Composite superfine slag powder for concrete and preparation method of composite superfine slag powder

Abstract

The invention discloses composite superfine slag powder for concrete and a preparation method of the composite superfine slag powder, and belongs to the field of superfine slag powder. Comprising the following raw materials in parts by mass: 80-90 parts of granulated blast furnace slag, 4-10 parts of silica fume and 2-5 parts of a stabilizer, and the stabilizer contains 10-30wt% of cerium oxide. The silica fume has higher pozzolanic activity, can accelerate an early hydration reaction, stimulates potential hydraulicity of the superfine slag powder, and can improve the compressive strength and stability of the concrete. By adding the stabilizer, phase change of beta-C2S in the slag can be inhibited, cerium oxide can fill lattice defects, hinder crystal nucleus reconstruction, inhibit conversion of beta-C2S into gamma-C2S without activity and induce beta-C2S to form a more stable structure, and by increasing the stability and content of beta-C2S in the slag, the stability and content of the gamma-C2S in the slag can be improved. The gel activity and the active substance content of the superfine slag powder are further improved, and the superfine slag powder with high activity index and stable performance is obtained.

Description

Technical Field

[0001] This invention relates to the field of slag powder, and particularly to a composite slag powder for concrete and its preparation method. Background Technology

[0002] With the continuous development of society, concrete, as the most basic building structural material, has seen rapid application and development. Cement, as the most important cementitious material in concrete, is also being used in increasing quantities. However, the cement industry is a heavily polluting and unsustainable industry that consumes large amounts of natural minerals and emits large amounts of greenhouse gases, sulfur dioxide, and dust, which does not conform to the scientific concept of green development.

[0003] To address this issue, developing new, environmentally friendly, high-performance concrete is a crucial direction for concrete research and development. During concrete preparation, it has been discovered that adding appropriate amounts of industrial waste to replace a portion of the cement not only allows for the recycling of industrial waste and reduces cement usage but also improves concrete performance. The chemical composition of slag is very similar to that of silicate cement clinker, and it possesses higher potential activity. Slag, after being ground to a certain fineness, is called slag powder. As a high-performance cementitious material that can effectively replace cement, slag powder, when added to concrete, not only increases its strength but also significantly enhances its overall performance. Concrete with high-quality slag powder exhibits good workability, rapid demolding, improved impermeability and frost resistance, and increased slump, making it one of the preferred building materials for key national construction projects such as airports, docks, hydropower projects, and bridges.

[0004] However, the current application rate of slag powder is small. High-grade slag powder has a low market share because its low activity index fails to meet the design requirements of building engineering. Moreover, slag is a polymer of crystals and glass. The glass is the main active component, and its content directly affects the activity of slag powder. The main active component in the glass is β-C2S, which has high hydraulic activity and is the main source of the cementitious activity of slag powder. However, during the production of slag powder, especially during grinding, the heat generated by the friction between the grinding rollers and grinding discs is difficult to dissipate in time. In particular, when extending the grinding time to obtain slag powder with a larger specific surface area in order to improve the activity of slag powder, a large amount of heat generated inside will accumulate during the grinding process. This will cause β-C2S to gradually transform into γ-C2S. γ-C2S has almost no activity and cannot participate in the hydration reaction, which will reduce the activity of slag powder. Furthermore, the phase transformation process is accompanied by volume expansion, which leads to microcracks and defects inside the slag particles, thus affecting the stability of various properties of the material when applied to concrete. Summary of the Invention

[0005] This invention provides a composite slag powder for concrete and its preparation method, which can solve the problem of low activity index of slag powder in the prior art.

[0006] In a first aspect, the present invention provides a composite slag powder for concrete, comprising the following raw materials in parts by weight: 80-90 parts of granulated blast furnace slag; 4-10 parts silica fume; Stabilizer 2-5 parts; The stabilizer contains 10–30 wt% cerium oxide.

[0007] Preferably, the specific surface area of ​​the composite slag powder is 430–550 m². 2 / kg.

[0008] More preferably, the composite slag powder comprises 30-34% SiO2, 1-1.5% Fe2O3, 16-18% Al2O3, 36-40% CaO, 7-10% MgO, and the balance; the balance includes TiO2, MnO2, CeO2, etc.

[0009] By adopting the above technical solution, the composite slag powder of the present invention uses granulated blast furnace slag as the main raw material and also incorporates silica fume. Compared with granulated blast furnace slag, silica fume has high pozzolanic activity, which can help promote the reaction with calcium hydroxide in the slag to generate more CSH gel. This not only accelerates the early hydration reaction of the slag powder but also shortens the hydration induction period by consuming calcium ions and hydroxide ions in the slag, further stimulating the potential hydraulic properties of the slag powder. Moreover, silica fume particles can fill the pores in the slag powder and the capillaries inside the concrete, reducing porosity and optimizing pore size distribution, thereby enhancing the cementing efficiency of the composite slag powder and strengthening the interfacial bonding strength with the concrete matrix.

[0010] By forming a slag-silica fume composite system, the compressive strength of concrete can be significantly improved, early hydration strength enhanced, and long-term strength growth supported, thereby improving the concrete's impermeability and volume stability. Furthermore, the lubricating properties of silica fume can reduce concrete segregation and seepage, improve pumpability, and expand its application range.

[0011] Stabilizers, including cerium oxide, are added to the slag powder. During the production of slag powder, thermal accumulation can accelerate or enhance the phase transformation of β-C2S (β-dicalcium silicate), resulting in inactive γ-C2S, which affects the activity index of the slag powder, leading to pulverization and loss of cementitious properties. To address this issue, cerium oxide is added to the slag powder to introduce cerium ions. The difference in radius between cerium ions and calcium ions in slag causes crystal nucleus expansion, reducing the atomic mobility of the phase transformation. Furthermore, the high charge state of cerium ions can be compensated for by vacancies or interstitial atoms, further hindering crystal nucleus reconstruction. The addition of cerium oxide can also induce β-C2S to form a more stable structure, thereby reducing the occurrence of phase transformation.

[0012] Meanwhile, the high silica content in silica fume can alter the crystal structure of β-C2S through solid solution or surface adsorption, and work with stabilizers to suppress the transformation, resulting in a structurally stable β-C2S lattice.

[0013] The stabilizer improved the β-C2S content and stability in the slag. The increased β-C2S content significantly enhanced the activity of the slag powder / concrete system, enabling rapid gel formation. The hydration products could form a dense cross-linked network with the aggregate interface, thereby reducing the porosity of the interface, improving the impermeability of the concrete, and thus delaying the corrosion of the internal steel reinforcement.

[0014] Furthermore, by inhibiting the phase transformation process of β-C2S and increasing its content and stability, more active dicalcium silicate can be retained. The calcium ions released after hydration can combine with silica and alumina in the slag powder, generating hydrated calcium silicate and hydrated calcium aluminate gels through a secondary hydration reaction. This increases the proportion of active forms and improves reaction efficiency. The large amount of gel generated during this process further fills the pores of concrete aggregates, improving the compressive strength of the concrete. Conversely, it reduces the decomposition of tricalcium silicate in the products, thereby inhibiting the formation of free calcium oxide and avoiding the risk of concrete cracking due to hydration expansion. Finally, not only can slag powder with a high activity index be obtained, but its application in concrete can also produce high-performance concrete materials.

[0015] Preferably, the stabilizer further includes 0-10 wt% of a sodium-based compound and 60-80 wt% of a phosphorus-based compound.

[0016] Preferably, the sodium-based compound includes one or a combination of two of sodium sulfate and sodium oxide.

[0017] Preferably, the phosphorus-based compound includes phosphate salts and / or phosphorus slag; the phosphate salts include one or more combinations of tricalcium phosphate, potassium phosphate, and calcium polyphosphate.

[0018] More preferably, the particle size of the phosphorus slag is 0.1 to 0.5 cm.

[0019] By adopting the above technical solution, sodium-based compounds and phosphorus-based compounds can also be added to the stabilizer. The phosphate ions in the phosphorus-based compounds can form a solid solution with the slag powder, improving the thermal stability of β-C2S. Furthermore, they can form complexes with cerium ions, reducing lattice stress caused by cerium ion doping and improving the stability of the solid solution. In addition, the phosphorus-based compounds can release phosphate ions during hydration, which react with calcium ions to become active sites, accelerating the hydration process.

[0020] The addition of sodium-based compounds can, on the one hand, compensate for charge, reduce the charge imbalance caused by cerium ion doping, reduce lattice distortion energy, and also reduce interfacial energy by preferentially adsorbing sodium ions at β-C2S grain boundaries, thus hindering the phase transformation process. On the other hand, the addition of sodium-based compounds can also accelerate the glass dissociation of slag powder by releasing sodium ions during the hydration stage, promote the breaking of molecular bonds, form more gel, and improve the activity of slag powder.

[0021] Preferably, the glass content of granulated blast furnace slag is ≥95%.

[0022] By adopting the above technical solution, the granulated blast furnace slag used in this invention has a high glass content. Glass is the only effective carrier for the potential hydraulic activity of slag. When the glass content increases, the silicon-oxygen bonds in the slag powder are more easily broken, thereby increasing the hydration reaction rate, accelerating glass dissociation and continuous gel formation. Furthermore, a high glass content means a decrease in the content of inert crystalline phases, thus improving the activity of the slag powder. The high glass content also provides a dispersion carrier for cerium oxide in the stabilizer, reducing agglomeration and improving the stability of β-C2S.

[0023] Furthermore, slag with high glass content can significantly improve the compressive strength of concrete and reduce strength decay. It can also improve impermeability and reduce water expansion rate by forming a dense gel structure and filling capillaries, effectively preventing concrete cracking.

[0024] Preferably, the silica fume is micro-nano silica fume; the average particle size of the micro-nano silica fume is 800 nm to 1 μm.

[0025] By adopting the above technical solution, the silica fume in this invention can be micro-nano silica fume. The intermediate particle size of micro-nano silica fume can more efficiently fill the voids between slag powder and aggregate particles, thereby significantly reducing porosity and improving the impermeability of concrete. Micro-nano silica fume can also be adsorbed on the surface of slag powder, reducing the water film thickness and inhibiting the directional growth of calcium hydroxide crystals, thereby improving the interfacial bonding strength and increasing the strength of concrete.

[0026] Micro- and nano-sized silica fume have a higher specific surface area and correspondingly higher reactivity, which can accelerate gel formation and improve the compressive strength of concrete. Furthermore, compared to nano-sized silica fume, micro- and nano-sized silica fume has a more suitable reaction rate, effectively avoiding early hydration reaction runaway caused by ultra-high specific surface area, while also ensuring the continued release of activity in the later stages.

[0027] Secondly, the present invention provides a method for preparing composite slag powder for concrete, comprising the following process steps: S1. Granulated blast furnace slag is passed through a 5mm square hole screen to remove large particulate impurities; S2. After sieving, the granulated blast furnace slag is dried with hot air; S3. Add silica fume and stabilizer to the dried granulated blast furnace slag, and stir evenly to obtain a mixture; S4. The obtained mixture is ground and then subjected to powder selection and grading to obtain composite slag powder for concrete.

[0028] Preferably, the hot air drying temperature in step S2 is 260–300°C.

[0029] Preferably, the grinding in step S4 includes one or more combinations of ball milling, vertical roller milling, vibratory milling and Raymond milling.

[0030] By adopting the above technical solution, the raw material is first coarsely screened to remove large particle impurities. Then, it is dried with hot air to reduce the moisture content in the granulated blast furnace slag, preventing excessive moisture from affecting the subsequent grinding process and increasing mill wear and energy consumption. The dried blast furnace slag is then mixed with stabilized silica fume. Because the amount of additives is small, it needs to be thoroughly mixed with the granulated blast furnace slag before grinding.

[0031] Finally, through powder selection and grading, the specific surface area of ​​the composite slag powder is controlled. Only slag powder with a certain specific surface area can fully exert its activity and play a decisive role in improving the strength and performance of concrete. In addition to adjusting the composition of slag powder, optimizing the production process can further help to obtain composite slag powder with excellent performance and relatively high strength.

[0032] The beneficial effects of this invention are: 1. The composite slag powder of the present invention uses granulated blast furnace slag and silica fume as the main raw materials. Silica fume has higher pozzolanic activity, which can accelerate the early hydration reaction, stimulate the potential hydraulic properties of slag powder, and improve the compressive strength and stability of concrete. Selecting micro-nano silica fume can more effectively fill the voids in the system, reduce the porosity of concrete, and enhance impermeability.

[0033] 2. The composite slag powder of this invention also contains a stabilizer. Cerium oxide in the stabilizer can suppress the β-C2S phase transition by filling lattice defects. Sodium-based compounds can help hinder the phase transition process, accelerate glass dissociation, and improve the activity of the slag powder. Phosphorus-based compounds can form a solid solution with the slag powder, thereby improving the stability of β-C2S and synergistically enhancing overall stability with cerium ions. The addition of the stabilizer can improve the stability and content of β-C2S in the slag, thereby increasing the gel activity of the slag powder, increasing the proportion of active silica and active alumina in the system, and inhibiting the formation of free calcium oxide, thus obtaining slag powder with high activity index and stable performance. Detailed Implementation

[0034] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0035] Example

[0036] Example 1: A composite slag powder for concrete was prepared according to the following process steps: S1. 85 parts of granulated blast furnace slag (glass content ≥95%) were passed through a 5mm square hole sieve to remove large particulate impurities; S2. After sieving, the granulated blast furnace slag is dried with hot air at a temperature of 280℃; S3. Add 7 parts silica fume (average particle size of 10 μm) and 4 parts stabilizer to the dried granulated blast furnace slag, and stir evenly to obtain a mixture; wherein the stabilizer includes 20 wt% cerium oxide, 5 wt% sodium oxide and 75 wt% phosphorus slag (average particle size of 0.3 cm). S4. The obtained mixture is vertically milled, and then subjected to powder classification to obtain composite slag powder for concrete. The specific surface area of ​​the obtained composite slag powder for concrete is controlled to be 500 m². 2 / kg.

[0037] Ash content tests were conducted on the obtained composite slag powder for concrete. The tests showed that the composite slag powder contained 32.08% SiO2, 1.23% Fe2O3, 16.85% Al2O3, 37.69% CaO, 9.36% MgO, and 2.79% balance.

[0038] Example 2: A composite slag powder for concrete is prepared according to the following process steps: S1. 80 parts of granulated blast furnace slag (glass content ≥95%) were passed through a 5mm square hole sieve to remove large particulate impurities; S2. After sieving, the granulated blast furnace slag is dried with hot air at a temperature of 280℃; S3. Add 4 parts silica fume (average particle size of 10 μm) and 2 parts stabilizer to the dried granulated blast furnace slag, and stir evenly to obtain a mixture; wherein the stabilizer includes 20 wt% cerium oxide, 5 wt% sodium oxide and 75 wt% phosphorus slag (average particle size of 0.3 cm). S4. The obtained mixture is vertically milled, and then subjected to powder classification to obtain composite slag powder for concrete. The specific surface area of ​​the obtained composite slag powder for concrete is controlled to be 500 m². 2 / kg.

[0039] Ash content tests were conducted on the obtained composite slag powder for concrete. The tests showed that the composite slag powder contained 31.98% SiO2, 1.23% Fe2O3, 16.67% Al2O3, 38.38% CaO, 9.01% MgO, and 2.73% balance.

[0040] Example 3: A composite slag powder for concrete was prepared according to the following process steps: S1. Pass 90 parts of granulated blast furnace slag (glass content ≥95%) through a 5mm square hole sieve to remove large particulate impurities; S2. After sieving, the granulated blast furnace slag is dried with hot air at a temperature of 280℃; S3. Add 10 parts of silica fume (average particle size of 10 μm) and 5 parts of stabilizer to the dried granulated blast furnace slag, and stir evenly to obtain a mixture; wherein the stabilizer includes 20 wt% cerium oxide, 5 wt% sodium oxide and 75 wt% phosphorus slag (average particle size of 0.3 cm). S4. The obtained mixture is vertically milled, and then subjected to powder classification to obtain composite slag powder for concrete. The specific surface area of ​​the obtained composite slag powder for concrete is controlled to be 500 m². 2 / kg.

[0041] Ash content tests were conducted on the obtained composite slag powder for concrete. The tests showed that the composite slag powder contained 33.21% SiO2, 1.31% Fe2O3, 16.21% Al2O3, 38.63% CaO, 9.13% MgO, and 1.51% balance.

[0042] Example 4, a composite slag powder for concrete, differs from Example 1 only in that the stabilizer includes 10 wt% cerium oxide, 10 wt% sodium oxide and 80 wt% phosphorus slag.

[0043] Example 5, a composite slag powder for concrete, differs from Example 1 only in that the stabilizer includes 30 wt% cerium oxide, 5 wt% sodium oxide and 65 wt% phosphorus slag.

[0044] Example 6, a composite slag powder for concrete, differs from Example 1 only in that the stabilizer includes 30 wt% cerium oxide and 70 wt% phosphorus slag.

[0045] Example 7: A composite slag powder for concrete, differing from Example 1 only in that an equal amount of micro-nano silica fume with an average particle size of 800 nm is used to replace silica fume with an average particle size of 10 μm.

[0046] Example 8: A composite slag powder for concrete, which differs from Example 1 only in that it uses an equal amount of granulated blast furnace slag with a glass content of ≥85% instead of granulated blast furnace slag with a glass content of ≥95%.

[0047] Comparative Example

[0048] Comparative Example 1 is a composite slag powder for concrete, which differs from Example 1 only in that it does not contain silica fume.

[0049] Comparative Example 2, a composite slag powder for concrete, differs from Example 1 only in that the amount of stabilizer added is 1 part.

[0050] Comparative Example 3, a composite slag powder for concrete, differs from Example 1 only in that the amount of stabilizer added is 7 parts.

[0051] Comparative Example 4, a composite slag powder for concrete, differs from Example 1 only in that the stabilizer does not include cerium oxide, and the stabilizer includes 5 wt% sodium oxide and 95 wt% phosphorus slag.

[0052] Comparative Example 5, a composite slag powder for concrete, differs from Example 1 only in that the stabilizer does not include phosphorus slag, and the stabilizer includes 80 wt% cerium oxide and 20 wt% sodium oxide.

[0053] Comparative Example 6, a composite slag powder for concrete, differs from Example 1 only in that no stabilizer is added.

[0054] Performance testing

[0055] 1. Activity test: According to the relevant records in GB / T 18046-2017 "Granulated blast furnace slag powder for use in cement, mortar and concrete", the activity index of the concrete slag powder obtained in the examples and comparative examples was tested after 7 days and 28 days of curing.

[0056] 2. Strength test: According to the relevant records in GB / T 17671-2021 "Test method for strength of cement mortar (ISO method)", the compressive strength of the slag powder for concrete obtained in the examples and comparative examples was tested after 3 days and 7 days of curing.

[0057] The results of the above experiments are shown in Table 1: Table 1 Performance test results

[0058] According to Table 1, and in conjunction with Examples 1, 2 to 6, it can be seen that the activity index and compressive strength of Examples 2 to 6 are not significantly different from those of Example 1, indicating that within the range provided by this invention, changing the raw material ratio and the proportion of stabilizer has no significant impact on the performance of the obtained composite slag powder for concrete.

[0059] Combining Examples 1 and 7, it can be seen that the activity index and compressive strength of Example 7 are increased compared to Example 1. The reason is that the silica fume used in Example 7 is micro-nano silica fume, which has a smaller particle size and a larger specific surface area. It can fill the pores in the concrete system more efficiently and can be adsorbed on the surface of slag powder to improve the interfacial bonding strength, thereby improving the concrete strength. At the same time, it also has higher reactivity and will not cause early hydration reaction runaway, ensuring that the activity can remain stable in both the early and late stages of the hydration reaction.

[0060] Combining Examples 1 and 8, it can be seen that the activity index and compressive strength of Example 8 are lower than those of Example 1. This is because the glass content of the granulated blast furnace slag used in Example 8 is lower than that of Example 1. As the main source of hydraulic activity in slag powder, the reduction in glass content will lead to a decrease in the gel formation rate and the dissociation rate of glass, resulting in a decrease in overall activity and compressive strength. Furthermore, the reduction in glass content will reduce the dispersion carrier of cerium oxide in the system, which will affect the stabilizing effect of the stabilizer on the slag to a certain extent.

[0061] Combining Example 1 and Comparative Example 1, it can be seen that the activity index and compressive strength of Comparative Example 1 are lower than those of Example 1. The reason is that no silica fume was added to the composite slag powder obtained in Comparative Example 1. On the one hand, this directly leads to a decrease in overall activity, because silica fume has higher reactivity than granulated blast furnace slag and can stimulate the potential hydraulic properties of slag powder. On the other hand, the presence of silica fume can help fill the pores inside the concrete, reduce the porosity, and optimize the pore size distribution. While improving the interfacial bonding strength between slag powder and concrete matrix, the resulting composite system can significantly improve the compressive strength of concrete.

[0062] Based on Examples 1, 2, 3, and 6, it can be seen that the activity index and compressive strength of Comparative Examples 2, 3, and 6 are all lower than those of Example 1, with the decrease being more pronounced in Comparative Example 6. This is because Comparative Examples 2, 3, and 6 mainly adjusted the amount of stabilizer added to the composite slag powder. Comparative Example 2 reduced the amount of stabilizer added, which increased the probability of β-C2S phase transformation due to heat accumulation during the production process of the composite slag powder, converting the active β-C2S into the inactive γ-C2S, thus affecting the activity index of the slag powder. Furthermore, the phase transformation process is accompanied by volume expansion, which affects the stability of the structure, leading to a decrease in compressive strength. Comparative Example 6, which did not add any stabilizer, showed an even more significant performance decline. In Comparative Example 3, an excessive amount of stabilizer was added. Excessive addition of cerium oxide led to excessive distortion of the β-C2S lattice, which in turn reduced activity and inhibited the dissociation of the glass in the slag powder. Moreover, excessive phosphorus compounds would compete with hydration products, thereby weakening the continuity of the gel matrix, resulting in decreased activity and reduced strength.

[0063] Based on Examples 1, 4, and 5, it can be seen that the activity index and compressive strength of Comparative Examples 4 and 5 are lower than those of Example 1. This is because the stabilizer in Comparative Example 4 does not contain cerium oxide. Cerium oxide is a key component of the stabilizer; its absence significantly affects the stabilizer's inhibitory effect on the β-C2S phase transition and reduces its ability to improve β-C2S stability. Therefore, the lack of cerium oxide increases the probability of β-C2S phase transition and decreases stability, thus affecting the performance of the composite slag powder. The stabilizer added to the slag powder in Comparative Example 5 does not contain phosphorus-based compounds. Phosphorus-based compounds can form solid solutions to a certain extent, inhibiting phase transitions while increasing hydration activity and reducing the content of free calcium oxide. Therefore, the lack of phosphorus-based compounds affects the activity and performance of the composite slag powder.

[0064] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A composite ground granulated blast furnace slag for concrete, characterized by, The raw materials include the following quality parts: Granulated blast furnace slag 80-90 parts; Silica fume 4-10 parts; Stabilizer 2-5 parts; The stabilizer contains 10-30 wt% of cerium oxide.

2. The composite ground granulated blast furnace slag for concrete according to claim 1, characterized by, The stabilizer further contains 0-10 wt% of sodium-based compounds and 60-80 wt% of phosphorus-based compounds.

3. The composite ground granulated blast furnace slag for concrete according to claim 2, characterized by, The sodium-based compounds include a combination of one or both of sodium sulfate and sodium oxide.

4. The composite ground granulated blast furnace slag for concrete according to claim 2, characterized by, The phosphorus-based compounds include phosphorus salt and / or phosphorus slag; the phosphorus salt includes a combination of one or more of tricalcium phosphate, potassium phosphate and calcium polyphosphate.

5. The composite ground granulated blast furnace slag for concrete according to claim 1, characterized by, The granulated blast furnace slag has a glass content of ≥95%.

6. The composite ground granulated blast furnace slag for concrete according to claim 1, characterized by, The silica fume is micro-nano silica fume; the micro-nano silica fume has an average particle size of 800 nm-1 μm.

7. The composite ground granulated blast furnace slag for concrete according to claim 1, characterized by, The specific surface area of the composite slag powder is 430-550 m 2 / kg.

8. A method for producing the composite mineral slag fine powder for concrete according to any one of claims 1 to 7, characterized by, The process includes the following steps: S1. Removing large-particle impurities from the granulated blast furnace slag through a 5 mm square hole sieve; S2. Hot air drying the granulated blast furnace slag after sieving; S3. Adding silica fume and stabilizer to the dried granulated blast furnace slag, stirring uniformly to obtain a mixture; S4. Grinding the obtained mixture, and then performing powder selection and grading treatment to obtain the composite slag micro-powder for concrete.

9. The method of claim 8, wherein the composite ground granulated blast furnace slag is prepared by mixing the ground granulated blast furnace slag and the fly ash in a weight ratio of 1:1 to 1:

3. The hot air drying temperature in the S2 step is 260-300 °C.

10. The method of claim 8, wherein the composite ground granulated blast furnace slag is prepared by mixing the ground granulated blast furnace slag and the fly ash in a weight ratio of 1:1 to 1:

3. The grinding in the S4 step includes a combination of one or more of ball milling, vertical roller milling, vibration milling and Raymond milling.

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