The rubber particles obtained from the grinding of waste tires can replace a portion of the fine aggregates in concrete, thus effectively reducing the level of environmental damage and saving resources. However, when concrete is mixed with rubber, it greatly reduces its strength. In this study, by introducing basalt fiber (BF) and polypropylene fiber (PF) as modified materials in rubberized concrete, the influence of the fiber type/volume ratio on the slump, water absorption, static uniaxial compression, and permeability of the rubberized concrete was tested. The axial compression stress–strain relationship was analyzed, the effect of the fiber type/volume ratio on the energy dissipation of the rubberized concrete during uniaxial compression was expounded, and a stress–strain constitutive model under uniaxial compression was established. The test results showed that the fiber reduces the fluidity and water absorption of the rubberized concrete. Compared with the polypropylene fiber, the basalt fiber increased the strength of the rubberized concrete, while the polypropylene fiber mainly inhibited the expansion and penetration of the macroscopic crack of the rubberized concrete. The mixing of the basalt fiber and polypropylene fiber significantly decreased the release rate of the elastic strain energy of the rubberized concrete, increased the dissipation energy, and thus improved its ductility and toughness. During a loading process under confining pressure, the permeability of the tested specimen decayed exponentially, and the fiber greatly enhanced the anti-permeability of the rubber concrete. With the rapid development of the global economy and society, the demand for concrete, the most commonly used building material worldwide, has risen sharply. Among them, natural river sand is one of the important raw materials for the preparation of concrete. However, long-term over-exploitation has led to the depletion of natural river sand resources, riverbed collapse, and a reduction in groundwater levels, which has ultimately seriously damaged the ecological environment ,2. ThereAt present, many scholars continue to study the effect of rubber as a fine aggregate on concrete. For instance, researchers have compared and analyzed the compressive strength and splitting tensile strength of rubber-aggregate concrete and ordinary concrete, finding that, compared with ordinary concrete, the compressive strength of rubber-aggregate concrete was reduced by a maximum of 85% and the splitting tensile strength was reduced by a maximum of 50% ,10,11. LAlthough rubber concrete has economic and environmental advantages compared to ordinary concrete, its greatest advantages are its fatigue resistance, weight, thermal conductivity, failure characteristics, and freeze–thaw resistance. However, the compressive strength of concrete is significantly reduced after the addition of rubber; thus, the safety of the concrete structure is not effectively guaranteed. Therefore, it is necessary to study and improve the strength of rubber concrete. In recent years, the introduction of fibers in concrete to enhance its strength has received extensive attention. In particular, the addition of fibers of different sizes or types can reduce the width of concrete cracks at different structural scales and significantly reinforcement the concrete strength ,26,27,28Basalt fiber (BF) is a continuous fiber made of basalt rock melted at 1450~1500 °C and drawn at a high speed through platinum-rhodium alloy wire drawing bushing. It belongs to green fiber. The elastic modulus of basalt fiber can reach 93~115 GPa; its tensile strength can reach 200~5000 MPa; and it has a good bonding performance with cement-based materials ,30. PolyIn view of the fact that rubber will significantly reduce the strength of concrete, in order to ensure the safety of rubber concrete buildings, it is designed to mix basalt fiber and polypropylene fiber in rubber concrete to prepare a new type of green and sustainable concrete . The slump and water absorption of BPRC were measured, and uniaxial compression and permeability tests under different confining pressures were carried out. The strengthening mechanism of basalt fiber (BF) and polypropylene fiber (PF) on rubber concrete was studied systematically.3. The rubber was obtained by crushing waste tires with a particle size of 1~2 mm and an apparent density of 1250 kg/m3. The main performance parameters of the basalt fiber and polypropylene fiber are shown in The cementitious material used in the present study was a common Portland cement with a compressive strength of 42.5 MPa at 28 days. The coarse aggregate was made of natural crushed stone with a particle size of 5~20 mm, while the fine aggregate was natural river sand with a fineness modulus of 2.65 and apparent density of 2345 kg/mVBF:VPF) was 1:0, 0:1, 1:2, 1:1, and 2:1. Using the absolute volume method [In order to maximize the use of the waste tires, this study fixed the rubber content at an equal volume to supersede 20% of the fine aggregate. The total volume ratio of the basalt fiber and polypropylene fiber was fixed at 1.5%, and the volume ratio ratio :The specimens were cylindrical with a diameter of 100 mm and a height of 200 mm. The test equipment used in this study was the WAW-2000D electro-hydraulic servo universal testing machine . A quasi-static loading process was simulated using the displacement-controlled loading method at a speed of 0.5 mm/min. During the test, the longitudinal deformation and axial force of the test block were collected automatically by the test system, and the displacements at both ends of the test block were measured by the displacement meter. Before the test, the two end surfaces of the test block were ground smooth and lubricated. Before the formal loading, each specimen was preloaded at a loading rate of 0.5 mm/min. When processing the results, three typical test stress–strain curves were selected from each group. Their average stress–strain curves were obtained through data processing, and the average curve was used as the analysis curve of this group of tests.K is the permeability; μ is the viscosity coefficient of the water; Q is the flow rate of the water infiltrating the specimen; L is the height of the specimen; A is the cross-sectional area of the water passing through; and p is the osmotic water pressure.The specimens were saturated with water the day before the test. The test equipment used in the present study was the TAW-2000 triaxial testing machine . The confining pressure was set to C = 3, 4, 5, 6, 7, and 8 MPa; the osmotic water pressure was set at a constant of 1.6 MPa; and the axial pressure was set at a constant of 1 kN. The calculation method used for determining the permeability is shown in Equation (2):1, BPRC2, and BPRC3, the slump reduction with an improve in the basalt fiber volume fraction, indicating that the basalt fiber has a greater influence on the slump of the rubber concrete than the polypropylene fiber.The influence of the fiber type/volume ratio on the slump of the rubber concrete is shown in 1, BPRC2, and BPRC3, the water absorption rate decreases with the increase in the volume fraction of the polypropylene fiber, indicating that the influence of the polypropylene fiber on the water absorption rate of the rubber concrete is greater than that of the basalt fiber.The water absorption of each group of specimens at the different curing ages is shown in (1)3 group and BFC group revealed similar performances in the elastic stage, the longest elastic time, and the largest slope, which indicated that the basalt fiber in the elastic stage of the rubber concrete lifting effect is more obvious than the polypropylene fiber.On the whole, the stress–strain curve of the fiber–rubber concrete is obviously fuller than that of the rubber concrete. At the initial stage of loading, the stress–strain curve is close to a straight line, and, at this stage, the slope of the fiber–rubber concrete is obviously larger than that of the rubber concrete. This shows that the fiber can effectively increase the stiffness of the rubber concrete and has a good elasticity. Because of the bridging effect of the fiber, the internal defects of the rubber concrete are reduced, and the elastic stage of fiber–rubber concrete is longer than that of the rubber concrete. Intuitively, the BPRC(2)3 group and BFC group being the largest. Compared with the RC group, the top of the fiber–rubber concrete curve is more rounded, while the PFC group is the most rounded, indicating that the polypropylene fiber is more conducive to improving the toughness of the rubberized concrete than the basalt fiber. It can be seen from the whole rising stage of the stress–strain curve that the basalt fiber and polypropylene fiber are both beneficial in improving the compressive capacity and deformation capacity of the rubber concrete.In the stage of rapid stress growth, the stress–strain relationship curve begins to bias from the straight line, with the growth rate of the strain greater than that of the stress at this stage. The slope of the curve decreased gradually, but the decreasing rate was different. The slope of the RC group is the smallest, with those of the BPRC(3)2 group declined the most slowly, mainly because the synergistic effect of the basalt fiber and polypropylene fiber improved the internal defects of the rubberized concrete so that it still had a better bearing capacity after compression failure.After the peak stress, the stress drops rapidly to the “inflection point” of the curve. Following the inflection point, the stress decreases slowly, and the stress–strain curve becomes convex toward the strain axis until ultimately reaching stability. After the peak stress, the stress of the RC group decreases rapidly, displaying obvious brittle failure, and the decline rate of the fiber–rubber concrete becomes significantly lower than that of the RC group, indicating that the fiber was beneficial in improving the ductility of the rubberized concrete and improving the brittle failure. Among them, the BPRCThe stress–strain curve from the uniaxial compression test is shown in VBF:VPF = 1:1, the peak stress is the largest, i.e., 23.24% higher than that of the rubberized concrete.The effect of the fiber type/volume ratio on the peak stress of the rubberized concrete is shown in cE is the elastic modulus.The effect of the fiber type/volume ratio on the elastic modulus of the rubber concrete is shown in To sum up, if only from the perspective of improving the peak stress and elastic modulus of rubber concrete, the volume ratio of the basalt fiber should be appropriately increased.U is the total strain energy per unit volume of the external force input; eU is the elastic strain energy stored in the concrete interior per unit volume; and dU is the dissipated energy per unit volume of concrete damage development.The essential characteristic of the physical change process of matter is the transformation of energy . The comσ is the stress; ε is the strain; and E is the initial elastic modulus.According to the stress–strain relationship, the calculation of the total strain energy, elastic strain energy, and dissipation energy under the unit volume of the external force input can be conducted using Equation (5):The total strain energy, dissipative energy, and elastic strain energy of each group of specimens in the process of compression failure are shown in 2 group maximum energy and dissipated energy. The total strain energy and dissipation energy of the BFC group are slightly larger than those of the PFC group. When the specimen was finally damaged under compression, compared with the RC group, the total strain energy of the BFC group, PFC group, and BPRC2 group increased by 62.98%, 57.62%, and 92.55%, respectively, and the dissipated energy increased by 62.79%, 57.58%, and 92.47%, respectively.It can be seen from 3 groups had the greatest increasing rate in the elastic strain energy before the peak elastic strain energy, indicating that basalt fiber is more advantageous than polypropylene fiber in increasing the rate of elastic strain energy of rubber concrete. Compared with the RC group, the BPRC2 group displayed the smallest decrease in the peak elastic strain energy, indicating that an appropriate fiber volume ratio was beneficial to the inhibition of the crack penetration velocity in the rubber concrete.It can be seen from The ratio of the elastic strain energy to the total strain energy represents the conversion rate of the elastic strain energy of the specimen during the process of compressive failure, and the ratio of the dissipated energy to the total strain energy represents the conversion rate of the dissipated energy of the specimen under the process of compressive failure. At present, the mechanical properties of rubber concrete/fiber–rubber concrete have been studied extensively by many scholars. However, the stress–strain constitutive model of rubber concrete/fiber–rubber concrete under uniaxial compression is seldom studied, and the failure characteristics of rubber concrete/fiber–rubber concrete are not fully understood. The four existing stress–strain constitutive models are combined , and the descending stage uses the rational fraction, as shown in Equation (7).Ascending stage:x and y are set according to a, b, and c are corrected by the peak stress, fiber type, and fiber volume ratio; and the least squares method is used to perform a regression analysis on the above parameters, with the calculation of the above parameters performed as follows in Equation (8):cσ is the peak stress; λ is the volume fraction of the basalt fibers; and η is the volume fraction of polypropylene fibers.Descending stage:In order to verify the accuracy of the stress–strain correction constitutive model established in this paper, the test curve was compared with the fitting curve, as shown in 1, BPRC2, and BPRC3 experiments, under the same confining pressure, the permeability of the polypropylene fiber increased gradually with the decrease in the volume fraction of the polypropylene fiber, thus also indicating that the polypropylene fiber is better than the basalt fiber at reducing the permeability of the rubberized concrete.(1)Both fibers reduce the slump of rubberized concrete, but the basalt fiber has a greater effect on the slump of the rubberized concrete than the polypropylene fiber. At the same curing time, the water absorption of the fiber–rubber concrete is lower than that of the RC, and the effect of the polypropylene fiber on the water absorption of the rubberized concrete is greater than that of the basalt fiber.(2)VBF to VPF is 1:1, the peak stress increases by 23.24% compared to that of the RC. The elastic modulus of the fiber–rubber concrete is larger than that of the RC, and the influence of the polypropylene fiber on the elastic modulus is limited. The elastic modulus of the PFC group is increased by 10.36% compared with the RC group.The fiber type/volume ratio has a significant effect on the RC peak stress, and the order of the effect in terms of fiber type is basalt fiber > polypropylene fiber. When the ratio of (3)The total strain energy and dissipation energy of the fiber–rubber concrete are obviously larger than those of the RC. Before the peak elastic strain energy, the fiber increases the elastic strain energy growth rate of the rubberized concrete, and, after the peak elastic strain energy, the fiber reduces the elastic strain energy reduction rate of the rubberized concrete, leading to obvious ductile failure characteristics.(4)Along with the characteristics of the fiber–rubber concrete in this paper, two parameters, namely the fiber type and fiber volume ratio, were introduced to establish a modified segmental stress–strain constitutive model. The model calculation results were in good agreement with the experimental results and can effectively reflect the effect of the fiber type/volume ratio on the constitutive behavior of the rubberized concrete.(5)The effect of the single-mixed basalt fiber on reducing the permeability of the rubber concrete is lower than that of the single-mixed polypropylene fiber, and the effect of the mixed fiber on reducing the permeability of the rubberized concrete is better than that of the single-mixed fiber.In this study, a new green and sustainable concrete (BPRC) was designed using rubber particle, basalt fiber, and polypropylene fiber and the effects of the fiber type/volume ratio on the workability, mechanical properties, and anti-permeability of the rubberized concrete were systematically studied. The main conclusions can be summarized as follows:


Candida (p < 0.001), and a higher fungal diversity (p = 0.005–0.04) and richness (p = 0.03) in the antibiotic-treated infants compared to the antibiotic-naïve ones at multiple timepoints. This indicates that the gut mycobiota could contribute to the long-term consequences of antibiotic treatments.Antibiotics are commonly used drugs in infants, causing disruptions in the developing gut microbiota with possible detrimental long-term effects such as chronic inflammatory diseases. The focus has been on bacteria, but research shows that fungi might have an important role as well. There are only a few studies on the infant gut fungal microbiota, the mycobiota, in relation to antibiotic treatment. Here, the aim was to investigate the impact of antibiotics on the infant gut mycobiota, and the interkingdom associations between bacteria and fungi. We had 37 antibiotic-naïve patients suffering from respiratory syncytial virus, of which 21 received one to four courses of antibiotics due to complications, and 16 remained antibiotic-naïve throughout the study. Fecal samples were collected before, during and after antibiotic treatment with a follow-up period of up to 9.5 months. The gut mycobiota was studied by Illumina MiSeq sequencing of the ITS1 region. We found that antibiotic use affected the gut mycobiota, most prominently seen as a higher relative abundance of  The gut microbiota is known to include bacteria, fungi, archaea, viruses and sometimes protozoa and is a major factor contributing to human health . Most miCompared to the bacterial gut microbiota, the gut mycobiota has fewer taxa and seems to be less stable ,11. VariThe first major exposure to microorganisms is through birth, and the infant gut has been observed to be colonized by fungi  as earlywww.kela.fi/tilastot, accessed on 2 February 2022; and statistics in Finland, www.stat.fi/til, accessed on 2 February 2022). The use of antibiotics during the critical time from conception to 2 years of age has been reported to cause both short-term problems including dramatic shifts of the gut fungal and bacterial microbiota and even sepsis, and further long-term consequences such as asthma, atopy, pediatric onset of Crohn’s disease and metabolic diseases [Many newborns receive antibiotics due to an infection during early years of life. In Finland, 26.5% of children < 5 years of age received at least one course of antibiotics in 2019  infection. Only antibiotic-naïve children were included. Fecal samples were collected before, during and after antibiotic treatment with a follow-up of up to 9.5 months. All fecal samples were immediately frozen at −20 °C until transported frozen to −70 °C where they were stored until analysis. At each sampling timepoint, questionnaires were filled out containing information on diet, probiotics and use of antibiotics. Additionally, information of birth mode, other possible diseases, growth and weight gain were available from the patient files. Preterm infants  or those with congenital malformations or syndromes were excluded. None of the infants had been traveling abroad. In analyses, the timepoints were calculated as time since the start of antibiotics, or time since the first sample for antibiotic-naïve patients. In the cases where multiple courses of antibiotics were administered to a patient, the days from the most recent antibiotic course were used in the timepoints. Therefore, the time of follow-up might be longer than the timepoint used in analyses.The fecal samples were thawed, and the bacterial and fungal DNA was extracted using the bead-beating method as previously described . The 16SThe ITS MiSeq sequencing read data were processed according to the DADA2 ITS pipeline . The reap-values for taxon-specific differences were corrected for false discovery rate . GeneraHochberg  and GeneHochberg  were use package .The study was approved by the Ethics committee of Helsinki and Uusimaa Hospital district. All guardians signed an informed consent to include their child in the study.The aim was to study the effect of antibiotics on the gut mycobiota. We analyzed samples from 37 antibiotic-naïve infants who were recruited prospectively and included in our previous report on the bacterial gut microbiota . All chiFungal amplicons generated from a total of 123 fecal samples obtained from the 37 recruited patients were sequenced. Out of these, 68 samples were derived from the 21 antibiotic-treated patients and 56 samples from the 16 control patients. Baseline samples of the antibiotic-treated patients were obtained from 12 patients. Background data of the study participants are presented in Saccharomyces was most prevalent (97%) with a relative abundance of 71%, followed by Malassezia  with a relative abundance of 8%, Candida  with a relative abundance of 9% and Cladosporium  with a relative abundance of 1%. The prevalence and relative abundance of all genera with a prevalence >5% is presented in p < 0.05) both at baseline and at all timepoints, except for the location of hospital, which was significant only when including all timepoints   . At the end of the study (>6 weeks after start of treatment) the phylum Basidiomycota was more abundant in the antibiotic-treated group (both amoxicillin and macrolide combined)  (Before the start of antibiotic treatment there was no significant difference in gut mycobiota composition between the groups. At 1–2 days after the start of treatment (during treatment), the amoxicillin-treated group had significantly higher relative abundance of the fungal genus e = 132) A. When ce = 3.8) A. Furthe = 10.9) B. DetailCandida at >6 weeks after start of treatment compared to controls . This difference was not significant for macrolide-treated infants, although the trend was similar with non-FDR-corrected p-value < 0.05, and fold change 22. Both the amoxicillin- , but notably the macrolide-treated  infants had significantly higher relative abundance of Malassezia at 3–6 weeks after the start of antibiotic treatment. Further, Basidiomycota was more abundant in the macrolide-treated group compared to controls at 3–6 weeks after the start of treatment .When comparing the groups of antibiotics used, the amoxicillin-treated infants had significantly higher relative abundance of p = 0.04, richness, p = 0.03), 1–2 weeks ((when comparing to control at 3–5 days) diversity, p = 0.005, richness, p = 0.03)) and >6 weeks  after the start of antibiotic treatment as seen in p = 0.0027).Finally, the antibiotic-treated group had significantly higher fungal diversity and richness at 3–5 days  at all timepoints, and these are presented in Interkingdom Spearman correlations were calculated at each timepoint for both the antibiotic-treated group and for those who remained antibiotic-naïve throughout the study. There were significant correlations (Candida and higher diversity and richness in antibiotic-treated infants.Here we investigated the effect of antibiotics on the infant gut mycobiota. This was carried out by MiSeq sequencing of the PCR-amplified ITS1 region from the DNA of fecal samples collected from both controls and antibiotic-treated infants at six different timepoints with a follow-up ranging over 9 months. All patients were naïve to any antibiotics at the first timepoint and controls were antibiotic-naïve throughout the follow-up. We observed that the use of antibiotics affected the gut mycobiota, characterized by an increased relative abundance of Clostridioides difficile infection. In children, however, C. difficile infections after antibiotic use is rare [Antibiotics may have a detrimental effect on both the bacterial and fungal gut microbiota, with consequences such as antibiotic-associated diarrhea and recurrent  is rare . The freSaccharomyces, Malassezia, Candida and Debaromyces were reported to make up the core gut mycobiota of infants across these studies [Debaromyces, which interestingly was not one of the most abundant genera. In addition to the difficulty in distinguishing colonizers from transient fungi [The healthy gut bacterial microbiota of infants is characterized by facultative anaerobic bacteria such as streptococci, enterococci and enterobacteria dominating the composition . There a studies ,49,50,51nt fungi  of the gnt fungi . In a Nont fungi . In our nt fungi , the mosnt fungi .In our previous study we showed that after introducing antibiotics the bacterial diversity and richness dropped significantly at 1–4 days, and then it rose again after cessation of antibiotic treatment. Additionally, we observed a rapid change in the bacterial composition during the antibiotic course with bifidobacteria already replaced by enterobacteria 4 days after the start of antibiotics. After the treatment ended, the bacterial microbiota started to recover by an increase of bifidobacteria, but there was still an increase of Firmicutes 6 months after the start of antibiotics . Here weBacteroidaceae, Bifidobacterium, Enterococcus, Bacillus and Haemophilus at baseline in our previous analysis with the same cohort [Candida was observed to be significantly more abundant in the antibiotic-treated infants compared to controls, while Saccharomyces was more abundant in the controls. The same trend was seen throughout. We also found that the fungal phylum Basidiomycota was relatively more abundant in the antibiotic-treated group at the end of the study. Further, we found that Basidiomycota was more abundant in the macrolide-treated infants compared to controls at >6 weeks after start of treatment, while Malassezia was more abundant in both amoxicillin- and macrolide-treated infants. Basidiomycota has been observed to be more abundant in IBD previously [The gut mycobiota was comparable between the control group and antibiotic-treated group before start of antibiotic treatment, while the antibiotic-treated group already had a higher relative abundance of the bacteria belonging to e cohort . This coeviously , suggesteviously .Candida has been observed to be elevated in inflammatory diseases [Candida is a yeast characterized by polymorphism, including both different growth forms and morphologies, of which particularly hyphae formation is observed to be associated with virulence [Candida albicans by limiting hyphae formation [Candida, have the opportunity to grow. Unfortunately, we do not have data on the absolute abundances of the fungi, but other studies have shown that overgrowth of Candida is a common side-effect of antibiotic treatments [Candida is elevated after antibiotic treatment and prevents re-establishment of Lactobacillus spp. in microbiome-disturbed mice [C. albicans, induce Th17 cells [Candida is a driver of inflammation, or whether it simply benefits from inflammation [While being a part of the healthy gut microbiota , Candidadiseases ,5,6,7,8,diseases ,29. Candirulence . In a reormation , which aormation . Since aeatments . Furtherbed mice . It has 17 cells ,57. Th1717 cells . Howeverammation .All infants included in this study had an RSV infection at baseline and therefore the observed differences between the study groups are unlikely to be due to the infection, but due to the antibiotics. Additionally, the infants had not received any antibiotics prior to being included in this study, i.e., all infants were antibiotic-naïve at recruitment. The relatively low number of patients, particularly the controls, is a limitation of this study, as in most pediatric studies. Finally, the fungal data were relative abundances and highly zero-inflated, meaning there was a high number of samples devoid of the given fungal taxa, which was considered by taking prevalence into account in all statistical analyses. Zero-inflation is observed in most, if not all, fungal microbiota studies, and therefore statistical tests designed for normally distributed data may produce unreliable results.Candida, and higher diversity and richness. This could indicate that aberrant gut mycobiota composition after antibiotic treatment could, together with the bacterial microbiota, be a cause of the long-term effects that antibiotics have on human health.Introduction of only a single course of antibiotics during the development of the gut mycobiota in infants caused a shift in the fungal gut composition, characterized by a higher relative abundance of


Non-destructive tests (NDTs) represent one of the solutions that aid engineers in evaluating the strength of materials. However, the results obtained using such tests are still questionable as they may be affected by different factors. One of these factors is the presence of steel reinforcement in concrete. An experimental investigation is presented in this study to investigate the effect of the single reinforcement steel bar on ultrasonic pulse velocity (UPV). Seven concrete beams, one containing no steel and the other six beams containing varying bar diameter and cover thicknesses, were tested. UPV measurements were obtained using the indirect method and then modified to eliminate the effect of the steel bar. To provide the scientific evidence to give a reliable and reasonable solution, a statistical analysis was also conducted. The results show that a large bar diameter and a small cover thickness significantly influence the measured UPV. Measured UPV with a spacing between transducers up to 500 mm can effectively be used to predict the compressive strength of concrete after the modification of the initial UPV. Concrete testing is a crucial procedure in a construction project or laboratory experiment. It is typically time-consuming and intractable, especially in a place where no samples can be taken from existing structures to be tested. At the same time, the non-destructive test (NDT) is becoming more popular in the built environment around the world. It is used to determine the integrity of a material, a component of the structure, or quantitatively measure some characteristic of an object. The NDT is a highly valuable technique that saves both material and financial resources in product evaluation, overhauling, and research.To determine the compressive strength of concrete, destructive coring tests, as well as NDT methods, such as the rebound hammer, ultrasonic tests, and radar, are widely used . HoweverTest methods are also categorised into penetration and nonpenetration modes. Because concrete typically exhibits variations in its material property even within a single member, concrete strengths are better obtained via penetration mode tests, such as in ultrasonic testing by passing through the entire cross-section of a member rather than part of it, as in the nonpenetration or reflection mode.An ultrasonic pulse velocity test is an in situ, non-destructive test to determine the homogeneity of the concrete. In this test, the strength of concrete can be assessed by measuring the ultrasonic pulse velocity (UPV) that passes through a concrete structure . In addiThe experimental apparatus for measuring UPV is advanced and convenient. The arrangement of transducers is also flexible and varies with the different situations. However, ultrasonic waves are known to be affected by the presence of embedded steel inside the concrete. Thus, it is necessary to quantitatively investigate the significance of the effect of steel.When dealing with the effect of steel in concrete on the estimation of the compressive strength of concrete, two scenarios need to be considered. First, it has been reported that when an ultrasonic wave crosses the steel bars in a direction that cuts through the cross-sectional areas, the summation of the cross-sectional areas of steel causes the wave velocity to increase ,7. SeconCurrently, steel-reinforced concrete structures are used extensively worldwide, but the presence of reinforcement causes considerable uncertainties due to the higher velocity of pulses in steel . It is mIn addition, in concrete it is always the case that that only one surface is appropriate for performing the ultrasonic pulse test. For instance: in a column with only one face exposed to the inner space, it is not always possible to apply the direct transmission. In order to obtain the quality of the concrete, indirect transmission is the only method. Therefore, the problem was raised, and this project is going to solve the contradiction of avoiding the use of the ultrasonic pulse velocity method in concrete structures if a single reinforced bar is present under the condition of indirect transmission. One of the methods of testing both steel and plastic bars is the self-excited acoustical system ,14.The present study aimed to investigate the quality of the concrete with the presence of a single reinforced steel bar by using an indirect transmission. So, it looks at the effect of the reinforcing steel bar diameter and concrete cover on the pulse velocity when it crosses the reinforced concrete medium. Three sizes of bar diameter and four concrete cover ranges were considered, so seven beams and twelve cubes were cast, namely, C20D20, C40D20, C60D12, C60D20, C60D32, and C80D20. By comparing beams C20D20, C40D20, C60D20, and C80D20, the effect of the concrete cover was able to be identified. Similarly, by comparing the beams C60D12, C60D20, and C60D32, the effect of the bar size was able to be investigated.It has been observed through the literature that there are existing experimental works to evaluate the concrete quality by UPV Measurements ,16,17. Hi.Identify the existence of the steel bar in the concrete: The information about concrete in a construction structure is always unknown, including whether the reinforcement exists or not. If the concrete is not reinforced, the analysis will be meaningless.ii.Analyse the pulse velocity with the steel bar existing: In this part, the calculation is performed to avoid the influence of the steel bar.iii.Perform a statistical analysis: This is to provide the scientific evidence to give a reliable and reasonable solution. On the basics of the statistical analysis, recommendations can be made.To achieve the objectives of the present study, different parts have been conducted:Previous studies have found that many factors influence UPV if the steel bar exists, such as concrete cover, bar size, corrosion, the bond between steel bar and concrete, the direction of steel bar, and the number of steel bars. However, in this study, only a single reinforcement is taken into consideration, and the steel bar is located at the middle line of a lateral cross-section. A deformed reinforcing steel bar with a grade of HRB500 (ASTM) was used in the study. Considering varying concrete cover thickness and the bar diameter, seven beams and twelve cubes were cast, as shown in The arrangement of the emitter and receiver transducers varies due to the length of the beam. Thus, a longer length of the beam is preferred. The cross-section has a limitation according to the British Standard . The sho2 at 28 days. The cement strength class was 42.5 N. The maximum coarse and fine aggregate had a size of 20 mm and 5 mm, and the type was crushed Basalt stone and river sand, respectively. The slump was in the range of 30–60 mm. The aim of having a concrete beam is to investigate the effect of the presence of a steel bar on the UPV. Thus, the concrete does not need a specific compressive strength. The concrete mix design is based on a water/cement ratio of 0.55 as the main factor, which directly influences the concrete strength. The ratio between cement and aggregates also has strong effects on the material capacity . AccordiThe Pundit Lab+ offered by Proceq, as shown in The distance (path length) between the transducers should be measured as accurately as possible to ensure the correct path length of the pulse. Adequate acoustic coupling of the transducers to the surface is also important to ensure transducer sensitivity. A thin layer of coupling agent should be applied to the transducer and the test surface . In someThere are 12 positions where the transducers are placed, as shown in Steel bar affects the transit time between transducers because the UPV in the steel bar is faster than that of concrete. If there is a path that makes the wave reach the receiver faster, it emphasises the influence of the steel bar. This can be observed by comparing the UPV results of the concrete beam with and without a steel bar. Therefore, this section aims to solve the UPV of concrete (tion (1) .(1)v=LTAssume that the transducers are placed on the points P(a), P(l), and the distance between two pints is The transit time will be the addition of the time passing through partly within concrete  and the vertical travel distance  within the concrete is Once the derivative of Let The negative value of In an infinite medium, the pulse velocity of steel is taken as 5900 m/s. It is known that the pulse velocity in steel bars decreases by a certain value if considered a concrete–steel medium. The pulse velocity of steel in a concrete medium with a bar diameter of us study ,(9)Vs=5Substituting the Where According to the Equation (10), the transit time , is shown in Theoretically, the UPV in the plain concrete is expected to be equal regardless of the location of transducers along the beam. However, practically, it can be seen that the average value of the UPV has a decreasing tendency with increased spacing between transducers, as shown in The percentage change of the UPV for the plain concrete beam does not show a unique relationship with the spacing between transducers, as shown in According to the British Standard , the eneAccording to Ndagi, A. et al. , “The puThe modified pulse velocity for the concrete medium using the measured pulse velocity of concrete beams with steel was calculated based on Equations (10)–(12). Modified pulse velocity is not applicable for the plain concrete beam as the beam does not have a steel bar.In all the cases, the modified UPV results have a similar trend with a plain concrete beam from 100 mm to 400 mm spacing between transducers, as shown in 3.The Pundit Lab guideline provides a method to estimate the compressive strength of concrete using the UPV value and the rebound number as shown in Equation (14) . In thision (15) . In thisconcrete  and rubbconcrete . This stIn the previous section, the average value with the standard deviation of the apparent and modified UPV was used to study the influence of the steel bar on the UPV measurements. However, the average value cannot represent the feature of each value when there are 66 data points of the transit time measured in one single beam with different spacing between transducers. It is difficult to interpret a single data point on its own. The implementation of summary statistics is an important method in the undertaking of any statistical analysis.Considering the full set of frequency data presented in This study was carried out to investigate the effect of steel bars in concrete on the UPV measurements. This study proposed a method to determine the UPV applicable for plain concrete in reinforced concrete by considering experimental evidence with plain concrete, varying cover thickness, and varying steel bar diameter. Based on the study and analysis, the following conclusions can be drawn.1.The existence of steel, mainly as reinforcement in the same direction of indirect UPV measurement, can significantly influence the measured UPV.2.Large bar diameter and small concrete cover thickness increase the UPV measurement using the indirect method.3.The measured indirect UPV data, which was influenced by the presence of steel, can be converted to a modified UPV using a mathematical approach.4.The modified UPV of concrete, with a cover thickness of 20 mm to 80 mm, can predict the UPV of plain concrete with an accuracy of 95% if the transducer’s spacing is between 100 mm and 500 mm, using indirect measurements. Transducer spacing can be further increased to 600 mm or 700 mm if the concrete cover thickness increases to 40 mm and 80 mm, respectively.5.Modified UPV accurately predicts the compressive strength of plain concrete. This was achieved using existing databases on UPV data for different types of concrete.6.This method of determining the indirect UPV of plain concrete in reinforced concrete elements should be carefully conducted. The results of this study do not support the situations with more than one steel bar in the longitudinal direction with the measurement, as more steel bars can influence the accuracy of the data. However, the steel bars in the lateral direction of the measurement will have minimal influence on the measured data.


Recently, substantial investigations were developed on a polyvinyl chloride (PVC)-carbon fiber-reinforced polymer (CFRP) confined concrete (PFCC) structure owing to its superior mechanical behavior and durability. However, a convenient and effective joint configuration between the PFCC columns and reinforced concrete (RC) beams still requires in-depth study. In the present work, the seismic performance of an RC beam to PFCC column exterior joint with steel tube connector (STC) is systematically studied. Eleven joint specimens are fabricated and tested, with the steel ratio of STC, reinforcement ratio of the frame beam, axial compression ratio, stirrup ratio of the joint and CFRP strips spacing as the design parameters. The experimental results, that is, 8 the failure modes, hysteretic response, ductility, strength, stiffness and energy dissipation, are analyzed. All specimens exhibit joint shear failure, although the joints with STC exhibit significantly better performance those of ordinary joint. In addition to reducing the axial compression ratio, the reinforcement ratio of the frame beam or increasing the stirrup ratio of the joint can also produce a positive effect. Furthermore, the numerical analysis of the exterior joints is performed; the calculated skeleton curves agree well with the test results, and additional parametric studies  are carried out based on the verified numerical model. Previous studies have proven that concrete-filled tube (CFT) systems can significantly enhance the mechanical properties and durability of encased concrete; CFT has emerged as one of the essential strengthening forms for high-rise and pile foundations ,2. In paHowever, owing to the corrosion of steel tubes, as well as the brittle fracture and high price of FRP materials ,7, severIt is well recognized that the connection between the CFT columns and reinforced concrete (RC) beams is an imperative research field for CFT systems ,16,17. CFor the beam-through system, the longitudinal bars of the RC beam can penetrate through the joint core directly, which significantly improves the integrity of the joint area. However, considering the discontinuity of the steel tube may weaken the confinement on the joint core concrete, a novel joint form  with the surrounded ring stirrups is employed in the joint core to confine the core concrete) is proposed . Wang etAs mentioned above, multiple studies have confirmed the feasibility of the joint with STC. Similar measures were applied to deal with connections between the PFCC columns and RC beams, and a series of static experiments and FE simulations were performed ,34,35,36Nevertheless, given the vulnerable portions in the earthquakes, it is far from sufficient to only conduct the investigations on the static performance of the developed joints ,38. MeanTo ensure that the loading conditions of the specimens were in accordance with the stress characteristics of the frame joints, a T-shaped joint consisting of the upper and lower columns and a unilateral frame beam were intercepted as the investigation objects. The overall appearance and detailed reinforcements of the specimens are plotted in A total of ten RC beam to PFCC column exterior joints with STC and one reference joint were manufactured. The design principle of “strong members, weak joint” was adopted because the main purposes of this experiment was to investigate the failure modes and seismic behavior of the composite joints. The impacts of the steel ratio of STC Additionally, the thickness of the PVC tubes adopted for the specimens was 7.8 mm and the outer diameter was 200 mm. Two layers of 0.111 mm thick CFRP strips are wrapped around the PVC tubes in the hoop direction, and the width of each layer is 20 mm. It is worth mentioning that an additional layer of CFRP strip is utilized at the PFCC column ends to prevent its premature failure. The stirrups of the PFCC columns and frame beams for all specimens are A10@150 and A10@100, respectively.4 Mpa, respectively. The main index properties of the steel material, PVC tubes and CFRP strips adopted in the test are measured according to GB/T 228.1-2010 [According to GB/T 50152-2012 , the cub8.1-2010 , GB/T 888.1-2010  and GB/T8.1-2010 , respectAs presented in y as the displacement amplitude until the specimen is destroyed or the load declines to 85% of the peak bearing capacity. However, considering the relatively poor deformability in the joint core of the designed specimens, the method of identifying the yield displacement Δy by the reinforcements yielding may result in the premature failure of the specimens. Consequently, in accordance with the crack development and reinforcements strain of the specimens in the pre-test, 6 mm is selected as the yield displacement in subsequent test. Nevertheless, regarding the subsequent seismic performance analysis, the veritable yield displacement is determined by the energy equivalence method [Referring to the test method specified in China Industry Standard JGJ/T 101-2015 , the dise method  based onTo facilitate the description of the experimental phenomenon, the components of the joints are denominated as shown in As expected, the shear failure of the joint core area is observed in all specimens, and the variation in the structural parameters has no apparent impact on the final failure mode. Meanwhile, the specimens exhibit similar crack mode except for an insignificant variance in the timing of crack appearance. The typical crack and failure mode are depicted in y, the oblique cracks are developed into the crossed oblique cracks and extends to the frame beam root and the cantilever beam. Until the peak bearing capacity is reached, the cracks present a stable development without new cracks occur, only the increase in the crack width. In this stage, the improvement in axial compression ratio can further accelerate the cracks development. When loading to the cycle with the displacement of 6Δy, severe concrete spalling is exhibited in the joint core area, an inevitable bond-slip between the STC and the joint concrete is observed, which indicates that the experiment is accomplished. There is no significant damage in the PFCC column during the whole loading process.At the initial loading stage, the specimens have no obvious cracks and exhibit elastic response. With the improvement of the displacement in the frame beam end , several oblique cracks emerge in the joint core area. Compared with the specimens PJ-2 and PJ-4, the above-mentioned oblique cracks of the specimen PJ-5 is accompanied with a higher displacement, which is mainly because the joint stirrups can provide a slight confinement for the surrounding concrete. At the displacement of 2ΔP and the corresponding vertical displacement Δ. All hysteretic curves are characterized by the significant pinching effect and residual deformation, the evolution of the generic hysteretic curves is described as follows.Before the specimens cracking, the hysteretic curves basically cycle linearly with a slight residual deformation. When the obvious crossed oblique cracks appearing in the joint core area, the hysteretic curves gradually progress into the elasto-plastic stage, in which stage, the growth rate of load is increasingly slower than the displacement, the pinching phenomenon is detected and becomes more pronounced with the increasing displacement. After the peak bearing capacity is reached, since the bond failure between the joint concrete and STC, the growth rate of load decreases drastically. Correspondingly, the apparent residual deformation and pinching effect is observed from the hysteretic loops, which indicates the significant degradation in strength and stiffness of the joints.Additionally, as illustrated in P-Δ skeleton curves for each specimen are also presented in The For an intuitive discussion of the test results, the peak loads and displacements  are plotted in Moreover, it is observed that the peak displacements of the specimens are principally determined by the stirrup ratio of the joint and the reinforcement ratio of the frame beam. With the improvement in stirrup ratio of the joint, the development of the core concrete cracks is further confined, and the joints present a stronger deformability. Meanwhile, the plastic hinge on the frame beam root is more prone to adequately develop with a smaller reinforcement ratio of the frame beam, the deformability of the joints can also be enhanced.The ductility coefficient is a crucial indicator to quantify the deformability of the RC structures in seismic design, which is defined as the ratio of the ultimate displacement e method , as illuThe ductility coefficients of the specimens PJ-0, PJ-1, PJ-2 and PJ-3 are 2.09, 2.46, 2.50 and 2.54, respectively. The ductility coefficient of the specimen PJ-3 is only slightly higher than that of the specimen PJ-1 attribute to the above-mentioned bond failure. Therefore, corresponding methods should be developed to avoid this phenomenon, such as welding ring bars or shear studs on the outer wall of STC. Alternatively, bonding  CFRP profiles on the surface of the joint area as additional shear reinforcement is an option worth investigating ,48,49,50Additionally, as the stirrup ratio of the joint increases, the confinement on the core concrete at the periphery of the STC is enhanced, which can effectively inhibit the extension of the joint concrete cracks, resulting in a stronger ductility of the specimens. The ductility coefficient of the specimen PJ-5 with a higher reinforcement ratio of the frame beam is 10.3% less than that of the specimen PJ-7. This may due to the higher reinforcement ratio inhibiting the generation of the plastic hinge. It is worth mentioning that, although the specimen PJ-6 exhibits a considerable peak bearing capacity in the above description, its ductility is the lowest among the specimens, this is because the increasing axial compression ratio will further accelerate the development of concrete cracks. Furthermore, the ductility coefficient of each specimen ranges from 2.03 to 3.12, which satisfies the requirement that the ductility coefficient of RC structures is not less than 2 .Since the cyclic loading is usually accompanied by a reduction in the bearing capacity for the identical displacement amplitude, the strength degradation coefficient To simplify the calculation, the strength degradation coefficient at the second cyclic loading is adopted, as depicted in In the specimens with the steel ratio of STC and stirrup ratio of the joint as the comparison parameters, the specimens PJ-3 and PJ-5 show the gentlest descending stage. Manifesting that the improvement in the steel ratio of STC and stirrup ratio of the joint are relatively effective methods to strengthen the joints. Significantly, the turning point of the specimen PJ-1 is earlier than that of the specimen PJ-6, which suggests that the improvement in axial compression ratio will accelerate the strength degradation. The strength degradation coefficient of the specimen PJ-7 is maintained above 0.8, indicating the joints with lower reinforcement ratio of the frame beam can perform a better stability of the bearing capacity.Stiffness is often described as the ability of the RC structures to resist the deformation. The loop stiffness As shown in The equivalent viscous damping ratio The development of the In addition, the impact of the stirrup ratio of the joint on the the Ref. , the effOpenSees is a finite element software for simulating the seismic response of engineering structures, which shows the advantages of short computation time-consumption and high solution efficiency. The skeleton curves of the exterior joint with STC under low cyclic loading is numerically simulated by the fiber beam-column element in the OpenSees, and the further parametric analysis of the joints is performed.(1) ConcreteThe ‘Concrete02′ and ‘Concrete03′ models are commonly adopted in OpenSees to simulate the concrete under seismic action since they can incorporate the stiffness degradation and hysteretic energy dissipation of the concrete during the loading and unloading. Nevertheless, in view of the time consumption of the concrete03 model, model concrete02 is introduced in the analysis models of the sandwiched concrete and ordinary concrete. The stress–strain relationship of the proposed model is illustrated in η from 5 to 5.5 to incorporate the confining effect of the STC, as shown in The properties of PVC-FRP confined concrete are defined according to the constitutive model proposed by Fang et al. , as show(2) SteelThe simulated results of the ‘steel02’ model are in good agreement with the cyclic loading tests on the steel materials. Meanwhile, the ‘steel02′ model can fully reveal the kinematic hardening effect and nonlinear combined isotropic. Thus, the ‘steel02′ model proposed by Filippou et al.  is utiliThe joint core area is modelled with fiber cross sections, as presented in To accurately model the joint core area subjected to low cyclic loading, the shear behavior of the panel zone should be specified. The diagonal strut model ,56 is suP strips . hb and Meanwhile, owing to the panel zone consists of the joint stirrups, sandwiched concrete and steel tube confined concrete, its shear behavior is distinct from the CFST structures. On the basis of the analytic results in Ref. , to compP-Δ skeleton curves are developed, as illustrated in Through the above modeling steps, the numerical P-Δ skeleton curves with the various parameters are illustrated in On the basis of the validated FE model, additional parameters which may influence the seismic behavior of the joints are further analyzed, for the purposes of improving the seismic design of this composite structure. The As illustrated in As illustrated in As illustrated in The final failure mode exhibited by all specimens is a joint shear failure. The increase in the stirrup ratio of the joint or the decline in the axial compression ratio can effectively confine the crack development of the joint concrete.The proposed joint with STC presents a superior seismic performance when compared with the ordinary joint. However, the strength of STC cannot be completely utilized owing to the premature bond failure between the joint concrete and STC.By increasing the steel ratio of STC or the stirrup ratio of the joint, the pinching effect of the hysteretic curves is controlled, the ductility and energy dissipation capacity are enhanced, and the strength degradation and stiffness degradation are delayed, while the increase in the reinforcement ratio of the frame beam and axial compression ratio presents the opposite effects.The higher stirrup ratio of the joint, axial compression ratio and steel ratio of STC develops a better contribution to the peak bearing capacity. Meanwhile, the peak displacement of the specimens observably increases as the stirrup ratio of the joint increases or the reinforcement ratio of the frame beam decreases.The numerical model of the joint is established by OpenSees, and it is verified that the developed model can well simulate the skeleton curves of the proposed joint.The parametric numerical analysis indicates that the peak bearing capacity increases with the concrete strength, height or diameter of the joint increase, while the increase in the height of the joint can also result in the reduction of the peak displacement. Considering the bearing capacity, deformability and construction convenience, it is recommended that the joint height be below 500 mm, the joint concrete strength be below C60 and the joint diameter not exceed 300 mm.Seismic behaviors were investigated on the RC beam to PFCC column exterior joint with STC through the experiment and numerical simulation in this study. The following conclusions can be obtained:


Surface damages usually occur in concrete structures. In order to restore the functions and prolong the service life of concrete structures, their surface damages should be repaired in time. This paper reviews the main requirements for repair materials for concrete structures and the most used inorganic repair materials, such as cement-based materials, alkali-activated materials and polymer modified inorganic repair materials. Moreover, techniques to characterize and even improve the interfaces between these repair materials and concrete substrate are summarized. Cement-based material has the advantages of good mechanical properties and consistency with concrete substrate while having the problems of high shrinkage and low flexibility. Polymer modified materials were found as having lower shrinkage and higher flexural strength. Increasing the roughness or humidity of the surface, adding fibers and applying interfacial agents can improve the bond strength between cement-based repair materials and concrete substrates. All of these repair materials and techniques can help to build a good interfacial bonding, and mechanisms of how they improve the interface are discussed in this article. These are of great importance in guaranteeing the effectiveness of the repair of the concrete surface and to guide the research and development of new repair materials. Cement concrete is currently the most widely used civil engineering construction material worldwide and has been applied in various civil infrastructures, such as roads, bridges, ports and tunnels. Under the external loads and environmental impacts, concrete structures are prone to be damaged, such as cracking and even spalling. In addition, inappropriate selection of raw materials, incorrect mixture design and irregular construction process may also cause damages to concrete, particularly regarding the cover protecting the reinforcement bars. These damages not only reduce the durability of structures, but also lead to structural unserviceability during service . To solvAt present, there is a huge demand for concrete structure repair worldwide. The investments on the repair and reinforcement of old constructions in the USA were estimated at 90 billion dollars in 2016 . In EuroThe effectiveness of surface repair is greatly dependent on the properties of the repair materials and the interface between the repair and concrete substrate . HoweverThe effectiveness of repair systems mainly depends on the performances of the repair materials. Usually, repair materials should have good mechanical performances, especially high early mechanical strength, strong bonding with substrates and appropriate workability. The China building materials industry standard JC/T2381-2016) for repair formulates the fundamental properties see  7]. The. The7]. 1-2016 foCement-based materials are the most widely used materials for repairing concrete structures. These materials not only have a good compatibility with the substrate, but also have advantages of good bonding with the substrate, high economic benefit and easy operations for repair. The most used binders in cement-based repair materials are Portland cement (PC), sulphoaluminate cement (SAC) and magnesium phosphate cement (MPC). In addition, blending materials, such as fly ash, blast furnace slag and silica fume, are usually used to modify the repair materials for better performance.Qian et al.  studied 2S and 3CaO∙3Al2O3∙3CaSO4. Hydration products with a large amount of crystalline water can not only provide a strong bonding capacity and shorten the setting time for emergent repairs, but also effectively reduce the shrinkage [Sulphoaluminate cement is also a fast-hardening binder, of which the main mineral components are Chrinkage . Yu et ahrinkage  studied hrinkage  also rephrinkage . Meanwhihrinkage  found thMagnesium phosphate cement made by mixing the magnesia and phosphate with some inert fillers in certain proportions is a new eco-friendly material because it consumes less resources and energy during production than other traditional cements. Compared to Portland cement mortar, MPC mortar features advantages of higher early strength, shorter setting time, better bonding performance ,19, lowe4·6H2O dissolves and the porosity of the mortar increases, causing a decrease in the mechanical strength. Therefore, MPC-based repair materials should not be applied in moist or underwater environments [Qiao et al.  studied ronments .In summary, cement-based materials with the properties of rapid hardening and high early mechanical strength are more suitable for the concrete repair materials. However, the effect of shrinkage of rapid hardening materials should be valued. Among the above cement-based materials, MPC shows better early mechanical properties, shorter setting time and lower shrinkage than PC and SAC.2) and alumina (Al2O3)-rich materials, such as fly ash (FA), blast furnace slag (BFS) and metakaolin (MK) [2 in the substrate will react with the SiO2 and Al2O3 in AAM to form calcium (natrium) silicoaluminate hydrate (C(N)ASH), thereby enhancing the interfacial adhesion [Alkali-activated material (AAM) is an environmentally friendly repair material because it causes little pollution during production and it presents desirable characteristics, such as high mechanical strength and resistance to chemical agents, better temperature stability, improved abrasion resistance and good adhesion to concrete substrates . Therefolin (MK) . When AAadhesion . Nunes eadhesion  found thadhesion  found thadhesion . Howeveradhesion  found thCement-based repair materials usually have problems of high shrinkage and low flexibility. Therefore, modification of cement-based repair materials by using organic materials has attracted lots of attention.The epoxy-modified cement mortar (EC) has been widely studied for concrete repair ,31,32 du2+ and chemical bonding, should be taken in consideration. Liu et al. [Asphalt mortar (AM) has been applied widely in repairing high-speed railways . Minh etu et al.  investigWang et al.  studied In summary, polymer-modified mortar generally has high mechanical strength, excellent durability and high bond strength with the substrates, but its setting time is usually longer than that of the non-modified ones.A follow-up survey on a large number of existing concrete repair projects showed that most of the repair materials cannot guarantee a long-term effective repair . Among tAccording to the literature , the intTherefore, effective bonding is required to withstand the aforementioned stresses, ensuring the integrity and functionality of repaired structures . The intThe bond strength between the cement-based repair material and the substrate can be evaluated by means of various testing methods, such as shear bond strength testing see , flexuraKim et al.  carried Through pull-out bond strength testing and double shear bond strength testing, Sadrmomtazi et al.  determinThrough the flexural bond strength tests and the split bond strength tests method, Karima et al.  investigIn summary, there are flexural bond strength tests to determine the bend resistance and monolithic failure mode of the repair interface; shear bond strength tests, slant shear tests and push-out tests to determine the shear resistance; and pull-out bond strength tests, split-pull bond strength tests and core pull-put bond strength tests to determine the tensile resistance. In addition, the nondestructive impact–echo technique provides a non-destructive method to evaluate the adhesive property of repair interface.The interfacial microstructure affects the bond strength between repair materials and substrate. Therefore, it is necessary to characterize their interfacial microstructure.Zhou et al.  characte2 in the old concrete substrate. Pang et al. [Qian et al.  used SEMg et al.  used a dM) and hardness (H) fluctuate are the interface regions. When the substrate has higher M and H values, the lowest values of M and H often appear in the interface region close to the overlay, and the maximum values of M and H are obtained in the near surface layer of the substrate, which can be attributed to the penetration of the new cement paste of overlay into the substrate.Sadowski et al.  employedThe quality of repair is affected not only by the repair material but also by external additives and the concrete substrate to be repaired . Feng etZanotti et al.  studied To improve the adhesion of the repair material and the concrete substrate, interfacial agents have been applied to the substrate surface. Fahim et al.  studied Based on the literature review above, there are technologies being developed to enhance the interfacial adhesion for concrete repair. Increasing the surface roughness of the concrete substrate and using interfacial agents can improve the interfacial bond strength between cement-based repair and concrete substrate under static loading .In this paper, the main requirements for cement-based repair materials for concrete structures were summarized. Mixtures and key properties of some cement-based repair materials and alkali-activated repair materials were introduced.According to the literature and application experience, the effectiveness of repair of a concrete surface is mainly dependent on the interface between the repair materials and concrete substrates. Therefore, the interfacial properties between cement-based materials and concrete substrate were concentrated on in this review. A comprehensive overview of the methods to evaluate their bond strengths was given. More importantly, characterization of the microstructure of the interface between repair materials and concrete substrates and the techniques to enhance their bond were summarized, as well. Based on the literature review, it can be concluded that the increase in roughness on the substrate surface, the use of polymer-based coupling agents on substrate surfaces and the use of fibers in repair materials can enhance the bonding strength between cement-based repair materials and concrete substrates. In addition, modification of cement-based repair materials with organic materials can also improve their bonding properties with concrete substrates.However, most of the studies on the bonding between repair materials and concrete substrates were carried out under static loads. It must be emphasized that, in practice, concrete structures usually withstand not only static loads but also repeating loads. Meanwhile, there are usually more pores and defects such as gaps and microcracks in the interfacial zone between repair materials and concrete substrates, which causes stress concentration to easily occur in the interface ,86,87,88


Aspergillus and Candida spp. is a recognized complication after lung transplantation, but knowledge of the incidence of Candida tracheobronchitis is lacking. The diagnosis relies on fungal cultures in bronchoalveolar lavage fluid (BALF), but cultures have low specificity. We aimed to evaluate the one-year incidence of fungal tracheobronchitis after lung transplantation and to assess the utility of diagnostic markers in serum and BALF to discriminate fungal tracheobronchitis from colonization. Ninety-seven consecutively included adult lung-transplant recipients were prospectively followed. BALF and serum samples were collected at 1, 3 and 12 months after transplantation and analyzed for betaglucan (serum and BALF), neutrophils (BALF) and galactomannan (BALF). Fungal tracheobronchitis was defined according to consensus criteria, modified to include Candida as a mycologic criterion. The cumulative one-year incidence of Candida and Aspergillus tracheobronchitis was 23% and 16%, respectively. Neutrophils of >75% of total leukocytes in BALF had 92% specificity for Candida tracheobronchitis. The area under the ROC curves for betaglucan and galactomannan in BALF to discriminate Aspergillus tracheobronchitis from colonization or no fungal infection were high (0.86 (p < 0.0001) and 0.93 (p < 0.0001), respectively). To conclude, the one-year incidence of fungal tracheobronchitis after lung transplantation was high and dominated by Candida spp. Diagnostic markers in BALF could be useful to discriminate fungal colonization from tracheobronchitis.Fungal tracheobronchitis caused by  Aspergillus spp. [Candida tracheobronchial infections, including infections localized to the anastomotic site, are also well-described [Aspergillus tracheobronchitis. However, despite being a recognized entity of fungal infection after lung transplantation, there is no established definition for probable Candida tracheobronchitis, implying that these infections are underreported. Knowledge of the incidence of fungal tracheobronchitis, including both Aspergillus and Candida spp., in this patient cohort is thus lacking.Invasive fungal infections constitute a major cause of morbidity and mortality after lung transplantation ,2. In a lus spp. ,7, but Cescribed ,7,8,9. Sescribed ,11. ThesCandida and Aspergillus spp. from respiratory specimens of lung-transplant recipients is a common occurrence during the first postoperative year [The diagnosis of fungal tracheobronchitis is based on histopathologic evidence of fungal invasion of bronchial tissue, but due to limited sensitivity and pertinent difficulties in obtaining tissue specimens for histopathologic analysis , the diaive year ,14, and Aspergillus cell-wall component galactomannan in BALF are widely used and recommended tools for the diagnosis of invasive pulmonary aspergillosis [A high neutrophil count in bronchoalveolar lavage fluid (BALF) from lung transplant recipients may be associated with lower respiratory tract infections ,16, but gillosis ,11, althgillosis . The utigillosis . HoweverThis prospective study aimed to assess the incidence of fungal tracheobronchitis during the first year after lung transplantation and to evaluate the utility of betaglucan in serum, and betaglucan, galactomannan and neutrophils in BALF as diagnostic tools for tracheobronchitis and as tools for discriminating tissue-invasive tracheobronchitis from fungal colonization.Aspergillus before transplantation were given four weeks of voriconazole or liposomal Amphotericin B treatment following transplantation. The study cohort was followed systematically during 12 months after transplantation, including clinical controls and bronchoscopies approximately at one, three and twelve months post-transplant and with additional bronchoscopies in response to clinical symptoms, according to the routine clinical follow-up protocol at the Sahlgrenska University Hospital Transplant Center. Clinical and laboratory data were recorded in an electronic case-report form, and serum and BALF samples were collected at all control episodes. Bronchoscopy procedures were recorded according to clinical routine. Transbronchial biopsies were collected at one and three months unless clinically contraindicated and at twelve months if clinically indicated. All biopsies were analyzed histopathologically for signs of acute rejection and for the presence of fungal elements.All adult Swedish patients accepted for lung transplantation at Sahlgrenska University Hospital in Gothenburg between May 2012 and December 2014 who gave oral and written consent to participate were prospectively and consecutively enrolled in the study. The final study cohort included all study patients who were alive two weeks after transplantation. The Swedish national protocol for immunosuppression after lung transplantation was followed, which at the time consisted of induction therapy with anti-thymocyte globulin and maintenance therapy with cyclosporine or tacrolimus in a tapering dose combined with mycophenolate mofetil and prednisone. Oral nystatin was given as antifungal prophylaxis for four weeks. Patients with respiratory tract colonization by Cell differential count; cultures for bacteria, yeast and mold; and direct microscopy for fungal elements were performed on BALF samples according to standard routines at the Sahlgrenska University Hospital’s Departments of Clinical Pathology and Clinical Microbiology, respectively. Galactomannan optical density indices (ODIs) were analyzed on BALF samples, using the Platelia™ Aspergillus Enzyme Immunoassay  according to the manufacturer’s instructions. The Glucatell assay kit  was used for measuring levels of betaglucan in serum and BALF samples according to the manufacturer’s instruction, which was modified to include heat pretreatment of samples at 75 °C. BALF samples were centrifuged at 10,000 rpm for 10 min, and aliquots of the supernatant were pretreated and analyzed according to the protocol for serum samples. Betaglucan results were reported between the minimum and maximum levels of detection (50–400 pg/mL). All analyses were performed consecutively on fresh patient samples.Candida tracheobronchitis, we took the liberty to extend the ISHLT criteria for fungal tracheobronchitis to also include positive cultures for Candida spp. in BALF as a mycological criterium for probable Candida tracheobronchitis. The classification of fungal tracheobronchitis was performed with the researchers blinded to the results of betaglucan and neutrophil count in BALF. Fungal colonization was defined as a BALF culture yielding Aspergillus or Candida spp. without fulfilling the definition of proven or probable fungal tracheobronchitis or invasive pulmonary aspergillosis. Patients who were first classified as colonized patients but at a later bronchoscopy episode fulfilled the criteria of tracheobronchitis were classified as patients with tracheobronchitis only. Acute rejection was defined as a transbronchial biopsy showing a rejection grade of A1 or higher according to the International Society for Heart and Lung Transplantation [The classification of proven or probable fungal tracheobronchitis was performed retrospectively and was based on the standardized international criteria for fungal infections in lung-transplant recipients formulated by the International Society for Heart and Lung Transplantation (ISHLT) . Patientantation .Candida and Aspergillus were performed separately. Galactomannan was evaluated only for patients with Aspergillus, excluding those patients where galactomannan was the only mycological criterion for the classification of Aspergillus tracheobronchitis. For scenarios with an acceptable area under the ROC curve (≥75%), further analyses of sensitivity and specificity at different cutoff levels were performed. Cutoff levels were chosen based on the results of the ROC curve analyses. The per-patient values for each diagnostic marker selected for the abovementioned evaluation were as follows. For patients with tracheobronchitis, the sample collected on the same day as the first fulfillment of the criteria defining the episode of tracheobronchitis was selected. For patients with fungal colonization, the sample collected on the same day as the first episode of positive fungal culture was selected. For patients with no evidence of fungi, the sample collected at the clinical control performed one month after transplantation was selected since all patients were still hospitalized and the vast majority of patients had a control performed at this point. A p-value < 0.05 was considered statistically significant.The cumulative one-year incidence of fungal tracheobronchitis was calculated by using a survival analysis. Patients who died before the end of the one-year follow-up time were treated as censored subjects. A comparison of the betaglucan levels, galactomannan indices and neutrophil counts in patients with fungal tracheobronchitis and fungal colonization was performed by using the Mann–Whitney test of mean ranks. Receiver operating characteristics (ROCs) curves were performed to assess the overall ability of each diagnostic marker to discriminate (1) fungal tracheobronchitis from colonization and (2) fungal tracheobronchitis from colonization or no evidence of fungi. Analyses for Aspergillus, all patients received antifungal prophylaxis with oral nystatin only according to clinical routine.A total of 105 eligible patients accepted for lung transplantation at the Sahlgrenska University Hospital gave informed consent to participate in the study. Six patients died while on the waiting list, and two patients died within two weeks after transplantation, resulting in 97 patients included in the study . The cliCandida or Aspergillus isolated from BALF at least once during the first year after transplantation (Candida tracheobronchitis (1 proven and 21 probable) and 15 episodes of Aspergillus tracheobronchitis (2 proven and 13 probable) in 31 patients. Six patients had an episode of Aspergillus tracheobronchitis following an earlier episode of Candida tracheobronchitis. Three patients with Aspergillus tracheobronchitis had concomitant signs of invasive Aspergillus pneumonia. The cumulative one-year incidence of fungal, Candida and Aspergillus tracheobronchitis was 33%, 23% and 16%, respectively. After transplantation, Candida tracheobronchitis occurred at a median of 0.8 months (range 0.2–12), while Aspergillus tracheobronchitis occurred at a median of 3.4 months (range 0.7–9.6). Among the 37 episodes classified as fungal tracheobronchitis, there was concomitant growth of potentially pathogenic bacteria in BALF in 14 episodes (38%): Pseudomonas aeruginosa (n = 6), Staphylococcus aureus (n = 4), Enterococcus spp. (n = 2) and other Gram-negative bacteria (n = 2). The histopathologic analysis of transbronchial biopsies showed signs of acute rejection in 4 (11%) out of these 37 episodes of tracheobronchitis. In 10 of the 37 episodes classified as fungal tracheobronchitis, no transbronchial biopsies were performed.In total, 61/97 (63%) had antation . There wCandida or Aspergillus, respectively, but without signs of tracheobronchitis, which was defined as colonization. Forty-four patients (45%) had no evidence of fungal colonization or tracheobronchitis during the 12 months of follow-up.Sixteen and eight patients had at least one culture from BALF with growth of Candida tracheobronchitis and patients with Candida colonization, there was a significant difference in mean ranks between the two groups (p = 0.04). There was a significant difference in the BALF betaglucan levels between patients with Aspergillus tracheobronchitis and patients with Aspergillus colonization (p = 0.03). The median neutrophil counts in BALF were higher in patients with Candida tracheobronchitis compared to patients with Candida colonization, as well as in patients with Aspergillus tracheobronchitis compared to patients with Aspergillus colonization. However, the difference in mean ranks was statistically significant only for patients with Candida tracheobronchitis and colonization (p = 0.02). The median galactomannan index in BALF was higher in patients with Aspergillus tracheobronchitis than in patients with Aspergillus colonization, and the difference in mean ranks between the groups was statistically significant (p = 0.04).The levels of the diagnostic markers in the different patient groups, including the number of analyzed samples for each group, are shown in Candida tracheobronchitis from colonization or (2) Candida tracheobronchitis from colonization or no evidence of fungi  and 0.79 , respectively).The results of all performed ROC curve analyses are provided as Aspergillus tracheobronchitis from colonization, only betaglucan in BALF had an acceptable area under the ROC curve . However, when comparing Aspergillus tracheobronchitis with Aspergillus colonization or no evidence of fungi, both betaglucan and galactomannan in BALF showed a high discriminatory ability  and 0.93 , respectively).For the discrimination of Candida tracheobronchitis (compared to Candida colonization or no evidence of fungi) and betaglucan and galactomannan in BALF for the diagnosis of Aspergillus tracheobronchitis (compared to Aspergillus colonization or no evidence of fungi) are shown in The results regarding the sensitivity and specificity of neutrophils in BALF for the diagnosis of Candida tracheobronchitis was higher than that of Aspergillus tracheobronchitis. We found that diagnostic markers such as betaglucan and galactomannan in BALF may help to discriminate between Aspergillus tracheobronchitis and colonization, and high neutrophil counts in BALF together with a culture yielding Candida may be indicative of Candida tracheobronchitis.In this prospective study of 97 lung-transplant recipients at Sweden’s largest center for cardiothoracic organ transplantations, the occurrence of fungi in the lower respiratory tract during the first year after transplantation was high. The one-year incidence of Aspergillus, as well as Candida spp., is a recognized infectious complication after lung transplantation, and treatment recommendations for both Aspergillus tracheobronchitis and Candida tracheobronchitis are included in international guidelines [Candida tracheobronchitis. The recommended criteria used in clinical studies to define fungal infections in lung-transplant recipients [Aspergillus tracheobronchitis but not for probable Candida tracheobronchitis. Reliable data on the incidence of Candida tracheobronchitis after lung transplantation are thus lacking. To the best of our knowledge, this is the first study reporting the incidence of fungal tracheobronchitis after lung transplantation, including tracheobronchial infections caused by Candida spp. Previous studies report one-year incidences of invasive fungal infections after lung transplantation of 3–14% [Candida tracheobronchitis in previous studies, considering that established definitions only allow for inclusion of proven cases of Candida tracheobronchitis. However, we are aware of the limitations associated with the inclusion of probable cases of infection based on a non-standardized case definition, and future studies are warranted to confirm our findings regarding the high incidence of Candida tracheobronchitis after lung transplantation.Fungal tracheobronchitis caused by idelines ,21. Despcipients ,11 incluof 3–14% , we founAspergillus spp. Diagnostic markers that could help diagnose fungal tracheobronchitis in the absence of a positive fungal culture would thus be of great value. On the other hand, in the transplanted population, treatment with antifungals may cause severe adverse events, as well as drug-drug interactions, and unnecessary antifungal treatment should be avoided. During the follow-up period of 12 months, Candida and Aspergillus spp. were isolated from BALF in 39% and 24% of all patients, respectively. Other studies report similar rates of Aspergillus colonization [Candida colonization [Fungal tracheobronchitis after lung transplantation is associated with bronchial complications  and excenization  and evennization ,26. Consnization .Candida tracheobronchitis from Candida colonization, and neutrophils in BALF could be a complementary tool for the diagnosis of Candida tracheobronchitis. High neutrophil counts in BALF after lung transplantation can also be seen in acute lung allograft rejection and infectious conditions other than fungal infection [Candida tracheobronchitis. The sensitivity, however, was very low, and a positive Candida culture in BALF, together with low neutrophil counts, does not rule out the possibility of a diagnosis of Candida tracheobronchitis.We found that high neutrophil counts in BALF could help to discriminate nfection ,28, but Aspergillus, betaglucan levels in BALF were significantly higher in patients with tracheobronchitis than in patients with colonization, and the ability of betaglucan in BALF to distinguish patients with Aspergillus tracheobronchitis from patients with colonization or no evidence of fungi was relatively high (area under the ROC curve of 0.86). The sensitivity and specificity of betaglucan in BALF for the diagnosis of Aspergillus tracheobronchitis, at a cutoff level of 110 pg/mL, was moderate ; however, at a higher cutoff level of 370 pg/mL, betaglucan in BALF could correctly identify 90% of all patients with Aspergillus tracheobronchitis, but at the expense of a low sensitivity. In contrast, betaglucan in BALF was not useful for the diagnosis of Candida tracheobronchitis. To the best of our knowledge, our study is the first to evaluate betaglucan in BALF specifically for the diagnosis of fungal tracheobronchitis in lung-transplant recipients. Two previous studies evaluating betaglucan in BALF for the diagnosis of invasive pulmonary aspergillosis in solid-organ-transplant [Aspergillus tracheobronchitis than for pulmonary aspergillosis.The available commercial betaglucan assays are recommended for serum samples; however, several previous studies ,32,33,34ansplant  recipienAspergillus tracheobronchitis and for the differentiation of tracheobronchitis from colonization are scarce. We found significantly higher galactomannan levels in BALF in patients with Aspergillus tracheobronchitis than in patients with only colonization. These findings align with previous studies comparing galactomannan indices in BALF in lung-transplant recipients with invasive pulmonary aspergillosis and Aspergillus colonization [Aspergillus tracheobronchitis showed a very high area under the ROC curve (0.93), with >90% specificity at cutoff levels >0.5. Galactomannan in BALF thus seems to be a useful tool not only for the diagnosis of invasive Aspergillus pneumonia but also for the diagnosis of Aspergillus tracheobronchitis.The measurement of galactomannan in BALF is a well-established and recommended method for the diagnosis of pulmonary aspergillosis in lung-transplant recipients ,12,36. Hnization ,38,39, aCandida tracheobronchitis. However, while waiting for a consensus definition for probable Candida tracheobronchitis in lung-transplant recipients to be published for use in future clinical studies, our attempt to address this important condition by adopting the consensus definitions of Aspergillus tracheobronchitis in a wider context of fungal origin may be acceptable and perhaps the most reasonable approach to be used at this point. Hence, our study contributes new data regarding the underreported condition of Candida tracheobronchitis and adds valuable information to the literature on infections in lung-transplant recipients.Our study has several limitations. As already mentioned, one major limitation is the use of a non-standardized definition for Similar to the majority of other studies on this subject, our study predominantly included probable rather than proven cases of fungal tracheobronchitis, where macroscopic bronchoscopic findings, along with microbiologic criteria, are decisive for the case classification . A limitAnother limitation is the somewhat limited size of the studied cohort, which resulted in wide confidence intervals for the results of comparative analyses. It also precluded a further sub-analysis of predictive values of the fungal markers at the different time points of clinical control during the first year after lung transplantation. Finally, the single-center design of this study warrants a certain level of caution regarding the generalization of the results.Candida was the dominating species. A standardized case definition for probable Candida tracheobronchitis is yet missing, and in the light of the results of our study, concern is raised regarding a possible underestimation of the true burden of fungal tracheobronchitis in previous epidemiologic studies on lung-transplant patients. However, the clinical relevance of fungal growth in BALF after lung transplantation is ambiguous. Our results suggest that diagnostic markers in BALF, such as neutrophils, betaglucan and galactomannan, may help to discriminate fungal colonization from tracheobronchitis. Further prospective studies assessing the predictive values of these diagnostic markers for fungal tracheobronchitis and their potential role as tools for surveillance of fungal infection after lung transplantation are warranted.We found a high one-year incidence of fungal tracheobronchitis in our lung-transplanted cohort, where