A straight-bonded prestressed tendon, a preparation method thereof and a straight-bonded prestressed construction method

Abstract

The present application relates to the technical field of building construction, in particular to a direct-bonding prestressed tendon, a preparation method thereof and a direct-bonding prestressed construction method. The direct-bonding prestressed tendon comprises prestressed steel, a hot-melt material layer and a heating assembly. The hot-melt material layer is wrapped on the surface of the prestressed steel, and the heating assembly is connected with the prestressed steel and used for heating the prestressed steel to melt the hot-melt material layer. The present application controls the melting and solidification of the hot-melt material by heating, actively regulates the bonding state of the prestressed tendon, solves the contradiction between the tension application period and the solidification speed of the traditional slow-bonding tendon, breaks through the storage time limit, supports recycling, is convenient to construct, has a durable structure and is suitable for various engineering scenes with high requirements for prestressed application timing and structural durability.

Description

Technical Field

[0001] This invention relates to the field of building construction technology, specifically to a direct-bonded prestressed tendon, its preparation method, and a direct-bonded prestressed construction method. Background Technology

[0002] Prestressed technology is widely used in modern civil engineering structures, especially in large-span, heavy-load, and crack-control-critical concrete structures, where it has irreplaceable advantages. In recent years, bonded prestressing technology, as a new type of prestressing that combines the construction convenience of unbonded prestressing with the durability of bonded prestressed structures, has gradually attracted attention and application in the engineering field.

[0003] Slow-setting prestressed tendons typically consist of prestressed steel strands, an outer sheath with regular transverse and longitudinal ribs, and a slow-setting adhesive filling the space between the prestressed steel strands and the sheath. During tensioning, the slow-setting adhesive exhibits specific thixotropic properties, allowing the prestressed tendon to slide freely within the adhesive layer. Subsequently, the slow-setting adhesive cures within a set time, bonding the prestressed steel strands and the sheath together to achieve a mechanical effect similar to bonded prestressing.

[0004] Currently, the retarding adhesives used in delayed-setting prestressing tendons mainly include thermosetting retarding adhesives and moisture-curing retarding adhesives. Thermosetting retarding adhesives are based on epoxy resin, combined with room-temperature or medium-temperature curing agents and various functional additives. They gradually cure at a predetermined time point under a specific ambient temperature, causing the prestressed steel strands to bond and interlock with the surrounding concrete, achieving effective adhesion. Moisture-curing retarding adhesives use a moisture-type latent curing agent as a key component. This curing agent undergoes a hydrolysis reaction after absorbing moisture, and its hydrolysis products further react with the epoxy resin to cure. Before the hydrolysis reaction occurs, there is no reaction between the curing agent and the epoxy resin; therefore, temperature has little impact on the curing process in the initial stage, exhibiting a certain degree of environmental adaptability.

[0005] However, existing retarded adhesives still have significant shortcomings:

[0006] First, there is an inherent contradiction between the tensioning service life and the later curing rate of retarded adhesives. Retarded adhesives need to maintain sufficient fluidity during the tensioning stage to ensure the prestressing tendons can slide freely and achieve effective tensioning. After tensioning, the retarded adhesive needs to cure rapidly to form an effective bond with the concrete as quickly as possible, improving the integrity and durability of the structure. However, the curing process of thermosetting and moisture-curing retarded adhesives is essentially an irreversible chemical reaction that continues once started. To ensure sufficient tensioning time, the initial retardation period of the adhesive must be extended, but this often leads to a corresponding slowdown in its later curing rate, affecting the early strength development of the structure and the construction progress. Conversely, if the curing rate is accelerated, premature hardening may occur before construction or during tensioning, resulting in the prestressing tendons being unable to be tensioned or increased tensioning resistance, seriously affecting construction quality and safety. Studies have shown that when the hardness of the retarded adhesive reaches 50D, the retarded prestressed steel strands can only fully work with the concrete, that is, achieve effective bond anchorage strength, which is usually achieved at about 70% of the curing period. Therefore, whether it is thermosetting or moisture-curing type prestressed steel strand, its prestressing tension is strictly limited by the tensioning service period, and the time for the structure to bear the operational load is also constrained by the curing period.

[0007] Secondly, the curing process of retarded adhesives is significantly affected by ambient temperature, making long-term stable storage difficult. Furthermore, existing retarded adhesives are primarily composed of epoxy resin, which cannot be recycled after curing, resulting in resource waste and environmental burden.

[0008] Therefore, there is a need for a prestressed tendon that can be controlled to cure, can be stored for a long time, and is recyclable. Summary of the Invention

[0009] (a) Technical problems to be solved

[0010] To address the problems of inconsistencies between the tensioning application period and curing rate, short storage period, and non-recyclability of existing retarded adhesives, this invention provides a direct-bonded prestressed tendon, its preparation method, and a direct-bonded prestressed construction method.

[0011] (II) Technical Solution

[0012] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0013] A type of directly bonded prestressed tendon includes prestressed steel, a hot-melt material layer, and a heating assembly;

[0014] The hot-melt material layer is wrapped around the surface of the prestressed steel, and the heating component is connected to the prestressed steel to heat the prestressed steel so that the hot-melt material layer melts.

[0015] As described above, in the case of directly bonded prestressed tendons, preferably, the prestressed steel is prestressed steel strand, prestressed steel wire, prestressed steel bar, or precision rolled threaded steel.

[0016] In the direct-bonded prestressed tendon as described above, preferably, the hot-melt material layer is polyurethane hot-melt adhesive, copolyester thermoplastic adhesive, or polyethylene resin.

[0017] In the direct-bonded prestressed tendon as described above, preferably, the hot-melt material layer includes a plurality of annular protrusions and annular recesses, wherein the annular protrusions and annular recesses are alternately connected.

[0018] The present invention also provides a method for preparing the above-mentioned directly bonded prestressed tendon, comprising the following steps:

[0019] S1: Heating prestressed steel to obtain hot prestressed steel;

[0020] S2: Coating the surface of hot-stressed steel with heated hot-melt material to obtain prestressed steel with a surface wrapped with hot-melt material layer;

[0021] S3: Annular protrusions and annular concave parts are pressed on the outer surface of the hot melt material layer, and after cooling, straight bonded prestressed tendons are obtained.

[0022] In the preparation method described above, preferably, in step S1, the prestressed steel is subjected to high-frequency induction heating to bring its temperature to 190-220℃.

[0023] In the preparation method described above, preferably, in step S2, a hot melt material heated to 190-220°C is coated on the surface of the hot prestressed steel.

[0024] The present invention also provides a direct-bonded prestressing construction method using the above-described direct-bonded prestressing tendons or the direct-bonded prestressing tendons prepared by the above-described preparation method, comprising the following steps:

[0025] A1: Arrange and fix the straight bonded prestressing tendons as required;

[0026] A2: Pour concrete around the prestressed tendons;

[0027] A3: Curing concrete until it reaches the specified strength;

[0028] A4: The prestressed steel in the straight bonded prestressed tendon is heated by a heating component, so that the hot melt material layer melts and bonds with the concrete;

[0029] A5: When the hot-melt material layer is in a molten state, the straight bonded prestressing tendons are tensioned and then fixed by anchors;

[0030] A6: Cut off the excess portion and seal the anchor.

[0031] In the direct bond prestressed construction method described above, preferably, in step A4, the prestressed steel is heated to 170-190°C using a heating assembly.

[0032] (III) Beneficial Effects

[0033] First, the direct-bonded prestressing tendons of this invention achieve active control of the bonding state through a hot-melt material layer and a heating component. During tensioning, the prestressed steel is heated by the heating component, melting the hot-melt material layer, allowing the prestressed steel to slide freely in the concrete. After tensioning is completed, heating is stopped, and the hot-melt material cools and solidifies naturally, achieving effective bonding with the concrete. Therefore, this invention overcomes the contradiction between the tensioning application period and the later curing rate caused by the irreversible chemical curing reaction of traditional retarded adhesives.

[0034] Secondly, the bonding process of this invention is controlled by external heating and does not rely on the chemical reaction process of the hot melt material itself. Therefore, it is not affected by ambient temperature and can achieve long-term stable storage, avoiding the problem of being unable to stretch due to excessive storage time. At the same time, the curing process of the hot melt material is reversible and has the possibility of recycling and reuse, solving the resource waste and environmental burden caused by the non-recyclability of epoxy-based retarded adhesives after curing.

[0035] Third, the direct-bonded prestressing tendon of the present invention eliminates the complex sheath structure of the traditional slow-bonded prestressing tendon, which is simple in construction and effectively avoids adhesive leakage caused by damage to the sheath end or the body, thereby preventing the problems of reduced bonding performance and pollution to the appearance of concrete. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of the single transverse rib straight bonded prestressing tendon of the present invention;

[0037] Figure 2 This is a schematic diagram of the structure of the ribless straight bonded prestressing tendon of the present invention;

[0038] Figure 3 This is a schematic diagram of the structure of the two longitudinal ribs straight bonded prestressing tendon of the present invention;

[0039] Figure 4 This is a schematic diagram of the structure of the three-longitudinal-rib straight bonded prestressing tendon of the present invention;

[0040] Figure 5 This is a schematic diagram of the structure of the four-longitudinal-rib straight bonded prestressing tendon of the present invention;

[0041] Figure 6 This is a schematic diagram illustrating the direct-bonded prestressing construction principle of the direct-bonded prestressing tendon of the present invention.

[0042] [Explanation of Labels in the Attached Image]

[0043] 1: Prestressed steel; 2: Hot melt material layer. Detailed Implementation

[0044] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0045] This invention provides a directly bonded prestressed tendon, comprising a prestressed steel 1, a hot-melt material layer 2, and a heating assembly. The hot-melt material layer 2 is wrapped around the surface of the prestressed steel 1, and the heating assembly is connected to the prestressed steel 1 to heat the prestressed steel 1 so that the hot-melt material layer 2 melts.

[0046] The direct-bonded prestressing tendons of this invention achieve active control of the bonding state through a hot-melt material layer and a heating component. During tensioning, the prestressed steel is heated by the heating component, melting the hot-melt material layer, allowing the prestressed steel to slide freely in the concrete. After tensioning is completed, heating is stopped, and the hot-melt material cools and solidifies naturally, achieving effective bonding with the concrete. Therefore, this invention overcomes the contradiction between the tensioning service life and the later curing rate caused by the irreversible chemical curing reaction of traditional retarded adhesives.

[0047] The bonding process of this invention is controlled by external heating and does not rely on the chemical reaction process of the hot melt material itself. Therefore, it is not affected by ambient temperature and can achieve long-term stable storage, avoiding the problem of being unable to stretch due to excessive storage time. At the same time, the curing process of the hot melt material is reversible and has the possibility of recycling and reuse, solving the resource waste and environmental burden caused by the non-recyclability of epoxy-based retarded adhesives after curing.

[0048] The direct-bonded prestressing tendon of the present invention also eliminates the complex sheath structure of the traditional slow-bonded prestressing tendon, with a simple structure, effectively avoiding adhesive leakage caused by damage to the sheath end or the main body, thereby preventing the problems of reduced bonding performance and pollution to the appearance of concrete.

[0049] Preferably, the prestressed steel can be prestressed steel strand, prestressed steel wire, prestressed steel bar, or precision-rolled threaded steel. The hot-melt material layer (i.e., thermoplastic material) can be a hot-melt adhesive, thermoplastic resin, etc., such as polyurethane hot-melt adhesive, copolyester thermoplastic adhesive (copolyester thermoplastic adhesive material), or polyethylene resin, etc.

[0050] The heating component can be an electric heater, etc. The electric heater heats the prestressed steel to a certain temperature, causing the encasing thermoplastic material to melt, thus allowing the prestressed steel to slide freely along the axial direction in the concrete. After the prestressing is completed, the electric heating is stopped, and the thermoplastic material cools and solidifies naturally, thereby bonding the prestressing tendons and concrete together to share the load.

[0051] like Figure 1-5 As shown, the outer surface of the thermoplastic material layer can be ribbed or unribbed; specifically, it can be... Figure 1 The single transverse rib shown is Figure 2 The ribless design shown Figure 3 The two longitudinal ribs shown Figure 4 The three longitudinal ribs shown Figure 5 The four longitudinal ribs shown are examples of this. The function of the ribs with uneven surfaces is to form a mechanical interlock with the concrete. If there are no ribs on the outer surface of the hot-melt material layer, the prestressed steel and concrete are bonded together by the chemical bonding force of the hot-melt material.

[0052] As a preferred embodiment, the hot-melt material layer includes multiple annular protrusions and annular recesses, with the annular protrusions and annular recesses being interlocked to form an interlocking structure that simultaneously has transverse rib peaks and transverse rib valleys.

[0053] This invention also provides a method for preparing directly bonded prestressed tendons, the specific steps of which are as follows:

[0054] Prestressed steel, such as prestressed steel strand coils, can be placed on a pay-off frame. The prestressed steel is then fed to a high-frequency induction heating device via a traction machine. The high-frequency induction heating device heats the prestressed steel to 190-220℃. After heating, the prestressed steel passes through a coating machine, which applies a layer of hot melt material, such as polyurethane hot melt adhesive, heated to 190-220℃, to the outside of the prestressed steel. A embossing machine then presses out raised and recessed transverse ribs on the outer surface of the polyurethane hot melt adhesive. After cooling and shaping in a cooling water tank, the traction machine transports the cooled, directly bonded prestressed tendons to a take-up machine for coiling.

[0055] Furthermore, the present invention also provides a method for direct-bonded prestressing construction using the above-described direct-bonded prestressing tendons or the direct-bonded prestressing tendons prepared by the above-described preparation method, comprising the following steps:

[0056] A1: Arrange and fix the straight bonded prestressing tendons as required.

[0057] A2: Pour concrete around the prestressed tendons.

[0058] A3: Curing concrete until it reaches the specified strength.

[0059] A4: The prestressed steel in the directly bonded prestressed tendons is heated by a heating component to 170-190℃, so that the hot melt material layer melts and bonds with the concrete.

[0060] A5: When the hot-melt material layer is in a molten state, the straight bonded prestressing tendons are tensioned and then fixed by anchors.

[0061] A6: Cut off the excess portion and seal the anchor.

[0062] Specifically, the construction methods for direct-bonded prestressed tendons can be divided into single-end tensioning and double-end tensioning methods, which are explained in detail below:

[0063] 1. Taking single-end tensioned straight-bonded prestressed tendons as an example, the construction process is explained as follows: Several straight-bonded prestressed tendons of a certain length and diameter of 15.2mm are cut using a cutting machine. A certain length of hot-melt material layer is melted at one end of each tendon using a hot air gun and then cleaned. Next, the spiral reinforcement, bearing plate, and extrusion anchors are installed, and the extrusion anchors are extruded using an extrusion machine. Then, the straight-bonded prestressed steel strands are laid out according to the drawings and fixed to the positioning reinforcement with tie wire. The fixed-end spiral reinforcement and bearing plate are fixed. The tensioning-end spiral reinforcement, bearing plate, and cavity mold are installed and fixed. Then, according to… Figure 6 As shown, two adjacent straight-bonded prestressed tendons are welded together using reinforcing bars with a diameter of not less than 16mm, pressing the anchor rings at their fixed ends. Concrete is then poured, and after it reaches the required strength, the formwork is cleaned. A hot air gun is used to melt and clean the hot-melt material layer on the prestressed steel strands outside the tensioning end bearing plate. A wedge anchor and jack are installed at the tensioning end of one of the straight-bonded prestressed tendons. The exposed prestressed tendon at the tensioning end and the tensioning end of the adjacent straight-bonded prestressed tendon with its cleaned adhesive layer are connected to either of the two wires at the output end of the electric heater, thus forming a current loop through these two straight-bonded prestressed tendons and the reinforcing bars welded to their fixed ends. The electric heater is then turned on, heating the straight-bonded prestressed tendons to 170-190℃ and maintaining this temperature. The jacks are used to tension the tendons to the tension control stress. After confirming that the tension control stress and the elongation of the prestressed steel strands meet the design requirements, the jacks are released, the anchors are secured, and finally, the tendons are cut and the anchors are sealed.

[0064] It should be noted that the electric heating measures for the fixed end of the single-end tensioned straight bonded prestressing tendon must be completed before pouring concrete.

[0065] 2. Taking double-end tensioned straight-bonded prestressed tendons as an example, the construction process is explained:

[0066] Cut several 15.2mm diameter straight bonded prestressing tendons of a certain length using a cutting machine. Arrange the tendons according to the drawings and fix them to the positioning tendons with tie wire. Install and fix the tensioning end spiral tendons, bearing plates, and cavity molds at both ends. Then pour concrete. After the concrete reaches its strength, clean the cavity molds. Use a hot air gun to melt and clean the hot melt material layer on the prestressing tendons outside the bearing plates at both ends of the tensioning ends of two adjacent straight bonded prestressing steel strands. Install a clamp anchor and jack at the tensioning end of one of the straight bonded prestressing tendons. Connect the exposed prestressing steel strands at the tensioning end and the tensioning ends of adjacent straight bonded prestressing steel strands with the cleaned adhesive layer to either of the two wires at the output end of the electric heating machine. Connect the two tensioning ends on the other side with a wire with clamps at both ends, thus forming a current loop through the two straight bonded prestressing steel strands and the connecting wire at the other end. Turn on the electric heating machine to heat the directly bonded prestressed tendons to 170-190℃ and keep them at that temperature. Tension them to the tension control stress using jacks. After confirming that the tension control stress and the elongation of the prestressed steel strands meet the design requirements, release the tension using jacks, anchor the tendons, and finally cut and seal the tendons.

[0067] The direct-bonded prestressing tendon of this invention uses a hot-melt material layer. Its bonding process is based on a physical phase change of heating and melting followed by cooling and solidification, without relying on a chemical curing reaction. This purely physical process is reversible and controllable, avoiding the tensioning application period limitations caused by the irreversibility of chemical curing. The curing is not affected by environmental temperature and humidity, allowing for precise control of the bonding timing. Furthermore, the material is reusable, fundamentally solving the problems of short storage period and non-recyclability caused by chemical reactions in traditional retarded adhesives.

[0068] The hot-melt material used in this invention forms a dense bonding layer after cooling, exhibiting excellent bond strength with concrete and prestressed steel. Tests have verified that it meets the current specifications for the mechanical performance requirements of bonded prestressed structures. The selected material possesses excellent resistance to aging, temperature changes, and environmental erosion. Its performance remains stable under long-term working conditions, and its bonding durability is reliable, effectively ensuring the safety and durability of the structure throughout its entire lifespan.

[0069] Furthermore, the hot-melt material of this invention bonds to concrete primarily through physical embedding and mechanical interlocking, without undergoing a chemical reaction and is insoluble in water or concrete slurry. After the structure reaches the end of its service life, the hot-melt material can be melted by heating, achieving non-destructive separation of the prestressing tendons from the concrete, facilitating recycling and reuse. The material itself possesses excellent thermal stability, can repeatedly undergo heating, melting, and cooling solidification processes without performance degradation, and remains stable under long-term variations in temperature and humidity, unaffected by external environmental factors, significantly improving resource utilization and reducing environmental burden.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A type of directly bonded prestressed tendon, characterized in that, It includes prestressed steel, a hot-melt material layer, and a heating assembly; the prestressed steel is prestressed steel strand, prestressed steel wire, prestressed steel bar, or precision-rolled threaded steel. The hot-melt material layer is wrapped around the surface of the prestressed steel. The heating component is connected to the prestressed steel and is used to heat the prestressed steel to melt the hot-melt material layer. The heating component is an electric heater, which heats the prestressed steel until the wrapped hot-melt material melts, thereby allowing the prestressed steel to slide freely in the concrete along the axial direction. After the prestressing is completed, the electric heating is stopped, and the hot-melt material cools and solidifies naturally, thereby bonding the prestressing tendons and concrete together to share the load. The hot melt material layer is polyurethane hot melt adhesive, copolyester thermoplastic adhesive, or polyethylene resin; The bonding process of the hot melt material is based on a physical phase transition of heating and melting followed by cooling and solidification, and this physical phase transition is reversible; the solidification process of the hot melt material is also reversible. The preparation method of directly bonded prestressed tendons includes the following steps: S1: Heat the prestressed steel to 190-220℃ to obtain hot prestressed steel; S2: Coating the surface of hot-stressed steel with a hot-melt material heated to 190-220℃ to obtain prestressed steel with a surface wrapped with a hot-melt material layer; S3: Annular protrusions and annular recesses are pressed onto the outer surface of the hot melt material layer, and after cooling, straight bonded prestressed tendons are obtained. The direct-bonded prestressing construction method using the aforementioned direct-bonded prestressing tendons includes the following steps: A1: Arrange and fix the straight bonded prestressing tendons as required; A2: Pour concrete around the prestressed tendons; A3: Curing concrete until it reaches the specified strength; A4: The prestressed steel in the straight bonded prestressed tendon is heated by a heating component, so that the hot melt material layer melts and bonds with the concrete; A5: When the hot-melt material layer is in a molten state, the straight bonded prestressing tendons are tensioned and then fixed by anchors; A6: Cut off the excess portion and seal the anchor. During tensioning, the prestressed steel is heated by a heating component, which melts the hot-melt material layer, allowing the prestressed steel to slide freely in the concrete. After tensioning is completed, heating is stopped, and the hot-melt material cools and solidifies naturally, achieving bonding with the concrete.

2. The directly bonded prestressed tendon according to claim 1, characterized in that, The hot-melt material layer includes multiple annular protrusions and annular recesses, with the annular protrusions and annular recesses being alternately connected.

3. A method for preparing a directly bonded prestressed tendon according to any one of claims 1-2, characterized in that, Includes the following steps: S1: Heating prestressed steel to obtain hot prestressed steel; S2: Coating the surface of hot-stressed steel with heated hot-melt material to obtain prestressed steel with a surface wrapped with hot-melt material layer; S3: Annular protrusions and annular concave parts are pressed on the outer surface of the hot melt material layer, and after cooling, straight bonded prestressed tendons are obtained.

4. The preparation method according to claim 3, characterized in that, In step S1, the prestressed steel is subjected to high-frequency induction heating to bring its temperature to 190-220℃.

5. The preparation method according to claim 3, characterized in that, In step S2, a hot melt material heated to 190-220°C is coated on the surface of the hot prestressed steel.

6. A method for direct-bonded prestressing construction using direct-bonded prestressing tendons prepared according to any one of claims 1-2 or the preparation method according to any one of claims 3-5, characterized in that, Includes the following steps: A1: Arrange and fix the straight bonded prestressing tendons as required; A2: Pour concrete around the prestressed tendons; A3: Curing concrete until it reaches the specified strength; A4: The prestressed steel in the straight bonded prestressed tendon is heated by a heating component, so that the hot melt material layer melts and bonds with the concrete; A5: When the hot-melt material layer is in a molten state, the straight bonded prestressing tendons are tensioned and then fixed by anchors; A6: Cut off the excess portion and seal the anchor.

7. The direct-bonded prestressed construction method according to claim 6, characterized in that, In step A4, the prestressed steel is heated to 170-190°C using a heating assembly.

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