Method for removing mortar attached to aggregate in air-entrained recycled concrete

Abstract

The present application discloses a method for removing mortar attached to aggregates of air-entrained regenerated concrete, which comprises vacuum water retention, and subjecting air-entrained concrete fragments to a dry pumping process and a wet pumping process. During the dry pumping process, the air-entrained concrete fragments are loaded into a vacuum pumping device and subjected to a first preset vacuuming process. After water is injected into the vacuum pumping device while maintaining the vacuum degree, a second preset vacuuming process is performed, thereby completing the wet pumping process. The air-entrained concrete fragments after the vacuum water retention treatment are subjected to freeze-thaw modification by water freezing and thawing. The method for removing mortar attached to aggregates of air-entrained regenerated concrete provided by the present invention improves the effect of freeze-thaw spalling through the vacuum water retention step. During the dry pumping process, negative pressure is used to open the pores and gaps in the mortar of the air-entrained concrete fragments. During the wet pumping process, water is injected while maintaining the vacuum degree. The opened pores and gaps absorb the injected water, so that the air-entrained concrete fragments are saturated, thereby improving the effect of subsequent mortar stripping.

Description

Technical Field

[0001] The invention relates to the technical field of recycling waste materials of concrete structures, and in particular to a method for removing mortar attached to aggregates of air-entrained recycled concrete. Background Art

[0002] Concrete structures offer numerous advantages over steel structures. However, concrete structures consume large quantities of natural aggregates, such as sand and gravel. With the continued increase in sand and gravel mining and the increasing attention paid to environmental issues, both sand and gravel production and prices are becoming increasingly unfavorable for businesses.

[0003] Correspondingly, the amount of existing construction waste generated is constantly increasing, and the reuse of construction waste is currently a hot topic in research and application. Metal and non-metallic materials (mainly aggregates and solid cement) in construction waste are all objects of recycling. In the process of aggregate regeneration, the recycled coarse aggregate is covered with a large amount of old mortar, and there are weak areas such as interface transition zones. As a result, compared with natural raw materials, there is a big gap in physical and mechanical properties, making it difficult to directly use and high-value utilization. At present, the modification technology of recycled aggregate can be divided into three categories according to different principles: adjusting the mix ratio; removing the old mortar attached to the surface of the recycled coarse aggregate; and strengthening the old mortar of the recycled coarse aggregate.

[0004] Chinese patent CN113117862A describes a method for rapidly removing old mortar from recycled concrete coarse aggregate, including primary impurity removal, crushing, high-temperature degradation, soaking in water, freeze-thaw peeling, vibration screening, mechanical vibration, high-pressure washing, and secondary impurity removal. This method can remove mortar attached to the surface of recycled coarse aggregate from ordinary concrete, producing recycled coarse aggregate with properties close to those of natural aggregate. However, similar methods to the above cannot handle frost-resistant air-entrained recycled concrete fragments, and the resulting mortar stripping effect does not meet application standards and is inefficient. Summary of the Invention

[0005] The main purpose of the present invention is to provide a method for removing mortar attached to aggregates of air-entrained regenerated concrete, aiming to solve the problem that the mortar attached to aggregates of air-entrained regenerated concrete cannot be removed with high quality in the existing method.

[0006] In order to achieve the above object, the first aspect of the present invention is to provide a method for removing mortar attached to aggregates of air-entrained regenerated concrete, comprising:

[0007] S1, the first impurity removal, screening the concrete blocks to obtain air-entrained concrete blocks;

[0008] S2, crushing, crushing the air-entrained concrete blocks into air-entrained concrete fragments;

[0009] S3, vacuum water retention, subjecting the air-entrained concrete fragments to a dry pumping process and a wet pumping process, wherein, in the dry pumping process, the air-entrained concrete fragments are placed in a vacuum pumping device and subjected to a first preset vacuum pumping process. After the dry pumping process is completed, water is injected into the vacuum pumping device while maintaining the vacuum degree, and then a second preset vacuum pumping process is performed to complete the wet pumping process;

[0010] S4, freeze-thaw spalling, the air-entrained concrete fragments after vacuum water retention treatment are subjected to freeze-thaw modification by water freezing and thawing, wherein the lowest temperature range during freeze-thaw spalling is -30 to -40°C, and the highest temperature is maintained at 15 to 25°C;

[0011] S5, vibrating screening, vibrating screening the air-entrained concrete fragments that have undergone freeze-thaw spalling;

[0012] S6, impact separation;

[0013] S7, second impurity removal;

[0014] The recycled aggregate is obtained by repeating steps S3 to S7 for a number of times according to the effect of removing the mortar attached to the aggregate.

[0015] Furthermore, when the water-cement ratio of the crushed air-entrained concrete block is less than the index A, the value range of the index A is 0.45 to 0.55, and step S2.5 is further included between step S2 and step S3, and the step S2.5 includes:

[0016] High temperature degradation: The air-entrained concrete fragments are subjected to high temperature degradation treatment, wherein the temperature range of high temperature degradation is 300°C to 400°C, and the time range of high temperature degradation is 6h to 18h.

[0017] Furthermore, the value of the indicator A is 0.5.

[0018] Furthermore, in step S3, the temperature range of high temperature degradation is 300° C. to 320° C., and the time range of high temperature degradation is 8 hours to 14 hours.

[0019] Furthermore, in the step S3, the first preset vacuuming process in the dry pumping process is to maintain a first preset negative pressure value for a first preset time period.

[0020] Furthermore, in the step S3, the second preset vacuuming process in the wet pumping process is to close the vacuuming device for a second preset time.

[0021] Furthermore, in the step S3, the second preset vacuuming process in the wet pumping process is to maintain the second preset negative pressure value for a third preset time period.

[0022] Furthermore, the step S4 includes:

[0023] The air-entrained concrete fragments after vacuum water retention treatment are subjected to freeze-thaw modification of at least one round of freezing and thawing, wherein the lowest freeze-thaw temperature range is -35 to -40°C and the highest temperature range is 20 to 25°C.

[0024] Furthermore, the step S4 includes:

[0025] The air-entrained concrete fragments after vacuum water retention treatment are subjected to freeze-thaw modification of at least two rounds of water freezing and thawing, wherein the lowest freeze-thaw temperature in the later freeze-thaw modification is higher than the lowest freeze-thaw temperature in the earlier freeze-thaw modification, and the highest freeze-thaw temperature in the later freeze-thaw modification is lower than the lowest freeze-thaw temperature in the earlier freeze-thaw modification.

[0026] Furthermore, the step S6 includes:

[0027] S6.1. Mechanical vibration: Place the air-entrained concrete fragments that have been vibrated and screened into a drum stone washer for mechanical vibration.

[0028] S6.2. High-pressure water flushing: Use high-pressure water to flush the air-entrained concrete fragments after mechanical vibration.

[0029] The method for removing mortar attached to aggregates of air-entrained regenerated concrete provided by the present invention improves the effect of freeze-thaw spalling through a vacuum water retention step. During the dry pumping process, negative pressure is used to open the pores and gaps in the mortar of the air-entrained concrete fragments. During the wet pumping process, water is injected while maintaining a vacuum degree. The opened pores and gaps absorb the injected water, so that the air-entrained concrete fragments are saturated. The lowest temperature range and the high temperature range in the freeze-thaw modification are limited, so that the pores and gaps in the air-entrained concrete fragments can be better dealt with, thereby improving the effect of subsequent mortar stripping. Finally, efficient removal of mortar attached to the outside of aggregates in the air-entrained regenerated concrete is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of a method for removing mortar attached to aggregates of air-entrained regenerated concrete according to a first embodiment of the present invention;

[0031] Figure 2 Schematic diagram of a method for removing mortar attached to aggregates of air-entrained regenerated concrete according to a second embodiment of the present invention;

[0032] Figure 3 It is a comparison of the mortar stripping effects of Examples 5, 3 and 1;

[0033] Figure 4 This is a comparison of the mortar stripping effects of Examples 6, 4, and 2;

[0034] Figure 5 The figure is a comparison of the mortar stripping effects of Examples 3, 2 and 1.

[0035] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0036] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0037] Those skilled in the art will understand that, unless otherwise stated, the singular forms "a", "an", "said", "above", and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present invention refers to the presence of the stated features, integers, steps, operations, elements, units, modules, and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, units, modules, components, and / or groups thereof. The term "and / or" used herein includes all or any units and all combinations of one or more associated listed items.

[0038] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0039] Reference Figure 1 The present invention provides a method for removing mortar attached to aggregates of air-entrained regenerated concrete, comprising:

[0040] S1, the first impurity removal, screening the concrete blocks to obtain air-entrained concrete blocks;

[0041] S2, crushing, crushing the air-entrained concrete blocks into air-entrained concrete fragments;

[0042] S3, vacuum water retention, subjecting the air-entrained concrete fragments to a dry pumping process and a wet pumping process, wherein, in the dry pumping process, the air-entrained concrete fragments are placed in a vacuum pumping device and subjected to a first preset vacuum pumping process. After the dry pumping process is completed, water is injected into the vacuum pumping device while maintaining the vacuum degree, and then a second preset vacuum pumping process is performed to complete the wet pumping process;

[0043] S4, freeze-thaw spalling, the air-entrained concrete fragments after vacuum water retention treatment are subjected to freeze-thaw modification by water freezing and thawing, wherein the lowest temperature range during freeze-thaw spalling is -30 to -40°C, and the highest temperature is maintained at 15 to 25°C;

[0044] S5, vibrating screening, vibrating screening the air-entrained concrete fragments that have undergone freeze-thaw spalling;

[0045] S6, impact separation;

[0046] S7, second impurity removal;

[0047] The recycled aggregate is obtained by repeating steps S3 to S7 for a number of times according to the effect of removing the mortar attached to the aggregate.

[0048] In the present invention, in the first impurity removal step S1, the concrete blocks (abandoned construction waste) are subjected to primary impurity removal to remove easily separable non-concrete construction waste and large masonry blocks, thereby obtaining air-entrained concrete blocks.

[0049] In the crushing step S2, suitable crushing equipment (such as a jaw crusher and a cone crusher) is selected to crush the air-entrained concrete blocks to obtain air-entrained concrete fragments with small particle sizes (such as less than 37.5 mm).

[0050] In the step of vacuum water retention in S3, vacuum water retention is performed, specifically including a dry extraction process and a wet extraction process. The dry extraction process can wait until the temperature of the air-entrained concrete fragments drops to room temperature, or the dry extraction process can be started before the temperature drops to room temperature.

[0051] During the dry pumping process of vacuum water retention, the air-entrained concrete fragments are placed in the vacuum pumping device and a first preset vacuum pumping process is performed. At this time, the negative pressure generated by the first preset vacuum pumping process opens the pores and gaps in the mortar of the air-entrained concrete fragments. For example, the first preset vacuum pumping process is to maintain the negative pressure in the vacuum pumping device at -0.098 MPa and maintain it for 3 hours.

[0052] During the wet pumping process for vacuum water retention, water is injected into the vacuuming device while maintaining a vacuum level. A second preset vacuuming process is then performed to complete the wet pumping process. The opened pores and voids absorb the injected water, saturating the air-entrained concrete fragments. The first preset vacuuming process can maintain a certain vacuum level for a certain period of time, or meet a certain vacuum curve. The second preset vacuuming process can maintain a certain vacuum level for a certain period of time, or meet a certain vacuum curve, or simply seal the vacuuming device (e.g., maintaining it for approximately 20 hours) without further vacuuming.

[0053] In step S4 of freeze-thaw spalling, the air-entrained concrete fragments, which have undergone vacuum water retention treatment, are subjected to a freeze-thaw and water-thaw process during freeze-thaw spalling. The minimum temperature during freeze-thaw spalling is between -30°C and -40°C, and the maximum temperature is maintained between 15°C and 25°C. During freeze-thaw spalling, the air-entrained concrete fragments are immersed in water, freezing and thawing the water and the concrete fragments together. During freeze-thaw spalling, the mortar attached to the aggregate is subjected to cumulative internal damage under the combined pore pressure created by water pressure, crystallization pressure, and low-temperature suction, resulting in increased microcracks, causing the attached mortar to spall from the aggregate surface. The air-entrained concrete fragments are immersed in water, freezing and thawing the water and the air-entrained concrete fragments together. The maximum temperature is preferably greater than 15°C, and the minimum temperature is preferably -40°C. During the freeze-thaw spalling process, the attached mortar is subjected to cumulative internal damage under the combined pore pressure created by water pressure, crystallization pressure, and low-temperature suction, causing increased microcracks, causing the attached mortar to spall from the aggregate surface. Specifically, to enhance the aforementioned forces, the minimum and high temperature ranges during freeze-thaw modification are limited, effectively addressing pores and voids in air-entrained concrete fragments. Freeze-thaw spalling includes at least one cycle of water freezing and thawing. This means multiple cycles of freeze-thaw spalling can be performed, often two to three cycles. The temperature and time conditions within each freeze-thaw modification cycle are not necessarily the same.

[0054] In the step of vibrating screening in S5, the mortar that has been peeled or easily peeled is separated from the air-entrained concrete fragments by vibrating screening. The type and mesh size of the vibrating screen can be various and are selected according to actual conditions.

[0055] In the S6 impact separation step, since only screening was performed in the S5 step, a large amount of mortar with a significantly weakened bonding degree exists on the surface of the aerated concrete fragments. At this time, impact separation is used to peel off the mortar. The specific impact separation method can be selected in a variety of ways, preferably one that does not damage the aggregate while achieving a peeling effect. For example, mechanical vibration is first completed in a drum stone washing machine, with a rolling collision at a speed of 50r / min for 30s. The attached mortar is peeled off by the mutual collision between the aerated concrete fragments themselves, and no other impurities are introduced in this process. Then, high-pressure water flow is used for flushing. On the one hand, the attached mortar is peeled off by the impact of the water flow, and at the same time, the peeled mortar is guided by the water flow.

[0056] In the second impurity removal step of S7, the second impurity removal can be performed by flotation, sedimentation, magnetism, manual methods, etc., so as to obtain recycled aggregate.

[0057] It should be noted that the number of repetitions of steps S3 to S7 is selected based on the effectiveness of removing the mortar attached to the aggregate. If, after three rounds of steps S3 to S7, the mortar stripping effect and the required standards are met, there is no need to continue. In the method for removing mortar attached to the aggregate of the present invention, multiple heating and cooling operations are performed. The heat from the above steps can be recycled to a certain extent using a heat pump to reduce overall energy waste. It should be noted that in steps S4 to S7, the mortar outside the aggregate of the aerated concrete fragments is continuously peeled off and continuously approaches the aggregate. However, until the mortar is confirmed to be completely solid, it is still designated as an aerated concrete fragment.

[0058] In summary, the freeze-thaw spalling effect is improved through the vacuum water retention step. During the dry pumping process, negative pressure is used to open the pores and voids in the mortar of the air-entrained concrete fragments. During the wet pumping process, water is injected while maintaining the vacuum degree. The opened pores and voids absorb the injected water, so that the air-entrained concrete fragments are saturated. The lowest temperature range and high temperature range in the freeze-thaw modification are limited, so that the pores and voids in the air-entrained concrete fragments can be better dealt with, thereby improving the effect of subsequent mortar stripping. Finally, the efficient removal of mortar attached to the outside of the aggregate in the air-entrained recycled concrete is achieved; no damage is caused to the aggregate, and the properties of the obtained recycled aggregate are closer to those of natural aggregate.

[0059] Reference Figure 2 In one embodiment, when the water-cement ratio of the crushed air-entrained concrete block is less than an index A, the value range of the index A is 0.45 to 0.55, and step S2.5 is further included between step S2 and step S3, and the step S2.5 includes:

[0060] High temperature degradation: The air-entrained concrete fragments are subjected to high temperature degradation treatment, wherein the temperature range of high temperature degradation is 300°C to 400°C, and the time range of high temperature degradation is 6h to 18h.

[0061] In the aforementioned embodiment, a vacuum water retention step was introduced, which improved the efficiency of mortar stripping during freeze-thaw spalling and eliminated the commonly used high-temperature degradation step. However, the above-mentioned methods for removing aggregate-attached mortar are less effective for cement mortars with lower water-cement ratios, that is, higher densities. In this embodiment, the AEC fragments were subjected to a high-temperature degradation treatment (e.g., in an oven) at a temperature range of 300°C to 400°C for a duration of 6 to 18 hours. The high-temperature degradation temperature was specifically increased to maximize the opening of gaps and pores created during the degradation process; the duration of the high-temperature degradation was also shortened to minimize the adverse effects on the performance of the AEC fragments. Degradation begins to intensify at 300°C, while the ultimate bearing temperature of typical cement materials is 500°C. In this embodiment, the temperature range of 300°C to 400°C was selected. If the water-cement ratio of the air-entrained recycled concrete matrix is ​​very low, such as less than 0.5, it is necessary to perform high-temperature degradation before the vacuum water retention step to dehydrate the cement matrix in the mortar of the air-entrained concrete fragments and make it brittle, thereby reducing the bonding ability and improving the effectiveness of subsequent vacuum water retention and freeze-thaw spalling.

[0062] In one embodiment, the value of the indicator A is 0.5.

[0063] In this embodiment, the value of the indicator A is precisely limited, and the water-cement ratio is set to 0.5 as the boundary, so as to obtain a comprehensive evaluation of efficiency and energy consumption.

[0064] In one embodiment, the vacuum water retention step of S3 is directly connected to the high temperature degradation step of S3, wherein the air entrained concrete fragments are placed in a high temperature state after the high temperature degradation is completed during the dry pumping process.

[0065] During the implementation process, it is even possible to combine the device used in the high-temperature degradation step of S3 with the vacuum device used in the vacuum water retention step of S3, so as to achieve, on the one hand, a reduction in energy consumption for high-temperature degradation (heating under vacuum conditions reduces the adverse heat dissipation), and on the other hand, to achieve direct dry and wet pumping processes under high-temperature conditions. At higher temperatures after high-temperature degradation, the pores and gaps in the mortar of the aerated concrete fragments are more likely to be opened during the dry pumping process. It should be noted that when the wet pumping process begins, the temperature of the aerated concrete fragments needs to be controlled (not too high) to avoid negative effects on the aggregate, especially when the wrapped mortar has been peeled off to a certain extent; in fact, during the dry pumping process, the temperature of the aerated concrete fragments continues to decrease, which has provided a basis for the wet pumping process.

[0066] In one embodiment, the temperature range of high temperature degradation in step S3 is 300° C. to 320° C., and the time range of high temperature degradation is 8 hours to 14 hours.

[0067] This embodiment provides more optimal high-temperature degradation temperatures and durations. Within these two ranges, both the high-temperature degradation effect and energy consumption are optimized. Specifically, a shorter treatment time at a higher temperature optimizes the effect. In particular, the presence of closed pores and voids in air-entrained recycled concrete makes high-temperature degradation of strength crucial.

[0068] In one embodiment, in step S3, the first preset vacuuming process in the dry pumping process is to maintain a first preset negative pressure value for a first preset time period.

[0069] In this embodiment, the purpose of the first preset vacuuming process is to provide a certain negative pressure condition during the dry pumping process. The specific negative pressure conditions can be selected in a variety of ways. For example, the negative pressure in the vacuuming device is maintained at -0.098 MPa for 3 hours. In other embodiments, the first preset vacuuming process is not limited to maintaining a constant negative pressure intensity, but rather meets a certain negative pressure value curve. The above negative pressure curve can be a gradually increasing negative pressure intensity.

[0070] In one embodiment, in step S3, the second preset vacuuming process in the wet pumping process is to close the vacuuming device for a second preset time.

[0071] In this embodiment, since the wet pumping process includes a water injection process, the vacuum device can be kept closed when the water injection submerges all the air-entrained concrete fragments. For example, during the dry pumping process, the negative pressure strength is maintained at -0.098 MPa for 3 hours; during the wet pumping process, the vacuum device can be kept closed for 21 hours.

[0072] In one embodiment, in step S3, the second preset vacuuming process in the wet pumping process is to maintain the second preset negative pressure value for a third preset time period.

[0073] In this embodiment, the second preset vacuuming process is similar to the first preset vacuuming process, and the second preset negative pressure value is maintained for a third preset time period. This is advantageous in situations where the vacuuming device has a poor sealing effect or the water injection does not submerge all the air-entrained concrete fragments. The second preset negative pressure value can be the same as the first preset negative pressure value.

[0074] In one embodiment, a stirring operation is performed during the dry pumping process and / or the wet pumping process.

[0075] In this embodiment, the introduction of a stirring operation during the dry pumping process can, on the one hand, enhance the effect of destroying pores and voids, and on the other hand, the stirring operation itself can also play a certain role in stripping the mortar, especially after high-temperature degradation. In the wet pumping process, the stirring operation can avoid mutual blocking between the aerated concrete fragments, open the re-closed pores and pores, and thus enhance the water absorption effect of the aerated concrete fragments, thereby improving the saturation state of the final aerated concrete fragments. The intensity of the stirring operation can be adjusted experimentally according to specific circumstances. In particular, the above-mentioned S3 vacuum water retention, S4 freeze-thaw peeling, S5 vibration screening, S6 impact separation to S7 second impurity removal operations can be repeated multiple times, and in the subsequent number of cycles, the stirring operation during the dry pumping process and / or the wet pumping process has a significant positive effect on the stripping of the mortar or the destruction of pores and voids.

[0076] In one embodiment, the step S4 includes:

[0077] The air-entrained concrete fragments after vacuum water retention treatment are subjected to freeze-thaw modification of at least one round of freezing and thawing, wherein the lowest freeze-thaw temperature range is -35 to -40°C and the highest temperature range is 20 to 25°C.

[0078] Compared to the previous embodiment, in this embodiment, the minimum temperature range and high temperature range for freeze-thaw modification are further limited. The air-entrained concrete blocks are immersed in water, freezing and thawing the water and concrete blocks together. During the freeze-thaw modification, the mortar attached to the aggregate is subjected to the total pore pressure formed by water pressure, crystallization pressure, and low-temperature suction, resulting in accumulated internal damage, increased microcracks, and thus peeling of the attached mortar from the aggregate surface. In particular, to increase the above forces, the minimum temperature range and high temperature range for freeze-thaw modification are limited, thereby better addressing the pores and voids in the air-entrained concrete fragments. In this embodiment, freeze-thaw modification is performed in three rounds, achieving a better peeling effect. It is worth noting that in this embodiment, whether the minimum and maximum temperatures in each round of freeze-thaw modification are consistent is still not limited. In other words, the specific process of each round of freeze-thaw modification can be different.

[0079] In one embodiment, the step S4 includes:

[0080] The air-entrained concrete fragments after vacuum water retention treatment are subjected to freeze-thaw modification of at least two rounds of water freezing and thawing, wherein the lowest freeze-thaw temperature in the later freeze-thaw modification is higher than the lowest freeze-thaw temperature in the earlier freeze-thaw modification, and the highest freeze-thaw temperature in the later freeze-thaw modification is lower than the lowest freeze-thaw temperature in the earlier freeze-thaw modification.

[0081] In this embodiment, the intensity of freeze-thaw modification is flexibly adjusted, with the intensity of the freeze-thaw modification at the front being greater and the intensity of the freeze-thaw modification at the back being weaker. This can improve processing efficiency and save processing energy while achieving the stripping goal.

[0082] In one embodiment, the step S6 includes:

[0083] S6.1. Mechanical vibration: Place the air-entrained concrete fragments that have been vibrated and screened into a drum stone washer for mechanical vibration.

[0084] S6.2. High-pressure water flushing: Use high-pressure water to flush the air-entrained concrete fragments after mechanical vibration.

[0085] In this embodiment, mechanical vibration is performed in a drum stone washer, with a rolling collision at 50 rpm for 30 seconds. This removes the attached mortar through the collision between the air-entrained concrete fragments, without introducing any other impurities. High-pressure water flushing, on the other hand, removes the attached mortar through the impact of the water flow, while also allowing the already removed mortar to be cleaned by the water flow.

[0086] Example 1:

[0087] A method for removing mortar attached to aggregates of air-entrained recycled concrete:

[0088] 1. The water-cement ratio of the parent concrete of air-entrained recycled concrete is 0.35A;

[0089] 2. Carry out primary impurity removal on abandoned construction waste, remove non-concrete construction waste that is easy to separate, and obtain air-entrained concrete blocks;

[0090] 3. Then, the air-entrained concrete blocks are crushed using a jaw crusher and a cone crusher to obtain air-entrained concrete fragments with a particle size of less than 37.5 mm;

[0091] 4. Place the air-entrained concrete fragments in a 300°C oven for 12 hours of high-temperature degradation;

[0092] 5. Place the prepared air-entrained concrete fragments in a vacuum water retention device for dry and wet extraction, with the water retention time being 24 hours;

[0093] Dry pumping process: Weigh sufficient dry air-entrained concrete fragments and put them into a woven mesh bag. Cover the bag with the lid, close the exhaust valve on the top and tighten the bolts around it symmetrically. After turning on the switch, use the vacuum device to pump the inside of the container to -0.098MPa and maintain it for 3 hours.

[0094] Wet pumping process: When the dry pumping process is completed, the water inlet valve will automatically open, and the water in the sorting box will be pressed into the container under the action of the pressure difference. When the predetermined water level is reached, the water inlet valve will automatically close and maintain the negative pressure state for 21 hours.

[0095] 6. The air-entrained concrete fragments after vacuum water retention are subjected to freeze-thaw spalling. The freeze-thaw spalling includes three freeze-thaw modifications. The freeze-thaw modification is in the form of water freezing and water thawing. The lowest temperature of freeze-thaw modification is -40°C, and the highest temperature of freeze-thaw modification is 15°C. Freeze-thaw modification is to immerse the air-entrained concrete fragments in water, and freeze and melt the water and the air-entrained concrete fragments together.

[0096] 7. After freeze-thaw peeling, the air-entraining concrete fragments are vibrated and screened to remove the peeled-off attached mortar.

[0097] 8. Use a drum stone washer to roll and collide the air-entrained concrete fragments at a speed of 50 revolutions per minute for 30 seconds;

[0098] 9. Use a high-pressure water gun to perform high-pressure washing on the air-entrained concrete fragments processed in the previous step;

[0099] 10. Then repeat steps 4 to 9 until recycled aggregate is obtained.

[0100] Comparative Example 1:

[0101] A method for removing mortar attached to aggregates of air-entrained recycled concrete. The difference between Comparative Example 1 and Example 1 is that, compared with the vacuum water retention step in Example 1, only natural water retention is performed in Comparative Example 1; the high-temperature degradation step is the same.

[0102] Comparative Example 2:

[0103] A method for removing mortar attached to aggregates of air-entrained regenerated concrete. The difference between Comparative Example 2 and Example 1 is that, compared with Example 1 having a high-temperature degradation step, Comparative Example 2 does not perform the high-temperature degradation step; the vacuum water retention step is the same.

[0104] Example 2:

[0105] A method for removing mortar attached to aggregates of air-entrained recycled concrete. The difference between Example 2 and Example 1 is that the water-cement ratio of the parent concrete is 0.5A; the high-temperature deterioration step and the vacuum water retention step are the same.

[0106] Comparative Example 3:

[0107] A method for removing mortar attached to aggregates of air-entrained recycled concrete. The difference between Comparative Example 3 and Example 2 is that, compared with the vacuum water retention step in Example 2, only natural water retention is performed in Comparative Example 3; the high-temperature degradation step is the same.

[0108] Comparative Example 4:

[0109] A method for removing mortar attached to aggregates of air-entrained regenerated concrete. The difference between Comparative Example 4 and Example 2 is that, compared with Example 2 having a high-temperature degradation step, Comparative Example 4 does not perform the high-temperature degradation step; the vacuum water retention step is the same.

[0110] Example 3:

[0111] A method for removing mortar attached to aggregates of air-entrained recycled concrete. The difference between Example 3 and Example 1 is that the water-cement ratio of the parent concrete is 0.65A; the high-temperature deterioration step and the vacuum water retention step are the same.

[0112] Comparative Example 5:

[0113] A method for removing mortar attached to aggregates of air-entrained recycled concrete. The difference between Comparative Example 5 and Example 3 is that, compared with the vacuum water retention step in Example 3, Comparative Example 5 only performs the natural water retention until the high-temperature degradation step is consistent.

[0114] Comparative Example 6:

[0115] A method for removing mortar attached to aggregates of air-entrained regenerated concrete. The difference between Comparative Example 6 and Example 2 is that, compared with Example 3 having a high-temperature degradation step, Comparative Example 6 does not perform the high-temperature degradation step; the vacuum water retention step is the same.

[0116]

[0117] The above table shows the number of modifications required to obtain recycled aggregates in Examples 1 to 3 and Comparative Examples 1 to 6, where modification refers to a round of steps of vacuum water retention (or natural water retention), freeze-thaw peeling, vibration screening, impact separation, and a second impurity removal. The modification of the comparative examples in which high-temperature degradation is absent ignores the high-temperature degradation step.

[0118] With reference to the effects of Example 2 and Comparative Example 3, the introduction of the vacuum water retention step reduced the number of modifications by 3 times.

[0119] Referring to the effects of Example 2 and Comparative Example 4, the introduction of the vacuum water retention step ensures that the number of modifications is still 2 even if the high-temperature degradation step is missing.

[0120] With reference to the effects of Example 3 and Comparative Example 5, the introduction of the vacuum water retention step reduced the number of modifications by 2 times.

[0121] Referring to the effects of Example 3 and Comparative Example 6, the introduction of the vacuum water retention step ensures that the number of modifications is still 2 even if the high-temperature degradation step is missing.

[0122] In reference example 1, since the water-cement ratio of the parent concrete of the air-entrained regenerated concrete is as low as 0.35A, it is difficult to achieve stripping without adding high-temperature degradation and vacuum water retention steps. The results of comparative examples 1 and 2 are not shown in the table, but are shown in the legend.

[0123] Reference Figures 3 to 5 The comparison method mainly reflects the influence of the water-cement ratio of the parent concrete on the stripping. The water absorption rate (calculated by weighing) and the mortar stripping rate (calculated by weighing) are used to judge the stripping effect of the mortars of Examples 1 to 3 and Comparative Examples 1 to 6, wherein both parameters can be used as judgment criteria.

[0124] Reference Figure 3 Comparative Examples 5, 3, and 1 all underwent high-temperature degradation, but only natural water retention was performed, with a step-wise decrease in the water-cement ratio. Comparative Example 1 failed to achieve mortar stripping, while Comparative Examples 5 and 3 completed stripping after 4 and 5 modifications, respectively.

[0125] Reference Figure 4 In the comparative examples 6, 4 and 2, vacuum water retention was performed, but high temperature degradation was not performed, and the water-cement ratio was stepped down. Comparative example 2 could not achieve mortar stripping, while comparative examples 6 and 4 completed stripping after 2 and 2 modifications, respectively.

[0126] Reference Figure 4 In the embodiment 3, 2 and 1, high temperature degradation and vacuum water retention are performed, and the water-cement ratio is stepped down. The peeling of the embodiment 3, 2 and 1 is completed after 2, 2 and 3 times respectively.

[0127] according to Figures 3 to 5 It can be seen that the water-cement ratio of the parent concrete of the air-entrained recycled concrete is low, which makes the stripping process more difficult, and the positive effect of the vacuum water retention step on mortar stripping is even better than high temperature deterioration.

[0128] In summary, the method for removing mortar attached to aggregates of air-entrained regenerated concrete provided by the present invention improves the effect of freeze-thaw spalling through the vacuum water retention step. During the dry pumping process, negative pressure is used to open the pores and gaps in the mortar of the air-entrained concrete fragments. During the wet pumping process, water is injected while maintaining a vacuum degree. The opened pores and gaps absorb the injected water, so that the air-entrained concrete fragments are saturated. The lowest temperature range and the high temperature range in the freeze-thaw modification are limited, so that the pores and gaps in the air-entrained concrete fragments can be better dealt with, thereby improving the effect of subsequent mortar stripping. Finally, efficient removal of mortar attached to the outside of aggregates in the air-entrained regenerated concrete is achieved.

[0129] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention's description and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for removing mortar attached to aggregates of air-entrained regenerated concrete, characterized in that: include: S1, the first impurity removal, screening the concrete blocks to obtain air-entrained concrete blocks; S2, crushing, crushing the air-entrained concrete blocks into air-entrained concrete fragments; S2.

5. High-temperature degradation. When the water-cement ratio of the crushed air-entrained concrete blocks is less than index A, the value range of index A is 0.45 to 0.

55. The air-entrained concrete blocks are subjected to high-temperature degradation treatment. The temperature range of high-temperature degradation is 300°C to 400°C, and the time range of high-temperature degradation is 6 hours to 18 hours. When the water-cement ratio of the crushed air-entrained concrete blocks is greater than or equal to index A, step S3 is directly performed after step S2. S3, vacuum water retention, subjecting the air-entrained concrete fragments to a dry pumping process and a wet pumping process, wherein, in the dry pumping process, the air-entrained concrete fragments are placed in a vacuum pumping device and subjected to a first preset vacuum pumping process. After the dry pumping process is completed, water is injected into the vacuum pumping device while maintaining the vacuum degree, and then a second preset vacuum pumping process is performed to complete the wet pumping process; The first preset vacuuming process is to maintain a first preset negative pressure value for a first preset time, and the second preset vacuuming process is to close the vacuuming device for a second preset time, or maintain the second preset negative pressure value for a third preset time. S4, freeze-thaw spalling, performing at least one round of freeze-thaw modification of the air-entrained concrete fragments after vacuum water retention treatment, wherein the minimum freeze-thaw temperature range is -35 to -40°C and the maximum temperature range is 20 to 25°C, and when performing at least two rounds of freeze-thaw modification of the air-entrained concrete fragments, the minimum freeze-thaw temperature of the subsequent freeze-thaw modification is higher than the minimum freeze-thaw temperature of the previous freeze-thaw modification, and the maximum freeze-thaw temperature of the subsequent freeze-thaw modification is lower than the minimum freeze-thaw temperature of the previous freeze-thaw modification; S5, vibrating screening, vibrating screening the air-entrained concrete fragments that have undergone freeze-thaw spalling; S6, impact separation, including: S6.

1. Mechanical vibration: Place the air-entrained concrete fragments that have been vibrated and screened into a drum stone washer for mechanical vibration. S6.2, high-pressure water flushing, using high-pressure water to high-pressure flush the air-entrained concrete fragments after mechanical vibration; S7, second impurity removal; The recycled aggregate is obtained by repeating steps S3 to S7 for a number of times according to the effect of removing the mortar attached to the aggregate.

2. The method for removing mortar attached to aggregates of air-entrained regenerated concrete according to claim 1, characterized in that: The value of the indicator A is 0.

5.

3. The method for removing mortar attached to aggregates of air-entrained regenerated concrete according to claim 1, characterized in that: In the step S3, the temperature range of high temperature degradation is 300° C. to 320° C., and the time range of high temperature degradation is 8 hours to 14 hours.

4. The method for removing mortar attached to aggregates of air-entrained regenerated concrete according to claim 1, characterized in that: In step S3, a stirring operation is performed during the dry pumping process and / or the wet pumping process.

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