Low-fiber-content high-toughness self-prestressed concrete

Abstract

This invention belongs to the technical fields of infrastructure construction, urban renewal, seismic reinforcement, and infrastructure improvement in cold regions, and discloses a low-fiber-content, high-toughness self-prestressed concrete. It achieves the dual goals of high toughness and crack-free service life in low-fiber-content concrete by controlling the volume deformation of a highly efficient expansion component. This invention controls the mass fraction (25 parts / 2000 parts - 45 parts / 2000 parts) and particle size (1 μm - 80 μm) of the highly efficient expansion component, and cures it with water for at least 3 days. The volume of the expanded highly efficient expansion component accounts for 2.5% - 4.5% of the total volume; thus, an equivalent flexural toughness of not less than 160 kJ / m is achieved with a low fiber volume content. 3 It achieves the goal of low cost and high toughness with a flexural strength of not less than 12 MPa. It has broad prospects in infrastructure construction, urban renewal, hydraulic structures, seismic reinforcement, and especially in upgrading infrastructure in cold regions.

Description

Technical Field

[0001] This invention relates to the technical fields of infrastructure construction, urban renewal, seismic reinforcement, and infrastructure improvement in cold regions, and particularly to a low-fiber-content, high-toughness self-prestressed concrete. Background Technology

[0002] Due to inadequate early design standards and deterioration from years of service, aging infrastructure urgently needs renewal, upgrading, and reinforcement. Taking widely used masonry structures as an example, seismic reinforcement and upgrading is one of the key tasks of urban renewal.

[0003] High-ductility concrete (ECC, SHCC, HDC, UHTCC) possesses high flexural toughness and high flexural strength, and can enhance the seismic performance of masonry structures through thin-layer spraying / coating. However, traditional high-ductility concrete for reinforcement typically has high cementitious material and fiber content.

[0004] The high amount of cementitious materials results in higher shrinkage of the high-ductility concrete itself, which makes it prone to confined cracking when used as a reinforcement thin layer. Application in areas with large diurnal and seasonal temperature differences will further exacerbate this cracking.

[0005] High material costs are one of the main bottlenecks limiting the large-scale application of high-ductility concrete. High fiber content is a major factor contributing to material costs. Traditional high-ductility concrete is usually reinforced with 1.5%-2% volumetric polyvinyl alcohol fiber (PVA fiber) or polyethylene fiber (PE fiber), and it is difficult to achieve high ductility characteristics by reducing the fiber content.

[0006] The fiber content and matrix strength of high-ductility concrete must be designed holistically to achieve both high ductility and high flexural strength. If the fiber content is insufficient, even with an increased matrix design strength, the fibers cannot provide sufficient bridging force after cracking, limiting the improvement in the concrete's flexural toughness. Water curing can reduce the risk of shrinkage cracking in high-ductility concrete and improve matrix strength; however, extending the water curing process enhances the shrinkage reduction process, which also increases the difficulty of achieving high toughness with low fiber content.

[0007] The present invention aims to achieve the dual goals of high toughness and crack-free service of low fiber content concrete by controlling the volume deformation of expansion components. Summary of the Invention

[0008] This invention aims to develop a low-fiber-content, high-ductility concrete through innovative material design and preparation methods. This concrete achieves multiple objectives, including low cost, high toughness, and self-prestressed performance to overcome shrinkage and temperature cracking. It overcomes many shortcomings of traditional reinforcement materials and can meet the needs of urban renewal, seismic reinforcement, and infrastructure upgrades in cold regions, demonstrating broad application prospects.

[0009] The technical solution of the present invention is as follows: a low fiber content, high toughness self-prestressed concrete, with the following component content, the total component is 2000 parts, including: 25 parts-45 parts of high-efficiency expansion component, 6 parts-12 parts of fiber, 200 parts-800 parts of cement, 400 parts-1200 parts of supplementary cementitious material, 300 parts-600 parts of fine aggregate, 200 parts-400 parts of water, 0 parts-30 parts of water-reducing agent, and 0 parts-10 parts of thickener; the particle size range of the high-efficiency expansion component is 1μm-80μm.

[0010] Furthermore, after the components are mixed and set, they are sprayed with water for curing for no less than 3 days. The particle size of the high-efficiency expansion component increases to 2.5μm-200μm, and the volume of the high-efficiency expansion component after expansion accounts for 2.5%-4.5% of the total volume of the low fiber content high toughness self-prestressed concrete.

[0011] Furthermore, the particle size range of the high-efficiency expansion component is 10μm-30μm; after each component is mixed and set, it is sprayed with water for curing for no less than 3 days, and the particle size of the high-efficiency expansion component increases to 25μm-75μm, and the volume of the high-efficiency expansion component after expansion accounts for 2.5%-4.5% of the total volume of the low fiber content high toughness self-prestressed concrete.

[0012] After the low-fiber-content, high-toughness self-prestressed concrete is applied to the reinforced structure, it is cured by water spraying for no less than 3 days. By controlling the expansion degree of the high-efficiency expansion component, its 28-day mechanical properties are made to meet the requirements of Class I high-ductility concrete, with an equivalent flexural toughness of no less than 160 kJ / m. 3 The flexural strength is not less than 12MPa; the volume deformation of the low fiber content high toughness self-prestressed concrete is characterized by expansion followed by shrinkage, and the shrinkage ratio after 90 days is less than 40% of the maximum expansion deformation.

[0013] The high-efficiency expanding component is one or more of the following: calcium oxide-based expanding agent, UEA expanding agent, and calcium sulfoaluminate expanding agent.

[0014] The fiber is one or more of the following: polypropylene fiber (PP fiber), polyethylene fiber, polyvinyl alcohol fiber, steel fiber, basalt fiber, carbon fiber, glass fiber, and fly ash fiber.

[0015] The fiber is polyethylene fiber, with a component content of 6 parts / 2000 parts to 9 parts / 2000 parts, more preferably 6 parts / 2000 parts to 8 parts / 2000 parts; the fiber length is 12mm to 18mm, preferably 15mm to 18mm; and the fiber strength is 1200MPa to 3600MPa.

[0016] The fiber strength is 1200MPa-2000MPa.

[0017] The fiber strength is 1200MPa-1600MPa.

[0018] The supplementary cementing material is one or more of the following: fly ash, mineral powder, silica fume, volcanic ash, steel slag powder, and metakaolin.

[0019] When the supplementary cementitious material is fly ash and mineral powder, the mineral powder accounts for 20%-100% of the supplementary cementitious material.

[0020] The fine aggregate is one or more of the following: manufactured sand, river sand, sea sand, desert sand, steel slag powder, tailings slag, limestone powder, and rubber powder.

[0021] The beneficial effects of this invention are as follows: By artificially controlling the expanded volume of the highly efficient expansive component, it acts as a micro-defect; inducing multi-crack formation without compromising concrete strength, it achieves high toughness with low fiber content. Simultaneously, the quantitative control of the highly efficient expansive component achieves the self-prestressed service characteristics of concrete. In other words, through the micro-defect design of the expansive component, the goals of self-prestressing and high toughness with low fiber content are simultaneously achieved. Attached Figure Description

[0022] Figure 1 A schematic diagram illustrating the principle of improving bending toughness through expansion defect control.

[0023] Figure 2 Schematic diagrams of concrete cracking for different examples; (a) without high-efficiency expansion component; (b) with high-efficiency expansion component at a ratio of 45 kg / m³. 3 Furthermore, the particle size distribution of the highly efficient expansion component (d) is: 10μm≤d≤30μm; (c) is the distribution ratio of the highly efficient expansion component at 45kg / m³. 3 Furthermore, the particle size distribution (d) of the highly efficient expanded component is 80 μm. <d≤200μm。 Detailed Implementation

[0024] 1. The effect of the dosage of highly efficient expansion components on volume deformation; Exemplary mix proportions are listed in Table 1. The cement is Portland cement, and the high-efficiency expansive component is calcium sulfoaluminate, UEA expansive agent, or calcium oxide composite, or alternatively, calcium sulfoaluminate, UEA expansive agent, and calcium oxide composite. The dosage of the high-efficiency expansive component is 20 kg / m³ in the C20, C25, C45, and C70 mix proportions. 3 25kg / m 3 45kg / m 3 70kg / m 3 Manufactured sand with a particle size of 40-80 mesh is used as ECC aggregate.

[0025] Table 1 Examples of different proportions (unit: kg / m³) 3 ) The example mixes were sprayed with water for 2 days and 3 days after pouring, respectively, and then placed in the air for curing until 90 days. Table 2 lists the free volume deformation of the example mixes, where... For maximum expansion deformation, The volumetric deformation value over 90 days. This represents the deformation shrinkage rate over 90 days.

[0026] Table 2 shows that with prolonged water curing time and increased dosage of the high-efficiency expansion component, the maximum volumetric expansion deformation increases, followed by a certain volumetric shrinkage. Among the formulations cured for 2 days, only C70 meets the self-prestressing criterion. After 3 days of water curing, the maximum expansion deformation of C20 is 1050 με, and the shrinkage rate after 90 days decreases from 93% to 60%, but still does not meet the self-stressing criterion. When the dosage of the high-efficiency expansion component is increased to C25, the shrinkage rate is 40%. Therefore, this invention recommends C25 as the minimum dosage of the high-efficiency expansion component and 3 days of water curing as the shortest curing time.

[0027] As the dosage of the high-efficiency expansive component increases to C70, the maximum expansion deformation after 3 days of water curing reaches 6500 με. Excessive expansion can affect the mechanical properties of high-ductility concrete and may also cause cracking and damage to the reinforced structure. Therefore, the maximum expansion needs to be limited. This invention limits the maximum dosage of the high-efficiency expansive component to 45 parts / 2000 parts.

[0028] Table 2 Free volume deformation of different stoichiometric ratios (unit: με) The density of the high-efficiency expanding component in this example is 2500 kg / m³. 3 In the C25 and C45 mix proportions, the volume of the high-efficiency expansive component before reaction is 1% and 1.8%, respectively. Given that the maximum expansion volume of calcium oxide and ettringite-based expansive agents is 2.5 times their pre-reaction volume, the volume of the high-efficiency expansive component after expansion is 2.5%-4.5% of the total concrete volume. This example shows that when the volume of the high-efficiency expansive component after expansion is less than 2.5%, the resulting defect volume is smaller, such as... Figure 2 As shown in (a), the expansion volume of the high-efficiency expansion component is insufficient to induce a sufficient number of cracks, resulting in limited improvement in equivalent flexural toughness. When the volume of the high-efficiency expansion component after expansion exceeds 4.5%, excessive expansion defects can easily lead to a decrease in concrete strength, causing adverse effects. Therefore, this invention suggests that the volume of the high-efficiency expansion component after expansion should account for 2.5%-4.5% of the total volume of low-fiber-content high-toughness self-prestressed concrete. The principle of micro-defect control over multi-crack initiation and flexural toughness can be seen in [the following text is incomplete and requires further context]. Figure 1 and Figure 2 .

[0029] 2. The effect of particle size of high-efficiency expansion components on the mechanical properties of high-ductility concrete; In this example, the PE fiber content is 9 g / L. After water curing for 3 days, the material is placed in air for 28 days before a bending test. For reinforced high-ductility concrete, the Class I standard is a flexural strength of not less than 12 MPa and an equivalent flexural toughness of not less than 160 kJ / m. 3 Although the C0 mix has high strength (14.1 MPa), it has a limited number of cracks, and its equivalent flexural toughness is only 115 kJ / m. 3 .

[0030] As shown in Table 3, when using a highly efficient expansion component with a micrometer diameter of less than 10 μm, the strength of C25 is reduced to some extent, but the flexural toughness is significantly improved to 161 kJ / m. 3 It just meets the Class I high-ductility concrete standard; it is foreseeable that when the particle size of the expansive component is less than 1μm, the resulting micro-defect size will be smaller, and the flexural toughness will be lower than the Class I high-ductility concrete standard. Further increasing the dosage of the high-efficiency expansive component to C45 significantly improves the equivalent flexural toughness.

[0031] For high-efficiency expansion component ratios with particle size ranges of 10μm-30μm, the expanded particle size of the high-efficiency expansion component can reach 25μm-75μm, which can induce crack formation without significantly reducing the strength of concrete. Figure 2 As shown in (b); in addition, in the C25-C45 admixture ratio, the volume of the expansion component after expansion is approximately 2.5%-4.5% of the total concrete volume. The particle size of micro-defects and the volume after expansion are both moderate. C25 and C45 achieve the dual goals of high flexural strength and high toughness, and both can meet the requirements of Class I high ductility concrete.

[0032] When the particle size of the high-efficiency expanding component increases to greater than 30 μm but less than 80 μm, a significant reduction in flexural strength is observed. Specifically, the flexural strength of C45 drops to 12.0 MPa. When the particle size of the high-efficiency expanding component is between 80 μm and 200 μm, the strength is significantly reduced, such as... Figure 2 As shown in (c), both the strength and equivalent flexural toughness are lower than those of Class I high ductility concrete.

[0033] For highly efficient expanding components based on calcium oxide and sulfoaluminate, the maximum volume expansion after full expansion is approximately 2.5 times. For highly efficient expanding components with a particle size of 80μm, the volume after expansion and deformation can reach 200μm. Excessively large defects can adversely affect the strength of concrete.

[0034] This invention utilizes the micro-defects generated after the expansion of a highly efficient expanding component to induce multi-crack formation, thereby improving flexural toughness. Simultaneously, the degree of expansion is designed and controlled to avoid mechanical reduction. Considering all factors, it is recommended that the dosage of the highly efficient expanding component be 25 parts / 2000 parts to 45 parts / 2000 parts; the particle size range of the highly efficient expanding component should be 1 μm to 80 μm, preferably 10 μm to 30 μm.

[0035] Table 3 Comparison of results for different particle size distributions 3. The effect of fiber content on mechanical properties; This example uses a high-efficiency expandable component with a particle size range of 10μm-30μm to study the effect of different PE fiber dosages on the flexural properties of high-ductility concrete. As shown in Table 4, when the PE fiber dosage increases from 20kg / m³, the effect is different. 3 Reduced to 12kg / m 3 The equivalent flexural toughness of C0 is 432 kJ / m. 3 Reduced to 155 kJ / m 3 Traditional ECC requires high fiber content to achieve high strength and flexural toughness.

[0036] This example of C45 achieves controlled multi-crack formation by designing a highly efficient expansion component with an expanded particle size of 25μm-75μm. Expansion micro-defects account for approximately 4.5% of the total concrete volume, thus significantly improving the equivalent flexural toughness to 312kJ / m². 3 As the fiber content decreases, both flexural strength and equivalent flexural toughness decrease accordingly. In this example, after the expansion micro-defect design, even with a fiber content of only 6 kg / m², the strength and equivalent flexural toughness both decrease. 3 (Equivalent to 0.6% volumetric admixture), the invented high-ductility concrete still meets the Class I high-ductility concrete design standards. It can simultaneously achieve the goals of low fiber content and high flexural toughness.

[0037] Table 4 Comparison of results with different fiber content

Claims

1. A low-fiber-content, high-toughness self-prestressed concrete, characterized in that, The low-fiber-content, high-toughness self-prestressed concrete has the following composition: a total of 2000 parts, including: 25-45 parts of high-efficiency expansive component, 6-12 parts of fiber, 200-800 parts of cement, 400-1200 parts of supplementary cementitious material, 300-600 parts of fine aggregate, 200-400 parts of water, 0-30 parts of water-reducing agent, and 0-10 parts of thickener; the high-efficiency expansive component has a particle size range of 1μm-80μm.

2. The low-fiber-content, high-toughness self-prestressed concrete according to claim 1, characterized in that, After the components are mixed and set, they are sprayed with water for curing for no less than 3 days. The particle size of the high-efficiency expansion component increases to 2.5μm-200μm, and the volume of the high-efficiency expansion component after expansion accounts for 2.5%-4.5% of the total volume of the low fiber content high toughness self-prestressed concrete.

3. The low-fiber-content, high-toughness self-prestressed concrete according to claim 1, characterized in that, The particle size range of the high-efficiency expansion component is 10μm-30μm; after each component is mixed and set, it is sprayed with water for curing for no less than 3 days, and the particle size of the high-efficiency expansion component increases to 25μm-75μm, and the volume of the high-efficiency expansion component after expansion accounts for 2.5%-4.5% of the total volume of the low fiber content high toughness self-prestressed concrete.

4. The low-fiber-content, high-toughness self-prestressed concrete according to claim 2 or 3, characterized in that, After the low-fiber-content, high-toughness self-prestressed concrete is applied to the reinforced structure, it is cured by water spraying for no less than 3 days. By controlling the expansion degree of the high-efficiency expansion component, its 28-day mechanical properties are made to meet the requirements of Class I high-ductility concrete, with an equivalent flexural toughness of no less than 160 kJ / m. 3 The flexural strength is not less than 12MPa; the volume deformation of the low fiber content high toughness self-prestressed concrete is characterized by expansion followed by shrinkage, and the shrinkage ratio after 90 days is less than 40% of the maximum expansion deformation.

5. The low-fiber-content, high-toughness self-prestressed concrete according to claim 1, characterized in that, The high-efficiency expanding component is one or more of the following: calcium oxide-based expanding agent, UEA expanding agent, and calcium sulfoaluminate expanding agent.

6. The low-fiber-content, high-toughness self-prestressed concrete according to claim 1, characterized in that, The fiber is one or more of the following: polypropylene fiber, polyethylene fiber, polyvinyl alcohol fiber, steel fiber, basalt fiber, carbon fiber, glass fiber, and fly ash fiber.

7. The low-fiber-content, high-toughness self-prestressed concrete according to claim 6, characterized in that, The fiber is polyethylene fiber, with a component content of 6 parts / 2000 parts to 9 parts / 2000 parts of material; fiber length of 12mm-18mm; and fiber strength of 1200MPa-3600MPa.

8. The low-fiber-content, high-toughness self-prestressed concrete according to claim 7, characterized in that, The fiber strength is 1200MPa-2000MPa.

9. The low-fiber-content, high-toughness self-prestressed concrete according to claim 8, characterized in that, The fiber strength is 1200MPa-1600MPa.

10. The low-fiber-content, high-toughness self-prestressed concrete according to claim 1, characterized in that, The supplementary cementing material is one or more of fly ash, mineral powder, silica fume, volcanic ash, steel slag powder, and metakaolin; the fine aggregate is one or more of manufactured sand, river sand, sea sand, desert sand, steel slag powder, tailings slag, limestone powder, and rubber powder.

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