Toughness Of Concrete Research Articles

Impact toughness and dynamic constitutive model of geopolymer concrete after water saturation

The dynamic compression test of geopolymer concrete (GC) before and after water saturation was carried out by the split Hopkinson pressure bar (SHPB). And the effects of water saturation and strain rate on impact toughness of GC were studied. Based on Weibull statistical damage distribution theory, the dynamic constitutive model of GC after water saturation was constructed. The results show that the dynamic peak strain and specific energy absorption of GC have strain rate strengthening effect before or after water saturation. The impact toughness of GC decreases after water saturation. The size distribution of GC fragments has fractal characteristics, and the fractal dimension of GC fragments after water saturation is smaller than that before water saturation. The dynamic constitutive model based on Weibull statistical damage distribution theory can accurately describe the impact mechanical behavior of GC after water saturation, and the model fitting curves are in good agreement with the experimental stress–strain curves.

Emphasis of Cyclic Loading on the Fracture Mechanism and Residual Fracture Toughness of High-Performance Concrete Considering the Morphological Properties of Aggregate

This research investigates the fatigue behaviour and fracture mechanics of high-performance concrete (HPC), including various compositions such as HPC with basalt aggregates (HPC-B), HPC with gravel (HPC-G), and high-strength coarse mortar (CM) under static and cyclic tensile loading within the special priority program SPP 2020. The study aims to integrate fracture mechanics into structural analysis to enhance design guidelines for slender cross-sections and safety-related high-performance structural components. The experimental investigations reveal HPC-B’s remarkable superiority, displaying its higher compressive strength, modulus of elasticity, and tensile strength compared to HPC-G and CM. A modified disk-shaped compact tension (MDCT) based on ASTM standards, aided by digital image correlation (DIC) unveils fracture behaviour, emphasizing fracture energy as a crucial parameter. HPC-B exhibits improved crack resistance and notch sensitivity reduction attributed to crushed basalt aggregates and an enhanced interfacial transition zone (ITZ). The research scrutinizes factors like material characterization, aggregate morphology, stress levels, and the displacement rate on crack formation. High-cycle fatigue tests show HPC-B’s superior performance, and the post-fatigue analysis reveals enhanced residual fracture toughness attributed to nano-level structural changes, stress redistribution and aggregate-matrix interaction. A 3D image analysis via Computed Tomography (CT) scans captures mesostructural crack propagation and provide quantitative insights. This research marks a significant shift from conventional aggregate-focused approaches and introduces a novel approach by integrating excess paste theory and mesoscale analysis, highlighting the critical role of aggregate choice in material characterization and mesoscale design in enhancing the structural efficiency of HPC. Furthermore, the study advances the understanding of HPC fatigue behaviour, emphasizing the interplay of aggregate types and morphologies and their dynamic response to cyclic loading, offering valuable insights for optimizing design guidelines and fostering innovation in structural engineering.

Effect of fiber addition on strength and toughness of rubberized concretes

In this paper, an experimental study was conducted to examine the static and dynamic behaviors of rubberized fiber-reinforced concrete (RFRC). Crumb rubber was partially replaced from sand at volume fractions of 0%, 5%, 10%, 15%, and 20%. Steel fibers (SFs) with fiber volume fractions (Vf%) of 0%, 0.5%, 1%, and 1.5% were used for the production of FRCs, while polypropylene fiber (PPF) with Vf% = 0.4% was adopted to produce others FRCs. A combination of 0.4% PPF and 1% SF was used for hybrid FRC. The static properties were evaluated through compression, indirect tension, and flexural tests. However, the drop weight impact test was conducted to assess the dynamic property by estimating the impact energy. It was observed that the replacement of sand with rubber reduced all mechanical properties of concrete. In the case of RFRC, a reduction in compressive strength, compared to samples without fibers, was noted, and this reduction increased with higher Vf%. Both toughness indices and fracture energy were affected slightly by increasing rubber percentages while markedly increased with higher Vf%. However, adding rubber and/or fibers enhanced the impact energy of concrete.

Influence of high temperatures on modes I and II fracture toughness and energy of nanoclay-reinforced polymer concrete

This paper investigates the influence of exposure to elevated temperatures on the fracture mechanics of polymer concrete (PC). The PC was synthesised using epoxy, silica sand, crushed basalt, and nanoclay. The prepared PC was exposed to temperatures of 24, 40, 60, 80, 100, 120 and 140°C for two hours, and the residual fracture toughness and fracture energy in mode I and mode II were studied. The three-point bending test was conducted on cracked semi-circular bend specimens with a crack angle of 0° (pure mode I) and 41° (pure mode II) to determine the fracture parameters. Subjection to high temperatures significantly increased the fracture toughness and fracture energy of the PC. The maximum fracture toughness and fracture energy were obtained after exposure to temperatures of 120°C and 140°C, respectively. Scanning electron microscopy was used to investigate the fracture surface of the PC. The type of fracture (brittle or ductile) of the PC before and after exposure to the target temperatures was evaluated. The mathematical relationships between modes I and II critical stress intensity factor (KIc and KIIc), as well as modes I and II fracture energy (GIf and GIIf) after exposure to high temperatures, were also determined.

An experimental and numerical study on the hybrid effect of basalt fiber and polypropylene fiber on the impact toughness of fiber reinforced concrete

As the civil aviation industry advances, higher requirements are put forward for the performance of airport cement pavement. The frequent takeoffs and landing of aircraft will cause continuous and large impact load on airport pavement, and combined with long-term natural factors, there will be various structural diseases. These diseases not only affect the service life of pavement, navigation safety. To enhance the impact resistance and durability of concrete, the incorporation of fiber has proven an effective approach, and basalt fibers (BF) and polypropylene fibers (PF) are selected as reinforcement materials in this study. Firstly, the effects of single BF and hybrid BF and PF on the mechanical properties of concrete were explored through compressive and flexural tests considering fiber volume contents (0.1%, 0.15, 0.2%) and lengths (6 mm, 9 mm, 12 mm). Then, the drop hammer impact test method, recommended by ACI committee 544, was refined to evaluate the impact resistance toughness of concrete. Finally, the numerical simulation of the impact test was established to explain the concrete impact damage mechanism. The results show that under less than 0.15% volume content, the single BF can effectively enhance the compressive strength, flexural strength, and impact resistance of concrete. Compared with the single BF, the combination of 12 mm BF and 6 mm PF yields favorable results, encompassing improved mechanical properties and impact resistance, thus exhibiting a positive hybrid effect. The increase in PF length (9 mm) leads to a reduction in compressive strength but an improvement in flexural strength and impact resistance. The simulation of the impact test is constructed and the accuracy is confirmed by comparing the impact times and failure patterns of the specimens. The tensile damage of plain concrete is much greater than the compressive damage, and the cracks will spread rapidly from the upper surface to the lower surface. Compared with plain concrete, the crack width of hybrid fiber reinforced concrete is larger, but the damage degree is more uniform. Fiber can absorb a large amount of impact energy, reduce the emergence of micro-cracks, and improve the impact toughness and toughness coefficient of concrete.

Mechanical performance study of basalt-polyethylene fiber reinforced concrete under dynamic compressive loading

In order to enhance concrete's impact resistance, this study investigates the effects of single basalt fiber and basalt-polyethylene hybrid fiber on concrete through split Hopkinson pressure bar (SHPB) tests, emphasizing their significance in engineering applications. A comparative analysis of the failure modes, dynamic compressive strength, dynamic compressive toughness, and dynamic growth factor of specimens was conducted under different strain rates and polyethylene fiber volume fractions. The study considered concrete damage, strain rate effect, and the toughening effect of fibers, introducing the damage factor, and establishing a dynamic damage constitutive model for fiber-reinforced concrete. The results showed that basalt-polyethylene fiber reinforced concrete (BPFRC) exhibited better impact resistance and deformation capability. There were improvements observed in dynamic compressive strength, dynamic compressive toughness, and dynamic growth factor. The addition of basalt fiber (BF) and polyethylene fiber (PE) played a buffering role in inhibiting crack propagation and slowing down the damage process. The optimum PE volume fraction for dynamic compressive strength was 0.1% at a strain rate of 60 s−1, 0.15% at a strain rate of 95 s−1, and 0.05% at a strain rate of 120 s−1, all with a BF volume fraction of 0.25%. The optimum fiber volume fractions for dynamic compressive toughness and dynamic peak toughness were consistent, both at 0.25% BF and 0.1% PE. The established dynamic damage constitutive model for fiber-reinforced concrete can effectively describe the impact resistance performance of BPFRC, and the experimental curves fit well with the constitutive curves. Furthermore, it was observed that BF acted as macrofibers, bridging to restrain the post-hardening cracking of concrete, while PE acted as microfibers, inhibiting the propagation of plastic cracks, reducing internal defects in concrete, and enhancing the ductility and toughness of concrete. Consequently, BPFRC holds significant potential value in engineering applications.

Evaluation of Flexural Toughness of Concrete Reinforced with High-Performance Steel Fiber.

In this study, a flexural test and residual stress evaluation using the aspect ratio (65 and 80) and steel fiber content (20, 30, and 40 kg/m3) as variables were conducted according to the EN 14651 standard to investigate the flexural toughness of concrete reinforced with high-performance arched steel fibers. The result of the flexural test show that the residual stress was 114.5% higher in the test specimen with high curvature and high content of arched steel fibers than that in the other conditions. In addition, the energy absorption capacity of arched steel fiber-reinforced concrete increased by 138.88% compared to concrete.

Residual fracture toughness and fracture energy of concrete with different strengths after fatigue loading

To evaluate the residual fracture toughness and fracture energy of concrete with different strengths after fatigue loading, the static, fatigue, and fatigue-static tests were conducted on 264 three-point bending (TPB) beams, respectively. The test results showed that the residual fracture toughness and fracture energy decreased rapidly at first and then steadily with the increase of the fatigue crack tip opening displacement and the number of fatigue cycles. For a given fatigue load level, the decrease rate of the residual fracture toughness increased with an increase in the concrete strength, but the decrease rate of the residual fracture energy decreased with increasing concrete strength. Finally, the degradation models for the residual fracture toughness and fracture energy of concrete were presented. When the tensile strength of concrete, the number of fatigue cycles, and the fatigue crack tip opening displacement are known, the residual fracture toughness and fracture energy of concrete after fatigue loading are determined. The research results are helpful to assess the safety of concrete structures in-service after fatigue loading.

Effect of Coarse Aggregate Size on the Performance of PE/HPP Hybrid Fiber Concrete

Three kinds of continuously graded coarse aggregates with maximum particle sizes of 10mm, 16mm and 20mm were selected from pebble and gravel respectively, then, Slump test, compressive strength test and bending toughness test were carried out to study the influence of maximum particle size of coarse aggregate on the workability, compressive strength, wear resistance and bending behaviour of PE/HPP hybrid fiber concrete. The results show that with the increase of the maximum particle size of coarse aggregate, the work performance, compressive strength and bending toughness of hybrid fiber concrete are improved.

Prediction model and measurement of fracture parameters in eco-friendly coarse copper slag-SFRSCC based on semi-circular bending test

This research has used 16 concrete mix designs containing 0.1, 0.3, and 0.5% steel fiber (SF), and 20, 30, 40, 50, and 60% copper slag (CS) to examine their fresh and hardened characteristics, and study their microstructural features with the help of scanning electron microscope (SEM) images. In addition, it has tried to evaluate the fracture characteristics of semi-circular bending (SCB) samples under loading modes I, I/II, II/I, and II. According to the results, increasing CS will improve the fresh concrete properties and reduce the negative SF effects on its performance. At 60% (fixed) CS, using 0.1% SF reduces the compressive strength by 10.08%, and applying 0.5% SF increases it by 17.24%, compared to the control sample. Increasing SF and CS improves the tensile strength of all concretes in the 14.02–86.02% range, compared to the control design. SEM images show that up to 30% replacement, the WCS-steel fiber reinforced self-compacting concrete (SFRSCC) microstructure is homogeneous, integrated and dense, and the fracture toughness and energy are higher under, respectively, pure loading modes II and I than other modes. Fracture toughness of concretes with the highest SF and CS volumes, compared to plain concrete, has increased 1.45, 1.61, 1.67, and 1.36 times under loading modes I, I/II, II/I, and II, respectively. Compared to ANN, using ALK to estimate the fracture features reduces the need for training data by 36.53%, and R2 (correlation coefficient) reduces by 0.91 and 1.52% for estimating the fracture energy and fracture toughness, respectively. Using ANN and ALK can provide a robust prediction model to estimate the fracture energy parameters of the CS-FRSCCs (R2 ≥ 0.970).

Strength and crack resistance of cement composites under multilevel reinforcement

The working hypothesis is confirmed that the required fracture toughness of structural concrete can be provided by multi-level reinforcement: at the level of the crystalline joint of cement stone – carbon nanotubes, and at the level of fine-grained concrete – various macro-sized fiber fibers (steel, polymer). Reinforcement of a crystalline splice with carbon nanotubes leads to an increase in tensile strength by 20 %, an increase in Young’s modulus. With dispersed reinforcement of concrete modified with nanoparticles at the level of fine-grained concrete, the tensile strength increases by 109 %, the critical stress intensity coefficient (crack resistance index) increases by 280 % at normal separation, and by 48 % at transverse shear.

Effect of Contents, Tensile Strengths and Aspect Ratios of Hooked-End Steel Fibers (SFs) on Compressive and Flexural Performance of Normal Strength Concrete

This study is a part of the study to simplify the reinforcing details of reinforced concrete (RC) structural members by substituting the conventional reinforcement with hooked-end steel fibers (SFs). This paper investigates the effects of SF strength, dosage and aspect (l/d) ratio on the compressive and flexural behaviors of normal strength concrete with specified compressive strength of 30 MPa. In this study, hooked-end SFs of high strength (2000–2400 MPa) and normal strength (1100–1200 MPa) were used with three l/d ratios of 64, 67 and 80. Hooked-end SFs were incorporated with three dosages of 20 kg/m3 (0.25 vol.%), 40 kg/m3 (0.50 vol.%) and 60 kg/m3 (0.75 vol.%). Eighteen steel fiber reinforced concrete (SFRC) mixes were mixed. To evaluate the compressive and flexural performance of each SFRC mixture, three SFRC cylindrical and prismatic specimens for each mixture were manufactured and tested, respectively. The test results that the inclusion of hooked-end SFs had little effect on the compressive strength, while it improved the toughness of concrete. Hooked-end SFs were also found to be effective in enhancing the flexural performance of concrete. The dosage and properties (strength and l/d ratio) of SFs significantly affect the residual flexural tensile strength (fR1 and fR3) at serviceability (SLS) and ultimate limit state (ULS) defined in fib Model Code 2010 (MC2010).

Effect of biochar on compressive strength and fracture performance of concrete

The production of cement aggravated the release of CO2 into the atmosphere. The replacement of cement by carbon neutral biochar will reduce CO2 emissions. In this study, therefore, the effects of biochar addition and age on compressive strength and fracture performance of concrete were investigated. The results revealed that the compressive strength, load bearing capacity, and initial fracture toughness of biochar-modified concrete increased firstly and then decreased with the increase of biochar addition. 1 wt% replacement of cement with biochar was identified as the optimal content in terms of compressive strength. For three-point bending beams, the biochar-modified concrete with 3 wt% replacement of cement with biochar showed better load bearing capacity and crack resistance, and the damage scale was lower at the same loading stage. The biochar addition reduced the ductility of concrete and fracture energy. When the biochar addition was 3 wt%, the fracture energy of biochar-modified concrete at different ages (7d, 14d and 28d) reduced by 3.6%, 33.3% and 33.2%, respectively, compared with that of plain concrete. The compressive strength, load bearing capacity and initial fracture toughness gradually increased with the increase of curing time. The replacement of cement by biochar promoted the compressive strength and fracture performance of concrete, which provided a CO2-reducing way for the production of concrete.

Compressive and flexural toughness indices of lightweight aggregate concrete reinforced with micro-steel fibers

There remains a lack of comprehensive investigations examining ductility of the fiber-reinforced lightweight aggregate concrete (LWAC) elements, necessitating a deeper exploration. The purpose of this study is to assess the effect of micro-steel fibers on the compressive and flexural toughness capacities of LWAC. A total of twenty-one LWAC mixtures were prepared, varying the test parameters of the compressive strength of concrete and fiber volume fraction. The toughness capacities of fiber-reinforced LWAC were calculated using the stress–strain curves in compression and flexural load–deflection curves measured for each specimen, in accordance with ASTM C1018. These were compared with those of the previous normal-weight concrete and LWAC specimens reinforced by single macro-steel fibers or a combination of macro-steel fibers and micro synthetic fibers. The effect of numerous fiber parameters on the toughness of concrete was considered as a function of the fiber reinforcing index. Simple closed-form equations from the literature were modified to reliably determine the compressive and flexural toughness indices of micro-steel fiber-reinforced LWAC. Additionally, the relationship between equivalent flexural strength ratio and flexural toughness indices was formulated from a regression analysis using test datasets. Test results showed that the addition of only 0.25% micro-steel fibers significantly enhanced strength and toughness in compression and flexure. Moreover, better dispersion of steel microfibers enabled greater LWAC strength and toughness increases through a denser restriction of crack propagation.

Experimental study on fracture and acoustic emission properties of internally cured concrete with super absorbent polymer subjected to high temperature

The three-point bending experiment was conducted on notched beams containing five different SAP contents to investigate the influence of high temperature on the fracture performance of Superabsorbent Polymer (SAP) concrete. Acoustic Emission (AE) technology was employed to monitor real-time crack propagation, and scanning electron microscopy (SEM) was utilized to analyze the micro-pore structure. The experimental results reveal the following findings. After exposure to high temperatures, the peak strength of SAP concrete continuously decreases. Compared to specimens at 20 °C, the strength loss after exposure to temperatures of 200 °C, 400 °C, and 600 °C is approximately 11%, 55%, and 87%, respectively. However, the introduction of SAP can reduce the proportion of strength loss in the concrete. Additionally, SAP improves the toughness of the concrete, with an increase in ductility coefficient ranging from 4.0 to 6.8 times as the loading temperature increases. Similar to the strength variation pattern, the initial fracture toughness of SAP concrete exhibits a significant decrease with increasing heating temperature. The loss in initiation toughness after exposure to temperatures of 200 °C, 400 °C, and 600 °C is approximately 11%, 42%, and 85%, respectively, while the loss in unstable fracture toughness is 11%, 46%, and 74%. Based on the experimental results, this study proposes two temperature-dependent fitting models for the peak strength and fracture toughness of SAP concrete, which are compared and validated with the experimental results. SEM analysis reveals a loose and porous internal structure in SAP concrete. Through the analysis of AE signals at different temperatures, the fracture process is elucidated based on the b-value method. Moreover, RA-AF analysis indicates that an increase in temperature reduces the proportion of tensile-type cracks in specimens with the same SAP content. From the temperature loaded results spanning 20 °C–600 °C, the proportion of tensile cracks decreases from 80% to 50%, indicating a transition in the failure mode from tension to shear. However, this trend is not significantly affected by the temperature increase, suggesting that the failure mode of the specimens is primarily determined by the internal pore structure of the concrete rather than the temperature load. The research findings provide experimental evidence for the application of SAP concrete in engineering projects.

Experimental study on recycled steel fiber-reinforced concrete under repeated impact

Abstract Recycled steel fiber comes from the waste produced by machining. Adding recycled steel fiber into concrete can significantly enhance the toughness of concrete. In order to study the impact toughness of recycled steel fiber-reinforced concrete, the drop weight repeated impact experiment method was used to study the performance of recycled steel fiber-reinforced concrete under repeated impact load. Four kinds of recycled steel fiber-reinforced concrete samples with different volume contents were designed and made, and the loading impact experiments under five working conditions were carried out. Taking the drop weight and drop height as changing parameters, the corresponding blow counts of the first crack and sample failure under the impact of the drop hammer are recorded, and the ductility coefficients of different samples are calculated. The results show that the impact resistance of the sample decreases significantly with the increase of the drop weight and drop height. With the increase of recycled steel fiber content, the impact toughness of the sample increases obviously. The impact toughness of recycled steel fiber-reinforced concrete under standard loading conditions is the best.

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.

Effect of Coarse Aggregate Grading on Mechanical Parameters and Fracture Toughness of Limestone Concrete

This work presents a discussion of the basic properties of broken mineral limestone aggregates with the specification of the properties affecting the fracture toughness of concretes made with these aggregates. To determine the influence of the grain-size distribution of coarse aggregates for each concrete series, two types of aggregate grain were used, with maximum grain sizes of 8 mm (series of concrete L1) and 16 mm (series of concrete L2). Fracture-toughness tests were carried out using mode I fractures in accordance with the RILEM Draft recommendations, TC-89 FMT. During the experiments the critical stress-intensity factor (KIcS) and crack-tip-opening displacements (CTODc) were determined. The main mechanical parameters, i.e., the compressive strength (fcm) and splitting tensile strength (fctm), were also assessed. Based on the obtained results, it was found that the grain-size distribution of the limestone aggregate influenced the concrete’s mechanical and fracture-mechanics parameters. The obtained results showed that the series-L2 concrete had higher strength and fracture-mechanics parameters, i.e.,: fcm—45.06 MPa, fctm—3.03 MPa, KIcS—1.22 MN/m3/2, and CTODc —12.87 m10−6. However, the concrete with a maximum grain size of 8 mm (series of concrete L1) presented lower values for all the analyzed parameters, i.e.,: fcm—39.17 MPa, fctm—2.57 MPa, KIcS—0.99 MN/m3/2, and CTODc —10.02 m10−6. The main reason for the lower fracture toughness of the concretes with smaller grain sizes was the weakness of the ITZ in this composite compared to the ITZ in the concrete with a maximum grain size of 16 mm. The obtained test results can help designers, concrete producers, and contractors working with concrete structures to ensure the more conscious composition of concrete mixes with limestone aggregates, as well as to produce precise forecasts for the operational properties of concrete composites containing fillers obtained from carbonate rocks.

Experimental study on using recycled polyethylene terephthalate and steel fibers for improving behavior of RC columns

In this research, the behavior of RC columns reinforced with recycled polyethylene terephthalate (PET) fibers and steel fibers (SFs) was experimentally investigated. The experimental work included testing of 8 columns with the dimensions of 150 × 150 × 1000 mm subjected to the axial loading up to failure. Three volume fractions (1%, 2%, and 3%) were considered for both PET fibers and SFs. The axial/lateral displacements of the columns and the transverse/vertical strains versus the loads of the bars were recorded. The peak load, yield load, failure mode, ductility, and stiffness of the columns were studied in detail. The effects of plastic fibers (PFs) and SFs on the concrete characteristics were experimentally examined. Using 2% SFs in the mix increased the compressive strength, tensile strength, and toughness of concrete by 12.7%, 87.6%, and 304.8%, respectively. Furthermore, enhancement rates of the ultimate load capacity, stiffness, and ductility of the columns with 2% SFs were 15.6%, 72.6%, and 34.29%, respectively. The ultimate load capacity, initial stiffness, and ductility of the columns reinforced with 1% PF fiber were 9.43%, 62.6%, and 19.4%, respectively, greater than those of the columns without fibers. The columns’ capacity was decreased with increasing SFs and PFs over 2%. An equation from ACI was used to predict the columns’ capacity and the results agreed well with the experimental results.

Experimental study on compressive behavior and failure characteristics of imitation steel fiber concrete under uniaxial load

The concrete columns suffer from spalling and flaking in the room and pillar mining method, which affects service performance. The energy absorption and deformation failure laws of fiber concrete structures under compression load need further study. In this study, four types of imitation steel fiber concrete specimens were prepared, and uniaxial compression experiments were carried out. Simultaneous photographic and acoustic emission monitoring was conducted to investigate the compression energy absorption, crack evolution, fracture surface fractal and RA/AF value characteristics of fiber concrete. The results obtained in the present work are as follows. Imitation steel fiber concrete showed the best compressive and energy absorption performance with a 0.4–0.6% fiber/mortar mass ratio. A higher dosage of fibers prolonged the yield time but also led to earlier macroscopic cracking. The bond between imitation steel fiber and matrix can disperse the stress, which significantly improved the toughness of concrete. For every 0.2% increase in fiber content, the pre-peak toughness index CTI and post-peak damage absorption energy FCEC increased by about 10% and 50%, respectively. Both plain concrete and fiber concrete specimens developed macroscopic cracks under local tensile stresses. The proportion of shear fracture in plain concrete reached 80.1% and dominated during the secondary crack development. The proportion of tension and shear fracture in fiber concrete was less disparate and showed a mixed pattern with synergistic action. The proportion of shear fractures gradually increased with the increase in fiber content. The calculated results of the RA/AF method corresponded well with the crack morphology. With the increase in fiber content, the bridging effect of fiber became more obvious, and the ability of specimens to resist cracking improved significantly. The fractal characteristics of the fracture surface of each specimen were investigated. The plain concrete specimens had a relatively complete surface when destroyed, and their fractal dimension was only 1.62, the lowest among all the specimens. The surface of fiber concrete was more fragmented, and their fractal dimension was higher, with the fractal dimension D increasing by 0.2–0.4 for each 0.2% increase in fiber content. This study can provide a reference for the fiber concrete pillar designs.