Anti-freezing and anti-cracking recycled aggregate and preparation method thereof

Abstract

The application relates to the field of recycled aggregate preparation, and specifically discloses a preparation method of recycled aggregate with anti-freezing and anti-cracking properties, characterized by comprising the following steps: S1, waste concrete is crushed and sieved to obtain recycled aggregate, and the particle size of the recycled aggregate is 5-30 mm; S2, the recycled aggregate is soaked in nano-silica dispersion liquid for 4-6 hours, taken out and dried; S3, a reinforcing agent is added, and stirring is carried out under pressure for 12-24 hours; the adding amount of the reinforcing agent is 10-20% of the mass of the recycled aggregate; the reinforcing agent comprises the following components: kaolin, cement, reinforcing fiber, fly ash, expansive soil and water; S4, the recycled aggregate obtained after the step S3 is dried for at least 7 days to obtain the recycled aggregate with anti-freezing and anti-cracking properties. The nano-silica dispersion liquid and the reinforcing agent synergistically act to better improve the strength and anti-freezing performance of the recycled aggregate, so as to improve the strength and anti-freezing performance of the concrete.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of concrete, in particular to a frost-resistant and anti-cracking recycled aggregate and a preparation method thereof. BACKGROUND

[0002] With the rapid development of the construction industry in China, the use of concrete is increasing year by year, and the resource of aggregate, which is the largest consumption in the preparation of concrete, is gradually decreasing. At the same time, a large amount of construction waste is produced, of which the most important is waste concrete. Therefore, the resource utilization of construction waste not only contributes to environmental protection, but also effectively alleviates the massive consumption of natural aggregate.

[0003] The aggregate formed by mixing the waste concrete after crushing, screening, grading and washing in a certain proportion is called recycled aggregate. During the production of recycled aggregate, some micro-cracks are often generated, and at the same time, the recycled aggregate often has defects such as high water absorption, high crushing rate and low strength due to the influence of the deterioration of raw materials during long-term use, thereby affecting the performance of concrete.

[0004] In winter in the north, after the rain, cold air comes, and the concrete prepared by the recycled aggregate is easy to absorb a large amount of water in the internal structure micro-crack and then freeze, which causes the micro-crack to further expand, resulting in cracking of the concrete, and at the same time, the strength of the concrete is greatly reduced, affecting the use of buildings and roads. SUMMARY

[0005] In order to improve the frost resistance and anti-cracking performance of concrete, the present application provides a frost-resistant and anti-cracking recycled aggregate and a preparation method thereof.

[0006] In a first aspect, the present application provides a preparation method of a frost-resistant and anti-cracking recycled aggregate, which adopts the following technical scheme:

[0007] A preparation method of a frost-resistant and anti-cracking recycled aggregate, characterized in that it comprises the following steps:

[0008] S1, crushing and screening the waste concrete to obtain a recycled aggregate, the particle size of the recycled aggregate being 5-30mm;

[0009] S2, soaking the recycled aggregate in a nano-silica dispersion liquid for 4-6h, and then taking out and drying;

[0010] S3, adding a reinforcing agent and stirring under pressure for 12-24h, the addition amount of the reinforcing agent being 10-20% of the mass of the recycled aggregate, and the reinforcing agent comprising the following components: kaolin, cement, reinforcing fiber, fly ash, swelling soil and water;

[0011] S4, drying the recycled aggregate obtained after the step S3 for at least 7d to obtain a frost-resistant and anti-cracking recycled aggregate.

[0012] By adopting the technical scheme, the nano-silica is adsorbed and precipitated into the open hole pores and micro-cracks of the recycled aggregate, and a nano-silica precipitation layer is formed on the surface of the recycled aggregate; the nano-particles that penetrate into the interior of the open hole pores of the recycled aggregate and the precipitation layer formed on the surface of the recycled aggregate together absorb calcium hydroxide enriched on the surface and in the pores of the recycled aggregate, the calcium hydroxide is formed in the strength development process of the recycled aggregate concrete, and the calcium hydroxide is generated into cementitious material with high strength through hydration, liquid phase or solid phase reaction, so as to improve the interfacial bonding strength between the recycled aggregate and the cement stone, realize in-situ strengthening of the recycled aggregate, and improve the strength and durability of the recycled aggregate concrete; meanwhile, the recycled aggregate is conveniently dispersed in the cement, the strengthening agent is conveniently introduced into the inner wall cracks of the recycled aggregate, and the bonding strength between the strengthening agent and the surface of the recycled aggregate is good.

[0013] The strengthening agent is composed of kaolin, cement, reinforcing fiber, fly ash, expansive soil and water; the kaolin has good compactness; the cement serves as a bonding material; the reinforcing fiber is attached to the surface and cracks of the recycled aggregate to improve the strength; the addition of the fly ash improves the strength of the recycled aggregate; and the expansive soil has strong water absorption and swelling properties; through stirring under a pressurized condition, the strengthening agent is filled into the cracks of the recycled aggregate, and the strength of the recycled aggregate is further improved.

[0014] Due to the water absorption and swelling properties of the expansive soil, a large number of independent micropores are formed in the recycled aggregate after drying, and the thermal expansion and cold shrinkage resistance of the recycled aggregate is improved; meanwhile, the cracks of the recycled aggregate are filled with the strengthening agent, and the micropores are in an independent state; due to the addition of the fly ash and kaolin, the water absorption of the surface of the recycled aggregate is reduced, so that water is not easily introduced into the independent micropores, and the cracks of the inner wall of the recycled aggregate are not expanded after freezing, so that the concrete applied with the recycled aggregate of the application has the characteristics of frost resistance and anti-cracking.

[0015] Optionally, the preparation method of the nano-silica dispersion liquid is as follows: the nano-silica is mixed in water, and ultrasonic stirring is performed; the mass concentration of the nano-silica dispersion liquid is 0.2-0.5 g / L.

[0016] By adopting the technical scheme, the nano-silica is uniformly dispersed through ultrasonic stirring, and the low mass concentration facilitates the formation of a gel thin layer on the surface of the recycled aggregate, so as to improve the bonding strength between the recycled aggregate and the strengthening agent.

[0017] Optionally, the strengthening agent comprises the following components in weight percentage: kaolin 3-3.5 parts, cement 1-1.5 parts, reinforcing fiber 2-2.3 parts, fly ash 0.5-1 part, expansive soil 1 part and water 2.5-3.5 parts.

[0018] By adopting the technical scheme, a large amount of kaolin is added to make the recycled aggregate have poor water absorption, and if the swelling soil is added too much, the recycled aggregate has strong water absorption, which can easily reduce the crack resistance of the concrete, and the addition of the reinforcing fiber and the fly ash can increase the strength of the recycled aggregate.

[0019] Optionally, the pressure in the S3 step is 0.5-0.7 MPa.

[0020] By adopting the technical scheme, the pressure is relatively small, which can not make the reinforcing agent fully enter the cracks of the recycled aggregate, and if the pressure is relatively large, the cracks can be easily expanded, which can affect the strength of the recycled aggregate.

[0021] Optionally, the reinforcing fiber is a mixture of one or more of glass fiber and carbon fiber.

[0022] By adopting the technical scheme, the glass fiber and the carbon fiber have high strength and good corrosion resistance, and are convenient for reinforcing the recycled aggregate.

[0023] Optionally, the diameter of the reinforcing fiber is less than 100 microns, and the length of the reinforcing fiber is 0.2-0.5 mm.

[0024] By adopting the technical scheme, the small particle size and length can make the reinforcing fiber enter the cracks of the recycled aggregate.

[0025] In a second aspect, the application provides an anti-freezing and anti-cracking recycled aggregate, which adopts the following technical scheme:

[0026] An anti-freezing and anti-cracking recycled aggregate is obtained by the preparation method of the anti-freezing and anti-cracking recycled aggregate.

[0027] By adopting the technical scheme, the recycled aggregate has good anti-freezing and anti-cracking properties, the concrete has good anti-freezing and anti-cracking properties, and the recycled aggregate is convenient for application in a climate that is cold and has more rain and low temperature to freezing.

[0028] In summary, the application has at least one of the following beneficial technical effects:

[0029] 1. The recycled aggregate is treated by the nano-silica dispersion liquid, which can make the recycled aggregate disperse in the cement, make the reinforcing agent enter the inner wall cracks of the recycled aggregate, and improve the bonding strength between the reinforcing agent and the surface of the recycled aggregate. The addition of the reinforcing agent can improve the strength of the recycled aggregate, and the swelling soil has strong water absorption and swelling properties, so that the reinforcing agent can be filled in the cracks of the recycled aggregate under the stirring condition of the pressure, which can further improve the strength of the recycled aggregate. The nano-silica dispersion liquid and the reinforcing agent can synergistically improve the strength and anti-freezing properties of the recycled aggregate, thereby improving the strength and anti-freezing properties of the concrete. DETAILED DESCRIPTION

[0030] The application is further described in detail below in connection with examples and comparative examples.

[0031] Raw materials

[0032] Kaolin 325 mesh; cement is Portland cement 42.5 grade; nano-silica 20 nm; glass fiber diameter 67 microns, length 0.5 mm; carbon fiber is short carbon fiber, diameter 80 microns, length 2 mm; fly ash 325 nm; swelling soil 325 mesh, water reducing agent is polycarboxylic acid water reducing agent.

[0033] Preparation example

[0034] Preparation example 1

[0035] Preparation of nano-silica, mix nano-silica in water, ultrasonic stirring, the mass concentration of nano-silica dispersion is 0.2 g / L.

[0036] Preparation example 2

[0037] Preparation of nano-silica, mix nano-silica in water, ultrasonic stirring, the mass concentration of nano-silica dispersion is 0.5 g / L.

[0038] Preparation example 3

[0039] Preparation of nano-silica, mix nano-silica in water, ultrasonic stirring, the mass concentration of nano-silica dispersion is 0.3 g / L.

[0040] Preparation example 4

[0041] Preparation of reinforcing agent: take kaolin, cement, reinforcing fiber, fly ash, swelling soil and water: the mass ratio of kaolin, cement, reinforcing fiber, fly ash, swelling soil and water is 3:1:2:0.5:1:2.5.

[0042] Preparation example 5

[0043] Preparation of reinforcing agent: take kaolin, cement, reinforcing fiber, fly ash, swelling soil and water: the mass ratio of kaolin, cement, reinforcing fiber, fly ash, swelling soil and water is 3.5:1.5:2.3:1:1:3.5.

[0044] Preparation example 6

[0045] Preparation of reinforcing agent: take kaolin, cement, reinforcing fiber, fly ash, swelling soil and water: the mass ratio of kaolin, cement, reinforcing fiber, fly ash, swelling soil and water is 3.3:1.3:2.1:0.8:1:3.

[0046] Preparation example 7

[0047] Preparation of the reinforcing agent: the difference from Preparation Example 6 is that the carbon fiber is replaced by the glass fiber in equal mass.

[0048] Preparation Example 8

[0049] Preparation of the reinforcing agent: the difference from Preparation Example 6 is that the addition amount of the kaolin is reduced, and the mass ratio of the kaolin, cement, reinforcing fiber, fly ash, expansive soil and water is 1:1.3:2.1:0.8:1:3.

[0050] Preparation Example 9

[0051] Preparation of the reinforcing agent: the difference from Preparation Example 6 is that the addition amount of the kaolin is increased, and the mass ratio of the kaolin, cement, reinforcing fiber, fly ash, expansive soil and water is 5:1.3:2.1:0.8:1:3.

[0052] Example 10

[0053] Preparation of the reinforcing agent: the difference from Preparation Example 6 is that the addition amount of the expansive soil is reduced, and the mass ratio of the kaolin, cement, reinforcing fiber, fly ash, expansive soil and water is 3.3:1.3:2.1:0.8:0.2:3.

[0054] Preparation Example 11

[0055] Preparation of the reinforcing agent: the difference from Preparation Example 6 is that the addition amount of the expansive soil is increased, and the mass ratio of the kaolin, cement, reinforcing fiber, fly ash, expansive soil and water is 3.3:1.3:2.1:0.8:3:3.

[0056] Preparation Example 12

[0057] Preparation of the reinforcing agent: the difference from Preparation Example 6 is that the addition amount of the cement is reduced, and the mass ratio of the kaolin, cement, reinforcing fiber, fly ash, expansive soil and water is 3.3:0.2:2.1:0.8:1:3.

[0058] Preparation Example 13

[0059] Preparation of the reinforcing agent: the difference from Preparation Example 6 is that the addition amount of the cement is increased, and the mass ratio of the kaolin, cement, reinforcing fiber, fly ash, expansive soil and water is 3.3:3:2.1:0.8:1:3.

[0060] Example

[0061] Example 1

[0062] A method for preparing a freeze-resistant and crack-resistant recycled aggregate, comprising the following steps:

[0063] S1, crushing and sieving the waste concrete to obtain a recycled aggregate, the particle size of the recycled aggregate being 5-30 mm;

[0064] S2, 50 kg of the recycled aggregate obtained in step S1 was weighed, soaked in 300 L of the nanosilica dispersion solution obtained in Preparation Example 1 for 4 h, and uniformly stirred by ultrasonic agitation, and then taken out and dried;

[0065] S3, the reinforcing agent obtained in Preparation Example 4 was added, and stirred under pressure for 12 h, the pressure was 0.7 MPa, and the amount of the reinforcing agent added was 10% of the mass of the recycled aggregate;

[0066] S4, the recycled aggregate obtained after step S3 was dried for 7 d to obtain the recycled aggregate resistant to freezing and cracking.

[0067] A recycled aggregate resistant to freezing and cracking, which is prepared by the above preparation method.

[0068] Example 2

[0069] A preparation method of a recycled aggregate resistant to freezing and cracking, comprising the following steps:

[0070] S1, waste concrete was crushed and sieved to obtain a recycled aggregate, and the particle size of the recycled aggregate was 5-30 mm;

[0071] S2, 50 kg of the recycled aggregate obtained in step S1 was weighed, soaked in 300 L of the nanosilica dispersion solution obtained in Preparation Example 2 for 6 h, and uniformly stirred by ultrasonic agitation, and then taken out and dried;

[0072] S3, the reinforcing agent obtained in Preparation Example 5 was added, and stirred under pressure for 24 h, the pressure was 0.5 MPa, and the amount of the reinforcing agent added was 20% of the mass of the recycled aggregate;

[0073] S4, the recycled aggregate obtained after step S3 was dried for 7 d to obtain the recycled aggregate resistant to freezing and cracking.

[0074] A recycled aggregate resistant to freezing and cracking, which is prepared by the above preparation method.

[0075] Example 3

[0076] A preparation method of a recycled aggregate resistant to freezing and cracking, comprising the following steps:

[0077] S1, waste concrete was crushed and sieved to obtain a recycled aggregate, and the particle size of the recycled aggregate was 5-30 mm;

[0078] S2, 50 kg of the recycled aggregate obtained in step S1 was weighed, soaked in 300 L of the nanosilica dispersion solution obtained in Preparation Example 3 for 5 h, and uniformly stirred by ultrasonic agitation, and then taken out and dried;

[0079] S3, the reinforcing agent obtained from Preparation Example 6 was added, and stirring was performed under pressure for 18 h at a pressure of 0.6 MPa, and the amount of the reinforcing agent added was 15% by mass of the recycled aggregate;

[0080] S4, the recycled aggregate obtained after the step S3 was air-dried for 7 d to obtain the freeze- and crack-resistant recycled aggregate.

[0081] A freeze- and crack-resistant recycled aggregate prepared by the above-described production method.

[0082] Example 4

[0083] The difference from Example 3 is that the reinforcing agent is obtained from Preparation Example 7.

[0084] Example 5

[0085] The difference from Example 3 is that the reinforcing agent is obtained from Preparation Example 8.

[0086] Example 6

[0087] The difference from Example 3 is that the reinforcing agent is obtained from Preparation Example 9.

[0088] Example 7

[0089] The difference from Example 3 is that the reinforcing agent is obtained from Preparation Example 10.

[0090] Example 8

[0091] The difference from Example 3 is that the reinforcing agent is obtained from Preparation Example 11.

[0092] Example 9

[0093] The difference from Example 3 is that the reinforcing agent is obtained from Preparation Example 12.

[0094] Example 10

[0095] The difference from Example 3 is that the reinforcing agent is obtained from Preparation Example 13.

[0096] Example 11

[0097] The difference from Example 3 is that the pressure intensity is 0.2 MPa.

[0098] Example 12

[0099] The difference from Example 3 is that the pressure intensity is 1 MPa.

[0100] Comparative Example

[0101] Comparative Example 1

[0102] The difference from Example 3 is that the recycled aggregate is not treated with the nano-silica dispersion liquid.

[0103] Comparative Example 2

[0104] The difference from Example 3 is that the recycled aggregate is not added with reinforcing agent.

[0105] Comparative Example 3

[0106] The difference from Example 3 is that the recycled aggregate is not treated with nano-silica dispersion liquid and reinforcing agent.

[0107] Comparative Example 4

[0108] The difference from Example 3 is that the stirring in the S3 step is not pressurized.

[0109] Performance detection test

[0110] Preparation of concrete test piece:

[0111] The recycled aggregate 50 kg, polycarboxylic acid water reducer 0.5 kg, cement 20 kg and water 7 kg are stirred uniformly, and the uniformly stirred concrete is loaded into a 100 mm*100 mm*100 mm test mold, covered with plastic wrap and cured for 24 h, then placed in a curing box for water curing for 28 d.

[0112] The compressive strength and splitting tensile strength test uses a WAW-2000 type universal testing machine.

[0113] The frost resistance test should be carried out according to the current national standard "Standard for Testing Methods of Long-term Performance and Durability of Ordinary Concrete" GB / T-50082-2009, 50 times of freeze-thaw cycle test, and the mass loss rate and compressive strength loss rate are calculated according to the test data.

[0114] Table 1

[0115]

[0116]

[0117] It can be seen from Examples 1-3 and Table 1 that the concrete prepared from the recycled aggregate according to the scheme of the application has good compressive strength and frost resistance.

[0118] It can be seen from the combination of embodiments 3, 5, 6 and table 1 that too much kaolin is added, which increases the strength of the concrete, but reduces the frost resistance of the concrete, because too much kaolin is added, which results in that the recycled aggregate has good compactness but poor toughness, and when the concrete expands and contracts with heat, the internal structure of the concrete is easily damaged, resulting in that the strength loss of the concrete is large after the freeze-thaw cycle test. When the amount of kaolin is small, the pores produced by the shrinkage of the swelling soil are difficult to become monomers, which makes the internal pores of the concrete too large, resulting in that the strength of the concrete is low, and the pores are further expanded after freezing, which makes the compressive strength of the concrete lose a lot.

[0119] It can be seen from the combination of embodiments 3, 7, 8 and table 1 that too much swelling soil is added, which results in too many internal pores of the concrete, reducing the compressive strength and frost resistance of the concrete; and when the amount of swelling soil is small, the internal structure of the swelling soil has small pores, the anti-expansion performance is small, and the frost resistance of the concrete is reduced.

[0120] It can be seen from the combination of embodiments 3, 9, 10 and table 1 that too little cement is added, which makes it difficult for the reinforcing agent to firmly bond to the surface of the recycled aggregate, thereby reducing the effect of the reinforcing agent, reducing the strength of the concrete and reducing the frost resistance of the concrete.

[0121] It can be seen from the combination of embodiments 3, 11, 12 and table 1 that too high or too low pressure strength will reduce the strength and frost resistance of the concrete.

[0122] It can be seen from the combination of embodiments 3 and comparative examples 1, 3 and table 1 that without the treatment of the nano-silica dispersion liquid, the dispersibility of the reinforcing agent on the surface of the recycled aggregate is poor, which reduces the compressive strength and frost resistance of the concrete.

[0123] It can be seen from the combination of embodiments 3 and comparative examples 2, 3 and table 1 that without the addition of the reinforcing agent, only the treatment of the relatively thin nano-silica dispersion liquid has little effect on the strength of the concrete

[0124] It can be seen from the combination of embodiments 3 and comparative example 4 and table 1 that in the scheme of the present application, the strength and frost resistance of the recycled aggregate are significantly improved through the treatment of nano-silica first and then the treatment of the reinforcing agent.

[0125] The specific embodiments are only an explanation of the present application, which is not a limitation of the present application, and those skilled in the art can make modifications to the embodiments without creative contribution after reading the 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 method for producing a freeze and crack resistant recycled aggregate, characterized by, The method comprises the following steps: S1, crushing and screening the waste concrete to obtain recycled aggregate, the particle size of the recycled aggregate being 5-30mm; S2, soaking the recycled aggregate in nano-silica dispersion liquid for 4-6h, taking out and drying; S3, adding a reinforcing agent, stirring under pressure for 12-24h, the adding amount of the reinforcing agent being 10-20% of the mass of the recycled aggregate, the reinforcing agent comprising the following components: kaolin, cement, reinforcing fiber, fly ash, expansive soil and water; S4, drying the recycled aggregate obtained after the step S3 for at least 7d to obtain the recycled aggregate resistant to freezing and cracking; The preparation method of the nano-silica dispersion liquid is as follows: mixing the nano-silica in water and stirring by ultrasonic wave, the mass concentration of the nano-silica dispersion liquid being 0.2-0.5g / L; The reinforcing agent comprises the following components by weight: kaolin 3-3.5 parts, cement 1-1.5 parts, reinforcing fiber 2-2.3 parts, fly ash 0.5-1 part, expansive soil 1 part and water 2.5-3.5 parts; The pressure in the step S3 is 0.5-0.7MPa.

2. A process for the preparation of a freeze and crack resistant recycled aggregate as claimed in claim 1, wherein: The reinforcing fiber is a mixture of one or more of glass fiber and carbon fiber.

3. A process for the preparation of a freeze and crack resistant recycled aggregate as claimed in claim 1, wherein: The diameter of the reinforcing fiber is less than 100 microns, and the length of the reinforcing fiber is 0.2-0.5mm.

4. A frost and crack resistant recycled aggregate, characterized in that, The method is obtained by any one of claims 1-3. The method is obtained by any one of claims 1-3.

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