Staphylococcus aureus or the less-virulent coagulase-negative staphylococci. Rapid identification and methicillin susceptibility determination with the Xpert MRSA/SA BC assay can improve management of S. aureus bloodstream infection and reduce inappropriate antibiotic use.Positive blood cultures showing Gram positive cocci in clusters signifies either We prospectively evaluated the Xpert MRSA/SA BC assay in comparison with culture, on samples referred to our laboratory in the Western Cape, South Africa. We interviewed attending clinicians upon culture result availability, to assess antibiotic choices and estimate potential impact of the assay.S. aureus 15/15, methicillin-susceptible S. aureus 42/42, coagulase-negative staphylococci 170/170). Time to final result could be reduced by approximately 30 h with the assay. Of the 178 patients with adequate antibiotic history, optimisation of antistaphylococcal therapy could have occurred more than 1 day sooner in 68.9% with S. aureus bloodstream infection . Six of the 11 patients with methicillin-resistant S. aureus bloodstream infection (54.5%) could have received anti-MRSA cover sooner. Fifty-four days of antibiotic therapy could have been spared, equating to 0.3 days  saved per patient, driven by broad-spectrum beta-lactams .Of the 231 samples included, there was 100% concordance between the Xpert MRSA/SA BC assay and culture (methicillin-resistant S. aureus bloodstream infection should be assessed.This assay has potential as an antimicrobial stewardship tool; costing and impact on clinical outcome in patients with The online version contains supplementary material available at 10.1186/s12879-021-05857-7. Staphylococcus aureus is a common cause of bloodstream infection (BSI) [on (BSI) , with a on (BSI) . In contS. aureus in positive blood culture broths showing Gram positive cocci in clusters (GPCC) on Gram stain, typically requires assessment of morphological and biochemical characteristics after overnight incubation. In addition, susceptibility testing is required to differentiate between methicillin-susceptible and methicillin-resistant S. aureus . These requirements can result in delayed initiation of appropriate therapy in patients with S. aureus BSI, with potentially adverse outcomes including secondary infectious complications [Differentiating between CoNS and ications , a higheications . Conversspa and the SCCmec-orfX junction (for S. aureus), and mecA (for methicillin resistance). Published studies, summarised in one paper [mec variants, were resolved in 2013 [The Xpert MRSA/SA BC System  differentiates between MRSA, MSSA and CoNS from positive blood cultures within approximately 1 h, using a real-time, semi-automated, nucleic acid-based test which targets ne paper , report We evaluated the Xpert MRSA/SA BC System (Xpert) and assessed the potential impact of implementation of this test as an antimicrobial stewardship tool in the patient population served by our laboratory in Cape Town, South Africa.S. aureus bloodstream infection, and reducing inappropriate antibiotic therapy in those with S. aureus and with coagulase-negative staphylococci. We performed a prospective observational study to evaluate the Xpert against the reference method of culture-based techniques, and to describe the potential impact of implementation of this assay in our setting by combining clinical history with attending clinician survey.We aimed to assess the performance and role of the Xpert in facilitating more appropriate antibiotic use in patients with The study took place from January to June 2016 at the National Health Laboratory Service (NHLS) Microbiology laboratory at Tygerberg Hospital in the Western Cape, South Africa. Tygerberg Hospital is a 1384-bedded referral hospital serving the northern and eastern subdistricts of the Cape Metro region, and the surrounding rural districts, including 4 regional hospitals and 17 district hospitals.Blood culture bottles were submitted from facilities throughout this drainage area at the clinicians’ discretion. The automated blood culture system in use is the BacT/Alert 3D Microbial Detection System  which includes anaerobic (FN Plus), aerobic (FA Plus) and paediatric bottles (PF Plus). These were kept at room temperature during transport, and were incubated as soon as possible after specimen receipt. After flagging positive, Gram stains are performed on an aliquot of the broth. All patients with positive blood cultures exclusively showing GPCC on Gram stain, were included. Blood culture specimens showing mixed morphology on Gram stain, and duplicate blood culture samples from the same patient, were excluded.Paediatric patients were defined as patients below the age of 13 years.Patients with positive blood cultures (indicating suspected sepsis) were defined as having community-acquired (CA) infection if the culture was collected < 72 h after admission, and hospital acquired (HA) infection thereafter; admission within the preceding 6 weeks was also considered a criterion for HA infection  .S. aureus was likely. During the study period, standard-of-care was to administer a carbapenem +/− vancomycin (for suspected MRSA) for presumed hospital-acquired sepsis.Empiric management of CA infections was based on local guidelines, with ceftriaxone or amoxicillin-clavulanate used for most infections; cloxacillin was recommended where Regional hospital guidelines in our drainage area advise a targeted approach of a semi-synthetic beta-lactamase stable penicillin (cloxacillin) for MSSA BSI, with vancomycin advised for MRSA BSI.Consecutive samples were processed in parallel using culture-based methods and Xpert, during weekdays between 8 am and 4 pm. The investigator performing the Xpert was blinded to the culture results.Culture-based methods entailed inoculation and overnight incubation of basic enriched agar media; Kirby-Bauer disk diffusion testing of an aliquot of broth against a standard anti-staphylococcal antibiotic panel; and identification using DNAse and Mannitol Salt Agar (MSA) plates. A rapid latex agglutination test was performed using the Pastorex Staph Plus kit  for indeterminate identification results. VITEK 2 Gram positive ID confirmation  was used at the discretion of the clinical microbiologist, and methicillin susceptibility was determined by cefoxitin disk diffusion testing using the Clinical and Laboratory Standards Institute (CLSI) guidelines .Batched Xpert testing was performed on blood culture bottles, which were stored at 35 °C following culture-based processing. The Xpert MRSA/SA BC G3 version 5  was performed as per manufacturer’s instructions. Briefly, 50 μl of blood culture broth was added to the vial containing the elution reagent and vortexed for 10 s. The contents of the vial were transferred to the test cartridge and loaded into the module. Xpert testing was performed as soon as possible after positivity; there was a maximum delay of 80 h for bottles flagging positive over a weekend. The results of the Xpert assay were not made available to the clinicians.The results of these methods were interpreted as summarised in Table S. aureus sepsis, or if the patient was admitted in an Intensive Care Unit (ICU). In all other cases, clinicians were contacted with the culture result, whether S. aureus or CoNS.As per standard practice, clinicians were contacted with the Gram stain result if the available clinical information or previous results suggested Modification: a change from an ineffective to a more effective agent, or the addition of a semisynthetic penicillin (MSSA) or glycopeptide (MRSA);De-escalation: a change in antibiotic to a narrower-spectrum, targeted antistaphylococcal agent, or cessation of some or all antibiotics;No change: no change to the empiric antibiotic regimen, or no antibiotics prescribed if the patient was not receiving antibiotics.Basic clinical and demographic information were obtained, including an antibiotic history. We surveyed the attending clinicians to assess whether knowledge of the culture and susceptibility result on the day the bottle flagged positive would have impacted antibiotic choice. This was categorised as:We regarded cephalosporins (with the exception of ceftazidime), beta-lactam–beta-lactamase inhibitors, carbapenems and vancomycin as being active against MSSA. Penicillin, ampicillin, amoxicillin, and ceftazidime were the beta-lactam agents regarded as being ineffective against MSSA.CoNS were considered significant only if reported as the likely cause for the patient’s clinical condition, as judged by the attending clinician.Days of antibiotic therapy saved were also evaluated during clinician interview, based on the empiric antibiotic regimen commenced and on clinician opinion as to whether an earlier result would have impacted antibiotic choice or duration .www.vassarstats.net) and EpiCalc 2000 v1.02  were used, with an α-level of 0.05 chosen. Continuous numerical variables were summarised using means and standard deviations for normally distributed variables, or medians and interquartile ranges (IQR) for variables not following a normal distribution. Binary categorical variables were summarised using proportions and 95% confidence intervals (CI). Comparison of selected independent proportions were evaluated using the z-test.Microsoft Excel, VassarStats  demonstrated only GPCC on Gram stain and 231 samples were included in the study  due to convenience sampling. Selected variables were compared between the participants included in the study and all patients for whom blood cultures were submitted showing Gram positive cocci in clusters on Gram stain, between January and June 2016. No differences in age, gender or ward location per organism type at blood culture sampling were noted, with the exception of a larger proportion of coagulase-negative staphylococci from patients admitted to surgical wards  and high care units/ICU  in the study population. Contribution of the bottle types is outlined in Table A valid Xpert result was initially obtained from 225/231 bottles . Of the remaining 6 assays, 2  were invalid  and were not repeated. Four were resulted as “error” with signal loss after initial amplification; two provided a valid result after repeat testing. The conservative failure rate was 1.7% (95% CI 0.7–4.4%), with 227 bottles yielding an interpretable result.Klebsiella pneumoniae (Gram negative bacilli missed on Gram stain) and a CoNS; the Xpert correctly assessed the CoNS.MSSA was present in 42 samples  and MRSA in 15 . CoNS were present as the sole isolate in 169 patients, and were part of mixed cultures in an additional 4 cases. Three of these 4 mixed cultures contained MSSA together with CoNS, were detected as MSSA by the Xpert, and were included as MSSA in the analysis. The fourth culture contained There was 100% concordance between the systems for the identification of MSSA, MRSA and CoNS. The Xpert assay had an overall sensitivity of 100% , and specificity of 100% . The positive and negative predictive values of the assay were both 100% (95% CIs 93.7–100% and 97.8–100% respectively). Analysis by MSSA, MRSA and CoNS is summarised in Supplementary Table mecA and methicillin resistance in CoNS, for the 169 isolates in which cefoxitin susceptibility on culture was known. The gene target, mecA, was detected in 85 of 88 CoNS isolates that were cefoxitin-resistant on culture  giving a positive predictive value of 86.7% (95% CI 78.6–92.1%). The specificity of detection of mecA in CoNS on Xpert was 84.0% (95% CI 74.5–90.4%) with a negative predictive value of 95.8% (95% CI 88.3–98.6%).We performed a subanalysis of The median time between blood culture positivity and final result authorisation was 31.3 h (interquartile range (IQR) 20.7–42.5 h).Of the 227 patients included, 50.7%  were males. The median age of the adults included was 43.0 years (IQR 31.0–58.0); the median age of the paediatric population was 71.5 days (IQR 17.8–325.0). Twenty-five adults  and 10 children  were admitted to an ICU at the time of blood culture collection. Sepsis was CA in 51.1% , HA in 38.3% ; and unknown in the remaining 10.6% . Only 1/11 with MRSA BSI reportedly had CA onset of infection .Adequate history regarding source of sepsis was obtained for 195 patients. Sixty-two patients  had an unclear source of sepsis. Respiratory tract infection was the most commonly identified suspected source overall  and in CA-infection . For HA-infection, 29 patients  had no clear source of sepsis; of those with known primary sources, the major foci were the respiratory tract and skin or skin structures .S. aureus BSI. The most commonly identified suspected source of sepsis  was skin or skin structure infection , followed by suspected respiratory tract infection . Source was undetermined at the time of clinician interview in 8 patients with S. aureus BSI (17.4%).Information on the suspected source of sepsis was obtained in 46 patients with Characteristics of the included patients can be found in Supplementary Table Adequate antibiotic history was obtained in 181 patients, including 34 with MSSA and 11 with MRSA BSI. Three patients were unclassified due to discordance between culture result, clinical history and antibiotic therapy; these were excluded from the analysis . The impact of the Xpert could be discerned by proxy if culture result availability approximated availability of the Gram stain result . Analysis by organism category  can be found in Supplementary Table The antibiotic changes over time are summarised in Fig. Most patients with MRSA BSI did not receive an MRSA-active agent until release of the final culture result Table . CessatiEmpiric cover: Empiric vancomycin was prescribed unnecessarily in 3/34 ; this could have been avoided if Xpert was used.In response to Gram stain availability: 2/34  received modifications to their antibiotic regimens in response to Gram stain result availability. In one case, vancomycin was started when the Gram stain became available, for suspected HA-sepsis. In the second, a non MSSA-active beta-lactam agent (ampicillin) was changed to an MSSA-active agent (cefotaxime).○ De-escalation to a semisynthetic penicillin in 18/25 ○ Modification to a more effective agent in the remaining 7/25 In response to final culture result availability: Overall, there was a change in antibiotic therapy on final result in 25 patients . These could have occurred at least 1 day earlier had the Xpert assay been used.For the 34 patients who had MSSA BSI, notable aspects of the antibiotic regimen include:Antibiotics were stopped in 13/133 patients on release of the final result indicating CoNS .S. aureus BSI and known antibiotic history could have received more appropriate antistaphylococcal therapy 1 day sooner, with adoption of the Xpert assay . Eleven of the 45 patients  were not receiving an agent with activity against their pathogen following Gram stain result availability (6 patients with MRSA and 5 with MSSA BSI).Overall, 31/45 patients with In the 178 patients with known antibiotic history, at least 32 days of exposure to a broad spectrum beta-lactam  could have been spared with earlier knowledge of the final result, equating to a reduction in broad spectrum beta-lactam use in 18.0% of the patients in this study .A further 5 days of vancomycin use could have been avoided, and 17 days of antibiotic therapy could have been spared for the other agents ; however, it must be noted that this is a conservative estimate as all beta-lactam agents were considered to have activity against MSSA in this analysis, although they may not be equally suitable for the treatment of MSSA BSI and some are associated with a higher odds of death [To our knowledge, this is the largest study assessing the potential impact of this assay to date. The median time saving to final result with use of this assay was approximately 30 h if the Xpert assay was performed immediately after microscopy, in line with previous estimates of a time saving of 24–48 h . This crof death .S. aureus therapy.More rapid administration of appropriate therapy can significantly impact mortality. In one study, the mean mortality rate was 59% for patients with MRSA BSI who were initially started on a semisynthetic penicillin, as opposed to 23–36% for patients initially started on vancomycin . The meaS. aureus BSI infection, this may still be regarded as advantageous, particularly when considered with the consequences of unnecessary antibiotic prescription.We estimated a reduction in broad spectrum beta-lactam antibiotic use in 18.0% of the cohort where antibiotic history was available, with 54 days of antibiotic therapy saved. This translates to a modest reduction in antibiotic days of therapy of 0.3 days per patient. When combined with the benefits shown in optimising therapy for We initially expected this assay to be of most use in reducing antibiotic therapy in patients with CoNS, as has been reported previously , but thiThe potential benefits described must be weighed against the expense of the assay, including additional labour, infrastructure and consumable costs. The total cost of the test may be prohibitive in a resource-constrained setting such as our own.S. aureus BSI rate was only 25.1% of all blood cultures with Gram positive cocci in clusters, and that methicillin resistance was detected in 26.3% of all S. aureus-containing blood cultures (similar to a contemporaneous study in our setting (27.1%) [Limitations to this study include that the  (27.1%) ); this r (27.1%) . SecondlS. aureus from CoNS on positive blood cultures with Gram positive cocci in clusters and in detecting methicillin resistance in S. aureus, and the assay may be an effective antimicrobial stewardship tool. Further studies may need to be performed in areas with differing blood culture contamination and MRSA rates. We demonstrated potential benefit in reducing time to appropriate therapy in the majority of patients with S. aureus bloodstream infection. Antibiotic modification based on the clinical response may have played a role in amplifying or attenuating the benefit observed in this study. We showed a modest reduction in antibiotics prescribed; studies limited to a more homogenous population may show a greater benefit. Additional studies assessing potential impact should focus on individual patient clinical status and outcomes, and should take into account source control, cost reduction in terms of antibiotic administration and hospital stay, and comprehensive costing.The Xpert MRSA/SA BC assay performed well in differentiating Additional file 1: Table S1. Diagnostic accuracy of the Xpert MRSA/SA BC assay on positive blood cultures containing Gram positive cocci in clusters on Gram stain, compared with culture-based methods (n = 227). A summary of the results of the evaluation of the Xpert assay for methicillin-resistant S. aureus, methicillin-susceptible S. aureus and coagulase-negative staphylococci.Additional file 2: Table S2. Characteristics of the included patients with blood cultures containing Gram positive cocci in clusters (n = 227). A summary of the basic demographic characteristics of the patients included in the diagnostic evaluation of the Xpert MRSA/SA BC assay, and the suspected source of sepsis in the 195 patients with clinical history on source of sepsis.Additional file 3: Table S3. Patients with Gram positive cocci in clusters on blood culture and adequate antibiotic history who were excluded from impact analysis due to discordance between culture result, clinical history and antibiotic therapy (n = 3). Further details on the three patients with adequate clinical history pertaining to antibiotic use who were excluded from analysis due to inconsistency between culture result, clinical history and antibiotic therapy.Additional file 4: Table S4. Evolution of antimicrobial therapy on Gram stain and culture result availability, in patients with Gram positive cocci in clusters on blood culture and known antibiotic history (n = 178). Action  in the 178 patients with known antibiotic history, in response to Gram stain and culture result release.Additional file 5: Table S5. Contribution of antibiotic agents to the days of antibiotic therapy saved in patients with known antibiotic history (n = 178). A summary of antibiotic days potentially saved, by antibiotic type, in this cohort with use of the Xpert MRSA/SA BC assay.


Older adults, particularly those from low-income communities, are disproportionately negatively affected by natural disasters. As the older adult population grows and natural disasters increase in frequency and intensity, social workers must consider their role in supporting the needs and safety of this population. Social workers practice in varied roles including policy advocate, service broker, and educator, all of which are crucial in disaster management. This systematic review summarizes the literature on the social work profession’s involvement with emergency management with older adults, and identifies gaps. Using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, authors searched AgeLine, CINAHL Complete, MEDLINE, PsycINFO, and Social Work Abstracts for peer-reviewed publications between January 1, 2009 and March 1, 2020. Examples of the terms searched include social work*, respon*, prepar*, disaster, crisis, emergency, geriatrics and older adults. The initial searches yielded 298 publications. After removing duplicates and screening articles for relevance based on titles and abstracts, 21 publications were retained for full review. A total of 11 articles met inclusion criteria. The body of literature identified was small. The majority of the publications constituted conceptual papers, textbook reviews, and letters to editors requesting greater emphasis on emergency management. Only three empirical studies were identified. Broadly, the publications discussed: (1) policies and resources; (2) needs; (3) capacity across practice settings; and (4) interventions. Findings reveal an underdeveloped area of social work practice, and highlight opportunities for researchers and practitioners to define gerontological social workers’ role in emergency management and detail best practice guidelines.


Mycobacterium tuberculosis isolate belonged to lineage 3 and harbored streptomycin resistance. We recommend reverse zoonosis prevention and determination of whether lemurs are able to maintain M. tuberculosis infection.We diagnosed tuberculosis in an illegally wild-captured pet ring-tailed lemur manifesting lethargy, anorexia, and cervical lymphadenopathy. Whole-genome sequencing confirmed the  Lemur catta) held at a nongovernmental organization facility in Southwestern Madagascar. The University of San Diego  provided ethics authorization (no. IACUC 0619-01).Tuberculosis (TB) is an ancient disease affecting a plethora of domestic and wild animals, including humans. In primates, TB can cause severe multisystemic disease. The prevalence of TB in lemurs within Madagascar is unknown; the most recent documented case occurred in 1973  (https://www.nanoporetech.com) long-read sequencing. We basecalled raw data using ONT Guppy software version 3.4.5. We performed read mapping using minimap2 version 2.17. For decontamination, we used a manually curated database including viral nontuberculosis mycobacteria and human sequences, augmented with L. catta genome (GenBank accession no. PVHV00000000) to improve host DNA filtering. Decontaminated reads were mapped to the M. tuberculosis H37Rv reference genome (accession no. NC_000962.3); we called single-nucleotide polymorphisms (SNPs) using bcftools version 1.10 (http://samtools.github.io/bcftools/bcftools.html) and masked repetitive regions (https://www.mykrobe.com) and confirmed streptomycin resistance (causative variant R83P/CCG4407954CGG) (M. tuberculosis lineage 3 consensus sequence to GenBank (accession no. PRJNA659624).We confirmed TB infection by PCR on the lymph node sample using GeneXpert MTB/RIF assay . However, lineage 3 isolates were previously isolated in humans from other regions of Madagascar (Suricata suricatta), banded mongoose (Mungos mungo), and Asian elephants (Elephas maximus)  in Madagascar, given the potential for reverse zoonotic and zoonotic transmission of TB and other infectious diseases.We present anatomopathologic and molecular diagnostics evidence that wild-born lemurs can become infected with and die from complications of TB. To minimize risk for transmission of TB between humans and lemurs, we recommend enforced prohibition of keeping wild-captured lemurs as pets, systematic clinical screening and microbiological testing of facility-based animals and staff who become ill, and necropsy of deceased lemurs. Because we do not know if lemurs are able to maintain M. tuberculosis infection in a ring-tailed lemur, Madagascar. Additional information about


T2 spectrum distribution curve gradually moves right, and the signal intensity of the larger pores increases.In order to study the deterioration and mechanism of dry–wet cycles and sulfate attack on the performance of concrete in seaside and saline areas, the deterioration of compressive strength of concrete with different water cement ratios under different erosion environments (sodium sulfate soaking at room temperature and coupling of dry–wet cycling and sodium sulfate) was studied here. At the same time, ICT  and NMR (nuclear magnetic resonance) techniques were used to analyze the internal pore structure of concrete under different erosion environments. The results show that the compressive strength under different erosion environments increases first and then decreases, and the dry–wet cycle accelerates the sulfate erosion. With the increase of dry and wet cycles, larger pores are filled with erosion products and developed into small pores in the early stage of erosion; in the later stage of erosion, the proportion of larger pores increases, and cracks occur inside the sample. In the process of sulfate soaking and erosion, the smaller pores in the concrete account for the majority. As the sulfate erosion continues, the  Concrete has become the most widely used engineering material due to its advantages of fast setting and hardening, low price, and good durability ,2,3,4,5.There are high concentrations of sulfate in the soil and groundwater in coastal areas, saline soil areas, acid rain coverage areas . ConcretSulfate corrosion is one of the main factors which affect the durability of concrete and the coupling between dry–wet cycles, and sulfate shows strong harm and complex mechanisms in corrosion of concrete. Therefore, it is of great significance to carry out research on the deterioration of concrete under the coupling of sulfate erosion and the dry–wet cycle. Many researchers have made a lot of achievements in the study of sulfate-eroded concrete ,12,13,14The appearance of concrete deterioration is the reduction of macro mechanical properties, while the reason for deterioration is the change of internal structure. At present, with regard to the mechanism research of sulfate eroding concrete, micro-analysis mainly for the composition and microstructure of erosion products is by technical means such as SEM ,25,26, XIn this paper, the deterioration of concrete with different mix ratios is considered under two erosion environments . The macroscopic performance of sulfate-eroded concrete is characterized by the compressive strength; at the same time, the evolution of the internal pore structure of concrete after sulfate-eroded is analyzed by ICT and NMR techniques.Ordinary Portland 42.5R cement was used in this experiment. Its chemical composition and main physical and mechanical properties are shown in 3 were used as coarse aggregates. The fly ash was produced by Weihe Power Plant in Shaanxi, China. Its chemical composition and physical properties are shown in Natural river sand with fineness module of 2.8 was used as fine aggregate. Natural crushed stones with continuous grading between 5 and 20 mm and bulk density of 1720 kg/mThe polycarboxylate superplasticizer was produced by Shandong Yousuo Chemical Technology Co., Ltd. The technical parameters are shown in Water to cement (W/C) ratios of 0.50 and 0.45 were adopted in this test, as shown in Two water to cement ratios, two erosion environments, and four different erosion ages were considered. Three samples were prepared for compressive test under each condition. Forty-eight samples were prepared in total.After pouring, the concrete specimens stood for 24 h and were then demolded. All specimens were put into a standard curing box for 28 days, with the temperature of 20 ± 2 °C and a relative humidity of 95%.2SO4 solution at room temperature (Group J), and the other group was under the coupling environment of dry–wet circulation and Na2SO4 solution erosion (Group D). The Na2SO4 solution in both groups had a mass fraction of 5%. During the erosion process, the solution was replaced every 30 days to prevent the concentration change of Na2SO4.The cured samples were divided into two groups. One group was immersed in Na(1)Immerse the cured sample in sodium sulfate solution for 15 h at a temperature of 25 °C.(2)Discharge the solution immediately after soaking and then air dry for 1 h.(3)Dry the sample at a temperature of 80 °C for 6 h.(4)After that, the samples were cooled by air for 1.5 h, and finally cooled for 0.5 h, with the cooling temperature of 25 °C.The treatment of Group D samples was carried out by a fully automatic machine for dry–wet circulation of sulfate, as shown in The above steps (1)~(4) indicated a dry–wet cycle of sulfate attack (1 d) and then were repeated in sequence until the end of the test.For the compression test, the sample size was 100 mm × 100 mm × 100 mm. The measured values were converted according to the standard size (150 mm × 150 mm × 150 mm), and the size conversion factor is 0.95. The universal testing machine of MTS, with the maximum test force of 2000 kN, was used here as shown in cK) is defined in this paper:fccn is the compressive strength of concrete after sulfate attack (MPa); fcc0 is the compressive strength of concrete without sulfate attack (MPa).The relative value of concrete compressive strength  were adopted in this paper to obtain the distribution of pores in the concrete. By comparison of the pore structure changes in the process of erosion, the effect of dry–wet cycles and sulfate attack on the pore evolution of concrete was analyzed.T2 spectrum distribution curve, which can reflect the internal pore distribution of concrete.The NMR test is mainly to detect the hydrogen nuclei in concrete, and gives the In this paper, the NMR testing instrument  was used, as shown in 2SO4 solution at room temperature with a water–cement ratio of 0.5 and 0.45, while D5 and D4 represent concrete samples under coupling of dry–wet circulation and Na2SO4 solution erosion with water–cement ratio of 0.5 and 0.45, respectively. For each erosion age, the compressive strength was the average value of 3 samples.The test results of compressive strength of concrete with different water–cement ratios under different erosion periods are shown in 2SO4 solution for 80 days, and the growth rate of group J5 is faster than that of group J4. The compressive strength of groups J5 and J4 at the peak increases to 111.0% and 107.8% of that of the uneroded concrete, respectively. Group D5 reaches the peak value after 40 dry–wet cycles of sulfate attack, while group D4 reaches the peak strength after 80 dry–wet cycles of sulfate attack. Compared with the uneroded samples, the peak compressive strength of D5 and D4 groups increases by 9.1% and 6.1%, respectively.It can be seen from As the age of erosion continues to increase, the compressive strength of concrete decreases at different rates. Compared with the peak compressive strength, after 120 days of erosion, the J5 and J4 groups respectively decrease by 6.3% and 2.0%, while the D5 and D4 groups decrease by 15.6% and 11.3%, respectively. It indicates that the effect of dry and wet circulation on the compressive strength of concrete is greater, and concrete with a larger water–cement ratio is more sensitive to sulfate attack.2SO4 solution penetrating into the concrete and forming corrosion products by the chemical reaction, which can fill the internal pores of concrete, and thus improve compressive strength. In the second stage, the compressive strength of concrete begins to decline, which may be caused by the continuous generation of corrosion products (ettringite and gypsum) squeezing the pore wall, accelerating the formation and development of cracks in concrete, and then resulting in the decreasing of compressive strength. Sulfate erosion products (ettringite and gypsum) are expansionary, with the increase of erosion age, erosion products increase, gradually fill and squeeze the pores inside the concrete, and finally may produce cracking. This caused the effect of ettringite and gypsum was at its maximum after 80 days of erosion.According to the curves of relative compressive strength of concrete in By comparing the results of J5 and D5, it can be seen that the compressive strength of J5 rises and falls at a relatively slow rate, while in group D5, the compressive strength decreases obviously after a short period of strength increase. It shows that dry–wet cycles make damages in concrete accumulate repeatedly and accelerate the deterioration of concrete.Referring to , pores i3 is significantly more than that of larger pores.It can be seen from 3 increases first and then decreases, while the proportion of pores larger than 0.01 mm3 shows a trend of decreasing first and then increasing.As shown in 42− in larger pores may react more fully with hydration products, and more erosion products will be generated in larger pores, which may promote larger pores evolving into small ones. At the same time, the continuous hydration reaction may also generate new smaller pores inside. Therefore, in the early stage of sulfate attack (0 to 40 dry–wet cycles), the proportion of pores in the range of 0~0.01 mm3 increases, while the proportion of pores larger than 0.01 mm3 is significantly reduced. Generally, compressive strength of concrete is improved in this period.It is known that the sulfate solution permeates into the concrete through the pores on the surface and forms insoluble substances by the chemical reaction with hydration products . With th3 decreases, and the proportion of pores larger than 0.01 mm3 increases. Concrete with larger water–cement ratio (D5) shows decreasing of compressive strength in this period.As sulfate attack continued, some pores in concrete are filled with erosion products. Hydration products are continuously consumed, which results in the decreasing of adhesion between aggregates. On the other hand, erosion products continuously generated have dilatability. The expansion force and crystallization pressure may induce cracking in concrete, and cracks will further expand and develop with the erosion of sulfate. Therefore, in the later stage of sulfate attack (40 dry–wet cycles to 80 dry–wet cycles), the proportion of pores in the range of 0 to 0.01 mmThe selection of CT images starts from the top of concrete. The surface and inner layers of D5 are located at about 5 and 25 mm, respectively, while the surface and inner layers of D4 are located at about 8 and 30 mm, respectively.Under the action of dry and wet cycles, sulfate reacts physically and chemically with the internal components of concrete. The generated erosion products cause cracking on the surface and interior of the concrete. There are three main types of cracks: mortar cracks, aggregate cracks, and aggregate–mortar interface cracks, which are indicated by yellow, green, and blue in From From the comparison between T2 spectrum distribution curve of pore fluid in concrete under soaking and erosion of Na2SO4 solution. The relaxation time on the horizontal axis reflects the radius of pore fluid. The larger relaxation time corresponds to the larger pore fluid radius.T2 spectrum distribution curves in 2SO4 solution, T2 spectrum distribution curves of J5 and J4 move to the right, that is, moving in the direction of the larger pore size, and the signal intensity of larger pores generally shows an increasing trend, which reveals the corrosion of sodium sulfate gradually penetrating into the interior of concrete.From the shape of 2SO4 solution for 57 days, the third peak of T2 spectrum curves of J4 has no significant change, while the third peak of J5 changes obviously, as shown in When concrete is soaked in NaT2 spectrum distribution curve reflects the hydrogen content inside the sample, that is, the pore fluid content of concrete. T2 spectrum area and peak proportion of pore fluid in concrete under sodium sulfate immersion and erosion.The area enclosed by the 2SO4 solution, the total area of T2 spectrum shows an increasing trend in general, which reflects the increasing of pore volume in concrete to some extent.As shown in 2SO4 solution for 21 days, the total area of T2 spectrum for J4 decreases. The reason for this may be that SO42− in sodium sulfate solution reacts with hydration products in concrete and then insoluble substances are generated, which fill larger pores, causing peak 3 in T2 spectrum to disappear. During the immersion in sodium sulfate solution (3 to 57 d), proportions of peak 3 and 4 (larger pores) for J4 are very small.When concrete is immersed in NaFrom As shown in During the period of sulfate attack from 39 to 57 d, the area proportion of peak 1 and peak 2 changes greatly. Compared with the value of 39 d, the area proportion of peak 1 and peak 2 for the J5 group respectively increases by −17.2%, 110.0%, while for the J4 group it increases by −12.7% and 85.9%, respectively. It may be due to the erosion products filling small pores and then reducing small pore volume. The pore walls are subject to expansion, causing the small pores to evolve into larger ones and then increasing the larger pore volume significantly. It can be found that the pore structure of concrete with larger water cement ratio has more significant changes.As sulfate attack continues, the proportion of peak 3 increases gradually, which respectively reaches 3.87% and 5.87% at 57 and 75 d for the J5 group, and reaches 1.92% at 75 d for the J4 group. In the early erosion, the proportion of peak 3 is relatively small, which indicates the change of pore structure is dominated by the development of smaller pores (peak 1 and peak 2).(1)Under the two erosion environments of group D and group J, the compressive strength of concrete shows the similar trend of first increasing and then decreasing, and the dry–wet cycles accelerate sulfate corrosion.(2)3 in group D accounts for the most, which increases first and then decreases with the increase of dry–wet cycles. In the early erosion, larger pores in concrete are filled with erosion products and develop into small pores. In the later stage of erosion, the proportion of small pores decreases, while the proportion of larger pores increases, and cracks appear inside concrete.According to ICT results, the number proportion of pores within the range of 0~0.01 mm(3)After 80 dry–wet cycles, obvious cracks appear on the surface and inner layers of D5 with larger water cement ratio. Cracks on the surface layer of concrete, mainly distributed on the edge of concrete. From the surface layer to inner layer, the number of cracks gradually decreases.(4)2SO4 solution, the T2 spectrum distribution of pore fluid for group J is dominated by peak 1, and the main peak is much higher than the sub-peak, which indicates that the proportion of smaller pore fluid in concrete is in the majority. With the increase of soaking time in Na2SO4 solution, the T2 spectrum distribution curve gradually moves toward the larger pore size, and the signal intensity of larger pores generally shows an increasing trend.Under soaking and erosion of NaThe objective of this research is to study the deterioration of dry–wet cycles and sulfate attack on the performance of concrete, the deterioration of compressive strength of concrete with different water cement ratios under different erosion environments (sodium sulfate soaking at room temperature and coupling of dry–wet cycling and sodium sulfate) was studied. At the same time, ICT  and NMR (nuclear magnetic resonance) techniques were used to analyze the internal pore structure of concrete under different erosion environments. Some main conclusions can be drawn as following:


Shigella, sapovirus, Shiga toxin-producing Escherichia coli, and Cryptosporidium were the leading antibiotic-treated diarrhea etiologies. Rotavirus caused 29.2% (24.5–35.2%) of antibiotic-treated cases, including the largest share in both the first and second years of life. Shigella caused 14.9% (11.4–18.9%) of antibiotic-treated cases, and was the leading etiology at ages 24–59 months. Our findings should inform the prioritization of vaccines with the greatest potential to reduce antibiotic exposure among children.Diarrhea is a leading cause of antibiotic consumption among children in low- and middle-income countries. While vaccines may prevent diarrhea infections for which children often receive antibiotics, the contribution of individual enteropathogens to antibiotic use is minimally understood. We used data from the Global Enteric Multicenter Study (GEMS) to estimate pathogen-specific incidence of antibiotic-treated diarrhea among children under five years old residing in six countries of sub-Saharan Africa and South Asia before rotavirus vaccine implementation. GEMS was an age-stratified, individually-matched case-control study. Stool specimens were obtained from children presenting to sentinel health clinics with newly-onset, acute diarrhea (including moderate-to-severe and less-severe diarrhea) as well as matched community controls without diarrhea. We used data from conventional and quantitative molecular diagnostic assays applied to stool specimens to estimate the proportion of antibiotic-treated diarrhea cases attributable to each pathogen. Antibiotics were administered or prescribed to 9,606 of 12,109 moderate-to-severe cases and 1,844 of 3,174 less-severe cases. Across all sites, incidence rates of clinically-attended, antibiotic-treated diarrhea were 12.2 , 10.2 (7.4–13.9) and 1.9 (1.3–3.0) episodes per 100 child-years at risk at ages 6 weeks to 11 months, 12–23 months, and 24–59 months, respectively. Based on the recommendation for antibiotic treatment to be reserved for cases with dysentery, we estimated a ratio of 12.6 (8.6–20.8) inappropriately-treated diarrhea cases for each appropriately-treated case. Rotavirus, adenovirus serotypes 40/41,  Shigella etiology), little is known about real-world diarrhea treatment practices in LMICs. We used data from a study of children experiencing diarrhea and matched, asymptomatic controls residing in LMICs of South Asia and sub-Saharan Africa to understand factors leading to antibiotic treatment of diarrhea cases, and the proportion of cases attributable to various enteric pathogens. We identify rotavirus and Shigella as the predominant causes of antibiotic-treated diarrhea at ages 0–23 months and 24–59 months; additional leading causes include adenovirus serotypes 40/41, sapovirus, Shiga toxin-producing Escherichia coli, and Cryptosporidium. We estimate that approximately 12.6 diarrhea cases receive antibiotics inappropriately for each appropriately-treated case in the study settings. Vaccines against prominent enteropathogens may substantially reduce antibiotic consumption among children in LMICs.Because diarrhea is the second-leading cause of antibiotic consumption among children in low- and middle-income countries (LMICs), effective vaccines against diarrheal pathogens may have the collateral benefit of reducing antibiotic exposure and resistance selection in these settings. Whereas antibiotic treatment is only recommended for diarrhea cases with blood in the stool (which suggests  Prevention of avoidable antibiotic consumption is a central goal of efforts to counter the growing threat of antimicrobial resistance . ChildhoStreptococcus pneumoniae [Randomized and observational studies in high-income settings have reported that vaccines against influenza  and Streeumoniae –11 reduceumoniae , there heumoniae ,13. EvidThe Global Enteric Multicenter Study (GEMS) –17 was uThe clinical protocol of the original study was approved by ethics committees of the University of Maryland, Baltimore, Maryland, United States, and at each of the participating field sites; parents or primary caretakers provided written informed consent for participating children at enrollment. This secondary analysis of the de-identified GEMS dataset was considered to be non-human subjects research and was therefore exempt from full review by the Committee for Protection of Human Subjects of the University of California, Berkeley.GEMS was a multi-site, age-stratified, individually-matched case-control study characterizing the incidence, etiology, and clinical consequences of diarrhea among children at four sites in sub-Saharan Africa  and three sites in South Asia . Participants were children ages 6 weeks to 59 months who belonged to routinely-censused populations, with demographic surveillance systems in place to record all births, deaths, and migrations. Enrollment of cases occurred at sentinel hospitals and health centers where children sought care for diarrhea. Sentinel hospitals and health centers  were selected which provided care to the largest number of children with diarrhea in each study region, and which offered appropriate infrastructure for computerized data management, secure freezer storage, at least intermittent internet access, the ability to ship specimens abroad, and laboratory capacity to perform coprocultures, antigen-detection tests, and nucleic acid-based assays. The design, procedures, and primary outcomes of GEMS have been reported previously –16,18. BThe study included a 3-year primary phase (GEMS-1) enrolling MSD cases as well as a 1-year follow-on phase (GEMS-1A) enrolling both MSD and LSD cases; due to an anticipated low enrollment, LSD cases were not enrolled in the Kenya site. Study personnel aimed to enroll the first 9 children with MSD (in the 3-year primary study) and the first 9 children with MSD or LSD (in the 1-year follow-on study) at each site, over each fortnight, within each of three age strata: infants ages 6 weeks to 11 months, toddlers ages 12–23 months, and young children ages 24–59 months. For each case, investigators aimed to enroll 1–3 matched controls from the community. Controls of the same age (±2 months for cases ages ≤23 months and ±4 months for cases ages 24–59 months), sex, and village or neighborhood were selected at random from demographic surveillance site databases and enrolled within 14 days of the case at home visits by field workers. Controls experiencing diarrhea in the preceding 7 days were ineligible. Standardized demographic, epidemiologic, and clinical information was collected by study personnel at enrollment, in consultation with parents or primary caretakers of children.All treatments that clinicians administered or prescribed to diarrhea cases at the primary enrollment visit were recorded. On the basis of these data, we defined clinically-attended, antibiotic-treated diarrhea cases as MSD or LSD cases who were administered antibiotics during the enrollment visit, or who received an antibiotic prescription at the enrollment visit. From this definition, we excluded cases diagnosed with other conditions that would justify antibiotic treatment, regardless of diarrhea symptoms; we considered these diagnoses to include pneumonia/lower respiratory-tract infection, meningitis or other invasive bacterial infection, and typhoid.Salmonella spp., Shigella spp., Campylobacter spp., Aeromonas spp., Vibrio cholerae, diarrheogenic Escherichia coli, rotavirus, adenovirus (serotypes 40 and 41), norovirus (serotypes GI and GII), sapovirus, astrovirus, Giardia lamblia, Entamoeaba histolytica, and Cryptosporidium spp.Microbiological procedures in GEMS have been described previously . BrieflyE. coli isolates as enteropathogenic, enteroaggregative, and Shiga toxin-encoding enterotoxigenic . Rotavirus, adenovirus, G. lamblia, E. histolytica, and Cryptosporidium spp. were detected via commercial immunoassays, and norovirus, sapovirus, and astrovirus were detected via multiplex reverse transcriptase (PCR).For this study, we used data obtained from both conventional diagnostic procedures  and quantitative molecular diagnostic assays  . Under cStool specimens from up to 300 randomly-selected MSD cases and the first available matched controls for each age stratum and study site from the primary study were retested using a custom TaqMan Array Card  with probe-based quantitative PCR (qPCR) assays for 32 enteropathogens, as described previously ,20. The S1 Text). Analyses were stratified for MSD and LSD cases. We also estimated adjusted attributable fractions using pathogen detection data from conventional assays, as applied in the primary analyses of the GEMS datasets [We used the diagnostic data produced by these assays to estimate the proportion of clinically-attended antibiotic-treated diarrhea cases caused by each pathogen, controlling for the presence and/or abundance of all other pathogens; for each pathogen, we refer to this quantity as the adjusted attributable fraction. We estimated adjusted attributable fractions using models that included the Cq value for each pathogen as covariates, similar to previous analyses ,21. We ddatasets ,15,22. DS1 Text).An initial cross-sectional healthcare utilization and attitudes survey was conducted within random samples of children belonging to the demographic surveillance population of each site, followed by brief serial surveys to document in-migration, out-migration, births, and deaths, as described previously . ParentsShigella etiology, we also estimated adjusted attributable fractions of clinically-attended, antibiotic-treated diarrhea associated with dysenteric and non-dysenteric Shigella infections. In addition, we estimated the ratio of incidence of inappropriate  to appropriate (dysenteric) antibiotic-treated cases in each setting. To understand differences in symptoms and management of diarrheal infections, we further estimated associations of detection of each pathogen with administration or prescription of an antibiotic (among MSD and LSD cases) and with dysentery and hospitalization (among MSD cases only). We detail the statistical approaches for these analyses in the supporting information (S1 Text).Because antibiotic treatment of dysentery is recommended based on the possibility of Data were available from 12,109 cases with MSD seeking care at sentinel hospitals and health centers recruited in the primary and follow-on studies between December, 2007 and November, 2012 . The oneTable 1). Concordant with World Health Organization guidelines [S2 Table). Contrary to current guidelines [In total, 9,606 children with MSD and 1,844 children with LSD were administered or prescribed antibiotics . Trimethoprim/sulfamethoxazole was the most common treatment in African sites for both MSD and LSD, while quinolones were more commonly used for MSD in the South Asian sites. Nearly all antibiotic-treated LSD cases in Bangladesh received azithromycin, whereas this drug was less commonly used in other settings.Predominant antibiotic choices varied by setting . In agreement with this finding, Shigella detection was associated with higher odds of dysentery among MSD cases. Within the South Asian GEMS study sites, Shigella was the only pathogen associated with higher odds of antibiotic administration or prescription, whereas detections of rotavirus, ST-ETEC, or V. cholerae O1 among MSD cases each predicted lower odds of antibiotic administration or prescription. Detections of these pathogens among MSD cases were also associated with lower odds of dysentery and higher odds of hospitalization. However, within the African sites, rotavirus-positive MSD cases were more likely than rotavirus-negative cases to be administered or prescribed antibiotics.Across all sites, adjusted odds of antibiotic administration or prescribing were higher in V. cholerae O1, Aeromonas, Shigella, and rotavirus were each associated with elevated odds of antibiotic administration or prescribing . These findings persisted in analyses stratified by region. In contrast to our observations in MSD, detections of rotavirus were associated with higher odds of antibiotic administration or prescribing in LSD in South Asian sites as well as African sites.Among LSD cases, detections of Tables 2 and 3). Rotavirus was associated with the greatest share of LSD cases resulting in antibiotic treatment across all ages, and with the greatest share of MSD resulting in antibiotic treatment during the first year of life . Although a minor contributor to clinically-attended, antibiotic-treated diarrhea during the first year of life, Shigella accounted for 23.4% (17.9–29.7%) and 23.7% (15.3–34.2%) of cases at ages 12–23 months and 24–59 months, respectively, and was thus the second-leading and leading etiology of antibiotic-treated cases at these ages (Table 2). In contrast to rotavirus, Shigella was associated with >4-fold greater fractions of clinically-attended, antibiotic-treated MSD cases than LSD cases, and was the leading cause of clinically-attended, antibiotic-treated MSD at ages 12–23 months as well as 24–59 months . In total, we estimated that 14.9% (11.4–18.9%) of clinically-attended, antibiotic-treated diarrhea was attributable to Shigella (Table 3). Our findings that rotavirus and Shigella were the leading causes of diarrhea did not differ in analyses based only on conventional diagnostic data (S9 Table), although qPCR data yielded higher adjusted attributable fraction estimates for these and most other pathogens .Rotavirus was the leading clinically-attended, antibiotic-treated diarrhea etiology overall and during both the first and second years of life, accounting for 34.2%  and 28.8% (22.9–37.2%) of cases in these age groups, respectively (Table 2). Of these pathogens, only ST-ETEC was a prominent cause of clinically-attended, antibiotic-treated diarrhea across all ages; we estimated that ST-ETEC accounted for 12.4% (0.0–29.4%) and 6.3% (3.2–12.4%) of cases at ages 12–23 months and 24–59 months, respectively. In contrast, by ages 24–59 months, adenovirus 40/41 and sapovirus each accounted for <3% of all clinically-attended, antibiotic-treated diarrhea.Adenovirus serotypes 40/41, sapovirus, and ST-ETEC were also important etiologies of antibiotic-treated diarrhea during the first year of life, accounting for 23.1% (0.0–43.3%), 21.4% (1.2–63.1%), and 10.3% (5.9–17.5%) of cases in this age group, respectively (Shigella was associated with roughly 2-fold greater fractions of cases in Bangladesh and Pakistan as compared to other sites (Tables 2 and 3). Additionally, V. cholerae O1 accounted for 3.3% (1.7–5.2%) and 5.4% (1.2–15.0%) of clinically-attended, antibiotic-treated diarrhea in India and Pakistan, respectively, but <1% of cases in each African site (Table 3). In contrast, estimates of the etiologic fraction for Cryptosporidium tended to be larger in the African sites than the South Asian sites.We noted several regional differences in etiologies of clinically-attended, antibiotic-treated diarrhea. Overall and within most age groups, Table 4). Whereas 52.4% (19.5–70.4%) and 24.5% (13.2–41.5%) of incident clinically-attended, antibiotic-treated diarrhea cases in Bangladesh and Pakistan experienced dysentery, the fraction was below 10% in all other settings. On this basis, the ratio of inappropriate to appropriate treatment of diarrhea cases with antibiotics ranged from 0.9 (0.4–4.1) in Bangladesh to 29.8 (16.6–75.3) in Mali. Accounting for the absolute incidence rates of clinically-attended, antibiotic-treated diarrhea in each setting, we estimated that the number of inappropriately-treated episodes per 100 children annually ranged from 1.5 (0.9–2.3) in Pakistan to 8.4 (6.2–11.2) in India.We estimated that dysentery occurred in only 17.5% (11.2–22.5%) of clinically-attended, antibiotic-treated diarrhea cases across all settings  and 12.2% (7.3–20.1%) of all clinically-attended, antibiotic-treated diarrhea cases at ages 12–23 months and 24–59 months, respectively (Table 5). This finding was consistent in all settings except Bangladesh and Pakistan, where the majority of antibiotic-treated, Shigella-attributable cases were dysenteric.Non-dysenteric cases accounted for over half of Fig 3). Consistent with this pattern, incidence rates declined with older age within each setting. Overall and within each age group, incidence rates were highest in India and lowest in Pakistan, where the fewest cases received antibiotics (Table 1).Across sites, we estimated incidence rates of 12.2 (9.0–17.8), 10.2 (7.4–13.9), and 1.9 (1.3–3.0) clinically-attended, antibiotic-treated diarrhea cases per 100 child-years at risk at ages 6 weeks to 11 months, 12–23 months, and 24–59 months, respectively . A similar pattern appeared in age-specific incidence of clinically-attended, antibiotic-treated diarrhea attributable to sapovirus and ST-ETEC, albeit less consistently. In contrast, Shigella-attributable incidence was highest among children ages 12–23 months in all settings. Similarly, incidence attributable to Vibrio cholerae O1 peaked at ages 12–23 months in India and Pakistan, where burden of this pathogen was greatest.Incidence rates of clinically-attended, antibiotic-treated diarrhea attributable to rotavirus, adenovirus 40/41, Fig 4). However, the relative contributions of MSD and LSD varied by pathogen. Point estimates suggested rotavirus, adenovirus 40/41, sapovirus, ST-ETEC, Cryptosporidium, and norovirus GII were each associated with a greater share of less-severe than moderate-to-severe episodes of clinically-attended, antibiotic-treated diarrhea. In contrast, we estimated that Shigella caused higher incidence of moderate-to-severe than less-severe cases overall and within each age group.Within each age group, LSD cases accounted for the majority of clinically-attended, antibiotic-treated diarrhea incidence  per appropriately-treated dysentery case in The Gambia, Mali, Mozambique, and India. A lower but substantial proportion of antibiotic-treated episodes were non-dysenteric in Bangladesh and Pakistan. Whereas this finding reflected lower rates of inappropriate antibiotic treatment in Pakistan, in Bangladesh this finding was instead driven by high prevalence of dysentery, as the proportion of non-dysenteric MSD and LSD cases receiving antibiotics resembled observations in other settings.Shigella detection was strongly associated with antibiotic administration or prescription in all settings. Left untreated, shigellosis is associated with severe adverse outcomes including mortality and growth faltering, independent of dysentery [Shigella infections exceeds the proportion with dysentery, current guidelines for antibiotic treatment of only dysenteric cases may be overly restrictive [Shigella could offer synergistic benefits, for instance by reducing the incidence of shigellosis cases that drive antibiotic use as well as reducing clinical suspicion of shigellosis and resulting empirical antibiotic treatment of diarrhea attributable to other causes. Moreover, expansion of multidrug-resistant Shigella lineages, most notably in South Asia, has resulted in a diminishing number of practical treatment options [Shigella.ysentery –33. Becatrictive ,33, infl options . The emeWhile general limitations of GEMS have been addressed previously , severalOur findings suggest that even a moderately effective rotavirus vaccination program could substantially reduce antibiotic consumption. For instance, 40–70% reductions in rotavirus diarrhea incidence reported in African settings after vaccine implementation  would trAntibiotic use endpoints merit inclusion in trials of vaccines against enteric pathogens to demonstrate whether prevention of diarrhea meaningfully reduces overall antibiotic consumption . ClusterS1 TextThe supporting information document includes further elaborations of methods (sections 1–5), 11 supplemental tables, and one supplemental figure, and citations to references in the supplemental text, as listed in the Table of Contents (page 1).(PDF)Click here for additional data file.


Sulfate induced degradation of concrete brings great damage to concrete structures in saline or offshore areas. The degradation mechanism of cast-in-situ concrete still remains unclear. This paper investigates the degradation process and corresponding mechanism of cast-in-situ concrete when immersed in sulfate-rich corrosive environments. Concrete samples with different curing conditions were prepared and immersed in sulfate solutions for 12 months to simulate the corrosion of precast and cast-in-situ concrete structures, respectively. Tests regarding the changes of physical, chemical, and mechanical properties of concrete samples were conducted and recorded continuously during the immersion. Micro-structural and mineral methods were performed to analyze the changes of concrete samples after immersion. Results indicate that the corrosion process of cast-in-situ concrete is much faster than the degradation of precast concrete. Chemical attack is the main cause of degradation for both precast and cast-in-situ concrete. Concrete in the environment with higher sulfate concentration suffers more severe degradation. The water/cement ratio has a significant influence on the durability of concrete. A lower water/cement ratio results in obviously better resistance against sulfate attack for both precast and cast-in-situ concrete. Sulfates, chlorides, and other corrosive sources are widely observed in soils, ground water, river water, and seawater in salty saline and offshore areas ,2,3,4,5.Experimental and theoretical studies regarding the degradation of concrete caused by sulfate attack have been well reported in recent decades. The corrosion products such as ettringite, gypsum, or thaumasite were reported after sulfate corrosion ,13. In a2SO4·10H2O, is several times greater than the volume of Na2SO4 [Concrete subjected to sulfate attack always results in great expansion as well as the risk of failure ,20,21. Tf Na2SO4 ,29,30. Tf Na2SO4 .It is clear that previous studies regarding the degradation of concrete induced by sulfate attack are of great importance for further research. By paying close attention to the published research, most of the previous studies were conducted on precast concrete samples. However, it should be pointed out that most concrete structures in salty saline or offshore areas are cast-in-situ concrete structures, especially for underground concrete structures. It should be noted that the construction processes of precast and cast-in-situ concrete structures are quite different. For cast-in-situ concrete, the corrosion process starts immediately after the casting of fresh concrete in the sulfate-rich environments, while for precast concrete structures, the hardening process has finished before being installed in the environment. Moreover, the effects of the water/cement ratio on the sulfate induced degradation of cast-in-situ concrete are rarely reported, which plays an important role in affecting the properties and safety of cast-in-situ structures. Consequently, the degradation process and mechanism between the precast and cast-in-situ concrete are quite different. Moreover, the safety of cast-in-situ concrete cannot be ensured if the design of cast-in-situ concrete structures is based on the research conducted on precast concrete samples. Thus, it is necessary to perform a specific experiment to reveal the degradation process and mechanism differences between the precast and cast-in-situ concrete.To study the degradation process and mechanism of cast-in-situ concrete caused by sulfate attack, concrete samples in cylinder shapes were prepared and immersed in sulfate solutions. Different curing conditions were used in the present study. To highlight the differences of specimens with different curing conditions, specimens cured for 12 h were described as cast-in-situ concrete and specimens cured for 28 days were described as precast concrete in the present study. Tests were conducted to record the physical, chemical, and mechanical properties changes during the 12-month immersion. The micro-structural and mineral properties of concrete were analyzed after immersion by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM) tests.To prepare concrete specimens, P.C. 32.5 R Portland cement  was used in the present experiment . The cheTo investigate the effects of water/cement ratio on the degradation of concrete caused by sulfate attack, three kinds of concrete samples were designed in the present study. Mixture proportions of concrete samples in the present study are listed in 2SO4 was selected to prepare sulfate corrosive solutions. The sulfate concentrations of different solutions were set at 0%, 3%, 5%, and 10% . Samples with modules were then put in the curing chamber with a temperature of 22 °C and relative humidity of >95%. The top and bottom surfaces of each specimen were sealed with epoxy resin. For precast concrete, the samples were cured for 28 days before being put into the solutions, while for cast-in-situ concrete, the samples were put into the solutions after being cured for 12 h.It should be noted that the specimens were put into an oven at a temperature of 60 °C for 48 h after being immersed in the solutions for 1, 3, 6, 9, and 12 months. To determine the diameter and weight changes of concrete samples during the immersion, a Vernier caliper and an electronic scale were selected to measure the diameter and weight of specimens. The diameter of each specimen was measured 5 times near the mid-height of specimens to obtain an average diameter. The weight of each specimen was weighed twice, and the average value was recorded.An unconfined compressive strength test was performed to determine the compressive strength of each specimen during the immersion. A loading system (the equipment model was POPWIL (HSR)) with a maximum capacity of 1000 kN was used to conduct the compressive strength test, and the loading rate during the tests was set as 5 kN/s.To determine the sulfate concentration in the concrete specimens, a drill was used to collect the powder samples by drilling perpendicular to the lateral surface of each specimen. Five powder samples (from the surface to a depth of 25 mm beneath the exposed surface of specimens) were obtained and sealed in the plastic zip bags. Each powder sample was mixed with 50 mL distilled water and put into a bottle for 48 h. Then the solution was filtered through filter paper to remove residues. The sulfate concentration of each solution was then determined by standard chemical titration .SEM , Shanghai, China) and XRD , Beijing, China) analyses were performed to observe the micro-structures and to determine the mineral composition of concrete samples after being immersed in sulfate solutions for 12 months. The element analysis , Shanghai, China)) was also performed in the SEM test to determine the corrosion products. The samples used in the SEM analysis were concrete core samples drilled from the lateral surface of specimens with a depth of 10 mm beneath the exposed surface. The powder samples used in the XRD analysis were drilled from the exposed surface with a depth of 5 mm and passed through a 75-µm sieve.It is well accepted that the micro-structural and mineral properties play an important role in affecting the basic physical and mechanical properties of concrete structures. Therefore, the results of the micro-structural and mineral analyses were given and discussed firstly. Additionally, sulfates penetrate concrete and react with concrete compositions to generate corrosion products and hence change the properties of concrete. Thus, the diffusion process of sulfates into concrete is subsequently introduced. Finally, results of other properties are given and discussed.To show the micro-structures of concrete after immersion in sulfate solutions for 12 months, SEM observation was conducted, and the results are presented in It is clear in the SEM images and EDS analysis results that sulfate corrosion products such as ettringite and gypsum were observed in both precast and cast-in-situ concrete samples. It should be noted that the peaks of Au and S shared little overlap in the EDS results, and a and b in the SEM images in The results of micro-structural and mineral analyses illustrate that the main corrosion products in both precast and cast-in-situ concrete were the same. Thus, one can conclude that both precast and cast-in-situ concrete mainly suffer chemical sulfate attack, especially when the concrete is fully immersed in the sulfate-rich environments. The peaks of sulfate hydrates detected in concrete indicated that crystallization of sulfates also occurred in the cracks and pores of concrete. However, it should be emphasized that fully immersed concrete samples stayed beneath the liquid surface all the time, and the evaporation process was not involved during the immersion. Thus, it was inferred that the crystallization hydrates of sulfates were generated during the 48-hours drying process instead of the immersion period.The generation of sulfate corrosion products would generally affect the properties of concrete in the following three ways. Firstly, the corrosion products would be generated and embedded in concrete, affecting the subsequent development of other properties. The reason is that the properties of sulfate-induced corrosion products and concrete are quite not the same. Secondly, the generated corrosion products would be gradually accumulated in the initial cracks and pores in concrete, influencing the density and strength of the outer layer of concrete. At last, it is well accepted that the corrosion products would cause great volume expansion by loading great pressure on the walls of internal cracks and pores, putting the outer layer of concrete under great tensile stress.Concentration of sulfates in different concrete samples was determined, and the results are shown in For precast concrete specimens, it is clear that the penetration of sulfate ions was relatively slow, especially for concrete immersed in 3% sulfate solution. The concentration of sulfates in concrete immersed in 5% and 10% sulfate solutions was higher and the penetration depth was deeper. Moreover, it is clear that the sulfate concentration in concrete with lower water/cement ratio is lower than that in concrete with greater water/cement ratio.As for cast-in-situ concrete, it was noticed that the sulfate concentration was relatively higher than that in precast concrete specimens. In addition, sulfates reached deeper depth in cast-in-situ concrete. Thus, sulfates diffused faster in cast-in-situ concrete, especially for concrete specimens with high water/cement ratio.2SO4 dissolve in water to form a sulfate solution in which sulfate ions can move freely. In the second step, sulfate ions would move from positions with higher sulfate concentrations to positions with lower sulfate concentrations. In this regard, the diffusion of sulfate ions is mainly motived by the concentration gradient between the concrete and the outer environments. In addition, it should be emphasized that the porosity of concrete also plays an important role in affecting the diffusion of sulfates. It is obvious that concrete with higher porosity can physically provide more paths for the penetration of sulfates. Thus, the sulfate concentration in concrete with a higher water/cement ratio is relatively high, while on the contrary, sulfates only reach a shallower depth beneath the exposed surface of concrete with a lower water/cement ratio. The diffusion of sulfates into concrete can be divided into two steps. In the first step, the soluble sulfates such as NaIt should be noted that the diffusion of sulfates in precast concrete and cast-in-situ concrete is different. First of all, sulfate ions can diffuse directly into concrete once the fresh concrete is put into the environment during the hardening process. Then, the penetrated sulfate ions can react with the cement composition to generate sulfate corrosion products such as gypsum and ettringite. The embedded corrosion products affect the integrity of concrete and hence increase the initial porosity of concrete. Additionally, the strength of sulfate induced corrosion products is relatively low, making it easier for expansive products to generate more cracks in the upcoming stage. Thus, the diffusion of sulfates in cast-in-situ concrete is easier and faster than that in precast concrete structures. It is clear that the porosity of concrete with different water/cement ratios is different. The porosity is lower when the water/cement ratio is lower, resulting in better waterproofness. Thus, it would be harder for an external sulfate solution to permeate into the internal concrete areas and hence decreases the diffusion speed of sulfate ions. Therefore, the sulfate concentration is low and the penetration depth is shallow in concrete with a lower water/cement ratio. Furthermore, concrete with a lower water/cement ratio has a higher tensile strength, making it difficult for sulfate corrosion products to generate new cracks, while for concrete with a high water/cement ratio, it would be easier for expansive products to extend initial cracks or generate new cracks, leading to a faster degradation.a is the change ratio, 0d is the initial diameter, and td is the diameter of the specimen after a specific immersion period of t. The results are shown in The diameter and weight of different specimens in different solutions were measured and recorded during the immersion. To give a clear comparison of diameter for different concrete specimens, the change ratios of diameter were calculated byThe comparison clearly indicates that concrete in sulfate solutions suffered radical expansion. For precast concrete specimens, the diameter showed a relatively stable increase tendency during the immersion. Only the specimen immersed in 10% sulfate solution showed a relatively slight decrease after the ninth month (with a water/cement ratio of 0.55). Additionally, one could observe that concrete in solution with a higher concentration of sulfates suffered more radical expansion in the early stage, indicating that concrete suffered more serious degradation when immersed in the environments with a relatively higher sulfate concentration. Compared to precast concrete specimens, it can be seen in For precast concrete samples, the weight increased quickly in the early corrosion stage and became relatively stable after nine months. Furthermore, there was a slight difference between the concrete in distilled water and sulfate solutions, which was caused by the accumulation of sulfate corrosion products. In addition, it can be seen that concrete immersed in solutions with higher sulfate concentration obviously experienced more fluctuation during the immersion, and the weight increment was relatively greater, especially at the early stage. However, it can be seen that the weight of cast-in-situ concrete experienced more significant changes during the 12-month immersion. The weight of specimens increased quickly at the early stage, then became stable or even began to decrease after the sixth month, especially for specimens immersed in 10% sulfate solution shown in c.To give a clear comparison of degradation between the precast and cast-in-situ concrete, the photos of the exposed surface of specimens after immersion are shown together. The image in It is clear that the diameter and weight of concrete samples are significantly affected by sulfate attack. In the early corrosion stage, sulfates penetrates internal concrete and reacts with concrete composition to generate ettringite and gypsum. The corrosion products are accumulated in the initial cracks and pores with immersion time. Soon after, the initial cracks are fully filled by the corrosion products, and excessive pressure is loaded on the walls of cracks and pores to cause volume expansion. During this stage, the diameter and weight of specimens increase with immersion time, while in the later corrosion stage, the excessive filling of corrosion products loads great pressure on the walls of the crack, causing the extending of initial cracks and generation of new cracks. Moreover, the development of a crack system on the concrete surface causes serious spalling and shedding of concrete powder and fragments, which cause a decrease of both the diameter and weight of concrete specimens. Therefore, the diameter of concrete specimens is a comprehensive result of the increase tendency induced by the proceeding of expansion and the decrease tendency induced by the falling off of concrete on the exposed surface. The weight of concrete specimens is a comprehensive result of the increase tendency induced by the accumulation of sulfate corrosion products and the decrease tendency induced by the shedding of concrete fragments. Furthermore, the diameter and weight of specimens are mainly controlled by the increase tendency in the early corrosion stage, while in the later stage, the decrease tendency plays the leading role. Hence both the diameter and weight of concrete specimens encounter a rapid decrease at the end of the immersion, especially for concrete with a high water/cement ratio immersed in the solution with a high sulfate concentration , the strength began to decrease after the ninth month, while for concrete specimens with water/cement ratios of 0.40 and 0.48, the strength remained increasing or stable even at the end of the immersion.It is noteworthy that the strength of cast-in-situ concrete increased quickly, and the value was relatively low in the early stage, while after that, the increase tendency of strength became stable or even began to decrease after the sixth month. In addition, one could notice that concrete lost more strength when immersed in the solutions with higher sulfate concentration.It is clearly illustrated in For precast concrete specimens, the hardening process and strength development were finished before being put into the sulfate solutions. Thus, sulfate ions had to penetrate internal concrete from the outside-in with immersion time. Sulfate ions penetrated the outer layer of concrete together with the permeating of pore water during the immersion. Then, the penetrated sulfate ions reacted with the concrete composition to generate corrosion products, which accumulated in the initial cracks and pores to cause expansion and degradation. Therefore, the degradation of precast concrete proceeded from the surface into the internal areas of the concrete gradually. However, for cast-in-situ concrete, the strength development of concrete was negatively affected in the early corrosion stage, since the hardening process of concrete was not complete during this stage. Hence, the strength of cast-in-situ concrete was lower than that of precast concrete, even when the specimens were immersed in the same sulfate solutions, especially when the sulfate concentration was high. It has to be emphasized that the water/cement ratio has a significant effect on the strength and resistance performance of concrete against sulfate attack. It is well accepted that concrete with a lower water/cement ratio always results in a relatively higher density and lower porosity. Therefore, the strength of specimens with lower water/cement ratio is relatively high. In addition, the porosity of concrete also plays a significant role in affecting the diffusion speed of sulfate ions, subsequently influencing the mechanical property of concrete. The generation and accumulation of sulfate corrosion products in the cracks and pores influence the properties of concrete. In the very early corrosion stage, the cracks and pores are not fully filled; hence, the accumulation of corrosion products do not affect the strength of concrete. Then, the excessive filling of corrosion products generate pressure on the walls of internal cracks and pores, making the concrete denser and causing a slight increase in strength. Then, initial cracks are extended and new cracks are generated, decreasing the strength of concrete to a large extent. In this regard, for concrete with a higher water/cement ratio, it takes less time for sulfates to penetrate internal concrete regions and brings a great deal of damage to concrete structures. Moreover, the tensile strength of the internal concrete area with a higher water/cement ratio is low, making it easier for sulfate corrosion products to generate new cracks and bring great damage.Experiments were performed to investigate the degradation of precast and cast-in-situ concrete caused by sulfate attack. Parameters regarding physical, chemical, and mechanical properties were determined and compared in detail. Methods of SEM, EDS, and XRD were used to reveal the micro-structural and mineral changes after immersion. Based on the experiments in the present study, the main conclusions are as follows:Degradation of both precast and cast-in-situ concrete is caused by chemical sulfate attack when the concrete is fully immersed in the sulfate-rich environments. The main corrosion products induced by sulfate attack are ettringite and gypsum.Sulfate attack results in great expansion and weight loss in the later corrosion stage, putting concrete structures in great danger, especially for cast-in-situ concrete structures. The diffusion of sulfates is faster in cast-in-situ concrete than that in the precast concrete due to the faster development of cracks in the cast-in-situ concrete.The faster strength increase of cast-in-situ concrete in the early corrosion stage is induced by the faster accumulation of corrosion products. Cast-in-situ concrete obviously suffers more strength loss during corrosion. Precast concrete has better resistance performance against sulfate attack than cast-in-situ concrete structures, indicating that precast concrete structures are more suitable in sulfate-rich environments.


F) on the critical stress intensity factor (KIC), fracture energy (GF), the deflection at failure(δ0), the critical crack mouth opening displacement (CMODC) and the critical crack tip opening displacement (CTODC) were studied. Through the analysis of test phenomena and test data such as the load-deflection (P-δ) curve, load-crack mouth opening displacement (P-CMOD) curve and load-crack tip opening displacement (P-CTOD) curve, the following conclusions are drawn: with the increase of the steel fiber volume fraction, some fracture parameters increase gradually and maintain a certain linear growth. The gain ratio of the fracture parameters increases significantly, and the gain effect is obvious. Through this law of growth, the experimental statistical formulas of fracture energy and the critical stress intensity factor are summarized.This study aimed to determine the influence of the volume fraction of steel fibers on the fracture parameters of concrete. Fifty notched steel-fiber-reinforced concrete (SFRC) beams and ordinary concrete beams with 100 mm × 100 mm × 515 mm were cast and tested via a three-point bending test. Among them, the type of steel fiber was the milling type (MF), and the volume fraction of steel fiber added was 0%, 0.5%, 1%, 1.5% and 2%, respectively. The effects of the steel fiber volume fraction (V Steel-fiber-reinforced concrete (SFRC) has been emerging as a widely used construction material that is suitable for many structural elements ,2,3. SFRSFRC is a composite material produced by the reinforcement of a cementitious matrix in which short-length steel fibers are randomly distributed. Compared with ordinary concrete, the incorporation of steel fibers is receiving growing attention, as it offers many advantages, such as tensile strengths, toughness and durability ,7,8,9,10The remarkable feature of steel fiber is that it hinders the development of macro cracks, delays the propagation of micro cracks to macro cracks and improves the ductility of micro cracks ,11,12,13F) [Fracture performance is important for the safety and durability of concrete structures. A basic ingredient for measuring the fracture process in quasi-brittle materials is the fracture energy (GF) . F. BencF)  reportedF) , a steelF)  studied F-GF), as well as the volume fraction of steel fibers and the critical stress intensity factor (VF-KIC) are established, where R2 = 0.97 and 0.99, respectively. This study can further promote the understanding and application of steel fiber reinforced concrete.In the literature, different methods have been proposed for estimating the fracture parameters experimentally: the direct uniaxial tension test, the wedge splitting test and bending tests . In ordeIn this test, according to CECS13:89 , PO42.5 F, the water dosage increased by 8 kg. In order to eliminate the influence of the strength variation of the matrix concrete on the test results, at the time of pouring SFRC, the ordinary concrete (OC) specimens with the same mix proportion as SFRC but without steel fiber were used as control specimens. The mix proportion of SFRC specimen and control group concrete is shown in According to CECS13:89 , the ref0/l, was 0.4. The design strength grade of SFRC was FC30.Notched three-point bending beams as shown in In order to improve the uniformity of the mixture of SFRC and the control group’s ordinary concrete (OC) specimens and to avoid segregation, a superplasticizer was used and the mixing time was prolonged. In order to make the fiber well distributed and avoid agglomeration, the slow dispersion method was adopted when adding steel fiber, and a forced mixer was used. The concrete of SFRC and its control group was mixed by forced mixer, formed by a shaking table, cured in the standard curing room  for 28 days, and then naturally cured and processed to the test room after maintenance. The experimental age was between 50 days and 70 days.The three-point bending test was carried out on a hydraulic press testing machine with a maximum capacity of 2000 kN. In order to ensure the continuous stability of the test process, the disc spring reinforcement device of the testing machine was used to strengthen the testing machine. The load sensor was used to measure the load of the notched three-point bending beam, and the measuring range of the sensor was 0–30 kN. In order to eliminate the influence of bearing deformation on the deflection test results, the deflection test beam was arranged directly above the support point of the three-point bending specimen, and the mid-span deflection is measured with a percentile meter. The CMOD clip extensometer was arranged at the bottom of the beam with a 3-mm thick alloy aluminum knife edge. The CTOD clip extensometer was fixed at the tip of the crack on the side of the beam with a knife edge.The continuous loading mode was adopted in the test, and the computer data acquisition system was used to realize the automatic data acquisition. The acquisition rate was different according to the type of the component, i.e., concrete component 2 times/s, SFRC component 1 time/s. The load deflection (P-δ) curve, load-CMOD (P-CMOD) curve and load-CTOD (P-CTOD) curve can be observed simultaneously. According to these test curves and the observation of test phenomena during the test, the fracture properties of SFRC can be analyzed qualitatively and quantitatively. The experimental loading and measurement device can be seen in IC)Calculation Formula of the Critical Stress Intensity Factor , S is the span of beam (mm), b is the width of the sample(mm), h is the height of the sample (mm) and a is the actual crack length (mm). The virtual crack length is used in this paper.In China, the KF) [0 is the area under the load-deflection curve (N·m), m is the total mass of specimens between supports (kg), g is the gravitational constant (N/kg), δ0 is the deflection at failure (mm), h is the height of the sample (mm), a0 is the depth of the notch (mm) and b is the width of the sample (mm).The Calculation Formula of Fracture Energy (GF) ,18(3)GFThe testing results of the fracture parameters of SFRC and OC are shown in In the correlation analysis of this paper, the gain ratio is used to reflect the reinforcement effect of steel fiber, which is defined as: gain ratio = mechanical performance index of SFRC/mechanical performance index of the corresponding control group’s concrete specimen. For example: fracture toughness gain ratio = fracture toughness of SFRC specimens/fracture toughness of OC specimens of the same mix proportion.F on KIC is shown in F, the KIC of SFRC specimens show a good increasing trend. For every 0.5% increase in the fiber fraction, the average increase in KIC is 33.7%. The KIC gain ratio of VF to SFRC can be seen in IC gain ratio of SFRC specimens is greater than 1, and with the increase of VF, the gain ratio shows a good increasing trend, the minimum gain ratio is 1.43, the maximum gain ratio is 3.45 and the average gain ratio is 2.275. Therefore, it can be considered that the addition of steel fiber improves the KIC of concrete.The effect of V2 = 0.9748. It can be seen that the increase of KIC is mainly affected by VF.According to the test results of KIC in this paper, the statistical analysis shows that:F are compared, as shown in The failure patterns of three-point bending specimens with different VF, the crack propagation path becomes more tortuous. Except for a small number of SFRC specimens with small content, some specimens were split in half, but most of the them were not completely split, which kept the integrity to a certain extent. On the other hand, the KIC of the ordinary concrete of the reference group and control group was small, and the bearing capacity of the specimens decreased rapidly after the test load reached the peak, which led to most of the specimens splitting into two parts. It can be judged that the addition of steel fiber greatly improves the fracture toughness of SFRC.It can be seen from the test process that the SFRC specimen can be clearly heard the sound of the fiber pulling out or breaking in the test. E.K. Tschegg  also obtF on the GF of SFRC. It can be seen, compared with the reference group concrete, that the addition of steel fiber greatly improves the fracture energy of concrete matrix, and with the increase of VF, GF keeps an obvious linear increasing trend. For every 0.5 percentage point increase in VF, GF increases between 30.53% and 71.14%, with an average increase of 47.22%. It can be seen from F gain ratio of SFRC specimens is between 5.88 and 20.52, and that the average gain ratio is 12.88. It can thus be seen that the addition of steel fiber greatly improves the energy absorption capacity of the concrete matrix.IC in this paper, the statistical analysis shows that:2 = 0.9966. It can be seen that the increase of GF is mainly affected by VF.According to the test results of KF conditions.F, the number of fibers across the cracks increases accordingly, and the ability to transfer stress is also relatively improved. The microcracks in the fracture process zone develop fully, and the absorbed external load energy increases accordingly, which is characterized by the increase of the peak load and ultimate deflection of the specimen. The test curve becomes fuller and the improvement of fracture performance is more sufficient.It can be seen from the figure that the deflection of concrete specimen is almost linear elastic before reaching the peak load. This result is consistent with the test results of Doo-Yeol Yoo . As the C and CTODC of matrix concrete, and that with the increase of VF, CMODC increases linearly, and the deflection corresponding to CMODC also increases obviously.From the test data analysis in The typical load-CMOD diagram and load-CTOD diagram of a group of SFRC specimens recorded during the bending test is shown in With the increase of the load, the steel fiber is gradually pulled out, and it connects the concrete across the cracks. The high content of steel fiber increases the bridging effect, which makes the steel-fiber-reinforced concrete show better ductility. In the test, the peak load and critical crack opening displacement of concrete specimens increased.F, the KIC of SFRC specimens showed a good increasing trend. For every 0.5% increase in the fiber volume rate, the average increase of KIC is 33.7%, and the average gain ratio is 2.275.The addition of steel fiber to concrete can obviously improve the fracture toughness of concrete. With the increase of VF, the GF and GF gain ratio of SFRC specimens showed a good increasing trend. In the range of VF, for every 0.5% increase of VF, the average gain ratio of GF is 47.22%, the average gain ratio is between 5.88 and 20.52, and the average gain ratio is 12.88.Adding steel fiber to concrete can obviously improve the fracture energy of concrete. With the increase of VWith the addition of steel fiber, the peak loads, the deflection at failure and the critical crack opening displacement of concrete specimens increased.F-GF and VF-KIC are established, where R2 = 0.97 and 0.99, respectively.Two test statistical equations of VThrough the analysis of the fracture behavior of concrete notched three-point bending beam specimens of SFRC and their control group, the following conclusions can be drawn: