Alkali-activated low-carbon cementing material for mechanically-chemically synergistically activating activity of steel slag and preparation method of alkali-activated low-carbon cementing material

Abstract

The invention discloses an alkali-activated low-carbon cementing material for mechanically-chemically synergistically activating the activity of steel slag and a preparation method of the alkali-activated low-carbon cementing material, and belongs to the technical field of metallurgical material solid waste resource utilization and cementing. In order to solve the problems that in the prior art, the use amount of an exciting agent is high, and strength improvement is limited, the preparation method comprises the steps that firstly, steel slag is ground for 35 min through a mechanical force means, then a grinding aid compounded by triethanolamine and triisopropanolamine is added into a grinding system, the mixing amount of the triisopropanolamine is 10%, and the grinding aid is added into the grinding system; finally, a composite cementing material is constructed from the steel slag powder, the mineral powder and the fly ash according to the mass ratio of 1: 3: 1, a triisopropanolamine modified polycarboxylate superplasticizer with the modulus of 1.2 is added to serve as an externally-doped alkali activator, and the cementing material is an alkali-activated low-carbon cementing material. The preparation method can be used for preparing the cementing material of which the dosage of the alkali activator is lower than that of the conventional dosage and the strength is greatly improved, so that resource transformation of the metallurgical waste slag is realized.

Description

Technical Field

[0001] An alkali-activated low-carbon cementitious material for synergistically activating the activity of steel slag by mechanical and chemical means and its preparation method belong to the fields of solid waste resource utilization and cementation technology in metallurgical materials. Technical Background

[0002] Steel slag, a major metallurgical solid waste generated during steelmaking, accounts for approximately 15%-20% of crude steel production. In 2022, my country's steel slag production reached 170 million tons, with a stockpile of 14.5 million tons, but the utilization rate has long been below 30%. Due to its high-temperature melting process, steel slag forms a dense crystalline structure, limiting the dissolution of active ions. This results in low cementitious activity and problems such as poor grindability and volume stability, thus restricting its application in the cement and concrete industries.

[0003] Alkali-activated gelled steel slag low-carbon cementitious materials are low-carbon building materials with cementitious properties formed by the hydration reaction of steel slag and auxiliary cementitious materials (such as mineral powder and fly ash) with an alkaline activator. These include single-component steel slag alkali-activated cementitious materials, steel slag-mineral powder composite cementitious materials, and ternary composite alkali-activated cementitious materials composed of steel slag, mineral powder, and fly ash. Among these, the ternary composite alkali-activated cementitious material composed of steel slag, mineral powder, and fly ash has complementary components due to the complementary nature of the three raw materials. Compared to a single-component steel slag alkali-activated system, it exhibits a more complete hydration reaction and a denser microstructure. The resulting hydrated calcium silicate gel (CSH gel) and ettringite (AFt) work synergistically, resulting in excellent mechanical properties. Furthermore, as it belongs to an alkali-activated steel slag cementitious system, its performance is adjustable; performance can be improved by adjusting the raw material ratio or optimizing the amount of alkaline activator.

[0004] Steel slag, containing potential cementing components such as tricalcium silicate (C3S) and dicalcium silicate (C2S) and widely sourced as metallurgical solid waste, has become a key research subject in the field of alkali-activated cementitious materials under the background of achieving the "dual carbon" target. Numerous studies have shown that the performance of alkali-activated steel slag cementitious materials depends on the degree of activation of the steel slag. Unoptimized alkali-activated steel slag cementitious materials suffer from problems such as poor grindability of steel slag and slow hydration reaction rate, resulting in low early strength and high activator dosage, which limits the large-scale application of steel slag. Therefore, considering the improvement effect of mechanical activation on the steel slag structure, we improved the mechanical properties of alkali-activated steel slag cementitious materials and the high-value utilization rate of steel slag by controlling the steel slag grinding time to 35 minutes to refine particles, compounding grinding aids to inhibit particle agglomeration, and adding water glass as an alkaline activator. Summary of the Invention

[0005] This invention relates to an alkali-activated low-carbon cementitious material and its preparation method for mechanically-chemically stimulating the activity of steel slag. Through a synergistic "mechanical activation-chemical activation" technical path, it achieves a dual technological breakthrough: on the one hand, it significantly reduces the amount of alkaline activator used, making it far lower than the 8%-12% dosage range of conventional alkali-activated steel slag cementitious materials; on the other hand, it significantly improves the mechanical properties of the cementitious material, with a 28-day compressive strength of up to 70.1 MPa, ultimately realizing the high-value-added resource conversion of metallurgical waste slag into steel slag.

[0006] The mechanical properties of an alkali-activated low-carbon cementitious material that synergistically activates the activity of steel slag can be controlled by adjusting the dosage of the alkali activator.

[0007] This invention relates to an alkali-activated low-carbon cementitious material for synergistically activating the activity of steel slag through mechanical and chemical processes. The preparation method is as follows: through the synergistic design of the entire process of "mechanical activation parameters - compound grinding aid - ternary system ratio - chemical activation parameters", the core of which is: by linking 35-minute grinding with 0.06% compound grinding aid, 'highly active steel slag powder' is provided to the ternary system; then, through 5% low-dosage, low-modulus activator, a closed loop of 'component complementarity - reaction acceleration - structural compaction' is achieved. This cementitious material is an alkali-activated low-carbon cementitious material. Attached Figure Description

[0008] Figure 1 This is a graph showing the effect of different grinding times on the specific surface area of ​​steel slag.

[0009] Figure 2 The graph shows the effect of different grinding times on the residue on a 45μm sieve.

[0010] Figure 3 The graph shows the effect of different grinding aid dosages on the specific surface area of ​​steel slag.

[0011] Figure 4 The graph shows the effect of different grinding aid dosages on the residue on a 45μm sieve.

[0012] Figure 5 The graph shows the relationship between different activator dosages and 28-day compressive strength.

[0013] Figure 6 This is a 3-day field emission scanning electron microscope image of the specimen with an activator dosage of 5%.

[0014] Figure 7 This is a 7-day field emission scanning electron microscope image of a specimen with an activator dosage of 5%.

[0015] Figure 8 This is a field emission scanning electron microscope image of a specimen with an activator dosage of 5% after 28 days. Detailed Implementation

[0016] The specific implementation method of the alkali-activated low-carbon cementitious material for synergistic mechanical-chemical activation of steel slag activity and its preparation method is as follows:

[0017] Add the pretreated steel slag (250g / part) to a variable frequency planetary ball mill (model SYMΦ500×500), and strictly control the grinding time to 35 minutes. Observe the mill's operating status every 10 minutes during the grinding process to avoid uneven grinding caused by material sticking to the walls. After grinding, immediately remove the steel slag powder and pass it through a 45μm sieve to determine the sieve residue and specific surface area.

[0018] An externally doped alkaline activator was prepared by esterification reaction between triisopropanolamine and polycarboxylate superplasticizer. The specific method is as follows: 10 g of triisopropanolamine was added to a 100 mL single-necked round-bottom flask and dissolved in 30 mL of dichloromethane. Then, 2 g of 4-dimethylaminopyridine was added and stirred at room temperature for 30 min. After that, 2 g of polycarboxylate superplasticizer was added and stirred in an ice-water bath for 3 h. Then, stirring was continued at room temperature for 12 h. After the reaction was completed, the product was dialyzed using a dialysis membrane with a molecular weight of 1000 and then freeze-dried to obtain 2.3 g of white solid powder.

[0019] The reaction formula is:

[0020] Before grinding begins, a special grinding aid, formulated with triethanolamine and triisopropanolamine in a 9:1 mass ratio (calculated as 0.06% of the steel slag mass), is uniformly sprayed onto the surface of the steel slag and stirred for 3 minutes to allow for initial mixing. This compound system, through molecular synergy, forms a stable adsorption layer during grinding, increasing the proportion of 3–30 μm active particles in the steel slag to over 51.78% and reducing the proportion of >80 μm coarse particles to below 10.88%, significantly improving the particle size distribution and providing a highly reactive interface for subsequent low-alkali activation.

[0021] Using NaOH, commercially available water glass with a modulus of 2.3 was adjusted to 1.2. Grinded steel slag was weighed according to a ratio of steel slag: mineral powder: fly ash = 1:3:1 (mass ratio), totaling 450g / set. This was added to a cement mortar mixer (model JJ-5) and dry-mixed for 2 minutes until uniformly mixed. Then, an external alkaline activator with a modulus of 1.2 was added at 5% (based on the total mass of the cementitious material), and mixing continued for 1 minute to initially mix the external alkaline activator with the dry material.

[0022] Add standard sand and tap water according to the following ratio: cementitious material: standard sand: water = 1:3:0.45 (mass ratio). First, stir at low speed for 30 seconds, then stir at high speed for 2 minutes to prepare a uniform mortar. Pour the mortar into a 40mm×40mm×160mm mold, place it on a vibrating table (amplitude 0.5mm) and vibrate for 120 seconds to remove air bubbles. After smoothing the surface of the mold, cover it with plastic wrap and let it stand at room temperature for 24 hours.

[0023] After demolding, the test blocks were placed in a standard constant temperature and humidity curing chamber (model SHBY-40A), with the temperature controlled at (20±1)℃ and the relative humidity ≥95%, and cured for 3 days, 7 days, and 28 days respectively. After curing to the corresponding age, the mechanical properties were tested using a cement mortar flexural and compressive strength tester (model JR-KZ300DS).

[0024] Figure 1 The effect of grinding time on the specific surface area of ​​steel slag was investigated. As the grinding time increased, the specific surface area first increased and then decreased, reaching a peak of 503 m² at 35 min. 2 / kg.

[0025] Figure 2 The effect of grinding time on the residue on a 45μm sieve was investigated. The residue on the 45μm sieve showed a trend of first decreasing and then increasing, reaching its lowest point at 35 min, where the residue was 9.2%.

[0026] The effect of compound grinding aid dosage on the proportion of 3-30μm particles is listed in Table 1. The polar groups (-OH, -NH) of triisopropanolamine are adsorbed on the surface of steel slag particles through hydrogen bonding and electrostatic interaction to form a monolayer. The adsorbed layer forms a lubricating film between particles, which reduces the friction coefficient between particles, lowers the surface free energy, and weakens the van der Waals forces between particles, thereby inhibiting secondary agglomeration and significantly improving the grinding effect. Table 1. Particle size distribution of steel slag with different dosages of compound grinding aid.

[0027] Figure 3 The effect of grinding aids on the specific surface area of ​​steel slag was investigated. The specific surface area initially increased and then decreased with varying grinding aid dosage, reaching a peak of 534 m² when the grinding aid dosage was 0.06%. 2 / kg.

[0028] Figure 4 The effect of grinding aid on the residue on a 45μm sieve showed a trend of first decreasing and then increasing, reaching its lowest point at 35 min, where the residue was 4.8%.

[0029] Figure 5The curves showing the relationship between different amounts of external activator and 28-day compressive strength are shown. The compressive strength of the mortar specimens shows an increasing trend with the increase of activator content. The compressive strength of the mortar specimens at 3d, 7d and 28d ages shows different degrees of increasing trend, and the compressive strength reaches 70.1 MPa when the amount of external activator is 5%.

[0030] Figure 6 The images show SEM images of specimens at 3 days of age when the external activator dosage is 5%. The amount of CSH gel is significantly increased, and the structure is denser (fiber-like or lamellar interwoven), showing that it has begun to encapsulate quartz crystals. The directional growth of needle-like ettringite (AFt) forms a "bridging" effect in the interfacial transition zone, strengthening the bond between particles and hydration products, thus increasing the 3-day compressive strength of the specimen to 29.7 MPa.

[0031] Figure 7 The images show SEM images of specimens at 7 days of age when the external activator dosage is 5%. The CSH gel exhibits an interwoven structure of "fiber bundles and flocs". The fiber bundles are connected by flocculent CSH gel to form a three-dimensional network structure, which provides good support for the cementitious material. The ettringite (AFt) crystals are needle-shaped and grow directionally in the gaps of the CSH gel network. Some ettringite (AFt) crystals are connected to the CSH gel fiber bundles at both ends to form a "bridging" structure, which improves the density of the hydration products.

[0032] Figure 8 The image shows a 28-day SEM image of a specimen with an external activator dosage of 5%. The hydration reaction has entered a stable period, at which point the raw material particles have completely depolymerized and repolymerized, forming a CSH gel with directional growth. The CSH gel generated outside the raw material particles further grows and interweaves with each other, forming a continuous three-dimensional network structure. The quartz crystals are completely encapsulated and the boundaries are indistinguishable. Eettsonite (AFt) continues to grow directionally, synergistically filling the interface transition zone with the CSH gel, making it free of obvious cracks. The overall structure achieves optimal density, providing good flexural and compressive strength for the steel slag-mineral powder cementitious material system.

Claims

1. An alkali-activated low-carbon cementitious material for steel slag that synergistically activates the activity of steel slag through a combination of mechanical and chemical processes, characterized in that... This material is a composite cementitious material formed by the mechanical-chemical synergistic activation of steel slag, mineral powder, and fly ash. Its English name is Alkali-activated steel slag low-carbon cementitious material, and its English abbreviation is AASS-LCCM. This material is prepared by adding alkaline activators to steel slag, mineral slag, and fly ash as the main raw materials.

2. The alkali-activated low-carbon cementitious material for steel slag according to claim 1 is characterized in that steel slag, mineral powder and fly ash are weighed according to a certain mass ratio, the steel slag is mechanically ground, a compound grinding aid is added during the grinding process, the treated steel slag is then mixed with mineral powder and fly ash, an alkaline activator is added, and then standard sand and water are added and stirred evenly to form a uniform mortar. After standard curing (temperature (20±1)℃, relative humidity ≥95%), an alkali-activated low-carbon cementitious material test block for steel slag is obtained.

3. The method for preparing an alkali-activated low-carbon cementitious material from steel slag according to claim 2, characterized in that... The mass ratio of steel slag, mineral powder and fly ash is 1:3:

1.

4. The method for preparing an alkaline-activated low-carbon cementitious material for steel slag according to claim 2, wherein the external alkaline activator is prepared by esterification reaction of triisopropanolamine and polycarboxylate superplasticizer. The specific method is as follows: 10g of triisopropanolamine is added to a 100mL single-necked round-bottom flask and dissolved in 30mL of dichloromethane. Then, 2g of 4-dimethylaminopyridine is added and stirred at room temperature. After 30min, 2g of polycarboxylate superplasticizer is added and stirred in an ice-water bath for 3h. Then, stirring is continued at room temperature for 12h. After the reaction is completed, the product is dialyzed using a dialysis membrane with a molecular weight of 1000 and then freeze-dried to obtain 2.3g of white solid powder.

5. The method for preparing an alkali-activated low-carbon cementitious material from steel slag according to claim 2, characterized in that... The compound grinding aid is a mixture of triethanolamine and triisopropanolamine, with the triisopropanolamine content being 10% and the compound grinding aid content being 0.06% of the steel slag grinding mass.

6. The method for preparing an alkali-activated low-carbon cementitious material from steel slag according to claim 2, characterized in that... The dosage of alkaline activator is 5% of the total mass of cementitious material (only 42%-62% of the conventional system's 8%-12%), and it can enable the cementitious material to achieve a 28-day compressive strength of 70.1 MPa, which is a significant improvement in strength compared to conventional high-dosage activator systems, achieving a technological breakthrough of "low dosage - high strength".

7. The method for preparing an alkali-activated low-carbon cementitious material from steel slag according to claim 1, characterized in that... The material has a strength of 70.1 MPa after 28 days.

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