A method for jointly improving the gelling activity of steel slag powder

Abstract

The present invention discloses a method for jointly modifying to improve the cementitious activity of steel slag, belonging to the technical field of resource utilization of steel slag. The method comprises the following steps: First, mix the steel slag and a high-temperature modifier, then conduct a heat treatment, break and grind after cooling, and then conduct a direct liquid-phase carbonation treatment. By matching different carbonation degrees based on different high-temperature modification alkalinity values, the present invention effectively combines the advantages of the two modification methods, fundamentally changes the mineral phase composition of the steel slag, improves the cementitious performance of the steel slag, enhances both the early and late strengths of the steel slag, and improves the soundness. The jointly modified steel slag has a high cementitious activity and can be incorporated into cement in a larger proportion, thereby improving the utilization rate of steel slag. At the same time, this treatment method can also reduce CO2 emissions and has high environmental, economic and social benefits.

Description

Technical Field

[0001] The present invention belongs to the technical field of resource utilization of steel slag, and particularly relates to a method for jointly modifying to improve the cementitious activity of steel slag powder. Background Technique

[0002] As a by-product generated in converter steelmaking, the output of steel slag is generally 10%-15% of the crude steel output. At present, a large amount of steel slag has not been effectively utilized and can only exist in the form of stacking. On the one hand, the stacked steel slag will occupy a large amount of land; on the other hand, with the washing of rainwater, heavy metal elements in the steel slag will leach out, bringing harm to the environment.

[0003] Since the steel slag contains mineral phases with cementitious activity such as C 3 S and C 2 S, the steel slag can be incorporated into cement as an auxiliary cementitious material. However, the current amount of steel slag incorporated into cement is not high mainly due to the following two reasons. One is that due to the very high temperature during the steelmaking process, the free calcium oxide crystals in the steel slag are very large and the hydration is slow. During the application in cement, it will gradually hydrate to generate calcium hydroxide, resulting in volume expansion and damaging the cement matrix; the other is that the temperature in the cement production process is 1450°C, while the temperature in the steelmaking process reaches above 1600°C, so the crystal grains of the steel slag mineral phase are relatively large and the mineral phase structure is relatively dense, with low hydration activity. If too much steel slag is incorporated into cement, it will cause a significant reduction in the cementitious activity of the steel slag cement composite material, making the performance indicators of the steel slag cement composite cementitious material not meet the standards. Therefore, to increase the amount of steel slag incorporated into cement, first, the soundness problem of steel slag needs to be solved, and second, the problem of its low cementitious activity needs to be solved.

[0004] The existing methods for improving the cementitious properties of steel slag include: 1) Physical activation, mainly by physical methods such as mechanical grinding to increase the specific surface area of steel slag so as to improve its hydration activity; 2) Chemical activation, mainly by adding certain chemical activators to steel slag to improve the hydration cementitious activity of steel slag, such as gypsum, hydroxides, etc.; 3) Thermal activation, mainly by changing the hydrothermal conditions during the hydration process of steel slag. Under high temperature and high pressure conditions, the Si-O bond and Al-O bond in the steel slag molecules are broken under the action of high temperature and high pressure to promote the further progress of the hydration reaction, such as autoclaving. The above treatment methods do not fundamentally change the mineral composition of steel slag and can only improve some properties of steel slag.

[0005] Patent (CN 111320400A, publication date: June 23, 2020) uses calcium-aluminum components to perform high-temperature reconstruction on steel slag, improving the hydration and cementitious activity of steel slag. The 28-day activity index of the high-temperature reconstructed steel slag is significantly improved compared to the original steel slag, while the improvement in the 7-day activity index is not significant. It can be seen that the improvement of the early strength of steel slag by high-temperature modification is not obvious. The reason is that whether calcium-aluminum components or siliceous components are added, the high-temperature modification of steel slag increases the C 2 S content in the steel slag, and C 2 S mainly provides the later strength, and C 3 S and C 3 A that provide the early strength are difficult to generate during the modification of steel slag.

[0006] The calcium-magnesium mineral phase, f-CaO, and f-MgO in the steel slag will react with CO 2 to form nano-scale calcium carbonate, which can promote the hydration reaction of the steel slag. Moreover, the generated calcium carbonate can also play a filling role, thus significantly improving the early strength of the steel slag. Patent (CN 107056202B, publication date: August 18, 2017) adds a mineral promoter to the steel slag-cement composite cementitious material to improve the activity of the easily carbonizable components of the steel slag-cement and promote the carbonation reaction of the steel slag, thereby improving the early strength of the steel slag. Patent (CN 113929334 B, publication date: January 14, 2022) proposes coupling acidification and carbonation to modify steel slag to improve the carbonation reaction rate of the steel slag and effectively eliminate f-CaO and f-MgO in the steel slag. However, due to the consumption of the hydration and cementitious active phase C 2 S in the steel slag during the carbonation process by reacting with CO 2 , the reduction of C 2 S is not conducive to the improvement of the later strength of the steel slag cement. Therefore, there is an urgent need to develop a modification method that can improve both the early and later strengths of steel slag. Summary of the Invention

[0007] To solve the above problems in the prior art, the present invention provides a method for improving the cementitious activity of steel slag powder by combined modification, which combines two modification methods: high-temperature hot-state modification and normal-temperature carbonation modification, makes full use of the advantages of the two modification methods, and improves both the early and later strengths of the steel slag.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] The present invention provides a method for improving the cementitious activity of steel slag by combined modification, including the following steps: First, mix the steel slag with a high-temperature modifier, then perform heat treatment, break and grind after cooling, and then perform direct liquid-phase carbonation treatment.

[0010] As a preferred embodiment of the present invention, the high-temperature modifier includes SiO2 , one or more of fly ash, slag and coal gangue; the mass percentage of the steel slag and the high-temperature modifier is (85-97%):(3-15%), and the sum of the mass percentages of the steel slag and the high-temperature modifier is 100%.

[0011] As a preferred embodiment of the present invention, it is heated to 1350-1500 °C, the heating treatment time is 25-35 min, and the cooling is specifically air-cooled to room temperature.

[0012] As a preferred embodiment of the present invention, it is ground to a specific surface area of the steel slag of 370±20 m 2 / kg.

[0013] As a preferred embodiment of the present invention, the direct liquid-phase carbonation treatment is carried out under stirring, the solid-liquid ratio is 1:(8-12), the reaction temperature is 20-30 °C, and CO 2 is introduced at a flow rate of 1 L / min, and the treatment time is 10-25 min.

[0014] As a preferred embodiment of the present invention, the stirring is magnetic stirring, and the stirring rate is 400-600 rpm.

[0015] As a preferred embodiment of the present invention, after the direct liquid-phase carbonation treatment, it further includes suction filtration and drying the obtained steel slag.

[0016] The present invention also provides a steel slag obtained by the method for improving the cementitious activity of steel slag by combined modification described above.

[0017] The present invention also provides the application of the above-mentioned steel slag in cement-based cementitious materials.

[0018] In the first step of high-temperature modification, the modifier and the steel slag react under high-temperature conditions, fundamentally changing the mineral composition and microstructure (grain size and mineral phase crystallinity) of the steel slag, increasing the content of C 2 S in the steel slag. On the one hand, it improves the later hydration activity of the steel slag, and on the other hand, it provides more calcium silicate mineral phases for the subsequent carbonation modification to absorb CO 2 , thereby reducing the emission of CO 2 ; in the second step of direct liquid-phase carbonation reaction, it further improves the cementitious activity and soundness of the steel slag. During the carbonation process of the steel slag, nano-scale calcium carbonate particles are generated, which can promote the hydration reaction of the steel slag, and the generated calcium carbonate can also play a filling role, thus significantly improving the early cementitious activity of the steel slag, enabling the present invention to promote the large-scale utilization of steel slag in the construction field.

[0019] For high-temperature modification and carbonation, they are respectively beneficial to the improvement of the later strength and the early strength of steel slag. However, carbonation will also consume the calcium silicate mineral phase in steel slag, and excessive carbonation will reduce its later strength. Combining the advantages of the two modification methods, the present invention proposes a new combined modification method, that is, matching different carbonation degrees based on different high-temperature modification alkalinity values.

[0020] For high-temperature modification, more calcium silicate cementitious mineral phases can be generated in the modified steel slag, which can improve the later activity index of steel slag. However, the improvement amplitude of the early activity index is not as obvious as that of the later stage. Only carbonation modification can significantly improve the early strength of steel slag, but the cementitious mineral phase calcium silicate phase will be continuously consumed during the carbonation process. Therefore, it is found that there is an optimal carbonation degree during the carbonation process. If excessive carbonation occurs, it is not conducive to the improvement of the later strength and may even lead to a decrease in the later strength.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention first adds siliceous components to reconstruct steel slag at high temperature to increase the content of C 2 S in steel slag, improve the later strength of the modified steel slag, and simultaneously eliminate free calcium oxide and free calcium oxide in a large proportion; on the other hand, after high-temperature modification of steel slag, C 2 S increases. The modified steel slag is directly treated by liquid-phase carbonation at room temperature, which improves the amount of CO 2 absorbed by steel slag. The reaction of C 2 S with CO 2 generates more nano-calcium carbonate, which can effectively improve the early strength of steel slag. By matching different carbonation degrees based on different high-temperature modification alkalinity values, the present invention effectively combines the two modification methods, makes full use of the advantages of the two modification methods, fundamentally changes the mineral phase composition of steel slag, improves the gelling performance of steel slag, improves the early and later strengths of steel slag, and significantly reduces the content of f-CaO in steel slag, thus improving the soundness of steel slag.

[0023] The combined-modified steel slag has high gelling activity and can be incorporated into cement in a larger proportion, thereby improving the utilization rate of steel slag and solving the problem of low utilization rate of steel slag. At the same time, CO 2 is fixed during the direct liquid-phase carbonation process of steel slag. Therefore, this treatment method can also reduce the emission of CO 2 , which conforms to the dual-carbon concept and has high environmental, economic and social benefits. Description of the Drawings

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0025] Figure 1 It is the process flow chart of the preparation of the combined modified steel slag in Example 1. Detailed implementation manners

[0026] Now, the various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation manners of the present invention. It should be understood that the terms used in the present invention are only for describing specific implementation manners and are not used to limit the present invention.

[0027] In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0028] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes the preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0029] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific implementation manners of the present invention specification, which are obvious to those skilled in the art. Other implementation manners obtained from the present invention specification are obvious to those skilled in the art. The present invention specification and embodiments are only exemplary.

[0030] Regarding the use of "comprising", "including", "having", "containing", etc. in this article, they are all open-ended terms, meaning including but not limited to.

[0031] The present invention provides a method for improving the cementitious activity of steel slag by combined modification, including the following steps: First, mix the steel slag and the high-temperature modifier, then perform heat treatment, break and grind after cooling, and then perform direct liquid-phase carbonation treatment.

[0032] In some embodiments, the high-temperature modifier includes one or more of SiO 2 , fly ash, slag and gangue; the mass percentage of steel slag and the high-temperature modifier is (85-97%):(3-15%), and the sum of the mass percentages of steel slag and the high-temperature modifier is 100%.

[0033] In some preferred embodiments, the high-temperature modifier is SiO 2 ; the mass percentage of steel slag and the high-temperature modifier is 92.6%:7.4%.

[0034] In some embodiments, it is heated to 1350-1500 °C, the heating treatment time is 25-35 min, and the cooling is specifically air cooling to room temperature.

[0035] In some preferred embodiments, it is heated to 1400 °C, the heating treatment time is 30 min, and the cooling is specifically air cooling to room temperature.

[0036] In some embodiments, it is ground to a specific surface area of the steel slag of 370±20 m 2 / kg.

[0037] In some embodiments, the direct liquid-phase carbonation treatment is carried out under stirring, the solid-liquid ratio is 1:(8-12), the reaction temperature is 20-30 °C, and CO 2 is introduced at a flow rate of 1 L / min, and the treatment time is 10-25 min.

[0038] In some preferred embodiments, the direct liquid-phase carbonation treatment is carried out under stirring, the solid-liquid ratio is 1:10, the reaction temperature is 25 °C, and CO 2 is introduced at a flow rate of 1 L / min, and the treatment time is 15 min.

[0039] In some embodiments, the stirring is magnetic stirring, and the stirring rate is 400-600 rpm.

[0040] In some preferred embodiments, the stirring is magnetic stirring, and the stirring rate is 500 rpm.

[0041] In some embodiments, after the direct liquid-phase carbonation treatment, it further includes suction filtration and drying the obtained steel slag.

[0042] The present invention also provides a steel slag obtained by the method for improving the cementitious activity of steel slag according to the above combined modification.

[0043] The present invention simultaneously provides the application of the above steel slag in cement-based cementitious materials.

[0044] In the following examples and comparative examples, the room temperature is 25 - 35°C; the chemical compositions of the steel slag and cement used in the following examples and comparative examples are shown in Table 1.

[0045] Table 1

[0046]

[0047] Example 1

[0048] The steel slag was subjected to combined modification by a method combining high - temperature modification and direct liquid - phase carbonation at room temperature. The specific steps are as follows:

[0049] First, the steel slag was crushed, ball - milled and screened with a crusher. The steel slag with a particle size passing through a 200 - mesh sieve and SiO 2 modifying agent were mixed evenly according to a mass percentage of 92.6%:7.4%, loaded into a magnesia crucible, placed in a muffle furnace, heated to 1400°C at a rate of 10°C / min, held for 30 min, taken out and air - cooled to room temperature, then crushed and ball - milled to a specific surface area meeting 370 ± 20 m 2 / kg. Then, the steel slag powder with a qualified specific surface area was added with water and CO 2 was introduced for direct liquid - phase carbonation treatment. The solid - liquid ratio was 1:10, the reaction temperature was 25°C, a magnetic rotor was used for stirring, the stirring rate was 500 rpm, CO 2 was introduced at a flow rate of 1 L / min, the reaction time was 15 min, and then filtration was carried out. Subsequently, the carbonated steel slag was dried at 45°C for 24 h. Finally, the combined - modified steel slag with a qualified specific surface area was incorporated into the reference cement at an addition amount of 30 wt% (i.e., the mass ratio of the combined - modified steel slag to the reference cement was 3:7), and mortar specimens were made according to GB / T 17671 - 2021, placed in a constant - temperature and constant - humidity curing box for curing, and the compressive strengths at 7 d and 28 d were detected. The results are shown in Table 2.

[0050] The process flow chart for the preparation of the combined - modified steel slag in this example is as Figure 1 shown.

[0051] Comparative Example 1

[0052] Mortar specimens were made from the reference cement according to GB / T 17671 - 2021, placed in a constant - temperature and constant - humidity curing box for curing, and the compressive strengths at 7 d and 28 d were detected. The results are shown in Table 2.

[0053] Comparative Example 2

[0054] The steel slag with a specific surface area meeting 370 ± 20 m 2The original steel slag at / kg was incorporated into the reference cement at an addition amount of 30 wt%, and mortar specimens were prepared in accordance with GB / T 17671-2021, placed in a thermo-hygrostat for curing, and their compressive strengths at 7 d and 28 d were tested. The results are shown in Table 2.

[0055] Comparative Example 3

[0056] First, the steel slag was crushed, ball-milled and screened by a crusher. The steel slag with a particle size below 200 mesh was taken and mixed with the modifier SiO 2 in a mass ratio of 92.6:7.4, placed in a magnesia crucible, and heated in a muffle furnace to 1400 °C at a rate of 10 °C / min, held for 30 min, taken out and air-cooled to room temperature, and then crushed and ball-milled to a specific surface area meeting 370±20 m 2 / kg. Finally, the high-temperature modified steel slag with a qualified specific surface area was incorporated into the reference cement at an addition amount of 30 wt%, and mortar specimens were prepared in accordance with GB / T 17671-2021, placed in a thermo-hygrostat for curing, and their compressive strengths at 7 d and 28 d were tested. The results are shown in Table 2.

[0057] Comparative Example 4

[0058] The original steel slag powder with a specific surface area meeting 370±20 m 2 / kg was added with water and CO 2 was directly subjected to liquid-phase carbonation treatment with a solid-liquid ratio of 1:10, a reaction temperature of 25 °C, stirred using a magnetic rotor at a stirring rate of 500 rpm, and CO 2 was introduced at a flow rate of 1 L / min for 15 min, and then suction filtration was carried out. Subsequently, the carbonated steel slag was dried at 45 °C for 24 h. Finally, the combined modified steel slag with a qualified specific surface area was incorporated into the reference cement at an addition amount of 30 wt%, and mortar specimens were prepared in accordance with GB / T 17671-2021, placed in a thermo-hygrostat for curing, and their compressive strengths at 7 d and 28 d were tested. The results are shown in Table 2.

[0059] Comparative Example 5

[0060] The steel slag with a particle size below 200 mesh was mixed with the SiO 2 modifier in a mass percentage of 92.6%:7.4%, placed in a magnesia crucible, and heated in a muffle furnace to 1400 °C at a rate of 10 °C / min, held for 30 min, taken out and air-cooled to room temperature, and then crushed and ball-milled to a specific surface area meeting 370±20 m 2 / kg. Then, the steel slag powder with a qualified specific surface area was added with water and CO 2 was directly subjected to liquid-phase carbonation treatment with a solid-liquid ratio of 1:10, a reaction temperature of 25 °C, stirred using a magnetic rotor at a stirring rate of 500 rpm, and CO2 It is introduced at a flow rate of 1 L / min for a reaction time of 5 min, and then suction filtration is carried out. Subsequently, the carbonated steel slag is dried at 45 °C for 24 h. Finally, the combined modified steel slag with a specific surface area meeting the requirements is incorporated into the reference cement at an addition amount of 30 wt%, and mortar specimens are prepared according to GB / T 17671-2021, placed in a thermo-hygrostat for curing, and their compressive strengths at 7 d and 28 d are tested.

[0061] Comparative Example 6

[0062] The steel slag with a particle size passing through a 200-mesh sieve and SiO 2 The modifier are mixed evenly according to a mass percentage of 92.6%:7.4%, loaded into a magnesia crucible, placed in a muffle furnace, heated to 1400 °C at a rate of 10 °C / min, held for 30 min, taken out and air-cooled to room temperature, and then crushed and ball-milled to a specific surface area meeting 370±20 m 2 / kg. After that, the steel slag powder with a qualified specific surface area is added with water and CO 2 is introduced for direct liquid-phase carbonation treatment, with a solid-liquid ratio of 1:10, a reaction temperature of 25 °C, stirred using a magnetic rotor at a stirring rate of 500 rpm, and CO 2 is introduced at a flow rate of 1 L / min for a reaction time of 30 min, and then suction filtration is carried out. Subsequently, the carbonated steel slag is dried at 45 °C for 24 h. Finally, the combined modified steel slag with a specific surface area meeting the requirements is incorporated into the reference cement at an addition amount of 30 wt%, and mortar specimens are prepared according to GB / T 17671-2021, placed in a thermo-hygrostat for curing, and their compressive strengths at 7 d and 28 d are tested.

[0063] Calculation of the activity index A of steel slag

[0064] The activity index A of steel slag can be calculated by Equation (1) according to GB / T51003 2014. In the formula, R t (MPa) is the strength of the pure cement mortar specimen at the corresponding age, and R 0 (MPa) is the strength of the steel slag-cement mortar at the corresponding age.

[0065] The calculation results of the activity index of the steel slag in Example 1 and Comparative Examples 1 to 4 are shown in Table 2.

[0066]

[0067] CO 2 Absorption rate (CO 2 Uptake) and calculation of carbonation degree (Carbonation degree)

[0068] CO 2The absorption rate can be calculated by formula (2) and formula (3), where m 105℃ is the weight of the steel slag sample after carbonization and drying at 105°C; is the weight loss of the sample at 640 - 840°C. The carbonation degree of the steel slag can be calculated by formula (4), where MWCa and MWCO 2 are the relative molecular masses of Ca and CO 2 , and Ca total is the total Ca content in the steel slag. The CO 2 absorption rates and carbonation degree calculation results in Example 1 and Comparative Examples 4, 5, and 6 are shown in Table 2.

[0069]

[0070]

[0071]

[0072] Table 2

[0073]

[0074] As can be seen from Table 2, Example 1 significantly improved the 7-day early hydration activity of the steel slag. The 28-day strength of Example 1 remained basically unchanged compared with Comparative Example 3, and the later strength of the steel slag was improved compared with Comparative Example 4. Therefore, the combined modification played a role in improving the cementitious activity of the steel slag, improving both the early strength and the later strength of the steel slag, which was beneficial to the incorporation of a larger proportion of steel slag into cement and opened up the prospect of large-scale utilization of steel slag. At the same time, compared with Example 1, the carbonation degree of Comparative Example 5 was lower, and the carbonation degree of Comparative Example 6 was higher. However, the 7-day and 28-day activity indices of the combined modified steel slag in Comparative Example 5 and Comparative Example 6 were lower than those in Example 1. It can be concluded that too low or too high carbonation degree is not conducive to the improvement of the hydration activity and strength of the steel slag.

[0075] The f-CaO content in Comparative Example 2 was 3.11%, and the f-CaO contents in Comparative Example 3, Comparative Example 4, and Example 1 were all lower than 0.5%. It can be seen that the modification changed the mineral phase structure of the steel slag and significantly improved the soundness of the steel slag fundamentally. The CO 2 absorption rate in Comparative Example 4 was 9.25%, and the CO 2 absorption rate in Example 1 was 6.66%. Direct liquid-phase carbonation treatment of the steel slag can not only improve the activity index of the steel slag but also achieve the fixation of CO 2 and reduce the emission of CO 2 .

[0076] Example 2

[0077] The steel slag is subjected to combined modification by combining high-temperature hot-state modification and room-temperature direct liquid-phase carbonation. The specific steps are as follows:

[0078] First, the steel slag is crushed, ball-milled, and screened by a crusher. The steel slag with a particle size smaller than 200 mesh is mixed with a fly ash modifier in a mass percentage of 85%:15%, loaded into a magnesia crucible, placed in a muffle furnace, heated to 1350°C at a rate of 10°C / min, held for 35 min, taken out and air-cooled to room temperature, and then crushed and ball-milled until the specific surface area meets 370±20 m 2 / kg. After that, the steel slag powder with a qualified specific surface area is subjected to direct liquid-phase carbonation treatment by adding water. The solid-liquid ratio is 1:8, the reaction temperature is 20°C, a magnetic rotor is used for stirring, the stirring rate is 400 rpm, and CO 2 is introduced at a flow rate of 1 L / min, the reaction time is 25 min, and then filtration is carried out. Subsequently, the carbonated steel slag is dried at 45°C for 24 h. Finally, the combined-modified steel slag with a qualified specific surface area is incorporated into the reference cement at an addition amount of 30 wt%, mortar test blocks are made in accordance with GB / T 17671-2021, placed in a constant temperature and humidity curing box for curing, and the compressive strengths at 7 d and 28 d are detected.

[0079] Example 3

[0080] The steel slag is subjected to combined modification by combining high-temperature hot-state modification and room-temperature direct liquid-phase carbonation. The specific steps are as follows:

[0081] First, the steel slag is crushed, ball-milled, and screened by a crusher. The steel slag with a particle size smaller than 200 mesh is mixed with a coal gangue modifier in a mass percentage of 97%:3%, loaded into a magnesia crucible, placed in a muffle furnace, heated to 1500°C at a rate of 10°C / min, held for 25 min, taken out and air-cooled to room temperature, and then crushed and ball-milled until the specific surface area meets 370±20 m 2 / kg. After that, the steel slag powder with a qualified specific surface area is subjected to direct liquid-phase carbonation treatment by adding water. The solid-liquid ratio is 1:12, the reaction temperature is 30°C, a magnetic rotor is used for stirring, the stirring rate is 600 rpm, and CO 2 is introduced at a flow rate of 1 L / min, the reaction time is 10 min, and then filtration is carried out. Subsequently, the carbonated steel slag is dried at 45°C for 24 h. Finally, the combined-modified steel slag with a qualified specific surface area is incorporated into the reference cement at an addition amount of 30 wt%, mortar test blocks are made in accordance with GB / T 17671-2021, placed in a constant temperature and humidity curing box for curing, and the compressive strengths at 7 d and 28 d are detected.

[0082] The compressive strengths of the mortar specimens at 7 days and 28 days, the 7-day activity index, the 28-day activity index and the f-CaO content of the steel slag in Example 2 and Example 3 are comparable to the test results of Example 1.

[0083] As described above, the above are only the preferred specific embodiments of the present invention, and the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A method for improving the cementitious activity of steel slag by combined modification, characterized in that, it comprises the following steps: First, mix the steel slag and the high-temperature modifier, then carry out heat treatment, break and grind after cooling, and then carry out direct liquid-phase carbonation treatment; The high-temperature modifier includes one or more of SiO 2 , fly ash, slag, and coal gangue; it is heated to 1350-1500 °C, the heating treatment time is 25-35 min, and the cooling is specifically air cooling to room temperature; The direct liquid-phase carbonation treatment is carried out under stirring, the solid-liquid ratio is 1:(8-12), the reaction temperature is 20-30 °C, and CO 2 is introduced at a flow rate of 1 L / min, and the treatment time is 10-25 min.

2. The method for improving the cementitious activity of steel slag by combined modification according to claim 1, characterized in that, the mass percentage of the steel slag and the high-temperature modifier is (85-97%)∶(3-15%), and the sum of the mass percentages of the steel slag and the high-temperature modifier is 100%.

3. The method for improving the cementitious activity of steel slag by combined modification according to claim 1, characterized in that, The specific surface area of the ground steel slag is 370 ± 20 m 2 / kg.

4. The method for improving the cementitious activity of steel slag by combined modification according to claim 1, characterized in that, the stirring is magnetic stirring, and the stirring rate is 400-600 rpm.

5. The method for improving the cementitious activity of steel slag by combined modification according to claim 1, characterized in that, after the direct liquid-phase carbonation treatment, it further includes a step of suction filtration and drying the obtained steel slag.

6. A steel slag obtained by the method for improving the cementitious activity of steel slag by combined modification according to any one of claims 1-5.

7. The application of the steel slag according to claim 6 in a cement-based cementitious material.

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