Method for preparing flow-state solidified soil through cooperation of construction waste recycled aggregate and steel slag micro-powder

Abstract

The invention belongs to the field of solid waste resource utilization, and particularly discloses a method for preparing flow-state solidified soil through cooperation of construction waste recycled aggregate and steel slag micro powder. The fluidized solidified soil is prepared from the following components in parts by weight: 40 to 60 parts of steel slag micro powder, 10 to 30 parts of recycled micro powder, 20 to 40 parts of recycled coarse aggregate, 15 to 30 parts of recycled fine aggregate, 10 to 20 parts of recycled fine aggregate, 25 to 40 parts of water and 0.5 to 1.5 parts of polycarboxylate superplasticizer. A steel slag micro powder and regenerated micro powder self-activated gelling system is adopted to replace a traditional gelling material and is matched with regenerated coarse, fine and fine aggregate three-stage grading to construct a close packing structure, and then staged CO2 mineralization treatment is performed, so that the solid waste mixing amount is increased, carbon emission is reduced, the drying shrinkage rate of the prepared flow-state solidified soil is greatly reduced, and the quality of the prepared flow-state solidified soil is improved. Meanwhile, the fluidity is regulated and controlled through the polycarboxylic acid water reducing agent, the constructability is guaranteed, and a low-carbon and high-efficiency path is provided for large-scale utilization of the construction waste and the steel slag.

Description

Technical Field

[0001] The present invention belongs to the field of solid waste resource utilization, and particularly relates to a method for collaboratively preparing fluidized solidified soil from recycled aggregates of construction waste and steel slag powder. Background Art

[0002] With the acceleration of urbanization, the generation of construction waste (such as discarded concrete, bricks and tiles, mortar, etc.) and steel slag (steel industry waste) is increasing. Both are bulk industrial solid waste.

[0003] In traditional civil engineering, cement-based solidification is often made with traditional binders like cement, which consumes significant amounts of natural resources and generates high carbon emissions. Therefore, there is an urgent need to develop a low-carbon, environmentally friendly, and fluidized solidification preparation technology that utilizes solid waste as an alternative to traditional materials, thereby achieving efficient resource utilization of construction waste and steel slag.

[0004] The traditional soil solidification process uses cement as the main binder and relies on chemical activators, which is costly and has large carbon emissions. When recycled aggregates from construction waste are used alone, the solidified soil has low strength and large shrinkage due to the porosity and high impurity content of the aggregates. When steel slag powder directly replaces cement, it has rapid early hydration and poor fluidity, requiring a large amount of water reducer for adjustment. In addition, unreasonable grading of a single aggregate will lead to high porosity and loose structure. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing fluidized solidified soil by synergistically combining recycled aggregates from construction waste and steel slag powder, so as to solve the problems proposed in the above-mentioned background technology that the traditional solidified soil process uses cement as the main cementitious material, relies on chemical activators, has high costs and large carbon emissions.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for preparing fluidized solidified soil by synergistically using recycled aggregate from construction waste and steel slag powder. The fluidized solidified soil comprises, by weight, 40-60 parts of steel slag powder, 10-30 parts of recycled powder, 20-40 parts of recycled coarse aggregate, 15-30 parts of recycled fine aggregate, 10-20 parts of recycled fine aggregate, 25-40 parts of water, and 0.5-1.5 parts of a polycarboxylate water reducer.

[0008] The preparation method comprises:

[0009] S1. Mix recycled coarse aggregate, fine aggregate and 60% of the total water, and stir until the surface is saturated and the surface is dry to obtain modified recycled aggregate;

[0010] S2. Add steel slag powder, recycled powder and water reducer to the modified recycled aggregate, dry mix to form a powder coating layer, then add the remaining water and stir until the fluidity reaches 180-220mm to form fluidized soil;

[0011] S3. After the fluidized soil is cast into shape, it is cured and demoulded and transferred to a mineralization kettle, where CO2 gas is introduced for staged mineralization treatment to obtain reinforced solid soil.

[0012] Preferably, the mineralization treatment temperature of the mineralization kettle is 50-70°C, the CO2 gas concentration is 50-99%, the CO2 gas flow rate is 0.5-1.5 L / min·kg, the pressure is 0.3-0.8 MPa, the humidity is 70-90%, and the time is 6-12 hours.

[0013] Preferably, the recycled coarse aggregate has a particle size of 5-10 mm, a crushing value ≤12%, and a red brick impurity content ≤20%; the recycled fine aggregate has a particle size of 0.15-2.36 mm, a methylene blue adsorption value ≤1.0 g / kg, and a mud content ≤3%; the recycled fine aggregate has a particle size of <0.15 mm and a pore filling rate ≥90%.

[0014] Preferably, the specific surface area of ​​the steel slag powder is ≥450m 2 / kg, free calcium oxide content is 5-10%, and alkalinity coefficient is ≥3.5.

[0015] Preferably, the regenerated micropowder is a product of grinding construction waste, with a particle size of ≤30 μm, a CaO content of ≥15%, and an activity index of ≥70%.

[0016] Preferably, the temperature of the curing and demoulding is 20-25°C and the time is 10-12 hours.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention adopts a self-activated cementitious system of steel slag micropowder and recycled micropowder to replace traditional cementitious materials, and uses a three-level gradation of recycled coarse, fine and micro aggregates to construct a tightly packed structure. The structure is then subjected to a staged CO2 mineralization treatment to increase the solid waste dosage and reduce carbon emissions. The drying shrinkage rate of the prepared fluidized solidified soil is greatly reduced, and the compressive strength and carbon fixation rate are improved. At the same time, the fluidity is regulated by a polycarboxylate water reducer to ensure constructability, thus solving the problems of high carbon, low strength and high shrinkage of traditional solidified soil, and providing a low-carbon and efficient path for the large-scale utilization of construction waste and steel slag. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort. Among them:

[0020] Figure 1It is a flowchart of the method steps of the present invention. DETAILED DESCRIPTION

[0021] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0022] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0023] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0024] As attached Figure 1 As shown:

[0025] Example 1: This example provides a method for preparing fluidized solidified soil by synergistically combining recycled aggregate from construction waste with steel slag powder. The fluidized solidified soil comprises, by weight, 40 parts of steel slag powder, 30 parts of recycled powder, 40 parts of recycled coarse aggregate, 15 parts of recycled fine aggregate, 10 parts of recycled fine aggregate, 40 parts of water, and 0.5 parts of a polycarboxylate water reducer.

[0026] The preparation method comprises:

[0027] S1. Mix recycled coarse aggregate, fine aggregate and 60% of the total water, and stir for 4 minutes until the surface is saturated and the surface is dry to obtain modified recycled aggregate;

[0028] S2. Add steel slag powder, recycled powder and water reducer to the modified recycled aggregate, dry mix for 2.5 minutes to form a powder coating layer, then add the remaining water and stir for 6 minutes until the fluidity reaches 205 mm to form fluidized soil;

[0029] S3. After the fluidized soil is cast into shape, it is cured and demoulded and transferred to a mineralization kettle, where CO2 gas is introduced for staged mineralization treatment to obtain reinforced solid soil.

[0030] The temperature of the mineralization kettle for mineralization treatment is 65°C. It is first cured at 0.3MPa and 50% CO2 concentration for 4 hours, and then raised to 0.8MPa and 99% CO2 concentration for curing for 8 hours.

[0031] Low-concentration CO2 first reacts with surface Ca(OH)2 to form crystal nuclei, and high-concentration CO2 accelerates internal carbonization to form a gradient mineralization structure; pressure increases the solubility of CO2, speeds up the reaction rate, and achieves a nano-CaCO3 filling rate ≥85%, and the permeability coefficient is controlled to 0.1-0.3cm / s, achieving a balance between water retention and water permeability.

[0032] Specifically, the particle size of the recycled coarse aggregate is 5-10 mm, the crushing value is 10%, and the red brick impurity content is 15%; the particle size of the recycled fine aggregate is 0.15-2.36 mm, the methylene blue adsorption value is ≤0.8 g / kg, the mud content is ≤3%; the particle size of the recycled fine aggregate is <0.15 mm, and the pore filling rate is 92%.

[0033] Specifically, the specific surface area of ​​steel slag powder is ≥450m 2 / kg, free calcium oxide content is 5-10%, and alkalinity coefficient is ≥3.5.

[0034] Specifically, the recycled micro powder is a product of grinding construction waste, with a particle size of ≤30 μm, a CaO content of ≥15%, and an activity index of ≥70%.

[0035] Specifically, the temperature for curing and demoulding is 25° C. and the time is 11 hours.

[0036] Example 2: This example provides a method for preparing fluidized solidified soil by synergistically combining recycled aggregate from construction waste with steel slag powder. The fluidized solidified soil comprises, by weight, 50 parts of steel slag powder, 20 parts of recycled powder, 30 parts of recycled coarse aggregate, 20 parts of recycled fine aggregate, 15 parts of recycled fine aggregate, 30 parts of water, and 1.0 part of a polycarboxylate water reducer.

[0037] The preparation method comprises:

[0038] S1. Mix recycled coarse aggregate, fine aggregate and 60% of the total water, and stir for 4 minutes until the surface is saturated and the surface is dry to obtain modified recycled aggregate;

[0039] By pre-mixing the recycled aggregate with part of the water, the porous characteristics of the recycled aggregate are utilized to allow the water to be pre-absorbed in the voids and then gradually released during the later hydration, thus achieving self-curing and reducing drying shrinkage.

[0040] S2. Add steel slag powder, recycled powder and water reducer to the modified recycled aggregate, dry mix for 2.5 minutes to form a powder coating layer, then add the remaining water and stir for 6 minutes until the fluidity reaches 205 mm to form fluidized soil;

[0041] Steel slag powder and recycled powder form a dense coating on the aggregate surface, which enhances the interfacial bonding strength and reduces the rapid hydration caused by direct contact of water with steel slag powder. Polycarboxylic acid water reducer is adsorbed on the surface of cementitious particles, releasing free water to ensure fluidity. Fluidity <180mm is prone to cause loose filling, and >220mm is prone to cause aggregate settlement, inhibiting the directional crystallization of Ca(OH)2, improving the workability of fluid soil (self-leveling), and reducing shrinkage cracks.

[0042] S3. After the fluidized soil is cast into shape, it is cured and demoulded and transferred to a mineralization kettle, where CO2 gas is introduced for staged mineralization treatment to obtain reinforced solid soil.

[0043] Under high temperature and pressure, CO2 diffuses into the interior and reacts with Ca(OH)2 to generate nano-CaCO3 (50-200nm); it fills the pores of the CSH gel, reducing the proportion of harmful pores with voids > 200nm, improving the bonding strength of the interface area, and controlling the CO2 concentration (50-99%) and flow rate (0.5-1.5L / min·kg) in stages to optimize the crystal morphology and improve the compressive strength and carbon fixation rate.

[0044] The temperature of the mineralization kettle for mineralization treatment is 65°C. It is first cured at 0.3MPa and 50% CO2 concentration for 4 hours, and then raised to 0.8MPa and 99% CO2 concentration for curing for 8 hours.

[0045] Low-concentration CO2 first reacts with surface Ca(OH)2 to form crystal nuclei, and high-concentration CO2 accelerates internal carbonization to form a gradient mineralization structure; pressure increases the solubility of CO2, speeds up the reaction rate, and achieves a nano-CaCO3 filling rate ≥85%, and the permeability coefficient is controlled to 0.1-0.3cm / s, achieving a balance between water retention and water permeability.

[0046] Specifically, the particle size of the recycled coarse aggregate is 5-10mm, the crushing value is 10%, and the red brick impurity content is 15%; the particle size of the recycled fine aggregate is 0.15-2.36mm, the methylene blue adsorption value is ≤10.8g / kg, the mud content is ≤3%, the particle size of the recycled fine aggregate is <0.15mm, and the pore filling rate is 92%. The recycled coarse aggregate constructs the skeleton, the recycled fine aggregate fills the large voids of the coarse aggregate, and the recycled fine aggregate fills the microscopic voids, further compacting the material so that the minimum void is less than 100nm. The gradient grading forms a tight stacking, reduces the porosity, reduces the water evaporation channels, improves the deformation resistance, and reduces the drying shrinkage rate.

[0047] Specifically, the specific surface area of ​​steel slag powder is ≥450m 2 / kg, the free calcium oxide content is 5-10%, the alkalinity coefficient is ≥3.5, and the free calcium oxide with a content of 5-10% releases Ca(OH)2 through hydration, providing a self-excited alkaline source with a pH ≥12.5.

[0048] Specifically, the recycled micropowder is a product of grinding construction waste, such as waste cement, with a particle size of ≤30μm, a CaO content ≥15%, and an activity index ≥70%. It undergoes a pozzolanic reaction in the alkaline environment of steel slag micropowder to generate CSH gel; at the same time, it acts as a fine aggregate to fill pores, realize the utilization of all components of construction waste, and improve the density of the cementitious system.

[0049] Specifically, the temperature for curing and demoulding is 25° C. and the time is 11 hours.

[0050] Comparative Example: The fluidized solidified soil ratio and preparation method are basically the same as those in Example 1, except that: 30 parts of ordinary cement are used instead of steel slag powder, only 50 parts of recycled coarse aggregate and 20 parts of recycled fine aggregate are used, and no mineralization treatment is performed, and only room temperature curing is performed for 28 days.

[0051] Performance testing:

[0052]

[0053]

[0054] Analysis of the results showed that increasing the amount of steel slag powder can enhance the alkaline excitation effect, but excessive use will lead to rapid early hydration, requiring the use of a water reducer to adjust the fluidity; the synergistic effect of recycled micropowder and tertiary aggregate significantly reduced the shrinkage rate, which was reduced by 40-50% compared with the control; staged mineralization curing increased the carbon fixation rate by more than 50%, and when the CO2 concentration increased from 50% to 99%, the nano-CaCO3 filling rate increased from 70% to 85%; the control group used ordinary cement and a single aggregate, so its strength, carbon fixation rate and shrinkage resistance were significantly lower than those of the present invention.

[0055] The free CaO in the steel slag powder is hydrated to provide an alkaline environment, stimulating the activity of the regenerated powder and forming a "steel slag-regenerated powder" self-activated gelling system, replacing chemical activators;

[0056] Mineralization-gradation synergistic strengthening: The three-level aggregate gradation reduces porosity, provides a uniform reaction space for CO2 mineralization, and the generated nano-CaCO3 fills the residual pores in the gradation, forming a dual reinforcement of "physical filling-chemical strengthening";

[0057] Low-carbon preparation path: The CO2 mineralization process simultaneously achieves carbon fixation and strength improvement, with a solid waste content of ≥90%. Compared with traditional processes, carbon emissions are reduced by more than 40%, meeting carbon neutrality requirements.

[0058] It will be appreciated that in the development of any actual embodiment, as in any engineering or design project, numerous implementation-specific decisions may be made. Such a development effort may be complex and time-consuming, but will, for those of ordinary skill having the benefit of this disclosure, be a routine undertaking of design, fabrication, and production without undue experimentation.

[0059] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for preparing fluidized solidified soil by synergistically using recycled aggregates from construction waste and steel slag powder, characterized in that: The fluidized solidification soil comprises, by weight, 40-60 parts of steel slag powder, 10-30 parts of recycled powder, 20-40 parts of recycled coarse aggregate, 15-30 parts of recycled fine aggregate, 10-20 parts of recycled fine aggregate, 25-40 parts of water, and 0.5-1.5 parts of polycarboxylate water reducer. The preparation method comprises: S1. Mix recycled coarse aggregate, fine aggregate and 60% of the total water, and stir until the surface is saturated and the surface is dry to obtain modified recycled aggregate; S2. Add steel slag powder, recycled powder and water reducer to the modified recycled aggregate, dry mix to form a powder coating layer, then add the remaining water and stir until the fluidity reaches 180-220mm to form fluidized soil; S3. After the fluidized soil is cast into shape, it is cured and demoulded and transferred to a mineralization kettle, where CO2 gas is introduced for staged mineralization treatment to obtain reinforced solid soil.

2. The method for preparing fluidized solidified soil by synergistically combining recycled aggregate from construction waste and steel slag powder according to claim 1, characterized in that: The mineralization treatment temperature of the mineralization kettle is 50-70°C, the CO2 gas concentration is 50-99%, the CO2 gas flow rate is 0.5-1.5L / min·kg, the pressure is 0.3-0.8MPa, the humidity is 70-90%, and the time is 6-12h.

3. The method for preparing fluidized solidified soil by synergistically combining recycled aggregate from construction waste and steel slag powder according to claim 1, characterized in that: The particle size of the recycled coarse aggregate is 5-10 mm, the crushing value is ≤12%, and the red brick impurity content is ≤20%. The particle size of the recycled fine aggregate is 0.15-2.36 mm, the methylene blue adsorption value is ≤1.0 g / kg, and the mud content is ≤3%. The particle size of the recycled fine aggregate is <0.15 mm, and the pore filling rate is ≥90%.

4. The method for preparing fluidized solidified soil by synergistically combining recycled aggregate from construction waste and steel slag powder according to claim 1, characterized in that: The specific surface area of ​​the steel slag powder is ≥450m 2 / kg, free calcium oxide content is 5-10%, and alkalinity coefficient is ≥3.

5.

5. The method for preparing fluidized solidified soil by synergistically combining recycled aggregate from construction waste and steel slag powder according to claim 1, characterized in that: The regenerated micro powder is a product of grinding construction waste, has a particle size of ≤30 μm, a CaO content of ≥15%, and an activity index of ≥70%.

6. The method for preparing fluidized solidified soil by synergistically combining recycled aggregate from construction waste and steel slag powder according to claim 1, characterized in that: The temperature of the curing and demoulding is 20-25° C., and the time is 10-12 hours.

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