High-anti-crack concrete based on sheath temperature shrinkage-core material phase change composite fiber and preparation method thereof

Abstract

This invention relates to the field of building materials technology, and proposes a high-crack-resistant concrete based on a sheath-core phase change composite fiber and its preparation method. The composite fiber has a core-shell structure, with the core material composed of porous metal fibers loaded with organic or inorganic phase change materials; the sheath material includes one or more of polyester, polypropylene, polyurethane, and high-density polyethylene; the sheath undergoes thermal shrinkage during heat treatment and coats the outside of the core material. By introducing the sheath-core phase change composite fiber into the concrete, this invention not only utilizes the latent heat of phase change to actively regulate the temperature field, but also introduces beneficial pre-stress within the concrete through the thermal shrinkage effect of the fiber sheath. This synergistically improves the crack resistance of the concrete from multiple dimensions, including "stress source control," "reducing the temperature difference between the inner and outer surfaces of the concrete," and "matrix reinforcement," while ensuring that its mechanical properties are not significantly reduced due to the introduction of the phase change material PCM.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to a high crack-resistant concrete based on sheath thermal shrinkage-core phase change composite fiber and its preparation method. Background Technology

[0002] Cracks in concrete, especially those caused by early-stage temperature and shrinkage stresses, are a global challenge affecting its durability and structural safety. Existing crack-resistant technologies are mainly divided into two categories: one is adding fibers (such as steel fibers and polypropylene fibers) to improve toughness and bridge cracks; the other is incorporating phase change materials to absorb the heat of hydration and regulate temperature rise. However, both of these technologies have inherent defects: (1) Ordinary fiber reinforcement: can only passively constrain crack propagation and cannot fundamentally reduce the driving forces that cause cracking—temperature stress and shrinkage stress. In other words, they are "treating the symptoms but not the root cause". (2) Direct application of phase change materials (PCM): whether directly incorporated or microencapsulated, the introduction of PCM usually deteriorates the mechanical properties of concrete and poses a risk of leakage under long-term cycling. In addition, the wall material of microcapsules has low strength and cannot contribute effective mechanical reinforcement.

[0003] While existing technologies combine PCM with fibers (such as the invention patent with publication number CN120328899A), they mostly employ simple surface loading, resulting in weak interfacial bonding, limited functionality, and failure to address the negative impact of PCM on matrix strength. Therefore, there is an urgent need for a synergistic reinforcing element capable of simultaneously achieving "active suppression of temperature stress" and "passive enhancement of the matrix's crack resistance." Summary of the Invention

[0004] In view of this, the present invention proposes a high crack-resistant concrete based on sheath thermal shrinkage-core phase change composite fiber and its preparation method. This concrete introduces a novel sheath thermal shrinkage-core phase change composite fiber, which not only actively regulates the temperature field by utilizing the latent heat of phase change, but also introduces beneficial pre-compression stress inside the concrete through the thermal shrinkage effect of the fiber sheath. This synergistically improves the crack resistance of the concrete from multiple dimensions such as "stress source control", "reducing the temperature difference between the inner and outer surfaces of the concrete" and "matrix reinforcement", and ensures that its mechanical properties are not significantly reduced due to the introduction of the phase change material PCM.

[0005] The technical solution of this invention is implemented as follows: Firstly, this invention provides a sheath-core phase change composite fiber with a temperature shrinkage mechanism. This composite fiber has a core-shell structure. The core material is composed of porous metal fibers loaded with organic or inorganic phase change materials. The sheath material includes one or more of polyester, polypropylene, polyurethane, or high-density polyethylene. The sheath shrinks under heat treatment and covers the outside of the core material. The core material is a phase change functional unit, and the sheath is a temperature shrinkage pre-stress unit. After the sheath shrinks under heat, a pre-stress state of "tensile sheath and compressive core material" is formed inside the fiber.

[0006] The sheath-core phase change composite fiber of the present invention, through its unique structural design, achieves seamless integration and functional synergy between "active temperature control" and "passive preloading" in the time series during the early hydration and shrinkage process of concrete. The specific mechanism of action is as follows:

[0007] Phase 1 (Temperature Rise Period, Active Temperature Control Dominates): In the initial stage of concrete pouring, the cement hydration reaction releases a large amount of heat, causing a rapid rise in internal temperature. When the temperature rises to the phase change temperature range (20-80℃) of the core material phase change material (PCM), the PCM undergoes a solid-liquid phase change, absorbing a large amount of latent heat (≥150 kJ / kg). This process is like embedding countless "miniature radiators" inside the concrete, effectively delaying the arrival of the concrete's temperature peak and reducing its maximum temperature rise (e.g., ...). Figure 2 As shown in the figure, it weakens the main driving force leading to temperature cracks—thermal stress—at its source.

[0008] The second stage (temperature drop period, passive prestressing activation): After the peak hydration heat has passed, the concrete enters the cooling and shrinkage stage. At this time, the sheath of the composite fiber (thermal shrinkage polymer) begins to play a crucial role. Because the coefficient of thermal expansion of the sheath material is much higher than that of the concrete matrix, its shrinkage deformation during cooling is strongly constrained by the surrounding concrete. This constraint forces the polymer sheath to generate a continuous and beneficial radial compressive stress on the concrete matrix. This prestress can actively counteract some of the shrinkage tensile stress generated during the cooling and drying process of the concrete, keeping the internal stress state of the concrete at a low level (e.g., ...). Figure 3 As shown in the figure, it greatly improves its crack resistance.

[0009] Synergistic Enhancement Effect: The two processes mentioned above are not independent but complementary. The more effective the temperature control of the core material PCM, the smaller the overall temperature drop and rate of the concrete. This not only directly reduces shrinkage stress but also provides a milder and more durable stress excitation environment for the sheath's thermal shrinkage, while providing the optimal development period for the increase in concrete strength. The pre-compression stress provided by the sheath provides a second line of defense for the residual tensile stress that was not completely eliminated during the heating stage of the PCM-absorbed concrete. This sequential synergy of "heat absorption and cooling first, followed by pre-compression and tensile strength" constitutes the dual, three-dimensional crack-resistant mechanism of this invention from "stress source control" to "stress field regulation," achieving a synergistic crack-resistant effect of 1+1>2.

[0010] Based on the above technical solutions, preferably, the porous metal fiber includes one or more of porous stainless steel fiber, porous nickel fiber and porous titanium fiber, with a porosity of 30%-60%, a pore size of 1-50μm, a fiber diameter of 0.1-1.0mm and a length of 10-50mm.

[0011] Based on the above technical solutions, preferably, the phase change material has a phase change temperature of 20-80℃ and a latent heat of phase change of not less than 150 kJ / kg. The phase change material is one or more of paraffin, fatty acids, or hydrated salts. The fatty acids are one or more of decanoic acid, lauric acid, myristic acid, and palmitic acid. The hydrated salts are one or more of disodium hydrogen phosphate dodecahydrate, barium hydroxide octahydrate, sodium sulfate decahydrate, and magnesium nitrate hexahydrate.

[0012] Based on the above technical solutions, preferably, the thickness of the sheath layer is 0.1-0.5 mm.

[0013] Based on the above technical solutions, preferably, the molecular weight of the polyester is 30,000 to 40,000, the molecular weight of the polypropylene is 8,000 to 10,000, the molecular weight of the high-density polyethylene is 150,000 to 200,000, and the molecular weight of the polyurethane is 60,000 to 80,000; the polyester is one or more of polybutylene terephthalate (PBT), polyethylene terephthalate (PET), and polyarylate; the shrinkage rate of the polyester, polypropylene, polyurethane, and high-density polyethylene is 2% to 10%, the shrinkage response temperature is 30 to 90°C, the tensile strength is 300 to 500 MPa, and the elastic modulus is 3 to 10 GPa.

[0014] Secondly, the present invention provides a method for preparing a sheath thermal shrinkage-core phase change composite fiber, comprising the following steps:

[0015] S11, porous metal fibers are immersed in a silane coupling agent solution, and after the process is completed, they are removed and dried to obtain surface-modified metal fibers;

[0016] S12, under vacuum and pressure conditions, the modified metal fiber is impregnated in molten phase change material, cooled after completion, and the fiber ends are sealed to obtain the core material;

[0017] S13, after preheating the core material of step S12, it is coated with one or more of molten polyester, polypropylene, polyurethane or high-density polyethylene to form a sheath layer, and then cooled and shaped to obtain composite fiber.

[0018] S14, the composite fiber coated in step S13 is heat-treated to obtain sheath shrinkage-core phase change composite fiber.

[0019] Based on the above technical solutions, preferably, the vacuum degree in step S12 is -0.09~-0.1MPa and the pressure is 0.5-1.0MPa; in step S14, heat treatment is carried out at a temperature of 90-120℃ for 5-30 minutes.

[0020] Thirdly, the present invention provides a high crack-resistant concrete based on sheath thermal shrinkage-core phase change composite fiber. The raw materials of the concrete, by weight, include 300-500 parts of cement, 800-1200 parts of coarse aggregate, 600-1000 parts of fine aggregate, 50-200 parts of mineral admixture, 4-15 parts of water-reducing agent, 150-200 parts of water, and 0.5-10 parts of sheath thermal shrinkage-core phase change composite fiber.

[0021] Fourthly, the present invention provides a method for preparing high crack-resistant concrete based on sheath thermal shrinkage-core phase change composite fiber, comprising the following steps:

[0022] S21, put cement, coarse aggregate, fine aggregate, and mineral admixture into a mixer and mix them evenly to obtain a dry mix;

[0023] S22, add water-reducing agent and water to dry mix, stir for 2-4 minutes to form cement concrete with good fluidity;

[0024] S23, add the sheath thermal shrinkage-core phase change composite fiber to the above cement concrete and stir slowly for 3-5 minutes to obtain a concrete mixture containing the sheath thermal shrinkage-core phase change composite fiber.

[0025] S24: Pour the concrete mixture into the mold, vibrate to compact it, and cure it to the specified age under conditions of temperature 20±2℃ and humidity above 95%.

[0026] Based on the above technical solutions, preferably, the coarse aggregate is continuously graded crushed stone with a particle size of 5-25mm, the fine aggregate is medium sand with a fineness modulus of 2.6-2.9, the mineral admixture is one or more of fly ash, granulated blast furnace slag powder and finely ground limestone powder, and the water-reducing agent is a polycarboxylate-based water-reducing agent.

[0027] The present invention provides a high crack-resistant concrete based on sheath thermal shrinkage-core phase change composite fiber and its preparation method, which has the following advantages over the prior art:

[0028] 1. Synergistic Crack Resistance Mechanism: The composite fiber created in this invention achieves a synergistic effect of "phase change heat absorption" and "thermal shrinkage pre-compression." When the concrete temperature changes, the sheath layer generates radial compressive stress on the surrounding matrix due to the mismatch in thermal expansion coefficients, actively offsetting part of the shrinkage tensile stress; simultaneously, the core material PCM absorbs heat within a specific temperature range, fundamentally suppressing temperature peaks and reducing temperature stress. These two mechanisms, one "passive" and one "active," form a dual line of defense.

[0029] 2. Mechanical property compensation: High-strength porous metal fibers are used as the carrier of phase change material PCM and wrapped with a polymer sheath layer. The fibers themselves are highly efficient reinforcing fibers, which perfectly compensate for the weakening of the matrix strength by PCM and can even improve the ultimate tensile strength and toughness of concrete.

[0030] 3. Excellent interface performance: Through silane modification and melt coating, the PCM is guaranteed to be leak-free, and there is a strong chemical bond and mechanical anchoring force between the fiber and the concrete matrix, resulting in high stress transfer efficiency.

[0031] 4. Comprehensive Improvement in Durability: The reduction in cracks directly enhances the concrete's impermeability and resistance to salt erosion. The phase change temperature regulation function effectively reduces the frequency of freeze-thaw cycles in frigid regions, further extending the structural lifespan. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the structure of the sheath thermal shrinkage-core phase change composite fiber of the present invention;

[0034] In the figure, 1-phase change material loaded in the core layer, 2-porous metal fiber in the core layer, and 3-thermally shrinkable fiber in the sheath layer;

[0035] Figure 2 This is a comparison chart of the temperature-time curves of the concrete of this invention and ordinary concrete during the early hydration process;

[0036] Figure 3 This is a comparison diagram of the early shrinkage stress development of the concrete of this invention and ordinary concrete. Detailed Implementation

[0037] 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 a part of the embodiments of the present invention, and not all of the 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.

[0038] In this invention, P·O 42.5 cement was selected, and the porous stainless steel fiber, porous nickel fiber and porous titanium fiber were purchased from Wuhan Xintu Engineering New Material Technology Co., Ltd., and the polycarboxylate superplasticizer was purchased from Wuhan Subo New Building Materials Co., Ltd.

[0039] Example 1

[0040] This embodiment provides a high crack-resistant concrete based on sheath thermal shrinkage-core phase change composite fiber and its preparation method. The concrete raw materials include 300 kg / m³ of cement (P·O 42.5). 3 Coarse aggregate (continuously graded granite with a particle size of 5-25mm) 1065 kg / m³ 3 Fine aggregate (medium sand with a fineness modulus of 2.6-2.9) 715 kg / m³ 3 180 kg / m³ of mineral admixtures 3 (Grade I fly ash 120 kg / m³) 3 Granulated blast furnace slag powder 60 kg / m 3 ), Polycarboxylate superplasticizer 4 kg / m 3 154 kg / m³ of water 3 Sheath thermal shrinkage-core phase change composite fiber 5 kg / m 3 .

[0041] The preparation method of the sheath thermal shrinkage-core phase change composite fiber includes the following steps:

[0042] S11, 1 kg of porous stainless steel fibers with a diameter of 0.2 mm, a length of 30 mm, a pore size of 20 μm, and a porosity of 45% were impregnated (2 cm of fiber was submerged) in a silane coupling agent (KH-550 silane coupling agent) solution (volume concentration 5%, immersion time 48 h). After the immersion was completed, the fibers were removed and dried (drying temperature was 100±5℃) to obtain surface-modified metal fibers.

[0043] S12, under a vacuum of -0.095 MPa and a pressure of 0.7 MPa, the modified metal fibers were impregnated (2 cm submerged) in molten phase change material paraffin at 85°C for 1.5 h. After immersion, the mixture was cooled to room temperature and micro-spot welded. The metal fiber ends and adjacent areas to be sealed were wiped with anhydrous ethanol to remove surface contaminants, followed by drying at room temperature for 10 min. A capacitor-powered automatic spot welding machine was used, placing the cleaned metal fibers in a special fixture, ensuring the ends to be sealed faced upwards. The automatic welding parameters were adjusted. Setting parameters: Welding energy E: 3.5J, charging voltage U: 150V (corresponding to capacitance C≈310μF, electrode pressure F: 1.5N, discharge time t: 2.5ms, upper electrode end radius R: 80μm, pulse count N: 2 times (first 3.0J, second 0.5J, interval 150ms); Welding execution: After alignment under a microscope, the welding program is started. Inspection: The weld joint morphology is bright and round. After heat aging at 95℃ for 2 hours, there is no paraffin seepage at the port, and the sealing performance is qualified.) The fiber port is sealed to obtain the core material;

[0044] S13, after preheating the core material from step S12 to 90°C, molten polyester (PET, molecular weight 30,000) and high-density polyethylene (molecular weight 200,000) are coated through a crosshead mold, with a mass ratio of 1:1, forming a sheath layer with a thickness of 0.2 mm. Then, it is cooled and shaped to obtain composite fiber.

[0045] S14. The composite fiber coated in step S13 is heat-treated at 100°C for 10 minutes to shrink the sheath layer and form a prestressed fiber, thus obtaining a sheath-core phase change composite fiber.

[0046] The preparation method of high crack-resistant concrete based on sheath thermal shrinkage-core phase change composite fiber includes the following steps:

[0047] S21, put cement, coarse aggregate, fine aggregate, and mineral admixture into a mixer and mix them evenly to obtain a dry mix;

[0048] S22, add water-reducing agent and water to dry mix, stir for 3 minutes (48 rpm) to form cement concrete with good fluidity;

[0049] S23, add the sheath thermal shrinkage-core phase change composite fiber to the cement mortar and stir slowly (25 rpm) for 4 minutes to obtain a concrete mixture containing the sheath thermal shrinkage-core phase change composite fiber;

[0050] S24: Pour the concrete mixture into the mold, vibrate to compact it, and cure it to the specified age under conditions of temperature 20±2℃ and humidity above 95%.

[0051] Example 2

[0052] The difference between Example 2 and Example 1 is that the amount of sheath thermal shrinkage-core phase change composite fiber used is 0.5 kg / m. 3 The rest of the content is the same as in Example 1.

[0053] Example 3

[0054] The difference between Example 3 and Example 1 is that the amount of sheath thermal shrinkage-core phase change composite fiber used is 3 kg / m. 3 The rest of the content is the same as in Example 1.

[0055] Example 4

[0056] The difference between Example 4 and Example 1 is that the amount of sheath thermal shrinkage-core phase change composite fiber used is 7 kg / m. 3 The rest of the content is the same as in Example 1.

[0057] Example 5

[0058] The difference between Example 5 and Example 1 is that the amount of sheath thermal shrinkage-core phase change composite fiber used is 10 kg / m. 3 The rest of the content is the same as in Example 1.

[0059] Example 6

[0060] This embodiment provides a high crack-resistant concrete based on sheath thermal shrinkage-core phase change composite fiber and its preparation method. The concrete raw materials include 500 kg / m³ of cement (P·O 42.5). 3 Coarse aggregate (continuously graded granite with a particle size of 5-25mm) 1200 kg / m³ 3 Fine aggregate (medium sand with a fineness modulus of 2.6-2.9) 1000 kg / m³ 3 Mineral admixtures (fly ash 140 kg / m³) 3 60 kg / m³ of slag powder 3 200kg / m 3 Polycarboxylate superplasticizer 15 kg / m 3 200 kg / m³ of water 3 Sheath thermal shrinkage-core phase change composite fiber 8 kg / m 3 .

[0061] The preparation method of the sheath thermal shrinkage-core phase change composite fiber includes the following steps:

[0062] S11. 0.5 kg of porous titanium fibers with a diameter of 0.1 mm, a length of 10 mm, a pore size of 1 μm, and a porosity of 30% were impregnated (2 cm of fiber was submerged) in a silane coupling agent (KH-550 silane coupling agent) solution (volume concentration 5%, immersion time 48 h). After the immersion was completed, the fibers were removed and dried (drying temperature 100±5℃) to obtain surface-modified metal fibers.

[0063] S12, under -0.09MPa vacuum and 1.0MPa pressure, the modified metal fiber was impregnated (2cm of fiber submerged) in molten phase change material fatty acid (lauric acid and decanoic acid, mass ratio 1:1) at 45℃, cooled after acceptance, and the fiber ends were sealed by micro-spot welding (same as Example 1) to obtain the core material.

[0064] S13. After preheating the core material from step S12 to 90°C, the core material is coated with molten polyester (polyarylate and PBT, with a molecular weight of 30,000 for polyarylate and 40,000 for PBT, and a mass ratio of 1:1) through a crosshead mold to form a sheath layer with a thickness of 0.1 mm. The composite fiber is then cooled and shaped.

[0065] S14. The composite fiber coated in step S13 is heat-treated at 120°C for 5 minutes to obtain a sheath thermal shrinkage-core phase change composite fiber.

[0066] The preparation method of high crack-resistant concrete based on sheath thermal shrinkage-core phase change composite fiber includes the following steps:

[0067] S21, put cement, coarse aggregate, fine aggregate, and mineral admixture into a mixer and mix them evenly to obtain a dry mix;

[0068] S22, add water-reducing agent and water to dry mix, stir for 2 minutes (48 rpm) to form cement concrete with good fluidity;

[0069] S23, add the sheath thermal shrinkage-core phase change composite fiber to the cement mortar and stir slowly (25 rpm) for 3 minutes to obtain a concrete mixture containing the sheath thermal shrinkage-core phase change composite fiber;

[0070] S24 involves pouring the concrete mixture into a mold, vibrating it to compact it, and curing it at a temperature of 18℃ and a humidity of over 95% until the specified age.

[0071] Example 7

[0072] This embodiment provides a high crack-resistant concrete based on sheath thermal shrinkage-core phase change composite fiber and its preparation method. The concrete raw materials include 420 kg / m³ of cement (P·O 42.5). 3 800 kg / m³ of coarse aggregate (continuously graded granite with a particle size of 5-25 mm) 3 Fine aggregate (medium sand with a fineness modulus of 2.6-2.9) 600 kg / m³ 3 Mineral admixtures (fly ash 30 kg / m³) 3 and slag powder 20 kg / m 3 50 kg / m 3 Polycarboxylate superplasticizer 5kg / m 3 150 kg / m³ of water 3 Sheath thermal shrinkage-core phase change composite fiber 2 kg / m 3 .

[0073] The preparation method of the sheath thermal shrinkage-core phase change composite fiber includes the following steps:

[0074] S11. Porous nickel fibers with a diameter of 1.0 mm, a length of 50 mm, a pore size of 50 μm, and a porosity of 60% were impregnated (2 cm of fiber was submerged) in a silane coupling agent (KH-550 silane coupling agent) solution (volume concentration 5%, immersion time 48 h). After the immersion was completed, the fibers were removed and dried (drying temperature 100±5℃) to obtain surface-modified metal fibers.

[0075] S12, under -0.1MPa vacuum and 0.5MPa pressure, the modified metal fiber was impregnated (2cm of fiber submerged) in molten phase change material hydrated salt (sodium sulfate decahydrate and magnesium nitrate hexahydrate, mass ratio 1:1) at 32.4℃, cooled after acceptance, and the fiber ends were sealed by micro-spot welding (same as Example 1) to obtain the core material;

[0076] S13. After preheating the core material from step S12 to 90°C, molten polypropylene (molecular weight 10,000) and polyurethane (molecular weight 80,000) are coated through a crosshead mold, with a mass ratio of 1:1, to form a sheath layer with a thickness of 0.5 mm. Then, the sheath is cooled and shaped to obtain composite fiber.

[0077] S14. The composite fiber coated in step S13 is heat-treated at 90°C for 30 minutes to obtain a sheath thermal shrinkage-core phase change composite fiber.

[0078] The preparation method of high crack-resistant concrete based on sheath thermal shrinkage-core phase change composite fiber includes the following steps:

[0079] S21, put cement, coarse aggregate, fine aggregate, and mineral admixture into a mixer and mix them evenly to obtain a dry mix;

[0080] S22, add water-reducing agent and water to dry mix, stir for 4 minutes (48 rpm) to form cement concrete with good fluidity;

[0081] S23, add the sheath thermal shrinkage-core phase change composite fiber to the cement mortar and stir slowly (25 rpm) for 5 minutes to obtain a concrete mixture containing the sheath thermal shrinkage-core phase change composite fiber;

[0082] S24 involves pouring the concrete mixture into a mold, vibrating it to compact it, and curing it at a temperature of 22℃ and a humidity of over 95% until the specified age.

[0083] Comparative Example 1

[0084] Compared with Example 1, Comparative Example 1 did not add sheath shrinkage-core phase change composite fiber, but only replaced it with fine aggregate of equal mass. The rest of the contents were the same as in Example 1.

[0085] Comparative Example 2

[0086] Compared with Example 1, Comparative Example 2 had an excessively high incorporation amount of sheath thermal shrinkage-core phase change composite fiber, specifically 30 kg / m². 3 The rest of the content is the same as in Example 1.

[0087] Comparative Example 3

[0088] Compared with Example 1, Comparative Example 3 had an excessively low incorporation amount of sheath thermal shrinkage-core phase change composite fiber, specifically 0.2 kg / m². 3 The rest of the content is the same as in Example 1.

[0089] Comparative Example 4

[0090] Compared with Example 1, Comparative Example 4 lacks the heat treatment step S14 in the preparation of the composite fiber, while the rest is the same as in Example 1.

[0091] Comparative Example 5

[0092] Compared with Example 1, in the preparation of the composite fiber, the porous metal fiber was not modified by silane coupling agent, but was directly impregnated with molten phase change material. The rest of the process was the same as in Example 1.

[0093] The concrete prepared in the examples and comparative examples was cured, and its compressive strength, splitting tensile strength, shrinkage, and crack resistance were tested according to the "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" (GB / T 50081-2019) and the "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete" (GB / T50082-2024). The fiber dispersion was observed at the cross-section. Simultaneously, a 1m×1m×1m concrete structure was poured using the concrete prepared in the examples and comparative examples, and the temperature rise of the concrete hydration heat was monitored by embedding a temperature sensor. The comparison results are shown in Table 1.

[0094] Table 1 Concrete Properties

[0095]

[0096] The results show that the sheath-core phase change composite fiber obtained by this invention can effectively improve the compressive strength and splitting tensile strength of concrete, significantly reduce the temperature rise of the heat of hydration in concrete, thereby reducing the internal and external temperature difference of solid concrete, and significantly improve the crack resistance of concrete. Furthermore, it exhibits good dispersibility in concrete within a suitable dosage range. Examples 1-5 show that, within a suitable range, as the dosage of the sheath-core phase change composite fiber increases, the compressive strength and splitting tensile strength increase accordingly, while the total crack area on a single surface decreases.

[0097] Compared with the concrete in Comparative Example 1 without the addition of sheath-core phase change composite fiber, the concrete with the addition of the sheath-core phase change composite fiber obtained by the present invention has good dispersion, higher compressive strength and splitting tensile strength, lower hydration heat temperature rise (the poured concrete entity will have a smaller internal surface temperature difference), and significantly improved crack resistance.

[0098] Compared with the concrete in Comparative Example 2, which incorporated an excessive amount of sheath-core phase change composite fiber, the concrete with an appropriate amount of the sheath-core phase change composite fiber obtained in this invention exhibits better dispersibility, higher compressive strength and splitting tensile strength, and significantly improved crack resistance.

[0099] Compared with the concrete of Comparative Example 3 with too low a dosage of sheath thermal shrinkage-core phase change composite fiber, the concrete with an appropriate amount of sheath thermal shrinkage-core phase change composite fiber obtained in this invention has higher compressive strength and splitting tensile strength, lower hydration heat temperature rise (the poured concrete will have a smaller internal surface temperature difference), and significantly improved crack resistance.

[0100] Compared with the concrete in Comparative Example 4, which incorporated the heat-treated sheath-core phase change composite fiber lacking step S14, the concrete with an appropriate amount of heat-treated sheath-core phase change composite fiber exhibited higher compressive strength and splitting tensile strength, and its crack resistance was significantly improved.

[0101] Compared with the concrete in Comparative Example 5, which incorporated sheath-core phase change composite fibers without silane coupling agent modification, the concrete with appropriate amounts of sheath-core phase change composite fibers modified with silane coupling agent exhibits better dispersibility, higher compressive strength and splitting tensile strength, lower hydration heat rise (the poured concrete will have a smaller internal surface temperature difference), and significantly improved crack resistance.

[0102] Figure 2 This is a comparison of the temperature-time curves of the concrete of this invention and ordinary concrete (Comparative Example 1) during the early hydration process. In the figure, the temperature peak of the curve of this invention is lower and appears later, effectively delaying the arrival of the temperature peak and reducing the maximum temperature rise, thereby weakening the main driving force leading to temperature cracks—thermal stress—from the root.

[0103] Figure 3 This is a comparison diagram of the early shrinkage stress development of the concrete of the present invention and ordinary concrete (Comparative Example 1). In the figure, the shrinkage stress of the concrete of the present invention is consistently lower than that of the control group, which keeps the internal stress state of the concrete at a low level and greatly improves its crack resistance.

[0104] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A sheath-core phase change composite fiber, characterized in that, The composite fiber has a core-shell structure. The preparation method of the core material is as follows: porous metal fibers are impregnated in a silane coupling agent solution to obtain surface-modified metal fibers; then, organic or inorganic phase change materials are loaded onto the modified metal fibers, and the ends of the metal fibers are sealed to obtain the core material. The sheath material includes one or more of polyester, polypropylene, polyurethane, and high-density polyethylene; the sheath is heat-shrinkable and covers the outside of the core material after heat treatment.

2. The sheath-core phase change composite fiber as described in claim 1, characterized in that, The porous metal fiber includes one or more of porous stainless steel fiber, porous nickel fiber and porous titanium fiber, with a porosity of 30%-60%, a pore size of 1-50μm, a fiber diameter of 0.1-1.0mm and a length of 10-50mm.

3. The sheath-core phase change composite fiber as described in claim 1, characterized in that, The phase change material is one or more of paraffin, fatty acids, or hydrated salts; the fatty acid is one or more of decanoic acid, lauric acid, myristic acid, and palmitic acid; and the hydrated salt is one or more of disodium hydrogen phosphate dodecahydrate, barium hydroxide octahydrate, sodium sulfate decahydrate, and magnesium nitrate hexahydrate.

4. The sheath-core phase change composite fiber as described in claim 1, characterized in that, The thickness of the sheath is 0.1-0.5 mm.

5. The sheath-core phase change composite fiber as described in claim 1, characterized in that, The molecular weight of the polyester is 30,000 to 40,000, the molecular weight of the polypropylene is 8,000 to 10,000, the molecular weight of the high-density polyethylene is 150,000 to 200,000, and the molecular weight of the polyurethane is 60,000 to 80,000; the polyester is one or more of polybutylene terephthalate, polyethylene terephthalate, and polyarylate.

6. The method for preparing a sheath-core phase change composite fiber as described in any one of claims 1-5, characterized in that, Includes the following steps: S11, porous metal fibers are immersed in a silane coupling agent solution, and after the process is completed, they are removed and dried to obtain surface-modified metal fibers; S12, under vacuum and pressure conditions, the modified metal fiber is impregnated in molten phase change material, cooled after completion, and the fiber ends are sealed to obtain the core material; S13, after preheating the core material from step S12, the molten sheath material is coated to form a sheath, and then cooled and shaped to obtain composite fiber; S14, the composite fiber coated in step S13 is heat-treated to obtain sheath shrinkage-core phase change composite fiber.

7. The method for preparing a sheath-core phase change composite fiber as described in claim 6, characterized in that, In step S12, the vacuum degree is -0.09~-0.1MPa and the pressure is 0.5-1.0MPa; in step S14, heat treatment is carried out at 90-120℃ for 5-30 minutes.

8. A high-crack-resistant concrete based on sheath thermal shrinkage-core phase change composite fiber, characterized in that, The raw materials of concrete, by weight, include 300-500 parts of cement, 800-1200 parts of coarse aggregate, 600-1000 parts of fine aggregate, 50-200 parts of mineral admixture, 4-15 parts of water-reducing agent, 150-200 parts of water, and 0.5-10 parts of sheath shrinkage-core phase change composite fiber prepared according to claim 6.

9. The method for preparing high crack-resistant concrete based on sheath thermal shrinkage-core phase change composite fiber as described in claim 8, characterized in that, Includes the following steps: S21, put cement, coarse aggregate, fine aggregate, and mineral admixture into a mixer and mix them evenly to obtain a dry mix; S22, add water-reducing agent and water to dry mix, stir for 2-4 minutes to form cement concrete with good fluidity; S23, add the sheath thermal shrinkage-core phase change composite fiber to the above cement concrete and stir slowly for 3-5 minutes to obtain a concrete mixture containing the sheath thermal shrinkage-core phase change composite fiber. S24: Pour the concrete mixture into the mold, vibrate to compact it, and cure it to the specified age under conditions of temperature 20±2℃ and humidity above 95%.

10. The method for preparing high crack-resistant concrete based on sheath thermal shrinkage-core phase change composite fiber as described in claim 9, characterized in that, The coarse aggregate is continuously graded crushed stone with a particle size of 5-25mm, the fine aggregate is medium sand with a fineness modulus of 2.6-2.9, the mineral admixture is one or more of fly ash, granulated blast furnace slag powder and finely ground limestone powder, and the water-reducing agent is a polycarboxylate-based water-reducing agent.

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