7Влияние гибридных волокон на раскрытие трещин в бетоне
Чиадигхикаоби Паскал Чимеремезе
Департамент строительства, Университет Афе Бабалола, Адо-Экити, (Экити штат, Нигерия), Департамент строительства, Российский Университет Дружбы Народов, chiadighikaobi.paschalc@abuad.edu.ng
Аль-муради Юнес Али Али
Теория и практика организационно-технологических и экономических решений в строительстве, Российский Университет Дружбы Народов
В данной статье приводится обзор работ по изучению характеристик гибридных волокон при включении их в бетонную смесь. Долговечность бетонной инфраструктуры определяется ее способностью поддерживать надежный уровень работоспособности и структурной целостности в условиях воздействия окружающей среды, которая может быть суровой, без необходимости проведения ремонтных работ в течение всего расчетного срока службы. Обычный бетон обладает относительно низкой прочностью на растяжение и пластичностью и поэтому подвержен образованию трещин. Трещины считаются путями проникновения в бетон газов, жидкостей и вредных растворителей, что приводит к раннему началу процессов разрушения бетона или арматурной стали. Основной целью данного исследования является выявление и понимание исследований по влиянию гибридных волокон и того, как эти смеси волокон повлияли на свойства бетона. Было доказано, что соответствующее включение стальных или неметаллических волокон повышает как способность к растяжению, так и пластичность фиброармированный бетон (ФАБ). Многие исследователи изучали повышение долговечности за счет использования ФАБ. В данной статье рассматриваются существенные доказательства того, что улучшенные характеристики ФАБ, используемого для строительства инфраструктуры, повышают его долговечность, главным образом, за счет перекрытия волокон и борьбы с трещинами. Данное исследование проведено на основе результатов лабораторных исследований в контролируемых условиях, мониторинга характеристик реальной инфраструктуры, построенной из ФАБ, и предыдущих обзорных работ.
Ключеые слова: фиброармированный бетон, гибридные волокна, трещины, прочность бетона, долговечность бетона
INTRODUCTION
Recent years have seen significant progress in the creation of a sustainable society. From an ecological standpoint, concrete structure maintenance has emerged as one of the most crucial challenges. Numerous concrete facilities constructed in Japan roughly 50 years ago have deteriorated. Therefore, thorough maintenance is required. The population of Japan has been declining, nevertheless, and as a result, labor- and money-saving maintenance systems are urgently needed. Additionally, access by engineers for inspection and maintenance is made difficult or impossible by the functional and/or environmental circumstances of infrastructures, such as metropolitan roadways and facilities for the disposal of radioactive waste.
In contrast to traditional concrete, which is a highly brittle material that develops microcracks even during curing and the early phases of strength development, reinforcement of concrete with randomly distributed short fibers reduces crack initiation and propagation.
After water, concrete is the material that is utilized the most frequently worldwide. It has been a popular building material because of its good compressive behavior, and its weak tension qualities are overcome using steel bars as reinforcement. Throughout their useful lives, concrete structures are prone to cracking. At various phases of their service life, various variables, such as plastic and drying shrinkage at an early age or freeze/thaw cycles
at a long-term stage, might result in cracks. Several methods can be used to reduce cracking, such as adding additional steel reinforcement bars or fiber reinforcement using the right mix design. However, some forms of cracks are still anticipated. As aggressive substances, such as chlorides, find their way into developed fissures in the concrete matrix, the structure's durability is compromised, and its useful life is shortened. Therefore, it is crucial to keep an eye on, manage, and fix concrete fractures. As cracks are not always visible or accessible, repairing them might not always be an option. According to reports, repair expenses account for half of Europe's annual building expenditure [1].
Steel bars help concrete withstand almost all types of loads and give structural members ductility, but they also have some drawbacks, including difficulty in controlling cracks and the penetration of substances that could cause steel to corrode [2]. To address these issues, concrete is provided with secondary reinforcement in the form of stress transfer bridges using dispersed fiber reinforcement [3]. Flexural strength (ff) and post-cracking properties of concrete can be improved by adding fibers to the concrete matrix, which increases the concrete's resistance to cracking. Micro, macro and meso fibers are the three categories into which fibers are separated based on their size [4]. Microfibers typically range in size from 6 to 20 mm in length and tens of microns in diameter. These were widely acknowledged as essential strategies for controlling plastic shrinkage. Microfibers are tiny, though, so even if concrete structures reach the large deformation zone, they provide only minimal structural benefits. Additionally, macro fibers, such as steel bar reinforcement, which are typically 30 to 60 mm long and more than 0.3 mm in diameter, can support loads and stop the spread of visible cracks after concrete matrix failure. Contrarily, meso-fibers are smaller than macro fibers but larger than microfibers, and they can, to a certain extent, fill the gaps between the micro and macro levels [4]. As can be seen, no single type of fiber can offer all-around strength, ductility, and resilience, so combining different fiber sizes is necessary to control reinforced concrete's multi-level cracking [5-7]. Table 1 provides an overview of the physical characteristics of common fiber types.
Table 1
Physical properties of commonly used fiber types in fiber reinforced concrete (FRC).
Types of Fibers Diameter Length Specific Tensile Elastic Ultimate
(Mm) (mm) Gravity (g/cm3) Strength (MPa) Modulus (GPa) Elongation (%)
Steel 5-1000 10-60 7.85 200-2600 195-210 0.5-5.0
Polyethylene (PE) 25-1000 0.96 80-600 1.4-5 12-100
High modulus PE 20-24 6-12 0.97 2500-3000 80-120 2.5-5
(HMPE)
As-spun 13 6 1.54 5800 180 3.5
phenylene-bensobisoxazole
(PBO-AS)
Polypropylene (PP) 10-200 5-50 0.90-0.91 310-760 3.5-14.7 6-15
Polyvinyl alcohol (PVA) 9-760 6-12 1.2-2.5 800-3600 20-80 4-12
Glass 6-35 10-50 2.54-2.70 1500-4000 72-80 2.5-4.8
Coconut 100-400 - 1.12-1.15 120-200 19-25 10-25
Jute 100-200 - 1.02-1.04 250-350 25-32 1.5-1.9
Asbestos 0.02-25 5-40 2.55-3.2 200-1800 164 2-3
Carbon 7-20 3-12 1.2-2 600-4000 200-390 0.4-11
Basalt 10-20 0.1-30 2.6-2.8 4100-4840 85-87 3.15
The best chance for concrete to self-heal is with fiber-reinforced cementitious composites (FRCCs). In actual applications, FRCCs are currently employed frequently and successfully. Durability and affordability are ensured because no special components are needed. By regulating the crack width and speeding up the precipitation of CaCO3, ubiquitous reinforcing fibers in the cement matrix can improve self-healing [8,9]. The issue of ensuring the durability of the healing agent is resolved because the healing process does not involve the fiber's reaction. Synthetic composite reinforcement fibers with high polarity (e. g. Particularly, the fibers that span a crack (e.g., PVA) have a high potential for self-healing precipitation [10].
Fiber reinforcement is frequently used to give the brittle cementitious matrix improved toughness and ductility. When used properly, the combination of two or more types of fibers achieves better engineering properties in concrete because of a beneficial synergistic effect, while the reinforcement of concrete with a single type of fiber may only slightly improve the desired properties. This entails combining various fiber types with concrete matrices that have different sizes, shapes, strengths, and moduli. To overcome the inherent limitations of their counterpart, the hybrid fiber (HF) draws on the unique characteristics of each of its constituent fibers. Microfibers with diameters of 10 to 40 meters (compared to 500 meters) are used to control microcracks in concrete, while macro fibers with diameters greater than that are used to control macrocracks to prevent the propagation and crack opening. The typical load-deflection curves for hybrid and conventional fiber reinforced concrete (FRC) are shown in comparison in Figure 1.
(a) (b)
Figure 1. Comparison of FRC: (a) Hybrid; (b) Conventional
Utilizing volume fractions of 1% and 0.035 percent of monofilament polypropylene and hooked-end steel fibers, the study [11] examined the mechanical characteristics of hybrid steel Polypropylene (PP) fiber concrete. The findings demonstrated that the hybrid steel-PP FRC had higher compressive strength (fc), tensile splitting strength (fst), and ff than plain concrete. Using volume fractions of 1 to 5 percent, Sukontasukkul [12] studied the tensile response of steel and PP fibers that are part of FRC both individually and in a hybrid system. The study's findings [12] demonstrated that the behavior of FRC using steel fibers was typical, i.e., the peak of the load occurred at the lowest deformation and was followed by a loaded fall to zero with no indication of a load recovery. In addition, PP fibers made the behavior of FRC more ductile than it was with just steel fibers. It demonstrated a standard double-peak response, i. e., the first peak happened at a small deformation, and the second peak happened at a large deformation. Li, Biao, et al. [13] used a steel-PP combination with three different types of steel fibers (straight, hooked-end, corrugated fiber, and
monofilament PP fibers) to study the flexural behavior of hybrid FRC. The findings indicated that PP fibers combined with all three types of steel fibers had a synergistic effect on improving flexural behavior. Hou et al. [14] examined how changes in temperature and stress affected the creep behavior of hybrid reactive powder concrete made with steel and polypropylene fibers. To achieve greater strength and prevent shrinkage cracking, it is recommended in literature to combine steel and PP fibers.
Smarzewski [15] looked at the flexural toughness of basalt/PP fiber-reinforced highperformance concrete (HPC) hybrids at total volume fractions of 1 and 2 percent, with proportions of 0/0, 100/0, 75/25, 50/50, 25/75, and 0/100 percent by volume. In terms of the flexural toughness of HPC, it was discovered that only 50/50 and 100 percent PP fibers produced the best results. The mechanical characteristics of HPC with basalt and PP fibers were examined in a different study [16]. It was discovered that the ff and /sthad increased. 0.15 percent basalt fibers and 0.033 percent PP fibers were discovered to be the optimal content for the best mechanical performance. Yan Chen et al. [17] examined the volumetric dosages of micro-size basalt, PP, and glass fibers in ultra-high-performance concrete (UHPC) at concentrations of 0.5 percent, 1.0 percent, 1.5 percent, 2.0 percent, and 2.5 percent. The fresh properties were found to be less affected by the addition of PP fibers, whereas the compressive strength increased with 0.5 percent of fibers and decreased with an increase in fiber volume. Increased and found to be comparable with these fibers were the toughness index and rupture modulus.
Pakravan et al. [18] investigated the impact of varying the ratios of PP and PVA fibers on the flexural behavior of cementitious composite concrete (ECC) beams. The variables taken into consideration were the ratios of PVA / PP fibers (75/25%, 50/50%, 100/0%, and 0/100%) at various fiber volume fraction contents (1.2% and 2%). The findings demonstrated that while hybrid fibers (PVA and PP) had little impact on ff, fibers increased the ff and ductility of the cement matrix. Additionally, the ductility of ECC was increased by substituting 25% of the volume of PVA fiber with PP fibers. Pakravan et al in another study [19] looked into the impact of hybrid PP and PVA fibers on the structural performance of Engineered Cementitious Composites (ECC) concrete elements that included fly ash as a cement substitute. Under a three-point bending test, the first-crack strength, post-crack strength, and toughness of the ECC concrete elements containing HF were investigated. The findings showed that partial replacement of PVA fibers with PP fibers with non-round cross-sectional shapes increased ductility and may be a promising way to lower the cost of producing ECC while also achieving improved deformability. et al. Feng. [20] investigated the fc and ff of hybrid fly ash fiber-reinforced concrete. According to the experimental findings, the addition of steel, PP, and PVA fibers improved the fc and ff. Additionally, it was discovered that the hybrid effects of SF-PP hybrid fiber-reinforced concrete and Steel-PVA hybrid fiber-reinforced concrete significantly increased the impact toughness of these materials. Large-scale engineered cementitious composite (ECC) concrete beams containing fly ash and reinforced with a combination of steel, PP, and PVA fibers of various lengths were studied for shear behavior by Ismail and Hassan [19]. The ultimate capacity and cracking moment of every test beam were compared to theoretical values predicted by some design code equations. In comparison to the NC beam, they discovered that the ECC beam exhibits better-cracking behavior, shear capacity, ductility, and energy absorption. Of all the ECC beams with other polymeric fibers, the PVA (8 mm) fiber reinforced ECC beam demonstrated the highest shear strength and ductility. While the use of steel fibers (13 mm) was most successful in enhancing the first crack load, ultimate load, ductility, and energy
absorption capacity, the beam reinforced with PP (19 mm) demonstrated the poorest performance.
DISCUSSION
Both macro and micro-level cracks can be effectively stopped by hybrid fiber-reinforced concrete. This is because the performance of the hybrid, which is the result of the fibers working well together, is greater than the sum of the performances of the individual fibers. The phrase "Positive Synergy Effect" refers to this phenomenon. The different hybrids are built using the fiber constitutive response, fiber dimensions, and fiber function as described below:
i. One type of fiber is stronger and stiffer and provides adequate first crack strength and ultimate strength, whereas the other type of fiber is more ductile or easily undergoes significant slippage to provide better toughness and strain capacity in the post crack zone.
ii. A smaller (micro) type of fiber that delays coalescence and early micro-crack control. The composite thus gains greater tensile strength. The composite's fracture toughness has significantly improved as a result of the addition of additional, larger fiber that is designed to stop the spread of macro-cracks.
iii. Where one type of fiber is intended to improve the fresh and early age properties, such as ease of production and controlling plastic shrinkage, the other type of fiber results in improved mechanical properties.
CONCLUSION
The mechanical characteristics of multi-scale hybrid fiber-reinforced concrete were reviewed in this study. It was found that adding more fiber types to a concrete mix increases the concrete's strength. A significant factor is also the ratio of each fiber type in the concrete. Every type of fiber is distinctive in some way. The property improvement in the concrete is a result of its singularity. It was found that the concrete properties are influenced by the fibers' incorporation sizes.
Impact of hybrid fibers on the crack healing of concrete Chiadighikaobi P.Ch., Al-muradi Yunes Ali Ali
Peoples Friendship University of Russia (RUDN University)
This article reviews past related works on the performance of hybrid fibers (HF) when incorporated in a concrete mix. The durability of a concrete infrastructure is defined by its ability to sustain reliable levels of serviceability and structural integrity in environmental exposure which may be harsh without any major need for repair intervention throughout the design service life. Conventional concrete has a relatively low tensile capacity and ductility and thus is susceptible to cracking. Cracks are pathways for gases, liquids, and deleterious solutes entering the concrete, which lead to the early onset of deterioration processes in the concrete or reinforcing steel. The main objective of this study is to identify and understand the research on the effect of HR and how these fiber mixtures have affected the properties of concrete. Appropriate inclusion of steel or non-metallic fibers has been proven to increase both the tensile capacity and ductility of fiber reinforced concrete (FRC). Many researchers have investigated durability enhancement using FRC. This paper reviews substantial evidence that the improved characteristics of FRC used to construct infrastructure, improve its durability through mainly the fiber bridging and control of cracks. This study is conducted on reported laboratory investigations under controlled conditions, the monitored performance of actual infrastructure constructed by FRC, and previous review work. Keywords: Fiber reinforced concrete, hybrid fibers, crack, concrete strength, concrete durability References
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