Recycled aggregate, method for its production and use thereof

Abstract

The application discloses a kind of recycled aggregate and its preparation method and application, it is related to building material field, including the following steps: taking waste concrete and removing impurities and crushing to obtain pretreated aggregate;Take pretreated aggregate and absorb internal treatment liquid to saturation to obtain pretreated saturated aggregate;The internal treatment liquid is water or freezing-point depressant aqueous solution;Pretreated saturated aggregate is placed in external treatment liquid and is repeatedly freeze-thaw treated, is filtered and dried to obtain freeze-thaw treated aggregate;The external treatment liquid is freezing-point depressant aqueous solution;The freezing temperature of freeze-thaw treatment is lower than the freezing point temperature of internal treatment liquid, higher than the eutectic point temperature of external treatment liquid, and the melting temperature is higher than the freezing point temperature of internal treatment liquid;Freeze-thaw treated aggregate is vibrated and classified, and the peeled attached mortar is removed to obtain recycled aggregate.The application reduces the mass water absorption and attached mortar content of recycled aggregate, improves the removal degree of attached mortar on recycled aggregate, and improves the quality of recycled aggregate.

Description

Technical Field

[0001] This application relates to the field of building materials, and in particular to a recycled aggregate, its preparation method, and its application. Background Technology

[0002] Waste concrete from construction waste can be crushed and screened to produce recycled aggregate. Using recycled aggregate to partially replace natural aggregate in concrete preparation can achieve the reuse of waste resources, reduce the consumption of natural resources, and improve sustainability. However, because recycled aggregate is coated with attached mortar, it has high porosity, high water absorption, and poor mechanical properties. When recycled aggregate is used to completely replace natural aggregate in the preparation of recycled concrete, the mechanical properties decrease significantly, especially in high-strength and high-performance concrete (according to the national standard "Technical Conditions for High-Performance Concrete" (GB / T 41054-2021), the cubic compressive strength of C100 concrete is not less than 100 MPa), which severely limits its application in high-strength and high-performance concrete materials.

[0003] Currently, to improve the quality of recycled aggregates, existing modification methods are mainly divided into two categories: mortar reinforcement and mortar removal. Mortar reinforcement includes carbonation and microbial mineralization, while mortar removal includes mechanical grinding, acid washing, and thermo-grinding. However, mortar reinforcement is costly and its quality is still difficult to approach that of natural aggregates due to the low strength of the waste concrete from demolished buildings. Even with reinforcement modification, it remains a weak point compared to high-strength, high-performance concrete. Mortar removal, on the other hand, has limited effectiveness in removing mortar and can easily cause secondary damage to the aggregates, leading to a decrease in the strength of high-strength, high-performance concrete. Summary of the Invention

[0004] In view of the shortcomings of the above-mentioned related technologies, this application provides a recycled aggregate, its preparation method and application.

[0005] Firstly, the method for preparing recycled aggregate provided in this application adopts the following technical solution:

[0006] A method for preparing recycled aggregate includes the following steps:

[0007] Step 1: Take waste concrete, remove impurities and crush it to obtain pretreated aggregate;

[0008] Step 2: Take pretreated aggregate and absorb the internal treatment liquid until saturated to obtain pretreated saturated aggregate;

[0009] The internal treatment solution is water or an aqueous solution of a freezing point depressant;

[0010] Step 3: Place the pretreated saturated aggregate in an external treatment liquid for repeated freeze-thaw treatment, filter and dry to obtain freeze-thaw treated aggregate;

[0011] The external treatment solution is an aqueous solution of a freezing point depressant;

[0012] The freezing temperature of the freeze-thaw treatment is lower than the freezing point temperature of the internal treatment liquid and higher than the eutectic point temperature of the external treatment liquid, while the melting temperature is higher than the freezing point temperature of the internal treatment liquid.

[0013] Step 4: Vibrate screen the freeze-thawed aggregate to remove the peeled-off attached mortar and obtain recycled aggregate.

[0014] Preferably, the pretreated aggregate has a particle size of 3-5 mm.

[0015] Preferably, the repeated freeze-thaw treatment includes drying the pretreated saturated aggregate after freeze-thaw treatment, soaking it again in the inner treatment solution until it is saturated, and then placing it in the outer treatment solution for another freeze-thaw treatment, or placing the pretreated saturated aggregate after freeze-thaw treatment in the outer treatment solution for a second freeze-thaw treatment.

[0016] Preferably, the repeated freeze-thaw treatment involves placing the pretreated saturated aggregate after freeze-thaw treatment in an external treatment liquid for another freeze-thaw treatment.

[0017] While the above approach, which involves re-immersing the pretreated saturated aggregate in the internal treatment solution and then re-freezing and thawing it in the external treatment solution, achieves better mortar stripping results than directly re-freezing and thawing the pretreated saturated aggregate in the external treatment solution, the difficulty of mortar stripping decreases after the initial freeze-thaw treatment. Even if the pretreated saturated aggregate is re-freezing and thawing it directly in the external treatment solution, only 2-4 cycles are required. However, the re-immersion step in the internal treatment solution is cumbersome and time-consuming. Therefore, choosing to re-freeze and thaw the pretreated saturated aggregate directly in the external treatment solution is preferable, as it helps reduce preparation costs and improve preparation efficiency.

[0018] Preferably, the freezing point lowering agent includes a salt with a eutectic point temperature with water below -15°C or an organic solute miscible with water.

[0019] Preferably, the freezing point lowering agent includes one or more of sodium chloride, calcium chloride, magnesium chloride, ethanol, and glycerol.

[0020] Preferably, the freezing point lowering agent is sodium chloride.

[0021] Preferably, when the internal treatment solution is water, the external treatment solution is a sodium chloride solution with a concentration of 1 wt.%-5 wt.%.

[0022] Preferably, when the internal treatment solution is water, the external treatment solution is a sodium chloride solution with a concentration of 1 wt.%-3 wt.%.

[0023] Preferably, when the internal treatment solution is water, the external treatment solution is a sodium chloride solution with a concentration of 1.5 wt.%.

[0024] Preferably, when the internal treatment solution is an aqueous solution of a freezing point depressant, the concentration of the freezing point depressant in the internal treatment solution does not exceed 1.5 wt.%, the concentration of the freezing point depressant in the external treatment solution is 1 wt.%-5 wt.%, and the mass concentration of the freezing point depressant in the external treatment solution is higher than that in the internal treatment solution.

[0025] Preferably, the freezing temperature of the freeze-thaw treatment is 10-20°C lower than the freezing point temperature of the internal treatment solution, and the thawing temperature is 10-20°C higher than the freezing point temperature of the internal treatment solution.

[0026] Preferably, the freezing duration of the freeze-thaw treatment is 3-5 hours, and the thawing duration of the freeze-thaw treatment is 1-3 hours.

[0027] Preferably, the freeze-thaw cycle number of the freeze-thaw treatment is 2-4 times.

[0028] Preferably, the step of taking pretreated aggregate and absorbing the internal treatment liquid until saturated to obtain pretreated saturated aggregate includes soaking the pretreated aggregate in the internal treatment liquid for 1-2 days.

[0029] Secondly, the recycled aggregate provided in this application adopts the following technical solution:

[0030] A recycled aggregate is prepared by the above-described method for preparing a recycled aggregate.

[0031] Preferably, the mortar content adhering to the recycled aggregate is less than 5 wt.%.

[0032] Preferably, the water absorption rate of the recycled aggregate is less than 2 wt.%.

[0033] Thirdly, the application of recycled aggregate in the preparation of fully recycled aggregate concrete provided in this application adopts the following technical solution.

[0034] The application of recycled aggregate in the preparation of fully recycled aggregate concrete, wherein the fully recycled aggregate concrete is composed of the following components in parts by weight: 12-17 parts cement, 3-5 parts limestone powder, 1 part silica fume, 6-7 parts quartz sand, 20-25 parts recycled aggregate, 3-4 parts water, and 0.1-0.3 parts water-reducing agent; wherein the recycled aggregate is the above-mentioned recycled aggregate.

[0035] In summary, this application includes at least one of the following beneficial technical effects:

[0036] 1. In this application, the pretreated aggregate is saturated with the internal treatment liquid and then placed in the external absorption liquid. A low-temperature solid-liquid coexistence system is constructed inside and outside the mortar to which the pretreated aggregate is attached for freeze-thaw treatment. During the freezing process, the internal treatment liquid and the external treatment liquid form an ice-unfrozen solution two-phase system. As the temperature decreases, the water in the internal treatment liquid freezes to form ice crystals. Driven by the interfacial pressure difference between the ice crystals and the unfrozen solution, the water in the unfrozen part of the internal and external treatment liquids is transported to the vicinity of the ice crystals in the mortar pores, causing them to continue to grow. This results in the ice crystals in the mortar pores continuously exerting outward pressure on the pore wall. This ice pressure increases with the increase of water content in the internal treatment liquid and the decrease of temperature. The external treatment liquid maintains an ice-unfrozen liquid two-phase system until the temperature drops to the eutectic point temperature of the external treatment liquid, thus maintaining the ice pressure applied to the mortar.

[0037] 2. The preparation method of this application reduces the water absorption rate and the content of adhering mortar in recycled aggregates, improves the removal of adhering mortar from recycled aggregates, and improves the quality of recycled aggregates.

[0038] 3. When the recycled aggregate prepared by the method of this application is applied to high-performance concrete, the compressive strength and flexural strength of the high-performance concrete sample are restored to 93%-95% of those of high-performance concrete prepared with natural basalt aggregate when it completely replaces natural basalt aggregate. This achieves the level of high-strength and high-performance concrete with a strength grade of C100. Compared with concrete prepared with untreated recycled aggregate, the comprehensive mechanical properties of the concrete are improved. Attached Figure Description

[0039] Figure 1 This is a process flow diagram of Embodiment 1 of the present invention;

[0040] Figure 2 This is a microscopic electron microscope image of the pretreated aggregate of Comparative Example 20 of the present invention;

[0041] Figure 3 This is a microscopic electron microscope image of the recycled aggregate of Embodiment 1 of the present invention;

[0042] Figure 4 This is a comparison chart showing the changes in the mass water absorption rate of recycled aggregates in Examples 1-8, Comparative Examples 1-13, pretreated recycled aggregates in Comparative Example 20, and natural basalt aggregates in Comparative Example 21 with the mass concentration of the freezing point depressant in the external treatment liquid and the number of freeze-thaw cycles.

[0043] Figure 5This is a comparison chart showing the changes in the mass water absorption rate of recycled aggregates in Examples 1-2, Comparative Example 8, and Comparative Examples 14-20 of the present invention with the composition of the internal and external treatment solutions and the number of freeze-thaw cycles.

[0044] Figure 6 This is a comparison chart showing the changes in the mortar content of the recycled aggregates in Examples 1-8, Comparative Examples 1-13, the pretreated recycled aggregates in Comparative Example 20, and the natural basalt aggregates in Comparative Example 21 with the concentration of the setting point depressant in the external treatment liquid and the number of freeze-thaw cycles.

[0045] Figure 7 This is a comparison chart showing the changes in the mortar content of the recycled aggregate in Examples 1-2, Comparative Example 8, and Comparative Examples 14-20 of the present invention with the composition of the internal and external treatment solutions and the number of freeze-thaw cycles. Detailed Implementation

[0046] The present application will be further described in detail below with reference to the embodiments. The following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified, specific conditions in the following embodiments were performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the methods used are conventional methods known in the art, and the consumables and reagents used are commercially available. Unless otherwise stated, the technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be applied to the present invention. The raw materials used in the embodiments and comparative examples are all commercially available.

[0047] Example 1

[0048] Example 1 of this application provides a recycled aggregate, the preparation process flow diagram of which is shown below. Figure 1 As shown, it is prepared by the following steps:

[0049] Waste concrete is cleaned to remove non-concrete impurities, and then crushed into small pieces using a jaw crusher to obtain pretreated aggregate with a particle size of 3-5 mm. The pretreated aggregate is then soaked in an internal treatment solution for 1 day to allow it to absorb the solution until saturated, resulting in pretreated saturated aggregate. The pretreated saturated aggregate is then subjected to freeze-thaw treatment in an external treatment solution. The freezing parameters are set to -20 ℃ for 3-5 h, and the thawing parameters are set to 20 ℃ for 1-2 h, resulting in freeze-thaw treated aggregate. This freeze-thaw cycle is repeated twice. The freeze-thaw treated aggregate is then vibrated and screened to remove any detached adhering mortar, resulting in recycled aggregate.

[0050] In this embodiment, the internal treatment solution is water, and the freezing point depressant in the external treatment solution is sodium chloride with a concentration of 1.5 wt.%.

[0051] Examples 2-8

[0052] This application provides a recycled aggregate in Examples 2-8. The difference between Examples 2-8 and Example 1 is that the concentration of the freezing point temperature reagent or the number of freeze-thaw cycles in the external treatment liquid in the preparation method of Examples 2-8 are as shown in Table 1 below.

[0053] Table 1:

[0054]

[0055] Example 9

[0056] Example 9 of this application provides a recycled aggregate. The difference between Example 9 and Example 1 is that the freezing point depressant in the external treatment solution of Example 9 is ethanol.

[0057] Example 10

[0058] Example 10 of this application provides a recycled aggregate. The difference between Example 10 and Example 1 is that the internal treatment liquid in Example 10 is an aqueous solution of a freezing point depressant, the freezing point depressant is sodium chloride, and the concentration of the freezing point depressant is 0.2 wt.%.

[0059] Comparative Examples 1-13

[0060] Comparative Examples 1-13 provide a recycled aggregate. The difference between Comparative Examples 1-13 and Example 1 is that the concentration of the freezing point temperature reagent or the number of freeze-thaw cycles in the external treatment liquid in the preparation method of Comparative Examples 1-13 are as shown in Table 2 below.

[0061] Table 2:

[0062]

[0063] Comparative Example 14

[0064] Comparative Example 14 provides a recycled aggregate. The difference between Comparative Example 14 and Example 1 is that in the preparation process of Comparative Example 14, the internal treatment liquid uses an aqueous solution of a freezing point depressant with the same concentration as the external treatment liquid.

[0065] Comparative Example 15

[0066] Comparative Example 15 provides a recycled aggregate. The difference between Comparative Example 15 and Comparative Example 14 is that Comparative Example 15 has one freeze-thaw cycle during the preparation process.

[0067] Comparative Example 16

[0068] Comparative Example 16 provides a recycled aggregate. The difference between Comparative Example 16 and Comparative Example 14 is that Comparative Example 16 has 4 freeze-thaw cycles during the preparation process.

[0069] Comparative Example 17

[0070] Comparative Example 17 provides a recycled aggregate. The difference between Comparative Example 17 and Example 1 is that in the preparation process of Comparative Example 17, the external treatment liquid is replaced with a sodium sulfate solution of equal mass concentration.

[0071] Comparative Example 18

[0072] Comparative Example 18 provides a recycled aggregate. The difference between Comparative Example 18 and Comparative Example 17 is that Comparative Example 18 has one freeze-thaw cycle during the preparation process.

[0073] Comparative Example 19

[0074] Comparative Example 19 provides a recycled aggregate. The difference between Comparative Example 19 and Comparative Example 17 is that Comparative Example 17 has 4 freeze-thaw cycles during the preparation process.

[0075] Comparative Example 20

[0076] Comparative Example 20 provides a recycled aggregate, which is the pretreated aggregate used in the preparation method of Example 1.

[0077] Comparative Example 21

[0078] Comparative Example 21 used natural basalt aggregate as a control.

[0079] Application Example 1

[0080] Application Example 1 of this application provides a fully alternative recycled aggregate concrete, which is prepared by the following method:

[0081] Take 15 parts of cement, 4 parts of limestone powder, and 1 part of silica fume and place them in a mixer and mix for 2 minutes. Take 3.6 parts of the mixing solution and add it to the mixer and mix for 2 minutes. Add 6.5 parts of quartz sand and 21 parts of recycled aggregate from Example 1 to the mixer and mix for 3 minutes to obtain a fresh slurry. Pour the fresh slurry into a mold to obtain a sample. After curing the sample in an environmental chamber at a temperature of 20 ℃ and a relative humidity (RH) ≥ 95% for 24 hours, demold it and then perform an additional 27 days of curing in the same environmental chamber to obtain fully replaced recycled aggregate concrete.

[0082] Application Comparative Example 1

[0083] Comparative Example 1 of this application provides a type of concrete. The difference between Comparative Example 1 and Example 1 is that the recycled aggregate of Comparative Example 20 is used to replace the recycled aggregate of Example 2 in Comparative Example 1.

[0084] Application Comparative Example 2

[0085] Comparative Example 2 of this application provides a type of concrete. The difference between Comparative Example 2 and Example 1 is that the natural basalt aggregate of Comparative Example 21 is used to replace the recycled aggregate of Example 2 in Comparative Example 2.

[0086] Testing and Inspection

[0087] (1) The recycled aggregate of Comparative Example 20 was examined using a scanning electron microscope, and the resulting scanning electron microscope image is shown below. Figure 2 As shown, the recycled aggregate of Example 1 was examined using a scanning electron microscope (SEM), and the resulting SEM image is shown below. Figure 3 As shown.

[0088] (2) Refer to GB / T 14685 The 2011 standard "Construction Gravel and Crushed Stone" tested the mass water absorption rate of recycled aggregates from Examples 1-8 and Comparative Examples 1-20, as well as the pretreated recycled aggregate from Comparative Example 20 and the natural basalt aggregate from Comparative Example 21. Some results are shown in Table 3. A comparison graph of the mass water absorption rate of recycled aggregates from Examples 1-8 and Comparative Examples 1-13, as well as the pretreated recycled aggregate from Comparative Example 20 and the natural basalt aggregate from Comparative Example 21, with the changes in the mass concentration of the freezing point lowering reagent in the external treatment solution and the number of freeze-thaw cycles is shown in the figure. Figure 4 As shown in the figure, the comparison graphs of the mass water absorption rate of the recycled aggregates of Examples 1-2, Comparative Example 8, and Comparative Examples 14-20 with the changes in the composition of the internal and external treatment solutions and the number of freeze-thaw cycles are as follows. Figure 5 As shown, Examples 1-2 and Comparative Example 8 are labeled as 0-1.5%-NaCl, Comparative Examples 14-16 are labeled as 1.5%-1.5%-NaCl, and Comparative Examples 17-19 are labeled as 0-1.5%-Na2SO4. The mortar content of the recycled aggregates in Examples 1-8 and Comparative Examples 1-20 was detected by thermal analysis, and some data are shown in Table 1. A comparison graph showing the changes in mortar content of the recycled aggregates in Examples 1-8 and Comparative Examples 1-13, and the pretreated recycled aggregate in Comparative Example 20, with the concentration of the setting point lowering reagent in the external treatment solution and the number of freeze-thaw cycles is shown below. Figure 6 As shown in the figure, the comparison graph of the mortar content of the recycled aggregates in Examples 1-2, Comparative Example 8, and Comparative Examples 14-20 with the changes in the composition of the internal and external treatment solutions and the number of freeze-thaw cycles is as follows. Figure 7 As shown, Examples 1-2 and Comparative Example 8 are labeled as 0-1.5%-NaCl, Comparative Examples 14-16 are labeled as 1.5%-1.5%-NaCl, and Comparative Examples 17-19 are labeled as 0-1.5%-Na2SO4.

[0089] Table 3:

[0090]

[0091] (3) The compressive strength and flexural strength of the concrete using the fully replaced recycled aggregate in Example 1, the concrete using Comparative Example 1, and the concrete using Comparative Example 2 were tested, and the results are shown in Table 4.

[0092] Table 4:

[0093]

[0094] Results Analysis

[0095] The following combination Figure 2-7 The experimental results provided in Tables 1-4 will be used to provide a detailed description of this application.

[0096] Figure 2 and Figure 3 The effects of the preparation method of Example 1 on the microstructure and composition of the pretreated aggregate were demonstrated. The results showed that the adhering mortar around the recycled aggregate of Example 1 was almost completely removed after treatment, and the microstructure of the internal natural aggregate did not suffer damage such as microcracks. This indicates that the preparation method of Example 1 can effectively remove the adhering mortar without damaging the internal natural aggregate. This is because, throughout the treatment process, the water absorption and permeability of the natural aggregate inside the recycled aggregate are much lower than those of the adhering mortar, and the transport efficiency of the unfrozen liquid decreases with increasing transport distance and decreasing permeability; therefore, the recycled aggregate was not damaged.

[0097] Table 3 Figure 4 and Figure 6This study demonstrates the effects of sodium chloride concentration in the external treatment solution and the number of freeze-thaw cycles on the peeling effect of recycled aggregate with attached mortar when the internal treatment solution is water. Mass water absorption rate and attached mortar content were used as the evaluation criteria. The results show that the presence of a setting point depressant in the external treatment solution significantly affects the peeling effect of the attached mortar. When the external treatment solution is water, the mass water absorption rate of the recycled aggregate is consistently higher than that of untreated recycled aggregate, and the attached mortar content is consistently higher than 30%. When the external treatment solution contains sodium chloride (a setting point depressant) and the number of freeze-thaw cycles is not less than two, the mass water absorption rate and attached mortar content of the resulting recycled aggregate are significantly reduced. The effect of sodium chloride concentration on the stripping effect is that it first increases and then decreases with increasing concentration. When the sodium chloride mass concentration in the external treatment solution is 1%-5%, the mass water absorption rate of the recycled aggregate is comparable to that of natural basalt aggregate after 4 freeze-thaw cycles, and the content of adhering mortar is less than 4%. When the sodium chloride mass concentration in the external treatment solution is 1.5% and 3%, the mass water absorption rate of the recycled aggregate is comparable to that of natural basalt aggregate after 2 freeze-thaw cycles. Considering the economy, the sodium chloride concentration is preferably 1.5%. The peeling efficiency was unsatisfactory when the sodium chloride concentration in the external treatment solution was 0.5% and 7%. The analysis suggests that this was due to two factors: the ice content inside the adhering mortar at low temperatures and the availability of unfrozen external solution. When the sodium chloride concentration in the external treatment solution was low, there was insufficient unfrozen external solution, limiting the rate of water migration to ice crystals. When the sodium chloride concentration in the external treatment solution was too high, the large concentration difference between the internal and external treatment solutions led to excessively rapid migration of chloride and sodium ions, causing external sodium chloride to quickly penetrate into the internal pore solution. This imbalance between the rate of freezing point reduction of the internal treatment solution and the rate of water freezing resulted in a decrease in ice crystal content, thus reducing the peeling efficiency.

[0098] Figure 5 and Figure 7 This study demonstrates the effects of the concentration of the setting point depressant in the internal treatment solution and the eutectic point temperature of the setting point depressant and water on the peeling effect of recycled aggregate-attached mortar. The results show that when the concentration of the setting point depressant in the internal treatment solution is high (consistent with the external treatment solution), the peeling effect decreases significantly. This is attributed to the introduction of sodium chloride into the mortar during the saturation treatment process of the internal treatment solution. The ionic effect of sodium chloride lowers the freezing point of the pore solution within the mortar and the ice content at low temperatures, thus leading to a decrease in peeling effect. When the internal treatment solution is water, and the sodium chloride in the external treatment solution is replaced with an equal concentration of sodium sulfate solution, the decrease in peeling effect is even more significant. This is because the eutectic point temperature of sodium sulfate and water is approximately -1.0 ℃, close to the freezing point of water. At low temperatures, the external treatment solution forms a solid-phase system of ice crystals and sodium sulfate crystals, which is insufficient to effectively provide unfrozen solution to the ice crystals within the mortar. Although the chemical erosion in the molten state and the expansion pressure of sodium sulfate crystals at low temperatures result in a peeling effect higher than when both the internal and external treatment solutions are water, the pressure cannot be sustained on the mortar, limiting the peeling effect.

[0099] Referring to Table 2, compared to the high-strength, high-performance concrete of Application Example 2 prepared using natural basalt aggregate, the compressive and flexural strengths of Application Example 1, prepared by replacing natural basalt aggregate with pretreated aggregate that has not undergone further treatment, decreased significantly, reaching only 82.3% and 71.4% of the original strength, respectively. In contrast, the compressive and flexural strengths of Application Example 1, prepared by replacing natural basalt aggregate with recycled aggregate prepared in Example 2, recovered to 93.0% and 95.5%, respectively, with a compressive strength exceeding 100 MPa, reaching the level of high-strength, high-performance concrete with a strength grade of C100.

[0100] In summary, this invention provides a method for preparing high-quality recycled aggregates suitable for high-strength, high-performance concrete. By introducing a freezing point-lowering agent into an external treatment liquid, a low-temperature ice crystal-unfrozen liquid solid-liquid system is formed. Driven by the pressure difference between the external ice crystals and the unfrozen liquid inside the mortar, the external unfrozen liquid is transported to the surface of the crystallized ice crystals, supporting their continuous growth. This generates continuous ice pressure at low temperatures, causing damage to the attached mortar. This process is influenced by both the internal ice content and the content of available external unfrozen liquid. Simultaneously, the transport of the unfrozen liquid is affected by the transport distance and permeability. The internal natural aggregates, with their low water absorption and permeability, are not damaged. This method protects the internal natural aggregates while improving the peeling effect and efficiency of the attached mortar during the preparation of recycled aggregates. When applied to fully replace high-performance recycled aggregate concrete, it improves the compressive and flexural strength of the recycled aggregate concrete, exceeding the strength requirements of high-strength, high-performance concrete with a strength grade of C100.

Claims

1. A method of producing recycled aggregate, characterized by: The method comprises the following steps: Step 1, taking waste concrete to remove impurities and crush to obtain pretreated aggregate; Step 2, taking the pretreated aggregate to absorb internal treatment liquid to saturation to obtain pretreated saturated aggregate; The internal treatment liquid is water or an aqueous solution of a freezing-point depressing agent; Step 3, placing the pretreated saturated aggregate in an external treatment liquid to perform repeated freeze-thaw treatment, filtering and drying to obtain freeze-thaw treated aggregate; The external treatment liquid is an aqueous solution of a freezing-point depressing agent; The freezing temperature of the freeze-thaw treatment is lower than the freezing point temperature of the internal treatment liquid and higher than the eutectic point temperature of the external treatment liquid, and the melting temperature is higher than the freezing point temperature of the internal treatment liquid; Step 4, performing vibration screening on the freeze-thaw treated aggregate to remove peeled and attached mortar to obtain recycled aggregate.

2. A method of producing recycled aggregate according to claim 1, characterised in that: The freezing-point depressing agent comprises a salt having a eutectic point temperature lower than -15℃ or an organic solute miscible with water.

3. A method of producing recycled aggregate according to claim 1, characterised in that: The freezing-point depressing agent comprises one or more of sodium chloride, calcium chloride, magnesium chloride, ethanol and glycerol.

4. The method of producing recycled aggregate according to claim 1, characterized in that: When the internal treatment liquid is water, the concentration of the freezing-point depressing agent in the external treatment liquid is 1 wt.%-5 wt.%.

5. The method of producing recycled aggregate according to claim 1, characterized in that: When the internal treatment liquid is an aqueous solution of a freezing-point depressing agent, the concentration of the freezing-point depressing agent in the internal treatment liquid is not more than 1.5 wt.%, the concentration of the freezing-point depressing agent in the external treatment liquid is 1 wt.%-5 wt.%, and the mass concentration of the freezing-point depressing agent in the external treatment liquid is higher than that in the internal treatment liquid.

6. The method of producing recycled aggregate according to claim 1, characterized in that: The freezing temperature of the freeze-thaw treatment is 10-20℃ lower than the freezing point temperature of the internal treatment liquid, and the melting temperature is 10-20℃ higher than the freezing point temperature of the internal treatment liquid.

7. The method of producing recycled aggregate according to claim 1, characterized in that: The freezing duration of the freeze-thaw treatment is 3-5 h, and the melting duration of the freeze-thaw treatment is 1-3 h.

8. The method of producing recycled aggregate according to claim 1, characterized in that: The freeze-thaw treatment is repeated for 2-4 times.

9. A recycled aggregate, characterized by: The recycled aggregate is prepared by the method of any one of claims 1-8.

10. Use of the recycled aggregate according to claim 9 for the production of a total replacement recycled aggregate concrete, characterized in that: The fully replaced recycled aggregate concrete is composed of the following components by weight: cement 12-17 parts, limestone powder 3-5 parts, silica fume 1 part, quartz sand 6-7 parts, recycled aggregate 20-25 parts, water 3-4 parts, and water reducing agent 0.1-0.3 parts; wherein the recycled aggregate is the recycled aggregate of claim 9.

Images