A highly corrosion-resistant concrete, its preparation method and application

Abstract

The present invention discloses a highly corrosion-resistant concrete, which is as follows by weight parts: 100 parts of cement, 100 - 125 parts of modified carbide slag powder, 125 - 250 parts of Class III fly ash, 20 - 50 parts of sodium hydroxide, 250 - 295 parts of water glass, 600 - 900 parts of common sand, 700 - 1200 parts of stones, 5 - 30 parts of silver-containing wastewater, and 5 - 50 parts of water; the modified carbide slag powder is obtained by calcining and grinding the waste residue mainly composed of calcium hydroxide after the hydrolysis of carbide to obtain acetylene gas; the calcination temperature is 500 - 600 °C, and the calcination time is 30 - 120 min; the average particle diameter is 20 - 50 μm; in the chemical composition of the modified carbide slag powder, CaO is 60 - 90%, Ca(OH)2 is 0 - 30%, MgO is 1 - 2%, SiO2 is 5 - 10%, Fe2O3 is 0.5% - 2.0%, and Al2O3 is 0.1% - 1.0%; the present invention makes resource utilization of Class III fly ash, carbide slag, and silver-containing wastewater, and greatly improves the chloride ion penetration resistance of concrete by enhancing the strength development and compensating shrinkage of the concrete.

Description

Technical Field

[0001] The present invention belongs to the technical field of concrete materials, and particularly relates to a highly corrosion-resistant concrete, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, hyperbolic thin-walled structures of large cooling towers have been widely used not only in thermal power but also in nuclear power. With the development of nuclear power technology, the construction of large-size and high-rise hyperbolic cooling towers has become more and more frequent, and the wall thickness has become thinner and thinner. The cooling tower structure involves large-volume structures, special-shaped and thin-walled structures, all of which have high workability and crack resistance requirements to meet the durability and safety design requirements. At the same time, the site selection of nuclear power plants is often close to the sea, and currently, the cooling towers of nuclear power projects are often designed with seawater cooling methods, which requires higher chloride ion penetration coefficients for the concrete of the cooling towers, and the design needs to meet less than 4×10-12m2 / s (28d or 56d).

[0003] As a common industrial solid waste, Class I and Class II fly ash have been fully applied in the construction field. At the same time, due to the problem of its own activity of low-grade fly ash (Class III), it cannot be applied and treated. Its continuous stacking has also had a huge impact on the ecological environment. This makes it an urgent problem to be solved to improve the utilization rate and application range of low-grade fly ash (Class III); in addition, carbide slag mainly comes from the production of polyvinyl chloride and vinyl acetate by the carbide method. For every 1 ton of polyvinyl chloride produced, about 1.45 tons of calcium carbide are consumed, and more than 1 ton of carbide slag is produced after each ton of calcium carbide is hydrolyzed. Therefore, more than 2 tons of carbide slag need to be discharged for every 1 ton of polyvinyl chloride produced. The quantity of carbide slag is large, the alkali content is high, and it also contains harmful substances such as sulfur and arsenic. If it is discharged without treatment, it will block the sewer, accumulate in the riverbed, and endanger fishery production.

[0004] Finally, silver-containing wastewater refers to wastewater containing a high concentration of silver ions in the industrial production process. Since silver has strong toxicity and bioaccumulation, it is particularly important to treat silver-containing wastewater. Summary of the Invention

[0005] Regarding that Class-Ⅲ fly ash can improve the strength of its alkali-activated geopolymer by the method of "calcium supplementation", and the modified carbide slag powder has a relatively high CaO content, and its CaO and Ca(OH)₂ contents can be adjusted by the calcination time. Therefore, using the modified carbide slag powder as the "calcium supplement" for Class-Ⅲ fly ash has the following benefits: 1. By adjusting the dosage of the modified ground carbide slag in the composite alkali-activated raw materials (Class-Ⅲ fly ash, carbide slag powder), the "calcium supplementation" effect of Class-Ⅲ fly ash can be achieved, and then the activation effect of Class-Ⅲ fly ash in the alkaline environment in the composite alkali-activated raw materials can be improved, thereby enhancing the strength and corrosion resistance of the overall concrete; 2. By adjusting the calcination time to change the contents of CaO and Ca(OH)₂, not only can the calcium supplementation effect of Class-Ⅲ fly ash be changed, but also Ca(OH)₂ in the modified ground carbide slag can be used as another alkali activator to activate the early activity of fly ash and improve the early strength of Class-Ⅲ fly ash concrete, making up for the problem of insufficient early strength of concrete.

[0006] Combined with the problems of difficult utilization and serious waste of Class-Ⅲ fly ash and the characteristics of carbide slag itself, the present invention provides a green highly corrosion-resistant seawater cooling tower concrete mainly composed of cement, Class-Ⅲ fly ash and carbide slag powder, and a preparation method thereof, which resourcefully utilizes Class-Ⅲ fly ash, carbide slag and silver-containing wastewater, and greatly improves the chloride ion penetration resistance of concrete by enhancing the strength development and compensating shrinkage of the concrete.

[0007] To achieve the above object, the technical solution is as follows:

[0008] A highly corrosion-resistant concrete, the composition of which is as follows by weight parts:

[0009] 100 parts of cement, 100 - 125 parts of modified carbide slag powder, 125 - 250 parts of Class-Ⅲ fly ash, 20 - 60 parts of sodium hydroxide, 250 - 295 parts of water glass, 600 - 900 parts of common sand, 700 - 1200 parts of stones, 5 - 30 parts of silver-containing wastewater, 5 - 50 parts of water.

[0010] According to the above solution, the cement used is P·O 42.5 cement, 300 m 2 / kg ≤ specific surface area ≤ 370 m 2 / kg.

[0011] According to the above solution, the modified carbide slag powder is obtained by calcining and grinding the waste residue mainly composed of calcium hydroxide after the hydrolysis of carbide to obtain acetylene gas; the calcination temperature is 500 - 600 °C, the calcination time is 30 - 120 min; the average particle diameter is 20 - 50 μm.

[0012] According to the above solution, in the chemical composition of the modified carbide slag powder, CaO is 60 - 90%, Ca(OH)₂ is 0 - 30%, MgO is 1 - 2%, SiO₂ is 5 - 10%, Fe₂O₃ is 0.5% - 2.0%, and Al₂O₃ is 0.1% - 1.0%.

[0013] According to the above solution, the fineness range of the Class III fly ash is 30 - 40%, the loss on ignition range is 3% - 8%, the CaO content in the chemical composition is 4 - 10%, the K₂O content is 1 - 4%, the SiO₂ content is 45 - 55%, the Fe₂O₃ content is 3% - 8%, and the Al₂O₃ content is 25% - 35%.

[0014] According to the above solution, the silver-containing wastewater is the wastewater containing high-concentration silver ions during the industrial production process, and the Ag + concentration is 2000 - 2500 mg / L.

[0015] According to the above solution, the concentration of the sodium silicate is 40 wt% and the modulus is 1.4.

[0016] According to the above solution, the purity of the sodium hydroxide is above 99.55 wt%.

[0017] According to the above solution, the common sand is medium sand, and its fineness modulus is between 2.3 - 3.0.

[0018] The preparation method of the above high corrosion-resistant concrete includes the following steps:

[0019] Mix the composite alkaline activator (sodium hydroxide, sodium silicate), water, and silver-containing wastewater to prepare an activator solution; mix the gravel, cement, Class III fly ash, modified carbide slag powder, and common sand, and then add the alkali-activated solution and mix and stir evenly to obtain the high corrosion-resistant cooling tower concrete.

[0020] The application of the above high corrosion-resistant concrete in seawater cooling towers.

[0021] During the long-term work process, the inventor found that compared with the extensive application of Class I and Class II fly ash in building materials, the application of low-grade (Class III) fly ash in the field of building materials is almost zero. The reason is that the fineness and activity of low-grade (Class III) fly ash are much lower than those of Class I and Class II fly ash. In addition, in the field of alkali-activated building materials, the strength and crack resistance of alkali-activated geopolymers of Class I and Class II fly ash are greatly improved compared with ordinary concrete, but the strength and crack resistance of alkali-activated geopolymers of Class III fly ash are far from sufficient.

[0022] The present invention organically combines and utilizes the physical and chemical properties among three industrial wastes, achieving the purpose of turning waste into treasure. First, considering that the content of CaO in low-grade fly ash (Grade III) is low and it cannot be directly applied to the preparation of concrete, and at the same time, it is also impossible to meet the strength requirements of low-grade fly ash (Grade III) geopolymers through alkali activation. By adjusting the dosage of modified ground carbide slag powder in the composite alkali-activated raw materials (Grade III fly ash, modified ground carbide slag powder), the "calcium supplementation" effect of Grade III fly ash can be achieved, increasing the content of CaO in the overall alkali-activated raw materials, and then the activation effect of Grade III fly ash in the composite alkali-activated raw materials under alkaline conditions can be improved; in addition, by adjusting the calcination time to change the content changes of CaO and Ca(OH)2, Ca(OH)2 in the modified ground carbide slag can be used as another alkali activator to stimulate the early activity of fly ash and improve the early strength of Grade III fly ash concrete, making up for the problem of insufficient early strength of concrete; second, due to the physical properties of fly ash itself, the addition of Grade III fly ash can effectively improve the chloride ion adsorption capacity of concrete; then, due to the prominent advantages of alkali activation such as low water demand, low hydration heat, good thermal stability, high crack resistance and water reduction, introducing partial alkali-activated materials in the preparation of concrete will further optimize the crack resistance performance of concrete. Finally, the addition of silver-containing wastewater weakens the erosion of chloride ions on concrete, greatly reducing the concentration of chloride ions penetrating into concrete, enabling the internal reaction degree of fly ash geopolymer cementing materials to be effectively improved under the action of low-concentration chloride ions, and further increasing the compactness of concrete.

[0023] The function of low-grade (Grade III) fly ash is not only as a raw material for alkali-activated geopolymers, but also beneficial to the "secondary hydration" reaction of fly ash after being incorporated into cement. The secondary hydration of fly ash is to absorb Ca(OH)2 generated by cement hydration in the cementitious system to generate C-S-H gel and calcium aluminate hydrate, improving the strength of the overall cementitious material. At the same time, calcium aluminate hydrate can combine with Cl - and CH to form Friedel salt, playing a role in solidifying CI - . In addition, fly ash particles are relatively large, with a hollow spherical structure, and there are complex pores on the surface that communicate with the internal cavities, increasing its specific surface area. It can not only adsorb a large amount of free chloride ions, further improving the adsorption of chloride ions. Finally, due to its large surface energy, C-S-H gel can also adsorb and solidify part of the chloride ions.

[0024] In the present invention, silver-containing wastewater is applied. Silver-containing wastewater refers to wastewater containing high-concentration silver ions in the industrial production process. When silver-containing wastewater is added, the Ag + ions can not only effectively reduce the erosion of chloride ions on the inside of concrete by reacting with chloride ions to produce precipitation, but also reduce the concentration of chloride ions entering the inside of concrete.

[0025] Due to the adsorption performance of fly ash to chloride ions and the internal reaction degree of fly ash geopolymer can be effectively improved under the action of low chloride ion concentration. The surface part of the concrete material close to the air side will preferentially contact with chloride ions and sulfate ions in the air, and react with Ag + to form a precipitate, reducing the chloride ion concentration invading into the interior of the concrete. Then, the reaction of the fly ash geopolymer in the deeper interior will be enhanced under the action of the infiltrated low-concentration chloride ions, which will enhance the strength and compactness of this part of the concrete, improve the impermeability and corrosion resistance of this part, and further effectively inhibit the invasion of chloride ions into the deeper concrete, avoiding the contact between steel bars and chloride ions, sulfate ions, etc., and improving the corrosion resistance of the concrete.

[0026] The alkali activation reaction principles involved in the present invention are of two types: 1. Fly ash generates sodium aluminosilicate hydrate under the activation of sodium silicate, and sodium hydroxide plays a role in adjusting the modulus of sodium silicate, which can effectively improve the strength of concrete; 2. Fly ash generates calcium silicate hydrate and calcium aluminate hydrate under the activation of calcium hydroxide, which can also effectively improve the strength of concrete.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. Due to the fineness and activity problems of low-grade (Grade III) fly ash itself, it cannot be applied to concrete. Here, through the "calcium supplementation" measure (that is, supplementing CaO to low-grade (Grade III) fly ash) and adjusting the amount of "calcium supplementation", the activation effect of low-grade (Grade III) fly ash in an alkaline environment is improved, so as to improve the strength and crack resistance of the alkali-activated geopolymer binder of Grade III fly ash, and the application way of low-grade (Grade III) fly ash in the construction field can be realized and improved; In addition, the present invention uses ground carbide slag powder as the "calcium supplementation" substance for low-grade (Grade III) fly ash alkali-activated geopolymer, which not only effectively utilizes the characteristic of high "CaO" content in the ground carbide slag powder, but also improves the utilization way of carbide slag;

[0029] 2. Ca(OH)2 in the modified ground carbide slag can be used as another alkali activator to activate the early activity of fly ash and improve the early strength of Grade III fly ash concrete, making up for the problem of insufficient early strength of concrete;

[0030] 3. In the present invention, the role of low-grade (Grade III) fly ash is not only as a raw material for alkali-activated geopolymer, but also beneficial to the "secondary hydration" reaction of fly ash after being incorporated into cement. The secondary hydration of fly ash is to absorb Ca(OH)2 generated by cement hydration in the cementitious system, generate C-S-H gel and calcium aluminate hydrate, improve the strength of the overall cementitious material, and C-S-H gel can also adsorb part of chloride ions due to its large surface energy; At the same time, calcium aluminate hydrate can combine with Cl- and CH generates Friedel's salt, which plays a role in solidifying Cl - . In addition, fly ash particles are relatively large, with a hollow spherical structure. There are complex pores on the surface that communicate with the internal cavities, increasing its specific surface area. It can not only adsorb a large amount of free chloride ions, but also further improve the adsorption of chloride ions. Therefore, combining the excitation effect improvement principle and anti-cracking improvement effect exerted by the above various materials will effectively improve the impermeability and corrosion resistance of the concrete of this seawater cooling tower.

[0031] 4. With the addition of the silver-containing wastewater in the present invention, Ag + ions can effectively reduce the erosion of chloride ions on the interior of the concrete by reacting with chloride ions to form precipitates. In addition, the internal reaction degree of the alkali-activated fly ash geopolymer can be effectively improved under the action of a low chloride ion concentration. And because the surface layer of the concrete material close to the air side will preferentially contact with chloride ions, sulfate ions, etc. in the air and react with Ag + to form precipitates, the chloride ion concentration invading the interior of the concrete is greatly reduced. At the same time, the alkali-activation reaction degree of the inner material is also effectively improved under the action of a low concentration of chloride ions. Therefore, it will further enhance the strength and compactness of this part of the concrete, improve the impermeability and corrosion resistance of this part, avoid the contact between steel bars and chloride ions, sulfate ions, etc., and improve the corrosion resistance of the concrete.

[0032] 5. Since the alkali activation has prominent advantages such as low water demand, low heat of hydration, good thermal stability, high anti-cracking and water-reducing properties, etc., therefore, introducing some alkali-activated materials in the preparation of concrete will further optimize the anti-cracking performance of the concrete.

[0033] 6. The present invention uses cement and grade III fly ash as the main raw materials for the seawater concrete of the high anti-cracking and corrosion-resistant cooling tower, and at the same time uses the ground fine electroslag powder after grinding as an external calcium source, sodium source, etc. It not only uses calcium oxide in the ground fine carbide slag powder as an external calcium source to solve the problem of insufficient strength of the alkali-activated grade III fly ash cementitious material, turning waste into treasure and harm into treasure, but also improves the utilization way of carbide slag in the field of building materials and alleviates the problem of carbide slag waste; in addition, the addition of silver-containing wastewater can not only effectively reduce the erosion of chloride ions on the concrete and reduce the chloride ion concentration entering the concrete, but also, because the internal reaction degree of the fly ash geopolymer cementitious material can be effectively improved under the action of a low concentration of chloride ions, therefore, on the basis of the silver ions reducing the chloride ion concentration invading the interior of the concrete, it will further improve the reaction degree and compactness of the concrete and further hinder the invasion of chloride ions.

[0034] 7. The preparation process of the present invention uses industrial waste as the main raw material to prepare alkali-activated materials, realizing the substitution of cement materials and reducing the demand for cement materials. This can not only alleviate the excessive consumption of limestone, clay, and energy in cement production, reducing the high energy consumption and high pollution problems brought by cement production, but also gradually eliminate the environmental pollution problems caused by the large accumulation of industrial solid waste. It meets the requirements of national environmental protection policies and has great application prospects. Detailed implementation manners

[0035] The following examples further illustrate the technical solutions of the present invention, but do not limit the protection scope of the present invention.

[0036] The detailed implementation manners provide a highly corrosion-resistant concrete, and its composition is as follows by weight parts:

[0037] 100 parts of cement, 100 - 125 parts of modified carbide slag powder, 125 - 250 parts of Class III fly ash, 20 - 60 parts of sodium hydroxide, 250 - 295 parts of water glass, 600 - 900 parts of common sand, 700 - 1200 parts of gravel, 5 - 30 parts of silver-containing wastewater, and 5 - 50 parts of water.

[0038] Specifically, the cement used is P·O 42.5 cement, with a specific surface area of 300 m 2 / kg ≤ specific surface area ≤ 370 m 2 / kg.

[0039] Specifically, the modified carbide slag powder is obtained by calcining and grinding the waste residue mainly composed of calcium hydroxide after the hydrolysis of carbide to obtain acetylene gas; the calcination temperature is 500 - 600 °C, the calcination time is 30 - 120 min; the average particle diameter is 20 - 50 μm; in the chemical composition of the modified carbide slag powder, CaO is 60 - 90%, Ca(OH)2 is 0 - 30%, MgO is 1 - 2%, SiO2 is 5 - 10%, Fe2O3 is 0.5% - 2.0%, and Al2O3 is 0.1% - 1.0%.

[0040] Specifically, the fineness range of the Class III fly ash is 30 - 40%, the loss on ignition range is 3% - 8%, the CaO content in the chemical composition is 4 - 10%, the K2O content is 1 - 4%, the SiO2 content is 45 - 55%, the Fe2O3 content is 3% - 8%, and the Al2O3 content is 25% - 35%.

[0041] Specifically, the silver-containing wastewater is the wastewater containing high-concentration silver ions in the industrial production process, and the Ag + concentration is 2000 - 2500 mg / L.

[0042] Specifically, the concentration of the water glass is 40 wt%, and the modulus is 1.4; the purity of the sodium hydroxide is above 99.55 wt%.

[0043] Specifically, the common sand is medium sand, and its fineness modulus is between 2.3 and 3.0.

[0044] The specific implementation manner also provides the preparation method of the above high corrosion-resistant concrete as follows:

[0045] Mix the composite alkaline activator (sodium hydroxide, water glass), water, and silver-containing wastewater to prepare an activator solution; mix the gravel, cement, Class III fly ash, modified carbide slag powder, and common sand, and then add the alkali-activated solution and mix and stir evenly to obtain high corrosion-resistant cooling tower concrete.

[0046] The composition design ratio of the specific embodiment is shown in Table 1.

[0047] Table 1

[0048]

[0049] The performance characterization results of the specific embodiment are shown in Table 2. Test the 100mm cube compressive strength in accordance with the "Standard Test Method for Physical and Mechanical Properties of Concrete" (CBT50081-2019), and test the rapid chloride ion diffusion coefficient DRCM and electric flux of the concrete in accordance with the "Standard Test Method for Long-Term Performance and Durability of Ordinary Concrete" (CB / T 50082-2009). According to the immersion corrosion resistance test method (Method K) in the "Test Method for Resistance of Cement to Sulfate Attack" (GB / T1749-2008), the mortar specimens are immersed in fresh water and SO4 2- solution (the SO4 2- concentration is 20000mg / L in the erosion solution respectively, and an erosion simulation test is carried out for 12 months). After immersion, measure the flexural strength of the specimens and calculate the corrosion resistance coefficient. Taking the corrosion resistance coefficient ≥ 0.80 as the qualified corrosion resistance and the judgment standard.

[0050] Table 2

[0051]

[0052]

[0053] It can be seen from the test data that the concrete specimens of the embodiments of the present invention exhibit good resistance to chloride ions and sulfate erosion, and maintain good mechanical properties. Among them, it can be observed from Example 7 that after "supplementing calcium" (CaO) to Class III fly ash with carbide slag powder, the concrete strength, chloride ion resistance and sulfate corrosion resistance can be effectively improved. This is because the key of the present invention lies in changing and adjusting the ratio of Class III fly ash to carbide slag powder in the alkali-activated raw materials. After "supplementing calcium" (CaO) to Class III fly ash with carbide slag powder, its various properties have all increased to varying degrees; at the same time, the uniform distribution of Class III fly ash will play an adsorption role on corrosive ions such as chloride ions; finally, the fly ash is evenly dispersed, and the adsorption performance of fly ash to chloride ions and the internal reaction degree of fly ash geopolymer can be effectively improved under the action of chloride ions. The alkali-activated hydration degree of fly ash in the cementitious system is improved, and then the strength and compactness of geopolymer concrete are also improved, and the impermeability and corrosion resistance of the concrete are improved.

[0054] Further observing Example 13, it can be known that the addition of a certain amount of silver ion-containing wastewater can further improve the chloride ion resistance of the concrete, and the mechanical properties also meet the standard requirements. This is because the surface part of the concrete material close to the seawater side will preferentially contact with chloride ions and sulfate ions in the seawater, so the strength and compactness of this part of the concrete will be preferentially improved, and the impermeability and corrosion resistance of this part will be improved. Furthermore, it can effectively reduce the contact between the more inner concrete and steel bars and chloride ions, sulfate ions, etc., and improve the corrosion resistance of the concrete.

[0055] It should be noted that the above-mentioned embodiments are only some of the preferred ways to implement the present invention, rather than all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Claims

1. A highly corrosion-resistant concrete, characterized in that The composition is calculated by weight as follows: 100 parts of cement, 100-125 parts of modified carbide slag powder, 125-250 parts of grade III fly ash, 20-50 parts of sodium hydroxide, 250-295 parts of water glass, 600-900 parts of ordinary sand, 700-1200 parts of gravel, 5-30 parts of silver-containing wastewater, and 5-50 parts of water; The modified carbide slag powder is obtained by calcining and grinding the waste slag with calcium hydroxide as the main component after acetylene gas is obtained by hydrolyzing calcium carbide; the calcination temperature is 500-600°C, the calcination time is 30-120min; the average particle diameter is 20-50μm; the chemical composition of the modified carbide slag powder is 60-90% CaO, 0-30% Ca(OH)2, 1-2% MgO, 5-10% SiO2, 0.5%-2.0% Fe2O3, and 0.1%-1.0% Al2O3; The grade III fly ash has a fineness range of 30-40%, a loss on ignition range of 3%-8%, a chemical composition of 4-10% CaO, 1-4% K2O, 45-55% SiO2, 3%-8% Fe2O3, and 25%-35% Al2O3; The silver-containing wastewater is wastewater containing a high concentration of silver ions during the industrial production process, with Ag + concentration being 2000 - 2500 mg / L.

2. The highly corrosion-resistant concrete according to claim 1, characterized in that The concentration of the water glass is 40wt% and the modulus is 1.

4.

3. The highly corrosion-resistant concrete according to claim 1, characterized in that The purity of the sodium hydroxide is above 99.55wt%.

4. The highly corrosion-resistant concrete according to claim 1, characterized in that The ordinary sand is medium sand, and its fineness modulus is between 2.3 and 3.

0.

5. The preparation method of the highly corrosion-resistant concrete according to any one of claims 1 to 4, characterized in that The following steps are involved: Sodium hydroxide, water glass, water and silver-containing wastewater are mixed to prepare an activator solution; gravel, cement, grade III fly ash, modified carbide slag powder and ordinary sand are mixed, and then the alkali activating solution is added, and the mixture is stirred evenly to obtain highly corrosion-resistant cooling tower concrete.

6. Use of the highly corrosion-resistant concrete according to any one of claims 1 to 4 in a seawater cooling tower.

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