Modified concrete waste slurry, and preparation method and application thereof

Abstract

The application discloses modified concrete waste slurry, a preparation method and application thereof, and belongs to the technical field of building material recycling. The modified concrete waste slurry comprises the following raw materials in parts by mass: 100 parts of concrete waste slurry, 0.01-0.05 parts of water reducing agent, 0.5-1.5 parts of formic acid, 0.1-1.5 parts of activating material, 0.03-0.6 parts of retarder and 0.03-0.1 parts of thickening agent. The modification of the concrete waste slurry efficiently activates the cementitious components in the waste slurry, and improves the adaptability of the waste slurry to fresh concrete. The modified concrete waste slurry is applied to the preparation of concrete, and has important significance for realizing the resource utilization of the waste slurry, reducing production cost and promoting the green transformation of the concrete industry.

Description

Technical Field

[0001] This invention belongs to the field of building material recycling technology, specifically relating to a modified concrete waste slurry, its preparation method, and its application. Background Technology

[0002] Waste slurry from ready-mixed concrete batching plants is a slurry remaining after the aggregates have been separated from the waste generated during the production, transportation, and site cleaning of ready-mixed concrete using pressure filtration technology. It mainly consists of cement hydration products, unhydrated cement, mineral admixtures, and fine aggregates, with a solids content typically ranging from 15% to 20%. Statistics show that a batching plant with an annual concrete production capacity of 500,000 cubic meters can generate approximately 36,000 tons of wet waste slurry annually (80% water content). Direct discharge or landfilling of this waste slurry will pollute water bodies, soil, and air due to its high alkalinity and suspended particles, increasing environmental costs for enterprises and potentially leading to environmental penalties. Traditional treatment methods primarily involve sedimentation followed by off-site transportation, but this approach suffers from high disposal costs and low resource utilization rates, wasting the potential value of cementitious materials and contradicting green production principles. Therefore, using waste slurry to replace a portion of the mixing water in concrete production is the most effective utilization method. However, without effective treatment, the solid particles in the waste slurry will lose their activity due to hydration hardening, preventing them from participating in the hydration reaction of fresh concrete and thus affecting the development of concrete strength. Furthermore, the high alkalinity of the waste slurry will cause the concrete to set prematurely, increasing slump loss and causing construction difficulties. Therefore, effective modification treatment of the waste slurry is necessary.

[0003] Most commercial concrete mixing plants directly replace fresh water with waste slurry in concrete production, but the utilization rate is low because waste slurry reduces the mechanical properties of concrete. Research on the modification of waste slurry is still limited. Existing technologies report methods for preparing nano-micron crystal nuclei additives by integrating waste slurry and wastewater from commercial concrete mixing plants for carbon fixation; methods for controlling waste slurry properties using slump-retaining agents; methods for using recycled water after pressure filtration and sedimentation to prepare polycarboxylate superplasticizers; and methods for incorporating slag and phosphogypsum into waste slurry to convert it into a slurry-like mineral admixture for concrete production. Overall, existing research generally suffers from complex modification methods, low utilization rates, and high costs, lacking widespread applicability.

[0004] The shortcomings of existing technologies highlight the necessity of efficient modification of waste slurry. Therefore, developing a waste slurry modification method that combines activity retention, dispersion stability, and intelligent control is of great significance for realizing the resource utilization of waste slurry, reducing production costs, and promoting the green transformation of the concrete industry. Summary of the Invention

[0005] In view of the above-mentioned prior art, the present invention provides a modified concrete waste slurry, its preparation method and application, which solves the problems in the prior art that concrete waste slurry will increase slump loss and reduce concrete strength, and that concrete waste slurry resources cannot be effectively utilized.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a modified concrete waste slurry is provided, comprising the following raw materials in parts by weight: 100 parts concrete waste slurry, 0.01-0.05 parts water-reducing agent, 0.5-1.5 parts formic acid, 0.1-1.5 parts activating material, 0.03-0.6 parts retarder, and 0.03-0.1 parts thickener; the activating material comprises the following raw materials in parts by weight: 3-5 parts potassium sulfate, 3-4 parts calcium bromide, 4-6 parts potassium silicate, 3-5 parts fumed nano silica, 78-86 parts silica fume, and 1-2 parts powder water-reducing agent.

[0007] The beneficial effects of the above-mentioned technical solution of the present invention are as follows: the waste slurry contains a large amount of calcium components (calcium hydroxide, calcium carbonate, ettringite, etc.). By adding modifying components, the calcium components are transformed into calcium formate and hydrated calcium silicate, which have a reinforcing effect on concrete. At the same time, the introduction of other functional additives effectively improves the hydration activity and workability of the waste slurry.

[0008] Based on the above technical solution, the present invention can be further improved as follows.

[0009] Furthermore, the solids content of the concrete waste slurry is 9.5%-10.5%.

[0010] Furthermore, the water-reducing agent is at least one of polycarboxylate water-reducing agent, naphthalene-based water-reducing agent, aliphatic water-reducing agent, aminosulfonate water-reducing agent, and melamine-based water-reducing agent; the concentration of formic acid is not less than 85%; the retarder is at least one of sodium gluconate, industrial sucrose, and maltodextrin; and the thickener is at least one of methyl cellulose ether, hydroxypropyl methyl cellulose ether, hydroxyethyl methyl cellulose ether, and carboxymethyl hydroxyethyl cellulose, with a viscosity range of 10w-15w.

[0011] Furthermore, the fumed nano-silica is hydrophilic; the silica fume is SF90 grade silica fume; and the powder water-reducing agent is at least one of polycarboxylate water-reducing agent, naphthalene-based water-reducing agent, aliphatic water-reducing agent, aminosulfonate water-reducing agent, and melamine-based water-reducing agent.

[0012] Furthermore, the method for preparing modified concrete waste slurry is characterized by comprising the following steps:

[0013] (1) Place the concrete waste slurry in the reactor and add water-reducing agent, and stir for 30-50 minutes at a speed of 35-45 rpm.

[0014] (2) Formic acidification stage: Formic acid is added to the mixture obtained in step (1), and the reaction is carried out for 2-2.5 hours;

[0015] (3) Preparation of activation material: Potassium sulfate, calcium bromide, potassium silicate, fumed nano silica, silica fume and powder water reducing agent are thoroughly mixed to prepare activation material;

[0016] (4) Activation and modification of waste slurry: Add activation material to the mixture obtained in step (2), with a rotation speed of 110-130 rpm, a temperature of 32-38℃, and a reaction time of 72-96 h;

[0017] (5) Add the retarder and thickener in sequence, and continue stirring for 10-20 minutes;

[0018] (6) When the temperature of the mixture obtained in step (5) drops to room temperature, ultrasonic dispersion treatment is performed. The ultrasonic frequency is 15-20kHz and the time is 5min to obtain modified concrete waste slurry.

[0019] Furthermore, the thickener was added in two batches, with a 10-minute interval between them.

[0020] The beneficial effects of the above-mentioned further technical solutions of the present invention are as follows: the retarder overcomes the shortcomings of waste slurry in promoting coagulation and increasing slump loss; the thickener is added in two stages to avoid local agglomeration and appropriately increase the consistency of the waste slurry; the modified waste slurry is subjected to ultrasonic dispersion treatment to make the waste slurry form a uniform suspension state, which is convenient for further application.

[0021] Furthermore, the application of modified concrete waste slurry in concrete preparation.

[0022] Furthermore, the concrete preparation includes the following raw materials in parts by weight: 280 parts cement, 60 parts fly ash, 850 parts medium sand, 1100 parts crushed stone, 11-105 parts water, 5.1 parts water-reducing agent, and 15-120 parts modified concrete waste slurry.

[0023] Furthermore, the cement is P·O 42.5R cement.

[0024] The beneficial effects of this invention are as follows: This invention uses formic acid to modify waste slurry, taking advantage of the high calcium content in the waste slurry to convert inert calcium components such as calcium hydroxide and calcium carbonate in situ into calcium formate, which has a reinforcing effect on cement, thus enhancing the reinforcing effect of the waste slurry. Simultaneously, formic acid can neutralize some calcium hydroxide, reducing the alkalinity of the waste slurry and significantly improving the ability of waste slurry to increase concrete slump. The formulated activating material has multiple mechanisms of action. On one hand, the active components can react with hydroxides in the waste slurry, reducing its alkalinity; fumed silica nanoparticles and silica fume particles, being at the micro-nano scale, can react with calcium hydroxide to promote the formation of hydrated calcium silicate crystal nuclei. On the other hand, when the modified waste slurry is added to concrete, potassium sulfate reacts with gypsum in the cement to produce calcium sulfate and potassium salts, promoting cement hydration; calcium bromide shortens the cement hydration induction period, generates a new hydration product, calcium aluminobromohydrate, and refines the pores of the concrete; potassium silicate mainly reacts with calcium hydroxide, promoting the formation of calcium silicate hydrate; the unreacted fumed silica and silica fume from the modified waste slurry stage can also play a nucleation role, inducing a large amount of hydration products and having a positive effect on promoting secondary hydration reactions. The multi-component combination of active materials exerts a good effect on reducing alkalinity and synergistic enhancement.

[0025] This invention modifies concrete waste slurry, in which the cementitious components are efficiently activated and the modifier components are optimized to produce a synergistic enhancement effect among the components, significantly improving the compatibility of waste slurry with fresh concrete. This is of great significance for realizing the resource utilization of waste slurry, reducing production costs, and promoting the green transformation of the concrete industry. Detailed Implementation

[0026] The specific embodiments of the present invention will be described in detail below with reference to examples.

[0027] Example 1

[0028] A modified concrete waste slurry, the raw materials for which are prepared include:

[0029] The mixture contains 100 parts concrete waste slurry, 0.01 parts water-reducing agent (polycarboxylate superplasticizer), 1.5 parts formic acid, 0.1 parts activating material, 0.3 parts retarder (sodium gluconate), and 0.03 parts thickener (methyl cellulose ether). The solid content of the concrete waste slurry is adjusted to 10.5% with water. The formic acid concentration is 85%. The effective ingredient content of sodium gluconate is 95%. The viscosity of methyl cellulose ether is 12w, and the effective ingredient content is 95%.

[0030] The activating material is a mixture of 3 parts potassium sulfate, 3 parts calcium bromide, 6 parts potassium silicate, 3 parts fumed nano silica, 78 parts silica fume, and 2 parts powder water-reducing agent (naphthalene-based water-reducing agent). Among them, the effective component content of potassium sulfate, calcium bromide, and potassium silicate is 98%; the fumed nano silica is hydrophilic and the effective component content is 99%; the silica fume is SF90 grade silica fume that meets GB / T 27690-2023.

[0031] The specific preparation steps for modified concrete waste slurry are as follows:

[0032] 1. Dilution and Formication Stage:

[0033] (1) Place the concrete waste slurry in a reactor with temperature control and stirring device, add water-reducing agent, adjust the speed to about 35 rpm, and stir for 50 min.

[0034] (2) Add formic acid to the mixture obtained in step (1) and react at room temperature for 2 hours to make the formic acid dispersed evenly and react fully.

[0035] 2. Activation stage:

[0036] (1) Preparation of activation material: Potassium sulfate, calcium bromide, potassium silicate, fumed nano silica, silica fume and powder water reducing agent are thoroughly mixed to prepare activation material.

[0037] (2) Activation and modification of waste slurry: Activation material is added to the mixture obtained after reaction with formic acid, the rotation speed is adjusted to 130 rpm, the temperature is raised to 36℃, and the reaction time is 96 h.

[0038] 3. Physical property regulation stage:

[0039] (1) Add retarder and thickener to the mixture obtained by activation and modification in sequence. Add the thickener in two batches with a 10-minute interval in between. Continue stirring for 20 minutes and then cool down.

[0040] (2) When the temperature drops to room temperature, the modified waste slurry is subjected to ultrasonic dispersion treatment at a frequency of 15kHz for 5min to obtain modified concrete waste slurry.

[0041] Example 2

[0042] A modified concrete waste slurry, the raw materials for which are prepared include:

[0043] The mixture contains 100 parts concrete waste slurry, 0.05 parts water-reducing agent (melamine-based water-reducing agent), 1.0 part formic acid, 1.0 part activating material, 0.6 parts retarder (maltodextrin), and 0.1 parts thickener (hydroxyethyl methyl cellulose ether). The solid content of the concrete waste slurry is adjusted to 9.5% with water; the formic acid concentration is 95%; the effective ingredient content of the maltodextrin is 95%; and the viscosity of the methyl cellulose ether is 10w, with an effective ingredient content of 95%.

[0044] The activating material is a mixture of 5 parts potassium sulfate, 3 parts calcium bromide, 4 parts potassium silicate, 3 parts fumed nano silica, 80 parts silica fume, and 1 part powder water-reducing agent (amine sulfonate water-reducing agent). Among them, the effective components of potassium sulfate, calcium bromide, and potassium silicate are 98%; the fumed nano silica is hydrophilic and the effective component content is 99%; the silica fume is SF90 grade silica fume that meets GB / T27690-2023.

[0045] The specific preparation steps for modified concrete waste slurry are as follows:

[0046] 1. Dilution and Formication Stage:

[0047] (1) Place the concrete waste slurry in a reactor with temperature control and stirring device, add water-reducing agent, adjust the speed to about 45 rpm, and stir for 30 minutes.

[0048] (2) Add formic acid to the mixture obtained in step (1) and react at room temperature for 2.5 h to make the formic acid dispersed evenly and react fully.

[0049] 2. Activation stage:

[0050] (1) Preparation of activation material: Potassium sulfate, calcium bromide, potassium silicate, fumed nano silica, silica fume and powder water reducing agent are thoroughly mixed to prepare activation material.

[0051] (2) Activation and modification of waste slurry: Activation material is added to the mixture obtained after reaction with formic acid, the rotation speed is adjusted to 130 rpm, the temperature is raised to 32℃, and the reaction time is 72 h.

[0052] 3. Physical property regulation stage:

[0053] (1) Add retarder and thickener to the mixture obtained by activation and modification in sequence. Add the thickener in two batches with a 10-minute interval in between. Continue stirring for 20 minutes and then cool down.

[0054] (2) When the temperature drops to room temperature, the modified waste slurry is subjected to ultrasonic dispersion treatment at a frequency of 20kHz for 5 minutes to obtain modified concrete waste slurry.

[0055] Example 3

[0056] A modified concrete waste slurry, the raw materials for which are prepared include:

[0057] The mixture contains 100 parts concrete waste slurry, 0.05 parts water-reducing agent (aliphatic water-reducing agent), 0.5 parts formic acid, 1.5 parts activating material, 0.03 parts retarder (industrial sucrose), and 0.05 parts thickener (hydroxypropyl methylcellulose ether). The solids content of the concrete waste slurry is adjusted to 10.5% with water; the formic acid concentration is 85%; the effective ingredient content of the industrial sucrose is 95%; and the viscosity of the methylcellulose ether is 15w, with an effective ingredient content of 95%.

[0058] The activating material is a mixture of 5 parts potassium sulfate, 4 parts calcium bromide, 6 parts potassium silicate, 5 parts fumed nano silica, 86 parts silica fume, and 2 parts powder water-reducing agent (naphthalene-based water-reducing agent). Among them, the effective component content of potassium sulfate, calcium bromide, and potassium silicate is 98%; the fumed nano silica is hydrophilic and the effective component content is 99%; the silica fume is SF90 grade silica fume that meets GB / T 27690-2023.

[0059] The specific preparation steps for modified concrete waste slurry are as follows:

[0060] 1. Dilution and Formication Stage:

[0061] (1) Place the concrete waste slurry in a reactor with temperature control and stirring device, add water-reducing agent, adjust the rotation speed to about 45 rpm, and stir for 50 min.

[0062] (2) Add formic acid to the mixture obtained in step (1) and react at room temperature for 2.5 h to make the formic acid dispersed evenly and react fully.

[0063] 2. Activation stage:

[0064] (1) Preparation of activation material: Potassium sulfate, calcium bromide, potassium silicate, fumed nano silica, silica fume and powder water reducing agent are thoroughly mixed to prepare activation material.

[0065] (2) Activation and modification of waste slurry: Add activation material to the mixture obtained after reaction with formic acid, adjust the rotation speed to 110 rpm, raise the temperature to 38℃, and react for 90 h.

[0066] 3. Physical property regulation stage:

[0067] (1) Add the retarder and thickener to the mixture obtained by activation and modification in sequence. Add the thickener in two batches with a 10-minute interval in between. Continue stirring for another 10 minutes and then cool down.

[0068] (2) When the temperature drops to room temperature, the modified waste slurry is subjected to ultrasonic dispersion treatment at a frequency of 20kHz for 5 minutes to obtain modified concrete waste slurry.

[0069] Examples 4-9

[0070] Modified waste slurry (modified concrete waste slurry prepared in Example 1) was added to concrete in different amounts. The raw materials for concrete preparation also included P·O 42.5R cement, fly ash, medium sand, crushed stone, water, and water-reducing agent (polycarboxylate water-reducing agent). The amounts of each raw material in each example are shown in Table 1. The preparation method includes the following steps:

[0071] (1) Add P·O 42.5R cement, fly ash, medium sand and crushed stone into the mixer and mix for 30 seconds to make the dry raw materials evenly mixed;

[0072] (2) Dissolve the water-reducing agent in 1 / 2 water and add the solution to the mixer. Then, use the remaining water to repeatedly wash the container holding the water-reducing agent. Pour the washing water into the mixer as well. Then, add the modified waste slurry to the mixer and continue mixing for 180 seconds.

[0073] (3) After mixing, the concrete is poured into the mold and cured for 24 hours. The mold is then removed and cured for 3 days and 28 days. The compressive strength is then tested.

[0074] Comparative Examples 1-6

[0075] Unmodified waste slurry (i.e., concrete waste slurry) is added to concrete in different amounts. The raw materials for concrete preparation also include P·O 42.5R cement, fly ash, medium sand, crushed stone, water and water-reducing agent (polycarboxylate water-reducing agent). The corresponding amounts of each raw material in each embodiment are shown in Table 1. The preparation steps are the same as above.

[0076] Table 1 Concrete mix proportions (unit: kg / m³) 3 )

[0077]

[0078] The slump and compressive strength of the concrete prepared in Examples 4-9 and Comparative Examples 1-6 were tested, and the test results are shown in Table 2.

[0079] Table 2 Slump and compressive strength of concrete

[0080]

[0081] Test results show that the slump loss of concrete in 1 hour is reduced by 70-90%, the 3-day compressive strength is increased by 10-30%, and the 28-day compressive strength can still be increased by 5-20%. Through modification, the disadvantages of unmodified concrete waste slurry, which increases slump loss and reduces concrete strength, are overcome, and the utilization rate of concrete waste slurry is significantly improved.

[0082] Although specific embodiments of the present invention have been described in detail with reference to examples, they should not be construed as limiting the scope of protection of this patent. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims are still within the scope of protection of this patent.

Claims

1. A modified concrete waste slurry, characterized by, The raw materials include the following components by mass: concrete waste slurry 100 parts, water reducing agent 0.01-0.05 parts, formic acid 0.5-1.5 parts, activating material 0.1-1.5 parts, retarder 0.03-0.6 parts and thickening agent 0.03-0.1 parts; the activating material includes the following components by mass: potassium sulfate 3-5 parts, calcium bromide 3-4 parts, potassium silicate 4-6 parts, fumed nano-silica 3-5 parts, silica fume 78-86 parts and powder water reducing agent 1-2 parts; the modified concrete waste slurry is prepared by the following steps: (1) placing the concrete waste slurry in a reactor and mixing in the water reducing agent, stirring at a speed of 35-45 rpm for 30-50 min; (2) formic acidization stage: mixing formic acid into the mixture obtained in step (1) and reacting for 2-2.5 h; (3) preparing the activating material: thoroughly mixing potassium sulfate, calcium bromide, potassium silicate, fumed nano-silica, silica fume and powder water reducing agent to prepare the activating material; (4) activating and modifying the waste slurry: mixing the activating material into the mixture obtained in step (2), stirring at a speed of 110-130 rpm at a temperature of 32-38℃ for 72-96 h; (5) sequentially adding the retarder and the thickening agent and continuing to stir for 10-20 min; (6) when the temperature of the mixture obtained in step (5) decreases to room temperature, performing ultrasonic treatment at a frequency of 15-20 kHz for 5 min to obtain the modified concrete waste slurry.

2. The modified concrete waste slurry according to claim 1, characterized in that: The solid content of the concrete waste slurry is 9.5%-10.5%.

3. The modified concrete waste slurry of claim 1, wherein: The water reducing agent is at least one of polycarboxylic acid water reducing agent, naphthalene series water reducing agent, aliphatic water reducing agent, amine sulfonate water reducing agent and melamine series water reducing agent; the concentration of the formic acid is not less than 85%; the retarder is at least one of sodium gluconate, industrial sucrose and malt dextrin; the thickening agent is at least one of methyl cellulose ether, hydroxypropyl methyl cellulose ether, hydroxyethyl methyl cellulose ether and carboxymethyl hydroxyethyl cellulose, with a viscosity range of 10-15 w.

4. The modified concrete waste slurry of claim 1, wherein: The fumed nano-silica is of hydrophilic type; the silica fume is SF90 grade silica fume; the powder water reducing agent is at least one of polycarboxylic acid water reducing agent, naphthalene series water reducing agent, aliphatic water reducing agent, amine sulfonate water reducing agent and melamine series water reducing agent.

5. The method of producing modified concrete waste slurry according to any one of claims 1 to 4, characterized in that, The method includes the following steps: (1) placing the concrete waste slurry in a reactor and mixing in the water reducing agent, stirring at a speed of 35-45 rpm for 30-50 min; (2) formic acidization stage: mixing formic acid into the mixture obtained in step (1) and reacting for 2-2.5 h; (3) preparing the activating material: thoroughly mixing potassium sulfate, calcium bromide, potassium silicate, fumed nano-silica, silica fume and powder water reducing agent to prepare the activating material; (4) activating and modifying the waste slurry: mixing the activating material into the mixture obtained in step (2), stirring at a speed of 110-130 rpm at a temperature of 32-38℃ for 72-96 h; (5) sequentially adding the retarder and the thickening agent and continuing to stir for 10-20 min; (6) when the temperature of the mixture obtained in step (5) decreases to room temperature, performing ultrasonic treatment at a frequency of 15-20 kHz for 5 min to obtain the modified concrete waste slurry. (6) When the temperature of the mixture obtained in step (5) is reduced to room temperature, ultrasonic treatment is performed at a frequency of 15-20 kHz for 5 min, to obtain the modified concrete waste slurry.

6. The method of claim 5, wherein: The thickening agent is added twice with an interval of 10 min.

7. Use of the modified concrete waste slurry according to any one of claims 1-4 in the preparation of concrete.

8. Use according to claim 7, characterized in that: The concrete is prepared from the following raw materials by mass: cement 280 parts, fly ash 60 parts, medium sand 850 parts, gravel 1100 parts, water 11-105 parts, water reducing agent 5.1 parts, and modified concrete waste slurry 15-120 parts.

9. Use according to claim 8, characterized in that: The cement is P·O 42.5R cement.

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