Phosphated ground polymer modified recycled aggregate and method of modifying and strengthening thereof

Abstract

The present application relates to a kind of phosphoric acid ground polymer modified recycled aggregate and its modified strengthening method.First, phosphoric acid, aluminum source material, water are used to prepare phosphoric acid excitation solution, then it is mixed with high-activity mineral admixture evenly to obtain phosphoric acid geopolymer slurry, then building waste is crushed, screened, washed, grinded to obtain recycled aggregate, finally recycled aggregate is added to phosphoric acid geopolymer slurry and impregnated modification, after taking out, heating and curing, obtain phosphoric acid ground polymer modified recycled aggregate.The present application uses phosphoric acid ground polymer to modify and strengthen the recycled aggregate from building solid waste, on the one hand, it reduces the loose mortar in recycled aggregate, on the other hand, it plays a good filling and strengthening effect on the pores and cracks in recycled aggregate, improves the mechanical properties of recycled aggregate, significantly reduces the crushing value and los angeles abrasion, not only solves the recycling problem of recycled aggregate, but also solves the resource utilization problem of solid waste such as slag powder.

Description

TECHNICAL FIELD

[0001] The application relates to a geopolymer and a building material solid waste recycling technology field, in particular to a phosphoric acid geopolymer modified recycled aggregate and a modified strengthening method thereof. BACKGROUND

[0002] A large amount of building solid waste will be generated in the process of urbanization, and if it cannot be effectively treated, it will not only occupy a large amount of land but also pollute the environment, so how to treat the building solid waste has become a problem to be solved in the sustainable development of cities. On the other hand, the construction of highways will consume a large amount of natural stone, leading to the exhaustion of natural stone resources. If the building solid waste can be processed into recycled aggregate and partially replace the natural stone, it will certainly have important significance for the sustainable development of highway construction. Unlike natural aggregate, recycled aggregate is usually composed of cement mortar and crushed aggregate, which makes the water absorption of recycled aggregate higher, the crushing value larger and the density smaller, and it is difficult to meet the technical specifications of aggregate in highway construction. Therefore, strengthening treatment of recycled aggregate to improve its performance is an important way to solve the application of recycled aggregate in highway construction.

[0003] Chinese patent CN108298849A discloses a method for strengthening treatment of recycled aggregate. The scheme uses dilute acetic acid to treat the surface of recycled aggregate, utilizes the chemical reaction between dilute acetic acid and cement mortar attached to the surface of recycled aggregate to remove part of the cement mortar on the surface of the auxiliary material, and thus achieves the purpose of reducing the water absorption of recycled aggregate and improving the quality of recycled aggregate. Chinese patent CN115893891A discloses a method for strengthening recycled aggregate. The recycled aggregate is soaked in an acid solution, and thus part of the adhering mortar is removed. However, in the above-mentioned scheme, only acid solution is used to dispose the recycled aggregate, which can only remove the mortar that is easy to peel off from the recycled aggregate, and cannot effectively reduce the micro-cracks in the recycled aggregate and cannot effectively improve the strength of the recycled aggregate. Chinese patent CN116750995A discloses a preparation method of a phosphoric acid geopolymer semi-rigid base material. The scheme uses phosphoric acid to activate silico-alumina solid waste, and then mixes and stirs the silico-alumina solid waste with graded gravel for paving, which avoids the complicated procedures of traditional alkali activation and reduces the construction difficulty. However, in the scheme, the molar ratio of Si / Al in the geopolymer slurry is 1-4, and the molar ratio of Si / P is 7-10, so the molar ratio of Al / P in the system is 1.75-10. Obviously, the amount of Al in the system is greater than that of P. In addition, the cement mortar in the recycled aggregate can also react with phosphoric acid, which will also increase the amount of phosphoric acid. However, in the phosphoric acid geopolymer, phosphoric acid as an activator is the core of the polycondensation reaction, and if the amount of phosphoric acid is insufficient, it will significantly affect the strength of the geopolymer. Therefore, the application increases the amount of phosphoric acid, so that the molar ratio of P / Al is 2-4:1, ensuring the amount of phosphoric acid in the system and enhancing the modification effect. SUMMARY

[0004] The present application aims to solve the problems of high cost, poor performance and high difficulty in the existing building waste recycling process, and provides a method for modifying and strengthening recycled aggregate with phosphoric acid-based geopolymer, which comprises the following steps:

[0005] (a) preparing a phosphoric acid activator solution with phosphoric acid, aluminum source material, water and other raw materials;

[0006] (b) mixing the phosphoric acid activator solution with high-activity mineral admixture uniformly to obtain a phosphoric acid-based geopolymer slurry;

[0007] (c) adding recycled aggregate to the phosphoric acid-based geopolymer slurry for impregnation modification, taking out the recycled aggregate wrapped with slurry after modification, and then performing heating and curing treatment to solidify the slurry on the surface of the recycled aggregate to obtain phosphoric acid-based geopolymer modified recycled aggregate.

[0008] Further, the preparation process of the phosphoric acid activator solution in step (a) is as follows: mix phosphoric acid, aluminum source material and water at 90℃±5℃, stir until the aluminum source material is completely dissolved, then cool the mixture to room temperature to obtain the phosphoric acid activator solution.

[0009] Further, the aluminum source material in step (a) is selected from at least one of aluminum hydroxide, aluminum oxide, aluminum metasilicate and aluminum metahydroxide. Since aluminum dihydrogen phosphate is an excellent phosphate binder, adding aluminum source material to phosphoric acid can react with phosphoric acid to form amorphous aluminum phosphate gel, thereby improving the activity of the activator solution.

[0010] Further, the mass fraction of water in the phosphoric acid activator solution prepared in step (a) is (30-70)%, and the molar ratio of P to Al is 2-4:1.

[0011] Further, the high-activity mineral admixture in step (b) is selected from at least one of metakaolin, fly ash and slag powder, and the particle size or size of the high-activity mineral admixture is 800-2000 mesh. Under the action of the phosphoric acid activator solution, the active components (such as silicon oxide and aluminum oxide) in the high-activity mineral admixture dissolve to form Si and Al monomers, which form long-chain or network oligomeric silica-alumina gel through condensation, and finally undergo condensation reaction with phosphoric acid monomers in the activator solution to form three-dimensional network structure of phosphoric acid-based geopolymer.

[0012] Further, the mass ratio of phosphoric acid activator solution to high-activity mineral admixture in step (b) is 1-3:1.

[0013] Further, the recycled aggregate in step (c) is obtained by crushing, screening, washing and grinding of construction waste, and the particle size is greater than 2.36mm.

[0014] Further, the step (c) is carried out under the condition of negative pressure (specifically 1-5 kPa), the dipping temperature is room temperature, the dipping time is not less than 30 min, and the dipping times are 1 or more. Through the dipping treatment, in addition to the loose mortar on the surface of the recycled aggregate is stripped, the phosphoric acid-based polymer slurry can also be ensured to fully penetrate into the recycled aggregate, and the pores, cracks, holes and the like of the recycled aggregate are filled.

[0015] Further, the curing temperature in the step (c) is 40-80 DEG C, and the curing time is not less than 12 h, so as to ensure that the phosphoric acid-based polymer is completely cured.

[0016] The second object of the present application is to provide a phosphoric acid-based polymer modified recycled aggregate, and each performance index meets the requirements of the Technical Specification for Construction of Highway Asphalt Pavement (JTG F40-2004), that is, the stone crushing value is ≯ 26%, the Los Angeles abrasion loss is ≯ 28%, the apparent relative density is ≮ 2.6, and the water absorption is ≯ 2%.

[0017] The principle of the present application is that the recycled aggregate is soaked in the phosphoric acid-based polymer under the condition of negative pressure, and the following two aspects are mainly achieved: one is that the phosphoric acid in the phosphoric acid-based polymer can react with the cement mortar on the surface of the recycled aggregate, so that part of the loose cement mortar is stripped, and the cement mortar is reacted to generate hydroxyapatite, so that the strength of the cement mortar is enhanced; the other is that the phosphoric acid-based polymer penetrates into the recycled aggregate, and the condensation reaction generates -O-Al-O-Si-O-P-O- gel, and the gel can fill the holes and cracks in the recycled aggregate after being cured, so that the strength of the recycled aggregate is enhanced again. Therefore, after the treatment of the phosphoric acid-based polymer, the recycled aggregate is effectively strengthened, and the problems of high water absorption and high crushing value of the recycled aggregate can be solved.

[0018] Compared with the prior art, the present application has the following advantages:

[0019] 1) The present application uses the phosphoric acid-based polymer to modify the recycled aggregate from the building solid waste, which not only reduces the loose mortar in the recycled aggregate, but also fills and enhances the holes and cracks in the recycled aggregate, so that the recycled aggregate is fully strengthened.

[0020] 2) The geopolymer in the present application can use fly ash, slag powder and other solid wastes as high-activity mineral admixtures, so that the resource utilization of the recycled aggregate and other solid wastes is solved, and the economic and environmental benefits are achieved;

[0021] 3) The recycled aggregate strengthening process provided by the present application has the advantages of simple operation, low cost, good product performance and the like, and is suitable for large-area popularization and application. Attached Figure Description

[0022] Figure 1 These are before-and-after photos of the recycled aggregate in Example 1 before and after reinforcement.

[0023] Figure 2 Comparative photographs of the phosphate-based polymers in Example 1 (left) and Example 4 (right);

[0024] Figure 3 The image shows a comparison of the XRD patterns of the recycled aggregate prepared in Example 1. Detailed Implementation

[0025] To enable those skilled in the art to fully understand the technical solution and beneficial effects of the present invention, the following description is provided in conjunction with specific embodiments and accompanying drawings.

[0026] The recycled aggregates used in the following embodiments and comparative examples were obtained by crushing, screening, and mechanically grinding waste concrete collected in the laboratory; the phosphoric acid used was all industrial grade phosphoric acid with a mass fraction of 85%; the aluminum source material used was alumina; and the highly active mineral admixture used was metakaolin with a mesh size of 1250 mesh. Its main chemical components and their mass percentages included: Al2O3 42.6%, SiO2 51.3%, and CaO 2.8%.

[0027] Example 1

[0028] 1) Preparation of phosphoric acid activation solution

[0029] In an oil bath environment at 90℃±5℃, a certain amount of phosphoric acid, water, and aluminum source material were added sequentially to the reactor, and the mixture was stirred using a magnetic stirrer until the aluminum source material was completely dissolved in the phosphoric acid. The resulting phosphoric acid activation solution had a P to Al molar ratio of approximately 3 and a water content of approximately 50%.

[0030] 2) Preparation of phosphate geopolymer slurry

[0031] The prepared phosphoric acid activating solution was mixed with highly active mineral admixtures at a weight ratio of 2:1, and stirred evenly using a mixer to obtain a phosphoric acid geopolymer slurry.

[0032] 3) Preparation of phosphate-based polymer-modified aggregates

[0033] The construction waste is sequentially subjected to crushing, screening, flushing, and grinding treatment to obtain recycled aggregate with a particle size of 4.75-9.5 mm. Under the condition of negative pressure of 3 kPa, 1000 g of recycled aggregate is added into 500 g of phosphoric acid geopolymer slurry according to a mass ratio of 2:1 for impregnation treatment for 2 h, so that the phosphoric acid geopolymer slurry fully penetrates into the recycled aggregate. After impregnation, the recycled coarse aggregate is taken out and heated at 60 ℃ for 12 h until the phosphoric acid geopolymer is completely cured, and finally the phosphoric acid geopolymer modified recycled aggregate is prepared.

[0034] Example 2

[0035] The specific steps of this example are substantially the same as those of Example 1, except that the molar ratio of P element to Al element in the phosphoric acid activating solution in step 1 is controlled to be 2.

[0036] Example 3

[0037] The specific steps of this example are substantially the same as those of Example 1, except that the molar ratio of P element to Al element in the phosphoric acid activating solution in step 1 is controlled to be 4.

[0038] Example 4

[0039] The specific steps of this example are substantially the same as those of Example 1, except that the water content in the phosphoric acid activating solution in step 1 is reduced to 30%.

[0040] Example 5

[0041] The specific steps of this example are substantially the same as those of Example 1, except that the water content in the phosphoric acid activating solution in step 1 is increased to 70%.

[0042] Example 6

[0043] The specific steps of this example are substantially the same as those of Example 1, except that the weight ratio of phosphoric acid activating solution to high-activity mineral admixture in step 2 is 1:1.

[0044] Example 7

[0045] The specific steps of this example are substantially the same as those of Example 1, except that the weight ratio of phosphoric acid activating solution to high-activity mineral admixture in step 2 is 3:1.

[0046] Example 8

[0047] The specific steps of this example are substantially the same as those of Example 1, except that the curing temperature in step 3 is 40℃.

[0048] Example 9

[0049] The specific steps of the present example are substantially the same as those of Example 1, except that the temperature of the curing in step 3 is 80°C.

[0050] Comparative Example 1

[0051] The specific steps of the present example are substantially the same as those of Example 1, except that the molar ratio of P element to Al element in the phosphoric acid activating solution in step 1 is 5.

[0052] Comparative Example 2

[0053] The specific steps of the present example are substantially the same as those of Example 1, except that the water content of the phosphoric acid activating solution in step 1 is 80%.

[0054] Comparative Example 3

[0055] The specific steps of the present example are substantially the same as those of Example 1, except that the weight ratio of the phosphoric acid activating solution to the high-activity mineral admixture in step 2 is 1:2.

[0056] Comparative Example 4

[0057] The specific steps of the present example are substantially the same as those of Example 1, except that the weight ratio of the phosphoric acid activating solution to the high-activity mineral admixture in step 2 is 4:1.

[0058] Comparative Example 5

[0059] The specific steps of the present example are substantially the same as those of Example 1, except that the temperature of the curing in step 3 is 20°C.

[0060] Comparative Example 6

[0061] The specific steps of the present example are substantially the same as those of Example 1, except that the temperature of the curing in step 3 is 100°C.

[0062] Blank Control Group

[0063] Raw (not subjected to any strengthening treatment) recycled aggregate.

[0064] The performance of the recycled aggregate samples in Examples 1-9, Comparative Examples 1-6, and the blank control group was tested in accordance with the Technical Specification for Construction of Highway Asphalt Pavement (JTG F40-2004) and the Test Procedures for Aggregate in Highway Engineering (JTG E42-2005), and the results are shown in Table 1 below.

[0065] Table 1 Comparison of the Performance of Different Recycled Aggregates

[0066]

[0067] The above results show that the mechanical properties of the recycled aggregate prepared by the phosphoric acid geopolymer strengthening measure are obviously improved, the water absorption is obviously reduced, and each technical index reaches the requirements of the pavement specification.

[0068] Figure 1 The figure is a comparison of the real object of the recycled aggregate before and after strengthening in embodiment 1 of the application. Figure 1 It can be obviously seen that the recycled aggregate is wrapped with a layer of geopolymer slurry after the modification treatment of the phosphoric acid geopolymer, and the performance of the geopolymer slurry has a decisive role on the performance of the recycled aggregate.

[0069] Figure 2 The figure is a comparison of the phosphoric acid geopolymer in embodiment 1 (left a) and embodiment 4 (right b). It can be seen from the figure that the phosphoric acid geopolymer in embodiment 1 and embodiment 4 has no obvious pores after curing, the structure is dense, and the strength is high. This shows that the pores and cracks of the recycled aggregate can be well filled when the recycled aggregate is modified by the phosphoric acid geopolymer, and the performance of the recycled aggregate is improved.

[0070] Figure 3 The figure is an XRD comparison of the recycled aggregate prepared in embodiment 1. It can be seen from the figure that the characteristic peak of calcium hydroxide in the modified recycled aggregate obtained after the treatment of the phosphoric acid geopolymer is obviously weakened, and at the same time, the characteristic peak of hydroxyapatite appears, which shows that the phosphoric acid in the phosphoric acid geopolymer reacts with calcium hydroxide in the recycled aggregate to generate hydroxyapatite. Secondly, the modified recycled aggregate appears a hump-shaped peak in the region of 25°, which is related to -O-Al-O-Si-O-P-O-. Therefore, the results confirm that the treatment of the recycled aggregate by the phosphoric acid geopolymer has the following two effects: one is to react with the hydration products in the cement mortar to reduce the content of the cement mortar; and the other is that the geopolymer can have a good wrapping effect on the recycled aggregate after curing, can fill the cracks and pores in the recycled aggregate, and improve the performance of the recycled aggregate.

[0071] The application is not limited to the above embodiments, and those skilled in the art can make several improvements and refinements without departing from the principles of the application, and these improvements and refinements are also regarded as within the protection scope of the application. The contents not described in detail in the specification belong to the prior art known to those skilled in the art.

Claims

1. A method for modifying and strengthening recycled aggregates with phosphate-based polymers, characterized in that... The method includes the following steps: preparing a phosphoric acid activation solution using phosphoric acid, aluminum source material, and water. Specifically, the phosphoric acid, aluminum source material, and water are mixed and stirred thoroughly at 90℃±5℃, and then cooled to room temperature to obtain a phosphoric acid activation solution. The mass percentage of water in the phosphoric acid activation solution is 30%-70%, and the molar ratio of P to Al is 2-4:

1. The phosphoric acid activation solution is mixed evenly with a highly active mineral admixture to obtain a phosphoric acid geopolymer slurry. The highly active mineral admixture is selected from at least one of metakaolin, fly ash, and slag powder, and its particle size is 800-2000 mesh. The recycled aggregate is mixed with the phosphoric acid geopolymer slurry for modification. The recycled aggregate is then removed and heated for curing to solidify the slurry adhering to its surface, finally obtaining phosphoric acid geopolymer-modified recycled aggregate.

2. The method as described in claim 1, characterized in that: The aluminum source material is selected from at least one of aluminum hydroxide, aluminum oxide, aluminum aluminate, and aluminum metaaluminate.

3. The method as described in claim 1, characterized in that: The mass ratio of phosphoric acid activating solution to highly active mineral admixture is 1-3:

1.

4. The method as described in claim 1, characterized in that: The recycled aggregate is obtained from construction waste through crushing, screening, washing, and grinding, and its particle size is greater than 2.36 mm.

5. The method as described in claim 1, characterized in that: Recycled aggregates were mixed with phosphate-based polymer slurry under negative pressure for impregnation modification. The impregnation temperature was room temperature, the impregnation time was not less than 30 minutes, and the impregnation was performed once or more.

6. The method as described in claim 1, characterized in that: The optimal temperature for health preservation is 40-80℃, and the duration should be no less than 12 hours.

7. A phosphate-based polymer-modified recycled aggregate, characterized in that: The recycled aggregate is prepared according to any one of claims 1-6, and has a stone crushing value ≤26%, Los Angeles abrasion loss ≤28%, apparent relative density ≥2.6, and water absorption ≤2%.

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