High-ductility low-shrinkage concrete and method for preparing the same

Abstract

The application discloses a kind of high toughness low shrinkage concrete and preparation method thereof.The concrete is composed of cementitious material system, aggregate, modified fiber and auxiliary material;Cementitious material system includes cement, mixed mineral admixture and micro-expansion component, mixed mineral admixture is metakaolin and zeolite powder compound, and micro-expansion component is calcium sulphoaluminate mineral powder;Modified fiber includes basalt fiber surface modified by silane coupling agent and polyvinyl alcohol fiber compound system.The preparation method of the application includes fiber modification, mixed mineral admixture activation, stirring, pouring molding and maintenance and the like steps.The concrete of the application has low shrinkage, high toughness and excellent mechanical properties, and can be widely used in building structure, bridge engineering and prefabricated component field.

Description

Technical Field

[0001] This invention relates to the field of concrete technology, specifically to a high-toughness, low-shrinkage concrete and its preparation method. Background Technology

[0002] As a multiphase composite system, concrete undergoes continuous energy release and evolution during its hydration and hardening process. When cement clinker minerals react with water, the breaking and reforming of chemical bonds releases a large amount of heat of hydration. Simultaneously, the nucleation, growth, and bonding of hydration products are accompanied by dynamic changes in local free energy. Due to the heterogeneity of the concrete's internal composition and structure—the differences in elastic moduli between aggregates and paste, the loose structure of the interface transition zone, and the uneven distribution of pores—energy is difficult to dissipate uniformly during transmission, easily leading to energy accumulation in weak areas. When the accumulated energy exceeds the fracture capacity of that area, it is suddenly released in the form of microcracks. These microcracks further expand and connect under service loads and environmental factors, eventually developing into visible macroscopic cracks. This energy evolution mechanism is the deep physical essence of concrete cracking. Once cracks form, they not only damage the integrity and aesthetics of the structure but also provide channels for the penetration of moisture and corrosive media, accelerating steel corrosion and concrete carbonation, ultimately leading to decreased structural durability or even failure.

[0003] Meanwhile, concrete inevitably undergoes various shrinkage deformations during the hardening process: chemical shrinkage caused by cement hydration, autogenous shrinkage due to water consumption during hydration, drying shrinkage caused by water evaporation, and cooling shrinkage due to temperature drop. These shrinkage deformations generate tensile stress when constrained by internal aggregates or external factors, further exacerbating energy accumulation. When the shrinkage tensile stress exceeds the tensile strength of the concrete, or the shrinkage strain exceeds the ultimate tensile value, cracking will also occur. Shrinkage and energy release are coupled; the strain energy generated by shrinkage accumulates locally, and the initiation of microcracks releases energy, creating a vicious cycle.

[0004] Existing crack prevention technologies mostly focus on physical blocking after cracks appear or post-cracking compensation for shrinkage deformation. For example, patent document CN116969725A proposes a high-crack-resistant, low-shrinkage ready-mixed concrete. By introducing components such as medium-heat cement, modified zeolite, and magnesium oxide expansion agent, it improves the shrinkage and crack resistance of concrete to a certain extent. However, this approach focuses on improving the volume stability and crack resistance of the concrete material itself, without fully considering the role of fiber reinforcement and toughening. It lacks effective resistance and inhibition for microcracks that have already formed, making it difficult to prevent crack propagation from the perspective of energy dissipation. Similarly, patent document CN121072241A discloses a fiber-reinforced concrete crack prevention method that blocks crack propagation by directional fiber placement, improving the crack resistance efficiency of concrete. However, this approach focuses on directional blocking after cracks appear, without addressing the shrinkage problem of concrete from the intrinsic material properties, and fails to eliminate the fundamental driving force for crack formation. The aforementioned existing technologies mostly focus on optimizing a single performance aspect. Whether focusing on low shrinkage, high crack resistance, or fiber crack resistance, most adopt a remedial approach after problems occur, failing to actively regulate the source of energy evolution and shrinkage synergy, and thus making it difficult to fundamentally suppress the initiation and propagation of microcracks.

[0005] Therefore, how to construct a technical solution that can actively regulate the energy release process, synergistically compensate for shrinkage deformation, and effectively dissipate crack propagation energy, starting from the fundamental process of concrete hydration and hardening, thereby inhibiting the initiation and propagation of microcracks and achieving a balance of low shrinkage, high toughness, and stress coordination, has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a high-toughness, low-shrinkage concrete and its preparation method, solving the technical problem that "existing single-modification technologies for concrete are difficult to balance energy dissipation and shrinkage compensation, resulting in poor crack resistance and high shrinkage rate".

[0007] To achieve the above objectives, the present invention is implemented using the following technical solution: In a first aspect, the present invention provides a high-toughness, low-shrinkage concrete, wherein the concrete, by weight, comprises: 60-80 parts cement, 20-30 parts mixed mineral admixtures, 3-8 parts micro-expansion components, 180-230 parts coarse aggregate, 120-160 parts fine aggregate, 0.5-1.2 parts water-reducing agent, 29-41 parts water, and 3-6 parts modified fiber; wherein the cement is P O42.5 grade ordinary Portland cement; the mixed mineral admixture is a compound system of metakaolin and zeolite powder; the micro-expansion component is calcium sulfoaluminate mineral powder; the water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent.

[0008] In this invention, the mass ratio of metakaolin to zeolite powder in the mixed mineral admixture is 1:(1~1.2), the total content of active SiO2 and Al2O3 in the metakaolin is ≥85%, and the specific surface area of ​​the zeolite powder is ≥400m². 2 / kg.

[0009] In this invention, the modified fiber is obtained by surface modification of basalt fiber and polyvinyl alcohol fiber by compounding and silane coupling agent; the mass ratio of basalt fiber to polyvinyl alcohol fiber is (1~2):1, the length of basalt fiber is 12~18mm and the tensile strength is ≥3500MPa, and the length of polyvinyl alcohol fiber is 8~12mm and the tensile strength is ≥1200MPa.

[0010] In this invention, the purity of the calcium sulfoaluminate mineral powder is ≥90%.

[0011] In this invention, the silane coupling agent is KH-550, and its dosage is 0.25~0.6% of the total mass of basalt fiber and polyvinyl alcohol fiber.

[0012] In this invention, the coarse aggregate is 5-16mm continuously graded basalt with a crushing value ≤10%, and the fine aggregate is medium sand with a fineness modulus of 2.6-2.9.

[0013] In this invention, the water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent.

[0014] Secondly, the present invention provides a high-toughness, low-shrinkage concrete and a method for preparing the same, comprising the following steps: (1) Basalt fiber and polyvinyl alcohol fiber are mixed, silane coupling agent KH-550 is added, and the mixture is stirred and left to stand to obtain modified fiber; (2) Mix and ball-mill metakaolin and zeolite powder to obtain a mixed mineral admixture; (3) Put cement, mixed mineral admixtures, calcium sulfoaluminate mineral powder, coarse aggregate and fine aggregate into a mixer for dry mixing, add water-reducing agent and water and mix, and finally add modified fiber in batches and continue mixing to obtain concrete mixture.

[0015] Specifically, in step (3), cement, mixed mineral admixtures, calcium sulfoaluminate mineral powder, coarse aggregate, and fine aggregate are first put into a mixer and dry-mixed for 1-2 minutes. Then, polycarboxylate-based high-efficiency water-reducing agent and water are added and wet-mixed for 3 minutes. Finally, modified fibers are added and mixing continues.

[0016] Specifically, the modified fiber in step (3) is added in three parts, with an interval of 30 seconds between each addition, and the mixture is stirred continuously for 3 to 4 minutes to finally obtain the concrete mixture.

[0017] Compared with the prior art, the beneficial effects achieved by the present invention are: (1) This invention achieves a balance between low shrinkage and high toughness by using the synergistic effect of a multi-component composite system of mixed mineral admixtures, micro-expansion components and fiber reinforcement to intervene in the energy release and shrinkage deformation of concrete in the early stage of hydration. This invention solves the problem of large shrinkage and poor toughness of concrete from the intrinsic material level and effectively inhibits the initiation and expansion of microcracks.

[0018] (2) In this invention, metakaolin and zeolite powder are combined to change the hydration process, transform high energy release into low energy continuous reaction, while maintaining stable internal humidity and reducing shrinkage driving force; calcium sulfoaluminate mineral powder transforms shrinkage strain energy into expansion energy and releases it in a controlled manner; basalt fiber and polyvinyl alcohol fiber are combined to form a three-dimensional support network, which dissipates crack expansion energy through debonding, pull-out and other mechanisms.

[0019] (3) The concrete of the present invention has both excellent mechanical properties and construction adaptability, meets the requirements of C40 strength grade, the water-cement ratio is controlled at 0.35~0.36, the workability of the mixture is good, and it is suitable for cast-in-place construction and precast component production. At the same time, the present invention, by adjusting the composition of the cementitious material system, makes the development rate of the elastic modulus of concrete more coordinated with the mechanical response under different constraint conditions. It can be widely used in building structures, bridge engineering, road engineering and various precast components, significantly improving the durability and service life of concrete structures and reducing the maintenance cost throughout the entire life cycle. Detailed Implementation

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

[0021] This invention provides a technical solution for a multi-component composite system consisting of mixed mineral admixtures, a micro-expansion component, and fiber reinforcement. The core of this solution lies in addressing the root causes of shrinkage and cracking at the intrinsic material level through the synergistic effect of these three functional components: the mixed mineral admixture is a blend of metakaolin and zeolite powder, utilizing its pozzolanic activity and porous structure to continuously release adsorbed water during cement hydration, achieving an internal curing effect, maintaining stable internal matrix humidity, and reducing self-shrinkage and drying shrinkage caused by capillary negative pressure; the micro-expansion component is calcium sulfoaluminate mineral powder, which generates ettringite crystals during hydration, producing moderate volume expansion to precisely compensate for the chemical shrinkage and partial drying shrinkage of concrete, achieving near-zero volume deformation; the fiber reinforcement component is basalt fiber... The combination of fiber and polyvinyl alcohol fiber forms a three-dimensional randomized support network inside the concrete. Through bridging, it hinders the initiation and propagation of microcracks, transforming brittle fracture into ductile fracture. Simultaneously, after surface modification treatment with silane coupling agent, chemical bonds are formed between the fiber and the matrix interface, further improving stress transfer efficiency. The synergistic effect of these three factors achieves a unity of low shrinkage, high toughness, and stress coordination. Specifically, shrinkage is reduced through internal curing and micro-expansion compensation, toughness is improved through fiber crack prevention and interface optimization, and the mechanical response of the precast and cast-in-place layers is synchronized by regulating the development rate of the elastic modulus, thereby reducing the driving force of interface stress concentration.

[0022] A method for preparing high-toughness, low-shrinkage concrete includes the following steps: (1) Basalt fiber and polyvinyl alcohol fiber are mixed to obtain mixed fiber. Silane coupling agent KH-550 is added, and the mixture is stirred for 30 min and then left to stand for 20-24 h to obtain modified fiber. (2) Mix metakaolin and zeolite powder and ball mill at 1000~2000 r / min for 20~45 min to obtain mixed mineral admixture; (3) By weight, add 60-80 parts of cement, 20-30 parts of mixed mineral admixture, 3-8 parts of calcium sulfoaluminate mineral powder, 180-230 parts of coarse aggregate, and 120-160 parts of fine aggregate into the mixer and dry mix for 1-2 minutes; then add 0.5-1.2 parts of polycarboxylate-based high-efficiency water-reducing agent and 29-41 parts of water, slowly add them into the mixer and mix for 3 minutes; finally, add a total of 3-6 parts of modified fiber in three batches, with an equal amount added each time and an interval of 30 seconds between each batch, and continue mixing for 3-4 minutes to obtain the concrete mixture.

[0023] In some preferred embodiments of the present invention, the mass ratio of the basalt fiber to the polyvinyl alcohol fiber is (1~2):1.

[0024] In some preferred embodiments of the present invention, the silane coupling agent KH-550 is 0.25~0.6% of the total mass of the mixed fibers.

[0025] In some preferred embodiments of the present invention, the mass ratio of metakaolin to zeolite powder is 1:(1~1.2).

[0026] In this invention, cement is P. O42.5 grade ordinary Portland cement; the water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent; the coarse aggregate is 5~16mm continuously graded basalt with a crushing value ≤10%; the fine aggregate is medium sand with a fineness modulus of 2.6~2.9; the basalt fiber length is 12~18mm with a tensile strength ≥3500MPa; the polyvinyl alcohol fiber length is 8~12mm with a tensile strength ≥1200MPa; the metakaolin has a total active SiO2 and Al2O3 content ≥85%; and the zeolite powder has a specific surface area ≥400m². 2 / kg.

[0027] Example 1; (1) Basalt fiber and polyvinyl alcohol fiber are mixed at a mass ratio of 1:1 to obtain mixed fiber. 0.25% of the total mass of the mixed fiber is added to silane coupling agent KH-550. After stirring for 30 min, the mixture is left to stand for 20 h to obtain modified fiber. (2) The metakaolin and zeolite powder were mixed at a mass ratio of 1:1 and ball-milled at 1000 r / min for 45 min to obtain a mixed mineral admixture; (3) By weight, add 60 parts of cement, 20 parts of mixed mineral admixture, 3 parts of calcium sulfoaluminate mineral powder, 230 parts of coarse aggregate and 120 parts of fine aggregate into the mixer and dry mix for 1 min; then add 0.5 parts of polycarboxylate-based high-efficiency water-reducing agent and 29 parts of water, slowly add them into the mixer and mix for 3 min; finally, add a total of 6 parts of modified fiber in three batches, with an equal amount added each time and an interval of 30 s between each batch, and continue mixing for 3 min to obtain concrete mixture.

[0028] Example 2; (1) Basalt fiber and polyvinyl alcohol fiber were mixed at a mass ratio of 1.5:1 to obtain mixed fiber. 0.5% of the total mass of the mixed fiber was added to the silane coupling agent KH-550. After stirring for 30 min, the mixture was left to stand for 22 h to obtain modified fiber. (2) The metakaolin and zeolite powder were mixed at a mass ratio of 1:1.1 and ball-milled at 1500 r / min for 30 min to obtain a mixed mineral admixture; (3) By weight, add 70 parts of cement, 25 parts of mixed mineral admixture, 5 parts of calcium sulfoaluminate mineral powder, 210 parts of coarse aggregate and 140 parts of fine aggregate into the mixer and dry mix for 1.5 min; then add 0.9 parts of polycarboxylate-based high-efficiency water-reducing agent and 35 parts of water, slowly add them into the mixer and mix for 3 min; finally, add a total of 4 parts of modified fiber in three batches, with an equal amount added each time and an interval of 30 s each time, and continue mixing for 3.5 min to obtain concrete mixture.

[0029] Example 3; (1) Basalt fiber and polyvinyl alcohol fiber are mixed at a mass ratio of 2:1 to obtain mixed fiber. 0.6% of the total mass of the mixed fiber is added to silane coupling agent KH-550. After stirring for 30 min, the mixture is left to stand for 24 h to obtain modified fiber. (2) The metakaolin and zeolite powder were mixed at a mass ratio of 1:1.2 and ball-milled at 2000 r / min for 20 min to obtain a mixed mineral admixture; (3) By weight, add 80 parts of cement, 30 parts of mixed mineral admixture, 8 parts of calcium sulfoaluminate mineral powder, 180 parts of coarse aggregate and 130 parts of fine aggregate into the mixer and dry mix for 2 minutes; then add 1.2 parts of polycarboxylate-based high-efficiency water-reducing agent and 41 parts of water, slowly add them into the mixer and mix for 3 minutes; finally, add a total of 6 parts of modified fiber in three batches, with an equal amount added each time and an interval of 30 seconds between each batch, and continue mixing for 4 minutes to obtain the concrete mixture.

[0030] Example 4; (1) Basalt fiber and polyvinyl alcohol fiber were mixed at a mass ratio of 1.2:1 to obtain mixed fiber. 0.3% of the total mass of the mixed fiber was added to the silane coupling agent KH-550. After stirring for 30 min, the mixture was left to stand for 22 h to obtain modified fiber. (2) The metakaolin and zeolite powder were mixed at a mass ratio of 1:1.1 and ball-milled at 1200 r / min for 35 min to obtain a mixed mineral admixture; (3) By weight, add 65 parts of cement, 25 parts of mixed mineral admixture, 4 parts of calcium sulfoaluminate mineral powder, 200 parts of coarse aggregate and 160 parts of fine aggregate into the mixer and dry mix for 1.5 min; then add 0.7 parts of polycarboxylate-based high-efficiency water-reducing agent and 33 parts of water, slowly add them into the mixer and mix for 3 min; finally, add a total of 5 parts of modified fiber in three batches, with an equal amount added each time and an interval of 30 s between each batch, and continue mixing for 3 min to obtain concrete mixture.

[0031] Example 5; (1) Basalt fiber and polyvinyl alcohol fiber were mixed at a mass ratio of 1.7:1 to obtain mixed fiber. 0.45% of the total mass of the mixed fiber was added to the silane coupling agent KH-550. After stirring for 30 min, the mixture was left to stand for 23 h to obtain modified fiber. (2) The metakaolin and zeolite powder were mixed at a mass ratio of 1:1.2 and ball-milled at 1500 r / min for 40 min to obtain a mixed mineral admixture; (3) By weight, add 75 parts of cement, 28 parts of mixed mineral admixture, 6 parts of calcium sulfoaluminate mineral powder, 210 parts of coarse aggregate and 150 parts of fine aggregate into the mixer and dry mix for 2 minutes; then add 1 part of polycarboxylate-based high-efficiency water-reducing agent and 38 parts of water, slowly add them into the mixer and mix for 3 minutes; finally, add a total of 3.5 parts of modified fiber in three batches, with an equal amount added each time and an interval of 30 seconds between each batch, and continue mixing for 3.5 minutes to obtain the concrete mixture.

[0032] Comparative Example 1; The difference between Comparative Example 1 and Example 2 is the difference in step (1). Step (1) is modified as follows: basalt fiber is added to 0.25% by mass of silane coupling agent KH-550, stirred for 30 min and left to stand for 20 h to obtain modified fiber; the remaining steps are the same as in Example 2.

[0033] Comparative Example 2; The difference between Comparative Example 2 and Example 2 is that step (1) is omitted, and step (3) is modified as follows: by weight, 75 parts of cement, 28 parts of mixed mineral admixture, 6 parts of calcium sulfoaluminate mineral powder, 210 parts of coarse aggregate, and 150 parts of fine aggregate are put into a mixer and dry-mixed for 2 minutes; then 1 part of polycarboxylate-based high-efficiency water-reducing agent and 38 parts of water are added slowly into the mixer and stirred for 3 minutes; finally, a total of 2 parts of basalt fiber and 2 parts of polyvinyl alcohol fiber are added in three batches, with equal amounts added each time and an interval of 30 seconds between each addition, and the mixture is stirred continuously for 3.5 minutes to obtain a concrete mixture; the remaining steps are the same as in Example 2.

[0034] Comparative Example 3; The difference between Comparative Example 3 and Example 2 is that step (2) is omitted, and step (3) is modified as follows: by weight, 70 parts of cement, 5 parts of calcium sulfoaluminate mineral powder, 210 parts of coarse aggregate and 140 parts of fine aggregate are put into the mixer and dry-mixed for 1.5 min; then 0.9 parts of polycarboxylate-based high-efficiency water-reducing agent and 26.3 parts of water are added slowly into the mixer and stirred for 3 min; finally, a total of 4 parts of modified fiber are added in three batches, with an equal amount added each time and an interval of 30 s each time, and stirred continuously for 3.5 min to obtain concrete mixture; the remaining steps are the same as in Example 2.

[0035] Comparative Example 4; The difference between Comparative Example 4 and Example 2 lies in step (3). Step (3) is modified as follows: by weight, 70 parts of cement, 25 parts of mixed mineral admixture, 210 parts of coarse aggregate, and 140 parts of fine aggregate are added to the mixer and dry-mixed for 1.5 min; then 0.9 parts of polycarboxylate-based high-efficiency water-reducing agent and 33 parts of water are added slowly to the mixer and stirred for 3 min; finally, a total of 4 parts of modified fiber are added in three batches, with an equal amount added each time and an interval of 30 s between each batch, and the mixture is stirred continuously for 3.5 min to obtain the concrete mixture; the remaining steps are the same as in Example 2.

[0036] Comparative Example 5; The difference between Comparative Example 5 and Example 2 lies in the difference in step (3). Step (3) is modified as follows: by weight, 70 parts of cement, 25 parts of metakaolin, 5 parts of calcium sulfoaluminate mineral powder, 210 parts of coarse aggregate, and 140 parts of fine aggregate are put into a mixer and dry-mixed for 1.5 min; then 0.9 parts of polycarboxylate-based high-efficiency water-reducing agent and 35 parts of water are added slowly into the mixer and stirred for 3 min; finally, a total of 4 parts of modified fiber are added in three batches, with an equal amount added each time and an interval of 30 s between each batch, and the mixture is stirred continuously for 3.5 min to obtain concrete mixture; the remaining steps are the same as in Example 2.

[0037] Test Results The concrete mixtures prepared in each embodiment and comparative example were cast into cubic specimens of 150mm×150mm×150mm, with 3 specimens per group. After casting, the specimens were covered with geotextile to retain moisture and pre-cured for 12 hours at an ambient temperature ≥15℃ and humidity ≥80%. The molds were then moved into a steam curing chamber, with the heating rate controlled at 10℃ / h. After heating to 55-60℃, the specimens were kept at a constant temperature for 16-18 hours. Then, the temperature was lowered to the ambient temperature at a rate of 8℃ / h. After steam curing, the specimens were demolded and continued to be covered with geotextile and watered for curing until 28 days of age, during which various tests were conducted.

[0038] Compressive strength test: The test was conducted according to GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete". An electro-hydraulic servo pressure testing machine was used for loading, with the loading rate controlled between 0.5 and 0.8 MPa / s. The failure load was recorded, and the compressive strength was calculated.

[0039] Drying shrinkage rate test: The test was conducted according to the contact method in GB / T50082-2009 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete". After curing the concrete mixture for 24 hours, the initial length (L0) was measured and the depth of the probe embedded was recorded as Lb. Then, the specimen was moved into a constant temperature and humidity shrinkage chamber with a temperature of 20±2℃ and a relative humidity of 60±5%. The specimen length (Lt) was measured at 1d, 3d, 7d, 14d and 28d respectively. The drying shrinkage rate ε was calculated according to the formula ε=(L0-Lt) / (L0-2×Lb).

[0040] Fracture toughness test: The fracture toughness of each concrete specimen was tested using the three-point method according to standard DL / T5332-2005. The specific results are shown in Table 1.

[0041] Table 1

[0042] The data in Examples 1-5 of Table 1 show that the concrete mixtures prepared using the multi-component composite system of mixed mineral admixtures, micro-expansion components, and fiber reinforcement described in this invention have a 28-day compressive strength ≥ 45.3 MPa, meeting the C40 strength grade requirements; and a 28-day drying shrinkage rate ≤ 271 × 10⁻⁶. -6 The shrinkage level is significantly lower than that of ordinary concrete; the fracture toughness is ≥3.8kJ / m. 2 They exhibited excellent crack resistance; among them, Example 2 showed the most balanced overall performance, with a 28-day compressive strength of 47.6 MPa and a drying shrinkage rate of 252 × 10⁻⁶ MPa. -6 Fracture toughness 4.2 kJ / m 2 This demonstrates a synergistic improvement in low shrinkage, high toughness, and good mechanical properties.

[0043] In Comparative Example 1, only basalt fiber was used without compounding with polyvinyl alcohol fiber. Its fracture toughness dropped to 3.2 kJ / m², and its compressive strength and shrinkage also deteriorated. This indicates that the compounding of basalt fiber and polyvinyl alcohol fiber is the key to improving the toughness of concrete. Single fiber is difficult to achieve the synergistic effect of three-dimensional reinforcement and ductile fracture.

[0044] Comparative Example 2 fibers were not surface-modified with silane coupling agent KH-550, and all other conditions were the same. The compressive strength and fracture toughness were inferior to those of Example 2. This shows that the surface modification treatment of fibers with silane coupling agent can effectively improve the interfacial bonding strength between fibers and concrete matrix, thereby enhancing the overall mechanical properties and crack resistance.

[0045] Comparative Example 3, without the addition of mixed mineral admixtures, showed a deterioration in drying shrinkage. This indicates that the absence of mixed mineral admixtures makes it difficult for the internal curing effect to be exerted, the internal humidity of the concrete decreases more rapidly, drying shrinkage increases significantly, and insufficient interface optimization leads to a decrease in toughness. This demonstrates that the internal curing and interface optimization effects of mixed mineral admixtures are indispensable.

[0046] Comparative Example 4, which did not include calcium sulfoaluminate mineral powder, demonstrates that the absence of the micro-expansion component leads to the disappearance of the shrinkage compensation effect, making it difficult to effectively suppress concrete shrinkage. This proves the importance of the micro-expansion compensation of calcium sulfoaluminate mineral powder.

[0047] In Comparative Example 5, the zeolite powder in the mixed mineral admixture was replaced with an equal amount of metakaolin. The absence of zeolite powder led to a weakening of the internal curing effect, and its unique adsorption-desorption effect was difficult to exert. This indicates that the combination of zeolite powder and metakaolin can achieve continuous internal curing and interface optimization.

[0048] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A high-toughness, low-shrinkage concrete, characterized in that, The concrete is composed of a cementitious material system, aggregates, modified fibers, and auxiliary materials; The cementitious material system includes cement, mixed mineral admixtures, and micro-expansion components; The mixed mineral admixture is a compound system of metakaolin and zeolite powder; The aggregates include coarse aggregates and fine aggregates; The modified fiber is obtained by surface modification of basalt fiber and polyvinyl alcohol fiber by silane coupling agent. The auxiliary materials include water-reducing agents and water.

2. The concrete according to claim 1, characterized in that, The concrete, by weight, comprises: 60-80 parts cement, 20-30 parts mixed mineral admixtures, 3-8 parts micro-expansion components, 180-230 parts coarse aggregate, 120-160 parts fine aggregate, 3-6 parts modified fiber, 0.5-1.2 parts water-reducing agent, and 29-41 parts water.

3. The concrete according to claim 1, characterized in that, The mass ratio of metakaolin to zeolite powder in the mixed mineral admixture is 1:(1~1.2).

4. The concrete according to claim 1, characterized in that, The micro-expansion component is calcium sulfoaluminate mineral powder with a purity of ≥90%.

5. The concrete according to claim 1, characterized in that, The mass ratio of basalt fiber to polyvinyl alcohol fiber in the modified fiber is (1~2):

1.

6. The concrete according to claim 1, characterized in that, The silane coupling agent is KH-550, and its dosage is 0.25~0.6% of the total mass of basalt fiber and polyvinyl alcohol fiber.

7. The concrete according to claim 1, characterized in that, The coarse aggregate is 5-16mm continuously graded basalt, and the fine aggregate is medium sand with a fineness modulus of 2.6-2.

9.

8. The concrete according to claim 1, characterized in that, The water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent.

9. A method for preparing high-toughness, low-shrinkage concrete as described in any one of claims 1-8, characterized in that, Includes the following steps: (1) Basalt fiber and polyvinyl alcohol fiber are mixed, silane coupling agent KH-550 is added, and the mixture is stirred and left to stand to obtain modified fiber; (2) Mix and ball-mill metakaolin and zeolite powder to obtain a mixed mineral admixture; (3) Put cement, mixed mineral admixtures, calcium sulfoaluminate mineral powder, coarse aggregate and fine aggregate into a mixer for dry mixing, add water-reducing agent and water and mix, and finally add modified fiber in batches and continue mixing to obtain concrete mixture.

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