The process of concrete cracking is a common problem because the first micro-cracks due to the loss of moisture may appear even before the concrete is loaded. The application of fracture mechanics allows for a better understanding of this problem. Steel-fiber-reinforced concrete (SFRC) samples with a notch were subjected to a three-point bending test, and the results for crack energy were used to analyze the concrete’s material properties. In this paper, an experimental and numerical analysis of SFRC with rapid changes in the force (F) crack mouth opening displacement (CMOD) curve (F-CMOD) is presented. In order to obtain the relevant F-CMOD diagrams, three-point bending tests were carried out with non-standard samples with a thickness equal to one-third of the width of standard samples. For analysis purposes, crimped steel fibers were adopted. A probabilistic analysis of the most important parameters describing the material in question, such as peak strength, post-cracking strength, crack mouth opening displacement (CMOD), fracture energy, and the post-cracking deformation modulus, was conducted. The tests and the analysis of their results show that the quasi-static numerical method can be applied to obtain suitable results. However, significant dynamic effects during experiments that influence the F-CMOD curves are hard to reflect well in numerical calculations. Concrete is the most widely used construction material in the building industry due to its versatility, durability, and feasible application. In order to meet the modern requirements of increasingly complex engineering structures, concrete reinforcements are applied to ensure the desired strength and adequate safety. The porous, heterogeneous structure of concrete with internal imperfections needs to be strengthened to improve its inherently low tensile strength, poor fracture toughness, brittleness, low deformation capacity, and low energy absorption ,2,3.In order to strengthen and improve the mechanical properties of concrete, various types of fibers can be applied to obtain a fiber-reinforced composite (FRC). Carbon or stainless steel fibers are used in FRCs . HoweverGlass, aramid, polypropylene, and basalt fiber additives ,7,8,9 caThe most commonly used fibers in concrete composites are steel fibers . The structural role of this type of fiber is to prevent or delay the propagation of cracks. Fibers can be treated as creating a bridging effect that also allows a homogeneous stress distribution in the concrete matrix ,14,15,16The strength of steel fibers, their geometry , the length of their embedding, their orientation, and their anchoring in concrete determine the strength of the bonds between the fibers and concrete, which plays an essential role in their tearing out due to the behavior of the composite matrix ,23. SteeIf the orientation of steel fibers in the structural elements is consistent with the direction of the main tensile stress, their ductility will be increased. Longbang Qing et al.  found duIn the literature related to the analysis of fiber-reinforced-concrete cracking, one can find various combinations of constitutive models adapted for concrete and for fiber material. An extensive review of both continuum and discrete mechanical concrete models, including crack simulation, was presented by Bolander et al. . The folThe Menétrey–Willam (M-W) model ,32 is alThe Drucker–Prager constitutive model ,34 (D-P)Willam and Warnke ,36 (W-W)The contact density model ,39 was fThe parabolic total strain crack model ,43 repreAnother type of constitutive model is a model of microplates ,45. The The actual concrete fracture specific energy ructures ,48. The ructures  presentsructures . The autructures  presenteAnother approach to the study of the problem of cracking fiber-reinforced concrete composites was proposed by the authors of the article . BearingThe authors improved the model by adopting explicit modeling of the fibers using interference elements between them and the cement matrix. In addition to the mechanical properties, the model also takes into account the geometric properties of the SFRC. The model adopted in this way was verified by means of uniaxial tensile and compression tests and analytical calculations. The results show that an increase in the fiber misorientation angle leads to a decrease in plasticity, while an increase in volume fractions  to solve the problem. A non-standard sample thickness of 1/3 of the width of standard samples was used, as well as an original approach to numerical calculations.Portland cement CEM I 42.5R produced by the Górażdże Cement Plant located in Chorula, Poland.according to the PN-EN 197 Standard was used. The basic physical and chemical properties presented by the cement manufacturer are shown in 3)Proportions of concrete mixtures . In order to reflect the actual behavior of the corrugated fibers, a linear-elastic material model and a material damage model with a material property degradation method were adopted for the analysis, in which the stiffness of the element was reduced as a function of the failure parameter. In terms of the analyzed displacements (crack mouth opening up to 4 mm), such a model is consistent with the realistic behavior of fibers when pulled out of concrete , and theA procedure written in GNU OCTAVE and LISP, similar to the method described in the publication , was useThe equation can represent the stiffness matrix of the bar element subject to failure  58]:(1):(1)58]:(d are given by the following equations [The failure parameters quations :(2)df=dfThe constitutive Menétrey–Willam  model wapression :(6)R¯i=RThe hardening–softening behavior represented by the yield surface evolution is defined by the functions ressions :(7)κi˙=αgiven by :(8)αc=1−E is Young’s modulus, giving the following relationship of the tension yield function for the energy dissipated during softening [The yield function in tension, nsion Gf :(11)Ωt=eoftening :(14)∫0∞ΩA detailed description of the Menétrey–Willam model can be found in .The analysis was based on a transient structural method  in orden vector . The loan vector  using tharameter :(16)δ=12Integrating the motion equations by means of the explicit method leads to several problems in the analyzed subject matter that make it impossible to apply. Among them, one can indicate the length of the time step necessary for a stable solution process, which leads to a very time-consuming calculation.The F-CMOD curves represent the main results of the experimental program where some points of interest can be distinguished . The fird fR,1.5  at 0.5 atermined . The subFor each sample, a similar failure propagation pattern can be observed after the first jump of the F-CMOD plot in the nominal phase of fiber work. After a sudden drop in force, the chart stabilizes, its shape is close to the horizontal position, and further jumps occur at intervals of about 5 mm until complete damage is attained. The jump value is approx. 2 kN.The jumps mentioned above in the force values do not appear in the F-CMOD mean and standard deviation plots, as shown in One particular point can be observed in this diagram, which also occurs for raw data d is beam depth, b is beam width.The fracture energy presented in Wt(d−a0)b, where WIn order to analyze the random changes in the fracture energy and parameters affecting the strength and deformation process of the bent samples , the essThe results of the numerical calculations are presented in The plots of the mean value, standard deviation, and skewness  give a sThe analysis in this paper described sample cracking during bending with a thickness similar to the correlation length usually assumed in the stochastic concrete analysis. A thickness of 1/3 of the standard thickness of concrete samples (50 mm) with steel fibers in the amount of 25 Taking into account the above discussion, the following conclusions can be made:1. Using cracking energy parameters, the authors presented another approach to identifying the mechanical properties of a concrete composite reinforced with steel fibers.2. The applied probabilistic analysis allowed us to obtain results describing the most important parameters of the tested material, such as peak strength, fracture toughness, crack opening displacement (CMOD), fracture energy, and modulus of elasticity after a fracture.3. The constitutive Menétrey–Willam model was used for the analysis, which helped solve the problem.4. To solve the problem, experimental studies were carried out on more samples (30 pcs.). The authors used a non-standard sample thickness of 1/3 of the width of standard models and an original approach to numerical calculations.5. In experimental studies, there was a tendency for a sudden decrease in strength with a concomitant increase in CMOD. This phenomenon did not occur when testing samples with greater thickness.6. The authors found good agreement between the experimental results and those obtained in the numerical simulation. However, the simulations did not show such significant drops in force with a simultaneous increase in CMOD.


The causes of cracks in concrete are varied, and regardless of their origin, these cracks invariably have a detrimental impact on the durability of concrete structures and escalate their maintenance costs. This paper presents a comprehensive review of current knowledge regarding the methods of self-healing in concrete, ranging from autogenic and improved autogenic self-healing to the autonomous self-healing of concrete. Particular emphasis is placed on the methods of autonomous concrete self-healing: the bacterial healing method, the crystalline hydrophilic additives healing method, and the capsule-based self-healing method. The hypothesis is that applying these self-healing methods could potentially prevent damages or cracks in concrete caused by freeze–thaw cycles, thereby extending the lifespan of concrete structures. The mechanism of action and current achievements in the field are provided for each method. Cracks in concrete (and in reinforced concrete) are a fairly common occurrence. In specific scenarios, these cracks in concrete do not cause harm and are entirely acceptable. In other instances, cracks are severe defects because they negatively impact the concrete’s strength, function, or appearance. Gardner et al. , in theiGolewski  categoriA frequent method of crack remediation (whether due to freeze–thaw or other causes) cited by Gardner et al.  is repaiIn the study conducted by Gardner et al. , nearly Autogenous healing is essentially a natural process induced by physical, chemical, and mechanical processes ,31, as dConcrete swelling is a slow and partially reversible process caused by water absorption of cement stone. Cracks healed solely by this method may leak again. According to Edvardsen , the max2 from the air enters the concrete and reacts with H2O, forming H2CO3. Subsequently, 2+ ions in the concrete to form CaCO3, which, once its solubility in water is exceeded, begins to deposit along the crack edges, healing them. According to Edvardsen [Continued hydration is, in fact, the hydration of unhydrated cement particles in concrete, with these unhydrated particles comprising up to 50% of the cement’s mass in conventional concrete . When co3 sediment/precipitate. Adding silicates to the concrete mix affects the pozzolanic reaction, the healing process duration, and the consumption of Ca(OH)2. The concrete grade is associated with the water-to-cement ratio, the binder’s ability to develop a substantial amount of CSH gel due to hydration, the type of binder, and its amount. Water presence is vital for the autogenous self-healing phenomenon because it enables chemical reactions and it is a transport medium for particles. In this context, water immersion is considered the most appropriate for healing, followed by wet–dry cycles [3 can quickly form due to the high availability of carbon dioxide (CO2) in the air. The maximum crack width that can be healed by autogenous healing is 150 µm [Due to the cracking process of concrete, tiny particles are detached and carried by water through the crack, blocking it and thus participating in the crack healing process. According to Meichsner and Röhling , this isy cycles . The lats 150 µm  or even s 150 µm . Althougs 150 µm , researc4 or MgSO4 solution) to improve the crack healing effect through the electrodeposition method. They concluded that both electrolyte solutions were equally effective, and the optimal CTAB amount was 1%, ensuring the most effective healing. Autonomous healing will be the subject of the next section.Improved autogenous healing refers to healing boosted by the addition of fibres  to the concrete that limit crack width or directly influence the uniform distribution of micro-cracks instead of macro-cracks or by replacing some of the binders with fly ash or slag, which slows down the hydration rate, thus reducing crack formation. Superabsorbent polymers have been reported as effective . In termAutonomous healing implies healing induced by “artificial means”. Autonomous self-healing techniques include the bacterial method, the application of crystalline hydrophilic additives, and the microencapsulation method . Each of4+) and carbonate ions CO32−, which leads to the formation of calcium carbonate. 2+, to deposit on the surface of their cell. Ca2+ ions react with CO32− in preparation for the deposition of calcium carbonate on the cell surface, which serves as the site of nucleation.Certain bacteria added to concrete create urease, which catalyzes urea into carbonate and ammonium, which results in an increase in the pH value of the concrete and an increase in the concentration of carbonate in the bacterial environment. These components further hydrolyze into ammonium . “Unprotected” refers to bacteria directly introduced into the concrete mix. Pseudomonas aeruginosa and Diaphorobacter nitroreducens showed a better ability to survive in concrete when protected.Çağatay Erşan et al.  investigBacillus sphaericus. Wang et al. [3)2·4H2O), group H includes samples with hydrogel, and group HS comprises samples with hydrogel on which bacteria are encapsulated. A crack was initiated on the concrete cylinders, and they were exposed to an environment of 60% and 95% humidity as well as to dry–wet cycles (1 h in water and 11 h in air at 60% humidity) for 4 weeks. No crack healing was recorded in 60% and 95% humidity, but there was crack healing during dry–wet cycles and in such a way that the best healing was recorded by the group of samples HS, followed by groups H and N, and the lowest healing was recorded by the mixture R. Zhang et al. [Sporosarcina pasteurii in alkali-activated concrete. They studied the self-healing of alkali-activated concrete with expanded glass granules without bacteria and concrete with bacteria  introduced into the concrete on a carrier of expanded glass granules. Cracks were initiated on the concrete samples, and their healing was monitored for 90 days. On concrete samples with bacteria  introduced on a carrier made of expanded glass granules, healing was monitored in water and during wet–dry cycles. Concrete with bacteria healed better than concrete without bacteria, and healing was more efficient in concrete cured with wet–dry cycles than in concrete cured in water. In another paper, Zhang et al. [Bacillus cohnii introduced directly into the concrete, and concrete with Bacillus cohnii introduced into the concrete on a carrier made of expanded perlite and expanded clay. The most effective healing was recorded with the mixture with Bacillus cohnii on expanded perlite, followed by the mixture with Bacillus cohnii on expanded clay. The mixture with Bacillus cohnii directly introduced into the concrete healed better than the reference mixture but worse than the mixtures with Bacillus cohnii on a carrier of expanded perlite or expanded clay. Microscopic analysis confirmed calcite crystals as healing products. Çağatay Erşan et al. [Pseudomonas aeruginosa and Diaphorobacter nitroreducens on a carrier of expanded clay and granular activated carbon and concluded that both types of bacteria are equally effective on both carriers in the self-healing process of cracked concrete. Microscopic examination of the concrete confirmed CaCO3 as a product of crack healing.Wang et al. , Zhang eg et al.  made foug et al.  investigg et al.  also stun et al.  investigBacillus pseudomycoides bacteria and control concrete. In order to initiate the self-healing process, a cylindrical sample with a crack was immersed in water at a temperature of 30 °C, which simulates the surrounding tropical temperature with a pH value of water of 7.8. The width of the crack was observed. The results of testing the compressive strength of concrete with bacteria were on average 16% higher than the compressive strength of the control concrete. This is attributed to the microbial deposition of calcium carbonate within the concrete core, as the microbial product filled the microcracks and pores of the concrete. In concrete with bacteria, the crack was completely healed through the deposition of microbes later identified as vaterite and calcite. Safiuddin et al. [Bacillus subtilis and Escherichia coli bacteria separately and in combination on concrete self-healing and compressive strength. Each bacteria was separately dosed into concrete in the amount of 2%, 3%, 4%, and 6% according to the weight of the cement, while in combination (50% each) they were dosed into concrete in the amount of 2% and 3% according to the weight of the cement. For testing compressive strength and monitoring self-healing, cubes were made, and for testing the tensile strength by splitting, cylindrical samples were prepared. It was concluded that cracks were completely healed within 48 h for 2% Bacillus subtilis, 32 h for 3% Bacillus subtilis, and 72 h for 4% Bacillus subtilis. The most favorable proportion of Bacillus subtilis bacteria for self-healing concrete would be 3%. Escherichia coli bacteria had no effect on self-healing. Separately, each of these bacteria had a positive effect on the development of compressive strength, with the bacterium Escherichia coli having a greater impact. Bacteria combined had a negative effect on the compressive strength of concrete. Separately, each of these bacteria had a positive effect on the development of splitting tensile strength, with Escherichia coli having a greater influence again. In their paper, Khaliq and Ehsan [Bacillus subtilis, which, in the form of a solution, was added directly to the concrete mixture (mixture two), via lightweight aggregate (LWA) soaked in the bacteria solution (mixture three) or via graphite nanoparticles (GNPs) soaked in the bacteria solution (mixture four), while the control mixture was mixture one. The compressive strength with the addition of Bacillus subtilis (mixture two) proved to be better at all studied concrete ages than the compressive strength of the control concrete (mixture one). The technique of introducing bacteria using the LWA method (mixture three) proved to be particularly effective. All mixes with bacteria showed better healing over time than the control mix (mixture one). For cracks initiated on the 3rd and 7th day of concrete age, the most effective method was the introduction of bacteria through GNP (mixture four), while in the case of cracks initiated on the 14th and 28th day of concrete age, the most effective method was the introduction of bacteria through LWA (mixture three).In addition to testing self-healing, the influence of bacteria on compressive strength was also tested, and Algaifi et al.  comparedn et al.  observednd Ehsan  used BacBacillus subtilis bacteria and compared their compressive strengths at the age of 7 and 28 days and their porosity. The results of their test showed that dead and live Bacillus subtilis cells had a negative effect on the compressive strength of the cement mortar samples, while Bacillus subtilis walls increased the compressive strength by 15%. The increase in the compressive strength of concrete with Bacillus subtilis cell walls is a direct consequence of the reduction in porosity of such concrete, and the reduction in porosity directly affects the increase in durability of such concrete. In their research, Jiang et al. [Bacillus subtilis (BS) in concrete. They prepared a reference concrete mix, a mix with coal, a mix with BS and calcium lactate as a nutrient, and a mix with coal mixed with BS and calcium lactate as a nutrient. The results show that the addition of BS to the mixture improved the compressive strength of the concrete in all observed periods, and this improvement was more pronounced when BS was immobilized with coal in the mixture. The mixture with BS showed reduced water absorption over time compared to the reference mixture, and the mixture with BS-immobilized coal showed a drastically reduced water absorption. The self-healing of concrete in water with a previously initiated crack was most pronounced in the mixture in which BS was immobilized with coal, and it was slightly less pronounced in the mixture with BS, while the least pronounced was in the reference mixture. SEM, EDS, and XRD analyses confirmed that the healing product is actually CaCO3. Achal et al. [Bacillus subtilis (BS). The addition of BS to the mortar increased the compressive strength of the mortar by 40%, reduced the porosity of the mortar by 50%, and significantly reduced chloride penetration and improved the healing of previously induced cracks. Namely, CaCO3, which forms in cracks as a self-healing product, is also generally formed in concrete with bacteria and densifies the concrete structure, thus positively affecting the durability properties, and mostly (depending on the type and concentration of the bacteria) also the mechanical properties of the concrete. The increase in the compressive strength of concrete with bacteria is a direct consequence of the decrease in porosity of such concrete, and the decrease in porosity directly affects the increase in durability of such concrete. The lower the water permeability coefficient, the better the effects of self-healing of cracks.In addition to self-healing and compressive strength, among Pei et al. , Jiang eg et al.  saturateg et al.  studied l et al.  comparedCrystalline admixtures (CA) are predominantly commercially available products from various manufacturers . They serve a dual purpose: reducing concrete permeability and healing cracks. Their recommended incorporation into concrete ranges from 0.3% to 2% according to the weight of the cement . The phyPrecipitation Reaction Mechanism—active chemicals penetrate the concrete with water and react with the free lime and oxides in the pores, forming crystalline materials that block pores and cracks. Water is a critical factor stimulating the crystal precipitation in the crack due to the reactive and hydrophilic nature of crystalline admixtures. The reaction between the active compound of the crystalline additive and tricalcium silicate in the presence of water forms a denser calcium silicate hydrate. The effect of the calcium additive can lead to pore clogging, creating a hydrophobic layer in the capillaries, or both. Crystalline additives block pores and, in doing so, deposit hydrates in the cracks to resist water ingress under pressure.2+ in concrete, forming an unstable complex that disperses in the pore solution. Complex ions are replaced with SiO32− on non-hydrated cement particles to form C–S–H gels and fill the pores. Active chemicals become free again and continue to diffuse in the solution. The primary identified products of hardened paste are ettringite and calcium silicate hydrate. The primary process for external crack healing is the formation of calcium carbonate, resulting from the action of calcium additives. The interaction of carbonate and bicarbonate ions leads to the precipitation of calcium carbonate, which is associated with increased material durability.Complexation Precipitation Reaction Mechanism—active chemicals bind with CaCombined Mechanism of Precipitation and Complexation Reactions—part of the active chemicals participates in the capillary crystallization reaction, while another part catalyzes the hydration of non-hydrated cement particles. Limestone formations react with tricalcium aluminate and form different calcium carboaluminates, such as hemi-carbo aluminate, mono-carbo aluminate, and tri-carbo aluminate. Silicate formations (ground quartz) react with calcium hydrate. Limestone formations have a much higher moisture absorption capacity. The high affinity between limestone formation and calcium aluminate favors the crystallization of mono-carbo aluminate over mono-sulfate. This process results in reduced porosity and an increase in the volume of hydrated phases.Condensation Crystallization Mechanism of Active Chemicals—these substances form insoluble crystals through condensation polymerization to fill cracks and pores.The following four mechanisms describe the self-healing process of concrete with crystalline admixtures :PrecipitThe mechanisms described above are schematically depicted in In their research, various authors observe the effect of such admixtures on concrete’s mechanical and durability properties and the concrete self-healing process. 2SO4 in the amount of 3 or 5% of the cement mass or Al2(SO4)3 in the amount of 3% of the cement mass. Cylindrical samples were made of concrete mixtures, on which a crack was generated, and the samples were placed in a device for measuring the speed of water flow. As the self-healing of the concrete progressed, the rate of water flow decreased. At the same time, the amount of self-healing product was monitored on the crack surfaces. The results show that all mixtures achieved a greater amount of self-healing product per crack and more intense self-healing than the control mixture, and the most effective in self-healing was the combination of CSA with crystalline hydrophilic additives. Roig-Flores et al. [In the following four studies, Park and Choi , Roig-Fls et al.  investigs et al.  investigs et al.  investigs et al.  analyze In their paper, Elsalamawy et al.  studied The following investigations ,73,74,75Reddy and Ravitheja  tested tZhang et al.  investigAzarsaa et al.  preparedThe encapsulation method is considered a versatile and effective strategy for self-healing. In capsule-based self-healing, the capsules provide mechanical protection to healing agents and release them upon being triggered by cracks (either through capsule rupture or diffusion), moisture, air, or changes in the pH of the pore solution in the matrix. When cracking is the trigger mechanism, capsules break, and the healing agent is drawn into the crack via capillary action . CapsuleResearchers, in their studies, utilize capsules that are either (1) mixed into the concrete or (2) embedded into previously drilled holes in the concrete or installed in molds/formwork before pouring the concrete mixture. Capsules mixed into the concrete are usually small and are referred to as microcapsules or nanocapsules due to their size, while the size of the latter type of capsule is measured in centimeters. Microcapsules/nanocapsules can be either single-component or multi-component capsules. The following four studies show the influence of capsules on crack self-healing. Milla et al.  explored2 melted at 120 °C and mixed at 800 RPM. The highest compressive strength was observed in the mortar with capsules made of paraffin melted at 75 °C and mixed at 600 RPM. Crack initiation and subsequent healing were monitored in these mortar samples over 1, 3, 7, and 10 days at room temperature. The mortar with the paraffin, wax, and nano SiO2 melted at 120 °C and mixed at 800 RPM showed the most successful healing. In final paper by Du et al. [2 melted at 120 °C and mixed at 800 RPM.In the subsequent three studies, Du et al. ,82,83 in2CO3 carrier in concrete mixes. They prepared three concrete mixtures, and on the samples they tested the compressive and tensile strength of the samples over time. Chloride penetration and crack healing were initiated at 7 and 28 days of age, and then the samples were immersed in water and a solution saturated with Ca(OH)2 for 28 days. The results show that ELWA, impregnated LWA protected by a coating of epoxy resin, curing reagent, and n-butyl glycidyl ether (mixture M3) provides the best compressive and tensile strengths of concrete over time, followed by LWA impregnated with Na2CO3 (mixture M2). Chloride penetration is the smallest in the mixture where LWA is saturated with Na2CO3 (mixture M2). The self-healing of cracks is best with the ELWA mixture (Mix M3), followed by the mixture with LWA soaked with Na2CO3 (Mix M2). Wang et al. [2 than in water. In their research, Wang et al. [Other researchers ,85,86,873. Apolinário de Oliveira et al. [2SiO3 solution to obtain an SS01 capsule shell or only with a Na2SiO3 solution to obtain an SS02 capsule shell. The capsules thus prepared were added to the mortar by replacing the volume of sand in the amount of 5, 10, and 20%, and prisms were made from the mortar and cured for 28 days in water. Flexural strength, compressive strength, and modulus of elasticity were tested on part of the prisms. A crack was initiated on part of the prisms by applying three-point bending, and they were placed in contact with water to stimulate the self-healing process. To evaluate the self-healing of the mortars, water absorption on the prisms was monitored on the 14th and 28th days, and the water absorption reduction coefficient was calculated from the water absorption. From the obtained results, it is evident that both types of capsules improve the mechanical properties of the mortar and that the SS02 capsules are more successful in this. Furthermore, the water absorption reduction coefficients increase as the proportion of both types of capsules in the mortar increases, and the reduction is greater with the use of SS01 capsules. In their research, Dong et al. [In the papers that follow, Feng et al. , Apolináa et al.  compareda et al.  producedg et al.  made micHilloulin et al. , in theiDeveloping suitable capsules is paramount for achieving encapsulated self-healing. In the context of self-healing concrete, capsules that can easily be mixed into the concrete and release the healing agent upon cracking are ideally required. Optimizing these properties would enable successful large-scale implementation in practical applications . MicrocaThis study systematically presents the state of the art of methods for concrete self-healing while emphasizing autonomous self-healing . It evaluates the diverse properties of concrete both before and after the self-healing process. The mentioned methods could serve as an intelligent approach to enhance the concrete’s resistance to freeze–thaw cycles and extend the lifespan of structures. Taking action during concrete mix preparation for incorporation into structures makes it possible to minimize damages/cracks resulting from freeze–thaw cycles, thereby significantly reducing the inspection labor and maintenance costs of such structures . The app


AAS offers great ecological advantages over OPC at some levels such as the utilization of industrial by-products and overcoming the issue of disposal, low energy consumption, and low greenhouse gas emission. Apart from these environmental benefits, the novel binder has shown enhanced resistance to high temperatures and chemical attacks. However, many studies have mentioned the risk of its considerably higher drying shrinkage and early-age cracking compared to OPC concrete. Despite the abundant research on the self-healing mechanism of OPC, limited work has been devoted to studying the self-healing behavior of AAS. Self-healing AAS is a revolutionary product that provides the solution for these drawbacks. This study is a critical review of the self-healing ability of AAS and its effect on the mechanical properties of AAS mortars. Several self-healing approaches, applications, and challenges of each mechanism are taken into account and compared regarding their impacts.Alkali-activated slag (AAS) has emerged as a potentially sustainable alternative to ordinary Portland cement (OPC) in various applications since OPC production contributed about 12% of global CO Infrastructures are always susceptible to severe changes in durability induced through multiple cracking. These changes are often related to the influence of shrinkage, mechanical loads, and/or environmental impact. Durability has a drastic influence on the structural resiliency and sustainability of concrete structures ,2,3,4. O3 and/or hydrating the unreacted cement particles and producing extra C-S-H in the crack flanks. Meanwhile, autonomic healing is activated through means of artificial healing materials, for instance, bacteria, chemical admixtures, or microencapsulation [Biological systems such as human organs and animal bodies are capable of self-healing and restoring their original functions. Scientists are inspired by this concept and realized the ability of concrete to heal cracks. Self-healing was discovered in cementitious material where concrete was found to heal cracks under normal conditions ,8. Nevilsulation ,2,11,12.2) is emitted into the atmosphere [2 emissions in 2020 were due to OPC production [In recent years, alkali-activated composites have been considered a strong competitor to replace ordinary Portland cement (OPC) concrete in various applications. The utilization of OPC is an energy-intensive process that consumes a large number of natural resources and releases a large amount of carbon dioxide gas. It was found that for the production of 1 ton of cement, 1.5 tons of raw materials is consumed and 1 ton of carbon dioxide gas  is one of the most important challenges of alkali-activated concrete, especially with a slag basis. It was reported that the shrinkage may reach about two to four times higher when compared to OPC ,23,24. TThe higher shrinkage reported in AAS composites compared to OPC is associated with the finer pore structure and lower stiffness, as illustrated in 2 into the external surface of the binder [Shrinkage takes place in two phases, plastic and hardening stages, and it is described as an inherent property of cementitious material. Slag paste and alkaline activators are the main materials in AAS concrete. Based on the different ways shrinkage takes place, it is classified into plastic, autogenous, drying, and carbonation shrinkages. Plastic (or young) shrinkage takes place immediately upon pouring concrete into a mold, and water evaporation is the main cause of this phenomenon. Autogenous shrinkage  is an unavoidable reduction in volume produced by the macroscopic process of self-desiccation and the chemical reaction of concrete. Autogenous shrinkage commonly occurs when concrete has a low cement-to-water ratio ,19. Dryie binder .3 prisms as per Australian Standard AS1012.13 at 23 °C for 24 h followed by exposure to 23 °C and 50% relative humidity (RH). Thus, the only way to differentiate between drying and autogenous shrinkage is to use the developed ring test or the generation of restrained shrinkage prisms by modifying the Australian Standard AS1012.13 [Consequently, the predominant shrinkage mechanisms in alkali-activated composites are autogenous and drying shrinkage, which are linked to losing the internal hydration water and the formation of capillary stress  and the S1012.13 ,28,29,30There are several ways mentioned in the literature to mitigate the high shrinkage in AAS. These ways include factors that might not only influence the shrinkage but might adversely affect mechanical and fresh properties of the produced concrete. As is clear from 2 [+ and OH−, retarding the hydration reaction. Although there was slight variation in the studies that explored mineral admixtures’ influence on shrinkage and strength, many scholars suggested that, generally, the mineral admixtures can help in reducing shrinkage but lead to a reduction in the strength of the AAS. A few suggested researchers [On the other hand, replacing the slag with mineral admixtures such as silica fume and fly ash would weaken the strength development. Several researchers ,22 explo2 . Moreoveearchers ,26 that earchers  stressedSimilar to the mineral admixtures, chemical admixtures could influence the shrinkage, especially regarding the expansion and shrinkage of concrete using shrinkage-reducing admixtures, expansive agents, and superabsorbent polymers. The idea mainly relies on reducing the surface tension of the pores by increasing the coarseness of the pore structure and increasing the micropores ,26. NeveFurthermore, fibers are another method that effectively controls shrinkage. The inclusion of fibers reduces shrinkage and enhances flexural strength through ties that resist tensile stresses resulting from pore capillaries. Fibers serve as a restraint in the composite, known as the fiber-bridging effect, creating composite stability and resisting any change in the paste volume. However, it should be highlighted that optimization of fiber dosage is an important aspect as it could negatively influence both shrinkage and strength. Puertas et al.  and HammAs curing affects the addition of fiber, it is a factor that affects the shrinkage. Shrinkage is reduced when elevated-temperature curing occurs as reported by Awoyera and Adesina . Their rAll these mitigation processes reduce the shrinkage up to a specific threshold; however, these processes might adversely affect the overall compressive and flexural strength or increase the embodied energy in AAS systems . FurtherNot only would shrinkage cracking be the main issue to overcome in AAS but also its high susceptibility to cracking because of the intrinsic brittleness ,36,37. GMany researchers ,11,40,41Cracks, on either a macro or micro scale, could significantly induce a series of problems in terms of deflection and aesthetics, interfering with durability and serviceability. Consequently, crack characterization of structural elements is controlled by the serviceability limit state based on the code and guidelines required for design. The crack width and depth should be the main aspect of self-healing technology; however, as shown, self-healing could provide a reduction in crack width of nearly 1 mm (≈970 µm) which exceeds the size of most of the limited cracks under serviceability loads as per ACI 318. Thus, several techniques and mechanisms are reviewed in the next section to understand how these mechanisms and techniques would work in healing the cracks of AAS structures.3 to seal/fill the cracks [Autogenous healing is the ability of concrete or the conventional ingredients of the cementitious matrix to recover from damage. The specific chemical composition of the cementitious matrix is the main reason for this process to take place . Generale cracks ,10,11. According to substantial experiments and practical application, an autogenous self-healing mechanism is a combination of complex chemical and physical processes. As stated by most of the studies in the literature ,10,11, vMore than one of the proposed causes can occur simultaneously. However, most of the mechanisms can partially fill the entrance of some cracks but cannot fill the crack. This could help in preventing the development of further cracks or control the deep penetration of harmful chemicals. Crystallization of calcium carbonate is the most effective method to heal the crack naturally. This is proved by the common observation of macroscopically and microscopically precipitated calcium carbonate on the crack surfaces as a white residue. Dissolving one of the cement hydration products in water is an essential condition for calcium hydroxide to be liberated and dissipated along the cracking surfaces ,10,11. T3 crystals depend on the pH, the surrounding temperature, the partial pressure of CO2, the calcite saturation, and the concentration of Ca2+ and Locations of CaCOsolution . The othsolution .3. The mechanical process comprises crack closing with the generated particles from the crushed concrete surface or impurities from water ingress [By observing surface cracks, calcium carbonate and calcium silicate hydrates were recognized as the main products of the self-healing process. The percentage of the formed C-S-H (<15%) was considerably lower than the percentage of the produced calcite which was 80%. It was realized that there is an obvious decline in the intensity of the self-healing efficiency after about 300 h . Autogen ingress . Different studies were conducted to study the efficiency of the autogenous self-healing mechanism and the factors affecting it. It was found that this process is effective for small crack sizes, however, sometimes larger crack widths (between 200 µm and 300 µm) were observed ,41,51,522 in the AAS mix led to higher Ca2+ concentration due to the low solubility of Ca(OH)2 at a high pH level before cracking takes place. Consequently, Ca2+ was not consumed during the geopolymerization process. After the activation process of AAS, Ca(OH)2 dissolved in the curing water, providing calcium carbonate precipitation [Limited research has been devoted to studying the autogenous self-healing property of AAS ,53,54. Tpitation  as illus3 through various intermolecular forces such as ionic bonding, hydrogen bonding, and van der Waals forces [The addition of polyvinyl alcohol (PVA) and polyethylene (PE) fibers showed a tendency towards enhancing the healing property of AAS ,57,58,59s forces . Anothers forces  tested tRecently, autonomous self-healing has attracted considerable attention. Autonomous concrete healing is an artificial healing mechanism that occurs when an appropriate healing agent is added to concrete. Accordingly, the healing and blocking of cracks can be carried out automatically without any external aid or repair at ambient room temperature. This type of healing takes place through chemical and biological processes ,44,45,52One of the new approaches in autonomous self-healing uses the injection of chemical compounds into concrete cracks. This chemical process could be carried out by mixing fresh concrete with (liquid) chemical reagents such as glue. For accomplishing this process, there are several methods, for example, hollow pipette and vessel networks containing glue and encapsulated glue. The hollow pipette concept is inspired by blood vessels in animals. These pipettes or vessels (classified by diameter size) provide a medium for storing functional components or healing agents. Pipettes are embedded within the composite matrix. When concrete is subjected to damage or cracking occurs, the healing material will flow out to start the healing process. Either the hollow pipettes or the vessel networks can be used to design a self-healing concrete based on passive or active mode. The passive mode uses hollow vessels that are not linked to an external glue source, while the active mode needs an external supply of glue for distribution . SystemsMethyl methacrylate, ethyl cranoacrylate, acrylic resin, and epoxy are different examples of healing materials (glue) that are suitable for filling the hollow pipettes. A network of vessels was applied within a concrete specimen for the distribution of glue. This brittle vessel network inside concrete was connected at one end to a glue supply, whereas the other end was sealed inside concrete. Another study proved that this technique used in a concrete specimen resulted in a 20% increase in the loading capacity under a subsequent flexural test . DespiteThe encapsulation technique was inspired by examples in nature, ranging from the macro scale (bird’s egg or seeds) to the micro scale (cells). Microencapsulation involves the development and preparation of capsules containing dyes that were originally for paper copying and eventually replaced with carbon paper. White et al.  developeMany researchers believed that this technique is versatile due to its efficiency in regaining the mechanical properties and the durability of concrete ,64. This2SiO3)) in the case of using one component as a healing agent for activation due to its ability to act individually. For the other two types, another substance, for example, dicyclopentadiene (DCPD), is required to achieve maximum efficiency. Practically, two or more component systems are found to be more complicated and have a high risk of inappropriate mixing that may cause inefficient crack healing. Moreover, optimum fluid with low viscosity is a vital factor for controlling the healing material transportation and penetration through the crack as well as solidifying in the desired locations [Different types of healing agents are used for the self-healing process as listed in ocations . Basicalocations ,64.Despite the remarkable progress accomplished in adopting this technique in OPC-based systems, no studies have introduced microcapsules in AAS-based composites and evaluated their performance.5Al3)(SiAl)O10(OH)5) and calcium carbonate (CaCO3) [This process is an environment-friendly mechanism that takes place by adding microorganisms to concrete. For that, it has been categorized as a biological strategy. The reason for choosing microorganisms is their wide availability . There are several types of microorganisms, for instance, bacteria, fungi, and viruses. Among these types, it was found that a certain strain of bacteria could be considered due to its ability to precipitate certain useful chemicals used in the design of biological self-healing concrete. These useful precipitation chemicals are polymorphic iron aluminum silicate ((Fe (CaCO3) ,41. For governing bacterial self-healing, there are two processes: (a) bacterial metabolism, and (b) enzymatic ureolysis. In the first mechanism, bacteria are present as a catalyst that converts the precursor compound into a filler material. The produced filler material is a calcium carbonate-based mineral that acts as a type of bio-cement and seals cracks . The rea2 starts a localized reaction with Ca(OH)2 within the crack mouth. As a result, five more CaCO3 molecules are produced [This type of reaction is six times more effective compared to autogenous self-healing as the produced COproduced . 2)2) into ammonium :Carbonate is simultaneously hydrolyzed to produce ammonia and carbonic acid: Carbonic acid is hydrolyzed into carbonate ions and hydrogen ions:Ammonia is spontaneously hydrolyzed to produce ammonium and hydroxide ions:The production of hydroxide ions increases the pH value and causes the overall equilibrium to form carbonate ions:2+) to form the precipitation of calcium carbonate (CaCO3) at the cell surface:The negative charge of the produced carbonate ions attracts the positively charged calcium ions  and (13)). This high-alkalinity solution is considered to be harsh for the bacteria’s survival. Furthermore, the fresh concrete’s temperature, which is around 70 °C, is too high for cell growth. Not only is temperature one of the drawbacks but so is water scarcity for cell growth once fresh concrete hardens. As a result, the chosen type of bacteria has to show high resistance against the high pH, temperature, and massive limitation of water . The bacaterials ,77,81,82The effects of bacteria on the compressive strength and transport properties of concrete are listed in 3 as previously stated by different researchers. Moreover, the tensile strength along with the tensile strain increased significantly by 150% and 234% during the reloading tests after crack healing [+2 ions in the AAS matrix. This led to reducing the diameters of capillary pores by about 37% and 23% in calcium hydroxide and zero calcium hydroxide specimens [Sporosarcina pasteuri in the crack healing property of AAS mortar was investigated using porous expanded recycled glass granules as bacterial carriers. Most of the crack surfaces under 100 μm were entirely healed after 5 months of curing. Bio-based samples showed enhanced crack healing with a maximum width of 140 μm. Increases in compressive strength of 7% and 14% have been observed for bacterial-based specimens incorporating calcium lactate and calcium chloride, respectively. The usage of a combination of bacterial nutrients  and porous expanded recycled glass granules led to a decrease in mechanical properties. However, the final strength increased by 7% due to the positive effect of the immobilized bacteria [According to the literature, few studies have investigated the self-healing property of alkali-activated concrete. Zhang et al.  explored healing ,59. The pecimens . The potbacteria . Consequbacteria ,54,98.The innovative technology of alkali-activated composites is known for its small carbon footprint and energy savings. These smart sustainable composites offer an eye-catching combination of good-quality mechanical properties and durability. However, degradation initiated at a very early stage may put a limitation on their usage as construction materials. The volumetric instability of AAS is two to four times higher than that of OPC composites. The finer pore structure of AAS, the lower stiffness, and the presence of alkali metals in the hydration products (C-S-A-H) are reported to be the main causes of this higher shrinkage. Based on this critical review, this research suggests producing smart alkali-activated composites with self-healing properties, which would provide a self-repairing structure with the minimal help of external maintenance.The natural self-healing mechanism could occur due to any of the following reasons: formation of calcium hydroxide or calcium carbonate, further hydration of the unreacted particles of cement, swelling of the hydrated cementitious matrix (C-S-H) in the crack flanks, or blocking of cracks by impurities in the curing water. More than one of the mentioned causes may occur.Clinker content in cement, hydration age, crack geometry, exposure condition, and addition of fiber or additives could enhance the efficiency of autogenous crack healing.Innovative techniques of chemical and biological self-healing have been proposed. The mentioned strategies are hollow vessels, encapsulation, and immobilization of bacteria. The idea of these methods is to prompt the intrinsic self-healing property of concrete to produce calcium ions and supply the cementitious matrix with external chemical or functional materials to provide better healing capacity.Bacterial-based bio-concrete is a remarkable solution because it showed enhanced results and an eco-friendly practical process. Nevertheless, the efficiency of the healing process depends on the proportion of the unreacted matrix that will respond to the introduced healing agent, and crack geometry and size play a vital role in predicting effective healing.From the available limited literature, it seems feasible to prompt the production of alkali-activated self-healing composites with a good crack-healing ratio and improved mechanical properties.Curing methods, including cycling air and wet methods, wetting and drying for just 24 h, wetting and air drying for 3 h, air drying, and oven drying. To date it is not clear which curing method would be suitable.Although it was stated that sodium concentration is a parameter, limited studies have mentioned the possibility for bacteria to die before activation; however, none of them mentioned the concentration percentage at which the bacteria will not be influenced.As discussed earlier, several parameters could influence the shrinkage of AAS and there are several solutions to overcome this shrinkage. The most commonly suggested is an autonomic healing solution. However, very few researchers work in this area, and the following points still need to be discussed:


Are antibiotics and antibiotic exposure timeframes associated with acute graft-vs-host disease (aGVHD) after allogeneic hematopoietic cell transplantation ?In this cohort study including 2023 patients and using 3 orthogonal approaches applied to antibiotic use between 7 days before and 30 days after allo-HCT procedures, several antibiotics and exposure timeframes were found to be associated with aGVHD rates. Most notably, carbapenems and penicillins with a β-lactamase inhibitor used during the first 2 weeks after allo-HCT were consistently associated with increased hazard of aGVHD.These findings suggest that aGVHD risk should be considered in antibiotic stewardship programs during allo-HCT. This cohort study uses 3 modeling methods to identify antibiotics and antibiotic exposure timeframes associated with hazard of acute graft-vs-host disease after allogenic hematopoietic cell transplantation. Certain antibiotic exposures have been associated with increased rates of acute graft-vs-host disease (aGVHD) after allogeneic hematopoietic cell transplantation . Since antibiotic exposure can both affect and be affected by infections, analyzing time-dependent exposure in the presence of multiple potential confounders, including prior antibiotic exposures, poses specific analytical challenges, necessitating both a large sample size and unique approaches.To identify antibiotics and antibiotic exposure timeframes associated with subsequent aGVHD.This cohort study assessed allo-HCT at a single center from 2010 to 2021. Participants included all patients aged at least 18 years who underwent their first T-replete allo-HCT, with at least 6 months of follow-up. Data were analyzed from August 1 to December 15, 2022.Antibiotics between 7 days before and 30 days after transplant.The primary outcome was grade II to IV aGVHD. The secondary outcome was grade III to IV aGVHD. Data were analyzed using 3 orthogonal methods: conventional Cox proportional hazard regression, marginal structural models, and machine learning.A total of 2023 patients  were eligible. Weeks 1 and 2 after HCT were the highest-risk intervals, with multiple antibiotic exposures associated with higher rates of subsequent aGVHD. In particular, exposure to carbapenems during weeks 1 and 2 after allo-HCT was consistently associated with increased risk of aGVHD , as was week 1 after allo-HCT exposure to combinations of penicillins with a β-lactamase inhibitor .In this cohort study of allo-HCT recipients, antibiotic choices and schedules in the early course of transplantation were associated with aGVHD rates. These findings should be considered in antibiotic stewardship programs. Currently, aGVHD risk is not considered in antibiotic stewardship programs.13Antibiotics disrupt the gut microbiota in recipients of allogeneic hematopoietic cell transplantation .21 Some antibiotics with potent antianaerobic activity  have been associated with more aGVHD,21 although other antianaerobic antibiotics, such as metronidazole, have been associated with lower rates of aGVHD.22 Antibiotics are used in complex clinical situations; therefore, their effects may depend on when they are administered in relation to clinical events and whether other antibiotics are given before, during, or afterward. In such circumstances, the conventional Cox model may produce biased estimates. Marginal structural models overcome this limitation and improve causal inference.23 The multifactorial nature of aGVHD pathogenesis24 necessitates a large sample size and special statistical methods to elucidate independent associations for antibiotics. We conducted a single-center, retrospective study using a large database with daily antibiotic exposure data for more than 2000 allo-HCT procedures and an integrated statistical approach consisting of 3 orthogonal methods: proportional hazards regression, marginal structural model, and machine learning.Several associations have been reported between antibiotics and aGVHD.STROBE) reporting guideline.This cohort study was approved by the Fred Hutchinson Cancer Center institutional review board. All patients provided written informed consent to participate in institutional database research. This study is reported following the Strengthening the Reporting of Observational Studies in Epidemiology .27 We considered oral and intravenous antibiotic exposures between 7 days before and 30 days after the procedure, with day 0 being the day of transplant. This interval was divided into 5 nonoverlapping intervals of approximately 1 week each. Antibiotics were classified into 17 classes: aminoglycosides, aztreonam, carbapenems, first- or second-generation cephalosporins, third- or higher-generation cephalosporins with or without a β lactamase inhibitor (2 separate groups), dalfopristin or quinupristin, fluoroquinolones, linezolid, macrolides, penicillins with or without a β lactamase inhibitor (2 separate groups), rifaximin, tetracyclines, trimethoprim-sulfamethoxazole, intravenous vancomycin, and oral vancomycin. Both inpatient and outpatient administrations were included. Patients received prophylactic antibiotics, usually fluoroquinolones, while neutropenic. Empirical treatment of neutropenic fever was generally third- or fourth-generation cephalosporins.We analyzed the allo-HCT database at the Fred Hutchinson Cancer Center with patients aged at least 18 years who underwent allo-HCT between 2010 and 2021, with at least 6 months of follow-up for survivors. Second allo-HCTs and ex vivo T-cell depleted allo-HCTs were not included. No other inclusion or exclusion criteria were used. Conditioning intensity and aGVHD staging and grading were defined according to the International Blood and Marrow Transplant Research criteria.We evaluated 2 end points: grade II to IV (primary end point) and grade III to IV (secondary end point) aGVHD. We used 3 models to find factors associated with grade II to IV aGVHD. To ensure model stability in the analysis of grade III to IV aGVHD using models 1 and 2, we considered all nonantibiotic variables but only statistically significant antibiotic variables from the analysis of grade II to IV aGVHD. The grade III to IV aGVHD models did not converge when all antibiotic exposures were included. Therefore, the results for grade III to IV aGVHD should be treated with caution.We fitted a multivariable proportional hazards model on the occurrence of aGVHD, in which death without GVHD was treated as a competing risk using the Fine and Gray model. The main variable was antibiotic exposure, coded as a binary categorical term per antibiotic class (each of the 9 most frequently used classes) and interval . Exposure to an antibiotic on different days of the same interval was assumed to have the same effect on GVHD hazard. Covariates in the model included factors most strongly associated with aGVHD in previous studies, including graft source, conditioning intensity, antithymocyte globulin use in conditioning, and an interaction term for donor type and GVHD prophylaxis. Two additional variables were included for neutrophil engraftment: a categorical variable coding whether neutrophil engraftment occurred or not and a continuous variable for days to neutrophil engraftment. For patients who did not engraft neutrophils, the median time to neutrophil engraftment was assigned to the latter variable. Thus, the regression coefficient for the categorical variable compares patients without neutrophil engraftment with a hypothetical patient experiencing neutrophil engraftment at median. We combined antibiotic use in adjacent intervals if there was perfect separation on event occurrence  to ensure model stability.After fitting the full model, we conducted model selection using a backward elimination procedure in which in each step, antibiotic exposures with similar associations (significant and consistently positive or negative or not significant) in adjacent intervals were combined over those intervals and assumed to have a constant effect on GVHD hazard or antibiotic exposures with no significant association across all 5 intervals were removed. Models with smaller Akaike information criterion (AIC) values were preferred. Hazard ratios (HRs) and 95% CIs were calculated.23 The same intervals as in model 1 were used for antibiotic exposures, and death without aGVHD was considered a competing risk. The same procedures as in model 1 were used to derive the final version of model 2.We used marginal structural models to estimate the association of time-dependent antibiotic exposures with aGVHD hazard in the presence of potentially confounding, previous, time-dependent antibiotic exposures. The model assumes that the vector of antibiotic exposures on a given day may depend on antibiotic exposures on the previous day and the baseline covariates, with antibiotic exposure probability estimated by a logistic regression model. The inverse-probability-of-treatment weighting approach with stabilized weight was used to estimate the model parameters (HRs and 95%CIs).28 a random forest feature selection algorithm, in R statistical software version 4.2.0 . For each antibiotic, exposure in a given interval was coded as a binary variable . Similarly, grade II to IV aGVHD was coded as a binary variable, 1 if the patient developed the outcome by day 180 after allo-HCT and zero otherwise. Because Boruta is not suitable for time-to-event or competing risk analysis, patients who died without aGVHD before day 180 were excluded. The goal in the Boruta algorithm is to classify the potential risk factors into important and unimportant features. Possible multicollinearity among important features does not pose a problem in this algorithm because all such variables are selected as important.We included 94 variables, including 85 antibiotic variables  as potential risk factors for aGVHD in the Boruta package,Z score is calculated based on the hits with which it determines the features that performed significantly better than shadow (classified as important) and those that performed significantly worse than shadow (classified as unimportant).Boruta operates in 5 steps. First, Boruta duplicates all features, shuffling the values of each added duplicate (“shadow” features), and merging original and shadow features into the same database. Second, Boruta trains a random forest classifier on the combined data set and determines the importance of each feature using 1 of the several available indices . Third, Boruta compares the score obtained for each original variable with the maximum score obtained from the shadow features. Original features with scores higher than this maximum receive a “hit” toward being important while those with scores lower than the maximum shadow score receive a “hit” toward being unimportant. Fourth, a set number of iterations (steps 1-3) are performed, assigning hits in each permutation. Finally, a P values were 2-sided, and statistical significance was set at P = .05. Data were analyzed from August 1 to December 15, 2022.All analyses were performed in R version 4.2.0. Analyses included 2023 patients   and several smaller cohorts.17 In another large series (approximately 1200 patients), exposure to carbapenems or piperacillin-tazobactam (grouped together as antianaerobic antibiotics) in the pre-engraftment period was associated with greater risk of aGVHD .16 By distinguishing different intervals and considering prior antibiotic exposures as time-dependent covariates, we found an association for carbapenems during weeks 1 and 2 after allo-HCT, with HRs ranging from 2.75 to 7.42.In this cohort study, we performed a comprehensive analysis of antibiotic exposures as a risk factor for aGVHD after allo-HCT. We included 94 variables  in 3 orthogonal analytical approaches using a database of more than 2000 allo-HCT procedures performed over a decade. The most consistent finding was the association for carbapenem exposure during week 1 (and to a lesser extent week 2) after allo-HCT. In murine studies, carbapenem led to the expansion of obligate anaerobic, mucus-degrading species, such as 16 Notably, exposure to any of the 9 most frequently used antibiotics in at least 1 of the 5 intervals was associated with greater hazard of aGVHD. This finding suggests that while specific bacteria may influence the risk of aGVHD, there are also more general patterns of microbiota injury that may be important in aGVHD pathogenesis. This hypothesis is supported by a 2012 study9 showing that large microbial fluctuations in the peritransplant interval may increase aGVHD risk. Weeks 1 and 2 after allo-HCT appeared to be the highest-risk intervals, with multiple antibiotic exposure associated with greater hazard of aGVHD. These intervals represent the pre-engraftment period, when the allogeneic graft is rapidly expanding and its immune effector cells are coming into contact with the changing gut microbiota. Studies have shown that microbiota changes start to occur within days after antibiotic exposure.30Another antibiotic class with a significant association during week 1 after allo-HCT was penicillins with a β lactamase inhibitor, with HRs ranging from 6.55 to 7.90. The most frequently used antibiotic in this class is piperacillin-tazobactam, found in some previous reports to be associated with greater risk of aGVHD or mortality from aGVHD.22 of ciprofloxacin plus metronidazole  vs ciprofloxacin (control group) during the first 5 weeks after HCT. A reduction of grade II aGVHD incidence by 50% was observed in the experimental group, and this was associated with a reduction of anaerobic bacteria in the stool .22 In addition, patients who developed grade II to IV aGVHD had a significantly higher anaerobic bacteria load in the stool.22 A few other gut decontamination studies observed similar results, including some that started this strategy before HCT.32 Most of these studies were performed in the premicrobiota era, thus the precise effect of the intervention on the microbiota and its possible involvement in the causal link cannot be ascertained.An unexpected finding was the association between pre-HCT exposure to penicillins with a β lactamase inhibitor and lower rates of both grade II to IV and III to IV aGVHD across all 3 methods. Although a statistically significant result was obtained only for grade II to IV aGVHD (model 2), the remarkably consistent pattern and similar HRs across models and for both end points may suggest a true biological relationship. The potential value of early broad-spectrum suppression of the gut microbiota and its possible protective effect against aGVHD has been debated for years. The best evidence for such an effect comes from a 1999 randomized trial by Beelen et alNCT03078010). Third, considering the negative association between pre-HCT use of penicillins with a β lactamase inhibitor and aGVHD, would pre-HCT use of this antibiotic class instead of fluoroquinolones reduce risk of aGVHD? Fourth, are patients with penicillin or cephalosporin allergies more likely to develop aGVHD (since they are more likely to receive carbapenems or piperacillin-tazobactam after HCT)? Fifth, could antibiotic exposures be used to identify patients at higher risk for aGVHD and direct them to microbiota therapeutic trials?In addition to mechanistic murine studies, there are many questions open to further investigation. First, are our findings consistent among different centers? Second, would posttransplant replacement of strong antianaerobic antibiotics with anaerobe-sparing antibiotics lead to less aGVHD? This could be tested in a randomized trial, and one such trial is currently ongoing (ClinicalTrials.gov identifier Enterococcus and methicillin-resistant Staphylococcus aureus infections in our patients were low during this study.34 Our Clostridioides difficile infection rates have been approximately 10% in the last several years.35 We see 1 to 3 infections with carbapenem-resistant Enterobacterales per year. Extended-spectrum β-lactamase colonization rates among our patients is approximately 3%.This study has some limitations. The reason for choosing a specific type of antibiotic among several possible choices cannot always be ascertained in retrospective studies, indicating the possibility of unmeasured confounders. Antibiotic use patterns partially depend on evolving local epidemiological patterns for common multidrug-resistant organisms. The rates of vancomycin-resistant 18 Various microbiota-targeted approaches are being tested to protect the microbiota during antibiotic use or restore it after injury.36 Examples of potentially protective treatments are nonselective luminal adsorbents, such as oral activated charcoal37 and selective luminal antibiotic degraders, such as β-lactamases38 and metallo-β-lactamases.39 Examples of potentially restorative treatments include prebiotics41 and fecal microbiota transplantation.45 If our results are replicated in independent cohorts, antibiotic-associated risk of aGVHD could become a consideration in antibiotic stewardship programs.The findings of this cohort study suggest that several antibiotics commonly used to treat neutropenic fever and infections after HCT were associated with increased rates of aGVHD. The most consistent finding in this study and prior reports, and with recent mechanistic support from murine studies, is a detrimental association of aGVHD with carbapenem exposure in weeks 1 and 2 after HCT. Avoiding this class of antibiotics early after transplant seems prudent. The challenge in current practice is the lack of antibiotics that are effective enough in prophylaxis or treatment but spare the commensal microbiota.


An estimated one third of antibiotics prescribed in the outpatient setting is considered unnecessary. We evaluated ambulatory antimicrobial use for a single system before and during the COVID-19 pandemic and assessed the impact of a system-based stewardship intervention on overall antibiotic selection and prescribing rates for indications with typically viral etiologies.Comparison of Antibiotic Use for Common Viral Respiratory Syndromes Prepandemic and Pandemic PeriodsChange in Antibiotic Use and Spectrum for Prepandemic and Pandemic PeriodsThis retrospective, quasi-experimental pre-post design evaluated rates of antibiotic prescribing for ambulatory setting in all ages across a large, multi-state healthcare system with encounters coded for common viral respiratory syndromes. Stewardship interventions were implemented starting July 2021 and included mandatory training on common upper respiratory infections for all Primary Care and Urgent Care clinicians, coupled with feedback on prescribing practices for targeted viral syndromes at quarterly intervals. Encounter volumes for ambulatory care clinicians were stratified by time period and common viral respiratory syndrome diagnosis (excluding COVID-19). Data on systemic antibiotic prescriptions collected from outpatient electronic health records (EHRs) was obtained during a prepandemic year (January 2019 - December 2019) and a pandemic year (January 2022 - December 2022). We compared the use of antibiotics for common viral respiratory syndromes between the two periods in the ambulatory setting and further evaluated for any changes in antibiotic selection.Ambulatory antibiotic utilization for common viral respiratory syndromes decreased from 54.3% (prepandemic) to 47.1% (pandemic), resulting in an absolute 7.2% reduction (p< 0.001). After adjusting for the decreased volume of common viral syndromes diagnosed during 2022, approximately 28,578 fewer antibiotics were prescribed during the COVID period.Associated with an intervention to optimize antimicrobial use, we witnessed an improvement in overall use and choice of antimicrobials during the pandemic in a single system.Melinda Mackey, MSN, RN, CPHQ, CCM, Pfizer, Inc: Advisor/Consultant Reese Cosimi, PharmD, Allergen: Advisor/Consultant


The necessary a priori bounds are found using a new version of the Bihari inequality that we prove here. We show that global solutions exist when f grows at most linearly in u, and also in some cases when the growth is faster than linear. We give examples of the new results for some fractional differential equations with nonlinearities related to some that occur in combustion theory. We also discuss in detail the often used alternative definition of Caputo fractional derivative and we show that it has severe disadvantages which restricts its use. In particular we prove that there is a necessary condition in order that solutions of the IVP can exist with this definition, which has often been overlooked in the literature.We prove existence of solutions, and particularly positive solutions, of initial value problems (IVPs) for nonlinear fractional differential equations involving the Caputo differential operator of order  We study the existence of continuous solutions, and particularly non-negative solutions, of initial value problems (IVPs) for nonlinear fractional differential equations (FDEs) involving the Caputo fractional differential operator of order entclass1pt{minimaα, as in –20.t in an interval , especially in cases where T can be arbitrarily large, which we call global solutions.One of our goals is to prove existence for all N acting in the space of continuous functions, using fixed point index theory or degree theory.We will employ the standard method of studying solutions via fixed points of the associated Volterra integral operator u which satisfies an extra condition so that N is a Volterra integral operator f is continuous. We suppose that f satisfies an N in our case.The IVP is written entclass1pt{minimaf satisfies a Lipschitz condition in the u variable. In the book of Diethelm [h]) is proved when f is continuous, see  is denoted by C or sometimes simply C and is endowed with the supremum norm f such that The space of functions that are continuous on  into C and AC into AC.C into AC.   is a continuous function u with Let  the IVP  on an inP denote the standard cone of non-negative continuous functions, that is,P inherits the norm of C.Let C and the existence of non-negative solutions in P, we will concentrate on the study of non-negative solutions when Since there is almost no difference between the arguments for existence of solutions in P of the nonlinear integral operator N defined byF is the Nemytskii operator We will study non-negative solutions of  via fixeWe will prove equivalence of these problems in Lemma F maps P into Let F maps P into P. Then there exists Let N in  ii) u is a solution of the IVP(i) holds. For Suppose that mentclass2pt{minimpt{minimiii) be satisfied. Then Now let  is continuous and t and is an w is non-decreasing, we have for a.e. t,W is a strictly increasing a, b are positive functions with We first consider the case when ondition  and sincsumption , for allbitrary,  holds. \a is only non-negative by taking a by a and b are non-decreasing functions. It is necessary that If a, b constants and supposed that W depends on a, b are constants.The original result was proved by Bihari who had estimate  does notcommon domain of definitionLet the hypotheses of Theorem Note that equality . \documeThe common domain of definition is needed otherwise mentclass2pt{minimk and u is replaced by f(u) for suitable functions f, k. They considered the case when a, b are positive functions by reduction to the case when a, b are constants using the same method as in the proof above. They did not check that certain functions are AC so that the integration step was not shown to be valid, some extra conditions on their functions are required to justify this.Butler and Rogers  gave a mWe have not been able to find the results of Theorems 1 and 2 in the literature when T, the third only gives a local estimate. We then give a fourth family of examples with T. These are cases where w(u) grows faster than linear, but to be valid for any T, such a function w must grow more slowly than We first consider three standard examples when In all the examples it is supposed that the hypotheses and notation of Theorem a, b are constants and is easy to calculate, we only state the result. In this case mentclass2pt{minima, b are constants and In fact, let l result .T, it can happen that a, b and In this case, for a given w is positive and increasing for u satisfies the boundLet We show how the Bihari inequality applies. Since the final estimate does not depend on the initial point mentclass2pt{minima, b by functions A, B as in Theorem Similarly, we can consider mentclass2pt{minimA slightly less general result than that of Example f is To obtain a priori bounds for the fractional integral equationw is a non-decreasing continuous function and a, b be positive bounded functions such that Let p and using the inequality Applying Hölder’s inequality in  gives\domentclass2pt{minimgiven in . This gigiven in . \documew is to take w when When This gives a result similar to Zhu  which is false in general. The proof uses Hölder’s inequality, as above, and then essentially gives the proof of the original Bihari inequality. In the equations (2.3), (2.4) of  into C by Proposition N is completely continuous. Now suppose that T], this is exactly the situation of Theorem N on the space N has a fixed point in Let mentclass2pt{minimmentclass2pt{minimmentclass2pt{minimution of  on the it, for example see [We will have T] for an arbitrary mentclass2pt{minim/p; then  has a glent}r>1;  has a loConsider growth assumption  in the fAnother variant where we can get global solutions is by using a special case of a Gronwall inequality for singular kernel integrals due to Webb [ Let \doThe condition T] such thatu(t), that is, the solution exists on .Suppose that ∈R+.Then  has a glThe proof is very similar to the proof of Theorem Since w is a non-decreasing continuous function with Assume that >0. Then  has a soSince her with , implieslu∈R+and  holds wiT]. If Let r≤1 then  has a glBy , there e).Hence,  with \domentclass2pt{minimu(t) by |u(t)| in the inequalities, and assuming inequalities on |f| such asWe have proved results for existence of non-negative solutions. By the same methods exactly similar results hold in u is the dimensionless temperature, and Motivated by some nonlinearities that arise in combustion theory, we study IVPs of first order FDEs of the formate, see . The reaied, see , 27 for 67], and  for \docThe existence and uniqueness of nonzero non-negative solutions of one or higher dimensional elliptic equations in combustion theory have been widely studied, for example in , 21, 28.g is continuous, h is continuous with We apply the results obtained in Sect. We say a solution Under the above hypotheses the IVP  has a pof satisfies the Carathéodory conditions since g, h are continuous. Also we havef is w continuous and non-decreasing. By Theorem Note that u is increasing, as shown by counter examples in .(1) If 1], then  has a gl(2) If m>1 then  has a pof is globally bounded and a solution exists on . Now suppose that f is T], and is positive for Let mentclass2pt{minimmentclass2pt{minimg(u) under suitable restrictions.Clearly we could replace The Caputo fractional derivative is frequently defined with the derivative and fractional integral taken in the reverse order to that of the R-L derivative, that is as Provisional Definition For t byAC, t, so we would have f continuousC. If It has often been claimed that for Therefore the definition must be as follows.For t.For This definition prevents having functions such as Lebesgue’s singular function. Moreover, it now follows simply that if f continuous, then clearly C into AC as shown in Cichoń-Salem  of the integral equation f is only assumed to be continuous, but these papers do not consider the necessary condition When we consider entclass1pt{minima


The subject of the article is to assess the suitability of over materials over a hundred years old that are embedded in historic building structures in conditions of contemporary utility challenges in residential and public buildings. It is based on an example of technical condition evaluation of a ceramic staircase erected in 1840 and a structure of two reinforced concrete staircases from the year 1910. As a part of in-situ and laboratory tests, the physical and mechanical parameters of unique historical materials  were determined. Then the conditions for their incorporation were inventoried and determined in order to save the unique material and technical solutions used in the first half of the 19th century and the first decade of the 20th century. The article is a summary of the research and analyzes carried out in terms of proper handling of historical materials, buildings and their elements that could still fulfill their original function and be a witness to the history of a certain era. Both a research case and an application case are described here. It will allow for the continuation of these studies directly in the facility, thus assessing the effectiveness and suitability of such methods for use in similar or other situations. The aim of this approach was to introduce a non-invasive reinforcing technique that would not change the valuable and authentic appearance of these historic structures. It would also not change their static schemes, and at the same time would ensure their proper load-bearing capacity, bearing in mind that the materials used here are not equivalent to current regulations and standards. The inspiration to take up the presented topic was the inquiry of the Provincial Office for the Protection of Monuments about the possibility of leaving and further to use the historic staircases in renovated buildings in new conditions. Designers of renovation, strengthening and modernization works had assigned these structures to demolition due to the low strength of concrete and because of currently not used technologies ,23,24,25Authors of the article decided to evaluate these materials and use them in structures in terms of suitability for today’s construction and operational requirements. As it was mentioned above, the subject of the research was over a hundred-year-old materials, of which the structure of three staircases marked as K1, K2 and K5 (ceramic) were made. The main idea was to leave them for further use in a new function of the building, i.e., the Centre for Vocational Education, and indicating the scope and solutions of their possible reinforcements. The research, the accurate inventory of three subjective structures and also the research of the elaboration ,30,31,32The ceramic (K5) and concrete K1, K2) staircases responsible for vertical communication in buildings have been so far used as fully-fledged load-bearing elements in a public utility facility , until it was shutdown. An object of this rank had to be regularly inspected, but at the time of performing these elaborations [, K2 staiIn terms of diagnostics, it is also important to refer to the applicable regulations and standards. For calculating the load-bearing capacity of the staircase structure, Polish Standards were used ,23,24,25The aim of the work was to make the research of building materials shown in  and to d2. It is the number of loads required to be transferred on communication areas in office buildings, schools, research institutes, banks and medical clinics. The specifics of the above-mentioned rooms do not differ much from those in hospitals and prison buildings, where the required operational loads are 1.0 kN/m2 less, the value being 3.0 kN/m2. This load is classified as a long-term, in fact it will be a short-term or even temporary load. In the combination of loads, only a part of it  described by the coefficient ψd = 0.35 could be assumed, but its full value was taken into account in the verification calculations due to the fact that these structures have already passed the technical service life that were assumed for them (over 100 years). The structures of all three staircases have been verified due to capacity of the load-bearing characteristic value of 4.0 kN/m2.Both values of permanent and functional loads were adopted on the basis of Polish Standards ,21, with2  were commonly used in concrete structures and concrete reinforced with iron (steel) bars [b = 140,000 kg/cm2) concrete was also used and iron for reinforcement bars with Ee = 210,000 kg/cm2 [The first tests of concrete compressive strength ,31,32, cel) bars ,33. In t“A derivation of formulas and calculation methods with small examplesA. Pure bending I. without considering concrete tensile stresses.e = 2,100,000 kg/cm2 to the modulus of elasticity of concrete εb = 140,000 kg/cm2(a) Simple reinforcement. The ratio of the modulus of elasticity of iron εe/εb = n = 2,100,000/140,000 = 15”εThe research of concrete structures from the beginning of 20th century indicated much higher strength parameters than assumed by their original designers. An example of this is the research carried out by another laboratory, which has checked the mechanical parameters of concrete and bricks by the request of the following article authors.Basing on the compression research of 3 concrete samples according to , it was 2 ranges from 3700 kg/cm2 (370 MPa) to 5800 kg/cm2 (580 MPa). According to the studies [It is similar with reinforcing steel . According to the study , the imm studies , the ten studies , where bThis section presents the results of research carried out for the structural elements made of reinforced concrete of the K1 staircase, which also had a reinforced concrete railing that served as the stringers of the running plates. The structural thickness of the running plate and landing is 13 cm, and the utility layer is 3 cm thick terrazzo a. The reAnother tested element of vertical communication was the K-2 staircase, which is fully monolithic. It was built by the P-3 slab . On both sides, it rests on 2 B-3 reinforced concrete stringers. In the level of the platforms the slabs rest on the new supporting structure, and the other side on the wall. They were connected with a massive B-3.1 reinforced concrete beam in the space between the running plates of the landing, probably in order to stiffen the entire structure. The staircase diagram is shown on It was not necessary to carry out a statistical analysis in this example and plan the experiment, because the samples were made to verify those presented in previous studies. The general aim was not a new experiment, but to determine the parameters of the existing structure, which was associated to limit the number of taken samples.On The tests of taken samples were carried out in the Pilot 4 testing machine in accordance with the applicable standards. The obtained results are presented in Tables in 2, the so-called class I masonry with Kc = up to 160 kg/cm2 (16 MPa), class II with Kc = ~100 kg/cm2 (10 MPa) and sand-lime with Kc = ~180 kg/cm2 (18 MPa). In fact, the strength class of the bricks was much higher, which is confirmed by most of the research carried out today. The current condition of masonry structures depends on the conditions in which they were used, as well as whether the maintenance and repair procedures have been carried out or not. The collected samples of bricks  from the walls of the building [In the first decades of the 20th century, ceramic bricks were commonly used, the so-called clinker—with compressive strength Kc = up to 640 kg/cmbuilding  have shobuilding , f = 28 This part of article describes tests of the ceramic and vaulted structural elements of the K5 staircase, which also served as a starting point for the verification calculations. The load-bearing structure of the staircase consists of ceramic running (bricks and mortar), landing and landing plates based on walls and iron (steel) beams. The main subject of the research and analysis of the structure in question if a brick was a running plate (vault with a thickness of ½ brick—12 cm) with an arc arrow up to 24 cm, shown above , on whicRepresentative sample No. 2 was taken from the landing . The sam3 and 1.08 g/cm3, respectively.Slag/the so-called slag mixed with tar, for which the bulk and tapped bulk densities were determined to be 0.89 g/cmFor each staircase, samples 8a–f were taken in the running plate and samples 9a–f in the landing plate. Results are presented in this section.The obtained results are presented in Basic statistics presented in the following figures were carried out for the research results .The values of internal forces in the vault were determined using Robot Autodesk Structural Analysis. The selected calculation results are shown on As mentioned in the studies ,27, the The obtained results are presented in Basic statistics presented in the following figures  were carStrength tests of 3 samples (tested in ) of concThe structure of the stairs is made of a running plate (13 cm thick) supported on the longitudinal wall of the staircase and a running string, which is also a reinforced balustrade. In the assumptions for the calculations, it was assumed that the balustrade is entirely a load-bearing stair cheek beam. It was also assumed that the P-1 running plate is freely supported on both sides, although in fact it can be fixed on one side in the above-mentioned “cheek”. Sclerometric and destructive tests were carried out on the concrete of running and landing slabs, as well as reinforcement iron (steel) inserts. Such an assumption would significantly reduce the span moment, the amount of deflection and the computationally required amount of reinforcement bars. The performed verification calculations showed that the inventoried number of reinforcing bars should be sufficient to transfer the moment, but their spacing does not meet the current code requirements , becauseThe problem was the not fully inventoried landing beam B-2, loaded with two large, concentrated forces originating from the reaction of the B-1cheek beams. With the existing cross-section, the bottom reinforcement in the form of 8 bars ø18  would be required, while only 2 such bars were inventoried. In the period when the staircases structures has been made, the concentration of reinforcement was used, which would be unacceptable at the present time . Such a large bending moment could be transferred by the parallelepiped I 200 × 200 (h = 200 mm and b = 200 mm), produced since 1902, which could easily fit into the cross-section of the B-2 beam.At the present times, the width of the beam could not be less than 42 cm. It cannot be ruled out that the existing reinforcement of the B-2 beam has not been fully inventoried or that there is an additional iron (steel) profile inside it. The cross-section of two ø18 iron inserts is FThe obtained results are presented in a = 3.59 cm2. This spacing (every 14 cm) is sufficient to carry the expected loads, therefore no additional reinforcements are provided for here. The situation is similar with the construction of the B-3 beam. It was recommended that, prior to the commencement of construction works, the size and spacing of the reinforcement inserts should be confirmed in an amount not less than 4ø16  with Fa = 7.40 cm2.The P-3 plate rests on both sides of the B-3 running beams’ cheeks and it cannot be ruled out that it is fixed in them. For this slab, the reinforcement was inventoried in the form of 7 bars ø8/per 1 m width  with FA very interesting element of the research was the assessment of over 100-year-old structures, especially the reinforced concrete. It was a pioneering period in the use of reinforced concrete. Despite the fact that the requirements then for the strength classes of materials, diameters and spacing of reinforcement inserts were significantly different from the present ones, the over 100-year service life of these structures proves that the solutions were properly adopted at the beginning of the 20th century. The authors of the research, wanting to keep the existing structures unchanged (to maintain their authenticity), without additional visible interference, proposed to strengthen them by implementing FRCM (Fibre Reinforced Cementitious Matrix) composite systems using carbon mesh of ceramic structures) and PBO (polyparaphenylene benzobisoxazol) mesh (for reinforced concrete structures). Both types of the nets differed from each other by the terms of strength, density and spacing of the carrying fibers. Carbon meshes were characterized by the same spacing of fibers and the same load capacity in two orthogonal directions . It should be not less than 1.5 MPa. The test should be carried out using the so-called Tear-off mushrooms by gluing them with epoxy glue to the smooth and cleaned surface, circumferential incision of the substrate and then tearing them off using a tear-off device, e.g., Positech AT-M. After starting the works, the wall load-bearing capacity should be assessed in the places of concentrated loads, i.e., in the places where the stringers, landings and platforms are supported. Such checking and possible strengthening of wall fragments would also occur when new stair structures rest on them. The application of the meshes should be preceded by preparatory works with the use of an appropriate concrete or construction ceramics re-profiling system when the substrate is uneven, peeling and with cavities. The system described above is used to strengthen reinforced concrete elements, mainly in the areas of bending, shear and torsional stresses. Strengthening the stair elements should be performed on the entire surfaces qualified for this purpose with the above-mentioned PBO composite meshes. As is the case with the reinforcement of masonry structures with carbon meshes, the application of PBO meshes must be preceded by consultation with a technical specialist of the system application, who will indicate to the contractor all the detailed requirements for its use in the case in question and confirm in writing that the application of the structure reinforcement system has been completed in accordance with all the requirements set by the manufacturer in the technical data sheets. It should be performed under strict supervision of authorized persons .2, but at the turn of the above-mentioned centuries, the dimensioning of the stair structure was taken into account already functional loads of 4.0 kN/m2 .A comprehensive diagnostic analysis of a building structure often requires the participation of people with appropriate qualifications and experience, which will allow for appropriate orientation and overall assessment of the problem under consideration ,52,53,54rding to —Figure 1“If the calculations are to be carried out for a strip with a width of b = 1.00 m, then the width of the stairs can be freely changed without reducing the correctness of the calculations. The average thickness of the steps 18/2 = 9 cm2operational load—400 kg/m2steps—180 kg/m2 total load—p = 1000 kg/m2landing plate—408 kg/m2plaster—12 kg/m2/10 × 100. Dimensioning should be carried out in accordance with table II in the formula book (page 14 no. 15), specifically for the compressive stress of concrete σb ≤ 40 kg/cm2 and for the tensile stress of iron σb ≤ 1000 kg/cm2.”Since the running plates of the stairs together with the landing plates are a load-bearing structure with many sub-pores, according to the guidelines of the Ministry, the bending moment in the middle of the board should be Mśr = plThe position of the authors of the publication is to preserve the historical substance to the highest degree of its authenticity, not mentioning about keeping them in general. It is difficult to carry out reliable research and analyzes in terms of determining the safety level of the structures left behind, the computational approach of which was completely different than the current one. Nevertheless, the inspection of the components of the staircases revealed that, despite over 100 years of exploitation, their deformations or scratches are not visually noticeable. So far, no measurements of this type have been carried out. The performed tests and verification calculations allow for the approval of these structures for further operation after taking into account the assumptions and requirements described above.Structure materials in historic buildings should not be classified as useless in relation to current regulations and standards, only because of their age. In the considered cases, parallel to the laboratory research of concrete and bricks, non-destructive tests were carried out for them using a “Schmidt hammer” sclerometer, which was calibrated on the basis of samples taken and destroyed in the laboratory. The main purpose of these tests was to check the homogeneity of the material structure on the entire surfaces of these structures, which was also confirmed. The quality of the constructions made in year 1840 and in 1910 should be considered as high, and their technical condition as very good.Currently, science is trying to look ahead towards the development and research of new materials, technologies, conducting advanced laboratory research, but there are still historical objects that are the national heritage of each region, which should be preserved for future generations in full technical efficiency and the highest degree of authenticity. Universal methods of strengthening, repairs and reinforcement have not yet been developed for them. This article not only attempts to justify such a necessity and to justify the preservation of these objects in a version corresponding to the original, but also to maintain their original function, but in the new conditions of the requirements set by building regulations and standards. What would science be if it did not transfer the results of its research to reality, even the one concerning “obsolete” constructions, one of which is over 180 years old and the other two over 110 years old? These are not standard and typical solutions, because such solutions in historic structures are still rare. We are dealing here with three different, and significantly different, technologies of performance of stairs with currently not used parameters, which have been subjected to multi-format researches and analyzes of materials, indicating simple but innovative reinforcement solutions, full responsibility for their implementation and operational safety. Reinforcing composite materials are already a well-known solution, but it mainly concerns the technology of their fixing with resins. As a way to strengthen the weakened parts of the structure, solutions based on the FRCM technology using carbon meshes and PBO have been proposed, which are described in detail in point 4 of the article, which are still in the research phase, especially in terms of their strength depending on adhesion to substrates and have not yet been fixed in standards.This approach to the problem of historical buildings is a significant part of the sustainable development strategy, because such buildings can still perform their original functions or can be used for other purposes. In this way, the need to deposit post-demolition waste in landfills that are already disappearing or is eliminated. Such solutions do not require the energy that is needed to produce new materials, transportation and erection of new facilities.