Subgeneration recycled coarse aggregate modification method suitable for sulfate dry and wet environment

Abstract

The invention relates to the technical field of building materials, and discloses a modification method of a next-generation recycled coarse aggregate suitable for a sulfate dry and wet environment. According to the modification method, Portland cement, fly ash, silica fume and Mg-Al hydrotalcite slurry are wrapped on the surface of the recycled coarse aggregate through a vacuum slurry wrapping technology, so that the compactness and sulfate attack resistance of the recycled coarse aggregate are remarkably improved. The apparent density of the modified aggregate is greater than or equal to 2330kg / m < 3 >, the water absorption rate is less than or equal to 5.6%, the crushing value is less than or equal to 21.6%, and the modified aggregate meets the III-class recycled coarse aggregate standard, is suitable for structural concrete engineering, and has environmental protection and economic benefits.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building materials, in particular to the technical field of recycled concrete, and especially to a modification method of next-generation recycled coarse aggregate suitable for sulfate dry-wet environment. BACKGROUND

[0002] Concrete is the most widely used building material in the world, but its production consumes a large amount of natural aggregate, and the landfill treatment of construction waste causes serious environmental burden. Although recycled aggregate concrete has environmental advantages, in the sulfate environment, the recycled aggregate is easy to cause internal erosion and lead to performance degradation due to carrying the sulfate erosion products in the original concrete. In the prior art, the modification methods of recycled aggregate are mostly focused on ordinary environments, and the adaptability to sulfate dry-wet cyclic environment is insufficient, and there is an urgent need for a modification method that can significantly improve the performance of recycled aggregate in sulfate environment. SUMMARY

[0003] The technical problem to be solved by the present application is to overcome the deficiencies in the prior art and provide a modification method of next-generation recycled coarse aggregate suitable for sulfate dry-wet environment. In the present application, a dense cement paste layer is formed on the surface of the recycled coarse aggregate by vacuum coating, which enhances the bonding force between the cement and the aggregate, and the added fly ash and silica fume effectively fill the micro-cracks and pores on the surface of the aggregate, and the Mg-Al hydrotalcite adsorbs free harmful anions, thereby improving the firmness of the aggregate and the stability of the overall structure. The mechanical properties of the recycled coarse aggregate modified by the method are improved, and it can be applied to structural concrete again.

[0004] The technical solution adopted by the present application to solve the technical problem is:

[0005] A modification method of next-generation recycled coarse aggregate suitable for sulfate dry-wet environment, specifically comprising the following steps:

[0006] Step S1, weigh the following components: 100 parts of recycled coarse aggregate, 80-100 parts of Portland cement, 40-80 parts of water, 0-15 parts of fly ash, 0-5 parts of silica fume, and 0-2 parts of Mg-Al hydrotalcite;

[0007] Step S2, uniformly stir the Portland cement, fly ash, silica fume, Mg-Al hydrotalcite and water, and then pour them into a vacuum container after ensuring that there is no dry powder or lump;

[0008] Step S3, pour the recycled coarse aggregate into the vacuum container, and seal the cover after stirring for 2-3 minutes;

[0009] Step S4, open the air valve on the cover of the vacuum container, and use a vacuum pump to apply a vacuum pressure of-0.6 to-1.0 bar to the vacuum container, and then stabilize the pressure for 5-8 minutes after the pressure gauge is stable;

[0010] Step S5, close the vacuum pump, open the inlet valve to make the vacuum container restore normal pressure, continue to soak for 5-8 minutes;

[0011] Step S6, filter out the slurry in the vacuum container to obtain the coated slurry recycled coarse aggregate, then dry on the iron mesh for 20-24 hours, then cover with wet cloth, and finally move into the standard curing room for 14 days to obtain the finished product of recycled concrete aggregate.

[0012] The addition of fly ash and silica ash can significantly improve the microstructure of the slurry, fill the pores in the recycled coarse aggregate, reduce the porosity, and improve the overall density. Fly ash has pozzolanic activity and participates in the hydration reaction to generate more gel products, which can improve the late strength. Silica ash has smaller particle size and stronger activity, which can significantly improve the performance of the interfacial transition zone. On this basis, the introduction of hydrotalcite can play its adsorption effect, effectively fix harmful ions and alkalize the environment, and further enhance the durability and long-term service performance of the concrete. This composite modification method is mature in technology, convenient to operate, suitable for engineering practical application, and has good economic and environmental friendliness.

[0013] In addition, the negative pressure environment can effectively exhaust the air in the pores of the recycled aggregate, help the cement slurry to penetrate more uniformly into the pores and cracks on the surface of the recycled aggregate, improve the density and strength, and thus improve the quality of the coated slurry. Under negative pressure environment, water and cement particles are in full contact, and the initial hydration reaction is accelerated. However, negative pressure environment can accelerate the evaporation of water, and thus accelerate the loss of water in the cement slurry, affecting the later hydration reaction. Therefore, after 5-8 minutes of negative pressure coating, it is converted to normal pressure for continued soaking.

[0014] Further, the preparation method of the recycled coarse aggregate is as follows: C35 natural aggregate concrete is subjected to 150 times of sulfate dry-wet cycle, then subjected to double crushing by a jaw crusher and a grinding crusher, and then subjected to washing by a high-pressure water gun to obtain the recycled coarse aggregate, wherein the washing pressure is 100-120 bar, and the washing time is 10-15 minutes.

[0015] The preparation method of the recycled coarse aggregate is limited. The double crushing by the jaw crusher and the grinding crusher, combined with the washing by the high-pressure water gun, can effectively remove impurities and loose particles on the surface of the aggregate, ensuring the cleanliness and uniformity of the aggregate. The high-pressure water gun washing can further reduce the micro-cracks on the surface of the aggregate and improve the overall quality of the aggregate.

[0016] Further, in step S1, the particle size of the recycled coarse aggregate ranges from 5 to 31 mm, the apparent density is 2250-2400 kg / m 3 , the water absorption is 5.0-8.0%, and the crushing value is 15-30%.

[0017] The particle size range, apparent density, water absorption rate and crushing value of the recycled coarse aggregate are limited to ensure 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 concrete can be ensured, further improving the overall performance of recycled concrete.

[0018] Further, in the step S1, the Portland cement has a strength grade of 42.5. Limiting the strength grade of the Portland cement to 42.5 ensures the strength and adhesion performance of the cement paste. Ordinary Portland cement has high early strength and durability, which can effectively improve the modification effect of recycled coarse aggregate and enhance the mechanical properties of recycled concrete.

[0019] Further, in the step S1, the fly ash is Grade I fly ash. Grade I fly ash has high activity and fineness, which helps to improve the density and workability of the cement paste. Limiting the use of Grade I fly ash can significantly improve the microstructure of the recycled coarse aggregate interface and improve the durability and later strength of the recycled concrete.

[0020] Further, in the step S1, the SiO2 content in silica ash is 94.8%. Silica ash has extremely high pozzolanic activity and ultra-fine particle characteristics, which can react with hydration products during hydration to generate more gel, filling the interfacial pores of recycled aggregate and significantly improving the density and mechanical properties of recycled concrete.

[0021] Further, in the step S1, the particle size of Mg-Al hydrotalcite is 10-80 nanometers, and the specific surface area is 10.1 m 2 / g. Mg-Al hydrotalcite has excellent adsorbability and dispersibility. Limiting the particle size and specific surface area helps it to be uniformly distributed in the cement-based system and fully play its physical filling and chemical activity role, optimizing the interface structure of recycled coarse aggregate and paste, thereby effectively improving the mechanical properties and durability of recycled concrete.

[0022] Further, in the step S5, the vacuum pump has an air pumping rate of 3.6 m 3 / h. Limiting the air pumping rate of the vacuum pump to 3.6 m 3 / h ensures that the vacuum barrel A can reach the required vacuum degree within a reasonable time. An appropriate air pumping rate can ensure that the slurry is uniformly wrapped around the aggregate surface, improving the modification effect.

[0023] Further, in the step S6, the wire mesh has a pore size of 4 mm. Limiting the pore size of the wire mesh to 4 mm ensures that excess slurry can be easily filtered, while preventing the aggregate from leaking out of the mesh. An appropriate pore size can ensure that the aggregate is evenly distributed during air drying, improving the quality of the modified aggregate.

[0024] Further, in the step S6, the standard curing room temperature is 20±2℃, 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 to form a stable cement paste wrapping layer. Appropriate curing conditions can further improve the physical properties and mechanical properties of the recycled coarse aggregate.

[0025] The present application has the following advantages:

[0026] (1) Improved mechanical properties: fly ash, silica fume and hydrotalcite can improve the interface structure, fill the pores, and improve the density and bonding force of hydration products, thereby improving the mechanical properties of the modified recycled coarse aggregate;

[0027] (2) Improved durability: the synergistic effect of fly ash, silica fume and hydrotalcite can reduce porosity, inhibit the intrusion of harmful ions and alkali-aggregate reaction, and improve the durability of the recycled coarse aggregate;

[0028] (3) Environmental protection and energy saving: recycled aggregate is prepared from construction waste in sulfate erosion areas, and its performance is improved through modification technology, which not only solves the problem of construction waste disposal in sulfate erosion areas, but also saves natural aggregate resources;

[0029] (4) The recycled coarse aggregate obtained by the method has an apparent density greater than 2330kg / m 3 , a water absorption less than 5.6%, and a crushing value less than 21.6%, and its physical properties meet the performance requirements of Class III recycled coarse aggregate, which can be used again in structural concrete engineering, improving the utilization level and utilization rate of recycled resources. DETAILED DESCRIPTION

[0030] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs.

[0031] It should be noted that the terms used herein are only for the purpose of describing the specific embodiments, and are not intended to limit the exemplary embodiments according to the present application. As used herein, the singular form also includes the plural form unless the context clearly indicates otherwise, and furthermore, it should be understood that when the terms "comprise" and / or "include" are used in the present description, they indicate the presence of the features, steps, operations, devices, components and / or combinations thereof.

[0032] The technical solutions of the present application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of the present application.

[0033] A modification method of a next-generation recycled coarse aggregate suitable for a sulfate dry-wet environment, specifically comprising the following steps:

[0034] Step S1, weigh the following components: 100 parts of recycled coarse aggregate, 80-100 parts of Portland cement, 40-80 parts of water, 0-15 parts of fly ash, 0-5 parts of silica fume, and 0-2 parts of Mg-Al hydrotalcite;

[0035] Step S2, uniformly stir the Portland cement, fly ash, silica fume, Mg-Al hydrotalcite, and water, and then pour them into a vacuum container after ensuring that there is no dry powder or lump;

[0036] Step S3, pour the recycled coarse aggregate into the vacuum container, stir for 2-3 minutes, and then seal the cover;

[0037] Step S4, open the air valve on the cover of the vacuum container, use a vacuum pump to apply a vacuum pressure of -0.6 to -1.0 bar to the vacuum container, and then stabilize the pressure for 5-8 minutes after the pressure gauge stabilizes;

[0038] Step S5, turn off the vacuum pump, open the air inlet valve to restore the vacuum container to normal pressure, and continue to soak for 5-8 minutes;

[0039] Step S6, filter out the slurry in the vacuum container to obtain slurry-coated recycled coarse aggregate, then air dry on a wire mesh for 20-24 hours, cover with a damp cloth, and finally move into a standard curing room for 14 days to obtain the finished product of recycled concrete aggregate.

[0040] The preparation method of the recycled coarse aggregate is as follows: C35 natural aggregate concrete is subjected to 150 times of sulfate dry-wet cycles, then subjected to double crushing by a jaw crusher and a roller mill, and finally subjected to washing by a high-pressure water gun to obtain the recycled coarse aggregate, wherein the washing pressure is 100-120 bar, and the washing time is 10-15 minutes.

[0041] In step S1, the particle size of the recycled coarse aggregate ranges from 5 to 31 mm, the apparent density is 2250-2400 kg / m 3 , the water absorption is 5.0-8.0%, and the crushing value is 15-30%.

[0042] In step S1, the Portland cement is ordinary Portland cement, and the strength grade is 42.5; the fly ash is grade I fly ash; the SiO2 content in the silica ash is 94.8%; the particle size of the Mg-Al hydrotalcite is 10-80 nanometers, and the specific surface area is 10.1 m 2 / g.

[0043] In step S5, the pumping rate of the vacuum pump is 3.6 m 3 / h.

[0044] In step S6, the mesh size of the iron wire mesh is 4 mm; the temperature in the standard curing room is 20±2℃, and the relative humidity is 95%±3%.

[0045] The recycled concrete aggregate prepared by the above method is subjected to physical performance test.

[0046] 1. Apparent density test

[0047] The sample is weighed according to the specification, and then is immersed in water until saturated, and then is put into a wide-mouth bottle. Water is injected, and the bottle opening is covered with a glass sheet. The bubbles are removed by shaking the bottle in up-down and left-right directions. After the bubbles are removed, water is added to the bottle until the water surface protrudes from the bottle opening, and then the glass sheet is quickly slid along the bottle opening to make it adhere to the water surface. After the water on the bottle is wiped off, the total mass of the sample, water, bottle and glass sheet (m1) is weighed. The sample in the bottle is poured into a shallow tray, and is placed in an oven at (105±5)℃ until the constant weight is reached. After being taken out, the sample is placed in a container with a cover and cooled to room temperature, and then the mass (m0) is weighed. The bottle is washed, and water is injected again. The glass sheet is tightly adhered to the water surface of the bottle opening, and the water on the bottle is wiped off, and then the mass (m2) is weighed.

[0048] The apparent density p is calculated according to the following formula, and the arithmetic mean of the results of two tests is taken as the measured value:

[0049]

[0050] Wherein p 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 sheet; m2 is the total mass of water, bottle and glass sheet; a t is the correction coefficient of the influence of water temperature on the apparent density, and is shown in Table 1.

[0051] Table 1 a t is the correction coefficient of the influence of water temperature on the apparent density

[0052]

[0053] 2. Water absorption test

[0054] The sample was weighed and placed in a container containing water, so that the water level was about 5 mm higher than the sample surface. After 24 h, the sample was taken out of the water, and the water on the surface of the sample was wiped dry with a wrung wet towel. The sample was immediately placed in a shallow dish and weighed (m2). The saturated surface-dry sample and the shallow dish were placed in an oven at (105±5) °C until the weight was constant. After being taken out, the sample and the shallow dish were placed in a container with a lid and cooled for 0.5-1 h. The total weight of the dried sample and the shallow dish (m1) was weighed, and the weight of the shallow dish (m3) was weighed.

[0055] The water absorption ω was calculated according to the following formula, and the arithmetic mean of two test results was taken as the measured value:

[0056]

[0057] where ω is the water absorption; m1 is the total weight of the dried sample and the shallow dish; m2 is the total weight of the saturated surface-dry sample and the shallow dish before drying; and m3 is the weight of the shallow dish.

[0058] 3. Crushed value test

[0059] The sample was placed in a crushed value index tester according to the specification, and was placed on the tester and uniformly loaded to 200 kN within 160-300 s, and then unloaded and taken out of the tester. The sample in the cylinder was poured out and weighed (m0), and the fine particles crushed were sieved out with a square hole sieve with a nominal diameter of 2.50 mm, and the mass of the sample remaining on the sieve (m1) was weighed.

[0060] The crushed value index δ was calculated according to the following formula, and the arithmetic mean of three test results was taken as the measured value:

[0061]

[0062] where δ is the crushed value index; m0 is the mass of the sample; and m1 is the mass of the sample remaining on the sieve after the crushed test.

[0063] In the present application, the apparent density, water absorption and crushed value of the modified recycled coarse aggregate prepared in the examples and comparative examples were measured according to GB / T 25177-2010 "Recycled Coarse Aggregate for Concrete".

[0064] The apparent density, water absorption and crushed value of the coarse aggregate used in the following examples and comparative examples were 2260 kg / m 3 , 7.3% and 27%, respectively, and the particle size was 5-31 mm.

[0065] Example 1

[0066] A modified method of the next generation recycled coarse aggregate suitable for sulfate dry and wet environment, specifically as follows:

[0067] Step S1, take the following weight parts of components: 100 parts of recycled coarse aggregate obtained by crushing C35 natural aggregate concrete subjected to 150 times of sulfate dry-wet cycles, 80 parts of Portland cement, 40 parts of water, 15 parts of fly ash, 5 parts of silica fume, and 2 parts of Mg-Al hydrotalcite (water-cement ratio 0.4);

[0068] Step S2, after uniformly stirring the cement, fly ash, silica fume, Mg-Al hydrotalcite, and water to ensure that there is no dry powder or lump, pour them into a vacuum container;

[0069] Step S3, pour the recycled coarse aggregate into the vacuum barrel, stir for 2-3 minutes, and then seal the cover;

[0070] Step S4, open the air exhaust valve on the cover of the vacuum barrel, use a vacuum pump to apply a vacuum pressure of -0.6 to -1.0 bar to the vacuum barrel, and after the pressure gauge stabilizes, stabilize the pressure for 5-8 minutes;

[0071] Step S5, turn off the vacuum pump, open the air inlet valve to restore the vacuum barrel to normal pressure, and continue to soak for 5-8 minutes;

[0072] Step S6, filter out the slurry in the vacuum barrel, then obtain the slurry-coated recycled coarse aggregate, air dry on a wire mesh for 20-24 hours, then cover with a damp cloth, and finally move to a standard curing room for 14 days to obtain the finished product recycled concrete aggregate.

[0073] Example 2

[0074] A method for modifying the next generation of recycled coarse aggregate suitable for sulfate dry-wet environment, specifically as follows:

[0075] Step S1, take the following weight parts of components: 100 parts of recycled coarse aggregate obtained by crushing C35 natural aggregate concrete subjected to 150 times of sulfate dry-wet cycles, 80 parts of Portland cement, 60 parts of water, 15 parts of fly ash, 5 parts of silica fume, and 2 parts of Mg-Al hydrotalcite (water-cement ratio 0.6);

[0076] Step S2, after uniformly stirring the cement, fly ash, silica fume, Mg-Al hydrotalcite, and water to ensure that there is no dry powder or lump, pour them into a vacuum container;

[0077] Step S3, pour the recycled coarse aggregate into the vacuum barrel, stir for 2-3 minutes, and then seal the cover;

[0078] Step S4, open the air exhaust valve on the cover of the vacuum barrel, use a vacuum pump to apply a vacuum pressure of -0.6 to -1.0 bar to the vacuum barrel, and after the pressure gauge stabilizes, stabilize the pressure for 5-8 minutes;

[0079] Step S5, turn off the vacuum pump, open the air inlet valve to restore the vacuum barrel to normal pressure, and continue to soak for 5-8 minutes;

[0080] Step S6, filter out the slurry in the vacuum barrel, then get the coated slurry recycled coarse aggregate, dry on the iron mesh piece for 20-24 hours, then cover with wet cloth, finally move into the standard curing room for 14d to get the finished product recycled concrete aggregate.

[0081] Example 3

[0082] A modified method for the next generation of recycled coarse aggregate suitable for sulfate dry-wet environment, specifically as follows:

[0083] Step S1, take the following weight parts of components: 100 parts of recycled coarse aggregate obtained by crushing C35 natural aggregate concrete subjected to 150 times of sulfate dry-wet cycles, 80 parts of Portland cement, 80 parts of water, 15 parts of fly ash, 5 parts of silica fume, and 2 parts of Mg-Al hydrotalcite (water-cement ratio 0.8);

[0084] Step S2, mix the cement, fly ash, silica fume, Mg-Al hydrotalcite and water uniformly, and then pour them into a vacuum container after ensuring that there is no dry powder or lump;

[0085] Step S3, pour the recycled coarse aggregate into the vacuum barrel, and seal the cover after stirring for 2-3 minutes;

[0086] Step S4, open the air valve on the cover of the vacuum barrel, and use the vacuum pump to apply a vacuum pressure of-0.6 to-1.0 bar to the vacuum barrel, and then stabilize the pressure for 5-8 minutes after the pressure gauge is stable;

[0087] Step S5, turn off the vacuum pump, open the air inlet valve to restore the pressure in the vacuum barrel to normal, and continue to soak for 5-8 minutes;

[0088] Step S6, filter out the slurry in the vacuum barrel, then get the coated slurry recycled coarse aggregate, dry on the iron mesh piece for 20-24 hours, then cover with wet cloth, finally move into the standard curing room for 14d to get the finished product recycled concrete aggregate.

[0089] Example 4

[0090] A modified method for the next generation of recycled coarse aggregate suitable for sulfate dry-wet environment, specifically as follows:

[0091] Step S1, take the following weight parts of components: 100 parts of recycled coarse aggregate obtained by crushing C35 natural aggregate concrete subjected to 150 times of sulfate dry-wet cycles, 80 parts of Portland cement, 80 parts of water, 15 parts of fly ash, 5 parts of silica fume, and 2 parts of Mg-Al hydrotalcite (water-cement ratio 0.8);

[0092] Step S2, mix the cement, fly ash, silica fume, Mg-Al hydrotalcite and water uniformly, and then pour them into a vacuum container after ensuring that there is no dry powder or lump;

[0093] Step S3, pour the recycled coarse aggregate into the vacuum barrel, seal the cover after stirring for 2-3 minutes;

[0094] Step S4, open the air valve on the cover of the vacuum barrel, use the vacuum pump to apply a vacuum pressure of-0.6 to-1.0 bar to the vacuum barrel, and stabilize the pressure for 5-8 minutes after the pressure gauge stabilizes;

[0095] Step S5, close the vacuum pump, open the air inlet valve to restore the vacuum barrel to normal pressure, and continue to soak for 5-8 minutes;

[0096] Step S6, filter out the slurry in the vacuum barrel, then get the slurry-coated recycled coarse aggregate, dry on the wire mesh for 20-24 hours, then cover with a wet cloth, and finally move into a standard curing room for 14d to get the finished product recycled concrete aggregate.

[0097] Comparative Example 1

[0098] A modified method of recycled coarse aggregate, specifically as follows:

[0099] Step S1, weigh the following components: 100 parts of recycled coarse aggregate obtained by crushing C35 natural aggregate concrete subjected to 150 cycles of sulfate salt dry-wet cycle, 100 parts of Portland cement, and 60 parts of water (water-cement ratio 0.6);

[0100] Step S2, mix the cement and water evenly, make sure there is no dry powder or lump, then pour into the vacuum container;

[0101] Step S3, pour the recycled coarse aggregate into the vacuum barrel, seal the cover after stirring for 2-3 minutes;

[0102] Step S4, open the air valve on the cover of the vacuum barrel, use the vacuum pump to apply a vacuum pressure of-0.6 to-1.0 bar to the vacuum barrel, and stabilize the pressure for 5-8 minutes after the pressure gauge stabilizes;

[0103] Step S5, close the vacuum pump, open the air inlet valve to restore the vacuum barrel to normal pressure, and continue to soak for 5-8 minutes;

[0104] Step S6, filter out the slurry in the vacuum barrel, then get the slurry-coated recycled coarse aggregate, dry on the wire mesh for 20-24 hours, then cover with a wet cloth, and finally move into a standard curing room for 14d to get the finished product recycled concrete aggregate.

[0105] Comparative Example 2

[0106] A modified method of recycled coarse aggregate, specifically as follows:

[0107] Step S1, take the following weight parts of components: 100 parts of recycled coarse aggregate obtained by crushing C35 natural aggregate concrete subjected to 150 times of sulfate salt dry-wet cycles, 80 parts of Portland cement, 60 parts of water, 15 parts of fly ash, and 5 parts of silica fume (water-cement ratio 0.6);

[0108] Step S2, after the cement, fly ash, silica fume and water are uniformly stirred to ensure that there is no dry powder or lump, pour them into a vacuum container;

[0109] Step S3, pour the recycled coarse aggregate into the vacuum barrel, stir for 2-3 minutes, and then seal the cover;

[0110] Step S4, open the air valve on the cover of the vacuum barrel, use the vacuum pump to apply a vacuum pressure of-0.6 to-1.0 bar to the vacuum barrel, and after the pressure gauge stabilizes, stabilize the pressure for 5-8 minutes;

[0111] Step S5, close the vacuum pump, open the air inlet valve to restore the vacuum barrel to normal pressure, and continue to soak for 5-8 minutes;

[0112] Step S6, filter out the slurry in the vacuum barrel, then obtain the slurry-coated recycled coarse aggregate, air dry on a wire mesh for 20-24 hours, then cover with a damp cloth, and finally move into a standard curing room for 14 days to obtain the finished product recycled concrete aggregate.

[0113] Comparative Example 3

[0114] A method for modifying recycled coarse aggregate, specifically as follows:

[0115] Step S1, take the following weight parts of components: 100 parts of recycled coarse aggregate obtained by crushing C35 natural aggregate concrete subjected to 150 times of sulfate salt dry-wet cycles, 100 parts of Portland cement, 60 parts of water, and 2 parts of Mg-Al hydrotalcite (water-cement ratio 0.6);

[0116] Step S2, after the cement, Mg-Al hydrotalcite and water are uniformly stirred to ensure that there is no dry powder or lump, pour them into a vacuum container;

[0117] Step S3, pour the recycled coarse aggregate into the vacuum barrel, stir for 2-3 minutes, and then seal the cover;

[0118] Step S4, open the air valve on the cover of the vacuum barrel, use the vacuum pump to apply a vacuum pressure of-0.6 to-1.0 bar to the vacuum barrel, and after the pressure gauge stabilizes, stabilize the pressure for 5-8 minutes;

[0119] Step S5, close the vacuum pump, open the air inlet valve to restore the vacuum barrel to normal pressure, and continue to soak for 5-8 minutes;

[0120] Step S6, filter out the slurry in the vacuum bucket, then obtain the coated slurry recycled coarse aggregate, dry on the iron wire mesh for 20-24 hours, then cover with wet cloth, and finally move into the standard curing room for curing for 14 days to obtain the finished product of recycled concrete aggregate.

[0121] The finished products prepared in Examples 1-4 and Comparative Examples 1-3 were sampled and subjected to physical performance tests, and the test results are shown in Table 2.

[0122] Table 2 Test results of Examples 1-4 and Comparative Examples 1-3

[0123]

[0124] Compared with the recycled coarse aggregate obtained by crushing C35 subjected to 150 times of sulfate salt dry-wet cycles before modification, the apparent density of the recycled coarse aggregate was 2260 kg / m 3 From the test results in Table 2, it can be seen that:

[0125] The recycled coarse aggregate obtained by crushing C35 subjected to 150 times of sulfate salt dry-wet cycles was coated with slurry with different water-binder ratios (0.4, 0.6, 0.8), and the apparent densities of the coated recycled coarse aggregate were 2330 kg / m 3 (Example 1), 2340 kg / m 3 (Example 2), and 2320 kg / m 3 (Example 3). It can be seen that, in terms of apparent density, the performance of the recycled coarse aggregate coated with slurry with different water-binder ratios was better than that of the unmodified recycled coarse aggregate, and the modification effect was best when the water-binder ratio was 0.6.

[0126] Compared with the recycled coarse aggregate obtained by crushing C35 subjected to 150 times of sulfate salt dry-wet cycles before modification, the water absorption of the recycled coarse aggregate was 7.3%, and from the test results in Table 2, it can be seen that:

[0127] The recycled coarse aggregate obtained by crushing C35 subjected to 150 times of sulfate salt dry-wet cycles was coated with slurry with different water-binder ratios (0.4, 0.6, 0.8), and the water absorptions of the coated recycled coarse aggregate were 5.5% (Example 1), 5.1% (Example 2), and 5.9% (Example 3). It can be seen that, in terms of water absorption, the performance of the recycled coarse aggregate coated with slurry with different water-binder ratios was better than that of the unmodified recycled coarse aggregate, and the modification effect was best when the water-binder ratio was 0.6.

[0128] Compared with the recycled coarse aggregate obtained by crushing C35 subjected to 150 times of sulfate salt dry-wet cycles before modification, the crushing index of the recycled coarse aggregate was 27%, and from the test results in Table 2, it can be seen that:

[0129] The recycled coarse aggregate obtained by crushing the C35 concrete subjected to 150 cycles of sulfate salt dry-wet cycle is modified by different water-binder ratio (0.4, 0.6, 0.8) slurry, and the crushing indexes of the recycled coarse aggregate are 24.4% (Example 1), 24.1% (Example 2) and 24.7% (Example 3) respectively, and it can be seen that the performance of the recycled coarse aggregate modified by the slurry of different water-binder ratio is better than that of the unmodified recycled coarse aggregate in terms of the crushing index, and the modification effect is best when the water-binder ratio is 0.6.

[0130] Compared with the apparent density, water absorption and crushing value of the modified recycled coarse aggregate in Example 2, which are 2340 kg / m3, 5.1% and 19.8% respectively, it can be seen from the test results in Table 2 that the apparent density, water absorption and crushing value of Comparative Example 1 are 2310 kg / m3, 6.2% and 21.9% respectively; the apparent density, water absorption and crushing value of Comparative Example 2 are 2320 kg / m3, 5.9% and 20.5% respectively; and the apparent density, water absorption and crushing value of Comparative Example 32 are 2320 kg / m3, 5.6% and 20.3% respectively. It can be seen that the addition of fly ash and silica fume improves the three indexes, and the optimization degree of single-doped Mg-Al hydrotalcite is similar, and the mixing of the three improves the three indexes again, which verifies the argument that the synergistic effect of the above three can reduce porosity, inhibit the invasion of harmful ions and improve the mechanical properties of the recycled coarse aggregate.

[0131] In summary, the performance of the recycled coarse aggregate modified by the slurry of the method is better in terms of the apparent density, water absorption and crushing index, the performance meets the performance requirements of the recycled coarse aggregate of Class III in the specification GB / T25177-2010 “Recycled Coarse Aggregate for Concrete”, and it is proved that the method is a modification method suitable for the next generation of recycled coarse aggregate in a sulfate salt dry-wet environment.

[0132] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions described in the foregoing examples can be modified, or some or all of the technical features can be replaced by equivalents; 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 application.

Claims

1. A method for modifying next-generation recycled coarse aggregate suitable for sulfate dry and wet environments, characterized by: The specific steps include: Step S1, weighing the following components in parts by weight: 100 parts of recycled coarse aggregate, 80-100 parts of Portland cement, 40-80 parts of water, 0-15 parts of fly ash, 0-5 parts of silica fume, and 0-2 parts of Mg-Al hydrotalcite; Step S2: Stir the Portland cement, fly ash, silica fume, Mg-Al hydrotalcite and water until there is no dry powder or lumps, and then pour the mixture into a vacuum container; Step S3: Pour the recycled coarse aggregate into a vacuum container, stir for 2 to 3 minutes, and then close the lid and seal; Step S4: Open the exhaust valve on the vacuum container cover and use a vacuum pump to apply a vacuum pressure of -0.6 to -1.0 bar to the vacuum container. After the pressure gauge stabilizes, maintain the pressure for 5 to 8 minutes. Step S5: Turn off the vacuum pump, open the air inlet valve to restore the vacuum container to normal pressure, and continue soaking for 5 to 8 minutes; Step S6: Filter out the slurry in the vacuum container to obtain the slurry-coated recycled coarse aggregate, which is then air-dried on a wire mesh for 20 to 24 hours, then covered with a wet cloth, and finally moved into a standard curing room for curing for 14 days to obtain the finished recycled concrete aggregate.

2. The method for modifying next-generation recycled coarse aggregate suitable for sulfate dry and wet environments according to claim 1, characterized in that: The preparation method of the recycled coarse aggregate is specifically as follows: C35 natural aggregate concrete is subjected to sulfate dry-wet cycles 150 times, then double-crushed by a jaw crusher and a grinding crusher, and then flushed by a high-pressure water gun with a flushing pressure of 100 to 120 bar and a flushing time of 10 to 15 minutes.

3. The method for modifying next-generation recycled coarse aggregate suitable for sulfate dry and wet environments according to claim 1, characterized in that: In step S1, the particle size of the recycled coarse aggregate is in the range of 5 to 31 mm, and the apparent density is in the range of 2250 to 2400 kg / m 3 , water absorption rate is 5.0~8.0%, and crushing value is 15~30%.

4. The method for modifying next-generation recycled coarse aggregate suitable for sulfate dry and wet environments according to claim 1, characterized in that: In step S1, the silicate cement is ordinary Portland cement with a strength grade of 42.

5.

5. The method for modifying next-generation recycled coarse aggregate suitable for sulfate dry and wet environments according to claim 1, characterized in that: In step S1, the fly ash is Class I fly ash.

6. The method for modifying next-generation recycled coarse aggregate suitable for sulfate dry and wet environments according to claim 1, characterized in that: In the step S1, the SiO2 content in the silica fume is 94.8%.

7. The method for modifying next-generation recycled coarse aggregate suitable for sulfate dry and wet environments according to claim 1, characterized in that: In step S1, the particle size of Mg-Al hydrotalcite is 10 to 80 nanometers, and the specific surface area is 10.1 m 2 / g.

8. The method for modifying next-generation recycled coarse aggregate suitable for sulfate dry and wet environments according to claim 1, characterized in that: In step S5, the vacuum pump has a pumping rate of 3.6 m / s. 3 / h.

9. The method for modifying next-generation recycled coarse aggregate suitable for sulfate dry and wet environments according to claim 1, characterized in that: In step S6, the pore size of the wire mesh is 4 mm.

10. The method for modifying next-generation recycled coarse aggregate suitable for sulfate dry and wet environments according to claim 1, characterized in that: In step S6, the temperature of the standard curing room is 20±2° C. and the relative humidity is 95%±3%.

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