Ultrahigh-strength light cement-based composite material and preparation method thereof

Abstract

The invention provides an ultrahigh-strength light cement-based composite material and a preparation method thereof, and belongs to the technical field of protective engineering materials.The ultrahigh-strength light cement-based composite material comprises an ultrahigh-strength layer, an ultrahigh-toughness layer and a buffer center layer; the ultrahigh-strength layer and the ultrahigh-toughness layer are arranged in an overlapped mode, and the buffer center layer is embedded in the ultrahigh-strength layer. The ultrahigh-strength layer is made of discontinuous short fiber doped cement-based composite materials, the ultrahigh-toughness layer is made of continuous fiber doped cement-based composite materials, and the buffer center layer is made of foam concrete materials. According to the ultrahigh-strength layer disclosed by the invention, by simulating a discontinuous stacking structure of a nanoscale of a biological shell, the front-side pit-digging effect formed by direct impact of a material impact-resistant projectile body is improved; the buffer center layer is embedded in the ultrahigh-strength layer, so that the stress transmitted to the ultrahigh-toughness layer is greatly reduced; the ultra-high toughness layer has ultra-high tensile strength and tensile strain, and impact energy is absorbed in modes of material deformation, crack propagation and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of protective engineering materials, and particularly relates to an ultra-high strength and lightweight cement-based composite material and a preparation method thereof. Background Art

[0002] Although traditional ultra-high performance concrete (UHPC) has ultra-high strength and toughness, its anti-penetration performance has a significant plateau effect. Research shows that when the compressive strength exceeds 120 MPa, the reduction rate of penetration depth and crater damage tends to level off. Traditional concrete materials are prone to explosive failure when subjected to high-speed penetration, generating flying debris and causing secondary injuries; in the field of anti-impact protection, traditional concrete materials have prominent problems such as high self-weight, significant brittleness, and mismatch of interlayer properties.

[0003] At present, improving the anti-penetration performance of concrete has shifted from traditional thickening and reinforcement to refined material-structure collaborative design. For example, the corrugated steel plate-confined multi-chamber gradient concrete proposed in patent CN202310261972.5 reduces the penetration depth by 64.7% compared with the traditional structure through the synergistic effect of the high-strength aggregate layer (corundum / ceramic balls) and fiber concrete. However, the current concrete with a density gradient stratified structure still faces problems such as (1) insufficient strength of the material itself; (2) the designed layered dense structure cannot fully disperse shock waves, resulting in spalling and overall failure. Summary of the Invention

[0004] In view of the technical problems existing in the background art, the present application provides an ultra-high strength and lightweight cement-based composite material and a preparation method thereof, aiming to solve the technical problems of insufficient material strength and the inability of the layered dense structure to fully disperse shock waves.

[0005] In a first aspect, an embodiment of the present application provides an ultra-high strength and lightweight cement-based composite material, including an ultra-high strength layer, an ultra-high toughness layer, and a buffer center layer; the ultra-high strength layer and the ultra-high toughness layer are stacked, and the buffer center layer is embedded in the ultra-high strength layer; the ultra-high strength layer is a cement-based composite material doped with discontinuous short fibers, the ultra-high toughness layer is a cement-based composite material doped with continuous fibers, and the buffer center layer is a foam concrete material.

[0006] In some embodiments, the thickness ratio of the ultra-high strength layer, the ultra-high toughness layer, and the buffer center layer is 1:(0.6 - 1.5):(0.1 - 0.5), and the area ratio of the ultra-high strength layer and the buffer center layer is 1:(0.5 - 0.7).

[0007] In some embodiments, the ultra-high strength layer comprises an ultra-high strength cement matrix and a plurality of discontinuous short fiber layers embedded in the ultra-high strength cement matrix. The discontinuous short fibers in the same discontinuous short fiber layer are arranged in the same direction, and the arrangement angles of the discontinuous short fibers in adjacent discontinuous short fiber layers form an included angle of -50° to 50°.

[0008] In some embodiments, by mass parts, the ultra-high strength layer cement matrix comprises 70 - 90 parts of cement, 10 - 30 parts of auxiliary cementitious material, 65 - 110 parts of fine aggregate, 0.08 - 4 parts of water reducing agent, and 16 - 22 parts of water; The discontinuous short fibers are copper-plated steel fibers or stainless steel fibers. The diameter of the discontinuous short fibers is 0.05 - 0.3 mm, the length of the discontinuous short fibers is 5 - 30 mm, and the tensile strength is ≥2000 MPa.

[0009] In some embodiments, the ultra-high toughness layer comprises an ultra-high toughness cement matrix and a plurality of continuous fiber layers embedded in the ultra-high toughness cement matrix. The continuous fibers in the same continuous fiber layer are arranged in the same direction, and the arrangement angles of the continuous fibers in adjacent continuous fiber layers form an included angle of -20° to 20°.

[0010] In some embodiments, by mass parts, the ultra-high toughness cement matrix comprises 70 - 100 parts of cement, 0 - 30 parts of auxiliary cementitious material, 0 - 130 parts of fine aggregate, 0.08 - 3 parts of water reducing agent, and 14 - 25 parts of water; The continuous fibers are one or several of PP fibers, PE fibers, aramid fibers, carbon fibers, etc. The diameter of the continuous fibers is 0.01 - 0.03 mm, and the tensile strength of the continuous fibers is ≥2000 MPa.

[0011] In some embodiments, the auxiliary cementitious material is a mixture of ultra-fine mineral powder and silica fume; The SiO2 content of the silica fume is ≥90%, and the specific surface area is ≥10000 m 2 / kg; The mineral powder is a mineral powder above S95 grade, and the specific surface area is ≥700m 2 / kg; The cement is ordinary Portland cement with a strength grade of 42.5 or above; The fine aggregate is high-aluminum aggregate or silicon carbide aggregate, and the fineness modulus is 1.6 - 2.2; The water reducing agent is a solid polycarboxylate water reducing agent.

[0012] In some embodiments, the buffer center layer comprises 70 - 100 parts of cement, 0 - 30 parts of auxiliary cementitious material, 0 - 30 parts of limestone powder, 0.08 - 3 parts of water reducing agent, 0.05 - 3.5 parts of foaming agent, 25 - 40 parts of water, and 1.5 - 6 parts of chopped fibers; The chopped fibers are one or several of PP fibers, PE fibers, PVA fibers, carbon fibers, etc. The diameter of the chopped fibers is 0.015 - 0.04 mm, the length of the chopped fibers is 5 - 30 mm, and the tensile strength is ≥ 2800 MPa; The supplementary cementitious material is a mixture of ultra-fine mineral powder and silica fume; The SiO₂ content of the silica fume is ≥ 90%, and the specific surface area is ≥ 10000 m 2 / kg; The mineral powder is a mineral powder above grade S95, and the specific surface area is ≥ 700 m 2 / kg; The cement is ordinary Portland cement with a strength grade above 32.5; The calcium carbonate content of the limestone powder is ≥ 90%, and the residue on a 80μm sieve is ≤ 10%; The water reducer is a solid polycarboxylate water reducer.

[0013] In a second aspect, an embodiment of the present application provides a method for preparing an ultra-high strength and lightweight cement-based composite material, including the following steps: S1. Prepare a buffer center layer: S11. Mix and stir cement, supplementary gel material, limestone powder, water reducer and water to form a concrete slurry; S12. Prepare foam from the foaming agent, add the foam to the concrete slurry and stir evenly, then pour, cure, and cut into a preset size to obtain the buffer center layer; S2. Prepare a green body of the ultra-high strength layer: S21. Mix and stir cement, supplementary cementitious material, fine aggregate, water reducer and water to form a first cement-based slurry; S22. Spread 1 / 20 - 1 / 7 of the cement slurry flat, and evenly sprinkle 1 / 20 - 1 / 7 of the discontinuous fiber short fibers on the surface of the first cement-based slurry in the same direction; S23. After the discontinuous short fibers enter the first cement-based slurry, repeat step S22 until the preset thickness is reached. Place the buffer center layer on the surface of the cement slurry, and continue to repeat step S22 until the upper surface of the first cement-based slurry is flush with the upper surface of the buffer center layer to obtain a buffer center layer / ultra-high strength layer green body; The spreading directions of the discontinuous short fibers in adjacent two layers form an angle of -50° to 50°; S3. Prepare a green body of the ultra-high toughness layer: S31. Mix and stir cement, supplementary cementitious material, fine aggregate, water reducer and water to form a second cement-based slurry; S32. Spread 1 / 15 - 1 / 5 of the continuous fibers in the same direction on the ultra-high strength layer green body, and pour 1 / 15 - 1 / 5 of the second cement-based slurry on the continuous fibers; S33. Repeat step S32 until the preset thickness is reached to obtain a buffer center layer / super high-strength layer green body / super high-toughness layer green body. The spreading directions of two adjacent layers of continuous fibers form an included angle of -20° to 20°. S4. Cure the buffer center layer / super high-strength layer green body / super high-toughness layer green body to obtain a super high-strength lightweight cement-based composite material.

[0014] In some embodiments, the curing conditions in step S4 are as follows: the temperature is 18 - 25°C, the humidity > 95%, and the time is 26 - 30 days; or steam curing for 2 days under the condition of 90°C.

[0015] Different from the prior art solutions, the beneficial effects of this application include: In the present invention, the super high-strength layer mimics the discontinuous stacking structure at the nanoscale of biological shells, uses common portland cement as the base material, and discontinuous fibers as the auxiliary reinforcing material. Through precision casting and molding to form a bionic structure, the cement-based composite material has excellent mechanical properties such as a compressive strength > 400 MPa, a tensile strength > 40 MPa, and a flexural strength > 80 MPa (2 - 3 times higher than the prior art, greatly reducing the cracking problem caused by insufficient material strength itself). High-hardness and high-modulus fine aggregates are used to improve the positive cratering effect formed by the material against the direct impact of the projectile.

[0016] Since the shock wave is usually a spherical wave, the stress acting on the periphery of the central part of the material is much greater than that of the edge material. And to ensure that the overall material does not fail, a buffer center layer is embedded in the super high-strength layer. The buffer center layer uses foam concrete material. On the one hand, through the foam concrete with uniform pores, the stress wave is reflected, refracted, and attenuated, greatly reducing the stress transmitted to the super high-toughness layer. On the other hand, the buffer center layer reduces the density of the overall structure through lightweight foam concrete.

[0017] The super high-toughness layer has a compressive strength > 150 MPa, a tensile strength > 30 MPa, a flexural strength > 60 MPa, and a tensile strain > 2%. It has super high tensile strength and tensile strain, and absorbs impact energy through material deformation, crack propagation, etc. The continuous fiber material consumes kinetic energy through fiber tensile fracture and interlayer slip, and in the anti-high-speed projectile penetration test, it completely achieves the effect of no trauma on the back surface.

[0018] The above description is only an overview of the technical solution of this application. In order to be able to understand the technical means of this application more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features, and advantages of this application more obvious and understandable, the following specifically gives the specific embodiments of this application. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] To more clearly illustrate the technical solution of this application, the accompanying drawings used in this application will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0020] Figure 1 It is a schematic structural diagram of a ultra-high strength and lightweight cement-based composite material in Embodiment 1 of this application.

[0021] Explanation of reference numerals: 1. Ultra-high toughness layer; 2. Continuous fiber; 3. Buffer center layer; 4. Ultra-high strength layer; 5. Discontinuous short fiber. Specific embodiments

[0022] The embodiments of the technical solution of this application will be described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of this application, so they are only examples and cannot be used to limit the protection scope of this application.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above accompanying drawing descriptions are intended to cover non-exclusive inclusion.

[0024] Some specific embodiments are listed below. It should be noted that the embodiments described below are exemplary and are only used to explain this application and cannot be understood as a limitation of this application. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in this field or according to the product specifications. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0025] I. Preparation method Embodiment 1 A ultra-high strength and lightweight cement-based composite material, as Figure 1 shown, includes an ultra-high strength layer 4, an ultra-high toughness layer 1 and a buffer center layer 3. The ultra-high strength layer 4 and the ultra-high toughness layer 1 are stacked. The ultra-high strength layer 4 is used to resist the direct impact of the projectile. The ultra-high toughness layer 1 is located inside and absorbs the impact energy through material deformation, crack propagation, etc.; the buffer center layer 3 is embedded in the ultra-high strength layer 4 on the side close to the ultra-high toughness layer 1. The side surface of the buffer center layer 3 is in contact with the ultra-high toughness layer 1. The buffer center layer 3 is located at the center of the ultra-high strength layer 4. The buffer center layer 3 is used to reflect, refract and attenuate the stress wave through the foam concrete with uniform pores, greatly reducing the stress transmitted to the ultra-high toughness layer 1.

[0026] The thicknesses of the ultra-high strength layer 4, the ultra-high toughness layer 1, and the buffer center layer 3 are 10 mm, 6 mm, and 5 mm respectively. The areas of the ultra-high strength layer 4 and the ultra-high toughness layer 1 are 90000 mm 2 , and the area of the buffer center layer 3 is 63000 mm 2 .

[0027] A preparation method of an ultra-high strength and lightweight cement-based composite material includes the following steps: S1. The buffer center layer uses foamed concrete with a density of 1500 kg / m 3 and a flexural strength of 12 MPa. The foamed concrete includes the following raw materials in parts by mass: 90 parts of PO42.5 cement, 10 parts of ultra-fine mineral powder, 10 parts of limestone powder, 1.2 parts of water reducing agent, 1 part of foaming agent, 30 parts of water, and 2 parts of short-cut PVA fiber (fiber diameter 0.015 mm, fiber length 10 mm, tensile strength ≥ 3000 MPa).

[0028] The preparation method of the buffer center layer includes the following steps: 1) Mix cement, auxiliary cementitious material, limestone powder, and water reducing agent evenly, add water, and continue to stir until it is completely in a homogeneous state to obtain concrete slurry.

[0029] 2) Dilute the foaming agent 40 times in water, then prepare foam in a foaming machine. The density of the prepared foam is 90 - 100 kg / m 3 ).

[0030] 4) Add the foam to the concrete slurry and stir evenly, then immediately pour it onto the II layer until it reaches the specified thickness, cure it in a standard curing room until it solidifies. The curing is steam curing at 90 °C for 2 days, demold it, and cut it into squares with a thickness of 5 mm and an area of 63000 mm 2 to obtain the buffer center layer.

[0031] S2. The ultra-high strength layer uses a cement-based composite material with a compressive strength > 600 MPa, a tensile strength > 70 MPa, and a flexural strength > 140 MPa. The cement-based composite material includes the following raw materials in parts by mass: 70 parts of PO52.5 cement, 20 parts of silica fume, 10 parts of mineral powder, 90 parts of high-aluminum aggregate (fineness modulus 1.6), 1 part of water reducing agent, 16 parts of water, and 100 parts of steel fiber (copper-plated steel fiber, diameter 0.12 mm, length 20 mm, tensile strength 2850 MPa).

[0032] The preparation method of the ultra-high strength layer blank includes the following steps: 1) Mix cement, auxiliary cementitious material, fine aggregate, and water reducing agent evenly, add water, and continue to stir until it is completely in a homogeneous state to form the first cement-based slurry.

[0033] 2) Place the mold on the vibrating table, and add 1 / 20 of the first cement-based slurry to make it spread flat on the bottom of the mold.

[0034] 3) Then evenly spread 1 / 20 of the fibers in the same direction, and wait until the fibers are completely immersed in the cement slurry.

[0035] 4) Pour the same amount of the first cement-based slurry as in step 2). After the slurry levels itself, then evenly spread the same amount of fibers as in step 3) at a 0° angle to the fibers in step 3). Wait until the fibers are completely immersed in the cement slurry and there are no air bubbles on the surface of the slurry.

[0036] 5) Repeat step 4) until a thickness of 5 mm is reached. Place the prefabricated buffer center layer at the symmetric position in the center of the mold. Repeat step 4) to fill the gap between the foam concrete and the mold and reach a thickness of 10 mm to obtain the buffer center layer / super high-strength layer green body.

[0037] S3. Prepare the super high-toughness layer green body: The super high-toughness layer uses a cement-based composite material with a compressive strength > 180 MPa, a tensile strength > 40 MPa, a flexural strength > 100 MPa, and a tensile strain > 2.8%. The cement-based composite material includes the following raw materials in parts by mass: 100 parts of PO52.5 cement, 70 parts of quartz sand aggregate (fineness modulus 2.2), 0.08 part of water reducer, 18 parts of water, and 6 parts of continuous UHMWPE fiber (fiber diameter 0.015 mm, fiber tensile strength ≥ 3400 MPa).

[0038] The preparation method of the super high-toughness layer green body includes the following steps: 1) Mix cement, auxiliary cementitious material, fine aggregate, and water reducer evenly, add water, and continue to stir until it is completely in a state to form the second cement-based slurry to be poured.

[0039] 2) Then lay 1 / 15 of the continuous fibers flat on the super high-strength layer green body in the same direction (the same direction as in step 2).

[0040] 3) Pour 1 / 15 of the second cement-based slurry to be poured along the same direction and translate it onto the continuous fiber layer.

[0041] 4) Wait until there are no air bubbles on the surface of the slurry, and repeat step 3) with the polymer laying direction forming a 0° angle with that in step 2).

[0042] 5) Pour 1 / 5 of the second cement-based slurry to be poured along the same direction and translate it onto the fiber layer.

[0043] 6) Repeat steps 2) to 5) until a thickness of 15 mm is reached, the buffer center layer / super high-strength layer green body / super high-toughness layer green body, and the areas of the super high-strength layer and the super high-toughness layer are 90000 mm2 。

[0044] S4. Cure the buffer center layer / super high-strength layer green body / super high-toughness layer green body at a temperature of 25 °C, a humidity > 95%, and for a time of 30 d to obtain a super high-strength lightweight cement-based composite material.

[0045] Example 2 The difference between Example 2 and Example 1 is that the thicknesses of the super high-strength layer 4, the super high-toughness layer 1, and the buffer center layer 3 are 10 mm, 15 mm, and 0.2 mm respectively, and the areas of the super high-strength layer 4 and the super high-toughness layer 1 are 90000 mm 2 , and the area of the buffer center layer 3 is 45000 mm 2 。

[0046] The preparation method of the super high-strength lightweight cement-based composite material in Example 2 includes the following steps: S1. The buffer center layer uses foamed concrete with a density of 1200 kg / m 3 and a flexural strength of 5 MPa. The foamed concrete includes the following raw materials in parts by mass: 70 parts of PO42.5 cement, 30 parts of ultra-fine mineral powder, 30 parts of limestone powder, 1.2 parts of water reducing agent, 1.3 parts of foaming agent, 40 parts of water, and 2 parts of short-cut PE fiber (fiber diameter 0.025 mm, fiber length 15 mm, tensile strength ≥ 3000 MPa).

[0047] The preparation method of the buffer center layer includes the following steps: 1) Mix the cement, supplementary cementitious material, limestone powder, and water reducing agent evenly, add water, and continue to stir until it is completely in a state to obtain a concrete slurry.

[0048] 2) Dilute the foaming agent 10 times in water, then prepare foam in a foaming machine, and the density of the prepared foam is 30 - 50 kg / m 3 ).

[0049] 4) Add the foam to the concrete slurry and stir evenly, then immediately pour it onto the II layer until it reaches the specified thickness, cure it in a standard curing room until it solidifies, cure it by steam curing at 90 °C for 2 days, demold it, and cut it into squares with a thickness of 0.2 mm and an area of 45000 mm 2 to obtain the buffer center layer.

[0050] S2. The ultra-high strength layer uses a cement-based composite material with a compressive strength > 400 MPa, a tensile strength > 40 MPa, and a flexural strength > 80 MPa. The cement-based composite material includes the following raw materials in parts by mass: 60 parts of PO42.5 cement, 30 parts of silica fume, 10 parts of slag powder, 130 parts of silicon carbide aggregate (fineness modulus 2.0), 1.2 parts of water reducer, 18 parts of water, and 80 parts of steel fiber (copper-plated steel fiber, diameter 0.3 mm, length 30 mm, tensile strength 2000 MPa).

[0051] The preparation method of the ultra-high strength layer blank includes the following steps: 1) Mix cement, auxiliary cementitious materials, fine aggregate, and water reducer evenly, add water, and continue to stir until it is completely in a state, forming a first cement-based slurry.

[0052] 2) Place the mold on the vibrating table, and add 1 / 7 of the first cement-based slurry to spread it evenly on the bottom of the mold.

[0053] 3) Then evenly spread 1 / 7 of the fiber in the same direction and wait for the fiber to be completely immersed in the cement slurry.

[0054] 4) Pour the same amount of the first cement-based slurry as in step 2). After the slurry levels itself, then evenly spread the same amount of fiber as in step 3) at an angle of 30° to the fiber in step 3). Wait for the fiber to be completely immersed in the cement slurry and there are no bubbles on the surface of the slurry.

[0055] 5) Repeat step 4) until a thickness of 9.8 mm is reached. Place the prefabricated buffer center layer at the symmetric position in the center of the mold, repeat step 4), fill the gap between the foam concrete and the mold, and reach a thickness of 10 mm to obtain the buffer center layer / ultra-high strength layer blank.

[0056] S3. Prepare the ultra-high toughness layer blank: The ultra-high toughness layer uses a cement-based composite material with a compressive strength > 150 MPa, a tensile strength > 30 MPa, a flexural strength > 60 MPa, and a tensile strain > 2%. The cement-based composite material includes the following raw materials in parts by mass: 100 parts of PO32.5 cement, 90 parts of quartz sand aggregate (fineness modulus 2.2), 1 part of water reducer, 18 parts of water, and 15 parts of continuous carbon fiber (fiber diameter 0.03 mm, fiber tensile strength ≥ 3400 MPa).

[0057] The preparation method of the ultra-high toughness layer blank includes the following steps: 1) Mix cement, auxiliary cementitious materials, fine aggregate, and water reducer evenly, add water, and continue to stir until it is completely in a state, forming a second cement-based slurry to be poured.

[0058] 2) Then, lay 1 / 5 of the continuous fibers flat on the ultra-high strength layer blank in the same direction (the same direction as in step 2).

[0059] 3) Pour 1 / 5 of the second cement-based slurry to be poured horizontally along the same direction onto the continuous fiber layer.

[0060] 4) Wait until no bubbles emerge on the surface of the slurry, and repeat step 3) with the laying direction of the polymer forming a 5° angle with that in step 2).

[0061] 5) Pour 1 / 5 of the second cement-based slurry to be poured horizontally along the same direction onto the fiber layer.

[0062] 6) Repeat steps 2) to 5) until a thickness of 15 mm is reached for the buffer center layer / ultra-high strength layer blank / ultra-high toughness layer blank, with the areas of the ultra-high strength layer and the ultra-high toughness layer being 90000 mm 2 .

[0063] S4. Cure the buffer center layer / ultra-high strength layer blank / ultra-high toughness layer blank at a curing temperature of 25°C, a humidity > 95%, and a time of 30 d to obtain the ultra-high strength lightweight cement-based composite material.

[0064] Comparative Example 1 A commercially available UHPC material in France, with a steel fiber volume fraction of 3% and a compressive strength > 200 MPa.

[0065] Comparative Example 2 A commercially available domestic UHPC material, with a steel fiber volume fraction of 3% and a compressive strength > 180 MPa.

[0066] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that no buffer center layer is set.

[0067] Comparative Example 4 The difference between Comparative Example 4 and Example 2 is that the ultra-high strength layer is cast by directly mixing fibers and cement slurry, and the ultra-high toughness layer is cast by directly mixing equal-length fibers and cement slurry.

[0068] Comparative Example 5 The difference between Comparative Example 5 and Example 2 is that the buffer center layer and the ultra-high strength layer have the same cross-sectional area.

[0069] II. Test Methods 1. Anti-high-speed projectile penetration test: The projectile impacts the material sample to be tested at high speed, and the damage depth and area of the sample are detected.

[0070] Projectile: 6 mm in diameter, single-head conical, and the projectile material is CAC304 high-strength copper alloy (yield strength 600 MPa, ultimate strength 850 MPa, Brinell hardness 330 HB).

[0071] III. Analysis of test results of various embodiments and comparative examples The ultra-high strength lightweight cement-based composite materials prepared in the embodiments and comparative examples were tested for resistance to high-speed projectile penetration. The test results are shown in Table 1 below.

[0072] Table 1 Test results of the materials prepared in various embodiments and comparative examples against high-speed projectile penetration

[0073] As can be seen from Table 1 above, the cement-based composite materials of Example 1 and Example 2 have excellent anti-penetration performance, especially anti-front penetration depth and anti-back delamination. Compared with Comparative Example 1, the front damage area and front damage volume of Example 1 were reduced by 47.3% and 49.0% respectively; and the back damage was completely eliminated. Compared with Comparative Example 2, the front damage area and front damage volume of Example 2 were reduced by 59.6% and 64.7% respectively; and the back damage was completely eliminated.

[0074] Compared with Example 1, Comparative Example 3 does not have a buffer center layer made of foam concrete, and the back of the material is still damaged by the stress wave generated by the impact. It can be seen that the ultra-high strength lightweight cement-based composite material used in the present invention and the ultra-high strength concrete layer can significantly reduce the penetration depth and the front damage area; buffer center layer: the foam concrete with uniform pores reflects, refracts and attenuates stress waves, greatly reducing the stress transmitted to the ultra-high toughness layer; the ultra-high toughness concrete in the ultra-high toughness layer fully dissipates energy through continuous fiber (such as UHMWPE) stretching and interlayer slippage, and the foam concrete pores refract and reflect stress waves, achieving the effect of no back cracking. In addition, the density of Example 1 and Example 2 is reduced by more than 10% compared with Comparative Example 1 and Comparative Example 2.

[0075] The fibers used in the ultra-high strength layer and the ultra-high toughness layer in Comparative Example 4 are directly mixed with cement slurry and cast. Compared with Example 2, the damage area on the front side of the obtained material and the proof damage depth are greatly improved, and the back side of the material is damaged by the stress wave generated by the impact, indicating that the fiber stacking structure of the invention can greatly improve the material's compressive, flexural and tensile mechanical properties.

[0076] In Comparative Example 5, the buffer center layer and the ultra-high strength layer have the same cross-sectional area, and the front damage area and the proof damage depth of the prepared material are slightly increased compared with those in Example 2, but the buffer center layer is damaged and cracked, indicating that embedding the buffer center layer in the ultra-high strength layer can reduce the stress wave transmission to the high toughness to obtain stress. The buffer center layer and the ultra-high strength layer have the same cross-sectional area, and without the peripheral protection of the ultra-high strength layer, the buffer center layer is easily damaged after being impacted.

[0077] It should be noted that this application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and embodiments with the same composition in terms of technical idea and the same function and effect within the scope of the technical solution of this application are all included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that those skilled in the art can think of to the embodiments, and other ways constructed by combining some constituent elements in the embodiments are also included in the scope of this application.

Claims

1. A super high-strength and lightweight cement-based composite material, characterized in that, It includes an ultra-high-strength layer, an ultra-high-toughness layer and a buffer center layer; the ultra-high-strength layer and the ultra-high-toughness layer are stacked, and the buffer center layer is embedded in the ultra-high-strength layer; the ultra-high-strength layer is a cement-based composite material doped with discontinuous short fibers, the ultra-high-toughness layer is a cement-based composite material doped with continuous fibers, and the buffer center layer is a foam concrete material.

2. The ultra-high strength and lightweight cement-based composite material according to claim 1, characterized in that, The thickness ratio of the ultra-high-strength layer, the ultra-high-toughness layer and the buffer center layer is 1:(0.6~1.5):(0.1~0.5); the area ratio of the ultra-high-strength layer and the buffer center layer is 1:(0.5~0.7).

3. The ultra-high strength and lightweight cement-based composite material according to claim 1, characterized in that, The ultra-high-strength layer includes an ultra-high-strength cement matrix and several layers of discontinuous short fiber layers embedded in the ultra-high-strength cement matrix. The discontinuous short fibers in the same layer of discontinuous short fiber layer are arranged in the same direction, and the arrangement angles of the discontinuous short fibers in adjacent two layers of discontinuous short fiber layers form an included angle of -50° to 50°.

4. The ultra-high strength and lightweight cement-based composite material according to claim 3, characterized in that By mass, the ultra-high-strength layer cement matrix includes 70~90 parts of cement, 10~30 parts of auxiliary cementitious material, 65~110 parts of fine aggregate, 0.08~4 parts of water reducer, and 16~22 parts of water; The discontinuous short fibers are copper-plated steel fibers, stainless steel fibers, the diameter of the discontinuous short fibers is 0.05~0.3mm, the length of the discontinuous short fibers is 5~30mm, and the tensile strength ≥2000MPa.

5. The ultra-high strength and lightweight cement-based composite material according to claim 1, wherein The ultra-high-toughness layer includes an ultra-high-toughness cement matrix and several layers of continuous fiber layers embedded in the ultra-high-toughness cement matrix. The continuous fibers in the same layer of continuous fiber layer are arranged in the same direction, and the arrangement angles of the continuous fibers in adjacent two layers of continuous fiber layers form an included angle of -20° to 20°.

6. The ultra-high strength and lightweight cement-based composite material according to claim 5, characterized in that, By mass, the ultra-high-toughness cement matrix includes 70~100 parts of cement, 0~30 parts of auxiliary cementitious material, 0~130 parts of fine aggregate, 0.08~3 parts of water reducer, and 14~25 parts of water; The continuous fibers are one or several of PP fibers, PE fibers, aramid fibers, carbon fibers, etc., the diameter of the continuous fibers is 0.01~0.03mm, and the tensile strength of the continuous fibers ≥2000MPa.

7. The ultra-high strength and lightweight cement-based composite material according to any one of claims 3 to 6, characterized in that, The auxiliary cementitious material is a mixture of ultra-fine mineral powder and silica fume; The SiO2 content of the silica fume is ≥90%, and the specific surface area is ≥10,000 m 2 / kg; The mineral powder is a mineral powder above S95 grade, with a specific surface area ≥ 700 m 2 / kg; The cement is ordinary Portland cement with a strength grade above 42.5; The fine aggregate is high-aluminum aggregate or silicon carbide aggregate with a fineness modulus of 1.6~2.2; The water reducer is a solid polycarboxylate water reducer.

8. The ultra-high strength and lightweight cement-based composite material according to claim 1, characterized in that, By mass, the buffer center layer includes 70~100 parts of cement, 0~30 parts of auxiliary cementitious material, 0~30 parts of limestone powder, 0.08~3 parts of water reducer, 0.05~3.5 parts of foaming agent, 25~40 parts of water, and 1.5~6 parts of chopped fibers; The chopped fibers are one or several of PP fibers, PE fibers, PVA fibers, carbon fibers, etc., the diameter of the chopped fibers is 0.015~0.04mm, the length of the chopped fibers is 5~30mm, and the tensile strength ≥2800MPa; The auxiliary cementitious material is a mixture of ultra-fine mineral powder and silica fume; The SiO2 content of the silica fume is ≥ 90%, and the specific surface area is ≥ 10,000 m 2 / kg; The mineral powder is a mineral powder above S95 grade, with a specific surface area ≥ 700 m 2 / kg; The cement is ordinary Portland cement with a strength grade above 32.5; The calcium carbonate content of the limestone powder is ≥ 90%, and the residue on a 80μm sieve is ≤ 10%. The water reducer is a solid polycarboxylate water reducer.

9. A method for preparing the ultra-high strength and lightweight cement-based composite material as described in claims 1 to 8, characterized in that, It includes the following steps: S1. Prepare a buffer center layer: S11. Mix and stir cement, auxiliary gel material, limestone powder, water reducer and water to form a concrete slurry; S12. Prepare foam from the foaming agent, add the foam into the concrete slurry and stir evenly. After casting and curing, cut it into a preset size to obtain the buffer center layer; S2. Prepare a ultra-high strength layer blank: S21. Mix and stir cement, auxiliary cementitious material, fine aggregate, water reducer and water to form a first cement-based slurry; S22. Lay 1 / 20 - 1 / 7 of the cement slurry flat, and evenly spread 1 / 20 - 1 / 7 of the discontinuous fiber short fibers in the same direction on the surface of the first cement-based slurry; S23. After the discontinuous short fibers enter the first cement-based slurry, repeat step S22 until the preset thickness is reached. Place the buffer center layer on the surface of the cement slurry, and continue to repeat step S22 until the upper surface of the first cement-based slurry is flush with the upper surface of the buffer center layer, obtaining a buffer center layer / ultra-high strength layer blank; The spreading directions of the discontinuous short fibers in adjacent two layers form an angle of -50° to 50°; S3. Prepare a ultra-high toughness layer blank: S31. Mix and stir cement, auxiliary cementitious material, fine aggregate, water reducer and water to form a second cement-based slurry; S32. Spread 1 / 15 - 1 / 5 of the continuous fibers in the same direction on the ultra-high strength layer blank, and pour 1 / 15 - 1 / 5 of the second cement-based slurry on the continuous fibers; S33. Repeat step S32 until the preset thickness is reached, obtaining a buffer center layer / ultra-high strength layer blank / ultra-high toughness layer blank; The spreading directions of the continuous fibers in adjacent two layers form an angle of -20° to 20°; S4. Cure the buffer center layer / ultra-high strength layer blank / ultra-high toughness layer blank to obtain a ultra-high strength lightweight cement-based composite material.

10. The preparation method of the ultra-high strength and lightweight cement-based composite material according to claim 9, characterized in that: The curing conditions in step S4 are: temperature is 18 - 25°C, humidity > 95%, time is 26 - 30d; or steam curing at 90°C for 2d.

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