durability. The interface transition zone between the coarse aggregate and mortar matrix is often the weakest link of conventional concrete. With the addition of RHA and nano partials like as NS and NA to the admixture, this weakness may be addressed, consequently enhancing the concrete’s strength. Mechanisms of these SCMs on concrete may be related to the fact that they function as Micro or Nano-sized fillers to reduce the Micro or Nano-sized pores in the hydration products of the cementitious materials and encourage the formation of a high-density C–S–H phase59. The cement producer is Khazar Cement Company . The cement fineness was 3230 60 and the final and initial setting times were 170 and 110 min, respectively. Besides, the 7 and 28 day compressive strengths and the specific weight of cement were 41 In the present work, a type II ordinary Portland cement is used as the main cementitious binder according to ASTM C 150Rice husk is provided by the rice milling industry since it is a byproduct, burnt for about 72 h in air in an uncontrolled burning process. The temperature range is between 400 and 600 °C. Gray RHA is used in the present study with a pH of 7.3. The size of NS particles with an average specific surface area of 193 61. Figure Natural river sand with a specific gravity of 2.63, fineness modulus of 2.64, water absorption of 1.3%, bulk density of 1720 62 is introduced in all the concrete mixtures as a weight percentage of the total cementitious materials. The superplasticizer was used to help disperse Nanoparticles throughout the concrete mixture, increase compaction, and improve the concrete workability. The characteristics of the superplasticizing admixture materials are given in Table A Type F polycarboxylate acid-based superplasticizer conforming with ASTM C494In this study, the water utilized for curing conditions was taken from the Caspian Sea. For determining the chemical properties of Caspian seawater, provided samples were analyzed. Table We cast four series of concrete samples . Then, samples are subjected to the experiments. PC signifies plain concrete and is considered as control concrete. The water to binder  ratio (W/C) employed for all mixtures is 0.5. RHAC10, RHAC15, and RHAC20 represent the concrete that contain 10, 15, and 20 wt % RHA, by the weight of cement. NSC1, NSC2, NSC3, NSC4, NSC5, NSC6, NSC7, and NSC8 signify the concrete that contain 1, 2, 3, 4, 5, 6, 7, and 8 wt % NS by the weight of cement. NAC1, NAC2, NAC3, and represent the concrete that contain 1, 2, 3, and 4 wt % nano-alumina by the weight of cement. Table 64 for determining the workability of freshly mixed concretes. For the workability test, a big pan, a slump cone , a ruler, and a steel tamping rod are utilized. Water was used for cleaning and moistening the internal surface of slump cone Fig. Standard slump tests are employed in accordance with ASTM C14365, three samples of concrete specimens were taken out of storage after 28 days of curing and scheduled to be tested on a certain day. After the elimination of water from the specimens’ surface, we transformed them into saturated surface dry (SSD) conditions. Then, the SSD weight of the specimens were specified in the air (C). Afterward, specimens were baked at 100–110 °C for 24 h. The weight of the specimens was then determined that represented their oven-dry weight while suspended in air (A). Later, the samples were placed under water in a bucket, following by determining the weight underwater (D). We also recorded the water temperature on test day (T), and the water density For conducting a density test based on ASTM C 64266, as shown in Fig. A 200-ton hydraulic concrete pressure testing machine was used for conducting compressive strength tests in accordance with ASTM C3967. Three samples were made  is used, followed by the post-hoc Tukey test. 69. Figure 70, NS73 and NA74 reduced the workability of the concrete. Furthermore, the incorporation of nanoclay75 and marble dust powder77 makes concrete mixtures stiffer, adversely influencing the workability of concrete. In addition, the workability of concrete containing recycled coarse aggregates (RCA) decreased as the percentage of RCA increased79. RHA has macro and mesoporous particles and their specific surface area increases with fineness. Water is absorbed by the surface of fine RHA and it is stored in its pores, which reduces free water and slump value32. Likewise, the increased reactivity of RHA could be another factor that contributes to the decrease in the concrete flow80. Specific area of NA and NS is larger than cement, which leads to greater water absorption and decreases the concrete slump. Also, NS has numerous unsaturated bonds and a large specific surface area that makes it simpler to attract water molecules for forming chemical bonds81. The low dosage of the NA Slump reliably indicates the concrete workability and is utilized for assessing the workability of different mixes of concrete containing the same amount of water. The greater the measured height of slump, the better the workability, which suggests easier flow of the concrete when it is poured. Nevertheless, it is not subjected to segregation at the same time82, who found that using adding 15% of RHA as cement replacement showed an increase by 26% of compressive strength at 28 days of curing. While 20% of RHA replacement showed equivalent in strength at 56 and 91 days of curing respectively. It can be because the RHA amount in the mix is higher than the amount needed for combining with the released lime during the hydration process, which results in excessive leaching of silica. Thus, it leads to a lack of strength as it replaces some of the cementitious material but has no contribution to strength83. Compressive strength is reduced for early-age concrete samples at 7 days in the presence of RHA in comparison with control concrete. The reason for such reduction in early-age strength is lower pozzolanic activity of RHA as an outcome of its coarser particles. Besides, it is likely that the reduced volume of hydration products related to a less favorable hydration rate leads to a decrease in early-age strength84. Studies86 have shown that even a small percentage of NS added to concrete while it is early age may dramatically increase the compressive strength. The improved compressive strength of NSCs at an early age is associated with the NS’s strong pozzolanic activity at an early age, while the improvement in 28-day compressive strength can be attributed to the C-S-H gel filling up voids and improved mortar-aggregated bonding. The space between the grains in the cement paste is filled by finer and smaller NS particles, which results in increasing the strength87. The compressive strength increases up to 2.0% NA replacements, then decreases, while the addition of 4.0% NA leads to samples with similar compressive strength, like CP. The reduction of compressive strength due to the addition of more than 2 % NA and 6.0% NS could be affected by the fact that the of NA and NS injected into the mix is more than the amount required for the combination with the freed lime during the hydration process. Besides, it can be associated with faults in the dispersion of NPs, forming weak zones. Heikal et al.88found that adding 1% NA to cement enhanced compressive strength by 30.67%. Similarly, Nazari and Riahi89 showed that the compressive strength of mortar could be significantly improved by introducing NA.Table 90, which is consistent with our findings for RHA. Similar to NS and NA, adding copper slag up to a certain percentage increases the compressive strength; after that, the compressive strength decreases91. Furthermore, replacing natural coarse aggregate with polypropylene92 and polyethylene terephthalate93 decreases the compressive strength of concrete.The RHA, NS, and NA may have a similar filler effect. However, NS is a very reactive pozzolanic material from a chemical viewpoint. When cement is hydrated, it combines with calcium hydroxide (CH) to create calcium silicate hydrate (C–S–H). The NS’s large specific surface area will accelerate cement hydration and pozzolanic reaction. Before the concrete samples were made for 24 h, the NS’s pozzolanic reaction might have begun, enhancing the early strengths. It’s possible that NS served as a reactive filler, which takes up space between cement and slag particles to stop bleeding and boost packing density of solid components. Given its size and form, RHA causes early-stage samples to exhibit delayed pozzolanic activity. The compressive strength of concrete mixes containing recycled coarse aggregate and natural coarse aggregate decreases as the percentage of RHA increases94 also showed that by adding 5%, 10%, 15%, and 20% RHA the density of concrete decreased. The increasing density of concrete is affected by amorphous silica concentration, fineness, and RHA replacement level. The pozzolanic activity and slower hydration of RHA blended cement can rationalize the loss in density of concrete above the 10% replacement. Due to the cement compatibility and high pozzolanic of RHA, a decline in the portlandite content of the matrix and an increase in the quantity of C S H products can result in improved pore structure of the concrete matrix95. With the replacement of the cement with NA and NS, the density is increased, which can be attributed to the cement paste hydration in particular. Hydration products become increasingly interconnected and compact as a unit. In comparison with the early age, the overall porosity showed a dramatic reduction. The small particle size of NA and NS has a filling impact, and they fill the space between un hydrated particles and voids from thicker cement paste, which lowers the the cement paste’s overall porosity.Figure The relationship between compressive strength and density, as well as the effect of RHA content is shown in Fig. 98 and NA99 resulted in an increase in concrete density. Furthermore, the incorporation of nano17, copper slag91 and marble dust75 increase the concrete density . In contrast to NS and NA, increasing amounts of waste expanded polystyrene100 and ethylene-vinyl acetate101 are added to concrete, resulting in a significant decrease in density. Similar to our results, Behera and Rahman showed that adding RHA decreased concrete density102.Several studies came to the same results as we did, namely that adding NS103 and Rezania et al.71 showed that adding 1–4% NA similarly reduced water permeability in concrete.Figure 104 reported the same decrease in the penetrability of the chloride ions with the increase in RHA dosage.Figure 107, NS110, and NA111 to concrete reduces chloride ion penetration and water absorption. Furthermore, adding nano112, while adding polyethylene terephthalate aggregates increases the depth of water penetration113. Moreover, adding of fly ash and coal gangue decreased the chloride diffusion coefficient114.The relationship between chloride penetrability and water penetration, as well as the effect of NS content is shown in Fig. According to results of Fresh properties, workability reduced with increasing amount of NA, RHA, and NS. The consistency of mortars is affected by the addition of NA, RHA, and NS, and NA as a partial replacement for cement. With an increase in the content of these SCMs, the water demand for the binder is also increased. Lowest workability was observed in the mix comprising 8% NS. NA, RHA, and NS have a large specific surface area because of their small particle size. In the process of concrete mixing, many unsaturated bonds improve the NA, RHA, and NS for absorbing more water molecules, leading to the reduction of concrete slump.In comparison with NA and RHA, the NS addition caused a significant increase in compressive strength in the early phases. Nevertheless, after 14 days, no noticeable difference was noted in the performance of concrete that contained NA, RHA, and NS. The highest compressive strength of all samples was observed in NSC6, followed by NSC5.With introducing RHA 10%, NS, and NA the concrete density increased. The increase in density is consistent with the results of depth of water and chloride ion penetration. The maximum increase in density was achieved by RHAC10, with an increase of 3.8% in comparison with the control sample.when cement was replaced by NA  in the Caspian Sea curing conditions on the durability and mechanical behavior of the concrete was analyzed. These materials were investigated concurrently by performing slump, density, compressive, chloride ion penetration, and permeability tests. As conclusion: