Experimental research on the direct shear behavior of fiber-reinforced concrete is often carried out using prisms molded with specific dimensions for a standardized test. However, the flow of fresh concrete in these molds can be different than in the case of a full-scale structural element. This is important considering that the flow direction highly influences the distribution and orientation of fibers. In addition, most of the studies did not relate their shear results to other mechanical properties. In contrast, this study attempted to deepen the experimental knowledge of the crack propagation of a steel fiber-reinforced concrete (SFRC) used in a full-scale prototype of a bridge box girder built in the laboratory. Prismatic specimens were sawn from webs and top flanges of this prototype. Serving as references, additional specimens were molded in wooden boxes. In a previous study of our research group, both had been tested under a three-point notched bending configuration maintaining test conditions proportional to the EN14651 specifications. From each of the previously flexurally tested specimens, two prismatic specimens suitable for the Fédération Internationale de la Précontrainte (FIP) shear test setup were extracted by adopting a cutting methodology that avoided the damage induced by the flexural tests to be part of the FIP specimens. These FIP specimens were tested in almost pure shear loading conditions for assessing the performance of SFRC. Computer tomography images and photos of the shear failure faces were used to determine the distribution and density of fibers. The results demonstrated that the peak loads were proportional to the fiber density at the shear failure section. Assuming that the SFRC conditions of the webs were representative of a common batching procedure in the construction industry, the results from the tests in specimens extracted from these webs were adopted to establish shear stress/flexural tensile stress ratios vs. crack mouth opening displacement curves. The curves belonging to cross-sections of a similar fiber density in the shear and flexural cases allowed for the proposal of a normalized crack-dilatancy relation composed of three stages of the crack propagation. In addition, a trilinear crack width–slip relation was established using the same set of specimens. The relevancy of this proposal is that the shear response can be estimated from a widely accepted standardized flexural test, which demands a simpler instrumentation and is also easier to execute than the shear setup. The load carrying capacity at serviceability and at the ultimate limit state conditions of constructive systems made by plain and reinforced concrete  increases with the contribution of fiber reinforcement due to the ability of fibers bridging cracks to support the load transferred between the crack faces and to restrain their width and sliding. Therefore, the inclusion of fibers results in a matrix of higher energy absorption capacity and post-cracking strength than the PC, but the fiber reinforcement efficiency depends on the volume and type of fibers, the quality of the matrix and the batching methods involved due to the influence of fiber distribution and orientation ,4,5,6,7.When fibers work as the shear reinforcement of beams, they are an efficient substitute of conventional stirrups by providing a diffuse reinforcement, delaying the failure mechanism and making it feasible to change the failure from brittle to ductile . When thThe distribution and orientation of fibers are highly influenced by the flow conditions of fresh concrete; fibers have the tendency to align orthogonally to the flow direction . Hence, Various experimental setups have been employed to determine the shear behavior of PC, RC and FRC; however, the difficulty of achieving pure shear in the cracking plane is a common characteristic. Overall, all these tests are more demanding in instrumentation in comparison with compression and bending cases, which are common for material characterization. Three setups were found to be the most utilized: the Z-type push-off test initially conceived for PC and RC , the modMost of the research campaigns utilized specimens molded with specific dimensions for the experimental tests. Considering that the mechanical response of FRC is highly influenced by the pouring method, among other variables, the execution of experimental tests with specimens extracted from a structure that can be more representative of the real behavior than molded specific-dimension prisms will provide more reliable results in terms of extracting conclusions and their use for supporting design guidelines and analytical and numerical models. Furthermore, few direct-shear studies provided a comprehensive characterization of the material. In addition to the shear results, most of them provided only the compressive strength. Therefore, the relationships between shear behavior and other mechanical properties have not been explored. In this context, it is desirable to relate the shear performance to results from an extensively adopted test, such as the EN 14651 flexural experiment . The EN1In order to understand the origin of the prisms experimentally tested, a description of the full-scale box girder prototype is given. In a previous study , an R/SFx and y axes represent the transverse and longitudinal directions of the mock-up, respectively. The placement of concrete started by pouring the content of the first buckets of fresh SFRC along the right corner. The flow direction of the content of every bucket is described in the top right corner of 3 (6W) and 8 × 8 × 32 cm3 (8W) prisms with a 45-degree inclination were extracted from the webs (3 (9TF) and 12 × 12 × 45 cm3 (12TF) prisms were obtained from the top flanges  and support (S1 and S2) loads were separated by spans 2 full cross-section, P1 and P2 to satisfy this requirement. To do so, the x represents the separation between the S1 and P2 loads and y represents the distance between the P2 loads  see ; for speP2 loads a. Then, ads y in a to guarb dimension from the full cross-section. Then, 15 × 5 × 3 was used for the 6 and 8 cm specimens. For the 9 cm and 12 cm prisms, 20 × 20 × 3 and 25 × 10 × 3 load plates were employed, respectively. A linear variable displacement transducer (LVDT) was fixed on both the front and rear surfaces of the prism to measure the slip of the sliding plane a. A clipThere are two edge factors, due to the sawing and wall, that are applied on the processed data of the mechanical response of the specimens. When sawing occurs during the extraction of specimens from the mock-up, the fibers near the sawn side are also cut; thus, it is considered that half of the fibers are not anchored anymore over a width of the half fiber length l (AFGC) , a sawinKrenchel  are η3D= factors ,53 that h. The limit of the wall and sawing effects is defined by two different lines, as depicted at the top of ith region affected by the saw cut, j = 1, 2 or 3 for 1D, 2D or 3D), kth region not affected for the saw cut, j = 1, 2 or 3 for 1D, 2D or 3D) and Thus, for any shear cross-section of any prism of the prototype, its position in The analysis of computer tomography (CT) images has served various purposes in the concrete research field, such as the study of microstructural damage, fiber distinction, aggregate and cement paste interaction and particle distribution ,55,56,57η is the fiber orientation factor. To consider isotropic conditions for the fiber orientation factor, i.e., a 3D random orientation, a value of 0.405 is proposed by Soroushian and Lee [2, considering a 3D fiber orientation (0.5) and CT scan images such as the one presented in ion (11) , where A and Lee  and a va and Lee . Hence, fined in  only forForty-seven tests were carried out under the setup detailed in ng, GfII ,62. BecaThe shear stress  and 2  of the mock-up a,c. BothThe distribution of fibers in the cross-sections was plotted in 2), with the exception of 8W-11A  registered in this specimen.The fracture energy of 8W-12B (1.99 N/mm) was the lowest in the group. This particular result indicates that the orientation of fibers and the arrangement of aggregates at the fracture plane might have been not so favorable for mobilizing the potential resisting mechanisms of the relatively high fiber density  are grouped as prisms of transverse direction (x-axis). Their test results are discussed first and are presented in y-axis  are grouped as prisms of longitudinal direction (y-axis) and are discussed subsequently . It can be inferred that the fibers aligned orthogonally to the flow direction of fresh concrete, as was found elsewhere [For the discussion of the results, the top flange prisms were separated according to the direction of their longitudinal axis with respect to the longitudinal axis of the box girder prototype which corresponds to the equently . From Talsewhere  and is eHaving established the influence of the SFRC flow direction on the mechanical response of both top-flange groups of specimens, the results of the prisms of the transverse direction are discussed first. The first crack of these prisms opened, on average, at 40% of the maximum stress a. The avip terms c and craip terms d indicat density b.y-axis in The results of the top flange specimens whose longitudinal axis is parallel to the longitudinal axis of the prototype (chw) occurs before 0.5 mm, and, subsequently, a rapid increase in either the crack width (12TF-7A and 9TF-2B) or a combination with the increase in the slip  were found. All cases experienced a complete separation of the specimen. By comparing chw and peakw, mixed relations were found, and considering that the experimental fiber densities were lower than both the theoretical density . The drop in the clip gauge of 9R-3A occurred at an early loading stage; thus, it is not included in On the crack-width vs. slip relation d, there The different sets were gathered in four groups: 6W-8Ws (W), 6R-12Rs (R), top flanges of the longitudinal direction (TF-L) and top flanges of the transverse direction (TF-T); then, average values and variation coefficients were obtained to summarize the mechanical parameters discussed previously. They are presented in T prisms  and theiIn The search of a relationship between shear and flexural tensile stresses was based on three motives. First, the scarcity of studies relating shear results with other mechanical characterization tests is a current research gap. In the case of steel fiber-reinforced concrete, it is important to establish the relation with the tensile properties considering the major contribution of fibers in this field. The EN14651 flexural test is one of the most widely accepted standards in the research community for indirectly determining the tensile properties of the material. Thus, if a bridge is created between both results, the shear behavior could be estimated from the parameters originated in flexural tests. A second motive relies on the fact that shear tests are more difficult to carry out than flexural tests. For the former, instrumentation is needed to control two simultaneous displacements, and, at the same time, other effects could influence the results, such as the relative rotation of crack surfaces in the FIP case, the flexural and arch action that can occur in the JSCE case and so on. Again, in the FIP case, the positioning of non-symmetric loads requires additional attention, and the available test setup cannot meet the required load spacing. Conversely, the EN14651 test requires less instrumentation to measure the crack opening at a half span, and loads are placed symmetrically . The third motive is the relevancy of establishing this relation from specimens extracted from real structural elements, avoiding the prisms molded with specific dimensions. The previous section proved the differences in mechanical performances despite the corrections of sawing and the wall effect. The flow of fresh concrete in real structures cannot be reproduced without using same-scale prototypes. Therefore, the possibility of obtaining this relation from a mock-up of a box girder strengthened the applicability of the results.To compare the shear and flexural behavior in terms of stress and crack width, curves of shear stress/flexural tensile stress ratios vs. CMOD were selected. This normalization of the crack dilatancy response, In addition, a relation between the crack width (response d was defThus, the experimental shear behavior of an SFRC could be estimated from EN14651-based flexural results by following the relations proposed.A normalized crack dilatancy law, The dispersion of the shear mechanical properties in a structural element can only be known by performing tests on specimens extracted from a prototype. The scatter of results occurred not only between points of extraction but also between two halves of the same specimen extracted. This study acquires value given that it quantitatively presents the variability of mechanical performance in a structural element. It strengthens the ideas that SFRC is a heterogenous material; thus, prototype construction is highly recommended to determine the actual mechanical response.The alignment of fibers perpendicular to the flow direction of fresh concrete was confirmed by the results of top-flange prisms. In addition, when fiber density increases, the point of the change in behavior from a controlled slip to a significant increase in it can be delayed.The batching method highly influenced the fiber density and the fiber orientation in the cross-sections. A proportional relation between the fiber density and the shear strength was found for the specimens extracted from the prototype model, but not for the reference specimens. Mode II fracture energy absorbed up to failure vs. fiber density did not display a clear trend. In a future work, the fiber orientation will be obtained, and inverse analysis will be carried out for the tests performed. The obtention of the fiber orientation will allow for the classification of the prisms in clusters according to the efficiency of the mechanical response of the fiber; thus, it is expected that the dispersion of results can be reduced.The experimental study of the crack propagation when shear loads were applied to prismatic specimens extracted from an SFRC full-scale box girder prototype allowed for the establishment of the following conclusions:


The digital twin concept lays the foundation of the virtual vibrational analytics suggested in the current paper. The latter presents extended virtual experiments aimed at determining the specific features of the optical spectra of the studied molecules that provide reliable express analysis of the body spatial structure and chemical content. Reduced graphene oxide was selected as the virtual experiment goal. A set of nanosize necklaced graphene molecules, based on the same graphene domain but differing by the necklace contents, were selected as the relevant DTs. As shown, the Raman spectra signatures contained information concerning the spatial structure of the graphene domains, while the molecule necklaces were responsible for the IR spectra. Suggested sets of general frequency kits facilitate the detailed chemical analysis. Express analysis of a shungite carbon, composed of rGO basic structural units, revealed the high ability of the approach. This term refers to a very wide class of new molecular formations called necklaced graphene molecules (NGMs), presenting nanometer-sized graphene domains surrounded with heteroatom necklaces of various compositions. The number of corresponding rGO compositions is countless, differing both in the shape and size of the graphene domain and in the content of the heteroatomic necklace. The name ‘necklaced graphene molecules’ is common to all of this richness and better reflects its principle personality than rGO, which was only attributed to a chemically synthesized product.It is unlikely that there is at least one person today working in the field of materials science who would not know the widely advertised high-tech material called reduced graphene oxide (rGO). Its “discovery” and a base surge of popularity over the past 10–15 years have been facilitated by the special euphoria of a new direction in materials science-graphenics. Nevertheless, humanity, without realizing it, is familiar with the body from the first bonfire, from the first shovel of coal thrown into the furnace, from the first filler of wheel tires, from the first … and this listing can be continued indefinitely. The ash from a burnt fire, the deposits of natural coal, synthetic black carbon, and, finally, a laboratory product of the chemical reduction of oxidized nanoscale graphite—this is a short list of these unique materials, which are known as The graphene era revealed the wide demand for rGO for various applications, which immediately required the formulation and implementation of a reliable analysis of this material, which exists only in solid form. The structure and chemical composition, as a fundamental principle, and the chemical and physical properties as its consequences, became the basis for the development of appropriate analytics. The complexity of the analyzed object and the lack of standard structural and compositional features have inevitably led to the multi-method nature of the required analysis. The diffraction of X-rays and thermal neutron flux, as a source of information about the components of the structure of a solid; thermal gravimetric analysis, as the first cut of the atomic composition in gross as well as in the detection of the presence of hydrogen in the samples; chemical elemental analysis for the presence of carbon, hydrogen, nitrogen, and sulfur atoms; X-ray photoelectron spectroscopic (XPS) analysis for the presence of carbon, oxygen, and atoms of other heavy elements; and energy dispersive spectroscopic analysis of the distribution of these atoms in the mass of a solid all together allowed us to proceed to the stage of creating models of the atomic structure of the sample. Next comes the final analytic stage—verification and approval or rejection of the proposed models. At this stage, the main attention is given to spectral methods of investigation, the primary place among which is occupied by the vibrational spectroscopy of IR absorption and the combinational scattering of light. The latter was discovered independently by Mandelstam and Landsberg in the USSR  and Ramasp2 amorphous carbons [virtual vibrational analytics (VVA) applied to complicated carbon materials such as rGO. The VVA fundamentals and facilities are considered in the current paper. Digital twins (DTs) and a proper computational code constitute the VVA core. The former, as in the previous cases [sp2 amorphous carbon with experimental analytics [The recent development of virtual vibrational spectrometry (VVS) ,11,12,13nalytics ,5,6, onlgeneral frequency (GF) concept. The latter is a particular spectral signature of a selected individual covalent bond observed in the corresponding IR and Raman spectra [general frequency kits (GFKs), attributed to sets of similar covalent bonds. A particular feature of the study concerns a simultaneous consideration of both the density of vibrations and the IR spectra of the relevant DTs, which forms the grounds of the wished spectral marks. A successive result of such an approach is illustrated by the example of a VVA consideration of a shungite carbon.The analytic ability of the vibrational spectroscopy of multiatomic molecules, once presented as sets of covalent bonds, is traditionally based on the  spectra ,15. SuccThe rest of this paper is organized as follows. A general description of the VVS technique as well as the formation of DTs are given in VVS is a chain of successive steps leading to digitalized vibrational analytics according to a general scheme.Here, DTs are the molecular models under study, a virtual device is a carrier of the selected software, and the IT product covers a large set of computational results related to the DTs under different actions in light of the software explored. In the current study, the virtual device HF Specrodyn, implementing the software CLUSTER-Z1 , provide−1 if not pointed otherwise. The intensities are reported in arbitrary units, normalized per maximum values within each spectrum. Since the number of vibrational modes composing the spectra under consideration is too large, the excessive fine structure, statistically suppressed in practice, is covered by trendlines averaged over either 50 or 100 points of linear dispersion of 0.003 ÷ 0.010 cm−1 each. The procedure was applied to the plots of the density of vibrations and the Raman scattering spectra.Throughout the paper, the virtual spectra are presented by stick-bars convoluted with a Gaussian bandwidth of 10 cm66 (DT I) but surrounded with different necklaces. The first group involved compositions with necklaces outside the graphene domain, namely C66H22 (DT II), C66O22 (DT III), C66(COOH)20 (DT IV), and C66(OH)22 (DT V). The former were composed of densely packed monoatomic hydrogen, forming a complete framing of the domain with sp2C–H methines. The second concerned monoatomic oxygen, providing the domain framing with carbonyls sp2C=O. The next two DTs were related to necklaces consisting of individual carbonyls sp2C–COOH and hydroxyls sp2C–OH. All of the models corresponded to the maximal dense packing. These DTs were supplemented with a similar set of compositions whose necklaces consisted of only four units each, C66O4 (DT VI), C66(COOH)4 (DT VII), and C66(OH)4 (DT VIII), respectively. The second group of DTs resulted from the incorporation of oxygen atoms among the carbon edges of the domain, thus substituting the latter and forming necklaces as groups of esters, lactones, and other compositions, namely, C60O6 (DT IX), C56O10 (DT X), C70O6 (DT XI), C56O14 (DT XII), C62O8 (DT XIII), and C60O12 (DT XIV). Equilibrium structures of the species are presented in Unlike the usual attitude toward models for computational spectroscopy, the design of DTs was not subject to the requirement of achieving the best agreement with the experiment. The task of the DT concept is to identify the main including the so far hidden patterns that are characteristic of a given object. The achievement of this result is ensured by the wide variability of the model modifications. Following this trend, two groups of DTs simulating the rGO of different spatial structure and chemical contents were selected for the study. These were NGMs based on the only  graphene domain Csp2C–C bond pool of the graphene domains only. The second concerns the dependence of the spectra on structural factors such as the size and shape of the NGMs, on one hand, and the molecule packing, on the other. As it turned out, the IR spectra of the NGMs were practically insensitive to the geometrical factors, but readily responded to changes in the chemical compositions of the necklaces. Conversely, the Raman spectra were highly dependent on the former factor due to the extreme lability of the graphene domain bond structure [I) on the background of its density of vibrations (DOV). The domain was a flat sheet that was 1.2 × 1.1 nm2 in size. As shown by the DOV trendline, the vibration spectrum was clearly divided into two parts from 20 to 1100 cm−1 and from 1100 to 1800 cm−1, respectively. This two-part character of the vibration spectrum of NGMs also remained in the crystalline state [A comprehensive VVS analysis of IR absorption and the Raman scattering spectra of bare graphene domains has only recently been conducted. . In lightructure ,25, but ne state ,26,27.sp2C–C–C bending, benzenoid ring breathing, and sp2C–C–C puckering (1100–700 cm−1), in-plane and out-of-plane sp2C–C–C bending (700–400 cm−1) accompanied with low-frequency breathings of the graphene domain as a whole. In contrast, the region of 1100–1800 cm−1 was related to a large set of sp2C–C stretching. As seen in the figure, Raman scattering mainly involved the latter with a particular favor toward high-frequency ones. These modes also formed in the IR absorption spectrum of the domain [According to the fundamental consideration of the vibrational spectrum of the benzene molecule , the fire domain . Both spe domain . The sime domain .I with not only the presence of a complicated necklace, but with a larger size of its graphene domain , that is, 2.2 × 2.0 nm2. As seen in the figure, the DT Raman spectrum drastically changed, presenting the transformation of a broad multiband structure toward a single-band one. Such a transformation of the Raman spectra was also repeated for the DTs involving bare and hydrogenated  graphene domains and became more pronounced in the case of the  graphene ones [sp2C–H stretching.The Raman spectrum in ene ones . The matene ones ,31. In f crystal ,27, the sp2 amorphous carbon structures, the linear dimensions of the domains were smaller than Aside from the domain size, two more factors come into play. The first is due to the high tendency of graphene domains to stacking. Indeed, the single-layer graphene sheets observed in a number of experiments were only of crystalline structures, the micron linear dimensions of which far exceeded all of the known characteristic dimensional parameters of the graphene crystal quasiparticles, so that their behavior obeys the solid-state laws. Natural packing of the sheets unambiguously led to the sample graphitization. In contrast, in almost all of the 3spC–C bond of 1.53 Å, so that the unpaired electrons of carbon atoms in the domain basal planes of neighboring layers cannot be paired. However, as has been shown theoretically [3spC–C bond can be considered broken when the interatomic distance is greater than or equal to 2.5 Å. Later on, the existence of “long” single 3spC–C bonds was forced to be admitted experimentally [sp2 hybridization. At the same time, the vibrations of carbon atoms are not limited in space, which is supported by the occurrence of special out-of-plane phonons in a multilayer graphene crystal, the existence of which significantly changes the form of its Raman spectrum [3dynamic spC–C bonds between the domain layers, supported with the displacement of carbon atoms between the layers toward each other [sp2C–C stretching caused by the presence of oxygen atoms in the molecule carbon core [sp2 amorphous carbons into a sign marking the stack structure of the substance. In fact, the doublet mark of the sp2 amorphous carbons disappeared when their BSU stacks were completely destroyed [Indeed, the distance between adjacent layers in graphite-like structures is close to the van der Waals diameter of a carbon atom and constitutes 3.35–3.50 Å [etically , a singlmentally . Howeverspectrum ,35,36,37ch other . Furtherbon core . Additiobon core ,35,36,37estroyed . On the sp2 amorphics [sp2C–C bonds of their graphene domains. In the case of DTs related to the considered NGMs [sp2C–C stretching −1 because of the tight interconnection between sp2C–C stretching in the DOV shown in sp2C–C bond structure, the less As shown by a detailed analysis of the Raman spectra of an extended set of morphics , the forred NGMs ,13, the brations . This feonfirmed .sp2 amorphics composed of BSUs with predetermined size [As for  domains ,43. A st domains ,45. Howened size  did not Concluding the description of the main characteristics of the vibrational spectra of graphene domains, I–V against the background of their DOVs. The set was opened by the reference spectra related to the bare  graphene domain DT I. As seen in the figure, the DOV spectra of all of the derivatives strongly retained the common two-part structure, definitely separating the high-frequency stretching from compositions of the deformational modes. In all the spectra, this division occurred at 1100 cm−1. The main changes in the DOVs concern the stretching part. A detailed comparison of the DT DOVs with the reference one can be traced in We started from the general overlook of the virtual spectra of the NGMs forming the DTs of the first group. Presented in sp2C–C bonds of the pattern graphene domains, caused by the corresponding necklaces, on one hand, as well as the appearance of additional heteroatom covalent bonds, on the other. As for the first fact, it is important to note that even the necklace, consisting of only one hydrogen atom, disturbed the distribution of the sp2C–C covalent bonds of the domains quite significantly [sp2 amorphous carbons in practice [As seen in ficantly . Despitepractice .sp2C–H modes provided the spectrum shape. When the necklace included only oxygen atoms  graphene domain caused by the derivatization. As seen in the figure, the hydrogenation concerned all of the vibrational modes. In turn, the plot in II makes it possible to use the reference data in the table belonging to the benzene molecule. As seen in the table, the suggested GFK was well-coherent with the reference data and correlated well with experimental data related to the NGMs, for which the methine-unit content of the necklaces was firmly established [The plot in ablished ,24,46.3spC–H2, 3spC–CH2, and 3spC–CH3. The HF Spectrodyn allows for the reliable consideration of all of the cases, based on the  graphene domain DTs, as was, say, in the case of 3spC–CH3 [Obviously, in practice, hydrogeneous necklaces of NGMs are much richer and may involve a variety of hydrogen-containing groups such as sp3C–CH3 . In its sp3C–CH3 ,20 offerOxygen is the second most frequent element present in carbon materials. Its atoms combine willingly to carbon ones, forming a wide spectrum of organic functionalities from carboxylic acids to ketones and ethers. sp2 amorphous carbons, which were thoroughly spectroscopically studied [I–V is given in III–V were substantially emptied to four units in each case. The corresponding DTs VI, VII, and VIII are shown in −1, in general. At the same time, the observed similarity of the spectra allows us to suggest quite reliable GFKs with the above-mentioned accuracy.As described in  studied ,8,24. A To achieve this goal, we needed reliable reference data similar to those of the benzene molecule discussed in the connection of the GFKs listed in III–V were treated in the manner described previously for the necklaced graphene hydrides in the previous section. The The calculated data related to DTs III is composed of monoatomic oxygens, the addition of which fully inhibits the dangling bonds of the edge carbon atoms. The circumference composition is extremely similar to that of polycarbonyls , sp2C–C (1500–1600 cm−1), and sp2C=O stretching (1800–1900 cm−1). Accordingly, stretching dominated in the IR spectrum, among which the sp2C–O–C ones covered the largest frequency area, sp2C–C ones presented carbon atom vibrations stimulated by the presence of chemically added oxygens [sp2C=O ones were the characteristic signature of carbonyls.The necklace of graphene oxide DT yls  graphene domain, form the basis of the second group of DTs. Their equilibrium structures are presented in XI provided the simplest IR spectrum, revealing mainly two types of vibrational modes related to the sp2C–O–C and sp2C=O stretching. It should be noted that the latter were characterized by 200 cm−1 less frequency in comparison with that of the DTs of the first group. This mode feature was repeatedly observed when acid anhydride and lactone OCCUs were present in the molecules [XII or pure lactones, located at the zigzag (DT XIII) and armchair (DT XIV) edges. All of the discussed peculiarities are presented in Acid anhydrides of DT olecules ,22,47,48In the present work, we abandoned the desire for a virtual substantiation of the experimental spectrum of certain molecules and focused on revealing the characteristic spectral characteristics inherent in the chosen class of molecules. The digital twin concept assists in achieving this goal. The concept lays the foundation of the virtual representations of physical objects or processes along with the connections of data and information that tie the two together ,51,52. ITo illustrate the possibilities of VVA, in this work, practical graphenics was chosen as an area that occupies one of the central places in modern materials science. Methodical approaches and the levels of analysis of the obtained results were presented for an important high-tech material such as reduced graphene oxide, thus demonstrating that VVA can already today be attributed to modern analytical methods of a new type.sp2 amorphous carbons, the DTs used in this work were molecular models constructed by taking into account the entire body of knowledge acquired to date concerning these solids. The central place in the information obtained is occupied by a clear idea of the multilevel structure of these solids, which is based on nanosized quasi-molecular formations, or BSUs, which are graphene domains, necklaced with heteroatoms that terminate dangling bonds of the domains edge atoms. The choice of these BSUs as DTs and the possibility of a wide variation in the size and chemical composition of their necklaces is the first fact, which ensures the successful implementation of the VVA. The second element of success is the correct choice of a virtual device that allows for a large number of calculations to be performed at the modern level of the molecular theory of the object under study. In this case, BSUs are stable polyatomic radicals, or molecules with open shells, which determine the use of the UHF version of the HF Spectrodyn as an effective device. A comparative analysis of a large set of calculated data obtained was the completion of the digital cycle. As a result of extensive virtual experiments carried out using two dozen DTs, started in a previous work [Since rGO belongs to the class of real ous work  and comp1.The carbon atoms of the graphene domains of the BSUs and heteroatoms of their necklaces participate in the optical vibrational spectra in different ways: the vibrations of the former form the Raman spectra of the BSUs, while the IR spectra are assigned to the vibrations of the heteroatoms of the necklaces.2.sp2 amorphics of various origins. Being multiband in the case of individual BSUs, the Raman spectrum accepts a standard D–G doublet view when packing the BSUs into stacks. In this case, the width of the bands depends on the linear size of the BSUs themselves and the thickness of the stacks. It sharply decreases with an increase in these parameters as their size approaches or exceeds the critical value determined by the mean free path of the optical phonons The carbon-domain nature of the Raman spectra underlies their unique uniform appearance for a wide range of 3.sp2 amorphous carbon, accommodating numerous types of rGOs. For example, the typical Raman spectrum of shungite carbon shown in These conclusions make it possible to carry out an express analysis of the structure of any 4.sp2 carbons strongly depend on the chemical content of the necklaces of their BSUs [The IR spectra of amorphous eir BSUs . It has 5.−1 blue shift of the former, on average.The DTs considered in the work, which are close in size to empirical BSUs, consist of a hundred atoms, due to which eigenvectors of harmonic vibrations of the molecules involve many hundreds of components. This makes the attribution of the considered vibrational mode to individual atomic pairs, or particular chemical bonds, practically impossible. However, the empirical IR spectra of amorphics retain a certain similarity to the spectra of small molecules, which allows us to speak about the selection of atomic compositions in the realization process of the absorption spectrum. However, if in the case of small molecules such selection leads to the formation of an extensive pool of GFs corresponding to individual covalent bonds, in the present case, we can speak about GFKs, implying the excitation of a set of bonds. In the present work, by changing the composition of the necklaces of the considered DTs in a given way, we succeeded in revealing the GFKs that are related to the composition of the BSU necklaces of different rGOs. A comparison of calculated data with the reference ones revealed a ~250 cm6.sp2 amorphous carbon based on the shape of its IR absorption spectrum. Thus, the IR spectrum of a shungite carbon in sp2C–H groups and sp2C=O carbonyls. There were no hydroxyls in the necklace, while a final conclusion concerning the presence of carboxyl groups, although extremely improbable [As listed in probable , should The given express analysis of the Raman and IR absorption spectra of an rGO sample is only the beginning of the in-depth analysis and is given as an example. Nevertheless, they provide a reliable entry level of analysis, requiring further confirmation using all of the advanced methods of analytical chemistry and spectroscopy .


Bitter peptides in the enzymatic hydrolysates were prepared and purified from wheat gluten using aqueous ethanol solutions and macroporous resin, which has opened a new road for the extraction and separation of bitter peptides. This report contains the release regularity of bitter peptides and the factors affecting the change of bitter intensity during enzymatic hydrolysis, providing a scientific basis for the research on debitterizing method. In this study, the effects of different degrees of hydrolysis (DH) and enzyme active sites on the bitter peptide content and bitter taste thresholds were discussed. The relationship between amino acid composition, molecular weight distribution, surface hydrophobicity and bitter taste thresholds was extensively researched. The results showed the exposure of hydrophobic amino acids and the bitterness intensity of the hydrolysates increased as the DH increased, and the bitterness of wheat gluten hydrolysates (WGHs) hydrolyzed by Alcalase was stronger than that of Trypsin. According to correlation analysis, the proportion of total hydrophobic amino acid is the first factor that affects the sensory properties of bitter peptide, and the release content of bitter peptides and the content of total bitter amino acids are the second, following by the content of peptide in the molecular weight range of 500–1,000 Da and the surface hydrophobicity. The amino acid sequence of bitter peptides from WGHs were identified and predicted using high performance liquid chromatography-mass spectrometry (HPLC-MS/MS) and bioinformatics. It was found that the molecular weight of most of the peptides was below 1,500 Da, and the Q value was higher than 5.86 kJ/mol. Wheat gluten (WG) is a relatively safe and inexpensive edible source of plant protein . The WGHIn recent years, researches , 13 on ePrevious research indicated that the bitter taste of peptides was caused by the hydrophobic groups interact with taste bud cells. The Q rule  proposedBased on the fact that bitter peptides are mostly composed of substances with strong hydrophobicity, the methods for separating bitter peptides from the enzymatic hydrolysates mainly include organic solvent extraction, macroporous resin adsorption, ultrafiltration, gel permeation chromatography, etc. . OrganicIn this study, WGHs with different DH hydrolyzed by Alcalase and Trypsin were prepared. The intention was to determine the effect of different DH and enzyme active sites of endopeptidase on the bitterness intensity of the resulting hydrolysates. A method that combining ethanol aqueous solution with macroporous adsorption resin was employed to extract bitter peptides from enzymatic hydrolysates, the effect of the amino acid composition, molecular weight distribution and average hydrophobicity of bitter peptides on bitter taste thresholds were studied. The main objective of the current research was to elucidate the changing characteristic of the bitterness intensity and clarify the internal reasons for the difference in bitterness of WGHs. Then sephadex gel  was usedWG (79% protein) was purchased from Beijing Rui Mai Jia He Co., Ltd. . Amylase, Alcalase 2.4 L and Trypsin were purchased from Novozymes . All other chemicals and solvents were of analytical grade.WG (15 g) was dissolved in 300 mL deionized water at thermostatic enzyme reactor, the suspension was adjusted to the appropriate temperature and pH depending on the respective enzyme used. Then, Alcalase (E/S = 1:20) and Trypsin (E/S = 1:20) was added to hydrolyze WG. During the hydrolysis process, the pH of the solution was kept constant by adding 1 mol/L sodium hydroxide. The proteolysis reaction was stopped at specific DH, with the hydrolysate immediately heat treatment in boiling water for 15 min. Then the resulting hydrolysates were centrifuged at 5,000 r/min for 15 min, the supernatants were freeze-dried and stored at 20°C . Alc-4, tot) during protein hydrolysis (The pH stat method was used to determine the DH of WGHs. The DH represents the percentage of broken peptide bonds (h) in the total peptide bonds ; For WG, htot = 8.38 mmol/ g; α is the dissociation degree of the amino group as a function of reaction temperature.In the formula, B is the volume of alkali solution consumed in the hydrolysis process (mL); Nb is the molar concentration of sodium hydroxide (mol/L); Mp is the mass of protein in the substrate (g); HLyophilized WGH was dissolved in deionized water at the concentration of 20% (w/v). Anhydrous ethanol was slowly added to the enzymatic hydrolysate until the concentration of ethanol in the solution system reached 40%. Then the solution was thorough mixed and sediment was removed after centrifugation . The supernatants were repeatedly extracted through 60 and 80% ethanol solution in accordance with the above operations. Finally, the ethanol extraction solvent was rotated and evaporated and the bitter peptide lyophilized powder was prepared. All the freeze-dried fractions were stored at 20°C before use .The extract was dissolved in ultra pure water at a concentration of 30 mg/mL and 30 mL was loaded onto DA201-C macroporous resin, the volume of the chromatographic column is 300 mL. The water-soluble impurities were eluted with ultra pure water, and then eluted with 80% volume fraction ethanol, which could completely elute the bitter peptides adsorbed on the column at a flow rate of 1 mL/min. The eluted components were collected at 220 nm and the ethanol solvent was removed by rotary evaporation, lyophilized to next step of separation. Alc-4M, Alc-12M, and Alc-20M are the bitter peptides purified from Alc-4, Alc-12 and Alc-20 by macroporous resin; Try-4M, Try-12M, and Try20M are the bitter peptides purified from Try-4, Try-12, and Try-20 by macroporous resin.Eight experienced sensory evaluators  evaluated the taste attributes of WGHs and bitter peptides. The sample solution at a concentration of 1% was randomly presented to the trained sensory evaluators. The evaluator rated the bitterness intensity of samples on a 10-point line scale, anchored with caffeine references: 0.3, 0.8, and 1.2 g/L, corresponding to the bitterness intensity of 2, 5, and 10, respectively . The samRelease content of bitter peptideThe total protein content was determined by Kjeldahl method (GB 5009.5-2016).The amino acid compositions in the bitter peptides were analyzed using amino acid analyzer. A certain amount of sample was hydrolyzed at 110°C for 24 h with 6 mol/L HCl in Hydrolysis tubes, Then the sample was transferred into a 50 mL volumetric ask and filtered. The filtrate was fully mixed and evaporated in a vacuum desiccator to remove hydrochloric acid, the residue was dissolved in 1 ml of water and evaporated again. Then the dried sample was dissolved in the sample diluent, ultrasonic for 1 min and filtered into the sample bottle for further analysis.The molecular weight (MW) distributions of bitter peptides were determined by high-performance gel-filtration chromatography with a TSK gel G2000 SWXL (300 mm × 7.8 mm) column and Waters 1525 liquid chromatograph system. The mobile phase used is acetonitrile/water/trifluoroacetic acid . The sample was monitored at wavelength of 220 nm and a column temperature of 30°C and a flow rate of 0.5 ml/min . The stao) of the relative fluorescence intensity against protein concentration, calculated by linear regression analysis, was used as an index of protein surface hydrophobicity.The fluorescence probe method  was usedBitter peptides were subjected to further separation separated by Sephadex G-25 gel chromatography column according to different molecular weight ranges. To clarify the key peptides accounting for the bitter taste sensation, the components with the strongest bitterness were selected through sensory evaluation and were analyzed by HPLC-MS/MS . The liqThe bitterness intensity of enzymatic hydrolysates is closely related to the type of enzymes and the DH. The release content of bitter peptides during enzymatic hydrolysis of WG is the ratio of the total protein content of the macroporous resin extracted components to the total protein content of the raw materials. As shown in Although the increase of the DH promotes the release of more hydrophobic bitter peptides, it also helps to improve the peptide nitrogen recovery rate and raw material utilization rate. Therefore, the DH and protein recovery rate should be improved as much as possible on the premise of controlling the bitterness in the actual production. In addition, different enzyme activities and enzyme active sites also affect the content of bitter peptides. Alcalase is helpful to generate more hydrophobic bitter peptides because it can open the hydrophobic structure region of protein and expose more hydrophobic groups. It can be inferred that the bitterness of enzymatic hydrolysates is related to the release of bitter peptide from the same change trend.The high bitterness intensity of bitter peptides indicates the small bitter taste thresholds of bitter peptides. Consequently, the bitterness intensity of the extracted components can reflect the bitter taste thresholds of bitter peptides. The bitter peptides with strong hydrophobicity from enzymatic hydrolysates were extracted by high concentration ethanol solution, and further purified by macroporous adsorption resin. As could be seen from Bitter peptide binding to bitter taste receptor must have two determining sites, namely binding unit and stimulating unit, and the space distance between the two sites should be maintained about 4.1 Å. The binding unit that determines the generation of bitterness contains at least three hydrophobic groups with large carbon chains, and the stimulating unit includes an α-amino group or hydrophobic group . TherefoThe amino acid composition of bitter peptides in hydrolysates hydrolyzed by Alcalase and Trypsin was shown in The MW distribution of bitter peptides extracted from the hydrolysates of Alcalase and Trypsin was shown in Compared to the bitter peptides with a low DH, Alc-20M and Tyr-20M have greatly improved the content of small peptides, the proportion of polypeptide with MW of 500–1,000 Da was 46.69 and 44.63%, which showed that the average relative MW of the peptides were rapidly reduced due to degradation by endopeptidases, the peptides with large MW were further hydrolyzed into peptides with smaller MW as the deepening of hydrolysis. The increase of the content of the oligopeptides with MW of 500–1,000 Da was consistent with the increase of the bitterness intensity of the corresponding bitter peptides, confirming the oligopeptides with MW of 500–1,000 Da resulted in a strong bitter taste. In addition, The MW distribution of bitter peptides hydrolyzed by Alcalase and Trypsin under the same DH was no significant difference, indicating that the difference of enzyme active sites had little effect on the MW distribution.The surface hydrophobicity of peptides represents the binding degree between hydrophobic groups and polar solution environment, which can measure the number of hydrophobic amino acid residues exposed in the protein, and also show the balance between the hydrophilic/hydrophobic groups of the protein. The surface hydrophobic of extraction components was higher than that of the hydrolysates, because the conformation of the protein was changed in the extraction process of bitter peptides by ethanol and macroporous adsorption resin, then the hydrophobic groups exposed by the unfolding of protein structure were easy to combine with the non-polar solution environment, and the original hydrophilic groups outside the bitter peptide were relatively reduced .As could be seen from The correlation among bitterness intensity, the release content of bitter peptides, the proportion of total hydrophobic amino acid, the proportion of the total bitter amino acid, the percentage of peptides in different molecular weight ranges and surface hydrophobicity of peptides was analyzed. It could be seen from r = 0.99). A high proportion of hydrophobic amino acids in a polypeptide will Make the bitterness heavier. The release content of bitter peptides and the content of total bitter amino acids are the second index that affected the sensory properties of bitter peptides (r = 0.98), followed by the peptides with molecular weight in the range of 500–1,000 Da and the surface hydrophobicity of peptides (r = 0.96). However, the peptides of molecular weight above 1,000 Da was negatively correlated with the bitterness of the hydrolysates, and the components with molecular weight <180 Da had a weak effect on the bitterness of hydrolysates. This indicated that the peptides with larger molecular weight and free amino acids had higher bitter taste thresholds, so they were not the factor causing the bitterness of the hydrolysates.The proportion of total hydrophobic amino acid in bitter peptide is the first index that affected the sensory properties of hydrolysates  and Cultivation Programme for Young Backbone Teachers in Henan University of Technology and Young Elite Scientists Sponsorship Program by Henan Association for Science and Technology (Grant No. 2021HYTP041).The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. 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Therefore, the PM concentrations in a subway station were analyzed considering air-conditioning diffuser arrangement and filtration efficiency, with the total ventilation flow rate of the station maintained constant. Dynamic analysis was performed under a worst-case scenario, wherein outdoor air was introduced through ground entrances and high-concentration dust  was introduced from stationary train cabins into the platforms through open platform screen doors (PSDs). Although the average PM concentrations were predicted to satisfy the reinforced criteria of Seoul under the existing operating conditions, the recommended limits were exceeded in certain local areas. To address this, the PM concentrations were predicted by changing the diffuser arrangement in the waiting room and maintaining the total ventilation flow rate constant. When the diffusers were placed near the waiting room walls, the PM10 and PM2.5 concentrations were reduced by approximately 10.5 and 5%, respectively, compared to the previous diffuser arrangement. Thus, the required PM concentration criteria were satisfied in nearly all areas of the target station, except for certain areas close to PSDs. The study findings can form the basis for improving the air quality of other subway stations.According to the stringent regulations on particulate matter (PM) concentrations in Seoul, Korea, the PM In 2016, subway users accounted for 59.3% of the public transportation users in Seoul, Korea . As subwntration . It can ntration , increasntration , and incntration .3 for PM10 and PM2.5 by 2024, respectively. The recently measured PM concentrations in the subway environment of Seoul were 111 μg/m3 for PM10 and 58 μg/m3 for PM2.5, which significantly exceed the required criteria [2.5 in the long underground passage of Shanghai South Railway Station, considering the inlet position and air velocity using the CFD method; they proposed a method to improve the air quality inside the underground passage.Therefore, stringent PM regulations have been introduced in Seoul, Korea; accordingly, the PM concentration criteria for subway stations must be maintained below 50 and 30 μg/mcriteria . Typicalcriteria . Woo et criteria  tested tcriteria  developecriteria  evaluatecriteria  reviewedcriteria  analyzedcriteria  used CFDcriteria  employedcriteria  analyzedcriteria  conducte2.5 and PM10 concentrations were predicted by changing the inlet/outlet arrangement, the flow rate of the ventilation system, and the filtration efficiency. The developed numerical method was used to measure the ventilation in the station, and the obtained results verified that the stringent PM regulations of Seoul were satisfied.Most existing studies predominantly focus on the concentration and spatial distribution characteristics of PM in subway environments, such as stations, tunnels, and train cabins. However, studies related to the influence of the overall vent arrangement in a station and the filtration efficiency on the air quality within the station are insufficient. Ideally, PM can be removed through the filters used in the air-handling unit (AHU) of the heating, ventilation, and air conditioning system. Moreover, cost-effectively achieving accurate filtration efficiency is essential for reducing the indoor PM concentration . In thisStation Y in the Seoul metropolitan area of Korea was selected as the target station for the analysis; Release 19.0 was used to analyze the airflow and PM concentration distribution in the target station. The airflow was assumed to be three-dimensional, steady, incompressible, and turbulent. The continuity and momentum equations were solved for the flow analysis [k–ε turbulence model was used for the turbulence analysis based on several previously reported studies that analyzed the airflow in the subway environment [The velocity inlet condition was applied to SA diffusers, and the velocity profile acquired in advance according to the flow rate was applied to each diffuser;The pressure outlet condition was applied to RA diffusers, and the target mass flow rate was set for the RA flow rate to be sucked through each diffuser;The no-slip condition was applied to all walls in the station, including ceilings, floors, and columns;The no-slip condition was applied to the walls and entrances of PSDs when they were closed, whereas the pressure outlet condition was applied to the entrances of PSDs when they were opened. This aided in implementing a scenario where the air flowed owing to the pressure difference between the platform and the cabins of a stationary train;Finally, the scenario of air flowing because of the pressure difference between the ground and underground station was implemented by setting the pressure outlet at the station entrances on the ground. The temperature and pressure in the computation domain were set to 20 °C and 101.3 kPa, respectively.ANSYS FLUENT analysis ,26,27. Tironment ,29,30,31ρ is the air density, t is the time, 2.5 and PM10 concentrations were set to 22 and 45 μg/m3, respectively. The moment at which the PM concentrations in the station reached their peaks during the operation of the ventilation system was assumed to be the time when a subway train halted at the station, causing the air to flow from the cabins to the platforms. To simulate this situation, the airflow and PM concentrations in the station were initially analyzed considering a steady-state condition with the PSDs closed. The PM2.5 and PM10 concentrations in the station were acquired after 20 s by analyzing the situation of PSDs being opened for 20 s and air flowing between the subway cabins and platforms in a transient state. The PM concentrations measured in the subway cabin were reflected in the simulation, wherein the PM2.5 and PM10 concentrations were set to 22 and 105 μg/m3, respectively.PM concentration transport was analyzed based on the Eulerian approach, i.e., the User-Defined Scalar transport equation (Equation (1)) was solved using the FLUENT :(1)∂ρϕ∂−5. The boundary conditions applied to each mesh level were identical to those used earlier. As indicated in the figure, the velocities were compared at seven arbitrary points; three points in the waiting room and four points on the platforms. The comparison based on the largest number of meshes (10 million) indicated that the error decreased with the increase in the number of meshes. When the number of meshes was approximately 5 million, the error was 0.41%. Therefore, the number of meshes was set to 5,446,743 for the analysis considering the calculation efficiency and accuracy.The grid independence test was performed by changing the number of meshes from approximately 0.5 to 10 million, based on a method reported in previous studies ,34 Figu. The conThe objective of this study was to propose an air-conditioning system that can satisfy the stringent PM concentration criteria of Seoul for subway stations by rearranging the diffusers in the station, adjusting the flow rate, and changing the filtration efficiency based on the existing air-conditioning system and filtration efficiency. To this end, three types of diffuser arrangement models were considered for the waiting room on the first basement floor, as indicated in 10 and PM2.5 concentration distributions at the height of the breathing line in the waiting room and platforms when the type A diffuser arrangement and operating flow rate  was lower than the ceiling height of the second basement floor, the average concentrations at the height of the breathing line were higher than those in the entire space. Although the platforms facing each other were symmetrically structured, the PM concentration distribution was different between the platforms. This is because the concentration distribution was affected by the flow pattern of the first basement floor as the platforms were connected to this floor through stairs. Both PM10 and PM2.5 concentrations exhibited a tendency to decrease as the distance from the PSDs increased. This can be attributed to the relatively clean airflow supplied from the SA diffusers, which were located immediately in front of the PSDs, serving as an air curtain and slightly blocking the airflow introduced from the subway cabins. Furthermore, relatively high PM concentrations were observed at both ends of the platforms. This is because although the airflow with high PM concentrations was introduced through the opened PSDs at both platform ends, no diffuser was placed in the outer areas of the pillars at these platform ends.low rate  of the c10 and PM2.5 concentration distributions at the height of the breathing line in the waiting room and platforms when the filtration efficiency was increased to 80% (Case 2) and 90% (Case 3), while the type A diffuser arrangement and operating flow rate , the average PM10 concentration in the platforms was predicted to be 31.1 μg/m3 at the height of the breathing line and 30.8 μg/m3 in the entire space, while the average PM2.5 concentration was predicted to be 13.8 μg/m3 at the height of the breathing line and 12.9 μg/m3 in the entire space. Therefore, despite the identical total ventilation flow rate and filtration efficiency, the PM10 and PM2.5 concentrations in the waiting room and platforms decreased by approximately 10.5 and 5%, respectively, for Case 4 (type B diffuser arrangement (angement ) compareangement ). The PMangement , whereinThe obtained results verified that the diffuser arrangement significantly impacted the air quality inside the subway station despite the application of the same ventilation flow rate. Additionally, among the different types of diffuser arrangements considered in this study, the type B diffuser arrangement was identified as the most favorable for reducing the PM concentrations in the station to satisfy the stringent PM concentration criteria of Seoul. However, diffusers in the type B model were placed only near the walls of the waiting room. Therefore, further analysis is required in terms of thermal comfort during cooling and heating operations. In addition, the flow rate of the diffusers near the waiting room walls was increased for the type B model because the diffusers in the central area were not used. This warrants further research on the influence of an increase in the local flow velocity and noise. To derive satisfactory results for the impact of thermal comfort, appropriate flow velocity, and noise in addition to PM concentration conditions, a detailed parametric study should be performed by changing the flow rate ratio of the diffusers in the central area and near the waiting room walls. In summary, as the airflow introduced from the ground and subway cabins significantly impact the PM concentrations in the station, reducing the airflow from the ground and PM concentrations in subway cabins is important in addition to improving the air-conditioning systems in subway stations.10 and PM2.5 concentrations at the height of the breathing line were predicted to be 33.5 and 12.0 μg/m3 for the first basement floor, whereas they were 36.4 and 14.2 μg/m3 for the second basement floor, respectively. Both the PM10 and PM2.5 concentrations on the platforms on the second basement floor were determined to be higher than those on the first basement floor. This can be attributed to the introduction of airflow with high PM concentrations from the subway cabins when the PSDs were opened, and to the insufficient number of diffusers in the relatively large platform space. When the filtration efficiency was increased from 70 to 90% under the operating conditions of the current air-conditioning system, the average PM concentrations in the station were predicted to satisfy the stringent regulations of Seoul; however, the criteria were exceeded in certain local areas. Therefore, three models with different diffuser arrangements were considered in this study. The analysis indicated that the PM10 concentration in the waiting room on the first basement floor was decreased by approximately 10.5% and the PM2.5 concentration by approximately 5% for the type B model, wherein the flow rate of the diffusers near the waiting room walls was increased. However, the type C model with an increased flow rate of the diffusers in the central area of the waiting room exhibited a deterioration in the air quality in both the waiting room and platforms. This is because the airflow introduced from the ground entrances was not effectively blocked or diluted. When the diffuser arrangement of type B was applied while maintaining the current total ventilation flow rate of station Y, the stringent PM concentration criteria of Seoul were predicted to be satisfied in all local areas on the first and second basement floors despite a filtration efficiency of 70%; however, certain areas close to the opened PSDs failed to satisfy the regulations. Nevertheless, the obtained results confirmed that an appropriate diffuser arrangement can significantly improve the indoor air quality in subway stations despite the use of low-grade filters. In the future, systematic and detailed research on thermal comfort, noise, and appropriate flow velocity is required, in addition to the PM concentrations, based on the diffuser arrangement and flow rate of each diffuser. The results of this study can form the basis for deriving suitable measures for reducing the PM concentrations in subway stations.In this study, the PM concentrations in a subway station were analyzed and compared according to different air-conditioning diffuser arrangements and filtration efficiencies. In the case of the current air-conditioning system operating conditions of station Y, the PM


The quality of bitumen is standardized by conventional tests. With the development of new techniques, rotational and oscillatory measuring systems are applied to evaluate bitumen under defined geometric, temperature, frequency, stress, and strain conditions that correspond to loads during asphalt production and service. Several studies have focused on determining the effect of composition on bitumen properties at service temperatures. However, there is a lack of information related to the effect of composition on viscosity at higher temperatures, which influences production processes. The different types of bitumen, samples of 50/70, 35/50, 45/80-75, and 25/55-60 bitumen, had different viscosity values in intervals corresponding to a confidence level of 95%. The viscosity–temperature relationship in temperature range of 120 to 180 °C was observed in values of 3.87 and 3.70 for unmodified bitumen and 3.09 and 3.22 for modified bitumen. The effect of differences in SARA fractions content on the variation in viscosity using regression analysis showed the importance of asphaltenes (direct correlation) and aromates (negative correlation) contents for 50/70 bitumen with a coefficient of linear regression above 0.7. In comparison, the strong effect of saturates and asphaltenes (negative correlation) and resins was identified for 45/80-75 bitumen samples with correlation of 0.5 to 0.7. The viscoelastic character of bitumen predetermines its use in asphalt mixtures for the construction of road pavements. It is known that the properties of bitumen, specified by softening point and penetration, do not allow enough polymer or crumb-rubber modified bitumen to predict the service performance of the asphalt mixture ,2. ConsiAt service temperatures , bitumen is highly viscous and its behavior is shown as a viscoelastic material. With their short time loading and low temperatures, binders behave elastic, with long time loading, viscoplastic strains occurring. In comparison, at higher temperatures  bitumen behavior corresponds to a flowing viscous liquid with a certain flow resistance  and is characterized by a temperature-dependent viscosity. For these non-Newtonian liquids, the viscosity is not a material constant  but it is dependent on the degree and duration of the applied load.The temperature dependence of bitumen viscosities is described by different mathematical models for different temperature regions. In the viscoelastic region, the Williams–Landers–Ferry (WLF) low equation is widely used to describe the temperature dependence of bitumen over a wide temperature range from bitumen glass-transition temperature Tg to Tg + 100 °C . In workPrediction of physical and rheological parameters and various testing methods need to be used to obtain relevant information. The performance of rotational tests is used to investigate more complex non-Newtonian flow behavior of liquids such as bitumen, which is important for the bitumen and asphalt processing . The rotational viscometer can influence the shear rate and identify the behavior of Newtonian fluids (fluids that have viscosity independent of the shear rate) and non-Newtonian fluids (both pseudoplastic and dilatant behavior) . Within The flow behavior of the material including bitumen is determined by its structure and chemical composition. Although according to the results of the SHRP program  it is veHofko et al.  emphasizThe research of bitumen thermoviscous behavior at the processing temperatures in relation to the composition of bitumen would help to explain the influence of bitumen composition on temperature sensitivity and processing temperatures in the production and laying of asphalt mixtures. Based on the above, this study investigates the possibility of the practical use of the dynamic viscosity measurements in the range of working temperatures for paving grade and modified bitumen to investigate thermoviscous properties as a qualitative parameter in relation to the composition of bitumen determined by means of elemental and compositional analysis.The physical properties of bitumen binders, which are in practice the most common indicators of their quality, were determined by conventional tests including the needle penetration at a temperature of 25 °C, and under specified conditions of load and loading duration according to EN 1426  and a soThe thermo-viscous behaviour of paving grade and modified bitumen samples was investigated using dynamic viscosity according to EN 13302 . The bas2, CO2, H2O, and SO2) are purified, separated into individual components and analyzed on a TCD detector. The analyzed results include all combustible sulfur, organic and inorganic , as well as all combustible carbon, organically bound and inorganically bound (CO32−). Gaseous combustion products are separated into individual components and analyzed using a thermal conductivity detector with an accuracy of <0.1%. This method is used to determine organic and inorganic sulfur and carbon, especially in petroleum products.With the aim to analyze the impact of chemical composition on bitumen properties, the group and elemental composition were determined. Elementary Vario Cube with TCD detection equipment was used to determine CHNS content . The basic principle of quantitative determination of CHNS content is the combustion of a sample in the oxygen stream at high temperatures (up to 1200 °C). Gaseous combustion products  were subjected to a further fractional procedure. Column chromatography was used for the separation of maltenes into saturates, aromates and resins. It involves passing maltenes in a weak solvent through a glass column of highly absorbent material. The sorbents were alumina 507C  and silica gel 60  impregnated with silver nitrate. The resins were separated into alumina and toluene as the mobile phase. The aromatics were separated from the saturated hydrocarbons on silver nitrate-modified silica gel and n-heptane as the mobile phase.The data presented in this paper were obtained from experimental measurements. Samples of paving-grade bitumen of 50/70 gradation (12 different samples) and 35/50 gradation (3 different samples) according to EN 12591, and polymer-modified bitumen 45/80-75 (5 different samples) and 25/55-60 (2 samples) in accordance with EN 14023 commonly used in practice for construction, repair and reconstruction of asphalt pavement layers in the Slovak Republic. The tested binders were obtained from different producers .The average values of the physical properties of all bitumen samples according to gradation are presented in In relation to physical test methods to determine the basic characteristics and performance-related bitumen properties, the elemental and group compositions were determined. The aim was to identify differences in CHNS and SARA content of the bitumen samples that could explain the differences in the thermoviscous behavior of bitumen. Based on current knowledge and the results of a conventional tests, the difference in the composition among the bitumen was expected.p-value was recorded less than the α . The chemical composition of bitumen is extremely complex and varies by crude oil sources, production process and chemical modification similar to the findings in [The average values and standard deviations of the CHNS and O content of the bitumen samples are presented in dings in , and thip-value 0.006). The other three hydrocarbon groups showed statistical insignificance . The highest content of asphaltenes as a key bitumen component that gives strength and stiffness to bitumen and is responsible for structure in bitumen was recorded for 25/55-60 bitumen, which corresponds to higher stiffness values . To compare viscosity data, the same test methodology was used: the same instrument, spindle, container, temperature, and test time for all test samples. The dynamic viscosity values of all tested bitumen samples at a temperature in the range of 120 to 190 °C are shown in The Saal equation  is the mResults of the measured dynamic viscosity in the temperature range of 120 to 190 °C have shown that different types of bitumen binders have different dynamic viscosity values. The dynamic viscosities of samples of the same bitumen type showed similarity between the values. This gives the possibility to define the viscosity limits at individual temperatures for various types of bitumen. The ranges of dynamic viscosity were determined using statistical prediction and confidence intervals that predict the value of a new observation based on the existing model, with a certain probability (1-α). The significance level α is set at 0.05 and corresponds to a 95% confidence level. Statistical intervals can be determined based on linear regression; therefore, the dependence log–log viscosity on log temperature was used to calculate. p < 0.05). Similarly, Anova analysis .Statistical Anova analysis of the results of the dynamic viscosity in a temperature range of 120 to 190 °C showed that the temperature  is a statistically significant element for viscosity values for paving grade bitumen binders 50/70 and the 35/50 gradation of bitumen and modified PMB 45/80-75 bitumen  and the correlation coefficient of the saturates content was 0.1 to 0.3. Quantitative analysis of the fraction composition of paving grade bitumen samples (50/70 and 35/50 samples) showed that as the asphaltene content increases and the resins and aromates content decreases, an increase in viscosity was observed. The impact of the saturates content was found to be small (correlation 0.0 to 0.18). In the case of PMB 45/80-75 samples modified by polymer, the analysis showed that as the resins content increases and asphaltenes and saturates contents decrease, an in-crease in viscosity was observed. The composition of unmodified and modified bitumen with a similar gradation was shown to have a different impact on the viscosity values.2 values are higher than 0.7, which can be assessed as the strong effect of the saturates at several temperatures. The important effect could also be seen with the content of resins and asphaltenes . The R2 values for the aromates are relatively low and their effect on dynamic viscosity can be assessed as marginal. Regarding the content of the effect of the SARA fraction on dynamic viscosities for 50/70 paving grade bitumen samples, the content of aromates and asphaltenes could be important, although the R2 values do not exceed 0.4. No correlation was observed between the effect of resins and saturates content. When analyzing 50/70 paving grade bitumen samples together with 35/50, the effect of the asphaltenes content could be significant. The effect of the other three compounds  seems to be unimportant because of the low coefficient of determination. The R2 values are even much lower. These results are shown to be similar at all test temperatures in the range of 120 to 190 °C.The significant effect of fraction content on dynamic viscosities is visible in the case of modified bitumen. The RIn this research, the dynamic viscosity at higher temperatures  was investigated and analyzed. These viscosities allow to set the appropriate temperature for mixing and compacting the asphalt mixture and thus characterize the workability of bitumen. In order to ensure good performance of the asphalt mixture, the temperature susceptibility of bitumen must be controlled .-The elemental composition of tested bitumen showed no differences in the content of individual elements between paving grade bitumen 50/70 and bitumen 35/50 samples from different producers, or between paving grade and modified bitumen PMB 45/80-75; based on the SARA analysis the bitumen groups tested differ in asphaltene content from the average values of 13.4% for bitumen 50/70 to 19.0% for bitumen 25/55-60; although the composition results did not show significant differences between bitumen, the dynamic viscosity results in the temperature range of 120 to 190 °C demonstrated differences in values;-The viscosity values of the bitumen samples of the same gradation at all evaluated temperatures in the range of 120 to 190 °C are similar and were in interval corresponding to a confidence level of 95%; the variations between the values are due to the different sources of crude oil and processing technology; different types of bitumen have different viscosity values , the highest values were observed for PMB 45/80-75 and PMB 25/55-60, followed 35/50 bitumen and the lowest values of 50/70;-The slope of the linear model expressing the viscosity–temperature relationship was observed as higher for paving grade bitumen 50/70 and bitumen 35/50, with a value of 3.87 and 3.70, respectively, compared to modified bitumen PMB 45/80-75 and PMB 25/55-60 with a value of 3.09 and 3.22; the SBS polymer has better compatibility with bitumen (aromates compound) and can influence viscosity;-The analysis of the SARA fraction composition of the bitumen on viscosity values showed that the impact of asphaltenes and aromates content is important for paving grade bitumen 50/70 (coefficient of linear regression above 0.7), as the asphaltenes content increases and decreasing the aromates content, an increase in viscosity was observed; in comparison, the strong effect of saturates of modified bitumen 45/80-75 was identified (coefficient of 0.7); the important effect could also be seen with the content of resins and asphaltenes (coefficient above the 0.5).The investigation was focused on the relationship between the composition (group) of bitumen identified SARA analysis and its thermoviscous properties determined in the rotational Brookfield viscometer. Fifteen samples of paving grade bitumen of two gradations and seven samples of polymer modified bitumen of two types were tested. The intention for the presented work was to investigate the influence of bitumen composition on its viscosity and the possibility of determining viscosity as an additional parameter for the assessment of binders. The following conclusions were summarized from the work:The research presented does not cover the overall range of bitumen binders. Continued research and further dynamic viscosity measurements should lead to the setting up of databases and the objectification of limits. Then it will be possible to use the viscosity parameter to assess the quality of the bitumen.