Foam concrete material capable of quickly responding to dry environment and prefabricated slab

Abstract

The invention relates to a foam concrete material capable of quickly responding to a dry environment and a prefabricated slab. The high-strength concrete is prepared from the following raw materials in parts by mass: 300 to 600 parts of cement, 150 to 300 parts of blast furnace slag, 20 to 50 parts of anhydrous calcium sulfate, 50 to 200 parts of micro-active aggregate, 7 to 10 parts of polypropylene fiber, 5 to 7 parts of polystyrene fiber, 100 to 300 parts of regenerated micro powder, 0.2 to 1 part of nano foaming agent, 2 to 6 parts of polycarboxylate superplasticizer mother liquor, 10 to 50 parts of AFt seed crystal and 0.1 to 0.2 part of hydroxypropyl methyl cellulose. According to the foam concrete prefabricated slab, part of cement is replaced by the recycled micro powder and the slag, and meanwhile, the micro-active aggregate is compounded with the AFt seed crystal, so that the problem that the shrinkage period of the foam concrete prefabricated slab is long is effectively solved, the utilization rate of solid waste resources is also increased, and the problem that the strength of foam concrete in the prior art is relatively low is solved.

Description

Technical Field

[0001] This invention relates to a foamed concrete material and precast slab that can quickly respond to dry environments, belonging to the technical field of foamed concrete materials. Background Technology

[0002] Foamed concrete, as a lightweight, heat-insulating, and sound-insulating green building material, is widely used in building walls, roof insulation, and foundation backfilling due to its advantages such as high strength, convenient construction, energy saving, and environmental protection. With the increasing demand for green building materials in the construction industry, the use of industrial solid waste to prepare foamed concrete has become an industry trend. This not only reduces raw material costs but also achieves the resource utilization of solid waste, aligning with the "dual-carbon" development strategy.

[0003] However, existing foamed concrete still faces many technical bottlenecks in practical applications, especially its shrinkage stability and mechanical property defects under natural curing conditions, which severely limit its application range and service life. Specifically, the shrinkage process of existing foamed concrete is characterized by its long cycle and uncontrollability: in natural use environments, its drying shrinkage and chemical shrinkage processes often last for months or even years, and long-term volume shrinkage will create continuous tensile stress inside the material; at the same time, due to the unevenness of the shrinkage process, tensile stress is prone to concentrate in weak parts such as wall joints and corners, which can lead to through cracks.

[0004] The aforementioned cracks not only damage the integrity of the wall structure, but also cause fireproof and waterproof coatings to peel off from the wall substrate, significantly reducing the protective performance of the coatings. In addition, existing foamed concrete generally has inherent defects such as low strength and poor crack resistance. Once cracks occur, they will further aggravate the deterioration of the material's performance and reduce the safety and durability of the building structure.

[0005] To address these issues, existing technologies often employ methods such as optimizing the proportions of cementitious materials and adding fiber reinforcing agents or water-reducing agents, but the results are not entirely satisfactory. On the one hand, while the addition of conventional fiber reinforcing agents can improve crack resistance to some extent, it is difficult to fundamentally shorten the shrinkage cycle. On the other hand, existing technologies for utilizing industrial solid waste are mostly limited to simple mixing, failing to fully leverage the synergistic effects of their active ingredients, and lacking targeted seeding and control methods. This makes it difficult to effectively improve the hydration process and microstructure of foamed concrete, and thus fails to simultaneously meet the multiple needs of solid waste utilization, shrinkage control, and mechanical property improvement.

[0006] Therefore, developing a foamed concrete material that can quickly respond to dry environments, effectively shorten the shrinkage cycle, and also possess high strength, excellent crack resistance, and enable efficient utilization of industrial solid waste has become an urgent technical problem to be solved in this field. Summary of the Invention

[0007] (a) Technical problems to be solved

[0008] To address the aforementioned problems in the prior art, this invention provides a foamed concrete material and precast slab that can quickly respond to dry environments. By using solid waste to replace conventional foamed concrete components and utilizing the characteristics and seed crystal effects of micro-active aggregates, it improves the technical problems of low strength and long shrinkage period of foamed concrete caused by traditional aggregates.

[0009] (II) Technical Solution

[0010] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0011] In a first aspect, the present invention provides a foamed concrete material that responds quickly to dry environments, comprising the following components by weight: 300-600 parts cement, 150-300 parts blast furnace slag, 20-50 parts anhydrous calcium sulfate, 50-200 parts micro-active aggregate, 7-10 parts polypropylene fiber, 5-7 parts polypropylene fiber, 100-300 parts recycled micro powder, 0.2-1 parts nano-foaming agent, 2-6 parts polycarboxylate superplasticizer mother liquor, 10-50 parts AFt seed crystals, and 0.1-0.2 parts hydroxypropyl methylcellulose;

[0012] The micro-active bone, polycarboxylate superplasticizer mother liquor, AFt seed crystals, and nano foam agent are packaged separately, while other remaining raw materials can be mixed together.

[0013] The foamed concrete material described above, preferably when used to prepare precast foamed concrete slabs, also contains 150 to 250 parts of water.

[0014] In the foamed concrete material described above, preferably, the cement is high-strength silicate 52.5 cement, and the aluminum phase content of the blast furnace slag is 15%~30%; the micro-active aggregate is solid waste cenospheres, which are modified by soaking in a certain alkaline solution; and the solid phase content of the polycarboxylate superplasticizer mother liquor is 45%~55%.

[0015] Furthermore, the solid waste cenospheres are fly ash cenospheres with an alumina content of 40% to 50%, and the particle size D50 of the solid waste cenospheres is 100 to 300 μm; the solid phase content of the polycarboxylate superplasticizer mother liquor is 50%.

[0016] In the foamed concrete material described above, preferably, the recycled micro powder is micro powder obtained by crushing and grinding waste concrete, with a particle size of 0.075~0.15mm.

[0017] In the foamed concrete material described above, preferably, the polypropylene fibers have a diameter of 18~48μm and a length of 6~8mm; and the polypropylene fibers have a diameter of 18~48μm and a length of 6~12mm.

[0018] For the foamed concrete material described above, preferably, the temperature of the drying environment is 35°C and the humidity is 25%.

[0019] In the foamed concrete material described above, preferably, the nano foaming agent is added by first physically foaming the nano foam to form nano foam.

[0020] Secondly, the present invention provides a method for preparing a precast foamed concrete slab that responds quickly to a dry environment, comprising the following steps:

[0021] S1. Prepare the raw materials according to the following mass parts: 300-600 parts cement, 150-300 parts blast furnace slag, 20-50 parts anhydrous calcium sulfate, 50-200 parts micro-active aggregate, 150-250 parts water, 7-10 parts polypropylene fiber, 5-7 parts polypropylene fiber, 100-300 parts recycled micro powder, 0.1-1 part nano foaming agent, 2-6 parts polycarboxylate superplasticizer mother liquor, 10-50 parts AFt seed crystals, and 0.1-0.2 parts hydroxypropyl methylcellulose;

[0022] S2. Raw material pretreatment:

[0023] First, soak the micro-active aggregate in an alkaline environment overnight for later use;

[0024] Cement, blast furnace slag, anhydrous calcium sulfate and recycled micro powder are mixed evenly to obtain dry powder material;

[0025] Add 40-60% of the total water and 40-60% of the total polycarboxylate superplasticizer mother liquor to the AFt seed crystals, and disperse them to prepare AFt seed crystal aqueous solution for later use;

[0026] Hydroxypropyl methylcellulose is dissolved in 5-10% of the remaining total water to prepare an HPMC aqueous solution;

[0027] S3. Add the soaked and drained micro-active aggregate to the above dry powder and stir until well mixed. Add the remaining water, polycarboxylate superplasticizer mother liquor and HPMC aqueous solution, stir at medium speed, and after the slurry state is stable, add the AFt seed crystal water agent, continue stirring, and then add polypropylene fiber and polypropylene fiber and continue stirring until well mixed.

[0028] S4. Add the foam prepared by physical foaming with the nano foaming agent, stir again to obtain slurry, fill the slurry into the precast slab mold, and after curing, obtain foamed concrete precast slabs with rapid response drying environment of composite micro-active aggregate.

[0029] In the preparation method described above, preferably, in step S2, the alkaline environment is an alkaline solution with a pH value of 10-12, and the soaking time is 20-24 hours.

[0030] Furthermore, the alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution.

[0031] In the preparation method described above, preferably, in step S2, the AFt seed water agent is prepared by an ultrasonic disperser for a time of 30-90 seconds.

[0032] In a preferred embodiment, in step S4, the physical foaming preparation method is foaming with a foaming machine.

[0033] In a preferred embodiment, in step S4, before the mold is used, an extremely thin sheet of ordinary iron is attached to the five surfaces of the mold, and lubricant is applied between the iron sheet and the mold; the maintenance method is to cover and maintain for 3 to 7 days.

[0034] (III) Beneficial Effects

[0035] The beneficial effects of this invention are:

[0036] The foamed concrete material provided by this invention, which responds quickly to dry environments, actively and rapidly completes most of the shrinkage and strength increase under high-temperature curing conditions through chemical means, so that the product reaches a dimensionally stable state before leaving the factory.

[0037] (1) The foamed concrete precast slab with composite micro-active aggregate that responds to rapid drying environment provided by the present invention uses recycled micro powder and slag to replace part of the cement and solid waste cenospheres as micro-active aggregate, which not only helps to improve the shrinkage problem of foamed concrete precast slab, but also greatly improves the utilization rate of solid waste resources, providing an effective solution for solving the problem of waste building materials in prefabricated building production plants.

[0038] (2) The method for preparing precast foamed concrete slabs that respond to rapid drying environments provided by this invention utilizes a pretreatment method to treat micro-active aggregates, namely solid waste cenospheres, so that the solid waste cenospheres act as an open-cell skeleton in the foamed concrete to strengthen the matrix. At the same time, the micro-active aggregates will dissolve some aluminum ions to generate ettringite in the high sulfate system, improving the interface between the foamed concrete matrix and the aggregates. This structure responds quickly to high-temperature drying environments and can reduce the shrinkage cycle of foamed concrete.

[0039] (3) The method for preparing precast foamed concrete slabs responsive to rapid drying environments provided by this invention incorporates AFt seed crystals in the foamed concrete, thereby controlling the crystal growth process in the matrix and generating two mechanistic reactions. First, according to Oswald's ripening law, the aspect ratio of AFt crystals decreases when seed crystals are involved, and these AFt crystals are mostly concentrated at the interface between the aggregate and the matrix, which can effectively improve the interface strength and the matrix strength. Second, the seed crystals can increase the activity of the micro-active aggregates, thereby increasing the amount of crystalline phase products.

[0040] (4) Under the same strength standard, the matrix of this invention has a higher acceptance of the amount of building micro powder than the general method. Its performance advantage comes from the lightweight aggregate that presents a skeleton after the reaction. Attached Figure Description

[0041] Figure 1 The image shows the product prepared in Example 1 of this invention. Detailed Implementation

[0042] This invention provides a scheme for using micro-active aggregates as lightweight aggregates in foamed concrete. By increasing the proportion of sulfates in the foamed concrete and incorporating AFt seed crystals (ettringite seed crystals), a foamed concrete slab that can rapidly complete its shrinkage process at a high temperature of 35°C is designed. This overcomes the problem of long shrinkage cycles in existing foamed concrete slabs and improves the low strength of existing foamed concrete. In this invention, AFt seed crystals refer to ettringite seed crystals, whose full chemical name is trisulfide-type hydrated calcium sulfoaluminate. It is synthesized from raw materials such as calcium hydroxide, aluminum sulfate, and calcium sulfate under normal temperature or low-temperature hydrothermal conditions and can be obtained using conventional preparation methods.

[0043] This invention provides a precast foamed concrete slab utilizing a rapid drying environment with composite micro-active aggregates, prepared from the following raw materials in the indicated mass ratios: 300-600 parts cement, 150-300 parts blast furnace slag, 20-50 parts anhydrous calcium sulfate, 50-200 parts micro-active aggregates, 150-250 parts water, 7-10 parts polypropylene fiber, 5-7 parts polypropylene fiber, 100-300 parts recycled micro powder, 0.2-1 parts nano-foaming agent, 2-6 parts polycarboxylate superplasticizer mother liquor, 10-50 parts AFt seed crystals, and 0.1-0.2 parts hydroxypropyl methylcellulose. This invention fully utilizes solid waste blast furnace slag to replace conventional foamed concrete components, leveraging the characteristics of micro-active aggregates and the effects of seed crystals to improve the problems of low strength and long shrinkage period in traditional foamed concrete.

[0044] This invention, through extensive experimental research, has discovered that using AFt seed crystals (ettringite seed crystals) as templates or seeds for the hydration reaction significantly accelerates the formation rate of ettringite (AFt). There is no need to wait for the crystals to slowly nucleate; the hydration products grow rapidly directly on the foreign seed crystals. The high-temperature environment further provides energy for the hydration reaction, causing the reaction rate to increase exponentially. The combination of seed crystals and high temperature enables the explosive and rapid formation of ettringite.

[0045] In this invention, anhydrous calcium sulfate (CaSO4) and blast furnace slag (providing active Al2O3) are used in the Ca(OH)2 environment provided by cement hydration to generate ettringite (3CaO·Al2O3·3CaSO4·32H2O). The formation of ettringite is accompanied by a significant volume expansion (approximately 120%). The micro-active aggregate itself has low activity, but under high temperature and high alkalinity conditions, the active SiO2 and Al2O3 on its surface are activated and participate in the reaction. On the one hand, it provides the aluminum phase, which reacts with sulfate to generate more ettringite; on the other hand, its own slowly dissolving pores provide internal space for the growth of ettringite.

[0046] The method provided by this invention utilizes the synergistic expansion of sulfate and micro-active aggregates. During the high-temperature curing period, precisely controlled ettringite is rapidly generated. This orderly chemical expansion precisely offsets and compensates for subsequent physical drying shrinkage. It's equivalent to pre-applying compressive stress within the concrete, ensuring that during subsequent drying, only this compressive stress is released without generating tensile stress, thus fundamentally preventing cracking. Furthermore, it shortens the natural shrinkage cycle, which can take years, to a high-temperature curing period of tens of hours. This means the product is essentially stable at the factory, and significant shrinkage leading to cracking almost completely disappears after on-site installation. Because shrinkage is completed before leaving the factory, the stress at the joints of the wall panels is greatly reduced, virtually eliminating the possibility of through-cracks. This directly ensures the integrity of the wall and the long-term effectiveness of fire-retardant coatings, significantly improving the durability and safety of the building.

[0047] The polypropylene fibers used in this invention preferably have a diameter of 18-48 μm and a length of 6 mm, primarily serving to prevent cracking and inhibit the generation and propagation of microcracks during the plastic stage and early hardening. The polypropylene fibers used preferably have a diameter of 18-48 μm and a length of 6-12 mm, primarily serving to resist cracking and inhibit drying shrinkage cracks in the later stages of hardening. The combination of these two fibers forms a three-dimensional network from microscopic to macroscopic, providing a second line of defense on top of the ettringite expansion system, significantly improving toughness and crack resistance.

[0048] The recycled micro-powder used in this invention is made from crushed and ground waste concrete, used to fill pores, improve pore structure, and increase later-stage strength. The nano-foaming agent used is a composite foam stabilizer-type anionic surfactant foam powder, used to ensure the formation of a fine, uniform, and closed pore structure, guaranteeing lightweight and thermal insulation properties. Polycarboxylate superplasticizer and hydroxypropyl methylcellulose are used to ensure good fluidity and water retention of the slurry at low water-cement ratios, preventing bleeding and stratification, and ensuring a uniform system. Hydroxypropyl methylcellulose also has a foam-stabilizing effect.

[0049] The cement used in this invention serves as the main binder, providing basic bonding ability and early strength. Studies have found that insufficient cement (less than 300 parts) fails to meet strength requirements, while excessive cement (more than 600 parts) leads to increased costs, excessive heat of hydration, and excessive shrinkage. Therefore, the preferred cement content is 300-600 parts. The micro-active aggregate is high-alumina solid waste cenospheres, specifically fly ash cenospheres with an alumina content of 40%-50% and a particle size D50 of 100-300 μm. It fills the voids between cement particles, improves the particle size distribution of the cement paste, and increases the density of the cement paste, thereby enhancing the strength and durability of the cement. Excessive use may negatively impact the cementitious properties. Therefore, the preferred micro-active aggregate content is 50-200 parts. Water, as a necessary condition for cement hydration, directly affects the degree of hydration, workability, and strength development of the cement. Studies have found that insufficient water usage (less than 150 parts) prevents cement from fully hydrating, leading to reduced strength; excessive water usage (more than 250 parts) makes the cement paste too thin, affecting workability and potentially causing increased shrinkage and decreased strength. Therefore, the preferred water usage is 150-250 parts. Nanofoam is used to reduce the density of cement products and improve thermal insulation, heat preservation, and sound insulation properties; excessive usage (more than 40 parts) may cause foam instability and reduced product strength; insufficient usage (less than 20 parts) will not achieve the required lightweight and thermal insulation effects. Therefore, the preferred nanofoam agent usage in this invention is 0.2-1 parts. Polycarboxylate superplasticizer mother liquor has highly efficient water-reducing properties, significantly improving the fluidity of cement paste and workability without increasing water usage, while also reducing the water-cement ratio and improving the strength and durability of cement paste. Excessive usage may lead to concrete segregation and bleeding; therefore, the preferred polycarboxylate superplasticizer mother liquor usage in this invention is 2-6 parts. Excessive use of AFt seed crystals can adversely affect the later performance of cement. Therefore, the preferred amount of AFt seed crystals is 10 to 50 parts. Excessive use of hydroxypropyl methylcellulose may cause the cement paste to be too viscous, affecting the construction operation. Therefore, the preferred amount of hydroxypropyl methylcellulose is 0.1 to 0.2 parts.

[0050] In the foamed concrete precast slab described above, preferably, the cement is high-strength silicate 52.5 cement.

[0051] In the foamed concrete precast slab described above, preferably, the polypropylene fibers have a diameter of 18-48 μm and a length of 6 mm; the polypropylene fibers have a diameter of 18-48 μm and a length of 6-12 mm; the recycled micro powder has a particle size of 0.075-0.15 mm; the nanofoam is formed by physical foaming with a nanofoaming agent; the aluminum phase content of the blast furnace slag, calculated as alumina, is 15%-30 wt%; the solid phase content of the water-reducing agent mother liquor is 45-55 wt%; the AFt seed crystals are prepared by hydrothermal synthesis followed by wet milling with an appropriate amount of dispersant; the micro-active aggregate is high-alumina phase solid waste cenospheres modified with a certain amount of alkali solution; the curing environment is set at 35°C and 25% humidity; and hydroxypropyl methylcellulose is a white powder.

[0052] The preferred material is solid waste cenospheres, which should be soaked in an alkaline solution with a pH of 11-12 for 20-24 hours before use.

[0053] This invention also provides a method for preparing precast foamed concrete slabs that can rapidly respond to dry environments, mainly including the following steps:

[0054] S1. Material Preparation: Prepare materials according to the following components, by weight: cement 300-600 parts, blast furnace slag 150-300 parts, anhydrous calcium sulfate 20-50 parts, micro-active aggregate (solid waste cenospheres) 50-200 parts, water 150-250 parts, polypropylene fiber 7-10 parts, polypropylene fiber 5-7 parts, recycled micro powder (micro powder obtained from crushing and grinding waste concrete) 100-300 parts, nano foam powder 0.2-1 parts, polycarboxylate superplasticizer mother liquor 2-6 parts, AFt seed crystals 10-50 parts, hydroxypropyl methylcellulose 0.1-0.2 parts;

[0055] Step 2: Prepare the mold for the foam concrete board. Attach an extremely thin sheet of ordinary iron to the five surfaces of the mold and apply a layer of lubricant between the iron sheet and the mold.

[0056] Step 3: Soak the micro-active aggregate in an alkaline environment overnight for later use;

[0057] Step 4: Add cement, blast furnace slag, anhydrous calcium sulfate, and recycled micro powder into a twin-shaft mixer and mix (200~300 r / min) for 120~240 s until uniformly mixed;

[0058] Step 5: Add AFt seed crystals to 40-60% of the total water and 40-60% of the total polycarboxylate superplasticizer mother liquor, and disperse the water-soluble agent using an ultrasonic disperser for 30-90 seconds to obtain AFt seed crystal water-soluble agent;

[0059] Take 5-10% of the remaining water, heat it to 40-50℃, add hydroxypropyl methylcellulose (HPMC), stir until completely dissolved, and prepare an HPMC aqueous solution for later use.

[0060] Step 6: Add the soaked and drained micro-active aggregate to the above dry powder and stir evenly (200~300r / min) for 120~180s to ensure that the aggregate is evenly dispersed in the dry powder system; then add the remaining water, polycarboxylate superplasticizer mother liquor and HPMC aqueous solution, stir at medium speed (400~500r / min) for 100~120s. After the slurry is stable, add the AFt seed crystal aqueous solution prepared in step 5 and continue stirring for 120s~240s; add polypropylene fiber and polypropylene fiber, and continue stirring for 120~180s to mix evenly.

[0061] Step 7: Finally, add the nano foaming agent to the mixer to form physically foamed foam, stir again for 120-180 seconds, and pour into the precast slab mold. After curing for 3-7 days, you will get a foamed concrete precast slab with a rapid drying environment and composite micro-active aggregate response.

[0062] In the preparation method described above, preferably, the alkaline environment has a pH value of 10-12 and a soaking time of 20-24 hours.

[0063] This invention provides a precast foamed concrete slab with a composite micro-active aggregate that responds quickly to a drying environment. It utilizes building micro-powder and slag to replace cement in the preparation of the foamed concrete slab. This invention leverages the micro-active characteristics of the aggregate to form a skeletal structure that responds quickly to temperature and humidity, significantly shortening the shrinkage cycle of the foamed concrete. Furthermore, this invention incorporates AFt seed crystals into the foamed concrete, effectively improving the aggregate-matrix interface and solving the problem of severe strength reduction when adding aggregates to ordinary foamed concrete.

[0064] It should be noted that the aluminum phase content of the blast furnace slag in this invention is 16-20%, and the aluminum phase content refers to the mass content of aluminum oxide.

[0065] To better explain and facilitate understanding of the present invention, specific embodiments are described in detail below. All materials used in the following embodiments are commercially available products. The polypropylene fibers used have a diameter of 18-48 μm and a length of 6 mm; the polypropylene fibers have a diameter of 18-48 μm and a length of 6-12 mm; the recycled micro-powder has a particle size of 0.075-0.15 mm; the micro-active aggregate is fly ash solid waste cenospheres with an alumina content of 45%, and the solid waste cenospheres have a particle size of 100-300 μm; the nano-foaming agent is a composite foam stabilizer type anionic surfactant foam powder purchased from Zhongshan Yifa Building Materials Co., Ltd.

[0066] Example 1

[0067] This embodiment provides a method for preparing a precast foamed concrete slab that can quickly respond to a dry environment, which includes the following steps:

[0068] Step 1, Material Preparation: Prepare materials according to the following components, by weight: 420 parts high-strength silicate 52.5 cement, 180 parts blast furnace slag (aluminum phase content of 17%), 30 parts anhydrous calcium sulfate, 60 parts micro-active aggregate (solid waste cenospheres), 210 parts water, 8 parts polypropylene fiber, 6 parts polypropylene fiber, 150 parts recycled micro powder (micro powder obtained from crushing and grinding waste concrete), 0.8 parts nano foaming agent, 2 parts polycarboxylate superplasticizer mother liquor with 50% solid phase content, 16 parts AFt seed crystals, and 0.15 parts hydroxypropyl methylcellulose.

[0069] Step 2: Prepare the mold for the foamed concrete board. The mold is 2400mm long, 600mm wide, and 100mm high. Arrange the iron sheets on the five surfaces of the mold as required.

[0070] Step 3: Soak the micro-active aggregate in an alkaline environment (sodium hydroxide solution) with a pH of 11-12 for 24 hours;

[0071] Step 4: Pour the dry powder materials such as cement, blast furnace slag, anhydrous calcium sulfate, and recycled micro powder into a twin-shaft mixer and mix evenly to obtain dry powder material.

[0072] Step 5: Add AFt seed crystals to half of the total water volume and total water-reducing agent in the aqueous solution, and disperse using an ultrasonic disperser for 60 seconds to obtain AFt seed crystal aqueous solution; take 10% of the remaining water volume, heat to 45℃, add HPMC, stir until completely dissolved, and prepare HPMC aqueous solution for later use.

[0073] Step 6: Add the soaked and drained micro-active aggregate to the above dry powder, stir at 300 r / min for 180 s until uniform, then add the remaining water, water-reducing agent and HPMC aqueous solution, stir at 500 r / min for 100 s, and after the slurry is stable, add the AFt seed crystal aqueous solution prepared in step 5, continue stirring for 240 s, add polypropylene fiber and polypropylene fiber, and continue stirring for 150 s to mix evenly.

[0074] Step 7: Finally, add the physically foamed foam (nano foaming agent is foamed using a foaming machine) to the mixer, stir again for 150 seconds, and pour into the precast slab mold. Before use, a very thin sheet of ordinary iron is attached to the five surfaces of the mold, and a layer of lubricating oil is applied between the iron sheet and the mold. Curing is carried out at room temperature for 5 days to obtain a foamed concrete precast slab with a rapid drying environment and composite micro-active aggregate response, resulting in a product such as... Figure 1 As shown.

[0075] Example 2

[0076] This embodiment provides a method for preparing a precast foamed concrete slab that can quickly respond to a dry environment, which includes the following steps:

[0077] Step 1, Material Preparation: Prepare materials according to the following components, by weight: 360 parts high-strength silicate 52.5 cement, 180 parts blast furnace slag (aluminum phase content of 19%), 30 parts anhydrous calcium sulfate, 90 parts micro-active aggregate (solid waste cenospheres), 210 parts water, 8 parts polypropylene fiber, 6 parts polypropylene fiber, 150 parts recycled micro powder (waste concrete powder), 0.7 parts nano foam, 2 parts polycarboxylate superplasticizer mother liquor, 20 parts AFt seed crystals, and 0.15 parts hydroxypropyl methylcellulose.

[0078] Step 2: Prepare the mold for the foamed concrete board. The mold is 2400mm long, 600mm wide, and 100mm high. Arrange the iron sheets on the five surfaces of the mold as required. Before casting, attach a very thin ordinary iron sheet to the five surfaces of the mold and apply a layer of lubricating oil between the iron sheet and the mold.

[0079] Step 3: Soak the micro-active aggregate in a sodium hydroxide solution with a pH of 11 for 24 hours;

[0080] Step 4: Pour cement, slag, anhydrous calcium sulfate, and recycled micro powder into a twin-shaft mixer and mix evenly to obtain dry powder.

[0081] Step 5: Add AFt seed crystals (i.e., ettringite seed crystals) to half of the total water volume and total water-reducing agent, and disperse using an ultrasonic disperser for 60 seconds to obtain AFt seed crystal aqueous solution.

[0082] Take 10% of the remaining water, heat it to 50°C, add HPMC, and stir until completely dissolved to prepare an HPMC aqueous solution for later use.

[0083] Step 6: Add the soaked and drained micro-active aggregate to the above dry powder, stir at 250 r / min for 160 s, and after it is uniform, add the remaining water, water-reducing agent and HPMC aqueous solution, stir at 450 r / min for 120 s, and after the slurry is stable, add the AFt seed crystal aqueous solution prepared in step 5, continue stirring for 180 s, add polypropylene fiber and polypropylene fiber, and continue stirring for 160 s to mix evenly.

[0084] Step 7: Finally, add the physically foamed foam (the nano foaming agent is first foamed by a foaming machine) to the mixer, stir again for 120 seconds, and pour it into the precast slab mold. Cure at room temperature with a film for 5 days to obtain a foamed concrete precast slab with a rapid drying environment and composite micro-active aggregate response.

[0085] Example 3

[0086] This embodiment provides a method for preparing a precast foamed concrete slab that can quickly respond to a dry environment, which includes the following steps:

[0087] Step 1, Material Preparation: Prepare materials according to the following components, by weight: 350 parts high-strength silicate 52.5 cement, 170 parts blast furnace slag (aluminum phase content of 18%), 30 parts anhydrous calcium sulfate, 115 parts micro-active aggregate (solid waste cenospheres), 200 parts water, 8 parts polypropylene fiber, 6 parts polypropylene fiber, 130 parts recycled micro powder (waste concrete powder), 0.6 parts nano foam, 2 parts polycarboxylate superplasticizer mother liquor with 50% solid phase content, 20 parts AFt seed crystals, and 0.15 parts hydroxypropyl methylcellulose.

[0088] Step 2: Prepare the mold for the foamed concrete board. The mold is 2400mm long, 600mm wide, and 100mm high. Arrange the iron sheets on the five surfaces of the mold as required. Before casting, attach a very thin ordinary iron sheet to the five surfaces of the mold and apply a layer of lubricating oil between the iron sheet and the mold.

[0089] Step 3: First, soak the micro-active aggregate in a sodium hydroxide solution with a pH of 12 for 24 hours;

[0090] Step 4: Pour the dry powder materials such as cement, blast furnace slag, anhydrous calcium sulfate, and recycled micro powder into a twin-shaft mixer and mix evenly to obtain dry powder material.

[0091] Step 5: Add AFt seed crystals (i.e., ettringite seed crystals) to half of the total water volume and total water-reducing agent, and disperse using an ultrasonic disperser for 60 seconds to obtain AFt seed crystal aqueous solution.

[0092] Take 10% of the remaining water, heat it to 50°C, add HPMC, and stir until completely dissolved to prepare an HPMC aqueous solution for later use.

[0093] Step 6: Add the soaked and drained micro-active aggregate to the above dry powder, stir at 200 r / min for 150 s until uniform, then add the remaining water, water-reducing agent and HPMC aqueous solution, stir at 450 r / min for 120 s, and after the slurry is stable, add the AFt seed crystal aqueous solution prepared in step 5, continue stirring for 150 s, add polypropylene fiber and polypropylene fiber, and continue stirring for 180 s to mix evenly.

[0094] Step 7: Finally, add the physically foamed foam (the nano foaming agent is first foamed by a foaming machine) to the mixer, stir again for 160 seconds, and pour it into the precast slab mold. Cure at room temperature with a film for 7 days to obtain a foamed concrete precast slab with a rapid drying environment and composite micro-active aggregate response.

[0095] Comparative Example 1

[0096] This comparative example is based on Example 1, but without the addition of micro-active aggregates. The amount of cement used is 480 parts, and the other raw materials and preparation methods are the same as in Example 1.

[0097] Comparative Example 2

[0098] This comparative example is based on Example 1, but without the addition of AFt seed crystals, and the amount of cement is adjusted to 436 parts. The other raw materials and preparation methods are the same as in Example 1.

[0099] The obtained product was subjected to dry density, drying shrinkage test (environment set at 35℃ and 25% humidity) and compressive strength test according to the "Foamed Concrete" JG / T 266-2011. The test results are shown in Table 1 below.

[0100] Table 1: Test results of each embodiment and comparative example

[0101]

[0102] The dry density of the precast foamed concrete slabs prepared in Examples 1-3 of this invention is 730~825 kg / m³, all meeting the requirements for lightweight foamed concrete (typically ≤1000 kg / m³). It is evident that by replacing part of the cement with solid waste such as recycled micro-powder, blast furnace slag, and solid waste cenospheres, the utilization rate of solid waste is significantly improved (the total amount of solid waste accounts for more than 30% of the base material) without sacrificing the lightweight properties of the material, thus meeting the requirements of the dual-carbon strategy and green building materials. Under a dry environment of 35℃ and 25% humidity, the 28-day shrinkage value of Examples 1-3 is only 3.2~4.0 mm / m, far lower than the natural shrinkage of existing foamed concrete (typically ≥6 mm / m, lasting for months to years). This indicates that after the micro-active aggregate in this invention is pretreated with alkali, the dissolved Al2O3 synergistically forms ettringite with anhydrous calcium sulfate and cement hydration products, and its volume expansion (about 120%) can accurately compensate for drying shrinkage. In addition, by adding AFt seed crystals, the rapid nucleation and growth of ettringite is accelerated, and the originally long shrinkage process is concentrated within a 3-7 day curing period, so as to achieve dimensional stability of the product before it leaves the factory.

[0103] The product of this invention strengthens the matrix structure by adding micro-active aggregates to form an open-pore skeleton; AFt seed crystals reduce the aspect ratio of ettringite and are concentrated at the aggregate-matrix interface, improving the interfacial bonding strength; the composite of polypropylene fibers and polypropylene fibers inhibits the propagation of microcracks at different stages, balancing strength and toughness. Therefore, the 7-day compressive strength of Examples 1-3 is 7.5~8.5MPa, far exceeding the high-strength requirement (≥5.0MPa) in the standard "Foamed Concrete" JG / T 266-2011. In contrast, Comparative Example 1, without the addition of micro-active aggregates, has an increased cement content and a significantly higher dry density; without the reaction space and additional Al2O3 provided by aggregates, shrinkage compensation is insufficient, resulting in a significant increase in shrinkage value; the matrix support is weakened: without the reinforcement of the aggregate skeleton, the strength is significantly reduced, 20% lower than that of Example 1. In Comparative Example 2, the absence of AFt seed crystals resulted in slow nucleation and disordered growth of ettringite, making it impossible to complete shrinkage compensation during the curing period, with shrinkage values ​​approaching those of traditional foamed concrete. Without seed crystals to regulate ettringite distribution, the aggregate-matrix interface was weak, leading to a significant decrease in strength, 27% lower than in Example 1. The lack of seed crystals also hindered the full participation of surface-active SiO2 and Al2O3 in the reaction, reducing crystalline phase products and decreasing matrix density. Therefore, this demonstrates the synergistic effect of the micro-active aggregates and AFt seed crystals used in this invention; both are indispensable, jointly achieving breakthroughs in shrinkage compensation, strength enhancement, and rapid drying response. Solid waste substitution (recycled micro-powder, blast furnace slag, solid waste cenospheres) not only reduces raw material costs but also optimizes the material's pore structure and hydration process, representing a key design that balances environmental protection and performance. Fiber blending and admixture control (polycarboxylate superplasticizer, hydroxypropyl methylcellulose) further ensured slurry fluidity and foam stability, providing support for achieving the core performance.

[0104] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art can make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A foamed concrete material that responds quickly to dry environments, characterized in that, It contains the following components by weight: 300-600 parts cement, 150-300 parts blast furnace slag, 20-50 parts anhydrous calcium sulfate, 50-200 parts micro-active aggregate, 7-10 parts polypropylene fiber, 5-7 parts polypropylene fiber, 100-300 parts recycled micro powder, 0.2-1 parts nano foaming agent, 2-6 parts polycarboxylate superplasticizer mother liquor, 10-50 parts AFt seed crystals, and 0.1-0.2 parts hydroxypropyl methylcellulose.

2. The foamed concrete material as described in claim 1, characterized in that, It also contains 150-250 portions of water.

3. The foamed concrete material as described in claim 1, characterized in that, The cement is high-strength silicate 52.5 cement, and the aluminum phase content of the blast furnace slag is 16~20wt% based on alumina; the micro-active aggregate is solid waste cenospheres; the solid phase content of the polycarboxylate superplasticizer mother liquor is 45~55wt%; the nano foaming agent is a composite foam stabilizer type anionic surfactant foam powder.

4. The foamed concrete material as described in claim 1, characterized in that, The recycled micro powder is made from crushed and ground waste concrete, and the particle size of the recycled micro powder is 0.075~0.15mm.

5. The foamed concrete material as described in claim 1, characterized in that, The polypropylene fiber has a diameter of 18~48μm and a length of 6~8mm; the polypropylene fiber has a diameter of 18~48μm and a length of 6~12mm.

6. A method for preparing a precast foamed concrete slab that rapidly responds to a dry environment, characterized in that, It includes the following steps: S1. Prepare the raw materials according to the following mass parts: 300-600 parts cement, 150-300 parts blast furnace slag, 20-50 parts anhydrous calcium sulfate, 50-200 parts micro-active aggregate, 150-250 parts water, 7-10 parts polypropylene fiber, 5-7 parts polypropylene fiber, 100-300 parts recycled micro powder, 0.2-1 part nano foaming agent, 2-6 parts polycarboxylate superplasticizer mother liquor, 10-50 parts AFt seed crystals, and 0.1-0.2 parts hydroxypropyl methylcellulose; S2. Raw material pretreatment: Soak the micro-active aggregate in alkaline solution overnight for later use; Cement, blast furnace slag, anhydrous calcium sulfate and recycled micro powder are mixed evenly to obtain dry powder material; Add 40-60% of the total water and 40-60% of the total polycarboxylate superplasticizer mother liquor to the AFt seed crystals, and disperse them to prepare AFt seed crystal aqueous solution for later use; Hydroxypropyl methylcellulose is dissolved in 5-10% of the remaining total water to prepare an HPMC aqueous solution; S3. Add the soaked and drained micro-active aggregate to the above dry powder and stir until well mixed. Add the remaining water, polycarboxylate superplasticizer mother liquor and HPMC aqueous solution, stir at medium speed, and after the slurry state is stable, add the AFt seed crystal water agent, continue stirring, and then add polypropylene fiber and polypropylene fiber and stir until well mixed. S4. Add the foam that has been physically foamed by the nano foaming agent, stir again to obtain a slurry, fill the slurry into the precast slab mold, and after curing, obtain a foamed concrete precast slab with a rapid response drying environment of composite micro-active aggregate.

7. The preparation method according to claim 6, characterized in that, In step S2, the pH value of the alkaline solution is 10-12, and the soaking time is 20-24 hours.

8. The preparation method according to claim 6, characterized in that, In step S2, during the preparation of the AFt seed water agent, an ultrasonic disperser is used for dispersion treatment, and the ultrasonic time is 30~90s.

9. The preparation method according to claim 6, characterized in that, In step S4, the physical foaming is achieved by using a foaming machine to generate foam.

10. The preparation method according to claim 6, characterized in that, In step S4, before the mold is used, an extremely thin iron sheet is attached to the five surfaces inside the mold, and lubricating oil is applied between the iron sheet and the mold. The maintenance method is to cover the film for 3-7 days.

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