Is framing antibiotic stewardship as a patient safety issue and emphasizing direct care staff engagement associated with reductions in antibiotic use across US long-term care facilities?In this quality improvement study including 439 long-term care facilities, participation in training on antibiotic stewardship from the Agency for Healthcare Research and Quality (AHRQ) was associated with a reduction in antibiotic use and urine culture collection. Fluoroquinolones, an antibiotic class targeted by the AHRQ safety program, had the greatest decrease.These results suggest that the AHRQ safety program provides a pragmatic framework for the development of antibiotic stewardship programs in long-term care facilities that may reduce antibiotic use. This quality improvement study examines the association between long-term care facility participation in an antibiotic reduction educational program and antibiotic use among facility residents. Antibiotic overuse in long-term care (LTC) is common, prompting calls for antibiotic stewardship programs (ASPs) designed for specific use in these settings. The optimal approach to establish robust, sustainable ASPs in LTC facilities is unknown.To determine if the Agency for Healthcare Research and Quality (AHRQ) Safety Program for Improving Antibiotic Use, an educational initiative to establish ASPs focusing on patient safety, is associated with reductions in antibiotic use in LTC settings.This quality improvement study including 439 LTC facilities in the US assessed antibiotic therapy data following a pragmatic quality-improvement program, which was implemented to assist facilities in establishing ASPs and with antibiotic decision-making. Training was conducted between December 2018 and November 2019. Data were analyzed from January 2019 to December 2019.Fifteen webinars occurred over 12 months (December 2018 to November 2019), accompanied by additional tools, activities, posters, and pocket cards. All clinical staff were encouraged to participate.Clostridioides difficile laboratory-identified events per 10 000 resident-days. All outcomes compared data from the baseline (January-February 2019) to the completion of the program (November-December 2019). Generalized linear mixed models with random intercepts at the site level assessed changes over time.The primary outcome was antibiotic starts per 1000 resident-days. Secondary outcomes included days of antibiotic therapy (DOT) per 1000 resident-days, the number of urine cultures per 1000 resident-days, and P = .02), with fluoroquinolones showing the greatest decrease at –0.21 starts per 1000 resident-days . The mean difference for antibiotic DOT per 1000 resident-days was not significant . Reductions in antibiotic starts and use were greater in facilities with greater program engagement (as measured by webinar attendance). While antibiotic starts and DOT in these facilities decreased by 1.12 per 1000 resident-days  and 9.97 per 1000 resident-days , respectively, no significant reductions occurred in low engagement facilities. Urine cultures per 1000 resident-days decreased by 0.38 . There was no significant change in facility-onset C difficile laboratory-identified events.Of a total 523 eligible LTC facilities, 439 (83.9%) completed the safety program. The mean difference for antibiotic starts from baseline to study completion per 1000 resident-days was –0.41 (95% CI, –0.76 to –0.07; Participation in the AHRQ safety program was associated with the development of ASPs that actively engaged clinical staff in the decision-making processes around antibiotic prescriptions in participating LTC facilities. The reduction in antibiotic DOT and starts, which was more pronounced in more engaged facilities, indicates that implementation of this multifaceted program may support successful ASPs in LTC settings. Over 70% of LTC residents may receive at least 1 course of antibiotics annually, with 40% to 75% of prescriptions deemed to be inappropriate or not concordant with guidelines.6 of antimicrobial stewardship interventions in LTC settings concluded that effective ASPs included those that incorporated multidisciplinary education with enduring material  as well as tools that integrate antimicrobial stewardship principles into the workflow patterns usually present in LTC settings. Useful educational material and tools for nurses and nurse assistants can aid in the gathering of appropriate clinical data  and the effective communication of findings with prescribers; for prescribers, these interventions can improve decision-making regarding indications to start and stop antibiotics after review of residents’ diagnostic test results and clinical status. These approaches informed the development and implementation of the Agency for Healthcare Research and Quality (AHRQ) Safety Program for Improving Antibiotic Use, an initiative to establish ASPs specific to LTC settings.A 2017 review7 In this quality improvement study, we examined the implementation of the AHRQ Safety Program in 439 LTC facilities across the US. We assessed process measures related to participation by staff and their association with antibiotic stewardship practices in LTC settings, such as rates of antibiotic use and total urine culture and Clostridioides difficile tests sent.The overarching goals of the AHRQ Safety Program were to establish sustainable ASPs that improve the use of antibiotics and enhance patient safety. Specifically, in LTC settings the safety program provided frontline nursing staff and prescribers with tools to incorporate antibiotic stewardship principles into routine decision-making by (1) emphasizing the importance of recognizing signs and symptoms that herald common infectious syndromes in LTC residents and (2) underscoring the importance of communication around antibiotic prescribing with clinical staff as well as residents and caregivers. The foundation of the safety program was drawn largely from the Comprehensive Unit-based Safety Program methodology, a patient safety approach that emphasizes the importance of improved teamwork, clinical best practices, and the science of safety.SQUIRE) version 2.0 reporting guideline.The AHRQ Safety Program was a quality improvement initiative aimed to assist LTC facilities in establishing antibiotic stewardship programs by addressing both facility culture and technical knowledge around antibiotic prescribing. The program was conducted from December 2018 to November 2019; changes in antibiotic use and process measures were compared in participating facilities from the beginning to the end of the program using a pre-post design. The AHRQ Safety Program was exempted from review and informed consent requirements by the institutional review board at the Johns Hopkins University School of Medicine as research that did not involve human participants. All methods and analysis were in compliance with the Standards for Quality Improvement Reporting Excellence Standards for Quality Improvement Reporting Excellence  events per 10 000 resident-days  and 25 oral antibiotics from January 2019 to December 2019, beginning the month following initiation of the safety program. Secondary outcomes included days of antibiotic therapy (DOT) per 1000 resident-days, total urine cultures collected per 1000 resident-days, and the number of facility-onset C difficile LabID events significantly higher or lower than expected when compared with either their individual historical data or the range of values obtained for the cohort were identified and contacted to review and reextract data when needed.Several steps were followed to ensure valid data collection. An informational onboarding webinar at the start of the safety program provided detailed instructions regarding data collection, and a standardized template was used to collect and upload data (eMethods 1 in the We used a pre-post design and compared the primary and secondary outcomes between the baseline (January 2019) and program completion periods (December 2019). Outcome measures were compared from the first 2 baseline months with the outcome measures from each subsequent bimonthly period to illustrate how the association of program training with outcomes evolved over the implementation period; engagement of facilities was measured by level of attendance of webinars  or educational credits claimed. Facilities were classified as high for engagement if more than 8 of 15 webinars were attended or an educational credit was claimed, low if 1 to 7 webinars were attended (or credit was claimed), and no engagement if zero webinars were attended (or credit claimed).P < .05 with 2-sided testing.The unit of analysis was the site, and the random effect analyzed was site-level. We used generalized linear mixed models assuming negative binomial distribution with a random intercept for LTC facility because there were zero prescriptions for certain antibiotic classes across months. Data analyses were conducted using SAS version 9.4 (SAS Institute Inc) and Stata version 16.1 (StataCorp LLC). Findings were considered significant at A total of 439 of 523 sites (83.9%) remained in the AHRQ Safety Program at the end of the 1-year period; mean (SD) bed capacity of these sites was 124.3 (96.0) beds. Common reasons for withdrawal included time limitations (22 sites), staff turnover (21 sites), or both (6 sites)  and 257 of 367 participating sites , respectively. Actions to improve antibiotic use and antibiotic use tracking significantly increased throughout the course of the safety program. Required in-service training for nurses on topics related to antibiotic use increased from 328 of 439 sites (74.7%) at the start of the safety program to 331 of 367 sites (90.2%) at the end (P < .001). Comparing the beginning and the end of the safety program, sites were more likely to develop antibiotic prescribing recommendations , perform postprescriptive review with feedback , implement formulary restriction of antibiotics , and track overall antibiotic use   and medical directors of 273 of 439 sites (62.2%) described themselves as being involved in antibiotic stewardship activities at their LTC facilities. By the end of the program, participation levels increased to 341  .P = .02). Similarly, antibiotic DOT decreased from 64.1 to 61.0 per 1000 resident-days, although the difference was not significant  (P < .001), from 8.3 to 7.2; differences in low  and no engagement facilities  were not significant. DOT in high-engagement facilities was reduced by 9.97 per 1000 resident-days , from 71.9 to 61.9; differences in low  and no engagement facilities  were not significant (P = .046) but not in IV antibiotics  across the entire cohort. Fluoroquinolone use decreased from 1.5 to 1.3 starts per 1000 resident-days (P = .002) and from 10.6 to 9.4 DOT per 1000 resident-days (P = .01) across all sites from the beginning to the end of the safety program  submitted comprehensive data for analysis of antibiotic use from the beginning to the end of the safety program. From baseline to the end of the program, antibiotic starts decreased from 7.9 to 7.5 per 1000 resident-days  . In a sunificant . The decnificant . There wP = .001) between January 2019 and December 2019. There was no statistically significant change in the number of facility-onset C difficile LabID events per 10 000 resident-days across the safety program . The reduction was significant between January and a study midpoint (May-June)  , nurses (on communicating infectious concerns with prescribers), family members , and program administration (on engaging senior executives). Engaging all staffing roles facilitates organizational culture change.The AHRQ Safety Program was designed to address unique challenges in the LTC setting and involve direct care staff in the antibiotic decision-making process. Most ASPs focus on educating physician prescribers in best practices or antibiotic prescribing guidelines. In LTC settings, nurses and nurse assistants are the backbone of the care system, serving as the point of contact between prescribers, family members, residents, and administration. Nurses and nurse assistants are well-positioned to serve as clear advocates for residents, particularly when it comes to patient safety and antibiotic prescribing practices, after receiving appropriate training in best practices around antibiotic prescribing.17 There is a growing body of evidence in older adults describing adverse events with fluoroquinolone use including prolonged corrected QT intervals, tendinitis, aortic dissections, seizures, peripheral neuropathy, psychological disturbances, and C difficile infections (CDI).20 The AHRQ Safety Program educated prescribers and direct care staff on the potential side effects associated with fluoroquinolone use through case-based examples combined with guidance for safer alternative therapies for common infections encountered in LTC settings. We observed significant reductions in both antibiotic starts and DOTs for fluoroquinolones. Despite the association between fluoroquinolone use and CDI rates, we did not observe a reduction in CDI across sites.Reductions in antibiotic use were more pronounced in facilities with greater engagement in the program, suggesting that variation in uptake of this quality improvement initiative was associated with key outcomes. Furthermore, antibiotic use decreased significantly for oral antibiotics compared with IV antibiotics. Oral antibiotics are used much more frequently in LTC settings, and case scenarios presented on the webinars were largely directed toward reducing oral antibiotics. It is possible that the lack of change in IV antibiotic use may reflect courses of antibiotics started in the acute-care setting and continued in postacute care. Reducing fluoroquinolone use was a specific target of the safety program given the concerning adverse event profile of fluoroquinolones, particularly in older adults. Because of a combination of their oral bioavailability, broad spectrum, and ease of dosing, fluoroquinolones are frequently prescribed in LTC as first-line agents, even when alternatives with a more favorable side effect profile exist.21 The common misperception by direct care staff or family members that changes in the appearance of urine  indicate a urinary tract infection (UTI) can lead to obtaining unnecessary urine cultures to assess for UTI.22 Up to 50% of residents in nursing homes will have bacteria in their urine, and prescribers often feel inclined to treat a positive culture even if antibiotics are not indicated.23 We targeted misconceptions about when to test for and treat UTIs by educating direct caregivers about sending urine cultures only when specific signs and symptoms were present.21 We saw a significant reduction in the number of urine cultures ordered from the beginning to the end of the safety program, emphasizing that diagnostic stewardship has an important role in reducing antibiotic use in LTC facilities.Unnecessary treatment of asymptomatic bacteriuria is one of the primary reasons antibiotics are prescribed inappropriately in nursing homes.26 Furthermore, we do not have comparative data available prior to the 1-year safety program. We did not want to discourage resource-limited LTC facilities from joining the program due to the need for onerous retrospective data collection. Additionally, we cannot discount the possibility of inaccuracies with antibiotic data collection by participating sites. Our lack of access to protected health information precluded our ability to ensure the integrity of antibiotic use data submitted from hospitals or an evaluation of appropriate antibiotic use. Nonetheless, rigorous steps were followed to maximize the likelihood of valid data submission, as previously described.There are several limitations to this study. Because the AHRQ Safety Program was a quality improvement initiative and not a research study, we limited data collection to information necessary to improve antibiotic prescribing practices. Evaluation to determine if specific aspects of the safety program had a greater association with the primary outcomes were not assessed. Previous evidence supports implementation of the safety program as a bundle of modules rather than as distinct components.27 Although seasonal trends may have had some impact on the high prescribing rates observed at the beginning of the safety program (in January), we compared these rates with data collected at the end of program (in December) where similar increases in antibiotic use in LTC are generally observed.28 No such increases were observed in our cohort.Seasonal trends can play a role in antibiotic use, and while data are limited, there are reports of increased antibiotic use in LTC facilities during the winter months, with antibiotic use particularly driven by an increase in respiratory infections.30 However, if this mandate impacted our results, an uptake in ASPs would have likely affected both baseline data as well as data at the conclusion of the study.Finally, changes in antibiotic usage identified in the safety program may have been affected by secular trends. The CMS mandated that LTC facilities have ASPs by 2017.Developing, implementing, and sustaining ASPs in LTC settings can be challenging due to frequent staff turnover and limited time and resources. Despite these challenges, the AHRQ Safety Program used patient-safety principles, multidisciplinary education, and a multitude of interactive tools aimed at incorporating stewardship principles into daily practice; high participation in the program was associated with a reduction in antibiotic use and improved outcomes. Data are needed to evaluate the sustainability of these interventions and their long-term effect on antibiotic use, resident outcomes, and staff and resident satisfaction.


Recycled aggregates (RA) from construction and demolition waste (CDW) instead of natural aggregates (NA) were analysed in the manufacture of new eco-friendly concrete. Fine (FRA) and coarse (CRA) recycled aggregates were used in different percentages as substitutes of natural sand and gravel, respectively. The results revealed that the use of RA in percentages of up to 50 wt.% is feasible. Additionally, RA were used to produce paving blocks in accordance with industrial requirements. Thus, values of water absorption lesser than 6.0% and tensile strength upper than 3.6 MPa were obtained, which are similar to those of a reference sample and within the limit values established by the regulations. These results were achieved by reducing the incorporation of cement, thereby saving production costs and minimizing environmental impact. Within Eurostat , being tEurostat . In turnthe CDRA , which ithe CDRA .CDW are comprised of a broad range of materials, such as concrete, ceramics, brick, rock, metal, plaster, wood, glass, soil and asphalt . CDW was treated to obtain RA with physical and mechanical properties similar to those of NA. Hence, the RA were obtained through mechanical pre-treatment  of the CDW. Firstly, the samples were crushed and passed through a sieve 12 mm. Secondly, the coarse fraction was ground and sieved through a 4.8-mm mesh sieve. Finally, two different grain size fractions were obtained, fine recycled aggregate (FRA) with a particle size < 4.8 mm, and coarse recycled aggregate (CRA) > 4.8 mm, which were used in this research. Regardless of the pre-treatment performed, RA showed a water absorption index higher than NA (sand and gravel) due to the presence of porous materials such as mortar, ceramic and clay  were provided by the precast concrete company “Montalbán y Rodríguez S.L.”, placed in the region of Murcia (Spain). Eco-friendly mortars and paving blocks were prepared using a high-activity water reducing/superplasticising additive based on polycarboxylates MasterCast 731 supplied by BASF Company to improve consistency.−2 and is composed of a mixture of clinker (97 wt.%) and natural gypsum (3 wt.%). The mixtures were moistened by spraying until a w/c ratio = 0.45 was reached, which is the optimum index for obtaining adequate consistency and a good workability used in the industrial process and which has been provided by the precast company. The moistened materials were homogenised and placed in steel moulds to obtain concrete cylindrical test specimens , which were finally vibrated as described in the UNE-EN 12390-3 standard . The mineralogical characterisation of the CDW, the recycled aggregates (fine and coarse) and the natural aggregates (sand and gravel) was carried out using the XRD (X-ray diffraction) technique in a Shimadzu diffractometer model XRD 6000, with Cuα radiation and operating at 1.2 kW (40 kV e 30 mA). The diffractograms were registered in the interval of 5–60° 2θ, with a step size of 1°/min. The main elements in the CDW and in the natural and recycled aggregates were examined using the energy dispersive X-ray fluorescence (EDXRF) technique in a Bruker S2 Ranger LE spectrometer fitted with a 50 W X-ray tube , Pd anode, XFlash® silicon drift detector with <135 eV resolution for Mn Kα and 100.000 cps, and equipped with a Peltier type cooling system (liquid nitrogen is not required) and primary filter tool changers with 9 positions possible. The trace elements were measured by inductively coupled plasma mass spectrometry (ICP-MS) by using an HP computer model HP4500®. The equipment was pre-calibrated with suitable standards.The consistency (self-compacting) of fresh concrete was calculated using a V-funnel test as established in the UNE-EN 12350-9  standardThe test specimens and paving units were immersed in water at a temperature of 20 ± 5 °C until they reached constant mass (immersed mass). Then, each specimen was dried using a cloth until the surface of the concrete is dull (wet mass). Finally, the materials were dried inside an oven at a temperature of 105 ± 5 °C until they reached a constant mass (dry mass). WA, BD and AP were determined according to the following equations:mw is the wet mass, md is the dry mass and mi is the immersed mass. Furthermore, in the case of regular and rectangular pavers, the best method of determining the BD is by using the md/mass volume ratio , which is calculated from the measured dimensions (ISO 5016 where ISO 5016 .For measuring specific gravity (SG), the samples were finely ground (< 62 μm) in order to open the entire closed porosity. A weighted mass from this powder was used to determine its true volume and, therefore, its true density, by displacing distilled water inside a pycnometer ISO 5018 .4\documT) test.T (MPa), P is the measured load at failure (N), S is the area of failure plane (mm2) and k is a correction factor (k=0.87) (UNE-EN 1338 σ (MPa), P is the measured load at failure (N) and A is the resisting area (mm2).The mechanical properties (compressive and tensile splitting strength) of the samples were compared with the properties of standards (without CDW), determined according to the requirements and test methods established in the UNE-EN 1338  standardAttending to Fig. Figure 2), Al (9.8 wt.% as Al2O3), Ca (6.1 wt.% as CaO), Fe (3.2 wt.% as Fe2O3), Mg (1.7 wt.% of MgO) and Ti (1.1 wt.% of TiO2). These results are similar to those found in the treated CDW fractions, whose main constituent is SiO2, 73.0 and 78.4 wt.% in CRA and FRA respectively. Regarding the NA, sand is mainly composed of SiO2 (90.6 wt.%) in the quartz form and Al2O3 (3.8 wt.%), according to the mineralogical study, while the gravel is mainly composed of SiO2 (63.2 wt.%), CaO (10.5 wt.%), Al2O3 (4.8 wt.%) and Fe2O3 (3.0 wt.%). On the other hand, Portland cement type I is composed of clinker and gypsum and mainly contains CaO, SiO2, Al2O3 and Fe2O3 .The major elemental analysis by XRF indicated a vast array of elements in CDW composition Table , mainly 3 in the RA, which also leads to increased LOI values, as its thermal decomposition produces CO2 emission.Furthermore, the loss on ignition (LOI) in CDW and RA ranged from 4.9 to 5.7 wt.% Table , and it In order to study the contaminants existing in the CDW, the trace elements (below 0.1 wt.%) were studied by ICP-MS Table . The mai2), calcite (CaCO3) and portlandite (Ca(OH)2). In addition, the diffractograms indicate the presence of minor phases such as calcium silicate hydrate or C-S-H (3CaO·2SiO2·3H2O), gypsum (CaSO4·2H2O) and ettringite (Ca6Al2(SO4)3(OH)12·26H2O). These results agree with those reported in other studies . Gravel only includes quartz as crystalline phase  met this requirement  of 2.2 g cm−3, and finally with those contain 100 wt.% CRA (0-100-7) of 2.1 g cm−3.Similar to the properties previously studied, the density (SG) increased lightly in the specimens with the highest cement content Table , becauseσ) and tensile splitting strength (T), as they are closely related to its potential to support stresses over time without failure. Therefore, both strengths allow a general assessment of the quality of the new concrete. Table The most relevant technological properties for assessing the performance of a concrete structure are compressive strength  although the best results were achieved by the specimens incorporating up to 25 wt.% FRA , 19.6 MPa (100-100-10), 21.5 MPa (100-100-20) and 26.3 MPa (100-100-30), Table Observation of the concrete specimens after the compressive strength test leads to the inference that the load distribution during the test Fig.  was homoT of the specimens, as it is expected.Moreover, the characteristic tensile splitting strength at 28 days for concrete made with RA (CRA and/or FRA) is shown in Table The cylindrical specimens after the tensile splitting strength test showed almost perfect longitudinal fracture, which is characteristic of samples subjected to a uniform longitudinal load distribution during the test Fig. .After studying the influence of the incorporation of the RA in the production of environmentally friendly concrete, the possibility of replacing NA with RA in the manufacture of constructive elements by using precast concrete elements such as paving block was evaluated Fig. , whose pUNE-EN 1338  establisTable 2 are emitted in the production of one ton of gravel or sand produced by open-cast mining, while this emission is reduced to 0.001 tons of CO2 emitted in the production of one ton of aggregates from CDW.Throughout its service life, concrete has an environmental impact resulting from different factors such as the production of the raw materials, its manufacture, its use and maintenance throughout its service life and, finally, its demolition. In this assessment, we will focus on the impact associated with the production of raw materials, specifically aggregates, assuming that the other variables are not significantly influenced by the use of natural or recycled aggregates. According to Pimiento and Restrepo , 0.008 t2 emission associated with the extraction of the aggregates necessary to manufacture 1 ton of precast concrete can be estimated as 7.4 kg  the CO2 emissions, other environmental benefits associated with the replacement of natural aggregates with recycled aggregates must be taken into account, such as reduction of the volume of extraction of limited raw materials, thus preserving natural resources; reduction of mining waste generated in the extraction of reduction of landfill requirements for mining waste resulting from the extraction of mining waste; and reduction of landfill requirements for mining waste. Therefore, the precast concrete in this study can be considered as environmentally friendly. However, it is clear that, in order to ensure that the manufacture of concrete incorporating recycled aggregates is assumed by the industry, it is necessary to ensure competitive manufacturing costs. In this sense, the production cost of recycled aggregates is 15% lower than that of gravel extraction and 27% lower than that of sand extraction (Varela Alberte But in addition to the advantages derived from lower COσ) and tensile splitting strength (T)). Additions of up to 50 wt.% of fine (50-0-7) or coarse (0-50-7) recycled aggregates or the substitution of 25 wt.% of each (sample 25-25-7) result in materials with similar properties to the reference materials. Moreover, the results are in accordance with the values established by the EHE-08 for concrete manufacture.In this study, the use of recycled aggregates in the manufacture of concrete paving blocks was analysed. Thus, the variability in the composition, the lower density and the higher water absorption of CDW are aspects to be borne in mind. In this sense, the addition of FRA and CRA increases the water absorption (WA) and the apparent porosity (AP) of concrete, reducing both its density and resistance . The water absorption below 6.0% (class 2 and mark B) and the characteristic tensile splitting strength above 3.6 MPa the minimum values established in the UNE-EN 1338 standard, which means that they can be used in pedestrian areas or areas with little traffic.


Social entrepreneurship (SE) is often presented in the literature as the key to solve many of this world’s persistent social problems. SE offers a special opportunity to address the 2030 Agenda for Sustainable Development and to boost the Sustainable Development Goals (SDGs). This research examines the effects of Service Learning (SL) on the SE of university students and to examine whether certain sociodemographic factors  are associated with students’ SE competence development when applying SL. Pre-service teachers (n = 98) of the degree in early childhood education applied a physical education SL programme. We used a quantitative method with a pre-experimental design, using pre-test and post-test measures. The findings obtained show a significant improvement on the SE competence of PSTs, so SL seems a good tool to develop it. The results that analyse the influence of socio-demographic factors do not show significant correlations. There are very few studies focusing on this objective, so it would be interesting to encourage the research community to provide more data in this area. In recent decades, higher education has been shifting from a directive and instructional approach to the use of active and experiential methodologies. This situation allows students to apply the acquired competences in real contexts, which is of vital importance in teacher education. In this vein, service learning (SL), is a methodology based on John Dewey’s experiential learning theory . SL seekhttps://sdgs.un.org/goals accessed on 27 October 2021). Specifically, our proposal, which focuses on the promotion of SE in PSTs, may be useful to enhance goal 1: economic growth must be inclusive to provide sustainable jobs and promote equality (no poverty); goal 4: obtaining a quality education is the foundation to improving people’s lives and sustainable development ; goal 5: gender equality is a necessary foundation for a prosperous and sustainable world ; goal 10: to reduce inequalities, policies should be universal in principle, paying attention to the needs of disadvantaged and marginalized populations ; goal 16: access to justice for all, and building effective, accountable institutions at all levels ; goal 17: revitalize the global partnership for sustainable development (partnerships).A surge of research interest in social entrepreneurship (SE) has flourished in the last decade, providing important insights regarding its role in fostering inclusive growth and institutional change . AlthougIn this sense, different studies with trainee teachers suggest that SL can foster knowledge, understanding, sensitivity and commitment in relation to the SDGs ,14. It iDriven by previous literature requests, this research analyses the effects of SL in the field of physical education ,16,17,18Previous research examining the effect of SL on SE in a North American university suggests that SL participation in the physical education field comes with an improvement in students’ social, personal, and innovative traits . TherefoWe consider it interesting to investigate the influence of socio-demographic factors, as the results may provide us with clues or recommendations that can serve as a guide for the implementation of future teaching innovation projects or for teachers to choose a certain strategy/include it or assess it in relation to the students they have to attend to and their characteristics.The present research has two objectives: to analyse the effects of SL on the SE of university students and to examine whether certain sociodemographic factors  are associated with students’ SEC development when applying SL. In this way, we will be able to compare the results obtained in each of the factors under study.Two hypotheses are put forward, on the one hand, that participation in the SL programme will significantly improve the SEC of university students, and on the other, that socio-demographic factors such as age, university entrance studies, family studies, previous participation in volunteering or associations, and employment situation will have an influence on the effects produced by the use of SL on the students’ SEC.This intervention experiment used a quantitative method with a pre-experimental design based on pre-test and post-test measures carried out with 98 PSTs. It examined the effect of participation in the SL programme on SEC and contrasted how sociodemographic factors may have been related to such an impact.All participants attended the annual course subject “Fundamentals of body language; motor games in early childhood education”, present in the 2nd year of the degree in early childhood education at Jaume I University, during the 2017/2018 academic year. This subject is focused on the development of contents of the physical education field, which are essential to promote children’s integral development. In addition, due to the idiosyncrasy inherent in this subject, a number of enriching interactions are promoted between PSTs and the children receiving the service.The sample was formed from a non-probability sampling, because it used a natural group and showed a bias regarding sex, because the majority of the students were female. This fact ruled out the gender variable for the investigation. However, such a distribution is not new, since most of the time, the number of females is higher in this context , a circuAccording to the curriculum and course syllabus, the reference subject aims to develop students’ skills to work body language in early childhood as well as to develop their motor domain through motor games. SL methodology was a strategy applied to develop the competences that PSTs had to acquire. Therefore, an SL programme was embedded in the subject. The design of such a programme was based on the quality guidelines established by the National Youth Leadership Council ; in addiWithin this programme, students were divided in groups of four or five members to carry out a direct SL project aimed at children with functional diversity and/or suffering from social exclusion. These children had some kind of motor and expressive impairment as a shared feature. Each group designed and carried out their own project. It was sketched bearing in mind the motor and social needs of the children, aspects that PSTs had identified in the diagnosis phase. Thus, the PSTs project consisted of designing and carrying out practical body language and motor game sessions with the aim of improving these areas as well as promoting social inclusion. The students could choose among six local organizations that had agreed to be involved in the programme. Each organization had a particular schedule; consequently, the projects could vary in terms of total length. In any case, all the groups were engaged in approximately eight hours of direct service . In addition to the time in direct contact with the children, PSTs had to undertake the rest of the phases integral to SL methodology. As a result, each pre-service teacher dedicated a total of 25 h on the project.Social Entrepreneurship Competency Scale (SECS) instrument was used [A Spanish version of the was used . This tot-tests for comparison of means and analysis of variance models (ANOVA) were used.Data were analysed using SPSS Version 26, using descriptive and inferential statistics. Specifically, α = 0.896 was obtained for Cronbach’s Alpha test, showing good internal consistency [t-test. The results showed significant differences (p < 0.05) for the SECS overall, as well as for all feature categories  for the ability to take risks and the ability to learn and evolve. The results for these features after applying the paired samples t-test were t(2) = −6.928, p = 0.020 and t(1) = −35.000, p = 0.018, respectively. However, we should note that 15 of the 17 features that make up the SEC improved in value from the pre- to the post-measurements. Creativity showed the same result for both measurements and only the ability to identify opportunities scored lower for the pre-test compared to the post-test measurement  with repeated measures was carried out to examine the individual effect of the seven factors on the results of the SECS between pre- and post-test measures. To do so, each of the factors was entered as a covariable in the ANOVA. p > 0.05). This means that all the factors influence the results of the scale.Results show significant differences when both analyses are combined and the global pre-test/post-test results of the SECS are compared. However, when using the ANOVA to analyse the influence of the factors with repeated measures, these do not appear for any of the six factors (Given that the study factors are grouped with different structure see , it is cNo significant differences were obtained in the analysis by factors. However, it is interesting to highlight some outcomes that arise from the analysis of the mean scores, which we summarize as follows: better mean scores are found as age increases; students who accessed from the high school achieved better social entrepreneurship results; the higher the family education, the better the SECS scores; having previous experience on social participation favoured the development of social entrepreneurship; participants who considered themselves progressive or liberal obtained better scores in social entrepreneurship after using SL, although the difference is small compared to those who defined themselves as conservative; and having work experience enhanced the acquisition of the social entrepreneurship features as a result of applying SL.The present study examines the impact of a SL programme applied through a subject within the field of the Didactics of Physical Education on the participant PSTs. Particularly, the first hypothesis focuses on the effects related to participants’ SEC, and the second on the sociodemographic outcomes that may influence such results.The findings obtained show a significant improvement on the SEC of PSTs; thus, the first hypothesis is accepted. Previous research had examined the effects of experiential methodologies applied in different contexts on students’ SEC  as well SEC, however, may be divided into different categories of features, namely personal, social, and innovative , and PSTIn fact, according to a recent systematic review on SL on physical education teacher education, many studies of the sample analysed focused on the impact of SL methodology on higher education students’ personal and social skills . In addiWith regard to the third category of features, which is related to innovative skills, the literature is less developed. Although research on social innovation is one of the four strands in which entrepreneurial social value creation is divided , the litlife-changing experience [The SECS has 17 specific features, among which 15 displayed an improvement in their value when pre-test and post-test scores were compared. This result is similar to that achieved by some authors ,45,46,47perience .The second hypothesis argued that sociodemographic factors could influence the participants’ SEC, but according to the results obtained, it has to be rejected, since no significant effects have been found. This finding is not surprising, since literature on SL examining the influence of students’ sociodemographic features is inconclusive. For example, regarding the age factor, two studies found that this feature could have an effect, and both agree on the fact that the older the students, the more significant the results ,24. HoweThe way of entering the university and relatives’ educational level could be other factors influencing the results of the present study, since they have been relevant in some cases regarding outcomes related to empathy and social and civic attitudes ,25. HoweMoving now to the factor focused on previous social participation, the literature suggests that volunteering or similar activities with underserved communities may be influenced by the participants’ previous experiences . In factFinally, employment status did not show any significant correlation with SEC development, similarly to previous results concerning social and civic attitudes . HoweverDespite the interesting results obtained, there exist some limitations that should be taken into consideration. For example, there was not a control group, and students were selected by means of convenience sampling. In this sense, a randomized controlled trial would have strengthened the validity of this study . In addiThis research has presented the results of applying a SL programme with PSTs in the field of physical education, aimed at analysing the effects of SL on the SEC of university students and examining the influence that socio-demographic factors may have on these effects. On the one hand, the results obtained show that the SL programme applied in the field of PSTs training through physical education is a useful tool for developing SEC. On the other hand, the analysis of the influence of socio-demographic factors does not show significant effects. There are very few studies focusing on this objective, so it would be interesting to encourage the research community to provide more data in this area. If research is carried out in this sense, it may offer clues for university teachers in the design and implementation of SL programmes in relation to the features of their students.


This paper deals with the cross-sectional analysis of the resistance of RC members subjected to a bending moment with or without axial forces. To determine section resistance, the nonlinear material law for concrete in compression is assumed according to Eurocode 2, taking into account the effect of concrete softening. It adequately describes the concrete behavior of RC members up to failure. The idealized stress–strain relation for the reinforcing steel is assumed. For the ring cross-section subjected to bending with axial force and for areas weakened by an opening, normalized resistances have been derived by integrating corresponding equilibrium equations. They are presented in the form of interaction curves and compared with the results of testing conducted on RC eccentrically loaded columns. Furthermore, the ultimate normalized bending moment has been derived for the RC rectangle subjected to bending without axial force. It was applied to the cross-sectional analysis of steel and concrete composite beams consisting of the RC rectangular core located inside a reversed TT-welded profile. Comparative analysis indicated good agreements between the proposed section models and experimental data. The objective of the paper is the dimensioning optimization of the considered cross-sections with the fulfillment of structural safety requirements. N and bending moment M and when the nonlinear material law for concrete is assumed, the task consists in the determining the unknown section strains. In this case, the problem is described mathematically by a set of two equations that are highly nonlinear and difficult to be solved. Therefore, a numerical optimization strategy must be employed [For structural safety reasons, the load-bearing capacity (resistance) of any designed or existing structures should satisfy the conditions of ultimate limit states. In recent years, intensive developments and advanced applications of RC structural members with the increased resistances are observed in newly designed and erected tower buildings. The resistance of RC (reinforced concrete) members subjected to bending with or without axial force is undertaken both as a structural and a practical task. Such members are commonly encountered in engineering practices, e.g., reinforced concrete columns, tower-like structures, steel and concrete composite columns and beams. In the formulation accepted in this paper, the resistance of RC cross-section is determined by the occurrence of the ultimate strains occurring anywhere in that section, which means that it depends both on the material laws and the geometrical characteristics of the section. With respect to material laws, a simplified approach is the most often used on the basis of the rectangular stress distribution in concrete, represented among others by Knauff . For theemployed .Newly designed floor slab systems are currently the subject of particular interest of designers because they provide a flat lower surface of finished floor slab. These systems consist of steel and concrete composite beams that are structurally connected with prefabricated or cast in situ slabs ,30,31,32In the presented considerations, two basic assumptions are made in which plane cross-sections remain in plane and the tensile strength of concrete is neglected.cσ-cε in compression for short term uniaxial loading is recommended for nonlinear structural analysis as follows [According to Eurocode 2, the stress–strain relation for concrete  follows .(1)σc=kFor both reinforcing and profile steels, the linear elastic–ideal plastic model is applied.R, inner radius r and thickness t = R − r is subjected to axial force N and bending moment M  and in reinforcing steel sε (‰) are given by the following.For the section under combined compression and bending, the relations for strains in concrete All angles are measured from the compressive to the tensile zone. The sectional equilibrium equation of the axial forces is described as follows.The sectional equilibrium equation of the bending moments about the symmetry axis of the section is expressed as follows.ϕ:Taking into account physical and geometrical relationships (1)–(3) in equilibrium Equations (4) and (5), the problem results in a purely mathematical task consisting in searching the indefinite integrals of the following functions of variable W1 = 1/(k − 2)k2; W2 = W1 + k/k2; and b = W1 − k1.Upon transformation, Equations (6) and (7) result in the following:ϕ + b) occurring in Equations (9) and (10) has been found as follows.An indefinite integral of function 1/–(12), normalized ultimate resistances μ is the reinforcement ratio; and α1 and α2 are angles determining the depth of the plastified zones of steel in compression and in tension, respectively.Here, Rmn-Rmm valid for the case, when both compressive and tensile strains occur in the analyzed section characterized by the following: the limiting value cu =ε −3.5‰; the concrete grade C20/25 (cmf = 28 MPa); ykf = 500 MPa; cmE = 30 GPa; substitute reinforcement ratio yk/fcmμ f = 0; 0.1; 0 ≤ sε ≤ 10‰ (The graphic interpretations of Equations (13)–(15) are the interaction diagrams with normalized resistances εs ≤ 10‰ . These cIn a similar manner, the corresponding formulae are obtained for the section that is entirely in compression. The relevant relationship for strains is given by the following.Rmn and Rmm are described in the following form:k1 = 2ε1/(ε2 − ε1) + 1; and k2 = −0.5 (ε2 − ε1)/cε1 shall be substituted.The formulae determining cross-sectional forces cuε | > |c1ε |, Equations (17) and (18) describe the ring cross-section at the stage of concrete instability (at failure). This means that Drucker’s stability postulates may not be satisfied [cε1 = −2.0 ‰; cu =ε −3.5‰), with a limitation to the values Rmm ≥ 0. All curves in cuε = cε1 = −2‰, the stability condition by Drucker is satisfied for any values of cε and sε. Thus, the obtained curves based on Equations (13)–(15) and Equations (17) and (18) can be regarded as the actual carrying capacity curves accepted in design codes. It is worth highlighting that these interaction diagrams (EC2) are very close to those based on the parabola–rectangle (parabola)  .uN and bending moment uM = uN⋅ e  and its percentage was μ = 1.024%. The properties of the steel rebars were established in turn by tensile test according to Polish Standard PN-EN ISO 6892-1:2010, [yk/fcmμ f = 0.2688. Using the derived Equations (13)–(18), the interaction chart Rmn-Rmm has been plotted. The effect of confinement of the column (stirrups) was not analyzed. The comparisons presented in Full-scale tests were carried out on four RC designed columns eccentrically loaded, with annular cross-section, denoted by Typ 2 . The out-3: 2011 . The rei-1:2010, . The colt and the width b is subjected to bending moment M without axial force , the normalized ultimate bending moment The presented section model can be applied for determining the resistance of composite steel and concrete beams, named BH beams, subjected to bending. The considered beams consist of a reinforced (RC) rectangular core placed inside a reversed TT-welded profile, as shown in HRmM determining the resistance of the considered BH beam is derived in terms of strains upon integrating the equilibrium equation of the bending moments about the horizontal axis of the RC core rectangle [L = 7.88 m. They were made of concrete with a mean compressive strength of cmf = 68 MPa, which was determined by a strength test according to Polish Standard PN-EN 12390-3:2011 . For the RC rectangle with the cross-section of 0.27 m × 0.35 m, the reinforcing steel with ykf = 500 MPa and the profile steel with Hykf = 460 MPa were used. The properties of the steels were established in turn by tensile tests according to Polish Standard PN-EN ISO 6892-1:2010. The setup of the tests is exhibited in cε, in reinforcing steels in compression s1ε and in tension sε2, as well as in the lower flange of profile steel Hfε, were measured in the middle section of the BH beam.Ultimate bending moment ectangle . In thisuM and resistances HRmM. The compressive strains in concrete reached ultimate values. The value of sε1 = −2.89‰ indicates that the plastic strains in the rebars in compression may have occurred. The values of HRmM have been calculated in accordance with derived Equations (23)–(26). It is worth noting that they are close to failure bending moments uM (relative differences 4.8–6.5%). This confirms very good agreements between resistances HRmM and the test results in ultimate bending moments uM.The failures of all BH beams manifested themselves by concrete crushing . Table 2The obtained solutions are presented in the form of interaction diagrams that satisfy the conditions of convexity in accordance with Drucker’s postulates. This means that they can be regarded as the actual carrying capacity curves.The proposed ring section models seem to have a wider application field than the previous ones, due to the assumptions of a noncentral layout of reinforcement and wall-edge strains. As a result, they are suitable for ring cross-sections with both the thin and moderate thicknesses. Furthermore, they can be easily adopted when structure strengthening is required by means of externally bonded CFRP, FRP or GFRP composites as well as for determining the resistance of composite steel and concrete columns.Using this approach, the similar formulae can be derived for other sections commonly encountered in the engineering practice, for example, a rectangle and the ones weakened by openings.It was proved that the computational results conform to those obtained by testing on RC eccentrically loaded columns.HRmM of the composite steel and concrete beams.The analytical solution was developed for the resistance of RC rectangle subjected to bending without axial forces to determine ultimate bending moment The comparisons made between the computational and test results of BH beams showed good agreements in ultimate bending moments.The above-developed models enabled the analysis of the behavior of RC members in the postcritical phase.They have been implemented in Excel to provide a useful tool for the dimensioning optimization of RC-designed members and structures that may result in a reduction in material consumption and a lesser impact on the environment.Further experimental work is needed concerning the postcritical behavior of RC members.The complete analytical solution has been found for the resistance of RC ring cross-sections subjected to bending with axial force, based on the nonlinear material law for concrete and taking into account the effect of concrete softening. It applies both to designed and existing members and structures. In this respect, it can be regarded as a valuable one in the theory of reinforced concrete:


This work experimentally investigated the corrosion process involving various concentrations of NaCl-Na2SO4 leading to the coupled erosion of concrete. The appearance, weight, and mechanical properties of the concrete were measured throughout the erosion process, and the Cl− and SO42− contents in concrete were determined using Cl− rapid testing and spectrophotometry, respectively. Scanning electron microscopy, energy spectrometry, X-ray diffractometry, and mercury porosimetry were also employed to analyze microstructural changes and complex mineral combinations in these samples. The results showed that with higher Na2SO4 concentration and longer exposure time, the mass, compressive strength, and relative dynamic elastic modulus gradually increased and large pores gradually transitioned to medium and small pores. When the Na2SO4 mass fraction in the salt solution was ≥10 wt%, there was a downward trend in the mechanical properties after exposure for a certain period of time. The Cl− diffusion rate was thus related to Na2SO4 concentration. When the Na2SO4 mass fraction in solution was ≤5 wt% and exposure time short, SO42− and cement hydration/corrosion products hindered Cl− migration. In a concentrated Na2SO4 environment (≥10 wt%), the Cl− diffusion rate was accelerated in the later stages of exposure. These experiments further revealed that the Cl− migration rate was higher than that of SO42−.The diffusion of sulfate (SO The coorrosion ,16,17,18− in concrete. Hussein et al. [− in concrete after different corrosion times in the marine environment. Luping [− enters concrete, a portion of these ions will react with cement hydration products, including tricalcium sulfate hydrate, to form Friedel’s salt in a process called “chloride bindin” [− remaining in the pore solution continues to diffuse into the interior through pores or cracks, ultimately accumulates around the steel bars [− attached to the surface of the steel bars exceeds a certain concentration, electrochemical corrosion of the steel bar may occur [To date, numerous scholars have carried out extensive NaCl exposure tests to study the diffusion and microstructural involvement of Cln et al.  studied n et al.  describe. Luping , Yuan [2. Luping , and Wan. Luping  each fou bindin” . The rem bindin” ,26. Meaneel bars . When thay occur , resultiay occur .2SO4 attack [2SO4 corrosion tests and found that as the Na2SO4 concentration in solution increased, the relative dynamic elastic modulus (RDEM) and compressive strength of concrete, and damage failure time all decreased significantly. Najjar [42− and the aluminates  of cement hydration products in concrete to produce ettringite (Aft) [2SO4 eroded concrete under a dry-wet cycle, the evolution of Aft was studied via thermal difference-thermogravimetry [2SO4 corrosion concrete and found that it is higher than the tensile strength of the matrix, this caused new microcracks to appear in the concrete, which decreased the concrete’s mechanical properties [Several scholars have also investigated the corrosion products, microstructure, mechanical properties, and mechanisms of concrete corrosion after Na4 attack ,31. Shan4 attack  conducte. Najjar  found thte (Aft) ,35,36. Ate (Aft) . After Navimetry . Bassuonavimetry  used scaoperties . Zhao [4operties  studied 2SO4 and NaCl. It is well established that, the erosion of concrete by chloride and sulfate involves complex physical and chemical reactions [− diffusion mechanism in concrete in a SO42−/ Cl− mixed environment. To date, research regarding the influence of sulfate in concrete on Cl− migration has been relatively limited, and there is insufficient experimental data to verify the relevant theoretical models. Therefore, it is necessary to fill the knowledge gaps related to the mechanical properties, Cl− diffusion rates, pores, and microstructure of concrete in NaCl-Na2SO4 environment. To probe the mixed SO42−/Cl− exposure experienced by reinforced concrete in saline soil environment, the appearance changes, weight loss, mechanical properties , and fineness of the concrete were examined after exposure to various concentrations of NaCl-Na2SO4 solutions  for different periods of time . This study aimed to understand the evolution of concrete structures during salt invasion, and the resulting chemical and physical changes. The experiments used NaCl-Na2SO4 solutions to corrode the concrete, and analyzed the resulting changes in the appearance, weight loss, and mechanical properties of the concrete, which revealed the influence of different Na2SO4 concentrations on Cl− migration. A capacitance mercury porosimeter was used to study the pore structure of the concrete after solutions exposure. Finally, SEM and XRD were used to analyze concrete microstructural changes, as well as corrosion products, and the evolution of ITZ with increasing Na2SO4 concentration.According to a literature survey, there are more than 1000 salt lakes scattered in Northwest China , and theeactions ,44. Howe2SO4 reagent  was obtained from Tianjin Beichen Fangzheng Reagent Factory. The matching ratios of concrete in the test are shown in Portland cement of P.O. 42.5  was selected to prepare concrete cube specimens. The chemical composition of the cement is shown in 2SO4 solutions were simulated by preparing five corrosion-resistant rectangular plastic boxes to store different concentrations of NaCl-Na2SO4 solutions, named CS0, CS0.5, CS1, CS2, and CS3 . After curing for 28 d, samples were placed into different solutions for infusion for different periods. Before foaming, 4 surfaces of a sample were covered with epoxy resin, leaving two opposite surfaces clear to ensure that SOConcrete samples were put in these various solutions for 30, 90, 180, 270, and 360 d. The sample should be placed in an oven at 50 °C for 48 h before testing.A sample weight was measured with an electronic scale with an accuracy of 0.01 g. An HYE-2000BS electro-hydraulic servo pressure testing machine  was used to test the compressive strength of concrete samples, with the loading speed controlled at 5 kN/s and average value of the compressive strength of 3 samples taken as the concrete compressive strength. A NELD-DTV dynamic elastic modulus tester  was used to test the dynamic elastic modulus of concrete samples and weights collected with an electronic scale with an accuracy of 0.1 g. Three identical samples were produced for each test and the average taken as the concrete RDEM, with the test frequency set to 3000–9000 Hz.− and SO42− was determined from powder extracted at different depths from concrete samples obtained depths using a percussion drill. Three holes were drilled in the resin-free surface, the powders mixed from different positions, sifted with a 0.63 mm sieve, and placed in an oven at 105 °C for 2 h until there is no significant change in the quality of the powders. A 2 g mass of each sample powder was mixed with distilled water and then left to dissolve its Cl− and SO42− for 48 h. The resulting solutions were passed through filter paper to remove remaining solids. A CLU-W  type Cl− content rapid tester and Ultraviolet-visible spectrophotometer (Shimadzu Enterprise Management (China) Co., Ltd., Shanghai, China) were used to measure the concentration of Cl− and SO42− in each sample. It should be noted that, due to the uneven distribution of aggregates in the concrete, at least three samples were measured to obtain relatively accurate Cl− and SO42− results.The concentration of ClSEM/EDS analyses of concrete samples were obtained using a Sigma 300 field emission scanning electron microscope  and the samples were photographed and elementally analyzed at different magnifications. X-ray diffractometry was performed using a Bruker D8 Advance instrument , with the voltage 40 kV, scanning speed 5°/min, and minimum current 100 mA. SEM/EDS test samples were produced by breaking a concrete sample, selecting a representative block, soaking it in absolute ethanol, and then placing it in an oven at 50 °C for 24 h. Powder samples for X-ray diffraction analysis were drilled 10 mm into a concrete sample surface with an electric hammer and filtered through a 0.075 mm sieve.Concrete pore analysis was performed using a YG-97A capacitive mercury porosimeter  to measure the sample pore structures after 30, 180, and 360 d of corrosion and to 25 mm (t − W0) × 100%/W0 . The weight changes for different solutions are presented in After specimens were attacked for 30, 90, 180, 270, and 360 d, the sample weights were recorded. Photos of these samples after being attacked to different solutions for the designated periods of time are shown in 2SO4 indicated that the surface pores in the CS0.5, CS1, CS2, and CS3 samples gradually increased with corrosion time. Simultaneously, the sharp shapes of cement paste around pores gradually adopted arc-shaped, and pore outer diameters gradually increased  is the change in compressive strength of concrete after corrosion n d, %; ∆fc,0 is the value of 28 d compressive strength of concrete before corrosion, MPa; ∆fc,n is after n days of corrosion compressive value of concrete, MPa;Uniaxial compressive strength is an important indicator for measuring the strength and damage characteristics of concrete materials in a corrosive environment and it can more intuitively reflect the relationship between the damage and the concentration and time of exposure to a corrosive solution. According to Equation (1), the loss of concrete compressive strength in different salt solutions was calculated.2SO4 for designated times were generally consistent regardless of the solutions composition (2SO4 content (≤ 5 wt%), no significant changes were observed on sample surfaces .2SO4. As the Na2SO4 concentration increased, RDEM decreased and the CS3 samples exhibited a downward trend. This indicted that the increased RDEM of the concrete during the initial salt corrosion stage was mainly due to cement hydration and the filling of pore structures upon NaCl and Na2SO4 corrosion, which increased concrete’s integrity and density. In concentrated Na2SO4 solution, as the concrete structure (to a certain depth) was damaged by corrosion products, new pores or cracks were generated in the samples, which reduced their RDEM. These results showed that the RDEMs of concrete in different salt solutions were basically consistent with the changes in compressive strength, however, the impact of Na2SO4 on compressive strength was more significant than on RDEM.As the corrosion time increased, its RDEM increased but the rate of increase tended to decelerate . The RDE2SO4 in samples at various depths during corrosion with different solutions were examined. The results involving Cl− and SO42− ions in the same solution were gathered to make a clear comparison ) generate Friedel’s salt and release SO42− at the same time [2SO4 concentration and longer times, AFm and Friedel’s salt reacted with SO42− to generate stable corrosion products Aft [2SO4 solution. Therefore, the diffraction peaks of Aft and Gyp in these samples gradually increased, whereas the intensity of Friedel’s salt and CH diffraction peaks gradually decreased. The Friedel’s salt diffraction peak was present in the diffraction pattern of the late-stage CS0.5 sample and early-stage CS1 and CS2 samples, but it did not appear in CS3 samples with high Na2SO4 concentration. This was mainly because the migration rate of Cl− in concrete was >100 times that of SO42−. After SO42− diffuses into the concrete, more Friedel’s salt was formed, and the small number of times that of SO42−. After SO42− diffused into the concrete, more Friedel’s salt was formed, and the small amount of SO42− only reacts with a portion the available Friedel’s salt to form Aft after it migrates into the concrete. In the CS2 samples, the Aft diffraction peak appeared relatively early and peak intensity relatively was relatively strong. Aft also appeared early in the CS3 samples. With extended exposure time, the CH and Aft peaks gradually disappeared, and the Gyp peak increased, which indicated that during concrete exposure to Na2SO4, Cl− and SO42− first react with Afm to form Friedel’s salt and Aft, and then Friedel’s salt reacts with SO42− to form Aft. Therefore, the peak intensities of Friedel’s salt and CH gradually decreases with the increase NaCl-Na2SO4 concentration and with the extension of erosion time. At this time, the peak corresponding to Aft gradually increased. However, if the concentration was too high or the attack too long, the peak associated with Friedel’s salt in the concrete disappeared, and that of Gyp gradually increased.The X-ray diffraction patterns of concrete sample attacked to NaCl-Nantensity . As the ame time . With hiucts Aft . Additio2O3∙CaCl2∙10H2O), Aft (3CaO∙Al2O3∙3CaSO4∙32H2O) and Gyp (CaSO4∙2H2O), and main corrosion reactions are as follows in Equations (3)–(9) [Examination of SEM and EDS results for samples after different exposure times enabled analysis of the microstructure and composition diagrams after salt solution exposure for various periods . The res (3)–(9) ,50,51,522SO4 solutions for various. The CS0 samples had a loose granular structure when exposed for 30 d, and a small amount of rod-like and net-like structures gradually appeared over time  the mortar and aggregate were tightly connected, (ii) there were more rod-shaped Aft crystals in the ITZ in the CS3 samples, and (iii) the ITZ was wider than that of the CS0 sample , middle pores (0.05–10 µm), and large pores (10–63 µm).The interior of concrete is a multiphase-porous composite material comprising of pores of various sizes and types. The pore structure is directly related to ion migration and the material’s mechanical properties. A YG-97A capacitive mercury porosimeter was used to analyze the concrete pore structure of samples that had been attacked to NaCl-Na2SO4 solution corrosion for 30, 180, or 360 d showed that the proportions of small, middle, and large pores of in the CS0 samples did not change significantly after different exposure times , the proportion of small pores and middle pores gradually decreased over time. After 360 d, the proportion of large pores had increased significantly, and the original small and middle pores were “smoothed”. Upon further increased Na2SO4 , the proportion of large pores decreased, and the proportion of small and medium pores increased up to 360 d. The pore distribution exhibited peaks in the range of small and medium pores, but the peaks corresponding to mesopores were more pronounced and spanned a larger distribution.The distribution of pores 25 mm from sample surfaces after NaCl-Nare times . The relThe distribution of pores at various depths after salt attack for 360 d showed that small and large pores in the CS0 samples were more common at depths between 0–25 mm than at depths of 25–50 mm, and mesopores showed the opposite trend f. In the2SO4 concentration and corrosion time, the corrosion products  gradually accumulated and filled the pores, cracks, and ITZ, thereby changing the pore distributions and allowing a transition from large pores to middle and small pores. As the Na2SO4 concentration, the crystal stress generated by the corrosion products caused small pores in a given sample to transform into large pores. Therefore, changes in the proportion of pore size further affected the diffusion of Cl− and SO42− ions and the mechanical properties of the concrete.These experimental results showed that the impact of NaCl in the salt solution on the concrete sample pore structure was not clear. With increased Na2SO4 (at a range concentrations) and salt solution exposure times were analyzed by examining changes in the appearance, weight, compressive strength, RDEM, and Cl− and SO42− diffusion depth in concrete samples. The depth of salt corrosion of concrete was observed, and a deterioration mechanism was proposed. XRD, SEM, EDS, and YG-97A capacitive mercury porosimeter analyses revealed changes in concrete minerals composition, microstructure, and pores contents after exposure to different salt solutions.In this study, the effects of NaCl (at a constant concentration), Na− and SO42− gradually migrated into the concrete samples through pores and cracks. Differences in concentration gradient, pores, and cracks were the main factor affecting ion diffusion. When the Na2SO4 concentration was ≤ 5%, as time passed or Na2SO4 increased, NaCl reacted with C-S-H and AFm to form Friedel’s salt and simultaneously release SO42−. Meanwhile, Na2SO4 reacted with cement hydration products of AFm Friedel’s salt to form the corrosion product Aft. Silicate and C-S-H in the concrete are required to provide Ca2+. During this process, C-S-H gradually shifted from a block to a honeycomb structure, which had lower strength. The corrosion products  filled the pores, cracks, and ITZ to certain. When the proportion of large holes in the sample decreased, the proportion of middle and small pores increased, and the concrete density increased. The crystal stress produced by the corrosion products was much smaller than the tensile strength of the matrix, and no new cracks generated. Coupled with the hardening effect of the cement, the mechanical properties  of the concrete were improved as a result of the increased density.During attack to different sodium salt solution, Cl2SO4 (≥10 wt%), as the attack time increased, corrosion products accumulated, and the concrete density during the early stages was higher than that in the low salt concentration samples. As a result, the mechanical properties were improved, and overall concrete quality increased. When a higher salt solution continued to corrode the samples, numerous Aft, Gyp, and Glauber’s salt crystals appeared inside. The same results were observed via XRD and SEM analyses. At this time, the corrosion products in pores and ITZ generated larger crystal stresses than the tensile strength of the matrix, which widened and extended the original concrete cracks until a large number of connected pores appeared and intersecting cracks appeared [2SO4 solutions. As a certain depth from the concrete surface, the ITZ widened, and new cracks were generated, thus decreasing the concrete’s mechanical properties and weight.When the salt solution contained more Naappeared ,54. In a− diffusion trends revealed that early in the exposure, the Cl− content in the concrete only exposure to NaCl was the highest, and as the Na2SO4 concentration increased, the produced Friedel’s salt hindered Cl− migration. However, Cl− diffusion was promoted in the late stage of corrosion by high-concentration NaCl-Na2SO4 solution.Following exposure to various salt solution concentrations for different periods of time, the Cl− diffusion at different concrete sample depths after exposure to NaCl-Na2SO4 solution showed that in the early stage, the concentration gradients inside the solution and concrete were quite different; Cl− and SO42− migrate rapidly, and the diffusion speed of Cl− faster than that of SO42− [2SO4 concentration in solution increased, the diffusion rate of SO42− also increased. As the exposure time increased, Cl− ions in the CS0 samples reacted with aluminate  to form a small amount of Friedel’s salt, which filled the interior, thus slightly hindering the migration of Cl−.Analysis of Clof SO42− ,55. As t2SO4 concentrations (≤ 5 wt%), Cl− and SO42− gradually migrated into the concrete; however, SO42− preferentially reacted with C-S-H, CH, or Friedel’s salt to form Aft, and Friedel’s salt was effectively corroded away by Na2SO4. A portion of the Cl− was also released to form free Cl− [− concentration in the pores to increase. At the same time, corrosion products filled the concrete pores, cracks, and ITZ, which changed the pore distribution in these samples, specifically, this caused the transition from large pores to middle and small pores, thereby hindering Cl− migration. In the Cl− diffusion process, corrosion products had a greater effect on Cl− than the concentration gradient in the pores, ultimately, the Cl− content in the CS0 samples was higher than that in the CS0.5 and CS1 samples.At low Nafree Cl− ,57,58, c2SO4 concentrations (≥10 wt%) indicated that in the initial stage of exposure, with increased time and Na2SO4 concentration, the pores, cracks, and ITZ were completely filled with Aft, Gyp, and Na2SO4 crystals, thus slowing the Cl− migration. However, due to the high Na2SO4 content in solution, the internal pores of the concrete released more Cl− ions, thus increasing the concentration gradient between the internal pores, which help the diffusion of Cl− ions in the concrete. As the attack continued, Na2SO4 corrosion products completely filled the pores and ITZ. At this point, crystal stresses generated by the corrosion products was less than the tensile force of the matrix, so no new microcracks were generated in the concrete. This was confirmed by the fact that the Cl− ion content at a depth 2.5 mm of in the CS2 sample was the smallest when the erosion occurred for 270 d. As the Na2SO4 concentration increased further, the corrosion products generated in the CS3 samples continued to accumulate, thereby, increasing the crystal stresses beyond the tensile stress of the matrix. This resulted in the production of new pores and cracks inside the sample, and was confirmed based on the fact that small and middle pores were occupied. As the salt ratio decreased, the proportion of large pores increased. Highly concentrated Na2SO4 solution (≥15 wt%) created new Cl− diffusion channels in the concrete samples attacked for 360 d. In addition, high Na2SO4 concentration released more Cl− ions, thus cresting comparable Cl− concentration in pores and cracks. Under the action of multiple factors , the Cl− in high concentrated Na2SO4 solution more easily diffused into the concrete samples. This was evidenced by the fact that the Cl− content was the highest at a depth 2.5 mm depth after exposure to CS3 solution for 360 d. Through these analyses, it was determined that under high Na2SO4 concentrations (≥10 wt%), the initial stage of exposure hindered Cl− diffusion. However, with increased concentration and exposure time, high Na2SO4 concentration facilitated Cl− diffusion.Examination of the samples attacked to higher Na2SO4 at 0, 2.5, 5, 10, or 15 wt%, Cl− diffusion into the pores and reacted in concrete samples in four stages , as the Na2SO4 concentration and exposure time increased, the mass, compressive strength, and RDEM gradually increased, and large pores gradually transformed to middle and small pores.Exposure to low-concentration of NaCl (5 wt%)-Na2SO4 (≥10 wt%), the compressive strength, RDEM, and mass of concrete samples increased with increased Na2SO4 concentration, but there was a downward trend after attack for a certain period of time.In solution with higher concentration of NaCl (5 wt%)-Na2SO4 solutions, the migration speed of Cl− was higher than that of SO42−.During the corrosion process by NaCl-Na− diffusion rate was related to the Na2SO4 concentration. Specifically, in an environment with a lower Na2SO4 concentration, Cl−, SO42− and cement hydration products hindered Cl− migration. In a more concentration Na2SO4 environment, the Cl− diffusion rate was hindered during the early stage of exposure, and the diffusion rate was promoted following longer corrosion periods.The Cl