Preparation method of autoclaved lightweight concrete plate
By using temperature-sensitive mineralized microcapsules and a segmented autoclaving temperature control strategy in autoclaved lightweight concrete slabs, tobermorite whiskers were generated, solving the problems of low bond strength between steel bars and concrete and failure of anti-rust coatings, thus achieving high strength and long-lasting anti-rust effect of the slabs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-02-11
- Publication Date
- 2026-04-24
AI Technical Summary
Existing autoclaved lightweight concrete slabs have low bond strength at the interface between steel reinforcement and lightweight concrete, making them prone to debonding. Furthermore, traditional anti-rust coatings for steel reinforcement are prone to failure under high temperature and pressure conditions, resulting in reduced durability and service life of the slabs.
A pre-coated layer is formed on the surface of steel bars using temperature-sensitive mineralization microcapsules. Tobermorite whiskers are generated through autoclaving-induced crystallization, achieving in-situ crystallization strengthening of the steel bar interface. Combined with silane-terminated modified styrene-acrylic emulsion and a segmented autoclaving temperature control strategy, the interfacial bonding strength and rust prevention performance are improved.
It significantly improves the interfacial bonding strength of the board and the rust prevention performance of the reinforcing steel, extends the service life of the board, and meets the requirements of buildings for mechanical performance and durability.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of autoclaved lightweight concrete (ALC) panel preparation technology, specifically a method for preparing autoclaved lightweight concrete panels. Background Technology
[0002] Autoclaved lightweight concrete (AFC) panels are widely used in building interior and exterior walls, floors, and other components due to their excellent properties such as light weight, thermal insulation, fire resistance, and sound insulation. Currently, AFC panels are typically reinforced with steel mesh cages to improve their mechanical properties. However, two major technical challenges exist in their actual preparation and use: First, the interfacial bond strength between the steel reinforcement and lightweight concrete is low, resulting in insufficient bond strength and easy debonding, which affects the overall load-bearing capacity of the panel. Second, traditional anti-rust coatings for steel reinforcement are mostly organic coatings, which are prone to thermal degradation and aging during autoclaving (high temperature and high pressure environment), leading to coating failure. This results in the steel reinforcement being susceptible to corrosion after long-term use, further reducing the durability and service life of the panel.
[0003] In existing technologies, physical modification methods such as mechanical scoring and sandblasting are often used to treat the surface of reinforcing bars to improve interfacial adhesion. However, these methods only achieve physical bonding, with limited improvement in interfacial strength. To solve the problem of reinforcing bar corrosion, increasing coating thickness or using expensive rust inhibitors are often employed, but these methods cannot simultaneously ensure the stability of the coating under autoclaving and the effectiveness of interfacial adhesion. Furthermore, some technologies attempt to add seed crystals to the slurry to induce interfacial reactions, but the seed crystals tend to react with the slurry prematurely, making it difficult to accurately generate a reinforcing phase in situ at the reinforcing bar-concrete interface, thus hindering the integration of protection and reinforcement.
[0004] Therefore, developing a method for preparing autoclaved lightweight concrete panels that can solve the above-mentioned technical pain points, achieve simultaneous improvement in long-term rust prevention of steel bars and interfacial bonding strength, and is simple in process and industrially applicable has become an urgent technical problem to be solved in this field. Summary of the Invention
[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing autoclaved lightweight concrete slabs. By utilizing the precise controlled release of temperature-sensitive mineralized microcapsules, in-situ crystallization strengthening of the steel reinforcement interface and long-term rust prevention are integrated, significantly improving the mechanical properties and durability of the slabs.
[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing autoclaved lightweight concrete slabs, comprising the following steps: S1, modification of the reinforcing mesh interface: immersing the rust-removed reinforcing mesh in a heat-responsive mineralizing rust-preventive slurry, removing it, draining and drying it to form a pre-coated layer with a thickness of 100μm-200μm on the surface of the reinforcing bars; the slurry contains temperature-sensitive mineralizing microcapsules; S2, slurry pouring and static curing: fixing the modified reinforcing mesh in a mold, pouring aerated concrete slurry, and static curing at 45℃-55℃. Curing time is 2.5-3.5 hours until the green body hardens to the cutting strength. During this stage, the temperature-sensitive mineralization microcapsules maintain structural integrity and do not react with the slurry. S3, Autoclaving-induced crystallization: The cut green body is sent into an autoclave and cured for 10-12 hours at 190℃-205℃ and 1.3MPa-1.6MPa steam pressure. During this process, the temperature-sensitive mineralization microcapsules undergo phase transformation and breakage, releasing the crystal nucleation inducer, and tobermorite whiskers grow in situ at the interface between the steel reinforcement coating and the concrete, forming a chemical anchoring layer.
[0007] Preferably, the preparation method of the temperature-sensitive mineralized microcapsules includes the following steps: a. Carrier activation: After calcining porous diatomaceous earth, it is immersed in a mixed dispersion of saturated calcium hydroxide and nano-aluminum powder, and impregnated under vacuum negative pressure for 2-3 hours to allow the calcium and aluminum active components to fill the pores of the diatomaceous earth. The material is then dried to obtain the mineralized core material; b. Capsule wall coating: The mineralized core material is dispersed in molten modified polyethylene wax, magnesium stearate is added as a dispersant, and a sealing layer with a melting point of 110℃-130℃ is formed on the surface of the mineralized core material by high-speed spray cooling granulation. The material is then sieved to obtain temperature-sensitive mineralized microcapsules with a particle size of 20μm-50μm.
[0008] Preferably, the mixed dispersion is prepared by calcium hydroxide, nano aluminum powder and deionized water in a weight ratio of 10:1:50; in step b, the weight ratio of mineralized core material to modified polyethylene wax is 1:0.5-1:0.8.
[0009] Preferably, the thermally responsive mineralized rust-preventive slurry is made from the following components in parts by weight: 30-40 parts of modified styrene-acrylic emulsion, 15-20 parts of the temperature-sensitive mineralized microcapsules, 10-15 parts of ultrafine cement, 5-8 parts of talc, 1-2 parts of film-forming aid, and 20-30 parts of water. The pH value of the slurry is adjusted to 11-13 to prevent steel reinforcement corrosion.
[0010] Preferably, the autoclaving in step S3 adopts a segmented temperature control strategy: constant temperature softening stage: maintaining 120℃-130℃ for 45min-60min to soften and melt the encapsulation layer of the temperature-sensitive mineralized microcapsules, exposing the internal mineralized core material; high temperature crystallization stage: rapidly heating to 190℃-205℃ and maintaining constant pressure to promote the reaction between the calcium and aluminum active components in the mineralized core material and the silica components that penetrate the coating to generate plate-shaped tobermorite.
[0011] Preferably, the modified styrene-acrylic emulsion is prepared as follows: Styrene, butyl acrylate, and acrylic acid are emulsion polymerized under the action of an initiator. In the later stage of polymerization, 3%-5% of vinyltrimethoxysilane is added for end-capping modification, so that the emulsion film can be cross-linked and cured through silicon-oxygen bonds under high temperature and pressure, without thermal degradation.
[0012] Preferably, the aerated concrete slurry comprises 55%-65% silica sand powder, 15%-20% quicklime, 10%-15% cement, 2%-4% dihydrate gypsum, and 0.08%-0.15% aluminum powder paste; the silica sand powder has a silica content ≥85%, a specific surface area ≥3000cm² / g, and the remainder is water.
[0013] Preferably, after curing in step S3, the precast coating of the steel mesh cage is transformed into a porous ceramic structure, the porosity of which is generated by the rupture of microcapsules, and the pores are filled with interwoven tobermorite crystals with a length of 5μm-20μm, and the interfacial bonding strength is increased by 30%-50% compared with that before modification.
[0014] An autoclaved lightweight concrete slab with a steel bar bond strength ≥ 5.5 MPa and a drying shrinkage value ≤ 0.50 mm / m.
[0015] Preferably, after the plate undergoes 50 freeze-thaw cycles, there are no rust spots at the interface of the reinforcing bars, and the mass loss rate is ≤2%.
[0016] Compared with existing technologies, this invention provides a method for preparing autoclaved lightweight concrete slabs, which has the following beneficial effects: Through the "low-temperature sealing and high-temperature core release" design of temperature-sensitive mineralized microcapsules, precise controlled release of the crystallization reaction is achieved. During the static curing stage, the microcapsule structure remains intact and does not interfere with the hardening of the green body. During the autoclaving stage, the microcapsules undergo phase transformation and rupture, releasing calcium-aluminum active components, which allow tobermorite whiskers to grow in situ at the steel-concrete interface, forming a chemical anchoring layer. This solves the problems of premature seed crystal reaction and poor interface strengthening effect in existing technologies. The interface bonding strength is increased by 30%-50% compared to the unmodified form.
[0017] A thermally responsive mineralized anti-rust slurry was prepared using silane-terminated modified styrene-acrylic emulsion. This emulsion can be cross-linked and cured under high temperature autoclaving without thermal degradation. Combined with the alkaline environment of slurry 11-13, it achieves the combination of early passivation and anti-rust of steel bars and long-term protection in the later stage, solving the pain points of traditional organic coating autoclaving failure and steel bar corrosion.
[0018] The segmented autoclaving and temperature control strategy first softens the microcapsule walls at a constant temperature of 120℃-130℃, and then induces crystallization at high temperature to ensure that tobermorite whiskers grow in a directional manner at the interface, further improving the interfacial bonding performance and the mechanical stability of the board. At the same time, the slurry uses silica sand powder with high silica content to provide sufficient silicon source for the formation of tobermorite, taking into account both the lightweight and high strength of the board. Detailed Implementation
[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0020] This invention provides a technical solution for the preparation of autoclaved lightweight concrete panels: In the examples, all raw materials used were conventional commercial products, including: porous diatomaceous earth calcined at 800℃ for 2 hours; nano-aluminum powder with a particle size of 50nm; modified polyethylene wax with a melting point of 110℃-130℃; vinyltrimethoxysilane added at 4% of the total monomer mass of the silane-terminated modified styrene-acrylic emulsion; silica sand powder with a silica content ≥85% and a specific surface area ≥3000cm² / g; and propylene glycol methyl ether acetate as the film-forming aid.
[0021] Test Method Description: All performance tests of this invention are strictly performed in accordance with relevant national / industry standards. The reference standards and detailed test steps are as follows to ensure the accuracy, objectivity and comparability of the test data. All test samples are autoclaved lightweight concrete slabs with a size of 600mm×200mm×75mm prepared in Examples 1 to 4 and Comparative Examples 1 to 6. Three parallel samples are set up for each test group, and the test results are taken as the average value (except for the condition of steel corrosion and the high temperature stability of the coating, which are qualitative judgments).
[0022] The reference standard for interfacial bond strength testing is: Technical Specification for Application of Autoclaved Aerated Concrete Panels (JGJ / T 17-2021), specifically referring to Section 6.3.2 "Method for Testing Interfacial Bond Strength".
[0023] Detailed testing steps: Sample preparation: Randomly cut 3 samples with a size of 100mm×100mm×75mm from each group of plates, grind the sample surface with a grinding wheel to remove surface dust and loose layer, and ensure that the test surface is flat and exposes the interface bonding area between the steel bar and the concrete; use epoxy resin to bond and fix the exposed end of the steel bar to the pull-out connector, and let it stand for 24 hours until the bond is firm.
[0024] Instruments and equipment: electronic universal pull-out testing machine (range 0-100kN, accuracy 0.01kN), grinding wheel, vernier caliper (accuracy 0.02mm), epoxy resin adhesive, pull-out connectors.
[0025] Test preparation: Fix the specimen with the bonded pull-out connector on the clamp of the pull-out testing machine, adjust the position of the clamp to ensure that the pull-out direction is consistent with the axis of the steel bar and perpendicular to the interface, and avoid eccentric tension during the test; use vernier calipers to measure the interface area between the steel bar and the concrete (accurate to 0.1 mm²) and record it as S.
[0026] Test procedure: Start the pull-out testing machine and use a uniform loading method with a loading speed controlled at 0.5 mm / min. Continue loading until the interface between the steel bar and the concrete debonds or fails, and record the maximum pull-out force F (unit: kN) at this time.
[0027] Data calculation: interfacial bond strength σ = F / S, where σ is in MPa, F is the maximum pull-out force (kN), and S is the interfacial bond area (mm²). Calculate the average value of 3 parallel samples as the interfacial bond strength test result of this group of plates, and retain 1 decimal place.
[0028] The reference standard for testing the bond strength of reinforcing bars is the "Code for Acceptance of Construction Quality of Concrete Structures" (GB 50204-2015), specifically Appendix E "Test Method for Bond Strength of Reinforcing Bars".
[0029] Detailed testing steps: Sample preparation: Randomly cut 3 samples with a size of 150mm×150mm×75mm from each group of plates, ensuring that the sample contains a complete steel bar segment (exposed length not less than 50mm), remove the loose rust and coating residue from the exposed end of the steel bar, and grind it smooth with a grinding wheel; use a steel bar cutter to cut the exposed end of the steel bar neatly to ensure uniform stress during testing.
[0030] Instruments and equipment: electronic universal testing machine (range 0-50kN, accuracy 0.01kN), rebar cutter, grinding wheel, vernier caliper, clamps (matched to the specifications of the rebar to avoid damaging the rebar during clamping).
[0031] Test preparation: Measure the nominal diameter d of the steel bar (accurate to 0.02 mm), and calculate the cross-sectional area of the steel bar A=πd² / 4; fix the sample on the lower clamp of the universal testing machine, adjust the upper clamp, clamp the exposed end of the steel bar, and ensure that the axis of the steel bar is consistent with the loading direction, without deviation or skew.
[0032] Test procedure: A uniform loading method was adopted, with the loading speed controlled at 0.3 mm / min. The loading continued until the steel bar and concrete slipped relative to each other, or the loading force reached its peak and then dropped to 80% of the peak value. The maximum loading force F (unit: kN) at this time was recorded.
[0033] Data calculation: Rebar bond force τ=F / A, where τ is in MPa, F is the maximum loading force (kN), and A is the cross-sectional area of the rebar (mm²). Calculate the average value of 3 parallel samples as the rebar bond force test result of this group of plates, and retain 1 decimal place.
[0034] The reference standard for testing drying shrinkage value is "Test Methods for Performance of Autoclaved Aerated Concrete" (GB / T 11969-2021), specifically Chapter 7 "Test Methods for Drying Shrinkage".
[0035] Detailed testing steps: Sample preparation: Randomly cut 3 samples with a size of 40mm×40mm×160mm from each group of plates. Grind the four sides and two ends of the sample with a grinding wheel to ensure that the sample size deviation meets the standard requirements (length deviation ≤±0.5mm). Place the sample in a standard curing chamber with a temperature of 20℃±2℃ and a relative humidity of 60%±5% for 72 hours to allow the sample to reach a stable state.
[0036] Instruments and equipment: drying shrinkage apparatus (accuracy 0.001mm), constant temperature and humidity curing chamber (temperature control accuracy ±2℃, humidity control accuracy ±5%), vernier calipers, grinding wheel, sample holder (to prevent sample deformation).
[0037] Initial length measurement: Take out the pre-cured sample and measure the initial length L0 of the sample (accurate to 0.001 mm) using a drying shrinkage tester. Measure once in each of the two mutually perpendicular directions of the sample and take the average of the two measurements as the initial length L0. After the measurement is completed, put the sample back into the standard curing chamber for continued curing.
[0038] Curing and Measurement: The samples were cured under standard curing conditions (20℃±2℃, relative humidity 60%±5%) for 28 days. During the curing period, the samples were taken out at 7 days, 14 days, and 28 days, and the corresponding lengths L7 and L were measured using a drying shrinkage tester. 14 L 28 The measurement method is the same as the initial length measurement, and the sample is immediately put back into the curing box after each measurement.
[0039] Data calculation: Drying shrinkage value ε=(L0-L t ) / L0×1000 (unit: mm / m), where L t L0 is the sample length (mm) after curing for t days (t=7, 14, 28), and L0 is the initial length (mm). In this invention, the 28-day drying shrinkage value is used as the test result, and the average value of 3 parallel samples is calculated and retained to 2 decimal places.
[0040] The reference standard for freeze-thaw cycle test (50 times) and steel corrosion and mass loss rate test is: "Standard for Test Methods of Long-term Performance and Durability of Concrete" (GB / T 50082-2009), specifically Chapter 4 "Slow Freezing Test Method".
[0041] Detailed testing steps: Sample preparation: Randomly cut 3 samples with a size of 100mm×100mm×75mm from each group of plates, grind the sample surface with a grinding wheel to remove floating dust and loose layer, rinse with clean water and wipe the surface dry; use an electronic balance (accuracy 0.01g) to measure the initial mass m0 (unit: g) of each sample and record the data; seal the sides of the sample with sealant (only the top and bottom test surfaces are left to simulate the water intrusion path in actual use).
[0042] Instruments and equipment: freeze-thaw tester (temperature control range -20℃ to 20℃, temperature control accuracy ±1℃), electronic balance (accuracy 0.01g), grinding wheel, clean water, sealant, magnifying glass (magnification 10x), vernier caliper.
[0043] Freeze-thaw cycle parameters: The slow freezing method is adopted, and one freeze-thaw cycle is 24 hours. The specific process is as follows: ① Freezing stage: The sample is placed in the freeze-thaw test chamber and kept at a temperature of -18℃±2℃ for 12 hours to ensure that the core temperature of the sample drops below -15℃; ② Melting stage: The frozen sample is taken out and immersed in clean water at 20℃±2℃ for 12 hours to ensure that the sample is completely thawed and the core temperature rises above 10℃; the number of cycles is set to 50.
[0044] Test procedure: Complete 50 freeze-thaw cycles according to the above freeze-thaw cycle parameters; during the cycle, observe whether the sample cracks or peels off. If serious damage occurs, record it in time and stop the test of the sample.
[0045] Mass loss rate calculation: After 50 freeze-thaw cycles, the sample is taken out, the loose particles on the surface are rinsed with clean water, the surface moisture is wiped dry, and the final mass m1 (unit: g) of the sample is measured with an electronic balance; the mass loss rate ω = (m0-m1) / m0 × 100%, the average value of 3 parallel samples is calculated, and one decimal place is retained.
[0046] Determination of steel bar corrosion: After freeze-thaw cycles, the sample is broken to expose the steel bar interface. A magnifying glass is used to observe whether rust spots or rust marks appear on the steel bar surface. The judgment criteria are: ① No corrosion: The steel bar surface is smooth, without any rust marks or rust spots; ② A small number of rust spots: Scattered, small rust spots appear on the steel bar surface, with a corrosion area ≤5%; ③ Obvious rust spots: A large number of rust spots appear on the steel bar surface, with a corrosion area >5%, or an obvious rust layer appears.
[0047] Reference standard for high temperature stability testing of coatings: Based on the characteristics of the autoclaving process of this invention, and referring to the "Test Method for Temperature Deterioration Resistance of Architectural Coatings" (GB / T 1733-1993), the test parameters were optimized in combination with the autoclaving curing conditions (190℃-205℃, 1.3MPa-1.6MPa).
[0048] Detailed testing steps: Sample preparation: Randomly cut 3 samples with a size of 100mm×100mm×75mm from each group of plates, ensuring that the precast coating on the surface of the steel bars in the sample is intact and undamaged; use a camera to photograph the initial state of the coating on the sample surface (record the color and integrity of the coating).
[0049] Instruments and equipment: autoclave (with autoclaving parameters consistent with the example, temperature control accuracy ±5℃, pressure control accuracy ±0.1MPa), camera, magnifying glass (10x magnification), and hair dryer.
[0050] Test procedure: Place the sample in an autoclave and cure it for 10-12 hours according to the autoclave parameters of the corresponding example / comparative example (temperature 190℃-205℃, pressure 1.3MPa-1.6MPa). After curing, close the autoclave and allow it to cool naturally to room temperature. Take out the sample and dry the surface moisture with a hair dryer.
[0051] Judgment criteria: The final state of the sample coating is photographed with a camera and observed with a magnifying glass to determine whether the high-temperature stability of the coating is qualified. The qualified criteria are: the coating has no cracks, no peeling, no thermal degradation, the surface color is basically uniform, it is firmly bonded to the surface of the steel bar, and there is no peeling or blistering. The unqualified criteria are: the coating has cracks, peeling, peeling, blistering, or thermal degradation (such as powdering, discoloration, carbonization).
[0052] Interface bond strength: Pull-out test was conducted in accordance with the "Technical Specification for Application of Autoclaved Aerated Concrete Panels" (JGJ / T17-2021). Three samples were tested in each group, and the average value was taken. Rebar bond strength: Tested according to the "Code for Acceptance of Construction Quality of Concrete Structures" (GB 50204-2015), with 3 samples tested in each group and the average value taken; Drying shrinkage value: Tested according to the "Test Method for Performance of Autoclaved Aerated Concrete" (GB / T 11969-2021), with a test environment of 20℃±2℃ and relative humidity of 60%±5%; Freeze-thaw cycle test: Referring to the "Standard for Test Methods of Long-term Performance and Durability of Concrete" (GB / T 50082-2009), the slow freezing method was adopted. After 50 freeze-thaw cycles, the corrosion of the steel reinforcement interface was observed, and the mass loss rate of the plate was calculated (mass loss rate = (mass before freeze-thaw - mass after freeze-thaw) / mass before freeze-thaw × 100%). High-temperature stability of coating: After autoclaving, observe the integrity of the coating on the surface of the steel bar. If there is no cracking, peeling or degradation, it is considered qualified.
[0053] Example 1 A method for preparing autoclaved lightweight concrete slabs specifically includes the following steps: Preparation of thermosensitive mineralized microcapsules: a. Carrier activation: Porous diatomaceous earth was calcined at 800℃ for 2 hours, removed and cooled, then immersed in a mixed dispersion prepared by calcium hydroxide, nano-aluminum powder and deionized water in a weight ratio of 10:1:50, and impregnated under vacuum for 2 hours. After removal, it was dried at 105℃ for 3 hours to obtain the mineralized core material; b. Capsule wall coating: The mineralized core material was mixed with modified polyethylene wax in a weight ratio of 1:0.5. The modified polyethylene wax was heated to 150℃ to melt, and the mineralized core material and magnesium stearate accounting for 0.3% of the total mass of the system were added. After stirring and dispersing evenly, the thermosensitive mineralized microcapsules with a particle size of 20μm (capsule wall melting point 110℃) were obtained by high-speed spray cooling granulation (spray pressure 0.3MPa, cooling temperature 25℃) and sieved.
[0054] Preparation of modified styrene-acrylic emulsion: Styrene, butyl acrylate, and acrylic acid were mixed in a weight ratio of 40:45:15. Ammonium persulfate initiator accounting for 0.8% of the total monomer mass was added, and emulsion polymerization was carried out at 75°C for 4 hours. In the later stage of polymerization, vinyltrimethoxysilane accounting for 3% of the total monomer mass was added, and the reaction was continued for 1 hour. After cooling to room temperature, the modified styrene-acrylic emulsion was obtained.
[0055] Preparation of thermally responsive mineralized rust-preventive slurry: Take 30 parts by weight of modified styrene-acrylic emulsion, 15 parts by weight of thermosensitive mineralized microcapsules, 10 parts by weight of ultrafine cement, 5 parts by weight of talc powder, 1 part by weight of film-forming aid, and 20 parts by weight of water. Mix and stir evenly, and adjust the pH value of the slurry to 11 with sodium hydroxide to obtain thermally responsive mineralized rust-preventive slurry.
[0056] Interface modification of steel mesh cage (S1): The steel mesh cage is sandblasted to remove rust (rust removal grade Sa2.5), immersed in the above-mentioned heat-responsive mineralized rust-preventive slurry, soaked for 10 minutes, taken out and drained, and then dried at 80℃ for 2 hours to form a pre-fabricated coating with a thickness of 100μm on the surface of the steel bar.
[0057] Slurry pouring and static curing (S2): Fix the modified steel mesh cage in the mold, pour in the aerated concrete slurry (components and mass fraction: silica sand powder 55%, quicklime 15%, cement 10%, dihydrate gypsum 2%, aluminum powder paste 0.08%, the remainder is water), stir evenly and pour, static curing at 45℃ for 3.5h, the green body hardens to the cutting strength, take it out and cut it into green bodies with specifications of 600mm×200mm×75mm.
[0058] Autoclaved Induced Crystallization (S3): The cut billet is sent into an autoclave and a segmented temperature control strategy is adopted: first, it is kept at 120℃ for 60 minutes (constant temperature softening section), then the temperature is rapidly increased to 190℃, the steam pressure is maintained at 1.3MPa, and it is cured for 12 hours (high temperature crystallization section). It is then taken out and cooled to room temperature to obtain autoclaved lightweight concrete slabs.
[0059] Example 2 A method for preparing autoclaved lightweight concrete slabs specifically includes the following steps: Preparation of thermosensitive mineralized microcapsules: a. Carrier activation: vacuum negative pressure impregnation for 2.5 h; b. Capsule wall coating: mineralized core material and modified polyethylene wax weight ratio 1:0.65, sieved to obtain thermosensitive mineralized microcapsules with a particle size of 35 μm (capsule wall melting point 120℃).
[0060] Preparation of modified styrene-acrylic emulsion: Vinyltrimethoxysilane was added at a rate of 4%.
[0061] Preparation of thermally responsive mineralized rust-preventive slurry: Take 35 parts by weight of modified styrene-acrylic emulsion, 18 parts by weight of thermosensitive mineralized microcapsules, 12 parts by weight of ultrafine cement, 6.5 parts by weight of talc, 1.5 parts by weight of film-forming aid, and 25 parts by weight of water, and adjust the pH value to 12.
[0062] Interface modification of steel mesh cage (S1): precast coating thickness 150μm.
[0063] Slurry pouring and static curing (S2): Aerated concrete slurry composition and mass fraction: silica sand powder 60%, quicklime 17.5%, cement 12.5%, dihydrate gypsum 3%, aluminum powder paste 0.12%, balance is water; static curing temperature 50℃, static curing time 3h.
[0064] Steam pressure induced crystallization (S3): Segmented temperature control: hold at 125℃ for 52 min, then raise the temperature to 198℃, steam pressure 1.45 MPa, cure for 11 h, the rest is the same as in Example 1.
[0065] Example 3 A method for preparing autoclaved lightweight concrete slabs specifically includes the following steps: Preparation of temperature-sensitive mineralized microcapsules: a. Carrier activation: vacuum negative pressure impregnation for 3 hours; b. Capsule wall coating: mineralized core material and modified polyethylene wax in a weight ratio of 1:0.8, and sieved to obtain temperature-sensitive mineralized microcapsules with a particle size of 50 μm (capsule wall melting point 130℃).
[0066] Preparation of modified styrene-acrylic emulsion: Vinyltrimethoxysilane was added at a rate of 5%.
[0067] Preparation of thermally responsive mineralized rust-preventive slurry: Take 40 parts by weight of modified styrene-acrylic emulsion, 20 parts by weight of thermosensitive mineralized microcapsules, 15 parts by weight of ultrafine cement, 8 parts by weight of talc powder, 2 parts by weight of film-forming aid, and 30 parts by weight of water, and adjust the pH value to 13.
[0068] Interface modification of steel mesh cage (S1): precast coating thickness 200μm.
[0069] Slurry pouring and static curing (S2): Aerated concrete slurry composition and mass fraction: silica sand powder 65%, quicklime 20%, cement 15%, dihydrate gypsum 4%, aluminum powder paste 0.15%, balance is water; static curing temperature 55℃, static curing time 2.5h.
[0070] Steam pressure induced crystallization (S3): Segmented temperature control: hold at 130℃ for 45 min, then raise the temperature to 205℃, steam pressure 1.6 MPa, cure for 10 h, the rest is the same as in Example 1.
[0071] Example 4 A method for preparing autoclaved lightweight concrete slabs specifically includes the following steps: Preparation of thermosensitive mineralized microcapsules: a. Carrier activation: After calcination of porous diatomaceous earth, it was impregnated under vacuum negative pressure for 2.5 h and dried to obtain mineralized core material; b. Capsule wall coating: The weight ratio of mineralized core material to modified polyethylene wax was 1:0.7, and the temperature-sensitive mineralized microcapsules with a particle size of 35 μm (capsule wall melting point 120℃) were obtained by sieving.
[0072] Preparation of modified styrene-acrylic emulsion: The optimal emulsion polymerization effect was achieved when the addition amount of vinyltrimethoxysilane was 4%.
[0073] Preparation of thermally responsive mineralized rust-preventive slurry: Take 36 parts by weight of modified styrene-acrylic emulsion, 18 parts by weight of thermosensitive mineralized microcapsules, 13 parts by weight of ultrafine cement, 7 parts by weight of talc, 1.6 parts by weight of film-forming aid, and 26 parts by weight of water, and adjust the pH value to 12.5.
[0074] Interface modification of steel mesh cage (S1): The coating thickness of 160μm is the best for coating adhesion.
[0075] Slurry pouring and static curing (S2): Aerated concrete slurry composition and mass fraction: silica sand powder 62%, quicklime 18%, cement 13%, dihydrate gypsum 3.2%, aluminum powder paste 0.13%, with the balance being water; static curing temperature 52℃, static curing time 2.8h, the green body hardening effect is optimal.
[0076] Steam pressure induced crystallization (S3): Segmented temperature control: hold at 128℃ for 50 min, then raise the temperature to 200℃, steam pressure 1.5 MPa, and cure for 10.5 h. The tobermorite whiskers grow most uniformly. The rest is the same as in Example 1.
[0077] In Comparative Example 1, no modification of the steel mesh cage interface was performed. After rust removal, the steel mesh cage was directly fixed in the mold. The remaining preparation steps, raw materials, and parameters were completely consistent with those in Example 2.
[0078] Comparative Example 2: When preparing the thermally responsive mineralized anti-rust slurry, no temperature-sensitive mineralized microcapsules were added, and the remaining preparation steps, raw materials, and parameters were completely consistent with those in Example 2.
[0079] In Comparative Example 3, when preparing temperature-sensitive mineralized microcapsules, ordinary polyethylene wax (melting point 80℃) was used for the capsule wall, and microcapsules with a particle size of 35μm were obtained by sieving. The remaining preparation steps, raw materials and parameters were completely consistent with those in Example 2 (static temperature 50℃, which is higher than the melting point of the capsule wall, causing the microcapsules to rupture prematurely).
[0080] Comparative Example 4: without segmented temperature control, the green body was directly fed into the autoclave, heated to 198°C and steam pressure 1.45 MPa, and cured for 11 hours. The remaining preparation steps, raw materials and parameters were completely consistent with those in Example 2.
[0081] In Comparative Example 5, when preparing the styrene-acrylic emulsion, vinyltrimethoxysilane was not added for end-capping modification, and ordinary styrene-acrylic emulsion was used. The remaining preparation steps, raw materials and parameters were completely consistent with those in Example 2.
[0082] In Comparative Example 6, the silica sand powder used in the aerated concrete slurry was ordinary silica sand powder with a SiO2 content of 80% and a specific surface area of 2800 cm² / g. All other preparation steps, raw materials, and parameters were completely consistent with those in Example 2. The autoclaved lightweight concrete slabs obtained in Examples 1-4 and Comparative Examples 1-6 were subjected to performance tests, specifically including interfacial bond strength (MPa), steel bond strength (MPa), drying shrinkage (mm / m), mass loss rate after 50 freeze-thaw cycles (%), steel corrosion, and high-temperature stability of the coating. Detailed test results are shown in Tables 1 and 2.
[0083] Table 1 Table 2 Based on the above test data, the following conclusions can be drawn: Through interface modification of the rebar mesh cage (coating with thermally responsive mineralized anti-rust slurry) and precise controlled release of temperature-sensitive mineralized microcapsules, it can be seen that the interface bonding strength and rebar bond strength of the embodiment are significantly better than all comparative examples. Among them, the interface bonding strength of Embodiment 2 reaches 4.8 MPa and the rebar bond strength reaches 5.8 MPa, which are 71.4% and 100% higher than Comparative Example 1 without interface modification, respectively, and 60.0% and 81.2% higher than Comparative Example 2 without microcapsules, respectively. The interface bonding performance and rebar anchoring effect are greatly improved. In the examples, the drying shrinkage value (0.42 mm / m-0.48 mm / m) was significantly lower than that of the processes without interface modification and without microcapsule (0.55 mm / m in Comparative Example 1 and 0.53 mm / m in Comparative Example 2), and both met the requirement of ≤0.50 mm / m. The mass loss rate after 50 freeze-thaw cycles (0.8%-1.3%) was much lower than that of the comparative examples (1.8%-3.5%). The particle size distribution (implying uniformity of the green body) and dimensional stability were better, meeting the stringent requirements of building panels for mechanical stability and durability. Pre-coated coatings and slurries prepared by silane-terminated modified styrene-acrylic emulsions in an alkaline environment (pH=11-13) showed significantly improved steel reinforcement corrosion protection compared to powders without silane-terminated treatment (comparative Example 5 showed a small number of rust spots and a mass loss rate of 2.2%). Furthermore, without silane-terminated modification, the coating's high-temperature stability was unsatisfactory (comparative Example 5 coating degraded and cracked), significantly increasing the risk of steel reinforcement corrosion. This indicates that silane-terminated modification and the alkaline environment of the slurry have a mutually reinforcing effect on long-term steel reinforcement corrosion protection. Simultaneously, silane-terminated modification also improves the adhesion between the coating and the steel reinforcement to a certain extent, thereby significantly improving the overall durability of the material. Thermosensitive mineralized microcapsules are embedded in a pre-coated layer. After steam pressing, the calcium-aluminum active components are released and react with SiO2 in the highly active silica sand powder to generate interwoven tobermorite whiskers. The interfacial bonding strength of Example 2 is 50.0% higher than that of Comparative Example 3 (capsule wall melting point is too low) where the microcapsule parameters do not match, 37.1% higher than that of Comparative Example 4 without segmented steam pressing, 54.8% higher than that of Comparative Example 6 (silica sand powder parameters do not match), 71.4% higher than that of Comparative Example 1 without interface modification, and 60.0% higher than that of Comparative Example 2 without microcapsules. Compared with all comparative examples that did not use the process of this invention, the interface strengthening effect and steel reinforcement anchoring ability are significantly improved, and the probability of steel corrosion in freeze-thaw environment is further reduced, which greatly extends the service life of the plate. The interface bonding strength (4.2MPa-5.0MPa) and rebar bond strength (5.5MPa-6.0MPa) of the embodiments are significantly improved compared with all comparative examples (2.8MPa-3.6MPa, 2.9MPa-3.6MPa). Among them, the preferred embodiment 4 has the best performance in all aspects, and the density of the SLM formed part (corresponding to the plate blank) is also better. The tensile related properties (rebar bond strength) of the embodiments are improved by more than 60% on average compared with the comparative examples, meeting the usage requirements of more building load-bearing components. Segmented autoclaving and temperature control reduce the problem of uneven growth of tobermorite whiskers (CSI-related hidden whisker uniformity), providing an environmental basis for the uniform growth of the interfacial chemical anchoring layer. The directional diffusion of calcium-aluminum active components and silicon components during gradient crystallization is jointly promoted by segmented autoclaving and temperature control and the precise release of microcapsules, further optimizing the interfacial bonding effect.
[0084] This invention utilizes five core technologies: rebar mesh interface modification, precise controlled release of temperature-sensitive mineralized microcapsules, segmented autoclaving temperature control, silane-terminated modified styrene-acrylic emulsion preparation, and selection of highly active silica sand powder. These technologies significantly improve the interfacial bonding strength, rebar rust prevention performance, dimensional stability, and durability of autoclaved lightweight concrete slabs, completely solving the core pain points of existing technologies such as poor rebar rust prevention, low interfacial bonding strength, high-temperature coating failure, and uncontrollable crystallization reaction.
[0085] The above are merely specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent substitutions, or modifications made based on the present invention to solve essentially the same technical problems and achieve essentially the same technical effects are all covered within the protection scope of the present invention.
Claims
1. A method for preparing autoclaved lightweight concrete slabs, characterized in that: Includes the following steps: S1. Reinforcing steel mesh interface modification: The rust-removed reinforcing steel mesh is immersed in a heat-responsive mineralizing rust-preventive slurry, taken out, drained and dried to form a pre-coated layer with a thickness of 100μm-200μm on the surface of the reinforcing steel; the slurry contains temperature-sensitive mineralizing microcapsules. S2. Slurry pouring and static curing: The modified steel mesh cage is fixed in the mold, and aerated concrete slurry is poured in. It is statically cured for 2.5-3.5 hours at 45℃-55℃ until the green body hardens and reaches the cutting strength. During this stage, the temperature-sensitive mineralized microcapsules maintain structural integrity and do not react with the slurry. S3. Autoclaving-induced crystallization: The cut billet is sent into an autoclave and cured for 10-12 hours at 190℃-205℃ and 1.3MPa-1.6MPa steam pressure. During this process, the temperature-sensitive mineralization microcapsules undergo phase transformation and breakage, releasing the crystal nucleation inducer, and tobermorite whiskers grow in situ at the interface between the steel reinforcement coating and the concrete, forming a chemical anchoring layer.
2. The method for preparing autoclaved lightweight concrete slabs according to claim 1, characterized in that: The preparation method of the temperature-sensitive mineralized microcapsules includes the following steps: a. Carrier activation: After calcining porous diatomaceous earth, it is immersed in a mixed dispersion of saturated calcium hydroxide and nano-aluminum powder, and impregnated under vacuum negative pressure for 2-3 hours to allow the calcium and aluminum active components to fill the pores of the diatomaceous earth. After drying, mineralized core material is obtained. b. Encapsulation: The mineralized core material is dispersed in molten modified polyethylene wax, and magnesium stearate is added as a dispersant. The encapsulation layer with a melting point of 110℃-130℃ is formed on the surface of the mineralized core material by high-speed spray cooling granulation. Thermosensitive mineralized microcapsules with a particle size of 20μm-50μm are obtained by sieving.
3. The method for preparing autoclaved lightweight concrete slabs according to claim 1, characterized in that: The mixed dispersion is prepared by calcium hydroxide, nano aluminum powder and deionized water in a weight ratio of 10:1:50; in step b, the weight ratio of mineralized core material to modified polyethylene wax is 1:0.5-1:0.
8.
4. The method for preparing autoclaved lightweight concrete slabs according to claim 1, characterized in that: The thermally responsive mineralized rust-preventive slurry is made from the following components in parts by weight: 30-40 parts of modified styrene-acrylic emulsion, 15-20 parts of the temperature-sensitive mineralized microcapsules, 10-15 parts of ultrafine cement, 5-8 parts of talc, 1-2 parts of film-forming aid, and 20-30 parts of water. The pH value of the slurry is adjusted to 11-13 to prevent steel reinforcement corrosion.
5. The method for preparing autoclaved lightweight concrete slabs according to claim 1, characterized in that: The autoclaving process in step S3 employs a segmented temperature control strategy: Constant temperature softening section: The temperature is maintained at 120℃-130℃ for 45min-60min to soften and melt the encapsulation layer of the temperature-sensitive mineralized microcapsules, exposing the internal mineralized core material. High-temperature crystallization stage: The temperature is rapidly increased to 190℃-205℃ and kept at constant pressure, which promotes the reaction between the calcium and aluminum active components in the mineralized core material and the siliceous components that penetrate the coating to generate plate-shaped tobermorite.
6. The method for preparing autoclaved lightweight concrete slabs according to claim 1, characterized in that: The modified styrene-acrylic emulsion is prepared as follows: Styrene, butyl acrylate, and acrylic acid are emulsion polymerized under the action of an initiator. In the later stage of polymerization, 3%-5% of vinyltrimethoxysilane is added for end-capping modification, so that the emulsion film can be cross-linked and cured through silicon-oxygen bonds under high temperature and pressure, without thermal degradation.
7. The method for preparing autoclaved lightweight concrete slabs according to claim 1, characterized in that: The aerated concrete slurry contains 55%-65% silica sand powder, 15%-20% quicklime, 10%-15% cement, 2%-4% dihydrate gypsum, and 0.08%-0.15% aluminum powder paste; the silica sand powder has a silica content ≥85%, a specific surface area ≥3000cm² / g, and the balance is water.
8. The method for preparing autoclaved lightweight concrete slabs according to claim 1, characterized in that: After curing in step S3, the precast coating of the steel mesh cage is transformed into a porous ceramic structure. Its porosity is generated by the rupture of microcapsules, and the pores are filled with interwoven tobermorite crystals with a length of 5μm-20μm. The interfacial bonding strength is increased by 30%-50% compared with that before modification.
9. An autoclaved lightweight concrete slab prepared by the method according to any one of claims 1-8, characterized in that: The bond strength of the reinforcing bars is ≥5.5MPa, and the drying shrinkage of the board is ≤0.50mm / m.
10. The autoclaved lightweight concrete slab according to claim 9, characterized in that: After undergoing 50 freeze-thaw cycles, the plate showed no rust spots at the steel reinforcement interface, and the mass loss rate was ≤2%.