A fully recycled concrete and its preparation method and application

Abstract

The present invention discloses a fully recycled concrete and its preparation method and application. The provided fully recycled concrete comprises the following components in parts by weight: 290 - 540 parts of cement, 1100 - 1200 parts of brick - concrete recycled coarse aggregate, 650 - 680 parts of brick - concrete recycled fine aggregate, 145 - 250 parts of water, 30 - 80 parts of steel fiber, 1.4 - 2.7 parts of polycarboxylate superplasticizer, and 40 - 60 parts of strengthening and toughening agent; the strengthening and toughening agent is formed by mixing an aqueous polyurethane - epoxy resin emulsion and a synergist in a mass ratio of 2 - 4:1. Compared with the prior art, the fully recycled concrete prepared by the present invention has good compressive strength, splitting tensile strength, axial compressive strength, chloride ion penetration resistance and frost resistance, and has a long service life.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete, and particularly to a fully recycled concrete and its preparation method and application. Background Art

[0002] The survey results show that the recycling rate of construction waste is insufficient. How to scientifically and effectively recycle construction waste has been a long-lasting research focus in the building materials industry. The engineering application of recycled concrete technology turns construction waste into treasure, saving concrete raw materials while also having social and economic benefits and environmental benefits. The fully recycled concrete prepared by simultaneously using recycled coarse and fine aggregates can not only alleviate the shortage of building resources to the greatest extent but also accommodate construction waste to the greatest extent, which conforms to the concepts of sustainable development and green development. However, most current research on recycled concrete focuses on the recycling and reuse of waste concrete, and its experience and conclusions are not applicable to construction waste mainly composed of brick-concrete structures. The reason is that brick-concrete recycled aggregates have higher porosity, crushing value, and water absorption, as well as lower apparent density compared with waste concrete recycled aggregates. Therefore, it is necessary to develop a fully recycled concrete mainly composed of brick-concrete recycled aggregates and having excellent mechanical properties and durability.

[0003] CN111320438A discloses a green and environment-friendly concrete and its preparation method. The green and environment-friendly concrete provided by this invention includes the following components in parts by weight: 180 - 220 parts of portland cement; 170 - 180 parts of water; 740 - 760 parts of medium sand; 800 - 860 parts of crushed stone; 210 - 240 parts of recycled concrete waste; 70 - 80 parts of fly ash; 160 - 190 parts of slag powder; 4 - 5 parts of water reducer; 2 - 3 parts of retarder; 8 - 12 parts of filling and strengthening material; 10 - 16 parts of diatomite; 25 - 35 parts of urea; 8 - 10 parts of soybean hull powder. The carbonation rate of the green and environment-friendly concrete in this invention is slower during long-term application, and it can generally maintain good and stable compressive strength, but its impermeability performance has not been improved.

[0004] CN118771823A discloses a coarse aggregate ultra-high performance concrete and its preparation method and application. The coarse aggregate ultra-high performance concrete of this invention includes 600 - 1000 parts of cement, 100 - 300 parts of silica fume, 100 - 200 parts of mineral admixture, 10 - 50 parts of water reducer, 600 - 1000 parts of fine aggregate, 200 - 600 parts of coarse aggregate, 50 - 200 parts of steel fiber, and 100 - 200 parts of water. Although the concrete provided by this invention has good compressive strength, elastic modulus, initial crack flexural strength, flexural strength, and fracture toughness, its frost resistance is poor, which is not conducive to long-term use. Summary of the Invention

[0005] In view of the above-mentioned defects of the prior art, the present invention provides a fully recycled concrete. By optimizing the paste-aggregate ratio, water-cement ratio and adopting a secondary mixing process, and simultaneously introducing a strengthening and toughening agent for synergistic use, the fully recycled concrete provided by the present invention has good compressive strength, splitting tensile strength, axial compressive strength, chloride ion penetration resistance and frost resistance.

[0006] To achieve the above object, the present invention provides a method for preparing a fully recycled concrete, which is characterized by comprising the following steps:

[0007] Add the brick-concrete recycled coarse aggregate and the brick-concrete recycled fine aggregate into a mixer and mix and stir for 110-130 s, add cement and 1 / 2 of the total mass of water, and continue to stir for 80-100 s; then add the remaining 1 / 2 of the water and the polycarboxylate superplasticizer, and continue to stir for 50-70 s; then evenly sprinkle in the steel fiber, stir for 160-200 s, and discharge to prepare the fully recycled concrete;

[0008] Or, add the brick-concrete recycled coarse aggregate and the brick-concrete recycled fine aggregate into a mixer and mix and stir for 110-130 s, add cement, the strengthening and toughening agent and 1 / 2 of the total mass of water, and continue to stir for 80-100 s; then add the remaining 1 / 2 of the water and the polycarboxylate superplasticizer, and continue to stir for 50-70 s; then evenly sprinkle in the steel fiber, stir for 160-200 s, and discharge to prepare the fully recycled concrete.

[0009] Preferably, the weight ratio of each raw material component is:

[0010] 290-540 parts of cement, 1100-1200 parts of brick-concrete recycled coarse aggregate, 650-680 parts of brick-concrete recycled fine aggregate, 145-250 parts of water, 30-80 parts of steel fiber, 1.4-2.7 parts of polycarboxylate superplasticizer;

[0011] Or, 290-540 parts of cement, 1100-1200 parts of brick-concrete recycled coarse aggregate, 650-680 parts of brick-concrete recycled fine aggregate, 145-250 parts of water, 30-80 parts of steel fiber, 1.4-2.7 parts of polycarboxylate superplasticizer, 40-60 parts of strengthening and toughening agent.

[0012] Preferably, the steel fiber is selected from one of corrugated steel fibers and end-hooked steel fibers.

[0013] Preferably, the strengthening and toughening agent is composed of an aqueous polyurethane-epoxy resin emulsion and a synergist mixed in a mass ratio of 2-4:1.

[0014] In the present invention, the aqueous polyurethane-epoxy resin emulsion has a good effect on improving the strength of concrete. It can form a network structure inside the concrete, fill the pores, enhance the bonding force between the aggregate and the cement paste, and improve the overall compressive strength. The polyurethane in the aqueous polyurethane-epoxy resin emulsion has flexibility and elasticity, which can disperse stress, thereby increasing the splitting tensile strength. Moreover, the polymer in the emulsion can strengthen the microstructure of the concrete, and together with the toughening effect of the polyurethane, it can jointly improve the axial tensile strength of the concrete. In addition, the aqueous polyurethane-epoxy resin emulsion also has a good effect on improving the impermeability durability and freeze-thaw resistance of the concrete. It can significantly enhance the chloride ion penetration resistance of the concrete. After the emulsion forms a film, it fills the pores, reduces the porosity and pore size, and effectively blocks the migration and diffusion of chloride ions. And during the freeze-thaw cycle, the polymer in the emulsion can relieve the internal stress concentration, reduce microcracks; at the microscopic level, it optimizes the pore structure of the concrete, reduces the content of freezable water, alleviates the freeze-thaw damage, and maintains the integrity of the concrete.

[0015] Preferably, the preparation method of the synergist comprises the following steps, by weight:

[0016] S1. Mix 1.5 - 3 parts by weight of eucommia gum with 95 - 105 parts by weight of toluene and stir until the eucommia gum is dissolved. Then add 0.3 - 0.4 parts by weight of hydrogen peroxide and 0.1 - 0.2 parts by weight of formic acid, and carry out a mixing reaction at 38 - 42 °C for 4 - 6 h to obtain a mixed solution; then add 8 - 12 parts by weight of water to the mixed solution and continue to stir for 0.5 - 2 h to obtain an epoxidized eucommia gum emulsion; mix 8 - 12 parts by weight of nano-clay with 95 - 105 parts by weight of water to obtain a suspension, and then add the suspension to the above epoxidized eucommia gum emulsion and continue to stir and react for 0.5 - 2 h. The product is precipitated with absolute ethanol, washed, and dried in vacuum at room temperature to obtain modified nano-clay;

[0017] S2. Mix 1.5 - 3 parts of the modified nano-clay prepared in step S1 above, 25 - 35 parts of absolute ethanol and 0.01 - 0.1 part of phytic acid, and place them in a mixing and stirring at 300 - 500 rpm and 75 - 85 °C for 3 - 5 h to obtain a mixed solution; centrifuge the mixed solution, collect the precipitate, wash it with water, and dry it in vacuum at 55 - 65 °C to obtain a nano-clay composite material, that is, the synergist.

[0018] Preferably, step S2 can also be, by weight:

[0019] Mix 1.5 - 3 parts of the modified nano - clay prepared in the above - mentioned step S1, 25 - 35 parts of absolute ethanol, 0.01 - 0.1 part of phytic acid and 0.01 - 0.05 part of corrosion inhibitor, and place them under mixing and stirring at 300 - 500 rpm and 75 - 85 °C for 3 - 5 h to obtain a mixed solution; centrifuge the mixed solution, collect the precipitate, wash it with water and then vacuum - dry it at 55 - 65 °C to obtain a nano - clay composite material, namely the synergist.

[0020] Further preferably, the corrosion inhibitor is selected from at least one of zinc chloride and cerous nitrate hexahydrate.

[0021] As a nano - enhancer, nano - clay can fill the pores of concrete, enhance the bonding force between the aggregate and the cement paste, and at the same time optimize the microstructure of concrete, thereby improving the overall uniformity, compactness and strength of concrete. Concrete added with nano - clay has a lower porosity and pore size, making it more difficult for chloride ions to migrate and diffuse inside the concrete, and the chloride - ion penetration resistance is significantly improved. In addition, during the freeze - thaw cycle, nano - clay can relieve the stress concentration inside the concrete, reduce the micro - cracks generated by freeze - thaw action, and maintain the integrity of the concrete. However, due to the easy agglomeration of nano - clay in concrete and its poor compatibility with water - borne polyurethane - epoxy resin emulsion, the uniformity of nano - clay in the concrete matrix will be reduced, resulting in local stress concentration, and at the same time affecting the rheological properties and workability of the concrete, which not only affects the overall performance of the concrete but also increases the construction difficulty of the concrete. Based on this, the nano - clay composite material prepared in the present invention is used as a synergist and mixed with water - borne polyurethane - epoxy resin emulsion as the strengthening and toughening agent of the fully recycled concrete of the present invention, which can effectively solve the problem of easy agglomeration of nano - clay in concrete and improve the problem of its poor compatibility with water - borne polyurethane - epoxy resin emulsion, and further improve the compressive strength, splitting tensile strength, chloride - ion penetration resistance and frost resistance of the fully recycled concrete with brick - mix aggregate of the present invention.

[0022] For the preparation method of the above synergist, the present invention first obtains epoxidized Eucommia ulmoides gum emulsion by subjecting Eucommia ulmoides gum to epoxidation reaction under the action of hydrogen peroxide and formic acid, and then mixes it with nano-clay. The epoxy groups introduced into the epoxidized Eucommia ulmoides gum emulsion react with the hydroxyl groups on the surface of the nano-clay through epoxy-ring opening reaction and are grafted onto the surface of the nano-clay, thereby preparing epoxidized Eucommia ulmoides gum modified nano-clay, which improves the surface activity of the nano-clay and introduces epoxy groups at the same time; then the modified nano-clay is mixed and reacted with phytic acid and corrosion inhibitor. Phytic acid contains multiple phosphoric acid groups, and these groups can react with the epoxy groups introduced by epoxidized Eucommia ulmoides gum to form strong chemical bonds, thereby grafting phytic acid onto the surface of the modified nano-clay; then the corrosion inhibition ions zinc ions or cerium ions in the corrosion inhibitor can react with the phosphoric acid groups in the phytic acid grafted onto the surface of the nano-clay to form stable coordination compounds, and thus are fixed onto the surface of the nano-clay, thereby preparing a nano-clay composite material, that is, the synergist of the present invention.

[0023] The present invention also provides a fully recycled concrete prepared by the above method.

[0024] The present invention also provides the application of the fully recycled concrete in bridges, roads and high-rise buildings.

[0025] In the present invention, steel fibers have the function of toughening and crack resistance, while concrete is a typical brittle material. When an appropriate amount of steel fibers are incorporated into the fully recycled concrete, the steel fibers can enhance the durability performance of the fully recycled concrete by improving the pore structure and interfacial transition zone, and give full play to its bridging effect, which can effectively improve the defects of low tensile strength, high brittleness and easy cracking of the concrete, and has an obvious enhancing effect on the overall performance of the fully recycled concrete.

[0026] The beneficial effects of the present invention:

[0027] 1. Compared with the prior art, in this paper, by using 100% brick-concrete recycled coarse and fine aggregates to replace natural aggregates, brick-concrete aggregate fully recycled concrete is configured, and steel fibers are incorporated on the basis of the brick-concrete aggregate fully recycled concrete, providing a reference basis for the efficient utilization of brick-concrete building solid waste; at the same time, by optimizing the paste-aggregate ratio, water-cement ratio and adopting a secondary mixing process, high-value and full-component utilization of brick-concrete building solid waste is realized, providing support for expanding the practical engineering application of fully recycled concrete. The fully recycled concrete provided by the present invention not only has excellent mechanical properties and toughness, but also has good chloride ion penetration resistance and frost resistance, and its frost resistance life in North China is between 20 and 30 years, and its durability performance is good.

[0028] 2. Compared with the prior art, the present invention prepares a nano-clay composite material by compound modification of nano-clay, and uses it as a synergist to be mixed with a waterborne polyurethane-epoxy resin emulsion as the strengthening and toughening agent for the fully recycled concrete of the present invention. It can effectively solve the problem of easy agglomeration of nano-clay in concrete and improve the problem of poor compatibility with the waterborne polyurethane-epoxy resin emulsion, further improving the compressive strength, splitting tensile strength, chloride ion penetration resistance and frost resistance of the brick-concrete aggregate fully recycled concrete of the present invention, which is beneficial to further improving the durability of the fully recycled concrete. Detailed implementation manners

[0029] The parameters and sources of the specific chemical substances used are as follows:

[0030] The brick-concrete recycled coarse aggregate is a recycled building material. It mainly comes from the construction waste after the demolition of abandoned brick-concrete structures. Through a series of processing such as crushing and screening, the components such as waste bricks and a small amount of concrete blocks are made into particulate materials with a particle size greater than 4.75 mm, and these particulate materials are the brick-concrete recycled coarse aggregate. In the embodiment, the brick-concrete recycled coarse aggregate has a particle size range of 4.75 mm to 31.5 mm and is sourced from Jin Ke Renewable Resources Co., Ltd. in Xuchang City, Henan Province;

[0031] The brick-concrete recycled fine aggregate is particulate material with a particle size less than 4.75 mm obtained from waste brick-concrete construction waste. It mainly contains components such as crushed bricks and mortar particles. In the embodiment, the brick-concrete recycled fine aggregate has a particle size range of 1.18 mm to 4.75 mm, fineness modulus: 2.62, and is sourced from Jin Ke Renewable Resources Co., Ltd. in Xuchang City, Henan Province;

[0032] Cement, which is P•O 42.5 grade cement, brand: Tianrui;

[0033] The polycarboxylate superplasticizer, model SPF-300, is sourced from Liaoning Kelong Fine Chemical Co., Ltd.;

[0034] The end-hooked steel fiber, diameter: 0.75 mm, average length: 35 mm, cross-section: circular, is sourced from Hebei Baihang Steel Products Factory;

[0035] The waterborne polyurethane-epoxy resin emulsion, model 5520-w-60A, brand: HEXION of the United States;

[0036] Eucommia gum, purity: >96%, brand: Shandong Beilong;

[0037] Nano-clay, particle size: 60 nm. Example 1

[0038] A preparation method for fully recycled concrete includes the following steps:

[0039] Add 1188 parts by weight of brick-concrete recycled coarse aggregate and 669 parts by weight of brick-concrete recycled fine aggregate into a mixer and mix and stir for 120 s, add 530 parts by weight of cement and 106 parts by weight of water, and continue to stir for 90 s; then add 106 parts by weight of water and 2.65 parts by weight of polycarboxylate superplasticizer, and continue to stir for 60 s; then evenly sprinkle 78 parts by weight of end-hooked steel fibers, stir for 180 s, and discharge to prepare all-recycled concrete. Example 2

[0040] A preparation method of all-recycled concrete includes the following steps:

[0041] Add 1188 parts by weight of brick-concrete recycled coarse aggregate and 669 parts by weight of brick-concrete recycled fine aggregate into a mixer and mix and stir for 120 s, add 530 parts by weight of cement, 50 parts by weight of strengthening and toughening agent and 106 parts by weight of water, and continue to stir for 90 s; then add 106 parts by weight of water and 2.65 parts by weight of polycarboxylate superplasticizer, and continue to stir for 60 s; then evenly sprinkle 78 parts by weight of end-hooked steel fibers, stir for 180 s, and discharge to prepare all-recycled concrete.

[0042] The strengthening and toughening agent is formed by mixing waterborne polyurethane-epoxy resin emulsion and synergist in a mass ratio of 3:1.

[0043] The preparation method of the synergist includes the following steps:

[0044] S1. Mix 2 parts by weight of eucommia gum with 100 parts by weight of toluene and stir until the eucommia gum is dissolved, then add 0.35 parts by weight of hydrogen peroxide and 0.14 parts by weight of formic acid, and carry out a mixing reaction at 40 °C for 5 h to obtain a mixed solution; then add 10 parts by weight of water to the mixed solution and continue to stir for 1 h to obtain an epoxidized eucommia gum emulsion; mix 10 parts by weight of nano-clay with 100 parts by weight of water and stir to obtain a suspension, then add the suspension to the above epoxidized eucommia gum emulsion and continue to stir and react for 1 h. The product is precipitated with absolute ethanol, washed, and dried in vacuum at room temperature to obtain modified nano-clay;

[0045] S2. Mix 2 parts by weight of the modified nano-clay prepared in the above step S1, 33 parts by weight of absolute ethanol and 0.06 parts by weight of phytic acid, place them at 400 rpm and 82 °C and mix and stir for 4 h to obtain a mixed solution; centrifuge the mixed solution, collect the precipitate, wash it with water and dry it in vacuum at 62 °C to obtain a nano-clay composite material, that is, the synergist. Example 3

[0046] A preparation method of all-recycled concrete, different from Example 2 in that the preparation method of the synergist includes the following steps:

[0047] S1. Mix 2 parts by weight of eucommia gum with 100 parts by weight of toluene and stir until the eucommia gum is dissolved. Then add 0.35 parts by weight of hydrogen peroxide and 0.14 parts by weight of formic acid, and mix and react at 40 °C for 5 h to obtain a mixed solution. Then add 10 parts by weight of water to the mixed solution and continue to stir for 1 h to obtain an epoxidized eucommia gum emulsion. Mix 10 parts by weight of nano-clay with 100 parts by weight of water to obtain a suspension, and then add the suspension to the above epoxidized eucommia gum emulsion and continue to stir and react for 1 h. The product is precipitated with absolute ethanol, washed, and dried under vacuum at room temperature to obtain modified nano-clay;

[0048] S2. Mix 2 parts by weight of the modified nano-clay prepared in the above step S1, 33 parts by weight of absolute ethanol, 0.06 parts by weight of phytic acid, and 0.03 parts by weight of zinc chloride, and place them at 400 rpm and 82 °C for mixing and stirring for 4 h to obtain a mixed solution. Centrifuge the mixed solution, collect the precipitate, wash it with water, and dry it under vacuum at 62 °C to obtain a nano-clay composite material, that is, a synergist. Example 4

[0049] A preparation method of all-recycled concrete, which is different from Example 2 in that the preparation method of the synergist includes the following steps:

[0050] S1. Mix 2 parts by weight of eucommia gum with 100 parts by weight of toluene and stir until the eucommia gum is dissolved. Then add 0.35 parts by weight of hydrogen peroxide and 0.14 parts by weight of formic acid, and mix and react at 40 °C for 5 h to obtain a mixed solution. Then add 10 parts by weight of water to the mixed solution and continue to stir for 1 h to obtain an epoxidized eucommia gum emulsion. Mix 10 parts by weight of nano-clay with 100 parts by weight of water to obtain a suspension, and then add the suspension to the above epoxidized eucommia gum emulsion and continue to stir and react for 1 h. The product is precipitated with absolute ethanol, washed, and dried under vacuum at room temperature to obtain modified nano-clay;

[0051] S2. Mix 2 parts by weight of the modified nano-clay prepared in the above step S1, 33 parts by weight of absolute ethanol, 0.06 parts by weight of phytic acid, and 0.03 parts by weight of cerous nitrate hexahydrate, and place them at 400 rpm and 82 °C for mixing and stirring for 4 h to obtain a mixed solution. Centrifuge the mixed solution, collect the precipitate, wash it with water, and dry it under vacuum at 62 °C to obtain a nano-clay composite material, that is, a synergist. Comparative Example 1

[0052] A preparation method of all-recycled concrete, which is different from Example 2 in that the preparation method of the synergist includes the following steps:

[0053] Mix 2 parts by weight of eucommia gum with 100 parts by weight of toluene and stir until the eucommia gum dissolves. Subsequently, add 0.35 parts by weight of hydrogen peroxide and 0.14 parts by weight of formic acid, and mix and react at 40 °C for 5 h to obtain a mixed solution. Then, add 10 parts by weight of water to the mixed solution and continue stirring for 1 h to obtain an epoxidized eucommia gum emulsion. Mix 10 parts by weight of nano-clay with 100 parts by weight of water and stir to obtain a suspension, and then add the suspension to the above epoxidized eucommia gum emulsion and continue stirring and reacting for 1 h. The product is precipitated with absolute ethanol, washed, and dried in vacuum at room temperature to obtain modified nano-clay, i.e., the synergist. Comparative Example 2

[0054] A preparation method of all-recycled concrete includes the following steps:

[0055] Add 1188 parts by weight of brick-concrete recycled coarse aggregate and 669 parts by weight of brick-concrete recycled fine aggregate into a mixer and mix and stir for 120 s. Add 530 parts by weight of cement, 50 parts by weight of the strengthening and toughening agent, and 106 parts by weight of water, and continue stirring for 90 s. Then add 106 parts by weight of water and 2.65 parts by weight of polycarboxylate superplasticizer, and continue stirring for 60 s. Then evenly sprinkle 78 parts by weight of end-hooked steel fibers, stir for 180 s, and discharge to prepare all-recycled concrete.

[0056] The strengthening and toughening agent is composed of an aqueous polyurethane-epoxy resin emulsion and nano-clay mixed in a mass ratio of 3:1. Comparative Example 3

[0057] A preparation method of all-recycled concrete includes the following steps:

[0058] Add 1188 parts by weight of brick-concrete recycled coarse aggregate and 669 parts by weight of brick-concrete recycled fine aggregate into a mixer and mix and stir for 120 s. Add 530 parts by weight of cement, 50 parts by weight of the strengthening and toughening agent, and 106 parts by weight of water, and continue stirring for 90 s. Then add 106 parts by weight of water and 2.65 parts by weight of polycarboxylate superplasticizer, and continue stirring for 60 s. Then evenly sprinkle 78 parts by weight of end-hooked steel fibers, stir for 180 s, and discharge to prepare all-recycled concrete.

[0059] The strengthening and toughening agent is an aqueous polyurethane-epoxy resin emulsion.

[0060] Test Example 1

[0061] Slump flow and mechanical property tests

[0062] Slump is one of the important indicators to measure the workability of fresh concrete mixture. Therefore, in this invention, the workability performance of concrete is tested by measuring the slumps of each example and comparative example. The slump test is carried out in accordance with the "Standard Test Method for Performance of Ordinary Concrete Mixtures" (GB / T 50080 - 2016).

[0063] Compressive strength, splitting tensile strength and axial tensile strength are important mechanical property indicators of concrete mixture. They play a crucial role in evaluating the quality and performance of concrete, and are of great significance for ensuring the safety and durability of concrete structures. Therefore, in this invention, the mechanical properties of concrete are tested by measuring the compressive strength, splitting tensile strength and axial tensile strength of each example and comparative example. The compressive strength and splitting tensile strength tests are carried out in accordance with the "Standard Test Method for Physical and Mechanical Properties of Concrete" (GB / T 50081 - 2019), and the test instrument used is the YAW - 3000 microcomputer - controlled constant - loading pressure testing machine; the axial tensile strength test is carried out in accordance with the "Standard Test Method for Physical and Mechanical Properties of Concrete" (GB / T 50081 - 2019), and the test instrument used is the WAW - 600D microcomputer - controlled universal testing machine.

[0064] The specific test results are shown in Table 1 below:

[0065] Table 1

[0066]

[0067] As can be seen from Table 1, by comparing Examples 1 - 4 with Comparative Examples 1 - 3, it is found that compared with Example 1, the slumps of Examples 2 - 4 and Comparative Examples 1 - 3 with added strengthening and toughening agents all decrease. The decreasing trends of Examples 2 - 4 and Comparative Example 1 are relatively small, while those of Comparative Examples 2 - 3 decrease significantly, with Comparative Example 3 showing the most significant decrease. The reason may be that the addition of waterborne polyurethane - epoxy resin emulsion will increase the viscosity of concrete, resulting in a decrease in slump, while the introduction of the synergist nano - clay composite material can form a network structure, which may improve the rheological properties of concrete and reduce the free flow of water, thus alleviating the decreasing trend of slump.

[0068] Comparing Examples 1-4 with Comparative Examples 1-3, it is found that the compressive strength, splitting tensile strength, and axial tensile strength of Examples 2-4 are significantly higher than those of Example 1 and Comparative Examples 1-3. Among them, Example 4 has the highest compressive strength, splitting tensile strength, and axial tensile strength, indicating that the toughening and strengthening agent prepared by mixing the nano-clay composite as a synergist with the waterborne polyurethane-epoxy resin emulsion is beneficial to improving the compressive strength, splitting tensile strength, and axial tensile strength of concrete, and is conducive to improving the mechanical properties of concrete. The reason may be that the introduction of epoxidized eucommia gum and phytic acid in the nano-clay composite improves the surface activity of the nano-clay, making it better dispersed in the concrete to form a uniform strengthening phase. Moreover, the nano-clay composite can form a uniformly distributed cross-linked network structure with the polymers in the waterborne polyurethane-epoxy resin emulsion, further strengthening the microstructure of the concrete. Therefore, the synergistic use of the nano-clay composite and the waterborne polyurethane-epoxy resin emulsion can not only effectively disperse stress, improve the density and strength of the concrete, but also improve the toughness and crack resistance of the concrete, reduce the generation and propagation of micro-cracks, and is beneficial to improving the tensile properties of the concrete. In addition, the nano-clay composite can improve the interfacial transition zone in the concrete, enhance the bonding force between the aggregate and the cement paste, and thus improve the overall performance of the concrete.

[0069] Comparing Example 3 with Example 4, it is found that the mechanical properties of Example 4 are better than those of Example 3. The reason may be that the corrosion inhibitor used in the preparation of the synergist in Example 3 is zinc chloride, while the corrosion inhibitor used in Example 4 is cerous nitrate hexahydrate. Compared with zinc ions (Zn 2+ ), cerium ions (Ce 3+ ), have a larger coordination number and stronger coordination ability, and can form stable coordination compounds with multiple phosphate groups in phytic acid. This coordination effect not only enhances the chemical stability of the nano-clay surface, enabling it to remain stable in the alkaline environment of the concrete and not easily hydrolyzed or ion-exchanged, but also is more conducive to improving the mechanical properties of the concrete.

[0070] Test Example 2

[0071] Chloride ion penetration resistance test

[0072] Chloride ion penetration resistance is one of the main research contents of the impermeability durability of concrete. The ease of entry of gases, liquids, ions, etc. into the interior of the concrete under the action of the external environment can reflect the strength of the concrete's impermeability performance. Chloride ions enter the interior of the concrete through the molecular movement caused by the concentration difference of chloride ions inside and outside the concrete specimen. Generally, it is represented by the chloride ion diffusion coefficient. The larger the chloride ion diffusion coefficient, the worse the chloride ion penetration resistance.

[0073] Referring to the standard of "Standard Test Method for Long-Term Performance and Durability of Ordinary Concrete" (GB / T 50082-2009), the rapid chloride migration coefficient method (RCM method) was used to conduct the chloride ion penetration resistance test. The specimens were cylindrical specimens with a size of φ100×50mm; the chloride ion diffusion coefficient D was calculated according to the test results. RCM , and according to the chloride ion diffusion coefficient D of the concrete in each example and comparative example RCM , the chloride ion penetration resistance performance of the concrete was evaluated. The evaluation method of the chloride ion penetration resistance performance of the concrete refers to the chloride ion diffusion coefficient standard in Table 2 below:

[0074] Table 2 Chloride Ion Diffusion Coefficient Standard

[0075]

[0076] The specific test results are shown in Table 3 below:

[0077] Table 3

[0078]

[0079] It can be seen from Table 3 that by comparing Examples 1-4 and Comparative Examples 1-3, it is found that compared with Example 1, the chloride ion diffusion coefficients of Examples 2-4 and Comparative Examples 1-3 all decreased, indicating that the introduction of the toughening and strengthening agent is beneficial to improving the chloride ion penetration resistance performance of the concrete. By comparing Examples 2-4 and Comparative Examples 1-3, it is found that the chloride ion diffusion coefficients of Examples 2-4 are significantly lower than those of Comparative Examples 1-3, and the evaluation of the chloride ion penetration resistance performance is "good". Among them, the chloride ion diffusion coefficient of Example 4 is the lowest, indicating that the toughening and strengthening agent prepared by mixing the nano-clay composite material as a synergist with the waterborne polyurethane-epoxy resin emulsion is beneficial to improving the chloride ion penetration resistance performance of the concrete. The reason may be that when the nano-clay composite material is added to the waterborne polyurethane-epoxy resin emulsion, due to the large specific surface area and layered structure of the nano-clay and the presence of epoxy-based eucommia gum and phytic acid grafted on its surface, it can be evenly distributed in the waterborne polyurethane-epoxy resin emulsion and form a dense cross-linked network structure, forming a uniform protective barrier to prevent the penetration of chloride ions. At the same time, due to the coordination effect of the corrosion inhibitor ions in the nano-clay composite material, the stability of this barrier is further enhanced, making it more difficult for chloride ions to migrate and diffuse inside the concrete, thereby steadily improving the chloride ion penetration resistance performance of the concrete. At the same time, the phosphate groups in the phytic acid on the surface of the nano-clay composite material and the corrosion inhibitor ions such as zinc ions (Zn 2+ ) or cerium ions (Ce 3+ ) can form stable chemical bonds with chloride ions, forming a chemical barrier effect, which can further prevent the penetration of chloride ions.

[0080] Comparing Comparative Example 3 and Example 4, it is found that the chloride ion penetration resistance of Example 4 is better than that of Example 3. The reason may be that the corrosion inhibitor used in the preparation of the synergist in Example 3 is zinc chloride, while the corrosion inhibitor used in Example 4 is cerous nitrate hexahydrate. Compared with zinc ions (Zn 2+ ), cerium ions (Ce 3+ ), have a larger coordination number and stronger coordination ability, and can form stable coordination compounds with multiple phosphate groups in phytic acid. This coordination effect not only enhances the chemical stability of the surface of the nano-clay, enabling it to remain stable in the alkaline environment of concrete and not being easily hydrolyzed or ion-exchanged, thereby effectively preventing the penetration of chloride ions in the long term, but also can form a denser chemical barrier to more effectively prevent the penetration of chloride ions.

[0081] Test Example 3

[0082] Freeze-thaw cycle test

[0083] Referring to the "Standard Test Method for Long-Term Performance and Durability of Ordinary Concrete" (GB / T 50082 - 2009), the freeze-thaw cycle test was carried out by the rapid freeze-thaw method. The specimen sizes were prismatic specimens of 100 mm×100 mm×400 mm and cubic specimens of 100 mm×100 mm×100 mm. The freeze-thaw cycle test was carried out using a walk-in multi-functional environmental simulation test system. The designed number of freeze-thaw cycles was 100 times. For the prismatic specimens, the mass and dynamic elastic modulus were measured every 50 freeze-thaw cycles, and the mass loss rate and relative dynamic elastic modulus loss were calculated; for the cubic specimens, the compressive strength was tested every 50 freeze-thaw cycles, and the strength loss was calculated;

[0084] The specific test results are shown in Table 4 below:

[0085] Table 4

[0086]

[0087] As can be seen from Table 4, by comparing Examples 1-4 and Comparative Examples 1-3, it is found that the mass loss rate and compressive strength loss rate of Examples 2-4 after 50 and 100 freeze-thaw cycles are significantly lower than those of Example 1 and Comparative Examples 1-3, and the relative dynamic elastic modulus is significantly higher than that of Example 1 and Comparative Examples 1-3. Among them, the mass loss rate and compressive strength loss rate of Example 4 after 50 and 100 freeze-thaw cycles are the lowest, and the relative dynamic elastic modulus is the highest. This shows that the toughening and strengthening agent prepared by mixing the nano-clay composite material as a synergist with the waterborne polyurethane-epoxy resin emulsion is beneficial to improving the freeze-thaw resistance of concrete. The reason may be that the introduction of epoxidized eucommia gum and phytic acid in the nano-clay composite material improves the surface activity of the nano-clay, making it better dispersed in the concrete, forming a uniform strengthening phase, improving the microstructure of the concrete, reducing the internal porosity, increasing the density and durability of the concrete, thereby improving the freeze-thaw resistance of the concrete. And the coordination effect of the corrosion inhibitor ions further enhances the stability of this strengthening phase, which is beneficial to further improving the freeze-thaw resistance of the concrete. The synergistic use of the nano-clay composite material and the waterborne polyurethane-epoxy resin emulsion can form a physical and chemical double barrier in the concrete, jointly improving the interfacial transition zone between the aggregate and the cement paste, enhancing the bonding strength and durability of the interface, and thus significantly improving the freeze-thaw resistance of the concrete.

[0088] By comparing Example 3 and Example 4, it is found that the freeze-thaw resistance of Example 4 is better than that of Example 3. The reason may be that the corrosion inhibitor used in the preparation of the synergist in Example 3 is zinc chloride, while the corrosion inhibitor used in Example 4 is cerium nitrate hexahydrate. Compared with zinc ions (Zn 2+ ), the coordination compound formed by cerium ions (Ce 3+ ) has higher chemical stability and can remain stable in the alkaline environment of the concrete, and is not easily hydrolyzed or ion-exchanged. This stability helps to maintain the structural integrity of the nano-clay composite material during the freeze-thaw cycle and reduce the generation of microcracks caused by chemical changes. However, the coordination compound formed by zinc ions (Zn 2+ ) is relatively unstable in the alkaline environment and is prone to hydrolysis or ion-exchange, resulting in the gradual failure of the chemical barrier and the easier generation of microcracks during the freeze-thaw cycle. Therefore, Example 4 has stronger freeze-thaw resistance.

Claims

1. A method for preparing fully recycled concrete, characterized in that: The following steps are involved: Add the brick-concrete recycled coarse aggregate and the brick-concrete recycled fine aggregate into a mixer and mix and stir for 110-130 seconds, add cement, a reinforcing and toughening agent and water accounting for 1 / 2 of the total mass of water, and continue to stir for 80-100 seconds; then add the remaining 1 / 2 of the water and a polycarboxylic acid high-performance water reducer, and continue to stir for 50-70 seconds; then evenly sprinkle the steel fiber, stir for 160-200 seconds, and discharge the material to prepare a fully recycled concrete; the weight ratio of each raw material component is: 290-540 parts of cement, 1100-1200 parts of brick-concrete recycled coarse aggregate, 650-680 parts of brick-concrete recycled fine aggregate, 145-250 parts of water, 30-80 parts of steel fiber, 1.4-2.7 parts of polycarboxylic acid high-performance water reducer, and 40-60 parts of reinforcing and toughening agent; The reinforcing and toughening agent is prepared by mixing a waterborne polyurethane-epoxy resin emulsion and a synergist at a mass ratio of 2-4:1; The synergist is prepared by the following method steps, calculated by weight: S1, 1.5-3 parts by weight of eucommia gum and 95-105 parts by weight of toluene are mixed and stirred until the eucommia gum is dissolved, and then 0.3-0.4 parts by weight of hydrogen peroxide and 0.1-0.2 parts by weight of formic acid are added, and the mixture is reacted at 38-42° C. for 4-6 hours to obtain a mixed solution; then 8-12 parts by weight of water are added to the mixed solution, and the mixture is stirred for 0.5-2 hours to obtain an epoxidized eucommia gum latex; 8-12 parts by weight of nanoclay are mixed and stirred with 95-105 parts by weight of water to obtain a suspension, and the suspension is added to the above-mentioned epoxidized eucommia gum latex, and the reaction is stirred for 0.5-2 hours, and the product is precipitated with anhydrous ethanol, washed, and dried in vacuo at room temperature to obtain modified nanoclay; S2, mixing 1.5-3 parts of the modified nanoclay prepared in the above step S1, 25-35 parts of anhydrous ethanol and 0.01-0.1 parts of phytic acid, placing the mixture at 300-500 rpm and 75-85°C and stirring for 3-5 hours to obtain a mixed solution; centrifuging the mixed solution, collecting the precipitate, washing it with water and vacuum drying it at 55-65°C to obtain a nanoclay composite material, i.e., a synergist; Alternatively, the step S2 comprises, by weight: 1.5-3 parts of the modified nanoclay prepared in step S1, 25-35 parts of anhydrous ethanol, 0.01-0.1 parts of phytic acid and 0.01-0.05 parts of a corrosion inhibitor are mixed, and the mixture is stirred at 300-500 rpm and 75-85° C. for 3-5 hours to obtain a mixed solution; the mixed solution is centrifuged, and the precipitate is collected, washed with water, and then vacuum dried at 55-65° C. to obtain a nanoclay composite material, i.e., a synergist; The corrosion inhibitor is cerous nitrate hexahydrate.

2. The method for preparing fully recycled concrete according to claim 1, characterized in that: The steel fiber is selected from one of a corrugated steel fiber and an end hook steel fiber.

3. A fully recycled concrete, characterized in that: Prepared by the method according to any one of claims 1 to 2.

4. Application of the fully recycled concrete as claimed in claim 3 in bridges, roads and high-rise buildings.

Images