A kind of low heat silicate cement and preparation method thereof

Abstract

The present invention relates to the technical field of low-heat cement, and discloses a low-heat silicate cement and a preparation method thereof, a low-heat silicate cement, wherein the low-heat silicate cement is obtained by mixing and grinding low-heat cement clinker and gypsum; the low-heat cement clinker is formed by pre-decomposing raw material powder, sintering in a cement kiln, mixing and melting with fly ash, and cooling after being discharged from the kiln; the raw material powder includes limestone, clay, iron ore and NaF additive. The present invention can improve the grindability of dicalcium silicate and tetracalcium aluminoferrite in low-heat cement clinker by dispersing a trace amount of NaF additive in the liquid phase during the sintering process of low-heat cement clinker, and can avoid the problem that aluminum colloid or iron colloid formed in the early stage of hydration is coated around C4AF and causes hydration stagnation of C4AF, thereby improving the hydration activity of C4AF, and promoting the rapid formation and interweaving of hydration products, and effectively improving the early strength of low-heat cement.

Description

Technical Field

[0001] The invention relates to the technical field of low-heat cement, and in particular to low-heat silicate cement and a preparation method thereof. Background Art

[0002] Low-heat Portland cement is based on dicalcium silicate (C2S) as the main mineral, which is about 25% lower than the main mineral tricalcium silicate (C3S) of traditional ordinary Portland cement. The clinker burning temperature can be reduced from 1450°C to 1300-1350°C, so the energy consumption required in the production process is reduced and the carbon emissions are reduced. At the same time, because the energy released by low-heat Portland cement during the hydration process is relatively low, the later strength is relatively high, and it also has more reliable durability.

[0003] The main feature of low heat cement is that the heat released during the hydration process is relatively low, which helps to control the temperature rise of concrete and reduce problems caused by thermal stress. However, it is precisely because of the low heat release of low heat cement that its early strength development is slow and requires special maintenance, such as wet maintenance, which increases the construction period and cost. This is the main reason restricting the application of low heat cement. In industry, low heat cement is often compounded with hydration-active sulphoaluminates, mineral admixtures, etc., or the hydration activity of low heat cement is improved by optimizing cement particle grading and other control methods, but these methods have limited effect on the improvement of hydration products. Summary of the invention

[0004] Based on the above problems, the present invention provides a low-heat silicate cement and a preparation method thereof, which can improve the grindability of dicalcium silicate and tetracalcium aluminoferrate in low-heat cement clinker, and at the same time avoid the problem of aluminum colloid or iron colloid formed in the early stage of hydration coating around C4AF and causing hydration stagnation of C4AF, thereby improving the hydration activity of C4AF and effectively improving the early strength of low-heat cement.

[0005] In order to achieve the above technical effects, the technical solution adopted by the present invention is:

[0006] A low-heat silicate cement, which is obtained by mixing and grinding low-heat cement clinker and gypsum; the low-heat cement clinker is formed by pre-decomposing raw material powder, sintering it in a cement kiln, mixing it with fly ash and melting it, and then cooling it after it is discharged from the kiln; wherein, by weight, the amount of fly ash is 1 to 6 parts, and the raw material powder includes 70 to 90 parts of limestone, 5 to 20 parts of clay, 1 to 7 parts of iron ore and 0.3 to 0.6 parts of NaF additive; during the sintering process, the temperature of the firing section in the cement kiln is controlled to be 1300 to 1350°C, and the temperature range of the lower transition zone near the kiln tail is 980 to 1030°C.

[0007] Furthermore, the low-heat cement clinker contains 40-60% dicalcium silicate, 5-15% tricalcium silicate, 1-6% tricalcium aluminate, 20-30% tetracalcium aluminoferrite, and the NaF is dissolved in the mineral crystal phase in the form of a solid solution.

[0008] Furthermore, in the low-heat Portland cement, the amount of the low-heat cement clinker is 80 to 90 parts, and the amount of the gypsum is 10 to 20 parts by weight.

[0009] Furthermore, in terms of mass percentage, the limestone comprises 8-14% SiO2, 1-3% Al2O3, 0.1-0.6% Fe2O3, 35-48% CaO, 0.3-1.8% MgO, 0.1-0.4% K2O, and 0.05-0.3% Na2O; the clay comprises 55-68% SiO2, 11-17% Al2O3, 2-8% Fe2 O3, 0.5-2.0% CaO, 1.4-2.8% MgO, 0.9-2.0% K2O, and 0.5-1.5% Na2O; the iron ore comprises 10-17% SiO2, 2-6% Al2O3, 62-69% Fe2O3, 0.1-0.6% CaO, 0.6-2.2% MgO, 0.5-2.0% K2O, and 0.5-1.3% Na2O.

[0010] Furthermore, the raw meal also includes volcanic ash, which includes, by mass percentage, 60-70% SiO2, 10-16% Al2O3, 2-5% Fe2O3, 0.5-3.5% CaO, 0.7-2.8% MgO, 0.5-1.0% K2O, and 0.5-1% Na2O.

[0011] In order to achieve the above technical effects, the present invention also provides a method for preparing low-heat silicate cement, which is used to prepare the low-heat silicate cement, comprising:

[0012] After crushing limestone, clay and iron ore according to the proportion, they are ground in a raw mill, and NaF additive is added to the raw mill to mix them evenly to form raw meal powder;

[0013] Pre-decomposing the raw material powder in a decomposition furnace;

[0014] The pre-decomposed raw material powder is fed from the kiln head of the cement kiln and enters the kiln for high-temperature sintering. The sintered material enters the grate cooler from the kiln tail for rapid cooling to obtain low-heat cement clinker. The temperature of the sintering section in the cement kiln is controlled to be 1300-1350℃, and the temperature range of the lower transition zone near the kiln tail is 980-1030℃.

[0015] After the formed low-heat cement clinker is cooled, it is put into a ball mill together with gypsum for grinding to obtain low-heat silicate cement.

[0016] Furthermore, a kiln cooling zone is set in the area 0 to 2 meters away from the kiln mouth at the kiln tail, and the temperature of the kiln cooling zone is controlled at 850 to 950°C; the discharge temperature of the raw meal powder in the decomposition furnace is 840 to 860°C.

[0017] Furthermore, during the mixed grinding process of low-heat cement clinker and gypsum, the temperature of the low-heat cement clinker entering the mill is lower than 50°C, and the material stays in the mill for more than 60 minutes.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. In the process of sintering low-heat cement clinker, a trace amount of NaF additive is dispersed in the liquid phase. The NaF dissolved in C2S and C4AF can improve the grindability of C2S and C4AF, thereby improving the grinding efficiency of low-heat cement clinker. Moreover, the NaF dissolved in C2S can also be used as a crystal stabilizer to reduce the transformation of β-type dicalcium silicate to γ-type dicalcium silicate during the cooling process, thereby ensuring the later strength of the low-heat cement.

[0020] 2. When low-heat silicate cement made from low-heat cement clinker is hydrated, a small amount of C4AF will release trace fluoride ions in the early stage of hydration. These trace fluoride ions can inhibit the formation of aluminum colloid and iron colloid in cement slurry due to their strong electronegativity and permeability, especially avoiding the problem of aluminum colloid or iron colloid formed in the early stage of hydration wrapping around C4AF and causing hydration stagnation of C4AF, thereby improving the hydration activity of C4AF; in addition, fluoride ions react with a small amount of aluminum colloid and iron colloid to produce floccules, which can also provide nucleation sites for hydration products, inducing the rapid formation of hydration products and interweaving them into a spatial network structure, thereby effectively improving the early strength of low-heat cement. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the XRD diagram of low heat cement clinker in Example 2;

[0022] Figure 2 This is the SEM image of the hardened cement paste in the cement mortar test block in Example 2. DETAILED DESCRIPTION

[0023] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0024] Embodiment 1:

[0025] A low-heat silicate cement, which is obtained by mixing and grinding low-heat cement clinker and gypsum; the low-heat cement clinker is formed by pre-decomposing raw material powder, sintering it in a cement kiln, mixing it with fly ash and melting it, and then cooling it after it is discharged from the kiln; wherein, by weight, the amount of fly ash is 1 to 6 parts, and the raw material powder includes 70 to 90 parts of limestone, 5 to 20 parts of clay, 1 to 7 parts of iron ore and 0.3 to 0.6 parts of NaF additive; during the sintering process, the temperature of the firing section in the cement kiln is controlled to be 1300 to 1350°C, and the temperature range of the lower transition zone near the kiln tail is 980 to 1030°C.

[0026] In this embodiment, the raw material powder used for sintering low-heat cement clinker includes 70-90 parts of limestone, 5-20 parts of clay, 1-7 parts of iron ore and 0.3-0.6 parts of NaF additive, wherein the limestone mainly provides calcium, the clay mainly provides silicon and aluminum, and the iron ore mainly provides iron. The cement kiln structure has the raw material feeding end as the kiln head and the high-temperature clinker discharging end as the kiln tail. There are also upper transition zones, sintering zones and lower transition zones from the kiln head to the kiln tail. The raw material powder is pre-decomposed in the decomposition furnace, and the limestone is decomposed to generate calcium oxide, which enters the cement kiln from the kiln head for sintering together with other raw materials. During the high-temperature sintering process of the raw materials in the cement kiln, Fe2O3 and Al2O3 are melted at high temperature to produce a liquid phase, and a liquid phase reaction occurs in the sintering zone, which promotes the formation of C3S, C2S, C3A, and C4AF. Since the iron phase is high and the aluminum phase is low in the liquid phase minerals during the sintering process of low-heat cement clinker, the liquid phase appears at a low temperature, which can ensure that the C2S and C4AF contents are high and the C3S and C3A contents are relatively low. In the process of the liquid phase entering the lower transition zone and the kiln tail from the sintering zone, the material gradually cools down, and C3S, C2S, C3A, and C4AF gradually form a stable crystalline phase structure, and a trace amount of sodium fluoride melt is dissolved in each crystalline phase to form a solid solution. On the one hand, NaF dissolved in C2S and C4AF can improve the grindability of C2S and C4AF due to the three-dimensional crystallization effect in the cooling process, which is convenient for improving the grinding efficiency of low-heat cement clinker; and NaF dissolved in C2S can also serve as a crystal stabilizer to reduce the transformation of β-type dicalcium silicate to γ-type dicalcium silicate in the cooling process, thereby ensuring the later strength of low-heat cement. On the other hand, the colloidal structure formed during the hydration of C4AF can be further wrapped around the surface of C2S and C4AF, hindering the further hydration of low-heat cement; and when the low-heat silicate cement made from low-heat cement clinker is hydrated, a small amount of C4AF can release trace fluoride ions after hydration. These trace fluoride ions can break the colloidal structure from the inside of the colloidal structure due to their strong electronegativity and permeability, further inhibiting the formation of aluminum colloids and iron colloids in the cement slurry, especially avoiding the problem of aluminum colloids or iron colloids formed in the early stage of hydration wrapping around C4AF and causing hydration stagnation of C4AF, thereby improving the hydration activity of C4AF; in addition, fluoride ions can also produce floccules after reacting with a small amount of aluminum colloids and iron colloids. These floccules can also provide nucleation sites for hydration products, inducing the rapid formation of hydration products and interweaving them into a spatial network structure, thereby effectively improving the early strength of low-heat cement.

[0027] Example 2

[0028] A method for preparing low-heat silicate cement, the specific preparation process is as follows:

[0029] Step 1: crush limestone, clay and iron ore according to the proportion, grind them in a raw mill, add NaF additive into the raw mill, and mix them evenly to form raw meal powder;

[0030] In this embodiment, since low heat Portland cement has one-way control over the clinker composition, mineral composition and cement performance and quality requirements, in this embodiment, the dicalcium silicate content in the low heat cement clinker should be controlled to be 40-60%, the tricalcium silicate content to be 5-15%, the tricalcium aluminate content to be 1-6%, the tetracalcium aluminoferrite content to be 20-30%, and the NaF is dissolved in the mineral crystal phase in the form of a solid solution, and the content of free calcium oxide is not more than 1.0%. In addition, considering the possible impact of control fluctuations in production on the quality of clinker, the KH value in the three rate values ​​is controlled to be 0.80±0.02, the SM value to be 2.8±0.1, and IM<1.

[0031] The contents of various raw material components in the raw material powder and coal ash in this embodiment are shown in Table 1 below:

[0032] Table 1 Content of each raw material in raw material powder and coal ash

[0033] name Loss on ignition <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> CaO MgO <![CDATA[K2O]]> <![CDATA[Na2O]]> limestone 38.18 10.36 1.78 0.45 46.07 0.69 0.26 0.11 clay 4.86 65.06 14.06 6.56 1.06 2.26 1.40 1.20 Iron Ore 10.09 15.37 2.93 64.90 0.29 1.43 1.98 1.12 Volcanic ash 4.30 66.97 14.87 4.93 2.74 2.43 0.74 0.15 coal ash / 45.09 26.36 8.68 10.33 2.31 1.27 0.42

[0034] Since the content of aluminum oxide in low-heat cement clinker is mainly brought in by clay, the clay ratio is kept constant in the batching control, and the aluminum content is controlled to fluctuate slightly. The three rate values ​​are adjusted to meet the control range requirements by adjusting the ratio of limestone, clay, iron ore, and volcanic ash. In this embodiment, the amount of coal ash is 3 parts by weight, and the raw material powder contains 85 parts of limestone, 12 parts of clay, 3.7 parts of iron ore, 0.3 parts of NaF additive, and 8 parts of volcanic ash.

[0035] Step 2: pre-decomposing the raw material powder in a decomposition furnace;

[0036] In this embodiment, the discharge temperature of the raw meal powder in the decomposition furnace is 840-860°C.

[0037] Step 3: Feed the pre-decomposed raw material powder from the kiln head of the cement kiln and enter the kiln for high-temperature sintering. The sintered material enters the grate cooler from the kiln tail for rapid cooling to obtain low-heat cement clinker;

[0038] Among them, the temperature of the firing section in the cement kiln is controlled to be 1300-1350℃;

[0039] Since the iron phase is high and the aluminum phase is low in the liquid phase mineral of low-heat silicate cement, the liquid phase viscosity is low and the clinker granulation strength is low, in this embodiment, a kiln cooling zone is set in the area 0 to 2 meters away from the kiln mouth at the kiln tail, and the temperature of the kiln cooling zone is controlled at 850 to 950° C. to ensure that the low-heat cement clinker is cooled to a certain temperature in the kiln and has sufficient granulation strength, and avoids the formation of flying sand after entering the grate cooler;

[0040] To ensure that the NaF melt can stably crystallize in the liquid phase, the temperature range of the lower transition zone at the kiln tail in this embodiment is 980-1030°C. The XRD pattern of the low-heat cement clinker obtained in this embodiment is as follows: Figure 1 As shown, the main minerals are C2S, C4AF, and a small amount of C3S and C3A.

[0041] Step 4: After the formed low-heat cement clinker is cooled, it is put into a ball mill together with gypsum for grinding to obtain low-heat silicate cement; in this embodiment, the amount of low-heat cement clinker is 85 parts, and the gypsum is natural gypsum, and the amount is 15 parts; and no grinding aid needs to be added separately during the grinding process to achieve a better grinding efficiency; during grinding, the low-heat cement clinker inlet temperature is lower than 50°C, and the material stays in the mill for more than 60 minutes.

[0042] Comparative test:

[0043] According to the test in GB / T26567-2011 cement raw material grindability test method (Bond method), grinding tests were carried out respectively, and the grinding work index of the test group and the control group were calculated; wherein the test group was a mixture of low-heat cement clinker and natural gypsum prepared according to the clinker and gypsum ratio of this embodiment, and the grinding work index of the mixture was obtained by analysis; the raw material components and amounts of the raw material powder and fly ash used in the control group were the same, but no NaF additive was added;

[0044] According to GB / T17671-2021 cement mortar strength test method (ISO), the cement obtained by grinding the control group and the test group was mixed with water and standard sand to prepare 40×40×160mm cement mortar specimens, and the compressive strength values ​​of cement mortar specimens of different ages were tested.

[0045] The two groups of test data are shown in Table 2:

[0046] Table 2 Cement performance data of the test group and the control group

[0047]

[0048] The above data show that the grindability of low-heat cement clinker added with NaF additive is significantly higher than that of cement clinker without NaF. This is because after the NaF dissolved in C2S and C4AF crystallizes, lattice defects are formed between the crystal phase interfaces, thereby improving the grindability of C2S and C4AF. Since the colloidal structure formed during the hydration of C4AF can further wrap around the surface of C2S and C4AF, it hinders the further hydration of low-heat cement; and when the low-heat silicate cement made from low-heat cement clinker is hydrated, a small amount of C4AF can release trace fluoride ions after hydration. These trace fluoride ions can react with positively charged aluminum colloids and iron colloids to form precipitates due to their strong electronegativity and permeability. In the early stage of hydration, the aluminum colloid or iron colloid wrapped around C4AF is removed, avoiding the problem of C4AF hydration stagnation caused by colloid coating in the early stage of hydration, thereby improving the hydration activity of C4AF and effectively improving the early strength of low-heat cement. In addition, the late strength of the experimental group is also significantly higher than that of the control group. This is because NaF dissolved in C2S can be used as a crystal stabilizer to reduce the transformation of β-type dicalcium silicate to γ-type dicalcium silicate during the cooling process, thereby ensuring the development of the late strength of low-heat cement. In addition, if Figure 2 As shown in the figure, there are certain flocs in the hardened cement paste, and there are flake hydration products around the flocs. This is because fluoride ions can also produce flocs after reacting with a small amount of aluminum colloid and iron colloid. These flocs can also provide nucleation sites for hydration products, inducing the rapid formation of hydration products and interweaving them into a spatial network structure. Therefore, this is also the reason why the early strength of the low-heat cement mortar test block in the control group of this embodiment can be further improved.

[0049] The above is an embodiment of the present invention. The above embodiments and the specific parameters in the embodiments are only for the purpose of clearly describing the invention verification process, and are not intended to limit the patent protection scope of the present invention. The patent protection scope of the present invention is still subject to its claims. Any equivalent structural changes made by using the contents of the description and drawings of the present invention should be included in the protection scope of the present invention.

Claims

1. A low heat silicate cement, characterized in that: The low heat Portland cement is obtained by mixing and grinding low heat cement clinker and gypsum; the low heat cement clinker is obtained by pre-decomposing raw material powder, sintering in a cement kiln, mixing with fly ash and melting, and cooling after being discharged from the kiln; wherein, by weight, the amount of fly ash is 3 parts, and the raw material powder contains 85 parts of limestone, 12 parts of clay, 3.7 parts of iron ore, 0.3 parts of NaF additive, and 8 parts of volcanic ash; during the sintering process, the temperature of the firing section in the cement kiln is controlled to be 1300-1350°C, and the temperature range of the lower transition zone near the kiln tail is 980-1030°C; the NaF is dissolved in the mineral crystal phase of the low heat cement clinker in the form of a solid solution, and the NaF dissolved in C2S serves as a crystal stabilizer to reduce the transformation of β-type dicalcium silicate to γ-type dicalcium silicate during the cooling process.

2. The low heat silicate cement according to claim 1, characterized in that: The low-heat cement clinker has a dicalcium silicate content of 40-60%, a tricalcium silicate content of 5-15%, a tricalcium aluminate content of 1-6%, and a tetracalcium aluminoferrite content of 20-30%.

3. The low heat silicate cement according to claim 1, characterized in that: In parts by weight, in the low-heat Portland cement, the low-heat cement clinker is used in an amount of 80 to 90 parts, and the gypsum is used in an amount of 10 to 20 parts.

4. The low heat silicate cement according to claim 1, characterized in that: In terms of mass percentage, the limestone comprises 8-14% SiO2, 1-3% Al2O3, 0.1-0.6% Fe2O3, 35-48% CaO, 0.3-1.8% MgO, 0.1-0.4% K2O, and 0.05-0.3% Na2O; the clay comprises 55-68% SiO2, 11-17% Al2O3, and 2-8% Fe2O3. 0.5-2.0% CaO, 1.4-2.8% MgO, 0.9-2.0% K2O, 0.5-1.5% Na2O; the iron ore comprises 10-17% SiO2, 2-6% Al2O3, 62-69% Fe2O3, 0.1-0.6% CaO, 0.6-2.2% MgO, 0.5-2.0% K2O, 0.5-1.3% Na2O.

5. The low heat silicate cement according to claim 1, characterized in that: The volcanic ash includes 60-70% SiO2, 10-16% Al2O3, 2-5% Fe2O3, 0.5-3.5% CaO, 0.7-2.8% MgO, 0.5-1.0% K2O, and 0.5-1% Na2O.

6. A method for preparing low heat Portland cement, the method being used for preparing the low heat Portland cement according to any one of claims 1 to 5, characterized in that: include: After crushing limestone, clay and iron ore according to the proportion, they are ground in a raw mill, and NaF additive is added to the raw mill to mix them evenly to form raw meal powder; Pre-decomposing the raw material powder in a decomposition furnace; The pre-decomposed raw material powder is fed from the kiln head of the cement kiln and enters the kiln for high-temperature sintering. The sintered material enters the grate cooler from the kiln tail for rapid cooling to obtain low-heat cement clinker. The temperature of the sintering section in the cement kiln is controlled to be 1300-1350℃, and the temperature range of the lower transition zone near the kiln tail is 980-1030℃. After the formed low-heat cement clinker is cooled, it is put into a ball mill together with gypsum for grinding to obtain low-heat silicate cement.

7. The method for preparing low heat Portland cement according to claim 6, characterized in that: The kiln tail is set in the area 0-2 meters away from the kiln mouth as a kiln cooling zone, and the temperature of the kiln cooling zone is controlled at 850-950°C; the discharge temperature of the raw meal powder in the decomposition furnace is 840-860°C.

8. The method for preparing low heat Portland cement according to claim 6, characterized in that: During the mixed grinding process of low-heat cement clinker and gypsum, the temperature of low-heat cement clinker entering the mill is lower than 50°C, and the material stays in the mill for more than 60 minutes.

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