This case study aimed to compare the differences in the durability and prestress loss between normal-weight-concrete (NC) and lightweight-aggregate-concrete (LWC) prestressed box girders, which were constructed at the same time in the same area, so as to verify the superiority of using synthetic lightweight aggregate (LWA) made from reservoir sediments in prestressed bridges. For the NCs and LWCs used in the prestressed box girders, the basic mechanical properties  were tested, as well as the durability properties (chloride ion penetration resistance and rapid chloride permeability). Then, through the prestress-monitoring system, the prestress losses of the two groups of prestressed box girders were tracked. The results of the durability test confirmed that LWC can inhibit the penetration of air, water, and chloride ions by strengthening the interfacial transition zone between the aggregate and the cement paste, thereby improving its durability. Moreover, the magnetic-flux prestress loss of the NC prestressed box girder reached 8.1%. In contrast, the magnetic-flux prestress losses on both sides of the LWC prestressed box girder were 4.6% and 4.9%, respectively. This verified that, under the same environmental conditions, the use of LWC produced less of a prestress loss than the use of NC. Lightwe3 . Since S3 . For exa3 ,13,14,153 . The uni3 , structu3 have been widely used in various structural projects, such as high-rise buildings, bridges, prestressed members, and offshore oil platforms, and their use in these contexts has shown good development and prospects [Expanded-shale, -clay, and -slate LWAs are highly absorbent, yet they are composed of vitrified silicates and are particularly durable . In addirospects ,28. Howerospects . This dirospects ,30. In Nrospects ,32. In crospects . Thereforospects ,35. In grospects ,37. In vrospects . Most ofrospects  uses a cMany studies have shown that LWCs perform much better than NCs under variable and dynamic loads ,41. In pThe creep control and shrinkage control of concrete are other important factors that affect the performance of prestressed concrete members ,47,48,49The surface of Taiwan is covered with a large amount of shale and slate, which is washed into rivers, turned into sediments, and accumulated in reservoirs, forming an excellent source of LWAs. In the past two decades, Taiwan has successfully sintered LWAs with excellent properties from reservoir sediment and applied them to structural engineering ,8,9. In 2/g; its chemical composition is shown in Cement: a locally produced Type I Portland cement, with a specific gravity of 3.15 and a fineness of 3550 cmSlag: purchased from Yu Qingtang Enterprise, Taichung, Taiwan; its specific gravity was 2.89, and its chemical composition is shown in Fly ash: taken from Taichung Thermal Power Plant, Taichung, Taiwan; its specific gravity was 2.32, and its chemical composition is shown in Silica fume: purchased from Elkem Taiwan, Taichung, Taiwan; its specific gravity was 2.1, and its chemical composition is shown in Water: general tap water, which was in line with the general quality requirements of concrete mixing water;Fine aggregate: a natural river sand with an FM value of 2.67, a specific gravity of 2.63, and a 24 h water absorption rate of 1.3%;Coarse aggregate: a natural crushed stone with a specific gravity of 2.64 and a 24 h water absorption rate of 0.7%;Lightweight aggregate: the appearance of the synthetic LWA obtained by using reservoir sediments used in this case study is shown in Superplasticizer: purchased from An-Yao Company; it met the requirements of ASTM C494-81  Type F.The materials used in this case study and their sources are described below:3, and a slag content of 90 kg/m3, while the LWC was made with a water–binder ratio of 0.39, a cement content of 296 kg/m3, and a supplementary cementitious material content of 243 kg/m3. The mix proportions of the two groups of concrete are shown in In this case study, the specimens of the control group (NC) and the experimental group (LWC) were made. Based on the design load of the prestressed box girders, the target values of the 28-day compressive strengths of the NC and LWC were 50 and 40 MPa, respectively. To ensure the strength and durability of the LWC, supplementary cementitious materials were incorporated, and a lower water-to-cement ratio was used. Considering the workability, strength, and durability of concrete, the amount of each material of the two groups of concrete was determined via trial mixing. The NC was made with a water–binder ratio of 0.36, a cement content of 364 kg/mBefore mixing the LWC, the LWAs were pre-wetted and soaked in a water tank for 24 h. During the pouring operation of the bridge, the sampling of the two groups of concrete and the preparation of the specimens were carried out simultaneously for subsequent concrete property tests. For each test age, three specimens were produced for each test. Air-dry unit weight and compressive-strength tests shared the same specimen. Three test specimens were produced for each age of compressive strength, with a total of 72 test specimens for the two groups of concrete. Three test specimens were made for each age of flexible strength, with a total of 24 test specimens for the two groups of concrete. Splitting tensile strength only produced three specimens for one test age, and the two groups of concrete had a total of six specimens. The elastic-modulus and compressive-strength tests shared the same specimen. Three specimens were produced for the drying shrinkage test, and there were six specimens in total for the two groups of concrete. In the creep test, three specimens were produced in each group, with a total of 18 concrete specimens in the two groups. The test items and specimen ages, as well as the test specifications of the basic properties and time-dependent deformation of the concrete, are shown in The air-dry unit weight of concrete cylinders (15 cm × 30 cm) at the age of 90 days was measured according to the ASTM C567 ), flexurIn essence, concrete is very chemically stable and has excellent durability. In view of this, when evaluating the durability of reinforced-concrete structures, the evaluation is mainly based on whether the steel bars are corroded and thereby damage the structure . RegardiThe ultrasonic test was carried out with reference to ASTM C597 . The ultThe chloride ion penetration test was carried out according to ASTM C1543  and CNS The configuration of the prestressed tendons of the NC and LWC prestressed box girders is shown in 3, respectively, while those of the LWC were 1817 and 1820 kg/m3, respectively. This shows that the unit weight of the LWCs was only about 76–78% of the NCs, which meant that replacing NC with LWC could reduce the weight of the whole structure by more than 20%, thereby achieving the purpose of reducing the inertial force during earthquakes. In addition, according to ACI 213R-14 [3.The test results of the air-dried unit weights of the two groups of concrete are shown in 3. Wu et al. [3. Accordingly, the compressive strength and density of the LWC in this study should be appropriate.The compressive-strength test results are shown in u et al.  used tufThe test results of the flexural strength are shown in The test results of the splitting tensile strength are shown in The elastic modulus is an important property of structural LWC in its application. The elastic modulus of LWC mainly depends on its density and strength . The tes3. However, there was a continuous supply of water in the pores of the LWAs. At the ages of 14, 28, 56, 90, 180, and 360 days, the drying shrinkage values of the LWC were 40.6%, 52.5%, 65.0%, 70.0%, 93.1%, and 109.3% of the NC, respectively. In the early stages (within six months), the drying shrinkage of the LWC was lower than that of the NC because the internal curing of the pre-soaked LWA could reduce autogenous shrinkage. But in the later period (after six months), the long-term shrinkage rate of the LWC was higher than that of the NC. This is because the LWA had lower stiffness and less restriction on the shrinkage. This is consistent with the research results in the literature [In the application of LWC, one issue worthy of attention is its potential cracking under restraint conditions. To reduce the risk of cracking, LWC must have low drying shrinkage and high tensile strength. Based on this, this study conducted a drying shrinkage test. The drying shrinkage test referred to the ASTM C157 . The speterature ,86.For accurate prestress-loss prediction, it is especially important to understand the creep behavior of concrete . The resIn order to understand the creep response of the LWC per unit of compressive stress, the value of its specific creep was also calculated, as shown in This study used an ultrasonic pulse velocity (UPV) test to evaluate the compactness of the two groups of concretes. The results of the UPV test are shown in 3. Its specimens were immersed in 20 ± 2 °C water until the testing age. The mix proportions of the cast concrete were 1:2.0:3.0:0.5 (binder: fine aggregate: coarse aggregate: W/C).The chloride ion penetration resistance test was carried out according to CNS 14795 . The sam3 at depths of 1.6–13 mm and 13–25 mm, respectively. However, under the same conditions, the chloride ions of the NC reached 1.490 and 1.420 kg/m3. The results showed that the increase in chloride ions in the LWC over a depth of 25 mm was much less than that in the NC. In other words, high-strength LWC could effectively resist chloride ion erosion. This is because although LWA has greater permeability, the protection provided by the cement matrix and the dense ITZ can enhance LWC’s resistance to chloride ion attack. This is consistent with the results in the literature [Chloride ion penetration is one of the most serious deterioration mechanisms affecting reinforced-concrete structures . Table 1terature ,103,104.In concrete, the quality of the aggregate–paste interface is a key factor affecting its long-term durability. Therefore, SEM observations were conducted on the ITZs of the two groups of concretes. The SEM observation results of the two groups of concrete after curing for 28 and 90 days are shown in In prestressed members, prestressing is the application of compressive stress to concrete in order to relieve the tensile strain caused by a load. The various reductions in the prestressing force are called the losses in prestressing, and it is an important topic in the design of prestressed members. In this case study, the prestress value, after the prestressed box girders were prestressed and anchored for 20 min, was used as the initial prestress. On the 3rd, 7th, 14th, 28th, 56th, 90th, 180th, 360th, 540th, and 720th days, prestress-loss monitoring was carried out a total of 11 times. The monitoring data are shown in The prestress-loss rates of the two groups of prestressed box girders during the two years after prestressing are shown in At present, the development of synthetic LWAs mainly uses industrial waste or municipal solid waste as raw materials. For example, slag, fly ash, reservoir sediment, waste TFT-LCD glass powder, paper sludge, tile-grinding sludge, water purification sludge, textile sludge, and other renewable resources are used to produce LWAs ,13,14,15This case study evaluated the basic mechanical properties and durability of synthetic lightweight-aggregate concrete made from reservoir sediments. It can be seen from the durability test results that the ultrasonic pulse velocity of the LWC used in this case was lower than that of the NC at different ages. However, the compactness of the LWC was estimated to be within the category of good quality based on regulatory standards. In addition, the chloride ion penetration test results showed that the probability of the chloride ion permeability of the LWC was very low at the age of 90 days. The test results using the CNS 14702 acid-soluble chloride ion content test method also showed that the increase in chloride ions inside the LWC over a depth of 25 mm was much less than that in the NC. This test result proved that the LWC used in this case study could effectively resist erosion by chloride ions and external moisture. This is consistent with the research results in the literature ,113,114.The above test results illustrated that the LWC with a compressive strength of 40 MPa was successfully manufactured from synthetic LWAs made from reservoir sediments, and its engineering properties complied with ACI 213R-14 . This inThis case study rigorously compared the durability and prestress-loss differences in NC and LWC prestressed box girders constructed simultaneously in the same area through comprehensive experimental methods. The test results verify the superiority of using synthetic LWA made from reservoir sediments in prestressed bridges. Under standard-curing conditions, the 28-day compressive strength of the LWC was 47.1 MPa, meeting the requirements of ACI 213R-14. Due to the internal-curing effect and lower elastic modulus of the LWA, the total dry shrinkage and total creep of the LWC were comparable to those of the NC. Furthermore, LWC can inhibit the infiltration of air, water, and chloride ions due to the reduced deformation and improved microstructure in its ITZ, thereby improving its durability. Notably, the magnetic-flux prestress loss of the NC prestressed box girder reached 8.1%. In contrast, the monitored values of the magnetic-flux prestress loss on both sides of the LWC prestressed box girder were 4.6% and 4.9%, respectively. This verified that, under the same environmental conditions, the use of LWC produced less of a prestress loss than the use of NC.


To describe the protocol for a multi-centre randomised controlled trial to determine whether treatment protocols monitoring daily CRP (C-reactive protein) or PCT  safely allow a reduction in duration of antibiotic therapy in hospitalised adult patients with sepsis.Multicentre three-arm randomised controlled trial.UK NHS hospitals.Hospitalised critically ill adults who have been commenced on intravenous antibiotics for sepsis.Three protocols for guiding antibiotic discontinuation will be compared: (a) standard care; (b) standard care + daily CRP monitoring; (c) standard care + daily PCT monitoring. Standard care will be based on routine sepsis management and antibiotic stewardship. Measurement of outcomes and costs. Outcomes will be assessed to 28 days. The primary outcomes are total duration of antibiotics and safety outcome of all-cause mortality. Secondary outcomes include: escalation of care/re-admission; infection re-lapse/recurrence; antibiotic dose; length and level of critical care stay and length of hospital stay. Ninety-day all-cause mortality rates will also be collected. An assessment of cost effectiveness will be performed.In the setting of routine NHS care, if this trial finds that a treatment protocol based on monitoring CRP or PCT safely allows a reduction in duration of antibiotic therapy, and is cost effective, then this has the potential to change clinical practice for critically ill patients with sepsis. Moreover, if a biomarker-guided protocol is not found to be effective, then it will be important to avoid its use in sepsis and prevent ineffective technology becoming widely adopted in clinical practice. Choosing the right antimicrobial drugs and doses is crucial because inappropriate antibiotic therapy is associated with two-to-fourfold increase in risk of death under these circumstances.Early, appropriate antimicrobial treatment for infection is a crucial part of emergency interventions aimed at improving sepsis survivorship. Fixed duration antibiotic courses (up to 14 days in some circumstances) have been widely used in the NHS because clinical signs and microbiology culture tests are not sufficiently useful for monitoring treatment efficacy in order to guide the decision to stop the administration of antibiotics. Daily clinical review of treatment and patient progress, performed alongside microbiology results and advice, do provide opportunities to limit patient exposure to broad-spectrum antibiotics while tailoring effective therapy for a proven infection – the so-called ‘Start smart - then focus’ approach.5Once commenced, the optimum duration of antibiotic treatment is less certain. This provides a potential opportunity to personalise the duration of antibiotic therapy which could lead to reductions in population antibiotic usage, adverse effects for patients, improved healthcare resource utilisation and downstream benefits relating to antimicrobial resistance – an urgent priority. These biomarkers, however, are part of a complex inflammatory response triggered not only by infection but by other stimuli such as trauma and surgery. Thus, unnecessarily prolonged antibiotic treatment may be commenced if guided solely by raised levels of these biomarkers as part of antibiotic initiation/escalation protocols. Alternatively, biomarker-guided antibiotic discontinuation protocols for critically ill patients have been associated with shorter treatment durations in some healthcare systems internationally8 and reduced mortality, but studies are at high risk of bias9 and with uncertain relevance to NHS practice. There is thus a need for a multicentre randomised controlled UK trial to determine whether an antibiotic treatment protocol based on monitoring CRP or PCT might safely allow a reduction in the duration of antibiotic therapy in patients with sepsis.Readily available circulating serum proteins such as C-reactive protein (CRP) and procalcitonin (PCT) – the most intensively researched biomarkers – are often raised in sepsis and usually fall in response to effective treatments.To determine whether treatment discontinuation protocols based on monitoring CRP or PCT in hospitalised adult patients with suspected sepsis reduces the duration of antibiotic therapy compared with standard care while maintaining treatment safety as measured by mortality 28 days after randomisation.To determine adherence to biomarker treatment protocols and their effects on antibiotic consumption, infection and antibiotic adverse events, critical care and hospital length of stay, acquisition cost of antibiotics, longer-term mortality and cost-effectiveness in the NHS setting.Standards of Reporting Trials) statement. Trial conduct has been planned in full conformance with the principles of the Declaration of Helsinki and Good Clinical Practice.This is a multicentre prospective, individual patient randomised, 3-arm, controlled, intervention-concealed clinical and cost effectiveness trial. The trial is managed by the Warwick Clinical Trials Unit and sponsored by the University of Manchester. The funding is provided by the National Institute for Health Research (NIHR) following a commissioned call from the Health Technology Assessment programme (15/99/02). The NHS main contractor is the Northern Care Alliance NHS Foundation Trust. The trial is coordinated by a Trial Management Group (TMG) and independent oversight is provided by a Trial Steering Committee (TSC) and a Data Monitoring Committee (DMC). The trial has been designed and will be reported in line with the CONSORT  antimicrobial therapy ;Severely immunocompromised not caused by sepsis (e.g. neutropenia less than 500 neutrophils/µl);Any patient given, or anticipated to receive an IL-6 receptor inhibitor drug (e.g. tocilizumab or sarilumab) during their acute hospital admission;All treatments for suspected sepsis likely to be stopped within 24 h of its initiation because of futility;Consent declined; orPreviously enrolled into this trial.Co-enrolment of study participants into other trials will be considered by the TMG using national guidance.Blood will be drawn daily in every trial patient participant from randomisation until discontinuation of antibiotics for the sepsis episode or discharge from hospital. The clinicians responsible for managing patients will receive daily standardised advice from the local research team on either standard care or on biomarker-guided antibiotic discontinuation. Advice will be based on daily serum testing of either (a) PCT or (b) CRP or (c) ‘no test’ (control group). The antibiotic discontinuation protocols are described alongside the standardised written advice for each group in Procalcitonin arm. Standard care with daily serum PCT measurement until antibiotic discontinuation or hospital discharge. Daily feedback to clinical team based on PCT discontinuation protocol .CRP arm. Standard care with daily serum CRP measurement until antibiotic discontinuation or hospital discharge. Daily feedback to clinical team based on CRP discontinuation protocol .For the randomly allocated intervention arms, patient research blood collection (minimum of 2 ml research sample per day) and serum biomarker laboratory testing (PCT or CRP) will commence within the first 24 h following the initiation of intravenous antibiotics for sepsis. Daily research blood sampling, laboratory testing and subsequent advice in every patient will continue until antibiotics for the sepsis episode have been discontinued. Research blood sampling will not recommence if antibiotics are subsequently re-introduced within the 28-day study period following patient randomisation. If a participant is discharged from hospital on a course of antibiotics for the initial sepsis episode, the trial intervention will cease at the time of discharge. Phlebotomy and samples will be handled in line with agreed local standard care practice.Daily blood sampling and delivery of sample to the laboratory. No biomarker testing of sample and feedback to clinical team will be based on usual care protocol . Patients will be reviewed daily by their medical team with documented decisions on antibiotic treatment guided by standard clinical assessment and review of microbiological culture results. Routinely available laboratory data, such as white blood cell counts, will remain part of standard care for all patients recruited to our proposed trial because these are part of the current standard of NHS care for patients with sepsis. Daily clinical review of all patients with sepsis, as a standard-of-care, will allow incorporation of the intervention protocols for daily assessment of antibiotic discontinuation described in Patients recruited to both control and intervention arms will receive standard NHS care for sepsis and antibiotic stewardship will follow Public Health England (PHE) guidance.Clinical effectiveness: Total duration (measured in days) of antibiotic treatment to 28 days following randomisationSafety: 28-day all-cause mortality following randomisationEffectiveness and safety outcome measures to 28 days following randomisation:Antibiotic duration (measured in days) and dose (measured as Defined Daily Dose) for the sepsis episodeTotal antibiotic dose (measured as Defined Dailey Dose)Unscheduled care escalation/re-admissionInfection relapse/recurrence requiring further antibiotic treatmentSuper-infection defined as new infection at a different anatomical siteSuspected clinically relevant antibiotic adverse reactionsTime to ‘fit’ for hospital dischargeAll-cause mortality will be determined at 90 daysHealth care system benefit outcomesAssessment of in-trial cost effectiveness (see below)Critical care unit length and level of stayHospital length of stay (days)Safety reportingSupplemental Material)Adverse event data .A total sample size of 2760 will be required to detect both a mean of 1-day (0.93 days to be precise) reduction in antibiotic duration  and a non-inferiority safety margin of 5.4%  assuming 28-day mortality is 15% in both arms (see ), (ii) recruitment centre and (iii) surgery within the last 72 h or not. Allocation concealment will be provided by a centralised 24-h web-based randomisation system located at Warwick Clinical Trials Unit.Patient participants will be allocated at random to PCT, CRP and usual care groups in a 1:1:1 ratio using a computer-generated randomisation sequence produced by the minimisation method. Stratification factors will be (i) sepsis severity  and standard care plus biomarker-guidance (CRP and PCT intervention groups), to maintain group concealment. Research blood samples will be allocated a unique research study number and will be transported to the laboratory. The research number will not reveal the identity of the patient to laboratory staff. A sample will be collected and transported to the laboratory each day for every recruited patient (control and intervention groups) until antibiotics are discontinued by the clinical team responsible for patient care.The trial website will be the route for routine reporting of research laboratory results and web-based automated advice will be generated for the clinical research teams daily for each patient. Automated, real-time, web-based, centre-specific, time-adaptive phasing factors will be used to maintain group concealment based on the speed of assays (CRP or PCT interventions) or no assay (control) for advice delivery. The clinical research team will deliver the daily written standardised advice to the clinicians responsible for patient care as described in Study biomarker values will not be reported back to routine clinical service or patient care records.Screening; recruitment; reasons for exclusion and intervention adherence will be audited throughout the study by using data recorded in screening logs, Case Report Forms (CRFs) and during site visits. Intervention adherence will be captured using specific data recorded in the CRFs of adherence to biomarker-guided advice on antibiotic discontinuation – and reasons for non-adherence will be documented if it occurs. These surveys indicated that CRP monitoring has not been used in the NHS as part of any defined antibiotic discontinuation protocols and there is considerable variation in CRP use in this setting. In addition, routine daily PCT measurement has not been widely adopted across the NHS to guide antibiotic duration decisions for sepsis, although the availability of PCT assays in the NHS has increased recently. Therefore, while we expect study centres to adopt a position of equipoise during the trial in terms of both protocolised CRP and PCT guided decisions on antibiotic duration, we accept that CRP may be measured outside of the study protocol if the treating clinician believes that this is an important part of a patient’s care. Any non-trial use of CRP in standard care that could impact on antibiotic treatment duration decisions will be recorded in the CRF and will be monitored at each site by the research team.A particular challenge for trials incorporating biomarker-guided antibiotic discontinuation protocols in sepsis is the variable but common use of CRP monitoring in this patient group, as identified by two independent national surveys of (a.) NHS hospitals and (b.) NHS clinical biochemistry service laboratories. Therefore, maintaining equipoise for the purposes of this trial involves avoiding PCT use in recruited patients. Any non-trial use of PCT to 28-days post randomisation will be reported as a protocol deviation and will be monitored at each site by the research team.The non-trial use of PCT presents a particular challenge because it has the potential to influence antibiotic treatment duration decisions. For non-trial use, study centres with access to routine PCT are likely to use identical PCT-guided antibiotic stopping rules to those in the trial protocol and that are recognised internationally.Data will be collected using a local paper CRF and web-based secure remote data capture system. Clinical data will be collected up to 28 days after randomisation as outlined in the study schematic  and detaPatient data on disease severity will be collected using the Case Mix Programme  and its equivalent in Scotland (Scottish Intensive Care Society Audit Group). All-cause mortality rates at 90 days will be collected using NHS Digital and equivalents in Northern Ireland and Scotland.The Medicines and Healthcare products Regulatory Agency (MHRA) confirmed that their approval for the trial is not required because clinical decisions about antibiotic initiation and drug choice are not the object of this study and will be at the clinical judgement of the treating clinicians.Ethical approval was from South Central – Oxford C Research Ethics Committee (REC) on 20th October 2017, Integrated Research Application System (IRAS) UK 209815 REC Ref: 17/SC/0434, and IRAS (Scotland) 234179, REC Ref: 17/SS/0125.The ADAPT-Sepsis trial aims to determine whether a treatment protocol based on monitoring CRP or PCT safely allows a reduction in duration of antibiotic therapy in adult patients with sepsis and to assess cost effectiveness. This will be the largest randomised trial evaluating biomarker-guided antibiotic discontinuation in sepsis to date. Based on this review, subsequent NICE guidance concluded that there is currently insufficient evidence to recommend routine adoption of PCT in the NHS. Furthermore, NICE recommended that research should be performed within the NHS for guiding decisions to stop antibiotic treatment in people with confirmed or highly suspected sepsis. NICE guidance also recognised that CRP is very likely to be monitored in the NHS during sepsis care, but there is a paucity of prospectively tested CRP-based algorithms and interventional data regarding efficacy and safety for guiding antibiotic duration. Therefore, the ADAPT-Sepsis trial has been designed to respond to these evidence gaps identified by NICE and has been funded by NIHR HTA following a specific commissioning brief call (15/99).The evidence-base for biomarker-guided antibiotic duration in sepsis was considered in a recent NIHR HTA commissioned systematic review. of intervention trials in sepsis revealed that PCT algorithms are based on multiple decision thresholds to guide antibiotic treatment in trial intervention arms, with final treatment decisions always remaining at the discretion of the treating clinician. Detailed PCT algorithms varied between studies; however, all discontinuation algorithms included a component that encouraged or strongly encouraged discontinuation of antibiotics when the PCT level was <0.25 µg/l and/or encouraged discontinuation of antibiotics when the PCT level was <0.5 µg/l. A fall in PCT from baseline by ⩾80% was incorporated into some algorithms to encourage antibiotic discontinuation.The health technologies being assessed are routinely available laboratory measured PCT and CRP-guided antibiotic discontinuation protocols aimed at safe reductions in antibiotic treatment duration. Antibiotic discontinuation protocol design was informed by the best available evidence. For PCT, a systematic review A CRP-based algorithm was compared with a PCT-guided algorithm in determining antibiotic duration – with both algorithms including antibiotic discontinuation rules based on relative declines and absolute biomarker thresholds. The CRP protocol had an absolute treatment discontinuation threshold at ⩽ 25 mg/l and relative discontinuation threshold when CRP fell by at least 50% from baseline. We could find no other prospectively tested CRP-based algorithm reporting interventional data regarding efficacy and safety for guiding antibiotic discontinuation.To the best of our knowledge, there is only one randomised trial using CRP-guided antibiotic treatment discontinuation in sepsis.810 ADAPT-Sepsis is the first trial internationally to incorporate an intervention concealment strategy aimed at reducing the risk of bias, improving trial quality and delivering the best evidence for patient care.The trial will adopt two threshold levels for both PCT and CRP antibiotic discontinuation guidance to embrace the best evidence identified by NICE and to align treatment advice that facilitates a biomarker intervention concealment strategy . RandomiIn conclusion, if this trial finds that a treatment protocol based on monitoring CRP or PCT safely allows a reduction in duration of antibiotic therapy, and is cost effective, then this has the potential to change clinical practice in terms of how patients with sepsis are managed. Moreover, if a biomarker-guided protocol is not found to be effective, then it will be important to avoid its use in sepsis and prevent ineffective technologies becoming widely adopted in clinical practice.Click here for additional data file.Supplemental material, sj-docx-1-inc-10.1177_17511437231169193 for biomArker-guided Duration of Antibiotic treatment in hospitalised Patients with suspecTed Sepsis (ADAPT-Sepsis): A protocol for a multicentre randomised controlled trial by Paul Dark, Gavin D Perkins, Ronan McMullan, Danny McAuley, Anthony C Gordon, Jonathan Clayton, Dipesh Mistry, Keith Young, Scott Regan, Nicola McGowan, Matt Stevenson, Simon Gates, Gordon L Carlson, Tim Walsh, Nazir I Lone, Paul R Mouncey, Mervyn Singer, Peter Wilson, Tim Felton, Kay Marshall, Anower M. Hossain and Ranjit Lall in Journal of the Intensive Care SocietyClick here for additional data file.Supplemental material, sj-docx-2-inc-10.1177_17511437231169193 for biomArker-guided Duration of Antibiotic treatment in hospitalised Patients with suspecTed Sepsis (ADAPT-Sepsis): A protocol for a multicentre randomised controlled trial by Paul Dark, Gavin D Perkins, Ronan McMullan, Danny McAuley, Anthony C Gordon, Jonathan Clayton, Dipesh Mistry, Keith Young, Scott Regan, Nicola McGowan, Matt Stevenson, Simon Gates, Gordon L Carlson, Tim Walsh, Nazir I Lone, Paul R Mouncey, Mervyn Singer, Peter Wilson, Tim Felton, Kay Marshall, Anower M. Hossain and Ranjit Lall in Journal of the Intensive Care Society


We observed a rebound in consumption of antibacterials for systemic use (ATC J01) in the community sector in the European Union/European Economic Area during 2021 and 2022, after an observed decrease between 2019 and 2020. The rates in 2022 returned to pre-COVID-19-pandemic levels and were exceeded in 13 countries. Although these patterns could partly be a result of changes in disease transmission during the study period, it could also reflect a lost opportunity to strengthen and reinforce prudent antibiotic use. In 2020, coinciding with the first year of the COVID-19 pandemic, the European Union (EU)/European Economic Area (EEA) saw a significant decrease in antibiotic consumption in the community sector [To better understand these changes, and specifically the timing and magnitude of the rebound period in 2021 and 2022, we analysed community sector consumption of antibacterials for systemic use group  group J01), quantified as defined daily doses (DDD) per 1,000 inhabitants per day   set an EHowever, between 2019 and 2022, we observed a high variability in the EU/EEA population-weighted mean community antibiotic consumption , in contIn the EU/EEA overall, as in 15 individual countries , there was no or marginal (less than +/−3%) change in antibiotic consumption between 2020 and 2021, while a rebound, that is, going back to the pre-pandemic levels of 2019, was apparent between 2021 and 2022 . The rebound occurred earlier between 2020 and 2021 for six countries . In contrast, five countries  reported a continued decrease in antibiotic consumption between 2020 and 2021  before a rebound in 2022  average and 3.At the EU/EEA level, there were no significant differences in 2022 consumption compared with the pre-pandemic quantities in 2019 for any of the antibiotic groups except for ‘macrolides, lincosamides and streptogramins’ (ATC group J01F), for which there was a statistically significant higher consumption in 2022 than in 2019 (p = 0.029). For individual countries, a more heterogeneous pattern was observed, with 13 countries reporting a higher consumption of macrolides, lincosamides and streptogramins in 2022 than in 2019 . Of thesThe unusual fluctuations seen in the EU/EEA antibiotic consumption between 2019 and 2022 highlight the need to better identify and understand the factors influencing antibiotic consumption in a pandemic context. The initial decrease in antibiotic consumption during the first phase of the COVID-19 pandemic has been attributed to non-pharmaceutical interventions generally reducing the spread of pathogens ,7, as weAlthough the resurgence of both viral and bacterial respiratory tract infections during the latter part of our study period -14 mightThere is a lack of patient-level information including prescription indications and actual use of antibiotics in ESAC-Net data, which derive mainly from sales and reimbursement records. Therefore, it is not possible to determine to which extent the observed rebound effect was driven by disease patterns or changes in behaviours. Nonetheless, observed variations across countries, both in the reduction of antibiotic consumption in 2020 and the subsequent rebound, suggest variations in potential inappropriate antibiotic use across countries. The 13 countries in which the rebound effect led to higher antibiotic consumption in 2022 compared with 2019, as well as the countries with the most ambitious reduction targets set out in the EU Council recommendation, now need to intensify measures to reduce unnecessary antibiotic use.Although the overall community antibiotic consumption increased from 2021 to 2022 in all studied EU/EEA countries, there was variation in the start of rebounds before 2022 and in the antibiotic subgroups involved in the rebounds. These differences suggest that the drivers of antibiotic consumption are country-specific, which might lead to variations in their trajectories of antibiotic consumption.Variations in consumption between 2019 and 2022 were also observed at antibiotic subgroup level, which reflects the complexity of reducing antibiotic consumption. At the EU/EEA level, the surge in consumption of ‘macrolides, lincosamides and streptogramins’ (ATC group J01F) in 2022 was largely driven by macrolide consumption -18. It iThe COVID-19-pandemic had a substantial impact on community antibiotic consumption in the EU/EEA between 2020 and 2022. Countries exhibited different patterns of antibiotic consumption, underlining the importance of understanding each country in its own context. Further examination into local prescribing and consumption behaviours for specific antibiotic groups can inform effective stewardship interventions and bring the EU/EEA closer to its antibiotic consumption targets for 2030.


Due to the reported decrease in the duration of primary care visits, it is important to assess provider adherence to guidelines when treating respiratory infections that are unlikely to necessitate antimicrobial treatment. This study aimed to investigate the relationship between the duration of visit and unnecessary antibiotic prescribing while considering patient and provider factors, including age, sex, race, and diagnosis.This retrospective, cross-sectional study used outpatient, office-based data from the National Ambulatory Medical Care Survey from 2009 to 2016. All patients with a primary diagnosis of bronchitis, viral respiratory tract infection, influenza, and viral pneumonia were included for analysis. Patients with diagnoses that almost always require an antibiotic were excluded. Diagnoses were identified using ICD-9 or ICD-10 codes. Inappropriate antibiotic use was identified using multum codes and defined as at least one prescribed oral antibiotic during the visit. Provider status was defined as physician only or other provider. Multivariate logistic regression was used to determine predictors of inappropriate antibiotic prescribing. Data weights were applied to all analyses to generate national estimates.A total of 226,250,589 patient visits were included in the analysis, of which 83,404,484 (36.9%) resulted in an inappropriately prescribed antibiotic. Patients prescribed antibiotics were older (median age 42 vs. 13 years) and more often White (82.4% vs. 79.6%). After adjustment for covariates, time spent with provider less than 15 minutes , patient age 18-64 years , other provider types only , and viral pneumonia diagnosis  were most strongly associated with inappropriate antibiotic prescribing.This study found that patients who spent less time with providers, had viral pneumonia, and were aged 18-64 years old were more likely to receive inappropriate treatment. Further investigation is necessary to determine reasons for inappropriate antimicrobial prescribing among outpatients.Kelly Reveles, PharmD, PhD, Ferring Pharmaceuticals: Advisor/Consultant|Ferring Pharmaceuticals: Honoraria


This study investigated the structural behavior of a beam–slab member fabricated using a steel C-Purlins beam carrying a profile steel sheet slab covered by a dry board sheet filled with recycled aggregate concrete, called a CBPDS member. This concept was developed to reduce the cost and self-weight of the composite beam–slab system; it replaces the hot-rolled steel I-beam with a steel C-Purlins section, which is easier to fabricate and weighs less. For this purpose, six full-scale CBPDS specimens were tested under four-point static bending. This study investigated the effect of using double C-Purlins beams face-to-face as connected or separated sections and the effect of using concrete material that contains different recycled aggregates to replace raw aggregates. Test results confirmed that using double C-Purlins beams with a face-to-face configuration achieved better concrete confinement behavior than a separate configuration did; specifically, a higher bending capacity and ductility index by about +10.7% and +15.7%, respectively. Generally, the overall bending behavior of the tested specimens was not significantly affected when the infill concrete’s raw aggregates were replaced with 50% and 100% recycled aggregates; however, their bending capacities were reduced, at −8.0% and −11.6%, respectively, compared to the control specimen (0% recycled aggregates). Furthermore, a new theoretical model developed during this study to predict the nominal bending strength of the suggested CBPDS member showed acceptable mean value (0.970) and standard deviation (3.6%) compared with the corresponding test results. The building industry is continually developing new composite structural members to replace conventional members  for a variety of reasons, including cost, availability of materials in the market, ease of fabrication, higher strength, better durability, and environment effects . In 1989Furthermore, concrete-filled steel tube (CFST) members showed sufficient structural behavior under different types of bending loads ,16,17,18According to the literature, existing studies investigated the bending behavior of CFST beams and concrete-filled PDS slabs separately. Recently, Liejy et al.  investigIn this study, six (6) full-scale beam–slab specimens were prepared using double steel C-Purlins beams connected from top to flange with profile steel sheet (PSS) deck slabs covered with dry board (DB) sheets. Each specimen was filled with a concrete mixture containing 0%, 50%, or 100% recycled aggregate. In addition, each specimen’s beam was fabricated with two pieces of C-Purlins either connected face-to-face or separated. The investigated CBPDS specimens’ nomenclature is described in This study adopted a new technique for filling CBPDS specimens with concrete that provided several equally distributed (40 × 80 mm at 340 mm c/c) openings along the contact surface between the deck slab and the beam, as shown in 3), and crushed limestone coarse aggregates . A high water/cement ratio (0.5) was used to increase the concrete mixture’s workability while it was poured inside the CBPDS specimens. In this study, combinations of four different waste materials were used as recycled aggregates , as shown in 3 for the CCA, 9.5 kg/m3 for the EPS, 600 kg/m3 for the CRA, and 1220 kg/m3 for the FGA. Three different concrete mixtures were prepared, each containing a different amount of recycled aggregates  which were replaced by volume with raw fine and raw coarse aggregates. The concrete mixtures were mainly prepared using Malaysian Portland cement (MS EN 197-1 CEM II/B-L 32.5N), washed sand , and tension stresses at bottom flanges of the C-Purlins beam part (CB). Generally, this performance was observed for all specimens regardless of the recycled aggregate composition of their concrete cores , and for both C-Purlins beam configurations. The specimens with double C-Purlins filled with the highest percentages of recycled aggregates (specimens CBPDS-DF100 and CBPDS-DS100) showed a typical steel outward buckling failure similar to the corresponding control specimens CBPDS-DF0 and CBPDS-DS0 (0% recycled aggregates), as compared in In addition, the same failure mode was observed for specimens CBPDS-DS0, CBPDS-DS50, and CBPDS-DS100 (double separate beam). However, the concrete core of these beams experienced earlier cracking failure than those with face-to-face connections; the latter configuration achieved better concrete confinement behavior, as it was fabricated in a tube shape ,45. GeneGenerally, CBPDS specimens’ bending behavior was expressed as a moment–deflection relationship, as shown in u) obtained at the peak values of all tested specimens’ moment–deflection curves are recorded in u values of the CBPDS specimens based on their infill concrete mixture  and according to their C-Purlins beam configuration (CBPDS-DF and CBPDS-DS). Generally, regardless of the C-Purlins connection type, specimens’ Mu values decreased as the recycled aggregate content increased, which is logical, as the concrete’s compressive strength usually decreased accordingly, as shown earlier in u value decreased approximately 7% when 50% of the raw aggregate was replaced with recycled aggregates, from 51.5 kN.m for specimen CBPDS-DF0 (control specimen) to 47.7 kN.m for specimen CBPDS-DF50. The Mu value decreased approximately 11% (46.1 kN.m) when 100% recycled aggregate was used (specimen CBPDS-DF100). Therefore, it can be concluding that replacing 100% of the raw aggregate with a combination of recycled aggregates reduced the suggested composite beam–slab specimens’ concrete cores’ self-weight by approximately 15%; their Mu values decreased approximately 9–11% with little effect on overall bending behavior.The ultimate bending strengths (Mu) to that at the yielding limit (δy) [Typically, for all tested specimens, the DI value was estimated from the deflection ratio at the ultimate bending limit (δmit (δy) , as illun) of the investigated composite beam–slab member (CFST beam carrying a PSSDB/PDS slab). Therefore, in this study, a new theoretical model was developed using the stress block theory, as shown in This model is limited to the concrete-filled composite CBPDS specimens prepared with rectangular steel tube beams and PSS deck slabs covered with dry board (DB) sheet subjected to static bending loads.The concrete cores achieved full interaction with the steel tube beams and PSS deck slabs, as no slip failures were recorded for the tested specimens see .The steel tube beams achieved full interaction with the PSS slabs, as no horizontal/vertical separations were recorded for the tested specimens see .The effects of C-Purlins lips were ignored.The effects of the infill concrete section below the NA was ignored, as it was subjected to tension stress and faced cracking failure .y-CB at the C-Purlins’ bottom flange (maximum tension stress) [s-pss), as it has not reached the yield limit  , as the cu and 0.8fu-DB is adopted for the concrete-filled PSS slab and DB sheet, respectively, as no crush failures were recorded for these two sections until the end of specimen tests  is assumed to be located at the beam–slab connection level (connection level of C-Purlins with PSS), as previously discussed in To simplify this model, the position of NA  equal to 0.8 and 0.7 are suggested for predicting the MThe steel tube members were classified as either slender, non-compact (semi-compact), or compact sections, according to how they buckle under compression stress ,49. SpecCB-flangeFy-CB . A CB-flange= fy-CB . (tCB . WCB)= f(only the bottom flange area)CB-webFy-CB . A CB-wed= fy-CB . (2 . tCB . DCB) . 0.5= fPSSFs-pss. A PSS= fy-CB/DCB .DPSS) . A PSS (excluded the bottom flanges area)= (fconFcu . A con= 0.8fcu . (3. (Wpss-t + Wpss-b)/2 . DPSS) . 0.5= 0.8fDBFu-DB . A DB= 0.8fu-DB . (beff .tDB)= 0.8fCB-flangeYCB-flange from the N.A = the distance of FCB − 1/2.tCB= DCB-webYCB-web from the N.A = the distance of FCB= 2/3.DPSSYPSS from the N.A = the distance of FPSS= 2/3.DconYcon from the N.A = the distance of FPSS= 2/3.DDBYDB from the N.A = the distance of FPSS + 1/2.tDB= DØ = 0.8 for CBPDS specimens (double face-to-face C-purlins beam) 0.7 for CBPDS specimens (double separate C-purlins beam)Based on the above assumptions and details presented in n values of the investigated CBPDS specimens are predicted using the new analytical model and compared with those obtained from the corresponding test results in The M➢Filling CBPDS specimens with infill material containing 50% and 100% of recycled aggregate had little effect on their flexural behavior. Thus, using a combination of different recycled aggregates  in the specimens’ concrete cores achieved a sufficient contribution, by reducing their self-weight approximately 15–18% and using less raw aggregate, which was considered an environmental improvement.➢Increasing the recycled aggregate content of the CBPDS specimens’ concrete materials to 50% and 100% reduced their ultimate bending strength by approximately 7–11% compared to the control specimen, due to reductions in their concrete compressive strengths. However, the specimen beams with double separate C-Purlins sections had slightly lower bending capacities than those with face-to-face connections. For example, the specimen with face-to-face C-Purlins beam and filled with 100% recycled concrete materials (CBPDS-DF100) achieved bending capacity equal to 46.1 kN.m, where this capacity reduced to 43 kN.m only when the C-Purlins beams were separated (CBPDS-DS100).➢Accordingly, the CBPDS specimens’ ductility indexes were reduced with increases of recycled aggregate content in their concrete cores; this is due to the reduction in their bending capacities. For example, the CBPDS-DF specimen filled with normal concrete (0% recycled aggregates) achieved a ductility index equal to 4.4, and this value reduced to 4.1 and 3.4 when the same specimen was filled with concrete mixture content 50% and 100%, respectively, of recycled aggregate.➢Based on the available experimental results, the newly developed theoretical model reasonably predicted the nominal bending capacity of the composite CBPDS with an acceptable mean value (0.970) and standard deviation (3.6%).➢Notably, further investigations are required for these composite CBPDS specimens concerning the influence of varied parameters and loading scenarios that have not yet been studied. The developed theoretical model needs further validation with more empirical and numerical data for improvement, in order to make it generally applicable to this type of composite beam–slab system (CFST beam carrying PDS slab system).The conclusions are summarized as follows:


Chloride ion attack is a major cause of concrete durability problems, and existing studies have rarely addressed the effects of damage zones. In this paper, an improved mesoscale model including five phases was constructed using the finite element software ABAQUS to study the diffusivity of chloride ions in cracked concrete. It was found that the damage zone is negligible when the crack width is less than 50 μm, while the width and depth of the damage zone are about 15 times the crack width and 15% of the crack depth when the crack is greater than 50 μm. The results show that the diffusion of chloride is greatly influenced by the crack width, while it is little-influenced by the crack shape. Low water–cement ratio and adequate hydration of the concrete are also key factors affecting chloride diffusion. In contrast, regular rounded aggregates have a positive effect on reducing chloride diffusion compared to irregularly shaped aggregates, and this effect becomes weaker with increasing service time. In addition, the protective layer can effectively prevent the diffusion of chloride in concrete. Therefore, when designing marine concrete, efforts should be made to ensure that the concrete has a low water–cement ratio, adequate hydration, less cracking and a protective layer. Chloride-induced corrosion of steel bars is a major cause of reduced durability of marine reinforced concrete (RC) , and bilRCs have extremely complex structures. At the microscopic scale, RCs can be seen as a unity of a solid matrix and micropores. Chloride diffusion is strongly dependent on the microstructural features. Tan et al.  reportedUnlike microscopic models, concrete is usually modeled at the mesoscale as a unity of four phases, including artificial cracks (ACs), cement paste (CP), aggregates (AGGs) and interfacial transition zones (ITZ) . It has It is important to note that existing studies rarely consider the effect of damage zones. It is crucial to construct a suitable model to predict the exact effect of different factors on chloride diffusion in cracked concrete. In this work, an improved five-phase mesoscale model including DZs is proposed to investigate the exact effect of different factors on chloride diffusion in concrete. The paper will be organized as follows. First, the propagation of the DZ is determined based on the comparison of experimental and simulation results. The reliability of the model is further verified by another set of experimental results. Then, using this model, the effects of the width as well as shape of the ACs, the water–cement ratio, the degree of hydration, the shape of the AGG and the protective layer on chloride diffusion are systematically investigated. Finally, based on the in-depth understanding of the above fundamental issues, valuable information for designing marine concrete will be presented. These insights on the exact effect of different factors on chloride diffusion should provide useful information for the design of marine concrete with appropriate compositions.ACs were created by inserting copper sheets of different widths into cylindrical concrete specimens  in experiments . The depW/C) [wAC and DAC, respectively.The model was constructed as follows. First, a three-phase model containing AGG, ITZ and CP was constructed by running a homemade program in ABAQUS software. (version number: ABAQUS 2020) Then, the other two phases, DZ and AC, were created by splitting two isolated regions in the CP. The cross section of this model is shown in W/C) . In the W/C) . Here, tW/C) . The widIn the numerical simulation, according to the mass diffusion equation and Fick’s law of diffusion, the concrete is considered to be fully saturated and only diffusion between seawater and concrete occurs . After t(a)ACsConsidering the differences in the five phases and their distinct effects on chloride diffusion, the following three factors are considered in constructing models:Under external loads, the width and depth of ACs are positively correlated within a certain range . The wid(b)Water–cement ratioW/C) and the degree of hydration (α) [W/C is 0.3 [W/C and α on chloride diffusion, four sets of samples with W/C of 0.3, 0.4, 0.5 and 0.6, respectively, were considered. For each sample, α was set to 0.8, 0.85 and 0.9, respectively.The porosity and pore structure of concrete are closely related to the water–cement ratio (tion (α) . It has C is 0.3 . The inc(c)AGG shapeIn real cases, AGG particles are not uniform in size and shape. To evaluate the possible influence of shape, AGGs with random shapes were also considered. The same gradation and volume ratio were adopted as that of the circular AGGs.DCP, m2/s) based on the general effective medium theory, treating CP as a two-phase material composed of capillary pores and solid cement gel [VP is the porosity of CP, W/C is the water–cement ratio and α is the degree of hydration.The specific model in this work consists of five phases. The diffusion behavior of chloride ions in each phase is completely different. For CP, Zheng and colleagues obtained an analytical solution for the chloride diffusion coefficient  and depth (fixed at 20 mm) as reported in . Peng et−11 m2/s, and is 6.56 × 10−10 m2/s, 1.06 × 10−9 m2/s, 1.23 × 10−9 m2/s and 2.22 × 10−9 m2/s in each of the four ACs. The simulation time was 37 days. The obtained diffusion depths of chloride in concrete with 4 different ACs are shown in The concrete was epoxy-coated except for the bottom surface and placed in a 1% chloride solution to ensure that the chloride diffused only in the direction perpendicular to the bottom. The chloride diffusion coefficient in CP is 1.34 × 10(a)The simulation results of this work are closer to the experimental data than , especia(b)There is a difference between the simulation results and the experimental data at the initial simulation time, which is more pronounced in the case with a smaller AC see a. This dThe resulting numerical model was used to simulate chloride diffusion in concrete. Data were collected on days 6, 12, 18.5, 25, 31 and 37, respectively. For clarity, the chloride distributions obtained at 6 days, 18.5 days and 37 days are shown in The above points show that the model can accurately describe the chloride diffusion behavior in concrete, especially when the immersion time is long and the AC is large. In the next section, we will turn to study the influence of different factors on the diffusion of chloride ions.−11 m2/s. The diffusion coefficients of chloride in different ACs can be calculated from Equation (3). The details of the four AC, DZ and chloride diffusion coefficients are summarized in In general, the wider the AC, the deeper the AC. To study the effect of cracks of different widths and depths and to further validate the reliability of the model, we constructed another set of ACs reported in . The widIt clearly shows that the diffusion depth increases with the AC depth . Taking It can be observed that the chloride concentration drops sharply with increasing depth, and the rate of decline decreases with increasing depth. For the same diffusion depth, the concentration of chloride ions increases with AC width. Taking a depth of 10 mm as an example, the chloride ion concentrations in concrete with ACs of 49.0 μm and 392 μm are 2.13‰ and 3.82‰, respectively. Note that the chloride concentration in the free solution was set to 1%. Therefore, the width and depth of ACs have a significant effect on the chloride diffusion in concrete.To further demonstrate the good reliability of our model, the experimental concentration of chloride ions  and the The simulation results of our model can describe the diffusion behavior of chloride ions well, especially in deeper regions (see data represented by solid lines and diamonds in each inset). These results again demonstrate the good reliability of our model and the necessity of considering the DZ effect when simulating chloride diffusion in concrete, especially with larger ACs.2.In the above discussion, the shape of the AC was simplified to a rectangle to save computational cost. However, in practical situations, ACs have various shapes, which may in turn affect chloride diffusion in concrete. To study the effect of AC shape, we here constructed ACs of six shapes, including rectangular (R), ladder-shaped (L), triangular (T), zigzag (Z), Y-shaped (Y) and branched (B)  is an important parameter that determines the mechanical properties of concrete, such as strength, hardness and durability, and has a great influence on the permeability of concrete [α) is another parameter closely related to porosity [W/C ratios and three α for each W/C ratio are considered. A rectangular AC with a width and length of 102.9 µm and 36.6 mm, respectively, was introduced into the concrete. The diffusion coefficient of chloride ions in AC is 12.5 × 10−10 m2/s. The diffusion coefficients of chloride ions in CP  calculated from Equations (1) and (2) are summarized in The water–cement ratio  and 15 mm (α = 0.9), respectively. To further clearly present the relationship between diffusion depth and water–cement ratio, the diffusion depths in concrete with different W/C ratios are shown as inset in W/C ratio.A quick look at the diffusion maps shows that chloride diffusion in concrete increases with W/C ratio, the degree of hydration has much less effect on chloride diffusion. To show this effect more clearly, the chloride diffusion depth in concrete with the same W/C ratio is shown in W/C ratio, the diffusion width is slightly larger in case with smaller α, and this trend is more pronounced when the W/C ratio is high. Another feature observed in W/C was a key parameter for designing concrete for marine environments [Compared with ronments .In the above discussion, all the simulations were performed by simplifying the AGGs to a regular sphere; however, in the real cases, the AGGs are usually irregular polyhedrons with different sizes and shapes. To evaluate the effect of different shapes on chloride diffusion in concrete, we modified the model here to replace regular AGGs with randomly shaped AGGs.The construction principle is to ensure the same gradation and volume ratio are the same as those of regular AGGs. Data were collected at 30, 60 and 90 days, respectively. The diffusion cloud maps of chloride are shown in An obvious difference between the simulation results and the experimental results is that, in the initial simulation stage, the simulation results are larger than the experimental results see . This diIn real cases, the concrete used in marine environments is coated with protective layer to reduce seawater corrosion . SchuereThe obtained outermost contours of chloride diffusion with and without PL are shown in (1)The damage zone around the crack is negligible when the crack width is less than 50 μm, but is not negligible when the crack width is greater than 50 μm. The propagation of the damage zone is about 15 times and 15% of the crack width and depth, respectively;(2)The chloride diffusion in concrete is greatly affected by the depth and width of cracks, and is hardly affected by the shape of cracks. Both the diffusion depth and concentration of chlorides increase with crack width;(3)The water–cement ratio also has a significant effect on the chloride diffusion in concrete. As the ratio increases, the diffusion depth increases almost linearly. For cement with the same water–cement ratio, the degree of hydration has little effect on the chloride diffusion depth, but can affect the diffusion width. The higher the degree of hydration, the narrower the diffusion width;(4)The AGG shape has a small effect on chloride diffusion. The diffusion in concrete with irregular aggregate is a little more serious than that in concrete with regular aggregate. The difference becomes smaller as the soaking time increases.In summary, an improved mesoscale model including a damage zone was proposed to simulate the diffusion behavior of chloride ions in concrete. The propagation of the DZ was determined from experimental data. Using this model, we studied the exact effects of cracks, water–cement ratio and aggregate shape on the chloride diffusion in concrete. The following results can be obtained:


The usage of weakly bonded ultra-high strength (WBUHS) rebars has emerged as a promising approach to enhance the resilience of concrete components due to their remarkable mechanical properties. To promote the application of WBUHS rebars, this paper presented an investigation on the seismic behavior of circular concrete columns reinforced with squarely arranged WBUHS rebars and externally confined by bolted steel tubes. Eight columns, including two reinforced with normal strength (NS) rebars and six reinforced with WBUHS rebars, were fabricated and tested under reversed cyclic lateral loading. Experimental results showed that the columns reinforced with WBUHS rebars exhibited remarkable drift-hardening capacity up to the drift of at least 5% as well as significantly reduced residual deformation even when subjected to relatively high axial compression with an axial load ratio of 0.33 in comparison to the traditional ductile columns reinforced with NS rebars. Notably, the precast columns reinforced with WBUHS rebars, with an embedment length of 20 times their diameter, behaved nearly identically in terms of resilience as cast-in-place columns. Additionally, a numerical analysis was performed to assess the hysteretic performance, and the analytical results, with consideration for the slippage of WBUHS rebars, were capable of capturing the hysteretic performance of test columns. As suggested from the recent catastrophic earthquakes, such as the 2008 Wenchuan earthquake, the 2011 Great East Japan earthquake, and the 2023 Turkey–Syria earthquake [The concept of “resilient cities” has garnered increasing attention within seismic design because it puts emphasis on reducing the permanent post-earthquake deformation and swift restoration of essential building functions ,5. NumerThe strengthening and/or repair of earthquake-damaged RC and masonry structures have experienced dramatic growth because of the frequent occurrence of earthquake disasters ,15. Init2) as well as low bond strength (3.0–4.0 N/mm2), relative to normal strength (NS) rebars [Another innovative alternative to materialize resilient concrete components involves the use of weakly bonded ultra-high strength (WBUHS) rebars with spiral grooves on their surfaces, the key aspect of which lies in their high yield strength 1275 N/mm) rebars . The for) rebars ,27,28,295 N/mm re) rebars . HoweverIn the meantime, there is a growing trend towards increased adoption of prefabricated and modular buildings, primarily motivated by the desire to enhance construction quality and reduce construction timelines. Consequently, it is of great significance to materialize the prefabrication of resilient structures reinforced with WBUHS rebars. Moreover, previous research has emphasized that achieving the optimal mechanical properties of UHS rebars requires secure anchoring with sufficient anchoring length at the ends ,32,33. TBased on the aforementioned background, the primary objectives of this research are: (1) to verify the resilience (referred to as drift-hardening capacity and self-centering capacity) of both cast-in-place and precast columns, and (2) to evaluate the seismic behavior of test columns using an analytical method capable of considering the slippage of WBUHS rebars. To this end, a total of eight concrete columns were fabricated and tested under reversed cyclic lateral loading, with experimental variables including reinforcement types (NS rebar or WBUHS rebar), axial load ratios (0.20 or 0.33), construction methods (cast-in-place or prefabrication), and shear span ratios (1.7 or 2.5). Of them, two ductile concrete columns were reinforced with NS rebars and confined by bolted steel tubes to serve as reference specimens, while the other six concrete columns were reinforced with WBUHS rebars and confined by bolted steel tubes to enhance their resilience. The test results were discussed in terms of hysteretic behavior, residual deformation, strain of reinforcements, equivalent viscous damping coefficient (EVDC) and axial deformation. Furthermore, a numerical analysis was performed to evaluate the hysteresis performance of test columns, and the comparison between analytical and experimental results was discussed.A total of eight concrete columns were designed, each composed of a loading stub of 400 × 350 × 350 mm, a circular column with a diameter of 300 mm, and a footing of 1000 × 540 × 400 mm (or 1000 × 500 × 400 mm for the specimens with a shear span ratio of 2.5). Both NS rebars and WBUHS rebars were squarely arranged and transversely confined by D6 deformed rebars with a hoop spacing of 100 mm, meeting the requirements of the hoop reinforcement ratio specified in the AIJ code . For NS For the purpose of preventing the early crushing of cover concrete and pursuing significant resilience up to large drift, all the specimens were externally confined by steel tubes with a thickness of 2.3 mm (PL2.3), to give a volumetric ratio of 3.1%. The steel tubes were fabricated by joining two premanufactured semicircular plates through HS bolts and nuts, and steel plates with 9 mm thickness (PL9) were added to prevent the local buckling of the flange see . To prev2 and a maximum coarse aggregate particle size of 20 mm, which is commonly employed for constructing the main supporting members. On the basis of the test performed on three cylinders (100 mm in diameter and 200 mm in height), the actual compressive strength (c′f) of the concrete for each loading day is presented in The specimens were cast using ready-mixed concrete with a nominal strength of 27 N/mmR, calculated by dividing the lateral displacement (Δ) at the loading point by the shear span (a). Two complete cycles were applied within 2% drift, followed by one cycle at subsequent drifts of 2.5%, 3%, 3.5%, 4%, 5% and 6%.The test apparatus and loading program of the test columns are illustrated in Δ) at the loading point and four vertical DTs (3–6) were placed to measure the axial deformation between the loading stub and footing. DTs (7–9) were used to monitor the displacement variation of the footing in real time during the loading process. Strain gages were attached to NS rebars, WBUHS rebars and steel tubes to serve the subsequent analysis of their mechanical properties.The location of displacement transducers (DTs) and strain gages is displayed as a/D = 1.7 became more pronounced and the corresponding range also expanded. Because a larger axial load ratio results in a higher stress level for the concrete in compressive side [Due to the confinement of steel tubes, it was challenging to observe the damage condition of the specimens during the loading process. ive side ,36.The measured lateral force versus drift relationships of the specimens are illustrated in The six concrete columns reinforced with WBUHS rebars exhibited ever-increasing lateral resistance without strength degradation but slow-growing residual deformation even up to a large drift of 5% , impn = 0.33 showed higher moment resistance, as the higher axial compression consistently led to a larger neutral axis depth or depth of compression zone. The residual drift was compared in Since the self-centering capacity was closely related to the behavior of reinforcements, the strain distribution of reinforcements along the column height at several controlling drifts was plotted in As drawn in As a critical index for evaluating the energy dissipation of engineering components, equivalent viscous damping coefficient (EVDC) of test columns was calculated following the method proposed by Chopra  and was n = 0.20 generally leveled off as drift increased. The columns with n = 0.33 showed increasing axial strain because an increase in the axial load will impose more compressive stresses on the column cross-section. However, the maximum axial strain was restricted to within 0.3% even when deformed to a drift of 4%, far below the peak strain of confined concrete. This suggests that the confinement effect provided by steel tubes can provide the resilient columns good axial stability at large drifts.The axial deformation between the footing and loading stub was measured via the average of the readings from four vertical DTs (3–6) see b when eaAccording to the fact stated in In this method, the following basic assumptions are made: (1) only WBUHS rebars resist tensile stress; (2) only the concrete part of the section remains plane after bending; (3) the constitutive laws of WBUHS rebars and concrete, respectively, follow the models proposed by Menegotto and Pinto  see Figa, and SuK) calculated based on the Sakino–Sun model (derived from welded steel tubes) [K value based on the Sakino–Sun model was adopted for the subsequent numerical analysis [It is worth highlighting that the strength-raising coefficient (l tubes)  tends toanalysis .The schematic diagram of section division and strain distribution are depicted in 1.Divide the column into three regions and discretize the joint and rocking region equally into tiny segments see a.2.oε at the center of section, and obtain the strain distribution of concrete cε along the depth of section  and slip 0S (=JS) of the WBUHS rebar in the first segment of the joint region. According to the relationships between the stress (k+f1) and slip (k+S1) listed by Equations (2) and (3), it is necessary to judge whether the boundary condition (see Equation (4)) is satisfied, if not, regive a 0f and 0S and repeat this process until Sn+1 = 0 is satisfied. Then the strain of WBUHS rebar sε can be obtained from the constitutive law.Give an initial stress kf and k+f1 represent the stress of the WBUHS rebar in the k-th segment and k + 1-th segment, respectively; kS, k+S1 and Sn+1 represent the slip of the WBUHS rebar in the k-th, k + 1-th and n + 1-th segment, respectively; kτ is the bond stress in the k-th segment; l represents the length of each segment; and d is the diameter of WBUHS rebar.4.0S (=RS) of the WBUHS rebar in the first segment of the rocking region based on Equation (5). The stress 0f (=Rf) of the rebar in the first segment of the rocking region can be computed by the same procedure shown in step (3).Calculate the slip RS and JS represent the slip of the WBUHS rebar in the rocking and jointing region, respectively; and sε and cε represent the strain of concrete and WBUHS rebars in the hinge region, respectively.5.Jf = Rf was satisfied.Obtain the target value of strain and stress of the WBUHS rebar assumed in step (3) by repeating steps (3)–(4) until 6.cF and sF borne by concrete and WBUHS rebars.Calculate the force 7.N = cF + sF was satisfied. If not, reassign a new center strain oε and repeat the process from step (2).Verify whether 8.V based on Equations (6) and (7).Calculate lateral force sf and cf represent the stress of WBUHS rebars and concrete, respectively; sA and cA represent the area of WBUHS rebars and concrete, respectively; sh and ch represent the distance from the acting point of force borne by WBUHS rebars and concrete to the neutral axis, respectively; N represents the applied axial force.9.R.Repeat the above steps until the target Exp.”, and the analytical results include two cases: one with consideration for the slippage of WBUHS rebars ”) and one without ”). On the one hand, the traditional analysis method, neglecting the bond–slip behavior of reinforcements ”), can effectively track the hysteretic performance of the two ductile concrete columns. However, it not only seems to overestimate the residual deformation and energy dissipation capacity but also results in an overestimation of the lateral resistance of the concrete columns reinforced with WBUHS rebars by 26.9–37.3%. On the other hand, the analysis results with consideration for the slippage of reinforcements ”) is capable of capturing the hysteretic performance of the test columns reinforced with WBUHS rebars, characterized by both remarkable drift-hardening capacity and an evident pinching effect.Anal. (no slip)” exhibits good agreement with the experimental results of the NS rebars strain, but the strain of WBUHS rebars increases at a rapid rate and reaches the yield strain at a drift lower than 2%, which inevitably leads to an overestimation of the lateral resistance at the early cyclic loads as compared with experimental results. The analysis result taking into account the slippage of reinforcements ”) can well predict the strain development trend of WBUHS rebars, indicating the validity and accuracy of the FSE method adopted in this paper.The phenomenon described above can be further explained by the comparison of reinforcement strain presented in This paper investigated the seismic behavior of circular concrete columns reinforced with WBUHS rebars and confined by bolted steel tubes. Eight concrete columns were fabricated and tested under reversed cyclic lateral loading simultaneously subjected to constant axial compression. Based on the experimental and analytical results, the following conclusions can be drawn.As compared with traditional ductile concrete columns, the concrete columns reinforced with WBUHS rebars exhibited significant drift-hardening capacity as well as self-centering capacity up to the drift of at least 5%.If the embedment length of the WBUHS rebar was 20 times its diameter, the precast concrete columns could exert almost the same excellent seismic performance as cast-in-place columns.The test columns under higher axial compression showed comparatively serious concrete damage, but larger moment resistance.The analytical results, considering the slippage of reinforcements, effectively predicted the strain development trend of WBUHS rebars, and demonstrated good agreement with the hysteretic performance of test columns reinforced with WBUHS rebars.In light of the significant drift-hardening capacity and good self-centering capacity exhibited by the concrete columns reinforced with WBUHS rebars and confined by steel tubes. The use of resilient concrete columns developed in this paper is applicable to the ground floors of mid- and high-rise buildings to reduce the need for maintenance and repairs, particularly for structures in high seismic-intensity areas.