An ultra-early-strength high-strength high-ductility cement-based composite material, a preparation method and applications thereof

Abstract

The application relates to the technical field of building materials in an extreme highland environment, and particularly discloses a super-early-strength high-strength high-ductility cement-based composite material, a preparation method and application. According to mass fractions, the composite material comprises the following components: cement 64-82 parts, mineral powder 12-16 parts, fly ash microbeads 6.2-8 parts, silica mortar 25-32 parts, limestone powder 8.3-11 parts, early-strength components 6.9-35 parts, sodium lignosulfonate 1.4-7 parts, quartz sand 40-60 parts, rubber particles 0.3-0.7 parts, polyethylene fibers 1.2-1.8 parts, water 17.5-21 parts, water reducing agent 1.2-1.6 parts, expanding agent 7.9-8.7 parts and defoaming agent 0.6-1.0 part. The composite material prepared by the application has the advantages that the 3h compressive strength reaches 13.5-22.8 MPa, the 28d ultimate tensile strain is 5.9-6.3%, the frost resistance grade reaches above F400, and the composite material is particularly suitable for repairing and replacing the expansion joints of roads and bridges in plateau areas.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology for extreme high-altitude environments, specifically relating to an ultra-early strength, high strength, and high ductility cement-based composite material, its preparation method, and its application. Background Technology

[0002] The harsh environment of the Qinghai-Tibet Plateau, with its daily temperature differences exceeding 30°C, strong radiation, and arid climate, causes a sharp decline in the durability of concrete. Internal freeze-thaw damage and external fatigue loads are the main causes of deterioration in road and bridge expansion joints in this region, leading to concrete failure at the expansion joints and a significant reduction in load-bearing capacity. Although the addition of silica fume, rubber aggregates, and steel fibers can improve the freeze-thaw resistance of concrete, the fatigue performance of concrete at expansion joints deteriorates rapidly under continuous vehicle loads, easily leading to concrete spalling and failure at the expansion joints, thus affecting driving safety.

[0003] Engineered cementitious composites (ECCs) possess high ductility and excellent crack control capabilities, making them promising candidates for fatigue resistance. However, ordinary ECCs typically exhibit compressive strengths below 60 MPa, and their freeze-thaw resistance is also insufficient to reach F300. Therefore, it is necessary to prepare high-strength (>80 MPa) ECCs to meet the requirements of expansion joints in high-altitude, high-frequency freeze-thaw regions. However, for the emergency repair of existing expansion joints, high-strength ECCs with early-strength properties are required. Current patents on early-strength ECCs show that they suffer from low early compressive strength, low ductility, and insufficient freeze-thaw resistance. Although calcium sulfoaluminate cement can achieve early-strength effects, its unstable byproducts can easily lead to later strength reduction and decreased durability.

[0004] Existing research indicates that the incorporation of rubber particles can effectively improve the freeze-thaw resistance of cement-based materials. As a flexible material, rubber particles can absorb the expansion stress during freeze-thaw cycles and block the penetration path of freeze-thaw water, thereby improving the material's freeze-thaw resistance. Studies have shown that the air-entraining effect of rubber can provide a site for the frost heave of concrete, reducing mass loss and the loss rate of dynamic elastic modulus. Service life prediction models based on freeze-thaw damage suggest that rubber-coated concrete can extend its service life by 19.57%–44.25% compared to ordinary concrete. However, rubber particles are hydrophobic, resulting in weak interfacial adhesion between the rubber and cement slurry, leading to a decrease in the strength of cement-based materials.

[0005] To improve the interfacial adhesion between rubber and cementitious matrix, researchers have attempted to modify the rubber surface using silane coupling agents. Silane coupling agents are hybrid molecules with the general structural formula YR-SiX3. The organic functional group at the Y-terminus can chemically react with the rubber polymer, while the hydrolyzable group at the SiX3-terminus can undergo hydrolytic condensation reactions with the hydroxyl groups on the surface of inorganic fillers, forming strong -Si-O-Si- covalent bonds. Studies have shown that silane coupling agents such as KH560 and KH550 can significantly enhance the chemical bonding at the rubber / cement interface, forming stronger bonds with CSH gel through the formation of Si-O-Si bonds. Furthermore, the particle size effect of ultrafine rubber powder allows it to fill the micropores in the cement matrix, forming a denser microstructure.

[0006] High-ductility cement-based composites, due to their low mortar-to-cement ratio and high cementitious content, exhibit high slurry viscosity, which is detrimental to construction. Furthermore, the high cementitious content in ECC leads to significant early autogenous shrinkage and later drying shrinkage, making the slurry prone to cracking and unsuitable for applications in high-freeze-thaw regions. While the use of a certain amount of expansive agent and water-absorbing resin can reduce autogenous shrinkage and drying shrinkage, the addition of expansive agent increases the slurry consistency, further hindering construction. Additionally, water-absorbing resin is prone to shear fracture during mixing, limiting its large-scale application in high-ductility cement-based composite systems. Summary of the Invention

[0007] To address the technical problems of low fluidity, insufficient early strength, low freeze-thaw resistance, and insufficient fatigue resistance in existing cement-based composite materials, this invention provides an ultra-early strength, high strength, and high ductility cement-based composite material, its preparation method, and its application.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] First, this invention provides an ultra-early strength, high strength, and high ductility cement-based composite material, comprising the following components by mass: 64-82 parts cement, 12-16 parts mineral powder, 6.2-8 parts fly ash microspheres, 25-32 parts silica fume, 8.3-11 parts limestone powder, 6.9-35 parts early strength component, 1.4-7 parts sodium lignosulfonate, 40-60 parts quartz sand, 0.3-0.7 parts rubber particles, 1.2-1.8 parts polyethylene fiber, 17.5-21 parts water, 1.2-1.6 parts water-reducing agent, 7.9-8.7 parts expanding agent, and 0.6-1.0 parts defoamer.

[0010] In this technical solution, ordinary silicate cement is used as the main cementitious material. Ultra-early strength is achieved through an early-strength component, sodium lignosulfonate acts as a retarding component to control setting time, silica fume improves rheology and density, rubber particles enhance frost resistance, and polyethylene fibers provide high ductility. The synergistic effect of these components gives the composite material ultra-early strength, high strength, high ductility, and excellent frost resistance.

[0011] As a further improvement of the present invention, the rubber particles are composite rubber particles composed of core-shell structured nano-SiO2 coated rubber particles, silane coupling agent grafted hydrophilic rubber particles, and micron-sized hydrophilic rubber powder in a mass ratio of 4:2-3:0.6-2.5.

[0012] Through extensive experimental research, the inventors discovered that combining rubber particles with three different modification methods and particle sizes can produce a significant synergistic effect. When these three are combined, a multi-level interfacial reinforcement system is formed, resulting in an unexpected improvement in freeze-thaw resistance while effectively compensating for the strength loss caused by the incorporation of a single rubber particle.

[0013] Partial component descriptions:

[0014] In this invention, the core-shell structured nano-SiO2-coated rubber particles refer to composite particles with styrene-butadiene rubber particles as the core and a nano-silica shell coating on the surface. The preparation process includes: using styrene-butadiene rubber particles with a particle size of 75–150 μm as the matrix, hydrolyzing and condensing tetraethyl orthosilicate on the surface of the rubber particles via a sol-gel method to form a uniformly coated nano-SiO2 shell (coating amount of 4%–6% of the rubber particle mass), thereby forming composite particles with a "soft core-hard shell" structure. In these core-shell structured rubber particles, the nano-SiO2 shell can form chemical bonds with CSH gel, a cement hydration product, significantly improving the interfacial bonding strength between the rubber particles and the cement matrix. Simultaneously, the shell protects the rubber particles from shear damage during stirring. Those skilled in the art can directly purchase the core-shell structured nano-SiO2-coated rubber particles from the market, or prepare them themselves according to the preparation methods provided in the invention description and specific embodiments section of this invention.

[0015] In this invention, the silane coupling agent-grafted hydrophilic rubber particles refer to modified rubber particles on which polar functional groups are introduced into the surface of waste tire rubber particles through a chemical grafting method. The preparation process includes: using 30-50 mesh waste tire rubber particles as raw material, and γ-aminopropyltriethoxysilane (KH550) or γ-glycidoxypropyltrimethoxysilane (KH560) as grafting agents, a heating reaction is carried out in an ethanol-water mixed solvent to form a Si-O-Si network structure on the rubber surface using the silane coupling agent, while simultaneously introducing polar functional groups such as amino (-NH2) or epoxy groups. The polar functional groups on the surface of these hydrophilic rubber particles can form chemical bonds with cement hydration products, densifying the interfacial transition zone (ITZ), significantly improving the compatibility between the rubber and the cement matrix, and reducing the surface contact angle from 110° (unmodified) to below 50°. Technicians can directly purchase the silane coupling agent grafted hydrophilic rubber particles from the market, or prepare them themselves according to the preparation methods provided in the Invention Content and Specific Embodiments section of this invention.

[0016] In this invention, the micron-sized hydrophilic rubber powder refers to ultrafine waste tire rubber powder that has undergone surface activation treatment. The preparation process includes: using 180-220 mesh waste tire rubber powder as raw material, performing surface activation treatment with saturated NaOH solution at 60-80°C for 1-2 hours to remove release agents such as zinc stearate from the rubber surface, exposing active sites, and simultaneously introducing hydroxyl (-OH) and carboxyl (-COOH) functional groups onto the rubber powder surface. This hydrophilic micron-sized rubber powder has a high specific surface area (approximately 1.5-2.0 m² / g), capable of filling micron-sized pores in cementitious matrices, optimizing pore structure, and simultaneously forming hydrogen bonds with cement hydration products to improve interfacial adhesion. Those skilled in the art can directly purchase the micron-sized hydrophilic rubber powder commercially, or prepare it themselves according to the preparation methods provided in the invention description and specific embodiments section of this invention.

[0017] As a further improvement of the present invention, the early strength component is composed of calcium aluminate and calcium formate in a mass ratio of 8:1.8 to 2.2, wherein the calcium aluminate has a particle size of 10 to 100 μm and the calcium formate has a particle size of 0.5 to 2 μm.

[0018] In this technical solution, calcium aluminate and calcium formate are compounded in a specific ratio to achieve hourly strength development. Calcium aluminate undergoes an extremely rapid hydration reaction, quickly generating hydration products such as ettringite, providing hourly early strength; calcium formate accelerates the hydration reaction of silicate cement and works synergistically with calcium aluminate to improve the early strength development rate.

[0019] As a further improvement of the present invention, the cement is ordinary Portland cement with a strength grade of 52.5; the mineral powder is S95 grade mineral powder with a particle size of 8-12 μm and an activity index of 95%-105%; the fly ash microspheres have a particle size of 2-30 μm; the quartz sand has a particle size of 0.075-0.38 mm and a fineness modulus of 1.4-1.6; the polyethylene fiber has a length of 12-18 mm, an equivalent diameter of 26-40 μm, a tensile modulus of 100-200 GPa, and a tensile strength of 3000-5000 MPa; the water-reducing agent is a polycarboxylate-type water-reducing agent with a water reduction rate greater than 40%; the expanding agent is a calcium oxide series expanding agent; and the defoamer is a polyether-type defoamer.

[0020] In this technical solution, the spherical particles of fly ash microspheres exhibit a "ball bearing effect," significantly reducing slurry viscosity and improving flowability during construction. Polyethylene fibers, with their high elastic modulus and high tensile strength, bridge cracks after matrix cracking, causing the material to exhibit strain hardening characteristics.

[0021] As a further improvement of the present invention, the silica slurry is composed of dense silica fume, water and high molecular weight polyelectrolyte dispersant in a mass ratio of 1:0.9-1.1:0.005-0.012, and its activity index is 130%-140%.

[0022] In this technical solution, pre-dispersing silica fume into a slurry solves the problems of easy agglomeration and increased viscosity of silica fume, while also improving the density of the slurry. As those skilled in the art will understand, the aforementioned dense silica fume refers to granular silica fume formed from unhydrated micron-sized amorphous silica powder through compaction or agglomeration treatment, with a bulk density of 300–600 kg / m³. Compared to undisturbed silica fume (bulk density 150–250 kg / m³), it is easier to transport and disperse, and can rapidly deagglomerate and exert its pozzolanic activity during stirring. The aforementioned high-molecular-weight polyelectrolyte dispersant is a polycarboxylic acid-based high-molecular-weight dispersant, specifically a polycarboxylic acid comb copolymer with a molecular weight of 20,000–40,000. It possesses both electrostatic repulsion and steric hindrance effects, effectively preventing the silica fume particles from re-agglomerating and improving the storage stability and dispersion uniformity of the silica fume slurry.

[0023] In this invention, the preparation method of the core-shell structured nano-SiO2 coated rubber particles may include: using styrene-butadiene rubber particles with a particle size of 75-150 μm as the core, coating the surface of the rubber particles with 4%-6% by mass of nano-silica through a sol-gel method, wherein the nano-silica particles have a particle size of 20-50 nm, to form composite particles with a soft core-hard shell structure.

[0024] In this invention, the preparation method of the silane coupling agent grafted hydrophilic rubber particles may include: washing 30-50 mesh waste tire rubber particles with anhydrous ethanol, using γ-aminopropyltriethoxysilane or γ-glycidoxypropyltrimethoxysilane as grafting agent, reacting in an ethanol-water mixed solvent at 60-80°C for 4-8 hours, and drying to obtain hydrophilic rubber particles with surface grafted polar functional groups.

[0025] In this invention, the preparation method of the micron-sized hydrophilic rubber powder may include: mechanically crushing 180-220 mesh waste tire rubber powder, surface activating it with saturated NaOH solution at 60-80°C for 1-2 hours, washing it until neutral, and then drying it to obtain hydrophilic micron-sized rubber powder with hydroxyl and carboxyl functional groups introduced on the surface.

[0026] This invention also provides a method for preparing an ultra-early strength, high strength, and high ductility cement-based composite material, comprising the following steps:

[0027] S1: Add the specified amounts of cement, mineral powder, fly ash microspheres, silica fume, limestone powder, quartz sand, rubber granules, expanding agent, and defoamer to a mixing container and dry mix at 300-360 rpm for 5-8 minutes to obtain the mixture.

[0028] S2: Add the water-reducing agent to the water and stir evenly. Then pour the mixture of water and water-reducing agent into the mixing container and mix with the mixture. Stir at 300-360 rpm for 3-5 minutes.

[0029] S3: Add polyethylene fibers to the mixing container and stir at 540-600 rpm for 5-6 minutes to obtain a slurry;

[0030] S4: Add the early strength component and sodium lignosulfonate to the slurry and stir for 2-4 minutes to obtain the composite material slurry.

[0031] In this technical solution, the early strength component and sodium lignosulfonate are added in the later stage of stirring. This can prevent the early strength component from coming into contact with the hydration environment too early, which would cause the slurry to solidify prematurely, avoid poor fiber dispersion, and ensure the uniformity of the composite material during construction and the stability of its mechanical properties.

[0032] This invention also provides the application of the above-mentioned ultra-early strength, high strength, and high ductility cement-based composite material in the emergency repair and renewal layer of road and bridge expansion joints in high-frequency freeze-thaw regions such as the Sichuan-Tibet Plateau.

[0033] Beneficial effects:

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1) The ultra-early strength, high strength and high ductility cement-based composite material prepared by this invention can solve the problem of high viscosity of traditional ECC by using ultra-dispersed nano silica slurry. The slurry fluidity is about 220-225 mm, which is much higher than the fluidity of traditional high strength ECC (less than 180 mm).

[0036] 2) The compressive strength of the ultra-early strength, high strength and high ductility cement-based composite material prepared by this invention at the early 3h, 6h and 12h are 13.5~22.8MPa, 19.6~28.1MPa and 33.8~41.8MPa, respectively. It is suitable for the replacement and emergency repair of concrete at the expansion joints of roads and bridges in high-altitude high-frequency freeze-thaw areas. Its early strength is significantly improved compared with the existing technology.

[0037] 3) This invention utilizes composite rubber particles, resulting in a significant synergistic effect among the three components. Experimental results show that the antifreeze synergy coefficient of the composite rubber particles reaches 6.14%, the antifreeze grade is improved to above F550, and the 28-day compressive strength retention rate exceeds 106%. Under the same usage conditions, this is far superior to single rubber particles (antifreeze grade F400~F450, strength retention rate 98.7%~103.9%), achieving a synergistic improvement in both antifreeze performance and mechanical properties.

[0038] 4) The ultra-early strength, high strength and high ductility cement-based composite material prepared by this invention has a compressive strength of over 90 MPa after 28 days, giving it a freeze-thaw resistance rating of over F450. At the same time, its ultimate tensile strain is 5.9~6.3%, which shows good fatigue resistance and can be used as an expansion joint material in high-altitude areas.

[0039] 5) The early strength, high strength and high ductility cement-based composite material prepared by this invention has an early strength self-shrinkage and a later 28-day drying shrinkage of less than 850 microstrain. It has good adaptability in the complex alternating wet and dry environment and strong wind drying environment in plateau areas and has no risk of cracking. Detailed Implementation

[0040] To enable those skilled in the art to better implement the present invention, the present invention will be further described below with reference to embodiments. However, it should be understood that the present invention is not limited to the following embodiments.

[0041] For ease of comparison, the raw materials used in the following examples and comparative examples are all from the same batch, and the specific parameters of the raw materials are as follows:

[0042] Cement: 52.5 strength grade ordinary Portland cement, commercially available;

[0043] Mineral powder: S95 grade mineral powder, particle size 10μm, activity index 98%, commercially available;

[0044] Fly ash microspheres: particle size 2~30μm, commercially available;

[0045] Silica slurry: It is prepared by mixing dense silica fume, water and polycarboxylate-based polymeric polyelectrolyte dispersant in a mass ratio of 1:1:0.01, and dispersed evenly by mechanical stirring, with an activity index of 136%.

[0046] Limestone powder: calcium carbonate content 75%, particle size 0.1~14μm, specific surface area 2.2m² / g, specific gravity 2.65g / cm³;

[0047] Calcium aluminate: particle size 10-100μm, specific gravity 2.95g / cm³, commercially available;

[0048] Calcium formate: particle size 0.5-2μm, specific gravity 1.70g / cm³, commercially available;

[0049] Sodium lignosulfonate: 100 mesh, bulk density 0.50 g / cm³, commercially available;

[0050] Quartz sand: particle size 0.075~0.38mm, fineness modulus 1.5, commercially available;

[0051] Polyethylene fiber: 12mm in length, 30μm in equivalent diameter, 150GPa in tensile modulus, 4000MPa in tensile strength, commercially available;

[0052] Polycarboxylate superplasticizer: water reduction rate 42%, commercially available;

[0053] Calcium oxide series expansion agent: density 2.7g / cm³, commercially available;

[0054] Polyether-type defoamer: density 1.0 g / cm³, commercially available.

[0055] The three modified rubber particles used in the following examples and comparative examples were prepared according to the following method:

[0056] Preparation of core-shell structured nano-SiO2 coated rubber particles:

[0057] 100g of styrene-butadiene rubber (SBR) particles with a diameter of 75-150μm were washed with anhydrous ethanol and dried. 10g of tetraethyl orthosilicate was dissolved in 50mL of anhydrous ethanol, and 5mL of deionized water and 0.1mol / L hydrochloric acid were added to adjust the pH to 3.6. The mixture was stirred and hydrolyzed in a 40℃ water bath for 30min to obtain a nano-SiO2 sol. The dried SBR particles were added to the sol, and the mixture was stirred continuously at 40℃ for 4h. After filtration, the particles were washed three times with anhydrous ethanol and dried under vacuum at 60℃ for 12h to obtain core-shell structured rubber particles coated with nano-SiO2. Thermogravimetric analysis showed that the nano-SiO2 coating amount was approximately 5.2% of the rubber particle mass. This method references the sol-gel method for preparing core-shell structured nanocomposite particles.

[0058] Preparation of hydrophilic rubber particles grafted with silane coupling agents:

[0059] 100g of 40-mesh waste tire rubber granules were washed with anhydrous ethanol and dried. 5g of γ-aminopropyltriethoxysilane (KH550) was dissolved in 200mL of an ethanol / water mixture (9:1 volume ratio), and the pH was adjusted to 5.1 with acetic acid. The rubber granules were added to the solution, and the mixture was stirred in a 70℃ water bath for 6 hours. After the reaction, the mixture was filtered, washed three times with anhydrous ethanol, and dried under vacuum at 80℃ for 8 hours to obtain rubber granules with surface-grafted hydrophilic functional groups. XPS analysis showed that the surface nitrogen content was approximately 1.8%, indicating successful KH550 grafting. The silane coupling agent formed a YR-SiX3 structure; the Y-terminus reacted with the rubber polymer, and the SiX3 terminus formed a -Si-O-Si- covalent bond with the hydroxyl groups on the surface of the inorganic filler.

[0060] Preparation of micron-sized hydrophilic rubber powder:

[0061] 100g of 200-mesh waste tire rubber powder was added to 500mL of saturated NaOH solution and stirred in a 70℃ water bath for 1.5h. After the reaction, the powder was repeatedly washed with deionized water until the pH of the filtrate reached 7.2, and then vacuum dried at 60℃ for 12h to obtain surface-activated ultrafine hydrophilic rubber powder. FTIR analysis showed characteristic absorption peaks of -OH and -COOH on the surface, indicating the successful introduction of hydrophilic functional groups.

[0062] Example 1:

[0063] Ultra-early strength, high strength, and high ductility cement-based composite materials were prepared according to the following method:

[0064] S1. Weigh the following raw materials according to the following parts by weight: 73.3 parts cement, 14.1 parts mineral powder, 7.1 parts fly ash microspheres, 28.3 parts silica fume slurry, 9.4 parts limestone powder, 0.5 parts ordinary rubber granules (80 mesh, unmodified), 50 parts quartz sand, 8.3 parts expanding agent, and 0.8 parts defoamer. Add the above raw materials to a mixing container and dry mix at 320 rpm for 6 minutes to obtain a mixture.

[0065] S2. Add 1.4 parts of water-reducing agent to 19.1 parts of water and stir evenly. Then pour the mixture of water and water-reducing agent into the mixing container and mix with the mixture. Stir at 320 rpm for 4 minutes.

[0066] S3. Add 1.5 parts of polyethylene fiber to the mixing container and stir at 570 rpm for 5.5 minutes to obtain a slurry.

[0067] S4. Add the early strength component (16.6 parts calcium aluminate and 4.2 parts calcium formate) and 4.2 parts sodium lignosulfonate to the slurry and stir rapidly for 3 minutes to obtain the composite material slurry.

[0068] Sample preparation: After the composite material slurry has initially set, it is demolded and denoted as sample A1.

[0069] Example 2:

[0070] The procedure is the same as in Example 1, except that the amounts of each component are adjusted. The specific plan is as follows:

[0071] S1. Weigh the following raw materials according to the following mass proportions: 81.9 parts cement, 15.8 parts mineral powder, 7.9 parts fly ash microspheres, 31.7 parts silica fume slurry, 10.5 parts limestone powder, 0.5 parts ordinary rubber granules (80 mesh, unmodified), 50 parts quartz sand, 8.3 parts expanding agent, and 0.8 parts defoamer. Dry mix at 300 rpm for 8 minutes.

[0072] S2. Add 1.4 parts of water-reducing agent to 17.5 parts of water and stir evenly. Stir at 300 rpm for 5 minutes.

[0073] S3. Add 1.5 parts of polyethylene fiber to the mixing container and stir at 540 rpm for 6 minutes.

[0074] S4. Add the early strength component (5.5 parts calcium aluminate and 1.4 parts calcium formate) and 1.4 parts sodium lignosulfonate to the slurry and stir rapidly for 3 minutes to obtain the composite material slurry.

[0075] Sample preparation: After the composite material slurry has initially set, it is demolded and denoted as sample A2.

[0076] Example 3:

[0077] The procedure is the same as in Example 1, except that the amounts of each component are adjusted. The specific plan is as follows:

[0078] S1. Weigh the following raw materials according to the following parts by weight: 64.6 parts cement, 12.5 parts mineral powder, 6.3 parts fly ash microspheres, 25.0 parts silica fume slurry, 8.3 parts limestone powder, 0.5 parts ordinary rubber granules (80 mesh, unmodified), 50 parts quartz sand, 8.3 parts expanding agent, and 0.8 parts defoamer. Dry mix at 360 rpm for 5 minutes.

[0079] S2. Add 1.4 parts of water-reducing agent to 20.8 parts of water and stir evenly. Stir at 360 rpm for 3 minutes.

[0080] S3. Add 1.5 parts of polyethylene fiber to the mixing container and stir at 600 rpm for 5 minutes.

[0081] S4. Add the early strength component (27.7 parts calcium aluminate and 6.9 parts calcium formate) and 6.9 parts sodium lignosulfonate to the slurry and stir rapidly for 3 minutes to obtain the composite material slurry.

[0082] Sample preparation: After the composite material slurry has initially set, it is demolded and designated as sample A3.

[0083] Example 4:

[0084] The procedure is the same as in Example 1, except that ordinary rubber particles are replaced with composite rubber particles. The composite rubber particles consist of core-shell structured nano-SiO2-coated rubber particles, silane coupling agent-grafted hydrophilic rubber particles, and micron-sized hydrophilic rubber powder in a mass ratio of 4:2.5:1.5. The specific scheme is as follows:

[0085] S1. Weigh the following raw materials according to the following parts by weight: 73.3 parts cement, 14.1 parts mineral powder, 7.1 parts fly ash microspheres, 28.3 parts silica fume slurry, 9.4 parts limestone powder, 0.5 parts composite rubber granules, 50 parts quartz sand, 8.3 parts expanding agent, and 0.8 parts defoamer. Add the above raw materials to a mixing container and dry mix at 320 rpm for 6 minutes to obtain a mixture.

[0086] S2. Add 1.4 parts of water-reducing agent to 19.1 parts of water and stir evenly. Then pour the mixture of water and water-reducing agent into the mixing container and mix with the mixture. Stir at 320 rpm for 4 minutes.

[0087] S3. Add 1.5 parts of polyethylene fiber to the mixing container and stir at 570 rpm for 5.5 minutes to obtain a slurry.

[0088] S4. Add the early strength component (16.6 parts calcium aluminate and 4.2 parts calcium formate) and 4.2 parts sodium lignosulfonate to the slurry and stir rapidly for 3 minutes to obtain the composite material slurry.

[0089] Sample preparation: After the composite material slurry has initially set, it is demolded and recorded as sample A4.

[0090] Comparative Example 1 (without early-strength component)

[0091] This comparative ratio does not include early-strength components or sodium lignosulfonate; the amounts of each component are adjusted according to the following formula. The specific scheme is as follows:

[0092] S1. Weigh the following raw materials according to the following mass proportions: 86 parts cement, 16.6 parts mineral powder, 8.3 parts fly ash microspheres, 33.3 parts silica fume slurry, 11.1 parts limestone powder, 0.5 parts ordinary rubber granules (80 mesh, unmodified), 50 parts quartz sand, 8.3 parts expanding agent, and 0.8 parts defoamer. Add the above raw materials to a mixing tank and dry mix at 320 rpm for 6 minutes to obtain a mixture.

[0093] S2. Add 1.4 parts of water-reducing agent to 16.6 parts of water and stir evenly. Then pour the mixture of water and water-reducing agent into the mixing tank and mix with the mixture. Stir at 320 rpm for 4 minutes.

[0094] S3. Add 1.5 parts of polyethylene fiber to the mixing tank and stir at 570 rpm for 5.5 minutes to obtain a slurry.

[0095] S4. Without adding early strength components and sodium lignosulfonate, proceed directly to the next step to obtain the composite material slurry.

[0096] Sample preparation: After the composite material slurry has initially set, it is demolded and denoted as sample D1.

[0097] Comparative Example 2 (only core-shell structured nano-SiO2 coated rubber particles added):

[0098] The procedure is the same as in Example 1, except that the rubber particles added in step S1 are only core-shell structured nano-SiO2 coated rubber particles, and the amount added is 0.5 parts. The specific scheme is as follows:

[0099] S1. Weigh the following raw materials according to the following mass proportions: 73.3 parts cement, 14.1 parts mineral powder, 7.1 parts fly ash microspheres, 28.3 parts silica fume slurry, 9.4 parts limestone powder, 0.5 parts core-shell structured nano-SiO2 coated rubber particles, 50 parts quartz sand, 8.3 parts expanding agent, and 0.8 parts defoamer. Dry mix at 320 rpm for 6 minutes to obtain the mixture.

[0100] S2~S5 are the same as in Example 1, and the resulting composite material is designated as comparative sample D2.

[0101] Comparative Example 3 (with only silane coupling agent added to graft hydrophilic rubber particles):

[0102] The procedure is the same as in Example 1, except that the rubber particles added in step S1 are only silane coupling agent-grafted hydrophilic rubber particles, and the amount added is 0.5 parts. The specific scheme is as follows:

[0103] S1. Weigh the following raw materials according to the following mass proportions: 73.3 parts cement, 14.1 parts mineral powder, 7.1 parts fly ash microspheres, 28.3 parts silica fume slurry, 9.4 parts limestone powder, 0.5 parts silane coupling agent grafted hydrophilic rubber particles, 50 parts quartz sand, 8.3 parts expanding agent, and 0.8 parts defoamer. Dry mix at 320 rpm for 6 minutes to obtain the mixture.

[0104] S2~S5 are the same as in Example 1, and the resulting composite material is designated as comparative sample D3.

[0105] Comparative Example 4 (only micron-sized hydrophilic rubber powder added):

[0106] The procedure is the same as in Example 1, except that the rubber particles added in step S1 are only micron-sized hydrophilic rubber powder, and the amount added is 0.5 parts. The specific scheme is as follows:

[0107] S1. Weigh the following raw materials according to the following mass proportions: 73.3 parts cement, 14.1 parts mineral powder, 7.1 parts fly ash microspheres, 28.3 parts silica fume slurry, 9.4 parts limestone powder, 0.5 parts micron-sized hydrophilic rubber powder, 50 parts quartz sand, 8.3 parts expanding agent, and 0.8 parts defoamer. Dry mix at 320 rpm for 6 minutes to obtain the mixture.

[0108] S2~S5 are the same as in Example 1, and the resulting composite material is designated as comparative sample D4.

[0109] Comparative Example 5 (core-shell + silane grafting only, without micron powder):

[0110] The procedure is the same as in Example 4, except that the composite rubber particles consist only of core-shell structured nano-SiO2 coated rubber particles and silane coupling agent-grafted hydrophilic rubber particles in a mass ratio of 4:2.5 (excluding micron-sized hydrophilic rubber powder), with a total addition amount of 0.5 parts. The specific scheme is as follows:

[0111] S1. Weigh the following raw materials according to the following parts by weight: 73.3 parts cement, 14.1 parts mineral powder, 7.1 parts fly ash microspheres, 28.3 parts silica fume slurry, 9.4 parts limestone powder, 0.5 parts composite rubber granules (core-shell + silane grafting only, excluding micronized powder), 50 parts quartz sand, 8.3 parts expanding agent, and 0.8 parts defoamer. Dry mix at 320 rpm for 6 minutes to obtain the mixture.

[0112] S2~S5 are the same as in Example 4, and the resulting composite material is designated as comparative sample D5.

[0113] Comparative Example 6 (core-shell + micron powder only, without silane grafting):

[0114] The procedure is the same as in Example 4, except that the composite rubber particles consist only of core-shell structured nano-SiO2-coated rubber particles and micron-sized hydrophilic rubber powder in a mass ratio of 4:1.5 (excluding silane coupling agent-grafted hydrophilic rubber particles), with a total addition amount of 0.5 parts. The specific scheme is as follows:

[0115] S1. Weigh the following raw materials according to the following mass proportions: 73.3 parts cement, 14.1 parts mineral powder, 7.1 parts fly ash microspheres, 28.3 parts silica fume slurry, 9.4 parts limestone powder, 0.5 parts composite rubber granules (core-shell + micronized powder only, excluding silane grafting), 50 parts quartz sand, 8.3 parts expanding agent, and 0.8 parts defoamer. Dry mix at 320 rpm for 6 minutes to obtain the mixture.

[0116] S2~S5 are the same as in Example 4, and the resulting composite material is designated as comparative sample D6.

[0117] Comparative Example 7 (Silane grafting only + micron powder, without core-shell):

[0118] The procedure is the same as in Example 4, except that the composite rubber particles consist only of silane coupling agent-grafted hydrophilic rubber particles and micron-sized hydrophilic rubber powder in a mass ratio of 2.5:1.5 (excluding core-shell structured nano-SiO2 coated rubber particles), with a total addition amount of 0.5 parts. The specific scheme is as follows:

[0119] S1. Weigh the following raw materials according to the following parts by weight: 73.3 parts cement, 14.1 parts mineral powder, 7.1 parts fly ash microspheres, 28.3 parts silica fume slurry, 9.4 parts limestone powder, 0.5 parts composite rubber granules (silane grafted + micronized powder only, excluding core and shell), 50 parts quartz sand, 8.3 parts expanding agent, and 0.8 parts defoamer. Dry mix at 320 rpm for 6 minutes to obtain the mixture.

[0120] S2~S5 are the same as in Example 4, and the resulting composite material is designated as comparative sample D7.

[0121] Performance verification experiment:

[0122] The composite material slurry samples and demolded composite material samples obtained in Examples 1 to 4 and Comparative Examples 1 to 7 were subjected to performance tests, as detailed below:

[0123] 1. Setting time and fluidity test

[0124] The setting time was tested according to GB / T 1346-2011 "Test Methods for Standard Consistency Water Requirement, Setting Time and Soundness of Cement", and the fluidity was tested according to GB / T 2419-2005 "Test Method for Flowability of Cement Mortar". The results are shown in Table 1.

[0125] Table 1. Condensation time and flowability of each sample

[0126]

[0127] As shown in Table 1, the addition of the early-strength component significantly shortened the setting time of the composite material, with the initial setting time controlled within the range of 21-33 minutes. This not only meets the requirement for rapid traffic reopening but also ensures a smooth construction window. The comparative example without the early-strength component had a setting time as long as 5.5 hours / 10 hours, which could not meet the requirements for rapid traffic reopening in emergency repair projects. The flowability of all examples and comparative examples was within the range of 218-223 mm, far exceeding that of traditional high-strength ECC (below 180 mm), indicating that the composite material of this invention has excellent workability.

[0128] 2. Mechanical properties and frost resistance testing

[0129] The compressive strength was tested according to GB / T 17671-1999 "Test Method for Strength of Cement Mortar (ISO Method)", the tensile properties were tested according to JC / T 2461-2018 "Test Method for Mechanical Properties of High-Ductility Fiber Reinforced Cement-Based Composite Materials", and the frost resistance was tested according to the rapid freezing method in GB / T 50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete". The results are shown in Table 2.

[0130] Table 2 Comparison of mechanical properties and freeze-thaw resistance of each sample

[0131]

[0132] *Note: The strength retention rate is calculated based on the 28-day compressive strength of 86.2 MPa of Comparative Example 1 (without early strength component).

[0133] The results in Table 2 show that:

[0134] (1) The key role of the early strength component: Comparing Comparative Example 1 and Example 1, it can be seen that after adding the early strength component, the composite material obtains a compressive strength of 13.5 MPa in 3 hours, while Comparative Example 1, which lacks the early strength component, has not yet solidified in 3 hours and its strength cannot be tested. This shows that the early strength component of the present invention is the key to achieving "ultra-early strength".

[0135] (2) Antifreeze effect of single rubber particles: Comparative Examples 2 to 4 show that single types of rubber particles can significantly improve the antifreeze performance, with antifreeze grades reaching F400~F450, but the strength retention rate is between 98.7% and 103.9%. Among them, the core-shell structured rubber particles (D2) performed the best, with an antifreeze grade of F450 and a strength retention rate of 103.9%, which is attributed to the enhancing effect of the nano-SiO2 shell on interfacial adhesion.

[0136] (3) Synergistic effect of ternary composite rubber particles: In Example 4, a core-shell structure, silane grafting, and micronized powder were compounded in a ratio of 4:2.5:1.5. After 200 freeze-thaw cycles, the relative dynamic elastic modulus reached 96.8%, and the freeze-thaw resistance grade was improved to F550 or higher (the relative dynamic elastic modulus was still higher than 60% after more than 550 freeze-thaw cycles), which is far superior to F400~F450 of single rubber particles. At the same time, the 28-day compressive strength reached 91.8 MPa, and the strength retention rate was as high as 106.5%, which is significantly better than all single rubber particle samples. This indicates that the three types of rubber particles produced a significant synergistic effect, achieving a synergistic improvement in freeze-thaw resistance and mechanical properties.

[0137] (4) Verification of the necessity of ternary synergy: Comparative Examples 5 to 7 show that when the total amount of rubber particles used is exactly the same, the antifreeze grade can only reach F400~F450 when only two types of rubber particles are used, which is significantly lower than F550 of the ternary compound. The antifreeze grade of Comparative Example 5 (core-shell + silane, no micron powder) is F450, the antifreeze grade of Comparative Example 6 (core-shell + micron, no silane) is F450, and the antifreeze grade of Comparative Example 7 (silane + micron, no core-shell) is F400, all of which are significantly lower than F550 of Example 4. This proves that all three types of rubber particles are indispensable, and only when all three work together can the best synergistic reinforcement effect be achieved. The inventors believe the reason may be that the nano-SiO2 shell of the core-shell rubber particles participates in the formation of CSH gel during the early stages of cement hydration, constructing a continuous and dense active transition layer at the rubber-matrix interface. This transition layer not only forms a high-strength chemical bond with the matrix but also provides an ideal adhesion substrate for the chemical anchoring of polar functional groups on the surface of the silane-grafted rubber particles. This allows the two rubber particles with different interface reinforcement mechanisms to form a nested "double-anchoring" structure in space. Simultaneously, the micron-sized hydrophilic rubber powder, with its ultrafine particle size, fills the micron-sized pores between the aforementioned "double-anchoring" structures, not only blocking the penetration channels of freeze-thaw water in the interface region but also providing a wrapping support for the shell of the core-shell rubber and the anchoring region of the silane-grafted rubber, thus constraining the propagation of microcracks in the interface transition zone. These three components thus construct a cyclic reinforcement system, resulting in a significant improvement in freeze-thaw resistance.

[0138] (5) Calculation of antifreeze synergy coefficient: Define the antifreeze synergy coefficient K = (ε ABC - max(ε A , ε B , ε C )) / max(ε A , ε B , ε C ) × 100%, where ε is the relative dynamic elastic modulus retention rate after 200 freeze-thaw cycles. max(ε) A, ε B , ε C =91.2% (Comparative Example 2, core-shell structure only), ε ABC = 96.8% (Example 4), and K = (96.8 - 91.2) / 91.2 × 100% = 6.1%. This synergy coefficient is positive, indicating that the ternary compound produced a significant synergistic effect. In contrast, the synergistic effect of the binary compound system was significantly weaker (the relative dynamic elastic modulus after freeze-thaw in Comparative Examples 5 to 7 did not exceed 91%, the synergy coefficient was negative, and there was no significant synergistic effect), further verifying the irreplaceable nature of the ternary compound.

[0139] 3. Shrinkage performance test

[0140] The shrinkage test was conducted according to the shrinkage test method in GB / T 50082-2009 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete", and the results are shown in Table 3.

[0141] Table 3. Autogenous shrinkage and drying shrinkage values ​​of each sample (unit: με)

[0142]

[0143] As shown in Table 3, the 7-day autogenous shrinkage and 28-day drying shrinkage of all samples with added early-strength components (Examples 1 to 4, Comparative Examples 2 to 7) were significantly lower than those of Comparative Example 1 without added early-strength components. Specifically, the 7-day autogenous shrinkage and 28-day drying shrinkage of Examples 1 to 4 were both below 850 με, far superior to the 2236 με and 912 με of Comparative Example 1, indicating that the composite material of the present invention has good volume stability and no risk of cracking in the dry, windy environment of high altitude. The addition of composite rubber particles had little effect on shrinkage performance, and all samples exhibited excellent volume stability.

Claims

1. A high-early-strength, high-strength, and high-ductility cement-based composite material, characterized in that, The product comprises the following components by weight: 64-82 parts cement, 12-16 parts mineral powder, 6.2-8 parts fly ash microspheres, 25-32 parts silica fume slurry, 8.3-11 parts limestone powder, 6.9-35 parts early strength component, 1.4-7 parts sodium lignosulfonate, 40-60 parts quartz sand, 0.3-0.7 parts rubber particles, 1.2-1.8 parts polyethylene fiber, 17.5-21 parts water, 1.2-1.6 parts water-reducing agent, 7.9-8.7 parts expanding agent, and 0.6-1.0 parts defoamer; the rubber particles are composite rubber particles composed of core-shell structured nano-SiO2 coated rubber particles, silane coupling agent grafted hydrophilic rubber particles, and micron-sized hydrophilic rubber powder in a weight ratio of 4:2-3:0.6-2.

5. The preparation method of silane coupling agent grafted hydrophilic rubber particles includes: washing 30-50 mesh waste tire rubber particles with anhydrous ethanol, using γ-aminopropyltriethoxysilane or γ-glycidoxypropyltrimethoxysilane as grafting agent, reacting in ethanol-water mixed solvent at 60-80℃ for 4-8h, and drying to obtain hydrophilic rubber particles with surface grafted polar functional groups. The preparation method of micron-sized hydrophilic rubber powder includes: surface activation treatment of 180-220 mesh waste tire rubber powder with saturated NaOH solution at 60-80℃ for 1-2 hours, washing until neutral and drying to obtain hydrophilic micron-sized rubber powder with hydroxyl and carboxyl functional groups introduced on the surface.

2. The ultra-early strength, high strength, and high ductility cement-based composite material according to claim 1, characterized in that, The early strength component is composed of calcium aluminate and calcium formate in a mass ratio of 8:1.8 to 2.2, wherein the calcium aluminate has a particle size of 10 to 100 μm and the calcium formate has a particle size of 0.5 to 2 μm.

3. The ultra-early strength, high strength, and high ductility cement-based composite material according to claim 1, characterized in that, The cement is ordinary Portland cement with a strength grade of 52.5; the mineral powder is S95 grade mineral powder with a particle size of 8-12 μm and an activity index of 95%-105%; the fly ash microspheres have a particle size of 2-30 μm; the quartz sand has a particle size of 0.075-0.38 mm and a fineness modulus of 1.4-1.6; the polyethylene fiber has a length of 12-18 mm, an equivalent diameter of 26-40 μm, a tensile modulus of 100-200 GPa, and a tensile strength of 3000-5000 MPa; the water-reducing agent is a polycarboxylate-type water-reducing agent with a water reduction rate greater than 40%; the expanding agent is a calcium oxide series expanding agent; and the defoamer is a polyether-type defoamer.

4. The ultra-early strength, high strength, and high ductility cement-based composite material according to claim 1, characterized in that, The silica slurry is composed of dense silica fume, water and high molecular weight polyelectrolyte dispersant in a mass ratio of 1:0.9-1.1:0.005-0.012, and its activity index is 130%-140%.

5. The ultra-early strength, high strength, and high ductility cement-based composite material according to claim 1, characterized in that, The preparation method of the core-shell structured nano-SiO2 coated rubber particles includes: using styrene-butadiene rubber particles with a particle size of 75-150 μm as the core, coating the surface of the rubber particles with 4%-6% by mass of nano-silica through a sol-gel method to form composite particles with a soft core-hard shell structure; the nano-silica particles have a particle size of 20-50 nm.

6. A method for preparing the ultra-early strength, high strength, and high ductility cement-based composite material according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1: Add the specified amounts of cement, mineral powder, fly ash microspheres, silica fume, limestone powder, quartz sand, rubber granules, expanding agent, and defoamer to a mixing container and dry mix at 300-360 rpm for 5-8 minutes to obtain the mixture. S2: Add the water-reducing agent to the water and stir evenly. Then pour the mixture of water and water-reducing agent into the mixing container and mix with the mixture. Stir at 300-360 rpm for 3-5 minutes. S3: Add polyethylene fibers to the mixing container and stir at 540-600 rpm for 5-6 minutes to obtain a slurry; S4: Add the early strength component and sodium lignosulfonate to the slurry and stir for 2-4 minutes to obtain the desired composite material.

7. The application of the ultra-early strength, high strength and high ductility cement-based composite material according to any one of claims 1 to 5 in the emergency repair and renewal layer of road and bridge expansion joints in high-frequency freeze-thaw regions.

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