A method for preparing recycled coarse aggregate concrete based on slurry mixing

Abstract

This invention discloses a method for preparing recycled coarse aggregate concrete based on slurry coating, comprising: preparing cement, mixing water, water-reducing agent, recycled coarse aggregate, and fine aggregate according to the designed mix proportion of concrete; dividing the mixing water into first-stage mixing water and second-stage mixing water; mixing cement, water-reducing agent, and first-stage mixing water to obtain cement paste; mixing recycled coarse aggregate with cement paste to obtain slurry-coated recycled coarse aggregate; and mixing fine aggregate, second-stage mixing water, and slurry-coated recycled coarse aggregate to obtain recycled coarse aggregate concrete; wherein, the mass of the first-stage mixing water is determined according to the type of recycled coarse aggregate and its natural saturation based on a fitted model. This invention requires no pretreatment of the recycled coarse aggregate; the technical performance of recycled aggregate concrete can be significantly improved simply by changing the order of material addition during the concrete mixing process.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, and specifically relates to a method for preparing recycled coarse aggregate concrete based on slurry mixing. Background Technology

[0002] With the continuous advancement of urbanization in my country, natural resources such as sand and gravel are being consumed in large quantities. At the same time, a large number of buildings that no longer meet development needs are being or are facing demolition, generating a massive amount of construction waste. It is estimated that my country generates approximately 1.55 billion to 2.55 billion tons of construction waste annually, with over 20 billion tons of untreated waste remaining. Currently, due to the scarcity of natural sand and gravel, the high-value resource utilization of demolition waste is receiving increasing attention. Processing it into recycled aggregates, which can partially or completely replace natural aggregates in concrete preparation, has excellent application prospects for use in building construction and road base courses.

[0003] Concrete performance is highly correlated with aggregate performance. The inherent defects in the technical performance of recycled aggregates result in recycled aggregate concrete having characteristics such as low strength and poor durability. Due to its poor technical performance, recycled aggregate concrete is rarely used in important structures. Strengthening and improving the quality of recycled aggregate concrete is an essential way to make high-value resources from it.

[0004] Currently, the main technologies for improving the performance of recycled aggregate concrete are to first modify the recycled aggregate and then apply the modified recycled aggregate to the preparation of concrete. Methodologically, these can be divided into particle shaping and reinforced grout repair methods. While these methods can improve the performance of recycled aggregate concrete to some extent, they have two main drawbacks: 1) The pretreatment process for the aggregate requires a significant amount of additional human and material resources, reducing the economic benefits of recycled aggregate; 2) The pretreatment process is largely limited to experimental research and cannot be applied on a large scale in engineering projects.

[0005] Therefore, it is imperative to develop a low-cost, high-efficiency method for improving the performance of recycled aggregate concrete that is applicable to engineering sites. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing a method for preparing recycled coarse aggregate concrete based on slurry coating and mixing. This method requires no pretreatment of the recycled coarse aggregate and can significantly improve the technical performance of recycled aggregate concrete simply by changing the order of material addition during the concrete mixing process.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing recycled coarse aggregate concrete based on slurry coating and mixing includes:

[0009] Prepare cement, mixing water, water-reducing agent, recycled coarse aggregate and fine aggregate according to the design mix proportion of concrete, and divide the mixing water into first-stage mixing water and second-stage mixing water.

[0010] Cement, water-reducing agent and first-stage mixing water are mixed and stirred to obtain cement paste;

[0011] The recycled coarse aggregate is mixed with cement paste to obtain the coated recycled coarse aggregate;

[0012] Fine aggregate, two-stage mixing water and recycled coarse aggregate after coating are mixed and stirred to prepare recycled coarse aggregate concrete;

[0013] The quality of the mixing water in the first stage is determined by calculation based on the type of recycled coarse aggregate and the natural saturation of the recycled coarse aggregate according to the fitting model.

[0014] The design strength grade of recycled coarse aggregate concrete is determined according to the classification of recycled coarse aggregate and the engineering requirements. The mix proportion design of recycled coarse aggregate concrete is carried out with reference to the relevant provisions in the "Specification for Mix Proportion Design of Ordinary Concrete" (JGJ55-2011).

[0015] The classification of recycled coarse aggregates shall be in accordance with the relevant requirements in "Recycled Coarse Aggregates for Concrete" (GB / T 25177-2010), and the strength grade of different categories of recycled coarse aggregates in concrete shall be in accordance with the relevant provisions in "Technical Specification for Application of Recycled Aggregates" (JGJ / T240-2011).

[0016] Furthermore, the recycled coarse aggregate is a type II recycled aggregate. Based on the extraction and fitting of experimental data, the fitting model suitable for type II recycled aggregate is as follows:

[0017] ,

[0018] Among them, S d1 This indicates the natural saturation of Class II recycled aggregate (the percentage ratio of the aggregate's natural moisture content to its 24-hour saturated water absorption rate); w 11 C1 represents the mass of the mixing water in the first stage; C1 represents the mass of cement in the concrete design mix proportion; C1 represents the predicted 28-day cubic compressive strength of Class II recycled aggregate concrete; R1 2 This indicates the correlation between the fitted model and the experimental data; the closer it is to 1, the better the fit.

[0019] Furthermore, the recycled coarse aggregate is Class III recycled aggregate. Based on the extraction and fitting of experimental data, the fitting model suitable for Class III recycled aggregate is as follows:

[0020] ,

[0021] Among them, S d2 This indicates the natural saturation of Class III recycled aggregate (the percentage ratio of the aggregate's natural moisture content to its 24-hour saturated water absorption rate); w 12 C2 represents the mass of the mixing water in the first stage; C2 represents the mass of cement in the concrete design mix proportion; C2 represents the predicted 28-day cubic compressive strength of Class III recycled aggregate concrete; R2 2 This indicates the correlation between the fitted model and the experimental data; the closer it is to 1, the better the fit.

[0022] Furthermore, when the recycled coarse aggregate is Class II recycled aggregate, the mass of the mixing water in the first stage is calculated according to the following method:

[0023] Substituting the values ​​of natural saturation of type II recycled aggregate and cement mass in the design mix proportion of concrete into the fitting model of type II recycled aggregate, we obtain the univariate quadratic relationship between the predicted cubic compressive strength of type II recycled aggregate concrete and the mixing water in the first stage.

[0024] The mass of the mixing water in the first stage is calculated by solving the quadratic relation using the formula for finding the maximum value of a parabola.

[0025] Furthermore, when the recycled coarse aggregate is Class III recycled aggregate, the mass of the mixing water in the first stage is calculated according to the following method:

[0026] Substituting the values ​​of natural saturation of Class III recycled aggregate and cement mass in the design mix proportion of concrete into the fitting model of Class III recycled aggregate, we obtain the univariate quadratic relationship between the predicted cubic compressive strength of Class III recycled aggregate concrete and the mixing water in the first stage.

[0027] The mass of the mixing water in the first stage is calculated by solving the quadratic relation using the formula for finding the maximum value of a parabola.

[0028] Furthermore, the mixing time for cement, water-reducing agent, and first-stage mixing water is 1-3 minutes; the mixing time for cement paste and recycled coarse aggregate is 1-3 minutes; and the mixing time for fine aggregate, second-stage mixing water, and recycled coarse aggregate coated with slurry is 1-3 minutes.

[0029] Furthermore, cement refers to the cement commonly used in concrete, including but not limited to ordinary Portland cement and Portland cement.

[0030] Furthermore, the water-reducing agent refers to the water-reducing agent commonly used in concrete, including but not limited to naphthalene-based high-efficiency water-reducing agents and polycarboxylate high-performance water-reducing agents.

[0031] Furthermore, the recycled coarse aggregate is obtained from construction demolition waste through crushing and screening, including but not limited to recycled concrete aggregate, recycled brick-concrete aggregate, and recycled brick aggregate, with a particle size range of 4.75 to 31.5 mm.

[0032] Furthermore, fine aggregate refers to the fine aggregate commonly used in concrete, including but not limited to natural river sand and manufactured sand, with a particle size range of 0.075 to 4.75 mm.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. This invention requires no pretreatment of recycled coarse aggregate. It can significantly improve the technical performance of recycled aggregate concrete simply by changing the order of feeding during the concrete mixing process. The compressive strength is 20-30% higher than that of recycled aggregate concrete prepared by ordinary mixing. It has the characteristics of low cost and high efficiency. It solves the problems of high cost, low efficiency and inapplicability to actual engineering of existing recycled aggregate concrete improvement processes. It has good feasibility in engineering practice and is conducive to the resource utilization of construction waste.

[0035] 2. Different types of recycled aggregates have significantly different water absorption rates, and their natural saturation varies with changes in environmental moisture. The water absorption and desorption behavior of aggregates on mixing water has a significant impact on concrete performance. This invention establishes a calculation model for the compressive strength of concrete based on different types of recycled aggregates, taking into account aggregate saturation and the amount of mixing water used in the first stage. By dynamically and precisely adjusting the amount of mixing water used in the first stage, the technical performance of recycled aggregate concrete can be significantly improved. Attached Figure Description

[0036] Figure 1 This is a flowchart illustrating an embodiment of the present invention of a method for preparing recycled coarse aggregate concrete based on slurry mixing.

[0037] Figure 2 A flowchart illustrating the process of preparing recycled coarse aggregate concrete using the conventional mixing method;

[0038] Figure 3 To be applicable to the calculation of the first-stage mixing water (w) of Class II recycled aggregate 11 The fitted model diagram;

[0039] Figure 4 To be applicable to the calculation of the first-stage mixing water (w) of Class III recycled aggregate 12 The fitted model diagram. Detailed Implementation

[0040] The present invention will be further described below with reference to specific embodiments. These embodiments are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0041] It should be noted that, unless otherwise stated, the technical or scientific terms used in this application should have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0042] Combination Figure 1 As shown in the figure, an embodiment of the present invention provides a method for preparing recycled coarse aggregate concrete based on slurry coating and mixing, comprising:

[0043] Prepare cement, mixing water, water-reducing agent, recycled coarse aggregate and fine aggregate according to the design mix proportion of concrete, and divide the mixing water into first-stage mixing water and second-stage mixing water.

[0044] Pour cement, water-reducing agent and first-stage mixing water into a mixer and mix for 1-3 minutes to obtain cement paste.

[0045] Pour recycled coarse aggregate into the mixer and mix it with cement paste for 1-3 minutes to obtain recycled coarse aggregate coated with paste.

[0046] Pour fine aggregate and secondary mixing water into the mixer, mix the fine aggregate, secondary mixing water and recycled coarse aggregate after coating for 1-3 minutes to obtain recycled coarse aggregate concrete.

[0047] The raw materials and properties of the embodiments of this invention are as follows:

[0048] Cement: PO 42.5 grade ordinary Portland cement is used, and its physical and mechanical properties comply with the relevant provisions of "General Portland Cement" (GB 175-2023).

[0049] Water-reducing agent: Powdered polycarboxylate high-performance water-reducing agent is used, with a water reduction efficiency of ≥25%.

[0050] Recycled coarse aggregate 1 (RCA-1): Derived from the concrete pavement layer of a road project, with a particle size range of 4.75~9.50mm. According to "Crushed Stone and Gravel for Construction" (GB / T 14685-2011), the apparent density of RCA-1 was measured to be 2706 kg / m³. 3 The water absorption rate is 4.54%. According to the "Recycled Coarse Aggregate for Concrete" (GB / T 25177-2010) and the "Technical Specification for Application of Recycled Aggregate" (JGJ / T240-2011), this aggregate is classified as Class II recycled aggregate and can be used in the preparation of concrete with strength grades of C40 and below.

[0051] Recycled coarse aggregate 2 (RCA-2): Derived from concrete components of a residential demolition project, with a particle size range of 4.75~9.50 mm. According to GB / T 14685-2011 "Construction Crushed Stone and Pebbles", the apparent density of RCA-2 was measured to be 2544 kg / m³.3 The water absorption rate is 6.62%. According to the "Recycled Coarse Aggregate for Concrete" (GB / T 25177-2010) and the "Technical Specification for Application of Recycled Aggregate" (JGJ / T240-2011), this aggregate is classified as Class III recycled aggregate and can be used in the preparation of concrete with strength grades of C25 and below.

[0052] Fine aggregate: Natural river sand with a particle size range of 0.075-4.75 mm. According to the "Sand for Construction" (GBT-1464-2011), the fineness modulus of the river sand is measured to be 3.17, indicating good gradation and an apparent density of 2621 kg / m³. 3 The crushing index and water absorption rate were 7.3% and 3.69%, respectively.

[0053] Water: Tap water in a certain area.

[0054] To maximize the applicability of this invention, in this embodiment, recycled coarse aggregate 1 (RCA-1) is used in the preparation of C40 concrete, and recycled coarse aggregate 2 (RCA-2) is used in the preparation of C25 concrete. The mix proportions for both types of concrete are designed according to the "Specification for Mix Proportioning Design of Ordinary Concrete" (JGJ55-2011), and the material proportions are shown in Table 1.

[0055] Table 1 Concrete Mix Proportions

[0056]

[0057] Example 1

[0058] RCA-1 was dried in a forced-air drying oven to constant weight, at which point the aggregate saturation was 0%. The mixing water (w) for the first stage was then calculated using the fitting formula for Class II recycled aggregate. 11 The dosage is 197 kg / m³ 3 Therefore, the second-stage mixing water (w) 21 The dosage is 43 kg / m³ 3 .according to Figure 1 The implementation process of the slurry mixing shown is used to prepare recycled aggregate concrete, and the cubic compressive strength of concrete specimens at 3, 7, and 28 days is tested.

[0059] Among them, the calculation of the first-stage mixing water (w) of Class II recycled aggregate is applicable. 11 The fitting model is as follows: Figure 3 As shown.

[0060] Comparative Example 1:

[0061] RCA-1 was dried in a forced-air drying oven until constant weight was achieved, at which point the aggregate saturation was 0%. The following method was used: Figure 2The conventional mixing method shown was used to prepare recycled aggregate concrete, and the cubic compressive strength of the concrete specimens was tested at 3, 7, and 28 days.

[0062] Example 2:

[0063] Pre-soak RCA-1 until the aggregate saturation is approximately 50%, then substitute the results into the fitting formula for Class II recycled aggregate to obtain the first-stage mixing water (w). 11 The dosage is 192 kg / m³ 3 Therefore, the second-stage mixing water (w) 21 The dosage is 48 kg / m³ 3 .according to Figure 1 The implementation process of the slurry mixing shown is used to prepare recycled aggregate concrete, and the cubic compressive strength of concrete specimens at 3, 7, and 28 days is tested.

[0064] Comparative Example 2:

[0065] Pre-soak RCA-1 until aggregate saturation is approximately 50%, using methods such as... Figure 2 The conventional mixing method shown was used to prepare recycled aggregate concrete, and the cubic compressive strength of the concrete specimens was tested at 3, 7, and 28 days.

[0066] Example 3:

[0067] Pre-soak RCA-1 until aggregate saturation is approximately 100%, then substitute the results into the fitting formula for Class II recycled aggregate to obtain the first-stage mixing water (w). 11 The dosage is 187 kg / m³ 3 Therefore, the second-stage mixing water (w) 21 The dosage is 53 kg / m³. 3 .according to Figure 1 The implementation process of the slurry mixing shown in the figure is used to prepare recycled aggregate concrete, and the cubic compressive strength of concrete specimens is tested at 3, 7, and 28 days.

[0068] Comparative Example 3:

[0069] Pre-soak RCA-1 until aggregate saturation is approximately 100%, using methods such as... Figure 2 The conventional mixing method shown was used to prepare recycled aggregate concrete, and the cubic compressive strength of concrete specimens was tested at 3, 7, and 28 days.

[0070] Example 4:

[0071] RCA-2 was dried in a forced-air drying oven to constant weight, at which point the aggregate saturation was 0%. The mixing water (w) for the first stage was then calculated using the fitting formula for Class III recycled aggregate. 12 The dosage is 182 kg / m³ 3 Therefore, the second-stage mixing water (w) 22 The dosage is 58 kg / m³ 3.according to Figure 1 The implementation process of the slurry mixing shown in the figure is used to prepare recycled aggregate concrete, and the cubic compressive strength of concrete specimens is tested at 3, 7, and 28 days.

[0072] Among them, the calculation of the first-stage mixing water (w) of Class III recycled aggregate is applicable. 12 The fitting model is as follows: Figure 4 As shown.

[0073] Comparative Example 4:

[0074] RCA-2 was dried in a forced-air drying oven until constant weight was achieved, at which point the aggregate saturation was 0%. The following method was used: Figure 2 The conventional mixing method shown was used to prepare recycled aggregate concrete, and the cubic compressive strength of concrete specimens was tested at 3, 7, and 28 days.

[0075] Example 5:

[0076] Pre-soak RCA-2 until the aggregate saturation is approximately 50%, then substitute the results into the fitting formula for Class III recycled aggregate to obtain the first-stage mixing water (w). 12 The dosage is 180 kg / m³ 3 Therefore, the second-stage mixing water (w) 22 The dosage is 60 kg / m³ 3 .according to Figure 1 The implementation process of the slurry mixing shown in the figure is used to prepare recycled aggregate concrete, and the cubic compressive strength of concrete specimens is tested at 3, 7, and 28 days.

[0077] Comparative Example 5:

[0078] Pre-soak RCA-2 until aggregate saturation is approximately 50%, using methods such as... Figure 2 The conventional mixing method shown was used to prepare recycled aggregate concrete, and the cubic compressive strength of concrete specimens was tested at 3, 7, and 28 days.

[0079] Example 6:

[0080] Pre-soak RCA-2 until aggregate saturation is approximately 100%, then substitute the results into the fitting formula for Class III recycled aggregate to obtain the first-stage mixing water (w). 12 The dosage is 178 kg / m³ 3 Therefore, the second-stage mixing water (w) 22 The dosage is 62 kg / m³ 3 .according to Figure 1 The implementation process of the slurry mixing shown in the figure is used to prepare recycled aggregate concrete, and the cubic compressive strength of concrete specimens is tested at 3, 7, and 28 days.

[0081] Comparative Example 6:

[0082] Pre-soak RCA-2 until aggregate saturation is approximately 100%, using methods such as... Figure 2 The conventional mixing method shown was used to prepare recycled aggregate concrete, and the cubic compressive strength of concrete specimens was tested at 3, 7, and 28 days.

[0083] The results of the 3, 7, and 28-day cubic compressive strength tests of concrete specimens from Examples 1-6 and Comparative Examples 1-6 are shown in Table 2.

[0084] Table 2. Test results of concrete compressive strength

[0085]

[0086] As shown in Table 2, compared with ordinary mixing, the present invention improves the compressive strength of recycled aggregate concrete at 3, 7 and 28 days to varying degrees. Among them, the improvement effect on the 28-day compressive strength of concrete can reach up to 29.0%, and the mechanical properties of concrete are significantly improved, further verifying the practicality of the present invention.

[0087] The present invention has been disclosed above with reference to preferred embodiments, but it is not intended to limit the present invention. All technical solutions obtained by adopting equivalent substitutions or equivalent transformations fall within the protection scope of the present invention.

Claims

1. A method for preparing recycled coarse aggregate concrete based on slurry coating and mixing, characterized in that, include: Prepare cement, mixing water, water-reducing agent, recycled coarse aggregate and fine aggregate according to the design mix proportion of concrete, and divide the mixing water into first-stage mixing water and second-stage mixing water. Cement, water-reducing agent and first-stage mixing water are mixed and stirred to obtain cement paste; The recycled coarse aggregate is mixed with cement paste to obtain the coated recycled coarse aggregate; Fine aggregate, two-stage mixing water and recycled coarse aggregate after coating are mixed and stirred to prepare recycled coarse aggregate concrete; The mass of the mixing water in the first stage is determined by the type of recycled coarse aggregate and the natural saturation of the recycled coarse aggregate according to the fitting model. The recycled coarse aggregate is a type II recycled aggregate, and the fitting model applicable to type II recycled aggregate is: ， in, S d1 Indicates the natural saturation of Class II recycled aggregate; w 11 This indicates the quality of the mixing water in the first stage; c 1 indicates the mass of cement in the concrete mix design; C 1 represents the predicted 28-day cubic compressive strength of Class II recycled aggregate concrete; R 1 2 This indicates the correlation between the fitted model and the experimental data; the recycled coarse aggregate is Class III recycled aggregate, and the fitted model applicable to Class III recycled aggregate is: ， in, S d2 Indicates the natural saturation of Class III recycled aggregate; w 12 This indicates the quality of the mixing water in the first stage; c 2 indicates the mass of cement in the concrete mix design; C 2 represents the predicted 28-day cubic compressive strength of Class III recycled aggregate concrete; R 2 2 This indicates the correlation between the fitted model and the experimental data.

2. The method for preparing recycled coarse aggregate concrete based on slurry mixing according to claim 1, characterized in that, When the recycled coarse aggregate is Class II recycled aggregate, the mass of the mixing water in the first stage is calculated according to the following method: Substituting the values ​​of natural saturation of type II recycled aggregate and cement mass in the design mix proportion of concrete into the fitting model of type II recycled aggregate, we obtain the univariate quadratic relationship between the predicted cubic compressive strength of type II recycled aggregate concrete and the mixing water in the first stage. The mass of the mixing water in the first stage is calculated by solving the quadratic relation using the formula for finding the maximum value of a parabola.

3. The method for preparing recycled coarse aggregate concrete based on slurry mixing according to claim 1, characterized in that, When the recycled coarse aggregate is Class III recycled aggregate, the mass of the mixing water in the first stage is calculated according to the following method: Substituting the values ​​of natural saturation of Class III recycled aggregate and cement mass in the design mix proportion of concrete into the fitting model of Class III recycled aggregate, we obtain the univariate quadratic relationship between the predicted cubic compressive strength of Class III recycled aggregate concrete and the mixing water in the first stage. The mass of the mixing water in the first stage is calculated by solving the quadratic relation using the formula for finding the maximum value of a parabola.

4. The method for preparing recycled coarse aggregate concrete based on slurry mixing according to claim 1, characterized in that, The mixing time for cement, water-reducing agent and first-stage mixing water is 1-3 minutes; the mixing time for cement paste and recycled coarse aggregate is 1-3 minutes; the mixing time for fine aggregate, second-stage mixing water and recycled coarse aggregate after coating is 1-3 minutes.

5. The method for preparing recycled coarse aggregate concrete based on slurry mixing according to claim 1, characterized in that, The cement is selected from ordinary Portland cement or Portland cement.

6. The method for preparing recycled coarse aggregate concrete based on slurry mixing according to claim 1, characterized in that, The water-reducing agent is selected from naphthalene-based high-efficiency water-reducing agents or polycarboxylate high-performance water-reducing agents.

7. The method for preparing recycled coarse aggregate concrete based on slurry mixing according to claim 1, characterized in that, The recycled coarse aggregate is selected from recycled concrete aggregate, recycled brick-concrete aggregate or recycled brick aggregate, with a particle size range of 4.75 to 31.5 mm.

8. The method for preparing recycled coarse aggregate concrete based on slurry mixing according to claim 1, characterized in that, The fine aggregate is selected from natural river sand or manufactured sand, with a particle size range of 0.075 to 4.75 mm.

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