Concrete preparation method adopting composite admixture to optimize performance

Abstract

The invention discloses a concrete preparation method adopting a composite admixture to optimize performance, which comprises the following steps: preparing raw materials, namely preparing cement, coarse aggregate, fine aggregate, water and components of a composite admixture system; preparing a composite admixture system; performing staged accurate addition and stirring parameter determination of the composite admixture system in the concrete preparation process; and completing concrete preparation and discharging. According to the invention, through accurate selection and optimal proportioning of the multi-component admixture, the synergistic effect among the components is fully utilized, and the antagonism is avoided or relieved, so that balanced improvement of multiple concrete performances which cannot be achieved by a single admixture is realized. According to the preparation method, on the premise that the workability of the concrete is not sacrificed, the compressive strength, the breaking strength, the impermeability, the freeze-thaw resistance and the carbonization resistance of the concrete are improved at the same time, and the drying shrinkage and cracking risks are remarkably reduced.

Description

Technical Field

[0001] This invention belongs to the field of concrete preparation technology, and particularly relates to a method for preparing concrete using composite admixtures to optimize performance. Background Technology

[0002] Concrete, as one of the most important and widely used structural materials in modern construction engineering, directly affects the safety, durability, and economy of engineering projects. With the continuous advancement of infrastructure construction and the increasing complexity of building structures, engineering practice has placed increasingly stringent performance requirements on concrete materials, such as higher strength, superior durability, better crack resistance, and more convenient construction and workability.

[0003] Patent application CN110577390A discloses a concrete preparation process. Its core technical idea is to improve the workability and performance of the mixture by finely adjusting the order of adding concrete raw materials.

[0004] Patent application CN110002810A discloses a type of concrete and its preparation process, which focuses on broadening the sources of concrete raw materials and improving its environmental performance. This patent introduces novel materials such as polyamide resin, polyimide fiber, and epoxy resin to effectively combine major cementitious materials such as cement, fly ash, and ceramic powder with manufactured sand and natural sand. Specific admixtures are then added for secondary mixing, resulting in concrete with specific physicochemical properties. This technical solution provides a new approach to reducing the dependence of traditional concrete production on natural resources and reducing carbon emissions through material substitution.

[0005] However, with the emergence of the concepts of high-performance and ultra-high-performance concrete and the increasing demand for their application in extreme service environments, some inherent characteristics of the aforementioned existing technologies at the principle level have gradually revealed their limitations in addressing new challenges. It is difficult to stably and efficiently produce concrete products that meet the growing demand for high performance while simultaneously considering cost-effectiveness. Therefore, a concrete preparation method is needed that can optimize concrete performance by adding composite admixtures to adapt to different construction requirements, while keeping the basic raw materials of concrete unchanged. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for preparing concrete using composite admixtures to optimize performance.

[0007] The present invention is achieved through the following technical solutions.

[0008] This invention provides a method for preparing concrete with optimized performance using composite admixtures, comprising the following steps: A1: Prepare raw materials, including cement, coarse aggregate, fine aggregate, water, and the components of the composite admixture system; A2: Preparation of a composite admixture system; A3: Precise addition of composite admixture systems in stages and determination of mixing parameters during concrete preparation; A4: Complete concrete preparation and discharge.

[0009] Preferably, the components of the composite admixture system include at least two or more of the following types of admixtures: water-reducing agent, retarder, early-strength agent, air-entraining agent, defoamer, expanding agent, shrinkage compensator, interface reinforcing agent, crystal-forming waterproofing agent, nano-scale mineral admixture, and cellulose ether.

[0010] Preferably, step A3 includes: B1: Initial wet mixing and first stage admixture addition: All coarse aggregate, fine aggregate and 70% to 80% of cement are added to a forced concrete mixer. Then, one or two of the components of the composite admixture system, such as water-reducing agent and retarder, are added to the mixer along with 70% to 80% of the mixing water for initial wet mixing. The mixing time is 90 to 120 seconds. B2: Main mixing and second-stage admixture addition. After the initial wet mixing is completed, add the remaining 20% ​​to 30% of cement to the mixer. Then, add one or more of the following components of the composite admixture system: drought-strength agent, air-entraining agent, defoamer, expansion agent, and cellulose ether, along with the remaining 20% ​​to 30% of mixing water, to the mixer for main mixing. The mixing time is 150 to 180 seconds. B3: Fine-tuning and third-stage admixture addition. After the main mixing is completed, one or more of the following components of the composite admixture system, namely shrinkage compensator, interface enhancer, crystal-forming waterproofing agent and nano-mineral admixture, are added to the mixer in batches or all at once for final mixing. The mixing time is 60 to 90 seconds.

[0011] Preferably, the water-reducing agent is a polycarboxylate-based water-reducing agent, the air-entraining agent is a rosin resin-based air-entraining agent, the defoamer is a polyether-modified silicone oil, and the interface reinforcing agent is an organosilane coupling agent.

[0012] Preferably, the retarder is sodium gluconate with a purity of not less than 98%, and its dosage is controlled between 0.05% and 0.3% of the cement mass.

[0013] Preferably, the early strength agent is calcium chloride with a purity of not less than 95%, and the amount of anhydrous calcium chloride is controlled between 1.0% and 2.0% of the cement mass.

[0014] Preferably, the expansive agent is a calcium sulfoaluminate type expansive agent with a fineness modulus of less than 400 mesh and an admixture amount of 6% to 10% of the cement mass.

[0015] Preferably, the shrinkage compensator is a calcium oxide-based shrinkage compensator with an active calcium oxide content of not less than 90%, a particle size distribution concentrated between 5 micrometers and 20 micrometers, and an admixture dosage of 1% to 3% of the cement mass.

[0016] Preferably, the nanoscale mineral admixture is nano-silica with an average particle size between 10nm and 50nm, a specific surface area of ​​not less than 200m² / g, and a purity of not less than 99.5%.

[0017] Preferably, the cellulose ether is hydroxypropyl methylcellulose with a viscosity of 15000 mPa·s and a degree of substitution of 1.8 to 2.0.

[0018] The beneficial effects of this invention are as follows: 1. Synergistic Effect of Composite Admixture System: Through precise selection and optimized proportioning of multi-component admixtures, this invention can fully utilize the synergistic effects between components, avoid or mitigate antagonistic effects, thereby achieving a balanced improvement in multiple concrete properties that cannot be achieved by a single admixture. For example, the synergistic effect of high-efficiency water-reducing agent and nano-silica can significantly improve the density of the paste and the degree of cement hydration, thereby enhancing strength and durability; the precise combination of retarder and accelerator can control setting time without sacrificing early strength development, balancing construction and performance.

[0019] 2. Simultaneous optimization of multiple performance indicators: The method of this invention can simultaneously improve the compressive strength, flexural strength, impermeability, freeze-thaw resistance, carbonation resistance, and significantly reduce the risk of drying shrinkage and cracking without sacrificing the workability of concrete. This simultaneous optimization of multiple performance indicators benefits from the systematic design and precise implementation of the synergistic effect of admixtures.

[0020] 3. Precision and Controllability of the Process: The precise metering and staged addition system employed in this invention, combined with mathematical model-optimized mix proportions, ensures high repeatability and stability in the concrete preparation process, significantly reducing the uncertainty and production costs associated with traditional trial-and-error methods. By programmatically controlling the timing of addition, flow rate, mixing speed, and time, predictable and precise adjustments to concrete performance are achieved.

[0021] 4. Improved resource utilization: By optimizing the performance of admixtures, the amount of cement used can be appropriately reduced while ensuring or even improving the performance of concrete, thereby reducing carbon emissions and resource consumption, which is in line with the concept of green and environmentally friendly production. Attached Figure Description

[0022] Figure 1This is a flowchart illustrating the present invention; Figure 2 This is a schematic diagram of the concrete preparation process of the present invention. Detailed Implementation

[0023] The technical solution of the present invention is further described below, but the scope of protection is not limited to what is described.

[0024] A method for preparing concrete with optimized performance using composite admixtures includes the following steps: A1: Prepare raw materials.

[0025] This step involves preparing the components of the cement, coarse aggregate, fine aggregate, water, and composite admixture system. The cement is silicate cement with a specific surface area ranging from 300 m² / kg to 450 m² / kg, a sulfur trioxide content not exceeding 3.5%, and a chloride ion content not exceeding 0.06%. The coarse aggregate is washed crushed stone with a maximum particle size of 25 mm, a mud content of less than 1.0%, and a crushing index of less than 10%. The fine aggregate is natural river sand or manufactured sand with a fineness modulus ranging from 2.3 to 3.0, a mud content of less than 2.0%, and a chloride ion content not exceeding 0.02%. The water is drinking water that meets the standards for concrete mixing water. The composite admixture system consists of at least two chemical or mineral admixtures with different functions and synergistic or antagonistic effects. The composition and physicochemical properties of this system will be detailed in subsequent steps.

[0026] A2: Prepare a composite admixture system.

[0027] This step is the core step for achieving performance optimization and precise control in this invention. The selection of components in the composite admixture system is based on a comprehensive analysis of the target concrete performance requirements and a deep understanding of the mechanisms of action of each admixture in cement hydration, paste rheology, and microstructure formation. The composite admixture system contains at least two or more of the following types of admixtures: high-efficiency water-reducing agents, retarders, early-strength agents, air-entraining agents, defoamers, expanding agents, shrinkage compensators, interface reinforcing agents, crystal-forming waterproofing agents, nano-scale mineral admixtures, or cellulose ethers.

[0028] The high-efficiency water-reducing agent is a polycarboxylate-based high-performance water-reducing agent. Its polyether side chain length ranges from 8 to 15 ethylene oxide units, its solid content is 40%, and its water reduction rate ranges from 25% to 40%. It has excellent dispersibility for cement particles.

[0029] The retarder is sodium gluconate with a purity of not less than 98%, and its dosage is controlled between 0.05% and 0.3% of the cement mass. It is used to adjust the setting time of concrete.

[0030] The early strength agent is calcium chloride with a purity of not less than 95%. The amount of anhydrous calcium chloride is controlled between 1.0% and 2.0% of the cement mass. It is used to accelerate cement hydration and improve early strength.

[0031] The air-entraining agent is a rosin resin-based air-entraining agent with a solid content of 15% and an air-entraining capacity ranging from 3% to 6%. It is used to improve the freeze-thaw resistance and workability of concrete.

[0032] The defoamer is a polyether-modified silicone oil with an active ingredient content of 20%. It is used to control and reduce the air bubble content in concrete mixtures to optimize the density and strength of hardened concrete.

[0033] The expansive agent is a calcium sulfoaluminate type expansive agent with a fineness modulus of less than 400 mesh. The dosage is 6% to 10% of the cement mass, and it is used to compensate for the shrinkage of concrete.

[0034] The shrinkage compensator is a calcium oxide-based shrinkage compensator with an active calcium oxide content of not less than 90% and a particle size distribution concentrated between 5 micrometers and 20 micrometers. The dosage is 1% to 3% of the cement mass, and it is used to reduce drying shrinkage through a micro-expansion mechanism.

[0035] The interface enhancer is an organosilane coupling agent with a methoxysilane active group content of 98%, used to enhance the interfacial bonding strength between cement matrix and aggregate.

[0036] Crystal-forming waterproofing agents are silicate-based active chemical substances with an average particle size of 50 micrometers and an active ingredient content of not less than 70%. They are used to form insoluble crystals inside concrete to fill capillary pores.

[0037] The nano-scale mineral admixture is nano-silica (SiO2), with an average particle size between 10nm and 50nm, a specific surface area of ​​not less than 200m² / g, and a purity of not less than 99.5%. It is used to improve the density of the slurry, enhance early strength, and improve durability.

[0038] The cellulose ether is hydroxypropyl methylcellulose (HPMC) with a viscosity of 15000 mPa·s (2% aqueous solution, 20℃) and a degree of substitution of 1.8 to 2.0. It is used to improve the water retention, thickening and anti-segregation properties of concrete.

[0039] The precise proportions of the composite admixture system are determined by the following method: First, threshold values ​​for several key performance parameters are set based on the performance indicators of the target concrete, such as compressive strength, flexural strength, modulus of elasticity, impermeability grade, carbonation resistance, freeze-thaw cycle count, drying shrinkage, slump, and spread.

[0040] Secondly, by designing orthogonal experiments or the response surface methodology (RSM) and other optimized experimental schemes, the synergistic and antagonistic effects of individual admixtures and their pairwise and triadic combinations under varying admixture dosage gradients were systematically investigated, thereby constructing a mathematical model of the relationship between each admixture component and concrete performance. This mathematical model is a multivariate nonlinear regression model, where the independent variable is the dosage of each admixture, and the dependent variable is each performance parameter. Finally, the mathematical model was solved using optimization algorithms to determine the composite admixture system components and their precise proportions that achieve the best overall benefit while satisfying all performance parameter thresholds. For example, in the preparation of high-strength, low-shrinkage concrete, the ratio of high-efficiency water-reducing agent to shrinkage compensator is not a simple linear relationship, but rather requires consideration of their combined effects on hydration rate, pore structure, and internal stress evolution. The preparation of the composite admixture system involves pre-weighing the selected components according to a determined precise proportion and pre-mixing or dispersing them according to their physical forms. Liquid components are premixed using high-shear mixing equipment to ensure uniform dispersion; solid components are uniformly mixed in a dry environment using a V-type mixer or a twin-screw mixer to prevent clumping. The mixed compound additive is stored in a sealed container to prevent moisture absorption or component degradation.

[0041] A3: Perform precise addition and mixing in stages.

[0042] This step involves adding specific components of the composite admixture at different times during the concrete mixing process in stages to adapt to the dynamic changes in cement hydration and paste rheological properties, avoiding improper initial contact and reaction between the components, thereby achieving precise control over concrete performance.

[0043] The precise addition and mixing process includes the following sub-steps: B1: Initial wet mixing and first-stage additive addition: First, all coarse aggregate, fine aggregate, and some cement are fed into a forced concrete mixer. The mixer is a twin-shaft forced mixer with a mixing speed of 30 revolutions per minute and a mixing capacity of 1 cubic meter.

[0044] Subsequently, the liquid components of the composite admixture system that have initial dispersing or retarding effects (e.g., 70% to 80% of the high-efficiency water-reducing agent and the entire amount of the retarder) are added to the mixer along with 70% to 80% of the mixing water. The addition process is carried out by a liquid metering pump at a constant flow rate, with a flow control accuracy of ±1%, ensuring uniform mixing of the liquid admixture and water. The liquid metering pump is controlled by a host computer and operates according to a preset addition program.

[0045] Perform initial wet mixing for 90 to 120 seconds. The purpose of this initial wet mixing is to fully wet the surface of the aggregates and to initially disperse the cement particles added in the early stages under the action of the water-reducing agent, forming a uniform paste coating layer. At the same time, the retarder begins to play its role in inhibiting premature setting of the cement.

[0046] B2: Main mixing and second-stage additive addition: After the initial wet mixing is complete, the remaining 20% ​​to 30% of the cement is added to the mixer. This addition is accomplished via a screw conveyor at a rate of 10 kg per second, with the amount added monitored in real-time by a weight sensor.

[0047] Next, the components of the composite admixture system that have air-entraining, early-strength, or interface-reinforcing effects (e.g., the entire amount of the air-entraining agent, the entire amount of the early-strength agent, and the entire amount of the interface-reinforcing agent) are added to the mixer along with the remaining 20% ​​to 30% of the mixing water. Liquid admixtures are added using a separate set of independent liquid metering pumps, while solid admixtures are added using a micro-powder metering device with a metering accuracy of ±0.5%. At this stage, the air-entraining agent begins to form uniform and stable microbubbles in the slurry, improving workability; the early-strength agent accelerates the hydration of the cement added later, compensating for any potential lag in strength development caused by the retarder; and the interface-reinforcing agent forms a more effective bond with the newly added cement particles and aggregate surfaces at this time.

[0048] Perform the main mixing for 150 to 180 seconds. This main mixing stage aims to thoroughly mix all components, ensure uniform dispersion of the admixture throughout the concrete mixture, and initiate the formation of the desired paste rheological properties.

[0049] B3: Fine-tuning and third-stage additive addition: After the main mixing is completed, a brief stoppage or low-speed mixing is performed to observe the initial workability of the concrete mixture. Workability is initially assessed by visually inspecting the uniformity and fluidity of the paste.

[0050] Based on preliminary assessment results, components in the composite admixture system that have the function of finely regulating the properties or microstructure of the paste (e.g., the remaining 0% to 10% of the high-efficiency water-reducing agent, the entire amount of the shrinkage compensator, the entire amount of the crystal-forming waterproofing agent, the entire amount of the nano-sized mineral admixture, or the entire amount of the cellulose ether) are added to the mixer in batches or all at once. The water-reducing agent added at this stage is used for final fine-tuning of the slump; the shrinkage compensator and crystal-forming waterproofing agent are added when the rheological properties of the paste are relatively stable, allowing for better uniform distribution in the cement matrix and the exertion of their long-term effects, avoiding initial over-hydration or uneven dispersion; the nano-sized mineral admixture, due to its extremely high specific surface area, helps avoid initial agglomeration and better fills the microporous structure when added at this stage; the cellulose ether added at this stage helps to precisely control water retention and viscosity, optimizing the final workability.

[0051] For liquid components, the addition method is injection via a liquid metering pump; for solid components, the addition method is feeding via a micro-powder metering device, with the addition accuracy maintained within ±0.5%.

[0052] Perform final mixing for 60 to 90 seconds. This final mixing stage aims to ensure that the admixtures added in the third stage are thoroughly mixed with the overall mixture and to finally adjust the workability of the concrete to the target value, preparing it for subsequent transportation, pouring, and vibration.

[0053] A4: Discharge. After final mixing, the prepared concrete mixture is unloaded from the mixer for transportation and pouring.

[0054] It can achieve synergistic enhancement of concrete performance, precise control at the microstructure level, and simultaneous optimization of multiple performance indicators, while significantly improving the accuracy and controllability of the process and contributing to the improvement of resource utilization.

[0055] Example 1: like Figure 1-2 As shown, this embodiment aims to prepare a C60 high-performance concrete with high strength, high durability, and good workability.

[0056] A method for preparing concrete with optimized performance using composite admixtures, comprising the following steps: A1: Prepare raw materials: Cement: P.O42.5 ordinary Portland cement, specific surface area 350m² / kg, sulfur trioxide content 3.0%, chloride ion content 0.03%.

[0057] Coarse aggregate: continuously graded crushed stone with a particle size of 5mm to 25mm, a mud content of 0.8%, and a crushing index of 8%.

[0058] Fine aggregate: medium sand, fineness modulus 2.7, mud content 1.5%, chloride ion content 0.01%.

[0059] Water: Complies with JGJ63 standard.

[0060] The composite admixture system consists of: high-efficiency water-reducing agent (polycarboxylic acid), retarder (sodium gluconate), defoamer (polyether-modified silicone oil), and nano-grade mineral admixture (nano-silica).

[0061] A2: Design and preparation of composite admixture systems: Based on the target C60 concrete performance requirements (28-day compressive strength ≥ 60 MPa, 90-day impermeability grade ≥ P12, slump 200 ± 20 mm), the following composite admixture system components and proportions (all based on cement mass percentages) were determined through optimization experiments using the Response Surface Methodology (RSM) method: High-efficiency water-reducing agent: 1.8%. This high-efficiency water-reducing agent is a polycarboxylate-based high-performance water-reducing agent with a solid content of 40%, a water reduction rate of 35%, and a polyether side chain length distribution range between 10 and 12 ethylene oxide units.

[0062] Retarder: 0.15%. The retarder is sodium gluconate with a purity of not less than 98%.

[0063] Defoamer: 0.02%. This defoamer is polyether-modified silicone oil with an active ingredient content of 20%.

[0064] Nano silica: 1.0%. This nano silica has an average particle size of 30 nm, a specific surface area of ​​250 m² / g, and a purity of 99.8%.

[0065] The high-efficiency water-reducing agent, retarder, and defoamer are all liquids, pre-mixed evenly according to the specified proportions, and stored in a liquid storage tank. Nano-silica is in powder form, pre-mixed physically with other powder components (such as some cement), or prepared as a 20% concentration dispersion to avoid later agglomeration. This embodiment uses a nano-silica dispersion.

[0066] A3: Precise addition of composite admixture systems in stages and determination of mixing parameters during concrete preparation; A4: Discharge the material and unload the prepared concrete.

[0067] The A3 step is specifically as follows: Concrete mix proportions (per cubic meter): 480 kg cement, 160 kg water, 1000 kg coarse aggregate, and 700 kg fine aggregate.

[0068] B1: Initial wet mixing and first-stage additive addition: First, 1000 kg of coarse aggregate, 700 kg of fine aggregate, and 240 kg (50%) of cement are fed into a twin-shaft forced concrete mixer.

[0069] Subsequently, 75% of the high-efficiency water-reducing agent (equivalent to 1.35% of the cement mass, or 8.1 kg of water-reducing agent solution), the entire amount of the retarder (equivalent to 0.15% of the cement mass, or 0.72 kg of sodium gluconate solution), and 120 kg (75%) of mixing water were added to the mixer. The liquid admixtures and water were injected through separate pipelines by a peristaltic pump at a constant flow rate, with a flow control accuracy of ±0.5%.

[0070] Perform initial wet mixing for 100 seconds.

[0071] B2: Main mixing and second-stage additive addition: After the initial wet mixing is complete, add the remaining 240 kg of cement to the mixer. The addition is completed via a screw conveyor.

[0072] Next, the entire amount of defoamer (i.e., 0.02% of the cement mass, equivalent to 0.1 kg of defoamer solution) and the remaining 40 kg (25%) of mixing water are added to the mixer. The defoamer is added using a separate liquid metering pump.

[0073] Perform the main mixing for 160 seconds.

[0074] B3: Fine-tuning and third-stage additive addition: After the main mixing is completed, a preliminary workability assessment is conducted.

[0075] Subsequently, the remaining 25% of the high-efficiency water-reducing agent (i.e., 0.45% of the cement mass, equivalent to 2.7 kg of water-reducing agent solution) and the entire amount of the nano-silica dispersion (i.e., 1.0% of the cement mass, equivalent to 4.8 kg of nano-silica solid) were added to the mixer. The water-reducing agent was added using a separate liquid metering pump, while the nano-silica dispersion was added using another set of liquid metering pumps.

[0076] Perform a final stirring for 80 seconds.

[0077] Testing revealed that the C60 concrete prepared in this embodiment achieved a 28-day compressive strength of 65.2 MPa, a 90-day impermeability grade of P16, a slump of 210 mm, a spread of 550 mm, and a drying shrinkage rate of 300 microstrains at 90 days, significantly lower than that of ordinary C60 concrete. These results demonstrate that through the synergistic design and precise multi-stage addition of composite admixtures, simultaneous optimization of high strength, high durability, and low shrinkage performance was achieved, while maintaining good workability.

[0078] Example 2: This embodiment aims to prepare a concrete with excellent crack resistance and freeze-thaw resistance, suitable for large-volume structures in cold regions.

[0079] like Figure 1-2 As shown, a method for preparing concrete with optimized performance using composite admixtures includes the following steps: A1: Prepare raw materials: Cement: P.O42.5 ordinary Portland cement, specific surface area 340m² / kg, sulfur trioxide content 3.2%, chloride ion content 0.04%.

[0080] Coarse aggregate: continuously graded crushed stone with a particle size of 5mm to 20mm, a mud content of 0.7%, and a crushing index of 9%.

[0081] Fine aggregate: natural river sand, fineness modulus 2.5, mud content 1.2%, chloride ion content 0.015%.

[0082] Water: Complies with JGJ63 standard.

[0083] The composite admixture system consists of: high-efficiency water-reducing agent (polycarboxylate), air-entraining agent (rosin resin), shrinkage compensator (calcium oxide-based), and crystal-forming waterproofing agent (silicate-based).

[0084] A2: Design and preparation of composite admixture systems: Based on the target concrete performance requirements (28-day compressive strength ≥ 40 MPa, freeze-thaw cycle resistance ≥ 300 cycles, drying shrinkage rate reduced by more than 30%, and impermeability grade ≥ P10), the following composite admixture system components and proportions (all based on cement mass percentages) were determined through orthogonal experiments and empirical model optimization: High-efficiency water-reducing agent: 1.5%. This high-efficiency water-reducing agent is a polycarboxylate-based high-performance water-reducing agent with a solid content of 35%, a water reduction rate of 30%, and a polyether side chain length distribution range of 8 to 10 ethylene oxide units.

[0085] Air-entraining agent: 0.03%. This air-entraining agent is a rosin resin-based air-entraining agent with a solid content of 15% and an air-entraining capacity ranging from 4% to 5%.

[0086] Shrinkage compensator: 2.0%. This shrinkage compensator is a calcium oxide-based shrinkage compensator with an active calcium oxide content of 92% and a particle size distribution concentrated between 10 and 15 micrometers.

[0087] Crystal-forming waterproofing agent: 1.5%. This crystal-forming waterproofing agent is a silicate-based active chemical substance with an average particle size of 55 micrometers and an active ingredient content of 75%.

[0088] Both the high-efficiency water-reducing agent and the air-entraining agent are liquids, which are pre-mixed evenly according to the specified ratio and then stored in liquid storage tanks. The shrinkage compensator and the crystal-forming waterproofing agent are powders, which are pre-mixed evenly in a dry environment using a V-type mixer and then stored in a sealed powder silo.

[0089] A3: Precise addition of composite admixture systems in stages and determination of mixing parameters during concrete preparation; A4: Discharge the material and unload the prepared concrete.

[0090] The A3 step is specifically as follows: Concrete mix proportions (per cubic meter): 380 kg cement, 150 kg water, 1080 kg coarse aggregate, and 680 kg fine aggregate.

[0091] B1: Initial wet mixing and first-stage additive addition: First, 1080 kg of coarse aggregate, 680 kg of fine aggregate, and 190 kg (50%) of cement are fed into a twin-shaft forced concrete mixer.

[0092] Subsequently, 60% of the high-efficiency water-reducing agent (i.e., 0.9% of the cement mass, equivalent to 3.42 kg of water-reducing agent solution) and 110 kg (73.3%) of mixing water were added to the mixer. The liquid admixture and water were injected through separate pipelines by an electromagnetic metering pump at a set flow rate, with a flow control accuracy of ±0.8%.

[0093] Perform initial wet mixing for 95 seconds.

[0094] B2: Main mixing and second-stage additive addition: After the initial wet mixing is completed, add the remaining 190 kg of cement into the mixer.

[0095] Next, the entire amount of air-entraining agent (i.e., 0.03% of the cement mass, equivalent to 0.114 kg of air-entraining agent solution) and the remaining 40 kg (26.7%) of mixing water are added to the mixer. The air-entraining agent is added using a separate liquid metering pump.

[0096] Perform the main mixing for 170 seconds.

[0097] B3: Fine-tuning and third-stage additive addition: After the main mixing is completed, a preliminary workability assessment is conducted.

[0098] Subsequently, the remaining 40% of the high-efficiency water-reducing agent (i.e., 0.6% of the cement mass, equivalent to 2.28 kg of water-reducing agent solution) was added to the mixer along with the entire amount of the premixed shrinkage compensator and crystal-forming waterproofing agent (i.e., 7.6 kg of shrinkage compensator and 5.7 kg of crystal-forming waterproofing agent). The water-reducing agent was added using a separate liquid metering pump, while the powdered admixtures were fed using a micro-powder metering device with a metering accuracy of ±0.5%.

[0099] Perform a final stirring for 85 seconds.

[0100] Testing revealed that the concrete prepared in this embodiment achieved a 28-day compressive strength of 43.5 MPa, withstanding 350 freeze-thaw cycles, and a drying shrinkage rate of 250 microstrains at 90 days (a 35% reduction compared to the baseline concrete), with a permeability grade of P14. These results demonstrate that the rational formulation and phased addition of the composite admixture successfully improved the crack resistance and freeze-thaw resistance of the concrete, meeting the application requirements under specific environmental conditions.

[0101] Example 3: This embodiment aims to prepare a type of concrete with rapid strength development and excellent early workability, suitable for emergency repairs or rapid construction projects.

[0102] like Figure 1-2 As shown, a method for preparing concrete with optimized performance using composite admixtures includes the following steps: A1: Prepare raw materials: Cement: PO 52.5 ordinary Portland cement, specific surface area 400m² / kg, sulfur trioxide content 3.3%, chloride ion content 0.05%.

[0103] Coarse aggregate: continuously graded crushed stone with a particle size of 5mm to 16mm, a mud content of 0.6%, and a crushing index of 7%.

[0104] Fine aggregate: manufactured sand, fineness modulus 2.8, mud content 1.8%, chloride ion content 0.02%.

[0105] Water: Complies with JGJ63 standard.

[0106] The composite admixture system consists of: high-efficiency water-reducing agent (polycarboxylate), early strength agent (calcium chloride), and cellulose ether (hydroxypropyl methylcellulose).

[0107] A2: Design and preparation of composite admixture systems: Based on the target concrete performance requirements (1-day compressive strength ≥ 20 MPa, 3-day compressive strength ≥ 35 MPa, 1-hour slump loss < 20 mm, and initial slump 180 ± 20 mm), the following composite admixture system components and proportions (all based on cement mass percentage) were determined using a multi-objective optimization algorithm: High-efficiency water-reducing agent: 1.2%. This high-efficiency water-reducing agent is a polycarboxylate-based high-performance water-reducing agent with a solid content of 45% and a water reduction rate of 38%. The polyether side chain length distribution ranges from 12 to 15 ethylene oxide units, and it has no significant inhibitory effect on early strength development.

[0108] Early strength agent: 1.5%. This early strength agent is anhydrous calcium chloride with a purity of not less than 95%.

[0109] Cellulose ether: 0.03%. This cellulose ether is hydroxypropyl methylcellulose (HPMC), with a viscosity of 15000 mPa·s (2% aqueous solution, 20℃) and a degree of substitution of 1.8.

[0110] The high-efficiency water-reducing agent is a liquid and is pre-stored in a liquid storage tank. The early-strength agent and cellulose ether are both in powder form. To ensure rapid early strength development, calcium chloride is pre-mixed with a portion of the cement and cellulose ether.

[0111] A3: Precise addition of composite admixture systems in stages and determination of mixing parameters during concrete preparation; A4: Discharge the material and unload the prepared concrete.

[0112] The A3 step is specifically as follows: Concrete mix proportions (per cubic meter): 450 kg cement, 145 kg water, 1050 kg coarse aggregate, and 690 kg fine aggregate.

[0113] B1: Initial wet mixing and first-stage additive addition: First, 1050 kg of coarse aggregate, 690 kg of fine aggregate, and 225 kg (50%) of cement are fed into a twin-shaft forced concrete mixer.

[0114] Subsequently, the entire amount of the high-efficiency water-reducing agent (i.e., 1.2% of the cement mass, equivalent to 5.4 kg of water-reducing agent solution) was added to the mixer along with 110 kg (75.9%) of mixing water. The liquid admixture and water were injected through separate pipelines by a gear pump at a constant flow rate, with a flow control accuracy of ±0.7%.

[0115] Perform initial wet mixing for 90 seconds.

[0116] B2: Main mixing and second-stage additive addition: After the initial wet mixing is completed, add the remaining 225kg of cement into the mixer.

[0117] Next, the entire amount of the accelerator (i.e., 1.5% of the cement mass, equivalent to 6.75 kg of anhydrous calcium chloride powder), the entire amount of the cellulose ether (i.e., 0.03% of the cement mass, equivalent to 0.135 kg of cellulose ether powder), and the remaining 35 kg (24.1%) of mixing water were added to the mixer. The accelerator and cellulose ether were added using a micro-powder metering device with a metering accuracy of ±0.3%.

[0118] Perform the main mixing for 150 seconds. At this stage, add an accelerator and cellulose ether. The accelerator accelerates cement hydration, while the cellulose ether improves the cohesiveness and water retention of the paste, ensuring that workability is not rapidly lost during the rapid setting process.

[0119] B3: Fine-tuning and third-stage additive addition: After the main mixing is completed, no additional additives are added. The mixer continues to mix for 20 seconds to ensure that all components are fully homogeneous.

[0120] Testing showed that the concrete prepared in this embodiment achieved a compressive strength of 22.8 MPa after 1 day and 38.1 MPa after 3 days, with an initial slump of 190 mm and a slump of 175 mm after 1 hour, resulting in a slump loss of only 15 mm. These results demonstrate that the synergistic design and precise, staged addition of the composite admixtures enabled rapid strength development and excellent early workability in the concrete, meeting the demands of rapid construction.

[0121] Comparative Example 1: This comparative example aims to prepare a standard C60 concrete with a mix proportion that is basically the same as that of Example 1. However, it adopts a traditional method in terms of admixture system and addition method, that is, it does not use the fine design and staged precise addition process of composite admixture system, but only uses a common high-efficiency water-reducing agent and adds it at once.

[0122] Raw material preparation: Cement: P.O42.5 ordinary Portland cement, specific surface area 350m² / kg, sulfur trioxide content 3.0%, chloride ion content 0.03%.

[0123] Coarse aggregate: continuously graded crushed stone with a particle size of 5mm to 25mm, a mud content of 0.8%, and a crushing index of 8%.

[0124] Fine aggregate: medium sand, fineness modulus 2.7, mud content 1.5%, chloride ion content 0.01%.

[0125] Water: Complies with JGJ63 standard.

[0126] Admixture: Polycarboxylate-based high-efficiency water-reducing agent (same type as the water-reducing agent in Example 1, but without retarders, defoamers, nano-silica, and other synergistic components). The dosage is 2.2% of the cement mass, added all at once.

[0127] Mix proportions (per cubic meter): 480 kg cement, 160 kg water, 1000 kg coarse aggregate, and 700 kg fine aggregate.

[0128] Stirring process: Step 1: Add all coarse aggregate, fine aggregate, and all cement into the twin-shaft forced concrete mixer.

[0129] Step 2: Add all the mixing water and all the high-efficiency water-reducing agent (2.2% of the cement mass, equivalent to 10.56 kg of water-reducing agent solution) to the mixer at once.

[0130] Step 3: Stir, set the total stirring time to 180 seconds.

[0131] Step 4: Discharge the material.

[0132] Testing showed that the C60 concrete prepared in this comparative example achieved a compressive strength of 61.0 MPa at 28 days, a permeability grade of P10 at 90 days, a slump of 200 mm, and a spread of 500 mm. The measured drying shrinkage rate at 90 days was 550 microstrain.

[0133] The performance data of the concrete prepared in Example 1 and Comparative Example 1 are compared as shown in the table below:

[0134] The comparative data clearly show that although Comparative Example 1 can also achieve a strength grade of C60 by increasing the amount of water-reducing agent, it has a significant gap with Example 1 of the present invention in terms of durability indicators (such as impermeability grade) and crack resistance (such as drying shrinkage rate). Example 1, while maintaining or even slightly improving workability, achieved a 6.9% increase in 28-day compressive strength and an improvement in impermeability grade from P10 to P16 through the systematic design and precise, phased addition of the composite admixture. Most notably, the drying shrinkage rate was reduced by approximately 45.5%. This significant reduction in shrinkage is of great engineering significance for improving the long-term durability and crack resistance of concrete structures. These quantitative comparative data fully demonstrate that the concrete preparation method of the present invention has significant technical advantages and non-obvious implications in achieving high-performance concrete, and can provide higher quality and more reliable concrete materials for practical engineering projects.

Claims

1. A method for preparing concrete with optimized performance using composite admixtures, characterized in that, Includes the following steps: A1: Prepare raw materials, including cement, coarse aggregate, fine aggregate, water, and the components of the composite admixture system; A2: Preparation of a composite admixture system; A3: Precise addition of composite admixture systems in stages and determination of mixing parameters during concrete preparation; A4: Complete concrete preparation and discharge.

2. The method for preparing concrete with optimized performance using composite admixtures as described in claim 1, characterized in that: The composite admixture system comprises at least two or more of the following types of admixtures: water-reducing agents, retarders, early-strength agents, air-entraining agents, defoamers, expanding agents, shrinkage compensators, interface reinforcing agents, crystal-forming waterproofing agents, nano-sized mineral admixtures, and cellulose ethers.

3. The method for preparing concrete with optimized performance using composite admixtures as described in claim 1, characterized in that: The A3 step includes: B1: Initial wet mixing and first stage admixture addition: All coarse aggregate, fine aggregate and 70% to 80% of cement are added to a forced concrete mixer. Then, one or two of the components of the composite admixture system, such as water-reducing agent and retarder, are added to the mixer along with 70% to 80% of the mixing water for initial wet mixing. The mixing time is 90 to 120 seconds. B2: Main mixing and second-stage admixture addition. After the initial wet mixing is completed, add the remaining 20% ​​to 30% of cement to the mixer. Then, add one or more of the following components of the composite admixture system: drought-strength agent, air-entraining agent, defoamer, expansion agent, and cellulose ether, along with the remaining 20% ​​to 30% of mixing water, to the mixer for main mixing. The mixing time is 150 to 180 seconds. B3: Fine-tuning and third-stage admixture addition. After the main mixing is completed, one or more of the following components of the composite admixture system, namely shrinkage compensator, interface enhancer, crystal-forming waterproofing agent and nano-mineral admixture, are added to the mixer in batches or all at once for final mixing. The mixing time is 60 to 90 seconds.

4. The method for preparing concrete with optimized performance using composite admixtures as described in claim 2, characterized in that: The water-reducing agent is a polycarboxylate-based water-reducing agent, the air-entraining agent is a rosin resin-based air-entraining agent, the defoamer is a polyether-modified silicone oil, and the interface reinforcing agent is an organosilane coupling agent.

5. The method for preparing concrete with optimized performance using composite admixtures as described in claim 2, characterized in that: The retarder is sodium gluconate with a purity of not less than 98%, and its dosage is controlled between 0.05% and 0.3% of the cement mass.

6. The method for preparing concrete with optimized performance using composite admixtures as described in claim 2, characterized in that: The early strength agent is calcium chloride with a purity of not less than 95%, and the amount of anhydrous calcium chloride is controlled between 1.0% and 2.0% of the cement mass.

7. The method for preparing concrete with optimized performance using composite admixtures as described in claim 2, characterized in that: The expansive agent is a calcium sulfoaluminate type expansive agent with a fineness modulus of less than 400 mesh and an admixture amount of 6% to 10% of the cement mass.

8. The method for preparing concrete with optimized performance using composite admixtures as described in claim 2, characterized in that: The shrinkage compensator is a calcium oxide-based shrinkage compensator with an active calcium oxide content of not less than 90%, a particle size distribution concentrated between 5 micrometers and 20 micrometers, and an admixture dosage of 1% to 3% of the cement mass.

9. A method for preparing concrete with optimized performance using composite admixtures as described in claim 2, characterized in that: The nanoscale mineral admixture is nano-silica, with an average particle size between 10nm and 50nm, a specific surface area of ​​not less than 200m² / g, and a purity of not less than 99.5%.

10. A method for preparing concrete with optimized performance using composite admixtures as described in claim 2, characterized in that: The cellulose ether is hydroxypropyl methylcellulose with a viscosity of 15000 mPa·s and a degree of substitution of 1.8 to 2.0.

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