A double-mixed concrete, a method for preparing the same and an application thereof

Abstract

This invention discloses a dual-blended concrete, its preparation method, and its application, relating to the field of concrete technology. The dual-blended concrete comprises the following components by weight: 100 parts cement, 20-35 parts slag powder, 15-35 parts limestone powder, 300-450 parts fine aggregate, 400-550 parts coarse aggregate, 60-85 parts water, and 0.8-2.0 parts polycarboxylate superplasticizer. This invention replaces fly ash with widely available and stable limestone powder, completely avoiding the influence of geographical, seasonal, and production capacity limitations on fly ash supply, ensuring the continuity of raw material supply and the stability of the mix proportion; and through a reasonable ratio of slag powder to limestone powder, the cement usage is reduced by 20%-30%; and early strength is improved, with excellent workability, making it suitable for high-performance projects requiring high-quality manufactured sand and gravel content and pumping heights ≥50 m.

Description

Technical Field

[0001] This invention relates to the field of concrete technology, and in particular to a double-blended concrete, its preparation method, and its application. Background Technology

[0002] In current concrete mix design, the use of a combination of Grade I fly ash and slag powder is often employed to partially replace cement in order to improve concrete durability and reduce costs. However, the supply of high-quality Grade I fly ash is limited by region, season, and production capacity, resulting in unstable supply and large quality fluctuations. This leads to poor continuity of raw materials for the dual-blended concrete, requiring frequent adjustments to the mix proportions and affecting the stability of project quality.

[0003] Although there have been attempts in existing technologies to use slag powder and limestone powder in combination to partially replace cement using industrial solid waste resources with stable sources, this system has not completely replaced the fly ash + slag powder combination system in actual engineering applications. This is mainly because insufficient optimization has resulted in the early strength and workability of manufactured sand with high stone powder content and high pumping requirements not reaching the ideal level, which limits its widespread application. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the present invention provides a double-blended concrete, its preparation method and application, the specific technical solution of which is as follows: A type of double-admixed concrete, by weight, comprises the following components: 100 parts cement, 20-35 parts slag powder, 15-35 parts limestone powder, 300-450 parts fine aggregate, 400-550 parts coarse aggregate, 60-85 parts water, and 0.8-2.0 parts polycarboxylate superplasticizer.

[0005] Preferably: The slag powder is of grade S95 or higher; The specific surface area of ​​the limestone powder is ≥400 m². 2 / kg, methylene blue value ≤1.2; The fine aggregate is manufactured sand with a fineness modulus of 2.6 to 3.2 and a stone powder content of 8% to 12%. The coarse aggregate is crushed stone with a continuous gradation of 5~31.5mm.

[0006] Preferably, the water-cement ratio of the dual-admixture concrete is 0.39~0.59, and the sand ratio is 42%~46%.

[0007] Preferably, it also includes a phosphogypsum-based composite modifier, the amount of which is 1% to 3% of the total mass of the cementitious material, wherein the cementitious material includes cement, slag powder and limestone powder.

[0008] Preferably, the phosphogypsum-based composite modifier is made from the following components in parts by weight: 70-80 parts phosphogypsum, 15-25 parts carbide slag, and 5-10 parts aluminum sulfate.

[0009] The present invention also provides a preparation method for preparing the dual-blended concrete as described in any one of the above claims, the preparation method comprising the following steps: S1. Dry-mix the cementitious materials and aggregates into a mixer until uniform, wherein the cementitious materials include cement, slag powder and limestone powder; S2. Add water and polycarboxylate superplasticizer, mix thoroughly with wet mix to obtain the double-blended concrete.

[0010] Preferably, the dry mixing time is 30-60 seconds, and the wet mixing time is 90-150 seconds.

[0011] Preferably, the cementitious material further includes a phosphogypsum-based composite modifier, which is prepared by the following steps: S01. Dry and pulverize phosphogypsum until the residue on a 0.08 mm square hole sieve is ≤10%, air dry and pulverize carbide slag, and mix it evenly with aluminum sulfate, then add water and stir to form a slurry; S02. Seal and age for 3-7 days; S03. Dry and pulverize until the residue on a 0.08 mm square hole sieve is ≤5%.

[0012] Preferably: In step S01, the water-to-solid ratio of the slurry is 0.3 to 0.4; In step S02, the pH after sealing and aging is 8.5~10.0.

[0013] The present invention also provides an application of double-blended concrete as described in any of the above claims, for pouring concrete for highway bridge piers, tunnel linings, culverts, or site hardening.

[0014] The dual-admixture concrete provided by this invention has the following beneficial effects: 1. Replacing fly ash with widely available and stable limestone powder completely avoids the impact of fly ash supply being affected by regional, seasonal, and production capacity limitations, ensuring the continuity of raw material supply and the stability of mix proportions; 2. By using a reasonable ratio of slag powder to limestone powder, the amount of cement used can be reduced by 20% to 30%; 3. Improved early strength and excellent workability, suitable for high-performance projects with high content of manufactured sand and gravel powder and pumping height ≥50 m. Detailed Implementation

[0015] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below. The description in this part is only exemplary and explanatory, and should not be used to limit the scope of protection of the present invention in any way.

[0016] This embodiment provides a double-admixture concrete, which, by weight, comprises the following components: 100 parts cement, 20-35 parts slag powder, 15-35 parts limestone powder, 300-450 parts fine aggregate, 400-550 parts coarse aggregate, 60-85 parts water, and 0.8-2.0 parts polycarboxylate superplasticizer.

[0017] Among them, limestone powder provides a micro-aggregate filling effect, filling the gaps between cement particles and improving the density of the mixture; at the same time, it plays a crystal nucleation effect, providing additional nucleation sites for cement hydration products and accelerating C3S hydration; in addition, the calcium carbonate in limestone powder reacts with the aluminum phase in cement to form aluminocarbonate, which further promotes the early hydration reaction, thereby significantly improving the early strength of concrete and making up for the defect of slow early hydration when traditional slag powder is used alone or improperly double-admixed.

[0018] Slag powder mainly plays a role in pozzolanic activity during the later stage of hydration. It reacts with Ca(OH)2 produced by cement hydration to generate additional CSH gel, contributing to the later strength increase and durability improvement (such as resistance to chloride ion penetration and carbonation).

[0019] Within a given range of total cementitious material content and water-cement ratio, the mass ratio of slag powder to limestone powder falls within a broad synergistic range of approximately 1:(0.43~1.75), achieving a balance between early-stage (limestone powder dominant) and later-stage (slag powder dominant) performance through mutual complementarity. Simultaneously, the micro-filling effect of limestone powder buffers the influence of aggregate powder in both fine and coarse aggregate systems. Combined with the dispersing effect of polycarboxylate superplasticizer, this ensures stable workability and minimal slump loss in the mixture, meeting high pumpability requirements.

[0020] The dual-admixture concrete provided in this embodiment has the following beneficial effects: 1. Replacing fly ash with widely available and stable limestone powder completely avoids the impact of fly ash supply being affected by regional, seasonal, and production capacity limitations, ensuring the continuity of raw material supply and the stability of mix proportions; 2. By using a reasonable ratio of slag powder to limestone powder, the amount of cement used can be reduced by 20% to 30%; 3. Improved early strength and excellent workability, suitable for high-performance projects with high content of manufactured sand and gravel powder and pumping height ≥50 m.

[0021] Furthermore: The slag powder is grade S95 or higher.

[0022] Limestone powder with a specific surface area ≥ 400 m²2 / kg, methylene blue value ≤1.2.

[0023] The fine aggregate is manufactured sand with a fineness modulus of 2.6 to 3.2 and a stone powder content of 8% to 12%.

[0024] The coarse aggregate is crushed stone with a continuous gradation of 5~31.5mm.

[0025] Specifically, high-grade slag powder has a high glass content and excellent activity index, ensuring efficient secondary hydration reaction in an alkaline environment, generating more CSH gel, which stably contributes to later strength and durability, avoiding performance fluctuations caused by insufficient activity of low-grade slag powder.

[0026] The high specific surface area of ​​limestone powder enhances the filling effect and nucleation effect of micro-aggregates, accelerating the early hydration of cement; the low methylene blue value indicates fewer clay impurities, avoiding the adsorption of water-reducing agents or interference with hydration by expansive minerals such as montmorillonite, thereby ensuring the efficiency of limestone powder in forming aluminate carbonates with the aluminum phase, improving early strength and maintaining the dispersion effect of polycarboxylate water-reducing agents.

[0027] Fine aggregate (manufactured sand) fineness modulus 2.6~3.2, stone powder content 8%~12%. Within this range, the stone powder content of manufactured sand is moderate. It works synergistically with externally added limestone powder to play a micro-filling role, optimize the particle size distribution curve, reduce porosity, improve the cohesiveness and water retention of the mixture, buffer the negative impact that high stone powder content may bring (such as excessive thickening), and ensure stable workability.

[0028] The continuous gradation of coarse aggregate forms a good skeleton, reduces the need for slurry, improves the overall density and strength of concrete, and at the same time reduces pumping resistance and improves construction performance in high-pumping scenarios.

[0029] Furthermore, the water-cement ratio of the double-admixed concrete is 0.39~0.59, and the sand ratio is 42%~46%.

[0030] Furthermore, it also includes a phosphogypsum-based composite modifier, which is added at 1% to 3% of the total mass of the cementitious materials, including cement, slag powder and limestone powder.

[0031] Among them, the phosphogypsum-based composite modifier forms a slow-release calcium sulfoaluminate system through pretreatment and aging. It slowly releases sulfate and aluminate ions in the early hydration stage of concrete, which react with Ca(OH)2 and aluminum phase generated by cement hydration to generate ettringite and monosulfide-type hydrated calcium sulfoaluminate, providing additional early strength contribution.

[0032] The alkaline component in the modifier (from carbide slag) neutralizes the residual acidity of phosphogypsum and improves the pH stability of the slurry; at the same time, the aging process consumes free acid, avoiding adsorption interference with the polycarboxylate superplasticizer, ensuring efficient dispersion of the superplasticizer and reducing slump loss.

[0033] Low dosage and aging treatment control the formation rate of ettringite and avoid the risk of delayed expansion; the modifier complements the carbon aluminate reaction of limestone powder and the secondary hydration of slag powder, further optimizing the structure of hydration products and improving density and durability.

[0034] Specifically, "phosphogypsum-based composite modifier" refers to a concrete admixture modified material made primarily from phosphogypsum (a solid waste generated during phosphoric acid production, mainly composed of CaSO4·2H4O, containing a small amount of impurity acid), a byproduct of industrial production, combined with an alkaline activator (carbide slag, providing Ca(OH)2) and a sulfoaluminate formation promoter (aluminum sulfate), through specific pretreatment. This modifier is a solid waste resource utilization type activator that enhances the activity of phosphogypsum through chemical modification, avoiding the acid interference or expansion risks that may result from its direct addition.

[0035] The preferred dosage of the modifier is 2% (as a percentage of the total mass of the cementitious materials), which is then dry-mixed with other cementitious materials (cement, slag powder, limestone powder). At this point, the total amount of cementitious materials is adjusted to 130-165 parts, and the amount of cement can be reduced by 5-10 parts to maintain a balanced water-cement ratio and strength.

[0036] Furthermore, the phosphogypsum-based composite modifier is made from the following components in parts by weight: 70-80 parts phosphogypsum, 15-25 parts carbide slag, and 5-10 parts aluminum sulfate.

[0037] Among them, phosphogypsum provides the main source of sulfate, forming the core component of ettringite, and its high proportion ensures sufficient early expansion compensation and strength contribution.

[0038] Carbide slag provides an alkaline environment (Ca(OH)2), which neutralizes the residual acid in phosphogypsum, increases the pH of the slurry, promotes the dissolution of aluminum sulfate and the formation of a slow-release system, and stimulates potential activity.

[0039] Aluminum sulfate supplements the active aluminum source, accelerates the formation of calcium sulfoaluminate, controls the reaction rate, and prevents excessive expansion.

[0040] This embodiment also provides a preparation method for preparing the dual-blended concrete as described in any one of the above embodiments, the preparation method comprising the following steps: S1. Dry mix the cementitious materials and aggregates in a mixer until uniform, wherein the cementitious materials include cement, slag powder and limestone powder.

[0041] S2. Add water and polycarboxylate superplasticizer, mix thoroughly with wet mix to obtain double-blended concrete.

[0042] In the dry mixing step (S1), the cementitious materials (cement, slag powder, limestone powder, and optionally phosphogypsum-based composite modifier) ​​and aggregates are dry mixed evenly. Mechanical shearing force is used to fully disperse the powder particles, reduce agglomeration, and ensure that the components are in uniform contact during subsequent hydration, thus avoiding strength fluctuations or poor workability caused by uneven water-cement ratios in some areas.

[0043] In the wet mixing step (S2), water and polycarboxylate superplasticizer are added and then wet-mixed. The three-dimensional dispersion effect of the superplasticizer releases the encapsulated water, improves the fluidity of the slurry, and activates the early hydration of cement and the synergistic effect of slag powder / limestone powder, ensuring that the mixture quickly reaches a uniform state.

[0044] Furthermore, the dry mixing time is 30-60 seconds, and the wet mixing time is 90-150 seconds.

[0045] Furthermore, the cementitious material also includes a phosphogypsum-based composite modifier, which is prepared through the following steps: S01. Dry and pulverize phosphogypsum until the residue on a 0.08 mm square hole sieve is ≤10%, air dry and pulverize carbide slag, and mix it evenly with aluminum sulfate, then add water and stir to form a slurry.

[0046] S02. Seal and age for 3-7 days.

[0047] S03. Dry and pulverize until the residue on a 0.08 mm square hole sieve is ≤5%.

[0048] Specifically, the phosphogypsum can be pre-treated and dried at 105℃ to constant weight, while the carbide slag can be naturally air-dried; after dry mixing, water is added to form a flowing slurry (with moderate consistency); aged in a sealed container at room temperature; and then pulverized by ball milling or Raymond milling after drying.

[0049] Furthermore: In step S01, the water-to-solid ratio of the slurry is 0.3 to 0.4.

[0050] In step S02, the pH after sealing and aging is 8.5~10.0.

[0051] This embodiment also provides an application of double-blended concrete as described in any of the above, for pouring concrete for highway bridge piers, tunnel linings, culverts, or site hardening.

[0052] Specific embodiments are provided below. These embodiments are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way.

[0053] Step 1: Raw Material Preparation Cement: Ordinary Portland cement P·O 42.5; Slag powder: S95 grade slag powder; Limestone powder: Methylene blue value 0.8; Fine aggregate: Manufactured sand, fineness modulus 2.78, stone powder content 9.6%; Coarse aggregate: Crushed stone, continuously graded 5~31.5mm; Water: Tap water; Polycarboxylate superplasticizer: solid content 30%.

[0054] All raw materials were placed in a laboratory environment (20~25℃, relative humidity 50%~60%) for 24 hours before the test to ensure that the temperature was uniform.

[0055] Step 2: Mix Design Cement: 320 kg; Slag powder: 74 kg; Limestone powder: 96 kg; Manufactured sand: 780 kg; Crushed stone: 910 kg; Water: 175 kg; Polycarboxylate superplasticizer: 4.8 kg.

[0056] Step 3: Concrete Mixing Cement, slag powder, limestone powder, manufactured sand and crushed stone are added into the mixer in sequence. The mixing speed is set to 35 r / min and dry-mixed for 45 s to ensure that the cementitious materials and aggregates are evenly mixed.

[0057] After pre-mixing the measured water with the polycarboxylate superplasticizer, add the mixture to the mixer in two batches, adjust the stirring speed to 45 r / min, and continue stirring for 120 s.

[0058] After mixing, the mixture is in a uniform plastic state with no obvious segregation or bleeding, and the outlet temperature is 22.6℃.

[0059] Step 4: Performance Testing of the Mixture According to GB / T 50080-2016, the slump and loss over time of the mixture were tested.

[0060] The test environment was 25 ℃ and 50% relative humidity.

[0061] The slump at the outlet was 198 mm; The slump was 187 mm after standing for 30 minutes. The slump was 176 mm after standing for 60 minutes. The slump was 158 mm after standing for 120 minutes.

[0062] Step 5: Specimen Molding and Curing Prepare 100 mm × 100 mm × 100 mm cubic compression test specimens according to GB / T 50081-2019.

[0063] After molding, the specimens were left to stand at room temperature for 24 hours before demolding. After demolding, place the product in a standard curing chamber for curing under the following conditions: temperature 20±1℃ and relative humidity ≥95%.

[0064] Step Six: Compressive Strength Test The compressive strength of the concrete specimens was tested at 7 days and 28 days using a pressure testing machine.

[0065] The test data are shown in Tables 1-1 and 1-2 below: Example 2

[0066] Step 1: Raw Material Preparation The raw materials used were the same as those in Example 1, and the samples were left to stand for 24 hours in a laboratory environment (20~25℃, relative humidity 50%~60%) before the test.

[0067] Step 2: Mix Design Cement: 340 kg; Slag powder: 78 kg; Limestone powder: 92 kg; Manufactured sand: 740 kg; Crushed stone: 930 kg; Water: 168 kg; Polycarboxylate superplasticizer: 5.1 kg.

[0068] Step 3: Concrete Mixing During the dry mixing stage, the rotation speed was 35 r / min and the time was 50 s.

[0069] During the wet mixing stage, the rotation speed was 45 r / min and the time was 130 s.

[0070] After mixing, the concrete mixture is uniform and dense, and the outlet temperature is 23.1℃.

[0071] Step 4: Performance Testing of the Mixture Tests were conducted according to GB / T 50080-2016: Slump at discharge: 186 mm; Slump after 30 minutes: 176 mm; Slump after 60 minutes: 164 mm; Slump after 120 min: 148 mm.

[0072] The mixture showed no obvious bleeding or segregation and exhibited good pumpability.

[0073] Step 5: Specimen Molding and Curing A 100 mm × 100 mm × 100 mm cubic specimen was used, and the standard curing conditions were the same as in Example 1.

[0074] Step Six: Compressive Strength Test The testing method is the same as in Example 1, and the test data are shown in Tables 2-1 and 2-2 below: Example 3

[0075] Step 1: Preparation of phosphogypsum-based composite modifier 1. Weighing raw materials Phosphogypsum: 15.0 kg; carbide slag: 4.0 kg; aluminum sulfate: 1.0 kg.

[0076] 2. Pulping and Mixing Add the above raw materials to a planetary mixer, add 7.0 kg of water, and mix for 20 minutes to form a uniform slurry.

[0077] 3. Aging treatment The slurry was sealed and left to stand for 5 days at an ambient temperature of 20-25℃.

[0078] The pH value of the slurry was measured to be 9.1 after aging.

[0079] 4. Drying and pulverizing The aged slurry was dried in an oven at 105℃ for 12 hours, then pulverized and passed through a 0.08 mm square hole sieve with a residue of ≤5%, to obtain phosphogypsum-based composite modifier powder.

[0080] Step 2: Raw Material Preparation The cement, slag powder, limestone powder, manufactured sand, crushed stone, water, and polycarboxylate superplasticizer are the same as in Example 1.

[0081] Step 3: Mix Design Cement: 300 kg; Slag powder: 80 kg; Limestone powder: 95 kg; Phosphogypsum-based composite modifier: 9.5 kg; Manufactured sand: 760 kg; Crushed stone: 915 kg; Water: 170 kg; Polycarboxylate superplasticizer: 4.9 kg.

[0082] Step 4: Concrete Mixing The phosphogypsum-based composite modifier is dry-mixed with cement, slag powder, and limestone powder in a mixer.

[0083] Dry mixing time: 60 s; Wet mixing time: 130 s; Exit temperature: 22.8℃.

[0084] Step 5: Performance Testing of the Mixture Tests were conducted according to GB / T 50080-2016: Slump at discharge: 202 mm; Slump after 60 minutes: 188 mm; Slump after 120 min: 172 mm.

[0085] Step 5: Specimen Molding and Curing A 100 mm × 100 mm × 100 mm cubic specimen was used, and the standard curing conditions were the same as in Example 1.

[0086] Step Six: Compressive Strength Test The test method is the same as in Example 1, and the test data are shown in Tables 3-1 and 3-2 below: Comparative Example 1 Step 1: Raw Material Preparation Cement: P·O 42.5; Fly ash: Grade II fly ash, loss on ignition 4.2%; Slag powder: Grade S95; Other raw materials are the same as in Example 1.

[0087] Step 2: Mix Design Cement: 320 kg; Fly ash: 85 kg; Slag powder: 35 kg; Manufactured sand: 760 kg; Crushed stone: 920 kg; Water: 175 kg; Polycarboxylate superplasticizer: 4.5 kg.

[0088] Step 3: Mixing and Testing The mixing and testing methods are the same as in Example 1.

[0089] Slump at discharge: 190 mm; Slump after 120 min: 138 mm.

[0090] Step 4: Specimen Molding and Curing The standard maintenance conditions are the same as in Example 1.

[0091] Step 5: Compressive Strength Test The testing method is the same as in Example 1, and the test data are shown in Tables 4-1 and 4-2 below. The data above shows that: The average 7-day compressive strength of Example 1 was approximately 28.9 MPa, significantly higher than the common early strength levels in traditional slag powder-only or fly ash systems. This indicates that limestone powder promotes early cement hydration through micro-filling and nucleation effects within the system. Its 28-day compressive strength reached approximately 46.0 MPa, demonstrating that the potential hydration reaction of the slag powder was fully utilized, and the dual-blending system can balance early and later strength development. With a manufactured sand powder content close to 10%, the concrete slump at the mixer was close to 200 mm, and the slump loss within 2 hours was minimal, with no significant bleeding or segregation. This indicates that the dual-blending system has good adaptability to high manufactured sand powder content.

[0092] Example 2, based on Example 1, prepared a higher-strength-grade dual-blended concrete by increasing the total amount of cementitious materials and appropriately reducing the water-cement ratio. Experimental results showed that the average 7-day compressive strength exceeded 32 MPa; the 28-day compressive strength stabilized at approximately 48.7 MPa; and the slump and its retention performance remained at a high level. These results indicate that the slag powder-limestone powder dual-blended system is not only suitable for medium-strength concrete but also exhibits good adjustability and engineering adaptability under higher strength conditions, meeting the performance requirements of construction scenarios such as high pumping speeds and high piers.

[0093] Example 3 further introduced a phosphogypsum-based composite modifier into the dual-blending system and tested the concrete performance under reduced cement dosage. Compared with Example 1, Example 3 showed the following significant changes: the average 7-day compressive strength of Example 3 was approximately 36.0 MPa, an increase of about 25% compared to Example 1, indicating that the phosphogypsum-based composite modifier can effectively construct an early sulfoaluminate reaction environment in the system, accelerating the early hydration of cement and slag powder. Even with reduced cement dosage, its 28-day compressive strength still increased to approximately 50.5 MPa, indicating that the modifier does not adversely affect later strength and has a good synergistic effect with the slag powder-limestone powder system. The slump loss of Example 3 within 120 minutes was significantly less than that of Example 1, indicating that the introduction of the modifier helps improve the rheological stability of the system, making it suitable for long-distance or high-altitude pumping construction.

[0094] A comparative system using a traditional fly ash and slag powder blend as a control was used. The test results showed that the average 7-day compressive strength was approximately 22.0 MPa, significantly lower than that of Examples 1 and 3; the 28-day compressive strength was approximately 42.2 MPa, indicating a generally low strength level; the slump decreased significantly over time, and the fluidity decreased noticeably after 2 hours. Furthermore, this system was highly sensitive to fluctuations in fly ash quality, exhibiting poor raw material stability and continuity.

[0095] The comparison shows that the present invention uses slag powder and limestone powder to replace fly ash, which not only avoids the adverse effects of fly ash supply and quality fluctuations, but also shows better comprehensive performance in terms of early strength, later strength and construction performance.

[0096] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be within the scope of protection of the present invention.

Claims

1. A double blended concrete, characterized in that, The product is made from the following components by weight: 100 parts cement, 20-35 parts slag powder, 15-35 parts limestone powder, 300-450 parts fine aggregate, 400-550 parts coarse aggregate, 60-85 parts water, and 0.8-2.0 parts polycarboxylate superplasticizer.

2. The double-blended concrete according to claim 1, characterized in that: The slag powder is of grade S95 or higher; The specific surface area of the limestone powder is > 400 m 2 / kg, methylene blue value < 1.2; The fine aggregate is manufactured sand with a fineness modulus of 2.6 to 3.2 and a stone powder content of 8% to 12%. The coarse aggregate is crushed stone with a continuous gradation of 5~31.5mm.

3. The dual-blended concrete of claim 1, wherein, The water-cement ratio of the double-admixed concrete is 0.39~0.59, and the sand ratio is 42%~46%.

4. The dual-blended concrete according to any one of claims 1 to 3, wherein It also includes a phosphogypsum-based composite modifier, which is added at 1% to 3% of the total mass of the cementitious materials, including cement, slag powder and limestone powder.

5. The dual-blended concrete of claim 4, wherein, The phosphogypsum-based composite modifier is made from the following components in parts by weight: 70-80 parts phosphogypsum, 15-25 parts carbide slag, and 5-10 parts aluminum sulfate.

6. A method of manufacture characterized by, The method for preparing the dual-blended concrete as described in any one of claims 1 to 5 comprises the following steps: S1. Dry-mix the cementitious materials and aggregates into a mixer until uniform, wherein the cementitious materials include cement, slag powder and limestone powder; S2. Add water and polycarboxylate superplasticizer, mix thoroughly with wet mix to obtain the double-blended concrete.

7. The preparation method according to claim 6, characterized in that, Dry mixing time is 30~60s, and wet mixing time is 90~150s.

8. The preparation method according to claim 6, characterized in that, The cementitious material also includes a phosphogypsum-based composite modifier, which is prepared through the following steps: S01. Dry and pulverize phosphogypsum until the residue on a 0.08 mm square hole sieve is ≤10%, air dry and pulverize carbide slag, and mix it evenly with aluminum sulfate, then add water and stir to form a slurry; S02. Seal and age for 3-7 days; S03. Dry and pulverize until the residue on a 0.08 mm square hole sieve is ≤5%.

9. The preparation method according to claim 8, characterized in that: In step S01, the water-to-solid ratio of the slurry is 0.3 to 0.4; In step S02, the pH after sealing and aging is 8.5~10.

0.

10. An application of the dual-admixture concrete as described in any one of claims 1 to 5, characterized in that, Used for pouring concrete for highway bridge piers, tunnel linings, culverts, or site hardening.

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