To analyse the prevalence of respiratory tract infection (RTI) episodes with and without antibiotic prescriptions in adult patients in Norwegian general practice during the period 2012–2019.Observational study linking data from the Norwegian Control and Payment for Health Reimbursements Database and the Norwegian Prescription Database. Episodes of acute RTIs in patients aged 18 years or older were identified and linked to antibiotic prescriptions dispensed within 7 days after diagnosis. We analysed annual infection rates and antibiotic prescription rates and antibiotics prescribed for the different RTI conditions.P = 0.205). Antibiotic prescription rate decreased from 37% of RTI episodes in 2012 to 23% in 2019 (P < 0.001). The reduction in prescribing was most pronounced for episodes coded with ICPC-2 symptom diagnoses, as well as upper RTIs, influenza, acute bronchitis and sinusitis. Prescriptions for phenoxymethylpenicillin decreased from 178 746 in 2012 to 143 095 in 2019, but increased as proportion of total antibiotic prescriptions from 40% in 2012 to 53% in 2019 (P < 0.001).RTI episode rate per 1000 inhabitants was 312 in 2012 and 277 in 2019, but showed no linear trend of change during the study period (This study demonstrates stable RTI episode rates and reduced antibiotic prescription rates for RTIs for adults in Norwegian general practice 2012–2019. We also observed a shift towards relatively more use of phenoxymethylpenicillin and less broad-spectrum antibiotics. These changes are in line with the aims of the Norwegian strategy against antibiotic resistance. Norwegian health authorities launched a National Strategy for Antibiotic Resistance in 2015, aiming to reduce the national antibiotic consumption by 30% expressed as defined daily dose (DDD) per 1000 inhabitants per day (DID) and reduce antibiotic prescriptions for respiratory tract infections (RTIs) by 20% by year 2020 compared to 2012 levels.5 Following the national strategy, the health authorities facilitated several voluntary quality improvement projects aiming for more appropriate prescribing in Norwegian hospitals and general practice. Among these projects, an audit-based course for primary care doctors was implemented in 2018,6 based on methods proven to be effective in a primary care setting.8Antimicrobial resistance (AMR) is a global threat to public health.9 Most of these prescriptions are usually attributed to general practitioners (GPs).9 Thus, GPs have a key role for the appropriateness of antibiotic use. RTIs account for approximately half of all antibiotic prescriptions in Norway.9 However, many of the RTIs seen in general practice are viral or self-limiting bacterial infections, and antibiotic treatment for mild infections, such as sinusitis and sore throat, have no or only a marginal effect.11 As well as prescribing an antibiotic when this is not warranted, a suboptimal choice of antibiotic is also considered as inappropriate antibiotic prescribing. The current national guidelines for Norwegian primary care recommend phenoxymethylpenicillin (PcV) as a first-line antibiotic for almost all acute RTIs,12 and beta-lactamase sensitive penicillin as percentage of the total antibiotic consumption is a national and European quality indicator.14 Studies on overprescribing in general practice have identified high proportions of inappropriate prescribing.15–17In Norway, 84% of all antibiotics for human use are prescribed outside hospitals and nursing homes.9 In 2019, the human antibiotic consumption in the community was 13.6 DID, while the European mean was 18.0 DID.18 Norway has a low ratio of broad- to narrow-spectrum antibiotics at 0.1, compared with the European mean ratio at 2.8.18From 2012 to 2019, Norway had achieved a 22% decrease in total human antibiotic consumption based on sales statistics from primary care, hospitals and nursing homes.To inform clinicians, policy makers and stewardship programmes, and to better understand the changes in antibiotic use, it is essential to monitor both the number of patients seeking their GP for infections, and the corresponding antibiotic prescriptions. In this study we aimed to analyse the prevalence of RTI episodes in adult patients treated in Norwegian general practice and the rate of dispensed antibiotic prescriptions, DDD per prescription and type of antibiotic for RTI treatment during the period 2012–2019.The study was approved by the Regional Committee for Medical and Health Research Ethics, REC South East (ref. 2016/2283), and the Norwegian Data Protection Authority (ref. 282558). The study was conducted in accordance with the Declaration of Helsinki and institutional standards.19 In Norway, antibiotics are available through prescription only.We conducted an observational study linking data from nationwide health registries. The study period was from 2012 to 2019. All Norwegian residents have access to public healthcare through the National Insurance Scheme and are assigned to a regular GP. In 2015, 99% of the population was assigned to a regular GP list, and most of the Norwegian population use their GP or the municipal GP-staffed out-of-hours (OOH) services when seeking medical help.20 For each claim, the database contains ID for patient and physician, date of contact and one or two diagnoses per contact according to the International Classification of Primary Care (ICPC-2).21 We obtained claims for all registered contacts  from GPs and OOH services with an infection related ICPC-2 diagnosis. The Norwegian Prescription database (NorPD) includes detailed information on all prescription drugs dispensed at Norwegian pharmacies.22 We obtained the following data from NorPD: encrypted IDs for patients and prescribers, prescription date, prescribed drug item categorized according to the Anatomical Therapeutic Chemical Classification (ATC) system, and DDD of prescription in accordance with the ATC/DDD index of 2019.23 Statistics Norway routinely collects demographic and geographic data on the Norwegian population.24 We extracted data on patient sex, and month and year of birth and death (if applicable). Data from the registries were linked using the unique personal identification number  assigned to all Norwegian residents. All databases cover the entire Norwegian population.The Norwegian Control and Payment for Health Reimbursements (KUHR) Database receives compensation claims from GPs and OOH services.JAC-AMR online) recorded during 2012–2019. We selected adult patients as both treatment guidelines and clinical decision-making in paediatric patients differ from adults. Patients were included from 1 January 2012. Further patients were included each month after their 18th birthday, along with new registrants in the KUHR database, and follow-up ended at study completion (31 December 2019) or the month of the patient’s death.We included all patients aged ≥18 years with a relevant diagnosis  was defined as the date of diagnosis if no RTI diagnoses had been recorded within the previous 30 days. If there were less than 30 days between diagnoses, the latter diagnosis was defined as a re-consultation and assigned to the initial episode. The 30-day period was based on previous comparable studies on RTI episodes.is Table . EpisodeWe included antibacterial agents for oral use (ATC code J01) excluding methenamine, nitrofurantoin, (piv)mecillinam and trimethoprim, because in Norway, these antibiotics are exclusively prescribed for urinary tract infections. For each RTI episode, we analysed the first antibiotic prescription dispensed within 7 days following a GP consultation. Antibiotic classes were grouped as tetracyclines (ATC code J01AA), PcV (J01CE02), other penicillins (J01C except J01CE02), macrolides (J01FA) and other antibiotics.Descriptive statistics were calculated with means and proportions for each year and for the entire study period. Age was analysed in groups from 18–24 years, then 10-year age groups up to >85 years. Annual RTI episode rates were calculated by dividing the number of episodes by number of inhabitants ≥18 years in the year of index date. To account for changes in the population, rates were age-and-sex-standardized using direct standardization using the Norwegian 2012 population as reference. The study mean RTI episode rates presented are the mean of yearly episode rates for the 8 year study period. Prescription rate was calculated as the proportion of episodes resulting in at least one dispensed antibiotic prescription. Relative proportions of the different antibiotic classes were calculated.For annual trends, we used linear regression with standardized yearly RTI episode rates over year for all diagnoses individually, and for total RTI episodes. Linear regression over year was also conducted for yearly prescription rate, DDD per prescription and proportion of each antibiotic class. Coefficients from the regressions are presented as mean yearly change with 95% CI.U-test to compare sexes and non-parametric ANOVA  to compare age groups. Chi-squared tests were used to compare differences between sexes and between age groups in prescription rates and penicillin proportion. As we observed different patterns in episode rates for age groups between men and women, we ran a linear regression with yearly episode rate over age group for each sex to test for linear trends.To test for differences in mean contacts per episode, we used the Mann–Whitney The significance level was set to 0.05. Means are presented with standard deviation (SD). STATA/SE v.16.1 (StataCorp LLC) was used for all calculations.P < 0.001), and did not change noticeably during the study period.During the study period, 2 931 421 adult patients were diagnosed with at least one RTI in general practice. At first consultation, 54% were women, mean age was 45.5 years (SD 19.5) (Table P of linear trend <0.001) and decreasing by age for women (P of linear trend <0.001) . Mean age of patients with pneumonia was 61.7 years (SD 19.3), for sinusitis 43.8 years (SD 15.4), for upper respiratory tract infection (URTI) 41.1 years (SD 17.4), and for tonsillitis 33.4 years (SD 13.1).Women had more episodes than men Table , and theP = 0.205) (Table P of linear trend = 0.003). The use of all other infection-specific ICPC-2 codes except acute bronchitis (R78), influenza (R80) and other RTI (R83) decreased .Antibiotics were prescribed for 29% (2 659 088) of all RTI episodes. Most prescriptions  were dispensed after the first GP contact, and 17% (461 404) after the second contact of the episode. Prescriptions dispensed the same day as the GP consultation comprised 83% (2 201 251) of all, whereas 9% (245 619) were dispensed on day two and 8% (212 218) between day 3 and 7. The overall prescription rates varied between age groups, with the least prescribing (27.3% of episodes) in 45–54-year-olds and the most (30.7% of episodes) in 65–64-year-olds during the study period (P of linear trend <0.001) (Table The antibiotic prescription rate declined from 37% (443 633/1 205 782) in 2012 to 23% (271 149/1 165 545) in 2019, corresponding to a 37% decrease throughout the study period (P of linear trend <0.001) (Table P of linear trend <0.001).PcV accounted for 47% of the antibiotic prescriptions during the study period; followed by macrolides (22%) and tetracyclines (17%) Table . Althoug1) Table . MacroliP of linear trend <0.001). Mean DDD per prescription increased for PcV from 13.7 (SD 4.3) in 2012 to 14.3 (SD 4.6) in 2019 (P < 0.001) and for other penicillins from 9.0 (SD 3.1) in 2012 to 9.4 (SD 2.7) in 2019 (P < 0.001)  during the study period. Overall, mean DDD per prescription increased from 11.6 DDD (SD 5.1) in 2012 to 12.5 DDD (SD 5.4) in 2019 ( during tP for difference <0.001). Men received a slightly higher proportion of PcV compared with women, with 47% versus 46% of all prescriptions (P for difference <0.001).Younger patients were more frequently treated with PcV. Patients aged 18–24 years received PcV in 64% of first prescriptions, whereas corresponding figures for patients aged 75–84 years and older than 85 years were 35% and 39%, respectively (The highest prescription rates were seen for tonsillitis (76%), pneumonia (66%) and otitis media (65%). From 2012 to 2019, the prescription rates decreased significantly for all infection-specific diagnoses except for tonsillitis and whooping cough Table . The larFigure This registry-based study demonstrated a stable rate of acute RTI episodes and a decreased antibiotic prescription rate for RTIs in adults in Norwegian general practice between 2012 and 2019. The antibiotic prescription rate decreased by almost 40% in 2019 compared with 2012. Reduced prescribing rates were seen for all RTI diagnoses except tonsillitis and whooping cough. PcV was the most frequently prescribed antibiotic for RTIs, and a relative increase in PcV use was seen compared to other antibiotics.29 which explains a high episode rate and a relatively high proportion of macrolides issued in 2012. A recent Norwegian study covering 2006–2015 reported an increased number of consultations in primary care, but a decreased proportion of RTI consultations.30 Studies from Swedish general practice from the same decade reported decreased consultation rates for RTIs and a corresponding decrease in antibiotic prescription rates.31 Also, both Danish and English primary care research have reported decreased antibiotic prescription rates.33Although we did not find a linear decrease in RTI episodes, we observed a change from 312 episodes per 1000 inhabitants in 2012 to 277 per 1000 in 2019. Norway experienced an epidemic of mycoplasma pneumoniae during the winter of 2011–2012,34 Interestingly, we observed that RTI episode rates increased with age for men, while decreasing with age for women. For both men and women, we observed relatively high RTI episode rates in the youngest age group mostly made up by patients aged 18 and 19 years, especially from 2016. This may reflect an absentee regulation for high school students implemented in 2016, urging students to see their GP to get a certificate of absence when unable to attend class.35 This may potentially contribute to antibiotic overuse, due to the positive association between RTI consultation rates and antibiotic prescription rates.37Women had more RTI episodes and more contacts per episode than men, which is in line with findings from Swedish general practice.38 An explanation for this is that our dataset did not include data from either hospitals or nursing homes. Elderly patients with more severe RTIs are more commonly treated in hospitals and about 40 000, mostly frail, are living in nursing homes.Older patients had on average more consultations per episode, and were diagnosed with more severe infections than younger patients. However, we did not find higher antibiotic prescription rates in the oldest age groups, consistent with previous studies on antibiotic use in the community.39 However, although the reduction in antibiotic prescription rate was larger for symptom-related episodes, we saw a significant decrease in prescriptions for the infection-specific diagnoses.We observed a relative increase in the use of symptom-related diagnoses (ICPC-2 R01-29) compared with infection-specific diagnoses (ICPC-2 R71-83) as well as increased use of the diagnosis URTI (R74). We assume that physicians tend to use more symptom-related diagnostic codes when deciding not to prescribe antibiotics and vice versa, on the basis of studies showing that the intention to prescribe influences the diagnostic labelling.40 We observed a decrease in sinusitis episode rates of 32%, combined with a reduction in antibiotic prescription rate of 26% while the proportion of PcV increased by 24%. Similar changes were observed for acute bronchitis. Both sinusitis and acute bronchitis have been specifically targeted by the Norwegian stewardship interventions in general practice.The increased use of the URTI diagnosis could partly explain the reduction in sinusitis episodes, as URTI and sinusitis have overlapping symptoms and accurate diagnosing of bacterial sinusitis in general practice is challenging.41 This is also reflected in the high proportions of narrow-spectrum penicillins out of the total antibiotic consumption in Scandinavia, with 21% in Norway, 27% in Denmark and 28% in Sweden.14 Although macrolide use decreased, it was still the second most commonly used antibiotic for RTIs accounting for 22% of prescriptions in the study period. This corresponds well with figures from Danish and British general practice.42 According to the Norwegian guidelines for antibiotic treatment of RTIs in primary care, macrolides are only recommended as first choice empirical treatment for atypical pneumonia, whooping cough and as an alternative to PcV in patients with penicillin allergy.12 Penicillin allergy is frequently self-reported by patients on the basis rashes and/or gastrointestinal symptoms, and although 8% of the population in the USA carries a history of penicillin allergy, <1 in 20 were really allergic when tested.43 Unverified penicillin allergy could represent a public health problem leading to use of unnecessary broad-spectrum antibiotics. Our results support the fact that there is still potential to further reduce macrolide prescribing in Norway.Our finding that PcV was the most frequently prescribed antibiotic for RTIs is in line with studies from general practice in Sweden and Denmark.The major strength of our study is the size of the dataset covering the entire Norwegian population. Linking data from different national registries by individual personal identification number gives the opportunity to obtain information across the public health system. However, the KUHR database does not receive any compensation claims from hospitals, nursing homes or commercial health care providers. There are currently no available statistics regarding the use of commercial primary care providers in Norway, but it is so far considered to be of negligible size.44To include all acute RTI episodes, we obtained all registered contacts, including phone and electronic communication. The diagnoses were obtained from the national reimbursement scheme that contain only one or two recorded diagnoses per claim, which in turn relies on the coding practices of the GPs. The ICPC-2 coding is necessary to generate compensation claims, and is not intended for research. A limitation of the KUHR database, compared to data from patient records, is the lack of information on clinical presentation and patient comorbidity. However, a reasonably good correspondence between medical record text and diagnosis coding in Norwegian general practice has been reported.7 the overall reduction in antibiotic prescriptions for RTIs may partly be attributed to more use of delayed prescribing.NorPD data includes dispensed antibiotics only, and the number of prescriptions not dispensed therefore remains unknown. That 8% of the prescriptions were dispensed between day 3 and 7 may represent delayed prescriptions. Considering that only about 60% of delayed prescriptions are filled at pharmacies, compared to 92% of ordinary antibiotic prescriptions,By only including antibiotics dispensed the first week after a GP-diagnosed RTI, we probably reduced the risk of including antibiotics given for other indications. However, the NorPD does not contain diagnoses for each prescription. That we only included the first prescription per RTI episode, may have led to an overestimation of narrow-spectrum penicillin if patients were prescribed a second antibiotic in cases of treatment failure.45 The definition of one DDD for PcV is 2 g,23 whereas the Norwegian primary care guidelines for treatment of pneumonia in adults recommend 4 g for 7 days, resulting in a prescription of 14 DDD.12 The DDD definition for macrolides and tetracyclines correspond better to the guideline recommendations. Thus, a shift towards more use of PcV would lead to increased mean DDD per prescription without necessarily reflecting enlarged prescribed doses.The NorPD only contains information on strength and size of the dispensed package of antibiotic, and no information about the prescribed dose or duration of the antibiotic course. We have, therefore, reported DDD per prescription as a standardized estimate of treatment dose and duration for each prescription. For penicillins, we observed increased mean DDDs per prescription during the study period. However, the DDD value defined by the WHO does not necessarily reflect the prescribed daily doses, as the dose vary according to diagnosis and patient characteristics.9The decreased rate of prescriptions per episode indicates that GPs’ prescribing practices contribute to the overall reduction in antibiotic consumption reported by the national surveillance programme.12 The reduction in RTI antibiotic prescribing was substantially larger than the overall reduction in antibiotic use reported in Norway during the period,9 demonstrating that the potential for change in antibiotic use for RTIs is larger than for other infections. To ensure further improvement of antibiotic use, it is important to establish a permanent system for quality improvement of antibiotic prescribing in general practice. It is also crucial to assess whether reducing antibiotic treatment too much may have undesirable effects such as increased rates of complications.So far, efforts to improve prescribing in Norwegian general practice have been time limited and project based. Our findings may reflect effects of these interventions, as reduced prescribing per RTI episode and increased use of PcV indicate an increased adherence to the national guidelines.This study demonstrates stable RTI episode rates and decreased antibiotic prescription rates for RTIs for adults in Norwegian general practice during 2012–2019. We also observed a shift towards relatively more use of phenoxymethylpenicillin and less use of broad-spectrum antibiotics. These changes are in line with the aims of the Norwegian AMR strategy.dlac135_Supplementary_DataClick here for additional data file.


Glass fiber reinforced polymer (GFRP) bars have been increasingly used as reinforcement in concrete structures. However, when the bars are exposed to high temperatures, there is a change in the internal structure of the polymer which affects the tensile strength of the matrix and its adhesion with the fibers, reducing the mechanical strength of the bar. In addition, with increasing temperature, the bar-concrete interface is also damaged by the decomposition of hydration products from the cement paste and the loss of surface adhesion. The intensity of these changes is associated with the type of resin used as a matrix since each polymer has its own molecular structure that provides a greater or lesser ability to resist the changes imposed by temperature. The present study evaluates the mechanical behavior of reinforced concrete containing different types of GFRP bars and subjected to temperatures of 150 °C, 300 °C, and 350 °C. The GFRP bars with three types of matrices  were mechanically evaluated under tension in two conditions: isolated and inserted into reinforced concrete specimens with a thickness of 20 mm, using two types of concrete (with and without silica fume). Degradation mechanisms at the bar/concrete interface were evaluated using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), differential thermal analysis (DTA), and bond techniques. The results showed that the type of matrix has a significant influence on the tensile behavior of GFRP bars, with the epoxy matrix showing the best performance, followed by bars with vinyl ester and polyester matrix resins. The use of silica fume improved the performance of the concrete coating and, consequently, improved the protection of GFRP bars, hindering the diffusion of oxygen and heat; bar/concrete adhesion was compromised by thermal degradation of GFRP bar ribs. The glass fiber reinforced polymer (GFRP) bar is a structural construction material that is attracting considerable attention due to its physical, chemical, and mechanical characteristics, such as electrochemical corrosion resistance, high strength-to-weight ratio, low thermal conductivity, electromagnetic transparency, and ease of manufacture, transport, and handling . CompareHowever, one of the main concerns regarding the use of FRP bars refers to the effect of temperature on their mechanical properties, since polymer matrices, mainly based on thermoset polymers (vinyl ester or epoxy) , undergoThe polymer molecules absorb thermal energy, which may weaken the intermolecular interactions and subsequently break the chemical bonds in the main chain of the polymer. Changes in color and texture have been verified in bars as a function of temperature and time of exposure to high temperature, which has been attributed to thermal decomposition of the polymer matrix  due to oThe effects of heating are propagated to the bottom of the bar, resulting in damage to the fiber/matrix interface and properties of the glass fibers with consequent loss of the mechanical properties of the GFRP bars. Recent studies have evaluated the properties of GFRP bars after exposure to high temperatures indicating a reduction in tensile strength of up to 40% ,10,11 deIn reinforced concrete structures, the damage to the GFRP bar due to the action of external agents, including the increase in temperature, is minimized by protecting the concrete cover, as observed by Alsayed et al. , NajafabWhen exposed to high temperatures, the cement paste of concrete undergoes changes in its chemical structure, with a reduction in mechanical strength and modulus of elasticity, which depends on the composition of the concrete. The presence of silica fume, for example, allows for greater resistance of the concrete to the action of high temperatures . As a coThese results have raised concerns about the structural performance of structural elements reinforced with GFRP bars exposed to high temperatures since most of a bar’s mechanical performance can be lost in the early stages of a fire. Exposure to fire is one of the most aggressive situations to which structures can be subjected during their useful life. Usually, building structures are protected by other protective measures, but as the fire progresses, the structural integrity needs to be maintained until the building is completely evacuated and the fire is extinguished. Thus, the knowledge of the effect of temperature on the behavior of concrete structures reinforced with FRP bars is fundamental for Civil Engineering.Thus, in order for GFRP bars to be used safely, in addition to the basic mechanical properties, it is necessary to determine the fire resistance of the bars, insulated or embedded in concrete, mainly due to the different types of polymeric matrices that can be used in the manufacturing of GFRP bars due to modifications of concrete with the addition of pozzolanic materials. The aim of this study is to analyze the effect of the type of polymer matrix used in the manufacture of GFRP bars and the effect of the type of concrete on the mechanical behavior and bond strength of reinforced concrete subjected to temperatures of 150 °C, 300 °C, and 350 °C. Degradation mechanisms at the bar/concrete interface were evaluated using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and differential thermal analysis (DTA) techniques.For the development of this study, GFRP bars were used with three types of matrices: isophthalic polyester (GFRP-P), vinyl ester (GFRP-V), and epoxy (GFRP-E). The nominal diameter of the bars used was 13 mm, with helical ribs, as shown in For the production of reinforced concrete elements, two types of concrete were produced  in order to verify the effect of the addition of pozzolan on the protection of the GFRP bars.3, a BET surface area of 1.4 m2/g, and an average equivalent diameter (D50) of 15.0 µm. The silica fume had a specific mass  of 2.32 g/cm3, a BET  surface area of 15.2 m2/g, and an equivalent diameter (D50), determined by laser granulometry , equal to 43.0 µm. A high initial strength cement was used with a specific mass of 3.13 g/cm3. The slump in the truncated cone was 170 ± 20 mm to maintain workability during the molding of the specimens.The reference concrete mix (REF) was defined based on the method proposed by the American Concrete Institute (ACI). A mass ratio of 1:2.50:2.40:0.65 was defined (cement + silica fume: sand: gravel: water), with the dimension maximum of the gravel being 9.5 mm, the silica fume content varying between 0% (REF) and 10% (SA-10), and replacing the cement content of 425.8 kg/mThe physical-mechanical properties of the concrete produced are shown in Note that the use of silica fume increased the compressive strength and the apparent specific weight of the concrete, reducing the open porosity of the material. No significant differences were observed in the diametral compressive strength and in the elastic modulus of the evaluated concretes.g) and close to the decomposition temperature of the polymeric matrix (Td). The specimens were heated at a rate of 10 °C/min until the target temperature, remaining at this level for 30 min [The GFRP bar specimens were tested at 23 °C and at high temperatures , above the glass transition temperatures , differential thermal analysis (DTA), and differential scanning calorimetry (DSC) were performed on the GFRP bars and cement paste, and a mass ratio of 1:0.65 was defined (cement + silica fume: water), with a silica fume content varying between 0% (REF) and 10% (SA-10), replacing the mass of cement.A TA Instruments SDT Q600 thermogravimetric analyzer , using approximately 10 mg per sample was used in the analysis. The tests were performed according to the procedures described in ASTM E1868  and ASTMThree 1.0 m-long specimens of each type of GFRP bar were prepared and subjected to the tensile test; 27 specimens without the concrete coating (GFRP-N) and 72 specimens with the concrete coating (GFRP-Y), as shown in The GFRP bar specimens without concrete coating (GFRP-N) and with the concrete coating (GFRP-Y) were prepared for the tensile test.GFRP barAn anchoring system had to be used at the ends of these specimens, following the procedures of the ASTM D 7205 standard , which rTo maintain the alignment between the GFRP bar and the metal tube, it was necessary to use PVC plastic bushings inside the tube and a wooden frame.2.GFRP bar with concrete coatingFor the preparation of the GFRP-Y specimens, in addition to protecting the ends of the GFRP bars, as described in the previous section, it was necessary to produce and mold the concrete.The GFRP bars were initially centered in a PVC tube of 48 cm in length and 53 mm in diameter, with the tube being filled with concrete. This procedure allowed the production of a reinforced concrete element with a covering layer 20 mm thick, which is the minimum value required by the design standard. Due to the thickness of the furnace used in the tests, it was not possible to evaluate concrete cover with greater thicknesses.After preparing the specimens, the tensile test was performed in a universal machine in an Instron 23-200 , with a load cell of 200 kN, equipped with a vertical electric oven. Initially, the specimens were positioned in this machine a,b. ThenAfter positioning the specimen, the oven was heated to the desired temperature, remaining at this temperature for 30 min, as described by . Then, tAfter heating the GFRP-Y specimens to temperatures of 150 °C, 300 °C, and 350 °C, as described in mτ) between the GFRP bars and the concrete was calculated using the value of the mean spacing between cracks and the diametrical compressive strength of the concrete at temperatures of 150 °C, 300 °C, and 350 °C [The bond strength  of the bar samples with the polyester matrix (P), vinyl ester (V), and epoxy (E) are shown in The first mass loss event was observed at about 100 °C, being attributed to the loss of chemically adsorbed water (intermolecular −OH) corresponding to 0.82%, 0.78%, and 0.69% in the GFRP bar samples with the polyester matrix, ester vinyl, and epoxy, respectively. At 300 °C, the mass loss was 3.76% (polyester matrix), 3.46% (vinyl ester matrix), and 2.87% (epoxy matrix), being associated with the breakage of the molecular chains of the polymer matrix .onset) of 389.4 °C (polyester matrix), 395.4 °C (vinyl ester matrix), and 366.0 °C (epoxy matrix), evidenced by the reduction of the derivative, reaching a well-defined valley in the DTG curve. At the end of this thermal event (Tendset), mass losses equal to 81.22% (polyester matrix), 75.65% (vinyl ester matrix), and 66.35% (epoxy matrix) were observed and were associated with the thermal degradation of the polymer chains.The TG curves showed a sharp slope at temperatures , 16.40% (vinyl ester matrix), and 25.78% (epoxy matrix), which may be associated with the presence of inorganic components with a higher decomposition temperature. Thus, the GFRP bar sample with the epoxy matrix showed the lowest mass loss, followed by the samples with vinyl ester and polyester matrix, respectively.g) and 300 °C (close to the beginning of the decomposition of the polymeric matrix of the GFRP bars).The glass transition temperature can be attributed to structural relaxation, since, beyond this temperature, the polymer’s ability to transfer stresses to the glass fibers is greatly impaired, having a negative effect on the tensile strength of GFRP bars. From the TG and DSC analyses, the exposure temperatures of the GFRP bars were chosen at 150 °C  and cement containing silica fume (SA-10) to high temperatures, thermogravimetric (TG) and differential thermal (DTA) analyses were performed at 28 days, as shown in Heating the REF and SA-10 pastes resulted in physical changes with similar thermal behavior. The first mass loss event was identified in the range between 40 °C and 100 °C, representing a loss of 12.3% and 13.4%, respectively, attributed to the effects of ettringite decomposition, which occurs at around 70–90 °C .The second thermal event occurs at 100 °C, with the intensified dehydration of cement pastes due to capillary water (free water), corresponding to 5.0% and 4.7% up to 150 °C, after which the lamellar water evaporates, being adsorbed and chemically associated with hydrated calcium silicate (CSH) crystals, corresponding to 5.0% and 4.8% up to 380 °C .Next, the calcium hydroxide (portlandite) decomposes into lime and water in the temperature range between 380 °C and 460 °C. The water composition of calcium hydroxide corresponds to 3.8% and 2.6%, respectively. These values, when multiplied by 4.11 , indicate the remaining content of lime in the sample, which corresponds to 15.6 and 10.7, respectively, indicating that portlandite was consumed in the SA-10 sample. Finally, the calcite decomposes, representing a mass loss of 2.1% and 1.4% for the REF and SA-10 pastes, respectively.The replacement of 10% of the cement mass by silica fume caused a pozzolanic reaction in the SA-10 cement paste, which reduced the amount of water in the ettringite, hydrated calcium silicate, portlandite, and calcite compounds, thus reducing the mass loss by dehydration. Therefore, the degradation of the cement paste occurred progressively with exposure to heat, which may compromise its mechanical properties. According to these results, it is observed that up to the temperature of 150 °C, there were no significant changes in the cement matrix.The thermal degradation suffered by the polymer matrix of the GFRP bars causes an increase in the interatomic spacing and the breaking of molecular bonds due to heating. Consequently, the interface between the polymer matrix and the glass fibers was damaged, reflecting a reduction in the transfer of forces between the fibers and the matrix. This loss of mechanical performance can be expressed in terms of the reduction of tensile strength values, as observed in These results corroborate the tensile strength losses reported by Wang et al. , who obsg of the polymer matrix). As the temperature increased to 300 °C, this color change intensified, and heat and toxic volatiles were released due to the thermal degradation of the polymer matrix [r matrix .As observed in insulated bars, there is a reduction in the strength of concrete reinforced with GFRP bars with the increase in temperature. However, due to the protection that the concrete coating provided the GFRP bars, damage to the tensile strength is less, as shown in In an attempt to establish a standard concrete thickness in concrete structures with GFRP bars, the CAN/CSA S806  standard3 and 18.2%, respectively, while for the SA-10 concrete these values were 2617.0 kg/m3 and 16.3, that is, the addition of silica fume promoted a greater barrier to the flow of fluids  resulting in greater thermal protection for the GFRP bars.Concerning the concrete types, heating with the addition of silica fume improves the protection of GFRP bars when compared to reference concrete, particularly at 150 °C. The effect of replacing 10% of the cement mass with silica fume caused a change in the pore structure of the concrete. The reference concrete (REF) presented density and apparent porosity of 2556.0 kg/mIn addition, the results of the thermogravimetric analysis showed a lower mass loss associated with the decomposition of calcium hydroxide (portlandite) in samples of the cementitious matrix with 10% silica fume, compared to the reference cement matrix, corresponding to 3.8% and 2.6%, respectively. This contributed to the reduction in microcracking of the cement matrix in the concrete samples with silica fume.The tendency to reduce the mechanical properties of GFRP bars after exposure to high temperatures corroborates the results obtained by several other authors ,12, who g) suffered a reasonable loss of tensile strength (16.9% and 12.2%), which intensified at 300 °C (27.5% and 22.5%), in addition to longitudinal cracks in the concrete specimen. At 350 °C, the longitudinal cracks in the overlay concrete were more evident, with a reduction in tensile strength of around 41.7% and 40.0%.It was observed that specimens heated to 150 °C  . The selAccording to ACI 440.1R-15 , the losr), and strain compatibility is established between the reinforcement and the concrete. New cracks are formed gradually, with relatively uniform spacing (s), in a process called multiple cracking, shown schematically in r < s < 2lr.After the first crack is formed, the force transmitted between the two parts of the cracked GFRP-Y specimen was performed only by bond stresses between the GFRP bar and the concrete. With the rupture of the chemical adhesion in the region close to the crack, the mechanical anchoring provided by the ribs is responsible for the largest portion of the adhesion. As the applied loads increase, a new crack forms at a certain distance from the initial crack called the transfer length , it is possible to define the position of a new crack that will occur when the stress in the concrete reaches the tensile strength value, that is, e et al. , the newBased on this concept, NBR 7477  establisIn another approach, the correlation between crack spacing and bond stress must consider the influence of the concrete coating , which rUsing the experimental values of crack spacing obtained in this study, it was possible to obtain the average bond strength (Equation (5)) and minimum and maximum values of bond stress, using Equation (4), for the Classical Theory, and Equation (6), for the FIB code 2010 . The resIt is observed that the reference reinforced concrete specimens (GFRP-Y-REF) heated to 150 °C showed a significant loss in bond strength , which intensified at temperatures of 300 °C  and 350 °C . Similar behavior was observed in the reinforced concrete specimens containing silica fume (GFRP-Y-SA10) heated to 150 °C , 300 °C , and 350 °C , for GFRP-P, GFRP-V, and GFRP-E bars, respectively.The heating of GFRP-C specimens caused physical and chemical changes in the concrete, such as dehydration of hydrated products (according to TG/DTA results), and changes to pore structure and microstructure. As a result, there was a reduction in the diametrical compressive strength of the concrete of 16.9% and 12.2% when heated to 150 °C; 27.5% and 22.5% when heated to 300 °C and 41.7% and 40.0% when heated to 350 °C, for concretes REF and SA-10, respectively.In addition to the type of resin, another factor that reduces the adhesion of the GFRP bar with increasing temperature is the difference in its geometry, as shown in Although the specimens of reinforced concrete with GFRP-E bars presented higher tensile strength at high temperatures, this was not observed in their behavior in terms of adhesion strength when compared to specimens reinforced with GFRP-E and GFRP-P bars. The lower bond strength loss of GFRP-V bars is a consequence of their geometric characteristics and the thermal stability of the vinyl ester matrix, with a relative rib area equivalent to 2.81, followed by 2.75 and 2.38 for GFRP-E and GFRP-P, respectively.p-values approximately equal to zero.The contribution of different parameters to the bond strength of the GFRP-Y specimens was investigated using multifactor analysis of variance, as shown in Furthermore, the GFRP-Y specimens with SA-10 concrete presented higher adhesion strength compared to the GFRP-Y specimens with REF concrete due to the reduction of interfacial porosity in the transition zone between the cementitious matrix and the surface of the GFRP bar. The favorable effect on adhesion caused by the addition of silica fume is explained by the fact that these particles filled the areas previously occupied by water in the transition zone. Thus, the densification of the transition zone occurs due to the presence of CSH formed from calcium hydroxide (CH) resulting from the pozzolanic reaction, as shown by the results of the thermogravimetric analysis, which indicated the reduction of the CH content in the cement paste with silica fume.The tensile strength of GFRP bars decreased significantly when subjected to high temperatures, with 350 °C being the critical temperature at which the decomposition of the polymer matrix occurred, releasing heat and toxic volatiles. GFRP bars exhibited elastic behavior even when heated at temperatures of 150 °C, 300 °C, and 350 °C, although there was a gradual reduction in displacement and consequently, a reduction in the load needed to achieve rupture;The 20 mm-thick concrete cladding increased protection against thermo-oxidative degradation resulting from exposure to high temperatures. At the temperature of 350 °C, this protection was compromised by the appearance of longitudinal cracks in the concrete due to the volumetric expansion of the GFRP bars;The influence of the GFRP matrix type was significant on the tensile behavior of the bars. In this sense, GFRP bars with epoxy matrix showed the best performance, followed by those with vinyl ester and polyester matrices. Thermoxidative degradation of the GFRP bar ribs resulted in a reduction in the capacity to transfer tension to the concrete, regardless of the type of coating concrete;Silica fume improved the performance of the concrete coating and, consequently, improved the protection of GFRP bars, making it difficult for oxygen and heat to diffuse towards the bars. As a result, concrete-coated GFRP bars exhibited better tensile behavior at elevated temperatures compared to GFRP bars that were directly exposed to heat.In this study, three types of GFRP bar  with and without concrete coating were exposed to temperatures of 150 °C, 300 °C, and 350 °C. From the results presented in this work, it is possible to conclude that:


For the bridge widening of long multi-span highway concrete continuous box girder with a conventional splicing structure, due to the large longitudinal difference deformation by concrete shrinkage and creep between the existing and new ones, the widened structure will have an overlarge bending deformation after widening, especially an obvious transverse deformation at the end of girder, which will lead to structural damage to the newly widened structure. To effectively absorb the difference deformation mentioned above, this study proposes a novel transverse splicing structure based on the folding effect of a corrugated steel plate (CSP) (hereinafter referred to as “the CSP splicing structure”). Then, a finite element structural analysis was performed on the mechanical properties of the widened structure with the CSP splicing structure, and compared to those of a widened structure adopting the conventional concrete splicing mode, to clarify the transverse load transferring mechanism of the structure. Finally, by conducting a sensitivity analysis on CSP thickness, corrugation length, splicing stitch width, and other structural parameters, a sound parameter combination scheme was put forward. According to the research results, to ensure effective utilization of the CSP folding effect, the corrugation pattern direction of CSP should be set as horizontal, and the wave angle as the degree of 90°. In addition, it mitigated the transverse tensile stress to effectively avoid concrete cracking feasibility on the top flange of the box girder at the end of the girder. This study offers a feasible way of avoiding the structural damage produced by an excess transverse deformation at the end of the girder after bridge widening of a long multi-span concrete continuous box girder. Economic development and population growth have put tremendous pressure on transportation services. Therefore, many existing highway bridges cannot meet the current increased traffic demands. Widening existing highway bridges not only requires less time to improve their capacity but also saves investment. A common way to do this is to build a new bridge side by side with the existing one and structurally connect the two bridge decks with an in situ concrete stitching slab. At present, the huge demand for bridge widening mainly comes from highway bridges, not railway bridges.Currently, integral widening, in which the new section of the structure is made continuous with the existing one, is attractive because it avoids the complication of a movement joint that would often be below a running carriageway . Under tThe interactions between the new and existing bridges are incurred by their different completion times, producing restraint stresses in the new and existing structures. For instance, the significant differences in their different completion times between the new and existing bridges would result in a series of deformation differences between them, including the longitudinal shrinkage and creep deformation of concrete, vertical foundation settlement, and so forth . To be sA practical engineering case described in the literature  involvesTo mitigate the adverse effect because of the different completion times of the new and existing bridges, the method of delayed splicing of the new and existing bridges for a period of six months is usually adopted worldwide to reduce the adverse effects of differences in deformation between the new and existing bridges on the widened structure ,9,10. HoOn the whole, as far as the widening structures of long concrete continuous girder bridges are concerned, the study on the interaction mechanism between the new and existing bridges and the countermeasures is still in the start-up stage, and the lack of related research results has severely hindered the further development of bridge-widening technologies and should be urgently addressed.In this study, a bridge of Beijing-Shanghai Expressway was taken as the engineering background. The bridge is a prestressed concrete continuous box girder bridge with a variable cross-section and a total length of 214 m, including a four-span of 40 + 2 × 67 + 40 m.The bridge deck is divided into 4-lane double-way, and the single-way box girder uses a single-box single-cell section, as shown in To effectively deal with the differences between the new and existing bridges in the longitudinal shrinkage and creep deformation of concrete after widening, this study proposes a novel transverse splicing structure based on the folding effect of a corrugated steel plate (CSP). By investigating its technical feasibility and force transferring mechanism and exploring its reasonable structural parameters, this study aims to offer a new solution to the splicing widening of long multi-span concrete continuous bridges.CSP is widely used in continuous box girder bridges with corrugated steel webs, mainly by virtue of its sound longitudinal folding effect. On the basis of such a longitudinal folding effect, two possible splicing structures were put forward, as shown in cuf, the axial compressive strength ckf, and tensile strength tkf, the elastic modulus cE of C50 concrete can be determined according to the reference [yf, the ultimate strength uf and the elastic modulus sE of Q345 steel plate concrete can be determined according to the reference [Before building the FE model, the mechanical properties of steel and concrete are listed in eference ,14. All The stress-strain relation of concrete damage constitutive in this paper is the concrete stress-strain relation suggested in Appendix C of the Code for Design of concrete Structures of China  as show.Shrinkage and creep coefficients were adopted according to the CEB-FIP model , and the relative humidity of the ambient environment was set at 60% .On this basis, two overall 3D finite element models were built for bridge widening. The overall dimensions of the two models followed the design drawings of the bridge under investigation in this study. Considering the different stress characteristics and thickness of structural members, two types of elements (3D solid elements and plate shell elements) were used for modeling: new and existing concrete box girders are both made of C50 concrete and simulated using eight-node hexahedral elements; CSP uses Q345 steel that is 10 mm in thickness and was simulated using four-node plane elements. The load case considers only the differences in concrete shrinkage and creep between the new and existing bridges, for which the structure produces transverse deformation, as shown in The data listed in (1) When the “CSP connection with vertical corrugation pattern” shown in (2) Under the “CSP connection scheme with horizontal corrugation pattern,” it was possible to effectively reduce the transverse displacement at the end of the girder of the widened bridge only when a right-angle CSP is adopted. According to the analysis, when there was a longitudinal deformation difference between the new and existing box girder flange plates, the CSP set between them produced longitudinal compression, inevitably resulting in transverse expansion of the CSP structure. However, such transverse expansion was resisted by both the new and existing flange plates on both sides, making it impossible for the CSP to bring its “folding effect” into play. In contrast, CSP bent at a right angle (“right-angle CSP” for short) avoided this problem and adapted well to the differences between the new and existing bridges in the longitudinal shrinkage and creep deformation of concrete. The splicing structure with a horizontal CSP for right-angle bending is discussed later.Based on the analysis of the above two types of CSP layout schemes, in this study, we proposed a horizontal CSP splicing structure bent at a right angle, which is applicable to the widening of a long-unit concrete continuous box girder bridge (hereinafter referred to as “the CSP splicing structure”), as shown in In the constitution of the structure, the first right-angle CSP is arranged continuously along the longitudinal splicing stitch, and the corrugation pattern direction was set as horizontal; the peaks and valleys of CSP were connected to the new and existing box girder flange plates using high-strength bolts, thus creating a transverse splicing structure. Next, a thin sheet steel isolated layer was prepared at the top of the CSP structure to bear the bridge deck pavement. Finally, a new bridge deck was paved on the entire spliced segment to form a flat bridge deck. The isolated layer can be welded together with the top surface of the box girder on one side and set free on the other side. In this way, it will neither restrict the longitudinal deformation of CSP nor cause it to slip out of service.In order to illustrate the working mechanism of the new splicing jointing structure, an analysis is conducted by taking a local structure with a length of 2 m longitudinally around the end support of the girder and building a refined local FE model, as shown in In the local refined finite element model, the new and existing box girder concrete, steel plate, and bolts were all simulated using solid elements, and the elements within the splicing part were refined again. The model has a total of 496,455 elements, and its boundary conditions are simulated as a hinging in the four corners at the bottom of the box girder. To be specific, CSP is connected to the new and existing flange plates by using four bolts of 20 mm in diameter and 15 d in anchorage depth, as shown in To effectively apply the effect of structural deformation difference, all the nodes on the end cross-section within the range of the new bridge are rigidly connected to the centroid node of the cross-section, followed by applying a longitudinal forced displacement at the mass centroid to simulate the longitudinal shrinkage and creep displacement difference between the existing and new bridges. According to the global finite element model shown in To investigate the differences in stress characteristics under the traditional splicing mode and the CSP splicing mode, two finite element models were built to stimulate two types of transverse splicing structures and then to analyze the widening structure. Three key sections were selected, as shown in The combination value of actions comprises dead weight, prestress, shrinkage creep, foundation post-construction settlement difference, lane load, and so forth. The selected analysis parameters included CSP thickness, CSP wavelength, and splicing stitch width. Given that the differences between the new and existing bridges in concrete shrinkage and creep and the foundation post-construction settlement are the main factors affecting the stress performance of the splicing widening structure, the parameter sensitivity analysis was performed mainly under the two action cases:Action case 1: The action of the differences between the new and existing bridges in concrete shrinkage and creep deformation;Action case 2: The action of the difference between the new and existing bridges in foundation post-construction settlement.The analysis results of the three parameters are listed in (1) (2) (3) Based on the analysis results of the sensitivity of parameters, in this study, for the sake of achieving a better splicing effect, two parameter value schemes are proposed, i.e., Scheme 1: right-angle CSP with a thickness of 10 mm, a splicing stitch width of 0.5 m, and a corrugation length of 0.5 m; Scheme 2: right-angle CSP with a thickness of 15 mm, a splicing stitch width of 0.75 m, and a corrugation length of 0.5 m. The advantages and disadvantages of the two parameter optimization schemes were further analyzed, as detailed in According to In conclusion, this study successfully demonstrated the scheme design and working mechanism of a CSP splicing structure based on a case study of a bridge of Beijing-Shanghai Expressway. The sensitivity of the relevant parameters was analyzed, and a better scheme design was put forward for this type of splicing structure. The results of this study are as follows:(1) When the “CSP connection scheme with a vertical corrugation pattern” is adopted, the corrugated steel plate with a right angle or an acute angle cannot effectively reduce lateral deformation at the end of the widened bridge girder, indicating that the corrugated steel plate almost does not exert a “folding effect.” When the “CSP connection scheme with a horizontal corrugation pattern” is adopted, only when the wave of right angle in the steel plate is adopted can the corrugated steel plate effectively exert the “folding effect,” and reduce the transverse deformation at the end of girder under the action of concrete shrinkage and creep deformation difference between the new and existing bridge. Based on the analysis results, the CSP splicing structure waved at the right angle is proposed and can be effectively applied to the transverse splicing widening of long multi-span concrete continuous box girder bridges.(2) When the CSP splicing structure is adopted as the widening stitch structure for the long multi-span concrete continuous box girder bridge, the maximum transverse deformation at the end of girder is about 20 mm, about 1/3 of that under the traditional splicing scheme. This indicates that the CSP splicing structure can adapt well to the action of the differences between the new and existing bridges in concrete shrinkage and creep deformation.(3) The working mechanism of the right-angle CSP is explained as follows. Due to the longitudinal deformation difference between the new and existing box girders, the deformation of the sheet steel is dominated by S-shaped bending deformation; the splicing structure has a strong ability to absorb longitudinal displacement, and the longitudinal restraint effect of the existing bridge on the new bridge is very small. As a result, the CSP splicing structure can adapt well to the differences between the new and existing bridges in the longitudinal shrinkage and creep deformation of concrete.(4) Under the combined action, when traditional splicing is adopted, the transverse tensile stress on the top flange plate at the end of girder of the existing bridge reaches 4.557 MPa, far exceeding the standard tensile strength of C50 concrete, making it necessary to take effective anti-cracking and reinforcement measures. In contrast, when the CSP splicing structure is adopted, both the maximum tensile stress on the top flange plate of the box girder of the existing bridge and the maximum principal tensile stress on the CSP are within the safe range, indicating that the comprehensive stress performance of the CSP splicing structure is obviously superior to that of the traditional splicing structures.(5) Through investigating the rules of the effects of CSP thickness, corrugation length, splicing stitch width, and other structural parameters on the stress characteristics of the widening structure, a sound parameter combination scheme was successfully established for the CSP splicing structure. The optimum CSP thickness, splicing stitch width, corrugation length, and waving angle were found to be 15 mm, 75 cm, 0.5 m, and right angle, respectively.


Concrete technology is adopted worldwide in construction due to its effectiveness, performance, and price benefits. Subsequently, it needs to be an eco-friendly, sustainable, and energy-efficient material. This is achieved by replacing or adding energy-efficient concrete materials from industries, such as ground granulated blast furnace slag, steel slag, fly ash, bottom ash, rice husk ash, etc. Likewise, copper slag is a waste material produced as molten slag from the copper industry, which can be used in concrete production. Copper slag can perform roles similar to pozzolans in the hydration process. This paper extends the comparative study of copper slag concrete with polypropylene fiber (PPF) subjected to destructive and non-destructive testing. Under destructive testing, compressive strength of concrete cubes, compressive strength of mortar cubes, splitting tensile tests on cylindrical specimens, and flexural tests on plain cement concrete were conducted and analysed. Ultrasonic pulse velocity and rebound hammer tests were performed on the samples as per IS13311-Part 1-1992 for non-destructive testing. The 100% replacement of copper slag exhibited a very high workability of 105 mm, while the addition of 0.8% PPF decreased the flowability of the concrete. Hence, the workability of concrete decreases as the fiber content increases. The density of the concrete was found to be increased in the range of 5% to 10%. Furthermore, it was found that, for all volume fractions of fiber, there was no reduction in compressive strength of up to 80% of copper slag concrete compared to control concrete. The 40% copper slag concrete was the best mix proportion for increasing compressive strength. However, for cement mortar applications, 80% copper slag is recommended. The findings of non-destructive testing show that, except for 100% copper slag, all mixes were of good quality compared to other mixes. Linear relationships were developed to predict compressive strength from UPV and rebound hammer test values. This relationship shows better prediction among dependent and independent values. It is concluded that copper slag has a pozzolanic composition, and is compatible with PPF, resulting in good mechanical characteristics.  Concrete is a versatile material, popular for its low cost and adaptability . It is tNatural resources are diminishing at their source due to recent development in urbanization and industrialization. Sand is one of such natural resources disappearing daily due to large mining operations utilized for construction . The ill2/kg and a bulk density of 1200 kg/m3, fine slag powder may be combined with free lime to replace 40–65% of total cement content. On the other hand, the coarser slag powder can be employed as an aggregate substitute in the concrete matrix [Researchers are interested in replacing bottom ash, blast furnace slag , copper e matrix . Despitee matrix ,22,23,24e matrix ,22,23. Ie matrix . Ground e matrix . Howevere matrix .2 to react with sulfate and reducing gypsum [Furthermore, because of the large particle size of slag, it has weaker cementing characteristics, which may decrease the bond between slag particles and calcium–silicate–hydrate gels ,29. Undeg gypsum . Due to g gypsum .Copper slag is a waste derivative obtained from the smelting and refining process during copper separation from copper ore . Using cMoreover, copper slag has an irregular glassy texture that does not absorb large quantities of water ,40. TherThe effect of copper slag on concrete strength after a 56- and 90-day curing period evidenced higher concrete strength, and in no case was the strength reduced. Additionally, each mix has a variation of high strength values compared to ordinary concrete ,45. The Slag concrete was also found to show better durability and higher corrosion resistance . The fer3 density was obtained from Jeetmull Pvt Ltd., Chennai, India. Ordinary Portland cement  was useFrom the obtained results of fundamental properties of copper slag, it was noted that the water absorption was 88% lower than for the sand. When copper slag is replaced at a higher rate, the unoccupied moisture content accumulates . SurplusCopper slag particles are available from 4.75 mm to 0.075 mm in size and exhibit a proper grading and good particle packing. 3, and the water–cement ratio was fixed as 0.41. The mix proportions and specimen details for various testing are listed in Concrete proportioning was conducted on copper slag replacement from 0% to 100% and fibrillated polypropylene fiber from 0% to 0.8%, in increments of 20% and 0.2%, respectively. Cement mortars were cast on a 1:3 ratio, in which the sand was replaced up to 100%. The cement content was taken as 360 kg/mThe slump and compacting tests were performed according to Indian standard IS-1199-1959  to analyThe UPV test is an in situ, qualitative, non-destructive testing methodology for concrete conducted per the procedure in IS: 13311:1992 . Before In the case of flaws and cavities, the time taken to travel for a particular path length is high, which indicates the lower velocity of sound waves, and results in poor quality of concrete. This velocity relates to the compressive strength of concrete. 3 cube at 28 days. The surface was cleaned and free from moisture content. The impact load was applied at a constant energy of 2.2 Nm. The number of trails against each measurement was entered as input data before starting the test. The impact energy is used so that the hammer spring rebounds against the concrete surface. The surface hardness of concrete is indicated as the compressive strength. According to BIS 13311—Part 2 [Concrete’s surface hardness is expressed as the non-destructive compressive strength of concrete. The uniformity of the concrete is affected by the compaction variability and variability in curing and temperature changes. 1—Part 2 , the est3 to 2850 kg/m3 [3, whereas the maximum density was 2810 kg/m3. The densities varied from 5% to 10% compared to control concrete.Copper slag is available in the fine aggregate state, and has a higher bulk density than river sand and crushed stone aggregate. The fineness modulus lies between sand and coarse aggregate. Copper slag occupies less volume than concrete due to its higher bulk density and specific gravity. These factors invariably influence the density of concrete. Hence, concrete with copper slag has higher density values, ranging from 2500 kg/m50 kg/m3 . A signiThe degree of compaction was determined using a compacting factor test. The compacting factor values of copper slag–PPF concrete ranged from 0.90 to 0.95, whereas the compacting factor of control concrete was 0.942. The high specific gravity of copper slag in concrete facilitates the self-settling of aggregates, resulting in void-free concrete. Conversely, PPF added to concrete occupies a specific volume, resulting in weight loss in partially compacted concrete. Hence, there was a slight decrease in compacting factor when PPF was added to the concrete. However, this difference had no influence, since the desirable compacting factor for manually compacted heavily reinforced sections is 0.90 to 0.95. The equivalent slump values analogous to the above-mentioned compacting factors start from 50 mm to 100 mm.From 2 at 180 days. PPF 0.6% can be used with 60% copper slag to produce workable concrete. After that, compressive strength decreases as copper slag replacement increases from 60% to 100%. The decrease in the compressive strength of concrete is due to the presence of freely available water in cement, but the strength value does not fall below the target mean strength or the compressive strength of control concrete. Replacement of 80% copper slag (2) at 180 days without fiber content. The 100% replacement of copper slag to fine aggregate exhibited higher strength than control concrete. Moreover, it was found that 100% copper slag replacement does not meet the mean target strength ,81,82. Aper slag  achievedCompressive strength results were obtained by casting and testing cement mortar cubes of size 70.6 mm × 70.6 mm × 70.6 mm at 7 and 28 days. In addition, various proportions of copper slag and polypropylene fiber constituting 180 specimens were tested; the results are tabulated in After 7 days, the C100P2 mix shows 44% higher compressive strength. Even when the sand was 100% replaced with copper slag, it showed 11% higher compressive strength than control concrete. Compared to control concrete, the C20P2 mortar mix exhibited a 133.31% increase in compressive strength after 7 days. This was due to the confinement of the mortar mix due to the PPF in the concrete. 2 and 37.33 N/mm2, respectively. This implies that the replacement of 20% and 80% copper slag produces 83% and 75% higher strength values than the reference mix. Copper slag replacement without PPF increased compressive strength by 11.13%, whereas the addition of PPF further improved the compressive strength by 25.57%. By no means did the compressive strength of any of the mixes fall below that of the control mix. Hence, the copper slag can be entirely replaced with sand in cement mortar application to maximize waste utilization. The compressive strengths of cement mortar at 28 days for C20P0 mix and C80P2 mix were 39.11 N/mmThe transit time in µs was noted for each cube specimen at 28 days of curing. The ultrasonic pulse velocity was calculated as per the formula in Equation (1). cf’ is the predicted compressive strength of concrete [Following Equations (2) to (4) are the compressive strength equations using UPV obtained by the previous researchers. Equations (5) and (6) are the equations derived in this study. concrete ,89.fc’ 2 values are nearer to 1; hence, values derived from the proposed equations fit well with the actual values.A rebound hammer expresses the relationship between the surface hardness and the compressive strength of concrete within the limiting error. Rebound hammer observations are discarded when the variation is more than 15%. Three continuous impacts were applied perpendicular to the reference plane. 2O3 and SiO2 [The main components in cement and copper slag are shown in and SiO2 . Since tand SiO2 . Aluminuand SiO2 . Hence, 2 is unavoidable in each mix proportion. We conclude that C–S–H gel formation increases as the replacement increases up to 60%, and further reduces due to excess water. Eventually, the strength decreases below the target level.Significant explanations were proposed regarding the SEM images of the cement aggregate matrix of the control concrete and copper slag-replaced concrete. Control concrete a showed -Copper slag has sharp angular lines and points that bond between aggregates. It has dimensional stability due to its high density. The density of the concrete increased within the range of 5% to 10%.-In line with the IS: 383-1970, the gradation of 40% of copper slag replaced with sand fits with zone II. Copper slag 20%, 60%, 80%, and 100% replacements satisfy zone I criterion, which shows that the particle sizes are coarser than sand.-Fiber-reinforced concrete alone gives equivalent or lower strength when compared to the control. From our results, copper slag addition leads to a 35% increase in the compressive strength of concrete. The application of copper slag for mortar shows better results, up to 80% replacement. Compressive strength increased to 75% was reported against the reference mix.-2 was perceived at the C40P4 mix, which was 31.58% greater than the control concrete. The maximum flexural strength of control concrete at 28 days for the C40P2 mix was 9.58 N/mm2, which is a 26.05% increase compared to control concrete.The split tensile test of concrete disclosed that the maximum split tensile strength of 3.54 N/mm-2 for 20% copper slag and 0.4% PPF, which was 83% higher than normal concrete.In cement mortar, the maximum compressive strength at 28 days was 39.11 N/mm-2 at 28 days, which was almost 75% greater than the compressive strength of the control mix.Even 80% copper slag in cement mortar produced a compressive strength of 37.11 N/mm-The concrete quality is good, and, in fact, excellent according to the ultrasonic pulse velocity test. In the rebound hammer test, 87% of results showed 30 to 40 MPa strength values, while only 13% fell below 30 MPa. The regression analysis designed to predict the compressive strength through NDT testing provided a better fit with the true values.-2 crystalline structure freely available in the microstructure of control concrete is depleted in copper slag concrete, since the copper slag consumes the unreacted Ca(OH)2 to produce C–S–H gel.The Ca(OH)This paper extends the comparative study of copper slag concrete with polypropylene fiber (PPF) subjected to destructive and non-destructive testing. Under destructive testing of compressive strength of concrete cubes, compressive strength of mortar cubes, splitting tensile test on cylindrical specimens, and flexural tests on plain cement concrete were conducted and analyzed. Ultrasonic pulse velocity and rebound hammer tests were performed as per IS13311-Part 1-1992 for non-destructive testing. In addition, this experimental work also analyzed the microstructure of the concrete and its mechanical properties through destructive, as well as non-destructive testing. The derived conclusions are listed as follows:


Second, a circumscribed central composite design was employed to add HEC as a thickening agent (formulation E2). The dissolution rates at 15, 30, 60, 120, and 240 min were used as responses. Partial least squares regression analysis indicated the effect of each component in delaying the release of Met HCl in the oral gel formulation. The optimized formulation E2-08 consisting of 1.88% Sod ALG, 0.63% HEC, and 1.00% calcium carbonate and two more formulations, E2-10 and E2-12 conformed to USP monograph for extended release. Other physicochemical properties, including floating lag time and duration, viscosity, and pH, measured for each batch and FT-IR spectrometry analysis showed no unexpected interaction between Met HCl and excipients. The current study suggests the potential use of a gastroretentive in situ oral gel for Met HCl helping patient compliance. This study highlights that a systematic approach based on DoE allows the formulation optimization.A gastroretentive in situ oral gel containing metformin hydrochloride (Met HCl) was prepared based on sodium alginate (Sod ALG), calcium carbonate, and hydroxyethylcellulose (HEC). The optimal composition of the formulation was explored based on the design of experiments (DoE). First, a 3 Metformin hydrochloride (Met HCl) is the most well-known biguanide, and it is used to treat type 2, non-insulin-dependent diabetes mellitus. While it has been the first choice for treating diabetes for a long time, a high-unit dose (500 mg or 1000 mg) and administration frequency hinder patient compliance. Swallowing a large tablet of Met HCl gives patients discomfort, and a relatively short elimination half-life calls for frequent administration (two to three times a day). Met HCl is mainly absorbed through the upper small intestine with bioavailability of ~50%. The absorption of Met HCl in the large intestine is negligible, and keeping Met HCl in stomach for a prolonged time can improve the bioavailability. The development of gastroretentive Met HCl with extended release provided a higher bioavailability than immediate release formulation. However, a large pill size remains a burden to patient compliance.® allows higher solubility and permeability for non-permeable lipophilic drug molecule [In biopharmaceutics classification system (BCS), Met HCl belongs to class III with high water solubility and low intestinal permeability. To enhance the permeability of the drug molecule, we can employ various approaches such as nanoemulsion drug delivery system (DDS), spray freeze drying, fatty acid excipients, self-microemulsifying (SME) DDS. Nanoemulsion DDS such as Pluronicsmolecule . It prommolecule . In a ramolecule . Spray fmolecule . Mokale molecule . Long-chmolecule . In addimolecule . SME DDSmolecule .To increase the bioavailability of class III compounds, gastroretentive DDS has been developed to prolong the time of absorption when the short retention time limits the biological availability. Gastroretentive DDS can benefit those drugs that are locally active in the stomach, such as misoprostol  and antaThe gastroretentive in situ oral gel system belongs to the floating system, and it has been widely used for antacid drug delivery . The susStudies have reported a variety of floating DDS for Met HCl mainly of tablet formulation . HoweverIn this study, we pursued to prepare a Met HCl in situ oral gel formulation with a short floating lag time and extended release property conforming to USP Dissolution <711>. In situ oral gel was prepared with Sod ALG and calcium carbonate, and hydroxyethyl cellulose was used as a thickener. To derive the optimal composition of the formulation, a systematic approach was attempted based on design of experiments (DoE).® Direct 8 Water Purification System from EMD Millipore . HPLC grade solvents were used for high-performance liquid chromatography.Met HCl was purchased from Farmhispania, S.A. . Alginic acid sodium salt from brown algae with medium viscosity (Sod ALG), sodium chloride, and hydrochloric acid fuming 37% were obtained from Sigma-Aldrich . Natrosol™ 250 hydroxyethylcellulose (HEC) HHX grade was purchased from Ashland . Calcium carbonate and sodium carbonate (USP grade) were obtained from Daejung . Gaviscon Double Action was purchased from Oxy Reckitt Benckiser . Purified water was prepared using a Milli-QThe pilot study for formulation E1 was first conducted to determine the proper composition of Sod ALG and calcium carbonate: Sod ALG and water indicated in To evaluate the sustained release of Met HCl from each formulation described above, in vitro dissolution test was performed in 900 mL of simulated gastric fluid with pH 1.2 at 37 °C using a USP paddle apparatus. The paddle speed was set at 50 rpm, and 12.5 g of formulation was added to dissolution basket to maintain the shape of gel. Samples, of 5 mL each, were taken at 15, 30, 60, 120, 240, 360, and 480 min . The conThe in vitro floating test was performed by modifying the previously described method . BrieflyTo evaluate the rheological property of Met HCl in situ oral gel, viscosity of the gel was measured using a DV2TLV viscometer from AMETEK Brookfield , keeping the torque within the range of 10~70% . The meaTo examine the formulation compatibility, Fourier-transform infrared spectroscopy (FTIR) was performed using a JASCO Fourier-Transform Infrared Spectrometer 4100  .® 4.0 from Sartorius Stedim  was employed to identify the design space and conditions for associated factors using DoE. In the pilot study of formulation E1, 32 full factorial design was used to investigate the influence of two variables: percent concentration of Sod ALG (X1) and equivalent of calcium carbonate (X2) compared to Sod ALG monomer. The percentage drug released in 15, 30, 60, 120, and 240 min were chosen as dependent variables .MODDE1), HEC (X2), and calcium carbonate (X3). The dissolution rate of Met HCl in situ oral gel at 15, 30, 60, 120, and 240 min was defined as response Y1, Y2, Y3, Y4, and Y5 each. We conducted a partial least squares regression analysis of dissolution rate for each study, using the MODDE® 4.0.For the formulation E2 of Met HCl in situ gel containing HEC, a circumscribed central composite design was used to systematically investigate the effect of each excipients. Three key variables were selected as independent factors: the concentrations of Sod ALG . For 120 and 240 min, predictive relevance Q2 values were low (Q2 < 0.5).Based on the study of formulation E1, we prepared formulation E2 containing HEC as a thickening agent. Design layouts for formulation E2 and corresponding dissolution rates are summarized in As shown in We could see from the dissolution study that batches E2-08, -10, and -12 conform to the USP monograph, and the better dissolution delay was observed in formulation E2 compared to E1. As seen in The viscosity of Met HCl in situ oral gel measured in triplicate are as summarized in −1 region and other areas did not show substantial changes.To see whether Met HCl has any undesirable interactions with Sod ALG and HEC, we analyzed the mixtures of Met HCl using FT-IR spectrometry. As seen in In this study, gastroretentive in situ oral gel formulations were prepared for Met HCl. In situ oral gel would be a good alternative to a tablet formulation with extended-release properties as it is easier to swallow. We could see that each excipient contributed to delaying the release of Met HCl. While Met HCl is quite stable in water , the sta


An increasing number of studies have shown the effects of time-restricted eating (TRE) on metabolic diseases and cardiovascular diseases associated with obesity. However, no bibliometric analyses were conducted in this field systematically. In our study, we aimed to visualize the publications about TRE to determine the frontiers and hotspots and then provide references and guidance for further studies. Publications about TRE were exported from the Web of Science Core Collection (WOSCC) database. VOSviewer 1.6.16 was adopted to perform the bibliometric analysis. In our study, a total of 414 publications with 298 articles and 116 reviews were included. The publications in this field showed an upward trend from 2016. A total of 2016 authors contributed to this field. The most productive authors were Satchidananda Panda, Krista A Varady and Emily NC Manoogian. All publications were distributed from about 624 organizations from 49 Countries/Regions. The leading institutions were the Salk Institute for Biological Studies, the University of California San Diego and the University of Alabama at Birmingham, and the most productive countries were the United States, the People’s Republic of China and Japan. All publications were from 182 journals, and the most productive journals were Nutrients, Frontiers in Nutrition and Cell Metabolism. The first highest cited reference with 991 citations was published in Cell Metabolism, and authored by Satchidananda Panda et al. There were four indicating research directions, and the keywords of the green cluster were time-restricted feeding, metabolism, circadian clock, and circadian rhythm. The keywords of the blue cluster were obesity, health, diet, and food intake. The keywords of the red cluster were intermittent fasting, weight loss, caloric restriction, and time-restricted eating. The keywords of the yellow cluster were insulin resistance, metabolic disease, cardiovascular disease, and caloric intake. The main research hotspots in the TRE field were TRE and circadian rhythm, TRE and obesity, TRE and metabolic disease, and TRE and cardiovascular disease. TRE represents new directions to evaluate the effects of the timing of eating on different diseases, especially obesity, Type 2 diabetes mellitus and cardiovascular disease. Previous studies have generated impressive data on the effects of TRE on metabolic diseases and cardiovascular diseases associated with obesity. More high-quality studies are needed to assess the mechanism and efficacy of TRE in a wide range of populations and diseases. Time-restricted eating (TRE) was an approach that all calorie intake is restricted within 12 h without reducing calories . It was via quantitative analysis of previous scientific literature. In our study, we conducted a bibliometric analysis of TRE to display the research status and draw visual maps and explored trends and hotspots in this field to provide the reference to future studies.An increasing number of studies have shown the effects of TRE on metabolic diseases and cardiovascular disease associated with obesity. However, these findings were not summarized and analyzed as a whole. Bibliometric analysis was widely used to investigate the developmental trends and main findings The Web of Science Core Collection (WoSCC) is widely used for bibliometric analysis, which is the most authoritative citation-based database with powerful indexing functions , 11. TheThe relevant records with “Full Record and Cited References” were exported in the format of “Plain Text.” The resulting set of publications was analyzed bibliometrically. The top 10 high-yield authors, institutions, country/region and journals according to publications and the characteristics of the top 20 highest cited publications were summarized.VOSviewer is a bibliometric tool which is developed for constructing and viewing bibliometric maps , 13. TheA total of 414 publications (298 articles and 116 reviews) were included, which was shown in A total of 2016 authors contributed to this field. Among them, Satchidananda Panda was the most productive author from the United States with 26 publications and an H-index of 15, followed by Krista A Varady with 12 publications and an H-index of 8, Emily NC Manoogian with 11 publications and an H-index of 5, Kelsey Gabel with nine publications and an H-index of 5 and Grant M Tinsley with 8 publications and an H-index of 6. Satchidananda Panda, Krista A Varady and Emily N C Manoogian were the most frequently cited authors. The co-authorship map of the authors was shown in the All publications were distributed from about 624 organizations from 49 Countries/Regions. The leading institutions were the Salk Institute for Biological Studies , University of California San Diego , the University of Alabama at Birmingham , University of Illinois (13 publications with 617 citations) and Texas Tech University (10 publications with 609 citations). The network visualization map of institutions was shown in All publications were from 182 journals. Among them, Nutrients was the most productive journal with 65 documents and 972 citations, which was followed by Frontiers in Nutrition with 13 documents and 101 citations, and Cell Metabolism with 10 documents and 3,224 citations. The most frequently cited journal was Cell Metabolism. The network visualization map of all journals was shown in The characteristics of the top 20 highest cited publications were summarized in The network visualization map of keywords was shown in To our best knowledge, this is the first study of bibliometric and visual analysis for TRE. In our study, a total of 414 publications with 298 articles and 116 reviews were included. The publications in this field showed an upward trend from 2016. A total of 2016 authors contributed to this field.The most productive authors were Satchidananda Panda, Krista A Varady, and Emily NC Manoogian. All publications were distributed from about 624 organizations from 49 Countries/Regions. The leading institutions were the Salk Institute for Biological Studies, the University of California San Diego and the University of Alabama at Birmingham, and the most productive countries were the United States, the People’s Republic of China and Japan. All publications were from 182 journals, and the most productive journals were Nutrients, Frontiers in Nutrition and Cell Metabolism. The first highest cited reference with 991 citations was published in Cell Metabolism, and authored by Satchidananda Panda et al. There were four indicating research directions, and the keywords of the green cluster were time-restricted feeding, metabolism, circadian clock, and circadian rhythm. The keywords of the blue cluster were obesity, health, diet, and food intake. The keywords of the red cluster were intermittent fasting, weight loss, caloric restriction, and time-restricted eating. The keywords of the yellow cluster were insulin resistance, metabolic disease, cardiovascular disease, and caloric intake.In this bibliometric analysis, most of the articles were published from the United States, the People’s Republic of China and Japan, and the percentage of articles from the United States was 44%(184/414). Of the top 10 institutions, seven were from the United States. Of the top 10 productive author, six were from the United States. In the field of TRE, the prominent contribution was from the United States. It indicates that the studies from other countries need to be enhanced.Through the combination of highest cited references and analysis of all keywords co-occurrence clusters, the research hotspots and frontiers were as follows: (1) TRE and circadian rhythm. In the top 20 highest cited references, five explored the TRE and the circadian rhythm, and the keywords of circadian clock and circadian were in the green cluster , 21, 25.This was the first study to conduct a bibliometric analysis of TRE. In our study, we displayed the research status and draw visual maps, and explored trends and hotspots in this field to provide the reference for future studies. There were several limitations in our study. First, all data were extracted from the WoSCC, and other databases such as Medline and Embase were not used. Second, only studies published in English were included. Finally, bias may still exist despite our normalization procedures. Further studies will provide new insight into this field.The main research hotspots in the TRE field were TRE and the circadian rhythm, TRE and obesity, TRE and metabolic disease, and TRE and cardiovascular disease. TRE represents new directions to evaluate the effects of the timing of eating on different diseases, especially for obesity, Type 2 diabetes mellitus and cardiovascular disease. Previous studies have generated impressive data on the effects of TRE on metabolic diseases and cardiovascular diseases associated with obesity. More high-quality studies are needed to assess the mechanism and efficacy of TRE in a wide range of populations and diseases.The original contributions presented in this study are included in the article/supplementary material, further inquiries can be directed to the corresponding authors.SW, XL, and YG were responsible for data collection, investigation, figures and tables construction, and writing the original draft. JH contributed to the discussion and final review and editing. All authors reviewed and edited the final manuscript.


Brittle fracture is a typical mechanical characteristic of high-strength self-compacting concrete, and the research on its toughening modification remains the highlight in the engineering field. To understand the effect of toughening materials  on the mechanical behavior of C80 high-strength self-compacting concrete under static loading, the failure mode, mechanical strength, strain field, and crack opening displacement (COD) of prepared high-strength self-compacting concrete under compressive, splitting, and flexural loads were studied based on digital image technology (DIC). The corresponding mechanism is also discussed. The results show that the hybrid of polymer latex powders, rubber particles, and polyethylene fibers can increase the crack path and inhibit the development of macrocracks in concrete, thus turning the fracture behavior of concrete from brittle to ductile. The addition of toughening materials reduced the compressive and flexural strengths of high-strength self-compacting concrete, but it increased the splitting strength. DIC showed that the incorporation of toughening materials promoted the redistribution of strain and reduced the degree of strain concentration in high-strength self-compacting concrete. The evolution of COD in high-strength self-compacting concrete can be divided into two stages, including the linear growth stage and the plastic yield stage. The linear growth stage can be extended by incorporating toughening materials. The COD and energy absorption capacity of concrete were enhanced with the addition of toughening materials, and the best enhancement was observed with the hybrid of polymer latex powders, rubber particles, and polyethylene fibers. Overall, this research provides a reference for exploring effective technical measures to improve the toughness of high-strength self-compacting concrete. Concrete is currently the most widely used engineering material. It has the advantages of easy access to raw materials and excellent mechanical properties, but it also exhibits the disadvantages of low tensile strength, high brittleness, and easy cracking. In the field of transportation engineering, the problem of durability in concrete structures has been the focus of attention due to the high brittleness and easy cracking of concrete ,2,3. In As we all know, concrete is a multi-phase composite material, and the incorporation of a single toughening material can only improve the performance of concrete in one aspect. If the toughness of concrete is to be enhanced comprehensively, the use of multi-scale toughness materials needs to be considered. For instance, some scholars ,10,11 haMoreover, concrete for transportation roads is also undergoing continuous technological updating with the rapid development of the transportation industry. As an example, high-strength self-compacting concrete is easy to construct and exhibits excellent performance. Thus, it is increasingly used in civil engineering ,17. HoweGiven the above, the aim of this research was to explore the effective way to enhance the toughness of high-strength self-compacting concrete and to investigate the toughening effect of hybrid toughening materials on the performance of high-strength self-compacting concrete. For this objective, a series of tests, including compressive, splitting, and three-point bending tests, were carried out on the high-strength self-compacting concrete containing macro and micro toughening materials. Accordingly, the mechanical behaviors and deformation characteristics of high-strength self-compacting concrete containing hybrid toughening materials were quantitatively evaluated and analyzed based on DIC technology. Overall, this work can provide new ideas and references for the preparation of high-toughness and high-strength concrete for transportation engineering.3, and an elastic modulus value of 3.4 MPa were used. A polymer latex powder (A) with the particle size of 80 μm and an apparent density of 950 kg/m3 was used, and its main component was a copolymer of ethylene vinyl acetate. The mix proportions and fresh properties of the concrete are listed in In this experiment, Portland cement , fly ash (FA), and silica fume (SF) were used as the binder materials, and the chemical composition and physical properties of the binder materials are shown in 500) of the fresh mixture was tested, and the fresh mixture was poured into molds. Then, 100 mm × 100 mm × 100 mm specimens were formed for compressive and splitting strength tests, and 100 mm × 100 mm × 400 mm specimens were formed for a three-point bending test. Three specimens were prepared for each test. The specimens were stored at room temperature and covered with plastic films to prevent the evaporation of the free water in the mixtures. After 24 h, the specimens were demolded and then subjected to standard curing (20 ± 1 ℃ and >95 % RH) for 56 d.The concrete strength grade of 80 MPa was designed in this work. The recommended dosage of toughening materials  referred to the previous experimental research ,23. In pThe compressive strength and splitting strength tests were stress-controlled, and the loading speed of the compressive strength test was 0.5 MPa/s, while that of the splitting strength test was 0.1 MPa/s. The three-point bending test was displacement-controlled, with a loading speed of 0.1 mm/min. The span of the three-point bending specimen was 300 mm. The test device for the above-mentioned tests is shown in DIC technology is a non-destructive measurement method that can obtain the full-field strain information of a specimen surface. In DIC analysis, a reference image is divided into many small blocks  is a common measurement for evaluating the toughness of concrete materials [ff/fc, the better the toughness of the concrete. ff/fc) of specimens incorporating toughening materials. It can be observed that the ff/fc values of specimens CAR and CARF increased with the addition of toughening materials compared with specimen C0. In particular, the ff/fc of specimen C0 was around 0.087, and the ff/fc values of specimens CAR and CARF were both greater than 0.100. This suggests that the incorporation of toughening materials could enhance the toughness of high-strength self-compacting concrete.The ratio of flexural strength to compressive strength  was set across the main crack and at a distance of about 5 mm from the bottom of the specimen. After that, the virtual extensometer was arranged every 20 mm along the main crack to the top of the specimen, with a total of five virtual extensometers. A schematic diagram of the virtual extensometers of a specimen is presented in max to carry out a normalization treatment . The relationship between COD and P/Pmax is shown in From the previous analysis, it was known that the stresses in the specimens were concentrated at their bottoms under the flexural load and that crack formation and connection led to the damage of the specimens with the increase in the load. Incorporating toughening materials brought about changes in both the crack morphology and the crack opening displacement (COD) of concrete. In order to quantitatively evaluate the influences of different toughening materials on the toughness of high-strength self-compacting concrete, we used DIC technology to analyze the displacement field under a flexural load and then obtained the influences of different toughening materials on the toughness of high-strength self-compacting concrete by quantitatively calculating COD. The specific process of calculating COD was as follows: First, the main crack was found in the strain field, and the first virtual extensometer  on the high-strength self-compacting concrete matrix resulted in an enhancement in the deformability of the concrete matrix. In addition, the COD of specimen C0 increased suddenly after reaching stage II, and specimen C0 failed. Although the COD of specimens CAR and CARF also increased after reaching stage II, specimens CAR and CARF still had load-bearing capacity. This demonstrates that the toughening materials provided a good energy absorption effect in high-strength self-compacting concrete, allowing the damaged energy inside the concrete to be released slowly and smoothly.As illustrated in DIC technology could successfully assess the crack expansion path and strain field of high-strength self-compacting concrete under an external load. The incorporation of rubber particles, polymer latex powders, and polyethylene fibers could increase the fracture path and inhibit the macrocrack expansion of high-strength self-compacting concrete. Moreover, the fracture mode of concrete with toughening materials changed from brittleness to ductility.The addition of toughening materials, i.e., rubber particles, polymer latex powders, and polyethylene fibers, reduced the compressive and flexural strengths of high-strength self-compacting concrete but enhanced its splitting strength.Incorporating toughening materials led to the redistribution of internal strains and the diminishment of stress concentration in high-strength self-compacting concrete under compressive and splitting loads, thus exhibiting a significant effect of inhibiting crack expansion. Meanwhile, the addition of toughening materials increased the ultimate strain under a flexural load, which improved the deformation capacity of the concrete.The evolution of crack opening displacement (COD) in high-strength self-compacting concrete could be divided into two stages, including the linear growth stage and the plastic yielding stage. Adding toughening materials could extend the linear growth stage and provide a good energy absorption effect in the plastic yielding stage of high-strength self-compacting concrete.The COD and energy absorption capacity of high-strength self-compacting concrete were improved by incorporating toughening materials. The best improvement was observed with the hybrid of rubber particles, polymer latex powders, and polyethylene fibers. This indicates that multiple types of toughening materials could effectively enhance the toughness of high-strength self-compacting concrete.Based on the results of this study, the following conclusions can be drawn: