Preparation method of C80-grade fully-recycled coarse aggregate concrete

Abstract

The invention relates to a preparation method of C80-grade fully-recycled coarse aggregate concrete, which comprises the following steps: firstly, infiltrating cement slurry into internal pores of recycled coarse aggregate in a negative pressure environment to form an enhancement layer, thereby obtaining the recycled coarse aggregate subjected to surface treatment; compounding with medium sand according to continuous grading to obtain a primary mixture; adding cement, silica fume and slag powder into the primary mixture, stirring and mixing, then adding a polycarboxylic acid water reducing agent and water, and stirring and mixing to obtain a mixture; placing the mixture in a curing atmosphere containing carbon dioxide, and carrying out primary curing at 25-30 DEG C and 0.5-0.7 MPa; carrying out secondary maintenance at the temperature of 30 to 40 DEG C under the pressure of 0.7 to 0.9 MPa; then carrying out maintenance for three times at the temperature of 40-50 DEG C and the pressure of 0.9-1.1 MPa; and finally, performing standard curing to obtain the C80-grade fully-recycled coarse aggregate concrete. Compared with the prior art, the C80-grade all-recycled coarse aggregate concrete is conveniently obtained by utilizing a multi-dimensional synergistic technology, the energy consumption and CO2 emission in the preparation process are controlled, and the C80-grade all-recycled coarse aggregate concrete has multiple advantages of convenience, low carbon and high strength.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology and relates to a method for preparing C80 grade fully recycled coarse aggregate concrete. Background Technology

[0002] With the acceleration of urbanization, the amount of construction solid waste generated continues to increase, among which the efficient recycling of waste concrete has become a global focus. Traditional landfill disposal not only occupies a large amount of land resources but may also cause environmental pollution problems. Crushing waste concrete into recycled coarse aggregate to replace natural sand and gravel is one of the key paths to achieving sustainable development in the construction industry. The application of recycled aggregate can significantly reduce dependence on natural resources while reducing energy consumption in the material production process. However, existing technologies still face core challenges in improving the performance of recycled aggregate concrete, especially when preparing high-strength concrete with 100% recycled coarse aggregate, it is difficult to balance strength, durability, and process economy.

[0003] The presence of old mortar layers on the surface, internal micro-cracks, and high porosity in recycled coarse aggregates makes their interfacial transition zones weak points in concrete structures. Traditional physical strengthening methods (such as mechanical grinding and high-pressure water jetting) can improve surface morphology, but their effectiveness in repairing internal defects is limited and energy consumption is high. Chemical modification techniques (such as silane impregnation) can improve durability, but they suffer from complex processes, high costs, and insufficient long-term durability. Furthermore, existing cementitious system designs often rely on high-volume mineral admixtures (such as slag powder and fly ash), which helps reduce costs but often leads to slow early strength development, making it difficult to meet the rapid construction requirements of C80 grade high-strength concrete. These technological shortcomings limit the widespread application of recycled aggregate concrete in high-strength engineering structures. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing C80 grade fully recycled coarse aggregate concrete based on multi-dimensional synergy. This method achieves high performance of recycled coarse aggregate through a multi-dimensional synergistic approach, including recycled aggregate reinforcement, optimized aggregate and sand blending, optimized mix design, and curing techniques. This technology is applicable to construction waste recycling, green and low-carbon concrete preparation, and engineering applications such as high-rise buildings and long-span bridges.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A method for preparing C80 grade fully recycled coarse aggregate concrete includes the following steps:

[0007] 1) Cement slurry is penetrated into the internal pores of recycled coarse aggregate in a negative pressure environment to form a reinforcing layer, resulting in surface-treated recycled coarse aggregate;

[0008] 2) The surface-treated recycled coarse aggregate and medium sand are blended according to continuous gradation to obtain the initial mixture;

[0009] 3) Add cement, silica fume, and slag powder to the initial mixture, stir and mix to obtain the remix;

[0010] 4) Add the polycarboxylate superplasticizer and water to the remixing material, stir and mix to obtain the mixture;

[0011] 5) Place the mixture in a curing atmosphere containing carbon dioxide and perform initial curing at 25-30℃ and 0.5-0.7MPa; then perform secondary curing at 30-40℃ and 0.7-0.9MPa; and finally perform tertiary curing at 40-50℃ and 0.9-1.1MPa.

[0012] 6) Standard curing yields C80 grade fully recycled coarse aggregate concrete.

[0013] This invention proposes a multi-dimensional synergistic optimization technical approach: enhancing the interfacial properties of recycled aggregates through surface strengthening, improving aggregate bulk density through gradation optimization, and synergistically regulating the hydration reaction using a composite cementitious material system. Furthermore, it innovatively introduces a segmented high-pressure-carbonation curing process, achieving synergistic effects of pore structure optimization and densification of hydration products through staged pressure and gas environment control. This technical system significantly reduces production energy consumption and carbon emissions while ensuring high strength (C80 grade) and high durability of concrete, providing new ideas for the high-value utilization of construction waste and the development of low-carbon concrete technology.

[0014] In some specific embodiments, the mass ratio of the recycled coarse aggregate, medium sand, cement, silica fume, slag powder, polycarboxylate superplasticizer, and water is 1000:(400-700):(350-400):(20-30):(50-100):(6-8):(150-160).

[0015] In some specific embodiments, the recycled coarse aggregate is a recycled coarse aggregate for concrete that meets the requirements of GB / T25177-2010, and the recycled coarse aggregate is selected from any one of Class I recycled coarse aggregate, Class II recycled coarse aggregate or Class III recycled coarse aggregate.

[0016] In some specific embodiments, the fineness modulus of the medium sand is 2-3.

[0017] In some specific embodiments, the cement is PO 42.5 grade cement.

[0018] In some specific embodiments, the specific surface area of ​​the silica fume is ≥200m². 2 / kg.

[0019] In some specific embodiments, the slag powder has a 28-day activity ≥105%.

[0020] In some specific embodiments, the water reduction rate of the polycarboxylate superplasticizer is 30-40%.

[0021] In some specific implementations, in step 1), the recycled coarse aggregate is saturated surface-dry recycled coarse aggregate.

[0022] In some specific implementations, in step 1), the negative pressure environment has a negative pressure of -0.8 to -1.5 MPa; and the thickness of the reinforcing layer is 0.5 to 1 mm.

[0023] In some specific implementations, in step 5), the volume content of carbon dioxide in the curing atmosphere is 20-30%.

[0024] This invention overcomes the performance bottleneck of high-strength recycled aggregate concrete by systematically integrating surface strengthening, gradation optimization, composite cementitious system design, and segmented high-pressure-carbonation synergistic curing technology. The method uses fully recycled coarse aggregate (replacement rate ≥80%) as its core, combined with multi-scale technology synergistic optimization, to achieve a synergistic improvement in high concrete strength (C80 grade), low carbon emissions, and high durability. It is suitable for engineering scenarios with stringent material performance requirements, such as super high-rise buildings and long-span bridges.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] This invention, through the use of 100% recycled coarse aggregate and a segmented carbonization curing process, significantly reduces carbon emissions compared to traditional methods, while also lowering clinker usage, resulting in a substantial decrease in the overall life-cycle carbon footprint. The concrete achieves a stable 28-day compressive strength of C80 grade, and its workability indicators, such as scalability and air content, are superior to similar recycled aggregate concretes. The chloride ion diffusion coefficient is as low as 2.0 × 10⁻¹² m³. 2 / s (RCM method) meets the durability requirements under harsh environments.

[0027] The results show that the recycled concrete prepared by this technology is both economical and environmentally friendly, providing an innovative solution for the resource utilization of construction waste and the achievement of "dual carbon" goals.

[0028] In summary, this invention overcomes three major technical barriers to the high-strength application of recycled aggregate concrete through systematic technological integration: weakened interfacial properties, high porosity, and insufficient synergy of the cementitious system. The synergistic effect of surface reinforcement layer design, gradation optimization, and the composite cementitious system solves the common problem of insufficient strength in recycled aggregate concrete. The segmented high-pressure carbonation curing technology achieves spatiotemporal matching between pore filling and hydration product generation through staged environmental control, balancing efficiency and performance. This technology does not rely on energy-intensive steam curing or complex chemical modification processes, exhibits strong process compatibility, and is easy to industrialize. Detailed Implementation

[0029] The present invention will now be described in detail with reference to specific embodiments.

[0030] A method for preparing C80 grade fully recycled coarse aggregate concrete based on multidimensional synergy includes the following steps:

[0031] (1) In terms of the reinforcement dimension of recycled aggregate, the surface of recycled coarse aggregate is reinforced: Select Class II recycled coarse aggregate (crushing index ≤12%, water absorption rate ≤5%, needle-like and flaky particle content ≤10%), spray a certain amount of water on its surface, and after reaching the saturated surface dry state, use negative pressure adsorption technology to adsorb a uniform cement slurry on the surface of recycled aggregate to form a 0.5-1mm reinforcement layer (this cement is not included in the water-cement ratio).

[0032] (2) In terms of the blending of recycled aggregate and sand, the aggregate gradation was optimized: the surface-reinforced recycled coarse aggregate was blended with medium sand, and the gradation was optimized based on the close packing model to achieve a bulk density of 1.65-1.70 g / cm³. 3 The porosity is 20-25%;

[0033] (3) In terms of mix proportion, the design is optimized using silica fume, slag powder, etc.: the cementitious material is compounded with the aggregate mixture, and the cementitious material is composed of cement (300-400 kg / m³). 3 It consists of silica fume (5-8% replacing cement) and viscosity-reducing slag powder (20-30% replacing cement), forming an aggregate-cement mixture. Then, a polycarboxylate superplasticizer (water reduction rate ≥30%) is added to reduce the water requirement to 150-170 kg / m³. 3 Mix the concrete and shape it to a slump of ≥220mm;

[0034] (5) In terms of curing, the segmented high pressure-carbonization synergistic curing technology was used: under the condition that the CO2 concentration in the high pressure curing chamber is 20-30%, the pressure is increased to 0.6MPa at 20-25℃ and cured for 2h to activate pore filling; the pressure is increased to 0.8MPa at 30-35℃ and cured for 4h to accelerate the generation of hydration products and reduce porosity; the pressure is increased to 1.0MPa at 40-45℃ and cured for 2h to strengthen the interface transition zone and densify the hydration products; and then the sample is placed in the standard curing environment for 28 days.

[0035] This embodiment is implemented based on the technical solution of the present invention, and provides detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiment.

[0036] In the following embodiments, unless otherwise specified, the raw materials, reagents or processing techniques are all conventional commercial products or conventional processing techniques in the art.

[0037] Based on the above method, three sets of C80 fully recycled coarse aggregate concrete were prepared, suitable for different engineering types, as follows:

[0038] Example 1

[0039] This embodiment utilizes multi-dimensional collaborative technology to achieve efficient preparation of C80 grade fully recycled coarse aggregate concrete, which can be applied to basic structural engineering, including super high-rise structures. The raw material mix proportions are shown in Table 1.

[0040] Table 1. Mix proportions of fully recycled coarse aggregate concrete in Example 1 (water-cement ratio 0.35)

[0041]

[0042]

[0043] The fully recycled aggregate concrete samples were prepared according to the following procedure:

[0044] 1) Surface strengthening treatment of recycled aggregate: Purchase commercially available recycled coarse aggregate of grade II that meets the national standard (GB / T 25177-2010). Spray water on its surface until the aggregate is fully wetted, and then let it air dry naturally for 1.0-2.0 hours until it reaches a saturated surface dry state. Then, in a negative pressure environment (using a Peiffer HiPace 800 vacuum pump), penetrate cement slurry into the internal pores of the recycled aggregate. Let it stand for 2 hours to form a dense 0.5-1mm reinforcing layer on the surface of the recycled aggregate through physical adsorption and chemical bonding (this cement is not included in the water-cement ratio), thereby improving the surface properties of the aggregate.

[0045] 2) Gradation optimization: The surface-treated recycled coarse aggregate and medium sand are blended according to a continuous gradation, and the aggregate bulk density is adjusted by vibrating sieving and manual sieving to achieve a density of 1.68 g / cm³. 3 The porosity is controlled within 20-25%, effectively reducing the filling voids;

[0046] 3) Cementitious system mixing: Add materials in sequence. First, dry mix the recycled aggregate and medium sand until uniform. Then add the composite cementitious material (cement, silica fume, slag powder) and dry mix (50 rpm for three minutes). Finally, add the water-reducing agent and water and stir until the slump is ≥220mm. Wet mix until the concrete fluidity meets the pumping requirements.

[0047] 4) Segmented high-pressure carbonization curing:

[0048] First stage (25℃ / 0.6MPa / 48h): A mixture of 25 vol% CO2 and air is introduced to the set pressure. Gas is replenished every 15 minutes to maintain the pressure, promoting the reaction of CO2 with cement hydration products to generate calcium carbonate gel, initially sealing capillary channels and reducing porosity.

[0049] The second stage (35℃ / 0.8MPa / 48h): Increasing the temperature and pressure accelerates the hydration reaction process, stimulates the potential activity of silica fume and slag powder, generates more CSH gel, and further densifies the aggregate interface transition zone.

[0050] The third stage (45℃ / 1.0MPa / 24h): Under high pressure, CO2 penetration depth is enhanced, filling deep pores, while the structure of the interface transition zone is optimized to improve impermeability and resistance to chemical corrosion.

[0051] After curing, the cement was transferred to a standard environment (temperature 20±2℃ and relative humidity 95%) for 28 days to complete the stabilization process of cement hydration reaction and carbonation products. Then, its compressive strength and chloride ion permeability coefficient (RCM method) were tested.

[0052] Example 2-3

[0053] An efficient preparation method for C80 grade fully recycled coarse aggregate concrete, differing from Example 1 only in that:

[0054] The proportions of each component were changed to those shown in Table 2. Other steps were the same as in Example 1. In addition, the compressive strength and chloride ion permeability coefficient of Examples 2 and 3 were also tested in this example.

[0055] Table 2. Mix proportions of fully recycled coarse aggregate concrete in Examples 2 and 3

[0056] Material <![CDATA[Dosage of Example 2 (kg / m 3 )]]> <![CDATA[Dosage of Example 3 (kg / m 3 ) <!-- 4 -->]]> Recycled coarse aggregate (Class II) 1000 1000 Medium sand (fineness modulus 2.5) 600 400 Cement (P·O 42.5) 400 360 silica ash 28 23.6 Viscosity-reducing slag powder 90 80 Polycarboxylate superplasticizer 6.0 6.4 water 155 158

[0057] Comparative Example 1

[0058] The preparation of a fully recycled coarse aggregate concrete differs from Example 1 only in that:

[0059] The recycled aggregate was not surface-strengthened and was directly used in step 2) to be compounded with medium sand according to continuous gradation. The rest was the same as in Example 1.

[0060] Comparative Example 2

[0061] The preparation of a fully recycled coarse aggregate concrete differs from Example 1 only in that:

[0062] In step 4), carbonization and curing are carried out at 45°C and 1.0 MPa for 48 hours, and the rest is the same as in the example.

[0063] The test results of the compressive strength (GB / T 50081-2019) and chloride ion permeability coefficient (GB / T 50082-2009) of the fully recycled coarse aggregate concrete in Examples 1-3 are shown in Table 3. The test results show that the 28-day compressive strength of the fully recycled coarse aggregate concrete prepared according to this invention can reach C80, and the chloride ion permeability coefficient is less than 2.0 × 10⁻¹² m² / s, which demonstrates the feasibility of this invention.

[0064] Table 3 Performance test results of Examples 1-3

[0065]

[0066]

[0067] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing C80 grade fully recycled coarse aggregate concrete, characterized in that, The method includes the following steps: 1) Cement slurry is penetrated into the internal pores of recycled coarse aggregate in a negative pressure environment to form a reinforcing layer, resulting in surface-treated recycled coarse aggregate; 2) The surface-treated recycled coarse aggregate and medium sand are blended according to continuous gradation to obtain the initial mixture; 3) Add cement, silica fume, and slag powder to the initial mixture, stir and mix to obtain the remix; 4) Add the polycarboxylate superplasticizer and water to the remixing material, stir and mix to obtain the mixture; 5) Place the mixture in a curing atmosphere containing carbon dioxide and perform initial curing at 25-30℃ and 0.5-0.7MPa; then perform secondary curing at 30-40℃ and 0.7-0.9MPa; and finally perform tertiary curing at 40-50℃ and 0.9-1.1MPa. 6) Standard curing yields C80 grade fully recycled coarse aggregate concrete.

2. The method for preparing C80 grade fully recycled coarse aggregate concrete according to claim 1, characterized in that, The mass ratio of the recycled coarse aggregate, medium sand, cement, silica fume, slag powder, polycarboxylate superplasticizer, and water is 1000:(400-700):(350-400):(20-30):(50-100):(6-8):(150-160).

3. The method for preparing C80 grade fully recycled coarse aggregate concrete according to claim 1, characterized in that, The recycled coarse aggregate is a recycled coarse aggregate for concrete that meets the requirements of GB / T25177-2010, and the recycled coarse aggregate is selected from any one of Class I, Class II or Class III recycled coarse aggregate.

4. The method for preparing C80 grade fully recycled coarse aggregate concrete according to claim 1, characterized in that, The fineness modulus of the medium sand is 2-3.

5. The method for preparing C80 grade fully recycled coarse aggregate concrete according to claim 1, characterized in that, The cement is PO 42.5 grade cement.

6. The method for preparing C80 grade fully recycled coarse aggregate concrete according to claim 1, characterized in that, The specific surface area of ​​the silica fume is ≥200m². 2 / kg.

7. The method for preparing C80 grade fully recycled coarse aggregate concrete according to claim 1, characterized in that, The slag powder has a 28-day activity ≥105%; the polycarboxylate superplasticizer has a water reduction rate of 30-40%.

8. The method for preparing C80 grade fully recycled coarse aggregate concrete according to claim 1, characterized in that, In step 1), the recycled coarse aggregate is saturated surface-dry recycled coarse aggregate.

9. The method for preparing C80 grade fully recycled coarse aggregate concrete according to claim 1, characterized in that, In step 1), the negative pressure environment has a negative pressure of -0.8 to -1.5 MPa; the thickness of the reinforcing layer is 0.5 to 1 mm.

10. The method for preparing C80 grade fully recycled coarse aggregate concrete according to claim 1, characterized in that, In step 5), the volume content of carbon dioxide in the curing atmosphere is 20-30%.

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