Method for preparing high performance concrete using construction waste recycled aggregate

Abstract

The application provides a method for preparing high-performance concrete by using construction waste recycled aggregate, comprising the following steps: S1, preparation of recycled coarse aggregate: taking waste concrete blocks, crushing into old concrete particles, and screening; treating carbon nanotubes with chitosan to obtain modified carbon nanotubes; adding the modified carbon nanotubes and methoxypropyl trimethoxysilane into the old concrete particles, stirring uniformly, and drying to obtain the recycled coarse aggregate; S2, preparation of powder: mixing the recycled coarse aggregate prepared in step S1 and fine aggregate to obtain the powder; S3, preparation of concrete: treating palm fibers with chitosan to obtain modified palm fibers; taking water, adding water reducing agent, cement, slag powder, palm ash, methoxypropyl trimethoxysilane and the modified palm fibers, and then adding the powder prepared in step S2, stirring uniformly, and obtaining the concrete. The method can significantly improve the compressive performance, splitting tensile performance and antibacterial performance of the concrete.

Description

Technical Field

[0001] This invention relates to the field of concrete preparation technology, and more specifically to a method for preparing high-performance concrete using recycled aggregates from construction waste. Background Technology

[0002] Construction waste mainly comes from waste and scrap generated during building construction, demolition, and urban infrastructure renovation. The large amount of construction waste generated puts great pressure on the urban environment and resource utilization. The application of recycled aggregates from construction waste helps reduce the emission of construction waste, reduce the environmental impact of the construction industry, and promote resource recycling.

[0003] Recycled aggregates from construction waste typically include crushed concrete, bricks, and tiles. These recycled aggregates can be used as concrete aggregates after appropriate processing. However, the crushing process causes numerous microcracks within the recycled aggregates due to accumulated damage, resulting in high porosity, high water absorption, low bulk density, and high crushing index, which differs from virgin materials. To improve the performance of recycled aggregates, it is necessary to modify the low-quality recycled aggregates obtained through simple crushing. How to modify recycled aggregates from construction waste to improve various properties of concrete is an urgent problem to be solved in this field. Summary of the Invention

[0004] In view of this, the present invention proposes a method for preparing high-performance concrete using recycled aggregates from construction waste, which can significantly improve the compressive strength, splitting tensile strength and antibacterial properties of concrete.

[0005] The technical solution of this invention is implemented as follows:

[0006] This invention provides a method for preparing high-performance concrete using recycled aggregates from construction waste, comprising the following steps:

[0007] S1. Preparation of recycled coarse aggregate: Take waste concrete blocks, crush them into old concrete particles, and sieve them; treat carbon nanotubes with chitosan to obtain modified carbon nanotubes; add the modified carbon nanotubes and methoxypropyltrimethoxysilane together to the old concrete particles, stir evenly, dry, and obtain recycled coarse aggregate.

[0008] S2. Preparation of powder: The recycled coarse aggregate and fine aggregate obtained in step S1 are mixed to prepare powder;

[0009] S3. Concrete preparation: Treat palm fibers with chitosan to obtain modified palm fibers; take water, add water-reducing agent, cement, slag powder, palm ash, methoxypropyltrimethoxysilane and modified palm fibers, then add the powder obtained in step S2, stir evenly to obtain concrete.

[0010] To further explain, in step S1, the particles are sieved using screens with apertures of 5mm and 20mm respectively. Particles larger than 20mm are further crushed until they are no larger than 20mm. Old concrete particles with a particle size of 5-20mm are selected.

[0011] To further explain, the preparation method of modified carbon nanotubes in step S1 includes the following steps:

[0012] S1-1. Chitosan is dissolved in acetic acid solution to obtain chitosan solution. The mass ratio of chitosan, acetic acid and water is 1:1:100.

[0013] S1-2. Carbon nanotubes were added to chitosan solution and reacted at 30-35℃ for 68 hours. The mixture was then filtered and dried to obtain modified carbon nanotubes.

[0014] The carbon nanotubes have an outer diameter of 4-8 nm and a length of 10-20 μm; the mass ratio of carbon nanotubes to chitosan is 1:3.

[0015] To further explain, in step S1, 5-8 parts by weight of modified carbon nanotubes and 0.2-0.4 parts by weight of methoxypropyltrimethoxysilane are added to 120-150 parts of old concrete particles, stirred evenly, and dried to obtain recycled coarse aggregate.

[0016] To further explain, in step S2, 120-150 parts by weight of recycled coarse aggregate and 100-130 parts by weight of fine aggregate are mixed to obtain powder; wherein the fine aggregate is river sand with a fineness modulus of 2.0-2.5.

[0017] To further explain, the preparation method of modified palm fiber in step S3 includes the following steps:

[0018] S3-1. Dissolve chitosan in acetic acid solution to obtain chitosan solution. The mass ratio of chitosan, acetic acid and water is 1:1:100.

[0019] S3-2. Immerse palm fibers in chitosan solution, soak for 3 hours and then dry to obtain modified palm fibers;

[0020] The palm fiber has a length of 20-30 mm and a diameter of 0.1-0.3 mm; the mass ratio of palm fiber to chitosan is 1:3.

[0021] To further explain, in step S3, by weight, take 30-40 parts of water, add 0.5-1 parts of water-reducing agent, 60-80 parts of cement, 20-30 parts of slag powder, 10-15 parts of palm ash, 0.025-0.05 parts of methoxypropyltrimethoxysilane and 0.5-1 parts of modified palm fiber, and then add 220-280 parts of the powder obtained in step S2, mix evenly, and obtain concrete.

[0022] To further explain, the palm ash in step S3 is palm ash with a particle size of 70-80μm and a silica content of 40-50%wt, collected after burning palm shells.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] (1) In this invention, carbon nanotubes are a high-strength and high-rigidity nanomaterial, and palm fibers have good toughness and tensile properties. Chitosan-modified carbon nanotubes and palm fibers have good bactericidal effects, effectively inhibiting the growth of various microorganisms inside concrete, thus giving concrete good antibacterial properties. In the chitosan modification step, the acidified carbon nanotubes and palm fibers have more active sites. Methoxypropyltrimethoxysilane can improve the dispersibility of modified carbon nanotubes and modified palm fibers, and at the same time react with the active groups on the modified carbon nanotubes and modified palm fibers to enhance the adhesion of modified carbon nanotubes in the cracks of recycled coarse aggregates and modified palm fibers in the cracks of concrete. The overall effect is to improve the compressive strength, splitting tensile strength and antibacterial properties of concrete.

[0025] (2) The fine particles in the palm ash of the present invention can fill the micropores in concrete and reduce the voids inside the concrete; the palm ash and modified palm fiber are compounded. After the palm ash and modified palm fiber are wetted with water, the palm ash slowly loses water in the hydration reaction, while the modified palm fiber slowly absorbs water and expands in volume. This is used to fill the cracks in the concrete and improve the compressive strength, splitting tensile strength and antibacterial properties of the concrete.

[0026] (3) In this invention, carbon nanotubes and palm ash are porous materials with large surface area and pore structure, and the concrete prepared can adsorb harmful gases.

[0027] (4) This invention uses waste concrete blocks to prepare recycled coarse aggregate. The slag powder, palm ash and palm fiber added later are also waste materials that are inexpensive and turn waste into treasure, which is of great significance to environmental protection. Detailed Implementation

[0028] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention.

[0029] Unless otherwise specified, the experimental methods used in the embodiments of this invention are all conventional methods.

[0030] Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.

[0031] In this embodiment of the invention, the carbon nanotubes have an outer diameter of 4-8 nm and a length of 10-20 μm; the fine aggregate is river sand with a fineness modulus of 2.0-2.5; the palm fiber has a length of 20-30 mm and a diameter of 0.1-0.3 mm; the water-reducing agent is a polycarboxylate high-efficiency water-reducing agent with a water reduction rate of 30%-45%; the cement is P.O42.5 silicate cement; the slag powder is S95 grade slag powder; and the palm ash is palm ash with a particle size of 70-80 μm and a silica content of 40-50% wt, collected after burning palm shells.

[0032] Example 1

[0033] A method for preparing high-performance concrete using recycled aggregates from construction waste includes the following steps:

[0034] S1. Preparation of recycled coarse aggregate: Take waste concrete blocks, crush them into old concrete particles, and sieve out old concrete particles of 5-20mm; treat carbon nanotubes with chitosan to obtain modified carbon nanotubes; add 50g of modified carbon nanotubes and 2g of methoxypropyltrimethoxysilane to 1200g of old concrete particles, stir evenly, and dry for 100-120min to obtain recycled coarse aggregate.

[0035] S2. Preparation of powder: Take 1200g of the recycled coarse aggregate obtained in step S1 and mix it with 1000g of river sand to prepare powder.

[0036] S3. Concrete preparation: Treat palm fibers with chitosan to obtain modified palm fibers; take 300g of water, add 5g of polycarboxylate superplasticizer, 600g of P.O42.5 silicate cement, 200g of S95 grade slag powder, 100g of palm ash, 0.25g of methoxypropyltrimethoxysilane and 5g of modified palm fibers, and then add 2200g of the powder obtained in step S2, stir evenly, and obtain concrete.

[0037] The preparation method of modified carbon nanotubes includes the following steps:

[0038] S1-1. Chitosan is dissolved in acetic acid solution to obtain chitosan solution. The mass ratio of chitosan, acetic acid and water is 1:1:100.

[0039] S1-2. Carbon nanotubes were added to chitosan solution and reacted at 30°C for 6 hours. The mixture was then filtered and dried for 60 minutes to obtain modified carbon nanotubes.

[0040] The mass ratio of carbon nanotubes to chitosan is 1:3.

[0041] The method for preparing modified palm fiber includes the following steps:

[0042] S3-1. Dissolve chitosan in acetic acid solution to obtain chitosan solution. The mass ratio of chitosan, acetic acid and water is 1:1:100.

[0043] S3-2. Immerse palm fibers in chitosan solution, soak for 3 hours and then dry to obtain modified palm fibers;

[0044] The mass ratio of palm fiber to chitosan is 1:3.

[0045] Example 2

[0046] A method for preparing high-performance concrete using recycled aggregates from construction waste includes the following steps:

[0047] S1. Preparation of recycled coarse aggregate: Take waste concrete blocks, crush them into old concrete particles, and sieve out old concrete particles of 5-20mm; treat carbon nanotubes with chitosan to obtain modified carbon nanotubes; add 60g of modified carbon nanotubes and 3g of methoxypropyltrimethoxysilane to 1400g of old concrete particles, stir evenly, and dry for 100-120min to obtain recycled coarse aggregate.

[0048] S2. Preparation of powder: Take 1400g of the recycled coarse aggregate obtained in step S1 and mix it with 1200g of river sand to prepare powder.

[0049] S3. Concrete preparation: Treat palm fibers with chitosan to obtain modified palm fibers; take 350g of water, add 7g of polycarboxylate superplasticizer, 700g of P.O42.5 silicate cement, 250g of S95 grade slag powder, 120g of palm ash, 0.35g of methoxypropyltrimethoxysilane and 8g of modified palm fibers, and then add 2600g of the powder obtained in step S2, stir evenly, and obtain concrete.

[0050] The preparation method of modified carbon nanotubes includes the following steps:

[0051] S1-1. Chitosan is dissolved in acetic acid solution to obtain chitosan solution. The mass ratio of chitosan, acetic acid and water is 1:1:100.

[0052] S1-2. Add carbon nanotubes to chitosan solution, react at 32℃ for 7h, filter, and dry for 60min to obtain modified carbon nanotubes.

[0053] The mass ratio of carbon nanotubes to chitosan is 1:3.

[0054] The method for preparing modified palm fiber includes the following steps:

[0055] S3-1. Dissolve chitosan in acetic acid solution to obtain chitosan solution. The mass ratio of chitosan, acetic acid and water is 1:1:100.

[0056] S3-2. Immerse palm fibers in chitosan solution, soak for 3 hours and then dry to obtain modified palm fibers;

[0057] The mass ratio of palm fiber to chitosan is 1:3.

[0058] Example 3

[0059] A method for preparing high-performance concrete using recycled aggregates from construction waste includes the following steps:

[0060] S1. Preparation of recycled coarse aggregate: Take waste concrete blocks, crush them into old concrete particles, and sieve out old concrete particles of 5-20mm; treat carbon nanotubes with chitosan to obtain modified carbon nanotubes; add 80g of modified carbon nanotubes and 4g of methoxypropyltrimethoxysilane to 1500g of old concrete particles, stir evenly, and dry for 100-120min to obtain recycled coarse aggregate.

[0061] S2. Preparation of powder: Take 1500g of the recycled coarse aggregate obtained in step S1 and mix it with 1300g of river sand to prepare powder.

[0062] S3. Concrete preparation: Treat palm fibers with chitosan to obtain modified palm fibers; take 400g of water, add 10g of polycarboxylate superplasticizer, 800g of P.O42.5 silicate cement, 300g of S95 grade slag powder, 150g of palm ash, 0.5g of methoxypropyltrimethoxysilane and 10g of modified palm fibers, then add 2800g of the powder obtained in step S2, stir evenly, and obtain concrete.

[0063] The preparation method of modified carbon nanotubes includes the following steps:

[0064] S1-1. Chitosan is dissolved in acetic acid solution to obtain chitosan solution. The mass ratio of chitosan, acetic acid and water is 1:1:100.

[0065] S1-2. Add carbon nanotubes to chitosan solution, react at 35℃ for 8 hours, filter, and dry for 60 minutes to obtain modified carbon nanotubes.

[0066] The mass ratio of carbon nanotubes to chitosan is 1:3.

[0067] The method for preparing modified palm fiber includes the following steps:

[0068] S3-1. Dissolve chitosan in acetic acid solution to obtain chitosan solution. The mass ratio of chitosan, acetic acid and water is 1:1:100.

[0069] S3-2. Immerse palm fibers in chitosan solution, soak for 3 hours and then dry to obtain modified palm fibers;

[0070] The mass ratio of palm fiber to chitosan is 1:3.

[0071] Comparative Example 1

[0072] A method for preparing high-performance concrete using recycled aggregates from construction waste includes the following steps:

[0073] S1. Preparation of recycled coarse aggregate: Take waste concrete blocks, crush them into old concrete particles, and sieve out old concrete particles of 5-20mm; add 80g carbon nanotubes and 4g methoxypropyltrimethoxysilane to 1500g old concrete particles, stir evenly, and dry for 100-120min to obtain recycled coarse aggregate.

[0074] S2. Preparation of powder: Take 1500g of the recycled coarse aggregate obtained in step S1 and mix it with 1300g of river sand to prepare powder.

[0075] S3. Concrete preparation: Take 400g of water, add 10g of polycarboxylate superplasticizer, 800g of P.O42.5 silicate cement, 300g of S95 grade slag powder, 150g of palm ash, 0.5g of methoxypropyltrimethoxysilane and 10g of palm fiber, and then add 2800g of the powder obtained in step S2. Stir evenly to obtain concrete.

[0076] Comparative Example 2

[0077] A method for preparing high-performance concrete using recycled aggregate from construction waste differs from Example 3 in the following aspects: S1. Preparation of recycled coarse aggregate: Take waste concrete blocks, crush them into old concrete particles, sieve out old concrete particles of 5-20mm, stir evenly, and dry for 100-120 minutes to obtain recycled coarse aggregate. The remaining steps are the same as in Example 3.

[0078] Comparative Example 3

[0079] A method for preparing high-performance concrete using recycled aggregates from construction waste differs from Example 3 in that methoxypropyltrimethoxysilane is not added in step S1. The remaining steps are the same as in Example 3.

[0080] Comparative Example 4

[0081] A method for preparing high-performance concrete using recycled aggregate from construction waste differs from Example 3 in the following aspects: S1. Preparation of recycled coarse aggregate: Take waste concrete blocks, crush them into old concrete particles, sieve out old concrete particles of 5-20mm, add 4g of methoxypropyltrimethoxysilane to 1500g of old concrete particles, stir evenly, and dry for 100-120min to obtain recycled coarse aggregate. The remaining steps are the same as in Example 3.

[0082] Comparative Example 5

[0083] A method for preparing high-performance concrete using recycled aggregates from construction waste differs from Example 3 in that methoxypropyltrimethoxysilane is not added in step S3. The remaining steps are the same as in Example 3.

[0084] Comparative Example 6

[0085] A method for preparing high-performance concrete using recycled aggregates from construction waste differs from Example 3 in the following steps: S3, Concrete preparation: Take 400g of water, add 10g of polycarboxylate superplasticizer, 800g of P.O42.5 silicate cement, 300g of S95 grade slag powder, 150g of palm ash, and then add 2800g of the powder obtained in step S2. Stir evenly to obtain concrete. The remaining steps are the same as in Example 3.

[0086] Comparative Example 7

[0087] A method for preparing high-performance concrete using recycled aggregates from construction waste, differing from Example 3 in that palm ash is not added in step S3. The remaining steps are the same as in Example 3.

[0088] Performance testing

[0089] 1. Compressive strength: Referring to GB / T50081-2002 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete", several standard cubic test blocks with a side length of 150mm were made, cured at room temperature for 28 days, and compressive strength was tested. The experimental results are shown in Table 1.

[0090] 2. Splitting tensile strength: Referring to GB / T50081-2002 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete", several standard test blocks with a size of 150mm*150mm*600mm were made, cured at room temperature for 28 days, and the splitting tensile strength was tested. The experimental results are shown in Table 1.

[0091] 3. Antibacterial performance: The antibacterial performance was tested using the microbial corrosion test method in patent authorization announcement number CN1307120C. The sample block size was selected as 4cm*4cm*10cm. The corrosion depth (mm) was used to represent the antibacterial performance. The test results are shown in Table 1.

[0092] Table 1

[0093] Compressive strength (MPa) Splitting tensile strength (MPa) Corrosion depth (mm) Example 1 49.2 6.6 0.0 Example 2 49.7 6.7 0.0 Example 3 50.1 6.9 0.0 Comparative Example 1 47.3 5.9 6.2 Comparative Example 2 38.5 5.1 3.6 Comparative Example 3 40.2 4.4 3.7 Comparative Example 4 38.8 5.4 3.6 Comparative Example 5 45.5 4.9 2.1 Comparative Example 6 40.8 4.0 3.9 Comparative Example 7 42.8 4.5 0.1

[0094] As can be seen from the table above, the concrete prepared in Example 3 has the best compressive strength, splitting tensile strength, and antibacterial properties. In Example 3, both chitosan-modified carbon nanotubes and palm fibers exhibit excellent bactericidal effects, effectively inhibiting the growth of various microorganisms inside concrete, thus giving the concrete good antibacterial properties. Carbon nanotubes are high-strength, high-rigidity nanomaterials, while palm fibers possess good toughness and tensile strength. Acidified carbon nanotubes and palm fibers have more active sites. Methoxypropyltrimethoxysilane can improve the dispersibility of modified carbon nanotubes and modified palm fibers, while enhancing the adhesion of modified carbon nanotubes in cracks of recycled coarse aggregates and modified palm fibers in concrete gaps. The fine particles in palm ash can fill the micropores in concrete, reducing internal voids. When palm ash and modified palm fibers are compounded, after being wetted with water, the palm ash slowly loses water during the hydration reaction, while the modified palm fibers slowly absorb water and expand in volume, thus filling cracks in the concrete. In Example 3, the overall effect improves the compressive strength, splitting tensile strength, and antibacterial properties of concrete. Compared with Example 3, the compressive strength, splitting tensile strength and antibacterial properties of the concrete were reduced to varying degrees. Comparative Example 1, lacking the steps of chitosan-modified carbon nanotubes and palm fiber (i.e., lacking acidification treatment), exhibited the worst antibacterial performance. Comparative Example 2, without modified carbon nanotubes and methoxypropyltrimethoxysilane in step S1, showed the worst compressive strength. Comparative Example 3, without methoxypropyltrimethoxysilane in step S1, significantly reduced the dispersibility of modified carbon nanotubes and their adhesion in cracks of recycled coarse aggregate. Comparative Example 4, without modified carbon nanotubes in step S1, showed results similar to Comparative Example 2. Examples 3 and Comparative Examples 2, 3, and 4 demonstrate the synergistic effect of modified carbon nanotubes and methoxypropyltrimethoxysilane. Comparative Example 5, without methoxypropyltrimethoxysilane in step S3, significantly reduced the dispersibility of modified palm fiber and its adhesion in concrete cracks. Comparative Example 6, without modified palm fiber and methoxypropyltrimethoxysilane in step S3, showed the worst splitting tensile strength. Comparative Example 7, without palm ash, exhibited more voids within the concrete.

[0095] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing high performance concrete using construction waste recycled aggregate, characterized by, Includes the following steps: S1. Preparation of recycled coarse aggregate: Take waste concrete blocks, crush them into old concrete particles, and sieve them; treat carbon nanotubes with chitosan to obtain modified carbon nanotubes; add the modified carbon nanotubes and methoxypropyltrimethoxysilane together to the old concrete particles, stir evenly, dry, and obtain recycled coarse aggregate. S2. Preparation of powder: Mix the recycled coarse aggregate and fine aggregate obtained in step S1 to obtain powder; S3. Concrete preparation: Treat palm fibers with chitosan to obtain modified palm fibers; take water, add water-reducing agent, cement, slag powder, palm ash, methoxypropyltrimethoxysilane and modified palm fibers, then add the powder obtained in step S2, stir evenly to obtain concrete. The preparation method of modified carbon nanotubes in step S1 includes the following steps: S1-1. Dissolve chitosan in acetic acid solution to obtain chitosan solution. The mass ratio of chitosan, acetic acid and water is 1:1:

100. S1-2. Add carbon nanotubes to chitosan solution, react at 30-35℃ for 6-8 hours, filter, and dry to obtain modified carbon nanotubes. The carbon nanotubes have an outer diameter of 4-8 nm and a length of 10-20 μm; the mass ratio of carbon nanotubes to chitosan is 1:

3. In step S1, by weight, 5-8 parts of modified carbon nanotubes and 0.2-0.4 parts of methoxypropyltrimethoxysilane are added to 120-150 parts of old concrete particles, stirred evenly, and dried to obtain recycled coarse aggregate. In step S2, 120-150 parts by weight of recycled coarse aggregate and 100-130 parts by weight of fine aggregate are mixed to obtain powder; wherein the fine aggregate is river sand with a fineness modulus of 2.0-2.

5. In step S3, by weight, take 30-40 parts of water, add 0.5-1 parts of water-reducing agent, 60-80 parts of cement, 20-30 parts of slag powder, 10-15 parts of palm ash, 0.025-0.05 parts of methoxypropyltrimethoxysilane and 0.5-1 parts of modified palm fiber, and then add 220-280 parts of the powder obtained in step S2. Mix evenly to obtain concrete.

2. The method of claim 1, wherein the high performance concrete is prepared by using the recycled aggregate of construction waste. In step S1, the sieving process involves sieving to obtain old concrete particles of 5-20mm.

3. The method of claim 1, wherein the high performance concrete is prepared by using the recycled aggregate of construction waste. The preparation method of modified palm fiber in step S3 includes the following steps: S3 1. Dissolve chitosan in acetic acid solution to obtain a chitosan solution, the mass ratio of chitosan, acetic acid and water being 1:1:100; S3 2. Soak the palm fiber in the chitosan solution, dry after soaking for 3 hours to obtain the modified palm fiber. The palm fiber has a length of 20-30 mm and a diameter of 0.1-0.3 mm; the mass ratio of palm fiber to chitosan is 1:

3.

4. The method of manufacturing high performance concrete using construction waste recycled aggregates as claimed in claim 1, wherein, Palm ash in step S3 is palm shell ash with a particle size of 80 80 μm, silica content 40-50% wt.

5. Concrete obtained by the method according to any one of claims 1-4.