Solid-waste-based high-performance concrete as well as preparation method and application thereof

Abstract

The invention provides solid-waste-based high-performance concrete as well as a preparation method and application thereof, and belongs to the technical field of concrete materials. The two solid wastes of the salt lake lithium magnesium extraction slag and the dredged sediment fly ash are used as raw materials, the seawater, the sea sand and the gravel are added to prepare the concrete, the obtained concrete is low in alkalinity, the concrete does not easily react with nuclear waste after being prepared into a nuclear waste storage container, the concrete cannot be corroded, and the service life of the concrete is prolonged. The prepared storage container can keep relatively high strength; in addition, two solid waste raw materials including the salt lake lithium magnesium extraction slag and the dredged sediment fly ash are recycled, and the energy-saving and environment-friendly development requirements are met.

Description

Technical Field

[0001] The present invention belongs to the technical field of concrete materials, and in particular relates to a solid waste-based high-performance concrete and a preparation method and application thereof. Background Art

[0002] With the continuous development of nuclear power generation technology, the disposal of low- and medium-level radioactive nuclear waste has become one of the key issues that need to be solved urgently. Whether it is stored in surface reservoirs, buried in shallow layers, or buried in abandoned mines and caves, nuclear waste must be sealed in storage containers to prevent radioactive contamination and environmental damage to the outside world.

[0003] In the related art, the material used for nuclear waste storage containers is mainly ordinary concrete, which has the advantage of low cost. On the basis of low cost, the storage container can be manufactured with a larger wall thickness to improve storage safety. However, the pH value of ordinary concrete is 12.5-13.5, which is highly alkaline and can react with some substances in nuclear waste to cause corrosion of concrete, affecting the overall strength of the storage container.

[0004] Waterways, rivers or waterways need to be regularly excavated and cleaned to improve water flow conditions, increase water depth or widen river channels. Sediments excavated from underwater are called dredged sediments. Dredged sediments mainly contain components such as silicon oxide and aluminum oxide, and the proportion of amorphous substances is relatively high. A large amount of magnesium slag is produced during the process of lithium extraction from salt lakes, and the magnesium oxide content in the magnesium slag is as high as 70%. Based on the above-mentioned composition characteristics, the magnesium slag produced by dredged sediments and lithium extraction from salt lakes meets the basic requirements for application in building materials, but the magnesium slag produced by dredged sediments and lithium extraction from salt lakes is usually treated as solid waste and directly landfilled, resulting in a waste of resources.

[0005] Therefore, it is necessary to provide a solid waste-based high-performance concrete and a preparation method and application thereof to solve the above problems. Summary of the invention

[0006] The present invention provides a solid waste-based high-performance concrete and a preparation method and application thereof. The concrete is prepared by taking two solid wastes, namely, lithium-magnesium slag extracted from salt lakes and fly ash from dredged sediments, as raw materials, adding seawater, sea sand and crushed stone. The obtained concrete has low alkalinity and is not easy to react with nuclear waste after being prepared into a nuclear waste storage container, so that the concrete will not be corroded, and the prepared storage container can maintain a high strength. The reuse of the two solid waste raw materials, namely, lithium-magnesium slag extracted from salt lakes and fly ash from dredged sediments, is also realized, thereby effectively solving at least one technical problem involved in the background technology.

[0007] In order to solve the above-mentioned technical problems, the present invention is achieved as follows: A solid waste-based high-performance concrete, comprising the following components in parts by weight: 100-400 parts of magnesium slag powder, 100-400 parts of dredged sediment fly ash, 500-800 parts of sea sand, 900-1200 parts of crushed stone, 5-30 parts of water reducer and 100-300 parts of sea water; the magnesium slag powder adopts the magnesium slag with a particle size of less than 600μm and a magnesium oxide content of 50-70% in the salt lake lithium extraction process; the dredged sediment is the sediment dredged from the waterway, river or channel, and the dredged sediment fly ash is the fly ash with a silicon oxide content of 40-60%, a calcium oxide content of 15-30% and an aluminum oxide content of 3-10% formed after the dredged sediment is burned at high temperature.

[0008] As a preferred improvement, the fineness modulus of sea sand is 2.5-2.7, and the apparent density is 2500-2600 kg / m 3 ; The gravel is a continuously graded gravel with a particle size of 5-15mm; the chloride ion content of seawater is 15-20g / L, and the magnesium ion content is 1-3g / L.

[0009] As a preferred improvement, the water reducing agent is a polycarboxylic acid-based water reducing agent having a water reducing efficiency of more than 20%.

[0010] A method for preparing the above-mentioned solid waste-based high-performance concrete comprises the following steps: Step S1, dry-mix 100-400 parts of magnesium slag powder and 100-400 parts of dredged sediment incineration fly ash according to weight parts, then add 100-300 parts of seawater, and stir evenly to form a slurry; Step S2, adding 500-800 parts of sea sand and 900-1200 parts of crushed stone into the slurry according to weight parts, and then adding 5-30 parts of water reducing agent, and stirring evenly to obtain concrete slurry; Step S3, pour the concrete slurry into the mold, place it at room temperature, cover it with plastic wrap, remove the mold after 24 hours, and then place it in a standard curing room for 28 days to obtain solid waste-based high-performance concrete.

[0011] As a preferred improvement, the following steps are also included before placing the product in a standard curing room for curing: Put it into the carbon dioxide curing room and cure it for 4-12 hours at a carbon dioxide concentration of 20%-100% and a pressure of 0.1-0.2MPa, then take it out.

[0012] An application of the solid waste-based high-performance concrete as described above is used as a casting material for nuclear waste storage containers.

[0013] The beneficial effects of the present invention are: (1) Using two solid wastes, lithium-magnesium slag from salt lakes and fly ash from dredged sediments, as raw materials, and adding seawater, sea sand and gravel to prepare concrete, this achieves waste recycling and meets the development needs of energy conservation and environmental protection; (2) The solid waste-based high-performance concrete provided by the present invention does not contain alkaline compounds such as calcium hydroxide and has a neutral pH value, which can effectively prevent the corrosion of concrete caused by the reaction between nuclear waste and concrete, ensure the strength of the storage container under long-term use, and avoid nuclear leakage. DETAILED DESCRIPTION

[0014] 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 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.

[0015] This embodiment provides a solid waste-based high-performance concrete, including the following components in parts by weight: 100-400 parts of magnesium slag powder, 100-400 parts of dredged sediment fly ash, 500-800 parts of sea sand, 900-1200 parts of crushed stone, 5-30 parts of water reducer and 100-300 parts of sea water; the magnesium slag powder adopts the magnesium slag with a particle size of less than 600μm and a magnesium oxide content of 50-70% in the salt lake lithium extraction process; the dredged sediment is the sediment dredged from the waterway, river or channel, and the dredged sediment fly ash is the fly ash with a silicon oxide content of 40-60%, a calcium oxide content of 15-30% and an aluminum oxide content of 3-10% formed after the dredged sediment is burned at high temperature.

[0016] The target product of the salt lake lithium extraction process is lithium. Therefore, magnesium exists as an impurity component in the salt lake lithium extraction process to form magnesium slag. The present invention reasonably utilizes the magnesium slag of the salt lake lithium extraction process, realizes the recycling of waste, and can reduce the mining of dolomite.

[0017] Dredged sediment refers to sediment dredged from waterways, rivers or channels, which mainly contains silicon oxide, aluminum oxide, calcium oxide and other components, and has a high proportion of amorphous substances, and can be used in building materials. In this embodiment, the dredged sediment is burned, and the fly ash after burning is used as a concrete ingredient, so as to realize the reuse of dredged sediment and meet the development needs of energy conservation and environmental protection.

[0018] Dredged sediments generally contain a large amount of corrupted organic components. If directly added to concrete, the organic components will continue to decay in the concrete system to produce gas and moisture, thereby forming a hollow structure inside the concrete and affecting the strength of the concrete. Therefore, the present invention decomposes the organic components in the dredged sediments into carbon dioxide and water through high-temperature combustion and then discharges them, leaving only the inorganic components.

[0019] The salt lake lithium-magnesium slag contains active magnesium oxide, and the dredged sediment fly ash mainly contains active silicon oxide, so the two will react to form hydrated magnesium silicate gel (MSH gel), which has a gelling effect and is used to replace the CSH gel in ordinary concrete. It is the source of concrete strength. The hydrated magnesium silicate gel itself is neutral and will not increase the alkalinity of the concrete system. It can well control the increase in the pH value of the concrete system and make the pH value of the concrete system neutral. The dredged sediment fly ash also contains some aluminum oxide and calcium oxide, so a small amount of aluminum silica gel (ASH gel) and CSH gel will be formed less. These hydration products make the pH value of the concrete neutral.

[0020] The sea sand is from Jiaozhou, Qingdao, with a fineness modulus of 2.5-2.7 and an apparent density of 2500-2600kg / m 3 , which mainly plays the role of fine aggregate in the concrete system; the continuously graded crushed stone with a particle size of 5-15mm mainly plays the role of coarse aggregate in the concrete system. The seawater is taken from the sea area near Jiaozhou Bay, Qingdao, with a chloride ion content of 15-20g / L and a magnesium ion content of 1-3g / L. The chloride ions in seawater and sea sand can react with the active magnesium oxide in magnesium slag to generate phase 5 (5Mg(OH)2·MgCl2·8H2O) and phase 3 (3Mg(OH)2·MgCl2·8H2O). Both phase 5 and phase 3 are fibrous crystals, which can play a role in fiber restraint and limit the loss of strength of concrete in the service environment.

[0021] The water reducing agent is a polycarboxylic acid-based water reducing agent with a water reducing efficiency of more than 20%, which is a conventional additive in the art and will not be described in detail in this embodiment.

[0022] This embodiment also provides a method for preparing solid waste-based high-performance concrete, comprising the following steps: Step S1, dry-mix 100-400 parts of magnesium slag powder and 100-400 parts of dredged sediment incineration fly ash according to weight parts, then add 100-300 parts of seawater, and stir evenly to form a slurry; Step S2, adding 500-800 parts of sea sand and 900-1200 parts of crushed stone into the slurry according to weight parts, and then adding 5-30 parts of water reducing agent, and stirring evenly to obtain concrete slurry; Step S3, pour the concrete slurry into the mold, place it at room temperature, cover it with plastic wrap, remove the mold after 24 hours, and then place it in a standard curing room for 28 days to obtain solid waste-based high-performance concrete.

[0023] As a preferred method, the following steps are also included before placing the product in a standard curing room for curing: Put it into the carbon dioxide curing room and cure it for 4-12 hours at a carbon dioxide concentration of 20%-100% and a pressure of 0.1-0.2MPa, then take it out.

[0024] The preparation method provided by the present invention first performs carbon dioxide curing before traditional curing. Under carbon dioxide conditions, the remaining magnesium oxide in the magnesium slag reacts with carbon dioxide to form magnesium carbonate, and magnesium hydroxide reacts with carbon dioxide to form hydrated hydroxy magnesium carbonate, thereby improving the strength of concrete. In addition, after carbon dioxide reacts with alkaline substances such as magnesium oxide and magnesium hydroxide, the alkalinity of the entire concrete can be reduced, making the pH value of the solid waste-based high-performance concrete neutral.

[0025] This embodiment also provides an application of solid waste-based high-performance concrete, which is used as a casting material for nuclear waste storage containers.

[0026] Nuclear waste contains many different types of substances, many of which react with strong acids or bases. For example, radioactive metal elements such as uranium, plutonium, and neptunium and their compounds will react with alkaline substances to undergo oxidation and dissolution. Some organic nuclear waste contains organic ion exchange resins, which will undergo hydrolysis and decomposition when encountering strong bases. Radioactive substances containing aluminum or magnesium can also react in a strong alkaline environment. For example, aluminum in nuclear waste can undergo the following reactions under alkaline conditions: 2Al+2OH - +6H2O→2[Al(OH)4] - +3H2(g).

[0027] The pH value of ordinary concrete is 12.5-13.5, which is highly alkaline and can react with nuclear waste. The solid waste-based high-performance concrete provided by the present invention does not contain alkaline compounds such as calcium hydroxide, and has a neutral pH value, which can effectively prevent nuclear waste from reacting with concrete to cause corrosion of concrete, ensure the strength of storage containers under long-term use, and avoid nuclear leakage.

[0028] Comparative Example 500 parts of cement were added to 198 parts of tap water and stirred into slurry, then 650 parts of river sand and 1060 parts of crushed stone were added and stirred, and 5 parts of water reducing agent were added and stirred to obtain concrete slurry. The slurry was poured into a mold, placed at room temperature, covered with plastic wrap, and removed from the mold after 24 hours, and placed in a standard curing room for 28 days to obtain a sample.

[0029] Example 1 250 parts of magnesium slag powder and 250 parts of fly ash from dredged sediment incineration were dry mixed, 198 parts of seawater were added, and stirred into slurry, then 650 parts of sea sand and 1060 parts of crushed stone were added, stirred, and 10 parts of water reducer were added to obtain concrete slurry. The slurry was poured into a mold, placed at room temperature, covered with plastic wrap, and removed from the mold after 24 hours, placed in a carbon dioxide curing room with a carbon dioxide concentration of 50% and a pressure of 0.1 MPa, and taken out after curing for 6 hours, and then placed in a standard curing room for 28 days to obtain a sample.

[0030] Example 2 375 parts of magnesium slag powder and 125 parts of fly ash from dredged sediment incineration were dry mixed, 198 parts of seawater were added, and stirred into slurry, then 650 parts of sea sand and 1060 parts of crushed stone were added, stirred, and 10 parts of water reducer were added to obtain concrete slurry. The slurry was poured into a mold, placed at room temperature, covered with plastic wrap, and removed from the mold after 24 hours, placed in a carbon dioxide curing room with a carbon dioxide concentration of 50% and a pressure of 0.1 MPa, and taken out after curing for 6 hours, and then placed in a standard curing room for 28 days to obtain a sample.

[0031] Example 3 250 parts of magnesium slag powder and 250 parts of fly ash from dredged sediment incineration were dry mixed, 198 parts of seawater were added, and stirred into slurry, then 650 parts of sea sand and 1060 parts of crushed stone were added, stirred, and 10 parts of water reducer were added to obtain concrete slurry. The slurry was poured into a mold, placed at room temperature, covered with plastic wrap, and removed from the mold after 24 hours, placed in a carbon dioxide curing room with a carbon dioxide concentration of 100% and a pressure of 0.1 MPa, and taken out after curing for 6 hours, and then placed in a standard curing room for 28 days to obtain a sample.

[0032] Example 4 250 parts of magnesium slag powder and 250 parts of fly ash from dredged sediment incineration were dry mixed, 198 parts of seawater were added, and stirred into slurry, then 650 parts of sea sand and 1060 parts of crushed stone were added, stirred, and 10 parts of water reducer were added to obtain concrete slurry. The slurry was poured into a mold, placed at room temperature, covered with plastic wrap, and removed from the mold after 24 hours, placed in a carbon dioxide curing room with a carbon dioxide concentration of 100% and a pressure of 0.2MPa, and taken out after curing for 6 hours, and then placed in a standard curing room for 28 days to obtain a sample.

[0033] Example 5 250 parts of magnesium slag powder and 250 parts of fly ash from dredged sediment incineration were dry mixed, 198 parts of seawater were added, and stirred into slurry, then 650 parts of sea sand and 1060 parts of crushed stone were added, stirred, and 10 parts of water reducer were added to obtain concrete slurry. The slurry was poured into a mold, placed at room temperature, covered with plastic wrap, and removed from the mold after 24 hours, and placed in a standard curing room for 28 days to obtain a sample.

[0034] Example 6 250 parts of magnesium slag powder and 250 parts of fly ash from dredged sediment incineration were dry mixed, 198 parts of tap water were added, and stirred into slurry, then 650 parts of river sand and 1060 parts of crushed stone were added, stirred, and 10 parts of water reducer were added to obtain concrete slurry. The slurry was poured into a mold, placed at room temperature, covered with plastic wrap, and removed from the mold after 24 hours, placed in a carbon dioxide curing room with a carbon dioxide concentration of 100% and a pressure of 0.2MPa, and taken out after curing for 6 hours, and then placed in a standard curing room for 28 days to obtain a sample.

[0035] The pH value of each sample of the comparative example and Examples 1-6 was tested. The test steps were as follows: 1g of the sample was crushed and ground to a particle size of less than 1mm, then immersed in 5g of deionized water, and the pH value of the solution was tested after 24 hours. In order to test the performance of the sample against radioactive metal corrosion, the slurry prepared in the comparative example and Examples 1-6 was inserted into an aluminum bar (Al 1050, 3mm*3mm*30mm), and the generated hydrogen content and the compressive strength after curing were tested. The test results are shown in the following table:

[0036] The comparative example is ordinary concrete, which has a higher pH value of 13.4 after 28 days of curing. Under strong alkaline conditions, the concrete reacts with the aluminum strip to generate 2.3 ml / cm 3 Hydrogen, and causes the concrete strength to drop by more than 50%.

[0037] Example 1 uses magnesium slag powder and fly ash from dredged sediment incineration to replace cement. The reaction product is mainly MSH gel. Carbon dioxide is used for curing. Carbon dioxide reacts with the remaining magnesium slag powder to make the remaining magnesium oxide and magnesium hydroxide content in the concrete. Therefore, the pH of the concrete is relatively low, which is 9.5. Under this pH condition, the reaction of aluminum strips is limited, generating 0.75 ml / cm 3 Hydrogen, concrete strength decreases less, by 15%. At the same time, seawater and sea sand are added, which react with magnesium slag powder to form fibrous phase 5 and phase 3, which play a limiting role in the decrease of concrete strength.

[0038] In Example 2, the ratio of magnesium slag powder to fly ash from incineration of dredged sediments is increased, so the concrete still contains some magnesium oxide and magnesium hydroxide after curing. Therefore, compared with Example 1, the pH is slightly higher, the generated hydrogen content is higher, and the degree of concrete strength reduction is higher than that of Example 1. Therefore, it is recommended that the ratio of magnesium slag powder to fly ash from incineration of dredged sediments does not exceed 50%.

[0039] Compared with Example 1, Examples 3 and 4 increase the concentration and pressure of carbon dioxide respectively, so that more carbon dioxide participates in the reaction, further reducing the remaining magnesium hydroxide and magnesium oxide content in the concrete. Therefore, the pH value is further reduced, the hydrogen content is reduced, and the decrease in the compressive strength of the concrete is limited.

[0040] Example 5 does not use carbon dioxide curing, so the pH is slightly higher, the generated hydrogen content is higher, and the degree of decrease in concrete strength is higher than that in Example 1.

[0041] Example 6 uses tap water and river sand, so phase 3 and phase 5 are not generated. At the same time, the remaining magnesium oxide and magnesium hydroxide content in the concrete is also increased, so the pH value is slightly higher than that of Example 1, the generated hydrogen is slightly more, and the decrease in the compressive strength of the concrete is also slightly higher than that of Example 1.

[0042] In summary, the ratio of magnesium slag powder to dredged sediment incineration fly ash should not exceed 50%, which has the best control effect on pH value and can effectively limit the corrosion of radioactive substances on concrete. In addition, the addition of seawater and sea sand and the use of carbon dioxide curing can further reduce the pH value of the system.

[0043] The embodiments of the present invention are described above, but the present invention is not limited to the above-mentioned specific implementation modes. The above-mentioned specific implementation modes are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the purpose of the present invention and the claims, all of which are protected by the present invention.

Claims

1. A solid waste-based high performance concrete, characterized in that: The composition comprises the following components in parts by weight: 100-400 parts of magnesium slag powder, 100-400 parts of dredged sediment fly ash, 500-800 parts of sea sand, 900-1200 parts of crushed stone, 5-30 parts of water reducer and 100-300 parts of sea water; the magnesium slag powder adopts the magnesium slag with a particle size of less than 600μm and a magnesium oxide content of 50-70% in the salt lake lithium extraction process; the dredged sediment is the sediment dredged from the waterway, river or channel, and the dredged sediment fly ash is the fly ash with a silicon oxide content of 40-60%, a calcium oxide content of 15-30% and an aluminum oxide content of 3-10% formed after the dredged sediment is burned at high temperature.

2. The solid waste-based high performance concrete according to claim 1, characterized in that: The fineness modulus of sea sand is 2.5-2.7, and the apparent density is 2500-2600kg / m 3 ; The gravel is a continuously graded gravel with a particle size of 5-15mm; the chloride ion content of seawater is 15-20g / L, and the magnesium ion content is 1-3g / L.

3. The solid waste-based high performance concrete according to claim 1, characterized in that: The water reducing agent is a polycarboxylic acid-based water reducing agent having a water reducing efficiency of more than 20%.

4. A method for preparing solid waste-based high performance concrete according to any one of claims 1 to 3, characterized in that: The steps include: Step S1, dry-mix 100-400 parts of magnesium slag powder and 100-400 parts of fly ash from dredged sediment incineration according to weight, then add 100-300 parts of seawater, and stir to form a slurry; Step S2, adding 500-800 parts of sea sand and 900-1200 parts of crushed stone into the slurry according to weight parts, and then adding 5-30 parts of water reducing agent, and stirring evenly to obtain concrete slurry; Step S3, pour the concrete slurry into the mold, place it at room temperature, cover it with plastic wrap, remove the mold after 24 hours, and then place it in a standard curing room for 28 days to obtain solid waste-based high-performance concrete.

5. The method for preparing solid waste-based high performance concrete according to claim 4, characterized in that: Before placing it in a standard curing room for curing, the following steps are also included: Put it into the carbon dioxide curing room and cure it for 4-12 hours at a carbon dioxide concentration of 20%-100% and a pressure of 0.1-0.2MPa, then take it out.

6. An application of the solid waste-based high performance concrete according to any one of claims 1 to 3, characterized in that: Used as casting material for nuclear waste storage containers.

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