There is a need to develop new construction materials with improved mechanical performance and durability that are low-priced and have environmental benefits at the same time. This paper focuses on the rheological, mechanical, morphological, and durability properties of synthetic and steel fiber reinforced self-compacting concrete (SCC) containing 5–15% metakaolin (M) by mass as a green replacement for Portland cement. Testing of the fresh mixes included a slump-flow test, density, and porosity tests. Mechanical properties were determined through compression and flexural strength. A rapid chloride penetrability test (RCPT) and the chloride migration coefficient were used to assess the durability of the samples. A scanning electron microscope (SEM) with energy dispersion spectrometry (EDS) was used to study the concrete microstructure and the interfacial transition zone (ITZ). The results show that a combination of metakaolin and hybrid fibers has a negative effect on the flowability of SCC. In contrast, the inclusion of M and hybrid fibers has a positive effect on the compressive and flexural strength of SCC. The fracture of SCC samples without fibers was brittle and sudden, unlike the fiber-reinforced SCC samples, which could still transfer a considerable load with increasing crack mouth opening deflection. Overall, the chloride migration coefficients were reduced by up to 71% compared to the control mix. The chloride reduction is consistent with the resulting compact concrete microstructure, which exhibits a strong bond between fibers and the concrete matrix. Concrete-based materials are constantly being developed with an aim to improve the mechanical performance and durability of structural concretes, as well as having environmental benefits at the same time. Self-compacting concrete (SCC) is widely used due to its main advantages over ordinary concrete, such as the possibility to fill the formwork even in the presence of dense reinforcement with no need for mechanical compaction, an easier concrete pumping procedure, shorter construction time, reduction in the amount of skilled labor needed onsite, no noise and vibration, and so on . The mai2Si2O7, is an environmentally friendly pozzolanic material obtained by calcining kaolinite clay at relatively moderate temperatures of 650 to 750 °C [2, and develops additional C-S-H gel, thus leading to an improved concrete microstructure and overall better performance of the concrete. Pozzolan metakaolin has been proven to enhance strength [The incorporation of supplementary cementitious materials (SCM) in the SCC mixture is becoming an increasing necessity. In the past, the main motivation for using SCM was to reduce costs, but now—in addition to improving the properties of concrete—various SCM are also used as a partial replacement for Portland cement to reduce carbon emissions . For exao 750 °C . Due to strength , permeabstrength , chloridstrength , and frestrength  in concrA few studies have been published on SCC that include both pozzolans and fibers as reinforcement. For example, Mahapatra and Barahi  evaluateTo investigate the combined effects of metakaolin and hybrid fibers on the fresh and hardening properties of SCC, eight concrete mixes were developed with a different mass percentage of metakaolin and the same amount of hybrid fibers. The experimental part of the study was carried out at the Faculty of Civil Engineering in Rijeka, Croatia.The typical ingredients used in the production of SCC are cement, a mineral admixture, coarse aggregate, fine aggregate, water, viscosity modifier, and superplasticizer. In the current study metakaolin (M) was also added to improve the workability, strength, and durability of SCC as SCM. According to previous studies of SCC containing M, the maximum amount which guarantees an increase in compressive strength is 15% of M by weight of cement . SynthetPortland cement (PC) CEM II/A-LL 42,5 R with high initial strength conforming to standard HRN EN 197-1 was used as the binder in all mixtures. The content of PC was 80–94% Portland clinker and 6–20% additives. Locally available mineral additive M was used as a partial replacement for cement in SCC at 5%, 10%, and 15% by weight of cement. 3 and a maximum grain size of 8 mm were used in the mixture preparation. The ratio of coarse aggregates to sand was kept constant and equal to 0.54:1. Dynamo SF 16S, a polycarboxylate superplasticizer for fresh concrete with low viscosity, was used in the production of SCC. Dynamo SF16 S has the best dispersing effect if added after the cement, admixtures, mineral additives and at least 80% of water are mixed. The recommended dosage is 0.2–2% in relation to the cement weight. The density of the superplasticizer used was 1 g/cm3 and chloride content was <0.1%. Viscosity modifying admixture (VMA) was added to control the rheology of the mix and increase cohesion and segregation resistance. Hooked-end steel fibers type DE 30/0.55 N, made by KrampeHarex, were used for hybrid SCC. The nominal diameter of the fiber is d = 0.55 mm and the nominal fiber length is L = 30 mm (aspect ratio L/d = 55). The tensile strength of the fibers reported by the manufacturer is 1350 N/mm2. The typical practical minimum dosage is 20 kg/m3. Synthetic fibers used in the SCC mixtures were the high-performance fibrillated microfibers Fibrofor High Grade 190 produced by Contec Fiber. The fibers are made of pure polyolefin with a bulk density of 0.91 g/cm3 and are environmentally friendly. The diameter of the microfibers is less than 0.03 mm, and the length of the fibers is 19 mm. The tensile strength was reported by the manufacturer as 400 N/mm2. For fibrillated microfibers, the typical dosage guideline is 1 kg/m3.Crushed limestone aggregates with a density of 2740 kg/mFor this experimental program, eight concrete mixes were made. The mixes were prepared with different replacements of the cement portion with metakaolin (up to 15% of the cement mass) and the same amount of hybrid fibers.3) and water-to-binder ratio (w/b = 0.4) were also kept constant for all mixes.The detailed proportions of the eight SCC mixes are listed in 3 of hooked end steel fibers and 1 kg/m3 of synthetic microfibers in the next four mixes . The main aim of this experimental investigation was to study the combined effects of M and hybrid fibers on the various properties of SCC and not to find the optimum content of hybrid fibers which results in the maximum improvement of mechanical properties. For this reason, the amount of synthetic and steel fibers was selected according to the recommendations given in engineering practice. Additionally, to better capture the influence of the combined effects of metakaolin and hybrid fibers on various properties, all other mix components, except the amount of M, were kept constant. Therefore, only one volume fraction of synthetic and steel fibers was considered. When hybrid fibers are neglected, the four mixes without fibers correspond to mixes SCC-0M, SCC-5M, SCC-10M, and SCC-15M without fibers.In the first four mixes  only the amounts of cement and metakaolin were varied. Hence, the first mixture was the SCC control mixture denoted as SCC-0M. In the next three mixtures , a certain amount of cement was replaced with M . The influence of the effects of metakaolin and hybrid fibers was studied by adding 50 kg/mWhen placing the concrete in molds only hand compaction was provided. For each concrete mix, the same test specimens were prepared: cubes with 150 mm sides to determine compressive strength, beams 100 mm × 100 mm × 400 mm to determine flexural tensile strength and fracture behavior, and cylinder samples with 100 mm diameter to determine chloride ion penetration resistance.The properties of fresh concrete mixes were tested according to current standards for SCC used in Europe. Testing of fresh SCC was carried out immediately after mixing had been completed and within a period of a maximum of 30 min to avoid losing the workability of the mixture. The various fresh properties of each SCC mixture with the same composition were measured two times.The properties required for the self-compatibility of concrete were characterized by testing the fresh mixtures, including with a slump-flow test method according to HRN EN 12350-8 .500 value). The slump value diameter for SCC concrete ranges between 550–850 mm, according to HRN EN 206 [500) or the efflux time in the V-funnel test. According to the European guidelines for SCC [500 are in the range of 2–5 s, and for V-funnel flow time are between 6–12 s. The time value does not measure the viscosity of SCC but it is related to it by describing the rate of flow. Concrete with low viscosity will have a very quick initial flow and then stop. In contrast, concrete with high viscosity may continue to creep forward over an extended time. Additionally, segregation and bleeding of fresh concrete were visually observed during the slump flow test and V-funnel test at T5min. Further, the density and porosity of the fresh concrete mixes were also measured. The air content of the concrete mixes was estimated according to the standard HRN EN 12350-7 [The flowability of SCC was determined by the slump flow test method by measuring the spread diameter and slump-flow time  in terms of total charge passed through concrete samples after 28 days of water curing was measured according to ASTM C 1202 . If the To eliminate the effects of heat on ion mobility and final Coulomb values in concrete samples with fibers, a modified ASTM C 1202 test was used . Linear U is the absolute value of the applied voltage (V), A is the cross-sectional area of the sample (m2), I is the current at 30 min after the voltage is applied (A) and L is the thickness of the sample (m). The length of the corrosion propagation stage until spalling of the concrete can be established by a linear correlation between the inverse concrete ER and the steel corrosion rate in µm Fe per year.The electrical resistivity for all mixtures corresponding to the electrical current measurements was calculated using Equation (1):3 solution. Chloride penetration depth was assessed by a colorimetric method. The average chloride penetration depth was determined on the concrete surface by a change in color in the presence of chloride ions, which chemically led to the formation of white AgCl product. The chloride migration coefficient was calculated using Equation (2) [nssmD is the non-steady-state migration coefficient (×10−12 m2/s), U is the absolute value of the applied voltage (V), T is an average value of the initial and final temperatures in the anolyte solution (°C), L is the thickness of the specimen (mm), t is the test duration in hours.In addition, chloride penetration was evaluated by calculating the chloride migration coefficient from the non-steady-state migration experiment. Similar to the RCPT, the cylindrical samples were kept under a potential difference between a cathode solution and anode solution according to the standard. After completion of the test, all tested samples were axially split into two pieces of fractured surfaces and sprayed with 0.1 M AgNOtion (2) :(2)Dnssm3 in size and placed in 96% ethanol to replace the pore solution and then dried in the ventilation oven at room temperatures. A precision etching and coating system (Gatan PECS II Model 685) with dual ion sources for the etching of solid samples was used for concrete coating with Pt. A JSM-7800F field emission scanning electron microscope equipped with (EDX) energy dispersive spectrometry was used to examine at different magnifications the microstructure of SCC samples and the interfacial transition zone (ITZ) between aggregates, binder pastes, and reinforced fibers.Cured SCC samples at the age of at least 28 days were smashed into pieces less than 1 cmThis section presents the results of the rheological, mechanical, and chloride permeability tests performed, as are those of the microstructure analysis on the bonds between the fractured SCC specimens and fibers.max) and longer flow time (T500) as compared with SCC with 0% M. This shows that concrete with M has a higher water demand. These results are in good agreement with studies by Vejmelková et al. [500 in the flow test with increasing M content, up to 27 s.Visually, all mixes were found to be homogeneous with no evidence of segregation or significant bleeding of the cement paste. As seen in á et al. . For SCCá et al. . The timFrom these results, it can be concluded that the reduction in flowability with increasing the proportion of metakaolin is greater in mixes with hybrid fibers than in mixes without them. The test results show good consistency and acceptable scatter in the case of a small amount of M. However, the scatter of test results for a specific concrete mixture is relatively high, especially for cases with a high content of M. In addition, it can be observed that the addition of fibers not only reduces slump flow diameter but also increases the scatter of test results. This can be attributed to the inhomogeneous distribution of fibers in the concrete matrix causing greater heterogeneity inside the mixture.The effect of metakaolin and hybrid fibers on the viscosity of fresh SCC is even greater. The rate of flow for SCC with metakaolin and hybrid fibers is much slower compared to the reference mixture. The V-funnel flow time was also measured. The time required to flow through the V-funnel apparatus increases along with the M content, ranging from 8–14 s for SCC mixes without fibers, while for all HySCC mixes flow was blocked due to the fibers. Consequently, concrete mixes containing hybrid fibers and 10% to 15% of M replacing cement by weight do not show the characteristics of the fresh SCC mixtures.The porosity of SCC mixes increases slightly with increasing the M content b. HoweveFrom Hence the rheological properties of SCC mixed with a combination of M and hybrid fibers are characterized by relatively high viscosity and cohesion. On the other hand, incorporation of M and fibers tends to reduce flowability, and this is most likely caused by the high reactivity of the M.In general, inclusion of hybrid fibers has a positive influence on the compressive strength of SCC. The SCC mix with hybrid fibers, HySCC-0M, shows about 9% higher compressive strength than SCC without fibers, SCC-0M. However, as the M content increases, the incorporation of the fibers becomes less significant. It can thus be concluded that the incorporation of M contributes more to the compressive strength than hybrid fibers. The SCC mixes with M and hybrid fibers showed an increase in compressive strength in the range of 9–31% compared to the SCC mix without fibers, SCC-0M. Consequently, the concrete mix with hybrid fibers and the highest percentage of M achieved the highest compressive strength, up to 31% higher than SCC-0M without M and fibers. In addition, From As can be seen in In the case of several SCC mixtures, it was clear that some of the bent fibers did not disperse which resulted in the uneven distribution of fibers. This may be attributed to the fact that the viscosity of the SCC mixtures was very significant, which negatively affected the fiber distribution and orientation inside fresh concrete . The reaThe rapid chloride permeability test (RCPT), concrete electrical resistivity, and chloride bulk diffusion test from non-steady-state migration were conducted to evaluate the performance of SCC containing metakaolin and fibers against chloride attack and chloride-induced corrosion.− ions located in the pore solution and on the composition of mineral admixtures. Since the alkali content in Portland cement is responsible for pore fluid transportation in concrete, changing the composition with a small dosage of M influences the curing regime, as the OH− in the pore fluid and particle packing density together enhance the resistance against chloride [The RCPT was performed in accordance with ASTM C1202, and the results were calculated as the average charge passed through at least four specimens a. The lichloride .As expected, chloride penetration increases when hybrid fibers are used. The congestion of fibers in a concrete mixture affects the self-compacting ability, which increases the pore structure and consequently the RCPT values . AnotherThe mixtures show a decrease in total charge passed for samples both with and without M content from 28 up to 56 days b. This cThe SCC electrical resistivity values support the findings from the RCPT. The resistivity values increased with the increasing M content, from 16 Ωm up to 92 Ωm without fibers, and from 7 Ωm up to 27 Ωm with fibers c. Replacnssm (×10−12 m2/s). For SCC samples without fibers, the chloride migration coefficient decreased from 49.98 × 10−12 m2/s to 14.53 × 10−12 m2/s when the M content was increased from 5% to 15%. Compared to the control mixture, the chloride migration coefficient was reduced by up to 71%. The calculated chloride migration coefficient appears to decrease exponentially with higher M content. Similar to the findings of Badogiannis et al. [s et al. , it can 3 solution. With the improved and more compact concrete structure, due to the pozzolanic reaction of M, the average depth of chloride migration decreased from 41.50 mm down to 12.70 mm.To acquire a sense of the concrete microstructure and the bonding degree between the hardened 28-day-old SCC and the synthetic and steel fibers, a scanning electron microscope (SEM) analysis was carried out . Figure 2 , which has a recognizable microstructure in the form of a “honeycomb” structure . In the 2 d. EttrinSEM-EDS and mapping test was performed to visually assess the different chemical composition on the concrete´s surface and the bond at the interface between the fibers and concrete matrix. SCC mixtures containing metakaolin and hybrid fibers require the addition of a larger amount of superplasticizer than SCC without fibers and M to ensure adequate self-compacting properties. With an increase in M, the flowability of SCC mixtures decreases slightly, while the viscosity and cohesive strength increase.Compressive strength generally increases with the increase in M content for both mixtures with and without fibers. The highest compressive strength is obtained for the SCC mix with hybrid fibers and the highest percentage of M, up to 31% higher than SCC without M and fibers. In addition, fiber-reinforced SCC mixes with 15% M have approximately 15% higher flexural strength values than SCC without M.To obtain better mechanical properties, the most important parameter for SCC is the distribution and orientation of the fibers. In the case of several SCC mixtures, it became clear that some of the bent fibers did not disperse, resulting in an uneven distribution of the fibers.The linear effect of chloride reduction is observed when the percentage of M is increased from 5% to 15% of the cement weight. Consequently, the calculated chloride migration coefficient appears to decrease with higher M content.The electrical resistivity increases with the increase in M content from 16 Ωm to 92 Ωm without fibers and from 7 Ωm to 27 Ωm with fibers.The microstructural investigation of the concrete reinforced with hybrid fibers confirmed the assumption of a strong bond between the fibers and concrete matrix. The crystallization products form a denser concrete structure with more filled pores.The test results emphasize the importance of the rheological properties of SCC such as adequate workability to ensure improved mechanical performance and durability. Hence, it is recommended to study the combined effects of metakaolin and hybrid steel and synthetic fibers at various volume fractions.The results of a comprehensive examination of a set of properties of fresh and hardened SCC mixes containing metakaolin and hybrid fibers fixed at only one volume fraction show that it is possible to obtain SCC with increased strength and durability. The conclusions of this study can be summarized as follows:Such high-performance SCC shows great potential for use in construction applications where higher crack resistance and resistance to chloride penetration are required.


It could be observed that the cubic compressive strength, axial compressive strength, and flexural strength increased and then decreased as the content of basalt fiber increased, while the permeability and porosity of the pervious concrete decreased with the increase in the basalt fiber content. The mesostructure of pervious concrete was also studied through industrial computed tomography (ICT); the testing phenomenon showed that the fibers had a significant influence on the arrangement of the aggregate, cement paste, and the interfacial transition zone, and excessive basalt fiber resulted in poor characteristics of the interfacial transition zone (ITZ) and inferior strength properties. It was found that incorporating a basalt fiber content of 4 kg/m3 could achieve a balance between the mechanical and physical properties of pervious concrete, which was suitable for structural applications.The aim of this study was to investigate the properties of fiber-reinforced pervious concrete. Ordinary cement, silica fume, coarse aggregate, and basalt fibers were used to produce the concrete mix. The fibers were mixed with pervious concrete at the levels of 0 kg/m Nowadays, various types of concrete gradually appear with the development of the economy, such as pervious concrete, fiber-reinforced concrete, and self-healing concrete ,2,3,4. AIn order to protect the environment, recycled aggregate is gradually being introduced as a partial replacement for natural coarse aggregate ,13,14. T2 of the cement [Supplementary cementitious materials could improve the mechanical and physical properties of concrete due to the effects of microfilling and pozzolanic reactivity ,24. Amone cement . Chen ete cement  studied e cement  found the cement  observedBesides the silica fume, another technique that is being widely used is fiber reinforcement. The reinforcing fibers could not only improve the seismic behavior of the structure ,30, but 3, 4 kg/m3, 6 kg/m3, and 8 kg/m3) on the mechanical and physical performance of pervious concrete. This paper is an attempt to establish a balance between the strength and permeability of pervious concrete. The cubic compressive strength, axial compressive strength, flexural tensile strength, permeability, porosity, acidic corrosion behavior, and mesostructure of pervious concrete were studied. The compressive strength and flexural tensile strength increased and then decreased with higher amounts of basalt fiber, while the porosity and permeability decreased as the basalt fiber content increased. Therefore, basalt fibers could achieve enhanced improvement in the physical and mechanical performance of pervious concrete. The research methodology is given in In this paper, we further investigated the effect of basalt fiber with different levels of content , and the performance index provided by this company is given in Silicon fume is collected and treated from the smoke and dust escaping from the waste gas in the process of melting industrial silicon and ferrosilicon at high temperature in an electric furnace. Adding an appropriate amount of silica fume can improve the fluidity, compactness, and strength of pervious concrete. The silica fume was purchased from Henan Yuanheng Environmental Protection Engineering Co., Ltd. , and the technical indexes given by the company are presented in The performance of pervious concrete is affected by the type, size, and porosity of the aggregate. In this paper, limestone was selected as the aggregate. The physical properties and grain size distribution of the aggregate were investigated, according to Chinese Code GB/T 14685-2011 , as presBasalt fiber could improve the mechanical and physical performance of concrete. The basalt fibers used in this paper were provided by Zhejiang Jinshi Co., Ltd. , and the material characteristics were tested and provided by the company, as shown in Polycarboxylate high-performance water reducer is used to reduce the water consumption in the preparation of pervious concrete, so as to improve the fluidity of the concrete. The Q8081PCA liquid equilibrium polycarboxylate acid high-performance water reducer was used in this paper, and the dosage of the water reducer was determined by the trial matching of the specimen. The water used in the pervious concrete was running water.3, 4 kg/m3, 6 kg/m3, and 8 kg/m3. The detailed mix design for the experiments is given in The impact of material additives was studied by adding basalt fiber into the concrete mix at the levels of 2 kg/mThe pervious concrete was designed to meet the requirements of Chinese Code CJJ/T 135-2009 . The cubTo fully investigate the compressive strength of the pervious concrete, two sizes of specimens were designed: (i). 100 mm × 100 mm × 100 mm, (ii). 100 mm × 100 mm × 400 mm. The groups (i) and (ii) were used to obtain the cubic compressive strength, axial compressive strength, and flexural tensile strength of the pervious concrete, respectively. The failure patterns of the cubic specimens are given in 3, which increases by 24% compared to the control specimen. The red dashed line in The compressive strength of concrete is related to the shape of the specimen. The prism specimen can better reflect the actual compressive strength of concrete than that of cube samples. Therefore, the axial compressive strength of the pervious concrete was tested in this paper. The failure patterns of concrete prisms under the action of axial load are given in 3) to 20.63 MPa for a basalt fiber content of 4 kg/m3, and then decreases to 18.00 MPa for a basalt fiber content of 8 kg/m3. The results also indicate that the addition of basalt fiber can improve the axial compressive strength of pervious concrete.The effect of basalt fiber on the axial compressive strength of the pervious concrete is presented in Pervious concrete is inevitably subjected to flexural and tensile loads in the practical usage process. Therefore, it is essential to study the flexural tensile strength to prevent the appearance of cracks in pervious concrete. 3, and then the strength value decreases to 2.84 MPa for the basalt fiber content of 8 kg/m3. In CJJ/T 135-2009 [The effect of basalt fiber on the flexural tensile strength of the pervious concrete is presented in 135-2009 , it is sCombining the results of the cubic compressive strength, axial compressive strength, and flexural tensile strength, it could be concluded that the mechanical properties of the fiber-reinforced pervious concrete can meet the requirements of CJJ/T 135-2009 , and thaT °C, Q is the amount of water seeping out within t seconds, L is the thickness of the specimen, A is the upper surface area of the specimen, H is the water level difference, and t is the time. The results of the calculation are shown in Cylinder specimens were prepared to obtain the permeability coefficient, as given in 3) and then slowly (2–8 kg/m3) with the increasing of the basalt fiber content. As can be seen, the permeability coefficient is roughly 2.9–7.1 mm/s, which is higher than the regulation of CJJ/T 135-2009 [As shown in 135-2009  , whose surface was at least 20 mm higher than the upper surface of the specimens, as shown in 3) is shown in The corrosion phenomenon of the specimens  was used to scan the specimen. The same trend can be seen from 3, 2 kg/m3, and 4 kg/m3), three failure modes could be observed, while for the specimens with a higher basalt fiber content (6 kg/m3 and 8 kg/m3), the failure was mainly along the ITZ. The same phenomenon could also be seen in the testing of axial compressive strength. Considering the changes in the strength value of mechanical performance, it could be concluded that the proper addition of basalt fiber helps to achieve the strength balance of the aggregate, cement paste, and the ITZ, which will ensure the strength of the specimen. Although excessive basalt fiber results in poor characteristics of the ITZ and inferior strength properties. As described in , perviouIt is widely accepted that porosity is vital to the mechanical performance and physical properties of pervious concrete. As described in the testing results of permeability and porosity, and taking the mesostructure of the fiber-reinforced pervious concrete into account, the addition of basalt fiber causes more cement to bond to the fibers, which blocks the pores in pervious concrete. It is also clear that porosity has a positive relationship with permeability, and the addition of basalt fibers does not change this trend. 3 (control samples) and 4 kg/m3, the cubic compressive strength and axial compressive strength increased by 24% and 39%, respectively, while the flexural tensile strength, permeability, and porosity were reduced by 17%, 42%, and 35%, respectively, with the 4 kg/m3 basalt fiber content. For the specimens for acidic corrosion of 0 day, 20 days, 40 days, and 60 days, the cubic compressive strength of the samples with a basalt fiber content of 4 kg/m3 was 21%, 12%, 14%, and 7% higher than that of the control specimens, respectively. All the testing results meet the requirements of specification, indicating that the optimum basalt fiber content should be determined as 4 kg/m3.In order to improve the physical and mechanical properties of pervious concrete and promote the application of pervious concrete in actual construction, the optimum basalt fiber content should be established. Comparing the samples with a basalt fiber content of 0 kg/m3, 4 kg/m3, 6 kg/m3, and 8 kg/m3. The strength testing, porosity testing, permeability testing, and acid corrosion testing were conducted on the testing specimen. The following conclusions were made:3 increased by 24% and 39%, respectively.The incorporation of basalt fiber enhances the cubic and axial compressive strength, and the compressive strength increases and then decreases with the increasing of the basalt fiber content. Compared to the matrix without basalt fiber, the cubic and axial compressive strength of the matrix with a basalt content of 4 kg/m3 reduces by 17%.The contribution of basalt fiber to the flexural strength of the concrete matrix reduces with the increasing of the basalt fiber content. Compared to the control samples, the flexural tensile strength of the matrix with a basalt fiber content of 4 kg/m3 were 42% and 35% lower than those of the control samples.A pervious concrete matrix incorporating basalt fiber showed a lower permeability and porosity than that of the mix without fiber. Moreover, the permeability coefficient and the porosity of the pervious concrete with a basalt fiber content of 4 kg/m3, the cubic compressive strengths of the matrix with acidic corrosion of 0 day, 20 days, 40 days, and 60 days were 21%, 12%, 14%, and 7% higher than those of the control group, respectively. The compressive strength increased and then decreased with the increase in the corrosion time, and the addition of basalt fibers does not change this trend.For the concrete matrix with the basalt fiber content of 4 kg/mThe testing results of ICT scanning indicated that the basalt fiber obviously affects the distribution of the cement paste and aggregate, hence affecting the physical and mechanical properties of the pervious concrete. The optimum basalt fiber content can realize the balance between the cement paste, aggregate, and the ITZ.This study investigated the effect of basalt fiber on the physical and mechanical properties of pervious concrete. To achieve the aim of this paper, the pervious concrete matrix was mixed incorporating basalt fiber at the level of 2 kg/mThe physical and mechanical properties of fiber-reinforced pervious concrete could satisfy the requirements of CJJ/T 135-2009. The obtained results indicated that it is possible to investigate whether pervious concrete is suitable for structural application by the addition of basalt fiber, which can maximize the application of pervious concrete.


The properties in the fresh state and mechanical properties of the test mixtures were investigated. Full-scale spun-cast concrete pipes having a 450 mm internal diameter were manufactured and tested using the three-edge bearing test. The compressive strength of the mixtures was largely insensitive to the dosage of the fibers. The splitting tensile strength of all fiber-reinforced concrete mixtures was higher than that of the reference mixture without fibers, with a 24% increase recorded for the concrete mixture incorporating 50 kg/m3 of bundled steel fibers relative to the reference mixture with no fibers. The flexural performance of the fiber-reinforced concrete mixtures was superior to that of the reference mixture without fibers in terms of flexural strength, toughness, residual strength, and crack control, with up to 28% higher flexural strength relative to the reference mixture without fibers. The three-edge bearing tests on full-scale spun-cast pipes incorporating steel fibers showed that the use of fibers is a promising alternative to the traditional steel cage in spun-cast concrete pipes.Spin casting is the oldest method of manufacturing precast concrete pipes among all existing methods. While improved concrete mixtures incorporating fibers for other methods of concrete pipe manufacturing, such as the vibration method and roller compaction method, have been developed, no such concrete mixture has yet been developed for spun-cast concrete pipes. This study was designed to explore the possibility of incorporating locally manufactured steel fibers and commercially available polypropylene fibers to develop an improved concrete mixture for use in the manufacturing of full-scale spun-cast concrete pipes. The used steel fibers were of two types, i.e., straight and bundled steel fibers, manufactured by cutting locally available long straight and bundled steel wires, respectively. Various dosages of steel fibers (i.e., 20, 30, 40, and 50 kg/m Most coca alone . The wor in 2050 . Wastewa in 2050 . The saf in 2050 . ConcretConcrete pipes are manufactured by various methods. The most adopted methods are vibration, roller compaction, and the spinning or centrifugal method . These mThe manufacturing of concrete pipes by the vibration method and roller compaction method is performed using computer-controlled automatic plants. These methods have the advantages of high efficiency, better quality control due to automation, and high concrete strength due to a low water/cementitious materials ratio. These methods have the additional advantage of producing concrete pipe with uniform concrete strength throughout the wall thickness. Due to these advantages, these methods are popular in North America and Europe. Manufacturing by the centrifugal method is performed either manually or using an automated plant. Due to the high initial investment and technical expertise required for an automated plant, spun-cast pipes are still manufactured manually in developing countries, including Pakistan. It is known that the centrifugal method of manufacturing concrete pipes results in the segregation of concrete ingredients, with larger particles tending to move towards the outer side and the smaller particles towards the inner side . This seThe tensile strength of plain concrete is low, and hence concrete pipes are vulnerable to cracking . As concStructural fibers such as steel fibers and polypropylene fibers are known to enhance the tensile strength, toughness, and resistance of concrete against cracking ,24,25,26Several researchers have explored the use of fibers in concrete pipes produced by either the vibration method or the roller compaction method ,46,47,48The application of fiber-reinforced concrete in manufacturing of precast concrete pipes has been a subject of research for the last two decades. The potential of using steel fibers or polypropylene fibers to replace conventional steel cages for the production of precast concrete pipes has been recognized in the EN standard BS EN 1916 , ASTM C1The materials used by a local concrete pipe manufacturer for the manufacturing of conventional spun-cast concrete pipes were employed in the current study. Ordinary Portland cement was used in all concrete mixtures. River sand having a fineness modulus of 2.15 and coarse aggregate having a nominal maximum size of 12.5 mm from a local crusher plant were used. The control concrete mixture was designed according to the guidelines of ACI 211.3R  with a t3 of concrete. The polypropylene fibers were added at dosages of 5, 10, 15, and 20 kg/m3.Locally manufactured steel fibers of two types and commercially available polypropylene fibers were used . One typA pan-type mixer with capacity of 56 L was used for mixing the concrete constituents, . Coarse The slump and the fresh-state density of concrete were measured immediately after the preparation of the mixture in accordance with ASTM C143  and ASTMThe 150 × 300 mm cylindrical specimens were tested in compression for compressive strength according to ASTM C39 . PlasterSplitting tensile strength testing was conducted on the 150 × 300 mm cylindrical specimens according to ASTM C496  Figure b. Each sThe flexural performance of the concrete mixtures was assessed in accordance with ASTM C1609  on the 13 of straight steel fibers was 5 mm as compared to 20 mm for the plain concrete mixture. However, the concrete mixture incorporating 20 kg/m3 of PP fibers showed zero slump. Similarly, the fresh density of the concrete also marginally decreased as the dosage of the fibers increased. For instance, the fresh density of the concrete mixture incorporating 50 kg/m3 of straight steel fibers was about 2% lower than that of the plain concrete mixture. This shows that the slight reduction in the slump resulting from the addition of the fibers in the dosages employed in this study did not significantly affect the level of consolidation of most of the fiber-reinforced concrete mixtures. However, the fresh density of the concrete mixture incorporating 20 kg/m3 of PP fibers was about 6% less than that of the plain concrete mixture without fibers. This was because the mixture had a zero slump and could not be consolidated sufficiently.Although the workability of fiber-reinforced concrete mixtures is best determined by vibration-based tests such as Vebe time test, the workability of the concrete mixtures tested in this study was evaluated using the slump test due to the simplicity of the test and its widespread use in the industry. The slump and fresh density results of the tested mixtures are given in 3 to 50 kg/m3. A similar trend was observed for the straight steel fibers. The increase in the dosage of the steel fibers increases the likelihood that cracks will be arrested by fibers crossing the cracks, thus leading to somewhat higher compressive strength [3 of PP fibers was 6% lower as compared to the plain concrete mixture without fibers. This is ascribed to the insufficient consolidation of the mixture due to a loss in workability [3).The results of the compressive strength tests are given in strength   showed sharp drops in load-carrying capacity after the peak load. This is due to the insufficient number of fibers available to bridge the crack [he crack . 3), those with bundled steel fibers (50 kg/m3), and those with PP fibers (20 kg/m3) dropped to 37%, 53%, and 43% of the respective peak loads at a deflection of about 0.17 mm. The specimens incorporating hybrid fibers (30 kg/m3 of bundled steel fibers and 10 kg/m3 of PP fibers) had a residual strength of about 70% of their peak load at the same deflection of 0.17 mm.The post-cracking behavior of fiber-reinforced concrete depends on the material, geometry, and dosage of the fibers used . The immFurthermore, the specimens incorporating straight steel fibers had the steepest rate of loss in residual strength, followed by the specimens incorporating bundled steel fibers. This is possibly because both kinds of steel fibers had a straight geometry with no hooks at the ends, which led to the pullout of the steel fibers from the concrete matrix at low bond stresses . By cont3. The residual strength of the bundled steel fibers was generally higher at smaller deflection (L/600 = 0.5 mm) as compared to the PP fibers, but lower at larger deflection (L/150 = 0.5 mm). The use of the hybrid fibers (bundled steel fibers and PP fibers) resulted in higher residual strengths at both smaller and larger deflections. For example, the specimens incorporating hybrid fibers (30 kg/m3 of bundled steel fibers and 10 kg/m3 of PP fibers) resulted in residual strengths of 4.39 MPa and 3.89 MPa at deflections of L/600 (0.5 mm) and L/150 (0.5 mm), respectively.A comparison of the residual strengths corresponding to deflections of L/600 (0.5 mm) and L/150 (2.0 mm) is given in 3 to 40 kg/m3. The straight steel fibers generally had lower toughness as compared to the bundled steel fibers at the same dosage. For instance, the toughness values of the straight steel fibers and bundled steel fibers were 12.0 J and 16.4 J, respectively, at the same dosage of 50 kg/m3. This was attributed to the superior post-peak performance of the bundled steel fibers. The PP fibers and the bundled steel fibers showed comparable toughness values at similar levels of dosage of the fibers, except that the bundled steel fibers had much lower toughness (3.5 J) at the first level of dosage used . This shows that the dosage of 20 kg/m3 of steel fibers is inadequate to improve the post-peak behavior of concrete [3 of bundled steel fibers and 10 kg/m3 of PP fibers) had a toughness of 27.6 J, which is the highest among all the specimens tested in this study.Toughness indicates the ability to maintain the load after cracking of the concrete matrix . The touconcrete . The hyb3 of PP fibers showed a secondary crack at a spacing of about 25 mm from the primary crack  displayed a prominent unstable crack propagation phase, and a loud tick sound was heard when the crack appeared and quickly propagated towards the compression face. The increase in the dosage of the fibers enhanced the ability of the specimen to hold the crack, and thus, mostly stable crack propagation was observed. The first point of the load vs. crack width curves corresponds to the peak load at which the crack is barely visible. The next points on the load vs. crack width curves depict the ability of the specimen to resist crack opening. In general, the load vs. crack width curves confirm the earlier findings on the basis of the load vs. deflection curves. The bundled steel fibers were more efficient in holding a crack as compared to the straight steel fibers. For instance, the loads corresponding to 0.26 mm crack width were 8.51 kN and 6.72 kN for the bundled steel fibers and the straight steel fibers, respectively. The specimens incorporating hybrid fibers (bundled steel fibers and PP fibers) were the most effective in controlling the crack width. The load at 0.26 mm crack width was 14.38 kN for the specimen incorporating hybrid fibers (30 kg/m3 of bundled steel fibers and 10 kg/m3 of PP fibers).Considering the intended application of the concrete mixtures for manufacturing spun-cast full-scale concrete pipes, the crack width was measured at discrete points during loading and plotted against the load . The craFurthermore, visual examination of the fracture surfaces of the specimens indicated that both the straight and the bundled steel fibers predominantly failed by fiber pullout, a,b. This3. The objective of this initial trial was to observe the behavior of the steel fibers in the spinning process. Accordingly, the concrete ingredients were mixed in a drum-type mixture according to the proportions given in To study the potential of incorporating the fibers into the manufacturing of full-scale spun-cast concrete pipes, full-scale pipes, having a 450 mm inside diameter and a 63 mm wall thickness, were manufactured at a local facility using the spinning technique. Concrete pipes are traditionally reinforced with a steel cage consisting of circumferential and longitudinal bars. For this study, initially, concrete pipe without any conventional cage was manufactured, incorporating straight steel fibers at a dosage of 20 kg/mThe pipe mold was mounted on two rollers which induced rotating motion to the mold . InitialThe centrifugal forces presented the biggest challenge to maintaining the uniform dispersion of the steel fibers in the spinning concrete. The visual inspection of the freshly cast concrete pipe revealed that the steel fibers, having much higher specific gravity (7.85), segregated towards the outer side of the wall of the pipe and that no steel fiber could be seen on the inside of the wall of the pipe .3 of the straight steel fibers, and concrete pipe with a conventional steel cage as well as 40 kg/m3 of the straight steel fibers were cast. The conventional steel reinforcement comprised six longitudinal bars of 4 mm diameter and circumferential rebar of 4 mm diameter spaced at 82 mm. In the second phase, four additional concrete pipes having an inside diameter of 450 mm and a wall thickness of 63 mm were manufactured. Plain concrete pipe without any reinforcement, conventional reinforced concrete pipe, concrete pipe with a conventional steel cage as well as 20 kg/mThe pipes were tested in three-edge bearing loading , followi3 of bundled steel fibers, as compared to the plain concrete mixture without fibers.The dosage and type of fibers generally showed little or no effect on the compressive strength of the fiber-reinforced concrete mixtures. However, some improvement in the compressive strength of up to 18% was observed for the concrete mixture incorporating 50 kg/m3 of bundled steel fibers and 10 kg/m3 PP fibers) exhibited much better improvement in flexural strength (24% higher), residual flexural strength at small and large deflections , and toughness (23 times higher) in comparison with the plain concrete mixture without fibers.The splitting tensile strength and flexural strength of all fiber-reinforced concrete mixtures were consistently higher as compared to the plain concrete mixture without fibers. The concrete mixture incorporating hybrid fibers  and low-specific-gravity fibers (such as PP fibers) can be an effective strategy to deal with the tensile stresses on both the inner and outer sides of the wall of a concrete pipe a with thickness too small to accommodate two layers of conventional rebar.This study explored the mechanical properties of various concrete mixtures incorporating steel and PP fibers in mono and hybrid forms at varying dosages with the aim to incorporate the fibers into concrete mixtures for the manufacturing of full-scale spun-cast concrete pipes. The following specific conclusions can be drawn from this study:


The steroid therapy efficacy in resolving hypoechoic lesions in SGs was evaluated in 36 cases. The presence of IgG4-related pancreaticobiliary disease with multiple hypoechoic lesions in SGs was reduced from 31 to 11 cases after steroid therapy, suggesting that multiple hypoechoic lesions in SGs are strongly associated with IgG4-positive cell infiltrations. Multiple hypoechoic lesions in SGs were observed in 53 cases, whereas submandibular swelling on palpation was observed in 21 cases of IgG4-related pancreaticobiliary diseases. A complemental diagnosis of IgG4-related pancreaticobiliary diseases without a histological diagnosis and steroid therapy was achieved in 57 and 68 cases without and with multiple hypoechoic lesions in SGs, respectively. In conclusion, multiple hypoechoic lesions in SGs are useful for the complemental diagnosis of IgG4-related pancreaticobiliary diseases.The diagnosis of autoimmune pancreatitis (AIP) and immunoglobulin G4-related sclerosing cholangitis (IgG4-SC) may require a somewhat invasive pathological examination and steroid responsiveness. This retrospective study assessed the complemental diagnosis of AIP and IgG4-SC using submandibular gland (SG) ultrasonography (US) in 69 patients, including 54 patients with AIP, 2 patients with IgG4-SC, and 13 patients with both AIP and IgG4-SC. The data from the physical examination and US of SGs to diagnose AIP ( Immunoglobulin G4-related disease (IgG4-RD) was recently established as a disease concept and is now widely recognized ,2,3. IgGn = 9) [AIP and IgG4-SC frequently involve diseases in other organs, such as sclerosing sialadenitis, sclerosing dacryoadenitis, retroperitoneal fibrosis, and pseudotumors. Information regarding the involvement of other organs increases diagnostic sensitivity. The histology of these lesions is similar to that of the pancreas in patients with AIP and includes an abundant infiltration of IgG4-positive plasma cells and lymphocytes with dense fibrosis ,9. Sclern = 9)  and the We investigated the hypoechoic nodules of SGs in patients with AIP and performed SG US in patients with IgG4-related disease at our hospital. Moreover, we previously reported that multiple hypoechoic lesions in SGs are a specific marker of AIP that can be objectively and noninvasively diagnosed by US ,13. HoweThe medical records of 69 patients, including 54 patients diagnosed with AIP, 2 patients diagnosed with IgG4-SC, and 13 patients diagnosed with both AIP and IgG4-SC at our institution between October 2003 and October 2020 were retrospectively reviewed. Therefore, the cohort included 67 AIP cases and 15 IgG4-SC cases. AIP was diagnosed according to the Japanese clinical diagnostic criteria  or ICDC ® instrument  at a frequency of 7.5 MHz. The thickest part of each SG was measured, and the characteristic features were analyzed by two US experts to reach a diagnosis. The SG findings were classified into homogeneous and multiple hypoechoic lesions based on the US . Two-group comparisons were conducted using paired n = 67) and IgG4-SC (n = 15) were analyzed. The SGs were evaluated by ultrasound in all cases. Based on US findings, the SGs were classified according to our previous reports into the following three groups: homogeneous, heterogeneous, and multiple hypoechoic lesions [ lesions ; multiplp < 0.001), 2 , and 11  cases with AIP, IgG4-SC, and both AIP and IgG4-SC, respectively  and 28  cases were positive using palpation of the SGs and SG thickness on US, respectively. Among the patients with IgG4-SC, multiple hypoechoic lesions were detected in 10 (67%) cases, whereas 3  and 6  cases were positive when using palpation of the SGs and SG thickness on US, respectively. In all cases, multiple hypoechoic lesions were detected in 53 (77%) cases, whereas 21  and 29  cases were positive when using palpation of the SGs and SG thickness on US, respectively.To clarify the usefulness of multiple hypoechoic lesions in the diagnosis of sialadenitis in patients with AIP and IgG4-SC, comparisons with other tests, including submandibular swelling on palpation and SG thickness on US, were performed . Among tp = 0.051). A noninvasive diagnosis of IgG4-SC was established in 87% and 93% of 15 cases without and with the use of multiple hypoechoic lesions in SGs, respectively (p = 0.540). A noninvasive diagnosis was established in all IgG4-related pancreaticobiliary diseases (combined AIP and IgG4-SC) in 65% and 81% of 69 cases without and with the use of multiple hypoechoic lesions of the SGs, respectively (p = 0.043).The comparison of the diagnosis of AIP or IgG4-SC using invasive examinations, such as the pathological examination and the effects of steroid therapy, with the diagnosis of sialadenitis using multiple hypoechoic lesions is shown in A list of cases that show the effect of the US findings of SGs in diagnosing AIP is provided in In a representative case, AIP was definitively diagnosed using the detection of the presence of sialadenitis based on multiple hypoechoic lesions a–f beforAfter steroid therapy, the focal enlargement of the pancreas on CT was less noticeable b and theThis study demonstrated that the identification of sialadenitis based on the US findings of multiple hypoechoic lesions in SGs may help avoid the use of invasive examinations, such as endoscopic ultrasound with fine-needle biopsy and steroid therapy, for the diagnosis of IgG4-related pancreaticobiliary diseases, including AIP and IgG4-SC. Thus, the noninvasive and objective diagnosis of multiple hypoechoic lesions in SGs using US might have wide utility for the complemental diagnosis of IgG4-related pancreaticobiliary diseases, which warrants future prospective studies in sialadenitis and IgG4-related diseases.The diagnosis of AIP and IgG4-SC was made easier after the establishment of the diagnostic criteria, such as the ICDC  for AIP The ultrasonographic findings of multiple hypoechoic nodules in SGs contributed to the noninvasive and sensitive diagnosis of sialadenitis in IgG4-related pancreaticobiliary diseases. We previously demonstrated that hypoechoic nodules are useful in differentiating AIP from pancreatic cancer . FurtherThe findings of the present study have several clinical implications. First, the characteristic findings of multiple hypoechoic nodules in the submandibular glands, which were present even in cases without palpation, can be an objective and sensitive diagnostic tool for IgG4-related sialadenitis. Second, the use of the ultrasonographic findings of multiple hypoechoic nodules in SGs reduced the number of cases requiring invasive testing for diagnosing IgG4-related pancreaticobiliary disease by 13%, as shown in n = 2), was not sufficient, which made it impossible to obtain statistically significant differences in some analyses, including the IgG4-SC cases alone. Second, considering both the decrease in hypoechoic nodules after the steroid treatment and the previously reported findings, we indirectly demonstrated that the hypoechoic nodules were caused by inflammation triggered by IgG4-positive cell infiltration; however, we could not establish a direct relationship between the pathological and US findings. We previously reported no hypoechoic nodules in the control group of pancreatic cancer when we compared the SGUS findings in pancreatic cancer and AIP [This study has several limitations inherent to its retrospective design. First, the number of cases included in the analysis, especially that of IgG4-SC alone ( and AIP ; howeverThe presence of multiple hypoechoic lesions in the SGs is a useful tool for the complemental diagnosis of IgG4-related pancreaticobiliary diseases without the use of steroids. The US findings also implied the presence of IgG4-positive cell infiltrations into the SGs. We hope that the findings of this study will contribute to the accurate diagnosis of IgG4-related pancreaticobiliary diseases without adverse effects on patients.


A new type of steel–concrete–steel composite structure was adopted and widely used in the immersed tunnel of the Shenzhen–Zhongshan access. The research on the mechanical behavior of the new composite structure under a high temperature of fire is of great engineering significance to the fire protection design of the structure. Both the model test and a numerical simulation were adopted to study the mechanical behavior and damage characteristics of the new composite structure under fire. The RABT standard temperature rise curve was used to simulate the temperature rising law under fire . The temperature distribution law inside the structure, the deformation development law of the roof and the crack distribution were analyzed based on the thermal–mechanical coupling analysis method. The results showed that the internal part of the composite structure close to the fire surface was directly affected by the high temperature, and the temperature presented a step distribution law, while the part far from the fire surface was affected by the lag effect of the temperature transfer, and the temperature presented a continuous growth law. The roof deformation presented a three-stage model of “rapid growth-deformation stability-deformation recovery” with time. The overall cracks of the composite structure showed a symmetrical distribution under fire. The composite structure presented a shear failure mode as a whole. The results could provide a reference for the study of fire resistance for the new composite structure and support the structural fire protection design of the immersed tunnel of the Shenzhen–Zhongshan access. China has now become the country with the largest scale, the largest number, the most challenging geological circumstance and structure forms, and the quickest development pace of highway tunnels in the world, thanks to the rapid development of China’s economic construction ,2,3. ChiSteel–concrete composite structural components are commonly utilized in building constructions as vertical and horizontal load-bearing components, and they are exposed to fire directly. As a result, the majority of research on the fire resistance of composite structures focuses on the construction of composite beam structures. Lennon and Moore 2003) conducted seven fire experiments on eight-story full-scale composite structures and discovered that steel–concrete composite beams could preserve stability and integrity even when deflected significantly . Wang et03 conducIn this paper, a study on the mechanical behavior of the steel–concrete–steel composite structure under a high temperature of fire was carried out based on the physical model test and numerical simulation analysis for the steel–concrete–steel composite structure used in the immersed tube tunnel of the Shenzhen–Zhongshan link, revealing the temperature transfer mechanism, component damage mode, and structural mechanical response characteristics in the internal structure of the composite structure under a high temperature of fire. Related results can provide a reference for the research on fire protection technology and fire mechanical behavior of steel–concrete–steel immersed tunnels.At present, the main tube structure of an immersed tunnel is mainly divided into reinforced concrete and steel plate concrete. The initial immersed tunnel adopted the form of a double steel plate or single steel plate. The outer steel plate was mainly used for waterproofing and as concrete pouring formwork, and the inner side was a reinforced concrete structure, so the outer steel plate was often not used as a load-bearing structure. With the advancement of immersed tunnel technology, in the 1980s, immersed tunnels with steel plate–concrete composite structures as the main bearing structure achieved engineering applications. In Japan, a new type of steel–concrete–steel composite structure was adopted in the Hong Kong Island Tunnel of Kobe Port: the inner structure was equipped with horizontal and vertical steel partitions, and different types of stiffeners were installed in the horizontal and vertical directions of the tunnel. The vertical and horizontal partitions and the inner and outer steel plates formed a whole to bear the external load, so that the component of the composite structure could fully utilize their respective material characteristics, as shown in The size of the steel–concrete–steel composite structural component was 2.9 m × 0.5 m × 0.5 m, the steel plate type was Q355B, the concrete label was C50, and there were horizontal and vertical steel plates, longitudinal T-ribs, welding studs, etc. The thickness of the steel plate at the top and bottom of the component was 10 mm, and the thickness of the transverse and longitudinal partitions was 4 mm. The specific structure of the steel structural component is shown in After the steel structure was fabricated, thermocouples were arranged inside the component, the concrete was poured and cured, and the curing time was not less than 7 days.During the test, internal thermocouples were used to measure the temperature transfer law at different positions inside the component, and wire-pull displacement gauges were used to measure the vertical deformation of the steel plate at the top of the component.The temperature measuring points inside the component were arranged nonuniformly along with the height of the section, and a total of four thermocouples were arranged on the measuring section. The distance between each measuring point and the upper surface of the steel plate at the bottom of the component was 0 mm (measuring point 1), 10 mm (measuring point 2), 240 mm (measuring point 3), and 470 mm (measuring point 4), respectively, as shown in A total of five pull-wire displacement gauges were arranged on the top of the component, and the ends of the pull-wire were fixed on the top plate of the component. The specific arrangement positions were as follows: 1 in the middle of the component’s clear span (measuring point 3), 1 at each of the 1/4 component’s clear span (measuring point 2 and 4), and 1 at each end on both sides (measuring point 1 and 5), as shown in The experiment was carried out with the test setup as shown in The damaged state of the component after the test is shown in Due to the influence of the high temperature, the crack development on the side of the component is obvious, and the main distribution positions of the cracks are shown in Firstly, the temperature distribution law in the steel–concrete–steel composite structure under the RABT heating curve was systematically analyzed. The temperature versus time curve for different sections in the component is shown in During the test, the temperature change rule of The temperature of The variation law of the displacement of different measuring points on the top plate is shown in In order to further analyze the mechanical behavior of the steel–concrete–steel composite structure under the action of the thermal–mechanical coupling, a comparative study was carried out between the numerical simulation and the physical model test results.The thermal parameters of steel and concrete are shown in The heat transfer coefficient of concrete cT—the temperature of the concrete (°C);The specific heat capacity of concrete 3. The heat required for water vaporization in one cubic meter of concrete is:Considering the influence of moisture on the concrete’s temperature, the main influence is the change of the concrete’s specific heat capacity, so the concrete’s specific heat capacity is corrected. Assuming that the vaporization of all water is completed between 90 °C and 110 °C, considering that the general concrete moisture content is 4%, and the vaporization heat of water  is 2257.2 kJ/kg, the density of concrete is taken as 2300 kg/mThe specific heat of concrete at 100 °C is 942.8 J/(kg·°C) according to Equation (2), so the heat required for one cubic meter of concrete to heat up to 20 °C is:Therefore, the specific heat value of concrete between 90 °C and 110 °C is:The specific heat of concrete in other temperature sections was taken according to Equation (2).There are three basic ways of transferring heat: heat conduction, heat convection, and heat radiation. In this model, the heat transfer modes of the flue gas in the overfire area were thermal convection and thermal radiation.2/°C.The comprehensive emissivity was taken from the American standard ANSI/AISC360-10 “Specification for Structural Steel Buildings” (2010), which comprehensively considers the emissivity of the flue gas and the influence of the radiation angle coefficient . The comc,Tσ—stress of concrete at high temperature;The tensile behavior of the concrete is linear elastic until the tensile strength. The stress–strain relationship of the compressive part of the high-temperature concrete adopts the high-temperature constitutive relationship proposed by Lie, as shown in Equation (6) .(6)σc,Tc,Tf—compressive strength of concrete at high temperature;c,Tε—strain of concrete at high temperature;cu,Tε—strain of concrete corresponding to peak stress at high temperatureT—temperature.c,TK—the reduction coefficient of concrete tensile strength at high temperature.The reduction coefficient of the concrete’s tensile strength at high temperature was set according to the provisions of European specification EC2, as shown in Equation (7) .(7)Kc,T5 N/mm2. The elastic modulus and yield strength reduction coefficient at high temperatures were taken according to the provisions of the Code for Fire Safety of Steel Building Structures GB51249, as shown in Equation (8) [Tχ—the reduction coefficient of strength of steel at high temperature;In the analysis, the constitutive model of the steel at different temperatures adopted the ideal elastic–plastic model. The yield strength of steel at room temperature was 355 MPa, and that of the elastic model was 2.06 × 10Tη—the reduction coefficient of Young’s modulus of steel at high temperature.Steel and concrete are homogeneous and isotropic structural materials, and their thermal parameters such as thermal conductivity and specific heat capacity are the same in each direction at the same temperature;A complete heat transfer between steel and concrete, ignoring the influence of contact thermal resistance;The influence of structural high-temperature mechanical response on structure temperature field distribution is not considered;There are many factors affecting the distribution of structural temperature fields under fire. In order to simplify the analysis process, the following assumptions were considered:The sequential thermal–mechanical coupling method was used to analyze the temperature field of the structure first, and then the results of the temperature analysis were applied to the mechanical model as loads to analyze the mechanical response of the model. The established finite element model is shown in (1)Comparative analysis of temperature transfer lawsThe comparison results of the temperature–time curves are shown in (2)Contrastive analysis of roof deformation lawsThe comparison results of the roof deformation laws are shown in (3)Distribution analysis of structural plastic zone under a high temperature of fireBased on the numerical simulation results, the plastic zone distribution of the steel–concrete–steel composite structure under a high temperature of fire was obtained, as shown in (4)Analysis of structural crack distribution under a high temperature of fireBased on the numerical simulation results, the tensile failure cloud diagram of the component concrete was obtained, as shown in (1)Under the RABT standard temperature rise curve, the area directly affected by the high temperature under fire in the steel–concrete–steel composite structure was within a range of about 10 cm from the fire surface, and within 3 cm away from the fire surface, the concrete showed a powdered state; the crack distribution modes in the composite structures under thermal–mechanical coupling were given.(2)The temperature transfer law of the measuring points at different depths of the combined structure were given: the temperature distribution of the measuring points closer to the fire surface presented a stepped distribution, and there was an obvious heating and cooling stage; the temperature of the far measuring points showed a continuous growth law due to the hysteresis effect of temperature transfer; the results of the numerical simulation and physical model test were compared to verify the temperature transfer law in the composite structure under a high temperature of fire.(3)The evolution law of the roof displacement of the composite structure was given: the overall deformation trend of the structural component under the action of thermal–mechanical coupling was that the middle sank and the two ends upturned. Affected by the high temperature of the fire, the roof deformation presented three distinct stages with time: a rapid growth stage, a deformation stabilization stage, and a deformation recovery stage. The results of the numerical simulation and physical model test were compared to verify the mechanical response mechanism of composite structure under the high temperature of fire.(4)The high temperature of fire had limited impact on the plastic development of the whole structure. The plastic zone was concentrated in the lower flange near the fire surface, and the plastic zone of the other parts was less distributed.(5)The composite structure presented a shear failure mode as a whole: the crack distribution of the whole component had good symmetry, a 45° oblique crack appeared on the line connecting the beam end support and the loading point, and the midspan cracks developed vertically.


A significant difference was also observed between the energy absorptions of the reinforced mixtures into steel fibers.Impact resistance of Portland cement concrete (PCC) is an essential property in various applications of PCC, such as industrial floors, hydraulic structures, and explosion-proof structures. Steel-fiber-fortified high-strength concrete testing was completed using a drop-weight impact assessment for impact strength. One mix was used to manufacture 320 concrete disc specimens cured in both humid and dry conditions. In addition, 30 cubic and 30 cylindrical specimens were used to evaluate the compressive and indirect tensile strengths. Steel fibers with hooked ends of lengths of 20, 30, and 50 mm were used in the concrete mixtures. Data on material strength were collected from impact testing, including the number of post-first-crack blows (INPBs), first-crack strength, and failure strength. Findings from the results concluded that all the steel fibers improved the mechanical properties of concrete. However, hooked steel fibers were more effective than crimped steel fibers in increasing impact strength, even with a smaller length-to-diameter ratio. Concrete samples containing hybrid fibers (hooked + crimped) also had lower compressive strength than the other fibers. Comparisons and analogies drawn between the test results and the static analyses  show that the  Concrete is the most used building material, with an annual consumption of well over 25 billion tons ,2,3,4,5.Concrete impact resistance is an essential property in various applications such as industrial floors, hydraulic structures, and explosion-proof structures. Given that the use of fiber-reinforced concrete in these structures is increasing, it is important to evaluate the impact resistance of concrete using different types of fibers. Among the various methods for assessing the impact strength of concrete, the drop-weight impact test proposed by ACI Committee 544  is the sSome factors, such as the test character or the heterogeneous nature of concrete, can cause the impact test results to be highly dispersed . VariousMany researchers have studied the effect of steel fibers on the mechanical properties of different types of concrete. A complete report on the characteristics of consumable steel fibers and the types of tests performed in previous studies is reported in According to Therefore, in this study, in the first stage, a complete study was performed on the research on fiber-containing concrete and information such as concrete type, the shape of steel fibers, fiber length, fiber diameter, the length-to-diameter ratio of fibers, and fiber consumption dose; the mechanical tests performed on concrete are reported in a table. In the next step, to study the effect of the shape and length of fibers, steel fibers in different sizes were used. Additionally, to investigate the effect of curing conditions on the mechanical properties of concrete, two completely different curing environments were planned. After the fabrication and processing of the samples, compressive, tensile, and impact strength tests were used to evaluate mechanical strength. In order to provide clearer results, the results of the experiments were analyzed by statistical analysis. The behavior of concrete under short-duration dynamic loads  is completely different from the behavior it exhibits under static load conditions. Therefore, the results of the present study can be considered a practical reference for projects that are of high importance, such as hospitals, nuclear power plants, tall buildings, etc. It is expected that the results of this study can provide useful information to civil engineers.3. The steel fibers utilized during this investigation had a tensile strength of 1140 MPa and were crimped and hooked  ratio of 0.4 and a cement grade of 450 kg/mAfter conducting the slump test, the concrete mixture was poured into 15 cm cubic molds for the compressive strength test and 30 × 15 cm cylindrical molds for the splitting tensile strength test . After 2The impact test was conducted in line with the drop-weight measurement recommended by ACI Group 544. As shown in CV% = is the sum of coefficients of variation percentages and allN = is the total number of mixtures.The tests were performed on hardened concrete after a curing period of 28 days. The test specification, the size of the samples, and the standards used are given in The 28-day specimens’ compressive strength was determined for humid and dry curing conditions, as shown in Examining fiber performance in concrete shows that 5 cm corrugated fibers increased the compressive strength of ordinary concrete by an average of 39%, while 3 cm and 2 cm corrugated fibers improved the compressive strength by 33% and 28%, respectively. A comparison of the mixtures’ compressive strengths indicates that the mixture containing 5 cm crimped fibers was 10%, 5%, and 9% stronger, on average, than F2, F3, and F3F2. This may be due to the longer length of the 5 cm wavy fibers compared to other fibers.p-value less than 0.05 means that the normal assumption was rejected. On the other hand, the Kruskal–Wallis test compares two or more groups of data. In the Kruskal–Wallis test, there was no significant difference between groups, as the p-value was greater than 0.5 [For each mixture and curing condition, 32 discs were tested for the drop-weight impact load. The number of blows required for the appearance of the first crack and for the final failure was determined in the tests. The results for the humid and dry curing conditions are given in than 0.5 .The results given in The coefficients of the variation of the first-crack impact strength for mixtures R, F2, F3, F5, and F2F3 in a humid environment were 27%, 33%, 77%, 36%, and 37%, respectively. The corresponding values for dry curing conditions were 29%, 32%, 88%, 41% and 44%, respectively. Thus, the impact strength data shows more dispersion for dry-cured concrete than those cured in humid conditions.p-values of less than 0.05, obtained by the Kolmogorov–Smirnov test, indicate that the data are not normally distributed. The normal probability shapes and histograms for different mixtures cured in humid conditions are plotted in As stated, p-value obtained for the first cracks of the reference concrete in a wet environment was 0.093, which confirms the above claim. Mixtures of F2 and F23 follow the normal distribution in p-value obtained by the K–S test showed a value greater than 0.15, which confirms their normal distribution. Mixtures of F3 and F5, however, do not follow the normal distribution due to the normal plot’s poor fit, shown in p-value of the K–S test was less than 0.01. p-value was equal to 0.141. Mixtures of F3 and F2F3 do not follow the normal distribution due to the poor representation in p-value confirms this result from the K–S test. Finally, the incorporation of F5, according to p-value equal to 0.093, shows a rarely normal distribution. p-values of 0.029, 0.000, 0.000, and 0.049, respectively. In addition, the corresponding p-values for dry curing conditions were 0.030, 0.001, 0.021 and 0.321, respectively. This indicates a significant improvement in the first-crack impact strength of high-strength concrete when the steel fibers were introduced separately compared to that of the high-strength control concrete.According to the average strength values presented in Similarities were observed in the strength of the first crack, the mean blows’ strength at failure, and the high-strength concrete containing 5 cm crimped steel fibers increasing from 2 cm crimped steel fibers. This demonstrates the effective role of a higher length/diameter ratio in increasing the impact strength of the concrete. Hooked fibers, however, have better performance in increasing the concrete’s strength compared to crimped fibers, even with a lower diameter ratio. In a dry environment, the average failure strength of conventional high-strength concrete is 129 blows, and the mean failure strength of F2, F3, F5, and F2F3 mixtures is 158, 237, 173, and 163, respectively b. As witTherefore, in dry environments, as in humid environments, the addition of steel fibers to high-strength concrete improves failure strength. Average impacts for failure in humid environments compared to dry environments for conventional high-strength concrete were 1.162 times, for concrete containing 2 cm crimped steel fiber 1.215 times, for 3 cm hooked steel fiber 1.919 times, for 5 cm crimped steel fiber 1.485 times, and for fiber composition 1.226 times. Similar to the strength of the first crack, the comparison of the failure strength coefficient of variation in the two environments also shows higher values in dry environments than in humid environments.p-value of the K–S test, which is equal to 0.068, is the result of a seldom normal distribution for this mixture. p-value for mixtures F2, F5, and F2F3 by the K–S test indicates a number greater than 0.15, which confirms the normal distribution of these mixtures. For the F3 mixture, p-value (0.087), show that a normal distribution is rare. Reference concrete in a dry environment also rarely shows a normal distribution due to the poor display in p-value for this mixture is equal to 0.075, which confirms its rarely normal distribution. The F2 mixture shows a normal distribution due to the relatively acceptable results of the normal plot with the histogram in p-value greater than 0.15 from the K–S test. Mixtures of F3, F5, and F2F3 do not follow the normal distribution due to poor representation of the fit between the normal plot and the histogram in p-value obtained from the K–S test for these mixtures also indicates abnormal distributions.p-values of 0.001, 0.000, 0.000, and 0.001, respectively. In dry environments, the values obtained were 0.003, 0.000, 0.002, and 0.058, respectively.The comparison in λ), has been defined by Cao [failN − firstN) to the impact energy absorbed by the first visible crack in the concrete (firstN). The ductility index (λ) and impact energy are defined by the following formula [λ = the ductility index, firstN = first visual crack, failN = ultimate crack, E = impact energy (J), m = mass of hammer, g = gravitation acceleration, and h = height of drop.In the field of impact resistance, in addition to first-crack strength and failure strength, a new term, the ductility index λ=λ) for different mixtures in The ductility index  of mixtures cured in humid and dry environments is shown in MAD and MAPE were used [The coefficient of determination .The presence of different steel fibers improves the tensile strength by 17% to 60%, and 3 cm hooked-end steel fibers allow the greatest increase in strength. The humid-cured samples also have higher tensile strength (up to 21%).The presence of steel fibers in concrete improves some parameters. For example, the number of blows for first-crack strength, failure strength, and energy absorption increase by 1.194–2.288 times, 1.224–3.033 times, and 1.83–6.5 times, respectively. Fiber shape also had an impact on the strength of the concrete, with the best performance being the 3 cm hooks.The comparison of F2 and F5 shows that taking into account the ratio of length to diameter, the presence of crimped fibers with a higher ratio of length to diameter has a better performance in increasing the strength of the first crack and failure.p-value.The relationships obtained in this study indicate a high correlation between first-crack strength and failure strength. Statistical analysis  also shows a more normal distribution of humid environments and a significant difference in steel-reinforced concrete by In addition to adding fibers to concrete, proper curing can also improve impact strength. This shows the importance of the hydration process for concrete.This study statistically analyzes the effect that different types of steel fibers have on the impact strength of high-strength concrete under different curing conditions, and it extracts the following results:


This retrospective observational study evaluated outpatient treatment patterns among patients with molecular-based viral diagnostic testing for suspected upper respiratory tract infections in the United States. Patients with a respiratory viral test were identified from 1 August 2016 to 1 July 2019 in a large national reference laboratory database linked to IQVIA’s prescription and medical claims databases. Antibiotic and influenza antiviral treatment patterns were reported up to 7 days post-test result. Predictors of antibiotic utilization were assessed using multivariable logistic regression. Among 9561 patients included in the study, 24.6% had evidence of ≥1 filled antibiotic prescription. Antibiotic utilization was higher in patients who tested negative for all viral targets  and patients positive for non-influenza viruses  compared with those influenza-positive only. Age ≥ 50 years and location outside of the northeast United States also predicted antibiotic utilization. Influenza antivirals were more common in influenza-positive patients compared with patients with other test results (32.5% vs. 3.6–9.0%). Thus, in this real-world study, antibiotic utilization was elevated in patients positive for non-influenza viruses, although antibiotics would generally not be indicated. Further research on pairing diagnostic tools with outpatient antibiotic stewardship programs is needed. Upper respiratory tract infections are common, with an estimated 500 million non-influenza respiratory infections in the United States (US) every year . DespiteOne aspect of antibiotic stewardship is diagnostic stewardship, ordering the right test to inform timely and appropriate test-guided treatments and improve patient care ,10. In tDespite our current repository of tools, including antibiotic stewardship programs and diagnostic testing, judicious antibiotic utilization remains suboptimal. In addition, the impact of molecular testing on treatment decisions is unclear, especially in the outpatient setting. This retrospective database study aims to describe outpatient antibiotic and influenza antiviral treatment patterns following molecular-based tests for acute respiratory tract infections and to explore predictors of antibiotic utilization in clinical practice.In total, 9561 patients received a respiratory viral test of interest in the large national reference laboratory database linked to IQVIA′s prescription claims (LRx) and medical claims (Dx) databases and met all study selection criteria . The demMost of the index viral tests were ordered during an influenza season (91.9%), with 46.2% of all tests ordered by primary care physicians and 34.6% ordered by pediatricians . The majIn total, 57.5% of the cohort tested negative for all viral targets, 22.5% tested positive for influenza, 20.8% tested positive for a non-influenza viral target, and 0.7% of patients were co-infected with influenza and a non-influenza virus. For each specific viral target, the highest positivity rates were observed for the combination rhinovirus/enterovirus test (25.2%), rhinovirus (22.7%), unspecified coronavirus (20.0%), and influenza A (14.9%) .Utilization of antibiotics and influenza antivirals in the cohort stratified by test result is described in In the logistic regression model among all patients, several characteristics were identified as significantly increasing the odds of antibiotic utilization . SpecifiIn this real-world study of patients with suspected upper respiratory tract infections, outpatient antibiotic prescribing was common and observed in about one-quarter of all patients who received molecular respiratory viral testing. Overall, we did not find a strong association between positive viral test results, particularly for non-influenza viruses, and a reduction in antibiotic prescribing. Compared with patients who only tested positive for influenza, those who tested positive for non-influenza viruses or negative for all viral targets had 28–33% higher odds of antibiotic utilization. Antibiotics are generally not indicated for the treatment of respiratory viruses or in the absence of an identified pathogen; therefore, this was a surprising finding. However, these results may be explained by several unmeasured factors. First, the antibiotic treatment decisions may have been informed by bacterial test results that were not observable in this study or the clinical suspicion of bacterial infection. This scenario seems probable based on our analysis of respiratory-related diagnosis codes, where patterns in the odds of antibiotic utilization matched up with the diagnosis tiers in the way one might expect , which suggests that the clinicians’ diagnoses may have warranted an antibiotic in some cases. Second, the timing and speed of the test results may have also played a role in impacting decision-making. In a retrospective study conducted by Rogers et al. of children hospitalized with an acute respiratory tract infection, the duration of antibiotic treatment was reduced by half a day if the positive test result was reported within 4 h compared with longer than 6 h . The impNevertheless, our findings of treatment patterns in the outpatient setting are consistent with previously conducted retrospective studies in inpatient settings, emergency departments, and hospital outpatient clinics, which suggest that respiratory viral testing alone may not be sufficient for improving appropriate antibiotic utilization ,16,18; rIn addition, this study investigated the association between patient characteristics and antibiotic utilization, which may help inform targeted outpatient antibiotic stewardship efforts. We observed that older adults ≥50 years of age had 27–40% higher odds of antibiotic treatment compared with younger adults, which aligns with prior studies of patients treated for respiratory tract infections in the emergency department setting ,27. In aAlthough there was no strong association between positive viral test results and antibiotic prescribing, we observed a favorable trend in higher antiviral utilization in the presence of a positive influenza test result 32.5%) compared with patients who tested positive for any non-influenza virus (3.6%) or negative for all viruses (9.0%). These findings of increased influenza antiviral use following testing have also been demonstrated in prior studies ,14,15, w.5% compaThe key strength of this study is the use of a nationally representative laboratory database linked to large pharmacy and medical claims databases in the United States, which allows for a comprehensive view of outpatient antibiotic and influenza antiviral utilization following receipt of a molecular-based viral test. Other studies examining the association between the results of viral testing for respiratory tract infections and treatment outcomes have typically used data from inpatient, emergency department, and urgent care settings in single institutions or limited analyses to pediatric or adult populations, whereas our study cohort reflects a variety of age categories, geographies, and insured populations. Given the majority of antibiotic expenditures occur in the outpatient setting  and the This retrospective observational study used data from a large national reference laboratory linked to IQVIA’s prescription claims (LRx) and medical claims (Dx) databases during the study period from 1 February 2016 to 31 July 2019 . The laboratory database consists of over one decade of laboratory data for approximately 150 million patients and is nationally representative of the U.S. population. Key information in the laboratory database includes patient demographics , diagnostic tests identified using Logical Observation Identifiers Names and Codes (LOINC) and lab test names, and test results. The LRx database captures information on dispensed prescriptions with 92% coverage of prescriptions from the retail channel, 72% coverage of standard mail service, and 76% coverage of long-term care facilities. The Dx database captures over one billion pre-adjudicated claims and three billion records obtained annually from approximately 800,000 office-based physicians and specialists, with 75% of American Medical Association providers captured. Medical claims from ambulatory and general health care sites  are also included in the Dx database. All data are Health Insurance Portability and Accountability Act (HIPAA)-compliant to protect patient privacy. The study dataset was created based on an HIPAA-compliant linking process using IQVIA’s patented and proprietary encryption algorithm ,40.Inclusion and exclusion criteria for patient selection are described in For the cohort of patients meeting all selection criteria, patient demographics and baseline clinical characteristics (including CCI and select comorbidities) were evaluated during the 6-month baseline period, and characteristics of the index test  were reported from data on the index date. Respiratory-related International Classification of Diseases Tenth Revision Clinical Modification (ICD-10-CM) diagnosis codes were grouped into three tiers based on previous publications ,5,41, whFollow-up measures included antibiotic utilization and influenza antiviral utilization, which were reported in the overall cohort stratified by three non-mutually exclusive categories of test results . Utilization was determined based on the presence of ≥1 pharmacy claim for an antibiotic or influenza antiviral picked up from a pharmacy on or up to 7 days after the index test result date.p-values < 0.05 were considered statistically significant. All analyses were conducted using SAS version 9.4 .Logistic regression was used to estimate the odds ratios (ORs) and 95% confidence intervals (CIs) for the association between patient demographic and baseline clinical characteristics and characteristics of the index test (including test result and respiratory-related diagnosis code tier on the index date). In summary, treatment with antibiotics for suspected respiratory tract infection in the outpatient setting was common in this large, real-world retrospective study. Although viral molecular testing had a demonstrated impact on patient management with influenza antivirals, its value on outpatient antibiotic utilization remains a topic for further exploration. Respiratory viral testing alone may not be sufficient for improving antibiotic utilization; expanding outpatient antimicrobial stewardship tools and further investigation into the barriers and facilitators of linking diagnostic test results with treatment decision-making are needed.