High-water-permeability concrete prepared from construction waste and preparation method of high-water-permeability concrete
By modifying the recycled aggregate of construction waste by diatomaceous earth, metakaolin and quicklime, and combining the use of reinforcement fibers and coupling agents, the poor adaptability of construction waste aggregate in concrete is solved, and the mechanical strength and long-term water permeability of permeable concrete are significantly improved.
Patent Information
- Application Number
- CN202510226613.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-27
- Publication Date
- 2025-06-17
AI Technical Summary
When construction waste is used as aggregate in concrete, the characteristics of frost resistance, shrinkage, creep or water absorption are greatly different from those of ordinary aggregates, resulting in poor adaptability and affecting the mechanical strength and long-term water permeability of permeable concrete.
By modifying the regenerated aggregate prepared by construction waste with diatomaceous earth, metakaolin and quicklime, a gelled material is formed to fill the pores of the aggregate, and the adaptability and pore structure of the aggregate to the concrete paddle is improved by adding reinforcement fibers and coupling agents.
It improves the adaptability of recycled aggregates of construction waste to concrete paddles, improves the mechanical strength and long-term water permeability of permeable concrete, reduces harmful large pores, and increases fine pores that are efficiently permeable and not easily blocked.
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Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of concrete, and more particularly to a highly permeable concrete prepared from construction waste and a preparation method thereof. Background Art
[0002] With the development of the urbanization process, a large amount of construction waste will be generated during the construction of new projects and the demolition of old buildings. In China, a large number of old buildings in urban and rural areas are mainly of masonry structure or mixed structure, and waste bricks and waste concrete account for a large proportion in these construction wastes. However, at present, our research on the recycling of these construction wastes is less, and the proportion of resource recycling is low. In most cases, the construction waste is landfilled or stacked. However, this will not only occupy and damage the land, but also pollute the surrounding environment.
[0003] Permeable concrete is made by mixing aggregate, cement, water and additives. Due to its high permeation efficiency, it is a green new type of pavement paving material. At present, permeable concrete has been widely used in the base construction of various permeable pavements such as sidewalks, community roads, and parking lots. At present, the main aggregate used in permeable concrete is still mostly natural sand and gravel. However, excessive exploitation of natural sand and gravel will also cause damage to the ecological environment. If construction waste can be applied to the preparation of permeable concrete, it can not only solve the problem of construction waste treatment, but also reduce the demand for natural aggregate in permeable concrete, which has great value and significance for environmental protection.
[0004] However, due to the large amount of impurities and complex composition in construction waste, most of the construction waste has great differences in properties such as frost resistance, shrinkage, creep or water absorption when used as aggregate compared with ordinary aggregate. This makes the compatibility of untreated construction waste with concrete paste poor, which will directly affect the overall mechanical strength of permeable concrete and is also prone to cracking. At the same time, due to the rough surface and excessive pores of the recycled aggregate made of construction waste, and the poor compatibility with the concrete paste, the aggregate made of construction waste cannot be effectively bonded with the concrete paste, and the prepared permeable concrete has more harmful large pores. Although the large pores can contribute to the excellent water permeability of the permeable concrete in the initial application, it is easy to adsorb impurities or be blocked by impurities after long-term use, resulting in blockage, and the water permeability of the permeable concrete will be greatly reduced over time, which is not conducive to long-term use and greatly affects the popularization and application of the process of preparing permeable concrete from construction waste. Summary of the Invention
[0005] In order to improve the compatibility of construction waste in concrete slurry and improve the comprehensive performance of permeable concrete with construction waste as aggregate, so that the permeable concrete not only has excellent mechanical strength, but also can maintain high water permeability for a long time, the present application provides a highly permeable concrete prepared from construction waste and its preparation method.
[0006] The highly permeable concrete prepared from construction waste provided by the present application adopts the following technical solutions: A highly permeable concrete prepared from construction waste, comprising the following raw materials in parts by weight: Cement: 300 - 360 parts; Modified recycled aggregate: 750 - 900 parts; Natural coarse aggregate: 500 - 600 parts; Ground granulated blast-furnace slag: 100 - 160 parts; Alkali activator: 50 - 75 parts; Reinforcing fiber: 45 - 70 parts; Coupling agent: 50 - 60 parts; Water-reducing agent I: 1.8 - 2.4 parts; Water: 126 - 160 parts; Wherein, the modified recycled aggregate is specifically prepared by mixing and modifying recycled aggregate with diatomite, metakaolin and quicklime, and the recycled aggregate is obtained by repeatedly crushing and screening construction waste.
[0007] By adopting the above technical solutions, the recycled aggregate prepared from construction waste is modified by using diatomite, metakaolin and quicklime. Diatomite can generate a gelling material with metakaolin and quicklime in water and fully adhere to and fill the internal and external pores of the construction waste recycled aggregate. Furthermore, the overall frost resistance, shrinkage, creep or water absorption and other characteristics of the construction waste recycled aggregate are improved, and the compatibility between the construction waste recycled aggregate and the concrete slurry is improved, so that the modified recycled aggregate can be effectively bonded with the concrete slurry. Moreover, through the adhesion and filling of diatomite, the pore structure on the surface of the construction waste recycled aggregate is greatly improved, reducing both the harmful large pore structure in the recycled aggregate and the proportion of harmful large pores in the prepared permeable concrete, while increasing the fine pores that are effectively permeable and not easily blocked, which is beneficial to further improving the water permeability of the permeable concrete, so that the permeable concrete can still have good water permeability after long-term use.
[0008] Optionally, the modified recycled aggregate includes modified recycled coarse aggregate with an average particle size of 4.75 - 13.2 mm and modified recycled fine aggregate with an average particle size less than 1 mm, and the mixing weight ratio of the modified recycled coarse aggregate to the modified recycled fine aggregate is (2 - 4):1.
[0009] By adopting the above technical solution, increasing the proportion of modified recycled coarse aggregate in the modified recycled aggregate is beneficial to improving the water permeability of permeable concrete, while adding a small amount of modified recycled fine aggregate can improve the pore structure of permeable concrete, reduce the harmful large-pore structure, and also improve the compactness in permeable concrete, which is beneficial to enhancing the mechanical strength of permeable concrete.
[0010] Optionally, the preparation method of the modified recycled aggregate includes the following steps: A1. Crush, wash, remove impurities, and screen the construction waste multiple times to obtain recycled aggregate with an average particle size less than 20 mm; fully mix the recycled aggregate with diatomite, and then place it in a furnace at 850 - 900 °C for continuous calcination for 2 - 3 h to obtain mixed recycled aggregate; fully mix metakaolin and quicklime to obtain a mixed powder, and then fully mix and stir evenly the mixed powder, water reducer II, and water to obtain a modified slurry; A2. Mix the mixed recycled aggregate obtained in step A1 with the modified slurry evenly at a weight ratio of 1:4, carry out vacuum filtration under reduced pressure and dry the filter residue, let it stand for no less than 24 h, then simply crush and screen the filter residue to obtain modified recycled coarse aggregate with an average particle size of 4.75 - 13.2 mm and secondary aggregate with an average particle size less than 4.75 mm, and further crush and grind the secondary aggregate until its average particle size is less than 1 mm to obtain modified recycled fine aggregate; A3. Fully mix the modified recycled coarse aggregate and the modified recycled fine aggregate obtained in step A2 at a weight ratio of (2 - 4):1 to obtain the modified recycled aggregate.
[0011] Optionally, in step A1, the mixing weight ratio of the recycled aggregate to the diatomite is 1:(0.4 - 0.6); the mixing weight ratio of the metakaolin to the quicklime is 1:(0.1 - 0.2), and the mixing weight ratio of the mixed powder, the water reducer II, and water is 1:(0.05 - 0.055):(0.4 - 0.55), where the water reducer II is a sulfonated melamine-based water reducer.
[0012] By adopting the above technical solution, diatomite can be fully mixed with recycled aggregates and fill the pores in the recycled aggregates. With the calcination of the mixed recycled aggregates, diatomite can expand moderately and preliminarily fill the pores of the recycled aggregates. The calcined diatomite is then combined with a modified slurry prepared in a specific proportion, which can form a cement-like gelling material that can dry and harden in water. Furthermore, the recycled aggregates can be fully modified by the gelling material, improving the aggregate properties such as the frost resistance, shrinkage, creep, or water absorption of the whole, and making it closer to natural aggregates. This is not only beneficial to improving the compatibility between the recycled aggregates made from construction waste and the concrete slurry, enhancing the mechanical strength of the permeable concrete, but also conducive to optimizing the pore structure in the permeable concrete, reducing the harmful large pores caused by the recycled construction waste aggregates in the permeable concrete, and improving the long-term water permeability of the permeable concrete.
[0013] Optionally, the alkali activator is a sodium silicate solution, and the molar ratio of SiO2 to Na2O in the sodium silicate solution is adjusted to 1.5 - 1.8 by sodium hydroxide.
[0014] By adopting the above technical solution, when the molar ratio of SiO2 to Na2O in the sodium silicate solution is 1.5 - 1.8, the formed permeable concrete not only has good mechanical strength but also has good water permeability.
[0015] Optionally, the reinforcing fiber is a mixture of cellulose fiber and polyvinyl alcohol fiber in a weight ratio of (1 - 2):(8 - 9).
[0016] By adopting the above technical solution, using a mixture of cellulose fiber and polyvinyl alcohol fiber as the reinforcing fiber of the permeable concrete, on the one hand, a small amount of cellulose fiber can improve the pore structure of the permeable concrete, reduce the large pores formed by the modified recycled aggregates prepared from construction waste, and refine the pore structure in the permeable concrete, which is beneficial to improving the compactness and mechanical strength of the permeable concrete and also beneficial to improving the long-term water permeability of the permeable concrete. Secondly, compared with polyvinyl alcohol fiber, cellulose fiber can be degraded by microorganisms. After long-term use, some cellulose fibers may be decomposed by microorganisms, and then a more complex fiber microporous structure may be formed in the permeable concrete, enabling the permeable concrete to still have good water permeability after long-term use.
[0017] Optionally, the average length of the reinforcing fiber is about 6 - 10 mm.
[0018] By adopting the above technical solution, when the average length of the reinforcing fiber is in the range of 6 - 10 mm, the formed permeable concrete not only has good mechanical strength after curing but also has a good pore structure and good water permeability.
[0019] Optionally, the coupling agent is specifically a mixture of silane coupling agent KH-550 and silane coupling agent KH-570, and the mixing weight ratio of the silane coupling agent KH-550 to the silane coupling agent KH-570 is 1:(1-2).
[0020] By adopting the above technical solution, it is beneficial to comprehensively improve the compatibility of modified recycled aggregate, natural coarse aggregate, reinforcing fiber and other reinforcing fillers with the concrete paste in this system, enabling the reinforcing fillers to achieve effective adhesion and combination with the concrete paste, which is beneficial to improving the bonding strength between the reinforcing fillers and the concrete paste, and further improving the mechanical strength of the permeable concrete.
[0021] Optionally, the water reducer I is specifically a polycarboxylate water reducer.
[0022] By adopting the above technical solution, the polycarboxylate water reducer can not only reduce the water consumption of the concrete paste, but also has outstanding advantages such as low dosage, good slump retention performance, and low concrete shrinkage rate. It is beneficial to ensure that while the permeable concrete has good water permeability, it can reduce the generation of harmful large pores in the permeable concrete, which is beneficial to improving the comprehensive performance of the permeable concrete.
[0023] In the second aspect, a preparation method of high-permeability concrete prepared from construction waste provided by this application adopts the following technical solution: A preparation method of high-permeability concrete prepared from construction waste, comprising the following steps: First, fully mix cement, modified recycled aggregate, natural coarse aggregate and slag powder, then add an alkali activator, a coupling agent, a water reducer and water, continue to stir and mix for 60-90 s, and batchwise add reinforcing fibers while stirring. When the addition of the reinforcing fibers is completed, continue to stir for 20-30 s to obtain high-permeability concrete.
[0024] By adopting the above technical solution, by controlling the stirring time, it is beneficial to fully and evenly mix the various raw materials. Secondly, while batchwise adding the reinforcing fibers and stirring and mixing, it can effectively improve the dispersion uniformity of the reinforcing fibers in the permeable concrete, which is beneficial to preventing the bonding and agglomeration of the reinforcing fibers in the concrete paste, and is beneficial to further improving the mechanical strength of the permeable concrete.
[0025] In summary, the technical solution of this application has at least any one of the following beneficial effects: 1. Modifying the recycled aggregate prepared from construction waste by using diatomaceous earth, metakaolin and quicklime is not only beneficial to improving the compatibility of the recycled aggregate from construction waste with the concrete slurry, so that the modified recycled aggregate can be effectively bonded with the concrete slurry, but also beneficial to reducing harmful large pores in the prepared permeable concrete, increasing the proportion of fine pores that are effectively permeable and not easy to be clogged, which is beneficial to further improve the permeability of the permeable concrete, so that the permeable concrete can still have good permeability after long-term use.
[0026] 2. By adding reinforcing fibers mixed with cellulose fibers and polyvinyl alcohol fibers, a small amount of cellulose fibers can improve the pore structure of permeable concrete, which is beneficial to improving the compactness and mechanical strength of permeable concrete, and also to improving the long-term water permeability of permeable concrete. Secondly, some cellulose fibers may be decomposed by microorganisms after long-term use, and then form a more complex fiber microporous structure in the permeable concrete, which is beneficial to make the permeable concrete still have good water permeability after long-term use. DETAILED DESCRIPTION
[0027] The present application is further described in detail below in combination with preparation examples, embodiments and comparative examples.
[0028] The cement used is specifically PO.42.5 grade silicate cement.
[0029] The sodium silicate solution was purchased from Kening New Materials, and the specific brand was industrial grade sodium silicate solution-4, in which the mass fraction of Na2O in the sodium silicate solution of this brand was 12.8%, and the initial modulus was 2.2 (the modulus is the molar ratio of SiO2 to Na2O).
[0030] Preparation Example [Preparation Example 1] A modified recycled aggregate is prepared by the following steps: A1. The construction waste is crushed, washed, impurity-removed and sieved for multiple times to obtain recycled aggregate with an average particle size of less than 20 mm; the recycled aggregate is fully mixed with diatomaceous earth in a weight ratio of 1:0.6, and then placed at 850° C. for continuous calcination for 3 hours to obtain mixed recycled aggregate; metakaolin and quicklime are fully mixed in a weight ratio of 1:0.1 to obtain a mixed powder, and then the mixed powder, water reducer II and water are fully mixed and stirred in a weight ratio of 1:0.05:0.55 to obtain a modified slurry; The water reducer II is a sulfonated melamine water reducer, and the specific brand is Melment F10.
[0031] A2. Take 100 kg of mixed recycled aggregate and 400 kg of modified slurry and mix them evenly for 30 minutes. Filter under reduced pressure and dry the filter residue. Let the filter residue stand for 24 hours, then simply crush and sieve the filter residue to obtain modified recycled coarse aggregate with an average particle size of 4.75-13.2 mm and secondary aggregate with an average particle size of less than 4.75 mm. The secondary aggregate is further crushed and ground until its average particle size is less than 1 mm to obtain modified recycled fine aggregate.
[0032] A3. The modified recycled coarse aggregate obtained in step A2 is fully mixed with the modified recycled fine aggregate in a weight ratio of 2:1 to obtain modified recycled aggregate.
[0033] [Preparation Example 2] A modified recycled aggregate is prepared by the following steps: A1. The construction waste is crushed, washed, impurity-removed and sieved for multiple times to obtain recycled aggregate with an average particle size of less than 20 mm; the recycled aggregate is fully mixed with diatomaceous earth in a weight ratio of 1:0.4, and then placed at 900°C for continuous calcination for 2 hours to obtain mixed recycled aggregate; metakaolin and quicklime are fully mixed in a weight ratio of 1:0.2 to obtain a mixed powder, and then the mixed powder, water reducer II and water are fully mixed and stirred in a weight ratio of 1:0.055:0.4 to obtain a modified slurry; The water reducer II is a sulfonated melamine water reducer, and the specific brand is Melment F10.
[0034] A2, take 100kg of mixed recycled aggregate and 400kg of modified slurry and mix them evenly for 30min, filter under reduced pressure and dry the filter residue, let the filter residue stand for 24h, then simply crush and sieve the filter residue to obtain modified recycled coarse aggregate with an average particle size of 4.75-13.2mm and secondary aggregate with an average particle size of less than 4.75mm, further crush and grind the secondary aggregate until its average particle size is less than 1mm, and obtain modified recycled fine aggregate; A3. The modified recycled coarse aggregate obtained in step A2 is fully mixed with the modified recycled fine aggregate in a weight ratio of 4:1 to obtain modified recycled aggregate.
[0035] [Preparation Example 3] A modified recycled aggregate, which is different from [Preparation Example 1] in that the mixing weight ratio of modified recycled coarse aggregate and modified recycled fine aggregate in the modified recycled aggregate is different.
[0036] In this preparation example, the modified recycled aggregate is prepared by mixing modified recycled coarse aggregate and modified recycled fine aggregate in a weight ratio of 4:1.
[0037] [Preparation Example 4] A modified recycled aggregate, which is different from [Preparation Example 1] in that the modified recycled aggregate does not contain modified recycled fine aggregate.
[0038]
Preparation Example 5
[0039] In this preparation example, in step A1, the recycled aggregate is directly taken and placed at 850 °C for high-temperature calcination to obtain calcined recycled aggregate, and in step A2, 20 kg of the calcined recycled aggregate is taken and mixed evenly with 80 kg of the modified slurry.
[0040]
Preparation Example 6
[0041] In this preparation example, in step A2, 100 kg of the mixed recycled aggregate is directly taken and stirred and mixed with 400 kg of water, and then the filter residue is subjected to reduced-pressure filtration and drying. Example
[0042]
Example 1
[0043] Among them, the modified recycled aggregate is specifically a modified mixed recycled aggregate prepared in [Preparation Example 1], the natural coarse aggregate is specifically crushed stone with an average particle size of 9.5 - 16 mm, the alkali activator is specifically a sodium silicate solution, and the modulus of the sodium silicate solution is adjusted to 1.5 by using sodium hydroxide. The water reducer I is a polycarboxylate water reducer, specifically the PCA-I series of Jiangsu Sobute New Materials Co., Ltd.
[0044] Among them, the reinforcing fiber is specifically composed of cellulose fiber and polyvinyl alcohol fiber mixed in a weight ratio of 1:9. That is, in this example, the reinforcing fiber includes 0.045 kg of cellulose fiber and 0.405 kg of polyvinyl alcohol fiber. And in this example, the average length of the reinforcing fiber is 6 mm.
[0045] Among them, the coupling agent is specifically composed of silane coupling agent KH-550 and silane coupling agent KH-570 mixed in a weight ratio of 1:1. That is, in this example, the coupling agent includes 2.5 kg of silane coupling agent KH-550 and 2.5 kg of silane coupling agent KH-570.
[0046] A preparation method of a highly permeable concrete, comprising the following steps: First, thoroughly dry-mix cement, modified recycled aggregate, natural coarse aggregate, and slag powder for 10 s, then add an alkali activator, coupling agent, water reducer I, and water, and continue stirring for 60 s. While stirring, add reinforcing fibers in multiple batches. After the addition of the reinforcing fibers is completed, continue stirring for 20 s to obtain highly permeable concrete.
[0047]
Example 2
[0048] Among them, the modified recycled aggregate is specifically a modified mixed recycled aggregate prepared in
Preparation Example 2
[0049] Among them, the reinforcing fibers are specifically composed of cellulose fibers and polyvinyl alcohol fibers mixed in a weight ratio of 2:8. That is, in this example, the reinforcing fibers include 0.14 kg of cellulose fibers and 0.56 kg of polyvinyl alcohol fibers. Moreover, in this example, the average length of the reinforcing fibers is 10 mm.
[0050] Among them, the coupling agent is specifically composed of silane coupling agent KH-550 and silane coupling agent KH-570 mixed in a weight ratio of 1:2. That is, in this example, the coupling agent includes 2 kg of silane coupling agent KH-550 and 4 kg of silane coupling agent KH-570.
[0051] A method for preparing a highly permeable concrete, comprising the following steps: First, thoroughly dry-mix cement, modified recycled aggregate, natural coarse aggregate, and slag powder for 10 s, then add an alkali activator, coupling agent, water reducer I, and water, and continue stirring for 90 s. While stirring, add reinforcing fibers in multiple batches. After the addition of the reinforcing fibers is completed, continue stirring for 30 s to obtain highly permeable concrete.
[0052]
Example 3
Example 1
[0053] In this example, the modified recycled aggregate is specifically a modified recycled aggregate prepared in
Preparation Example 3
[0054]
Example 4
[0055] In this embodiment, the modified recycled aggregate is specifically selected as a kind of modified recycled aggregate prepared in [Preparation Example 4].
[0056]
Example 5
[0057] In this embodiment, the modulus of the sodium silicate solution selected as the alkali activator is adjusted to 1.8 by sodium hydroxide.
[0058]
Example 6
[0059] In this embodiment, the modulus of the sodium silicate solution selected as the alkali activator is adjusted to 1.2 by sodium hydroxide.
[0060]
Example 7
[0061] In this embodiment, the reinforcing fiber is specifically composed of cellulose fiber and polyvinyl alcohol fiber mixed in a weight ratio of 2:8, that is, in this embodiment, the reinforcing fiber includes 0.09 kg of cellulose fiber and 0.36 kg of polyvinyl alcohol fiber.
[0062]
Example 8
[0063] In this embodiment, the average length of the reinforcing fiber is 10 mm.
[0064] Comparative example
Comparative Example 1
[0065] In this comparative example, the modified recycled concrete is replaced equally with the recycled aggregate prepared in step A1 of [Preparation Example 1], wherein the recycled aggregate still needs to be crushed and screened to obtain recycled coarse aggregate with a particle size in the range of 4.75 - 13.2 mm and recycled fine aggregate with a particle size less than 1 mm, and the added recycled aggregate needs to be mixed by the recycled coarse aggregate and the recycled fine aggregate in a weight ratio of 2:1.
[0066]
Comparative Example 2
[0067] In this comparative example, the modified recycled aggregate is specifically selected as a kind of modified recycled aggregate prepared in [Preparation Example 5].
[0068] [Comparative Example 3] A kind of pervious concrete, which is different from [Example 1] in the modified recycled aggregate.
[0069] In this comparative example, the modified recycled aggregate is specifically selected as a kind of modified recycled aggregate prepared in [Preparation Example 6].
[0070] Performance test data Preparation of samples to be tested: Pour the concrete prepared in Examples 1-8 and Comparative Examples 1-3 into standard cube specimens with side lengths of 150mm * 150mm * 150mm according to the requirements of Chapter 4 in the "Standard Test Method for Mechanical Properties of Ordinary Concrete" (GB / T 50081-2020), and cure for 28 days. If there are special specimen sizes for the following tests, prepare them according to the specimen shapes and sizes required for the tests, and cure for 28 days.
[0071] 1. Detection of water permeability coefficient: Refer to Appendix C in the "Pervious Pavement Bricks and Pervious Road Panels" (GB / T 25993-2023) for detection, and record the water permeability coefficient (mm / s) of the pervious concrete specimens prepared in each example and comparative example at the standard temperature, where the standard temperature is 15°C.
[0072] 2. Test of long-term water permeability performance: Place the pervious concrete specimens prepared in each example and comparative example on the outdoor ground, and they can be normally exposed to sunlight, wind, and rain. Store them outdoors for 6 months. After the storage time, clean them, and then dry them and conduct the water permeability coefficient test again.
[0073] 3. Compressive strength: Refer to Section 5 in the "Standard Test Method for Physical and Mechanical Properties of Concrete" (GB / T 50081-2002) for detection, and record the compressive strength (MPa) of the pervious concrete prepared in each example and comparative example.
[0074] 4. Continuous porosity: Refer to Appendix B in the "Technical Specification for Pervious Cement Concrete Pavement" (CJJ / T 135-2009, 2023 Edition) for detection, and record the continuous porosity (%) of the pervious concrete prepared in each example and comparative example.
[0075] Table 1 Partial performance data of pervious concrete Combining Example 1 with Comparative Examples 1-3 and referring to the data in Table 1, it can be seen that under the same water-cement ratio, in Example 1, diatomite, metakaolin and quicklime were used to modify the recycled aggregate prepared from construction waste, and the modified recycled aggregate was added to the cement concrete. The prepared permeable concrete can have compressive strength, and the permeability index and porosity are relatively medium, predicting that the long-term permeability performance of the permeable concrete is good. This may be because the diatomite that is fully mixed and calcined with the construction waste recycled aggregate can generate a gelling material in water with metakaolin and quicklime and fully adhere to fill the internal and external pores of the construction waste recycled aggregate. This not only improves the overall frost resistance, shrinkage, creep or water absorption and other properties of the construction waste recycled aggregate, enhances the compatibility between the construction waste recycled aggregate and the concrete paste, enabling the modified recycled aggregate to achieve effective bonding with the concrete paste, and thus making the permeable concrete have good performance; moreover, through the adhesion and filling of diatomite, the pore structure on the surface of the construction waste recycled aggregate is greatly improved, the harmful large pore structure in the recycled aggregate is reduced, and at the same time, the proportion of harmful large pores in the prepared permeable concrete is reduced, and the fine pores that can effectively permeate water and are not easily blocked increase, which is beneficial to further improving the permeability performance of the permeable concrete, so that the permeable concrete can still have good permeability performance after long-term use.
[0076] Specifically, comparing Example 1 with Comparative Example 1, it can be seen that in Comparative Example 1, unmodified construction waste recycled aggregate was added. Although the prepared permeable concrete has a high porosity and excellent permeability coefficient, its compressive strength is very low and does not meet the national standard requirements; comparing Example 1 with Comparative Example 2, it can be seen that in Comparative Example 2, only metakaolin and quicklime were used to generate a gelling substance in water to modify the surface of the construction waste recycled aggregate. Although it can initially improve the compatibility between the construction waste recycled aggregate and the concrete paste and increase the compressive strength of the permeable concrete, it still causes more harmful large pores to be generated in the permeable concrete. Therefore, its porosity and permeability index are still in a relatively high range. Comparing Example 1 with Comparative Example 3, it can be seen that in Comparative Example 3, only diatomite was simply mixed with the construction waste recycled aggregate and soaked in water. Then this modification method is just equivalent to directly adding unmodified recycled aggregate and diatomite to the cement concrete. Although diatomite can improve the pore structure of the permeable concrete to a certain extent and can appropriately reduce the generation of large harmful pores, it fails to solve the problem of poor compatibility between the construction waste recycled aggregate and the cement concrete and the inability to generate effective bonding. Therefore, the compressive strength of the permeable concrete is still in a relatively low range.
[0077] Combining Example 1 with Examples 3 - 4 and considering the data in Table 1, it can be seen that as the proportion of modified recycled coarse aggregate in the modified recycled aggregate increases, the permeability index and porosity of the permeable concrete will increase accordingly, while the compressive strength of the permeable concrete will decrease. In order to maintain good compressive strength of the permeable concrete and reduce the proportion of harmful large pores, it is recommended that the mixing weight ratio of modified recycled coarse aggregate to modified recycled fine aggregate in the modified recycled aggregate be (2 - 4):1, and the pore structure of the permeable concrete can be further improved by the modified recycled fine aggregate.
[0078] Combining Example 3 with Examples 5 - 6 and considering the data in Table 1, it can be seen that when the modulus of the sodium silicate solution in the alkali activator is adjusted from 1.5 to 1.8, the compressive strength of the permeable concrete decreases accordingly, but the permeability coefficient and porosity increase slightly; when the modulus of the sodium silicate solution in the alkali activator is further decreased from 1.5 to 1.2, the compressive strength of the permeable concrete drops sharply, and the drop amplitude is larger than that when the modulus is increased from 1.5 to 1.8. At the same time, the permeability coefficient and porosity of the permeable concrete decrease. This may be because the modulus of the sodium silicate solution in the alkali activator is specifically the ratio of SiO 2 to Na 2 O. When the modulus of the sodium silicate solution is higher than 1.5, as the modulus increases, the proportion of Na2O decreases, and the amount of OH - produced by the hydrolysis of the sodium silicate solution will gradually decrease, making it difficult to stimulate the decomposition of cement and slag powder. It may cause the formed pore structure to become larger and the porosity to become higher. And SiO4 4- also has a too high concentration, increasing its own polymerization degree and making it difficult to react with Ca 2+ and other ions. Therefore, it may lead to a decrease in the strength of the formed hydration products and a decrease in the compressive strength of the permeable concrete; when the modulus of the sodium silicate solution is lower than 1.5, although the proportion of Na2O is high, a large amount of OH - can promote the decomposition of cement and slag powder, which will further improve the fluidity of the concrete paste, make the pore structure further shrink and the porosity decrease. However, due to the low proportion of SiO4 4- , the double excitation becomes single excitation. Therefore, it may also lead to the low strength of the formed hydration products, which will affect the compressive strength of the permeable concrete.
[0079] Combining Example 3 with Examples 7 - 8 and considering the data in Table 1, it can be seen that when the proportion of cellulose fibers in the reinforcing fibers increases, the compressive strength and porosity of the permeable concrete change little, but its permeability coefficient and the permeability performance after long - term placement are significantly improved. This may be because cellulose fibers can improve the pore structure of the permeable concrete, increasing the proportion of effective fine pores in the permeable concrete, thereby enhancing the water permeability of the permeable concrete. In addition, cellulose fibers can be degraded by microorganisms. After long - term placement and use, some cellulose fibers may be degraded by the environment or microorganisms that penetrate into the concrete with water, and a more complex fiber microporous structure is formed in the permeable concrete. Therefore, it can still have good water permeability performance after long - term placement, and the decline rate of its permeability coefficient is reduced. In addition, when the average length of the reinforcing fibers increases to 10 mm, the compressive strength of the permeable concrete increases slightly, while its permeability coefficient and porosity both decrease.
[0080] This specific embodiment is only an interpretation of the present application, and it does not limit the present application. Those skilled in the art can make non - creative modifications to this specific embodiment as needed after reading this specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.
Claims
1. A highly permeable concrete prepared from construction waste, characterized in that: It includes the following raw materials in parts by weight: Cement: 300-360 parts; Modified recycled aggregate: 750-900 parts; Natural coarse aggregate: 500-600 parts; Slag powder: 100-160 parts; Alkali activator: 50-75 parts; Reinforcement fiber: 4.5-7 parts; Coupling agent: 50-60 parts; Water reducing agent I: 1.8-2.4 parts; Water: 126-160 parts; The modified recycled aggregate is prepared by mixing and modifying recycled aggregate including diatomaceous earth, metakaolin and quicklime, and the recycled aggregate is obtained by repeatedly crushing and screening construction waste.
2. The highly permeable concrete prepared from construction waste according to claim 1, characterized in that: The modified recycled aggregate includes modified recycled coarse aggregate with an average particle size of 4.75-13.2 mm and modified recycled fine aggregate with an average particle size of less than 1 mm, and the mixing weight ratio of the modified recycled coarse aggregate to the modified recycled fine aggregate is (2-4):
1.
3. The highly permeable concrete prepared from construction waste according to claim 2, characterized in that: The preparation method of the modified recycled aggregate comprises the following steps: A1. The construction waste is crushed, cleaned, impurity-removed and sieved for multiple times to obtain recycled aggregate with an average particle size of less than 20 mm; the recycled aggregate is fully mixed with diatomaceous earth, and then placed at 850-900° C. for continuous calcination for 2-3 hours to obtain mixed recycled aggregate; metakaolin and quicklime are fully mixed to obtain a mixed powder, and then the mixed powder, water reducer II and water are fully mixed and stirred to obtain a modified slurry; A2, the mixed recycled aggregate obtained in step A1 and the modified slurry are uniformly mixed in a weight ratio of 1:4, and the filter residue is filtered under reduced pressure and dried, and the filter residue is allowed to stand for not less than 24 hours, and then the filter residue is simply crushed and sieved to obtain modified recycled coarse aggregate with an average particle size of 4.75-13.2 mm and secondary aggregate with an average particle size of less than 4.75 mm, and the secondary aggregate is further crushed and ground until its average particle size is less than 1 mm to obtain modified recycled fine aggregate; A3. The modified recycled coarse aggregate obtained in step A2 is fully mixed with the modified recycled fine aggregate in a weight ratio of (2-4):1 to obtain modified recycled aggregate.
4. The highly permeable concrete prepared from construction waste according to claim 3, characterized in that: In the step A1, the mixing weight ratio of the recycled aggregate to the diatomaceous earth is 1:(0.4-0.6); the mixing weight ratio of the metakaolin to the quicklime is 1:(0.1-0.2), and the mixing weight ratio of the mixed powder, the water reducer II and water is 1:(0.05-0.055):(0.4-0.55), wherein the alkaline water agent II is a sulfonated melamine type water reducer.
5. The highly permeable concrete prepared from construction waste according to claim 1, characterized in that: The alkaline activator is a sodium silicate solution, wherein the molar ratio of SiO2 to Na2O in the sodium silicate solution is adjusted to 1.5-1.8 by sodium hydroxide.
6. The highly permeable concrete prepared from construction waste according to claim 1, characterized in that: The reinforcing fibers are cellulose fibers and polyvinyl alcohol fibers mixed in a weight ratio of (1-2): (8-9).
7. The highly permeable concrete prepared from construction waste according to claim 6, characterized in that: The average length of the reinforcing fibers is 6-10 mm.
8. The highly permeable concrete prepared from construction waste according to claim 1, characterized in that: The coupling agent is specifically a mixture of silane coupling agent KH-550 and silane coupling agent KH-570, and the mixing weight ratio of the silane coupling agent KH-550 to the silane coupling agent KH-570 is 1:(1-2).
9. The highly permeable concrete prepared from construction waste according to claim 1, characterized in that: The water reducer I is specifically a polycarboxylic acid water reducer.
10. The method for preparing highly permeable concrete from construction waste according to any one of claims 1 to 9, characterized in that: The following steps are involved: First, cement, modified recycled aggregate, natural coarse aggregate and slag powder are fully mixed, and then alkali activator, coupling agent, water reducer and water are added, and stirring is continued for 60-90s. Reinforcing fibers are added in batches while stirring. After the reinforcing fibers are added, stirring is continued for 20-30s to obtain highly permeable concrete.