Prestressed steel fiber concrete and preparation method thereof

Abstract

The invention belongs to the technical field of cement-based composite material preparation, and particularly discloses prestressed steel fiber concrete and a preparation method thereof. The preparation method comprises the following steps: S1, testing initial setting time and final setting time of different types of cement, and selecting a matrix raw material; s2, adding a mineral admixture into the matrix raw material selected in S1, uniformly mixing with water, adding steel fibers, stirring, and pouring to obtain steel fiber concrete; and S3, performing thermal curing on the steel fiber reinforced concrete poured in the step S2, and naturally cooling to room temperature to obtain the prestressed steel fiber reinforced concrete. The invention discloses prestressed steel fiber reinforced concrete and a preparation method thereof, a base material in the prestressed steel fiber reinforced concrete is in a pre-pressed state, and the initial crack strength of the material can be improved under the action of an external load, so that steel fibers play a role in strengthening and toughening before cracking.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of cement-based composites, and particularly relates to a prestressed steel fiber concrete and a preparation method thereof. Background Art

[0002] As a high-performance cement-based composite material, steel fiber concrete can significantly improve the tensile, flexural, impact and crack resistance properties of the material by incorporating steel fibers into the concrete matrix. The strengthening mechanism of traditional steel fiber concrete mainly relies on the bridging effect of steel fibers after the matrix cracks: when the external load causes the matrix to crack, the steel fibers transfer stress across the cracks, delaying the crack propagation, thereby improving the toughness and load-bearing capacity of the material. However, this strengthening effect only appears after the matrix cracks. In the stage before the matrix cracks, due to the high strain synchronization between the steel fibers and the matrix, the steel fibers can hardly play a role in crack resistance or strengthening. This limitation results in a low initial cracking strength of traditional steel fiber concrete, and the material is prone to reduce its durability due to the propagation of microcracks during long-term use.

[0003] In recent years, researchers have tried to improve the performance of steel fiber concrete through prestress technology. For example, prestressed steel fibers are embedded in the concrete or an external prestress application device is used to pre-tension the steel fibers in the matrix and compress the matrix, thereby improving the crack resistance of the material. However, such methods have problems of complex process and high cost, and the application of prestress is easily restricted by construction conditions, and it is difficult to achieve a uniform prestress distribution. In addition, traditional prestress technology has extremely high requirements for the bond strength between the steel fibers and the matrix interface. If the interface bond is insufficient, prestress failure is likely to occur.

[0004] On the other hand, the application of the difference in thermal expansion coefficient in the prior art mostly focuses on reducing the internal stress of the material, such as suppressing temperature cracks by matching the thermal expansion coefficients of the aggregate and the cement paste. However, how to actively utilize the difference in thermal expansion coefficient to form a prestress effect in concrete has not been fully explored. Summary of the Invention

[0005] The present invention aims to provide a prestressed steel fiber concrete and a preparation method thereof. In this prestressed steel fiber concrete, the matrix material is in a pre-compressed state, and under the action of an external load, it can improve the initial cracking strength of the material, enabling the steel fibers to play a role in strengthening and toughening before cracking.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0007] A preparation method of a prestressed steel fiber concrete includes the following steps:

[0008] S1. Test the initial setting and final setting times of different cements, and select the matrix raw materials;

[0009] S2. Add mineral admixtures to the matrix raw materials selected in S1, mix them evenly with water, add steel fibers and mix well, then pour to obtain steel fiber concrete;

[0010] S3. Conduct heat curing on the steel fiber concrete completed in S2, and naturally cool it to room temperature to obtain prestressed steel fiber concrete.

[0011] Preferably, in S1, select cement with an initial setting time of 15 - 40 min, a final setting time of 20 min - 60 min, and a fast hardening speed and small autogenous shrinkage as the matrix raw material.

[0012] Preferably, in S2, the mineral admixture is one or both of fly ash and silica fume.

[0013] Preferably, in S3, the steel fibers are directionally distributed in the steel fiber concrete.

[0014] Preferably, in S3, the heat curing temperature is 100 °C.

[0015] Preferably, in S3, the heat curing time is determined according to the initial and final setting times of different cements, and the heat curing time is not less than the final setting time of the cement.

[0016] The present invention also provides the prestressed steel fiber concrete prepared by the described preparation method.

[0017] Compared with the prior art, the present invention has the following advantages and technical effects:

[0018] The present invention discloses a prestressed steel fiber concrete and its preparation method. By directionally regulating the difference in the thermal expansion coefficients of steel fibers and the concrete matrix and combining with the heat curing process, a prestressed state is constructed inside the material to enhance the early crack resistance and toughening effect of steel fibers. Select steel fibers with a high linear expansion coefficient as the reinforcing phase, and at the same time incorporate mineral admixtures into the matrix raw materials to reduce their thermal expansion coefficients and improve the density, forming a significant thermal expansion difference between the steel fibers and the matrix. During the heat curing process, the matrix hardens and forms a firm bond with the steel fibers. When the temperature drops, the steel fibers pull the matrix to shrink due to a larger shrinkage amount, and a stress balance state of pre-tensioned steel fibers and pre-compressed matrix is formed after being restricted by the matrix. Combining with the directional distribution of steel fibers to enhance the stress transfer efficiency and selecting a matrix raw material with small autogenous shrinkage to reduce interference factors, the matrix needs to offset the internal pre-compressive stress first when bearing external loads, thereby improving the initial crack strength, and the steel fibers inhibit the initiation of microcracks through tensile stress before the matrix cracks due to the pre-tensioned state.

[0019] Through the coordination of the thermophysical properties of the material and the curing process, the present invention transforms the reinforcement effect of steel fibers from the traditional post-cracking bridging to the active crack resistance before cracking. Tests show that the matrix shrinkage increases with the increase of the steel fiber content, and the initial cracking strength is increased by more than 20% compared with the traditional materials. At the same time, the durability is improved through the pre-compressive stress and the dense structure, achieving a key breakthrough in the performance of cement-based composites.

[0020] The technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the schematic diagram of the formation principle of the prestress of the non-coordinated deformation of steel fiber - matrix;

[0022] Figure 2 is the preparation flow chart of prestressed steel fiber concrete;

[0023] Figure 3 is the shrinkage of the steel fiber concrete specimen during the whole cooling process of the prestressed steel fiber concrete provided in Examples 1 - 3;

[0024] Figure 4 is the shrinkage of the steel fiber concrete specimen during the whole cooling process of the prestressed steel fiber concrete provided in Examples 4 - 6. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0026] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the field to which the present invention belongs.

[0027] Source of test materials:

[0028] In the present invention, unless otherwise specified, other test materials and instrument equipment are all conventional test materials in the field and can be obtained through commercial channels.

[0029] In Examples 1 - 6 of the present invention, the schematic diagram of the formation principle of the prestress of the non-coordinated deformation of steel fiber - matrix is as Figure 1 shown;

[0030] Examples 1 - 6 of the present invention refer to the Figure 2 shown preparation flow chart of prestressed steel fiber concrete.

[0031] Example 1

[0032] A preparation method of prestressed steel fiber concrete, comprising the following steps:

[0033] S1. The initial setting and final setting time of different cements were tested. The initial setting time was 16 minutes, the final setting time was 22 minutes, and the high-belite sulphoaluminate cement with fast hardening speed and small self-shrinkage was used as the matrix raw material;

[0034] S2, pour 1.536kg of the matrix material selected in S1, 0.307kg of fly ash, and 0.645L of water into a mortar mixer and stir thoroughly. Mix evenly, add 1.0% of round straight 304 stainless steel fiber by volume and mix for 3 minutes, wherein the steel fiber has a diameter of 0.5mm and a length of 30mm. Pour the mixed mixture into a triple mold with dimensions of 40mm in height, 40mm in width, and 160mm in length, pre-embed copper nail probes at both ends, and assist with appropriate vibration to enhance density. The dispersed phase steel fibers are oriented and distributed so that the fiber direction is parallel to the long side direction of the specimen, thereby obtaining steel fiber concrete;

[0035] S3. The steel fiber concrete poured in S2 was heat-cured at 100°C for 40 minutes and naturally cooled to room temperature to obtain prestressed steel fiber concrete. The test was repeated three times to prepare 3 portions of prestressed steel fiber concrete.

[0036] Example 2

[0037] A method for preparing prestressed steel fiber concrete comprises the following steps:

[0038] S1. The initial setting and final setting time of different cements were tested. The initial setting time was 16 minutes, the final setting time was 22 minutes, and the high-belite sulphoaluminate cement with fast hardening speed and small self-shrinkage was used as the matrix raw material;

[0039] S2, pour 1.536kg of the matrix material selected in S1, 0.307kg of fly ash, and 0.645L of water into a mortar mixer and stir thoroughly. Mix evenly, add 0.5% by volume of round straight 304 stainless steel fiber and mix for 3 minutes, wherein the steel fiber has a diameter of 0.5mm and a length of 30mm. Pour the mixed mixture into a triple mold with dimensions of 40mm in height, 40mm in width, and 160mm in length, pre-embed copper nail probes at both ends, and assist with appropriate vibration to enhance density. The dispersed phase steel fiber is oriented and distributed so that the fiber direction is parallel to the long side direction of the specimen, and steel fiber concrete is obtained;

[0040] S3. The steel fiber concrete poured in S2 was heat-cured at 100°C for 40 minutes and naturally cooled to room temperature to obtain prestressed steel fiber concrete. The test was repeated three times to prepare 3 portions of prestressed steel fiber concrete.

[0041] Example 3

[0042] A method for preparing prestressed steel fiber concrete comprises the following steps:

[0043] S1. The initial setting and final setting time of different cements were tested. The initial setting time was 16 minutes, the final setting time was 22 minutes, and the high-belite sulphoaluminate cement with fast hardening speed and small self-shrinkage was used as the matrix raw material;

[0044] S2, pour 1.536kg of the matrix material selected in S1, 0.307kg of fly ash, and 0.645L of water into a mortar mixer and stir thoroughly. Mix evenly, add 0% of round straight 304 stainless steel fiber by volume and mix for 3min, wherein the steel fiber has a diameter of 0.5mm and a length of 30mm, pour the mixed mixture into a triple mold with a size of 40mm in height, 40mm in width, and 160mm in length, embed copper nail probes at both ends, and vibrate appropriately to enhance density. The dispersed phase steel fiber is oriented and distributed so that the fiber direction is parallel to the long side direction of the specimen, and obtain steel fiber concrete;

[0045] S3. The steel fiber concrete poured in S2 was heat-cured at 100°C for 40 minutes and naturally cooled to room temperature to obtain prestressed steel fiber concrete. The test was repeated three times to prepare 3 portions of prestressed steel fiber concrete.

[0046] Example 4

[0047] A method for preparing prestressed steel fiber concrete comprises the following steps:

[0048] S1. The initial setting and final setting time of different cements were tested. The initial setting time was 16 minutes, the final setting time was 22 minutes, and the high-belite sulphoaluminate cement with fast hardening speed and small self-shrinkage was used as the matrix raw material;

[0049] S2, pour 1.536kg of the matrix material selected in S1, 0.307kg of fly ash, and 0.829L of water into a mortar mixer and stir thoroughly. Mix evenly, add 1.0% of round straight 304 stainless steel fiber by volume and mix for 3 minutes, wherein the steel fiber has a diameter of 0.5mm and a length of 30mm. Pour the mixed mixture into a triple mold with a size of 40mm in height, 40mm in width, and 160mm in length, pre-embed copper nail probes at both ends, and assist with appropriate vibration to enhance density. The dispersed phase steel fiber is oriented and distributed so that the fiber direction is parallel to the long side direction of the specimen, and steel fiber concrete is obtained;

[0050] S3. The steel fiber concrete poured in S2 was heat-cured at 100°C for 40 minutes and naturally cooled to room temperature to obtain prestressed steel fiber concrete. The test was repeated three times to prepare 3 portions of prestressed steel fiber concrete.

[0051] Example 5

[0052] A preparation method of prestressed steel fiber concrete, comprising the following steps:

[0053] S1. Test the initial setting and final setting times of different cements. The initial setting time is 16 min and the final setting time is 22 min. Use high belite sulphoaluminate cement with a fast hardening speed and small autogenous shrinkage as the matrix raw material;

[0054] S2. Pour 1.536 kg of the matrix raw material selected in S1, 0.307 kg of fly ash, and 0.829 L of water into a mortar mixer and stir well to mix evenly. Add round straight 304 stainless steel steel fibers with a volume fraction of 0.5% and mix for 3 min. Among them, the diameter of the steel fibers is 0.5 mm and the length is 30 mm. Pour the mixed mixture into a triple mold with a height of 40 mm, a width of 40 mm, and a length of 160 mm. Embed copper nail probes at both ends and assist with appropriate vibration to enhance densification. The dispersed phase steel fibers are distributed directionally, making the fiber direction parallel to the long side direction of the specimen to obtain steel fiber concrete;

[0055] S3. For the steel fiber concrete completed in S2 pouring, conduct heat curing at 100 °C for 40 min and naturally cool to room temperature to obtain prestressed steel fiber concrete. Conduct three repeated tests to prepare 3 portions of prestressed steel fiber concrete.

[0056] Example 6

[0057] A preparation method of prestressed steel fiber concrete, comprising the following steps:

[0058] S1. Test the initial setting and final setting times of different cements. The initial setting time is 16 min and the final setting time is 22 min. Use high belite sulphoaluminate cement with a fast hardening speed and small autogenous shrinkage as the matrix raw material;

[0059] S2. Pour 1.536 kg of the matrix raw material selected in S1, 0.307 kg of fly ash, and 0.829 L of water into a mortar mixer and stir well to mix evenly. Add round straight 304 stainless steel steel fibers with a volume fraction of 0% and mix for 3 min. Among them, the diameter of the steel fibers is 0.5 mm and the length is 30 mm. Pour the mixed mixture into a triple mold with a height of 40 mm, a width of 40 mm, and a length of 160 mm. Embed copper nail probes at both ends and assist with appropriate vibration to enhance densification. The dispersed phase steel fibers are distributed directionally, making the fiber direction parallel to the long side direction of the specimen to obtain steel fiber concrete;

[0060] S3. The steel fiber concrete poured in S2 was heat-cured at 100°C for 40 minutes and naturally cooled to room temperature to obtain prestressed steel fiber concrete. The test was repeated three times to prepare 3 portions of prestressed steel fiber concrete.

[0061] The effects of the prestressed steel fiber concrete provided in the above-mentioned embodiments 1-6 were verified through the following tests.

[0062] In order to capture the degree of non-coordinated deformation between the steel fiber and the matrix, the present invention uses a shrinkage test to confirm the prestress effect in the matrix. The steel fiber concrete after heat curing in Examples 1-6 is placed under a comparator and naturally cooled to room temperature. The comparator continuously monitors the shrinkage of the steel fiber concrete specimen during the entire cooling process. The test results are taken as the average of the three specimens. The test results are as follows: Figures 3 - 4 shown.

[0063] The non-coordinated deformation caused by the difference in thermal expansion coefficients and mutual constraints between the steel fibers and the matrix causes additional shrinkage of the cement matrix. Figure 3 and Figure 4 The results of the matrix shrinkage test during the cooling process after thermal curing show that during the cooling time, the shrinkage of the cement matrix with 304 stainless steel fiber added is higher than that of the matrix without steel fiber. And with the increase of the volume fraction of steel fiber, the shrinkage of the matrix gradually increases, that is, more steel fibers play a role in pulling the matrix to shrink, making the matrix in a pre-stressed state. When external loads act, the pre-stress stress on the matrix can be offset first, so that the steel fiber can play a reinforcing and crack-resisting role in the uncracked stage of the matrix, which is of great significance to improving the tensile, crack resistance and toughness properties of cement-based materials.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A preparation method of prestressed steel fiber concrete, characterized in that It includes the following steps: S1. Test the initial setting time and final setting time of different cements, and select the matrix raw materials; S2. Add mineral admixtures to the matrix raw materials selected in S1, mix them evenly with water, add steel fibers and mix, and then pour to obtain steel fiber concrete; S3. Perform heat curing on the steel fiber concrete completed in S2, and naturally cool it to room temperature to obtain prestressed steel fiber concrete.

2. The preparation method according to claim 1, characterized in that, In S1, select the cement with an initial setting time of 15 - 40 min, a final setting time of 20 min - 60 min, and a fast hardening speed and small autogenous shrinkage as the matrix raw material.

3. The preparation method according to claim 1, characterized in that, In S2, the mineral admixture is one or both of fly ash and silica fume.

4. The preparation method according to claim 1, characterized in that, In S3, the steel fibers are directionally distributed in the steel fiber concrete.

5. The preparation method according to claim 1, characterized in that, In S3, the heat curing temperature is 100 °C.

6. According to the preparation method described in claim 1, it is characterized in that In S3, the heat curing time is determined according to the initial setting time and final setting time of different cements, and the heat curing time is not less than the final setting time of the cement.

7. The prestressed steel fiber concrete prepared by the preparation method according to any one of claims 1 - 6.

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