Multi-solid waste synergic autoclaved aerated concrete material and preparation method thereof

Abstract

This invention provides a multi-solid-waste synergistic autoclaved aerated concrete material and its preparation method, belonging to the field of solid waste resource utilization building materials technology. This invention uses solid waste aggregate, sludge residue, industrial solid waste powder, and desulfurized gypsum as raw materials. These materials are ground separately according to differences in hardness and activity, allowing the solid waste aggregate to retain coarse particles, while the sludge residue and desulfurized gypsum form a fine filler. This filler is then co-ground with the solid waste powder and aged in a sealed environment, allowing it to adhere to the surface of the solid waste aggregate to form a core-shell structure. Cement and lime are added, and pre-hydration with atomized water generates cementitious bridges. Aluminum powder paste is kneaded with desulfurized gypsum and then dry-mixed with lime to form a double-layer protective gas-generating agent. After main mixing, the material is poured, allowed to stand, and cut. The green body is cooled to a set temperature window through single-layer ventilation and then placed in an autoclave for gradient autoclaving curing to obtain the multi-solid-waste synergistic autoclaved aerated concrete material. This invention solves technical problems such as the difficulty in matching the synergistic activity of multiple solid wastes, insufficient strength stability of products with high waste content, and failure in controlling cracks in aerated concrete.

Description

Technical Field

[0001] This invention relates to the field of building materials technology for the resource utilization of solid waste, specifically to a multi-solid waste synergistic autoclaved aerated concrete material and its preparation method. Background Technology

[0002] Currently, the resource utilization of industrial solid waste in the autoclaved aerated concrete (AAC) field has made some progress, and the application of waste residues such as fly ash and desulfurized gypsum in AAC is becoming increasingly mature. However, when a large amount of solid wastes from different sources with different physicochemical properties are introduced into the same system at the same time, due to the significant differences in hardness, particle shape, water demand, and reactivity of each solid waste, simple blending or simultaneous grinding is insufficient to achieve matching and coordination of the particle size distribution and reaction sequence of each component. This results in poor slurry stability and difficulty in controlling the uniformity of pore structure under high waste residue content, leading to large fluctuations in product strength and high drying shrinkage.

[0003] To address the aforementioned issues, CN117486573B discloses an autoclaved aerated concrete (AAC) material, slab, and building structure. By introducing functional components such as inorganic hydrophobic agents, organic hydrophobic agents, and ionic liquid mineralizers, and combining carbonation with surface hydrophobic post-treatment, it achieves a significant reduction in the water absorption rate of AAC. However, achieving hydrophobic functionality through a large number of admixtures and relying on post-treatment processes to improve surface properties leads to complex raw material types and high costs. Furthermore, the hydrophobic effect is mainly concentrated on the surface and pore wall modification levels, failing to address the homogenization problem of multi-solid waste compound systems from the perspective of solid waste particle accumulation and interfacial reactions. CN119219373A discloses an autoclaved aerated concrete material and its preparation method. By adding graphene oxide to support calcium carbonate and graphene oxide, the nucleation-inducing effect of graphene oxide is used to generate a multi-level nano-needle structure inside the material to fill the capillary pores, which effectively reduces the drying shrinkage value. However, it relies on artificially synthesized nanomaterials as the functional core. Its preparation process involves two complex steps: graphene oxide synthesis and calcium carbonate loading. In large-scale production, there are dual constraints of cost and quality stability. Moreover, the scheme aims to compensate for the existing pore defects by nano-filling, but fails to reduce the generation of original defects from the perspective of synergistic activation of solid waste raw materials.

[0004] In summary, existing technologies still struggle to achieve high solid waste utilization, uniform pore structure, and stable product strength simultaneously when processing multiple solid wastes to co-prepare autoclaved aerated concrete without requiring large amounts of additives. Therefore, there is an urgent need to develop a co-preparation method based on the differences in the physical properties of solid wastes, including graded grinding, core-shell structure construction, double-layer gas-generating agent coating, and gradient autoclaving. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a multi-solid-waste synergistic autoclaved aerated concrete material and its preparation method. This invention uses solid waste aggregates, sludge residue, industrial solid waste powder, and desulfurized gypsum as raw materials. These materials are ground separately according to differences in hardness and activity, allowing the solid waste aggregates to retain coarse particles, while the sludge residue and desulfurized gypsum form a fine filler. This filler is then co-ground with the solid waste powder and aged in a sealed environment, allowing it to adhere to the surface of the solid waste aggregates and form a core-shell structure. Cement and lime are added, and pre-hydration with atomized water generates cementitious bridges. Aluminum powder paste is kneaded with desulfurized gypsum and then dry-mixed with lime to form a double-layer protective gas-generating agent. After main mixing, the material is poured, allowed to stand, and cut. The green body is cooled in a single layer to a set temperature window before being placed in an autoclave and cured under gradient autoclaving to obtain the multi-solid-waste synergistic autoclaved aerated concrete material. This invention solves technical problems such as the difficulty in matching the synergistic activity of multiple solid wastes, insufficient strength stability of products with high waste content, and failure in controlling cracks in aerated concrete.

[0006] This invention proposes a multi-solid-waste synergistic autoclaved aerated concrete material. The total amount of raw materials, excluding water, is 100 parts by weight. The solid raw materials are calculated on a dry basis, and the aluminum powder paste is calculated on a commercial wet paste basis. The raw materials include the following components: 28-42 parts of industrial solid waste powder, 8-16 parts of sludge residue, 3-8 parts of desulfurized gypsum, 8-14 parts of quicklime, 5-10 parts of cement, 0.05-0.15 parts of aluminum powder paste, and the remainder is solid waste aggregate; an additional 55-68 parts of total water are added, which includes 0.6-1.2 parts of atomized water and the remainder of main mixing water.

[0007] This invention also proposes a method for preparing autoclaved aerated concrete material with synergistic effects of multiple solid wastes, the specific technical solution of which is as follows: Step 1: After crushing and screening the solid waste aggregate, it is ground into coarse powder using low-energy grinding. Then, the sludge residue and desulfurized gypsum are mixed and ball-milled to obtain fine mixed powder.

[0008] Step 2: Coarse powder, fine mixed powder and industrial solid waste powder are put into a grinding mill for mixing and grinding. Then the material is transferred to a sealed container for static aging. After aging, the material is dry mixed with cement and quicklime. Then atomized water is sprayed in and stirred to pre-hydrate, so as to obtain pre-hydrated composite dry material.

[0009] Step 3: Take desulfurized gypsum and aluminum powder paste and knead them together. Then take quicklime and dry mix it with the kneaded material to obtain a double-layer protective gas-generating agent. Put the pre-hydrated composite dry material and the gas-generating agent into a mixer, add water and mix them. After primary and secondary mixing, pour the mixture into a mold.

[0010] Step 4: Place the poured material in a constant temperature environment for static curing. After curing, demold and cut the material. Then, ventilate and cool the cut material in a single layer and transfer it into an autoclave. After autoclaving in a heated isothermal platform and a high-temperature constant pressure section, the material is removed from the autoclave and cooled naturally to obtain the required concrete material.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The three-stage particle gradation system enables the coarse particle skeleton, fine filler and ultrafine active body to form a continuous particle size coverage in space. After the slurry is poured, the sedimentation of coarse particles is hindered by the suspension and support of fine particles. The reactivity of fine particles is fully exerted under autoclaving conditions and transformed into cement products, which grow on the surface of coarse particles and bind the coarse particles and the matrix into a whole.

[0012] 2. The double-layer aluminum powder coating structure in the gas generator delays the start of the gas generation process from the moment water is added. During the delay, the stirring paddle pushes the aluminum powder coating to all areas of the slurry to achieve spatial uniformity. Subsequently, concentrated gas generation is triggered synchronously in all areas. The density of nucleation sites of bubbles in the slurry tends to be consistent along all directions of the mold box, which reduces the probability of large-diameter defect holes and avoids the risk of local cracking caused by stress concentration at the edges of a few large holes.

[0013] 3. Under the anchoring effect of the cementitious bridge, the core-shell structure maintains a certain structural integrity in the initial stage of water addition and stirring, so that the shell layer of industrial solid waste powder gradually peels off and disperses in the slurry during the stirring process, rather than being released in a concentrated manner, resulting in local agglomeration and uneven dispersion. This avoids the delamination shrinkage and surface peeling defects caused by the difference in humidity between the surface and the interior due to the rapid evaporation of moisture on the surface of the green body in conventional processes.

[0014] 4. Under autoclaving conditions, the siliceous and calcareous components undergo hydrothermal reaction to generate crystals, which preferentially nucleate and grow to fill microcracks on the crack walls. This transforms the microcracks into whisker-interwoven suture bands. When the product is subjected to tensile stress, the whisker bridging and pull-out energy dissipation mechanism prevents the cracks from expanding into through cracks, thereby improving the bending strength and impact resistance of the sample. Attached Figure Description

[0015] Figure 1 The graphs show the changes in temperature and pressure over time during autoclaving of the plates in Example 10 and Comparative Example 10, where a is the graph of sample temperature changing over time and b is the graph of sample pressure changing over time. Figure 2 The images show crack scanning images of the plate material of Example 10 and Comparative Example 10 before and after autoclaving, where a is before autoclaving of Example 10, b is before autoclaving of Comparative Example 10, c is after autoclaving of Example 10, and d is after autoclaving of Comparative Example 10. Figure 3 A comparison diagram of the crack widths of the plate material in Example 10 and Comparative Example 10 before and after autoclaving. Figure 4 The graph shows the variation of the bond stress of the steel bars in Example 10 and Comparative Example 10 as a function of slip. Figure 5The images show local dry density distribution heatmaps of the plates from Examples 10 and Comparative Example 7, where a is the plate from the Examples and b is the plate from the Comparative Example. Detailed Implementation

[0016] The autoclaved aerated concrete material described below is further detailed, but this does not limit the scope of protection of this application, which is defined by the claims. Certain specific details disclosed provide a comprehensive understanding of the various disclosed embodiments. However, those skilled in the art will know that embodiments can be implemented using other materials, etc., without employing one or more of these specific details.

[0017] This invention proposes a method for preparing autoclaved aerated concrete material using a combination of solid wastes, the specific technical solution of which is as follows: 1. Separate grinding Solid waste aggregate and desulfurized gypsum were ground separately to obtain coarse-grained powder and fine-mixed powder with different particle sizes. The pore wall structure and strength of autoclaved aerated concrete depend on the balance between the bulk density of raw material particles and the hydrothermal reactivity. Solid waste aggregate is mainly composed of quartz, which has high hardness and strong chemical inertness. During autoclaving, it mainly exists as an unreacted residual skeleton phase. However, if the solid waste aggregate is ground to a fine particle size, it will not only lead to a significant increase in the water demand of the slurry, but also destroy its volume stability function as a rigid skeleton. Therefore, it is necessary to control the grinding endpoint of solid waste aggregate in the coarse particle range so that it can play a skeleton support role in the slurry and reduce the volume shrinkage during the gas generation and static curing stages.

[0018] Sludge and desulfurized gypsum have low hardness. After being ground to a fine particle size, their specific surface area increases and the surface defects of the particles increase. This accelerates the rate at which silicon, aluminum, and calcium ions dissolve in the subsequent hydrothermal reaction, allowing them to participate more fully in the formation of hydration products.

[0019] 2. Construction of a three-level particle size distribution system After mixing and grinding the three powders, the mixture is aged in a sealed environment. Structural reinforcement is then achieved through dry mixing with cement and quicklime, followed by pre-hydration with atomized water. Under the mechanical action of a grinding mill, industrial solid waste powder and solid waste aggregate particles undergo relative movement and collision. During kinetic energy transfer, the industrial solid waste powder is pushed onto the surface of the solid waste aggregate particles, forming a physical adhesion and creating a particle configuration with the solid waste aggregate as the core and the solid waste powder as the outer shell. During the sealed, static aging period, this adhesion state gains sufficient time without external mechanical disturbance. Van der Waals forces and electrostatic attraction stabilize the contact between the powder and aggregate, further solidifying the core-shell configuration. At this point, coarse particles act as the rigid core of the skeleton, fine particles are distributed in the gaps between the coarse particles, and ultrafine particles adhere to the surface of the coarse particles to form a shell layer, initially constituting the solid-phase skeleton of a three-level particle size distribution system.

[0020] The addition of cement and quicklime introduces calcareous components into the system. The added atomized water forms a thin water film at the particle contact points instead of free water, thereby triggering the surface hydration reaction of cement and quicklime. The resulting early-stage hydrated calcium silicate gel bridges span the interface between the solid waste powder shell and the solid waste aggregate core, transforming physical adhesion into chemical anchoring and mechanically reinforcing the core-shell structure. The pre-hydrated composite dry material retains the function of the solid waste powder shell gradually releasing during the initial stage of subsequent water addition and mixing, while avoiding secondary agglomeration of the powder during storage and transportation.

[0021] 3. Preparation of a double-layer protective gas-generating agent Separately, desulfurized gypsum and aluminum powder paste are kneaded together and coated with quicklime to form a double-layer protective gas-generating agent. This agent is then mixed with pre-hydrated composite dry material and poured into a mold. When the desulfurized gypsum is kneaded with the gas-generating aluminum powder paste, the surface of the aluminum powder particles is coated with desulfurized gypsum micro-powder. Subsequently, when quicklime is dry-mixed with the kneaded material, the lime powder is further adsorbed onto the outside of the gypsum layer. After the aluminum powder particles are sequentially coated by the desulfurized gypsum and quicklime, a double-layer coated gas-generating agent is formed, blocking the contact between its surface and water and alkaline substances. When the gas-generating agent is added to the mixer in dry powder form, the coating layer is consumed sequentially after water is added, causing the aluminum powder surface to be exposed to water lag behind the water addition time. During this lag, the stirring action ensures that the gas-generating agent particles achieve a uniform spatial distribution in the slurry.

[0022] When the pre-hydrated composite dry material and the gas-generating agent are added to the mixer and mixed with water, the slurry gradually becomes homogenized, and the gas-generating agent particles migrate to different areas with the flow of the slurry. After being poured into the mold, the gas-generating reaction starts simultaneously in all areas of the slurry. Hydrogen nucleates on the surface of the aluminum powder particles and forms bubbles. These bubbles rise in the slurry and drive its expansion. The water in the slurry serves as both the hydration reaction medium and the gas-generating reaction medium. The hydration reaction causes the slurry to gradually lose its fluidity, while the hydrogen produced by the gas-generating reaction forms bubbles in the slurry and drives its expansion and solidification. Because the gas-generating agent is evenly distributed in the slurry and each particle starts gas generation simultaneously, the nucleation density of bubbles is consistent in all areas of the mold, and the expansion process of bubbles in each area proceeds synchronously. After the slurry loses its fluidity, the bubbles are fixed in the matrix, forming closed spherical pores. The pore walls are composed of hydration products and unreacted particles. The pore wall thickness between adjacent pores is uniform, with no through-holes. The porosity phase is solidified inside the product.

[0023] 4. Hydrothermal curing After casting, the material is kept at a constant temperature for static curing and gas generation before being cut, cooled, and then placed in an autoclave for steam pressure curing. Finally, it is cooled to obtain the finished product. The cast slurry undergoes hydration and gas generation reactions simultaneously in a constant temperature environment. The hydration reaction causes the slurry to gradually lose its fluidity and gain strength, while the hydrogen produced by the gas generation reaction forms bubbles in the slurry and drives its expansion. At the same time, the rates of the two reactions must be kept in harmony so that the bubbles complete their expansion and shaping before the slurry loses its fluidity.

[0024] After reaching the required cutting strength, the material is demolded and cut to the target size. However, the cut body still contains a large amount of unreacted active components and free water. Single-layer ventilation cooling allows the body to cool down under uniform humidity. By controlling the temperature difference between the surface and inner layers of the body, through-cracks that cannot be repaired are avoided. Autoclaving after entering the autoclave utilizes a combination of a heated isothermal platform and a high-temperature constant-pressure section, allowing the siliceous and calcareous components to react under hydrothermal conditions to generate hydration products. During this process, the micro-powder shell layer adhering to the surface of the solid waste aggregate transforms into tobermorite and hydrated calcium silicate crystals. This crystal layer adheres to the surface of coarse particles and extends outward into the matrix, continuously contacting the surrounding hydration product matrix, forming the interface transition phase between the skeleton core and the matrix. Simultaneously, the hydration products preferentially nucleate and fill micro-defects on the walls of some micro-cracks. After depressurization and exiting the autoclave, the hydration products remain stable, thus obtaining the desired concrete material.

[0025] The present invention can be better understood from the following embodiments and comparative examples. However, those skilled in the art will readily understand that the descriptions in the embodiments are for illustrative purposes only and should not, and will not, limit the invention as described in detail in the claims. Table 1 provides basic information on the raw materials used in the embodiments.

[0026] Table 1 Raw Material Information Table

[0027] Example 1

[0028] This embodiment uses 1000 kg of raw materials excluding water, and employs the following raw materials: 300 kg of silt, 120 kg of sludge and waste residue, 54 kg of desulfurized gypsum, 340 kg of Class II fly ash, 80 kg of P·O42.5 ordinary Portland cement, 105 kg of quicklime, and 1.0 kg of aluminum powder paste. Of the desulfurized gypsum, 48 kg is used for ball milling with the sludge and waste residue, 6 kg is used for the inner coating of the aluminum powder paste, 90 kg of quicklime is used for pre-hydration of the composite dry material, and 15 kg is used for the outer coating of the aluminum powder paste. An additional 585 kg of water is added, including 10 kg of atomizing water and 575 kg of main mixing water.

[0029] S1: Dry the silt to a moisture content of no more than 1.0%, crush it with a jaw crusher, and then screen it through a 5mm vibrating screen. The undersize material is fed into a low-energy rod mill and ground at 20r / min for 40min. The intermediate fraction of 200~500μm is taken as coarse powder. Then, 120kg of sludge waste residue and 48kg of desulfurized gypsum are mixed and fed into a ball mill with a ball-to-material ratio of 6:4. The mixture is ball-milled at 25r / min for 30min. The output is screened through a 45μm sieve and the undersize material is taken as fine mixed powder.

[0030] S2: The coarse powder and fine mixed powder obtained in S1 are fed together with 340 kg of fly ash into a scrubbing mill. The scrubbing mill is filled with 35% zirconia microspheres. Then, it is ground at 120 r / min for 12 min. After discharge, it is transferred to a sealed container and left to stand and age for 24 h at 25℃ and 65% relative humidity. After aging, 80 kg of cement and 90 kg of quicklime are added to the material and dry-mixed at 40 r / min for 2 min. Then, 10 kg of atomized water is sprayed in through a 0.5 mm nozzle at a pressure of 0.4 MPa. Then, it is stirred at 40 r / min for 15 min to obtain the prehydrated composite material.

[0031] S3: Take another 6 kg of desulfurized gypsum and 1 kg of aluminum powder paste and put them into a kneader. Knead them at 50 r / min for 5 min at 30℃ to obtain an inner layer coated with aluminum powder. Then add 15 kg of quicklime and dry mix it with the kneaded material at 40 r / min for 4 min to obtain a double-layer protective gas generating agent with a gas generation start delay time of 25~30 s. Put the pre-hydrated composite material and the double-layer protective gas generating agent obtained in S2 into a mixer and add 575 kg of main mixing water. First, stir at a low speed of 60 r / min for 60 s, then stir at a high speed of 120 r / min for 120 s. Then pour the slurry into a 600 mm × 240 mm × 100 mm steel mold.

[0032] S4: Place the mold in a static curing chamber at 48℃ and relative humidity ≥90% for 3 hours. After the compressive strength of the green body reaches 0.3MPa, cut it into 600mm×200mm×100mm blocks using 0.8mm steel wire at a speed of 2.0m / min. Then place the blocks on a ventilated rack with a layer spacing of 300mm and ventilate them in a single layer at 25℃ and relative humidity 65% ​​for 30 minutes to uniformly cool the temperature, so that the temperature at the center of the green body drops to 35~45℃ and the temperature difference between the center and the surface is ≤8℃. Then transfer the green body into an autoclave and evacuate the autoclave to -0.07MPa. Gradient autoclaving is performed by introducing saturated steam. The first gradient is to raise the temperature to 115℃ at 1.2℃ / min and hold for 30 min. The second gradient is to raise the temperature to 145℃ at 0.8℃ / min and hold for 30 min. Finally, the third gradient is to raise the temperature to 185℃ at 0.6℃ / min. The autoclave is then kept at constant temperature and pressure for 6.5 h. After the curing is completed, the steam is turned off and the pressure is reduced to 0.1 MPa at 0.3 MPa / min. The pressure is then naturally reduced to atmospheric pressure and the temperature inside the autoclave does not exceed 80℃. The autoclave is then opened and the product is removed. After naturally cooling to 25℃, the desired autoclaved aerated concrete material is obtained.

[0033] Example 2

[0034] The difference from the preparation method in Example 1 is as follows: S1: Take 299.5 kg of silt, 160 kg of sludge and waste residue, and 72 kg of desulfurized gypsum; S2: Take 280 kg of fly ash, 100 kg of cement, 70 kg of quicklime, and spray in 6 kg of atomized water; S3: Take another 8 kg of desulfurized gypsum, 0.5 kg of aluminum powder paste, and 10 kg of quicklime to obtain a double-layer protective gas generator with a gas generation start delay time of 15~20 s. Add 544 kg of process water. All other steps are the same.

[0035] Example 3

[0036] The difference from the preparation method in Example 1 is as follows: S1: Take 278.5 kg of silt, 80 kg of sludge and waste residue, and 27 kg of desulfurized gypsum; S2: Take 420 kg of fly ash, 50 kg of cement, 120 kg of quicklime, and spray in 10 kg of atomized water; S3: Take another 3 kg of desulfurized gypsum, 1.5 kg of aluminum powder paste, and 20 kg of quicklime to obtain a double-layer protective gas generator with a gas generation start delay time of 35~40 s. Add 670 kg of process water. All other steps are the same.

[0037] Example 4

[0038] The difference from the preparation method in Example 1 is as follows: S1: Grinding time is 30 min, ball-to-material ratio is 5:4, ball mill speed is 20 r / min, and ball milling time is 25 min; S2: The spindle speed of the grinding machine is 110 r / min, the grinding time is 10 min, the aging temperature is 20℃, the aging time is 20 h, the diameter of the atomizing water nozzle is 0.2 mm, the spraying pressure is 0.2 MPa, the pre-hydration stirring speed is 30 r / min, and the time is 10 min; S3: Kneading temperature is 20℃, kneading time is 2min, low speed mixing time is 45s, and high speed mixing time is 90s; S4: Curing temperature 45℃, curing time 2h, blank strength at cutting time 0.2MPa, cutting speed 1.5m / s, first gradient curing temperature 110℃, curing time 20min, second gradient curing temperature 135℃, curing time 20min, third gradient curing temperature 175℃, curing time 5h, the remaining steps are the same.

[0039] Example 5

[0040] The difference from the preparation method in Example 1 is as follows: S1: Grinding time is 45 min, ball-to-material ratio is 8:4, ball mill speed is 40 r / min, and ball milling time is 45 min; S2: The spindle speed of the grinding machine is 150 r / min, the grinding time is 20 min, the aging temperature is 35℃, the aging time is 30 h, the diameter of the atomizing water nozzle is 0.7 mm, the injection pressure is 1.0 MPa, the pre-hydration stirring speed is 60 r / min, and the stirring time is 25 min; S3: Kneading temperature is 35℃, kneading time is 8min, low speed mixing time is 90s, and high speed mixing time is 180s. S4: Curing temperature 60℃, curing time 5h, blank strength at cutting time 0.5MPa, cutting speed 3m / s, first gradient curing temperature 130℃, curing time 45min, second gradient curing temperature 160℃, curing time 45min, third gradient curing temperature 200℃, curing time 8h, the remaining steps are the same.

[0041] Example 6

[0042] The difference from the preparation method in Example 1 is as follows: S1: Replace the silt with quartz sand, and the rest of the steps are the same.

[0043] Example 7

[0044] The difference from the preparation method in Example 1 is as follows: S2: Replace fly ash with slag powder, and the rest of the steps are the same.

[0045] Example 8

[0046] The difference from the preparation method in Example 1 is as follows: S1: Replace the silt with river sand, and the rest of the steps are the same.

[0047] Example 9

[0048] The difference from the preparation method in Example 1 is as follows: S2: Replace fly ash with zeolite powder, and the rest of the steps are the same.

[0049] Example 10

[0050] The difference from the preparation method in Example 1 is as follows: S3: Replace the casting mold with a 6500mm×650mm×200mm steel mold with a corrosion-resistant steel mesh placed inside; S4: Cut the blank into plates with dimensions of 6000mm×600mm×200mm. The remaining steps are the same.

[0051] Comparative Example 1 The difference from the preparation method in Example 1 is as follows: S1: Mix 300kg of silt, 120kg of sludge residue, 48kg of desulfurized gypsum, and 340kg of fly ash together and then put them into a ball mill to ball mill until D50=25μm; S2: Directly age the mixture obtained in S1, and the remaining steps are the same.

[0052] This comparative example prepares concrete material without tertiary particle size distribution.

[0053] Comparative Example 2 The difference from the preparation method in Example 1 is as follows: S3: Without adding desulfurization gypsum and quicklime, use an equal mass of silt to make up the difference. Directly add 1 kg of aluminum powder paste to the mixer and mix it with the pre-hydrated composite dry material. All other steps are the same.

[0054] This comparative example prepares a concrete material with a double-layer encapsulated structure of aluminum powder-free foaming agent.

[0055] Comparative Example 3 The difference from the preparation method in Example 1 is as follows: S2: After aging, dry mix with cement and quicklime, without spraying in atomized water, and the rest of the steps are the same.

[0056] This comparative example demonstrates the preparation of concrete materials for cementless bridge anchorage.

[0057] Comparative Example 4 The difference from the preparation method in Example 1 is as follows: S4: For autoclaving, the 115℃ and 145℃ heat preservation platforms are eliminated. Instead, the temperature is directly increased to 185℃ at a rate of 0.6℃ / min for constant temperature and pressure curing. All other steps are the same.

[0058] This comparative study demonstrates the preparation of concrete materials without microcrack repair.

[0059] Comparative Example 5 The difference from the preparation method in Example 1 is as follows: S2: After grinding and extruding, the material is not sealed and aged. It is directly dry-mixed with cement and quicklime, and then sprayed with atomized water for stirring. The remaining steps are the same.

[0060] This comparative study demonstrates the preparation of core-shell-free concrete materials.

[0061] Comparative Example 6 The difference from the preparation method in Example 1 is as follows: S3: After the desulfurized gypsum and aluminum powder paste are kneaded together, no quicklime is added. The missing mass is made up by silt. All other steps are the same.

[0062] This comparative example prepares a concrete material lacking an outer lime protective shell and a gas-generating agent.

[0063] Comparative Examples 7-12 The difference from the preparation method in Example 10 is that: Boards were prepared according to the differences in Comparative Examples 1 to 6.

[0064] Experimental Example 1 According to GB / T 11968-2020 "Autoclaved Aerated Concrete Blocks" and GB / T 11969-2020 "Test Methods for Performance of Autoclaved Aerated Concrete", 100mm×100mm×100mm cubic specimens were cut from the middle of the concrete blocks prepared in Examples 1-9 and Comparative Examples 1-6 using a cutting machine. The specimens were placed in an electric heating drying oven and dried at 65℃ to constant weight. After being removed and cooled to room temperature, a pressure testing machine was used to continuously and uniformly load the specimen at a loading rate of 2.5kN / s until the specimen failed. The failure load value F was recorded, and the compressive strength was calculated according to the formula f=F / A, where f is the compressive strength and A is the area of ​​the specimen subjected to pressure.

[0065] 100mm×100mm×100mm cubic specimens were cut from the middle of the concrete blocks prepared in Examples 1-9 and Comparative Examples 1-6 using a cutting machine. The specimens were placed in an electric heating drying oven and dried at 65°C until the difference between two consecutive weighings did not exceed 0.1%. The specimens were then removed and placed in a desiccator to cool to room temperature. The dry mass of each specimen was then weighed, and the dimensions and volume of each specimen were measured to calculate the dry density of the sample.

[0066] Table 2 Compressive strength and dry density of blocks from the examples and comparative examples

[0067] As can be seen from Table 2, the compressive strength of the concrete blocks prepared in the examples is higher than that in the comparative examples, and the dry density is lower than that in the comparative examples. This indicates that the process in the examples achieves continuous stacking of coarse skeleton and fine filler through three-level particle gradation, slow-release dispersion of fly ash and time-sequential release of silt moisture through core-shell structure and cement bridge anchoring, uniform gas generation starting point and consistent bubble nucleation density through double-layer aluminum powder coating, and selective filling and repair of microcracks by hydrothermal products through cooling pre-cracking and gradient autoclaving. The synergistic effect of each process step enables the product to obtain higher strength at a lower density.

[0068] Comparative Example 1 did not undergo separate grinding. All four types of solid waste were ball-milled to a uniform particle size. The silt did not retain a coarse skeleton. After the slurry was poured, the coarse particles settled without the support of fine particles. After hardening, the density of the product was unevenly distributed along the height direction. At the same time, excessive grinding of fly ash led to a reduction in surface active sites and insufficient generation of hydration products, thus limiting the improvement of strength.

[0069] Comparative Example 2 did not undergo aluminum powder paste coating. The aluminum powder was added directly to the mixer and generated gas prematurely before the slurry was evenly distributed. The bubbles became excessively concentrated in certain areas and merged into large pores. Under pressure, the stress concentrated at the edge of the large pores and expanded preferentially. After hardening, the pore structure was uneven, so the strength could not be effectively exerted.

[0070] Comparative Example 3 did not undergo pre-hydration with atomized water. There was no cementitious bridge anchoring between the fly ash shell and the silt core. After adding water and stirring, the core-shell structure disintegrated instantly upon contact with water. The fly ash was released in the form of agglomerates. The silt core released adsorbed water in advance, disrupting the water-solid ratio balance. The hydration products were unevenly distributed, resulting in inconsistent matrix density after hardening.

[0071] Comparative Example 4, which was cured by autoclaving without an isothermal platform, had no silicon-rich surface deposits on the crack walls. The nucleation and induction periods of crystals on the crack walls and inside the matrix were the same in the high-temperature section. Microcracks could not be selectively filled and remained open, resulting in a reduced effective load-bearing cross-sectional area. Under pressure, stress was concentrated at the crack tips and could not be dissipated through whisker bridging. Therefore, the compressive strength was lower than that of the example and the dry density was increased.

[0072] Comparative Example 5 was not subjected to sealed aging, and the fly ash powder did not have sufficient static time to complete the adhesion on the silt surface. The core-shell structure was missing, the fly ash existed in a free state and agglomerated during stirring, the activity of the pozzolanic ash could not be fully exerted, and the amount of hydration products generated was insufficient. Therefore, the compressive strength was lower than that of the example and the dry density was increased.

[0073] Comparative Example 6 did not undergo dry mixing with quicklime on the outer layer. The aluminum powder was only coated with a single layer of desulfurized gypsum. Without the dual protection of heat release and delayed penetration from lime hydration, the gypsum layer dissolved rapidly in the alkaline slurry. The aluminum powder was exposed prematurely and generated gas in advance. The density of bubble nucleation was inconsistent along the direction of the mold box. After hardening, the uniformity of the pore structure was poor, and the effective load-bearing cross-sectional area was unevenly distributed. Therefore, the mechanical properties were worse than those of the Example and the dry density was larger.

[0074] Experimental Example 2 According to GB / T 15762-2020 (XG1-2022) "National Standard for Autoclaved Aerated Concrete Slabs - Amendment No. 1", concrete slabs prepared in Example 10 and Comparative Examples 7-12 were supported on a test bench. The calculated span was 95% of the slab's design length. A concentrated load was applied at the mid-span using a surcharge method, with each load being 10% of the estimated ultimate load. After holding the load for 5 minutes, the mid-span deflection value was recorded. Loading continued until the slab showed initial cracks, and the initial crack load and deflection were recorded. Loading continued until the slab failed, and the ultimate failure load and maximum deflection were recorded. The sample bearing capacity test coefficient was calculated based on the ratio of the ultimate failure load to the design load.

[0075] Specimens containing a single longitudinal steel bar were cut along the length of the concrete slabs prepared in Examples 10 and 7-12, respectively. Each end of the steel bar was left with a length of not less than 100 mm for clamp installation. The specimens were placed on a material testing machine, with the steel bar perpendicularly passing through the hole in the center of the perforated iron plate. The top end was aligned with the upper end of the steel bar, ensuring that the axes of the top end, the steel bar, and the hole in the iron plate were perpendicularly coincident. The testing machine was started and a downward load was applied at a speed of 100-150 N / s to push the steel bar out of the aerated concrete matrix. The maximum load value F during the pushing process was recorded. The adhesion force of the steel bar was calculated according to the formula τ=F / (π·d·l), where d is the nominal diameter of the steel bar and l is the actual length of the steel bar embedded in the aerated concrete matrix.

[0076] Table 3. Bending load and steel reinforcement adhesion of the plates in the examples and comparative examples

[0077] As can be seen from Table 3, the concrete slab prepared in Example 10 has better load-bearing capacity, maximum deflection, and steel reinforcement adhesion than the comparative example, indicating that the synergistic effect of each step of the process in Example 10 improves the slab in terms of load-bearing capacity, flexural stiffness, and interfacial bonding strength.

[0078] Comparative Example 7 did not undergo separate grinding, and the silt did not retain a coarse particle skeleton. After pouring, the settlement of coarse particles led to an increase in the density gradient along the thickness direction of the slab, resulting in a dense lower layer and a loose upper layer. During pouring, the steel mesh underwent slight displacement due to local slurry density fluctuations, which reduced the uniformity of the surrounding matrix. After hardening, the bond force between the matrix and the steel bars was uneven at different cross-sections along the slab length. Under load, the path of stress transmission from the steel bars to the matrix was discontinuous. At the same time, the density gradient also reduced the flexural stiffness of the slab.

[0079] In Comparative Example 8, the aluminum powder paste was not coated. The aluminum powder generated gas prematurely before the slurry was evenly distributed in space. The bubbles gathered around the steel mesh and formed large, interconnected or semi-connected pore defects. The actual contact area between the steel surface and the matrix was reduced. Local pores in the interface area disrupted the bond continuity. Under load, the shear force transmission between the steel and the matrix was hindered. At the same time, the large pore defects served as strain concentration areas during bending deformation, which increased the deflection.

[0080] In Comparative Example 9, no atomized water pre-hydration was performed. The core-shell structure disintegrated instantly upon contact with water, causing fly ash to be released in the form of agglomerates. The particles inside the agglomerates could not be hydrated, resulting in weak phase regions in the matrix. These weak phase regions were the first to generate microcracks and propagate when the plate was subjected to bending loads. At the same time, the stress fields of the weak phase regions and the steel-matrix interface were superimposed. When the local interface shear stress exceeded the adhesion limit, interface debonding occurred prematurely, resulting in a decrease in load-bearing capacity and an increase in deflection.

[0081] In Comparative Example 10, the autoclaving was not performed with an isothermal platform. Microcracks were not filled and repaired during the curing process. Open cracks formed through or semi-through weak surfaces inside the plate. If microcracks exist at the interface between the steel reinforcement and the matrix, they directly reduce the effective adhesion area. At the same time, these cracks expand rapidly under bending loads and connect with the stress field around the steel reinforcement, resulting in decreased adhesion, reduced load-bearing capacity, and increased deflection.

[0082] Comparative Example 11 was not subjected to sealed aging, and the lack of a core-shell structure caused the fly ash to exist in a free state and agglomerate during stirring. The amount of matrix hydration products generated was insufficient and the distribution was severely uneven, resulting in extremely low overall strength. The interface transition zone between the steel reinforcement and the matrix became the weakest link due to the lack of sufficient hydration products for bonding, resulting in severely insufficient adhesion. At the same time, the extremely low-strength matrix cracked rapidly when bent, exhibiting the lowest load-bearing capacity and the highest deflection.

[0083] Comparative Example 12 did not undergo external lime dry mixing. The aluminum powder was only coated with a single layer of gypsum and then dissolved rapidly in the alkaline environment. The inconsistent exposure time of the aluminum powder resulted in large differences in the nucleation density of bubbles along the direction of the mold box, and extremely poor uniformity of the pore structure. In some areas around the reinforcing bars, loose zones were formed due to excessive accumulation of bubbles. The bonding between the matrix and the reinforcing bars in the loose zones was almost ineffective, and the adhesion was extremely low. At the same time, the presence of loose zones also caused the deformation of the plate to be concentrated in these areas under bending loads.

[0084] Experimental Example 3 The concrete slab prepared in Example 10 is denoted as H, and the concrete slab prepared in Comparative Example 10 without gradient autoclaving is denoted as C1. Before casting the samples, small-diameter K-type thermocouples resistant to autoclaving are placed. Three stations are set along the length of the slab, 500 mm from each end and at the middle. Each station has a central measuring point 100 mm from the top surface and a near-surface measuring point 5 mm from the top surface. An additional steam temperature measuring point is set inside the autoclave. After the sample is ventilated and homogenized, it is placed in the autoclave. The thermocouple leads are passed through the autoclave body using a pressure-resistant connector. The autoclave temperature, surface temperature, center temperature, and pressure are continuously recorded at 5-minute intervals using a data acquisition device. The integral of the center-surface temperature difference is calculated to compare the differences in the thermal history between the two groups. Figure 1 As shown.

[0085] Figure 1In Figure a, the temperature at each measuring point of samples H and C1 changes over time, and in Figure b, the pressure changes over time. It can be seen that at 115℃ and 145℃, both the autoclave temperature and pressure of sample H plateaued. The temperature at the center of the billet continuously caught up with the surface temperature on these plateaus. When entering the high-temperature section at 185℃, the temperature difference between the center and the surface was minimal. However, sample C1 skipped the plateau and directly heated up, so the center temperature never kept up with the surface temperature. When entering the high-temperature section, the difference between the two was significant. This indicates that the isothermal plateau of gradient autoclaving provides time for heat to be conducted from the surface to the center, making the internal temperature of the billet as uniform as possible before entering the high-temperature section. This reduces the difference in thermal expansion and contraction at various points in the cross-section and lowers residual stress.

[0086] Experiment Example 4 Micropillars measuring 3mm × 3mm × 8mm were cut from samples H and C1 using a low-vibration diamond wire saw, prioritizing those containing natural microcracks. After cutting, they were placed in thin-walled polyimide sleeves. Three 100-200μm zirconia spheres were fixed on the sample holder as external registration markers. A high-resolution CT scan was performed before autoclaving. The seal was then removed, and the micropillars were placed in porous alumina or PEEK heat-resistant sample baskets. They were cured in the same autoclave as the H and C1 plates, respectively. After removal from the autoclave, they were allowed to cool naturally to room temperature and re-mounted in the same CT sample holder. A post-autoclaving scan was performed using the same parameters. Global affine registration was first performed to compensate for overall shrinkage, followed by local rigid registration of the crack ROI. Thirty cross-sections were selected at equal intervals on the same crack skeleton, and the width was calculated using a local thickness algorithm. The sample mean was used as an independent replicate for statistical comparison. The scanning results and statistical results are shown below. Figures 2-3 As shown.

[0087] from Figure 2 As can be seen, before steaming, sample H had a clear and continuous dark crack line. After steaming, the crack line was largely filled by hydrothermal products, and the two walls were almost in contact. Sample C1 also had a clear crack before steaming. After steaming, although the crack became thinner, the dark line was still clearly distinguishable and the path was continuous, indicating that the crack was not effectively filled and remained open.

[0088] from Figure 3 As can be seen, the crack width of sample H decreased significantly before and after autoclaving, while the crack width of sample C1 did not change much. This indicates that due to gradient autoclaving, the crack wall of sample H preferentially adsorbed silicate ions to form a silica-rich surface layer during the heating stage. In the high-temperature stage, the nucleation induction period of tobermorite on the crack wall was shorter than that inside the matrix. Therefore, the crystals preferentially grew inward and filled the crack. In contrast, no silica-rich layer was deposited on the crack wall of sample C1. The crystals grew synchronously on the crack wall and inside the matrix, without selective filling. Therefore, the repair effect on the crack was limited.

[0089] Experimental Example 5 Specimens were cut from the plates of samples H and C1 along the longitudinal reinforcement, with each single reinforcement bar positioned at the center of the cross-section, exposing at least 100 mm of reinforcement at each end, and retaining 100 mm of effective bond length in the middle. The specimens were placed on a rigid bearing plate with a central hole, and two LVDTs were positioned on either side of the free end of the reinforcement bar to measure the slippage of the reinforcement bar relative to the matrix. During loading, a 50 N preload was applied, followed by a loading rate of 120 N / s to approximately 80% of the estimated peak value. Displacement control was then switched to 0.10 mm / min until a slippage of 1.20 mm was achieved. Load and slippage data were collected simultaneously. The bond stress was calculated using τ = F / (π·d·l), and the bond stress-slip curve was plotted. Figure 4 As shown.

[0090] The slab prepared in Comparative Example 7 was designated C2. Samples H and C2 were equilibrated in the same environment until their mass stabilized. Two-dimensional attenuation data (length-thickness) were obtained using X-ray transmission scanning. Measurement areas were set every 250 mm along the length direction, and a 25×11 grid was formed by layering samples every 20 mm along the thickness direction. An attenuation-dry density calibration curve was established using a standard aerated concrete block with known dry density. After moisture content correction, the local equivalent dry density at each grid point was calculated. Samples were taken from at least 10 representative locations, and the measured dry density was used for verification; the difference was not to exceed 15 kg / m³. 3 The calibration is considered valid, and the final output is a thermal map of the dry density distribution of the board material, as shown in the following figure. Figure 5 As shown.

[0091] from Figure 4 As can be seen, the peak value of the H curve of sample is higher and the decline after the peak is slower, indicating that the interface debonding is a gradual failure. Crack repair keeps the interface mechanically interlocked and frictionally engaged. In contrast, the peak value of the C2 curve of sample is lower and the decline after the peak is sharp, indicating that the interface debonding is a brittle one-time failure. The crack is not repaired and the interface crack remains open.

[0092] Figure 5 The local dry density thermal map of the sample shows that the density distribution of sample H plate is uniform from top to bottom, with no sedimentation or stratification. In contrast, the density of sample C2 is low on the upper surface and high on the lower surface, showing a clear vertical gradient. This indicates that the coarse particles in sample C2 have undergone free sedimentation and accumulation in the slurry.

Claims

1. A multi-solid-waste synergistic autoclaved aerated concrete material, characterized in that: The total amount of raw materials excluding water is 100 parts by weight, of which solid raw materials are calculated on a dry basis and aluminum powder paste is calculated on a wet basis. The raw materials include: 28-42 parts of industrial solid waste powder, 8-16 parts of sludge residue, 3-8 parts of desulfurization gypsum, 8-14 parts of quicklime, 5-10 parts of cement, 0.05-0.15 parts of aluminum powder paste, and the remainder is solid waste aggregate; an additional 55-68 parts of total water are added, which includes 0.6-1.2 parts of atomized water and the remainder of main mixing water.

2. The multi-solid-waste synergistic autoclaved aerated concrete material according to claim 1, characterized in that: The concrete material is composed of a solid skeleton, a porous phase, and an interfacial transition phase. The solid skeleton has the solid waste aggregate as a rigid skeleton core. The sludge and the desulfurized gypsum are distributed in the gaps between the aggregates. The porous phase is a closed pore formed by bubbles generated by the gas-generating agent. The interfacial transition phase is a layer of tobermorite and hydrated calcium silicate crystals formed on the surface of the coarse particles of the solid waste aggregate after hydrothermal reaction.

3. The multi-solid-waste synergistic autoclaved aerated concrete material according to claim 1, characterized in that: The concrete material can be prepared into concrete blocks and concrete slabs.

4. A method for preparing a multi-solid-waste synergistic autoclaved aerated concrete material according to any one of claims 1 to 3, characterized in that, It is prepared through the following steps: S1: After crushing and screening solid waste aggregate, it is ground in a low-energy process to obtain coarse powder. Then, sludge residue and desulfurized gypsum are mixed and ball-milled to obtain fine mixed powder. S2: Coarse powder, fine mixed powder and industrial solid waste powder are fed into a rubbing mill for mixing and grinding. The material is then transferred to a sealed container for static aging. After aging, the material is dry-mixed with cement and quicklime. Then, atomized water is sprayed in and stirring is continued to pre-hydrate the material to obtain pre-hydrated composite dry material. S3: Take desulfurized gypsum and aluminum powder paste and knead them together. Then take quicklime and dry mix it with the kneaded material to obtain a double-layer protective gas generator. Put the pre-hydrated composite dry material and the gas generator into the mixer, add water and mix them. After primary and secondary mixing, pour the mixture into the mold. S4: Place the poured material in a constant temperature environment for static curing. After curing, demold and cut the material. Then, ventilate and cool the cut material in a single layer and transfer it into an autoclave. After gradient autoclaving, remove the material from the autoclave and allow it to cool naturally to obtain the required concrete material.

5. The method for preparing a multi-solid-waste synergistic autoclaved aerated concrete material according to claim 4, characterized in that: The solid waste aggregate mentioned in S1 is one or more of silt, quartz sand, and river sand.

6. The method for preparing a multi-solid-waste synergistic autoclaved aerated concrete material according to claim 4, characterized in that: The low-energy grinding time of S1 is 30~50min, and the solid waste aggregate is ground into coarse particles of 200~500μm; the ball-to-material ratio during ball milling is (5:4)~(8:4), the ball mill speed is 20~40r / min, and the ball milling time is 25~45min.

7. The method for preparing a multi-solid-waste synergistic autoclaved aerated concrete material according to claim 4, characterized in that: The industrial solid waste powder mentioned in S2 is one or more of fly ash, slag powder, and zeolite powder.

8. The method for preparing a multi-solid-waste synergistic autoclaved aerated concrete material according to claim 4, characterized in that: The spindle speed of the grinding machine described in S2 is 110~150 r / min; the grinding time is 10~20 min; the aging temperature is 20~35℃ and the aging time is 20~30 h; the nozzle diameter for spraying atomized water is 0.2~0.7 mm and the spraying pressure is 0.2~1.0 MPa; the stirring speed during pre-hydration is 30~60 r / min and the pre-hydration time is 10~25 min.

9. The method for preparing a multi-solid-waste synergistic autoclaved aerated concrete material according to claim 4, characterized in that: The kneading temperature of S3 is 20~35℃, and the kneading time is 2~8min; in the double-layer protective gas-generating agent, the mass ratio of the desulfurized gypsum to the aluminum powder paste is (2:1)~(16:1), and the mass ratio of the quicklime to the kneaded material is (10:9)~(40:9); the gas generation start delay time of the double-layer protective gas-generating agent is 15~40s; the primary stirring time is 45~90s, and the secondary stirring time is 90~180s.

10. The method for preparing a multi-solid-waste synergistic autoclaved aerated concrete material according to claim 4, characterized in that: The static curing temperature described in S4 is 45~60℃, and the curing time is 2~5h; the blank strength during cutting is 0.2~0.5MPa, and the cutting speed is 1.5~3m / s; the gradient autoclaving includes three gradients, wherein the first gradient curing temperature is 110~130℃, and the curing time is 20~45min; the second gradient curing temperature is 135~160℃, and the curing time is 20~45min; and the third gradient curing temperature is 175~200℃, and the curing time is 5~8h.

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