Phase change material loaded steel fiber and preparation method and application thereof

Abstract

The invention discloses a phase-change material loaded steel fiber as well as a preparation method and application thereof, and belongs to the technical field of concrete preparation. Paraffin and the like are used as phase-change materials, the phase-change temperature of the phase-change materials is well matched with the peak value of hydration heat of concrete, a large amount of heat can be absorbed in the hydration process of the concrete, the internal temperature rise of the concrete is effectively reduced, the temperature stress is reduced, and cracks are inhibited; the steel fiber loaded with the phase-change material is subsequently doped into the concrete according to the doping amount of 40-60kg / m < 3 >, and the reinforcing effect of the steel fiber and the temperature control effect of the phase-change material have a synergistic effect, so that the strength and toughness of the concrete are remarkably improved, and the concrete has better mechanical properties and durability; an innovative thought and an effective way are provided for preparation of a high-performance concrete material, and the method has a wide application prospect and huge economic benefits in the field of constructional engineering.

Description

Technical Field

[0001] The present invention relates to the field of concrete preparation, and in particular to a steel fiber loaded with a phase change material, a preparation method thereof and an application thereof. Background Art

[0002] In the field of construction engineering, concrete, as the most widely used building material, its performance directly affects the project quality and structural safety. During the concrete pouring process, the hydration of cement will release a large amount of heat, resulting in a sharp rise in the internal temperature of the concrete. When the internal and external temperature difference is too large, temperature stress is extremely likely to be generated, causing the concrete to crack, seriously affecting the durability and stability of the concrete structure. At the same time, ordinary concrete has inherent defects such as low tensile strength and poor toughness, which limit its application in projects with high material performance requirements such as high-rise buildings and long-span bridges.

[0003] To solve the above problems, in the prior art, there is a method of preparing phase change concrete by encapsulating a phase change material with aggregate. Although it can adjust the hydration heat, it will reduce the strength of the concrete. In addition, there are mainly three ways to incorporate the phase change material into the concrete. One is to use a pipeline to encapsulate a flowable phase change material. Although this method can effectively improve the temperature control efficiency of the phase change material, it has the same disadvantages as the condenser pipe. Due to the temperature gradient in the area near the cooling pipe, thermal stress will cause the concrete to crack. Therefore, this design has extremely high requirements for the quality of construction personnel in the environment. The second is the microcapsule encapsulation method, which is to coat the phase change material with a polymer film material to form fine particles and then incorporate them into the concrete. In the existing literature, adding 5wt% of PCM to the mortar can reduce the peak temperature by 20% and delay the appearance time of the peak temperature by 40% under the condition of semi-adiabatic temperature rise, but the compressive strength is reduced by 34%. The phase change concrete prepared by this process has obvious temperature regulation effect, but it has high cost, complex preparation process, and significant reduction effect on strength.

[0004] And currently, one of the most promising phase change material encapsulation methods for engineering applications is to encapsulate the phase change material in low-cost lightweight aggregate by using a vacuum encapsulation process. It encapsulates paraffin with ceramsite, replacing 10% of the coarse aggregate. Under laboratory conditions, the peak temperature is reduced by 8.5°C, and the 28-day concrete strength is reduced by 18%.

[0005] In the above prior art, although the incorporation of the phase change material has a good temperature regulation effect on the concrete, it significantly reduces the concrete strength.

[0006] Based on the above problems, a steel fiber loaded with a phase change material, a preparation method thereof and an application thereof are proposed. Summary of the Invention

[0007] The purpose of the present invention is to provide a steel fiber loaded with a phase change material, a preparation method thereof and an application thereof to solve the problems in the background art.

[0008] To achieve the above object, the present invention provides a method for preparing steel fibers loaded with a phase change material, comprising the following steps:

[0009] First, place the phase change material in a heating device and heat it at a heating rate of 3 - 10 °C / min until the phase change temperature of the phase change material is reached, and keep it warm for 10 - 30 min to convert the phase change material into a liquid;

[0010] Then, vacuum package the phase change material using a vacuum packaging device, fix the hollow steel fibers at the packaging station, inject the liquid phase change material into the hollow steel fibers through a diversion tube, and after the packaging is completed, cool it until the phase change material solidifies to obtain steel fibers loaded with the phase change material.

[0011] Preferably, the phase change material is one or more of paraffin, organic fatty acids, and composite phase change materials.

[0012] Preferably, the phase change temperature is 30 - 60 °C.

[0013] Preferably, the diameter of the hollow steel fibers is 3 - 5 mm and the wall thickness is 0.1 - 1 mm.

[0014] Preferably, during the vacuum packaging process, the vacuum degree is 1×10 -3 ~1×10 -5 Pa, the temperature is 30 - 60 °C, and the vacuum packaging time is 5 - 15 min.

[0015] The present invention also provides steel fibers loaded with a phase change material, and the steel fibers loaded with the phase change material are obtained by the above preparation method.

[0016] Preferably, the steel fibers loaded with the phase change material are applied to the field of concrete preparation to regulate the hydration heat of the concrete and increase the strength and toughness of the concrete.

[0017] Preferably, the specific way of applying the steel fibers loaded with the phase change material to concrete preparation is: incorporating the steel fibers loaded with the phase change material into the concrete, wherein the dosage of the steel fibers is 40 kg / m 3 ~60 kg / m 3 .

[0018] Therefore, the steel fibers loaded with a phase change material, the preparation method thereof, and the application thereof according to the present invention have the following beneficial effects:

[0019] (1) In terms of the preparation method of the present invention, the heating rate, phase change temperature (40 - 60 °C), and heat preservation time of the phase change material are precisely controlled to ensure that the phase change material is completely liquefied, laying a foundation for subsequent encapsulation. The vacuum encapsulation process with specific vacuum degree, temperature (5 - 15 °C), and encapsulation time, combined with hollow steel fibers of appropriate size, effectively ensures the encapsulation stability of the phase change material, prevents leakage, and improves the quality reliability of the steel fibers loaded with the phase change material.

[0020] (2) In the present invention, paraffin and the like are used as the phase change material, and its phase change temperature has good adaptability to the temperature at which the peak value of concrete hydration heat appears. It can absorb a large amount of heat during the concrete hydration process, effectively reduce the internal temperature rise of the concrete, reduce the temperature stress, and inhibit the generation of cracks. The steel fibers loaded with the phase change material are incorporated into the concrete at a dosage of 40 - 60 kg / m 3 . The strengthening effect of the steel fibers themselves and the temperature control effect of the phase change material act synergistically, significantly improving the strength and toughness of the concrete, enabling the concrete to have better mechanical properties and durability, providing innovative ideas and effective ways for the preparation of high-performance concrete materials, and having broad application prospects and huge economic benefits in the field of construction engineering.

[0021] (3) After the steel fibers loaded with the phase change material prepared by the method protected by the present invention are doped with concrete, the peak temperature under semi-adiabatic temperature rise conditions is reduced by 15%, the time when the peak temperature appears is delayed by 30%, the compressive strength is increased by 15%, the flexural strength is increased by 8%, the cracking time is delayed by 2 - 5 h, and the number of cracks is reduced by 20% - 40%.

[0022] The technical solution of the present invention will be further described in detail below through the drawings and embodiments. Description of the Drawings

[0023] Figure 1 It is a schematic structural diagram of the steel fibers loaded with the phase change material in the embodiment of the present invention. Detailed Embodiments

[0024] The technical solution of the present invention will be further described below through the drawings and embodiments.

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention.

[0026] Embodiment 1

[0027] Select paraffin wax as the phase change material and place it in a heating device. Heat it at a heating rate of 3°C / min. When the temperature reaches 40°C, keep it warm for 30 minutes to completely convert the paraffin wax into a liquid;

[0028] Prepare hollow steel fibers with a diameter of 3 mm and a wall thickness of 0.1 mm. Use a vacuum packaging device with a vacuum degree of up to 1×10-3 Pa to fix the hollow steel fibers at the packaging station. In an environment with a temperature of 40°C, inject liquid paraffin into the hollow steel fibers through a diversion tube, and the vacuum packaging time is 15 minutes;

[0029] Adopt the air-cooling method, set the wind speed to 5 m / s, and cool the encapsulated phase change material steel fibers. Control the cooling rate at 2°C / min until the paraffin wax cools and solidifies to obtain the phase change material steel fibers with load.

[0030] Incorporate the prepared phase change material steel fibers with load into C50 concrete, and the steel fiber dosage is 40 kg / m 3 .

[0031] Example 2

[0032] Select paraffin wax as the phase change material and put it into a heating device. Heat it at a heating rate of 7°C / min. When the temperature rises to 40°C, keep it warm for 20 minutes to convert the paraffin wax into a liquid state.

[0033] Take hollow steel fibers with a diameter of 4 mm and a wall thickness of 0.5 mm, and use a vacuum packaging device with a vacuum degree of 1×10 -4 Pa. In an environment with a temperature of 40°C, fix the hollow steel fibers well, inject liquid paraffin through a diversion tube, and the vacuum packaging time is 10 minutes.

[0034] Adopt the water-cooling method, set the coolant temperature to 15°C, and control the cooling rate at 5°C / min to cool the encapsulated steel fibers until the paraffin wax solidifies to complete the preparation of the phase change material steel fibers with load.

[0035] Incorporate the phase change material steel fibers with load into C50 concrete at a dosage of 50 kg / m 3 .

[0036] Comparative Example 1

[0037] Prepare hollow steel fibers with a diameter of 3 mm and a wall thickness of 0.1 mm without any filling treatment.

[0038] Incorporate the hollow steel fibers into concrete, and the steel fiber dosage is 40 kg / m 3 , for concrete preparation.

[0039] Comparative Example 2

[0040] Select paraffin as the phase change material, place it in a heating device, heat it at a heating rate of 3°C / min, and keep it at 40°C for 30 minutes after the temperature reaches 40°C to completely convert the paraffin into a liquid;

[0041] Prepare hollow steel fibers with a diameter of 3 mm and a wall thickness of 0.1 mm;

[0042] Under the environment of 40°C, directly add the liquid paraffin and hollow steel fibers to the mixing process of C50 concrete, where the paraffin dosage is 40 kg / m 3 , and the steel fiber dosage is also 40 kg / m 3 . Use a forced mixer, first dry mix the cement, sand, and gravel for 1 minute, then add the liquid paraffin and steel fibers, and at the same time inject water and water reducer, and wet mix for 3 minutes to make each component evenly mixed;

[0043] Pour the mixed concrete into a mold and cure it for 28 days under standard curing conditions (temperature 20±2°C, relative humidity ≥95%) to obtain a concrete specimen with double admixture of paraffin and steel fiber.

[0044] Comparative Example 3

[0045] Select paraffin as the phase change material, place it in a heating device, heat it at a heating rate of 3°C / min, and keep it at 40°C for 30 minutes after the temperature reaches 40°C to completely convert the paraffin into a liquid;

[0046] Prepare ceramsite with a particle size of 5 - 10 mm and a porosity of 30%, place the ceramsite in an environment of 40°C, and inject paraffin into the ceramsite pores by vacuum packaging

[0047] Adopt the natural cooling method, and cool the ceramsite adsorbed with paraffin in the room temperature (25°C) environment until the paraffin cools and solidifies to obtain ceramsite encapsulated phase change material.

[0048] Mix the prepared ceramsite encapsulated phase change material into C50 concrete, and the dosage is 40 kg / m 3 .

[0049] Taking ordinary concrete as the reference, test the concretes prepared in the above Examples 1 and 2 and Comparative Examples 1 - 3, and the results are shown in Tables 1 - 3 below.

[0050] Table 1 Peak temperature and occurrence time

[0051] Peak temperature (°C) Appearance time (h) Reference (ordinary concrete) 68 12 Example 1 58 16 Example 2 54 17.8 Comparative Example 1 68 12 Comparative Example 2 59 16 Comparative Example 3 60 15

[0052] Table 2 Compressive strength and flexural strength

[0053]

[0054]

[0055] Table 3 Cracking test

[0056] Cracking time (h) Number of cracks (pieces) Reference (ordinary concrete) 10 25 Example 1 13 13 Example 2 12.5 11 Comparative Example 1 12 17 Comparative Example 2 11 19 Comparative Example 3 9.8 22

[0057] As can be seen from the above table, compared with ordinary concrete, in Examples 1 and 2, under the semi-adiabatic temperature rise condition, the peak temperature is reduced by 15%, and the occurrence time of the peak temperature is delayed by 30%; the compressive strength is increased by about 15%, and the flexural strength is increased by 8%; the cracking time is delayed by 2 - 5 h, and the number of cracks is reduced by 20% - 40%.

[0058] In Comparative Example 1, when compared with the reference concrete and Example 1, the hollow steel fiber concrete without filled phase change material only relies on the physical strengthening effect of the hollow steel fiber, and cannot effectively regulate the hydration heat. The temperature stress generated inside the concrete due to the hydration heat cannot be relieved, and cracks are likely to appear.

[0059] In Comparative Example 2, the mechanical properties such as the compressive strength and flexural strength of the concrete specimens with double admixture of paraffin and steel fibers are significantly reduced compared with the reference concrete and Example 1. This is because the compatibility between the liquid paraffin and the concrete matrix is poor. During the hardening process of the concrete, the paraffin gradually cools and solidifies, and the volume shrinkage generates voids, destroying the compactness of the internal structure of the concrete; at the same time, the paraffin forms a weak interface in the concrete and cannot cooperate with the steel fibers to strengthen the concrete, resulting in a decrease in the overall mechanical properties.

[0060] In Comparative Example 3, the mechanical property indexes such as the compressive strength and flexural strength of the concrete incorporated with ceramsite encapsulated phase change material are all reduced to varying degrees compared with the reference concrete and Example 1. This is because the strength of the ceramsite itself is lower than that of the steel fiber, and its interfacial bonding property with the concrete matrix is weak, and it is likely to become a weak link inside the concrete under the action of load, resulting in a decrease in the mechanical properties of the concrete.

[0061] In summary, it can be seen that when the steel fiber loaded with the phase change material prepared by the protected solution of the present invention is incorporated into the concrete, the prepared concrete has a reduced hydration heat while the mechanical properties are improved.

[0062] Therefore, for a steel fiber loaded with a phase change material, its preparation method and application according to the present invention, using paraffin and the like as the phase change material, the phase change temperature of which has good adaptability with the temperature at which the peak of the concrete hydration heat appears, can absorb a large amount of heat during the concrete hydration process, effectively reduce the internal temperature rise of the concrete, reduce the temperature stress, and inhibit the generation of cracks; subsequently, the steel fiber loaded with the phase change material is 40 - 60 kg / m 3When the admixture is incorporated into concrete, the reinforcing effect of the steel fiber itself and the temperature control effect of the phase change material act synergistically, significantly improving the strength and toughness of the concrete, endowing the concrete with better mechanical properties and durability, providing innovative ideas and effective ways for the preparation of high-performance concrete materials, and having broad application prospects and huge economic benefits in the field of construction engineering.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and such modifications or equivalent replacements do not make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A preparation method of steel fibers loaded with phase change materials, characterized in that, It includes the following steps: First, place the phase change material in a heating device and heat it at a heating rate of 3 - 10 °C / min until the heating temperature reaches the phase change temperature of the phase change material, and keep it warm for 10 - 30 min to convert the phase change material into a liquid; Then, use a vacuum packaging device to vacuum package the phase change material, fix the hollow steel fiber at the packaging station, inject the liquid phase change material into the hollow steel fiber through a diversion tube, and cool it after packaging. After the phase change material solidifies, the steel fiber loaded with the phase change material is prepared.

2. The preparation method of a steel fiber loaded with a phase change material according to claim 1, characterized in that: The phase change material is one or more of paraffin, organic fatty acid, and composite phase change material.

3. The preparation method of a steel fiber loaded with a phase change material according to claim 1, characterized in that: The phase change temperature is 30 - 60 °C.

4. The preparation method of a steel fiber loaded with a phase change material according to claim 1, characterized in that: The diameter of the hollow steel fiber is 3 - 5 mm, and the wall thickness is 0.1 - 1 mm.

5. The preparation method of a steel fiber loaded with a phase change material according to claim 1, characterized in that: During the vacuum packaging process, the degree of vacuum is 1×10 -3 ~1×10 -5 Pa, the temperature is 30 to 60 °C, and the vacuum packaging time is 5 to 15 minutes.

6. A steel fiber loaded with a phase change material, characterized in that: The steel fiber loaded with the phase change material is prepared by the preparation method according to any one of claims 1 - 5 above.

7. A steel fiber loaded with a phase change material according to claim 6, characterized in that: Apply the steel fiber loaded with the phase change material to the field of concrete preparation to regulate the hydration heat of the concrete and increase the strength and toughness of the concrete.

8. A steel fiber loaded with a phase change material according to claim 7, characterized in that, The specific method of applying the phase change material - loaded steel fiber to concrete preparation is as follows: Incorporate the phase change material - loaded steel fiber into the concrete, where the dosage of the steel fiber is 40 kg / m 3 ~60 kg / m 3 .

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