Geopolymer-based ultra-high performance concrete and preparation method thereof

Abstract

The invention discloses geopolymer-based ultra-high performance concrete and a preparation method thereof. The geopolymer-based ultra-high performance concrete comprises the following components in parts by weight: 50-70 parts of an industrial solid waste-based gel material, 8-15 parts of a composite alkali foaming agent, 3-8 parts of a nano reinforcing agent, 10-20 parts of copper-plated steel fibers, 20-30 parts of graded aggregate and 0.5-1.5 parts of a functional additive, according to the prepared geopolymer-based ultra-high performance concrete, the industrial solid waste-based gel material is used for replacing traditional cement to reduce carbon emission, the composite alkali activator and the graded aggregate are matched, the early-stage strength is improved, the 28-day compressive strength is larger than or equal to 180 MPa, and the drying shrinkage rate is reduced to 260 mu epsilon.

Description

Technical Field

[0001] This invention belongs to the field of concrete and its preparation, and particularly relates to a geopolymer-based ultra-high performance concrete and its preparation method. Background Technology

[0002] Traditional ultra-high performance concrete (UHPC) relies on a binary combination of 52.5R grade Portland cement and high-purity silica fume as its core cementitious system. A typical UHPC formulation uses 500-800 kg of cement and 100-150 kg of silica fume per cubic meter. This means that the cement raw material stage alone generates significant CO2 emissions. If the energy consumption for silica fume production and the mining and transportation of quartz aggregates are taken into account, the peak carbon emissions over the entire life cycle of traditional UHPC can reach 780 kg CO2 / m³. 3 It far exceeds the 280kg CO2 / m³ of ordinary concrete. 3 The baseline. Meanwhile, the global supply chain for high-quality silica fume is facing a severe crisis, with declining silica fume production causing nearly 30% of UHPC projects to be delayed due to raw material shortages. Therefore, to reduce carbon emissions and silica fume usage, geopolymer-based concrete is being considered as an alternative technology in existing research.

[0003] However, the existing system suffers from three major structural defects: First, early strength development is severely delayed. The 3-day compressive strength of a typical alkali-activated slag system under standard curing conditions is far lower than that of cement-based UHPC, leading to a prolonged demolding cycle and hindering construction efficiency. Second, volume stability deterioration is a prominent issue. The 28-day drying shrinkage of fly ash-slag-based polymers in environments with high relative humidity is two times or more than that of cement-based systems. Third, the high-value utilization of industrial solid waste encounters a technological ceiling. When the total content of fly ash and granulated blast furnace slag exceeds 80%, the material performance exhibits a precipitous decline. More seriously, impurities such as residual carbon and heavy metal ions in solid waste can undergo toxic polymerization reactions, causing a 28-day strength fluctuation coefficient >15%.

[0004] Currently, only 12% of UHPC projects under construction use geopolymer systems, and these projects struggle to simultaneously meet the three core performance indicators: 28-day compressive strength ≥ 180 MPa; and life-cycle carbon emissions ≤ 150 kg CO2 / m³. 3 Drying shrinkage ≤300με.

[0005] This technological predicament severely restricts the process of industrial solid waste resource utilization. my country has over 3.5 billion tons of stockpiled fly ash and an annual increase of 320 million tons of slag, but the high-value-added consumption for UHPC (Ultra-High-Hybrid Polymer) accounts for less than 5% of annual production. A large amount of solid waste is forced into landfills, occupying arable land and creating dual pressures on environmental protection and the economy. Therefore, developing geopolymer-based UHPCs with ultra-high mechanical properties, ultra-low carbon emissions, and excellent durability has become a strategically crucial area for solving the carbon neutrality problem in the building materials industry. Summary of the Invention

[0006] Purpose of the invention: The technical problem to be solved by the present invention is to provide a geopolymer-based ultra-high performance concrete and its preparation method, so as to solve the problems of low compressive strength and high carbon dioxide emissions of ultra-high performance concrete in the prior art.

[0007] Technical solution: The geopolymer-based ultra-high performance concrete provided by the present invention comprises the following components by weight: 50-70 parts of industrial solid waste-based gel material, 8-15 parts of composite alkali-invigorating agent, 3-8 parts of nano-reinforcing agent, 10-20 parts of copper-plated steel fiber, 20-30 parts of graded aggregate, and 0.5-1.5 parts of functional additives.

[0008] Furthermore, the specific surface area of ​​the industrial solid waste-based gel material is ≥600m². 2 / kg, and the industrial solid waste-based gel material is fly ash, slag and red mud, and the CaO / SiO2 molar ratio in the industrial solid waste-based gel material is 0.65-0.85, and the content of ferric oxide is 2-4%.

[0009] Furthermore, the composite alkali activator includes water glass with a modulus of 1.4-1.8 and sodium hydroxide, wherein the mass of sodium hydroxide accounts for 15-25% of the total mass of the composite alkali activator.

[0010] Furthermore, the nano-reinforcing agent is nano-silica and carbon nanotubes, and the mass of carbon nanotubes is 1-3% of the mass of the nano-reinforcing agent.

[0011] Furthermore, the copper-plated steel fiber has a length of 10-15mm and an aspect ratio of 60-80.

[0012] Furthermore, the graded aggregate is quartz sand and basalt, and the mass ratio of quartz sand to basalt is (2-3):1. Furthermore, the functional additive is prepared by the following method: heating an aqueous solution of polycarboxylate superplasticizer to 60-70°C, then stirring and adding an organosilicon defoamer emulsion at a speed of 150-200 rpm, followed by adding a silane coupling agent at a mass of 0.4-0.5‰ of the functional additive, and reacting for 30-50 minutes.

[0013] Furthermore, the polycarboxylate superplasticizer is 0.4-1 parts, and the silicone defoamer is 0.1-0.5 parts.

[0014] Furthermore, the composite alkali activator is prepared by the following method: first, water glass is diluted with water to a density of 1.25-1.35 g / cm³. 3Subsequently, sodium hydroxide solution was uniformly injected into water glass solution, stirred and maintained at a temperature of 38-42℃. After sufficient reaction, nano ZnO dispersion was added, and the mixture was aged for 22-26 hours under an inert atmosphere and at a temperature of 40-45℃ to obtain a composite alkali activator with a viscosity of 300-400 cP.

[0015] The present invention also provides a method for preparing the above-mentioned geopolymer-based ultra-high performance concrete, comprising the following steps: (1) The industrial solid waste-based gel material was ball-milled and activated for 1.8-2.2 h until the specific surface area was ≥600 m². 2 / kg; (2) After mixing the industrial solid waste-based gel material with graded aggregates evenly, add the composite alkali activator and continue stirring until a uniform slurry is formed; add nano-reinforcing agent, copper-plated steel fiber and functional additives to the slurry, continue stirring evenly, and then form it by high-frequency vibration. (3) The material formed in step (2) is cured in stages. First, it is cured under saturated steam at 78-82℃ for 23-50h; then it is cured under dry heat at 58-62℃ for 46-50h; finally, it is cured in water at 19-21℃ until the desired age is reached to obtain geopolymer-based ultra-high performance concrete material.

[0016] Beneficial effects: Compared with the prior art, the significant advantages of the present invention are: The geopolymer-based ultra-high performance concrete prepared by the present invention reduces carbon emissions by using industrial solid waste-based gel materials instead of traditional cement, and improves early strength by combining composite alkali activators and graded aggregates, with a 28-day compressive strength ≥180MPa and a drying shrinkage rate reduced to 260με. Detailed Implementation

[0017] The technical solution of the present invention will be further described in detail below with reference to the embodiments.

[0018] It should be noted that all raw materials used in this invention are commercially available. The graded aggregate used in the following examples is a mixture of quartz sand with a particle size of 0.1-0.3 mm and basalt with a particle size of 0.3-0.5 mm, in a mass ratio of 3:1; the density of the fly ash microspheres is 0.7-0.8 g / cm³. 3 The copper-plated steel fiber has a diameter of 0.2 mm and a length of 12 mm; the ferric oxide content in the red mud is 25%; and the CaO / SiO2 molar ratio in fly ash, slag, and red mud is controlled at 0.7.

[0019] The preparation method of the composite alkali activator used in the following examples is as follows: first, water glass is diluted with water to a density of 1.32 g / cm³. 3Subsequently, sodium hydroxide solution was uniformly injected into water glass solution, stirred, and allowed to react fully at 40°C. Then, nano ZnO dispersion was added, and the mixture was aged for 22 hours under an inert atmosphere at 45°C to obtain a clear and transparent composite alkali activator with a viscosity of 400 cP. The amounts of water glass and sodium hydroxide added were based on the component contents in Table 1-4.

[0020] The preparation method of the functional additive used in the following examples is as follows: the aqueous solution of polycarboxylate superplasticizer is heated to 70°C, and then the silicone defoamer emulsion is added dropwise while stirring at 200 rpm. Subsequently, 0.5‰ of the mass of the functional additive is added as silane coupling agent, and the reaction is carried out for 350 min to obtain the functional additive. The amount of polycarboxylate superplasticizer and silicone defoamer added is based on the component content in Table 1-4.

[0021] Example 1 The component contents of the geopolymer-based ultra-high performance concrete of Example 1 are shown in Table 1 below.

[0022] Table 1

[0023] Example 1: The preparation method of geopolymer-based ultra-high performance concrete includes the following steps: (1) Preparation of industrial solid waste-based gel material: Weigh each component of the industrial solid waste-based gel material and process it in a planetary ball mill at 500 rpm for 2.2 h. The grinding ball gradation is Φ5mm:Φ10mm=3:1 until the industrial solid waste-based gel material is ball-milled to a specific surface area of ​​652 m². 2 / kg.

[0024] (2) Gradient mixing: First, dry mix industrial solid waste-based gel material and graded aggregate at 120 rpm for 90 s; then add composite alkali activator and stir at 140 rpm for 60 s; finally add nano-reinforcing agent, copper-plated steel fiber and functional additives and stir at 190 rpm for 60 s.

[0025] (3) Vibrate the above mixed slurry at a high frequency of 120Hz for 180s with an amplitude of 0.5mm to obtain the molding material.

[0026] (4) Step curing: Place the molded material under 80℃ saturated steam for 24h; then cure it in a 60℃ oven for 48h, with humidity ≤30% in a dry heat environment; finally cure it in water at 20℃ for 26d until it reaches its age.

[0027] Example 2 The component content of the polymer-based ultra-high performance concrete in Example 2 is shown in Table 2 below, and the preparation method is the same as that in Example 1.

[0028] Table 2 Example

[0029] The component content of the geopolymer-based ultra-high performance concrete of Example 3 is shown in Table 3 below, and the preparation method is the same as that of Example 1.

[0030] Table 3 Example

[0031] The component content of the geopolymer-based ultra-high performance concrete of Example 4 is shown in Table 4 below, and the preparation method is the same as that of Example 1.

[0032] Table 4

[0033] The geopolymer-based ultra-high performance concrete prepared in Examples 1-4 was tested for chloride ion penetration resistance and drying shrinkage according to the standard of GB / T 50082 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete". The results are shown in Table 5.

[0034] Table 5

[0035] As shown in Table 5, the geopolymer-based ultra-high performance concrete prepared in this invention achieves a dual leap in material performance and environmental benefits by constructing a three-level synergistic mechanism of "chemical activation-nanofilling-fiber toughening": while ensuring a 28-day compressive strength ≥180MPa, the carbon emissions throughout the entire life cycle are reduced to ≤150kg CO2 / m³. 3 Combining the stabilizing effect of the iron phase component in red mud on the silicon-aluminum framework, a geopolymer from industrial solid waste-based cementitious materials, namely fly ash + slag + red mud, is used to replace cement, reducing carbon emissions. Furthermore, the early strength of the geopolymer is enhanced through gradient stirring and the use of an alkali activator. Specifically, red mud, fly ash, and slag are stirred evenly, and then a composite alkali activator is added. Through the modulus control of water glass and the synergistic effect of NaOH, the formation of a three-dimensional network [NASH] gel framework is accelerated. This reacts synchronously with the Fe2O3 nanocrystal nuclei in the red mud, reducing the nucleation barrier and promoting heterogeneous nucleation of reactants on the gel phase surface, thus improving the early strength of the geopolymer, i.e., a 28-day compressive strength ≥180 MPa. Next, nano-SiO2 is added to fill the capillary pores, and carbon nanotubes react with Ca through surface -COOH functional groups. 2+The formation of ionic bonds reduces drying shrinkage, and the matching of the expansion coefficients of the graded aggregates basalt and quartz sand with the geopolymer matrix further reduces the drying shrinkage to 260 με. This solution not only addresses the problem of industrial solid waste treatment but also improves the later-stage performance of ultra-high performance concrete through the combination of graded aggregates, gradient mixing, and stepped curing processes.

[0036] In addition to the above embodiments, it should be noted that the specific surface area of ​​the industrial solid waste-based gel material described in this invention needs to be ≥600m². 2 / kg, and the CaO / SiO2 molar ratio in the industrial solid waste-based gel material can be 0.65-0.85, and the content of ferric oxide can be 2-4%. The CaO / SiO2 molar ratio is controlled by adjusting the proportion of coal ash, slag and red mud in the scheme.

[0037] The technical effects claimed by this invention can be achieved by using the preparation process and the parameter range defined in this invention, and therefore no further examples will be provided to support these claims.

Claims

1. A geopolymer-based ultra-high performance concrete, characterized in that, It includes the following components by weight: 50-70 parts of industrial solid waste-based gel material, 8-15 parts of composite alkali osmotic agent, 3-8 parts of nano-reinforcing agent, 10-20 parts of copper-plated steel fiber, 20-30 parts of graded aggregate, and 0.5-1.5 parts of functional additives.

2. The geopolymer-based ultra-high performance concrete according to claim 1, characterized in that, The steel slag powder contains ≥45% A(CaO+MgO).

3. The geopolymer-based ultra-high performance concrete according to claim 1, characterized in that, The specific surface area of ​​the industrial solid waste-based gel material is ≥600m² / kg, and the industrial solid waste-based gel material is fly ash, slag and red mud, and the CaO / SiO2 molar ratio in the industrial solid waste-based gel material is 0.65-0.85, and the content of ferric oxide is 2-4%.

4. The geopolymer-based ultra-high performance concrete according to claim 1, characterized in that, The composite alkali activator includes water glass with a modulus of 1.4-1.8 and sodium hydroxide, wherein the mass of sodium hydroxide accounts for 15-25% of the total mass of the composite alkali activator.

5. The geopolymer-based ultra-high performance concrete according to claim 1, characterized in that, The nano-reinforcing agent is nano-silica and carbon nanotubes, and the mass of carbon nanotubes is 1-3% of the mass of the nano-reinforcing agent.

6. The geopolymer-based ultra-high performance concrete according to claim 1, characterized in that, The copper-plated steel fibers are 10-15mm long and have an aspect ratio of 60-80.

7. The geopolymer-based ultra-high performance concrete according to claim 1, characterized in that, The functional additive is prepared by the following method: heating an aqueous solution of polycarboxylate superplasticizer to 60-70°C, then stirring and adding an organosilicon defoamer emulsion at a speed of 150-200 rpm, followed by adding a silane coupling agent at a mass of 0.4-0.5‰ of the functional additive, and reacting for 30-50 minutes.

8. The geopolymer-based ultra-high performance concrete according to claim 7, characterized in that, The polycarboxylate superplasticizer is 0.4-1 parts, and the silicone defoamer is 0.1-0.5 parts.

9. The geopolymer-based ultra-high performance concrete according to claim 1, characterized in that, The composite alkali activator is prepared by the following method: water glass is first diluted with water to a density of 1.25-1.35 g / cm³. 3 Subsequently, sodium hydroxide solution was uniformly injected into water glass solution, stirred and maintained at a temperature of 38-42℃. After sufficient reaction, nano ZnO dispersion was added, and the mixture was aged for 22-26 hours under an inert atmosphere and at a temperature of 40-45℃ to obtain a composite alkali activator with a viscosity of 300-400 cP.

10. A method for preparing geopolymer-based ultra-high performance concrete according to any one of claims 1-9, characterized in that, Includes the following steps: (1) The industrial solid waste-based gel material was ball-milled and activated for 1.8-2.2 h until the specific surface area was ≥600 m². 2 / kg; (2) After mixing the industrial solid waste-based gel material with graded aggregates evenly, add the composite alkali activator and continue stirring until a uniform slurry is formed; add nano-reinforcing agent, copper-plated steel fiber and functional additives to the slurry, continue stirring evenly, and then form it by high-frequency vibration. (3) The material formed in step (2) is cured in stages. First, it is cured under saturated steam at 78-82℃ for 23-50h; then it is cured under dry heat at 58-62℃ for 46-50h; finally, it is cured in water at 19-21℃ until the desired age is reached to obtain geopolymer-based ultra-high performance concrete material.

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