Steel Fiber Dosage Research Articles

Experimental Performance Study on Axial Compressive Load-Bearing Capacity of Steel Slag Micropowder Ecotype UHPC of Short Columns Steel Pipe

In order to study the axial compression performance of steel pipe concrete short columns filled with steel slag micronized ultra-high-performance concrete (UHPC), this paper designs 27 steel pipe UHPC short columns for axial compression test and compares and analyzes the axial compression performance of the specimens in terms of the damage mode, the deformation curve, and the coefficient of strength enhancement, which is aimed at investigating the differences in the actual load-bearing performance of steel pipe UHPC short columns through changes in the aspect ratio, concrete type, and steel content rate, and so on. The purpose of this paper is to compare and analyze the axial compressive performance of the specimens in terms of damage mode and strength enhancement factor in order to investigate the difference in the actual bearing capacity performance of steel pipe UHPC short columns through the changes in length-to-diameter ratio, concrete type, and steel content. The test results show that the axial compressive performance of steel slag powder steel pipe UHPC short columns is greatly affected by the L/D ratio and steel content; the specimen bearing capacity increases with the increase in the wall thickness of the steel pipe and decreases slightly with the increase in the L/D ratio, and the steel fibers can effectively improve the deformation of the concrete so as to enhance the composite effect with the steel pipe; the contribution of the core UHPC to improve the value of bearing capacity accounts for a higher percentage when UHPC with 1% steel fiber dosage and 20% coarse aggregate dosage gave the best uplift with no change in the type of steel pipe. In this paper, the axial compression test bearing capacity results of steel slag micro powder steel pipe UHPC short column are compared with the calculated bearing capacity results of domestic and international specifications and analyzed from the perspectives of perimeter compression strength, steel fiber mixing of core concrete, and the relevant parameter design suggestions for high-strength steel pipe concrete specimens are put forward.

Optimization of Ultra-High Performance Concrete Based on Response Surface Methodology and NSGA-II.

This study systematically investigated three influential factors-water-to-binder ratio, cement/sand ratio, and steel fiber content-that significantly impact the performance of ultra-high-performance concrete (UHPC). Utilizing the Response Surface Methodology (RSM) with a Central Composite Design (CCD), 20 carefully designed mix proportions underwent comprehensive experimental testing. Through rigorous statistical analysis, models were established to elucidate the complex relationships between the specified factors and the overall properties of UHPC. Variance analysis reveals significant effects of the three factors on UHPC performance, with workability and compressive strength increasing with higher cement/sand ratios while flexural strength decreases. Moreover, increased water-to-binder ratios exhibit substantial negative impacts on both 28-day compressive and flexural strengths. Despite adversely affecting workability, higher steel fiber dosages contribute positively to mechanical performance. Furthermore, Monte Carlo sampling and the multi-objective non-dominated sorting genetic algorithm-II (NSGA-II) were employed to validate the reliability of the statistical model and to conduct multi-objective optimization. The final UHPC mix design obtained consists of a cement/sand ratio of 1.12, a water/binder ratio of 0.16, and a steel fiber content of 2.94%. Experimental results yielded a slump flow of 802 mm, compressive strength of 122.7 MPa, and flexural strength of 24.3 MPa.

Autogenous shrinkage prediction models and microstructure of UHPC with single or binary addition of an expansive agent and steel fibers

The low water/binder ratio of ultra-high performance concrete (UHPC) often results in its high autogenous shrinkage. Our study explored the effect of the single or binary addition of a CaO-based expansive agent (CEA) and steel fibers on flowability, compressive strength, flexural strength, microstructure, and autogenous shrinkage of UHPC. X-ray diffraction (XRD), thermogravimetric (TG) analysis, scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) were applied to reveal the effects of CEA and steel fibers on hydration products and microstructure characteristics of UHPC. Experimental results show that the autogenous shrinkage of UHPC decreased markedly with the single or binary addition of CEA and steel fibers. Relative to the control group, autogenous shrinkage of UHPC with 2.5% dosage of single steel fibers, 6% dosage of single CEA, and binary addition of 2.5% steel fibers and 6% CEA decreased 17.8%, 10.9%, and 30.8% at 180 days, respectively. Steel fibers could enhance the mechanical performance of UHPC; nevertheless, they would decrease the flowability of UHPC. Meanwhile, the addition of CEA in the UHPC mixture not only maintained the mechanical properties and flowability but also decreased the autogenous shrinkage. Diffraction peak intensity and endothermic peak of Ca(OH)2 and the pore volume of 10–50 nm diminished with the content of CEA; however, that of C-S-H gel and ettringite increased. The prediction accuracy of nine shrinkage models (FHWA model, Lee model, Yoo model, JSCE model, B4 model, JonassonH model, Eurocode 2 model, CEB model, and DilgerW model) is analyzed with RE, Rnew2, and autogenous shrinkage of UHPC in this paper.

Mechanical Properties and Microanalytical Study of Concrete Reinforced with Blended Corn Straw and Scrap Steel Fibers.

Fiber concrete exhibits superior performance in various aspects compared to plain concrete and has been widely researched and applied worldwide. However, many industrially made fibers are expensive, and their cost has to be considered before use; thus, it would be economically valuable to find inexpensive fibers with excellent properties to make fiber concrete. Rural areas have many rich straw resources to be disposed of; at the same time, the rapid development of the automobile industry has introduced a large number of used tires containing steel wire with a very low reuse rate. These two low-cost materials can be processed to make fibers, making the study of mechanical properties regarding their incorporation into concrete practically significant for reducing the cost of fiber concrete. Based on this, a three-factor, three-level orthogonal test was conducted to investigate the effects of different dosages of corn straw fibers and scrap steel fibers, as well as the water-cement ratio, on the mechanical properties of concrete. The optimum level of each factor for blended straw-waste-steel-fiber concrete with different mechanical properties was obtained using the polar and ANOVA methods. It was found that the compressive strength, splitting tensile strength, flexural strength, and impact resistance of the specimens after fiber dosing were better than those of plain concrete specimens with the same water-cement ratio. The maximum improvement was 14.96% in cubic compressive strength, 42.90% in tensile strength, and 16.30% in flexural strength, while the maximum improvement in impact energy consumption at the final crack was 228.03%. Combined with SEM microanalysis, the two fibers formed a stronger whole with the C-S-H gel. When the specimen was subjected to load, the two fibers were able to withstand part of the load, thus enhancing the load-bearing capacity. Finally, the optimal mix ratio of blended straw-scrap-steel-fiber concrete was determined to be 0.8% corn straw fibers by volume, 0.6% scrap steel fibers by volume, and a 0.45 water-cement ratio by combining the weights of the levels of each factor under its four different mechanical properties through hierarchical analysis. This analysis of mechanical properties provides a reference for practical applications in future projects.

Bond performance and constitutive model of steel bar in G-UHPC under cyclic loading

The increasing embrace of the low-carbon and environmentally sustainable construction approach has opened exciting opportunities for using environmentally friendly geopolymer based ultra-high-performance concrete (G-UHPC) in engineering structures, drawing significant attention to its performance. Seismic performance is a crucial factor in structural design, and it is greatly affected by the bond behavior between steel bar and concrete. As a result, a thorough understanding of the bond behavior of steel bars to G-UHPC provides essentially theoretical support for the structural design and nonlinear finite element analysis of G-UHPC structures, which is vital for their widespread implementation in earthquake engineering. This study tested 54 specimens from 18 groups to examine the bond performance of G-UHPC and steel bars under cyclic loading. The influence of concrete and steel bar types, protective layer thickness, bond length, and steel fiber on critical bond performance indicators were evaluated, and the bond stress-slip hysteretic and skeleton curves were analyzed. Subsequently, based on the experimental data, a constitutive model was proposed to predict the bond stress-slip relationship of steel bars and G-UHPC under cyclic loading. The results indicated that the steel bars exhibited superior bond performance with G-UHPC as compared to NSC. The bond and residual strength between steel rebars and G-UHPC was approximately 1.73 times and 3 times greater, respectively, in comparison with that between NSC and steel rebars. Increasing the strength of steel bars only resulted in a limited 2 % improvement in bond strength. The steel bar diameter, protective layer thickness, bond length, and the dosage and length of steel fibers in G-UHPC significantly influenced the bond performance. The addition of irregular-shaped steel fibers to G-UHPC has demonstrated potential in improving energy consumption, with the most remarkable enhancement observed for the inclusion of twisted steel fibers. Specifically, the incorporation of twisted steel fibers signally enhanced the energy consumption to approximately 1.3 times the energy dissipation as compared to straight steel fibers with the same dosage and aspect ratio. In addition, the accuracy of the proposed constitutive model has been validated.

Effect of Basalt/Steel Individual and Hybrid Fiber on Mechanical Properties and Microstructure of UHPC.

Ultra High-Performance Concrete (UHPC) is a cement-based composite material with great strength and durability. Fibers can effectively increase the ductility, strength, and fracture energy of UHPC. This work describes the impacts of individual or hybrid doping of basalt fiber (BF) and steel fiber (SF) on the mechanical properties and microstructure of UHPC. We found that under individual doping, the effect of BF on fluidity was stronger than that of SF. Moreover, the compressive, flexural, and splitting tensile strength of UHPC first increased and then decreased with increasing BF dosage. The optimal dosage of BF was 1%. At a low content of fiber, UHPC reinforced by BF demonstrated greater flexural strength than that reinforced by SF. SF significantly improved the toughness of UHPC. However, a high SF dosage did not increase the strength of UHPC and reduced the splitting tensile strength. Secondly, under hybrid doping, BF was partially substituted for SF to improve the mechanical properties of hybrid fiber UHPC. Consequently, when the BF replacement rate increased, the compressive strength of UHPC gradually decreased; on the other hand, there was an initial increase in the fracture energy, splitting tensile strength, and flexural strength. The ideal mixture was 0.5% BF + 1.5% SF. The fluidity of UHPC with 1.5% BF + 0.5% SF became the lowest with a constant total volume of 2%. The microstructure of hydration products in the hybrid fiber UHPC became denser, whereas the interface of the fiber matrix improved.

Research on the Performance of Steel Strand-Reinforced Reactive Powder Concrete with Mixed Steel Fibers and Basalt Fibers under the Salt Dry–Wet Erosion

In this study, the properties of steel strand-reinforced reactive powder concrete (RPC) with mixed steel fibers and basalt fibers were investigated. The volume ratios of steel fibers and basalt fibers ranged from 0% to 2%. The reinforcement ratio of steel strands was 1%. The flexural strength and toughness were measured. Moreover, the impact toughness was determined. The studies were carried out under an erosion environment with chlorides and sulfates. The electrical resistance and the ultrasonic velocity were obtained to assess the salt corrosion resistance performance of steel strand-reinforced RPC. The results show that the addition of basalt fibers and steel fibers can improve the mechanical strength, ultrasonic velocity, flexural toughness, and impact toughness and decrease the performance degradation of the steel strand-reinforced RPC under the conditions of dry–wet alternations of NaCl and Na2SO4 solutions. Basalt fibers and steel fibers can improve the steel strand-reinforced RPC’s flexural strength by rates of up to 13.1% and 28.7%, respectively. Moreover, the corresponding compressive strength increases by 10.3% and 18.3%. The flexural strength decreases by 11.2~33.6% and 7.3~22.7% after exposure to the NaCl and Na2SO4 dry–wet alternations. Meanwhile, the corresponding compressive strength decreases by 22.1~38.9% and 14.6~41.3%. The electrical resistance increases with the addition of basalt fibers and decreases with the increasing dosages of steel fibers. The steel strand-reinforced RPC with the assembly units of 1% steel fibers and 1% basalt fibers shows the optimal mechanical properties and salt resistance considering its wet–dry alternation performance. The properties of steel strand-reinforced RPC decrease more rapidly after undergoing NaCl erosion than Na2SO4 erosion.

Experimental Study on the Flexural Performance of Steel-Polyvinyl Alcohol Hybrid Fiber-Reinforced Concrete.

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 (fL) and residual flexural strength (fR,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.

Experimental Study of Mechanical Properties and Theoretical Models for Recycled Fine and Coarse Aggregate Concrete with Steel Fibers.

With diminishing natural aggregate resources and increasing environmental protection efforts, the use of recycled fine aggregate is a more sustainable approach, although challenges persist in achieving comparable mechanical properties. Exploration into the incorporation of steel fibers with recycled aggregate has led to the development of steel-fiber-reinforced recycled aggregate concrete. This study investigates the shrinkage performance and compressive constitutive relationship of steel fiber recycled concrete with different steel fibers and recycled aggregate dosages. Initially, based on different replacement rates of recycled coarse aggregate and different volume contents of steel fiber, experimental results demonstrate that as the replacement rate of recycled coarse aggregate increases, shrinkage also increases, while the addition of steel fiber can mitigate this effect. An empirical shrinkage model for steel fiber recycled concrete under natural curing conditions is also proposed. Subsequently, based on the uniaxial compression test, findings indicate that with an increasing replacement rate of recycled fine aggregate, the peak stress and elastic modulus of concrete decrease, accompanied by an increase in peak strain, and the addition of steel fiber limits concrete crack development and enhances its brittleness while the peak stress and strain of recycled fine aggregate concrete are enhanced. However, the steel fiber volume percentage has a negligible effect on the elastic modulus. A constitutive relationship for concrete considering the effects of recycled fine aggregate and steel fiber is also proposed. This finding provides foundational support for the influence patterns of steel fiber dosage and recycled aggregate ratio on the mechanical properties of steel fiber recycled concrete.

Time-Dependent Behavior of Ultra-High Performance Concrete Beams under Long-Term Bending Loads

In the past, scholars have studied the creep of UHPC, mainly in compression and tension but not bending creep. In this research, 20 ultra-high performance concrete (UHPC) beams were tested for bending creep under long-term loading, and the changes of beam deflection, temperature, and humidity with time were obtained for 445 days of continuous loading. The deflection patterns of UHPC beams with time were analyzed for different steel fiber content, curing systems, water/binder ratio, sand/binder ratio, and stress levels. The results showed that steel fiber had an obvious inhibition effect on initial deflection, but a dosage of steel fiber too high would offset part of the inhibition effect of steel fiber on creep. The use of heat treatment had a better inhibition of creep in the later stage of UHPC, but heat treatment must be matched with necessary moisture content, and hot water maintenance was the most efficient. Both a high water/binder ratio and high stress level increased the bending creep of the specimen. Bending creep increased with the increase in the sand/binder ratio. Therefore, attention should be paid to the total amount and ratio of cementitious materials and fine aggregates in UHPC.

Performance of Steel Fiber Reinforced Concrete under Different Cooling Methods at High Temperature

Performance of Steel Fiber Reinforced Concrete under Different Cooling Methods at High Temperature

Flexural Experiments on B58 Type Railway Sleepers with Different Dosages of Steel Fibers

The flexural strengths and toughnesses of 15 post-tensioned B58 type railway sleepers produced at the Turkish State Railroads Sivas Plant using C40 class concrete with addition of hooked steel fibers at dosages of 0, 20, 30, 40, 50 kg/m3 were experimentally determined. Four-point flexural experiments were applied to them in one month after their production and proper curing. Three cylindrical samples of 15×30 cm dimensions taken from the first and the fourth batches apiece were subjected to standard compression tests with compressometer rings mounted on each sample after having been cured in 21 °C water tank for 28 days, resulting in their compressive strengths and elasticity moduluses. Modeling a railway sleeper as a post-tensioned reinforced-concrete beam, the maximum load it can resist in the experimented configuration was calculated by the ultimate-strength method using its dimensions and material properties. The experimentally-measured maximum load carried by the reference sleeper without any steel fibers was found to be 1.34 times the theoretically-calculated value, and the same ratio was found to be 1.59 for the sleepers having steel fibers of 40 kg/m3 dosage, accounting for an increase of 18%. And, the experimentally-measured toughness of the sleepers with 40 kg/m3 dosage steel fibers was found to be 23% greater than that of the reference sleepers.

The investigation and estimation of flexural strength in shear-critically designed RC beams considering the steel fiber content

Despite numerous studies investigating the effectiveness of steel fibers in RC members subjected to various loading conditions, the majority ignored the impact of the interaction between the tensile reinforcement ratio, compressive strength of fibrous concrete, and steel fiber dosage. This paper aimed to inspect and quantify the effects of hooked-end steel fiber dosage on the bending behavior of RC beams considering the interaction arising from various longitudinal reinforcement ratios. For this purpose, an extensive and hybrid investigation involving both experimental and numerical techniques was conducted. In the experimental part, an investigation was carried out to evaluate the contribution of a specific amount of fiber ratio and various aspect ratios to the behavior of large-scale RC beams having a shear-deficient design. Three beams with a 0.5% hooked-end steel fiber ratio and one without fibers but with a minimum amount of stirrups were produced, and three-point bending tests were conducted. All beams having fibers utilized full flexural strength as in the beam with stirrups. Once the experimental studies were completed, the numerical models were then developed and validated with those of experimental three-point bending tests using the non-linear finite element code VecTor2 to establish a basis for the comprehensive parametric study. The parametric study consisted of 33 analyses. Rebar and volumetric fiber ratios were selected to be variables, and the ratios adopted were within the typical range used in structural engineering applications. Based on the regression analysis a linear and a quadratic model were proposed for estimating the yield and peak strength depending on the steel fiber content. Finally, the obtained models were verified using work from the literature and found to be effective in forecasting the strength of shear-deficient RC beams with 0.8%, 1.0%, and 1.2% tensile reinforcement ratios and hooked end steel fibers (0.5 to 1.5%).

Experimental Study and Bearing Capacity Calculation of Compression-Reinforced Concrete Columns Strengthened with Ultra-High-Performance Concrete

A total of five ultra-high-performance concrete (UHPC)-strengthened reinforced concrete (RC) columns and one RC column were built and subjected to eccentric compression testing to examine the force performance of UHPC-strengthened eccentrically compressed plain RC columns. This experimental study examined the crack progression, the damage morphology, the deformation ability, the maximum load-carrying capacity, and the ductile properties of the eccentrically compressed columns. It also investigated the impacts of eccentricity, the reinforcement thickness, and the addition of steel fibers on the effectiveness of reinforcement. The cracking load, peak load, and ductility coefficient of the UHPC-reinforced specimens were increased by 100.28%, 172.30%, and 56.30%, respectively, compared with the RC column at an initial eccentricity of 50 mm. As the eccentricity distance increased, the bearing capacity of the UHPC eccentrically compressed specimens decreased, and the deformation capacity increased. Increasing the steel fiber dosage within the appropriate range decreased the crack width of the specimen. The addition of 2% steel fiber resulted in a 24.8% increase in cracking load, an 8.96% increase in peak load, and a 2.60% increase in ductility coefficient compared to the addition of 1% steel fiber. However, the reinforcing effect of UHPC was weakened under high eccentric pressures. Based on the theory of concrete structure and mechanical principles, the formula for calculating the compressive bearing capacity of RC columns strengthened with high-performance concrete was proposed. The results of calculating the positive section bearing capacity of eccentrically compressed RC columns reinforced with high-performance concrete are in good agreement with the test values. The results of this paper provide an experimental basis and theoretical foundation for the cross-sectional design of UHPC eccentrically compressed columns.

Magnetic Alignment of Micro Steel Fibers Embedded in Self-Compacting Concrete

Steel fiber reinforced cementitious composites (SFRCC) have emerged as one of the most efficient techniques to improve the flexural capacity and ductility performance of concrete. However, one of the most significant shortcomings is the randomness of steel fibers direction in the concrete matrix, which influences the extent of mechanical enhancement for a limited fiber content. An experimental approach to control the direction of steel fibers embedded in self-compacting concrete is presented in this study, which is based on generating a driving rotating force to overcome the viscous impeding forces acting onto the embedded fiber. The mechanical performance of micro steel fiber reinforced self-compacting concrete members was investigated. A uniform magnetic field of 9.8×10-3 Tesla generated by a cylindrical powered coil was capable of aligning micro steel fibers embedded in fresh self-compacting concrete along the desired direction. The testing program included seven beam specimens of size of 100 ×100 x 500 mm3. The micro steel fiber contents considered were 0.35%, 0.70%, and 1.05% by volume. Fiber volume fraction of 0.35% was the optimum dosage for magnetic alignment as it achieved the highest extents of mechanical enhancement. The concrete specimens reinforced with 0.35% of steel fiber content have exhibited enhancement rates of 5%, 28%, and 30% in four-point failure load, maximum mid-span deflection, and compressive strength, respectively. Based on the visual analysis of cross-sectional images, the highest orientation factor achieved was 0.91 when steel fiber dosage was 0.35%, whereas the random non-magnetized steel fiber reinforced beams achieved an orientation factor ranging from 0.30 to 0.50.

An Overview on the Dispersion of Steel Fiber in Ultra-High-Performance Concrete

Abstract Ultra-high-performance concrete (UHPC) is widely recognized for its high toughness, which is directly affected by the dispersion of steel fiber and its loading mode. To investigate the reinforcement effect of steel fiber, this paper summarizes the influencing factors, evaluation methods, and theoretical models of steel fiber dispersion in UHPC. First, the results reveal that a scientifically designed mixture can reduce the cost of steel fiber dosage in UHPC and improve fiber dispersion by adjusting matrix rheological properties. The optimum plastic viscosity of the slurry should range from 30 to 80 Pa·s for achieving the best fiber dispersion effect. Second, during slurry placement, the orientation of fibers in UHPC can be improved by up to 80 % through flow induction and the wall effect, which increases the bending strength, tensile strength, and toughness of UHPC matrix by 5–67 %, 30–90 %, and 13–200 %, respectively. Moreover, although the dispersion of fiber in two-dimensional space has been extensively studied, further characterization in three-dimensional space is required. Lastly, some theoretical simulation results have been achieved on fiber orientation, but factors such as aggregate or reinforcement must be considered.

Mechanical performance evaluation of steel fiber-reinforced concrete (FRC) based on multi-mechanical indicators from split hopkinson pressure bar (SHPB) test

Fiber-reinforced concrete (FRC) is a new composite material composed of various fibers and a cement matrix that has been widely used and developed in the construction engineering field. In this paper, split Hopkinson pressure bar (SHPB) tests are carried out with the aim of investigating the mechanical properties and failure characteristics of FRC containing different types and dosages of steel fibers. The main findings are as follows: At a fiber content of 0 %–3.5 %, the strength of FRC shows two trends: continuously increasing and then decreasing. The ductility of hooked-end steel fiber-reinforced concrete (HFRC) is better than that of hybrid steel fiber-reinforced concrete (HSFRC) and straight steel fiber-reinforced concrete (SFRC) under static loads, whereas the ductility of HSFRC is better than that of SFRC and HFRC under dynamic loads. Straight steel fibers (SF) are better than hooked-end steel fibers (HF) in improving tensile toughness but worse than HF in improving compressive toughness. In terms of the degree of failure, NFRC and HFRC were the most severely fragmented, whereas SFRC and HSFRC exhibited better integrity. Finally, based on the multi-mechanical indicators of the FRC, a comprehensive performance evaluation method and optimization suggestions for the FRC are proposed. This provides theoretical support for the application of FRC as seismic-resistant materials in reinforced structures (i.e., anti-slide piles, retaining walls, and beam structures) of rocky landslides in strong seismic areas, which have important engineering significance.

Freeze-Thaw resistance and mechanical properties of UHPC reinforced with a lower amount of hybrid fibers

Sustainable development is becoming critical in many industrial fields, including building materials. The rapid development of the construction industry in Kazakhstan requires construction materials having high-quality, low maintenance, and good durability. The main durability issue of construction material associated with Kazakhstan’s severe climate is the volume change of water in concrete caused by the freezing and thawing (F-T) cycles, which threatens the material’s strength and microstructure. Therefore, ultra-high-performance concrete (UHPC), a relatively new material with high compressive and tensile strength and improved microstructural properties, is suggested. Nevertheless, a limited number of researches have been done regarding the F-T resistance of UHPC. This research focuses on the effect of combining two types of fibers (steel and polypropylene (PP) fibers) on the compressive, flexural, and direct tensile strength and F-T resistance of UHPC. Test results indicated higher dosages of PP fiber in UHPC increased strength before exposure to F-T cycles. Adding PP fiber to UHPC led to more prolonged strains for each UHPC mixture. However, adding more steel fibers was beneficial for UHPC exposed to F-T cycles. Although mixtures with high steel fiber dosage presented a more brittle type of failure and lower strain values than mixtures with higher PP fiber dosage, the compressive, flexural, and tensile strength of UHPC mixtures containing higher steel fiber dosages increased after 90F-T cycles. Relative dynamic modulus of elasticity (RDME), which is a common indicator of F-T resistance of concrete, tends to increase for all tested mixtures, with the highest values belonging to ones with higher steel fiber dosage. Hence, it is suggested that UHPC with higher steel fiber dosage is more beneficial in terms of the F-T resistance of UHPC.

Experimental Investigation on the Impact of Micro-Steel Fibers on the Flat Slabs' Punching Shear Resistance

This research examined the effects of micro-straight steel fiber percentage and column form on the punching shear of SFRC slabs. Fibers made of micro steel with a diameter of 0.2 mm and a length of 13mm with an aspect ratio equal to 65 were used. The fiber content varied between 0.5%, 1%, and 1.5% by volume. Four different types of concrete mixes were adopted and tested. Experimental results showed that when the percentage of steel fibers in SFRC increased, its compressive strength, flexural strength, splitting tensile strength, and direct tensile strength improved. This investigation applied a monotonic load to eight cast slabs (two each of conventional concrete of square and circular column sections of the equivalent area while the other six slabs were made with steel fiber concrete. The dimensions of each slab were (920 x 920 x 80 ) mm. Each slab specimen had essential, edge-based support with square and round column sections. It has been demonstrated that slabs with square column sections endured a relatively higher ultimate load than slabs with circular column segments when the steel fiber dosage was 0.5% or 1.0%. Still, at a steel fiber dosage of 1.5%, circular column segment slabs approached the ultimate load of square column segment slabs. The heterogeneous behavior in concrete can be attributed to the random and unequal distribution of steel fibers throughout the material. There were only flexural fractures visible on the tensile face of the slab. New fractures emerged in the center of the slab as the load increased.

Compressive strength and impact strength of preplaced aggregate fibre reinforced concrete

A new form of concrete composites known as prepacked aggregates fiber reinforced concrete (PAFRC) has recently attracted the research community's attention. Preparing PAFRC involves inserting and packing coarse aggregate fibers in a mold. Afterward, a cement grout that has a high flowability is injected into the gaps between the particles to complete the construction. This study aimed to examine PAFRC's resistance to impact using a drop weight impact test. Four mixtures were prepared with three different dosages (1, 3 and 5%) of steel fibres. All of the specimens were put through an impact test as per the recommendations of the ACI Committee 544. The impact resistance of PAFRC specimens dosed with 1, 3, and 5% steel fibres was increased by 7.86, 20.64, and 30.57 times, respectively, compared to those without fibres. The information that was gleaned from this analysis serves as a baseline for more extensive scientific research into PAFRC when it is being affected by an impact.