The presented article concentrates on the influence of various concrete additives in the form of fibers on the mechanical parameters of concrete so as to obtain the effect of gradual changes in these parameters, which is very important in the transition zone of the railway track. Steel, polymer and glass fibers, as well as concrete without additives, were accepted for the study. The effect of additives on the consistency of the mixture, compressive strength, frost resistance and elastic modulus was studied. The research concerned concrete samples and models of elements of the ballastless railway surface, i.e., track slab and concrete block supports. The track slab model was made of concrete without additives, while the models of supports were made both without and with additives. The studies were carried out in laboratory conditions. As a result, the tested concrete samples with various additives were ranked so that they could be used as a material for elements of the railway surface in the transition zones of engineering facilities on railway roads, which is important from the point of view of reducing the threshold effect occurring in these zones. Detailed laboratory tests were presented, the results of these studies were discussed, and final conclusions were drawn regarding the technology of materials and the methodology of constructing the transition zones of the railway surface in order to avoid or at least reduce the threshold effect existing in such zones. In previous practice, concrete additives in the form of mineral ingredients or chemical admixtures were used for two reasons: (1) to obtain concretes with increased strength parameters, and (2) to use waste raw materials and to increase the recycling rate. This article describes the use of concrete additives in the form of various fibers in order to obtain a gentle change of the strength parameters of fragments of the railway surface on the section of the transition zone in order to eliminate, or at least reduce, the impact of the threshold effect on the dynamic interactions at the interface of the rail vehicle with the railway track.With the development of construction, there is an increase in demand for concretes with high strength parameters. Due to the occurrence of concrete shrinkage, it is not possible to increase the cement content in it indefinitely. For this reason, a number of mineral additives and chemical admixtures have been used for concrete for decades ,2,3,4. OThe use of various concrete additives to obtain materials with different, slightly changing strength parameters has not been the subject of research described in the available literature. This type of research was initiated in the work presented in . This arThe composition of the concrete mix intended for the track slab has been designed on the basis of the method of three equations in accordance with the requirements set out in the technical documents ,24,25,26Due to the fact that block supports are prefabricated elements and the design of the concrete mix is a trade secret, the components of concrete intended for block supports were selected on the basis of information obtained from the manufacturer of the ÖBB-PORR system and analogies to the requirements set out in “the Technical Conditions for the Execution and Acceptance of Prestressed Concrete Sleepers and Turnouts Id-101” . In ordeZ2—concrete with the addition of steel fibers, Z3—concrete with the addition of polymer fibers, Z4—concrete with the addition of glass fibers, Z5—reference concrete, without the addition of fibers.For concrete mixes, fine aggregate 0/2 from the Żabiny mine  and granite coarse aggregate with fractions 2/8 and 8/16 from the Graniczna mine  were used. The concrete mix intended for the Z1 track slab was made using CEM I 42.5 N/NA cement from the WARTA company , while CEM 42.5 R cement from the CEMEX company  was used to make the concrete mix intended for Z2–Z5 block supports. The properties of the cements used are shown in The dosage of fibers in individual mixtures meets the requirements specified by the manufacturer and the standard provisions ,29.3 of concrete mix. The concrete mix intended for Z3 block supports uses Polyex Duro polymer fibers from the Astra company  with a length of 25 mm, in the amount of 4.5 kg/m3 of concrete mix. The Z4 blend uses CemFil Hp Macro glass fibers from the Serra-Ciments company  with a length of 36 mm in the amount of 1 kg/m3 of concrete mix. The dosage of the fibers was based on the manufacturer’s recommendations and the standard provisions [In the concrete mix intended for block supports Z2, steel fibers for concrete were used, from the Siatpol company  with a length of 50 mm in the amount of 25 kg/movisions ,30. The The first study that was carried out was the study of the consistency of the concrete mix. The consistency of the mixture was determined by the Abrams cone fall method. The consistency test was carried out in accordance with PN-EN 12350-2:2011 Concrete mix tests—part 2: Consistency testing by the cone fall method .Another test was the compressive strength test of cement concrete samples. This test was performed on cubic samples with dimensions of 150 mm × 150 mm × 150 mm in accordance with the provisions of PN-EN 12390-3:2019 Concrete tests—Part 3: Compressive strength of samples for testing . Due to The next study aimed at determining the parameters of the designed cement concretes was the study of the frost resistance of concrete. This test was carried out by the usual method in order to verify the degree of frost resistance F assumed at the design stage of the mixture. However, this degree in the assumptions corresponds to the N index, which is equal to the number of expected years of use of the structure. The usual method makes it possible to take into account the degree of internal destruction of concrete, characterized by the decreased strength of the sample, as well as the external destruction, determined by the loss of mass of the sample. The frost resistance test was carried out in accordance with PN-88/B-06250:1988 Ordinary concrete . The tesIn order to determine the physical parameters of the designed cement concretes, a study of the elastic modulus was carried out. Cylindrical samples with a diameter of 150 mm and a height of 300 mm were prepared for the study. The study of elastic modulus was carried out using two methods. The first method consisted in determining the modulus of elasticity using the resonant method. In this method, the modulus of elasticity is determined by the propagation of the waves in the sample. Vibrations are caused by hitting a ball of a properly selected diameter on the base of the cylinder. Based on the measured wave, the device determines the frequency of vibrations and the modulus of elasticity of the tested material. This test is a non-destructive test of the element under study. The test was carried out with the use of the JAMES INSTRUMENT V-E-400 testing machine . In the The main part of the experimental research was to determine the impact of the stiffness and strength of block supports on the strength of the entire ballastless surface, and thus on the strength of the track plate made of cement concrete. According to the adopted model, there are tensions of concrete in the track plate. At the same time, under the block supports, the forces from the wheeled vehicle cause the concrete to stretch downwards, and in the middle of the length of the slab the phenomenon of lifting the slab is triggered. The plate load model adopted for the cross-sectional test is shown in Due to the research possibilities, in order to check the tensile strength when bending the track plate with embedded block supports, a laboratory sample constituting 30% of the actual dimensions was prepared. The dimensions of the sample on which the tests were carried out were 100 mm × 150 mm × 750 mm and were adapted to the forms equipped by the laboratory. The tests  were carThis destruction consists in settling or washing the foundation from the central part of the support. The stress value of the samples is based on the following formula.Wg—index of the bending strength of the rectangular cross-section relative to the vertical axis.P—force acting on the sample (kN), z—distance of force from the support—0.05 m, Another test aimed at determining the strength of block supports on the strength of the entire surface was to check the strength of the longitudinal section. The purpose of this test was to check the load capacity in the direction along the track, derived from the axle load of the bogie of the AEG12X locomotive, with a spacing of 2.60 m. The axle load of the locomotive is 210 kN. The plate load model adopted for longitudinal section testing is shown in In order to check the tensile strength when bending along the surface, samples measuring 10 × 15 × 100 cm were prepared. The construction of the surface was made on a scale of 0.3. It is therefore the same scale factor as in the case of cross-sectional testing. In addition to the limited availability of large molds for making samples, the choice of scale factor in this study was dictated by the capabilities of the strength testing machine. Additionally to the limited availability of large molds for making samples, the choice of scale factor in this study was dictated by the capabilities of the strength testing machine. A sample after the bending strength testing is shown in The research was carried out for four types of block supports. The load was applied, as in the previous test, in the middle of the block supports. Support points are adopted at a distance of 5 cm from the edge. The stress values in the samples were determined in the same way as in the previous test, i.e., according to Equation (1).The results of measuring the consistency of the concrete mix are presented in The greatest cone fallout was observed in the case of concrete without the addition of fibers and with steel fibers. The smallest for concrete with the addition of glass fibers. The reason for this is the effect of fibers on the workability and consistency of the mixture. Fine polymer and glass fibers propagated in the mixture, improving its stability. Steel fibers, due to their greater rigidity and larger size, did not provide this property. Concrete without the addition of fibers, as a reference result, confirms this thesis.The compressive strength test was carried out for concrete used for the production of block supports and concrete used to make a concrete slab. Below in Based on the presented results, it can be concluded that the use of fibers slightly increased the compressive strength of concrete intended for block supports. The average strength of concrete without the addition of Z5 fibers is 68.5 MPa, while the strength of concrete with the addition of fibers is from 71.7 MPa for Z2 concrete, to 76.9 MPa for Z4 concrete, which is a strength increase of 4.7% to 12.3%. Although fibers have a greater impact on the increase in tensile strength than on compression, the conducted research shows that their use significantly increases the compressive strength and thus the class of concrete. In addition, it should be stated that the strength reserve is acceptable and allows us to assume that the concrete intended for the slab (Z1) and block supports (Z2–Z5) has been designed correctly.The frost resistance test was carried out for concrete intended for the production of block supports and concrete intended for making a concrete slab. Below in Based on the analysis of the obtained results, it should be concluded that all concrete samples meet the standard requirements. The permissible maximum loss in weight of samples after the frost resistance test should not exceed 5%, and the decrease in strength in relation to comparative samples not exposed to frost should not exceed 20%. All designed concretes are characterized by a loss of mass below 0.5% and a decrease in strength below 4%, which significantly exceeds the standard requirements. The research also shows that the use of fibers improved the frost resistance parameters of concrete intended for block supports in relation to the reference concrete Z5. In the case of steel fibers, the Z2 sample, the average strength decrease is reduced by 45.2% compared to the average strength decrease of concrete without fibers, and the average loss weight is reduced by 26.5%. For concrete with polymer fibers, Z3 concrete, the average strength decrease is reduced by 27.5%, and the average loss weight is reduced by 17.6%. When it comes to concrete with glass fibers, Z4 samples, the average strength decrease is reduced by 39% compared to the average strength decrease of concrete without fibers, and the average loss weight is reduced by 5.6%. Both due to the compressive strength and loss of mass after the impact of negative temperatures, concrete with the use of steel fibers looks the most advantageous. In terms of the decrease in compressive strength, Z4 concrete with glass fibers is not much worse, but in the case of a loss of mass, it is characterized by slightly more favorable results than concrete without fibers.As in the case of previous tests, the test of the modulus of elasticity was carried out for concrete intended for a concrete slab and concrete block supports with fibers and reference concrete without the addition of fibers. In the non-destructive method, based on the frequency of vibrations propagating in the sample, the modulus of elasticity was determined by the method of propagation of the wave in the sample. In the classical method, the modulus of elasticity was calculated on the basis of the recorded deformation of the sample during loading according to Formula (2). The results of the elastic modulus for individual samples determined by method one are summarized in σ—compressive stress increment (MPa);∆ε—sample deformation.∆The results obtained by the resonant method are higher, but the difference between the results in relation to the classical method is about 2% to 4%. In both test methods used, the influence of the addition of fibers on the modulus of elasticity of cement concrete can be seen. The highest modulus of elasticity in both resonance and load tests is characterized by samples with glass fibers, whose modulus of elasticity is greater than concrete without fibers in the resonant method by 4.8% and in the classical method by 3.9%. Slightly worse are samples with polypropylene fibers, whose elastic modulus is higher by 4.2% in the resonance method and in the classical method by 3.8%. Steel fibers, whose elastic modulus is higher by 1.4% in the resonance method, and by 1.2% in the classical method, have the least positive effect.In order to determine the influence of the strength parameters of block supports on the concrete slab, tensile strength tests at bending described in Based on the analysis of the presented results, it should be concluded that the fibers used in the concrete of block supports affect the tensile strength when bending the concrete slab. The highest tensile strength during bending has a plate with supports in which glass fibers are used, and the smallest with supports in which concrete without the addition of fibers is used. Glass fibers in concrete intended for block supports increased the tensile strength of the plate at bending by 17.5% compared to block supports in which no fibers were used. Steel fibers increased the tensile strength of the plate at bending by 10.7%, and polypropylene fibers by only 1.2%. It should also be noted that the degree to which individual fibers affect does not depend either on the compressive strength of the cement concrete or on the modulus of elasticity. The key in this case is how the material of block supports cooperates with the concrete slab in the transfer of loads.Another important study is to determine the influence of the material from which block supports were made on the tensile strength of the concrete slab in a longitudinal system. In this case, as before, the tests were performed on laboratory samples prepared on a scale of 0.3. The research was carried out for a concrete slab using block supports without fibers (Z5) and with the addition of fibers (Z2–Z4). The results of the study are presented in In the case of the longitudinal system, one can also notice increased tensile strength when bending the concrete slab after using reinforcing fibers in block supports. However, in the longitudinal arrangement, the difference in the results is not as large as in the case of the transverse arrangement. In the longitudinal system, block supports with glass fibers also had the best effect on increasing the tensile strength when bending the concrete slab and increased it by 8.6%. For the transverse system, it was 17.5%. Polypropylene and steel fibers increased the strength of the concrete slab by 7.5% and 7.1%, respectively. In the case of the longitudinal system, you can see a much more favorable effect of polypropylene fibers on the tensile strength when bending the concrete slab than in the case of the transverse system, where this benefit was only 1.2%. In the case of the longitudinal system, you can see a slightly more correlation of the impact of the increase in tensile strength when bending the concrete slab with the compressive strength of the concrete block supports. However, it is not possible to talk about a full correlation due to the value of standard deviations of the obtained results, which indicate that each type of fibers used equally affects the tensile strength of the concrete slab.On the basis of the conducted research, it can be concluded that individual strength results depend on the reinforcing fibers used. Samples with the addition of glass fibers are the most advantageous in the strength tests carried out, which are shown in In the case of compression , the nexIn the case of frost resistance of cement concrete , samplesAnalyzing the modulus of elasticity of concrete samples , it can Taking into account the influence of reinforcing fibers on the work of the concrete slab supporting the block supports, it should be noted that the most advantageous variant is the use of glass fibers in block supports, thanks to which the concrete slab is characterized by the highest tensile strength in both longitudinal and transverse systems. In the case of steel fibers, the tensile strength of the concrete slab at bending is reduced by about 0.4 MPa. For polypropylene fibers, the strength is lower by about 1 MPa. The least favorable effect on the strength of the concrete slab is the use of block supports without the addition of fibers, which is shown in The analyses carried out above show that the most advantageous in terms of strength and proper work of the surface is the use of glass fibers in block supports, which at the same time increase the strength of concrete intended for block supports and increase tensile strength when bending the concrete slab constituting support for block supports.Having in mind the above discussion one may conclude what follows.Finally, it should be stated that when changing the rail support in the transition railway sections, in order to eliminate the threshold effect, it is necessary to use a proper sequence of various reinforcing fibers in the set of railway concrete elements, which will properly affect the total rigidity of the track system in the transition zone.This article is a continuation of the research described in , in whicThe next step in the test cycle could be the use of an experimentally proven computational model , which w


Prior studies in the literature show promising results regarding the improvements in strength and durability of concrete upon incorporation of glass fibers into concrete formulations. However, the knowledge regarding glass fiber usage in concrete is scattered. Moreover, this makes it challenging to understand the behavior of glass fiber-reinforced concrete. Therefore, a detailed review is required on glass fiber-reinforced concrete. This paper provides a compressive analysis of glass fiber-reinforced composites. All-important properties of concrete such as flowability, compressive, flexural, tensile strength and modulus of elasticity were presented in this review article. Furthermore, durability aspects such as chloride ion penetration, water absorption, ultrasonic pulse velocity (UPV) and acid resistance were also considered. Finally, the bond strength of the fiber and cement paste was examined via scanning electron microscopy. Results indicate that glass fibers improved concrete’s strength and durability but decreased the concrete’s flowability. Higher glass fiber doses slightly decreased the mechanical performance of concrete due to lack of workability. The typical optimum dose is recommended at 2.0%. However, a higher dose of plasticizer was recommended for a higher dose of glass fiber (beyond 2.0%). The review also identifies research gaps that should be addressed in future studies. The construction industry is one of the world’s most rapidly growing sectors. Concrete is a widely applied construction material in the construction industry and is critical to its success ,2. ConcrIn compression, conventional concrete (CC) is usually strong but not in the domain of tension ,6. When Over the past few decades, there has been a growing concern about applying fibers instead of conventional materials to reinforce or rehabilitate concrete structures ,11,12,13Fibers may lower the overall cost of construction by substituting the conventional and energy-intensive techniques of wiring mesh and steel reinforcing bars with fibers . As a reGlass fibers (GF) were first employed as a mortar and concrete reinforcement in 1931 . They ar3. The tensile strength of glass fibers ranges from 1000 MPa to 3400 MPa with elastic modulus from 29 to 84 GPa. Furthermore, GF has a significantly higher modulus of elasticity than synthetic fibers, although not as high as steel or carbon fibers. They can withstand high temperatures and begin to weaken at about 700–900 °C [The color of glass fiber used in concrete is mostly light white, as shown in 0–900 °C . The hig0–900 °C . This is0–900 °C . TherefoVarious studies have also shown that fiber incorporation in the concrete improves engineering assets of concrete such as tensile capacity, flexural capacity, impact resistance, ductility and force carrying capacity even after cracks . NeverthThe fiber type, length, diameter, and quantity of fiber employed may all influence the implementation of fiber-reinforced composites. High fiber content is generally required for composites to work well and achieve high performance. For improved concrete performance, the ideal content is equally vital. Many researchers are focusing on glass fibers rather than steel fibers. Steel fibers are expensive and prone to thermal expansion and corrosion problems. Nevertheless, the understanding of glass fibers in concrete is sporadic, and no one can simply assess its significance in concrete. As a result, this study emphasizes the physical qualities of glass fibers, as well as the fresh assets, mechanical properties, and durability of concrete with the incorporation of glass fibers. A good outcome will also inspire future researchers to examine the selection and employment of glass fibers in practical applications.Song et al.  discoverOur study indicated that age bears no effect on the CPM of glass fiber-reinforced concrete. GF failed to enhance the CPM of the sample as compared to control specimens. In the presence of GF, it is impossible to achieve consistent distribution of concrete ingredients. These results corroborate those of Fenu et al. . When glIn the glass fiber specimens, point accumulation of glass fibers and a lack of a proper mortar cover surrounding the fibers cause cracks to appear around the fibers, eventually leading to concrete rupture as shown in The relationship between CPM and FLS is seen in According to one study, increasing the volume percentage of glass fibers in self-compacting concrete (SCC) from 0 to 1.5 percent enhanced the modulus of elasticity . A studyChlorides may cause corrosion in reinforced steel if they manage to permeate into the concrete. These represent some of the most significant problems that may be identified in concrete structures globally. The chloride-ion permeabilities of the SCC composites are shown in The water absorption test determines how quickly the exterior- and inner-concrete surfaces absorb water. The test involves determining the rise in density of samples due to water absorption with time after the sample has been subjected to water. Because water includes numerous harmful substances that soak into concrete, causing concrete disintegration and resulting in decreased durability, more water absorption leads to lower durability.The impact of GF on water absorption was much better than that of PPF. When the water/binder ratio was 0.30, adding 1.35 percent GF reduced the specimen’s water absorption from 3.49 percent to 1.99 percent, with a maximum reduction of 43.0 percent. Meanwhile, adding 0.45 percent PPF reduced water absorption from 3.49 percent to 3.12 percent, with a maximum reduction of 10.6 percent . CompareUltrasonic pulse velocity (UPV) assessment validates the integrity and quality of mechanical strength of concrete by measuring the velocity and attenuation of an ultrasonic wave travelling through concrete at a depth of approximately 6 feet. Smaller-speed regions have smaller compactness and mechanical capacity than greater-speed regions. The Rebound hammer test is a non-damaging concrete assessment procedure that evaluates the concrete’s mechanical capacity rapidly and simply. The homogeneity of plain concrete may be reduced by adding fibers. Concrete is graded according to the UPV values and rebound numbers specified in the appropriate standard codes. The steel fiber-reinforced concrete surface hardness was found as a hard layer. The surface hardness of the GF-reinforced concrete matrix was lower than that of RCC, and it was evaluated as a good layer. In comparison to ordinary concrete, reinforced concrete has poor homogeneity. The reinforced concrete containing a large fiber volume improved the homogeneity in this study. As the amount of fibers rose, the pulse velocity dropped. Concrete with steel fibers have a lower pulse velocity than concrete with glass fibers. When compared to reinforced vibrated concrete, reinforced SCC exhibited higher uniformity .Concrete creep is the deformation of a structure caused by a sustained load. When concrete is exposed to continuous pressure or stress, its shape may be altered. Over a period of 50 years, a study on the creep behavior of pultruded GFRP revealed a typical reduction in instantaneous longitudinal; flexural stiffness of pultruded profile of around 50%, and it was predicted that for a period of one year, the flexural stiffness will be in the range of 75–80% of elastic. It is also expected that after one year of loading, creep deflection would grow by up to 35 percent, and after 50 years, increase by up to 100 percent . AnotherConcrete shrinkage and volume reduction occur due to moisture loss, which eventually results in cracks and more concrete deformation. Early-stage shrinkage (polyolefin or capillary shrinkage), autogenous shrinkage, carbonation shrinkage, and drying shrinkage are the four types of shrinkage. Early-stage shrinkage in new concrete is caused by a moisture exchange from the surface to the environment (by evaporation) and a mass exchange via the concrete to the surface. After casting, polyolefin shrinkage is detected in the early hours, which may be avoided by optimizing the mix design and curing properly. Carbonation shrinkage is caused by interactions between hardened cement paste and carbon dioxide . This prWhen w/b is 0.30, SEM pictures of GFRC specimens are shown in The excellent fiber–matrix bonding quality made it possible for GF to increase the concrete’s strength qualities and reduce water absorption. The GF filled the gaps and decreased porosity since its surface was covered by a firmly cemented cement matrix. The GF-30-135 45 cement matrix structure (water to binder ratio 0.30 and GF 1.35 percent) was dense and less porous, as illustrated in When w/b is 0.35, the SEM images of the GFRC sample are shown in It has been stressed in numerous research works and studies that the content of the fibers used to strengthen the composite material is quite significant. A greater fiber content is not always beneficial. Although fiber reinforcement is known to increase material mechanical characteristics, it generally only does so to a certain amount, beyond which the qualities begin to deteriorate. Therefore, a composite material’s ideal fiber composition is critical for achieving the greatest outcomes. Physical parameters such as fiber length, fiber count, and fiber distribution should be considered . In concOther matrices have been employed to generate high-performance composites using fibers . The mecGFRC is becoming an increasingly popular and commonly utilized material. Both in structural materials, and items associated with the construction process. In addition, modest architectural features, are being manufactured with GF to create more appealing, durable, and safer public places . Glass fOne of the most troubling issues in the early stages of GRC development was the durability of the glass fibers, which grew brittle over time owing to the alkalinity of the cement mortar. Significant progress has been achieved since then, and the issue is now essentially eliminated with new forms of alkali-resistant glass fibers and mortar additives that inhibit the processes behind GRC embrittlement .The study focused on composites made of glass fibers. The key qualities of concrete, such as mechanical durability and microstructure, were considered. Following are the conclusions reached after a thorough examination and discussion of the findings.Glass fibers have a negative impact on concrete flowability due to their higher surface area, which increases resistance to flow.Glass fibers did not show significant improvement in compressive strength. Tensile and flexural capacity, on the other hand, were significantly enhanced. This is a result of the glass fibers’ ability to resist cracking.The surface hardness of glass fiber-reinforced concrete is lower than that of steel fiber-reinforced concrete, which is rated as a good layer.Glass fibers reduce the permeability of concrete to chloride-ions due to crack prevention.Glass fibers increase the performance of concrete in a maritime environment.The optimal dosage of fibers is affected by the water to binder ratio, according to preliminary study of SEM observation. The major causes for this are the dramatic increases in pore size and quantity caused by the coupling effect of increased water/binder ratio and fiber content. The impact of the water/binder ratio should be addressed when considering the effect of fibers on the mechanical or microstructural qualities of concrete.The performance of concrete in harsh environments should be thoroughly examined.With regard to the creep and dry shrinkage qualities of glass fiber-reinforced concrete, there is no information available.It is essential to explore the thermal characteristics of glass-based composites.According to some research, glass fibers do not considerably improve the compressive capacity of concrete. As a result, further research using various pozzolanic materials is needed to increase the compressive capacity of glass fiber-reinforced concrete.


Some of the primary problems of construction are brittleness and low the mechanical properties of good thermal insulation materials. Heat-insulating foam concrete has a low thermal conductivity. However, it is practically impossible to transport it over long distances since corners are cracked during transportation, the structure is broken, and, in principle, the fragility of this material is a big problem for modern buildings. The purpose of this study was to develop a heat-insulating foam concrete with improved characteristics by experimentally selecting the optimal dosage of polypropylene fiber and a nanomodifying microsilica additive. Standard methods for determining the characteristics of fiber foam concrete were used as well as the method of optical microscopy to study the structure of the composite. It has been established that the use of polypropylene fiber with the optimal reinforcement range from 1% to 3% allows us to achieve an improvement in the mechanical and physical characteristics of fiber foam concrete. The optimal dosage of the nanomodifier introduced instead of a part of the binder (10%) and polypropylene fiber (2%) by weight of the binder was determined. The maximum values of increments in mechanical characteristics were 44% for compressive strength and 73% for tensile strength in bending. The values of the thermal conductivity coefficient at optimal dosages of the nanomodifier and fiber decreased by 9%. The absence of microcracking at the phase boundary between the polypropylene fiber and the hardened cement–sand matrix due to nanomodification was noted. Some of the main problems of construction are fragility and the low mechanical performance of good thermal insulation materials. So, low-density foam concrete has good thermal insulation ability, but it is practically impossible to transport it over long distances since corners are broken during transportation, the structure is broken, and, in principle, the fragility of this material is a big problem for modern builders. In this regard, the actual direction of building materials science is the search for ways to find the optimal relationship between the density and strength of heat-insulating concretes. At the same time, modern materials science puts forward the creation of new and improvement of existing building materials and technologies for their production as the main tasks.3. The structure of this material is characterized by a multitude of randomly arranged air voids, which were formed in the concrete mixture due to the addition of a foaming agent [The most relevant and progressive building materials include heat-insulating concretes, among which foam and fiber foam concretes stand out—some of the most popular in practical construction due to their properties, economy, reliability, and durability ,2. Foam ng agent . As for ng agent ,6,7 noteThe main raw materials for the preparation of foam concrete are cement, foaming agent, sand, and water for mortar. Ordinary Portland cement, quick-hardening Portland cement, sulfate-resistant Portland cement, and high alumina cement can be used as a binder in foam concrete and as additional materials to replace part of the cement in the range from 10% to 70% in place of materials such as microsilica, fly ash, lime, ground granulated blast-furnace slag, and others. As a rule, various additional components in addition to the main raw material are used to improve the mechanical and physical characteristics ,23,24,25After considering the modifiers and nanomodifiers that are used for concrete, another important criterion for the compatibility of these nanomodifiers with foam concentrates should be noted. The blowing agent is a key component for foam concrete and regulates the density of concrete due to the amount of air bubbles formed in the cement paste mixture. Protein-based and synthetic-based foam concentrates are the most common in practice; protein-based foam concentrates are characterized by the formation of a more durable and closed-cell structure with a stable network of air cavities. When using synthetic foam concentrates, this causes much greater expansion and makes it possible to achieve a lower density ,36,37,38The goal of this study is to develop a heat-insulating foam concrete with improved characteristics by experimentally selecting the optimal dosage of polypropylene fiber and a nanomodifying microsilica additive. Tasks to achieve the set goal are as follows:(1)Determination of a rational optimal dosage of polypropylene fiber, which allows to achieve the maximum improvement in the mechanical and physical characteristics of fiber foam concrete;(2)Determination of the optimal dosage of the nanomodifying microsilica additive;(3)Revealing the dependences of the mechanical and physical characteristics of fiber foam concrete on the values of dosages of polypropylene fiber and silica fume;(4)Determination of further research prospects.The scientific novelty of the work lies in obtaining new dependences of the characteristics of foam concrete on the dosages of polypropylene fiber and a nanomodifying microsilica additive. Theoretical and experimental studies were carried out to evaluate the effectiveness of the use of polypropylene fibers in foam concrete technology, both separately and in combination with a nanomodifying additive. According to the results of analytical studies, the optimal ranges of the percentage of fiber reinforcement were previously determined and, during experimental studies, the most optimal dosages of fiber and silica fume were determined, at the values of which the best physical and mechanical characteristics of foam concrete are observed.To ensure the correctness and reliability of the results obtained, a methodological decision was made to use Portland cement without additives, which made it possible to evaluate the influence of additives and their complex effect, regardless of the additives contained in the Portland cement. As the initial filler, quartz sand with known characteristics was taken because quartz sand is not reactive, and it allows us to evaluate the influence of certain modifiers in its pure form so that the scientific novelty is distinguished by reliability, correctness, reproducibility, and repeatability. Foaming agent PB-2000 was adopted based on the results of a literature review ,36,37,38The properties of Portland cement were tested according to GOST 30744 «Cements. Methods of testing with using polyfraction standard sand», sand, according to GOST 8735 «Sand for construction work. Testing methods». The properties of the foaming agent and fiber are taken from the manufacturer.Microsilica MK-85  was used as a modifying additive for scientific research. The chemical composition of microsilica is presented in It follows from Thus, all received materials, after their additional verification and comparison of their own laboratory data with the data of manufacturing plants, made it possible to set and determine specific research methods.(1)Making samples;(2)Testing and examination of the obtained samples.Research methods were based on normative and technical proven methods and were reduced to two stages:-Water-solid ratio W/T = 0.49;-The ratio of sand and cement P/C = 0.3;-3.Foaming agent content PO = 5.25 kg/mFoam concrete samples were made in laboratory conditions. For the manufacture of all samples, the following parameters of concrete mixtures were adopted :-Water-sThe sand was preliminarily sifted through a standard set of KSI sieves  to obtain the required fraction of 0.16–0.315 mm.-Hydraulic press IP-1000 ;-Device for determining thermal conductivity ITP-MG4 ;-Laboratory oven ShS-80-01 SPU ;-Metal measuring ruler 500 mm ;-Laboratory scales HT-5000 ; caliper ShTs-I-250–0.05 ;-A device for measuring deviations from the plane NPL-1 and a device for measuring deviations from perpendicularity NPR-1 .The dosed ingredients—water, Portland cement, microsilica, fiber, and sand—were successively loaded into a CA 400/500 laboratory turbulent mixer with a capacity of 50 L and a rotor speed of 620 rpm . Mixing of all components was carried out until the fiber was evenly distributed over the volume of the concrete mixture. Next, with the mixer activator stopped, a dosed foaming agent was poured in and the mixture was poured for 4 min. The prepared mixtures were poured into metal molds previously lubricated with mineral oil. Forms with foam and fiber-reinforced concrete mixtures were slightly compacted by tapping on a metal table and smoothing with a ruler. Further, the samples hardened under normal conditions with a temperature of (20 ± 2) °C and relative humidity of the air (95 ± 5)%. After 3 days after manufacture, the samples were removed from the molds, and they continued to harden under normal conditions until reaching 28 days of age. The sequence, time, speed of mixing, and the order of introduction of materials are adopted according to previous studies . TestingThe study of the structure of fiber foam concrete samples was carried out on an MBS-10 microscope .-Compressive and tensile strength in bending was determined according to GOST 10180 “Concretes. Methods for strength determination using reference specimens”;-The average density was determined according to GOST 12730.1 “Concretes. Methods of determination of density”;-Release humidity was determined according to GOST 12730.2 “Concretes. Method of determination of moisture content”;-Thermal conductivity was determined according to GOST 7076 “Building materials and products. Method of determination of steady-state thermal conductivity and thermal resistance”.The physical and mechanical characteristics of the fiber foam concrete samples and the control composition were determined by the following methods:Before conducting the main part of the experimental studies to study the effect of the content of microsilica additive introduced instead of a part of the cement and the percentage of dispersed reinforcement with polypropylene fiber on the physical and mechanical characteristics of fiber foam concrete, preliminary studies were carried out to identify the optimal range of the percentage of fiber reinforcement, the plan of which is shown in During the main part of the experimental studies, a total of 22 series of samples were made and tested with different values of the percentage of fiber reinforcement with polypropylene fiber and the content of the nanomodifying microsilica additive. The experimental research program is shown in The results of experimental studies of the effect of the percentage of fiber reinforcement on the physical and mechanical characteristics of foam concrete are shown in The compressive strength curve of the test samples of fiber foam concrete  at variox is the dosage of polypropylene fiber; R2 is the coefficient of determination.Here The dependence curve of tensile strength in bending of fiber foam concrete samples at various dosages of polypropylene fiber is approximated by the equation:The change in tensile strength in bending is similar to the nature of the change in compressive strength. Thus, the increases in tensile strength in bending at dosages of polypropylene fibers of 1%, 2%, 3%, 4%, and 5% were 15%, 34%, 24%, 2%, and 0%, respectively. At a fiber dosage of 6%, the drop in strength was 10%.Control and evaluation of the strength of fiber foam concrete samples were carried out in accordance with GOST 18105 “Concretes. Rules for control and assessment of strength”. The standard deviation of strength values does not exceed 5%, and the coefficient of strength variation is not more than 4%, which meets the requirements of the standard.From The control and evaluation of the average density of fiber foam concrete samples was carried out in accordance with GOST 27005 “Light-weight and cellular concretes. Rules for control and assessment density” and for release moisture in accordance with GOST 13015 “Concrete and reinforced concrete products for construction. General technical requirements. Rules for acceptance, marking, transportation and storage”. The variation in the results of the average density (no more than 2%) and release moisture (no more than 4.5%) of each sample turned out to be less than the ranges allowed by the standards.The dependence of the thermal conductivity of fiber foam concrete samples at various dosages of polypropylene fiber is approximated by the equationFrom The control and evaluation of the thermal conductivity of fiber foam concrete samples was carried out in accordance with GOST 7076 “Building materials and products. Method of determination of steady-state thermal conductivity and thermal resistance”. The variation of thermal conductivity results for each sample does not exceed 2% and turned out to be less than the ranges allowed by the standards.According to the results of a study aimed at identifying the optimal range of fiber reinforcement, it was found that the most optimal range of polypropylene fiber is its content in foam concrete in an amount of 1% to 3%. The best values of the physico-mechanical characteristics of fiber foam concrete were recorded when the fiber dosage was 2% by weight of cement. Later, when conducting experimental studies on the production of fiber foam concrete nanomodified with the addition of microsilica, the range of dispersed reinforcement in the amount of 1–3% was adopted.The results of experimental studies of the influence of the content of microsilica additive introduced instead of part of the cement and the percentage of dispersed reinforcement with polypropylene fiber on the strength characteristics of fiber foam concrete are presented in The graph in Based on the values of the compressive strength of the fiber foam concrete samples, it can be said that the most optimal dosage of silica fume, introduced instead of a part of the cement, is a dosage of 10%, since it is at this percentage of replacement that the highest compressive strength value was recorded, which amounted to 1.69 MPa for the composition of the type F14. As for the most optimal dosage of polypropylene fiber, its value is 2% by weight of the binder component. Compositions of type F2, F5, F8, F11, F14, F17, and F20 at different dosages of microsilica, but the same value of dispersed reinforcement equal to 2%, showed the best values of compressive strength, which are respectively equal to 1.51 MPa, 1.55 MPa, 1.62 MPa, 1.63 MPa, 1.69 MPa, 1.61 MPa, and 1.52 MPa.The graph in The flexural tensile data results shown in The results of experimental studies of the influence of the content of microsilica additive introduced instead of a part of cement, and the percentage of dispersed reinforcement with polypropylene fiber on the physical characteristics of fiber foam concrete are presented in 3, and the release moisture values ranged from 20% to 25%. Thus, the analysis of From The best value of the thermal conductivity of the test samples of fiber foam concrete was recorded for the composition of type F14, where the replacement of part of the cement with the addition of silica fume was 10%. Thus, as in the case of strength characteristics, the dosage of microsilica of 10% is the best. As for the percentage of fiber reinforcement, at a dosage of 2%, the lowest values of thermal conductivity are observed.The photographs show differences in the pore macrostructure between the two samples. So, the porous macrostructure of the control sample of foam concrete in Next, consider After testing on the specified sample, the absence of microcracking at the phase boundary between the polypropylene fiber and the reinforced cement–sand matrix due to nanomodification is well monitored. The nature of the micropore structure makes it possible to register the positive influence of the combined effect of dispersed reinforcement and nanomodification. Thus, on the example of the fundamental relationship between the composition of the micro- and macrostructure and the properties of the material, the positive influence of the proposed recipe–technological factors has been proved.Let us analyze the mechanism of the processes occurring in the fundamental nature of the structure formation of foam concrete of the obtained type. Due to the fact that at the micro level the pore structure acquires a denser packing of particles, microporosity decreases, macroporosity increases due to the strengthening of interpore partitions, volume is preserved, and concrete shrinkage is reduced. Thus, the density of the material, due to the preservation of the volume at the same level, is reduced. At the same time, interpore partitions acquire a denser packing of particles at the micro level, and at the macro level the foam concrete structure acquires a more perfect pore structure, the pores become monodisperse, large, and all this has a positive effect on the thermal insulation properties of the final product .When fiber is added, the internal forces in the concrete are redistributed. Those microcracks that occurred in the absence of fiber reinforcement under mechanical, static, and dynamic effects on such concrete are absent with the introduction of fiber, which has some damping, softening effect. The reduction of microcrack formation, which has been established by studies both at the macro level and at the micro level with the help of a microscope, makes it possible to improve not only the structure of this concrete but also its properties ,45,46.The combined effect of nanomodification with microsilica and fiber reinforcement with polypropylene fibers improves both the mechanical and physical properties of foam concrete. It is in this connection that its strength indicators, as well as the thermal conductivity index, have improved.It is known that the strength of cellular concrete largely depends on the physical and mechanical properties of the material of interpore partitions, in particular, on its density. However, in real materials, dense packing of solid particles in interpore walls is usually not achieved due to the angularity and roughness of the particles ,35,47,48Let us carry out a comparative analysis of the results obtained in this study with data obtained by other authors. In , the effIn , the effIn , the autComparison with works ,29,31 co(1)The use of polypropylene fibers in the range from 1% to 3% by weight of the binder makes it possible to improve the mechanical and physical characteristics of fiber foam concrete; the best values of the strength and physical characteristics of fiber foam concrete are recorded at a dosage of polypropylene fiber of 2%;(2)The optimal dosage of the nanomodifying microsilica additive introduced instead of a part of the binder is 10%;(3)The maximum values of increments in mechanical characteristics were 44% for compressive strength and 73% for tensile strength in bending, the values of the coefficient of thermal conductivity of fiber foam concrete at optimal dosages of the nanomodifier and polypropylene fiber decreased by 9%, and the use of polypropylene fiber and microsilica in the ranges considered in this study does not reflect a clear dependence of density and release moisture on the dosage of fiber and nanomodifier;(4)The results obtained in the course of the study make it possible to determine further research prospects for structural, heat-insulating, and structural foam concrete and considering the possibility of improving their characteristics and significantly increasing the reliability of enclosing load-bearing structures made of such materials.Thus, based on the results of the study, the following conclusions can be drawn:


Cement production is environmentally unsustainable due to the high anthropogenic carbon emissions produced. Supplementary cementitious materials (SCMs), derived from the by-products of different industries, have been deemed an effective way to reduce carbon emissions. The reduction in carbon emissions is achieved by lowering the clinker factor of cement, through a partial replacement with an SCM. Sugarcane Bagasse Ash (SCBA) is produced as an agricultural waste from the sugarcane industry and has gained a lot of attention for being a feasible and readily available pozzolanic material, underutilised as an SCM. This study evaluates alkali-activated sugarcane bagasse ash’s mechanical and durability performance, at varied contents, in binary blended cement concrete and ternary blended cement concrete containing silica fume (SF). Potassium Hydroxide (KOH), used as the alkali activator, is intended to enhance the reactivity of the ash, with the possibility of a high-volume SCBA content. The mechanical performance was investigated by compressive and split tensile strength tests, and durability performance was investigated using the Oxygen Permeability Index (OPI) test. In addition, a micro-CT porosity test was conducted to assess how the microstructure and porosity of the concrete affect the mechanical and durability performance. The results indicated that using SCBA in a ternary blend with SF can significantly improve the overall performance and create less porous concrete. At 30% SCBA and 10% SF replacement, the performance tests revealed the highest mechanical strength and the lowest permeability, outperforming the control concrete and the binary blended cement concrete containing only SCBA. Sugarcane Bagasse Ash (SCBA) is produced as a secondary product from the sugarcane industry. Bagasse is produced during the extraction of sugar from sugarcane; this bagasse is considered a waste product that is then burnt as a fuel for electricity generation [Global warming has become a very big concern to the future of civilisation and creating a sustainable and environmentally conscious method of development is paramount. Ordinary Portland Cement (OPC) is one of the major ingredients used in concrete. However, OPC production produces copious amounts of carbon dioxide  and blending with SF. Alkali activation can potentially improve the early age pozzolanic reactivity of SCBA by contributing to an early alkaline environment, compared to that later provided by cement hydration—Ca(OH)products . The alkproducts ,19. It itrolysis . Using tThe addition of SF (micro-silica) can provide synergetic effects in improving the microstructure and nucleation sites to form cement hydration. SF is known to be highly amorphous and finely grained; that is, improved pozzolanic activity and micro-filler effects for improved reactivity, pore size, aggregate interfacial refinement, and better packing density . CombiniThis study is poised to take advantage of the alkali activation and SF inclusion to assess the performance of concrete with a high volume of SCBA contents. This is done by replacing Portland cement (PC) of 30% and 50% with alkali-activated SCBA and blending with 10% SF as separate mixtures. This is to understand how these two SCMs interact with each other and the potential to use SCBA as an SCM at these relatively high replacement percentages. It should be noted that this study does not intend to isolate and quantify the effect of alkali activation; hence, the activator content was kept constant for all mixes, except the control. The performance of the mixtures was assessed by compressive and splitting tensile tests for mechanical strength and oxygen permeability index (OPI) tests for durability. To explain the obtained results for the performance of the mixtures and identify the influence of the SCMs, characterisations of the SCMs were undertaken, mortar samples of each mix were characterised, and micro-CT scans were carried out on the concrete samples to assess the microstructure.This study is significant as it shows how using a SCBA replacement of 30% in a ternary blend with 10% SF can produce concrete that outperforms the binary blend at the same SCBA replacement and control (Portland cement), in terms of mechanical and durability performance. By using this alkali-activated ternary blend, the limitations of using SCBA replacements up to a maximum of 20–25% can be overcome. This research is fundamental in producing environmentally sustainable concrete for the future. It indicates that up to 40% of the cement can be replaced while producing no negative effect on performance. This will significantly reduce the clinker factor of the cement and, consequentially, reduce carbon emissions.2/kg). SCBA was sourced as raw ash from Kwa-Zulu Natal in South Africa. Graded river sand  was used as the fine aggregate, and 19 mm quarry stone was used as the coarse aggregate. Potassium Hydroxide (KOH) was used as the alkali activator and intended to enhance the pozzolanic reactivity. KOH was chosen as it has an ionic size K+ of 152 pm. This is very small and will accelerate the dissolution process of the aluminosilicate minerals [® Fluid Premia 310 , a modified polycarboxylate polymer. This plasticiser was required to achieve the correct workability while maintaining a constant water-to-border ratio. The materials used and the characteristics of each are shown in The cementitious materials comprised PC (CEM II 52.5N), processed SCBA (90% passing through the 45 microns sieve size), and SF . Calcination has been shown to increase the pozzolanic activity of SCBA ,10,22. K3 throughout. The slump range of 50–90 mm was maintained using the superplasticiser. KOH was added to all mixes containing SCMs at a dosage of 1% with respect to the binder weight and then subtracted from the water mass to ensure that the w/b ratio was consistent. The mix proportions for a 1000-litre mix are shown in The mix designs were developed according to the Cement and Concrete Institute (C&CI) design method based on the ACI Standard 211.1-91 . The watX-ray fluorescence (XRF) analysis was used to obtain the chemical (oxide) composition of the SCMs (processed SCBA and SF) using a PANalytical AXIOS XRF spectrometer, Malvern Panalytical (Pty) Ltd., Aimelo, The Netherlands.Qualitative and quantitative X-ray diffraction (XRD) analysis was conducted on the raw SCBA, processed SCBA, and SF to determine the mineralogical characteristics of these cementitious materials. By this, the influence of SCBA calcination can be observed. In addition to these cementitious materials, the sample of each concrete mix was analysed at a curing age of 21 days. A backloading preparation method was used for the XRD analysis. Hence, the prerequisite for the testing procedure was that all samples were to be tested in powder form so that they could be placed into the backloaded sample holder. The (mortar) sample was prepared by hand grinding the concrete samples using a mortar and pestle and sifting out the coarse aggregate. The mortar samples were analysed to identify the hydration extent and observe the influence of the adopted approaches .The diffractograms were obtained using a Malvern Panalytical Aeries diffractometer, Malvern Panalytical (Pty) Ltd., Aimelo, The Netherlands. This diffractometer had a PIXcel detector, and fixed slits with Fe-filtered Co-Kα radiation. The phases were identified using X’Pert Highscore plus software, Malvern Panalytical (Pty) Ltd., Aimelo, The Netherlands, and the specific crystalline phase amounts (percentage of weight) were obtained using the Rietveld Method. The Internal Standard Method was used to obtain the amorphous phase amount (percentage of weight). Further, 20% addition of silicon was added as the internal standard as it is 100% crystalline and nonreactive with the cementitious materials and mortars. The addition of silicon as the internal standard allowed the phase quantity of the samples to be rescaled to 20% silicon. Thus, absolute phase quantities could be obtained, with the specific deviation to 100% weight percentage, constituting the resulting amorphous phase amount.Scanning electron microscopy (SEM) was carried out to determine the morphology of the SCMs . The equipment used to obtain the SEM images was a Zeiss MERLIN Field Emission SEM, Carl Zeiss AG, Jena, Germany, with a voltage of 10 kV.SANS 5861-2:2006a  and SANSThe preparation of the test specimens for the OPI test was done following SANS 3001-CO3-1:2015 [The compressive strength test was conducted in accordance with SANS 5863:2006e . This teThe split tensile strength test was conducted following SANS 6253:2006f . This teThis test method was conducted in accordance with ASTM C311:2018  and ASTMThe OPI test was conducted per SANS 3001-CO3-2:2015 . This tePorosity analysis is the method of determining the pore spaces or voids present inside the concrete. It is used to assess the concrete’s durability  properties for the transport properties. The Micro-CT (Micro Computer Tomography) scanner was a General Electric V TomeX L240 system, General Electric, Wunstorf, Germany. This system used an X-ray source and detector to obtain 2D images, which were then combined to create a 3D representation of the reconstructed 2D images . The X-rThis analysis was conducted to assess the porosity of the different concrete mixes. It could be analysed through qualitative visualisation of the spatial distribution of voids present in the concrete  and/or qThe results of the XRF analysis are shown in The results from the XRD analysis are represented by mineral names, which correspond to the specific group of minerals, as shown in From Portlandite is the natural form of calcium hydroxide (Ca(OH)₂) and is used up for pozzolanic reactions of SCMs. A pozzolanic reaction is from the amorphous and partially crystalline siliceous phases in the SCMs reacting with the calcium hydroxide produced during hydration to yield calcium silicate hydrate (C-S-H) gel . From thA further decrease in the calcium hydroxide phase is observed in the ternary blends containing SCBA and SF (Mixes 4 and 5). Mixes 4 and 5 have a portlandite weight percentage of 0.4% and 0.2%, respectively. This proves a very high amount of pozzolanic activity in these mixes, as Mix 5 is close to 0% portlandite. Portlandite was decreased significantly more in the ternary blends than the binary blends at the same SCBA replacement percentage. This supports the fact that the amorphous nature of SF has significantly increased the pozzolanic activity during hydration. The combination of these two SCMs produced high reactivity. The high reactivity could also be attributed to the use of KOH as the alkali activator, as KOH helps raise the pH to a level that can start and maintain the pozzolanic reactions . It shouThe amorphous weight percentages represented in The SEM results obtained for the unprocessed SCBA are shown in The processed SCBA SEM images  show thaThese structures, normally in an elongated oval shape, have been observed to be carbon particles in SCBA . The parThe SF SEM results are shown in The workability of every mix was designed to have a slump that falls within a range of 50–90 mm. This was achieved using different contents of the superplasticiser. Therefore, the amount of superplasticiser required varied depending on the SCM’s type and content. The results from the SAI test at 7 and 28 days of curing are 0.775 and 0.845, respectively. The results show that the 7- and 28-day SAI is above the minimum value of 0.75, stipulated in ASTM C618:2018 . The SAIThe results from the compressive strength test are shown in The main cause of the low compressive strength results obtained in high-volume SCBA blended cement concrete can be associated with low early reactivity. The high-volume SCBA causes a dilution effect, leading to delayed pozzolanic reaction, and is common to most silica-based SCMs, causing higher strength only at much later curing ages, such as 90 days . The stuThis study used KOH as an alkali activator to increase the early reactivity by creating a high alkaline environment. The dissolution of Al and Si from the SCBA and SF is accelerated, forming a polymeric gel that enhances early age mechanical performance . The sin2 from the XRD results. The SF  used allows for a good reduction (40%) of Portland cement and higher strength at 28 days. Mix 4 is adjudged to the optimum mix, with about 2% higher strength than the control. Similar results were also reported by Chindaprasirt et al. [The improved increase between Mixes 2 and 4 and Mixes 3 and 5 also indicates that adding SF can significantly improve pozzolanic activity, rather than just SCBA. These are supported by the increased consumption of Ca(OH)t et al. , which ft et al.  found thThe results from the split tensile strength test are shown in The ternary blends (Mix 4 and 5) show a similar pozzolanic trend as the compressive strength. Mix 4 is observed to be the optimum mix for this test as well, achieving the highest split tensile strength out of all mixes. Mix 4 was 0.26% higher than the control at 28 days. The ternary blends achieved better results than the mix with only SCBA at 28 days. At 30% SCBA replacement, Mix 4 achieved a strength that was 5.83% higher than Mix 2. For 50% SCBA replacement, Mix 5 achieved a strength that was 17.76% higher than Mix 3. This proves the synergetic effects of SF with SCBA. The increased strength results achieved with the addition of SF in both mechanical strength tests can be attributed to the enhanced aggregate matrix bond by interfacial refinement  and micrTransport properties within concrete cause different mechanisms of deterioration  to effectively ingress through the microstructural pores of the concrete and cause durability problems. The Oxygen Permeability Index (OPI) test is a durability index that effectively assesses the resistance of concrete to oxygen permeation. The primary objective of the durability index test is to assess the cover zone that is intended to protect the reinforcement in the concrete . The OPIThe results from the OPI test are shown in The results follow the same trend noticed in both the compressive and split tensile strength tests. All OPI values that have been calculated are greater than 10, which indicates that the expected durability performance in terms of gas permeation is excellent for all mixes. The binary blends (Mix 2 and 3) have lower OPI than the control and decrease as the replacement percentage increases. The ternary blend of Mix 4 achieved the highest OPI, being 1.91% higher than the control and 2.30% higher than Mix 2 (without SF). It is evident that SF helped decrease the permeability of the concrete and created more durable concrete . Mix 5 achieved the lowest OPI; that is, the high volume of 50% SCBA content produces concrete with a higher permeability which can be associated with less densification due to the lesser C-S-H observed in the XRD results.From From the pore size distributions by volume in The study conducted by Naik  found thWhen comparing the mechanical strength results to porosity, it is noted that Mixes 3 and 5 achieved the lowest strengths and the highest porosity. Porosity is one of the major determining factors for strength in concrete; with the decreasing compressive strength obtained with an increase in porosity , the intThough a morphostructural investigation (SEM) on the mechanically tested mixtures were not reported, the quantitative XRD and porosity analyses corroborate the mechanical results, giving insights into the morphology and microstructure, respectively. C-S-H results from the XRD highlight the extent of cement hydration/bonding, while the oxygen permeability (mean K) and XCT scan results highlight the microstructural properties, including the interconnectivity of pores.This study focused on evaluating the mechanical and durability performance of using a binary blend of SCBA with Portland cement in concrete and a ternary blend of SCBA, SF, and Portland cement, with the addition of an alkali activator. The conclusions that can be drawn from this study are as follows.Processing the SCBA through calcination resulted in a material that possessed better pozzolanic properties than the raw SCBA. The processed SCBA has a very high silica content and a low LOI. Moreover, the processed SCBA had an increase of 12.3% in the amorphous phase and a 10.8% decrease in the crystalline quartz phase.SF possessed exceptional pozzolanic properties, with a high silica content and a low LOI, superior to the processed SCBA. In addition, SF possesses essentially an amorphous phase at 96.1% and fine spherical particles confirmed by SEM images.The XRD analysis of the cement mortar samples at 21 days confirmed pozzolanic reaction due to the SCMs with decreasing portlandite content. This, with the SAI results, indicates that both SCBA and SF have good pozzolanic reactivity in concrete. The amorphous SF helped produce a higher amount of the C-S-H phase (Mix 4). This high amount of C-S-H phase helped increase the strength and improve the microstructure of the concrete, which consequently improved the durability. At 28 days of age, the compressive and tensile strength of the ternary blend supersedes that of the plain concrete, allowing for up to 40% cement reduction without detrimental effects.The results from the OPI test showed that all mixes achieved indices that can be considered excellent (>10). A similar trend to the the mechanical strength tests was observed in the OPI test. The SCBA binary blends resulted in a lower OPI than the control and decreased further as the replacement percentage increased. The ternary blend of Mix 4 achieved the highest OPI. This indicates that the addition of SF produces better mechanical performance and creates a more durable concrete.The interconnectivity of the pores has an impact on the permeability of the concrete more than the porosity. This is portrayed by Mix 4, with higher porosity than the control, although with higher resistance to oxygen permeation. Higher porosity impacts the mechanical performance of the concrete, as portrayed by Mixes 3 and 5, having the lowest strength and the highest porosity.This study proves that when SF is added at 10% content as a ternary blend with SCBA, SCBA can be added up to 30% and still produce concrete with better mechanical and durability performance than the control (plain concrete). This research shows how the limitations of using high-volume SCBA can be curtailed . The findings presented in this study are fundamental in producing a more environmentally sustainable future of construction and can positively influence the concrete industry. Up to 40% of the cement content in the concrete can be replaced while providing enhanced performance characteristics at the same time. This will significantly reduce the clinker factor of the cement and consequently reduce carbon emissions. Further studies are required to optimise the alkali content/activation and achieve similar or higher early age strength as the control with high-volume SCBA.


Among the 139,259 prescriptions with antibiotics, 37.82%  included two or more antibiotics, 55.29%  included parenteral antibiotics, and 56.62%  included Watch group antibiotics. The binary logistic regression indicated that (1) female patients were slightly less likely to be prescribed antibiotics than males (adjusted odds ratio (OR) = 0.954, 95% confidence interval [CI] [0.928–0.981]; p = 0.001); and (2) compared to patients aged ≤5 years, those who were 6–15 years old , 16–60 years old , and >60 years old  were more likely to be prescribed antibiotics. The overuse and irrational use of antibiotics in PHC settings remain major healthcare challenges in rural Guangdong. Thus, it is imperative to implement targeted antimicrobial stewardship (AMS) policies to address this problem.Overuse and inappropriate use of antibiotics are important contributors to bacterial antimicrobial resistance (AMR), especially in ambulatory primary healthcare (PHC) settings in low- and middle-income countries. This study aimed to investigate antibiotic prescription patterns among patients with acute respiratory infections (ARIs) in rural PHC facilities in the Guangdong Province, China. A total of 444,979 outpatient prescriptions were extracted from the electronic medical record system of 35 township health centers (THCs) and 2 community health centers (CHCs) between November 2017 and October 2018. We used the chi-square test to analyze the antibiotic prescription patterns and binary logistic regression to explore patient-related factors associated with antibiotic prescriptions. Of the 162,742 ARI prescriptions, 85.57% ( Antimicrobial resistance (AMR) is an increasingly serious problem that threatens global public health . A previOveruse and irrational use of antibiotics are major drivers fueling the development of bacterial AMR , especiaAntibiotic consumption is usually expressed in defined daily doses (DDDs). In China, 4.2 billion DDDs were consumed in 2015 , placingIn China, the PHC system has substantially helped reduce the burden of diseases, performing 53% of outpatient (4.1 billion visits) and 16% of inpatient  care in 2020 ,17,18,19Acute respiratory infections (ARIs) are commonly observed in PHC facilities . PatientEven though Guangdong is one of the wealthiest provinces in China, it includes Shaoguan City, which is located in the north and considered one of the poorest areas. In rural Shaoguan, much of the younger population has temporarily moved to cities for employment, leaving behind children and elderly relatives. Our study covered two rural counties in Shaoguan, Lechang and Nanxiong. In 2018, Lechang County had 419,500 permanent residents, with an annual gross domestic product (GDP) of USD 4503 per person , and NanWe extracted 444,979 outpatient prescriptions from the electronic medical record system of 35 THCs and 2 CHCs in these two counties between November 2017 and October 2018. The electronic medical records contained basic patient information: name, medical card number, sex, age, disease diagnosis ), chronic diseases, drug regimen, and prescription cost. The ARI diagnoses in our study included URTIs, coded by ICD-10 as J00 = acute nasopharyngitis (common cold), J01 = acute sinusitis, J02 = acute pharyngitis, J03 = acute tonsillitis, J04 = acute laryngitis and tracheitis, J05 = acute obstructive laryngitis (croup) and epiglottitis, and J06 = multiple acute upper respiratory tract infections of unknown sites; and the LRTI, J20 = acute bronchitis . The chrMicrosoft Excel (version 2019) was used to filter electronic medical records. First, prescriptions with missing critical information  and without an ARI diagnosis  were excluded. Next, among all prescriptions containing at least one ARI diagnosis, we further excluded those presenting other possible bacterial infections , as it was essential to ensure that antibiotics were prescribed only for ARIs. Lastly, in the selected ARI prescriptions, we screened those containing at least one antibiotic for systemic use and defined them as “ARI antibiotic prescriptions” . We classified the antibiotics used in our study according to the 2022 Anatomical Therapeutic Chemical (ATC) classification system recommended by the World Health Organization (WHO) . ConsideAntibiotic prescription patterns were evaluated using primary and secondary outcome indicators. The primary outcome indicator was the rate of ARI antibiotic prescriptions. The secondary outcome indicators were expressed as the proportion of ARI antibiotic prescriptions, including parenteral antibiotics (intravenous (IV) or intramuscular (IM) administration), oral antibiotics, multiple antibiotics, AWaRe group of antibiotics, ATC group of antibiotics, and antiviral drugs. These key indicators were calculated as follows:Antibiotic prescription rate = number of ARI prescriptions including at least one antibiotic for systemic use/total number of enrolled ARI prescriptions ×100%.Parenteral antibiotic proportion = number of ARI prescriptions including at least one parenteral antibiotic/total number of ARI antibiotic prescriptions ×100%.Oral antibiotic proportion = number of ARI prescriptions in which all included antibiotics were oral antibiotics/total number of ARI antibiotic prescriptions ×100%.Multiple antibiotic proportion = number of ARI prescriptions including two or more individual antibiotic agents/total number of ARI antibiotic prescriptions ×100%.Access group antibiotic proportion = number of ARI prescriptions in which all included antibiotics were Access group antibiotics/total number of ARI antibiotic prescriptions × 100%.Watch group antibiotic proportion = number of ARI prescriptions including at least one antibiotic of the Watch group but without any antibiotic of the Reserve group or Not recommended group/total number of ARI antibiotic prescriptions × 100%.Reserve group antibiotic proportion = number of ARI prescriptions including at least one antibiotic of the Reserve group but without any antibiotic of the Not recommended group/total number of ARI antibiotic prescriptions × 100%.Not recommended group antibiotic proportion = number of ARI prescriptions including at least one antibiotic of the Not recommended group/total number of ARI antibiotic prescriptions × 100%.Proportion of each ATC group of antibiotics = number of ARI prescriptions including at least one antibiotic from one ATC group/total number of ARI antibiotic prescriptions ×100%.Proportion of antibiotics combined with antiviral drugs = number of ARI antibiotic prescriptions including at least one antiviral drug/total number of ARI antibiotic prescriptions ×100%.p < 0.05.The statistical analysis was performed using the SPSS statistics software . We analyzed the overall antibiotic prescription patterns and stratified ARI prescriptions by sex , age , and presence or absence of chronic diseases. We calculated the median prescription cost and interquartile range (IQR). We used the chi-square test to compare differences in antibiotic prescription patterns in the defined population groups and binary logistic regression (Enter method) to explore possible patient-related factors associated with antibiotic prescriptions. The covariates included patients’ age, sex, hypertension and diabetes status. Statistical significance was set at n = 85,685) belonged to male patients and 47.35%  to females. The majority  of patients in this sample were ≤60 years old, with the highest proportion  of patients being aged ≤5 years, and with only 10.53%  being >60 years old. Moreover, 95.51%  lacked chronic diseases, and only 4.49% (n = 7312) were diagnosed with hypertension and/or diabetes. The most commonly identified diagnoses of ARIs were multiple acute upper respiratory tract infections of unknown sites (ICD-10 code J06) , followed by acute bronchitis (ICD-10 code J20) , acute pharyngitis (ICD-10 code J02) , and acute tonsillitis (ICD-10 code J03)   .n = 139,259) were prescribed at least one antibiotic, with 37.82%  of them including multiple antibiotics. Moreover, 55.29%  comprised parenteral antibiotics. According to the AWaRe classification, Watch group antibiotics accounted for the highest proportion , followed by the Access group  and the Not recommended group , while no Reserve group antibiotics  were prescribed , first-generation cephalosporins , macrolides , and extended-spectrum penicillins  (n = 235)  was the most common antibiotic for all ARIs in the sample, followed by amoxicillin , cefixime , and ceftriaxone . When evaluating the prescribed individual antibiotic agent per ARI diagnosis, we found that erythromycin was the most frequent for ICD-10 code J00 (55.41%), levofloxacin and metronidazole for J01 (17.27%), amoxicillin for J02 (14.80%), amoxicillin–clavulanic acid for J03 (22.34%), cefixime for J04 (24.55%), cefalexin for J06 (17.62%), and azithromycin for J20 (15.70%)  . In relan = 235) . Regardi(15.70%) .n = 63,861) of the antibiotic prescriptions included at least one antiviral drug. Based on the median prescription cost, the average ARI antibiotic prescription cost was higher than that of ARI prescriptions without antibiotics (USD 3.60 vs. USD 2.17)  .p = 0.373). Despite the sex, more than half of the patients were prescribed parenteral antibiotics (p = 0.089), and approximately 38% were prescribed multiple antibiotics (p = 0.901). However, male patients were prescribed a higher proportion of antibiotics in the Watch group  and antibiotics combined with antiviral drugs  than female patients (p < 0.001)  .p < 0.001). Additionally, general practitioners (GPs) tended to prescribe parenteral antibiotics  and multiple antibiotics  according to the patient’s increasing age. Moreover, patients aged ≤5 years received a higher proportion of antibiotics from the Watch group  and antibiotics combined with antiviral drugs  when compared to other age groups (p < 0.001)  .p < 0.001), the proportion of Watch group antibiotics was beyond 56% , and the proportion of antibiotics combined with antiviral drugs was more than 41% . The groups showed significant differences in the route of administration and the number of antibiotics prescribed. Patients with chronic diseases received a higher proportion of parenteral antibiotics  and multiple antibiotics  than those without chronic diseases (p < 0.001), but showed a lower proportion of prescriptions for macrolides and penicillins/beta-lactamase inhibitors (p < 0.001)  .p = 0.001). As evidenced before, we confirmed that patients aged >5 years were more likely to be prescribed antibiotics, particularly those aged >60 years . Moreover, patients with hypertension appeared less prone to receiving antibiotics than those without hypertension . However, there was no significant difference in antibiotic prescriptions between patients with and without diabetes   = 0.954, 95% confidence interval [CI] [0.928–0.981]; = 0.128) .Our study demonstrates that antibiotic overuse and improper use in patients presenting ARIs are prevalent in rural PHC facilities in Guangdong, China. The antibiotic prescription rate was excessively high, as well as the proportions of multiple antibiotics, parenteral, and Watch group antibiotics. Moreover, we found that patients’ sex and age were key factors associated with GPs’ prescription behaviors in the studied PHC facilities.We found that 85.57% of the total ARI prescriptions in the eligible sample included at least one antibiotic, in line with a previous report from a systematic review in China, where 91.1% of outpatients with URTIs were prescribed antibiotics in PHC settings . HoweverAmong all ARI antibiotic prescriptions in our study, 37.82% included multiple antibiotics, a slightly lower figure than previously reported for URTI outpatients in Chinese PHC settings (55.5%) , but sigWe also found that more than half of the ARI antibiotic prescriptions (55.29%) included parenteral antibiotics, a much higher rate than that recommended by the WHO (less than 20%)  and thosOur study identified that Watch group antibiotics were more frequently prescribed for ARIs than those in the Access group (56.62% vs. 40.77%), in accordance with previous reports on children under 18 years old with respiratory tract infections in outpatient PHC settings in Beijing, China (89.0% vs. 10.5%) . The WHOThe observed patterns in our study notably deviate from the Chinese national guidelines, according to which ARIs are mainly viral and should not be treated with antibiotics unless accompanied by evidence of bacterial infection ,43. FurtIn our study, female patients with ARIs were less likely to be prescribed antibiotics than male patients. Zhao et al. found similar results in a larger-scale study of patients with URTIs in ambulatory and emergency departments of secondary and tertiary hospitals in 28 provinces of China .Regarding age, our results indicate that patients were more likely to be prescribed parenteral antibiotics as they became older, consistent with the findings in rural Anhui, China . In addiPatients with ARIs presenting chronic diseases were prescribed parenteral and multiple antibiotics at a higher proportion. This is also related to the fact that most of these patients  were over 60 years of age in our study, suggesting a strong link between this age group, the route of administration, and prescription of multiple antibiotics, as previously stated. Moreover, it is worth mentioning that the low prevalence of chronic diseases (4.49%) in our study might be related to the fact that most (60.89%) patients presenting ARIs were ≤15 years old.Despite the implementation of China’s zero-markup drug policy to eliminate profit from medicine sales, financial incentives may still exist for medical institutions . Before Irrational antibiotic prescriptions can also be attributed to diagnostic uncertainty ,49,50. IAnother important factor may be the lack of GPs’ professional knowledge and training on antibiotic use, leading to improper use of antibiotics ,18. In 2In addition, patient expectations and demands may influence irrational antibiotic prescriptions . PatientAs evidenced, urgent actions should be adopted to control the overuse and inappropriate use of antibiotics for ARIs and improve the situation in rural PHC institutions in Guangdong, China.First, the government should increase funding for rural PHC institutions to reduce financial dependence on drug sales, and strengthen diagnostic equipment, especially for POCT services. POCT, as a diagnostic test performed near or at the site of patient care, provides faster test results than traditional laboratory testing . ParticuSecond, improving antibiotic use awareness among GPs and patients is imperative. Examples of measures include strengthening GPs’ professional training, encouraging the study of clinical guidelines, and implementing prescription peer review ,58. SpecThird, the government should strengthen the supervision of antibiotic prescriptions in PHC institutions. A study in Shenzhen, China, indicated that strict enforcement of AMS interventions  implemented by local health authorities could make substantial and constant reductions in antibiotic prescriptions in PHC settings . MoreoveFinally, simple metrics for antibiotic prescriptions should be developed that are easily understood by GPs and policymakers, for the purpose of assessing and improving the quality of antibiotic prescriptions more accurately. The proportion of each WHO AWaRe antibiotic group, the percentage of parenteral administration, and the ratio of broad-to-narrow-spectrum antibiotics comprise good examples to follow ,62,63. Hn = 162,742), providing strong evidence of irrational antibiotic prescription practices. Moreover, this analysis contributes to implementing targeted AMS policies in rural PHC facilities. Nonetheless, it presents some apparent limitations. First, the antibiotic prescription rate of outpatient ARI prescriptions may have been slightly biased after excluding prescriptions with missing diagnosis and/or drug regimen. However, they accounted for only 3.85%  of the total number extracted.Our study covered 35 THCs and 2 CHCs in rural areas, with a large sample size , which may also affect the decision to prescribe antibiotics, were not analyzed in the selected ARI prescriptions. Future studies should include more cities and provinces and control more confounding variables to improve the generalizability of the findings.Third, quality indicators of antibiotic use required for AMS implementation, for example, adherence to guidelines, could not be analyzed in our study due to insufficient information in the electronic medical record system in rural PHC settings . However, since antibiotics are generally not required for ARIs, we have been able to demonstrate the overuse and irrational use of antibiotics in a general sense.Finally, our study did not include antibiotic prescriptions from village clinics and community health stations (PHC facilities are one level lower than THCs and CHCs), fields that should also be explored for a more comprehensive understanding of antibiotic prescription practices in rural PHC settings in China.Irrational antibiotic prescription for ARIs is a serious concern in rural PHC facilities in Guangdong, China. GPs often overprescribe antibiotics, including parenteral antibiotics, Watch group antibiotics, and multiple combinations of them. We found that patients’ sex and age are critical factors associated with this issue. Targeted AMS interventions are required to improve rational prescription practices in these settings. Potential implementations should be focused on, but not be limited to, enhancing funding, diagnostic equipment, healthcare provider and patient education, and antimicrobial surveillance, as well as implementing the WHO AWaRe’s metrics, and developing feasible quality indicators adapted to the local context.


Despite limitations to coal combustion energy production, many countries face the still-unresolved problem of utilising the wastes from fluidised bed coal combustion. One direction of rational utilisation can be using these wastes in the building materials industry. The study aimed to analyse the possibility of using fluidised bed combustion fly ashes as a partial substitute for cement in the underwater concrete (UWC). Two groups of concrete mixes were tested, containing 20 to 50% of fluidised bed combustion fly ashes. Investigations of the rheological properties of the concrete mixes and the mechanical performance of the hardened concrete confirmed the possibility of replacing cement in UWC with fluidised bed combustion fly ash up to 30% of the cement mass. The higher content of the fly ashes significantly worsens the UWC strength as well as the consistency and wash-out loss of the concrete mixes, excluding its use in underwater concreting.  Countries with mainly coal-based energetics face problems utilizing the large volume of fly ashes, the by-products of combustion. In recent years, Poland has become Europe’s largest producer of coal . In 2020Fluidized bed combustion (FBC) fly ashes have a different chemical composition than the fly ashes from conventional coal dust combustion. The difference is a result of the lower temperature of FBC, which is 800–900 °C, compared to conventional beds, in which the coal is combusted at 1400–1700 °C . The preThe physico-chemical properties of fluidized bed combustion fly ashes (FBCFAs) depend mainly on the combusted fuel and combustion technology ,16,17.Large amounts of sulfates, mainly the anhydrite, and free calcium oxide in the fluidized bed combustion fly ashes limit their use in the cement composites ,19,20. T2 and heavy metals emission but also causes some stabilization of the chemical composition of the combustion products, including fly ashes. Investigations of new types of FBC fly ashes are intensively conducted in the countries facing a significant problem with re-using the rising amount of FBCFAs. The ashes are utilized to neutralize the acidic soil components, to fertilize soil, to improve water transport in the soil, to limit fertilizers and fine-soil-fractions wash-out [The introduction of still new systems of the fluidized bed combustion not only leads to the limitation of COwash-out ,26. An iwash-out . These fwash-out ,7. Cemenwash-out ,12,27,28wash-out ,30,31. Hwash-out ,33,34. TThe paper aims to demonstrate the possibility of using FBC fly ash in underwater concrete mixes. The concrete mixes with different water to binder ratios w/b (0.40 and 0.46) were analyzed in the presented investigations. The percentage of FBCFA ranged from 20 to 50% of the cement mass. The investigation covered 10 underwater concrete compositions. The compressive strength of the concrete after 28 and 56 days of underwater curing was determined. The penetration depth of the water under pressure was tested after 28 days of underwater curing. The consistency and wash-out loss of the UWC mixes were determined, and the results were analyzed from the point of view of the underwater concreting technology . 3, gravel of 2–8 mm and 8–16 mm fractions, natural sand 0–2 mm and tap water. The grain size distribution curves of the sand and gravel are presented in 3. The chemical composition of the used FBCFA and cement are presented in The following materials were used to prepare the tested UWC: Portland cement CEM I 42.5N with the specific density of 3.1 g/cmTwo series of concrete mixes were designed with the water to binder ratio w/b equal to 0.4 and 0.48 and with variable content of cement and superplasticizer. The amount of AWA was adjusted proportionally to the binder content, 1% of the binder mass. The concrete mixes contained different volumes of FBCFA, which was added as a partial substitute for the cement. The concrete mixes’ compositions are presented in The UWC mixes were prepared in the laboratory mixer with 30 L. The concrete specimens were prepared in cubic steel molds 100 × 100 × 100 mm. The molds were first placed at the bottom of the container, which was then filled with water until the water level was 20 cm above the upper edge of the mold. Then, the concrete mix was cast directly from above the water table without smoothing the formed surface of the concrete . The speThe method for determining wash-out loss for the concrete mix has been developed in Belgium. The method has been standardized in the USA and described in the instruction CRD-C61-89A . The proThe pipe was filled with water up to the level of 1700 ± 5 mm.The container with the cover was weighed, and the concrete mix sample with a mass slightly exceeding 2000 g was placed in the container.i) was again measured; it should be 2000 ± 20 g.The concrete mix in the container was compacted using the metal rod, and the container walls were cleaned from the leaking concrete mix. The mass of the concrete mix .After 15 s, after the container had fallen to the bottom, it was pulled out in a time not longer than 5 ± 1 s. The excess water was removed from the container, leaving it to drain for 2 min, and then the container was weighed  was calculated after each test. The mass loss D after the third immersion was accepted as the final result. The wash-out loss of UWC mixes were determined immediately after mixing the components and one hour after the mixing in the laboratory mixer.The loss of mass of the concrete mix sample was the difference between MThe consistency of the UWC mixes was determined using the flow table according to the European Standard EN 12350-5 . The tesThe concrete specimens’ compressive strength was determined according to the European Standard EN 12390-3  after 28The watertightness of the concrete was determined by testing the depth of water penetration under pressure. The test was determined according to EN 12390-8 [The results of UWC mixes consistency testing, according to EN 12350-5 , are pre3 and w/b = 0.48 had the consistency of SCC mix or close to it. All concrete mixes from the C0.48 series obtained flow diameters above 400 mm after 0 and 60 min. Such a flow is recommended for UWC mixes in the German Standard DIN 1045-2 [3, the flow diameter above 400 mm was noted after mixing the components of the concrete mix CR0.4-0 without fly ash addition. Despite using a large amount of superplasticizer SP, the strong influence of FBCFA content on consistency of the tested UWC mixes was observed. This effect was particularly significant when the FBCFA content exceeded 30% of the cement mass. The used volume of SP was very high in these concrete mixes, exceeding even 3% of the binder mass, and significantly affected the UWC mixes’ production cost. Only slight changes in the consistency with time were observed in the case of the UWC mixes with w/b = 0.48. The reason for this could be the properly adjusted SP content in this series of concrete mixes. In the case of the mixes with w/b = 0.4, when the content of FBCFA increased, the rise of water demand led to a significant worsening of workability and consistency despite the high amount of SP admixture. The results of consistency testing are presented in The effect of the binder content on the tested concrete mixes’ consistency was visible. The UWC mixes with the binder content of 400 kg/mN 1045-2 . HoweverThe results of UWC mixes’ wash-out loss testing according to CRD-C61-89A  are presThe wash-out loss D was increasing with the growth of FBCFA content in the tested UWC mixes. An effect of AWA content on D value was visible after 60 min. from the mixing of the components. This effect was demonstrated by decreasing the D value compared to the values obtained immediately after mixing components. According to the American recommendation , the wasThe UWC compressive strength testing results after 28 and 56 days of curing are presented in The high binder content in the UWC mix generated more considerable wash-out loss and worsening of the mix’s workability, which can finally increase the volume of the micropores and macropores in concrete. A lack of sufficient water to wet the high volume of the fly ash can also result in a fall in the compressive strength. According to , increasThe results of testing water penetration depth are presented in The initial increase in the tightness of concrete was a result of concrete’s structure compaction in the range of the capillary pores by FBCFA microparticles. As presented in , an addi3) were selected for testing. Besides the strength tests, which are the basis for UWC designing, the investigation focused on the effect of FBCFA addition on the rheological properties of UWC mixes. Considering the underwater concreting technology, meeting the requirements regarding the consistency and wash-out loss is obligatory and decides on the future mechanical performance of the hardened underwater concrete. Two series of concrete mixes with large and medium binder content (530 and 400 kg/mDue to the complexity of UWC mixes’ composition and the use of two acting opposite admixtures, superplasticizer and viscosity modifier, the problem of using FBCFA as the cement’s substitute is difficult. The FBCFA content higher than 30% of the cement mass makes it impossible to design the concrete mix with the consistency and wash-out loss suitable for adequately placing it in the formwork under water. Obtaining the constant-in-time rheological properties of UWC mixes containing a large volume of FBCFA requires using a tremendous amount of superplasticizer, high above the content recommended by the producers, which also increases the cost of the concrete mix. The large volume of FBCFA also worsens the UWC compressive strength and tightness.3, with the use of up to 30% FBCFA in the composition of the binder, enables the production of UWC with the compressive strength close to the reference concrete and a consistency suitable for placing the concrete mix under water. The highest compressive strength after 56 days was achieved by concretes with 20% FBCFA content. The strength of these concretes was on average 10% higher than that of concrete without the addition of FBCFA. The advantages of FBCFA addition are an increase in the tightness of concrete and the improvement of corrosion resistance.Limitation of the binder content in UWC mix to 400 kg/m