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ЗАРУБЕЖНЫЙ ОПЫТ
УДК 666.9
Flexural behaviour of fiber reinforced concrete beams specimens strengthened by hybrid fibers
Asasira Naome, Kunda Kunda, Ngango Justin, Zefack Mac Rollin, Department of Civil Engineering, Peoples Friendship University of Russia (RUDN University), Moscow, Russia
Keywords: basalt fiber, steel fiber, polypropylene fiber, Flexural strength of FRC.
Concrete structural beams are brittle in nature. The brittleness causes weakness and failure of the beams. These are big challenges in concrete structural construction. To find solution to these issues, the objective of this paper which is an experimental analysis is done to study the effect of different hybrid basalt, steel, glass, and polypropylene fibers when added in concrete beam specimens (rectangular prisms) separately as dispersed fiber for concrete strength. These types of concrete beams can be used in construction engineering for effective, durable, and reliable structures. Using fibers for concrete beam reinforcement has a positive economic effect as regular maintenance is not needed because of the properties when compared to concrete beam not reinforced with dispersed hybrid fibers to protect the steel rod reinforcement. Different percentages of these hybrid fibers (0,3%, 0,6%, and 0,9% and control mixture without fiber 0%) are incorporated in the concrete mixes separately to check and investigate their effect on the flexural strength of concrete beams specimens of size 100 x 100x 300 mm. Thirteen sets of concrete mixtures were used of which each set produced 9 rectangular prisms which were tested for flexure on the day 7, day 14 and day 28 per 3 rectangular prisms. The experimental results showed that addition of fiber increased the flexural strength of the concrete prism. 0.9% fiber gave the best flexural strength in all the four hybrid fibers with basalt fiber given the highest flexural strength on the day 28. During and after the testing, basalt fiber reinforced concrete showed more plasticity with lower cracks than the hybrid fiber reinforced concrete.
Изгибающее поведение образцов фибробетонных балок, усиленных гибридными волокнами
Асасира Наоме, Кунда Кунда, Нганго Джустин, Зефак Мак Роллин, Департамент строительства, Российский университет дружбы народов (РУДН), Москва, Россия
Ключевые слова: строительное производство, базальтовое волокно, стальное волокно, полипропиленовое волокно, прочность на изгиб фибрами армированых бетонах.
Бетонные конструктивные балки находят применение в строительном производстве. Тем не менее, они хрупкие по своей природе. Хрупкость вызываетслабостьиразрушение балок. Это вызываетбольшие проблемы в строительстве бетонных конструкций. Для решения этих проблем в данной работе, которая представляет собой экспериментальный анализ, было проведено исследование влияния различных гибридных базальтовых, стальных, стеклянных и полипропиленовых волокон при добавлении их в образцы бетонных балок (прямоугольные призмы) отдельно в качестве дисперсной фибры для прочности бетона. Эти типы бетонных балок могут использоваться в строительстве для создания эффективных, долговечных и надежных конструкций. Использование фибры для армирования бетонных балок имеет положительное значение, так как не требует регулярного ухода за ними из-за их свойств по сравнению с бетонной балкой, не армированной дисперсными гибридными волокнами для защиты арматуры стального стержня. Различные процентные соотношения этих гибридных фибр (0,3%, 0,6% и 0,9% и контрольнная смесь без волокна 0%) добавляются в бетонные смеси отдельно для проверки и исследования их влияния на прочность при изгибе образцов бетонных балок размером 100 х 100 х 300 мм. Использовано 13 комплектов бетонных смесей, из которых каждый комплект выпустил 9 прямоугольных призм, которые были испытаны на изгиб на 7-й день, 14-й и 28-й день на 3-х прямоугольных призмах. Результаты эксперимента показали, что добавление фибры повысило прочность бетонной призмы на изгиб. 0,9% фибра дала наибольшую прочность на изгиб во всех четырех гибридных фибрах с базальтовым волокном, при этом наибольшая прочность на изгиб была достигнута на 28 день. Во время и после испытаний базальтобетон показал большую пластичность с более низкими трещинами, чем гибридный армированный фиброй бетон. Полученные экспериментальные данные могут быть в дальнейшем использованы для подсчета экономического эффекта.
The addition of fibers in concrete to enhance the concrete strength is an ancient practice [1]. Fibers are produced for structural usage in many forms like basalt, carbon, steel, glass, and others, however, the use of steel fibers in concrete is still the most popular. Enhanced spalling strength, ductility, and toughness of concrete is found by adding 1.5 % volumetric ratio of steel fibers. Using this percentage, different studies show that concrete compressive strength is enhanced up to 15 % [2], 37 % [3], and 10 % [4]. In the research work [5] the results show that inclusion of basalt and glass fibers, separately, in concrete mix reduced the workability of
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this mix. Further in the results, it was observed that the splitting tensile strength of concrete increases up to 40 % when adding 1,0 % basalt fibers, with no improvement in strength when 0.50 % glass fiber was added. Steel-polyethylene fibers are used in reinforced cementitious composites [6]. Which showed that polyethylene fibers improve strain capacity while steel fibers improve ultimate tensile strength. Comparing hybrid polyvinyl-alcohol fibers used in strengthening mortar matrix with different types of light weight sand [7]. It is observed that the ultimate load capacities of the strengthened composites are almost the same irrespective of volume fractions of light weight sand. Effect of adding different percentages of steel, basalt, and glass fibers separately on the behavior of reinforced concrete beams, are presented in much research done in [8-14], however, the impact of adding hybrid fibers [15], by combining different types and volumetric ratios of these three fibers, on high strength concrete compressive and splitting tensile strengths as well as on beam flexural load-deflection behavior is still under discussion.
This paper focuses on investigating hybrid fibers of different percentages to identify which the fiber produces the best flexural strength and at what percentage. This investigation is based on solving the brittleness in concrete which caused failure of concrete structures.
This fiber reinforced concrete comprises of the below listed materials its concrete mix.
• Cement as binder 380 kg/m3.
• Sand with the fineness modulus of 2.7 = 585 kg/m3.
• Crushed granite with the fraction of 5-20 mm = 1005 kg/m3.
• Silica fume = 125 kg/m3.
• Water = 187,5 l/m3.
• Chopped basalt fiber (BF) of 20 mm length, diameter 15 micrometer for BF reinforced 24 kg/m3 (figure 1).
• Steel fiber (SF) of 50 mm length, 1mm for SF reinforced 24 kg/m3 (figure 2).
• Polypropylene fiber (PPF) of 25 mm length, diameter 60 micrometer for BF reinforced 24 kg/m3 (figure 3).
• Glass fiber (GF) of 12 mm length, diameter 15 micrometer for BF reinforced 24 kg/m3 (figure 4).
A total of 13 (thirteen) sets of conventional concrete mix were prepared for the rectangular prisms. From each of the sets, 9 (three) concrete rectangular prisms were made. The following percentages of fibers for each concrete were investigated: 0,3%, 0,6%, 0,9% and the control sample of 0% (concrete without fiber).
The flexural strengths were testing on concrete rectangular prisms of dimensions 100mm x 100mm x 300mm. The rectangular prisms are molded in a metallic
Fig.3. Polypropylenefiber Fig.4. Glassfiber
form. After pouring the concrete mix in the molds, the molds were kept in water bath covered with polyethylene at room temperature (20 ± 2)oC. Two days after, the concrete rectangular prisms were removed from the molds and kept in the curing cupboard till the 28th day when concrete rectangular prisms were tested for flexural strength.
The results of experimental tests conducted on basalt fiber reinforced concrete (BFRC) rectangular prisms and steel fiber reinforced concrete (SFRC) rectangular prisms, glass fiber reinforced concrete (GFRC) and polypropylene fiber reinforced concrete (PPFRC) are illustrated in table 1 and figures 5, 6, and 7. The results in table 1 are average results gotten from each of the three specimens from each set per day.
The results in table 1 and figures 5-7 show BFRC has more flexural strength than the other FRC. At day 28 curing period, BFRC obtained a maximum flexural strength of 6,72 MPa with incorporation of 0,9% BF while SFRC 6.05 MPa with
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«Экономика строительства» № 4 (70) /2021
Table 1
Flexural test results of fiber reinforced concrete (FRC)
Curing period, Days Average Flexural Strength (Ff ) of FRC, MPa
BFRC, % SFRC,%
0 0,3 0,6 0,9 0 0,3 0,6 0,9
7 3,12 3,62 4,31 5,92 3,12 3,59 4,02 5,28
14 3,29 4,05 4,96 6,11 3,29 3,65 4,61 5,53
28 3,77 4,69 5,24 6,72 3,77 4,23 4,95 6,05
GFRC PPFRC
0 0,3 0,6 09 0 0,3 0,6 0,9
7 3,12 3,31 3,91 5,07 3,12 3,19 3,53 4,82
14 3,29 3,74 4,27 5,29 3,29 3,44 4,11 5,03
28 3,77 3,99 4,51 5,85 3,77 3,61 4,26 5,71
incorporation of 0,9% SF. GFRC at 0,9% GF obtained 5,85 MPa while PPFRC at 0,9% PPF obtained 5,71 MPa. During test, it was discovered that BFRC took longer time to reach its maximum flexural strength which is attributed to the ductile nature of basalt fiber.
Fig.5. Comparison of the flexural strength of FRC on day 7
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Fig.6. Comparison of the flexural strength ofFRC on day 14
Fig.7. Comparison of the flexural strength of FRC on day 28
From the experimental test results, a noticeable increase in the flexural strength of the concrete rectangular prisms were seen with increase addition of hybrid fibers. Weight differences of the FRC were observed on the day 28. The Upon failure of the concretes, addition of fiber reduced the crack visibility on the concrete specimens with BFRC having more crack resistance ability.
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Авторы
Департамент строительство, Российский университет дружбы народов (РУДН), Москва, Россия
Асасира Наоме, e-mail: [email protected]; Кунда Кунда, e-mail: [email protected]; Нганго Джустин, e-mail: [email protected]; Зефак Мак Роллин, e-mail: [email protected]
