Cement-free solid waste-based cementitious material, preparation method and application thereof

Abstract

The application relates to the technical field of building materials, and discloses a cement-free solid-waste-based cementitious material and a preparation method and application thereof. The cementitious material is prepared from slag powder, fly ash, steel slag powder, desulfurization gypsum, cement and a solid alkaline synergist according to specific proportions by weight; the preparation method adopts a two-step dry mixing process, bulk solid waste raw materials are first put into a mixer for sufficient premixing and homogenization, then a synergist composed of anhydrous sodium carbonate and sodium hydroxide is added for secondary dispersion mixing, and a dynamic feeding checking mechanism based on the feedback of intermediate semi-finished product liquid-phase pH value detection results is established. Through the synergistic effect of strong alkali excitation of the solid synergist and coagulation adjustment of the sulfate, rapid depolymerization of aluminosilicate glass and dense gel construction are realized, which is beneficial to solving the storage and transportation problem of the liquid excitation agent, reduces carbon emission, and improves the volume stability and mechanical strength of the material.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a cement-free solid waste-based cementitious material, its preparation method, and its application. Background Technology

[0002] Cement-free solid waste-based cementitious materials refer to materials that utilize industrial solid wastes such as fly ash and slag as main raw materials. Through the action of an alkali activator, the silica-alumina raw materials undergo depolymerization and condensation reactions to form a hardened material with mechanical strength. Cement-free solid waste-based cementitious materials do not require traditional Portland cement, thus helping to reduce energy consumption and carbon dioxide emissions. These materials show promising applications in civil engineering and resource recycling.

[0003] Existing technologies for preparing cement-free solid waste-based cementitious materials typically employ a physical mixing process, which involves mixing fly ash and slag powder in a specific ratio, followed by activation with sodium silicate or sodium hydroxide solution. In this mixed system, the slag powder contains a significant amount of highly active calcium aluminosilicate glass, which can rapidly dissolve and undergo hydration reactions under alkaline conditions. Fly ash, on the other hand, is primarily composed of relatively dense spherical glass microspheres; its deagglomeration requires high activation energy, resulting in a relatively slow reaction rate.

[0004] Due to the significant differences in reaction kinetics between fly ash and slag powder, a competitive inhibition effect occurs between them in the same reaction system. Slag powder preferentially reacts with the alkali activator to generate hydration products, which then coat the surface of fly ash particles, blocking the diffusion channels between the alkali activator and fly ash. This prevents fly ash from fully participating in the geopolymerization reaction, resulting in it only playing a physical filling role. The insufficient reaction of fly ash leads to an uneven microstructure within the cementitious system, with defects and pores in the gel skeleton. Consequently, the macroscopic mechanical properties of cement-free solid waste-based cementitious materials exhibit high brittleness and low toughness. Furthermore, because the formed gel network has limited chemical binding capacity for alkali metal ions, free alkali metal ions easily migrate with moisture to the surface of cement-free solid waste-based cementitious materials, causing efflorescence, which is detrimental to the water resistance and long-term durability of these materials. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a cement-free solid waste-based cementitious material, its preparation method, and its application. The aim is to solve the problems in existing technologies where the difference in reaction kinetics between fly ash and slag powder leads to insufficient fly ash reaction, resulting in brittleness, low toughness, and susceptibility to efflorescence in cement-free solid waste-based cementitious materials.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of this invention provides a cement-free solid waste-based cementitious material, made from dry powder raw materials comprising the following parts by weight: The mixture comprises: 300-700 parts slag powder; 100-300 parts fly ash; 100-200 parts steel slag powder; 100-200 parts desulfurized gypsum; 0-100 parts cement; and 4.5-5.5 parts solid alkaline synergist. The solid alkaline synergist is used to adjust the pH of the liquid phase system to above 12.0 during the initial mixing of the solid waste-based cementitious material with water, thereby depolymerizing the aluminosilicate glass in the slag powder, fly ash, and steel slag powder.

[0007] By adopting the above technical solution, this invention achieves the synergistic activation of dry powdering of all solid waste components. The core reaction mechanism is described below: Alkalinity regulation and vitreous depolymerization mechanism: This invention introduces a specific ratio of solid alkaline synergist. Upon mixing the cementitious material with water, the solid alkaline synergist rapidly dissolves and ionizes, releasing a high concentration of hydroxide ions, thus raising the pH of the liquid system to above 12.0. This high alkalinity environment breaks down the silicon-oxygen and aluminum-oxygen bonds in the glassy network structure on the surface of slag powder, fly ash, and steel slag powder. After the glassy network depolymerizes, it releases active calcium ions, silicate ions, and aluminate ions.

[0008] Multi-component solid waste synergistic hydration hardening mechanism: The active ions released during depolymerization migrate in the liquid phase and undergo chemical bonding reactions. Slag powder provides the main calcium and silica components, forming a hydrated calcium silicate gel framework; fly ash supplements the alumina components, promoting the formation of hydrated calcium aluminosilicate gel and optimizing the pore structure; steel slag powder acts as an active micro-aggregate to fill the voids, and the slowly released alkalinity from the steel slag powder maintains an alkaline environment in the later stages of the system, preventing reaction stagnation; sulfate ions provided by desulfurized gypsum react with the dissolved aluminum phase to form ettringite crystals, constructing an early-stage strength framework. The specific reaction process is as follows: Dissolution and ionization: Anhydrous sodium carbonate and sodium hydroxide dissolve in water and ionize into sodium ions, carbonate ions and hydroxide ions.

[0009] Network depolymerization: The silicon-oxygen bonds and aluminum-oxygen bonds in the vitreous network break under the action of hydroxide ions, generating silicate ions, aluminate ions and calcium ions.

[0010] Condensation into gel: Calcium ions, silicate ions and aluminate ions undergo condensation reaction in an aqueous environment to form hydrated calcium aluminosilicate gel.

[0011] Crystal growth: Calcium ions, aluminate ions and sulfate ions combine in an aqueous environment to form ettringite crystals.

[0012] Performance advantages: This technology replaces unstable liquid activators, achieving complete dry powdering of the material and solving the problems of liquid transportation and storage. Simultaneously, through precise stoichiometric activation, the material can still achieve excellent mechanical properties even with no cement or extremely low cement content (0-100 parts), significantly reducing carbon emissions during the production of cementitious materials.

[0013] Preferably, the solid waste-based cementitious material is made from raw materials comprising the following parts by weight: 660-680 parts slag powder; 110-120 parts fly ash; 110-120 parts steel slag powder; 95-105 parts desulfurized gypsum; 4.8-5.2 parts solid alkaline synergist; and 0 parts cement.

[0014] By adopting the above technical solution, without using any silicate cement, and by optimizing the bulk density and activity matching of each solid waste component, and utilizing the strong activating effect of solid alkaline synergists, a pure solid waste cementitious material with excellent mechanical properties can be obtained.

[0015] Preferably, the slag powder is S95 grade granulated blast furnace slag, and the specific surface area of ​​the slag powder is 500-550 m². 2 / kg; the fly ash is low-calcium fly ash, and the specific surface area of ​​the fly ash is 550-590m². 2 / kg; the steel slag powder is hot-pollinated steel slag, and the specific surface area of ​​the steel slag powder is 400-450m². 2 / kg; the desulfurized gypsum is a dry powder with a moisture content of less than 1%, and the specific surface area of ​​the desulfurized gypsum is 500-550m². 2 / kg. By adopting the above technical solution, the specific surface area of ​​each component is limited, increasing the contact area between solid waste particles and the alkaline liquid phase, thus accelerating the reaction rate. The physical filling effect of the micro-powder optimizes the pore size distribution of the hardened body, improving the material's density and impermeability. Limiting the moisture content of the desulfurized gypsum to less than 1% prevents the moisture in the raw materials from pre-reacting with the alkaline synergist during storage, ensuring the product's storage stability.

[0016] Preferably, the solid alkaline synergist is composed of anhydrous sodium carbonate and sodium hydroxide; more preferably, the mass ratio of anhydrous sodium carbonate to sodium hydroxide is 1:(1.4-1.6).

[0017] By adopting the above technical solution, sodium hydroxide provides an initial high alkalinity environment, which rapidly destroys the glass structure; while providing alkalinity, anhydrous sodium carbonate can react with dissolved calcium ions to generate fine calcium carbonate crystal nuclei, induce the precipitation and growth of hydration products, and act as a buffer to maintain the alkalinity balance in the later stage of the reaction.

[0018] A second aspect of this invention provides a method for preparing a cement-free solid waste-based cementitious material, comprising the following steps: (a) Weigh out the slag powder, fly ash, steel slag powder, desulfurized gypsum and cement by weight, put them into a mixer for dry premixing, so that the components are macroscopically dispersed evenly to obtain the semi-finished cementitious material. (b) Add the weighed solid alkaline enhancer to the semi-finished cementitious material, mix and stir it a second time, adjust the alkalinity of the liquid phase of the system with the solid alkaline enhancer, and discharge the material to obtain the finished solid waste-based cementitious material.

[0019] By adopting the above technical solution, the two-step dry mixing process achieves the following technical effects: To prevent localized agglomeration: First, mix a large amount of base solid waste evenly, then add a small amount of solid alkaline synergist to prevent the synergist from coming into contact with a single solid waste at too high a concentration, which could lead to localized agglomeration or crusting.

[0020] Improved activation uniformity: Secondary mixing ensures that trace amounts of synergist are highly dispersed in the macroscopic powder, guaranteeing that the pH value of each micro-region in the system rises uniformly when water is added later, reducing the dispersion of mechanical strength caused by uneven alkalinity distribution.

[0021] Extended shelf life: The stepwise contact between solid waste raw materials and synergists minimizes the deliquescence effect of moisture in the air on the synergists.

[0022] Preferably, in step (a), the dry premixing speed is 25-35 r / min and the mixing time is 25-35 minutes; in step (b), the secondary mixing speed is 25-35 r / min and the mixing time is 4-6 minutes.

[0023] By adopting the above technical solutions, the low-speed, long-time premixing ensures the macroscopic uniformity of large-volume materials; the short-time secondary mixing ensures the dispersion of synergists and prevents material heating or physical segregation caused by excessive stirring.

[0024] Preferably, the solid alkaline synergist is prepared by dry mixing anhydrous sodium carbonate and flake sodium hydroxide at a high speed of 450-550 r / min in an environment with a relative humidity of less than 40% and then vacuum sealing.

[0025] By adopting the above technical solution, high-speed dry mixing in a low-humidity environment avoids the absorption of moisture by sodium hydroxide and uses mechanical force to initially combine the two alkaline components; vacuum sealing further isolates carbon dioxide and moisture, maintaining the high chemical activity of the synergist.

[0026] Preferably, the preparation method further includes a quality control step: Before step (b), a small amount of the semi-finished cementitious material obtained in step (a) is dispersed in water to test the pH value. The amount of solid alkaline synergist added is checked based on the test results to ensure that the final system pH value is not lower than 12.0.

[0027] By adopting the above technical solution, a dynamic batching control mechanism based on pH feedback was established. Because the chemical composition of different batches of solid waste raw materials (especially steel slag powder and fly ash) fluctuates significantly, their acidity and alkalinity can easily differ. Through intermediate testing, the amount of synergist added is dynamically adjusted to avoid the impact of raw material fluctuations on the final reaction environment. This ensures that the liquid-phase reaction environment of each batch of product can stably reach the depolymerization threshold of pH 12.0 or higher, thereby guaranteeing the stability of product quality.

[0028] This invention provides a cement-free solid waste-based cementitious material, its preparation method, and its application. It has the following beneficial effects: 1. This invention utilizes a solid alkaline synergist to construct a liquid phase environment with a pH value greater than 12.0 in the initial stage of mixing. This helps to depolymerize the aluminosilicate glass network on the surface of slag powder and fly ash, releasing active silicon-oxygen and aluminum-oxygen monomers. This helps to overcome the problem of the solid waste raw materials' low alkalinity preventing them from solidifying and hardening, promotes the formation of a dense structure in the slurry, helps to reduce the leaching concentration of harmful ions, and thus ensures the environmental safety of the materials.

[0029] 2. This invention introduces sulfate ions into desulfurized gypsum, thereby regulating the crystal transformation of hydration products and the slurry setting rate. Sulfate ions preferentially react with the dissolved aluminate phase to form needle-shaped ettringite, inhibiting the formation of flaky hydrated calcium aluminate that easily leads to rapid coagulation. The generated ettringite crystals are used to construct an early strength framework, which helps to solve the technical problems of slow early strength development and uncontrollable setting time in single solid waste systems.

[0030] 3. This invention employs a synergistic activation strategy of composite alkaline components and steel slag powder, which improves the volume stability and later strength development of the material. At the same time, it utilizes the micro-expansion effect generated by the magnesium-containing components in the steel slag and the crystallization expansion of ettringite to effectively compensate for the drying shrinkage of the cementitious material, significantly reduce the shrinkage rate and increase the softening coefficient, thereby improving the crack resistance and water resistance durability of the material. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0032] Preparation Examples 1-5 Preparation Example 1: This preparation example provides a method for preparing synergist C1 for activating the activity of solid waste, including the following steps: Weigh out 400.0 g of analytical grade anhydrous sodium carbonate and 600.0 g of analytical grade flake sodium hydroxide. Simultaneously add both raw materials to a high-speed mixer equipped with a sealed lid, and dry mix at 500 rpm for 5 minutes at room temperature and relative humidity below 40%. After the materials are uniformly mixed, immediately remove and vacuum seal the mixture to obtain a white powdered synergist C1, in which the mass ratio of anhydrous sodium carbonate to sodium hydroxide is 1:1.5, used for subsequent pH adjustment of the gelling system.

[0033] Preparation Example 2: This preparation example provides a method for preparing synergist C2 for industrial production, including the following steps: Weigh out 20.0 kg of industrial-grade anhydrous sodium carbonate (purity ≥98%) and 30.0 kg of industrial-grade sodium hydroxide (purity ≥96%). Add the raw materials to a V-type mixer, start the mixing program, and set the mixing time to 15 minutes to ensure that powders of different densities are fully and uniformly dispersed. After discharge, package the mixture in a moisture-proof manner to obtain synergist C2. This synergist strictly adheres to a 1:1.5 mass ratio formulation design, aiming to verify the feasibility of using industrial-grade raw materials in practical applications.

[0034] Preparation Example 3: This preparation example provides a method for preparing pretreated highly active slag powder K1, including the following steps: S95 grade granulated blast furnace slag was selected as the raw ore and fed into a ball mill for mechanical grinding via an elevator. The particle size of the slag powder was shaped and refined by controlling the gradation of the grinding media and the grinding time. After grinding, the powder was separated by an air classifier, and particles with a specific surface area of ​​525 m² were selected. 2 The fine powder fraction is obtained by passing it through a 0.045mm square-hole sieve, with the residue rate controlled within 5%. The resulting powder is designated as slag powder K1, and its physical properties fall within the 500-550 μm range specified in the claims. 2 / kg is preferably near the center value of the range.

[0035] Preparation Example 4: This preparation example provides a method for preparing pretreated fly ash F1, including the following steps: Low-calcium F-type fly ash (loss on ignition 1.8%) was selected and fed into an ultrafine grinding mill for activation grinding. The grinding process focused on breaking down the hard outer shell of the fly ash's spherical glassy structure to expose the internal active silica-alumina components. Online monitoring with a laser particle size analyzer showed that when the powder's specific surface area reached 570 m² / g, the desired particle size was achieved. 2Grinding is stopped when the particle size reaches / kg, the material is discharged and sieved to remove impurities, yielding fly ash F1. This fineness meets the 550-590 μm requirement of the claim. 2 / kg of high activity range.

[0036] Preparation Example 5: This preparation example provides a method for preparing pretreated steel slag powder G1, including the following steps: Hot-pouring steel slag with an aging period of over 6 months was selected, crushed, and magnetically separated to remove iron before being fed into a vertical mill. Due to the high hardness of the steel slag, a multi-stage grinding process was employed to grind the steel slag to a specific surface area of ​​430 m². 2 / kg. The resulting steel slag powder G1 has extremely low metallic iron content and high hydration activity, meeting the requirements of claim 400-450m. 2 / kg parameter requirements.

[0037] Examples 1-10: Example 1: This embodiment provides a method for preparing a cement-free solid waste-based cementitious material, including the following steps: Weigh out 675.0g of S95 grade slag powder K1 obtained in Preparation Example 3, 112.5g of fly ash F1 obtained in Preparation Example 4, 112.5g of steel slag powder G1 obtained in Preparation Example 5, and 100.0g of desulfurized gypsum conforming to national standard GB / T21371. The cement content in this formula is 0.

[0038] The weighed solid waste raw materials are put into a double cone mixer, the mixer is started and the speed is adjusted to 30 rpm, and the mixture is continuously mixed for 30 minutes to make the components uniformly dispersed on a macroscopic scale, so as to obtain a semi-finished cementitious material.

[0039] A small amount of the semi-finished cementitious material was taken and dispersed in deionized water at a solid-liquid ratio of 1:10. After stirring for 10 minutes, the pH value of the supernatant was measured. The initial pH value was found to be below 12.0. Then, 5.0 g of the synergist C1 prepared in Preparation Example 1 was added to the semi-finished product in the mixer. This amount accounted for 0.5% of the total mass of the cementitious material. The mixer was restarted and stirred for another 5 minutes at the same speed. The alkalinity of the system was adjusted using the solid synergist until the pH value of the system stabilized above 12.0, thus obtaining the finished cement-free solid waste-based cementitious material.

[0040] Mortar molding was performed according to GB / T17671-2021 standard. The resulting cementitious material was mixed with standard sand and water at a mortar-to-mortar ratio of 1:3 and a water-to-cement ratio of 0.5 in a cement paste mixer. The mixing program was set as follows: first, low-speed mixing at 140 r / min for 30 seconds; then, high-speed mixing at 285 r / min for 30 seconds after adding sand; a 90-second pause; and finally, high-speed mixing for 60 seconds. After discharge, the slurry was poured into triple molds measuring 40 mm × 40 mm × 160 mm and compacted 60 times at 60 times / min on a vibrating table. The surface was smoothed, covered with plastic wrap, and placed in a standard curing chamber at a temperature of 20 ± 2℃ and a relative humidity of not less than 95% for static curing. After 24 hours, the mold was removed, and curing continued under the same conditions until the specified age.

[0041] Example 2: This embodiment provides a method for preparing a high-strength solid waste-based cementitious material, including the following steps: Weigh out 662.5g of S95 grade slag powder K1 obtained in Preparation Example 3, 111.25g of fly ash F1 obtained in Preparation Example 4, 111.25g of steel slag powder G1 obtained in Preparation Example 5, 100.0g of desulfurized gypsum conforming to national standard GB / T21371, and 10.0g of P·O42.5 grade ordinary Portland cement. The cement content in this formula is 10.0g.

[0042] The weighed raw materials were added to a double cone mixer. The mixer was started and the speed was adjusted to 30 rpm. Mixing was continued for 30 minutes to ensure that the trace cement and other solid waste components were macroscopically and uniformly dispersed, resulting in a semi-finished cementitious material. A small amount of the semi-finished cementitious material was taken and dispersed in deionized water at a solid-liquid ratio of 1:10. After stirring for 10 minutes, the pH value of the supernatant was measured. The initial pH value was found to be below 12.0. Therefore, 5.0 g of the synergist C1 prepared in Preparation Example 1 was added to the semi-finished material in the mixer. This amount accounted for 0.5% of the total mass of the cementitious material. The mixer was started again and stirred at the same speed for 5 minutes to adjust the alkalinity of the system using the solid synergist until the pH value of the system stabilized above 12.0, resulting in a high-strength solid waste-based cementitious material product.

[0043] Mortar molding was performed according to GB / T17671-2021 standard. The resulting cementitious material was mixed with standard sand and water at a mortar-to-mortar ratio of 1:3 and a water-to-cement ratio of 0.5 in a cement paste mixer. The mixing program was set as follows: first, low-speed mixing at 140 r / min for 30 seconds; then, high-speed mixing at 285 r / min for 30 seconds after adding sand; a 90-second pause; and finally, high-speed mixing for 60 seconds. After discharge, the slurry was poured into triple molds measuring 40 mm × 40 mm × 160 mm and compacted 60 times at 60 times / min on a vibrating table. The surface was smoothed, covered with plastic wrap, and placed in a standard curing chamber at a temperature of 20 ± 2℃ and a relative humidity of not less than 95% for static curing. After 24 hours, the mold was removed, and curing continued under the same conditions until the specified age.

[0044] Example 3: This embodiment provides a method for preparing a solid waste-based cementitious material containing trace amounts of cement, comprising the following steps: Weigh out 637.5g of S95 grade slag powder K1 obtained in Preparation Example 3, 106.25g of fly ash F1 obtained in Preparation Example 4, 106.25g of steel slag powder G1 obtained in Preparation Example 5, 100.0g of desulfurized gypsum conforming to national standard GB / T21371, and 50.0g of P·O42.5 grade ordinary Portland cement. The cement content in this formula is 50.0g.

[0045] The weighed raw materials were added to a double cone mixer. The mixer was started and the speed was adjusted to 30 rpm. Mixing was continued for 30 minutes to ensure that the components were macroscopically uniformly dispersed, resulting in a semi-finished cementitious material. A small amount of the semi-finished cementitious material was taken and dispersed in deionized water at a solid-liquid ratio of 1:10. After stirring for 10 minutes, the pH value of the supernatant was measured. The initial pH value was found to be slightly lower than 12.0. 5.0 g of the synergist C1 prepared in Preparation Example 1 was then added to the semi-finished material in the mixer. This amount accounted for 0.5% of the total mass of the cementitious material. The mixer was started again and stirred at the same speed for 5 minutes to adjust the alkalinity of the system using the solid synergist until the pH value of the system stabilized above 12.0, thus obtaining the finished solid waste-based cementitious material.

[0046] Mortar molding was performed according to GB / T17671-2021 standard. The resulting cementitious material was mixed with standard sand and water at a mortar-to-mortar ratio of 1:3 and a water-to-cement ratio of 0.5 in a cement paste mixer. The mixing program was set as follows: first, low-speed mixing at 140 r / min for 30 seconds; then, high-speed mixing at 285 r / min for 30 seconds after adding sand; a 90-second pause; and finally, high-speed mixing for 60 seconds. After discharge, the slurry was poured into triple molds measuring 40 mm × 40 mm × 160 mm and compacted 60 times at 60 times / min on a vibrating table. The surface was smoothed, covered with plastic wrap, and placed in a standard curing chamber at a temperature of 20 ± 2℃ and a relative humidity of not less than 95% for static curing. After 24 hours, the mold was removed, and curing continued under the same conditions until the specified age.

[0047] Example 4: This embodiment provides a method for preparing a cement-free solid waste-based cementitious material, including the following steps: Weigh out 652.5g of S95 grade slag powder K1 obtained in Preparation Example 3, 108.75g of fly ash F1 obtained in Preparation Example 4, 108.75g of steel slag powder G1 obtained in Preparation Example 5, 100.0g of desulfurized gypsum conforming to national standard GB / T21371, and 30.0g of P·O42.5 grade ordinary Portland cement. The cement content in this formula is 30.0g.

[0048] The weighed raw materials were added to a double cone mixer. The mixer was started and the speed was adjusted to 30 rpm. Mixing was continued for 30 minutes to ensure that the components were macroscopically uniformly dispersed, resulting in a semi-finished cementitious material. A small amount of the semi-finished cementitious material was taken and dispersed in deionized water at a solid-liquid ratio of 1:10. After stirring for 10 minutes, the pH value of the supernatant was measured. The initial pH value was found to be below 12.0. Therefore, 5.0 g of the synergist C1 prepared in Preparation Example 1 was added to the semi-finished product in the mixer. This amount accounted for 0.5% of the total mass of the cementitious material. The mixer was started again and stirred at the same speed for 5 minutes to adjust the alkalinity of the system using the solid synergist until the pH value of the system stabilized above 12.0, thus obtaining the finished solid waste-based cementitious material.

[0049] Mortar molding was performed according to GB / T17671-2021 standard. The resulting cementitious material was mixed with standard sand and water at a mortar-to-mortar ratio of 1:3 and a water-to-cement ratio of 0.5 in a cement paste mixer. The mixing program was set as follows: first, low-speed mixing at 140 r / min for 30 seconds; then, high-speed mixing at 285 r / min for 30 seconds after adding sand; a 90-second pause; and finally, high-speed mixing for 60 seconds. After discharge, the slurry was poured into triple molds measuring 40 mm × 40 mm × 160 mm and compacted 60 times at 60 times / min on a vibrating table. The surface was smoothed, covered with plastic wrap, and placed in a standard curing chamber at a temperature of 20 ± 2℃ and a relative humidity of not less than 95% for static curing. After 24 hours, the mold was removed, and curing continued under the same conditions until the specified age.

[0050] Example 5: This embodiment provides a method for preparing a cement-free solid waste-based cementitious material, comprising the following steps: weighing a total of 660.0g of S95 grade slag powder K1 obtained in Preparation Example 3, a total of 110.0g of fly ash F1 obtained in Preparation Example 4, a total of 110.0g of steel slag powder G1 obtained in Preparation Example 5, 100.0g of desulfurized gypsum conforming to national standard GB / T21371, and 20.0g of P·O42.5 grade ordinary Portland cement, wherein the cement content in this formula is 20.0g.

[0051] The weighed raw materials were added to a double cone mixer. The mixer was started and the speed was adjusted to 30 rpm. Mixing was continued for 30 minutes to ensure that the components were macroscopically uniformly dispersed, resulting in a semi-finished cementitious material. A small amount of the semi-finished cementitious material was taken and dispersed in deionized water at a solid-liquid ratio of 1:10. After stirring for 10 minutes, the pH value of the supernatant was measured. The initial pH value was found to be below 12.0. Therefore, 5.0 g of the synergist C1 prepared in Preparation Example 1 was added to the semi-finished product in the mixer. This amount accounted for 0.5% of the total mass of the cementitious material. The mixer was started again and stirred at the same speed for 5 minutes to adjust the alkalinity of the system using the solid synergist until the pH value of the system stabilized above 12.0, thus obtaining the finished solid waste-based cementitious material.

[0052] Mortar molding was performed according to GB / T17671-2021 standard. The resulting cementitious material was mixed with standard sand and water at a mortar-to-mortar ratio of 1:3 and a water-to-cement ratio of 0.5 in a cement paste mixer. The mixing program was set as follows: first, low-speed mixing at 140 r / min for 30 seconds; then, high-speed mixing at 285 r / min for 30 seconds after adding sand; a 90-second pause; and finally, high-speed mixing for 60 seconds. After discharge, the slurry was poured into triple molds measuring 40 mm × 40 mm × 160 mm and compacted 60 times at 60 times / min on a vibrating table. The surface was smoothed, covered with plastic wrap, and placed in a standard curing chamber at a temperature of 20 ± 2℃ and a relative humidity of not less than 95% for static curing. After 24 hours, the mold was removed, and curing continued under the same conditions until the specified age.

[0053] Example 6: This embodiment provides a method for preparing a finely proportioned cementitious material without cement solid waste, comprising the following steps: Weigh out 633.4g of S95 grade slag powder K1 obtained in Preparation Example 3, 103.3g of fly ash F1 obtained in Preparation Example 4, 103.3g of steel slag powder G1 obtained in Preparation Example 5, and 100.0g of desulfurized gypsum conforming to national standard GB / T21371. The cement content in this formula is 0.

[0054] The weighed solid waste raw materials were added to a double cone mixer. The mixer was started and the speed was adjusted to 30 rpm. Mixing was continued for 30 minutes to ensure that the components were macroscopically uniformly dispersed, resulting in a semi-finished cementitious material. A small amount of the semi-finished cementitious material was taken and dispersed in deionized water at a solid-liquid ratio of 1:10. After stirring for 10 minutes, the pH value of the supernatant was measured. The initial pH value was found to be below 12.0. Therefore, 4.7 g of the synergist C1 prepared in Preparation Example 1 was added to the semi-finished product in the mixer. This amount accounted for 0.5% of the total mass of the cementitious material. The mixer was started again and stirred at the same speed for 5 minutes to adjust the alkalinity of the system using the solid synergist until the pH value of the system stabilized above 12.0, resulting in a finished cement-free solid waste-based cementitious material.

[0055] Mortar molding was performed according to GB / T17671-2021 standard. The resulting cementitious material was mixed with standard sand and water at a mortar-to-mortar ratio of 1:3 and a water-to-cement ratio of 0.5 in a cement paste mixer. The mixing program was set as follows: first, low-speed mixing at 140 r / min for 30 seconds; then, high-speed mixing at 285 r / min for 30 seconds after adding sand; a 90-second pause; and finally, high-speed mixing for 60 seconds. After discharge, the slurry was poured into triple molds measuring 40 mm × 40 mm × 160 mm and compacted 60 times at 60 times / min on a vibrating table. The surface was smoothed, covered with plastic wrap, and placed in a standard curing chamber at a temperature of 20 ± 2℃ and a relative humidity of not less than 95% for static curing. After 24 hours, the mold was removed, and curing continued under the same conditions until the specified age.

[0056] Example 7: This embodiment provides a method for preparing a cement-free binder with high content of fly ash and steel slag, including the following steps: Weigh out 600.0g of S95 grade slag powder K1 obtained in Preparation Example 3, 150.0g of fly ash F1 obtained in Preparation Example 4, 150.0g of steel slag powder G1 obtained in Preparation Example 5, and 100.0g of desulfurized gypsum conforming to national standard GB / T21371. The cement content in this formula is 0. Add the weighed solid waste materials to a double cone mixer, start the mixer and adjust the speed to 30 rpm, and mix continuously for 30 minutes to ensure uniform macroscopic dispersion of all components, obtaining a semi-finished cementitious material. Take a small amount of the semi-finished cementitious material and disperse it in deionized water at a solid-liquid ratio of 1:10. After stirring for 10 minutes, let it stand and test the pH value of the supernatant. The initial pH value was found to be below 12.0. Then, add 5.0g of synergist C1 obtained in Preparation Example 1 to the semi-finished product in the mixer. This addition amount accounts for 0.5% of the total mass of the cementitious material. Restart the mixer and continue stirring for 5 minutes at the same speed. Use the solid synergist to adjust the alkalinity of the system until the pH value of the system stabilizes above 12.0, thus obtaining the cement-free solid waste-based cementitious material product.

[0057] Mortar molding was performed according to GB / T17671-2021 standard. The resulting cementitious material was mixed with standard sand and water at a mortar-to-mortar ratio of 1:3 and a water-to-cement ratio of 0.5 in a cement paste mixer. The mixing program was set as follows: first, low-speed mixing at 140 r / min for 30 seconds; then, high-speed mixing at 285 r / min for 30 seconds after adding sand; a 90-second pause; and finally, high-speed mixing for 60 seconds. After discharge, the slurry was poured into triple molds measuring 40 mm × 40 mm × 160 mm and compacted 60 times at 60 times / min on a vibrating table. The surface was smoothed, covered with plastic wrap, and placed in a standard curing chamber at a temperature of 20 ± 2℃ and a relative humidity of not less than 95% for static curing. After 24 hours, the mold was removed, and curing continued under the same conditions until the specified age.

[0058] Example 8: This embodiment provides a method for preparing a cement-free solid waste-based cementitious material with high steel slag content, including the following steps: weighing a total of 600.0g of S95 grade slag powder K1 obtained in Preparation Example 3, a total of 120.0g of fly ash F1 obtained in Preparation Example 4, a total of 180.0g of steel slag powder G1 obtained in Preparation Example 5, and 100.0g of desulfurized gypsum conforming to the national standard GB / T21371. The cement content in this formula is 0.

[0059] The weighed solid waste raw materials were added to a double cone mixer. The mixer was started and the speed was adjusted to 30 rpm. Mixing was continued for 30 minutes to ensure that the components were macroscopically uniformly dispersed, resulting in a semi-finished cementitious material. A small amount of the semi-finished cementitious material was taken and dispersed in deionized water at a solid-liquid ratio of 1:10. After stirring for 10 minutes, the pH value of the supernatant was measured. The initial pH value was found to be below 12.0. Therefore, 5.0 g of the synergist C1 prepared in Preparation Example 1 was added to the semi-finished product in the mixer. This amount accounted for 0.5% of the total mass of the cementitious material. The mixer was started again and stirred at the same speed for 5 minutes to adjust the alkalinity of the system using the solid synergist until the pH value of the system stabilized above 12.0, resulting in a finished cement-free solid waste-based cementitious material.

[0060] Mortar molding was performed according to GB / T17671-2021 standard. The resulting cementitious material was mixed with standard sand and water at a mortar-to-mortar ratio of 1:3 and a water-to-cement ratio of 0.5 in a cement paste mixer. The mixing program was set as follows: first, low-speed mixing at 140 r / min for 30 seconds; then, high-speed mixing at 285 r / min for 30 seconds after adding sand; a 90-second pause; and finally, high-speed mixing for 60 seconds. After discharge, the slurry was poured into triple molds measuring 40 mm × 40 mm × 160 mm and compacted 60 times at 60 times / min on a vibrating table. The surface was smoothed, covered with plastic wrap, and placed in a standard curing chamber at a temperature of 20 ± 2℃ and a relative humidity of not less than 95% for static curing. After 24 hours, the mold was removed, and curing continued under the same conditions until the specified age.

[0061] Example 9: This embodiment provides a method for preparing a cementitious material without cement solid waste and low slag content, including the following steps: Weigh out 300.0g of S95 grade slag powder K1 obtained in Preparation Example 3, 300.0g of fly ash F1 obtained in Preparation Example 4, 200.0g of steel slag powder G1 obtained in Preparation Example 5, and 200.0g of desulfurized gypsum conforming to national standard GB / T21371. The cement content in this formula is 0.

[0062] The weighed solid waste raw materials were added to a double cone mixer. The mixer was started and the speed was adjusted to 30 rpm. Mixing was continued for 30 minutes to ensure that the components were macroscopically uniformly dispersed, resulting in a semi-finished cementitious material. A small amount of the semi-finished cementitious material was taken and dispersed in deionized water at a solid-liquid ratio of 1:10. After stirring for 10 minutes, the pH value of the supernatant was measured. The initial pH value was found to be below 12.0. Therefore, 5.0 g of the synergist C1 prepared in Preparation Example 1 was added to the semi-finished product in the mixer. This amount accounted for 0.5% of the total mass of the cementitious material. The mixer was started again and stirred at the same speed for 5 minutes to adjust the alkalinity of the system using the solid synergist until the pH value of the system stabilized above 12.0, resulting in a finished cement-free solid waste-based cementitious material.

[0063] Mortar molding was performed according to GB / T17671-2021 standard. The resulting cementitious material was mixed with standard sand and water at a mortar-to-mortar ratio of 1:3 and a water-to-cement ratio of 0.5 in a cement paste mixer. The mixing program was set as follows: first, low-speed mixing at 140 r / min for 30 seconds; then, high-speed mixing at 285 r / min for 30 seconds after adding sand; a 90-second pause; and finally, high-speed mixing for 60 seconds. After discharge, the slurry was poured into triple molds measuring 40 mm × 40 mm × 160 mm and compacted 60 times at 60 times / min on a vibrating table. The surface was smoothed, covered with plastic wrap, and placed in a standard curing chamber at a temperature of 20 ± 2℃ and a relative humidity of not less than 95% for static curing. After 24 hours, the mold was removed, and curing continued under the same conditions until the specified age.

[0064] Example 10: This embodiment provides a method for preparing a solid waste-based cementitious material with high cement content, including the following steps: Weigh out 500.0g of S95 grade slag powder K1 obtained in Preparation Example 3, 150.0g of fly ash F1 obtained in Preparation Example 4, 150.0g of steel slag powder G1 obtained in Preparation Example 5, 100.0g of desulfurized gypsum conforming to national standard GB / T21371, and 100.0g of P·O42.5 grade ordinary Portland cement. The cement content in this formula is 100.0g, accounting for 10% of the total mass.

[0065] The weighed raw materials were added to a double cone mixer. The mixer was started, and the speed was adjusted to 30 rpm. Mixing was continued for 30 minutes to ensure that the cement and solid waste components were macroscopically and uniformly dispersed, resulting in a semi-finished cementitious material. A small amount of the semi-finished cementitious material was taken and dispersed in deionized water at a solid-liquid ratio of 1:10. After stirring for 10 minutes, the pH value of the supernatant was measured. The initial pH value was found to be below 12.0. Therefore, 5.0 g of the synergist C1 prepared in Preparation Example 1 was added to the semi-finished material in the mixer. This amount accounted for 0.5% of the total mass of the cementitious material. The mixer was started again, and stirring was continued for 5 minutes at the same speed. The alkalinity of the system was adjusted using the solid synergist until the pH value of the system stabilized above 12.0, resulting in the finished solid waste-based cementitious material.

[0066] Mortar molding was performed according to GB / T17671-2021 standard. The resulting cementitious material was mixed with standard sand and water at a mortar-to-mortar ratio of 1:3 and a water-to-cement ratio of 0.5 in a cement paste mixer. The mixing program was set as follows: first, low-speed mixing at 140 r / min for 30 seconds; then, high-speed mixing at 285 r / min for 30 seconds after adding sand; a 90-second pause; and finally, high-speed mixing for 60 seconds. After discharge, the slurry was poured into triple molds measuring 40 mm × 40 mm × 160 mm and compacted 60 times at 60 times / min on a vibrating table. The surface was smoothed, covered with plastic wrap, and placed in a standard curing chamber at a temperature of 20 ± 2℃ and a relative humidity of not less than 95% for static curing. After 24 hours, the mold was removed, and curing continued under the same conditions until the specified age.

[0067] Comparative Examples 1-6: Comparative Example 1: Compared with Example 1, the difference is that no synergist C1 was added, and the hydration was carried out only by utilizing the slight alkalinity of the raw materials themselves. The proportions of the other raw materials (slag, fly ash, steel slag, gypsum) and the preparation steps are the same.

[0068] Comparative Example 2: Compared with Example 1, the difference is that 5.0g of synergist C1 was replaced with an equal mass of pure flake sodium hydroxide (analytical grade), while the other raw material ratios and preparation steps were the same.

[0069] Comparative Example 3: Compared with Example 1, the difference is that 5.0g of synergist C1 was replaced with an equal mass of pure anhydrous sodium carbonate (analytical grade), while the other raw material ratios and preparation steps are the same.

[0070] Comparative Example 4: Compared with Example 1, the difference is that steel slag powder G1 was not added, but replaced with an equal mass of fly ash F1. The total amount of other raw materials and preparation steps are the same.

[0071] Comparative Example 5: Compared with Example 1, the difference is that desulfurized gypsum was not added, but replaced with an equal mass of S95 grade slag powder K1. The total amount of other raw materials and preparation steps are the same.

[0072] Comparative Example 6: Compared to Example 1, the difference lies in replacing 5.0 g of synergist C1 with an equal mass of commercially available instant sodium silicate powder (modulus 2.0), while the remaining raw material ratios and preparation steps are the same. Test Examples 1-2 Test Example 1: Feasibility and Environmental Safety Verification of the Reaction Mechanism of the Gelation System This test case aims to verify the effectiveness of the synergist of the present invention in regulating the pH value of the solid waste system, explore the effect of sulfate on coagulation time, and verify the material's ability to solidify heavy metals.

[0073] The experimental steps are as follows: Fresh slurries were prepared according to the formulations of Example 1 (optimal group without cement), Example 5 (low-cement group), Comparative Example 1 (group without synergist), and Comparative Example 5 (group without desulfurized gypsum). At 5 minutes, 30 minutes, 60 minutes, and 120 minutes after mixing, 50g samples of the slurry were taken from the mixer and dispersed in deionized water at a solid-liquid ratio of 1:10. After magnetic stirring for 5 minutes, the mixture was allowed to stand and filtered. The pH value of the filtrate was measured using a high-precision pH meter to characterize the evolution of alkalinity in the liquid phase.

[0074] Meanwhile, in accordance with GB / T1346 standard, the initial setting time and final setting time of each group of slurries were determined using a Vicat apparatus. The change in the depth of the test needle was recorded; if the slurry had not set within 48 hours, it was recorded as not set.

[0075] For hardened specimens that have reached a curing age of 28 days, leaching toxicity tests were conducted according to the HJ / T299 standard. The specimens were crushed and sieved, and acidic extractant was added at a liquid-to-solid ratio of 10:1. The mixture was then shaken on a rotary shaker for 18 hours. After filtration, the concentrations of chromium (Cr) and lead (Pb) in the leachate were determined using inductively coupled plasma mass spectrometry to evaluate the environmental safety of the material.

[0076] Table 1. System alkalinity evolution, coagulation characteristics, and leaching toxicity test data in conclusion: The test data in Table 1 show that the intervention of the synergist and the synergistic effect of sulfate are key to the formation of the system of this invention. In Examples 1 and 5, after the addition of the synergist, the pH value of the slurry remained above 12.21 for 120 minutes. This high-alkaline environment effectively depolymerized the glassy network on the surface of slag and fly ash, providing the silicon-oxygen tetrahedron and aluminum-oxygen tetrahedron active monomers required for the reaction. The initial setting time of Example 1 was 218 minutes, and the final setting time was 342 minutes, indicating that the system has a suitable construction window.

[0077] In contrast, Comparative Example 1, without the addition of synergists, could only maintain a weakly alkaline environment of around pH 10.51 due to the weak hydrolysis of the raw materials themselves. It could not overcome the potential energy barrier of glass depolymerization, resulting in the slurry remaining in a fluid state without solidification after 48 hours. Furthermore, due to the lack of dense hydration product encapsulation, its leaching concentration of heavy metal chromium was as high as 0.452 mg / L.

[0078] Comparative Example 5 reveals the setting mechanism of sulfate ions in desulfurized gypsum. In the absence of gypsum, although the pH value was as high as 12.51, the initial setting time of the slurry was shortened to 43 minutes, exhibiting a significant rapid setting phenomenon. This is because, in the absence of sulfate ions, the dissolved aluminate phase rapidly combines with calcium ions to form platy hydrated calcium aluminate, resulting in a loss of fluidity. In contrast, the sulfate ions present in Example 1 effectively slowed the initial reaction rate by forming needle-like ettringite that coats the particle surface, ensuring workability and contributing to early skeletal strength through the formation of ettringite.

[0079] Test Example 2: Comparison of Mechanical Properties and Analysis of Volume Stability. This test example aims to verify the advantages of the formulation of the present invention in terms of strength development and durability by comparing the mechanical strength, drying shrinkage rate and water resistance of each embodiment and comparative example, and focuses on examining the influence of different activation methods and solid waste ratios on material properties.

[0080] The experimental procedures are as follows: The compressive strength of the mortar blocks prepared in Examples 1-10 and Comparative Examples 1-6 was tested according to GB / T17671 standard, and the compressive strength data at 3 days, 7 days, and 28 days were recorded. Another set of blocks was tested for 28-day drying shrinkage according to JC / T603 standard. The demolded specimens were placed in a constant temperature and humidity chamber at 20±2℃ and 50±4% relative humidity, and their length change rate was measured to evaluate the volumetric stability of the material.

[0081] Simultaneously, the softening coefficient of the material was tested to characterize its water resistance. After soaking the test block in water for 48 hours following 28 days of curing, the saturated compressive strength was measured, and the ratio of this strength to the compressive strength under oven-dry conditions was calculated.

[0082] Table 2. Test data on mechanical properties and durability of cementitious materials in each group. Note: Comparative Example 1 was not hardened, so its strength and shrinkage rate could not be tested; therefore, "--" is used to indicate this. in conclusion: Table 2 shows the performance advantages of the technical solution of this invention. Examples 1-10 all exhibit good mechanical properties, with the cement-free group (Example 1) achieving a 28-day strength of 42.3 MPa and a softening coefficient of 0.88, proving that the pure solid waste system can completely replace traditional cement under reasonable alkali-sulfate activation. Examples 2 and 10 show that the introduction of trace amounts of cement can further increase the strength to approximately 45 MPa, but the increase is not exponentially greater than that of the cement-free group, further proving that the core strength of this invention still originates from the activation by solid waste.

[0083] The differences in the comparative data revealed the roles of each component: Comparative Example 2 (pure sodium hydroxide) showed high early strength (29.1 MPa at 3 days), but its strength declined at 28 days (30.8 MPa). This was due to the strong alkali causing poor crystallinity and uneven distribution of the reaction products. In contrast, Comparative Example 3 (pure sodium carbonate) had low early strength (12.4 MPa at 3 days) and slow growth in the later stages. The composite synergist used in this invention (Example 1) balanced the early and late strength, achieving stable growth throughout the entire lifespan.

[0084] Although Comparative Example 6 (water glass activated) showed acceptable strength, its 28-day drying shrinkage rate was as high as 0.124%, nearly three times that of Example 1 (0.045%). This indicates that the gel generated by water glass activation experiences high shrinkage stress after drying, making it extremely prone to cracking. In contrast, this invention achieves long-term volume stability through the combination of a solid synergist with trace amounts of steel slag (containing magnesium components that cause micro-expansion) and gypsum (containing ettringite that causes micro-expansion). Furthermore, Comparative Example 4 (without steel slag) exhibited low strength, indicating that the high density characteristics of steel slag and the active minerals contribute to the matrix density. Comparative Example 5 (without gypsum) had a 3-day strength of only 6.8 MPa, further confirming that the formation of ettringite is a key mechanism for providing early strength.

Claims

1. A cement-free solid waste-based cementitious material, characterized in that, Made from dry powder ingredients comprising the following parts by weight: 300-700 parts of slag powder; 100-300 parts fly ash; 100-200 parts of steel slag powder; 100-200 parts of desulfurized gypsum; Cement 0-100 parts; 4.5-5.5 parts of solid alkaline synergist; The solid alkaline synergist is used to adjust the pH value of the liquid phase system to above 12.0 in the initial stage of mixing the cement-free solid waste-based cementitious material with water, and is used to depolymerize the aluminosilicate glass in the slag powder, fly ash and steel slag powder.

2. The cement-free solid waste-based cementitious material according to claim 1, characterized in that, Made from the following ingredients in parts by weight: 660-680 parts of slag powder; 110-120 parts fly ash; 110-120 parts of steel slag powder; 95-105 parts of desulfurized gypsum; Solid alkaline synergist 4.8-5.2 parts; 0 parts cement.

3. The cement-free solid waste-based cementitious material according to claim 1, characterized in that, The slag powder is S95 grade granulated blast furnace slag, and the specific surface area of ​​the slag powder is 500-550 m². 2 / kg; the fly ash is low-calcium fly ash, and the specific surface area of ​​the fly ash is 550-590m². 2 / kg; the steel slag powder is hot-pollinated steel slag, and the specific surface area of ​​the steel slag powder is 400-450m². 2 / kg; the desulfurized gypsum is a dry powder with a moisture content of less than 1%, and the specific surface area of ​​the desulfurized gypsum is 500-550m². 2 / kg.

4. The cement-free solid waste-based cementitious material according to claim 1, characterized in that, The solid alkaline synergist is composed of anhydrous sodium carbonate and sodium hydroxide.

5. The cement-free solid waste-based cementitious material according to claim 4, characterized in that, The mass ratio of anhydrous sodium carbonate to sodium hydroxide is 1:(1.4-1.6).

6. A method for preparing the cement-free solid waste-based cementitious material according to any one of claims 1 to 5, characterized in that, Includes the following steps: (a) Weigh out the slag powder, fly ash, steel slag powder, desulfurized gypsum and cement by weight, put them into a mixer for dry premixing, so that the components are macroscopically dispersed evenly to obtain the semi-finished cementitious material. (b) Add the weighed solid alkaline enhancer to the semi-finished cementitious material, mix and stir it a second time, adjust the alkalinity of the liquid phase of the system with the solid alkaline enhancer, and discharge the material to obtain the finished cement-free solid waste-based cementitious material.

7. The method for preparing a cement-free solid waste-based cementitious material according to claim 6, characterized in that, In step (a), the dry premixing speed is 25-35 r / min and the mixing time is 25-35 minutes; in step (b), the secondary mixing stirring speed is 25-35 r / min and the mixing time is 4-6 minutes.

8. The method for preparing a cement-free solid waste-based cementitious material according to claim 6, characterized in that, The solid alkaline synergist is prepared by dry mixing anhydrous sodium carbonate and flake sodium hydroxide at high speed of 450-550 r / min in an environment with relative humidity below 40% and then vacuum sealing.

9. The method for preparing a cement-free solid waste-based cementitious material according to claim 6, characterized in that, It also includes quality control steps: Before step (b), a small amount of the semi-finished cementitious material obtained in step (a) is dispersed in water to test the pH value. The amount of solid alkaline synergist added is checked based on the test results to ensure that the final system pH value is not lower than 12.

0.

10. The application of the cement-free solid waste-based cementitious material according to any one of claims 1 to 5 in the preparation of precast components, building repair materials and 3D printed building materials.

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