Negative-temperature early-strength concrete as well as preparation method and application thereof

Abstract

The invention relates to the technical field of concrete material preparation, in particular to negative temperature early strength concrete and a preparation method and application thereof. The concrete comprises cement, aggregate, an additive and water. In each cubic meter of the concrete, the doping amount of the cement is 320kg / m < 3 >-475kg / m < 3 >, the maximum mass ratio of the water to the cement is not more than 0.45, the mass ratio of the aggregate to the cement is limited in a range of 3.5-4.6, the doping amount of the additive is 0.9%-1.3% of the doping amount of the cement, and the water reducing rate of the additive is limited in a range of 25%-30%; wherein the aggregate comprises sand and gravel, and the sand ratio is 38%-42.5%. By adding a proper amount of additives and reasonably optimizing the doping proportion of the raw material components, the anti-compression and anti-freezing performance suitable for engineering construction in extreme environments such as high-cold and ultrahigh-altitude permanent permafrost regions and the like is endowed with the anti-compression and anti-freezing performance; the problems of low work efficiency, complex process, difficulty in quality guarantee, difficulty in cost control and the like in road and bridge engineering construction in the high-cold and ultrahigh-altitude permafrost region are systematically solved.

Description

Technical Field

[0001] This invention relates to the field of concrete material preparation technology, specifically to a low-temperature early-strength concrete, its preparation method, and its application. Background Technology

[0002] Construction of bridges and roads in high-altitude, ultra-high-temperature permafrost regions presents numerous challenges due to their distinct climatic characteristics, with very limited applicable experience. For example, the project area, located in the plateau temperate semi-arid climate zone, is characterized by extremely high altitude and frigid climate: long hours of sunshine, strong solar radiation, large annual temperature range, distinct wet and dry seasons; cold and windy winters, and cool but frequent thunderstorms in summer. The average annual temperature is only 1.7℃, with an extreme difference of over 59℃ between the highest and lowest temperatures; precipitation is concentrated from June to September, with annual evaporation far exceeding precipitation, resulting in low relative humidity; abundant sunshine, numerous days with strong winds (up to 17.8 m / s) concentrated in specific periods, a short frost-free period, and a high number of thunderstorm days. These unique geographical and climatic conditions pose severe challenges to key issues in engineering construction, such as construction efficiency, construction technology and quality, and cost control, requiring effective solutions.

[0003] Concrete is a key material in engineering construction, and its performance is of paramount importance. Currently, while some patents disclose concrete materials suitable for high-altitude or cold-climate engineering areas, such as patents with application numbers CN201310694362.0 and CN202211629123.2, the concrete material disclosed in patent CN202211629123.2 exhibits low compressive strength in its test specimens at -5℃, reaching a maximum of only 19.6 MPa. Although the concrete material disclosed in patent CN201310694362.0 shows higher compressive strength in its test specimens at -15℃, the excessive use of water-reducing agents and antifreeze agents in this concrete easily leads to problems such as aggregate settling, poor cohesion, and excessively delayed setting, increasing construction difficulty. Furthermore, the uneven internal structure after hardening results in a significant reduction in strength and durability. Therefore, there is an urgent need to develop concrete materials suitable for high-altitude and ultra-high-temperature permafrost regions to ensure their construction and service performance in high-altitude and cold environments. Summary of the Invention

[0004] The purpose of this invention is to provide a low-temperature early-strength concrete, its preparation method, and its application. By introducing admixtures and rationally optimizing the concrete mix proportions, the concrete is made suitable for high-altitude and ultra-high-temperature permafrost regions, ensuring its construction and service performance in high-altitude and cold environments.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a negative temperature early strength concrete, comprising cement, aggregate, admixture and water; Calculated by volumetric method, the cement content in each cubic meter of concrete is 320 kg / m³. 3 -475kg / m 3 The water-to-cement mass ratio shall not exceed 0.45, the aggregate-to-cement mass ratio shall be limited to the range of 3.5-4.6, the admixture content shall be 0.9%-1.3% of the cement content, and the water reduction rate of the admixture shall be limited to the range of 25%-30%; wherein the aggregate comprises sand and crushed stone, and the sand content shall be any value of 38%-42.5%.

[0006] Furthermore, the admixture is a mixture comprising at least a water-reducing agent, an air-entraining agent, and an early-strength antifreeze agent; the water-reducing agent is an SMS polycarboxylate-based water-reducing agent, the early-strength antifreeze agent is a high-efficiency pumpable chlorine-free and / or chloride salt rust-inhibiting antifreeze agent, and the air-entraining agent is an anionic surfactant.

[0007] Furthermore, the crushed stone includes a first crushed stone and a second crushed stone, and the mass ratio of the first crushed stone to the second crushed stone is 1:(2.1-2.5). The particle size of the first crushed stone is 5mm-10mm, and the particle size of the second crushed stone is 10mm-25mm.

[0008] Furthermore, when the structural form of the project is an underground structure, the compressive strength of the concrete is not less than 35 MPa, the mass ratio of water to cement in the concrete is any value between 0.3 and 0.4, the amount of admixture added is 0.9% to 1.1% of the amount of cement added, and the concrete pouring temperature is limited to the range of 0℃ to 10℃.

[0009] Furthermore, when the structural form of the project is an above-ground structure, the compressive strength of the concrete is not less than 40 MPa, the mass ratio of water to cement in the concrete is any value between 0.3 and 0.38, and the amount of admixture added is 1.0% to 1.2% of the amount of cement added.

[0010] This application also provides a design method for the above-mentioned mix proportion of negative temperature early strength concrete, including the following steps: S1. Based on the structural form and performance requirements of the engineering construction, and taking into account the climate, geology, construction conditions and raw material properties, select the required raw materials, and design multiple concrete mix proportions with the water-cement ratio or the amount of admixture as variables. S2. Mix each group of concrete evenly to form a concrete mixture. Test the slump of the concrete mixture and the compressive strength of the hardened concrete mixture. Select the group with the best overall performance and determine it as the preliminary mix proportion of the concrete. S3. Based on the preliminary mix proportion, adjust the water-cement ratio, redesign multiple sets of concrete mix proportions, and conduct performance tests on the concrete mixtures formed after mixing. Select the set with the best comprehensive performance and determine it as the ideal mix proportion of the concrete. S4. Prepare concrete according to the ideal mix ratio, and conduct standard curing test and negative temperature curing test on the concrete. Record and compare the compressive strength growth, and conduct frost resistance test to verify the durability of the concrete.

[0011] Further, in step S4, the standard curing test includes limiting the concrete placement temperature to the range of 5℃-15℃, preparing compressive strength test blocks and frost resistance test blocks under 7-day and 28-day standard curing, conducting a comparative analysis of the compressive strength growth of the compressive strength test blocks, and conducting frost resistance performance testing on the frost resistance test blocks.

[0012] Further, in step S4, the negative temperature curing test includes limiting the concrete placement temperature to the range of 0℃-10℃, and preparing compressive strength test blocks and frost resistance test blocks under negative temperature curing for 7 days and 28 days under preset temperature conditions. The compressive strength of the compressive strength test blocks is compared and analyzed, and the frost resistance of the frost resistance test blocks is tested. The preset temperature is any value from -15℃ to 0℃.

[0013] Furthermore, in step S2, the slump of the concrete mixture is limited to the range of 160mm-220mm, and the compressive strength of the hardened concrete mixture is not less than 35MPa.

[0014] This application also provides for the application of the aforementioned low-temperature early-strength concrete, including its application in permafrost regions where the extreme temperature is not lower than -50°C.

[0015] The beneficial effects of this invention are as follows: The negative-temperature early-strength concrete provided in this application, by adding an appropriate amount of admixtures and rationally optimizing the mixing ratio of raw material components, can endow it with compressive and frost resistance properties suitable for engineering construction in extreme environments such as high-altitude and ultra-high-altitude permafrost regions. In this way, it can systematically solve the problems of low efficiency, complex processes, difficulty in ensuring quality, and difficulty in controlling costs in road and bridge construction in high-altitude and ultra-high-altitude permafrost regions, and provide reliable technical support for high-quality road and bridge construction in high-altitude and cold regions.

[0016] The negative-temperature early-strength concrete mix design method provided in this application can select raw materials based on factors such as climate, geology, construction conditions, and raw material characteristics, according to the engineering structural form and performance requirements, and rationally design the concrete mix proportion, so that the concrete can fully meet the construction and production requirements of high-altitude and ultra-cold regions in terms of various performance indicators. Simultaneously, it can track the service life of structures to form evolution patterns, thereby constructing a complete set of technical benefit evaluations based on the whole life cycle concept. This design method is of great significance for solving technical application problems such as process and quality control and performance evaluation in similar projects, and for supporting the practical application and construction of projects in high-altitude and ultra-cold permafrost regions.

[0017] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0018] Figure 1 This is the curve showing the relationship between the 7-day glue-to-water ratio and compressive strength of concrete in Example 1 of this invention; Figure 2 This is the curve showing the relationship between the 28-day glue-to-water ratio and compressive strength of concrete in Example 1 of this invention; Figure 3 This is a slump test diagram of concrete in actual application according to Embodiment 1 of the present invention; Figure 4 This is a diagram showing the on-site temperature detection of concrete upon placement in the formwork during actual application in Embodiment 1 of the present invention. Figure 5 This is the curve showing the relationship between the 7-day glue-to-water ratio and compressive strength of concrete in Example 2 of this invention; Figure 6 This is the curve showing the relationship between the 28-day glue-to-water ratio and compressive strength of concrete in Example 2 of this invention; Figure 7 This is a slump test diagram of concrete in actual application according to Embodiment 2 of the present invention; Figure 8 This is a diagram showing the on-site temperature detection of concrete during actual application in Embodiment 2 of the present invention. Detailed Implementation

[0019] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. In the description of the present invention, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances. Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0020] The negative-temperature early-strength concrete shown in a preferred embodiment of this application mainly comprises cement, aggregates, and water. Calculated by volumetric method, the cement content per cubic meter of concrete is limited to 320 kg / m³. 3 -475kg / m 3Within a certain range, to ensure the concrete has sufficient strength. The water-to-cement ratio, or water-cement ratio, must not exceed 0.45. This is used to regulate the pore structure of the concrete, significantly improving its density and durability, thereby ensuring that the concrete maintains stable performance even in extreme environments. The aggregate-to-cement ratio is limited to the range of 3.5-4.6 to ensure a good balance between the workability and mechanical properties of the concrete. The aggregate includes sand and crushed stone, with a sand ratio of 38%-42.5%. This helps ensure that the workability, strength, and durability of the concrete are optimal. To ensure that the concrete exhibits good strength, durability, and other workability properties even in harsh environments such as high-altitude and ultra-high-temperature permafrost regions, admixtures are also introduced into the concrete. Furthermore, based on the water-cement ratio, the admixture dosage is limited to 0.9%-1.3% of the cement dosage. This admixture effectively improves the workability of concrete, reduces water consumption, and enhances its strength and durability. Simultaneously, the water-reducing rate of the admixture is limited to 25%-30%, allowing it to work synergistically with water and cement to further improve concrete workability, providing strong support for the long-term stable use of concrete in extreme environments. By strictly adhering to industry standards to limit cement dosage, combining a rationally designed water-cement ratio, and adjusting the admixture dosage and water-reducing rate based on the water-cement ratio, this negative-temperature early-strength concrete is suitable for extreme environmental conditions such as high-altitude and ultra-high-cold permafrost regions. This negative-temperature early-strength concrete with this mix design not only systematically solves a series of problems faced in road and bridge construction in high-altitude and ultra-high-cold permafrost regions, such as low construction efficiency, complex construction processes, difficulty in ensuring quality, and challenges in cost control, but also provides solid and reliable technical support for the high-quality construction of road and bridge projects in high-altitude and ultra-high-cold regions. In some embodiments, concrete may also include raw material components such as slag powder and fly ash.

[0021] Crushed stone, as a crucial aggregate component of concrete, directly impacts various concrete properties, especially compressive strength. To ensure excellent compressive strength, crushed stone can encompass a variety of sizes. While using only large-diameter crushed stone can create a continuous skeleton within the concrete, effectively transferring stress and enhancing compressive strength, the large inter-particle voids prevent tight packing, resulting in low density and poor durability. Conversely, using only small-diameter crushed stone requires more cement paste to form a good bond due to their large surface area, increasing cement usage and material costs. Using both large and small-diameter crushed stone allows the smaller particles to fill the voids between the larger ones, creating a tightly packed structure, reducing internal porosity, and significantly improving density. Based on these characteristics, concrete incorporating various crushed stone sizes is particularly suitable for projects requiring high fluidity or pumping, ensuring no segregation or stratification during transport and a uniform, dense structure after pouring to meet engineering performance requirements. In one embodiment, the crushed stone includes a first crushed stone and a second crushed stone, wherein the first crushed stone has a particle size of 5mm-10mm and the second crushed stone has a particle size of 10mm-25mm. Furthermore, based on the requirements of the actual engineering project, with the minimum porosity or maximum bulk density of the continuous gradation as the optimal standard, the mass ratio of the first crushed stone and the second crushed stone is limited to 1:(2.1-2.5). In other embodiments, the second crushed stone may also be a mixture comprising particles with a particle size of 10mm-20mm and 20mm-25mm (or 20mm-30mm). Additionally, a third crushed stone with a particle size of 0mm-4.75mm may be introduced into the aggregate.

[0022] In this application, all admixtures used are obtained through conventional commercial channels and are mixtures composed of multiple components. For example, in this embodiment and other embodiments, the admixture is a mixture including at least a water-reducing agent, an air-entraining agent, and an early-strength antifreeze agent. The water-reducing agent is an SMS polycarboxylate-based water-reducing agent. This water-reducing agent can adsorb onto cement particles in a "comb-like" manner, generating a "three-dimensional" repulsive effect. This effectively regulates the setting time of concrete while ensuring rapid early strength development, meeting the needs of different construction conditions. Furthermore, this type of water-reducing agent features low dosage, high water reduction rate, minimal slump loss over time, and suitability for double-admixed concrete. It imparts good workability and low shrinkage to concrete, making it an ideal green and environmentally friendly admixture for configuring high-strength, high-performance concrete. The main technical indicators of this SMS polycarboxylate-based high-performance water-reducing agent include: antifreeze type, specific gravity of 1.07±0.015, and pH value of 7-8. The early-strength antifreeze agent is a high-efficiency pumpable, chloride-free type (JW-3) and / or chloride salt rust-inhibiting type (JW-3A) antifreeze agent to ensure the long-term durability of concrete structures. This type of antifreeze agent is a multi-functional, high-efficiency composite antifreeze agent that can simultaneously solve the technical requirements of pumpable antifreeze and early-strength during winter construction. It is a high-water-reducing, high-early-strength, effectively lowers the freezing point of concrete liquid phase, is chloride-free and low-alkali, and is a 3C-certified environmentally friendly product. It can be used for various cast-in-place pumped concretes at temperatures above -15℃. The main technical indicators of this antifreeze agent include: the powder is a grayish-brown powder, the aqueous solution is a brownish-brown liquid, the specific gravity is 1.15±0.015, the pH value is 7-9, the powder fineness is 0.315mm, and the sieve residue is <15%. The air-entraining agent is an anionic surfactant material used to effectively improve the workability of concrete and enhance its resistance to freeze-thaw cycles and durability. For example, it is a rosin amine soap synthesized and converted from rosin thermal polymer and sodium rosinate. This air-entraining agent has both air-entraining and dispersing effects, and can be used as an air-entraining agent for concrete and a plasticizer for mortar. It significantly alters the workability of concrete and mortar, improves various performance indicators of concrete and mortar, thereby increasing the impermeability of concrete by more than 2 times and the freeze-thaw resistance by more than 12 times. The main technical indicators of this air-entraining agent include: effective ingredient ≥78%, pH value 7-9 (5% aqueous solution), foaming rate ≥3.5 times, and defoaming time ≥7 hours.

[0023] In this application, ordinary Portland cement can be used, for example, cement manufactured by Qinghai Hongyang Cement Co., Ltd., with a specification of P•O42.5 and an apparent density of 3.020. The first crushed stone can be crushed stone manufactured by K3327 Crushed Stone Plant, with a specification of 5-10mm and an apparent density of 2734. The second crushed stone can be crushed stone manufactured by K3327 Crushed Stone Plant, with a specification of 10-25mm and an apparent density of 2.717. The first and second crushed stones are then mixed in a ratio of 30% and 70%, respectively, resulting in a specification of 5-25mm and an apparent density of 2.725. The third crushed stone can be manufactured sand manufactured by K3327 Crushed Stone Plant, with a specification of 0mm-4.75mm and an apparent density of 2.630. The mixing water can be well water from the Nagqu Ando mixing plant, preferably groundwater from the region, with a density of 1.0. The water-reducing agent used is SMS polycarboxylate-based high-performance water-reducing agent produced in Shanxi, with a density of 1.052.

[0024] In high-altitude and ultra-high-flying permafrost regions, when engineering projects are constructed with above-ground structures, such as using concrete to build beams, retaining walls, foundation stones, piers, column-beam systems, pile-beam systems, pile foundations, abutment caps, abutment walls, back walls, retaining walls, guardrails, precast pile-slab walls, circular culverts, box culvert bodies, and cap stones, extensive experimental research indicates that the required concrete specifications include: a design strength of 40 MPa, a frost resistance grade of F300, a freeze-thaw environment rating of D5, a slump of 160 mm-200 mm, and a spread of [missing information]. The air content is 4.5%-5.5%. In one embodiment, when the structural form of the engineering construction is an above-ground structure, the mass ratio of water to cement in the concrete is limited to the range of 0.3-0.38, and the amount of admixture added is 1.1% of the cement content. By limiting the water-to-cement ratio, it helps to optimize the pore structure of the concrete, improve its density and durability, and by optimizing the amount of admixture added, effectively improve the workability of the concrete, so that the performance of the concrete meets the above-mentioned index requirements, making it applicable to high-altitude and ultra-high-cold permafrost areas and meeting the various requirements of above-ground structure construction.

[0025] In high-altitude, ultra-high-cold permafrost regions, when the structural form of engineering construction is underground, such as underground pile foundations, extensive experimental research has shown that the required concrete specifications include: design strength of 35 MPa, frost resistance grade of F300, freeze-thaw environment rating of D5, slump of 180 mm-220 mm, and spread of [missing information]. The air content is 5%-6%. In one embodiment, the compressive strength of the concrete is limited to not less than 35MPa, and the mass ratio of water to cement in the concrete is limited to 0.3-0.4, and the amount of admixture is 1% of the cement content, so that the performance of the concrete meets the above-mentioned requirements and satisfies the various requirements for underground structure construction.

[0026] This application also provides a design method for the above-mentioned mix proportion of negative temperature early strength concrete, which includes the following steps: S1. Based on the structural form and performance requirements of the engineering construction, and taking into account the climate, geology, construction conditions and raw material properties, select the required raw materials, and design multiple concrete mix proportions with the water-cement ratio or the amount of admixture as variables. S2. Mix each batch of concrete evenly to form a concrete mixture. Test the slump and compressive strength of the concrete mixture after hardening. Select the batch with the best overall performance and determine it as the preliminary mix proportion of the concrete. S3. Based on the preliminary mix proportion, adjust the water-cement ratio, redesign multiple sets of concrete mix proportions, and conduct performance tests on the concrete mixtures formed after mixing. Select the set with the best comprehensive performance and determine it as the ideal mix proportion for concrete. S4. Prepare concrete according to the ideal mix proportion, and conduct standard curing test and negative temperature curing test on the concrete. Record and compare the compressive strength growth of the concrete, and conduct a freeze-thaw resistance test to verify the durability of the concrete.

[0027] In step S1, based on the structural form and performance requirements of the project, and taking into account factors such as local climate characteristics, geological conditions, construction conditions, and raw material characteristics, various raw materials are selected to prepare the necessary concrete mix design. Then, based on this, multiple concrete mix design schemes with different parameter combinations are rationally designed.

[0028] In step S2, concrete is trial-mixed according to the concrete mix design in step S1, and each batch of concrete is thoroughly mixed to form a concrete mixture. Then, according to relevant industry standards and specifications, key performance indicators such as the slump and hardened compressive strength of the concrete mixture are tested to evaluate its fluidity and hardened compressive strength, thereby measuring the corresponding mechanical properties of the concrete. Afterwards, based on the test results, a reasonable evaluation method is used to comprehensively consider the importance and influence of each performance indicator, and the mix design with the best overall performance is selected. This mix design is then used as the initial mix design for the concrete.

[0029] In step S3, based on the preliminary mix proportions determined in step S2, the proportions of some raw materials in the concrete are adjusted in a targeted manner, and multiple sets of concrete mix proportion schemes are redesigned. Performance tests are then conducted on the concrete mixtures formed from each of the redesigned sets. Through data analysis and comparison, the set with the best overall performance is selected and determined as the ideal mix proportion for the concrete.

[0030] In step S4, concrete is prepared according to the determined ideal mix proportion. Standard curing tests and negative temperature curing tests are then conducted on the prepared concrete. The compressive strength growth under different temperature conditions is recorded and compared in detail. Simultaneously, a frost resistance test is performed. Based on the test results, the workability of the trial-mixed concrete is comprehensively verified to ensure it meets the actual engineering requirements. If the test results meet the requirements, the ideal mix proportion can be used as the final mix proportion for the project. If there are deficiencies, the reasons need to be further analyzed, the mix proportion optimized and adjusted, and the test re-verified.

[0031] In one embodiment, step S4, the standard curing test includes controlling the temperature of raw materials within the range of 0℃-10℃ during concrete mixing, controlling the concrete's outlet temperature by adjusting the water temperature, and limiting the concrete's placement temperature to within the range of 5℃-15℃. Then, compressive strength test blocks and frost resistance test blocks are prepared under 7-day and 28-day standard curing conditions. A comparative analysis of the compressive strength growth of the compressive strength test blocks is performed to evaluate the strength development trend of concrete under different curing conditions. The frost resistance test blocks are tested to comprehensively verify the concrete's frost resistance under normal conditions. In this embodiment and other embodiments, step S4, the negative temperature curing test includes limiting the concrete placement temperature within the range of 0℃-10℃. Then, under preset temperature conditions, compressive strength test blocks and frost resistance test blocks are prepared under 7-day and 28-day negative temperature curing conditions. A comparative analysis of the compressive strength growth of the compressive strength test blocks is performed to explore the strength growth law of concrete under negative temperature conditions. The frost resistance test blocks are tested to evaluate the frost resistance performance of concrete under negative temperature conditions. The preset temperature is any value between -15℃ and 0℃.

[0032] In one embodiment, in step S2, the slump of the concrete mixture is limited to the range of 160mm-220mm to ensure that the concrete mixture has good fluidity and plasticity, while avoiding problems such as segregation, bleeding, or difficulty in shaping caused by excessively large or small slumps. The compressive strength of the hardened concrete mixture is not less than 35MPa to ensure that it can withstand the design load and long-term environmental effects, ensuring the stability and reliability of the engineering structure.

[0033] This application also provides the application of the aforementioned negative temperature early strength concrete, including its application in high-altitude and ultra-high-temperature permafrost regions. This negative temperature early strength concrete can effectively overcome the adverse effects of low temperature, permafrost and other adverse factors on concrete construction and performance, providing reliable technical support and material guarantee for infrastructure construction in these regions.

[0034] The following examples all use a high-altitude, ultra-high-cold permafrost region as the project area. This project area has a plateau temperate semi-arid climate, characterized by long hours of sunshine, strong solar radiation, large annual temperature range, and distinct wet and dry seasons. Winters are cold and windy, while summers are cool and prone to thunderstorms. The average annual temperature is 1.7℃, with an extreme maximum of 26.5℃ and an extreme minimum of -32.5℃. The average annual precipitation is 459.3 mm, mostly concentrated from June to September, with a maximum daily precipitation of 50.4 mm. The annual evaporation is 1852.3 mm, and the average annual relative humidity is 54%. The average annual sunshine duration is 2925.2 hours. The average annual wind speed is 2.4 m / s, with 52.4 days of strong winds (wind speed 17.8 m / s) per year, the most frequent wind direction being SW, mainly concentrated from December to March of the following year. The frost-free period is 53 days, and the number of thunderstorm days per year is 74.3.

[0035] Example 1 The project involves above-ground construction, specifically highway construction in permafrost regions, using piers as an example. Design requirements are: design strength of 40 MPa, frost resistance grade of F300, freeze-thaw environment rating of D5, slump of 160mm-200mm, and spread of [missing information]. The gas content is 4.5%-5.5%.

[0036] S1. Based on the structural form of the engineering construction and in accordance with the provisions of the "Technical Specification for Design and Construction of Highways in Seasonally Frozen Soil Areas" JTG / T D31-06-2017, taking into account climate, geology, construction conditions and raw material performance, ordinary Portland cement, first crushed stone with a nominal particle size of 5mm-10mm, second crushed stone with a nominal particle size of 10mm-25mm, sand, admixtures and water are selected as raw materials. With the water-cement ratio or the amount of admixture added as variables, multiple groups of concrete with different mix proportions are designed.

[0037] S2. Mix each batch of concrete thoroughly to form a concrete mixture. Test the slump and compressive strength of the hardened concrete mixture, and select the batch with the best overall performance to determine the preliminary mix proportion. This preliminary mix proportion is: cement content of 475 kg / m³. 3 The water-cement ratio is 0.32, the mass ratio of aggregate to cement is limited to 3.63, the sand ratio is 38.1%, and the amount of admixture added is 1.1% of the cement content.

[0038] S3. Based on the initial mix proportion, adjust the cement admixture ratio, i.e., adjust the water-cement ratio, and fine-tune the admixture amount of each component in the aggregate based on the water-cement ratio. Redesign multiple sets of concrete with different mix proportions. The mix proportions of the multiple sets of concrete are shown in Table 1. Perform performance tests on the concrete mixtures formed after mixing these concretes. The test structural components are shown in Table 2. Select the set with the best overall performance, i.e., the concrete mix proportion with a water-cement ratio of 0.35, and determine its ideal concrete mix proportion.

[0039] Table 2 shows that the concrete with a water-cement ratio of 0.32 exhibits the highest compressive strength, indicating a denser internal structure and stronger bond between aggregates and cementitious materials, thus giving the concrete higher load-bearing capacity. However, the concrete with this mix proportion has a lower slump, indicating poor flowability during construction. This may lead to difficulties in pouring and insufficient compaction, increasing construction difficulty and cost, thus requiring optimization of its economic performance. The concrete with a water-cement ratio of 0.35, while having slightly lower compressive strength than the concrete with a water-cement ratio of 0.32, still has an acceptable compressive strength. Furthermore, the air content of this concrete is 4.5%, meeting the basic strength requirements of engineering structures. The slump of the concrete with this water-cement ratio is suitable, exhibiting good workability and effectively ensuring the quality of concrete pouring and construction efficiency. Therefore, the concrete with a water-cement ratio of 0.35 is ultimately selected as the ideal mix proportion.

[0040] S4. Concrete was prepared according to the ideal mix proportions, and standard curing and negative temperature curing tests were conducted. Specifically, during the standard curing test, the concrete outlet temperature was controlled by adjusting the water temperature, limiting the concrete placement temperature to approximately 10℃. Compressive strength and frost resistance test blocks were prepared under 7-day and 28-day standard curing conditions. The compressive strength growth of the compressive strength test blocks was compared and analyzed, and the frost resistance of the frost resistance test blocks was tested. During the negative temperature curing test, the concrete placement temperature was limited to approximately 4℃. Subsequently, compressive strength and frost resistance test blocks were prepared under -3℃ and -10℃ conditions for 7-day and 28-day negative temperature curing, respectively. The compressive strength growth of the compressive strength test blocks was compared and analyzed, and the test results are shown in Table 3. The frost resistance of the frost resistance test blocks was tested.

[0041] The concrete test blocks prepared using the ideal mix proportions showed the following results: After 7 days of curing at room temperature, the effective strength was 45.2 MPa, reaching 113% of the design strength; after 28 days of curing at room temperature, the effective strength was 55.3 MPa, reaching 138% of the design strength; after 7 days of curing at -3℃, the effective strength was 41.9 MPa, reaching 105% of the design strength; after 28 days of curing at -3℃, the effective strength was 53.4 MPa, reaching 134% of the design strength; after 7 days of curing at -10℃, the effective strength was 37.3 MPa, reaching 93% of the design strength; and after 28 days of curing at -10℃, the effective strength was 53.0 MPa, reaching 133% of the design strength. All these results meet the requirements for on-site construction.

[0042] Freeze-thaw resistance tests were conducted on the frost-resistant test blocks. After 300 freeze-thaw cycles, the relative durability index of the frost-resistant test blocks reached 84.7%, indicating that the frost resistance of the concrete meets the design standards. This further demonstrates that by scientifically designing the concrete mix proportions and using admixtures to control the air content and air bubble spacing, a balanced and suitable combination of mechanical properties and freeze-thaw durability can be achieved.

[0043] Comparative strength tests were conducted on concrete with the ideal mix proportion under different curing times. The results are shown in [Table]. Figure 1 , Figure 2 As shown in the figure, after 7 days of curing, the compressive strength of the concrete reached 113% of the design strength, which is 45 MPa; after 28 days of curing, the compressive strength stabilized above 55 MPa, meeting the strength requirements of C40 concrete. Furthermore, during the curing period, the temperature and humidity of the concrete were well controlled, and the specimens showed no abnormal deformation or cracking, indicating that this mix proportion concrete has excellent workability and is suitable for the main construction of this structural project.

[0044] The concrete mix based on this ideal mix proportion will be used in the construction production process for trial production. For example... Figure 3 , Figure 4 As shown, according to on-site measurements, the slump of the concrete is 200mm, the concrete pouring temperature is 10.5℃, and all initial performance indicators meet the construction requirements.

[0045] After concrete pouring and formwork removal, a comprehensive inspection of the relevant structure was conducted. On-site curing was carried out according to specifications, and the concrete strength was tested after 28 days. The results of the 28-day standard-cured compressive strength test showed a cube compressive strength of 47.7 MPa, reaching 119% of the design strength; the rebound strength using the rebound method was 43.0 MPa, reaching 108% of the design strength. These data indicate that the concrete exhibits excellent strength performance at 28 days. Based on the above test data and on-site construction conditions, the concrete mix design demonstrates good performance in terms of slump, placement temperature control, and strength development, and all performance indicators meet the construction and production requirements of high-altitude, cold, and ultra-high-altitude regions.

[0046] Example 2 The project involves an underground structure. Taking the foundation piles as an example, the design requirements are: design strength of 35 MPa, frost resistance grade of F300, freeze-thaw environment grade of D5, slump of 180mm-220mm, and spread of... The gas content is 5%-6%.

[0047] In step S2, the preliminary mix proportion obtained is: cement content is 456 kg / m³. 3 The water-cement ratio is 0.34, the mass ratio of aggregate to cement is limited to 3.77, the sand ratio is 40.1%, and the amount of admixture added is 1.0% of the cement content.

[0048] In step S3, the cement admixture ratio and aggregate admixture ratio were adjusted specifically to redesign multiple sets of concrete with different mix proportions. The mix proportions of these concrete sets are shown in Table 4. Performance tests were conducted on the concrete mixtures formed after mixing, and the test structural components are shown in Table 5. The set with the best overall performance was selected, i.e., the concrete mix proportion with a water-cement ratio of 0.37, and its ideal mix proportion was determined.

[0049] As shown in Table 5, the concrete with a water-cement ratio of 0.34 exhibits high compressive strength, but also high slump, and its economic performance needs further optimization. Concrete with a water-cement ratio of 0.40, on the other hand, shows lower compressive strength. Therefore, a water-cement ratio of 0.37 is selected as the ideal mix proportion for concrete.

[0050] In step S4, concrete was prepared according to the ideal mix proportion, and standard curing test and negative temperature curing test were conducted on the concrete. The test conditions for the standard curing test and negative temperature curing test were the same as those in Example 1, and the test results are shown in Table 6.

[0051] The concrete test blocks prepared using the ideal mix proportions showed the following results: After 7 days of curing at room temperature, the effective strength was 41.7 MPa, reaching 119% of the design strength; after 28 days of curing at room temperature, the effective strength was 48.4 MPa, reaching 138% of the design strength; after 7 days of curing at -3℃, the effective strength was 36.1 MPa, reaching 103% of the design strength; after 28 days of curing at -3℃, the effective strength was 47.0 MPa, reaching 134% of the design strength; after 7 days of curing at -10℃, the effective strength was 33.5 MPa, reaching 96% of the design strength; and after 28 days of curing at -10℃, the effective strength was 44.5 MPa, reaching 127% of the design strength. All these results meet the requirements for on-site construction.

[0052] Freeze-thaw resistance tests were conducted on the frost-resistant test blocks. After 300 freeze-thaw cycles, the relative durability index of the frost-resistant test blocks reached 84.0%, indicating that the frost resistance of the concrete meets the design standards. This further demonstrates that by scientifically designing the concrete mix proportions and using admixtures to control the air content and air bubble spacing, a balanced adaptation between mechanical properties and freeze-thaw durability can be achieved.

[0053] Comparative strength tests were conducted on concrete with the ideal mix proportion under different curing times. The results are shown in [Table]. Figure 5 , Figure 6 As shown in the figure, after 7 days of curing, the compressive strength of the concrete reached 119% of the design strength, which was 41.7 MPa; after 28 days of curing, the compressive strength stabilized above 48 MPa, meeting the strength requirements of C35 concrete. Furthermore, during the curing period, the temperature and humidity of the concrete were well controlled, and the specimens showed no abnormal deformation or cracking, indicating that this mix proportion concrete has excellent workability and is suitable for the main construction of this structural project.

[0054] The concrete mix based on this ideal mix proportion will be used in the construction production process for trial production. For example... Figure 7 , Figure 8As shown, on-site measurements revealed that the concrete slump was 220 mm and the concrete placement temperature was 4.3℃, with all initial performance indicators meeting construction requirements. The integrity of the constructed pile was tested using acoustic wave transmission. The results showed that while some individual acoustic parameters at multiple measuring points exhibited slight deviations from the normal range, the remaining key acoustic parameters remained within the normal thresholds. Furthermore, the received acoustic waveform remained generally good, with only slight distortion observed at a few measuring points, which did not significantly affect the overall waveform characteristics. Based on the comprehensive test results and in accordance with relevant specifications and criteria, the pile's structural integrity was assessed as Class I. This indicates that the pile's structural integrity is good and meets design and usage requirements.

[0055] Therefore, it can be seen that the concrete provided in this application fully meets the construction and production requirements of high-altitude and frigid regions in terms of various performance indicators. This not only provides a technical foundation for subsequent similar projects to address specific issues encountered in the application of technology in terms of process and quality control, performance evaluation, etc., when facing actual construction scenarios, but also provides strong support and guarantee for the practical application and construction operations of engineering projects in high-altitude and frigid permafrost regions.

[0056] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0057] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A type of low-temperature early-strength concrete, characterized in that, Includes cement, aggregates, admixtures, and water; Calculated by volumetric method, the cement content in each cubic meter of concrete is 320 kg / m³. 3 -475kg / m 3 The water-to-cement mass ratio shall not exceed 0.45, the aggregate-to-cement mass ratio shall be limited to the range of 3.5-4.6, the admixture content shall be 0.9%-1.3% of the cement content, and the water reduction rate of the admixture shall be limited to the range of 25%-30%; wherein the aggregate comprises sand and crushed stone, and the sand content shall be any value of 38%-42.5%.

2. The negative-temperature early-strength concrete as described in claim 1, characterized in that, The admixture is a mixture comprising at least a water-reducing agent, an air-entraining agent, and an early-strength antifreeze agent; the water-reducing agent is an SMS polycarboxylate-based water-reducing agent, the early-strength antifreeze agent is a high-efficiency pumpable chlorine-free and / or chloride salt rust-inhibiting antifreeze agent, and the air-entraining agent is an anionic surfactant.

3. The negative-temperature early-strength concrete as described in claim 1, characterized in that, The crushed stone includes a first crushed stone and a second crushed stone, and the mass ratio of the first crushed stone to the second crushed stone is 1:(2.1-2.5). The particle size of the first crushed stone is 5mm-10mm, and the particle size of the second crushed stone is 10mm-25mm.

4. The negative-temperature early-strength concrete as described in any one of claims 1-3, characterized in that, When the structural form of the project is an underground structure, the compressive strength of the concrete shall not be less than 35 MPa, the mass ratio of water to cement in the concrete shall be any value between 0.3 and 0.4, the amount of admixture shall be 0.9% to 1.1% of the amount of cement, and the concrete temperature shall be limited to the range of 0℃ to 10℃.

5. The negative-temperature early-strength concrete as described in any one of claims 1-3, characterized in that, When the structural form of the project is an above-ground structure, the compressive strength of the concrete shall not be less than 40 MPa, the mass ratio of water to cement in the concrete shall be any value between 0.3 and 0.38, and the amount of admixture shall be 1.0% to 1.2% of the amount of cement.

6. The method for designing the mix proportion of negative-temperature early-strength concrete according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Based on the structural form and performance requirements of the engineering construction, and taking into account the climate, geology, construction conditions and raw material properties, select the required raw materials, and design multiple concrete mix proportions with the water-cement ratio or the amount of admixture as variables. S2. Mix each group of concrete evenly to form a concrete mixture. Test the slump of the concrete mixture and the compressive strength of the hardened concrete mixture. Select the group with the best overall performance and determine it as the preliminary mix proportion of the concrete. S3. Based on the preliminary mix proportion, adjust the water-cement ratio, redesign multiple sets of concrete mix proportions, and conduct performance tests on the concrete mixtures formed after mixing. Select the set with the best comprehensive performance and determine it as the ideal mix proportion of the concrete. S4. Prepare concrete according to the ideal mix ratio, and conduct standard curing test and negative temperature curing test on the concrete. Record and compare the compressive strength growth of the concrete, and conduct a freeze-thaw resistance test to verify the durability of the concrete.

7. The preparation method as described in claim 4, characterized in that, In step S4, the standard curing test includes limiting the concrete placement temperature to the range of 5℃-15℃, and then preparing compressive strength test blocks and frost resistance test blocks under 7-day and 28-day standard curing conditions. The compressive strength of the compressive strength test blocks is compared and analyzed, and the frost resistance of the frost resistance test blocks is tested.

8. The preparation method as described in claim 4, characterized in that, In step S4, the negative temperature curing test includes limiting the concrete placement temperature to the range of 0℃-10℃, and preparing compressive strength test blocks and frost resistance test blocks under negative temperature curing for 7 days and 28 days under preset temperature conditions. The compressive strength of the compressive strength test blocks is compared and analyzed, and the frost resistance of the frost resistance test blocks is tested. The preset temperature is any value from -15℃ to 0℃.

9. The preparation method as described in claim 4, characterized in that, In step S2, the slump of the concrete mixture is limited to the range of 160mm-220mm, and the compressive strength of the hardened concrete mixture is not less than 35MPa.

10. The application of the negative-temperature early-strength concrete according to any one of claims 1-3, characterized in that, Including applications in permafrost regions where extreme temperatures are not lower than -50°C.

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