High slump retention and high fluidity concrete based on fully recycled coarse aggregate and its mixing process

Abstract

The present invention relates to a high slump retention and high fluidity concrete based on fully recycled coarse aggregate and its mixing process. The raw materials per cubic meter of the concrete include the following components: 200 - 250 kg of cement, 150 - 200 kg of mineral admixture, 700 - 800 kg of manufactured sand, 1000 - 1100 kg of recycled coarse aggregate, 6.0 - 7.5 kg of admixture, and 170 - 200 kg of mixing water. Through the synergistic effect of technologies such as "high-volume mineral admixture technology", "admixture compounding technology", "pretreatment technology for recycled coarse aggregate", and "mixing process design technology", the present invention significantly improves the slump retention performance and fluidity of the fully recycled coarse aggregate concrete, strengthens the mortar strength adhered to the recycled coarse aggregate, and improves the defects in the interfacial transition zone, realizing the high slump retention, high fluidity of the concrete and the full replacement of the recycled coarse aggregate, and is suitable for popularization and application in ready-mixed concrete.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete materials, and in particular to a high slump retention and high fluidity concrete based on fully recycled coarse aggregate and its mixing process. Background Art

[0002] Processing waste concrete into recycled aggregate and preparing new concrete can solve the problem of waste concrete disposal, and at the same time alleviate the shortage of natural aggregate resources, with extensive social, environmental and economic benefits, which is conducive to the sustainable development of the construction industry.

[0003] However, there are still many technical bottlenecks in using recycled coarse aggregate to prepare concrete and apply it in the engineering field. This is because the surface of recycled coarse aggregate is rough, with a layer of hardened cement mortar attached, and microcracks are generated due to damage during the crushing process, resulting in defects such as high porosity, large water absorption, small bulk density and high crushing value. As a result, the workability of the prepared concrete has a large time-dependent loss and poor retention performance, making it difficult to meet the requirements of long-distance transportation and on-site pouring construction of concrete. Currently, physical strengthening methods and chemical strengthening methods are mainly used to strengthen recycled coarse aggregate. The physical strengthening method mainly removes the hardened cement mortar attached to the surface of recycled coarse aggregate through mechanical force, and the chemical strengthening method mainly uses a slurry or chemical reagent with certain activity to treat the surface and microcracks of recycled coarse aggregate. Both of these methods can improve the quality of recycled coarse aggregate, thereby improving the performance of recycled coarse aggregate concrete. However, these methods are cumbersome to operate, require special equipment for grinding or long-term chemical soaking treatment, have a long cycle, and will greatly increase production costs and pollute the environment, making it difficult to meet the large-scale concrete production demand and restricting the full substitution application of recycled coarse aggregate in ready-mixed concrete.

[0004] Chinese Patent CN201711330560.3 discloses a preparation method of mineral admixture and a self-compacting concrete, which is prepared by compounding fly ash, slag powder, silica fume and metakaolin; wherein the first mixture is mixed according to the mass ratio of fly ash to slag powder of 0.6 - 1.5, the second mixture is mixed according to the mass ratio of silica fume to metakaolin of 0.8 - 1.2, and then the first mixture and the second mixture are mixed again according to the mass ratio of 4:1 and put into a ball mill for further grinding and refinement, and 1% - 2.5% of gel dispersant and polyacrylamide are added and dispersed evenly, and stirred step by step at a constant temperature. After the reaction is complete, it is filtered and dried, and the mineral admixture is obtained after screening. However, in this patent, the mineral admixture is ground and modified, and silica fume is added, resulting in a large specific surface area and increased water demand, reducing the workability of the concrete. Summary of the Invention

[0005] The object of the present invention is to provide a high slump-retention and high fluidity concrete based on fully recycled coarse aggregate and its mixing process, so as to solve the problems such as fast slump loss, poor fluidity and low replacement rate of recycled coarse aggregate concrete. Through the synergistic effect of technologies such as "high-volume mineral admixture technology", "compound admixture technology", "pretreatment technology of recycled coarse aggregate" and "mixing process design technology", the present invention greatly improves the slump retention performance and fluidity of fully recycled coarse aggregate concrete, strengthens the strength of the mortar attached to the recycled coarse aggregate and improves the defects in the interfacial transition zone, realizing high slump-retention, high fluidity of concrete and full replacement of recycled coarse aggregate, and is suitable for popularization and application in ready-mixed concrete.

[0006] The object of the present invention can be achieved by the following technical solutions:

[0007] A high slump-retention and high fluidity concrete based on fully recycled coarse aggregate, the raw materials of each cubic meter of the concrete include the following components:

[0008] Cement 200 - 250 kg,

[0009] Mineral admixture 150 - 200 kg,

[0010] Manufactured sand 700 - 800 kg,

[0011] Recycled coarse aggregate 1000 - 1100 kg,

[0012] Admixture 6.0 - 7.5 kg,

[0013] Mixing water 170 - 200 kg.

[0014] Further, the cement is 42.5-grade portland cement.

[0015] Further, the mineral admixture is composed of fly ash, ground granulated blast-furnace slag and metakaolin, and the mass percentages of the fly ash, ground granulated blast-furnace slag and metakaolin are (40 - 60):(30 - 40):(10 - 20). The water demand ratio of the mineral admixture is not greater than 100%. By limiting the ratio and water demand ratio of the mineral admixture, the purpose is to reduce the hydration rate of the cementitious material while not reducing the free water content in the concrete system.

[0016] Still further, the fly ash is Class II fly ash.

[0017] Still further, the ground granulated blast-furnace slag is S95 ground granulated blast-furnace slag.

[0018] Still further, the residue on the 45μm square-hole sieve of the metakaolin is ≤ 4.0%.

[0019] By adopting the above "high-volume mineral admixture technology" solution, on the one hand, the high-volume mineral admixture reduces the early hydration reaction rate of the cementitious material system, prolongs the initial setting time of the concrete, and is beneficial to improving the slump retention performance of the all-recycled coarse aggregate concrete; on the other hand, the micro-particles of the cementitious material fill each other. First, it can release the free water wrapped by the paste particles, which is beneficial to improving the fluidity of the all-recycled coarse aggregate concrete. Second, metakaolin can reduce the total porosity of the recycled coarse aggregate concrete, improve the compactness of the concrete, and thus improve the strength and impermeability of the all-recycled coarse aggregate concrete.

[0020] Furthermore, the fineness modulus of the manufactured sand is 2.6 - 3.2, MB < 1.0, and the stone powder content is 3 - 6%. The smaller the MB value in the manufactured sand, the less mud it contains, and the better the finally prepared concrete.

[0021] Furthermore, the recycled coarse aggregate has a particle size of 5 - 25 mm, a continuous grading, the content of needle-like and flaky particles is not more than 8%, the saturated water absorption rate is not more than 5%, and the crushing value is not more than 16%.

[0022] By adopting the above preferred sand and stone aggregate solutions, the aggregate gradation can be controlled, and by using the principle of the densest packing of aggregates, the densest packing of the concrete aggregate system can be achieved, improving the fluidity and strength of the all-recycled coarse aggregate concrete.

[0023] Furthermore, the admixture is a composite admixture. Calculated by 100 parts by weight, it consists of the following components: 20 - 30 parts by weight of water reducer, 5 - 10 parts by weight of hydroxycarboxylate, and the rest is water.

[0024] Furthermore, the water reducer is a polycarboxylate superplasticizer, and the water reduction rate is not less than 25%.

[0025] Furthermore, the hydroxycarboxylate is sodium tartrate, industrial grade, and the purity is not less than 85%.

[0026] By adopting the above "admixture compounding technology" solution, on the one hand, the polycarboxylate superplasticizer can effectively improve the fluidity of the all-recycled coarse aggregate concrete. On the other hand, sodium tartrate and the water reducer form competitive adsorption on the surface of cement particles. First, the hydroxyl groups (-OH) on sodium tartrate react with free Ca 2+ and other substances in the alkaline environment of the cement paste to form unstable complexes, prolonging the initial setting time of the concrete and being beneficial to improving the slump retention performance of the all-recycled coarse aggregate concrete. Second, as the cement hydration proceeds, the unstable complexes decompose by themselves, and the water reducer molecules in the liquid phase are adsorbed onto the surface of cement particles, improving the fluidity of the all-recycled coarse aggregate concrete.

[0027] The polycarboxylate superplasticizer and sodium tartrate together form a composite admixture, and its main purpose is to regulate the water consumption and cement hydration, and then control the workability of recycled aggregate concrete. It is necessary to cooperate with other technical means to solve the problem of slump loss of recycled aggregate concrete.

[0028] Furthermore, the mixing water is composed of first mixing water and second mixing water. The mass percentage of the first mixing water is 35-50%, and the mass percentage of the second mixing water is 50-65%.

[0029] Furthermore, the first mixing water is a chemical solution. By weight of 100 parts, it is composed of the following components: 2.0-5.0 parts by weight of sodium methyl silicate, 1.0-3.0 parts by weight of aluminum sulfate, and the rest is water.

[0030] Furthermore, the second mixing water is tap water.

[0031] By adopting the above "pretreatment technology for recycled coarse aggregate" scheme, on the one hand, the first mixing water pretreats the recycled coarse aggregate, reduces the adsorption capacity of the recycled coarse aggregate for free water and superplasticizer during the later mixing process, ensures the effective content of the superplasticizer in the concrete system, and improves the slump retention performance and fluidity of the recycled aggregate concrete; on the other hand, during the pretreatment process of the recycled coarse aggregate, the chemical solution penetrates into the interior of the old mortar. The Si-O of sodium methyl silicate is easy to combine with Si-O-Si on the surface of the old mortar, making the surface denser. Aluminum sulfate enters the interior of the attached mortar and reacts with calcium hydroxide to generate needle-shaped ettringite crystals that block the capillary channels of the attached mortar, playing multiple functions such as densification, strengthening, and curing, strengthening the strength of the attached mortar of the recycled coarse aggregate and improving the defects in the interfacial transition zone, and thus improving the strength of the recycled aggregate concrete.

[0032] In addition, the present invention also provides a mixing process for high slump-retention and high-fluidity concrete based on all-recycled coarse aggregate, and the specific steps are as follows:

[0033] S1. Put the first mixing water and the recycled coarse aggregate into a mixing pan and stir.

[0034] S2. Then add mineral admixtures, admixtures and the second mixing water and continue to stir.

[0035] S3. Finally, add manufactured sand and stir until uniform to obtain concrete.

[0036] Furthermore, in step S1, the stirring time is 45-60 s.

[0037] Furthermore, in step S2, the stirring time is 30-60 s.

[0038] Further, in step S3, the stirring time is 30 to 60 s.

[0039] By adopting the above "stirring process design technology" solution, first, the recycled coarse aggregate is pretreated by mixing and stirring with the first mixing water; then, the cementitious material, water reducer, and the second mixing water are added and stirred continuously to form a cement paste, which further fills the pores, cracks, and the interfacial transition zone between the old mortar and the original coarse aggregate of the recycled coarse aggregate, enhancing the strength of the recycled coarse aggregate and further improving the later strength of the all-recycled coarse aggregate concrete; finally, the manufactured sand is added and stirred to obtain the all-recycled coarse aggregate concrete with high slump retention and high fluidity.

[0040] In the concrete production process of the present invention, a pretreatment process is directly added to solve the problems of water absorption, water reducer absorption, and low strength of recycled aggregates. In the existing patented technologies, only the recycled aggregates are modified to reduce the water absorption rate, without involving reducing the dosage of water reducer and enhancing its effect.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] Through the synergistic effect of a series of technologies, the slump retention performance of the all-recycled coarse aggregate concrete is greatly improved, and the strength of the mortar attached to the recycled coarse aggregate is enhanced and the defects in the interfacial transition zone are improved, realizing high slump retention, high fluidity of the concrete, and full replacement of the recycled coarse aggregate, which is suitable for popularization and application in ready-mixed concrete. Specific Embodiments

[0043] The present invention will be described in detail below with reference to specific embodiments. These embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but the protection scope of the present invention is not limited to the following embodiments.

[0044] The raw materials in the following embodiments are as follows:

[0045] (1) Cement: P·O42.5 cement;

[0046] (2) Mineral admixture: Class II fly ash, S95 slag powder, and metakaolin, with a water demand ratio of 98%;

[0047] (3) Manufactured sand: fineness modulus of 3.0, MB value of 0.9, and stone powder content of 4.5%;

[0048] (4) Recycled coarse aggregate: The recycled coarse aggregate produced by Shanghai Xuzhong Renewable Resources Utilization Co., Ltd., with a particle size of 5 - 25 mm continuous grading, saturated water absorption rate of 4.8%, water content of 1.0%, crushing value of 15.5%, and content of needle-like and flaky particles of 7%;

[0049] (5) Water reducing agent: The polycarboxylate high-performance water reducing agent produced by China State Construction Western Construction New Materials Technology Co., Ltd. with a water reducing rate of 28% is used;

[0050] (6) Sodium tartrate, sodium metasilicate, aluminum sulfate: Industrial grade, all are commercially available products;

[0051] (7) Water: Tap water.

[0052] Unless otherwise specified, the equipment used in the following examples is all conventional equipment in the field; unless otherwise specified, the reagents used are all commercially available products or prepared by conventional methods in the field. Those not described in detail in the following examples can be achieved by conventional experimental means in the field.

[0053] Some embodiments of the present invention will be described in detail below. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0054] Example 1

[0055] This example provides a high slump retention and high fluidity concrete based on fully recycled coarse aggregate. The raw materials per cubic meter of the concrete include the following components: 200 kg of cement, 150 kg of mineral admixture, 700 kg of manufactured sand, 1100 kg of recycled coarse aggregate, 6.0 kg of admixture, and 170 kg of mixing water. Among them, the mineral admixture consists of 90 kg of Class II fly ash, 45 kg of S95 blast furnace slag powder, and 15 kg of metakaolin. The admixture consists of 20 parts by weight of polycarboxylate high-performance water reducing agent, 10 parts by weight of sodium tartrate, and 70 parts by weight of water. The mixing water consists of 60 kg of the first mixing water and 110 kg of the second mixing water. The first mixing water consists of 2 parts by weight of sodium metasilicate, 1 part by weight of aluminum sulfate, and 97 parts by weight of water.

[0056] In addition, this example also provides a mixing process for a high slump retention and high fluidity concrete based on fully recycled coarse aggregate, and the specific steps are as follows:

[0057] S1, Put the first mixing water and the recycled coarse aggregate into the mixing pot and stir for 45 s;

[0058] S2, Then add the cementitious material, water reducing agent, and the second mixing water and continue to stir for 60 s;

[0059] S3, Finally, add the manufactured sand and stir for 30 s until uniform, and a high slump retention and high fluidity concrete based on fully recycled coarse aggregate is obtained.

[0060] Example 2

[0061] This embodiment provides a high slump-retention and high fluidity concrete based on fully recycled coarse aggregate and its mixing process. The raw material mix ratio per cubic meter of the concrete is shown in Table 1. Among them, the first mixing water formula is shown in Table 2, and the admixture formula is shown in Table 3. The mixing process is the same as that in Embodiment 1, and the mixing time for each step is shown in Table 4.

[0062] Embodiment 3

[0063] This embodiment provides a high slump-retention and high fluidity concrete based on fully recycled coarse aggregate and its mixing process. The raw material mix ratio per cubic meter of the concrete is shown in Table 1. Among them, the first mixing water formula is shown in Table 2, and the admixture formula is shown in Table 3. The mixing process is the same as that in Embodiment 1, and the mixing time for each step is shown in Table 4.

[0064] Embodiment 4

[0065] This embodiment provides a high slump-retention and high fluidity concrete based on fully recycled coarse aggregate and its mixing process. The raw material mix ratio per cubic meter of the concrete is shown in Table 1. Among them, the first mixing water formula is shown in Table 2, and the admixture formula is shown in Table 3. The mixing process is the same as that in Embodiment 1, and the mixing time for each step is shown in Table 4.

[0066] Embodiment 5

[0067] This embodiment provides a high slump-retention and high fluidity concrete based on fully recycled coarse aggregate and its mixing process. The raw material mix ratio per cubic meter of the concrete is shown in Table 1. Among them, the first mixing water formula is shown in Table 2, and the admixture formula is shown in Table 3. The mixing process is the same as that in Embodiment 1, and the mixing time for each step is shown in Table 4.

[0068] Embodiment 6

[0069] This embodiment provides a high slump-retention and high fluidity concrete based on fully recycled coarse aggregate and its mixing process. The raw material mix ratio per cubic meter of the concrete is shown in Table 1. Among them, the first mixing water formula is shown in Table 2, and the admixture formula is shown in Table 3. The mixing process is the same as that in Embodiment 1, and the mixing time for each step is shown in Table 4.

[0070] Comparative Example 1

[0071] This comparative example provides a concrete prepared without adding mineral admixtures and using conventional admixtures. The raw materials per cubic meter of the concrete include the following components: 350 kg of cement, 700 kg of manufactured sand, 1100 kg of recycled coarse aggregate, 6.0 kg of conventional admixture, and 170 kg of mixing water. Among them, the conventional admixture is a polycarboxylate superplasticizer, and the mixing water and mixing process are the same as those in Embodiment 1.

[0072] Comparative Example 2

[0073] This comparative example provides a concrete prepared without adding mineral admixtures. The raw materials per cubic meter of the concrete include the following components: 350 kg of cement, 700 kg of manufactured sand, 1100 kg of recycled coarse aggregate, 6.0 kg of admixture, and 170 kg of mixing water. Among them, the admixture, mixing water, and mixing process are the same as those in Example 2.

[0074] Comparative Example 3

[0075] This comparative example provides a concrete prepared with conventional admixtures. The raw materials per cubic meter of the concrete include the following components: 220 kg of cement, 200 kg of mineral admixture, 750 kg of manufactured sand, 1000 kg of recycled coarse aggregate, 6.8 kg of conventional admixture, and 180 kg of mixing water. Among them, the mineral admixture consists of 80 kg of Class II fly ash, 80 kg of S95 blast furnace slag powder, and 40 kg of metakaolin. The conventional admixture is a polycarboxylate superplasticizer, and the mixing water and mixing process are the same as those in Example 3.

[0076] Comparative Example 4

[0077] This comparative example provides a concrete mixed with tap water. The raw materials per cubic meter of the concrete include the following components: 220 kg of cement, 200 kg of mineral admixture, 740 kg of manufactured sand, 1040 kg of recycled coarse aggregate, 7.0 kg of admixture, and 180 kg of mixing water. Among them, the mineral admixture consists of 100 kg of Class II fly ash, 80 kg of S95 blast furnace slag powder, and 20 kg of metakaolin. The mixing water is tap water, and the admixture and mixing process are the same as those in Example 4.

[0078] Comparative Example 5

[0079] This comparative example provides a concrete. The raw materials per cubic meter of the concrete are the same as those in Example 5.

[0080] In addition, this comparative example also provides a mixing process for concrete, and the specific steps are as follows:

[0081] Directly mix and stir the cement, mineral admixture, manufactured sand, recycled coarse aggregate, admixture, and mixing water to obtain concrete.

[0082] Comparative Example 6

[0083] This comparative example provides a concrete. The raw materials per cubic meter of the concrete include the following components: 250 kg of cement, 100 kg of fly ash, 100 kg of blast furnace slag powder, 750 kg of manufactured sand, 1000 kg of recycled coarse aggregate, 7.2 kg of polycarboxylate superplasticizer, and 200 kg of mixing water. Directly mix and stir the cement, fly ash, blast furnace slag powder, manufactured sand, recycled coarse aggregate, polycarboxylate superplasticizer, and mixing water to obtain concrete.

[0084] Table 1 Mix proportion of fully recycled coarse aggregate concrete (kg / m 3 )

[0085]

[0086]

[0087] Table 2 Formula of the first mixing water (by 100 parts by weight)

[0088] Example Sodium methyl silicate Aluminum sulfate Water 1 2.0 1.0 97.0 2 5.0 3.0 92.0 3 3.0 2.0 95.0 4 3.5 2.5 94.0 5 4.5 2.5 93.0 6 5.0 1.0 94.0

[0089] Table 3 Formula of admixture (by 100 parts by weight)

[0090] Example Polycarboxylate superplasticizer Sodium tartrate Water 1 20 10 70 2 20 5 75 3 30 10 60 4 30 5 65 5 25 10 65 6 25 5 70

[0091] Table 4 Mixing time of examples (s)

[0092]

[0093]

[0094] Performance detection

[0095] The slump test of concrete was carried out in accordance with the relevant provisions of the "Standard Test Method for Properties of Ordinary Concrete Mixtures" (GB / T 50080-2016); the compressive strength test was carried out in accordance with the relevant provisions of the "Standard Test Method for Physical and Mechanical Properties of Concrete" (GB / T 50081-2019); the electric flux test was carried out in accordance with the relevant provisions of the "Standard Test Method for Long-Term Performance and Durability of Ordinary Concrete" (GB / T 50082-2009).

[0096] The slump, compressive strength and electric flux of the concretes of Examples 1-6 and Comparative Examples 1-5 were tested, and the test results are shown in Table 5.

[0097] Table 5 Test results of slump, compressive strength and electric flux of concrete

[0098]

[0099] From Example 2 and Comparative Example 2, it can be seen that the present invention adopts the technology of large dosage of mineral admixtures: the mineral admixtures described in Example 2 are composed of Class II fly ash, S95 slag powder and metakaolin, and the water demand ratio is 98%. Mineral admixtures were not added in Comparative Example 2. The present invention limits the proportion of mineral admixtures and the water demand ratio, aiming to reduce the hydration rate of the cementitious material, extend the initial setting time of the concrete, which is beneficial to improving the slump retention performance of the fully recycled coarse aggregate concrete. At the same time, it does not reduce the free water content in the concrete system and releases the free water wrapped by the paste particles, which is beneficial to improving the fluidity of the fully recycled coarse aggregate concrete.

[0100] It can be seen from Example 3 and Comparative Example 3 that the present invention adopts an admixture compounding technique: the admixture described in Example 3 is a composite admixture, which, based on 100 parts by weight, consists of the following components: 30 parts by weight of water reducer, 10 parts by weight of hydroxycarboxylate, and the rest is water. The conventional admixture in Comparative Example 3 is a polycarboxylate superplasticizer. It is proved that on the one hand, the polycarboxylate superplasticizer in the composite admixture can effectively improve the fluidity of the all-recycled coarse aggregate concrete; on the other hand, sodium tartrate and the water reducer form competitive adsorption on the surface of cement particles, prolonging the initial setting time of the concrete, which is beneficial to improving the slump retention performance of the all-recycled coarse aggregate concrete and enhancing the fluidity of the all-recycled coarse aggregate concrete.

[0101] It can be seen from Example 4 and Comparative Example 4 that the present invention improves the mixing water: the first mixing water described in Example 4 is a chemical solution, which, based on 100 parts by weight, consists of the following components: 3.5 parts by weight of sodium methyl silicate, 2.5 parts by weight of aluminum sulfate, and the rest is water. The first mixing water in Comparative Example 4 is tap water. It is proved that the first mixing water pre-treats the recycled coarse aggregate, reducing the adsorption capacity of the recycled coarse aggregate for free water and water reducer during the subsequent mixing process, ensuring the effective content of the water reducer in the concrete system, and improving the slump retention performance and fluidity of the recycled coarse aggregate concrete. During the pre-treatment process of the recycled coarse aggregate, the chemical solution penetrates into the interior of the old mortar. The Si-O of sodium methyl silanolate is easily combined with Si-O-Si on the surface of the old mortar, making the surface denser. Aluminum sulfate enters the interior of the attached mortar and undergoes a chemical reaction with calcium hydroxide to generate needle-shaped ettringite crystals that block the capillary pore channels of the attached mortar, performing various functions such as densification, strengthening, and curing, strengthening the strength of the attached mortar of the recycled coarse aggregate and improving the defects in the interfacial transition zone, thereby enhancing the strength of the recycled coarse aggregate concrete.

[0102] It can be seen from Example 5 and Comparative Example 5 that the present invention adopts a step-by-step process design: that is, first, the recycled coarse aggregate is pre-treated by mixing and stirring the first mixing water and the recycled coarse aggregate; then, the cementitious material, water reducer, and the second mixing water are added and stirred continuously to form a cement paste, further filling the pores, cracks, and interfacial transition zone between the old mortar and the original coarse aggregate of the recycled coarse aggregate. By adding a pre-treatment link, the problems of water absorption, water reducer absorption, and low strength of the recycled aggregate are solved.

[0103] In summary, by the synergistic effect of technologies such as "high-volume mineral admixture technology", "compound admixture technology", "pretreatment technology for recycled coarse aggregate", and "mixing process design technology", the slump retention performance of fully recycled coarse aggregate concrete can be significantly improved, the strength of the mortar attached to the recycled coarse aggregate is enhanced, and the defects in the interfacial transition zone are improved, achieving high slump retention, high fluidity of concrete, and full replacement of recycled coarse aggregate. The initial slump of the fully recycled coarse aggregate concrete prepared by the present invention is not less than 230 mm, the slump after 2 hours is not less than 220 mm, the slump loss is not less than 10 mm, the spread after 2 hours is not less than 550 mm, and the workability meets the requirements of high slump retention and high fluidity concrete. At the same time, the 28-day compressive strength of the prepared fully recycled coarse aggregate concrete is between 35.9 and 53.5 MPa, which can meet the strength requirements of C30 to C45, and the 28-day electric flux is less than 1100 C. The recycled coarse aggregate concrete technology formed by the present invention is suitable for popularization and application in ready-mixed concrete.

[0104] The above description of the embodiments is to enable those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A high slump retention and high fluidity concrete based on fully recycled coarse aggregate, characterized in that, The raw materials per cubic meter of the concrete include the following components: Cement: 200 - 250 kg, Mineral admixture: 150 - 200 kg, Machine-made sand: 700 - 800 kg, Recycled coarse aggregate: 1000 - 1100 kg, Admixture: 6.0 - 7.5 kg, Mixing water: 170 - 200 kg; The mineral admixture consists of fly ash, ground granulated blast-furnace slag and metakaolin. The mass percentages of fly ash, ground granulated blast-furnace slag and metakaolin are (40 - 60):(30 - 40):(10 - 20), and the water demand ratio of the mineral admixture is not greater than 100%; The mixing water consists of first mixing water and second mixing water. The mass percentage of the first mixing water is 35 - 50%, and the mass percentage of the second mixing water is 50 - 65%; The first mixing water is a chemical solution, which consists of the following components by 100 parts by weight: sodium methyl silicate 2.0 - 5.0 parts by weight, aluminum sulfate 1.0 - 3.0 parts by weight, and the rest is water; The second mixing water is tap water; The admixture is a composite admixture, which consists of the following components by 100 parts by weight: water-reducing agent 20 - 30 parts by weight, hydroxycarboxylate 5 - 10 parts by weight, and the rest is water; The mixing process of high slump-retention and high fluidity concrete based on all recycled coarse aggregate is as follows: S1. Put the first mixing water and the recycled coarse aggregate into the mixing pan and stir; S2. Then add the mineral admixture, the admixture and the second mixing water and continue to stir; S3. Finally, add the machine-made sand and stir until uniform to obtain the concrete.

2. The high slump retention and high fluidity concrete based on fully recycled coarse aggregate according to claim 1, wherein The fly ash is Class II fly ash; The ground granulated blast-furnace slag is S95 ground granulated blast-furnace slag; The residue on 45μm square hole sieve of the metakaolin is ≤4.0%; 3. A high slump retention and high fluidity concrete based on fully recycled coarse aggregate according to claim 1, characterized in that, The fineness modulus of the machine-made sand is 2.6 - 3.2, MB < 1.0, and the stone powder content is 3 - 6%; The particle size of the recycled coarse aggregate is 5 - 25 mm, with continuous grading, the content of needle-like and flaky particles is not greater than 8%, the saturated water absorption rate is not greater than 5%, and the crushing value is not greater than 16%; 4. A high slump retention and high fluidity concrete based on fully recycled coarse aggregate according to claim 1, characterized in that, The water-reducing agent is a polycarboxylate superplasticizer, and the water-reducing rate is not less than 25%; The hydroxycarboxylate is sodium tartrate, industrial grade, and the purity is not less than 85%.

5. A mixing process for a highly slump-retentive and highly fluid concrete based on fully recycled coarse aggregate as described in any one of claims 1-4, characterized in that, The specific steps are as follows: S1. Put the first mixing water and the recycled coarse aggregate into the mixing pan and stir; S2. Then add the mineral admixture, the admixture and the second mixing water and continue to stir; S3. Finally, add the machine-made sand and stir until uniform to obtain the concrete.

6. The mixing process of a high slump retention and high fluidity concrete based on fully recycled coarse aggregate according to claim 5, characterized in that, In step S1, the stirring time is 45 - 60 s; In step S2, the stirring time is 30 - 60 s; In step S3, the stirring time is 30 - 60 s.

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