A solid waste-based high-performance concrete, its preparation method and application

Abstract

The present invention provides a solid waste-based high-performance concrete, its preparation method and application, belonging to the technical field of concrete materials. The present invention uses two kinds of solid wastes, namely magnesium slag from lithium extraction in salt lakes and fly ash from dredged sediment, as raw materials, and adds seawater, sea sand and crushed stones to prepare concrete. The obtained concrete has a lower alkalinity and is not likely to react with nuclear waste easily after being made into a nuclear waste storage container, thus not causing corrosion of the concrete. The prepared storage container can maintain a relatively high strength. Moreover, the present invention also realizes the reuse of two kinds of solid waste raw materials, namely magnesium slag from lithium extraction in salt lakes and fly ash from dredged sediment, meeting the development requirements of energy conservation and environmental protection.

Description

Technical Field

[0001] The present invention belongs to the technical field of concrete materials, and particularly relates to a solid waste-based high-performance concrete, a preparation method thereof, and an 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 problems to be solved urgently. Whether it is stored in a surface repository, buried in a shallow stratum, or buried in abandoned mines and caves, the nuclear waste needs to be sealed in a storage container to prevent radioactive contamination and environmental damage to the outside world.

[0003] In related technologies, the materials used for nuclear waste storage containers are mainly ordinary concrete. Ordinary concrete storage containers have the advantage of low cost, and the storage containers can be manufactured with a relatively large wall thickness at a relatively low cost to improve the storage safety. However, the pH value of ordinary concrete is between 12.5 and 13.5, with a relatively high alkalinity, which can react with some substances in the nuclear waste, causing corrosion of the concrete and affecting the overall strength of the storage container.

[0004] Waterways, river channels, or shipping lanes need to be excavated and cleaned regularly to improve the water flow conditions, increase the water depth, or widen the river channel. The sediment excavated from underwater is called dredged sediment, which mainly contains components such as silicon oxide and aluminum oxide, and has a relatively high proportion of amorphous substances; a large amount of magnesium slag is generated during the process of extracting lithium from salt lakes, and the magnesium oxide content in the magnesium slag is as high as 70%. Based on the above component characteristics, the dredged sediment and the magnesium slag generated from lithium extraction from salt lakes meet the basic requirements for application in building materials. However, the dredged sediment and the magnesium slag generated from lithium extraction from salt lakes are usually regarded as solid waste and are treated by direct landfill, resulting in a waste of resources.

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

[0006] The present invention provides a solid waste-based high-performance concrete, a preparation method thereof, and an application thereof. Using two solid wastes, namely magnesium slag from lithium extraction from salt lakes and fly ash from dredged sediment, as raw materials, seawater, sea sand, and crushed stone are added to prepare concrete. The obtained concrete has a lower alkalinity and is not likely to react with nuclear waste after being prepared into a nuclear waste storage container, thus not causing corrosion of the concrete. The prepared storage container can maintain a relatively high strength; and the reuse of the two solid waste raw materials, namely magnesium slag from lithium extraction from salt lakes and fly ash from dredged sediment, is also realized, thereby effectively solving at least one technical problem involved in the background art.

[0007] In order to solve the above technical problems, the present invention is implemented as follows:

[0008] A solid waste-based high-performance concrete, comprising the following components in parts by weight:

[0009] 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 seawater; the magnesium slag powder is magnesium slag with a particle size less than 600 μm and a magnesium oxide content of 50 - 70% in the lithium extraction process from salt lakes; the dredged sediment is the sediment dredged from waterways, river channels or shipping lanes, and the dredged sediment fly ash is fly ash formed after the dredged sediment is burned at high temperature, with a silica content of 40 - 60%, a calcium oxide content of 15 - 30%, and an alumina content of 3 - 10%.

[0010] As a preferred improvement, the fineness modulus of the sea sand is 2.5 - 2.7, and the apparent density is 2500 - 2600 kg / m 3 ; the crushed stone is continuously graded crushed stone with a particle size of 5 - 15 mm; the chloride ion content of the seawater is 15 - 20 g / L, and the magnesium ion content is 1 - 3 g / L.

[0011] As a preferred improvement, the water reducer is a polycarboxylate-based water reducer with a water reduction efficiency of more than 20%.

[0012] A preparation method of the above-mentioned solid waste-based high-performance concrete, comprising the following steps:

[0013] Step S1, dry-mix 100 - 400 parts of magnesium slag powder and 100 - 400 parts of dredged sediment incineration fly ash in parts by weight, and then add 100 - 300 parts of seawater and stir evenly to form a slurry;

[0014] Step S2, add 500 - 800 parts of sea sand and 900 - 1200 parts of crushed stone to the slurry in parts by weight, and then add 5 - 30 parts of water reducer, and stir evenly to obtain a concrete slurry;

[0015] Step S3, pour the concrete slurry into a mold, place it at room temperature, cover it with plastic wrap, demold it after 24 hours, and then place it in a standard curing room for 28 days to obtain the solid waste-based high-performance concrete.

[0016] As a preferred improvement, before placing it in the standard curing room for curing, the following steps are further included:

[0017] Place it in a carbon dioxide curing room and cure it for 4 - 12 hours under the conditions of a carbon dioxide concentration of 20% - 100% and a pressure of 0.1 - 0.2 MPa, and then take it out.

[0018] An application of the above-mentioned solid waste-based high-performance concrete, used as a casting material for nuclear waste storage containers.

[0019] The beneficial effects of the present invention are as follows:

[0020] (1) Using two solid wastes, namely magnesium slag from lithium extraction from salt lakes and dredged sediment fly ash, as raw materials, and adding seawater, sea sand, and crushed stone to prepare concrete, the reuse of waste is realized, meeting the development needs of energy conservation and environmental protection;

[0021] (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 of nuclear waste with concrete, ensure the strength of the storage container during long-term use, and avoid nuclear leakage. Detailed implementation mode

[0022] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0023] This implementation mode provides a solid waste-based high-performance concrete, which includes the following components in parts by weight:

[0024] 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 reducing agent, and 100 - 300 parts of seawater; the magnesium slag powder is magnesium slag with a particle size less than 600 μm and a magnesium oxide content of 50 - 70% in the lithium extraction process from salt lakes; the dredged sediment is the sediment dredged from waterways, river channels or shipping lanes, and the dredged sediment fly ash is fly ash formed after the high-temperature combustion of the dredged sediment, with a silica content of 40 - 60%, a calcium oxide content of 15 - 30%, and an alumina content of 3 - 10%.

[0025] The target product of the lithium extraction process from salt lakes is lithium. Therefore, magnesium exists as an impurity component in the lithium extraction process from salt lakes to form magnesium slag. The present invention reasonably utilizes the magnesium slag in the lithium extraction process from salt lakes, realizes the reuse of waste, and can reduce the exploitation of magnesite.

[0026] The dredged sediment refers to the sediment dredged from waterways, river channels or shipping lanes, mainly containing components such as silica, alumina, and calcium oxide, with a relatively high proportion of amorphous substances, and can be applied to building materials. In this implementation mode, the dredged sediment is subjected to combustion treatment, and the fly ash after combustion is taken as the ingredient of the concrete, realizing the reuse of the dredged sediment and meeting the development needs of energy conservation and environmental protection.

[0027] Dredged sediments generally contain a large amount of corrupt organic components. If directly added to concrete, the organic components will continuously decompose in the concrete system, generating gas and moisture, thus forming a cavity structure inside the concrete and affecting the strength of the concrete. Therefore, in the present invention, the organic components in the dredged sediments are decomposed into carbon dioxide and water by high-temperature combustion and then discharged, only retaining their inorganic components.

[0028] The lithium extraction magnesium slag from salt lakes contains reactive magnesium oxide, and the dredged sediment fly ash mainly contains reactive silica. Therefore, the two will react to form magnesium silicate hydrate gel (M-S-H gel), which has a gelling effect and is used to replace the C-S-H gel in ordinary concrete, and is the source of the strength of the concrete. The magnesium silicate hydrate gel itself is neutral and will not increase the alkalinity of the concrete system. It can well control the increase of the pH value of the concrete system, making the pH value of the concrete system slightly neutral. The dredged sediment fly ash also contains some aluminum oxide and calcium oxide. Therefore, a small amount of aluminosilicate gel (A-S-H gel) and less C-S-H gel will also be formed. These hydration products all make the pH value of the concrete slightly neutral.

[0029] The sea sand is the sea sand from the Jiaozhou area of Qingdao, with a fineness modulus of 2.5 - 2.7 and an apparent density of 2500 - 2600 kg / m 3 , and mainly plays the role of fine aggregate in the concrete system; the crushed stone with a continuous gradation of 5 - 15 mm mainly plays the role of coarse aggregate in the concrete system. The seawater is taken from the sea area near Jiaozhou Bay in Qingdao, with a chloride ion content of 15 - 20 g / L and a magnesium ion content of 1 - 3 g / L. The chloride ions in the seawater and sea sand can react with the reactive magnesium oxide in the magnesium slag to form phase 5 (5Mg(OH)2·MgCl2·8H2O) and phase 3 (3Mg(OH)2·MgCl2·8H2O). Both phase 5 and phase 3 are fibrous crystals and can play a fiber constraint role to limit the strength loss of the concrete in the service environment.

[0030] The water reducer is a polycarboxylate-based water reducer with a water reduction efficiency of more than 20%. It belongs to the conventional additive components in this field, and this embodiment will not elaborate on it.

[0031] This embodiment also provides a preparation method for solid waste-based high-performance concrete, including the following steps:

[0032] Step S1, dry-mix 100 - 400 parts of magnesium slag powder and 100 - 400 parts of dredged sediment incineration fly ash evenly by weight, and then add 100 - 300 parts of seawater and stir evenly to form a slurry;

[0033] Step S2, add 500 - 800 parts of sea sand and 900 - 1200 parts of crushed stone to the slurry by weight, and then add 5 - 30 parts of water reducer, and stir evenly to obtain a concrete slurry;

[0034] 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 cure it in a standard curing room for 28 days to obtain the solid waste-based high-performance concrete.

[0035] As a preferred method, the following steps are also included before curing in the standard curing room:

[0036] Place it in a carbon dioxide curing room and cure it for 4 - 12 hours under the conditions of a carbon dioxide concentration of 20% - 100% and a pressure of 0.1 - 0.2 MPa, and then take it out.

[0037] Before the traditional curing in the preparation method provided by the present invention, carbon dioxide curing is carried out first. Under the carbon dioxide condition, the remaining magnesium oxide in the magnesium slag will react with carbon dioxide to form magnesium carbonate, and magnesium hydroxide will react with carbon dioxide to form hydrated hydroxy magnesium carbonate, improving the concrete strength. In addition, after carbon dioxide reacts with alkaline substances such as magnesium oxide and magnesium hydroxide, the overall alkalinity of the concrete can also be reduced, making the pH value of the solid waste-based high-performance concrete slightly neutral.

[0038] This embodiment also provides an application of the solid waste-based high-performance concrete, which is used as a casting material for nuclear waste storage containers.

[0039] Nuclear waste contains various different types of substances, and many of them will react with strong acids or strong bases. For example, radioactive metal elements such as uranium, plutonium, and neptunium and their compounds will undergo oxidation, dissolution and other reactions with alkaline substances. Some organic nuclear waste contains organic ion exchange resins, etc., and will undergo hydrolysis, decomposition and other chemical reactions 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 reaction under alkaline conditions:

[0040] 2Al + 2OH - + 6H2O → 2[Al(OH)4] - + 3H2(g).

[0041] The pH value of ordinary concrete is between 12.5 - 13.5, and the alkalinity is relatively high. Therefore, it can react with nuclear waste. However, the solid waste-based high-performance concrete provided by the present invention does not contain alkaline compounds such as calcium hydroxide, and the pH value is slightly neutral, which can effectively prevent the reaction between nuclear waste and concrete from causing corrosion of the concrete, ensure the strength of the storage container during long-term use, and avoid nuclear leakage.

[0042] Comparative example

[0043] Add 500 parts of cement and 198 parts of tap water, stir into a slurry, then add 650 parts of river sand and 1060 parts of gravel, stir, add 5 parts of water reducing agent and stir to obtain a concrete slurry. Pour the slurry into a mold, place it at room temperature, cover it with plastic wrap, remove the mold after 24 hours, and place it in a standard curing room for 28 days to obtain a sample.

[0044] Example 1

[0045] Dry mix 250 parts of magnesium slag powder and 250 parts of incineration fly ash of dredged sediment, add 198 parts of seawater, stir into a slurry, then add 650 parts of sea sand and 1060 parts of gravel, stir, add 10 parts of water reducing agent and stir to obtain a concrete slurry. Pour the slurry into a mold, place it at room temperature, cover it with plastic wrap, remove the mold after 24 hours, place it in a carbon dioxide curing room with a carbon dioxide concentration of 50% and a pressure of 0.1 MPa, cure for 6 hours and then take it out, and then place it in a standard curing room for 28 days to obtain a sample.

[0046] Example 2

[0047] Dry mix 375 parts of magnesium slag powder and 125 parts of incineration fly ash of dredged sediment, add 198 parts of seawater, stir into a slurry, then add 650 parts of sea sand and 1060 parts of gravel, stir, add 10 parts of water reducing agent and stir to obtain a concrete slurry. Pour the slurry into a mold, place it at room temperature, cover it with plastic wrap, remove the mold after 24 hours, place it in a carbon dioxide curing room with a carbon dioxide concentration of 50% and a pressure of 0.1 MPa, cure for 6 hours and then take it out, and then place it in a standard curing room for 28 days to obtain a sample.

[0048] Example 3

[0049] Dry mix 250 parts of magnesium slag powder and 250 parts of incineration fly ash of dredged sediment, add 198 parts of seawater, stir into a slurry, then add 650 parts of sea sand and 1060 parts of gravel, stir, add 10 parts of water reducing agent and stir to obtain a concrete slurry. Pour the slurry into a mold, place it at room temperature, cover it with plastic wrap, remove the mold after 24 hours, place it in a carbon dioxide curing room with a carbon dioxide concentration of 100% and a pressure of 0.1 MPa, cure for 6 hours and then take it out, and then place it in a standard curing room for 28 days to obtain a sample.

[0050] Example 4

[0051] Dry mix 250 parts of magnesium slag powder and 250 parts of incineration fly ash of dredged sediment, add 198 parts of seawater, stir into a slurry, then add 650 parts of sea sand and 1060 parts of gravel, stir, add 10 parts of water reducing agent and stir to obtain a concrete slurry. Pour the slurry into a mold, place it at room temperature, cover it with plastic wrap, remove the mold after 24 hours, place it in a carbon dioxide curing room with a carbon dioxide concentration of 100% and a pressure of 0.2 MPa, cure for 6 hours and then take it out, and then place it in a standard curing room for 28 days to obtain a sample.

[0052] Example 5

[0053] Dry-mix 250 parts of magnesium slag powder and 250 parts of incineration fly ash of dredged sediment, add 198 parts of seawater, stir into a slurry, then add 650 parts of sea sand and 1060 parts of crushed stone, stir, add 10 parts of water reducing agent and stir to obtain a concrete slurry. Pour the slurry into a mold, place it at room temperature, cover it with plastic wrap, remove the mold after 24 hours, and cure it in a standard curing room for 28 days to obtain a sample.

[0054] Example 6

[0055] Dry-mix 250 parts of magnesium slag powder and 250 parts of incineration fly ash of dredged sediment, add 198 parts of tap water, stir into a slurry, then add 650 parts of river sand and 1060 parts of crushed stone, stir, add 10 parts of water reducing agent and stir to obtain a concrete slurry. Pour the slurry into a mold, place it at room temperature, cover it with plastic wrap, remove the mold after 24 hours, put it into a carbon dioxide curing room with a carbon dioxide concentration of 100% and a pressure of 0.2 MPa, cure for 6 hours and then take it out, and then cure it in a standard curing room for 28 days to obtain a sample.

[0056] Test the pH values of the samples of the comparative example and Examples 1-6. The test steps are as follows: Crush and grind 1 g of the sample to a particle size less than 1 mm, then soak it in 5 g of deionized water, and test the pH value of the solution after 24 hours. In order to test the performance of the samples against radioactive metal corrosion, insert the slurries prepared in the comparative example and Examples 1-6 into aluminum bars (Al 1050, 3 mm * 3 mm * 30 mm), test the hydrogen content generated, and the compressive strength after the curing is completed. The test results are shown in the following table:

[0057]

[0058] The comparative example is ordinary concrete. Its pH is relatively high after 28 days of curing age, which is 13.4. Under strong alkaline conditions, the concrete reacts with the aluminum bar, generating 2.3 ml / cm 3 of hydrogen gas, and causing the concrete strength to decrease by more than 50%.

[0059] Example 1 uses magnesium slag powder and incineration fly ash of dredged sediment to replace cement. The reaction product is mainly M-S-H gel. At the same time, carbon dioxide curing is adopted. Carbon dioxide reacts with the remaining magnesium slag powder, reducing the content of residual magnesium oxide and magnesium hydroxide in the concrete. Therefore, the pH of the concrete is relatively low, which is 9.5. Under this pH condition, the reaction of the aluminum bar is limited, generating 0.75 ml / cm 3 of hydrogen gas, and the decrease in concrete strength is relatively small, which is 15%. At the same time, seawater and sea sand are added, which react with the magnesium slag powder to generate fibrous phases 5 and 3, restricting the decrease in concrete strength.

[0060] In Example 2, the proportion of magnesium slag powder to incineration fly ash of dredged sediment was increased. Therefore, after curing, the concrete still contained some magnesium oxide and magnesium hydroxide. As a result, the pH was slightly higher than that in Example 1, the hydrogen content generated was higher, and the degree of concrete strength reduction was higher than that in Example 1. Therefore, it is recommended that the proportion of magnesium slag powder to incineration fly ash of dredged sediment should not exceed 50%.

[0061] Compared with Example 1, in Example 3 and Example 4, the concentration and pressure of carbon dioxide were increased respectively, and more carbon dioxide participated in the reaction, further reducing the content of residual magnesium hydroxide and magnesium oxide in the concrete. As a result, the pH value was further reduced, the hydrogen content was reduced, and the reduction of the concrete compressive strength was limited.

[0062] In Example 5, carbon dioxide curing was not adopted. Therefore, the pH was slightly higher, the hydrogen content generated was higher, and the degree of concrete strength reduction was higher than that in Example 1.

[0063] In Example 6, tap water and river sand were used. Therefore, Phase 3 and Phase 5 were not generated. At the same time, the content of residual magnesium oxide and magnesium hydroxide in the concrete also increased. As a result, the pH value was slightly higher than that in Example 1, slightly more hydrogen was generated, and the reduction amount of the concrete compressive strength was also slightly higher than that in Example 1.

[0064] In summary, when the proportion of magnesium slag powder to incineration fly ash of dredged sediment does not exceed 50%, the control effect on the pH value is the best, which can effectively limit the corrosion of radioactive substances on the concrete. In addition, adding seawater and sea sand and adopting carbon dioxide curing can further reduce the pH value of the system.

[0065] The embodiments of the present invention have been described above. However, the present invention is not limited to the above specific embodiments. The above specific embodiments are merely illustrative rather than restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many forms without departing from the spirit and scope protected by the claims of the present invention, and all of them belong to the protection scope of the present invention.

Claims

1. A solid waste-based high-performance concrete, characterized in that, Comprising the following components by weight parts: 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 reducing agent and 100 - 300 parts of seawater; the magnesium slag powder is magnesium slag with a particle size less than 600μm and a magnesium oxide content of 50 - 70% in the lithium extraction process from salt lakes; the dredged sediment is the sediment dredged from waterways, river channels or shipping lanes, and the dredged sediment fly ash is fly ash formed after the high-temperature combustion of the dredged sediment, with a silica content of 40 - 60%, a calcium oxide content of 15 - 30% and an alumina content of 3 - 10%; the chloride ion content of the seawater is 15 - 20g / L and the magnesium ion content is 1 - 3g / L.

2. The solid waste-based high-performance concrete according to claim 1, wherein The fineness modulus of the sea sand is 2.5 - 2.7, and the apparent density is 2500 - 2600 kg / m 3 ; The crushed stone is continuously graded crushed stone with a particle size of 5 - 15 mm.

3. The solid waste-based high-performance concrete according to claim 1, wherein, The water reducing agent is a polycarboxylate-based water reducing agent with a water reducing efficiency of more than 20%.

4. A preparation method of the solid waste-based high-performance concrete according to any one of claims 1 to 3, characterized in that, Including the following steps: Step S1, dry mix 100 - 400 parts of magnesium slag powder and 100 - 400 parts of dredged sediment incineration fly ash by weight parts, and then add 100 - 300 parts of seawater and stir evenly to form a slurry. Step S2, add 500 - 800 parts of sea sand and 900 - 1200 parts of crushed stone to the slurry by weight parts, and then add 5 - 30 parts of water reducing agent, and stir evenly to obtain a concrete slurry. Step S3, pour the concrete slurry into a 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 the solid waste-based high-performance concrete.

5. The preparation method of the solid waste-based high-performance concrete according to claim 4, wherein, Before placing it in the standard curing room for curing, it also includes the following steps: Place it in a carbon dioxide curing room and cure it for 4 - 12 hours under the conditions of a carbon dioxide concentration of 20% - 100% and a pressure of 0.1 - 0.2MPa, and then take it out.

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

Images