Phosphogypsum solidification agent for cement-based materials and use in concrete

Abstract

The application discloses a phosphogypsum solidifying agent for cement-based materials and application in concrete, and relates to the technical field of building materials.The solidifying agent is composed of the following components in mass fraction: phosphogypsum 20-35 parts, slag powder 30-50 parts, Portland cement clinker 10-20 parts, limestone powder 5-15 parts, sodium sulfate 1-3 parts, and triethanolamine 0.05-0.2 parts.The application combines water-washing and neutralization treatment of phosphogypsum with slag powder, Portland cement clinker and limestone powder, and uses sodium sulfate and triethanolamine as a composite activator, and combines with the process steps of atomization spraying and aging treatment, so that the components of the solidifying agent fully act and form a synergistic effect, the interference of impurities in the phosphogypsum on the hydration process of the cement-based material can be effectively reduced, and the reaction activity and structural compactness of the cementitious material system can be improved.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, and in particular relates to a phosphogypsum curing agent for cement-based materials and its application in concrete. Background Technology

[0002] Phosphogypsum is an industrial byproduct of wet-process phosphoric acid production. Its main component is calcium sulfate dihydrate, along with small amounts of soluble phosphorus, fluorine, and organic matter. Due to its large production volume and complex impurity composition, the resource utilization of phosphogypsum has been a key focus in the field of industrial solid waste treatment. In the building materials sector, phosphogypsum can be used to produce cement retarders, gypsum boards, and cementitious materials. However, the presence of impurities can affect the hydration process and performance stability of cement-based materials, limiting its large-scale application in cementitious material systems.

[0003] Slag powder is a powdery material obtained by grinding granulated blast furnace slag. It possesses potential hydration activity and can undergo hydration reactions to generate cementitious products under alkaline or sulfate-activated conditions. Adding slag powder to cement-based materials not only facilitates the disposal of industrial solid waste but also improves certain material properties. Limestone powder, as a commonly used mineral admixture, mainly functions as a micro-aggregate filler; its appropriate addition can improve the workability of freshly mixed slurry. The application technologies of these industrial by-products and mineral materials in cement-based materials have been researched and accumulated over many years.

[0004] The main technical obstacle to the application of phosphogypsum in cement-based materials lies in the fact that its soluble phosphorus and fluorine impurities interfere with the normal hydration reaction of cement and slag, affecting the formation and development of cementitious strength. Existing treatment methods include pretreatment processes such as washing, neutralization, and calcination, but these are costly or complex. There are also existing technologies that combine phosphogypsum with slag and cement, but these often fail to balance the workability, mechanical properties, and durability of the curing agent, especially when the phosphogypsum content is high, leading to significant fluctuations in material properties and limiting its widespread application in concrete engineering. Therefore, the following solutions are proposed to address these issues. Summary of the Invention

[0005] The purpose of this invention is to provide a phosphogypsum curing agent for cement-based materials and its application in concrete. Through the synergistic effect of phosphogypsum with slag powder, cement clinker and composite activator, the adverse effects of phosphogypsum impurities on cement hydration can be improved, the mechanical properties and durability of the curing agent can be enhanced, and the problem of unstable performance of existing phosphogypsum curing agents can be solved.

[0006] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution:

[0007] This invention relates to a phosphogypsum curing agent for cement-based materials, characterized in that the curing agent is composed of the following components in parts by weight: 20-35 parts phosphogypsum, 30-50 parts slag powder, 10-20 parts silicate cement clinker, 5-15 parts limestone powder, 1-3 parts sodium sulfate, and 0.05-0.2 parts triethanolamine.

[0008] Furthermore, the phosphogypsum is an industrial wet-process phosphoric acid byproduct, which is treated by washing, neutralizing, and drying. Its pH value is 6.5-7.5, its calcium sulfate dihydrate content is ≥85%, and its particle size range is 20-50 μm.

[0009] Furthermore, the slag powder is obtained by grinding granulated blast furnace slag, and its specific surface area is ≥400. Activity index ≥95%.

[0010] Furthermore, the mineral composition of the silicate cement clinker contains ≥50% tricalcium silicate.

[0011] Furthermore, the limestone powder is obtained by crushing and grinding natural limestone, with a particle size range of 10-45 μm and a calcium carbonate content of ≥90%.

[0012] A method for preparing a phosphogypsum curing agent for cement-based materials includes the following steps:

[0013] S1: Mix phosphogypsum and slag powder to obtain premix A;

[0014] S2: Add silicate cement clinker and limestone powder to premix A and continue stirring to obtain mixture B;

[0015] S3: Dissolve sodium sulfate and triethanolamine in water to prepare a liquid activator solution;

[0016] S4: Add the liquid activator solution to mixture B by atomized spraying and stir continuously to obtain a curing agent mixture in a wet state;

[0017] S5: Place the resulting curing agent mixture in a sealed container for aging;

[0018] S6: After aging, the mixture is dried to a moisture content of ≤2%, then crushed and sieved to obtain the finished phosphogypsum curing agent.

[0019] Further, in step S1, the stirring speed is 200-300 rpm and the stirring time is 5-8 minutes; in step S2, the stirring speed is 150-250 rpm and the stirring time is 6-10 minutes.

[0020] Further, the mass concentration of the liquid activator solution in step S3 is 10% to 20%; the stirring speed in step 4) is 200 rpm, and the stirring time is 8 to 12 minutes.

[0021] Furthermore, the aging time in step S5 is 12 to 24 hours, and the aging temperature is controlled at 20 to 30°C; the drying temperature in step S6 is 60 to 80°C.

[0022] The application of a phosphogypsum curing agent for cement-based materials in concrete includes the following steps:

[0023] The phosphogypsum curing agent is used to replace ordinary Portland cement at a ratio of 10% to 30% of the cement mass, and is mixed with coarse aggregate, fine aggregate, water and other admixtures to prepare a concrete mixture.

[0024] The mixing sequence is as follows: first, dry mix the coarse and fine aggregates with the curing agent for 30 seconds, then add the cement and dry mix for 30 seconds, and finally add the water and water-reducing agent and wet mix for 120 seconds.

[0025] The mixed concrete is poured into the mold, vibrated to compact it, and cured under standard curing conditions until the specified age.

[0026] The present invention has the following beneficial effects:

[0027] 1. This invention uses two types of industrial solid waste, phosphogypsum and slag powder, as raw materials. By pre-treating the phosphogypsum through water washing and neutralization, the negative impact of impurities on the performance of cement-based materials is reduced. This technical solution realizes the large-scale resource utilization of industrial by-product phosphogypsum, reduces the mining and consumption of natural gypsum, and provides a high-value-added utilization method for granulated blast furnace slag. In the process of preparing cement-based materials, replacing some traditional cementitious materials with solid waste is beneficial to reducing carbon emissions in the production of building materials, which meets the technical requirements of green and low-carbon development, and takes into account environmental benefits while ensuring the basic performance of materials.

[0028] 2. This invention constructs a multi-component synergistic system through the composite proportion design of phosphogypsum, slag powder, silicate cement clinker, and limestone powder. The calcium sulfate component provided by phosphogypsum can undergo a hydration reaction with the aluminosilicate component in slag powder under the action of an activator to generate hydration products with cementitious properties. Limestone powder acts as a micro-aggregate filler in the system and can also provide nucleation sites for hydration products, promoting the uniformity of the hydration reaction. The silicate cement clinker ensures the stable performance of the basic cementitious properties of the system. The interaction of each component helps to form a dense hardened body structure.

[0029] 3. This invention uses sodium sulfate and triethanolamine as a composite activator, which is uniformly dispersed in the mixture by liquid spraying. Sodium sulfate can provide sulfate ions to participate in the hydration reaction of slag, while triethanolamine helps to improve the fluidity of the slurry and regulate the hydration process. An aging process is set in the preparation process to allow the activator to fully contact the powder material and undergo a preliminary reaction, and then the finished product is obtained after drying. This process is conducive to the uniform distribution of the activator in the system, so that the chemical activation effect and the physical mixing effect complement each other and improve the overall efficiency of the curing agent.

[0030] 4. When the curing agent of this invention is used in concrete, the limestone powder in its components can improve the water retention and cohesiveness of fresh concrete, and the triethanolamine helps to regulate the setting time and fluidity retention capacity. The cementitious products generated during the hydration process can fill the internal pores of the concrete, making the structure of the hardened concrete more compact. The formation of this compact structure helps to slow down the penetration of external corrosive media, has a positive impact on the durability of concrete such as resistance to chloride ion penetration, and at the same time helps to maintain volume stability and reduce the tendency of shrinkage deformation.

[0031] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram comparing the compressive strength of each sample at 7 days and 28 days in this invention.

[0034] Figure 2 This is a schematic diagram showing the comparison of electrical flux over 56 days according to the present invention. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0036] Please see Figure 1-2 As shown, the present invention provides a phosphogypsum curing agent for cement-based materials, the curing agent being composed of the following components in parts by weight:

[0037] 20-35 parts phosphogypsum; 30-50 parts slag powder; 10-20 parts silicate cement clinker; 5-15 parts limestone powder; 1-3 parts sodium sulfate; 0.05-0.2 parts triethanolamine;

[0038] The phosphogypsum is a byproduct of industrial wet-process phosphoric acid production. It is used after washing, neutralization, and drying. Its pH value is 6.5–7.5, calcium sulfate dihydrate content is ≥85%, and particle size is controlled within the range of 20–50 μm. The slag powder is obtained by grinding granulated blast furnace slag, with a specific surface area ≥400. The activity index is ≥95%. The silicate cement clinker is a general-purpose silicate cement clinker with a tricalcium silicate content ≥50% in its mineral composition. The limestone powder is obtained by crushing and grinding natural limestone, with a particle size range of 10-45μm and a calcium carbonate content ≥90%. The sodium sulfate is industrial anhydrous sodium sulfate with a purity ≥98%. The triethanolamine is industrial grade with a purity ≥85%.

[0039] The present invention also provides a method for preparing the phosphogypsum curing agent, comprising the following steps:

[0040] S1: Add phosphogypsum and slag powder to a horizontal mixer in proportion, and stir at 200-300 rpm for 5-8 minutes to ensure that the two are fully mixed and uniform, so as to obtain premix A;

[0041] S2: Add silicate cement clinker and limestone powder to premix A, and continue to stir at a speed of 150-250 rpm for 6-10 minutes to obtain mixture B;

[0042] S3: Dissolve sodium sulfate and triethanolamine in a small amount of water beforehand to prepare a liquid activator solution with a mass concentration of 10% to 20%, stir well and let stand for later use;

[0043] S4: The liquid activator solution prepared in step S3 is slowly added to mixture B by atomized spraying. During the spraying process, the speed of the stirrer is kept at 200 rpm and the stirring is continued for 8 to 12 minutes to make the liquid evenly distributed and fully adsorbed on the surface of the powder, so as to obtain the curing agent mixture in a wet state.

[0044] S5: Place the mixture obtained in step S4 in a sealed container and age it for 12 to 24 hours to allow the activator to fully penetrate and react with each component. The aging temperature is controlled at 20 to 30°C.

[0045] S6: After aging, the mixture is sent to an airflow drying device and dried at 60-80℃ until the moisture content is ≤2%. After crushing and sieving, the finished phosphogypsum curing agent is obtained.

[0046] The present invention also provides a method for applying the phosphogypsum curing agent in concrete, comprising the following steps:

[0047] S1: The phosphogypsum curing agent is used to replace ordinary Portland cement at a ratio of 10% to 30% of the cement mass, and is mixed with coarse aggregate, fine aggregate, water and other admixtures to prepare a concrete mixture.

[0048] S2. The mixing sequence is as follows: First, dry mix the coarse and fine aggregates with the curing agent for 30 seconds, then add the cement and dry mix for 30 seconds, and finally add the water and water-reducing agent and wet mix for 120 seconds to ensure that each component is evenly dispersed.

[0049] S3: Pour the mixed concrete into the mold, vibrate it to make it dense, smooth the surface and cover it with a moisturizing film. Cure it under standard curing conditions (temperature 20±2℃, relative humidity ≥95%) until the specified age.

[0050] This invention constructs a multi-component synergistic curing system by synergistically combining phosphogypsum with slag powder, cement clinker, limestone powder, and a composite activator. Calcium sulfate in the phosphogypsum reacts with aluminosilicate in the slag powder under the action of the activator to form ettringite and hydrated calcium silicate gel, significantly improving the early strength and impermeability of cement-based materials. Limestone powder provides micro-aggregate effect and nucleation sites, promoting the uniform distribution of hydration products. Sodium sulfate and triethanolamine synergistically provide sulfate ions to participate in the hydration reaction and improve slurry fluidity, enhancing the workability of the curing agent.

[0051] In the following Examples 1-3 and Comparative Examples 1-3:

[0052] All raw materials are from the same batch to ensure comparability;

[0053] The phosphogypsum is a byproduct of the wet-process phosphoric acid production at a chemical plant in Hubei Province. After washing and neutralization, it has a pH of 7.0, a calcium sulfate dihydrate content of 88%, and a particle size of 30 μm. The slag powder is grade S95 with a specific surface area of ​​420. The cement clinker is P·I 42.5 grade silicate cement clinker; the limestone powder has a calcium carbonate content of 92% and a particle size of 15μm; the sodium sulfate has a purity of 98%; and the triethanolamine has a purity of 85%.

[0054] Example 1:

[0055] A phosphogypsum curing agent, comprising, by weight: 25 parts phosphogypsum, 40 parts slag powder, 15 parts cement clinker, 10 parts limestone powder, 2 parts sodium sulfate, and 0.1 parts triethanolamine. The preparation method is the same as described above.

[0056] Example 2:

[0057] A phosphogypsum curing agent, comprising, by weight: 30 parts phosphogypsum, 35 parts slag powder, 12 parts cement clinker, 12 parts limestone powder, 1.5 parts sodium sulfate, and 0.15 parts triethanolamine. The preparation method is the same as described above.

[0058] Example 3:

[0059] A phosphogypsum curing agent, comprising, by weight: 20 parts phosphogypsum, 45 parts slag powder, 18 parts cement clinker, 8 parts limestone powder, 2.5 parts sodium sulfate, and 0.08 parts triethanolamine. The preparation method is the same as described above.

[0060] Comparative Example 1:

[0061] Compared to Example 1, sodium sulfate and triethanolamine were not added, while the remaining components remained the same. The preparation of the liquid activator and the aging process were omitted during the preparation process.

[0062] Comparative Example 2:

[0063] Compared to Example 1, phosphogypsum was replaced with natural gypsum, while the other components remained the same.

[0064] Comparative Example 3:

[0065] Commercially available slag cement does not contain phosphogypsum curing agent.

[0066] The curing agents used in the above examples and comparative examples were used to replace 20% of the P·O 42.5 cement by mass to prepare C30 concrete. The 7-day and 28-day compressive strengths and the 56-day electrical flux were measured, and the results are shown in the table below:

[0067] Sample 7-day compressive strength (MPa) 28-day compressive strength (MPa) 56d electric flux (C) Example 1 28.5 42.3 890 Example 2 27.8 41.5 920 Example 3 29.2 43.1 850 Comparative Example 1 22.1 35.6 1350 Comparative Example 2 26.3 39.2 1120 Comparative Example 3 24.5 37.8 1280

[0068] As can be seen from the table, the embodiments of the present invention are superior to the comparative examples in terms of compressive strength and chloride ion penetration resistance, indicating that the phosphogypsum curing agent can effectively improve the mechanical properties and durability of concrete under the synergistic effect of the activator. Comparative Example 1 lacks an activator, resulting in insufficient hydration reaction and decreased performance; Comparative Example 2 uses natural gypsum instead of phosphogypsum, but due to the lack of trace components and crystal characteristics of phosphogypsum, the effect is slightly inferior; Comparative Example 3 is a commercially available product, not optimized for the phosphogypsum system, and its performance is moderate.

[0069] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0070] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A phosphogypsum curing agent for cement-based materials, characterized in that, The curing agent is composed of the following components in parts by weight: 20-35 parts phosphogypsum, 30-50 parts slag powder, 10-20 parts silicate cement clinker, 5-15 parts limestone powder, 1-3 parts sodium sulfate, and 0.05-0.2 parts triethanolamine.

2. The phosphogypsum curing agent for cement-based materials according to claim 1, characterized in that, The phosphogypsum is an industrial wet-process phosphoric acid byproduct. After being washed, neutralized, and dried, it has a pH value of 6.5–7.5, a calcium sulfate dihydrate content of ≥85%, and a particle size range of 20–50 μm.

3. The phosphogypsum curing agent for cement-based materials according to claim 1, characterized in that, The slag powder is obtained by grinding granulated blast furnace slag, and its specific surface area is ≥400. Activity index ≥95%.

4. The phosphogypsum curing agent for cement-based materials according to claim 1, characterized in that, The mineral composition of the silicate cement clinker contains ≥50% tricalcium silicate.

5. The phosphogypsum curing agent for cement-based materials according to claim 1, characterized in that, The limestone powder is obtained by crushing and grinding natural limestone, with a particle size range of 10-45 μm and a calcium carbonate content of ≥90%.

6. A method for preparing a phosphogypsum curing agent for cement-based materials as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1: Mix phosphogypsum and slag powder to obtain premix A; S2: Add silicate cement clinker and limestone powder to premix A and continue stirring to obtain mixture B; S3: Dissolve sodium sulfate and triethanolamine in water to prepare a liquid activator solution; S4: Add the liquid activator solution to mixture B by atomized spraying and stir continuously to obtain a curing agent mixture in a wet state; S5: Place the resulting curing agent mixture in a sealed container for aging; S6: After aging, the mixture is dried to a moisture content of ≤2%, then crushed and sieved to obtain the finished phosphogypsum curing agent.

7. The method for preparing the phosphogypsum curing agent for cement-based materials according to claim 6, characterized in that, The stirring speed in step S1 is 200-300 rpm and the stirring time is 5-8 minutes; the stirring speed in step S2 is 150-250 rpm and the stirring time is 6-10 minutes.

8. The method for preparing the phosphogypsum curing agent for cement-based materials according to claim 6, characterized in that, The mass concentration of the liquid activator solution in step S3 is 10% to 20%; the stirring speed in step 4) is 200 rpm and the stirring time is 8 to 12 minutes.

9. The method for preparing the phosphogypsum curing agent for cement-based materials according to claim 6, characterized in that, The aging time in step S5 is 12 to 24 hours, and the aging temperature is controlled at 20 to 30°C; the drying temperature in step S6 is 60 to 80°C.

10. The application of a phosphogypsum curing agent for cement-based materials as described in any one of claims 1 to 5 in concrete, characterized in that, Includes the following steps: The phosphogypsum curing agent is used to replace ordinary Portland cement at a ratio of 10% to 30% of the cement mass, and is mixed with coarse aggregate, fine aggregate, water and other admixtures to prepare a concrete mixture. The mixing sequence is as follows: first, dry mix the coarse and fine aggregates with the curing agent for 30 seconds, then add the cement and dry mix for 30 seconds, and finally add the water and water-reducing agent and wet mix for 120 seconds. The mixed concrete is poured into the mold, vibrated to compact it, and cured under standard curing conditions until the specified age.

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