Lightweight carbon fiber concrete for building external wall and preparation method of lightweight carbon fiber concrete

Abstract

The invention relates to light carbon fiber concrete for a building outer wall and a preparation method thereof, and belongs to the technical field of building materials. The concrete is prepared from the following components in parts by weight: 300 to 320 parts of ordinary Portland cement, 460 to 480 parts of fine aggregate, 940 to 980 parts of coarse aggregate, 35 to 40 parts of glass beads, 10 to 13.5 parts of modified carbon fibers, 5.5 to 6.8 parts of a water reducing agent and 115 to 125 parts of water, a surface modifier integrating dispersing, coagulation accelerating and toughening is grafted on the surface of the modified carbon fiber through coupling, when the modified carbon fiber is applied to lightweight concrete, effective regulation and control on a fiber-cement matrix interface are realized through the synergistic effect of a surface organic structure, and excellent comprehensive performance with high strength and high toughness is obtained.

Description

A lightweight carbon fiber concrete for building exterior walls and its preparation method Technical Field

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

[0002] Carbon fiber reinforced concrete (CFRC) is an advanced composite material with cement-based concrete as the continuous phase and carbon fiber as the dispersed phase, achieving significant improvements in tensile strength, flexural toughness, impact resistance, and fatigue resistance. Based on these superior properties, CFRC exterior walls are lightweight and high-strength, enabling large-format thin-panel designs and significantly reducing the load requirements on the main structure. Furthermore, its excellent plasticity and toughness make it easy to fabricate complex irregular-shaped components such as curved and hyperboloidal surfaces, meeting the aesthetic demands of modern architecture. In addition, it fundamentally solves the problems of corrosion, weathering, and freeze-thaw damage in exterior wall materials, resulting in low life-cycle costs. Therefore, CFRC is considered an important direction for achieving high performance, lightweight, and aesthetically pleasing building envelopes.

[0003] However, according to existing research, the full realization of the performance of carbon fiber concrete is highly dependent on the performance of the interfacial transition zone between the fiber and the concrete matrix. An ideal interface should possess high strength to effectively transfer loads, while also possessing high toughness to buffer stress concentration and prevent interfacial debonding. Unfortunately, carbon fibers themselves are composed of highly graphitized crystals with extremely high surface chemical inertness, low surface energy, and are extremely smooth. This results in poor wetting between the carbon fiber and hydrophilic cement hydration products, leading to weak physical bonding. This "weak interface" problem significantly reduces the reinforcing and toughening effects of the fiber, and the actual measured performance indicators of the composite material (especially toughness and fracture energy) are far lower than theoretical predictions, severely restricting its safe and reliable application in long-span, high-stress, or complex irregular-shaped exterior wall structures.

[0004] To overcome this interface bottleneck, existing technologies mainly modify the carbon fiber surface from two dimensions: physical and chemical.

[0005] Physical modification mainly includes surface oxidation etching (such as air oxidation, nitric acid treatment, and plasma bombardment) and surface sizing coating. Surface oxidation aims to etch grooves on the fiber surface and introduce oxygen-containing functional groups using strong oxidants. The former increases surface roughness to strengthen mechanical interlocking, while the latter increases surface energy and may enhance adhesion through hydrogen bonding. Sizing involves coating the fibers with a thin layer of epoxy resin or other polymer "slurry" at the factory, mainly to protect the fibers and improve wettability with the subsequent resin matrix. However, for cementitious matrices, the mechanical anchoring force provided by simple physical roughening is limited; and most sizing agents designed for organic resin matrices have poor compatibility with cement paste, and may even hinder cement hydration, causing the interface to become a new weak point. Therefore, these methods have limited improvement on the macroscopic mechanical properties of composite materials, especially tensile and flexural strength, and lack stability.

[0006] Chemical modification: In recent years, more forward-looking research has focused on functionalizing the surface of carbon fibers by grafting active groups that can actively participate in or promote cement hydration reactions. For example, using technologies such as silane coupling agents and dopamine biomimetic coatings, molecular layers rich in amino, carboxyl, or silanol groups are grafted onto the fiber surface. These active groups can coordinate or chemically react with calcium ions and silicate ions in the cement paste, inducing hydration products (mainly calcium silicate hydrate CSH gel) to preferentially and densely nucleate and grow on the fiber surface, thereby forming a "strong hydration layer" around the fiber. This method can significantly improve the chemical bond strength between the fiber and the matrix, and the compressive and flexural strength of the composite material can usually achieve considerable increases.

[0007] However, this strong hydration layer strategy inherently harbors a new and more serious technical flaw: interfacial brittleness. Cement hydration gels, especially those that form rapidly in the early stages and have high structural density, are essentially brittle inorganic ceramic materials. The strong hydration layer forcibly formed on the fiber surface often results in a highly brittle region with a denser structure but fewer defects and extremely poor deformation capacity due to intense interfacial reactions and low local water-cement ratios. While this region has high hardness, it has low fracture toughness. Under external forces, especially dynamic loads, impacts, or complex stress states (such as the bending and torsional coupling of irregularly shaped components), stress is highly concentrated at the interface. The brittle strong hydration layer cannot dissipate energy through plastic deformation, making it highly susceptible to sudden brittle fracture. This fracture mode manifests as sudden debonding at the interface, with the fibers being "brittlely pulled out," failing to fully utilize their high tensile strain capacity. This results in the composite material exhibiting "strong but not tough" characteristics, with poor impact resistance and post-cracking load-bearing capacity. In the application of irregularly shaped exterior wall panels, this brittle interface poses a potential safety hazard, limiting the material's application in scenarios with complex shapes and high seismic fortification requirements. Summary of the Invention

[0008] In order to solve the technical problems mentioned in the background art, the purpose of this invention is to provide a lightweight carbon fiber concrete for building exterior walls and a method for preparing the same.

[0009] The objective of this invention can be achieved through the following technical solutions:

[0010] A lightweight carbon fiber concrete for building exterior walls comprises, by weight: 300-320 parts ordinary silicate cement, 460-480 parts fine aggregate, 940-980 parts coarse aggregate, 35-40 parts vitrified microspheres, 10-13.5 parts modified carbon fiber, 5.5-6.8 parts water-reducing agent, and 115-125 parts water.

[0011] The concrete is prepared by premixing ordinary silicate cement, fine aggregate, vitrified microspheres and modified carbon fiber, then adding coarse aggregate and mixing evenly, and adding water-reducing agent dissolved in water to obtain concrete.

[0012] The modified carbon fiber is prepared by the following method:

[0013] Step A1: Add boron trifluoride diethyl ether to polyoxyethylene ether for premixing, heat to 50-65℃, slowly add epichlorohydrin and stir for 4-5 hours, then add sodium hydroxide solution and continue to heat to 80-90℃ and reflux for 2.5-3.5 hours. After the reaction is completed, concentrate the reaction solution by rotary evaporation under reduced pressure, filter, extract with dichloromethane, separate and dry to obtain intermediate 1;

[0014] Furthermore, the ratio of hydroxyl content of polyoxyethylene ether, epichlorohydrin, boron trifluoride ethyl ether, and sodium hydroxide solution is 0.1 mol: 0.102-0.105 mol: 0.2-0.3 mL: 80-120 mL, the mass fraction of sodium hydroxide solution is 15-20 wt%, epichlorohydrin ring-opens with the terminal hydroxyl group of polyoxyethylene ether, and then ring-closes under strong alkalinity to introduce a terminal epoxy structure;

[0015] Preferably, the polyoxyethylene ether has an EO number of 5-10. The ether segments formed after ring opening at this EO number have a more superior effect on improving the overall performance of concrete.

[0016] Step A2: Premix intermediate 1 with anhydrous acetone, cool to below 5°C in an ice-water bath, slowly add diethylenetriamine and stir for 1.5-2 hours, then continue the reaction at 30-40°C in a water bath for 6-9 hours. After the reaction is complete, remove the acetone by rotary evaporation to obtain intermediate 2.

[0017] Furthermore, the ratio of epoxy content, diethylenetriamine, and anhydrous acetone in intermediate 1 is 0.1 mol: 50 mmol: 150-200 mL. The terminal epoxy structure of intermediate 1 undergoes ring-opening with the primary amine of diethylenetriamine to form a compound containing bibranched polyoxyethylene ether segments with diethylenetriamine as a bridge.

[0018] Step A3: Premix intermediate 2,3-bromopropyltrimethoxysilane and anhydrous DMF under dry nitrogen protection, heat to 60-80℃ and stir for 5-8 hours, cool and add iodomethane and pressurize to 0.3-0.5 MPa, control the temperature at 50-70℃ and reflux for 10-15 hours. After the reaction is completed, pour into cold diethyl ether to precipitate and obtain the surface modifier.

[0019] Furthermore, the ratio of intermediate 2, 3-bromopropyltrimethoxysilane, iodomethane, and anhydrous DMF is 50 g: 20-30 mmol: 55-90 mmol: 50-80 mL. 3-bromopropyltrimethoxysilane is substituted with the secondary amine in intermediate 2 molecule, and then quaternized with highly reactive iodomethane.

[0020] Step A4: Disperse the surface modifier in an ethanol aqueous solution and adjust the pH to 4-5 with glacial acetic acid to prepare a treatment solution. Add short-cut carbon fibers and disperse them ultrasonically. Then heat the solution to 60-70℃ and stir for 2-3 hours. After the reaction is complete, filter out the carbon fibers, wash with water, and dry to obtain modified carbon fibers.

[0021] Furthermore, the concentration of the surface modifier in the treatment solution is 2.2-2.8 wt%, and the bath ratio of the short-cut carbon fibers to the treatment solution is 1:30-35; the trimethoxysilane structure in the surface modifier is hydrolyzed and coupled to the carbon fiber surface for loading.

[0022] Preferably, the length of the short-cut carbon fiber is 10-20mm, which improves the strength and toughness of the carbon fiber and makes it suitable for exterior wall construction.

[0023] The beneficial effects of this invention are:

[0024] This invention successfully synthesizes a carbon fiber surface modifier that integrates dispersion, setting acceleration, and toughening properties, and covalently grafts it onto the surface of carbon fibers. When applied to lightweight concrete, the modified carbon fibers, through the synergistic effect of their surface organic structures, effectively regulate the fiber-cement matrix interface, achieving excellent comprehensive properties that combine high strength and high toughness. Its beneficial effects are specifically reflected in the following aspects:

[0025] First, it achieves initial uniform dispersion of fibers in the slurry and enrichment of cement particles at the interface. The quaternary ammonium salt cation structure at the center of the modifier molecule plays a dual key role. First, in the multiphase mixture of concrete, the electrostatic repulsion between the quaternary ammonium salt cations grafted onto the fiber surface effectively prevents the aggregation of carbon fibers due to van der Waals forces, ensuring that the fibers are uniformly dispersed in the matrix in monofilament form, which is a prerequisite for exerting its reinforcing effect. Second, the particle surfaces in the early stages of cement hydration and the surface of the main hydration product CSH gel are usually negatively charged under alkaline conditions. The quaternary ammonium salt cations on the fiber surface, through strong electrostatic adsorption, can directionally enrich and pull the negatively charged cement particles and hydration product precursors closer to the fiber interface region, which is equivalent to significantly increasing the local cement particle concentration at the interface, laying the material basis for the subsequent formation of a dense interfacial transition zone.

[0026] Secondly, it synergistically promotes the rapid formation of a dense and robust hydration gel structure in the interfacial region. Building upon the electrostatic adsorption and enrichment of cement particles, the long polyoxyethylene ether chains in the modifier molecules further play a crucial physicochemical regulatory role. Polyoxyethylene ether chains possess extremely strong hydrophilicity and flexibility; the ether oxygen atoms (-O-) in their molecular chains can interact with water molecules and Ca2+. 2+ The formation of coordination by cations plays a crucial role. On one hand, it creates a structural water film on the fiber surface, optimizing the local hydration environment. On the other hand, these long chains act as a "flexible template," guiding the orderly growth of hydration products (such as CSH gel) around them, avoiding the formation of poorly structured, porous gels due to limited reaction space. Meanwhile, studies have indicated that polyoxyethylene ether molecules can influence the morphology and migration of calcium ions, potentially fine-tuning the nucleation and early growth of hydrated calcium silicate. The electrostatic enrichment of quaternary ammonium salts, combined with the template-guiding and environmental-regulating effects of polyoxyethylene ether chains, synergistically promote the formation of a more dense, rationally crystallized, and chemically bonded "reinforced hydration layer" at the fiber-matrix interface, thus providing an interfacial strength far exceeding that of physical bonding.

[0027] Third, the flexible energy dissipation mechanism of the polyoxyethylene ether molecular chain effectively toughens the brittle hydrated gel. This is the core of this invention's superiority over existing "strong hydration" technologies. While the aforementioned interface-reinforced hydration layer exhibits high strength, it remains essentially a brittle inorganic material. In the surface modifier molecules of this invention, the long-chain polyoxyethylene ether structure connecting the rigid quaternary ammonium salt center and the fiber anchoring point acts as a deformable "flexible buffer unit." When the composite material is subjected to load, stress is transferred to the interface, and microcracks or stress concentrations occur in the brittle hydrated gel layer, the long polyoxyethylene ether chains, tightly bound to it through physical interactions such as hydrogen bonds and van der Waals forces, can undergo viscoelastic deformations such as stretching, slippage, and conformational changes. This process effectively absorbs and dissipates fracture energy, blunts crack tips, and prevents microcracks from propagating into macroscopic destructive cracks. In other words, the polyoxyethylene ether chain introduces a controllable "plastic" component into the rigid inorganic gel, transforming the potentially sudden brittle interface fracture into a destructive process requiring more energy and exhibiting extensibility. This was directly confirmed in the performance tests: the bending toughness index and the number of impacts of the embodiment of the present invention far exceeded those of the comparative example 2, which only formed a strong hydration layer, proving the effectiveness of the flexible toughening mechanism.

[0028] In summary, this invention truly achieves a balance and unity between "strength" and "toughness," providing key technical guarantees for the safe and reliable application of carbon fiber concrete in building exterior walls under complex stress, especially irregular curved exterior walls. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1: Preparation of carbon fiber concrete, the specific implementation process is as follows:

[0031] 1. Preparation of modified carbon fibers

[0032] Step A1: Add boron trifluoride ethyl ether premix to polyoxyethylene ether, heat to 50℃, slowly add epichlorohydrin and stir for 4 hours, then add sodium hydroxide solution and continue heating to 80℃ and reflux for 3 hours. The polyoxyethylene ether uses TERGITOL 15-S-5 type raw material (EO number 5), the mass fraction of sodium hydroxide solution is 15wt%, and the ratio of hydroxyl content of polyoxyethylene ether, epichlorohydrin, boron trifluoride ethyl ether and sodium hydroxide solution is 0.1mol:0.102mol:0.2mL:80mL. After the reaction is completed, concentrate the reaction solution by rotary evaporation under reduced pressure, filter, extract with dichloromethane, separate and dry to obtain intermediate 1.

[0033] Step A2: Take intermediate 1 and anhydrous acetone, premix them, cool them to below 5°C in an ice-water bath, slowly add diethylenetriamine and stir for 1.5 h, then continue the reaction at 30°C in a water bath for 6 h. The epoxy content of intermediate 1 and the ratio of diethylenetriamine to anhydrous acetone are 0.1 mol: 50 mmol: 150 mL. After the reaction is completed, remove the acetone by rotary evaporation to obtain intermediate 2.

[0034] Step A3: Take intermediate 2,3-bromopropyltrimethoxysilane and anhydrous DMF, premix them under dry nitrogen protection, heat to 60℃ and stir for 5h, cool and add iodomethane, then pressurize to 0.3MPa with dry nitrogen and reflux at 50℃ for 12h. The ratio of intermediate 2,3-bromopropyltrimethoxysilane, iodomethane and anhydrous DMF is 50g:20mmol:55mmol:50mL. After the reaction is completed, pour into cold diethyl ether to precipitate and obtain the surface modifier.

[0035] Step A4: Disperse the surface modifier in an ethanol aqueous solution and adjust the pH to 5 with glacial acetic acid to prepare a treatment solution. Control the concentration of the surface modifier in the treatment solution to 2.2 wt%. Add 10 mm short-cut carbon fibers at a bath ratio of 1:30 and ultrasonically disperse. Then heat to 60℃ and stir for 2.5 h. After the reaction is completed, filter to remove the carbon fibers and wash with water and dry to obtain modified carbon fibers.

[0036] 2. Preparation of lightweight carbon fiber concrete

[0037] The following components are prepared by weight: 300 parts of ordinary silicate cement, P.O42.5 type cement; 470 parts of fine aggregate, using manufactured sand with a fineness modulus of 2.3-3.0; 940 parts of coarse aggregate, using 5-20mm continuously graded crushed stone; 35 parts of vitrified microspheres, using raw materials with a fineness of 20 mesh; 10 parts of modified carbon fiber, prepared in this embodiment; 5.5 parts of water-reducing agent, using PY-01 type raw material; and 115 parts of water.

[0038] Ordinary silicate cement, fine aggregate, vitrified microspheres and modified carbon fiber are added to a mixer for premixing, then coarse aggregate is added and mixed evenly. Water-reducing agent is dissolved in water and added to the mix to obtain concrete.

[0039] Example 2: Preparation of carbon fiber concrete, the specific implementation process is as follows:

[0040] 1. Preparation of modified carbon fibers

[0041] Step A1: Add boron trifluoride ethyl ether premix to polyoxyethylene ether, heat to 55℃, slowly add epichlorohydrin and stir for 4 hours, then add sodium hydroxide solution and continue heating to 80℃ and reflux for 2.5 hours. The polyoxyethylene ether uses TERGITOL 15-S-5 type raw material (EO number 5), the mass fraction of sodium hydroxide solution is 15wt%, and the ratio of hydroxyl content of polyoxyethylene ether, epichlorohydrin, boron trifluoride ethyl ether and sodium hydroxide solution is 0.1mol:0.103mol:0.3mL:100mL. After the reaction is completed, concentrate the reaction solution by rotary evaporation under reduced pressure, filter, extract with dichloromethane, separate and dry to obtain intermediate 1.

[0042] Step A2: Take intermediate 1 and anhydrous acetone, premix them, cool them to below 5°C in an ice-water bath, slowly add diethylenetriamine and stir for 1.5 h, then continue the reaction at 35°C in a water bath for 7 h. The epoxy content of intermediate 1 and the ratio of diethylenetriamine to anhydrous acetone are 0.1 mol: 50 mmol: 200 mL. After the reaction is completed, remove the acetone by rotary evaporation to obtain intermediate 2.

[0043] Step A3: Take intermediate 2,3-bromopropyltrimethoxysilane and anhydrous DMF, premix them under dry nitrogen protection, heat to 65℃ and stir for 6h, cool and add iodomethane, then pressurize to 0.3MPa with dry nitrogen and reflux at 50℃ for 10h. The ratio of intermediate 2,3-bromopropyltrimethoxysilane, iodomethane and anhydrous DMF is 50g:25mmol:60mmol:70mL. After the reaction is completed, pour into cold diethyl ether to precipitate and obtain the surface modifier.

[0044] Step A4: Disperse the surface modifier in an ethanol aqueous solution and adjust the pH to 5 with glacial acetic acid to prepare a treatment solution. Control the concentration of the surface modifier in the treatment solution to 2.5 wt%. Add 10 mm short-cut carbon fibers at a bath ratio of 1:30 and ultrasonically disperse. Then heat to 60℃ and stir for 2 hours. After the reaction is completed, filter to remove the carbon fibers and wash with water and dry to obtain modified carbon fibers.

[0045] 2. Preparation of lightweight carbon fiber concrete

[0046] The following components are prepared by weight: 320 parts of ordinary silicate cement, P.O42.5 type cement; 460 parts of fine aggregate, using manufactured sand with a fineness modulus of 2.3-3.0; 980 parts of coarse aggregate, using 5-20mm continuously graded crushed stone; 38 parts of vitrified microspheres, using raw materials with a fineness of 20 mesh; 101 parts of modified carbon fiber, which is self-made in this embodiment; 6 parts of water-reducing agent, using PY-01 type raw material; and 120 parts of water.

[0047] Ordinary silicate cement, fine aggregate, vitrified microspheres and modified carbon fiber are added to a mixer for premixing, then coarse aggregate is added and mixed evenly. Water-reducing agent is dissolved in water and added to the mix to obtain concrete.

[0048] Example 3: Preparation of carbon fiber concrete, the specific implementation process is as follows:

[0049] 1. Preparation of modified carbon fibers

[0050] Step A1: Add boron trifluoride ethyl ether premix to polyoxyethylene ether, heat to 65℃, slowly add epichlorohydrin and stir for 5h, then add sodium hydroxide solution and continue heating to 90℃ and reflux for 3.5h. The polyoxyethylene ether uses TERGITOL 15-S-9 type raw material (EO number 9), the mass fraction of sodium hydroxide solution is 20wt%, and the ratio of hydroxyl content of polyoxyethylene ether, epichlorohydrin, boron trifluoride ethyl ether and sodium hydroxide solution is 0.1mol:0.105mol:0.2mL:120mL. After the reaction is completed, concentrate the reaction solution by rotary evaporation under reduced pressure, filter, extract with dichloromethane, separate and dry to obtain intermediate 1.

[0051] Step A2: Take intermediate 1 and anhydrous acetone, premix them, cool them to below 5°C in an ice-water bath, slowly add diethylenetriamine and stir for 2 hours, then continue the reaction at 40°C in a water bath for 9 hours. The epoxy content of intermediate 1 and the ratio of diethylenetriamine to anhydrous acetone are 0.1 mol: 50 mmol: 200 mL. After the reaction is completed, remove the acetone by rotary evaporation to obtain intermediate 2.

[0052] Step A3: Take intermediate 2,3-bromopropyltrimethoxysilane and anhydrous DMF, premix them under dry nitrogen protection, heat to 80℃ and stir for 8h, cool and add iodomethane, then pressurize to 0.5MPa with dry nitrogen and reflux at 70℃ for 15h. The ratio of intermediate 2,3-bromopropyltrimethoxysilane, iodomethane and anhydrous DMF is 50g:25mmol:80mmol:80mL. After the reaction is completed, pour into cold diethyl ether to precipitate and obtain the surface modifier.

[0053] Step A4: Disperse the surface modifier in an ethanol aqueous solution and adjust the pH to 4 with glacial acetic acid to prepare a treatment solution. Control the concentration of the surface modifier in the treatment solution to 2.5 wt%. Add 20 mm short-cut carbon fibers at a bath ratio of 1:35 and ultrasonically disperse. Then heat to 70℃ and stir for 3 hours. After the reaction is completed, filter to remove the carbon fibers and wash with water and dry to obtain modified carbon fibers.

[0054] 2. Preparation of lightweight carbon fiber concrete

[0055] The following components are prepared by weight: 320 parts of ordinary silicate cement (P.O42.5 type); 480 parts of fine aggregate (manufactured sand with a fineness modulus of 2.3-3.0); 970 parts of coarse aggregate (continuously graded crushed stone of 5-20mm); 40 parts of vitrified microspheres (raw material with a fineness of 20 mesh); 13.5 parts of modified carbon fiber (self-made in this embodiment); 6.8 parts of water-reducing agent (PY-01 type raw material); and 125 parts of water.

[0056] Ordinary silicate cement, fine aggregate, vitrified microspheres and modified carbon fiber are added to a mixer for premixing, then coarse aggregate is added and mixed evenly. Water-reducing agent is dissolved in water and added to the mix to obtain concrete.

[0057] Example 4: Preparation of carbon fiber concrete, the specific implementation process is as follows:

[0058] 1. Preparation of modified carbon fibers

[0059] Step A1: Add boron trifluoride ethyl ether premix to polyoxyethylene ether, heat to 65℃, slowly add epichlorohydrin and stir for 5h, then add sodium hydroxide solution and continue heating to 90℃ and reflux for 3h. The polyoxyethylene ether uses TERGITOL 15-S-9 type raw material (EO number 9), the mass fraction of sodium hydroxide solution is 18wt%, and the ratio of hydroxyl content of polyoxyethylene ether, epichlorohydrin, boron trifluoride ethyl ether and sodium hydroxide solution is 0.1mol:0.105mol:0.3mL:110mL. After the reaction is completed, concentrate the reaction solution by rotary evaporation under reduced pressure, filter, extract with dichloromethane, separate and dry to obtain intermediate 1.

[0060] Step A2: Take intermediate 1 and anhydrous acetone, premix them, cool them to below 5°C in an ice-water bath, slowly add diethylenetriamine and stir for 1.5 h, then continue the reaction at 40°C in a water bath for 8 h. The epoxy content of intermediate 1 and the ratio of diethylenetriamine to anhydrous acetone are 0.1 mol: 50 mmol: 180 mL. After the reaction is completed, remove the acetone by rotary evaporation to obtain intermediate 2.

[0061] Step A3: Take intermediate 2,3-bromopropyltrimethoxysilane and anhydrous DMF, premix them under dry nitrogen protection, heat to 75℃ and stir for 8 hours, cool and add iodomethane, then pressurize to 0.5 MPa with dry nitrogen and reflux at 60℃ for 15 hours. The ratio of intermediate 2,3-bromopropyltrimethoxysilane, iodomethane and anhydrous DMF is 50 g: 30 mmol: 90 mmol: 80 mL. After the reaction is completed, pour into cold diethyl ether to precipitate and obtain the surface modifier.

[0062] Step A4: Disperse the surface modifier in an ethanol aqueous solution and adjust the pH to 4 with glacial acetic acid to prepare a treatment solution. Control the concentration of the surface modifier in the treatment solution to 2.8 wt%. Add 20 mm short-cut carbon fibers at a bath ratio of 1:33 and ultrasonically disperse. Then heat to 70℃ and stir for 3 hours. After the reaction is completed, filter to remove the carbon fibers and wash with water and dry to obtain modified carbon fibers.

[0063] 2. Preparation of lightweight carbon fiber concrete

[0064] The following components are prepared by weight: 310 parts of ordinary silicate cement (P.O42.5 type); 475 parts of fine aggregate (manufactured sand with a fineness modulus of 2.3-3.0); 960 parts of coarse aggregate (continuously graded crushed stone of 5-20mm); 40 parts of vitrified microspheres (raw material with a fineness of 20 mesh); 12.7 parts of modified carbon fiber (self-made in this embodiment); 6.2 parts of water-reducing agent (PY-01 type raw material); and 125 parts of water.

[0065] Ordinary silicate cement, fine aggregate, vitrified microspheres and modified carbon fiber are added to a mixer for premixing, then coarse aggregate is added and mixed evenly. Water-reducing agent is dissolved in water and added to the mix to obtain concrete.

[0066] Comparative Example 1 uses the same basic ratio as Example 4, and commercially available hydrophilic sized carbon fibers are cut to the same length and replaced with the modified carbon fibers in equal amounts. The rest of the implementation process is the same.

[0067] Comparative Example 2 used the same basic formulation as Example 4, and treated the carbon fibers with a "dopamine-silica sol" composite coating according to existing technology. Specifically, the carbon fibers were immersed in a Tris-HCl buffer solution (pH=8.5) containing 2 g / L dopamine hydrochloride, shaken at room temperature for 24 h, removed, washed, and dried. Then, they were immersed in nano-silica sol (SiO2 content 20%) for 10 min, removed, and dried. Coated carbon fibers were cut to the same length, and the modified carbon fibers were replaced in equal amounts; the remaining procedures were the same.

[0068] Sample preparation method: Pour concrete into the mold, vibrate it for 30 seconds using a vibrating table, cover the surface with plastic film and let it stand at room temperature for 24 hours. After demolding, place it under the same conditions for curing for 28 days.

[0069] Compressive strength: In accordance with GB / T 50081-2019 standard, 100mm×100mm×100mm cubic specimens were used for testing at 28 days of age.

[0070] Flexural strength and flexural toughness: Referring to JGJ / T 221-2010 standard, a four-point bending test was conducted using a 100mm×100mm×400mm prism specimen. In addition to recording the peak load (flexural strength), the flexural toughness index (Ib) was calculated based on the load-deflection curve. 20 This is used to quantitatively evaluate the post-cracking load-bearing and energy absorption capacity of materials.

[0071] Direct tensile properties: The ultimate tensile strength was determined with reference to the China Engineering Construction Standardization Association standard CECS 13:2009.

[0072] Impact resistance: Refer to the drop hammer impact test method recommended by ACI 544.2R-89 standard, use a disc specimen with a diameter of 150mm and a thickness of 64mm, and record the number of impact hammers the specimen withstands when it first cracks.

[0073] The specific test results are shown in Table 1:

[0074] Table 1

[0075]

[0076] As can be seen from the test results in Table 1, in terms of strength, the introduction of modified carbon fiber in the examples is significantly better than the existing sized carbon fiber reinforcement system in terms of compressive strength and tensile strength. Compared with the dopamine composite coated carbon fiber reinforcement of Comparative Example 2, Comparative Example 2 has a slightly higher compressive strength than Example 4. The analysis may be that the strong hydration effect forms a hydration gel, which significantly improves the interfacial bonding ability, thus resulting in higher compressive strength, but lower tensile strength. Combining the flexural strength and bending toughness index, it can be found that Comparative Example 2 shows obvious brittleness, especially the bending toughness index is significantly reduced, which has the disadvantage of being strong but not tough.

[0077] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0078] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A lightweight carbon fiber concrete for building exterior walls, characterized in that, The composition by weight is as follows: 300-320 parts ordinary silicate cement, 460-480 parts fine aggregate, 940-980 parts coarse aggregate, 35-40 parts vitrified microspheres, 10-13.5 parts modified carbon fiber, 5.5-6.8 parts water-reducing agent, and 115-125 parts water; wherein, the modified carbon fiber is prepared by the following method: Step A1: Add boron trifluoride ether to polyoxyethylene ether for premixing, heat to 50-65℃, slowly add epichlorohydrin and stir for 4-5 hours, then add sodium hydroxide solution and continue to heat to 80-90℃ and reflux for 2.5-3.5 hours to prepare intermediate 1; Step A2: Premix intermediate 1 with anhydrous acetone, cool to below 5℃ in an ice-water bath, and slowly... Add diethylenetriamine and stir for 1.5-2 hours, then continue the reaction in a water bath at 30-40℃ for 6-9 hours to prepare intermediate 2; Step A3: Premix intermediate 2, 3-bromopropyltrimethoxysilane and anhydrous DMF under dry nitrogen protection, heat to 60-80℃ and stir for 5-8 hours, cool, add iodomethane and pressurize to 0.3-0.5 MPa, reflux at 50-70℃ for 10-15 hours to prepare surface modifier; Step A4: Disperse the surface modifier in an ethanol aqueous solution and adjust the pH to 4-5 with glacial acetic acid to prepare a treatment solution, add short-cut carbon fibers and ultrasonically disperse, then heat to 60-70℃ and stir for 2-3 hours to prepare modified carbon fibers.

2. The lightweight carbon fiber concrete for building exterior walls according to claim 1, characterized in that, The ratio of hydroxyl content of polyoxyethylene ether, epichlorohydrin, boron trifluoride ethyl ether and sodium hydroxide solution is 0.1 mol: 0.102-0.105 mol: 0.2-0.3 mL: 80-120 mL, and the mass fraction of sodium hydroxide solution is 15-20 wt%.

3. The lightweight carbon fiber concrete for building exterior walls according to claim 2, characterized in that, The EO number of polyoxyethylene ether is 5-10.

4. The lightweight carbon fiber concrete for building exterior walls according to claim 3, characterized in that, The ratio of epoxy content, diethylenetriamine and anhydrous acetone in intermediate 1 was 0.1 mol: 50 mmol: 150-200 mL.

5. The lightweight carbon fiber concrete for building exterior walls according to claim 4, characterized in that, The ratio of intermediate 2,3-bromopropyltrimethoxysilane, iodomethane and anhydrous DMF is 50 g: 20-30 mmol: 55-90 mmol: 50-80 mL.

6. The lightweight carbon fiber concrete for building exterior walls according to claim 5, characterized in that, The concentration of the surface modifier in the treatment solution is 2.2-2.8 wt%, and the bath ratio of the short-cut carbon fiber to the treatment solution is 1:30-35.

7. The lightweight carbon fiber concrete for building exterior walls according to claim 6, characterized in that, The length of chopped carbon fiber is 10-20mm.

8. A method for preparing lightweight carbon fiber concrete for building exterior walls according to any one of claims 1-7, characterized in that, The specific method is as follows: ordinary silicate cement, fine aggregate, vitrified microspheres and modified carbon fiber are premixed, then coarse aggregate is added and mixed evenly, and water-reducing agent is dissolved in water and added to the mixture to obtain concrete.

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