A kind of recycled aggregate concrete and its preparation method and application

Abstract

The invention discloses a recycled aggregate concrete and a preparation method and application thereof, belonging to the technical field of environmentally friendly building materials. The recycled aggregate concrete, by weight, comprises the following raw materials: 250-270 parts of cement, 1800-1900 parts of silicate-modified recycled aggregate, 100-110 parts of fly ash, 0.5-1.5 parts of water reducer, and 140-150 parts of water. The waste concrete is wetted with water, freeze-dried, and mechanically crushed to a particle size of 5-25 mm; impurities are removed by screening, and after washing, it is first placed in an alkali solution and soaked for 2-4 hours, and then added to a micro-powder silicate solution, wrapped for 0.5-1 hour, to obtain silicate-modified recycled aggregate. The present invention solves the key technical problems of the application of recycled aggregate in concrete by optimizing the processing method and mix design of recycled aggregate, and provides a green and low-carbon recycling scheme for bridge engineering waste.

Description

Technical Field

[0001] The invention belongs to the technical field of environmentally friendly building materials, and specifically relates to recycled aggregate concrete and a preparation method and application thereof. Background Art

[0002] The resource utilization of waste concrete can effectively recycle waste concrete for secondary use, reduce production costs and protect the natural environment. The resource utilization of waste concrete has attracted widespread attention. Among them, crushing these waste concrete and adding them as recycled aggregate to newly prepared concrete is a common method, which has relatively low cost and technical requirements and is theoretically easier to promote and apply on a large scale.

[0003] However, the actual situation is that the strength and water absorption resistance of concrete prepared by directly using recycled aggregates formed by crushing waste concrete to replace natural aggregates are not ideal, and the performance gap with natural aggregate concrete is large. Research and analysis found that this is mainly due to the high water absorption rate caused by the large number of cracks and pores in the recycled aggregate itself. After entering the concrete, it will strongly absorb the moisture in the cement material at its interface, resulting in insufficient hydration of the cement material and failure to generate sufficient hydration products, resulting in poor interface bonding between the recycled aggregate and the concrete matrix, and the concrete is prone to cracking when subjected to load. At the same time, there are a large number of pores and channels at the interface, and the cracks and pores of the recycled aggregate itself provide more sufficient diffusion and migration channels for water, chloride ions, etc., resulting in insufficient impermeability of concrete, which is not only easy to cause corrosion of steel bars in concrete, but also a large number of chloride ions in seawater can easily cause serious corrosion to steel bars in concrete; at the same time, insufficient impermeability can also easily cause freeze-thaw damage to concrete.

[0004] The waste generated from bored pile heads in bridge projects has a complex composition, containing impurities such as concrete, steel bars, drilling mud residues and soil deposits. If direct doping is used, its strength will inevitably be difficult to meet the concrete technical requirements in bridge projects. Therefore, how to effectively recycle the waste concrete generated in bridge projects and reduce material waste and construction waste stacking pressure during construction is an urgent problem to be solved. Summary of the invention

[0005] One of the purposes of the present invention is to provide a recycled aggregate concrete to solve the problem of poor strength performance of recycled concrete;

[0006] The second object of the present invention is to provide a method for preparing recycled aggregate concrete to solve the problem of resource waste in bridge engineering;

[0007] A third object of the present invention is to provide an application of recycled aggregate concrete.

[0008] The purpose of the present invention can be achieved through the following technical solutions:

[0009] In a first aspect, a recycled aggregate concrete comprises the following raw materials in parts by weight:

[0010] 250-270 parts of cement, 1800-1900 parts of silicate modified recycled aggregate, 100-110 parts of fly ash, 0.5-1.5 parts of water reducer, and 140-150 parts of water.

[0011] Furthermore, the silicate modified recycled aggregate is prepared by the following steps:

[0012] The waste concrete is soaked in water, freeze-dried, and then mechanically crushed to a particle size of 5-25 mm; impurities are removed by screening, and after washing, it is first soaked in alkaline solution for 2-4 hours, and then added to a micro-powder silicate solution and wrapped for 0.5-1 hour to obtain silicate-modified recycled aggregate.

[0013] Furthermore, the alkali solution is a sodium hydroxide solution with a mass concentration of 1-3%.

[0014] Furthermore, the mass concentration of the micro-powder silicate solution is 5-10%.

[0015] Furthermore, the cement is ordinary Portland cement with a strength grade of ≥42.5.

[0016] Furthermore, the fly ash is Class F fly ash, with a fineness of ≤45 μm and a sieve residue of ≤12%.

[0017] Furthermore, the water reducing agent is a polycarboxylic acid-based water reducing agent, and the water reduction rate is ≥25%.

[0018] In a second aspect, a method for preparing recycled aggregate concrete comprises the following steps:

[0019] Weigh each raw material according to its weight, dry-mix the silicate modified recycled aggregate for 25-35 seconds, then add cement and fly ash, and continue dry-mixing for 50-70 seconds to obtain a mixed material; dissolve the water reducer in water, add it to the mixed material, and wet-mix it for 150-200 seconds to obtain recycled aggregate concrete.

[0020] The third aspect is the application of recycled aggregate concrete in bridge engineering.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention effectively improves the physical properties of recycled aggregates, reduces their water absorption and increases their strength by optimizing the processing method of recycled aggregates. The waste concrete is soaked in alkali solution to generate alkali-aggregate reaction, produce alkali silicate gel, and then is wrapped by micro-powder silicate to fill the gaps between cement particles and further form a gel with hydration products; in addition, micro-powder silicate can also react with calcium hydroxide in cement to generate additional CSH gel, which further enhances the density and strength of concrete by filling cracks and pores, and enhances its overall strength and stability, thereby achieving the purpose of extending the service life.

[0023] 2. The mix design method adopted by the present invention fully considers the characteristics of recycled aggregates, so that the prepared concrete has good working performance and mechanical properties. By optimizing the processing method and mix design of recycled aggregates, the key technical problems of the application of recycled aggregates in concrete are solved, providing a green and low-carbon recycling solution for bridge engineering waste.

[0024] 3. The application of the present invention can significantly reduce the treatment cost of bridge engineering waste and reduce the demand for natural aggregates, thus having significant environmental and economic benefits. DETAILED DESCRIPTION

[0025] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Preparation Example 1

[0027] Silicate modified recycled aggregate is prepared by the following steps:

[0028] The waste concrete was moistened with water, placed in a freezer for freeze drying, and then mechanically crushed to a particle size of 5-25 mm using a mechanical crushing device; impurities and oversized particles were sieved to remove impurities and oversized particles, and surface dust was removed by washing with clean water; then, it was first soaked in a 2% mass concentration sodium hydroxide solution for 3 hours, and then added to a 7% mass concentration micro-powder silicate solution, wrapped for 0.75 hours, and finally naturally air-dried for 24 hours to obtain silicate-modified recycled aggregate.

[0029] Example 1

[0030] A recycled aggregate concrete, comprising the following raw materials in parts by weight:

[0031] 250 parts of ordinary Portland cement with strength grade ≥42.5, 1800 parts of silicate modified recycled aggregate prepared in Preparation Example 1, 100 parts of Class F fly ash (fineness ≤45μm, sieve residue ≤12%), 0.5 parts of polycarboxylic acid water reducer (ART-M611 produced by Jiangsu Aolaite New Materials Co., Ltd.), and 140 parts of water;

[0032] The method for preparing the recycled aggregate concrete comprises the following steps:

[0033] Weigh the raw materials according to the above weight proportions, put the silicate modified recycled aggregate into a mixer and dry mix for 30 seconds, then add cement and fly ash, continue dry mixing for 60 seconds to obtain a mixed material; dissolve the water reducer in water, slowly add it into the mixer, wet mix for 180 seconds, pour the obtained recycled aggregate concrete into a mold, vibrate it to make it dense, and cure it under standard conditions for 28 days.

[0034] Example 2

[0035] A recycled aggregate concrete, comprising the following raw materials in parts by weight:

[0036] 255 parts of ordinary Portland cement with strength grade ≥42.5, 1825 parts of silicate modified recycled aggregate prepared in Preparation Example 1, 102 parts of Class F fly ash (fineness ≤45μm, sieve residue ≤12%), 0.8 parts of polycarboxylic acid water reducer (ART-M611 produced by Jiangsu Aolaite New Materials Co., Ltd.), and 142 parts of water;

[0037] The method for preparing the recycled aggregate concrete comprises the following steps:

[0038] Weigh the raw materials according to the above weight proportions, put the silicate modified recycled aggregate into a mixer and dry mix for 30 seconds, then add cement and fly ash, continue dry mixing for 60 seconds to obtain a mixed material; dissolve the water reducer in water, slowly add it into the mixer, wet mix for 180 seconds, pour the obtained recycled aggregate concrete into a mold, vibrate it to make it dense, and cure it under standard conditions for 28 days.

[0039] Example 3

[0040] A recycled aggregate concrete, comprising the following raw materials in parts by weight:

[0041] 260 parts of ordinary Portland cement with strength grade ≥42.5, 1850 parts of silicate modified recycled aggregate prepared in Preparation Example 1, 105 parts of Class F fly ash (fineness ≤45μm, sieve residue ≤12%), 1.0 part of polycarboxylic acid water reducer (ART-M611 produced by Jiangsu Aolaite New Materials Co., Ltd.), and 145 parts of water;

[0042] The method for preparing the recycled aggregate concrete comprises the following steps:

[0043] Weigh the raw materials according to the above weight proportions, put the silicate modified recycled aggregate into a mixer and dry mix for 30 seconds, then add cement and fly ash, continue dry mixing for 60 seconds to obtain a mixed material; dissolve the water reducer in water, slowly add it into the mixer, wet mix for 180 seconds, pour the obtained recycled aggregate concrete into a mold, vibrate it to make it dense, and cure it under standard conditions for 28 days.

[0044] Example 4

[0045] A recycled aggregate concrete, comprising the following raw materials in parts by weight:

[0046] 265 parts of ordinary Portland cement with strength grade ≥42.5, 1875 parts of silicate modified recycled aggregate prepared in Preparation Example 1, 108 parts of Class F fly ash (fineness ≤45μm, sieve residue ≤12%), 1.2 parts of polycarboxylic acid water reducer (ART-M611 produced by Jiangsu Aolaite New Materials Co., Ltd.), and 148 parts of water;

[0047] The method for preparing the recycled aggregate concrete comprises the following steps:

[0048] Weigh the raw materials according to the above weight proportions, put the silicate modified recycled aggregate into a mixer and dry mix for 30 seconds, then add cement and fly ash, continue dry mixing for 60 seconds to obtain a mixed material; dissolve the water reducer in water, slowly add it into the mixer, wet mix for 180 seconds, pour the obtained recycled aggregate concrete into a mold, vibrate it to make it dense, and cure it under standard conditions for 28 days.

[0049] Example 5

[0050] A recycled aggregate concrete, comprising the following raw materials in parts by weight:

[0051] 270 parts of ordinary Portland cement with strength grade ≥42.5, 1900 parts of silicate modified recycled aggregate prepared in Preparation Example 1, 110 parts of Class F fly ash (fineness ≤45μm, sieve residue ≤12%), 1.5 parts of polycarboxylic acid water reducer (ART-M611 produced by Jiangsu Aolaite New Materials Co., Ltd.), and 150 parts of water;

[0052] The method for preparing the recycled aggregate concrete comprises the following steps:

[0053] Weigh the raw materials according to the above weight proportions, put the silicate modified recycled aggregate into a mixer and dry mix for 30 seconds, then add cement and fly ash, continue dry mixing for 60 seconds to obtain a mixed material; dissolve the water reducer in water, slowly add it into the mixer, wet mix for 180 seconds, pour the obtained recycled aggregate concrete into a mold, vibrate it to make it dense, and cure it under standard conditions for 28 days.

[0054] Comparative Preparation Example 1

[0055] A recycled aggregate is prepared by the following steps:

[0056] The waste concrete is soaked in water, placed in a freezer for freeze-drying, and then mechanically crushed to a particle size of 5-25 mm using a mechanical crushing device; impurities and oversized particles are removed by sieving, and surface dust is removed by washing with clean water. The concrete is naturally air-dried for 24 hours to obtain recycled aggregate.

[0057] Comparative Example 1

[0058] A recycled aggregate concrete, which is different from Example 1 in that only the silicate modified recycled aggregate is replaced by the recycled aggregate prepared in Comparative Preparation Example 1, and the other components and preparation methods remain the same.

[0059] Comparative Example 2

[0060] A natural aggregate concrete, which is different from Example 1 in that only the silicate modified recycled aggregate is replaced by the natural aggregate, and the other components and preparation methods remain the same.

[0061] Comparative Preparation Example 2

[0062] A mechanically ground recycled aggregate is prepared by the following steps:

[0063] The waste concrete is soaked in water, placed in a freezer for freeze-drying, and then mechanically crushed to a particle size of 5-25 mm using a mechanical crushing device; impurities and oversized particles are removed by screening, and surface dust is removed by washing with clean water. The surface of the recycled aggregate is then mechanically ground to remove the old mortar attached to the surface, and naturally air-dried for 24 hours to obtain mechanically ground recycled aggregate.

[0064] Comparative Example 3

[0065] A recycled aggregate concrete, which is different from Example 1 in that only the silicate-modified recycled aggregate is replaced by the mechanically ground recycled aggregate prepared in Comparative Preparation Example 2, and the other components and preparation methods remain the same.

[0066] Comparative Example 4

[0067] A recycled aggregate concrete, which is different from Example 1 in that the weight portion of silicate modified recycled aggregate is replaced by 2200 parts, and the other components and preparation methods remain the same.

[0068] Comparative Example 5

[0069] A recycled aggregate concrete, which is different from Example 1 in that ordinary Portland cement is replaced by slag Portland cement, and the other components and preparation methods remain the same.

[0070] The concrete prepared in Examples 1-5 and Comparative Examples 1-5 was subjected to a concrete compressive strength test according to GB / T 50080-2016 Standard for Testing Performance of Ordinary Concrete Mixtures. The test results are shown in Table 1.

[0071] Table 1

[0072]

[0073] It can be seen from Table 1 that the modification treatment method of immersing the micro-powder silicate in alkali solution can effectively improve the interface bonding force between the recycled aggregate and the concrete matrix, so that the prepared concrete has a strong compressive strength.

[0074] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0075] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A recycled aggregate concrete, characterized in that: According to weight parts, it includes the following raw materials: 250-270 parts of cement, 1800-1900 parts of silicate modified recycled aggregate, 100-110 parts of fly ash, 0.5-1.5 parts of water reducer, 140-150 parts of water; The silicate modified recycled aggregate is prepared by the following steps: The waste concrete is soaked in water, freeze-dried, and then mechanically crushed to a particle size of 5-25 mm; impurities are removed by screening, and after washing, it is first soaked in alkaline solution for 2-4 hours, and then added to a micro-powder silicate solution and wrapped for 0.5-1 hour to obtain silicate-modified recycled aggregate; The alkali solution is a sodium hydroxide solution with a mass concentration of 1-3%; Waste concrete is soaked in alkali solution, an alkali-aggregate reaction occurs, producing alkali silicate gel, which is then wrapped by micro-powder silicate to fill the gaps between cement particles and further form a gel with hydration products; micro-powder silicate can also react with calcium hydroxide in cement to generate additional CSH gel.

2. The recycled aggregate concrete according to claim 1, characterized in that: The mass concentration of the micro-powder silicate solution is 5-10%.

3. The recycled aggregate concrete according to claim 1, characterized in that: The cement is silicate cement with a strength grade of ≥42.

5.

4. The recycled aggregate concrete according to claim 1, characterized in that: The fly ash is Class F fly ash, with a fineness of ≤45 μm and a sieve residue of ≤12%.

5. The recycled aggregate concrete according to claim 1, characterized in that: The water reducing agent is a polycarboxylic acid-based water reducing agent, and the water reducing rate is ≥25%.

6. A method for preparing recycled aggregate concrete as claimed in claim 1, characterized in that: The following steps are involved: Weigh each raw material according to its weight, dry-mix the silicate modified recycled aggregate for 25-35 seconds, then add cement and fly ash, and continue dry-mixing for 50-70 seconds to obtain a mixed material; dissolve the water reducer in water, add it to the mixed material, and wet-mix it for 150-200 seconds to obtain recycled aggregate concrete.

7. Use of the recycled aggregate concrete as claimed in claim 1 in bridge engineering.

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