Green low-carbon c30 self-compacting concrete using dry-mixed mortar tail powder and preparation method thereof

Abstract

The present application relates to the technical field of concrete materials, and particularly relates to a kind of green low-carbon C30 self-compacting concrete using dry-mixed mortar tail powder and a preparation method thereof, comprising the following steps: S1, pre-slurry: dry-mixed mortar tail powder is screened to obtain pre-slurry; S2, composite cementitious material preparation; S3, self-compacting concrete preparation.The present application classifies pre-slurry by fine screening of dry-mixed mortar tail powder according to particle size, separates superfine powder, and densifies the composite cementitious material by mixing cement, fly ash and other components, to further mix the components uniformly, effectively solves the performance decline or instability problem caused by tail powder, and obtains C30 self-compacting concrete with excellent comprehensive performance.

Description

Technical Field

[0001] This invention relates to the field of concrete materials technology, specifically to a green, low-carbon C30 self-compacting concrete using dry-mixed mortar tailings and its preparation method. Background Technology

[0002] Dry-mixed mortar tailings, as an industrial byproduct, lead to significant instability in the performance of high-strength concrete when used in its preparation. A large part of this instability stems from the fact that ultrafine powder (typically particles smaller than 200 mesh) often constitutes around 40% of the dry-mixed mortar tailings by weight. This portion readily absorbs moisture and clumps, making it difficult to disperse during concrete mixing. It creates localized weak points and traps large amounts of free water, significantly impacting the homogeneity and final strength development of the concrete. More problematic is that these ultrafine particles possess a large specific surface area, unpredictably adsorbing high-efficiency water-reducing agents and other chemical admixtures, leading to agent inactivation, accelerated loss of concrete fluidity, and even abnormal setting. Given its high proportion, simply sieving it out would drastically reduce the economic viability of using dry-mixed mortar tailings in concrete preparation. Furthermore, the halogen salts that may be present in dry-mixed mortar tailings pose long-term durability risks such as erosion and alkali-aggregate reactions, severely restricting the workability, mechanical properties, and long-term durability of the concrete.

[0003] There are few existing technologies for applying dry-mixed mortar tailings to C30 self-compacting concrete. A related technology is CN 103936369A, which discloses a C30 grade single-particle recycled self-compacting concrete. The self-compacting concrete is characterized by its raw material components being cement, recycled coarse aggregate, natural coarse aggregate, fine aggregate, water, additional water, fly ash, and admixtures, with a water-cement ratio of 0.37. The raw material components, calculated by weight fraction, are: cement 1 part by weight; recycled coarse aggregate 0.70–1.53 parts by weight; natural coarse aggregate 0.66–1.64 parts by weight; fine aggregate 1.90 parts by weight; water 0.47 parts by weight; additional water 0.04–0.08 parts by weight; fly ash 0.26 parts by weight; and admixtures 0.006–0.007 parts by weight. The recycled self-compacting concrete meets relevant requirements for fluidity, filling properties, segregation resistance, time loss, and strength. It facilitates construction while reducing concrete production costs. Simultaneously, it addresses the issue of construction waste disposal, alleviating resource depletion pressures. It is environmentally friendly, has a simple preparation method, and is suitable for industrial production. CN107352906A provides a C30 grade steel slag sand self-compacting concrete with a water-cement ratio controlled between 0.3 and 0.7. The raw material components, calculated by weight fraction, include: 2-10 parts by weight of steel slag sand; 2-10 parts by weight of glass microspheres; 2-10 parts by weight of cement; 5-7 parts by weight of natural coarse aggregate; 2-5 parts by weight of recycled coarse aggregate; 2-10 parts by weight of sand; 1.3-1.7 parts by weight of fly ash; and 2-10 parts by weight of water. The resulting self-compacting concrete exhibits good fluidity, gap-passing ability, and segregation resistance, meeting strength requirements. It facilitates construction while reducing concrete production costs, has a simple preparation method, and is suitable for industrial production. CN116425487A discloses a C30 self-compacting concrete and its preparation method, relating to the field of concrete materials. The self-compacting concrete includes raw material cement, mineral admixtures, fine aggregate, coarse aggregate, water-reducing agent, modified fibers, and water. The modified fibers comprise, from the inside out, a fiber layer, an alkali-resistant polyurethane adhesive layer, a water-absorbing and expanding layer, and a sodium polyacrylate protective layer. The water-absorbing and expanding layer is made of inorganic water-absorbing mineral material, and the length of the modified fibers is 3-5 μm. The above technologies all propose improvements for different aggregates or powders, but have not encountered the problems associated with tailings in dry-mixed mortar. Summary of the Invention

[0004] To address the above problems, the present invention provides...

[0005] Specifically, it is a method for preparing green, low-carbon C30 self-compacting concrete using dry-mixed mortar tailings, comprising the following steps: S1, Precast slurry: The tailings of the dry-mixed mortar are sieved: Sieve out ultrafine powders below 200 mesh, powders of 150-200 mesh, powders of 80-150 mesh, and powders of 20-80 mesh; Based on a total weight of 100%, prepare graded tail powder, in which the proportion of 150-200 mesh particle size powder is 20%-30%, the proportion of 80-150 mesh particle size powder is controlled to be 50%-60%, and the remainder is 20-80 mesh particle size powder. The graded tailings powder is mixed with water at a mass ratio of 1:3-5, stirred and allowed to stand, and then dehydrated to obtain a pre-made slurry with a water content of 40-50%. S2. Preparation of composite cementitious material: By mass, 100 parts of ultrafine powder, 300-500 parts of cement, 100-200 parts of fly ash, 5-15 parts of expanding agent and 1-5 parts of viscosity modifier are mixed and densified to obtain composite cementitious material. S3. Concrete preparation: Under mixing conditions, add 100-110 parts of composite cementitious material, 100-110 parts of pre-wetted coarse sand, and 180-200 parts of pre-wetted coarse aggregate to 100 parts of precast grout by weight. At the same time, add 0.5%-1.5% of water-reducing agent and 0.01%-0.05% of air-entraining agent by weight of composite cementitious material, and add 0-5 parts of mixing water. Continue mixing until the mixture is uniform to obtain green low-carbon C30 self-compacting concrete.

[0006] In the S1 precast slurry stage, this scheme avoids the risks of directly using ultrafine powders through sieving and gradation reconstruction. Ultrafine powders smaller than 200 mesh are first sieved out to separate them from the immediate reaction slurry system, preventing them from instantly adsorbing large amounts of free water and water-reducing agents due to their high specific surface area during mixing, thus avoiding workability loss and homogeneity degradation over time. Subsequently, coarser-grained powders (20-200 mesh) are used to prepare gradation tailings, which are then mixed with a large amount of water (1:3-5) and dehydrated. This process is essentially prehydration and granulation, allowing the easily hygroscopic fine particles to absorb water and become saturated under controlled conditions, forming a precast slurry with stable moisture content. This effectively seals their water-absorbing capacity, preventing them from fiercely competing for water during final concrete synthesis, thereby ensuring workability stability. In the S2 composite cementitious material preparation stage, the separated ultrafine powders are reintroduced, but in a fundamentally different way: they are pre-mixed and densified with cement, fly ash, and viscosity modifiers. This step aims to fully utilize the dry-mixed mortar tailings and, through densification, agglomerate the tailings, ensuring thorough contact with cement, fly ash, and other materials. Furthermore, this dense mixture, acting as a unified slow-release unit, slows down the contact rate between ultrafine powder and free water, preventing localized concentrated hydration. If the cementitious material is not densified, uneven dispersion of ultrafine powder will exacerbate the risk of concrete shrinkage and cracking. Pre-wetting of coarse sand and coarse aggregate is a routine operation. During the S3 concrete synthesis stage, the pre-prepared mortar (serving as a stable fine aggregate and water source), pre-wetted coarse sand and coarse aggregate (to prevent them from competing for water), and pretreated composite cementitious material are mixed sequentially. This effectively prevents the dry microparticles within the graded tailings from causing localized bleeding and clumping during concrete mixing, thus avoiding weak areas of strength.

[0007] Preferably, the particle size of the dry-mixed mortar tailings is ≤800μm.

[0008] Preferably, the process of stirring and settling followed by dehydration is as follows: stirring for 5-15 minutes at a speed of 100-300 rpm, followed by settling for 20-40 minutes, and dehydration to obtain a pre-made slurry with a water content of 40-50%.

[0009] The dehydration process can also remove most of the harmful substances such as soluble halogen salts.

[0010] Preferably, in S2, the densification process involves grinding using a dry ball mill to obtain a loose bulk density of 1.8-2.1 g / cm³. 3 Composite cementitious material.

[0011] Loose bulk density is an indicator for evaluating the densifying effect of composite cementitious materials. Typically, the loose bulk density of cement is between 1.2 and 1.6 g / cm³. 3 If the loose density of the composite cementitious material is less than 1.8 g / cm³ 3This indicates that the densification effect is only average, and there may be problems such as uneven mixing and unaggregated ultrafine powders. However, generally speaking, the loose density after densification is unlikely to exceed 2.1 g / cm³. 3 .

[0012] Preferably, in S2, the viscosity modifier is a cellulose ether or a warming agent; the swelling agent is a calcium sulfoaluminate-based swelling agent.

[0013] Preferably, in S2, the cement is PO 42.5 ordinary Portland cement; and the fly ash is Grade I fly ash.

[0014] Preferably, in S3, the stirring speed of the stirring conditions is 30-70 rpm.

[0015] Preferably, in S3, the water-reducing agent is a polycarboxylate-based high-performance agent; the air-entraining agent is a rosin resin-based air-entraining agent or a saponin-based air-entraining agent.

[0016] The anchoring groups of polycarboxylate superplasticizer molecules are specifically adsorbed onto the surface of cement, fly ash, and ultrafine tailings particles through electrostatic forces. The extended polyether side chains generate a strong steric hindrance effect in water, pushing away the flocculated particle clusters, thereby achieving dispersion, releasing free water, reducing viscosity, and improving fluidity. The viscosity modifier forms a large number of hydrogen bonds with water molecules through hydroxyl and other groups on the molecular chain, and they entangle with each other to form a continuous three-dimensional hydration network structure in the entire solution phase, which slows down the kinetics of the diffusion and adsorption of subsequently added polycarboxylate superplasticizer molecules to the particle surface.

[0017] Preferably, in S3, the coarse aggregate is continuously graded crushed stone with a particle size of 5-16mm, the content of needle-like and flaky particles is not greater than 8%, and the crushing index is not greater than 12%; the coarse sand is river sand with a fineness modulus of 3.3-3.7.

[0018] This solution also proposes a green, low-carbon C30 self-compacting concrete prepared by the above-mentioned method using dry-mixed mortar tail powder.

[0019] Compared with the prior art, the present invention has the following advantages: 1. In terms of component design, this invention improves the aggregate gradation by finely separating and directionally utilizing the tailings powder of dry-mixed mortar according to particle size, and by introducing coarse sand and aggregates. At the same time, it achieves the preparation of high-performance C30 concrete through the coordinated action of functional auxiliary materials such as expansion agents, water-reducing agents, and air-entraining agents.

[0020] 2. This invention achieves a clump-breaking effect by separating ultrafine powder from dry-mixed mortar tailings and densifying it with cement and other components. Simultaneously, it redistributes the remaining particle sizes of the dry-mixed mortar tailings to obtain more stable tailings. During the preparation of the precast slurry, the water content is controlled, and then the remaining components are added. Under stirring, all components are thoroughly and uniformly mixed, ultimately producing green, low-carbon C30 self-compacting concrete. Detailed Implementation

[0021] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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.

[0022] In the embodiments and comparative examples of this invention: The particle size of dry-mixed mortar tailings is ≤800μm; The expanding agent is calcium sulfoaluminate; The viscosity modifier is cellulose ether or warm roller gum; The stress reliever is sodium saccharin; The cement is PO 42.5 ordinary Portland cement; The fly ash is classified as Class I fly ash. The water-reducing agent is a high-performance polycarboxylate-based agent; The air-entraining agent is a rosin resin-based air-entraining agent or a saponin-based air-entraining agent; Pre-wet the coarse sand and coarse aggregate separately with 2% water by weight; The coarse aggregate is continuously graded crushed stone with a particle size of 5-16mm, and its needle-like and flaky particle content is 7.5%, and its crushing index is 11.2%; the coarse sand is river sand with a fineness modulus of 3.5.

[0023] Example 1 A method for preparing green, low-carbon C30 self-compacting concrete using dry-mixed mortar tailings includes the following steps: S1, Precast slurry: The tailings of the dry-mixed mortar are sieved: Sieve out ultrafine powders below 200 mesh, powders of 150-200 mesh, powders of 80-150 mesh, and powders of 20-80 mesh; Based on a total weight of 100%, the graded tail powder is prepared, of which 25% is 150-200 mesh particle size powder, 55% is 80-150 mesh particle size powder, and the remainder is 20-80 mesh particle size powder. The graded tailings powder was mixed with water at a mass ratio of 1:4, stirred for 10 minutes at a speed of 200 rpm, and then allowed to stand and settle for 30 minutes. After dehydration, a pre-made slurry with a water content of 45% was obtained. S2. Preparation of composite cementitious material: By weight, 100 parts of ultrafine powder, 400 parts of cement, 150 parts of fly ash, 10 parts of expanding agent, and 3 parts of cellulose ether are mixed and compacted. The mixture is then ground using a dry ball mill to obtain a loose density of 1.95 g / cm³. 3 Composite cementitious materials; S3. Concrete preparation: Under a mixing condition of 50 rpm, add 105 parts of composite cementitious material, 105 parts of pre-wetted coarse sand and 190 parts of pre-wetted coarse aggregate to 100 parts of precast grout by weight. At the same time, add 1.0% water-reducing agent and 0.03% rosin resin air-entraining agent by weight of composite cementitious material. Continue mixing until the mixture is uniform to obtain green low-carbon C30 self-compacting concrete.

[0024] Example 2 A method for preparing green, low-carbon C30 self-compacting concrete using dry-mixed mortar tailings includes the following steps: S1, Precast slurry: The tailings of the dry-mixed mortar are sieved: Sieve out ultrafine powders below 200 mesh, powders of 150-200 mesh, powders of 80-150 mesh, and powders of 20-80 mesh; Based on a total weight of 100%, the graded tail powder is prepared, of which 20% is 150-200 mesh particle size powder, 60% is controlled to be 80-150 mesh particle size powder, and the remainder is 20-80 mesh particle size powder. The graded tailings powder was mixed with water at a mass ratio of 1:3, stirred for 15 minutes at a speed of 100 rpm, and then allowed to stand and settle for 40 minutes. After dehydration, a pre-made slurry with a water content of 40% was obtained. S2. Preparation of composite cementitious material: By weight, 100 parts of ultrafine powder, 300 parts of cement, 200 parts of fly ash, 5 parts of expanding agent, and 1 part of warm wheel adhesive are mixed and compacted. The mixture is then ground using a dry ball mill to obtain a loose density of 1.8 g / cm³. 3 Composite cementitious materials; S3. Concrete preparation: Under 30 rpm mixing conditions, add 100 parts by weight of composite cementitious material, 110 parts by weight of pre-wetted coarse sand and 180 parts by weight of pre-wetted coarse aggregate to 100 parts by weight of precast grout. At the same time, add 0.5% by weight of water-reducing agent and 0.01% by weight of saponin air-entraining agent of composite cementitious material, add 3 parts by weight of mixing water, and continue mixing until uniformly mixed to obtain green low-carbon C30 self-compacting concrete.

[0025] Example 3 A method for preparing green, low-carbon C30 self-compacting concrete using dry-mixed mortar tailings includes the following steps: S1, Precast slurry: The tailings of the dry-mixed mortar are sieved: Sieve out ultrafine powders below 200 mesh, powders of 150-200 mesh, powders of 80-150 mesh, and powders of 20-80 mesh; Based on a total weight of 100%, the graded tail powder is prepared, of which 30% is 150-200 mesh particle size powder, 50% is controlled to be 80-150 mesh particle size powder, and the remainder is 20-80 mesh particle size powder. The graded tailings powder was mixed with water at a mass ratio of 1:5, stirred for 5 minutes at a speed of 300 rpm, and then allowed to stand and settle for 20 minutes. After dehydration, a pre-made slurry with a water content of 50% was obtained. S2. Preparation of composite cementitious material: By weight, 100 parts of ultrafine powder, 500 parts of cement, 100 parts of fly ash, 15 parts of expanding agent, and 5 parts of cellulose ether are mixed and compacted. The mixture is then ground using a dry ball mill to obtain a loose density of 2.1 g / cm³. 3 Composite cementitious materials; S3. Concrete preparation: Under a mixing condition of 70 rpm, add 110 parts of composite cementitious material, 100 parts of pre-wetted coarse sand and 200 parts of pre-wetted coarse aggregate to 100 parts of precast grout by weight. At the same time, add 1.5% water-reducing agent and 0.05% rosin resin air-entraining agent by weight of composite cementitious material. Continue mixing until the mixture is uniform to obtain green low-carbon C30 self-compacting concrete.

[0026] Example 4 A method for preparing green, low-carbon C30 self-compacting concrete using dry-mixed mortar tailings includes the following steps: S1, Precast slurry: The tailings of the dry-mixed mortar are sieved: Sieve out ultrafine powders below 200 mesh, powders of 150-200 mesh, powders of 80-150 mesh, and powders of 20-80 mesh; Based on a total weight of 100%, the graded tail powder is prepared, of which 22% is 150-200 mesh particle size powder, 58% is controlled to be 80-150 mesh particle size powder, and the remainder is 20-80 mesh particle size powder. The graded tailings powder was mixed with water at a mass ratio of 1:3.5, stirred for 12 minutes at a speed of 150 rpm, and then allowed to stand and settle for 35 minutes. After dehydration, a pre-made slurry with a water content of 42% was obtained. S2. Preparation of composite cementitious material: By weight, 100 parts of ultrafine powder, 350 parts of cement, 180 parts of fly ash, 7 parts of expanding agent, and 2 parts of warm wheel adhesive are mixed and compacted. The mixture is then ground using a dry ball mill to obtain a loose density of 1.85 g / cm³. 3 Composite cementitious materials; S3. Concrete preparation: Under a mixing condition of 40 rpm, add 102 parts of composite cementitious material, 108 parts of pre-wetted coarse sand and 185 parts of pre-wetted coarse aggregate to 100 parts of precast grout by weight. At the same time, add 0.8% water-reducing agent and 0.02% saponin air-entraining agent by weight of composite cementitious material, add 4 parts of mixing water, and continue mixing until uniformly mixed to obtain green low-carbon C30 self-compacting concrete.

[0027] Example 5 A method for preparing green, low-carbon C30 self-compacting concrete using dry-mixed mortar tailings includes the following steps: S1, Precast slurry: The tailings of dry-mixed mortar with a particle size ≤800μm were screened: Sieve out ultrafine powders below 200 mesh, powders of 150-200 mesh, powders of 80-150 mesh, and powders of 20-80 mesh; Based on a total weight of 100%, the graded tail powder is prepared, of which 28% is 150-200 mesh particle size powder, 52% is controlled to be 80-150 mesh particle size powder, and the remainder is 20-80 mesh particle size powder. The graded tailings powder was mixed with water at a mass ratio of 1:4.5, stirred for 8 minutes at a speed of 250 rpm, and then allowed to stand and settle for 25 minutes. After dehydration, a pre-made slurry with a water content of 48% was obtained. S2. Preparation of composite cementitious material: By weight, 100 parts of ultrafine powder, 450 parts of cement, 120 parts of fly ash, 13 parts of expanding agent, and 4 parts of cellulose ether are mixed and compacted. The mixture is then ground using a dry ball mill to obtain a loose density of 2.05 g / cm³. 3 Composite cementitious materials; S3. Concrete preparation: Under 60 rpm mixing conditions, add 108 parts by weight of composite cementitious material, 102 parts by weight of pre-wetted coarse sand and 195 parts by weight of pre-wetted coarse aggregate to 100 parts by weight of precast grout. At the same time, add 1.2% by weight of water-reducing agent and 0.04% by weight of rosin resin air-entraining agent of composite cementitious material, add 1 part of mixing water, and continue mixing until uniformly mixed to obtain green low-carbon C30 self-compacting concrete.

[0028] Comparative Example 1 The only difference from Example 1 is that the composite gel material was not prepared by densification.

[0029] Comparative Example 2 The only difference from Example 1 is that the dry-mixed mortar tailings were not graded, and all components such as dry-mixed mortar tailings, cement, and coarse aggregates of the corresponding mass were directly mixed evenly.

[0030] Comparative Example 3 The only difference from Example 1 is that, based on a total weight of 100%, the graded tail powder is prepared, in which the proportion of 150-200 mesh particle size powder is 40%, the proportion of 80-150 mesh particle size powder is controlled to be 40%, and the remainder is 20-80 mesh particle size powder.

[0031] Comparative Example 4 The only difference from Example 1 is that, based on a total weight of 100%, the graded tail powder is prepared, wherein the proportion of 150-200 mesh particle size powder is 10%, the proportion of 80-150 mesh particle size powder is controlled to be 70%, and the remainder is 20-80 mesh particle size powder. Comparative Example 5 The only difference from Example 1 is that the water content of the pre-mixed slurry is 60%.

[0032] Comparative Example 6 The only difference from Example 1 is that no pre-prepared slurry was prepared first, and all the water was reserved as mixing water: the graded tailings, composite gel material, pre-wetted coarse aggregate, pre-wetted coarse sand, etc. were pre-stirred and then mixed with mixing water until uniform.

[0033] Comparative Example 7 The only difference from Example 1 is that in S3, the pre-made slurry is added to the pre-mixed materials such as composite gel material, pre-wetted coarse aggregate, and pre-wetted coarse sand.

[0034] Comparative Example 8 The only difference from Example 1 is that the loose bulk density after densification is 1.7 g / cm³. 3 .

[0035] Performance testing: 1.28d compressive strength: tested according to GB / T 50081-2019 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete".

[0036] 2. Number of freeze-thaw cycles: The number of freeze-thaw cycles when the mass loss is ≤5%, and the curing time for self-compacting concrete is 28 days.

[0037] 3. Impermeability grade: Tested by the stepwise pressure method in GB / T 50082-2019 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete", with a curing time of 28 days for self-compacting concrete.

[0038] 4. Impact toughness: Tested according to the drop hammer impact test method recommended by ACI-544. The curing time for self-compacting concrete is 28 days.

[0039] Table 1 shows a comparison of the performance data of the examples and the comparative examples.

[0040] Table 1 Performance data of the examples and comparative examples

[0041] The ultrafine powder below 200 mesh, which accounts for about 40% of the dry-mixed mortar tailings, is prone to moisture absorption and clumping, and is difficult to disperse. It will form weak points in the concrete and trap free water. At the same time, its large specific surface area will disorderly adsorb water-reducing agents, leading to admixture failure, increased loss of fluidity over time, and abnormal setting. Furthermore, the halogens contained in the tailings can also cause durability risks such as sulfate attack and alkali-aggregate reaction, which seriously restricts its application in high-strength concrete. Simply sieving out the ultrafine powder will significantly reduce economic efficiency. The embodiment involves finely sieving and classifying the tailings of dry-mixed mortar according to particle size. After separating the ultrafine powder, it is densified with components such as cement and fly ash to prepare a composite cementitious material. This not only achieves the rational utilization of ultrafine powder but also avoids localized concentrated hydration caused by its rapid contact with free water. At the same time, the remaining particle size powder is resized and pre-mixed into a slurry, allowing the easily hygroscopic particles to absorb water and become saturated in advance, thus sealing their water absorption capacity. Combined with the pre-wetting of coarse sand and coarse aggregate and a reasonable feeding sequence, the components are mixed evenly, effectively solving the performance degradation or instability problems caused by tailings and exhibiting better comprehensive performance.

[0042] Compared with the examples, Comparative Example 1, due to the lack of densification treatment of the composite cementitious material, resulted in uneven dispersion of ultrafine powder and failure to deagglomerate, exacerbating the risk of concrete shrinkage and cracking, leading to a decline in performance; Comparative Example 2, without grading the dry-mixed mortar tail powder, allowed ultrafine powder to directly participate in the mixing, failing to address the issues of moisture absorption, clumping, and adsorption of water-reducing agents, severely impacting the homogeneity and strength development of the concrete; Comparative Examples 3 and 4, due to deviations in the proportion of each particle size in the graded tail powder from the optimized range, disrupted the rationality of the aggregate gradation, affecting the density of the internal structure of the concrete, thus resulting in performance inferior to the examples; Comparative Example 5... The precast grout had an excessively high water content, exceeding its stable range, which disrupted the internal moisture balance and structural integrity of the concrete, reducing its overall performance. In Comparative Example 6, no precast grout was prepared; all water was used as mixing water. The dry fine powder in the graded aggregate was prone to localized bleeding and clumping during mixing, forming weak areas and resulting in poor performance. Comparative Example 7 altered the feeding sequence, adding the precast grout to other pre-mixed materials. This caused the precast grout to clump due to water, making it difficult to disperse and resulting in uneven mixing of components. This prevented the precast grout from fully functioning as a stabilizing fine aggregate and water source, affecting the concrete's performance. Comparative Example 8, after densification, did not achieve the expected loose density, resulting in slightly worse overall performance, but still showing significant improvement compared to Comparative Example 1.

[0043] The above description is only a preferred embodiment 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 scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing green, low-carbon C30 self-compacting concrete using dry-mixed mortar tailings, characterized in that, Includes the following steps: S1, Precast slurry: The tailings of the dry-mixed mortar are sieved: Sieve out ultrafine powders below 200 mesh, powders of 150-200 mesh, powders of 80-150 mesh, and powders of 20-80 mesh; Based on a total weight of 100%, prepare graded tail powder, in which the proportion of 150-200 mesh particle size powder is 20%-30%, the proportion of 80-150 mesh particle size powder is controlled to be 50%-60%, and the remainder is 20-80 mesh particle size powder. The graded tailings powder is mixed with water at a mass ratio of 1:3-5, stirred and allowed to stand, and then dehydrated to obtain a pre-made slurry with a water content of 40-50%. S2. Preparation of composite cementitious material: By mass, 100 parts of ultrafine powder, 300-500 parts of cement, 100-200 parts of fly ash, 5-15 parts of expanding agent and 1-5 parts of viscosity modifier are mixed and densified to obtain composite cementitious material. The densification process involves grinding the material using a dry ball mill to obtain a bulk density of 1.8-2.1 g / cm³. 3 Composite cementitious materials; S3. Concrete preparation: Under mixing conditions, add 100-110 parts of composite cementitious material, 100-110 parts of pre-wetted coarse sand, and 180-200 parts of pre-wetted coarse aggregate to 100 parts of precast grout by weight. At the same time, add 0.5%-1.5% of water-reducing agent and 0.01%-0.05% of air-entraining agent by weight of composite cementitious material, and add 0-5 parts of mixing water. Continue mixing until the mixture is uniform to obtain green low-carbon C30 self-compacting concrete.

2. The preparation method according to claim 1, characterized in that, The particle size of the dry-mixed mortar tailings is ≤800μm.

3. The preparation method according to claim 1, characterized in that, The process of stirring and settling followed by dehydration is as follows: stirring for 5-15 minutes at a speed of 100-300 rpm, followed by settling for 20-40 minutes, and dehydration to obtain a pre-mixed slurry with a water content of 40-50%.

4. The preparation method according to claim 1, characterized in that, In S2, the viscosity modifier is cellulose ether or warm sizing agent; the swelling agent is calcium sulfoaluminate-based swelling agent.

5. The preparation method according to claim 1, characterized in that, In S2, the cement is PO 42.5 ordinary Portland cement; the fly ash is Grade I fly ash.

6. The preparation method according to claim 1, characterized in that, In S3, the stirring speed of the stirring conditions is 30-70 rpm.

7. The preparation method according to claim 1, characterized in that, In S3, the water-reducing agent is a polycarboxylate-based high-performance water-reducing agent; the air-entraining agent is a rosin resin-based air-entraining agent or a saponin-based air-entraining agent.

8. The preparation method according to claim 1, characterized in that, In S3, the coarse aggregate is continuously graded crushed stone with a particle size of 5-16mm, the content of needle-like and flaky particles is not greater than 8%, and the crushing index is not greater than 12%; the coarse sand is river sand with a fineness modulus of 3.3-3.

7.

9. A green, low-carbon C30 self-compacting concrete prepared by the preparation method according to any one of claims 1-8, utilizing dry-mixed mortar tailings.

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