A carbonated hardened low-calcium cement and methods of making and hardening the same

Abstract

The present application aims at the problems of excessive consumption of traditional cement limestone resources, excessive energy consumption and high carbon emission, and provides a carbonated hardened low-calcium cement and a preparation and hardening method thereof, which is a hardening method for curing low-calcium cement by CO2 carbonation. The mass percentage composition of cement raw material components is: limestone: 60-70%, sandstone or clay or silica ash: 15-25%, phosphogypsum, fluorogypsum or desulfurization gypsum: 5-25%, component A: 0.5-2%. Component A is composed of the following raw material components in mass percentage: fluorite 0-50%, barium slag: 0-50%, lithium slag 0-50%, wood ash 0-50%, industrial sodium carbonate 0-30%. The composition design of carbonated hardened cement clinker minerals is C2S: 10-90%, C5S2$: 10-90%, C$: 0-5%, C4A3$: 0-10%, etc. In the present application, the limestone required for the cement clinker is lower than that of ordinary Portland cement clinker, the calcination temperature is reduced by 200-350 DEG C than that of ordinary Portland cement clinker, and the energy consumption and carbon emission are significantly lower than those of Portland cement; the low-calcium cement is hardened by CO2 carbonation curing, which can make the cement obtain excellent mechanical properties within 2 hours.

Description

Technical Field

[0001] This invention belongs to the field of building materials and relates to a low-calcium cement cured by CO2 carbonation and its preparation and hardening method. Background Technology

[0002] The cement industry is a resource- and energy-intensive industry, and also a high-carbon emission industry. The energy consumption of the cement industry mainly comes from the calcination energy consumption in the clinker calcination process, including the following two aspects: (1) The decomposition process of carbonates in raw materials. In the calcination process of cement clinker, it is necessary to calcine at a high temperature of 500-900℃ to gradually decompose CaCO3 in the raw materials into CaO. About 50% of the theoretical heat consumption of calcination comes from the high-temperature decomposition of calcium carbonate. (2) The high-temperature calcination process of clinker minerals. The main mineral components of traditional silicate cement clinker are tricalcium silicate (C3S, about 55-65%), dicalcium silicate (C2S, about 20-30%), tricalcium aluminate (C3A, about 7-15%), and tetracalcium aluminoferrite (C4AF, about 10-18%). In order to obtain excellent mechanical strength and early activity, a large amount of C3S exists in the clinker minerals, and a large amount of limestone resources are required for calcination of this mineral. To ensure the formation of a high proportion of C3S high-calcium mineral phase in clinker, the clinker firing temperature typically needs to reach around 1450℃. Therefore, the design of the high-calcium mineral (C3S) component in cement clinker is the fundamental reason for the high energy consumption and carbon emissions during the formation of traditional silicate cement clinker.

[0003] The cement industry is facing immense pressure to reduce carbon emissions and urgently needs breakthroughs in key low-carbon and zero-carbon technologies. This invention proposes a low-calcium cement clinker mineral system that utilizes CO2 carbonation curing for rapid hardening and provides its hardening method. The limestone content of the cement clinker in this invention is lower than that of ordinary silicate cement clinker, which can consume industrial waste such as phosphogypsum. The calcination temperature is 200-350℃ lower than that of ordinary silicate cement clinker, resulting in significantly lower energy consumption and carbon emissions compared to traditional silicate cement. The low-calcium cement of this invention, hardened by CO2 carbonation curing, can achieve excellent mechanical properties within 2 hours. The CO2 absorption during the cement hardening process of this invention enables CO2 recycling, which is of great significance for energy conservation and carbon reduction in the cement industry. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of excessive limestone resource consumption, excessive energy consumption, and serious carbon emissions in the existing cement technology. It proposes a low-calcium cement mineral composition and preparation method that is cured by CO2 carbonation, and provides a method for curing low-calcium cement by CO2 carbonation.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A carbonation-hardened low-calcium cement, wherein the carbonation-hardened low-calcium cement is cement clinker mineral prepared from a variety of raw materials.

[0007] The raw materials include the following components: limestone: 60%–70%, sandstone or clay or silica fume: 15%–25%, phosphogypsum, fluorogypsum or desulfurized gypsum: 5%–25%, component A: 0.5%–2%, and the sum of the mass percentages of the above components is 100%.

[0008] Furthermore, the mineralized component A is composed of the following raw material components by mass percentage: fluorite 0-50%, barium slag 0-50%, lithium slag 0-50%, wood ash 0-50%, and industrial sodium carbonate 0-30%. The sum of the mass percentages of the above components is 100%.

[0009] Furthermore, the limestone contains 48-56% CaO. The sandstone, clay, or silica fume contains 70-99.9 wt.% SiO2.

[0010] The cement clinker minerals mentioned above include the following components: C2S (including β-C2S, α' ... L -C2S (one or more combinations of amorphous C2S): 10-90%, calcium sulfosilicate (abbreviated as: C5S2$): 10-90%, C$: 0-5%, C4A3$: 0-10%, the remainder being miscellaneous. Preferably, C2S: 10%-50%, C5S2$: 60-90%, C$: 0-2%. The sum of the mass percentages of the above components is 100%.

[0011] A method for preparing the above-mentioned carbonation-hardened low-calcium cement includes the following steps:

[0012] (1) Raw material batching calculation and preparation

[0013] Calculate the amount of raw materials needed based on the chemical composition of each raw material and the mineral composition of the target cement clinker.

[0014] (2) Raw material grinding and premixing homogenization

[0015] Limestone, sandstone, silica fume, clay, phosphogypsum, fluorogypsum, or desulfurized gypsum, along with component A, are dried and then mixed, crushed, and ground according to their mass fraction ratios. After pre-homogenization, qualified raw materials are obtained.

[0016] (3) Calcination of clinker:

[0017] Raw materials are calcined in a kiln at a controlled temperature of 1100–1250℃ for 1–5 hours, followed by rapid or natural cooling to produce low-calcium cement clinker.

[0018] (4) After calcining the cement clinker obtained in step (3), quickly cool or naturally cool it to room temperature, and then grind it to obtain low-calcium cement.

[0019] Furthermore, in step (1), the fineness of the raw material is controlled by passing it through a 0.08mm square hole sieve.

[0020] Furthermore, in step (4), the low-calcium cement clinker is ground to a Blaine specific surface area of ​​300–400 m². 2 / kg.

[0021] A method for hardening the aforementioned carbonation-hardened low-calcium cement includes the following steps:

[0022] (1) Add water to low-calcium cement and mix evenly to obtain a mixture.

[0023] (2) Press the mixture obtained in step (1) into a shape to obtain a test block.

[0024] (3) Harden the test block in an environment containing CO2 gas to obtain a hardened test block.

[0025] Furthermore, in step (1), the mass ratio of water to low-calcium cement is 0.1 to 0.3:1, preferably 0.15 to 0.2:1.

[0026] Furthermore, in step (2), the initial porosity of the pressed and molded specimen before hardening is controlled to be between 5% and 35%, preferably between 15% and 25%. Initial porosity refers to the ratio of the gas phase volume (excluding the volume of low-calcium cement and water) to the specimen volume after pressing and molding. Control methods include, but are not limited to, pressure control during pressing and controlling the mass of the mixture within a fixed pressing volume space.

[0027] Furthermore, in step (3), the hardening time is 0.5 to 24 hours, preferably 1 to 3 hours. The hardening environment conditions include, but are not limited to, pure CO2 gas, CO2-containing industrial waste gas, etc., with a gas pressure of 0.05 MPa to 0.5 MPa, preferably 0.1 to 0.3 MPa.

[0028] Another feature of this invention is that, in the preparation process of the low-calcium cement, the CO2-containing gas generated during the calcination of the low-calcium cement raw materials can be used in the hardening process to achieve CO2 recycling.

[0029] The beneficial effects of this invention are as follows:

[0030] (1) Compared with traditional silicate cement clinker, the calcination temperature is 200-350℃ lower. Low-temperature calcination will reduce energy consumption and CO2 emissions.

[0031] (2) Compared with traditional silicate cement clinker, less limestone is used, thereby reducing energy consumption for carbonate decomposition and reducing CO2 emissions.

[0032] (3) It can consume industrial waste such as phosphogypsum and fluorogypsum, reducing environmental pressure.

[0033] (4) Low-calcium cement hardens quickly and can achieve excellent mechanical properties within 2 hours.

[0034] (5) The hardening process absorbs CO2, which further reduces CO2 emissions and realizes CO2 recycling. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail through the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0036] For the raw materials and their chemical composition in the following examples, please refer to Table 1:

[0037] Table 1 Chemical composition of raw materials

[0038]

[0039] Example 1

[0040] The above eight raw materials were dried at 105℃ for 24 hours, then crushed and ground to pass through a 0.08mm square-hole sieve. The following components were then weighed according to their weight percentages: limestone 69.6%, sandstone 23.2%, phosphogypsum 5.5%, and component A 1.7%, wherein component A is composed of: fluorite 20%, wood ash 15%, lithium slag 10%, barium slag 25%, and sodium carbonate 30%. The weighed raw materials were placed in a planetary ball mill and thoroughly mixed to obtain a uniformly mixed powdery raw meal.

[0041] Add 8% water by mass to powdered cement raw meal, mix well, and press into round discs with a diameter of about 50 mm and a thickness of about 5 mm using a tablet press. After drying, place the raw meal discs into a high-temperature kiln and heat to 900℃ at a rate of 5℃ / min, hold for 0.5 h, and then raise the calcination temperature to 1100℃ and hold for 5 h. After calcination, remove the low-calcium cement clinker and allow it to cool naturally to room temperature. Grind the low-calcium cement clinker to a Blaine specific surface area of ​​376 m² / g. 2 / kg yields low-calcium cement.

[0042] Water at a mass ratio of 0.2% was added to the prepared low-calcium cement, and the mixture was stirred until homogeneous to obtain a paste. A specimen with an initial porosity of 10% was obtained by controlling the mass of the paste within a fixed compression space of 2cm × 2cm × 2cm. This specimen was placed in a reactor filled with 99.9% CO2 gas, and the gas pressure was adjusted to 0.3 MPa. The carbonation reaction times were 2 hours and 24 hours, respectively.

[0043] Example 2

[0044] The above eight raw materials were dried at 105℃ for 24 hours, then crushed and ground to pass through a 0.08mm square-hole sieve. The following components were then weighed according to their weight percentages: limestone 67.9%, sandstone 20.7%, phosphogypsum 10.6%, and component A 0.8%, where component A is composed of: fluorite 20%, wood ash 10%, lithium slag 15%, barium slag 50%, and sodium carbonate 5%. The weighed raw materials were placed in a planetary ball mill and thoroughly mixed to obtain a uniformly mixed powdery raw meal.

[0045] Add 8% water by mass to powdered cement raw meal, mix well, and press into round discs with a diameter of about 50 mm and a thickness of about 5 mm using a tablet press. After drying, place the raw meal discs into a high-temperature kiln and heat to 900℃ at a rate of 5℃ / min, hold for 0.5 h, and then raise the calcination temperature to 1250℃ and hold for 1 h. After calcination, remove the low-calcium cement clinker and cool it rapidly to room temperature using a fan. Grind the low-calcium cement clinker to a Blaine specific surface area of ​​391 m². 2 / kg yields low-calcium cement.

[0046] Water at a mass ratio of 0.2 was added to the prepared low-calcium cement, and the mixture was stirred until homogeneous to obtain a paste. A specimen with an initial porosity of 10% was obtained by controlling the mass of the paste within a fixed compression space of 2cm × 2cm × 2cm. This specimen was placed in a reactor filled with 99.9% CO2 gas, and the gas pressure was adjusted to 0.2 MPa. The carbonation reaction times were 2 hours and 24 hours, respectively.

[0047] Example 3

[0048] The above eight raw materials were dried at 105℃ for 24 hours, then crushed and ground to pass through a 0.08mm square-hole sieve. The following components were then weighed according to their weight percentages: limestone 62.0%, sandstone 19.6%, phosphogypsum 17.8%, and component A 0.6%, where component A is composed of: fluorite 35%, wood ash 15%, lithium slag 15%, barium slag 25%, and sodium carbonate 10%. The weighed raw materials were placed in a planetary ball mill and thoroughly mixed to obtain a uniformly mixed powdery raw meal.

[0049] Add 8% water by mass to powdered cement raw meal, stir well, and press into round discs with a diameter of about 50 mm and a thickness of about 5 mm using a tablet press. After drying, place the raw meal discs into a high-temperature kiln and heat to 900℃ at a rate of 5℃ / min, hold at that temperature for 0.5 h, and then raise the calcination temperature to 1170℃ and hold for 2.5 h. After calcination, remove the low-calcium cement clinker and allow it to cool naturally to room temperature. Grind the low-calcium cement clinker to a Blaine specific surface area of ​​388 m² / g. 2 / kg yields low-calcium cement.

[0050] Water at a mass ratio of 0.2 was added to the prepared low-calcium cement, and the mixture was stirred until homogeneous to obtain a paste. A specimen with an initial porosity of 10% was obtained by controlling the mass of the paste within a fixed compression space of 2cm × 2cm × 2cm. This specimen was placed in a reactor filled with 99.9% CO2 gas, and the gas pressure was adjusted to 0.2 MPa. The carbonation reaction times were 2 hours and 24 hours, respectively.

[0051] Example 4

[0052] The above eight raw materials were dried at 105℃ for 24 hours, then crushed and ground to pass through a 0.08mm square-hole sieve. The following components were then weighed according to their weight percentages: limestone 61.1%, sandstone 18.5%, phosphogypsum 19.4%, and component A 1%, wherein component A is composed of: fluorite 35%, wood ash 15%, lithium slag 15%, barium slag 10%, and sodium carbonate 25%. The weighed raw materials were placed in a planetary ball mill and thoroughly mixed to obtain a uniformly mixed powdery raw meal.

[0053] Add 8% water by mass to powdered cement raw meal, mix well, and press into round discs with a diameter of about 50 mm and a thickness of about 5 mm using a tablet press. After drying, place the raw meal discs into a high-temperature kiln and heat to 900℃ at a rate of 5℃ / min, hold for 0.5 h, and then raise the calcination temperature to 1150℃ and hold for 3 h. After calcination, remove the low-calcium cement clinker and cool it rapidly to room temperature using a fan. Grind the low-calcium cement clinker to a Blaine specific surface area of ​​398 m² / g. 2 / kg yields low-calcium cement.

[0054] Water at a mass ratio of 0.2 was added to the prepared low-calcium cement, and the mixture was stirred until homogeneous to obtain a paste. A specimen with an initial porosity of 10% was obtained by controlling the mass of the paste within a fixed compression space of 2cm × 2cm × 2cm. This specimen was placed in a reactor filled with 99.9% CO2 gas, and the gas pressure was adjusted to 0.5 MPa. The carbonation reaction times were 2 hours and 24 hours, respectively.

[0055] Example 5

[0056] Example 5 uses the same low-calcium cement as Example 4. The molding method is as follows:

[0057] Water at a mass ratio of 0.3 was added to the prepared low-calcium cement, and the mixture was stirred until homogeneous to obtain a paste. A specimen with an initial porosity of 5% was obtained by controlling the mass of the paste within a fixed compression space of 2cm × 2cm × 2cm. This specimen was placed in a reactor filled with 99.9% CO2 gas, and the gas pressure was adjusted to 0.5 MPa. The carbonation reaction times were 2 hours and 24 hours, respectively.

[0058] Example 6

[0059] Example 6 uses the same low-calcium cement as Example 4. The molding method is as follows:

[0060] Water at a mass ratio of 0.1 was added to the prepared low-calcium cement, and the mixture was stirred until homogeneous to obtain a paste. A specimen with an initial porosity of 20% was obtained by controlling the mass of the paste within a fixed compression space of 2cm × 2cm × 2cm. This specimen was placed in a reactor filled with 99.9% CO2 gas, and the gas pressure was adjusted to 0.05 MPa. The carbonation reaction times were 2 hours and 24 hours, respectively.

[0061] Example 7

[0062] Example 7 uses the same low-calcium cement as Example 4. The molding method is as follows:

[0063] Water at a mass ratio of 0.15 was added to the prepared low-calcium cement, and the mixture was stirred until homogeneous to obtain a paste. A specimen with an initial porosity of 15% was obtained by controlling the mass of the paste within a fixed compression space of 2cm × 2cm × 2cm. This specimen was placed in a reactor filled with 99.9% CO2 gas, and the gas pressure was adjusted to 0.05 MPa. The carbonation reaction times were 0.5 h and 24 h, respectively.

[0064] Example 8

[0065] Example 8 uses the same low-calcium cement as Example 4. The molding method is as follows:

[0066] Water at a mass ratio of 0.15 was added to the prepared low-calcium cement, and the mixture was stirred until homogeneous to obtain a paste. A specimen with an initial porosity of 10% was obtained by controlling the mass of the paste within a fixed compression space of 2cm × 2cm × 2cm. This specimen was placed in a reactor filled with 99.9% CO2 gas, and the gas pressure was adjusted to 0.5 MPa. The carbonation reaction times were 0.5 h and 2 h, respectively.

[0067] Example 9

[0068] Example 9 uses the same low-calcium cement as Example 4. The molding method is as follows:

[0069] Water at a mass ratio of 0.15 was added to the prepared low-calcium cement, and the mixture was stirred until homogeneous to obtain a paste. A specimen with an initial porosity of 15% was obtained by controlling the mass of the paste within a fixed compression space of 2cm × 2cm × 2cm. This specimen was placed in a reactor filled with industrial waste gas containing approximately 30% CO2, and the gas pressure was adjusted to 0.5 MPa. The carbonation reaction times were 2 hours and 24 hours, respectively.

[0070] The specific surface area of ​​the cement prepared in Examples 1 to 9 was tested according to the "Brainwood Method for Determination of Specific Surface Area of ​​Cement GB / T8074-2008" using a cement Brainwood specific surface area meter. Compressive strength was tested according to national standards. Carbon sequestration of the cement specimens was calculated using TG testing of CO2 loss on ignition. The mineral composition of the low-calcium cement clinker was analyzed and calculated using XRD full-spectrum fitting quantitative analysis technology. Specific results are shown in Table 2.

[0071] Table 2 Mineral composition, compressive strength, and carbon sequestration of low-calcium cement

[0072]

[0073] As can be seen from the above embodiments and the test results in Table 2, the firing temperature of the low-calcium cement clinker of the present invention is 200-350°C lower than that of traditional silicate cementitious materials; thanks to the advantages of C5S2S and C2S minerals, less limestone is used; it can consume industrial waste such as phosphogypsum; it can achieve hardening through industrial waste gas containing CO2, and can obtain excellent mechanical properties in a short time (less than 2 hours); the low-calcium cement clinker can be naturally cooled. Based on the above advantages, the CO2 emissions during the production process of the low-calcium cement product of the present invention are significantly reduced compared with traditional silicate cement.

[0074] The above-described embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A low-calcium cement that hardens through carbonation, characterized in that, The carbonation-hardened low-calcium cement is cement clinker mineral prepared from a variety of raw materials; The raw materials include the following components: limestone: 60%~70%, sandstone or clay or silica fume: 15%~25%, phosphogypsum, fluorogypsum or desulfurized gypsum: 5%~25%, mineralized component A: 0.5%~2%, and the sum of the mass percentages of the above components is 100%. The mineralized component A is composed of the following raw material components by mass percentage: fluorite 0-50%, barium slag 0-50%, lithium slag 0-50%, wood ash 0-50%, and industrial sodium carbonate 0-30%; the sum of the mass percentages of the above components is 100%. The limestone contains 48-56% CaO; the sandstone, clay, or silica fume contains 70-99.9 wt.% SiO2. The composition of the cement clinker minerals is designed as follows: C2S: 10%~50%, C5S2 60-90%, C : 0~2%; the sum of the mass percentages of the above components is 100%.

2. The low-calcium cement with carbonation hardening according to claim 1, characterized in that, The C2S mentioned is β-C2S, α' L -C2S, one or more combinations of amorphous C2S.

3. A method for preparing carbonation-hardened low-calcium cement according to any one of claims 1-2, characterized in that, Includes the following steps: (1) Raw material batching calculation and preparation Calculate the amount of raw materials used based on the chemical composition of each raw material and the mineral composition of the target cement clinker; (2) Raw material grinding and premixing homogenization Limestone, sandstone, silica fume, clay, phosphogypsum, fluorogypsum, or desulfurized gypsum, and mineral component A are dried and then mixed, crushed, and ground according to the mass fraction ratio. After pre-homogenization, qualified raw materials are obtained. (3) Calcination of clinker: Raw materials are calcined in a kiln, with the calcination temperature controlled at 1100~1250℃ and the holding time at 1~5 hours. The materials are then rapidly cooled or naturally cooled to obtain low-calcium cement clinker. (4) After calcining the cement clinker obtained in step (3), quickly cool or naturally cool it to room temperature, and then grind it to obtain low-calcium cement; In the preparation process of the aforementioned low-calcium cement, the CO2-containing gas generated during the calcination of the low-calcium cement raw materials can be used in the hardening process to achieve CO2 recycling.

4. The method for preparing carbonation-hardened low-calcium cement according to claim 3, characterized in that, In step (1), the fineness of the raw material is controlled by passing it through a 0.08mm square-hole sieve; in step (4), the low-calcium cement clinker is ground to a Blaine specific surface area of ​​300~400m². 2 / kg.

5. A method for hardening low-calcium cement by carbonation hardening as described in any one of claims 1-2, characterized in that, Includes the following steps: (1) Add water to low-calcium cement and mix evenly to obtain a mixture; the mass ratio of water to low-calcium cement is 0.1~0.3:1; (2) Press the mixture obtained in step (1) into a test block; control the initial porosity of the pressed test block before hardening to be between 5% and 35%; (3) Harden the test block in an environment containing CO2 gas for 0.5~24h to obtain a hardened test block; wherein the gas pressure of the hardening environment is 0.05MPa~0.5MPa.

6. The method for hardening low-calcium cement by carbonation hardening according to claim 5, characterized in that: In step (1), the mass ratio of water to low-calcium cement is 0.15~0.2:1; In step (2), the initial porosity of the pressed and molded test block before hardening is controlled to be between 15% and 25%. In step (3), the hardening time is 1 to 3 hours and the gas pressure in the hardening environment is 0.1 MPa to 0.3 MPa.

7. The method for hardening low-calcium cement by carbonation hardening according to claim 6, characterized in that, In step (3), the hardening environmental conditions include: pure CO2 gas and industrial waste gas containing CO2.

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