The adhesion strength of fibre-reinforced repair concrete under hot coastal conditions

In this study, high strength concrete of 75 MPa compressive strength was investigated. The experimental program was designed to study the effect of fibers and hybrid fibers (steel and polypropylene fibers) on the fresh (workability and wet density) and hardened properties (compressive strength, splitting strength, flexural strength and dry density) of high strength concrete. Results show that decreases in slump flow of all concrete mixtures containing steel, polypropylene and hybrid fibers compared with control mix (0% fiber). Hybrid high strength concrete with steel and polypropylene fibers showed superior compressive, splitting, flexural strengths over the others concrete without or with single fibers content. The test results indicate that the maximum increase in compressive and flexural strengths are obtains with the hybridization ratio (70%steel + 30% polypropylene) and were equal to 14.54% and 23.34% respectively, compared with the control mix. While, the maximum increase in splitting tensile strength with (100% steel fiber + 0 polypropylene) is 21.19%. KEYWORDS: High strength concrete, Fibers, Hybrid fibers high strength concrete, Mechanical properties.

This paper investigates the effect of high temperatures on the compressive strength, flexural strength, and splitting tensile strength of ultra-high-performance concrete (UHPC), and ultra-high-performance, fiber-reinforced concrete (UHPFRC). The experimental variables in this study were fiber type, fiber content, and high-temperature exposure levels. Three different types of fibers were evaluated, including steel fibers, polypropylene (PP), and polyvinyl alcohol (PVA) fibers. Six concrete mixes were prepared with and without different combinations of fibers. One mix was made with no fibers. Others were made with either steel fibers alone; a hybrid of steel fibers and PVA; and a hybrid system of steel, PP, and PVA fibers. These mixes were tested under a range of temperatures and compared for strength. The UHPC and UHPFRC were exposed to high temperatures at 100°C, 300°C, 400°C, and 500°C for 3 hours. The results showed that UHPFRC did not exhibit any significant degradation when exposed to 100°C. However, reductions of approximately 18% to 25%, 12% to 22%, and 14% to 25% in the compressive strength, splitting tensile strength, and flexural strength were observed when the UHPFRC was exposed to 400°C. UHPFRC made of steel fibers showed higher mechanical properties after exposure to 400°C compared to UHPFRC made of PP and PVA fibers. The results also demonstrate the use of PVA and/or PP fibers, along with steel fiber, to withstand the effects of highly elevated temperature and prevent spalling of UHPC after exposure to elevated temperature. The observed spalling was a direct result of the melting and evaporation of PVA and/or PP fibers when exposed to high temperature, an effect that was confirmed using scanning electron microscopy.

Influence of a hybrid combination of steel and polypropylene fibers on concrete toughness

One of the most important characteristics of concrete is its resistance to tensile and bending. In order to improve these two characteristics, some fibers can be used to form fiber-reinforced concrete. There are many fibers, which may be synthetic or natural, that can be used and their properties can be applied in the formation of concrete that resists many external and internal forces, including polyester, glass, polypropylene, and steel fiber. The incorporation of steel (SF) and polypropylene fiber (PF) and the examination and the comparison of engineering characteristics of high strength concrete (HSC) are the principal objectives of this examination. The general method used in this research is by adopting one high strength concrete mix. However, the work and concrete mixes are divided into 3 groups. The first group includes 0% steel fiber with polypropylene fiber in proportions (0, 0.1 0.2, 0.3, 0.4 and 0.5%). The second groups includes 0.5% steel fiber with polypropylene fiber (0, 0.1 0.2, 0.3, 0.4 and 0.5%) and finally the third group includes 1.0% steel fiber with polypropylene fiber (0, 0.1 0.2, 0.3, 0.4 and 0.5%). Compared to the mixture of regular concrete, the improvement in tensile, compressive flexural strength is the main advantage of the mixture, which has been observed after adding the used percentage of used fibers, which has been deduced from this research as the placement of fibers in the mixture intensified the strength features of mixtures. The maximum compressive strength, flexural tensile strength has been recorded for P0.2+S1.0 with polypropylene increasing percentage of 15.30, 15.32 and 15.317% and steel increasing percentage of 34.03, 36.51 and 36.41% respectively.

Ultra-high performance concretes (UHPC) are advanced cement-based materials characterised by superior mechanical properties with respect to normal and high-strength concretes; however, their dense and compact matrix can facilitate the onset of spalling at high temperatures. This problem is often coped up by adding polypropylene (PP) fibres to the mix design, alone or with other types of fibres; steel fibres enhance the material’s tensile capacity. The paper presents a series of tests on two UHPC types (150 and 180 N/mm2) with PP fibres (0.27% of volume) and variable content of steel fibres (0% to 1.92%), aimed at investigating the residual mechanical properties of the material after high temperature exposure. The experimental results are compared to available research on small UHPC specimens exposed to high temperatures, with dosages in PP fibres from 0.03% to 2%, and in steel fibres from 0 to 3%. The results of this research demonstrate that UHPCs need hybrid fibre reinforcement (PP + steel) to withstand high temperatures, and that the residual strength increases after 200 °C exposure, at all steel fibre dosages; this is in line with literature. Available research also shows that strength loss is possible in hot conditions, as found in the present research, while PP fibres alone do not always prevent the occurrence of spalling in small UHPC samples.

Mechanical and durability properties of high-strength concrete containing steel and polypropylene fibers

Flexural strength at high temperatures of a high strength steel and polypropylene fibre concrete

In this study, high strength concrete of 75 MPa compressive strength was investigated. Theexperimental program was designed to study the effect of fibers and hybrid fibers (steel andpolypropylene fibers) on the fresh (workability and wet density) and hardened properties(compressive strength, splitting strength, flexural strength and dry density) of high strengthconcrete. Results show that decreases in slump flow of all concrete mixtures containing steel,polypropylene and hybrid fibers compared with control mix (0% fiber). Hybrid high strengthconcrete with steel and polypropylene fibers showed superior compressive, splitting, flexuralstrengths over the others concrete without or with single fibers content. The test resultsindicate that the maximum increase in compressive and flexural strengths are obtains with thehybridization ratio (70%steel + 30% polypropylene) and were equal to 14.54% and 23.34%respectively, compared with the control mix. While, the maximum increase in splitting tensilestrength with (100% steel fiber + 0 polypropylene) is 21.19%.

High strength concrete (HSC) posses more problems, since it has less ductility in comparison with normal strength concrete (NSC). To overcome this problem was reinforced with fibers and hybrid fibers. The effects of fibers and hybrid fibers upon the properties of high-strength concrete mixtures containing superplasticizing admixtures have been investigated. The properties of fibrous high-strength concrete and high-strength concrete are compared. Results showed that decrease in workability of all concrete mixtures containing polypropylene, glass and hybrid fibers compared with control mix. It was found that the addition polypropylene fibers increase the suitable w/c ratio to save the workability from 0.24 to 0.26, 0.27 and 0.29 at 0.5, 1.0 and 1.5 volume fraction respectively. While the w/c ratio increased to 0.35 when the 0.4% glass fiber was added. HSC with 1.5% polypropylene fibers showed superior splitting and flexural strengths over the other concrete without or with fibers, compared with HSC without fibers the increasing were 30.76% and 25.61% respectively. At 28-day age, fibrous high-strength concrete showed higher compressive, splitting and flexural strengths than the high-strength concrete, depending upon the types and volume fraction of fibers. The results obtained demonstrate that the addition of the hybrid fibers to the high strength concrete showed that the ratio of (0.7% polypropylene+0.12% glass fibers) at volume fraction 0.82% gives better fresh and hardened properties than the ratio (0.3% polypropylene+0.28% glass fibers) at volume fraction 0.58%. The maximum increase in compressive strength, splitting strength and flexural strength of high strength concrete contains (0.7% polypropylene+0.12% glass fibers) were 9.57%, 15.38% and 14.04% respectively.

Fiber-reinforced concrete (FRC) has become increasingly important in recent decades due to its superior mechanical properties, especially flexural strength and toughness, compared to normal concrete. FRC has also received significant attention because of its superior fire resistance performance compared to non-fiber concrete. In recent years, studies on the mechanical performance, fire design, and post-fire repair of thermally damaged fibrous and non-fibrous concrete have gained importance. In particular, there are very few studies in the literature on the mechanical performance and flexural behavior of steel and basalt hybrid fiber concretes after high temperature and water re-curing. This study aims to determine the mechanical properties and toughness of concrete containing steel fiber (SF) and basalt fiber (BF) after ambient and high temperature (400 °C, 600 °C, and 800 °C). Additionally, this study aimed to examine the changes in fire-damaged FRCs as a result of water re-curing. In this context, high temperature and water re-curing were carried out on non-fibrous concrete (control) and four different fiber compositions: in the first mixture, only steel fibers were used, and in the other two mixtures, basalt fibers were substituted at 25% and 50% rates instead of steel fibers. Furthermore, in the fifth mixture, basalt fibers were replaced by polypropylene fibers (PPFs) to make a comparison with the steel and basalt hybrid fiber-reinforced mixture. This study examined the effects of different fiber compositions on the ultrasonic pulse velocity (UPV) and compressive and flexural strength of the specimens at ambient temperature and after exposure to elevated temperatures and water re-curing. Additionally, the load–deflection curves and toughness of the mixtures were determined. The study results showed that different fiber compositions varied in their healing effect at different stages. The hybrid use of SF and BF can improve the flexural strength before elevated temperature and particularly after 600 °C. However, it caused a decrease in the recovery rates, especially after re-curing with water in terms of toughness. Water re-curing provided remarkable improvement in terms of mechanical and toughness properties. This improvement was more evident in steel–polypropylene fiber-reinforced concretes.

Comparison of mechanical properties of concrete and design thickness of pavement with different types of fiber-reinforcements (steel, glass, and polypropylene)

The goal of this study is to assess the fresh and hardened properties of self-compacting concrete (SCC) prepared using locally available materials. This research includes also the impact of polypropylene (PP), steel and hybrid fibers on the same properties. In addition, the mechanical properties of SCC specimens (with and without fibers) at high temperatures, including as compressive, tensile, and flexural strengths, will be determined. Four different SCC mixtures (with and without fibers) are prepared, tested, and assessed in order to attain these goals. The specimens were heated to various temperatures (200, 400, 600, and 800) at a rate of 5 degrees Celsius per minute for each test. The temperature was remained constant at the target temperature for one hour before cooling to ensure a consistent temperature throughout the specimen. According to the test results, all of the mixes have good consistency and workability in terms of filling and passing ability. In addition, the inclusion of fibers lowered the workability of SCC slightly. Also, the compressive, tensile, and flexural strengths improved with increasing temperature up to 200 °C and dropped at temperatures over 200 °C, according to these findings. Within the SCC, the PP fibers lowered and removed the risk of spalling. Concrete mixtures containing steel fibers and hybrid fibers have the finest mechanical characteristics and spalling resistance as temperature rises. Weight losses were lower in SCC mixtures with PP and steel fibers than in those without PP and steel fibers. As the temperature rose, all SCC mixes lost mass and UPV decreased until the samples spalled (as in plain SCC and SCC with steel fibers) or were questionable (as in SCC with PP and SCC with hybrid fibers). Doi: 10.28991/cej-2021-03091779 Full Text: PDF

Hybrid fibres addition in concrete proved to be a promising method to improve the composite mechanical properties of the cementitious system. Fibre combinations involving different fibre lengths and moduli were added in high strength slag based concrete to evaluate the strain hardening properties. Influence of hybrid fibres consisting of steel and polypropylene fibres added in slag based cementitious system (50% CRL) was explored. Effects of hybrid fibre addition at optimum volume fraction of 2% of steel fibres and 0.5% of PP fibres (long and short steel fibre combinations) were observed in improving the postcrack strength properties of concrete. Test results also indicated that the hybrid steel fibre additions in slag based concrete consisting of short steel and polypropylene (PP) fibres exhibited a the highest compressive strength of 48.56 MPa. Comparative analysis on the performance of monofibre concrete consisting of steel and PP fibres had shown lower residual strength compared to hybrid fibre combinations. Hybrid fibres consisting of long steel-PP fibres potentially improved the absolute and residual toughness properties of concrete composite up to a maximum of 94.38% compared to monofibre concrete. In addition, the relative performance levels of different hybrid fibres in improving the matrix strain hardening, postcrack toughness, and residual strength capacity of slag based concretes were evaluated systematically.

Fire-induced spalling is one of the concerns with the use of high-strength concrete (HSC) in structural applications. Some recent studies have recommended addition of polypropylene and/or steel fibers to overcome such spalling. This paper presents results from fire resistance tests on the comparative fire performance of HSC columns with and without fibers. Four reinforced concrete (RC) columns made of HSC with plain (no fibers), polypropylene, steel, and hybrid fibers, as well as one RC column made of conventional normal-strength concrete (NSC), were tested under different fire conditions. Data from these tests are utilized to evaluate comparative fire behavior of RC columns made of plain and fiber-reinforced HSC. In addition, an analytical study is carried out to evaluate relative changes in porosity and temperature-induced pore pressure in NSC and HSC, and its effect on spalling behavior and fire resistance of HSC columns. Results from fire resistance experiments and numerical studies show that hybrid-fiber-reinforced HSC columns exhibit better fire performance compared to polypropylene- or steel-fiber-reinforced or plain HSC columns.

The effect of polypropylene fibers, steel fibers and hybrid polypropylene - steel fibers which consist of (50% polypropylene fiber+50% steel fiber), with various volume fractions 0.25%, 0.75% and 1.25% on the flexural behavior of Reinforced concrete T-beams under static load was investigated in this research.To carry out this research ten concrete mixes were prepared one for reference high strength concrete (without fiber), and the other contain all types and volume fractions of fibers. For eachmix three reinforced concrete T-beams, three cubes (150×150×150mm) and three cylinders (150×300mm) were casted. Water cement ratio was constant 0.38, silica fume with ratio of 10% as a partial replacement by weight of cement and super plasticizer with ratio of 3% by weight of the cementitious material were add to enhance the bond between fiber and cement matrix.28-day compressive strength and split tensile strength tests were made on hardened concrete specimen. The result showed that polypropylene fiber had little effect on mechanical properties of the high strength concrete. Compressive strength and splitting tensile strength of the steel fiber-reinforced concrete improved with increasing the volume fraction, achieving 24.5%, 43%, respectively, at 1.25% volume fraction. On the other hand, the addition of Hybrid fiber to high strength concrete improved compressive strength and splitting tensile stress with slight decrease as compared with the best improvement.All of the reinforced concrete T-beams were tested in flexure using controlled displacement two point loads applied on simply supported T-beams, during this test the load and deflection at mid span were measured. The result shows that the addition of polypropylene fiber had a little effect on the behavior of reinforced concrete T-beam at first steps of loading until yielding load, while, it was more effective in improving ductility and toughness (energy absorption) where the ultimate load and max deflection were increased with increasing volume fraction. The addition of steel fiber increased the cracking load, yield load and ultimate load capacity with increasing volume fraction, at the same time reduce deflection. The ductility improved by the addition of steel fiber, but this improvement decreased with increasing the volume fraction. The addition of hybrid fiber improved crack load, yield load, ultimate load, ductility and toughness at all steps of loading.