Low-shrinkage ultrahigh-strength high-ductility cement-based material and preparation method thereof

Abstract

The invention discloses a low-shrinkage, ultrahigh-strength and high-ductility cement-based material and a preparation method thereof, and belongs to the technical field of building materials, the cement-based composite material is prepared by taking fine river sand, cement, slag and silica fume as main raw materials, taking ultrahigh molecular weight synthetic fiber as a microcosmic energy consumption component, and adding super absorbent resin and magnesium oxide, after mixing treatment, the cement-based composite material with low shrinkage, compressive strength of more than 120 MPa and ductility of more than 6% under a uniaxial tensile load is obtained; a traditional shrinkage reducing scheme has great influence on the performance of the ultrahigh-strength and high-ductility cement-based material, a traditional expanding agent and an internal curing shrinkage reducing method are referred to, a composite shrinkage reducing technology is finely designed, and the influence of the traditional expanding agent and the internal curing shrinkage reducing method on the performance of the material is avoided; and self-shrinkage and drying shrinkage are inhibited at the same time by utilizing the synergistic effect of the two components, so that the problems of early-stage shrinkage and later-stage shrinkage of the ultrahigh-strength high-ductility concrete are solved, and large-volume and large-scale application of the ultrahigh-strength high-ductility concrete is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and in particular to a low-shrinkage, ultra-high-strength, high-ductility cement-based composite material and a preparation method thereof. Background Art

[0002] In recent years, the accelerated urbanization process and infrastructure upgrades have placed higher demands on the comprehensive performance of building materials, especially in complex engineering scenarios such as high-rise buildings, earthquake-resistant areas, and extreme climate regions. The strength of traditional concrete materials cannot meet the increasingly complex engineering needs, and they have inherent defects such as high brittleness. Although traditional ultra-high performance concrete can improve the structural bearing capacity and significantly enhance toughness by adding steel fibers, it is essentially a strain-softening material with significantly insufficient tensile properties. In order to meet the stringent requirements of modern engineering, new cement-based materials with ultra-high strength, high tensile ductility, and volume stability are urgently needed.

[0003] Traditional ultra-high-strength, high-ductility cement-based materials, like traditional high-performance concrete, require extremely low water-cement ratios and high cement usage to achieve ultra-high strength. Mineral admixtures such as silica fume and slag are used, leading to significant shrinkage. Furthermore, to achieve high ductility, the fibers must be evenly dispersed, leading to the use of finer river sand, which further increases shrinkage. This significant shrinkage can lead to concentrated cracks at restraints early on, significantly reducing structural strength and integrity. According to statistics, the global annual repair cost of concrete shrinkage cracking amounts to tens of billions of dollars.

[0004] However, with the continuous development of new materials and technologies, low-shrinkage, ultra-strength, high-ductility cement-based composites have become potential alternatives to traditional ultra-high performance concrete. However, traditional concrete shrinkage reduction methods are not applicable to ultra-strength, high-ductility cement-based composites. For example, ultra-high performance concrete does not require fine-tuning of steel fiber dispersion and matrix fracture properties during shrinkage reduction; and shrinkage reduction schemes for low-strength, high-ductility materials are not sensitive to the effects of strength. Specifically, the currently commonly used method of adding shrinkage reducers will reduce compressive strength, while the addition of expansion agents alone will significantly change the design properties of the matrix, affecting multi-crack cracking performance and reducing tensile ductility. In addition, the water-absorbing aggregates added in ordinary internal curing schemes will affect fiber dispersion and also reduce ductility.

[0005] In this context, the development of low-shrinkage, ultra-high-strength and high-ductility cement-based composite materials has become an urgent issue that needs to be addressed in the industry. Summary of the Invention

[0006] To address the above-mentioned problems, the present invention aims to provide a low-shrinkage, ultra-high-strength, high-ductility cement-based material and its preparation method. Through the concept of multi-scale material design, the present invention combines the composite shrinkage reduction technology of superabsorbent resin and magnesium oxide expansion agent with the refined nano-modification, fiber reinforcement, and strain hardening properties of traditional ultra-high-strength, high-ductility cement-based composite materials. The development of low-shrinkage, ultra-high-strength, high-ductility cement-based composite materials represents an important path to breaking through the performance bottlenecks of traditional materials. By optimizing the gelling components, regulating the fiber-matrix interface, and introducing superabsorbent resin and magnesium oxide, this material system can achieve a 6% tensile elongation while maintaining a compressive strength of 120 MPa. Its autogenous shrinkage is 60%-80% lower than that of ordinary high-strength concrete, thereby achieving structural safety and durability without reinforcement.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows: A low-shrinkage, ultra-high-strength, high-ductility cement-based material is a composite material. The cement-based composite material uses fine river sand, cement, slag, and silica fume as main raw materials, uses ultra-high molecular weight synthetic fibers as microscopic energy-consuming components, and is supplemented with super absorbent resin and magnesium oxide. After mixing, a low-shrinkage cement-based composite material with a compressive strength of >120 MPa and a ductility of >6% under uniaxial tensile load is obtained.

[0008] The low-shrinkage, ultra-high-strength, high-ductility cement-based material of the present invention comprises the following components in parts by weight: 60-85 parts of cement, 10-40 parts of silica fume, 35 parts of river sand, 30-55 parts of slag, 16-20 parts of water, 1.6-2.0 parts of ultra-high molecular weight synthetic fiber, 1.8-2.2 parts of water reducer, 0.02-0.05 parts of super absorbent resin, and 4-6 parts of magnesium oxide.

[0009] The cement of the present invention is at least one of Portland cement, ordinary Portland cement, Portland pozzolana cement, Portland slag cement, and Portland fly ash cement, and has a 28-day compressive strength of 52.5 MPa or greater. The restrictions on cement type and 28-day compressive strength of 52.5 MPa or greater are primarily due to the exceptionally high strength of low-shrinkage, ultra-high-strength, high-ductility cement-based materials; exceeding these limits would compromise the strength of the material.

[0010] The silica fume of the present invention comprises greater than 92% by mass of silicon dioxide; the mass percentage of silicon dioxide having a particle size of less than 1 μm in the silicon dioxide is greater than 50%; the content of the silica fume is limited mainly in view of the ultra-high strength of the low-shrinkage, ultra-high-strength, and high-ductility cement-based material. According to the closest packing theory of particles, the high content of silicon dioxide in the silica fume and the nanometer-level particle size ensure the ultra-high strength of the material.

[0011] The 28-day activity index of the slag of the present invention must reach or exceed 95%, and the content of active calcium, silicon, aluminum and other inorganic substances must be greater than 30%; the activity of the slag is limited mainly considering the ultra-high strength of the low-shrinkage, ultra-high-strength, high-ductility cement-based material. According to the calculation of the degree of pozzolanic reaction, the content of active calcium, silicon, aluminum and other inorganic substances in the slag must be greater than 30% to meet the ultra-high strength of the low-shrinkage, ultra-high-strength, high-ductility cement-based material.

[0012] The superabsorbent resin of the present invention should have a water absorption rate greater than 90 g / g and a maximum particle size of no more than 100 μm. Extensive theoretical and experimental research has shown that superabsorbent resins with excessively large particle sizes can leave large voids within low-shrinkage, ultra-high-strength, and high-ductility cementitious materials, affecting their compressive strength and preventing them from meeting ultra-high-strength requirements.

[0013] The magnesium oxide of the present invention is lightly calcined magnesium oxide, with a maximum particle size not exceeding 200 μm. Extensive theoretical and experimental research has shown that lightly calcined magnesium oxide increases its reaction rate, allowing it to compensate for shrinkage at an early stage. Magnesium oxide with excessively large particle sizes can produce large expansion products within low-shrinkage, ultra-high-strength, high-ductility cement-based materials, affecting their compressive strength and preventing them from meeting ultra-high-strength requirements.

[0014] The aggregate of the present invention is fine river sand with a particle size not exceeding 0.6 mm. Extensive theoretical and experimental research has shown that if the aggregate particle size exceeds 0.6 mm, it will seriously affect the uniformity of the fibers, thereby affecting the ductility of the low-shrinkage, ultra-high-strength, high-ductility cement-based material.

[0015] The ultra-high molecular weight synthetic fiber of the present invention is at least one of polyethylene fiber, Kevlar fiber, and carbon fiber, and has a length of 8 to 12 mm and a diameter of 24 to 38 μm. The ultra-high molecular weight synthetic fiber is limited primarily because theoretical calculations of the design of ultra-high-strength, high-ductility cement-based composite materials reveal that exceeding this range severely impacts the ductility of the low-shrinkage, ultra-high-strength, high-ductility cement-based material.

[0016] The water reducer of the present invention is a liquid polycarboxylic acid-based water reducer with a solids content greater than 50% and a water reduction rate greater than 40%. This limitation is primarily due to considerations regarding the preparation process of low-shrinkage, ultra-high-strength, and high-ductility cementitious materials. Exceeding this range, especially when the silica fume content is high, can severely impact the fresh slurry, thereby affecting the strength and ductility of the low-shrinkage, ultra-high-strength, and high-ductility cementitious materials.

[0017] The present invention provides a method for preparing a low-shrinkage, ultra-high-strength, high-ductility cement-based material, comprising the following steps: 1) Dry-mix a certain amount by weight of Portland cement, ordinary Portland cement, pozzolana Portland cement, slag Portland cement, or fly ash Portland cement, silica fume, slag, magnesium oxide, and fine river sand in a mixer for 3 to 5 minutes to obtain a uniform dry mix; 2) Mix a certain amount of water reducer with tap water and stir for 2 to 3 minutes to obtain a uniform mixture; 3) Pour the mixed liquid into the dry mix and stir for 5-8 minutes to obtain a uniformly mixed ultra-high-strength matrix; 4) Add polyethylene fiber, Kevlar fiber or carbon fiber to the mortar and stir for 3 to 5 minutes to ensure that the synthetic fiber is fully and evenly dispersed in the ultra-high-strength matrix; 5) Add the super absorbent resin to the ultra-high strength cement-based material containing ultra-high molecular weight synthetic fibers and stir for 3 to 5 minutes to ensure that the super absorbent resin is fully and evenly dispersed in the ultra-high strength cement-based material; 6) Pour the ultra-high-strength cement-based material containing super absorbent resin and ultra-high molecular weight synthetic fiber into the mold and form it, then cover it with plastic film for curing; The mixer in the preparation method of the present invention is a body mixer with a rotation speed of 140 to 285 r / min. The mold in the preparation method of the present invention is a steel or PE plastic mold. The plastic film in the preparation method of the present invention is a PE plastic wrap.

[0018] The advantages of the present invention are: (1) The present invention uses fine river sand, cement, slag and silica fume as main raw materials, adopts ultra-high molecular weight synthetic fiber as micro energy-consuming component, and adds super absorbent resin and magnesium oxide. After mixing, a low shrinkage, ultra-high strength, high ductility cement-based composite material with low shrinkage, compressive strength exceeding 120MPa, and ductility under uniaxial tensile load reaching 6% is obtained. The low shrinkage, ultra-high strength and high ductility cement-based composite material can alleviate the problems of large shrinkage of ultra-high performance concrete, meet the needs of major modern complex engineering structures, and improve structural strength, safety performance and durability. The ultra-high compressive strength and high tensile elongation of the low shrinkage, ultra-high strength and high ductility cement-based composite material of the present invention make it the preferred material for unreinforced structures, and can give full play to the unique advantages of the material's intrinsic properties in modern large-scale complex engineering.

[0019] (2) The preparation method of the low-shrinkage, ultra-high-strength, high-ductility cement-based composite material of the present invention is simple and easy to operate, and is suitable for large-scale engineering construction with a large amount of concrete. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the total shrinkage development diagram of ordinary ultra-high performance concrete and Example 1, Example 2, Example 3, and Example 4.

[0021] Figure 21 is a uniaxial tensile stress-strain curve of the cement-based composite material obtained in Example 1.

[0022] Figure 3 This is a uniaxial tensile stress-strain curve of the cement-based composite material obtained in Example 2.

[0023] Figure 4 The uniaxial tensile stress-strain curve of the cement-based composite material obtained in Example 3 is shown.

[0024] Figure 5 This is a uniaxial tensile stress-strain curve of the cement-based composite material obtained in Example 4.

[0025] Figure 6 Graph showing the relationship between tensile strength and tensile strain for Examples 1 to 4. DETAILED DESCRIPTION

[0026] The present invention will be described in further detail below with reference to the accompanying drawings and specific implementation methods.

[0027] The material of the present invention is incomparable to general high-ductility cement-based composite materials (ECC, STCC, or HTCC) or ultra-high performance concrete (UHPC or UHPFRCC) on the market, and cannot be obtained by repeated experiments using preparation technologies in existing literature. Example 1

[0028] The low shrinkage, ultra-high strength, high ductility cement-based material proposed in the present invention has a mix ratio as shown in Table 1 (parts by weight): Table 1 Mixing ratio of cement-based composite materials in Example 1

[0029] The cement is silicate cement; the fiber is polyethylene fiber with a length of 12 mm and a diameter of 38 μm.

[0030] A method for preparing a shrinkage ultra-high strength and high ductility cement-based composite material proposed by the present invention comprises the following steps: 1) Dry mix cement, silica fume, slag, magnesium oxide and fine river sand in a mixer for 3 to 5 minutes to obtain a uniform dry mix; 2) Mix the water reducer with tap water and stir for 2-3 minutes to obtain a uniform mixture; 3) Pour the mixed liquid into the dry mix and stir for 5-8 minutes to obtain a uniformly mixed ultra-high-strength matrix; 4) Add polyethylene fiber to the mortar and stir for 3 to 5 minutes to ensure that the polyethylene fiber is fully and evenly dispersed in the ultra-high-strength matrix; 5) Add the super absorbent resin to the ultra-high strength cement-based material containing polyethylene fibers and stir for 3 to 5 minutes to ensure that the super absorbent resin is fully and evenly dispersed in the ultra-high strength cement-based material; 6) The ultra-high-strength cement-based material containing the super absorbent resin and the polyethylene fiber is poured into a mold, formed, covered with a plastic film, and cured in an environment of 25°C and 95% relative humidity for 28 days to obtain a low-shrinkage ultra-high-strength cement-based material. Example 2

[0031] The low shrinkage, ultra-high strength, high ductility cement-based material proposed in the present invention has a mix ratio as shown in Table 2 (parts by weight): Table 2 Mixing ratio of cement-based composite materials in Example 2

[0032] The cement is pozzolana silicate cement; the fiber is Kevlar fiber with a length of 12 mm and a diameter of 24 μm.

[0033] A method for preparing a shrinkage ultra-high strength and high ductility cement-based composite material proposed by the present invention comprises the following steps: 1) Dry mix cement, silica fume, slag, magnesium oxide and fine river sand in a mixer for 3 to 5 minutes to obtain a uniform dry mix; 2) Mix the water reducer with tap water and stir for 2-3 minutes to obtain a uniform mixture; 3) Pour the mixed liquid into the dry mix and stir for 5-8 minutes to obtain a uniformly mixed ultra-high-strength matrix; 4) Add Kevlar fiber to the mortar and stir for 3 to 5 minutes to ensure that the Kevlar fiber is fully and evenly dispersed in the ultra-high-strength matrix; 5) Add the super absorbent resin to the ultra-high strength cement-based material containing Kevlar fiber and stir for 3 to 5 minutes to ensure that the super absorbent resin is fully and evenly dispersed in the ultra-high strength cement-based material; 6) The ultra-high-strength cement-based material containing the super absorbent resin and Kevlar fiber is poured into a mold, formed, covered with a plastic film, and cured in an environment of 25°C and 95% relative humidity for 28 days to obtain a low-shrinkage ultra-high-strength cement-based material. Example 3

[0034] The low shrinkage, ultra-high strength, high ductility cement-based material proposed in the present invention has a mix ratio as shown in Table 3 (parts by weight): Table 3 Mixing ratio of cement-based composite materials in Example 3

[0035] The cement is slag silicate cement; the fiber is carbon fiber with a length of 12 mm and a diameter of 24 μm.

[0036] A method for preparing a shrinkage ultra-high strength and high ductility cement-based composite material proposed by the present invention comprises the following steps: 1) Dry mix cement, silica fume, slag, magnesium oxide and fine river sand in a mixer for 3 to 5 minutes to obtain a uniform dry mix; 2) Mix the water reducer with tap water and stir for 2-3 minutes to obtain a uniform mixture; 3) Pour the mixed liquid into the dry mix and stir for 5-8 minutes to obtain a uniformly mixed ultra-high-strength matrix; 4) Add carbon fiber to the mortar and stir for 3 to 5 minutes to ensure that the carbon fiber is fully and evenly dispersed in the ultra-high strength matrix; 5) Add the super absorbent resin to the ultra-high strength cement-based material containing carbon fibers and stir for 3 to 5 minutes to ensure that the super absorbent resin is fully and evenly dispersed in the ultra-high strength cement-based material; 6) The ultra-high-strength cement-based material containing the super absorbent resin and the carbon fiber is poured into a mold, formed, covered with a plastic film, and cured in an environment of 25°C and 95% relative humidity for 28 days to obtain a low-shrinkage ultra-high-strength cement-based material. Example 4

[0037] The low shrinkage, ultra-high strength, high ductility cement-based material proposed in the present invention has a mix ratio as shown in Table 1 (parts by weight): Table 4 Mixing ratio of cement-based composite materials in Example 4

[0038] The cement is fly ash silicate cement; the fiber is polyethylene fiber with a length of 12 mm and a diameter of 24 μm.

[0039] A method for preparing a shrinkage ultra-high strength and high ductility cement-based composite material proposed by the present invention comprises the following steps: 1) Dry mix cement, silica fume, slag, magnesium oxide and fine river sand in a mixer for 3 to 5 minutes to obtain a uniform dry mix; 2) Mix the water reducer with tap water and stir for 2-3 minutes to obtain a uniform mixture; 3) Pour the mixed liquid into the dry mix and stir for 5-8 minutes to obtain a uniformly mixed ultra-high-strength matrix; 4) Add polyethylene fiber to the mortar and stir for 3 to 5 minutes to ensure that the polyethylene fiber is fully and evenly dispersed in the ultra-high-strength matrix; 5) Add the super absorbent resin to the ultra-high strength cement-based material containing polyethylene fibers and stir for 3 to 5 minutes to ensure that the super absorbent resin is fully and evenly dispersed in the ultra-high strength cement-based material; 6) The ultra-high-strength cement-based material containing the super absorbent resin and the polyethylene fiber is poured into a mold, formed, covered with a plastic film, and cured in an environment of 25°C and 95% relative humidity for 28 days to obtain a low-shrinkage ultra-high-strength cement-based material.

[0040] The performance of the composite materials obtained in Examples 1 to 4 was tested, and the results are shown in Tables 5 and Figures 1 to 5 As shown: Table 5 Test results of relevant parameters

[0041] It can be seen from the technical indicators of the above tests that the low-shrinkage, ultra-high-strength, high-ductility cement-based material prepared in the embodiment of the present invention has excellent compressive strength (>120 MPa) and excellent tensile elongation (>6%).

[0042] It should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any combination or equivalent transformation based on the above embodiments falls within the scope of protection of the present invention.

Claims

1. A low shrinkage, ultra-high strength and high ductility cement-based material, wherein the cement-based material is a composite material, characterized in that: The cement-based composite material is made of fine river gravel, cement, slag and silica fume as main raw materials, uses ultra-high molecular weight synthetic fibers as microscopic energy-consuming components, and is added with super absorbent resin and magnesium oxide. After mixing, a low-shrinkage cement-based composite material with a compressive strength of more than 120 MPa and a ductility of more than 6% under uniaxial tensile load is obtained.

2. The low shrinkage, ultra-high strength and high ductility cement-based material according to claim 1, characterized in that: The weight proportions of the components in the cement-based composite material are as follows: 60-85 parts of cement, 10-40 parts of silica fume, 35 parts of river sand, 30-55 parts of slag, 16-20 parts of water, 1.6-2.0 parts of ultra-high molecular weight synthetic fiber, 1.8-2.2 parts of water reducer, 0.02-0.05 parts of super absorbent resin, and 4-6 parts of magnesium oxide.

3. The low shrinkage, ultra-high strength and high ductility cement-based material according to claim 2, characterized in that: The cement is at least one of Portland cement, ordinary Portland cement, pozzolana Portland cement, slag Portland cement and fly ash Portland cement, and the 28-day compressive strength of the cement is ≥52.5 MPa.

4. The low shrinkage, ultra-high strength, high ductility cement-based material according to claim 2, characterized in that: The silica fume is greater than 92% by mass of silicon dioxide; the mass percentage of silicon dioxide with a particle size of less than 1 μm in the silicon dioxide is greater than 50%; the 28-day activity index of the slag must reach or exceed 95%, and the content of active calcium, silicon, aluminum and other inorganic substances must be greater than 30%; the particle size of the fine river sand does not exceed 0.6 mm.

5. The low shrinkage, ultra-high strength and high ductility cement-based material according to claim 2, characterized in that: The ultra-high molecular weight synthetic fiber is at least one of polyethylene fiber, Kevlar fiber, and carbon fiber. The ultra-high molecular weight synthetic fiber has a length of 8 to 12 mm and a diameter of 24 to 38 μm.

6. The low shrinkage, ultra-high strength and high ductility cement-based material according to claim 2, characterized in that: The water reducer is a liquid polycarboxylic acid water reducer with a solid content of >50% and a water reduction rate of >40%.

7. The low shrinkage, ultra-high strength, high ductility cement-based material according to claim 2, characterized in that: The water absorption rate of the super absorbent resin should be greater than 90g / g, and the maximum particle size should not exceed 100 μm.

8. The low shrinkage, ultra-high strength, high ductility cement-based material according to claim 2, characterized in that: The magnesium oxide is light-burned magnesium oxide, and its maximum particle size does not exceed 200 μm.

9. Application of the low shrinkage, ultra-high strength and high ductility cement-based material according to claim 1 in large and complex building structures without steel bars.

10. A method for preparing a low shrinkage, ultra-high strength, high ductility cement-based material according to claim 2, characterized in that: The preparation method comprises the following steps: 1) Dry-mix silicate cement, ordinary silicate cement, pozzolanic silicate cement, slag silicate cement, or fly ash silicate cement with silica fume, slag, magnesium oxide, and fine river sand in a mixer for 3 to 5 minutes to obtain a uniform dry mix; 2) Mix the water reducer with tap water and stir for 2-3 minutes to obtain a uniform mixture; 3) Pour the mixed liquid into the dry mix and stir for 5-8 minutes to obtain a uniformly mixed ultra-high-strength matrix; 4) Add polyethylene fiber, Kevlar fiber or carbon fiber to the mortar and stir for 3 to 5 minutes to ensure that the synthetic fiber is fully and evenly dispersed in the ultra-high strength matrix; 5) Add the super absorbent resin to the ultra-high strength cement-based material containing ultra-high molecular weight synthetic fibers and stir for 3 to 5 minutes to ensure that the super absorbent resin is fully and evenly dispersed in the ultra-high strength cement-based material; 6) pouring the ultra-high-strength cement-based material containing the super absorbent resin and the ultra-high molecular weight synthetic fiber into a mold for shaping, and covering with a plastic film for curing; removing the mold, and curing the ultra-high-strength cement-based material containing the super absorbent resin and the ultra-high molecular weight synthetic fiber in an environment at 20-30° C. and a relative humidity greater than 90% for 28 days to obtain a low-shrinkage, ultra-high-strength, high-ductility cement-based material.

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