Method for analyzing impact resistance of nano-toughened ultra-high performance concrete

Abstract

The application provides a kind of nano toughening super high performance concrete impact resistance performance analysis method, it is related to hydraulic engineering material analysis technical field, including: preparation nano toughening super high performance concrete sample;Through impact resistance test to the sample of nano toughening super high performance concrete, mass loss test result is obtained;Wherein the impact resistance test is provided with several groups of different test parameters;Through nano indentation test to the sample of nano toughening super high performance concrete carries out micro test, the micro test result is analyzed, and micro fracture toughness evaluation result is obtained, the analysis of the impact resistance performance of multi-dimensional nano toughening super high performance concrete can be carried out.

Description

Technical Field

[0001] This invention relates to the field of hydraulic engineering material analysis technology, and more specifically, to a method for analyzing the impact and abrasion resistance of nano-toughened ultra-high performance concrete. Background Technology

[0002] Existing methods for analyzing the impact and abrasion resistance of concrete have the following shortcomings: traditional testing methods, such as the sand-blowing gun method, the underwater steel ball method, and the rotary abrasion method, cannot realistically simulate the impact-cutting composite damage process of high-speed sand-laden water flow on concrete, and the test condition parameters are limited to a single setting, making it impossible to simulate the actual situation by combining multiple parameters in various ways; at the same time, the evaluation index is limited, making it impossible to analyze the multi-dimensional impact and abrasion resistance of nano-toughened ultra-high performance concrete. Summary of the Invention

[0003] In view of this, the present invention proposes a method for analyzing the impact and abrasion resistance of nano-toughened ultra-high performance concrete to solve the problems existing in the prior art.

[0004] To achieve the above objectives, this invention proposes a method for analyzing the impact and abrasion resistance of nano-toughened ultra-high performance concrete, comprising: Samples of nano-toughened ultra-high performance concrete were prepared. The nano-toughened ultra-high performance concrete samples were tested by impact and grinding failure test to obtain mass loss test results; the impact and grinding failure test was set with several different test parameters. Microscopic tests were conducted on samples of nano-toughened ultra-high performance concrete using nano-indentation tests. The results of these microscopic tests were analyzed to obtain an assessment of the microscopic fracture toughness.

[0005] Optionally, the preparation process of nano-toughened ultra-high performance concrete samples includes: Cellulose nanofibers were diluted in deionized water, and polycarboxylate superplasticizer was added to the diluted suspension for magnetic stirring and ultrasonic dispersion to obtain a cellulose nanofiber suspension. Cement and silica fume were stirred, and sand was added during the stirring process. After stirring, water and the suspension were added and mixed. After mixing, fiber-reinforcing material was added and stirred to set the mixture, thus preparing a sample of nano-toughened ultra-high performance concrete material.

[0006] Optionally, the process of the impact and abrasion test includes: The surface of a nano-toughened ultra-high performance concrete sample was subjected to surface impact by a high-speed sand jet abrasive jet instrument, and the mass loss test results were obtained, wherein the mass loss test results are the mass loss index of the sample.

[0007] Optionally, the test parameters for the abrasion test include abrasion angle, sand content, and flow rate.

[0008] Optionally, the process of analyzing the microscopic test results includes: Obtain microscopic test results, wherein the microscopic test results include indentation load-displacement curves and loading-unloading curves; The fracture energy is extracted and calculated from the microscopic test results. The total energy and elastic energy are obtained from the indentation load-displacement curve and the loading and unloading curve. The loading and unloading energy constants are calculated by fitting the indentation load-displacement curve and the loading and unloading curve. The fracture energy is calculated based on the loading and unloading energy constants, the total energy and the elastic energy. The fracture energy release rate is calculated based on the fracture energy, and the micro-fracture toughness assessment result is obtained based on the fracture energy release rate and the material parameters of the sample, wherein the micro-fracture toughness assessment result is the critical stress intensity factor.

[0009] Optionally, the nano-toughened ultra-high performance concrete sample is tested by abrasion test, and abrasion damage morphology image is obtained. The abrasion damage morphology image is used to visually represent the morphology of the nano-toughened ultra-high performance concrete sample after abrasion damage.

[0010] Optionally, after obtaining the mass loss test results and the microfracture toughness assessment results, the following may also be included: Based on the mass loss test results and microfracture toughness evaluation results, samples of nano-toughened ultra-high performance concrete were screened to obtain the required nano-toughened ultra-high performance concrete samples; among them, samples whose mass loss test results and microfracture toughness evaluation results exceeded the threshold were retained.

[0011] On the other hand, the present invention provides a nano-toughened ultra-high performance concrete impact and abrasion resistance analysis system for performing the above-described method.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention establishes a systematic method for analyzing the erosion resistance of nano-toughened ultra-high performance concrete, achieving the following technical effects: Firstly, a multi-condition simulation test system covering erosion angle, sand content, and erosion speed is constructed for the first time using a high-speed sand-carrying water jet method, which can realistically reflect the erosion failure process of hydraulic structures under complex service environments. Secondly, a multi-scale correlation evaluation system between macroscopic performance and microscopic fracture toughness is established. The fracture toughness of cement paste and the interface transition zone is quantitatively characterized through nanoindentation tests. Combined with X-CT three-dimensional damage morphology analysis and BSE-EDS interface morphology characterization, the intrinsic laws governing the improvement of erosion resistance by cellulose nanofibers through multiple mechanisms such as filling pores, bridging microcracks, and enhancing interfacial bonding are revealed. This provides scientific evaluation methods and technical support for the performance optimization of erosion-resistant materials for hydraulic concrete. Attached Figure Description

[0013] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. In the drawings: Figure 1 This is a schematic diagram of the sand-carrying water jet grinding process in an embodiment of the present invention; Figure 2 This is a diagram showing the depth loss of a UHPC eroded by sand-laden water with different sand contents in an embodiment of the present invention. Figure 3 This is a diagram showing the mass loss of a UHPC being eroded by sand-laden water with different sand contents in an embodiment of the present invention. Figure 4 This is a graph showing the depth loss of a UHPC being eroded by sand-laden water flow at different erosion speeds in an embodiment of the present invention. Figure 5 This is a diagram showing the mass loss of a UHPC being milled by sand-laden water flow at different milling speeds in an embodiment of the present invention. Figure 6 This is a correlation analysis diagram of grinding speed and mass loss in an embodiment of the present invention; Figure 7 This is a schematic diagram of the nanoindentation load-displacement curves and total energy, plastic properties, and elastic properties in an embodiment of the present invention; Figure 8 The load-depth curves and UHPC cement paste fracture toughness statistics of the samples in the embodiments of the present invention are shown. Figure 9 This is an X-CT analysis of wear damage profiles with different CNFs contents in an embodiment of the present invention; Figure 10 This is a wear damage profile diagram under X-CT analysis condition A1 in this embodiment of the invention. Detailed Implementation

[0014] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0015] This embodiment proposes a method for analyzing the erosion resistance of nano-toughened ultra-high performance concrete (UHPC). To systematically investigate the erosion resistance of UHPC, and addressing the problem of erosion damage to cement-based materials caused by high-speed sediment-laden water flow in hydraulic engineering, this invention is guided by simulating real-world complex working conditions. Multiple erosion damage tests are designed based on three core influencing factors: erosion angle, sediment content, and flow velocity. The erosion angle covers typical working conditions from small angles (e.g., 30 degrees) to large angles (e.g., 90 degrees), and the sediment content is set with low, medium, and high concentration gradients (e.g., 30 kg / m³). 3 55kg / m 3 100kg / m 3 The flow rate is also selected from characteristic values ​​in the high-speed range (such as 30 m / s and 40 m / s), and the grinding environment in actual engineering is fully simulated through parameter combination.

[0016] This invention provides concrete impact and abrasion resistance testing content, including: Experimental Apparatus: The instrument used in this invention is a high-speed sand jet milling apparatus, consisting of a control center and the instrument body. The control center dynamically adjusts the speed of the multi-stage centrifugal pump (0~500 rpm) using frequency conversion speed regulation technology, combined with real-time feedback data from the electromagnetic flowmeter, to achieve precise water pressure control (±0.1 MPa) from 0 to 15 MPa. Simultaneously, through a double-helix conveyor linked with a weighing sensor, the gear speed is controlled (0~50 rpm) to achieve a sand content of 0.1~0.8 kg / m³. 3 Precise mixing. The instrument itself includes a high-pressure water system driven by a multi-stage centrifugal pump, a 50L sand storage tank with a vibration anti-clogging device, plastic nozzles, and angle-shifting sample clamps. Its working principle is to use a water pump to pressurize water to a set value, mix it with sand in the sand storage tank, and then spray it onto the sample surface through the nozzle according to the set parameters.

[0017] The specific process is as follows: First, a multi-stage centrifugal pump pressurizes water to 0~15 MPa and delivers it to the contraction section, dynamically adjusting the water pressure using frequency conversion speed regulation technology. Then, manufactured sand (particle size 0.1~0.16 mm) in the sand storage tank is pneumatically vibrated to break the arching effect and quantitatively transported to the mixing chamber via a double-screw conveyor. The negative pressure effect of the high-speed water flow forms a solid-liquid two-phase flow, and the sand content in the water flow can be adjusted to over 100 kg / m³. The mixed sand-laden water flow is then impacted and fixed onto the sample surface of the metal stage through a plastic nozzle (d=2 mm). The spray angle can be adjusted from 0~90 degrees, as shown in Figure 1.

[0018] Experimental Method: Different abrasion angles (α), abrasion speeds (v), and sand content (C) were set to comprehensively evaluate the abrasion resistance of sand-laden water flow to ultra-high performance concrete (UHPC). The controlled variable method was used, and the experimental conditions are shown in Table 1.

[0019] Table 1

[0020] The abrasive used in the experiment was manufactured sand with a particle size of 0.1~0.16 mm, and the sample was a concrete block with a size of 50×50×10 mm.

[0021] The preparation process includes: diluting cellulose nanofibers in deionized water, adding polycarboxylate superplasticizer to the diluted suspension, and then magnetically stirring and ultrasonically dispersing to obtain a suspension of cellulose nanofibers; stirring cement and silica fume, adding sand during the stirring process, adding water and the suspension after stirring, adding fiber-reinforcing material after mixing and stirring to shape, and preparing a test block of nano-toughened ultra-high performance concrete material.

[0022] The concrete test block mixes included samples with CNFs content (cement mass) of 0%, 0.05%, 0.1%, and 0.15%, and a sample containing a mixture of 0.1% by mass of cellulose nanofibers (CNFs), 2% by volume of copper-plated steel fibers, and 0.5% by volume of PVA fibers, numbered REF, C05, C10, C15, and CSF, respectively. All samples had a water-cement ratio of 0.17 and a binder-mortar ratio of 1.0. To compare the impact and abrasion resistance of nanofibers, a control group of samples containing 2 vol% steel fibers was used, designated SF. The materials of the control group were identical to those of the concrete test blocks except for CNFs. The mix proportions and mechanical properties of the control group are shown in Tables 2 and 3. Table 2 shows the mix proportions of the steel fiber-containing samples, and Table 3 shows the working and mechanical properties of the steel fiber-containing samples. The curing regime involved placing the extracted samples in a steam curing chamber at 60°C for 72 hours before testing their mechanical properties.

[0023] The experimental procedure is as follows: ① Sample pretreatment: After the concrete sample preparation and curing are completed, it is placed in a 60℃ oven to dry for 2 hours to ensure that the surface is dry; ② Pre-test weighing: The dried concrete sample is accurately weighed and the initial mass is recorded; ③ Post-test treatment: After the test, the sample is dried again to constant weight (mass error controlled within ±0.001g), and the mass loss during the grinding process is calculated by using the mass data before and after the test.

[0024] Table 2

[0025] Table 3

[0026] Research schemes for the impact and abrasion resistance of concrete under different working conditions include: The effect of the grinding angle on the sample follows this pattern: within the range of 30–45 degrees, the grinding depth gradually decreases with increasing angle; within the range of 45–90 degrees, the grinding depth increases with increasing angle. When the grinding angle is 30 degrees and the sand content is 100 kg / m³... 3 At a velocity of 40 m / s, the sample with added cellulose nanofibers (CNFs) exhibited excellent impact and abrasion resistance, particularly compared to steel fibers, with the abrasion depth decreasing from 2.82 mm to 2.23 mm, a reduction of approximately 20.92%. When CNFs were mixed with steel fibers, the two significantly improved the impact and abrasion resistance of UHPC through a synergistic effect. Specifically, CNFs effectively suppressed microcrack propagation through a nanoscale toughening mechanism, while steel fibers constrained macroscopic cracking through a three-dimensional network structure. Under abrasion conditions of 30 degrees Celsius, the toughening effect of nanofibers was particularly prominent, improving the impact and abrasion resistance of UHPC by approximately 29.33% compared to the group with steel fibers alone. This indicates that in small-angle impact scenarios, nanofibers and steel fibers form a multi-scale reinforcement system, which can achieve gradient dissipation of impact energy, thereby significantly delaying the impact and abrasion damage of UHPC.

[0027] To evaluate the effect of nanofibers on the impact and abrasion resistance of UHPC, this study used mass loss as a quantitative indicator and conducted a comparative analysis from the perspective of material mass damage. Analysis of the influence of different CNF dosages on the mass loss of UHPC after impact and abrasion showed that, under 30-degree impact and abrasion conditions, the mass loss of UHPC was significantly correlated with the nanofiber dosage. Specifically, when the CNF dosage was 0.05 wt.% and 0.15 wt.%, it was significantly lower than that of the single-doped steel fiber group, with a mass loss reduction of approximately 18.56%. The multi-scale synergistic toughening mechanism demonstrated a significant advantage in optimizing the impact and abrasion resistance of UHPC: under impact and abrasion conditions from 30 to 90 degrees, the mass loss of the CNF / steel fiber hybrid system was significantly lower than that of the single-doped steel fiber group. This phenomenon fully confirms the synergistic effect of the "macro-micro" multi-scale reinforcement system.

[0028] Relevant tests were conducted to investigate the impact of sand content: Sediment content refers to the mass of sediment particles contained in a unit volume of sediment-laden water flow. The test was conducted to correct the sediment content by measuring the volume of sediment-laden water flow and the mass of sand within it over 10 seconds; the correction test was performed three times. The abrasion depth results for different sediment contents are shown below. Figure 2 As shown in the figure, the grinding depth increases with increasing sand content. Once the sand content reaches 55 kg / m³, the grinding depth increases further. 3 Within this range, the scouring depth remains relatively constant. This is related to the energy dissipation of the flow due to sediment movement in the sediment-laden flow. Some sediment creates resistance to the flow, leading to a reduction in the impact energy of the sediment-laden flow. Therefore, within the range of 55~100 kg / m 3Within a certain range, the scouring depth tends to stabilize with increasing sediment content. During the scouring process of high sediment-content water flow, the effect of a mixture of CNFs and steel fibers is significantly better than that of steel fibers alone. This may be because in high sediment-content water flow, steel fibers inhibit the development of macroscopic cracks but cannot suppress the continued development of smaller-scale cracks, while CNFs, through a "bridging" effect and interfacial reinforcement, significantly delay the initiation and propagation of microcracks with a width less than 1 μm.

[0029] Mass loss of UHPC after grinding with different sand contents, such as Figure 3 As shown, under the impact of sand-laden water with low sediment content, the mass loss of the sample containing steel fibers exceeded that of the sample containing only CNFs, indicating that CNFs have better resistance to abrasion under the scouring effect of sand-laden water with low sediment content. This phenomenon can be attributed to the intrinsic defects of the steel fiber-slurry interface transition zone (ITZ). Under the impact of sand-laden water with low sediment content, the impact of the water flow first makes the weak area of ​​the fiber-matrix interface a stress concentration source, leading to the initiation and propagation of microcracks. When the crack width exceeds the micron-level critical threshold, the internal damage evolution of the material enters the stage dominated by macroscopic cracking. At this time, although nanofibers delay the microcrack propagation rate through the "bridging" effect, the initial defects of the steel fiber-slurry interface limit the ability of the composite system to completely suppress the formation and connection of the macroscopic crack network, ultimately resulting in a continuous increase in the mass loss due to abrasion. Under the impact of high sediment content, the impact of the water flow may be weakened due to the resistance of sediment, thus reducing this effect.

[0030] The morphology after grinding shows that at low sand content (30 kg / m³)... 3 Under normal operating conditions, the abrasive action of the sand-laden water flow only causes shallow wear on the material surface, without exposing the aggregate or significant depth loss. However, with increasing sand content, especially at 100 kg / m³, the wear becomes more pronounced. 3 Under these conditions, the impact and abrasion damage of concrete is exacerbated. From the perspective of the failure mechanism, sand particles in water with high sand content impact the sample surface at high speed, and their kinetic energy is converted into stress concentration inside the material, leading to the initiation and propagation of microcracks in the matrix. CNFs improve the impact and abrasion resistance of concrete in two ways: First, CNFs are uniformly dispersed in the matrix and form a high-strength interfacial bond with cement hydration products (such as CSH gel) through hydrogen bonds, constructing a "nano-bridging network" between steel fibers and the matrix, effectively inhibiting debonding at the fiber-matrix interface; Second, the high aspect ratio of CNFs enables them to bridge the microcrack tip, dissipating the impact load energy through the "crack deflection" and "nanofiber pull-out energy dissipation" mechanisms, thus delaying the process of crack propagation from the micrometer scale to the millimeter scale.

[0031] Tests were conducted to investigate the impact of grinding speed: This experiment calculates the scouring velocity by measuring the volume of sand-laden water flow within 10 seconds. A calibration test was conducted three times. The effect of different scouring velocities on the scouring depth of the UHPC is as follows: Figure 4 As shown in the figure, the grinding depth increases with increasing grinding speed. At a grinding speed of 20 m / s, the grinding depth of CNFs with a dosage of 0.05 wt.% decreased by approximately 22.39% compared to the SF group. Under the condition of high sand content and low-speed grinding, the silt particles in the sand-laden water flow act on the material surface through high-frequency, low-energy impacts. At this time, the nanoscale toughening and strengthening mechanism of CNFs shows its advantage, effectively inhibiting the initiation and propagation of microcracks, thereby maintaining the integrity of the material surface. The 0.05 wt.% dosage exhibits the best anti-grinding performance. This phenomenon stems from the ideal dispersion state of the fibers at this dosage, which can form a continuous reinforcing network in the matrix while avoiding the agglomeration defects caused by high dosages, thus constructing a denser protective structure inside the UHPC and achieving efficient dissipation of low-speed impact energy.

[0032] Mass loss of UHPC due to sediment-laden water flow at different velocities, such as Figure 5 As shown in the figure, the mass loss follows a pattern consistent with the depth, increasing with the increase of the grinding speed. Under the grinding condition of sand-laden water flow at a velocity of 20 m / s, UHPC with a CNFs content of 0.15 wt.% exhibits the lowest mass loss rate, indicating that this content has a significant inhibitory effect on surface layer peeling. The grinding speed and mass loss are directly proportional, and their linear correlation equation is shown in the figure. Figure 6 As shown.

[0033] In the microstructure of the samples after grinding, at lower flow velocities, the grinding damage was mainly concentrated in the loss of the slurry, and the surface damage of the samples with CNFs was relatively small. When the water flow velocity reached 40 m / s, the aggregate was exposed, and the damage was concentrated at the interface between the aggregate and the slurry.

[0034] Testing and research on the micromechanical properties of concrete: The micromechanical properties of UHPC significantly influence its impact and abrasion resistance. To quantitatively characterize the toughening effect of nanocellulose fibers (CNFs) on the cement matrix, this invention employs a nanoindentation testing system to test the fracture toughness of cement mortar. The fracture toughness obtained from nanoindentation testing can serve as an indicator of micro-toughness. High-toughness materials can absorb impact energy through plastic deformation and crack bridging, thereby delaying crack initiation and propagation, and reducing damage caused by impact and abrasion. Under impact loads, nano-toughened UHPC materials, through CNFs, reduce the microcrack width in the cement slurry and adjust the bridging stress at the fiber-matrix interface, thus reducing impact and abrasion losses.

[0035] Fracture toughness calculation theory: The fracture toughness of cement paste was calculated based on an improved energy method. The detailed calculation process is as follows: Typical indentation load-displacement curves during loading and unloading are as follows: Figure 7 As shown. P m It is the maximum load, h m It is the maximum head displacement, h f It is the residual displacement, h c This is the vertical distance of contact, i.e., the contact depth. The area under the loading curve and the constant load platform represents the total energy in the loading process W2+W5, and the area under the unloading curve represents the elastic recovery energy in the unloading process W4. Based on the concept proposed by Attaf, reference load energies W1+W2 and W3+W4 related to the linear loading and unloading paths are defined. Wherein, W1 represents the area under the linear loading path, W2 represents the area of ​​the difference between the actual loading curve and the linear loading path, W3 represents the area under the linear unloading path, W4 represents the elastic holding energy, and W5 represents the energy during the holding phase. During the loading and unloading phases, the ratio of the reference energy to the actual energy is defined as the loading and unloading energy constant. (1) (2) Where V t and V e These represent the loading energy constant and the unloading energy constant, respectively. The introduction of these two parameters effectively eliminates the influence of the maximum load. They are used to quantitatively describe the characteristics of the loading and unloading curves, providing a more accurate and independent method for analyzing the mechanical behavior related to the loading and unloading processes.

[0036] The loading and unloading phases of the test curve follow a simple power function: (3) Where P is the load. h α is the indentation depth, m and n are the power exponents of the loading and unloading curves, and α and β are constants. The relationship between the energy constant and the power index can be obtained by combining the equations.

[0037] (4) (5) Ignoring the energy dissipated through heat and contact displacement during indentation, the fracture energy can be determined as follows: The total work done by the indenter may involve all possible mechanical states, namely elastic, plastic, and fracture processes. Therefore, the fracture energy can be expressed as: (6) Where W is subscripted with T, E, PP, and C, representing total energy, elastic energy, pure plastic energy, and fracture energy, respectively. Total energy and elastic energy can be obtained by directly reading the load depth curve or by fitting the curve using the aforementioned power function. By assuming that the effect of fracture on elastoplastic deformation is averaged across the entire load curve, the ratio of pure plastic energy to total energy can be estimated using the following equation: (7) Where hf represents the residual displacement after complete unloading, and hl represents the displacement at the end of loading.

[0038] By combining formulas (5) and (6), the fracture energy can be obtained as follows: (8) Critical stress intensity factor K c It refers to the fracture toughness of a material, which can be measured by the fracture energy release rate G. c To determine: (9) (10) Where E and ν are the elastic modulus and Poisson's ratio of the material, which can be obtained directly from the indentation unloading curve; A c This represents the area of ​​the fracture energy release region and the contact area (hm) at the maximum penetration depth. For the Berkovich indenter, the maximum crack area Ac = 24.5hm. 2 .

[0039] Fracture toughness calculation results: Nanoindentation testing was used to quantitatively evaluate the microfracture toughness of the ITZ (internal zone) surrounding the UHPC matrix and embedded aggregates. Toughness implies the ability of the material to absorb more energy and undergo plastic deformation before fracture, which also provides favorable conditions for resisting crack propagation. All tests were conducted at room temperature with a Berkovich indenter. A 5×5 indentation grid was selected around the cement paste for testing. To ensure the accuracy of the results, possible interactions between two adjacent indentation points and interference from aggregates should be avoided; therefore, the spacing between indentation points was set to 20 μm. The test used a trapezoidal loading scheme, initially loading at a constant rate of 20 mN / min to a peak load of 50 mN, then holding for 10 s to eliminate the possible effects of creep deformation, and finally unloading at a constant rate of 30 mN / min.

[0040] Box plots of fracture toughness values ​​of blocky cement paste for four groups of samples (REF, C05, C10, C15) obtained from nanoindentation tests are shown below. Figure 8As shown in the figure, comparing the cement paste fracture toughness values ​​of UHPC with different CNFs dosages, it can be clearly seen that the REF group without CNFs has a smaller box height, which means that the fracture toughness values ​​are more concentrated and less dispersed. The average fracture toughness of the REF group without CNFs is 1.00 MPa / m. 1 / 2 When 0.05 wt.%, 0.1 wt.%, and 0.15 wt.% CNFs were incorporated into the UHPC matrix, the height of the cell increased, indicating a greater dispersion in the fracture toughness distribution. Furthermore, it is noteworthy that the cell gradually shifted upwards with the addition of CNFs. The average fracture toughnesses of the samples containing 0.05 wt.%, 0.10 wt.%, and 0.15 wt.% CNFs were 1.51, 1.46, and 1.57 MPa / m, respectively. 1 / 2 Compared to the control group, this represents an improvement of approximately 50%. This also explains why, under the abrasion of sand-laden water at 30 degrees Celsius, the abrasion depth and mass loss of UHPC with single nanofiber doping are reduced compared to that with single steel fiber doping.

[0041] Samples in groups C05 and C15 generally exhibited better abrasion resistance than those in group C10. The improvement in abrasion resistance was analyzed from the perspective of fracture toughness distribution at the aggregate interface. Contour plots clearly illustrated the influence of CNFs on the cement paste and aggregate interface. Further analysis of the wear depth of samples under abrasion by sand-laden water flow at different angles showed that the sample containing 0.05 wt.% CNFs had a significantly smaller wear depth compared to samples with other CNFs. This is mainly due to the improved fracture toughness of the cement paste, effectively inhibiting the increase in abrasion depth. In the fracture toughness contour plot of the UHPC matrix near the aggregate in the sample containing 0.05 wt.% CNFs, the matrix fracture toughness in the area near the aggregate was lower than that in the area far from the aggregate, confirming the existence of an intermediate temperature zone (ITZ) between the aggregate and the matrix, which is the initiation point of failure. The fracture toughness of the aggregate-paste interface of sample C05 was approximately 1.6 MPa / m. 1 / 2 This also indicates a strong bond between the aggregate and the slurry. Higher fracture toughness means that when UHPC is exposed to the abrasive action of sand-laden water, the interface can withstand greater stress before crack propagation and fracture occur.

[0042] Verification of the grinding damage morphology of UHPC after grinding at different angles: To verify the abrasion damage morphology of UHPC after abrasion at different angles, X-ray CT was used to statistically analyze the volume of abrasion pits. This analysis aimed to understand the mechanism by which nanofibers enhance the abrasion resistance of UHPC under a 45-degree sand-laden water flow. The morphology of abrasion pits in samples with different CNFs contents under condition A2 is shown in the figure. Figure 9As shown in the figure, obvious cracks exist in the aggregate at the edge of the grinding pit, especially in the REF group. Cracks along the aggregate-slurry interface can also be seen around the grinding pit. Compared with the REF group, the grinding pit volume of the sample incorporating CNFs decreased by 31.83%, especially in the sample with CNFs content of 0.15 wt.%. This indicates that CNFs act as fiber "bridging" during the grinding process of sand-laden water, preventing slurry spalling and the formation of aggregate-slurry interface cracks. The addition of CNFs promotes the production of more hydration products, enhances the encapsulation of the aggregate-slurry interface, and inhibits the formation of microcracks.

[0043] In summary, the surface cement paste of UHPC is initially damaged upon the onset of the sand-laden water flow. As the sand-laden water continues to abrade, water penetrates into the concrete, transporting moisture along internal crack channels. Under the impact of the water flow, the cement paste is gradually removed, and the aggregates are increasingly exposed directly to the water flow's impact load. Subsequently, smaller aggregates, mostly fine particles with smooth surfaces, are exposed to the sand-laden water flow. Cracks initiate and widen at the aggregate-paste interface. Ultimately, the bottom of the abrasion pit forms an uneven surface dominated by coarse aggregates, with a significantly higher roughness than the initial surface.

[0044] Under the abrasive action of a 30°C sand-laden water flow, the UHPC sample with CNFs as the sole additive exhibited significantly lower abrasive volume loss than the UHPC sample with steel fibers as the sole additive. The abrasive damage was as follows: Figure 10 As shown, the REF group samples clearly exhibit a narrow and elongated shape at one end of the grinding pit. This is due to the high brittleness and low tensile strength of the cement-based material itself, leading to stress concentration under tangential force and easily forming a narrow and elongated wear area. However, the UHPC samples with CNFs added show improved fracture toughness, reducing localized brittle fracture. Therefore, when subjected to sand-laden water flow, the material can distribute stress more evenly, reducing localized concentrated wear, resulting in a smoother, wider semi-circular boundary of the grinding pit. The CSF group samples show less volume loss, which is related to the toughening effect of CNFs in the cement paste and its own pore structure. Although the CSF group samples have a larger open pore volume, they have the lowest porosity, which can effectively reduce the loss caused by pore structure collapse and inhibit the generation and development of microcracks. Compared with the SF group samples with only steel fibers, the CSF group shows a reduction of approximately 29.85% in volume loss. Furthermore, the volume loss of the C05 group samples decreased by approximately 14.77% compared to the SF group samples. These data are sufficient to demonstrate that the nanoscale toughening of CNFs significantly improves the impact and wear resistance of steel fiber-containing UHPC.

[0045] The addition of CNFs increased the fracture toughness of UHPC from 1.0 MPa / m in the REF group. 1 / 2Increased to 1.5 MPa / m 1 / 2 The improved fracture toughness fundamentally alters the stress transmission mechanism of impact loads. At the microscopic level, CNFs suppress the propagation of internal microcracks through a dual mechanism of "building a bridging network and suppressing the tip effect." When sand-laden water impacts and induces microcracks, CNFs distributed at the crack tips generate bridging forces due to their high aspect ratio (>20), increasing the energy required for crack propagation. This nanoscale reinforcement effect reduces the stress concentration factor, promoting the uniform dispersion of impact loads through nonlinear deformation at the fiber-matrix interface, thus preventing cracks caused by stress concentration within the concrete. The volume of CNFs added in the samples is 0.1-1 mm. 3 The number of pores in the sample is reduced compared to the REF group. This difference in pore structure has a key impact on the evolution of abrasion damage: during the abrasion process of sand-laden water flow, when the energy caused by the impact of sand particles is transferred in the sample containing CNFs, the uniform pore distribution and the small number of large-volume pores, as well as the high density of the interfacial transition zone (ITZ), avoid the chain reaction damage caused by the collapse of the pore structure.

[0046] The improvement of UHPC's impact and abrasion resistance by nanofibers stems not only from their nanoscale toughening effect but also from their systematic optimization of the microstructure of cement-based materials. Nano-toughened ultra-high performance impact and abrasion resistant concrete compensates for the shortcomings of traditional steel fiber reinforced concrete in controlling nanoscale defects by regulating the density of the interfacial transition zone, refining the pore structure, and constructing a micro-network structure.

[0047] The morphology of the interfacial transition zone (ITZ) and EDS-based elemental analysis provide an explanation for the improved abrasion resistance of UHPC by CNFs. BSE images of samples with different CNF contents showed unhydrated cement and pores in the UHPC slurry, particularly near the aggregate-slurry interface where pores and microcracks were present. With the incorporation of CNFs, the probability of microcracks and pores in the cementitious system significantly decreased. This phenomenon indicates that CNFs, with their nanoscale size, effectively fill the existing pore structure in the material. Furthermore, CNFs also help accelerate the cement hydration process. During this process, more hydration products are generated, further filling and refining the microstructure, resulting in a significant improvement in the overall density and uniformity of the material.

[0048] The grayscale contrast in the BSE micrographs helps assess the quality of the cement paste-aggregate interaction at the ITZ. Clearly, good bonding characterized by continuous and blurred phase boundaries improves the abrasion resistance of UHPC compared to poor bonding with macro / micro cracks and porosity. EDS spectroscopy allowed us to further analyze the chemical composition near the ITZ. Four elements (C, O, Si, and Ca) were selected from a large number of detected chemical elements based on their concentrations, sufficient to distinguish the primary phases. Elemental calcium migrated and enriched at the aggregate-paste interface upon the addition of CNFs. This indicates the generation of more calcium-containing hydration products at the aggregate-paste interface, which can fill interfacial pores and increase interfacial density. The enhanced mechanical interlocking between aggregate and paste improves interfacial bonding. Larger grain sizes reduce the number of grain boundaries per unit volume, lowering the probability of microcrack initiation and potentially increasing the overall strength of the crystals. This contributes to improved compactness in the interfacial transition zone (ITZ), reducing porosity and microcracks. Furthermore, the high surface area of ​​CNFs enables them to bond with cement-based materials, especially in weaker regions. Additionally, the presence of CNFs can effectively transfer shear forces between nanofibers and cement, thus helping to control deformation in weaker regions of UHPC.

[0049] Simultaneously, nanofibers promote the generation of hydration products, filling the gaps between aggregate and paste, optimizing the pore structure of concrete, and reducing the number of harmful pores larger than 1 μm that become weak points in load transfer and channels for the intrusion of harmful substances, thus refining the pores. Furthermore, the addition of CNFs plays a role in "spatial confinement": during the hardening process of cement paste, CNFs uniformly dispersed in the pore solution form a physical barrier, restricting the disordered accumulation of cement particles and guiding the orderly growth of hydration products at the nanoscale. For the interfacial transition zone, CNFs may adsorb onto the aggregate surface, enhancing the adhesion between paste and aggregate through chemical bonds such as hydrogen bonding, increasing the CSH gel content at the interface, reducing the width of the aggregate-paste interface transition zone, and decreasing microcracks and porosity within the concrete.

[0050] In summary, the addition of CNFs to UHPC improves and alters the pore structure, which is one of the reasons for its improved abrasion resistance. The following is the effect of CNFs on the pore structure during cement hydration: During the pre-induction period of hydration, CNFs adsorb onto the surface of cement particles due to electrostatic attraction, forming a cross-linked network. When the cement particles come into contact with water, a hydration reaction occurs immediately. To maintain valence balance, Ca... 2+ and OH -The cement particles enter the solution. At this stage, the pores are mainly the original spacing between cement particles, depending on the packing density between the cement-based materials. The original surface structure of C3S is destroyed, forming a calcium-deficient, silicon-rich amorphous layer. As the reaction proceeds, C3A and gypsum continue to dissolve, producing needle-like hydration products, and an amorphous protective film gradually covers the entire surface. CNFs and needle-like hydration products occupy larger pores through physical filling, thereby reducing the size of the original pores. The unfilled pore portions are retained to form capillary pores. Simultaneously, the functional groups on the CNFs surface begin to adsorb water molecules, creating conditions for subsequent hydration reactions. The protective film covering the cement particles marks the end of the hydration pre-induction period. 2+ Through diffusion into the thin film, some of the carbon dioxide is adsorbed by the negative charge on the film surface, forming a diffused electric double layer. CNFs adsorb Ca from the solution via electrostatic interactions. 2+ This promotes the uniform distribution of hydration products and initiates the formation of gel pores around CNFs. The film prevents the leakage of silicate ions formed by the dissolution of unhydrated particles inside, but it will rupture when the osmotic pressure limit is reached.

[0051] During the accelerated hydration period, Ca 2+ and SiO4 2- At CSH saturation, a large amount of CSH grows. More CSH gel forms on and around the CNFs surface, leading to an increase in gel pores. The physical space of the CNFs restricts the unlimited growth of the CSH gel, preventing overfilling and deformation of local pores, thus maintaining a relatively stable size and shape of the gel pores. During hydration deceleration, the cement hydration reaction rate begins to decrease, and the growth of CSH gel gradually slows down. At this stage, CNFs continue to stabilize the wall structure of the gel pores through hydrogen bonds and electrostatic interactions on the surface, preventing pore deformation due to shrinkage. The filling effect of CSH reduces the formation of capillary, mesopore, and macropores. Furthermore, under the abrasive action of sand-laden water flow, CNFs form a nanoscale network structure within the slurry, effectively dispersing the initial wear and related microcrack formation on the UHPC surface caused by the water flow. Microcrack formation is related to the tensile strain of the UHPC at the impact point; once the tensile strain at the impact point exceeds the tensile strain of the UHPC, microcracks will form. However, the presence of CNFs fills the pores in the microstructure and acts as a "bridging" mechanism, enhancing the fracture toughness of the cement slurry. Meanwhile, CNFs limit stress concentration at the crack tip during microcrack propagation, increase the energy required for crack propagation, help counteract crack accumulation, and enhance the abrasion resistance of cement paste at this stage.

[0052] In summary, CNFs reduce the formation of harmful pores during cement hydration, generate more hydration products, enhance the hardness of the cement paste, and resist the abrasive loss of UHPC surfaces caused by sediment in sand-laden water flows. The "bridging" effect of nanofibers prevents the generation and propagation of cracks in the cement paste, improves the fracture toughness of the aggregate-paste interface, and slows down the rate of aggregate exposure. This microscopic improvement in the properties of the UHPC cement paste results in a macroscopic enhancement of the UHPC's abrasion resistance.

[0053] This experiment investigated the impact and abrasion resistance of UHPC under different working conditions. The impact and abrasion resistance mechanism was analyzed from aspects such as fracture toughness, loss morphology, and aggregate / slurry interface. The main conclusions are as follows: (1) The addition of CNFs to UHPC improves its abrasion resistance, especially under the abrasion of sand-laden water at an angle of 30 degrees. CNFs improve the abrasion resistance of concrete more than steel fibers, with a 20.92% decrease in depth loss, and a 18.56% and 14.77% decrease in mass loss and volume loss, respectively. In addition, the multi-scale toughening of CNFs and steel fibers improves the abrasion resistance of UHPC in the environment of high speed, high sand content and small angle sand-laden water flow.

[0054] (2) The microfracture toughness of UHPC incorporating CNFs was significantly improved, with an increase of more than 50%. This phenomenon is directly attributed to the effective filling of micropores by nanofibers and their "bridging" role in crack propagation. Nanoindentation tests revealed that the fracture toughness of the 0.05 wt.% incorporation group exhibited a "high in the middle and low on both sides" distribution in the aggregate-slurry interface transition zone (ITZ). This indicates that the addition of CNFs improved the fracture toughness of the interface, thereby optimizing the impact and abrasion resistance of UHPC.

[0055] (3) CNFs with high specific surface area provide a large number of nucleation sites for cement hydration, promote the generation of hydration products, fill the pores at the aggregate-slurry interface, and enhance interfacial bonding. At the same time, the network structure jointly constructed by CNFs and steel fibers significantly improves the abrasion resistance of UHPC under vertical abrasion by sand-laden water flow, especially when the erosion angle exceeds 60 degrees, effectively reducing abrasion damage and improving the durability of UHPC.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for analyzing the impact and abrasion resistance of nano-toughened ultra-high performance concrete, characterized in that, include: Samples of nano-toughened ultra-high performance concrete were prepared. The nano-toughened ultra-high performance concrete samples were tested by impact and grinding failure test to obtain mass loss test results; the impact and grinding failure test was set with several different test parameters. Microscopic tests were conducted on samples of nano-toughened ultra-high performance concrete using nano-indentation tests. The results of these microscopic tests were analyzed to obtain an assessment of the microscopic fracture toughness.

2. The method according to claim 1, characterized in that, The preparation process of nano-toughened ultra-high performance concrete samples includes: Cellulose nanofibers were diluted in deionized water, and polycarboxylate superplasticizer was added to the diluted suspension for magnetic stirring and ultrasonic dispersion to obtain a cellulose nanofiber suspension. Cement and silica fume were stirred, and sand was added during the stirring process. After stirring, water and the suspension were added and mixed. After mixing, fiber-reinforcing material was added and stirred to set the mixture, thus preparing a sample of nano-toughened ultra-high performance concrete material.

3. The method according to claim 1, characterized in that, The process of impact grinding failure test includes: The surface of a nano-toughened ultra-high performance concrete sample was subjected to surface impact by a high-speed sand jet abrasive jet instrument, and the mass loss test results were obtained, wherein the mass loss test results are the mass loss index of the sample.

4. The method according to claim 1, characterized in that, The test parameters for the abrasion damage test include abrasion angle, sand content, and flow rate.

5. The method according to claim 1, characterized in that, The process of analyzing the microscopic experimental results includes: Obtain microscopic test results, wherein the microscopic test results include indentation load-displacement curves and loading-unloading curves; The fracture energy is extracted and calculated from the microscopic test results. The total energy and elastic energy are obtained from the indentation load-displacement curve and the loading and unloading curve. The loading and unloading energy constants are calculated by fitting the indentation load-displacement curve and the loading and unloading curve. The fracture energy is calculated based on the loading and unloading energy constants, the total energy and the elastic energy. The fracture energy release rate is calculated based on the fracture energy, and the micro-fracture toughness assessment result is obtained based on the fracture energy release rate and the material parameters of the sample, wherein the micro-fracture toughness assessment result is the critical stress intensity factor.

6. The method according to claim 1, characterized in that, The nano-toughened ultra-high performance concrete samples were tested by abrasion and impact failure tests, and abrasion and impact damage morphology images were obtained. These images are used to visually represent the morphology of the nano-toughened ultra-high performance concrete samples after abrasion and impact failure.

7. The method according to claim 1, characterized in that, After obtaining the mass loss test results and the microfracture toughness assessment results, the following is also included: Based on the mass loss test results and microfracture toughness evaluation results, samples of nano-toughened ultra-high performance concrete were screened to obtain the required nano-toughened ultra-high performance concrete samples; among them, samples whose mass loss test results and microfracture toughness evaluation results exceeded the threshold were retained.

8. A system for analyzing the impact and abrasion resistance of nano-toughened ultra-high performance concrete, characterized in that, Used to perform the method described in any one of claims 1-7.

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