Concomitant administration of resveratrol and quercetin prevented the acquisition of heroin CPP, while resveratrol, quercetin, and magnolol blocked heroin-triggered reinstatement. Magnolol, quercetin, and β-catechin blocked naloxone-precipitated heroin withdrawal and increased striatal IL-6 concentration (p < 0.01). Resveratrol administration was associated with significantly higher withdrawal scores compared to those of the control animals (p < 0.0001). The results of this study show that different polyphenols target specific behavioral domains of heroin addiction in a CPP model and modulate the increase in striatal inflammatory cytokines TNF-α and IL-6 observed during naloxone-precipitated heroin withdrawal. Further research is needed to study the clinical utility of polyphenols and to investigate the intriguing finding that resveratrol enhances, rather than attenuates naloxone-precipitated heroin withdrawal.We have examined the effects of four different polyphenols in attenuating heroin addiction using a conditioned place preference (CPP) paradigm. Adult male Sprague Dawley rats received heroin  in escalating doses starting from 10 mg/kg, i.p. up to 80 mg/kg/d for 14 consecutive days. The rats were treated with distilled water (1 mL), quercetin (50 mg/kg/d), β-catechin (100 mg/kg/d), resveratrol (30 mg/kg/d), or magnolol (50 mg/kg/d) through oral gavage for 7 consecutive days, 30 min before heroin administration, starting on day 8. Heroin withdrawal manifestations were assessed 24 h post last heroin administration following the administration of naloxone (1 mg/kg i.p). Heroin CPP reinstatement was tested following a single dose of heroin (10 mg/kg i.p.) administration. Striatal interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-α) were quantified (ELISA) after naloxone-precipitated heroin withdrawal. Compared to the vehicle, the heroin-administered rats spent significantly more time in the heroin-paired chamber ( Heroin is a highly addictive illicit opiate that represents one of the main contributors to the global burden of illness . In the Current pharmacological treatment options for heroin addiction target µ opioid receptors as either full agonists, such as methadone, partial agonists, such as buprenorphine—which is also a ĸ-antagonist—or full antagonists, such as naltrexone ,7,8. BesIllicit drug use, including opiates, is associated with dysregulated immune signaling ,14, withPeroxisome proliferator-activated receptor-alpha (PPAR-α) is known to regulate cellular inflammatory response ,21, and Yunusoglu et al. examined the effect of resveratrol on alcohol-induced conditioned place preference (CPP) in mice. Pretreatment with resveratrol, dose dependently, impaired ethanol preference acquisition, reinstating and facilitating the extinction of alcohol CPP . FurtherConditioned place preference (CPP) is a valid and reliable method used to assess the rewarding properties of various drugs of abuse , such asAdult inbred male Sprague Dawley rats weighing 180 to 210 g (n = 88) were used for the experiments. The study was conducted according to the guidelines of the Declaration of Helsinki and approved by the Animal Care and Use Committee of the Egyptian National Research Center (protocol #19-220/20/11/2019). The rats were housed in standard plastic cages, with 4 animals/cage, in a controlled environment  and food/water were provided ad libitum.Rats were randomly assigned to two cohorts. The first cohort (n = 56) was used to establish CPP to test naloxone-precipitated withdrawal, and to assay striatal IL-6 and TNF-α concentration. The second cohort (n = 32) was established to test heroin-triggered reinstatement. Rats in the first cohort were assigned to one of five groups: (1) control (n = 8), (2) heroin + quercetin (n = 12), (3) heroin + resveratrol (n = 12), (4) heroin + β-catechin (n = 12), and (5) heroin + magnolol (n = 12). Rats in the second cohort were assigned to one of six groups (n = 8 each): (1) vehicle negative control, (2) heroin positive control, (3) quercetin, (4) resveratrol, (5) β-catechin, and (6) magnolol.Heroin was provided from the Criminal Justice Laboratories under the permission of the Ministry of Justice, Cairo, Egypt. Resveratrol , quercetin , β-catechin , and magnolol  were obtained from a local pharmacy as dietary supplements. We discarded the capsule, which contains inactive ingredients such as cellulose, gelatin, rice flour, silica, and maltodextrin. The content of the capsule contains the active substance only. We dissolved the active ingredient in distilled water to the required concentration to be administered orally at 1 mL doses.(A)Habituation: Before the start of the procedure, the rats were habituated to the place preference laboratory room for one hour. During the preconditioning phase (1 day), the animals were allowed to freely explore the whole apparatus for 15 min. The time spent in each chamber, while the door is open, was recorded (unconditioned preference), and then the animals were returned to their home cages.Establishing CPP: The following day, control rats received saline , while heroin-primed rats received heroin in the least preferred chamber in escalating doses, starting from 10 mg/kg, i.p. up to 80 mg/kg daily for 14 consecutive days . The rats received treatments for heroin CPP starting on day 8. Animals were administered polyphenols  after 24 h of the last heroin dose (between 8:00 a.m. and 12:00 p.m.) to precipitate withdrawal, and they were observed in a transparent cylinder arena for a 30 min test period to detect withdrawal symptoms; scores were recorded manually in real time by a blinded observer . SpecifiTesting for the effect of naloxone-precipitated withdrawal on spontaneous locomotor activity using an open field: On day 16, the rats were screened in an open field at the end of the experiment for 5 min . Each rat was placed in the center of the field (100 × 100 cm white box), and the number of squares crossed, as well as the vertical rears, were monitored by a blind observer in real time.Testing for the effect of naloxone-precipitated withdrawal on anxiety using elevated plus maze (EPM): Following the open field experiment, the rats were tested for anxiety using EPM. The maze was raised 40 cm off the floor with two equal crossed arms (10 cm wide and 100 cm long), and one arm was closed by 30 cm high walls. Animals were placed at the intersection facing one open arm and allowed to freely move; the time spent in the open or closed arm, in addition to the number of entries into any of the arms, was recorded in real time by a blinded observer. Maze sessions of 5 min each were held after 90 min of naloxone-induced withdrawal .Testing for the effect of naloxone-precipitated withdrawal on sucrose preference: On day 17 , the rats were deprived of food for 12 h, starting at 8:00 p.m. and continuing until 8:00 a.m. the next day, and were placed in individual cages and provided two regular 200 mL bottles: one containing 3% sucrose solution and the other containing tap water. On the next day (8:00 a.m.), the volumes of sucrose-containing water and plain water were recorded after 24 h. Sucrose intake was calculated: sucrose preference = sucrose intake/total intake (sucrose + water intake) × 100 (28).Euthanasia and brain tissue collection: The rats were euthanized by decapitation under light anesthesia after the end of the sucrose preference test on day 17. Brain tissues were dissected and stored at −80 °C for molecular assay A.Conditioned place preference (first cohort)(B)Heroin-triggered-reinstatement (second cohort)After establishing heroin CPP as described above, the rats were kept in normal housing conditions for 6 days, without heroin exposure. On the day 7, the rats were challenged in the CPP drug-linked chamber by a single heroin dose administration , whereas polyphenols were administered orally from day 8 to day 21, and the last dose was administered 30 min before heroin challenge. Reinstatement was assessed as the time spent in the drug-linked chamber B. At the®, Houston, TX, USA). After adding samples/standards, a biotinylated detection antibody specific for Rat TNF-α or IL-6 and Avidin-Horseradish Peroxidase (HRP) conjugate were added successively to each well and incubated. The optical density of TNF-α or IL-6 conjugated with the biotinylated detection antibody was measured spectrophotometrically at a wavelength of 450 nm using a plate reader . The OD value is proportional to the concentration.The micro-ELISA plate was pre-coated with an antibody specific to Rat TNF-α or IL-6  Concomitant administration of resveratrol and quercetin prevented the acquisition of heroin CPP  spent significantly more time in the heroin-paired chamber . Resveratrol and quercetin administration concomitant with heroin successfully prevented heroin preference and reduced the percentage of time spent in the heroin-paired chamber compared to the administration of heroin alone. . Neither magnolol nor β-catechin administration reduced heroin preference, according to one way ANOVA, followed by Dunnett’s multiple comparisons test, against Her + Veh control group, n = 6–10 animals per group.Daily heroin administration for 14 days established heroin dependence [F = 6.198, Magnolol, quercetin, and β-catechin block naloxone-precipitated heroin withdrawal, prevent rapid weight loss during withdrawal, and reduce withdrawal-associated anxiety-like behaviorp < 0.0001 for both, p < 0.0001 p = 0.3 vs. Her + Veh, p = 0.9, p < 0.01, *** p < 0.001, **** p < 0.0001).Opiate withdrawal manifestations measured 24 h post last heroin administration showed significantly higher scores in both spontaneous and naloxone-induced withdrawal . Animals subjected to heroin administration along with resveratrol, quercetin, and magnolol spent significantly less time in the heroin-paired chamber compared to the heroin+ vehicle group  triggered reinstatement, as evidenced by the significant increase in the percentage of time spent in the heroin-paired chamber compared to the vehicle .A single heroin dose triggered reinstatement, as evidenced by the percentage of time spent in the heroin-paired chamber, as assessed by one-way ANOVA F = 6.983, p < 0.001, p < 0.01 respectively), while resveratrol and β-catechin attenuated the heroin-induced increase in striatal IL-6 concentration . On the other hand, quercetin accentuated IL-6 concentration (p < 0.0001)  .The results of this study show that different polyphenols target specific behavioral domains of heroin addiction in a CPP model and modulate the increase in striatal inflammatory cytokines TNF-α and IL-6 observed during naloxone-precipitated heroin withdrawal.Specifically, quercetin blocked the acquisition of heroin CPP, reduced withdrawal manifestations and heroin-triggered reinstatement, prevented heroin-induced sucrose preference, and accentuated the heroin-induced increase in striatal IL-6 concentration. Interestingly, quercetin prevented certain aspects of naloxone-precipitated heroin withdrawal, such as rapid wight loss and anxiety-like behavior.Our results are in accordance with those of Singh et al., who reported that repeated administration of quercetin (25 and 50 mg/kg) for 9 days suppressed naloxone-precipitated morphine (10 mg/kg) withdrawal . On the The current results show that resveratrol, like quercetin, blocked the acquisition of heroin CPP and heroin-triggered reinstatement. However, it was associated with significantly higher withdrawal scores compared to heroin control, but unlike quercetin, resveratrol attenuated the heroin-induced increase in striatal TNF-α and IL-6 concentrations. Our results are the first, to the best of our knowledge, to report the effect of resveratrol on heroin addiction. Few studies have examined the effects of resveratrol on the attenuating behavioral manifestations of other substance. Yunusoglu et al. examined the effect of resveratrol on alcohol-induced conditioned place preference (CPP) in mice. Pretreatment with resveratrol  30 min prior to ethanol administration impaired acquisition, and reinstatement of alcohol induced CPP and facilitated the extinction of alcohol CPP . As such(A) receptors (as reported for quercetin), then the efficacy of these compounds in the treatment of depression and anxiety should be examined.In the case of β-catechin, our results show that it failed to block the acquisition of heroin CPP or to attenuate naloxone-precipitated heroin withdrawal, but it prevented heroin-triggered reinstatement. Shutto et al. reported that resveratrol (40 mg/kg s.c.) enhanced the acute effect of cocaine on locomotor activity . The autUnlike quercetin and resveratrol, magnolol failed to block the acquisition of heroin CPP, but it successfully prevented heroin-triggered reinstatement. In addition, magnolol attenuated naloxone-precipitated heroin withdrawal, prevented rapid wight loss and anxiety-like behavior associated with naloxone-precipitated heroin withdrawal, and attenuate heroin-induced increase in striatal TNF-α concentration. More studies focused on this unique property of magnolol in attenuating heroin withdrawal manifestations are required.(A) receptors (as reported for quercetin), then the efficacy of these compounds in the treatment of depression and anxiety should be examined.Shutto et al. reported that resveratrol (40 mg/kg s.c.), enhanced the acute effect of cocaine on locomotor activity . The autPPAR-γ agonists can block rewarding properties of drugs through stimulating the mesolimbic dopaminergic neurotransmission ,49. The At the molecular level, we examined two neuroinflammatory markers in the striatum, IL-6 and TNF-α, following naloxone-induced heroin withdrawal. Our results show that magnolol, which successfully blocked withdrawal manifestations, attenuated the heroin-induced increase in striatal TNF-α, while quercetin was also associated with an increase in striatal IL-6 concentration. Magnolol attenuates the increase in pro-inflammatory cytokines such as IL-1β, IL-6 and TNF-α ,57,58,59On the other hand, resveratrol attenuated striatal TNF-α, and β-catechin attenuated striatal IL-6 concentrations. Both resveratrol and β-catechin were of limited value in attenuating withdrawal manifestations. These results highlight the complexity of the neuroimmunological changes that take place during heroin use and the effects of different polyphenols on immune markers.Heroin and other exogenous opiates exert neuromodulatory effects through both immune suppression and activation, depending on the stage of drug use . Acute mThe effects of individual polyphenols on the immune system are also complex. For example, resveratrol modulates the immune response, with both anti-inflammatory ,73 and iQuercetin also exhibits immunomodulatory activities through inhibiting the secretion of inflammatory cytokines and improving immune function [reviewed in ,82,83,84β-Catechin is a natural immune enhancer present in several plants such as green tea leaves, black grapes, and cherries ,89,90. OThe role of PPAR-γ activation cannot be neglected. PPAR-γ expression functions as a vital regulator in NF-κappaB-mediated inflammation . It was Clinical data relative to the use of these compounds in drug use and dependence is not present. However, quercetin, resveratrol, and catechin were investigated clinically in many other disorders such as diabetes, cancer, arthritis, or neurodegenerative diseases, while magnolol was investigated in dental and periodontal studies (clinicaltrials.gov; review ,100,101.The results of this study should be viewed in light of its limitations. First, we examined only adult male rats and could not comment on the efficacy of tested compounds in adolescents or female rats. Second, we did not examine different doses or the optimal therapeutic window for the efficacy of polyphenols for different stages of drug use. Third, we investigated only IL-6 and TNF-α following naloxone-precipitated withdrawal and did not examine other neuroimmune markers during acquisition or reinstatement. Future studies are needed to expand on the current findings and examine other neuroinflammatory markers at each stage of heroin addiction. Despite these limitations, the results of this study lend more evidence to the potential therapeutic benefits of PPAR agonists in reversing certain behavioral manifestations of heroin use and highlight the immunomodulatory function of these compounds, with some concerns for worsening behavioral manifestations of heroin withdrawal. Further preclinical research is needed to gain more insight into the utility of natural polyphenols in treating heroin use disorder in human subjects.Despite these limitations, our current results show that four different polyphenols, with known modulatory effects at the PPAR-γ, are effective in attenuating different aspects of heroin addiction. Quercetin and resveratrol could be effective in blocking heroin relapse, while quercetin and magnolol may be utilized in reducing the severity of heroin withdrawal. Resveratrol use during early heroin abstinence might aggravate withdrawal manifestations. Β-catechin was of limited value in opioid withdrawal, but it blocked reinstatement and relapse to heroin. Proof of concept pilot clinical trials are needed to test the potential efficacy of these compounds in treating patients with heroin use disorder.


In this investigation, a comprehensive assessment was conducted on the cooperative effects of Super Absorbent Polymers (SAP), limestone powder, and white cement within the realm of fair-faced concrete. We discerned that while white cement augments the color vibrancy of the concrete, its accelerated hydration rate potentially induced early-stage cracks and compromised performance. To mitigate these challenges, SAP was incorporated to regulate early hydration, and limestone powder was introduced as a fortifying agent to bolster the mechanical robustness of the concrete. Our findings highlighted not only the capability of SAP to enhance concrete workability and longevity but also the pivotal role of limestone powder in amplifying its mechanical attributes. Microscopic evaluations, undertaken via Scanning Electron Microscopy (SEM), unveiled the potential of both SAP and limestone powder in refining the microstructure of the concrete, thereby elevating its performance metrics. Synthesizing the research outcomes, we pinpointed an optimal amalgamation of SAP, limestone powder, and white cement in fair-faced concrete, offering a valuable reference for prospective architectural applications. In recent years, fair-faced concrete has garnered widespread attention in the architectural realm due to its natural, minimalist appearance and superior engineering properties . With adSuper Absorbent Polymers (SAP) have taken center stage in concrete research ,14. TheiSimilarly, the role of limestone powder in concrete is undeniable ,32. It nNevertheless, despite the positive impact of both SAP and limestone powder on the performance of fair-faced concrete, questions remain regarding their interaction with white cement and how, collectively, they influence both the aesthetics and mechanical properties of the concrete . Recent In conclusion, the use of white cement in fair-faced concrete has been deeply researched and widely applied. Simultaneously, both SAP and limestone powder are receiving increasing attention due to their beneficial effects on concrete performance. However, the synergistic utilization of these three materials to achieve optimal fair-faced concrete performance remains a challenge. This study aims to delve deep into the interactions of these materials within fair-faced concrete, hoping to offer more insights and recommendations for practice.In this study, white Portland cement (strength grade 42.5 and fineness of 300 mesh) was sourced from Aalborg Portland (Anqing) Co., Ltd., Anqing, China. The research also utilized Class II fly ash and Ordinary Portland cement, the chemical composition of which is detailed in The control group ,42,43,44During the sample preparation, white cement, water, coarse aggregate, and fine aggregate were initially combined to ensure a homogenous mixture. During this mixing phase, Super Absorbent Polymer (SAP) was incrementally added based on the desired proportion, ensuring its even dispersion throughout the concrete slurry. Limestone powder was subsequently incorporated in a stepwise manner, with continued mixing to ascertain its thorough integration with the slurry. Once the mixture was prepared, it was transferred to pre-arranged molds. To achieve an even distribution within the mold and to eliminate potential air bubbles, a vibrator was employed. The poured concrete was then subjected to a controlled curing environment with consistent temperature and humidity for a duration of 28 days, ensuring the concrete fully solidified and reached its optimal performance characteristics. Post-curing, the concrete specimens were demolded from their molds.The workability of fair-faced concrete was investigated using the slump test. This test was rigorously conducted following the protocols set out in the “Standards for Performance Tests of Ordinary Concrete Mixtures GB/T50080-2016)” [080-2016”The standard cube compressive strength and splitting tensile strength tests were carried out in accordance with the Standards for Test Methods of Mechanical Properties of Ordinary Concrete (GB/T50081-2002) . Cubic sThis study performed the Rapid Chloride Permeability Test (RCPT) following the Chinese Standard for Long-term Performance and Durability of Ordinary Concrete (GBT50082-2009) . CylindrThis study conducted SEM tests to observe the microstructure characteristics of fair-faced concrete at different magnifications. Samples with a length of 1 cm, a width of 1 cm, and a thickness of 3 mm were prepared from the core part of specimens cured for 28 d. One side was smoothed with sandpaper to serve as the bottom for sticking, and the other side was used for viewing under SEM (TESCAN MIRA LMS).The specific experimental scheme and procedure are illustrated in (1)The impact of SAP on the workability of fair-faced concreteFrom (2)The impact of water absorption on the workability of fair-faced concreteFrom (3)The impact of limestone on the workability of fair-faced concreteFrom The criteria taken from the Chinese Standard for inspection and assessment of concrete durability (JGJ/T193-2009)  are pres(1)Impact of white cement on the durability of fair-faced concrete(2)Impact of SAP on the durability of fair-faced concreteThe inconsistencies observed in these results could stem from several factors. Firstly, when the SAP content surpasses the optimal threshold, the SAP particles might become oversaturated, leading to the creation of minute voids. These minuscule cavities could serve as pathways of minimal resistance, resulting in a heightened RCPT value due to increased permeability. Secondly, while an adequate amount of SAP can offer internal curing to the concrete, thus delaying cement hydration, both an excessive and insufficient quantity of SAP may disrupt the concrete’s microstructure, leading to compromised physical properties. These elements collectively account for the inconsistent RCPT values observed at certain SAP dosages.(3)Impact of limestone on the durability of fair-faced concrete(1)Influence of white cement on the strength of fair-faced concreteFair-faced concrete samples were prepared by mixing ordinary cement with white cement at mass ratios of 0%, 25%, 50%, 75%, and 100%. Compressive strength tests and split tensile strength tests were performed on the samples after curing for 3 d, 7 d, and 28 d. The test results are shown in 3S content in white cement, which accelerates the hydration reaction rate and promotes early strength gain in fair-faced concrete [concrete . The ear(2)Effect of SAP content on the mechanical properties of fair-faced concreteTo improve the quality of fair-faced concrete made with a combination of white cement and ordinary cement, a study was conducted where varying amounts of SAP were added. The cement content used was 50%, and SAP in concentrations of 0%, 0.2%, 0.3%, 0.4%, and 0.5% were included after being pre-absorbed ten times. The effect of SAP concentration on the strength of the resulting fair-faced concrete at different ages is presented in (3)Effect of SAP water absorption ratio on fair-faced concreteThe pre-absorbed water ratio refers to the ratio of the weight of SAP after pre-absorption to the weight of SAP. In this study, fair-faced concrete with SAP content of 0.2% was created by adding SAP with pre-absorbed water ratios of 5, 10, and 15 to a cement mixture containing 50% white cement and 50% ordinary cement. The findings are illustrated in (4)Effect of limestone powder on the mechanical properties of fair-faced concreteAs depicted in However, at a limestone powder content of 30%, there is a slight reduction in the compressive strength of the SAP white fair-faced concrete at the 3-day and 7-day marks. This can be attributed to the intensification of the dilution effect as the limestone powder content rises. Consequently, the early-stage hydration products of the white fair-faced concrete surpass those of the standard white fair-faced concrete. Nevertheless, as the curing age progresses, a notable increase of 11.6% in compressive strength is observed at 28 days. Based on the 28-day standard curing results, the inclusion of limestone powder is evidently advantageous for enhancing the compressive strength of SAP white fair-faced concrete. A limestone powder content of 20% yields the most prominent overall strength enhancement.To further delve into the statistical significance of the effects of different factors such as SAP concentration, limestone content, and white cement content on the properties of fair-faced concrete, an Analysis of Variance (ANOVA) was conducted .p-value is a measure that helps determine the significance of the results. A smaller p-value indicates stronger evidence against a null hypothesis, suggesting the factor has a significant effect. Typically, a p-value less than 0.05 is considered statistically significant. The p-value calculation results are shown in The factors were treated as independent variables, while the properties of the concrete, including slump value, RCPT value, compressive strength, and tensile strength, were treated as dependent variables. The main objective was to determine if the variations in the means of these properties were significant across different levels of the factors. In statistics, the p-value between the SAP concentration and each response variable was below the conventional significance level (0.05), indicating that the SAP concentration has a statistically significant effect on the workability, durability, and mechanical properties of the concrete. The ANOVA results showed that the limestone content also had a significant influence on the properties of the concrete, especially on its compressive and tensile strengths. The variance analysis indicated that white cement content significantly affected the durability of the fair-faced concrete, especially its RCPT value.It can be seen from 3A produced during the hydration process of white cement might be associated with its distinct color and an increase in early strength. However, it is worth noting that while white cement can amplify the color saturation of concrete, its faster hydration rate might adversely affect other properties of the concrete, potentially leading to early cracking. Despite these challenges, due to its superior color and aesthetic appeal, the application of white cement in architectural decoration, road and bridge construction, and other aesthetically demanding areas continues to grow.Through a series of experimental studies, it can be seen from It can be seen from 1 = 60, a1 = 0.5, and b1 = 1.5, while subsequent measurements for Sample B produced L2 = 80, a2 = 0.2, and b2 = 1.0. The color difference between the two samples was then calculated using the respective color difference formula.Two types of concrete samples were selected for comparison in the study. Sample A utilized traditional ordinary Portland cement, while Sample B incorporated white cement. To ensure the accuracy of the test, all other ingredients and curing conditions for both samples were kept consistent. A high-precision colorimeter, capable of measuring L, a, and b values, was employed to determine the color of the concrete samples. Initial measurements of Sample A yielded LAfter inputting the values, we obtain:The color difference value ΔE = 20.1 indicates a significant color variation between the two concrete samples. This is primarily attributed to the use of white cement, which results in Sample B having a whiter and brighter color than Sample A. Given that the color difference surpasses the commonly accepted range , it can be concluded that white cement has a pronounced effect on the color of fair-faced concrete.Scanning Electron Microscopy (SEM) was employed to investigate the microstructural changes in fair-faced concrete with and without the incorporation of Super Absorbent Polymer (SAP). All SEM micrographs were acquired under consistent imaging conditions to ensure comparability. Details of the accelerating voltage and magnification are provided in the respective figure captions.A closer examination of the regions surrounding the spherical fly ash particles is facilitated by 2). The enhanced presence of these hydration products suggests that the limestone powder, in synergy with the SAP, has promoted the hydration process of the white cement. This microstructural observation underscores the potential benefits of introducing limestone powder into SAP-composite white cement concrete, as it appears to augment the density and integrity of the matrix, potentially translating to improved mechanical properties and durability.In (1)Microstructure and mechanical propertiesThe strength and durability of concrete largely depend on its pore structure. Smaller, evenly distributed pores help enhance the compactness and mechanical properties of concrete. The addition of SAP can influence the pore structure. In the early stages of curing, the SAP releasing water might increase porosity, but in the later stages, due to the continuous hydration water provided by SAP, it helps fill these pores, thereby improving strength.White cement and limestone powder react with water in the presence of moisture, forming hydrated calcium silicate (C-S-H) and other hydration products. These hydration products fill the voids in the original mixture, thereby strengthening the structure of the concrete. Specifically, the inclusion of SAP provides additional moisture, facilitating the formation of more C-S-H gel, which in turn enhances the strength and durability of the concrete.(2)Microstructure and durabilityElectrical flux is commonly used to evaluate the compactness and durability of concrete. A lower electrical flux indicates better compactness and durability. From the documentation, the combined use of white cement and SAP can significantly reduce electrical flux, which microscopically indicates a better pore structure and distribution of hydration products.The durability of concrete is also related to the size and distribution of pores. Smaller pores and even distribution help prevent the penetration of corrosive substances, thereby enhancing the durability of the concrete. The addition of SAP and limestone powder helps optimize the pore structure, thereby strengthening the concrete’s durability.(3)Microstructure and impermeabilityThe impermeability of concrete is related to the connectivity of the pores. The lower the pore connectivity, the better the impermeability of the concrete. The addition of SAP and limestone powder helps reduce pore connectivity, thereby enhancing the concrete’s resistance to permeation.The macroscopic properties of fair-faced concrete, such as strength, durability, and impermeability, are influenced by its microstructure. The pore structure, formation and distribution of hydration products, and pore connectivity all affect the performance of concrete at the microscopic level. The addition of SAP and limestone powder helps optimize these microstructures, thereby enhancing the macroscopic properties of fair-faced concrete.(1)Microstructure of SAP and Fair-Faced ConcreteThe primary function of SAP is to absorb and store a significant amount of moisture within the concrete and gradually release this moisture during the curing process. This process impacts the microstructure of the concrete, particularly the distribution and size of the pores. In the early stages of concrete curing, the water released from SAP might lead to an increase in porosity, affecting the compactness of the concrete at the microscopic level. This could influence the concrete’s appearance, resulting in more visible pores or cracks on its surface. However, in the later stages of curing, the moisture provided by SAP supports the continuous hydration of the cement, filling these pores, thereby enhancing the concrete’s compactness and visual uniformity.(2)Microstructure of Fair-faced Concrete with Limestone PowderLimestone powder, as a mineral admixture, can enhance the microstructure of concrete. Its filler effect aids in reducing porosity and increasing the compactness of the concrete. Aesthetically, limestone powder can render a smoother and more uniform surface to the concrete. Additionally, it can impart a more consistent coloration, contributing to a more visually appealing appearance of the concrete.(3)Relationship between Microstructure and Aesthetic PropertiesThe microstructure of concrete, especially the distribution and size of its pores, directly influences its appearance. Concrete with fewer pores and uniform distribution typically presents a superior appearance devoid of extensive cracks and voids. The incorporation of SAP and limestone powder both impact the microstructure of the concrete, consequently affecting its visual characteristics. Specifically, they both can enhance the compactness of the concrete, leading to improved surface uniformity and aesthetic appeal.The aesthetic properties of fair-faced concrete are intricately linked to its microstructure. Both SAP and limestone powder, as admixtures, can enhance the appearance of concrete by improving its microstructural attributes. Specifically, they both contribute to increasing the compactness of the concrete, resulting in a more uniform and visually appealing appearance.(1)Influence of SAP on the Microstructure of Fair-faced ConcreteThe primary role of Super Absorbent Polymers (SAP) in concrete is to absorb substantial amounts of water and gradually release this moisture during the concrete’s curing process. This released moisture creates minute pores, thereby affecting the concrete’s structure at the microscopic level. After the addition of SAP, the 28-day electrical flux of white cement fair-faced concrete is lower than that of concrete without SAP. This suggests that the microstructure of the concrete with SAP is more compact with fewer pores.(2)Effect of Limestone Powder on the Microstructure of Fair-faced ConcreteLimestone powder, as a mineral admixture, serves to fill minute voids in concrete, thereby enhancing its microstructural compactness. This filling effect contributes to the overall mechanical performance of the concrete. When the limestone powder content is at 30%, combined with 0.3% SAP, the concrete’s mechanical properties are optimized. This underscores the significance of limestone powder in refining the microstructure of concrete.(3)Relationship between Microstructure and Mechanical PropertiesThe mechanical properties of concrete, such as compressive strength and tensile strength, are largely dependent on its microstructure. Concrete with smaller, uniformly distributed pores typically exhibits higher strength. The addition of both SAP and limestone powder impacts the microstructure of the concrete. Specifically, they both contribute to enhancing the compactness of the concrete, subsequently improving its mechanical performance. The microstructure of fair-faced concrete is intricately linked to its mechanical properties. Both SAP and limestone powder can enhance the mechanical performance of concrete by optimizing its microstructure. For instance, the data mentioned above indicates that when the SAP content is at 0.3% and the limestone powder content is at 30%, the 28-day compressive strength of the concrete is about 20% higher than other combinations. This significant enhancement can be attributed to the ameliorating effects of SAP and limestone powder on the microstructural attributes of the concrete.(1)The Superabsorbent Polymer (SAP) is pivotal in white cement fair-faced concrete. This is largely attributed to its ability to regulate the hydration of the concrete, especially in the early stages. By gradually releasing moisture during the curing process, SAP ensures continuous hydration of the cement. This is crucial as white cement, while enhancing the color vibrancy of concrete, has an accelerated hydration rate that could lead to early-stage cracks. By mitigating this challenge, SAP ensures the longevity and workability of the concrete. Through extensive testing and evaluations, SAP content of 0.3% has emerged as the optimal proportion for delivering superior concrete performance.(2)Limestone powder serves a dual purpose in the realm of fair-faced concrete. Firstly, as a mineral admixture, it significantly bolsters the mechanical properties of the Concrete, acting as a fortifying agent. Secondly, its presence refines the concrete’s microstructure, as evidenced by Scanning Electron Microscopy (SEM) evaluations. These microscopic evaluations have unveiled the profound impact of limestone powder on the concrete’s performance metrics. Through a series of experiments, a combination of 30% limestone powder content with 0.3% SAP has been determined to provide the optimal comprehensive performance for the concrete.(3)The beauty of fair-faced concrete is not just skin-deep. Its aesthetic properties are intricately linked to its microstructure. The uniformity, color vibrancy, and overall aesthetic appeal of the concrete are significantly dictated by the fine-tuning of its microstructure. By optimizing the proportions of SAP and limestone powder, not only is the mechanical robustness of the concrete enhanced, but its aesthetic appeal also sees marked improvement.(4)p-values associated with the factors underscore their influence on the properties of fair-faced concrete. For instance, the significance of SAP concentration aligns with its observed effect on workability and microstructure. Similarly, the importance of limestone content in enhancing mechanical strengths is statistically validated.The results of the ANOVA reinforce the observations made in the previous sections. The significant (5)This investigation is more than just a theoretical exploration; it holds pragmatic value. By shedding light on the synergistic effects of SAP, limestone powder, and white cement, the research offers invaluable insights into the optimal formulations for white cement fair-faced concrete. These findings are not just academically significant but hold substantial relevance for real-world engineering applications. Architects, civil engineers, and construction professionals can leverage these insights to produce superior quality fair-faced concrete, combining aesthetic appeal with mechanical robustness.


The splitting tensile test of concrete under the same condition was carried out simultaneously. The damage phenomenon and test results of the axial tensile test and splitting tensile test of concrete were compared and analyzed, and the applicability of the new developed device in the concrete axial tensile test was verified.In order to study the axial tensile properties of polypropylene fiber reinforced concrete, an axial tensile test device for concrete is developed in this paper. The device is composed of three parts: rigid frame, spherical hinge and puller, and specimen fabrication part. The test device can accurately measure the tensile strength and peak tensile strain of concrete, and perfectly solves the eccentricity problem of concrete specimens under tension. It can measure the post peak segment tensile strain, such that the whole process tensile stress–strain curve can be obtained. The axial tensile test of polypropylene fiber concrete was carried out using the above test device, and the results show that the tensile strength of concrete can be clearly improved by adding polypropylene fiber, which makes the tensile failure of concrete show certain plastic characteristics. The test results show that with the increase in fiber content, the tensile strength of concrete increases first and then decreases. The effects of polypropylene fiber content and curing age on the tensile properties of concrete were studied and the optimum polypropylene fiber content was determined. When the fiber content is 0.9 kg/m Polypropylene fiber has excellent mechanical properties, good corrosion resistance and low price. Adding a proper amount of polypropylene fiber into concrete can obviously improve the mechanical properties and crack resistance of concrete5. The plastic shrinkage of concrete can be reduced by 12–25% when 0.1–0.3% polypropylene fiber is added. In addition, the splitting tensile strength and flexural strength of concrete after 7 and 28 days can be increased, and the tensile–compressive ratio at 28 days can be increased by 46%. Obviously, polypropylene fibers can significantly improve the performance of concrete8.The addition of polypropylene fibers to concrete can provide significant benefits, improved economy and sustainability. For example, the combination of fiber and concrete can enhance the crack resistance of concrete10 and bending test11. The tensile strength is calculated according to the empirical formula, whereas the internal stress state of the specimen is more complicated; the error of the measured tensile strength is larger, and the ultimate tensile strain and the tensile stress–strain curve of concrete cannot be measured12. The axial tensile test is the most suitable method to test the tensile strength of concrete13. Several scholars have performed experiments in this regard.At present, most of the researches on the mechanical properties of concrete are focused on the performance of concrete under compression and bending loads, while studies on the axial tensile behavior of concrete have been rare. At present, the tensile strength of concrete is mainly measured by the indirect method, including splitting test14 conducted a three-point bending test and an axial tensile test at the same time. In the axial tensile test, cylindrical concrete specimens were used. Moreover, an axial tensile testing device was developed. The two ends of the specimens were clamped by a metal fixture to exert tensile force, but this approach does not take any measures to eliminate eccentricity. Kim et al.15 used a dumbbell specimen with variable section, and the stress concentration was reduced by the variable section, so that the middle part of the specimen was a uniform tensile zone. Liao et al.16 designed a set of concrete axial tensile device and clamp and carried out direct and indirect tensile tests on concrete at the same time. Kasagani and Rao17 developed an external clamp-type concrete fixture that secures the upper and lower ends of concrete and sets a pull ring at both ends to eliminate the eccentricity of the specimen. This method was used to measure the rising section of tensile stress–strain curve of concrete. The experimental work was carried out under uni-axial tension with 0.1%, 0.2%, 0.3%, 0.4%, 0.50% fiber volumes of Mono Glass Fibers, and the results showed that the strength, deformation capacity and energy absorption capacity were higher for Graded Glass Fiber Reinforced concrete than for Mono Glass Fiber Reinforced Concrete.Julia et al.18 designed prismatic specimens with embedded steel bars, in which the steel bars on both ends were welded to steel plates to exert tension on the concrete. Chun and Yoo19 used dog-bone concrete specimens for the tensile strength tests of steel fiber reinforced concrete. The size of specimens was small, and the width of tension zone was only 25 mm. It was found that the tensile test is easily affected by eccentricity and size effects.Chrysanidis and PanoskaltsisIn summary, the main problems of concrete axial tensile test device are as follows: (1) the size of the specimen is too small and the shape of the specimen is unreasonable, and the test results are affected by the size effect and stress concentration. The internal tensile stress of the test piece is not uniform, which leads to the distortion of test results. (2) Eccentricity will easily occur during the test. (3) The concrete will break immediately after cracking, thus the descending segment of the tensile stress–strain curve cannot be measured.In order to solve the current challenges in the axial tensile test of concrete, a set of concrete axial tensile test equipment was developed in this work. The axial tensile test of polypropylene fiber concrete was carried out using this device, and the tensile strength, peak tensile strain and the whole process curve of tensile stress–strain were determined. Based on the test data, the effect of polypropylene fiber on the tensile properties of concrete was analyzed. The axial tensile test and splitting tensile test of concrete were carried out simultaneously under the same condition. Finally, according to the stress state inside the specimen and the test data, the applicability of the new test device in the study of the tensile properties of concrete was verified.20. The second test method involves embedding a reinforcement at both ends of the concrete specimen. The uniform tensile zone is formed in the middle of the specimen, and the tensile force is transmitted through the adhesive force between the steel bar and concrete22. In the third test method, also called the bonding method, the steel plate is pasted on both ends of the concrete specimen, and the tensile force is directly applied to the specimen24. However, all of these three methods indirectly test the tensile strength and have obvious defects. Thus, the failure of the test will easily occur, and the downward section of the stress–strain curve cannot be obtained.Three common test methods exist for the concrete axial tension test. The first test method uses some kind of fixture. The clamp is fixed outside the concrete specimen, and the tension is transmitted by the friction force with the concrete surface25. Herein, based on the above analysis, a set of axial tension test device is developed. The device is composed of three parts: rigid frame, spherical hinge and puller, and specimen fabrication part, as shown in Fig. The success of concrete axial tensile test mainly depends on two aspects: the first is whether the eccentricity of the specimen can be avoided, and the second is whether the stress concentration of the specimen can be solvedFigure There are two main reasons for eccentricity in the axial tensile test: one is the deviation of the specimen placement position, and the other is the error of the test device itself because the pullers in the test device are not on the same axis.In order to solve the eccentricity problem, the spherical hinge part and puller are designed, as shown in Fig. Considering that concrete is easy to be poured and formed, a dumbbell-shaped concrete specimen and mold are designed. The dimensions of the mold and concrete specimen are shown in Fig. Compared with other tensile test devices, this test device provides the following benefits: (1) the device is easy to install and disassemble. When used with the universal testing machine, the tensile strength, peak tensile strain and the whole-process tensile stress–strain curve of concrete can be accurately measured. (2) The operation of tensile test is simple, and the mold can be designed as needed for making a concrete specimen. The preparation of the specimen can be done easily. The dumbbell-shaped specimen is convenient for transferring the tensile force and forming a uniform tensile zone in the middle of the specimen. The measured tensile strength is closer to the true value. (3) The rigid frame in the device and the specimen are pulled at the same time, and the post-peak section tensile stress–strain curve of concrete can be measured. (4) The spherical joint in the device effectively eliminates eccentricity, which makes the specimen always keep the axial tension state. (5) The device is not only limited to testing the tensile strength of concrete, but also can be used to assess the tensile strength of other easily formed materials; hence, it has potential for wide application.In order to directly test the tensile strength, peak stress and full tension stress–strain curve of polypropylene fiber reinforced concrete, the axial tensile test is carried out using the newly developed test device.The design strength grade of polypropylene fiber reinforced concrete is C30, the cement is P.O 42.5 ordinary portland cement, the particle size of gravel is 5–20 mm, the fineness modulus of fine aggregate is 2.5, and the coarse and fine aggregates are well graded. The concrete mix proportion is as follows, cement:water:sand:gravel = 337.95:4.875:634.79:1232.25. The mechanical properties of polypropylene fiber are summarized in Table The amounts of cement, water, sand and fiber are calculated and determined. Before the pouring of the sample, the coarse aggregate was first cleaned and air-dried. In the mixing process, the coarse aggregate and sand were added at first, the mixture was stirred for 60 s, then cement and half water were added, the mixture was stirred for 30 s, then polypropylene fiber was added twice, and the mixture was stirred for 60 s. Finally, the other half water and water-reducing agent were added to stir the mixture for 180 s, and water and polypropylene fiber were added in two stages to achieve the required stirring state. Then the slump of each sample was measured immediately after mixing. Subsequently, the mixed concrete is poured into dumbbell-shaped and cube-shaped molds, which are vibrated evenly on a vibrating table. After the completion of the casting and demoulding, the sample should be immediately moved to the standard concrete curing room where the temperature and humidity are constant, the temperature of the curing room is constant at 20 ± 2 °C, and the relative humidity is not less than 95%. During curing, the specimens are protected from damage.3, 0.3 kg/m3, 0.6 kg/m3, 0.9 kg/m3, 1.2 kg/m3, and 1.5 kg/m3. Three different curing ages are considered, namely, 14 days, 28 days and 60 days. Based on the above two factors, 18 groups of specimens are prepared. Each group of specimens includes 4 dumbbell-shaped specimens and 6 cube specimens. The dumbbell-shaped specimen is fabricated using the above mold, and the side length of the cube specimen is 150 mm.In the axial tensile test of polypropylene fiber concrete, two factors are mainly considered: the content of polypropylene fiber and curing age. The length of the polypropylene fiber is 19 mm. Six different fiber contents are designed, namely, 0 kg/mF of the testing machine, the tensile strain ε0 of the round steel, and the tensile strain ε of the concrete specimen are recorded. The tensile force F0 of the concrete specimen is:The axial tensile test of concrete is carried out using the above device. The main test steps are shown in Fig. E0 denotes the elastic modulus of the round steel, A denotes the cross-sectional area of the round steel on both sides, and ε0 is the tensile strain of the round steel.In the above formula, The axial tensile strength of concrete specimens is:Ac denotes the cross sectional area in the middle of the concrete specimen.In the above formula, Based on the above test data, the tensile strength, peak tensile strain and full process tensile stress–strain of polypropylene fiber concrete are obtained.3, 0.3 kg/m3, 0.6 kg/m3, 0.9 kg/m3, 1.2 kg/m3, and 1.5 kg/m3, respectively.Eighteen groups of axial tensile tests of fiber reinforced concrete were carried out using our self-developed axial tensile test device. The test results are shown in Table 3, the pulled polypropylene fiber can be observed on the fracture surface. The change law of concrete tensile strength with the polypropylene fiber content is shown in Fig. 3, 0.6 kg/m3, 0.9 kg/m3, 1.2 kg/m3 and 1.5 kg/m3, the tensile strength is increased by 17%, 27%, 43%, 38%, and 29%, respectively. With the increase in fiber content, the tensile strength of concrete rises first and then declines. When the fiber content is 0.9 kg/m3, the increase in the tensile strength of concrete is the most obvious.As shown in Fig. 26, and bubbles and irregular holes will appear at the fiber overlap, which in turn increases the probability of internal defects in the concrete, thus the tensile strength of the concrete is reduced.The uniformly distributed polypropylene fiber will connect the weak area between the cement matrix and the aggregate. When the concrete is in tension, the fiber will share part of the tension, which improves the tensile strength of the concrete. Because the fiber is non-directionally distributed in the concrete, when the fiber content is large, the fiber agglomeration phenomenon will occur in the concreteThe influence of curing age on the tensile strength of concrete is shown in Fig. 3, 0.3 kg/m3, 0.6 kg/m3, 0.9 kg/m3, 1.2 kg/m3, and 1.5 kg/m3, the ratio of 14 days tensile strength to 28 days tensile strength is 0.904, 0.901, 0.903, 0.933, 0.936, and 0.936 respectively. The tensile strength at 60 days is increased very little; compared with the tensile strength at 28 days, it is increased by 7.4%, 2.3%, 2.6%, 4.2%, 8.3%, and 7.8%, respectively. The tensile strength of concrete with different fiber contents remains stable with the curing age. Therefore, it can be considered that the tensile strength of polypropylene fiber concrete increases rapidly in the first 14 days. During this period, the hydration reaction inside the concrete is intense, which is the key period for the performance improvement of concrete. After 14 days, the tensile strength of polypropylene fiber concrete does not increase much and basically reaches stability.The strength of polypropylene fiber concrete increases rapidly in the early stage. At the curing time of 14 days, the tensile strength has reached more than 90% of the tensile strength of that at 28 days. When the fiber content is 0 kg/m3 and without polypropylene fiber, respectively. The reason for choosing PFRC-28-0.9 is that when the curing age is 28 days, the mechanical properties of concrete are improved the most when the content of polypropylene fiber is 0.9 kg/m3, and the stress–strain curve of the specimen is the smoothest and most representative.The typical stress–strain curves of polypropylene fiber reinforced concrete and ordinary concrete are shown in Fig. The tensile stress–strain curve of concrete can be divided into the following stages: elastic stress stage, crack propagation stage, falling stage, and failure stage, so as to show the whole tensile process of fiber reinforced concrete.Elastic stress stage: this corresponds to the OA and OE sections, where the stress–strain curve is close to a straight line, and the stress growth rate is fast. In the OE stage, the polypropylene fiber and concrete matrix are under tension together, so the polypropylene fiber concrete can bear greater tensile force than ordinary concrete.EF segment of the curve and is the microcrack development stage. The stress–strain curve appears an inflection point at E, and the slope decreases. At this time, microcracks in the concrete gradually expand and the strain increases. With the continuous increase in tensile stress, microcracks develop to a certain extent, and the polypropylene fiber begins to bear tensile force, which prevents the further development of microcracks. The microcracks in the specimen gradually connect and penetrate to form the main crack, the force transmission path in the concrete decreases, and the stress of the specimen declines. At this time, the polypropylene fibers mainly play the role of crack resistance. In this stage, the stress–strain curve begins to become gentle and the growth rate of strain is accelerated. Compared with polypropylene fiber reinforced concrete, ordinary concrete has no obvious crack propagation stage, and when the tensile stress reaches the peak stress value, the fracture surface quickly forms and the tensile capacity is lost, which also leads to the peak strain of ordinary concrete being lower than that of polypropylene fiber reinforced concrete. Some concrete specimens with low fiber content will also break quickly after reaching the peak stress and show no obvious falling curve. This is because of the low fiber content. In addition, the tensile strength of the fiber and the bonding force with the concrete are insufficient, so the improvement of the tensile performance of the concrete is limited.Fracture propagation stage: this corresponds to the FG and AB stages of the stress–strain curve. At this stage, the stress–strain curve of polypropylene fiber concrete will drop in a fluctuating manner, because the fiber at the fracture surface will be pulled off or pulled out after being subjected to the tensile force. However, the falling stage of ordinary concrete is approximately linear without the crack resistance effect of polypropylene fiber, and the specimen is rapidly destroyed.Descent phase: this corresponds to the Failure stage: this corresponds to the GH and CD stages of stress–strain curve. For polypropylene fiber concrete, point G represents the residual stress of fiber concrete. After point G, the stress–strain curve enters the convergence stage, the stress decreases to the minimum and does not change, and the strain increases rapidly. At this time, the specimen is completely destroyed, and most of the fibers are pulled off or pulled out. Ordinary concrete is completely pulled off after point C, and the stress becomes zero.Figure 3 and 0.6 kg/m3, compared with ordinary concrete, the influence of the fiber content on the tensile stress–strain curve shape is mainly reflected in the following aspects: the development process of microcracks in the elastic stage is obviously shorter, the slope of the curve becomes smaller, and the peak strain increases. The ductility of the concrete is improved after the fiber dimension is added.When the polypropylene fiber content is 0.3 kg/m3, 1.2 kg/m3 and 1.5 kg/m3, the stress–strain curve shape is more gentle, the curvature of the peak point becomes larger, and the sharp point disappears. There is a relatively obvious slow growth and decline before and after reaching the peak stress. In the descending stage, the higher the fiber content, the more gentle the descending section of the stress–strain curve, the fuller the overall shape of the curve, and the more the residual strength and strain are improved. The residual strength increases slightly with the increase in fiber content, which increase is within 0.2 MPa. When the fiber content is above 0.9 kg/m3, the process of stress–strain curve from peak stress to final convergence is longer.When the polypropylene fiber content is 0.9 kg/mThe significance of comparing the axial tension test with the splitting tension test is to point out the difference between an indirect tension test and a direct tension test. It shows the limitation of indirect test represented by the splitting tensile test, whereas the new test device and test method are more reliable and can reflect the true tension state of concrete.At the time of making dumbbell-shaped concrete specimens, cube specimens were also made with the same mix ratio and fiber content. The side length of the cube specimen is 150 mm, and this specimen is used to carry out the splitting tensile test.The concrete cube specimen is taken out from the curing box, a line is drawn at the center line of the top and bottom surfaces of the specimen, and the position of the splitting surface is preliminarily determined. The arc cushion block is installed on the universal testing machine. To avoid the influence of eccentricity on the test results, the arc-shaped cushion block is aligned with the centerline of the top and bottom surfaces of the specimen. The specimen is loaded in an equal strain manner until it is destroyed. The pressure F of the testing machine is recorded when the test piece is split. The main steps of splitting tensile test are shown in Fig. fts denotes the splitting tensile strength of concrete; F denotes the pressure when the specimen is split; A is the split surface area of the test piece. The splitting tensile strength of fiber reinforced concrete is shown in Table In the above formula, 27, which is only an approximate expression of the tensile strength of materials.At present, the splitting tensile test is frequently used to test the tensile strength. The operation is simple and the deviation of test results is small. As shown in Fig. When comparing the axial tensile strength and splitting tensile strength of fiber reinforced concrete, it can be seen that there is a deviation between the two tensile strengths; the splitting tensile strength is greater than the axial tensile strength under the same condition. When the curing age is 14 days, the difference between the two tensile strengths is scattered, ranging from 0.17 to 0.67 MPa. Moreover, the difference decreases with the increase in fiber content. When the curing age is 28 days, the difference between the two tensile strengths is relatively average at about 0.5 MPa, and is not affected by the fiber content. When the curing age is 60 days, the difference between the two tensile strengths is relatively large, and the average difference is 0.59 MPa. There is no obvious change law with the fiber content. The change law of the difference between the two tensile strengths and the fiber content is shown in Fig. The main reasons why the splitting tensile strength is generally higher than the axial tensile strength are as follows:The formula of splitting tensile strength is derived on the assumption that concrete is a homogeneous ideal elastic body. However, the size of sand and gravel aggregate in the concrete is randomly distributed. Concrete is a heterogeneous body formed by cement stone and aggregate bonding, and is not an ideal elastic body. This leads to a deviation between the theoretical results and the real strength.In the splitting tensile test, the failure surface is relatively fixed. It is always on the center line between the upper and lower cushion strips, but this section is not necessarily the weak surface of the concrete. However, the failure surface of the axial tensile test is uncertain, and the crack will appear on a weak surface of the tensile zone in the middle of the specimen. This is the main reason why the axial tensile strength is less than the splitting tensile strength.The production and curing of concrete specimens, the distribution and density of aggregates, the quality of raw materials, the concrete mix ratio, and other test conditions cannot be completely the same. The above factors cause the actual test and theoretical derivation results to be inconsistent.To sum up, the strength measured by the axial tensile test is the tensile strength of concrete under uniaxial tension, which is the most direct and true result without any theoretical assumptions. Furthermore, it allows the measurement of tensile stress–strain curve of concrete, which cannot be achieved by the splitting tensile test.In this paper, to solve the existing problems in the axial tensile test of concrete, an axial tensile test device for concrete is developed. It is composed of three parts: rigid frame, spherical hinge and puller, and specimen fabrication part. The test device is easy to install and disassemble, and can effectively eliminate eccentricity in the test process and avoid stress concentration failure. Combined with a universal testing machine, the tensile strength, peak tensile strain and tensile stress–strain curve of concrete can be accurately measured.3, the tensile strength of concrete reaches the maximum value. The longer the curing age, the higher the tensile strength of polypropylene fiber concrete, while the tensile strength of polypropylene fiber concrete does not increase after the curing age exceeds 28 days.The axial tensile test of polypropylene fiber concrete was carried out by using the newly developed axial tensile test device. The test results show that with the increase in fiber content, the tensile strength of concrete increases first and then decreases. When the fiber content is 0.9 kg/mThe splitting tensile test of concrete under the same conditions was carried out simultaneously. Compared with the axial tensile strength, the splitting tensile strength of concrete is generally larger, the dispersion is high, and there is no obvious regularity. The tensile strain and tensile stress–strain curves of concrete cannot be measured by the splitting tensile test. The applicability of the new developed device in the tensile test of concrete is further verified.The application of the newly developed test device is not only limited to the tensile strength test of concrete, but also the testing of tensile strength of other easily molded materials. Therefore, the test device can be widely used.


Uncomplicated urinary tract infections (uUTIs) are among the most prevalent infections worldwide. Currently, treatments are limited by antimicrobial resistance and antibiotic allergy/intolerance. There is an unmet need for new oral antibiotics active against uropathogens resistant to current treatments. Gepotidacin is a novel, bactericidal, first-in-class triazaacenaphthylene antibiotic that inhibits bacterial DNA replication by a distinct mechanism of action and binding site and provides well-balanced inhibition of two Type II topoisomerase enzymes. Gepotidacin is under investigation for treatment of uUTI.5 cfu/mL) susceptible to nitrofurantoin. Therapeutic success was combined clinical success (complete resolution of symptoms) and microbiological success  without additional systemic antimicrobials. Data below are from a predefined interim analysis (IA) with efficacy/futility stopping criteria, conducted by an Independent Data Monitoring Committee (IDMC).EAGLE-2 (NCT04020341) and EAGLE-3 (NCT04187144) were near-identical global Phase 3, randomized, parallel-group, double-blind, non-inferiority (10% margin) studies comparing the efficacy and safety of oral gepotidacin  to nitrofurantoin  for the treatment of uUTI. Eligible female patients were aged ≥12 years with ≥2 uUTI symptoms and urinary nitrite or pyuria . Per latN=1474; EAGLE-3: N=1512) were included in the IA. See A total of 2986 randomized patients (EAGLE-2: In two large Phase 3 trials using the latest, stringent, FDA efficacy endpoint, gepotidacin demonstrated non-inferiority in one trial and superiority in the other versus nitrofurantoin in the treatment of uUTI with an acceptable safety and tolerability profile. These data will be further described. Gepotidacin has the potential to be a useful oral antibiotic to treat uUTI and its evaluation in Phase 3 trials is an important step in addressing a significant unmet need.


Three days of nitrofurantoin at 100 mg twice daily is recommended as first-line treatment for uncomplicated urinary tract infection (UTI) in evidence-based guidelines across the UK. A review of international guidelines shows that the evidence base has been interpreted in very different ways. UK guidelines are unusual in promoting short (3 day) courses, and we find little direct evidence to support this. Although ‘short’ courses of antibiotics for other agents may provide optimum balance between providing effective treatment whilst reducing selective pressure driving resistance amongst colonizing microbial flora, it remains unclear that course lengths can be extrapolated to nitrofurantoin. Three days of nitrofurantoin may indeed be a useful intervention in a large group of patients. However, without supporting evidence and because clinical response should be expected to vary widely, it is unclear that establishing and promoting an antibiotic duration for UTI is the best approach to optimizing prescribing in this important area. The consequences of suboptimal management in terms of persistence or recrudescence of infection also remain unclear.6 Evidence-based guidelines attempt to optimize prescribing for UTI by standardizing antibiotic therapy to a set duration.Urinary tract infection (UTI) is one of the most commonly seen bacterial infections in general practice,7 Nitrofurantoin provides good empirical cover of uropathogens, reaches high concentrations in the bladder9 and has a low impact on endogenous resident microflora.10 Moreover, a greater proportion of trimethoprim prescribing to nitrofurantoin prescribing at general practice level in adult women was significantly associated with a higher incidence of trimethoprim-resistant Escherichia coli bacteraemia in bacteraemias reported from January 2012 to December 2014 to the national mandatory surveillance programme.11 In 2016/17, a reduction in the trimethoprim to nitrofurantoin prescribing ratio for uncomplicated UTI was incentivized through the NHS England Quality Premium.12 This incentivization contributed to increasing the use of nitrofurantoin for 3 days, in line with UK national guidelines.13Oral options for treating uncomplicated UTI are limited by increasing antibiotic resistance to trimethoprim and safety concerns surrounding fluoroquinolones. In the UK, this has led to an increased use of nitrofurantoin.In this article, we compare the recommendations made on the use of nitrofurantoin in guidelines internationally. In the context of widespread variation in clinical response and tensions between under-treating and over-treating, we analyse how the evidence base has been interpreted in guidance on how best to manage uncomplicated UTI.We conducted a review of guidelines for the use of nitrofurantoin internationally in the treatment of uncomplicated lower UTI. The aim of the review was to capture the level of variation globally surrounding recommendations on nitrofurantoin.Mixed methods were utilized in order to identify guidance, searching for the latest version of guidelines on lower UTI published between January 2010 and January 2023. This was because no one search method consistently yielded relevant and specific results. In PubMed and Google Scholar, a combination of different search terms using the terms ‘urinary tract infection’ or ‘UTI’ or ‘cystitis’ and ‘guidance’ or ‘guideline’ or ‘recommendation’ was used. Results pages, filtered by relevance, were searched until results consistently became no longer relevant. Repositories of national clinical guidelines were searched using the terms ‘urinary tract infection’ or ‘UTI’ or ‘cystitis’, specifically the Guidelines International Network and Guideline Central. The official webpages of major uro-gynaecological, microbiological, infectious diseases and general practice organizations were searched. Reference lists of previous research and guidelines were also searched for citations of guidelines.14 Lower UTI was defined as an infection of the urinary bladder. Guidance related to recurrent UTI, upper UTI and complicated UTI was excluded. Guidance published in languages other than English were translated by E.K. No guidance, once identified, was unable to be translated. The search was not restricted by country but it is possible and indeed probable that guidelines, especially those written in languages other than English, were not captured by this English-language search. However, the aim of comparing recommendations on nitrofurantoin globally to ascertain the level of variation in guidance internationally was achieved.Uncomplicated UTI was defined according to the European Association of Urology classification, which is limited to ‘non-pregnant women with no known relevant anatomical and functional abnormalities within the urinary tract or comorbidities.’Identifying outlying recommendations on nitrofurantoin course length in some guidance, we then reviewed and analysed the evidence cited in support of these outlying recommendations. Firstly, this involved identifying which studies included in the systematic reviews cited had arms using nitrofurantoin as an intervention. Secondly, we evaluated these arms individually for their relevance and applicability to the recommendation made in terms of antibiotic agent, dosage and duration. No comparative methodology to compare between studies for quality of evidence was necessary given the nature of the findings.Finally, we discuss evidence pertaining to outlying nitrofurantoin interventions that was not cited in the guidance recommending these interventions. This was in order to discuss the recommendation itself, based on available evidence, as well as to evaluate the evidence upon which recommendations were based. Evidence was previously known to the authors and mixed methods searches yielded no further relevant results.15 and SIGN16 recommend a 3 day course of nitrofurantoin 100 mg modified-released (MR) twice daily or 50 mg four times a day as first-line treatment for women presenting with symptoms of uncomplicated UTI who are assessed to be in need of antibiotics. The Norwegian Directorate for Health recommends a 3 day course of nitrofurantoin 50 mg three times daily.36 The Finnish Medical Association recommends a 3 day course of 75 mg twice daily.37 The German College of General Practitioners and Family Physicians guideline also recommends considering a 3 to 5 day course of 100 mg twice daily.27 The Belgian EBM PracticeNet guideline31 recommends a 3 to 5 day course of nitrofurantoin but the dose is higher, with 100 mg recommended three times daily. Meanwhile, most other guidance internationally recommends longer courses of nitrofurantoin. A major international guideline from the IDSA and ESCMID jointly recommends a 5 day course of 100 mg twice daily,18 and the European Association of Urology (EAU)14 recommends a 5 day course of 50–100 mg four times daily, or 100 mg (MR) twice daily.Twenty-seven guidelines from major organizations internationally were identified. There is widespread variation in recommendations on nitrofurantoin use globally Table . In part40 is presented by NICE, SIGN and the Norwegian Directorate for Health as evidence for ‘short’ courses of 3 days of nitrofurantoin for treating acute UTI in non-pregnant women. The equal efficacy of 3 day and 5 day courses was a finding independent of antibiotic class used. However, the review did not include any trials that had nitrofurantoin courses of less than 7 days as a study arm. As noted by the authors, the drug in the 3 day group was a quinolone in nearly all of the studies, with no direct evidence for the use of 3 days of nitrofurantoin 100 mg twice daily, the current recommended therapy in the UK for acute uncomplicated UTI in women.A Cochrane Library systematic review of evidence comparing the efficacy of 3 day courses with 5 day courses of antibioticsin vitro resistance rates. NICE cites a meta-analysis of randomized controlled trials,41 and two Cochrane systematic reviews,43 as evidence supporting nitrofurantoin as first-line antibiotic choice for non-pregnant women. SIGN cites one of these Cochrane systematic reviews.42 The meta-analysis compared fosfomycin with 7 day courses of nitrofurantoin and found no significant difference.41 One of the Cochrane reviews compared trials involving quinolones only.43 The other Cochrane review42 included one small clinical trial,44 where 3 days of nitrofurantoin was compared with 3 days of trimethoprim/sulfamethoxazole 160/800 mg twice daily, 3 days of cefadroxil 500 mg twice daily, and amoxicillin 500 mg twice daily. Not only was nitrofurantoin found to be inferior in terms of clinical cure to trimethoprim/sulfamethoxazole , but the dosage of nitrofurantoin used in the study was 100 mg four times daily, double that of current UK recommendations.The Norwegian Directorate for Health presents no trial evidence on the choice of antibiotic, citing 40 and of the equal effectiveness of 7 days of nitrofurantoin to fosfomycin41 and β-lactams and trimethoprim/sulfamethoxazole.42 No direct evidence on the clinical efficacy of 3 days of 100 mg nitrofurantoin MR twice daily (or 50 mg immediate release four times daily) is presented by NICE, SIGN or the Norwegian Directorate for Health’s evidence review. There is some evidence on 3 days of 100 mg nitrofurantoin four times daily, which demonstrated it to be inferior to 3 days of amoxicillin, cefadroxil and trimethoprim/sulfamethoxazole.44Therefore, the current UK recommendation for a 3 day course of 100 mg nitrofurantoin MR twice daily is based on evidence of the equal effectiveness of 3 day quinolones and 5 day courses of other antibiotics,45The limitations of the evidence base are not recognized in the guidance of NICE or SIGN. In contrast, previous SIGN guidance on UTIs from 2012 noted that the recommendation of 3 days of nitrofurantoin differed from IDSA recommendations and that ‘there is no direct evidence comparing three days nitrofurantoin with seven days nitrofurantoin.’46 The data on 3 day courses come from the small US clinical trial analysed above44 using 3 days of nitrofurantoin at a dosage of 100 mg four times daily, and from a 2002 study from Belgium47 also using 3 days of nitrofurantoin at a dosage of 100 mg four times daily. The study found that a 3 day course of nitrofurantoin was significantly more effective than placebo for uncomplicated UTI but noted that it was ‘surprising to have so few patients in the treated group with completely resolved symptoms after three days’ with 37% symptomatic cure, and that ‘patients should be informed about the frequent persistence of some symptoms after three days of nitrofurantoin treatment, despite the apparently successful bacteriological eradication.’ Therefore, there is no direct evidence for the Finnish recommendation of 75 mg nitrofurantoin twice daily for 3 days nor is there evidence directly comparing 3 day courses of nitrofurantoin with longer courses.The Finnish guideline does not cite systematic reviews but recommends a 3 day course of nitrofurantoin on the basis that ‘the microbiological and clinical responses achieved with nitrofurantoin do not differ from each other in different studies where treatment times have been either 3, 5 or 7 days. A direct comparison of nitrofurantoin treatments of different lengths has not been made.’47 cited in the Finnish guidance is not cited by NICE, SIGN or the Norwegian guideline. As in the US trial,44 the dosage in this trial, which showed 37% symptomatic cure after 3 days of treatment with nitrofurantoin, is double that of current UK guidance, at 100 mg four times daily.There is some, albeit very little, evidence available on 3 day courses of nitrofurantoin in addition to that cited in guidance that recommends this intervention. The Belgian trial7 (using data on 3 day courses of nitrofurantoin47) demonstrated equivalent clinical efficacy of nitrofurantoin to trimethoprim/sulfamethoxazole, ciprofloxacin and amoxicillin when used for 5 or 7 days (79%–92%), but diminished clinical efficacy when used for 3 days (61%–70%). This review was not prioritized by NICE, as the Cochrane review42  was established to be of higher quality by the committee using NICE’s interim process guide.48 Neither systematic review provides evidence that a 3 day course of nitrofurantoin 100 mg twice daily is clinically equivalent to a 5 or 7 day course, or alternative antibiotics.A systematic review and meta-analysis in 201549 Treatment failure was defined as re-prescription of a common urinary antibiotic  within 31 days of finishing initial treatment. Results showed increased treatment failure of 18.9% after 3 days of nitrofurantoin, compared with 13.1% at 5 days and 12.5% at 7 days. This led the authors to conclude that 3 day courses of nitrofurantoin were less effective than 5 or 7 day courses.Evidence on 3 day courses of nitrofurantoin was published following high re-prescription rates in the Netherlands between 1992 and 1997.‘Short’ courses of antimicrobial therapy are intended to be the shortest course length that maintains clinical efficacy. This optimizes the benefit of the antibiotic to the patient whilst minimizing side effects and reducing selective pressure driving antimicrobial resistance amongst microbial flora.51 The challenge in this approach is to identify the shortest course that will be clinically effective for the most people. However, both microbiological clearance and symptomatic resolution may be poor measures of clinical efficacy, even in patients who did have bacterial infection, as symptoms may be caused by residual inflammation.We have been unable to identify any trial evidence on the clinical efficacy of the current recommended first-line therapy in the UK for uncomplicated UTI. NICE extrapolates that 3 days of nitrofurantoin is non-inferior to longer courses of nitrofurantoin because this is the case for other antibiotics. Antibiotics, however, vary in their wide range of different pharmacokinetics and modes of action. It is therefore not clear that course lengths can be extrapolated between drug classes without supporting clinical evidence.52The variation between recommendations internationally reflects both the uncertain foundations upon which evidence-based guidelines are written, and the limits of what can be safely concluded from evidence. A conclusion that there is more evidence for longer courses of nitrofurantoin than shorter, 3 day courses, ignores the paucity of evidence for either, and that the total absence of any evidence for current recommended practice means that comparisons cannot be made. Looking ahead, the National Institute for Health and Care Research (NIHR)-funded DurATIon-UTI trial, which started in August 2022 at the University of Oxford, UK, and is set to conclude in August 2025, will provide evidence on clinical efficacy of durations of 1, 2, 3, 4 and 5 day courses of nitrofurantoin, at currently recommended dosages.40–43 Genetic bacterial resistance and diagnostic uncertainty notwithstanding, this could be due to multiple host and pathogen factors such as individual immune response, microbiotic make-up53 and bacterial virulence.55 Moreover, response could well differ across different episodes of infection in the same patient. A study from 1984 compared single-dose (50 mg four times in 1 day) nitrofurantoin with nitrofurantoin 50 mg four times daily for 10 days.56 Single dose and 10 days were equally effective (95%–97% cure rate). It could be that in some patients with lower UTI, very short courses of even a single dose may be as effective as longer courses. In other patients though, 3 day courses are clearly ineffective. Treating for longer may resolve symptoms in a larger proportion of patients, although it may of course involve over-treating others, and data on longer courses of nitrofurantoin still demonstrate considerable rates of treatment failure.57–60 One possible explanation for this could be that whereas nitrofurantoin retains in vitro efficacy against a large proportion of urinary isolates derived from clinical settings, this may not correlate well with in vivo efficacy.Evidence-based clinical guidelines that recommend antibiotic durations by indication are useful in primary care where ongoing assessment is limited compared with hospital settings. However, the concept of a course length in itself is limited. Evidence suggests that different patients respond differently to the same antibiotic.61 in pointing out there may be ways of customizing duration of therapy to the patient’s response in primary care settings. Patients could be advised to contact the prescriber if symptoms resolve prior to finishing the course or else simply to stop treatment when they feel better. Another way of incorporating the expectation of individual variance in clinical efficacy into guideline care would involve a greater commitment to sharing uncertainty with clinicians and patients.62 Such efforts are underway in the WikiGuidelines initiative,63 which aims to ‘create guidelines with the humility of uncertainty.’ Pushing for greater compliance towards predefined course durations without the evidence to support it, especially without sharing the uncertainty of the evidence base, may risk a loss of confidence in recommended interventions. Certainly, there is a need for better safety-netting and guidance on the common clinical scenario of treatment failure in uncomplicated UTI.We join others