CN108249854B - Fiber-reinforced cement-based ultra-high ductility concrete mixed with seawater and its preparation - Google Patents

Abstract

The invention relates to seawater-stirred fiber-reinforced cement-based ultra-high-ductility concrete and a preparation method thereof, wherein the ultra-high-ductility concrete is prepared by the following method: (1) adding the cement, the sand and the fly ash into a stirrer according to the formula, stirring the dry powder for 2-3min, and fully and uniformly mixing; (2) continuously adding the water reducing agent and the seawater, and stirring the slurry for 1-2 min; (3) then adding a thickening agent and polyethylene fibers, and fully stirring for 2-3 min; (4) and after stirring, transferring to a mold, vibrating for 1-2min for molding, maintaining, and demolding to obtain the target product. Compared with the prior art, the ultra-high ductility concrete has strong tensile strength and ductility, good micro-crack distribution performance and energy consumption performance, no obvious difference in mechanical properties compared with the ultra-high performance concrete prepared by fresh water, capability of realizing the construction of a concrete structure without reinforcing steel bars, and suitability for the fields of island construction and the like.

Description

Fiber-reinforced cement-based ultra-high ductility concrete mixed with seawater and its preparation

technical field

The invention relates to the technical field of building materials, in particular to a seawater-stirred fiber-reinforced cement-based ultra-high ductility concrete and its preparation.

Background technique

In the next few decades, my country is bound to build a large number of infrastructures such as civil and military terminals, offshore airports, offshore wind power stations, offshore lighthouses and radar stations, island and reef border fortifications, and the demand for concrete is huge. If traditional reinforced concrete is used for island reef construction, a large amount of cement, fresh water and sand and gravel need to be transported from inland areas, which will not only affect the construction period, but also greatly increase the construction cost. In fact, islands and coastal areas are rich in seawater and sea sand resources. If seawater and sea sand can be used to configure concrete, it will greatly reduce the construction cost of islands and reefs and improve construction efficiency. However, the use of seawater and sea sand to prepare concrete brings durability problems. The main reason is that seawater and sea sand contain a large amount of sodium chloride and various inorganic salts. The presence of these salts can cause severe steel corrosion, resulting in a reduction in the service life of concrete.

With the introduction of chopped fiber reinforcement technology, concrete gradually overcomes the shortcomings of poor tensile properties and insufficient ductility. According to reports, the tensile ductility of steel fiber reinforced concrete is 0.5% to 1.0%, and the axial tensile strength is between 3MPa and 15MPa; the tensile strength of the specially designed polyvinyl alcohol fiber reinforced cement-based composite (PVA-ECC) It is about 3MPa to 7MPa, and the ultimate tensile strain is about 2% to 4%. Therefore, if seawater can be used to prepare a steel-free UHDCC structure, the problem of steel corrosion (concrete carbonization, chloride ion erosion, etc.) that has plagued the engineering community for many years will be cured.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a seawater-stirred fiber-reinforced cement-based ultra-high ductility concrete and its preparation in order to overcome the above-mentioned defects in the prior art. With good crack control ability, energy dissipation ability and durability, it is a building material that can be used for non-reinforced construction, so the corrosion problem of steel reinforcement in seawater environment can be effectively avoided. This product is designed to solve the technical problems of high brittleness of existing cement-based materials, poor crack control ability and poor durability of steel bar corrosion in seawater environment.

The object of the present invention can be realized through the following technical solutions:

A fiber-reinforced cement-based ultra-high ductility concrete stirred by seawater, comprising the following components by weight: 900-950 parts of cement, 400-450 parts of sand, 400-450 parts of fly ash, and 2.5-4.5 parts of water reducing agent , 0.5-1.5 parts of thickener, 300-350 parts of sea water, 10-20 parts of polyethylene fiber.

Preferably, the cement is composite Portland cement or ordinary Portland cement, and its 28-day compressive strength is greater than or equal to 52.5 MPa, its 28-day flexural strength is greater than or equal to 7.0 MPa, and its specific surface area is greater than or equal to 300 m ² /kg. Limiting the amount of cement is mainly due to the consideration of the strength of the ultra-high ductility concrete material. Beyond the limited range, it will have a certain impact on the strength of the ultra-high ductility concrete material.

Preferably, the sand is ultra-fine sand, the size of which is 70 mesh to 110 mesh, and the maximum particle size does not exceed 0.25mm. The limited amount of sand is mainly due to the strength of ultra-high ductility concrete materials, beyond the limited range, it will have a certain impact on the strength of ultra-high ductility concrete materials.

Preferably, the fly ash is first-grade fly ash with a specific surface area of ≥700 m ² /kg and a density of 2.6 g/cm ³ . Limiting the amount of fly ash is mainly due to the consideration of the strength of ultra-high ductility concrete materials. Beyond the limited range, it will have a certain impact on the strength of ultra-high ductility concrete materials.

Preferably, the seawater is ordinary coastal seawater, its Cl ^- content is 10000-20000 mg/L, and the salinity is 20-30‰. The limited amount of seawater is mainly due to the consideration of the strength of the ultra-high ductility concrete material and the preparation process. Beyond the limited range, it will have a certain impact on the strength of the ultra-high ductility concrete material. Too much seawater reduces the strength of the material, and too little seawater. Do not stir.

Preferably, the polyethylene fiber has a diameter of 30-45 μm, a length of 8-12 mm, an aspect ratio of >200, an elongation at break of 2-3%, and a tensile strength of 2000-4000 MPa. Limiting the amount of polyethylene fiber is mainly due to the strength and ductility of the ultra-high ductility concrete material and the preparation process. Beyond the limited range, it will have a certain impact on the strength and ductility of the ultra-high ductility concrete material. Too much is not easy. Mixing, too little will reduce the strengthening effect of the cement base, which will reduce the strength and ductility of the material.

Preferably, the water-reducing agent is a general-purpose polycarboxylate water-reducing agent, the solid content of which is 40-50%, and the water-reducing rate is greater than or equal to 40%. The limited amount of water reducing agent is mainly due to the consideration of the preparation process of ultra-high ductility concrete materials. Beyond the limited range, it will have a certain impact on the preparation of ultra-high ductility concrete materials. Too much will make the slurry too thin. Too little will make the slurry too thick, which is not conducive to the dispersion of fibers.

Preferably, the thickener is a common starch ether thickener. Limiting the amount of thickener is mainly due to the consideration of the preparation process of ultra-high ductility concrete materials. Beyond the limited range, it will have a certain impact on the fluidity of ultra-high ductility concrete materials.

The preparation method of the fiber-reinforced cement-based ultra-high ductility concrete stirred by sea water comprises the following steps:

(1) Add cement, sand and fly ash into the mixer according to the formula, mix dry powder for 2-3min, and mix well;

(2) Continue to add water reducing agent and seawater, and stir the slurry for 1-2min;

(3) then add thickener and polyethylene fiber, fully stir for 2-3min;

(4) After the stirring, transfer to the mold, vibrate for 1-2 minutes to form, maintain, and demould to obtain the target product.

Preferably, the curing temperature in step (4) is 20-25° C., the humidity is 85-95%, and the curing is performed to a predetermined age.

The working principle of the fibers added in the present invention is mainly the interaction with the microcracks. The interaction between fibers and microcracks is complex, especially when the fibers pass through the cracks at an oblique angle, which is common due to the random arrangement of fibers in the mortar matrix. However, the most important and fundamental interactions supporting the stress-crack response arise from the disengagement and sliding of each individual fiber as it cracks. If the fibers don't have any slippage, they will break, not connecting the two sides of the crack. However, if the sliding is too large and the connection with the composite material is lost, the micro-cracks lose their planar crack shape and become macro-cracks.

In ultra-high ductile concrete, slip is not just a simple friction process, but also includes a slip-hardening response, meaning that during slip, the sliding resistance of the interface between the fibers and the surrounding mortar increases. The slip-hardening response of this fiber-matrix interface determines the specific stress-crack relationship of the composite at the mesoscopic level at the level of a single fiber, so it must be strictly controlled. Therefore, the nonlinear slip-hardening response is the result of careful design such that the fibers slip out of the matrix material and fail. During sliding, the fiber surface is "stripped" by rough matrix channels, with the deepest fiber ends experiencing the greatest damage due to the longest sliding distance. This debonding results in a "swell" effect on the remaining tethered fibers, making them tighter with the matrix channel, requiring greater force to pull out.

Different from the PVA fibers used by general researchers, the present invention uses polyethylene fibers. Compared with PVA fibers, PE fibers have higher strength and elastic modulus. More importantly, unlike the hydrophilicity of PVA, PE fibers are hydrophobic, which can reduce the chemical bonding force between the fibers and the matrix, and the fibers are not easy to break during the pull-out process. At the same time, polyethylene fibers play the role of toughening the concrete matrix in the present invention, so that the concrete can produce continuous fine and dense cracks. Fiber diameter, aspect ratio, breaking strength and breaking elongation are affected by fiber manufacturers on the one hand. On the other hand, it is obtained from theoretical calculation and experimental deployment. If the length-diameter ratio of the fiber is too large, it is easy to cause the fiber to break. fine cracks.

Through theoretical calculation based on the initial cracking strength criterion and the steady-state cracking criterion, the two strain hardening indexes PSH (J′ _b /J _ti p and σ _cu /σ _fc ) should be greater than 3 and 1.2, respectively, to ensure that the seawater-mixed cement-based concrete is The material can obtain good steady-state multi-crack development by incorporating polyethylene fibers with a volume fraction of about 2%, achieve strain strengthening, and greatly improve the ultimate tensile strength and tensile strength. It combines mechanical properties such as compressive strength, tensile strength, and tensile strength with working properties such as setting time and fluidity. When the early tensile strength, tensile ductility, compressive strength and late strength are significantly improved, sufficient setting time and fluidity are also guaranteed.

Compared with the prior art, the present invention has the following advantages:

(1) It maintains ultra-high axial tensile ductility while achieving high tensile strength. When the age is 28d, the tensile strength exceeds 8MPa, and the axial tensile elongation exceeds 6%, which is 10% of the existing UHPC materials. times higher than the elongation, close to the ductility of steel.

(2) It has good micro-crack distribution performance and good energy dissipation performance.

(3) The preparation method is simple, the source of raw materials is wide, the economic cost is low, and it is suitable for large-scale industrial construction applications, and seawater is used as stirring water, which is environmentally friendly and green.

Description of drawings

FIG. 1 is a uniaxial tensile stress-strain diagram of the ultra-high ductility concrete of the present invention.

Detailed ways

A fiber-reinforced cement-based ultra-high ductility concrete stirred by seawater, comprising the following components by weight: 900-950 parts of cement, 400-450 parts of sand, 400-450 parts of fly ash, and 2.5-4.5 parts of water reducing agent , 0.5-1.5 parts of thickener, 300-350 parts of sea water, 10-20 parts of polyethylene fiber.

As a preferred embodiment of the present invention, the cement is composite Portland cement or ordinary Portland cement, and its 28-day compressive strength is greater than or equal to 52.5 MPa, its 28-day flexural strength is greater than or equal to 7.0 MPa, and its specific surface area is greater than or equal to 52.5 MPa. 300m ² /kg. Limiting the amount of cement is mainly due to the consideration of the strength of the ultra-high ductility concrete material. Beyond the limited range, it will have a certain impact on the strength of the ultra-high ductility concrete material.

As a preferred embodiment of the present invention, the sand is ultra-fine sand, the specification of which is 70 mesh to 110 mesh, and the maximum particle size does not exceed 0.25mm. The limited amount of sand is mainly due to the strength of ultra-high ductility concrete materials, beyond the limited range, it will have a certain impact on the strength of ultra-high ductility concrete materials.

As a preferred embodiment of the present invention, the fly ash is first-grade fly ash with a specific surface area of ≥700 m ² /kg and a density of 2.6 g/cm ³ . Limiting the amount of fly ash is mainly due to the consideration of the strength of ultra-high ductility concrete materials. Beyond the limited range, it will have a certain impact on the strength of ultra-high ductility concrete materials.

As a preferred embodiment of the present invention, the seawater is ordinary coastal seawater, its Cl ^- content is 10000-20000 mg/L, and the salinity is 20-30‰. The limited amount of seawater is mainly due to the consideration of the strength of the ultra-high ductility concrete material and the preparation process. Beyond the limited range, it will have a certain impact on the strength of the ultra-high ductility concrete material. Too much seawater reduces the strength of the material, and too little seawater. Do not stir.

As a preferred embodiment of the present invention, the polyethylene fiber has a diameter of 30-45 μm, a length of 8-12 mm, an aspect ratio of >200, an elongation at break of 2-3%, and a tensile strength of 2000 -4000MPa. Limiting the amount of polyethylene fiber is mainly due to the strength and ductility of the ultra-high ductility concrete material and the preparation process. Beyond the limited range, it will have a certain impact on the strength and ductility of the ultra-high ductility concrete material. Too much is not easy. Mixing, too little will reduce the strengthening effect of the cement base, which will reduce the strength and ductility of the material.

As a preferred embodiment of the present invention, the water-reducing agent is a general-purpose polycarboxylate water-reducing agent, the solid content of which is 40-50%, and the water-reducing rate is greater than or equal to 40%. The limited amount of water reducing agent is mainly due to the consideration of the preparation process of ultra-high ductility concrete materials. Beyond the limited range, it will have a certain impact on the preparation of ultra-high ductility concrete materials. Too much will make the slurry too thin. Too little will make the slurry too thick, which is not conducive to the dispersion of fibers.

As a preferred embodiment of the present invention, the thickener is a common starch ether thickener. Limiting the amount of thickener is mainly due to the consideration of the preparation process of ultra-high ductility concrete materials. Beyond the limited range, it will have a certain impact on the fluidity of ultra-high ductility concrete materials.

The preparation method of the fiber-reinforced cement-based ultra-high ductility concrete stirred by sea water comprises the following steps:

(1) Add cement, sand and fly ash into the mixer according to the formula, mix dry powder for 2-3min, and mix well;

(2) Continue to add water reducing agent and seawater, and stir the slurry for 1-2min;

(3) then add thickener and polyethylene fiber, fully stir for 2-3min;

(4) After the stirring, transfer to the mold, vibrate for 1-2 minutes to form, maintain, and demould to obtain the target product.

As a preferred embodiment of the present invention, the curing temperature in step (4) is 20-25° C., the humidity is 85-95%, and the curing is performed to a predetermined age.

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

Unless otherwise specified, the materials used in the following examples are all commercially available chemical raw materials that are commonly used in the field.

Example 1

The raw materials of the seawater-stirred fiber-reinforced cement-based ultra-high ductility concrete prepared in this example are: P.O.52.5 ordinary Portland cement, first-class fly ash, sand, water reducing agent, thickener, seawater and polyethylene fibers , among which, the polyethylene fiber length in Table 1 is 12mm, and the aspect ratio is 400. The specific formula is shown in Table 1, and each part in the table is the content by weight.

Table 1 embodiment 1 product formula

label cement sand fly ash thickener water reducer water polyethylene fiber 1 930 400 400 1 4 330.0 20

The specific preparation process is as follows:

(1) Add cement, sand and fly ash into the mixer, mix dry powder for 2-3min, and mix well;

(2) Add the water reducing agent and seawater into the mixer, stir the slurry for 1-2min, and fully stir it evenly;

(3) Add thickener and polyethylene fiber, and fully stir for 2-3min;

(4) After the stirring, transfer to the mold, vibrate for 1-2 minutes to form, carry out maintenance, and maintain to the specified age to release the mold to obtain the product.

The mechanical properties of the obtained products are shown in Table 2.

Table 2 Example 1 product mechanical properties test test results

age Ultimate tensile strength MPa Tensile strain % 28d 8.88 6.14

Figure 1 is an example of a uniaxial tensile stress-strain diagram at an age of 28 days; it can be seen from the figure that the reading of the force sensor increases rapidly after the start of loading, while the reading of the extensometer increases slowly. When the load reaches about 1kN to 1.5kN, the first crack appears on the specimen, and the load decreases slightly. At this time, the bridging fibers at the crack begin to play their role, which improves the bearing capacity of the section and makes the crack width gradually tend to Stablize. With the increase of the load, fine cracks gradually appeared on the surface of the specimen, and the load-displacement curve continued to rise in fluctuations. When the ultimate stress is reached, the cracks are controlled to appear and reach the limit of the bridging force of the section. The width of the cracks begins to gradually increase, and the bearing capacity of the specimen slowly decreases. At this stage, the sound of fibers being pulled can be heard. In the end, the specimen was completely pulled off and completely destroyed, but this process also happened slowly, and no sudden breaking occurred.

Example 2-5

Compared with Example 1, most of them are the same, except that the product formula is adjusted accordingly:

The product formula of table 3 embodiment 2-embodiment 5

label cement sand fly ash thickener water reducer seawater polyethylene fiber Example 2 900 420 420 0.5 2.5 300 10 Example 3 950 450 450 1.5 4.5 350 15 Example 4 910 430 430 1.2 3 310 11 Example 5 920 440 410 0.8 3.5 340 18

Comparative Examples 1-3

Compared with Example 1, most of them are the same, except that its product formula is adjusted accordingly:

Table 4 Product formulations of Comparative Examples 1-3

label cement sand fly ash thickener water reducer seawater polyethylene fiber Comparative Example 1 930 400 400 1 4 330.0 0 Comparative Example 2 930 400 400 1 4 330.0 5 Comparative Example 3 930 400 400 1 4 330.0 35

According to the above formula, the preparation method in Example 1 is used to make a product, and the results of its mechanical properties are shown in Table 4 below.

Table 5 Test results of mechanical properties of products in Comparative Examples 1-3

Numbering age Ultimate tensile strength MPa Tensile strain % Comparative Example 1 28d 1.5 0.04 Comparative Example 2 28d 2.5 3.5 Comparative Example 3 28d -(Cannot stir) -

The foregoing description of the embodiments is provided to facilitate understanding and use of the invention by those of ordinary skill in the art. It will be apparent to those skilled in the art that various modifications to these embodiments can be readily made, and the generic principles described herein can be applied to other embodiments without inventive step. Therefore, the present invention is not limited to the above-mentioned embodiments, and improvements and modifications made by those skilled in the art according to the disclosure of the present invention without departing from the scope of the present invention should all fall within the protection scope of the present invention.

Claims (5)

1. a fiber-reinforced cement-based ultra-high ductility concrete stirred by seawater, is characterized in that, comprises the component of following parts by weight: 900-950 parts of cement, 400-450 parts of sand, 400-450 parts of fly ash, 2.5-4.5 parts of water agent, 0.5-1.5 parts of thickener, 300-350 parts of sea water, 10-20 parts of polyethylene fiber; The diameter of the polyethylene fiber is 30-45μm, the length is 8-12mm, the aspect ratio is >200, the elongation at break is 2-3%, and the tensile strength is 2000-4000MPa; The cement is composite Portland cement or ordinary Portland cement, and its 28-day compressive strength is greater than or equal to 52.5 MPa, its 28-day flexural strength is greater than or equal to 7.0 MPa, and its specific surface area is greater than or equal to 300 m ² /kg; The sand is ultra-fine sand, its specification is 70 mesh-110 mesh, and the maximum particle size does not exceed 0.25mm; The fly ash is first-grade fly ash, its specific surface area is ≥700m ² /kg, and the density is 2.6g/cm ³ ; The water-reducing agent is a general-purpose polycarboxylate water-reducing agent, the solid content of which is 40-50%, and the water-reducing rate is greater than or equal to 40%. 2. the fiber-reinforced cement-based ultra-high ductility concrete of a kind of seawater stirring according to claim 1, is characterized in that, described seawater is common coastal seawater, and its Cl ^- content is 10000～20000mg/L, salinity 20-30‰. 3. The fiber-reinforced cement-based ultra-high ductility concrete stirred by seawater according to claim 1, wherein the thickener is a common starch ether thickener. 4. the preparation method of the fiber-reinforced cement-based ultra-high ductility concrete stirred by seawater as described in any one of claims 1-3, is characterized in that, comprises the following steps: (1) Add cement, sand and fly ash into the mixer according to the formula, mix dry powder for 2-3min, and mix well; (2) Continue to add water reducing agent and seawater, and stir the slurry for 1-2min; (3) then add thickener and polyethylene fiber, fully stir for 2-3min; (4) After the stirring, transfer to the mold, vibrate for 1-2 minutes to form, maintain, and demould to obtain the target product. 5. the preparation method of the fiber-reinforced cement-based ultra-high ductility concrete stirred by seawater according to claim 4, is characterized in that, the temperature of curing in step (4) is 20-25 ℃, and humidity is 85-95%, and curing to a predetermined age.

Images