A method for producing precast concrete slabs based on ultrasonic-assisted accelerated curing

Abstract

This invention discloses a method for producing precast concrete slabs based on ultrasonic-assisted accelerated curing, specifically relating to the field of precast concrete slab production technology. The method includes the following steps: S1, mold preparation; S2, concrete mixing and pouring; S3, ultrasonic-assisted accelerated curing; S4, static demolding. Utilizing the principle of acoustic cavitation accelerating the hydration reaction, when high-power ultrasonic waves propagate in a solid-liquid two-phase medium like cement paste, the periodic alternation of sound pressure causes microbubble nuclei in the liquid phase to undergo periodic expansion, compression, and even transient collapse. The instantaneous collapse of the bubbles generates extreme high-temperature and high-pressure shock waves in local micro-regions. Although these extreme physical conditions are limited to the microscopic scale, they effectively break down the early hydration product films (C-S-H gel film and ettringite film) covering the surface of unhydrated cement particles, continuously exposing the fresh, unhydrated cement surface to water, thereby accelerating the hydration process. Simultaneously, the cavitation shock waves promote further refinement of cement particles, increase the reaction surface area, significantly shorten curing time, improve production efficiency, and greatly increase mold turnover rate and production line capacity.

Description

Technical Field

[0001] This invention relates to the field of precast concrete slab production technology, and in particular to a method for producing precast concrete slabs based on ultrasonic-assisted accelerated curing. Background Technology

[0002] Precast concrete slabs are core load-bearing and enclosure components in prefabricated building systems, widely used in structural parts such as floor slabs, wall panels, and roof panels. In industrialized production scenarios, the production efficiency of precast slabs directly depends on the time required for concrete to reach demolding strength after pouring. The shorter this time window, the higher the mold turnover rate, the greater the output per unit time, and the lower the overall production cost.

[0003] Currently, steam curing is the mainstream process for accelerating concrete hardening in the domestic and international precast concrete slab production industry. A typical steam curing regime consists of: a 2-3 hour static rest period, a 1-2 hour heating period, a 4-6 hour constant temperature period (60-80℃), and a 1-2 hour cooling period, for a total curing cycle of approximately 8-12 hours. This lengthy curing process constitutes a core bottleneck in the precast slab production line. Furthermore, the high-temperature saturated steam required for steam curing relies on coal-fired or gas-fired boilers, resulting in enormous energy consumption. The process also involves significant temperature gradients and thermal expansion stress, which can easily induce micro-cracks within the precast slabs, affecting the product's durability and long-term mechanical properties.

[0004] To shorten curing time, the industry has tried alternative solutions such as electrothermal curing, microwave curing, and infrared curing. Among them, electrothermal curing heats the concrete by embedding resistance wires in the mold or using electric heating templates, but it still suffers from problems such as uneven temperature field and low thermal efficiency; microwave curing uses the dielectric heating effect of microwaves on polar molecules to achieve volumetric heating of concrete, with a fast heating rate but limited penetration depth, making it difficult to uniformly heat thick precast slabs, and the equipment cost is high; infrared curing is a surface radiation heating method, which makes it difficult to achieve uniform curing of concrete thickness.

[0005] Early research focused on using ultrasound for non-destructive testing of concrete. In recent years, the role of ultrasound in promoting cement hydration has been explored. The acoustic cavitation effect and mechanical vibration effect induced by low-frequency power ultrasound (20-40kHz) in cement paste can accelerate the dissolution of cement particles and the nucleation process of hydration products, promote the early formation of CSH gel, and at the same time, ultrasonic vibration helps to eliminate micro air bubbles in the paste and improve the microstructure of the aggregate-paste interface transition zone.

[0006] However, in practical engineering applications, existing technologies have the following systemic defects: it is difficult to develop ultrasonic application schemes for precast slab size effects and large-volume casting scenarios. The planar dimensions of precast slabs are usually several square meters and the thickness is 60-150 mm. Simple single-point ultrasonic application cannot achieve effective coverage of the entire slab. The attenuation of ultrasonic energy in concrete limits the effective range of action. At the same time, precast slabs often use special materials such as self-compacting concrete (containing high-dosage water-reducing agents), fiber-reinforced concrete, or lightweight aggregate concrete. The ultrasonic parameters need to be matched with the specific mix proportions to avoid problems such as uneven fiber dispersion, lightweight aggregate floating, or incompatibility between water-reducing agents and ultrasonic cavitation.

[0007] Therefore, there is an urgent need for a method for producing precast concrete slabs to solve the aforementioned problems in the existing technology. Summary of the Invention

[0008] The main objective of this invention is to provide a method for producing precast concrete slabs based on ultrasonic-assisted accelerated curing, which can achieve effective ultrasonic coverage of the entire slab, ensure the effective effect of ultrasonic energy in the concrete, and match the ultrasonic parameters with the specific mix proportions to ensure uniform dispersion of fibers and materials inside the precast slab.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A method for producing precast concrete slabs based on ultrasonic-assisted accelerated curing, the method comprising the following steps:

[0011] S1. Mold preparation;

[0012] S2. Concrete preparation and pouring;

[0013] S3. Ultrasonic-assisted accelerated curing;

[0014] S4. Static stop demolding;

[0015] In a preferred embodiment of the present invention, step S1 is specifically implemented as follows: a release agent is applied to the inner surface of the assembled mold; the mold includes a bottom mold and four side molds, the lower surface of the bottom mold is provided with several ultrasonic transducer mounting positions, and the side molds are provided with detachable sealing baffles to seal the mold during the ultrasonic treatment stage and suppress moisture evaporation;

[0016] In a preferred embodiment of the present invention, step S2 is specifically implemented as follows: a concrete mixture is prepared according to a preset mix ratio; the mixture is injected into a mold through a material distribution device, and the pouring process is supplemented by an attached vibrator on the bottom or side wall of the mold to achieve preliminary compaction, with the vibration duration being 10-30 seconds; after pouring, the concrete surface is initially scraped smooth.

[0017] In a preferred embodiment of the present invention, step S3 is specifically implemented as follows: an ultrasonic transducer is installed in the ultrasonic transducer mounting position. After the concrete is poured and initially leveled, before the initial setting of the concrete begins, the ultrasonic transducer array arranged at the bottom of the mold is activated to perform ultrasonic treatment on the precast concrete slab inside the mold.

[0018] In a preferred embodiment of the present invention, in step S3, the operating frequency range of the ultrasonic transducer is 20-40 kHz, and the power density applied to the concrete is in the range of 0.3-1.5 W / cm². 2 Calculated based on the planar area of ​​the precast slab.

[0019] In a preferred embodiment of the present invention, the specific calculation method of step S3 includes:

[0020] S3.1 Determine the duration of ultrasonic treatment for the foundation based on the thickness H (in mm) of the precast slab:

[0021] T0 = ​​0.5H + 5

[0022] It should be noted that normal use is possible when H≤100mm, and when H>100mm, a higher value should be used and an auxiliary ultrasonic treatment should be added to the upper surface.

[0023] S3.2 Adjustment time based on the 28-day design compressive strength grade of concrete:

[0024] T=T0×k1

[0025] k1 is the incentive coefficient;

[0026] When the concrete strength grade is C30-C40, k1=1.0;

[0027] When the concrete strength grade is C45-C60, k1=0.8-0.9;

[0028] When the concrete strength grade is C60 or above, k1 = 0.7-0.8.

[0029] S3.3 Adjust the frequency and power according to whether it contains fibers:

[0030] The concrete contains no fibers, operates at a frequency of 30-40kHz, and has a power density P0 = 0.8-1.5W / cm³. 2 ;

[0031] The concrete contains steel or carbon fibers, with a frequency of 25-30kHz and a power density P0 = 0.5-1.0 W / cm³. 2 ;

[0032] The concrete contains low-modulus fibers such as PVA or glass fibers, with a frequency of 20-28kHz and a power density P0 = 0.3-0.8 W / cm³. 2 .

[0033] S3.4 Adjust the power according to the concrete density:

[0034] P = P0 × k2

[0035] Density < 1800 kg / m³ 3 k2=0.7;

[0036] Density 1800-2400 kg / m³ 3 k2=1;

[0037] Density > 2400 kg / m³ 3 k2=1.2.

[0038] In a preferred embodiment of the present invention, in step S3, the ultrasonic transducer adopts an intermittent working mode, with a single continuous working time of 5-15 seconds and an interval of 3-10 seconds.

[0039] In a preferred embodiment of the present invention, in step S3, the ultrasonic transducer array comprises multiple independent ultrasonic transducer units arranged in a row-column rectangular array on the lower surface of the bottom mold. The center-to-center distance between adjacent ultrasonic transducer units is set to an integer multiple of half the wavelength of ultrasonic waves in concrete to ensure uniform ultrasonic energy coverage across the entire plane of the precast slab.

[0040] In a preferred embodiment of the present invention, in step S3, the single ultrasonic transducer unit can be independently controlled to turn on and off and output power, so as to perform zoned differentiated processing according to the differences in thickness or material composition of different areas of the precast slab.

[0041] In a preferred embodiment of the present invention, when the precast slab uses functionally graded concrete, that is, when the concrete density and / or strength change continuously along the thickness direction, each independent unit of the array ultrasonic transducer in step S3 is set with different output power according to the concrete density corresponding to its location. Higher density areas correspond to higher power, and lower density areas correspond to lower power, thereby achieving differentiated ultrasonic processing that matches the material gradient.

[0042] In a preferred embodiment of the present invention, the ultrasonic transducer array in step S3 is fixedly installed at a fixed station below the mold conveying track of the production line. After the mold is transported to the station by the conveying system, the ultrasonic transducer array is lifted from below and comes into close contact with the lower surface of the bottom mold to form acoustic coupling.

[0043] In a preferred embodiment of the present invention, step S4 is implemented as follows: after the ultrasonic treatment is completed, the precast concrete slab continues to be statically cured in the mold until it reaches the demolding strength and is then demolded; after demolding, the precast slab can be subsequently subjected to natural curing or standard curing as needed.

[0044] In a preferred embodiment of the present invention, in step S3, the time window for starting ultrasonic treatment is 5-20 minutes after the concrete is poured, that is, when the concrete mixture has completed initial settlement and is left to stand but has not yet entered the initial setting stage.

[0045] In a preferred embodiment of the present invention, in step S3, a coupling layer is provided between the ultrasonic transducer array and the bottom mold to ensure that ultrasonic energy is effectively transmitted into the mold and the interior of the concrete.

[0046] In a preferred embodiment of the present invention, the coupling layer material is selected from one of high-temperature resistant silicone rubber, epoxy resin acoustic coupling agent, or metal foil.

[0047] In a preferred embodiment of the present invention, in step S3, when the thickness of the precast slab exceeds 100mm, a movable ultrasonic application device is added to the upper surface of the concrete to apply auxiliary ultrasonic waves to the concrete from above, so as to compensate for the energy attenuation of the bottom mold ultrasonic waves in the thickness direction.

[0048] In a preferred embodiment of the present invention, in step S3, during the ultrasonic treatment process, a temperature sensor is used to monitor the internal temperature of the concrete in real time. When the internal temperature rise exceeds 55°C, the ultrasonic power is automatically reduced or the interval time is extended to avoid the generation of thermally induced microcracks.

[0049] As a preferred embodiment of the present invention, the method for producing precast concrete slabs based on ultrasonic-assisted accelerated curing further includes step S5 and post-processing.

[0050] In a preferred embodiment of the present invention, step S5 is specifically implemented by: subjecting the upper surface of the demolded precast slab to high-pressure water jet rinsing to form a rough surface to enhance the bond strength with the on-site cast concrete.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] 1. This method utilizes the principle of acoustic cavitation to accelerate the hydration reaction. When high-power ultrasound propagates in a solid-liquid two-phase medium like cement slurry, the periodic alternation of sound pressure causes microbubble nuclei in the liquid phase to undergo periodic expansion, compression, and even transient collapse. The instantaneous collapse of the bubbles generates extreme high-temperature and high-pressure shock waves in local micro-regions. Although these extreme physical conditions are limited to the microscopic scale, they can effectively break down the early hydration product films (CSH gel film and ettringite film) covering the surface of unhydrated cement particles, continuously exposing the fresh, unhydrated cement surface to water, thereby accelerating the hydration process. At the same time, the cavitation shock waves promote further refinement of cement particles, increase the reaction specific surface area, significantly shorten curing time, improve production efficiency, and greatly increase mold turnover rate and production line capacity.

[0053] 2. This method generates mechanical vibration through ultrasonic waves. The mechanical vibration of the ultrasonic waves induces high-frequency micro-amplitude oscillations in the concrete mixture. On the one hand, this oscillation enhances the relative motion and collision frequency between cement particles and water molecules, promoting the mass transfer rate of the dissolution-precipitation process. On the other hand, the micro-vibration drives the aggregation, floating and discharge of microbubbles, reducing the porosity of hardened concrete, especially the content of harmful macropores (>200nm), thereby improving density and final strength, and improving the quality of precast components.

[0054] 3. This method utilizes the acoustic flow effect to activate the interfacial transition zone. When ultrasound encounters the surface of aggregate particles or fibers, it generates an acoustic flow effect, creating a steady-state microscale liquid circulation near the solid surface. This continuously scours the aggregate or fiber surface, breaking down the water-rich film layer formed at the interface due to internal stratification. This promotes the directional deposition and dense arrangement of hydration products in the interfacial zone, significantly improving the microstructure of the aggregate-slurry and fiber-slurry interfacial transition zone and fully leveraging the fiber reinforcement efficiency. For fiber-reinforced precast concrete slabs, the mechanical vibration and acoustic flow effect of ultrasound can effectively eliminate the weak interfacial layer around the fibers caused by slurry shrinkage or bubble adhesion, promoting the dense deposition of hydration products on the fiber surface. This improves the fiber-matrix interfacial bond strength, allowing the reinforcing and toughening effects of the fibers to be more fully realized.

[0055] 4. This method utilizes some of the energy from ultrasound to convert into heat in the medium, causing a moderate increase in concrete temperature. This overall gentle heating, combined with the localized high temperature in the cavitation micro-zones, produces a significant synergistic acceleration effect. Traditional steam curing generates a significant temperature gradient along the thickness of the precast slab during the heating phase, with a surface-to-core temperature difference of 20-30°C. The resulting differential thermal expansion stress often leads to the initiation of microcracks. The ultrasonic treatment of this invention induces a uniform temperature rise, with a temperature difference across the entire slab typically less than 5°C, and the maximum temperature is controllable. This fundamentally eliminates the conditions for the formation of heat-induced microcracks, which is beneficial for improving the impermeability, frost resistance, and long-term durability of the precast slab.

[0056] 5. This method utilizes electrically driven ultrasonic transducers. Compared to traditional steam curing, which dissipates a large amount of heat into the environment and pipelines and has low thermal energy utilization, the electrically driven ultrasonic transducers allow energy to act directly on the interior of the concrete, resulting in high energy utilization efficiency. The overall energy consumption is only 15-25% of that of steam curing, and there is no need for a boiler room and steam pipeline network, which reduces the infrastructure investment and operation and maintenance costs of the production line.

[0057] 6. This method utilizes ultrasound to improve the micro-density of concrete, enhancing its mechanical properties and impermeability. The degassing effect of ultrasound can significantly reduce the porosity of hardened concrete, especially the content of harmful macropores. Increased micro-density can improve the compressive strength, flexural strength, and modulus of elasticity of precast slabs, while reducing the chloride ion permeability coefficient and water absorption rate. Attached Figure Description

[0058] Figure 1 This is a schematic diagram of the process for producing precast concrete slabs based on ultrasonic-assisted accelerated curing according to the present invention. Detailed Implementation

[0059] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0060] Example 1:

[0061] Self-compacting precast concrete floor slab, 80mm thick

[0062] S1. Mold Preparation

[0063] A modular steel mold with a detachable bottom mold is used, with internal dimensions of 4500mm (length) × 2400mm (width) × 80mm (height). The bottom mold is made of 8mm thick Q345B steel plate, with a flat mounting surface milled on the lower surface for coupling with the ultrasonic transducer array. The side molds are connected to the bottom mold with bolts. Four attached vibrators are pre-installed on the lower surface of the bottom mold.

[0064] An ultrasonic transducer array is arranged on the lower surface of the bottom mold. The ultrasonic transducer array contains 60 piezoelectric ultrasonic transducer units in 6 rows × 10 columns. Each unit has a rated power of 100W and a resonant frequency of 28kHz. The units are arranged in a rectangular array with a center-to-center distance of 350mm between adjacent units. The length of the bottom mold is 4500mm, the diameter of each unit is 60mm, and the distance between the center of the units at both ends is 150mm. Therefore, the core spacing of 10 units along the length is approximately (4500-300) / 9=467mm; the core spacing of 6 units along the width of 2400mm is approximately (2400-300) / 5=420mm. The core spacing range is 350-467mm, which is approximately 16-21 times the half wavelength of 28kHz ultrasonic waves in initially set concrete, thus meeting the requirements for uniform coverage.

[0065] The upper surface of each ultrasonic transducer unit, which is the contact surface with the bottom mold, is coated with a 1mm thick high-temperature resistant silicone rubber coupling layer to ensure effective transmission of ultrasonic energy. A lightweight aluminum alloy sealing baffle is hinged to the top of the mold side mold, which can be closed during casting and ultrasonic treatment to suppress moisture evaporation.

[0066] The inner surface of the mold is uniformly coated with water-based release agent using automated spraying equipment.

[0067] S2, Concrete mix design and pouring

[0068] The concrete used in this embodiment is self-compacting concrete with a concrete grade of C50. The higher the strength grade, the higher the activity of the cement, and the shorter the required ultrasonic excitation time can be.

[0069] Their combinations are shown in Table 1.

[0070] Ordinary Portland cement 400 S95 grade slag powder 100 silica ash 30 river sand 780 gravel 900 Polycarboxylate superplasticizer 6.5 water 155

[0071] Table 1

[0072] The fineness modulus of the river sand is 2.6.

[0073] The self-compacting concrete has a water-cement ratio of 0.31, a slump extension of 680 mm, and a V-shaped funnel outflow time of 12 s, meeting the performance requirements of self-compacting concrete.

[0074] The mixture is injected into the mold through a movable hopper. After the mixture is placed, the attached vibrator is activated, and the vibration lasts for 15 seconds to help the concrete fill the corners of the mold and remove large air bubbles. After vibration, the surface is initially smoothed with a scraper.

[0075] S3, Ultrasonic-assisted accelerated curing

[0076] This step is the core innovation of the present invention: after the concrete has been poured and leveled, the sealing baffle is closed 8 minutes later.

[0077] The ultrasonic transducer array is activated in intermittent operation mode: 10 seconds of continuous operation followed by a 5-second pause, repeated continuously. The ultrasonic frequency is 28kHz, and the output power of each unit is set to 80W, corresponding to a power density of approximately 0.56W / cm². 2 The total duration of the ultrasonic treatment was 35 minutes.

[0078] During the process, the temperature sensor embedded in the center of the mold monitored the concrete temperature in real time. The temperature gradually rose from the initial 25℃ to the peak 43℃, without exceeding the preset upper limit of 55℃, and the power reduction protection was not triggered throughout the process.

[0079] S4, Static Demolding

[0080] After ultrasonic treatment, the sealing baffle was opened. The precast slab continued to cure statically in the mold for 2.5 hours. During this time, the surface hardness of the concrete was tested using a rebound hammer, and the converted strength was approximately 16 MPa, meeting the demolding strength requirements. Demolding was successful, and the surface of the precast slab was smooth, with intact edges and no visible cracks.

[0081] Performance tests were conducted on standard specimens of the precast components, and the test results are as follows:

[0082] After demolding, the specimens were cured under standard conditions for 28 days. Core samples were taken for performance testing and compared with a control group with the same mix proportion and traditional steam curing. The results are shown in Table 2.

[0083] Demolding time (h) 3.1 12 Demolding strength (MPa) 16.2 18.5 28-day compressive strength (MPa) 65.3 61.8 28-day splitting tensile strength (MPa) 4.8 4.2 <![CDATA[Chloride ion permeability coefficient (×10 -12 m 2 / s)]]> 3.2 4.5 Porosity (%) 8.5 10.2 Comprehensive maintenance energy consumption (kWh / m³) 8.5 52.0

[0084] Table 2

[0085] As shown in Table 2, this invention, while significantly shortening the curing time, achieves higher 28-day compressive strength, lower porosity, and significantly improved durability compared to the steam-cured group. Energy consumption is also greatly reduced.

[0086] Example 2:

[0087] PVA fiber-reinforced lightweight aggregate concrete precast wall panel, 120mm thick

[0088] S1. Mold Preparation

[0089] The mold cavity dimensions are 3000mm (length) × 1800mm (width) × 120mm (height);

[0090] S2, Concrete mix design and pouring

[0091] The concrete used in this embodiment is PVA fiber-reinforced lightweight aggregate concrete, and its mix proportions are shown in Table 3.

[0092] cement 380 fly ash 120 Shale Ceramsite 450 Pottery Sand 200 PVA fiber (40μm in diameter, 12mm in length) Volumetric doping 1.5% Polycarboxylate superplasticizer 4.2 water 150

[0093] Table 3

[0094] S3, Ultrasonic-assisted accelerated curing

[0095] Since the concrete in this embodiment contains PVA fibers, to avoid the potential adverse effects of high-frequency ultrasound on the fiber-matrix interface, the ultrasonic frequency was selected as 25kHz, the single-unit power was set to 65W, and the power density was approximately 0.46W / cm³. 2 The intermittent mode is adjusted to 8 seconds of operation followed by 7 seconds of rest, with a total ultrasound treatment time of 40 minutes.

[0096] Since the plate thickness is 120mm, a movable ultrasonic application device is added above the mold. During the second half of the ultrasonic treatment, i.e., 20-40 minutes, auxiliary ultrasonic waves are applied to the concrete surface from above to compensate for the energy attenuation of the bottom mold ultrasonic waves in the thickness direction.

[0097] S4, Static Demolding

[0098] After ultrasonic treatment, demold after static curing to meet the demolding strength requirements.

[0099] Performance tests were conducted on standard specimens of the precast components, and the test results are as follows:

[0100] Demolding time (h) 3.8 12 Demolding strength (MPa) 14.5 13.8 28-day compressive strength (MPa) 32.4 30.1 28-day splitting tensile strength (MPa) 3.6 2.9 28-day flexural strength (MPa) 5.2 4.3 Fiber-matrix interfacial bond strength (MPa) 2.8 2.1 <![CDATA[Chloride ion permeability coefficient (×10 -12 m 2 / s)]]> 5.8 8.2 Porosity (%) 11.2 14.5 <![CDATA[Dry shrinkage value (×10⁻ 6 , 90 days)]]> 520 610 Thermal conductivity (W / (m·K)) 0.41 0.45

[0101] This invention significantly shortens the demolding time of PVA fiber-containing lightweight aggregate concrete precast slabs from 12 hours under steam curing to 3.8 hours, fully verifying the outstanding accelerating effect of ultrasound on the early strength development of fiber-reinforced concrete systems. The 28-day flexural strength, 28-day splitting tensile strength, and fiber-matrix interfacial bond strength are significantly improved compared to the steam-cured control group, proving that the acoustic flow effect of ultrasound effectively eliminates the water-rich film layer formed on the PVA fiber surface due to internal delamination, promoting the dense deposition of hydration products on the fiber surface. Secondly, the degassing effect of ultrasonic treatment reduces the porosity and chloride ion permeability coefficient of the specimens, significantly improving impermeability. The 90-day drying shrinkage value is reduced, which is beneficial to the long-term dimensional stability and crack resistance of the precast wall panels.

[0102] The slight decrease in thermal conductivity proves that ultrasound promotes a denser microstructure and more uniform pore distribution in the slurry, which can improve the thermal insulation performance of the wall panel.

[0103] It should be noted that all embodiments in this application are described in a related manner, and the same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

Claims

1. A method for producing precast concrete slabs based on ultrasonic-assisted accelerated curing, characterized in that, Includes the following steps: S1. Mold preparation; S2. Concrete preparation and pouring; S3. Ultrasonic-assisted accelerated curing; S4. Static stop demolding.

2. The method for producing precast concrete slabs based on ultrasonic-assisted accelerated curing according to claim 1, characterized in that: The specific implementation of step S1 is as follows: a release agent is applied to the inner surface of the assembled mold; the mold includes a bottom mold and four side molds, the lower surface of the bottom mold is provided with several ultrasonic transducer mounting positions, and the side molds are provided with detachable sealing baffles.

3. The method for producing precast concrete slabs based on ultrasonic-assisted accelerated curing according to claim 2, characterized in that: The specific implementation method of step S2 is as follows: prepare concrete mixture according to preset mix ratio; inject the mixture into the mold through a material distribution device, and use an attached vibrator on the bottom or side wall of the mold to achieve preliminary compaction during the pouring process; after pouring, perform preliminary leveling on the concrete surface.

4. The method for producing precast concrete slabs based on ultrasonic-assisted accelerated curing according to claim 3, characterized in that: The specific implementation of step S3 is as follows: an ultrasonic transducer is installed in the ultrasonic transducer installation position. After the concrete is poured and initially leveled, before the initial setting of the concrete begins, the ultrasonic transducer array arranged at the bottom of the mold is activated to perform ultrasonic treatment on the precast concrete slab in the mold.

5. The method for producing precast concrete slabs based on ultrasonic-assisted accelerated curing according to claim 4, characterized in that: In step S3, the ultrasonic transducer operates at a frequency range of 20-40 kHz, and the power density applied to the concrete ranges from 0.3-1.5 W / cm². 2 Calculated based on the planar area of ​​the precast slab.

6. The method for producing precast concrete slabs based on ultrasonic-assisted accelerated curing according to claim 5, characterized in that: The specific calculation method for step S3 includes: S3.1 Determine the duration of ultrasonic treatment for the foundation based on the thickness H (in mm) of the precast slab: T0 = ​​0.5H + 5; S3.2 Adjustment time based on the 28-day design compressive strength grade of concrete: T = T0 × k1; k1 is the incentive coefficient; When the concrete strength grade is C30-C40, k1=1.0; When the concrete strength grade is C45-C60, k1=0.8-0.9; When the concrete strength grade is C60 or above, k1 = 0.7-0.8; S3.3 Adjust the frequency and power according to whether it contains fibers: The concrete contains no fibers, operates at a frequency of 30-40kHz, and has a power density P0 = 0.8-1.5W / cm³. 2 ; The concrete contains steel or carbon fibers, with a frequency of 25-30kHz and a power density P0 = 0.5-1.0 W / cm³. 2 ; The concrete contains low-modulus fibers such as PVA or glass fibers, with a frequency of 20-28kHz and a power density P0 = 0.3-0.8 W / cm³. 2 ; S3.4 Adjust the power according to the concrete density: P = P0 × k2 Density < 1800 kg / m³ 3 k2=0.7; Density 1800-2400 kg / m³ 3 k2=1; Density > 2400 kg / m³ 3 k2=1.

2.

7. The method for producing precast concrete slabs based on ultrasonic-assisted accelerated curing according to claim 6, characterized in that: In step S3.1, normal use is performed when H≤100mm, and a higher value is taken and an auxiliary ultrasonic treatment is added to the upper surface when H>100mm.

8. The method for producing precast concrete slabs based on ultrasonic-assisted accelerated curing according to any one of claims 4 or 5, characterized in that: In step S3, the ultrasonic transducer array comprises multiple independent ultrasonic transducer units arranged in a row-column rectangular array on the lower surface of the bottom mold. The center-to-center distance between adjacent ultrasonic transducer units is set to an integer multiple of half the wavelength of ultrasonic waves in concrete to ensure uniform ultrasonic energy coverage across the entire plane of the precast slab.

9. The method for producing precast concrete slabs based on ultrasonic-assisted accelerated curing according to claim 8, characterized in that: In step S3, the single ultrasonic transducer unit can be independently controlled to turn on and off and output power, so as to perform zoned differentiated processing according to the differences in thickness or material composition of different areas of the precast slab.

10. The method for producing precast concrete slabs based on ultrasonic-assisted accelerated curing according to claim 4, characterized in that: In step S3, a coupling layer is provided between the ultrasonic transducer array and the bottom mold.

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