A method for synergistically enhancing recycled aggregate based on pressurized carbonization and diammonium phosphate
Patent Information
- Application Number
- CN202610235665.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-02-27
- Publication Date
- 2026-09-25
AI Technical Summary
[0019]本发明采用协同改性机理，利用碳化反应主要发生在旧砂浆内部，生成的碳酸钙有效填充了微米级的大孔隙；随后进行的DAP浸泡，利用磷酸根离子的渗透，在碳化尚未完全填充的微孔隙及骨料外表面生成羟基磷灰石，由内而外形成了“碳酸钙填充核-羟基磷灰石致密壳”的复合强化结构。
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Figure CN122809780A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of building material preparation and solid waste resource utilization technology, specifically to a method for synergistically improving the physical and mechanical properties of recycled aggregates by combining pressure carbonization technology with phosphate solution soaking. Background Technology
[0002] With the acceleration of urbanization, the demolition of numerous old buildings has generated a massive amount of construction waste. Recycled aggregates obtained from crushing and screening waste concrete are a key way to replace natural aggregates and achieve sustainable development in the construction industry. However, recycled aggregates are often coated with a large amount of porous, low-strength old cement mortar, and there are numerous microcracks and interface transition defects between the aggregates and the old mortar. This results in recycled aggregates generally having high water absorption and high crushing index, severely limiting their application in high-performance concrete. Currently, carbon dioxide mineralization curing has become a relatively mature and widely used technology in the field of recycled aggregate modification. Carbonation modification can convert unstable calcium hydroxide in old mortar into stable calcium carbonate, improving the density of the aggregate to some extent. However, existing carbonation technologies have significant performance bottlenecks: rapidly generated calcium carbonate crystals easily clog surface pores, preventing carbon dioxide from penetrating deeper, making it difficult for the modification effect to reach the microcracks inside the aggregate, resulting in limited performance improvement. To break through the performance ceiling of single carbonation, the introduction of more efficient chemical strengthening methods has become inevitable. Phosphate solution (especially diammonium phosphate) soaking modification has attracted much attention due to its unique mineralization mechanism. The core principle is that phosphate ions (PO43-) in the solution penetrate into the aggregate pores and react in situ with calcium ions (Ca2+) in the old mortar to form hydroxyapatite. Hydroxyapatite is the main inorganic component of vertebrate bone and tooth enamel in nature, possessing extremely high mechanical strength and chemical stability. Compared to calcium carbonate (calcite, Mohs hardness approximately 3) formed by carbonization, hydroxyapatite has a higher hardness (Mohs hardness approximately 5). More importantly, hydroxyapatite crystals tend to grow in needle-like or flower-like clusters; this special micromorphology allows for tighter interlocking and filling of nanoscale micropores that calcium carbonate particles cannot access. However, existing studies often treat diammonium phosphate as a single modification method, neglecting its synergistic potential with the carbonized matrix. Direct soaking with diammonium phosphate without pretreatment can lead to a rapid reaction rate, resulting in loose accumulation of the product on the surface. Therefore, how to use carbonized modified aggregate as a precursor and then use biomass minerals generated from diammonium phosphate for secondary strengthening to form a multi-level dense structure from the inside out is currently the key technical challenge to solve the defects of recycled aggregate and achieve high-quality resource utilization. Summary of the Invention
[0003] The purpose of this invention is to provide a method for synergistic reinforcement of recycled aggregates based on pressure carbonization and diammonium phosphate. This method combines the filling effect of pressure carbonization on large internal pores with the crystal strengthening effect of diammonium phosphate on micropores and surfaces, significantly reducing the water absorption rate of recycled aggregates and improving their crushing strength.
[0004] The present invention adopts the following technical solution:
[0005] A method for synergistically reinforcing recycled aggregates based on pressure carbonization and diammonium phosphate includes the following steps:
[0006] S1. Pre-treat the recycled aggregate to achieve the specified moisture content;
[0007] S2. The pretreated recycled aggregate is placed in a high-concentration carbon dioxide gas atmosphere to carry out a carbonization reaction;
[0008] S3. Soak the carbonized recycled aggregate in a diammonium phosphate solution;
[0009] S4. Remove the soaked recycled aggregate and let it stand for curing to obtain modified recycled aggregate.
[0010] Furthermore, the humidity is specified as 60% ± 5% in S1.
[0011] Furthermore, in S1, the recycled aggregate is placed under constant temperature and humidity conditions to achieve a specified humidity level. The constant temperature and humidity conditions are: temperature 20℃; the curing time is 4 days, which aims to make the internal moisture of the recycled aggregate evenly distributed and reach a balance between air drying and moisture absorption.
[0012] Furthermore, the concentration of carbon dioxide gas in S2 is 99%-99.9%.
[0013] Furthermore, the pressure of the carbon dioxide gas atmosphere is not less than 120 kPa.
[0014] Furthermore, S2 specifically involves: placing the pretreated recycled aggregate in a high-concentration carbon dioxide gas atmosphere for carbonization reaction; using a pressurized carbonization chamber, first extracting the air from the chamber to a negative pressure of 100 kPa, and then filling it with carbon dioxide gas at a concentration of 99.9%; filling the chamber until the gas pressure reaches 150 kPa, and maintaining this pressure for carbonization reaction for 3 days; monitoring the gas pressure inside the chamber in real time during the reaction process, and promptly replenishing carbon dioxide gas to maintain a constant pressure of 150 kPa when the gas pressure drops.
[0015] Furthermore, the concentration of the diammonium phosphate solution in S3 is 0.8-1.2 mol / L.
[0016] Furthermore, in step S3, the recycled aggregate is sealed and soaked in a diammonium phosphate solution.
[0017] Furthermore, the curing conditions in S4 are: temperature 20℃, relative humidity RH=60%; curing time is 1 day.
[0018] Furthermore, the recycled aggregate in S1 is recycled coarse aggregate obtained by crushing and screening waste concrete, with a particle size range of 5-20mm; the pretreatment includes: screening and washing the recycled aggregate, drying it, and placing it in a constant temperature and humidity environment for curing to achieve a humidity balance state. The screening and washing adopts a water washing method to remove floating dust and soil adhering to the surface of the aggregate.
[0019] This invention employs a synergistic modification mechanism, utilizing the fact that the carbonation reaction mainly occurs inside the old mortar, and the generated calcium carbonate effectively fills the micron-sized large pores; the subsequent DAP soaking utilizes the penetration of phosphate ions to generate hydroxyapatite on the micropores that have not been fully filled by carbonation and on the outer surface of the aggregate, forming a composite reinforced structure of "calcium carbonate filling core - hydroxyapatite dense shell" from the inside out. Attached Figure Description
[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0021] Figure 1 This is a flow chart of the pressurized carbonization and diammonium phosphate synergistic enhancement process of the present invention;
[0022] Figure 2 This is a sample image of recycled aggregate modified by pressure carbonization and diammonium phosphate in accordance with the present invention.
[0023] Figure 3 This is a performance comparison diagram between the modified aggregate and ordinary recycled aggregate in Example 1 of the present invention;
[0024] Figure 4 This invention provides a comparison of the performance of recycled aggregates that have undergone only carbonization modification in its embodiments.
[0025] Figure 5 This is a comparison of the performance of recycled aggregates modified only by soaking in an embodiment of the present invention. Detailed Implementation
[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and 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.
[0027] This invention discloses a method for synergistically reinforcing recycled aggregates based on pressure carbonization and diammonium phosphate, comprising the following steps:
[0028] S1. Pre-treat the recycled aggregate to achieve the specified moisture content;
[0029] S2. The pretreated recycled aggregate is placed in a high-concentration carbon dioxide gas atmosphere to carry out a carbonization reaction;
[0030] S3. Soak the carbonized recycled aggregate in a diammonium phosphate solution;
[0031] S4. Remove the soaked recycled aggregate and let it stand for curing to obtain modified recycled aggregate.
[0032] Optionally, the humidity is specified in S1 as 50%-70%, wherein the humidity is preferably specified as 60%±5%.
[0033] Specifically, in S1, the recycled aggregate is placed under constant temperature and humidity conditions to achieve a specified humidity level. The constant temperature and humidity conditions are: temperature 20℃; the curing time is 4 days, which aims to make the internal moisture of the recycled aggregate evenly distributed and reach a balance between air drying and moisture absorption.
[0034] Optionally, the concentration of carbon dioxide gas in S2 is 99%-99.9%, preferably 99.9%.
[0035] Specifically, the pressure of the carbon dioxide gas atmosphere is not less than 120 kPa, preferably not less than 150 kPa.
[0036] Specifically, S2 involves: placing the pretreated recycled aggregate in a high-concentration carbon dioxide gas atmosphere for carbonization reaction; using a pressurized carbonization chamber, first extracting the air from the chamber to a negative pressure of 100 kPa, and then filling it with carbon dioxide gas at a concentration of 99.9%; filling the chamber until the gas pressure reaches 150 kPa, and maintaining this pressure for carbonization reaction for 3 days; monitoring the gas pressure inside the chamber in real time during the reaction process, and promptly replenishing carbon dioxide gas to maintain a constant pressure of 150 kPa when the gas pressure drops.
[0037] Optionally, the concentration of the diammonium phosphate solution in S3 is 0.8-1.2 mol / L, preferably 1 mol / L.
[0038] Optionally, in step S3, the recycled aggregate is sealed and soaked in a diammonium phosphate solution.
[0039] Optionally, the curing conditions in S4 are: temperature 20℃, relative humidity RH=60%; curing time is 1 day.
[0040] Optionally, the recycled aggregate in S1 is recycled coarse aggregate obtained by crushing and screening waste concrete, with a particle size range of 5-20mm; the pretreatment includes: screening and washing the recycled aggregate, drying it, and placing it in a constant temperature and humidity environment for curing to achieve a humidity balance state. The screening and washing adopts a water washing method to remove floating dust and soil adhering to the surface of the aggregate.
[0041] To further disclose the embodiments of the present invention, the following embodiments are provided.
[0042] Example 1
[0043] The specific operation steps of this embodiment 1 are as follows:
[0044] S1 Aggregate Preparation and Moisture Balancing Pretreatment: Select recycled coarse aggregate obtained from crushed waste concrete, with a particle size range of 5-20mm; screen and wash the aggregate to thoroughly remove surface dust, dry it, and then place it in a constant temperature and humidity chamber. Set the chamber temperature to 20℃ and the relative humidity (RH) to 60% for 4 days of constant temperature and humidity curing. This step aims to adjust the moisture content in the pores of the old mortar, as overly dry or oversaturated pores are not conducive to CO2 transport and reaction.
[0045] S2. Negative pressure replacement and pressurized carbonization treatment: The pretreated recycled aggregate is removed and placed in a specially designed pressurized carbonization box ( Figure 1 The following steps are performed: (1) Vacuum treatment: Start the vacuum pump and extract the air in the box to a negative pressure of 100 kPa, and maintain it for 5-10 minutes. This step aims to use negative pressure to overcome capillary resistance and expel the air in the deep pores of the aggregate. (2) Pressurized filling: Fill the box with carbon dioxide gas with a purity of 99.9% until the gas pressure in the box reaches 150 kPa. (3) Constant pressure reaction: Maintain carbonization at this pressure for 3 days. During the process, the pressure sensor is used to monitor in real time. Once the reaction consumes gas and causes the gas pressure to drop, carbon dioxide gas is added to maintain a constant pressure of 150 kPa.
[0046] S3. DAP Solution Immersion: After carbonization, the aggregate was removed and immediately placed in a container containing a 1 mol / L diammonium phosphate (DAP) solution. The liquid was ensured to completely cover the aggregate. The container was sealed and left to soak at 20°C. To verify the effect of soaking time, three different soaking durations were set in this embodiment: 1 day (CD1), 7 days (CD7), and 14 days (CD14). During this process, the DAP solution penetrated the surface layer and microcracks of the aggregate, reacting in situ with calcium hydroxide and some calcium carbonate to form a dense hydroxyapatite precipitate.
[0047] S4. Finished Product Curing: After soaking, pour out the solution and place the moistened aggregate again in a curing environment of 20℃ and 60% humidity for 1 day. This step allows the reaction products adhering to the surface of the aggregate to dehydrate and solidify under constant temperature and humidity, forming a hard protective layer, thus obtaining modified recycled aggregate.
[0048] The specific modification process is shown in the attached instruction manual. Figure 2 As shown, the modified sample is as per the attached instruction manual. Figure 3 As shown.
[0049] Performance testing and result analysis: The water absorption rate and crushing value of the aggregate prepared above were tested in accordance with the "Standard for Quality and Testing Methods of Sand and Stone for Ordinary Concrete" (JGJ 52-2021).
[0050] (1) Comparison benchmark: Unmodified recycled aggregate from the same batch was selected as the comparison example. The test results showed that the water absorption rate of the unmodified recycled aggregate was 5.77% and the crushing value was 11.15%. These values are higher than those of natural aggregate, but are within the typical range of recycled aggregate.
[0051] (2) Modification effect: The modified aggregates in this embodiment that have undergone DAP soaking treatment for different times are compared with the comparative example. Specific data are shown in the appendix of the instruction manual. Figure 3 As shown in the figure. Analysis reveals that after the synergistic modification of the recycled aggregate using the "pressure carbonization + DAP soaking" method described in this invention, both the water absorption rate and crushing value were significantly improved. This indicates that the calcium carbonate produced by carbonation and the hydroxyapatite generated by the reaction with DAP effectively synergistically filled the aggregate pores and strengthened the interfacial transition zone. Specifically, as the soaking time increased (from 1 day to 14 days), the reduction in crushing value showed an increasing trend, with a maximum decrease of 24.5%, indicating that prolonged soaking facilitates the deep penetration of phosphate ions into the aggregate and the continuous generation of strengthening products. It is also noteworthy that the crushing value decreased by 18.6% after only 1 day of soaking (CD1), demonstrating that the modification method of this invention can achieve a highly efficient reaction in a short time, ensuring both modification effectiveness and production efficiency, and possessing good engineering application value.
[0052] Comparative Example 1
[0053] 1. Preparation of Modified Recycled Aggregate: This comparative example aims to explore the modification effect of a single pressure carbonization process. The specific operating steps are as follows: Steps S1 and S2 described in Example 1 were strictly followed. After the carbonization reaction was completed for 3 days and the aggregate was removed, the subsequent DAP solution soaking step was not performed. The carbonized aggregate was directly placed in the same environment as in Example 1 for static aging, thus obtaining the single carbonization modified aggregate.
[0054] 2. Performance Testing and Result Analysis: The performance of the prepared single carbonized aggregate was tested under the same conditions. For example... Figure 4 The test data showed that, compared with the unmodified original recycled aggregate, the water absorption rate of the aggregate obtained in this comparative example decreased by only 2.1%, and the crushing value decreased by only 2.3%. This slight change is in stark contrast to the sample soaked in DAP for 1 day in Example 1 (water absorption rate decreased by 10.0%, and crushing value decreased by 18.6%), confirming that, in the absence of subsequent phosphate synergistic strengthening, the effect of single pressure carbonization treatment on improving the performance of this batch of recycled aggregate is negligible.
[0055] 3. Results Analysis: Based on the data differences between Example 1 and this comparative example, the reasons are analyzed as follows: During the crushing, shaping, and stockpiling process, recycled aggregates inevitably undergo prolonged exposure to the natural environment. During this period, the old mortar adhering to the aggregate surface undergoes a slow natural carbonization reaction with carbon dioxide in the air, resulting in most of the surface active component (calcium hydroxide) being converted into calcium carbonate. Therefore, when artificial pressure carbonization is performed again, the modification effect is difficult to penetrate further due to the lack of reaction substrate, leading to a bottleneck in performance improvement. However, in this invention (Example 1), after introducing the DAP soaking step, phosphate ions can undergo a phosphating replacement reaction with the calcium carbonate already formed on the surface, converting the relatively soluble calcium carbonate into the more stable and harder hydroxyapatite. This successfully overcomes the modification failure problem caused by the natural carbonization of old aggregates, achieving a significant leap in performance.
[0056] Comparative Example 2
[0057] Compared to Example 1, only the DAP immersion treatment described in step 4 was performed, without prior carbonization modification.
[0058] 1. Preparation of Modified Recycled Aggregate: This comparative example aims to investigate the modification effect of a single DAP solution immersion process. The specific operation steps are as follows: After the recycled aggregate was subjected to the same screening, drying, and pretreatment as in Example 1, the pressurized carbonization step was skipped, and the aggregate was directly immersed in a 1 mol / L diammonium phosphate (DAP) solution. The aggregate was sealed at 20°C and immersed for 1 day, 7 days, and 14 days respectively. Afterwards, it was removed, drained, and cured for 1 day under the same conditions as in Example 1 to obtain a single chemically immersion modified aggregate.
[0059] 2. Performance testing and results analysis: such as Figure 5 As shown, the aggregates prepared above were subjected to performance tests under the same conditions. The test data showed that, compared with the unmodified original recycled aggregates, the water absorption rate of the aggregates obtained in this comparative example increased by 6.1% - 15.7%, while the crushing value decreased only slightly by 0.5% - 8.3%. Compared with Example 1, its modification effect showed obvious negative effects or ineffectiveness.
[0060] 3. Results Analysis: The main reason for the above-mentioned anomaly is that the surface of the uncarbonized recycled aggregate has a large amount of highly reactive calcium hydroxide. When a high-concentration DAP solution directly contacts the aggregate surface, phosphate ions react with the large amount of calcium ions on the surface to form a loose, rough calcium phosphate salt deposit layer. This leads to two consequences: First, this rapidly formed loose deposit layer not only fails to fill the internal pores, but also increases the water-holding capacity of the aggregate surface due to its high specific surface area and porous structure, resulting in an increase in water absorption instead of a decrease; Second, the rapid precipitation on the surface creates a "shielding effect," blocking the channels for the solution to penetrate into the deep microcracks inside the aggregate, causing the modification to remain only on a very thin surface layer, unable to build a reinforcing skeleton that penetrates the interior of the aggregate, and therefore contributing negligibly to the overall compressive strength.
[0061] This embodiment demonstrates the scientific validity of the "carbonization followed by soaking" process route in this invention (Example 1): carbonization first consumes the excessively active calcium ions on the surface and fills the large pores, reducing the surface reaction rate, thereby forcing the subsequent DAP solution to penetrate deep into the micropores and slowly crystallize in the depths, achieving true deep strengthening.
[0062] In summary, the technical solutions adopted in the embodiments of the present invention have the following advantages:
[0063] Synergistic modification mechanism: The carbonation reaction mainly occurs inside the old mortar, and the generated calcium carbonate effectively fills the micron-sized macropores. Subsequent DAP soaking utilizes the penetration of phosphate ions to generate hydroxyapatite in the micropores that are not yet fully filled by carbonation and on the outer surface of the aggregate. Hydroxyapatite has lower solubility and higher hardness than calcium carbonate, and the two form a composite strengthening structure of "calcium carbonate-filled core-hydroxyapatite dense shell" from the inside out.
[0064] Process optimization: The carbonization process of "vacuuming first and then pressurizing" is adopted to eliminate air resistance in the pores, allowing CO2 to penetrate into the core area of the aggregate; the humidity balance of the pretreatment ensures the optimal medium environment required for the carbonization reaction.
[0065] Significantly improved performance: After treatment by the method of this invention, the water absorption rate of recycled aggregate is reduced by 7.6% - 11.5%, and the crushing value is reduced by 18.6% - 24.5%, which significantly improves its workability and mechanical properties in concrete.
[0066] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.
Claims
1. A method for synergistically reinforcing recycled aggregates based on pressure carbonization and diammonium phosphate, characterized in that, Includes the following steps: S1. Pre-treat the recycled aggregate to achieve the specified moisture content; S2. The pretreated recycled aggregate is placed in a high-concentration carbon dioxide gas atmosphere to carry out a carbonization reaction; S3. Soak the carbonized recycled aggregate in a diammonium phosphate solution; S4. Remove the soaked recycled aggregate and let it stand for curing to obtain modified recycled aggregate.
2. The method according to claim 1, characterized in that, The humidity is specified as 60% ± 5% in S1.
3. The method according to claim 2, characterized in that, In step S1, the recycled aggregate is placed under constant temperature and humidity conditions to achieve a specified humidity level. The constant temperature and humidity conditions are: temperature 20℃; the curing time is 4 days, which aims to make the internal moisture of the recycled aggregate evenly distributed and reach a balance between air drying and moisture absorption.
4. The method according to claim 1, characterized in that, The carbon dioxide gas concentration in S2 is 99%-99.9%.
5. The method according to claim 4, characterized in that, The pressure of the carbon dioxide gas atmosphere is not less than 120 kPa.
6. The method according to claim 5, characterized in that, S2 specifically involves: placing the pretreated recycled aggregate in a high-concentration carbon dioxide gas atmosphere for carbonization reaction; using a pressurized carbonization chamber, first extracting the air from the chamber to a negative pressure of 100 kPa, and then filling it with carbon dioxide gas at a concentration of 99.9%; filling the chamber until the gas pressure reaches 150 kPa, and maintaining this pressure for carbonization reaction for 3 days; monitoring the gas pressure inside the chamber in real time during the reaction process, and promptly replenishing carbon dioxide gas when the gas pressure drops to maintain a constant pressure of 150 kPa.
7. The method according to claim 1, characterized in that, The concentration of the diammonium phosphate solution in S3 is 0.8-1.2 mol / L.
8. The method according to claim 1, characterized in that, In step S3, the recycled aggregate is sealed and soaked in a diammonium phosphate solution.
9. The method according to claim 1, characterized in that, The curing conditions in S4 are: temperature 20℃, relative humidity RH=60%; curing time is 1 day.
10. The method according to claim 1, characterized in that: The recycled aggregate in S1 is recycled coarse aggregate obtained by crushing and screening waste concrete, with a particle size range of 5-20mm. The pretreatment includes: screening and washing the recycled aggregate, drying it, and curing it in a constant temperature and humidity environment to achieve a humidity balance. The screening and washing is done by water washing to remove floating dust and soil adhering to the surface of the aggregate.