Modified concrete waste slurry as well as preparation method and application thereof

Abstract

The invention discloses modified concrete waste slurry as well as a preparation method and application thereof, and belongs to the technical field of recycling of building materials. The modified concrete waste slurry is prepared from the following raw materials in parts by mass: 100 parts of concrete waste slurry, 0.01 to 0.05 part of a water reducing agent, 0.5 to 1.5 parts of formic acid, 0.1 to 1.5 parts of an activating material, 0.03 to 0.6 part of a retarder and 0.03 to 0.1 part of a thickening agent. By modification of the waste concrete slurry, a gelling component in the waste slurry is efficiently activated, and the adaptability of the waste slurry and fresh concrete is improved; the modified concrete waste slurry is applied to preparation of concrete, and has important significance on recycling of the waste slurry, reduction of production cost and promotion of green transformation of the concrete industry.

Description

Technical Field

[0001] The invention belongs to the technical field of building material recycling, and particularly relates to a modified concrete waste slurry and a preparation method and application thereof. Background Art

[0002] Waste slurry from commercial concrete mixing plants is the residual slurry generated during the production, transportation, and site cleaning of ready-mixed concrete. This slurry is formed after aggregates are separated through filter pressing. It primarily consists of cement hydration products, unhydrated cement, mineral admixtures, and fine aggregate, typically with a solids content of 15% to 20%. According to statistics, a concrete mixing plant with an annual production capacity of 500,000 cubic meters generates approximately 36,000 tons of wet waste slurry (80% moisture content) annually. If the waste slurry is directly discharged or landfilled, its highly alkaline components and suspended particles can pollute water, soil, and air, increasing environmental costs and even leading to penalties. Traditional treatment methods, primarily sedimentation followed by external transport, present high disposal costs and low resource utilization. This waste not only wastes the potential value of cementitious materials but also violates the principles of green production. Therefore, using waste slurry to replace part of the mixing water in concrete production is the most effective method. However, if not effectively treated, the solid particles in the waste slurry will lose their activity due to hydration and hardening, making them unable to participate in the hydration reaction of fresh concrete, thereby affecting the strength development of concrete. In addition, the high alkalinity of the waste slurry will accelerate the setting of concrete, increase slump loss, and cause construction difficulties. Therefore, effective modification of the waste slurry is necessary.

[0003] Most commercial concrete mixing plants directly use waste slurry to partially replace clean water in concrete production. However, since waste slurry can reduce the mechanical properties of concrete, its utilization rate is relatively low. Research on the modification of waste slurry is relatively limited. Prior art reports include methods for preparing nano- and micron-sized crystal nucleus additives using integrated carbon fixation of waste slurry and wastewater from commercial concrete mixing plants, methods for regulating the properties of waste slurry using slump-preventing blending agents, the use of recycled water after filter press sedimentation to prepare polycarboxylate water reducers, and the addition of slag and phosphogypsum to waste slurry before converting the waste slurry 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 promotion significance.

[0004] The shortcomings of existing technologies highlight the need for efficient waste slurry modification. Therefore, developing waste slurry modification methods that maintain activity, stabilize dispersion, and enable intelligent control is crucial for recycling waste slurry, reducing production costs, and promoting a green transformation in the concrete industry. Summary of the Invention

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

[0006] In order to achieve the above-mentioned object, the technical solution adopted by the present invention is: providing a modified concrete waste slurry, comprising the following raw materials in parts by weight: 100 parts of concrete waste slurry, 0.01-0.05 parts of water reducer, 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 thickener; the activating material comprises the following raw materials in parts by weight: 3-5 parts of potassium sulfate, 3-4 parts of calcium bromide, 4-6 parts of potassium silicate, 3-5 parts of fumed nano-silica, 78-86 parts of silica fume and 1-2 parts of powder water reducer.

[0007] The beneficial effect of the above technical solution adopted by the present invention is that the waste slurry contains a large amount of calcium components (calcium hydroxide, calcium carbonate, ettringite, etc.). By adding modifying components, the calcium components are converted into calcium formate and calcium silicate hydrate that have a reinforcing effect on concrete. At the same time, the introduction of other functional additives effectively improves the hydration activity and working performance of the waste slurry.

[0008] On the basis of the above technical solution, the present invention can also be improved as follows.

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

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

[0011] Furthermore, the fumed nano-silica is hydrophilic; the silica fume is SF90 grade silica fume; and the powder water reducer is at least one of a polycarboxylic acid water reducer, a naphthalene water reducer, an aliphatic water reducer, an aminosulfonate water reducer and a melamine water reducer.

[0012] Furthermore, the preparation method of modified concrete waste slurry is characterized by comprising the following steps: (1) Place the waste concrete slurry in the reactor and add the water reducer, stirring at a speed of 35-45 rpm / min for 30-50 minutes; (2) Formic acidification stage: formic acid is added to the mixture obtained in step (1) and reacted for 2-2.5 hours; (3) Preparation of activation material: Potassium sulfate, calcium bromide, potassium silicate, fumed nano-silica, silica fume and powder water reducer are fully mixed to prepare activation material; (4) Activation modification of waste pulp: adding activation material to the mixture obtained in step (2), with a rotation speed of 110-130 rpm / min, a temperature of 32-38°C, and a reaction time of 72-96 h; (5) Add retarder and thickener in sequence and continue stirring for 10-20 minutes; (6) When the temperature of the mixture obtained in step (5) drops to room temperature, ultrasonic dispersion treatment is performed at an ultrasonic frequency of 15-20 kHz for 5 minutes to obtain modified concrete waste slurry.

[0013] Furthermore, the thickener was added twice with an interval of 10 min.

[0014] The beneficial effects of the above-mentioned further technical solution adopted in the present invention are: the retarder overcomes the shortcomings of the waste slurry in accelerating coagulation and increasing the slump loss, the thickener is added twice to avoid local agglomeration and appropriately improve the consistency of the waste slurry; the modified waste slurry is subjected to ultrasonic dispersion treatment to form a uniform suspension state of the waste slurry, which is convenient for further application.

[0015] Furthermore, the modified concrete waste slurry is used in the preparation of concrete.

[0016] Furthermore, the prepared concrete includes the following raw materials in parts by mass: 280 parts of cement, 60 parts of fly ash, 850 parts of medium sand, 1100 parts of crushed stone, 11-105 parts of water, 5.1 parts of water reducing agent and 15-120 parts of modified concrete waste slurry.

[0017] Furthermore, the cement is P·O 42.5R cement.

[0018] The beneficial effects of the present invention are as follows: the present invention uses formic acid to modify the 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 into calcium formate, which has a reinforcing effect on cement, thereby enhancing the reinforcing effect of the waste slurry. At the same time, formic acid can neutralize part of the calcium hydroxide, reducing the alkali content of the waste slurry, which is significantly effective in overcoming the increase in concrete collapse caused by waste slurry. The formulated activated material has multiple mechanisms of action. On the one hand, the active components can react with the hydroxides in the waste slurry to reduce the alkalinity of the waste slurry: the gas-phase nano-silica and silica fume particles are at the micro-nano level and can react with calcium hydroxide to promote the formation of calcium silicate hydrate crystal nuclei. On the other hand, when the modified waste slurry is added to concrete, potassium sulfate reacts with the gypsum in the cement to produce calcium sulfate and potassium salt, promoting cement hydration. Calcium bromide shortens the cement hydration induction period, generating a new hydration product, hydrated calcium bromoaluminate, and refining concrete pores. Potassium silicate primarily reacts with calcium hydroxide, promoting the formation of hydrated calcium silicate. Unreacted fumed nanosilica and silica fume in the modified waste slurry also act as a nucleation agent, inducing the formation of large amounts of hydration products and promoting secondary hydration reactions. The multi-component active material combination exerts a significant alkalinity-reducing and synergistic enhancement effect.

[0019] In the present invention, concrete waste slurry is modified, wherein the cementitious components are efficiently activated and the modifier components are optimized, so that a synergistic enhancement effect is produced between the components, and the compatibility of the waste slurry with fresh concrete is significantly improved. 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 DESCRIPTION

[0020] The specific implementation methods of the present invention are described in detail below with reference to the embodiments.

[0021] Example 1 A modified concrete waste slurry, prepared from raw materials including: 100 parts of concrete waste slurry, 0.01 parts of water reducer (polycarboxylate water reducer), 1.5 parts of formic acid, 0.1 parts of activating material, 0.3 parts of retarder (sodium gluconate), and 0.03 parts of thickener (methyl cellulose ether); wherein, the solid content of the concrete waste slurry is adjusted to 10.5% by using clean water; the formic acid concentration is 85%; the active ingredient content in the sodium gluconate is 95%; the viscosity of the methyl cellulose ether is 12w, and the active ingredient content is 95%.

[0022] The activation material is prepared by thoroughly mixing 3 parts of potassium sulfate, 3 parts of calcium bromide, 6 parts of potassium silicate, 3 parts of fumed nano-silica, 78 parts of silica fume, and 2 parts of a powder water reducer (naphthalene-based water reducer); the active ingredient content of potassium sulfate, calcium bromide, and potassium silicate is 98%; the fumed nano-silica is hydrophilic and has an active ingredient content of 99%; and the silica fume is SF90 grade silica fume that meets GB / T 27690-2023.

[0023] The specific preparation steps of modified concrete waste slurry are as follows: 1. Dilution and formic acidification stage: (1) Place the waste concrete slurry in a reactor equipped with temperature control and stirring devices, add a water reducer, adjust the speed to about 35 rpm / min, and stir for 50 minutes.

[0024] (2) Formic acid was added to the mixture obtained in step (1) and reacted at room temperature for 2 h to allow the formic acid to be evenly dispersed and fully reacted.

[0025] 2. Activation stage: (1) Preparation of activation materials: Potassium sulfate, calcium bromide, potassium silicate, fumed nano-silica, silica fume, and powdered water reducer are fully mixed to prepare activation materials.

[0026] (2) Activation modification of waste pulp: Add activation material to the mixture obtained after the reaction with formic acid, adjust the rotation speed to 130 rpm / min, increase the temperature to 36 °C, and the reaction time to 96 h.

[0027] 3. Physical properties regulation stage: (1) Add retarder and thickener to the activated and modified mixture in sequence. Add thickener twice with an interval of 10 minutes in between. Continue stirring for 20 minutes and then cool down.

[0028] (2) When the temperature drops to room temperature, the modified waste slurry is subjected to ultrasonic dispersion treatment at a frequency of 15 kHz for 5 minutes to obtain modified concrete waste slurry.

[0029] Example 2 A modified concrete waste slurry, prepared from raw materials including: 100 parts of concrete waste slurry, 0.05 parts of water reducer (melamine-based water reducer), 1.0 parts of formic acid, 1.0 parts of activating material, 0.6 parts of retarder (maltodextrin), and 0.1 parts of thickener (hydroxyethyl methylcellulose ether); wherein, the solid content of the concrete waste slurry is adjusted to 9.5% by using clean water; the formic acid concentration is 95%; the effective ingredient content of maltodextrin is 95%; the viscosity of methylcellulose ether is 10w, and the effective ingredient content is 95%.

[0030] The activation material is prepared by thoroughly mixing 5 parts of potassium sulfate, 3 parts of calcium bromide, 4 parts of potassium silicate, 3 parts of fumed nano-silica, 80 parts of silica fume, and 1 part of a powder water reducer (aminosulfonate water reducer); the active ingredient content of potassium sulfate, calcium bromide, and potassium silicate is 98%; the fumed nano-silica is hydrophilic and has an active ingredient content of 99%; the silica fume is SF90 grade silica fume that meets GB / T27690-2023.

[0031] The specific preparation steps of modified concrete waste slurry are as follows: 1. Dilution and formic acidification stage: (1) Place the waste concrete slurry in a reactor equipped with temperature control and stirring device, add water reducer, adjust the speed to about 45 rpm / min, and stir for 30 minutes.

[0032] (2) Formic acid was added to the mixture obtained in step (1) and reacted at room temperature for 2.5 h to allow the formic acid to be evenly dispersed and fully reacted.

[0033] 2. Activation stage: (1) Preparation of activation materials: Potassium sulfate, calcium bromide, potassium silicate, fumed nano-silica, silica fume, and powdered water reducer are fully mixed to prepare activation materials.

[0034] (2) Activation modification of waste pulp: Add activation material to the mixture obtained after the reaction with formic acid, adjust the rotation speed to 130 rpm / min, increase the temperature to 32 °C, and the reaction time is 72 h.

[0035] 3. Physical properties regulation stage: (1) Add retarder and thickener to the activated and modified mixture in sequence. Add thickener twice with an interval of 10 minutes in between. Continue stirring for 20 minutes and then cool down.

[0036] (2) When the temperature drops to room temperature, the modified waste slurry is subjected to ultrasonic dispersion treatment at a frequency of 20 kHz for 5 minutes to obtain modified concrete waste slurry.

[0037] Example 3 A modified concrete waste slurry, prepared from raw materials including: 100 parts of concrete waste slurry, 0.05 parts of water reducer (aliphatic water reducer), 0.5 parts of formic acid, 1.5 parts of activating material, 0.03 parts of retarder (industrial sucrose), and 0.05 parts of thickener (hydroxypropyl methyl cellulose ether); among them, the solid content of the concrete waste slurry is adjusted to 10.5% by clean water; the formic acid concentration is 85%; the effective ingredient content of industrial sucrose is 95%; the viscosity of methyl cellulose ether is 15w, and the effective ingredient content is 95%.

[0038] The activation material is prepared by thoroughly mixing 5 parts of potassium sulfate, 4 parts of calcium bromide, 6 parts of potassium silicate, 5 parts of fumed nano-silica, 86 parts of silica fume, and 2 parts of a powder water reducer (naphthalene-based water reducer); the active ingredient content of potassium sulfate, calcium bromide, and potassium silicate is 98%; the fumed nano-silica is hydrophilic and has an active ingredient content of 99%; and the silica fume is SF90 grade silica fume that meets GB / T 27690-2023.

[0039] The specific preparation steps of modified concrete waste slurry are as follows: 1. Dilution and formic acidification stage: (1) Place the waste concrete slurry in a reactor equipped with temperature control and stirring devices, add a water reducer, adjust the speed to about 45 rpm / min, and stir for 50 minutes.

[0040] (2) Formic acid was added to the mixture obtained in step (1) and reacted at room temperature for 2.5 h to allow the formic acid to be evenly dispersed and fully reacted.

[0041] 2. Activation stage: (1) Preparation of activation materials: Potassium sulfate, calcium bromide, potassium silicate, fumed nano-silica, silica fume, and powdered water reducer are fully mixed to prepare activation materials.

[0042] (2) Activation modification of waste pulp: Add activation material to the mixture obtained after the reaction with formic acid, adjust the rotation speed to 110 rpm / min, raise the temperature to 38 °C, and the reaction time to 90 h.

[0043] 3. Physical properties regulation stage: (1) Add retarder and thickener to the activated and modified mixture in sequence. Add thickener twice with an interval of 10 minutes in between. Continue stirring for 10 minutes and then cool down.

[0044] (2) When the temperature drops to room temperature, the modified waste slurry is subjected to ultrasonic dispersion treatment at a frequency of 20 kHz for 5 minutes to obtain modified concrete waste slurry.

[0045] Example 4-Example 9 The modified waste slurry (modified concrete waste slurry prepared in Example 1) was added to concrete in different amounts. The raw materials for preparing the concrete also included P·O 42.5R cement, fly ash, medium sand, crushed stone, water and a water reducer (polycarboxylate water reducer). The corresponding amounts of the raw materials in each example are shown in Table 1. The preparation method includes the following steps: (1) Add P·O 42.5R cement, fly ash, medium sand, and gravel into a mixer and stir for 30 seconds to mix the dry materials evenly; (2) Dissolve the water reducer in 1 / 2 of the water and add the solution to the mixer. Use the remaining water to repeatedly wash the container containing the water reducer. Pour the washing water into the mixer. Then add the modified waste pulp into the mixer and continue stirring for 180 seconds. (3) After mixing, the concrete is placed in a mold and removed after standard curing for 24 hours. The concrete is then cured for the 3rd and 28th days and the compressive strength is tested.

[0046] Comparative Example 1-Comparative Example 6 Unmodified waste slurry (i.e., concrete waste slurry) was added to concrete in different amounts. The raw materials for preparing the concrete also included P·O 42.5R cement, fly ash, medium sand, crushed stone, water, and a water reducer (polycarboxylate water reducer). The corresponding amounts of each raw material in each embodiment are shown in Table 1. The preparation steps were the same as above.

[0047] Table 1 Concrete mix ratio (unit: kg / m 3 ) Example P·O 42.5R cement fly ash medium sand gravel water water reducer Unmodified waste pulp Modified waste pulp Example 4 280 60 850 1100 103.7 5.1 -- 17 Example 5 280 60 850 1100 88.4 5.1 -- 34 Example 6 280 60 850 1100 73.1 5.1 -- 51 Example 7 280 60 850 1100 42.5 5.1 -- 85 Example 8 280 60 850 1100 27.2 5.1 -- 102 Example 9 280 60 850 1100 11.9 5.1 -- 119 Comparative Example 1 280 60 850 1100 103.7 5.1 17 -- Comparative Example 2 280 60 850 1100 88.4 5.1 34 -- Comparative Example 3 280 60 850 1100 73.1 5.1 51 -- Comparative Example 4 280 60 850 1100 42.5 5.1 85 -- Comparative Example 5 280 60 850 1100 27.2 5.1 102 -- Comparative Example 6 280 60 850 1100 11.9 5.1 119 -- The slump and compressive strength of the concrete prepared in Examples 4 to 9 and Comparative Examples 1 to 6 were tested, and the test results are shown in Table 2.

[0048] Table 2 Slump and compressive strength of concrete Example Initial slump (mm) 1h slump (mm) 3d compressive strength (MPa) 28d compressive strength (MPa) Comparative Example 1 195 160 17.6 34.2 Example 4 195 185 19.4 36.6 Comparative Example 2 186 167 16.8 34.7 Example 5 200 196 20.3 37.8 Comparative Example 3 180 151 17.3 35.1 Example 6 197 190 21.3 38.3 Comparative Example 4 170 143 15.6 34.5 Example 7 199 190 20.8 38.9 Comparative Example 5 175 154 16.3 35.3 Example 8 189 185 21.4 39.6 Comparative Example 6 170 133 15.2 34.3 Example 9 190 185 23.6 40.4 Test results show that the 1-hour slump loss of concrete is reduced by 70-90%, the 3-day compressive strength is increased by 10-30%, and the 28-day compressive strength is further improved by 5-20%. This modification overcomes the shortcomings of unmodified concrete waste slurry, which increases slump loss and reduces concrete strength, and significantly improves the utilization rate of concrete waste slurry.

[0049] Although the specific embodiments of the present invention have been described in detail in conjunction with the embodiments, this should not be construed as limiting the scope of protection of this patent. Within the scope described by the claims, various modifications and variations that can be made by those skilled in the art without creative work still fall within the scope of protection of this patent.

Claims

1. A modified concrete waste slurry, characterized in that: The invention comprises the following raw materials in parts by weight: 100 parts of waste concrete slurry, 0.01-0.05 parts of water reducer, 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 thickener; the activating material comprises the following raw materials in parts by weight: 3-5 parts of potassium sulfate, 3-4 parts of calcium bromide, 4-6 parts of potassium silicate, 3-5 parts of fumed nano-silica, 78-86 parts of silica fume and 1-2 parts of powdered water reducer.

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

3. The modified concrete slurry according to claim 1, characterized in that: The water reducer is at least one of a polycarboxylate water reducer, a naphthalene water reducer, an aliphatic water reducer, an aminosulfonate water reducer and a melamine water reducer; the concentration of the formic acid is not less than 85%; the retarder is at least one of sodium gluconate, industrial sucrose and maltodextrin; the thickener is at least one of methyl cellulose ether, hydroxypropyl methyl cellulose ether, hydroxyethyl methyl cellulose ether and carboxymethyl hydroxyethyl cellulose, and the viscosity range is 10w-15w.

4. The modified concrete waste slurry according to claim 1, characterized in that: The fumed nano-silica is hydrophilic; the silica fume is SF90 grade silica fume; and the powder water reducer is at least one of a polycarboxylic acid water reducer, a naphthalene water reducer, an aliphatic water reducer, an aminosulfonate water reducer and a melamine water reducer.

5. The method for preparing modified concrete waste slurry according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) Place the waste concrete slurry in the reactor and add the water reducer, stirring at a speed of 35-45 rpm / min for 30-50 minutes; (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; (3) Preparation of activation material: Potassium sulfate, calcium bromide, potassium silicate, fumed nano-silica, silica fume and powder water reducer are fully mixed to prepare activation material; (4) Activation modification of waste pulp: adding activation material to the mixture obtained in step (2), with a rotation speed of 110-130 rpm / min, a temperature of 32-38°C, and a reaction time of 72-96 h; (5) Add retarder and thickener in sequence and continue stirring for 10-20 minutes; (6) When the temperature of the mixture obtained in step (5) drops to room temperature, ultrasonic treatment is performed at an ultrasonic frequency of 15-20 kHz for 5 minutes to obtain modified concrete waste slurry.

6. The method for preparing modified concrete waste slurry according to claim 5, characterized in that: The thickener was added twice with an interval of 10 minutes.

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

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

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