An ultra-high strength and ultra-high toughness concrete and a preparation method thereof

Abstract

The application discloses a kind of super high strength super high toughness concrete and its preparation method, the process of the preparation method is: based on the design of concrete slurry mix proportion of close packing theory, select the slurry formula of initial strength not less than 60MPa with fluidity not less than 180mm as benchmark mix proportion;Select steel fiber as end hook type steel fiber, utilize board or steel plate according to the size requirement of test piece to carry out formwork support, then end hook type steel fiber is laid in the range of support with steel fiber cage, steel fiber is staggered in the range of support to form macroscopic steel fiber space skeleton;According to benchmark mix proportion, slurry is prepared, then slurry is infiltrated into the steel fiber space skeleton built, after slurry completely infiltrates steel fiber space skeleton, vibration;After that, curing formwork is removed to obtain super high strength super high toughness concrete.Solve the problem of agglomeration effect caused by too high fiber content, meet the unified requirement of concrete material strength and toughness in engineering.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of civil engineering and protective engineering technology, in particular to a kind of super high strength super high toughness concrete and its preparation method. BACKGROUND

[0002] On the one hand, the development of civil engineering technology, the pursuit of higher and more complex building forms, puts higher requirements on the strength and toughness of concrete materials for civil engineering.

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

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

[0005] Compared with conventional concrete, UHPC has high compressive strength (100-150 MPa), and is usually mixed with short-cut fibers (length generally 13 mm), which has limited crack resistance. The material has insufficient toughness when the structure deforms greatly and there are large cracks.

[0006] ECC is prepared with randomly oriented organic fiber reinforced cement-based composite material, which has the characteristics of multi-crack cracking and strain hardening, and good tensile toughness. However, due to the lower matrix strength (20-40 MPa) and smaller elastic modulus of the reinforcing fiber (generally polyethylene fiber and polyvinyl alcohol fiber), the strength of ECC does not increase significantly compared with conventional concrete, and the elastic modulus is lower than that of conventional concrete (15-22 GPa). Therefore, the high dynamic load capacity of ECC is limited compared with conventional concrete, and even in some aspects (such as penetration resistance), it is not as good as conventional concrete.

[0007] In addition, in the traditional concrete material mixing process, there is an upper limit (2%-3%) for the amount of fiber. When the amount exceeds the limit, fiber clumping and fiber segregation phenomena are likely to occur, forming a large number of initial defects in the concrete, which rapidly reduces the mechanical properties of fiber concrete and causes serious adverse consequences. Therefore, it is urgent to develop a new construction process to develop a kind of concrete with super high strength and super high toughness. SUMMARY

[0008] The application aims at overcoming the deficiencies in the prior art and providing an ultrahigh-strength and ultrahigh-toughness concrete and a preparation method thereof. The concrete can have both ultrahigh strength and ultrahigh toughness. The preparation method uses high-performance and high-fluidity cement-based paste as a permeation material, adopts a fiber skeleton mechanical building technology to form two types of random and / or directional fiber spatial skeletons, and reasonably controls the fiber content in cooperation with a vibration table to solve the problem of agglomeration caused by excessive fiber content, meet the unified requirements of strength and toughness of the concrete material in engineering, and significantly improve the mechanical properties.

[0009] To achieve the above-mentioned purpose, the technical solution adopted by the application is:

[0010] In the first aspect, the application provides a preparation method of an ultrahigh-strength and ultrahigh-toughness concrete, and the process of the preparation method is:

[0011] Design the mix proportion of the concrete paste based on the close packing theory, select a paste formula with a fluidity of not less than 180 mm and an initial strength of not less than 60 MPa as the reference mix proportion;

[0012] Build a steel fiber spatial skeleton: select an end-hook type steel fiber, use a wooden board or a steel board to support the template according to the size requirements of the test piece, and then lay a steel fiber cage in the supporting range with the end-hook type steel fiber. The steel fibers are interlaced with each other in the supporting range to form a macroscopic steel fiber spatial skeleton;

[0013] Permeate the concrete: prepare the paste according to the reference mix proportion, and then permeate the paste into the built steel fiber spatial skeleton. Shake after the paste completely permeates the steel fiber spatial skeleton;

[0014] Then, maintain and demold to obtain the ultrahigh-strength and ultrahigh-toughness concrete.

[0015] Further, the steel fiber spatial skeleton is a random steel fiber spatial skeleton and / or a directional steel fiber spatial skeleton.

[0016] Further, the structure of the random steel fiber spatial skeleton is constructed by two methods of natural fiber accumulation or electromagnetic field regulation:

[0017] Firstly, after supporting, the mechanical equipment is used to preliminarily scatter the steel fibers to preliminarily form a steel fiber skeleton. The template is vibrated together with the preliminary steel fiber skeleton to control the steel fiber content by controlling the vibration time to form a random steel fiber spatial skeleton.

[0018] The second kind is that the steel fiber is magnetized by a one-way electromagnetic field when leaving the factory, so that the steel fiber leaves the factory with magnetism; a one-way electromagnetic field is constructed in the supporting range by an electromagnet group; the steel fiber is scattered by a mechanical device, the strength of the electromagnetic field is adjusted so that the steel fiber is in a partial suspended state, the gravity is offset, the random distribution of the steel fiber in the space is realized, and the mixing amount is controlled by the strength of the electromagnetic field.

[0019] Further, the construction of the oriented steel fiber space skeleton adopts two methods:

[0020] The first kind is that the end-hook type steel fiber is used to build a three-dimensional steel fiber cage by a prefabricated method;

[0021] The second kind is that the steel fiber is magnetized by a one-way electromagnetic field when leaving the factory, so that the steel fiber leaves the factory with magnetism; a one-way electromagnetic field is constructed in the supporting range by an electromagnet group; the steel fiber is scattered by a mechanical device, the strength of the electromagnetic field is adjusted so that the steel fiber is in a partial suspended state, the gravity is offset, the random distribution of the steel fiber in the space is realized, and the mixing amount is controlled by the strength of the electromagnetic field.

[0022] In the second aspect, the application provides a super-high-strength and super-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 polymer-based slurry as a permeation material, includes a fiber space skeleton, and the permeation material is permeated in the fiber space skeleton; the fiber is a fiber that can build a space skeleton and can be used with the permeation material.

[0023] Further, the permeation material does not contain coarse aggregate, wherein the maximum particle size of the raw material is not more than 40 mesh; the high-performance and high-fluidity cement-based slurry is composed of a cementitious material, a fine aggregate, water and a water reducing agent, and the cementitious material includes cement, silica fume and blast furnace slag.

[0024] Further, the fiber includes at least one of a fiber, a carbon fiber, a basalt fiber, a glass fiber or an artificial fiber, and the fiber has an end hook or a protruding support part.

[0025] Compared with the prior art, the application has the following beneficial effects:

[0026] The super-high-strength and super-high-toughness concrete has excellent mechanical properties, a certain margin and greatly reduced dependence on raw materials. At the same time, the maintenance condition is natural maintenance, which breaks the limitation of the need for heating maintenance of UHPC.

[0027] When the content of steel fiber exceeds 2.5% in the traditional stirring preparation of UHPC, the fluidity of UHPC rapidly decreases, which leads to the rapid increase of internal defects, and the mechanical properties decrease with the continuous increase of the content of steel fiber. The high-performance high-fluidity cement-based slurry can realize the large content of steel fiber in steel fiber concrete by pre-setting the spatial skeleton of steel fiber.

[0028] If the content of steel fiber is too high in the preparation of traditional steel fiber concrete, the steel fiber skeleton cannot be controlled, the uniformity is poor, and the content is difficult to control. The ultra-high strength and ultra-high toughness concrete can control the content of steel fiber, improve the uniformity of steel fiber distribution, and control the steel fiber skeleton by pre-magnetizing the steel fiber and constructing the electromagnetic field in the support range.

[0029] The application realizes the target indicators of ultra-high strength (ultimate compressive strength 200-400 MPa) and ultra-high toughness (bending strength 50-100 MPa, ultimate tensile strain ≥3%, toughness 5×10 3 ~5×10 4 N / m) of the ultra-high strength and ultra-high toughness concrete. The existing high-performance concrete with fiber mixed in the form of raw materials, such as UHPC and ECC, uses common short straight steel fiber (length 13 mm, diameter 0.2 mm) or polyethylene fiber, which cannot realize the construction of spatial skeleton. In this application, the fiber with end hook and other protrusions is used to form the construction of spatial skeleton, and the high-performance high-fluidity cement-based slurry is infiltrated into the spatial skeleton of the fiber. The mechanism of the steel fiber content of the high-performance high-fluidity cement-based slurry for enhancing and toughening the matrix changes compared with the matrix introduced by the raw material form, and the characteristics of the constitutive model gradually develop from strain softening to strain hardening, and finally show obvious strain hardening characteristics. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a comparison chart of the compressive stress-strain curve in an embodiment.

[0031] Figure 2 It is a comparison chart of the bending stress-deflection curve in an embodiment. DETAILED DESCRIPTION

[0032] In order to further understand the content, characteristics and effects of the application, the following embodiments are exemplified, and are described in detail as follows:

[0033] The ultra-high strength and ultra-high toughness concrete of the application is composed of high-performance high-fluidity cement-based or geopolymer-based slurry and fiber spatial skeleton.

[0034] Further, the high-performance high-fluidity cement-based paste is composed of cementitious material, fine aggregate, water and water reducing agent, wherein the cementitious material is cement, silica fume and blast furnace slag.

[0035] The preliminary mixing ratio design is based on the close packing theory, and the paste formula with fluidity not less than 180 mm and initial strength not less than 60 MPa is selected as the reference mixing ratio.

[0036] The fiber space framework in the application is a three-dimensional space structure composed of fibers, and has a certain structural effect.

[0037] The random fiber space framework is constructed by natural accumulation or electromagnetic field regulation of fibers, and has a bird nest-like appearance, is distributed in multiple directions and maintains a certain discreteness, and has the characteristic of uniform stress distribution in all directions.

[0038] The directional fiber space framework is constructed by a prefabricated steel fiber net, and is linearly arranged in three dimensional directions.

[0039] Further, the fibers include but are not limited to steel fibers, carbon fibers, basalt fibers, glass fibers, artificial fibers and other fibers that can build a space framework and can be used with high-performance high-fluidity cement-based paste.

[0040] The preparation method of the above-mentioned super-high-strength super-high-toughness concrete includes four steps of preparing a high-performance high-fluidity paste, building a steel fiber space framework, permeating and forming, and curing.

[0041] I. Building a steel fiber space framework:

[0042] The construction of the random steel fiber space framework is constructed by two methods of natural accumulation or electromagnetic field regulation of fibers:

[0043] Firstly, after supporting, the steel fibers are preliminarily scattered by mechanical equipment to preliminarily form a steel fiber framework; the formwork together with the preliminary steel fiber framework is vibrated, and the amount of steel fibers is controlled by controlling the vibration time to form a random steel fiber space framework;

[0044] Secondly, the steel fibers are unidirectionally magnetized by a unidirectional electromagnetic field when they are delivered from the factory, so that the steel fibers have magnetism when they are delivered from the factory; a horizontal and vertical double-directional plane electromagnetic field is constructed in the supporting range by an electromagnetic group; then the steel fibers are scattered by mechanical equipment, the steel fibers are partially suspended by adjusting the strength of the electromagnetic field to offset the gravity, the random distribution of the steel fibers in space is realized, and the amount of the steel fibers is controlled by the strength of the electromagnetic field.

[0045] Two methods are used to construct the directional steel fiber space skeleton:

[0046] The first method involves using hook-shaped steel fibers to construct a three-dimensional steel fiber cage through prefabrication.

[0047] The second method involves unidirectionally magnetizing the steel fibers with a unidirectional electromagnetic field at the factory, making them magnetic; constructing a unidirectional electromagnetic field within the support area using an electromagnet assembly; transporting the steel fibers to the support area in single layers using conveyor belts and other mechanical equipment; and simultaneously adjusting the strength of the electromagnetic field to ensure unidirectional arrangement of the steel fibers, thus achieving the construction of a directional steel fiber spatial skeleton within the space.

[0048] The construction of a steel fiber spatial framework can also combine randomized steel fiber spatial frameworks with oriented steel fiber spatial frameworks.

[0049] II. Preparation of high-performance, high-flowability slurries:

[0050] Step 1, Weighing: Based on the continuous packing theory, design the mix proportion of the concrete slurry, and select a slurry formula with a fluidity of not less than 180 mm and an initial strength of not less than 60 MPa as the benchmark mix proportion; weigh all raw materials according to the benchmark mix proportion;

[0051] Step 2, dry material mixing: After wetting the mixing pot with tap water, add silica fume, cement, blast furnace slag and quartz sand in proportion and mix evenly to obtain the initial mixture;

[0052] Step 3, stirring: Weigh and stir the water and water-reducing agent evenly, then add the initial mixture from Step 2 and continue stirring for 10 minutes to obtain a high-performance, high-flowability slurry.

[0053] III. Infiltration casting:

[0054] Step 1: Stir the high-performance, high-flowability slurry until uniform, and pour it into the constructed steel fiber space frame by seepage pouring.

[0055] Step 2: Pour high-performance, high-flowability slurry in layers, and gently vibrate after the slurry has completely filled the steel fiber space frame.

[0056] Step 3: After slight vibration, cover the upper surface of the prepared specimen to prevent moisture loss.

[0057] IV. Maintenance:

[0058] Step 1: Remove the mold after curing under natural conditions for 1 day;

[0059] Step 2: Curing outdoors for 28 days to obtain ultra-high strength and ultra-high toughness concrete.

[0060] The raw material in the present application does not contain coarse aggregate, wherein the maximum particle size of the raw material is not more than 40 mesh; the infiltrating material has high fluidity (more than 180 mm) and high strength (more than 60 MPa), and the fluidity can ensure the infiltration in the supporting range during the infiltration process, and form the concrete with excellent overall performance.

[0061] Embodiment 1

[0062] The preparation method of the super-high-strength and super-high-toughness concrete comprises the following steps:

[0063] (1) Raw material ratio and selection

[0064] The super-high-strength and super-high-toughness concrete is composed of cementitious material, fine aggregate, water and water reducing agent, and the cementitious material is composed of cement, silica fume and blast furnace slag.

[0065] According to the required amount, the specific raw materials are as follows: cement, blast furnace slag, silica fume, quartz sand, water and water reducing agent. The cement, blast furnace slag and silica fume are cementitious materials, the sand is fine aggregate, the cement is ordinary portland cement with a strength grade of 52.5; the blast furnace slag is S95 grade blast furnace slag; the silica fume is 1000 mesh high-performance silica fume with a mass percentage of silicon dioxide of 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 with a water reducing efficiency of not less than 35%. Based on the continuous packing theory, the preliminary mix ratio design is carried out, the slurry with a fluidity of 190 mm and a strength of 60-70 MPa is selected, and the reference mix ratio of the high-performance and high-fluidity cement-based slurry is obtained. The concrete with super-high strength, super-high blast resistance, super-high toughness after cracking and durability is prepared.

[0066] (2) Construction of steel fiber space framework

[0067] The fiber is an end-hook type steel fiber, and the steel fiber space framework is pre-built within the supporting range. The construction of the steel fiber space framework includes formwork supporting and determination of the steel fiber space framework.

[0068] Formwork supporting: wood or steel plates are used to support the formwork according to the size requirements of the test piece.

[0069] Determination of the random steel fiber space framework, method 1: (1) use a conveyor belt or other mechanical equipment to preliminarily scatter the steel fibers, and preliminarily form the steel fiber framework; (2) vibrate the formwork together with the preliminarily formed steel fiber framework, and control the amount of steel fibers by controlling the vibration time;

[0070] Determination of random steel fiber space framework, method 2: (1) The steel fiber is magnetized in a single direction by a single electromagnetic field when it leaves the factory, so that the steel fiber leaves the factory with magnetism; (2) A horizontal and vertical plane electromagnetic field is constructed in the supporting range by an electromagnet group; (3) The steel fiber is thrown by mechanical equipment such as a conveyor belt, and the strength of the electromagnetic field is adjusted to make the steel fiber partially suspended, offsetting gravity, achieving random distribution of the steel fiber in space, and the dosage can be controlled by the strength of the magnetic field.

[0071] Determination of directional steel fiber space framework, method 1: A three-dimensional directional steel fiber cage is built by prefabrication;

[0072] Determination of directional steel fiber space framework, method 2: (1) The steel fiber is magnetized in a single direction by a single electromagnetic field when it leaves the factory, so that the steel fiber leaves the factory with magnetism; (2) A single-direction electromagnetic field is constructed in the supporting range by an electromagnet group; (3) The steel fiber is transported to the supporting range in a single layer by mechanical equipment such as a conveyor belt; (4) The strength of the electromagnetic field is adjusted to make the steel fiber unidirectional, achieving the construction of the directional steel fiber space framework in space.

[0073] (3) Pouring concrete

[0074] Step 1, weighing: weigh various raw materials according to the reference mix ratio;

[0075] Step 2, pre-construct steel fiber space framework;

[0076] Step 3, dry material mixing: wet the mixing pot with tap water, then add silica fume, cement, blast furnace slag, and quartz sand in proportion and mix for 5-10 minutes to get the initial mixture;

[0077] Step 4, weigh and mix water and water reducing agent uniformly for 1-2 minutes, then add the initial mixture obtained in step 3 and mix uniformly for 5-10 minutes;

[0078] Step 5, molding: after mixing step 4 uniformly, pour into the constructed steel fiber space framework, and gently vibrate after the slurry completely fills the framework;

[0079] (4) Curing

[0080] Step 1, remove the formwork after 1 day of natural curing;

[0081] Step 2, move the test block to natural conditions for curing until 28 days.

[0082] (5) Determination of mechanical properties

[0083] 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 of age.

[0084] Example 2

[0085] Experimental raw materials: P52.5 cement, silica fume, S95 blast furnace slag, polycarboxylate superplasticizer, 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.

[0086] ① Raw material mixing ratio

[0087] Cement: silica fume: mineral powder: quartz sand: water: superplasticizer: steel fiber = 1:0.28:0.14:1.2:0.2:0.04:0.78 (mass ratio).

[0088] ② Preparation of test pieces

[0089] According to the mixing ratio in ①, directional fiber space skeleton and random fiber space skeleton are respectively used to prepare ultra-high strength and ultra-high toughness concrete test blocks;

[0090] Meanwhile, UHPC and ECC test blocks are prepared based on the mixing ratio in the existing process. The UHPC test block is configured according to the aforementioned raw material mixing ratio; the ECC test block adopts the aforementioned mixing ratio, and the fiber is PE fiber with a volume content of 2%, and the mass ratio of the remaining cement, silica fume, mineral powder, quartz sand, water and superplasticizer is the same as that of the ultra-high strength and ultra-high toughness concrete. The test blocks poured are removed from the mold after 1 day of curing under natural conditions.

[0091] ③ Test piece curing

[0092] The test pieces are moved to the natural conditions for curing for 28 days.

[0093] ④ Test piece mechanical property test

[0094] The compressive and flexural strength tests of UHPC, ECC and ultra-high strength and ultra-high toughness concrete are carried out after curing to the specified age. The test results of the mechanical properties of UHPC, ECC and ultra-high strength and ultra-high toughness concrete are compared as shown in Figure 1 and Figure 2 .

[0095] Through the comparison of the above results, it can be found that compared with UHPC and ECC, the ultra-high strength and ultra-high toughness concrete has certain improvement in compressive strength, which is 1.5 times and 2.8 times respectively; compared with UHPC and ECC, the ultra-high strength and ultra-high toughness concrete has certain improvement in compressive toughness, which is 12.3 times and 135.1 times respectively; compared with UHPC and ECC, the ultra-high strength and ultra-high toughness concrete has certain improvement in flexural strength, which is 2.3 times and 4.1 times respectively; compared with UHPC and ECC, the ultra-high strength and ultra-high toughness concrete has certain improvement in flexural toughness, which is 7.8 times and 2.2 times respectively.

[0096] The application is applicable to the prior art where not otherwise indicated.

Claims

1. A method for producing an ultra-high strength and ultra-high toughness concrete, characterized by, The preparation method comprises the following steps: The mixing proportion of the concrete slurry is designed based on the close packing theory, and a slurry formula with a fluidity of not less than 180 mm and an initial strength of not less than 60 MPa is selected as a reference mixing proportion; The steel fiber space framework is built: the end-hook type steel fiber is selected, the formwork support is carried out according to the size requirement of the test piece by using the wood board or the steel plate, then the steel fiber cage is laid in the support range by using the end-hook type steel fiber, and the steel fibers are staggered in the support range to form the macroscopic steel fiber space framework; The steel fiber space framework is a random steel fiber space framework, and the structure of the random steel fiber space framework is constructed by electromagnetic field regulation and control: the steel fiber is unidirectionally magnetized by the unidirectional electromagnetic field when the steel fiber is factory-delivered, so that the steel fiber is factory-delivered with magnetism; the horizontal and vertical plane electromagnetic field is constructed in the support range by using the electromagnet group; then the steel fiber is scattered by using the mechanical equipment, the strength of the electromagnetic field is adjusted to make the steel fiber reach the partial suspended state, the gravity is offset, the random distribution of the steel fiber in the space is realized, and the content is controlled by the strength of the electromagnetic field; The concrete is infiltrated: the slurry is prepared according to the reference mixing proportion, then the slurry is infiltrated into the built steel fiber space framework, and the slurry is vibrated after the slurry fully infiltrates the steel fiber space framework; Then the curing and form removal are carried out to obtain the super-high-strength and super-high-toughness concrete; The static and dynamic mechanical properties of the super-high-strength and super-high-toughness concrete at the ages of 7 days, 14 days and 28 days are measured; The slurry does not contain coarse aggregate, and the maximum particle size of the raw material is not more than 40 mesh. The ultimate compressive strength of the ultra-high strength and ultra-high toughness concrete is 200-400 MPa, the bending strength is 50-100 MPa, the ultimate tensile strain is greater than or equal to 3%, and the toughness is 5*10 3 ~5*10 4 N / m; in the process of infiltration, the slurry ensures infiltration within the supporting range, and forms the concrete with excellent overall performance.

2. An ultra-high strength and ultra-high toughness concrete, obtained by the method according to claim 1, characterized in that, The super-high-strength and super-high-toughness concrete uses the high-performance and high-fluidity cement-based slurry or the high-performance and high-fluidity polymer-based slurry as the infiltrated material, comprises a fiber space framework, and the infiltrated material is infiltrated in the fiber space framework; the fiber is a fiber that can build a space framework and can be used with the infiltrated material.

3. The ultra-high strength, ultra-high ductility concrete according to claim 2, wherein, The high-performance and high-fluidity cement-based slurry is composed of cementitious materials, fine aggregates, water and water reducing agents, and the cementitious materials include cement, silica fume and blast furnace slag.

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