Vacuum slurry wrapping modification method for recycled concrete aggregate

Abstract

The invention relates to the technical field of building materials, and discloses a modification method for vacuum slurry wrapping of recycled concrete aggregate. According to the modification method, a compact cement paste layer is formed on the surface of the recycled coarse aggregate in a vacuum paste wrapping manner, so that the bonding force between cement and the aggregate is enhanced, and microcracks and pores on the surface of the aggregate are filled. According to the recycled coarse aggregate obtained through the method, the apparent density is larger than 2330 kg / m < 3 >, the water absorption rate is smaller than 5.6%, the crushing value is smaller than 21.6%, the physical performance of the recycled coarse aggregate meets the performance requirement of III-type recycled coarse aggregate, the recycled coarse aggregate can be used for structural concrete engineering again, and the utilization level and the utilization rate of renewable resources are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of building materials, and in particular to a modification method for vacuum slurry wrapping of recycled concrete aggregates. Background Art

[0002] Concrete is the most widely used building material in the world, with an annual output of nearly 20 billion tons. Large-scale concrete production has led to the overconsumption and shortage of natural resources, such as natural aggregates. In addition, the demolition of buildings at the end of their service life generates a large amount of construction waste. It is reported that more than 3 billion tons of construction waste are generated globally every year. These construction wastes are usually landfilled, having a negative impact on the environment. In order to handle construction waste in an environmentally friendly manner and save natural coarse aggregate resources, scholars have proposed processing and crushing construction waste into aggregates for the production of recycled aggregate concrete. As a sustainable building material, recycled aggregate concrete has unique advantages and broad application prospects.

[0003] Due to the high porosity of the mortar attached to the recycled coarse aggregates and the generation of some microcracks during the crushing process of construction waste, the mechanical properties and durability of recycled aggregate concrete are worse than those of natural concrete. To improve the performance of recycled coarse aggregates, attention should be focused on strengthening the mortar adhered to the surface of recycled coarse aggregates and the interfacial transition zone; the proposed modification technology based on the strengthening of recycled coarse aggregates will be beneficial to fundamentally improve the performance of recycled aggregate concrete, thereby realizing its large-scale application in structural engineering. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: to overcome the deficiencies in the prior art and provide a modification method for vacuum slurry wrapping of recycled concrete aggregates. By means of vacuum slurry wrapping, the present invention forms a dense cement paste layer on the surface of recycled coarse aggregates, enhances the bonding force between cement and aggregates, and fills the microcracks and pores on the surface of aggregates, thereby improving the firmness of aggregates and the stability of the overall structure. The mechanical properties of the recycled coarse aggregates modified by this modification method are all improved, and they can be reused in structural concrete.

[0005] The technical solution adopted by the present invention to solve its technical problems is:

[0006] A modification method for vacuum slurry wrapping of recycled concrete aggregates specifically includes the following steps:

[0007] Step S1: Weigh the following components in parts by weight: 100 parts of recycled coarse aggregates, 100 parts of Portland cement, and 40 - 80 parts of water;

[0008] Step S2: Put the recycled aggregates into vacuum bucket A and then close and seal the lid;

[0009] Step S3: Stir the cement and water evenly. After ensuring that there is no dry powder or lumps, pour them into container bucket B and keep container bucket B unsealed.

[0010] Step S4: Connect vacuum bucket A and container bucket B with a rubber hose. A hose valve is installed on the rubber hose and keep the hose valve in the closed state.

[0011] Step S5: Open the air extraction valve of vacuum bucket A. Apply a vacuum of -0.6 to -1.0 bar to vacuum bucket A using a vacuum pump. After the pressure gauge stabilizes, maintain the pressure for 5 to 8 minutes.

[0012] Step S6: Open the hose valve and pump the slurry in container bucket B into negative pressure vacuum bucket A. After the slurry level in vacuum bucket A is flush with the surface of the accumulated aggregate, continue to pump in the slurry for 30 to 50 seconds, then close the hose valve and keep vacuum bucket A in a vacuum state for 5 to 8 minutes.

[0013] Step S7: Turn off the vacuum pump, open the air inlet valve of vacuum bucket A to make vacuum bucket A return to normal pressure, and continue to soak for 5 to 8 minutes.

[0014] Step S8: Filter the slurry in vacuum bucket A, then obtain the slurry-coated recycled coarse aggregate, air-dry it naturally on a wire mesh sheet for 20 to 24 hours, then cover it with a wet cloth, and finally move it into a standard curing room for curing for 7d to obtain the finished recycled concrete aggregate.

[0015] Through the vacuum slurry coating technology, a uniform cement slurry coating layer can be formed on the surface of the recycled coarse aggregate, enhancing the bonding force between the aggregate and the cement slurry. This method can effectively fill the microcracks and pores on the surface of the aggregate, improving the physical properties of the aggregate, such as apparent density, water absorption rate, and crushing value, thereby improving the mechanical properties and durability of recycled concrete. In addition, this method is simple to operate, suitable for large-scale production, and has high economic and environmental benefits.

[0016] In addition, the negative pressure environment can effectively discharge the air in the pores of the recycled aggregate, helping the cement slurry to penetrate more evenly into the pores and cracks on the surface of the recycled aggregate, improving the density and strength, thereby enhancing the slurry coating quality. In the negative pressure environment, water and cement particles are in full contact, accelerating the initial hydration reaction. However, the negative pressure environment will accelerate the evaporation of water, and then cause the water in the cement slurry to be lost faster, affecting the later hydration reaction. Therefore, after 5 to 8 minutes of negative pressure slurry coating, it is changed to normal pressure and continue to soak for slurry coating.

[0017] Furthermore, in step S1, the particle size range of the recycled coarse aggregate is 5 to 20 mm, the apparent density is 2250 to 2350 kg / m 3 , the water absorption rate is 5.0 to 8.0%, and the crushing value is 20 to 30%.

[0018] The particle size range, apparent density, water absorption rate, and crushing value of the recycled coarse aggregate are limited, ensuring that the basic physical properties of the recycled coarse aggregate meet the requirements of Class III recycled coarse aggregate. By controlling these parameters, the stability and strength of the modified aggregate in the concrete can be guaranteed, further improving the overall performance of the recycled concrete.

[0019] Furthermore, the preparation method of the recycled coarse aggregate in step S1 is as follows: The natural aggregate concrete is double-crushed by a jaw crusher and a grinding crusher, and then obtained by flushing with a high-pressure water gun. The flushing pressure is 100 - 120 bar, and the flushing time is 10 - 15 min.

[0020] The preparation method of the recycled coarse aggregate is limited. Through the double crushing of the jaw crusher and the grinding crusher, combined with the flushing of the high-pressure water gun, impurities and loose particles on the surface of the aggregate can be effectively removed, ensuring the cleanliness and uniformity of the aggregate. The flushing with the high-pressure water gun can further reduce the microcracks on the surface of the aggregate and improve the overall quality of the aggregate.

[0021] Furthermore, the Portland cement in step S1 is ordinary Portland cement with a strength grade of 42.5. The strength grade of the Portland cement is limited to 42.5, ensuring the strength and bonding performance of the cement paste. Ordinary Portland cement has high early strength and durability, which can effectively improve the modification effect of the recycled coarse aggregate and enhance the mechanical properties of the recycled concrete.

[0022] Furthermore, in step S4, the two ends of the rubber hose are respectively at the upper part of the side wall of vacuum bucket A and the bottom of the side wall of container bucket B. The connection position of the rubber hose is limited, ensuring that the slurry can flow smoothly from container bucket B into vacuum bucket A, and the liquid level height can be accurately controlled. This connection method can effectively avoid slurry backflow or leakage, ensuring the smooth progress of the vacuum slurry coating process.

[0023] Furthermore, in step S4, the rubber hose is a pressure-resistant rubber hose. The rubber hose is limited to be a pressure-resistant rubber hose, which can withstand the negative pressure during the vacuum slurry coating process, ensuring the sealing and stability of the system. The use of the pressure-resistant rubber hose can effectively prevent slurry leakage or hose rupture, improving the safety and reliability of the modification process.

[0024] Furthermore, in step S5, the air extraction rate of the vacuum pump is 3.6 m 3 / h. The air extraction rate of the vacuum pump is limited to 3.6 m 3 / h, ensuring that vacuum bucket A can reach the required vacuum degree within a reasonable time. An appropriate air extraction rate can ensure that the slurry evenly coats the surface of the aggregate, improving the modification effect.

[0025] Further, in the step S8, the aperture of the wire mesh sheet is 4 mm. The aperture of the wire mesh sheet is limited to 4 mm to ensure that the excess slurry can be smoothly filtered, while preventing the aggregate from leaking out through the mesh holes. An appropriate aperture can ensure the uniform distribution of the aggregate during the air-drying process and improve the quality of the modified aggregate.

[0026] Further, in the step S8, the temperature of the standard curing room is 20 ± 2°C and the relative humidity is 95% ± 3%. The temperature and humidity conditions of the standard curing room are limited to ensure that the modified aggregate can be fully hydrated during the curing process and form a stable cement paste coating layer. Appropriate curing conditions can further improve the physical and mechanical properties of the recycled coarse aggregate.

[0027] The beneficial effects of the present invention are as follows: The present invention is reasonably designed and has the following advantages:

[0028] (1) Improve the mechanical properties. The vacuum slurry wrapping method can form a dense cement paste layer on the surface of the aggregate, enhance the bonding force between the cement and the aggregate, and thus improve the mechanical properties of the recycled coarse aggregate;

[0029] (2) Improve the durability performance. The cement paste can fill the microcracks and pores on the surface of the aggregate, reduce the penetration of water and harmful substances, and improve the durability performance of the recycled coarse aggregate;

[0030] (3) Environmental protection and energy saving. Using construction waste to prepare recycled aggregate and improving its performance through modification technology not only solves the problem of construction waste treatment but also saves natural aggregate resources;

[0031] (4) The apparent density of the recycled coarse aggregate obtained by this method is greater than 2330 kg / m 3 , the water absorption rate is less than 5.6%, and the crushing value is less than 21.6%. Its physical properties meet the performance requirements of Class III recycled coarse aggregate and can be used again in structural concrete projects, improving the utilization level and utilization rate of recycled resources. Description of the Drawings

[0032] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0033] Figure 1 It is a diagram showing the relationship between cumulative intrusion and pore size obtained by ordinary slurry wrapping and vacuum slurry wrapping tests, where (a) is ordinary slurry wrapping (Comparative Example 2), and (b) is vacuum slurry wrapping (Example 2);

[0034] Figure 2 It is a graph showing the relationship between the cumulative pore area and pore size obtained from ordinary slurry coating and vacuum slurry coating tests, where (a) is ordinary slurry coating (Comparative Example 2), and (b) is vacuum slurry coating (Example 2). Detailed implementation manners

[0035] It should be noted that the following detailed descriptions are all illustrative and are intended to provide further explanations for this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs.

[0036] It should be noted that the terms used herein are only for describing specific implementation manners and are not intended to limit the exemplary implementation manners according to this application. As used herein, unless the context clearly indicates otherwise, the singular forms also include the plural forms. In addition, it should also be understood that when the terms "include" and / or "comprise" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or their combinations.

[0037] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0038] A modified method for vacuum slurry coating of recycled concrete aggregates specifically includes the following steps:

[0039] Step S1: Weigh the following components in parts by weight: 100 parts of recycled coarse aggregates, 100 parts of portland cement, and 40 - 80 parts of water;

[0040] Step S2: Put the recycled aggregates into vacuum bucket A and then close and seal the lid;

[0041] Step S3: Stir the cement and water evenly to ensure there is no dry powder or lumps, and then pour them into container bucket B, keeping container bucket B unsealed;

[0042] Step S4: Connect vacuum bucket A and container bucket B through a rubber hose, and install a hose valve on the rubber hose, keeping the hose valve in a closed state;

[0043] Step S5: Open the air extraction valve of vacuum bucket A, apply a vacuum of -0.6 to -1.0 bar to vacuum bucket A using a vacuum pump, and keep the pressure stable for 5 - 8 minutes after the pressure gauge stabilizes;

[0044] Step S6: Open the hose valve, pump the slurry in container barrel B into the negative-pressure vacuum barrel A. After the slurry level in the vacuum barrel A is flush with the surface of the accumulated aggregate, continue to pump in the slurry for 30 - 50 seconds, then close the hose valve and maintain the vacuum state of the vacuum barrel A for 5 - 8 minutes;

[0045] Step S7: Turn off the vacuum pump, open the air inlet valve of the vacuum barrel A to make the vacuum barrel A return to normal pressure, and continue to soak for 5 - 8 minutes;

[0046] Step S8: Filter the slurry in the vacuum barrel A, then obtain the slurry-coated recycled coarse aggregate, air-dry it naturally on the wire mesh for 20 - 24 hours, then cover it with a wet cloth, and finally move it into the standard curing room for curing for 7d to obtain the finished recycled concrete aggregate.

[0047] In step S1, the particle size range of the recycled coarse aggregate is 5 - 20 mm, the apparent density is 2250 - 2350 kg / m 3 , the water absorption rate is 5.0 - 8.0%, and the crushing value is 20 - 30%.

[0048] The preparation method of the recycled coarse aggregate in step S1 is: the natural aggregate concrete is double-crushed by a jaw crusher and a grinding crusher, and then obtained by flushing with a high-pressure water gun. The flushing pressure is 100 - 120 bar, and the flushing time is 10 - 15 min.

[0049] In step S1, the Portland cement is ordinary Portland cement with a strength grade of 42.5.

[0050] In step S4, both ends of the hose are respectively the upper part of the side wall of the vacuum barrel A and the bottom of the side wall of the container barrel B, and the hose is a pressure-resistant hose.

[0051] In step S5, the air extraction rate of the vacuum pump is 3.6 m 3 / h.

[0052] In step S8, the aperture of the wire mesh is 4 mm; the temperature of the standard curing room is 20 ± 2°C, and the relative humidity is 95% ± 3%.

[0053] Perform physical property tests on the recycled concrete aggregate prepared by the above vacuum slurry coating modification method.

[0054] 1. Apparent density experiment

[0055] Weigh the sample according to the specification, soak the sample in water until saturated, and then put it into a wide-mouth bottle. Pour in water, cover the bottle mouth with a glass slide, and remove the air bubbles by shaking the bottle up, down, left and right. After all the air bubbles are removed, add water to the bottle until the water surface bulges out of the bottle mouth edge, and then quickly slide the glass slide along the bottle mouth to make it close to the water surface of the bottle mouth. After drying the water on the outside of the bottle, weigh the total mass of the sample, water, bottle and glass slide (m1); pour the sample in the bottle into a shallow dish and dry it in an oven at (105±5)°C until constant weight; take it out, put it in a covered container and cool it to room temperature, then weigh the mass (m0); wash the bottle, refill it with water, make the glass slide close to the water surface of the bottle mouth, and weigh the mass (m2) after drying the water on the outside of the bottle.

[0056] The apparent density ρ shall be calculated according to the following formula, and the arithmetic mean of the results of two tests shall be used as the measured value:

[0057]

[0058] where ρ is the apparent density; m0 is the mass of the sample after drying; m1 is the total mass of the sample, water, bottle and glass slide; m2 is the total mass of water, bottle and glass slide; α t is the correction coefficient for the influence of water temperature on the apparent density, see Table 1 for details.

[0059] Table 1 α t is the correction coefficient for the influence of water temperature on the apparent density

[0060]

[0061] 2. Water absorption test

[0062] Weigh the sample and place it in a container filled with water so that the water surface is about 5 mm higher than the surface of the sample. After 24 hours, take out the sample from the water, wipe the water on the surface of the particles with a wrung-out wet towel, and immediately weigh the mass (m2) of the sample on a shallow dish; place the saturated surface-dry sample together with the shallow dish in an oven at (105±5)°C and dry it until constant weight. After taking it out, put it in a covered container and cool it for 0.5 - 1 h, weigh the total mass of the dried sample and the shallow dish (m1), and weigh the mass of the shallow dish (m3).

[0063] The water absorption ω shall be calculated according to the following formula, and the arithmetic mean of the results of two tests shall be used as the measured value:

[0064] ω = (m2 - m1) × 100%

[0065] m1 - m3

[0066] where ω is the water absorption; m1 is the total mass of the dried sample and the shallow dish; m2 is the total mass of the saturated surface-dry sample and the shallow dish before drying; m3 is the mass of the shallow dish.

[0067] 3. Crushing value test

[0068] Place the specimen in the crusher value indicator according to the specification, put it on the testing machine, and evenly apply a load of 200 kN within 160 - 300 s and keep it stable for 5 s, then unload the load and take out the measuring cylinder. Pour out the specimen in the cylinder and weigh its mass (m0). Sieve out the crushed fine particles with a square-hole sieve with a nominal diameter of 2.50 mm, and weigh the mass of the specimen remaining on the sieve (m1).

[0069] The crushing value index δ shall be calculated according to the following formula, and the arithmetic mean of the results of three tests shall be taken as the measured value:

[0070] δ= m0 - m1 ×100%

[0071] m0

[0072] Where δ is the crushing value index; m0 is the mass of the specimen; m1 is the mass of the specimen remaining after the crushing test.

[0073] In the present invention, the apparent density, water absorption rate and crushing value of the modified recycled coarse aggregate prepared in the examples and comparative examples are measured according to GB / T 25177—2010 "Recycled Coarse Aggregate for Concrete".

[0074] The apparent density, water absorption rate and crushing value of the coarse aggregate used in the following examples and comparative examples are 2280 kg / m 3 , 6.7% and 25% respectively, and the particle size is 5 - 20 mm. The cement is ordinary Portland cement with a strength of 42.5.

[0075] Example 1

[0076] A modified method for vacuum slurry coating of recycled concrete aggregate is as follows:

[0077] Step S1: Weigh the following components by weight: 100 parts of recycled coarse aggregate obtained by crushing C25 concrete, 100 parts of Portland cement, and 60 parts of water (water-cement ratio 0.6); the apparent density of C25 concrete is 2260 kg / m 3 , the water absorption rate is 7.1%, and the crushing value is 27.3%;

[0078] Step S2: Put the recycled aggregate into vacuum bucket A and then close and seal the lid;

[0079] Step S3: Put the cement and water into container bucket B, stir evenly to ensure that there is no dry powder or lumps, and keep container bucket B unsealed;

[0080] Step S4: Connect vacuum bucket A and container bucket B through a rubber hose, and install a rubber hose valve on the rubber hose, and keep the rubber hose valve in the closed state;

[0081] Step S5: Open the air extraction valve of vacuum bucket A, apply a vacuum of -0.6 to -1.0 bar to vacuum bucket A using a vacuum pump, and keep the pressure stable for 5 to 8 minutes after the pressure gauge stabilizes.

[0082] Step S6: Open the hose valve, pump the slurry in container bucket B into negative pressure vacuum bucket A. After the slurry level in vacuum bucket A is flush with the surface of the stacked aggregate, continue to pump in the slurry for 30 to 50 seconds, then close the hose valve, and keep vacuum bucket A in a vacuum state for 5 to 8 minutes.

[0083] Step S7: Turn off the vacuum pump, open the air inlet valve of vacuum bucket A to make vacuum bucket A return to normal pressure, and continue to soak for 5 to 8 minutes.

[0084] Step S8: Filter out the slurry in vacuum bucket A, then obtain the wrapped-slurry recycled coarse aggregate, air-dry it naturally on the wire mesh for 20 to 24 hours, then cover it with a wet cloth, and finally move it into the standard curing room for curing for 7 days to obtain the finished recycled concrete aggregate.

[0085] Example 2

[0086] A modified method for vacuum wrapping of recycled concrete aggregate is as follows:

[0087] Step S1: Weigh the following components by weight: 100 parts of recycled coarse aggregate obtained by crushing C35 concrete, 100 parts of Portland cement, and 60 parts of water (water-binder ratio 0.6); the apparent density of C35 concrete is 2280 kg / m 3 , water absorption rate is 6.7%, and crushing value is 25.2%.

[0088] Step S2: Put the recycled aggregate into vacuum bucket A and then close and seal the lid.

[0089] Step S3: Put the cement and water into container bucket B, stir evenly to ensure there is no dry powder or lumps, and keep container bucket B unsealed.

[0090] Step S4: Connect vacuum bucket A and container bucket B through a hose, and a hose valve is installed on the hose. Keep the hose valve in a closed state.

[0091] Step S5: Open the air extraction valve of vacuum bucket A, apply a vacuum of -0.6 to -1.0 bar to vacuum bucket A using a vacuum pump, and keep the pressure stable for 5 to 8 minutes after the pressure gauge stabilizes.

[0092] Step S6: Open the hose valve, pump the slurry in container bucket B into negative pressure vacuum bucket A. After the slurry level in vacuum bucket A is flush with the surface of the stacked aggregate, continue to pump in the slurry for 30 to 50 seconds, then close the hose valve, and keep vacuum bucket A in a vacuum state for 5 to 8 minutes.

[0093] Step S7: Turn off the vacuum pump, open the intake valve of vacuum bucket A to make the vacuum bucket A return to normal pressure, and continue to soak for 5 - 8 minutes;

[0094] Step S8: Filter the slurry in vacuum bucket A, then obtain the wrapped-slurry recycled coarse aggregate, air-dry it naturally on the wire mesh for 20 - 24 hours, then cover it with a wet cloth, and finally move it into the standard curing room for curing for 7d to obtain the finished recycled concrete aggregate.

[0095] Example 3

[0096] A modified method for vacuum wrapping slurry of recycled concrete aggregate is as follows:

[0097] Step S1: Weigh the following components by weight: 100 parts of recycled coarse aggregate obtained by crushing C45 concrete, 100 parts of Portland cement, and 60 parts of water (water-binder ratio 0.6); The apparent density of C45 concrete is 2300 kg / m 3 , water absorption rate is 6.1%, and crushing value is 22.7%;

[0098] Step S2: Put the recycled aggregate into vacuum bucket A and then close the lid and seal it;

[0099] Step S3: Put the cement and water into container bucket B, stir evenly to ensure there is no dry powder or lumps, and keep container bucket B unsealed;

[0100] Step S4: Connect vacuum bucket A and container bucket B through a rubber hose, and install a rubber hose valve on the rubber hose, and keep the rubber hose valve in the closed state;

[0101] Step S5: Open the air extraction valve of vacuum bucket A, use a vacuum pump to apply a vacuum of -0.6 - -1.0 bar to vacuum bucket A, and keep the pressure stable for 5 - 8 minutes after the pressure gauge is stable;

[0102] Step S6: Open the rubber hose valve, pump the slurry in container bucket B into the negative pressure vacuum bucket A, continue to pump in the slurry for 30 - 50 seconds after the slurry level in vacuum bucket A is flush with the surface of the accumulated aggregate, close the rubber hose valve, and keep vacuum bucket A in a vacuum state for 5 - 8 minutes;

[0103] Step S7: Turn off the vacuum pump, open the intake valve of vacuum bucket A to make the vacuum bucket A return to normal pressure, and continue to soak for 5 - 8 minutes;

[0104] Step S8: Filter the slurry in vacuum bucket A, then obtain the wrapped-slurry recycled coarse aggregate, air-dry it naturally on the wire mesh for 20 - 24 hours, then cover it with a wet cloth, and finally move it into the standard curing room for curing for 7d to obtain the finished recycled concrete aggregate.

[0105] Example 4

[0106] A modification method for vacuum slurry wrapping of recycled concrete aggregates is as follows:

[0107] Step S1: Weigh the following components by weight: 100 parts of recycled coarse aggregates obtained by crushing C35 concrete, 100 parts of Portland cement, and 40 parts of water (water-binder ratio 0.4);

[0108] Step S2: Put the recycled aggregates into vacuum bucket A and then close and seal the lid;

[0109] Step S3: Put the cement and water into container bucket B, stir evenly to ensure there is no dry powder or lumps, and keep container bucket B unsealed;

[0110] Step S4: Connect vacuum bucket A and container bucket B through a rubber hose, and install a rubber hose valve on the rubber hose, keeping the rubber hose valve in the closed state;

[0111] Step S5: Open the air extraction valve of vacuum bucket A, use a vacuum pump to apply a vacuum of -0.6 to -1.0 bar to vacuum bucket A, and keep the pressure stable for 5 to 8 minutes after the pressure gauge is stable;

[0112] Step S6: Open the rubber hose valve, pump the slurry in container bucket B into negative pressure vacuum bucket A. After the slurry liquid level in vacuum bucket A is flush with the surface of the stacked aggregates, continue to pump in the slurry for 30 to 50 seconds, then close the rubber hose valve, and keep vacuum bucket A in a vacuum state for 5 to 8 minutes;

[0113] Step S7: Turn off the vacuum pump, open the air inlet valve of vacuum bucket A to make vacuum bucket A return to normal pressure, and continue to soak for 5 to 8 minutes;

[0114] Step S8: Filter out the slurry in vacuum bucket A, then obtain the slurry-wrapped recycled coarse aggregates, air-dry them naturally on a wire mesh sheet for 20 to 24 hours, then cover them with a wet cloth, and finally transfer them to a standard curing room for curing for 7d to obtain the finished recycled concrete aggregates.

[0115] Example 5

[0116] A modification method for vacuum slurry wrapping of recycled concrete aggregates is as follows:

[0117] Step S1: Weigh the following components by weight: 100 parts of recycled coarse aggregates obtained by crushing C35 concrete, 100 parts of Portland cement, and 80 parts of water (water-binder ratio 0.8);

[0118] Step S2: Put the recycled aggregates into vacuum bucket A and then close and seal the lid;

[0119] Step S3: Put the cement and water into container bucket B, stir evenly to ensure there is no dry powder or lumps, and keep container bucket B unsealed;

[0120] Step S4: Connect the vacuum bucket A and the container bucket B with a rubber hose. A rubber hose valve is installed on the rubber hose, and keep the rubber hose valve in the closed state;

[0121] Step S5: Open the air extraction valve of the vacuum bucket A, and use a vacuum pump to apply a vacuum of -0.6 to -1.0 bar to the vacuum bucket A. After the pressure gauge stabilizes, maintain the pressure for 5 to 8 minutes;

[0122] Step S6: Open the rubber hose valve, and pump the slurry in the container bucket B into the negative pressure vacuum bucket A. After the slurry level in the vacuum bucket A is flush with the surface of the accumulated aggregate, continue to pump in the slurry for 30 to 50 seconds, then close the rubber hose valve, and maintain the vacuum state of the vacuum bucket A for 5 to 8 minutes;

[0123] Step S7: Turn off the vacuum pump, open the air inlet valve of the vacuum bucket A to make the vacuum bucket A return to normal pressure, and continue to soak for 5 to 8 minutes;

[0124] Step S8: Filter the slurry in the vacuum bucket A, then obtain the wrapped-slurry recycled coarse aggregate, air-dry it naturally on a wire mesh for 20 to 24 hours, then cover it with a wet cloth, and finally move it into a standard curing room for curing for 7d to obtain the finished recycled concrete aggregate.

[0125] Comparative Example 1

[0126] A common method for wrapping slurry of recycled concrete aggregate is as follows: Weigh the following raw materials in parts by weight: 100 parts of recycled coarse aggregate obtained by crushing C25 concrete, 100 parts of Portland cement, and 60 parts of water (water-binder ratio 0.6); Mix the cement and water in a mixing container and stir well until there are no dry powder particles to form a uniform cement slurry. Add the dried recycled coarse aggregate into the cement slurry and use a mixer to stir well for 8 to 10 minutes to ensure that the surface of the aggregate is evenly covered with the cement slurry; Filter the excess slurry from the wrapped-slurry recycled coarse aggregate in the mixing bucket and air-dry it naturally on a wire mesh for 24 hours, then cover it with a wet cloth and move it into a standard curing room for curing for 7d to obtain a common wrapped-slurry recycled coarse aggregate.

[0127] Comparative Example 2

[0128] A common method for wrapping slurry of recycled concrete aggregate is as follows: Weigh the following raw materials in parts by weight: 100 parts of recycled coarse aggregate obtained by crushing C35 concrete, 100 parts of Portland cement, and 60 parts of water (water-binder ratio 0.6); Mix the cement and water in a mixing container and stir well until there are no dry powder particles to form a uniform cement slurry. Add the dried recycled coarse aggregate into the cement slurry and use a mixer to stir well for 8 to 10 minutes to ensure that the surface of the aggregate is evenly covered with the cement slurry; Filter the excess slurry from the wrapped-slurry recycled coarse aggregate in the mixing bucket and air-dry it naturally on a wire mesh for 24 hours, then cover it with a wet cloth and move it into a standard curing room for curing for 7d to obtain a common wrapped-slurry recycled coarse aggregate.

[0129] Comparative Example 3

[0130] A common slurry coating method for recycled concrete aggregates, specifically: Weigh the following raw materials in parts by weight: 100 parts of recycled coarse aggregates obtained by crushing C45 concrete, 100 parts of Portland cement, and 60 parts of water (water-binder ratio 0.6); Mix the cement and water in a stirring container and stir thoroughly until there are no dry powder particles to form a uniform cement slurry; Add the dried recycled coarse aggregates to the cement slurry and use a mixer to stir thoroughly for 8 - 10 minutes to ensure that the surface of the aggregates is evenly covered with the cement slurry; Filter the excess slurry from the slurry-coated recycled coarse aggregates in the stirring bucket and air-dry them naturally on a wire mesh sheet for 24 hours, then cover them with a wet cloth and transfer them to a standard curing room for curing for 7 days to obtain a common slurry-coated recycled coarse aggregate.

[0131] Comparative Example 4

[0132] A common slurry coating method for recycled concrete aggregates, specifically: Weigh the following raw materials in parts by weight: 100 parts of recycled coarse aggregates obtained by crushing C35 concrete, 100 parts of Portland cement, and 40 parts of water (water-binder ratio 0.4); Mix the cement and water in a stirring container and stir thoroughly until there are no dry powder particles to form a uniform cement slurry; Add the dried recycled coarse aggregates to the cement slurry and use a mixer to stir thoroughly for 8 - 10 minutes to ensure that the surface of the aggregates is evenly covered with the cement slurry; Filter the excess slurry from the slurry-coated recycled coarse aggregates in the stirring bucket and air-dry them naturally on a wire mesh sheet for 24 hours, then cover them with a wet cloth and transfer them to a standard curing room for curing for 7 days to obtain a common slurry-coated recycled coarse aggregate.

[0133] Comparative Example 5

[0134] A common slurry coating method for recycled concrete aggregates, specifically: Weigh the following raw materials in parts by weight: 100 parts of recycled coarse aggregates obtained by crushing C35 concrete, 100 parts of Portland cement, and 80 parts of water (water-binder ratio 0.8); Mix the cement and water in a stirring container and stir thoroughly until there are no dry powder particles to form a uniform cement slurry; Add the dried recycled coarse aggregates to the cement slurry and use a mixer to stir thoroughly for 8 - 10 minutes to ensure that the surface of the aggregates is evenly covered with the cement slurry; Filter the excess slurry from the slurry-coated recycled coarse aggregates in the stirring bucket and air-dry them naturally on a wire mesh sheet for 24 hours, then cover them with a wet cloth and transfer them to a standard curing room for curing for 7 days to obtain a common slurry-coated recycled coarse aggregate.

[0135] For the finished products prepared in Examples 1 - 5 and Comparative Examples 1 - 5, samples were taken for physical property tests, and the test results are shown in Table 2.

[0136] Table 2 Test Results of Examples 1 - 5 and Comparative Examples 1 - 5

[0137]

[0138] Compared with the recycled coarse aggregates obtained by crushing C25, C35, and C45 before modification, the apparent densities are 2260 kg / m 3 、2280 kg / m 3 、2300 kg / m 3 respectively. It can be seen from the test results in Table 2 that:

[0139] (1) When the water-binder ratio is 0.6, the apparent densities of the recycled coarse aggregates after ordinary slurry coating modification are 2280 kg / m 3 (Comparative Example 1), 2300 kg / m 3 (Comparative Example 2), 2310 kg / m 3 (Comparative Example 3) respectively, while the apparent densities of the recycled coarse aggregates after vacuum slurry coating modification are 2300 kg / m 3 (Example 1), 2320 kg / m 3 (Example 2), 2330 kg / m 3 (Example 3) respectively. By comparison, in terms of apparent density, for the recycled coarse aggregates obtained by crushing different-strength concretes, the vacuum slurry coating effect is better than that of ordinary slurry coating;

[0140] (2) The apparent densities of the recycled coarse aggregates obtained by crushing C35 concrete after being coated with slurries with different water-binder ratios (0.4, 0.6, 0.8) through ordinary slurry coating modification are 2310 kg / m 3 (Comparative Example 4), 2300 kg / m 3 (Comparative Example 2), 2290 kg / m 3 (Comparative Example 5) respectively, while the apparent densities after vacuum slurry coating modification are 2320 kg / m 3 (Example 4), 2320 kg / m 3 (Example 2), 2300 kg / m 3 (Example 5) respectively. By comparison, in terms of apparent density, for the recycled coarse aggregates obtained by slurry coating modification with different water-binder ratio slurries, the vacuum slurry coating effect is better than that of ordinary slurry coating.

[0141] Compared with the recycled coarse aggregates obtained by crushing C25, C35, and C45 before modification, the water absorption rates are 7.1%, 6.7%, and 6.1% respectively. It can be seen from the test results in Table 2 that:

[0142] (1) When the water-binder ratio is 0.6, the water absorption rates of the recycled coarse aggregates modified by ordinary slurry coating are 6.7% (Comparative Example 1), 6.3% (Comparative Example 2), and 5.9% (Comparative Example 3) respectively, while the water absorption rates of the recycled coarse aggregates modified by vacuum slurry coating are 6.4% (Example 1), 6.1% (Example 2), and 5.6% (Example 3) respectively. By comparison, in terms of water absorption rate, for the recycled coarse aggregates obtained by crushing different-strength concrete, the vacuum slurry coating effect is better than that of ordinary slurry coating;

[0143] (2) The water absorption rates of the recycled coarse aggregates obtained by crushing C35 concrete after being modified by slurries with different water-binder ratios (0.4, 0.6, 0.8) through ordinary slurry coating are 6.4% (Comparative Example 4), 6.3% (Comparative Example 2), and 6.4% (Comparative Example 5) respectively, while the water absorption rates after vacuum slurry coating are 6.1% (Example 4), 6.1% (Example 2), and 6.3% (Example 5) respectively. By comparison, in terms of water absorption rate, for the recycled coarse aggregates modified by slurries with different water-binder ratios through slurry coating, the vacuum slurry coating effect is better than that of ordinary slurry coating.

[0144] Compared with the crushing indexes of the recycled coarse aggregates obtained by crushing C25, C35, and C45 before modification, which are 27.3%, 25.2%, and 22.7% respectively, it can be seen from the test results in Table 2 that:

[0145] (1) When the water-binder ratio is 0.6, the crushing indexes of the recycled coarse aggregates modified by ordinary slurry coating are 25.0% (Comparative Example 1), 24.1% (Comparative Example 2), and 22.1% (Comparative Example 3) respectively, while the crushing indexes of the recycled coarse aggregates modified by vacuum slurry coating are 24.4% (Example 1), 23.4% (Example 2), and 21.6% (Example 3) respectively. By comparison, in terms of crushing index, for the recycled coarse aggregates obtained by crushing different-strength concrete, the vacuum slurry coating effect is better than that of ordinary slurry coating;

[0146] (2) The crushing indexes of the recycled coarse aggregates obtained by crushing C35 concrete after being modified by slurries with different water-binder ratios (0.4, 0.6, 0.8) through ordinary slurry coating are 24.4% (Comparative Example 4), 24.1% (Comparative Example 2), and 24.7% (Comparative Example 5) respectively, while the crushing indexes after vacuum slurry coating are 23.9% (Example 4), 23.4% (Example 2), and 24.3% (Example 5) respectively. By comparison, in terms of crushing index, for the recycled coarse aggregates modified by slurries with different water-binder ratios through slurry coating, the vacuum slurry coating effect is better than that of ordinary slurry coating.

[0147] For the finished products prepared in Example 2 and Comparative Example 2, after sampling, tests on the relationship between cumulative intrusion and pore size and the relationship between cumulative pore area and pore size were carried out, and the test results are as Figure 1 (Graph of the relationship between cumulative intrusion and pore size) and Figure 2As shown in the (Relationship Diagram between Cumulative Pore Area and Pore Size).

[0148] Figure 1 In it, by comparing a (Comparative Example 2) with b (Example 2), it can be seen that after the mercury intrusion test on the aggregate with ordinary slurry coating, the cumulative intrusion total reaches 0.1466 ml / g, while the test data of the aggregate after vacuum slurry coating modification drops to 0.1170 ml / g;

[0149] Figure 2 In it, by comparing a (Comparative Example 2) with b (Example 2), it can be seen that after the mercury intrusion test on the aggregate with ordinary slurry coating, the cumulative pore area reaches 21.267 m 2 / g, while the test data of the aggregate after vacuum slurry coating modification drops to 19.050 m 2 / g;

[0150] It can be seen from the analysis of the two groups of data that compared with ordinary slurry coating modification, the total amount of pores in the recycled aggregate after vacuum slurry coating modification is smaller, and the overall pore area is smaller.

[0151] In summary, in the slurry coating modification test of recycled coarse aggregate obtained by crushing three different strengths of concrete, the apparent density, water absorption rate and crushing index performance of the recycled coarse aggregate with vacuum slurry coating modification are all better than those of ordinary slurry coating modification; the same result is also obtained in the slurry coating modification experiments with two different water-binder ratios; its performance meets the performance requirements of Class III recycled coarse aggregate in the specification GB / T25177—2010 "Recycled Coarse Aggregate for Concrete", indicating that the vacuum slurry coating method of the present invention is a high-performance slurry coating modification method for recycled aggregate.

[0152] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for modifying recycled concrete aggregate by vacuum coating, characterized in that: The specific steps include: Step S1, weigh the following components in parts by weight: 100 parts of recycled coarse aggregate, 100 parts of Portland cement, and 40-80 parts of water; Step S2, placing the recycled aggregate into the vacuum barrel A and sealing it with the lid closed; Step S3, mix cement and water evenly, ensure that there is no dry powder or lumps, and then pour them into container barrel B, keeping container barrel B unsealed; Step S4, the vacuum barrel A is connected to the container barrel B through a hose, a hose valve is installed on the hose, and the hose valve is kept in a closed state; Step S5, open the exhaust valve of the vacuum barrel A, use a vacuum pump to apply a vacuum of -0.6 to -1.0 bar to the vacuum barrel A, and stabilize the pressure for 5 to 8 minutes after the pressure gauge stabilizes; Step S6, open the hose valve, pump the slurry in the container barrel B into the negative pressure vacuum barrel A, and continue to pump the slurry for 30 to 50 seconds after the slurry level in the vacuum barrel A is flush with the surface of the accumulated aggregate, close the hose valve, and keep the vacuum state of the vacuum barrel A for 5 to 8 minutes; Step S7, turn off the vacuum pump, open the air inlet valve of vacuum barrel A to restore the vacuum barrel A to normal pressure, and continue soaking for 5 to 8 minutes; Step S8, filter out the slurry in the vacuum barrel A, and then obtain the slurry-coated recycled coarse aggregate, air-dry it on the wire mesh for 20 to 24 hours, then cover it with a wet cloth, and finally move it into a standard curing room for curing for 7 days to obtain the finished recycled concrete aggregate.

2. The method for modifying recycled concrete aggregate by vacuum coating according to claim 1, characterized in that: The particle size of the recycled coarse aggregate in step S1 is in the range of 5 to 20 mm, and the apparent density is in the range of 2250 to 2350 kg / m 3 , water absorption rate is 5.0-8.0%, and crushing value is 20-30%.

3. The method for modifying recycled concrete aggregate by vacuum coating according to claim 1, characterized in that: The preparation method of the recycled coarse aggregate in step S1 is as follows: the natural aggregate concrete is crushed by a jaw crusher and a grinding crusher, and then washed by a high-pressure water gun, with a washing pressure of 100 to 120 bar and a washing time of 10 to 15 minutes.

4. The method for modifying recycled concrete aggregate by vacuum coating according to claim 1, characterized in that: The silicate cement in step S1 is ordinary Portland cement with a strength grade of 42.

5.

5. The method for modifying recycled concrete aggregate by vacuum coating according to claim 1, characterized in that: In step S4, the two ends of the hose are respectively the upper part of the side wall of the vacuum barrel A and the bottom part of the side wall of the container barrel B.

6. The method for modifying recycled concrete aggregate by vacuum coating according to claim 1, characterized in that: In the step S4, the rubber hose is a pressure-resistant rubber hose.

7. The method for modifying recycled concrete aggregate by vacuum coating according to claim 1, characterized in that: In step S5, the vacuum pump has a pumping rate of 3.6 m / s. 3 / h.

8. The method for modifying recycled concrete aggregate by vacuum coating according to claim 1, characterized in that: In step S8, the pore size of the wire mesh is 4 mm.

9. The method for modifying recycled concrete aggregate by vacuum coating according to claim 1, characterized in that: In step S8, the temperature of the standard curing room is 20±2° C. and the relative humidity is 95%±3%.

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