Preparation method of steel slag-based cementing material

Abstract

The invention belongs to the technical field of steel slag resource utilization, and particularly relates to a preparation method of a steel slag-based cementing material. Comprising the following steps: S1, preparing raw materials: drying and grinding steelmaking steel slag to obtain steel slag micro powder, respectively dissolving an alkaline exciting agent, a sulfate exciting agent and hydrolyzable polymerized silane in water, and mixing to obtain a composite exciting agent solution; s2, activation: performing plasma activation on the steel slag micro powder through a normal-pressure low-temperature plasma jet device in a dense-phase pneumatic conveying manner to obtain activated steel slag micro powder; and S3, preparation of a cementing material: immediately performing dry mixing on the activated steel slag micro powder and aggregate, slowly adding a composite exciting agent solution, performing vibration molding, and curing to a specified age to obtain a cementing material product. According to the method, denser and firmer anchoring points are provided for polymerized silane through plasma activation, a three-dimensional siloxane network is formed in situ through Si69, the breaking strength and toughness of the material are greatly improved, and generation and extension of microcracks are inhibited.

Description

Technical Field

[0001] This invention belongs to the field of steel slag resource utilization technology, and particularly relates to a method for preparing steel slag-based cementitious materials. Background Technology

[0002] Steel slag is a large amount of solid waste generated during the steel industry. Its stockpiling not only occupies a lot of land but also poses a potential pollution risk to the environment. Grinding steel slag and using it as a cementing material is an important way to realize its high-value resource utilization.

[0003] Currently, mainstream steel slag cementitious material preparation technologies mainly involve activating the steel slag through mechanical grinding or a single activator (such as an alkaline substance), followed by aggregate mixing and molding. While the process is simple, it relies on high amounts of cement or lime, resulting in low strength and poor durability of the cementitious material, insufficient utilization of steel slag, and significant resource waste and environmental burden. Existing technologies have the following shortcomings: 1. Insufficient activation of steel slag activity Traditional methods rely solely on mechanical grinding or a single alkaline activator, which is insufficient to effectively disrupt the stable structure of silicates and aluminates in steel slag. This results in inadequate release of active SiO2 and Al2O3, low hydration reaction efficiency, and poor early strength of the cementitious material.

[0004] 2. Poor interface integration performance There is a lack of chemical bonding between steel slag powder and aggregates (such as quartz sand), and there are weak links in the interface transition zone. After hardening, it is prone to cracking, has low flexural strength, and insufficient durability (such as poor impermeability and carbonation resistance).

[0005] 3. Resource utilization and environmental protection issues Traditional techniques require the addition of large amounts of cement or lime to adjust the setting time, which limits the amount of steel slag (usually <50%) and results in low resource utilization. At the same time, industrial solid waste is not fully utilized (such as steel slag stockpiling pollutes the environment), which does not meet the requirements of green building materials. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing steel slag-based cementitious materials to solve the problems existing in the prior art.

[0007] The technical solution adopted by this invention to solve its technical problem is: A method for preparing a steel slag-based cementitious material includes the following steps: S1. Raw material preparation: Steel slag is dried and ground to obtain steel slag powder. Alkaline activator, sulfate activator and hydrolyzable polymerizable silane are dissolved in water and then mixed to obtain a composite activator solution. S2. Activation: Steel slag powder is activated by plasma activation through an atmospheric pressure low temperature plasma jet device using a dense phase pneumatic conveying method to obtain activated steel slag powder. S3. Preparation of cementitious material: The activated steel slag powder and aggregate are immediately dry-mixed to obtain a dry mixture. The composite activator solution is slowly added to the dry mixture and stirred for 5-10 minutes to form a uniform slurry. The slurry is poured into a mold and vibrated to form the product. After curing at a temperature of 20±2℃ and a humidity of ≥90% for 24-48 hours, the product is demolded and cured according to standard until the specified age is obtained to obtain the cementitious material product.

[0008] Furthermore, in step S1, the specific surface area of ​​the steel slag powder is 200-300 m² / kg.

[0009] Furthermore, in step S1, the alkaline activator is a mixture of sodium hydroxide and sodium aluminate in a mass ratio of 1:0.5~1, the sulfate activator is sodium sulfate, and the hydrolyzable polymerizable silane is bis-(γ-triethoxysilylpropyl)tetrasulfide. The dry matter mass concentration of the composite activator solution is 8~15%, wherein the mass ratio of alkaline activator, sulfate activator, and hydrolyzable polymerizable silane to steel slag powder is as follows: alkaline activator 3~8%, sulfate activator 2~5%, and hydrolyzable polymerizable silane 1~3%.

[0010] Furthermore, in step S2, plasma activation uses helium or a helium-oxygen mixture as the working gas, and is performed for 5 to 10 seconds at a power of 1.5 to 4 kW, with an output temperature of 60 to 80°C.

[0011] Furthermore, the plasma-activated steel slag powder has a specific surface area of ​​700~1000m² / kg.

[0012] Furthermore, the aggregate mentioned in step S3 is quartz sand with a particle size ≤ 5 mm and a SiO2 mass content of not less than 95%, and the mass ratio of activated steel slag powder to aggregate is 7~8:3~2.

[0013] The present invention has the following beneficial effects: 1. This invention uses atmospheric pressure low temperature plasma jet to activate the surface of steel slag powder, replacing the traditional time-consuming mechanical activation process. It has high activation efficiency, creates a better reaction interface for subsequent chemical activation, and significantly reduces energy consumption.

[0014] 2. Hydrolyzable polymerizable silane Si69 is selected to replace the traditional silane coupling agent. This polymerizable silane undergoes in-situ interfacial polymerization to form a three-dimensional network structure that can interweave with the hydration products of steel slag, forming a tough organic-inorganic interpenetrating network structure in the interfacial transition zone, thereby greatly improving the flexural strength and toughness of the material.

[0015] 3. The highly active surface created by plasma activation greatly promotes the hydrolysis and bonding efficiency of polymeric silanes, while the three-dimensional network formed by polymeric silanes can effectively stabilize and protect the active surface created by plasma activation. The two work together to improve the compressive strength and flexural strength of cementitious materials.

[0016] 4. The cementitious material prepared by this invention has a high content of steel slag powder, eliminating the need for cement clinker and realizing the high-value utilization of industrial solid waste. Moreover, the plasma process itself is a dry, low-pollution green technology, which is in line with the development direction of green building materials. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Example 1

[0018] S1. Raw material preparation: Steel slag is dried at 105℃ to constant weight and then ground in a vertical mill to a specific surface area of ​​265m² / kg to obtain steel slag powder. 10kg of steel slag powder is weighed out for later use.

[0019] Preparation of the composite activator solution: Weigh 312.5g NaOH, 187.5g NaAlO2, 350g Na2SO4, and 200g bis-(γ-triethoxysilylpropyl)tetrasulfide (abbreviated as Si69). Dissolve NaOH and NaAlO2 in water to prepare an alkaline solution. Dissolve Na2SO4 in water. Premix Si69 with a small amount of anhydrous ethanol and then dissolve it in water. Finally, mix the three solutions and adjust the total amount of water to make the dry matter concentration of the composite activator solution 10%.

[0020] S2. Activation: The above-mentioned steel slag powder is conveyed by dense-phase pneumatic conveying through a helium atmospheric pressure low-temperature plasma jet device with a power set at 3kW and a processing time of 6 seconds to obtain activated steel slag powder. The discharge temperature of the treated steel slag powder is approximately 70℃, and the specific surface area is measured to increase to 920m² / kg.

[0021] S3. Preparation of cementitious material: Hot activated steel slag powder and quartz sand (particle size ≤5mm, SiO2 mass content 96.8%) are rapidly dry-mixed at a mass ratio of 7.5:2.5 to obtain a dry mixture. The composite activator solution is slowly added to the dry mixture and stirred for 8 minutes to form a uniform slurry. The slurry is poured into a mold and vibrated to form the product. After curing at a temperature of 20±2℃ and a humidity of ≥90% for 36 hours, the product is demolded and cured according to standard until the specified age is obtained to obtain the cementitious material product.

[0022] Its mechanical properties were tested according to national standards, and the results were: 28-day compressive strength 78.5 MPa, 28-day flexural strength 13.2 MPa. Example 2

[0023] S1. Raw material preparation: Steel slag is dried at 105℃ to constant weight and then ground in a vertical mill to a specific surface area of ​​280m² / kg to obtain steel slag powder. 10kg of steel slag powder is weighed out for later use.

[0024] Preparation of the composite activator solution: Weigh 200g NaOH, 100g NaAlO2, 200g Na2SO4, and 100g bis-(γ-triethoxysilylpropyl)tetrasulfide (abbreviated as Si69). Dissolve NaOH and NaAlO2 in water to prepare an alkaline solution. Dissolve Na2SO4 in water. Premix Si69 with a small amount of anhydrous ethanol and then dissolve it in water. Finally, mix the three solutions and adjust the total amount of water to make the dry matter concentration of the composite activator solution 8%.

[0025] S2. Activation: The above-mentioned steel slag powder is conveyed by dense-phase pneumatic conveying through a helium atmospheric pressure low-temperature plasma jet device with a power set at 1.5kW and a processing time of 5 seconds to obtain activated steel slag powder. The discharge temperature of the treated steel slag powder is approximately 70℃, and the specific surface area is measured to increase to 718m² / kg.

[0026] S3. Preparation of cementitious material: Hot activated steel slag powder and quartz sand (particle size ≤5mm, SiO2 mass content 96.8%) are rapidly dry mixed at a mass ratio of 7:3 to obtain a dry mixture. A composite activator solution is slowly added to the dry mixture and stirred for 5 minutes to form a uniform slurry. The slurry is poured into a mold and vibrated to form the product. After curing at a temperature of 20±2℃ and a humidity of ≥90% for 24 hours, the product is demolded and continued to be cured according to standard until the specified age to obtain the cementitious material product.

[0027] Its mechanical properties were tested according to national standards, and the results were: 28-day compressive strength 73.6 MPa, 28-day flexural strength 11.4 MPa. Example 3

[0028] S1. Raw material preparation: Steel slag is dried at 105℃ to constant weight and then ground in a vertical mill to a specific surface area of ​​230m² / kg to obtain steel slag powder. 10kg of steel slag powder is weighed out for later use.

[0029] Preparation of the composite activator solution: Weigh 400g NaOH, 400g NaAlO2, 500g Na2SO4, and 300g bis-(γ-triethoxysilylpropyl)tetrasulfide (abbreviated as Si69). Dissolve NaOH and NaAlO2 in water to prepare an alkaline solution. Dissolve Na2SO4 in water. Premix Si69 with a small amount of anhydrous ethanol and then dissolve it in water. Finally, mix the three solutions and adjust the total amount of water to make the dry matter concentration of the composite activator solution 15%.

[0030] S2. Activation: The above-mentioned steel slag powder is conveyed via dense-phase pneumatic conveying through an atmospheric pressure low-temperature plasma jet device using a helium-oxygen mixture as the working gas. The power is set to 1.5kW, and the processing time is 10 seconds to obtain activated steel slag powder. The discharge temperature of the processed steel slag powder is approximately 80℃, and the measured specific surface area increases to 952m² / kg.

[0031] S3. Preparation of cementitious material: Hot activated steel slag powder and quartz sand (particle size ≤5mm, SiO2 mass content 96.8%) are rapidly dry-mixed at a mass ratio of 8:2 to obtain a dry mixture. The composite activator solution is slowly added to the dry mixture and stirred for 10 minutes to form a uniform slurry. The slurry is poured into a mold and vibrated to form the product. After curing at a temperature of 20±2℃ and a humidity of ≥90% for 48 hours, the product is demolded and continued to be cured according to standard until the specified age to obtain the cementitious material product.

[0032] The mechanical properties of cement mortar were tested according to the national standard GB / T17671-2021 "Test Method for Strength of Cement Mortar". The results were: 28-day compressive strength 82.1 MPa and 28-day flexural strength 14.1 MPa.

[0033] Comparative Example 1: This comparative example uses the steel slag powder obtained in Example 1. In the activation step, ball milling is used instead of plasma activation. The ball mill speed is 20-30 r / min, and the grinding times are 30 min and 60 min, respectively. The mass ratio of steel balls to steel slag powder is 5:1. During the ball milling process, an appropriate amount of anhydrous ethanol is added as a grinding aid.

[0034] Comparative Sample 1: Activated steel slag powder obtained after grinding for 30 minutes; Comparative Sample 2: Activated steel slag powder obtained after grinding for 60 min; Test sample: Activated steel slag powder obtained in Example 1.

[0035] The activation results are compared in Table 1 below: Table 1: Comparison of specific surface area of ​​activated steel slag powder Process Initial specific surface area m² / kg Specific surface area after activation m² / kg Comparative sample 1 Ball milling 30 min 265 410 Comparative sample 2 Ball milling 60 min 265 480 Test sample Plasma activation 6 seconds 265 920 As shown in Table 1, mechanical activation via ball milling has limited effectiveness in increasing specific surface area. Ball milling is a physical process of crushing from the outside in, and its efficiency decreases sharply as particle size decreases. Extending the grinding time from 30 min (comparison sample 1) to 60 min did not increase the specific surface area beyond 500; further extending the time would only exponentially increase energy consumption and prolong the activation time. In contrast, plasma activation is essentially surface nanostructuring rather than simple grinding. High-energy particle bombardment can create nanopores and defects on the surface in a very short time, forming a highly reactive amorphous layer, thus significantly increasing the specific surface area. Furthermore, plasma treatment effectively breaks up particle agglomeration. Ball-milled micropowders, due to their high surface energy, tend to agglomerate tightly, and the surface area inside these agglomerates is immeasurable. Plasma bombardment provides the energy to break up these agglomerates, making the particles more dispersed and releasing the hidden internal surface area.

[0036] Comparative Example 2: This embodiment compares the strength of cementitious material products obtained under different process conditions.

[0037] Comparative Sample 3: A cementitious material product obtained by preparing activated steel slag micro powder through the cementitious material preparation steps. The cementitious material preparation steps are basically the same as those in Example 1. The difference is that the activated steel slag micro powder is Comparative Sample 2, and the activator is NaOH: 4% and NaAlO2: 2% (by mass ratio of steel slag micro powder). Comparative Sample 4: A cementitious material product obtained by preparing activated steel slag micro powder through a cementitious material preparation step. The cementitious material preparation step is basically the same as that in Example 1. The difference is that the activated steel slag micro powder is Comparative Sample 2, and the activator is NaOH: 4%, NaAlO2: 2%, Na2SO4: 3%, and silane coupling agent KH550: 2% (as a percentage of the mass of the steel slag micro powder). Comparative Sample 5: The cementitious material product obtained by the cementitious material preparation steps of activated steel slag micro powder. The activator and cementitious material preparation steps are basically the same as those in Example 1. The difference is that the activated steel slag micro powder is Comparative Sample 2. Test sample: cementitious material product obtained in Example 1.

[0038] The results are shown in Table 2 below: Table 2: Comparison of strength of cementitious material products obtained under different process conditions Sample name Compressive strength (MPa) Flexural strength (MPa) 3 days Comparative sample 3 18.5 3.5 Comparative sample 4 25 4.6 Comparative sample 5 30.5 5.8 Test sample 35.2 7.1 7 days Comparative sample 3 30.2 4.8 Comparative sample 4 42 6.5 Comparative sample 5 52.5 8.2 Test sample 58.8 9.8 28 days Comparative sample 3 45.5 6.2 Comparative sample 4 58 8.6 Comparative sample 5 68 10.5 Test sample 78.5 13.2 As can be seen from the table above, the compressive and flexural strengths of the control sample 3 obtained by the traditional method were not ideal in the early stage (3 days, 7 days) or the final age of 28 days; the control sample 4 added silane coupling agent KH550 as an activator on the basis of the traditional method, but the improvement effect was only average; the control sample 5 used the composite activator solution of the present invention, and the compressive and flexural strengths were further improved; the test sample was the cementitious material product obtained by the present invention, which used plasma-activated steel slag powder and the composite activator solution of the present invention, and the compressive and flexural strengths were improved again.

[0039] This is because traditional methods, relying solely on mechanical grinding or a single alkaline activator, are insufficient to effectively disrupt the stable structure of silicates and aluminates in steel slag. This results in a low upper limit for specific surface area improvement, leading to insufficient release of active SiO2 and Al2O3, low hydration reaction efficiency, and poor early strength of the cementitious material. While adding silane coupling agent KH550 as an activator to the traditional method can improve strength to some extent, the improvement is minimal. This is because the mechanism of action of silane coupling agent KH550 involves hydrolysis and bonding, ultimately forming a monomolecular capping layer. Its organic functional group (-NH2) faces outwards and can be used to connect with organic phases.

[0040] Bis-(γ-triethoxysilylpropyl)tetrasulfide (Si69) possesses tetrasulfide bonds. Through hydrolysis, covalent bonding, and condensation, Si69 forms a three-dimensional, cross-linked polysiloxane network in situ. This network interpenetrates and entangles with steel slag hydration products (such as CSH gel), forming a tough, organic-inorganic hybrid interface phase. Its long tetrasulfide chains are flexible, capable of absorbing and dissipating energy, thus significantly improving the material's flexural strength and toughness, and inhibiting the generation and propagation of microcracks. The three-dimensional cross-linked network exhibits higher chemical and mechanical stability and better durability than a monolayer. Meanwhile, the high specific surface area, nanoscale pores, and numerous defects created by plasma activation provide an abundance of reaction sites for alkaline activators and sulfates, maximizing the efficiency and depth of chemical activation. The plasma-activated surface has more dangling bonds and hydroxyl groups, providing denser and stronger anchoring points for polymerized silanes, resulting in a denser and more stable interfacial polymer network. The three-dimensional siloxane network formed in situ by Si69 can effectively fix and protect the highly active surface created by plasma, preventing "secondary aggregation" or "passivation" before use, and ensuring that the activation effect is maximized.

[0041] The above embodiments are merely descriptions of preferred embodiments of the present invention and are not intended to limit the concept and scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the design concept of the present invention should fall within the protection scope of the present invention.

[0042] The technologies, shapes, and structures not described in detail in this invention are all known technologies.

Claims

1. A method for preparing a steel slag-based cementitious material, characterized in that, Includes the following steps: S1. Raw material preparation: Steel slag is dried and ground to obtain steel slag powder. Alkaline activator, sulfate activator and hydrolyzable polymerizable silane are dissolved in water and then mixed to obtain a composite activator solution. S2. Activation: Steel slag powder is activated by plasma activation through an atmospheric pressure low temperature plasma jet device using a dense phase pneumatic conveying method to obtain activated steel slag powder. S3. Preparation of cementitious material: The activated steel slag powder and aggregate are immediately dry-mixed to obtain a dry mixture. The composite activator solution is slowly added to the dry mixture and stirred for 5-10 minutes to form a uniform slurry. The slurry is poured into a mold and vibrated to form the product. After curing at a temperature of 20±2℃ and a humidity of ≥90% for 24-48 hours, the product is demolded and cured according to standard until the specified age is obtained to obtain the cementitious material product.

2. The method for preparing steel slag-based cementitious material according to claim 1, characterized in that, The specific surface area of ​​the steel slag powder in step S1 is 200~300m² / kg.

3. The method for preparing steel slag-based cementitious material according to claim 1, characterized in that, In step S1, the alkaline activator is a mixture of sodium hydroxide and sodium aluminate in a mass ratio of 1:0.5~1, the sulfate activator is sodium sulfate, and the hydrolyzable polymerizable silane is bis-(γ-triethoxysilylpropyl)tetrasulfide. The dry matter mass concentration of the composite activator solution is 8~15%, wherein the mass ratio of alkaline activator, sulfate activator, and hydrolyzable polymerizable silane to steel slag powder is as follows: alkaline activator 3~8%, sulfate activator 2~5%, and hydrolyzable polymerizable silane 1~3%.

4. The method for preparing steel slag-based cementitious material according to claim 1, characterized in that, In step S2, plasma activation uses helium or a helium-oxygen mixture as the working gas, and is performed for 5 to 10 seconds at a power of 1.5 to 4 kW, with an output temperature of 60 to 80°C.

5. The method for preparing steel slag-based cementitious material according to claim 4, characterized in that, The plasma-activated steel slag powder has a specific surface area of ​​700~1000m² / kg.

6. The method for preparing steel slag-based cementitious material according to claim 1, characterized in that, The aggregate in step S3 is quartz sand with a particle size ≤5mm and a SiO2 mass content of not less than 95%. The mass ratio of activated steel slag powder to aggregate is 7~8:3~2.