Recycled coarse aggregate concrete and method for producing the same

Abstract

The application provides a recycled coarse aggregate concrete and a preparation method thereof, and uses waste concrete to prepare recycled coarse aggregate, fills the gaps generated in the breaking process of the recycled coarse aggregate by carrying out grafting reaction on the gelatinized starch permeating into the gaps of the recycled coarse aggregate, and reduces the water absorption rate of the coarse aggregate to ensure the quality of the concrete. After the starch free radical solution permeating into the gaps of the recycled coarse aggregate and the unsaturated monomer carry out polymerization reaction, a nearly continuous structure is formed, and the bonding strength of the recycled coarse aggregate and other components is increased. With the increase of the addition proportion of the starch free radical solution, the release amount of the cement hydration heat is also reduced to a certain extent, so that the formula is also helpful for reducing the temperature stress of the concrete and reducing the cracking of the concrete.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of building materials, and particularly relates to a concrete added with recycled coarse aggregate and a preparation method thereof. BACKGROUND

[0002] According to statistics, about 15-20 billion cubic meters of concrete are poured in China every year, and the sand and stone content accounts for about 70% of the concrete. Therefore, more than 1.1 billion cubic meters of sand and stone need to be mined every year to prepare concrete. As a non-renewable resource in the short term, sand and stone will inevitably become scarce. At present, natural sand and stone cannot meet the demand, and the supply-demand contradiction is increasingly prominent. In the process of new house construction, house demolition is inevitable, and a large amount of waste concrete is generated in the process. The treatment of waste concrete is facing severe challenges.

[0003] The waste concrete contains coarse aggregate that can be reused, but a large number of microcracks will be generated inside the recycled aggregate during the forced crushing and separation process, and a part of the "old mortar" will be attached to the surface. In the crushing process, a large number of microcracks will be generated in the recycled coarse aggregate due to mechanical action, resulting in a large water absorption rate and a large quality loss rate, which seriously affects the quality of the concrete. Compared with natural concrete, the recycled concrete will form various forms of interface transition zones inside, affecting the mechanical properties and durability of the concrete. At present, the industry generally strengthens the recycled coarse aggregate by chemical slurry strengthening method. The recycled coarse aggregate is soaked in chemical slurry of different properties to fill the microcracks of the recycled coarse aggregate and improve its quality.

[0004] A concrete coarse aggregate is disclosed in Chinese patent (CN202211487398.7, publication date: March 7, 2023). The recycled coarse aggregate is strengthened by using cement exosmosis Kim powder slurry, nano-silica sol, and modified organic silicon resin. The combination of nano-silica sol and exosmosis Kim powder slurry can repair the internal cracks of the soaked recycled coarse aggregate, make the grain shape of the aggregate round and the edges and corners not prominent, and make the aggregate more easily distributed uniformly and the aggregate interface more dense. After the solution formed by mixing the modified organic silicon resin and the catalyst is sprayed and solidified into a film, it can plug the unfilled pores and microcracks on the surface of the recycled coarse aggregate, so that the aggregate surface is covered with a thin film, the water absorption rate is reduced, and the strength is improved. Although this technology improves the strength of the concrete added with the aggregate to some extent by plugging the cracks and pores, the organic silicon resin covering the surface of the aggregate can easily cause the coarse aggregate to separate from the mixture components. In addition, the use of nano-silica sol and modified organic silicon resin to strengthen the aggregate has complex operation procedures and high cost, which is not conducive to the wide promotion of the technology.

[0005] A kind of recycled coarse aggregate concrete and its preparation method are disclosed in Chinese patent (CN201911345625.0, publication date: May 1, 2020), which mixes natural coarse aggregate, recycled coarse aggregate, cement, blast furnace slag, natural river sand, waste plastic, water reducing agent and water to prepare recycled coarse aggregate concrete.Although this technology uses recycled coarse aggregate, blast furnace slag, waste plastic and other waste resources to reduce production costs, the recycled coarse aggregate is only subjected to miscellaneous, magnetic separation, crushing, screening, leaching and drying treatment, and no other treatment is performed on its defects, so the performance of the concrete product still needs to be improved. SUMMARY

[0006] The purpose of the present application is to provide a kind of recycled coarse aggregate concrete and its preparation method to solve the problem of difficult efficient recycling of waste concrete in the prior art.The technical solution provided by the present application is as follows:

[0007] First, the waste concrete is treated:

[0008] The waste concrete material is crushed and vibrated, and the obtained waste concrete pieces are screened.The pieces with a particle size of 5-15 mm are selected by a screening machine as recycled coarse aggregate blanks.The recycled coarse aggregate blanks are washed with water and dried.The specific surface area of the washed and dried recycled coarse aggregate blanks is measured by nitrogen adsorption method, and the specific surface area is required to be greater than 3000 m2 / kg to ensure that there are enough gaps and holes inside, and the water absorption rate of the recycled coarse aggregate blanks is required to be less than 18%.If the specific surface area test result does not meet the requirements, the vibration time, frequency and intensity need to be adjusted.Furthermore, the vibration time, frequency and intensity need to be adjusted in time for waste concrete from different sources.

[0009] A starch solution with a mass concentration of 20%-30% is prepared using cassava starch or corn starch.To ensure good dispersion of the starch in the solution, sodium dodecyl benzene sulfonate, sodium polyacrylate, sodium citrate and the like are selected as dispersants, and the addition amount is 0.1%-0.3% of the mass of the starch.Heat to 60-70℃ to gelatinize the starch.Add 0.5-0.8% of benzoyl peroxide based on the mass of the starch to the gelatinized starch solution, and react for 1-2 h to obtain a starch free radical solution.

[0010] Add the prepared starch free radical solution to the washed and dried recycled coarse aggregate blanks, and mix thoroughly according to a weight ratio of 10-50:1 to obtain recycled coarse aggregate.The specific surface area of the above-mentioned recycled coarse aggregate is measured by nitrogen adsorption method after drying, and the specific surface area is less than 1000 m2 / kg.

[0011] The recycled coarse aggregate concrete is prepared according to the following steps (all parts by weight):

[0012] Mix 60-80 parts of recycled coarse aggregate, 0.5-0.8 parts of initiator, and 3-20 parts of unsaturated monomer in a mixer for 5 minutes.

[0013] in:

[0014] The initiator is one or a combination of two of the following: ammonium persulfate, sodium persulfate, and potassium persulfate.

[0015] The unsaturated monomers are one or a combination of two of acrylamide, acrylic acid, and methacrylic acid.

[0016] Add 100 parts of silicate cement, 30-60 parts of admixture, and 50-100 parts of fine aggregate to the well-mixed recycled coarse aggregate, initiator, and unsaturated monomer, and continue mixing for 3 minutes.

[0017] in:

[0018] The admixture is any one or a mixture of two of the following: fly ash, kaolin, attapulgite, and limestone powder.

[0019] The fine aggregate is any one or a combination of two of the following: quartz sand, manufactured sand, and washed sand.

[0020] Add 2-5 parts of polycarboxylate superplasticizer and 10-30 parts of water to the above mixture, and continue wet mixing for 3-5 minutes to obtain recycled coarse aggregate concrete.

[0021] Compared with existing technologies, this invention has the following advantages: 1. By grafting the gelatinized starch that has seeped into the gaps of recycled coarse aggregate, the gaps generated during the crushing process of recycled coarse aggregate are filled, reducing the water absorption rate of the coarse aggregate and ensuring concrete quality. 2. After the starch free radical solution that has seeped into the gaps of recycled coarse aggregate undergoes a polymerization reaction with the unsaturated monomers, a near-continuous structure is formed, increasing the bonding strength between the recycled coarse aggregate and other components. 3. As the proportion of starch free radical solution added increases, the release of heat of hydration of cement is also reduced to a certain extent, so this formula also helps to reduce concrete temperature stress and reduce concrete cracking. Detailed Implementation

[0022] The embodiments of the present invention will now be described.

[0023] Waste concrete material is compacted and vibrated, and the resulting fragments are screened to obtain fragments with a particle size of 5-15mm. The fragments are then washed with water and dried to obtain recycled coarse aggregate blocks. The specific surface area is determined using the nitrogen adsorption method, and is 3260㎡ / kg. The water absorption rate of this recycled coarse aggregate block is 15.1%.

[0024] Example 1:

[0025] A 20% (w / w) cassava starch solution was prepared using cassava starch. Sodium dodecylbenzenesulfonate was selected as the dispersant and added at 0.1% of the starch mass. The solution was heated to 60°C to gelatinize the starch. Benzoyl peroxide (0.5% of the starch mass) was then added to the gelatinized starch solution, and the reaction was allowed to proceed for 1.5 hours to obtain a starch free radical solution. This starch free radical solution was then thoroughly mixed with recycled coarse aggregate blocks at a weight ratio of 1:50 to obtain recycled coarse aggregate. 0.5 parts ammonium persulfate and 5 parts acrylamide were added to 60 parts of the recycled coarse aggregate, and the mixture was stirred for 5 minutes. 100 parts silicate cement, 30 parts a mixture of fly ash and kaolin in a 1:1 ratio, and 30 parts washed sand were then added, and the mixture was stirred for another 3 minutes. Finally, 4 parts polycarboxylate superplasticizer and 30 parts water were added, and the mixture was wet-mixed for 3 minutes to obtain recycled coarse aggregate concrete S1.

[0026] Example 2:

[0027] A 25% (w / w) cassava starch solution was prepared using cassava starch. Sodium polyacrylate was selected as the dispersant and added at 0.2% of the starch mass. The solution was heated to 65°C to gelatinize the starch. Benzoyl peroxide (0.65% of the starch mass) was then added to the gelatinized starch solution, and the reaction was allowed to proceed for 1.5 hours to obtain a starch free radical solution. This starch free radical solution was then thoroughly mixed with recycled coarse aggregate blocks at a weight ratio of 1:30 to obtain recycled coarse aggregate. 0.6 parts sodium persulfate and 10 parts methacrylic acid were added to 70 parts of the recycled coarse aggregate, and the mixture was stirred for 5 minutes. Then, 100 parts silicate cement, 60 parts attapulgite, and 30 parts quartz sand were added, and the mixture was stirred for another 3 minutes. Finally, 5 parts polycarboxylate superplasticizer and 25 parts water were added, and the mixture was wet-stirred for 3 minutes to obtain recycled coarse aggregate concrete S2.

[0028] Example 3:

[0029] A 30% (w / w) cassava starch solution was prepared using cassava starch. Sodium citrate was selected as the dispersant and added at 0.3% of the starch mass. The solution was heated to 70°C to gelatinize the starch. Benzoyl peroxide (0.8% of the starch mass) was then added to the gelatinized starch solution, and the reaction was allowed to proceed for 2 hours to obtain a starch free radical solution. This starch free radical solution was then thoroughly mixed with recycled coarse aggregate blocks at a weight ratio of 1:10 to obtain recycled coarse aggregate. 0.7 parts potassium persulfate and 15 parts acrylic acid were added to 80 parts of the recycled coarse aggregate, and the mixture was stirred for 5 minutes. 100 parts silicate cement, 35 parts limestone powder, and 30 parts washed sand were then added, and the mixture was stirred for another 3 minutes. Finally, 5 parts polycarboxylate superplasticizer and 10 parts water were added, and the mixture was wet-mixed for 3 minutes to obtain recycled coarse aggregate concrete S3.

[0030] Example 4:

[0031] A 20% corn starch solution was prepared using corn starch. Sodium polyacrylate was selected as the dispersant and added at 0.2% of the starch mass. The solution was heated to 65°C to gelatinize the starch. Benzoyl peroxide (0.6% of the starch mass) was then added to the gelatinized starch solution, and the reaction was allowed to proceed for 1 hour to obtain a starch free radical solution. This starch free radical solution was then thoroughly mixed with recycled coarse aggregate blocks at a weight ratio of 1:50 to obtain recycled coarse aggregate. 0.5 parts potassium persulfate and 5 parts acrylamide were added to 60 parts of the recycled coarse aggregate, and the mixture was stirred for 5 minutes. 100 parts silicate cement, 30 parts of an admixture (a 1:1 mixture of fly ash and limestone powder), and 30 parts washed sand were then added, and the mixture was stirred for another 3 minutes. Finally, 4 parts polycarboxylate superplasticizer and 30 parts water were added, and the mixture was wet-mixed for 3 minutes to obtain recycled coarse aggregate concrete S4.

[0032] Example 5:

[0033] A 25% corn starch solution was prepared using corn starch, with sodium citrate added as a dispersant at 0.1% of the starch mass. The solution was heated to 70°C to gelatinize the starch. Benzoyl peroxide (0.6% of the starch mass) was then added to the gelatinized starch solution, and the reaction was allowed to proceed for 1 hour to obtain a starch free radical solution. This starch free radical solution was then thoroughly mixed with recycled coarse aggregate blocks at a weight ratio of 1:30 to obtain recycled coarse aggregate. 0.6 parts ammonium persulfate and 10 parts methacrylic acid were added to 80 parts of the recycled coarse aggregate, and the mixture was stirred for 5 minutes. Next, 100 parts silicate cement, 40 parts of an admixture (a 1:1 mixture of attapulgite and kaolin), and 40 parts manufactured sand were added, and the mixture was stirred for another 3 minutes. Finally, 5 parts polycarboxylate superplasticizer and 20 parts water were added, and the mixture was wet-mixed for 3 minutes to obtain recycled coarse aggregate concrete S5.

[0034] Example 6:

[0035] A 30% corn starch solution was prepared using corn starch. Sodium dodecylbenzenesulfonate was selected as the dispersant and added at 0.2% of the starch mass. The solution was heated to 65°C to gelatinize the starch. Benzoyl peroxide (0.7% of the starch mass) was then added to the gelatinized starch solution, and the reaction was allowed to proceed for 1.2 hours to obtain a starch free radical solution. This starch free radical solution was then thoroughly mixed with recycled coarse aggregate blocks at a weight ratio of 1:10 to obtain recycled coarse aggregate. 0.7 parts sodium persulfate and 15 parts acrylic acid were added to 70 parts of the recycled coarse aggregate, and the mixture was stirred for 5 minutes in a mixer. 100 parts silicate cement, 60 parts of an admixture (a 1:1 mixture of fly ash and limestone powder), and 35 parts manufactured sand were then added, and the mixture was stirred for another 3 minutes. Finally, 5 parts polycarboxylate superplasticizer and 15 parts water were added, and the mixture was wet-mixed for 3 minutes to obtain recycled coarse aggregate concrete S6.

[0036] Comparative example:

[0037] Mix 60 parts of recycled coarse aggregate blocks, 0.5 parts of ammonium persulfate, and 5 parts of acrylamide in a mixer for 5 minutes. Then add 100 parts of silicate cement, 30 parts of an admixture (a 1:1 mixture of fly ash and kaolin), and 30 parts of washed sand, and continue mixing for 3 minutes. Finally, add 4 parts of polycarboxylate superplasticizer and 30 parts of water, and wet mix for 3 minutes to obtain recycled coarse aggregate concrete comparative example D1.

[0038] The recycled coarse aggregate concretes S1-S6 and comparative example D1 were analyzed and tested as follows (the test temperature was room temperature, 23℃):

[0039] In each embodiment, the recycled coarse aggregate blocks were mixed with starch free radical solution and then dried, and their specific surface area was tested using the nitrogen adsorption method.

[0040] The 28-day compressive strength of concrete samples was tested in accordance with GB / T 50081-2019 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete".

[0041] The heat of hydration was measured using a microcalorimeter (TAM-AI R), and the cumulative heat release was compared.

[0042] The specific test data for each sample are shown in the table below:

[0043]

[0044]

[0045] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A type of recycled coarse aggregate concrete, characterized in that, Its components, by weight, include the following components: 100 parts of silicate cement 30-60 parts of admixture, 60-80 parts recycled coarse aggregate 50-100 parts fine aggregate, 2-5 parts of polycarboxylate superplasticizer Initiator 0.5-0.8 parts, 3-20 parts of unsaturated monomers 10-30 parts water; The recycled coarse aggregate is obtained by the following steps: Step 1: Compact and vibrate the waste concrete material to obtain several fragments; Step 2: Screen the fragments obtained in Step 1. Use a screening machine to screen fragments with a particle size of 5-15mm as recycled coarse aggregate blanks. Step 3: Wash the recycled coarse aggregate blocks obtained in Step 2 with water and dry them for later use; Step 4: Prepare a starch solution with a mass concentration of 20%-30%, add a dispersant of 0.1%-0.3% of the starch mass, heat to 60-70℃ to gelatinize, then add benzoyl peroxide of 0.5-0.8% of the starch mass, and react for 1-2 hours to obtain a starch free radical solution. Step 5: Thoroughly mix the recycled coarse aggregate blocks that have been cleaned and dried in Step 3 with the starch free radical solution in Step 4 at a weight ratio of 10-50:1 to obtain recycled coarse aggregate; The dispersant mentioned in step four is one or a combination of two of sodium dodecylbenzenesulfonate, sodium polyacrylate, and sodium citrate.

2. The recycled coarse aggregate concrete as described in claim 1, characterized in that, The specific surface area of ​​the recycled coarse aggregate blocks after washing and drying in step three is greater than 3000 m². 2 / kg.

3. The recycled coarse aggregate concrete as described in claim 1, characterized in that, In step three, the water absorption rate of the recycled coarse aggregate blocks after cleaning and drying is less than 18%.

4. The recycled coarse aggregate concrete as described in claim 1, characterized in that, The recycled coarse aggregate obtained in step five, after drying, has a specific surface area of ​​less than 1000 m². 2 / kg.

5. The recycled coarse aggregate concrete as described in claim 1, characterized in that, The admixture is any one or a mixture of two of the following: fly ash, kaolin, attapulgite, and limestone powder.

6. The recycled coarse aggregate concrete as described in claim 1, characterized in that, The fine aggregate is any one or a combination of two of the following: quartz sand, manufactured sand, and washed sand.

7. The recycled coarse aggregate concrete as described in claim 1, characterized in that, The initiator is one or a combination of two of ammonium persulfate, sodium persulfate, and potassium persulfate.

8. The recycled coarse aggregate concrete as described in claim 1, characterized in that, The unsaturated monomer is one or a combination of two of acrylamide, acrylic acid, and methacrylic acid.

9. The method for preparing recycled coarse aggregate concrete according to any one of claims 1-8, characterized in that, Includes the following steps: S1: Mix the recycled coarse aggregate, initiator, and unsaturated monomer obtained in step five in a mixer for 5 minutes; S2: Add silicate cement, admixtures, and fine aggregates to the mixture obtained in S1, and stir for 3 minutes; S3: Add water and polycarboxylate superplasticizer to the mixture obtained in S2, and continue wet mixing for 3-5 minutes to obtain the recycled coarse aggregate concrete.

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