Cracking Stage Research Articles

Effect of Using ECC Layer on the Flexural Performance of RC Beams Previously Strengthened with EB CFRP Laminates

This paper studies the efficiency of applying an engineered cementitious composite (ECC) layer to the tensile surface of (RC) beams that were previously strengthened using externally bonded (EB) carbon fiber-reinforced polymer (CFRP) laminates. One control and ten strengthened RC beams were produced and tested utilizing a four-point loading regime. For strengthened beams, two beams were kept strengthened using only CFRP, and additional ECC layers were added to the rest of the strengthened beams. The CFRP width and overlap length and position were among the test factors. Experimental results revealed that strengthening RC beams with CFRP laminates enhanced both the stiffness and flexural capacity of beams. Additional enhancements were obtained through the application of the additional ECC layers. The existence of the ECC layer alongside the CFRP laminate improved the flexural capacity by 102% and 125% when using CFRP widths of 50 mm and 100 mm, respectively, and the stiffness was improved by an average value of 318%. Three-dimensional (3D) finite element models (FEMs) were developed using ABAQUS software and verified against the experimental results to model the response of the tested beams. The verified model was used to conduct a parametric study to consider the effect of the ECC layer thickness and the reinforcement ratio on the strengthened beam behavior. The numerical results revealed that the effect of the reinforcement ratio was more significant than the ECC layer thickness in enhancing the load-displacement response, especially after the cracking stage.

Torsional behavior of GFRP-reinforced concrete pontoon decks with and without an edge cutout

Using glass fiber-reinforced polymer (GFRP) bars in precast concrete pontoon decks in aggressive marine environments would eliminate corrosion problems encountered with steel reinforcement. Although wave action usually subjects pontoon decks to torsion, but little is known about the behavior of such structures. Moreover, nothing is known about the effects of cutouts on the torsional behavior of pontoon decks. This study experimentally investigated the torsional behavior of GFRP-reinforced concrete (RC) pontoon decks in terms of the effect of edge cutouts, reinforcement-bar distribution, and rotation direction. The results show that the bar configuration affected the failure behavior and torsional capacity of the GFRP-reinforced concrete decks under torsion. The decks with double-layer reinforcement exhibited slower and narrower cracking growth in the post-cracking stage than the decks with single-layer reinforcement. In addition, the edge cutouts reduced the cracking torque of the solid rectangular decks by an average 17%. The torsional behavior of the GFRP-reinforced planks can be accurately described by the ACI318-14 equation in the cracking stage, while the decks’ post-cracking torsional rigidity can be predicted accurately from the contribution of the GFRP bars.

Morphological and mechanical characterization of reinforcement in cracked elements exposed to chloride-induced corrosion

In Reinforced Concrete (RC) structures exposed to chloride-rich environments, reinforcement corrosion might be already initiated (especially at crack location). A deep knowledge on the correlation between the mechanical properties of corroded bars and corrosive attack morphology, useful for the evaluation of the residual bearing capacity of structure, is still lacking. In this paper, morphological and mechanical characterization of steel reinforcement embedded in RC specimens (with and without fibers) both in cracked stage and subjected to cyclic exposure to a 5 % NaCl solution for 280 days was carried out. Although a chloride content higher than the critical chloride threshold was also measured in correspondence of uncracked concrete, corrosive attacks were observed only in correspondence of cracks. Pits were mostly characterized by a shallow morphology, which led to a rebar diameter loss ranging between 1 and 10 %. Furthermore, the results showed that both yielding and ultimate load of corroded rebars can be predicted by combining circular residual cross-section and mechanical properties of uncorroded rebars.

Kinetic study of asphaltenes phase separation in supercritical water upgrading of heavy oil

Supercritical water upgrading heavy oil is a promising way to produce light oil and gas. To understand the reactions pathways and the role of supercritical water during the upgrading process, experiments were carried out in a batch reactor at 380–440 °C and reaction times up to 2900 min. The products were classified as gas, coke and liquid products which were further separated into saturates, aromatics, resins and asphaltenes. A kinetic model including aromatics and resins partially dissolved in both supercritical water phase and oil phase was developed. This model could fit experimental data well and interpret effects of supercritical water solubility for aromatics and resins on heavy oil upgrading process. Further, supercritical water upgrading process was divided into three stages: pre-induction primary cracking stage, post-induction primary cracking stage and gas-generation stage. This work provides an in-depth understanding of mechanism of heavy oil upgrading in supercritical water.

Matrix and fabric contribution on the tensile behaviour of fabric reinforced cementitious matrix composites

Fabric reinforced cementitious matrix (FRCM) are a type of sustainable materials for structures strengthening and envisaging to develop new construction solutions. However, the wide range of possible combinations of fabric and cementitious matrixes makes it necessary to study the particular contribution of mortar and fabric in the composite action of the FRCM. In this line, this study presents the experimental, analytical and numerical evaluation of the tensile behaviour of FRCM composites. 85 FRCM specimens of different thicknesses were manufactured, with one or two embedded fabrics of different type of fibres and geometry. Fabrics made of coated vegetal fibres were also considered to be compared with commercial fabrics of coated synthetic fibres. The results show a significant increase of the ultimate tensile strength with the increase of the FRCM thickness due to a residual contribution of the mortar after the cracking stage. The analytical model was effective for the cases that showed a cracking stabilization stage. However, the numerical model allows a closer approximation to experimental results because of considering the mortar contribution in the post-cracking stage.

Mechanical properties of concrete containing recycle concrete aggregates and multi-walled carbon nanotubes under static and dynamic stresses

The growing demand for natural aggregates in the construction industry has motivated researchers to utilize recycled concrete aggregates (RCA) to preserve the natural resources and provide sustainable structure. However, the use of RCA in concrete applications has revealed defects in performance with low strength and rapid collapse under static and dynamic loads, respectively. Thus, the objective of present research is to improve these properties by using multi-walled carbon nanotubes (MWCNT). This study involves evaluating the fresh and hardened properties of recycled aggregate concrete (RAC) modified with different levels of MWCNT. The study involves RCA (i.e., 0 %, 25 %, 50 %, 75 % and 100 %) as replacement for natural aggregates, and MWCNT (i.e., 0.05 %, 0.1 % and 0.25 %) as weight of cement. The experimental testing consists of 240 specimens prepared from different mixtures. Workability is assessed using slump tests. Mechanical properties including static compressive strength and dynamic impact resistance are evaluated at 7 and 28 days. Experimental results show that incorporating MWCNT at all levels significantly reduces the slump values for all specimens. On the other hand, the compressive strength is increased by adding MWCNT to the concrete samples. The compressive strength of the RAC increased by as much as 70 % when modified with MWCNT. Furthermore, the inclusion of MWCNT is found to significantly increase the impact resistance of RAC specimens with percentage developments reaching approximately 11–508 % and 110–679 % at 7 and 28 days, respectively, at both first crack and failure stages. The dosage of 0.1 % MWCNT is shown to exhibit the highest percentage enhancement in impact resistance among the other nano levels. The failure patterns and cracks propagation are presented as well.

Environment-Assisted Crack Initiation in Aluminum Alloys Studied by Local Probe Techniques

Environment-assisted crack initiation in aluminum alloys is strongly related to the physical and chemical reactivity of intermetallic particles (IMPs) whatever their location, i.e., at grain boundaries or in the matrix. Therefore, this paper first focuses on the most recent contribution of microscale local probe techniques to the study of processes occurring at the coarse IMPs that need to be taken into account in the initiation stage of environment-assisted cracking (EAC). A critical review of microscale electrochemistry, chemistry, and analysis of the influence of stress on IMPs leading to the microscale analysis of crack incubation is presented. Moreover, the contribution of hydrogen to the initiation of EAC remains a widely debated issue. Therefore, the second part of this paper more specifically reviews and summarizes the contribution of some specific local probe techniques to a better understanding of the contribution of hydrogen enrichment to environment-assisted crack initiation. The remaining challenges in future studies needed to fully elucidate hydrogen-assisted cracking mechanisms at the microscale are discussed.

Bulk and intramolecular carbon isotopic compositions of hydrocarbon gases from laboratory pyrolysis of oil shale of the Green River Formation: Implications for isotope structures of kerogens

Evaluation of intramolecular isotope distributions within organic compounds can provide important insights into gas formation processes and structural properties of gas-generating precursors, such as kerogen, bitumen, and oil, in natural reservoirs. Until recently, little has been known about the intramolecular isotope distributions within kerogens. In this study, we conducted systematic pyrolysis experiments of gas generation from a lacustrine oil shale of the Eocene Green River Formation under hydrous and anhydrous conditions (equivalent maturity or Easy %Ro: 0.76 to 3.27 at 310 to 480 °C for 3 to 50 days), measuring gas yields and compositions, as well as bulk and position-specific (PS) carbon isotope compositions. Gas generation processes were investigated in combination with kinetic Monte Carlo (kMC) simulations on a model Type I kerogen based on the chemical structures of oil shale of the Green River Formation. The comparison of our experimental results with kMC modelling indicates a series of β-scission, radical isomerization, and recombination reactions better represent the bulk isotope compositions of propane in the pyrolysis of the oil shale of the Green River Formation, but the ΔCc-t (= δ13Ccen – δ13Cter) values of propane at Easy %Ro > 1.5 can be better simulated by a simple combination of propyl groups with H radicals. Combining our previous works on marine shale of the Woodford Formation and Springfield Coal Member of the Carbondale Formation, PS carbon isotopes of propane indicate that in the lacustrine shales of the Green River Formation and the marine Woodford Shale, propane is sourced from CC bond cleavage, while CO bond cracking generates propane from coal at the initial kerogen cracking stage. At high maturity, the differences of late-stage propane production among the source rocks lead to the different bulk and PS C kinetic isotope effects of propane. Our findings suggest that the δ13C at the terminal position of propane precursors is likely up to 3.6‰ higher than at the central position in the Green River kerogen, while they are similar in the marine shale of Woodford Formation. In addition, the δ13C at the central position of propyl groups attached to heteroatom compounds is relatively more positive in the Springfield Coal Member of the Carbondale Formation than in Green River kerogen. A comparison of intramolecular C isotopes of propyl groups in the kerogens with their bulk δ13C, based on the PS δ13C of early-generated propane, contributes to our understanding of heterogeneities of isotopic structures of sedimentary organic matter.

Investigation of the sulfur enrichment mechanism on the catalyst in the FCC process of waste tire pyrolytic oil

The high sulfur content of polymer solid waste (like waste tires) pyrolytic oil limits its application as feedstock in fluidized catalytic cracking (FCC), while there are fewer studies on the effect of sulfur on catalysts. To explore the mechanisms of sulfur enrichment on the catalyst, the distribution characteristics of sulfur in the spent catalysts were investigated and the conversion behavior of sulfur during the FCC process of the waste tire pyrolytic oil was analyzed. The results showed that the species of sulfur in the catalyst before and after the FCC process could be well distinguished by using combined physicochemical analysis method. Sulfur mainly existed in the form of sulfates in the spent catalysts and part of the sulfur was confirmed to be bound to the catalysts matrix. The enrichment of sulfur in the catalysts was probably due to the direct and indirect migration of sulfur compounds in waste tire pyrolytic oil in the catalytic cracking stage, rather than SO2 adsorption on the catalyst in the flue gas purification stage. Furthermore, it was suggested that the sulfur-containing compounds reacted with the oxygen-containing functional groups to form sulfones and/or sulfates on the surface of the catalysts. These findings contribute to the clean utilization of solid waste and to a better understanding of the catalyst deactivation mechanism in the FCC processes.

A practical approach for monitoring reinforcement corrosion in steel fiber reinforced concrete elements exposed to chloride rich environments

AbstractThe use of fibers in Reinforced Concrete (RC) elements changes their cracking pattern, leading to narrower and more closely spaced cracks. In addition, the presence of fibers can improve the steel‐to‐concrete bond behavior reducing the steel‐to‐concrete interface damage after cracking. Cracks and steel‐to‐concrete interface damage work like paths, for aggressive agents, to reach the rebar in cracking elements, reducing the initiation period of the corrosion process, and favoring the corrosion at the intersection between cracks and reinforcement. In this context, this article discusses an experimental program on tension ties mechanically cracked and exposed to a chloride‐rich environment with the purpose to check and eventually adequate the typical electrochemical measurements, used in the case of RC elements, for Steel Fiber Reinforced Concrete (SFRC). Adjustments related to degradation morphology and interference of steel fibers are proposed and used on Fiber Reinforced Concrete (FRC) elements for monitoring the influence of cracks and fibers on corrosion propagation. Finally, these proposed modifications were checked and validated against the results obtained by monitoring SFRC beams in the cracked stage.

Multi-mode fusion BP neural network model with vibration and acoustic emission signals for process pipeline crack location

Vibration fatigue occurs easily in offshore platform pipelines that have been in service for several years. Timely damage detection and the detection of fatigue cracks are of great significance to ensure safe production. To accurately locate pipe cracks, a multi-mode fusion crack location model is proposed in this paper. The model combines two location methods based on vibration signals and acoustic emission (AE) signals through a backpropagation (BP) neural network. The natural frequencies of a large number of crack models at different locations were obtained by combining vibration modal test and finite element simulation results. A large number of acoustic emission signal time differences of cracks at different positions were obtained by simulating the acoustic emission signals at the initiation and propagation stages of cracks with the pencil-lead break method. The multi-mode fusion model was trained by experimental and simulation data, and the positioning effect of the model was verified. The results showed that training the neural network based on multi-mode data could effectively avoid the over-fitting of the network and improve the training effect. Compared with the method based on single information or only a weighted average method, this model could effectively improve the accuracy of crack location and reduce the fluctuations of the location errors, and the location results were more reliable.

Post-High-Temperature Exposure Repeated Impact Response of Steel-Fiber-Reinforced Concrete

The response of plain and fibrous concrete to the scenario of fired structures exposed to repeated impacts from falling fragmented building elements and other objects is experimentally investigated in this study. The experimental program included the casting and testing of specimens with 0%, 0.5%, and 1.0% hooked-end steel fibers (SFs) under the ACI 544-2R repeated-impact test. The impact test was conducted using cylindrical disk specimens, while 100 mm cubes were used to evaluate the residual compressive strength and weight loss. From each mixture, six disks and three cubes were heated to high temperatures of 200, 400, and 600 °C, while a similar set of specimens were tested without heating as a reference group. The results show that SF could significantly improve cracking impact resistance and dramatically boost failure impact numbers. The retained percentage improvements were the highest for specimens heated to 600 °C, which were approximately 250% at the cracking stage and 1680% at the failure stage for specimens with 1.0% SF. The test results also show that the repeated-impact resistance dramatically deteriorated at high temperatures, where the maximal residual cracking and failure impact numbers after exposure to 200, 400, and 600 °C were approximately 20% and 40%, 4% and 7%, and 2.2% and 4%, respectively.

Resistivity Response of Thermally Treated Granite During the Compression Test.

To determine the stress and damage state of rock mass is important for many geotechnical engineering. To study the feasibility of resistivity measurement in characterizing the damage and stress state, the resistivity measurement, uniaxial compression test, and incremental loading–unloading compression test were carried out on granite samples with different porosities (induced by different treatment temperatures). Results show that the resistivity is very sensitive to thermal damage and mechanical damage during compression. The evolution of resistivity can not only quantify thermal damage but also clearly indicate the critical stress (crack closure stress and crack damage stress) and damage stage during compression. In addition, the resistivity evolution was quite different in the pore closure stage, elastic deformation stage, and unstable cracking stage during the loading–unloading process, which is useful in field stress and damage state identification for field monitoring. The conductive mechanism variation during compression was discussed using the Archie equation considering crack volume strain evolution during the mechanical damage process. Overall, the resistivity measurement holds great potential in geotechnical engineering for field monitoring.

Research on the Evolution of Shield Segment Cracks Based on Acoustic Emission and CMOD.

In order to explore the cracking law and failure characteristics of segments, a model test of shield segment cracking was conducted. The microscopic and macroscopic crack evolution process of the segment is studied by using acoustic emission detection technology and crack opening displacement (CMOD). According to the acoustic emission signal and CMOD, characteristics generated in the process of segment cracking, in the form of numerical value, the evolution characteristics of each stage of segment cracking are directly reflected. Based on acoustic emission energy and CMOD, the segment cracking damage model was established to determine the segment fracture damage degree. The result shows that segment cracking can be divided into three stages, and the acoustic emission detection results and CMOD have different degrees of change in each cracking stage. This proves that both the acoustic emission acquisition results and CMOD can be used as evaluation indicators of damage degree. Acoustic emission can accurately identify the crack evolution process, and the yield strengthening is an important stage of crack damage evolution. The damage data points in this stage account for 76.83% of all the damage data points, the occurrence rate of damage data points is 0.225 s, and the density of data points in the damaged area is 3.219 × 10−4 mm3, which is larger than the other two stages. The segment cracking damage model can effectively reflect the segment cracking degree and provide a reference for the actual segment cracking assessment.

Kinetic and equilibrium reactions on natural and laboratory generation of thermogenic gases from Type II marine shale

The phenomenon that laboratory pyrolysis experiments produce much wetter gases than those in natural reservoirs is a long-recognized and debated problem in the investigation of natural gases in sedimentary basins. In this study, we explore the discrepancy by pyrolyzing a type II kerogen from the Woodford Shale in Oklahoma, compared with the previous results on the produced natural gases from the Arkoma Basin generated from the same source rock (Liu et al., 2019) with the discussion of gas and isotopic compositions at bulk and position-specific (PS) levels. An improved GC-pyrolysis-GC IRMS method is applied for the determination of PS δ13C of propane produced in the pyrolysis of the Woodford Shale at Easy %Ro from 0.76 to 3.27. Kinetic and thermodynamic considerations of the chemical and isotopic compositions of the natural and laboratory pyrolysis gases suggest that the generation of light hydrocarbons involves uni-directional cracking reactions, exchange reactions with water, and likely reversible reactions among light hydrocarbons and other H-containing volatiles. After the gas generation in the unconventional Woodford Shale reservoirs, the C1-C4 gases might have approached close to chemical equilibrium of C1-C3 and isotope equilibrium of C2-C1 and C3-C1 pairs at their peak temperatures. The capping H for the generation of C1-C4 in the Woodford Shale gases appears to have experienced at least partial exchange with the water, while that in the pyrolysis gases is only originated from organic-bound compounds with large kinetic isotope effects (KIE). Our findings indicate that elevated compound-specific and PS δ13C values of propane in the wet-gas cracking stage are significantly influenced by the breakdown of the thermally stable compounds (e.g., remaining kerogen, residues). A first synthesis of PS δ13C and δ2H isotopic compositions of propane from this study and the literature data suggests relatively similar isotopic structures of propane precursors in kerogens. This study demonstrates that PS isotope analysis of propane can contribute to identifying various geological (e.g., maturation, wet-gas cracking, H exchange, diffusion) and biodegradation processes.

Gas generation and intramolecular isotope study in laboratory pyrolysis of the Springfield coal from the Illinois Basin

Position-specific (PS) isotopes of propane have been proposed as a potential geochemical tool to decipher various geological processes (e.g., thermal cracking, biodegradation, H exchange) in natural reservoirs. The limited studies have been conducted on the PS isotopes of propane from the pyrolysis gases from marine shales, and natural gases sourced from lacustrine and marine kerogens, but little is known on gases produced from the humic kerogen. This study investigated the PS δ13C of propane in the closed-system pyrolysis of the Springfield coal, Illinois Basin, Indiana, at 310 to 470 °C (Easy %Ro: 0.76 to 3.07). The C kinetic isotope effect (KIE) of CH4 produced in both this study and previous low-temperature pyrolysis of the same coal indicates the cleavage of CO bonds is the main generation pathway at the early kerogen cracking stage, followed by the breakdown of alkyl groups. At the wet-gas cracking stage, C3H8 production from thermally stable compounds has a significant influence on the bulk and position-specific C KIE in the pyrolysis of marine Woodford kerogen and Springfield coal. According to the PS δ13C of propane, the central site is likely more enriched in 13C and the δ13C of the terminal site is relatively heterogeneous within the propyl group attached to different functional groups of the gas-prone kerogen. Our findings based on the pyrolysis experiments and natural gas samples indicate thermal cracking and biodegradation appear to alter the δ13Ccen values more significantly than the δ13Cter values of propane. The larger magnitude of ΔCc-t in the kMC simulations (Peterson et al., 2018) compared with those from the marine shale and coal possibly implies the non-random distributions of 13C of propane precursors in the kerogens. As a new dimension of intramolecular isotopic information of propane, the PS δ13C values can contribute to fingerprinting the gas origins and identifying the various geological processes (e.g., kerogen cracking, wet-gas cracking, microbial activities) in sedimentary basins.

An Investigation into the Densification-Affected Deformation and Fracture in Fused Silica under Contact Sliding.

Subsurface damage of fused silica optics is one of the major factors restricting the performance of optical systems. The densification-affected deformation and fracture in fused silica under a sliding contact are investigated in this study, via three-dimensional finite element analysis (FEA). The finite element models of scratching with 70.3° conical and Berkovich indenters are established. A refined elliptical constitutive model is used to consider the influence of densification. The finite element models are experimentally verified by elastic recovery, and theoretically verified by hardness ratio. Results of densification and plastic deformation distributions indicate that the accuracy of existent sliding stress field models may be improved if the spherical/cylindrical yield region is replaced by an ellipsoid/cylindroid, and the embedding of the yield region is considered. The initiation sequence, and the locations and stages of radial, median, and lateral cracks are discussed by analyzing the predicted sliding stress fields. Median and radial cracks along the sliding direction tend to be the first cracks that emerge in the sliding and unloading stages, respectively. They coalesce to form a big median–radial crack that penetrates through the entire yield region. The fracture behavior of fused silica revealed in this study is essential in the low-damage machining of fused silica optics.

Experimental study of reinforced concrete beams reinforced with hybrid spiral-hooked end steel fibres under static and impact loads

Discrete short steel fibres were proposed to be mixed with concrete for arresting cracks and enhancing the post-cracking resistance. It has been proven in previous tests that spiral steel fibres possessed markedly higher bonding to concrete matrix, leading to significantly improved performance of steel fibre reinforced concrete (SFRC) in terms of crack controllability, impact resistance, deformability and energy absorption capability. However, at the initial stage of cracking, SFRC reinforced with spiral fibres has relatively lower resistance to crack opening as compared to that reinforced with other types of steel fibres because of spiral shape stretching. To overcome this shortcoming, in the present study, short hooked-end steel fibres that exhibit high pull-out resistance at the crack initiation stage were mixed with spiral steel fibres in the normal-strength concrete matrix. A total volume fraction of 1% of hybrid steel fibres was mixed to cast SFRC specimens. With various mix ratios between spiral and hooked-end fibres considered, five batches of SFRC specimens were tested. Uniaxial compressive tests and four-point bending tests were carried out to compare the mechanical properties of SFRC materials with hybrid fibres while three-point bending tests on SFRC structural beams under static, drop-weight impact and post-impact static loading tests were conducted to investigate the structural performances. An equal dosage of hooked-end and spiral fibres was found to outperform other blend proportions to provide synergetic reinforcement to concrete matrix in terms of post-cracking resistance, energy absorption capacity and post-impact performance.

Influence of Clay Content on Crack Evolution of Clay–Sand Mixture

Clay particles have an important influence on the cracking of clay–sand mixture, but the quantitative relationships between the clay content and crack evolution of the clay–sand mixture are still not clear. In order to explore the crack evolution process of the clay–sand mixture under different clay content conditions, we prepared nine groups of saturated clay–sand mixture samples with different clay contents and carried out drying experiments and Brazilian tests. The geometric dimensions and development forms of soil cracking were quantitatively analyzed by taking pictures of the sample cracks, image processing, and weighing the variation of the soil mass at the corresponding time during the drying process. The results showed that when the clay content was greater than 50%, the development process of the clay–sand mixture cracks can be divided into three stages: the formation stage of main cracks, the generation stage of the autonomously derived secondary fractures, and the stage of cracks widening. When it was less than 50%, the cracks in the development process of clay–sand mixture cracks had the characteristics of short length, dense crack spacing, no main cracks, and no obvious stage. The clay could add the tensile strength of the mixture and restrain crack development. The clay content had a significant effect on the shrinkage cracking and crack development process of soil, which shows that with the increase in the clay content, the tensile strength increases and restrains the crack development; the crack rate increases continuously and the width of cracks become larger; the lower the clay content, the lower is the crack rate and the smaller is the average crack width. The water content of samples with different clay soil contents all nonlinearly decreased with the increase in drying time, and the corresponding residual water content increased with the increase in the clay soil content at the same time. The water content of initial cracking, stable crack length, stable crack width, and stable block of the clay–sand mixture increased with the increase in the clay content, and the water content of the stable crack length was the same as that of the stable block number.

Experimental Research on Fracture Characteristics of Reactive Powder Concrete in Different Volume Content of Steel Fiber

The fracture characteristics of reactive powder concrete in different volume content of steel fiber are researched in this paper, combining with the photoelastic coating method and the mathematical analytical software MATLAB. More precisely, the wholly integrated initiation, stable propagation, and final failure stages of precast cracks in three-point bending specimens of reactive powder concrete in different volume content of steel fiber are directly recorded and systematically analyzed. Besides, the photoelastic fringe distribution graphs from the vicinity of the precast cracks of specimens are obtained. Based on the experimental results and fracture mechanics theory, the mechanical property of reactive powder concrete, fracture energy, ductility index, initial fracture toughness, and unstable fracture toughness are quantitatively and qualitatively analyzed. The research achievements indicate that there is a stable crack propagation process before the instability failure of the three-point bending beam specimen of reactive powder concrete. The fracture process of the structure includes three stages, namely, the crack initiation, stable propagation, and instability failure. The order of the photoelastic fringe, critical effective crack length, crack initiation load, and maximum load of test parameters in the three-point bending beam specimen of reactive powder concrete increases with the increase of the fiber volume ratio. Based on the numerical treatment for the whole curves of each specimen group, the softening curve and the double fracture parameters of reactive powder concrete are obtained. Besides, the calculated critical effective joint length, initiation toughness, toughness increment, and unstable fracture toughness increase with the increase of the steel fiber volume ratio, by analyzing the measured initiation load, maximum load, and critical effective joint length. The research results can be treated as an important basis and reference for the engineering design and safety assessment of reactive powder concrete.