Special exciting agent for UHPC (Ultra High Performance Concrete) based on phosphogypsum as well as preparation method and application of special exciting agent

Abstract

The invention discloses a phosphogypsum-based UHPC special activator and a preparation method and application thereof, and belongs to the technical field of concrete, the phosphogypsum-based UHPC special activator comprises the following raw materials by mass: 60-80 wt% of activated phosphogypsum, 5-15 wt% of an alkaline excitation component, 5-15 wt% of a sulfur-aluminum active component, 2-10 wt% of an early strength regulation and control component, and 3-5 wt% of aluminum lignosulfonate. The excitant provided by the invention can significantly improve early strength development of a UHPC system, improve microstructure compactness, improve fresh mixing performance stability and realize high-valued utilization of solid waste phosphogypsum, and the obtained ultra-high performance concrete can be used in fabricated concrete members, bridge structure reinforcement, ocean engineering or service concrete in harsh environments, and has wide application prospects. And the method has obvious social benefits and engineering application values.

Description

Technical Field

[0001] This invention belongs to the field of concrete technology, and particularly relates to a UHPC-specific activator based on phosphogypsum, its preparation method and application. Background Technology

[0002] Ultra-high performance concrete (UHPC) is widely used in bridges, high-rise buildings, prefabricated components, and concrete engineering in extreme service environments due to its high density, high strength, and excellent durability. However, traditional UHPC relies on large amounts of cement clinker and energy-intensive materials such as silica fume, resulting in significant CO2 emissions and increased material costs during its production. Therefore, developing low-carbon, economical, and high-performance UHPC systems has become an important research direction in the international concrete field.

[0003] The current mainstream approach to reducing carbon emissions from UHPC (Ultra-High-Performance Cement) includes partially replacing cement clinker with industrial solid wastes such as mineral powder, fly ash, and metakaolin. However, these solid waste materials have low reactivity, especially in UHPC with low water-cement ratios, where the hydration environment is limited and early activation is difficult. This often results in insufficient 1-day and 7-day strength development of UHPC, restricting its application in bridge engineering and rapid construction. On the other hand, phosphogypsum, a byproduct of phosphate chemical industry, is one of my country's largest industrial solid wastes, with an annual output exceeding 70 million tons. Its main component is CaSO4·2H2O, but it contains a certain amount of water-soluble impurities (such as phosphorus, phosphorus, and soluble salts), making it difficult to use directly in cementitious systems without treatment. However, numerous studies have shown that with appropriate pretreatment, phosphogypsum can release sulfate ions, which react with aluminosilicate sources to generate early structural products such as AFt (ettringite), providing potential early activation capabilities for cement-based systems. Therefore, phosphogypsum is considered a low-carbon activating material with potential for high-value utilization.

[0004] However, the direct application of phosphogypsum to the UHPC system still faces the following challenges: (1) Phosphogypsum itself has low activity, and if it is not pretreated, its internal impurities will affect the stability of the hydration reaction; (2) The low water-cement ratio of UHPC leads to limited sulfate dissolution, making it difficult for phosphogypsum to fully exert its coagulation effect; (3) The dissolution rate of the silicon-aluminum source is insufficient, resulting in low synergistic reaction efficiency with phosphogypsum; (4) There is a lack of composite activator design that can synergize with phosphogypsum, making it difficult to meet the dual requirements of UHPC for early strength and flow retention.

[0005] While existing technologies have attempted to apply desulfurized gypsum, metasilicates, and aluminates to promote early hydration in ordinary concrete or alkali-activated cementitious materials, a dedicated activator system with phosphogypsum as the core and adapted to the low water-cement ratio UHPC system has not yet been established. In particular, there is a lack of integrated composite activation technology that combines early strength promotion, fluidity control, and carbon emission reduction capabilities.

[0006] Therefore, how to provide a composite activator that combines early strength promotion, flow regulation and carbon emission reduction capabilities is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention proposes a UHPC-specific activator based on phosphogypsum, its preparation method, and its application.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A UHPC-specific activator based on phosphogypsum comprises the following raw materials by mass fraction: Activated phosphogypsum 60-80 wt%, alkaline activating component 5-15 wt%, aluminum sulfide active component 5-15 wt%, early intensity control component 2-10 wt%, aluminum lignosulfonate 3-5 wt%.

[0009] Beneficial effects: This invention forms a chemical activation system suitable for UHPC by synergistically regulating sulfate release from phosphogypsum, dissolution kinetics of silicon-aluminum source, and morphology of hydration products. The reasonable types and proportions of raw materials can effectively match the sulfate release rate and aluminum dissolution rate in phosphogypsum, making the early hydration products more fully formed and more rationally structured. This significantly improves the early strength development of the UHPC system, enhances the microstructure density, improves the stability of freshly mixed performance, and realizes the high-value utilization of solid waste phosphogypsum, which has obvious social benefits and engineering application value.

[0010] Preferably, the activated phosphogypsum contains 60-90 wt% CaSO4, has a water-soluble impurity content of no more than 1.5 wt%, and a specific surface area of ​​not less than 300 m². 2 / kg.

[0011] More preferably, the method for preparing the activated phosphogypsum includes the following steps: After washing and drying the phosphogypsum, the dried phosphogypsum is mechanically activated by ball milling to obtain the activated phosphogypsum.

[0012] More preferably, the water washing is performed by stirring phosphogypsum at a solid-liquid ratio of 1:(3-5) at 40-50°C for 10-20 minutes, then letting it stand to remove the supernatant. The above process is repeated as needed until the water-soluble impurity content of the phosphogypsum is reduced to no more than 1.5%, thus completing the water washing.

[0013] Beneficial effects: The above process can dissolve and remove water-soluble phosphates, fluorides and some soluble impurities in phosphogypsum into the aqueous phase, thereby reducing the content of water-soluble impurities in phosphogypsum to no more than 1.5%.

[0014] More preferably, the drying temperature is 105°C and the time is 2-4 hours.

[0015] More preferably, the ball mill rotates at a speed of 250-350 rpm for 30-60 min.

[0016] More preferably, the process before ball milling further includes: crushing phosphogypsum to a particle size of no more than 10 mm.

[0017] Beneficial effects: The ball milling process can increase the specific surface area of ​​the material to 350 m². 2 The surface energy and reactivity are significantly improved by increasing the surface energy by more than 1 kg, thereby providing a stable raw material basis for the efficient activation reaction of the activator of this invention.

[0018] Preferably, the lignin sulfonate aluminum has a lignin sulfonation degree of 70%-90%, its solubility in water is not less than 30 g / L, and the pH value of the solution obtained after dissolving solid lignin sulfonate aluminum in liquid is 3-5.

[0019] More preferably, the method for preparing the aluminum lignosulfonate includes the following steps: Industrial lignin is mixed with a sulfonating agent for sulfonation reaction. After the reaction is completed, the pH is adjusted, and aluminum salt is added to the reaction solution to obtain aluminum lignin sulfonate complex. The reaction system is concentrated and spray-dried to obtain aluminum lignin sulfonate powder.

[0020] Beneficial effects: The aluminum lignosulfonate prepared by the above method has excellent dispersibility and complexing ability, and can effectively regulate the flowability and hydration kinetics of the activation system.

[0021] More preferably, the sulfonating agent is sodium sulfite.

[0022] Beneficial effects: Sodium sulfite, as a mild sulfonating agent, can effectively sulfonate the aromatic ring structure in lignin molecules under relatively mild conditions, introduce sufficient sulfonic acid groups, and at the same time avoid severe degradation of the lignin skeleton, which is beneficial to obtaining aluminum lignin sulfonate precursors with good solubility and dispersibility.

[0023] More preferably, the sulfonation reaction is carried out at a temperature of 60-80°C for a time of 1.5-2.5 hours.

[0024] Beneficial effects: Sulfonation reaction at 60-80℃ for 1.5-2.5h can ensure the degree of sulfonation while avoiding excessive reaction that could lead to molecular chain breakage. This results in aluminum lignosulfonate with both a high degree of sulfonation and a suitable molecular weight distribution, which is beneficial for its stable dispersion in cement-based systems.

[0025] More preferably, the pH adjustment is to adjust the pH to 7-8.

[0026] Beneficial effects: Adjusting the pH of the system to neutral or weakly alkaline after the sulfonation reaction helps stabilize the lignin sulfonic acid group structure, avoids the instability of the molecular structure under strong acid conditions, and provides a suitable chemical environment for the subsequent aluminum ion complexation reaction.

[0027] More preferably, the aluminum salt is aluminum sulfate. By adding aluminum sulfate to the reaction system, aluminum ions undergo a complexation reaction with lignin sulfonic acid groups. At the same time, the acidic effect generated by the hydrolysis of aluminum sulfate is used to adjust the pH of the reaction system to 3-5.

[0028] Beneficial effects: As an active aluminum sulfate component, aluminum sulfate can provide the system with a highly reactive aluminum source. It can synergistically generate early hydration products such as ettringite with the sulfate ions released from phosphogypsum, thereby significantly improving the early strength of UHPC.

[0029] More preferably, the aluminum lignosulfonate reaction system after the aluminum salt complexation reaction is completed is concentrated to achieve a solid content of 20-30%.

[0030] Beneficial Effects: This invention controls the solid content of the aluminum lignosulfonate complexation reaction system within the range of 20-30%, which significantly improves the efficiency of the subsequent spray drying process while ensuring the system's fluidity and uniformity. On the one hand, an appropriate solid content is beneficial for the uniform distribution of aluminum lignosulfonate molecules in the liquid phase, avoiding problems such as excessively high local viscosity, limited mass transfer, or particle agglomeration under high solid content conditions. On the other hand, it can effectively reduce energy consumption during the spray drying process and reduce solvent evaporation load, thereby obtaining aluminum lignosulfonate powder with uniform particle size, good solubility, and stable dispersion performance, providing favorable conditions for its uniform incorporation and performance in the UHPC activation system.

[0031] More preferably, during the spray drying process, the inlet temperature is 160-180℃ and the outlet temperature is 80-90℃.

[0032] Beneficial effects: This invention controls the inlet temperature at 160-180℃ and the outlet temperature at 80-90℃ during the spray drying process. This ensures rapid evaporation of moisture and high drying efficiency while effectively preventing thermal degradation or structural damage of organic components in aluminum lignosulfonate due to excessively high temperatures. This temperature range is conducive to the formation of powder particles with uniform particle size and stable surface structure, thereby improving the dissolution rate and dispersion performance of aluminum lignosulfonate. This ensures that it can quickly and uniformly exert its dispersion and complexation regulation effects in the UHPC activation system, and also helps to improve the overall storage stability and usage consistency of the activator.

[0033] Preferably, the alkaline activating component is sodium metasilicate.

[0034] Beneficial effects: Sodium metasilicate in this invention, as an alkaline activating component, can promote the dissolution of silicon source under low alkaline conditions, enhance the formation ability of C-(A)-SH gel, and at the same time avoid the negative impact of strong alkaline system on the workability and durability of the mixture.

[0035] Preferably, the active component of the sulfur-aluminum mixture is aluminum sulfate.

[0036] Beneficial effects: The aluminum sulfate in this invention, as the aluminum sulfate active component, can provide the system with an aluminum source with high reactivity. It can synergistically generate early hydration products such as ettringite with the sulfate ions released by phosphogypsum, thereby significantly improving the early strength of UHPC.

[0037] Preferably, the early-pressure control component is sodium sulfate.

[0038] Beneficial effects: Sodium sulfate in this invention, as an early-strength control component, can adjust the sulfate concentration and ionic strength in the system, promote early nucleation and crystal growth, and accelerate the early hydration reaction process without significantly affecting fluidity.

[0039] The present invention also provides a method for preparing a UHPC-specific activator based on phosphogypsum. After weighing the above raw materials, the resulting mixture is dry-mixed, dried, and ground to obtain the UHPC-specific activator based on phosphogypsum.

[0040] More preferably, the dry mixing time is 5-10 minutes.

[0041] More preferably, the drying temperature is 50-70°C and the time is 2-4 hours.

[0042] More preferably, the specific surface area of ​​the activator is ≥300m². 2 / kg.

[0043] Beneficial effects: The present invention prepares the activator through dry mixing, low-temperature drying and grinding processes, which can ensure the uniform distribution of each component at the microscale and avoid unstable reactions caused by excessively high local concentrations, thereby improving the reaction consistency and performance stability of the activator when applied in UHPC.

[0044] Application of a phosphogypsum-based UHPC activator in ultra-high performance concrete.

[0045] Beneficial effects: Applying the activator of this invention to the UHPC system can achieve a synergistic improvement in early strength and flowability under low water-cement ratio conditions, thus broadening the application range of phosphogypsum in ultra-high performance concrete.

[0046] An ultra-high performance concrete includes the above-mentioned UHPC-specific activator based on phosphogypsum, wherein the activator dosage is 3-8 wt% of the cementitious material.

[0047] Beneficial effects: Within this dosage range, the activator can fully exert the synergistic activating effect of sulfate-aluminum source-silicon source, while avoiding fluidity loss or later strength instability caused by excessive dosage, thus balancing performance and economy.

[0048] More preferably, the water-cement ratio of the ultra-high performance concrete is 0.16-0.22.

[0049] Beneficial effects: This water-cement ratio range can meet the requirements of UHPC for high density and high strength, and can also match the dispersion and activation characteristics of the activator of this invention, ensuring that the mixture has good workability.

[0050] Application of an ultra-high performance concrete in prefabricated concrete components, bridge structure reinforcement, marine engineering, or concrete used in harsh environments.

[0051] Beneficial effects: The UHPC prepared by the activator of this invention has high strength, high density and excellent durability, and is particularly suitable for prefabricated components, bridge structure reinforcement and concrete for marine or harsh environments, which can significantly extend the service life of the structure and reduce maintenance costs.

[0052] Compared with the prior art, the present invention has the following advantages and technical effects: Compared to conventional phosphogypsum-based low-carbon high-performance concrete without the activator of this invention, the activator of this invention significantly reduces the overall carbon emissions of the system because it reduces the amount of clinker and strong alkali materials used. Simultaneously, the addition of aluminum lignosulfonate improves the initial fluidity of the concrete slurry, reduces fluidity loss, decreases segregation and sedimentation differences, and significantly increases the 7-day and 28-day compressive strength, thus significantly improving the stability of both fresh and hardened properties. Furthermore, the activator provided by this invention significantly reduces concrete porosity, improves impermeability and durability, making low-carbon UHPC prepared using this activator suitable for prefabricated concrete components, ultra-high-performance bridge structure reinforcement, marine engineering structures, and concrete materials serving in harsh environments, thus broadening the application range of concrete. Detailed Implementation

[0053] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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.

[0054] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to specific embodiments.

[0055] Unless otherwise specified, all raw materials used in the embodiments of this invention were purchased through commercial channels; Industrial lignin is derived from black liquor byproducts produced during the alkaline pulping process in the paper industry. The alkali lignin is obtained through the following steps for recycling: (1) The black liquor produced during the alkali pulping process is sent to a multi-effect evaporator for evaporation and concentration to achieve a solid content of 40% by mass, thus obtaining concentrated black liquor. Under mechanical stirring, a 10% hydrochloric acid solution is slowly added dropwise to the concentrated black liquor at a rate of 5 mL per minute, while the pH value of the system is monitored in real time. The acid addition is stopped when the pH value of the system is adjusted to 2.5, and stirring is continued for 30 min to allow the alkali lignin to fully precipitate and form a lignin suspension.

[0056] (2) The above lignin suspension was filtered using a plate and frame vacuum filter at a pressure of 0.08 MPa. The filter cake was collected to obtain crude lignin precipitate. The obtained crude lignin precipitate was placed in a constant temperature water bath and washed with deionized water at 25°C using a resuspension-filtration method. The washing was repeated three times to remove residual inorganic salts and soluble impurities. The washed lignin precipitate was placed in a vacuum drying oven and dried at 80°C for 12 h to obtain a brownish-red powdered industrial alkali lignin product.

[0057] Phosphogypsum is a byproduct of the wet-process phosphoric acid industry, with a CaSO4 content of 60-90% and a water-soluble impurity content of no more than 1.5%. The cement is ordinary Portland cement PO 52.5; The mineral powder is S95 grade slag powder; The quartz sand used is a three-graded quartz sand, which is obtained by mixing quartz sand of different particle size ranges in a certain mass ratio, specifically: The first-grade quartz sand has a particle size of 0.15-0.30 mm. The second-grade quartz sand has a particle size of 0.30-0.60 mm. The third-grade quartz sand has a particle size of 0.60-1.18 mm. The above three types of quartz sand are mixed in a mass ratio of 3:4:3 to form a three-graded quartz sand. The steel fiber is a single copper-plated steel fiber with a length of 13 mm and a tensile strength ≥2500 MPa; Polycarboxylate superplasticizer is a high-performance polycarboxylate superplasticizer with a solid content of approximately 25%.

[0058] Unless otherwise specified, room temperature or normal temperature in the embodiments of the present invention refers to 25±3℃.

[0059] Example 1 An activator for low-carbon ultra-high performance concrete (UHPC) based on phosphogypsum, comprising the following raw materials by mass fraction: The composition consists of 60 wt% activated phosphogypsum, 15 wt% sodium metasilicate, 15 wt% aluminum sulfate, 7 wt% sodium sulfate, and 3 wt% aluminum lignosulfonate.

[0060] A method for preparing a low-carbon ultra-high performance concrete (UHPC) activator based on phosphogypsum includes the following steps: (1) Activation of phosphogypsum: Phosphogypsum was mixed in 45°C warm water at a solid-liquid ratio of 1:4 and stirred at 300 rpm for 15 min to dissolve water-soluble phosphates, fluorides and some soluble impurities into the aqueous phase. After standing for 10 min, the supernatant was removed by filtration to reduce the water-soluble impurity content of the phosphogypsum to no more than 1.5%. Subsequently, the washed phosphogypsum was dried at 105°C for 3 h, then crushed to no more than 10 mm and ball-milled at 300 rpm for 45 min to achieve a specific surface area of ​​350 m². 2 The surface energy and reactivity of the phosphogypsum are significantly improved by increasing the concentration of CaSO4 to above 80%, thereby obtaining activated phosphogypsum. After the above treatment, the phosphogypsum can simultaneously meet the requirements of 80% CaSO4 content, water-soluble impurities not exceeding 1.5%, and a specific surface area of ​​not less than 300 m². 2 / kg requirement.

[0061] (2) Preparation of aluminum lignin sulfonate: Industrial lignin was selected as the raw material and added to sodium sulfite. A sulfonation reaction was carried out at 70°C for 2 hours. After the reaction, the pH of the system was adjusted to 7.5, and aluminum sulfate was added to the reaction solution to adjust the pH to 4, generating an aluminum lignin sulfonate complex. The obtained product was concentrated to a solid content of 25% and dried in a spray dryer at an inlet temperature of 170°C and an outlet temperature of 85°C to obtain aluminum lignin sulfonate powder with a sulfonation degree of 80%, a solubility of not less than 30 g / L, and a pH of 4.0 when dissolved in water. The aluminum lignin sulfonate prepared by the above method has excellent dispersibility and complexing ability, and can effectively regulate the flowability and hydration kinetics of the activated system.

[0062] (3) Preparation of activator: Weigh out activated phosphogypsum, sodium metasilicate, aluminum sulfate, sodium sulfate and aluminum lignosulfonate according to the proportion, dry mix for 8 min, dry at 60℃ for 3 h, and then grind to a specific surface area ≥300 m². 2 / kg, thus obtaining the UHPC-specific activator based on phosphogypsum.

[0063] Example 2 An activator for low-carbon ultra-high performance concrete (UHPC) based on phosphogypsum, comprising the following raw materials by mass fraction: The composition consists of 70 wt% activated phosphogypsum, 10 wt% sodium metasilicate, 10 wt% aluminum sulfate, 6 wt% sodium sulfate, and 4 wt% aluminum lignosulfonate.

[0064] A method for preparing a special activator for low-carbon ultra-high performance concrete (UHPC) based on phosphogypsum, using the raw materials described in this embodiment, with the remaining process steps and parameters being the same as in Example 1.

[0065] Example 3 An activator for low-carbon ultra-high performance concrete (UHPC) based on phosphogypsum, comprising the following raw materials by mass fraction: The composition includes 80 wt% activated phosphogypsum, 5 wt% sodium metasilicate, 5 wt% aluminum sulfate, 10 wt% sodium sulfate, and 5 wt% aluminum lignosulfonate.

[0066] A method for preparing a special activator for low-carbon ultra-high performance concrete (UHPC) based on phosphogypsum, using the raw materials described in this embodiment, with the remaining process steps and parameters being the same as in Example 1.

[0067] Example 4 An activator for low-carbon ultra-high performance concrete (UHPC) based on phosphogypsum, comprising the following raw materials by mass fraction: The composition consists of 75 wt% activated phosphogypsum, 12 wt% sodium metasilicate, 12 wt% aluminum sulfate, 2 wt% sodium sulfate, and 4 wt% aluminum lignosulfonate.

[0068] A method for preparing a special activator for low-carbon ultra-high performance concrete (UHPC) based on phosphogypsum, using the raw materials described in this embodiment, with the remaining process steps and parameters being the same as in Example 1.

[0069] Comparative Example 1 An activator for low-carbon ultra-high performance concrete (UHPC) based on phosphogypsum, comprising the following raw materials by mass fraction: The composition consists of 80 wt% activated phosphogypsum, 8 wt% sodium metasilicate, 8 wt% aluminum sulfate, and 4 wt% sodium sulfate.

[0070] A method for preparing a low-carbon ultra-high performance concrete (UHPC) activator based on phosphogypsum, using the raw materials described above in this comparative example, with the remaining process steps and parameters being the same as in Example 1.

[0071] Comparative Example 2 An activator for low-carbon ultra-high performance concrete (UHPC) based on phosphogypsum, comprising the following raw materials by mass fraction: The composition consists of 75 wt% activated phosphogypsum, 10 wt% sodium metasilicate, 10 wt% aluminum sulfate, and 5 wt% sodium sulfate.

[0072] A method for preparing a low-carbon ultra-high performance concrete (UHPC) activator based on phosphogypsum, using the raw materials described above in this comparative example, with the remaining process steps and parameters being the same as in Example 1.

[0073] Comparative Example 3 An activator for low-carbon ultra-high performance concrete (UHPC) based on phosphogypsum, comprising the following raw materials by mass fraction: The composition consists of 65 wt% activated phosphogypsum, 15 wt% sodium metasilicate, 15 wt% aluminum sulfate, and 5 wt% sodium sulfate.

[0074] A method for preparing a low-carbon ultra-high performance concrete (UHPC) activator based on phosphogypsum, using the raw materials described above in this comparative example, with the remaining process steps and parameters being the same as in Example 1.

[0075] Comparative Example 4 A low-carbon ultra-high performance concrete (UHPC) activator based on phosphogypsum differs from Example 2 only in that it does not include aluminum lignosulfonate, and the mass ratio of activated phosphogypsum, sodium metasilicate, aluminum sulfate, and sodium sulfate is still 60:15:15:5.

[0076] A method for preparing a low-carbon ultra-high performance concrete (UHPC) activator based on phosphogypsum, using the raw materials described above in this comparative example, with the remaining process steps and parameters being the same as in Example 1.

[0077] Comparative Example 5 A low-carbon ultra-high performance concrete (UHPC) activator based on phosphogypsum differs from Example 2 only in that it does not include aluminum sulfate, and the mass ratio of activated phosphogypsum, sodium metasilicate, sodium sulfate and aluminum lignosulfonate is still 60:15:5:5.

[0078] A method for preparing a low-carbon ultra-high performance concrete (UHPC) activator based on phosphogypsum, using the raw materials described above in this comparative example, with the remaining process steps and parameters being the same as in Example 2.

[0079] Comparative Example 6 A low-carbon ultra-high performance concrete (UHPC) activator based on phosphogypsum differs from Example 2 only in that it does not include sodium sulfate, and the mass ratio of activated phosphogypsum, sodium metasilicate, aluminum sulfate, and aluminum lignosulfonate is still 60:15:5:5.

[0080] A method for preparing a low-carbon ultra-high performance concrete (UHPC) activator based on phosphogypsum, using the raw materials described above in this comparative example, with the remaining process steps and parameters being the same as in Example 2.

[0081] Comparative Example 7 A low-carbon ultra-high performance concrete (UHPC) activator based on phosphogypsum is different from Example 2 only in that it uses phosphogypsum raw material directly without activation treatment, while the other raw materials and addition amounts are the same as in Example 2.

[0082] A method for preparing a low-carbon ultra-high performance concrete (UHPC) activator based on phosphogypsum, using the raw materials described above in this comparative example, with the remaining process steps and parameters being the same as in Example 2.

[0083] Comparative Example 8 Using sodium hydroxide solution as an alkaline activator, specifically using caustic soda flakes as raw material, dissolving it in water and cooling it to room temperature yields a sodium hydroxide solution with a concentration of 5 wt.%.

[0084] Application Examples 1-4 A low-carbon ultra-high performance concrete, using the activators obtained in Examples 1-4, specifically includes the following raw materials by mass fraction: The composition consists of 27.50% cement, 8.00% mineral powder, 54.20% quartz sand, 1.80% phosphogypsum (unactivated phosphogypsum raw material), 0.80% steel fiber, and 6.70% water. Simultaneously, the activator obtained in Examples 1-4 and the polycarboxylate superplasticizer are added, with the activator added at 5% of the total mass of the cementitious materials (cement and mineral powder) and the polycarboxylate superplasticizer added at 1% of the total mass of the cementitious materials.

[0085] A method for preparing low-carbon ultra-high performance concrete includes the following steps: The above-mentioned cement, mineral powder, quartz sand, and phosphogypsum were dry-mixed for 2 minutes. Water, polycarboxylate superplasticizer, and activator were added and stirred for 2 minutes. Steel fibers were then added and stirred for 1 minute to obtain concrete slurry. The prepared concrete slurry was poured into molds and cured under standard conditions (temperature 20±2℃, relative humidity ≥95%) until the specified age to obtain concrete specimens.

[0086] Compare and contrast examples 1-7 The only difference from Application Example 1 is that the activator in Example 1 is replaced with the activators obtained in Comparative Examples 1-7 by equal mass, while the other raw materials, process steps and parameters are the same as in Application Example 1.

[0087] Comparative Application Example 8 A low-carbon, ultra-high-performance concrete comprises the following raw materials by mass fraction: The composition includes 27.5% cement, 8.00% mineral powder, 54.20% quartz sand, 1.80% phosphogypsum (unactivated phosphogypsum raw material), 0.80% steel fiber, 6.70% water, 0.80% sodium hydroxide solution obtained from Comparative Example 8, and 0.20% polycarboxylate superplasticizer. The cementitious material is cement and mineral powder, the amount of sodium hydroxide solution added is equivalent to 5% of the total mass of the cementitious material, and the amount of polycarboxylate superplasticizer added is 1% of the total mass of the cementitious material.

[0088] A method for preparing low-carbon ultra-high performance concrete includes the following steps: Cement, mineral powder, quartz sand, and phosphogypsum were dry-mixed for 2 minutes. Water, polycarboxylate superplasticizer, and sodium hydroxide solution were added and stirred for 2 minutes. Steel fibers were then added and stirred for 1 minute to obtain concrete slurry. The prepared concrete slurry was poured into molds and cured under standard conditions (temperature 20±2℃, relative humidity ≥95%) until the specified age to obtain concrete specimens.

[0089] Technical effects: The low-carbon ultra-high performance concrete slurries and specimens prepared in Application Examples 1-4 and Comparative Application Examples 1-8 were subjected to performance tests under standard conditions, including compressive strength, fluidity, and porosity, in order to comprehensively evaluate the activation efficiency of the activator and its impact on the performance of UHPC.

[0090] The compressive strength test was conducted according to GB / T 17671-2021 "Test Method for Strength of Cement Mortar (ISO Method)" and the commonly used mechanical property test methods of UHPC. The specific steps were as follows: the uniformly mixed concrete slurry was placed into a 40 mm × 40 mm × 40 mm cubic mold in two layers and compacted by vibration. After standing at room temperature for 24 h, the mold was removed. The specimens were then placed in a standard curing room with a temperature of 20 ± 2℃ and a relative humidity of not less than 95% and cured until the specified age. At 3 d, 7 d and 28 d, compression loading was performed using an electro-hydraulic servo pressure testing machine. The loading rate was controlled at 2.4 ± 0.2 kN / s. The average value of the test results of 3 specimens in each group was taken as the compressive strength of that group.

[0091] The fluidity test was conducted according to the slump spread test method in GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures". The slump spreader was placed in the center of a smooth glass plate. The mixed concrete slurry was filled into the conical mold of the flowability tester within 10 seconds, and the upper surface was leveled. Then, without compaction, the conical mold was lifted vertically to allow the slurry to flow freely. The initial spread diameter formed by the free flow of the slurry was recorded, and the spread diameter was recorded again after 30 minutes of settling. The fluidity loss rate was calculated based on this. By comparing the initial fluidity and the 30-minute fluidity changes of the application example with those of the control application example, the effect of the activator on the dispersibility and fluid retention capacity of the fresh mixture can be evaluated.

[0092] Porosity testing was conducted using the vacuum saturation method, according to GB / T 50082-2009 "Test Methods for Long-Term Performance and Durability of Ordinary Concrete". The specific method was as follows: 28-day-old concrete specimens were dried in an oven until their mass became constant, and their dried mass (M1) was measured. The specimens were then immersed in water and vacuum-saturated for 1 hour to ensure complete saturation of the internal pores. After removal and rapid wiping off surface moisture, the saturated mass (M2) was measured. Finally, the saturated specimens were suspended in water and their underwater mass (M3) was measured. The total porosity of the specimens was calculated using the formula P = (M2 − M1) / (M2 − M3) × 100%. Three specimens from each group were used to measure porosity, and the average value was taken as the final result. This method accurately reflects the density of the internal pore structure of UHPC, thus evaluating the effect of the activator on microstructure optimization.

[0093] The test results of compressive strength, flowability and porosity of concrete specimens obtained using Examples 1-4 and Comparative Examples 1-4 are shown in Table 1: Table 1 As shown in Table 1, the introduction of the activator of this invention significantly improves the mechanical properties and structural density of phosphogypsum-based high-performance concrete. In contrast, in Comparative Application Example 8, the limited effective dissolution of silica-alumina sources in the system due to the use of only sodium hydroxide for alkali activation resulted in insufficient early strength, significant loss of fluidity, and high internal porosity. In contrast, in Comparative Examples 1-3, with the gradual increase of sodium metasilicate, aluminum sulfate, and sodium sulfate content in the activator, the early and later compressive strengths of the concrete showed a continuous upward trend, improved fluidity, and gradually decreased porosity, indicating that the activator can effectively regulate the release of sulfate ions and the dissolution kinetics of the aluminum-silicon source, promoting the synergistic formation of C-(A)-SH gel and AFt crystals. In Comparative Application Example 4, the lack of effective organoaluminum dispersion and complexation regulation in the system due to the absence of aluminum lignosulfonate led to insufficient particle dispersion during hydration and a decrease in the uniformity of the slurry structure. As shown in Table 1, the 3-day, 7-day, and 28-day compressive strengths of Application Example 4 were 70 MPa, 92 MPa, and 140 MPa, respectively, all lower than those of Application Examples 1 and 2, which used the activator of this invention. Simultaneously, its 30-minute flowability loss reached 33%, significantly higher than the application example system, and the porosity also increased to 0.128, indicating a deterioration in both the system's density and the stability of its freshly mixed properties. Compared to other comparative examples, Example 1, due to the addition of aluminum lignosulfonate, further improved the slurry dispersibility, reduced flowability loss, and lower porosity, indicating a more uniform and dense microstructure. Example 2 achieved the highest three-year compressive strength, best flowability retention, and lowest porosity, demonstrating that the aluminum lignosulfonate in this invention can synergistically interact with other raw materials in the system, thereby significantly enhancing the overall effect of the activator and showcasing the comprehensive advantages of the activator in promoting hydration reactions, increasing early nucleation rates, and improving interfacial structure. In summary, the activator obtained by the present invention can significantly improve the strength and density of UHPC while maintaining good fluidity by reasonably controlling the types and proportions of raw materials of each component. Among them, Example 2 is the activator system with the best overall performance.

[0094] Furthermore, comparative analysis of the material composition and performance results between the corresponding use cases and comparative application examples reveals that the activator system of this invention, while ensuring a significant improvement in the mechanical properties of UHPC, effectively reduces the system's dependence on high-clinker and strong-alkali activating materials. Compared to comparative application example 8, which uses sodium hydroxide for activation, the clinker content in the system of this invention is significantly reduced, resulting in an overall reduction in carbon emissions of approximately 25-40%. The reduction in clinker content contributes approximately 15-25% to the reduction in carbon emissions, while the reduction in alkaline activating materials contributes approximately 10-15%.

[0095] Meanwhile, as shown in Table 1, the initial flowability of Application Example 1 and Application Example 2 using the activator of the present invention is significantly higher than that of the comparative application examples. The flowability loss rate at 30 min is reduced from 30-40% in the comparative application example system to no more than 22-25%, a decrease of about 30-45%, indicating that the activator of the present invention can significantly improve the flow retention performance of UHPC mixtures.

[0096] Regarding durability, the porosity of the application example system decreased from 0.140 in comparative application example 8 to no more than 0.110, a reduction of approximately 20-25%, indicating a denser internal structure. Further analysis of the impermeability and freeze-thaw durability test results shows that the UHPC prepared using the activator of this invention exhibits approximately 30-40% improved impermeability. After 100 freeze-thaw cycles, its mass loss rate decreased from 3-5% in the comparative application example system to less than 2%, demonstrating excellent long-term service stability.

[0097] In summary, the UHPC-specific activator based on phosphogypsum provided by this invention can significantly improve the mechanical properties, fresh mix stability, and durability of concrete while reducing carbon emissions, demonstrating promising prospects for engineering applications.

[0098] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A UHPC-specific activator based on phosphogypsum, characterized in that, Raw materials including the following mass fractions: Activated phosphogypsum 60-80 wt%, alkaline activating component 5-15 wt%, aluminum sulfide active component 5-15 wt%, early intensity control component 2-10 wt%, aluminum lignosulfonate 3-5 wt%.

2. The UHPC-specific activator based on phosphogypsum according to claim 1, characterized in that, The activated phosphogypsum contains 60-90 wt% CaSO4, no more than 1.5 wt% water-soluble impurities, and has a specific surface area of ​​not less than 300 m². 2 / kg.

3. The UHPC-specific activator based on phosphogypsum according to claim 1, characterized in that, The lignin sulfonate aluminum has a lignin sulfonation degree of 70%-90% and a solubility of not less than 30 g / L in water.

4. The UHPC-specific activator based on phosphogypsum according to claim 1, characterized in that, The alkaline activating component is sodium metasilicate.

5. The UHPC-specific activator based on phosphogypsum according to claim 1, characterized in that, The active component of the sulfur-aluminum mixture is aluminum sulfate.

6. The UHPC-specific activator based on phosphogypsum according to claim 1, characterized in that, The early-pressure control component is sodium sulfate.

7. A method for preparing a UHPC-specific activator based on phosphogypsum as described in any one of claims 1-6, characterized in that, After weighing the raw materials, the resulting mixture is dry-mixed, dried, and ground to obtain the UHPC-specific activator based on phosphogypsum.

8. The application of a UHPC-specific activator based on phosphogypsum as described in any one of claims 1-6 in ultra-high performance concrete.

9. A type of ultra-high performance concrete, characterized in that, Includes the UHPC-specific activator based on phosphogypsum as described in any one of claims 1-6, wherein the dosage of the UHPC-specific activator is 3-8 wt% of the mass of the cementitious material.

10. The application of the ultra-high performance concrete as described in claim 9 in prefabricated concrete components, bridge structure reinforcement, marine engineering, or concrete used in harsh environments.

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