Green concrete taking recycled aggregate as raw material and preparation method

Abstract

The invention provides a preparation method of green concrete with recycled aggregate as a raw material, which comprises the following steps: S1, preparing gypsum water, mixing gypsum powder with water, and stirring to prepare the gypsum water; s2, regenerated broken stone prepared from construction waste is added into gypsum water to be soaked, the liquid level above the gypsum water is pressurized, and the liquid pressure of the gypsum water is increased; and S3, removing the pressurizing plate, when the gypsum water starts to thicken and reduce the flowability, filtering out the gypsum water to only remain the regenerated gravel solid, and standing and solidifying the remaining solid to form the required regenerated coarse aggregate. The preparation method comprises the following steps: S1, mixing and stirring cement, limestone macadam, recycled coarse aggregate, fly ash and machine-made sand to obtain a dry mixture; s2, adding a water reducing agent and a reinforcing agent into the mixing water, and dissolving to form a mixed solution; and S3, gradually adding the mixed solution into the dry mixture, and uniformly stirring to prepare the green concrete. According to the green concrete prepared from the recycled coarse aggregate, resources can be recycled, environmental pollution is reduced, and the performance strength of the concrete can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of concrete, and in particular to green concrete using recycled aggregate as raw material and a preparation method thereof. Background Art

[0002] Recycled aggregate concrete primarily involves dismantling discarded concrete, fired bricks, and ceramic tiles from old buildings, sorting, cleaning, and crushing them, and then mixing them in a certain proportion to create a new concrete. The preparation and application of recycled concrete not only addresses environmental pollution caused by construction waste but also effectively replaces some natural aggregates, reducing construction projects' reliance on natural aggregates and reducing the amount of natural aggregate mined. This, in turn, contributes to a certain degree of ecological protection and sustainable development. However, due to the poor particle shape, large particle size, rough surface, large voids, and high water absorption of recycled aggregate, its workability and construction properties are inferior to those of conventional concrete, and its compressive strength is also relatively low. Summary of the Invention

[0003] In order to overcome the problems existing in the background technology, the present invention provides a green concrete using recycled aggregate as raw material and a preparation method to solve the technical problems of poor working performance and construction performance and low compressive strength of recycled aggregate concrete.

[0004] To achieve the above objectives, the invention is implemented through the following technical solutions: A green concrete using recycled aggregate as raw material, comprising the following raw materials in parts by weight: 180-280 parts of cement; 100-130 parts fly ash; 600-1000 parts of virgin coarse aggregate; 200-500 parts of recycled coarse aggregate; 800-1200 parts fine aggregate; 5-10 parts of water reducer; 20-50 parts of enhancer; 150-170 parts mixing water; The recycled coarse aggregate is formed by processing recycled gravel formed by sorting, washing and crushing construction waste; the recycled gravel has a mud content of 1.4%, a crushing index of 18%, a needle-like particle content of 6%, and a water absorption rate of 3.4%.

[0005] Preferably, the processing steps of the recycled coarse aggregate are as follows: S1, preparing gypsum water, mixing gypsum powder with water and stirring to make gypsum water; S2. Immerse the recycled crushed stones made from construction waste in gypsum water, and apply pressure to the liquid surface above the gypsum water to increase the liquid pressure of the gypsum water. S3. Remove the pressure plate. When the gypsum water begins to thicken and its fluidity decreases, filter out the gypsum water until only the solid recycled crushed stones remain, and let the remaining solid stand and solidify to form the required recycled coarse aggregate.

[0006] Preferably, the water-cement ratio of the gypsum water is 0.5 - 0.8.

[0007] Preferably, when preparing the gypsum water, add a retarder to delay the setting of the gypsum water.

[0008] Preferably, the original coarse aggregate uses limestone crushed stones with a size of 5 - 31.5 mm; the mud content is 0.1%, the crushing index is 8%, the content of needle-like and flaky particles is 3%, and the water absorption rate is 0.1%.

[0009] Preferably, the fine aggregate uses manufactured sand with a size of 0 - 4.75 mm.

[0010] A preparation method of green concrete using recycled aggregate as raw material includes the following steps. Preparation of recycled coarse aggregate: S1. Prepare gypsum water by mixing gypsum powder and water and stirring. S2. Immerse the recycled crushed stones made from construction waste in gypsum water, and apply pressure to the liquid surface above the gypsum water to increase the liquid pressure of the gypsum water. S3. Remove the pressure plate. When the gypsum water begins to thicken and its fluidity decreases, filter out the gypsum water until only the solid recycled crushed stones remain, and let the remaining solid stand and solidify to form the required recycled coarse aggregate.

[0011] Preparation method of green concrete: S1. Mix cement, limestone crushed stones, recycled coarse aggregate, fly ash, and manufactured sand and stir to obtain a dry mix. S2. Add a water reducer and a strengthening agent to the mixing water and dissolve to form a mixed liquid. S3. Then gradually add the mixed liquid to the dry mix and stir evenly to make green concrete.

[0012] Preferably, the retarder uses citric acid or borax.

[0013] Preferably, the fly ash is Class F Grade II fly ash, with a water demand ratio of 95%, a loss on ignition of 3.1%, a fineness of 19.3%, and 7-day and 28-day activity indices of 57% and 76% respectively.

[0014] The beneficial effects of the present invention are as follows: The recycled coarse aggregate prepared by soaking and pressurizing the recycled crushed stone made from construction waste with gypsum water improves the performance of the recycled crushed stone. Through the soaking and pressurization of gypsum water, the gypsum water penetrates into the voids and cracks between the recycled crushed stones. After the gypsum water undergoes a hydration reaction and initially solidifies to reduce fluidity, the excess gypsum water is filtered out. The voids, cracks, and pits on the surface of the recycled crushed stones remain with gypsum gel. After the gypsum gel cures, a high-performance recycled coarse aggregate with good compactness and a smooth surface is formed. The green concrete made with this recycled coarse aggregate can not only recycle resources and reduce environmental pollution but also improve the performance strength of the concrete. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a test diagram of the slump of concrete.

[0016] Figure 2 It is a test diagram of the spread of concrete. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] In order to make the objectives, technical solutions, and beneficial effects of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings for the convenience of those skilled in the art to understand.

[0018] Embodiment 1 Select the following raw materials in parts by mass to make concrete; 186 parts of cement; Use P·O42.5 grade cement, whose standard consistency water requirement is 26.4%, specific surface area is 348 m2 / kg, initial setting time and final setting time are 180 min and 245 min respectively, and the compressive strengths at 3 d and 28 d are 22.6 MPa and 49.1 MPa respectively.

[0019] 112 parts of fly ash; The fly ash is Class F Grade II fly ash, with a water demand ratio of 95%, a loss on ignition of 3.1%, a fineness of 19.3%, and activity indices at 7 d and 28 d of 57% and 76% respectively; 664 parts of natural coarse aggregate; Use limestone crushed stone of 5 - 31.5 mm; The mud content is 0.1%, the crushing index is 8%, the content of needle-like and flaky particles is 3%, and the water absorption rate is 0.1%; 284 parts of recycled coarse aggregate; It is formed by processing the recycled crushed stone obtained by sorting, cleaning, and crushing construction waste; The mud content of the recycled crushed stone is 1.4%, the crushing index is 18%, the content of needle-like and flaky particles is 6%, and the water absorption rate is 3.4%; 949 parts of fine aggregate; Use manufactured sand of 0 - 4.75 mm.

[0020] 6.72 parts of water reducer; using a retarding polycarboxylate superplasticizer with a solid content of 10%, a water reduction rate of 28%, and a recommended dosage of 1.6% - 2.0%.

[0021] 22 parts of enhancer; using a powder enhancer with a moisture content of 0.35%, a water demand ratio of 100%, a fineness of 0.9%, a specific surface area of 346 m2 / kg, a 28-day concrete compressive strength ratio of 103%, and a 28-day shrinkage ratio of 97%.

[0022] 163 parts of mixing water; using domestic tap water.

[0023] Preparation method of concrete using the above raw materials: Processing of recycled coarse aggregate: S1, Prepare gypsum water by mixing gypsum powder and water and stirring; the water-cement ratio of the gypsum water is 0.6, and a retarder is added to delay the setting of the gypsum water; S2, Add the recycled crushed stone made from construction waste into the gypsum water and apply pressure to the liquid level above the gypsum water to increase the liquid pressure of the gypsum water; use a pressure plate that fits tightly with the opening of the container containing the gypsum water to apply pressure from the liquid level of the gypsum water to increase the pressure of the gypsum water, so that the gypsum water penetrates into the voids and cracks in the recycled crushed stone; S3, Remove the pressure plate. When the gypsum water starts to thicken and its fluidity decreases, filter out the gypsum water leaving only the solid of the recycled crushed stone, and let the remaining solid stand and solidify to form the required recycled coarse aggregate; delaying the setting of the gypsum water by the retarder enables the gypsum water to have sufficient time to penetrate into the voids and cracks in the recycled crushed stone, and waiting for the gypsum water to solidify can increase the strength of the prepared concrete.

[0024] Preparation of concrete S4, Mix cement, limestone crushed stone, recycled coarse aggregate, fly ash, and manufactured sand to obtain a dry mix; S5, Add the water reducer and enhancer into the mixing water to dissolve and form a mixed liquid; S6, Then gradually add the mixed liquid into the dry mix and stir evenly to make green concrete.

[0025] Comparative Example 1 186 parts of cement; 112 parts of fly ash; 664 parts of primary coarse aggregate; using limestone crushed stone of 5 - 31.5 mm; 284 parts of recycled coarse aggregate; using recycled crushed stone formed after sorting, cleaning, and crushing of construction waste; 949 parts of fine aggregate; using manufactured sand of 0 - 4.75 mm; 6.72 parts of water reducer; 22 parts of enhancer; 163 parts of mixing water; Preparation method of concrete using the above raw materials: S1. Directly mix and stir cement, limestone gravel, recycled gravel, fly ash, and manufactured sand to obtain a dry mixture; S2. Add water reducing agent and strengthening agent to the mixing water and dissolve to form a mixed solution; S3. Then gradually add the mixed solution to the dry mixture and stir evenly to make green concrete.

[0026] Example 2 208 parts of cement; 124 parts of fly ash; 687 parts of primary coarse aggregate; use limestone gravel of 5 - 31.5 mm; 294 parts of recycled coarse aggregate; obtained by treating the recycled gravel formed by sorting, cleaning, and crushing construction waste through the gypsum water treatment method in Example 1; 869 parts of fine aggregate; use manufactured sand of 0 - 4.75 mm; 7.81 parts of water reducing agent; 26 parts of strengthening agent; 163 parts of mixing water; Preparation method of concrete using the above raw materials: S1. Directly mix and stir cement, limestone gravel, treated recycled coarse aggregate, fly ash, and manufactured sand to obtain a dry mixture; S2. Add water reducing agent and strengthening agent to the mixing water and dissolve to form a mixed solution; S3. Then gradually add the mixed solution to the dry mixture and stir evenly to make green concrete.

[0027] Comparative Example 2 208 parts of cement; 124 parts of fly ash; 687 parts of primary coarse aggregate; use limestone gravel of 5 - 31.5 mm; 294 parts of recycled coarse aggregate; use the recycled gravel formed by sorting, cleaning, and crushing construction waste; 869 parts of fine aggregate; use manufactured sand of 0 - 4.75 mm; 7.81 parts of water reducing agent; 26 parts of strengthening agent; 163 parts of mixing water; Preparation method of concrete using the above raw materials: S1. Directly mix and stir cement, limestone gravel, recycled gravel, fly ash, and manufactured sand to obtain a dry mixture; S2. Add water reducing agent and strengthening agent into mixing water to dissolve and form a mixed solution; S3. Then gradually add the mixed solution into the dry mix and stir evenly to make green concrete.

[0028] Conduct workability test and compressive strength test on the concrete made by the above different methods according to "Test Methods for Performance of Ordinary Concrete Mixtures" GB / T 50080-2016 and "Standard for Test Methods of Physical and Mechanical Properties of Concrete" GBT 50081-2019. The analysis table obtained is as follows: Table 1 As can be seen from Table 1, for Examples 1 and 2 of the concrete made with recycled coarse aggregate treated with gypsum water, compared with Comparative Examples 1 and 2 of the concrete directly made with recycled crushed stone, their compressive strength has been significantly improved. Moreover, their slump and spread have both increased, which is beneficial for transportation during pouring and has better self-compacting property.

[0029] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A green concrete made from recycled aggregates, characterized in that: Comprising raw materials in the following parts by weight, 180 - 280 parts of cement; 100 - 130 parts of fly ash; 600 - 1000 parts of natural coarse aggregate; 200 - 500 parts of recycled coarse aggregate; 800 - 1200 parts of fine aggregate; 5 - 10 parts of water reducer; 20 - 50 parts of strengthening agent; 150 - 170 parts of mixing water; Among them, the recycled coarse aggregate is formed after sorting, cleaning and crushing construction waste to form recycled crushed stones for processing; the mud content of the recycled crushed stones is 1.4%, the crushing index is 18%, the content of needle - like and flaky particles is 6%, and the water absorption rate is 3.4%.

2. The green concrete using recycled aggregate as raw material according to claim 1, characterized in that: The processing steps of the recycled coarse aggregate are as follows: S1, Prepare gypsum water by mixing gypsum powder and water and stirring; S2, Add the recycled crushed stones made of construction waste into the gypsum water and soak, and apply pressure to the liquid surface above the gypsum water to increase the liquid pressure of the gypsum water; S3, Remove the pressure plate. When the gypsum water begins to thicken and its fluidity decreases, filter out the gypsum water leaving only the solid of the recycled crushed stones, and let the remaining solid stand and solidify to form the required recycled coarse aggregate.

3. A green concrete using recycled aggregate as raw material according to claim 2, characterized in that: The water - cement ratio of the gypsum water is 0.5 - 0.

8.

4. A green concrete made from recycled aggregates according to claim 2 or 3, characterized in that: When preparing gypsum water, add a retarder to delay the setting of the gypsum water.

5. A green concrete made from recycled aggregates as claimed in claim 1, wherein: The natural coarse aggregate uses limestone crushed stones of 5 - 31.5 mm; the mud content is 0.1%, the crushing index is 8%, the content of needle - like and flaky particles is 3%, and the water absorption rate is 0.1%.

6. A green concrete made from recycled aggregates as claimed in claim 1, wherein: The fine aggregate uses manufactured sand of 0 - 4.75 mm.

7. A green concrete made from recycled aggregates as claimed in claim 4, wherein: The retarder uses citric acid or borax.

8. A green concrete made from recycled aggregate as claimed in claim 1, wherein: The fly ash is Class F Grade II fly ash, with a water demand ratio of 95%, a loss on ignition of 3.1%, a fineness of 19.3%, and 7 - day and 28 - day activity indices of 57% and 76% respectively.

9. A preparation method of green concrete using recycled aggregate as raw material, comprising the following steps, Preparation of recycled coarse aggregate: S1, Prepare gypsum water by mixing gypsum powder and water and stirring; S2, Add the recycled crushed stones made of construction waste into the gypsum water and soak, and apply pressure to the liquid surface above the gypsum water to increase the liquid pressure of the gypsum water; S3, Remove the pressure plate. When the gypsum water begins to thicken and its fluidity decreases, filter out the gypsum water leaving only the solid of the recycled crushed stones, and let the remaining solid stand and solidify to form the required recycled coarse aggregate; Preparation method of green concrete: S1, Mix cement, limestone crushed stones, recycled coarse aggregate, fly ash and manufactured sand and stir to obtain a dry - mixed material; S2, Add the water reducer and the strengthening agent into the mixing water and dissolve to form a mixed liquid; S3, Then gradually add the mixed liquid into the dry - mixed material and stir evenly to make green concrete.

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