A solid waste-based high-activity carbon-fixing low-calcium gelling material and its preparation method

Abstract

The invention discloses a solid waste-based high-activity carbon-fixing low-calcium cementitious material and a preparation method thereof. The cementitious material uses 69-85 parts of calcareous waste slag, 7-26 parts of siliceous waste slag and 5-10 parts of iron ore as raw materials. The main mineral phases of the cementitious material are 30-55% of γ-C2S, 30-50% of β-C2S, 20-10% of C3S and 5-10% of f-CaO. The cementitious material is fired at a heating rate of 5-20°C / min within a temperature range of 1100-1250°C, and then cooled, crushed and ball-milled to obtain the solid waste-based high-activity carbon-fixing low-calcium cementitious material. The low-calcium cementitious material prepared by the present invention has excellent properties such as high activity, easy grinding, early strength and high strength. At the same time, it greatly reduces the material production cost, calcination energy consumption and grinding power consumption, realizes the recycling of various industrial solid wastes, and solves the problem of slow later strength development due to excessively fast early carbonization rate of cementitious materials. It is of great significance to the industrial production of carbonization-hardening cementitious materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and in particular relates to a solid waste-based high-activity carbon-fixing low-calcium cementitious material and a preparation method thereof. Background Art

[0002] The high carbon emissions of the cement industry mainly come from the production process of cement: (1) the high temperature formation of clinker mineral C3S; (2) the thermal decomposition of carbonates in raw materials, of which the heat consumption of CaCO3 decomposition accounts for about 46% of the theoretical heat consumption of clinker. Therefore, the fundamental reason for the high energy consumption of cement clinker burning lies in the composition design of high calcium minerals (C3S). The high calcium minerals in the clinker easily cause the calcination temperature to be too high (1450℃), and a large amount of high-quality limestone and coal power resources are consumed, CO2, NO X and SO3 emissions. Therefore, designing a clinker composition based primarily on low-calcium minerals, based on cement production processes, can help alleviate the cement industry's energy (coal) and resource (limestone) consumption and environmental impact (CO2). However, low-calcium calcium silicate minerals have low hydration activity, and conventional standard curing methods cannot provide sufficient mechanical properties. Therefore, effectively stimulating the reactivity of low-calcium calcium silicate minerals has become a major technical challenge.

[0003] In calcium silicate systems, C3S, C2S, C3S2, and CS all exhibit high carbonization reactivity. This is particularly true for the low-hydration-activity minerals β-C2S, γ-C2S, C3S2, and CS. These minerals, while adhering to low-calcium design principles, can be activated through carbonization, resulting in excellent performance and providing new insights into the development of novel low-calcium cementitious materials. Currently, the sintering of these cementitious materials relies primarily on analytically pure chemical reagents and industrial-grade raw materials, resulting in high preparation costs and impracticality for industrial production. Furthermore, the rapid early strength development of these cementitious materials hinders the steady increase in later strength, limiting their application and development.

[0004] Patent CN 105347706 A discloses a method for preparing a self-pulverizing low-calcium cement and its preforms. The cement is composed primarily of 30-45% C3S2, 45-65% α-CS, and 5-10% f-CaO. Patent CN 111393051 A invents a grinding-free, carbonization-hardening cement clinker and its preparation method. The cement clinker incorporates the limiting component f-CaO into its mineral composition, achieving self-pulverization of the clinker through cooling and expansion. Patent CN 111393050A discloses a method for preparing a γ-C2S-based cementitious material. The cementitious material is composed primarily of γ-C2S and contains small amounts of β-C2S and C3S2. While these methods reduce carbon emissions and grinding power consumption during cement production to a certain extent, they still use natural raw materials such as limestone, sandstone, and iron ore, resulting in high preparation costs and impracticality for large-scale industrial production. Patent CN 111393049 A discloses a method for activating and modifying γ-C2S. By doping it with a mixture of metal ions, the specific surface area of ​​the γ-C2S is increased, thereby enhancing its carbonization reactivity. However, this modification method is complex and costly. Furthermore, while activation modification improves the early carbonization strength of the cementitious material, it has little effect on its later strength and is prone to unstable later strength development. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the present invention aims to provide a solid waste-based high-activity carbon-fixing low-calcium cementitious material and a preparation method thereof, breaking through the traditional silicate cement mineral composition, and using industrial solid waste to synthesize a clinker system with low-calcium carbon-fixing minerals γ-C2S, β-C2S and C3S2 as the main mineral components, solving the problems of high preparation cost, high calcination energy consumption, and slow later strength development of existing carbonization-hardening cementitious materials. At the same time, it realizes the recycling of various industrial solid wastes and absorbs and seals CO2, with significant economic and environmental benefits.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A solid waste-based high-activity carbon-fixing low-calcium cementitious material, expressed in parts by weight, wherein the main mineral phases include: γ-C2S: 30-55 parts, β-C2S: 30-50 parts, C3S2: 0-10 parts, and f-CaO: 5-10 parts.

[0008] A method for preparing a solid waste-based high-activity carbon-fixing low-calcium gelling material comprises the following steps:

[0009] Step 1) using a traditional "two grinding and one calcining" calcination process, according to a designed calcium-silicon ratio of 1.7-4.0, 69-85 parts of calcareous waste slag, 7-26 parts of siliceous waste slag and 5-10 parts of iron ore are crushed, ball-milled, batched and homogenized to obtain a raw material for preparing a cementitious material;

[0010] Step 2) Add 10%-15% deionized water or anhydrous ethanol to the above raw materials, stir evenly and press into shape under a pressure of 5-30 MPa, place in an oven at 60-105°C for 6-24 hours to constant weight, pre-sinter and calcine in a muffle furnace, cool, and ball mill at a speed of 450 r / min for 10-30 minutes until less than 10% of the residue passes through an 80 μm square hole sieve to obtain a solid waste-based high-activity carbon-fixing low-calcium cementitious material.

[0011] Step 3) The solid waste-based high-activity carbon-fixing low-calcium cementitious material obtained in step 2) is also added with 10%-15% deionized water or anhydrous ethanol, stirred evenly, and then continuously pressed for 15-20 seconds in a 20mm*20mm*20mm steel mold at a molding pressure of 5-30MPa. After curing in a carbonization reactor for 8-24 hours, it is placed in a standard curing room with a temperature of 20±5°C and a humidity of ≥90% for standard curing to the specified age.

[0012] According to the above scheme, the calcareous waste residue in step 1) includes one or more of fly ash from municipal solid waste incineration, steel slag, waste concrete, and carbide slag, and its CaO content is ≥45%.

[0013] According to the above scheme, the siliceous waste slag in step 1) includes one or more of furnace slag, mineral slag, and calcium-silicon slag, and its SiO2 content is ≥60%.

[0014] According to the above scheme, the crushed particle size in step 1) is 3-6 mm.

[0015] According to the above scheme, the grinding process in step 1) is: ball milling at a speed of 500 r / min for 15-45 min, and the fineness is less than 10% of the residue on the 80 μm square hole sieve.

[0016] According to the above scheme, the pre-sintering process in step 2) is: heating to 800-950°C at a heating rate of 5°C / min and keeping warm for 1-2 hours.

[0017] According to the above scheme, in step 2), the calcination process is as follows: the temperature is raised to 1100° C.-1250° C. at a rate of 5-20° C. / min and kept at that temperature for 1-3 hours.

[0018] According to the above scheme, the cooling rate in step 2) is: rapid cooling at a rate of 150-180°C / min for 1-2 hours, and then natural cooling (~20°C / min) to room temperature.

[0019] According to the above scheme, the carbonization curing system in the carbonization reactor in step 3) is: CO2 pressure 0.1-0.5MPa, concentration 10%-99%, temperature 20℃-60℃.

[0020] Compared with the prior art, the solid waste-based high-activity carbon-fixing low-calcium cementitious material and its preparation method described in the present invention have the following advantages:

[0021] (1) The cementitious material of the present invention uses industrial solid waste as raw material and has a low calcination temperature (1100-1250°C). Compared with ordinary Portland cement, it can save 60%-100% of natural resources such as limestone and clay, reduce coal consumption by 15%-30%, and reduce carbon emissions by more than 30%.

[0022] (2) The cementitious material of the present invention is mainly composed of β-C2S, γ-C2S, C3S2 and f-CaO. During the cooling process, f-CaO absorbs moisture and expands. The local expansion stress generated inside the clinker makes its structure loose, and the power consumption of grinding is reduced by more than 30% compared with ordinary Portland cement.

[0023] (3) The cementitious material of the present invention is mainly carbonized for curing in the early stage. Each ton of cementitious material can seal 250-300 kg of CO2, and the content of alkaline substances such as f-MgO and f-CaO is not strictly controlled.

[0024] (4) The cementitious material of the present invention contains 30%-50% β-C2S (with hydration activity). The continuous hydration of this mineral can steadily improve the later strength of cement, thereby improving the density and strength of the carbonization-hardened cementitious material from the source. Compared with methods such as significantly increasing the CO2 pressure and adding metal ion compounds, the cost is low and the process is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 (a) XRD diffraction pattern of solid waste-based high-activity carbon-fixing and low-calcium sintered clinker at Ca / Si=3.0

[0026] Figure 1 (b) XRD diffraction pattern of solid waste-based high-activity carbon-fixing and low-calcium sintered clinker at Ca / Si=3.6 DETAILED DESCRIPTION

[0027] In order to better understand the present invention, the present invention is further described below with reference to specific examples. Obviously, the described embodiments are only preferred embodiments of the present invention and are not intended to limit the present invention.

[0028] Example 1

[0029] A solid waste-based high-activity carbon-fixing low-calcium gelling material and a preparation method thereof, comprising the following steps:

[0030] Step 1. According to the calcium-silicon design ratio of 3.0, 81 parts of ground calcareous waste slag-municipal domestic waste incineration fly ash (MSWIFA), 19 parts of siliceous waste slag-incineration furnace slag (BA) and 5 parts of iron ore are mixed in a ball mill at a speed of 500r / min for 15min, 10% deionized water is added, and the test blocks are pressed into 20mm*20mm*20mm cubic test blocks at a molding pressure of 10MPa. The test blocks are dried in an 80℃ drying oven for 8h to constant weight, and then pre-burned in a muffle furnace at 950℃ for 30min at a heating rate of 10℃ / min, and then continued to rise to 1150℃ and calcined for 60min at the same heating rate. The test blocks are first rapidly cooled at 150℃ / min for 30min, then naturally cooled (~20℃ / min), and ball-milled at 450r / min for 10min to obtain a solid waste-based high-activity carbon-fixing low-calcium cementitious material.

[0031] Step 2: Take 90 parts of the gelling material prepared in step 1, add 10 parts of deionized water, stir evenly, press into 20mm*20mm*20mm cubic test blocks with a pressure of 10MPa, put into a carbonization reactor (CO2 pressure 0.5MPa, CO2 concentration 20%, temperature 25°C) and cure for 24 hours, then place in a curing room with a temperature of 20±5°C and a humidity ≥90% for standard curing to the specified age.

[0032] The solid waste-based high-activity carbon-fixing low-calcium cementitious material in this embodiment was subjected to X-ray diffraction testing and carbonization curing to obtain a carbonized product. The mechanical properties of the carbonized product were tested in accordance with JGJ / T70-2009 "Standard for Test Methods for Basic Properties of Building Mortar", and the degree of carbonization of the product was evaluated using the calcium carbonate loss on ignition method.

[0033] After testing, the sintered clinker contains 37% β-C2S, 48% γ-C2S, 10% C3S2 and 5% f-CaO (see Figure 1 (a)), the compressive strength after carbonization for 24 hours is 46.3 MPa, the degree of carbonization is 36.1%, and the compressive strength after 28 days is 71.4 MPa.

[0034] The principle of the present invention is:

[0035] Starting from the breakthrough of traditional silicate mineral composition design, γ-C2S and C3S2, two hydrated inert low-calcium minerals, are used as the main components. Taking advantage of their high carbonization activity, carbonization curing is carried out to obtain excellent early mechanical strength. The specific reaction process is shown in formula (1) and formula (2):

[0036] γ-C2S+(2-x)CO2+yH2O→(2-x)CaCO3+C x SH y (Formula 1)

[0037] C3S2+(3-x)CO2+yH2O→(3-x)CaCO3+C x S2H y (Formula 2)

[0038] However, due to the rapid development of early carbonization strength, the dense protective layer makes the material's later strength development unstable. Therefore, the hydrated mineral β-C2S is also a design focus. Continuous hydration is used to stably provide the material's later strength, thereby improving the density and strength of the carbonization-hardened cementitious material from the source. Compared with methods such as significantly increasing CO2 pressure and adding metal ion compounds, this method is less costly and simpler to process. Because early carbonization curing is less affected by the content of alkaline substances, the present invention attempts to design f-CaO as an expansive component. f-CaO reacts with water (in a humid environment) to form Ca(OH)2, which expands in volume by approximately 1.3 times. The local expansion stress formed within the hardened material makes its structure loose and easy to grind.

[0039] Example 2

[0040] A method for preparing a solid waste-based high-activity carbon-fixing low-calcium gelling material comprises the following steps:

[0041] Step 1. According to the calcium-silicon design ratio of 3.6, 84 parts of ground calcareous waste slag-MSWIFA, 16 parts of siliceous waste slag-BA and 5 parts of iron ore are mixed in a ball mill at a speed of 500r / s for 15min, 10% deionized water is added, and the test blocks are pressed into 20mm*20mm*20mm cubic test blocks at a molding pressure of 15MPa. The test blocks are placed in a 105℃ drying oven and dried for 6h to constant weight. The test blocks are placed in a muffle furnace at 950℃ for pre-burning for 30min at a heating rate of 5℃ / min, and then the temperature is continued to rise to 1150℃ and calcined for 60min at the same heating rate. The test blocks are first rapidly cooled at 180℃ / min for 15min, and then naturally cooled (~20℃ / min) to room temperature. The test blocks are ball-milled at 500r / min for 10min to obtain a solid waste-based high-activity carbon-fixing low-calcium cementitious material.

[0042] Step 2: Take 90 parts of the gelling material prepared in step 1, add 10 parts of deionized water, stir evenly, and press into a 20mm*20mm*20mm cubic test block at a pressure of 10MPa. Place it in a carbonization reactor (CO2 pressure 0.5MPa, CO2 concentration 99%, temperature 25°C) and cure for 24 hours. Then, place it in a curing room with a temperature of 20±5°C and a humidity ≥90% for standard curing to the specified age.

[0043] The solid waste-based high-activity carbon-fixing low-calcium cementitious material in this embodiment was subjected to X-ray diffraction testing and carbonization curing to obtain a carbonized product. The mechanical properties of the carbonized product were tested in accordance with JGJ / T70-2009 "Standard for Test Methods for Basic Properties of Building Mortar", and the degree of carbonization of the product was evaluated using the calcium carbonate loss on ignition method.

[0044] After testing, the sintered clinker contains 43% β-C2S, 41% γ-C2S, 8% C3S2 and 8% f-CaO (see Figure 1 (b)), the compressive strength after carbonization for 24 hours is 43.7 MPa, the degree of carbonization is 32.2%, and the compressive strength after 28 days is 76.9 MPa.

Claims

1. A method for preparing a solid waste-based high-activity carbon-fixing low-calcium cementitious material, characterized in that: The following steps are involved: Step 1) Using a conventional "two-grinding-one-calcining" calcination process, according to a designed calcium-silicon ratio of 1.7-4.0, 69-85 parts of calcareous waste slag, 7-26 parts of siliceous waste slag, and 5-10 parts of iron ore are crushed, ball-milled, batched, and homogenized to obtain a raw material for preparing a cementitious material; Step 2) Add 10%-15% deionized water or anhydrous ethanol to the above raw materials, stir evenly, press into shape under a pressure of 5-30 MPa, bake in an oven at 60-105°C for 6-24 hours to constant weight, pre-sinter in a muffle furnace, calcine, and cool; the pre-sintering process is: heating to 800-950°C at a rate of 5°C / min, and keeping warm for 1-2 hours; the calcining process is: heating to 1100-1250°C at a rate of 5-20°C / min, and keeping warm for 1-3 hours; the cooling process is: heating to 15 Rapid cooling at a cooling rate of 0-180°C / min for 1-2 hours, and then cooling to room temperature at a cooling rate of 20°C / min; finally, ball milling at a rotation speed of 450 r / min for 10-30 minutes until less than 10% of the residue passes through an 80 μm square hole sieve, to obtain a solid waste-based high-activity carbon-fixing low-calcium cementitious material, wherein the main mineral phases thereof include, by weight, 30-55 parts of γ-C2S, 30-50 parts of β-C2S, 0-10 parts of C3S2, and 5-10 parts of f-CaO; Step 3) The solid waste-based high-activity carbon-fixing low-calcium cementitious material obtained in step 2) is also added with 10%-15% deionized water or anhydrous ethanol, stirred evenly, and then continuously pressed for 15-20 seconds in a 20mm*20mm*20mm steel mold at a molding pressure of 5-30MPa. After curing in a carbonization reactor for 8-24 hours, it is placed in a standard curing room with a temperature of 20±5°C and a humidity of ≥90% for standard curing to the specified age.

2. The method for preparing a solid waste-based high-activity carbon-fixing low-calcium cementitious material according to claim 1, characterized in that: The calcareous waste residue in step 1) includes one or more of fly ash from municipal solid waste incineration, steel slag, waste concrete, and carbide slag, and its CaO content is ≥45%.

3. The method for preparing a solid waste-based high-activity carbon-fixing low-calcium cementitious material according to claim 1, characterized in that: The siliceous waste slag in step 1) includes one or more of furnace slag, mineral slag, and calcium-silicon slag, and the SiO2 content thereof is ≥60%.

4. The method for preparing a solid waste-based high-activity carbon-fixing low-calcium cementitious material according to claim 1, characterized in that: The crushed particle size in step 1) is 3-6 mm.

5. The method for preparing a solid waste-based high-activity carbon-fixing low-calcium cementitious material according to claim 1, characterized in that: The ball milling process in step 1) is as follows: ball milling at a rotation speed of 500 r / min for 15-45 min, and the fineness is less than 10% of the residue on the 80 μm square hole sieve.

6. The method for preparing a solid waste-based high-activity carbon-fixing low-calcium cementitious material according to claim 1, characterized in that: The carbonization curing system in the carbonization reactor in step 3) is as follows: CO2 pressure 0.1-0.5 MPa, concentration 10%-99%, temperature 20-60°C.

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