Process for removing impurities from construction waste and waste cement blocks using xylene

Abstract

The application relates to the technical field of resource utilization of construction waste, and discloses a construction waste and waste cement block xylene impurity removal process. In the process, waste cement blocks and waste concrete blocks in the construction waste are subjected to sorting, crushing and screening to obtain recycled aggregates, the aggregates are subjected to pre-washing with clean water to remove loose impurities, and then are subjected to xylene treatment liquid soaking under specific solid-liquid ratio and temperature conditions, and are subjected to ultrasonic oscillation or mechanical stirring to strengthen mass transfer; after treatment, the aggregates are subjected to solid-liquid separation, distillation and purification, and then are recycled, and the aggregates are subjected to washing and drying to obtain high-quality recycled aggregates. The application has excellent impurity removal effect, does not damage the original structure of the aggregates, can realize recycling of the solvent, does not cause pollution of acidic waste water, has strong process adaptability, and can significantly reduce the water absorption rate and crushing index of the treated recycled aggregates, so that the treated recycled aggregates can meet the preparation requirements of medium and high-grade concrete, and the application realizes high-value and green resource utilization of the construction waste.

Description

Technical Field

[0001] This invention relates to the field of construction waste resource utilization technology, specifically a xylene removal process for construction waste and waste cement blocks. Background Technology

[0002] With the acceleration of urbanization and urban renewal in my country, the annual amount of construction waste has exceeded 3 billion tons, of which waste concrete blocks and waste cement blocks account for more than 60%. Preparing them into recycled aggregates is the core way to achieve the reduction and resource utilization of construction waste.

[0003] However, recycled aggregates have inherent performance defects: their surface is covered with a large amount of hardened cement paste, and there are a large number of microcracks and pores inside. At the same time, they contain impurities such as plastics, asphalt, and organic admixture residues, which result in high water absorption, high crushing index, and poor interfacial bonding performance with new cement stone. They can only be used in low-end scenarios such as roadbed backfilling and low-grade concrete, and cannot be applied to medium and high-grade structural concrete, which seriously limits the high-value utilization of construction waste.

[0004] Currently, the mainstream recycled aggregate processing technologies in the industry have significant shortcomings: mechanical crushing and grinding methods are energy-intensive, do not thoroughly remove attached slurry, and are prone to over-crushing of aggregates, resulting in low yield; acid etching modification methods such as hydrochloric acid and phosphoric acid can remove surface cement slurry, but they easily corrode the native silicate interface of the aggregate, causing a decrease in aggregate strength, while generating a large amount of acidic wastewater, resulting in extremely high environmental treatment costs; high-temperature calcination methods have huge energy consumption and carbon emissions, making industrial-scale promotion difficult; conventional organic modification is mostly surface coating treatment, which cannot penetrate into the pores of the aggregate to achieve deep impurity removal, resulting in limited modification effects.

[0005] Therefore, there is an urgent need to develop a recycled aggregate impurity removal and modification process that is thorough, does not damage the aggregate itself, is environmentally friendly, and is easy to industrialize, in order to solve the long-standing technical pain points in the industry. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a xylene impurity removal process for construction waste and waste cement blocks. Utilizing the strong permeability, organic solubility, and interfacial swelling effect of xylene, it deeply removes organic impurities and weak interfacial layers from recycled aggregates while avoiding damage to the original structure of the aggregates. This results in a significant improvement in the performance of recycled aggregates, and the solvent can be recycled, with no highly polluting wastewater discharge. It is also compatible with existing industrial production lines.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a xylene removal process for construction waste and waste cement blocks, comprising the following steps:

[0008] Step S1 Raw material pretreatment: The waste cement blocks and waste concrete blocks in the construction waste are sorted and separated. After removing non-hard impurities such as steel bars, plastics, and wood, the recycled aggregates are crushed and screened to obtain the preset particle size. Step S2 Pre-cleaning treatment: The recycled aggregate obtained in step S1 is rinsed with clean water to remove surface dust and loose mud powder, and the surface water is drained to obtain pre-cleaned aggregate. Step S3 Xylene impurity removal and modification: Immerse the pre-cleaned aggregate in xylene treatment solution, control the solid-liquid mass ratio to 1:(1.2-3), and keep it at 25-60℃ for 1-6 hours. During the soaking process, use ultrasonic vibration or mechanical stirring to enhance mass transfer and complete the impurity removal and modification treatment. Step S4 Solid-liquid separation and solvent recovery: The material processed in step S3 is subjected to solid-liquid separation to obtain modified wet aggregate and xylene waste liquid; the xylene waste liquid is filtered and treated by vacuum distillation to recover xylene, which is then recycled for the impurity removal and modification process in step S3. Step S5 Post-processing: Rinse the modified wet aggregate with clean water 2-3 times to remove residual solvent on the surface, and then dry it to constant weight to obtain high-quality recycled aggregate after impurity removal and modification.

[0009] Further, in step S1, the crushing includes jaw crushing for coarse crushing and cone crushing for fine crushing, and the recycled aggregate obtained by screening is recycled coarse aggregate with a particle size of 5-10mm, 10-20mm or 20-31.5mm; or recycled fine aggregate with a particle size of 0.15-5mm; or recycled micro powder with a particle size ≤0.15mm.

[0010] Furthermore, in step S3, the xylene treatment solution is pure xylene or a xylene-ethanol mixture, wherein the volume fraction of xylene is ≥90%.

[0011] Furthermore, in step S3, the ultrasonic oscillation power is 300-600W, the frequency is 25-40kHz, the ultrasonic time is 30%-50% of the total immersion time, and an intermittent start-up mode is adopted.

[0012] Furthermore, in step S3, the mechanical stirring speed is 80-150 rpm, and the stirring method is continuous stirring or intermittent stirring.

[0013] Furthermore, in step S4, the vacuum degree of vacuum distillation is -0.08 to -0.1 MPa, the distillation temperature is 80-110℃, and the xylene recovery rate is ≥95%.

[0014] Furthermore, in step S5, the drying temperature is 100-110℃, and the aggregate moisture content is dried to ≤0.5%.

[0015] Furthermore, after step S5, a surface passivation treatment step is also included: immersing the dried recycled aggregate in a 1%-3% (w / w) silane coupling agent ethanol solution for 10-30 minutes, then removing it, draining it, and drying it a second time to obtain interface-reinforced recycled aggregate.

[0016] Beneficial technical effects The xylene of this invention has extremely strong penetrability, enabling it to penetrate into the interfacial transition zone of aggregate-cement paste. It specifically dissolves and swells residual organic admixtures (such as water-reducing agents) and incompletely hydrated organic polymer impurities in this zone. This dissolution and swelling effect targeting organic matter disrupts the physical bonding support network of inorganic cement hydration products at the microscopic level. This causes the waste cement paste originally attached to the aggregate surface to become loose due to loss of anchoring force, and it can easily detach with intermittent ultrasonic vibration. This method not only thoroughly dissolves organic impurities such as plastic residues, asphalt, and organic admixture residues on the surface and within the pores of recycled aggregate, but also penetrates into the interfacial transition zone of aggregate-cement paste, swelling and weakening the interfacial hydration products, making the attached weak cement paste easy to detach. The impurity and paste removal effect is far superior to traditional water washing methods, solving the core defect of weak interfaces in recycled aggregates. The xylene of this invention is a neutral organic solvent that has no corrosive effect on silicate virgin aggregates such as quartz and feldspar. This avoids the damage to the original structure of aggregates caused by traditional acid etching methods, ensures the basic mechanical strength of recycled aggregates, and solves the industry problem of "damaging aggregates while removing slurry" in acid etching methods.

[0017] The xylene used in the process of this invention can be recycled at a rate of over 95% through vacuum distillation, resulting in no acidic wastewater discharge and only a small amount of distillation residue that can be centrally and harmlessly treated. This significantly reduces environmental treatment costs and meets the requirements of green production under the dual-carbon context. The process of this invention is simple, has a short processing cycle, and consumes far less energy than high-temperature calcination and prolonged mechanical grinding. It can be directly adapted to existing construction waste recycled aggregate production lines without large-scale equipment modifications, possessing strong potential for industrial-scale application. The recycled aggregate processed by this invention exhibits a 30%-50% reduction in water absorption, a 20%-35% reduction in crushing index, and a significant decrease in porosity and void ratio. This meets the requirements for preparing C30 and higher grade concrete, achieving high-value resource utilization of construction waste. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with specific embodiments.

[0020] Example 1 Step S1 Raw material pretreatment: Sorting waste cement blocks and waste concrete blocks from construction waste, removing non-hard impurities such as steel bars, plastics, and wood, and then screening them to obtain recycled coarse aggregate with a particle size of 20-31.5mm after jaw coarse crushing and cone fine crushing.

[0021] Step S2 Pre-cleaning treatment: Rinse the recycled aggregate with clean water to remove surface dust and loose mud powder, drain the surface moisture, and obtain pre-cleaned aggregate.

[0022] Step S3 Xylene impurity removal and modification: Pure xylene was used as the treatment solution, with a solid-liquid mass ratio of 1:3, and the solution was soaked at 60℃ for 6 hours; ultrasonic vibration was used to enhance mass transfer, with an ultrasonic power of 600W and a frequency of 40kHz, and the ultrasonic time was 50% of the total soaking time, using an intermittent start-up mode.

[0023] Step S4 Solid-liquid separation and solvent recovery: Solid-liquid separation yields modified wet aggregate and xylene waste liquid. After filtration, the waste liquid is distilled under reduced pressure at a vacuum of -0.1 MPa and a distillation temperature of 110℃ to recover xylene (recovery rate ≥95%), which is then recycled for impurity removal and modification.

[0024] Step S5 Post-processing: The modified wet aggregate is rinsed three times with clean water to remove residual solvent on the surface, and then dried at 110℃ to constant weight. The aggregate moisture content is ≤0.5%, thus obtaining high-quality recycled aggregate.

[0025] Surface passivation treatment: The dried recycled aggregate is immersed in a 3% (w / w) silane coupling agent ethanol solution for 30 minutes, then drained and dried again to obtain interface-reinforced recycled aggregate.

[0026] Example 2 Step S1 Raw material pretreatment: After sorting and removing impurities, the raw material is subjected to jaw crushing and cone crushing, and then screened to obtain recycled coarse aggregate with a particle size of 10-20mm.

[0027] Step S2 Pre-cleaning treatment: Rinse with clean water and drain to obtain pre-cleaned aggregate.

[0028] Step S3 Xylene impurity removal and modification: A xylene-ethanol mixed solution (xylene volume fraction 95%) was used as the treatment solution with a solid-liquid mass ratio of 1:2.1. The solution was kept at 42℃ for 3.5 hours. Mechanical stirring was used to enhance mass transfer at a stirring speed of 115 rpm and a continuous stirring method was adopted.

[0029] Step S4 Solid-liquid separation and solvent recovery: After solid-liquid separation, the waste liquid is filtered and distilled under reduced pressure at a vacuum of -0.09 MPa and a distillation temperature of 95°C to recover xylene (recovery rate ≥95%) and recycle it.

[0030] Step S5 Post-processing: Rinse twice with clean water spray, dry at 105℃ to constant weight, aggregate moisture content ≤0.5%, to obtain high-quality recycled aggregate.

[0031] Surface passivation treatment: Immerse in a 2% (w / w) silane coupling agent ethanol solution, soak for 20 minutes, then remove and drain, and dry a second time to obtain interface-reinforced recycled aggregate.

[0032] Example 3 Step S1 Raw material pretreatment: After sorting and removing impurities, the raw material is subjected to jaw crushing and cone crushing, and then screened to obtain recycled coarse aggregate with a particle size of 5-10mm (or recycled fine aggregate with a particle size of 0.15-5mm).

[0033] Step S2 Pre-cleaning treatment: Rinse with clean water and drain to obtain pre-cleaned aggregate.

[0034] Step S3 Xylene impurity removal and modification: A xylene-ethanol mixed solution (xylene volume fraction 90%) was used as the treatment solution with a solid-liquid mass ratio of 1:1.2. The solution was kept at 25℃ for 1 hour. Ultrasonic oscillation was used to enhance mass transfer with an ultrasonic power of 300W and a frequency of 25kHz. The ultrasonic time was 30% of the total soaking time, and an intermittent start-up mode was adopted.

[0035] Step S4 Solid-liquid separation and solvent recovery: After solid-liquid separation, the waste liquid is filtered and distilled under reduced pressure at a vacuum of -0.08 MPa and a distillation temperature of 80°C to recover xylene (recovery rate ≥95%) and recycle it.

[0036] Step S5 Post-processing: Rinse twice with clean water spray, dry at 100℃ to constant weight, aggregate moisture content ≤0.5%, to obtain high-quality recycled aggregate.

[0037] Surface passivation treatment: Immerse in a 1% (w / w) silane coupling agent ethanol solution, soak for 10 minutes, then remove and drain, and dry a second time to obtain interface-reinforced recycled aggregate.

[0038] Comparative Example 1 Construction waste cement blocks / concrete blocks of the same batch and particle size as in Example 2 were taken, sorted and impurities removed, and then ground by jaw crusher and ball mill, and screened to obtain recycled aggregate of the same specifications.

[0039] After rinsing with clean water and drying at 105℃ to a moisture content of ≤0.5%, the processed recycled aggregate is obtained, without any further modification or passivation treatment.

[0040] Comparative Example 2 Take pre-cleaned aggregate of the same batch and particle size as in Example 2 (same as steps S1-S2 in Example 2).

[0041] Immerse in a 10% hydrochloric acid solution and soak at room temperature for 3.5 hours with mechanical stirring throughout (115 rpm).

[0042] After solid-liquid separation, the aggregate is repeatedly rinsed with clean water until neutral, and dried at 105℃ until the moisture content is ≤0.5%, without subsequent passivation treatment.

[0043] Comparative Example 3 Take pre-cleaned aggregate of the same batch and particle size as in Example 2 (same as steps S1-S2 in Example 2).

[0044] The surface was continuously rinsed with high-pressure clean water (pressure 0.8MPa) for 30 minutes to remove impurities and some of the attached cement paste.

[0045] Dry at 105℃ until the moisture content is ≤0.5%, without any modification or passivation treatment.

[0046] Comparative Example 4 Steps S1-S2 are completely consistent with those in Example 2, and pre-cleaned aggregate of the same specifications is obtained.

[0047] Step S3 Xylene impurity removal and modification: A xylene-ethanol mixed solution (xylene volume fraction 80%, lower than the 90% requirement of this invention) was used, and the other parameters (solid-liquid ratio 1:2.1, temperature 42℃, soaking for 3.5h, mechanical stirring at 115rpm) were the same as in Example 2.

[0048] Steps S4-S6 are completely consistent with those in Example 2, resulting in processed recycled aggregate.

[0049] I. Performance Testing Methods All performance tests of recycled aggregates in the examples and comparative examples were conducted in accordance with the national standard "Recycled Coarse Aggregate for Concrete" (GB / T25177-2010). Additionally, interfacial bond strength testing (an industry-standard method) was performed. The test indicators were water absorption, crushing index, apparent porosity, and interfacial bond strength. The specific test methods are as follows: (a) Water absorption rate test (saturated water absorption rate) 1. Take recycled aggregate from each sample, sieve out needle-shaped and flaky particles, select about 1000g of aggregate with a particle size of 10-20mm, dry it in an oven at 105°C until constant weight, cool it to room temperature and weigh it, and record the mass as m1 (accurate to 0.1g). 2. Place the dried aggregate into a water container, add water until the aggregate is completely submerged, and let it stand for 24 hours, ensuring that the water level is at least 20mm above the aggregate surface during this period; 3. Remove the saturated aggregate, gently wipe off the surface moisture with a damp towel (do not wipe away the moisture in the internal pores), and immediately weigh the saturated aggregate. Record the weight as follows: (Accurate to 0.1g); 4. Formula for calculating water absorption rate:

[0050] Three parallel tests were conducted, and the arithmetic mean was taken as the final result.

[0051] (ii) Crushing index test 1. Take recycled aggregate samples from each sample, sieve them into 10-20mm particle sizes, dry them in an oven at 105℃ to constant weight, cool them to room temperature, and then load them into a crushing index tester in three layers. After each layer is loaded, compact it evenly with a metal rod 25 times. Finally, level the surface and weigh the loaded aggregate, recording the weight as follows: (Accurate to 1g); 2. Place the measuring instrument on the press and apply pressure to 200kN at a uniform loading rate of 500N / s. After stabilizing the pressure for 5 seconds, unload the instrument. 3. Pass all the compressed aggregate through a 2.36mm square-hole sieve, weigh the remaining aggregate, and record the mass as follows: (Accurate to 1g); 4. Crushing index calculation formula:

[0052] Three parallel tests were conducted, and the arithmetic mean was taken as the final result.

[0053] (III) Apparent porosity test The determination was made using a combination of the water displacement method and the volumetric method. 1. Take approximately 500g of the dried aggregate sample to constant weight, weigh it, and record the mass as m. d ; 2. Place the aggregate in a water container and vacuum it to -0.09 MPa. Hold the pressure for 30 minutes, then add water until the aggregate is submerged. Continue to hold the pressure for 15 minutes to fully saturate the aggregate pores with water. 3. Place the saturated aggregate in a mesh basket, immerse it in water, and weigh it. Record the buoyant weight as m. w ; 4. Remove the saturated aggregate, wipe off the surface moisture, and weigh the saturated mass, recording it as m. s ; 5. Formula for calculating apparent porosity:

[0054] Three parallel tests were conducted, and the arithmetic mean was taken.

[0055] (iv) Interfacial bond strength test (split tensile test, industry standard) 1. Prepare concrete test blocks by mixing recycled aggregate with P·O42.5 ordinary Portland cement. The aggregate content is 100% of the coarse aggregate in the concrete, the water-cement ratio is 0.45, and the test blocks are 100mm×100mm×100mm cubes. Standard curing (20±2℃, relative humidity ≥95%) for 28 days. 2. Place the cured test block on a press and use a splitting tensile device to apply pressure at a loading rate of 0.05 MPa / s until the test block splits along the aggregate-cement stone interface. Record the splitting failure load F. 3. Formula for calculating interfacial bond strength: (A is the area of ​​the split surface), 5 parallel tests were conducted, and the arithmetic mean was taken after removing outliers.

[0056] II. Specific Test Data All samples were selected from 10-20mm recycled coarse aggregate as the test object. Examples 1-3 were samples of the xylene impurity removal process in this test, and Comparative Examples 1-4 were samples of the traditional process / parameter deviation process. The core performance test data are shown in the table below. All data are the average results after multiple tests, and the accuracy is retained to two decimal places.

[0057] Table 1: Performance Tests

[0058] As shown in Table 1, the core performance of Examples 1-3 is excellent, with water absorption rate ≤4.0%, crushing index ≤15.0%, apparent porosity ≤10.0%, and interfacial bond strength ≥2.7MPa, which fully meets the performance requirements of recycled coarse aggregate for medium and high grade concrete of C30 and above; among them, Example 1 has the best treatment effect. Comparative Example 1 (mechanical crushing and grinding method) and Comparative Example 3 (conventional water washing method): The water absorption rate, crushing index, and apparent porosity are all significantly higher, and the interfacial bonding strength is extremely low. Due to the lack of deep impurity removal, a large amount of thin cement paste still adheres to the surface of the aggregate, and the internal porosity is not effectively improved. It can only meet the requirements of roadbed backfilling and low-grade concrete. Comparative Example 2 (hydrochloric acid etching method): Although the performance is improved compared to the mechanical method / water washing method, the acid etching corrodes the original silicate structure of the aggregate, resulting in a higher crushing index and insufficient interfacial bonding strength. It cannot meet the standards of medium and high-grade concrete and generates acidic wastewater, which is not environmentally friendly. Comparative Example 4 (xylene volume fraction 80%): Because the xylene content does not meet the requirement of ≥90% of this invention, the organic impurity removal and interfacial swelling effect is greatly reduced. The internal impurities of the aggregate are not completely removed, and the performance is far lower than that of the examples, which reflects the strict requirements of this process on the xylene treatment solution ratio. Compared with the traditional water washing method (Comparative Example 3), the water absorption rate of Example 2 of this process is reduced by 52.7%, the crushing index is reduced by 57.0%, the apparent porosity is reduced by 55.8%, and the interfacial bonding strength is increased by 102.8%, which fully demonstrates the deep modification effect of the xylene impurity removal process.

[0059] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0060] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A xylene removal process for construction waste and waste cement blocks, characterized in that, Includes the following steps: Step S1 Raw material pretreatment: The waste cement blocks and waste concrete blocks in the construction waste are sorted and separated. After removing non-hard impurities such as steel bars, plastics, and wood, the recycled aggregates are crushed and screened to obtain the preset particle size. Step S2 Pre-cleaning treatment: The recycled aggregate obtained in step S1 is rinsed with clean water to remove surface dust and loose mud powder, and the surface water is drained to obtain pre-cleaned aggregate. Step S3 Xylene impurity removal and modification: Immerse the pre-cleaned aggregate in xylene treatment solution, control the solid-liquid mass ratio to 1:(1.2-3), and keep it at 25-60℃ for 1-6 hours. During the soaking process, use ultrasonic vibration or mechanical stirring to enhance mass transfer and complete the impurity removal and modification treatment. Step S4 Solid-liquid separation and solvent recovery: The material processed in step S3 is subjected to solid-liquid separation to obtain modified wet aggregate and xylene waste liquid; the xylene waste liquid is filtered and treated by vacuum distillation to recover xylene, which is then recycled for the impurity removal and modification process in step S3. Step S5 Post-processing: Rinse the modified wet aggregate with clean water 2-3 times to remove residual solvent on the surface, and then dry it to constant weight to obtain high-quality recycled aggregate after impurity removal and modification. In step S1, the crushing includes jaw crushing for coarse crushing and cone crushing for fine crushing. The recycled aggregate obtained by screening is recycled coarse aggregate with a particle size of 5-10mm, 10-20mm or 20-31.5mm; or recycled fine aggregate with a particle size of 0.15-5mm; or recycled micro powder with a particle size ≤0.15mm.

2. The xylene removal process for construction waste and waste cement blocks according to claim 1, characterized in that, In step S3, the xylene treatment solution is pure xylene or a xylene-ethanol mixture, wherein the volume fraction of xylene is ≥90%.

3. The xylene removal process for construction waste and waste cement blocks according to claim 1, characterized in that, In step S3, the ultrasonic oscillation power is 300-600W, the frequency is 25-40kHz, the ultrasonic time is 30%-50% of the total immersion time, and an intermittent start-up mode is adopted.

4. The xylene removal process for construction waste and waste cement blocks according to claim 1, characterized in that, In step S3, the mechanical stirring speed is 80-150 rpm, and the stirring method is continuous stirring or intermittent stirring.

5. The xylene removal process for construction waste and waste cement blocks according to claim 1, characterized in that, In step S4, the vacuum degree of vacuum distillation is -0.08 to -0.1 MPa, the distillation temperature is 80-110℃, and the xylene recovery rate is ≥95%.

6. The xylene removal process for construction waste and waste cement blocks according to claim 1, characterized in that, In step S5, the drying temperature is 100-110℃, and the aggregate moisture content is dried to ≤0.5%.

7. The xylene removal process for construction waste and waste cement blocks according to claim 1, characterized in that, The step S5 is followed by a surface passivation treatment step: the dried recycled aggregate is immersed in a 1%-3% silane coupling agent ethanol solution for 10-30 minutes, then taken out, drained, and dried a second time to obtain interface-reinforced recycled aggregate.

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