CN110304883A - A kind of virgin fiber cement-based composite material and preparation method thereof - Google Patents

Abstract

The invention discloses a virgin fiber cement-based composite material and a preparation method thereof, and relates to the field of building materials. The primary fiber cement-based composite material is composed of water 280-300kg/m ³ , cement 310-330kg/m ³ , fine sand 680-700kg/m ³ , fly ash 680-700kg/m ³ , primary fiber 24-28kg/ m ³ , water reducing agent 10-15kg/m ³ , adhesive 0.15-0.18kg/m ³ . The invention adopts the native fiber to replace the PVA fiber in the traditional engineering cement-based composite material, which can greatly reduce the production cost of the cement-based composite material, and the compressive and tensile strengths of the obtained native fiber cement-based composite material reach 40-50Mpa, 4 ‑5Mpa, and has the characteristics of strain-hardening performance, super toughness, and multi-crack cracking, which can meet the requirements of specific engineering applications.

Description

A kind of virgin fiber cement-based composite material and preparation method thereof

technical field

The invention belongs to the technical field of building materials, and in particular relates to a virgin fiber cement-based composite material and a preparation method thereof.

Background technique

Concrete is the most widely used building material in modern social engineering construction. Although concrete has a series of advantages such as high compressive strength, simple material acquisition, low cost, and wide application range, its shortcomings such as low tensile strength, easy cracking and high brittleness cannot be ignored. Studies have shown that the tensile-compression ratio of concrete is only 1/10-1/7, and the ultimate elongation under tension is only 0.01%-0.06%, so it shows obvious brittle characteristics when it fails. The cracking of concrete will lead to the intrusion of harmful media in the external environment, resulting in a series of problems such as the decline of structural bearing capacity and the aging of internal materials, which will eventually lead to the degradation of mechanical properties of components or structures and the failure of durability, which seriously reduces the service life of concrete structures.

At present, the economies of various countries in the world are developing rapidly, and the economic losses caused by the destruction of concrete structures and the corrosion of internal steel bars in developed countries every year have become an unbearable burden for the government, and my country is no exception. According to the American Society of Civil Engineers (ASCE) report, the annual expenditure on bridge repair alone in the United States has increased to 9 billion US dollars, and the indirect economic loss caused by this has exceeded 54 billion US dollars. In addition, the 11 reinforced concrete viaducts on the British island of England, from the original construction to 1989, cost up to 4,500 pounds just for their maintenance, which is 1.6 times the cost, and it is estimated that they will still consume a lot in the future. costs for maintenance. In Japan and South Korea, annual building maintenance and repair costs will soon exceed investment in new construction. The above all reflect that the economic losses caused by the durability of concrete are far beyond people's expectations. In recent years, my country has carried out large-scale infrastructure construction, and built a large number of concrete structures such as residential buildings, shopping malls, ports, and highways. According to the engineering experience of some developed countries for many years, in the future, my country will enter a stage of rapid growth in building repair and even demolition and reconstruction, and the heavy maintenance and reconstruction work will consume huge manpower and material resources, which will be my country's national economic development. unprecedented challenges. Therefore, under the existing technical and economic level, in order to control the cracks of concrete to meet the functional requirements of the components and related standards, and to ensure the concrete structure has good durability and reliability, the selection of good toughness, green environmental protection and good durability building materials are necessary.

The above shortcomings of concrete materials are essential and cannot be solved by the improvement of their own materials. Therefore, the "composite" technical idea is mainly used to improve and improve the performance of cement-based materials. According to this idea, the US National Materials Advisory Board (NMAB) proposed the concept of cement-based composite materials in 1980, which is a series of composite materials based on cement materials. When fiber is used as a reinforcing material, the concept of fiber-reinforced cement-based composite material is obtained, which uses cement paste, cement mortar or concrete as the base material, and uses discontinuous short fibers or continuous long fibers as reinforcements. assembled composite material. Fibers added to cement substrates can play three major roles: crack resistance, reinforcement, and toughening. At present, fiber-reinforced concrete (FRC) and high-performance fiber-reinforced concrete (HPFRC), which have been widely used, belong to this category. Traditional fiber reinforced concrete (FRC) such as steel fiber reinforced cement-based composite materials, carbon fiber reinforced cement-based composite materials and glass fiber reinforced cement-based composite materials are all composite materials composed of concrete as base material and fiber as reinforcement. Although the tensile strength, deformation capacity and dynamic load resistance performance of concrete can be greatly improved, and the strain-hardening characteristics can also be realized under tensile (bending) load, these materials require high fiber content and high processing and molding process requirements. , the construction cost is difficult to control, and the crack width is not easy to control under the load, and it often shows the characteristics of strain softening under the direct tensile load, while showing high toughness, often at the expense of wider harmful cracks. These greatly limit the popularization and application of FRC in engineering.

In order to further improve the toughness and crack resistance of concrete, the early high-performance fiber reinforced cement represented by reactive powder concrete (RPC), mortar mixed with steel fiber concrete (SIFCON), and mortar poured steel fiber mesh concrete (SIMCON) has appeared. Matrix Composite (HPFRCC). Different from traditional FRC, this material can show strain-hardening characteristics and multiple cracks that can be observed with the naked eye during the tensioning process, and has high toughness and strong energy absorption capacity. However, in the early stage of HPFRCC, high fiber content was required. High fiber content increased the project cost, and high fiber content led to difficult construction and production. These factors restricted the large-scale application of HPFRCC materials in engineering. To this end, some scholars have made improvements on the basis of traditional fiber reinforced concrete (FRC) and high-performance fiber-reinforced cementitious composites (HPFRCC). Preparation method" (CN109293303A), the concrete is composed of cement, silica fume, boron nitride powder, sand, polyvinyl alcohol fiber, crushed stone, fly ash, coal gangue powder, phosphorus slag powder, water reducing agent, dispersion activator, It is prepared from modified graphene oxide dispersion and water; at the same time, Yuan Hui of Fuzhou University proposed "a high-performance environmental protection concrete and its preparation method" (CN 108675748A), the concrete contains artificial aggregate, active powder, sulfuric acid Aluminum salt cement, natural sand, concentrated modified liquid of papermaking black liquor, modified lignin fiber, dicyclopentadiene modified unsaturated polyester, medical stone powder, potassium water glass, nanocomposite filler, _SiO2 aerogel, Water reducing agent, modified intercalating agent, flame retardant, sodium acetate and water. Compared with traditional cement-based composite materials, the maximum crack of this type of patent has been reduced, but due to the existence of crushed stone, the maximum crack width is still more than 500mm. The price of cellulose fibers is still high, which cannot effectively reduce the cost, and the amount of cement used is still high. In addition, the materials prepared by this type of patent still belong to the category of concrete, and concrete is a brittle material with poor toughness and high resistance. The tensile strength and bond strength are low, the elastic modulus is high and the deformation ability is poor.

It can be seen from the above that future materials must meet high safety, high durability, high environmental protection and good economy in order to be invincible in building structural materials. In order to overcome the brittleness and strain softening characteristics of concrete materials, people began to study cement-based materials with strain-hardening properties by means of micro and mesoscopic mechanics. The fiber-reinforced cement-based composite material with cracking characteristics meets the requirements of sustainable development society for high safety and high durability of infrastructure construction. ECC was first proposed by Professor Li from the University of Michigan in the early 1990s based on the basic principles of meso-mechanics and fracture mechanics. The basic design concept of this material. The ECC material uses cement, mineral aggregates and quartz sand with a particle size of not more than 150 μm as the matrix, without coarse aggregates, and uses short fibers as reinforcement materials. When the fiber volume permeability is not more than 2%, the ultimate tensile strain obtained by the direct tensile test can reach more than 3%, and many fine cracks with a width of less than 50 μm are formed during the stretching process. One of the main differences between ECC and traditional fiber reinforced concrete (FRC) and high-performance fiber-reinforced cementitious composites (HPFRCC) is that the components of the material are based on meso-mechanical design. Mortar is the matrix, so it belongs to the category of cement. At present, the fibers used in ECC at home and abroad are mainly concentrated in synthetic fibers such as polyvinyl alcohol (PVA) and polypropylene (PP). Adding synthetic fibers to ECC can overcome the shortcomings of traditional concrete materials such as easy cracking and high brittleness, and improve the durability of the structure. However, the production of this synthetic fiber will cause environmental pollution and high cost, which does not meet the sustainable development requirements of green energy saving. As a renewable organic fiber in nature, virgin fiber has the advantages of abundant resources and low price. Therefore, the selection of virgin fibers for reinforcing cement-based materials can significantly reduce energy consumption without affecting human health, which is an inevitable requirement for the sustainable development of modern society.

SUMMARY OF THE INVENTION

In view of the above problems, the present invention provides a virgin fiber cement-based composite material and a preparation method thereof. The cement-based composite material has high ductility, high crack resistance and high durability, and is suitable for ordinary high-performance concrete under complex environmental conditions. Design requirements of all kinds of engineering and construction.

To achieve the above object, the present invention adopts the following technical solutions:

A primary fiber cement-based composite material, the raw materials used and the amount thereof include: water 280-300kg/m ³ , cement 310-330kg/m ³ , fine sand 680-700kg/m ³ , fly ash 680-700kg/m ^3. Virgin fiber 24-28kg/m ³ , water reducing agent 10-15kg/m ³ , adhesive 0.15-0.18kg/m ³ .

Wherein, the cement is ordinary Portland cement with a strength of 42.5.

The gradation of the fine sand is as follows: a square hole sieve with a size of 1.18mm, the pass rate of fine sand is 100%; a square hole screen with a size of 0.6mm, the pass rate of fine sand is 44.6%; the square hole size of 0.3mm sieve, the pass rate of fine sand is 10.8%; for a square hole sieve with a size of 0.15mm, the pass rate of fine sand is 0%.

The fly ash is Class I fly ash, the 45μm sieve balance is not more than 12%, the water demand ratio is not more than 95%, and the main active chemical components are SiO ₂ and Al ₂ O ₃ , and the hydrogen produced by cement hydration. Alumina can react to form a cementitious product, which plays the role of densely filled concrete.

The diameter of the primary fiber is 30-40 μm, the length is 10-20 mm, the elastic modulus is 15-30 GPa, and the elongation is 6-8%, and it includes ramie fiber, flax fiber, sisal fiber, apocynum fiber, cotton Any one or more of the fibers.

The water reducing agent is a polycarboxylate water reducing agent, and its water reducing rate is more than 20%.

The binder is hydroxypropyl methyl cellulose, and its function is to improve the dispersibility of cement-sand, greatly improve the plasticity and water retention of mortar, and has the effect of preventing cracks and enhancing the strength of cement.

The preparation method of the virgin fiber cement-based composite material comprises the following steps:

Step 1: Put cement, fly ash and fine sand into the mixer in sequence, and pre-mix for 2 minutes;

Step 2: Then sprinkle the adhesive evenly while stirring, and stir for 5 minutes (the adhesive will swell into a gel in cold water. after adding water);

Step 3: Gradually add water and water reducer, stirring until a homogeneous mixture is produced;

Step 4: Gradually add virgin fibers and continue to mix for 3 minutes until the fibers are evenly dispersed;

Step 5: Pour the mixed mortar prepared in step 4 into the mold, vibrate, demould after 24 hours, and standardize for 28 days to obtain the virgin fiber cement-based composite material.

For the prior art, the advantages of the present invention are as follows:

First, in the proportion of the cement-based composite material, the original fiber is used to replace the steel fiber, PVA fiber, etc. to play a bridging role, which can greatly reduce the cost of the cement-based composite material;

Second, the virgin fiber cement-based composite material of the present invention exhibits the characteristics of multiple cracks. After the first crack of the material begins to occur, it will not gradually expand until it penetrates like ordinary concrete, but the number of cracks will continue to increase. The width does not increase, and the multi-point cracking crack width in the saturated state is less than 50 μm, and its excellent crack control ability is very beneficial to the requirements of concrete engineering for crack width control;

Third, the primary fiber cement-based composite material of the present invention has unique strain-hardening performance and super toughness, and its tensile strain value is greater than 3%, which significantly changes the brittleness characteristics of traditional cement concrete and can overcome many defects caused by material brittleness. ;

Fourth, the compressive strength of the cement-based composite material reaches 40-50Mpa, and the tensile strength reaches 4-5Mpa, and its mechanical properties are good and meet the requirements of specific engineering applications.

Description of drawings

FIG. 1 is a multi-slit cracking diagram presented by the virgin fiber cement-based composite material of the present invention.

Detailed ways

In order to make the content of the present invention easier to understand, the technical solutions of the present invention will be further described below with reference to specific embodiments, but the present invention is not limited thereto.

Example 1:

A virgin fiber cement-based composite material, its raw material formula is: water 280kg/m ³ , 42.5 grade ordinary Portland cement 310kg/m ³ , fine sand 680kg/m ³ , fly ash 680kg/m ³ , ramie fiber 24kg /m ³ , polycarboxylate water reducing agent 10kg/m ³ , binder hydroxypropyl methylcellulose 0.15kg/m ³ .

Example 2

A virgin fiber cement-based composite material, the raw material formula is: water 290kg/m ³ , 42.5 grade ordinary Portland cement 320kg/m ³ , fine sand 690kg/m ³ , fly ash 690kg/m ³ , flax fiber 26kg /m ³ , polycarboxylate water reducing agent 12kg/m ³ , binder hydroxypropyl methylcellulose 0.16kg/m ³ .

Example 3

A primary fiber cement-based composite material, the raw material formula is: water 280kg/m ³ , 42.5 grade ordinary Portland cement 310kg/m ³ , fine sand 680kg/m ³ , fly ash 700kg/m ³ , apocynum fiber 28kg/m ³ , polycarboxylate water reducer 15kg/m ³ , binder hydroxypropyl methylcellulose 0.18kg/m ³ .

The gradation of the fine sand used above is: a square hole sieve with a size of 1.18mm, the fine sand passing rate is 100%; a square hole sieve with a size of 0.6mm, the fine sand passing rate is 44.6%; the square hole size is 0.3mm. sieve, the pass rate of fine sand is 10.8%; for a square hole sieve with a size of 0.15mm, the pass rate of fine sand is 0%.

The fly ash used is grade I fly ash, the 45μm sieve balance is not more than 12%, the water demand ratio is not more than 95%, and the main active chemical components are SiO ₂ and Al ₂ O ₃ .

The diameter of the ramie fiber used is 30~40μm, the length is 10~20mm, the elastic modulus is 15~30GPa, and the elongation is 6~8%.

The water reducing rate of the polycarboxylate water reducing agent used is greater than 20%.

The preparation method of the virgin fiber cement-based composite material is as follows: sequentially putting cement, fly ash and fine sand into a mixer, pre-mixing for 2 minutes; then evenly adding the binder hydroxypropyl methylcellulose powder while stirring , and stir for 5 min; gradually add water and water reducing agent to the dry mixture, and stir until a homogeneous mixture is produced; gradually add virgin fibers and continue to mix for 3 min until the fibers are uniformly dispersed; pour the prepared mixed mortar into the mold, and vibrate tamping, demoulding after 24 hours, and standard curing for 28 days to obtain a virgin fiber cement-based composite material.

Comparative Example 1 ECC cement-based material

The same as the preparation method of the embodiment, the difference is that the raw material formula of the ECC cement-based material unit test piece is: water 280kg/m ³ ; 42.5 grade ordinary Portland cement 310kg/m ³ , fine sand 680kg/m ³ , Fly ash 680kg/m ³ , PVA fiber 24kg/m ³ , polycarboxylate water reducer 10kg/m ³ , binder hydroxypropyl methylcellulose 0.15kg/m ³ .

Among them, the diameter of the PVA fiber used is 39 μm, the length is 12 mm, the elastic modulus is not less than 42.8 GPa, and the elongation is not less than 6%.

Comparative example 2 C30 concrete unit specimen

The same as the preparation method of the embodiment, the difference is that the raw material formula of the common C30 concrete unit test piece is: water 200kg/m ³ ; 42.5 grade ordinary Portland cement 400kg/m ³ ; sand 630kg/m ³ ; stone 1280kg /m ³ ;

In order to verify the properties of the virgin fiber cement-based composite material prepared by the present invention, the performance test of the virgin fiber cement-based composite material obtained by the present invention is carried out.

(1) Cube compression test

The cube compression test uses a 70.7 × 70.7 mm × 70.7 mm test block. The test piece is demolded after 24 hours of molding, placed in a standard curing room for 28 days, and taken out to dry for 3 hours before the test to prepare for the test. Prepare 3 test blocks for each group of mix ratios to complete the compression test. The test indicators are elastic modulus and compressive strength.

(2) Uniaxial tensile test

The uniaxial tensile test uses a thickness × width × length = 50mm × 50mm × 190mm test block, the test piece is demolded after 24 hours , placed in a standard curing room for 28 days , and taken out to dry 3 hours before the test to prepare for the test. Four test blocks were prepared for each group of mix ratios to complete the tensile test. The test indicators are cracking strength, tensile strength, maximum tensile strain, elastic modulus and fracture energy.

The examples and ECC were tested under the same conditions as ordinary C30 concrete, and the results are shown in Table 1.

Table 1 Performance comparison table

It can be seen from Table 1 that although the strength of the native fiber cement-based composite material is lower than that of ECC, it is still greater than the compressive strength of ordinary C30 cement concrete. At the same time, the maximum tensile strain of the native fiber cement-based composite material reaches 4%. It is much higher than the maximum tensile strain of ordinary concrete, which basically meets the ductility requirements of most concrete buildings. In addition, the present invention uses virgin fibers to replace PVA fibers in traditional engineering cement-based composite materials (ECC), which can greatly reduce the production cost of cement-based composite materials, and is suitable for large-scale promotion and application in the construction field.

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims (8)

1. a primary fiber cement-based composite material, is characterized in that, raw material used and consumption thereof comprise: water 280-300kg/m ³ , cement 310-330kg/m ³ , fine sand 680-700kg/m ³ , fly ash 680-700kg/m ³ , virgin fiber 24-28kg/m ³ , water reducing agent 10-15kg/m ³ , adhesive 0.15-0.18kg/m ³ . 2 . The virgin fiber cement-based composite material according to claim 1 , wherein the cement is ordinary Portland cement with a strength of grade 42.5. 3 . 3. The primary fiber cement-based composite material according to claim 1, wherein the gradation of the fine sand is: a square-hole sieve with a size of 1.18mm, the fine sand passing rate is 100%; the size is 0.6mm The pass rate of fine sand is 44.6% for the square hole sieve with the size of 0.3mm; the pass rate for fine sand is 10.8% for the square hole sieve with the size of 0.3mm; 4 . The primary fiber cement-based composite material according to claim 1 , wherein the fly ash is grade I fly ash, and its 45 μm sieve balance is not more than 12%, and the water demand ratio is not more than 95%. 5 . 5. The primary fiber cement-based composite material according to claim 1, wherein the primary fiber has a diameter of 30 to 40 μm, a length of 10 to 20 mm, an elastic modulus of 15 to 30 GPa, and an elongation of 6 to 60 μm. 8%, which includes any one or more of ramie fiber, flax fiber, sisal fiber, apocynum fiber and cotton fiber. 6 . The virgin fiber cement-based composite material according to claim 1 , wherein the water-reducing agent is a polycarboxylate water-reducing agent, and its water-reducing rate is greater than 20%. 7 . 7. The virgin fiber cement-based composite material according to claim 1, wherein the binder is hydroxypropyl methylcellulose. 8. a preparation method of primary fiber cement-based composite material as described in any one of claims 1-7, is characterized in that, comprises the following steps: Step 1: Put cement, fly ash and fine sand into the mixer in sequence, and pre-mix for 2 minutes; Step 2: Then evenly sprinkle the adhesive while stirring, and stir for 5 minutes; Step 3: Gradually add water and water reducer, stirring until a homogeneous mixture is produced; Step 4: Gradually add virgin fibers and continue to mix for 3 minutes until the fibers are evenly dispersed; Step 5: Pour the mixed mortar prepared in step 4 into the mold, vibrate, demould after 24 hours, and standardize for 28 days to obtain the virgin fiber cement-based composite material.