A fiber-reinforced recycled ultra-high performance concrete and its preparation method

Abstract

The present invention relates to the technical field of ultra-high performance concrete, and specifically discloses a fiber-reinforced recycled ultra-high performance concrete. Its raw materials by mass parts include: 50-100 parts of cement, 20-50 parts of fly ash, 20-30 parts of recycled coarse aggregate, 60-80 parts of fine aggregate, 5-15 parts of hybrid fiber, 1-5 parts of steel fiber, 5-10 parts of epoxy resin, 1-2 parts of water reducer, 5-10 parts of doping agent, and 2-4 parts of curing agent; the raw materials of the doping agent by mass parts include: 1-2 parts of graphene oxide, 0.01-0.1 parts of cerium acetate, and 1-5 parts of ammonia water with a mass fraction of 5-15%. The present invention also discloses a preparation method of the above-mentioned fiber-reinforced recycled ultra-high performance concrete. The present invention has excellent compressive strength, crack resistance and freeze-thaw resistance effects, the matrix microstructure is dense, the impermeability is good, and the structural durability is effectively improved; at the same time, the construction performance is good, which is beneficial to its popularization and application in actual projects.

Description

Technical Field

[0001] The present invention relates to the technical field of ultra-high performance concrete, and in particular to a fiber-reinforced recycled ultra-high performance concrete and a preparation method thereof. Background Art

[0002] Ultra-high performance concrete is made of raw materials such as cement, mineral admixtures, aggregates, fibers, chemical admixtures and water. It is a high-toughness cement-based composite material with ultra-high mechanical properties and ultra-high impermeability.

[0003] Ultra-high performance fiber-reinforced concrete is an ideal application material for engineering structures that tend to develop into larger spans, lighter structures and more assembled structures due to its high density, ultra-high strength and excellent durability.

[0004] However, ultra-high performance concrete is added with 1-2% steel fiber. Current research shows that the steel fiber in traditional ultra-high performance concrete is affected by the structural size and its dispersion is difficult to ensure, which causes higher internal stress inside the ultra-high performance concrete material and even more microcracks, thus affecting the durability of the structure.

[0005] In order to solve the problem of large autogenous volume shrinkage of ultra-high performance concrete, technical measures such as adding chemical admixtures are often adopted. Although the shrinkage of ultra-high performance concrete is reduced to a certain extent, there are still certain problems. The addition of chemical admixtures can easily reduce the mechanical properties of the matrix, and the low-temperature resistance is poor, and the strength loss after freezing and thawing is large, which needs to be solved urgently. Summary of the invention

[0006] The purpose of the present invention is to solve the shortcomings of the prior art and to propose a fiber-reinforced recycled ultra-high performance concrete and a preparation method thereof.

[0007] A fiber-reinforced recycled ultra-high performance concrete, whose raw materials include, by mass, 50-100 parts of cement, 20-50 parts of fly ash, 20-30 parts of recycled coarse aggregate, 60-80 parts of fine aggregate, 5-15 parts of mixed fiber, 1-5 parts of steel fiber, 5-10 parts of epoxy resin, 1-2 parts of water reducer, 5-10 parts of dopant, and 2-4 parts of curing agent; the raw materials of the dopant include, by mass, 1-2 parts of graphene oxide, 0.01-0.1 parts of cerium acetate, and 1-5 parts of ammonia water with a mass fraction of 5-15%.

[0008] Preferably, the cement is CEMI type 52.5R grade ordinary Portland cement.

[0009] Preferably, the water reducing agent is a polycarboxylic acid-based high-performance water reducing agent.

[0010] Preferably, the curing agent is curing agent T31.

[0011] Preferably, the dopant is prepared by the following steps: adding graphene oxide to deionized water and stirring evenly, adding cerium acetate and ultrasonically treating for 1-2 hours, adding ammonia water dropwise thereto and continuing ultrasonic treatment for 10-20 minutes, hydrothermally reacting at 180-200° C. for 10-20 hours, naturally cooling to room temperature, centrifuging, washing, and vacuum drying.

[0012] More preferably, the ultrasound frequency is 5-15 kHz.

[0013] Preferably, the hybrid fiber is prepared by the following specific steps: aluminum silicate fiber and basalt fiber are mixed evenly, heated to a molten state, extruded and spun, cooled, and then sent to a sodium hydroxide solution for ultrasonic treatment for 10-20 minutes, filtered, washed, vacuum dried, soaked in water, added with 3-aminopropyltrimethoxysilane for ultrasonic treatment for 1-2 hours, added with nano titanium dioxide and continued ultrasonic treatment for 10-30 minutes, filtered, washed, and vacuum dried.

[0014] More preferably, the mass ratio of aluminum silicate fiber, basalt fiber, 3-aminopropyltrimethoxysilane and nano-titanium dioxide is 5-10:10-20:1-2:1-5.

[0015] More preferably, the frequency of ultrasonic treatment after feeding into the sodium hydroxide solution is 5-12 kHz.

[0016] More preferably, the frequency of ultrasonic treatment after adding 3-aminopropyltrimethoxysilane is 4-10 kHz.

[0017] The method for preparing the fiber-reinforced recycled ultra-high performance concrete comprises the following steps:

[0018] S1. Mixing recycled coarse aggregate, fine aggregate and water to obtain premixed aggregate;

[0019] S2, cement and fly ash are mixed evenly, mixed fiber, steel fiber, epoxy resin, water reducer and water are added thereto and stirred for 1-3 minutes, premixed aggregate, dopant and curing agent are added and stirred for 10-30 seconds to obtain a premix;

[0020] S3. Discharge the material, put it into the mold and vibrate it for 1-2 minutes, cover it with plastic film, and naturally cure it for 20-40 hours. Remove the plastic film and naturally cure it for 20-40 days.

[0021] Beneficial effects:

[0022] The present invention partially replaces steel fibers with non-metallic hybrid fibers to form a multi-scale fiber system of steel fibers and hybrid fibers, which greatly improves the bearing capacity of the engineering structure while reducing the amount of steel fibers.

[0023] In the hybrid fibers, aluminum silicate fibers and basalt fibers are compounded and melted, and the resulting fibers are combined with nano-titanium dioxide in the presence of 3-aminopropyltrimethoxysilane, thereby making the titanium dioxide lipophilic. This can effectively promote the uniform dispersion of the hybrid fibers in the epoxy resin, and after curing, it can significantly improve the ability of concrete to resist stress, effectively solve the problem of large spontaneous volume shrinkage, prevent the occurrence of cracks, and at the same time improve the overall concrete's absorption of impact energy and enhance the concrete's impact resistance.

[0024] The present invention adopts a compound of hybrid fibers and steel fibers. The steel fibers have excellent mechanical properties, and the hybrid fibers have extremely good dispersibility. The two produce a synergistic effect, which can enhance the utility of the fiber system from micro to macro and improve the durability of the structure. Further, by combining cerium oxide on a two-dimensional graphene sheet with a special structure, not only are the two highly stable, but also can be compounded with the hybrid fibers. On the one hand, the present invention can inhibit the expansion of microcracks inside the cured concrete and enhance the compressive strength of the system. On the other hand, the dopant can strengthen the microstructure of the concrete, significantly improve the interface defects between the aggregate and the mortar, and effectively enhance the density. The product has excellent low-temperature mechanical properties and good freeze-thaw resistance.

[0025] The invention has excellent compressive strength, crack resistance and freeze-thaw resistance, a dense matrix microstructure, good impermeability, and effectively improves structural durability; at the same time, it has good construction performance, which is conducive to its promotion and application in actual engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a comparison chart of the compressive strength and flexural strength of the fiber-reinforced recycled ultra-high performance concrete obtained in Example 5 and Comparative Examples 1-2.

[0027] Figure 2 This is a comparison chart of the uniaxial tensile strength and uniaxial tensile strain of the fiber-reinforced recycled ultra-high performance concrete obtained in Example 5 and Comparative Examples 1-2.

[0028] Figure 3 This is a comparison chart of the early-age autogenous shrinkage and chloride ion diffusion coefficient of the fiber-reinforced recycled ultra-high performance concrete obtained in Example 5 and Comparative Examples 1-2.

[0029] Figure 4 This is a comparison chart of the strength loss rate of the fiber-reinforced recycled ultra-high performance concrete obtained in Example 5 and Comparative Examples 1-2 after 100 freeze-thaw cycles. DETAILED DESCRIPTION

[0030] The present invention will be further explained below in conjunction with specific embodiments.

[0031] The recycled coarse aggregate used below was purchased from Zhengzhou Yuanmufa Environmental Protection Technology Co., Ltd., and the quality grade is Grade I (GB / T25177-2010 "Recycled Coarse Aggregate for Concrete"). After the incoming material inspection, the aggregate screening results are shown in Table 1:

[0032] Table 1 Recycled coarse aggregate gradation

[0033]

[0034]

[0035] The fine aggregate used in the following is machine-made sand, and the parameters are as follows: diameter between 0-4.75 mm, fineness modulus of 2.8, stone powder content of 6.0%, mud block content of 0.2%, and crushing index of 22%.

[0036] The polycarboxylic acid-based high-performance water-reducing agent used below was purchased from Shandong Tongmu New Material Technology Co., Ltd.

[0037] The steel fibers used below were purchased from Anping County Lianmou Steel Fiber Manufacturing Co., Ltd., with a diameter of 0.2±0.02 mm, a length of 0.4 mm, and a tensile strength of ≥2850 MPa.

[0038] Example 1

[0039] A fiber-reinforced recycled ultra-high performance concrete, whose raw materials include: 50kg of CEMI type 52.5R grade ordinary Portland cement, 20kg of grade II fly ash, 20kg of recycled coarse aggregate, 60kg of fine aggregate, 5kg of mixed fiber, 1kg of steel fiber, 15kg of epoxy resin E5, 1kg of polycarboxylic acid high-performance water reducer, 5kg of dopant, and 12kg of curing agent T3.

[0040] The dopant raw materials include: 1 kg of graphene oxide, 0.01 kg of cerium acetate, and 1 kg of ammonia water with a mass fraction of 5%.

[0041] The dopant is prepared by the following specific steps: adding graphene oxide to 20 kg of deionized water and stirring evenly, adding cerium acetate and ultrasonically treating for 1 hour at an ultrasonic frequency of 5 kHz, adding ammonia water dropwise thereto and continuing ultrasonic treatment for 10 minutes, sending it into a polytetrafluoroethylene-lined high-pressure reactor, hydrothermally reacting at a temperature of 180° C. for 10 hours, naturally cooling to room temperature, centrifuging, washing, and vacuum drying.

[0042] The hybrid fiber was prepared by the following specific steps: 5 kg of aluminum silicate fiber and 10 kg of basalt fiber were mixed evenly, heated to a molten state, extruded and spun, cooled to obtain fibers with a length of 5 mm and a diameter of 0.05 mm, and then sent to 50 kg of 0.5 mol / L sodium hydroxide solution for ultrasonic treatment for 10 min at an ultrasonic frequency of 5 kHz, filtered, washed, vacuum dried, immersed in 50 kg of water, added with 1 kg of 3-aminopropyltrimethoxysilane for ultrasonic treatment for 1 h at an ultrasonic frequency of 4 kHz, added with 1 kg of nano titanium dioxide and continued ultrasonic treatment for 10 min, filtered, washed, and vacuum dried.

[0043] The method for preparing the fiber-reinforced recycled ultra-high performance concrete comprises the following steps:

[0044] S1. Mix recycled coarse aggregate, fine aggregate and 10 kg water, and stir at a speed of 500 r / min for 50 seconds to obtain premixed aggregate;

[0045] S2, CEMI type 52.5R grade ordinary Portland cement and grade II fly ash are mixed evenly, mixed fiber, steel fiber, epoxy resin E51, polycarboxylic acid high-performance water reducer, 10kg water are added thereto, stirred at a speed of 500r / min for 1min, premixed aggregate, dopant, and curing agent T31 are added, and stirring is continued for 10s to obtain a premix;

[0046] S3, discharge the material, put it into the mold and vibrate it for 1 minute, cover it with PET film, cure it under natural conditions for 20 hours, remove the PET film, and cure it under natural conditions for 20 days.

[0047] Example 2

[0048] A fiber-reinforced recycled ultra-high performance concrete, whose raw materials include: 100 kg of CEMI type 52.5R grade ordinary Portland cement, 50 kg of grade II fly ash, 30 kg of recycled coarse aggregate, 80 kg of fine aggregate, 15 kg of mixed fiber, 5 kg of steel fiber, 10 kg of epoxy resin E51, 2 kg of polycarboxylic acid high-performance water reducer, 10 kg of doping agent, and 14 kg of curing agent T3.

[0049] The dopant raw materials include: 2 kg of graphene oxide, 0.1 kg of cerium acetate, and 5 kg of ammonia water with a mass fraction of 15%.

[0050] The dopant is prepared by the following specific steps: adding graphene oxide to 40 kg of deionized water and stirring evenly, adding cerium acetate and ultrasonically treating for 2 hours at an ultrasonic frequency of 15 kHz, adding ammonia water dropwise thereto and continuing ultrasonic treatment for 20 minutes, sending it into a polytetrafluoroethylene-lined high-pressure reactor, hydrothermally reacting at a temperature of 200° C. for 20 hours, naturally cooling to room temperature, centrifuging, washing, and vacuum drying.

[0051] The hybrid fiber was prepared by the following specific steps: 10 kg of aluminum silicate fiber and 20 kg of basalt fiber were mixed evenly, heated to a molten state, extruded and spun, cooled to obtain fibers with a length of 15 mm and a diameter of 0.2 mm, and then sent to 100 kg of 1.2 mol / L sodium hydroxide solution for ultrasonic treatment for 20 min at an ultrasonic frequency of 12 kHz, filtered, washed, vacuum dried, immersed in 100 kg of water, added with 2 kg of 3-aminopropyltrimethoxysilane for ultrasonic treatment for 2 h at an ultrasonic frequency of 10 kHz, added with 5 kg of nano titanium dioxide and continued ultrasonic treatment for 30 min, filtered, washed, and vacuum dried.

[0052] The method for preparing the fiber-reinforced recycled ultra-high performance concrete comprises the following steps:

[0053] S1. Mix recycled coarse aggregate, fine aggregate and 20 kg of water, and stir at a speed of 1000 r / min for 100 s to obtain premixed aggregate;

[0054] S2, CEMI type 52.5R grade ordinary Portland cement and grade II fly ash are mixed evenly, mixed fiber, steel fiber, epoxy resin E51, polycarboxylic acid high-performance water reducer, 20kg water are added thereto, stirred at a speed of 1000r / min for 3min, premixed aggregate, dopant, and curing agent T31 are added, and stirring is continued for 30s to obtain a premix;

[0055] S3, discharge the material, put it into the mold and vibrate it for 2 minutes, cover it with PET film, and cure it under natural conditions for 40 hours. Remove the PET film and cure it under natural conditions for 40 days.

[0056] Example 3

[0057] A fiber-reinforced recycled ultra-high performance concrete, whose raw materials include: 70kg of CEMI type 52.5R grade ordinary Portland cement, 40kg of grade II fly ash, 22kg of recycled coarse aggregate, 75kg of fine aggregate, 8kg of mixed fiber, 4kg of steel fiber, 17kg of epoxy resin E5, 1.7kg of polycarboxylic acid high-performance water reducer, 7kg of dopant, and 13.5kg of curing agent T3.

[0058] The dopant raw materials include: 1.3 kg of graphene oxide, 0.07 kg of cerium acetate, and 4 kg of ammonia water with a mass fraction of 8%.

[0059] The dopant is prepared by the following specific steps: adding graphene oxide to 25 kg of deionized water and stirring evenly, adding cerium acetate and ultrasonically treating for 100 minutes at an ultrasonic frequency of 8 kHz, adding ammonia water dropwise thereto and continuing ultrasonic treatment for 18 minutes, sending it into a polytetrafluoroethylene-lined high-pressure reactor, hydrothermally reacting at a temperature of 185° C. for 17 hours, naturally cooling to room temperature, centrifuging, washing, and vacuum drying.

[0060] The hybrid fiber was prepared by the following specific steps: 7 kg of aluminum silicate fiber and 17 kg of basalt fiber were mixed evenly, heated to a molten state, extruded and spun, cooled to obtain fibers with a length of 8 mm and a diameter of 0.15 mm, and then sent to 70 kg of 1 mol / L sodium hydroxide solution for ultrasonic treatment for 12 min at an ultrasonic frequency of 10 kHz, filtered, washed, vacuum dried, immersed in 70 kg of water, added with 1.7 kg of 3-aminopropyltrimethoxysilane for ultrasonic treatment for 80 min at an ultrasonic frequency of 7 kHz, added with 2 kg of nano titanium dioxide and continued ultrasonic treatment for 25 min, filtered, washed, and vacuum dried.

[0061] The method for preparing the fiber-reinforced recycled ultra-high performance concrete comprises the following steps:

[0062] S1. Mix recycled coarse aggregate, fine aggregate and 13 kg of water, and stir at a speed of 900 r / min for 85 seconds to obtain premixed aggregate;

[0063] S2, CEMI type 52.5R grade ordinary Portland cement and grade II fly ash are mixed evenly, mixed fiber, steel fiber, epoxy resin E51, polycarboxylic acid high-performance water reducer, 14kg water are added thereto, stirred at a speed of 700r / min for 2.5min, premixed aggregate, dopant, and curing agent T31 are added, and stirring is continued for 15s to obtain a premix;

[0064] S3, discharge the material, put it into the mold and vibrate it for 1.5 minutes, cover it with PET film, and cure it under natural conditions for 35 hours. Remove the PET film and cure it under natural conditions for 25 days.

[0065] Example 4

[0066] A fiber-reinforced recycled ultra-high performance concrete, whose raw materials include: 90kg of CEMI type 52.5R grade ordinary Portland cement, 30kg of Class II fly ash, 28kg of recycled coarse aggregate, 65kg of fine aggregate, 12kg of mixed fiber, 2kg of steel fiber, 19kg of epoxy resin E5, 1.3kg of polycarboxylic acid high-performance water reducer, 9kg of dopant, and 2.5kg of curing agent T3.

[0067] The dopant raw materials include: 1.7 kg of graphene oxide, 0.03 kg of cerium acetate, and 2 kg of ammonia water with a mass fraction of 12%.

[0068] The dopant is prepared by the following specific steps: adding graphene oxide to 35 kg of deionized water and stirring evenly, adding cerium acetate and ultrasonically treating for 80 minutes at an ultrasonic frequency of 12 kHz, adding ammonia water dropwise thereto and continuing ultrasonic treatment for 12 minutes, sending it into a polytetrafluoroethylene-lined high-pressure reactor, hydrothermally reacting at a temperature of 195° C. for 13 hours, naturally cooling to room temperature, centrifuging, washing, and vacuum drying.

[0069] The hybrid fiber was prepared by the following specific steps: 9 kg of aluminum silicate fiber and 13 kg of basalt fiber were mixed evenly, heated to a molten state, extruded and spun, cooled to obtain fibers with a length of 12 mm and a diameter of 0.1 mm, and then sent to 90 kg of 0.6 mol / L sodium hydroxide solution for ultrasonic treatment for 18 min at an ultrasonic frequency of 6 kHz, filtered, washed, vacuum dried, immersed in 90 kg of water, added with 1.3 kg of 3-aminopropyltrimethoxysilane for ultrasonic treatment for 100 min at an ultrasonic frequency of 5 kHz, added with 4 kg of nano titanium dioxide and continued ultrasonic treatment for 15 min, filtered, washed, and vacuum dried.

[0070] The method for preparing the fiber-reinforced recycled ultra-high performance concrete comprises the following steps:

[0071] S1. Mix recycled coarse aggregate, fine aggregate and 17 kg of water, and stir at a speed of 600 r / min for 95 seconds to obtain premixed aggregate;

[0072] S2, CEMI type 52.5R grade ordinary Portland cement and grade II fly ash are mixed evenly, mixed fiber, steel fiber, epoxy resin E51, polycarboxylic acid high-performance water reducer, 12kg water are added thereto, stirred at a speed of 900r / min for 1.5min, premixed aggregate, dopant, and curing agent T31 are added and stirred for 25s to obtain a premix;

[0073] S3, discharge the material, put it into the mold and vibrate it for 1.5 minutes, cover it with PET film, cure it under natural conditions for 25 hours, remove the PET film, and cure it under natural conditions for 35 days.

[0074] Example 5

[0075] A fiber-reinforced recycled ultra-high performance concrete, whose raw materials include: 80kg of CEMI type 52.5R grade ordinary Portland cement, 35kg of Class II fly ash, 25kg of recycled coarse aggregate, 70kg of fine aggregate, 10kg of mixed fiber, 3kg of steel fiber, 18kg of epoxy resin E5, 1.5kg of polycarboxylic acid high-performance water reducer, 8kg of dopant, and 13kg of curing agent T3.

[0076] The dopant raw materials include: 1.5 kg of graphene oxide, 0.05 kg of cerium acetate, and 3 kg of ammonia water with a mass fraction of 10%.

[0077] The dopant is prepared by the following specific steps: adding graphene oxide to 30 kg of deionized water and stirring evenly, adding cerium acetate and ultrasonically treating for 90 minutes at an ultrasonic frequency of 9 kHz, adding ammonia water dropwise thereto and continuing ultrasonic treatment for 15 minutes, sending it into a polytetrafluoroethylene-lined high-pressure reactor, hydrothermally reacting at a temperature of 192° C. for 15 hours, naturally cooling to room temperature, centrifuging, washing, and vacuum drying.

[0078] The hybrid fiber was prepared by the following specific steps: 8 kg of aluminum silicate fiber and 15 kg of basalt fiber were mixed evenly, heated to a molten state, extruded and spun, cooled to obtain fibers with a length of 10 mm and a diameter of 0.12 mm, and then sent to 80 kg of 0.8 mol / L sodium hydroxide solution for ultrasonic treatment for 15 min at an ultrasonic frequency of 9 kHz, filtered, washed, vacuum dried, immersed in 80 kg of water, added with 1.5 kg of 3-aminopropyltrimethoxysilane for ultrasonic treatment for 90 min at an ultrasonic frequency of 6 kHz, added with 3 kg of nano titanium dioxide and continued ultrasonic treatment for 20 min, filtered, washed, and vacuum dried.

[0079] The method for preparing the fiber-reinforced recycled ultra-high performance concrete comprises the following steps:

[0080] S1. Mix recycled coarse aggregate, fine aggregate and 15 kg water, and stir at a speed of 800 r / min for 90 s to obtain premixed aggregate;

[0081] S2, CEMI type 52.5R grade ordinary Portland cement and grade II fly ash are mixed evenly, mixed fiber, steel fiber, epoxy resin E51, polycarboxylic acid high-performance water reducer, 13kg water are added thereto, stirred at a speed of 800r / min for 2min, premixed aggregate, dopant, and curing agent T31 are added, and stirring is continued for 20s to obtain a premix;

[0082] S3, discharge the material, put it into the mold and vibrate it for 1.5 minutes, cover it with PET film, and cure it under natural conditions for 32 hours. Remove the PET film and cure it under natural conditions for 30 days.

[0083] Comparative Example 1

[0084] A fiber-reinforced recycled ultra-high performance concrete, whose raw materials include: 80kg of CEMI type 52.5R grade ordinary Portland cement, 35kg of Class II fly ash, 25kg of recycled coarse aggregate, 70kg of fine aggregate, 10kg of mixed fiber, 3kg of steel fiber, 18kg of epoxy resin E5, 1.5kg of polycarboxylic acid high-performance water reducer, 8kg of dopant, and 13kg of curing agent T3.

[0085] The dopant raw material includes: 1.5 kg of graphene oxide and 0.05 kg of cerium acetate. The dopant is prepared by the following specific steps: mixing graphene oxide and cerium acetate.

[0086] The hybrid fiber was prepared by the following specific steps: 8 kg of aluminum silicate fiber and 15 kg of basalt fiber were mixed evenly, heated to a molten state, extruded and spun, cooled to obtain fibers with a length of 10 mm and a diameter of 0.12 mm, and then sent to 80 kg of 0.8 mol / L sodium hydroxide solution for ultrasonic treatment for 15 min at an ultrasonic frequency of 9 kHz, filtered, washed, vacuum dried, immersed in 80 kg of water, added with 1.5 kg of 3-aminopropyltrimethoxysilane for ultrasonic treatment for 90 min at an ultrasonic frequency of 6 kHz, added with 3 kg of nano titanium dioxide and continued ultrasonic treatment for 20 min, filtered, washed, and vacuum dried.

[0087] The method for preparing the fiber-reinforced recycled ultra-high performance concrete comprises the following steps:

[0088] S1. Mix recycled coarse aggregate, fine aggregate and 15 kg water, and stir at a speed of 800 r / min for 90 s to obtain premixed aggregate;

[0089] S2, CEMI type 52.5R grade ordinary Portland cement and grade II fly ash are mixed evenly, mixed fiber, steel fiber, epoxy resin E51, polycarboxylic acid high-performance water reducer, 13kg water are added thereto, stirred at a speed of 800r / min for 2min, premixed aggregate, dopant, and curing agent T31 are added, and stirring is continued for 20s to obtain a premix;

[0090] S3, discharge the material, put it into the mold and vibrate it for 1.5 minutes, cover it with PET film, and cure it under natural conditions for 32 hours. Remove the PET film and cure it under natural conditions for 30 days.

[0091] Comparative Example 2

[0092] A fiber-reinforced recycled ultra-high performance concrete, whose raw materials include: 80kg of CEMI type 52.5R grade ordinary Portland cement, 35kg of Class II fly ash, 25kg of recycled coarse aggregate, 70kg of fine aggregate, 10kg of mixed fiber, 3kg of steel fiber, 18kg of epoxy resin E5, 1.5kg of polycarboxylic acid high-performance water reducer, 8kg of dopant, and 13kg of curing agent T3.

[0093] The dopant raw materials include: 1.5 kg of graphene oxide, 0.05 kg of cerium acetate, and 3 kg of ammonia water with a mass fraction of 10%.

[0094] The dopant is prepared by the following specific steps: adding graphene oxide to 30 kg of deionized water and stirring evenly, adding cerium acetate and ultrasonically treating for 90 minutes at an ultrasonic frequency of 9 kHz, adding ammonia water dropwise thereto and continuing ultrasonic treatment for 15 minutes, sending it into a polytetrafluoroethylene-lined high-pressure reactor, hydrothermally reacting at a temperature of 192° C. for 15 hours, naturally cooling to room temperature, centrifuging, washing, and vacuum drying.

[0095] The hybrid fiber was prepared by the following specific steps: 8 kg of aluminum silicate fiber and 15 kg of basalt fiber were mixed evenly, heated to a molten state, extruded and spun, cooled to obtain fibers with a length of 10 mm and a diameter of 0.12 mm, and then sent to 80 kg of 0.8 mol / L sodium hydroxide solution for ultrasonic treatment for 15 min at an ultrasonic frequency of 9 kHz, filtered, washed, and vacuum dried.

[0096] The method for preparing the fiber-reinforced recycled ultra-high performance concrete comprises the following steps:

[0097] S1. Mix recycled coarse aggregate, fine aggregate and 15 kg water, and stir at a speed of 800 r / min for 90 s to obtain premixed aggregate;

[0098] S2, CEMI type 52.5R grade ordinary Portland cement and grade II fly ash are mixed evenly, mixed fiber, steel fiber, epoxy resin E51, polycarboxylic acid high-performance water reducer, 13kg water are added thereto, stirred at a speed of 800r / min for 2min, premixed aggregate, dopant, and curing agent T31 are added, and stirring is continued for 20s to obtain a premix;

[0099] S3, discharge the material, put it into the mold and vibrate it for 1.5 minutes, cover it with PET film, and cure it under natural conditions for 32 hours. Remove the PET film and cure it under natural conditions for 30 days.

[0100] According to T / CECS 864-2021 "Ultra-High Performance Concrete Test Method Standard", the fiber-reinforced recycled ultra-high performance concrete obtained in Example 5 and Comparative Examples 1-2 was subjected to performance tests.

[0101] like Figures 1 to 3 As shown, the fiber-reinforced recycled ultra-high performance concrete obtained in Example 5 has the highest compressive and flexural strengths, the highest uniaxial tensile strength and uniaxial tensile strain, and the lowest early-age autogenous shrinkage and chloride ion diffusion coefficient, all of which are better than those of Comparative Examples 1-2 (P < 0.05).

[0102] The fiber-reinforced recycled ultra-high performance concrete specimens obtained in Example 5 and Comparative Examples 1-2 were then immersed in 20±2°C water for 4 days, and the immersion water level was 25.0±5.0mm higher than the top surface of the specimen; after the immersion was completed, the specimen was taken out and the moisture on the surface of the specimen was wiped off, and the appearance dimensions were measured and weighed; each specimen was placed in a specimen box and placed in a freeze-thaw box, leaving a 20mm gap between the specimen and the wall of the specimen box; and in the quick freezing test, clean water should be injected into the specimen box, and the height of the water level was 50mm higher than the specimen; when the temperature in the freeze-thaw box dropped to -18°C, the timing started, and the freezing time in each freeze-thaw cycle was 4h. After the freezing was completed, water at a temperature of 19.0±1.0°C was immediately added, and the water addition time was within 10min. The water level was more than 20mm higher than the specimen, and the thawing time was 4h; after the thawing was completed, the freeze-thaw cycle was considered to be over, and the next freeze-thaw cycle could be carried out.

[0103] The freeze-thaw test was stopped after 100 freeze-thaw cycles, the compressive strength of the specimens was tested, and the strength loss rate was calculated.

[0104] Strength loss rate = 1-compressive strength of the sample after 100 freeze-thaw cycles ÷ original compressive strength of the sample × 100%

[0105] like Figure 4 As shown, the fiber-reinforced recycled ultra-high performance concrete obtained in Example 5 has the lowest strength loss rate after freeze-thaw and the best anti-freeze-thaw effect, which are better than those of Comparative Examples 1-2 (P < 0.05), proving that the samples obtained in the present invention have excellent low-temperature mechanical properties.

[0106] The applicant believes that the reason for the above results is that the present invention adopts aluminum silicate fiber and basalt fiber to be compounded and melted, and the obtained fiber is combined with nano titanium dioxide under the cooperation of 3-aminopropyltrimethoxysilane, so that titanium dioxide has good lipophilicity, which can effectively promote the uniform dispersion of hybrid fiber in epoxy resin, and can significantly improve the ability of concrete to resist stress after curing, effectively solve the problem of large spontaneous volume shrinkage, prevent cracks from occurring, and at the same time improve the absorption of impact energy by the whole concrete, and enhance the impact resistance of concrete. The hybrid fiber and steel fiber are compounded, and the two produce a synergistic effect, which can improve the utility of the fiber system from micro to macro, and improve the durability of the structure; further, by combining cerium oxide on the two-dimensional graphene sheet with a special structure, not only the two have high stability, but also can be compounded with the hybrid fiber. On the one hand, the present invention can inhibit the expansion of microcracks inside the cured concrete and enhance the compressive strength of the system. On the other hand, the dopant can strengthen the microstructure of the concrete, significantly improve the interface defects between the aggregate and the mortar, effectively enhance the density, and the product has excellent low-temperature mechanical properties and good anti-freeze-thaw effect.

[0107] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A fiber-reinforced recycled ultra-high performance concrete, characterized in that: The raw materials include, by mass: 50-100 parts of cement, 20-50 parts of fly ash, 20-30 parts of recycled coarse aggregate, 60-80 parts of fine aggregate, 5-15 parts of mixed fiber, 1-5 parts of steel fiber, 5-10 parts of epoxy resin, 1-2 parts of water reducing agent, 5-10 parts of doping agent, and 2-4 parts of curing agent; The dopant raw materials include, by mass: 1-2 parts of graphene oxide, 0.01-0.1 parts of cerium acetate, and 1-5 parts of ammonia water with a mass fraction of 5-15%; The dopant is prepared by the following steps: adding graphene oxide to deionized water and stirring evenly, adding cerium acetate and ultrasonically treating for 1-2 hours, dropping ammonia water therein and continuing ultrasonically treating for 10-20 minutes, hydrothermally reacting at 180-200° C. for 10-20 hours, naturally cooling to room temperature, centrifuging, washing, and vacuum drying; The hybrid fiber is prepared by the following specific steps: aluminum silicate fiber and basalt fiber are mixed evenly, heated to a molten state, extruded and spun, cooled, and then sent to a sodium hydroxide solution for ultrasonic treatment for 10-20 minutes, filtered, washed, vacuum dried, soaked in water, added with 3-aminopropyltrimethoxysilane for ultrasonic treatment for 1-2 hours, added with nano titanium dioxide and continued ultrasonic treatment for 10-30 minutes, filtered, washed, and vacuum dried.

2. The fiber-reinforced recycled ultra-high performance concrete according to claim 1, characterized in that: The cement is CEMI type 52.5R grade ordinary Portland cement.

3. The fiber-reinforced recycled ultra-high performance concrete according to claim 1, characterized in that: The water reducing agent is a polycarboxylic acid-based high-performance water reducing agent.

4. The fiber-reinforced recycled ultra-high performance concrete according to claim 1, characterized in that: The curing agent is curing agent T31.

5. The fiber-reinforced recycled ultra-high performance concrete according to claim 1, characterized in that: During the preparation of the dopant, the ultrasonic frequency is 5-15kHz.

6. The fiber-reinforced recycled ultra-high performance concrete according to claim 1, characterized in that: The mass ratio of aluminum silicate fiber, basalt fiber, 3-aminopropyltrimethoxysilane and nano-titanium dioxide is 5-10:10-20:1-2:1-5.

7. The fiber-reinforced recycled ultra-high performance concrete according to claim 1, characterized in that: The frequency of ultrasonic treatment after feeding into the sodium hydroxide solution is 5-12 kHz; the frequency of ultrasonic treatment after adding 3-aminopropyltrimethoxysilane is 4-10 kHz.

8. A method for preparing the fiber-reinforced recycled ultra-high performance concrete according to any one of claims 1 to 7, characterized in that: The steps include: S1. Mixing recycled coarse aggregate, fine aggregate and water to obtain premixed aggregate; S2, cement and fly ash are mixed evenly, mixed fiber, steel fiber, epoxy resin, water reducer and water are added thereto and stirred for 1-3 minutes, premixed aggregate, dopant and curing agent are added and stirred for 10-30 seconds to obtain a premix; S3. Discharge the material, put it into the mold and vibrate it for 1-2 minutes, cover it with plastic film, and naturally cure it for 20-40 hours. Remove the plastic film and naturally cure it for 20-40 days.

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