Recycled concrete and preparation method thereof

Abstract

The invention discloses recycled concrete and a preparation method thereof, and belongs to the technical field of concrete. The recycled concrete is prepared from 600 to 800 parts of modified recycled coarse aggregate, 300 to 400 parts of river sand, 300 to 400 parts of cement, 60 to 80 parts of modified fiber, 70 to 80 parts of fly ash, 70 to 80 parts of silica fume, 1 to 3 parts of an active agent, 1 to 3 parts of a polycarboxylate superplasticizer and 190 to 210 parts of water. The modified recycled aggregate and the modified fiber are jointly subjected to CO2 mineralization treatment, the durability of the recycled concrete is comprehensively improved through the synergistic effect of the modified recycled aggregate and the modified fiber, the obtained recycled concrete has good mechanical performance, meanwhile, cracking caused by the defects that the recycled aggregate is small in density, high in water absorption rate, poor in interface bonding force and the like can be reduced, and the service life of the recycled concrete is prolonged. The permeation and erosion of corrosive ions are reduced, and the comprehensive durability of the concrete is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of concrete, and particularly relates to a recycled concrete and a preparation method thereof. BACKGROUND

[0002] The recycled concrete refers to recycled aggregate formed by crushing, washing and grading of waste concrete blocks, mixed with natural aggregate such as sand and gravel according to a certain proportion and grading, partially or wholly replaced by natural aggregate, and then added with cement, water and the like to form new concrete. A large amount of construction waste (such as concrete produced by demolishing old buildings) is produced in the world every year, the recycled concrete can replace part of the natural aggregate, reduce the dependence on non-renewable resources such as sand and gravel; the production of natural aggregate needs mining, transportation and processing, while the recycled aggregate can utilize the waste concrete nearby, reduce the transportation distance and energy consumption, and indirectly reduce carbon emissions; the construction waste accounts for 30%-40% of the total amount of urban waste, and the recycled concrete technology can significantly reduce the landfill amount, reduce land occupation and environmental pollution. Therefore, the core of the recycled concrete is to realize the resource utilization of construction waste, reduce the mining of natural resources and waste landfill, and meet the concept of circular economy and sustainable development.

[0003] With the acceleration of urbanization construction, the recycled concrete has been widely used in non-structural engineering such as road base, slope protection and drainage facilities, and gradually penetrates into structural engineering (such as beams and columns). However, the recycled aggregate has some old cement mortar attached to the surface, and a large number of cracks exist on the surface and inside due to damage accumulation in the crushing production process, so compared with the natural aggregate, the recycled aggregate has the disadvantages of small density, high water absorption rate and poor interfacial bonding force, and thus the workability and mechanical properties of the recycled concrete are significantly lower than those of ordinary concrete. In the service process, due to the high water absorption rate and poor interfacial bonding force, the recycled concrete is prone to cracking, which causes some erosive ions to penetrate, and thus the durability of the concrete structure is significantly reduced. Therefore, how to improve the durability of the recycled concrete becomes a technical problem to be solved. SUMMARY

[0004] The present application aims to provide a recycled concrete which has good mechanical properties and can reduce cracking caused by the disadvantages of the recycled aggregate such as small density, high water absorption rate and poor interfacial bonding force, reduce the penetration and erosion of erosive ions, and improve the comprehensive durability of the concrete.

[0005] To achieve the above technical purpose, the technical solution adopted by the present application is as follows: A kind of recycled concrete, it is made of the following weight parts of raw materials: modified recycled coarse aggregate 600-800 parts, river sand 300-400 parts, cement 300-400 parts, modified fiber 60-80 parts, fly ash 70-80 parts, silica ash 70-80 parts, active agent 1-3 parts, polycarboxylic acid water reducing agent 1-3 parts, water 190-210 parts;The active agent is carboxymethyl chitosan, nanometer silicon dioxide sol, sodium gluconate according to (1.2-1.5) :(1.8-2.5) :1.

[0006] Further, the modified recycled coarse aggregate is prepared by the following method: Step 1) crush and sieve the construction waste, take the recycled coarse aggregate with particle size of 5-25 mm, wash the surface dust, and dry to constant weight at 105±5 ℃; Step 2) immerse the dry aggregate in CaCl2 solution according to the solid-liquid ratio, place it in an ultrasonic cleaning tank for ultrasonic treatment for 20 minutes, and then separate the solid and liquid to obtain the activated coarse aggregate; Step 3) mix the activated coarse aggregate with a polyethyleneimine / sodium alginate composite solution according to the solid-liquid ratio, stir and react at 60 ℃ for 1 h, then separate the solid and liquid after the reaction to obtain the modified recycled coarse aggregate.

[0007] Further, the solid-liquid ratio of the dry aggregate to the CaCl2 solution in step 2) is 1:3 w / v.

[0008] Further, the concentration of the CaCl2 solution is 1.5 mol / L.

[0009] Further, the polyethyleneimine / sodium alginate composite solution in step 3) is prepared by the following method: slowly add polyethyleneimine to a 0.1 wt% sodium alginate solution so that the final solution has a polyethyleneimine concentration of 0.1 wt%, and then adjust the pH of the solution to 9.0-10.0 with 0.1 mol / L NaOH to obtain the solution.

[0010] Further, the solid-liquid ratio of the activated coarse aggregate to the polyethyleneimine / sodium alginate composite solution in step 3) is 1:5 w / v.

[0011] Further, the modified fiber is prepared by the following method: A. immerse polyvinyl alcohol fibers in a dopamine-Tris buffer solution, stir at room temperature for 10-16 hours, take out the fibers and dry them in an oven at 60 ℃ for 6 h to obtain pretreated fibers; B. immerse the pretreated fibers in a 1.5-2.0 mol / L CaCl2 solution, stir at 30-40 ℃ for 50-60 min, then take out the fibers and dry them to obtain the modified fibers.

[0012] Further, the dopamine-Tris buffer solution has a pH of 8.5 and a dopamine hydrochloride concentration of 1-5 g / L.

[0013] Further, the nanosilica sol has a solid content of 30%, a particle size of 5-20 nm, and a pH of 10-11.

[0014] The application further provides a preparation method of the recycled concrete. S1: preparing modified recycled coarse aggregate; S2: preparing modified fiber; S3: mixing the modified recycled coarse aggregate and the modified fiber uniformly, and then transferring into a CO2 mineralization reactor, and introducing 15% CO2 and 85% N2 mixed gas, and reacting at 0.5 MPa and 60 DEG C for 2 hours, to obtain premix one; S4: mixing cement, the premix one and water uniformly, adding an active agent and stirring for 5 minutes, adding a water reducing agent and stirring for 3 minutes, and then adding the remaining materials in proportion and stirring sufficiently, to obtain a uniform recycled concrete mixture; S5: pouring, vibrating and curing according to a conventional concrete construction method.

[0015] The application modifies the surface of the recycled coarse aggregate, and forms an organic template layer on the surface; the surface of the polyvinyl alcohol fiber is modified, and dopamine is self-polymerized on the fiber surface to form a strong-adhesion polydopamine (PDA) coating layer and adsorb a large amount of Ca 2+ ions; the modified recycled coarse aggregate and the modified fiber are mixed, and then subjected to CO2 mineralization treatment at the same time, to form CO3 2- / HCO3 - ions on the surface of the modified recycled aggregate and the organic template layer, and react with Ca 2+ ions adsorbed on the surface of the organic template layer to generate nanoscale CaCO3 particles; CO3 2- / HCO3 - ions on the surface of the modified fiber react with Ca 2+ ions adsorbed on the surface of the modified fiber to form micron / nanoscale CaCO3 crystals in situ on the fiber surface; meanwhile, the modified recycled aggregate and the modified fiber can form bridging CaCO3 crystals, or the crystals grown on the surfaces of the two are interlocked / interwoven to form a strong physical anchoring connection; meanwhile, the amino groups on the surface of the PDA form coordination bonds or ionic bonds with the CaCO3 crystals, to enhance the chemical combination, and greatly strengthen the direct connection between the aggregate and the fiber, to directly transfer part of the load from the aggregate to the fiber, and significantly improve the toughening, crack resistance and tensile resistance effect; the two synergistically improve the mechanical properties of the concrete.

[0016] The active agent of the present application can improve the workability of concrete, solve the defects of recycled aggregate, promote cement hydration, optimize the microstructure, reduce the interface debonding caused by shrinkage or load by improving the bonding force between the paste and the aggregate, and reduce the risk of micro-crack propagation. Combined with the crack resistance of modified fibers, the crack resistance coefficient of concrete is significantly improved, and the durability of concrete is enhanced.

[0017] The present application has the following beneficial effects: 2. The modified recycled coarse aggregate and the modified fiber form micron / nanometer level CaCO3 on the surface through co-mineralization treatment, and generate a “calcium carbonate bridge” or a crystal interweaving structure at the interface between the two. This physical anchoring significantly enhances the connection strength between the aggregate and the fiber, enabling the load to be directly transmitted from the aggregate to the fiber, thereby greatly improving the tensile, crack resistance and toughening effect of the concrete; the polydopamine coating on the surface of the modified fiber adsorbs a large amount of Ca 2+ ions, forming stronger mechanical engagement and chemical bonding with cement hydration products, improving the bonding performance of the fiber and the paste, and further enhancing the mechanical properties of the concrete.

[0018] 3. The mineralized layer and the organic template layer formed on the surface of the modified recycled aggregate effectively fill the cracks and pores inside the aggregate, significantly reducing its water absorption, thereby reducing cracking and the penetration of erosive ions caused by water penetration during service; the PDA / CaCO3 layer on the surface of the modified fiber has better compatibility with cement hydration products, forming a dense interface transition zone that effectively blocks the penetration of sulfate ions, chloride ions and other erosive ions, prolonging the service life of the concrete structure; the two work together to comprehensively improve the durability of recycled concrete.

[0019] 4. The present application realizes the dual goals of high performance and resource utilization of recycled concrete through innovation in materials, interfaces and processes, providing a reliable technical solution for green utilization of construction waste, with environmental, economic and social benefits. DETAILED DESCRIPTION

[0020] The technical solutions of the present application will be further described below in conjunction with specific embodiments, but are not limited thereto. The cement of the present application is P.O 42.5 Portland cement.

[0021] Example 1 A recycled concrete made from the following raw materials by weight: modified recycled coarse aggregate 600 kg, river sand 300 kg, cement 300 kg, modified fiber 60 kg, fly ash 70 kg, silica fume 70 kg, active agent 1 kg, polycarboxylic acid water reducer 1 kg, and water 190 kg.

[0022] The modified recycled coarse aggregate is prepared by the following method: Step 1) crushing and screening the construction waste, taking the recycled coarse aggregate with a particle size of 5-25 mm, washing the surface dust, and drying at 105±5℃ until constant weight; Step 2) immersing the dried aggregate in a 1.5 mol / L CaCl2 solution according to a solid-liquid ratio of 1:3 w / v, placing it in an ultrasonic cleaning tank for ultrasonic treatment for 20 minutes, and then separating the solid and liquid to obtain the activated coarse aggregate; Step 3) mixing the activated coarse aggregate with a polyethyleneimine / sodium alginate composite solution according to a solid-liquid ratio of 1:5 w / v, stirring at 60℃ for 1h, and then separating the solid and liquid after the reaction to obtain the modified recycled coarse aggregate.

[0023] The polyethyleneimine / sodium alginate composite solution in step 3) is prepared by slowly adding polyethyleneimine to a 0.1wt% sodium alginate solution to obtain a final solution with a polyethyleneimine concentration of 0.1wt%, and then adjusting the pH of the solution to 9.0 with 0.1mol / L NaOH.

[0024] The modified fiber is prepared by the following method: A. immersing polyvinyl alcohol fibers in a dopamine-Tris buffer solution, stirring at room temperature for 10-16 hours, taking out the fibers and drying them in an oven at 60℃ for 6h to obtain pretreated fibers; B. immersing the pretreated fibers in a 1.5 mol / L CaCl2 solution, stirring at 30℃ for 60 minutes, and then taking out the fibers and drying them to obtain the modified fibers.

[0025] The dopamine-Tris buffer solution has a pH of 8.5 and a dopamine hydrochloride concentration of 1g / L.

[0026] The active agent is carboxymethyl chitosan, nano-silica sol, and sodium gluconate in a ratio of 1.2:1.8:1; the nano-silica sol has a solid content of 30%, a particle size of 20nm, and a pH of 10.0.

[0027] A method for preparing the recycled concrete comprises the following steps: S1: preparing modified recycled coarse aggregate; S2: preparing modified fibers; S3: mixing the modified recycled coarse aggregate and the modified fibers uniformly, then transferring them into a CO2 mineralization reaction kettle, introducing 15% CO2 and 85% N2 mixed gas, and reacting at 60℃ for 2 hours under a pressure of 0.5MPa to obtain premix one; S4: mixing cement, premix one, and water uniformly, then adding an active agent and stirring for 5 minutes, adding a water reducing agent and stirring for 3 minutes, and then adding the remaining materials according to the proportion and stirring thoroughly to obtain a uniform recycled concrete mixture. S5: pouring, vibrating and curing according to the conventional concrete construction method.

[0028] Example 2 A recycled concrete is prepared from the following raw materials by weight: modified recycled coarse aggregate 800 kg, river sand 400 kg, cement 400 kg, modified fiber 80 kg, fly ash 80 kg, silica fume 80 kg, active agent 3 kg, polycarboxylate superplasticizer 3 kg, and water 210 kg.

[0029] The modified recycled coarse aggregate is prepared by the following method: Step 1) crushing and sieving the construction waste, taking the recycled coarse aggregate with a particle size of 5-25 mm, washing the surface dust, and drying at 105±5℃ until constant weight; Step 2) immersing the dried aggregate in a 1.5 mol / L CaCl2 solution according to a solid-liquid ratio of 1:3 w / v, placing it in an ultrasonic cleaning tank for ultrasonic treatment for 20 minutes, and then separating the solid and liquid to obtain the activated coarse aggregate; Step 3) mixing the activated coarse aggregate with a polyethyleneimine / sodium alginate composite solution according to a solid-liquid ratio of 1:5 w / v, stirring at 60℃ for 1h, and then separating the solid and liquid after the reaction to obtain the modified recycled coarse aggregate.

[0030] The polyethyleneimine / sodium alginate composite solution in Step 3) is prepared by the following method: slowly adding polyethyleneimine to a 0.1wt% sodium alginate solution so that the final solution has a polyethyleneimine concentration of 0.1wt%, and adjusting the solution pH to 10.0 with 0.1mol / L NaOH.

[0031] The modified fiber is prepared by the following method: A. immersing polyvinyl alcohol fibers in a dopamine-Tris buffer solution, stirring at room temperature for 10-16 hours, taking out the fibers and drying them in an oven at 60℃ for 6h to obtain pretreated fibers; B. immersing the pretreated fibers in a 2.0 mol / L CaCl2 solution, stirring at 40℃ for 50 minutes, and then taking out the fibers and drying them to obtain the modified fibers.

[0032] The dopamine-Tris buffer solution has a pH of 8.5 and a dopamine hydrochloride concentration of 5 g / L.

[0033] The active agent is carboxymethyl chitosan, nano-silica sol, and sodium gluconate in a ratio of 1.5:2.5:1; the nano-silica sol has a solid content of 30%, a particle size of 5nm, and a pH of 11.

[0034] A method for preparing the above-mentioned recycled concrete, comprising the following steps: S1: preparing modified recycled coarse aggregate; S2: preparing modified fiber; S3: After the modified recycled coarse aggregate and the modified fiber are uniformly mixed, they are transferred into a CO2 mineralization reaction kettle, 15% CO2 and 85% N2 mixed gas is introduced, the pressure is 0.5 MPa, and the reaction is carried out at 60°C for 2 hours. After the reaction is completed, a premix is obtained; S4: After the cement, the premix and water are uniformly mixed, the active agent is first added and stirred for 5 min, then the water reducing agent is added and stirred for 3 min, and then the remaining materials are added in proportion, and fully stirred to obtain a uniform recycled concrete mixture; S5: Pouring, vibrating and curing are carried out according to the conventional concrete construction method.

[0035] Example 3 A kind of recycled concrete, it is made of the following weight parts of raw materials: modified recycled coarse aggregate 700 kg, river sand 350 kg, cement 350 kg, modified fiber 70 kg, fly ash 75 kg, silica fume 75 kg, active agent 2 kg, polycarboxylic acid water reducing agent 2 kg, water 200 kg.

[0036] The modified recycled coarse aggregate is prepared by the following method: Step 1) The construction waste is crushed and sieved, the recycled coarse aggregate with a particle size of 5-25 mm is taken, the surface dust is washed, and the dried aggregate is dried to constant weight at 105±5°C; Step 2) The dried aggregate is immersed in a 1.5 mol / L CaCl2 solution according to a solid-liquid ratio of 1:3 w / v, and is treated by ultrasonic cleaning for 20 minutes in an ultrasonic cleaning tank. The solid-liquid separation is carried out to obtain the activated coarse aggregate. Step 3) The activated coarse aggregate is mixed with a polyethyleneimine / sodium alginate composite solution according to a solid-liquid ratio of 1:5 w / v, and is stirred and reacted at 60°C for 1h. After the reaction is completed, the solid-liquid separation is carried out to obtain the modified recycled coarse aggregate.

[0037] The polyethyleneimine / sodium alginate composite solution in step 3) is prepared by the following method: 0.1wt% sodium alginate solution is slowly added with polyethyleneimine, so that the concentration of polyethyleneimine in the final solution is 0.1wt%, and the pH of the solution is adjusted to 10.0 with 0.1mol / L NaOH.

[0038] The modified fiber is prepared by the following method: A. The polyvinyl alcohol fiber is immersed in a dopamine-Tris buffer solution, stirred at room temperature for 10-16 hours, taken out and dried in a 60°C oven for 6h to obtain pretreated fiber; B. The pretreated fiber is immersed in a 1.8 mol / L CaCl2 solution, and after stirring at 35℃ for 55 min, the fiber is taken out and dried to obtain the modified fiber.

[0039] The dopamine-Tris buffer solution has a pH of 8.5 and a dopamine hydrochloride concentration of 3 g / L.

[0040] The active agent is carboxymethyl chitosan, nano-silica sol, and sodium gluconate in a ratio of 1.4:2:1; the nano-silica sol has a solid content of 30%, a particle size of 10 nm, and a pH of 10.5.

[0041] A method for preparing the above-mentioned recycled concrete, comprising the following steps: S1: preparing modified recycled coarse aggregate; S2: preparing modified fiber; S3: After the modified recycled coarse aggregate and the modified fiber are uniformly mixed, they are transferred into a CO2 mineralization reaction kettle, 15% CO2 and 85% N2 mixed gas is introduced, the pressure is 0.5 MPa, and the reaction is carried out at 60℃ for 2 hours, and after the reaction is completed, a premixing material I is obtained; S4: After the cement, the premixing material I, and water are uniformly mixed, the active agent is first added and stirred for 5 min, then the water reducing agent is added and stirred for 3 min, and then the remaining materials are added in proportion, and fully stirred to obtain a uniform recycled concrete mixture; S5: The construction method of conventional concrete is used for pouring, vibrating, and curing to obtain the recycled concrete.

[0042] Comparative Example 1 A recycled concrete is prepared from the following raw materials by weight: recycled coarse aggregate 700 kg, river sand 350 kg, cement 350 kg, polyvinyl alcohol fiber 70 kg, fly ash 75 kg, silica fume 75 kg, active agent 2 kg, polycarboxylic acid water reducing agent 2 kg, and water 200 kg. The recycled coarse aggregate is obtained by crushing and sieving construction waste, taking coarse aggregate with a particle size of 5-25 mm, washing the surface dust, and drying at 105±5℃ to constant weight.

[0043] A method for preparing the above-mentioned recycled concrete, comprising the following steps: S1: After the recycled coarse aggregate and the polyvinyl alcohol fiber are uniformly mixed, they are transferred into a CO2 mineralization reaction kettle, 15% CO2 and 85% N2 mixed gas is introduced, the pressure is 0.5 MPa, and the reaction is carried out at 60℃ for 2 hours, and after the reaction is completed, a premixing material I is obtained; S2: After the cement, the premixing material I, and water are uniformly mixed, the active agent is first added and stirred for 5 min, then the water reducing agent is added and stirred for 3 min, and then the remaining materials are added in proportion, and fully stirred to obtain a uniform recycled concrete mixture; S3: pouring, vibrating and curing according to the conventional concrete construction method.

[0044] Comparative Example 2 A recycled concrete, whose raw material composition and preparation method are basically the same as those of Example 3, the only difference being that the polyvinyl alcohol fiber is not modified.

[0045] Comparative Example 3 A recycled concrete, whose raw material composition and preparation method are basically the same as those of Example 3, the only difference being that the recycled coarse aggregate is not modified. The recycled coarse aggregate is obtained by directly crushing and sieving the construction waste to obtain coarse aggregate with a particle size of 5-25 mm, washing the surface dust, and drying at 105±5℃ until constant weight.

[0046] Comparative Example 4 A recycled concrete, whose raw material composition and preparation method are the same as those of Example 3, the only difference being that the CO2 mineralization treatment step S3 is omitted (directly skip S3, mix the modified aggregate and modified fiber, and then enter S4).

[0047] Comparative Example 5 A recycled concrete, whose raw material composition and preparation method are basically the same as those of Example 3, the only difference being that no active agent is added.

[0048] Performance Test The recycled concrete prepared in Examples 1-3 and Comparative Examples 1-4 was tested for 28d compressive strength and 28d flexural strength, and the test method was in accordance with GB / T50081-2016 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete". The test results are shown in Table 1.

[0049] Table 1: Test Results of Mechanical Properties From the results of Table 1 above, it can be seen that the 28d compressive strength and 28d flexural strength of Example (1-3) are significantly higher than all the comparative examples, and close to the level of high-performance concrete. This proves that the modified recycled aggregate of the present application is used in combination with modified fibers and at the same time is subjected to CO2 mineralization, which synergistically improves the mechanical properties. Comparative Example 1 (without modification) has the lowest performance (28d compressive strength 30.2 MPa), reflecting the defects of ordinary recycled aggregate (small density, poor interfacial bonding). Comparative Example 2 (fiber not modified) and Comparative Example 3 (aggregate not modified) have medium performance, indicating that single modification is effective, but the effect is limited. Comparative Example 4 has better performance than Comparative Examples 2 / 3, but is lower than Examples 1-3, which shows that the modified recycled aggregate is used in combination with modified fibers and at the same time is subjected to CO2 mineralization, which has a synergistic effect. In Comparative Example 5, the 28d compressive strength and flexural strength are both reduced. This is because the active agent, nano-silicon dioxide (filling pores) and carboxymethyl chitosan (thickening and water retention), can optimize the hydration process and improve the density; sodium gluconate adjusts the setting time and improves the early strength development. Its absence leads to weak interfacial bonding.

[0050] The carbonation depth, chloride ion penetration resistance and frost resistance of the concrete were detected according to GB / T 50082-2009 “Standard for Testing Methods of Long-term Performance and Durability of Ordinary Concrete”, wherein the chloride ion penetration test used the rapid chloride migration (RCM) method; the frost resistance used the mass loss rate after 300 freeze-thaw cycles. The specific results are shown in Table 2.

[0051] Table 2 Durability test results From the content of Table 2, it can be seen that the durability of Example (1-3) is overall optimal: the carbonation depth is much lower than that of Comparative Examples 1-5; the chloride ion permeability coefficient is lower; and the loss rate after 300 freeze-thaw cycles is also significantly lower than that of Comparative Examples 1-5. Comparative Example 1 has the worst performance, because the high water absorption of the recycled aggregate and the poor interfacial bonding result in serious ion penetration and freeze-thaw damage. Comparative Example 2 (unmodified fiber) and Comparative Example 3 (unmodified aggregate) have moderate durability, indicating that the pores of the unmodified aggregate are not filled and erosion is easy to occur. Comparative Example 4 has better durability than Comparative Examples 2 / 3 but is weaker than the examples, proving that the mineralized layer is crucial for sealing micro-cracks. The absence of active agents in Comparative Example 5 leads to a decrease in mechanical strength, an increase in chloride ion permeability coefficient, and an increase in freeze-thaw loss rate. The organic template layer (polyethyleneimine / sodium alginate) and the mineralized CaCO3 of the modified recycled coarse aggregate in the present application effectively fill the aggregate cracks (reduce water absorption), and the PDA / CaCO3 layer of the modified fiber forms a dense interface with the cement paste, blocking ion penetration. The synergistic effect of the two improves the mechanical properties and durability of the recycled concrete, achieving resource utilization (building waste utilization) and high performance. The active agent also has an irreplaceable synergistic effect on the improvement of the durability of the present application by optimizing the interfacial transition zone (ITZ) structure of the paste-aggregate and reducing porosity.

[0052] It should be noted that the above examples are only part of the preferred modes of implementing the present application, not all. Obviously, based on the above examples of the present application, all other examples obtained by a person of ordinary skill in the art without creative labor should fall within the scope of the present application.

Claims

1. Recycled concrete, characterized in that, It is made from the following weight parts of raw materials: modified recycled coarse aggregate 600-800 parts, river sand 300-400 parts, cement 300-400 parts, modified fiber 60-80 parts, fly ash 70-80 parts, silica ash 70-80 parts, active agent 1-3 parts, polycarboxylic acid water reducing agent 1-3 parts, water 190-210 parts; the active agent is carboxymethyl chitosan, nano silicon dioxide sol, sodium gluconate in the ratio of (1.2-1.5): (1.8-2.5):

1.

2. Recycled concrete according to claim 1, characterized in that The modified recycled coarse aggregate is prepared by the following method: Step 1) crush and sieve the construction waste, take the recycled coarse aggregate with a particle size of 5-25mm, wash the surface dust, and dry to constant weight at 105±5℃; Step 2) immerse the dry aggregate in a CaCl2 solution according to the solid-liquid ratio, place it in an ultrasonic cleaning tank for ultrasonic treatment for 20 minutes, and then separate the solid and liquid to obtain the activated coarse aggregate; Step 3) mix the activated coarse aggregate with a polyethyleneimine / sodium alginate composite solution according to the solid-liquid ratio, stir and react at 60℃ for 1h, then separate the solid and liquid after the reaction to obtain the modified recycled coarse aggregate.

3. Recycled concrete according to claim 2, characterized in that, The solid-liquid ratio of the dry aggregate to the CaCl2 solution in step 2) is 1:3 w / v.

4. Recycled concrete according to claim 3, characterized in that The concentration of the CaCl2 solution is 1.5 mol / L.

5. The recycled concrete of claim 2, wherein, The polyethyleneimine / sodium alginate composite solution in step 3) is prepared by the following method: slowly add polyethyleneimine to a 0.1wt% sodium alginate solution so that the final solution has a polyethyleneimine concentration of 0.1wt%, and then adjust the pH of the solution to 9.0-10.0 with 0.1 mol / L NaOH.

6. The recycled concrete of claim 2, wherein, The solid-liquid ratio of the activated coarse aggregate to the polyethyleneimine / sodium alginate composite solution in step 3) is 1:5 w / v.

7. The recycled concrete of claim 1, wherein, The modified fiber is prepared by the following method: A. immerse polyvinyl alcohol fibers in a dopamine-Tris buffer solution, stir at room temperature for 10-16 hours, take out the fibers and dry them in an oven at 60℃ for 6h to obtain pretreated fibers; B. immerse the pretreated fibers in a 1.5-2.0 mol / L CaCl2 solution, stir at 30-40℃ for 50-60min, then take out the fibers and dry them to obtain modified fibers.

8. Recycled concrete according to claim 7, characterized in that The dopamine-Tris buffer solution has a pH of 8.5 and a dopamine hydrochloride concentration of 1-5 g / L.

9. The recycled concrete of claim 1, wherein, The nano silicon dioxide sol has a solid content of 30%, a particle size of 5-20nm, and a pH of 10-11.

10. A method of producing the recycled concrete according to any one of claims 1 to 9, characterized in that, It includes the following steps: S1: preparing modified recycled coarse aggregate; S2: preparing modified fiber; S3: after mixing the modified recycled coarse aggregate and the modified fiber evenly, transfer them into a CO2 mineralization reaction kettle, introduce 15% CO2 and 85% N2 mixed gas, and react at 60℃ for 2 hours under a pressure of 0.5MPa to obtain premix one; S4: after mixing cement, premix one and water evenly, first add the active agent and stir for 5min, then add the water reducing agent and stir for 3min, and finally add the remaining materials according to the proportion and stir thoroughly to obtain a uniform recycled concrete mixture; S5: Pouring, vibrating and curing are carried out according to the conventional concrete construction method.

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