Ultrahigh-strength and ultrahigh-toughness concrete and preparation method thereof

Abstract

The invention relates to ultrahigh-strength ultrahigh-toughness concrete and a preparation method thereof, and the process of the preparation method is as follows: designing the mix proportion of concrete slurry based on a close packing theory, and selecting a slurry formula with the fluidity of not less than 180mm and the initial strength of not less than 60MPa as a reference mix proportion; steel fibers are selected as end hook type steel fibers, a wood plate or a steel plate is used for formwork supporting according to the size requirement of the test piece, then a steel fiber cage is laid with the end hook type steel fibers within the supporting range, and the steel fibers are staggered with one another to form a macroscopic steel fiber space framework within the supporting range; preparing slurry according to a standard mixing ratio, then infiltrating the slurry into the built steel fiber space framework, and vibrating after the steel fiber space framework is completely infiltrated with the slurry; and then curing and form removal are performed to obtain the ultrahigh-strength ultrahigh-toughness concrete. The problem of agglomeration effect caused by too high fiber mixing amount is solved, and the unified requirements on the strength and toughness of concrete materials in engineering are met.

Description

Technical Field

[0001] The invention relates to the technical field of civil engineering and protective engineering, and in particular to ultra-high strength and ultra-high toughness concrete and a preparation method thereof. Background Art

[0002] On the one hand, the development of civil engineering technology and the pursuit of higher and more complex building forms have put forward higher requirements on the strength and toughness of concrete materials used in civil engineering.

[0003] On the other hand, concrete structure is the most important and common structural form in protective engineering, and has obvious characteristics of high precision and high strength, which poses new challenges to the protective capacity of protective engineering and the performance of the concrete materials used.

[0004] With the development of building materials, emerging materials such as ultra-high performance concrete (UHPC) and engineered cementitious concrete (ECC) are gradually being used in engineering.

[0005] Compared with conventional concrete, UHPC has high compressive strength (100~150 MPa) and is usually mixed with chopped fibers (generally 13 mm in length). It has limited crack resistance and cannot ensure toughness when the structure undergoes large deformation and large cracks exist in the material.

[0006] ECC is made of random organic fiber reinforced cement-based composite materials. It has the characteristics of multi-crack cracking, strain hardening and good tensile toughness. However, due to the low matrix strength (20-40 MPa) and the small elastic modulus of the reinforcing fibers (generally polyethylene fibers and polyvinyl alcohol fibers), the strength of ECC is not significantly improved compared with conventional concrete, and the elastic modulus is lower than that of conventional concrete (15-22 GPa). Therefore, its strong dynamic load capacity is limited compared with conventional concrete, and even some aspects (such as anti-penetration ability) are not as good as conventional concrete.

[0007] In addition, in the traditional concrete material mixing process, there is an upper limit on the fiber content (2%~3%). When the content exceeds the limit, fiber agglomeration and fiber segregation are likely to occur, forming a large number of initial defects inside the concrete, causing the mechanical properties of fiber concrete to decline rapidly, resulting in serious adverse consequences. Therefore, it is urgent to adopt a new construction process to develop a concrete that can have both ultra-high strength and ultra-high toughness. Summary of the invention

[0008] The purpose of the present invention is to overcome the deficiencies in the prior art and provide an ultra-high strength and ultra-high toughness concrete and a preparation method thereof. The concrete can have both ultra-high strength and ultra-high toughness. The preparation method uses high-performance and high-fluidity cement-based slurry as the infiltration material, adopts fiber skeleton mechanical construction technology to form two types of random and / or directional fiber space skeletons respectively, and reasonably controls the fiber content in conjunction with a vibration table to solve the agglomeration effect problem caused by excessive fiber content, meet the unified requirements for the strength and toughness of concrete materials in engineering, and significantly improve its mechanical properties.

[0009] To achieve the above purpose, the technical solution adopted by the present invention is: In a first aspect, the present invention provides a method for preparing ultra-high strength and ultra-high toughness concrete, the process of the preparation method is: The mix ratio of concrete paste is designed based on the close packing theory, and the paste formula with fluidity not less than 180mm and initial strength not less than 60MPa is selected as the benchmark mix ratio; Build a steel fiber space skeleton: Select end hook steel fiber, use wooden boards or steel plates to support the template according to the size requirements of the specimen, and then lay steel fiber cages with end hook steel fibers within the support range. The steel fibers are interlaced with each other within the support range to form a macroscopic steel fiber space skeleton; Infiltration concrete: prepare the slurry according to the standard mix ratio, then infiltrate the slurry into the constructed steel fiber space frame, and vibrate after the slurry completely infiltrates the steel fiber space frame; After that, the formwork is removed for curing to obtain ultra-high strength and ultra-high toughness concrete.

[0010] Furthermore, the steel fiber space skeleton is a random steel fiber space skeleton and / or a directional steel fiber space skeleton.

[0011] Furthermore, the structure of the random steel fiber space skeleton is constructed by two methods: natural fiber accumulation or electromagnetic field regulation: The first method is to use mechanical equipment to initially scatter steel fibers after support to initially form a steel fiber skeleton; vibrate the template together with the initial steel fiber skeleton, and control the amount of steel fibers by controlling the vibration time to form a random steel fiber space skeleton; The second method is to magnetize the steel fibers unidirectionally through a unidirectional electromagnetic field when they leave the factory, so that the steel fibers are magnetic when they leave the factory; a bidirectional horizontal and vertical planar electromagnetic field is constructed within the support range through an electromagnet group; then the steel fibers are scattered using mechanical equipment, and the strength of the electromagnetic field is adjusted to make the steel fibers partially suspended, offsetting gravity and achieving random distribution of steel fibers in space, and the dosage is controlled by the strength of the magnetic field.

[0012] Furthermore, the oriented steel fiber space skeleton is constructed using two methods: The first method uses end hook steel fibers to build a three-dimensional steel fiber cage through prefabrication; The second method is to magnetize the steel fibers unidirectionally through a unidirectional electromagnetic field when they leave the factory, so that the steel fibers are magnetic when they leave the factory; construct a unidirectional electromagnetic field within the support range through an electromagnet group; use mechanical equipment to transport the steel fibers to the support range in a single layer; and at the same time, adjust the strength of the electromagnetic field to make the steel fibers unidirectionally arranged, thereby realizing the construction of a directional steel fiber space skeleton in space.

[0013] In a second aspect, the present invention provides an ultra-high strength and ultra-high toughness concrete obtained by the preparation method. The concrete uses a high-performance and high-fluidity cement-based slurry or a high-performance and high-fluidity geopolymer-based slurry as an infiltration material, including a fiber space skeleton, and the infiltration material is infiltrated into the fiber space skeleton; the fiber is a fiber that can build a space skeleton and can be used in combination with the infiltration material.

[0014] Furthermore, the infiltration material does not contain coarse aggregate, wherein the maximum particle size of the raw material does not exceed 40 meshes; the high-performance and high-fluidity cement-based slurry is composed of cementitious materials, fine aggregates, water, and a water reducing agent, wherein the cementitious materials include cement, silica fume, and blast furnace slag.

[0015] Furthermore, the fiber includes at least one of fiber, carbon fiber, basalt fiber, glass fiber or artificial fiber, and the fiber has an end hook or a protruding supporting portion.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The ultra-high strength and ultra-high toughness concrete of the present invention has excellent mechanical properties and a certain degree of abundance, which greatly reduces the dependence on raw materials. At the same time, the curing conditions are natural curing, which gets rid of the limitation that UHPC needs heating curing.

[0017] When UHPC is prepared by traditional mixing, when the steel fiber content exceeds 2.5%, the fluidity of UHPC decreases rapidly, resulting in a surge in the number of internal defects, and the mechanical properties decrease as the steel fiber content continues to increase. By pre-setting the steel fiber space skeleton and then infiltrating high-performance and high-fluidity cement-based slurry, it is possible to achieve a large amount of steel fiber in steel fiber concrete.

[0018] If the steel fiber content of traditional steel fiber concrete is too high during preparation, the steel fiber skeleton cannot be adjusted, the uniformity is poor, and the content is difficult to control. Ultra-high strength and ultra-high toughness concrete adjusts the content of the steel fiber space skeleton by pre-magnetizing the steel fibers and constructing an electromagnetic field within the support range. This can control the steel fiber content, improve the uniformity of steel fiber distribution, and regulate the steel fiber skeleton.

[0019] The present invention realizes the ultra-high strength (ultimate compressive strength 200-400 MPa) and ultra-high ductility (flexural strength 50-100 MPa, ultimate tensile strain ≥3%, toughness 5×10 3 ~5×10 4 N / m). The existing high-performance concretes that incorporate fibers in the form of mixed raw materials are UHPC and ECC, and the fibers used are commonly used short straight steel fibers (length 13 mm, diameter 0.2 mm) or polyethylene fibers, neither of which can achieve the construction of a spatial skeleton. In this application, fibers with protrusions such as end hooks are used to form the construction of a spatial skeleton, and a high-performance and high-fluidity cement-based slurry penetrates into the fiber spatial skeleton. The reinforcement and toughening mechanism of the high-performance and high-fluidity cement-based slurry due to the addition of steel fibers changes compared to the introduction of the matrix in the form of mixed raw materials. The characteristics of its constitutive model gradually develop from strain softening to strain hardening, and finally show obvious strain strengthening characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 1 is a comparison diagram of compressive stress-strain curves in an embodiment.

[0021] Figure 2 A comparison diagram of bending stress-deflection curves in an embodiment. DETAILED DESCRIPTION

[0022] In order to further understand the content, features and effects of the present invention, the following embodiments are given as examples and described in detail as follows: The ultra-high strength and ultra-high toughness concrete of the present invention consists of two parts: a high-performance and high-fluidity cement-based or geopolymer-based slurry and a fiber space skeleton.

[0023] Furthermore, the high-performance and high-fluidity cement-based slurry is composed of a cementitious material, fine aggregate, water, and a water reducing agent, wherein the cementitious material is cement, silica fume, and blast furnace slag.

[0024] Based on the Close Packing Theory, a preliminary mix design was conducted, and a slurry formula with a fluidity of not less than 180 mm and an initial strength of not less than 60 MPa was selected as the benchmark mix. Furthermore, the high-performance and high-fluidity slurry mix was adjusted based on the density and mechanical properties.

[0025] The fiber space skeleton in the present invention is a three-dimensional space structure composed of fibers, which has a certain structural effect. The fiber space skeleton includes a random fiber space skeleton and / or an oriented fiber space skeleton.

[0026] The random fiber space skeleton is constructed by natural fiber stacking or electromagnetic field regulation. It looks like a bird's nest. It is distributed in multiple directions and maintains a certain discreteness. It has the characteristic of uniform stress distribution in all directions.

[0027] The oriented fiber space frame is constructed from a prefabricated steel fiber mesh that is arranged linearly in three dimensions.

[0028] Furthermore, the fibers include but are not limited to steel fibers, carbon fibers, basalt fibers, glass fibers, artificial fibers, and the like that can construct a space skeleton and can be used in combination with a high-performance, high-fluidity cement-based slurry.

[0029] The preparation method of the ultra-high strength and ultra-high toughness concrete includes four steps: preparing high-performance and high-fluidity slurry, building a steel fiber space skeleton, infiltration casting, and curing. The specific steps are: 1. Build a steel fiber space skeleton: The structure of random steel fiber space skeleton is constructed by two methods: natural fiber stacking or electromagnetic field regulation: The first method is to use mechanical equipment to initially scatter steel fibers after support to initially form a steel fiber skeleton; vibrate the template together with the initial steel fiber skeleton, and control the amount of steel fibers by controlling the vibration time to form a random steel fiber space skeleton; The second method is to magnetize the steel fibers unidirectionally through a unidirectional electromagnetic field when they leave the factory, so that the steel fibers are magnetic when they leave the factory; a bidirectional horizontal and vertical planar electromagnetic field is constructed within the support range through an electromagnet group; then the steel fibers are scattered using mechanical equipment, and the strength of the electromagnetic field is adjusted to make the steel fibers partially suspended, offsetting gravity and achieving random distribution of steel fibers in space, and the dosage is controlled by the strength of the magnetic field.

[0030] The oriented steel fiber spaceframe is constructed using two methods: The first method uses end hook steel fibers to build a three-dimensional steel fiber cage through prefabrication; The second method is to magnetize the steel fibers unidirectionally through a unidirectional electromagnetic field when they leave the factory, so that the steel fibers are magnetic when they leave the factory; construct a unidirectional electromagnetic field within the support range through an electromagnet group; use mechanical equipment such as conveyor belts to transport the steel fibers to the support range in a single layer; and at the same time, adjust the strength of the electromagnetic field to make the steel fibers unidirectionally arranged, thereby realizing the construction of a directional steel fiber space skeleton in the space.

[0031] The steel fiber space skeleton can also be constructed by combining the random steel fiber space skeleton with the directional steel fiber space skeleton.

[0032] 2. Preparation of high performance and high fluidity slurry: Step 1, weighing: design the mix ratio of concrete paste based on the continuous stacking theory, select a paste formula with fluidity not less than 180 mm and initial strength not less than 60 MPa as the benchmark mix ratio; weigh various raw materials according to the benchmark mix ratio; Step 2, dry material mixing: wet the stirring pot with tap water, then add silica fume, cement, blast furnace slag, and quartz sand in proportion and mix evenly to obtain a primary mixture; Step 3, stirring: After weighing and evenly stirring water and water reducing agent, add the initial mixture of step 2, and continue stirring for 10 minutes to obtain a high-performance and high-fluidity slurry.

[0033] 3. Infiltration molding: Step 1, stirring the high-performance and high-fluidity slurry until it is uniform, and pouring it into the constructed steel fiber space skeleton by infiltration pouring; Step 2: Layered infiltration of high-performance and high-fluidity slurry, and slight vibration after the slurry completely permeates the steel fiber space skeleton; Step 3, after slight vibration, cover the upper surface of the prepared specimen to prevent moisture loss.

[0034] 4. Maintenance: Step 1, remove the mold after curing for 1 day under natural conditions; Step 2: Curing for 28 days under outdoor conditions to obtain ultra-high strength and ultra-high toughness concrete.

[0035] The infiltration material of the present invention does not contain coarse aggregate, wherein the maximum particle size of the raw material does not exceed 40 meshes; the infiltration material has high fluidity (above 180 mm) and high strength (above 60 MPa), and this fluidity can ensure penetration within the support range during the infiltration process to form concrete with excellent overall performance.

[0036] Embodiment 1: The method for preparing ultra-high strength and ultra-high toughness concrete in this embodiment comprises the following steps: (1) Raw material ratio and selection Ultra-high strength and ultra-high toughness concrete is composed of cementitious materials, fine aggregate, water, and water reducing agent. The cementitious materials are cement, silica fume, and blast furnace slag.

[0037] According to the required dosage, the specific raw materials used are as follows: cement, blast furnace slag, silica fume, quartz sand, water, and water reducing agent. Among them, cement, mineral powder and silica fume are cementitious materials, and sand is fine aggregate. The cement is ordinary Portland cement with a strength grade of 52.5; the blast furnace slag is S95 grade mineral powder; the silica fume is 1000 mesh high-performance silica fume, and its silica mass percentage is not less than 95%; the quartz sand is 40~70 mesh and 70~120 mesh quartz sand mixed in a ratio of 1:1; the water reducing agent is a polycarboxylic acid high-efficiency water reducing agent, and the water reducing efficiency is not less than 35%. Based on the continuous stacking theory, a preliminary mix ratio design is carried out, and a slurry with a fluidity of 190mm and a strength of 60-70MPa is selected to obtain a benchmark mix ratio of high-performance and high-fluidity cement-based slurry. Prepare concrete with ultra-high strength, ultra-high explosion resistance, ultra-high toughness after cracking and durability.

[0038] (2) Construction of steel fiber space frame The fiber is a hook-end steel fiber, and a steel fiber space skeleton is pre-built within the support range. The construction of the steel fiber space skeleton includes the determination of the formwork and the steel fiber space skeleton.

[0039] Formwork support: Use wooden or steel plates to support the formwork according to the size requirements of the specimen.

[0040] Determination of the spatial skeleton of random steel fibers, method 1: (1) using mechanical equipment such as conveyor belts to initially scatter steel fibers to form a preliminary steel fiber skeleton; (2) vibrating the template together with the preliminary steel fiber skeleton, and controlling the amount of steel fibers by controlling the vibration time; Determination of the spatial skeleton of random steel fibers, method 2: (1) When the steel fibers leave the factory, they are unidirectionally magnetized through a unidirectional electromagnetic field to make them magnetic when leaving the factory; (2) A bidirectional planar electromagnetic field is constructed within the support range through an electromagnet group; (3) The steel fibers are scattered using mechanical equipment such as conveyor belts, and the strength of the electromagnetic field is adjusted to make the steel fibers partially suspended to offset gravity, thereby achieving random distribution of steel fibers in space, and the dosage can be controlled by the strength of the magnetic field.

[0041] Determination of the directional steel fiber space skeleton, Method 1: Build a three-dimensional steel fiber cage by prefabrication; Determination of the oriented steel fiber space skeleton, method 2: (1) When the steel fibers leave the factory, they are unidirectionally magnetized through a unidirectional electromagnetic field to make the steel fibers magnetic when leaving the factory; (2) A unidirectional electromagnetic field is constructed within the support range through an electromagnet group; (3) The steel fibers are transported in a single layer to the support range using mechanical equipment such as conveyor belts; (4) At the same time, the strength of the electromagnetic field is adjusted to make the steel fibers unidirectionally arranged, thereby realizing the construction of the oriented steel fiber space skeleton of the steel fibers in the space.

[0042] (3) Cast-in-place concrete Step 1, weighing: weigh various raw materials according to the benchmark ratio; Step 2, pre-build the steel fiber space frame; Step 3, dry material mixing: wet the stirring pot with tap water, then add silica fume, cement, blast furnace slag, and quartz sand in proportion and mix evenly for 5-10 minutes to obtain the primary mixture; Step 4, weigh water and water reducing agent and stir evenly for 1-2 minutes, then add the primary mixture obtained in step 3 and mix evenly for 5-10 minutes; Step 5, molding: After stirring step 4 until evenly mixed, infiltrate into the constructed steel fiber space skeleton, and vibrate slightly after the slurry completely permeates the skeleton; (4) Maintenance Step 1, demoulding after curing for 1 day under natural conditions; Step 2: Move the test pieces to natural conditions and cure for 28 days.

[0043] (5) Determination of mechanical properties Strength test: Determine the static and dynamic mechanical properties of ultra-high strength and ultra-high toughness concrete at 7 days, 14 days and 28 days.

[0044] Embodiment 2: Experimental raw materials: P52.5 cement, silica fume, S95 blast furnace slag, polycarboxylic acid high-efficiency water reducer, quartz sand, river sand, tap water, 5D special-shaped steel fiber, conventional short straight steel fiber (length 12 mm, diameter 0.2 mm), polyethylene (PE) fiber.

[0045] ①Raw material ratio Cement: silica fume: mineral powder: quartz sand: water: water reducer: steel fiber = 1:0.28:0.14: 1.2:0.2:0.04:0.78 (mass ratio).

[0046] ② Specimen preparation With the mix ratio in ①, ultra-high strength and ultra-high toughness concrete test blocks were made according to the directional fiber space skeleton and the random fiber space skeleton respectively; At the same time, UHPC and ECC test blocks were prepared based on the mix ratio in the existing process. The UHPC test blocks were configured according to the aforementioned raw material mix ratio; the ECC test blocks adopted the aforementioned mix ratio, and the fiber used PE fiber with a volume content of 2%. The mass ratios of the remaining cement, silica fume, mineral powder, quartz sand, water and water reducer were the same as those of ultra-high strength and ultra-high toughness concrete. The cast test blocks were placed under natural conditions for curing for 1 day before demolding.

[0047] ③ Specimen maintenance The test pieces were moved to natural conditions and cured for 28 days.

[0048] ④Test specimen mechanical properties test The compressive and flexural strength tests of UHPC, ECC and ultra-high strength and ultra-high toughness concrete were carried out after curing to the specified age. Figure 1 and Figure 2 As shown: By comparing the above results, it can be found that compared with UHPC and ECC, ultra-high strength and ultra-high toughness concrete has a certain improvement in compressive strength, which are 1.5 times and 2.8 times respectively; compared with UHPC and ECC, ultra-high strength and ultra-high toughness concrete has a certain improvement in compressive toughness, which are 12.3 times and 135.1 times respectively; compared with UHPC and ECC, ultra-high strength and ultra-high toughness concrete has a certain improvement in flexural strength, which are 2.3 times and 4.1 times respectively; compared with UHPC and ECC, ultra-high strength and ultra-high toughness concrete has a certain improvement in flexural toughness, which are 7.8 times and 2.2 times respectively.

[0049] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A method for preparing ultra-high strength and ultra-high toughness concrete, characterized in that: The process of the preparation method is: The mix ratio of concrete paste is designed based on the close packing theory, and the paste formula with fluidity not less than 180mm and initial strength not less than 60MPa is selected as the benchmark mix ratio; Build a steel fiber space skeleton: Select end hook steel fiber, use wooden boards or steel plates to support the template according to the size requirements of the specimen, and then lay steel fiber cages with end hook steel fibers within the support range. The steel fibers are interlaced with each other within the support range to form a macroscopic steel fiber space skeleton; Infiltration concrete: prepare the slurry according to the standard mix ratio, then infiltrate the slurry into the constructed steel fiber space frame, and vibrate after the slurry completely infiltrates the steel fiber space frame; After that, the formwork is removed for curing to obtain ultra-high strength and ultra-high toughness concrete.

2. The preparation method according to claim 1, characterized in that: The steel fiber space skeleton is a random steel fiber space skeleton and / or a directional steel fiber space skeleton.

3. The preparation method according to claim 2, characterized in that: The structure of the random steel fiber space skeleton is constructed by two methods: natural fiber accumulation or electromagnetic field regulation: The first method is to use mechanical equipment to initially scatter steel fibers after support to initially form a steel fiber skeleton; vibrate the template together with the initial steel fiber skeleton, and control the amount of steel fibers by controlling the vibration time to form a random steel fiber space skeleton; The second method is to magnetize the steel fibers unidirectionally through a unidirectional electromagnetic field when they leave the factory, so that the steel fibers are magnetic when they leave the factory; a bidirectional horizontal and vertical planar electromagnetic field is constructed within the support range through an electromagnet group; then the steel fibers are scattered using mechanical equipment, and the strength of the electromagnetic field is adjusted to make the steel fibers partially suspended, offsetting gravity and achieving random distribution of steel fibers in space, and the dosage is controlled by the strength of the magnetic field.

4. The preparation method according to claim 2, characterized in that: The oriented steel fiber space frame is constructed in two ways: The first method uses end hook steel fibers to build a three-dimensional steel fiber cage through prefabrication; The second method is to magnetize the steel fibers unidirectionally through a unidirectional electromagnetic field when they leave the factory, so that the steel fibers are magnetic when they leave the factory; construct a unidirectional electromagnetic field within the support range through an electromagnet group; use mechanical equipment to transport the steel fibers to the support range in a single layer; and at the same time, adjust the strength of the electromagnetic field to make the steel fibers unidirectionally arranged, thereby realizing the construction of a directional steel fiber space skeleton in space.

5. An ultra-high strength and ultra-high toughness concrete, obtained by the preparation method according to any one of claims 1 to 4, characterized in that: The concrete uses high-performance high-fluidity cement-based slurry or high-performance high-fluidity geopolymer-based slurry as the infiltration material, including a fiber space skeleton, and the infiltration material is infiltrated into the fiber space skeleton; the fiber is a fiber that can build a space skeleton and can be used in combination with the infiltration material.

6. The ultra-high strength and ultra-high toughness concrete according to claim 5, characterized in that: The infiltration material does not contain coarse aggregate, wherein the maximum particle size of the raw material does not exceed 40 meshes; the high-performance and high-fluidity cement-based slurry is composed of cementitious materials, fine aggregates, water, and a water reducing agent, wherein the cementitious materials include cement, silica fume, and blast furnace slag.

7. The ultra-high strength and ultra-high toughness concrete according to claim 5, characterized in that: The fiber comprises at least one of fiber, carbon fiber, basalt fiber, glass fiber or artificial fiber, and the fiber has end hooks or protruding support parts.

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