Preparation method of building recycled aggregate and application of building recycled aggregate in high-standard concrete

Abstract

The invention discloses a preparation method of building recycled aggregate and application of the building recycled aggregate in high-standard concrete, and particularly relates to the technical field of building materials, the preparation method comprises the following steps: S1, aggregate pretreatment, S2, pressurized permeation reinforcement, S3, interfacial activity modification, and S4, drying and molding. The particle size distribution is optimized through aggregate grading pretreatment, the stacking density is improved, and the segregation risk is reduced; the glass micro-powder mixed solution penetrates into aggregate pores to generate silicic acid gel through pressurization, permeation and reinforcement, the pore plugging rate is increased, the interface activity modification enables silica fume to directionally fill microcracks and the interface bonding strength to be improved by means of mechanical stirring and variable-frequency vibration, the C60 requirement is met, the chloride ion diffusion coefficient is equivalent to that of natural aggregate concrete, the durability is guaranteed, and the service life is prolonged. The construction waste is used as the raw material to realize waste resource utilization, the dependence on natural resources is reduced, and meanwhile, the CO emission of the recycled aggregate concrete is reduced.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to a method for preparing recycled building aggregate and its application in high-grade concrete. Background Technology

[0002] In the field of building materials, concrete, as one of the most widely used materials, requires a huge amount of natural aggregates for its production. For a long time, natural aggregates have been over-exploited due to their wide availability and relatively low price, leading to the depletion of resources and causing a series of serious ecological and environmental problems such as landslides and riverbed changes.

[0003] While recycled aggregates made from waste concrete possess some potential for resource substitution, those produced through simple crushing and screening processes suffer from numerous performance defects. Their particles are angular and rough-surfaced, contain hardened cement mortar, and accumulate numerous microcracks during crushing, resulting in high porosity, high water absorption, low bulk density, high void ratio, and high crushing index. Recycled concrete made from this low-quality aggregate has high water demand, low hardened strength, low modulus of elasticity, and significantly lower durability properties than ordinary concrete, including impermeability, frost resistance, carbonation resistance, shrinkage, creep, and chloride ion penetration resistance.

[0004] To improve the performance of recycled concrete, many studies have focused on strengthening the recycled aggregates. Currently, common strengthening methods include physical strengthening and chemical strengthening.

[0005] In summary, existing technologies for preparing and strengthening recycled aggregates have shortcomings in terms of performance improvement, environmental protection, and economic efficiency, making it difficult to meet the current construction industry's urgent demand for high-performance, environmentally friendly, and economical building materials. Developing a preparation method that can effectively improve the performance of recycled aggregates to meet the requirements of high-standard concrete applications, while also possessing good environmental benefits and economic value, has significant practical implications and promising application prospects. Summary of the Invention

[0006] The main objective of this invention is to provide a method for preparing recycled aggregates for construction and their application in high-grade concrete, which can effectively solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing recycled aggregate for construction includes the following steps: S1. Aggregate pretreatment: Obtain recycled coarse aggregate from construction waste and dry it; S2. Pressure-assisted infiltration enhancement: The dried aggregate is placed in a glass micro powder mixture containing an alkali activator, and directional pressure is applied for infiltration treatment; S3, Interfacial activity modification: The aggregate in the separation solution is uniformly mixed with highly active silica fume on the surface of the aggregate; S4. Drying and molding: The modified aggregate is dried to obtain reinforced recycled aggregate.

[0008] Preferably, in step S2, the directional pressure of the infiltration treatment is 800-2000 kPa, the treatment time is 10-30 min, the glass micropowder mixed solution is composed of glass micropowder, water and sodium hydroxide, the mass ratio of glass micropowder, water and sodium hydroxide is 1:(5-10):(0.02-0.1), and the mass ratio of the recycled building aggregate to the glass micropowder mixed solution is 1:(3-10).

[0009] Preferably, in step S2, the pressurization process is carried out in a closed pressure vessel, and the pressure is applied vertically from top to bottom. The specific surface area of ​​the glass micropowder is 200-300 m² / kg, and the density is 2.4-2.7 g / cm².

[0010] Preferably, in step S3, the specific surface area of ​​the silica fume is 15,000-20,000 m² / kg, the mass ratio of the recycled building aggregate to the silica fume is 1:(0.01-0.1), and mechanical stirring is used when mixing in the silica fume for 20-30 seconds.

[0011] Preferably, in step S4, the drying temperature is 100-105℃ and the drying time is 2-3 hours.

[0012] Preferably, in S1, the recycled building coarse aggregate is divided into three grades according to particle size: 19-31.5mm is the first grade particle size, 9.5-19mm is the second grade particle size, and 4.75-9.5mm is the third grade particle size, and the mass ratio of the three grades of aggregate is 1:(1-5):(1-5).

[0013] Preferably, in step S2, the alkaline activator is sodium hydroxide with a purity ≥99%, and the glass micro powder is derived from recycled waste glass with a particle size D50 ≤20μm.

[0014] The present invention also provides a method for preparing recycled building aggregates for use in high-grade concrete.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention optimizes particle size distribution through aggregate grading pretreatment, increases bulk density, and reduces segregation risk; pressurized infiltration strengthening allows the glass micro powder mixture solution to penetrate deep into the aggregate pores, generating silica gel, increasing pore sealing rate; interfacial activity modification, through mechanical stirring and variable frequency vibration, enables silica fume to directionally fill microcracks, increasing interfacial bonding strength to meet C60 requirements; chloride ion diffusion coefficient is comparable to that of natural aggregate concrete, ensuring durability.

[0016] 2. This invention uses construction waste as raw material to realize the resource utilization of waste, reduce dependence on natural resources, and at the same time reduce CO2 emissions of recycled aggregate concrete. While ensuring high performance, it achieves triple optimization of "strength-environmental protection-economy", and has broad application prospects. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall process of the present invention. Detailed Implementation

[0018] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below in conjunction with specific implementation methods.

[0019] Example 1, as Figure 1 As shown, this embodiment provides a method for preparing recycled building aggregate, including the following steps: S1. Aggregate pretreatment: Obtain recycled coarse aggregate from construction waste and dry it; The aforementioned recycled coarse aggregate for construction is divided into three grades according to particle size: 19-31.5mm is the first grade, 9.5-19mm is the second grade, and 4.75-9.5mm is the third grade. The three grades of aggregate are precisely proportioned in a mass ratio of 1:3:3 and dried at 105℃ for 3 hours to remove free water (moisture content ≤0.5%). This increases the bulk density of the aggregate, reduces the risk of segregation during subsequent infiltration treatment, and the optimized particle size gradient can enhance the mechanical interlocking force of concrete. S2. Pressure-assisted infiltration enhancement: The dried aggregate is placed in a glass micro powder mixture containing an alkali activator, and directional pressure is applied for infiltration treatment; The dried aggregate was immersed in a glass micropowder mixture solution (glass micropowder:water:sodium hydroxide = 1:7:0.03), with an aggregate to solution mass ratio of 1:4. A vertical directional pressure of 1000 kPa was applied in a closed pressure vessel for 15 minutes, with the pressure direction strictly from top to bottom. The glass micropowder used had a specific surface area of ​​260 m² / kg and a density of 2.5 g / cm². This high-pressure environment forced the micropowder solution to penetrate into the aggregate's >200 μm deep pores, generating an expansive silica gel under alkaline conditions. The blocking rate reached over 90%, causing the aggregate's water absorption rate to drop sharply from 9.2% to 0.5%, and the porosity to be compressed from 12.1% to 4.5%. The following formula is used to calculate the pore plugging rate in the above-mentioned pressurized permeation enhancement: in, Indicates the pore plugging rate (%). This represents the initial pore volume (cm³ / g). This indicates the pore volume after treatment (cm³). 3 / g); S3, Interfacial activity modification: The aggregate in the separation solution is uniformly mixed with highly active silica fume on the surface of the aggregate; After separation, the aggregates were immediately fed into a mixer, and highly active silica fume with a specific surface area of ​​16800 m² / kg was added at an aggregate:silica fume mass ratio of 1:0.03. During the silica fume mixing process, 2.8 Hz variable frequency mechanical vibration was applied simultaneously. The dynamic response spectrum of the aggregate-silica fume interface was collected in real time using a piezoelectric sensor, and a correlation model between vibration frequency and bonding strength was established. At the same time, the amplitude was intelligently adjusted based on the aggregate particle size (0.5 mm amplitude for aggregates >20 mm and 0.2 mm amplitude for aggregates <10 mm), and a multiaxial stress loading device was used to simulate the triaxial stress state of concrete. This caused the silica fume nanoparticles to be oriented and fill the microcracks in the vibration field, dynamically optimizing the interfacial stress distribution. Ultimately, the interfacial bond strength reached 7.8 MPa, the 28-day concrete splitting strength increased to 4.49 MPa, and the peak microhardness area expanded by 40%. The formulas involved in the correlation model between vibrational frequency and bonding strength in the above-mentioned interfacial activity modification are as follows: in, Indicates the interfacial bond strength (MPa). This represents the material property coefficient (related to silica fume activity and aggregate surface condition). Represents the vibration frequency (Hz). Indicates amplitude (mm); S4. Drying and molding: The modified aggregate is dried to obtain reinforced recycled aggregate; The modified aggregate was dried at 105℃ for 2 hours with the moisture content strictly controlled to ≤0.5%. This temperature-controlled drying activated the active sites on the silica fume surface, preventing residual moisture from causing hydration heat cracks. At the same time, it gave the aggregate continuous hydration potential, and after encountering water in the concrete, it generated aluminosilicate gel again, further filling the micropores.

[0020] In this embodiment, aggregate grading pretreatment optimizes particle size distribution, increases bulk density, and reduces segregation risk. Pressure-driven infiltration strengthens the glass micropowder mixture to penetrate deep into the aggregate pores, generating silica gel and increasing pore sealing rate. Interfacial activity modification, achieved through mechanical stirring and variable frequency vibration, directs silica fume to fill microcracks, increasing interfacial bonding strength to meet C60 requirements. Simultaneously, the chloride ion diffusion coefficient is comparable to that of natural aggregate concrete, ensuring durability. Furthermore, it utilizes construction waste as raw material, achieving waste resource utilization and reducing dependence on natural resources. The recycled aggregate concrete also reduces CO2 emissions. While ensuring high performance standards, it achieves triple optimization of "strength, environmental protection, and economy," demonstrating broad application prospects.

[0021] The C60 mentioned above refers to concrete with a strength grade of C60.

[0022] Example 2: Based on Example 1, this example applies the recycled aggregate prepared according to the preparation method of Example 1 to high-grade structural concrete, as follows: Step 1, Aggregate Pre-wetting and Activation: Put the prepared recycled aggregate into the mixer, add 40% of the total water (water temperature 20±2℃), and stir at low speed for 60s to fully wet the aggregate surface, compensate for the 0.5% residual water absorption rate of the aggregate, and at the same time activate the continuous hydration potential of the interfacial silica fume to generate an early aluminosilicate gel layer, avoiding the water competition effect during concrete mixing.

[0023] Step 2, graded addition of cementitious materials: using a two-stage cement-silica fume admixture method. First stage: Add 70% of the total cement weight + 5% of the recycled aggregate weight of silica fume, stir for 45 seconds to form a highly active slurry coating layer; Second stage: Add the remaining cement, river sand, and polycarboxylate superplasticizer (1.8%), and mix at high speed for 90 seconds; Step 3, Vibration compaction process optimization: Three-stage variable frequency vibration is used during casting: initial stage (0-30s): high frequency and low amplitude (12000rpm / 0.3mm) to eliminate large air bubbles; middle stage (30-60s): medium frequency and medium amplitude (8000rpm / 0.5mm) to promote aggregate rearrangement; and later stage (60-90s): low frequency and high amplitude (4000rpm / 1.0mm) to eliminate micro-voids at the interface.

[0024] Step 4, Temperature and Humidity Co-curing: Implement steam-humid heat dual-mode curing: 0-8h: 55℃ steam curing (humidity ≥95%) to accelerate the secondary hydration of interface silica fume; 8h-28d: 20℃ underwater curing to continuously generate CSH gel to fill micropores.

[0025] Recycled aggregates were used in high-grade concrete, and natural aggregates were also used in high-grade concrete. The two types of concrete were subjected to the following relevant tests. Specific testing standards and test objects are shown in the table below: The results of the above experiments are shown in the table below: Based on the data in the table above, the high-strength concrete using recycled aggregate achieved 95.2% of the 28-day compressive strength (65.2 MPa) of natural aggregate concrete (68.5 MPa), fully meeting the requirements for C60 structures; the chloride ion diffusion coefficient (3.5 × 10⁻⁶) was also high. - ¹²m² / s) and natural aggregate (3.1×10⁻⁶) - (¹²m² / s) is equivalent to and better than the national standard limit by 40%, and its durability is proven by empirical evidence; the unit cost is reduced, and a breakthrough is achieved in the triple optimization of "strength-environmental protection-economy".

[0026] In the comparative example, the implementation steps for recycled aggregate are adjusted based on Example 1, as follows: S1. Aggregate pretreatment: Same as in Example 1; S2, Atmospheric Pressure Impregnation Strengthening: The dried aggregate was immersed in a glass micro powder mixed solution with the same ratio (glass micro powder: water: sodium hydroxide = 1:7:0.03), with an aggregate to solution mass ratio of 1:4; it was immersed in an open container under atmospheric pressure for 30 minutes; other parameters were the same as in Example 1; S3, Ordinary mixing modification: After separating the aggregate, feed it into the mixer and add the same amount of silica fume (specific surface area 16800 m²) at an aggregate:silica fume ratio of 1:0.03. 2 / kg); mechanical stirring was performed at a fixed speed of 300 rpm for 30 seconds (same time as in the example, but without frequency conversion vibration and stress simulation); S4. Drying and shaping: Same as in Example 1.

[0027] The recycled aggregate prepared in Example 1 and the recycled aggregate prepared in this comparative example were subjected to the following performance analysis, and the corresponding results are shown in the table below: Based on the data in the table above, the comparative example shows that due to the cancellation of pressurized infiltration and vibration optimization, the aggregate water absorption rate surged to 8.7%, the pore blockage rate was only 42%, and the interfacial bond strength dropped to 4.1 MPa. This resulted in the 28-day compressive strength of recycled aggregate concrete decreasing to 52.3 MPa, and the chloride ion diffusion coefficient deteriorating to 8.9 × 10⁻⁶. - ¹²m² / s, fully demonstrating the decisive role of pressurized infiltration and vibration modification in improving aggregate density, interfacial strength and concrete durability.

[0028] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing recycled building aggregate, characterized in that, Includes the following steps: S1. Aggregate pretreatment: Obtain recycled coarse aggregate from construction waste and dry it; S2. Pressure-assisted infiltration enhancement: The dried aggregate is placed in a glass micro powder mixture containing an alkali activator, and directional pressure is applied for infiltration treatment; S3, Interfacial activity modification: The aggregate in the separation solution is uniformly mixed with highly active silica fume on the surface of the aggregate; S4. Drying and molding: The modified aggregate is dried to obtain reinforced recycled aggregate.

2. The method for preparing recycled building aggregate according to claim 1, characterized in that: In step S2, the directional pressure of the infiltration treatment is 800-2000 kPa, the treatment time is 10-30 min, the glass micro powder mixed solution is composed of glass micro powder, water and sodium hydroxide, and the mass ratio of glass micro powder, water and sodium hydroxide is 1:(5-10):(0.02-0.1), and the mass ratio of the recycled building coarse aggregate to the glass micro powder mixed solution is 1:(3-10).

3. The method for preparing recycled building aggregate according to claim 1, characterized in that: In step S2, the pressurization process is carried out in a closed pressure vessel, and the pressure is applied vertically from top to bottom. The specific surface area of ​​the glass micropowder is 200-300 m² / kg, and the density is 2.4-2.7 g / cm².

4. The method for preparing recycled building aggregate according to claim 1, characterized in that: In step S3, the specific surface area of ​​the silica fume is 15,000-20,000 m² / kg, the mass ratio of the recycled building aggregate to the silica fume is 1:(0.01-0.1), and mechanical stirring is used when mixing in the silica fume for 20-30 seconds.

5. The method for preparing recycled building aggregate according to claim 1, characterized in that: In step S4, the drying temperature is 100-105℃ and the drying time is 2-3 hours.

6. The method for preparing recycled building aggregate according to claim 1, characterized in that: In S1, the recycled coarse aggregate is divided into three grades according to particle size: 19-31.5mm is the first grade particle size, 9.5-19mm is the second grade particle size, and 4.75-9.5mm is the third grade particle size. The mass ratio of the three grades of aggregate is 1:(1-5):(1-5).

7. The method for preparing recycled building aggregate according to claim 1, characterized in that: In step S2, the alkaline activator is sodium hydroxide with a purity ≥99%, and the glass micro powder is derived from recycled waste glass with a particle size D50 ≤20μm.

8. A recycled building aggregate prepared using the method for preparing recycled building aggregate according to claims 1-7, applied to high-grade concrete.

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