In recent decades, many cities have become densely populated due to increased urbanization, and the transportation infrastructure system has been heavily used. The downtime of important parts of the infrastructure, such as tunnels and bridges, seriously affects the transportation system’s efficiency. For this reason, a safe and reliable infrastructure network is necessary for the economic growth and functionality of cities. At the same time, the infrastructure is ageing in many countries, and continuous inspection and maintenance are necessary. Nowadays, detailed inspections of large infrastructure are almost exclusively performed by inspectors on site, which is both time-consuming and subject to human errors. However, the recent technological advancements in computer vision, artificial intelligence (AI), and robotics have opened up the possibilities of automated inspections. Today, semiautomatic systems such as drones and other mobile mapping systems are available to collect data and reconstruct 3D digital models of infrastructure. This significantly decreases the downtime of the infrastructure, but both damage detection and assessments of the structural condition are still manually performed, with a high impact on the efficiency and accuracy of the procedure. Ongoing research has shown that deep-learning methods, especially convolutional neural networks (CNNs) combined with other image processing techniques, can automatically detect cracks on concrete surfaces and measure their metrics . However, these techniques are still under investigation. Additionally, to use these data for automatically assessing the structure, a clear link between the metrics of the cracks and the structural condition must be established. This paper presents a review of the damage of tunnel concrete lining that is detectable with optical instruments. Thereafter, state-of-the-art autonomous tunnel inspection methods are presented with a focus on innovative mobile mapping systems for optimizing data collection. Finally, the paper presents an in-depth review of how the risk associated with cracks is assessed today in concrete tunnel lining. After decades of increased urbanization, many cities have become densely populated, and the transportation infrastructure has been heavily utilized. Concrete infrastructure such as tunnels, bridges, and roads often constitutes an important part of the infrastructure network. The downtime of these structures has a huge impact on the efficiency of transportation capacity; therefore, it is important to minimize this downtime to ensure cities’ functionality and economic growth. At the same time, the majority of concrete infrastructure is ageing, and continuous inspections are needed to ensure the safety of these structures. Concrete infrastructure can today be designed for a technical lifespan of up to 120 years, but it needs to be maintained to ensure safety. Inspections must be conducted to detect, observe, and measure damage such as cracks, water, and leaching, which can lead to decreased structural capacity. Cracks are a common initiation to the degradation of concrete and reinforcement, water often accelerates the deterioration, and leaching is common in structures with one-sided water pressure, such as tunnels [Nowadays, tunnels have become a more attractive alternative when road and railway networks need to be improved, and they have increased in both total length and number . One of Automated, cost-effective, and exhaustive approaches for inspecting tunnels can, therefore, significantly increase the efficiency of inspections, improve the conditions for human activities, decrease the downtime of infrastructure and facilitate the transfer of knowledge . In receThe inspection is usually followed by an assessment of the structural condition. In this phase, the risk associated with the observed damage is evaluated with respect to the structural capacity and stability of the infrastructure. Commonly, these evaluations are used to classify infrastructure using condition classes adopted as the foundation for maintenance planning. If effective, the maintenance program helps reduce costs, decrease the number of temporary closures, increase public safety, and ensure adequate service levels. However, there are no internationally accepted standard procedures for conducting tunnel assessment and maintenance, which represents an open problem.This paper presents a review of existing methods used to optimize data collection and inspection for tunnel monitoring and to assess the risk associated with damage in the concrete lining used as a rock support based on scientific papers and national guidelines. The paper is organized as follows: Over time, damage to the concrete lining, such as cracking and leaching, that is visible is inevitable . Cracks Reinforced concrete is the most commonly used support material for tunnels. Different types of support systems are used for tunnels depending on the strength and quality of the rock mass, alongside other factors, such as span length, type of tunnel, and height of overburdened rock mass. For a case with low-strength rock, it is commonly assumed that the support system must carry the entire weight of the rock mass. In such a case, an arch made of reinforced concrete is a typical support system. For a tunnel in good-quality rock, the rock mass can often support its weight through arch action; here, fiber-reinforced shotcrete, i.e., sprayed concrete, is often used in combination with rock bolts to support the tunnel. Shotcrete is directly sprayed on the rock surface and sticks to the surface through the use of set accelerators and high pneumatic pressure used during application. Depending on the tunnel requirements and the amount of infiltrating water, shotcrete can be complemented with different solutions to reduce the amount of water inside the tunnel. In It should be noted that the post cracking response significantly varies between fiber-reinforced and conventional reinforced shotcrete, which should be considered in the assessment, see, e.g., Sjölander . MoreoveWhen concrete cracks, the stiffness of the material locally decreases. As mentioned, cracks do not necessarily have a direct impact on the structural capacity of the tunnel lining. The impact of the crack with respect to the structural capacity depends on the length and width of the crack and on factors such as the direction of the crack with respect to the tunnel. Moreover, the cause of cracking has a significant effect on its impact, and the structural post cracking performance of the concrete lining must also be considered. Cast reinforced concrete has strain-hardening behavior, meaning the structure can carry an increased load after cracking. Fiber-reinforced shotcrete, on the other hand, has normally a strain-softening behavior, which implies that the load-carrying capacity decreases after the first crack is formed . This isLoad-independent cracks caused by, e.g., restrained shrinkage or swelling of the concrete;Load-induced cracks caused by, e.g., loose blocks or deformation of the tunnel.If possible, cracks should be divided into two categories to facilitate the assessment of the associated risk:Nordström et al.  also sugFor concrete lining, load-independent cracks, caused before or after hardening, are commonly found in tunnels. Ansell  reportedShrinkage and other load-independent cracks can often be considered harmless ; howeverTypically, load-induced cracks originate from the loads caused by the deformation of the rock or soil, water pressure, or the deadweight of a loose block. Here, the French guideline  makes anHorizontal cracks are orientated parallel to the tunnel direction, and several horizontal cracks commonly occur in succession. Single horizontal cracks are uncommon. The risk associated with cracking is low, but the formation of such cracks may decrease the stiffness and cause the localized rupture of a lining. However, as long as no rapid deformation occurs at these sections, it is suggested that no actions should be taken . VerticaBased on experimental testing by Holmgren , FernandMost guidelines on how cracks influence the structural capacity of concrete lining are based on empirical knowledge, but few scientific studies have been devoted to the risk of cracks in tunnel linings. However, Su et al.  investigHere, the results showed a decreased structural capacity of approximately 5% when a crack was present. This result indicates that the direct influence from narrow cracks with a limited depth is negligible with respect to the structural capacity. Xu et al.  combinedIn a tunnel, the primary rock support is in direct contact with the rock mass and is therefore affected by the groundwater. Because a dry traffic environment is desirable, preventive actions, such as grouting or watertight membranes, are adopted to reduce the contact between groundwater and rock support. However, such systems are rarely completely successful, and part of the tunnel and the concrete is therefore subjected to a one-sided hydro-static pressure. This can lead to erosion or an accelerated leaching process, which is discussed further below. Infiltrating water in the tunnel is a sign of lost water tightness or failure of installed drains in the tunnel. Over time, the water pressure, in combination with cracks, may lead to internal erosion. This loss in material volume is strongly correlated to a reduced strength of the material . A more During construction, water may be present on the rock surface. This can result in a low-quality or nonexisting bond between concrete and rock . Thus, pDuring the leaching process, calcium hydroxide (CH) is dissolved in water and transported to the concrete surface through a slow diffusion process or with the flow of water, which is a much faster process. When particles of CH react with the carbon dioxide  using specific software packages such as the Mobile Mapping GeoTracker, which only facilitate data visualization see . The opeIn the last decades, different image-based approaches have been widely investigated to overcome all these drawbacks and to develop an automatic procedure for damage detection. The aim is to speed up the procedure of infrastructure monitoring and achieve the efficient automatic extraction of defects. Some examples are edge-detection algorithms, percolation methods, and principal component analysis (PCA), see, e.g., ,59,60. RCommonly, the assessment of damaged concrete lining is divided into local and global effects. First, local effects, i.e., individual damages, are separately assessed. This means that the impact of each damage is first assessed. This should be performed with respect to the structural capacity and the prescribed functionality of the structural part. For example, a crack in a waterproof membrane likely does not affect the structural stability but may significantly reduce the functionality. Second, the tunnel is divided into sections, and the structural condition and functionality are assessed based on the combined effect of all local damage in that section.Most of the published papers on maintenance focus on developing autonomous inspection and damage detection methods. Farrar and Lieven  expresseIn its essence, damage diagnostics and the subsequent planning of required maintenance is an optimization problem that must find a sufficient balance between the cost of maintenance and the required level of safety of the tunnel. Different strategies to optimize maintenance are presented in the literature, see, e.g., Ai and Yuan , Baji etTo the best of our knowledge, only a few studies and research projects focusing on autonomous tunnel assessment of concrete tunnels exist. In the literature, a quantification of tunnel lining level of degradation was proposed using the Tunnel Lining Crack Index (TCI) . The TCIFrom a commercial point of view, a few companies have recently investigated new approaches for tunnel assessment. Among them, ETS s.r.l. developed the ETS management and identification of the risk for existing tunnels (MIRET) approach, which combines the ARCHITA system with AI technologies to detect defects from the high-resolution images ,89. MIREPerforming a quantitative assessment of damage to concrete structures has not received much attention from the scientific community, and few papers focus on how to assess individual damages. However, some countries have established national guidelines to increase the quality of inspections and obtain more consistent results from their inspectors. A summary of some of these guidelines is presented below.In Sweden, road and railway tunnels on the public transportation network are divided into a functionality class that ranges from TK0 to TK3 . Here, tThe French Road Administration has issued a guideline for tunnel inspection  and a liSimilar to the French guidelines , a definIn As shown above, different national guidelines differently assess the risk associated with cracks. The main reason for this is that the support of tunnels is designed differently depending on the quality of the rock mass and the expected load on the support. Thus, a risk system should be developed for every type of tunnel support. The structural capacity and risk with respect to cracks in reinforced cast concrete have been well studied, see, e.g., ,93,94. HIn recent years, robotic and mobile mapping systems have been developed for automatically acquiring data in tunnels and improving the inspection protocol. This technology is mature and already exists on the market.Damage detection is still mainly performed manually, which has a high impact on the efficiency and accuracy of the procedure. However, the interest from the scientific community in developing and improving deep learning algorithms is constantly improving the efficiency and accuracy of damage detection.Some indications, such as preferred orientation and common crack widths, exist for load-induced and load-independent cracks. However, it can be concluded that the cause of cracking is difficult to determine in an automated way on the first inspection. Over time, cracks caused by shrinkage or temperature, i.e., load-independent cracks, tend to be stable. Hence, the cause of cracking can be better estimated after several inspections. The experimental tests reported in the literature indicated that cracks with limited width  have no direct impact on the structural capacity of the concrete lining.Different methodologies to assess the safety of the tunnel and the need for maintenance are, nowadays, adopted together with recommended threshold values for assessing the risk associated with cracks in concrete lining based on national standards. It can be noted that a significant difference exists between the national guidelines. The threshold values contain a combination of numeric values and descriptive text. This makes the guidelines difficult to use in an automated process in which only numeric values can be used. Furthermore, neither theoretical reasoning nor experimental testing is provided to give any scientific background to the selected threshold values for cracks presented in the guidelines. Thus, the values are most likely determined based on a combination of empirical knowledge and subjective engineering judgement. To increase the understanding of the risk associated with cracks in the concrete lining, numerical simulations or more experimental testing is one possible way forward.This paper reviewed the methods and technologies for inspecting and assessing concrete tunnels. Scientific papers and commercial solutions for improving the objectivity and accuracy of tunnel monitoring were presented. Additionally, scientific papers and national guidelines for tunnel assessment were reviewed and presented in detail in this paper. Based on this review, the following conclusions can be drawn:To summarize the current state of research, it seems likely that automated inspections and assessments of tunnels will be implemented in the coming years. This review showed that the technology to efficiently and semiautonomously capture data from a tunnel is mature and, to some extent, already available on the market. Moreover, the efficiency and accuracy of deep learning algorithms to automatically detect cracks and other defects are constantly improving. Here, further research should focus on proof of concept on a large scale, i.e., the accuracy of detecting cracks in different tunnels and environments must be shown. The results should not only be compared with the ground truth, i.e., labeled data, but also with the results from human in situ inspection. This way, the accuracy and efficiency of automated and human inspections can be compared. Lastly, a foundation for an automated assessment system must be developed, and threshold values for cracks and other damages must be suggested. In this area, more research is required.


This research investigates the effects of iron tailings content on the mechanical properties and durability of concrete under dry–wet cycling and negative temperature conditions (−10 °C), where iron tailings replace river sand at rates of 0%, 10%, 20%, and 30%. A variety of tests were conducted on the iron tailings concrete, including compressive strength, flexural strength, splitting tensile strength, mass loss, and relative dynamic modulus, and its pore characteristics were analyzed using low-field nuclear magnetic resonance (NMR) experiments. The results reveal that when 20% of the river sand was replaced with iron tailings, the concrete achieved optimal splitting strength, compressive strength, and flexural strength at 28 days, improving by 0.46 MPa, 3.14 MPa, and 0.41 MPa, respectively, compared to conventional concrete. Furthermore, the concrete containing this proportion of iron tailings demonstrated superior mechanical properties and durability in both negative temperature conditions and dry–wet cycling experiments. Due to the excellent physical and chemical properties of iron tailings, they enhance the performance of concrete when incorporated in appropriate quantities. The fine granularity of iron tailings helps to compensate for the granularity defects in concrete aggregates by filling internal voids, optimizing the pore structure, and improving the concrete’s density and integrity. This enhances the concrete’s mechanical properties and its resistance to external solutions and harmful ion penetration. Additionally, the active substances in iron tailings promote the hydration reaction of cement, leading to the formation of an increased amount of C-S-H gel and other hydration products in the cement system. Iron tailings are among the significant by-products of mining operations and a major component of industrial solid waste. As the steel industry develops, the proportion of iron tailings in industrial solid waste has been continuously increasing . The annOwing to the simple and energy-efficient production process of iron tailings concrete (ITC), it effectively addresses the environmental concerns related to iron tailings resources. In recent years, researchers from around the world have extensively studied the utilization of iron tailings in concrete, making strides in the preparation and performance testing of ITC. A multitude of studies suggest that although the excellent water absorption and substantial specific surface area of iron tailings may increase water usage in concrete and diminish its workability ,15, the Currently, there is a noticeable research gap concerning the changes in mechanical properties and failure mechanisms of ITC under complex environmental factors. Iron tailings are widely distributed in the eastern region of China. Whether ITC can be widely used depends on whether it can withstand the influence of climate and environment in the eastern region. As a common environmental factor in the eastern region of China, the dry–wet cycle and negative temperature effect have an important impact on the performance and structure of iron tailings concrete. During these cycles, iron tailings concrete is exposed to fluctuating humidity and temperature conditions, potentially resulting in water penetration, chemical reactions, and other effects that lead to intricate changes in its properties. This study examines the mechanical properties of iron tailings concrete with varying river sand substitution rates after dry–wet cycles and negative temperature, ultimately determining the optimal substitution rate of iron tailings for fine aggregate. By analyzing the water content and porosity of iron tailings concrete, the study investigates the enhancement mechanism of iron tailings on concrete’s mechanical properties. This provides valuable insights for optimizing the mix proportion of iron tailings concrete and improving the durability of concrete structures.Type I ordinary Portland cement 42.5 R was used as cementitious material in this test. The basic physical properties of the cement are shown in Fine aggregates: The iron tailings were mined from the LiZhu iron tailings repository area in Zhejiang Province, China. The fineness modulus of iron tailings is 1.29 and that of river sand is 2.49, respectively. The particle size distribution of iron tailings and river sand is shown in Coarse aggregates: The coarse aggregate uses crushed stone with a continuous gradation of 5–16 mm in particle size. The physical properties of coarse aggregate are shown in 3 were prepared for each group of concrete specimens.The concrete mix proportions can be found in 3 specimens were prepared for testing compressive strength, weight loss, and splitting tensile strength after 0, 20, 40, 60, 80, and 100 dry–wet cycles in different solutions and after negative temperature. The experimental process is shown in Guided by the GBT50082-2009 , the tes3 cubes. For the flexural strength, the 400 mm × 100 mm × 100 mm were used for testing, and the loading speed was selected at 0.001 mm/s, 0.01 mm/s, 0.1 mm/s, and 1 mm/s. In this case, the double-K criterion is used to calculate the cracking toughness and instability toughness [0.5); QF is the cracking load, which is determined from the load–crack opening displacement process curve (kN); mg is the self-weight of the specimen between effective spans (kN). Converted from the total mass S/L as0.5); Fmax is the instability load (kN); ac the effective crack length (mm).The compressive strength, splitting tensile strength, and flexural strength were tested in a 1000 kN MTS microcomputer-controlled electro-hydraulic servo universal testing machine by changing the chuck. The compressive strength and split tensile strength were investigated by testing 100 mmoughness . The for2 spectra of the sample after vacuum pressure saturation. Additionally, by utilizing the test standard sample’s NMR T2 spectra, establish a calibration line and calculate the sample’s porosity. The formula for calculating the pore size of concrete can be expressed as follows:ρ represents the transverse surface relaxation strength of porous media, in units of μm/ms, and its value varies depending on the sample; S represents the surface area of the pores; V is the volume of the pores. The ρ of concrete is generally 3–10 μm/ms. Based on experience, ρ is usually set to 5 μm/ms.Using the MacroMR12-100H-GS low-field NMR (nuclear magnetic resonance) spectrometer, test the NMR Tcr represents the radius of the pores. By substituting Equation (4) into Equation (3), the T2 relaxation time distribution image can be transformed into the pore size distribution image of concrete. This allows for an intuitive analysis of the pore size distribution in each test sample.Assume the pores are perfect spheres:The compressive strength and splitting tensile strength of the iron tailings concrete were tested after 28 days of standard curing, and the flexural strength was tested under different loading rates . To minimize experimental error, six specimens were tested in each group. The average value was then calculated and used as the experimental result, which is illustrated in Using hydrogen atomic nuclei as the detection target, we have drawn the T2 spectral test curve  and the After calibrating the standard specimens and normalizing their volumes, the calculated moisture content and porosity of the four groups of concrete specimens are shown in The weight loss data of specimens subjected to dry–wet cycles were measured and presented in The mass of specimens in each group exhibited a trend of initially increasing and then decreasing with an increase in the number of dry–wet cycles when a water solution was used as the medium for dry–wet cycle testing. After 20 dry–wet cycles, the mass of OPC, ITC10, ITC20, and ITC30 increased by 4%, 6%, 7%, and 3%, respectively. The increase in concrete mass during the first 20 cycles of dry–wet conditions can be attributed to the reaction of unhydrated clinker in the concrete with water, producing more cementitious materials. The moisture penetrated further into the interior of the concrete as the number of dry–wet cycles increased, leading to the generation and development of micro-cracks and the peeling of aggregates due to water erosion, resulting in weight loss of the concrete specimens. After 100 dry–wet cycles, OPC experienced a weight loss of 39%, while ITC20 exhibited a weight loss of only 34%, demonstrating the best performance. This suggests that the appropriate addition of iron tailings helps to enhance the concrete’s resistance to erosion by the water solution and strengthen the overall integrity of the concrete.2+ in the C-S-H gel to form chlorides. When the environment becomes dry, these chlorides crystallize within the concrete, leading to the formation of cracks and peeling on the concrete surface. Concurrently, the precipitated chlorides form crystals on the surface of the concrete, affecting its appearance. Additionally, with the reduction of C-S-H gel, the mechanical properties and durability of the concrete begin to decline [The weight loss rate and corresponding apparent changes in concrete after chloride salt dry–wet cycles are shown in  decline . A visib3S in cement after the concrete absorbs water, resulting in the formation of more C-S-H gel. This process reduces porosity and optimizes the microstructure of the concrete, thereby enhancing its dynamic modulus of elasticity [2·H2O crystals and magnesium salt crystals). These complex salts do not grow sufficiently in the initial stage, filling the concrete internally and improving its compactness. However, as the dry–wet cycles continue, the expansive stress generated by the complex salt crystals increases. When the expansive force exceeds the adhesive force between the aggregates and the mortar, the concrete begins to form damage, and the relative dynamic elastic modulus starts to decrease. Iron tailings concrete, due to its higher compactness and weaker erosion by the water-soluble solution, slows down the damage rate.The magnitude of the relative dynamic elastic modulus reflects the ability of a material to resist elastic deformation, with higher values indicating a smaller likelihood of elastic deformation occurring. In this article, we present the variation of the relative dynamic elastic modulus of concrete after undergoing dry–wet cycles , which iasticity . Subsequ2·H2O and magnesium salt crystals, it also includes complex salts such as CaCl·Ca(OH)2·nH2O) [)2·nH2O) . This leThe compressive strength and splitting strength of concrete after dry–wet cycles are shown in 2·nH2O complex salt formed by the reaction of chloride salt with cement rapidly increases, leading to the formation of micro-cracks in the concrete. On one hand, this causes specimen deterioration, and on the other hand, it promotes further intrusion of chloride ions in subsequent cycles. Furthermore, the infiltrating chloride ions react chemically with the cement hydration products, destroying the balance between Ca(OH)2 and C-S-H gel, causing the C-S-H gel to decompose and lose its binding ability [From  ability .2O3 components in the iron tailings react chemically with water to produce alkaline substances during concrete formation. This reaction promotes cement hydration during hardening, leading to more complete hydration. Consequently, this process significantly reduces the initial defects in concrete during hardening, resulting in a notable increase in fracture toughness and instability toughness at a macro-scale [The relationship between the cracking resistance of ITC under negative temperature action, the substitution rate, and the loading rate is depicted in ro-scale . Figure ro-scale In conclusion, the replacement doping demonstrates a more pronounced effect on the fracture toughness and instability fracture toughness at negative temperatures. It is suggested that the optimum replacement admixture level for recycled concrete using this type of iron tailings sand to replace conventional sand should be controlled at around 20% to show optimum crack resistance, while the loading rate is optimum at 0.1 mm/s.Based on the results of the mechanical properties tests in a single environment, 20% iron tailings was initially determined as the optimum admixture, and the mechanical properties were investigated under the combined effect of negative temperature and dry–wet cycles . The resThe optimal replacement rate of iron tailings for river sand is 20%, at which point the concrete exhibits the smallest porosity and the best mechanical performance.The incorporation of iron tailings increases the water demand of concrete, which promotes the hydration reaction of cement, resulting in increases in mass, relative dynamic elastic modulus, and mechanical performance during the early stages of the dry–wet cycle tests.At a single factor of negative temperature, the best crack resistance was achieved at a 20% iron tailings replacement admixture rate. This crack resistance was higher than that of the same concrete material at room temperature. Moreover, the greatest fracture toughness value was achieved at a controlled loading rate of 0.1 mm/s.In a combined negative temperature and dry–wet cycle environment, the mechanical properties of concrete with a 20% iron tailings replacement rate surpass those of standard concrete.In this paper, a comparative analysis of the mechanical properties of iron tailings concrete at room temperature, under negative temperature, and in a dry–wet cycle environment was conducted. We found that the research method of using tailings waste, which both pollutes the environment and occupies land resources, to quantitatively replace non-renewable fine aggregate sand to manufacture recycled concrete is feasible and made a preliminary attempt for the research and application of iron tailings sand recycled concrete in the monsoon frost zone. The main findings from this research can be summarized as follows:


To demonstrate that a syndromic stewardship intervention can safely reduce antipseudomonal antibiotic use in the treatment of inpatient diabetic foot infections (DFIs).From November 2017 through March 2018, we performed an antimicrobial stewardship intervention that included creation of a DFI best-practice guideline, implementation of an electronic medical record order set, and targeted education of key providers. We conducted a retrospective before-and-after study evaluating guideline adherent antipseudomonal antibiotic use 1 year before and after the intervention using interrupted time-series analysis.University of Nebraska Medical Center, a 718-bed academic medical center in Omaha, Nebraska.The study included 193 adults aged ≥19 years (105 in the preintervention group and 88 in the postintervention group) admitted to non–intensive care units whose primary reason for antibiotic treatment was diabetic foot infection (DFI).Guideline-adherent use of antipseudomonal antibiotics increased from 39% before the intervention to 68% after the intervention (P ≤ .0001). Antipseudomonal antibiotic use decreased from 538 days of therapy (DOT) per 1,000 DFI patient days (PD) before the intervention to 272 DOT per 1,000 DFI PD after the intervention (P < .0001), with a statistically significant decrease in both level of use and slope of change. We did not detect any changes in length of stay, readmission, amputation rate, subsequent positive Clostridioides difficile testing, or mortality.Our 3-component intervention of guideline creation, implementation of an order set, and targeted education was associated with a significant decrease in antipseudomonal antibiotic use in the management of inpatient DFIs. DFIs are common and should be considered as opportunities for syndromic stewardship intervention. Syndromic stewardship interventions have been used by ASPs to reduce unnecessary antibiotic use and to improve patient care in common infections. In 2010, 77,491 hospital discharges were attributed to diabetic foot infections (DFIs), making this a common hospital-managed infection. However, published strategies to improve antibiotic use in these cases are lacking.Antimicrobial stewardship programs (ASPs) are an integral part of the United States public health strategy to combat the emergence of antimicrobial resistant bacteria. A few reports have suggested that adherence to antibiotic prescribing guidelines in DFI is suboptimal, but when guidelines are followed, improved outcomes have been observed. Clinical decision support systems (CDSSs) have been utilized with the goal of improving guideline-adherent treatment for infectious diseases, although mixed success has been reported. In DFI, CDSS associated with guideline adherence and reduction in unnecessary antibiotic use has not been reported.National guidelines for the treatment of DFI were published in 2012 and include antibiotic recommendations based upon severity and prior culture data.Pseudomonas aeruginosa was an uncommon DFI pathogen, present in 1 (2%) of 56 cases, but DFI was empirically treated in 41 (73%) of 56 cases. This finding suggested that DFI was an excellent opportunity for a syndromic stewardship intervention. Between November 2017 and March 2018, we conducted a 3-part ASP intervention that included provider education and the creation of an institutional management guideline and DFI order set in the electronic medical record (EMR). We evaluated the effect of this intervention  on DFI antibiotic use and clinical outcomes.A review of DFIs at our institution (July 2014–June 2015) revealed that The University of Nebraska Medical Center (UNMC) is a 718-bed, academic medical center located in Omaha, Nebraska. Institution-specific guidelines for the treatment of common infectious diseases with associated EMR order sets  has been a core strategy of the program, coupled with audit and feedback.International Classification of Diseases Tenth Revision (ICD-10) codes for DFI. Code E8-E13 identifies patients with diabetes mellitus and among these, they must have had at least 1 of the following codes: 0J, 0Q, 0S, 0Y for procedures involving lower extremity tissue, bones or joints or A48.0, I96, L02, L03, L97, M86 Z44, Z89 identifying gangrene, cellulitis, abscess, ulcer, osteomyelitis, or limb loss. Code definitions are included in the Supplementary Material. Cases were manually reviewed, and only cases in which infection was described as originating in the foot were included. Infections originating at the ankle and above were excluded, as were surgical wound infections. If an infection was present or suspected at any other site not contiguous with the foot, the case was excluded. Additional exclusion criteria included intensive care unit (ICU) admission, transfer from an outside hospital, admission to non-IM/FM or hospitalist services , puncture wound or foreign body present, or admitted from hospice. Only the first admission for DFI was included. All patients were unique.We retrospectively assessed empiric antibiotic use in hospitalized patients with DFI before and after a stewardship intervention. Guideline-adherent antibiotic use was measured before the intervention  and was compared to guideline-adherent antibiotic use after the intervention , excluding an implementation period . We included adults aged ≥19 years (19 is the age of majority in Nebraska) who had been admitted to general medical wards through internal medicine (IM) or family medicine (FM) practices and received antibiotic treatment for a DFI. The IM and FM services include hospitalist teams and comprise >90% of DFI admissions. We identified eligible cases using  Infection was defined as having a wound present with at least 2 of the following: swelling, erythema, tenderness, warmth, or purulence. Severe infection was defined as an infection plus ≥2 of the following within 8 hours of admission: fever or hypothermia (temperature >38.0°C or <36.0°C), heart rate >90 beats per minute, respiratory rate >20 breaths per minute, or white blood cell count (WBC) >12,000/µL. Infections without evidence of systemic inflammatory response were consider nonsevere. Empiric coverage for P. aeruginosa was considered guideline adherent only if risk factors for P. aeruginosa were present . Empiric coverage was defined as the first systemic antibiotic regimen received. Topical antibiotics were excluded. Antibiotic use was measured in days of therapy (DOT), whereas any dose of an antibiotic in a single day constituted 1 day of therapy. Formulary antipseudomonal antibiotics included meropenem, piperacillin/tazobactam, cefepime, ceftazidime, aztreonam, levofloxacin, ceftolozane-tazobactam, ceftazidime-avibactam, and aminoglycosides. Only deep-tissue cultures were evaluated; they were categorized as having been obtained via surgical debridement (operative or bedside), amputation, or bone biopsy. All other wound cultures were excluded.The presence of a DFI and infection severity were defined based on national guidelines.A). This guideline was reviewed by our local ASP committee and was made available online. Recommendations included defining severity and risk factors for resistant pathogens, such as MRSA and P. aeruginosa, with empiric antibiotic recommendations based upon these factors. Additionally, a comprehensive DFI admission order set was created in the EMR with severity- and risk-factor–stratified empiric antibiotic orders available. The order set included options for additional consultation , suggestions for appropriate imaging and laboratory tests, as well as options for other medications including insulin.In July 2017, we produced an institutional guideline for the management of DFIs modeled after national guidelines and supplemented by local microbiologic data and formulary preferences . Our ASP conducts audit and feedback but did not specifically target DFI for review. The UNMC Institutional Review Board classified this work as a quality improvement project.Between November 2017 and March 2018, education was provided to clinicians who commonly prescribe antibiotics in DFIs. Emergency medicine residents received 1 session, hospitalists including advanced practice providers received 1 session, internal medicine residents received 1 session, and family medicine residents and attending physicians received 2 sessions. Content included education on local microbiology highlighting the rarity of We collected demographic, clinical, laboratory, microbiologic, and treatment data. EMR order-set use was tabulated via request from our local EMR team. Online guideline document downloads were collected using local information technology resources. For vital signs, maximum or minimum values along with maximum WBCs within 8 hours of admission were recorded. To calculate the Elixhauser comorbidity score for each patient, ICD-10 codes from the source encounter file were parsed using SAS codes. If any of the predetermined ICD codes for a particular condition existed for a patient in the source file, that patient was said to have that condition and was assigned the standard Elixhauser score for that condition. All Elixhauser scores for each condition were summed to yield the final Elixhauser comorbidity index for each patient.Conditions that make up the Elixhauser comorbidity index included peripheral vascular disorders, depression, lymphoma, metastatic cancer, solid tumor without metastasis, renal failure, and congestive heart failure.Clostridioides difficile testing within 30 days of admission, 30-day mortality, and 1-year mortality.The primary end point of interest in this study was adherence to empiric antipseudomonal antibiotic use guidelines. Secondary outcomes included antipseudomonal antibiotic use measured in DOT per 1,000 DFI patient days (PD), length of stay (LOS), 30-day readmission, amputation, subsequent positive t test or Mann-Whitney test was used to compare continuous data.Descriptive statistics including means, standard deviations, medians, minimums, maximums, counts, and percentages were used to summarize the data. Categorical data were compared between the 2 periods using the Fisher exact test. The independent sample A negative binomial regression model for interrupted time series was used to compare the change in adherence rates prior to and after the intervention. We hypothesized that the intervention was associated with both a level change and a slope change in the rate of antipseudomonal therapy prescribed between the 2 periods following the approach outlined by Bernal et al.In total, 874 cases were identified and reviewed, and 681 were excluded  rates, LOS, and amputation rate, were not significantly different between the 2 periods . The antipseudomonal antibiotic DOT per 1,000 DFI PD decreased as well: 538.3 in the preintervention period versus 272.9 in the postintervention period (P < .0001). Guideline adherence to antipseudomonal antibiotic use recommendations improved in the postintervention group: 41 of 105 (39%) in the preintervention period versus 60 of 88 (68%) in the postintervention period (P < 0.0001). Most of this decrease was related to the avoidance of antipseudomonal antibiotics when not recommended.A decrease in the rate of empiric antipseudomonal antibiotic use was observed in the postintervention group: 68 of 105 (64.7%) in the preintervention period versus 35 of 88 (39.7%) in the postintervention period . We conducted an interrupted time-series analysis to explore the changes in the level and slope between the 2 periods , and the order set was used 41 times during the postintervention period. Order-set usage remained stable, with 49 uses in the 11 months after the postintervention period .Pseudomonas aeruginosa was an uncommon DFI pathogen. In comparing the preintervention and postintervention periods, we did not detect differences in important patient-centered outcomes such as mortality, readmission, length of stay, or rates of CDI and amputation. These findings indicate that avoiding empiric antipseudomonal antibiotics in DFI patients admitted to general medical floors is safe when local rates of Pseudomonas causing infection are low. Similar interventions targeting skin and soft-tissue infections, and DFI specifically, have yielded reductions in the use of broad-spectrum antibiotics without subsequent increases in adverse clinical outcomes.Our syndromic stewardship intervention was associated with a significant decrease in empiric and overall antipseudomonal antibiotic use in the postintervention period. We targeted antipseudomonal antibiotics because we, and others, had found that Our intervention was relatively simple; we utilized 3 components: (1) an evidence-based, locally customized, DFI treatment guideline available on our ASP website; (2) targeted education to providers who frequently manage DFI cases; and (3) implementation of an order set in the EMR.Our guideline document provided antibiotic recommendations based on infection severity, pathogen-specific risk factors, local microbiologic data, and formulary preferences. Measuring guideline downloads could not be assessed with location specificity beyond the level of the state of Nebraska, but our website has an established reputation at our institution as a source of guidance on treatment of common infections. Access and review of a guideline, however, does not equate to implementation or causation. We were not able to specifically link online utilization to treatment decisions, although no other interventions were performed during the study period to limit antipseudomonal antibiotic use in skin and soft-tissue infections, sepsis, or DFI.When developing our education, we targeted those who most frequently prescribe antibiotics for DFI at our institution , and we presented local microbiologic and treatment data in the context of national guidelines to demonstrate opportunities for improvement. Our guideline excluded orders not supported by guidelines  while making correct management easy. Along with orders needed for the care of complex diabetic patients , we included all items needed for DFI management: support for determining infection severity, prepopulated antibiotic orders, medical and surgical consultations, preferred imaging, vascular studies, etc. The order set was a “one-stop shop” for DFI admissions. The order set was used 41 times during the postintervention period among 88 cases, suggesting that 100% adoption is not necessary for a successful intervention.Coupling the guideline and education with a EMR order set also likely contributed to our success. Order sets should be efficiency tools that provide convenient access to best practices.We had concern about order-set use degradation over time because much of the education targeted residents and one-third of internal medicine and family medicine residents exit the programs yearly. During the 11 months following our postintervention period (April 2019–February 2020), the order set was utilized an additional 49 times, suggesting durability. Residency training is heavily dependent on practice passed down from senior to junior, and we believe that our practice-improving recommendations have been integrated into this process. Despite our efforts, a substantial portion of patients were not treated in a guideline-adherent manner. This may have occurred for a variety of reasons, including care by providers not included in education , incomplete penetrance of our education, and other clinical factors. Severe DFI was specifically mentioned as a situation in which combination therapy with vancomycin and piperacillin-tazobactam may be appropriate. During this study, we noted significant decreases in piperacillin-tazobactam use, but we also noted subsequent increases in the use of cefepime. Specific to DFI, we detected an overall decrease in antipseudomonal antibiotic use, suggesting that clinicians changed their spectrum of the therapy rather than replacing one antipseudomonal agent with another. We did not specifically capture the presence of osteomyelitis, although we do not expect the diagnosis of osteomyelitis (which is often not established at the time empiric antibiotics are selected) to have had an effect on empiric antibiotic choices. Additionally, similar LOS and amputation rates between groups does not indicate that major differences in rates of osteomyelitis were present. Other unmeasured factors may also have influenced antibiotic use, although no major changes were made in the activities of the ASP nor were DFIs specifically targeted for review. Although no significant differences were detected in patient-centered outcomes , this study was not powered to detect differences in these outcomes, and these results should be interpreted with caution.This study had several limitations. Case selection bias may have been introduced by our retrospective design. This was a single-center study, and our results may not be generalizable to other centers. One potential confounder was that additional education was provided around the beginning of the intervention period when clinicians were recommended to generally avoid vancomycin and piperacillin-tazobactam combination therapy to reduce the risk of kidney injury.Overall, this pattern of creating a DFI institutional guideline, best-practice order set coupled with targeted education was associated with a safe and significant reduction in antipseudomonal antibiotic use. Our experience suggests that DFI should be recognized as an additional opportunity for syndromic stewardship intervention for hospitals and healthcare systems.


Concrete sleepers used in railway engineering are subject to damage, such as cracks and breakage. Damaged concrete sleepers undergo changes to their material and structural properties, including response, mode shape, and natural frequency. Therefore, we have proposed modal testing in this study to quantitatively evaluate the structural integrity of concrete sleepers. The results of modal testing were compared with those of numerical analysis and visual inspection. In addition, an impact hammer test was conducted to evaluate the structural performance of damaged concrete sleepers. The results show that natural-frequency analysis using the modal-testing technique can usefully complement visual inspection for structural performance evaluation in the field. The dynamic response, natural frequency, mode shape, damping ratio, and other material and structural characteristics of concrete structures often change when the structure is damaged. Concrete sleepers are frequently damaged in the course of railway operation; poor materials and construction, manufacturing defects, environmental factors, repeated loads, and the driving characteristics of trains are among the internal and external factors responsible for concrete damage. Cracks in concrete sleepers are caused by structural and material factors. These cracks are enlarged by repeated loads of trains and exposure to the atmospheric environment. When exposed to the atmosphere, cracks expand owing to neutralization and freezing–thawing action, resulting in damage to track components .According to South Korean standards, damaged sleepers  are idenIn the case of sleepers with axial cracks and with resilience pads attached to the lower part, the lateral resistance is reduced in the curved rail. Excessive lateral pressure occurs owing to poor contact between the bottom of the sleeper and the ballast because of the cant imbalance while the train is running. Such excessive lateral pressure generates high stress in the axial direction of the sleeper as the stress is concentrated in the structurally weak landfill in the sleeper .In the track-facility performance evaluation of South Korea , shown iIn operating urban passenger lines, concrete sleepers can only be visually inspected at night . This limits the working time to ~3 h or less, making it difficult in practice to evaluate the condition of the numerous sleepers in the field.Indoor and outdoor experiments have been conducted in South Korea and overseas to study damage to sleepers.Choi  analyzedRemennikov and Kaewunruen  analyzedKaewunruen and Remennikov ,6,7,8 inTaherinezhad et al.  investigYou and Kaewunruen  evaluateYou et al.  confirmeKaewunruen and Remennikov  confirmeFerdous et al.  analyzedChoi et al.  analyzedLee et al.  experimeMost of the non-destructive testing studies on concrete sleepers were conducted by Remennikov and Kaewunruen. Based on the research by Remennikov and Kaewunruen, the structural integrity of concrete sleepers was confirmed through non-destructive testing of sleepers installed in Korea.In South Korea, most of the experimental and numerical research has been conducted on the cracks in concrete sleepers, however, there exists no research on crack integrity through non-destructive testing. This study focuses on post-tensioned concrete sleepers, which are buried in gravel or concrete tracks; in this case, only the surfaces of the sleepers can be visually inspected. Depending on the type of track, it is buried in a gravel or concrete roadbed; thus, only the upper surface of the concrete sleeper can be inspected. Consequently, the condition evaluation grade of the sleeper is determined based on the condition of the upper surface.In the structure damage detection method using changes in dynamic characteristics of structures when a structure changes physically, such as appearance of cracks, the dynamic characteristics of the structure also change.In this study, we conducted an impact hammer test, which is a portable non-destructive test, to evaluate more quantitatively the structural integrity of 20 damaged concrete sleepers in the field and analyzed the correlation between damage and changes in dynamic characteristics.We conducted on-site visual inspections of 20 concrete sleepers that were designated for replacement because of damage. In sleeper #5 shown in In a visual inspection at night, the inspector would only be able to observe the condition of the top surface and would thus judge #13 and #5 to be similar. Moreover, although the cracks in the axial direction were similar in all three sleepers, #18, which has more damaged areas, may be evaluated as being in the worst state.We conducted modal tests on damaged concrete-sleeper specimens collected from the operating line, as shown in The FRF is the ratio of dynamic response to impact load; it allows us to calculate the characteristics of dynamic responses in the frequency domain and the relationship between mass and stiffness. Through FRF, values can be estimated in the range below the natural frequency in the case of dynamic stiffness and the range exceeding the natural frequency in the case of dynamic mass.Two frequency bands occurred in all sleepers when excited with an impact hammer.As shown in Based on the FRF analysis results, the measured natural frequencies of the 20 damaged concrete sleepers were divided into first and second modes, as shown in We performed a Gaussian probability density analysis using the measured natural frequencies of each mode, as shown in 2. 7 N/m) and the damage to the concrete sleepers directly affected it. Contrarily, the dynamic mass was constant for each sleeper as shown in d) of free vibration. If the damping ratio is small  .(1)δ=lnWe calculated the damping ratio in the free-vibration region for each sleeper, as shown in The natural frequencies of the concrete sleepers were analyzed numerically using ANSYS Workbench Ver. 2021 R2 , a generNodes and elements were calculated automatically during their generation in the ANSYS Workbench program. The mesh of the sleeper contained 242,085 nodes and 144,779 elements. The element size of the sleeper was assumed to be 20 mm. In the numerical analysis, we modeled both normal and damaged sleepers under the impact load (700 N) and boundary conditions used in the modal test. Additionally, as shown in The mode shapes and corresponding frequencies of the concrete sleepers are shown in As shown in After comparing and analyzing the natural frequencies of the damaged concrete sleepers, a modal test was performed on the damaged concrete sleepers in the field.We compared the analytical and measured natural frequencies of two concrete sleepers whose crack propagation patterns appear to have similar damage states . According to the FRF-based estimation results, the change in dynamic mass caused by the damage to concrete sleepers was negligible, whereas dynamic stiffness significantly differed among sleepers. Furthermore, the measured damping ratio of each sleeper was 3 ± 0.5%, which is the material damping level of concrete; this indicates that the effect of sleeper damage on the damping ratio was small.A comparative analysis of the modal-testing, analytical, and visual-inspection results showed that the measured natural frequencies of the two concrete sleepers classified as similarly damaged in the visual inspection were, respectively, 20 and 49% smaller than the calculated natural frequency under normal conditions. This experimentally and analytically demonstrates the limitations of evaluating the structural integrity of concrete sleepers solely by their visual state.Natural-frequency analysis through modal testing can be used for quantitatively evaluating the structural integrity of many sleepers easily in a short time. Therefore, considering the difficulty of night-time inspections on operational lines, the proposed modal-testing method provides a complementary method of visual-inspection-based sleeper-condition assessment in the field.This study proposed impact hammer testing, a portable technique that can be easily applied in the field for quantitative assessment of the structural integrity of concrete sleepers. We proved the validity of the modal-testing approach by comparing the results of field testing, numerical analysis, and visual inspection. The results are as follows:


We very much appreciate the interest in our study and the valuable issues raised by Dr. Yilmaz and Dr. Selek in their Letter to the Editor regarding our analysis about the association between antibiotic application and oncological outcomes in head-and-neck squamous cell carcinoma (HNSCC) patients undergoing (chemo)radiation , 2.We fully agree that further studies exploring potential differences among the different classes of antibiotics in terms of their impact on the oral microbiome are necessary. For instance, in a retrospective study including patients treated with immune checkpoint inhibitors, broad-spectrum antibiotics were found to negatively impact patients’ response rate, whereas narrow-spectrum antibiotics did not . HoweverDr. Yilmaz and Dr. Selek pointed out that neither the evidence-based protocol used nor the authors’ rationale for choosing that protocol were provided for single-shot antibiotic administration immediately prior to central port catheter insertions. The rationale for using single-shot antibiotics prior to port catheter insertions is related to findings that the prevalence of port catheter infections can be reduced by this approach . FollowiEven though the suggested analysis in which the oncological outcomes between long-term and short-term antibiotic application are compared was not performed in our study, we provided data regarding differences in the oncological outcomes related to the number of applied antibiotic courses. Furthermore, we conducted an analysis, in which the duration of antibiotic treatment (as a continuous variable) was analyzed regarding its prognostic impact on survival and locoregional control; this analysis did not show a relationship between the duration of antibiotics administration and survival or tumor control rates. It should be pointed out that another study concerning the relationship between antibiotics application and oncological outcomes in HNSCC patients undergoing (chemo)radiation observed a stronger reduction in survival if patients received several courses of antibiotic treatments .We agree with Dr. Yilmaz and Dr. Selek regarding the necessity to further examine the microbiome radiation and antibiotic treatment) in the different head-and-neck sub-regions, given the known differences in the microbiome composition . Further


The mechanical properties and impact resistance of conventional self-compacting concrete (SCC) need to be further improved. In order to explore the dynamic and static mechanical properties of copper-plated steel-fiber-reinforced self-compacting concrete (CPSFRSCC), the static mechanical properties and dynamic mechanical properties of CPSFRSCC with a different volume fraction of copper-plated steel fiber (CPSF) are tested, and a numerical experiment is carried out to analyze the experimental results. The results show that the mechanical properties of self-compacting concrete (SCC) can be effectively improved by adding CPSF, especially for the tensile mechanical properties. The static tensile strength of CPSFRSCC shows a trend that increases with the increase in the volume fraction of CPSF and then reaches the maximum when the volume fraction of CPSF is 3%. The dynamic tensile strength of CPSFRSCC shows a trend that increases first and then decrease with the increase in the volume fraction of CPSF, and then reaches the maximum when the volume fraction of CPSF is 2%. The results of the numerical simulation show that the failure morphology of CPSFRSCC is closely related to the content of CPSF; with the increase in the volume fraction of CPSF, the fracture morphology of the specimen gradually evolves from complete fracture to incomplete fracture. Self-compacting concrete (SCC), a special kind of concrete, is widely used in construction engineering, underground space engineering, and other fields because it does not need artificial vibration and can rely on its own gravity to fill density. It also has strong fluidity and filling, as well as strong segregation resistance and water resistance ,2,3. HowResearch shows that an effective method to improve the performance of concrete is the addition of fiber materials into concrete ,11,12,13To sum up, although researchers are carrying out research on how CPSF improves the performance of concrete, reports on how CPSF affects the performance of SCC with CPSF are rare. In addition, how to improve the mechanical properties of copper-plated steel-fiber-reinforced concrete (CPSFRCC) according to the characteristics of CPSF to improve the performance of CPSFRCC under impact loading is also worth further exploration. In this paper, in order to explore the influence of the volume fraction of CPSF on the dynamic and static mechanical properties of CPSFRCC, CPSFRCC specimens with various volume fraction of CPSF were configured separately. A series of dynamic and static mechanical experiments were applied to the dynamic and static mechanical properties test of CPSFRCC specimens with a different volume fraction of CPSF. The effects of volume fraction of CPSF on the static compressive strength, static tensile strength, dynamic tensile strength, dynamic growth factor, and failure mode of CPSFRC are discussed. In addition, the numerical simulation software ABAQUS 2021 was applied to simulate the SHPB experiment of CPSFRC to verify the experimental results. The results provide a theoretical basis for the evaluation of engineering structures using copper-plated steel-fiber-reinforced concrete.3. The water reducer with a water-reduction rate of ≥45% can be selected. Many types of steel fibers are designed, manufactured, and used in engineering construction. Steel fibers, such as flat, hook, and wave, are commonly used [CPSFRCC, a high-performance concrete prepared by adding CPSF to the foundation of ordinary SCC, is generally prepared by coarse aggregate, fine aggregate, inorganic cementitious material, high-performance admixture, and water according to appropriate proportions. The raw materials used in the CPSFRCC in the test involved in this paper are as follows: Portland cement, natural river sand, quartz powder, fly ash, water, water reducer, and CPSF. P.052.5 ordinary Portland cement produced by Hejin Yumen was selected, and its performance met the requirements of Chinese standard JGJ/T283-2012. Studies show that the use of some quartz powder instead of natural river sand can effectively improve the fluidity of self-compacting concrete slurry ; therefonly used . Long stIn this experiment, the mix proportion of C60 strength grade CPSFRSCC was determined, as shown in In order to control variables, all CPSFRSCC specimens underwent the same processing and curing process. In this paper, the production of CPSFRSCC specimens was improved using the production method of ordinary steel fiber self-compacting concrete (SFRSCC) specimens. In order to make the most effective use of CPSF, in the process of making CPSF specimens, the CPSF should be uniformly distributed in the concrete matrix as much as possible. Therefore, the natural river sand, quartz powder, fly ash, cement, and water-reducing agent were mixed and stirred for 3 min to ensure that the concrete had good fluidity. Then, the CPSF was evenly spread into the container, fully stirred for at least 3 min, and finally slowly added. The water was fully stirred for at least 6 min, so that the CPSF could be evenly distributed in the mixing material as much as possible, effectively avoiding the influence of adding water first, which causes the steel fiber to be bound by the cement so it cannot be dispersed. All the specimens experienced the same curing process. After the completion of production, the mold  with slu3, the wave velocity was 5190 m/s, and the elastic modulus was 195 GPa.The split Hopkinson pressure bar (SHPB) shown in E, The SHPB experiment was based on two assumptions: the one-dimensional stress wave assumption and the uniform stress distribution assumption ,39. The The Brazilian disk-splitting method is widely used in the tensile properties of brittle materials, such as concrete, due to the difficulty of the directly tensile strength testing of such brittle materials ,41.The tP represents the loading load when the specimen fails; and A and P represents the loading load when the specimen fails; and D, L, and The static mechanical properties of specimens were tested using an RMT-150 rock mechanical performance test machine a. The RMIt can be observed from Compared with the static compressive strength, the effect of adding CPSF on the splitting tensile strength of SCC is more obvious. The splitting tensile strength of concrete specimens with different volume fractions of CPSF increased by 18.1%, 36.1%, 37.5%, 40.1%, 45.6%, and 47.74% compared with CPRF0, showing a disciplined increased with the increase in the volume fraction of CPSF. The above experimental phenomenon is consistent with the findings of Xu et al.  in the eThe stress–strain curves of CPSFRSC with different volume fractions of CPSF under virous average impact velocity can be obtained by processing the strain signals obtained in the experiment according to the method described in It can be seen from Initial stage: In the initial stage of dynamic loading, the gap between the internal pores and the aggregate of the specimen is closed due to the loading of the stress wave transmitted along the direction of the bar, showing a slow strain hardening growth stage from the curve.Elastic stage: The elastic stage of curve occurs after the initial stage. Similar to other concrete materials, in this stage, the curve shows an approximately linear growth relationship with the accumulation of strain. Some studies show that concrete materials usually reach the elastic stage limit when stress reaches 75% of the peak stress , which aYield stage: With the continuous loading of impact loading and the accumulation of strain, the curve shows a trend in strain softening behavior and a nonlinear growth relationship with the accumulation of strain. The gap between the internal apertures and the aggregate begins to develop continuously, and the specimen shows the characteristics of plastic deformation.Failure stage: With the continuous development of the apertures in the specimen and the gap between the aggregates, different degrees of cracks and fracture surfaces are produced. With the further loading of impact loading, the continuous development and interconnection of cracks and fracture surfaces lead to the fragmentation of the specimen, and stress reaches the peak on the curve. However, the specimen after failure still has a certain bearing capacity in a short time, which can be seen from the slow decline after the curve reaches the peak rather than the cliff-like decline.DIF, Equation (7)) to investigate the strain rate effect of concrete materials under dynamic loading [DIF of CPSFRSC with different volume fractions of CPSF under various degrees of strain rate is calculated and statistically shown in The average dynamic tensile strength of CPSFRSCC under different loading strain rates is shown in  loading . The DIFDIF of CPSFRSCC specimens under various loading strain rates shows the same trend. The DIF of CPSF0.5 and CPSF1 fluctuates near the initial value and even shows a slight downward trend. When the volume fraction of CPSF reaches 1.5% and 2.0%, the DIF of CPSFRSCC specimens is significantly enhanced and reaches the maximum value when the volume fraction is 2.0%. However, the DIF of CPSFRSCC specimens does not increase continuously with the increase in volume fraction. When the volume fraction is 2.5% and 3.0%, it begins to decrease, and the DIF value of CPSFRSCC specimens is lower than that of CPSF0.It can be observed from The above phenomenon shows that CPSF has a significant effect on the dynamic tensile strength of CPSFRSCC. When the concrete matrix is subjected to tensile stress cracking, fine cracks are first generated, then the cracks gradually develop and concentrate; finally, macroscopic cracks are formed, which eventually lead to the fracture of the concrete specimen. CPSF is distributed randomly in the specimen and combines with the concrete matrix to form a fiber–concrete composite. When CPSFRSCC is subjected to tensile loading, the fine cracks encounter steel fibers during the development process, the steel fibers are pulled out from the concrete matrix, and the process of being pulled out consumes additional energy, which makes CPSFRSCC have better tensile performance than conventional concrete.In summary, the addition of CPSF delays the development of microcracks and the transformation of microcracks to macrocracks by consuming additional energy. Therefore, CPSFRSCC shows the trend that tensile strength increases with the increase in the volume fraction of CPSF. When the volume fraction of CPSF exceeds 2%, the dynamic tensile strength of CPSFRSCC decreases, which may be due to the uneven distribution of a large amount of CPSFs in the SCC matrix. The fiber produces agglomerates, which makes CPSF form a non-uniform complex and leads to the formation of a new weak area bearing external force inside the specimen, resulting in the dynamic tensile strength of CPSFRSCC decreasing instead of increasing.−1 to 147.3 s−1) is shown in In the SHPB dynamic splitting test, the whole process of CPSFRSCC specimen failure is photographed by a high-speed camera. Four failure images of CPSFRSCC at different times are selected in turn, and the failure process of seven different CPSF volume fractions are analyzed. The dynamic splitting failure process of the CPSFRSCC specimen under a loading air pressure of 0.2 MPa  model [The CDP model is selected as the constitutive model of the CPSFRSCC specimen in this simulation according to the method given in the literature . The modC) model  is selecA straight line of 12 mm is randomly generated in a disk model with a diameter of 65 mm and a height of 35 mm  to repreIt can be observed from It seems that there are some differences in the final failure mode of CPSFRSCC in the experiment and numerical simulation. In the SHPB experiment, almost all of the CPSFRSCC specimens are complete failures; only a few specimens with a higher volume fraction of CPSF are not completely broken, while only the specimens without CPSF and the specimens with a lower volume fraction of CPSF are completely broken in the numerical simulation. This phenomenon has also appeared in other studies ,53. ChenThe static compressive strength and static tensile strength of CPSFRSCC can be improved by adding CPSF, and the improvement in static tensile strength is more obvious. The tensile strength of CPSFRSCC increases with the increase in the volume fraction of CPSF and reaches its maximum value when the volume fraction of CPSF is 3%.The dynamic tensile strength of CPSFRSCC increases first and then decreases with the increase in the volume fraction of CPSF, reaching its maximum value when the volume fraction of CPSF is 2%. When the volume fraction of CPSF exceeds 2%, the dynamic tensile strength decreased, but the peak tensile strength remains higher than that of conventional SCC. In addition, with the increase in strain rate, CPSFRSCC shows an obvious strain rate effect.The results of numerical simulation show that CPSF has a significant effect on the failure morphology of SCC. The crack width decreases slightly, and the specimen is almost completely broken when 0.5% and 1% of CPSF are mixed; the crack width decreases obviously and the width of both ends of the crack is greater than the width of the crack near the center of the disk specimen, and the specimen is not completely broken when 1.5%, 2%, 2.5%, and 3% of CPSF are mixed.In order to study the mechanical properties of CPSFRSCC under static and dynamic loads with different volume fractions of CPSF, the static and dynamic mechanical properties of CPSFRSCC are investigated by static mechanical testing, dynamic mechanical testing, and numerical simulation analysis. The conclusions are as follows:


Use of the double-gating mode implemented on the modern hybrid photon counting system EIGER2 helps to suppress the influence of beam fluctuations in pump–probe experiments at synchrotron radiation facilities and provides better data quality. Understanding and control of thermal transport in solids at the nanoscale are crucial in engineering and enhance the properties of a new generation of optoelectronic, thermoelectric and photonic devices. In this regard, semiconductor superlattice structures provide a unique platform to study phenomena associated with phonon propagations in solids such as heat conduction. Transient X-ray diffraction can directly probe atomic motions and therefore is among the rare techniques sensitive to phonon dynamics in condensed matter. Here, optically induced transient heat conduction in GaAs/AlAs superlattice structures is studied using the EIGER2 detector. Benchmark experiments have been performed at the Austrian SAXS beamline at Elettra–Sincrotrone Trieste operated in the hybrid filling mode. This work demonstrates that drifts of experimental conditions, such as synchrotron beam fluctuations, become less essential when utilizing the EIGER2 double-gating mode which results in a faster acquisition of high-quality data and facilitates data analysis and data interpretation. Assuming that the SL structure is again in the steady state after 3.46 µs , as the background image, the unpumped image was recorded with the counter B shifted by a half-period of the reference storage ring time frame. This period also corresponds to the maximum delay time between the pump and the probe signal. The X-ray detector was operated in 16-bit mode so that 65 536 X-ray pulses were recorded for every counter at a fixed delay time. The frequency of the trigger pulse train that is sent to the detector is doubled compared with the laser repetition rate. The laser wavelength was tuned to 515 nm . The energy per pulse was set to 6 µJ while the laser beam diameter was set to 0.5 mm, resulting in a fluence of 3 mJ cm−2 at the sample plane. Note the laser beam stabilization system  has been used to stabilize the position with an accuracy of 99.8%. The X-ray beam size was set to 0.35 × 0.1 mm (H × V), which results in an almost square footprint in the θ/2θ configuration at the scattering vector value q = 22.2 ± 0.8 nm−1 [Fig. 2a)]. No laser or X-ray radiation damage was observed. The details of spatial overlap of the laser and X-ray beams are given by Burian et al. . The error propagation was calculated using the formalism described by Burian et al.  and 2(b), respectively. A θ–2θ rocking-curve scan shows outstanding agreement of the real SL structure with simulations performed using dynamical scattering theory . The evaluated SL period is 10.76 nm (4.53 nm of GaAs/6.23 nm of AlAs), resulting in a total SL thickness of 538 nm that agrees with SEM measurements [Fig. 2b)]. Prior to pump–probe experiments the SL was thermalized. The downshift (Δq = 0.8 × 10−3 nm−1) of the SL 0th-order diffraction peak after laser-induced thermalization implies that the averaged SL temperature has been raised to 306.7 K, which has been further used as the SL initial temperature for simulations of transient heat conduction (see Section 3.2The GaAs/AlAs SL structure was grown on a GaAs(001) substrate using the molecular beam epitaxy technique. Such structures exhibit a small lattice mismatch (∼0.2%) with interfacial mixing of less than ∼3 monolayers ]. Under such conditions the largest signal contrast is expected due to the peak broadening and its shift towards lower q as a consequence of pump-induced heating of the SL. In Fig. 3a), counter A corresponds to the signal obtained in a single-gating experiment and counter B corresponds to the unpumped signal . The advantages of double-gate mode can be clearly seen from Fig. 3b), where beam instabilities as observed in the single-gating experiment  vanish by simply dividing the signal of counter A with counter B, or alternatively they can be subtracted.In order to obtain a temporal overlap of laser and single X-ray pulses the transient signal was measured at a fixed scattering vector magnitude of 22.19 nm−1 Fig. 3, which ai.e. across the 0th and ±1st order SL peaks, as a function of delay time between the optical pump and X-ray probe, are displayed in Fig. 4g)]. The downshift of all three SL peaks, Δq = (7 ± 0.5) × 10−4 nm−1, has been observed due to the transient SL temperature rise ΔT = 5.7 ± 0.4 K that corresponds to a 10 fm expansion of the single unit cell constituting the SL.The absolute difference signals (|counter A − counter B|) measured at variable incidence angles, For further analysis and comparison with theoretical predictions, we nevertheless use the normalized differential signal  given bySL Fig. 5 brings d3.3.udkm1Dsim toolbox . This is not surprising since the reduction in cross-plane thermal conductivity is a well studied phenomenon in GaAs/AlAs SL structures  both reduced specific heat and group velocity determine the rise and immediate response of the SL-normalized transient differential signal. These findings have been achieved using the upgraded version of the picosecond pump–probe X-ray diffraction/scattering setup at the Austrian SAXS beamline at Elettra–Sincrotrone Trieste. We have shown that use of the double-gating mode implemented in the hybrid photon counting detector (EIGER2) helps to supress the influence of beam fluctuations and provide better data quality. The laser feedback system on the other hand kept a laser beam trajectory with 99.8% accuracy, avoiding sample temperature fluctuations. The best match between experimental and modelled data is obtained with 50 to 65% reduced specific heat, group velocity and phonon mean free path that resulted in a 12.5-fold decrease of thermal conductivity. Our findings suggest that better temporal resolution at a shorter timescale (<100 ps) is required in order to complete a full picture of dynamical response of optically excited GaAs/AlAs SL structures. Nevertheless, for timescales above 100 ps the pump–probe setup at the Austrian SAXS beamline demonstrates its high potential. A new class of experiments on bio-structures in liquid, photo-switchable systems, T-jump experiments in water 5.et al. (2012The following additional reference is cited in the supporting information: Durbin  al. 2012.10.1107/S1600576723004302/jl5061sup1.pdfSupporting information file. DOI: