Low-carbon high-anti-cracking cementitious material for mass concrete and preparation method thereof

Abstract

The present application relates to the technical field of building materials, and particularly relates to a low-carbon high-anti-cracking cementitious material for mass concrete and a preparation method thereof, wherein the cementitious material comprises, by weight, 81-85 parts of a cementitious component, 3.2-3.8 parts of an activator, 5.5-5.8 parts of a shrinkage compensation component and 4-5.3 parts of a performance adjusting component. The present application uses a large amount of fly ash, slag powder and steel slag powder, which are industrial solid wastes, so that the amount of cement clinker is reduced to less than 30%, and compared with the traditional cementitious material, the carbon emission is reduced by more than 50%, and a large amount of industrial waste is absorbed, which meets the development direction of green building materials.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a low-carbon, high-crack-resistant cementitious material for large-volume concrete and its preparation method. Background Technology

[0002] Mass concrete refers to concrete structures with large dimensions that require technical measures to control temperature stress and cracking caused by heat of hydration. During the hardening process, this type of concrete generates a large amount of heat of hydration, causing a rapid rise in internal temperature. Subsequently, during the cooling phase, due to the temperature difference between the inside and outside and shrinkage, temperature cracks and shrinkage cracks are easily generated, severely affecting the integrity and durability of the structure.

[0003] Currently, the following methods are commonly used in engineering to control temperature cracks in large-volume concrete: Using low-heat cement: The heat of hydration is relatively low, but the early strength development is slow and the cost is high; Pre-cooled aggregate: complex process, high energy consumption; Laying cooling water pipes: increases construction costs and difficulty; Adding mineral admixtures, such as fly ash and mineral powder, can reduce the heat of hydration, but excessive amounts can affect early strength.

[0004] However, these traditional methods have significant shortcomings. On the one hand, they often fail to fundamentally solve the problem of heat accumulation in hydration; on the other hand, in pursuing low heat of hydration, the mechanical properties and durability of concrete may be sacrificed. Furthermore, the cement production process is a major source of carbon emissions, with the global cement industry contributing approximately 8 parts of CO2 emissions, which contradicts the global promotion of "green building" and "carbon neutrality" policies.

[0005] In recent years, researchers have attempted to develop new cementitious materials using industrial solid waste, but some limitations still exist: First, the amount of solid waste added is limited, and the carbon emission reduction effect is not significant; second, the mechanism of synergistic effect of multiple solid wastes is unclear, and improper proportions can easily lead to performance degradation; third, there is a lack of systematic optimization for the crack resistance of large-volume concrete. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned shortcomings and provide a low-carbon, high-crack-resistant cementitious material for mass concrete and its preparation method, which can make large-volume use of industrial solid waste, significantly reduce heat of hydration and carbon emissions, while ensuring mechanical properties and crack resistance.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a low-carbon, high-crack-resistant cementitious material for mass concrete, comprising, by weight: 81-85 parts cementitious component, 3.2-3.8 parts activator, 5.5-5.8 parts shrinkage compensation component and 4-5.3 parts performance regulating component.

[0008] Furthermore, the cementitious component comprises 18-25 parts cement clinker, 28-35 parts fly ash, 20-22 parts slag powder, and 8-12 parts steel slag powder.

[0009] Furthermore, the cement clinker is silicate cement with a specific surface area of ​​350-450 m² / kg.

[0010] Furthermore, the activator comprises 1.2-1.8 parts sodium silicate, 0.8-1.2 parts sodium sulfate, and 0.8-1.2 parts calcium nitrate.

[0011] Furthermore, the shrinkage compensation component comprises 3-4 parts magnesium oxide expanding agent and 1.8-2.5 parts hemihydrate gypsum.

[0012] Furthermore, the performance regulating components include 2-3 parts silica fume, 0.7-1 parts of nanocrystalline nucleus early strength agent, and 1.2-1.3 parts of polylactic acid water-reducing agent.

[0013] Furthermore, the nanocrystalline nucleus early strength agent comprises calcium salt and composite silicon salt in a molar ratio of 1:1, with a particle size ≤100nm and a specific surface area ≥50m² / kg.

[0014] The preparation method of low-carbon, high-crack-resistant cementitious materials for mass concrete includes the following steps: S1. Prepare raw materials: Prepare gelling components, activators, shrinkage compensation components and performance conditioning components according to the proportions; S2. Preliminary mixing: Add fly ash, slag powder, and steel slag powder to a high-efficiency mixer in proportion and mix until the materials are uniform; S3. Add activator: After pre-mixing sodium silicate, sodium sulfate and calcium nitrate evenly, add them to the material that has been mixed evenly in S2, and continue mixing; S4. Mixing all components: Continue to add cement clinker, magnesium oxide expansion agent, hemihydrate gypsum, silica fume, nanocrystalline nucleus early strength agent and polycarboxylate superplasticizer to S3, and mix for 10-15 minutes until all components are mixed evenly.

[0015] Furthermore, prior to step S1, the raw materials undergo pretreatment, including the following steps: (1) Fly ash air separation: using air separation technology to separate ultrafine particles from fly ash raw materials, wherein the fineness of the ultrafine particles is ≤20μm; (2) Grinding of solid waste powder: The slag powder and steel slag powder are respectively fed into a fluidized bed air jet mill for grinding. The specific surface area of ​​the slag powder is ≥400m² / kg and the specific surface area of ​​the steel slag powder is ≥450m² / kg. (3) Drying of gypsum: Drying and dehydrating dihydrate gypsum at 150-180℃ to produce hemihydrate gypsum with a dehydration rate of 60-80%.

[0016] Furthermore, in S3, the activator is added to the uniformly mixed material in S2 using a solution spray.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention reduces the amount of cement clinker to below 30% by using large amounts of industrial solid waste such as fly ash, slag powder, and steel slag powder. Compared with traditional cementitious materials, carbon emissions are reduced by more than 50%, while a large amount of industrial waste is disposed of, which is in line with the development direction of green building materials. 2. This invention utilizes the low heat of hydration of fly ash and slag powder to reduce the temperature rise of large-volume concrete from the source. At the same time, through the synergistic expansion effect of magnesium oxide expansion agent and steel slag powder, it compensates for the shrinkage during the temperature drop stage of concrete, thus significantly improving crack resistance. 3. This invention overcomes the defect of low early strength in high-content solid waste cementitious materials by optimizing the component ratio and adding chemical activators, and the strength continues to increase in the later stage, with the 90-day strength being 10-20% higher than that of traditional cement concrete; 4. By rationally grading polycarboxylate superplasticizers and various micro powders, the rheological properties of cementitious materials are improved, the viscosity is reduced, and the pouring uniformity and compactness of large-volume concrete are enhanced. Attached Figure Description

[0018] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is the data on the development of hydration heat in various cementitious material systems of this invention.

[0019] Figure 2 This data represents the development of compressive strength in various cementitious material systems of this invention.

[0020] Figure 3 The data on the adiabatic temperature rise of the concrete prepared according to this invention and that of conventional methods are presented. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Please see Figure 1-3 .

[0023] Example 1: The low-carbon, high-crack-resistant cementitious material for mass concrete comprises, by weight: 82 parts cementitious component, 3.5 parts activator, 5.5 parts shrinkage compensation component, and 4 parts performance modifier component; The cementitious components include 20 parts cement clinker, 30 parts fly ash, 22 parts slag powder, and 10 parts steel slag powder; The activator comprises 1.5 parts sodium silicate, 1 part sodium sulfate, and 1 part calcium nitrate; The shrinkage compensation component comprises 3.5 parts magnesium oxide expanding agent and 2 parts hemihydrate gypsum; The performance-adjusting components include 2 parts silica fume, 0.8 parts of nanocrystalline nucleus early strength agent, and 1.2 parts of crack-resistant polylactic acid water-reducing agent.

[0024] The preparation method of low-carbon, high-crack-resistant cementitious materials for mass concrete includes the following steps: The pretreatment of raw materials includes the following steps: (1) Fly ash air separation: using air separation technology to separate ultrafine particles from fly ash raw materials, wherein the fineness of the ultrafine particles is ≤20μm; (2) Grinding of solid waste powder: The slag powder and steel slag powder are respectively fed into a fluidized bed air jet mill for grinding. The specific surface area of ​​the slag powder is 420 m² / kg and the specific surface area of ​​the steel slag powder is 480 m² / kg. (3) Gypsum drying: Dihydrate gypsum is dried and dehydrated at 165℃ to produce hemihydrate gypsum with a dehydration rate of 70%; S1. Prepare raw materials: Prepare gelling components, activators, shrinkage compensation components and performance conditioning components according to the proportions; S2. Preliminary mixing: Add fly ash, slag powder, and steel slag powder to a high-efficiency mixer in proportion and mix until the materials are uniform; S3. Add activator: After pre-mixing sodium silicate, sodium sulfate and calcium nitrate evenly, add the activator to the material that has been mixed evenly in S2 using a solution spray, and continue mixing; S4. Mixing all components: Continue to add cement clinker, magnesium oxide expansion agent, hemihydrate gypsum, silica fume, nanocrystalline nucleation early strength agent and polycarboxylate superplasticizer to S3. Mix for 15 minutes until all components are evenly mixed. After sampling and testing, package to obtain a low-carbon, high-crack-resistant cementitious material for mass concrete.

[0025] Example 2: The low-carbon, high-crack-resistant cementitious material for mass concrete comprises, by weight: 85 parts cementitious component, 3.8 parts activator, 5.8 parts shrinkage compensation component, and 4.4 parts performance modifier component; The cementitious components include 18 parts cement clinker, 35 parts fly ash, 20 parts slag powder, and 12 parts steel slag powder. The activator comprises 1.8 parts sodium silicate, 0.8 parts sodium sulfate, and 1.2 parts calcium nitrate; The shrinkage compensation component comprises 4 parts magnesium oxide expanding agent and 1.8 parts hemihydrate gypsum; The performance-adjusting components include 2.5 parts silica fume, 0.7 parts powdered nanocrystalline nuclei early strength agent, and 1.2 parts crack-resistant polylactic acid water-reducing agent.

[0026] The preparation method differs from Example 1 only in that the slag powder is ground to a specific surface area of ​​450 m² / kg and the steel slag powder is ground to a specific surface area of ​​500 m² / kg.

[0027] Example 3: The low-carbon, high-crack-resistant cementitious material for mass concrete comprises, by weight: 81 parts cementitious component, 3.2 parts activator, 5.5 parts shrinkage compensation component and 5.3 parts performance modifier component; The cementitious components include 25 parts cement clinker, 28 parts fly ash, 20 parts slag powder, and 8 parts steel slag powder. The activator comprises 1.2 parts sodium silicate, 1.2 parts sodium sulfate, and 0.8 parts calcium nitrate; The shrinkage compensation component comprises 3 parts magnesium oxide expanding agent and 2.5 parts hemihydrate gypsum; The performance-adjusting components include 3 parts silica fume, 1 part nanocrystalline nucleus early strength agent, and 1.3 parts crack-resistant polylactic acid water-reducing agent.

[0028] The preparation method is the same as in Example 1.

[0029] Comparative Example 1: In this comparative example, fly ash was added only to the cement clinker at a mass ratio of 30%.

[0030] Performance tests were conducted on Examples 1-3, Comparative Example 1, and conventional ordinary Portland cement (PO 42.5). The test items and results are shown in Table 1 below. Figure 1-2 : Table 1 Physical and mechanical properties of various cementitious materials

[0031] Table 2. Hydration heat development data for various cementitious material systems (J / g)

[0032] Figure 3 Compressive strength development data (MPa) of various cementitious material systems

[0033] Based on the above test results: 1. Specific surface area: According to the data in Table 1, the specific surface area of ​​Examples 1-3 is 475-510 m² / kg, which is much higher than that of traditional cement (350 m² / kg) and Comparative Example 1 (380 m² / kg). This indicates that the cementitious material powder prepared in this application has finer particles and a better proportion of active components, which can improve the contact area of ​​the cementitious material hydration reaction and lay a structural foundation for the continuous growth of strength and full reaction of components in the later stage. 2. Standard consistency water consumption: The water consumption of Examples 1-3 is 25.8-27.2%, which is lower than that of traditional cement (27%) and Comparative Example 1 (28.3%). This indicates that the cementitious material slurry prepared in this application is superior, requires less water for mixing, and can effectively reduce the free water content in the system, thereby reducing the porosity in the later stage and improving the density of the hardened body. 3. Setting time: Traditional cement sets and sets the fastest, and early hardening can easily lead to rushed construction and early cracking risks. The setting time of Comparative Example 1 is significantly longer, which will greatly prolong the construction and maintenance cycle and reduce the efficiency of project construction. In this application, the setting time of Examples 1-3 is moderate and controllable, which not only avoids the construction defects caused by the rapid setting of traditional cement, but also solves the problem of slow setting of a single modified system (Comparative Example 1), thus meeting the rhythm of conventional civil construction. 4. Compressive strength: Early strength (3 days, 7 days). Traditional cement has the highest early strength. The early strength of the example is slightly lower than that of traditional cement, but far better than that of Comparative Example 1, which meets the requirements for early demolding and load-bearing foundation use in engineering. Mid-term strength (28 days): Example 3 has a compressive strength of 52.6 MPa, which significantly exceeds that of traditional cement (48.9 MPa). Example 1 is basically the same as traditional cement, and Example 2 is close to traditional cement. The mid-term mechanical properties fully meet the standards and have advantages. In terms of late-stage and long-term strength (45-180 days), the strength of traditional cement almost stagnates after 90 days, with a very low growth rate; while the strength of the embodiment in this application continues to grow steadily, with a strength of 55.2~60.3 MPa at 90 days and a maximum of 62.0 MPa at 180 days, which is much higher than that of traditional cement and Comparative Example 1. 5. Heat of hydration: Data from all ages (1 day to 28 days) show that traditional cement has the highest heat of hydration at each stage, with intense hydration reactions and a large amount of heat released in the early stages. This can easily lead to thermal stress in large-volume components, inducing temperature cracks. The heat of hydration in Comparative Example 1 is reduced, but the reduction is limited. The heat of hydration in Examples 1 to 3 of this application is significantly reduced at each age. The heat of hydration at 1 day is only 115 to 135 J / g, which is much lower than the 210 J / g of traditional cement. The heat of hydration at 3 days, 7 days, and 28 days is also significantly better than that in Comparative Example 1. 6. Drying shrinkage performance: Traditional cement has a shrinkage value as high as 425×10 -6 Comparative Example 1 is 385 × 10 -6 The embodiment is only 275×10 -6 -295×10 -6 The shrinkage rate is significantly reduced. The lower drying shrinkage can effectively inhibit the drying shrinkage deformation of cementitious materials in the later stage of hardening, reduce the drying shrinkage cracks, deformation and hollowing problems of walls, floors and structures, and significantly improve the durability and appearance integrity of building materials.

[0034] Mass concrete was prepared using the cementitious material prepared in Example 1 and compared with conventional cement concrete of the same strength grade. The results are shown in the table below. Figure 3 As shown: Table 4 Comparison of performance of mass concrete

[0035] Table 5 Adiabatic temperature rise data

[0036] Based on the above data: 1. Flowability: The concrete of this invention has a slump of 210mm and a spread of 550mm, which are 2.4% and 5.8% higher than traditional concrete, respectively. The mixture has better flowability, filling properties and workability, and is more adaptable to pumping construction. It can meet the pouring construction needs of large-volume, large-span complex structures and reduce construction resistance. 2. Setting performance: The initial setting time and final setting time are extended by 21.4% and 19.0% respectively, effectively slowing down the hydration reaction rate. Large-volume concrete involves large single-pour volumes and poor heat dissipation; a longer setting time avoids concentrated hardening in a short period, facilitating layered and segmented construction and reducing the formation of cold joints. 3. Compressive strength: Early strength: 3d compressive strength is 22.5MPa, which is 16.0% lower than that of traditional concrete. This is a normal phenomenon caused by the low hydration activity and slow hydration reaction of cementitious materials, which is consistent with the characteristics of extended setting time and less heat release in early hydration. Medium- to long-term strength: 28-day compressive strength increased by 4.5%, and 90-day strength increased significantly by 18.5%, demonstrating the advantages of continuous hydration and steady strength growth in the later stages. Large-volume structures are mostly long-term projects, and excellent later-stage strength development can significantly improve the structure's long-term load-bearing capacity and safety reserve. 4. Heat of hydration: The large-volume concrete prepared in this application has an overall adiabatic temperature rise peak of 42.5℃, which is 27.0% lower than that of traditional concrete. The hydration temperature rise of the concrete of this invention is much lower than that of traditional concrete throughout all curing ages, with a temperature rise difference of up to 16.7℃ per day. The concentrated heat release during hydration in the early stage is effectively suppressed. The temperature rise tends to be gradual in the later stage, and the final temperature rise difference after 28 days is still 5.1℃. The core cause of cracking in large-volume concrete is the concentrated release of hydration heat, which leads to excessive internal and external temperature difference and excessive temperature stress. Low hydration temperature rise can reduce the temperature gradient and temperature shrinkage stress from the root cause. 5. Crack resistance: The cracking index of the concrete of this invention is only 0.32%, which is 62.4% lower than that of traditional concrete. Combined with the low temperature rise characteristics, it fully proves that the cementitious material system of this invention can effectively inhibit the generation of temperature cracks and shrinkage cracks, perfectly solve the industry pain point of easy cracking of large-volume concrete, and improve the overall structure and appearance quality. 6. Durability: The chloride ion diffusion coefficient decreased by 45.9%, indicating that the internal structure of concrete is denser, the porosity is lower, and the resistance to the penetration of harmful ions is greatly improved. In coastal, saline-alkali, and corrosive environments, it can effectively delay the corrosion of steel bars and the deterioration of the matrix, and significantly extend the service life of large-volume hydraulic, underground, and municipal structures. 7. Environmental performance: The concrete of this invention emits only 218 kg CO2 / m³ of carbon per unit, which is 43.4% less than that of traditional concrete. This significantly reduces cement usage and the consumption of high-carbon-emission clinker, aligning with the construction industry's policies on low-carbon emission reduction and green building materials development, and combining engineering and ecological benefits.

[0037] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A low-carbon, high-crack-resistant cementitious material for mass concrete, characterized in that, By weight, it includes: 81-85 parts gelling component, 3.2-3.8 parts activator, 5.5-5.8 parts shrinkage compensation component and 4-5.3 parts performance conditioning component.

2. The low-carbon, high-crack-resistant cementitious material for mass concrete according to claim 1, characterized in that, The cementitious components include 18-25 parts cement clinker, 28-35 parts fly ash, 20-22 parts slag powder, and 8-12 parts steel slag powder.

3. The low-carbon, high-crack-resistant cementitious material for mass concrete according to claim 2, characterized in that, The cement clinker is silicate cement with a specific surface area of ​​350-450 m² / kg.

4. The low-carbon, high-crack-resistant cementitious material for mass concrete according to claim 1, characterized in that, The activator comprises 1.2-1.8 parts sodium silicate, 0.8-1.2 parts sodium sulfate, and 0.8-1.2 parts calcium nitrate.

5. The low-carbon, high-crack-resistant cementitious material for mass concrete according to claim 1, characterized in that, The shrinkage compensation component comprises 3-4 parts magnesium oxide expanding agent and 1.8-2.5 parts hemihydrate gypsum.

6. The low-carbon, high-crack-resistant cementitious material for mass concrete according to claim 1, characterized in that, The performance-adjusting components include 2-3 parts silica fume, 0.7-1 parts of nanocrystalline nucleus early strength agent, and 1.2-1.3 parts of polylactic acid water-reducing agent.

7. The low-carbon, high-crack-resistant cementitious material for mass concrete according to claim 6, characterized in that, The nanocrystalline nucleus early strength agent has a particle size ≤100nm and a specific surface area ≥50m² / kg.

8. The method for preparing a low-carbon, high-crack-resistant cementitious material for mass concrete according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Prepare raw materials: Prepare gelling components, activators, shrinkage compensation components and performance conditioning components according to the proportions; S2. Preliminary mixing: Add fly ash, slag powder, and steel slag powder to a high-efficiency mixer in proportion and mix until the materials are uniform; S3. Add activator: After pre-mixing sodium silicate, sodium sulfate and calcium nitrate evenly, add them to the material that has been mixed evenly in S2, and continue mixing; S4. Mixing all components: Continue to add cement clinker, magnesium oxide expansion agent, hemihydrate gypsum, silica fume, nanocrystalline nucleus early strength agent and polycarboxylate superplasticizer to S3, and mix for 10-15 minutes until all components are mixed evenly.

9. The method for preparing low-carbon, high-crack-resistant cementitious material for mass concrete according to claim 8, characterized in that, Prior to step S1, the raw materials undergo pretreatment, including the following steps: (1) Fly ash air separation: using air separation technology to separate ultrafine particles from fly ash raw materials, wherein the fineness of the ultrafine particles is ≤20μm; (2) Grinding of solid waste powder: The slag powder and steel slag powder are respectively fed into a fluidized bed air jet mill for grinding. The specific surface area of ​​the slag powder is ≥400m² / kg and the specific surface area of ​​the steel slag powder is ≥450m² / kg. (3) Drying of gypsum: Drying and dehydrating dihydrate gypsum at 150-180℃ to produce hemihydrate gypsum with a dehydration rate of 60-80%.

10. The method for preparing low-carbon, high-crack-resistant cementitious material for mass concrete according to claim 8, characterized in that, In step S3, the activator is added to the material that was mixed evenly in step S2 using a solution spray.

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