Preparation process of green building material based on building waste recycling and product

Abstract

The application relates to the technical field of building materials, and discloses a green building material preparation process based on building waste recycling and a product, the process comprises the following steps: building waste regeneration micro powder is put into a stirrer for low-speed stirring, an acid etching solution is uniformly added, an inert coating layer on the surface of the building waste regeneration micro powder is dissolved, and gas is released; after the end, granulated blast furnace slag micro powder and an alkaline polycondensation solution are synchronously added, the stirring speed is increased to a strong shearing mode during the adding, the internal network of the slurry is destructed to realize shear thinning, then the stirring speed is reduced to low speed to restore the slurry structure viscosity, the product is unloaded and molded, and the final product is obtained through vibration curing. The technical scheme of acid-alkali asynchronous decoupling control is adopted, the acid etching solution is used to treat the regeneration micro powder at a low speed in the early preparation stage, the carbonized film on the surface of the material is stripped, and the technical effect of discharging the interface wrapping gas in advance and exposing the internal active silicon aluminum core is achieved.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a green building materials preparation process and product based on the recycling of construction waste. Background Technology

[0002] The accelerated pace of urban renewal has led to the demolition of old buildings, generating massive amounts of waste concrete and bricks. Grinding this construction waste into recycled powder and then converting it into green building materials is a crucial pathway for resource recycling. This approach not only alleviates the environmental pressure from landfills but also reduces the building materials industry's reliance on natural mineral raw materials. Currently, the engineering sector urgently needs to improve the actual conversion rate of construction waste. Utilizing waste materials on a large scale to replace conventional building material raw materials has become a practical requirement for low-carbon construction and sustainable development.

[0003] Currently, conventional processes for processing this type of recycled micropowder mainly rely on single-stage mixed alkali activation technology. Most preparation methods involve centrally feeding solid powders such as waste micropowder and granulated blast furnace slag into a mixing device, followed by direct introduction of high-concentration alkaline activators such as sodium silicate or sodium hydroxide for one-pot mixing. This type of process has a relatively simple overall operation flow. It requires minimal modification to existing production line mixing equipment and is easy to scale up. The highly active slag component in the formulation can rapidly depolymerize in a strongly alkaline environment. The material undergoes a rapid hydration reaction in the early stages of molding, quickly achieving the basic mechanical strength required for demolding, thus realizing the basic recycling of solid waste resources.

[0004] Old construction waste typically undergoes long-term natural weathering. The surface of the finely ground recycled microparticles is generally coated with a solidified film of calcium carbonate. Conventional alkaline activation solutions are unable to dissolve this inert coating layer in a short time. The active aluminosilicate core inside the microparticles is physically sealed, resulting in the high-volume waste microparticles merely acting as inert fillers within the system. The added highly active slag instantly generates a large number of hydrated flocs upon contact with strong alkaline solutions. These nascent flocs quickly encapsulate free water within the system. The high concentration of solid powder then undergoes rapid rheological changes, exhibiting early pseudo-coagulation and stickiness. Conventional constant-speed stirring methods are insufficient to break up these dense agglomerates. During production, the only option is often to passively increase the amount of mixing water. Excess water evaporates during the later hardening stage of the material, inevitably leaving dense interconnected pores within the matrix. The hydration framework of purely inorganic geopolymers is inherently quite rigid. When the material undergoes chemical self-shrinkage during curing, the rigid network lacks elastic deformation buffer space. The internally accumulated shrinkage stress cannot find a way to dissipate, and the building material is very prone to developing micro-cracks, making it difficult to meet the application requirements of high-standard projects. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a green building material preparation process and product based on the recycling of construction waste. This addresses the technical problems in existing conventional alkali-activated solid waste building material preparation processes, such as the low reactivity caused by the inert coating layer on the surface of the recycled micropowder, and the early false coagulation and stickiness of the slurry caused by reaction rate mismatch, as well as the high brittleness and easy shrinkage and cracking of the hardened body.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a green building material preparation process based on the recycling of construction waste, employing the following technical solution: A green building material preparation process based on the recycling of construction waste includes the following steps: (1) Put the recycled micro powder of construction waste into a mixer, set it to low speed at room temperature, add acidic etching solution at a uniform speed to mix, and use the acidic etching solution to dissolve the inert coating layer on the surface of the recycled micro powder of construction waste and release gas. (2) After the low-speed stirring in step (1) is completed, granulated blast furnace slag powder and alkaline condensation liquid are added to the mixer simultaneously; during the addition of granulated blast furnace slag powder and alkaline condensation liquid, the mixer is switched to strong shear mode to increase the stirring speed, and the internal network of the slurry is deconstructed through strong shear action to achieve shear thinning of the slurry. (3) After maintaining the strong shear mode of step (2), reduce the speed of the mixer to low speed to restore the viscosity of the slurry structure. Then unload the material and pour it into the mold. After vibration molding and curing, the final product is obtained.

[0007] By adopting the above technical solution, this invention transforms the original single-stage mixing and activation process of solid-phase powders into an acid-base heterogeneous decoupling control process. Its main consideration lies in creating a time-series intervention window for rheological properties. Specifically, the reaction mechanism and effects are manifested in the synergistic effect of the following reaction system: In the initial low-speed mixing stage, hydrogen ions in the acidic etching solution react with the calcium carbonate film on the surface of the recycled construction waste powder. The main chemical reaction process is as follows: 2H + + CaCO3→ Ca 2+ + H2O + CO2↑.

[0008] The main function of this reaction is to strip away the chemically inert outer shell that hinders the hydration of the internal active substances. During the reaction, the released carbon dioxide gas gradually escapes from the slurry due to the local disturbance caused by low-speed stirring. This not only clears the microscopic venting channels but also exposes the potentially hydration-active aluminosilicate core inside the regenerated micropowder.

[0009] Subsequently, with the introduction of slag powder and alkaline condensation liquid, the system environment rapidly changes from acidic to alkaline, and silicate ions undergo in-situ condensation reactions with the calcium ions released earlier. At this point, if conventional low-speed stirring is maintained, false coagulation of the slurry is often induced due to excessively rapid local reactions.

[0010] To resolve this contradiction, this process incorporates a strong shear mode during the feeding phase, utilizing high-frequency mechanical shear stress to disrupt the early-formed hydration flocculation structure and polymer physical cross-linking network. Under strong shear force, the molecular chains within the system untangle and align themselves along the shear flow field, exhibiting a macroscopic shear-thinning physical rheological phase transition. This allows high-concentration solid powders to achieve homogeneous dispersion at a lower water-cement ratio, thus mitigating to some extent the risk of hydration product agglomeration caused by localized high-alkalinity regions.

[0011] When the strong shear is removed and the stirring speed is reduced, the electrostatic forces within the system regain dominance due to the influence of van der Waals forces and hydrogen bond recombination. The polymer macromolecular chains rotate and re-entangle, and the slurry exhibits significant thixotropic recovery characteristics, with a rapid increase in structural viscosity. This recovery of rheological properties can effectively limit the segregation and stratification of high-density slag powder and low-density recycled powder under gravity, ensuring the stability of the slurry during the unloading and molding stage, thus contributing to obtaining a final product with a uniform and dense internal structure.

[0012] Preferably, based on 100 parts by weight of solid powder, the solid powder consists of 55-65 parts by weight of recycled construction waste micro powder and 35-45 parts by weight of granulated blast furnace slag micro powder; the specific surface area of ​​the recycled construction waste micro powder is 400-460 m². 2 / kg; Granulated blast furnace slag powder meets the S95 grade technical indicators, with a specific surface area of ​​400-430m². 2 / kg.

[0013] By adopting the above technical solutions and controlling the ratio and specific surface area range of recycled micropowder and slag micropowder, a relatively reasonable physical gradation can usually be constructed at the microscale. Considering the inherent disadvantage of the low early reaction rate of recycled micropowder, the slag micropowder provides the main highly active silicon-aluminum source in the early stage of alkali activation. This complementarity of material properties is often more conducive to the establishment of the matrix's early compressive strength.

[0014] Preferably, based on 100 parts by weight of solid powder, the acidic etching solution is made from the following raw materials in parts by weight: 12.21 to 13.00 parts of water; 0.46 to 0.87 parts of polyvinyl alcohol, with a degree of alcoholysis of 87% to 89% and an average degree of polymerization of 1700 to 1800; 1.061 to 1.729 parts of anhydrous citric acid; 0.736 to 1.200 parts of aluminum sulfate octadecylhydrate; and 0.015 to 0.0504 parts of polyoxypropylene polyoxyethylene glycerol ether, with a number-average molecular weight of 2500 to 3500 g / mol.

[0015] By employing the above technical solution, anhydrous citric acid serves as the primary source of free protons, working in conjunction with aluminum sulfate octadechydrate to adjust the pH of the system and simultaneously replenishing the liquid phase with free aluminum ions. Polyvinyl alcohol with a degree of alcoholysis of 87%–89% contains retained unhydrolyzed acetate side groups. When these groups interact with polyoxypropylene polyoxyethylene glycerol ethers of a specific molecular weight distribution, they can often adsorb onto the exposed surface of the regenerated micropowder after etching, forming a steric hindrance protective film. This protective film can, to some extent, limit the excessive dissolution of calcium ions in the acidic stage and lay the molecular chain foundation for rheological regulation in the subsequent alkaline stage.

[0016] Preferably, the preparation method of the acidic etching solution includes: continuously stirring polyvinyl alcohol in water, heating to 85-90°C and stirring for 45-60 minutes until completely dissolved; after naturally cooling to room temperature, adding anhydrous citric acid and aluminum sulfate octadecylhydrate in sequence and stirring until completely dissolved; then adding polyoxypropylene polyoxyethylene glycerol ether dropwise and homogenizing at 100-150 rpm for 5 minutes to obtain the acidic etching solution.

[0017] By employing the above technical solution, controlling the heating to 85–90°C to dissolve polyvinyl alcohol helps to fully destroy the polymer crystallization region, thereby allowing the molecular chains to fully extend. The addition of anhydrous citric acid and aluminum sulfate after natural cooling to room temperature is largely to prevent polyvinyl alcohol from undergoing degradation, dehydration, or excessive intermolecular cross-linking condensation reactions in a high-temperature, strong acid environment, thus maintaining the long-term stability of the acidic etching solution.

[0018] Preferably, based on 100 parts by weight of solid powder, the alkaline condensation solution is made from the following raw materials in parts by weight: 4.30 to 6.30 parts of water; 0.30 to 0.70 parts of sodium tetraborate decahydrate; 0.40 to 0.60 parts of naphthalene sulfonate formaldehyde condensate; and 8.60 to 12.50 parts of sodium silicate aqueous solution, wherein the modulus of the sodium silicate aqueous solution is 1.8 to 2.2 and the Baume degree is 38 to 42, and its equivalent solid sodium silicate content is 3.268 to 5.00 parts.

[0019] By employing the above technical solution, the sodium silicate aqueous solution not only provides the hydroxyl environment required for alkali activation but also serves as the primary source of active silicon-oxygen tetrahedral monomers. The borate ions dissociated from sodium tetraborate decahydrate in solution react with adjacent hydroxyl groups on the polyvinyl alcohol segments within the system, forming a borate ester crosslinking network with dynamic, reversible breakage and recombination characteristics. Simultaneously, naphthalene sulfonate formaldehyde condensate acts as an anionic surfactant, providing electrostatic repulsion to disperse solid particles. The physicochemical effects of these three factors are synergistic, jointly influencing the network deconstruction and recovery behavior during subsequent rheological phase transition processes.

[0020] Preferably, the preparation method of the alkaline condensation solution includes: adding sodium tetraborate decahydrate and naphthalene sulfonate formaldehyde condensate to water and stirring until dissolved; then adding an aqueous solution of sodium silicate and stirring at 200-300 rpm for 10-15 minutes to obtain the alkaline condensation solution.

[0021] By adopting the above technical solution, and following the order of first dissolving sodium tetraborate and naphthalene sulfonate formaldehyde condensate and then introducing a high-concentration sodium silicate aqueous solution, the possibility of salting out and agglomerating organic components in a local high-salt and high-alkalinity environment can be reduced to a certain extent, thereby promoting the homogeneous dispersion of effective components in the alkaline condensation solution.

[0022] Preferably, in step (1), the speed of low-speed stirring is 30-50 rpm, and the time of maintaining low-speed stirring is 5-10 min; in step (3), the speed of low-speed stirring is 30-50 rpm, and the time of maintaining low-speed stirring is 1-2 min.

[0023] By adopting the above technical solution, the initial low-speed period of 5-10 minutes is actually to allow for a relatively sufficient solid-liquid contact interface for the penetration of the acidic solution into the micro-powder pores and for the subsequent decarburization and degassing reaction. The low-speed operation of 1-2 minutes set in the later stage of the reaction basically matches the rheological relaxation time period required for polymer network reconstruction and van der Waals force recovery.

[0024] Preferably, the specific operation method of step (2) is as follows: granulated blast furnace slag powder is fed into the mixer by a screw conveyor, and alkaline condensation liquid is evenly sprayed into the mixer by a high-pressure atomizing nozzle, and the two are added synchronously within 45 to 75 seconds; from the 20th to 40th second after the addition of granulated blast furnace slag powder and alkaline condensation liquid, the mixer is switched to strong shear mode, and the stirring speed is increased to 120 to 160 rpm; and before the speed is reduced in step (3), the strong shear mode is maintained for 1.5 to 3 minutes.

[0025] By adopting the above technical solution, practice has shown that the 20-40 seconds after the initial feeding is often the rheological critical point where slag powder easily induces rapid flocculation in a strongly alkaline environment. Applying high-frequency mechanical shear at 120-160 rpm at this specific point can timely sever the nascent hydrated flocculent structure and release the free water trapped within the flocculent body. This control over the timing is beneficial for promoting the shear-thinning effect and improving the fluidity of the high-concentration mineral system.

[0026] Preferably, in step (3), the curing conditions are as follows: the molded specimen is placed in a standard curing room with a temperature of 20±2℃ and a relative humidity of ≥95% for 24 hours and then demolded, and the curing continues until the specified test age.

[0027] By adopting the above technical solutions, maintaining a constant temperature and high humidity external curing environment can alleviate the increase in capillary shrinkage pressure caused by the rapid evaporation of free water in the slurry to a certain extent, thereby reducing the risk of plastic shrinkage cracking of the product and providing a basic guarantee for the strength development of the final structure.

[0028] Secondly, the present invention provides a green building material product based on the recycling of construction waste, which adopts the following technical solution: A green building material product based on the recycling of construction waste, wherein the product is prepared by the green building material preparation process based on the recycling of construction waste as described in any one of claims 1-9.

[0029] By adopting the above technical solution, this product, through in-situ curing and molding using a time-decoupled acid-base activation and rheological phase change intervention process, achieves a dense microscopic interface structure and stable macroscopic mechanical properties. The specific mechanism and product structure are as follows: Because the pretreatment stage removes the inert film such as calcium carbonate from the surface of the recycled micropowder, the weak interface transition zone that is common in traditional recycled solid waste building materials is significantly weakened. The exposed potentially active aluminosilicates and granulated blast furnace slag micropowder dissolve and recombine in an alkaline environment, often intertwining to form a continuous and relatively homogeneous inorganic spatial network, providing a strong chemical bonding basis for the solid particles.

[0030] At the same time, the early venting operation combined with the strong shear compaction in the middle stage physically restricts the large accumulation of free water, which to some extent blocks the possibility of interconnected capillary pores caused by the later water evaporation, and helps to reduce the total porosity of the hardened matrix.

[0031] Furthermore, the dynamic polymer network formed by the polyvinyl alcohol molecular chains and borate ions within the system interpenetrates and cross-links into the inorganic matrix after the product is finally cured. This near-interpenetrating network microstructure can typically dissipate strain energy when the matrix is ​​subjected to external stress, thereby improving the compressive strength and resistance to brittle cracking of the product, providing a feasible path for the high-volume and high-value-added conversion of construction waste.

[0032] This invention provides a green building material preparation process and product based on the recycling of construction waste. It has the following beneficial effects: 1. This invention employs an acid-base heterogeneous decoupling control technique. In the initial stage of preparation, the regenerated micropowder is treated with low-speed stirring using an acidic etching solution to peel off the carbonized film on the material surface. This achieves the technical effect of prematurely removing interfacial encapsulated gases and exposing the internal active silicon-aluminum core. Compared to the existing technology that directly mixes waste micropowder with an alkaline activator in a one-pot process, this application avoids the physical obstruction of the hydration process by the inert shell, solving the shortcomings of low utilization rate and low reactivity of regenerated micropowder in conventional activation processes.

[0033] 2. This invention employs a high-frequency mechanical shearing technique that intervenes at a specific rheological critical period. The rotational speed is suddenly increased during the 20-40 second phase after the addition of slag powder and alkaline solution, promptly cutting off the nascent hydrated flocs. This achieves the technical effect of forcibly releasing internally trapped water and promoting shear thinning of the high-concentration slurry. Compared to existing technologies that maintain a single fixed rotational speed throughout or rely solely on water-reducing agents for adjustment, this method actively intervenes in particle aggregation behavior through physical phase change, solving the problem of insufficient localized false coagulation caused by early reaction rate mismatch in multi-component solid waste powders.

[0034] 3. This invention employs a technical solution that interweaves organic dynamic crosslinking with an inorganic polycondensation framework. It utilizes the dynamic bond network formed by polyvinyl alcohol and sodium tetraborate in an alkaline environment, which is directly interwoven within the three-dimensional skeleton of the geopolymer. This achieves the technical effect of constructing a microscopic interpenetrating network system and enhancing stress dissipation capacity. Compared to existing building material preparation methods that rely solely on unidirectional curing of inorganic aluminosilicates, this composite structure improves the mechanical conduction characteristics of the hardened body and solves the common problems of excessive brittleness and easy shrinkage cracking in high-content recycled construction waste products. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the three-stage rheological response of different slurry systems in the test examples of the present invention. Detailed Implementation

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Unless otherwise specified, all chemical reagents are commercially available industrial grade or analytical grade products; the recycled construction waste powder, granulated blast furnace slag powder, and additives are all commercially available industrial products that meet the corresponding requirements.

[0038] Recycled construction waste powder: made from waste concrete blocks through initial crushing and grinding, with a specific surface area controlled at 400 m². 2 / kg to 460m 2 / kg, the particle surface contains calcium carbonate in a carbonized state and a thin film of calcium silicate hydrate.

[0039] Granulated blast furnace slag powder: meets the technical specifications of S95 grade industrial slag powder, with a specific surface area controlled at 400 m². 2 / kg to 430m 2 / kg.

[0040] Anhydrous citric acid: CAS number 77-92-9.

[0041] Aluminum sulfate octahydrate: CAS number 7784-31-8.

[0042] Polyvinyl alcohol: CAS number 9002-89-5, the main repeating units are ethylene alcohol unit [-CH2-CH(OH)-] and unhydrolyzed vinyl acetate unit [-CH2-CH(OCOCH3)-], the degree of alcoholysis is controlled at 87% to 89%, and the average degree of polymerization is controlled at 1700 to 1800.

[0043] Polyoxypropylene polyoxyethylene glycerol ether: CAS No. 9082-00-2, is a nonionic block copolymer prepared by copolymerization of glycerol with propylene oxide and ethylene oxide, with a number average molecular weight controlled between 2500 g / mol and 3500 g / mol.

[0044] Sodium silicate aqueous solution: CAS No. 1344-09-8, modulus controlled between 1.8 and 2.2, Baumé degree controlled between 38 and 42, solid content based on supplier test value or drying method determination value; in each preparation example, the amount of sodium silicate used after conversion is controlled between 3.0% and 5.0% of the total mass of solid powder.

[0045] Sodium tetraborate decahydrate: CAS number 1303-96-4.

[0046] Naphthalene sulfonate formaldehyde condensate: CAS number 36290-04-7.

[0047] Preparation Example 1: This preparation example provides a method for preparing a composite liquid activator suitable for 100.0 kg of solid powder, including the following steps: (1) Preparation of acidic etching solution: Weigh 12.21 kg of water, add 640.0 g of polyvinyl alcohol under continuous stirring, heat to 88 °C and keep stirring for 50 minutes until the polyvinyl alcohol is completely dissolved; after naturally cooling to room temperature, add 1537.0 g of anhydrous citric acid and 1066.0 g of aluminum sulfate octadecahydrate in sequence, and stir until completely dissolved; then add 31.0 g of polyoxypropylene polyoxyethylene glycerol ether dropwise, and stir homogenously at 120 rpm for 5 minutes to obtain acidic etching solution; (2) Preparation of alkaline condensation solution: Weigh 6.01 kg of water, add 500.0 g of sodium tetraborate decahydrate and 500.0 g of naphthalene sulfonate formaldehyde condensate, and stir until dissolved; then add 10.0 kg of sodium silicate aqueous solution, the modulus of sodium silicate aqueous solution is 2.0, the Baume degree is 40, and the solid content is 40.0% by drying method, which is equivalent to 4.0 kg of solid sodium silicate; then stir at 250 rpm for 12 minutes to obtain alkaline condensation solution.

[0048] Preparation Example 2: This preparation example provides a method for preparing a composite liquid activator suitable for 100.0 kg of solid powder, including the following steps: (1) Preparation of acidic etching solution: Weigh 12.30 kg of water, add 460.0 g of polyvinyl alcohol under continuous stirring, heat to 85 °C and keep stirring for 45 minutes until the polyvinyl alcohol is completely dissolved; after naturally cooling to room temperature, add 1061.0 g of anhydrous citric acid and 736.0 g of aluminum sulfate octadecahydrate in sequence, and stir until completely dissolved; then add 15.0 g of polyoxypropylene polyoxyethylene glycerol ether dropwise, and stir homogenously at 100 rpm for 5 minutes to obtain acidic etching solution; (2) Preparation of alkaline condensation solution: Weigh 6.30 kg of water, add 300.0 g of sodium tetraborate decahydrate and 400.0 g of naphthalene sulfonate formaldehyde condensate, and stir until dissolved; then add 8.60 kg of sodium silicate aqueous solution, the modulus of sodium silicate aqueous solution is 1.8 and the Baume degree is 38. The solid content is 38.0% by drying method, which is equivalent to 3.268 kg of solid sodium silicate; then stir at 200 rpm for 10 minutes to obtain alkaline condensation solution.

[0049] Preparation Example 3: This preparation example provides a method for preparing a composite liquid activator suitable for 100.0 kg of solid powder, including the following steps: (1) Preparation of acidic etching solution: Weigh 13.00 kg of water, add 870.0 g of polyvinyl alcohol under continuous stirring, heat to 90 °C and keep stirring for 60 minutes until the polyvinyl alcohol is completely dissolved; after naturally cooling to room temperature, add 1729.0 g of anhydrous citric acid and 1200.0 g of aluminum sulfate octadechydrate in sequence, and stir until completely dissolved; then add 50.4 g of polyoxypropylene polyoxyethylene glycerol ether dropwise, and stir homogenously at 150 rpm for 5 minutes to obtain acidic etching solution; (2) Preparation of alkaline condensation solution: Weigh 4.30 kg of water, add 700.0 g of sodium tetraborate decahydrate and 600.0 g of naphthalene sulfonate formaldehyde condensate, and stir until dissolved; then add 12.50 kg of sodium silicate aqueous solution, the modulus of sodium silicate aqueous solution is 2.2 and the Baume degree is 42. The solid content is 40.0% as determined by the drying method, which is equivalent to 5.0 kg of solid sodium silicate; then stir at 300 rpm for 15 minutes to obtain alkaline condensation solution.

[0050] Example 1: This embodiment provides a green building material preparation process based on the recycling of construction waste, including the following steps: (1) Weigh 60.0 kg of recycled construction waste powder and put it into a twin-shaft forced mixer. Set the stirring speed to 40 rpm at room temperature, pump the acidic etching solution prepared in Preparation Example 1 into the mixer at a constant speed, and maintain low-speed stirring for 7 min. (2) After the low-speed stirring is completed, 40.0 kg of granulated blast furnace slag powder is fed into the mixer through a screw conveyor, and the alkaline condensation liquid prepared in Preparation Example 1 is evenly sprayed into the mixer through a high-pressure atomizing nozzle. The granulated blast furnace slag powder and alkaline condensation liquid are added synchronously within 60 seconds. At 30 seconds after the addition of granulated blast furnace slag powder and alkaline condensation liquid, the mixer is switched to strong shear mode through a frequency converter to increase the stirring speed to 140 rpm. (3) Maintain the strong shear mode for 2 minutes, then reduce the stirring speed to 40 rpm and stir at low speed for 1.5 minutes. After stirring, open the discharge port to discharge the material, inject the resulting slurry into the standard mold, and vibrate it on the vibrating table to form the mold. Place the molded specimen in a standard curing room with a temperature of 20±2℃ and a relative humidity of ≥95% for 24 hours, then demold it and continue curing until the specified test age.

[0051] Example 2: This embodiment provides a green building material preparation process based on the recycling of construction waste, including the following steps: (1) Weigh 65.0 kg of recycled construction waste powder and put it into a twin-shaft forced mixer. Set the stirring speed to 50 rpm at room temperature, pump the acidic etching solution prepared in Preparation Example 3 into the mixer at a constant speed, and maintain low-speed stirring for 10 min. (2) After the low-speed stirring is completed, 35.0 kg of granulated blast furnace slag powder is fed into the mixer by a screw conveyor, and the alkaline polycondensation liquid prepared in Preparation Example 3 is evenly sprayed into the mixer by a high-pressure atomizing nozzle. The granulated blast furnace slag powder and alkaline polycondensation liquid are added synchronously within 75 s. At 40 s from the start of adding the granulated blast furnace slag powder and alkaline polycondensation liquid, the mixer is switched to strong shear mode by a frequency converter, so that the stirring speed is increased to 160 rpm. (3) Maintain the strong shear mode for 3 minutes, then reduce the stirring speed to 50 rpm and stir at low speed for 2 minutes. After stirring, open the discharge port to discharge the material, inject the resulting slurry into the standard mold, and vibrate it on the vibrating table to form the mold. Place the molded specimen in a standard curing room with a temperature of 20±2℃ and a relative humidity of ≥95% for 24 hours and then demold it. Continue curing until the specified test age.

[0052] Example 3: This embodiment provides a green building material preparation process based on the recycling of construction waste, including the following steps: (1) Weigh 55.0 kg of recycled construction waste powder and put it into a twin-shaft forced mixer. Set the stirring speed to 30 rpm at room temperature, pump the acidic etching solution prepared in Example 2 into the mixer at a constant speed, and maintain low-speed stirring for 5 min. (2) After the low-speed stirring is completed, 45.0 kg of granulated blast furnace slag powder is fed into the mixer by a screw conveyor, and the alkaline condensation liquid prepared in Preparation Example 2 is evenly sprayed into the mixer by a high-pressure atomizing nozzle. The granulated blast furnace slag powder and alkaline condensation liquid are added synchronously within 45 seconds. At 20 seconds after the addition of granulated blast furnace slag powder and alkaline condensation liquid, the mixer is switched to strong shear mode by a frequency converter to increase the stirring speed to 120 rpm. (3) Maintain the strong shear mode for 1.5 min, then reduce the stirring speed to 30 rpm and stir at low speed for 1 min; after stirring, open the discharge port to discharge the material, inject the resulting slurry into the standard mold, and vibrate it on the vibrating table to form it; place the molded specimen in a standard curing room with a temperature of 20±2℃ and a relative humidity of ≥95% for 24 h and then demold it, and continue curing until the specified test age.

[0053] Example 4: This embodiment provides a green building material preparation process based on the recycling of construction waste, including the following steps: (1) Weigh 60.0 kg of recycled micro powder from construction waste and put it into a twin-shaft forced mixer. Set the stirring speed to 40 rpm at room temperature, pump the acidic etching solution prepared in Preparation Example 1 into the mixer at a constant speed, and maintain low-speed stirring for 5 min. (2) After the low-speed stirring is completed, 40.0 kg of granulated blast furnace slag powder is fed into the mixer by a screw conveyor, and the alkaline polycondensation liquid prepared in Preparation Example 1 is evenly sprayed into the mixer by a high-pressure atomizing nozzle. The granulated blast furnace slag powder and alkaline polycondensation liquid are added synchronously within 45 s. At 20 s from the start of adding the granulated blast furnace slag powder and alkaline polycondensation liquid, the mixer is switched to strong shear mode by a frequency converter, so that the stirring speed is increased to 140 rpm. (3) Maintain the strong shear mode for 1.5 min, then reduce the stirring speed to 40 rpm and stir at low speed for 1 min; after stirring, open the discharge port to discharge the material, inject the resulting slurry into the standard mold, and vibrate it on the vibrating table to form it; place the molded specimen in a standard curing room with a temperature of 20±2℃ and a relative humidity of ≥95% for 24 h and then demold it, and continue curing until the specified test age.

[0054] Example 5: This embodiment provides a green building material preparation process based on the recycling of construction waste, including the following steps: (1) Weigh 60.0 kg of recycled micro powder from construction waste and put it into a twin-shaft forced mixer. Set the stirring speed to 50 rpm at room temperature, pump the acidic etching solution prepared in Preparation Example 1 into the mixer at a constant speed, and maintain low-speed stirring for 7 min. (2) After the low-speed stirring is completed, 40.0 kg of granulated blast furnace slag powder is fed into the mixer through a screw conveyor, and the alkaline polycondensation liquid prepared in Preparation Example 1 is evenly sprayed into the mixer through a high-pressure atomizing nozzle. The granulated blast furnace slag powder and alkaline polycondensation liquid are added synchronously within 60 seconds. At 30 seconds after the addition of granulated blast furnace slag powder and alkaline polycondensation liquid, the mixer is switched to strong shear mode through a frequency converter to increase the stirring speed to 160 rpm. (3) Maintain the strong shear mode for 2 minutes, then reduce the stirring speed to 50 rpm and stir at low speed for 1.5 minutes; after stirring, open the discharge port to discharge the material, inject the resulting slurry into the standard mold, and vibrate it on the vibrating table to form it; place the molded specimen in a standard curing room with a temperature of 20±2℃ and a relative humidity of ≥95% for 24 hours and then demold it, and continue curing until the specified test age.

[0055] Comparative Example 1: The difference between this comparative example and Example 1 is that it does not employ a step-by-step etching and liquid-liquid activation process, but instead uses a conventional single-phase alkali activation system. Specifically, 60.0 kg of recycled construction waste powder and 40.0 kg of granulated blast furnace slag powder were mixed evenly and then added to a mixer. A mixed activation solution prepared from 21.0 kg of water, 10.0 kg of sodium silicate aqueous solution, and 1.5 kg of sodium hydroxide was directly added. The modulus of the sodium silicate aqueous solution was 2.0, and the Baume degree was 40. The total liquid mass of the mixed activation solution was 32.5 kg, the same as in Example 1. This system did not contain anhydrous citric acid, aluminum sulfate octadecylhydrate, polyvinyl alcohol, polyoxypropylene polyoxyethylene glycerol ether, sodium tetraborate decahydrate, or naphthalene sulfonate formaldehyde condensate. Subsequently, the mixture was stirred at a constant speed of 140 rpm for 3.5 min, and then directly discharged and poured into a mold. The remaining conditions were the same as in Example 1.

[0056] Comparative Example 2: The difference between this comparative example and Example 1 is that: no polyoxypropylene polyoxyethylene glycerol ether is added during the preparation of the acid etching solution, and an equal mass of water is used to replace the polyoxypropylene polyoxyethylene glycerol ether, so that the total liquid mass and liquid-solid ratio of the system are consistent with those of Example 1, and the other conditions are the same as those of Example 1.

[0057] Comparative Example 3: The difference between this comparative example and Example 1 is that the order of material addition is changed. Specifically, in step (1), 60.0 kg of recycled construction waste powder and 40.0 kg of granulated blast furnace slag powder are simultaneously added to a twin-shaft forced mixer, and then acidic etching solution is pumped in at a uniform speed for mixing; in step (2), alkaline polycondensation solution is sprayed in only through a high-pressure atomizing nozzle, and the other conditions are the same as in Example 1.

[0058] Comparative Example 4: The difference between this comparative example and Example 1 is that the naphthalene sulfonate formaldehyde condensate in the alkaline condensation solution is replaced by an equal mass of commercially available conventional polycarboxylate-based high-efficiency water-reducing agent solid powder, while the other conditions are the same as in Example 1.

[0059] Comparative Example 5: The difference between this comparative example and Example 1 is that: no polyvinyl alcohol is added during the preparation of the acidic etching solution, and no sodium tetraborate decahydrate is added during the preparation of the alkaline polycondensation solution. In addition, equal masses of water are used to replace polyvinyl alcohol and sodium tetraborate decahydrate, so that the total liquid mass and liquid-solid ratio of the system are consistent with those of Example 1. All other conditions are the same as those of Example 1.

[0060] Comparative Example 6: The difference between this comparative example and Example 1 is that anhydrous citric acid is not added during the preparation of the acid etching solution, and an equal mass of water is used to replace anhydrous citric acid, so that the total liquid mass and liquid-solid ratio of the system are consistent with those of Example 1. The other conditions are the same as those of Example 1.

[0061] Test Example 1: This test case aims to verify the physical laws governing strong shear-induced rheological phase transition and the anti-slip condensation mechanism.

[0062] The testing steps are as follows: (1) Extract the slurry that was immediately discharged at the end of step (2) in Example 1, Comparative Example 4 and Comparative Example 5 respectively as test objects, and slowly inject it into the test tank of the rotational rheometer with a coaxial cylindrical clamp. Set the circulating water bath system to keep the test temperature constant at 20°C and let it stand for 2 minutes to eliminate the influence of shear history caused by the injection.

[0063] (2) Conduct steady-state shear rate scan test, and set the shear rate from 0.1s using the control program. -1 Increased continuously in logarithmic form up to 200s -1 The apparent viscosity and shear stress parameters of the slurry at each sampling point were recorded.

[0064] (3) Replace with fresh slurry samples in the same condition and conduct a three-stage thixotropic recovery test. The first stage applies 0.1s. -1 The initial static network viscosity was collected by running at a constant low shear rate for 60 seconds; in the second stage, the shear rate was instantaneously increased to 160 seconds. -1 And maintain for 60 seconds; in the third stage, the shear rate is instantly restored to 0.1 seconds. -1 Continuously monitor the dynamic changes in apparent viscosity over 180 seconds.

[0065] Each group of slurry samples was tested in parallel three times. The data in Table 1 are average values, and the relative deviation of a single test does not exceed 5%. The test data are shown in Table 1.

[0066] Table 1: Apparent viscosity test data of slurry at different shear stages The apparent viscosity changes of the slurries in Examples 1, 4, and 5 under the low-shear, high-shear, and recovery stages are as follows: Figure 1 As shown.

[0067] According to Table 1 and Figure 1 The data, in Example 1, was obtained in 0.1s. -1 The apparent viscosity at low shear rates is 19.34 Pa·s, and when the shear rate is increased to 160 s⁻¹, the viscosity decreases. -1 At that time, the apparent viscosity decreased to 0.38 Pa·s; when the shear rate recovered to 0.1 s⁻¹, the viscosity decreased to 0.38 Pa·s. -1After 180 seconds, the apparent viscosity recovered to 18.23 Pa·s. These results indicate that the slurry of Example 1 exhibits high structural viscosity under low shear conditions, demonstrates significant shear thinning characteristics under strong shear, and shows good viscosity recovery after the strong shear is removed. This rheological response matches the system design of polyvinyl alcohol and sodium tetraborate decahydrate participating in the formation of a dynamic reversible network, which is beneficial for balancing fluidity and structural recovery during mixing, conveying, and molding of the slurry.

[0068] Compared to Example 1, Comparative Example 5 did not contain polyvinyl alcohol and sodium tetraborate decahydrate, and its [result] was [decreased / concentrated] in 0.1s. -1 The initial apparent viscosity at low shear rates was 5.12 Pa·s, significantly lower than that of Example 1. After the strong shear was removed, the apparent viscosity gradually increased from 2.03 Pa·s to 16.89 Pa·s. This result indicates that in the absence of the dynamic network constructed from polyvinyl alcohol and sodium tetraborate decahydrate, the early structural viscosity of the slurry is low, and subsequent viscosity growth depends more on the formation of inorganic gels and interparticle aggregation within the system. Compared to Example 1, Comparative Example 5 exhibits weaker controllability in shear response and structural recovery processes, which is detrimental to maintaining stable construction operation.

[0069] Comparative Example 4, after replacing the naphthalene sulfonate formaldehyde condensate with a commercially available conventional polycarboxylate superplasticizer, exhibited higher apparent viscosity at all shear rates, with the highest apparent viscosity at 160 s⁻¹. -1 The apparent viscosity under strong shear conditions remains 9.54 Pa·s; when the shear rate recovers to 0.1 s⁻¹... -1 Subsequently, the apparent viscosity further increased to 71.05 Pa·s. This result indicates that in the strongly alkaline, multivalent metal ion coexisting system involved in this embodiment, the polycarboxylate superplasticizer's effect on maintaining the slurry dispersion state is weaker than that of the naphthalene sulfonate formaldehyde condensate. The naphthalene sulfonate formaldehyde condensate, in combination with the polyvinyl alcohol-borate dynamic network, helps reduce flow resistance during the strong shear stage and improves the structural recovery state of the slurry after shear removal.

[0070] Test Example 2: This test case aims to verify the chemical kinetic evolution of acid etching-delayed activation and precipitation-driven nucleation.

[0071] The testing steps are as follows: (1) In-situ sequential injection method was used for isothermal calorimetry testing. Solid powder with a total mass of 5.00 g was weighed according to the solid mass ratios in Example 1, Comparative Example 1 and Comparative Example 6. For Example 1 and Comparative Example 6, the corresponding proportion of recycled construction waste powder was placed in a glass ampoule for micro-isothermal calorimetry, and the corresponding proportion of granulated blast furnace slag powder was pre-placed in an openable solid compartment; for Comparative Example 1, the recycled construction waste powder and granulated blast furnace slag powder were pre-mixed evenly and then placed in an ampoule.

[0072] (2) Extract the corresponding liquid components according to the liquid mass ratio in each embodiment and comparative example. For Example 1 and Comparative Example 6, the acidic etching solution and the alkaline polycondensation solution were respectively loaded into a dual-channel in-situ syringe; for Comparative Example 1, the mixed excitation solution was loaded into a single-channel in-situ syringe.

[0073] (3) Place the ampoule in the calorimeter test channel, set the system constant temperature environment to 20℃ and balance the baseline. For Example 1 and Comparative Example 6, first inject the corresponding acidic etching solution into the recycled construction waste powder in the ampoule, and define the moment when the acidic etching solution begins to contact the recycled construction waste powder as the test zero point; after reaching the corresponding scaled etching time, open the solid compartment to release the granulated blast furnace slag powder, and simultaneously inject the alkaline polycondensation solution. For Comparative Example 1, inject the mixed activation solution once at the test zero point. Continuously collect the heat flow rate signal released by the mixed materials, set the test time to 72h, and the system synchronously integrates and calculates the cumulative heat release, with the acquisition frequency set to record data once per minute.

[0074] Each sample group was tested in parallel three times. The data in Table 2 are average values, and the relative deviation of a single test does not exceed 5%. The test data are shown in Table 2.

[0075] Table 2: Statistical Table of Hydration Heat Release Characteristic Parameters of Slurries of Different Systems According to the data in Table 2, the peak exothermic time in the initial stage of Example 1 was 0.13 h, and the highest heat flux in the initial stage was 5.28 mW / g; the peak exothermic time in the main hydration stage was 15.61 h, the peak heat flux in the main hydration stage was 12.83 mW / g, and the total cumulative heat release over 72 h was 224.67 J / g. These results indicate that the reaction process in Example 1 exhibits a phase separation between the initial low-intensity exothermic stage and the subsequent main hydration exothermic stage. This exothermic characteristic corresponds to the sequential process of first contacting the acidic etching solution with the recycled micro-powder from construction waste, followed by the introduction of granulated blast furnace slag micro-powder and alkaline polycondensation solution. This process helps to reduce the degree of concentrated heat release in the early stages and maintain a high cumulative heat release level in the subsequent hydration polycondensation reaction.

[0076] Comparative Example 1 used a single-phase alkali-activated system. Its initial exothermic peak time was 0.06 h, and the highest heat flux in the initial stage reached 38.15 mW / g. No independent exothermic peak was observed in the main hydration stage, and the total cumulative heat release over 72 h was 185.32 J / g. Compared to Example 1, Comparative Example 1 showed a higher heat flux peak in the early stage of the reaction, indicating that the early dissolution and gel formation processes were more concentrated after the strong alkali-activated liquid came into direct contact with the composite powder. This reaction process enabled the system to rapidly form a reaction product coating layer in the early stage, and the subsequent reaction persistence was lower than that of Example 1, manifested in a reduced total cumulative heat release over 72 h.

[0077] Comparative Example 6, without the addition of anhydrous citric acid as a complexing etchant, exhibited a peak heat flux of 1.14 mW / g in the initial stage, a delayed exothermic peak time of 26.43 h in the main hydration stage, a peak heat flux of 5.76 mW / g in the main hydration stage, and a cumulative total heat release of 151.09 J / g over 72 h. Compared to Example 1, Comparative Example 6 showed lower initial exothermic intensity, peak exothermic peak during main hydration, and cumulative total heat release. This indicates that the absence of anhydrous citric acid in the pre-etching and complexing process limits the subsequent ion exchange and hydration condensation reactions of the recycled construction waste powder surface passivation layer, resulting in a reduced overall reaction rate.

[0078] In summary, Example 1, through the process sequence of acidic etching solution pretreatment and simultaneous introduction of slag micropowder and alkaline polycondensation solution, achieved a more coordinated reaction process in terms of early exothermic intensity, the appearance time of the main hydration peak, and the total cumulative exothermic amount. This result is consistent with the technical objective of this invention: to improve the degree to which regenerated micropowder participates in the gel network construction by controlling reaction kinetics in stages.

[0079] Test Example 3: This test case aims to evaluate the differences in the macroscopic working performance and exhaust densification index of each system at the actual construction operation level.

[0080] The testing steps are as follows: (1) According to the standard specifications, the instant slurry after mixing is layered and put into the standard slump cylinder. After compaction, it is lifted vertically and steadily. The diameters of the slurry in two mutually perpendicular directions are measured after it is spread out. The average value of the two is taken as the initial slump expansion. Then the remaining slurry is placed in a sealed container and left to stand. Samples are taken at 30 min and 60 min respectively to repeat the above expansion test and record the flowability data over time.

[0081] (2) Take a portion of the instant slurry and put it into a truncated cone mold. After smoothing the surface, place it in a standard curing chamber with a temperature of 20℃ and a relative humidity of 95% and let it stand. Use a standard Vicat apparatus to periodically determine the initial setting and final setting times. During the test, record the depth of the probe sinking and the distance between the probe and the bottom plate until the standard judgment limit for initial setting and final setting is met.

[0082] (3) The instant grout was poured into a standard mold of 40mm×40mm×160mm, vibrated and shaped, and then cured in a standard curing room at a temperature of 20±2℃ and a relative humidity of ≥95% for 24 hours before demolding. The curing continued until 28 days. The specimens were then placed in a drying oven at 60℃ and dried to constant weight. The external dimensions of the specimens were measured and the constant weight was measured. The apparent density of the hardened body after 28 days was calculated by dividing the constant weight by the apparent volume of the specimen.

[0083] The fluidity, setting time, and apparent density of the hardened body of each group of slurries were tested in triplicate. The data in Table 3 are average values, and the relative deviation of a single test does not exceed 5%. The test data are shown in Table 3.

[0084] Table 3: Test data on macroscopic working properties of slurry and densification index of hardened body According to the data in Table 3, the initial slump spread of Examples 1 to 5 was 268 mm to 282 mm, the 60-minute spread was 238 mm to 251 mm, the initial setting time was 178 min to 192 min, the final setting time was 246 min to 268 min, and the apparent density of the hardened body after 28 days was 2271 kg / m³. 3 Up to 2292kg / m 3 The above results indicate that, under the formulation and process conditions specified in this invention, the slurry maintains high fluidity over time within 60 minutes and has a setting time range suitable for casting; at the same time, the apparent density of the hardened body remains at a high level, indicating that the material has a good densification state after molding.

[0085] Comparative Example 2, without the addition of polyoxypropylene polyoxyethylene glycerol ether, had an initial slump spread of 265 mm, a 60-minute spread of 225 mm, an initial setting time of 182 min, and a final setting time of 253 min. Compared with the Example Group, the changes in fluidity and setting time were smaller; however, its apparent density after 28 days of hardening was 1865 kg / m³. 3 The results show that polyoxypropylene polyoxyethylene glycerol ether has a relatively limited effect on the initial fluidity and setting time of the slurry, but a significant impact on the apparent density of the hardened body. Considering the characteristics of gas generation during the acid etching stage of this system, the addition of polyoxypropylene polyoxyethylene glycerol ether is beneficial to improving the venting state during the acid etching stage and reducing the adverse effects of residual gas on the densification of the hardened body.

[0086] Comparative Example 3 altered the material addition sequence, allowing the granulated blast furnace slag powder to enter the acid etching stage earlier and contact the acid etching solution together with the recycled construction waste powder. Its initial slump spread was 185 mm, the spread at 30 min was 120 mm, the spread at 60 min was 0 mm, the initial setting time was 45 min, and the final setting time was 78 min. Compared to the example group, Comparative Example 3 showed significantly reduced flowability and setting time, indicating that the material addition sequence has a significant impact on the system's construction operation time. This result demonstrates that distinguishing the acid etching stage of the recycled construction waste powder from the simultaneous introduction stage of the granulated blast furnace slag powder and alkaline condensation solution helps reduce early uncontrolled thickening and maintains the slurry's operability before molding.

[0087] Comparative Example 4 used a commercially available conventional polycarboxylate superplasticizer to replace the naphthalene sulfonate formaldehyde condensate. Its initial slump spread was 150 mm, and the spread at 30 min and 60 min was 0 mm. The initial setting time was 55 min, the final setting time was 92 min, and the apparent density of the hardened body after 28 days was 1980 kg / m³. 3 Compared to the example group, Comparative Example 4 showed lower initial fluidity, fluidity over time, and apparent density of the hardened body, and a significantly shorter setting time. This result indicates that in the strongly alkaline environment of this system, where multiple valent metal ions coexist, the polycarboxylate-based high-efficiency water-reducing agent is less effective than the naphthalene sulfonate formaldehyde condensate in maintaining slurry fluidity. The naphthalene sulfonate formaldehyde condensate, when combined with the stepwise activation process of this invention, is beneficial for maintaining the slurry dispersion state and the molding operation window.

[0088] Test Example 4: This test case aims to evaluate the quantitative indicators of the macroscopic physical and mechanical properties of each system under standard curing conditions.

[0089] The testing steps are as follows: (1) Extract the instant slurry from the mixer during the preparation of Examples 1 to 5, and Comparative Examples 1, 5 and 6 as test objects. Fill the standard triple mold with an internal size of 40mm×40mm×160mm and vibrate it continuously on a high-frequency vibration table to remove the residual air mixed in until the surface is covered with slurry and no air bubbles overflow. Then use a scraper to smooth the surface along the edge of the mold.

[0090] (2) The molded specimens were placed in a standard curing room with a temperature of 20±2℃ and a relative humidity of not less than 95% and left to cure for 24 hours. After reaching the initial demolding strength, they were numbered and the mold was removed. The exposed specimens after demolding were placed in the same standard curing room and cured for 7 days and 28 days respectively.

[0091] (3) After reaching the specified test age, remove the specimen and wipe off the surface moisture, then place it on a computer-controlled constant stress flexural and compressive strength testing machine. Adjust the loading rate to 50 N / s and conduct a three-point bending flexural test, record the peak load at the time of specimen fracture, and calculate the flexural strength. Collect the half-section specimens after flexural fracture, and conduct a compressive strength test in a fixture with a compression area of ​​40 mm × 40 mm at a loading rate of 2400 N / s, record the failure load, and calculate the average compressive strength of a single set of specimens.

[0092] Each group of test specimens shall contain no fewer than 3 specimens. The data in Table 4 are average values, and the relative deviation of a single group of tests shall not exceed 5%. The test data are shown in Table 4.

[0093] Table 4: Test data of compressive and flexural strength of each system at different ages According to the data in Table 4, the compressive strength of Examples 1 to 5 at 7 days of age ranged from 43.52 MPa to 47.33 MPa, and the flexural strength ranged from 6.95 MPa to 7.85 MPa; at 28 days of age, the compressive strength ranged from 56.41 MPa to 62.59 MPa, and the flexural strength ranged from 9.47 MPa to 10.51 MPa. These results indicate that, under the formulation and stepwise preparation process defined in this invention, the resulting hardened body exhibits high early strength and late strength development levels under standard curing conditions. Combined with the aforementioned fluidity, setting time, and apparent density test results of the hardened body, the improved mechanical properties of the example groups correspond to the maintenance of slurry handling properties, densification of the hardened body, and the participation of regenerated micropowder in the construction of the inorganic gel network.

[0094] Comparative Example 1 used a conventional single-phase alkali-activated system, with a 28-day compressive strength of 31.62 MPa and a 28-day flexural strength of 5.37 MPa, lower than that of the Example Group. This result indicates that, under the same solid-phase powder composition, when directly using a single-phase alkali-activated method, the early reaction is concentrated, and the subsequent strength development level is lower than that of the step-by-step etching and liquid-based activation processes. Compared to Comparative Example 1, Example 1 pre-treated the recycled micro-powder from construction waste with an acidic etching solution and simultaneously introduced granulated blast furnace slag micro-powder and alkaline polycondensation solution in the subsequent stage, which is beneficial to increasing the degree to which the solid-phase powder participates in the hydration polycondensation reaction, thereby improving the compressive and flexural strength of the hardened body.

[0095] Comparative Example 6, without the addition of anhydrous citric acid as a complexing etchant, exhibited a 28-day compressive strength of 26.75 MPa and a 28-day flexural strength of 4.61 MPa, lower than that of the Example Group and Comparative Example 1. This result indicates that the absence of anhydrous citric acid in the pre-etching and complexing process significantly limits the passivation layer on the surface of the recycled construction waste powder, reducing the effective participation of the recycled powder in the system. The Example Group, through an acidic etching stage involving anhydrous citric acid, improved the surface condition of the recycled powder, facilitating the formation of a bonding interface between the inorganic gel and the recycled powder surface, and enhancing the overall mechanical properties of the hardened body.

[0096] Comparative Example 5, without the addition of polyvinyl alcohol and sodium tetraborate decahydrate, exhibited a 28-day compressive strength of 21.36 MPa and a 28-day flexural strength of 3.94 MPa, which were among the lowest levels in the test groups. This result indicates that in the absence of the dynamic network constructed by polyvinyl alcohol and sodium tetraborate decahydrate, the rheological control ability of the slurry during the reaction process decreases, and the stability of particle dispersion and gel formation is lower than that of the Example Group. In the Example Group, the dynamic network formed by the combination of polyvinyl alcohol and sodium tetraborate decahydrate, combined with the dispersing effect of the naphthalenesulfonate formaldehyde condensate, helps to reduce disordered flocculation and structural defects, and improves the compressive and flexural strength of the hardened body.

[0097] Test Example 5: This test case aims to verify the system's ability to solidify free alkali metal ions and its performance in preventing moisture migration-induced efflorescence.

[0098] The testing steps are as follows: (1) Test blocks with dimensions of 40mm×40mm×160mm that were cured for 28 days in Examples 1 to 5 and Comparative Example 1 were selected as test objects. The test blocks were dried in a 60℃ drying oven until the mass was constant. The four long strip sides of the test blocks were sealed with epoxy resin, leaving only the square cross-sections at both ends as test surfaces. The test blocks were placed in a constant temperature water bath with the bottom surface immersed in water for 3mm. The mass change of the test blocks after absorbing water was measured periodically, and the capillary water absorption coefficient of the test blocks was calculated.

[0099] (2) Take test blocks from the same batch and place them in a sealed polytetrafluoroethylene container containing 2000 mL of deionized water, and implement a wet-dry cycle program. A single cycle is set to soak in water at 20°C for 24 h, and then transfer to a dry environment at 60°C for 24 h.

[0100] (3) At the end of the 7th, 14th and 28th soaking stages of the wet-dry cycle, 15 mL of leachate sample was taken from each container and a 2% (v / v) nitric acid solution was added for micro-acidification. The treated sample was injected into an inductively coupled plasma atomic emission spectrometer to determine the concentration of free sodium ions in the liquid phase.

[0101] Each group of test blocks shall contain no fewer than 3 pieces. The data in Table 5 are average values, and the relative deviation of a single group of tests shall not exceed 5%. The test data are shown in Table 5.

[0102] Table 5: Test data of capillary water absorption coefficient and sodium ion leaching concentration of each system sample blocks According to the data in Table 5, the capillary water absorption coefficients of Examples 1 to 5 are 0.131 kg / (m²). 2 ·h 0.5 ) to 0.155 kg / (m 2 ·h 0.5 After 28 wet-dry cycles, the sodium ion concentration in the leachates of Examples 1 to 5 ranged from 19.43 mg / L to 23.12 mg / L. These results indicate that, under the formulation and stepwise preparation process conditions defined in this invention, the hardened body exhibits a low capillary water absorption coefficient and maintains a low sodium ion leaching level after multiple wet-dry cycles. This result corresponds to the higher apparent density and better structural compaction of the hardened bodies in the Example group.

[0103] Comparative Example 1 used a conventional single-phase alkali activation system, with a capillary water absorption coefficient of 0.876 kg / (m²). 2 ·h 0.5 The sodium ion concentration in the leachate was significantly higher than that in the example group. After the 7th, 14th, and 28th wet-dry cycles, the sodium ion concentrations in the leachate were 156.42 mg / L, 284.15 mg / L, and 412.87 mg / L, respectively, all higher than those in the example group. This result indicates that the addition of sodium hydroxide to a conventional single-phase alkali-activated system results in a higher initial content of free alkali metal ions. Simultaneously, the higher capillary water absorption coefficient of the hardened body facilitates water entry and migration during wet-dry cycles, thereby increasing the sodium ion leaching level.

[0104] In the example group, no additional sodium hydroxide was introduced. Instead, an aqueous solution of sodium silicate and sodium tetraborate decahydrate were used in the network construction, reducing the initial enrichment of free sodium ions. Combined with the venting effect during the acid etching stage, the subsequent gel precipitation reaction, and the vibration molding process, the number of through-pores and interface gaps inside the hardened body of the example group was reduced, and the capillary water migration path was restricted. As a result, the example group exhibited a lower capillary water absorption coefficient and a lower sodium ion leaching concentration under wet-dry cycling conditions, which is beneficial for reducing the tendency of surface alkali blooming during service.

[0105] In summary, the example group, through the combined effects of a low-free alkali metal ion formulation, stepwise etching activation, and densification of the hardened body, effectively suppressed moisture migration and sodium ion efflorescence. This result aligns with the technical objective of this invention: reducing efflorescence and improving the service stability of green building materials.

[0106] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A green building material preparation process based on the recycling of construction waste, characterized in that, Includes the following steps: (1) The recycled micro powder of construction waste is put into a mixer and stirred at low speed at room temperature. Acidic etching solution is added at a uniform speed for mixing. The acidic etching solution is used to dissolve the inert coating layer on the surface of the recycled micro powder of construction waste and release gas. (2) After the low-speed stirring in step (1) is completed, granulated blast furnace slag powder and alkaline polycondensation liquid are added to the mixer simultaneously; During the addition of the granulated blast furnace slag powder and alkaline condensation liquid, the mixer is switched to strong shear mode to increase the stirring speed; (3) After maintaining the strong shear mode of step (2), reduce the speed of the mixer to low speed to restore the viscosity of the slurry structure. Then unload the material and pour it into the mold. After vibration molding and curing, the final product is obtained.

2. The green building material preparation process based on the recycling of construction waste according to claim 1, characterized in that, Based on 100 parts by weight of solid powder, the solid powder consists of 55-65 parts by weight of the recycled construction waste micro powder and 35-45 parts by weight of the granulated blast furnace slag micro powder. The specific surface area of ​​the recycled construction waste powder is 400-460 m². 2 / kg; the granulated blast furnace slag powder meets the S95 grade technical indicators, with a specific surface area of ​​400-430m². 2 / kg.

3. The green building material preparation process based on the recycling of construction waste according to claim 2, characterized in that, Based on 100 parts by weight of solid powder, the acidic etching solution is prepared from the following raw materials in parts by weight: Water 12.21–13.00 parts; Polyvinyl alcohol (PVA) 0.46–0.87 parts, wherein the degree of alcoholysis of PVA is 87%–89% and the average degree of polymerization is 1700–1800; Anhydrous citric acid 1.061–1.729 parts; Aluminum sulfate octahydrate, 0.736–1.200 parts; 0.015 to 0.0504 parts of polyoxypropylene polyoxyethylene glycerol ether, wherein the number average molecular weight of the polyoxypropylene polyoxyethylene glycerol ether is 2500 to 3500 g / mol.

4. The green building material preparation process based on the recycling of construction waste according to claim 3, characterized in that, The preparation method of the acidic etching solution includes: The polyvinyl alcohol is added to water with continuous stirring, the temperature is raised to 85-90°C and kept at this temperature with stirring for 45-60 minutes until completely dissolved; after naturally cooling to room temperature, the anhydrous citric acid and aluminum sulfate octadecahydrate are added in sequence and stirred until completely dissolved; then the polyoxypropylene polyoxyethylene glycerol ether is added dropwise and homogenized at 100-150 rpm for 5 minutes to obtain an acidic etching solution.

5. The green building material preparation process based on the recycling of construction waste according to claim 2, characterized in that, Based on 100 parts by weight of solid powder, the alkaline polycondensation solution is made from the following raw materials in parts by weight: Water 4.30–6.30 parts; Sodium tetraborate decahydrate, 0.30–0.70 parts; 0.40–0.60 parts of naphthalene sulfonate formaldehyde condensate; The sodium silicate aqueous solution comprises 8.60 to 12.50 parts, wherein the modulus of the sodium silicate aqueous solution is 1.8 to 2.2 and the Baume degree is 38 to 42, which is equivalent to 3.268 to 5.00 parts of solid sodium silicate.

6. The green building material preparation process based on the recycling of construction waste according to claim 5, characterized in that, The preparation method of the alkaline polycondensation solution includes: Add the sodium tetraborate decahydrate and naphthalene sulfonate formaldehyde condensate to water and stir until dissolved; then add the sodium silicate aqueous solution and stir at 200-300 rpm for 10-15 minutes to obtain an alkaline condensation solution.

7. The green building material preparation process based on the recycling of construction waste according to claim 1, characterized in that, In step (1), the speed of the low-speed stirring is 30-50 rpm, and the low-speed stirring time is 5-10 min; In step (3), the speed of the low-speed stirring is 30-50 rpm, and the low-speed stirring time is 1-2 min.

8. The green building material preparation process based on the recycling of construction waste according to claim 1, characterized in that, The specific operation method of step (2) is as follows: Granulated blast furnace slag powder is fed into the mixer via a screw conveyor, and alkaline condensation liquid is evenly sprayed into the mixer via a high-pressure atomizing nozzle, with both being added synchronously within 45 to 75 seconds. From the 20th to 40th second after the addition of the granulated blast furnace slag powder and alkaline polycondensation liquid, the mixer is switched to strong shear mode to increase the stirring speed to 120 to 160 rpm; and before the speed is reduced in step (3), the strong shear mode is maintained for 1.5 to 3 minutes.

9. The green building material preparation process based on the recycling of construction waste according to claim 1, characterized in that, In step (3), the curing conditions are as follows: after curing the molded specimen in a standard curing room with a temperature of 20±2℃ and a relative humidity of ≥95%, the specimen is demolded and cured until the specified test age is reached.

10. A green building material product based on the recycling of construction waste, characterized in that, The product is prepared using the green building material preparation process based on the recycling of construction waste as described in any one of claims 1 to 9.

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