Preparation method of recycled coarse aggregate concrete based on slurry wrapping and mixing

Abstract

The invention discloses a preparation method of recycled coarse aggregate concrete based on slurry wrapping and mixing, which comprises the following steps: preparing cement, mixing water, a water reducing agent, recycled coarse aggregate and fine aggregate according to the designed mixing proportion of concrete, and dividing the mixing water into first-stage mixing water and second-stage mixing water; cement, a water reducing agent and first-stage mixing water are mixed and stirred, and cement paste is obtained; mixing and stirring the recycled coarse aggregate and cement paste to obtain slurry-coated recycled coarse aggregate; mixing and stirring the fine aggregate, the second-stage mixing water and the slurry-coated recycled coarse aggregate to prepare recycled coarse aggregate concrete; wherein the mass of the first-stage mixing water is calculated and determined according to the category of the recycled coarse aggregate and the natural saturation of the recycled coarse aggregate according to a fitting model. The recycled coarse aggregate does not need to be subjected to any pretreatment, and the technical performance of the recycled aggregate concrete can be remarkably improved only by changing the feeding sequence in the concrete mixing process.

Description

Technical Field

[0001] The invention belongs to the technical field of building materials, and in particular relates to a method for preparing recycled coarse aggregate concrete based on slurry mixing. Background Art

[0002] With the continuous advancement of urbanization in my country, natural resources such as sand and stone are consumed in large quantities. At the same time, a large number of buildings that do not meet the needs of development are being or are facing demolition, generating a large amount of construction waste. It is estimated that my country generates about 1.55 to 2.55 billion tons of construction waste each year, and the accumulated untreated construction waste also reaches more than 20 billion tons. At present, due to the shortage of natural sand and stone, the high-value resource utilization of construction demolition waste has received attention. Processing it into recycled aggregates, partially or completely replacing natural aggregates to prepare concrete, has good application prospects for housing construction or road base, etc.

[0003] The performance of concrete is highly correlated with the performance of aggregate. The inherent defects of the technical performance of recycled aggregate make recycled aggregate concrete have the characteristics of low strength and poor durability. Recycled aggregate concrete is also rarely used in important structures due to its poor technical performance. Strengthening and improving the quality of recycled aggregate concrete is an essential way to utilize its high-value resources.

[0004] At present, the technology for improving the performance of recycled aggregate concrete mainly involves first improving the recycled aggregate and then applying the improved recycled aggregate to the preparation of concrete. The methods can be mainly divided into particle shaping method and reinforced slurry repair method. Although the above reinforcement methods can improve the performance of recycled aggregate concrete to a certain extent, they are accompanied by two major disadvantages: 1) The pretreatment process of aggregates requires additional consumption of a large amount of manpower and material resources, which reduces the economic benefits of recycled aggregates; 2) The pretreatment process is basically limited to experimental research and cannot be applied on a large scale in engineering.

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

[0006] The purpose of the present invention is to address the deficiencies in the prior art and to propose a method for preparing recycled coarse aggregate concrete based on slurry mixing. The method does not require any pretreatment of the recycled coarse aggregate and can significantly improve the technical performance of the recycled aggregate concrete by simply changing the feeding sequence in the concrete mixing process.

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

[0008] A method for preparing recycled coarse aggregate concrete based on paste mixing, comprising:

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

[0010] Mixing cement, water reducing agent and first-stage mixing water to obtain cement paste;

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

[0012] The fine aggregate, the second-stage mixing water and the recycled coarse aggregate after being coated with paste are mixed and stirred to prepare recycled coarse aggregate concrete;

[0013] Among them, the quality of the mixing water in the first stage is determined by calculating the fitting model based on the type of recycled coarse aggregate and the natural saturation of the recycled coarse aggregate.

[0014] Among them, the design strength grade of recycled coarse aggregate concrete is determined according to the classification of recycled coarse aggregate and engineering requirements, and the mix design of recycled coarse aggregate concrete is carried out in accordance with the relevant provisions of the "Ordinary Concrete Mix Design Code" (JGJ55-2011).

[0015] The classification of recycled coarse aggregate shall refer to the relevant requirements of "Recycled Coarse Aggregate for Concrete" (GB / T 25177-2010), and the application strength grades of different types of recycled coarse aggregate in concrete shall refer to the relevant provisions of "Technical Code for Application of Recycled Aggregate" (JGJ / T240-2011).

[0016] Furthermore, the recycled coarse aggregate is Class II recycled aggregate. By extracting and fitting the experimental data, the fitting model applicable to Class II recycled aggregate is:

[0017] ,

[0018] Among them, S d1 It represents the natural saturation of Class II recycled aggregate (the ratio of the natural moisture content of aggregate to the saturated water absorption rate of aggregate in 24 hours); w 11 represents the mass of mixing water in the first stage; c1 represents the mass of cement in the concrete design mix; C1 represents the predicted value of the 28-day cubic compressive strength of Class II recycled aggregate concrete; R1 2 It represents the correlation between the fitting model and the experimental data. The closer it is to 1, the better the fitting relationship is.

[0019] Furthermore, the recycled coarse aggregate is Class III recycled aggregate. By extracting and fitting the experimental data, the fitting model applicable to Class III recycled aggregate is:

[0020] ,

[0021] Among them, S d2 It represents the natural saturation of Class III recycled aggregate (the ratio of the natural moisture content of aggregate to the saturated water absorption rate of aggregate in 24 hours); w 12 represents the mass of mixing water in the first stage; c2 represents the mass of cement in the concrete design mix; C2 represents the predicted value of 28-day cubic compressive strength of Class III recycled aggregate concrete; R2 2 It represents the correlation between the fitting model and the experimental data. The closer it is to 1, the better the fitting relationship is.

[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 natural saturation of Class II recycled aggregate and the cement mass in the design mix ratio of concrete into the fitting model of Class II recycled aggregate, the quadratic relationship between the predicted value of the cubic compressive strength of Class II recycled aggregate concrete and the first-stage mixing water was obtained.

[0024] The quadratic relationship is solved according to the parabola maximum value formula to calculate the mass of mixing water in the first stage.

[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 natural saturation of Class III recycled aggregate and the cement mass in the design mix ratio of concrete into the fitting model of Class III recycled aggregate, the quadratic relationship between the predicted value of the cubic compressive strength of Class III recycled aggregate concrete and the first-stage mixing water was obtained.

[0027] The quadratic relationship is solved according to the parabola maximum value formula to calculate the mass of mixing water in the first stage.

[0028] Furthermore, the mixing time of cement, water reducing agent and first-stage mixing water is 1-3 min; the mixing time of cement paste and recycled coarse aggregate is 1-3 min; the mixing time of fine aggregate, second-stage mixing water and recycled coarse aggregate after coating is 1-3 min.

[0029] Furthermore, cement is cement generally used in concrete, including but not limited to ordinary Portland cement, silicate cement, etc.

[0030] Furthermore, the water reducing agent is a water reducing agent generally used in concrete, including but not limited to naphthalene-based high-efficiency water reducing agent, polycarboxylic acid high-performance water reducing agent, and the like.

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

[0032] Furthermore, the fine aggregate is the fine aggregate generally used in concrete, including but not limited to natural river sand, machine-made sand, etc., 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. The present invention does not require any pretreatment of the recycled coarse aggregate. The technical performance of the recycled aggregate concrete can be significantly improved by simply changing the order of feeding in the concrete mixing process. The compressive strength is increased by 20-30% compared with the recycled aggregate concrete prepared by ordinary mixing. It has the characteristics of low cost and high efficiency, and solves the problems of high cost, low efficiency and inability to be applied to actual projects in the existing recycled aggregate concrete improvement process. It has good feasibility in actual engineering and is conducive to the resource utilization of construction waste.

[0035] 2. The water absorption rate of different types of recycled aggregates varies greatly, and their natural saturation will change with the change of water content in the environment. The water absorption and desorption behavior of aggregates on mixing water will have a significant impact on the performance of concrete. Based on different types of recycled aggregates, the present invention establishes a calculation model for the compressive strength of concrete with aggregate saturation and the amount of mixing water in the first stage. By dynamically and finely adjusting the mixing water in the first stage, the technical performance of recycled aggregate concrete can be greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a flow chart of an implementation of a method for preparing recycled coarse aggregate concrete based on paste mixing according to an embodiment of the present invention;

[0037] Figure 2 The implementation flow chart of preparing recycled coarse aggregate concrete by ordinary mixing method;

[0038] Figure 3 It is suitable for calculating the mixing water (w 11 )’s fitted model diagram;

[0039] Figure 4 It is suitable for calculating the mixing water (w 12 ) of the fitted model. DETAILED DESCRIPTION

[0040] The present invention will be further described below in conjunction with specific examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention.

[0041] It should be noted that, unless otherwise specified, the technical terms or scientific terms used in this application should have the common meanings understood by those skilled in the art to which the invention belongs.

[0042] Combination Figure 1 As shown, a method for preparing recycled coarse aggregate concrete based on paste mixing according to an embodiment of the present invention comprises:

[0043] Prepare cement, mixing water, water reducing agent, recycled coarse aggregate and fine aggregate according to the designed mix ratio 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 prepare cement paste;

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

[0046] Pour fine aggregate and second-stage mixing water into the mixer, mix the fine aggregate, second-stage mixing water and the 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 the present invention are as follows:

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

[0049] Water reducing agent: Use powdered polycarboxylic acid high-performance water reducing agent with a water reducing efficiency of ≥25%.

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

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

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

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

[0054] In order to maximize the applicability of the present invention, the recycled coarse aggregate 1 (RCA-1) is used in the preparation of C40 concrete, and the recycled coarse aggregate 2 (RCA-2) is used in the preparation of C25 concrete. The mix ratios of the two concretes are designed according to the "Common Concrete Mix Design Code" (JGJ55-2011), and the material ratios are shown in Table 1.

[0055] Table 1 Concrete mix ratio

[0056] Example 1

[0057] RCA-1 was placed in a blast drying oven and dried to constant weight. At this time, the aggregate saturation was 0%. Substituting it into the fitting formula of Class II recycled aggregate, the first-stage mixing water (w 11 ) dosage is 197 kg / m 3 , so the second stage mixing water (w 21 ) dosage is 43 kg / m 3 .according to Figure 1 The implementation process of paste mixing shown is used to prepare recycled aggregate concrete, and the cubic compressive strength of concrete specimens is tested at 3, 7, and 28 days.

[0058] Among them, it is applicable to the calculation of the first-stage mixing water (w 11 ) is fitted to the model Figure 3 shown.

[0059] Comparative Example 1:

[0060] RCA-1 was placed in a blast drying oven and dried to constant weight. At this time, the aggregate saturation was 0%. Figure 2 The recycled aggregate concrete was prepared by the ordinary mixing method shown in the figure, and the cubic compressive strength of the concrete specimens was tested at 3, 7, and 28 days.

[0061] Embodiment 2:

[0062] Pre-soak RCA-1 until the aggregate saturation is about 50%, and substitute it into the fitting formula of Class II recycled aggregate to obtain the first-stage mixing water (w 11 ) dosage is 192 kg / m 3 , so the second stage mixing water (w 21 ) dosage is 48 kg / m 3 .according to Figure 1 The implementation process of paste mixing shown is used to prepare recycled aggregate concrete, and the cubic compressive strength of concrete specimens is tested at 3, 7, and 28 days.

[0063] Comparative Example 2:

[0064] Pre-soak RCA-1 until the aggregate saturation is about 50%, using Figure 2 The recycled aggregate concrete was prepared by the ordinary mixing method shown in the figure, and the cubic compressive strength of the concrete specimens was tested at 3, 7, and 28 days.

[0065] Embodiment 3:

[0066] Pre-soak RCA-1 until the aggregate saturation is about 100%, and substitute it into the fitting formula of Class II recycled aggregate to obtain the first-stage mixing water (w 11 ) dosage is 187 kg / m 3 , so the second stage mixing water (w 21 ) dosage is 53 kg / m 3 .according to Figure 1 The recycled aggregate concrete was prepared by the implementation process of the paste mixing shown in the figure, and the cubic compressive strength of the concrete specimens was tested at 3, 7, and 28 days.

[0067] Comparative Example 3:

[0068] Pre-soak RCA-1 until the aggregate saturation is about 100%, using Figure 2 The recycled aggregate concrete was prepared by the ordinary mixing method shown in the figure, and the cubic compressive strength of the concrete specimens was tested at 3, 7, and 28 days.

[0069] Embodiment 4:

[0070] RCA-2 was placed in a blast drying oven and dried to constant weight. At this time, the aggregate saturation was 0%. Substituting it into the fitting formula of Class III recycled aggregate, the first-stage mixing water (w 12 ) dosage is 182 kg / m 3 , so the second stage mixing water (w 22 ) dosage is 58 kg / m 3 .according to Figure 1The recycled aggregate concrete was prepared by the implementation process of the paste mixing shown in the figure, and the cubic compressive strength of the concrete specimens was tested at 3, 7, and 28 days.

[0071] Among them, it is applicable to the calculation of the first-stage mixing water (w 12 ) is fitted to the model Figure 4 shown.

[0072] Comparative Example 4:

[0073] RCA-2 was placed in a forced air drying oven and dried to constant weight. At this time, the aggregate saturation was 0%. Figure 2 The recycled aggregate concrete was prepared by the ordinary mixing method shown in the figure, and the cubic compressive strength of the concrete specimens was tested at 3, 7, and 28 days.

[0074] Embodiment 5:

[0075] Pre-soak RCA-2 until the aggregate saturation is about 50%, and substitute it into the fitting formula of Class III recycled aggregate to obtain the first-stage mixing water (w 12 ) dosage is 180 kg / m 3 , so the second stage mixing water (w 22 ) dosage is 60 kg / m 3 .according to Figure 1 The recycled aggregate concrete was prepared by the implementation process of the paste mixing shown in the figure, and the cubic compressive strength of the concrete specimens was tested at 3, 7, and 28 days.

[0076] Comparative Example 5:

[0077] Pre-soak RCA-2 to about 50% aggregate saturation, using Figure 2 The recycled aggregate concrete was prepared by the ordinary mixing method shown in the figure, and the cubic compressive strength of the concrete specimens was tested at 3, 7, and 28 days.

[0078] Embodiment 6:

[0079] Pre-soak RCA-2 until the aggregate saturation is about 100%, and substitute it into the fitting formula of Class III recycled aggregate to obtain the first-stage mixing water (w 12 ) dosage is 178 kg / m 3 , so the second stage mixing water (w 22 ) dosage is 62 kg / m 3 .according to Figure 1 The recycled aggregate concrete was prepared by the implementation process of the paste mixing shown in the figure, and the cubic compressive strength of the concrete specimens was tested at 3, 7, and 28 days.

[0080] Comparative Example 6:

[0081] Pre-soak RCA-2 until the aggregate saturation is about 100%, using Figure 2The recycled aggregate concrete was prepared by the ordinary mixing method shown in the figure, and the cubic compressive strength of the concrete specimens was tested at 3, 7, and 28 days.

[0082] The test results of 3, 7, and 28 d cubic compressive strength of the concrete test blocks of Examples 1 to 6 and Comparative Examples 1 to 6 are shown in Table 2.

[0083] Table 2 Concrete compressive strength test results

[0084] It can be seen from the data in Table 2 that, compared with ordinary mixing, the present invention has different degrees of improvement on the 3-, 7- and 28-day compressive strength of recycled aggregate concrete, among which 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, which further verifies the practicability of the present invention.

[0085] The present invention has been disclosed above with preferred embodiments, but they are not intended to limit the present invention. Any technical solutions obtained by adopting equivalent replacement or equivalent transformation solutions fall within the protection scope of the present invention.

Claims

1. A method for preparing recycled coarse aggregate concrete based on paste mixing, characterized in that: include: Prepare cement, mixing water, water reducing agent, recycled coarse aggregate and fine aggregate according to the designed mix ratio of concrete, and divide 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; The recycled coarse aggregate is mixed with cement paste to obtain the recycled coarse aggregate coated with cement paste; The fine aggregate, the second-stage mixing water and the recycled coarse aggregate after being coated with paste are mixed and stirred to prepare recycled coarse aggregate concrete; Among them, the quality of the mixing water in the first stage is determined by calculating the fitting model based on the type of recycled coarse aggregate and the natural saturation of the recycled coarse aggregate.

2. The method for preparing recycled coarse aggregate concrete based on paste mixing according to claim 1, characterized in that: The recycled coarse aggregate is Class II recycled aggregate, and the fitting model applicable to Class II recycled aggregate is: ， Among them, S d1 Indicates the natural saturation of Class II recycled aggregate; w 11 represents the mass of mixing water in the first stage; c1 represents the mass of cement in the concrete design mix; C1 represents the predicted value of the 28-day cubic compressive strength of Class II recycled aggregate concrete; R1 2 Indicates the correlation between the fitted model and the experimental data.

3. The method for preparing recycled coarse aggregate concrete based on paste mixing according to claim 1, characterized in that: The recycled coarse aggregate is Class III recycled aggregate, and the fitting model applicable to Class III recycled aggregate is: ， Among them, S d2 Indicates the natural saturation of Class III recycled aggregate; w 12 represents the mass of mixing water in the first stage; c2 represents the mass of cement in the concrete design mix; C2 represents the predicted value of 28-day cubic compressive strength of Class III recycled aggregate concrete; R2 2 Indicates the correlation between the fitted model and the experimental data.

4. The method for preparing recycled coarse aggregate concrete based on paste mixing according to claim 2, 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 natural saturation of Class II recycled aggregate and the cement mass in the design mix ratio of concrete into the fitting model of Class II recycled aggregate, the quadratic relationship between the predicted value of the cubic compressive strength of Class II recycled aggregate concrete and the first-stage mixing water was obtained. The quadratic relationship is solved according to the parabola maximum value formula to calculate the mass of mixing water in the first stage.

5. The method for preparing recycled coarse aggregate concrete based on paste mixing according to claim 3, 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 natural saturation of Class III recycled aggregate and the cement mass in the design mix ratio of concrete into the fitting model of Class III recycled aggregate, the quadratic relationship between the predicted value of the cubic compressive strength of Class III recycled aggregate concrete and the first-stage mixing water was obtained. The quadratic relationship is solved according to the parabola maximum value formula to calculate the mass of mixing water in the first stage.

6. The method for preparing recycled coarse aggregate concrete based on paste mixing according to claim 1, characterized in that: The mixing time of cement, water reducer and first-stage mixing water is 1-3 min; the mixing time of cement paste and recycled coarse aggregate is 1-3 min; the mixing time of fine aggregate, second-stage mixing water and recycled coarse aggregate after coating is 1-3 min.

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

8. The method for preparing recycled coarse aggregate concrete based on paste mixing according to claim 1, characterized in that: The water reducer is selected from naphthalene-based high-efficiency water reducer or polycarboxylic acid high-performance water reducer.

9. The method for preparing recycled coarse aggregate concrete based on paste 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, and the particle size ranges from 4.75 to 31.5 mm.

10. The method for preparing recycled coarse aggregate concrete based on paste mixing according to claim 1, characterized in that: The fine aggregate is selected from natural river sand or machine-made sand, and the particle size ranges from 0.075 to 4.75 mm.

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