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Francesco Tornabene Subscribe SciFeed Recommended Articles Related Info Link Google Scholar More by Authors Links on DOAJ Beskopylny, A. N. Shcherban, E. M. Stel’makh, S. A. Mailyan, L. R. Meskhi, B. Chernil’nik, A. El’shaeva, D. on Google Scholar Beskopylny, A. N. Shcherban, E. M. Stel’makh, S. A. Mailyan, L. R. Meskhi, B. Chernil’nik, A. El’shaeva, D. on PubMed Beskopylny, A. N. Shcherban, E. M. Stel’makh, S. A. Mailyan, L. R. Meskhi, B. Chernil’nik, A. El’shaeva, D. /ajax/scifeed/subscribe Article Views Citations - Table of Contents Altmetric share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up ... Endorse textsms ... Comment Need Help? Support

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Get Information clear JSmol Viewer clear first_page settings Order Article Reprints Font Type: Arial Georgia Verdana Font Size: Aa Aa Aa Line Spacing:    Column Width:    Background: Open AccessArticle Influence of Variatropy on the Evaluation of Strength Properties and Structure Formation of Concrete under Freeze-Thaw Cycles by

Alexey N. Beskopylny 1,* ORCID

Evgenii M. Shcherban 2 ORCID

Sergey A. Stel’makh 3 ORCID

Levon R. Mailyan 4,

Besarion Meskhi 5 ORCID

Andrei Chernil’nik 3 ORCID

and

Diana El’shaeva 3 1 Department of Transport Systems, Faculty of Roads and Transport Systems, Don State Technical University, 344003 Rostov-on-Don, Russia 2 Department of Engineering Geology, Bases, and Foundations, Don State Technical University, 344003 Rostov-on-Don, Russia 3 Department of Unique Buildings and Constructions Engineering, Don State Technical University, Gagarin Sq. 1, 344003 Rostov-on-Don, Russia 4 Department of Roads, Don State Technical University, 344003 Rostov-on-Don, Russia 5 Department of Life Safety and Environmental Protection, Faculty of Life Safety and Environmental Engineering, Don State Technical University, 344003 Rostov-on-Don, Russia * Author to whom correspondence should be addressed. J. Compos. Sci. 2023, 7(2), 58; https://doi.org/10.3390/jcs7020058 Received: 15 December 2022 / Revised: 10 January 2023 / Accepted: 31 January 2023 / Published: 4 February 2023 (This article belongs to the Section Composites Modelling and Characterization) Download Download PDF Download PDF with Cover Download XML Browse Figures Versions Notes

Abstract: The resistance of concrete structures to the impact of cyclic freezing and thawing is one of the key long-term characteristics, which further determines the operation and its service life. To date, the resistance to alternating freeze-thawing cycles under various operating conditions of concrete structures has been little studied related to several manufacturing processes: simple vibrated, variotropic centrifuged, and improved variotropic vibrocentrifuged. The purpose of this study is to investigate the effect of heavy concrete manufacturing technology on the resistance of concrete to alternate freezing and thawing in an aggressive environment of 5% sodium chloride solution, as well as to study the trend in strength characteristics and weight loss of vibrated, centrifuged and vibrocentrifuged concretes after a series of freezing and thawing cycles. Standardized techniques for assessing the characteristics of concrete and scanning electron microscopy were used. Vibrated, centrifuged, and vibrocentrifuged concretes made from the same raw materials have differences in weight loss of 4.5%, 3%, and 2%, respectively, and in strength of 15.0%, 13.5%, and 10%, respectively, when tested for frost resistance in similar environments after 15 cycles by the accelerated method. Centrifuged and especially vibrocentrifuged variotropic concrete have greater resistance and endurance to cycles of alternate freezing and thawing compared to vibrated. Keywords: frost resistance of concrete; variotropic structure of concrete; freeze-thaw cycles; durability of concrete; compressive strength 1. IntroductionCurrently, one of the primary subjects for the premature concrete structures’ destruction operated in various aggressive conditions is the insufficient resistance of concrete to cyclic effects of alternate freeze-thaw [1], carbonation [2], loading [3,4], moistening, and drying [5,6], as well as to various types of corrosive effects [7]. The resistance of concrete to alternate freezing and thawing is one of the key long-term characteristics, which further determines the service life of the concrete and reinforced concrete structures made of geopolymer concrete [8], ordinary concrete [9], waste concrete [10], and pavement concrete [11,12]. Currently, the mechanism of destruction of a concrete composite during freezing and thawing, as well as the impact of various composition and technological factors on the frost resistance of concrete, are actively studied by scientists from all over the world. Table 1 presents an overview of cutting-edge research on this topic.To understand the process of frost destruction of cement concrete, several main factors that determine the frost resistance of concrete are distinguished. From a methodological point of view, these factors can be divided into technological (the method of selecting the composition of concrete, the technology for manufacturing concrete and reinforced concrete products, etc.) and prescription (chemical [23] and mineral additives, such as fly ash [24,25] and slag [26], ilmenite mud waste [27], various types of fiber, water-cement ratio, a fineness of grinding of Portland cement clinker, use of recycled aggregate concrete [28,29,30] and etc.). A rational combination of technological and prescription factors directly affects the structure of the concrete composite at all its levels. Porosity parameters “under freezing and thawing conditions are important for assessing the frost resistance of concrete” [31,32]. The porosity of the HCP is divided into several types, namely: the total porosity of the HCP, the porosity of hydrated cement, capillary porosity, open and closed porosity [33,34]. Formulas for calculating all the above types of porosity of the HCP are presented in Table 2.Of all the types of porosity considered, the greatest influence on the frost resistance of concrete and its durability is exerted by closed porosity, or rather, the ratio of the volume of conditionally closed pores to open pores [34,35,36]. The capillary porosity of centrifuged concrete can be reduced by using a superplasticizer or a complex additive in the form of a mixture of a superplasticizer and an air-entraining additive. In addition, the use of the above additives contributes to a closer fit of the mortar part to coarse and fine aggregates. Moisture migration paths, which are radially directed channels in the mortar part of the inner layer, go around coarse and fine aggregates in the outer and middle layers. Loose adhesion in contact with the aggregate, and its orientation to the outer surface, revealed in the studies of the structure, are associated with compaction under the action of the centrifugal force of the cement paste in the gaps between the grains of fine and coarse aggregates, which leads to the separation of water precisely at their surfaces, facing outward. In concrete mixtures with additives, the initial water content decreased due to the plasticizing effect. The amount of free liquid in mixtures with additives is much less, and during centrifugation, filtration channels either did not form at all or became thinner. The uniform distribution of filler over the wall thickness indicates a change in compaction processes in concrete using a superplasticizer during centrifugation molding. In this case, the squeezing and movement of free water in the compacted mixture plays a lesser role, and a greater role is played by the movement of the bound mass of cement slurry [37].An important aspect in the study and control of the frost resistance of concrete is the possibility of predicting the residual resource or the service life of products and structures [38,39]. Another important aspect of studying the durability of concrete is the modeling of reinforced concrete structures, as well as the very mechanism of chloride penetration, considering the heterogeneity of concrete and reinforcement coatings [40,41]. To assess the frost resistance of concrete, as well as products and structures made of it, various methods were used to control the characteristics of concrete (nonlinear resonant vibration diagnostics [42], ultrasonic method [43], numerical study [44]), such as seismic resistance [45], dynamic mechanical properties [46], strength, including its distribution over the thickness of reinforced concrete elements [43].Thus, the studies reviewed above were carried out on the assumption that resistance of concrete to various alternating influences, including freezing and thawing, is estimated by the integral characteristics of their structure, that is, averaged. At the same time, the works devoted to the research of centrifuged samples and their frost resistance, thus, had an approximate character [37,47]. The scientific novelty of this article is the first studied resistance to alternating cycles of freezing and thawing under various operating and influencing conditions of concrete of various structures: simple vibrated, variotropic centrifuged, and improved variotropic vibrocentrifuged. To fully evaluate the frost resistance of variotropic centrifuged concretes, one should proceed from the theoretical assumption proposed by us about the multilayer nature of such concrete, and, thereby, the differentiation of the properties of such concrete over the section of the element. Thus, the specific goal can be formulated, which is presented below.The primary goal of this study is to investigate the effect of heavy concrete manufacturing technology on the resistance of concrete to alternate freezing and thawing in an aggressive environment of 5% sodium chloride solution, as well as to study the trend in strength characteristics and weight loss of vibrated, centrifuged and vibrocentrifuged concretes after a series of freezing and thawing cycles. 2. Materials and Methods 2.1. MaterialsPortland cement CEM I 52.5N manufactured by JSC “SEBRYAKOVCEMENT” (Mikhailovka, Russia) was applied as a binder with the following characteristics: residue on a sieve 0.08 mm, characterizing the fineness of grinding—1.8% (specific surface—340 m2/kg); the beginning point of setting is 155 min; the end is 240 min; uniformity of volume change—0 mm; normal density—26%; compressive strength after 28 days—56.0 MPa; tensile strength in bending—8.2 MPa. Clinker composition: tricalcium silicate C3S—64.3%; dicalcium silicate C2S—14.7%; tetracalcium aluminoferrite C4AF—12.6%; tricalcium aluminate C3A—5.7%; magnesium oxide MgO—2.7%.Crushed sandstone of fractions from 5 to 10 mm and more than 10 to 20 mm according to GOST 8267 [48] from the Sokolovsky quarry (Novoshakhtinsk, Russia) was a coarse aggregate. The main characteristics of crushed stone are presented in Table 3.The river sand of the Kagalnitsky quarry (village Kagalnik, Russia) had the following characteristics: fineness modulus, 1.43; the content of dust and clay particles is 0.8%; clay content in lumps—1.1%; bulk density—1397 kg/m3. 2.2. MethodsVibrated, centrifuged, and vibrocentrifuged concretes were made from concrete mixtures, their compositions are provided in Table 4.The composition of the vibrated concrete was assigned according to GOST 27006 [50], while the composition of centrifuged and vibrocentrifuged concrete was determined according to VSN 1-90 [51].The preparation of the concrete mixture for vibrated, centrifuged, and vibrocentrifuged concrete structures was carried out according to the same method, which included the following steps: dosing of the concrete mixture components; loading cement and sand into a laboratory concrete mixer and mixing them for 60 s; loading coarse aggregate and mixing for 60 s; the introduction of mixing water and mixing the mixture to a homogeneous consistency. Determination of the density and mobility of the concrete mixture was carried out by following GOST 10181 “Concrete mixtures. Methods of testing” [52].Further, the manufacture of vibrated concrete samples included the following technological steps: pouring the concrete mixture into metal molds FK-50 (NPO LaborKomplekt, Moscow, Russia) and vibrating them on a laboratory vibration platform.The manufacture of centrifuged and vibrocentrifuged samples included the following technological steps: loading the concrete mixture into the assembled mold; distribution of the concrete mixture in the form for 70 s at a rotation speed of 150 rpm; compaction of the concrete mix within 220 s at 700 rpm.The manufactured vibrated, centrifuged, and vibrocentrifuged samples were kept in a normal hardening chamber for one day, after which they were removed from the molds and again kept in a normal hardening chamber for 27 days until full strength was gained.After 28 days of hardening, the centrifuged and vibrocentrifuged prototypes were sawn according to the scheme shown in Figure 1.The plan of experimental studies of vibrated, centrifuged, and vibrocentrifuged concrete samples is shown in Figure 2.Thus, for all experimental studies, 15 series of vibrated, 15 series of centrifuged, and 15 series of vibrocentrifuged samples were made.All technological and testing equipment used in the course of experimental studies, as well as measuring instruments, are presented in Table 5.Tests of samples for compressive strength were carried out according to the GOST 10180 method [54].Samples were tested for the effects of alternate freezing and thawing by following the third accelerated method of GOST 10060 [55]. Test conditions are shown in Table 6.Control samples of concrete were soaked in a 5% aqueous solution of sodium chloride at a temperature of 20 ± 2 °C before testing for strength.After saturation in water, the experimental samples were located in a freezer in containers closed at the top and filled with a 5% sodium chloride aqueous solution. So, the distance between the walls of the containers and the walls of the chamber was at least 50 mm. The temperature in the closed chamber was set to −(50 ± 5) °C and maintained for at least 2.5 h. Then the temperature was raised to −10 °C for 1.5 h, and afterward the samples were thawed in 5% chloride solution aqueous sodium at a temperature of (20 ± 2) °C for at least 1.5 h. After each cycle of freezing-thawing, the samples were weighed and tested for compressive strength. Photos of control samples, as well as the process of their testing, are presented in Figure 3 and Figure 4.The processing of test results for samples subjected to alternate freezing and thawing was conducted according to the formulas presented in Table 7.Samples are considered to have passed the frost resistance test if the following ratio is observed: X m i n ″ ≥ 0.9 X m i n ′ SEM analysis of the samples was conducted on a Carl Zeiss Microscopy electron microscope with a magnification of 500 and 1000 times. 3. ResultsTest results of vibrated, centrifuged, and vibrocentrifuged concrete samples subjected to alternate freezing and thawing are presented in Table 8, Table 9, Table 10 and Table 11.Based on the data presented in Table 9, it can be concluded that the condition X m i n ″ ≥ 0.9 X m i n ′ is performed up to the sixth cycle inclusive, which means that the test of vibrated concrete samples for frost resistance is considered positive. According to Table 4 of GOST 10060, these samples have a frost resistance grade of F1200. However, with a further continuation of the tests, a more intense drop in compressive strength is seen, and the weight loss exceeds 2%, which is unacceptable according to the requirements of GOST 10060.According to the data presented in Table 10, the fulfillment of the condition X m i n ″ ≥ 0.9 X m i n ′ for centrifuged concrete samples is observed up to cycle 10 inclusive. According to Table 4 from GOST 10060, these samples have a frost resistance grade of F1300.According to the results presented in Table 11, the fulfillment of the condition X m i n ″ ≥ 0.9 X m i n ′ for vibrocentrifuged concrete samples was observed up to cycle 13 inclusive. According to Table 4 of GOST 10060, these samples have a frost resistance grade of F1400.Figure 5 shows photos of vibrated, centrifuged, and vibrocentrifuged concrete samples after 15 cycles of freezing and thawing.Concrete specimens undergoing freezing and thawing can be characterized by the following common defects: peeling of the specimen surface and chipping of the ribs. However, it is visually seen that the centrifuged and vibrocentrifuged samples are damaged to a lesser extent than the vibrated ones, which is confirmed by the results of determining their strength characteristics.For a visual interpretation of the test results of samples of vibrated, centrifuged, and vibrocentrifuged concrete, dependencies were plotted (Figure 6 and Figure 7), showing the loss of compressive strength (∆Rb) and weight loss (∆m) after each cycle of freezing and thawing in percentage terms.Figure 5 shows that the loss of compressive strength of vibrated samples is more intense with an augmentation of the number of freeze-thaw cycles than for centrifuged or vibrocentrifuged samples. As for the curves illustrating the weight loss of the samples after each cycle of freezing and thawing, they are of the same nature as the change in compressive strength. After 15 cycles of the accelerated frost resistance test method, the weight loss of vibrated, centrifuged, and vibrocentrifuged concrete was 4.5%, 3%, and 2%, respectively, and strength—15%, 13.5%, and 10%, respectively. According to the results of statistical processing, the coefficient of variation of the obtained results is in the range of 6.5% to 7.5%.For a more complete assessment of experimental studies of the concrete strength, research on the microstructure of samples of hardened cement paste (HCP) made by vibration, centrifugation, and vibrocentrifugation was carried out after 15 cycles of freezing and thawing. Photographs of the microstructure of the samples are shown in Figure 8, Figure 9 and Figure 10.The samples of cement paste made using vibrocentrifugation technology have a denser crystalline intergrowth (Figure 10). As for the cement gel, in samples made using centrifugal compaction technologies, it is observed more than in vibrated concrete (Figure 8, Figure 9 and Figure 10). The higher frost resistance of concretes made using the technology of centrifugation and vibrocentrifugation can be explained by the different nature of the porosity of these concretes and the large number of reserve pores per unit volume. When concrete saturated with water freezes, due to the formation of ice crystal growth, hydrostatic pressure will arise in the remaining liquid. Under the action of this pressure, the liquid can move into the reserve pores, and tensile stresses will not arise in the crystalline intergrowth of the HCP [56].At the initial stage of concrete structure formation, mixing water forms a system of interconnected capillary and large pores in concrete, arranged in a chaotic manner throughout the entire volume of the composite. Further, under the conditions of continued hydration of the cement, the total and capillary porosity of the HCP decrease, since the volume occupied by the cement hydration products, together with the pores between the crystalline neoplasms, is several times, approximately 2.2 times, greater than the volume of non-hydrated cement. Thus, the system of interconnected pores becomes conditionally discrete, as it is separated by cement gel. This structure of the HCP makes concrete less permeable, and the main condition for its formation is “the initial value of the water-cement ratio” [34]. Macrostructure of concretes produced using the technology of centrifugal compaction is uneven. Conventionally, it can be divided into three layers: inner, middle, and outer. Previously, in [57,58,59,60], the characteristics of various layers of centrifuged and vibrocentrifuged concrete were studied, and according to the results of the studies, the outer layer of these concretes is the most durable. The higher strength characteristics of the middle and outer layers are primarily due to the lower water-cement ratio of these layers and the location of the main part of coarse aggregate in them, respectively, due to this, they will have a higher density and lower permeability and, as a result, higher frost resistance. 4. DiscussionThe primary reason for the destruction of concrete under conditions of alternate freezing and thawing is the pressure on the walls of pores and the mouths of microcracks created by freezing water. When freezing, water expands in volume by more than 9%. The expansion of water is prevented by the hard skeleton of concrete, in which very high stresses can occur. The repetition of freezing and thawing leads to a gradual softening of the concrete structure and to its destruction. First, the protruding faces begin to collapse, then the surface layers, and gradually the destruction spreads deep into the concrete body. The stresses caused by the difference in the coefficients of thermal expansion of the concrete components and the temperature-humidity gradient will also have some influence.The frost resistance of concrete depends on its structure, especially on the nature of porosity, since the latter will determine the volume and distribution of ice formed in the body of concrete at negative temperatures, and, consequently, the value of the stresses that arise and the intensity of the process of weakening the concrete structure [56].The trend of concrete strength loss (in %) on freeze-thaw cycles, shown in Figure 6, can be represented as a regression equation with a determination coefficient R2 for vibrated (1), centrifuged (2), and vibrocentrifuged (3) concretes Δ R b V = 0.00325 + 0.804 x + 0.0158 x 2 , R 2 = 0.97 Δ R b C = − 0.285 + 0.30 x + 0.0464 x 2 , R 2 = 0.98 Δ R b V C = 0.0678 + 0.0587 x + 0.0422 x 2 , R 2 = 0.99 Trends in concrete mass loss (in %) by freeze-thaw cycles, shown in Figure 7 can be represented as a regression equation with the coefficient of determination R2 for vibrocentrifuged (4), centrifuged (5), and vibrocentrifuged (6) concretes Δ m V = − 0.141 + 0.286 x , R 2 = 0.989 Δ m C = − 0.107 + 0.0765 x + 0.0080 x 2 , R 2 = 0.99 Δ m V C = − 0.0461 + 0.0408 x + 0.00616 x 2 , R 2 = 0.978 Concrete, as a composite material, has a capillary-porous structure. In general, the structure of concrete can be considered at three levels (Figure 11).Of all these structures, the structure of the HCP and its pore space has the most significant effect on the frost resistance of concrete.The concretes considered in this study are made using different technologies and have, respectively, different macro- and microstructures. If we consider the formation of concrete structure made by vibration, then in this method of compaction, in the process of vibration impact on the concrete mix, large and dense aggregates fall under the vibration force, and small and light grains rise. Thus, this technology creates differences in the properties of concrete along the height of the section. That is, vibration leads to variatropy.In the case of centrifuged technology, variatropy has a different nature. This is expressed in the difference in the concrete properties in the annular cross section. The essence of the centrifugal method of manufacturing a product lies in the process of rotation at a certain speed of a mold with a plastic concrete mixture evenly distributed in it, a pressing pressure arises, under the influence of which the particles of the solid phase approach each other and weakly bound water with finely dispersed fractions suspended in it is displaced from the cement paste. The pressure is distributed unevenly over the thickness of the entire product: its maximum value is fixed on the outer wall of the product and the minimum on the inner wall. Thus, the compaction of the concrete mixture during centrifugation is accompanied by a change in the water-cement ratio across the wall thickness, and, as a result, the porosity of the product itself changes throughout its entire thickness [47].The higher resistance of heavy concretes made by centrifugation and especially vibrocentrifugation technologies to the effects of alternating cycles of freezing and thawing, in comparison with vibrated ones, can be explained by the difference in the nature of the pore structure of these concretes [34,47,56]. Let us consider the obtained results and discuss them from the point of view of the pore structure. As already mentioned by us earlier and confirmed by numerous studies by other authors [31,32,33,34,35,36,56], vibrated concrete with a simple structure has an open porosity and is thus subject to rather facilitated penetration of moisture from the outside, through the outer layer of concrete and, thereby, is at risk of less resistance to freezing and thawing. This is due, firstly, to easier penetration of moisture through the pores in the outer layer, and thus, unclosed porosity creates a capillary structure of concrete, in which, when frozen, the moisture particles contained in the capillaries lead to the destruction of concrete from the inside. This emphasizes the difference and the advantage of heterogeneous structures of centrifuged concrete due to the protected outer layer from moisture penetration.As we have obtained in previous studies [57,58,59,60,61,62,63,64] and in the studies of other authors [37,47,65], a denser wall of the outer layer of centrifuged concretes with a variotropic structure allows one to control not only the mechanical characteristics but also the physical characteristics of concrete, such as the density over the cross section and thus the capillary micro- and macrostructure. An even greater effect is expressed in improved variotropic structures of concretes made using the vibrocentrifugation method. In such structures, we control the capillary porosity of concrete, its nature, isolation, and closeness, strengthening the outer layer. The properties of the middle layer became closer to the values of the outer one. This creates a double layer of protection against additional moisture, and the capillaries are even more reliably protected from internal stresses and, accordingly, the destruction of concrete during freeze and thaw cycles. It is these structural and physical phenomena during the formation of such concretes that determine their great resistance and endurance to cycles of alternate freezing and thawing. 5. ConclusionsThis study presents the results of testing concretes made using vibrating, centrifuging, and vibrocentrifuging technologies. According to the test results of concretes subject to the influence of alternate freezing and thawing, the following conclusions can be drawn:(1)Vibrated, centrifuged, and vibrocentrifuged concretes made from the same raw materials have differences in weight loss and strength when tested for frost resistance in similar environments: −According to the condition X m i n ″ ≥ 0.9 X m i n ′ , vibrated concretes are considered to have passed the frost resistance test after six cycles of freezing and thawing, while the maximum mass loss was 1.7%;−According to the condition X m i n ″ ≥ 0.9 X m i n ′ centrifuged concretes are considered to have passed the frost resistance test after 10 cycles of freezing and thawing, while the maximum weight loss was 1.4%;−According to the condition X m i n ″ ≥ 0.9 X m i n ′ , vibrocentrifuged concretes are considered to have passed frost resistance tests after 13 cycles of freezing and thawing, while the maximum weight loss was 1.3%;−The maximum value of strength loss after 15 cycles of freezing and thawing of vibrated concrete was 15%, for centrifuged concretes—13.5%, and for vibrocentrifuged ones—10%.(2)The advantage of variotropic structures of centrifuged concretes due to the protection of a denser outer layer from moisture penetration compared to conventional concrete structures was noted and explained; even more, this effect is observed in vibrocentrifuged concretes, allowing one to control the capillary porosity of concrete, its nature, closedness, and closeness, strengthening the outer layer. The properties of the middle layer became closer to the values of the outer one; a double layer of protection against additional moisture is created, and the capillaries are even more reliably protected from internal stresses and destruction of concrete during freeze and thaw cycles. It is these structural and physical phenomena during the formation of such concretes that determine their great resistance and endurance to cycles of alternate freezing and thawing.(3)The durability of variotropic concretes, characterized by resistance to alternating cycles of freezing and thawing, is higher than that of conventional concretes with other things being equal.Further research is planned in the direction of studying the behavior of variotropic structure concrete under the action of wetting and drying cycles, as well as comparing such concrete with conventional structure concrete. Author ContributionsConceptualization, S.A.S., E.M.S., A.N.B. and A.C.; methodology, S.A.S., E.M.S. and D.E.; software, S.A.S., E.M.S., A.N.B. and D.E.; validation, A.C., S.A.S., E.M.S. and A.N.B.; formal analysis, A.C., S.A.S. and E.M.S.; investigation, D.E., L.R.M., S.A.S., E.M.S., A.N.B. and B.M.; resources, B.M.; data curation, S.A.S., E.M.S. and A.C.; writing—original draft preparation, S.A.S., E.M.S. and A.N.B.; writing—review and editing, S.A.S., E.M.S. and A.N.B.; visualization, S.A.S., E.M.S. and A.N.B.; supervision, L.R.M. and B.M.; project administration, L.R.M. and B.M.; funding acquisition, A.N.B. and B.M. All authors have read and agreed to the published version of the manuscript.FundingThis research received no external funding.Institutional Review Board StatementNot applicable.Informed Consent StatementNot applicable.Data Availability StatementThe study did not report any data.AcknowledgmentsThe authors would like to acknowledge the administration of Don State Technical University for their resources and financial support.Conflicts of InterestThe authors declare no conflict of interest.ReferencesLehner, P.; Koubová, L.; Rosmanit, M. Study of Effect of Reference Time of Chloride Diffusion Coefficient in Numerical Modelling of Durability of Concrete. Buildings 2022, 12, 1443. [Google Scholar] [CrossRef]Yu, Q.; Guo, B.; Li, C. Effects of CO2 Concentration and the Uptake on Carbonation of Cement-Based Materials. Materials 2022, 15, 6445. [Google Scholar] [CrossRef] [PubMed]Chinnasamy, Y.; Joanna, P.S.; Kothanda, K.; Gurupatham, B.G.A.; Roy, K. 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Figure 1. Scheme of sawing centrifuged and vibrocentrifuged samples: (a) top view; (b) general view. Figure 1. Scheme of sawing centrifuged and vibrocentrifuged samples: (a) top view; (b) general view. Jcs 07 00058 g001

Figure 2. Experiment plan. Figure 2. Experiment plan. Jcs 07 00058 g002

Figure 3. Photo of control samples. Figure 3. Photo of control samples. Jcs 07 00058 g003

Figure 4. Photos of the testing process of control samples: (a) before destruction; (b) after destruction. Figure 4. Photos of the testing process of control samples: (a) before destruction; (b) after destruction. Jcs 07 00058 g004

Figure 5. Photos of the main samples after 15 cycles of freezing and thawing: on the left—vibrated; in the center—centrifuged; on the right—vibrocentrifuged. Figure 5. Photos of the main samples after 15 cycles of freezing and thawing: on the left—vibrated; in the center—centrifuged; on the right—vibrocentrifuged. Jcs 07 00058 g005

Figure 6. Compressive strength loss of vibrated (V), centrifuged (C), and vibrocentrifuged (VC) concretes depending on the number of freeze and thaw cycles. Figure 6. Compressive strength loss of vibrated (V), centrifuged (C), and vibrocentrifuged (VC) concretes depending on the number of freeze and thaw cycles. Jcs 07 00058 g006

Figure 7. Weight loss of vibrated (V), centrifuged (C), and vibrocentrifuged concrete (VC) samples depending on the number of freeze and thaw cycles. Figure 7. Weight loss of vibrated (V), centrifuged (C), and vibrocentrifuged concrete (VC) samples depending on the number of freeze and thaw cycles. Jcs 07 00058 g007

Figure 8. Vibrated samples: (a) 500×; (b) 1000×. Figure 8. Vibrated samples: (a) 500×; (b) 1000×. Jcs 07 00058 g008

Figure 9. Centrifuged samples: (a) 500×; (b) 1000×. Figure 9. Centrifuged samples: (a) 500×; (b) 1000×. Jcs 07 00058 g009

Figure 10. Vibrocentrifuged samples: (a) 500×; (b) 1000×. Figure 10. Vibrocentrifuged samples: (a) 500×; (b) 1000×. Jcs 07 00058 g010

Figure 11. Structure of concrete at different levels. Figure 11. Structure of concrete at different levels. Jcs 07 00058 g011

Table 1. Overview of studies on the topic of frost resistance of concrete and ways to improve it. Table 1. Overview of studies on the topic of frost resistance of concrete and ways to improve it. Reference NumberResearch TopicsMain Results[13]The influence of alternate freezing—thawing and corrosion of metal rods on the change in the mechanical properties of concreteAlternate freezing and thawing have a negative effect on the structure of micropores, increases their diameter, and contribute to the acceleration of corrosion processes.[14]Influence of air-entraining and mineral additives on the frost resistance of concreteThe authors selected rational dosages of additives that make it possible to obtain concretes with improved frost resistance characteristics. The optimal dosage of fly ash was 5.06%, ground blast furnace slag 6.75%, microsilica 7.77%, and the most effective air content in the concrete mix was in the range of 4 ± 0.5%.[15,16]Influence of Microsilica Additive and Various Synthetic Fibers on the Frost Resistance of ConcreteAccording to the results of studies [15], the lowest rate of weight loss of samples after multiple cycles of freezing and thawing, as well as the best strength characteristics, were recorded for samples with a microsilica and fiber content of 10% and 1%. The maximum augmentation in compressive strength was 26.6% and flexural strength was 29.17%. In [16], the addition of synthetic fibers in the amount of 7 kg/m3 of the concrete mixture improves the strength characteristics of the composite, increases its modulus of elasticity, and also helps to maintain “the structural integrity of the concrete during its repeated freezing and thawing” [16].[17,18,19,20]Influence of different types of fibers on the frost resistance of concreteIn [17], authors studied the effectiveness of jute fibers in concrete under freezing-thawing conditions. The addition of jute fibers in road concrete contributes to an increase in the impact strength index, and this further positively affects the frost resistance of concrete. “The addition of steel fiber in an amount of 1–2.5%” [18] to concrete provides an increase in both strength characteristics and the durability coefficient calculated from the results of freezing and thawing tests. In [19], the addition of micro synthetic fiber in an amount of 0.15% makes it possible to obtain composites with improved strength and durability. This effect of the introduction of micro synthetic fibers is explained by the authors as the creation of a more flexible system with air pores that resist the expansion forces of freezing water. In studies conducted in [20], it was found that the use of steel and polypropylene fibers has an approximately equivalent effect on the frost resistance of concrete. Therefore, from an economic point of view, the use of polypropylene fibers is the most profitable.[21]Influence of limestone addition on frost resistance of various types of concreteThe authors found that the addition of limestone to aerated concrete and non-aerated concrete mixtures significantly affects the frost resistance of concrete. Weight loss and strength reduction in various types of concrete considered in this study after 100 freeze-thaw cycles do not exceed acceptable limits.[22]Influence of hydrophobic and ice-phobic treatment of concrete surface on its durabilitySuperhydrophobic coatings for concrete based on hydrophobic emulsions with nano powders have been obtained, which make it possible to impart a nanotexture to the already existing “complex roughness of the material. Concrete treated with this type of coating exhibited a pronounced ice-phobic character, a parameter that goes beyond the freeze-thaw characteristics normally controlled for cement-based composites” [22]. Table

Table 2. Types of porosity of the HCP. Table 2. Types of porosity of the HCP. Type of PorosityCalculation FormulaExplanation Total porosity P t = ( W C − 0.23 α ) ρ c 1 + ρ c · W C W C —water-cement ratio; α —degree of hydration of cement; ρ c —cement density, g/cm3;0.23—coefficient taking into account the mass of water chemically bound by cement.This type of porosity means the volume of all pores enclosed between individual solid structural components (not fully hydrated clinker grains and cement hydration products)Porosity of hydrated cement P h = α ( C + 0.23 C ) V o · 0.28 ( C ρ c + C · W C ) = 0.19 α · ρ c 1 + ρ c · W C C, W—consumption, respectively, of cement and water per 1 m³ of cement paste; V o —the volume occupied by 1 g of hydrated cement, equal (according toT. Powers) 0.567 cm3/g;0.28—minimum porosity of hydrated cement (at α = 1 и W C = 0.38 )This type of porosity means the volume of all pores enclosed between the particles of hydrated cementCapillary porosity P c = P 0 − P h = ρ c ( W C − 0.42 α ) 1 + ρ c · W C Capillary porosity directly depends on the water-cement ratio and the degree of hydration. The lower the W/C and the higher the degree of cement hydration, the lower the value of this type of porosityOpen porosity P o = W m · ρ 0 ( h c p ) ρ W m —water absorption of cement stone by weight,%; ρ 0 ( h c p ) —density of hardened cement paste, kg/L; ρ —water density, kg/L.These types of porosity are opposite to each other. Closed pores cannot be filled with water either when concrete is immersed in water or by capillary suction, respectively, open pores can be filled with waterClosed porosity P c l = P t − P o Table

Table 3. Crushed stone (CS) characteristics. Table 3. Crushed stone (CS) characteristics. CS SizeThe Content of Lamellar and Needle-Shaped Grains, % by WeightGrade of Crushed Stone according to CrushabilityGOST 8267 [48]The Content of Dust and Clay Particles,% by MassGrade of Crushed Stone for Frost Resistance according to GOST 82675–106.710000.1530010–205.312000.12300 Table

Table 4. Proportions of mixtures and their workability. Table 4. Proportions of mixtures and their workability. Forming TechnologyWorkability CharacteristicCement, kg/m3Water, L/m3CS, kg/m3Sand, kg/m3VibrationCone draft—3.5 cm (P1 according to GOST 7473 [49])3751681014746CentrifugationCone draft—2.3 cm (P1 according to GOST 7473)3871821143692Vibrocentrifugation Table

Table 5. List of used laboratory instruments. Table 5. List of used laboratory instruments. Name of the Technological OperationApplied EquipmentProduction of concrete mixLaboratory concrete mixer BL-10 (ZZBO, Zlatoust, Russia)Fabrication of vibrated samplesLaboratory vibration platform SMZh-539-220A (IMASH, Armavir, Russia)Production of centrifuged and vibrocentrifuged samples of the annular sectionLaboratory vibrocentrifuge [53]Keeping samples for 28 daysNormal hardening chamber “RNPO RusPribor” (St. Petersburg, Russia)Sawing centrifuged samplesStone-cutting machine (Helmut, Moscow, Russia)Laboratory experimental studies“IP-1000” (“NPK TEHMASH”, Neftekamsk, Republic of Bashkortostan, Russia); laboratory oven ShS-80-01 SPU (Smolensk SKTB SPU, Smolensk, Russia); freezer NTTK (−60 °C) (VNIR, Moscow, Russia); calipers; laboratory scales (Laborkomplekt, Moscow, Russia) Table

Table 6. Test conditions for concrete specimens. Table 6. Test conditions for concrete specimens. Test ConditionsSaturation EnvironmentFreezing Environment and TemperatureEnvironment and Defrosting Temperature5% aqueous sodium chloride solution5% aqueous solution of sodium chloride, −(50 ± 5) °C5% aqueous solution of sodium chloride, (20 ± 2) °C Table

Table 7. Formulas for calculating the physical characteristics of vibrated and centrifuged concrete. Table 7. Formulas for calculating the physical characteristics of vibrated and centrifuged concrete. Type of ImpactFormulaDescriptionFreeze-Thaw Δ m = m − m 1 m · 100 Δ m is the change in the mass of the samples, %; m is the mass of the sample before freezing and thawing, g; m 1 is the mass of the sample after freezing and thawing, g. X a v = ∑ X i n X a v is average value of strength, MPa; X i is the strength of a single sample, MPa; n is the number of samples. σ n = W m α σ n is standard deviation; W m is the range of single values of concrete strength in a series; α by Table 6 GOST 10060 V m = σ n X cp V m is the coefficient of variation. X m i n ′ = X cp ′ − t β σ n ′ X m i n ′ is the lower limit of the confidence interval for control samples; t β is Student’s coefficient with confidence probability σ n ′ = 0.95, taken according to Table 7 of GOST 10060, depending on the number of samples tested. X m i n ″ = X cp ″ − t β σ n ″ X m i n ″ is the lower limit of the confidence interval for the main samples; t β Student’s coefficient with confidence probability σ n ″ = 0.95, taken according to Table 7 of GOST 10060, depending on the number of test samples. Table

Table 8. Results of tests of control samples. Table 8. Results of tests of control samples. Type of ImpactAverage Compressive Strength of Control Samples, MPaVibrated ConcreteCentrifuged ConcreteVibrocentrifuged ConcreteFreeze-thaw45.3 ( X m i n ′ = 44.0)51.1 ( X m i n ′ = 48.5)54.2 ( X m i n ′ = 52.2) Table

Table 9. Test results of vibrated samples subjected to alternate freezing and thawing. Table 9. Test results of vibrated samples subjected to alternate freezing and thawing. Number of Freeze and Thaw CyclesAverage Mass CHANGE of Samples, %Average Compressive Strength of Samples in a Series, MPa X m i n ″ , MPa 1045.042.820.744.040.230.643.941.040.743.840.251.243.839.961.743.539.772.143.038.682.241.937.692.440.937.2102.940.637.2113.240.037.2123.539.735.1133.739.334.7144.038.834.7154.338.734.6 Table

Table 10. Results of tests of centrifuged samples subjected to alternate freezing and thawing. Table 10. Results of tests of centrifuged samples subjected to alternate freezing and thawing. Number of Freeze and Thaw CyclesAverage Mass Change of Samples, %Average Compressive Strength of Samples in a Series, MPa X m i n ″ , MPa 1051.048.92050.947.830.150.547.640.350.347.150.549.947.060.549.846.770.849.146.281.248.846.091.348.045.7101.447.744.9111.845.943.3122.045.542.9132.144.841.9142.644.641.8152.844.241.3 Table

Table 11. Results of tests of vibrocentrifuged samples subjected to alternate freezing and thawing. Table 11. Results of tests of vibrocentrifuged samples subjected to alternate freezing and thawing. Number of Freeze and Thaw CyclesAverage Mass Change of Samples, %Average Compressive Strength of Samples in a Series, MPa X m i n ″ , MPa 1054.152.12054.052.53053.952.440.253.652.150.453.452.060.553.051.570.652.951.480.752.650.790.952.149.5101.051.448.4111.151.148.2121.250.547.7131.349.947.3141.849.146.5152.148.645.7 Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content. © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/). Share and Cite MDPI and ACS Style

Beskopylny, A.N.; Shcherban, E.M.; Stel’makh, S.A.; Mailyan, L.R.; Meskhi, B.; Chernil’nik, A.; El’shaeva, D. Influence of Variatropy on the Evaluation of Strength Properties and Structure Formation of Concrete under Freeze-Thaw Cycles. J. Compos. Sci. 2023, 7, 58. https://doi.org/10.3390/jcs7020058

AMA Style

Beskopylny AN, Shcherban EM, Stel’makh SA, Mailyan LR, Meskhi B, Chernil’nik A, El’shaeva D. Influence of Variatropy on the Evaluation of Strength Properties and Structure Formation of Concrete under Freeze-Thaw Cycles. Journal of Composites Science. 2023; 7(2):58. https://doi.org/10.3390/jcs7020058

Chicago/Turabian Style

Beskopylny, Alexey N., Evgenii M. Shcherban, Sergey A. Stel’makh, Levon R. Mailyan, Besarion Meskhi, Andrei Chernil’nik, and Diana El’shaeva. 2023. "Influence of Variatropy on the Evaluation of Strength Properties and Structure Formation of Concrete under Freeze-Thaw Cycles" Journal of Composites Science 7, no. 2: 58. https://doi.org/10.3390/jcs7020058

AMA Style

Chicago/Turabian Style

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