A high-durability low-carbon fiber concrete and its preparation method

Abstract

The invention discloses a high-durability low-carbon fiber concrete, which is composed of the following raw materials in parts by mass: 260-500 parts of low-carbon cement, 900-1100 parts of coarse aggregate, 500-900 parts of fine aggregate, 20-40 parts of modified coated fibers, 150-180 parts of water, and 5-10 parts of admixtures; the modified coated fibers are selected from plant fibers and steel fibers, and have a length of 2-3 cm and a diameter of 10-20 μm; the coating thickness is 0.5-1 mm; and the preparation method comprises the following steps: removing moisture from the fibers; applying a reinforcing primer on the fiber surface; and spraying a single-component heat-curing adhesive on the primer surface; the low-carbon cement of the invention obtains strength and performance through carbonization curing, and simultaneously utilizes the exothermic characteristic of the carbonization reaction to cure the coating on the modified fibers. The obtained coating can prevent the fibers from being eroded by CO2 diffusion, improve the corrosion resistance of the fibers, and strengthen the bonding force of the internal structure of the concrete, thereby improving the mechanical properties and durability of the fiber concrete.

Description

Technical Field

[0001] The invention belongs to the technical field of building materials, and particularly relates to a high-durability low-carbon fiber concrete and a preparation method thereof. Background Art

[0002] Fiber concrete is usually a cement-based composite material composed of cement paste, mortar or concrete as the base material and discontinuous short fibers or continuous long fibers as the reinforcing material; the fibers can improve the tensile strength, impact resistance, and impermeability of concrete.

[0003] Traditional fiber concrete uses raw materials including cement and fiber. Traditional cement is a material with high energy consumption and high CO2 emissions. The plant fiber and steel fiber in the fiber are affected by the material properties and application environment. In humid and corrosive environments, they are easily corroded, leading to the failure of the concrete structure and causing huge economic losses.

[0004] Patent CN114620973A discloses a fiber concrete and a preparation method thereof. The method mainly modifies plant fibers. The types of modified fibers are relatively single, and the modification process of the plant fibers is relatively complicated. The preparation requirements are relatively high and the difficulty is great.

[0005] In addition, low-carbon concrete can only obtain mechanical and other properties after a carbonization curing process, and CO2 diffusion during the carbonization curing process will accelerate the erosion of fibers. Summary of the Invention

[0006] The purpose of the present invention is to provide a high-durability low-carbon fiber concrete and a preparation method thereof. The low-carbon cement obtains strength and performance through carbonization curing, and at the same time utilizes the exothermic characteristics of its carbonization reaction to cure the coating on the modified fiber. The obtained coating can avoid the erosion of CO2 diffusion on the fiber, and while improving the corrosion resistance of the fiber, it can also strengthen the bonding force of the internal structure of the concrete, thereby improving the mechanical properties and durability of the fiber concrete.

[0007] In order to achieve the above purpose, the technical solutions adopted are as follows:

[0008] A high-durability low-carbon fiber concrete, composed of the following raw materials in parts by mass:

[0009] 260-500 parts of low carbon cement, 900-1100 parts of coarse aggregate, 500-900 parts of fine aggregate, 20-40 parts of modified coated fiber, 150-180 parts of water, and 5-10 parts of admixture.

[0010] According to the above scheme, the modified coating fiber is one of plant fiber and steel fiber, with a length of 2-3 cm and a diameter of 10-20 μm; the coating thickness is 0.5-1 mm.

[0011] According to the above scheme, the preparation method of the modified coated fiber includes the following steps:

[0012] (1) Remove moisture from the fiber;

[0013] (2) Apply reinforcing primer to the fiber surface;

[0014] (3) spraying a single-component heat-curing adhesive on the surface of the primer.

[0015] According to the above scheme, the composition of the enhanced primer is as follows in percentage by mass:

[0016] Sodium methyl silicate 1-5%; sodium silicate 40-60%; the balance is water.

[0017] According to the above scheme, the composition of the one-component heat-curing adhesive includes, by mass:

[0018] 80-100 parts of bisphenol S epoxy resin, 15-20 parts of triethylene glycol amine; 10-20 parts of polythiol; 8-12 parts of dibutyl phthalate, 5-10 parts of nano-TiO2, and 90-150 parts of glass microspheres.

[0019] According to the above scheme, in step (3), the single-component heat-curing adhesive is sprayed twice, and the time interval between the two times is 2 to 5 hours.

[0020] According to the above scheme, the polythiol is prepared by chain extension reaction of dipentaerythritol hexa(3-mercaptopropionate) ester and triethylene glycol diglycidyl ether in a molar ratio of 1:(1.1-1.3) as raw materials, triethylamine as catalyst, and reaction at 80-90°C for 8-12h.

[0021] According to the above scheme, the particle size of the nano-TiO2 is 20 to 30 nm.

[0022] According to the above solution, the calcium-silicon ratio of the low carbon cement is 1.4-2.0.

[0023] The method for preparing the above-mentioned high-durability low-carbon fiber concrete comprises the following steps:

[0024] 1) Premix the coarse and fine aggregates, then add low carbon cement and mix evenly;

[0025] 2) adding the modified coated fiber, water and admixtures and mixing evenly to obtain a concrete mixture, which is then poured into a mold for casting;

[0026] 3) The obtained molded product is placed in a CO2 curing environment for carbonization curing.

[0027] According to the above scheme, the carbonization maintenance system is:

[0028] CO2 concentration is 20-100 vol%, curing temperature is 40-80°C, curing pressure is 0.1-1.0 MPa, and curing time is 6-24 hours.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The mineral components of carbonized cement have the characteristics of high carbonization and low hydration activity. Only after the carbonization curing process can mechanical and other properties be obtained. Carbonation reaction is an exothermic reaction. Therefore, after carbonization curing, the temperature inside the concrete of concrete products prepared with low-carbon cement will increase. In the single-component heat-curing adhesive of the present invention, the main resin is bisphenol S type epoxy resin, the curing agent is polythiol, and the accelerator is triethylene glycol amine, which catalyzes the polythiol curing agent; the plasticizer is dibutyl phthalate, and the filler is glass microbeads; according to the principle of "like dissolves like", nano-TiO2 does not need hydrophobic modification and can be directly incorporated into the adhesive. Nano-TiO2 can enter the interior of the concrete and fill the internal voids, making the connection between the fiber and the concrete stone structure denser, reducing the penetration and erosion of external moisture and CO2 when the concrete is used.

[0031] The single-component heat-curing adhesive of this invention is a viscous liquid at room temperature and slowly solidifies at temperatures between 65 and 80 degrees Celsius. The cured adhesive forms a protective layer around the fibers, enhancing their corrosion resistance. It also strengthens the connection between the fibers and the concrete substrate, increasing the concrete's internal stability and density, and improving its overall performance.

[0032] The sodium silicate in the reinforcing primer reacts with the water and calcium hydroxide in the concrete to produce silicate gel, which fills the gaps in the contact layer between the fiber and the concrete and increases the strength of the concrete. During the carbonization curing process, the diffusion of CO2 will accelerate the erosion of the fiber. The interior of the carbonized product is low in alkalinity. Sodium methyl silicate is a hydrophobic surfactant that can form a film on the surface to prevent the water dissolved in CO2 from eroding the fiber.

[0033] The fiber of the present invention can be used as a reinforcing material to improve the tensile strength, impact resistance and toughness of concrete products, reduce the demoulding breakage rate during the preparation of low-carbon concrete, and have significant economic benefits for the industrial preparation of low-carbon concrete products. The carbonization exothermic effect of low-carbon cement and the characteristics of carbonization curing heating are utilized to cure the single-component adhesive, which is environmentally friendly and highly efficient. The curing of the single-component heating curing adhesive does not require a very high ambient temperature, the process is simple, and the product quality is stable. The corrosion resistance of the modified fiber is improved, and the cured adhesive improves the bonding strength between the fiber and the concrete substrate, thereby improving the mechanical properties and durability of the low-carbon concrete. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0035] The low-carbon cement used in the embodiment has C3S2, CS and C2S as the main mineral phases, and the calcium-silicon ratios are 1.4 and 1.7 respectively; the ordinary Portland cement used is PO42.5 cement.

[0036] The natural coarse aggregate used is provided by Huaxin Aggregate (Wuxue) Company. Its lithology is dolomite and limestone, with a particle size of 5 to 10 mm, continuous grading, needle- and flake-shaped particle content (mass percentage) of 1.8%, crushing value of 10%, and saturated surface dry water absorption of 0.9%.

[0037] The fine aggregate used is dolomite machine-made sand, which has a fineness modulus of 3.0, a stone powder content of 4.4%, an MB value of 0.25, a crushing value of 22%, and a moisture content of 1%.

[0038] Two types of enhanced primers were prepared:

[0039] The mass percentages of the components of No. 1 reinforcing primer are: 1% sodium methyl silicate, 58% sodium silicate, and 41% water.

[0040] The mass percentages of the components of No. 2 enhanced primer are: 3% sodium methyl silicate, 45% sodium silicate, and 52% water.

[0041] There are two types of one-component heat-curing adhesives:

[0042] The composition of 1# is: 85 parts of bisphenol S epoxy resin, 18 parts of triethylene glycol amine; 13 parts of polythiol; 10 parts of dibutyl phthalate, 6 parts of nano-TiO2, and 120 parts of glass microspheres.

[0043] The composition of 2# is: 94 parts of bisphenol S epoxy resin, 13 parts of triethylene glycol amine; 13 parts of polythiol; 10 parts of dibutyl phthalate, 4 parts of nano-TiO2, and 113 parts of glass microspheres.

[0044] The modified fibers include ephedra fiber and steel fiber, both of which have a length of 2 cm and a diameter of 15 μm.

[0045] The admixture is a naphthalene-based water reducer with a water reduction rate of 20%.

[0046] Preparation of polythiol curing agent: The molar ratio of dipentaerythritol hexa(3-mercaptopropionic acid) ester and triethylene glycol diglycidyl ether is 1:1.1, and triethylamine is used as a catalyst to react at 80°C for 10 hours to obtain the product by chain extension reaction.

[0047] Preparation of modified coated fiber 1: Ephedra fiber was dried in an oven at 60°C for 24 hours to remove moisture; a reinforcing primer was applied to the surface; and 1# single-component heat-curing adhesive was sprayed on the surface of the reinforcing primer twice with an interval of 3 hours.

[0048] Preparation of modified coated fiber 2: The above process was repeated, replacing the ephedra fiber with steel fiber.

[0049] Preparation of modified coated fiber 3: Repeat the above process and use 2# single-component heat-curing adhesive.

[0050] Example 1

[0051] A high-durability fiber low-carbon concrete, the preparation method of which comprises the following steps:

[0052] 1) Weigh the following raw materials: 350 parts of low carbon cement, 950 parts of coarse aggregate, 800 parts of machine-made sand, 160 parts of water, 6 parts of water reducer, and 130 parts of modified coated fiber; wherein the calcium-silicon ratio of low carbon cement is 1.4;

[0053] 2) Stirring the aggregate for 30 seconds to premix evenly; then adding low carbon cement and stirring for 60 seconds until evenly mixed; finally adding the modified coated fiber 1, water and admixtures and stirring for 60 to 120 seconds to obtain a concrete mixture; pouring the concrete mixture into a mold and casting;

[0054] 3) placing the obtained formed green body in a CO2 curing environment for carbonization curing to obtain a fiber concrete product, wherein the CO2 curing conditions adopted are: concentration 80%, temperature 50°C, carbonization pressure 0.3MPa, and carbonization time 12h.

[0055] Example 2

[0056] Example 1 was repeated, except that a different low carbon cement was used, and the calcium-silicon ratio was 1.7.

[0057] Example 3

[0058] Example 1 was repeated except that modified coated fiber 2 was used.

[0059] Example 4

[0060] Example 1 was repeated except that modified coated fiber 3 was used.

[0061] Example 5

[0062] Example 1 was repeated, except that the carbonization curing temperature was 40°C.

[0063] Example 6

[0064] Example 1 was repeated, except that the concrete mix ratio used was different. The mix ratio of this example was: 280 parts of low carbon cement, 800 parts of coarse aggregate, 520 parts of machine-made sand, 140 parts of water, 4 parts of water reducer, and 20 parts of modified coated fiber.

[0065] Example 7

[0066] Example 1 was repeated, except that the concrete mix ratio used was different. The mix ratio of this example was: 410 parts of low carbon cement, 1010 parts of coarse aggregate, 800 parts of machine-made sand, 170 parts of water, 8 parts of water reducer, and 30 parts of modified coated fiber.

[0067] Comparative Example 1

[0068] Example 1 was repeated, except that the low carbon cement was replaced with PO42.5 cement, and no carbonization curing process was performed.

[0069] Comparative Example 2

[0070] Example 1 was repeated, except that the ephedra fiber used was not subjected to a modification process.

[0071] Comparative Example 3

[0072] Example 1 was repeated except that no carbonization curing process was performed.

[0073] Comparative Example 4

[0074] Example 1 was repeated except that no fiber was added.

[0075] Comparative Example 5

[0076] Example 1 was repeated, except that the modified coated fiber 1 was only coated with a reinforcing primer without being sprayed with a one-component heat-curing adhesive.

[0077] Comparative Example 6

[0078] Example 1 was repeated, except that the modified coated fiber 1 was not coated with a reinforcing primer, but was directly sprayed with a one-component heat-curing adhesive.

[0079] Performance testing methods

[0080] The fiber concrete prepared in Examples 1 to 7 and Comparative Examples 1 to 6 was subjected to performance tests in accordance with JTG 3420-2020 “Test Procedure for Cement and Cement Concrete in Highway Engineering”. The results are shown in Table 1.

[0081] Table 1

[0082]

[0083]

[0084] As can be seen from Table 1:

[0085] Combining Comparative Example 1 with Examples 1-7 and Table 1, it can be seen that the 28d compressive strength of Comparative Example 1 is less than that of Examples 1-5, and the crack area and 200 freeze-thaw cycle strength loss rate of Comparative Example 1 are greater than those of Examples 1-5. Because the carbonization reaction is rapid relative to the ordinary hydration reaction, the heat release is concentrated and dissipated slowly, and the internal temperature of the concrete product can be rapidly increased, the single-component curing adhesive wrapped in the outer layer of the fiber cannot be quickly and effectively cured, which weakens the connection force between the fiber and the concrete substrate, and the resulting fiber concrete has average performance.

[0086] Combining Comparative Example 2 with Examples 1-7 and Table 1, it can be seen that the 28d compressive strength of Comparative Example 2 is less than that of Examples 1-5, and the cracking area and the strength loss rate of the 200-cycle freeze-thaw specimen of Comparative Example 2 are greater than those of Examples 1-5, indicating that the single-component heat-curing adhesive can improve the density inside the concrete, improve the interface transition zone, and improve the mechanical properties and durability of the concrete.

[0087] Combining Comparative Example 3 with Examples 1-7 and Table 1, it can be seen that the 28d compressive strength of Comparative Example 3 is much smaller than that of Examples 1-5, and the cracking area and the strength loss rate of the 200-cycle freeze-thaw specimen of Comparative Example 3 are greater than those of Examples 1-5, indicating that low-carbon cement requires carbonization curing to stimulate strength, and low-calcium cement cannot improve the performance of concrete by simply adding fibers without carbonization curing.

[0088] Combining Comparative Example 4 with Examples 1-7 and Table 1, it can be seen that the crack area and the strength loss rate of the 200-cycle freeze-thaw specimen of Comparative Example 4 are greater than those of Examples 1-7, indicating that although the fiber can improve the mechanical properties of low-carbon concrete, the carbonization curing will cause the pH value inside the concrete to decrease, and the dissolution of CO2 in water will accelerate the corrosion of the fiber, which will have an adverse effect on the durability of the concrete.

[0089] Combining Comparative Examples 5 and 6 with Examples 1-7 and Table 1, it can be seen that the cracking area and the strength loss rate of the 200-cycle freeze-thaw specimens of Comparative Examples 5 and 6 are greater than those of Examples 1-7, indicating that the single-component heat-curing adhesive can strengthen the connection between the fiber and the concrete stone structure during the carbonization and heating process, and enhance the corrosion resistance of the fiber, thereby improving the durability of the fiber concrete; the enhanced primer makes the single-component heat-curing adhesive evenly distributed on the fiber surface, optimizing the connection and anti-corrosion effect of the single-component heat-curing adhesive.

[0090] The above results show that the fiber low-carbon concrete prepared in Examples 1 to 7 has high compressive strength, small cracking area, and good freeze-thaw resistance; based on the characteristics of low-carbon cement having high carbonization activity and reaction heat generation, a single-component heat-curing adhesive is used to improve the durability of the fiber, enhance the internal linking force and density of the concrete, and improve the mechanical properties and long-term performance of the concrete, which has important economic and social benefits.

[0091] The above embodiments are merely examples for illustrative purposes only and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications may be made based on the above descriptions. It is not necessary and impossible to enumerate all implementation methods here. Therefore, any obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A high-durability low-carbon fiber concrete, characterized in that It is composed of the following raw materials in parts by mass: 260~500 parts of low carbon cement, 900~1100 parts of coarse aggregate, 500~900 parts of fine aggregate, 20~40 parts of modified coated fiber, 150~180 parts of water, 5~10 parts of admixture; The modified coated fiber is one of plant fiber and steel fiber, has a length of 2-3 cm and a diameter of 10-20 μm; the coating thickness is 0.5-1 mm; and the preparation method of the modified coated fiber comprises the following steps: (1) Remove moisture from the fiber; (2) applying a reinforcing primer on the fiber surface; the reinforcing primer comprises the following components by mass percentage: 1-5% sodium methyl silicate; 40-60% sodium silicate; and the balance being water; (3) spraying a one-component heat-curing adhesive on the surface of the primer; the composition of the one-component heat-curing adhesive is calculated by mass: 80-100 parts of bisphenol S epoxy resin, 15-20 parts of triethylene glycol amine, 10-20 parts of polythiol, 8-12 parts of dibutyl phthalate, 5-10 parts of nano-TiO2, and 90-150 parts of glass microspheres.

2. The high-durability low-carbon fiber concrete according to claim 1, characterized in that The polythiol is prepared by chain extension reaction of dipentaerythritol hexa(3-mercaptopropionic acid) ester and triethylene glycol diglycidyl ether in a molar ratio of 1:(1.1-1.3) as raw materials, using triethylamine as a catalyst, and reacting at 80-90° C. for 8-12 hours.

3. The high-durability low-carbon fiber concrete according to claim 1, characterized in that In step (3), the single-component heat-curing adhesive is sprayed twice, and the time interval between the two times is 2 to 5 hours.

4. The high-durability low-carbon fiber concrete according to claim 1, characterized in that The calcium-silicon ratio of the low carbon cement is 1.4-2.

0.

5. The method for preparing the high-durability low-carbon fiber concrete according to claim 1, characterized in that The following steps are involved: 1) Premix the coarse and fine aggregates evenly, then add low carbon cement and mix well; 2) Add modified coated fiber, water and admixtures and mix evenly to obtain a concrete mixture, which is then poured into a mold for molding; 3) The obtained molded product is placed in a CO2 curing environment for carbonization curing.

6. The method for preparing high-durability low-carbon fiber concrete according to claim 5, characterized in that The carbonization maintenance system is: CO2 concentration is 20~100vol%, curing temperature is 40~80℃, curing pressure is 0.1~1.0MPa, and curing time is 6~24h.

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