Fast setting special adhesive for non-shrinkage and non-slippage, non-shrinkage and non-slippage prestressed steel strand and its preparation and use method

Abstract

The application discloses a quick-curing type slow-bonding special adhesive, a slow-bonding prestressed steel strand and a preparation and use method thereof. The quick-curing type slow-bonding special adhesive comprises, by weight, 40-60 parts of a matrix resin, 5-10 parts of a latent curing agent, 5-15 parts of a microcapsule thixotropic agent, 10-20 parts of a lubricating filler, 1-2 parts of a coupling agent and 0.5-2 parts of an acoustic-sensitive nano cavitation agent. The microcapsule thixotropic agent is internally wrapped with a core material serving as a polymerization accelerator. The acoustic-sensitive nano cavitation agent can produce a microcosmic cavitation effect under the action of ultrasonic waves, so that the microcapsule thixotropic agent is broken and the core material is released. The released core material contacts with the matrix resin and the latent curing agent, and a hotspot generated by ultrasonic cavitation is heated to activate the latent curing agent, so as to jointly trigger the matrix resin to generate a curing reaction. The quick-curing type slow-bonding prestressed steel strand prepared from the quick-curing type slow-bonding special adhesive achieves the goals of controllable reaction, rapid curing after tensioning and uniform curing.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to fast-curing slow-bonding special adhesives, slow-bonding prestressed steel strands, and their preparation and application methods. Background Technology

[0002] Slow-bonded prestressing technology combines the advantages of convenient construction of unbonded prestressing and the good mechanical properties of bonded prestressing. Its core involves coating the surface of the steel strands with a special adhesive. This adhesive maintains a low viscosity (slow-setting state) during the tensioning stage, allowing the steel strands to slide freely within the sheath. After tensioning and anchoring, the adhesive needs to cure within a certain time, allowing the steel strands to bond with the sheath, thus integrating the slow-bonded prestressed steel strands with the surrounding concrete.

[0003] Currently, there are two main methods for curing loosely bonded prestressed steel strands: natural curing and heat curing. These two methods have significant drawbacks: (1) Natural curing: The curing cycle is relatively long, usually 360-240 days, which seriously affects the time for the structure to be put into use later. (2) Heat curing: The method of triggering by electric heating has high energy consumption, slow response, and difficulty in ensuring uniform curing. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a fast-curing slow-bonding special adhesive, slow-bonding prestressed steel strand and its preparation and use methods, which solves the technical problems of long curing cycle, poor curing uniformity and the need to improve the controllability of curing process of existing slow-bonding prestressed steel strand.

[0006] (II) Technical Solution

[0007] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0008] In a first aspect, embodiments of the present invention provide a fast-curing, slow-bonding adhesive, comprising, by weight: 40-60 parts of a base resin, 5-10 parts of a latent curing agent, 5-15 parts of a microcapsule thixotropic agent, 10-20 parts of a lubricating filler, 1-2 parts of a coupling agent, and 0.5-2 parts of a sound-sensitive nano-cavitation agent.

[0009] The microcapsule thixotropic agent contains a core material that serves as a polymerization accelerator.

[0010] The acoustically sensitive nano-cavitation agent can generate a microscopic cavitation effect under the action of ultrasound, causing the microcapsule thixotropic agent to rupture and release the core material. The released core material comes into contact with the matrix resin and the latent curing agent. At the same time, the hot spots generated by the ultrasonic cavitation heat up to activate the latent curing agent, which together triggers the curing reaction of the matrix resin.

[0011] In a preferred embodiment of the present invention, the fast-curing slow-bonding adhesive has a base resin that is a modified epoxy resin or a polyurethane prepolymer.

[0012] Latent curing agents are dicyandiamide micro powder or imidazole derivatives;

[0013] The core material of the microcapsule thixotropic agent is an amine accelerator, and the wall material of the microcapsule thixotropic agent is urea-formaldehyde resin or melamine-formaldehyde.

[0014] The lubricating filler is at least one of graphite powder, molybdenum disulfide, and wax powder;

[0015] The coupling agent is a silane coupling agent;

[0016] The acoustically sensitive nanocavitation agent is a hydrophobically modified porous silica nanosphere.

[0017] Among them, modified epoxy resin or polyurethane prepolymer has high bonding strength and toughness, which can adapt to the high stress state of prestressed steel strands. The combination of dicyandiamide / imidazolium (latent agent) and amine accelerator for low-temperature rapid curing exhibits high reactivity, high crosslinking density after curing, and excellent mechanical properties. Urea-formaldehyde resin or melamine-formaldehyde wall material has suitable brittleness and strength threshold, capable of withstanding the shear force during production coating without cracking, and also shattered by the microjets generated by the collapse of ultrasonic cavitation bubbles. Graphite / molybdenum disulfide / wax powder provides an extremely low coefficient of friction, ensuring smooth tensioning of the steel strands; silane coupling agents build chemical bridges between the inorganic steel strands and organic resins, preventing debonding. The surface of hydrophobically modified porous silica or hollow glass microspheres contains numerous micro-nano cavitation cavities, which can significantly amplify ultrasonic energy and improve triggering efficiency.

[0018] In a preferred embodiment of the present invention, the wall thickness of the microcapsule thixotropic agent in the fast-curing, slow-adhesion adhesive is 1-5 μm, and the average particle size of the microcapsule thixotropic agent is 10-50 μm.

[0019] The particle size of the acoustically sensitive nanocavitation agent is 50-300 nm.

[0020] The optimal wall thickness for microcapsule thixotropic agents is 1-5 μm. Too thin a wall can easily break during production, leading to failure, while too thick a wall requires excessively high ultrasonic energy to break it, which generates a large amount of heat, negatively impacting the curing effect. A microcapsule particle size of 10-50 μm ensures both trigger point density and uniform dispersion.

[0021] Secondly, embodiments of the present invention provide a fast-curing, slow-bonding prestressed steel strand, comprising a steel strand, a sheath, and at least one acoustic waveguide wire, as well as the fast-curing, slow-bonding special adhesive.

[0022] The sheath is fitted over the outside of the steel strand, and a fast-curing, slow-bonding special adhesive is filled between the steel strand and the sheath.

[0023] The acoustic waveguide wire is inserted into the sheath and completely embedded in a fast-curing, slow-bonding adhesive; both ends of the acoustic waveguide wire protrude from the sheath.

[0024] The end of the acoustic waveguide wire extending from the sheath is used to apply ultrasonic waves;

[0025] When stress is applied to the steel strand, the ultrasonic waves transmitted along the acoustic waveguide wire can break the microcapsule structure of the microcapsule thixotropic agent with the assistance of acoustically sensitive nano-cavitation agent, thereby triggering the curing of the fast-curing slow-bonding special adhesive.

[0026] Among them, the fast-curing, slow-bonding prestressed steel strand incorporates an acoustic waveguide wire directly wrapped inside the adhesive and running the entire length, solving the problems of large attenuation and insufficient energy at the far end of externally coupled ultrasonic waves. Ultrasonic waves are transmitted with low loss along the metal wire, ensuring sufficient triggering energy throughout the entire length of the tens of meters of steel strand. Because the waveguide wire is completely wrapped in the adhesive, cavitation occurs within the adhesive, achieving uniform triggering and avoiding the uneven curing phenomenon caused by traditional heat curing. Furthermore, the acoustic waveguide wire is directly embedded in the adhesive during the sheathing process, simplifying the operation. Both ends of the acoustic waveguide wire extend out of the sheath; on-site operation only requires clamping the ends, eliminating the need for complex pre-embedded heating pipes and significantly simplifying the preparation and construction procedures of prestressed steel strands.

[0027] In a preferred embodiment of the present invention, the fast-setting, slow-bonding prestressed steel strand has a sheath with multiple transverse ribs and at least two longitudinal ribs evenly distributed around its outer periphery. The transverse ribs are arranged circumferentially around the sheath, with a certain spacing between them. The longitudinal ribs extend continuously along the sheath's axial direction, and the inner side of each longitudinal rib has a groove extending continuously along the sheath's axial direction with its opening facing the sheath's central axis. The longitudinal ribs are evenly distributed circumferentially around the sheath. Each longitudinal rib contains an acoustic waveguide wire, and the number of longitudinal ribs can be greater than the number of acoustic waveguide wires. The number of acoustic waveguide wires can be adjusted as needed.

[0028] The acoustic waveguide wire is located in the groove of the longitudinal rib, and the groove is filled with a fast-curing, slow-bonding special adhesive.

[0029] The longitudinal ribs utilize grooves to accommodate the acoustic waveguide wires, preventing displacement and twisting during extrusion, covering, or tensioning, thus ensuring the integrity of the acoustic wave transmission channel. The grid-like structure formed by the transverse and longitudinal ribs significantly increases the mechanical interlocking force between the sheath and the surrounding concrete, preventing the steel strands from slipping in the concrete and improving structural safety.

[0030] In a preferred embodiment of the present invention, the fast-setting, slow-bonding prestressed steel strand has a waveguide wire with a diameter of 1-1.5 mm made of stainless steel or copper-clad steel wire.

[0031] The acoustic impedance of the acoustic waveguide is >40×10⁻⁶. 6 kg / (m 2 ·s).

[0032] The acoustic waveguide wire is made of stainless steel or copper-clad steel wire, and its acoustic impedance is >40×10⁻⁶. 6 kg / (m 2 The high sound velocity and low attenuation of the metal ensure that the ultrasonic energy can be efficiently transmitted to the far end of the steel strand, while the 1-2mm diameter takes into account both flexibility and axial strength.

[0033] Thirdly, embodiments of the present invention provide a method for preparing the fast-curing, slow-bonding prestressed steel strand, comprising the following steps:

[0034] S1. Mix the matrix resin, latent curing agent, lubricating filler, and coupling agent evenly in an environment of <40℃ to obtain the first mixture;

[0035] S2. Reduce the temperature of the first mixture to below 25°C, add microcapsule thixotropic agent and sound-sensitive nano cavitation agent, and stir and mix well while keeping the temperature below 25°C and the rotation speed <200 rpm to obtain a fast-curing slow-bonding special adhesive.

[0036] S3. Using an extrusion coating process, a fast-curing, slow-bonding special adhesive is evenly coated onto the surface of the steel strand, with the coating thickness controlled at 1.5-2.5mm. The acoustic waveguide wire is then attached to the surface of the fast-curing, slow-bonding special adhesive.

[0037] S4. The sheath is extruded and wrapped around the outer periphery of the steel strand coated with a fast-curing, slow-bonding special adhesive to prepare the fast-curing, slow-bonding prestressed steel strand.

[0038] The matrix resin is a liquid thermosetting resin (such as liquid modified epoxy resin or liquid polyurethane prepolymer) or a low-viscosity resin solution.

[0039] In the preparation method of fast-setting prestressed steel strand, the matrix is ​​strictly controlled at <40℃, and microcapsule thixotropic agents and acoustically sensitive nano-cavitation agents are added at <25℃ to avoid the risk of premature rupture of microcapsules or activation of latent agents due to frictional heat or ambient temperature during the production process, thus ensuring the product qualification rate.

[0040] Fourthly, embodiments of the present invention provide a method for using the aforementioned fast-setting, slow-bonding prestressed steel strand, comprising the following steps:

[0041] Step 1: Lay the fast-setting, slow-bonding prestressed steel strands according to the design requirements;

[0042] Step 2: Pour concrete. Once the concrete reaches the design strength, tension the steel strands.

[0043] Step 3: Connect at least one exposed end of the acoustic waveguide wire to the energy output end of the ultrasonic transducer, and start the ultrasonic transducer to apply ultrasonic waves to the acoustic waveguide wire to trigger the curing of the fast-curing slow-bonding adhesive.

[0044] In a preferred embodiment of the present invention, in step 3 of the method of use, the ultrasonic wave applied to the acoustic waveguide wire is a pulse-modulated ultrasonic wave with a duty cycle of 10%-20%, a peak power of 300-400W, and an output frequency of 20-28kHz.

[0045] The ultrasonic wave is pulse-modulated, with a low duty cycle of 10%-20% and a high peak power of 300-400W, creating a high-energy impact and intermittent heat dissipation mode. When the pulse is on, the high peak power generates strong cavitation to break up the microcapsules; when the pulse is off, the gap dissipates heat to prevent local overheating and carbonization of the adhesive or melting of the sheath caused by continuous waves. This minimizes average power while ensuring effective triggering, reducing energy consumption.

[0046] In a preferred embodiment of the present invention, in the method of use, step 3, the total duration of applying ultrasonic waves to the acoustic waveguide wire is 5-8 minutes.

[0047] During the application of ultrasound, a frequency conversion scanning mode is used to control the output frequency of the ultrasound to fluctuate periodically based on the set center frequency, and the frequency fluctuation range is kept within the instantaneous output frequency of 20-28kHz.

[0048] The variable frequency scanning mode dynamically changes the wavelength of the ultrasonic waves on the waveguide wire, causing the standing wave nodes (energy troughs) to continuously move along the length of the steel strand. This ensures that the entire length of the steel strand experiences energy peaks within a total duration of 5-8 minutes, promoting uniform curing.

[0049] Frequency window locking: The instantaneous frequency is strictly limited to 20-28kHz, avoiding the noise zone that the human ear is sensitive to, while also being in the golden frequency band where the metal waveguide has the highest transmission efficiency and the strongest cavitation effect, ensuring maximum triggering efficiency. Only a short processing time of 5-8 minutes is required to achieve complete solidification triggering, greatly improving project progress compared to the traditional solidification wait of several hours or even days.

[0050] (III) Beneficial Effects

[0051] The beneficial effects of this invention are as follows: The fast-curing, slow-bonding adhesive, the slow-bonding prestressed steel strand, and their preparation and application methods of this invention are as follows. The fast-curing, slow-bonding adhesive adopts a sound-chemical synergistic triggering mechanism: a specific combination of acoustic-sensitive nano-cavitation agent and microcapsule thixotropic agent is introduced to construct a unique sound-chemical response system. The nano-cavitation agent lowers the cavitation threshold, enabling a strong microscopic cavitation effect to be generated even under low-power ultrasound. This effect precisely breaks the microcapsules, releasing the core material (accelerator), and combined with the slight temperature rise of the cavitation hotspot, instantly activates the latent curing agent, triggering the resin to begin a cross-linking reaction (curing reaction). In addition, the heat generated by the reaction of the accelerator, latent agent, and resin accelerates curing, achieving complete curing within 1 hour. The Shore hardness of the fast-curing, slow-bonding adhesive and the friction coefficient of the fast-curing, slow-bonding prestressed steel strand both meet the standards.

[0052] Fast-curing, slow-bonding adhesives are used in prestressed steel strands. The components work synergistically: the matrix resin provides the mechanical framework, lubricating fillers ensure smooth tensioning, and coupling agents enhance interfacial bonding. Acoustic-sensitive nano-cavitation agents, with their large specific surface area, provide numerous cavitation nucleation sites and disperse uniformly within the resin matrix without settling, ensuring that ultrasonic energy is uniformly converted into mechanical destructive force in three-dimensional space. The acoustic-sensitive nano-cavitation agents and microencapsulated thixotropic agents assist in controlled triggering of ultrasonic intervention, accelerating the curing reaction rate and improving the uniformity of the curing reaction. Compared to existing technologies, fast-curing, slow-bonding prestressed steel strands achieve controllable reaction, rapid post-tensioning curing, and uniform curing. Attached Figure Description

[0053] Figure 1 The fast-curing, slow-bonding prestressed steel strand prepared in Example 1 of this invention;

[0054] Figure 2 This is a partial cross-sectional view of the fast-curing, slow-bonding prestressed steel strand prepared in Example 1 of the present invention.

[0055] [Explanation of Labels in the Attached Image]

[0056] 1. Steel strand; 2. Sheath; 3. Acoustic waveguide wire; 4. Fast-curing, slow-bonding adhesive; 5. Horizontal ribs; 6. Vertical ribs; 61. Groove. Detailed Implementation

[0057] 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.

[0058] To better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present invention can be understood more clearly and thoroughly, and that the scope of the present invention can be fully conveyed to those skilled in the art.

[0059] Example 1

[0060] This embodiment provides a method for preparing a fast-setting, slow-bonding prestressed steel strand, including the following steps:

[0061] (1) Raw material preparation

[0062] 50 parts of matrix resin: specifically, E-51 epoxy resin and flexible epoxy diluent are mixed at a ratio of 4:1.

[0063] 8 parts of latent curing agent: dicyandiamide micro powder (particle size <10μm);

[0064] Ten parts of microencapsulated thixotropic agent with an average particle size of 25 μm: core material is triethylenetetramine (TETA); wall material is urea-formaldehyde resin with a wall thickness of 3 μm; the mass ratio of core material to wall material is 90-97:3-10.

[0065] 15 parts of lubricating filler: flake graphite powder (325 mesh) and molybdenum disulfide powder are mixed in a 1:1 ratio.

[0066] 1.5 parts coupling agent: KH-560 silane coupling agent;

[0067] 1.0 part of acoustically sensitive nano-cavitation agent: hydrophobically modified porous silica nanospheres (particle size 150nm).

[0068] The preparation method of the microcapsule thixotropic agent is as follows:

[0069] 1) Emulsification and protection of core material: Water-soluble TETA is converted into a stable water-in-oil (W / O) emulsion to prevent it from reacting prematurely in subsequent acidic environments.

[0070] Add 100 parts TETA and 25 parts dibutyl phthalate (DBP) to a dry beaker and stir until homogeneous. DBP acts as a co-solvent, reducing the surface tension of TETA and increasing its hydrophobicity. Add 6 parts Span-80 emulsifier and stir at 800 rpm for 20 minutes in a 40°C water bath to form a homogeneous oil phase mixture (core material emulsion). At this point, TETA is encapsulated in the oil phase micro-regions and is temporarily not in contact with external water.

[0071] 2) Preparation of low molecular weight hydroxymethylurea prepolymer: Add 50 parts deionized water and 5 parts urea to a reaction vessel and stir to dissolve; adjust the pH value to 8.0-8.5 with triethanolamine; slowly add 12 parts 37% formaldehyde solution; heat to 70℃ and keep the reaction at this temperature for 40 minutes until the solution is clear and transparent to obtain hydroxymethylurea prepolymer solution; it is necessary to maintain alkalinity during this stage to prevent urea and formaldehyde from prematurely condensing into precipitate;

[0072] 3) Add 1 part of styrene-maleic anhydride copolymer (SMA) dispersant (pre-dissolved in a small amount of hot water) to the hydroxymethyl urea prepolymer solution prepared in 2), and stir until homogeneous; SMA is the key to controlling the microcapsule particle size, and the higher its concentration, the smaller the particle size;

[0073] The core material emulsion prepared in step 1) is slowly poured into a solution of hydroxymethyl urea prepolymer containing SMA;

[0074] Use a high-shear emulsifier at 2000-2500 rpm and shear at 45°C for 15-20 minutes; take samples and observe them under a microscope, adjusting the speed and time until the oil droplet size distribution is concentrated at 20-30 μm (target 25 μm).

[0075] Add 0.2 parts of ammonium chloride (or slowly add 10% dilute hydrochloric acid) to slowly lower the pH of the system to 3.0-3.5. Hydroxymethylurea begins to condense. Due to the interfacial tension on the surface of the oil droplets, the polymer preferentially deposits on the surface of the oil droplets to form the primary wall material. Slowly raise the temperature to 55-60℃ at a rate of 1℃ / min and keep the reaction at this temperature for 3-4 hours. Take samples regularly for microscopic examination to observe the increase in wall material thickness. When the wall thickness reaches about 3μm (estimated by particle size change or SEM sampling) and the microcapsules are spherical and non-adhesive, stop the reaction.

[0076] 4) Allow the microcapsule suspension to cool naturally to room temperature. Wash the suspension 3-4 times with weakly alkaline warm water (40℃). Centrifuge the suspension (2000 rpm, 5 minutes) to remove unreacted urea, formaldehyde, and free TETA. Dry the filter cake in a vacuum oven at 40-45℃ for 12 hours. The dried microcapsules may have slight agglomeration. They need to be gently sieved through a 200-mesh (75μm) sieve to obtain free-flowing powdered microcapsules.

[0077] It should be noted that in addition to TETA, the core material of the microcapsules also contains a small amount of DBP, but DBP does not affect the subsequent curing reaction. In fact, it facilitates the curing reaction. Upon microcapsule rupture, DBP rapidly reduces local viscosity, helping TETA diffuse more quickly into the epoxy resin matrix. DBP also better wets the surface of the steel strand and the epoxy matrix, eliminating microscopic voids and resulting in a more uniform curing reaction.

[0078] (2) Preparation of fast-curing, slow-bonding prestressed steel strand

[0079] S1: At 35°C, the matrix resin, dicyandiamide powder, lubricating filler, and KH-560 prepared in (1) are added to a high-speed disperser and stirred at 800 rpm for 30 minutes to obtain the first mixture.

[0080] S2: Cool the first mixture to 20°C, add microcapsule thixotropic agent and acoustic nano cavitation agent, adjust the speed to 150 rpm, stir at low speed for 20 minutes to obtain a fast-curing slow-bonding special adhesive.

[0081] S3: Using an extrusion coating process, adhesive is applied to the surface of the steel strand, controlling the coating thickness to 2.0mm. A 1.5mm diameter 304 stainless steel wire (acoustic impedance 45×10) is then used. 6 kg / (m 2 •s)) is attached to the surface of the adhesive layer, with the stainless steel wire corresponding to the groove position inside the longitudinal rib of the sheath;

[0082] S4: See also Figure 1 and Figure 2 The process involves extruding an HDPE sheath 2 (this sheath has multiple transverse ribs 5 and two longitudinal ribs 6 grooves) to cover steel strand 1 coated with a fast-curing, slow-bonding adhesive 4. The acoustic waveguide wires are then embedded into the grooves 61 of the longitudinal ribs 6 under the influence of the adhesive, resulting in a 50-meter-long fast-curing, slow-bonding prestressed steel strand product. It should be noted that there can be 3 or 4 longitudinal ribs, etc., evenly distributed around the sheath. The number of acoustic waveguide wires is optional and can be less than the number of longitudinal ribs.

[0083] Example 2

[0084] This embodiment provides performance testing of the fast-curing, slow-bonding prestressed steel strand prepared in Example 1; tensioning the fast-curing, slow-bonding prestressed steel strand to a certain strength; clamping the exposed ends of the acoustic waveguide wire with the coupling of ultrasonic transducers respectively; activating the ultrasonic transducers to apply ultrasonic waves to the acoustic waveguide wire; the ultrasonic waveform is pulse-modulated ultrasonic wave with a duty cycle of 15%, a peak power of 350W, a center frequency of 24kHz, and a frequency conversion scanning range of 22-26kHz; applying ultrasonic waves for 7 minutes triggers the curing of the fast-curing, slow-bonding special adhesive.

[0085] The performance tests mainly targeted the fast-curing, slow-bonding prestressed steel strands and the fast-curing, slow-bonding adhesive used inside them. See Table 1 for details.

[0086] Table 1

[0087]

[0088] Example 3

[0089] This embodiment provides a method for preparing a fast-setting, slow-bonding prestressed steel strand, including the following steps:

[0090] (1) Raw material preparation

[0091] 55 parts of matrix resin: MDI-based polyurethane prepolymer (NCO content 8%);

[0092] 6 parts of latent curing agent: blocked imidazole derivative;

[0093] 12 parts of microcapsule thixotropic agent with an average particle size of 40 μm: the core material is isophorone diamine (IPDA); the wall material is melamine formaldehyde with a wall thickness of 4.5 μm; the mass ratio of core material to wall material is 90-97:3-10.

[0094] 18 parts of lubricating filler: polyethylene wax powder;

[0095] 2 parts coupling agent: KH-550 silane coupling agent;

[0096] 1.5 parts of acoustically sensitive nano-cavitation agent: hydrophobically modified porous silica nanospheres (particle size 150nm).

[0097] The preparation method of the microcapsule thixotropic agent is as follows:

[0098] 1) 95 parts of isophorone diamine (IPDA) need to be pre-dried to remove moisture; the wall material monomers are 3.5 parts of melamine and 8.7 parts of formaldehyde solution (37% wt, formalin); SMA is used as the emulsifier; triethanolamine (for alkalinity), acetic acid or citric acid (for acidity) are used as the pH adjusters; deionized water is used as the dispersion medium.

[0099] 2) Preparation of hydroxymethyl melamine: In a four-necked flask equipped with a mechanical stirrer, thermometer, reflux condenser, and pH meter, add deionized water and formaldehyde solution (the molar ratio of formaldehyde to melamine is approximately 3:1 to ensure complete hydroxymethylation); add melamine; adjust the pH to 8.5-9.0 (alkaline environment) with triethanolamine; heat to 70℃ and maintain the temperature for 60 minutes until the melamine is completely dissolved, forming a transparent hydroxymethyl melamine prepolymer solution; stop heating and cool the solution to 50-55℃ for later use;

[0100] 3) Emulsification and dispersion: Add 140 parts of 4% SMA (emulsifier) ​​aqueous solution to another container and adjust the pH to 8.0; slowly add the dried IPDA core material; turn on the high-speed shear emulsifier at 2000 rpm and shear emulsify for 15-20 minutes to prepare the O / W emulsion;

[0101] Key control point: At this point, the size of the droplet directly determines the final particle size of the microcapsules. To obtain an average particle size of 40 μm, it is necessary to monitor in real time with a microscope and adjust the shear rate and emulsification time. The faster the shearing, the smaller the particle size; and vice versa.

[0102] Slowly add the prepolymer solution prepared in step 2) to the above O / W emulsion while stirring at 400 rpm until the mixture is homogeneous. At this time, the pH of the system should be maintained at 8.0-8.5 to prevent the prepolymer from self-polymerizing prematurely.

[0103] 4) In-situ polymerization and coating: The pH of the system is slowly adjusted to 4.0-4.5 with dilute acetic acid solution, and the temperature is raised to 55-60℃ and kept constant. During this stage, the prepolymer migrates from the aqueous phase to the oil / water interface and undergoes a condensation reaction on the surface of the IPDA droplets to form a primary wall film. The reaction time is 1.5 hours.

[0104] During the sampling and observation, it was observed that the surface of the droplets gradually became rough and hardened;

[0105] 5) Wall thickness increase and curing: Slowly increase the temperature to 75℃ and continue the reaction for 2 hours;

[0106] High temperature accelerates polycondensation, causing oligomers to cross-link further, resulting in thicker and denser wall material;

[0107] Wall thickness control: The wall thickness is controlled by adjusting the mass ratio of melamine / formaldehyde to the core material; after the reaction is completed, the pH is adjusted to 7.0 with NaOH solution to terminate the reaction.

[0108] 6) Filter the product and wash the filter cake repeatedly with 40℃ warm water 3-4 times to remove unreacted monomers, free formaldehyde and residual emulsifiers; vacuum dry the filter cake at 50℃ until the moisture content is <0.5%; sieve (200 mesh) to remove a small amount of oversized particles or clumps to obtain free-flowing white powder microcapsules.

[0109] (2) Preparation of fast-curing, slow-bonding prestressed steel strand

[0110] S1: At 30°C, the matrix resin, blocked imidazole derivative, lubricating filler, and KH-550 prepared in (1) are added to a high-speed disperser and stirred at 800 rpm for 40 minutes to obtain the first mixture.

[0111] S2: Cool the first mixture to 15°C, add microcapsule thixotropic agent and acoustic nano cavitation agent, adjust the speed to 120 rpm, stir at low speed for 25 minutes to obtain a fast-curing slow-bonding special adhesive.

[0112] S3: Using an extrusion coating process, adhesive is applied to the surface of the steel strand, with the coating thickness controlled at 2.2mm. A 1.8mm diameter copper-clad steel wire (acoustic impedance 42×10⁻⁶) is then used. 6 kg / (m 2 •s)) is attached to the surface of the adhesive layer, with the stainless steel wire corresponding to the groove position inside the longitudinal rib of the sheath;

[0113] S4: See also Figure 1 and Figure 2 The HDPE sheath (with multiple transverse ribs and two longitudinal rib grooves) is extruded to cover the steel strand coated with adhesive. The acoustic waveguide wire is embedded in the longitudinal rib groove under the push of the adhesive, thus preparing a fast-curing, slow-bonding prestressed steel strand with a length of 30 meters.

[0114] Example 4

[0115] This embodiment provides performance testing of the fast-curing, slow-bonding prestressed steel strand prepared in Example 3; the fast-curing, slow-bonding prestressed steel strand is tensioned to a certain strength; the exposed ends of the acoustic waveguide wire are coupled and clamped with ultrasonic transducers respectively; the ultrasonic transducers are activated to apply ultrasonic waves to the acoustic waveguide wire; the ultrasonic waveform is pulse-modulated ultrasonic wave with a duty cycle of 20%, a peak power of 330W, a center frequency of 20kHz, and a frequency conversion scanning range of 20-24kHz; the ultrasonic waves are applied for 8 minutes to trigger the curing of the fast-curing, slow-bonding special adhesive.

[0116] The performance testing method for this product is described in Example 1, and the test results are shown in Table 2.

[0117] Table 2

[0118]

[0119] Comparative Example 1

[0120] This comparative example provides an application of a slow-bonding prestressed steel strand, differing from Example 2 in that: an ultrasonic transducer is activated to apply ultrasonic waves to the waveguide wire. The ultrasonic waves are continuous waves with a power of 55W (close to the average power of Example 1) and a frequency of 24kHz. The ultrasonic waves are applied for 6 minutes to trigger the curing of the fast-curing slow-bonding adhesive. The remaining steps are the same.

[0121] It was found that the adhesive at the inlet end of the cured slow-bonded prestressed steel strand turned black and brittle, while the middle part softened and failed to cure. The analysis showed that the heat accumulation generated by the ultrasound damaged the resin, and the ultrasound was affected by the external medium, resulting in a lower energy transmission efficiency to the far end.

[0122] Comparative Example 2

[0123] This comparative example provides an application of a slow-bonding prestressed steel strand, which differs from Example 4 in that: an ultrasonic transducer is activated to apply ultrasonic waves to the waveguide wire. The ultrasonic waves are pulsed waves with a fixed frequency of 24 kHz for 6 minutes, triggering the curing of the fast-curing slow-bonding adhesive. The remaining steps are the same.

[0124] It was found that the near end cured well, while the far end (8-10m) showed insufficient curing reaction and extremely low strength. The reason for this may be that the standing wave caused this location to be at a node, resulting in insufficient mechanical strength for the ultrasonic fragmentation of the microcapsules.

[0125] Comparative Example 3

[0126] This comparative example provides a method for preparing a slow-bonded prestressed steel strand, which differs from Example 1 in that: 1.0 part of acoustically sensitive nano-cavitation agent was not added.

[0127] The remaining steps and conditions are the same as in Example 1.

[0128] The performance testing method for this product is described in Example 1, and the test results are shown in Table 3.

[0129] Table 3

[0130]

[0131] Based on the above embodiments and comparative examples, the following analysis is performed:

[0132] Examples 1 to 4 show that slow-bonded prestressed steel strands can achieve low-friction tensioning and high-strength rapid curing under different resin systems, and all indicators meet and exceed current standards.

[0133] Comparing Comparative Examples 1 and 2 with Examples 2 and 4, it can be seen that ultrasonic pulse modulation and frequency conversion scanning can solve the problems of uniformity and thermal damage during the curing of long-distance steel strands.

[0134] Comparing Comparative Example 3 with Example 1, it is evident that without the addition of acoustically sensitive nano-cavitation agents, the cavitation threshold of ultrasound in the medium increases, the cavitation bubble density decreases, and the cavitation intensity weakens. The Shore hardness significantly decreases, and the failure mode deteriorates from cohesive failure to interfacial debonding. These results strongly demonstrate the crucial role of acoustically sensitive nano-cavitation agents in the rapid and uniform curing of adhesives.

[0135] 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 fast-curing, slow-bonding adhesive, characterized in that, It includes, by weight: 40-60 parts of matrix resin, 5-10 parts of latent curing agent, 5-15 parts of microencapsulated thixotropic agent, 10-20 parts of lubricating filler, 1-2 parts of coupling agent and 0.5-2 parts of acoustically sensitive nano-cavitation agent; The microcapsule thixotropic agent contains a core material that serves as a polymerization accelerator. The acoustically sensitive nano-cavitation agent can generate a microscopic cavitation effect under the action of ultrasound, causing the microcapsule thixotropic agent to rupture and release the core material; the released core material comes into contact with the matrix resin and the latent curing agent, and at the same time, the hot spot generated by the ultrasonic cavitation heats up to activate the latent curing agent, which together triggers the curing reaction of the matrix resin. Among them, the acoustically sensitive nanocavitation agent is a hydrophobically modified porous silica nanosphere.

2. The fast-curing, slow-setting adhesive as described in claim 1, characterized in that, The matrix resin is a modified epoxy resin or a polyurethane prepolymer; Latent curing agents are dicyandiamide micro powder or imidazole derivatives; The core material of the microcapsule thixotropic agent is an amine accelerator, and the wall material of the microcapsule thixotropic agent is urea-formaldehyde resin or melamine-formaldehyde. The lubricating filler is at least one of graphite powder, molybdenum disulfide, and wax powder; The coupling agent is a silane coupling agent.

3. The fast-curing, slow-bonding adhesive as described in claim 2, characterized in that, The wall material thickness of the microcapsule thixotropic agent is 1-5 μm; the average particle size of the microcapsule thixotropic agent is 10-50 μm. The particle size of the acoustically sensitive nanocavitation agent is 50-300 nm.

4. A fast-curing, slow-bonding prestressed steel strand, characterized in that, It includes steel strand, sheath and at least one acoustic waveguide wire, and the fast-curing slow-bonding adhesive as described in any one of claims 1 to 3; The sheath is fitted over the outside of the steel strand, and a fast-curing, slow-bonding special adhesive is filled between the steel strand and the sheath. The acoustic waveguide wire is inserted into the sheath and completely embedded in a fast-curing, slow-bonding adhesive; both ends of the acoustic waveguide wire protrude from the sheath. The end of the acoustic waveguide wire extending from the sheath is used to apply ultrasonic waves; When stress is applied to the steel strand, the ultrasonic waves transmitted along the acoustic waveguide wire can break the microcapsule structure of the microcapsule thixotropic agent with the assistance of acoustically sensitive nano-cavitation agent, thereby triggering the curing of the fast-curing slow-bonding special adhesive.

5. The fast-setting, slow-bonding prestressed steel strand as described in claim 4, characterized in that, The outer periphery of the sheath is evenly distributed with multiple transverse ribs and at least two longitudinal ribs; the multiple transverse ribs are arranged around the circumference of the sheath and are distributed at a certain interval between them; the longitudinal ribs extend continuously along the axial direction of the sheath and the inner side of the longitudinal ribs is provided with a groove that extends continuously along the axial direction of the sheath and faces the central axis of the sheath. The acoustic waveguide wire is located in the groove of the longitudinal rib, and the groove is filled with a fast-curing, slow-bonding special adhesive.

6. The fast-setting, slow-bonding prestressed steel strand as described in claim 5, characterized in that, The acoustic waveguide wire is made of stainless steel or copper-clad steel wire with a diameter of 1-1.5 mm. The acoustic impedance of the acoustic waveguide is >40×10⁻⁶. 6 kg / (m 2 ·s).

7. A method for preparing the fast-curing, slow-bonding prestressed steel strand according to any one of claims 4 to 6, characterized in that, Includes the following steps: S1. Mix the matrix resin, latent curing agent, lubricating filler, and coupling agent evenly in an environment of <40℃ to obtain the first mixture; S2. Reduce the temperature of the first mixture to below 25°C, add microcapsule thixotropic agent and sound-sensitive nano cavitation agent, and stir and mix well while keeping the temperature below 25°C and the rotation speed <200 rpm to obtain a fast-curing slow-bonding special adhesive. S3. Using an extrusion coating process, a fast-curing, slow-bonding special adhesive is evenly coated onto the surface of the steel strand, with the coating thickness controlled at 1.5-2.5mm. The acoustic waveguide wire is then attached to the surface of the fast-curing, slow-bonding special adhesive. S4. The sheath is extruded and wrapped around the outer periphery of the steel strand coated with a fast-curing, slow-bonding special adhesive to prepare the fast-curing, slow-bonding prestressed steel strand.

8. The method of using the fast-setting, slow-bonding prestressed steel strand as described in any one of claims 4 to 6, or the fast-setting, slow-bonding prestressed steel strand prepared by the preparation method of claim 7, characterized in that... Includes the following steps: Step 1: Lay the fast-setting, slow-bonding prestressed steel strands according to the design requirements; Step 2: Pour concrete. Once the concrete reaches the design strength, tension the steel strands. Step 3: Connect at least one exposed end of the acoustic waveguide wire to the energy output end of the ultrasonic transducer, and start the ultrasonic transducer to apply ultrasonic waves to the acoustic waveguide wire to trigger the curing of the fast-curing slow-bonding adhesive. In step 3, the ultrasonic waves applied to the acoustic waveguide wire are pulse-modulated ultrasonic waves with a duty cycle of 10%-20%, a peak power of 300-400W, and an output frequency of 20-28kHz.

9. The method of use as described in claim 8, characterized in that, In step 3, the total duration of applying ultrasound to the acoustic waveguide wire is 5-8 minutes; During the application of ultrasound, a frequency conversion scanning mode is used to control the output frequency of the ultrasound to fluctuate periodically based on the set center frequency, and the frequency fluctuation range is kept within the instantaneous output frequency of 20-28kHz.

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