Carbon fiber foam concrete and method for manufacturing the same

Abstract

The application belongs to the technical field of building materials, and particularly relates to carbon fiber foam concrete and a preparation method thereof. The carbon fiber foam concrete comprises the following raw materials: cement carbon fiber slurry, cement, carbon fiber and water; foaming liquid, foaming agent and water. The preparation method comprises the following steps: mixing cement and carbon fiber, adding water to form cement carbon fiber slurry; mixing the foaming agent and water to form foaming liquid; preparing foam from the foaming liquid; introducing the foam into the cement carbon fiber slurry to form carbon fiber foam cement slurry; and shaping, solidifying and curing the carbon fiber foam cement slurry to obtain the carbon fiber foam concrete. The application solves the problem of relatively low strength of the existing ordinary foam concrete.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a carbon fiber foam concrete and its preparation method. Background Technology

[0002] With the development of the construction industry, lightweight, high-strength, and environmentally friendly building materials have become important research directions. Foamed concrete (FC) is a lightweight and environmentally friendly building material that can be used in various civil engineering applications. Therefore, its performance optimization has received widespread attention. Foamed concrete is a microporous lightweight material. As a type of porous concrete, it exhibits excellent physical and mechanical properties such as lightweight, high strength, energy saving, waste utilization, thermal insulation, and heat insulation due to its large number of closed pores. However, it also has some obvious drawbacks, such as relatively low strength, high brittleness, insufficient durability, poor buffering performance, low yield stress, and poor compressive, tensile, impact, and crack resistance. These shortcomings largely limit its further promotion and application in some high-performance engineering projects. Summary of the Invention

[0003] In view of the problems existing in the prior art, the purpose of this invention is to provide carbon fiber foamed concrete and its preparation method, so as to solve the problem of relatively low strength of ordinary foamed concrete, as well as the problems of high brittleness, insufficient durability, poor buffering performance and low yield stress of ordinary foamed concrete, and the problems of poor compressive strength, tensile strength, impact resistance and crack resistance of ordinary foamed concrete.

[0004] The technical solution of the present invention is as follows: The present invention provides a carbon fiber foamed concrete, which is composed of cement carbon fiber slurry and foaming liquid; the cement carbon fiber slurry is composed of cement, carbon fiber and water; the foaming liquid is composed of foaming agent and water.

[0005] Based on the aforementioned technical methods, the microstructure and mechanical properties of foamed concrete are significantly improved by cleverly incorporating carbon fiber and foaming agents into cement, thereby effectively enhancing its strength, brittleness, durability, and cushioning performance. This solves the problems of relatively low strength, high brittleness, insufficient durability, and poor cushioning performance of ordinary foamed concrete.

[0006] Preferably, the volume ratio of foaming agent to water is 1:40. By precisely controlling the ratio of foaming agent to water, the overall performance of foamed concrete is significantly improved, giving it higher strength and reliability in engineering applications. Furthermore, according to multiple tests, the foam is most stable when the volume ratio of foaming agent to water is 1:40. Because foam has a half-life, the prepared foam needs to be stirred and used immediately. Preferably, the ratio of cement carbon fiber slurry to foaming liquid is 270~300:1 (g:mL). Preferably, the foaming agent is selected from protein-based foaming agents. Protein-based foaming agents are selected from animal protein foaming agents or plant protein foaming agents used in tunnel boring machines. Preferably, the carbon fiber foamed concrete possesses at least one of the following characteristics: the length of the carbon fiber is 3~12mm; the carbon fiber content, by volume, is 0.18%~0.60%; and the density of the carbon fiber foamed concrete is 500~1200 kg / m³. 3 Specifically, the carbon fiber length is 3, 6, or 12 mm. Specifically, the carbon fiber content, by volumetric weight, is 0.18%, 0.36%, 0.48%, or 0.60%. Specifically, the density of the carbon fiber foamed concrete is 500 kg / m³. 3 700 kg / m 3 900 kg / m 3 Or 1200 kg / m 3 Carbon fiber foamed concrete possesses at least one of the following characteristics: the length of the carbon fiber is 6 mm; the carbon fiber content, on a volumetric basis, is 0.48%; and the density of the carbon fiber foamed concrete is 500 kg / m³. 3 Carbon fiber foamed concrete possesses at least one of the following characteristics: the length of the carbon fiber is 6 mm; the carbon fiber content, on a volumetric basis, is 0.36%; and the density of the carbon fiber foamed concrete is 500 kg / m³. 3 By precisely controlling the length of carbon fibers, the dynamic compressive strength of foamed concrete was enhanced, and it could effectively bridge microcracks in the matrix. Simultaneously, the fiber dispersion within the matrix was good, allowing it to fully exert its reinforcing effect. Long-term experimental research showed that when the volumetric carbon fiber content was 0.48%, the compressive strength of foamed concrete was significantly enhanced. The experiments also revealed that unfiber-added foamed concrete exhibited typical brittle failure characteristics under impact loading, while the addition of carbon fibers greatly improved its toughness. In particular, specimens with a carbon fiber content of 0.48% maintained good integrity under impact, with a significantly reduced degree of fragmentation. Experimental research also showed that, based on precise control of the carbon fiber incorporation length, further controlling the density of carbon fiber foamed concrete to 500 kg / m³... 3 This can further improve the tensile and compressive strength of fiber foam concrete.

[0007] This invention also provides a method for preparing carbon fiber foamed concrete, comprising the following steps: 1) mixing cement and carbon fiber, adding water to form a cement-carbon fiber slurry; 2) mixing a foaming agent and water to form a foaming liquid; 3) forming foam from the foaming liquid in step 2); 4) introducing the foam into the cement-carbon fiber slurry to form a carbon fiber foamed cement slurry; 5) molding, solidifying, and curing the carbon fiber foamed cement slurry to obtain carbon fiber foamed concrete. By mixing cement and carbon fiber first, and then adding water, the carbon fiber can be effectively and evenly dispersed in the cement matrix, reducing carbon fiber agglomeration and significantly improving the homogeneity of the concrete; the method in steps 2) and 3) can generate stable and uniform foam to ensure the consistency and stability of foam pore size; after the foam is formed, introducing the foam into the cement-carbon fiber slurry allows for precise adjustment of the target density of the foamed concrete by controlling the amount of foam added; molding, solidifying, and curing the carbon fiber foamed cement slurry ensures sufficient hydration and strength development of the fiber foamed concrete.

[0008] Preferably, step 1) includes: mixing cement and carbon fiber, thoroughly dry-mixing, then adding water and stirring for 2 minutes to form a homogeneous cement-carbon fiber slurry; step 4) includes: introducing foam into the cement-carbon fiber slurry and stirring for 1 minute to form a homogeneous carbon fiber foam cement slurry; step 5) includes: pouring the carbon fiber foam cement slurry into a standard test mold, smoothing the surface, allowing it to solidify at room temperature for 24 hours, demolding, and curing to obtain carbon fiber foam concrete. Preferably, curing is carried out in a standard curing room with a temperature of 18~22℃ and a relative humidity of ≥95% for 28 days. Thorough stirring in step 1) forms a homogeneous cement-carbon fiber slurry, ensuring further dispersion of carbon fibers and uniform slurry; thorough stirring in step 4) ensures the formation of a homogeneous carbon fiber foam cement slurry; "smoothing the surface" effectively eliminates surface air bubbles and unevenness; placing the mold at room temperature for 24 hours facilitates initial setting and molding; curing treatment effectively ensures full hydration and strength development of the fiber foam concrete, preparing it for subsequent mechanical property testing.

[0009] The beneficial effects of this invention are:

[0010] (1) The carbon fiber foamed concrete of the present invention significantly improves the microstructure and mechanical properties of foamed concrete by cleverly adding carbon fiber and foaming agent to cement, thereby effectively improving the strength, brittleness, durability, buffering performance and yield stress of foamed concrete. (2) The preparation method of carbon fiber foamed concrete of the present invention, by mixing the weighed cement and carbon fiber according to the design ratio and dry mixing thoroughly, can make the carbon fiber uniformly dispersed in the cement matrix, thereby reducing the carbon fiber agglomeration phenomenon and improving the homogeneity of concrete; by controlling the amount of foam added, the target density of foamed concrete can be precisely controlled; by using "smoothing the surface", surface air bubbles and non-uniformity are effectively eliminated; through curing treatment, the full hydration and strength development of fiber foamed concrete are effectively ensured, preparing for subsequent mechanical property testing. Attached Figure Description

[0011] Figure 1 The image shows the test results of the compressive strength of carbon fiber foam concrete. Figure 2 The graph shows the compressive strength coefficient of carbon fiber foam concrete. Figure 3 The image shows the tensile strength test results of carbon fiber foam concrete. Figure 4 The result is a graph showing the tensile strength coefficient of carbon fiber foam concrete. Figure 5 The compressive stress-strain curve of carbon fiber foam concrete; Figure 6 The strain curve of the compression test of carbon fiber foam concrete; Figure 7 The image shows the damage results of carbon fiber foam concrete. Figure 8 The tensile stress-strain curve of carbon fiber foam concrete; Figure 9 The strain curve of the tensile test of carbon fiber foam concrete; Figure 10 The flowability results of carbon fiber foam concrete are shown in the figure. Without CF: no CF. Figure 11 The dynamic compressive stress-strain curve of carbon fiber foam concrete; Figure 12 The dynamic compressive strength results of carbon fiber foam concrete with different carbon fiber lengths are shown in the figure. Figure 13 The dynamic compressive strength results of carbon fiber foam concrete with different fiber content are shown in the figure. Figure 14 The left figure shows the dynamic compressive stress-strain curve; the right figure shows the energy consumption of carbon fiber foam concrete. Figure 15 (1) Typical failure mode diagram of the specimen without carbon fiber; (2) Failure mode diagram of the specimen under different air pressures when the carbon fiber content is 0.48%; Figure 16 This is a schematic diagram of the cross-sectional porous structure of the specimen; Figure 17 This is a graph showing the aperture distribution. Figure 18 This is a schematic diagram of the microstructure of CFFC; Figure 19 This is a schematic diagram of the EDS scan results of the specimen. Detailed Implementation

[0012] The present invention will be further described in detail below through embodiments, but in no way is the invention limited.

[0013] The experimental raw materials used in the following examples are as follows: (1) The cement used in the experiment was ordinary Portland cement (PO42.5) produced by a company in Jiangxi Province. The initial and final setting times were 160 and 300 (min), respectively, and the 28-day compressive and flexural strengths were 46 MPa and 7 MPa, respectively. Its physicochemical composition parameters are shown in Table 1. (2) The experiment used plant protein foaming agent used in tunnel shields. The foaming ratio was about 21~25. The appearance was a brownish liquid with a density of 1.01~1.02 g / cm³. 3 Solid content: mass fraction after drying ≥35%, pH value: 9~10, with low water bleeding, high stability and high foaming ratio, and its various properties are shown in Table 2. (3) The carbon fiber (CF) used in the experiment was provided by Taili Carbon Fiber Co., Ltd., and its various properties are shown in Table 3.

[0014] Table 1. Composition of Silicate Cement PO42.5

[0015]

[0016] Table 2 Basic Physical Properties of Plant Protein Foaming Agents

[0017]

[0018] Table 3 Basic Properties of Carbon Fiber

[0019]

[0020] Example: Preparation method of carbon fiber foamed concrete, the steps are as follows: 1) Raw material preparation and dry mixing: Mix the weighed cement and carbon fiber according to the design ratio, and dry mix thoroughly to make the carbon fiber uniformly dispersed in the cement matrix, so as to reduce the agglomeration of carbon fiber and improve the homogeneity of concrete. 2) Cement carbon fiber slurry preparation: Mix cement and water at a water-cement ratio of 0.4 and stir for 2 minutes to form a homogeneous cement carbon fiber slurry, ensuring that the carbon fiber is further dispersed and the slurry is uniform. 3) Foam preparation: Mix foaming agent and water at a volume ratio of 1:40 and stir evenly to form a stable foaming liquid. Then, inject the weighed foaming liquid into the foaming machine to generate stable and uniform foam, ensuring the consistency and stability of foam pore size. 4) Foam introduction into cement carbon fiber slurry: Slowly introduce the prepared foam into the uniformly stirred carbon fiber cement slurry. Adjust the target density of foamed concrete (FC) by controlling the amount of foam added. Continue stirring for 1 minute until a homogeneous carbon fiber foamed cement slurry is formed. 5) Pouring and setting: Pour the mixed carbon fiber foamed cement slurry into the standard test mold and smooth the surface with a scraper to eliminate surface air bubbles and unevenness. After completion, place the mold at room temperature for 24 hours to allow initial setting. 6) Demolding and curing: After the slurry has completely solidified, carefully demold the specimen. Then transfer it to a standard curing room (temperature 20±2℃, relative humidity ≥95%) for curing for 28 days to ensure that the carbon fiber foamed concrete is fully hydrated and develops strength, in preparation for subsequent mechanical property testing. After curing, carbon fiber foamed concrete is obtained. In this embodiment, a total of 48 sets of specimens were designed. The specific component parameters of each set of specimens are shown in Table 4. In Table 4, specimen number 0.18CF(3) / FC-500 indicates that the carbon fiber volume content in the carbon fiber foamed concrete is 0.18%, the carbon fiber length is 3mm, and the density of the carbon fiber foamed concrete is 500 kg / m³. 3 per m 3 The carbon fiber foamed concrete contained 323.128 kg of cement, 129.251 kg of water, 0.762 kg of carbon fiber, and 47.621 kg of foam. The remaining specimens were numbered accordingly.

[0021] Table 4 Summary of Specimen Parameters

[0022]

[0023] Testing and Analysis: (I) Testing of Static Mechanical Properties of Carbon Fiber Foamed Concrete: 1. Static Compressive Strength Test: The compressive strength of carbon fiber foamed concrete was tested using a Chenxin Electronic Universal Testing Machine. The testing method was based on the "Foamed Concrete" standard JG / T 266-2011. The steps were as follows: After the specimen was cured, the specimen was removed and the surface was wiped dry; after checking that the appearance and dimensions (100mm × 100mm × 100mm) were correct, the specimen was placed on the bearing plate of the universal testing machine; the center of the specimen was aligned with the center of the bearing plate; the instrument was started and the load was applied uniformly according to the specification at a displacement control of 2mm / min for compression; until the specimen failed and the maximum failure load F was recorded. The formula for calculating the compressive strength is shown in Equation (I).

[0024] (I); In formula (I): f c — Compressive strength of the specimen, in MPa; F — Failure load of the specimen, in N; A — Contact area of ​​the specimen, in mm 2 The result is as follows Figure 1 As shown.

[0025] Figure 1 (a) Figure 1 (b) Figure 1 (c) and Figure 1 (d) The density of carbon fiber foamed concrete is 500 kg / m³. 3 700 kg / m 3 900 kg / m 3 and 1200 kg / m 3 The compressive strength of carbon fiber foam concrete made with carbon fibers of different lengths and volume fractions was determined. Figure 1 As shown in (a), compared to the undoped carbon fiber group, the compressive strength reaches its maximum, increasing by 88.4%, when 6mm long carbon fibers are incorporated at a doping rate of 0.48%. Furthermore, the compressive strength increases by 41.6% as the carbon fiber content increases from 0.18% to 0.48%. When the content increases from 0.48% to 0.60%, the compressive strength increases by 2.4%. Similar results can be obtained for different densities, such as... Figure 1(b) to 1(d). At the same length and density, the compressive strength of carbon fiber foamed concrete increased with increasing carbon fiber volume content, and the growth trend gradually slowed down, reaching its maximum at a carbon fiber content of 0.48%. Therefore, compared to plain foamed concrete (composed of cement, water, and foam), carbon fiber foamed concrete exhibits a slower water transfer process. The strength improvement of foamed concrete mainly comes from matrix hydration; in the case of carbon fiber-added foamed concrete, the strength is fully developed under sufficient moisture conditions. At a content of 0.48%, the carbon fiber content achieves its maximum enhancing effect on compressive strength. At this level, the carbon fiber is optimally distributed, effectively improving compressive performance by inhibiting microcrack propagation and enhancing structural integrity. When the content exceeds 0.48%, carbon fibers begin to aggregate, as shown in the SEM image (…). Figure 18 As shown in the figure, aggregation leads to uneven distribution and stress concentration points, thus reducing the effectiveness and compressive strength of the carbon fibers. Therefore, 0.48% is the optimal carbon fiber content to maximize compressive strength and provide the best performance in terms of compressive strength. When the admixture is constant, the carbon fiber length also shows an advantage in improving the compressive strength of foam. The results show that the compressive strength of foamed concrete first increases and then decreases with the increase of carbon fiber length. The compressive strength reaches its maximum value when the carbon fiber length is 6 mm. This is because the 6 mm carbon fiber length can better bridge the microcracks in the matrix, and the carbon fiber dispersion in the matrix is ​​also better, which can give full play to its reinforcing effect. However, when the carbon fiber length increases to 12 mm, the compressive strength decreases. This is because excessively long carbon fibers are prone to entanglement and agglomeration during the mixing process, resulting in uneven distribution of carbon fibers in the matrix, thereby reducing the overall compressive strength of the material.

[0026] Compressive strength coefficient: To more intuitively represent the relationship between the volume content and length variation of carbon fiber and the compressive strength of CFFC specimens, the compressive strength coefficient of carbon fiber foamed concrete was tested. The calculation formula is shown in equation (II).

[0027] (II); In formula (II), f c (N) represents the compressive strength observed in the CFFC specimen after the addition of carbon fiber, f c0 Kc represents the compressive strength of CFFC specimens without carbon fiber, and Kc is the compressive strength coefficient. The results of the compressive strength coefficient of carbon fiber reinforced foamed concrete (CFFC) varying with carbon fiber volume content at different density grades are shown below. Figure 2 As shown. Figure 2 (a) Figure 2 (b) and Figure 2(c) The compressive strength coefficients of carbon fiber foam concrete of different densities with different volumetric carbon fiber admixtures when the carbon fiber lengths are 3 mm, 6 mm, and 12 mm, respectively. Figure 2 (d) is the compressive strength coefficient of carbon fiber foam concrete of different densities made of carbon fiber of different lengths when the carbon fiber volume content is 0.48%.

[0028] from Figure 2 (a) ~ Figure 2 Analysis in (c) shows that the addition of carbon fiber effectively improves its compressive strength, exhibiting an initial increase followed by a decrease, reaching its maximum at 0.48%. Figure 2 As shown in (d), at the maximum carbon fiber content (0.48%), the carbon fiber contributes to the CFFC specimen at 500 kg / m². 3 Density level exhibits the most significant reinforcing effect. The introduction of carbon fibers creates a continuous network structure, effectively filling these pores through bridging, thereby significantly increasing the overall compressive strength of the CFFC specimen. Furthermore, excessively long carbon fibers may lead to insufficiently tight alignment and aggregation, reducing the reinforcing effect. At a suitable carbon fiber incorporation length, a density of 500 kg / m³ is achieved. 3 The compressive strength of foamed concrete can be increased to 6.09 MPa, which is 52.3% higher than that of foamed concrete without carbon fiber, with a density of 500 kg / m³. 3The compressive strength of the foamed concrete can be increased to 6.65 MPa, which is 33% higher than that of foamed concrete without carbon fiber, and its compressive strength is much higher than that of foamed concrete of the same density grade currently on the market. The length and dosage of carbon fiber are important factors affecting the compressive strength of foamed concrete. Appropriate carbon fiber dosage and length are beneficial to the development of compressive strength. After the addition of carbon fiber, the carbon fiber is distributed in all directions in the foamed concrete to form a three-dimensional network structure, which restricts the generation and development of cracks. At the same time, it will also transfer the external force borne by the foamed concrete through deformation, thereby reducing the number of weak points in the foamed concrete and improving the overall integrity. However, excessive dosage may lead to carbon fiber agglomeration, which will reduce the strength of the material. The results show that with the increase of carbon fiber dosage, the compressive strength of foamed concrete first increases and then decreases. When the carbon fiber dosage is 0.48%, the compressive strength reaches the maximum value. This proves that the dosage of 0.48% not only ensures the uniform distribution of carbon fiber in the matrix, but also ensures the bonding force between carbon fiber and matrix, and can give full play to the reinforcing effect of carbon fiber. When the carbon fiber dosage increases to 0.60%, the compressive strength decreases. Excessive carbon fiber content can cause carbon fiber agglomeration in the matrix, increasing the interaction between carbon fibers and thus reducing the adhesion between the carbon fibers and the matrix. Furthermore, too much carbon fiber during mixing can easily cause foam rupture and foam coalescing, resulting in the formation of many large bubbles and causing the foamed concrete to exhibit inhomogeneity. Therefore, a high carbon fiber content is detrimental to the compressive strength of foamed concrete.

[0029] 2. Uniaxial Tensile Strength Test: This test used a Chenxin Electronic Universal Testing Machine and employed a uniaxial tensile method. The carbon fiber foam concrete prepared in the example was subjected to a static uniaxial load test according to GB / T 50081-2019. The specimen dimensions were 100mm × 100mm × 300mm. A uniform load was applied, and tension was controlled at a displacement of 0.5mm / min until the specimen fractured. Data was recorded, and the arithmetic mean of three specimen measurements was taken as the tensile strength value of the group of specimens. The formula for calculating tensile strength is shown in Equation (Ⅲ).

[0030] (III); In formula (III): f f P represents the tensile strength of the specimen, in MPa; P represents the failure load of the specimen, in N; A represents the contact area of ​​the specimen, in mm. 2 The tensile strength results of CFFC specimens with different carbon fiber lengths and contents at various density grades are as follows: Figure 3 As shown. Figure 3 (a) Figure 3 (b) Figure 3 (c) and Figure 3 (d) The density of carbon fiber foamed concrete is 500 kg / m³. 3700kg / m 3 900kg / m 3 and 1200kg / m 3 The tensile strength of carbon fiber foam concrete made of carbon fibers with different lengths and volume fractions.

[0031] from Figure 3 (a) ~ Figure 3 As shown in (d), under the same density and carbon fiber length, the tensile strength of the specimens increases with the increase of carbon fiber content. The most significant improvement in tensile strength is observed when the CF volume content is 0.48%. When the length is 6 mm, the tensile strength of the specimen with a carbon fiber content of 0.48% increases by 250% compared to the undoped carbon fiber group. When the content of 6 mm long carbon fibers increases from 0.18% to 0.48%, the tensile strength increases by 72.3%. This indicates that carbon fiber can improve the tensile strength of foamed concrete; and that the ability of carbon fiber to prevent cracking can improve the uniformity of foamed concrete. Figure 3 (c) It can be seen that as the carbon fiber content increases from 0.48% to 0.60%, the strength decreases by 9.8%. This indicates that the carbon fiber content is another important factor affecting the tensile strength of foamed concrete. An appropriate amount of carbon fiber can effectively improve the tensile properties of the matrix, while excessive content leads to the aggregation of carbon fibers in the matrix, enhancing the interaction between carbon fibers and thus reducing the bonding force between the carbon fibers and the matrix, thereby reducing the strength of the material. Figure 3 (a) ~ Figure 3 (d) It can be seen that, under the same density and volumetric admixture, the effect of carbon fiber length on the tensile strength of carbon fiber foamed concrete first increases and then decreases. The influence of carbon fiber length on the tensile strength of foamed concrete is mainly reflected in the interaction between carbon fiber and the matrix. Carbon fiber acts as a bridge in the matrix, effectively dispersing stress and improving the tensile strength of the material. The results show that with the increase of carbon fiber length, the tensile strength of foamed concrete first increases and then decreases. Figure 3 In (b), when the carbon fiber length is extended from 3 mm to 6 mm with a carbon fiber content of 0.48%, the tensile strength increases by 71.1%. Figure 3 (c) Conversely, with the same carbon fiber content, the tensile strength decreased by 7.0% when the carbon fiber length increased from 6 mm to 12 mm, because the longer carbon fibers were prone to kinking inside the specimen. This demonstrates that a carbon fiber length of 6 mm not only bridged the microcracks in the matrix well, but also provided good dispersion of the carbon fibers in the matrix, fully utilizing their reinforcing effect. However, when the carbon fiber length increased to 12 mm, the tensile strength decreased. This is because excessively long carbon fibers are prone to entanglement and agglomeration during stirring, resulting in uneven distribution of carbon fibers in the matrix, thereby reducing the overall tensile properties of the material.

[0032] Tensile strength coefficient: To more intuitively represent the relationship between the volume content and length variation of carbon fiber and the tensile strength of CFFC specimens, the relative tensile strength coefficient of carbon fiber foam concrete was tested: the calculation formula is shown in equation (Ⅳ).

[0033] (Ⅳ); In formula (Ⅳ), f t (N) represents the tensile strength of the CFFC specimen containing carbon fiber, f t0 K represents the tensile strength of the CFFC specimen without carbon fiber. t K represents the relative tensile strength coefficient. K0 for CFFC varies with different density grades. t The results of the change in carbon fiber volume content are as follows Figure 4 As shown. Figure 4 (a) Figure 4 (b) and Figure 4 (c) K values ​​of carbon fiber foam concrete of different densities with different volumetric carbon fiber admixtures when the carbon fiber lengths are 3 mm, 6 mm, and 12 mm, respectively. t , Figure 4 (d) represents the K values ​​of carbon fiber foam concrete of different densities made from carbon fibers of different lengths when the carbon fiber volume content is 0.48%. t .

[0034] from Figure 4 It can be seen that the tensile strength of CFFC is significantly improved after the addition of carbon fiber, and the tensile strength first increases and then decreases, reaching the maximum when the carbon fiber content is 0.48%. Figure 4 In (a), the tensile strength coefficients for the four different contents are 1.3, 1.66, 2.03 and 1.81, respectively, equivalent to 500 kg / m². 3 The increase in tensile strength of carbon fiber is more pronounced in low-density CFFC than in high-density CFFC. All other things being equal, the density is 500 kg / m³. 3 The CFFC is more affected by the carbon fiber bonding, and this enhancement effect on the tensile properties of CFFC weakens as the density grade of CFFC increases. Figure 4 In (b), the density is 500 kg / m³. 3 The tensile strength and density of CFFC are 1200 kg / m³. 3 The increase of 1.7 compared to the previous value indicates that carbon fiber has a more significant reinforcing effect in low-density FC, and that carbon fiber has high stiffness. When FC is subjected to external tension, cracks tend to propagate from the edge region of the specimen, and carbon fiber prevents further crack propagation by dispersing stress. Figure 4 (b) and Figure 4(c) shows that, with constant carbon fiber content and density, increasing the carbon fiber length from 6 mm to 12 mm reduces the relative tensile coefficient, thus worsening the tensile properties of the foamed concrete. This indicates that the length of the carbon fiber is related to K. t Closely related. Figure 4 In (d), the tensile strength coefficient first increases and then decreases with the increase of carbon fiber length, reaching its maximum at a length of 6 mm. Therefore, the test results show that the optimal combination for modifying carbon fiber to improve the tensile properties of FC is: carbon fiber length of 6 mm and carbon fiber content of 0.48%.

[0035] 3. The effect of carbon fiber on the strength of foamed concrete of different density grades: From Figure 4 It can be seen that carbon fiber has a significant effect on improving the tensile strength of foamed concrete of different densities. For example, carbon fiber significantly improves the tensile strength of 500 kg / m³ foamed concrete. 3 700kg / m 3 900kg / m 3 and 1200kg / m 3 The peak strength of the specimens increased by an average of 357%, 206%, 161%, and 53%, and the peak strain increased by an average of 367%, 180%, 207%, and 84%. This indicates that carbon fiber can significantly improve the performance of 500 kg / m² specimens. 3 Density grade significantly affects the compressive and tensile strength of foamed concrete. At lower densities, the FC matrix material exhibits a relatively loose structure with weaker interaction with carbon fibers. Although the increase in tensile strength after adding carbon fibers is limited, the inherently low tensile strength of FC makes the improvement significant. At higher densities, the interaction between the FC matrix material and carbon fibers is stronger, while FC itself already possesses high tensile strength. Although the addition of carbon fibers improves tensile strength, the relative improvement is not as pronounced as at lower densities. With increasing carbon fiber length, the compressive and tensile strengths of the foamed concrete first increase and then decrease. At the same density and dosage, the maximum compressive and tensile strength is reached when the carbon fiber length is 6 mm. This demonstrates that in low-density foamed concrete, longer carbon fibers can better bridge cracks in the matrix, thereby improving compressive and tensile strength. When the carbon fiber length increases to 12 mm, the compressive and tensile strength decreases, indicating that excessively long carbon fibers are prone to entanglement and agglomeration during mixing, leading to uneven distribution of carbon fibers in the matrix and reducing the overall strength of the material. For 700 kg / m³... 3 For high-density foamed concrete, the carbon fiber length exhibits a similar trend in tensile and compressive strength. At 900 kg / m³... 3 In high-density foamed concrete, the length of carbon fibers still has a significant impact on tensile and compressive strength. For 1200 kg / m³... 3In high-density foamed concrete, the length of carbon fibers has a relatively small impact on tensile and compressive strength. When the carbon fiber length is 6 mm, the tensile and compressive strength increases slightly, but the difference is not significant compared to 3 mm and 12 mm carbon fibers. Because the matrix of high-density foamed concrete is relatively dense, the dispersion of carbon fibers within the matrix is ​​poor, making it difficult to fully exert their reinforcing effect. The results show that the carbon fiber content affects the tensile and compressive strength of 500 kg / m³ foamed concrete. 3 The density grade of foamed concrete significantly affects its compressive and tensile strength. With increasing carbon fiber content, the compressive strength of foamed concrete initially increases and then decreases. The maximum compressive and tensile strength is reached when the carbon fiber content is 0.48%. Appropriate amounts of carbon fiber can effectively disperse stress and improve the tensile and compressive properties of the matrix. However, when the carbon fiber content increases to 0.60%, the tensile and compressive strength decreases because excessive content leads to carbon fiber agglomeration, reducing the overall strength of the material. For 700 kg / m³... 3 For foamed concrete of various density grades, the effect of carbon fiber content on tensile and compressive strength also shows a similar trend. At 900 kg / m³... 3 In foamed concrete of various density grades, the carbon fiber content still has a significant impact on tensile and compressive strength. For 1200 kg / m³... 3 For foamed concrete of different density grades, the effect of carbon fiber content on tensile and compressive strength is relatively small. When the carbon fiber content is 0.36%, the compressive strength increases slightly, but the difference is not significant compared to 0.18% and 0.48% carbon fiber content. Because the matrix of high-density foamed concrete is relatively dense, the dispersion of carbon fiber within the matrix is ​​poor, making it difficult to fully exert its reinforcing effect. In summary, the influence of carbon fiber on the strength of foamed concrete of different densities is multifaceted. Both the length and content of carbon fiber have a significant impact on the compressive and tensile strength of foamed concrete. The reinforcing effect of carbon fiber is most significant in low-density foamed concrete, while its reinforcing effect is relatively small in high-density foamed concrete. Simultaneously, the incorporation of carbon fiber can also improve the microstructure and durability of foamed concrete, further enhancing its engineering applicability.

[0036] 4. Test on the failure mode of carbon fiber foamed concrete: Compression tests were conducted on the carbon fiber foamed concrete prepared with 0.48CF(6) / FC-500 in the examples, and on the carbon fiber foamed concrete prepared under the same conditions but without carbon fiber. The stress-strain curves obtained are as follows: Figure 5 As shown. From Figure 5As can be seen, the two curves exhibit similar trends. In the initial loading stage, all curves show small compressive loads, attributed to the small gap between the specimen and the test fixture. Subsequently, the compressive stress increases linearly, indicating that the specimen is mainly in the elastic deformation stage. After reaching the peak load, the curves gradually decrease, indicating that the material has entered the plastic yielding stage. The stress-strain curves show that, due to the presence of the plastic yielding stage, CFFC exhibits good deformation capacity and excellent energy absorption characteristics. During the compression test, two-dimensional digital image correlation (DIC) technology was used to monitor the strain field distribution on the specimen surface to further analyze its potential failure mechanism. The results are as follows: Figure 6 As shown. Figure 6 (a) The density of undoped carbon fiber is 500 kg / m³ 3 foamed concrete, Figure 6 (b) A carbon fiber with a volumetric carbon content of 0.48% and a length of 6 mm, having a density of 500 kg / m³. 3 Foamed concrete.

[0037] Figure 6 Presenting the corresponding compression test process Figure 5 Typical compressive strain contour distributions of specimens at different stages (labeled A, B, C, and D). In the initial stage, the material mainly undergoes elastic deformation, and the strain distribution in the central working region of the CFFC is relatively uniform. The elastic strain inside the material is recoverable, and no obvious microcracks are observed on the specimen surface. After the load reaches its peak, the stress level drops sharply ( Figure 5 In stage B, crack propagation and penetration lead to internal damage accumulation in the material. The DIC strain contour plot clearly shows that the high strain concentration region closely matches the fine transverse cracks appearing in the specimen. The initiation of these cracks promotes lateral slip, and stress fluctuations occur near this critical value as strain increases. Subsequently, the stress-strain curve enters the plastic plateau stage (…). Figure 5 (Middle stage C), corresponding DIC contour map ( Figure 6 (C) shows that at this stage, the specimen approached its ultimate failure load. Due to its low strength and numerous internal pores, spalling occurred at the ends and surrounding areas. The crack in the upper part of the specimen continued to propagate, eventually forming a through crack. This indicates that the internal cell wall structure of the material had been severely damaged and ultimately failed. Figure 6 Mid-stage D). Figure 7 In (a): (A), (B), (C), and (D) represent the density of 500 kg / m³ without added carbon fiber, respectively. 3 Foamed concrete, with a volumetric admixture of 0.48% and carbon fiber with a length of 6 mm, has a density of 700 kg / m³. 3 Carbon fiber foam concrete, made with carbon fibers of 0.48% by volume and 6mm in length, has a density of 900 kg / m³.3 Carbon fiber foam concrete, made with carbon fibers of 0.48% volumetric weight and 6mm length, has a density of 1200 kg / m³. 3 The failure condition of carbon fiber foamed concrete after tensile testing. Figure 7 In (b): (A), (B), (C), and (D) represent densities of 500 kg / m³ without added carbon fiber. 3 Foamed concrete, with a volumetric admixture of 0.18% and 3mm long carbon fiber, has a density of 700 kg / m³. 3 Carbon fiber foam concrete, made with carbon fibers of 0.36% by volume and 6mm in length, has a density of 900kg / m³. 3 Carbon fiber foam concrete, made with carbon fibers of 0.48% by volume and 12mm in length, has a density of 1200 kg / m³. 3 The damage condition of carbon fiber foamed concrete after compression testing. Figure 7 (b) Failure of foamed concrete specimens with and without carbon fiber after compression testing under the same conditions. For details on the failure modes of ordinary foamed concrete specimens (components of ordinary foamed concrete: water, cement, and foam), please refer to [link to relevant documentation]. Figure 7 (b) of (A). From Figure 7 It can be seen that, compared with ordinary foamed concrete, the specimens incorporating carbon fiber still exhibited crack development as the main failure mode, but their plasticity was significantly improved, the degree of spalling after failure was significantly reduced, and the overall structure remained basically intact. This is mainly attributed to the high strength of carbon fiber, which effectively improved the toughness and reduced the brittleness of the specimens after incorporation into foamed concrete. In contrast, the specimens without carbon fiber showed obvious spalling on the surface. Figure 7 (b) shows that carbon fiber can effectively prevent crack propagation in foamed concrete through bridging effects, significantly improving the failure mode and enhancing the toughness of the specimens. Further comparison... Figure 7 As shown in (A), (B), (C), and (D) of (b), the degree of failure of the specimens intensifies with increasing carbon fiber content. This is because although carbon fiber can improve the strength of foamed concrete, there is an interfacial transition zone between the carbon fiber and the cement matrix. Under greater pressure, cracks easily propagate along this transition zone, eventually forming through cracks. On the other hand, the failure mode of the specimens did not change significantly with different carbon fiber contents, indicating that the incorporation of carbon fiber mainly affects the degree of failure, while its impact on the failure mode is relatively small. Figure 7 (a) The failure condition of the carbon fiber reinforced foamed concrete specimen after tensile testing. From Figure 7As shown in (a), there are no microcracks on either side of the main crack, and the crack can appear anywhere within the gauge length, exhibiting strong randomness. During the tensile process, the fracture surface becomes increasingly smooth with increasing carbon fiber content and specimen density under tensile load. Under conditions of higher carbon fiber content and longer carbon fiber length, the carbon fiber pull-out phenomenon at the fracture site is more pronounced. This indicates that the carbon fiber plays a bridging role in the specimen, thereby improving the tensile strength and load-bearing capacity of the material. Figure 7 The study revealed that when the carbon fiber volume fraction was 0.18%, the fracture of the CFFC specimen mainly manifested as a straight crack forming along the waistline of the compaction block. However, when the carbon fiber volume fraction increased to 0.48%, the crack exhibited a tortuous shape, thus improving the material's toughness. Further increasing the carbon fiber volume fraction to 0.60% resulted in not only a main crack extending along a tortuous path but also the formation of multiple secondary cracks, significantly enhancing the overall toughness of the material. The addition of carbon fiber significantly altered the failure mode of foamed concrete. Foamed concrete without carbon fiber typically exhibits brittle failure under pressure; once cracks form, they propagate rapidly, leading to sudden fracture. However, with the addition of carbon fiber, the failure mode of foamed concrete tends towards ductile failure. This is because carbon fiber acts as a bridge in the matrix; when cracks form, the carbon fiber can withstand some tensile stress, preventing further crack propagation. Specifically, during compression, the crack propagation rate of foamed concrete with carbon fiber is slowed, and the specimen can maintain a certain load-bearing capacity after reaching peak stress, exhibiting better ductility. Furthermore, the addition of carbon fiber alters the failure mode of foamed concrete during tensile testing. Without carbon fiber, cracks in foamed concrete typically propagate rapidly along the weakest section during tension, leading to rapid specimen fracture. However, with the addition of carbon fiber, crack initiation and propagation are hindered during tension, resulting in a more tortuous crack propagation path and a slower fracture process. This ductile failure mode contributes to improving the impact resistance and durability of foamed concrete.

[0038] Figure 8 Typical stress-strain curves of CFFC specimens in tensile tests are shown, and stress-strain curves of FC are also included for comparative analysis. Figure 8 In China: the density of 0% CFFC is 500 kg / m³. 3 The carbon fiber volume content is 0; the density of 0.48% CFFC is 500 kg / m³. 3 The carbon fiber volume fraction is 0.48%, and the carbon fiber length is 6 mm. From... Figure 8It can be seen that the FC specimen experienced an initial linear elastic stage before reaching its peak strength (0.03 MPa), followed by specimen failure (stage C). At the peak stress point, the curve gradually decreased, due to crack propagation or local carbon fiber pull-out. The descending branch of the stress-strain curve indicates low residual stress, and no obvious oscillations were observed on the curve after specimen fracture. The ascending branch of FC mainly represents the linear elastic stage, which lasts almost throughout the entire deformation process. In contrast, the CFFC specimen, due to the reinforcement of carbon fibers, does not immediately undergo brittle failure after reaching its peak strength. The stress-strain curve of CFFC exhibits typical mechanical properties of carbon fiber reinforced foamed cement-based materials. In the initial stage, the material exhibits linear elasticity at low strain, followed by a rapid decrease in stress, corresponding to the formation of the first crack (matrix failure), and entering the plastic deformation stage. Within the plastic zone, the material can still withstand a certain proportion of the peak strength with increasing displacement, attributed to the frictional slip and pull-out effects of the carbon fibers. With increasing carbon fiber content, the area under the curve of the CFFC specimen gradually increases, indicating an improvement in its energy absorption capacity. During the tensile strength test of CFFC, DIC (Digital Image Correlation) was used to monitor the strain field distribution and analyze crack initiation and propagation behavior. The results are as follows: Figure 9 As shown. Figure 9 The density of CFFC in (a) is 500 kg / m³. 3 (a) The carbon fiber volume content is 0; (b) The density of CFFC is 500 kg / m³. 3 The carbon fiber volume content is 0.48%, and the length of the carbon fiber is 6mm. Figure 9 For different stages (corresponding) Figure 8 Typical tensile strain modes of specimens A, B, C, and D in the diagram. Figure 9 It is evident that as the damaged area gradually expands under longitudinal tensile loading and propagates in the transverse direction, the longitudinal tensile strain of both types of specimens increases. The transverse expansion of the failure zone indicates that the crack gradually penetrates the material structure. The distribution and transmission mechanism of strain under concentrated loads (with and without carbon fibers) were also investigated. The results show that the confined region at the center of the FC-CF specimen (foamed concrete specimens with and without carbon fibers) exhibits a high strain field, while the strain of the CFFC specimen is uniformly distributed throughout the entire material. This can be attributed to the high modulus properties of carbon fibers, which effectively inhibit transverse crack propagation and, through close bonding with the surrounding matrix, effectively transfer and disperse stress, thereby improving the overall tensile strength of the material.

[0039] 5. Flowability Test: The carbon fiber foamed concrete prepared in the example was poured into a flowability test chamber with dimensions of 600mm×200mm×200mm. After standing for 1 minute, the maximum distance it could freely flow on a horizontal surface was measured. The effects of different carbon fiber dosages and lengths on the flowability of the foamed concrete were recorded, and the changes in the flowability of the slurry under different variables were compared. The test results are as follows: Figure 10 As shown. From Figure 10 As can be seen, the fluidity decreases with increasing carbon fiber content. When the carbon fiber content reaches 0.60%, the fluidity decreases from 22 mm to 9 mm. This demonstrates that the externally added short-cut carbon fibers form a three-dimensional randomized network structure in foamed concrete, significantly increasing the friction and tensile force between the carbon fibers and fine aggregates. Increasing the carbon fiber content means increasing the number of carbon fibers, thus significantly increasing the consumption of cement paste, making the mortar more viscous, and leading to a decrease in the paste's flowability. Increasing the carbon fiber length also leads to decreased fluidity. This demonstrates that longer carbon fibers are more likely to form aggregates and interlock in the mixture, thus significantly increasing the internal resistance of the mixture and reducing its fluidity. Under the same dosage conditions, the effect of adding 12 mm carbon fibers on the fluidity of cement mortar is smaller than that of 6 mm carbon fibers. This is because 12 mm carbon fibers are easier to disperse in cement mortar than 6 mm carbon fibers, resulting in less clumping. Although both have the same specific surface area, at the same volume dosage, the number of 6 mm carbon fibers is twice that of 12 mm carbon fibers, making it easier to form a network overlap in the mortar, thereby enhancing the barrier effect. Shorter carbon fibers, with a higher number of strands, are more difficult to disperse in mortar, leading to a more significant decrease in fluidity. In summary, the addition of carbon fibers significantly alters the failure mode of foamed concrete, transforming it from brittle to ductile failure, effectively improving the material's ductility and impact resistance. Regarding mechanical properties, the length and dosage of carbon fibers have a significant impact on the compressive and tensile strength of foamed concrete. A 6mm carbon fiber length shows the best effect in improving strength; an appropriate carbon fiber dosage (0.36%) can significantly improve the strength of foamed concrete, while excessive dosage will reduce material properties due to carbon fiber agglomeration. The addition of carbon fibers reduces the fluidity of foamed concrete; as the carbon fiber dosage and length increase, the fluidity decreases. This is because carbon fibers form a reinforcing skeleton structure in the concrete, increasing the internal friction of the mortar and restricting its free flow.

[0040] (II) Dynamic Compression Performance Testing of Carbon Fiber Foamed Concrete: Dynamic Mechanical Experiment: The dynamic mechanical properties of carbon fiber foamed concrete were studied using a split Hopkinson bar (SHPB) experimental system. Foamed concrete specimens of different densities were selected and prepared into cylindrical shapes with a diameter of 75 mm and a height of 37.5 mm. During the experiment, the impact speed of the impact bar was precisely controlled to achieve impact loading conditions under different strain rates. Stress wave signals were collected using strain gauges, and the deformation and failure process of the specimens were recorded using a high-speed camera to accurately obtain parameters such as the stress-strain relationship, failure mode, and dynamic strength of the foamed concrete under dynamic impact. The SHPB dynamic compression testing equipment was used to comprehensively and systematically analyze the failure mode, dynamic compressive strength, dynamic compression stress-strain curve, and dynamic compression energy consumption index of foamed concrete under different carbon fiber lengths and dosages, exploring its dynamic compression mechanical properties. Using carbon fiber volume content and carbon fiber length as independent variables, 90 samples were collected in each group (0.18%, 0.36%, 0.48%, 0.60%; 3 mm, 6 mm, 12 mm) with 6 samples per group to ensure the reliability and accuracy of the experimental data. The specimen was a circular disc with a diameter of d = 75 mm and a thickness of 37.5 mm. Before loading the specimen, it needed to be polished and then coated with Vaseline to ensure that the two surfaces were parallel and uniformly stressed within the plane during impact, thus avoiding data deviation due to uneven stress. This experiment used three air pressures (0.2 MPa, 0.25 MPa, and 0.3 MPa) (corresponding to three strain rates, automatically acquired by the ultra-dynamic strain gauge acquisition system under different air pressure impacts) for quasi-dynamic testing.

[0041] 1. Dynamic compressive strength: In static mechanical tests, the performance improvement effect on low-density foamed concrete was particularly significant when the carbon fiber length was 6mm and the volumetric admixture was 0.48%. Therefore, in the dynamic compression test, a carbon fiber length of 6mm and a density of 500kg / m³ were selected. 3 Impact tests were conducted on the specimens. The dynamic strength of foamed concrete specimens with different carbon fiber content under three pneumatic impact loads is shown in the figure. Figure 11 As shown in (a, b, c). From Figure 11It is evident that the addition of carbon fiber significantly improves the impact strength of foamed concrete. At an air pressure of 0.2 MPa, the stresses of specimens with 0–0.60% carbon fiber content were 1.16 MPa, 1.58 MPa, 1.87 MPa, 2.28 MPa, and 1.89 MPa, respectively. Under the four carbon fiber volume fractions, the corresponding strengths of the foamed concrete increased by 6.6%, 37.9%, 49.2%, and 38.6%, respectively. At an air pressure of 0.25 MPa, the stresses of specimens with 0–0.60% carbon fiber content were 1.91 MPa, 2.43 MPa, 2.65 MPa, 3.45 MPa, and 2.98 MPa, respectively. Under the four carbon fiber volume fractions, the corresponding strengths of the foamed concrete increased by 21.4%, 27.9%, 44.6%, and 35.9%, respectively. When the air pressure was 0.3 MPa, the stresses of the specimens with 0% to 0.60% carbon fiber content were 2.48 MPa, 3.15 MPa, 3.21 MPa, 4.20 MPa, and 4.05 MPa, respectively. At the four carbon fiber volumetric dosages, the strength of the foamed concrete increased by 21.3%, 22.7%, 40.9%, and 38.8%, respectively, reaching its maximum at a dosage of 0.48%. The dynamic compressive stress-strain curve of carbon fiber foamed concrete can be divided into an ascending segment, a plateau segment, and a softening and descending segment. In the ascending segment, the stress-strain curve of carbon fiber foamed concrete is approximately linear in the early stage, indicating an elastic phase. Figure 11 In the study, the elastic modulus initially increased and then decreased with increasing carbon fiber content. When the carbon fiber volume content was 0.60% compared to 0.48%, the addition of carbon fiber caused the foamed concrete to initially increase and then decrease. This indicates that excessive carbon fiber addition leads to increased internal defects in the foamed concrete and carbon fiber agglomeration, thus affecting the overall material performance. The stress-strain curves show that the addition of carbon fiber significantly improved the impact toughness of the foamed concrete. In the plateau section, the material exhibited a stable stress level, indicating that carbon fiber can effectively absorb and dissipate impact energy, improving the material's impact resistance.

[0042] Dynamic compression performance test: To more intuitively illustrate the effect of carbon fiber length on the dynamic compression performance of foamed concrete, a carbon fiber volume fraction of 0.48% and a density grade of 500 kg / m³ were selected. 3 The analysis focused on carbon fiber foamed concrete. The dynamic strength of carbon fiber foamed concrete under different air pressures (0.2 MPa, 0.25 MPa, and 0.3 MPa) was as follows: Figure 12 As shown. By Figure 12It is known that, with the same carbon fiber content, the dynamic compressive strength increases with increasing air pressure under different air pressures. This proves that as the air pressure increases, the dynamic compressive strength also increases, exhibiting an effect of increased strain rate. Under the same strain rate, the dynamic compressive strength first increases and then decreases with increasing carbon fiber length, indicating that there is a maximum dynamic compressive strength within a certain carbon fiber length, and the dynamic compressive strength decreases when the carbon fiber is too long. When the carbon fiber is too long, it is prone to agglomeration in foamed concrete. Agglomeration leads to the formation of localized clusters of carbon fibers within the concrete, rather than uniform dispersion. This agglomeration disrupts the homogeneity of the concrete, causing stress concentration and thus reducing the impact strength of the specimen. Furthermore, when the carbon fiber is too long, the bonding force may be insufficient to support the stress transmission of the carbon fiber, leading to interface failure between the carbon fiber and the matrix, thereby reducing strength. The performance improvement effect of carbon fiber foamed concrete shows significant differences when facing different impact intensities. Specifically, at lower impact intensities, the addition of carbon fiber has a more significant effect on improving the strength of foamed concrete, while at higher impact intensities, this effect is relatively weakened. Dynamic compression performance test of carbon fiber foamed concrete with different carbon fiber content. Figure 13 The carbon fiber content at 0.2 MPa pressure is compared with that of a carbon fiber with a density of 500 kg / m³. 3 The influence of the dynamic compressive strength of foamed concrete is due to Figure 13 It is known that under the same air pressure, the strength of foamed concrete varies with different carbon fiber dosages. For a given carbon fiber length, the reinforcing effect is most significant when the carbon fiber dosage is 0.48%. Taking 6mm as an example, at 0.2MPa air pressure, the strengths of specimens with carbon fiber dosages of 0.18%~0.60% are 1.58MPa, 1.87MPa, 2.28MPa, and 1.89MPa, respectively. At 0.2MPa air pressure, the maximum stress increased by 36.9%, 49.2%, and 37.6% for lengths of 3, 6, and 12mm compared to no carbon fiber, respectively. This indicates that there is a maximum dynamic compressive strength within a certain carbon fiber dosage range; excessive dosage will decrease the dynamic compressive strength. Too much carbon fiber increases the difficulty of dispersion; unevenly dispersed carbon fiber cannot fully exert its reinforcing effect and instead becomes a weak point within the foamed concrete matrix, thus affecting its strength. Excessive carbon fiber can exacerbate stress concentration, especially in areas where carbon fiber aggregates and at the interface between carbon fiber and the matrix. Stress concentration can cause the stress in these areas to exceed the material's load-bearing capacity, leading to the generation and propagation of microcracks.

[0043] Dynamic compression energy dissipation test: To quantitatively evaluate the energy dissipation characteristics of carbon fiber foamed concrete under dynamic impact loading, an energy absorption density index was constructed using dynamic stress-strain curves obtained from Hopkinson bar compression (SHPB) tests. This index is defined as the impact energy absorbed per unit volume of the specimen. The integral area of ​​the curve (i.e., the shaded area) intuitively reflects the energy accumulation and dissipation mechanism of the material throughout the entire process from elastic deformation and plastic flow to structural instability. Its value is closely related to the carbon fiber reinforcement effect, the pore structure collapse mode, and the crack propagation path. Its physical characterization can be achieved through integral calculation of the dynamic compression stress-strain curve, such as... Figure 14 As shown in the left figure, calculate according to formula (V): (V); In formula (V), S is the energy consumption value, in J; σ is the stress, in MPa; μ is the ultimate strain, dimensionless. Carbon fibers with a length of 6 mm have a density of 500 kg / m³. 3 The dynamic compressive energy consumption of carbon fiber foamed concrete with different carbon fiber admixtures under air pressures of 0.2 MPa, 0.25 MPa, and 0.3 MPa is shown in the figure. Figure 14 As shown in the right figure, the dynamic compression energy consumption of foamed concrete exhibits a significant strain rate increase effect, with energy consumption increasing with increasing air pressure. For example, without carbon fiber, the energy consumption at air pressures of 0.2 MPa, 0.25 MPa, and 0.3 MPa is 5.2 J, 7.5 J, and 12.8 J, respectively. This is because at high strain rates, both the peak stress and ultimate strain of the foamed concrete increase, leading to increased energy consumption. On the other hand, carbon fiber can improve the energy consumption capacity of foamed concrete; with increasing carbon fiber content, energy consumption first increases and then decreases. Taking 0.2 MPa as an example, the energy consumption at carbon fiber content of 0-0.60% is 5.2 J, 6.1 J, 7.3 J, 9.4 J, and 7.6 J, respectively. This indicates that carbon fiber improves the energy consumption of foamed concrete within a certain content range, but the effect is not significant when the content is too high. The reason is that, as shown in the porosity and average pore size data in the micro-mechanism analysis in (III), with the increase of carbon fiber content, both the average pore size and porosity decrease, and the addition of carbon fiber improves the performance and integrity of the foamed concrete matrix.

[0044] 2. Test on the failure modes of carbon fiber in carbon fiber foamed concrete. Figure 15This paper demonstrates the dynamic failure morphology of specimens with different carbon fiber volume fractions under varying gradient impact pressures. The experimental results show that the baseline specimens without carbon fiber, due to insufficient matrix strength and a lack of effective energy dissipation mechanisms, underwent complete pulverization failure under high stress levels (0.25 MPa, 0.3 MPa). At an impact strength of 0.2 MPa, the specimens without carbon fiber exhibited typical brittle fracture characteristics: the main crack rapidly propagated along the shock wave propagation direction, forming a penetrating fracture surface; the fragments exhibited irregular polyhedral shapes; and due to the lack of bridging effect from carbon fiber, significant interface separation occurred between the fragments. This indicates that the specimens without carbon fiber exhibit typical brittle fracture characteristics under impact loading. With increasing carbon fiber content, the failure morphology of the specimens showed a significant improvement in toughness. The crack propagation path was constrained by the bonding effect between the carbon fiber and the matrix interface, resulting in bifurcation and deflection phenomena, and the fragmentation was significantly alleviated. Under the same 0.2 MPa air pressure, the carbon fiber foamed concrete specimen with a carbon fiber content of 0.48% was more intact than the specimen without carbon fiber, with only a few fragments breaking and no spalling. This indicates that carbon fiber effectively improves the impact toughness of foamed concrete through stress transfer and crack passivation mechanisms. Through dynamic compression mechanical property tests, the failure mode, dynamic compression stress-strain curve, and dynamic compression energy consumption of carbon fiber foamed concrete under three air pressures were studied. The conclusions are: (1) The dynamic compression strength of foamed concrete has a typical strain rate effect, and the dynamic compression strength increases with increasing air pressure. Under the same air pressure conditions, when the carbon fiber length is constant, the dynamic compression strength first increases and then decreases with increasing carbon fiber content. The dynamic compression strength reaches its maximum value when the carbon fiber content is 0.48%. (2) When the carbon fiber content is 0.48%, the three carbon fiber lengths have different effects on the reinforcement of foamed concrete under three air pressures. When the air pressure is constant, the dynamic compression strength decreases with increasing carbon fiber length. When the air pressure is 0.2MPa, the maximum dynamic strength of 3, 6, and 12 mm lengths increases by 36.9%, 49.2%, and 37.6% respectively compared with the non-carbon fiber content; when the air pressure is 0.25MPa, the dynamic strength of 3, 6, and 12 mm lengths increases by 40%, 45.2%, and 41.8% respectively compared with the non-carbon fiber content; when the air pressure is 0.3MPa, the dynamic strength of 3, 6, and 12 mm lengths increases by 34.9%, 41.2%, and 38.5% respectively compared with the non-carbon fiber content. (3) The dynamic pressure energy consumption of foamed concrete exhibits a typical strain rate effect. As the air pressure increases, the energy consumption of carbon fiber foamed concrete increases. The energy consumption first increases and then decreases with the increase of carbon fiber content. The energy consumption performance is better when the carbon fiber content is 0.48%, reaching 9.4J, 14.6J, and 18.6J respectively under the three air pressures. (4) Carbon fiber foamed concrete shows a more significant improvement effect when facing lower impact strength.However, as impact strength gradually increases, the effect of adding carbon fiber on strength improvement becomes less significant.

[0045] (III) Microscopic Mechanism Analysis: The microstructure of carbon fiber foamed concrete is the key foundation for revealing its macroscopic mechanical property changes. Based on the study of the static and dynamic mechanical properties of carbon fiber foamed concrete, the microscopic characteristics of carbon fiber foamed concrete were explored and its mechanical property mechanism was explained in depth using SEM scanning electron microscopy, EDS energy dispersive spectroscopy, XRD diffraction, and MIP mercury porosimetry.

[0046] 1. Pore Structure Analysis of Carbon Fiber Foamed Concrete. In this study, pores refer to the air pores introduced through the foaming agent. First, the cross-section of the foamed concrete was photographed using a stereomicroscope; several images were randomly taken from each specimen, as shown below. Figure 16 Subsequently, the obtained images were processed, and key pore structure parameters, including porosity, average pore diameter, pore area, and pore size, were measured and analyzed using specialized image processing software, providing precise data support for the microstructure research of foamed concrete. Porosity: Figure 17 It demonstrated the use of carbon fiber with a length of 6mm and a foam density of 500kg / m. 3 Under certain conditions, the effect of different carbon fiber contents on the pore size distribution of foamed concrete was investigated. Where a, b, c, and d correspond to carbon fiber contents of 0.18%, 0.36%, 0.48%, and 0.60%, respectively. The horizontal axis represents pore size, and the vertical axis represents the pore volume of the corresponding pore size. From... Figure 17 It can be seen that compared with foamed concrete containing less carbon fiber (0.18% CFFC), the number of fine pores inside the foamed concrete decreases significantly with the increase of carbon fiber content, while the number of large pores on the outside increases, making the overall pore distribution more uneven. This indicates that the addition of carbon fiber can effectively inhibit the growth of pores inside the foamed concrete, but it also leads to the unevenness of the pore structure. Further analysis shows that in foamed concrete with 0.6% carbon fiber (0.6% CFFC), the proportion of pore volume in the 0-200μm, 200-400μm, and >800μm ranges is higher than that in 0.18% CFFC without carbon fiber, while the proportion of pores in the 400-800μm range is relatively low. This indicates that the presence of carbon fiber causes a significant polarization in the pore distribution, both inhibiting further expansion of pores and causing some pores to expand outward after being compressed internally, forming larger pore structures, such as... Figure 16 and Figure 17As shown, the role of carbon fiber in foamed concrete has a dual nature. On the one hand, carbon fiber can provide support during foam dispersion, reducing the probability of foam breakage and coalescence, thereby improving the stability of the slurry and effectively preventing formwork collapse. This is due to the high strength and high modulus of carbon fiber, which allows it to form a support network in the slurry, enhancing the uniformity of the foam and improving the overall structural stability of the concrete. On the other hand, the addition of carbon fiber also leads to an expansion of the pore distribution, causing changes in the pore structure of the concrete. This is because carbon fiber may affect the generation and distribution of air bubbles, leading to an increase in the size or non-uniformity of the pores inside the foamed concrete, thus affecting the mechanical properties and durability of the material to some extent. Average pore size and specific surface area: Table 5 shows the average pore size and specific surface area for a carbon fiber length of 6 mm and a foam density of 500 kg / m³. 3 The structural parameters of foamed concrete with different carbon fiber content are shown in Table 5 below, outlining the pore structure. The reason for the significant difference between the intermediate pore diameter (V) calculated using the volume method and the intermediate pore diameter (A) calculated using the area method is as follows: Intermediate pore diameter (V) refers to the pore diameter corresponding to the median pore volume when pores of different diameters are arranged in terms of pore volume; intermediate pore diameter (A) refers to the pore diameter corresponding to the median pore surface area when pores of different diameters are arranged in terms of pore surface area. For pores of the same volume but different diameters, the pore with the smaller diameter has a larger surface area. Generally, the intermediate pore diameter (V) is larger than the intermediate pore diameter (A).

[0047] Table 5 Calculation results of pore structure parameters

[0048]

[0049] Carbon fiber has a certain influence on the macroscopic morphology of foamed concrete pores. Foamed concrete without carbon fiber has more pores and larger pore size deviations, with the median pore size (V) exceeding 42,864.34 nm. After adding carbon fiber, the median pore size decreases. With further increases in carbon fiber content, the pores tend to become smaller and more uniform. However, when the carbon fiber content exceeds a certain amount, it no longer improves the pore structure morphology. Data shows that the porosity of specimens with 0.48% and 0.60% carbon fiber content is not significantly different. The average pore size uniformity decreases compared to specimens with 0.36%-0.60% carbon fiber content. Microscopic electron microscopy also reveals a more pronounced disordered distribution of carbon fiber within the specimen cross-section compared to lower carbon fiber content, forming a disordered carbon fiber-foamed concrete support system. Figure 18As shown, the effect of carbon fiber on the pore size of foamed concrete is due to the partial defoaming phenomenon caused by carbon fiber incorporation. This manifests as the elimination of relatively weak large air bubbles, while smaller air bubbles with better quality and smaller pore size are retained. Therefore, with the increase of carbon fiber content, the pore size of the bubbles in the specimen becomes smaller and more uniform. However, when the carbon fiber content is excessive, small air bubbles will also be eliminated when mixed with a large amount of carbon fiber. The microstructure also shows that the elimination of small air bubbles is accompanied by the synthesis of large air bubbles and the generation of interconnected air bubbles, which again leads to an increase in air bubble inhomogeneity.

[0050] 2. Microstructure Analysis. To further analyze the internal structure of the CFFC specimens after testing, scanning electron microscopy (SEM) was used to characterize the damaged areas. The SEM images clearly show the distribution of microbubbles in all specimens. Figure 18 As shown, the low-density foamed concrete FC has more closed pores on its surface, while the ordinary foamed concrete (without carbon fiber) specimen ( Figure 18 In (a) (A) the pores exhibit larger diameters and more perforations in the pore walls, forming numerous interconnected pores. Furthermore, the presence of numerous micropores in the ordinary matrix is ​​the primary reason for its lower compressive and tensile strength.

[0051] With the incorporation of carbon fiber, such as Figure 18 As shown in (B and C in b), the phenomenon of pore wall rupture is significantly reduced, the pore wall thickness is increased, and the pore structure tends to be stable. Figure 18(A) B and C show the bonding interface between carbon fiber and the concrete matrix. Carbon fiber monofilaments are deeply embedded within the matrix and interwoven in the form of carbon fiber bundles. Similarly, the pulled-out carbon fiber surfaces are covered with a thick layer of hydration products, which effectively enhances the bond strength between the carbon fiber and the concrete matrix. Furthermore, some carbon fibers are embedded in the concrete matrix. When the interface is damaged and cracks appear, the carbon fibers anchored in the matrix experience slight slippage, forming frictional resistance, thus coordinating deformation and making the stress distribution within the concrete more uniform. The addition of carbon fiber not only significantly reduces the pore structure of foamed concrete but also effectively compensates for the inherent defects of porous materials. Insufficient carbon fiber content or excessively short carbon fiber length may reduce the bond strength between the carbon fiber and the cement foam matrix, leading to relative slippage and making the specimen more prone to cracking under stress. With increasing carbon fiber content, the number of pores further decreases, and the pore wall thickness further increases. When the specimen reaches peak stress and fails, it can be observed that the fractured matrix still adheres to the carbon fiber surface and is subsequently pulled out. However, excessive carbon fiber content or excessively long carbon fibers can easily lead to carbon fiber aggregation within the matrix, reducing dispersion and weakening the overall structural uniformity. Overly long carbon fibers may knot and bend during mixing, affecting their bridging effect and creating weak areas within the specimen. SEM images further reveal the failure characteristics of CFFCs under different load conditions (tension and compression). Figure 18 As shown in (a, B), under tensile load, the fractured matrix adheres to the carbon fiber surface, accompanied by fiber pull-out, indicating that carbon fibers can effectively enhance the integrity of the matrix under tension. Under compressive load, however, bending and pull-out of the carbon fibers are observed, further verifying the significant impact of tensile and compressive loads on foamed concrete structures. Figure 18 (b in B) and Figure 18 (b, C) As can be seen, carbon fiber is a multifilament structure composed of multiple monofilaments, with numerous tiny voids between the monofilaments. During mixing, the yarn structure tends to loosen, increasing the internal voids, allowing cement particles to easily fill them. After hardening, the shrinkage of the cement further enhances the bond strength between the yarn and the concrete matrix. Furthermore, all the monofilaments within the yarn can collectively bear the load, effectively inhibiting the propagation of cracks within the concrete matrix and improving overall strength. Hydration product analysis: EDS analysis was performed on the powder extracted from the carbon fiber foam concrete specimens. Figure 19The EDS spectra revealed four main crystals in the recycled foamed concrete (hydration products generated after the experiment): hydrated calcium silicate (CSH), quartz (SiO2), calcium hydroxide (Ca(OH)2), and calcite (CaCO3). This indicates that the hydration products of ordinary and carbon fiber reinforced foamed concrete are essentially the same, and also suggests that carbon fibers are inert within the foamed concrete matrix, hardly reacting with the concrete to generate new substances. Recycled micro-powder and fly ash (typical byproducts from the coal-fired industry) contain a large amount of SiO2, which reacts during cement hydration to generate large amounts of water and calcium silicate. However, the addition of carbon fibers led to an increase in the intensity of the diffraction peaks of calcium hydroxide and quartz, indicating an increase in their crystallinity and content. Therefore, carbon fibers affect the hydration process of recycled foamed concrete, accelerating the formation of calcium hydroxide crystals and increasing the amount of unreacted SiO2 crystals. Thus, the increase in compressive strength of carbon fiber reinforced foamed concrete is mainly due to the toughening and crack-resistant properties of carbon fibers being greater than their effect on the hydration process. Surface elemental analysis of the experimental CFFC specimens was performed using EDS. The microstructure morphology of the hydration products after field emission line scanning electron microscopy is shown in the figure below. Figure 19 As shown. From Figure 19 As can be seen, bulk crystals, such as calcium aluminate, calcium hydroxide, and CSH gel, are present in the specimen. These hydration products effectively fill the voids in the FC, improving the density and hardness of the specimen structure. The microstructure also revealed the presence of Ca5Si6O. 16(OH)*4H2O is a calcium silicate hydrate. This compound has a large specific surface area, strong surface activity, and a tendency to aggregate. The microstructure also shows the presence of carbon fiber networks and flocculent structures, which helps to improve the mechanical properties of the specimen. The hydration products adhere to the carbon fiber surface, fill the pores, and enhance gelation. This process increases the bonding between carbon fibers, effectively improving the compressive and tensile properties of the specimen. In general, the incorporation of carbon fibers and hydration products significantly improves the compressive and tensile strength of the specimen. In summary, 1) the increase in carbon fiber incorporation can effectively reduce the fine pores in foamed concrete, thereby changing the pore distribution. The role of carbon fibers is to inhibit the expansion of pores on the one hand, and to make the pore structure more uneven on the other hand, which may lead to a polarized trend in pore distribution. 2) the addition of carbon fibers significantly affects the pore size distribution. When 0.6% carbon fibers are incorporated, the pore volume of 0-200μm and larger than 800μm is increased compared with foamed concrete without carbon fibers, indicating that carbon fibers promote the formation of large pores to a certain extent. 3) SEM images revealed the microstructural characteristics of carbon fiber foamed concrete, showing the pore distribution, the bonding interface between carbon fibers and the matrix, and the distribution of hydration products. The introduction of carbon fibers effectively improved the pore structure, enhanced the integrity of the matrix, and exhibited different failure characteristics under different loading conditions. 4) Carbon fibers can effectively improve the pore structure of foamed concrete, reduce the formation of large pores, and also promote the bonding between the matrix and carbon fibers, resulting in better mechanical properties of the foamed concrete under stress. However, excessive dosage or excessively long carbon fibers may lead to carbon fiber aggregation, affecting the dispersion effect and thus the uniformity of the overall structure.

[0052] In summary, the carbon fiber foamed concrete prepared by the method of this invention has the following advantages: 1) The mechanical properties of carbon fiber foamed concrete are significantly improved. Carbon fibers can significantly increase the peak tensile stress and peak strain of the specimen. With the increase of carbon fiber volume fraction and carbon fiber length, the compressive strength and tensile strength of CFFC show a trend of first increasing and then decreasing. 2) Carbon fibers are more effective in enhancing the strength of low-density CFFC. For a density of 500 kg / m³... 3In the CFFC specimens, the addition of carbon fiber increased the tensile strength and compressive strength by 250% and 88.5%, respectively. 3) When the carbon fiber volume fraction was 0.48% and the length was 6mm, the peak tensile stress, peak strain, and compressive strength of carbon fiber foamed concrete all reached their maximum values. The addition of carbon fiber changed the compression failure mode of FC, changing from longitudinal compression failure to shear compression failure and transverse compression failure; in the tensile test, the fracture surface tended to flatten with increasing density. The addition of carbon fiber prevented crack propagation. 4) The dynamic compressive strength and energy consumption of foamed concrete both exhibited typical strain rate effects, increasing with increasing air pressure. Under the same air pressure, the dynamic compressive strength first increased and then decreased with increasing carbon fiber content, reaching its maximum value at a content of 0.48%. Meanwhile, at air pressures of 0.2MPa, 0.25MPa, and 0.3MPa, the carbon fiber length had different reinforcing effects; the dynamic compressive strength decreased with increasing carbon fiber length, with 6mm carbon fiber showing the best reinforcing effect. 5) The energy dissipation capacity of carbon fiber foamed concrete varies with air pressure and carbon fiber content. At a content of 0.48%, the energy consumption at three air pressures reaches 9.4 J, 14.6 J, and 18.6 J, respectively. The carbon fiber reinforcement effect is more significant at lower impact strengths, but gradually weakens with increasing impact strength. 6) Foamed concrete without carbon fiber exhibits typical brittle failure characteristics under impact loads. However, with the increase of carbon fiber content (0.18%–0.60%), the failure mode of the specimens gradually shifts towards a more resilient mode. Among them, the specimen with a carbon fiber content of 0.48% maintains better integrity under impact, with a significantly reduced degree of fragmentation. This indicates that carbon fiber effectively improves the impact toughness of foamed concrete through stress transfer and crack passivation mechanisms. 7) The incorporation of carbon fiber significantly improves the microstructure and mechanical properties of foamed concrete. SEM analysis shows that carbon fiber reinforced foamed concrete (CFFC) exhibits increased pore wall thickness, a more stable pore structure, enhanced bond strength between carbon fibers and the matrix, and suppressed crack propagation, thereby improving the material's impact toughness. Under tensile conditions, carbon fibers effectively bridge cracks and enhance the overall integrity of the matrix; under compressive conditions, carbon fibers provide additional support, reduce stress concentration, and improve the material's toughness. However, excessive carbon fiber content may affect its dispersibility and reduce structural uniformity. XRD and EDS analyses indicate that carbon fibers are inert in foamed concrete, but their incorporation affects the hydration process, accelerating calcium hydroxide formation and increasing CSH gel content, resulting in a denser matrix. The network structure of carbon fibers, combined with hydration products, improves the compressive and tensile strength of the specimens while effectively filling pores and enhancing the overall stability of the material. Therefore, appropriate carbon fiber incorporation can significantly improve the comprehensive performance of foamed concrete, giving it higher strength and reliability in engineering applications.

[0053] The above embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention.

Claims

1. A carbon fiber foamed concrete, characterized in that, It is composed of cement carbon fiber slurry and foaming liquid; The cement carbon fiber slurry is composed of cement, carbon fiber and water; The foaming liquid is composed of a foaming agent and water; The volume ratio of the foaming agent to water is 1:40; The ratio of the cement carbon fiber slurry to the foaming liquid is 270~300:1 in g:mL. The carbon fiber foamed concrete has the following characteristics: The length of the carbon fiber is 6 mm; The carbon fiber content, on a volumetric basis, is 0.48%. The density of the carbon fiber foam concrete is 500 kg / m³. 3 .

2. The carbon fiber foamed concrete according to claim 1, characterized in that, The foaming agent is selected from protein-based foaming agents.

3. A method for preparing carbon fiber foamed concrete as described in claim 1 or 2, characterized in that, Includes the following steps: (1) Mix cement and carbon fiber, add water to form cement-carbon fiber slurry; (2) Mix the foaming agent and water to form a foaming liquid; (3) The foaming liquid described in step (2) is made into foam; (4) The foam is introduced into the cement carbon fiber slurry to form carbon fiber foam cement slurry; (5) The carbon fiber foam cement slurry is molded, solidified and cured to obtain carbon fiber foam concrete.

4. The preparation method according to claim 3, characterized in that, The step (1) includes: mixing cement and carbon fiber, thoroughly dry mixing, then adding water and stirring for 2 minutes to form a homogeneous cement-carbon fiber slurry; And / or, step (4) includes: introducing the foam into the cement carbon fiber slurry, stirring for 1 minute to form a homogeneous carbon fiber foam cement slurry; And / or, step (5) includes: pouring the carbon fiber foam cement slurry into a standard test mold, smoothing the surface, allowing it to solidify at room temperature for 24 hours, demolding, curing, and obtaining carbon fiber foam concrete.

5. The preparation method according to claim 4, characterized in that, The curing process is carried out in a standard curing room with a temperature of 18~22℃ and a relative humidity of ≥95% for 28 days.

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