Steel Polypropylene Fiber Research Articles

Research on mechanical properties of steel-polypropylene fiber concrete and application of beam structure

Concrete faces the difficulties of low tensile strength and poor crack resistance in building structures. In order to remedy this deficiency. In this paper, steel-polypropylene hybrid fiber reinforced concrete (SPFRC) was prepared by adding steel fiber (SF) and three kinds of polypropylene fiber (PF) to C50-grade concrete. The mechanical properties and microstructure of SPFRC were studied with different fiber combinations and content, obtaining the best hybrid combination. Based on this, the bending resistance and cracking of SPFRC beam members were investigated. The results demonstrate that the addition of fiber improves the compressive strength of ordinary concrete by 0.16% ∼ 17.69%, the splitting tensile strength by 15.18% ∼ 47.45%, and the bending strength by 3.54% ∼ 26.77%. Compared with single-fiber concrete, the hybrid fiber can achieve better internal microstructure, which further enhances the mechanical properties of the material. Hybrid fibers overlap within concrete beams, effectively redistributing stress and inhibiting the formation and propagation of cracks. For the three types of SPFRC beams, the cracking load is increased by 14.29% ∼ 28.57% compared with PC beam, the ultimate bearing capacity is increased by 9.68% ∼ 19.35%. The optimal dosage is determined as 1.0% SF, 0.6% Embossed polypropylene fiber (PBF). It provides reference for the application of SPFRC in flexural members.

Damage-fracture mechanism analysis of steel-polypropylene fiber reinforced recycled concrete based on acoustic emission and digital image correlation

The engineering application of recycled aggregate concrete is significant for resource conservation and environmental protection. However, the applied range of recycled aggregate concrete is greatly limited due to microscopic defects such as microcracks in recycled aggregate. Steel-polypropylene fiber reinforced recycled concrete (SPRAC) makes up for the defects brought by recycled aggregate to a certain extent due to the action of hybrid fiber. To further promote the practical application of SPRAC, it is crucial to evaluate its damage-fracture mechanic's response mechanism under different hybrid fiber admixtures and recycled aggregate replacement rates. For this purpose, the following work is carried out in this paper: firstly, SPRAC beam specimens with different substitution rates of hybrid fiber and recycled aggregate were prepared; and the damage-fracture process of specimens under four-point bending load was monitored in real-time by using acoustic emission and digital image correlation techniques to analyze the influence of hybrid fiber and recycled aggregate on the flexural properties and damage-fracture characteristics of SPRAC; the inherent relationship between the acoustic emission rise time/amplitude (RA) and the average frequency (AF) is utilized to classify the crack type of SPRAC in the course of the data analysis; the b-value is also analyzed to assess the crack evolution process in SPRAC, and the corresponding warning thresholds are given.; strain and displacement fields on the specimen surface are analyzed using the digital image correlation; finally, the microscopic results of SPRAC are also given to better understand the damage-fracture evolution mechanism of SPRAC. Results show that the flexural strength and fracture toughness of SPRAC decreased nonlinearly with the increase of recycled aggregate content; on the contrary, the addition of hybrid fiber improved the mechanical properties of SPRAC. The study in this paper provides a new method to characterize the damage-fracture mechanism of SPRAC under bending loads quantitatively. It provides a reference for the engineering application of SPRAC.

Mechanical Properties of Fully Recycled Aggregate Concrete Reinforced with Steel Fiber and Polypropylene Fiber.

The study and utilization of fully recycled aggregate concrete (FRAC), in which coarse and fine aggregates are completely replaced by recycled aggregates, are of great significance in improving the recycling rate of construction waste, reducing the carbon emission of construction materials, and alleviating the ecological degradation problems currently faced. In this paper, investigations were carried out to study the effects of steel fiber (0.5%, 1.0%, and 1.5%) and polypropylene fiber (0.9 kg/m3, 1.2 kg/m3 and 1.5 kg/m3) on the properties of FRAC, including compressive strength, splitting tensile strength, the splitting tensile load-displacement curve, the tensile toughness index, flexural strength, the load-deflection curve, and the flexural toughness index. The results show that the compressive strength, splitting tensile strength, and flexural strength of fiber-reinforced FRAC were remarkably enhanced compared with those of ordinary FRAC, and the maximum increase was 56.9%, 113.3%, and 217.0%, respectively. Overall, the enhancement effect of hybrid steel-polypropylene fiber is more significant than single-mixed fiber. Moreover, the enhancement of the crack resistance, tensile toughness, and flexural toughness obtained by adding steel fiber to the FRAC is more significant than that obtained by adding polypropylene fiber. Furthermore, adding polypropylene fiber alone and mixing it with steel fiber showed different FRAC splitting tensile and flexural properties.

Mechanical Properties and Development of Steel Fiber, Polypropylene Fiber and Steel-Polypropylene Fiber Concrete Structures

Fibre concrete is a commonly improved concrete. Compared with ordinary concrete, it has more excellent characteristics and has been widely used in engineering structures and other fields. This paper describes the mechanical properties of polypropylene fibres, steel fibres, and hybrid fibres (steel fibres and polypropylene fibres); it discusses the use and development of these three kinds of fibre concrete in various professional fields. Steel fibre concrete overcomes the shortcomings of concrete, such as low tensile strength, slight ultimate elongation, brittle, et al., with excellent tensile, flexural, shear, crack resistance, fatigue resistance, high toughness and other properties, has been applied in the field of hydraulics, roads and bridges, construction and other engineering fields. Polypropylene has better crack and impact resistance because of its ability to be uniformly dispersed in the concrete; chemically stable, simple construction has been widely used in the world. Steel-polypropylene hybrid fibre concrete has excellent mechanical properties and economy due to the integration of steel fibres and polypropylene fibres with high strength and toughness. It has a broader prospect in the application of engineering materials.

Study on the Fracture Resistance of Mixed Fiber Concrete Lining in a Reverse Fault Tunnel

With the increasing complexity of engineering environments in tunnel construction, some projects are located in areas with adverse geological conditions, including areas prone to fault movements and other geological hazards. Fiber-reinforced concrete can significantly enhance structural performance in such challenging conditions. Currently, the application of high-performance steel-polypropylene fiber in tunnel linings and its anti-fault performance are quite limited. Therefore, this paper focuses on studying the application of steel-polypropylene mixed fiber-reinforced concrete in tunnel lining under reverse fault movements. In this paper, the constitutive relationship of mixed fiber-reinforced concrete is modified based on literature data. Utilizing the Najar formula, fiber-related variables were designed, and a three-dimensional numerical simulation model of a reverse fault tunnel was established. By designing various parameter combination cases, the structural response of tunnel linings was calculated and studied. then the influence patterns of mixed fiber parameters on the anti-fault performance of tunnel linings are summarized, the relationships between main variables are explored, and a reasonable value range for the two fibers is determined, which can provide guidance for practical engineering.

Study on mechanical properties and microstructure of steel-polypropylene fiber coal gangue concrete

Incorporating coal gangue into the concrete matrix can realize the utilization of solid waste and reduce the use of natural aggregate. To improve the mechanical properties of coal gangue concrete, this paper designs four-level and four-factor orthogonal tests with coal gangue ceramide substitution rate, coal gangue ceramide sand substitution rate, steel fiber content, and polypropylene fiber content as independent variables. Through multidimensional data analysis of the test results, The main and secondary factors of compressive strength of hybrid fiber coal gangue concrete from strong to weak are the replacement rate of coal gangue ceramic sand, the replacement rate of coal gangue ceramic grain, the content of steel fiber and the content of polypropylene fiber. The optimal content is 30% coal gangue ceramic particle, 25∼30% coal gangue ceramic sand, 0.75∼1% steel fiber, and 0.2% polypropylene fiber. The grey prediction model GM (1, 5) is obtained, which can predict the concrete strength well within the range selected in this paper. The influence of fiber and coal gangue on the microstructure was studied by scanning electron microscopy, and the influence law of interfacial transition zone on the strength of concrete was explored, which provided a theoretical basis for the study of solid waste utilization of coal gangue.

Analysis on rheological and workability properties of steel-polypropylene fibers reinforced self-compacting concrete with recycled coarse and fine aggregates

Rheological and workability properties are important for the design of steel-polypropylene fibers reinforced recycled aggregates self-compacting concrete (SPFRA-SCC). In this work, the rheological and workability behavior of SPFRA-SCC was investigated to provide guideline for structural application. The SPFRA-SCC mixtures were prepared with various combined replacement contents of recycled coarse aggregate (RCA) and recycled fine aggregate (RFA). Meanwhile, the influences of steel-polypropylene fibers (milling steel fiber and polypropylene fiber) with different combined volume fractions, silica fume and fly ash on the rheological and workability properties of SPFRA-SCC were also studied. Modified-Bingham and Herschel-Bulkley models were employed to describe the rheological behavior of SPFRA-SCC. Based on the experimental results, the multi-output least-squares support vector regressor (MLS-SVR) method was adapted to predict the rheological parameters of SPFRA-SCC. Test results showed that RCA, RFA, and hybrid steel-polypropylene fibers had a negative effect on the workability and rheological properties of SPFRA-SCC, while appropriate content of silica fume and fly ash could ameliorate the rheological and workability parameters. Both Modified-Bingham and Herschel-Bulkley models could characterize the shear thickening behavior of SPFRA-SCC, and MLS-SVR method could be well applicable to predicate a close estimation of rheological parameters based on the experimental results.

Hybridisation effect of steel–polypropylene fibres in high-volume fly ash concrete

The paper presents the results of an investigation conducted to investigate the effects of hybrid fibres (polypropylene (PP) and steel (S) fibres on the workability, compressive strength, flexural strength and flexural toughness of high-volume fly ash concrete (HVFAC). Different combinations of PP and S fibres (PP fibre 0–100% and S fibre 100–0%) were incorporated to a total fibre volume fraction of 1.0%. Three different code methods were used for a comparative evaluation of various properties of the HVFAC (toughness, residual strength, cracking strength, etc.). It was found that the mixes with a higher percentage of PP fibre resulted in lower workability as compared to the mixes made with a higher percentage of S fibres. The HVFAC mix made with 25% PP fibre and 75% S fibre showed the best results of all concrete mixes and this combination is thus considered to be the most appropriate for fibre hybridisation in HVFAC.

Post-heating flexural behavior of reinforced concrete beam with lap-spliced bar and feasibility of improving flexural performance by adding hybrid fibers

Using bar splices in reinforced concrete structures is inevitable due to transportation and construction limitations. On the other hand, executing lap splices in flexural members such as beams allows these members to potentially fail at the splice zone before reaching their ultimate flexural capacity. The failure of the beam at the splice location results from different factors, one of which is the exposure of concrete members to elevated temperatures. To address this, the flexural behavior of beams with lap-spliced bars after exposure to heat was examined, and the feasibility of improving their flexural performance by incorporating hybrid steel-polypropylene fibers was studied in the work. Here, 24 reinforced concrete beam specimens were constructed in 12 groups and exposed to the four-point bending test. Variables considered in the manufacturing and testing of these specimens included the splicing method (continuous reinforcement, simple lap splice, and hooked-end lap splice), concrete mix type (plain and fiber-reinforced), and exposure temperature (25 and 600 °C). Parameters under study included the load–deflection behavior, crack pattern, cracking load, ultimate load, failure mode, initial stiffness, effective stiffness, energy-absorption capacity, and ductility of the beams. The results indicated that exposing the spliced concrete beams to elevated temperatures changed the failure mode from flexural to splitting; however, adding hybrid fibers to the concrete mix improved the behavior of these members, with a more pronounced improvement in the specimens with the hooked-end splice. In addition, the simultaneous use of the hooked-end splice and hybrid fibers in the beams that had been exposed to heat prevented the splitting failure mode in these members. Furthermore, splicing the bar in the heated and unheated beam specimens lowered the energy-absorption capacity and ductility of the beams. The addition of fibers improved the energy absorption and ductility of the heated and unheated specimens, and the beams with the hooked-end splice showed a more significant improvement.

Cyclic tensile behavior of ultra-high performance concrete with hybrid steel-polypropylene fiber: Experimental study and analytical model

The present study deals with the effect of steel-polypropylene hybrid fiber on the tensile stress–strain behavior of ultra-high performance concrete (UHPC) subjected to monotonic and cyclic loading. Eight batches of UHPC samples with hybrid fibers were tested, with the failure process monitored by acoustic emission (AE) technique synchronously. The failure mechanism of UHPC and reinforcing mechanism of hybrid fibers were analyzed based on the combination of AE source location and scanning election microscope (SEM) observation results. The results indicated that the inclusion of hybrid steel-polypropylene fibers in UHPC matrix contributes to the enhancement of tensile mechanical performance with respect to the tensile strength, peak strain and especially the tensile toughness. Moreover, the relationship between plastic strain accumulation and envelope unloading strain during cyclic tension presents a linear pattern and appears insensitive to the variation of fiber parameters. However, the hybrid fibers significantly contribute to alleviation of the elastic stiffness degradation of UHPC during the cyclic tension. Based on the stiffness degradation process, a damage evolution law characterized by an exponential equation associated with fiber reinforcement indexes is proposed. Notably, the failure of UHPC specimen stems from concurrent macro-crack propagation and multiple cracking behavior throughout the whole loading process, which is improved due to the multi-scale reinforcement effect of hybrid fibers. Finally, in consideration of the effect of hybrid fibers, an analytical constitutive model is developed to generalize the tensile behavior of UHPC, and the comparisons yield a close estimation with test results in current research and literature.

Experimental and Numerical Analysis of Steel-Polypropylene Hybrid Fibre Reinforced Concrete Deep Beams.

This work experimentally and numerically explored how varied steel-polypropylene fibre mixtures affected simply supported reinforced concrete deep beams. Due to their better mechanical qualities and durability, fibre-reinforced polymer composites are becoming more popular in construction, with hybrid polymer-reinforced concrete (HPRC) promising to increase the strength and ductility of reinforced concrete structures. The study evaluated how different combinations of steel fibres (SF) and polypropylene fibres (PPF) affected beam behaviour experimentally and numerically. The study's focus on deep beams, research of fibre combinations and percentages, and integration of experimental and numerical analysis provide unique insights. The two experimental deep beams were the same size and were composed of hybrid polymer concrete or normal concrete without fibres. Fibres increased deep beam strength and ductility in experiments. The calibrated concrete damage plasticity model in ABAQUS was used to numerically calibrate HPRC deep beams with different fibre combinations at varied percentages. Based on six experimental concrete mixtures, calibrated numerical models of deep beams with different material combinations were investigated. The numerical analysis confirmed that fibres increased deep beam strength and ductility. HPRC deep beams with fibre performed better than those without fibres in numerical analysis. The study also determined the best fibre percentage to improve deep beam behaviour where a combination of 0.75% SF and 0.25% PPF was recommended to enhance load-bearing capacity and crack distribution, while a higher content of PPF was suggested for reducing deflection.

Axial tensile behavior of hybrid steel-polypropylene fiber reinforced high-strength lightweight concrete

In practical engineering, concrete materials are mainly damaged by tension, especially for high-strength lightweight concrete (HSLC) whose tensile performance is not as satisfactory as ordinary concrete under the same compressive strength. Adding fibers is one of the most effective methods to improve the tensile properties of concrete. In this study, the tensile behavior of hybrid fiber reinforced HSLC was investigated through direct tensile test. The tensile stress-strain curve was obtained and the tensile toughness was calculated. Furthermore, the cracking process was measured and captured synchronously by digital image correlation (DIC) measurement. The results indicated that hybrid fibers enhanced the tensile properties of HSLC at both micro and macro levels. Polypropylene fibers increased the tensile toughness of HSLC by inhibiting the propagation of micro-cracks. Steel fibers improved the peak stress, peak strain, and tensile toughness of HSLC by extending the propagation path of macro-cracks and restraining the increase of the width of macro-cracks. According to the test results, an equation for the axial tensile stress-strain curve of the hybrid fiber reinforced HSLC related to fiber characteristic parameters was formulated, which can be used as a reference for engineering design.

Experimental Study on High Strength Concrete with partial replacement of fine aggregate using polypropylene steel fiber

The present study is to investigates changes polypropylene used with various percentages such as 0%,0.5%,1%,1.5%,2%,2.5% in M25 grade of concrete. In this investigation, OPC 53 grade cement, fine and coarse aggregates were utilized. Further, the characteristics of each construction materials and polypropylene properties were determined under the laboratory tests. Afterwards, the specimens were constructed as per Indian standards then sent for seven days, fourteen days, and twenty-eight days curing, then the specimens were tested under the Tension, compression and flexural strength test. The attained maximum compression strength, tensile strength and flexural strength were 22.15N/mm2,3.81N/mm2,5.2 N/mm2, respectively. Finally, these highest strengths of polypropylene concrete, were achieved by 2.5% polypropylene used in concrete.

Effect of hybrid steel-polypropylene fiber on punching shear behavior of flat slab with an opening

This research aimed to gain a better understanding of how the addition of fiber influences the punching shear capacity of two-way slabs by conducting an experiment into the structural behavior of flat slabs with and without a square opening using different volume fractions of hybrid steel-polypropylene fiber (0%, 0.9%, 1.05% and 1.8%). Ten 700 × 700 × 70 mm slabs were divided into five pairs, with two samples used as control samples (with and without openings), and eight other samples with different volume fraction of fibers. Results showed that an increase in fiber content enhanced the shear strength of the slabs. For example, as the volume fraction of hybrid fiber increased from 0.0 to 1.8%, the ultimate load increased by 52% for slabs without an opening and up to 42% for slabs with an opening.

Flexural fatigue behavior of hybrid steel-polypropylene fiber reinforced high-strength lightweight aggregate concrete

Compared with ordinary concrete, high-strength lightweight aggregate concrete (HSLC) can remarkably attenuate self-weight in engineering structures. However, the fatigue performance of ordinary concrete is better than that of HSLC. Herein, the flexural fatigue behavior, including fatigue life and crack propagation process, of hybrid fiber (HF) reinforced HSLC under different stress levels (S = 0.85, 0.80 and 0.75) was investigated. A further analysis on the fatigue life and crack propagation rate of HF reinforced HSLC was also conducted by two-parameter Weibull distribution (2PWD) and Paris law, respectively. The results indicated that the fatigue life of all specimens followed the 2PWD under various stress levels. Compared to the single fiber reinforced HSLC, the HF reinforced HSLC exhibited minimum crack propagation rates, the longest duration of stable development stage and fatigue life. The fatigue life equation was established with double logarithmic fatigue equation by considering failure probability. Furthermore, the expression of crack propagation rate with respect to crack length of each group of specimens was proposed under various stress levels.

Damage characteristics of hybrid fiber reinforced concrete under the freeze-thaw cycles and compound-salt attack

This paper presents an experimental investigation on the damage characteristics and microstructures of hybrid fiber reinforced concrete (HFRC) subjected to the freeze-thaw（F-T）cycles and compound- salt attack. The effect of steel fiber content and steel-polypropylene fiber hybridization on the apparent morphology, mass loss, relative dynamic elastic modulus (RDEM), mechanical strengths in terms of compressive and flexural strengths were studied. The damage mechanism was explored based on an analysis of pore structures of specimens. The results showed that the F-T cycle has adverse effect on the physical and mechanical properties of specimens. The addition of fibers alleviates the damage degree of concrete, and the fiber hybridization shows more pronounced effect. Results from the porosity analysis indicate the pore sizes of 1.2HFRC are mainly distributed within 40 nm and those of OC are within 60 nm. The volume of larger pore size of 1.2HFRC increases less than the others after salt F-T cycles. Finally, based on Weibull distribution function, evolution equations for the salt-frozen damage of HFRC are developed by a combination of strength attenuation and RDEM degradation. The research results provide theoretical basis and reference for the practical application and building maintenance of fiber reinforced concrete.

Experimental study on seismic performance of hybrid steel-polypropylene fiber-reinforced recycled aggregate concrete-filled circular steel tube columns

In this paper, 1 recycled aggregate concrete-filled circular steel tube column (RACFST) and 11 hybrid steel-polypropylene fiber-reinforced recycled aggregate concrete-filled circular steel tube (HFRACFST) columns were designed given the variables of steel fiber (SF) volume content (Vsf = 0.6 %,1.2 %,1.8 %), polypropylene fiber (PPF) content fractions (Vpf = 0.05 %,0.10 %,0.15 %), concrete strengths (C40, C50, C60), thickness of steel tube (t = 2.70 mm, 3.65 mm, 4.50 mm), axial compression ratios (n = 0.25, 0.35, 0.45). Then the influence of variables on hysteretic curves, ductility, energy dissipation and stiffness degradation were studied experimentally using the pseudo-static tests. Subsequently, the restoring force models of HFRACFST were proposed based on the experimental results. The results indicated that: (1) The incorporation of HF (hybrid steel-polypropylene fiber) could enhance the hysteretic behaviour of HFRACFST columns. An increase in PPF content had little effect on the lateral bearing capacity and energy dissipation capability. Nevertheless, it could improve the ductility to some extent. As the SF content increased, the lateral bearing capacity, energy dissipation capability and ductility of the specimens increased. (2) An increase in concrete strength resulted in the increase of the bearing capacity and energy dissipation capability, but led to inferior ultimate deformation and ductility. (3) The comprehensive hysteretic behaviour was improved significantly as the thickness of steel tube increased, especially in the energy dissipation capability. (4) The specimens with higher axial compression ratio experienced inferior ultimate deformation and ductility. (5) The ductility indexes of all specimens were higher than 3.0. The yielding elastic and ultimate elastoplastic drift ratios were in the ranges 0.012–0.013 and 0.038–0.054, respectively. The hysteretic performance of HFRACFST columns could satisfy the requirement of seismic design. It is feasible to apply the HFRACFST columns to vertical load-bearing structures in the seismic zones.

An elastoplastic damage constitutive model for hybrid steel-polypropylene fiber reinforced concrete

An appropriate constitutive model to characterize the mechanical behavior of fiber reinforced concrete (FRC) plays a critical role in accurate prediction of structural performance. In this study, an elastoplastic damage constitutive model is developed for hybrid steel-polypropylene fiber reinforced concrete (HFRC), which can predict the versatile mechanical responses of HFRC as a result of various hybrid fiber inclusions. For plasticity growth, the Willam-Warnke five-parameter failure envelope is modified in the effective stress space to govern the yield condition of HFRC, while a nonlinear Drucker-Prager type plastic potential function is proposed to control the non-associated plastic flow. Regarding the damage evolution, the damage criterion and evolution laws are established in the Cauchy stress space, in which the plastic hardening and unilateral behaviors are taken into consideration. Upon two parallel integration algorithms to describe the development of plasticity and damage, as well as the identification of fiber-dependent parameters, the proposed model is numerically implemented and then validated by the experimental results from available research. The comparisons between the numerical predictions and the test results at both material scale and structural scale solidly demonstrate the capacity of the model in capturing the main features of HFRC when subjected to different loading paths.

Mechanical Properties of Hybrid Steel-Polypropylene Fiber Reinforced High Strength Concrete Exposed to Various Temperatures

Combining different types of fibers inside a concrete mixture was revealed to improve the strength properties of cementitious matrices by monitoring crack initiation and propagation. The contribution of hybrid fibers needs to be thoroughly investigated, taking into consideration a variety of parameters such as fibers type and content. In this paper, the impact of integrating hybrid steel-polypropylene fibers on the mechanical properties of the concrete mixture was investigated. Hybrid fiber-reinforced high-strength concrete mixtures were tested for compressive strength, tensile strength, and flexural strength. According to the results of the experiments, the addition of hybrid fibers to the concrete mixture improved the mechanical properties significantly, more than adding just one type of fiber for specimens exposed to room temperature. Using hybrid fibers in the concrete mixture increased compressive, tensile, and flexural strength by approximately 50%, 53%, and 46%, respectively, over just using one type of fiber. Furthermore, results showed that including hybrid fibers into the concrete mixture increased residual compressive strength for specimens exposed to high temperatures. When exposed to temperatures of 200 °C, 400 °C, and 600 °C, the hybrid fiber reinforced concrete specimens maintained 87%, 65%, and 42% of their initial compressive strength, respectively. In comparison, the control specimens, which were devoid of fibers, would be unable to tolerate temperatures beyond 200 °C, and an explosive thermal spalling occurred during the heating process.

Interfacial bond characteristics of polypropylene fiber in steel/polypropylene blended fiber reinforced cementitious composite

This paper investigates for the first time the interfacial bond characteristics of polypropylene fiber in blended hybrid steel-polypropylene fiber reinforced concrete, which contributes to improving the polypropylene fiber utilization efficiency and then promoting the overall performance of the composite. Single-sided fiber pullout tests were performed on 21 groups of macro polypropylene fiber pullout specimens. The complete fiber pullout load-slip responses were captured, and the fiber interfacial properties were analyzed for different hybrid fiber dosage, fiber embedded length and matrix length. Results show that partial fiber rupture with a non-zero residual pullout load is the dominant failure mode. Increasingly severe abrasion at the PF surface is observed during the pullout process, resulting in a strain hardening behavior after a bent-over point is reached in a typical pullout load-slip curve. An appropriate polypropylene fiber addition in the concrete matrix can effectively improve the maximum pullout load, residual pullout load, the pullout energy, and the contribution of polypropylene fibers is more critical than that of steel fibers. Besides, the reinforcement of polypropylene fibers on the toughness and cracks resistance is proven to be more pronounced in plain concrete than that in high-strength concrete. Finally, theoretical analyses were performed on the polypropylene fiber direct pullout problem and the frictional bond stress vs. slippage relation is obtained with hybrid fiber content taken into account. The research provides a base for an optimized hybrid fiber reinforced concrete with high fiber efficiency and less cement consumption.