Regenerated micro-powder green cement and preparation method thereof

Abstract

The application discloses a kind of recycled micro powder green cement and preparation method thereof.Recycled micro powder green cement includes the following raw materials: cement, recycled micro powder, fly ash, hydrophobic nanosilica, sodium silicate and ferric sulfate;Its preparation method is: immerse recycled micro powder in hydrochloric acid solution, stir, filter and dry, grind, then add other raw materials and stir evenly.When raw materials are uniformly mixed and then water is added, hydrophobic nanosilica will fill in the fine pores of recycled micro powder, improve the compactness of concrete, inhibit concrete cracking, sodium silicate decomposes and precipitates gum, realize the adhesion between hydrophobic nanosilica particles and recycled micro powder, which is beneficial to prolong the durability of anti-cracking effect, ferric sulfate can also react with calcium hydroxide in concrete to form a precipitate, block the internal voids of concrete to form support, further improve the anti-cracking effect of concrete, and improve the recycling rate of waste concrete resources, which helps to promote the use of recycled micro powder.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of cement, more particularly, it relates to a recycled micro-powder green cement and a preparation method thereof. BACKGROUND

[0002] With the continuous expansion of the scale of urban reconstruction in China and the continuous updating of old buildings in cities, a large amount of waste concrete is generated by the demolition of a large number of old buildings and structures. At present, the traditional disposal methods such as open-air stacking and landfill are still mainly used for the disposal of construction waste concrete, which not only occupies a large amount of land, but also causes great harm to the environment and personal safety. In recent years, China has begun to speed up the recycling of waste concrete, which mainly focuses on the reuse of coarse and fine aggregates to form recycled aggregates. In the process of forming recycled aggregates, a large amount of recycled micro-powder is inevitably produced.

[0003] At present, recycled micro-powder is mainly used as a filler. Some studies have replaced part of the cement to produce concrete, but the recycled micro-powder has a large water absorption, which leads to a fast hydration reaction rate. Directly mixing recycled micro-powder into cement may cause the formed concrete to shrink and crack, which affects the popularization and use of recycled micro-powder and needs to be improved. SUMMARY

[0004] In order to improve the problem that directly mixing recycled micro-powder into cement may cause the formed concrete to crack, the present application provides a recycled micro-powder green cement and a preparation method thereof.

[0005] In a first aspect, the present application provides a recycled micro-powder green cement, which adopts the following technical solution:

[0006] A recycled micro-powder green cement, comprising the following raw materials in parts by weight: 200-250 parts of cement, 50-80 parts of recycled micro-powder, 25-40 parts of fly ash, 20-30 parts of hydrophobic nano-silicon dioxide, 5-10 parts of sodium silicate, and 10-15 parts of ferric sulfate.

[0007] By adopting the above technical solution, a large number of micro-pores exist in the recycled micro-powder, and the hydrophobic nano-silicon dioxide particles have the characteristics of hydrophobicity and nano-filling. When the raw materials are uniformly mixed and then water is added, the hydrophobic nano-silicon dioxide will be filled in the micro-pores of the recycled micro-powder. Since the hydrophobic nano-silicon dioxide particles themselves do not consume wetting water and can expel water from around their own particles, they will not cause free water to be consumed and form voids at the original position, thereby improving the density of the concrete, inhibiting the cracking of the concrete, and improving the anti-cracking effect of the concrete.

[0008] Ferric sulfate dissolves in water to form an acidic environment, while sodium silicate dissolves in water in an alkaline state. When it encounters acid, it decomposes and precipitates into colloidal precipitates, thereby achieving adhesion between hydrophobic nano-silica particles and recycled micropowder, inhibiting the loss of hydrophobic nano-silica, thereby delaying the decrease in concrete density and helping to prolong the durability of the concrete's anti-cracking effect. Ferric sulfate can also react with calcium hydroxide in concrete to form ferric hydroxide and calcium sulfate precipitates, which block the internal voids of the concrete to form support, inhibit cracks formed in the concrete due to plastic shrinkage, further improve the concrete's anti-cracking effect, and reduce the occurrence of cracking in concrete made with the addition of recycled micropowder.

[0009] Preferably, the raw materials further include 30-40 parts by weight of rubber powder.

[0010] By adopting the above technical solution, the rubber powder particles have good elasticity. Dispersing them inside the concrete can inhibit the cracking of the concrete. When micro cracks are generated inside the concrete, they can prevent the micro cracks from expanding to form macro cracks and thus cause damage to the concrete. The easy deformation property of the rubber powder can reduce the stress generated inside the concrete due to changes in humidity or temperature, thereby further improving the crack resistance of the concrete.

[0011] Preferably, the preparation method of the hydrophobic nano-silica is to place the nano-silica particles at a temperature of 40-60°C under vacuum conditions and dry them for 3-5 hours, then immerse the nano-silica particles in 100 times the volume of an organic solvent, ultrasonically disperse them for 1-1.5 hours, and then dropwise add octadecyltriethoxysilane, the mass ratio of octadecyltriethoxysilane to nano-silica particles is 3:1, stir and reflux at 50-60°C for 5-6 hours to obtain a suspension, then centrifuge to remove the supernatant, and then wash and dry the filter residue, and grind it to obtain hydrophobic nano-silica.

[0012] By adopting the above technical solution, after surface modification with octadecyltriethoxysilane, the surface of the nano-silica particles has hydrophobic carbon chains, which makes them have good hydrophobic effect. In addition, the cost of octadecyltriethoxysilane is low, which is conducive to reducing the manufacturing cost of concrete.

[0013] In a second aspect, the present application provides a method for preparing recycled micro-powder green cement, which adopts the following technical solution:

[0014] A method for preparing recycled micropowder green cement comprises the following steps: immersing 50-80 parts of recycled micropowder in a 10% (v / v) hydrochloric acid solution, stirring for 10-15 minutes, filtering and drying, grinding, and then adding 200-250 parts of cement, 25-40 parts of fly ash, 20-30 parts of hydrophobic nano-silica, 5-10 parts of sodium silicate and 10-15 parts of ferric sulfate and stirring and mixing.

[0015] By adopting the above technical solution, the recycled micropowder is pretreated before the raw materials are mixed. The recycled micropowder contains a large amount of hydrated calcium silicate. Hydrochloric acid is used to react with the recycled micropowder, thereby chemically modifying the surface of the recycled micropowder, reducing the specific surface area of ​​the recycled micropowder and the hydrophilic coefficient of the recycled micropowder, thereby reducing the water absorption of the recycled micropowder and inhibiting concrete cracking.

[0016] Preferably, 200-250 parts of cement, 50-80 parts of recycled micropowder, 25-40 parts of fly ash, 20-30 parts of hydrophobic nano-silica, 5-10 parts of sodium silicate, 10-15 parts of ferric sulfate and 30-40 parts of rubber powder are stirred and mixed.

[0017] Preferably, half of the hydrophobic nano-silica and 30-40 parts of rubber powder are ground for 6-8 minutes, the remaining hydrophobic nano-silica and 50-80 parts of regenerated micropowder are stirred and mixed, and then the mixture of the ground hydrophobic nano-silica and rubber powder, 25-40 parts of fly ash, 5-10 parts of sodium silicate and 10-15 parts of ferric sulfate are added and stirred and mixed.

[0018] By adopting the above technical solution, the hardness of the hydrophobic nano-silica particles is greater than the hardness of the rubber powder particles, and the particle size of the hydrophobic nano-silica particles is smaller than the particle size of the rubber powder particles. Part of the hydrophobic nano-silica is used to grind and mix the rubber powder. The hydrophobic nano-silica particles rub the surface of the rubber powder particles, thereby increasing the surface roughness of the rubber powder particles, making the rubber powder surface easier to adsorb and seal bubbles, thereby improving the stability and uniformity of the gas distribution in the concrete, reducing the bubble size, and increasing the elastic modulus of the concrete, thereby improving the toughness and crack resistance of the concrete.

[0019] In summary, this application has the following beneficial effects:

[0020] 1. Since the present application adopts hydrophobic nano-silica, sodium silicate and ferric sulfate, when the raw materials are evenly mixed and then water is added, the hydrophobic nano-silica will fill the fine pores of the recycled micro-powder, thereby improving the density of the concrete and inhibiting concrete cracking. The sodium silicate decomposes and separates out colloidal precipitates, thereby achieving adhesion between the hydrophobic nano-silica particles and the recycled micro-powder, which is beneficial to prolonging the durability of the concrete's anti-cracking effect. The ferric sulfate can also react with the calcium hydroxide in the concrete to form a precipitate, which blocks the internal voids of the concrete to form support, further improving the concrete's anti-cracking effect. Moreover, the present application uses waste such as recycled micro-powder and fly ash as raw materials, fully utilizing waste resources, thereby improving the reuse rate of waste concrete resources, and helping to promote the popularization and use of recycled micro-powder.

[0021] 2. The method of the present application utilizes hydrochloric acid to react with the regenerated micropowder, thereby chemically modifying the surface of the regenerated micropowder, reducing the specific surface area of ​​the regenerated micropowder, and lowering the hydrophilic coefficient of the regenerated micropowder, thereby reducing the water absorption of the regenerated micropowder and inhibiting concrete cracking.

[0022] 3. The method of the present application utilizes partially hydrophobic nano-silica to grind and mix rubber powder. The hydrophobic nano-silica particles rub the surface of the rubber powder particles, thereby increasing the surface roughness of the rubber powder particles, making the surface of the rubber powder easier to adsorb and seal bubbles, thereby improving the stability and uniformity of the gas distribution in the concrete, reducing the bubble size, and increasing the elastic modulus of the concrete, thereby improving the toughness and crack resistance of the concrete. DETAILED DESCRIPTION

[0023] The present application is further described in detail below with reference to the embodiments.

[0024]

[0025] It should be noted that % (v / v) refers to volume percentage.

[0026] Unless otherwise specified, the raw materials used in the following embodiments can be obtained from common commercial sources.

[0027] Preparation example of raw materials

[0028] Preparation Example 1

[0029] Preparation of hydrophobic nano-silica: Under a relative vacuum degree of -0.1 MPa, the nano-silica particles are placed at a temperature of 40°C and dried for 5 hours, and then the nano-silica particles are immersed in 100 times the volume of an organic solvent and ultrasonically dispersed for 1 hour. Then, octadecyltriethoxysilane is added dropwise, and the mass ratio of octadecyltriethoxysilane to nano-silica particles is 3:1. The suspension is stirred and refluxed at 50°C for 6 hours to obtain a suspension, which is then centrifuged to remove the supernatant. The filter residue is washed with NN-dimethylformamide and anhydrous ethanol four times respectively, and then dried under a relative vacuum degree of -0.1 MPa and a temperature of 60°C for 8 hours, and then ground through a 600-mesh sieve to obtain hydrophobic nano-silica.

[0030] Preparation Example 2

[0031] Preparation of hydrophobic nano-silica: Under a relative vacuum degree of -0.1 MPa, the nano-silica particles are placed at a temperature of 60°C and dried for 3 hours, and then the nano-silica particles are immersed in 100 times the volume of an organic solvent and ultrasonically dispersed for 1.5 hours. Then, octadecyltriethoxysilane is added dropwise, and the mass ratio of octadecyltriethoxysilane to nano-silica particles is 3:1. The suspension is stirred and refluxed at 60°C for 5 hours to obtain a suspension, which is then centrifuged to remove the supernatant. The filter residue is washed with NN-dimethylformamide and anhydrous ethanol four times respectively, and then dried under a relative vacuum degree of -0.1 MPa and a temperature of 60°C for 8 hours, and then ground through a 600-mesh sieve to obtain hydrophobic nano-silica.

[0032] Preparation Example 3

[0033] Preparation of hydrophobic nano-silica: Under a relative vacuum degree of -0.1 MPa, the nano-silica particles are placed at a temperature of 50°C and dried for 4 hours, and then the nano-silica particles are immersed in 100 times the volume of an organic solvent and ultrasonically dispersed for 1.5 hours. Then, octadecyltriethoxysilane is added dropwise, and the mass ratio of octadecyltriethoxysilane to nano-silica particles is 3:1. The suspension is stirred and refluxed at 55°C for 6 hours to obtain a suspension, which is then centrifuged to remove the supernatant. The filter residue is washed with NN-dimethylformamide and anhydrous ethanol four times respectively, and then dried under a relative vacuum degree of -0.1 MPa and a temperature of 60°C for 8 hours, and then ground through a 600-mesh sieve to obtain hydrophobic nano-silica.

[0034] Example

[0035] Example 1

[0036] The present application discloses a regenerated micropowder green cement, which includes the following raw materials: cement, regenerated micropowder, fly ash, hydrophobic nano-silica, sodium silicate and ferric sulfate. The hydrophobic nano-silica is prepared by Preparation Example 1, and the content of each component is shown in Table 1 below.

[0037] The preparation method of the regenerated micro-powder green cement comprises the following steps: stirring and uniformly mixing cement, regenerated micro-powder, fly ash, hydrophobic nano-silica, sodium silicate and ferric sulfate.

[0038] Example 2

[0039] The difference from Example 1 is that the hydrophobic nano-silica is prepared by Preparation Example 2, and the addition amount of each raw material is different. The content of each component is shown in Table 1 below.

[0040] Example 3

[0041] The difference from Example 1 is that the hydrophobic nano-silica is prepared by Preparation Example 3, and the addition amount of each raw material is different. The content of each component is shown in Table 1 below.

[0042] Example 4

[0043] The difference from Example 1 is that rubber powder is added to the raw materials, and the content of each component is shown in Table 1 below.

[0044] The preparation method of the regenerated micro-powder green cement comprises the following steps: stirring and uniformly mixing cement, regenerated micro-powder, fly ash, hydrophobic nano-silica, sodium silicate, ferric sulfate and rubber powder.

[0045] Example 5

[0046] The difference from Example 4 is that the preparation method is different.

[0047] The preparation method of recycled micro-powder green cement includes the following steps: grinding half of the hydrophobic nano-silica and rubber powder for 6 minutes, stirring and mixing the remaining hydrophobic nano-silica and recycled micro-powder, and then adding the ground mixture of hydrophobic nano-silica and rubber powder, fly ash, sodium silicate and ferric sulfate and stirring and mixing.

[0048] Example 6

[0049] The difference from Example 1 is that the preparation method is different.

[0050] The preparation method of recycled micro-powder green cement includes the following steps: immersing the recycled micro-powder in 10% (v / v) hydrochloric acid solution, stirring for 10 minutes, filtering and drying, grinding through a 400-mesh sieve, and then adding cement, fly ash, hydrophobic nano-silica, sodium silicate and ferric sulfate and stirring and mixing.

[0051] Example 7

[0052] The present application discloses a regenerated micropowder green cement, which includes the following raw materials: cement, regenerated micropowder, fly ash, hydrophobic nano-silica, sodium silicate, ferric sulfate and rubber powder. The hydrophobic nano-silica is prepared by Preparation Example 1, and the content of each component is shown in Table 1 below.

[0053] The preparation method of recycled micropowder green cement includes the following steps: immersing the recycled micropowder in a 10% (v / v) hydrochloric acid solution, stirring for 10 minutes, filtering and drying, grinding through a 400-mesh sieve, taking half of the hydrophobic nano-silica and rubber powder and grinding for 6 minutes, stirring and mixing the remaining hydrophobic nano-silica and the treated recycled micropowder, and then adding the ground mixture of the hydrophobic nano-silica and rubber powder, fly ash, sodium silicate and ferric sulfate and stirring and mixing.

[0054] Example 8

[0055] The application discloses a recycled micro-powder green cement, which comprises the following raw materials: cement, recycled micro-powder, fly ash, hydrophobic nano-silicon dioxide, sodium silicate, ferric sulfate and rubber powder, the hydrophobic nano-silicon dioxide is prepared by the preparation example 2, and the content of each component is shown in the following table 1.

[0056] The preparation method of the recycled micro-powder green cement comprises the following steps: submerging the recycled micro-powder in a 10% (v / v) hydrochloric acid solution, stirring for 15 min, filtering and drying, grinding through a 400-mesh sieve, grinding half of the hydrophobic nano-silicon dioxide and the rubber powder for 8 min, stirring and uniformly mixing the remaining hydrophobic nano-silicon dioxide and the treated recycled micro-powder, and then adding the mixture of the hydrophobic nano-silicon dioxide and the rubber powder after grinding, the fly ash, the sodium silicate and the ferric sulfate.

[0057] Example 9

[0058] The application discloses a recycled micro-powder green cement, which comprises the following raw materials: cement, recycled micro-powder, fly ash, hydrophobic nano-silicon dioxide, sodium silicate, ferric sulfate and rubber powder, the hydrophobic nano-silicon dioxide is prepared by the preparation example 3, and the content of each component is shown in the following table 1.

[0059] The preparation method of the recycled micro-powder green cement comprises the following steps: submerging the recycled micro-powder in a 10% (v / v) hydrochloric acid solution, stirring for 15 min, filtering and drying, grinding through a 400-mesh sieve, grinding half of the hydrophobic nano-silicon dioxide and the rubber powder for 8 min, stirring and uniformly mixing the remaining hydrophobic nano-silicon dioxide and the treated recycled micro-powder, and then adding the mixture of the hydrophobic nano-silicon dioxide and the rubber powder after grinding, the fly ash, the sodium silicate and the ferric sulfate.

[0060] Comparative example

[0061] Comparative example 1

[0062] The difference from the example 1 is that the cement without adding the hydrophobic nano-silicon dioxide, the sodium silicate and the ferric sulfate in the raw materials is used as a blank control group.

[0063] Comparative example 2

[0064] The difference from the example 1 is that the sodium silicate is replaced by calcium silicate, and the content of each component is shown in the following table 1.

[0065] Comparative example 3

[0066] The difference from the example 1 is that the ferric sulfate is replaced by sodium sulfate, and the content of each component is shown in the following table 1.

[0067] Comparative example 4

[0068] The difference from the example 1 is that the ferric sulfate is not added, and the content of each component is shown in the following table 1.

[0069] Comparative Example 5

[0070] The difference between Comparative Example 4 is that sodium silicate is replaced by calcium silicate, and the content of each component is shown in Table 1 below.

[0071] Table 1 Component Content Table

[0072]

[0073]

[0074] Performance Test Test

[0075] (1) Anti-cracking test (characterized by cracking index): the cement prepared by each example is prepared into a concrete sample according to the ratio of cement: sand: stone: water: water reducing agent of 1:0.5:0.4:0.45:0.03, and the cracking index of each example and comparative example is detected according to the standard GB / T 29417-2012 "Cement Mortar and Concrete Drying Shrinkage and Cracking Performance Test Method", and the test results are shown in Table 2 below.

[0076] (2) Anti-cracking performance durability test: the concrete sample prepared by the cement prepared by Example 1 and Comparative Examples 2, 4-5 is detected according to the standard GB / T 29417-2012 "Cement Mortar and Concrete Drying Shrinkage and Cracking Performance Test Method" to detect the cracking index, and then the concrete sample is immersed in deionized water, and after 24h, the cracking index is detected again, and the test results are shown in Table 2 below

[0077] Table 2 Test Results of Each Example and Comparative Example

[0078]

[0079]

[0080] In summary:

[0081] 1. It can be seen from Example 1 and Example 4 in combination with Table 2 that the addition of rubber powder in cement can improve the anti-cracking performance of the prepared concrete, and the reason may be that the rubber powder particles have good elasticity, which can inhibit the cracking of concrete and hinder the expansion of microcracks in concrete to form macrocracks and cause concrete damage, thereby improving the anti-cracking performance of concrete.

[0082] 2. From Example 1 and Examples 4-5 and Table 2, it can be seen that mixing and grinding the hydrophobic nano-silica and rubber powder before mixing the raw materials is beneficial to improving the crack resistance of the prepared concrete. The reason may be that the hardness of the hydrophobic nano-silica particles is greater than the hardness of the rubber powder particles, and the particle size of the hydrophobic nano-silica particles is smaller than the particle size of the rubber powder particles. Grinding and mixing the rubber powder with hydrophobic nano-silica can increase the surface roughness of the rubber powder particles, making the rubber powder surface more susceptible to adsorption and closed bubbles, thereby improving the stability and uniformity of the gas distribution in the concrete, reducing the bubble size, and increasing the elastic modulus of the concrete, thereby improving the toughness and crack resistance of the concrete.

[0083] 3. Combining Examples 1 and 6 with Table 2, it can be seen that treating the regenerated micropowder with hydrochloric acid before mixing the raw materials can improve the crack resistance of the resulting concrete. This may be because the regenerated micropowder contains a large amount of hydrated calcium silicate. The hydrochloric acid reacts with the regenerated micropowder to chemically modify the surface of the regenerated micropowder, reducing the specific surface area of ​​the regenerated micropowder and the hydrophilic coefficient of the regenerated micropowder, thereby reducing the water absorption of the regenerated micropowder and inhibiting concrete cracking.

[0084] 4. Combining Example 1 and Comparative Examples 1-2, 4-5, and Table 2, it can be seen that the co-addition of sodium silicate and ferric sulfate to the raw materials can improve the durability of the crack resistance of the prepared concrete. The reason may be that ferric sulfate dissolves in water to form an acidic environment, while sodium silicate dissolves in water in an alkaline state. When it is exposed to acid, it decomposes and precipitates into a colloidal precipitate, which achieves adhesion between the hydrophobic nano-silica particles and the regenerated micropowder, inhibits the loss of hydrophobic nano-silica, and thus delays the decrease in concrete density, which is conducive to prolonging the durability of the concrete's anti-cracking effect.

[0085] 5. Combining Example 1 and Comparative Example 3 with Table 2, it can be seen that the addition of ferric sulfate to the raw materials can improve the crack resistance of the prepared concrete. The reason may be that ferric sulfate can react with calcium hydroxide in the concrete to form ferric hydroxide and calcium sulfate precipitates, which block the internal voids of the concrete to form support, inhibit cracks formed in the concrete due to plastic shrinkage, and further improve the crack resistance of the concrete.

[0086] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for preparing recycled micro-powder green cement, characterized in that: The following steps are involved: Immerse 50-80 parts of regenerated micropowder in 10% (v / v) hydrochloric acid solution, stir for 10-15 minutes, filter, dry, and grind. Take half of 20-30 parts of hydrophobic nano-silica and 30-40 parts of rubber powder and grind for 6-8 minutes. Stir and mix the remaining hydrophobic nano-silica and regenerated micropowder. Then add the ground mixture of hydrophobic nano-silica and rubber powder, 200-250 parts of cement, 25-40 parts of fly ash, 5-10 parts of sodium silicate and 10-15 parts of ferric sulfate and stir and mix.

2. The method for preparing recycled micro-powder green cement according to claim 1, characterized in that: The preparation method of the hydrophobic nano-silica comprises the following steps: drying the nano-silica particles at a temperature of 40-60° C. for 3-5 hours under vacuum conditions, immersing the nano-silica particles in 100 times the volume of an organic solvent, ultrasonically dispersing the nano-silica particles for 1-1.5 hours, dropwise adding octadecyltriethoxysilane in a mass ratio of octadecyltriethoxysilane to the nano-silica particles of 3:1, stirring and refluxing at 50-60° C. for 5-6 hours to obtain a suspension, centrifuging to remove the supernatant, washing and drying the filter residue, and then grinding to obtain the hydrophobic nano-silica.

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