Biological self-healing concrete (BSHC) offers a sustainable and economical way of increasing the lifespan of structures vulnerable to cracking. In recent decades, an enormous research effort has been dedicated to developing and optimizing the bacterial healing process. Nevertheless, most studies have been carried out under laboratory conditions. To verify the effectiveness and longevity of the embedded healing systems under normal service conditions, field studies on BSHC structures must be performed. In the present study, BSHC beams were designed as a structural part of a prototype footbridge. To select the optimal BSHC mix composition, a series of laboratory tests were also carried out. Laboratory tests have shown that the healing ratio in BSHC elements under rain-simulating healing conditions was several times higher in comparison to control specimens. Based on the laboratory results, the BSHC mix composition was selected and applied for structural bridge beams. To the best of the authors’ knowledge, the present study reports the first application of BSHC in a prototype footbridge. The long-term data gathered on the healing process in a humid continental climate zone will allow the benefits of biological self-healing to be quantitatively evaluated and will pave the way for the further optimization of this material. Concrete is a versatile structural material best known for its high compressive strength, excellent formability and low cost. Recent developments in concrete technology have further broadened the application of this outstanding material. For example, concrete may feature ultra-high bending strength and toughness, the ability to self-consolidate, extreme lightness or the ability to heal cracks itself. Its primary deficiency, however, remains its low tensile strength, making it susceptible to cracking. Once a crack opens, water, oxygen and salts easily penetrate inside, causing corrosion of reinforcement, deterioration of concrete and, consequently, shortening the service life of the structure. Cracking is the most detrimental defect in concrete structures; bridges and underground and water-retaining infrastructures are among the most vulnerable objects .One of the most promising technologies to inhibit the detrimental effect of cracks is the development of self-healing concrete. The idea of self-healing involves the recovery of material integrity without any human intervention, thereby saving on maintenance and repair costs. A bacterial approach which is based on the utilization of calcium carbonate-precipitating bacteria has emerged as one of the most sustainable and effective techniques in the development of self-healing concretes .In recent decades, an enormous research effort has been dedicated developing and optimizing the bacterial healing process. The identification of suitable bacteria strains, efficient microbial metabolic processes and bacteria encapsulation techniques, along with the optimization of concrete composition, have been comprehensively studied and are well summarized in several review papers ,4,5. HowTo examine the benefits of bacterial self-healing concrete under real environmental conditions, several field studies have been performed in the Netherlands ,16, BelgA wastewater treatment tank and water reservoir constructed in the Netherlands  had direAn inspection pit constructed in Belgium  featured3 of BSHC was produced and poured in a wall segment with a length of 18 m. Despite the massive application of biological concrete, only several cracks developed between the bottom slab and side wall of the lock chamber. Consequently, the field data gathered on crack healing in a hydraulic environment was rather limited. A large amount of BSHC was applied for a lock channel wall segment in China . In totaA wall panel with a height of 1.8 m and width of 1 m was constructed from BSHC and tested in open air conditions in the United Kingdom [In general, studying the healing efficiency of BSHC in field conditions is quite challenging. If a structure operates under normal service conditions, very few cracks may develop ,17 or thPinus sylvestris, the most common tree species in Lithuania. Four tree-like cantilever trusses (two from each side) were designed as the main load-bearing elements of the bridge, while the central part acts as a simply supported beam. This bridge design presents benefits with regard to the installation and replacement of the central bridge part. The bridge having replaceable beams allows us to perform several consecutive studies of healing performance under real environmental conditions, as beams may easily be dismantled and replaced after the study is finished. Moreover, this design enables cracks to be induced in the beams under laboratory conditions before installation on the bridge. The total span of the bridge prototype was 7.2 m (2.8 + 1.6 + 2.8 m), sufficient to pass a small water stream in the Botanical Gardens of Vilnius University . The loc2 was assumed according to [The bridge prototype was designed for normal pedestrian use. Consequently, the characteristic value of a uniformly distributed load of 5 kN/mrding to . The mosUltra-high-performance fiber-reinforced concrete (UHPC) was selected as the structural material for the tree-like trusses due to the extremely complex shape of these structures. The strain-hardening behavior of UHPC allowed us to eliminate the use of bar reinforcement, which was critical for the thin and curved web elements. A detailed specification of the material and structural design of the trusses, however, is outside of the scope of the present study. Here, we instead focus on the design and testing of the central BSHC beams. Further sections give more information on the material composition, crack formation and laboratory and field studies of biological concrete elements.B. pseudofirmus bacteria strain  was used  were performed (Laboratory tests on BSHC specimens were conducted in two stages. At the first stage (Series 1), the was used A. At theerformed B. These ®, Aalborg, Denmark) was used for the production of BSHC. The healing agent was prepared by impregnating expanded clay particles  with 80 g/L calcium lactate pentahydrate solution, 1 g/L yeast extract and 1 × 108 CFU/mL of bacterial (B. pseudofirmus or B. cohnii) spores, as described in [Due to its lower concentration of toxic metal oxides, white Portland cement  after 98 days of regular water spray. Control specimens also exhibited marginal crack closure, with a 3% healing ratio over 98 days. The autogenous healing of plain concrete is a well-known phenomenon and is mostly related to the swelling of concrete, continued hydration of cement and mechanical blocking of cracks by fine particles [Crack widths in the reinforced specimens were repeatedly measured after 28 and 98 days of healing. The obtained variation of healing ratio over time for Series 1 and Series 2 specimens is shown in articles , where bB. cohnii bacteria), where healing ratios of 17% and 2% were observed for biological and control specimens, respectively. The healing ratios of Series 1 and Series 2 are compared in Similar healing ratios were obtained for Series 2 specimens  and the addition of steel fibers . Silica fume was used as a pigment in the BSHC mix, avoiding the color contrasts between UHPC trusses and BSHC beams, whereas steel fibers were added (78 kg/m3) to secure the required shear strength. The concrete mix was prepared using the same rotating pan mixer . The average compressive strength, established in accordance with BS EN 12390 [Laboratory tests have shown that comparable healing efficiency was observed using both the EN 12390 , was 26.The shape and number of reinforcing bars for the beams were selected based on two requirements: (i) sufficient strength to withstand the design loads; and (ii) the formation of 10–15 cracks in the central part of the beam. After several numerical simulations using the ATENA nonlinear finite element software , the finAs predicted by the numerical simulation, 12–15 visible cracks formed in the side profiles of the beams A,B. For Although the healing ratio may not fully characterize the healing process in reinforced concrete elements, such an approach was used due to the position of the inspected beams. Existing methods in water or gas permeability measurement ,23 may hThe most challenging process in the construction of the prototype footbridge was the production of the tree-like trusses. The idea of 3D-printing the trusses was excluded due to existing challenges in printing fiber-reinforced concretes. Often, 3D-printed structures suffer from difficult buildability and exhibit a high degree of anisotropy. Moreover, constitutive models for such materials have not yet been developed . ConsequThe cantilever design of the bridge required a relatively massive foundation. The bridge abutment was placed on four piles with a diameter of 0.4 m and a depth of 1.8 m, sufficient to resist uplifting forces from the cantilever action D. The coBiological self-healing concrete offers a sustainable and economical way of increasing the lifespan of structures vulnerable to cracking. This new approach to repair has attracted a tremendous number of research efforts towards developing a suitable and reliable biological healing system. Nevertheless, most of these studies have been carried out under laboratory conditions. B. pesudofirmus and B. cohnii bacteria strains . These healing ratios were several times higher in comparison to control specimens, which exhibited healing ratios of 2–3%. However, the final healing ratios of BSHC elements were significantly lower in comparison to those that have been reported elsewhere from water-immersed specimens [In the present study, BSHC beams were designed as a structural part of a prototype footbridge. To select the optimal composition of the biological concrete mix, a series of laboratory tests were carried out. The healing process was examined in specifically designed rain-simulating water basins, with dry-wet cycles repeated two times per day. These healing conditions were considered to be more realistic in comparison to the commonly used practices of full water immersion or healing in 100% RH rooms. Laboratory tests have shown that comparable healing ratios were obtained in BSHC specimens using both the pecimens . Most liThe upscaling of BSHC specimens is essential for evaluating the healing performance of reinforced concrete elements. Moreover, the healing process may be affected by environmental effects that are very different to ideal laboratory conditions. Freeze-thaw cycling, fluctuations in temperature and humidity, and natural rain or fog may compromise bacterial viability and, consequently, healing efficiency. The prototype footbridge constructed allows the real-time healing process under natural environmental conditions to be studied. The long-term data gathered on the healing process in a humid continental climate zone will allow the benefits of biological self-healing to be quantitatively evaluated and will pave the way for the further optimization of this material.


When the calcium stearate content is within 1.8%, the pore size tends to increase (0.547 to 0.631 mm). With increase in the fly ash content, the strength of foam concrete gradually decreases, and the dry bulk density first decreases and then increases. When the blending ratio of fly ash is 10–40%, the thermal conductivity gradually decreases; an extreme thermal conductivity of 0.0824 W/(m·K) appears at the blending ratio of 40%, and the dry bulk density is 336 kg/m3.Foam concrete is fire resistant and durable and has broad applicability as a building insulation material. However, cement has high energy consumption and causes pollution, necessitating an environment-friendly cementitious material to replace the cement used to prepare foam concrete. In this study, foam concrete was prepared through chemical foaming. The influence of the foaming agent material, foam stabiliser, and fly ash on the basic properties of the foam concrete, including the dry bulk density, compressive strength, and thermal conductivity, was studied, and the pore structure was characterised. The results show that with an increase in the hydrogen peroxide (H With increased focus on global energy conservation and emission reduction, building energy conservation, as an important part of energy conservation and emission reduction, has attracted extensive attention of researchers globally ,2. Build3, but the utilisation rate of fly ash was only 20%. Li et al. [3. Li [3. The research shows that fly ash can obviously improve the strength of foam concrete and has stronger fluidity; however, it was found that there was a need to increase greatly the amount of foam required to achieve the specified design plastic density.Foam concrete is a typical inorganic wall thermal insulation material. It has many advantages, such as light weight, good environmental protection performance, good thermal insulation performance, high scope for industrialisation, and convenient construction ,7. Howevi et al.  studied . [3. Li  showed t. [3. Li  showed t. [3. Li  prepared. [3. Li  studied Generally, the thermal insulation performance of foam concrete can be improved by increasing the porosity . Lian et2O2) and foam stabiliser  were used to prepare a cement-based fly ash foam concrete. According to the changes in the water–binder ratio and blending ratio of H2O2, calcium stearate, and fly ash, the influence of different parameters on the strength, dry bulk density, and thermal conductivity of foam concrete was studied. In addition, the influence of different parameters on the pore structure of foam concrete was studied through an image analysis method. The research results can provide technical support for the widespread application of fly ash foam concrete.It can be seen that the existing research on foam concrete has mostly focused on the influence of the composition on the performance, whereas the influence of pore structure has been neglected. The most remarkable feature of foam concrete structure is its high porosity, which makes it very different from ordinary concrete in performance. Therefore, it is of great significance to study the porosity of foam concrete for improving its performance. In this study, a foaming agent , and the results are listed in Foam concrete was prepared using the chemical foaming method. The fixed water–binder ratio was 0.56. The foaming agent contents were 5.5%, 6%, 6.5%, 7%, and 7.5% (A1–A5); the corresponding amounts of foam stabiliser were 1.2%, 1.4%, 1.6%, 1.8%, and 2.0% , respectively, and the replacement rates of fly ash were 0%, 10%, 20%, 30%, 40%, 50%, and 60% , respectively. The foam concrete test blocks were prepared according to these proportions, and the physical and mechanical properties were tested. In order to prevent the specimen from collapsing and reduce the setting time of foam concrete, a certain amount of lithium carbonate was added to foam concrete based on the previous experimental research. The preparation is illustrated by the flow chart in 0). The drying process was repeated after an interval of 4 h, and the mass difference was not allowed to exceed 0.5% of the mass of the test piece. The dry bulk density was calculated as3; M0-mass of test piece after drying, g; V-volume of test piece, mm3.Three indicators were tested according to the requirements in JG/T 266–2011 . The sizAccording to GB/T 10294-2008 , the sizAccording to Chinese JG/T 266–2011 , the curThe pore structure parameters of foam concrete were measured using the image analysis method. After 28 days of curing, the test piece was placed in an electric oven and heated at (80 ± 5) °C for 24 h. A cutting tool was used to cut along the direction parallel to the porous surface, and an abrasive paper was used to remove the powder particles on the surface. The sample was photographed using an AO-HD208CD electron microscope to obtain the image information, as shown in Foaming agent is one of the basic raw materials for preparing foam concrete. The foaming agent reacts chemically in the evenly mixed slurry to generate a large amount of gas, which is distributed in the slurry and gradually trapped in the hardened concrete with the solidification of the slurry, forming a uniform and stable porous structure ,30. Ther3, which is 4.42% lower than that of foam concrete with 1.2% H2O2. This is because the water in the formed pore structure will gradually decrease until it is completely consumed during the hydration process. The mechanical and elastic strengths of the original liquid film are improved under the action of calcium stearate, enabling the liquid film to better withstand the external forces without breaking. Therefore, the stability of the bubbles is improved, escaping of the bubbles is reduced, the number of pores per unit volume is increased, and dry bulk density of the foam concrete is decreased. However, when the calcium carbide content increases from 1.8% to 2.0%, the dry density of the foam concrete increases, which may be because of the consistency of the cement paste and the increase in bubble formation resistance. When the dissolution of calcium stearate reaches the limit, the excessive calcium stearate causes a delay in hydration to a certain extent, resulting in a decrease in the compressive strength and an increase in the dry bulk density [The addition of the foam stabiliser causes the dry bulk density of the foam concrete to decrease first and then increase b. When t density .3, which is much lower than that foam concrete with 0–20% fly ash. This is because the density of fly ash is lower than that of cement. If fly ash is used to replace a part of the cement, the density of the foam concrete will naturally decrease. Secondly, fly ash can effectively reduce the friction resistance between the pastes as well as reduce the resistance to bubble formation during foaming. However, when the fly ash content reaches 50–60%, the dry bulk density of foam concrete increases slightly, which may be due to further reduction in the cement content of the system. Very high fly ash content makes the slurry flow rapidly, affecting the foaming effect, and the trapped gas escapes, thus increasing the dry bulk density [With the increase in fly ash content, the dry bulk density of foam concrete shows a trend towards initial decrease and subsequent increase c. When t density .2O2 is very large, the number of pores in the system is too high, the pore walls become thin, and the number of connected pores is relatively large, resulting in decreased strength [It can be seen from strength ,34. The strength .2O3 and SiO2 siliceous materials in fly ash and cement are mixed with water to generate alkaline activators such as Ca(OH)2 and further generate hydrated calcium silicate gel, which also contributes to the strength of the foam concrete cement stone [The effect of fly ash on the strength of foam concrete is shown in nt stone ,37,38.Thermal conductivity characterises the thermal insulation performance of the material . Foam co2O2 increases (5.5~7.5%), the thermal conductivity decreases. The thermal conductivity values of foam concrete with 5.5%, 6%, 6.5%, 7%, and 7.5% H2O2 content were 0.1507, 0.1472, 0.1435, 0.1423, and 0.1421 W/(m·K), respectively. With the addition of the foaming agent, the porosity of the foam concrete increases and dry bulk density decreases. However, the high porosity is not conducive to heat conduction. Therefore, thermal conductivity shows a downward trend.It can be seen from The thermal conductivity of the foam concrete decreases first and then increases with increase in the calcium stearate content, as shown in It can be seen from 3) and the minimum thermal conductivity (0.0824 W/(m·K)), and its strength is 0.63 MPa. Although it does not have advantages in strength compared with conventional concrete and geopolymer concrete, foam concrete is a lightweight thermal insulation material. In this paper, river sand is not added to the preparation of foam concrete, which makes it not usable in load-bearing structures but can be used in roof insulation, subgrade backfill, and other projects, meeting relevant standards.From the comprehensive dry bulk density and thermal conductivity results, when the content of fly ash is 40%, foam concrete has the minimum dry bulk density , the number of bubbles introduced in the foam concrete system increases, porosity gradually increases, fusion probability between the bubbles increases, probability of small aperture bubbles merging into large aperture bubbles increases, and dry bulk density gradually decreases [2O2 content from the perspective of the pore structure.In the foam concrete system, the foaming agent is the key material for pore formation. After high-speed mixing, the foaming agent is evenly dispersed in the slurry. The bubbles in the foam concrete system gradually set and harden with the solidification of the slurry and finally form a porous structure. It can be seen from ecreases . When thIt can be seen from Adding fly ash as a mineral admixture in foam concrete can help in achieving more uniform pore distribution ,44. Fly 2O2, calcium stearate, and fly ash on the strength, dry bulk density, thermal conductivity, and pore structure of foam concrete were studied. A foam concrete insulation material capable of effectively utilising the solid waste fly ash and delivering the basic performance requirements was prepared.The effects of different contents of H(1)The dry bulk density, strength, and thermal conductivity of foam concrete decrease with the increase in foaming agent.(2)3, the compressive strength is 1.57 MPa, and the thermal conductivity is 0.1439 W/(m·K).With the addition of foam stabilizer, the dry bulk density and thermal conductivity of foam concrete decrease first and then increase, while the compressive strength increases first and then decreases. When the optimum content of foam stabilizer is 1.8%, the dry bulk density of foam concrete is 648 kg/m(3)3) and the minimum thermal conductivity (0.0824 W/(m·K)), and the strength is 0.63 MPa.The dry bulk density and thermal conductivity of foam concrete decrease first and then increase with the increase of fly ash, while the compressive strength decreases gradually. When the content of fly ash is 40%, foam concrete has the minimum dry bulk density (336 kg/m(4)2O2 content (5.5~7.5%), the porosity gradually increases, and the pore size tends to increase. The appropriate content can improve the pore structure of foam concrete. When the content of foam stabilizer is less than 1.8%, the pore size tends to increase. A small amount of fly ash (10–20%) has the morphological effect of improving the pore structure of foam concrete and making the pore size smaller. When the content of fly ash is 40%, the performance is the best, and the porosity is the highest. The pore size distribution is more uniform, which makes it possible to control the pore structure, significantly reduce the dry bulk density of foam concrete, and significantly reduce the thermal conductivity.With the increase of HIn this paper, the strength of foam concrete made of fly ash is low. In order to improve foam concrete for application in practical projects, the strength of fly ash foam concrete can be improved by alkali excitation technology, and fibre can be added to improve its crack resistance in future research. In addition, the influence of the materials constituting foam concrete on durability performance, especially frost resistance, also needs to be studied in the future.


The development of new drugs for idiopathic pulmonary fibrosis strongly relies on preclinical experimentation, which requires the continuous improvement of animal models and integration with in vivo imaging data. Here, we investigated the lung distribution of bleomycin (BLM) associated with the indocyanine green (ICG) dye by fluorescence imaging. A long-lasting lung retention (up to 21 days) was observed upon oropharyngeal aspiration (OA) of either ICG or BLM + ICG, with significantly more severe pulmonary fibrosis, accompanied by the progressive appearance of emphysema-like features, uniquely associated with the latter combination. More severe and persistent lung fibrosis, together with a progressive air space enlargement uniquely associated with the BLM + ICG group, was confirmed by longitudinal micro-computed tomography (CT) and histological analyses. Multiple inflammation and fibrosis biomarkers were found to be increased in the bronchoalveolar lavage fluid of BLM- and BLM + ICG-treated animals, but with a clear trend toward a much stronger increase in the latter group. Similarly, in vitro assays performed on macrophage and epithelial cell lines revealed a significantly more marked cytotoxicity in the case of BLM + ICG-treated mice. Also unique to this group was the synergistic upregulation of apoptotic markers both in lung sections and cell lines. Although the exact mechanism underlying the more intense lung fibrosis phenotype with emphysema-like features induced by BLM + ICG remains to be elucidated, we believe that this combination treatment, whose overall effects more closely resemble the human disease, represents a valuable alternative model for studying fibrosis development and for the identification of new antifibrotic compounds. Idiopathic pulmonary fibrosis (IPF) is a heterogeneous, chronic disease characterized by progressive lung scarring and impaired pulmonary function, ultimately leading to respiratory failure and death. A truly resolving pharmacological therapy has yet to be identified, and lung transplantation often remains the only treatment option , 2. EvenHowever, this model does not faithfully reproduce all the main features of the human disease and some drawbacks, such as the spontaneous resolution of fibrosis and a significant degree of interanimal variability, have been reported , 7. EvenWe thus mixed ICG with BLM to monitor lung distribution and exposure following OA in mice through an in vivo imaging system (IVIS). Surprisingly, and in stark contrast with the very short half-life commonly observed with intravenously administered ICG , we founFemale inbred C57Bl/6j  mice were purchased from Envigo, Italy . Before use, animals were acclimatized for 7–10 days to the local vivarium conditions , having free access to regular rodent chow and softened tap water. Sterile sunflower seeds and hydrogel were supplied as diet integration to prevent excessive body weight loss.Animals were housed five per cage under standard conditions at our animal facility, in compliance with the procedures and principles outlined in the European Directive 2010/63 UE, Italian D.Lgs 26/2014 and the revised “Guide for the Care and Use of Laboratory Animals” . All animal procedures were conducted in an AAALAC  certified facility at Chiesi Farmaceutici and were authorized by the Italian Ministry of Health with protocol number 809/2020-PR and by the internal AWB .A visual analog scale (0–10) for pain assessment was assessed daily by a designated veterinarian or trained technicians. VAS ≥6 and/or body weight loss ≥ 20% were considered as humane endpoints, as well as signs of dyspnea or apathy evaluated by a designated veterinarian.The solutions instilled via OA were prepared as follows:days 0 and 4, whereas Sal + ICG and BLM + ICG were administered once, at day 0 .Bleomycin hydrochloride  was diluted in 0.9% NaCl at a working concentration of 0.5 mg/mL (BLM); indocyanine green  was dissolved in sterile water and diluted with saline  at a working concentration of 2.5 mg/mL . The solution was prepared in a vial covered with aluminum foil to prevent light exposure and was used immediately after solubilization preparation to avoid compound precipitation; BLM and ICG were dissolved at 1 mg/mL and 5 mg/mL concentrations, respectively, and then mixed (1:1 volume ratio) to obtain the final BLM + ICG solution. Sal and BLM were administered twice (indicated as “TW”), at For each solution, 50 µL was administered to mice as described previously , 16; brin = 15) and Sal + ICG (n = 15), BLM (n = 15) and BLM + ICG (n = 36).Three independent experiments were carried out. As follows, the total number of mice used per group: Sal  .Ex = 790 nm, λEm = 840 nm) fluorescent signal was quantified in calibrated (radiant efficiency) units [(photons/s/cm2/str)/(µW/cm2)] in Sal + ICG and BLM + ICG mice using the software Living Image version 4.3.1. . Mice were imaged in a prone position at 0, 7, 14, and 21 days after OA treatment; an average of total fluorescence signal emitted from the chest region was calculated for each mouse. Two representative Sal and BLM mice were also imaged as negative controls. At each time point, subgroups of mice were euthanized, and lungs were collected for histological analysis. Before formalin fixation, lungs were imaged for ex vivo fluorescence detection as already described. Thereafter, two paraffin-embedded lung slides from Sal + ICG and BLM + ICG samples were cut with 5-µm thickness and fluorescence at 800 nm detected by Odyssey (LI-COR Biosciences - GmbH).ICG . Mice were lightly anesthetized with 2% isoflurane and images were acquired with the following parameters: 90 KV, 88 µA, and total scan time of 4 min . The “high speed” acquisition protocol was used, and a respiratory-gated technique was applied. The entire set of projection radiographs was reconstructed using a filtered back-projection algorithm with a Ram-Lak filter and resulted in two stacks of 512 slices with a nominal resolution of 50 µm.Micro-computed tomography (micro-CT) was performed at The reconstructed datasets were analyzed with Analyze software . Following the analysis protocol, CT scans were filtered and then converted from gray levels to CT numbers .For the quantitative assessment of the aeration degrees, the total lung volume was extracted from the reconstructed image , 15 throThe hypo- and non-aerated lung tissue areas refer to those with a low gas/tissue ratio, which was previously developed to quantify lung fibrosis progression and evaluate antifibrotic drug efficacy .g for 10 min at 4°C. The cell pellet was resuspended in 0.2 mL of phosphate buffer solution (PBS), and leukocytes and cell populations were determined using an automated cell counter , while supernatants were frozen at −80°C. At a later time, BAL supernatants were thawed, and the levels of multiple cytokines and chemokines were determined, using a Magnetic Luminex Assay , according to the manufacturer’s instructions; neutrophil elastase and total TGF-β1 levels were determined with the SimpleStep ELISA Kit (Abcam) and the LEGEND MAX Total TGF-β1 ELISA Kit (Biolegend), respectively.At 7, 14, and 21 days, after the in vivo imaging, subsets of 5 , 5 (BLM), 5 , and 12 (BLM + ICG) mice were euthanized with an overdose of anesthetic followed by bleeding from the abdominal aorta. Bronchoalveolar lavage fluid (BALF) was then harvested by gently washing the lungs with 0.6-mL sterile Hank’s balanced salt solution (HBSS) containing 1 mM ethylenediaminetetraacetic acid (EDTA) and 100 mM 4-(2-hydroxy-ethyl)-1-piperazineethansulphonic acid (HEPES); the collected fluid was centrifuged at 300 After BAL collection, the lungs were removed and inflated with a cannula through the trachea by gentle infusion of 0.6 mL of 10% neutral-buffered formalin and fixed for 24 h. For histological assessment, the samples were dehydrated in a graded ethanol series, clarified in xylene, and paraffin-embedded. Sections of 5-μm thickness were cut with a rotary microtome  and then stained with hematoxylin and eosin (H&E) and Masson’s trichrome (TM), according to the manufacturer’s specifications (Histo-Line Laboratories). The whole slide images (WSIs) were acquired by the NanoZoomer S-60 Digital slide scanner  for analysis. Three sections for each lung sample were stained with TM and scored on a scale of 0–8 by two independent investigators who were blinded to the treatments. Fibrotic modifications were assessed morphologically and semiquantitatively graded according to the scale defined by Ashcroft et al.  and modiParaffin-embedded sections (4-μm thickness) were dewaxed and processed as described previously . SectionDigital slide images (NDPITools) were uploaded, recorded, and analyzed with QuPath (version 0.2.3), an open-source software for image analysis . DAPI stAlveolar air spaces enlargement and alveolar destruction, in accordance with emphysema definition , were hihttps://med.nyu.edu/nolanlab) for the MLI quantification and Visiopharm’s Quantitative Digital Pathology software  for the AAA.The mean linear intercept (MLI) and alveolar airspace area (AAA) were semiautomatically detected, through morphological and color-thresholding tools, using an ImageJ plug-in (1) image borders detection, 2) identification of histological structures, 3) airways size categorization, and 4) airspace size metrics.MLI provides the mean free distance between gas exchange surface in the acinar airway complex . MLI was1) Image borders detection: The purpose of this step is to determine the working area available for quantitative analysis. A combination of three “image classes” was used for training the decision forest classifier, an ensemble learning method that takes advantage of constructing a multitude of classifiers, to recognize the image principal pixels. The postprocessing step in combination with “morphological tools”  allows this application to define the lung profile, surrounding the tissue and excluding the outside.2) Identification of histological structures: Decision Forest algorithm was trained by an experienced operator to recognize blood vessels, airways, and tissue  found in the histological image stained with TM. The identification of blood vessels and airways from the whole section was possible, particularly, following a postprocessing list with a specific order.3) Airways size categorization: Focusing only on airways, with the help of “morphological tools” designed on Visiopharm to highlight different sizes, it was possible to proceed with a dimensional categorization of the “alveolar air spaces”: normal (0–100 μm), medium (101–300 μm), and large (≥ 300 μm).4) Airspace size metrics: The last application, working on labeled region, returns quantitative data generated by algorithms with “calculation options.” This was applied to the airways categories, allowing definition of the percentage occupied by each of three categories of total lung structure.g at room temperature. LA-4 were cultured in F-12K nutrient mixture  + 1X penicillin/streptomycin  + 15% FBS , whereas RAW 264.7 were cultured in DMEM  + 1X penicillin/streptomycin/glutamine  + 10% FBS. A subcultivation ratio of 1:3 was generally applied in T-75 flasks every 2–3 days and confluence was carefully evaluated with an inverted microscope (×10 magnification). The passage range of 5–10 was considered for in vitro experiments. Experiments were repeated at least three times with similar results.Murine macrophage  and epithelial  cell lines were purchased from ATCC and grown in T-75 flasks (Corning) until they reached the 80% of confluence. For subculture, they were detached from plate using 0.025% Trypsin-EDTA solution  and centrifuged for 4 min at 125 After 24 h from seeding, cells were starved for 3 h using the same culture medium supplemented with 2% FBS. 2X solutions of ICG and BLM were freshly prepared in culture medium to achieve final concentrations of 0.01 and 0.1 mg/mL for ICG, as reported in previous studies –32, and LA-4 were seeded on glass coverslips (Sigma-Aldrich) positioned inside 12 multiwell plates. After treatment, cells were fixed with paraformaldehyde 4% and stained with 4′,6-diamidino-2-phenylindole, dihydrochloride  for 5 min. After three washings with PBS, the cytoplasmatic or nuclear ICG uptake (red) was evidenced with fluorescence microscope Nikon Eclipse Ti2 (Nikon) and cell nuclei were highlighted in blue.4 cells/well) in 0.5 mL of complete medium in 48 multiwell plates. After treatment, the supernatants were replaced with 0.5 mg/mL thiazolyl blue tetrazolium bromide  diluted in serum-free culture medium. Plates were then incubated for 2 h at 37°C. The deposition of violet crystals in the bottom well reveals the presence of metabolic active and vital cells. The solution was then removed, and crystals were dissolved in 0.2 mL of dimethyl sulfoxide . Absorbance was immediately quantified using a plate reader  at 570 nm wavelength and optical densities (O.D.) were quantified through the Microplate Manager Software 6 version 6.3 (Bio-Rad). At each time point of observation, the viability was measured in triplicate for both the cell lines, and biological replicates were performed at least twice with similar results. Results were expressed as % of vital cells compared with untreated cells as control (considered as 100% by default) at each time point.Cells were seeded (5 × 10CASP7), Mm01204974_m1 (FAS), and Mm00725412_s1 (ACTA2) were used to measure the expression of CASP7, FAS, and ACTA2 genes, using GAPDH as housekeeping gene. RT-qPCR was performed with QuantStudio 7 Flex Real-Time PCR System (Thermo Fisher Scientific). Cycle threshold (Ct) for each gene and sample was recorded and 2-ΔΔCt analysis was conducted using untreated RAW 264.7 or LA-4 as controls (fold change corresponding to 1).After 4 h and/or 24 h treatment, RAW 264.7 and LA-4 cells were washed with Hank’s balanced salt solution (HBSS), and RNA was extracted using the RNeasy Plus Mini kit (Qiagen) following the instructions protocol. The concentration of RNA was measured using the NanoDrop 2000 (Thermo Fisher Scientific) and retrotranscribed using SuperScript VILO Master Mix (Invitrogen). TaqMan Assays Mm00432322_m1 (P < 0.05 (*) was considered as statistically significant.Statistical analyses were performed using Prism 8 software . All data are presented as mean ± SEM. One- or two-way analysis of variance (ANOVA) was performed, followed by Sidak’s or Tukey’s multiple comparisons post hoc tests. Normal distribution was assessed through Shapiro–Wilk test accompanied by visual inspection of QQ-plots. Sample size was calculated with a priori Power Analysis (G*Power Version 3.1.2) considering Ashcroft Score as endpoint. For all the applied tests, a We initially traced lung accumulation and distribution of OA-administered ICG, alone and in combination with BLM, by in vivo fluorescence analysis. Representative in vivo fluorescence images of Sal, BLM, Sal + ICG, and BLM + ICG mice in prone position and ex vivo lung-associated signals at different time points are shown in day 7 and gradually decreased thereafter, both in vivo and ex vivo. At day 21, a sizeable ICG signal could still be detected  lung segmentations in Normo-, hypo-, non-aerated, and hyperinflated lung areas, as revealed by micro-CT analysis, were thus considered hallmarks of lung compartments with distinctive gas/tissue ratios. Although hypo- and non-aerated lung parenchyma is diagnostic of different degrees of fibrosis, alveolar air space enlargement as seen in hyperinflated areas represents the micro-CT imaging correlate of an emphysema-like phenotype.days 7, 14, and 21, using Sal- and Sal + ICG-treated mice as controls, respectively. As shown in P < 0.001 vs. Sal + ICG) and non-aerated  areas at all the investigated time points, with a peak for both types of abnormal compartments at day 14. A similar increase in underaerated areas was observed at day 14 in BLM-treated animals but it reached statistical significance  only for hypo-aerated tissue. In fact, the fractional occurrence of non-aerated tissue, which is indicative of more severe fibrotic lesions, was 5 ± 1% at day 14 in the BLM group but more than twice as much (12 ± 2%) in the case of the BLM + ICG group.Accordingly, individual lung compartments of animals belonging to the BLM-only and the BLM + ICG groups were quantitatively imaged at days 7, 14, and 21.Hyperinflated tissue areas containing bubble-like shaped structures were not detectable in BLM-treated mice nor in the Sal + ICG or Sal controls, but they were clearly visible in the BLM + ICG group and time-dependently increased at days 7, 14, or 21 and on parallel tissue samples derived from Sal- and BLM-treated mice , was revealed by Ashcroft score measurements performed at the different time points, with a clear trend toward further worsening at day 14 (days 14 and 21 (P < 0.05). Indeed, as shown in days 7 (P < 0.05), 14, and 21 (P < 0.01). Conversely, mild to moderate lesions were markedly lower in the BLM + ICG compared with the BLM-only group (P < 0.01), which displayed the highest frequency of moderate rather than severe lesions at all time points. Both BLM groups, however, featured a significantly higher abundance of moderate to severe lesions compared with the control Sal + ICG and Sal groups (P < 0.01), which did not differ significantly from each other.Alveolar walls collapse and destruction, with a marked enlargement of alveolar airspaces, was already visible in lung tissue samples from BLM + ICG animals at rphology A. No sucrphology A and B. t day 14 C. Even hOverall, BLM + ICG-treated mice displayed significantly more severe fibrotic lesions compared with BLM-only animals at all time points, with morphologically distinctive signs of an emphysema-like alteration, most notably, a marked enlargement of the alveolar air space not observed in the latter group. The Ashcroft score of the Sal + ICG, Sal, BLM + ICG, and BLM groups was highly correlated with micro-CT parameters such as normo-, hypo-, and non-aerated areas E.days 7, 14, or 21. We determined expression levels of Collagen I and FAP-1α, a protein associated with matrix remodeling .Immunofluorescence assays were performed on controls , BLM-only-treated, and BLM + ICG mice euthanized at modeling A–D. A coday 14 in both BLM + ICG and BLM-only-treated mice . FAP-1α, the other cellular component we used as a biomarker, is a type II transmembrane protein that is upregulated in activated fibroblasts within areas of active tissue remodeling , whereas a nonsignificant increase was detected in BLM mice relative to the control Sal group. Moreover, FAP-1α expression levels were much higher in BLM + ICG than in BLM-only mice at days 7 and 14  at day 21. This was accompanied by a loss of tissue resulting from coarctation and scarring due to the establishment of emphysematous-like conditions.Quantification of the Collagen I signal revealed a peak at ted mice E. Even tmodeling , 34, parP < 0.05 at days 14 and 21) along with a significant decrease of the “medium-size” air space category, compared with the Sal + ICG group.As shown in day 21 and were not detected at any of the examined time points in the Sal + ICG or the BLM-only groups.As revealed by a mean linear intercept analysis performed on the same micrographs C, markedThe observed changes in MLI, but also in the alveolar airspace area, are once again strongly indicative of an emphysema-like alteration, as initially suggested by micro-CT imaging data, which highlighted the presence of multiple and well-detectable low-density, bubble-shaped structures within the lung parenchyma.As inflammation is an early hallmark of bleomycin-induced fibrosis, we evaluated the development of pulmonary inflammation by measuring the number of inflammatory cells  and cytoday 7 in BALFs from BLM + ICG compared with Sal + ICG mice , which did not exhibit any appreciable inflammatory response signature at any of the examined time points  could still be detected at this time point (P < 0.01) was also apparent at day 14 , including neutrophils, macrophages, and eosinophils, were all significantly increased at e points A–E. Thisme point A and C. t day 14 D, indicadays 7 and 14 . As in the case of BLM + ICG, inflammatory cells  in the BLM-only group returned to basal levels at day 21, thus pointing once again to the fully reversible nature of the inflammatory response associated with the early phase of BLM-induced lung fibrosis. In addition to the lack of any appreciable effect of the BLM-only treatment on neutrophils and eosinophils, a significantly reduced increase in WBCs and macrophages (P < 0.05) was observed in this group, at day 7, compared with BLM + ICG-treated animals. A similar, albeit not significant trend was observed for lymphocytes at days 7 and 14, thus indicating the induction of a synergistic enhancement of multiple inflammatory cell types by BLM + ICG compared with BLM- and ICG-only treatments. This effect was partly mirrored by a parallel, statistically significant increase, especially at day 7, of 7 of the 17 tested cytokines (nine were not detectable) in the BALFs from BLM + ICG compared with control Sal + ICG animals . Also notable, and in keeping with the emphysema-like phenotype highlighted by micro-CT and histomorphometric analyses, was the striking elevation of elastase levels detected in the BALFs of BLM + ICG- but not Sal + ICG-treated animals . Given the presumable neutrophil origin of elastase, which is considered a hallmark of emphysema and is used as an experimental tool to induce this particular lung pathology (P < 0.01) at day 7.As expected, BLM was the second most effective treatment at increasing the levels of all inflammatory cell types except neutrophils and eosinophils at athology , the obsathology B. We alsathology G. Even tday 7. At variance with the BLM-only group, in which active caspase-3 was detected in cell nuclei at day 14, apoptotic cells were visible at all time points in the BLM + ICG group, as confirmed by cleaved Caspase-3 signal quantification (P < 0.01), as well as in BLM mice (P < 0.01), at each of the examined time points. On the other hand, as regard the BLM group, a significant increase in cleaved caspase-3 with respect to the Sal control group was detected only at day 14 (P < 0.05), whereas a slightly, not significantly, higher signal was observed at the other time points.As revealed by in vivo data, the BLM + ICG combination triggered a strong tissue reaction  ultimately causing lung fibrosis with emphysema-like features after OA administration. To gain initial insight into the molecular bases of this reaction, we investigated the effects of BLM and ICG, both alone and in combination, both in vitro, through cell-based assays, and ex vivo, on paraffin-embedded lung sections. The morphological appearance of apoptosis is shown in fication E. In BLMP < 0.05 and P < 0.01, respectively), whereas no appreciable detrimental effect was observed at the lower (3 µg/mL) concentration . ICG, instead, did not affect cell viability at either concentration after 4 h, but caused a dose-dependent reduction of cell viability at both concentrations after 24 h. The lowest concentrations of BLM and ICG , which proved to be ineffective alone after a 4 h incubation, were thus selected for subsequent combination studies. As shown in P < 0.01) at both 4 and 24 h. Also, apparently unique to the combined BLM + ICG treatment was the synergistic activation of the early extrinsic apoptotic pathway, as suggested by the results of a targeted gene expression analysis that revealed a significant upregulation at 4 h of the mRNAs coding for the death receptor Fas , as well as compared with cells treated with BLM (P < 0.01) or ICG (P < 0.05) alone  alone E.A, ICG but not BLM alone significantly reduced cell viability at 4 and 24 h (P < 0.01 vs. untreated cells). Also with this cell line, however, a much more pronounced loss of viability was induced by the combined BLM + ICG treatment . As in the case of RAW 264.7 cells, loss of cell viability was paralleled by a marked, albeit only partially significant, upregulation of the proapoptotic FAS and CASP7 mRNAs, which was only detectable in BLM + ICG-treated cells .The effect of BLM and ICG and their combination was also tested in the mouse lung epithelial cell line LA-4. As shown in Supplemental Fig. S6D, the red fluorescence signal associated with the ICG dye displayed an exclusively cytoplasmic localization both in cells treated with ICG alone as well as with the BLM + ICG combination.Because of their more favorable morphology compared with macrophages, epithelial LA-4 cells also allowed us to investigate the subcellular localization of the fluorescent dye ICG after a 24 h treatment. As shown by the representative fluorescence microscopy images presented in Supplemental Fig. S6Although our primary goal was to investigate the lung distribution of BLM associated with a fluorescent dye, we unexpectedly found that ICG displays long-lasting lung retention upon OA administration. Moreover, the BLM + ICG combination triggered a severely aggravated form of pulmonary fibrosis which, unlike the fibrotic phenotype commonly observed in the BLM-only model widely used by our and many other laboratories , 15, 16,Long-lasting lung persistency of ICG has similarly never been reported before. However, we documented the presence of ICG, coadministered with BLM, inside epithelial cells and a persistent (up to 21 days) ICG-associated fluorescence signal in the lungs. A possible explanation for these divergent behaviors may reside in the well-known ability of ICG to tightly bind to proteins as well as phospholipids (PLs), with a significant change in its fluorescence  properties , 38. GivWe used multiple experimental approaches, both in vivo and in vitro, to comparatively characterize the lung pathology caused by the BLM + ICG and the BLM-only treatments and to begin to elucidate the mechanisms underlying their quantitative and qualitative different effects. Indeed, as revealed by total Ashcroft score and fibrosis severity assessments based on frequency distribution, the fibrotic phenotype induced by the BLM + ICG combination was significantly more severe than that observed upon BLM instillation. Importantly, the fibrosis enhancement elicited by BLM + ICG was always accompanied by the appearance of hyperinflated areas that were uniquely detected in BLM + ICG-treated mice by micro-CT. The latter areas were interpreted as signs of an emphysema-like lung tissue alteration: an interpretation that was corroborated by the results of histomorphometric and mean linear intercept analyses, both of which highlighted a significant increase of the alveolar air spaces within the lung parenchyma. The increase in air space size was particularly striking at 21 days after OA administration of BLM + ICG and led to a significant reduction of parenchymal tissue.day 21 fibroblasts were still activated in BLM + ICG mice, as revealed by FAP-1α quantification, the levels of Collagen I were not significantly increased. Importantly, we showed that in vivo detection of FAP-1α can assess the fibrotic activity of BLM + ICG-mediated injury, as was recently reported for the BLM model , in which neutrophils, but often also eosinophils, are considered the main inflammatory cells .day 7, of neutrophil-derived elastase, a proteolytic enzyme causally associated with emphysema development and widely used as an experimental tool to induce this particular lung pathology  coding for two known drivers of the extrinsic apoptotic pathway. In the case of macrophages, this was paralleled by the upregulation of the mRNA coding for the myofibroblast formation marker α-smooth muscle actin (ACTA2) and by the switch from a round to a spindle-like morphology, which has previously been associated with a proinflammatory, rather than wound-healing, phenotype  triggered by the combined administration of the two compounds cannot be simply ascribed to a generalized, necrotic/cytotoxic effect, but rather to a subtler apoptotic, morphological, and likely function-modifying transition.We have described a new, more comprehensive model of lung fibrosis that may represent a useful addition to the currently available toolkit for pulmonary disease drug discovery. As pointed out by the multiple lines of evidence presented in this work, the BLM + ICG combination may allow to overcome a major shortcoming of the commonly used BLM model, namely, the fact that lung fibrosis induced by a BLM-only treatment starts to spontaneously resolve after 14 days, thus hindering the achievement of a proper time-window for testing the efficacy of new drug candidates. In fact, BLM + ICG-induced fibrosis develops early and maintains a high level of severity after 21 days. Although the fibrotic peak occurs at 14 days, the BLM + ICG-induced injury is associated with progressive emphysema-like features that resemble human IPF, as well as certain forms of COPD. A lung fibrosis animal model alternative to bleomycin is strongly needed; in fact, Nintedanib, an approved drug for IPF , as wellFrom a methodological point of view, the present data also document the importance of functional micro-CT analysis as a crucial exploratory tool for longitudinal, qualitative as well as quantitative in vivo monitoring of disease progression.We thus strongly believe that a continuous and integrated refinement of both the animal models and the bioanalytical tools  that are applied to pharmacologically oriented studies of lung fibrosis and other pulmonary pathologies are essential prerequisites for a successful preclinical investigation with a high potential for clinical translation.All animal experiments described herein were approved by the intramural animal-welfare committee for animal experimentation of Chiesi Farmaceutici under protocol number: 809/2020-PR and complied with the European Directive 2010/63 UE, Italian D.Lgs 26/2014.The data sets used and/or analyzed during the current study are available from the corresponding author on reasonable request.10.6084/m9.figshare.20014943https://doi.org/10.6084/m9.figshare.20014943.Supplemental Fig. S1: 10.6084/m9.figshare.20015039https://doi.org/10.6084/m9.figshare.20015039.Supplemental Fig. S2: 10.6084/m9.figshare.20015912https://doi.org/10.6084/m9.figshare.20015912.Supplemental Fig. S3: 10.6084/m9.figshare.21355290https://doi.org/10.6084/m9.figshare.21355290.Supplemental Fig. S4: 10.6084/m9.figshare.21355368https://doi.org/10.6084/m9.figshare.21355368.Supplemental Fig. S5: 10.6084/m9.figshare.21776369https://doi.org/10.6084/m9.figshare.21776369.Supplemental Fig. S6: 10.6084/m9.figshare.20015948https://doi.org/10.6084/m9.figshare.20015948.Supplemental Table S1: This study was fully supported by Chiesi Farmaceutici S.p.A.This study was fully supported by Chiesi Farmaceutici S.p.A. F.F.S., G.V., and A.G. are employees of Chiesi Farmaceutici S.p.A., which supported the research work. None of the other authors has any conflicts of interest, financial or otherwise, to disclose.A.G., E.F., and F.F.S. conceived and designed research; A.G., E.F., and Z.K. performed experiments; L.M., R.C., M.Z., and L.L. analyzed data; A.G., A.K., C.W.G.M.L., G.D., and F.F.S. interpreted results of experiments; E.F., L.M., R.C., M.Z., L.L., and Z.K. prepared figures; A.G., G.V., and F.F.S. drafted manuscript; A.K., C.W.G.M.L., G.D., and G.V. edited and revised manuscript; A.G., E.F., L.M., R.C., M.Z., L.L., Z.K., A.K., C.W.G.M.L., G.D., G.V., and F.F.S. approved final version of manuscript.


In this paper, the environmental characteristics and corrosion degree of concrete in a 41-year-old steelworks were investigated, and the neutralization life prediction of the concrete structure was carried out. The results showed that the temperature, relative humidity, CO2 concentration, and SO2 concentration in the steelworks were 1.32, 0.62, 1.28, and 13.93 times higher than those of the general atmospheric environment, respectively. These environmental characteristics in various sections were significantly different. The appearance change of concrete in the ingot casting bay was more serious than that of concrete in the billet bay. Both the compressive strength of concrete in the ingot casting bay and billet bay decreased, and the strength in the billet bay was relatively low. The neutralization depth of concrete in the ingot casting bay was 2.35 times larger than that of concrete in the billet bay. The prediction model of concrete neutralization depth was established, and the remaining neutralization service life in the ingot casting bay and billet bay were 194.68 a and 202.07 a, respectively.Iron and steel industry emits a large amount of CO Moreover, iron ore contains the sulfur element, which inevitably produces SO2 in the process of mining and processing [2 emissions in 2019 were 11.198 billion tons [2 emissions that generated by China’s steel industry accounted for 14% of total CO2 emissions [2 emissions generated by China’s steel industry in 2015 were 1.37 million tons, which accounted for 7.36% of China’s total SO2 emissions [Steel is the most widely used and consumed alloy in the world. China is the largest steel producer in the world . The steocessing . Accordiion tons , and themissions . The SO22 and SO2 can react with alkaline hydration products. Thrangavel [2 reacted with Ca(OH)2 and decreased the pore-solution pH of concrete, and Niu [2 could also reduce the alkalinity of concrete. Once pore-solution pH drops to about 9, the protective film of the rebars is destroyed, and the rebars begin to corrode [2 and SO2 resistance of concrete. To achieve this goal, the study on the neutralization of concrete under the combined action of CO2 and SO2 should be accomplished.The pore-solution pH of ordinary Portland cement concrete is usually between 12.5 to 13.5 , and thirangavel  found th and Niu  and Pavl corrode . Excessi2 or SO2. According to the theoretical analysis [2 reacted with calcium compounds of hydration products to form CaCO3. SO2 reacted with all calcium compounds, including CaCO3, and converted them into calcium sulfates and calcium sulfoaluminates [3 increased the compactness of concrete, so the carbonation of concrete increased the compressive strength. Li [At present, the research on concrete neutralization mainly focuses on the action of single COanalysis , laboratanalysis ,17, and analysis ,19 of couminates . Calciumuminates . Once pHuminates . The decuminates . CaCO3 ingth. Li  and Rostngth. Li  verifiedngth. Li .2 and SO2, mainly focusing on the neutralization mechanism. Pavlik [2 and CO2. Lean [2 in concrete was faster than that of SO2 at the same volume concentration. Furthermore, the concentration of CO2 was higher than that of SO2 in an industrial environment. Therefore, the essence of concrete sulfuration was the reaction between SO2 and carbonation products under the action of CO2 and SO2.There is little research on concrete neutralization under the combined action of CO. Pavlik  investig. Pavlik  found thO2. Lean  observed2 and SO2, especially in terms of the degree of concrete performance degradation. Therefore, the corrosion damage and life prediction of concrete structures in a 41-year-old steelworks of Wuhan Iron and Steel Corp. (WISCO) were studied in the present work. The environmental characteristics such as temperature, relative humidity, CO2 concentration, and SO2 concentration in various sections of the steelworks were monitored, respectively. The appearance, cover thickness, neutralization depth, and compressive strength of concrete in the ingot casting bay and billet bay were analyzed, respectively. The prediction model of neutralization depth of concrete in the steelworks was established, and the remaining neutralization service life in the ingot casting bay and billet bay were predicted.To sum up, there are few research results on the concrete neutralization under the combined action of CO2 and SO2, are generated in the process of steelmaking. Therefore, the corrosion damage to concrete structures in the steelworks is serious. Taking a 41-year-old steelworks of WISCO as an example, the research group investigated the environmental characteristics and corrosion damage of concrete structures from August to October 2013.The industrial environment of steelworks is a typical environment with high temperatures and high concentrations of acid gas. The temperatures of molten iron and molten steels are 1250–1350 °C and 1600–1700 °C, respectively. Therefore, steelworks are exposed to a high-temperature environment for a long time. Besides, a large amount of acid gases, such as COWISCO was located in Qingshan District, Wuhan City. The main building of the steelworks was built in 1972, and it was divided into seven sections: charging bay, acceptance bay, converter bay, casting bay, ingot casting bay, billet bay, and granulating slag bay. Among them, the ingot casting bay and billet bay were the concrete bent construction. The ingot casting bay was a single slope bent structure with a span of 24 m and a column spacing of 37. The bent frame column of the billet bay adopted the diagonal web member double-wing column.The concrete consisted of ordinary Portland cement, with natural river sand as the fine aggregate and crushed limestone as the coarse aggregate. Both the design thicknesses of concrete cover in the ingot casting bay and billet bay were 30 mm, and the concrete mark of the column was 400. According to Chinese standard GB 50010-2010 , the chaThe temperature in the steelworks was tested by the temperature and humidity recorder , and the data were collected hourly. The layout of measuring points was based on the Chinese standard GB/T 18204.13-2000 . There wThe relative humidity in the steelworks was tested by the temperature and humidity recorder, and the data were collected hourly. The arrangement of measuring points was the same as that of measuring points for temperature monitoring. The average of all measuring points in each section was the average relative humidity in the section. The average of all sections was the average relative humidity in the steelworks.2 concentration in the steelworks was monitored by using the carbon dioxide detector , and the data were collected hourly. The layout of measuring points was the same as that of measuring points for temperature monitoring. The average of all measuring points in each section was the average CO2 concentration in the section, and the average of all sections was the average CO2 concentration in the steelworks.The CO2 concentration in the steelworks was monitored by using the sulfur dioxide detector , and the data were collected hourly. The layout of measuring points was the same as that of measuring points for temperature monitoring. The average of all measuring points in each section was the average SO2 concentration in the section, and the average of all sections was the average SO2 concentration in the steelworks.The SOThe thickness of concrete cover in the steelworks was tested by a rebar scanner  with a measuring range of 70 mm. Concrete columns were randomly selected to test the thickness of concrete cover. Each column had 30 testing zones, which were evenly distributed on two symmetrical measurable surfaces of the column. The thickness of concrete cover in each testing zone was tested along the direction of the main reinforcement of the column, and the average value of all testing zones in each column was the average thickness of concrete cover of the column.The neutralization depth test method of concrete in Chinese standard JCJ/T 23-2011  was adopThe compressive strength of concrete was tested by the rebound method according to JCJ/T 23-2011, and the test was carried out by using a rebound hammer . The selection of concrete columns was the same as that of columns for testing the concrete cover thickness. Two testing zones were selected for each column, and they were arranged on two symmetrical measurable surfaces of the column. The measuring points in each testing zone were not less than 16. The measuring points should be evenly distributed, and the distance between two adjacent measuring points should not be less than 20 mm. The distance between the measuring points and the exposed steel bars or embedded parts was not less than 30 mm. The measuring points should not appear on stones and pores, and each measuring point bounced only once. After removing three maximum values and three minimum values, the arithmetic mean value of the remaining measuring points was the average rebound value of the testing zone. The average rebound value of the two testing zones was the final strength of the column. The equivalent value of concrete compressive strength was converted according to the rebound value of compressive strength and the neutralization depth.The temperature in the steelworks is shown in The relative humidity in the steelworks is shown in 2 concentration in the steelworks is shown in 2 concentration in the steelworks was 944.5 mg/m3. According to the relevant information from the Wuhan Environmental Protection Bureau (WHEPB), the CO2 concentration of the atmospheric environment in the Qingshan District was 740.5 mg/m3 [2 concentration in the steelworks was 1.28 times higher than that of the general atmospheric environment. In addition, there were significant differences in the CO2 concentrations in various sections, and the CO2 concentrations in the charging bay, acceptance bay, converter bay, casting bay, ingot casting bay, billet bay, and granulating slag bay were 1084.3, 791.2, 1117.6, 974.3, 1039.4, 846.6, and 758.2 mg/m3, respectively. Therefore, CO2 concentration in all sections of the steelworks was higher than that of the general atmospheric environment, and the maximum value was 1.51 times higher than that of the general atmospheric environment.The CO.5 mg/m3 . Therefo2 concentration in the steelworks is shown in 2 concentration in the steelworks was 0.78 mg/m3. According to the relevant information from WHEPB, the SO2 concentration of the atmospheric environment in the Qingshan District was 0.056 mg/m3 [2 concentration in the steelworks was 13.93 times higher than that of the general atmospheric environment. There were significant differences in the SO2 concentrations in various sections. The SO2 concentrations in the charging bay, acceptance bay, converter bay, casting bay, and ingot casting bay were 1.29, 1.17, 1.03, 0.96 and 1.03 mg/m3, respectively. No obvious SO2 was detected in the billet bay and granulating slag bay. Therefore, the SO2 concentration in the charging bay was the largest, which was 20.04 times higher than that of the general atmospheric environment.The SO56 mg/m3 . Therefo2 existed in the ingot casting bay and reacted with hydration products of concrete, resulting in the sulfuration reaction of concrete. Sulfuration could lead to the spalling and damage of concrete [2 in the billet bay, and therefore, there was only some damage on the surface of concrete caused by mechanical collision.The appearance of concrete in the ingot casting bay and billet bay of the steelworks is shown in concrete . Therefop-value was 0.81 at a significant level α = 0.05 by using Shapiro-Wilk. Therefore, the thickness of the concrete cover was in accordance with the normal distribution. In summary, the thickness of concrete cover in the steelworks basically met the structural design requirements.The thickness of concrete cover in the steelworks is listed in As shown in The neutralization depth of concrete in the steelworks is listed in 2 concentration and temperature in the ingot casting bay were 1.23 times and 1.11 times higher than those in the billet bay, respectively. In addition, the presence of SO2 in the ingot casting bay led to the cracking of concrete and accelerated the neutralization rate. Therefore, the neutralization depth of concrete in the ingot casting bay was larger, and it was 2.35 times larger than that in the billet bay.As shown in As shown in 2 [The compressive strength of concrete in the steelworks is listed in 2  and some2 ,36, suchAs shown in As shown in XC is the carbonation depth of concrete, mm; k is the carbonation coefficient, mm/d0.5; t is the carbonation exposure duration, d.It is verified by a large number of researchers that the carbonation depth of concrete varies linearly with the square root of exposure time ,41,42,432 acid gas in the billet bay, and therefore, the neutralization depth of concrete in the billet bay is the carbonation depth. The carbonation depth of concrete is affected by environmental parameters and material properties. In this paper, temperature, relative humidity, and CO2 concentration are the environmental parameters, and compressive strength is the material property of concrete. Therefore, Equation (1) can be expressed as:k0 is the undetermined parameter; k1, k2 and k3 are the carbonation influence coefficients of the temperature and humidity, CO2 concentration and compressive strength, respectively.There is only CO2 concentration, and compressive strength can be calculated as follows:T is the temperature, °C; RH is the relative humidity, %; CC is the concentration of CO2, %; and fcuk is the compressive strength of concrete, MPa.According to the literature , the carSubstituting Equations (3), (4), and (5) into Equation (2), the carbonation depth of concrete can be expressed as:2 concentration, concrete compressive strength, concrete neutralization depths, and neutralization ages in the billet bay into Equation (6), k0 is calculated and the frequency distribution histogram of k0 is shown in k0 were 7.66, 3.16, and 0.41, respectively. The p-value of k0 was 0.13 at the significant level α = 0.05 by using Shapiro-Wilk. Therefore, k0 in the steelworks followed the normal distribution.The neutralization depth of concrete in the billet bay is the carbonation depth. Substituting the test values of the temperature, relative humidity, CO2 concentration in the steelworks is much lower than that of CO2. However, SO2 can lead to the expansion and cracking of concrete, which accelerates the concrete neutralization. Therefore, the neutralization depth of concrete in the ingot casting bay can be expressed as:k5 is the neutralization influence coefficient of SO2 concentration.SO2 concentration, concrete compressive strength, neutralization ages in the ingot casting bay into Equation (6), the average of carbonation depth of concrete in the ingot casting bay is 9.97 mm. Combining the average carbonation depth and the neutralization depths of concrete in the ingot casting bay, k5 is calculated and the frequency distribution histogram of k5 is shown in k5 were 1.64, 0.50, and 0.31, respectively. The p-value of k5 was 0.30 at the significant level α = 0.05 by using Shapiro-Wilk. Therefore, k5 in the steelworks followed the normal distribution.Substituting the test values of the temperature, relative humidity, COCS = 0, k5 = 1.In conclusion, the neutralization depth of concrete in the steelworks is expressed as:2 and SO2 diffuse into concrete and react with the alkaline hydration products. Once the concrete cover is completely neutralized, the protective effect on the rebars is lost, and therefore, the rebars begin to corrode. The neutralization service life of concrete takes the initial time of steel bar corrosion as the end of the structural life. Therefore, the beginning of the steel bar corrosion is the sign of neutralization service life assessment criteria of concrete structure.c is the thickness of concrete cover, mm; x0 is the neutralization remain, mm; X(t) is the neutralization depth of concrete, mm; and t is the neutralization age, d.COTherefore, the limit state function of the neutralization service life of concrete is:According to the literature , the neux0 are shown in x0 between the ingot casting bay and billet bay, and x0 in the billet bay was much larger than that in the ingot casting bay. The average, standard deviation, and coefficient of variation of x0 in the ingot casting bay were −0.67, 0.22, and −0.33 mm, respectively. As well, the average, standard deviation, and coefficient of variation of x0 in the billet bay were 20.10, 3.66, and 0.18 mm, respectively. This was because the relative humidity in the billet bay was much larger than that in the ingot casting bay. The p values of x0 in the ingot casting bay and billet bay were 0.63 and 0.89 at the significant level α = 0.05 by using Shapiro-Wilk, respectively. Therefore, both neutralization remains of concrete in the ingot casting bay and billet bay followed the normal distribution.Neutralization remains of concrete in the ingot casting bay and billet bay of the steelworks are calculated according to Equation (11). The frequency distribution histograms of Substituting the calculation results of Equations (8) and (11) into Equation (10), the neutralization service life of concrete in the ingot casting bay and billet bay of the steelworks were 235.68 a and 243.07 a, respectively. Therefore, the remaining neutralization service life in the ingot casting bay and billet bay were 194.68 a and 202.07 a, respectively.2 concentration, and SO2 concentration in the steelworks were 1.32, 0.62, 1.28, and 13.93 times higher than those of the general atmospheric environment, respectively. Besides, those environmental parameters in various sections were significantly different. The temperature, relative humidity, and CO2 concentration in the ingot casting bay were 1.11, 0.55, and 1.23 times higher than those in the billet bay, respectively. The SO2 concentration in the ingot casting bay was 1.03 mg/m3, and there was no obvious SO2 in the billet bay. The appearance change of concrete in the ingot casting bay was more serious than that of concrete in the billet bay. Both the compressive strength of concrete in the ingot casting bay and billet bay of the steelworks decreased, and the compressive strength in the ingot casting bay was 1.23 times larger than that in the billet bay. The neutralization depth in the ingot casting bay was 2.35 times higher than that in the billet bay. The prediction model of the neutralization depth of concrete was established, and the remaining neutralization service life of concrete in the ingot casting bay and billet bay were 194.68 a and 202.07 a, respectively.In this study, the environmental characteristics and corrosion degree of concrete in a 41-year-old steelworks were analyzed, and the neutralization life prediction of the concrete structure was carried out. The average temperature, relative humidity, CO


In addition, we exemplifythe use of Raman spectroscopy as a tool for analyzing coordinationcages, exploiting alkyne and nitrile reporter functional groups thatare contained within the host and guest, respectively.Thehost–guestchemistry of coordination cages continuesto promote significant interest, not least because confinement effectscan be exploited for a range of applications, such as drug delivery,sensing, and catalysis. Often a fundamental analysis of noncovalentencapsulation is required to provide the necessary insight into thedesign of better functional systems. In this paper, we demonstratethe use of various techniques to probe the host–guest chemistryof a novel Pd 2L4 cage has been investigated. This cage shows a strongaffinity toward dicyanoarene compounds, with affinities ranging from103 to 104 M−1. NMR spectroscopyand X-ray crystallography reveal that the guests are bound throughCH···N hydrogen-bonding and CH···πinteractions, with subtle distortions also affecting the binding strength.The use of Raman spectroscopy as a tool for analyzing coordinationcages, exploiting alkyne and nitrile reporter groups, is also highlighted.The host−guest chemistry of a novel Pd It can also provide compelling evidenceas to which noncovalent interactions may be key to binding.6 Solution host–guest studies, using techniques such as 1H NMR spectroscopy and spectrophotometric methods, are alsokey, not least because many of the most important applications occurin this phase. It is especially important to show that encapsulationobserved in the solid state persists in solution, where sometimesthe competition from a vast excess of even weakly interacting solventmolecules can disrupt the interactions that drive binding.Analysis of the interactionsthat govern encapsulation phenomenais crucial for an understanding of the metallosupramolecular host–guestcomplexes that find application in areas such as catalysis, drug delivery,molecular recognition, and separation.15 They are also advantageous because they can be applied to both solution-and solid-phase  samples. Raman analysisof metalloorganic cages is underexplored; however, there are clearopportunities.17 Specifically, the alkyne functionalgroup, which is often used as a structurally rigid spacer unit inmany coordination assemblies, is a widely used RS handle. This isbecause its stretching frequency generates intense peaks18 and is both highly sensitive to changes in thelocal environment20 and direct chemical modification.21 It also occurs in a largely silent region ofthe spectrum, which, in particular, has made it a popular choice foranalyzing suitably labeled biomolecules within cells.18IRand Raman (RS) spectroscopy have been much less widely usedfor probing host–guest compounds. However, they are powerfulmethods for analyzing molecular structure and can be used to monitorthe changes in specific vibrational modes of the guest and host uponcomplexation.1. We have previously studied the host–guestchemistryof 1  where there arefew other signals. We herein describe the use of RS as a complementarytool for probing the binding properties of a Pd2L4 metalloorganic cage, exploiting a dual-labeled, alkyne–nitrilehost–guest system  it was hoped that their vertically aligned nitrilegroups could simultaneously interact with both pockets of the H-bonddonors in a fashion analogous to that of quinone⊂1 and (b) there are several dicyanoarenes that are commercially available.To accommodate the larger separation between the nitrile N atoms ofthe dicyanoarene guests compared to the interoxygen distance in aquinone, we targeted cage 2 4Pd](OTf)2 in equal amounts of CH3CN/CH2Cl2 led to formation of the expected [Pd2L4](OTf)4 structure, as evidenced by NMR spectroscopy . Anion metathesis with the noncoordinatingtetrakisborate (BArF) gave [Pd2L4](BArF)4 (2). We havepreviously described how the use of BArF counteranions can maximizehost–guest interactions with neutral organic molecules.22d cage 2 1b, which2 was characterizedby a variety of NMR techniques and electrospray ionizationmass spectrometry . In addition,crystals suitable for single-crystal X-ray diffraction were grownfrom the diffusion of diethyl ether into a solution of 2 in CH2Cl2 over 2 days. The crystal structureof 2 .27 Interestingly, the structure also shows an unexpectedfeature: two BArF counterions are partially protruding into the cavity.These anions are interacting with the cage in the same manner; eachforms interactions between the two CF3 groups from a singleBArF aryl ring and the o-pyridyl H atoms that usuallyH-bond to carbonyl guests , while in contrast, anotherstretching mode B ν(CN) was assigned to the IR band at 2220cm–1. This mode has a small polarization value,which will result in weak (if any) Raman scattering. In TCDCB, we propose that these two modes are detected.31] Because of the highly fluorescent nature of DCA, we were unable to collect a full Raman spectrum; however, a partialRaman spectrum was acquired at 785 nm laser excitation that identifieda CN stretching mode at 2220.8 cm–1. For the host–guestcomplexes, the naphthalene Raman bands at 1385 and 1626 cm–1 were consistently red-shifted compared to 2, whilethe 1458 cm–1 Raman band was generally unaffectedby guest encapsulation. In addition, the modes at 1597 and 1574 cm–1 were both red-shifted upon encapsulation of DCN and TCDCB but were both blue-shifted uponencapsulation of DCA. These results indicate that theRaman spectral shifting of the lantern structure is directly impactedby the size and chemical nature of the encapsulated guest molecule.We have also made a generalcomparison of the spectral frequencydifferences between 1H NMR spectroscopy. Several spectra were recordedwith increasing equivalents of DCN with respect to 2 . These experimentsshow that the alkyne stretching frequency of 2 shiftsfrom 2221.0 to 2219.2 cm–1 upon the addition of3.5 equiv of DCN. Significantly, no further shift isobserved, even after the addition of 16 equiv of DCN,with only an increase in the intensity of the signal for free DCN (2231.5 cm–1). These results indicatethat we are observing the binding and saturation of 2 at low equivalents of DCN, which is consistent withour NMR data. This represents the first example (to the best of ourknowledge) of the detection of a host–guest coordination cagecomplex using RS.Last, we examined solution-state experiments, focusing on the alkyne–nitrileregion of the RS, because these two groups cannot be directly detectedusing 2L4 cage compound. This metallosupramolecular structureshows selective and high-affinity binding toward a range of dicyanoarenecompounds. A combination of X-ray crystallography and 1H NMR spectroscopy has provided insight into guest encapsulation,revealing subtle features that affect the relative affinities of differentspecies. Further analysis using RS has shown that this can be a complementaryand informative technique, exploiting reporter functional groups thatare present in many different coordination assemblies. We continueto use these methods to probe the noncovalent chemistry of cage compounds,paving the way to new opportunities in various applications, frommagnetism30 to catalysis.We have described thehost–guest chemistry of a novel Pd


In this study, an artificial intelligence tool called gene expression programming (GEP) has been successfully applied to develop an empirical model that can predict the shear strength of steel fiber reinforced concrete beams. The proposed genetic model incorporates all the influencing parameters such as the geometric properties of the beam, the concrete compressive strength, the shear span-to-depth ratio, and the mechanical and material properties of steel fiber. Existing empirical models ignore the tensile strength of steel fibers, which exercise a strong influence on the crack propagation of concrete matrix, thereby affecting the beam shear strength. To overcome this limitation, an improved and robust empirical model is proposed herein that incorporates the fiber tensile strength along with the other influencing factors. For this purpose, an extensive experimental database subjected to four-point loading is constructed comprising results of 488 tests drawn from the literature. The data are divided based on different shapes (hooked or straight fiber) and the tensile strength of steel fiber. The empirical model is developed using this experimental database and statistically compared with previously established empirical equations. This comparison indicates that the proposed model shows significant improvement in predicting the shear strength of steel fiber reinforced concrete beams, thus substantiating the important role of fiber tensile strength. The concept of fiber-reinforced building materials is by no means new, ancient West Asia, Africa, and South America were the earliest civilizations that were familiar with reinforcing adobe bricks with straw fibers . Much deShear failure is one of the most dangerous types of failure, due to its inherent uncertainty and catastrophic nature. In order to avoid this sudden and explosive failure, typical vertical web reinforcement is provided that is spaced at varying intervals. However, the provision of web reinforcement can be challenging if the available space is narrow, irregular, and congested. In such cases, as pointed out earlier, steel fiber reinforcement can be used to effectively increase the shear strength. Although the use of steel fibers, such as metal chips and screws, started as early as 1910 . ConsequCongestion of reinforcing bars at beam-column intersection and placement of concrete in such a region has been a challenging problem for a long time. Steel fiber reinforced concrete (SFRC) has been suggested as one of the potential alternatives. Wang and Lee  have shoBuilding design codes such as ACI has encouraged the use of steel fiber as a replacement for minimum stirrups . It may,Recently, a new technique of machine learning models has been able to predict the mechanical properties of concrete with higher accuracy. Several evolutionary algorithms for the shear capacity predictions of steel fiber reinforced (SFRC) concrete beams are proposed by different researchers. For instance, two models using multi-expression programming are proposed by Sarveghadi et al. . GreenouThe study is motivated by a similar investigation by Sabetifar et al. , where aThe shear failure of a structural element built from concrete is very dangerous because of the greater uncertainty and the catastrophic nature of failure . This haIdentifying key influencing parameters is the most important step toward generating an accurate model. The influencing factors chosen for modeling the shear behavior of steel fiber reinforced concrete (SFRC) beams herein are the concrete compressive strength, the tensile reinforcement ratio, the span to depth ratio, the fiber aspect ratio, the number of fibers in concrete, the fiber tensile strength, and the span of a beam. Of special interest in these parameters is the fiber tensile strength, which has been overlooked by all the previous studies ,27,28,29Khuntia et al.  have shoFinally, the effect of steel fiber tensile strength has a significant influence on the steel fiber reinforced concrete (SFRC) beams. Studies have shown that the toughness and the shear strength of the RC beam can be increased by improving the tensile strength of the steel fiber . MoreoveBy increasing the reinforcement ratio l action ,32,33.By increasing the effective depth By decreasing the shear span to depth ratio , the normalized shear capacity is increased, as indicated in By increasing the fiber volume fraction This section is concerned with a parametric study performed to enhance the understanding of important factors influencing the shear strength of steel fiber reinforced concrete (SFRC) beams. The aim is to create a set of circumstances across which only one parameter, affecting the outcome of interest, varies. To achieve this objective in the current parametric study, it is essential to make concrete compressive strength uniform, so that its confounding effect is minimized. Therefore, the shear strength values are normalized with respect to the concrete compressive strength to create a circumstance in which the effect of the compressive strength on the outcome is small in comparison with other varying key factors under study. There exists some discrepancy in the literature on whether to normalize with respect to square root or cube root of concrete compressive strength . TherefoBy increasing the fiber’s mechanical and geometric properties, such as increasing the length of fiber or the tensile strength The increase in the diameter of the fiber results in decreasing the shear strength of a steel fiber reinforced concrete (SFRC) beam as shown in The increase in the tensile strength of the steel fiber tends to increase the shear strength of a steel fiber reinforced (SFRC) concrete beam shown in The effect of aggregate size in the steel fiber reinforced concrete (SFRC) beam is observed in Although the shear strength benefits of steel fiber reinforced concrete (SFRC) have been known for a very long time, a systematic study in this context started in the mid-1980s. Much development has taken place since, and various types of steel fiber reinforced concrete (SFRC) have been proposed based on the properties of concrete and steel fibers.Many analytical and experimental investigations have highlighted the effectiveness of steel fibers in enhancing the shear strength of steel fiber reinforced concrete (SFRC) beams, provided care is taken in the selection of these fibers. The details of the experimental results of the shear strength of steel fiber reinforced concrete (SFRC) beams are summarized in Based on the experimental investigation, numerous researchers have proposed prediction equations for the shear strength of steel fiber reinforced concrete (SFRC) beams. These equations are given in An extensive experimental database of 488 experiments of steel fiber reinforced concrete (SFRC) beams without the shear reinforcement is considered for proposing a GEP model. Moreover, only those experiments are reported in this study that have failed in shear. The experimental studies have been undertaken by several other researchers ,101,102 Gene expression programming (GEP)  is a genGEP  selects Over the past decade, structural engineering has seen a significant increase in the use of GEP. Many authors have used GEP to create models for estimating structural component capacities ,20,21. RIn this section, the proposed GEP models for steel fiber reinforced (SFRC) concrete beams are discussed. The GEP  models gThe accuracy of any empirical model is strongly dependent on training and validation sets. It has been shown by several researchers ,108 thatAnother measure is the average absolute error (AAE), expressing the arithmetic average between the model and the experimental observations. The AAE isA commonly used measure to test model reliability is the coefficient of determination  and (8), the approach proposed by Gandomi et al.  is emploxi) are the max and min of the estimated output over the The 2 = 0.97, which shows better prediction when compared to the other available models. In addition, higher performance factor and lower average absolute error suggest the merit of the current model. The model of Imam et al. [The graphical plots of experimental and predicted values are demonstrated herein. It can be seen from m et al.  demonstrThe Chaabene and Nehdi model  has one The remaining models reflect a greater difference in the predictive performance, see Sensitivity analysis is carried out to assess the contribution of each input variable to the predicted value. The frequency values of these variables are presented in It is observed that an increase in the concrete compressive strength, reinforcement ratio, fiber volume, and fiber tensile strength, each increases the shear strength of steel fiber reinforced concrete (SFRC) beams. Contrarily, an increase in the span to depth ratio, the beam effective depth, and the aggregate diameter, each result in a decrease in the shear strength of the beam.The proposed empirical equation can accurately determine the shear strength of steel fiber reinforced concrete (SFRC) beams by incorporating all the aforementioned influencing factors. Moreover, the behavior of different influencing parameters in the proposed model shows consistency with the experimental data.Statistical investigation demonstrates the accuracy and validity of the proposed model, as the values obtained from the statistical analysis are very close to the benchmark values. More specifically, 0.97 of coefficient of determination (R2) is close to the benchmark value of 1.00, which indicates the higher reliability of the proposed model. Similarly, the performance factor of the proposed model is 1.00, which is also the benchmark value. The average absolute error (AAE) of the model is 16%, which firmly confirms the accuracy of the proposed model.A particular virtue of the proposed model is that it can approximate the shear capacity of the steel fiber reinforced concrete beam more closely than other available models. A comparison is made with fourteen different models to evidence the predictive ability of the developed model.In conclusion, it is believed that the proposed regression model offers a robust predictive apparatus for determining the shear capacity of steel fiber reinforced concrete (SFRC) beams. Hence, the model can be confidently prescribed for the shear design of these beams.In future work, it is planned to conduct experimental and numerical studies investigating the effect of steel fiber strength on the shear capacity of steel fiber reinforced concrete (SFRC) beams. This can also be an effective way to further validate the current GEP model.The present study is aimed at developing an efficient genetic shear capacity model of steel fiber reinforced concrete (SFRC) beams in the absence of stirrups. In contrast to the available shear capacity models, the important influencing parameter of fiber tensile strength is implemented in the current model resulting in higher accuracy. A total number of 488 experiments are employed to estimate the shear strength of steel fiber reinforced concrete (SFRC) beams, out of which 190 experiments are used to validate the proposed model. The proposed genetic model is benchmarked against 14 previous empirical or semi-analytical models. The following conclusions are drawn: