An ultra-low-carbon magnesia slag cement, a preparation method and application thereof

Abstract

The application provides an ultra-low-carbon magnesia slag cement, which is made of the following raw materials in percentage by weight: granulated blast furnace slag 36-95%, gypsum raw material 3-40%, magnesia raw material 0.5-5%, cement mixing material 0-50% and coagulation-adjusting and strength-promoting component 0-5%; the magnesia raw material is a material with free magnesia and / or magnesium hydroxide as the main active mineral, and the sum of the free magnesia and the magnesium hydroxide is not more than 3.25% of the total weight of the raw material. The application also provides a method for preparing the ultra-low-carbon magnesia slag cement and application of the ultra-low-carbon magnesia slag cement in preparing concrete, mortar, cement products and grouting material. The ultra-low-carbon magnesia slag cement has a faster hydration hardening speed, higher early and later strength.

Description

Technical Field

[0001] This invention belongs to the field of inorganic building materials, specifically relating to an ultra-low carbon magnesium oxide slag cement. Background Technology

[0002] Granulated blast furnace slag is a byproduct obtained during pig iron smelting in a blast furnace, consisting mainly of silicates and aluminosilicates. After quenching and granulation, the granulated blast furnace slag forms an amorphous silica-calcium-aluminum glassy substance, typically containing over 80% amorphous material. Researchers have discovered that using gypsum as a sulfate activator and silicate cement clinker, silicate cement, or calcium oxide as an alkaline activator can activate the granulated blast furnace slag, producing a hydraulic cementitious material. This material is known as supersulfate cement in Europe and gypsum-slag cement in my country. This type of cement exhibits excellent properties such as low heat of hydration, strong impermeability, and resistance to sulfate attack, while also having low emissions and low energy consumption. However, it also suffers from long setting time, slow hardening speed, low early strength, and low later strength, limiting its application in engineering projects.

[0003] Granulated blast furnace slag itself possesses a certain degree of hydration activity. Upon contact with water, it rapidly hydrates, forming a dense layer of hydration products on its surface. This layer isolates the water from the granulated blast furnace slag particles, preventing further hydration. Research has found that a cement pore solution with suitable alkalinity can break down this dense hydration product layer, activating and initiating the rehydration of the granulated blast furnace slag. Once hydration of the granulated blast furnace slag is initiated, the alkaline environment of the pore solution can be maintained, achieving self-acceleration of hydration. Subsequently, calcium and aluminum dissolve from the granulated blast furnace slag, forming calcium ions and aluminate ions, respectively. These then further react with gypsum to gradually produce ettringite crystals. Therefore, silicate cement, silicate cement clinker, or calcium oxide is often added to persulfate cement or gypsum-slag cement as an alkaline activator. Upon contact with water, these react to generate calcium hydroxide, providing hydroxide ions to the cement solution and ensuring an alkaline environment. However, excessive calcium hydroxide production leads to an excessively high concentration of calcium ions in the cement pore solution, which in turn affects the dissolution of calcium ions in granulated blast furnace slag and inhibits its hydration. Furthermore, excessively high alkalinity is also detrimental to the formation of ettringite; as alkalinity increases, both the rate and quantity of ettringite formation decrease. Therefore, insufficient addition of silicate cement, silicate cement clinker, or calcium oxide cannot effectively activate the activity of granulated blast furnace slag, resulting in slow cement hardening and low early strength. Increasing the amount of silicate cement, silicate cement clinker, or calcium oxide can improve early hydration activity to some extent, improving setting time and early strength to some extent. However, excessively high calcium ion concentrations in the solution will inhibit the hydration of granulated blast furnace slag in the middle and later stages, leading to a significant decrease in later strength and failing to meet engineering requirements. Summary of the Invention

[0004] The primary objective of this invention is to provide a cement material with faster hydration and hardening speed and higher early and late strength.

[0005] A second object of the present invention is to provide a method for preparing the cement.

[0006] A third objective of this invention is to provide the application of the cement in the preparation of concrete, mortar, cement products, and grouting materials.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides an ultra-low carbon magnesium oxide slag cement, which is made from the following raw materials by weight percentage: 36%~95% granulated blast furnace slag, 3%~40% gypsum raw materials, 0.5%~5% magnesium oxide raw materials, 0%~50% cement admixtures and 0%~5% setting and strength-promoting components.

[0009] In the ultra-low carbon magnesium oxide slag cement of the present invention, the magnesium oxide raw material is a material with free magnesium oxide and / or magnesium hydroxide as the main active minerals. The sum of free magnesium oxide and magnesium hydroxide does not exceed 3.25% of the cement weight; preferably, the sum of free magnesium oxide and magnesium hydroxide accounts for 0.325% to 3.25% of the cement weight, more preferably 1.2% to 3.25% of the cement weight, even more preferably 1.8% to 2.8% of the cement weight, and even more preferably 1.95% to 2.6% of the cement weight.

[0010] In the ultra-low carbon magnesium oxide slag cement of the present invention, the magnesium oxide raw materials can be selected from any one or a combination of at least two of industrial magnesium oxide, magnesium hydroxide, light-burned magnesium oxide, light-burned dolomite, light-burned magnesite, light-burned magnesite, magnesium oxide expanding agent, brucite, light magnesium oxide, active magnesium oxide, and heavy magnesium oxide; preferably, the magnesium oxide raw materials are any one or a combination of at least two of light-burned magnesium oxide, light-burned dolomite, magnesium oxide expanding agent, and magnesium hydroxide; more preferably, the magnesium oxide raw materials are a mixture of light-burned magnesium oxide and light-burned dolomite, magnesium oxide expanding agent, and / or magnesium hydroxide.

[0011] In the ultra-low carbon magnesium oxide slag cement of the present invention, the gypsum raw material is any one or a combination of at least two of dihydrate gypsum, anhydrite, hemihydrate gypsum, α-type high-strength gypsum, desulfurized gypsum, phosphogypsum, or fluorogypsum; preferably, the gypsum raw material is any one or a combination of at least two of dihydrate gypsum, anhydrite, desulfurized gypsum, or phosphogypsum; more preferably, the gypsum raw material is a mixture of desulfurized gypsum with dihydrate gypsum, anhydrite, and / or phosphogypsum.

[0012] The preferred ultra-low carbon magnesium oxide slag cement of this invention is made from the following raw materials in weight percentages: 48%~93% granulated blast furnace slag, 5%~40% gypsum-based raw materials, 0.5%~4% magnesium oxide-based raw materials, 0%~46.5% cement admixtures, and 0%~5% setting and strength-enhancing components; more preferably, it is made from the following raw materials in weight percentages: 58%~88% granulated blast furnace slag, 10%~35% gypsum-based raw materials, 1%~4% magnesium oxide-based raw materials, 0%~31.5% cement admixtures, and setting and strength-enhancing components. The strengthening component is 0%~5%; more preferably, it is made from the following raw materials by weight percentage: 63%~83% granulated blast furnace slag, 15%~35% gypsum raw materials, 2%~3% magnesium oxide raw materials, 0%~20% cement admixtures and 0%~5% setting and strengthening component; even more preferably, it is made from the following raw materials by weight percentage: 70%~78% granulated blast furnace slag, 20%~28% gypsum raw materials, 2% magnesium oxide raw materials, 0%~8% cement admixtures and 0%~5% setting and strengthening component.

[0013] In the preferred ultra-low carbon magnesium oxide slag cement of the present invention, the cement admixture is any one or a combination of at least two of the following: fly ash, limestone, steel slag, silica fume, quartz, sandstone, tuff, zeolite, pumice, coal gangue, or pozzolanic admixture; preferably, the cement admixture is any one or a combination of at least two of the following: fly ash, limestone, or steel slag.

[0014] In the preferred ultra-low carbon magnesium oxide slag cement of the present invention, the setting-regulating and strength-promoting component is any one or a combination of at least two of sodium hydroxide, potassium hydroxide, calcium hydroxide, calcium oxide, industrial aluminum sulfate, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, sodium silicate, sulfoaluminate cement, sulfoaluminate cement clinker, citric acid, sodium citrate, or sodium gluconate; preferably, the setting-regulating and strength-promoting component is selected from any one or a combination of at least two of sodium hydroxide, calcium hydroxide, sulfoaluminate cement clinker, or citric acid.

[0015] In a preferred embodiment of the present invention, the specific surface area of ​​the raw materials used to prepare the ultra-low carbon magnesium oxide slag cement is 200~1000 m². 2 / kg; preferably, the specific surface area of ​​the raw material is 300~800 m² / kg. 2 / kg; more preferably, the specific surface area of ​​the raw material is 420~800 m². 2 / kg.

[0016] Secondly, the present invention provides a method for preparing the ultra-low carbon magnesium oxide slag cement, the specific steps of which include: mixing all the raw materials in the specified proportions and then grinding them together to a specific surface area of ​​200~1000 m². 2 / kg;

[0017] or,

[0018] The specific steps include: grinding the granulated blast furnace slag of the specified proportion separately to a specific surface area of ​​200-1000 m². 2 / kg, grind all remaining raw materials together to a specific surface area of ​​300-800m². 2 / kg, then mix the two powders evenly.

[0019] Thirdly, the present invention also provides the application of the ultra-low carbon magnesium oxide slag cement in the preparation of concrete, mortar, cement products, and grouting materials.

[0020] In the preparation of ultra-low carbon magnesium oxide slag cement described in this invention, the addition of magnesium oxide raw materials provides a more suitable alkaline environment for the activation of granulated blast furnace slag, and avoids the problems of inhibited hydration of granulated blast furnace slag and slowed growth of ettringite caused by excessive alkalinity and increased calcium ion concentration. Therefore, compared with the prior art, the ultra-low carbon magnesium oxide slag cement of this invention has superior strength properties. In particular, compared with supersulfate cement / gypsum slag cement, the ultra-low carbon magnesium oxide slag cement of this invention has a faster hydration and hardening speed and higher early and late strength. Detailed Implementation

[0021] The following describes the solution and technical effects of the present invention in further detail by way of examples, but the solution of the present invention is not limited to the specific examples listed.

[0022] Examples 1-6. Ultra-low carbon magnesium oxide slag cement and its strength testing

[0023] Ultra-low carbon magnesium oxide slag cement, as shown in Table 1 below, is prepared by weight percentage from 75%~79.5% granulated blast furnace slag, 20% desulfurized gypsum and the balance of light-burned magnesium oxide, wherein the free magnesium oxide content in the light-burned magnesium oxide is 65%.

[0024] The preparation steps include: as shown in Table 1 below, mixing all raw materials according to the raw material proportions and then grinding them together until the specific surface area is 420 m². 2 After mixing the free magnesium oxide (MgO) at a ratio of 0.325% to 3.25%, the free magnesium oxide content is controlled to obtain ultra-low carbon magnesium oxide slag cement.

[0025] The compressive strength of the mortar of the ultra-low carbon magnesium oxide slag cement in Examples 1-6 was tested according to the national standard GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)" with a water-cement ratio of 0.5 and a mortar-mortar ratio of 1:3. The test results are shown in Table 1.

[0026] Table 1. Mix proportions and compressive strengths of ultra-low carbon magnesium oxide slag cement in Examples 1-6

[0027] .

[0028] As shown in Table 1, when the content of free magnesium oxide in the cement raw materials is controlled within the range of 0.325% to 3.25%, the cement in all examples exhibits excellent early and late strength. With the increase of the amount of lightly calcined magnesium oxide in the cement raw materials, the 1-day strength of the cement continuously increases, while the 3-day and 28-day strengths show a trend of first increasing and then decreasing. The cement exhibits optimal overall strength when the content of free magnesium oxide in the cement is between 1.3% and 3.25%, especially between 1.95% and 2.6%.

[0029] Examples 7-13. Ultra-low carbon magnesium oxide slag cement and its strength test

[0030] Ultra-low carbon magnesium oxide slag cement, as shown in Table 2 below, is prepared by weight percentage from 58% to 95% granulated blast furnace slag, 3% to 40% desulfurized gypsum and the balance (2%) light-burned magnesium oxide, wherein the free magnesium oxide content in the light-burned magnesium oxide is 65%.

[0031] The preparation steps include: as shown in Table 2 below, mixing all raw materials according to the raw material proportions and then grinding them together until the specific surface area is 420 m². 2 After mixing the free magnesium oxide (MgO) at a ratio of 1.3% per kg, the resulting ultra-low carbon magnesium oxide slag cement is obtained.

[0032] The compressive strength of the mortar of the ultra-low carbon magnesium oxide slag cement in Examples 7-13 was tested according to the national standard GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)" with a water-cement ratio of 0.5 and a mortar-mortar ratio of 1:3. The test results are shown in Table 2.

[0033] Table 2. Mix proportions and compressive strengths of ultra-low carbon magnesium oxide slag cement in Examples 7-13

[0034] .

[0035] As shown in Table 2, when the content of free magnesium oxide in the cement raw materials is controlled at 1.3%, the cement in all examples exhibits excellent early and late strength. With the increase of desulfurized gypsum content in the cement raw materials, the 1-day, 3-day, and 28-day strengths of the cement all show a trend of first increasing and then decreasing, and reach the highest values ​​simultaneously when the desulfurized gypsum content is 28%.

[0036] Examples 14-19. Ultra-low carbon magnesium oxide slag cement and its strength test

[0037] The ultra-low carbon magnesium oxide slag cement, as shown in Table 3 below, is prepared by weight percentage from 78% granulated blast furnace slag, 20% desulfurized gypsum and the balance (2%) light-burned magnesium oxide, wherein the free magnesium oxide content in the light-burned magnesium oxide is 65%.

[0038] The preparation steps include: as shown in Table 3 below, all raw materials in each embodiment are mixed according to the raw material mixing ratio and then ground together to different specific surface areas, and then mixed evenly, controlling the free magnesium oxide weight percentage content to be 1.3% to obtain ultra-low carbon magnesium oxide slag cement.

[0039] The compressive strength of the mortar of the ultra-low carbon magnesium oxide slag cement in Examples 14-19 was tested according to the national standard GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)" with a water-cement ratio of 0.5 and a mortar-mortar ratio of 1:3. The test results are shown in Table 3.

[0040] Table 3. Mix proportions and compressive strengths of ultra-low carbon magnesium oxide slag cement in Examples 14-19

[0041] .

[0042] Table 3 shows that when the free magnesium oxide content in cement raw materials is controlled at 1.3%, ideal early and later strengths can be obtained when cement is ground to various specific surface areas. As the specific surface area of ​​cement raw materials increases, the 1-day and 3-day strengths of cement continuously improve, reaching 420m... 2 / kg ~1000m 2 It exhibits superior early and late strength at a specific surface area of ​​ / kg, especially at 500m². 2 / kg ~800m 2 The overall compressive strength of cement reaches its maximum when the specific surface area is / kg.

[0043] Examples 20-25. Ultra-low carbon magnesium oxide slag cement and its strength test

[0044] Ultra-low carbon magnesium oxide slag cement, as shown in Table 4 below, is prepared by weight percentage from 73% or 78% granulated blast furnace slag, 20% or 25% gypsum-based raw materials and the balance (2%) light-burned magnesium oxide, wherein the free magnesium oxide content in the light-burned magnesium oxide is 65%.

[0045] The preparation steps include: as shown in Table 4 below, mixing all raw materials in each embodiment according to the raw material mixing ratio and then grinding them together until the specific surface area is 420m². 2 / kg, then mix evenly, and control the free magnesium oxide weight percentage to 1.3% to obtain ultra-low carbon magnesium oxide slag cement.

[0046] The compressive strength of the ultra-low carbon magnesium oxide slag cement from Examples 20-25 was tested according to the national standard GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)" with a water-cement ratio of 0.5 and a mortar ratio of 1:3. The test results are shown in Table 4.

[0047] Table 4. Mix proportions and compressive strengths of ultra-low carbon magnesium oxide slag cement in Examples 20-25

[0048] .

[0049] As shown in Table 4, regardless of the type of gypsum raw material used, as long as the content of free magnesium oxide in the cement raw materials is controlled at 1.3%, the cement can achieve ideal early and later strength. When using a single type of gypsum raw material, compared with desulfurized gypsum, dihydrate gypsum has a slightly lower calcium sulfate content, resulting in slightly lower cement strength; anhydrite has a slower dissolution rate and a higher calcium sulfate content, resulting in lower early strength and higher later strength; phosphogypsum contains a small amount of impurities, affecting its activity, thus reducing cement strength. However, when multiple gypsum raw materials, including desulfurized gypsum, are mixed and incorporated, both the early and later strength of the cement are improved compared to using desulfurized gypsum alone.

[0050] Examples 26-31. Ultra-low carbon magnesium oxide slag cement and its strength test

[0051] Ultra-low carbon magnesium oxide slag cement, as shown in Table 5 below, is prepared by weight percentage from 76% or 78% granulated blast furnace slag, 20% gypsum-based raw materials, and the balance (2% or 4%) magnesium oxide-based raw materials. The magnesium oxide-based raw materials are selected from any one or more mixtures of light-burned magnesium oxide, light-burned dolomite, magnesium oxide expanding agent, and magnesium hydroxide. The free magnesium oxide content in light-burned magnesium oxide, light-burned dolomite, and magnesium oxide expanding agent is 65%, 70%, and 80%, respectively, and the purity of magnesium hydroxide is 90%.

[0052] The preparation steps include: as shown in Table 5 below, mixing all raw materials in each embodiment according to the raw material mixing ratio and then grinding them together until the specific surface area is 420m². 2 / kg, then mix evenly, and control the free magnesium oxide weight percentage in it within the range of 0.325%~3.25% to obtain ultra-low carbon magnesium oxide slag cement.

[0053] The ultra-low carbon magnesium oxide slag cement of Examples 26-31 was tested for mortar compressive strength according to the national standard GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)" with a water-cement ratio of 0.5 and a mortar ratio of 1:3. The test results are shown in Table 5.

[0054] Table 5. Mix proportions and compressive strengths of ultra-low carbon magnesium oxide slag cement in Examples 26-31

[0055] .

[0056] As shown in Table 5, regardless of the type of magnesium oxide raw material used, as long as the content of free magnesium oxide in the cement raw material is controlled within the range of 0.325% to 3.25%, the cement can achieve ideal early and late strength. When using a single magnesium oxide raw material, light-burned magnesium oxide provides the best late strength. Compared to light-burned magnesium oxide, the use of light-burned dolomite results in increased early strength but decreased late strength. The use of magnesium oxide expanding agents slightly increases early strength but slightly decreases late strength. Magnesium hydroxide dissolves faster and has fewer effective components, thus increasing early strength but slightly decreasing late strength. However, when using a mixture of multiple magnesium oxide raw materials containing light-burned magnesium oxide, both the early and late strength of the cement are improved compared to using light-burned magnesium oxide alone.

[0057] Examples 32-41. Ultra-low carbon magnesium oxide slag cement and its strength test

[0058] Ultra-low carbon magnesium oxide slag cement, as shown in Table 6 below, is prepared by weight percentage from 36% to 78% granulated blast furnace slag, 20% or 12% desulfurized gypsum, 2% light-burned magnesium oxide, and the balance cement admixture. The cement admixture is any one or a combination of at least two of fly ash, limestone, or steel slag, and the free magnesium oxide content in the light-burned magnesium oxide is 65%.

[0059] The preparation steps include: as shown in Table 6 below, mixing all raw materials in each embodiment according to the raw material mixing ratio and then grinding them together until the specific surface area is 420m². 2 / kg, then mix evenly, and control the free magnesium oxide weight percentage to 1.3% to obtain ultra-low carbon magnesium oxide slag cement.

[0060] The ultra-low carbon magnesium oxide slag cement of Examples 32-41 was tested for mortar compressive strength according to the national standard GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)" with a water-cement ratio of 0.5 and a mortar-mortar ratio of 1:3. The test results are shown in Table 6.

[0061] Table 6. Mix proportions and compressive strengths of ultra-low carbon magnesium oxide slag cement in Examples 32-41

[0062] .

[0063] As shown in Table 6, regardless of whether cement admixtures are added, as long as the content of free magnesium oxide in the cement raw materials is controlled at 1.3%, the cement can achieve ideal early and later strength. When cement admixtures are added, compared with not adding them, the addition of fly ash leads to a decrease in strength; the addition of limestone leads to a decrease in strength, but its early and later strength is higher than that of fly ash; the addition of steel slag increases the early strength of cement, but leads to a decrease in later strength.

[0064] Examples 42-46: Ultra-low carbon magnesium oxide slag cement and its strength test

[0065] Ultra-low carbon magnesium oxide slag cement, as shown in Table 7 below, is prepared by weight percentage from 67% to 78% granulated blast furnace slag, 20% desulfurized gypsum, 2% light-burned magnesium oxide, and the balance of cement admixtures and setting-regulating and strength-promoting components. The cement admixtures are fly ash, and the setting-regulating and strength-promoting components are selected from any one or a combination of at least two of sodium hydroxide, calcium hydroxide, sulfoaluminate cement clinker, or citric acid. The free magnesium oxide content in the light-burned magnesium oxide is 65%.

[0066] The preparation steps include: as shown in Table 7 below, mixing all raw materials in each embodiment according to the raw material mixing ratio and then grinding them together until the specific surface area is 420m². 2 / kg, then mix evenly, and control the free magnesium oxide weight percentage to 1.3% to obtain ultra-low carbon magnesium oxide slag cement.

[0067] The compressive strength of the ultra-low carbon magnesium oxide slag cement in Examples 42-46 was tested according to the national standard GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)" with a water-cement ratio of 0.5 and a mortar ratio of 1:3. The test results are shown in Table 7.

[0068] Table 7. Mix proportions and compressive strengths of ultra-low carbon magnesium oxide slag cement in Examples 42-46

[0069] .

[0070] As shown in Table 7, regardless of whether cement admixtures and setting-regulating and strength-promoting components are added, as long as the content of free magnesium oxide in the cement raw materials is controlled at 1.3%, the cement can achieve ideal early-age strength and later-age strength. When setting-regulating and strength-promoting components are added, compared with not adding them, the addition of sodium hydroxide and calcium hydroxide increases early-age strength but decreases later-age strength; the addition of citric acid decreases early-age strength but increases later-age strength.

[0071] Comparative Examples 1-6. Slag Cement and its Strength Testing

[0072] As a control, slag cement was prepared according to the mix proportions shown in Table 8 below, wherein the free magnesium oxide content in the lightly calcined magnesium oxide was 65%.

[0073] The preparation steps include: as shown in Table 8 below, all raw materials in each comparative example are mixed according to the raw material mixing ratio and then ground together to the corresponding specific surface area, and then mixed evenly to obtain slag cement.

[0074] The slag cement samples from Comparative Examples 1-6 were tested for compressive strength of their mortar according to the national standard GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)", with a water-cement ratio of 0.5 and a mortar-mortar ratio of 1:3. The test results are shown in Table 8.

[0075] Table 8. Comparative proportions and compressive strengths of slag cement

[0076] .

[0077] As shown in Table 8, in Comparative Example 1, no magnesium oxide raw materials were added, so the activity of the granulated blast furnace slag was not activated, and hydration was almost impossible, resulting in consistently very low cement compressive strength. Comparative Example 2 had excessive magnesium oxide raw materials, leading to an excessively high content of free magnesium oxide. While this activated the granulated blast furnace slag in the early stages, the resulting excessive alkalinity inhibited the hydration of the granulated blast furnace slag in the later stages, resulting in cement with only high early strength and insufficient later strength. Comparative Example 4 had excessive gypsum raw materials, resulting in a large amount of residual gypsum in the hydration product system and insufficient granulated blast furnace slag powder, thus failing to generate enough ettringite. Therefore, its cement's early compressive strength was only slightly better than Comparative Example 3, but both its early and later strengths were significantly lower than those of the embodiments of this invention. In Comparative Example 5, only the raw materials were ground to 120 μm. 2 The specific surface area of ​​the raw materials was insufficient, resulting in low activity and consistently significantly lower cement compressive strength compared to the embodiments of this invention. Conversely, grinding the raw materials to 1200 m² as described in Comparative Example 6 improved the specific surface area. 2 While cement can achieve higher early strength at a specific surface area of ​​ / kg, its later strength is inferior to that of the embodiments of the present invention, and the process cost is too high.

[0078] In summary, the ultra-low carbon magnesium oxide slag cement of the present invention, by adding an appropriate amount of magnesium oxide raw materials and controlling the content of free magnesium oxide in the hydration raw materials, enables the granulated blast furnace slag to be activated and hydrated in the most suitable alkaline environment, thereby enabling the cement to obtain ideal early strength and later strength.

Claims

1. An ultra-low carbon magnesia slag cement, characterized by, The material is made from the following raw materials by weight percentage: 36%~95% granulated blast furnace slag, 3%~40% gypsum-based raw materials, 0.5%~5% magnesium oxide-based raw materials, 0%~50% cement admixtures, and 0%~5% setting-regulating and strength-promoting components; the magnesium oxide-based raw materials are materials with free magnesium oxide and / or magnesium hydroxide as the main active minerals, and the sum of the free magnesium oxide and magnesium hydroxide accounts for 0.325%~3.25% of the total weight of the raw materials; the setting-regulating and strength-promoting components are any one or a combination of at least two of potassium hydroxide, calcium hydroxide, calcium oxide, industrial aluminum sulfate, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, sodium silicate, sulfoaluminate cement, sulfoaluminate cement clinker, citric acid, sodium citrate, or sodium gluconate.

2. The ultra-low carbon magnesia slag cement according to claim 1, characterized in that: It is made from the following raw materials by weight percentage: 58%~88% granulated blast furnace slag, 10%~35% gypsum raw materials, 1%~4% magnesium oxide raw materials, 0%~31.5% cement admixtures and 0%~5% setting and strength-promoting components.

3. The ultra-low carbon magnesia slag cement according to claim 1, wherein: It is made from the following raw materials by weight percentage: 70%~78% granulated blast furnace slag, 20%~28% gypsum raw materials, 2% magnesium oxide raw materials, 0%~8% cement admixtures and 0%~5% setting and strength-promoting components.

4. The ultra-low carbon magnesia slag cement according to any one of claims 1 to 3, characterized in that: The sum of the free magnesium oxide and magnesium hydroxide accounts for 1.95% to 2.6% of the total weight of the raw materials.

5. The ultra-low carbon magnesia slag cement according to any one of claims 1 to 3, characterized in that: The magnesium oxide raw materials are selected from any one or at least a combination of two of the following: industrial magnesium oxide, magnesium hydroxide, light-burned magnesium oxide, light-burned dolomite, light-burned magnesite, light-burned magnesite, magnesium oxide expanding agent, brucite, light magnesium oxide, active magnesium oxide, and heavy magnesium oxide.

6. The ultra-low carbon magnesia slag cement according to any one of claims 1 to 3, wherein: The magnesium oxide raw material is a mixture of lightly calcined magnesium oxide, lightly calcined dolomite, magnesium oxide expanding agent and / or magnesium hydroxide.

7. The ultra-low carbon magnesia slag cement according to any one of claims 1 to 3, wherein: 0.1 < x < 0.

3. The gypsum raw materials mentioned are any one or a combination of at least two of the following: dihydrate gypsum, anhydrite, hemihydrate gypsum, α-type high-strength gypsum, desulfurized gypsum, phosphogypsum, or fluorogypsum.

8. The ultra-low carbon magnesia slag cement according to any one of claims 1 to 3, wherein: The gypsum raw material is a mixture of desulfurized gypsum, dihydrate gypsum, anhydrite, and / or phosphogypsum.

9. The ultra-low carbon magnesia slag cement according to any one of claims 1 to 3, wherein: The cement admixture is any one or a combination of at least two of the following: fly ash, limestone, steel slag, silica fume, quartz, sandstone, tuff, zeolite, pumice, coal gangue, or pozzolanic admixture.

10. The ultra-low carbon magnesia slag cement according to any one of claims 1 to 3, wherein: The raw material has a specific surface area of 200-1000 m 2 / kg.

11. The ultra-low carbon magnesia slag cement according to any one of claims 1 to 3, wherein: The raw material has a specific surface area of 420-800 m 2 / kg.

12. Process for the production of the ultra-low-carbon magnesia-slag cement according to any one of claims 1 to 11, characterized in that, The specific steps include: mixing all raw materials in proportion and then grinding them together until the specific surface area is 200~1000 m². 2 / kg; or, grind granulated blast furnace slag separately to a specific surface area of ​​200–1000 m². 2 / kg, grind all remaining raw materials together in proportion to achieve a specific surface area of ​​300-800m². 2 / kg, and then mix the two powders evenly in proportion.

13. The application of the ultra-low carbon magnesium oxide slag cement according to any one of claims 1-11 in the preparation of concrete, mortar, cement products, and grouting materials.