Concrete track slab admixture and method of manufacture

Abstract

The application discloses a concrete track slab mixing material and a preparation method, relates to the technical field of high-speed railway component construction, and through the nucleation effect of a nanocrystalline core early strength agent, the cement hydration process is greatly accelerated, the compressive strength of sleeper concrete is significantly improved after 12h of steam curing, the 1d activity index far exceeds the standard requirement, the rapid demolding requirement of the sleeper is met, and defects such as corner drop and cracks are effectively reduced; the pozzolanic effect of superfine mineral powder and silica fume is continuously exerted, the micro aggregate filling effect of a high polymer viscosity reducer is used, the later strength of the concrete continuously grows, meanwhile, the dense filling effect of the high polymer viscosity reducer makes the internal structure of the concrete more compact, the chloride ion penetration resistance and the frost resistance are significantly improved, and the service life of the sleeper is prolonged.

Description

Technical Field

[0001] This invention relates to the field of high-speed railway component construction technology, and in particular to a concrete track slab admixture and its preparation method. Background Technology

[0002] As a crucial component of high-speed railway track structures, ballastless track has gradually replaced traditional ballasted track, becoming the primary structural form for high-speed railways due to its significant advantages such as strong geometric shape retention and reduced maintenance workload. Among these, twin-block ballastless sleepers occupy a core application position in current high-speed railway construction due to their outstanding characteristics, including simple structure, high efficiency of factory prefabrication, convenient on-site construction, and economical overall construction costs.

[0003] In existing high-speed railway double-block ballastless sleeper production practices, steam curing is commonly used to promote the early strength development of concrete in order to improve mold turnover efficiency and ensure construction progress. The typical procedure is as follows: after concrete pouring and molding, steam curing is performed for approximately 12 hours until the core concrete of the sleeper reaches the designed demolding strength (usually not less than 45 MPa), at which point demolding, stacking, and subsequent natural curing can proceed. To reduce hydration heat and improve the long-term volume stability of concrete, existing technologies often use mineral admixtures (such as fly ash, ground granulated slag powder, etc.) to replace a portion of the cement in equal amounts, thus forming the cementitious material system of the sleeper concrete.

[0004] However, when facing the growing dual demands for early demolding efficiency and long-term durability, existing railway sleeper concrete preparation technologies rely solely on ordinary composite admixture systems made from fly ash or mineral powder. While these systems can partially reduce the heat of hydration and facilitate later strength growth, their early hydration activity is relatively low. Within the specified 12-hour steam curing period, they often fail to stably reach the 45MPa strength required for demolding. This results in frequent appearance defects such as chipped corners and microcracks at the edges and corners of the sleepers during demolding, which not only damages the dimensional accuracy and appearance quality of the components but also creates potential durability risks. Summary of the Invention

[0005] The main objective of this invention is to propose a concrete track slab admixture and its preparation method. This aims to address the shortcomings of existing technologies in meeting the growing dual demands for early demolding efficiency and long-term durability. While conventional composite admixture systems relying solely on fly ash or mineral powder can partially reduce the heat of hydration and facilitate later strength growth, their early hydration activity is relatively low. Consequently, they often fail to stably reach the required 45MPa strength for demolding within the specified 12-hour steam curing period. This results in frequent defects such as chipped corners and microcracks at the edges and corners of the sleepers during demolding, which not only damages the dimensional accuracy and appearance quality of the components but also poses a potential durability risk.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a concrete track slab admixture, comprising, by mass fraction, the following materials: Silicate cement: 35-45%; Ultrafine mineral powder: 25-35%; Silica fume: 10-15%; Sodium sulfate: 1-2.5%; Nanocrystalline nucleus early strength agent: 0.5-2%; High molecular weight viscosity reducer: 0.5-1.5%; Water-reducing agent: 0.3-0.6%; Defoamer: 0.1–0.25%; The nanocrystalline nucleus early strength agent is a solid powder composed of nano-sized hydrated calcium silicate particles and an inorganic dispersion carrier. The effective component content of the nano-sized hydrated calcium silicate is 30% to 40%, the average particle size is 50 to 100 nm, and the specific surface area is ≥800,000 m² / g. The sodium sulfate is industrial-grade anhydrous sodium sulfate with a purity of ≥98%.

[0007] In one embodiment, the silicate cement is P·O 52.5 cement, with a 3-day compressive strength ≥30MPa, a 28-day compressive strength ≥52.5MPa, and a specific surface area of ​​300~350m² / kg.

[0008] In one embodiment, the ultrafine mineral powder is S95 grade or above granulated blast furnace slag powder with a specific surface area of ​​400-450 m² / kg, a 7-day activity index ≥75%, a 28-day activity index ≥95%, and a fluidity ratio ≥95%.

[0009] In one embodiment, the silica fume is semi-densified silica fume with SiO2 content ≥90%, specific surface area ≥15000m² / kg, 28d activity index ≥105%, and water requirement ratio ≤125%.

[0010] In one embodiment, the inorganic dispersion carrier is silica fume or metakaolin.

[0011] In one embodiment, the polymer viscosity reducer is an inorganic polymer mineral material composed of one or more of metakaolin, zeolite powder or diatomaceous earth that have been calcined at high temperature and surface modified, with a particle size of 5-50 μm and a bulk density of 0.4-0.8 g / cm3.

[0012] In one embodiment, the water-reducing agent is a powdered polycarboxylate water-reducing agent with a water reduction rate ≥25% and a solid content ≥98%; the defoamer is a powdered polyether defoamer with a defoaming rate ≥80% and a solid content ≥98%.

[0013] Based on the same technical concept, in a second aspect, the present invention also proposes a method for preparing the concrete track slab admixture material described in the first aspect, comprising the following steps: Preparation of intermediates for nanocrystalline nuclei early strength agents; Silicate cement, ultrafine mineral powder, silica fume, sodium sulfate, polymer viscosity reducer, and the intermediate of the nanocrystalline nucleus early strength agent are added to a mixing container according to the mass percentages described in the first aspect, and then mixed to prepare the concrete track slab admixture.

[0014] In one embodiment, the step of preparing the nanocrystalline nucleus early strength agent intermediate includes: A hydrated calcium silicate suspension with a solid content of 15% and silica fume are added to a reaction vessel at a preset mass ratio; wherein, the preset mass ratio is hydrated calcium silicate suspension: silica fume = 1:2; After stirring the reactor for a first target time, a mixture is obtained; wherein, the first target time is 30 minutes. The mixture is vacuum dried at a preset temperature for a second target time to obtain the material to be crushed; wherein the preset temperature is 60°C and the second target time is 24 hours. The material to be crushed is pulverized and sieved to obtain the nanocrystalline nucleus early strength agent intermediate; wherein the content of the hydrated calcium silicate in the nanocrystalline nucleus early strength agent intermediate is 25%, and the average particle size is 50nm to 100nm.

[0015] Based on the same technical concept, in a third aspect, the present invention also proposes a method for manufacturing concrete material for track slabs, comprising the following steps: The concrete aggregate is put into the preset mixing equipment and dry-mixed for a first preset time; wherein, the concrete aggregate used in 1m³ of concrete, by mass fraction, includes sand: coarse aggregate: fine aggregate = 708kg: 808kg: 347kg. The cementitious material and the concrete track slab admixture described in the second aspect are jointly added to the preset mixing equipment and dry-mixed for a second preset time; wherein, the mass of the cementitious material used per m³ of concrete is 405 kg, and the amount of the concrete track slab admixture is 10% of the cementitious material; Water and admixtures are added to the preset mixing equipment and mixed for a third preset time to produce the concrete material.

[0016] The technical solution of this invention significantly accelerates the cement hydration process through the nucleation effect of nanocrystalline nucleus early strength agents, resulting in a significant increase in the compressive strength of railway sleeper concrete after 12 hours of steam curing. The 1-day activity index far exceeds standard requirements, meeting the need for rapid demolding of railway sleepers and effectively reducing defects such as chipping and cracking. The pozzolanic effect of ultrafine mineral powder and silica fume continues to exert its effect, combined with the micro-aggregate filling effect of polymeric viscosity reducers, leading to a sustained increase in the later-stage strength of the concrete. Simultaneously, the dense filling effect of the polymeric viscosity reducers makes the internal structure of the concrete more compact, significantly improving its resistance to chloride ion penetration and freeze-thaw resistance, thus greatly extending the service life of the railway sleepers. The ball-bearing effect of the agent and the dispersing effect of the water-reducing agent work synergistically to significantly improve the fluidity of concrete and significantly reduce the water demand ratio, solving the problem of decreased fluidity after the addition of silica fume. This facilitates construction and molding, resulting in a smooth and defect-free surface. All components are solid powders, which have good storage stability, low transportation costs, convenient metering, and easy uniform mixing, making them suitable for industrial production. The use of ultrafine mineral powder, an industrial by-product, to replace part of the cement reduces cement usage and lowers carbon emissions. The nanocrystalline nucleus early strength agent has a low dosage and high efficiency, and does not introduce harmful components such as chloride ions. The polymer viscosity reducer is an inorganic material, which is environmentally friendly and meets the requirements of sustainable development. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0018] Figure 1 A flowchart illustrating the method for preparing concrete materials provided by this invention.

[0019] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0022] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0023] This invention proposes a concrete track slab admixture and its preparation method.

[0024] Please see Figure 1 For ease of understanding, this concrete track slab admixture, by mass fraction, includes the following materials: Silicate cement: 35-45%; Ultrafine mineral powder: 25-35%; Silica fume: 10-15%; Sodium sulfate: 1-2.5%; Nanocrystalline nucleus early strength agent: 0.5-2%; High molecular weight viscosity reducer: 0.5-1.5%; Water-reducing agent: 0.3-0.6%; Defoamer: 0.1–0.25%; The nanocrystalline nucleus early strength agent is a solid powder composed of nano-sized hydrated calcium silicate particles and an inorganic dispersion carrier. The effective component content of the nano-sized hydrated calcium silicate is 30% to 40%, the average particle size is 50 to 100 nm, and the specific surface area is ≥800,000 m² / g. The sodium sulfate is industrial-grade anhydrous sodium sulfate with a purity of ≥98%.

[0025] In one embodiment, the silicate cement is P·O 52.5 cement, with a 3-day compressive strength ≥30MPa, a 28-day compressive strength ≥52.5MPa, and a specific surface area of ​​300~350m² / kg.

[0026] In one embodiment, the ultrafine mineral powder is S95 grade or above granulated blast furnace slag powder with a specific surface area of ​​400-450 m² / kg, a 7-day activity index ≥75%, a 28-day activity index ≥95%, and a fluidity ratio ≥95%.

[0027] In one embodiment, the silica fume is semi-densified silica fume with SiO2 content ≥90%, specific surface area ≥15000m² / kg, 28d activity index ≥105%, and water requirement ratio ≤125%.

[0028] In one embodiment, the inorganic dispersion carrier is silica fume or metakaolin.

[0029] In one embodiment, the polymer viscosity reducer is an inorganic polymer mineral material composed of one or more of metakaolin, zeolite powder or diatomaceous earth that have been calcined at high temperature and surface modified, with a particle size of 5-50 μm and a bulk density of 0.4-0.8 g / cm3.

[0030] In one embodiment, the water-reducing agent is a powdered polycarboxylate water-reducing agent with a water reduction rate ≥25% and a solid content ≥98%; the defoamer is a powdered polyether defoamer with a defoaming rate ≥80% and a solid content ≥98%.

[0031] The composition of the admixture in the five embodiments of the present invention is shown in Table 1 below: Table 1. Raw material components and proportions of the composite admixture

[0032] Table 2 shows the performance of cement mortar after incorporating the composite admixtures in Examples 1-5.

[0033] Table 2 Performance of Cement Mortar

[0034] As shown in Table 2, after replacing the reference cement with the early-strength admixtures from Examples 1-5, the 1-day mortar activity index all reached over 165%, far exceeding the standard requirement of 125%; the 28-day mortar activity index all reached over 126%, exceeding the standard requirement of 100%; and the mortar water demand ratio was controlled within 103%, meeting the requirement of ≤105% in TB / T 3397-2015 "CRTS Double-Block Ballastless Track Concrete Sleepers". Among them, Example 5, with the highest dosage of nanocrystalline nucleus early-strength agent (1.8%), achieved a 1-day activity index of 175%, showing the most significant early strength improvement effect; Example 3, with the highest dosage of polymer viscosity reducer (1.2%), achieved a 28-day activity index of 131%, showing the best later strength development.

[0035] Table 3. C60 concrete mix proportions (kg / m3)

[0036] When adding the composite admixture of this invention, it is added internally at 10% of the total mass of cementitious materials, that is, 405 kg of standard cement and 45 kg of composite admixture, and the amount of external admixture is 1%.

[0037] Table 4 shows the performance of concrete after incorporating the composite admixtures in Examples 1-5.

[0038] Table 4. Concrete Performance

[0039] Table 4 shows that the 12-hour steam-cured compressive strength of Examples 1-5 all reached above 54 MPa, a significant improvement compared to the comparative example, with Example 5 reaching the highest at 57.2 MPa, proving that the nucleation effect of the nanocrystalline nucleus early strength agent can significantly accelerate cement hydration. The 7-day strength all reached above 69.8 MPa, and the 28-day strength reached above 77.5 MPa, both showing significant improvements compared to the comparative example, with Example 3 exhibiting the highest 28-day strength. This demonstrates that the filling effect of the polymer viscosity reducer and the pozzolanic effect of the mineral admixtures synergistically lead to continuous strength growth. The 56-day electrical flux all decreased to below 760°C, a reduction of 39%-44% compared to the comparative example, with Example 3 showing the lowest. After 100 freeze-thaw cycles, the relative dynamic modulus of elasticity all reached above 94%, far exceeding the 90.3% of the comparative example, indicating significant improvement in resistance to chloride ion penetration and freeze-thaw resistance.

[0040] In this embodiment, the nucleation effect of the nanocrystalline nucleation early strength agent significantly accelerates the cement hydration process, resulting in a significant increase in the compressive strength of the sleeper concrete after 12 hours of steam curing. The 1-day activity index far exceeds the standard requirements, meeting the need for rapid demolding of the sleeper and effectively reducing defects such as corner chipping and cracking. The pozzolanic effect of ultrafine mineral powder and silica fume continues to exert its influence, combined with the micro-aggregate filling effect of the polymer viscosity reducer, causing the concrete's later-stage strength to continue to increase. At the same time, the dense filling effect of the polymer viscosity reducer makes the internal structure of the concrete more compact, significantly improving its resistance to chloride ion penetration and freeze-thaw resistance, thus greatly extending the service life of the sleeper. The ball-bearing effect of the agent and the dispersing effect of the water-reducing agent work synergistically to significantly improve the fluidity of concrete and significantly reduce the water demand ratio, solving the problem of decreased fluidity after the addition of silica fume. This facilitates construction and molding, resulting in a smooth and defect-free surface. All components are solid powders, which have good storage stability, low transportation costs, convenient metering, and easy uniform mixing, making them suitable for industrial production. The use of ultrafine mineral powder, an industrial by-product, to replace part of the cement reduces cement usage and lowers carbon emissions. The nanocrystalline nucleus early strength agent has a low dosage and high efficiency, and does not introduce harmful components such as chloride ions. The polymer viscosity reducer is an inorganic material, which is environmentally friendly and meets the requirements of sustainable development.

[0041] Based on the same technical concept, in a second aspect, the present invention also proposes a method for preparing the concrete track slab admixture material described in the first aspect, comprising the following steps: S100, preparation of nanocrystalline nucleus early strength agent intermediate; S200. Silicate cement, ultrafine mineral powder, silica fume, sodium sulfate, polymer viscosity reducer, and the intermediate of the nanocrystalline nucleus early strength agent are added to a mixing container according to the mass percentages described in the first aspect and mixed to prepare the concrete track slab admixture.

[0042] Specifically, this embodiment aims to provide a method for preparing admixtures that can significantly improve the early demolding strength of concrete track slabs while taking into account the workability and long-term volume stability of the mixture. In the production scenario of double-block ballastless sleepers, after the concrete is poured and formed, it usually needs to undergo a steam curing process of about 12 hours. Demolding can only be carried out when the compressive strength of the core concrete of the sleeper reaches not less than 45MPa. In the prior art, the cementitious material system that simply introduces fly ash or ordinary slag powder has a slow hydration reaction process during this limited steam curing period, resulting in insufficient early strength reserve. This is a direct cause of edge and corner defects and micro-cracks in the sleeper during the demolding stage.

[0043] The concrete track slab admixture prepared by this method, through the nucleation-inducing effect provided by the nanocrystalline nucleus early-strength agent intermediate, synergistically combines the optimized particle packing structure composed of ultrafine mineral powder and silica fume with the sulfate-activating effect of sodium sulfate. Within the predetermined 12-hour steam curing cycle, it stably achieves an early compressive strength exceeding 45 MPa, effectively solving the frequent problems of edge defects and microcracks during the demolding process of double-block ballastless sleepers. Simultaneously, the introduction of a polymer viscosity reducer ensures the workability of the mixture under the high specific surface area powder system. This technical solution not only meets the industrial requirements for rapid mold turnover in the production of high-speed railway ballastless track components but also takes into account the volume stability and durability requirements of the concrete structure during long-term service.

[0044] In one embodiment, step S100 includes: S110. A hydrated calcium silicate suspension with a solid content of 15% and silica fume are added to the reactor at a preset mass ratio; wherein, the preset mass ratio is hydrated calcium silicate suspension: silica fume = 1:2. S120. After stirring the reactor for a first target time, a mixture is obtained; wherein, the first target time is 30 min. S130. Vacuum dry the mixture at a preset temperature for a second target time to obtain the material to be crushed; wherein, the preset temperature is 60°C and the second target time is 24 hours. S140. The material to be crushed is pulverized and sieved to obtain the nanocrystalline nucleus early strength agent intermediate; wherein the content of the hydrated calcium silicate in the nanocrystalline nucleus early strength agent intermediate is 25%, and the average particle size is 50nm to 100nm.

[0045] Specifically, firstly, a hydrated calcium silicate suspension with a solid content of 15% and silica fume are added to the reactor at a preset mass ratio. The hydrated calcium silicate suspension with a solid content of 15% refers to a stable suspension containing 15% by mass of hydrated calcium silicate solid particles, pre-synthesized in a liquid-phase reaction system; the liquid medium is typically water. Using this suspension as a precursor material for the intermediate ensures that the hydrated calcium silicate is uniformly dispersed in the liquid phase at the nanoscale in the initial stage, avoiding hard agglomeration caused by re-dispersion after drying. In this step, the silica fume not only serves as an active mineral admixture component in the subsequent blending materials but also acts as a dispersion carrier and isolation medium in the intermediate preparation process. The hydrated calcium silicate suspension and silica fume are added at the preset mass ratio of 1:2. Here, based on the total mass of the suspension, for every 1 part by mass of suspension added, 2 parts by mass of silica fume powder are added. The extremely fine spherical morphology and high specific surface area of ​​the silica fume particles enable them to fully adsorb the liquid phase medium in the suspension and effectively encapsulate and isolate the hydrated calcium silicate nanoparticles.

[0046] Subsequently, the reaction vessel is stirred for a first target duration to obtain a homogeneous mixture. In this step, the reaction vessel refers to a closed or open reaction container equipped with a mechanical stirring device, preferably made of stainless steel or enamel to prevent corrosion. The first target duration is specifically defined as 30 minutes. Within this time interval, the stirring blades are controlled to rotate at an appropriate linear speed (e.g., 1.5 m / s to 3.0 m / s) to ensure that the 15% solid content hydrated calcium silicate suspension and silica fume powder are fully in contact, mutually wetting each other to form a homogeneous slurry mixture. The stirring duration must be sufficient to completely wet the surface of the silica fume particles with the suspension, while avoiding excessive shearing that could damage the original nanostructure of the hydrated calcium silicate.

[0047] Subsequently, the resulting mixture is vacuum dried under a preset temperature condition for a second target duration to obtain the material to be crushed. In this step, the preset temperature condition is specifically 60°C, and the second target duration is specifically 24 hours. The slurry mixture obtained in the aforementioned steps is spread evenly on a tray inside a vacuum drying oven, with the material layer thickness preferably controlled between 1 cm and 3 cm. The vacuum pump is turned on to reduce the absolute pressure inside the drying oven to the range of -0.08 MPa to -0.095 MPa, while the heating temperature is set and maintained at 60°C. Under this low-temperature vacuum environment, the boiling point of the liquid medium (water) is significantly reduced, enabling rapid evaporation and removal at temperatures far below the atmospheric pressure boiling point.

[0048] Finally, the material to be crushed is pulverized and sieved to obtain the nanocrystalline nucleus early strength agent intermediate. The blocky material to be crushed, after vacuum drying, is fed into an air jet mill or vibratory mill. By adjusting the speed of the classifying wheel or the filling rate of the grinding media, the pulverization intensity is controlled so that the hydrated calcium silicate agglomerates wrapped in silica fume are dissociated into powder with the target particle size distribution. The pulverized powder is then sieved through a sieve of a specified mesh size to retain excessively large coarse particles. The final product obtained after the above treatment is the nanocrystalline nucleus early strength agent intermediate defined by this method. In this intermediate product, the content of hydrated calcium silicate is 25%, a value based on the solid content of the hydrated calcium silicate suspension in the original feed and the amount of silica fume, calculated through material balance to determine the solid phase composition ratio; simultaneously, the average particle size of the intermediate powder is 50 nm to 100 nm. It should be clarified that the average particle size referred to here is the secondary particle size (i.e., the particle size of the composite particle formed by the silica fume carrier and the loaded calcium silicate) measured by laser particle size analyzer or scanning electron microscope image analysis, rather than the primary particle size of the calcium silicate crystal nucleus alone.

[0049] Based on the same technical concept, in a third aspect, the present invention also proposes a method for manufacturing concrete material for track slabs, comprising the following steps: S400. Add concrete aggregate to a pre-set mixing device and dry mix for a first pre-set time; wherein, the concrete aggregate used in 1m³ of concrete, by mass fraction, includes sand: coarse aggregate: fine aggregate = 708kg: 808kg: 347kg.

[0050] Specifically, in this step, the concrete aggregate refers to the granular inorganic materials that constitute the concrete skeleton structure. Its specific composition and dosage are clearly defined as follows: for every 1 m³ of concrete prepared, by mass, it includes 708 kg of sand, 808 kg of coarse aggregate, and 347 kg of fine aggregate. Here, the sand typically refers to natural river sand or clean manufactured sand with a fineness modulus between 2.3 and 3.0; the coarse aggregate refers to crushed stone with a nominal particle size of 5 mm to 20 mm in continuous gradation; and the fine aggregate refers to fine-grained aggregate with a nominal particle size less than 5 mm. These aggregates, together with the aforementioned "sand," form a gradient in particle size distribution, jointly constituting an optimized aggregate packing structure. In this embodiment, the preset mixing equipment is preferably a twin-shaft forced concrete mixer with a nominal capacity of not less than 1.5 m³, whose mixing blades and tank clearance are adjustable, enabling high-intensity shear mixing of dry-hard or low-plasticity concrete. The first preset time is preferably 30 to 45 seconds. After the aggregates of the above three particle sizes are added into the mixing equipment according to the mass ratio, they are first dry-mixed without the introduction of liquid water.

[0051] S500. The cementitious material and the concrete track slab admixture described in the second aspect are put into the preset mixing equipment and dry-mixed for a second preset time; wherein, the mass of the cementitious material used for 1m³ of concrete is 405kg, and the amount of the concrete track slab admixture is 10% of the cementitious material.

[0052] Specifically, in this step, the cementitious material refers to an inorganic powder material that can undergo a hydration reaction and generate binding capacity under the action of mixing water. Its main component is silicate cement, and it may also contain a certain proportion of mineral admixtures. Its dosage is specifically limited to: for every 1 m³ of concrete prepared, the total mass of the cementitious material is 405 kg. The dosage of the admixture is 10% of the mass of the cementitious material, that is, 40.5 kg of the admixture is added per cubic meter of concrete. The second preset time is preferably 45 to 60 seconds. The cementitious material and the admixture are then added together to a mixing device already containing premixed aggregates, and dry mixing continues in an anhydrous state.

[0053] S600. Water and admixtures are added to the preset mixing equipment and mixed for a third preset time to produce the concrete material.

[0054] The amount of water used is adjusted according to the target slump or spread requirements of the concrete, and is usually characterized by the water-cement ratio (the mass ratio of water to cementitious materials). In this embodiment, the preferred water-cement ratio range is 0.28 to 0.32. The third preset time is preferably 120 to 150 seconds. The metered mixing water is evenly added to the dry-mixed powder-aggregate mixture through the spray device of the mixing equipment, and the forced mixing program is started. In the initial stage of mixing, water molecules rapidly wet the surface of cement particles and ultrafine powder in the admixtures, initiating the dissolution and hydration reaction of cement clinker minerals. At this time, the nanocrystalline nucleation early strength agent intermediate particles uniformly dispersed in the cementitious material system rapidly adsorb calcium ions and silicate ions in the surrounding liquid phase, providing a large number of non-uniform nucleation sites, significantly reducing the nucleation barrier of hydration products such as hydrated calcium silicate gel. It can be further clarified that the preferred amount of water is 132 kg.

[0055] The above description is merely an exemplary embodiment of the present invention and does not limit the scope of the present invention. Any equivalent structural transformations made based on the technical concept of the present invention and the contents of the specification and drawings of the present invention, or direct / indirect applications in other related technical fields, are included within the protection scope of the present invention.

Claims

1. A concrete track slab admixture, characterized in that, By mass fraction, it includes the following materials: Silicate cement: 35-45%; Ultrafine mineral powder: 25-35%; Silica fume: 10-15%; Sodium sulfate: 1-2.5%; Nanocrystalline nucleus early strength agent: 0.5-2%; High molecular weight viscosity reducer: 0.5-1.5%; Water-reducing agent: 0.3-0.6%; Defoamer: 0.1–0.25%; The nanocrystalline nucleus early strength agent is a solid powder composed of nano-sized hydrated calcium silicate particles and an inorganic dispersion carrier. The effective component content of the nano-sized hydrated calcium silicate is 30% to 40%, the average particle size is 50 to 100 nm, and the specific surface area is ≥800,000 m² / g. The sodium sulfate is industrial-grade anhydrous sodium sulfate with a purity of ≥98%.

2. The concrete track slab admixture as described in claim 1, characterized in that, The silicate cement is P·O52.5 cement, with a 3d compressive strength ≥30MPa, a 28d compressive strength ≥52.5MPa, and a specific surface area of ​​300~350m² / kg.

3. The concrete track slab admixture as described in claim 2, characterized in that, The ultrafine mineral powder is S95 grade or above granulated blast furnace slag powder with a specific surface area of ​​400-450 m² / kg, a 7-day activity index ≥75%, a 28-day activity index ≥95%, and a fluidity ratio ≥95%.

4. The concrete track slab admixture as described in claim 3, characterized in that, The silica fume is semi-densified silica fume with SiO2 content ≥90%, specific surface area ≥15000m² / kg, 28d activity index ≥105%, and water requirement ratio ≤125%.

5. The concrete track slab admixture as described in claim 4, characterized in that, The inorganic dispersion carrier is silica fume or metakaolin.

6. The concrete track slab admixture as described in claim 5, characterized in that, The polymer viscosity reducer is an inorganic polymer mineral material composed of one or more of metakaolin, zeolite powder or diatomaceous earth that have been calcined at high temperature and surface modified, with a particle size of 5-50 μm and a bulk density of 0.4-0.8 g / cm3.

7. The concrete track slab admixture as described in claim 6, characterized in that, The water-reducing agent is a powdered polycarboxylate water-reducing agent with a water reduction rate ≥25% and a solid content ≥98%; the defoamer is a powdered polyether defoamer with a defoaming rate ≥80% and a solid content ≥98%.

8. A method for preparing a concrete track slab admixture as described in any one of claims 1 to 7, characterized in that, Includes the following steps: Preparation of intermediates for nanocrystalline nuclei early strength agents; The mixture comprises silicate cement, ultrafine mineral powder, silica fume, sodium sulfate, a polymer viscosity reducer, and the aforementioned nanocrystalline nucleation early strength agent intermediate. The mixture is added to a mixing container according to the mass percentage as described in claim 1 and mixed to prepare the concrete track slab admixture.

9. The method for preparing the concrete track slab admixture as described in claim 8, characterized in that, The step of preparing the nanocrystalline nucleus early strength agent intermediate includes: A hydrated calcium silicate suspension with a solid content of 15% and silica fume are added to a reaction vessel at a preset mass ratio; wherein, the preset mass ratio is hydrated calcium silicate suspension: silica fume = 1:2; After stirring the reactor for a first target time, a mixture is obtained; wherein, the first target time is 30 minutes. The mixture is vacuum dried at a preset temperature for a second target time to obtain the material to be crushed; wherein the preset temperature is 60°C and the second target time is 24 hours. The material to be crushed is pulverized and sieved to obtain the nanocrystalline nucleus early strength agent intermediate; wherein the content of the hydrated calcium silicate in the nanocrystalline nucleus early strength agent intermediate is 25%, and the average particle size is 50nm to 100nm.

10. A method for manufacturing concrete material for track slabs, characterized in that, Includes the following steps: The concrete aggregate is put into the preset mixing equipment and dry-mixed for a first preset time; wherein, the concrete aggregate used in 1m³ of concrete, by mass fraction, includes sand: coarse aggregate: fine aggregate = 708kg: 808kg: 347kg. The cementitious material and the concrete track slab admixture as described in claim 8 or 9 are jointly added to the preset mixing equipment and dry-mixed for a second preset time; wherein, the mass of the cementitious material used per m³ of concrete is 405 kg, and the amount of the concrete track slab admixture is 10% of the cementitious material; Water and admixtures are added to the preset mixing equipment and mixed for a third preset time to produce the concrete material.

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