High-shellfish cement-based sulfate-erosion-resistant special concrete as well as preparation method and application thereof

Abstract

The invention discloses high-bainite cement-based sulfate-erosion-resistant special concrete as well as a preparation method and application thereof, and belongs to the field of building materials. Aiming at the problems of low early strength, poor corrosion resistance and poor dry and wet adaptability of the existing sulfate-resistant concrete, the concrete takes high belite cement as a main gelling component, and is matched with auxiliary gelling components containing sulphoaluminate cement, silica fume and the like, the aggregate contains functional fine aggregate, the water-binder ratio is 0.28-0.35, and a specific chemical additive is supplemented. Three-stage variable-frequency stirring is adopted for preparation, and water retention and wet maintenance are carried out for more than or equal to 14 days after pouring. The 90-day sulfate attack resistance coefficient is larger than or equal to 1.5 (4000 mg / L sulfate radical), the 7-day compressive strength is larger than or equal to 40 MPa, the total porosity is smaller than or equal to 15%, and the composite material is suitable for the environment (such as an ocean tidal zone and a salinized soil roadbed) with the sulfate radical of 2000-8000 mg / L and the wetting and drying alternation of larger than or equal to 3 times / month, and performance and economical efficiency are both considered.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a high-carbon cement-based special concrete resistant to sulfate attack, its preparation method and applications, and is particularly suitable for engineering structures subjected to high-concentration sulfate attack and alternating wet and dry environments. Background Technology

[0002] In various complex environments such as marine engineering, saline soil foundations, areas with fluctuating groundwater levels, and industrial wastewater treatment ponds, concrete materials are subjected to long-term sulfate erosion. This erosion leads to a significant reduction in concrete strength, structural cracking, and even eventual failure. The main mechanism of sulfate erosion lies in the chemical reaction between sulfate ions and hydration products within the concrete, such as calcium hydroxide (Ca(OH)2) and aluminum trisilicate (C3A), to form gypsum and ettringite. These newly formed substances expand in volume, thereby inducing internal stress and compromising the integrity of the concrete structure.

[0003] Currently, commercially available sulfate-resistant concrete mainly uses silicate cement with low C3A content, or improves its erosion resistance by adding mineral admixtures such as fly ash and slag. However, these methods have some significant limitations in practical applications: First, the early strength is low. Cement with low C3A content has a slower hydration rate, resulting in a compressive strength of less than 30 MPa within 7 days. This characteristic makes it difficult to meet the requirements of rapid construction and limits its application in emergency projects.

[0004] Secondly, its corrosion resistance is insufficient. Single mineral admixtures have limited effect on refining the pores of concrete. In harsh environments with sulfate ion concentrations exceeding 4000 mg / L, after a year of corrosion resistance testing, its corrosion resistance coefficient is mostly below 1.2, making it difficult to effectively resist long-term erosion.

[0005] Furthermore, it has poor adaptability to alternating wet and dry conditions. During the wet and dry cycle, conventional concrete is prone to shrinkage and cracking due to moisture evaporation. This cracking accelerates the penetration of corrosive media, further exacerbating the damage to the concrete.

[0006] High-belite cement (C2S content ≥50%) exhibits good resistance to sulfate attack due to its low heat of hydration, stable later-stage strength, and low C3A content (≤5%). However, its insufficient early-stage strength still limits its widespread application in practical engineering. On the other hand, although sulfoaluminate cement has high early-stage strength, its production cost is high and its long-term volume stability is poor, which also limits its application.

[0007] Therefore, how to effectively balance early strength, corrosion resistance, and economy through multi-component synergistic design has become a key technical problem that urgently needs to be solved in the field of sulfate-resistant concrete. A breakthrough in this area will provide more reliable technical support for the application of concrete in special environments such as marine engineering and saline soil foundations. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a high-bearing cement-based sulfate-resistant special concrete, its preparation method, and its applications. Through the synergistic design of cementitious materials, functionalized aggregate configuration, and process optimization, it achieves the technical effects of high early strength, excellent sulfate resistance, and adaptability to alternating wet and dry environments. To achieve the above objectives, the present invention adopts the following technical solution: This invention first discloses a high-biological-weight cement-based special concrete resistant to sulfate attack, the key being that it is prepared from raw materials comprising the following components: Cementitious materials, the dosage is 380-450 kg / m³; aggregate; Chemical admixtures; And water; The water-to-binder ratio is 0.28-0.35; The cementitious material is composed of a main cementitious component and an auxiliary cementitious component, by weight percentage: The main cementitious component is high belite cement, with a C3A content ≤3% and a C2S content ≥50%, accounting for 50%-70% of the total weight of the cementitious material; The auxiliary cementitious component accounts for 30%-50% of the total weight of the cementitious material and includes sulfoaluminate cement, silica fume, ultrafine fly ash microspheres, nano silica, and highly active metakaolin. The sulfoaluminate cement grade is ≥42.5, the silica fume specific surface area is ≥20000m² / kg, the ultrafine fly ash microspheres have a particle size of 0.1-1μm and a loss on ignition of ≤3%, the nano silica has a particle size of 5-50nm and a purity of ≥99%, and the highly active metakaolin has an Al2O3 content of ≥40%. The cementitious material has a hydration degree of ≥90% after 28 days, and the critical pore size of the hardened concrete is ≤50nm and the permeability coefficient is ≤1×10⁻⁶. -12 cm / s. Furthermore, the auxiliary cementitious component, based on a percentage of the total weight of the cementitious material, comprises the following components: Sulfoaluminate cement: 5%-10%; Silica fume: 3%-7%; Ultrafine fly ash microspheres: 10%-15%; Nano silica: 1%-2%; Highly active metakaolin: 5%-10%; The auxiliary cementitious component works synergistically with the main cementitious component to ensure that the Ca(OH)2 content in the concrete hydration products is ≤5% and the Ca / (Si+Al) ratio of C-(A)-SH gel is ≤1.0. Furthermore, in the auxiliary gelling component: The weight ratio of the sulfoaluminate cement to the nano-silica is 4:1 to 6:1. Under this ratio, the aspect ratio of AFt crystals is ≤2, which can avoid microcracks caused by needle-like crystals. The weight ratio of silica fume to ultrafine fly ash microspheres is 1:2~3. Under this ratio, the bulk density of the cementitious system is ≥1.8g / cm³, and the filling density is increased by more than 20% compared with that of a single admixture. Furthermore, the aggregates include coarse aggregates, fine aggregates, and functional micro-aggregates; calculated per cubic meter of concrete: The coarse aggregate is crushed stone with a continuous gradation of 5-25mm; The fine aggregate is machine-made medium sand from gradation zone II; The functional fine aggregate is grade I fly ash with a particle size of 1-10μm and a water requirement ratio of ≤95%, and a dosage of 50-70kg. The functional micro-aggregate and ultrafine fly ash microspheres form a continuous "micron-submicron" gradation filling, making the total porosity of the concrete ≤15%. Furthermore, the coarse aggregate has a crushing value ≤10%, a needle-like and flaky particle content ≤8%, and a dosage of 1000-1080 kg / m³; the fine aggregate has a stone powder content of no more than 5% by weight, a fineness modulus of 2.3-3.0, and a dosage of 600-700 kg / m³. Furthermore, the chemical additive includes: Polycarboxylate-based high-performance water-reducing agents, with a dosage of 1.0%-1.8% of the total weight of cementitious materials, enable concrete to achieve an initial spread of ≥650mm and a spread loss of ≤80mm within 1 hour. The water-retaining and thickening agent is hydroxypropyl methylcellulose ether with a viscosity of 40000±5000 mPa·s. The dosage is 0.05%-0.15% of the total weight of the cementitious materials, so that the bleeding rate of concrete is ≤0.5%. The retarder, sodium gluconate, is added at a dosage of 0.02%-0.05% of the total weight of the cementitious materials to control the initial setting time of concrete at 6-8 hours and the final setting time at 10-12 hours. Secondly, this invention also discloses a method for preparing the above-mentioned high-biological-content cement-based sulfate-resistant special concrete, the key of which is that it includes the following steps: S1: Powder premixing: The high belite cement, sulfoaluminate cement, silica fume, ultrafine fly ash microspheres, nano silica and highly active metakaolin are put into a mixer and dry-mixed at a low speed of 25-35 rpm for 2-3 minutes to form a homogeneous cementitious powder with a homogeneity variation coefficient ≤3%; S2: Preparation of mortar: Add fine aggregate and 60%-70% of the total water volume of the homogeneous cementitious powder obtained in S1 to the mixing water, wherein sodium gluconate has been dissolved in the mixing water. Stir at a medium speed of 40-50 rpm for 3-4 minutes to form a uniform mortar. During the stirring process, the material temperature is controlled at 15-25℃. S3: Preparation of concrete mixture: Add coarse aggregate, chemical admixture and remaining mixing water to the mortar obtained in S2, and stir at high speed of 55-65 rpm for 3-5 minutes to obtain a uniform and cohesive concrete mixture with an expansion of ≥600mm and a slump loss over time of ≤100mm / h. Furthermore, the polycarboxylate-based high-performance water-reducing agent and hydroxypropyl methylcellulose ether are pre-dissolved in the remaining mixing water to form an additive solution with a solid content of 30%-40%; the solution is added dropwise at a rate of 5-10 mL / s.

[0009] Furthermore, maintenance steps are included after S3: S4: After the concrete mixture is poured and formed, cover it with plastic film or wet cloth for water retention and curing within 1 hour. The curing environment temperature is ≥10℃. S5: After final setting, remove the covering and use fresh water spraying or immersion curing at 20-25℃ for no less than 14 days to ensure that the concrete has a 90-day compressive strength ≥60MPa and a sulfate erosion resistance coefficient ≥1.5 under the condition of sulfate concentration 4000mg / L.

[0010] Finally, the present invention also provides the use of concrete prepared according to the concrete described above or according to the method described above, the key feature of which is for use in corrosive environments with sulfate ion concentrations of 2000-8000 mg / L and wet-dry alternation frequency ≥3 times / month, said environments including marine tidal zone revetment structures, wet-dry alternation layers of saline soil roadbeds, tunnel linings in groundwater level fluctuation zones, and bottom slabs of industrial wastewater recycling ponds.

[0011] Compared with the prior art, the significant advantages of the present invention are: 1. Significantly improved early strength. This invention utilizes the complementary properties of high-belite cement and sulfoaluminate cement through the synergistic design of cementitious materials, combined with the role of auxiliary cementitious components, to enable concrete to form a relatively dense structure in the early stages. The compressive strength can reach over 40MPa at 7 days, meeting the needs of rapid construction and applicable to emergency engineering projects.

[0012] 2. Excellent resistance to sulfate attack. The auxiliary cementitious components work synergistically with the main cementitious components to reduce the Ca(OH)2 content in the hydration products of concrete and optimize the Ca / (Si+Al) ratio of C-(A)-SH gel. At the same time, the functional micro-aggregates and ultrafine fly ash microspheres form a continuous "micron-submicron" gradation filling, which reduces the total porosity of concrete, the critical pore size, and the permeability coefficient. Under the condition of sulfate concentration of 4000 mg / L, the sulfate attack resistance coefficient is ≥1.5 after 90 days, which can effectively resist long-term sulfate attack.

[0013] 3. Adaptability to alternating wet and dry environments. The rational use of chemical admixtures, such as polycarboxylate-based high-performance water-reducing agents, ensures the workability of concrete, water-retaining and thickening agents reduce bleeding rate, and retarders control setting time. This allows concrete to reduce volume shrinkage and cracking caused by water evaporation during alternating wet and dry processes, thereby improving its durability in such environments.

[0014] 4. Excellent economic efficiency. This invention, while ensuring concrete performance, balances material usage through multi-component synergistic design, avoiding the use of high-cost materials alone, reducing production costs, improving product cost-effectiveness, and demonstrating promising market application prospects. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Additional aspects and advantages of this invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. It should be understood that the following description is merely illustrative and not intended to limit the invention.

[0016] The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used herein, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0017] The present invention provides a high-biological-content cement-based special concrete resistant to sulfate attack, which is prepared from raw materials comprising the following components: Cementitious materials, the dosage is 380-450 kg / m³; aggregate; Chemical admixtures; And water; The water-to-binder ratio is 0.28-0.35; The cementitious material is composed of a main cementitious component and an auxiliary cementitious component, by weight percentage: The main cementitious component is high belite cement, with a C3A content ≤3% and a C2S content ≥50%, accounting for 50%-70% of the total weight of the cementitious material; The auxiliary cementitious component accounts for 30%-50% of the total weight of the cementitious material and includes sulfoaluminate cement, silica fume, ultrafine fly ash microspheres, nano-silica, and highly active metakaolin. The sulfoaluminate cement grade is ≥42.5, the silica fume specific surface area is ≥20000 m² / kg, the ultrafine fly ash microspheres have a particle size of 0.1-1 μm and a loss on ignition ≤3%, the nano-silica has a particle size of 5-50 nm and a purity ≥99%, and the highly active metakaolin has an Al₂O₃ content ≥40%. The cementitious material has a 28-day hydration degree ≥90%, and the hardened concrete has a critical pore size ≤50 nm and a permeability coefficient ≤1×10⁻⁶. -12 cm / s.

[0018] Aggregates play a crucial role in concrete, acting as both a skeleton and filler, and are essential for improving its strength and stability. The aggregates selected in this invention have undergone careful screening in terms of gradation and performance. The fine aggregates used are manufactured medium sand from gradation zone II. This type of medium sand has good particle shape and gradation, enabling it to form a relatively dense packing structure in concrete, reducing porosity, and thus improving the compactness and impermeability of the concrete.

[0019] Chemical admixtures also play a crucial role in concrete preparation. They can improve concrete workability, regulate setting time, and enhance strength and durability. The chemical admixtures used in this invention undergo rigorous formulation and screening to ensure effective synergy with cementitious materials and aggregates. For example, they can reduce the water content of concrete, improve its fluidity, making it easier to pour and vibrate during construction, thus ensuring uniformity and density. Simultaneously, chemical admixtures can also, to some extent, inhibit internal chemical reactions within the concrete, reducing the damage caused by sulfate attack to the concrete structure.

[0020] Water is a crucial component in concrete preparation, and its dosage and water-cement ratio directly affect concrete performance. This invention controls the water-cement ratio within the range of 0.28-0.35, ensuring sufficient fluidity and plasticity for easy construction while avoiding reduced strength and durability due to an excessively high water-cement ratio. A suitable water-cement ratio promotes full hydration of the cementitious materials, forming a dense microstructure, thereby improving the concrete's resistance to sulfate attack.

[0021] Through precise proportioning and strict control of each component, the high-biological-weight cement-based sulfate-resistant special concrete prepared by this invention exhibits excellent performance. In practical applications, it can maintain stable structure and performance for a long time in harsh environments containing sulfates, greatly extending the service life of concrete structures and providing reliable material support for various engineering constructions. This special concrete has broad application prospects in marine engineering, underground engineering, and other engineering fields susceptible to sulfate corrosion.

[0022] In specific implementation, the auxiliary cementitious component, based on its percentage of the total weight of the cementitious material, consists of the following components: Sulfoaluminate cement: 5%-10%; Silica fume: 3%-7%; Ultrafine fly ash microspheres: 10%-15%; Nano silica: 1%-2%; Highly active metakaolin: 5%-10%; The auxiliary cementitious component works synergistically with the main cementitious component to ensure that the Ca(OH)2 content in the concrete hydration products is ≤5% and the Ca / (Si+Al) ratio of C-(A)-SH gel is ≤1.0.

[0023] This unique component ratio allows the auxiliary cementitious components to fully exert their advantages. Appropriate addition of sulfoaluminate cement can accelerate the early strength development of concrete and provides certain anti-erosion properties; within a proportion range of 5%-10%, it can effectively enhance the concrete's early resistance to sulfate attack. Silica fume has high pozzolanic activity; at a proportion of 3%-7%, it can fill the pores in concrete, increase its density, enhance its impermeability, and further block the intrusion of sulfate ions.

[0024] At a content of 10%-15%, ultrafine fly ash microspheres can improve the workability of concrete, making it easier to mix and construct. They also participate in the hydration reaction, consuming some Ca(OH)2 and optimizing the microstructure of concrete. Although nano-silica accounts for only 1%-2%, its extremely small particle size and huge specific surface area can significantly improve the strength and durability of concrete, promote the formation of C-(A)-SH gel, and reduce the Ca / (Si+Al) ratio.

[0025] Highly active metakaolin, within the range of 5%-10%, can synergize with other auxiliary cementitious components to further reduce the Ca(OH)2 content in concrete hydration products, resulting in a denser microstructure. When the auxiliary and primary cementitious components work synergistically, controlling the Ca(OH)2 content in concrete hydration products to ≤5% and the C-(A)-SH gel Ca / (Si+Al) ratio to ≤1.0, the concrete exhibits superior resistance to sulfate attack. This is because the lower Ca(OH)2 content reduces the likelihood of reacting with sulfate to form expansive products, while the appropriate C-(A)-SH gel Ca / (Si+Al) ratio ensures the stability and erosion resistance of the gel structure, thereby significantly improving the long-term stability and service life of concrete in sulfate-containing environments.

[0026] In this embodiment, the auxiliary gelling component includes: The weight ratio of the sulfoaluminate cement to the nano-silica is 4:1 to 6:1. Under this ratio, the aspect ratio of AFt crystals is ≤2, which can avoid microcracks caused by needle-like crystals. The weight ratio of silica fume to ultrafine fly ash microspheres is 1:2~3. Under this ratio, the bulk density of the cementitious system is ≥1.8g / cm³, and the filling density is increased by more than 20% compared with that of a single admixture. Meanwhile, this ratio fully activates the activity of the auxiliary cementitious components, enabling them to better participate in the hydration reaction of concrete. The appropriate weight ratio of sulfoaluminate cement to nano-silica makes the AFt crystals more regularly shaped during formation, not only avoiding the microcrack problems that may be caused by needle-like crystals, but also enhancing the stability of the internal structure of concrete. Furthermore, the specific weight ratio of silica fume to ultrafine fly ash microspheres increases the bulk density and filling compactness of the cementitious system, further reducing the porosity inside the concrete.

[0027] This optimized ratio also improves the workability of concrete. During concrete mixing, the synergistic effect between the auxiliary cementitious components improves the fluidity of the mixture, facilitating construction. Furthermore, after hardening, the concrete's impermeability and frost resistance are significantly enhanced. Improved impermeability means that external sulfate solutions are less likely to penetrate the concrete, further strengthening its resistance to sulfate attack. Improved frost resistance ensures the long-term performance of concrete in cold environments, reducing structural damage caused by freeze-thaw cycles.

[0028] Furthermore, this ratio of auxiliary cementitious components also offers certain economic advantages. By rationally utilizing materials such as sulfoaluminate cement, nano-silica, silica fume, and ultrafine fly ash microspheres, production costs can be reduced while ensuring high concrete performance. This is because these materials can, to some extent, replace part of the main cementitious components, and their inherent performance advantages can compensate for any performance loss that might result from such substitution, achieving a good balance between performance and cost.

[0029] In practical applications, the aggregate includes coarse aggregate, fine aggregate, and functional micro-aggregate; calculated per cubic meter of concrete: The coarse aggregate is crushed stone with a continuous gradation of 5-25mm; The fine aggregate is machine-made medium sand from gradation zone II; The functional fine aggregate is grade I fly ash with a particle size of 1-10μm and a water requirement ratio of ≤95%, and a dosage of 50-70kg. The functional micro-aggregate and ultrafine fly ash microspheres form a continuous "micron-submicron" gradation filling, making the total porosity of the concrete ≤15%. This "micron-submicron" continuous gradation filling method not only reduces the total porosity of concrete but also optimizes the pore structure, making the pores finer and more uniformly distributed. This characteristic further enhances the compactness of concrete, thereby improving its resistance to impermeability, frost damage, and sulfate attack. Regarding coarse aggregate, 5-25mm continuously graded crushed stone can form a stable skeleton structure in concrete, providing good mechanical support. Meanwhile, the machine-made medium sand in gradation zone II, with its reasonable particle shape and gradation, can increase the fluidity and cohesiveness of the concrete mixture while filling the voids in the coarse aggregate, which is beneficial for mixing, transportation, and pouring during construction. Grade I fly ash, as a functional fine aggregate, with a particle size of 1-10μm and a water requirement ratio ≤95%, can exert a pozzolanic effect and a micro-aggregate effect in concrete. The pozzolanic effect causes fly ash to react with calcium hydroxide produced during cement hydration, generating hydration products with cementitious properties, further improving the strength and durability of concrete. The micro-aggregate effect refers to the ability of fine fly ash particles to fill the voids between cement particles, improving the microstructure of concrete. When functional micro-aggregates and ultrafine fly ash microspheres form a continuous "micron-submicron" gradation, particles of different sizes fill each other, making the internal structure of concrete more compact. This dense structure effectively prevents the intrusion of harmful external substances such as sulfate solutions and moisture, reducing the risk of chemical erosion and physical damage to concrete. Simultaneously, because the total porosity is ≤15%, the migration and expansion of internal moisture are limited when concrete undergoes freeze-thaw cycles, reducing structural damage caused by freeze-thaw cycles and ensuring the long-term stability and service life of concrete in harsh environments.

[0030] Specifically, the coarse aggregate has a crushing value ≤10%, a needle-like and flaky particle content ≤8%, and a dosage of 1000-1080 kg / m³; the fine aggregate has a stone powder content of no more than 5% by weight, a fineness modulus of 2.3-3.0, and a dosage of 600-700 kg / m³.

[0031] Strict control over the various indicators and dosages of coarse and fine aggregates is essential to ensure that concrete achieves ideal performance. For coarse aggregates, a lower crushing value indicates higher strength, enabling them to withstand greater pressure without easily breaking, thus providing stable support in the concrete structure. A lower content of needle-like and flaky particles allows for a more compact and regular arrangement of coarse aggregates in the concrete, reducing voids and enhancing its density. For fine aggregates, a low stone powder content prevents excessive stone powder from affecting the bond between cement and aggregates, while a suitable fineness modulus helps to better blend fine and coarse aggregates, forming a good gradation and further improving the workability and strength of the concrete. By precisely setting the dosage ranges of coarse and fine aggregates, it is possible to achieve rational material utilization and reduce costs while ensuring the strength and durability of the concrete. Simultaneously, an appropriate aggregate ratio also helps control the workability of the concrete, such as fluidity and water retention, ensuring smooth pouring and vibration during construction and guaranteeing construction quality.

[0032] In this embodiment, the chemical additive includes: Polycarboxylate-based high-performance water-reducing agents, with a dosage of 1.0%-1.8% of the total weight of cementitious materials, enable concrete to achieve an initial spread of ≥650mm and a spread loss of ≤80mm within 1 hour. The water-retaining and thickening agent is hydroxypropyl methylcellulose ether with a viscosity of 40000±5000 mPa·s. The dosage is 0.05%-0.15% of the total weight of the cementitious materials, so that the bleeding rate of concrete is ≤0.5%. The retarder, sodium gluconate, is added at a dosage of 0.02%-0.05% of the total weight of the cementitious materials to control the initial setting time of concrete at 6-8 hours and the final setting time at 10-12 hours. These chemical admixtures play a crucial synergistic role in concrete. The appropriate addition of polycarboxylate-based high-performance water-reducing agents not only significantly improves the initial spread of concrete, allowing it to flow better and fill the formwork during pouring, but also effectively controls spread loss within one hour, ensuring the concrete maintains good workability for a certain period and preventing construction disruptions due to excessive spread loss. The use of the water-retaining and thickening agent hydroxypropyl methylcellulose ether significantly reduces the bleeding rate of concrete, preventing water from leaching out and ensuring the uniformity and stability of the concrete's internal structure, thus improving its durability. The incorporation of the retarder sodium gluconate precisely controls the initial and final setting times of the concrete. A suitable initial setting time allows construction workers sufficient time for mixing, transporting, pouring, and vibrating the concrete, while proper control of the final setting time helps the concrete fully develop its strength during subsequent curing, ensuring the overall quality of the concrete structure. By precisely controlling the type and dosage of these chemical admixtures, concrete can meet strength and durability requirements while possessing good workability to adapt to the construction needs of different projects.

[0033] Based on the foregoing description, this invention also discloses a method for preparing high-bibium cement-based sulfate-resistant special concrete, comprising the following steps: S1: Powder premixing: The high belite cement, sulfoaluminate cement, silica fume, ultrafine fly ash microspheres, nano silica and highly active metakaolin are put into a mixer and dry-mixed at a low speed of 25-35 rpm for 2-3 minutes to form a homogeneous cementitious powder with a homogeneity variation coefficient ≤3%; S2: Preparation of mortar: Add fine aggregate and 60%-70% of the total water volume of the homogeneous cementitious powder obtained in S1 to the mixing water, wherein sodium gluconate has been dissolved in the mixing water. Stir at a medium speed of 40-50 rpm for 3-4 minutes to form a uniform mortar. During the stirring process, the material temperature is controlled at 15-25℃. S3: Preparation of concrete mixture: Add coarse aggregate, chemical admixture and remaining mixing water to the mortar obtained in S2, and stir at high speed of 55-65 rpm for 3-5 minutes to obtain a uniform and cohesive concrete mixture with an expansion of ≥600mm and a slump loss over time of ≤100mm / h. In this method, the powder premixing step uses low-speed dry mixing, which allows the various cementitious materials to be initially and evenly mixed under gentle stirring conditions, avoiding agglomeration or uneven distribution of some materials due to excessive stirring speed. Low-speed stirring also reduces material dusting and loss, ensuring full utilization of the powder. Controlling the homogeneity variation coefficient to ≤3% ensures the quality stability of the cementitious powder, laying the foundation for the subsequent preparation of high-performance concrete.

[0034] When preparing mortar, some of the mixing water is first dissolved with sodium gluconate. This serves two purposes: firstly, to ensure that the retarder is evenly dispersed in the concrete system, thus better controlling its setting time; and secondly, to control the material temperature between 15-25℃ during medium-speed mixing. This temperature range is conducive to the stable hydration reaction of cement and other cementitious materials, preventing the hydration reaction from being affected by excessively high or low temperatures, thereby ensuring the quality and performance of the mortar.

[0035] When preparing concrete mixtures, high-speed mixing ensures that coarse aggregates, chemical admixtures, and residual mixing water are fully integrated with the mortar, forming a uniform and cohesive state. A spread of ≥600mm ensures good fluidity of the concrete during pouring, allowing it to smoothly fill gaps in formwork and reinforcing bars; a slump loss over time of ≤100mm / h ensures the stability of the concrete's workability over a certain period, preventing excessive slump loss from affecting construction quality during transportation and construction.

[0036] The entire preparation method, through precise control of each step—from powder mixing to mortar formation and final concrete mix preparation—ensures the performance and quality of high-bearing cement-based sulfate-resistant special concrete. This method is suitable not only for small-batch laboratory preparation but also for large-scale industrial production based on actual engineering needs, providing reliable material support for various projects threatened by sulfate attack. Furthermore, the method is relatively simple to operate, easy to master, and possesses high practicality and potential for widespread application.

[0037] Preferably, the polycarboxylic acid-based high-performance water-reducing agent and hydroxypropyl methylcellulose ether are pre-dissolved in the remaining mixing water to form an additive solution with a solid content of 30%-40%; the solution is added dropwise at a rate of 5-10 mL / s.

[0038] This drip-addition method allows the admixture solution to mix more evenly with other materials, avoiding problems such as excessively high or low concentrations caused by concentrated addition. During the drip-addition process, the high-speed mixing equipment operates continuously, enabling the solution to rapidly diffuse throughout the mixture, fully utilizing the effects of polycarboxylate superplasticizer and hydroxypropyl methylcellulose ether. Polycarboxylate superplasticizer can significantly reduce the water-cement ratio of concrete, improving its fluidity and strength; hydroxypropyl methylcellulose ether helps improve the water retention and cohesiveness of concrete, preventing segregation and bleeding during transportation and pouring. By controlling the solid content and drip rate of the admixture solution, the performance of the concrete can be precisely adjusted to better meet the needs of different projects. In practical applications, the solid content and drip rate parameters can be flexibly adjusted according to the environmental conditions and specific requirements of the project to achieve optimal results. For example, when constructing in high-temperature environments, the content of polycarboxylate superplasticizer can be appropriately increased while accelerating the drip rate to ensure that the concrete has good fluidity and workability in a short time. In low-temperature environments, the solid content of the admixture solution can be reduced, the dripping rate slowed down, and premature concrete setting prevented. This flexible adjustment method allows high-bearing cement-based sulfate-resistant special concrete to exhibit excellent performance under various working conditions.

[0039] In practical applications, maintenance steps are also included after S3: S4: After the concrete mixture is poured and formed, cover it with plastic film or wet cloth for water retention and curing within 1 hour. The curing environment temperature is ≥10℃. S5: After final setting, remove the covering and use fresh water spraying or immersion curing at 20-25℃ for no less than 14 days to ensure that the concrete has a 90-day compressive strength ≥60MPa and a sulfate erosion resistance coefficient ≥1.5 under the condition of sulfate concentration 4000mg / L.

[0040] This curing method effectively prevents moisture loss from the concrete, providing a favorable environment for cement hydration and promoting strength gain and sulfate resistance. During curing, close monitoring of temperature and humidity is crucial. If the temperature drops below 10℃, appropriate insulation measures, such as covering with insulating materials, should be implemented to prevent freezing and performance degradation. Simultaneously, the water quality for freshwater spraying or immersion curing must be strictly controlled to ensure it is free of harmful substances that could affect concrete performance. Throughout the curing cycle, designated personnel should regularly inspect the concrete's condition, recording key parameters such as temperature and humidity. This allows for timely adjustments to the curing strategy, ensuring the concrete ultimately meets design performance requirements. This allows the high-bearing capacity of the high-bearing cement-based sulfate-resistant special concrete to leverage its advantages in practical projects, extending the project's service life and reducing maintenance costs.

[0041] The concrete described above or the concrete prepared according to the method described above is intended for use in corrosive environments with sulfate ion concentrations of 2000-8000 mg / L and a wet-dry alternation frequency of ≥3 times / month. The environments include marine tidal zone revetment structures, wet-dry alternation layers of saline soil roadbeds, tunnel linings in groundwater level fluctuation zones, and bottom slabs of industrial wastewater recycling ponds.

[0042] This type of concrete exhibits significant advantages in the aforementioned corrosive environments. In marine tidal zone revetment structures, it can withstand frequent wet-dry cycles and high concentrations of sulfate ions, effectively resisting seawater erosion and chemical corrosion, ensuring the stability and durability of the revetment structure, and reducing safety hazards and repair costs caused by structural damage. For saline soil subgrade wet-dry alternating layers, it can prevent sulfate ions in the soil from eroding and damaging the subgrade, enhancing its bearing capacity, and avoiding problems such as subgrade settlement and cracking, thereby ensuring road smoothness and driving safety.

[0043] In tunnel lining in areas with fluctuating groundwater levels, this concrete can resist groundwater erosion and wet-dry cycles, preventing cracks and spalling in the lining structure, extending the tunnel's service life, and reducing maintenance difficulty and costs. In its application to the bottom slab of industrial wastewater recycling tanks, it effectively resists the erosion of sulfate ions in industrial wastewater, preventing leakage and damage to the bottom slab, ensuring the normal operation of the recycling tank, and avoiding wastewater leakage that could pollute the surrounding environment.

[0044] Furthermore, this type of concrete can also be applied in similar harsh environments, such as the seepage prevention layer of mine tailings ponds and wastewater treatment ponds in chemical industrial parks. In these environments, it also demonstrates excellent resistance to sulfate attack, providing reliable material protection for related projects. Moreover, with the continuous improvement of performance requirements for building materials, this type of concrete is expected to be promoted and applied in more fields, providing an effective solution to addressing engineering durability issues in complex environments.

[0045] The following examples, combined with experimental data and results, will verify this technical solution: Raw material preparation High-belite cement: C3A=2.8%, C2S=55%, 3-day strength 28MPa, 28-day strength 52MPa; Sulfoaluminate cement: grade 42.5, 3-day strength 45MPa; Silica fume: specific surface area 22000m² / kg, SiO₂ ≥ 90%; Ultrafine fly ash microspheres: particle size 0.3-0.8μm, loss on ignition 2.5%; Nano-silica: Particle size 20-30nm, purity 99.5%; Highly active metakaolin: Al2O3=42%, specific surface area 12000m² / kg; Coarse aggregate: 5-25mm continuously graded crushed stone, crushing value 8%, needle-like and flaky content 6%; Fine aggregate: machine-made medium sand, fineness modulus 2.6, stone powder content 4%; Functional fine aggregate: Grade I fly ash, particle size 3-8μm, water requirement ratio 92%; Chemical admixtures: polycarboxylate superplasticizer (20% solids content), hydroxypropyl methylcellulose ether (viscosity 42000 mPa·s), sodium gluconate (industrial grade).

[0046] Formulation Design of Examples 1-3 and Comparative Examples 1-3 The component dosages for each embodiment and comparative embodiment, calculated per cubic meter of concrete, are shown in Table 1 below:

[0047] Preparation process Examples 1-3 and Comparative Examples 2-3 were all prepared according to the method of the present invention: S1: Dry mix the powder (30 rpm, 2.5 minutes); S2: Add fine aggregate and 70% water (containing sodium gluconate), stir at 45 rpm for 3.5 minutes; S3: Add coarse aggregate, remaining water and admixtures (water-reducing agent and cellulose ether pre-dissolved), stir at 60 rpm for 4 minutes; Curing: Cover with a thin film after pouring, and immerse in water for 14 days after final setting (temperature 20℃).

[0048] Comparative Example 1: No functional fine aggregates were added; all other aspects were the same as in Example 1. Comparative Example 3: Ordinary silicate cement (C3A=8%) was used instead of high belite cement, and the rest was the same as in Example 1.

[0049] Performance test results According to the national standards GB / T50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete" and GB / T17671-1999 "Test Methods for Strength of Cement Mortar", the results are shown in Table 2 below:

[0050] *Note: The sulfate resistance coefficient is the ratio of the compressive strength after 90 days of curing in a sulfate concentration of 4000 mg / L solution to the compressive strength after 90 days of curing in freshwater at the same age.

[0051] Results Analysis The sulfate resistance coefficients of Examples 1-3 (1.53-1.62) were significantly higher than those of the comparative examples, indicating that the synergistic effect of the cementitious system of the present invention (high belite cement + sulfoaluminate cement + multi-mineral admixture) can effectively improve corrosion resistance. Compared with Example 1 (non-functional fine aggregate), the porosity and permeability coefficient were significantly increased, proving that the dual filling effect of "ultrafine fly ash microspheres + grade I fly ash" can refine the pore structure. Compared with Example 2 (without ultrafine fly ash microspheres), the large loss of expansion and high shrinkage rate demonstrate the importance of ultrafine fly ash microspheres to workability and volume stability. Compared with Example 3 (ordinary silicate cement), the corrosion resistance coefficient was only 0.95, verifying the key role of low C3A content in high belite cement in inhibiting sulfate attack.

[0052] Industrial applicability The high-sulfate-resistant cement-based special concrete of this invention, through multi-component synergistic design and process optimization, exhibits excellent durability and mechanical properties in high-concentration sulfate and alternating wet-dry environments. It can be widely applied in projects such as marine tidal zones, saline soil subgrades, tunnels in areas with fluctuating groundwater levels, and industrial wastewater treatment plants, demonstrating significant economic and environmental benefits. Its technical effects are as follows: Excellent resistance to sulfate attack: Through the synergistic effect of "high belite cement + sulfoaluminate cement + multi-mineral admixture", the Ca(OH)2 content is reduced (≤5%), the pores are refined (critical pore size ≤50nm), and the corrosion resistance coefficient is ≥1.5 after 90 days at a sulfate concentration of 4000mg / L. Strength and workability balance: Sulfoaluminate cement compensates for early strength, with a 7-day compressive strength ≥40MPa and a 28-day compressive strength ≥60MPa; polycarboxylate superplasticizer and cellulose ether work synergistically, with an initial spread ≥650mm and a 1-hour loss ≤80mm; Adaptable to alternating wet and dry environments: Double filling (ultra-fine fly ash microspheres + primary fly ash) ensures a total porosity ≤15%, and with 14 days of wet curing, the shrinkage rate is ≤200×10⁻⁶. -6 This significantly reduces the risk of cracking. It is economically viable: with an industrial solid waste content of 40%-50%, the cost is reduced by 15%-20% compared to pure sulfoaluminate concrete, and carbon emissions are reduced by more than 60%.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-bearing cement-based special concrete resistant to sulfate attack, characterized in that, It is prepared from raw materials including the following components: Cementitious materials, the dosage is 380-450 kg / m³; aggregate; Chemical admixtures; And water; The water-to-binder ratio is 0.28-0.35; The cementitious material is composed of a main cementitious component and an auxiliary cementitious component, by weight percentage: The main cementitious component is high-belite cement, with a C3A content ≤3% and a C2S content ≥50%, accounting for 50%-70% of the total weight of the cementitious material; The auxiliary cementitious component accounts for 30%-50% of the total weight of the cementitious material and includes sulfoaluminate cement, silica fume, ultrafine fly ash microspheres, nano silica, and highly active metakaolin. The sulfoaluminate cement grade is ≥42.5, the silica fume specific surface area is ≥20000m² / kg, the ultrafine fly ash microspheres have a particle size of 0.1-1μm and a loss on ignition of ≤3%, the nano silica has a particle size of 5-50nm and a purity of ≥99%, and the highly active metakaolin has an Al2O3 content of ≥40%. The cementitious material has a hydration degree of ≥90% after 28 days, and the critical pore size of the hardened concrete is ≤50nm and the permeability coefficient is ≤1×10⁻⁶. -12 cm / s.

2. The concrete according to claim 1, characterized in that, The auxiliary cementitious component, by percentage of the total weight of the cementitious material, consists of the following components: Sulfoaluminate cement: 5%-10%; Silica fume: 3%-7%; Ultrafine fly ash microspheres: 10%-15%; Nano silica: 1%-2%; Highly active metakaolin: 5%-10%; The auxiliary cementitious component works synergistically with the main cementitious component to ensure that the Ca(OH)2 content in the concrete hydration products is ≤5% and the Ca / (Si+Al) ratio of C-(A)-SH gel is ≤1.

0.

3. The concrete according to claim 2, characterized in that, In the auxiliary gelling component: The weight ratio of the sulfoaluminate cement to the nano-silica is 4:1 to 6:

1. Under this ratio, the aspect ratio of AFt crystals is ≤2, which can avoid microcracks caused by needle-like crystals. The weight ratio of silica fume to ultrafine fly ash microspheres is 1:2~3. Under this ratio, the bulk density of the cementitious system is ≥1.8g / cm³, and the filling density is increased by more than 20% compared with that of a single admixture.

4. The concrete according to any one of claims 1-3, characterized in that, The aggregates include coarse aggregates, fine aggregates, and functional micro-aggregates; calculated per cubic meter of concrete: The coarse aggregate is crushed stone with a continuous gradation of 5-25mm; The fine aggregate is machine-made medium sand from gradation zone II; The functional fine aggregate is grade I fly ash with a particle size of 1-10μm and a water requirement ratio of ≤95%, and a dosage of 50-70kg. The functional micro-aggregate and ultrafine fly ash microspheres form a continuous "micron-submicron" gradation filling, making the total porosity of the concrete ≤15%.

5. The concrete according to claim 4, characterized in that, The coarse aggregate has a crushing value ≤10%, a needle-like and flaky particle content ≤8%, and a dosage of 1000-1080 kg / m³; the fine aggregate has a stone powder content of no more than 5% by weight, a fineness modulus of 2.3-3.0, and a dosage of 600-700 kg / m³.

6. The concrete according to claim 1 or 5, characterized in that, The chemical admixture includes: Polycarboxylate-based high-performance water-reducing agents, with a dosage of 1.0%-1.8% of the total weight of cementitious materials, enable concrete to achieve an initial spread of ≥650mm and a spread loss of ≤80mm within 1 hour. The water-retaining and thickening agent is hydroxypropyl methylcellulose ether with a viscosity of 40000±5000 mPa·s. The dosage is 0.05%-0.15% of the total weight of the cementitious materials, so that the bleeding rate of concrete is ≤0.5%. The retarder, sodium gluconate, is added at a dosage of 0.02%-0.05% of the total weight of the cementitious materials to control the initial setting time of concrete at 6-8 hours and the final setting time at 10-12 hours.

7. A method for preparing high-biological-weight cement-based sulfate-resistant special concrete as described in any one of claims 1-6, characterized in that, Includes the following steps: S1: Powder premixing: The high belite cement, sulfoaluminate cement, silica fume, ultrafine fly ash microspheres, nano silica and highly active metakaolin are put into a mixer and dry-mixed at a low speed of 25-35 rpm for 2-3 minutes to form a homogeneous cementitious powder with a homogeneity variation coefficient ≤3%; S2: Preparation of mortar: Add fine aggregate and 60%-70% of the total water volume of the homogeneous cementitious powder obtained in S1 to the mixing water, wherein sodium gluconate has been dissolved in the mixing water. Stir at a medium speed of 40-50 rpm for 3-4 minutes to form a uniform mortar. During the stirring process, the material temperature is controlled at 15-25℃. S3: Preparation of concrete mixture: Add coarse aggregate, chemical admixture and remaining mixing water to the mortar obtained in S2, and stir at high speed of 55-65 rpm for 3-5 minutes to obtain a uniform and cohesive concrete mixture with an expansion of ≥600mm and a slump loss over time of ≤100mm / h.

8. The method according to claim 7, characterized in that, In step S3, the polycarboxylic acid-based high-performance water-reducing agent and hydroxypropyl methylcellulose ether are pre-dissolved in the remaining mixing water to form an additive solution with a solid content of 30%-40%; the solution is added by dropping, with a dropping rate of 5-10 mL / s.

9. The method according to claim 7, characterized in that, The S3 step is followed by maintenance steps: S4: After the concrete mixture is poured and formed, cover it with plastic film or wet cloth for water retention and curing within 1 hour. The curing environment temperature is ≥10℃. S5: After final setting, remove the covering and use fresh water spraying or immersion curing at 20-25℃ for no less than 14 days to ensure that the concrete has a 90-day compressive strength ≥60MPa and a sulfate erosion resistance coefficient ≥1.5 under the condition of sulfate concentration 4000mg / L.

10. Use of concrete according to any one of claims 1-6 or concrete prepared by the method according to any one of claims 7-9, characterized in that, This material is intended for use in corrosive environments with sulfate ion concentrations of 2000-8000 mg / L and a wet-dry alternation frequency of ≥3 times / month. These environments include marine tidal zone revetment structures, wet-dry alternation layers of saline soil roadbeds, tunnel linings in groundwater level fluctuation zones, and bottom slabs of industrial wastewater recycling ponds.

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