Search Results (18)

Recent research indicates that high-strength bolts could be more effectively and efficiently used to connect steel girders and fabricated decks or retrofit existing composite girders than headed studs. To reduce the number of bolt shear connectors and, thus, further accelerate the construction of composite girders, high-strength large bolts could be an excellent alternative, resulting in greater concrete stress below the bolt. Also, hybrid fiber-reinforced concrete (HFRC) has better tensile ductility and strength than that of ordinary concrete (OC). Therefore, this study tried to design eighteen push-out test specimens, including different configurations of bolt shear connectors, to investigate the static properties of post-installed, high-strength, large-bolt shear connectors with fabricated HFRC/OC slabs. The experimental results indicated that the capacity and initial stiffness of a high-strength large through-bolt shear connector was the smallest. The fiber might enhance the capacity and initial stiffness of bolt shear connectors. Increasing the bolt diameter can significantly enhance the initial stiffness and load-bearing capacity, while the clearance of the bolt hole had a great influence on the capacity, initial stiffness, and slippage of the post-installed high-strength large-bolt shear connector. Finally, the capacity equation and slip behavior of post-installed, high-strength, large-bolt shear connector with fabricated HFRC deck were obtained using the regression method, which could provide the reference for their design. Full article

This paper explores the impact of steel–PVA hybrid fibers (S-PVA HF) on the flexural performance of panel concrete via three-point bending tests. Crack development in the concrete is analyzed through Digital Image Correlation (DIC) and Scanning Electron Microscope (SEM) experiments, unveiling the underlying mechanisms. The evolution of cracks in concrete is quantitatively analyzed based on fractal theory, and a predictive model for flexural strength (PMFS) is established. The results show that the S-PVA HF exhibits a synergistic effect in enhancing and toughening the concrete at multi-scale. The crack area of steel–PVA hybrid fiber concrete (S-PVA HFRC) is linearly correlated with deflection (δ), and it further reduces the crack development rate and crack area compared to steel fiber-reinforced concrete (SFRC). The S-PVA HF improves the proportional ultimate strength (f_L) and residual flexural strength (f_R,j) of concrete, and the optimal flexural performance of concrete is achieved when the steel fiber dosage is 1.0% and the PVA fiber dosage is 0.2%. The established PMFS of hybrid fiber-reinforced concrete (HFRC) can effectively predict the flexural strength of concrete. Full article

Freeze–thaw (F-T) is one of the principal perils afflicting concrete pavements. A remedial strategy used during construction encompasses the integration of hybrid fibers into the concrete matrix. An extant research gap persists in elucidating the damage mechanism inherent in hybrid steel fiber (SF)- and basalt fiber (BF)-reinforced concrete subjected to F-T conditions. This paper empirically investigated the durability performance of hybrid fiber-reinforced concrete (HFRC) subjected to F-T cycles. The impact of SF/BF hybridization on mass loss, abrasion resistance, compressive strength, flexural strength, damaged layer thickness, and the relative dynamic modulus of elasticity (RDME) was examined. The damage mechanism was explored using micro-hardness and SEM analysis. The results indicate that incorporating hybrid SF/BF effectively enhances the F-T resistance of concrete and prolongs the service life of concrete pavement. The mechanisms underlying these trends can be traced back to robust bonding at the fiber/matrix interface. Randomly dispersed SFs and BFs contribute to forming a three-dimensional spatial structure within the concrete matrix, suppressing the expansion of internal cracks caused by accumulated hydrostatic pressure during the F-T cycle. This research outcome establishes a theoretical foundation for the application of HFRC to concrete pavements in cold regions. Full article

Concrete is a brittle material due to its poor tensile strength; consequently, concrete tends to crack or peel under an applied external load. Previous studies have investigated the effect of incorporating fiber into concrete, which can improve its tensile strength. In this study, the static and dynamic mechanical characteristics of three types of fiber-reinforced concrete (FRC) were examined: carbon-fiber-reinforced concrete (CFRC); Kevlar-fiber-reinforced concrete (KFRC); and a combination of both, known as carbon/Kevlar-hybrid-fiber-reinforced concrete (HFRC). This study created concrete specimens by pneumatically dispersing carbon and Kevlar fibers and mixing them with cement to comprise 1% of the weight. The mixture was then combined with aggregates and water to form the concrete specimens. When compared with the benchmark concrete specimens, it was found that the compressive strength of the CFRC, KFRC, and HFRC specimens increased by about 19% to 50%, the bending strength increase by about 8% to 32%, and the splitting strength increased by about 4% to 36%. Specifically, the HFRC made with the 24 mm carbon and Kevlar fibers displayed the most significant mechanical strength in a static state. Furthermore, the HFRC showed superior resistance to impact compared to the benchmark concrete specimens across various impact energies, with the 24 mm carbon and Kevlar fiber HFRC showing the highest resistance. The inclusion of fibers in the split Hopkinson pressure bar (SHPB) test demonstrated a notable increase in the maximum strength, particularly in the case of the 12 mm carbon fiber combined with the 24 mm Kevlar fiber in the HFRC specimen. Full article

To study the dynamic tensile mechanical properties of steel polypropylene hybrid fiber reinforced concrete (SP-HFRC) after high temperature, split Hopkinson pressure bar (SHPB) dynamic splitting tests were carried out, and the optimal fiber content combination was obtained. With the plain concrete (PC) as the control, the effects of fiber addition on energy dissipation and failure forms of concrete specimens after high temperatures were analyzed. LS-DYNA software was used to simulate the dynamic splitting test. The results show that the splitting strength of specimens increases first and then deteriorates with the increase of temperature. After high temperatures, HFRC has a positive and negative fiber hybrid effect. Among the studied fiber mixture combinations, S1PP0.2 (1 vol% steel fiber + 0.2 vol% polypropylene fiber) concrete has the best splitting resistance. Compared with PC, the splitting strength increases by 106.8% at 25 °C and 128.2% at 800 °C. From the perspective of energy, we can conclude that adding hybrid fiber can significantly improve the dynamic splitting and tensile toughness of concrete after high temperatures, and defining damage variables can better characterize the damage degree of concrete. PC cracks seriously after high temperatures, while S1PP0.2 concrete cracks but does not disperse at 800 °C, showing ductile failure characteristics. By modifying some parameters of the HJC model, the state of high-temperature concrete mechanical properties can be better characterized after deterioration. The simulated failure process shows an excellent agreement with the experimental results. Full article

The incorporation of reinforcements is a necessity to compensate for the deficiency that concrete presents with its fragile behavior and low deformation capacity. One of the solutions to improve tensile performance is the addition of fiber in random distributions throughout the volume. However, this strategy can compromise the compressive strength of concrete; consequently, the purpose of this study was to analyze the compressive strength of conventional concrete with hybrid fiber reinforcement. A behavioral equation of compressive strength as a function of the hybridization of three types of fibers (steel, polypropylene, and carbon) was determined. This equation accounted for the proportions, as well as the binary and tertiary combinations, of fibers. Results showed that the effective participation of metallic fibers and their combination with synthetic fibers contributed positively to the performance of fiber-reinforced concrete. The gain in axial compression strength reached values in the range of 10% to 19% depending on the content of total fibers and their combination, without problems in the production process. Full article

In this study, aramid fiber (Kevlar^® 29 fiber) and carbon fiber were added into concrete in a hybrid manner to enhance the static and impact mechanical properties. The coupling agent presence on the surface of carbon fibers was spotted in Scanning Electron Microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) graphs. The carbon fiber with a coupling agent affected the mechanical strength of the reinforced concrete. At 1% fiber/cement weight percentage, the hybrid fiber-reinforced concrete (HFRC) prepared using Kevlar fiber and carbon fiber of 12 and 24 mm in length under different mix proportions was investigated to determine the maximum mechanical strengths. From the test results, the mechanical strength of the HFRC attained better performance than that of the concrete with only Kevlar or carbon fibers. Foremost, the mix proportion of Kevlar/carbon fiber (50–50%) significantly improved the compressive, flexural, and splitting tensile strengths. Under different impact energies, the impact resistance of the HFRC specimen was much higher than that of the benchmark specimen, and the damage of the HFRC specimens was examined with an optical microscope to identify slippage or rupture failure of the fiber in concrete. Full article

Combining different fiber types may improve the mechanical properties of fiber reinforced concrete. The present study is focused on investigating hybrid fiber reinforced concrete (HFRC) with steel and basalt fiber. Mechanical properties of fiber reinforced fine-grained concrete are investigated. The results demonstrate that using optimal steel and basalt fiber reinforcement ratios avoids concrete mixtures’ segregation and improves their homogeneity. Concrete with hybrid steel and basalt fiber reinforcement has higher strength. Effective methodology for proper design of HFRC compositions was proposed. It is based on the mathematical experiments planning method. The proposed method enables optimal mix proportioning of high-strength fine-grained concrete with hybrid steel and basalt fiber reinforcement. Full article

In order to solve the problem of highly brittle shaft lining under dynamic loading, a combination of hybrid fiber concrete mixed with steel and polypropylene fiber is proposed to make shaft lining. C60, the concrete commonly used in shaft lining, was selected as the reference group. The static mechanical properties, dynamic mechanical properties, and crack failure characteristics of the hybrid fiber concrete were experimentally studied. The test results showed that compared to the reference group concrete, the compressive strength of the hybrid fiber-reinforced concrete did not significantly increase, but the splitting tensile strength increased by 60.4%. The split Hopkinson compression bar results showed that the optimal group peak stress and peak strain of the hybrid fiber concrete increased by 58.2% and 79.2%, respectively, and the dynamic toughness increased by 68.1%. The strain distribution before visible cracks was analyzed by the DIC technology. The results showed that the strain dispersion phenomenon of the fiber-reinforced concrete specimen was stronger than that of the reference group concrete. By comparing the crack failure forms of the specimens, it was found that compared to the reference group concrete, the fiber-reinforced concrete specimens showed the characteristics of continuous and slow ductile failure. The above results suggest that HFRC has significantly high dynamic splitting tensile strength and compressive deformation capacity, as well as a certain anti-disturbance effect. It is an excellent construction material for deep mines under complex working conditions. Full article

The bending performance of a basalt-polypropylene fiber-reinforced concrete (HBPFRC) was characterized by testing 24,400 × 100 × 100 mm³ prismatic specimens in a four-point bending test JSCE-SF4 configuration. The type and content of both fibers were varied in order to guarantee different target levels of post-cracking flexural performance. The results evidenced that mono-micro basalt fiber reinforced concrete (BFRC) allows the increase of the flexural strength (pre-cracking stage), while macro polypropylene fiber reinforced concrete (PPFRC) can effectively improve both bearing capacity and ductility of the composite for a wide crack width range. Compared with the plain concrete specimens, flexural toughness and equivalent flexural strength of macro PPFRC and the hybrid fiber-reinforced concrete (HFRC) increased by 3.7–7.1 times and 10–42.5%, respectively. From both technical and economic points of view, the optimal mass ratio of basalt fiber (BF) to polypropylene fiber (PPF) resulted in being 1:2, with a total content of 6 kg/m³. This HFRC is seen as a suitable material to be used in sewerage pipes where cracking control (crack formation and crack width control) is of paramount importance to guarantee the durability and functionality of the pipeline as well as the ductility of the system in case of local failures. Full article

This article proposes hybrid fiber-reinforced concrete (HFRC) mixed with polyvinyl alcohol fiber (PVA) and polypropylene steel fiber (FST) as a wall construction material to improve the bearing capacity and durability of frozen shaft lining structures in deep alluvium. According to the stress characteristics and engineering environment of the frozen shaft lining, the strength, impermeability, freeze–thaw damage, and corrosion resistance are taken as the evaluation and control indexes. The C60 concrete commonly used in freezing shaft lining is selected as the reference group. Compared to the reference group, the test results show that the compressive strength of HFRC is similar to that of the reference concrete, but its splitting tensile strength and flexural strength are higher; according to the strength test, the optimum mixed content of 1.092 kg/m³ PVA and 5 kg/m³ FST are obtained. According to the impermeability test results, the mixing of PVA and FST can improve the impermeability resistance of concrete. For the freeze–thaw cycle test results, the mixing of PVA and FST can improve the frost resistance of concrete; based on the 120 days sulfate corrosion test, the mixing of PVA and FST will improve the corrosion resistance of concrete. Full article

To address the temperature cracking of concrete in frozen shaft linings in extra-thick alluvial layers in coal mines, a novel shaft lining structure of coal mines consisting of hybrid-fiber-reinforced concrete (HFRC) was developed. Using the Finite Element Method (FEM), a numerical simulation test of the HFRC shaft lining structure with four factors and three levels was carried out, and the mechanical characteristics of the shaft lining structure were obtained. The results show that under a uniform surface load, the maximum hoop stress position of the HFRC shaft lining presents a transition trend from the inside surface to the outside surface; the hoop strain of shaft lining concrete is always a compressive strain, and the inside surface is greater than the outside surface. The empirical formula for the ultimate capacity of this new type of shaft lining structure was obtained by fitting. Compared with the model test results, the maximum relative error of the calculated value is only 6.69%, which provides a certain reference value for designing this kind of shaft lining structure. Full article

This paper experimentally investigates the blast-resistant characteristics of hybrid fiber-reinforced concrete (HFRC) panels by contact detonation tests. The control specimen of plain concrete, polypropylene (PP), polyvinyl alcohol (PVA) and steel fiber-reinforced concrete were prepared and tested for characterization in contrast with PP-Steel HFRC and PVA-Steel HFRC. The sequent contact detonation tests were conducted with panel damage recorded and measured. Damaged HFRC panels were further comparatively analyzed whereby the blast-resistance performance was quantitively assessed via damage coefficient and blast-resistant coefficient. For both PP-Steel and PVA-Steel HFRC, the best blast-resistant performance was achieved at around 1.5% steel + 0.5% PP-fiber hybrid. Finally, the fiber-hybrid effect index was introduced to evaluate the hybrid effect on the explosion-resistance performance of HFRC panels. It revealed that neither PP-fiber or PVA-fiber provide positive hybrid effect on blast-resistant improvement of HFRC panels. Full article

To address the cracking and leaking of concrete in frozen shaft linings in deep and thick topsoil layers in coal mines, hybrid-fiber-reinforced concrete (HFRC) was developed. First, the composition of the reference concrete was obtained by investigating high-strength concrete commonly used in shaft linings, and two dosages of polyvinyl alcohol fiber (PVAF) and polypropylene plastic steel fiber (PPSF) were obtained by the mixing test. Then, tests of early cracks of concrete were conducted; results showed that HFRC could almost avoid early cracks, exhibiting an advantage in early crack resistance. Thus, HFRC can play a significant role in improving the durability of frozen shaft linings in complex underground environments. Furthermore, a series of mechanical property tests were carried out. The results showed that the compressive strength of HFRC was similar to that of the reference concrete, but the tensile and flexural strength of HFRC was 42.7% and 35.1% higher than that of the reference concrete, respectively. Finally, an analog simulation model test of shaft linings was conducted. The new type of shaft lining structure containing hybrid fibers (HFs) exhibited plastic deformation characteristics under load, and the maximum hoop strain was −3562 με. It addressed the problem of high brittleness of frozen shaft lining structures of ordinary high-strength concrete and improved the toughness and crack resistance. HFRC is an ideal material for frozen shaft lining structures in deep and thick topsoil. Full article

In order to establish accurate compressive constitutive model of Hybrid Fiber-Reinforced Concrete (HFRC), 10 groups of HFRC specimens containing polyvinyl alcohol (PVA), polypropylene (PP), and steel fibers are designed and compressive testing is conducted. On the basis of summarizing and comparing the existing research, accuracy of various stress-strain constitutive model is compared and the method of calculating fitting parameters is put forward, peak stress, peak strain, and elastic modulus of specimens with different fiber proportion are analyzed, the calculation expressions of each fitting parameter are given. The results show that, under the condition that the volume of the hybrid fiber is 2% with the proportion of the steel fiber increase, the strength of the specimen increases, the peak strain decreases slightly, and the elastic modulus increases significantly. In specimens mixed with PVA-PP hybrid fiber, with the increase of PVA fiber proportion, the peak stress and elastic modulus of the material are improved, and the peak strain are decreased. The existing stress-strain expressions agree well with the tests. Accuracy of exponential model proposed in this paper is the highest, which can be applied in engineering and nonlinear finite element analysis of components. Full article