Self-curing low-carbon concrete for flues and chimneys and construction method of self-curing low-carbon concrete

Abstract

The invention relates to self-curing low-carbon concrete for flues and chimneys and a construction method of the self-curing low-carbon concrete for flues and chimneys, and the concrete comprises the following components in parts by mass: 270-290 parts of low-calcium clinker; 10 to 15 parts of lithium slag; 70 to 90 parts of mineral powder; 30 to 40 parts of monopotassium phosphate; 10 to 15 parts of active magnesium oxide; 10 to 15 parts of barium carbonate; 7-8 parts of a polycarboxylic acid water reducer; 0.5 to 1 part of boric acid and 0.5 to 1 part of a silane-based water repellent; 1.5 to 2.5 parts of polypropylene fiber; 120 to 130 parts of water; 800 to 900 parts of coarse aggregate; and 650 to 750 parts of fine aggregate. According to the invention, hydration of the low-calcium clinker can be effectively activated, and the early strength of concrete is improved; flue gas pollutants are cured in multiple modes such as active magnesium oxide and barium carbonate two-stage sulfur locking, and the concrete has the advantages of being fast in early strength development, excellent in sulfate corrosion resistance, low in carbon, environmentally friendly, high in pollutant curing capacity and the like.

Description

Technical Field

[0001] This invention relates to the field of concrete, specifically to a self-curing low-carbon concrete for flues and chimneys and its construction method. Background Technology

[0002] The lining structure of industrial chimneys (especially flue gas emission systems from coal-fired, oil-fired, or biomass boilers) is exposed to harsh service environments for extended periods. The concrete materials must not only withstand temperature fluctuations of 80-150°C, but also resist sulfur dioxide (SO2) and nitrogen oxides (NOx) in the flue gas, in addition to carbon dioxide. x The chimney is susceptible to corrosion from acidic gases such as SO2. However, traditionally widely used ordinary silicate cement-based concrete suffers from significant durability defects. During its hydration process, it generates a large amount of calcium hydroxide [Ca(OH)2], which readily reacts with penetrating acidic gases such as SO2 to produce expansive sulfate products (such as ettringite and gypsum). Furthermore, acidic substances in flue gas can corrode other components of the concrete. This continuous sulfate and acidic corrosion leads to internal volume expansion of the concrete, ultimately causing cracking, spalling, and even structural failure, seriously threatening the safe operation and service life of the chimney.

[0003] To address these issues, existing technologies typically employ two main strategies: one is to increase the density and alkali reserve of the matrix by increasing cement usage or using higher-grade cement or higher-strength concrete; the other is to coat the concrete surface with acid-resistant and corrosion-resistant coatings (such as resin, glass flake mortar, etc.) to form a physical barrier, or to crystallize on the concrete surface to form a chemical barrier. However, both approaches have significant drawbacks: increasing cement usage or raising the concrete strength grade not only significantly increases material costs but also directly leads to an increase in the carbon footprint of concrete products, contradicting environmental carbon reduction goals; simultaneously, coating with corrosion-resistant layers adds extra complexity to construction, material costs, and maintenance burdens, and the coating itself is also at risk of aging and failure. Furthermore, it is noteworthy that the flue gas emitted from chimneys is itself polluting, and the waste heat and abundant CO2 gas it carries are not effectively recovered and utilized, which not only causes air pollution but also signifies a waste of energy and carbon resources.

[0004] In recent years, low-calcium silicate cement-based cementitious materials have attracted attention as a potential solution. These materials significantly reduce the amount of Ca(OH)2 generated during hydration by optimizing mineral composition (e.g., increasing belite (β-C2S) content and decreasing allite (C2S) content) and sintering specific carbonation-active mineral phases (e.g., CS / C3S2), fundamentally reducing the risk of sulfur dioxide erosion and expansion. More innovatively, these materials are suitable for carbon dioxide (CO2) curing. During carbonation curing, residual Ca(OH)2 and some other calcium components react with CO2 to form stable calcium carbonate (CaCO3), while this process also promotes the hydration reaction of the slowly hydrating β-C2S. This dual-action mechanism effectively improves the density and overall performance of concrete and has a carbon fixation effect. Its carbon emissions over its entire life cycle are significantly lower than those of ordinary silicate cement concrete, demonstrating significant environmental advantages.

[0005] However, the widespread application of this technology is still limited by key bottlenecks. In engineering scenarios such as chimneys requiring rapid turnover or early load bearing, the slow strength development of traditional low-calcium cement-based materials severely restricts their practical engineering application potential. Furthermore, chimney environments often contain significant amounts of acidic gases and high temperatures. Therefore, there is an urgent need to develop new technologies or material modification methods that can effectively improve the early hydration activity and strength development rate of low-calcium cement-based materials to overcome existing obstacles and fully leverage their advantages in the construction of high-temperature resistant, corrosion-resistant, and low-carbon chimneys. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a self-curing low-carbon concrete for flues and chimneys and its construction method, thereby solving the technical problem of slow early strength growth of low-calcium cement-based materials used in chimneys in the prior art.

[0007] To achieve the above-mentioned technical objectives, the technical solution provided by this invention is as follows: In a first aspect, the present invention provides a self-curing low-carbon concrete for flue gas ducts and chimneys, comprising the following components by weight: low-calcium clinker: 270-290 parts; lithium slag: 10-15 parts; mineral powder: 70-90 parts; potassium dihydrogen phosphate: 30-40 parts; active magnesium oxide: 10-15 parts; barium carbonate: 10-15 parts; polycarboxylate superplasticizer: 7-8 parts; boric acid: 0.5-1 part; silane-based water-repellent agent: 0.5-1 part; polypropylene fiber: 1.5-2.5 parts; water: 120-130 parts; coarse aggregate: 800-900 parts; fine aggregate: 650-750 parts.

[0008] Secondly, the present invention provides a construction method for self-curing low-carbon concrete for flue and chimney, comprising the following steps: S1, mixing the components of low-carbon concrete in proportion to obtain concrete; S2, spraying concrete on the base surface, and curing flue exhaust gas after the concrete has set.

[0009] Compared with the prior art, the beneficial effects of the present invention include: This invention utilizes potassium dihydrogen phosphate to disrupt the passivation layer on the surface of β-dicalcium silicate, effectively activating the hydration of low-calcium clinker and improving the early strength of concrete. The addition of active magnesium oxide, which reacts with water to release heat internally, facilitates curing. Simultaneously, the active magnesium oxide efficiently adsorbs and catalyzes the conversion of infiltrated sulfur and nitrogen gases, and fills nanopores to reduce permeability. The dissolution of barium carbonate provides Ba. 2+ With the infiltrated SO4 2- The reaction produces an extremely stable and non-expanding BaSO4 precipitate, thus achieving a "two-stage sulfur locking" effect; nitrogen fixation is achieved through the combination of potassium dihydrogen phosphate and barium carbonate; therefore, this invention solidifies flue gas pollutants (SO2 / NO) through multiple mechanisms. x This invention reduces energy consumption and emissions from end-of-pipe treatment and improves the durability of concrete. It can directly utilize flue gas for steam curing, shortening construction and curing time. The concrete of this invention has the characteristics of rapid early strength development, excellent resistance to sulfate attack, low carbon and environmental protection, and strong ability to solidify pollutants. Detailed Implementation

[0010] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0011] To address the issue of slow strength development of traditional low-calcium cement-based materials in engineering scenarios such as chimneys that require rapid turnover or early load bearing, this invention provides a self-curing low-carbon concrete for flues and chimneys and its construction method. This concrete is a corrosion-resistant chimney concrete that utilizes flue gas for synergistic carbonation strengthening. Furthermore, this invention utilizes flue gas and carbon dioxide for curing, which can effectively solidify pollutants. It features a short construction cycle, energy conservation and emission reduction, and is conducive to widespread adoption.

[0012] In a first aspect, the present invention provides a self-curing low-carbon concrete for flue gas ducts and chimneys, comprising the following components by weight: low-calcium clinker: 270-290 parts; lithium slag: 10-15 parts; mineral powder: 70-90 parts; potassium dihydrogen phosphate: 30-40 parts; active magnesium oxide: 10-15 parts; barium carbonate: 10-15 parts; polycarboxylate superplasticizer: 7-8 parts; boric acid: 0.5-1 part; silane-based water-repellent agent: 0.5-1 part; polypropylene fiber: 1.5-2.5 parts; water: 120-130 parts; coarse aggregate: 800-900 parts; fine aggregate: 650-750 parts.

[0013] Preferably, the mineral composition of low-calcium clinker includes: Ca 14 The content of Mg2(SiO4)8 is 50–60 wt.%, the content of β-Ca2SiO4 is 30–40 wt.%, and the content of Ca2Al2SiO7 is 6–10 wt.%; the specific surface area of ​​the low-calcium clinker is ≥450 m². 2 / kg.

[0014] Preferably, the lithium slag composition, based on oxides, includes: SiO2 40–50 wt.%, Al2O3 18–25 wt.%, Li2O 0.5–1.5 wt.%; and the specific surface area of ​​the lithium slag is 400–500 m². 2 / kg, loss on ignition ≤5 wt.%.

[0015] Preferably, the mineral powder used is S95 grade mineral powder.

[0016] Preferably, the potassium dihydrogen phosphate has a purity of ≥99.0% and a particle size D50 ≤50 μm.

[0017] Preferably, the active magnesium oxide has a particle size of 0.1–1 μm and a specific surface area ≥300 m². 2 / kg.

[0018] Preferably, the barium carbonate has a purity greater than 90% and a specific surface area less than 400 m². 2 / kg.

[0019] Preferably, the concentration of boric acid used is greater than 99%.

[0020] Preferably, the water reduction rate of the polycarboxylate superplasticizer is ≥25%.

[0021] Preferably, the coarse aggregate is a mixture of first basalt with a particle size of 5-8 mm and second basalt with a particle size of 8-12 mm in a mass ratio of 6:4.

[0022] Preferably, the fine aggregate is a mixture of quartz sand and lithium slag powder in a mass ratio of 6.5:3.5 to 7.5:2.5, and the fineness modulus of the fine aggregate is 2.7 to 2.9.

[0023] Preferably, the active ingredient in the silane-based water-repellent agent is ≥20%; more preferably, the silane-based water-repellent agent is Wacker BS1001, which is well compatible with other components in concrete.

[0024] Secondly, the present invention provides a construction method for self-curing low-carbon concrete for flues and chimneys, comprising the following steps: S1, mix the components of low-carbon concrete in proportion to obtain concrete; S2, spray concrete onto the base surface, and perform flue gas curing after the concrete has set.

[0025] It is understood that this invention is applicable to the maintenance or repair of existing flue chimneys, and the base surface needs to be treated. For example, it may be necessary to remove the loose layer on the inner wall of the chimney, thoroughly remove the loose layer, oil stains, and floating dust on the inner wall of the chimney using high-pressure water jetting to expose a solid base surface, sandblast to remove rust from the rusted areas of the reinforcing steel, apply a rust inhibitor (an epoxy-based rust inhibitor can be used) to the reinforcing steel area, and then spray a nano-silica sol interface agent onto the base surface. The SiO2 content of the nano-silica sol interface agent used is ≥30%; the spraying amount of the nano-silica sol interface agent is 0.2~0.4kg / m². 2 After spraying, allow it to stand and penetrate for 20-40 minutes.

[0026] Preferably, in step S2, the concrete is sprayed in two layers, with the second layer being sprayed after the first layer of concrete has initially set.

[0027] More preferably, the polypropylene fiber length in the first layer of concrete is 5-7 mm, and the polypropylene fiber length in the second layer of concrete is 10-14 mm. This invention improves initial crack resistance by using short-fiber concrete to spray the first layer, while also compensating for minor defects on the substrate surface, facilitating the spraying of the second layer of concrete (the main concrete).

[0028] More preferably, the spraying angle of the first layer of concrete is 70° to 80°.

[0029] More preferably, the thickness of the first layer of concrete spraying is 5-8 mm.

[0030] In a further preferred embodiment, after the first layer of concrete has initially set, a roughening treatment is applied before spraying a second layer of concrete.

[0031] More preferably, the thickness of the second layer of concrete spraying is 13-16 mm.

[0032] Preferably, in step S2, the temperature of the flue gas is 80–120°C, and it contains 10–15% CO2 by volume; and within 12 hours of flue gas curing, a 4–6 wt% Na2CO3 solution is sprayed every 3–4 hours, with a spraying volume of 0.15–0.25 L / m³. 2 .

[0033] This invention utilizes flue gas for curing, which contains a certain amount of CO2 and is typically at a temperature of 80–120°C, facilitating carbonation. Furthermore, this invention maintains surface alkalinity by spraying Na2CO3 solution, further promoting carbonation curing. However, excessively high Na2CO3 solution concentration is detrimental to carbonation curing, while excessively low concentration leads to excessive moisture. Too short a spray interval results in excessive moisture affecting concrete performance, while too long an interval can contribute to the formation of an alkaline environment.

[0034] Preferably, the chimney includes a coal / oil boiler chimney, a biomass power plant chimney, or a chemical plant flue gas chimney.

[0035] Main mechanism of action and advantages of this invention: First, it significantly improves early strength: This invention uses potassium dihydrogen phosphate to destroy the passivation layer on the surface of β-C2S, effectively activating the hydration of low-calcium clinker (especially β-C2S). Combined with the promotion of hydration by carbon dioxide in flue gas and the curing by residual heat, magnesium oxide can also react with water to exothermically cure internally, thus overcoming the bottleneck of slow early strength development in low-calcium systems.

[0036] Second, it exhibits excellent resistance to sulfate attack and its ability to solidify acidic gases: (1) Adopting a "two-stage sulfur locking mechanism": First stage: Activated magnesium oxide efficiently adsorbs and catalyzes the conversion of infiltrated SO2 and NO. x (For example, NO2), while filling nanopores to reduce permeability. The main reactions include: 2MgO + 2SO2+ O2→ 2MgSO4 (1) MgO + 2NO2 → Mg(NO3)2 (2) Second stage: Barium carbonate (BaCO3) dissolution provides Ba 2+ With the infiltrated SO4 2- The reaction produces an extremely stable and non-expanding BaSO4 precipitate. This mechanism fundamentally blocks the reaction pathway for the formation of expansive ettringite and gypsum in traditional concrete. The main reactions include: Ba 2+ + SO4 2- → BaSO4(3) (2) It has a certain nitrogen fixation capacity: NO can be converted into NO2 by transition metal oxides in lithium slag, and NO2 originally in the flue gas is adsorbed by magnesium oxide to produce Mg(NO3)2; calcium hydroxide produced by the hydration of low-calcium clinker can also adsorb NO2 to produce Ca(NO3)2; potassium dihydrogen phosphate and barium carbonate react with it: KH2PO4+Mg(NO3)2→KMgPO4·H2O+2HNO3(4) Ca(NO3)2 + BaCO3 → Ba(NO3)2 + CaCO3 (reversible) (5) 5Ba 2+ +3PO4 3- +OH - →Ba5(PO4)3OH (prevents reversible reaction) (6) Among them, reaction (5) is a reversible reaction, but reaction (6) occurs under the action of phosphate, causing reaction (5) to proceed to the right, preventing the reversible reaction, and making nitrogen completely fixed in the barium phosphate (Ba5(PO4)3OH) lattice.

[0037] Simultaneously, in the CO2 environment of the flue gas, free Ca(NO3)2 is converted into calcium nitrate carbonate (Ca2NO3CO3·11H2O). 2Ca 2+ +NO 3- +CO3 2- +11H2O→Ca2NO3CO3·11H2O (7) In summary, this invention provides multiple methods for solidifying flue gas pollutants (SO2 / NO). x This reduces energy consumption and emissions from end-of-pipe treatment and improves the durability of concrete.

[0038] Third, it has outstanding low-carbon and environmental benefits: Active carbon sequestration: Utilizing CO2 from flue gas for carbonation curing not only promotes hydration but also permanently seals CO2 within the concrete in the form of stable carbonates (CaCO3, MgCO3). The reaction mechanism is as follows: (1) β-C2S consumes calcium hydroxide in a carbon dioxide environment, which accelerates the hydration rate, promotes carbonization (as shown in reaction (8)) and accelerates hydration (as shown in reaction (9)): Ca(OH)2+CO2→CaCO3+H2O (8) 2Ca2SiO4+4H2O→3CaO·2SiO2·3H2O+Ca(OH)2(9) (2) Calcium silicate (Ca 14 Mg2(SiO4)8 undergoes directional decomposition in a CO2 environment: Ca 14Mg2(SiO4)8+14CO2→14CaCO3+2MgO+8SiO2 (10) The generated magnesium oxide can further solidify carbon dioxide, while silicon dioxide continues to participate in the volcanic ash effect to form CSH gel.

[0039] Fourth, the construction is simple and environmentally friendly. Steam curing is carried out directly using flue gas, which reduces construction and curing time and shortens the construction cycle.

[0040] The present invention will be further described in detail below through specific embodiments. To avoid redundancy, some raw materials are described below: The mineral composition of low-calcium clinker mainly includes: Ca 14 Mg2(SiO4)8 content 52 wt.%, β-Ca2SiO4 content 38 wt.%, Ca2Al2SiO7 content 7 wt.%; specific surface area 550 m² 2 / kg.

[0041] The silane-based hydrophobic agent is specifically Wacker BS 1001.

[0042] Water reduction rate of polycarboxylate superplasticizer: 30%.

[0043] The fine aggregate is a mixture of quartz sand and lithium slag powder in a mass ratio of 6.5:3.5 to 7.5:2.5, and the fineness modulus of the fine aggregate is 2.8.

[0044] Example 1 A self-curing low-carbon concrete for flues and chimneys, comprising the following components by weight: 280 parts low-calcium clinker; 12 parts lithium slag; 80 parts mineral powder; 35 parts potassium dihydrogen phosphate; 12 parts activated magnesium oxide; 12 parts barium carbonate; 7.5 parts polycarboxylate superplasticizer; 0.8 parts boric acid; 0.6 parts silane hydrophobic agent; 1.8 parts polypropylene fiber; 125 parts water; 850 parts coarse aggregate; 700 parts fine aggregate.

[0045] A construction method for self-curing low-carbon concrete for flues and chimneys includes the following steps: S1, Mix the components according to the above proportions to obtain concrete; S2. To simplify the operation and ensure specimen uniformity, concrete was directly poured into a standard mold. Curing with flue gas began within 2 hours of the concrete's final setting. Curing was divided into two stages: Stage 1 (0-12 hours): Spraying with 5% Na2CO3 solution (0.2 L / m³) every 4 hours. 2Maintain surface alkalinity; Phase 2 (12-24h): Natural exposure, curing process with high-temperature flue gas introduced throughout (temperature between 80 and 120°C, carbon dioxide volume concentration of approximately 10%); after 24h, stop introducing flue gas and allow natural cooling in preparation for testing.

[0046] Example 2 A self-curing low-carbon concrete for flues and chimneys, comprising the following components by weight: 280 parts low-calcium clinker; 15 parts lithium slag; 80 parts mineral powder; 35 parts potassium dihydrogen phosphate; 12 parts activated magnesium oxide; 12 parts barium carbonate; 7.5 parts polycarboxylate superplasticizer; 0.8 parts boric acid; 0.6 parts silane hydrophobic agent; 1.8 parts polypropylene fiber; 125 parts water; 850 parts coarse aggregate; 700 parts fine aggregate.

[0047] The curing method for concrete construction in this embodiment is the same as in Embodiment 1.

[0048] Example 3 A self-curing low-carbon concrete for flues and chimneys, comprising the following components by weight: 280 parts low-calcium clinker; 12 parts lithium slag; 80 parts mineral powder; 40 parts potassium dihydrogen phosphate; 12 parts activated magnesium oxide; 12 parts barium carbonate; 7.5 parts polycarboxylate superplasticizer; 0.8 parts boric acid; 0.6 parts silane hydrophobic agent; 1.8 parts polypropylene fiber (12mm length); 125 parts water; 850 parts coarse aggregate; 700 parts fine aggregate.

[0049] The curing method for concrete construction in this embodiment is the same as in Embodiment 1.

[0050] Comparative Example 1 An existing type of concrete, by weight, comprises the following components: 300 parts of P·O 42.5 cement; 80 parts of mineral powder; 10 parts of silica fume; 7 parts of water-reducing agent; 130 parts of water; 850 parts of coarse aggregate; and 700 parts of fine aggregate.

[0051] Maintenance method: Standard steam curing (40℃ water spray curing for 12 hours → 60℃ steam curing for 12 hours).

[0052] Comparative Example 2 (without active magnesium oxide and barium carbonate) A self-curing low-carbon concrete for flues and chimneys, comprising the following components by weight: 280 parts low-calcium clinker; 12 parts lithium slag; 80 parts mineral powder; 35 parts potassium dihydrogen phosphate; 7.5 parts polycarboxylate superplasticizer; 0.8 parts boric acid; 0.6 parts silane hydrophobic agent; 1.8 parts polypropylene fiber; 125 parts water; 850 parts coarse aggregate; 700 parts fine aggregate.

[0053] The curing method for concrete construction in this comparative example is the same as in Example 1.

[0054] Comparative Example 3 Compared with Example 1, the only difference is that the curing method is different. In this comparative example, the concrete is naturally cured after final setting (ambient temperature 20±5℃, humidity ≥60%) for 28 days; the concrete component ratio is the same as in Example 1.

[0055] Comparative Example 4 Compared with Example 1, the only difference is that potassium dihydrogen phosphate is removed, while the other steps and conditions are the same as in Example 1.

[0056] Performance testing The test items include: compressive strength, resistance to sulfate attack, CO2 emissions, and pollutant solidification (SO2 / NO2). x Adsorption capacity), the specific test methods and results are as follows: 1. Compressive strength test: The compressive strength of the concrete specimens obtained in Examples 1-3 and Comparative Examples 1-4 were tested according to GB / T 50081-2019. The results are shown in Table 1 below.

[0057] Table 1 Compressive strength of Examples 1-3 and Comparative Examples 1-4

[0058] As shown in Table 1, Examples 1-3 achieved a strength of 48.1-50.2 MPa after 36 hours of curing, which is far superior to Comparative Example 3 (38.2 MPa @ 28 days) cured naturally, and close to or exceeds that of ordinary cement concrete cured by steam (Comparative Example 1). In Comparative Example 2, the removal of active magnesium oxide and barium carbonate is problematic. Active magnesium oxide (MgO) reacts with water to release heat, and this exothermic effect effectively promotes the hydration of the cementitious material, especially in the early stages, thus positively impacting early strength. Barium carbonate (BaCO3) primarily functions as a sulfur lock-in agent, but its dissolution provides Ba... 2+ The components involved in the reaction and the formation of precipitates may also contribute to the early microstructure density. In Comparative Example 2, the removal of these two components resulted in the loss of the internal heat source and some contribution to structure formation, leading to a decrease in early strength. This demonstrates that the present invention effectively overcomes the slow early hydration defect of low-calcium clinker through the synergistic effect of phosphate activation, lithium slag pozzolanic effect, exothermic effect of activated magnesium oxide, and residual heat curing, thereby effectively improving early strength.

[0059] 2. Resistance to sulfate attack: In accordance with GB / T 50082-2024, a wet-dry cycle test of 5% sodium sulfate solution was conducted, and the mass change rate and compressive strength retention rate were calculated. The results are shown in Table 2 below.

[0060] Table 2. Resistance to sulfate attack in Examples 1-3 and Comparative Examples 1-3

[0061] As shown in Table 2, after soaking in 5% Na2SO4 solution for 60 days, Examples 1-3 exhibited stable quality and a strength retention rate >92%, significantly superior to ordinary concrete (Comparative Example 1, strength retention rate 78%, increased mass) and Comparative Example 2 lacking magnesium oxide / barium carbonate (strength retention rate 81%, increased mass). This fully demonstrates the effectiveness of the "dual-stage sulfur-locking" mechanism (magnesium oxide adsorption + barium carbonate precipitation) in blocking the expansionous sulfate erosion pathway.

[0062] 3. CO2 emissions (life cycle assessment) Evaluation method: Calculate 1m 3 CO2 emissions during the concrete production process were calculated, covering the entire chain from material production to construction, 50-year service life, and disposal. The results are shown in Table 3 below.

[0063] Table 3 CO2 emissions of Examples 1-3 and Comparative Examples 1-3

[0064] Note: Due to the poor corrosion resistance of ordinary concrete, it requires 8 repairs during its 50-year service life (each repair emits +76kg CO2 / m³). 3 ).

[0065] As shown in Table 3, the net CO2 emissions of Examples 1-3 are approximately 300 kg / m³. 3 The yield is significantly lower than that of ordinary concrete considering multiple repairs (comparative example 1,954 kg / m³). 3 ) and naturally cured low-calcium concrete (comparative example 3,363 kg / m³) 3 Magnesium oxide production generates a significant amount of carbon dioxide. Comparative Example 2, which does not include magnesium oxide, has lower carbon emissions, but this is detrimental to early strength and sulfur fixation. This demonstrates the comprehensive low-carbon benefits brought by carbonization for carbon fixation, emission reduction, energy conservation, and long service life.

[0066] 4. Pollutant solidification test (SO2 / NO) x (Adsorption capacity) Test method: After curing, the concrete is broken up, and the pore fluid is extracted with deionized water to detect SO4 content. 2- NO3 - Mg 2 + The content was calculated, and the amount of curing was determined. The results are shown in Table 4 below.

[0067] Table 4 shows the amount of contaminant solidification in the concrete specimens obtained from the examples and comparative examples.

[0068] As shown in Table 4, Examples 1-3 of the present invention have effects on SO2 and NO. x Curing amount (SO4) 2- 10.3-12.1 mg / g, NO3 - 8.5-9.2 mg / g) and Mg 2+ The utilization rate (78%-82%) was significantly higher than all comparative examples. This demonstrated the efficient purification of flue gas pollutants during the curing process using the concrete's own components.

[0069] In summary, this invention successfully solves the key technical bottlenecks of traditional chimney concrete, such as poor durability, high carbon emissions, low early strength, and unutilized waste heat and pollutants from flue gas. It provides a high-performance, green, low-carbon, economical, and efficient chimney lining concrete with features such as rapid early strength development, excellent resistance to sulfate attack, low carbon emissions, environmental friendliness, and strong pollutant solidification ability.

[0070] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A self-curing low-carbon concrete for flues and chimneys, characterized in that, By weight, it includes the following components: low-calcium clinker: 270-290 parts; lithium slag: 10-15 parts; Mineral powder: 70-90 parts; Potassium dihydrogen phosphate: 30-40 parts; Activated magnesium oxide: 10-15 parts; Barium carbonate: 10-15 parts; Polycarboxylate superplasticizer: 7-8 parts; Boric acid: 0.5-1 part; Silyl hydrophobic agent: 0.5-1 part; Polypropylene fiber: 1.5-2.5 parts; Water: 120-130 parts; coarse aggregate: 800-900 parts; fine aggregate: 650-750 parts.

2. The self-curing low-carbon concrete for flues and chimneys according to claim 1, characterized in that, The mineral composition of the low-calcium clinker includes: Ca 14 The low-calcium clinker contains 50–60 wt.% Mg2(SiO4)8, 30–40 wt.% β-Ca2SiO4, and 6–10 wt.% Ca2Al2SiO7; its specific surface area is ≥450 m². 2 / kg.

3. The self-curing low-carbon concrete for flues and chimneys according to claim 1, characterized in that, The lithium slag, based on oxides, comprises: 40–50 wt.% SiO2, 18–25 wt.% Al2O3, and 0.5–1.5 wt.% Li2O; the specific surface area of ​​the lithium slag is 400–500 m². 2 / kg, loss on ignition ≤5 wt.%.

4. The self-curing low-carbon concrete for flues and chimneys according to claim 1, characterized in that, The mineral powder used is S95 grade mineral powder; The potassium dihydrogen phosphate has a particle size D50 ≤ 50 μm.

5. The self-curing low-carbon concrete for flues and chimneys according to claim 1, characterized in that, The active magnesium oxide has a particle size of 0.1–1 μm and a specific surface area ≥300 m². 2 / kg; The specific surface area of ​​the barium carbonate is less than 400 m². 2 / kg; The water reduction rate of polycarboxylate superplasticizer is ≥25%.

6. The self-curing low-carbon concrete for flues and chimneys according to claim 1, characterized in that, The coarse aggregate is a mixture of first basalt with a particle size of 5-8 mm and second basalt with a particle size of 8-12 mm at a mass ratio of 6:

4. The fine aggregate is a mixture of quartz sand and lithium slag powder in a mass ratio of 6.5:3.5 to 7.5:2.5, and the fineness modulus of the fine aggregate is 2.7 to 2.

9.

7. A construction method for self-curing low-carbon concrete for flues and chimneys, characterized in that, Includes the following steps: S1, mix the components of the self-curing low-carbon concrete for flue and chimney as described in any one of claims 1-6 in proportion to obtain concrete; S2, spray concrete onto the base surface, and perform flue gas curing after the concrete has set.

8. The construction method for self-curing low-carbon concrete for flues and chimneys according to claim 7, characterized in that, In step S2, the concrete is sprayed in two layers. The second layer of concrete is sprayed after the first layer of concrete has initially set.

9. The construction method for self-curing low-carbon concrete for flues and chimneys according to claim 8, characterized in that, The polypropylene fibers in the first layer of concrete are 5-7 mm long, and the polypropylene fibers in the second layer of concrete are 10-14 mm long. The thickness of the first layer of concrete spraying is 5-8 mm; After the first layer of concrete has initially set, it is roughened before the second layer of concrete is sprayed on. The thickness of the second layer of concrete spraying is 13-16 mm.

10. The construction method for self-curing low-carbon concrete for flues and chimneys according to claim 7, characterized in that, In step S2, the temperature of the flue gas is 80–120℃, containing 10–15% CO2 by volume; and within 12 hours of flue gas curing, a 4–6 wt% Na2CO3 solution is sprayed every 3–4 hours, with a spraying volume of 0.15–0.25 L / m³. 2 .

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