A freeze-thaw resistant recycled concrete and a method of manufacturing the same

Abstract

The application relates to the technical field of recycled concrete, in particular to a freeze-thaw resistant recycled concrete and a preparation method thereof. The freeze-thaw resistant recycled concrete comprises the following raw materials: Portland cement, fine aggregate, coarse aggregate, ceramsite, water, a polycarboxylate water reducing agent and an air entraining agent. The fine aggregate comprises natural fine aggregate and modified recycled fine aggregate, the weight percentage of the modified recycled fine aggregate in the fine aggregate is 20-80%, the coarse aggregate comprises natural coarse aggregate and modified recycled coarse aggregate, the weight percentage of the modified recycled coarse aggregate in the coarse aggregate is 20-80%, the modified recycled fine aggregate and the modified recycled coarse aggregate are prepared by soaking in a modified liquid, and the modified liquid comprises the following raw materials: an anionic surfactant, a non-ionic penetrant, a dimethicone emulsion, a silane coupling agent and water. The freeze-thaw resistant recycled concrete has the advantages of improving the freeze-thaw resistance of the recycled concrete.

Description

Technical Field

[0001] This application relates to the technical field of recycled concrete, and in particular to a freeze-thaw resistant recycled concrete and its preparation method. Background Technology

[0002] With the further development of urbanization, old buildings are being demolished, generating a large amount of construction waste. Recently, my country has placed increasing emphasis on the reuse of waste concrete. The sand and gravel obtained after crushing waste concrete is called recycled aggregate, which can be used in concrete preparation. However, the surface of recycled aggregate is coated with hardened cement mortar, resulting in low apparent density and high water absorption and porosity. Therefore, recycled concrete made from recycled aggregate is prone to crystallization and expansion of free water in low-temperature environments, leading to high internal expansion pressure in the recycled concrete specimen and causing cracks. After repeated freeze-thaw cycles, the surface of the recycled concrete exhibits cracking, peeling, and detachment. The poor freeze-thaw resistance of recycled concrete severely restricts its development and application in the construction industry. Summary of the Invention

[0003] To improve the freeze-thaw resistance of recycled concrete, this application provides freeze-thaw resistant recycled concrete and its preparation method.

[0004] In the first aspect, this application provides a freeze-thaw resistant recycled concrete, which adopts the following technical solution:

[0005] A freeze-thaw resistant recycled concrete comprises the following raw materials in parts by weight: 350-370 parts of silicate cement, 620-640 parts of fine aggregate, 1000-1100 parts of coarse aggregate, 60-100 parts of ceramsite, 160-175 parts of water, 30-40 parts of polycarboxylate superplasticizer, and 1.0-1.5 parts of air-entraining agent;

[0006] The fine aggregate includes natural fine aggregate and modified recycled fine aggregate, wherein the modified recycled fine aggregate accounts for 20-80% of the weight of the fine aggregate;

[0007] The coarse aggregate includes natural coarse aggregate and modified recycled coarse aggregate, wherein the modified recycled coarse aggregate accounts for 20-80% of the weight of the coarse aggregate;

[0008] The modified recycled fine aggregate and the modified recycled coarse aggregate are obtained by soaking in a modifying liquid, the modified liquid comprising the following raw materials: anionic surfactant, nonionic penetrant, polydimethylsiloxane emulsion, silane coupling agent and water.

[0009] Preferably, the modified recycled fine aggregate accounts for 40% of the weight of the fine aggregate, and the modified recycled coarse aggregate accounts for 60% of the weight of the coarse aggregate.

[0010] By adopting the above technical solution, simultaneously adding anionic surfactants and nonionic penetrants to the modified liquid, the compressive strength and freeze-thaw cycle count of the resulting recycled concrete are improved to a certain extent. This indicates that the addition of anionic surfactants and nonionic penetrants allows the hydroxyl-terminated polydimethylsiloxane emulsion and silane coupling agent in the modified liquid to penetrate more fully into the pores of the recycled fine and coarse aggregates, reaching more of the surface of the recycled fine and coarse aggregates and the pore surface, greatly reducing the water absorption of the fine and coarse aggregates. Furthermore, the expanded clay aggregate, under high mechanical strength, is not easily compressed, maintaining its own pores, which allows it to better absorb water molecules, hindering water molecule penetration without affecting the compressive strength of the concrete. In addition, the air-entraining agent forms closed air bubbles, which also hinder water molecule penetration. These three factors combined make it difficult for free water to penetrate and migrate in the recycled concrete, greatly improving its freeze-thaw resistance.

[0011] Preferably, the modified liquid comprises the following raw materials in parts by weight: 0.2-0.5 parts of anionic surfactant, 0.3-0.6 parts of nonionic penetrant, 10-15 parts of hydroxyl-terminated polydimethylsiloxane emulsion, 1-1.5 parts of silane coupling agent, and 100-120 parts of water.

[0012] By adopting the above technical solution and limiting the addition ratio of each raw material in the modified liquid, the modification effect of recycled aggregate can be optimized.

[0013] Preferably, the anionic surfactant is sodium dodecylbenzenesulfonate or sodium dodecyl sulfate.

[0014] By adopting the above technical solution, the anionic surfactants selected are sodium dodecylbenzenesulfonate or sodium dodecyl sulfate, both of which can work synergistically with nonionic penetrants to allow the hydroxyl-terminated polydimethylsiloxane emulsion and silane coupling agent in the modified liquid to penetrate more fully into the pores of the recycled fine aggregate and recycled coarse aggregate.

[0015] Preferably, the nonionic penetrant is sorbitol fatty acid ester or nonylphenol polyoxyethylene ether.

[0016] Preferably, the modifying liquid used for the modified recycled coarse aggregate also includes 1-3 parts by weight of high-density material with a particle size range of 700-900 mesh.

[0017] By adopting the above technical solution, adding high-density terreus with a certain particle size to the modification liquid can fill the larger pores of the recycled aggregate while modifying it, thereby further reducing the water absorption of the recycled aggregate.

[0018] Preferably, the particle size of the ceramsite is in the range of 50-70 mesh.

[0019] Secondly, this application provides a method for preparing freeze-thaw resistant recycled concrete, employing the following technical solution:

[0020] A method for preparing freeze-thaw resistant recycled concrete includes the following preparation steps:

[0021] Silicate cement, fine aggregate, coarse aggregate, ceramsite, and polycarboxylate superplasticizer are mixed together, then water and air-entraining agent are added, and mixing continues to obtain freeze-thaw resistant recycled concrete.

[0022] By adopting the above technical solution, the recycled concrete produced can maintain good compressive strength and also exhibit excellent freeze-thaw resistance.

[0023] In summary, this application includes at least one of the following beneficial technical effects:

[0024] 1. The simultaneous addition of anionic surfactants and nonionic penetrants to the modified liquid resulted in improved compressive strength and freeze-thaw cycle count of the recycled concrete. This indicates that the addition of anionic surfactants and nonionic penetrants allows the hydroxyl-terminated polydimethylsiloxane emulsion and silane coupling agent in the modified liquid to penetrate more fully into the pores of the recycled fine and coarse aggregates, reaching more of the surface and pore surfaces of the recycled fine and coarse aggregates, significantly reducing their water absorption. Furthermore, the expanded clay aggregate, under high mechanical strength, is not easily compressed, maintaining its porosity and better absorbing water molecules, hindering water molecule penetration without affecting the compressive strength of the concrete. Additionally, the air-entraining agent forms closed air bubbles, which also hinder water molecule penetration. These three factors combined make it difficult for free water to penetrate and migrate in the recycled concrete, greatly improving its freeze-thaw resistance.

[0025] 2. The recycled concrete prepared in this application has a freeze-thaw cycle count of 272 or more in water, with a maximum of 423; and a freeze-thaw cycle count between 263 and 396 in salt water. Meanwhile, the compressive strength of the recycled concrete can be maintained above 52.5 MPa, with a maximum of 63.2 MPa. This indicates that the recycled concrete prepared in this application has good freeze-thaw performance and excellent compressive strength, demonstrating excellent comprehensive performance and greatly enhancing the application potential of recycled concrete. Detailed Implementation

[0026] The following provides a more detailed explanation of this application in conjunction with specific details.

[0027] raw material

[0028] The preparation method of the recycled fine aggregate and recycled coarse aggregate used in this application is as follows: The crushed aggregate is fed into a 5X series crushing and shaping machine for producing manufactured sand. The linear speed of the 5X series crushing and shaping machine for producing manufactured sand is 100m / s. The shaped recycled aggregate particles are subjected to a rolling screen twice. The particles with a particle size range of 3-5mm are recycled fine aggregate; the particles with a particle size range of 5-25mm are recycled coarse aggregate. The silicate cement is P.O42.5R; the polycarboxylate superplasticizer is LA-8Q; the natural fine aggregate is natural sand with a particle size of 3-5mm; the natural coarse aggregate is crushed stone with a particle size of 5-16mm; the air-entraining agent is fatty alcohol polyoxyethylene ether, model AEO-7; the remaining raw materials are all commercially available products.

[0029] Preparation Example

[0030] Preparation Example 1

[0031] A modified recycled fine aggregate, the preparation method of which is as follows:

[0032] Add 55 kg of modifying liquid to 100 kg of recycled fine aggregate, then stir and mix at 500 rpm, and then bake in an oven at 150℃ for 5 h to obtain modified recycled fine aggregate; wherein, the raw materials and the amount of each raw material in the modifying liquid are shown in Table 1; wherein, the anionic surfactant is sodium dodecylbenzenesulfonate; the nonionic penetrant is sorbitan fatty acid ester, model S-80; and the silane coupling agent is silane coupling agent KH550.

[0033] Table 1. Raw materials and amounts (kg) used in the preparation of the modified liquid in Example 1.

[0034]

[0035]

[0036] Preparation Example 2

[0037] A modified recycled coarse aggregate, the preparation method of which is as follows:

[0038] Add 50 kg of modifying liquid to 100 kg of recycled coarse aggregate, then stir and mix at 500 rpm, and then bake in an oven at 150°C for 6 hours to obtain modified recycled fine aggregate; the modifying liquid used is the same as that used in Preparation Example 1.

[0039] Preparation Example 3

[0040] A modified recycled coarse aggregate, which differs from Preparation Example 2 in that its modification liquid also includes 2 kg of meta-high teratogen, the meta-high teratogen having a particle size range of 700-900 mesh; the remaining steps are the same as those in Preparation Example 2.

[0041] Example

[0042] Example 1

[0043] A freeze-thaw resistant recycled concrete, the raw materials and their quantities are shown in Table 2, and its preparation method is as follows:

[0044] Silicate cement, fine aggregate, coarse aggregate, ceramsite, and polycarboxylate superplasticizer are mixed together, then water and air-entraining agent are added, and mixing continues to obtain freeze-thaw resistant recycled concrete.

[0045] The fine aggregate includes natural fine aggregate and modified recycled fine aggregate, with the same particle size. The modified recycled fine aggregate accounts for 20% of the total weight of the fine aggregate. The modified recycled fine aggregate is from Preparation Example 1. The coarse aggregate includes natural coarse aggregate and modified recycled coarse aggregate, with the same particle size. The modified recycled coarse aggregate accounts for 20% of the total weight of the coarse aggregate. The modified recycled coarse aggregate is from Preparation Example 2.

[0046] The particle size range of ceramsite is 50-70 mesh.

[0047] Table 2. Raw materials and their quantities (kg) in Example 1

[0048] Silicate cement 360 fine aggregate 630 coarse aggregate 1050 Expanded clay 80 water 170 Polycarboxylate superplasticizer 35 Entraining agent 1.2

[0049] Example 2

[0050] A freeze-thaw resistant recycled concrete differs from Example 1 in that its modified recycled coarse aggregate is derived from Preparation Example 3, while the remaining steps are the same as in Example 1.

[0051] Example 3

[0052] A freeze-thaw resistant recycled concrete differs from Example 2 in that its modified recycled fine aggregate accounts for 40% of the weight of the fine aggregate, while the remaining steps are the same as in Example 2.

[0053] Example 4

[0054] A freeze-thaw resistant recycled concrete differs from Example 2 in that its modified recycled fine aggregate accounts for 60% of the weight percentage of the fine aggregate, while the remaining steps are the same as in Example 2.

[0055] Example 5

[0056] A freeze-thaw resistant recycled concrete differs from Example 2 in that its modified recycled fine aggregate accounts for 80% of the weight percentage of the fine aggregate, while the remaining steps are the same as in Example 2.

[0057] Example 6

[0058] A freeze-thaw resistant recycled concrete differs from Example 3 in that its modified recycled coarse aggregate accounts for 40% of the weight percentage of the coarse aggregate, while the remaining steps are the same as in Example 3.

[0059] Example 7

[0060] A freeze-thaw resistant recycled concrete differs from Example 3 in that its modified recycled coarse aggregate accounts for 60% of the weight percentage of the coarse aggregate, while the remaining steps are the same as in Example 3.

[0061] Example 8

[0062] A freeze-thaw resistant recycled concrete differs from Example 3 in that its modified recycled coarse aggregate accounts for 80% of the weight percentage of the coarse aggregate, while the remaining steps are the same as in Example 3.

[0063] Comparative Example

[0064] Comparative Example 1

[0065] A freeze-thaw resistant recycled concrete differs from Example 1 in that the anionic surfactant and nonionic penetrant added to the modification liquid used in the preparation of the modified recycled coarse aggregate and modified recycled fine aggregate are replaced with water, while the remaining steps are the same as in Example 1.

[0066] Comparative Example 2

[0067] A freeze-thaw resistant recycled concrete differs from Example 1 in that the anionic surfactant added to the modification liquid used in the preparation of the modified recycled coarse aggregate and modified recycled fine aggregate is replaced with water, while the remaining steps are the same as in Example 1.

[0068] Comparative Example 3

[0069] A freeze-thaw resistant recycled concrete differs from Example 1 in that the nonionic penetrant added to the modifying liquid used in the preparation of the modified recycled coarse aggregate and modified recycled fine aggregate is replaced with water, while the remaining steps are the same as in Example 1.

[0070] Comparative Example 4

[0071] A freeze-thaw resistant recycled concrete differs from Example 1 in that the expanded clay aggregate is replaced with an equal mass of rubber powder, the particle size of which is 50-70 mesh. The remaining steps are the same as in Example 1.

[0072] Performance testing

[0073] Detection methods / test methods

[0074] Reclaimed freeze-thaw resistant concrete was prepared according to the preparation methods in Examples 1-8 and Comparative Examples 1-4. The concrete was poured into concrete molds with dimensions of 100mm×100mm×100mm. After molding, the specimens were cured under standard curing conditions for 28 days. The specimens were then tested according to the following testing methods. The test results are shown in Table 3.

[0075] Compressive strength: The compressive strength of the above-mentioned cured specimens was tested in accordance with GB / T50081-2010 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete".

[0076] Freeze-thaw cycle testing:

[0077] The specimens were tested using reagent #1: The specimens were removed from the curing area 4 days before the freeze-thaw experiment. First, a visual inspection was performed, and then the specimens were immersed in water at 20°C. The water level should be 20 mm above the specimens during immersion. The specimens were used for the test after 4 days of immersion. Each freeze-thaw cycle was controlled to be completed within 2-4 hours, with the thawing time not less than 1 / 4 of the total freeze-thaw time. At the end of freezing and thawing, the core temperature of the specimens should be controlled at -17±2°C and 8±2°C, respectively. The time required for each specimen to drop from 6°C to -15°C should not be less than 1 / 2 of the freezing time.

[0078] The specimens were tested using reagent #2: The specimens were removed from the curing area 4 days before the freeze-thaw experiment. First, a visual inspection was performed. Then, they were immersed in a 3.5 wt% sodium chloride solution at 20°C, with the liquid level 20 mm above the specimen. The specimens were used for testing after 4 days of immersion. Each freeze-thaw cycle was controlled to be completed within 2-4 hours, with the thawing time not less than 1 / 4 of the total freeze-thaw time. At the end of freezing and thawing, the core temperature of the specimen should be controlled at -17±2°C and 8±2°C, respectively. The time required for each specimen to cool from 6°C to -15°C should not be less than 1 / 2 of the freezing time.

[0079] Record the number of freeze-thaw cycles at which cracks or peeling first appeared on the specimen during the two testing processes described above.

[0080] Table 3 shows the test results of Examples 1-8 and Comparative Examples 1-4.

[0081]

[0082]

[0083] As can be seen from Examples 1-8, Comparative Examples 1-4, and the test data in Table 3, the recycled concrete prepared in this application has a freeze-thaw cycle count of 272 or more in water, with a maximum of 423; the freeze-thaw cycle count in salt water is between 263 and 396; and the compressive strength of the recycled concrete can be maintained above 52.5 MPa, with a maximum of 63.2 MPa. This indicates that the recycled concrete prepared in this application has good freeze-thaw performance and excellent compressive strength, demonstrating excellent overall performance and greatly enhancing the application potential of recycled concrete.

[0084] The test data from Examples 1 and Comparative Examples 1-3 show that the simultaneous addition of anionic surfactants and nonionic penetrants to the modified liquid improves the compressive strength and freeze-thaw cycle count of the recycled concrete. This indicates that the addition of anionic surfactants and nonionic penetrants allows the hydroxyl-terminated polydimethylsiloxane emulsion and silane coupling agent in the modified liquid to penetrate more fully into the pores of the recycled fine and coarse aggregates, reaching more of the surface and pore surfaces of the recycled fine and coarse aggregates, thus significantly reducing their water absorption. Combining Examples 2-8 and their test data, it can be seen that as the proportion of modified recycled fine and coarse aggregates gradually increases, the freeze-thaw cycle count of the recycled concrete gradually increases, indicating that modified recycled fine and coarse aggregates help improve the freeze-thaw resistance of recycled concrete. Furthermore, considering both the compressive strength and freeze-thaw resistance of recycled concrete, the optimal addition proportions are 40% for modified recycled fine aggregates and 60% for modified recycled coarse aggregates.

[0085] The test data from Examples 1-2 show that by adding a certain particle size of high-density terreus to the modification liquid, the larger pores of the recycled aggregate can be filled while modifying it, thereby further reducing the water absorption of the recycled aggregate.

[0086] The test data from Example 1 and Comparative Example 4 show that although both rubber powder and ceramsite may absorb water molecules and hinder their permeation due to their porous structure, making it difficult for free water to migrate during crystallization, rubber powder is easily compressed during the drying process of recycled concrete, resulting in reduced porosity and lower mechanical strength. Replacing it with ceramsite, however, allows for higher mechanical strength, reduces the likelihood of compression, maintains its porosity, and enhances both the freeze-thaw resistance and mechanical properties of the recycled concrete.

[0087] The embodiments described above are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A freeze-thaw resistant recycled concrete, characterized by: It comprises the following raw materials by weight: 350-370 parts of Portland cement, 620-640 parts of fine aggregate, 1000-1100 parts of coarse aggregate, 60-100 parts of ceramsite, 160-175 parts of water, 30-40 parts of polycarboxylate superplasticizer and 1.0-1.5 parts of air entraining agent; The fine aggregate comprises natural fine aggregate and modified recycled fine aggregate, and the modified recycled fine aggregate accounts for 20-80% of the weight percentage of the fine aggregate; The coarse aggregate comprises natural coarse aggregate and modified recycled coarse aggregate, and the modified recycled coarse aggregate accounts for 20-80% of the weight percentage of the coarse aggregate; The modified recycled fine aggregate and the modified recycled coarse aggregate are prepared by soaking in a modifying liquid, and the modifying liquid comprises the following raw materials by weight: 0.2-0.5 parts of anionic surfactant, 0.3-0.6 parts of non-ionic penetrant, 10-15 parts of hydroxyl-terminated polydimethylsiloxane emulsion, 1-1.5 parts of silane coupling agent and 100-120 parts of water; The anionic surfactant is sodium dodecyl benzene sulfonate or sodium dodecyl sulfate; The non-ionic penetrant is sorbitan fatty acid ester or nonylphenol polyoxyethylene ether; The modifying liquid for the modified recycled coarse aggregate further comprises 1-3 parts by weight of metakaolin with a particle size range of 700-900 mesh; The ceramsite has a particle size range of 50-70 mesh.

2. The freeze-thaw resistant recycled concrete according to claim 1, characterized in that: The modified recycled fine aggregate accounts for 40% of the weight percentage of the fine aggregate, and the modified recycled coarse aggregate accounts for 60% of the weight percentage of the coarse aggregate.

3. A method of producing the freeze-thaw regenerating concrete according to any one of claims 1 to 2, characterized by: It comprises the following preparation steps: The Portland cement, fine aggregate, coarse aggregate, ceramsite and polycarboxylate superplasticizer are stirred and blended, then the water and air entraining agent are added, and the stirring is continued to obtain the freeze-thaw resistant recycled concrete. The fine aggregate comprises natural fine aggregate and modified recycled fine aggregate, and the modified recycled fine aggregate accounts for 20-80% of the weight percentage of the fine aggregate; The coarse aggregate comprises natural coarse aggregate and modified recycled coarse aggregate, and the modified recycled coarse aggregate accounts for 20-80% of the weight percentage of the coarse aggregate; The modified recycled fine aggregate and the modified recycled coarse aggregate are prepared by soaking in a modifying liquid, and the modifying liquid comprises the following raw materials by weight: 0.2-0.5 parts of anionic surfactant, 0.3-0.6 parts of non-ionic penetrant, 10-15 parts of hydroxyl-terminated polydimethylsiloxane emulsion, 1-1.5 parts of silane coupling agent and 100-120 parts of water; The anionic surfactant is sodium dodecyl benzene sulfonate or sodium dodecyl sulfate; The non-ionic penetrant is sorbitan fatty acid ester or nonylphenol polyoxyethylene ether; The modifying liquid for the modified recycled coarse aggregate further comprises 1-3 parts by weight of metakaolin with a particle size range of 700-900 mesh; The ceramsite has a particle size range of 50-70 mesh. The modified recycled fine aggregate accounts for 40% of the weight percentage of the fine aggregate, and the modified recycled coarse aggregate accounts for 60% of the weight percentage of the coarse aggregate. It comprises the following preparation steps: The Portland cement, fine aggregate, coarse aggregate, ceramsite and polycarboxylate superplasticizer are stirred and blended, then the water and air entraining agent are added, and the stirring is continued to obtain the freeze-thaw resistant recycled concrete.

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