Micro-expansion low-heat portland cement-based concrete material, method for preparing same, and use thereof

Abstract

This application discloses a micro-expansion low-heat silicate cement-based concrete material, its preparation method, and its application, belonging to the field of concrete engineering technology. Each cubic meter of micro-expansion low-heat silicate cement-based concrete material comprises 78-92 kg of water, 82-161 kg of micro-expansion low-heat silicate cement, 28-105 kg of fly ash, 476-608 kg of sand, and 1286-1696 kg of aggregate. The dosage of naphthalene-based water-reducing agent is 0.4 wt%-0.6 wt%, and the dosage of air-entraining agent is 0.014 wt%-0.018 wt%. The air content of the concrete material in the mixed state is 4%-5%, and the slump is 35-50 mm. Through the synergistic proportioning of water, micro-expansion low-heat silicate cement, fly ash, sand, and aggregate, the low heat of hydration and micro-expansion characteristics of micro-expansion low-heat silicate cement are fully utilized.

Description

Technical Field

[0001] This application belongs to the field of concrete engineering technology, specifically relating to a micro-expansion low-heat silicate cement-based concrete material, its preparation method, and its application. Background Technology

[0002] Micro-expansion low-heat silicate cement is a type of cement with dicalcium silicate (C2S) as the main mineral. Its C2S content is usually not less than 40%. Compared with medium-heat silicate cement, micro-expansion low-heat silicate cement has the advantage of low heat of hydration, which can be reduced by more than 50%. It can reduce the peak temperature rise inside large-volume concrete and reduce temperature stress, thereby enhancing crack resistance from the material itself.

[0003] However, the current mix design for micro-expansion low-heat silicate cement with aggregates and water-reducing agents still follows the technical system of medium-heat silicate cement or ordinary silicate cement, which makes it difficult to fully utilize the micro-expansion effect and crack resistance advantages of micro-expansion low-heat silicate cement. Summary of the Invention

[0004] This application discloses a micro-expansion low-heat silicate cement-based concrete material, its preparation method, and its application, in order to solve the problem that the existing technology has defects in the mix design of micro-expansion low-heat silicate cement with aggregates, water-reducing agents, etc., which makes it difficult to fully utilize the micro-expansion effect and crack resistance advantages of micro-expansion low-heat silicate cement.

[0005] To solve the above-mentioned technical problems, this application is implemented as follows: In a first aspect, this application discloses a micro-expansion low-heat silicate cement-based concrete material. Each cubic meter of the concrete material comprises 78-92 kg of water, 82-161 kg of micro-expansion low-heat silicate cement, 28-105 kg of fly ash, 476-608 kg of sand, and 1286-1696 kg of aggregate. The concrete material also includes a naphthalene-based water-reducing agent and an air-entraining agent. The naphthalene-based water-reducing agent is added at a dosage of 0.4 wt%-0.6 wt%, and the air-entraining agent is added at a dosage of 0.014 wt%-0.018 wt%. The concrete material has an air content of 4% to 5% and a slump of 35 to 50 mm in the mixed state. The aggregates include secondary, tertiary, or quaternary aggregates. The secondary aggregates include medium and small stones in a mass ratio of (45-60):(40-55). The tertiary aggregates include large, medium, and small stones in a mass ratio of (40-50):(20-30):(20-30). The quaternary aggregates include extra-large, large, medium, and small stones in a mass ratio of (25-35):(20-30):(20-25):(20-30).

[0006] In some embodiments, the water-cement ratio in the concrete material is 0.35 to 0.55, and the fly ash content is 25 wt% to 35 wt%.

[0007] In some embodiments, the bulk density of the secondary aggregate in its stacked state is 1550~1595 kg / m³. 3 The porosity is 40-45%; under vibratory compaction, the density of the secondary aggregate is 1810-1860 kg / m³. 3 And the porosity is 33%~36%; And / or, in the stacked state, the bulk density of the three-graded aggregate is 1600~1640 kg / m³. 3 The porosity is 39%~42%; under vibratory compaction, the density of the three-graded aggregate is 1840~1860 kg / m³. 3 And the porosity is 30%~36%; And / or, in the packed state, the bulk density of the four-grade aggregate is 1600~1640 kg / m³. 3 The porosity is 40%~43%; under vibratory compaction, the density of the four-grade aggregate is 1850~1890 kg / m³. 3 And the porosity is 30%~34%.

[0008] In some embodiments, when the aggregate includes the secondary aggregate, each cubic meter of the concrete material includes 579-1018 kg of medium aggregate and 514-933 kg of small aggregate.

[0009] In some embodiments, when the aggregate includes the three-graded aggregate, each cubic meter of the concrete material includes 591-653 kg of the large stones, 443-490 kg of the medium stones, and 443-490 kg of the small stones.

[0010] In some embodiments, when the aggregate includes the four-graded aggregate, each cubic meter of the concrete material includes 497-511 kg of the extra-large stone, 333-341 kg of the large stone, 414-426 kg of the medium stone, and 414-428 kg of the small stone. In some embodiments, the secondary aggregate comprises medium aggregate and fine aggregate in a mass ratio of 50:50; The three-graded aggregate comprises large stones, medium stones, and small stones in a mass ratio of 40:30:30; The four-grade aggregate comprises extra-large stones, large stones, medium stones, and small stones in a mass ratio of 30:20:25:25.

[0011] In some embodiments, the micro-expansion low-heat silicate cement contains dicalcium silicate content ≥40 wt%, tricalcium aluminate content ≤3 wt%, and magnesium oxide content of 4.0 wt%~4.5 wt%.

[0012] Secondly, this application also provides a method for preparing a micro-expansion, low-heat silicate cement-based concrete material, comprising the following steps: By weight, the following components are used to prepare each cubic meter of concrete: 78-92 kg of water, 82-161 kg of micro-expansion low-heat silicate cement, 28-105 kg of fly ash, 476-608 kg of sand, 1286-1696 kg of aggregate, naphthalene-based water-reducing agent, and air-entraining agent. The naphthalene-based water-reducing agent is added at a dosage of 0.4 wt%-0.6 wt%, the air-entraining agent at a dosage of 0.014 wt%-0.018 wt%, and the aggregate is secondary grade. The aggregate can be classified into three-stage, four-stage, or mixed aggregates. The two-stage aggregates consist of medium and small stones in a mass ratio of (45-60):(40-55); the three-stage aggregates consist of large, medium, and small stones in a mass ratio of (40-50):(20-30):(20-30); and the four-stage aggregates consist of extra-large, large, medium, and small stones in a mass ratio of (25-35):(20-30):(20-25):(20-30). The aggregate and sand are put into a mixer and stirred. Then, the micro-expansion low-heat silicate cement and the fly ash are added and stirred. Finally, the water, the naphthalene-based water-reducing agent and the air-entraining agent are added and stirred to obtain a mixture. The mixture has an air content of 4% to 5% and a slump of 35 to 50 mm in the mixed state. After the mixture is poured into shape and cured, concrete material is obtained.

[0013] Thirdly, this application also provides the application of the aforementioned micro-expansion low-heat silicate cement-based concrete material in large-volume hydraulic concrete.

[0014] This application discloses a micro-expansion low-heat silicate cement-based concrete material. Each cubic meter of the concrete material includes 78-92 kg of water, 82-161 kg of micro-expansion low-heat silicate cement, 28-105 kg of fly ash, 476-608 kg of sand, and 1286-1696 kg of aggregate. The concrete material also includes a naphthalene-based water-reducing agent and an air-entraining agent. The naphthalene-based water-reducing agent is added at a dosage of 0.4 wt%-0.6 wt%, and the air-entraining agent is added at a dosage of 0.014 wt%-0.018 wt%. The concrete material is mixed... The air content in the combined state is 4%~5% and the slump is 35~50mm; the aggregate includes secondary aggregate, tertiary aggregate or quaternary aggregate. The secondary aggregate includes medium stone and small stone with a mass ratio of (45~60):(40~55); the tertiary aggregate includes large stone, medium stone and small stone with a mass ratio of (40~50):(20~30):(20~30); the quaternary aggregate includes extra-large stone, large stone, medium stone and small stone with a mass ratio of (25~35):(20~30):(20~25):(20~30). In this application, the low heat of hydration and micro-expansion characteristics of the low-heat silicate cement are fully utilized through the synergistic proportioning of water, micro-expansion low-heat silicate cement, fly ash, sand, aggregate, naphthalene-based water-reducing agent, and air-entraining agent. Simultaneously, by optimizing the gradation ratio and dosage range of the two-, three-, and four-grade aggregates, the aggregates are made densely packed, reducing the porosity, thereby reducing the amount of cementitious paste, lowering the total heat of hydration, and forming an interlocking rigid aggregate skeleton, providing a stable constraint boundary for micro-expansion stress and improving the volume stability of the concrete material. Furthermore, the dosage of the naphthalene-based water-reducing agent is controlled at 0.4wt%~0.6wt%, and the dosage of the air-entraining agent is controlled at 0.014wt%~0.018wt%. The addition of wt% ensures that the slump of the mixture is stable at 35~50mm and the air content is stable at 4%~5%, guaranteeing workability and freeze-thaw durability, avoiding segregation, bleeding, or strength loss. This optimizes the mechanical properties, durability, and crack resistance of concrete materials, making it suitable for large-volume hydraulic concrete projects with stringent temperature control and crack prevention requirements. Detailed Implementation

[0015] The technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0016] It should be understood that the phrase "one embodiment" or "an embodiment" throughout the specification means that a specific feature, structure, or characteristic related to the embodiment is included in at least one embodiment of this application. Therefore, "in one embodiment" or "in an embodiment" appearing throughout the specification does not necessarily refer to the same embodiment. Furthermore, these specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments.

[0017] Micro-expansion low-heat silicate cement is a type of cement with dicalcium silicate (C2S) as its main mineral composition. Its C2S content is typically no less than 40%, and its tricalcium aluminate (C3A) content is controlled below 3%. It also possesses micro-expansion properties through the introduction of an appropriate amount of magnesium oxide (MgO). Compared to medium-heat silicate cement, this micro-expansion low-heat silicate cement has the advantage of low heat of hydration, which can be reduced by more than 50%. This reduces the peak temperature rise inside large-volume concrete and lowers temperature stress. Simultaneously, during the temperature drop and shrinkage process, the delayed micro-expansion generated by MgO hydration in the micro-expansion low-heat silicate cement can compensate for the volume shrinkage of the concrete, thereby enhancing crack resistance from the material's fundamental source.

[0018] However, current mix design for micro-expansion low-heat silicate cement still follows the technical system of medium-heat silicate cement or ordinary cement, lacking optimization based on its "low-heat, micro-expansion, and high crack resistance" characteristics. Specifically, it has the following technical defects: Regarding the compatibility of admixtures, since the mineral composition, particle morphology and surface charge characteristics of micro-expansion low-heat silicate cement differ from those of medium-heat cement, when conventional polycarboxylate superplasticizers are used in combination with them, problems such as abnormal adsorption rate of superplasticizers and mismatch of dispersion performance often occur, leading to frequent phenomena such as segregation, bleeding and caking of the mixture. Furthermore, there is a lack of standards and adjustment schemes for the dosage of superplasticizers and air-entraining agents for micro-expansion low-heat silicate cement.

[0019] In terms of aggregate gradation, the combination ratio of coarse aggregates in grade II, grade III, and grade IV is mostly determined by engineering experience. The gradation combination has not been systematically optimized through quantitative tests of "bulk density-compact density-void ratio", resulting in low bulk density and high void ratio of aggregates, loose internal structure of concrete, and difficulty in ensuring compactness.

[0020] Regarding the mix proportion parameters, key parameters such as water content and sand ratio were not accurately matched according to the aggregate gradation type. The dosage of water-reducing agent and air-entraining agent was not coordinated with the hydration characteristics of micro-expansion low-heat silicate cement. Problems such as excessive water content, unstable air content control, and insufficient matching between water-cement ratio and binder dosage were found, making it difficult to fully realize the micro-expansion effect and crack resistance advantages of micro-expansion low-heat silicate cement.

[0021] Therefore, the aforementioned technical defects lead to multiple difficulties in the engineering application of micro-expansion low-heat silicate cement: poor compatibility of admixtures makes it difficult to stably control the workability of the mixture, easily resulting in segregation or insufficient fluidity, affecting construction efficiency and pouring quality; lack of quantitative optimization of aggregate gradation leads to insufficient concrete density and high porosity, which not only weakens mechanical properties but also reduces durability properties such as impermeability and frost resistance, and may even weaken the effective transmission of the MgO micro-expansion effect; mismatched mix proportion parameters make it difficult to achieve synergy among hydration heat control, expansion process and mechanical development, and an effective crack compensation mechanism cannot be formed during the temperature drop and shrinkage stage.

[0022] To address the above issues, this application provides a micro-expansion, low-heat silicate cement-based concrete material. Each cubic meter of the concrete material comprises 78-92 kg of water, 82-161 kg of micro-expansion, low-heat silicate cement, 28-105 kg of fly ash, 476-608 kg of sand, and 1286-1696 kg of aggregate. The concrete material also includes a naphthalene-based water-reducing agent and an air-entraining agent. The naphthalene-based water-reducing agent is added at a dosage of 0.4 wt%-0.6 wt%, and the air-entraining agent is added at a dosage of 0.014 wt%-0.018 wt%. It should be noted that, based on the above formula, the water-cement ratio is 0.29~0.77, and the fly ash content is 15%~56%, where the water-cement ratio = water ÷ (cement + fly ash), and the fly ash content = fly ash ÷ (cement + fly ash) × 100%.

[0023] The air content of the concrete material in the mixed state is 4%~5% and the slump is 35~50mm.

[0024] Aggregates include secondary, tertiary, or quaternary aggregates. Secondary aggregates include medium and small stones in a mass ratio of (45~60):(40~55); tertiary aggregates include large, medium, and small stones in a mass ratio of (40~50):(20~30):(20~30); and quaternary aggregates include extra-large, large, medium, and small stones in a mass ratio of (25~35):(20~30):(20~25):(20~30).

[0025] In this application, micro-expansion low-heat silicate cement-based concrete material refers to concrete material formed by mixing, molding, and curing micro-expansion low-heat silicate cement as the core cementitious material, compounded with fly ash, sand, aggregate, water-reducing agent, air-entraining agent and water.

[0026] Among them, micro-expansion low-heat silicate cement is a type of cement with dicalcium silicate (C2S) as the main mineral composition, with a C2S mass ratio of not less than 40%, tricalcium aluminate (C3A) mass ratio of not more than 3%, and magnesium oxide (MgO) mass ratio of 4.0%~4.5%. This micro-expansion low-heat silicate cement has the characteristics of low heat of hydration, micro-expansion to compensate for shrinkage, and high crack resistance. It can reduce the peak temperature rise of large-volume concrete and, during the temperature drop stage, compensate for volume shrinkage through the delayed micro-expansion of MgO, thus inhibiting crack formation from the material itself.

[0027] Fly ash includes Grade I fly ash (water requirement ≤95%), Grade II fly ash (water requirement ≤105%), or Grade III fly ash (water requirement ≤115%). The active components of fly ash undergo a secondary pozzolanic reaction with the calcium hydroxide generated during the hydration of micro-expansion low-heat silicate cement. This reaction refines the pore structure, improves the interfacial transition zone, reduces early hydration heat, and enhances the later strength and durability of concrete materials.

[0028] The sand is medium sand used in hydraulic concrete, with a fineness modulus of 2.3 to 3.0 and a mud content of no more than 3.0%. The sand fills the voids between aggregates in the concrete material and, together with the cementitious material paste, forms mortar that coats the surface of the aggregates, giving the mixture the necessary fluidity and cohesiveness.

[0029] The aggregate is made from crushed hydraulic limestone and is divided into extra-large stones, large stones, medium stones, and small stones. In some embodiments, the particle size of extra-large stones is 80mm~150mm, the particle size of large stones is 40mm~80mm, the particle size of medium stones is 20mm~40mm, and the particle size of small stones is 5mm~20mm.

[0030] In some embodiments, the amount of aggregate per cubic meter of concrete material is within the range of one or any two of 1286 kg, 1300 kg, 1350 kg, 1400 kg, 1500 kg, 1600 kg, 1650 kg and 1696 kg.

[0031] Aggregates act as the skeleton in concrete, bearing most of the load. Their gradation affects the bulk density and porosity, which in turn determines the compactness and volume stability of the concrete material. Depending on the project requirements, extra-large, large, medium, and small stones are combined to form secondary, tertiary, or quaternary aggregates.

[0032] In this embodiment, the mass ratio of medium-sized stones to large stones in the secondary aggregate is (45~60):(40~55). This ratio range allows for a reasonable particle size distribution between medium-sized and small stones. The medium-sized stones act as a coarse skeleton, while the small stones act as fillers. The two interlock, achieving a high bulk density and low porosity in the packed state. Preferably, the mass ratio of medium-sized stones to large stones in the secondary aggregate is 50:50.

[0033] In a three-grade aggregate, the mass ratio of large stones, medium stones, and small stones is (40~50):(20~30):(20~30), which effectively fills the gaps between large stones with medium stones, and further fills the gaps between medium stones with small stones, forming a tightly packed structure with progressively interlocking aggregates. Preferably, the mass ratio of large stones, medium stones, and small stones in the three-grade aggregate is 40:30:30.

[0034] When the mass ratio of extra-large stones, large stones, medium stones, and small stones in the four-grade aggregate is (25~35):(20~30):(20~25):(20~30), the large skeleton voids formed by the extra-large stones are effectively filled by the large stones, the voids between the large stones are further filled by the medium stones, and the voids between the medium stones are finely filled by the small stones, forming a multi-level interlocking and densest packing structure, so that the aggregate system achieves the minimum porosity and maximum bulk density on a macroscopic scale. Preferably, the mass ratio of extra-large stones, large stones, medium stones, and small stones in the four-grade aggregate is 30:20:25:25.

[0035] The above aggregate combination system reduces voids in the structure, enhances the density of the aggregate skeleton, restricts the free shrinkage of the cementitious paste, and reduces drying shrinkage and autogenous shrinkage. This complements the micro-expansion characteristics of micro-expansion low-heat silicate cement, jointly inhibiting crack formation. Simultaneously, it reduces the volume of cementitious paste required to fill voids, lowering the amount of micro-expansion low-heat silicate cement used and the total heat of hydration. For large-volume concrete, the reduction in total heat of hydration means a decrease in peak temperature rise and temperature stress. Combined with the low heat of hydration inherent in micro-expansion low-heat silicate cement, this allows for better control of internal temperature rise within a safer range, fundamentally reducing the risk of temperature cracks. Furthermore, the reduced amount of cementitious material results in a moderate paste thickness, avoiding increased drying shrinkage and decreased volume stability caused by excessive paste thickness. This allows the micro-expansion effect of MgO in micro-expansion low-heat silicate cement to be more effectively transferred to the aggregate interface.

[0036] The water used is drinking water that meets the standards for water used in hydraulic concrete. It serves as the medium for the hydration reaction of micro-expansion low-heat silicate cement and imparts fluidity to the mixture. The amount of water used and the water-cement ratio together determine the strength and durability of the concrete.

[0037] In some embodiments, the naphthalene-based water-reducing agent is a high-efficiency water-reducing agent of β-naphthalenesulfonic acid formaldehyde condensate. The sulfonic acid groups in its molecular structure are adsorbed on the surface of micro-expansion low-heat silicate cement particles, generating electrostatic repulsion and steric hindrance effects, which fully disperse the micro-expansion low-heat silicate cement particles, release the encapsulated water, improve fluidity at the same water-cement ratio, or reduce the water consumption while maintaining the slump, thereby reducing the water-cement ratio, increasing strength, and reducing porosity.

[0038] In some embodiments, the naphthalene-based water-reducing agent is of type JM-II, type FDN9001, or type ZB-1A.

[0039] The air-entraining agent is a rosin thermal polymer air-entraining agent. Its molecules have hydrophobic and hydrophilic groups. During the stirring process, it is directionally adsorbed at the gas-liquid interface, reducing the surface tension and introducing a large number of uniformly distributed microbubbles with a pore size of less than 200μm and a spacing coefficient of no more than 0.25mm. These microbubbles act as ball bearing lubricants in the mixture, which can improve the fluidity of the mixture. At the same time, they cut off the capillary channels and improve the concrete's resistance to freeze-thaw cycles and impermeability.

[0040] In some embodiments, the air-entraining agent is of type ZB-1G, type PC-2, or type AIR202.

[0041] It should be noted that the dosage of naphthalene-based water-reducing agent refers to the percentage of the mass of the naphthalene-based water-reducing agent (by solids content) to the total mass of the cementitious material. The total mass of the cementitious material is the sum of the masses of low-heat silicate cement and fly ash.

[0042] Since micro-expansion low-heat silicate cement uses dicalcium silicate (C2S) as the main mineral, with a C2S mass ratio of not less than 40% and a tricalcium aluminate (C3A) mass ratio of not more than 3%, the surface charge density of its particles has poor adsorption matching with polycarboxylate superplasticizers. On the other hand, naphthalene superplasticizers, as β-naphthalenesulfonic acid formaldehyde condensates, have negatively charged sulfonic acid groups in their molecular structure, which can be adsorbed onto the surface of micro-expansion low-heat silicate cement particles through electrostatic repulsion, forming a stable double electric layer structure, which allows the cement particles to be fully dispersed and release the encapsulated free water.

[0043] Therefore, when the dosage of naphthalene-based water-reducing agent is controlled within the range of 0.4 wt% to 0.6 wt%, the sulfonic acid groups of the naphthalene-based water-reducing agent can be fully adsorbed onto the surface of micro-expansion low-heat silicate cement particles, making the cement particles uniformly dispersed. This, in turn, allows the cementitious material paste to uniformly coat the aggregate surface, forming a dense and homogeneous mixture. This eliminates abnormal phenomena such as segregation, bleeding, and caking, ensuring that the internal structure of the hardened concrete is uniform and free of water-rich areas. Consequently, the mixture can achieve a target slump of 35 to 50 mm without the need for additional water, ensuring that the water-cement ratio is stably controlled within the optimized range of 0.35 to 0.55, thus guaranteeing the density and strength of the concrete. At the same time, the naphthalene-based water-reducing agent at this dosage does not adversely interfere with the hydration process of micro-expansion low-heat silicate cement. It matches the mild hydration exothermic characteristics of micro-expansion low-heat silicate cement, resulting in stable and orderly early strength development. It will not affect the demolding progress due to excessive retarding, and it fully utilizes the advantage of the continuous strength growth of micro-expansion low-heat silicate cement in the later stage. More importantly, the uniformly dispersed cementitious material system allows the hydration products of the MgO micro-expansion component in the micro-expansion low-heat silicate cement to be evenly distributed, enabling the micro-expansion stress to be transmitted to the aggregate interface and the entire concrete material, compensating for the shrinkage caused by temperature drop. This allows the advantages of micro-expansion low-heat silicate cement, namely "low heat of hydration, micro-expansion, and high crack resistance", to be maximized.

[0044] The air-entraining agent dosage refers to the percentage of the air-entraining agent's mass relative to the total mass of the cementitious material. The air-entraining agent is a rosin-based thermopolymer surfactant whose molecules are directionally adsorbed at the gas-liquid interface, reducing surface tension and introducing a large number of uniformly distributed microbubbles with a pore size less than 200 μm and a spacing coefficient no greater than 0.25 mm during stirring. Controlling the air-entraining agent dosage within the range of 0.014 wt% to 0.018 wt% introduces sufficient air bubbles, allowing the air content to be stably controlled at 4% to 5%. This air content range exhibits excellent bubble stability and size distribution in micro-expansion low-heat silicate cement systems, with the bubble spacing coefficient meeting frost resistance requirements, achieving a frost resistance grade of F200 or higher. Simultaneously, the ball-bearing lubrication effect of the bubbles synergistically complements the dispersing effect of the naphthalene-based water-reducing agent, improving the fluidity of the micro-expansion low-heat silicate cement mixture under low water-cement ratio conditions, stabilizing the slump at 35 to 50 mm, and preventing strength reduction due to excessively high air content. This results in a significant improvement in durability while maintaining mechanical properties. Furthermore, the dosage range of this air-entraining agent does not interfere with the hydration process of the MgO micro-expansion agent in the micro-expansion low-heat silicate cement. The bubble system provides a fine space for the uniform distribution of MgO hydration products, avoiding local concentration of expansion stress and making the micro-expansion effect more uniformly compensate for temperature drop shrinkage.

[0045] Air content refers to the percentage of uniformly distributed microbubbles in fresh concrete relative to the total volume of the concrete, expressed as a percentage (%). Air content affects the freeze-thaw resistance, fluidity, and strength of concrete. In this application, the air content in the mixed state is limited to 4.0%~5%. This range was determined experimentally using an air-entraining agent dosage of 0.014 wt%~0.018 wt% in a micro-expansion low-heat silicate cement system. This ensures that the concrete material achieves a freeze-thaw resistance grade of F200 or higher without reducing strength due to excessive air content. Simultaneously, the ball-bearing lubrication effect of the microbubbles improves the early fluidity of the micro-expansion low-heat silicate cement.

[0046] The air content is determined according to the air pressure method or water pressure method in the "Test Procedure for Hydraulic Concrete" (DL / T 5150) or the "Standard for Test Methods of Performance of Ordinary Concrete Mixtures" (GB / T 50080). During the test, the freshly mixed concrete is placed into the measuring bowl of the air content meter, compacted by tamping and vibration, the surface is leveled, the bowl lid is tightened, and pressure balance is established by injecting water to release air. The pressure gauge value is read, and the air content value is obtained by comparing with the calibration curve.

[0047] In the micro-expansion low-heat silicate cement of this application embodiment, the mass percentage of dicalcium silicate is ≥40 wt%, the mass percentage of tricalcium aluminate is ≤3 wt%, and the mass percentage of magnesium oxide is 4.0 wt%~4.5 wt%.

[0048] In some embodiments, the chemical composition and mass percentage of each chemical component of the micro-expansion low-heat silicate cement are as follows: CaO 58.74 wt%, SiO2 22.82 wt%, Al2O3 3.55 wt%, Fe2O3 4.28 wt%, MgO 4.18 wt%, SO3 2.96 wt%, R2O 0.32 wt%, and loss on ignition 1.59%. The corresponding mineral composition, as determined by XRD, is approximately 60 wt% dicalcium silicate (C2S), approximately 2 wt% tricalcium aluminate (C3A), and 4.18 wt% magnesium oxide (MgO), thus endowing the micro-expansion low-heat silicate cement with low heat of hydration and micro-expansion characteristics.

[0049] In some embodiments, the water-cement ratio in the concrete material is 0.35 to 0.55, and the fly ash content is 25 to 35 wt%.

[0050] The water-cement ratio refers to the ratio of the mass of water to the total mass of the cementitious materials. The water-cement ratio is a parameter that determines the strength, durability, and heat of hydration of concrete. In this application, the water-cement ratio is limited to 0.35 to 0.55, meaning the mass of water is 0.35 to 0.55 times the total mass of the cementitious materials. For large-volume hydraulic concrete, this water-cement ratio is beneficial for improving the density and crack resistance of the concrete material.

[0051] In some embodiments, the water-cement ratio in the concrete material is a range of one or both of 0.35, 0.40, 0.42, 0.45, 0.50, and 0.55.

[0052] In this concrete material, the fly ash content is 25-35 wt%, where fly ash content refers to the ratio of fly ash mass to the total mass of cementitious materials. Within this content range, the pozzolanic active components of fly ash (active SiO2 and Al2O3) react with calcium hydroxide generated during the hydration of micro-expansion low-heat silicate cement in a secondary pozzolanic reaction, producing low-calcium-to-silica hydrated calcium silicate gel. This gel fills capillary pores, refines the pore structure, improves the density of the interfacial transition zone, and enhances the later-stage strength and durability of the concrete. Simultaneously, the low early-stage hydration activity of fly ash slows down the hydration heat release rate of the cementitious material system, reducing the peak hydration heat. Combined with the low hydration heat characteristic of micro-expansion low-heat silicate cement itself, this further reduces the internal temperature rise of large-volume concrete, decreases temperature stress, and inhibits the formation of temperature cracks from the material's origin.

[0053] Meanwhile, the fly ash content of 25 wt%~35 wt% synergistically enhances the micro-expansion effect of MgO in micro-expansion low-heat silicate cement: this content range allows the secondary pozzolanic reaction of fly ash and the delayed micro-expansion of MgO to match each other in time history. In the early stage of hydration, fly ash plays a role in cooling and heat reduction, providing a suitable temperature environment for MgO hydration; in the middle and late stages of hydration, the pozzolanic reaction of fly ash consumes calcium hydroxide, reduces the alkalinity of the pore solution, optimizes the uniformity of MgO hydration products distribution, and enables the expansion stress to be uniformly transmitted along the aggregate interface, avoiding local stress concentration, realizing the synchronization of the expansion process and the temperature drop and shrinkage process, and improving the crack resistance safety margin of concrete.

[0054] In some embodiments, the fly ash content is a range of one or both of 25 wt%, 28 wt%, 30 wt%, 33 wt%, and 35 wt%.

[0055] In some embodiments, the bulk density of the secondary aggregate in the stockpiled state is 1550~1595 kg / m³. 3 The porosity is 40%~45%; the compacted density of the secondary aggregate under vibratory conditions is 1810~1860 kg / m³. 3 The porosity is 33%~36%.

[0056] It should be noted that bulk density, compacted density, and porosity are physical quantities that characterize the quality of aggregate particle gradation and the degree of packing density. Their definitions and measurement methods are as follows: Bulk density refers to the mass of aggregate per unit volume (including the volume of aggregate particles and the volume of voids between particles) in a packed state. It is usually determined by the volumetric cylinder method according to the "Test Procedure for Hydraulic Concrete" (DL / T 5150) or "Construction Gravel and Crushed Stone" (GB / T 14685). The aggregate is dropped freely from a specified height into the volumetric cylinder until it overflows, then leveled and weighed to obtain the density.

[0057] Compact density refers to the mass per unit volume of aggregate under vibratory compaction. It is measured by weighing the aggregate particles after they have been compacted to the densest possible arrangement using a vibrating table or by layered tamping.

[0058] The porosity is calculated based on the relationship between bulk density or compacted density and apparent density of aggregate. The formula is: porosity (%) = (1 - bulk density or compacted density / apparent density of aggregate) × 100%. Apparent density of aggregate is determined according to standard methods.

[0059] The higher the bulk density and the lower the porosity, the more reasonable the mix of aggregate particles. The gaps between large particles are filled by medium-sized particles, and the gaps between medium-sized particles are filled by small particles, forming the densest packing state.

[0060] In the embodiments of this application, for secondary aggregates (composed of medium stone and fine stone), the bulk density is relatively high (1550~1595 kg / m³) in the stockpiled state. 3 The high density and low porosity (40%~45%) of this gradation combination indicate that it has high packing efficiency in the packing state, with small void volumes between aggregate particles. This means that the volume of cementitious paste required to fill these voids in concrete mix design is correspondingly reduced. The reduction in paste volume directly reduces the amount of cementitious materials used, thereby reducing the total heat of hydration of micro-expansion low-heat silicate cement, which is beneficial for improving temperature control and crack prevention in large-volume concrete. At the same time, the reduction in paste volume allows the cementitious paste to coat the aggregate surface more evenly, avoiding increased drying shrinkage and decreased volume stability caused by excessive paste thickness. This allows the micro-expansion effect of micro-expansion low-heat silicate cement to be more effectively transferred to the aggregate interface, forming a synergistic crack resistance mechanism.

[0061] For secondary aggregates (composed of medium and small stones), the compaction density is increased to 1810~1860 kg / m³ under vibratory compaction. 3The porosity decreased to 33%~36%, indicating that the aggregate mix could achieve the densest arrangement of aggregate particles after mechanical vibration. When the mixture was poured into the mold and vibrated, the aggregate particles tended to be densely packed under vibration, and the porosity was further compressed from 40%~45% in the packed state to 33%~36%. This means that the aggregate particles formed a denser skeleton structure through displacement and rearrangement, which improved the elastic modulus, reduced creep deformation, and made the micro-expansion stress of the micro-expansion low-heat silicate cement more effectively compensate for temperature drop shrinkage. On the other hand, the dense arrangement of the aggregate skeleton restricted the free shrinkage of the cementitious paste, reduced drying shrinkage and autogenous shrinkage, complementing the micro-expansion characteristics of the micro-expansion low-heat silicate cement and jointly inhibiting crack formation.

[0062] In some embodiments, the bulk density of the three-graded aggregate in its stockped state is 1600~1640 kg / m³. 3 The porosity is 39%~42%; the compacted density of the three-grade aggregate under vibratory compaction is 1840~1860 kg / m³. 3 The porosity is 30%~36%.

[0063] In this embodiment, for three-grade aggregate, the bulk density in the stockpiled state is relatively high (1600~1640 kg / m³). 3 The low porosity (39%~42%) indicates that this gradation combination has a high packing efficiency during natural packing. The small void volume between aggregate particles means that the volume of cementitious material paste required to fill the voids is reduced accordingly, which reduces the amount of micro-expansion low-heat silicate cement and the total heat of hydration, and is conducive to promoting the temperature control and crack prevention performance of large-volume concrete.

[0064] For graded aggregates, the bulk density is higher than that of graded aggregates (1550~1595 kg / m³). 3 This is because the three-gradation method increases the amount of large stone components. The coarse skeleton formed by the large stones provides more space for the filling of medium-sized aggregates, which further improves the overall packing efficiency.

[0065] For graded aggregates, the compacted density is 1840~1860 kg / m³ under vibratory compaction. 3 The porosity is 30%~36%. This variation indicates that the aggregate composition can achieve the densest arrangement of aggregate particles after mechanical vibration. The aggregate particles form a rigid skeleton through displacement and rearrangement. This skeleton provides a stable constraint boundary for the uniform distribution of MgO micro-expansion hydration products in micro-expansion low-heat silicate cement while bearing the load. This allows the expansion stress to be uniformly transmitted along the aggregate interface, avoiding local concentration of expansion stress in the paste-rich area, and achieving precise matching between the expansion process and the temperature drop shrinkage process.

[0066] Three-grade aggregates are typically used in general parts of large-volume structures or areas with low pumping heights. Their aggregate particle size is between that of two-grade and four-grade aggregates, which has both good packing density and maintains a certain degree of flowability.

[0067] In some embodiments, the bulk density of the graded aggregate in its stockped state is 1600~1640 kg / m³. 3 The porosity is 40%~43%; the compacted density of graded aggregate under vibratory compaction is 1850~1890 kg / m³. 3 The porosity is 30%~34%.

[0068] In this embodiment, the large skeleton voids formed by the extra-large stones of the four-grade aggregate are effectively filled by the large stones, the voids between the large stones are further filled by the medium stones, and the voids between the medium stones are finely filled by the small stones, forming the densest packing structure of multi-level interlocking, so that the aggregate system achieves the minimum porosity and the maximum packing density on a macroscopic scale.

[0069] For graded aggregates, in the stockpiled state, the higher bulk density (1600~1640 kg / m³) 3 The high density and low porosity (40%~43%) of this gradation combination indicate that it already has extremely high packing efficiency during natural packing, with a reduced void volume between aggregate particles. Compared to two- and three-grade aggregates, four-grade aggregates, by introducing extra-large stone components, construct a more coarse skeleton system. The macroscopic voids between extra-large stones are filled stepwise by large, medium, and small stones, achieving the highest packing density and the lowest porosity under the same cementitious material dosage. This means that the volume of cementitious material paste required to fill the aggregate voids is significantly reduced, lowering the dosage of micro-expansion low-heat silicate cement and the total heat of hydration. This is of great significance for temperature control and crack prevention in large-volume concrete, especially suitable for engineering components such as ultra-high arch dams and gravity dams where the heat of hydration control is extremely stringent.

[0070] For graded aggregates, the compaction density is increased to 1850~1890 kg / m³ under vibratory compaction conditions. 3 The porosity decreased to 30%~34%, indicating that this gradation combination can achieve the ultimate compaction of aggregate particles after mechanical vibration. The compacted density of the fourth-grade aggregate under vibration is higher than that of the third-grade aggregate (1840~1860 kg / m³). 3 ) and secondary mix (1810~1860kg / m 3The porosity is lower than that of three-grade aggregates (30%~36%) and two-grade aggregates (33%~36%), demonstrating the superior packing efficiency of multi-grade aggregates after vibration. Under vibration, aggregate particles are displaced and rearranged, forming an interlocking rigid skeleton of extra-large stones, large stones, medium stones, and small stones. This skeleton not only bears the main load of concrete, increases the elastic modulus, and reduces creep deformation, but also provides the most stable and effective constraint boundary for the uniform distribution of MgO micro-expansion hydration products in micro-expansion low-heat silicate cement. Table 1 shows the proportion of medium stones in two-grade, three-grade, and four-grade aggregates, as well as the density and porosity of each grade of aggregate in the packed and vibrated states.

[0071] Table 1 Bulk density and porosity of different aggregate gradations

[0072] In some embodiments, when the aggregate includes secondary aggregate, each cubic meter of concrete material includes 579-1018 kg of medium aggregate and 514-933 kg of small aggregate.

[0073] In this embodiment, the combination of 579~1018 kg of medium aggregate and 514~933 kg of small aggregate enables the aggregate to achieve a high bulk density and low porosity in the stockpiled state. The volume of cementitious material paste required to fill the voids is reduced, which reduces the amount of micro-expansion low-heat silicate cement and the total heat of hydration. When combined with the low heat of hydration characteristics of low-heat silicate cement, it can reduce the peak temperature rise of large-volume concrete and reduce temperature stress.

[0074] In some embodiments, when the aggregate includes three-graded aggregate, each cubic meter of concrete material includes 591-653 kg of large stones, 443-490 kg of medium stones, and 443-490 kg of small stones.

[0075] In this embodiment, large stones form a stable coarse aggregate framework as the first-level skeleton, medium stones are embedded in the gaps between large stones to fill and transmit force, and small stones further fill the fine gaps between medium stones, so that the aggregate achieves a high bulk density and a low porosity in the stacked state. The volume of cementitious material paste required to fill the gaps is reduced, which reduces the amount of micro-expansion low-heat silicate cement and the total heat of hydration. When combined with the low heat of hydration characteristics of micro-expansion low-heat silicate cement, the peak temperature rise of large-volume concrete can be reduced.

[0076] In some embodiments, when the aggregate includes four-graded aggregate, each cubic meter of concrete material includes 497-511 kg of extra-large stone, 333-341 kg of large stone, 414-426 kg of medium stone, and 414-428 kg of small stone.

[0077] In this embodiment, extra-large stones form a coarse aggregate framework as the first-level skeleton, with a dosage of 497-511 kg ensuring adequate spacing between the extra-large stone particles; large stones, at a dosage of 333-341 kg, are embedded in the gaps between the extra-large stones, serving a filling and force-transferring function; medium stones, at a dosage of 414-426 kg, further fill the gaps between the large stones; and small stones, at a dosage of 414-428 kg, act as the finest filler, filling the tiny gaps between the medium stones. This results in an aggregate with extremely high bulk density and extremely low porosity in its stacked state, achieving a bulk density of 1600-1640 kg / m³. 3 The porosity is reduced to 40%~43%. This multi-stage filling mechanism minimizes the volume of cementitious material paste required to fill aggregate voids, reducing the amount of micro-expansion low-heat silicate cement and the total heat of hydration. Combined with the low heat of hydration characteristic of micro-expansion low-heat silicate cement itself, the internal temperature rise of large-volume concrete can be controlled at a low level, reducing the peak temperature stress and achieving the goal of reducing temperature cracks from the material's origin.

[0078] This application also provides a method for preparing a micro-expansion, low-heat silicate cement-based concrete material, including the following steps: Step 1: By weight, when preparing one cubic meter of concrete material, take 78-85 kg of water, 82-161 kg of micro-expansion low-heat silicate cement, 28-105 kg of fly ash, 476-608 kg of sand, 1286-1696 kg of aggregate, 0.44-1.6 kg of naphthalene-based water-reducing agent (equivalent to a naphthalene-based water-reducing agent dosage of 0.4-0.6 wt%), and 0.03-0.05 kg of air-entraining agent (equivalent to an air-entraining agent dosage of 0.014-0.018 wt%).

[0079] The aggregates are classified as secondary, tertiary, or quaternary aggregates. Secondary aggregates include medium and small stones in a mass ratio of (45~60):(40~55); tertiary aggregates include large, medium, and small stones in a mass ratio of (40~50):(20~30):(20~30); and quaternary aggregates include extra-large, large, medium, and small stones in a mass ratio of (25~35):(20~30):(20~25):(20~30).

[0080] Step 2: Add aggregate and sand into a mixer and mix. Then add micro-expansion low-heat silicate cement and fly ash and continue mixing. Finally, add water, naphthalene-based water-reducing agent and air-entraining agent and mix to obtain a mixture. The water-cement ratio of the mixture is 0.35~0.55, the air content in the mixed state is 4%~5%, and the slump is 35~50mm.

[0081] Step 3: After pouring the mixture into shape, cure it to obtain micro-expansion low-heat silicate cement-based concrete material.

[0082] In this step, curing is crucial to ensuring the full hydration reaction of the micro-expansion low-heat silicate cement, the effective exertion of the micro-expansion effect, and the achievement of various performance indicators of the concrete. After pouring and molding, the concrete surface should be covered with a moisture-retaining material or water-retaining curing measures should be taken. During the curing period, the concrete surface should be kept moist to avoid interruption of hydration or shrinkage cracks due to water evaporation. For large-volume concrete, it is advisable to cover it with plastic film and insulation blankets promptly after pouring to control the temperature difference between the inside and surface of the concrete to not exceed 25°C, preventing temperature cracks. The curing period should not be less than 28 days.

[0083] During the curing process, mechanical damage to the concrete surface should be avoided. After demolding, timely moist curing should be carried out to ensure that the concrete continues to hydrate under moist conditions, so that the secondary pozzolanic reaction of fly ash in the cementitious material system can be fully carried out, the pore structure can be refined, and the density of the interface transition zone can be improved, thereby ensuring that the concrete's compressive strength, ultimate tensile value, impermeability grade and frost resistance grade meet the design requirements.

[0084] This application also provides the application of micro-expansion low-heat silicate cement-based concrete materials, specifically in the application of hydraulic engineering large-volume concrete.

[0085] For the above-mentioned large-volume hydraulic concrete embodiments, it includes the aforementioned micro-expansion low-heat silicate cement-based concrete material and can achieve the same technical effect. To avoid repetition, it will not be described again here. For relevant details, please refer to the description of the micro-expansion low-heat silicate cement-based concrete material embodiments.

[0086] To make the purpose, technical solution, and beneficial effects of this application clearer, the application is further described below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application.

[0087] The present application will be described in detail below through embodiments.

[0088] Example 1 When preparing each cubic meter of concrete material, the following components are used: 84 kg of water, 140 kg of micro-expansion low-heat silicate cement, 47 kg of Grade I fly ash, 555 kg of sand, 503 kg of extra-large aggregate, 335 kg of large aggregate, 419 kg of medium aggregate, and 419 kg of small aggregate (i.e., the mass ratio of extra-large aggregate, large aggregate, medium aggregate, and small aggregate is 30:20:25:25). The dosage of JM-II naphthalene-based water-reducing agent is 0.45 wt%, or 0.84 kg, and the dosage of ZB-1G type air-entraining agent is 0.014 wt%, or 0.026 kg. The micro-expansion low-heat silicate cement used is from the Jiahua brand, and its main components and mass percentages are as follows: CaO 58.74%, SiO2 22.82%, Al2O3 3.55%, Fe2O3 4.28%, MgO 4.18%, SO3 2.96%, R2O 0.32%, and loss on ignition 1.59%.

[0089] Aggregates and sand are added to a mixer and mixed. Then, micro-expansion low-heat silicate cement and fly ash are added and mixed. Finally, water, naphthalene-based water-reducing agent and air-entraining agent are added and mixed to obtain a mixture.

[0090] After the mixture is poured into shape and cured, concrete material is obtained.

[0091] Example 2 When preparing one cubic meter of concrete material, the following components are used: 86 kg of water, 112 kg of micro-expansion low-heat silicate cement, 60 kg of fly ash, 555 kg of sand, 622 kg of large aggregate, 467 kg of medium aggregate, and 467 kg of small aggregate (i.e., the mass ratio of large aggregate, medium aggregate, and small aggregate is 40:30:30). The dosage of JM-II naphthalene-based water-reducing agent is 0.5 wt%, or 0.86 kg, and the dosage of ZB-1G type air-entraining agent is 0.016 wt%, or 0.028 kg.

[0092] Aggregates and sand are added to a mixer and mixed. Then, micro-expansion low-heat silicate cement and fly ash are added and mixed. Finally, water, naphthalene-based water-reducing agent and air-entraining agent are added and mixed to obtain a mixture.

[0093] After the mixture is poured into shape and cured, concrete material is obtained.

[0094] Example 3 When preparing one cubic meter of concrete material, the following components are used: 92 kg of water, 138 kg of micro-expansion low-heat silicate cement, 46 kg of fly ash, 557 kg of sand, 746 kg of medium aggregate, 670 kg of small aggregate (i.e., the mass ratio of medium aggregate to small aggregate is 53:48), 0.55 wt% (1.01 kg) of JM-II naphthalene-based water-reducing agent, and 0.017 wt% (0.031 kg) of ZB-1G type air-entraining agent.

[0095] Aggregates and sand are added to a mixer and mixed. Then, micro-expansion low-heat silicate cement and fly ash are added and mixed. Finally, water, naphthalene-based water-reducing agent and air-entraining agent are added and mixed to obtain a mixture.

[0096] After the mixture is poured into shape and cured, concrete material is obtained.

[0097] Comparative Example 1 The difference from Example 1 is that the four-grade aggregate contains 550 kg of extra-large stone, 300 kg of large stone, 450 kg of medium stone, and 376 kg of small stone (extra-large stone: large stone: medium stone: small stone = 35:19:29:24).

[0098] The performance of the mixtures and concrete materials prepared in the above examples and comparative examples was tested. The test results are shown in Table 2. The test methods included: (1) The slump of the mixture shall be determined in accordance with the provisions of GB / T 50080 "Standard for Test Method of Performance of Ordinary Concrete Mixture" or DL / T5150 "Test Procedure for Hydraulic Concrete".

[0099] (2) The gas content of the mixture shall be determined by the gas pressure method or the water pressure method in accordance with the provisions of GB / T 50080 or DL / T 5150.

[0100] (3) The compressive strength of concrete materials shall be determined in accordance with GB / T 50081 "Standard for Test Methods of Physical and Mechanical Properties of Concrete" or DL / T 5150. The mixture shall be cast into cubic specimens with a side length of 150 mm and cured under standard curing conditions (temperature 20℃±2℃, relative humidity above 95%) until the specified age (28 days, 90 days). The specimens shall be removed, the surface wiped dry, and placed between the upper and lower plates of a pressure testing machine. The specimens shall be continuously and uniformly loaded at a loading rate of 0.5 MPa / s to 0.8 MPa / s until failure. The failure load shall be recorded, and the compressive strength shall be calculated according to the following formula: f=P / A, where f is the compressive strength (MPa), P is the failure load (N), and A is the bearing area of ​​the specimen (mm²). 2 The result is accurate to 0.1 MPa, and the arithmetic mean of the three test specimens is taken as the compressive strength value of the group of specimens.

[0101] (4) The ultimate tensile strength (axial tensile strength) of concrete materials shall be determined in accordance with the provisions of DL / T 5150 "Test Procedure for Hydraulic Concrete". The mixture shall be cast into axial tensile specimens that meet the requirements (usually prism specimens with a maximum aggregate size of more than 3 times). The specimens shall be cured under standard curing conditions to the specified age (90 days). Tie rods shall be pre-embedded at both ends of the specimens or the specimens shall be connected to the testing machine by bonding. The specimens shall be continuously and uniformly loaded at a loading rate of 0.08 MPa / s to 0.12 MPa / s until the specimens fail. The failure load shall be recorded, and the axial tensile strength shall be calculated by the following formula: ft =P / A, where f t Where P is the axial tensile strength (MPa), P is the failure load (N), and A is the cross-sectional area of ​​the specimen (mm²). The ultimate tensile value is expressed as the axial strain at failure and is determined by a deformation measuring device mounted on the specimen, with the result accurate to 1×10⁻⁶. -6 .

[0102] (5) The impermeability grade of concrete materials shall be determined by the stepwise pressure method in accordance with GB / T 50082 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete" or DL / T 5150. The mixture shall be cast into frustum or cylindrical impermeability specimens and cured to the specified age. The specimens shall be sealed and placed in an impermeability tester. Starting from a water pressure of 0.1 MPa, the pressure shall be increased by 0.1 MPa after 8 hours, and then increased by 0.1 MPa every 8 hours until water seepage appears on the end face of 3 out of 6 specimens. The test shall be stopped when the maximum water pressure is recorded and the impermeability grade shall be calculated by the following formula: W = 10H - 1, where H is the maximum water pressure (MPa) when water seepage occurs in 3 specimens, and the impermeability grade is represented by W.

[0103] (6) The freeze-thaw resistance grade of concrete materials shall be determined by the rapid freezing method in accordance with the provisions of GB / T 50082 or DL / T 5150. The mixture shall be cast into prism specimens of 100mm×100mm×400mm and cured to the specified age. The specimens shall be placed in a rapid freeze-thaw tester and subjected to freeze-thaw cycles between -18℃±2℃ and 5℃±2℃. Each freeze-thaw cycle shall be completed within 2h~4h. After every 25 freeze-thaw cycles, the relative dynamic elastic modulus and mass loss rate of the specimen shall be measured. The test shall be stopped when the relative dynamic elastic modulus drops to 60% of the initial value or the mass loss rate reaches 5%. The number of freeze-thaw cycles at this time shall be recorded as the freeze-thaw resistance grade, which shall be represented by F. For example, F200 means that the requirements are still met after 200 freeze-thaw cycles.

[0104] Table 2

[0105] As can be seen from Table 2, Examples 1 to 3 achieved higher 28-day and 90-day compressive strength, ultimate tensile strength, and higher impermeability and frost resistance by using appropriate water-reducing agent dosage, air-entraining agent dosage, and graded aggregate ratio. However, Comparative Example 1, due to its aggregate gradation deviating from the most compact packing ratio of Example 1, resulted in a decrease in air content and a decline in strength and durability indicators, further confirming the important influence of aggregate gradation optimization on concrete performance.

[0106] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0107] Although optional embodiments of the present application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the optional embodiments as well as all changes and modifications falling within the scope of the embodiments of the present application.

[0108] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used merely to distinguish one entity from another, and do not necessarily require or imply any such actual relationship or order between these entities. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or terminal device. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or terminal device that includes that element. The technical solutions provided in this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the principles and implementation methods of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A micro-expansion, low-heat silicate cement-based concrete material, characterized in that, The concrete material per cubic meter comprises 78-92 kg of water, 82-161 kg of micro-expansion low-heat silicate cement, 28-105 kg of fly ash, 476-608 kg of sand, and 1286-1696 kg of aggregate. The concrete material also includes a naphthalene-based water-reducing agent and an air-entraining agent. The naphthalene-based water-reducing agent is added at a dosage of 0.4 wt%-0.6 wt%, and the air-entraining agent is added at a dosage of 0.014 wt%-0.018 wt%. The concrete material has an air content of 4% to 5% and a slump of 35 to 50 mm in the mixed state. The aggregates include secondary, tertiary, or quaternary aggregates. The secondary aggregates include medium and small stones in a mass ratio of (45-60):(40-55). The tertiary aggregates include large, medium, and small stones in a mass ratio of (40-50):(20-30):(20-30). The quaternary aggregates include extra-large, large, medium, and small stones in a mass ratio of (25-35):(20-30):(20-25):(20-30).

2. The micro-expansion low-heat silicate cement-based concrete material according to claim 1, characterized in that, The concrete material has a water-cement ratio of 0.35 to 0.55 and a fly ash content of 25 wt% to 35 wt%.

3. The micro-expansion low-heat silicate cement-based concrete material according to claim 1, characterized in that, In the stockpiled state, the bulk density of the secondary aggregate is 1550~1595 kg / m³. 3 The porosity is 40%~45%; under vibratory compaction, the compacted density of the secondary aggregate is 1810~1860 kg / m³. 3 And the porosity is 33%~36%; And / or, in the stacked state, the bulk density of the three-graded aggregate is 1600~1640 kg / m³. 3 The porosity is 39%~42%; under vibratory compaction, the density of the three-graded aggregate is 1840~1860 kg / m³. 3 And the porosity is 30%~36%; And / or, in the packed state, the bulk density of the four-grade aggregate is 1600~1640 kg / m³. 3 The porosity is 40%~43%; under vibratory compaction, the density of the four-grade aggregate is 1850~1890 kg / m³. 3 And the porosity is 30%~34%.

4. The micro-expansion low-heat silicate cement-based concrete material according to claim 1, characterized in that, When the aggregate includes the secondary aggregate, each cubic meter of the concrete material includes 579~1018 kg of medium aggregate and 514~933 kg of small aggregate.

5. The micro-expansion low-heat silicate cement-based concrete material according to claim 1, characterized in that, When the aggregate includes the three-graded aggregate, each cubic meter of the concrete material includes 591-653 kg of the large stone, 443-490 kg of the medium stone, and 443-490 kg of the small stone.

6. The micro-expansion low-heat silicate cement-based concrete material according to claim 1, characterized in that, When the aggregate includes the four-grade aggregate, each cubic meter of the concrete material includes 497-511 kg of the extra-large stone, 333-341 kg of the large stone, 414-426 kg of the medium stone, and 414-428 kg of the small stone.

7. The micro-expansion low-heat silicate cement-based concrete material according to claim 1, characterized in that, The secondary aggregate comprises medium stone and fine stone in a mass ratio of 50:50; The three-graded aggregate comprises large stones, medium stones, and small stones in a mass ratio of 40:30:30; The four-grade aggregate comprises extra-large stones, large stones, medium stones, and small stones in a mass ratio of 30:20:25:

25.

8. The micro-expansion low-heat silicate cement-based concrete material according to claim 1, characterized in that, The micro-expansion low-heat silicate cement contains dicalcium silicate content ≥40 wt%, tricalcium aluminate content ≤3 wt%, and magnesium oxide content of 4.0 wt%~4.5 wt%.

9. A method for preparing a micro-expansion, low-heat silicate cement-based concrete material, characterized in that, Includes the following steps: By weight, the following components are used to prepare each cubic meter of concrete: 78-92 kg of water, 82-161 kg of micro-expansion low-heat silicate cement, 28-105 kg of fly ash, 476-608 kg of sand, 1286-1696 kg of aggregate, naphthalene-based water-reducing agent, and air-entraining agent. The naphthalene-based water-reducing agent is added at a dosage of 0.4 wt%-0.6 wt%, the air-entraining agent at a dosage of 0.014 wt%-0.018 wt%, and the aggregate is secondary grade. The aggregate can be classified into three-stage, four-stage, or mixed aggregates. The two-stage aggregates consist of medium and small stones in a mass ratio of (45-60):(40-55); the three-stage aggregates consist of large, medium, and small stones in a mass ratio of (40-50):(20-30):(20-30); and the four-stage aggregates consist of extra-large, large, medium, and small stones in a mass ratio of (25-35):(20-30):(20-25):(20-30). The aggregate and sand are put into a mixer and stirred. Then, the micro-expansion low-heat silicate cement and the fly ash are added and stirred. Finally, the water, the naphthalene-based water-reducing agent and the air-entraining agent are added and stirred to obtain a mixture. The mixture has an air content of 4% to 5% and a slump of 35 to 50 mm in the mixed state. After the mixture is poured into shape and cured, concrete material is obtained.

10. The application of the micro-expansion low-heat silicate cement-based concrete material as described in any one of claims 1 to 8 in large-volume hydraulic concrete.

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