Steel fiber reinforced cementitious composite material, method for preparing same, and use thereof

Abstract

The application discloses a kind of steel fiber reinforced cement-based composite material and its preparation method, application, the mass ratio of each component in the composite material is as follows: refractory bauxite sand 220~250 parts, cement 70~80 parts, fly ash 15~20, silica fume 5~10 parts, calcined high-alumina powder 6~9 parts, water reducing agent 0.8~1.2 parts, water 28~32 parts;Modified steel fiber volume content is 1.0%~1.5%;Among them, modified steel fiber is modified by silane coupling agent hydrolysate to obtain.The application introduces refractory bauxite sand to replace traditional aggregate to reduce the thermal expansion of the system, a dense chemical bonding layer is formed on the surface of the modified steel fiber, and the active calcined high-alumina powder is used to realize the filling of micro-cracks and the recovery of mechanical properties in the damaged interface transition zone after disaster recovery, the three synergies form a full-scale fire prevention and disaster self-repair system, effectively guarantee the safety of the structure after disaster, and greatly reduce the cost and difficulty of post-disaster reinforcement.

Description

Technical Field

[0001] This invention belongs to the field of cement-based composite materials, specifically relating to a steel fiber reinforced cement-based composite material with resistance to high-temperature damage and post-disaster self-repair function, its preparation method, and its application. Background Technology

[0002] Concrete, as a core material for infrastructure such as roads, bridges, and rail transit, is consumed in enormous quantities annually. As transportation construction extends into extreme environments, concrete structures not only bear increasing traffic loads but also face potential threats from extreme high-temperature environments such as fires and explosions. [1] High temperatures can cause the decomposition of chemical components within the cementitious materials of concrete and non-uniform thermal expansion, leading to the initiation and connection of microcracks. [2] Especially for steel fiber reinforced cementitious composites with high strength and toughness, the maintenance of their macroscopic mechanical properties is highly dependent on the interfacial transition zone (ITZ) between the fiber and the cement matrix. [3] The interface transition zone, being the weakest link within the material, is highly susceptible to performance degradation under extreme high-temperature conditions. The physicochemical instability of traditional silicate aggregates at high temperatures (such as limestone decomposition and quartz phase transformation) exacerbates thermal stress concentration within the cement matrix, leading to brittle structural failure and severely weakening the service safety and durability of infrastructure. [4] .

[0003] Currently, to improve the high-temperature resistance of cement-based composite materials, both domestically and internationally, the main methods adopted include adding polypropylene fibers to the cement matrix, increasing mineral admixtures, and optimizing aggregate gradation. [5] While adding polypropylene fibers can create pressure relief channels through high-temperature melting to prevent bursting, the resulting voids significantly reduce the density and post-disaster residual strength of cement-based composite materials. [6] While adding mineral admixtures such as fly ash or silica fume as auxiliary cementitious materials can improve the matrix density at room temperature, after exposure to temperatures above 500℃, the hydration products of the cement matrix undergo severe dehydration. Furthermore, due to the lack of support from a refractory skeleton, cement-based composite materials are prone to significant volume shrinkage and strength reduction. [7] Existing interfacial reinforcement methods mostly rely on optimizing aggregate gradation to achieve physical roughening. However, this method cannot alleviate the radial delamination of the interface between steel fibers (high thermal expansion coefficient) and cement matrix (low thermal expansion coefficient) caused by thermal mismatch at the chemical level. This leads to an irreversible loss of the crack-resistant and toughening performance of steel fibers after high temperature. [8] .

[0004] To address the limitations of the existing technologies, this invention proposes a steel fiber reinforced cement-based composite material with resistance to high-temperature damage and post-disaster self-repair functions, as well as its preparation method and application, to solve the practical problems of severe deterioration of the interface transition zone, collapse of the physical properties of the cement matrix, and loss of toughness of steel fiber reinforced cement-based composite materials under extreme high temperatures in transportation engineering.

[0005] References

[0006] [1] Jiang Chao, Ge Yuqing, Gu Xianglin, et al. Fire resistance of carbonized and corroded concrete structures [J]. Journal of Civil Engineering, 2025, 58(11):1-12.

[0007] [2] Lei Mingfeng, Xiao Fenglong, Zhang Hu, et al. Study on damage mechanism and mechanical properties of self-compacting steel fiber reinforced concrete under fire [J]. Journal of Railway Science and Engineering, 2024, 21(10):4201-4213.

[0008] [3] Shen Haiyang, Liu Linghui, Ren Lei. Study on mechanical properties of lightweight aggregate concrete under high temperature [J]. Journal of Railway Science and Engineering, 2022, 19(10):2976-2983.

[0009] [4] GUO Shuaicheng, REN Jinghua, YANG Ting, et al. Influences of surface treatment on the mechanical performances of carbon and basalttextiles-reinforced concretes under harsh environments[J]. Composites Part B:Engineering, 2022, 246: 110195.

[0010] [5] XU Qiqi, JIANG Xuepeng, ZHANG Zhiyun, et al. Experimental study on residual mechanical properties of steel-PVA hybrid fiber high performance concrete after high temperature[J]. Construction and Building Materials, 2025, 458: 139735.

[0011] [6] He Bei, Zhang Hongen, Zhu Xinping, et al. Research progress on mechanical properties and degradation mechanism of ultra-high performance concrete under high temperature environment [J]. Journal of the Chinese Ceramic Society, 2024, 52(11):3470-3481.

[0012] [7] BOUHAFS F, EZZIANE M, AYED K, et al. Effect of water re-curing on the physico-mechanical and microstructural properties of self-compacting concrete reinforced with steel fibers after exposure to high temperatures[J]. Construction and Building Materials, 2024, 413: 134805.

[0013] [8] ZHOU Ao, YU Zechuan, WEI Huinan, et al. Understanding the toughening mechanism of silane coupling agents in the interfacial bonding insteel fiber-reinforced cementitious composites[J]. ACS Applied Materials & Interfaces, 2020, 12(39): 44163-44171. Summary of the Invention

[0014] This invention aims to provide a steel fiber reinforced cement-based composite material with mature technology, excellent interface performance, and the ability to be applied in transportation infrastructure, exhibiting resistance to fire and high-temperature damage and post-disaster self-repair capabilities, as well as its preparation method and application. It mainly addresses the practical problems of severe deterioration of the interface transition zone, collapse of the physical properties of the cement matrix, and loss of toughness in steel fiber reinforced cement-based materials under extreme high temperatures in transportation engineering. Through the synergistic effect of refractory skeleton construction, interface chemical modification, and active minerals, a composite material preparation scheme with high-temperature damage inhibition and post-disaster toughness self-repair capabilities is proposed.

[0015] To achieve the above objectives, the present invention adopts the following technical solution:

[0016] In a first aspect, the present invention provides a steel fiber reinforced cement-based composite material, wherein the mass ratio of each component is as follows: refractory bauxite sand, cement, fly ash, silica fume, calcined high-alumina powder, water-reducing agent, water = 220~250 : 70~80 : 15~20 : 5~10 : 6~9 : 0.8~1.2 : 28~32; the volume content of modified steel fiber is 1.0%~1.5%;

[0017] The modified steel fibers were obtained by modifying the silane coupling agent hydrolysate.

[0018] Based on the above technical solutions, this invention constructs a full-scale fire protection and self-repair system by utilizing the synergistic effect of refractory bauxite sand, activated calcined high-alumina powder to build a refractory skeleton, and silane coupling agent to modify steel fibers: (1) Refractory bauxite sand with extremely low thermal expansion coefficient and high refractoriness completely replaces traditional silicate aggregates to build a stable low-expansion refractory skeleton, thereby suppressing thermal stress concentration from a physical perspective; (2) Calcined high-alumina powder is introduced as an active self-repairing component, and its chemical activity after high temperature is used to induce secondary hydration during the post-disaster curing stage to fill damaged microcracks; (3) On the basis of this stable skeleton, a dense Fe-O-Si chemical bond layer is constructed on the surface of steel fibers through a condensation reaction using silane coupling agent, thereby strengthening the interfacial thermal stability and alleviating thermal mismatch peeling phenomena at the molecular scale. This multi-scale synergistic modification method not only significantly improves the residual fracture toughness of cement-based composite materials at extreme high temperatures, but also endows cement-based composite materials with superior post-disaster performance self-repair capabilities, providing a scientific and efficient technical solution for high-temperature damage protection and low-cost rapid repair of transportation infrastructure.

[0019] Preferably, the fineness of the calcined high-alumina powder is 200-400 mesh, more preferably 300 mesh, and the Al2O3 content is not less than 85%; in high-performance cement-based composite materials, the fineness of the powder is usually required to reach above 200 mesh to ensure the filling effect and reactivity.

[0020] Preferably, the refractory bauxite sand has a particle size distribution between 0.15 mm and 0.6 mm, and an Al2O3 content of not less than 75%.

[0021] Preferably, the volume ratio of the silane coupling agent hydrolysate is: silane coupling agent: anhydrous ethanol: deionized water = 1:(8-12):(2-4), with a preferred ratio of 1:9:2.5; the silane coupling agent is γ-aminopropyltriethoxysilane (KH-550) with a purity of not less than 98%.

[0022] Preferably, the steel fiber is a straight steel fiber with a length of 25-35mm, an aspect ratio of 60-80, and a tensile strength of not less than 1100MPa.

[0023] Preferably, the fly ash is low-calcium grade I fly ash, i.e., the calcium oxide content is not higher than 10%; the silica fume contains not less than 95% silicon dioxide (SiO2).

[0024] Preferably, the water-reducing agent is a polycarboxylate-based high-performance water-reducing agent with a water reduction rate of 25%-30%.

[0025] Preferably, the cement is any one of ordinary silicate cement and aluminate cement, preferably aluminate cement; aluminate cement has excellent refractory properties and good material compatibility with refractory bauxite sand and calcined high alumina powder, and is more suitable for self-repair after high temperature disaster damage.

[0026] Secondly, the present invention also provides a method for preparing steel fiber reinforced cement-based composite materials, the method comprising the following steps:

[0027] (1) Multiphase dry material mixing: Add refractory bauxite sand, cement, fly ash, silica fume, calcined high alumina powder and modified steel fiber to a mixer and dry mix for 2-5 minutes to obtain a dry material mixture. Use physical friction to assist the fiber in being evenly dispersed in the composite powder system and to construct a preliminary refractory skeleton.

[0028] (2) Wet mixing: Add an aqueous solution containing water-reducing agent to the dry mixture and stir at a constant speed for 3-5 minutes until the mixture reaches the required fluidity;

[0029] (3) Molding and curing: Casting and molding, and standard curing are carried out to obtain the steel fiber reinforced cement-based composite material;

[0030] The steel fibers are modified using the following method:

[0031] Preparation and hydrolysis of modified solution: Mix anhydrous ethanol and deionized water in a certain proportion, add silane coupling agent KH-550 and place on a magnetic stirrer. Stir continuously at 25℃-35℃ for 30-60 minutes to obtain silane coupling agent hydrolysate, ensuring that silane molecules are fully hydrolyzed to form a stable silanol solution.

[0032] Steel fiber surface modification treatment: Immerse the steel fiber in the prepared silane coupling agent hydrolysate for 10-15 minutes, take it out and place it in a constant temperature drying oven, heat treat it at 60℃-80℃ for 1-3 hours to obtain modified steel fiber; the heat treatment promotes the condensation reaction between the silanol molecules on the fiber surface and the hydroxyl groups on the fiber surface to form a strong Fe-O-Si chemical bond.

[0033] The condensation and curing of silane coupling agents on the substrate surface is typically completed within 1-3 hours. Too short a time results in incomplete reaction, while too long a time does not meet the efficiency requirements for industrial preparation. In laboratory or industrial production, the mixing of dry powders is usually controlled within 2-5 minutes to ensure that the various mineral components (especially silica fume and high alumina powder) are fully dispersed and do not generate excessive heat accumulation.

[0034] Thirdly, this invention also provides an application of steel fiber reinforced cement-based composite material for repairing cement-based composite materials damaged by high-temperature disasters above 600 degrees Celsius: immersion curing or spray curing for 7-28 days, utilizing calcined high-alumina powder and residual active mineral components (incompletely hydrolyzed cement particles, fly ash, and active silica in silica fume, etc.) in the cement matrix for secondary hydration under the guidance of the interface modification layer, thereby achieving the filling of microcracks in the transition zone of the damaged interface and the restoration of mechanical properties.

[0035] The standard performance characterization points for cement-based composite materials are typically 7 days and 28 days. For secondary hydration repair processes, preliminary mechanical recovery can be observed at 7 days, while the design strength can be reached at 28 days.

[0036] The advantages of this invention compared to existing repair materials:

[0037] (1) This invention utilizes silane coupling agent to construct an organic-inorganic hybrid protective layer on the surface of steel fiber. Through stable Fe-O-Si chemical bonds, it effectively alleviates the thermal mismatch caused by the mismatch of thermal expansion coefficients between steel fiber and cement matrix under extreme high temperature, so that the physical continuity of the interface transition zone can still be maintained between steel fiber and cement matrix after high temperature of 600℃.

[0038] (2) The present invention combines the introduction of refractory bauxite sand and calcined high alumina powder to construct an excellent inorganic refractory skeleton. Compared with ordinary fiber-reinforced cement-based materials, it still has excellent residual energy consumption capacity after high temperature damage. Its instability fracture toughness improvement rate can reach more than 70%, which can effectively prevent the brittle collapse of building structures after encountering extreme high temperature environments such as fire, and effectively ensure structural safety.

[0039] (3) With the specific composition ratio of calcined high alumina powder, fly ash and silica fume, the cement-based composite material can still retain a large number of active sites after high temperature; after re-curing, the interfacial microhardness of the material can be significantly restored, and the compressive strength recovery rate can reach more than 18.06%, which greatly reduces the cost and difficulty of post-disaster reinforcement of transportation facilities.

[0040] (4) The material system and preparation process used in this invention do not require complex special equipment, the modified liquid can be recycled, and the prepared cement-based composite material has good working performance and is suitable for large-scale application in high-performance precast component plants or large infrastructure sites. Attached Figure Description

[0041] Figure 1 The results of compressive strength tests on specimens from different groups;

[0042] Figure 2 The results of flexural strength tests for specimens from different groups;

[0043] Figure 3 The results of instability toughness tests on specimens from different groups;

[0044] Figure 4 The fracture energy test results are for specimens from different groups;

[0045] Figure 5 To monitor the amplitude of peak load by acoustic emission (AE) during the fracture process of specimens from different groups;

[0046] Figure 6 To monitor the relative cumulative energy of acoustic emission (AE) during the fracture process of specimens from different groups;

[0047] Figure 7 Photographs of fracture toughness and acoustic emission tests on specimen 1 in Example 1;

[0048] Figure 8 This is a photograph of the fracture surface of the specimen in Example 1. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0050] The purpose of this invention is to provide a steel fiber reinforced cementitious composite material with excellent high-temperature resistance and self-healing ability for high-temperature damage, as well as its preparation method and applications. This aims to solve the technical bottlenecks of existing fiber-reinforced cementitious materials under extreme high-temperature conditions such as fires, including poor thermophysical stability of ordinary silicate aggregates, severe deterioration of the interfacial transition zone (ITZ) due to thermal mismatch between steel fibers and the cement matrix, loss of toughness, and lack of post-disaster repair activity. This invention uses ordinary silicate cement as the cementitious matrix and innovatively introduces refractory bauxite sand to construct an aggregate skeleton with a low thermal expansion rate. It also synergistically utilizes fly ash, silica fume, and calcined high-alumina powder as micro-aggregate fillers and the secondary hydration effect after high-temperature treatment. The core technology involves using a silane coupling agent to modify the surface of the steel fibers, constructing a high-temperature stable organic-inorganic hybrid molecular film on the fiber surface through a condensation reaction. This establishes a strong chemical bond (Fe-O-Si) between the steel fibers and the matrix, effectively inhibiting ITZ pore expansion and stress concentration-induced physical debonding under high-temperature conditions. By precisely optimizing the interface modification process and the dosage of high-alumina components, this invention not only significantly improves the fracture toughness of materials at room temperature, but also, after experiencing high-temperature damage at 600°C and above, utilizes the reserves of active substances such as calcined high-alumina powder within the matrix, combined with a specific re-curing process, to induce the directional growth of hydration products at the modified interface, achieving a significant recovery in microhardness and self-repair of interfacial micro-damage. Ultimately, a high-performance cement-based composite material with a "highly stable skeleton, strong and tough interface, and efficient repair" under extreme high-temperature conditions is obtained, providing a practical technical solution for improving the fire safety of transportation infrastructure and reducing post-disaster maintenance costs.

[0051] In industry, the applications of bauxite sand and high-alumina powder are mostly limited to refractory bricks and linings for industrial furnaces and kilns, or as industrial abrasives. In the field of cement-based composite materials for conventional transportation infrastructure, a technical solution utilizing both to synergistically construct a refractory framework and combining it with interfacial chemical modification to improve fire resistance has not been reported in existing publicly available technologies.

[0052] This invention utilizes the extremely high chemical stability and low thermal expansion coefficient of refractory bauxite sand to construct a stable physical support framework. Unlike conventional silicate aggregates (such as quartz sand) which undergo drastic volume expansion due to phase transformation near 573℃, this invention fundamentally alleviates the volume instability of conventional silicate aggregates at high temperatures. Furthermore, it selects activated calcined high-alumina powder to utilize its residual chemical activity after undergoing high-temperature thermal activation. Under post-disaster maintenance conditions, it can act as a key repair source to induce secondary hydration reactions, generating aluminate-based hydration products, thereby achieving directional filling of damaged microcracks.

[0053] Unless otherwise specified, all reagents used in the following examples are commercially available chemical reagents.

[0054] The cementing material used in this invention is P.O42.5 grade ordinary Portland cement; the fly ash is low-calcium grade I fly ash; the silica content of the silica fume is ≥95%; the calcined high-alumina powder is 800 mesh high-alumina bauxite powder with an Al2O3 content ≥85%; the aggregate is refractory bauxite sand with a particle size distribution of 0.15mm-0.6mm; the steel fiber is straight steel fiber with a length of 30mm and an aspect ratio of 60; the silane coupling agent is γ-aminopropyltriethoxysilane (KH-550) with a purity ≥98%; and the water-reducing agent is a polycarboxylate-based high-performance water-reducing agent with a water reduction rate of 25%~30%.

[0055] Example 1,

[0056] This embodiment provides a steel fiber reinforced cement-based composite material, which contains the following components by mass ratio: refractory bauxite sand: cement: fly ash: silica fume: calcined high alumina powder: water-reducing agent: water = 250: 80: 15: 5: 8: 1.0: 30; the volume content of modified steel fiber is 1.5%; in the interface modification liquid of steel fiber, the volume ratio of KH-550: anhydrous ethanol: deionized water is 1: 9: 2.5.

[0057] Preparation method:

[0058] (1) Weigh each component according to the mass ratio and volume ratio for later use;

[0059] (2) Mix anhydrous ethanol, deionized water and KH-550, and stir magnetically at 30°C for 45 min to obtain a fully hydrolyzed modified solution (silane coupling agent hydrolysate).

[0060] (3) After immersing the steel fiber in the modification solution for 15 minutes, take it out and place it in an 80℃ constant temperature drying oven for 2 hours to form a dense Fe-O-Si chemical bond layer on the surface of the steel fiber, thus obtaining modified steel fiber.

[0061] (4) Using a cement paste mixer, dry mix refractory bauxite sand, cement, fly ash, silica fume, calcined high alumina powder and modified steel fiber for 3 minutes to obtain a dry mixture.

[0062] (5) Then add an aqueous solution containing water-reducing agent and mix for 5 minutes, then pour and cure.

[0063] Example 2,

[0064] This embodiment provides a steel fiber reinforced cementitious composite material within the range of the claimed proportions. The mass ratio of each component is as follows: river sand: cement: fly ash: silica fume: calcined high alumina powder: water-reducing agent: water = 220:70:15:5:8:1.0:30; the volume content of modified steel fiber is 1.5%, and the steel fiber modification method is the same as in Example 1.

[0065] Preparation method:

[0066] The weighed refractory bauxite sand, cement, fly ash, silica fume, calcined high alumina powder and modified steel fiber were dry-mixed for 3 minutes, then water and water-reducing agent were added and wet-mixed for 5 minutes. The mixture was then poured into molds and cured. The pouring and curing conditions were the same as in Example 1.

[0067] Comparative Example 1,

[0068] This comparative example provides a common steel fiber reinforced cementitious material (conventional river sand group, the main component of which is silicon dioxide, which expands dramatically in volume at 573℃). The mass ratio of each component is as follows: river sand: cement: fly ash: silica fume: calcined high alumina powder: water-reducing agent: water = 250:108:0:0:0:1.0:30; the volumetric content of steel fiber is 1.5%, and the steel fiber is not subjected to any surface modification treatment.

[0069] Preparation method:

[0070] Weighed cement, river sand and unmodified steel fiber were dry-mixed for 3 minutes, water and water-reducing agent were added and wet-mixed for 5 minutes, and then poured into molds and cured. The pouring and curing conditions were the same as in Example 1.

[0071] Comparative Example 2,

[0072] This comparative example provides a steel fiber reinforced cementitious composite material containing calcined high-alumina powder modification and steel fiber modification, but using only ordinary river sand. The mass ratio of each component is: river sand: cement: fly ash: silica fume: calcined high-alumina powder: water-reducing agent: water = 250: 80: 15: 5: 8: 1.0: 30; the volume content of steel fiber is 1.5%, and the steel fiber does not undergo surface modification treatment.

[0073] Preparation method:

[0074] Weighed river sand, cement, fly ash, silica fume, calcined high-alumina powder and unmodified steel fiber were dry-mixed for 3 minutes, water and water-reducing agent were added and wet-mixed for 5 minutes, and then poured into molds and cured. The pouring and curing conditions were the same as in Example 1.

[0075] Comparative Example 3,

[0076] This comparative example provides a steel fiber reinforced cementitious composite material containing refractory bauxite sand and calcined high-alumina powder modified but without steel fiber modification. The mass ratio of each component is: refractory bauxite sand: cement: fly ash: silica fume: calcined high-alumina powder: water-reducing agent: water = 250: 80: 15: 5: 8: 1.0: 30; the volume content of steel fiber is 1.5%, and the steel fiber is not surface modified.

[0077] Preparation method:

[0078] The weighed refractory bauxite sand, cement, fly ash, silica fume, calcined high alumina powder and unmodified steel fiber were dry-mixed for 3 minutes, water and water-reducing agent were added and wet-mixed for 5 minutes, and then poured into molds and cured. The pouring and curing conditions were the same as in Example 1.

[0079] Comparative Example 4,

[0080] This comparative example provides a steel fiber reinforced cementitious composite material containing refractory bauxite sand and modified steel fibers, but without the use of calcined high-alumina powder modification. The mass ratio of each component is: refractory bauxite sand: cement: fly ash: silica fume: calcined high-alumina powder: water-reducing agent: water = 250: 108: 15: 5: 0: 1.0: 30; the volume content of steel fibers is 1.5%, and the steel fibers are modified according to the method of Example 1.

[0081] Preparation method:

[0082] The weighed cement, refractory bauxite sand, fly ash, silica fume and modified steel fiber were dry-mixed for 3 minutes, water and water-reducing agent were added and wet-mixed for 5 minutes, and then poured into molds and cured. The pouring and curing conditions were the same as in Example 1.

[0083] The proportions of each component and the steel fiber modification methods in Examples 1-2 and Comparative Examples 1-4 are summarized in Table 1. Comparative Example 1 uses conventional river sand and ordinary cement, without adding fly ash, silica fume, calcined high-alumina powder, modified steel fibers, or refractory bauxite sand. Comparative Example 1 serves as the benchmark group for Examples 1-2 and other comparative examples. The flexural and compressive strengths of different groups of specimens were measured using the flexural and compressive strength test method in "Test Method for Strength of Cement Mortar (ISO Method)" (GB / T 17671-2021) and summarized in Tables 2a and 2b. The fracture toughness of different groups of specimens was measured using the three-point bending test method in "Test Procedure for Fracture of Hydraulic Concrete" (DL / T 5332-2005) and summarized in Tables 3a and 3b. The damage evolution characteristic parameters of the entire fracture process were collected in real time by an acoustic emission (AE) monitoring system and summarized in Tables 4a and 4b. The fracture toughness and acoustic emission test photos of the specimen in Example 1 are shown below. Figure 7 The test photograph of the fracture surface of the specimen in Example 1 is shown below. Figure 8 Standard curing is performed at 20±2℃, followed by baking at 600℃ for 1 hour. Further curing conditions include immersion in water at 20±2℃ or constant-temperature spray curing for 7-28 days.

[0084] Table 1. Mixing ratios and modification methods of Examples 1-2 and Comparative Examples 1-4

[0085]

[0086] Table 2a Compressive strength test results of specimens in different groups before and after high temperature treatment at 600℃ and after re-curing

[0087]

[0088] Table 2b Results of flexural strength tests on specimens of different groups before and after high-temperature treatment at 600℃ and after subsequent curing

[0089]

[0090] According to Table 2a and Table 2b, Figure 1-2 It can be seen that, compared with Comparative Examples 1-4, Examples 1 and 2 both exhibited excellent resistance to high-temperature damage and post-disaster self-repair performance, which stems from the deep synergy of physical framework, chemical bonding, and active repair. Specifically, compared with Comparative Example 2, which used ordinary river sand, the refractory bauxite sand in Example 1 constructed a stable physical framework support through its low thermal expansion coefficient, effectively avoiding the structural collapse caused by phase transformation expansion of ordinary aggregates, resulting in a significantly better increase in compressive strength after high temperature than the comparative examples; compared with Comparative Example 3, which did not modify steel fibers, Example 1 showed significant advantages in residual flexural strength and recovery of strength after re-curing at high temperature, proving that the Fe-O-Si chemical bonding layer can significantly alleviate thermal mismatch delamination and maintain the bridging and toughening effect of steel fibers; compared with Comparative Example 4, which did not contain calcined high-alumina powder, the flexural strength of Example 1 recovered to 97.7% of the level at room temperature after re-curing, quantitatively verifying the secondary hydration repair activity of calcined high-alumina powder after thermal activation. Quantitative comparison revealed that the combined performance improvement of Comparative Examples 2 and 4 compared to Comparative Example 1 (conventional river sand group) during the re-curing stage (compressive strength 25.7%, flexural strength 15.38%) was still significantly lower than that of Example 1 (compressive strength 45.2%, flexural strength 29.23%), directly demonstrating a significant synergistic enhancement effect between the refractory skeleton and the active self-healing component. Both Example 1 and Example 2, used as boundary verification, achieved a comprehensive improvement in high-temperature resistance and self-healing performance through systematic reinforcement via physical support, interface stabilization, and active filling.

[0091] Table 3a. Fracture toughness test results of specimens in different groups before and after high temperature treatment at 600℃ and after re-curing.

[0092]

[0093] Table 3b: Fracture energy test results of specimens from different groups before and after high-temperature treatment at 600℃ and after re-curing.

[0094]

[0095] According to Tables 3a and 3b, Figure 3-4It can be seen that, compared with Comparative Examples 1-4, Examples 1 and 2 both exhibited the best fracture performance and toughening recovery ability. Specifically, compared with Comparative Example 2 using ordinary river sand, Example 1 showed the highest level of instability toughness and fracture energy after high temperature, proving that the refractory bauxite sand skeleton can effectively suppress the thermal damage of aggregates under extreme temperature rise and maintain the stability of the material's macroscopic fracture performance. Compared with Comparative Example 3 without steel fiber modification, Example 1 showed a 78.57% increase in instability toughness after experiencing a high temperature of 600℃, and the fracture energy also remained at a high level of 46.65 N / m, demonstrating the decisive role of the Fe-O-Si chemical bonding interface in alleviating fiber-matrix thermal mismatch and ensuring the toughening effect of fiber bridging under extreme high temperatures. Compared with Comparative Example 4 without calcined high alumina powder, the fracture energy of Example 1 recovered to 82.4% of the room temperature level after re-curing, quantitatively characterizing the effective repair and reconstruction of the microstructure of the damaged interface transition zone (ITZ) by the thermal activation activity of high alumina powder. Quantitative analysis of the improvement rate reveals that the sum of the improvement rates of Comparative Example 2 and Comparative Example 4 compared to Comparative Example 1 (e.g., a 70.59% increase in instability toughness after high temperature and a 70.62% increase in fracture energy) is significantly lower than the actual performance of Example 1 (78.57% and 74.39%, respectively). This directly demonstrates the significant technical synergy between physical skeleton protection and active secondary hydration, achieving a systematic strengthening of the toughness level of cement-based composite materials and efficient self-repair after disasters.

[0096] Table 4a. Peak load amplitude test results of acoustic emission (AE) monitoring during fracture process of specimens in different groups.

[0097]

[0098] Table 4b: Relative cumulative energy test results of acoustic emission (AE) monitoring during fracture process of specimens in different groups

[0099]

[0100] According to Tables 4a and 4b, Figure 5-6It can be seen that, compared with Comparative Examples 1-4, Examples 1 and 2 exhibit the most significant acoustic emission (AE) activity and energy dissipation characteristics during the fracture process. Specifically, compared with Comparative Example 2, which uses ordinary river sand, Example 1 shows a significant advantage in peak AE amplitude and relative cumulative energy after high temperature, demonstrating that the refractory bauxite sand skeleton effectively inhibits the violent initiation of macroscopic thermal cracks and maintains the energy-bearing capacity of the matrix during fracture. Compared with Comparative Example 3, which does not modify steel fibers, the RA-AF signal of Example 1 shows a longer and denser shear signal characteristic, demonstrating that the Fe-O-Si chemical bonding layer can still ensure tight adhesion and slip between the steel fibers and the matrix after high temperature, significantly improving the energy dissipation efficiency during fiber pull-out. Compared with Comparative Example 4, which does not contain calcined high-alumina powder, Example 1 shows a 75.36% increase in cumulative AE energy recovery after re-curing, far exceeding the 59.42% of Comparative Example 4, quantitatively verifying the repair effect of the secondary hydration products of high-alumina powder on the microstructure of the damaged interface transition zone (ITZ). Furthermore, through comparative analysis of the improvement magnitude, it was found that the sum of the performance improvement magnitudes of Comparative Example 2 and Comparative Example 4 compared to Comparative Example 1 during the re-curing stage (peak amplitude 65.85%, cumulative energy 72.46%) was lower than the actual performance of Example 1. From the perspective of acoustic monitoring, it was intuitively demonstrated that there is a significant technical synergy between physical skeleton protection and active secondary hydration, which realizes a deep enhancement of the material's micro-damage evolution mechanism and macro-energy dissipation capacity.

[0101] In summary, bauxite sand and calcined high-alumina powder have a synergistic effect, forming an excellent inorganic refractory skeleton. Compared with ordinary fiber-reinforced cement-based materials, the cement-based composite material of this invention still has excellent residual energy dissipation capacity after experiencing high-temperature damage. Furthermore, the combination of calcined high-alumina powder with fly ash and silica fume allows the cement-based composite material to retain a large number of residual active mineral components after high temperatures, resulting in high performance recovery capacity after re-curing. Modified steel fibers can maintain the physical continuity of the interface transition zone between the steel fibers and the cement matrix at high temperatures. The synergistic effect of these three components forms a full-scale fire protection and post-disaster self-repair system, which can effectively improve the resistance of transportation facilities to high-temperature damage in extreme high-temperature environments and enable them to have post-disaster self-repair capabilities, effectively ensuring the structural safety after a disaster and greatly reducing the cost and difficulty of post-disaster reinforcement of transportation facilities.

[0102] The above description is only used to illustrate the technical solution of the present invention and is not intended to limit it. Any modifications or substitutions made by other people skilled in the art to the technical solution, as long as they do not depart from the connotation of the technical solution of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A steel fiber reinforced cementitious composite material, characterized in that, The mass ratio of each component is as follows: refractory bauxite sand: cement: fly ash: silica fume: calcined high alumina powder: water-reducing agent: water = 220~250: 70~80: 15~20: 5~10: 6~9: 0.8~1.2: 28~32; the volume content of modified steel fiber is 1.0%~1.5%; wherein, the modified steel fiber is obtained by modification with silane coupling agent hydrolysate.

2. The steel fiber reinforced cementitious composite material according to claim 1, characterized in that, The calcined high-alumina powder is made of 200-400 mesh high-alumina bauxite powder with an Al2O3 content of not less than 85%.

3. The steel fiber reinforced cementitious composite material according to claim 2, characterized in that, The refractory bauxite sand has a particle size distribution between 0.15 mm and 0.6 mm, and an Al2O3 content of not less than 75%.

4. The steel fiber reinforced cementitious composite material according to claim 3, characterized in that, The volume ratio of the silane coupling agent hydrolysate is: silane coupling agent: anhydrous ethanol: deionized water = 1:9:2.5; the silane coupling agent is γ-aminopropyltriethoxysilane.

5. The steel fiber reinforced cementitious composite material according to claim 4, characterized in that, The steel fibers are straight steel fibers with a length of 25-35mm, an aspect ratio of 60-80, and a tensile strength of not less than 1100MPa.

6. The steel fiber reinforced cementitious composite material according to claim 4, characterized in that, The fly ash is low-calcium grade I fly ash, and the silica content in the silica ash is not less than 95%.

7. The steel fiber reinforced cementitious composite material according to claim 4, characterized in that, The water-reducing agent used is a polycarboxylate-based high-performance water-reducing agent with a water reduction rate of 25%-30%.

8. The steel fiber reinforced cementitious composite material according to claim 4, characterized in that, The cement used is either ordinary silicate cement or aluminate cement.

9. A method for preparing steel fiber reinforced cementitious composite material according to any one of claims 1-8, comprising the following steps: (1) Weigh out refractory bauxite sand, cement, fly ash, silica fume, calcined high alumina powder and modified steel fiber according to the mass ratio, stir for 2-5 minutes to obtain a dry mixture; (2) Add an aqueous solution containing a water-reducing agent to the dry mixture and stir until the required fluidity is achieved to obtain the mixture; (3) Casting and molding, and standard curing are performed to obtain the steel fiber reinforced cement-based composite material.

10. The application of the steel fiber reinforced cementitious composite material according to any one of claims 1-8, characterized in that, For repairing cement-based composite materials damaged by high-temperature disasters: immersion curing or spray curing for 7-28 days, utilizing calcined high-alumina powder and residual active mineral components in the cement matrix for secondary hydration under the guidance of the interface modification layer, to achieve filling of microcracks in the transition zone of the damaged interface and restoration of mechanical properties.

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