Green low-carbon recycled concrete and preparation method thereof

Abstract

The application relates to the field of building materials, and particularly discloses green low-carbon recycled concrete and a preparation method thereof. The green low-carbon recycled concrete comprises the following raw materials in parts by weight: 3-6 parts of slag, 30-50 parts of modified recycled sand, 8-10 parts of recycled powder, 40-50 parts of cement, 5-8 parts of water-soluble phenolic resin, 0.2-0.5 parts of an additive, 1-3 parts of a dispersant, 5-7 parts of water glass and 60-80 parts of water, wherein the modified recycled sand is obtained through carbonization modification after being impregnated with a modified solution; and the preparation method comprises the following steps: uniformly stirring the slag, the recycled powder, the cement, the additive and the water glass to obtain dry powder, then continuously stirring and mixing the dry powder, water glass and half of the water to obtain a mixture for standby; heating the water to 50-70 DEG C, then stirring the weighed modified recycled sand, the water-soluble phenolic resin and the dispersant for 3-5 min, adding the mixture and continuously stirring for 3-5 min to obtain the green low-carbon recycled concrete. The composition has the advantages of high compressive strength and good durability.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of building materials, in particular to green low-carbon recycled concrete and a preparation method thereof. BACKGROUND

[0002] With the acceleration of urbanization, a large amount of construction waste and waste concrete is generated, which has caused serious pollution and resource waste problems to the environment. In order to cope with this challenge, green low-carbon recycled concrete emerges as the times require. It can not only effectively reduce the emission of construction waste, but also reduce the dependence on natural resources and achieve sustainable development by recycling and reusing waste concrete.

[0003] However, the surface of recycled aggregate may be covered with old cement paste, and new cracks and damages may be formed during the crushing process, resulting in a large porosity, a complex interface and a large number of needle-like particles. These characteristics make the mechanical properties of recycled aggregate concrete significantly different from those of ordinary concrete. SUMMARY

[0004] In order to improve the compressive strength and durability of recycled concrete, the application provides a green low-carbon recycled concrete and a preparation method thereof.

[0005] In a first aspect, the application provides a green low-carbon recycled concrete, which adopts the following technical solution:

[0006] A green low-carbon recycled concrete comprises the following raw materials by weight:

[0007] 3-6 parts of slag, 30-50 parts of modified recycled sand, 8-10 parts of recycled powder, 40-50 parts of cement, 5-8 parts of water-soluble phenolic resin, 0.2-0.5 parts of additive, 1-3 parts of dispersant, 5-7 parts of water glass and 60-80 parts of water, wherein the modified recycled sand is obtained by impregnating a modified solution and then carbonizing modification.

[0008] By adopting the above technical solution, the raw material components are scientifically proportioned, and the environment-friendly recycled materials such as slag, modified recycled sand and recycled powder are combined, and an appropriate amount of cement and water-soluble phenolic resin are used as a bonding and reinforcing agent. The additive and dispersant optimize the performance of the concrete, the water glass improves the durability, and finally an appropriate amount of water is used for mixing. This effectively reduces the exploitation of natural resources, promotes the recycling of waste materials, and at the same time, the synergistic effect of the components improves the mechanical properties and durability of the concrete, achieving the dual goals of energy saving and sustainable development.

[0009] Optionally, the preparation process of the modified recycled sand is as follows:

[0010] (1) crushing and screening waste concrete to obtain aggregate with a diameter of less than 4.75 mm;

[0011] (2) After the above-mentioned aggregate is put into a modified solution of polyacrylamide, chitosan and calcium hydroxide and stirred uniformly, it is left to stand, and after completion, carbonation treatment is carried out by passing in carbon dioxide, and after completion, modified recycled sand is obtained.

[0012] By adopting the above technical solution, the soaking treatment makes each modified molecule penetrate into the recycled aggregate, and the carbonation treatment by passing in carbon dioxide utilizes the reaction between carbon dioxide and active substances (such as calcium hydroxide) in the recycled aggregate to generate stable compounds such as carbonates, fills the pores and micro-cracks inside the aggregate, and makes the originally loose aggregate structure more compact, thereby improving the compressive strength of the aggregate.

[0013] After the concrete is crushed and sieved to obtain aggregate of a suitable particle size, the aggregate is immersed in a modified solution, polyacrylamide penetrates into the surface and internal voids of the aggregate, fills the pores, refines the pore structure, and can reduce the content of calcium hydroxide and change its form, making it change from a larger parallel accumulation layered structure to a smaller edge corrosion structure, improving the reactivity of calcium hydroxide with carbon dioxide in the carbonation process, and in the presence of polyacrylamide, the C-S-H phase has a higher Ca / Si ratio and a higher carbonation rate, promoting the formation of calcite-type calcium carbonate with higher stability. Further, polyacrylamide can improve the interfacial activity of recycled aggregate and enhance the bonding strength with other raw materials, thereby improving the overall performance of recycled concrete. At the same time, it can also wrap the surface of the carbonation product, improve the dispersibility of the product, avoid the problem of agglomeration and accumulation, and significantly improve the compressive strength of the modified recycled sand.

[0014] Further carbonation treatment can significantly reduce the water absorption of recycled aggregate and improve its impermeability and durability. At the same time, the carbonation product can also enhance the bonding force between the aggregate and the mortar and improve the performance of the interfacial transition zone of the recycled aggregate.

[0015] The addition of calcium hydroxide as an additional calcium source further improves the improvement effect after carbonation treatment, and the addition of chitosan, which is rich in functional groups such as amino and hydroxyl groups, can react with metal ions such as calcium ions, act as a template for the growth of calcium carbonate crystals, guide the growth direction of calcium carbonate crystals, and generate more stable calcite-type calcium carbonate, which helps to improve the strength and stability of the aggregate.

[0016] Optionally, the standing time in step 1 is 60-80 min.

[0017] In step 2, the concentration of carbon dioxide is 20-25%, the gas flow rate is 4-4.5 L / min, the temperature is 20-25℃, and the passing-in time is 30-60 min.

[0018] By adopting the technical scheme, the carbon dioxide concentration, gas flow rate, temperature and passing-in time affect the final carbonation effect, and determine the diffusion speed of carbon dioxide molecules on the aggregate surface and the reaction efficiency. Proper concentration and gas flow rate help the carbon dioxide molecules to be uniformly distributed and fully contact with the aggregate, proper temperature is conducive to the rapid diffusion and penetration of carbon dioxide molecules, and long enough passing-in time can ensure that the carbonation reaction is fully carried out, thereby improving the carbonation effect.

[0019] Optionally, the adding weight ratio of polyacrylamide, chitosan and calcium hydroxide in the modification solution is 0.5-0.8:0.3:1.2-1.5.

[0020] By adopting the technical scheme, proper ratio is conducive to realizing the preliminary modification of the aggregate and improving the strength and water absorption resistance of the aggregate.

[0021] Optionally, the polyacrylamide is anionic polyacrylamide with a molecular weight of 7-9 million.

[0022] By adopting the technical scheme, the high-molecular-weight polymer has more active groups and is adsorbed on the aggregate surface, which is conducive to further reaction modification in the subsequent concrete hydration process, and controlling the molecular weight of the polyacrylamide between 7-9 million can ensure its reaction activity while enabling it to better penetrate into the aggregate for reaction and better fill cracks, thereby improving the strength of the aggregate.

[0023] Optionally, the dispersant is any one of lignin sulfonates.

[0024] By adopting the technical scheme, lignin sulfonates have excellent dispersing performance and stability, and can effectively interact with high-molecular-weight substances such as polyacrylamide, thereby achieving better dispersion effect.

[0025] Optionally, the additive is sodium hexametaphosphate.

[0026] By adopting the technical scheme, sodium hexametaphosphate can react with hydroxyl ions in concrete to produce phosphorus attachments, which help the hardening process of concrete and improve the compressive strength of concrete. Further, sodium hexametaphosphate can complex with calcium ions in concrete to control the hydration reaction rate, reduce water loss, and enhance the hardening and strength of concrete. At the same time, sodium hexametaphosphate can also control the concentration of chloride ions and salt, reduce concrete cracks, and enhance durability and persistence.

[0027] Optionally, the raw material further includes 2-5 parts of a polyhydric alcohol.

[0028] By adopting the technical scheme, the polyhydric alcohol can improve the reactivity of each raw material, increase the dissolution of metal ions such as calcium, silicon, aluminum and iron in the regenerated powder and slag, promote the hydration reaction, generate ettringite, calcium carbonate and other fillers to fill the pores of the concrete, prevent the penetration of water, and thus improve the compressive strength and durability of the concrete.

[0029] In a second aspect, the application provides a preparation method of green low-carbon recycled concrete, which adopts the following technical scheme:

[0030] A preparation method of green low-carbon recycled concrete comprises the following steps:

[0031] (1) The slag, regenerated powder, cement, additive and water glass are uniformly stirred to obtain dry powder, and then the water glass and half of the water are added and continuously stirred to obtain a mixture for standby;

[0032] (2) The water is heated to 50-70℃, and then the modified recycled sand, water-soluble phenolic resin and dispersant are added and stirred for 3-5min, and then the mixture is added and continuously stirred for 3-5min to obtain the green low-carbon recycled concrete.

[0033] By adopting the technical scheme, in the alkaline environment of cement hydration, the molecules of water-soluble phenolic resin can play a unique chemical role to enhance the strength and stability of the concrete. This helps to improve the durability of the concrete and prolong the service life.

[0034] In summary, the application has the following beneficial effects:

[0035] 1. By scientifically proportioning each raw material component, using water-soluble phenolic resin, additive, dispersant and water glass and other additives to cooperate with each other, the performance of the concrete in terms of mechanical properties and durability is improved. Further, the recycled sand is modified, and through the synergistic effect of soaking, carbonization treatment and various modifiers, the physical and chemical properties of the recycled aggregate are effectively improved, and the compressive strength and durability of the recycled concrete are improved.

[0036] 2. The recycled aggregate and recycled powder produced from waste concrete are applied to the concrete, which not only improves the economic benefit, but also endows the recycled concrete with high carbon reduction characteristics. At the same time, a large amount of waste is used as raw material, which reduces the production cost and improves the economic benefit. DETAILED DESCRIPTION

[0037] The application will be further described in detail below in combination with examples.

[0038] In the examples, the specific conditions not specified are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, but are conventional products that can be purchased on the market.

[0039] The water-soluble phenolic resin is purchased from Jinan Shanhai Chemical Technology Co., Ltd., model number: 2402.

[0040] Preparation example of raw material and / or intermediate

[0041] Preparation example 1

[0042] A modified recycled sand, the preparation comprising the following steps:

[0043] (1) crushing and screening the waste concrete to obtain aggregates with a diameter less than 4.75 mm;

[0044] (2) 5 kg of polyacrylamide, 3 kg of chitosan, and 13.5 kg of calcium hydroxide are put into 100 kg of water to stir and dissolve, to obtain a modified aqueous solution, 50 kg of aggregates are put into the modified aqueous solution to stir and mix uniformly, then stand for 70 min of immersion, and then carbonation treatment is performed by introducing carbon dioxide into the solution for 45 min, the concentration of carbon dioxide is 22%, the gas flow rate is 4 L / min, and the temperature is 23℃, to obtain the modified recycled sand after completion;

[0045] The anionic polyacrylamide is purchased from Zibo Lanlqing High Polymer Material Co., Ltd., with a molecular weight of 8 million.

[0046] Preparation example 2

[0047] A modified recycled sand, the preparation comprising the following steps:

[0048] (1) crushing and screening the waste concrete to obtain aggregates with a diameter less than 4.75 mm;

[0049] (2) 0.65 kg of polyacrylamide, 3 kg of chitosan, and 15 kg of calcium hydroxide are put into 100 kg of water to stir and dissolve, to obtain a modified aqueous solution, 50 kg of aggregates are put into the modified aqueous solution to stir and mix uniformly, then stand for 60 min of immersion, and then carbonation treatment is performed by introducing carbon dioxide into the solution for 60 min, the concentration of carbon dioxide is 20%, the gas flow rate is 4.5 L / min, and the temperature is 20℃, to obtain the modified recycled sand after completion;

[0050] The anionic polyacrylamide is purchased from Zibo Lanlqing High Polymer Material Co., Ltd., with a molecular weight of 8 million.

[0051] Preparation example 3

[0052] A modified recycled sand, the preparation comprising the following steps:

[0053] (1) crushing and screening the waste concrete to obtain aggregates with a diameter less than 4.75 mm;

[0054] (2) 8 kg of polyacrylamide, 3 kg of chitosan and 12 kg of calcium hydroxide are put into 100 kg of water to stir and dissolve to obtain a modified aqueous solution, 50 kg of aggregate is put into the modified aqueous solution to stir uniformly, then it is left to stand and soak for 80 min, carbon dioxide is introduced into it for carbonization treatment for 30 min, the concentration of carbon dioxide is 25%, the gas flow rate is 4 L / min, the temperature is 25°C, and the modified recycled sand is obtained after completion;

[0055] The anionic polyacrylamide is purchased from Zibo Lan'erqing High Polymer Material Co., Ltd. and has a molecular weight of 8 million.

[0056] Preparation Example 4

[0057] A modified recycled sand, which is different from that of Preparation Example 1 in that the polyacrylamide used in the present preparation example is cationic polyacrylamide, which is purchased from Langfang Xingrui Chemical Building Material Co., Ltd.

[0058] Comparative Preparation Example 1

[0059] A modified recycled sand, the preparation comprising the following steps:

[0060] (1) The waste concrete is crushed and sieved to obtain aggregate with a diameter of less than 4.75 mm;

[0061] (2) 5 kg of polyacrylamide, 3 kg of chitosan and 13.5 kg of calcium hydroxide are put into 100 kg of water to stir and dissolve to obtain a modified aqueous solution, 50 kg of aggregate is put into the modified aqueous solution to stir uniformly, then it is left to stand and soak for 70 min, and the modified recycled sand is obtained after being taken out and dried;

[0062] The anionic polyacrylamide is purchased from Zibo Lan'erqing High Polymer Material Co., Ltd. and has a molecular weight of 8 million.

[0063] Example

[0064] Example 1

[0065] A green low-carbon recycled concrete, the preparation comprising the following steps:

[0066] (1) 4.5 kg of slag, 10 kg of recycled powder, 25 kg of cement and 0.3 kg of sodium hexametaphosphate (additive) are stirred uniformly to obtain dry powder, then 6 kg of water glass and 35 kg of water are added and continue to stir and mix uniformly to obtain a mixture;

[0067] (2) The remaining water is heated to 60°C, then 30 kg of modified recycled sand, 8 kg of water-soluble phenolic resin and 2 kg of sodium lignosulfonate (dispersant) are stirred for 3 min, then they are put into the mixture and continue to stir for 5 min to obtain the green low-carbon recycled concrete; the modified recycled sand is obtained by Preparation Example 1; the D50 particle size of the recycled powder is 30 μm.

[0068] Example 2

[0069] A green low-carbon recycled concrete, the preparation comprising the following steps:

[0070] (1) 3 kg of slag, 9 kg of recycled powder, 30 kg of cement and 0.5 kg of sodium hexametaphosphate (admixture) are stirred uniformly, and after obtaining the dry powder, 5 kg of water glass and 30 kg of water are added and continue to be stirred and mixed uniformly to obtain a mixture;

[0071] (2) The remaining water is heated to 50℃, and then 50 kg of modified recycled sand, 6.5 kg of water-soluble phenolic resin and 3 kg of sodium lignosulfonate (dispersant) are stirred for 4 min, and then added into the mixture and continue to be stirred for 4 min to obtain a green low-carbon recycled concrete; the modified recycled sand is prepared by the preparation example 1; the D50 particle size of the recycled powder is 30 μm.

[0072] Example 3

[0073] A green low-carbon recycled concrete, the preparation comprising the following steps:

[0074] (1) 6 kg of slag, 8 kg of recycled powder, 20 kg of cement and 0.2 kg of sodium hexametaphosphate (admixture) are stirred uniformly, and after obtaining the dry powder, 7 kg of water glass and 40 kg of water are added and continue to be stirred and mixed uniformly to obtain a mixture;

[0075] (2) The remaining water is heated to 70℃, and then 40 kg of modified recycled sand, 5 kg of water-soluble phenolic resin and 1 kg of sodium lignosulfonate (dispersant) are stirred for 5 min, and then added into the mixture and continue to be stirred for 3 min to obtain a green low-carbon recycled concrete; the modified recycled sand is prepared by the preparation example 1; the modified recycled sand is prepared by the preparation example 1; the D50 particle size of the recycled powder is 30 μm.

[0076] Example 4

[0077] A green low-carbon recycled concrete, which is different from example 1 in that the modified recycled sand used in this example is prepared by the preparation example 2.

[0078] Example 5

[0079] A green low-carbon recycled concrete, which is different from example 1 in that the modified recycled sand used in this example is prepared by the preparation example 3.

[0080] Example 6

[0081] A green low-carbon recycled concrete, which is different from example 1 in that the modified recycled sand used in this example is prepared by the preparation example 4.

[0082] Example 7

[0083] A green low-carbon recycled concrete, different from Example 1, is that the dispersant used in this example is a fatty alcohol polyoxyethylene ether.

[0084] Example 8

[0085] A green low-carbon recycled concrete, different from Example 1, is that this example further includes 2 kg of propylene glycol (a polyhydric alcohol).

[0086] Example 9

[0087] A green low-carbon recycled concrete, different from Example 1, is that this example further includes 5 kg of propylene glycol (a polyhydric alcohol).

[0088] Comparative Example

[0089] Comparative Example 1

[0090] A green low-carbon recycled concrete, different from Example 1, is that no water-soluble phenolic resin is added in this comparative example.

[0091] Comparative Example 2

[0092] A green low-carbon recycled concrete, different from Example 1, is that the recycled sand in this comparative example is obtained by crushing and sieving waste concrete to obtain an aggregate with a diameter of less than 4.75 mm.

[0093] Comparative Example 3

[0094] A green low-carbon recycled concrete, different from Example 1, is that the modified recycled sand prepared by Comparative Preparation Example 1 is used in this comparative example.

[0095] Performance detection test

[0096] Detection method / test method

[0097] The mixtures of each example and comparative example are injected into a test mold, and are vibrated on a high-frequency vibration table until the test piece is formed, then leveled, placed in a laboratory natural environment for 24 h, then demolded, and finally cured for 60 d under standard curing conditions for testing.

[0098] Compressive strength: 100 mm x 100 mm x 100 mm cubic test pieces are used, the loading rate is 1 Mpa / s, and the compressive strength of the test block at 25℃ is tested according to GB / T50081-2002 "Standard Test Methods for Mechanical Properties of Ordinary Concrete";

[0099] Anti-chloride ion permeability test: according to the electric flux method in GB / T50082-2009 "Standard for testing methods of long-term performance and durability of ordinary concrete", the anti-chloride ion permeability test is carried out on the concrete, the cylindrical test piece with a diameter of 100 mm and a height of 50 mm is used for the test, the epoxy resin is used as the sealing material, the surface of the sea sand recycled concrete test piece reaching the test age is cleaned, the resin is used to seal the side of the test piece and fill the holes on the surface, the treated test piece is placed in the concrete vacuum saturation machine, after the vacuum saturation treatment is completed, the electric flux of the concrete test block is tested by using the electric flux tester, the smaller the electric flux, the better the durability of the concrete, the test solution is a 3.0% NaCl solution, and the evaluation is shown in Table 1:

[0100] Table 1: Evaluation of concrete electric flux and chloride ion permeability

[0101] Total electric flux (C) Chloride ion permeability of concrete ＞4000 High 2000-4000 Medium 1000-2000 Low 100-1000 Very low ＜100 Negligible

[0102] Table 2: Test results

[0103]

[0104]

[0105] It can be seen from Examples 1-3 and Comparative Example 1 in combination with Table 1 that the experimental data of Examples 1-3 are better than those of Comparative Example 1, which shows that the addition of water-soluble phenolic resin can play a unique chemical role in the alkaline environment of cement hydration and enhance the strength of concrete.

[0106] It can be seen from Examples 1-3 and Comparative Example 2 in combination with Table 1 that the experimental data of Examples 1-3 are better than those of Comparative Example 2, which shows that the modification treatment of recycled sand by the method of the present application can significantly reduce the water absorption of recycled aggregate and improve its impermeability and durability.

[0107] It can be seen from Examples 1-3 and Comparative Example 3 in combination with Table 1 that the experimental data of Examples 1-3 are better than those of Comparative Example 3, which shows that the impregnation treatment of aggregate can promote the carbonation reaction of aggregate, and the impregnation treatment can help to improve the crystal form of calcium carbonate generated by carbonation reaction, forming more stable and higher strength aggregate, and the modified molecules attached to the surface of the aggregate can improve the reactivity of the aggregate and the bonding strength between the aggregate and other raw materials, thereby improving the strength and durability of the concrete.

[0108] It can be seen from Examples 1, Examples 4-6 in combination with Table 1 that the experimental data of Examples 1, Examples 5-6 are better than those of Example 7, which shows that the use of anionic polyacrylamide has a modification effect, and it has better hydrophilicity, high viscosity and other characteristics, which can significantly improve the coagulation and durability of the aggregate and concrete, and improve the strength of the concrete.

[0109] It can be seen from the combination of Example 1 and Example 7 and Table 1 that the experimental data of Example 1 is better than that of Example 7, which shows that the selection of dispersant affects the properties of recycled concrete, and the selection of lignin sulfonate as dispersant has better dispersing performance and stability, can interact with the modified molecules adsorbed on the surface of aggregate, achieve better dispersion effect, and thus improve the compressive strength and durability of concrete.

[0110] It can be seen from the combination of Example 1 and Example 8-9 and Table 1 that the experimental data of Example 8-9 is better than that of Example 1, which shows that the addition of polyhydric alcohol can improve the reactivity of each raw material in concrete, promote the progress of hydration reaction, generate more ettringite, calcium carbonate and other substances to fill the pores, and thus improve the compressive strength and durability of concrete.

[0111] The specific embodiments are only an explanation of the present application, which is not a limitation of the present application, and those skilled in the art can make modifications to the embodiments without creative contribution after reading the present specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A green low-carbon recycled concrete, characterized in that, The raw materials include the following weight parts: slag 3-6 parts, modified recycled sand 30-50 parts, recycled powder 8-10 parts, cement 40-50 parts, water-soluble phenolic resin 5-8 parts, sodium hexametaphosphate 0.2-0.5 parts, dispersant 1-3 parts, water glass 5-7 parts, and water 60-80 parts, the modified recycled sand is obtained by impregnating a modified solution and then carbonizing modification; The preparation process of the modified recycled sand is as follows: (1) crushing and screening the waste concrete to obtain aggregate with a diameter less than 4.75 mm; (2) putting the aggregate into a modified solution of polyacrylamide, chitosan and calcium hydroxide, stirring uniformly, standing, and then carbonizing treatment by passing in carbon dioxide, and obtaining the modified recycled sand after completion; 2. The green low-carbon recycled concrete according to claim 1, characterized in that: The standing time in step (2) is 60-80 min; The concentration of carbon dioxide in step (2) is 20-25%, the gas flow rate is 4-4.5 L / min, the temperature is 20-25℃, and the passing-in time is 30-60 min.

3. The green low-carbon recycled concrete according to claim 1, characterized in that: The weight ratio of polyacrylamide, chitosan and calcium hydroxide in the modified solution is 0.5-0.8:0.3:1.2-1.

5.

4. The green low-carbon recycled concrete according to claim 1, characterized in that: The polyacrylamide is an anionic polyacrylamide with a molecular weight of 7-9 million.

5. The green low-carbon recycled concrete according to claim 1, characterized in that: The dispersant is any one of lignin sulfonate.

6. The green low-carbon recycled concrete according to claim 1, characterized in that: The raw materials further include 2-5 parts by weight of a polyhydric alcohol.

7. A method of producing the green low-carbon recycled concrete according to any one of claims 1 to 5, characterized by, The method includes the following steps: (1) stirring the slag, recycled powder, cement and sodium hexametaphosphate uniformly to obtain dry powder, then adding water glass and half of the water and continuing to stir and mix uniformly to obtain a mixture for standby; (2) heating the remaining water to 50-70℃, then adding the weighed modified recycled sand, water-soluble phenolic resin and dispersant and stirring for 3-5 min, then adding the mixture and continuing to stir for 3-5 min to obtain green low-carbon recycled concrete.

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