Low-carbon controllable low-strength material based on residual concrete slurry and waste residues and preparation method of low-carbon controllable low-strength material

Abstract

The invention discloses a low-carbon controllable low-strength material based on residual concrete slurry and waste residue and a preparation method thereof, and the preparation method comprises the following steps: stirring the residual concrete slurry, recycled water and molasses to obtain diluted and retarded pretreated residual slurry; mixing the pretreated residual slurry, fine waste residues, coarse waste residues and recycled water in proportion to prepare a material mixture; and finally, transporting, pouring, filling, hardening and forming. The cement hardening performance of the concrete residual slurry is utilized, solid waste resource utilization is achieved through residual slurry pretreatment, the fluidity of the prepared controllable low-strength material ranges from 200 mm to 350 mm, the density ranges from 1500 kg / m < 3 > to 1750 kg / m < 3 >, the 28d unconfined compressive strength ranges from 0.2 MPa to 8.3 MPa, the performance requirements of ACI 229R controllable low-strength materials are met, the filling performance and the bearing capacity of the material are good, and the controllable low-strength material is suitable for large-scale production. And different backfill or filling engineering requirements such as backfill of pipeline grooves and filling of foundation pit fertilizer grooves can be met, and the advantages of low carbon, environmental protection and cost are achieved.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical engineering materials technology, specifically relating to a low-carbon, controllable, low-strength material based on concrete residue and waste residue, and its preparation method. Background Technology

[0002] Controlled low-strength material (CLSM), as a self-compacting filler, possesses characteristics such as high fluidity, self-filling, and self-compacting properties, and is widely used in various geotechnical engineering projects. Current CLSM mainly uses cement as the core binder, combined with admixtures such as fly ash and mineral powder, and aggregates such as natural sand and manufactured sand. This presents the following problems:

[0003] 1. High cement usage (50~200kg / m³) leads to high material costs, and the cement production process generates significant carbon emissions. Producing 1 ton of cement results in high material costs. Approximately 0.732 tons of grade cement were discharged. This results in CLSM having a cement carbon footprint of 36.6~146.4 kg. / m³;

[0004] 2. The centrifugal residue generated during the production of prestressed concrete pipe piles (1-2 tons per cubic meter of concrete) has a low utilization rate, high transportation and disposal costs, and is prone to environmental pollution. The bonding properties of the unhydrated cement and mineral admixtures it contains are not fully utilized.

[0005] 3. Fine waste residue (fine particles less than 0.15mm) and coarse waste residue (particles of 0.15~5mm) generated by concrete mixing plants are difficult to recycle for concrete production due to poor particle size distribution and high mud powder content. The cost of off-site transportation and disposal is high, and stockpiling takes up space and poses environmental risks.

[0006] 4. Current CLSM production relies on cement and mineral admixtures, natural or artificial sand, and fresh water, resulting in high resource consumption, which does not meet the needs of green and low-carbon development.

[0007] Therefore, developing a low-carbon CLSM (Concentrated Solid Waste Components) that utilizes industrial waste to replace traditional raw materials and its preparation technology has become the key to solving the above problems. Summary of the Invention

[0008] This invention aims to solve the technical problems of existing controllable low-strength materials (CLSM) relying on cement as the core cementing material, resulting in high costs and large carbon emissions, as well as low utilization rates, high treatment costs, and environmental pollution of industrial waste such as concrete residue, fine and coarse waste residue from concrete mixing plants. The invention provides a low-strength material with all solid waste components, low carbon emissions, environmental friendliness, low cost, and controllable performance, as well as its preparation method, to achieve the dual goals of on-site resource utilization of industrial waste and green upgrading of engineering materials.

[0009] The present invention relates to a low-carbon, controllable, low-strength material based on concrete residue and slag, which is composed of the following solid waste components and a retarder in the following mass ratios (per cubic meter of material):

[0010] 184~911kg of residual concrete binder (dry basis), 62~262kg of fine waste residue (dry basis), 310~420kg of coarse waste residue (dry basis), 452~635kg of recycled water, and 0.092~1.822kg of molasses (i.e., 0.05%~0.20% of the mass of dry-basis residual concrete binder).

[0011] The concrete residue binder (i.e., pretreated concrete residue) is obtained by diluting concrete residue with water and pretreating it with molasses. It has a density of 1.4~2.0 g / cm³, a solid content of 50%~90%, and a fluidity retention time of 4~10 h.

[0012] Preferably, the concrete slurry is industrial waste generated during the centrifugal molding process of PHC pipe piles (prestressed high-strength concrete pipe piles), with a solid content of 65%~90% and a density of 1.6~2.0 g / cm³. Cement and mineral admixtures account for 60%~90% of the slurry mass (dry basis), and the initial fluidity of the slurry is 200~400 mm. The concrete slurry is mixed with ISO standard sand at a mass ratio of 1:1 to prepare mortar specimens (size 40mm×40mm×160mm). The mortar specimens have a 7-day compressive strength of 40~65MPa and a 28-day compressive strength of 50~75MPa. The total solid waste content can reach over 95%, which significantly reduces the land occupation cost and secondary pollution risk of industrial solid waste disposal, while also reducing the consumption of natural sand, cement, and other resources, thus significantly reducing resource consumption.

[0013] Preferably, the molasses content is 0.05% to 0.20% of the dry weight of the concrete slurry binder. This ensures that the pretreated concrete slurry binder maintains its fluidity for 4 to 10 hours and retains good hydration and bonding properties, while also guaranteeing that the produced controllable low-strength concrete slurry material can set and harden within 24 hours after pouring. Tests show that untreated concrete slurry loses its fluidity quickly, decreasing to 60 mm in about one hour, essentially losing its fluidity, which is detrimental to production applications. When the molasses content is 0.05% to 0.20% of the concrete slurry, the slurry fluidity (≥150 mm) can be maintained for 4 to 10 hours, and the setting time does not exceed 24 hours, which better meets the requirements of production and construction. Excessive molasses content will cause excessive retardation, affecting the setting and hardening time and early strength of the CLSM, delaying subsequent construction. The appropriate molasses content is 0.05%-0.20% of the mass of the concrete slurry-based binder (dry basis).

[0014] Table 1. Effect of molasses content on the retention of concrete slurry fluidity

[0015]

[0016] Preferably, the fine waste residue is ultrafine particles smaller than 0.15mm obtained by natural sedimentation and separation of residual slurry from concrete mixing plants in a sedimentation tank;

[0017] The fine waste residue mainly consists of ultrafine particles, clay particles, partially hydrated cementitious materials (cement and mineral admixtures) and their hydration products in concrete aggregates;

[0018] The coarse waste residue is obtained by separating and dewatering the residual slurry from the concrete mixing plant through a sand and gravel separation system, with a particle size of less than 5mm.

[0019] The coarse waste residue is mainly composed of natural sand particles, artificial sand particles, fine crushed stone particles, and a small amount of hardened cement and mortar.

[0020] Its particle size distribution meets the following requirements: particles with a diameter of 2.36mm to 5mm account for 30% to 50%, particles with a diameter of 1.18mm to 2.36mm account for 15% to 30%, particles with a diameter of 0.15mm to 1.18mm account for 20% to 40%, and particles smaller than 0.15mm account for no more than 15%.

[0021] The coarse waste residue has a fineness modulus of 2.3 to 3.3, a crushing value of ≤30%, and a mud content of ≤5%.

[0022] A method for preparing a low-carbon, controllable, low-strength material based on concrete residue and slag includes the following steps:

[0023] S1: Pretreatment of Excess Concrete Slurry: The centrifugal excess slurry of the prestressed concrete pipe pile, the recycled water from the mixing plant, and the molasses admixture are added to the mixing tank at a mass ratio of 100:(0~75):(0.05~0.20). The mixture is stirred at 60~80 r / min for 3~5 min until uniform. Stirring is continued to ensure the uniformity of the excess slurry and prevent the sedimentation and segregation of some denser solid particles. The density and solid content are tested to ensure that the density of the pretreated concrete excess slurry binder meets the requirement of 1.4~2.0 g / cm³.

[0024] ① Molasses solution content = Molasses solids content / Molasses solution solids content;

[0025] ② The density of the pretreated concrete slurry-based binder was tested according to standard ASTM D6023-2016;

[0026] ③ The solids content and moisture content of the residual concrete slurry after pretreatment were tested using the drying method:

[0027] Solid content of residual slurry in pretreated concrete = Mass of dried sample / Mass of undried sample;

[0028] Moisture content of residual slurry in pretreated concrete = (mass of sample before drying - mass of sample after drying) / mass of sample before drying;

[0029] S2: Moisture content test of solid components: The actual moisture content of fine waste residue and coarse waste residue was determined by drying method (105℃±5℃, dried to constant weight), with the moisture content of fine waste residue being 100%~200% and the moisture content of coarse waste residue being 0%~15%.

[0030] S3: Production mix proportion correction: Based on the dry basis mix proportion described in claim 1, calculate the actual amount of each component according to the following formula:

[0031] ① Amount of wet fine waste residue = Amount of dry fine waste residue × (1 + Measured moisture content of fine waste residue);

[0032] ② Amount of wet coarse waste residue = Amount of dry coarse waste residue × (1 + Measured moisture content of coarse waste residue);

[0033] ③ Moisture content of residual cementitious material in pretreated concrete = Amount of residual cementitious material in wet pretreated concrete × Measured moisture content of residual cementitious material in wet pretreated concrete;

[0034] ④ Actual amount of recycled water added = Total water consumption in dry mix proportion - Moisture content of wet pretreated concrete slurry binder - Moisture content of wet fine waste residue - Moisture content of wet coarse waste residue;

[0035] S4: Preparation of mixture: The pretreated concrete residue binder, wet fine waste residue, wet coarse waste residue and actual added recycled water are sequentially put into a forced mixer and stirred at 60~80r / min for 5~10min until the mixture is uniform and free of lumps. The discharge temperature is controlled at 5~35℃.

[0036] S5: Transportation, pouring and curing: Controlled low-strength material mixtures are transported by concrete mixer trucks, with a transportation time of ≤3 hours. They are poured using methods such as chutes and pumps, and after setting and hardening, they form controlled low-strength materials.

[0037] Preferably, in step S1, the molasses has a solid content of 40%~60% and a pH value of 5.0~7.0. Its function is to slow down the cement hydration rate in the residual concrete slurry and extend the fluidity retention time and usable time of the residual concrete slurry. The raw materials are mostly industrial waste, which are inexpensive to obtain and can even be recycled for a fee. Compared with traditional cement-based controllable low-strength filler materials, the production cost is reduced by 35%~70%, while saving the cost of solid waste treatment and creating additional revenue for enterprises. Molasses can also be replaced by cement retarder such as lignin sulfonate (byproduct of papermaking wood pulp), sodium gluconate, and white sugar.

[0038] Preferably, in step S4, the mixture needs to be tested for quality before discharge. If the fluidity is less than 200 mm, recycled water is added, with each addition amount ≤ 5% of the total water consumption. If the fluidity is greater than 350 mm, coarse waste residue is added, with each addition amount ≤ 10% of the dry basis coarse waste residue consumption. After adjustment, stir for 1~2 minutes before discharge.

[0039] Preferably, the recycled water used in the material preparation process meets the following criteria:

[0040] pH value: 9~14;

[0041] Insoluble matter content: ≤30000 mg / L;

[0042] Soluble content: ≤10000 mg / L;

[0043] Content: ≤3500mg / L;

[0044] Alkali content: ≤1500 mg / L;

[0045] SO4 2－ Content: ≤2700mg / L;

[0046] The prepared controllable low strength material (CLSM) has the following physical and mechanical properties: density 1502~1750kg / m³, flowability 235~295mm, water bleeding rate ≤5%, 7-day unconfined compressive strength 0.19~7.0MPa, and 28-day unconfined compressive strength 0.32~9.5MPa.

[0047] Through residual slurry pretreatment and mixing, the material performance in the preferred solution can be maintained for more than 3 hours, with a bleeding rate of ≤5%. The mechanical properties and working properties are synergistically matched, adapting to different engineering load-bearing and filling requirements, and applicable to a wide range of scenarios.

[0048] The technical effects and advantages of this invention are as follows:

[0049] 1. Highly innovative and filling a technological gap: It is the first time that concrete residue has been proposed as the core cementing material to completely replace cement and mineral admixtures, and to prepare controllable low strength material (CLSM) in conjunction with various industrial wastes and by-products. This solves the industry pain points of low utilization rate of concrete residue and high carbon and high cost of traditional CLSM. The technical route is novel and feasible.

[0050] 2. Outstanding green sustainability: The raw materials are all industrial waste and recycled materials, with a carbon footprint close to zero. The preparation process has virtually no additional carbon emission links, reducing carbon emissions by more than 70% compared to conventional controllable low-strength materials. There are no new pollutant emissions during the production process, realizing the closed-loop utilization of "waste-recycled resources-engineering materials". This is in line with the development trend of green building materials and meets the needs of "dual carbon" goals and "zero waste city" construction.

[0051] 3. The product is highly designable and adaptable to a wide range of scenarios: The prepared controllable low-strength material has good flowability, filling and self-compacting properties, and its flowability, strength and other properties can be adjusted by mix design to meet the needs of different geotechnical engineering scenarios such as trench backfilling, foundation pit filling, bridge abutment and culvert backfilling, roadbed and subbase filling, etc., making it highly applicable.

[0052] 4. Win-win economic and social benefits: On the one hand, it creates new economic growth points for concrete pipe pile plants and mixing plants, transforming waste into marketable geotechnical engineering materials; on the other hand, it reduces resource consumption and environmental pollution, lowers carbon emissions, and helps the industry's green transformation, thus possessing significant economic and social value.

[0053] 5. The production process is optimized based on existing concrete production technology, requiring no complex equipment modification. The mix proportion calculation method is simple and clear, and the quality control standards are clear. Enterprises in the industry can quickly master and scale up production, and the prospects for promotion and application are broad. Attached Figure Description

[0054] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0055] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0056] The present invention will be described in detail below with reference to five specific embodiments. The concrete residue used in each embodiment comes from the production process of PHC pipe piles (prestressed high-strength concrete pipe piles). The fine waste residue, coarse waste residue and recycled water all come from the slurry recycling and treatment system of the concrete mixing plant of the precast component factory. Molasses is an industrial by-product (containing 50% solids and pH value 5.5).

[0057] Example 1

[0058] 1. Raw material parameters

[0059] Excess concrete mortar: density 1.8 g / cm³, solid content 78.8%, moisture content 21.2%, fluidity 320 mm (GB8077 Cement Paste Fluidity Method); The 7-day compressive strength of 40 mm × 40 mm × 160 mm mortar specimens prepared by mixing excess concrete mortar and ISO standard sand at a mass ratio of 1:1 was 52.6 MPa, and the 28-day compressive strength was 63.8 MPa.

[0060] Molasses: 50% solids content;

[0061] Fine waste residue (wet state): moisture content 150%;

[0062] Coarse waste residue (wet state): moisture content 7.0%, fineness modulus 2.4, crushing value 22%, mud content 3.1%;

[0063] Recycled water: pH 12.5, insoluble matter content 8270 mg / L.

[0064] 2. Mix design

[0065] Dry base mix proportion (per cubic meter): 184 kg of residual concrete binder, 262 kg of fine waste residue, 420 kg of coarse waste residue, 635 kg of recycled water, and 0.277 kg of molasses (i.e., 0.15% of the mass of the dry base concrete binder).

[0066] Preparation of pre-treated concrete slurry: The centrifugal slurry of prestressed concrete pipe piles, recycled water from the mixing plant, and molasses with a solid content of 50% are mixed evenly at a mass ratio of 100:33:0.30 to obtain a pre-treated slurry with a density of 1.50 g / cm³, a solid content of 59.1%, and a moisture content of 40.9%. The dosage is 312 kg (i.e., 184 kg ÷ 59.1%).

[0067] Production mix ratio (per cubic meter): 312 kg of pretreatment residue, 655 kg of wet fine waste residue (i.e., 262 kg × (1 + 150%)), 449 kg of wet coarse waste residue (i.e., 420 kg × (1 + 7%)), and 85 kg of recycled water (i.e., 635 kg - 312 kg × 40.9% - 262 × 150% - 420 × 7%).

[0068] 3. Preparation process

[0069] Preparation of pre-treated concrete slurry: The centrifugal slurry of prestressed concrete pipe piles, recycled water from the mixing plant, and molasses with a solid content of 50% were added to the mixing tank at a mass ratio of 100:33:0.30. The mixture was stirred at 65 r / min for 4 min. The density was measured to be 1.50 g / cm³, the solid content was 59.1%, and the solid content was 40.9%.

[0070] Moisture content test: The moisture content of wet fine waste residue was 150% and that of wet coarse waste residue was 7.0% as measured by the drying method.

[0071] Preparation of mixture: 312 kg of pretreatment residue, 655 kg of wet fine waste residue, 449 kg of wet coarse waste residue, and 85 kg of replenished recycled water were sequentially added to the mixer and stirred at 60 r / min for 8 min until uniform. The discharge temperature was 22℃.

[0072] Transportation and pouring: The controllable low-strength material mixture is transported to the construction site by concrete mixer truck and poured into the foundation pit trench (volume 280m³) by pumping. The mixture fills and compacts by its good fluidity and its own weight, without the need for vibration.

[0073] 4. Performance test results

[0074] Density: 1502 kg / m³ (ASTM D6023-2016 standard);

[0075] Flowability: 295 mm (ASTM D6103-04 standard);

[0076] 7-day unconfined compressive strength: 0.19 MPa (ASTM D4832 standard);

[0077] 28-day unconfined compressive strength: 0.32 MPa (ASTM D4832 standard);

[0078] Bleeding rate: 3.8% (ASTM C940 standard).

[0079] Example 2

[0080] 1. Raw material parameters

[0081] Excess concrete mortar: density 1.8 g / cm³, solid content 78.8%, moisture content 21.2%, fluidity 320 mm (GB8077 Cement Paste Fluidity Method); The 7-day compressive strength of 40 mm × 40 mm × 160 mm mortar specimens prepared by mixing excess concrete mortar and ISO standard sand at a mass ratio of 1:1 was 52.6 MPa, and the 28-day compressive strength was 63.8 MPa.

[0082] Molasses: 50% solids content;

[0083] Fine waste residue (wet state): moisture content 150%;

[0084] Coarse waste residue (wet state): moisture content 7.0%, fineness modulus 2.4, crushing value 23%, mud content 3.3%;

[0085] Recycled water: pH 12.5, insoluble matter content 8270 mg / L.

[0086] 2. Mix design

[0087] Dry base mix proportion (per cubic meter): 369 kg of residual concrete binder, 225 kg of fine waste residue, 420 kg of coarse waste residue, 571 kg of recycled water, and 0.553 kg of molasses (i.e., 0.15% of the mass of residual concrete binder).

[0088] Preparation of pre-treated concrete slurry: The centrifugal slurry of prestressed concrete pipe piles, recycled water from the mixing plant, and molasses with a solid content of 50% are mixed evenly at a mass ratio of 100:10:0.30 to obtain a pre-treated slurry with a density of 1.68 g / cm³, a solid content of 71.6%, and a moisture content of 28.4%, with a dosage of 515 kg (i.e., 369 kg ÷ 71.6%).

[0089] Production mix ratio (per cubic meter): 515 kg of pretreatment residue, 562 kg of wet fine waste residue (i.e., 225 kg × (1 + 150%)), 449 kg of wet coarse waste residue (i.e., 420 kg × (1 + 7%)), and 57.84 kg of recycled water (i.e., 571 kg - 515 kg × 28.4% - 225 × 150% - 420 × 7%).

[0090] 3. Preparation process

[0091] Preparation of pre-treated concrete slurry: The centrifugal slurry of prestressed concrete pipe piles, recycled water from the mixing plant, and molasses with a solid content of 50% were added to the mixing tank at a mass ratio of 100:10:0.30. The mixture was stirred at 70 r / min for 3 min. The density was measured to be 1.68 g / cm³, the solid content to be 71.6%, and the moisture content to be 28.4%.

[0092] Moisture content test: The moisture content of wet fine waste residue was 150% and that of wet coarse waste residue was 7.0% as measured by the drying method.

[0093] Preparation of the mixture: 515 kg of pretreatment residue, 562 kg of wet fine waste residue, 449 kg of wet coarse waste residue, and 57.84 kg of recycled water were added into the mixer in sequence and stirred at 60 r / min for 7 min until uniform. The discharge temperature was 24℃.

[0094] Transportation and pouring: The controllable low-strength material mixture is transported to the construction site by concrete mixer truck and backfilled into the municipal pipe trench (50m long, 0.5m wide, and 1.2m deep) by chute. The mixture fills the trench densely by relying on its good fluidity and its own weight, which makes the construction speed fast, does not require vibration, and reduces construction noise.

[0095] 4. Performance test results

[0096] Density: 1585 kg / m³ (ASTM D6023-2016 standard);

[0097] Flowability: 270 mm (ASTM D6103-04 standard);

[0098] 7-day unconfined compressive strength: 1.3 MPa (ASTM D4832 standard);

[0099] 28-day unconfined compressive strength: 2.0 MPa (ASTM D4832 standard);

[0100] Bleeding rate: 2.6% (ASTM C940 standard).

[0101] Example 3

[0102] 1. Raw material parameters

[0103] Excess concrete mortar: density 2.0 g / cm³, solid content 88.7%, moisture content 11.3%, fluidity 260 mm (GB8077 Cement Paste Fluidity Method); The 7-day compressive strength of 40 mm × 40 mm × 160 mm mortar specimens prepared by mixing excess concrete mortar and ISO standard sand at a mass ratio of 1:1 was 61.9 MPa, and the 28-day compressive strength was 73.2 MPa.

[0104] Molasses: 50% solids content;

[0105] Fine waste residue (wet state): moisture content 150%;

[0106] Coarse waste residue (wet state): moisture content 7.0%, fineness modulus 2.4, crushing value 24%, mud content 3.5%;

[0107] Recycled water: pH 12.4, insoluble matter content 7690 mg / L.

[0108] 2. Mix design

[0109] Dry base mix proportion (per cubic meter): 565 kg of residual concrete binder, 191 kg of fine waste residue, 375 kg of coarse waste residue, 518 kg of recycled water, and 0.848 kg of molasses (i.e., 0.15% of the mass of residual concrete binder).

[0110] Preparation of pre-treated concrete slurry: The centrifugal slurry of prestressed concrete pipe piles, recycled water from the mixing plant, and molasses with a solid content of 50% are mixed evenly at a mass ratio of 100:12.5:0.30 to obtain a pre-treated slurry with a density of 1.80 g / cm³, a solid content of 78.8%, and a moisture content of 21.2%, with a dosage of 718 kg (i.e., 565 kg ÷ 78.8%).

[0111] Production mix ratio (per cubic meter): 718 kg of pretreatment residue, 478 kg of wet fine waste residue (i.e., 191 kg × (1 + 150%)), 401 kg of wet coarse waste residue (i.e., 375 kg × (1 + 7%)), and 53 kg of recycled water (i.e., 518 kg - 718 kg × 21.2% - 191 × 150% - 375 × 7%).

[0112] 3. Preparation process

[0113] Preparation of pre-treated concrete slurry: The centrifugal slurry of prestressed concrete pipe piles, recycled water from the mixing plant, and molasses with a solid content of 50% were added to the mixing tank at a mass ratio of 100:12.5:0.30. The mixture was stirred at 75 r / min for 3 min. The density was measured to be 1.80 g / cm³, the solid content to be 78.8%, and the moisture content to be 21.2%.

[0114] Moisture content test: The moisture content of wet fine waste residue was 150% and that of wet coarse waste residue was 7.0% as measured by the drying method.

[0115] Preparation of the mixture: 718 kg of pretreatment residue, 478 kg of wet fine waste residue, 401 kg of wet coarse waste residue, and 53 kg of replenished recycled water were sequentially added to the mixer and stirred at 60 r / min for 7 min until uniform, to obtain a controllable low-strength material mixture.

[0116] Transportation and pouring: The controllable low-strength material mixture is transported to the construction site by concrete mixer trucks and the pile holes (0.6m in diameter and 8m in depth) are filled by direct unloading. The mixture fills the pile holes by its own fluidity and gravity, which not only has high construction efficiency, but also reduces construction vibration and noise.

[0117] 4. Performance test results

[0118] Density: 1650 kg / m³ (ASTM D6023-2016 standard);

[0119] Flowability: 235 mm (ASTM D6103-04 standard);

[0120] 7-day unconfined compressive strength: 2.7 MPa (ASTM D4832 standard);

[0121] 28-day unconfined compressive strength: 4.1 MPa (ASTM D4832 standard);

[0122] Bleeding rate: 1.8% (ASTM C940 standard).

[0123] Example 4

[0124] 1. Raw material parameters

[0125] Excess concrete mortar: density 2.0 g / cm³, solid content 88.7%, moisture content 11.3%, fluidity 260 mm (GB8077 Cement Paste Fluidity Method); The 7-day compressive strength of 40 mm × 40 mm × 160 mm mortar specimens prepared by mixing excess concrete mortar and ISO standard sand at a mass ratio of 1:1 was 61.9 MPa, and the 28-day compressive strength was 73.2 MPa.

[0126] Molasses: 50% solids content;

[0127] Sediment (wet state): Moisture content 150%;

[0128] Coarse waste residue (wet state): moisture content 7.0%, fineness modulus 2.4, crushing value 25%, mud content 3.8%;

[0129] Recycled water: pH 11.5, insoluble matter content 6560 mg / L.

[0130] 2. Mix design

[0131] Dry base mix proportion (per cubic meter): 792 kg of residual concrete binder, 96 kg of fine waste residue, 345 kg of coarse waste residue, 475 kg of recycled water, and 1.189 kg of molasses (i.e., 0.15% of the mass of the residual concrete binder).

[0132] Preparation of pre-treated concrete slurry: The centrifugal slurry of prestressed concrete pipe piles, recycled water from the mixing plant, and molasses with a solid content of 50% are added to the mixing tank at a mass ratio of 100:12.5:0.30 and mixed evenly to obtain a pre-treated slurry with a density of 1.80 g / cm³, a solid content of 78.8%, and a moisture content of 21.2%, with a dosage of 1005 kg (i.e., 792 kg ÷ 78.8%).

[0133] Production mix ratio (per cubic meter): 1005 kg of pretreatment residue, 240 kg of wet fine waste residue (i.e., 96 kg × (1 + 150%)), 369 kg of wet coarse waste residue (i.e., 345 kg × (1 + 7%)), and 93.8 kg of recycled water (i.e., 475 kg - 1005 kg × 21.2% - 96 × 150% - 345 × 7%).

[0134] 3. Preparation process

[0135] Preparation of pre-treated concrete slurry: The centrifugal slurry of prestressed concrete pipe piles, recycled water from the mixing plant, and molasses with a solid content of 50% were added to the mixing tank at a mass ratio of 100:12.5:0.30 and mixed evenly. The mixture was stirred at 80 r / min for 3 min. The density was measured to be 1.80 g / cm³, the solid content was 78.8%, and the moisture content was 21.2%.

[0136] Moisture content test: The moisture content of wet fine waste residue was 150% and that of wet coarse waste residue was 7.0% as measured by the drying method.

[0137] Preparation of the mixture: 1005 kg of pretreatment residue, 240 kg of wet fine waste residue, 369 kg of wet coarse waste residue, and 93.8 kg of recycled water were added to the mixer in sequence and stirred at 60 r / min for 8 min until uniform to obtain a controllable low-strength material mixture.

[0138] 4. Performance test results

[0139] Density: 1720 kg / m³ (ASTM D6023-2016 standard);

[0140] Flowability: 265 mm (ASTM D6103-04 standard);

[0141] 7-day unconfined compressive strength: 5.4 MPa (ASTM D4832 standard);

[0142] 28-day unconfined compressive strength: 7.7 MPa (ASTM D4832 standard);

[0143] Bleeding rate: 1.1% (ASTM C940 standard).

[0144] Example 5

[0145] 1. Raw material parameters

[0146] Excess concrete mortar: density 2.0 g / cm³, solid content 88.7%, moisture content 11.3%, fluidity 260 mm (GB8077 Cement Paste Fluidity Method); The 7-day compressive strength of 40 mm × 40 mm × 160 mm mortar specimens prepared by mixing excess concrete mortar and ISO standard sand at a mass ratio of 1:1 was 61.9 MPa, and the 28-day compressive strength was 73.2 MPa.

[0147] Molasses: 50% solids content;

[0148] Sediment (wet state): Moisture content 150%;

[0149] Coarse waste residue (wet state): moisture content 7.0%, fineness modulus 2.4, crushing value 25%, mud content 3.8%;

[0150] Recycled water: pH 11.5, insoluble matter content 6560 mg / L.

[0151] 2. Mix design

[0152] Dry base mix proportion (per cubic meter): 911 kg of residual concrete binder, 62 kg of fine waste residue, 310 kg of coarse waste residue, 452 kg of recycled water, and 1.366 kg of molasses (i.e., 0.15% of the mass of residual concrete binder).

[0153] Preparation of pre-treated concrete slurry: The centrifugal slurry of prestressed concrete pipe piles, recycled water from the mixing plant, and molasses with a solid content of 50% are added to the mixing tank at a mass ratio of 100:12.5:0.30 and mixed evenly to obtain a pre-treated slurry with a density of 1.80 g / cm³, a solid content of 78.8%, and a moisture content of 21.2%, with a dosage of 1156 kg (i.e., 911 kg ÷ 78.8%).

[0154] Production mix ratio (per cubic meter): 1156 kg of pretreatment residue, 155 kg of wet fine waste residue (i.e., 62 kg × (1 + 150%)), 332 kg of wet coarse waste residue (i.e., 310 kg × (1 + 7%)), and 92 kg of recycled water (i.e., 452 kg - 1156 kg × 21.2% - 62 × 150% - 310 × 7%).

[0155] 3. Preparation process

[0156] Preparation of pre-treated concrete slurry: The centrifugal slurry of prestressed concrete pipe piles, recycled water from the mixing plant, and molasses with a solid content of 50% were added to the mixing tank at a mass ratio of 100:12.5:0.30 and mixed evenly. The mixture was stirred at 80 r / min for 3 min. The density was measured to be 1.80 g / cm³, the solid content was 78.8%, and the moisture content was 21.2%.

[0157] Moisture content test: The moisture content of wet fine waste residue was 150% and that of wet coarse waste residue was 7.0% as measured by the drying method.

[0158] Preparation of the mixture: 1156 kg of pretreatment residue, 155 kg of wet fine waste residue, 332 kg of wet coarse waste residue, and 92 kg of replenished recycled water were sequentially added to the mixer and stirred at 60 r / min for 8 min until uniform, to obtain a controllable low-strength material mixture.

[0159] 4. Performance test results

[0160] Density: 1750 kg / m³ (ASTM D6023-2016 standard);

[0161] Flowability: 250 mm (ASTM D6103-04 standard);

[0162] 7d unconfined compressive strength: 7.0 MPa (ASTM D4832 standard);

[0163] 28-day unconfined compressive strength: 9.5 MPa (ASTM D4832 standard);

[0164] Bleeding rate: 0.8% (ASTM C940 standard).

[0165] The strength grades and practical applications of each embodiment are shown in Table 2. The dry-based raw material mix proportions for controllable low-strength materials (CLSM) are shown in Table 3, the production mix proportions are shown in Table 4, and the correlation analysis between the properties of the prepared CLSM materials and the dry-based raw material mix proportion parameters is shown in Table 5. The water-cement ratio (W / B) refers to the mass ratio of total water consumption to dry-based concrete slurry binder, and the water-solid ratio (W / S) refers to the mass ratio of total water consumption to the total mass of solid particles in the system, including dry-based concrete slurry binder, dry-based fine waste residue, and dry-based coarse waste residue.

[0166] Table 2 Performance parameters and practical scenarios of each embodiment

[0167]

[0168] Table 3. Dry basis raw material proportions for each embodiment (unit: kg / m³) 3 )

[0169]

[0170] Table 4 Production mix proportions for each embodiment

[0171]

[0172] Table 5. Correlation analysis between material properties and dry-basis raw material proportioning parameters in each embodiment.

[0173]

[0174] As shown in Tables 3 and 5, the higher the amount of residual concrete binder (dry basis), the higher the strength of the controllable low strength material (CLSM). The strength of CLSM decreases exponentially with its water-binder ratio (W / B) and increases linearly with the reciprocal of the water-binder ratio (W / B), 1 / (W / B) (or B / W). The mathematical fitting formula is:

[0175] 28-day unconfined compressive strength = 5.3366 × [1 / (W / B)] - 1.3985;

[0176] The greater the total water consumption, the greater the water-to-solid ratio (W / S) of the controllable low strength material (CLSM), and the greater the fluidity of the CLSM (except for Example 3). In addition, reducing the amount of fine waste residue (see Examples 3-5) helps to improve the fluidity of the CLSM.

[0177] The less total water consumption, the smaller the water-to-solid ratio (W / S) of controllable low-strength materials (CLSM), and the greater the density of CLSM.

[0178] The less total water consumption, the smaller the water-to-solid ratio (W / S) of controllable low-strength materials (CLSM), and the lower the CLSM bleeding rate.

[0179] The production mix proportions for various embodiments of low-carbon controllable low-strength materials (CLSM) based on concrete slurry and waste residue are shown in Table 4. CLSM with lower strength grades and higher fluidity should preferably use low-density pretreated concrete slurry as a binder, while CLSM with higher strength grades should use high-density pretreated concrete slurry as a binder. The fluidity of CLSM can be adjusted by varying the amounts of fine and coarse waste residue; reducing the amount of fine waste residue helps improve the fluidity of CLSM.

[0180] The core of strength control: The mass ratio of the amount of residual concrete binder (dry basis) and the total water content to the amount of residual concrete binder (dry basis) (i.e., water-binder ratio W / B) is the key to regulating the strength of CLSM. The more residual concrete binder (dry basis) and the smaller the water-binder ratio W / B, the higher the strength of the controllable low-strength material prepared.

[0181] Flowability adaptation logic: The lower the strength, the higher the total water consumption, which easily meets the requirements of high flowability and self-filling and self-compacting; the higher the strength, the lower the total water consumption, and the lower the flowability. By optimizing the amount of fine waste residue and coarse waste residue, the flowability can reach more than 200mm, which meets the requirements of self-filling and self-compacting.

[0182] Environmental protection and cost synergy: All strength grades achieve full solid waste resource utilization. The higher the strength, the more concrete slurry binder is used, and the higher the cement substitution, resulting in more significant carbon emission reduction and cost savings. For example, high-strength concrete slurry-based CLSM has a carbon footprint that is reduced by about 90% (about 150 kg CO2 / m³) and a cost reduction of 50% to 70% compared to traditional cement-mineral admixture composite cementitious material-based CLSM.

[0183] The applicant further declares that while the above embodiments illustrate the implementation and preparation methods of the present invention, the present invention is not limited to the above-described embodiments, meaning that the present invention must rely on the above methods and structures to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the selected implementation methods, additions to steps, and selections of specific methods all fall within the scope of protection and disclosure of the present invention.

[0184] This invention is not limited to the above-described embodiments. All methods that employ similar structures and approaches to achieve the objectives of this invention are within the scope of protection of this invention.

Claims

1. A low-carbon, controllable, low-strength material based on concrete residue and waste, characterized in that, It is prepared from the following solid waste components and retarder in the following mass ratio: 184~911kg of concrete residue binder, 62~262kg of fine waste residue, 310~420kg of coarse waste residue, 452~635kg of recycled water, and 0.092~1.822kg of molasses (converted to solids). The concrete residue binder is obtained by diluting the centrifuged residue of prestressed concrete pipe piles with water and pre-treating it with molasses modification. It has a density of 1.4~2.0 g / cm³, a solid content of 50%~90%, and a fluidity retention time of 4~10 h.

2. The low-carbon, controllable low-strength material based on concrete residue and slag according to claim 1, characterized in that, The concrete slurry is an industrial waste generated during the centrifugal molding process of prestressed concrete pipe piles. It has a solid content of 65% to 90% and a density of 1.6 to 2.0 g / cm³. Cement and mineral admixtures account for 60% to 90% of the slurry mass. The initial fluidity of the slurry is 200 to 400 mm. Mortar specimens are prepared by mixing the concrete slurry with ISO standard sand at a mass ratio of 1:

1. The mortar specimens have a 7-day compressive strength of 40 to 65 MPa and a 28-day compressive strength of 50 to 75 MPa.

3. The low-carbon, controllable low-strength material based on concrete residue and slag according to claim 1, characterized in that, The fine waste residue is ultrafine particles smaller than 0.15mm obtained by natural sedimentation separation of the residual slurry from the concrete mixing plant in a sedimentation tank; The fine waste residue mainly consists of ultrafine particles, clay particles, partially hydrated cementitious materials and their hydration products in concrete aggregates. The coarse waste residue is obtained by separating and dewatering the residual slurry from the concrete mixing plant through a sand and gravel separation system, with a particle size of less than 5mm. The coarse waste residue is mainly composed of natural sand particles, artificial sand particles, fine crushed stone particles, and a small amount of hardened cement and mortar. Its particle size distribution meets the following requirements: particles with a size of 2.36mm to 5mm account for 30% to 50%, particles with a size of 1.18mm to 2.36mm account for 15% to 30%, particles with a size of 0.15mm to 1.18mm account for 20% to 40%, and particles smaller than 0.15mm account for no more than 15%. The coarse waste residue has a fineness modulus of 2.3 to 3.3, a crushing value of ≤30%, and a mud content of ≤5%.

4. A method for preparing a low-carbon, controllable, low-strength material based on concrete residue and slag, characterized in that, Includes the following steps: S1: Pretreatment of Excess Concrete Slurry: The centrifugal excess slurry of prestressed concrete pipe piles, recycled water from the mixing plant, and molasses admixture are added to the mixing tank at a mass ratio of 100:(0~75):(0.05~0.20). The mixture is stirred at 60~80 r / min for 3~5 min until homogeneous. Stirring is continued to ensure the homogeneity of the pretreated excess concrete slurry and prevent the sedimentation and segregation of some denser solid particles. The density, solid content, and moisture content are tested to ensure that the density of the pretreated excess concrete slurry binder meets the requirement of 1.4~2.0 g / cm³. ① Molasses solution content = Molasses solids content / Molasses solution solids content; ② The density of the pretreated concrete slurry-based binder was tested according to standard ASTM D6023-2016; ③ The solids content and moisture content of the pretreated concrete slurry-based binder were tested using the drying method: Solid content of residual slurry in pretreated concrete = Mass of dried sample / Mass of undried sample; Moisture content of residual concrete slurry after pretreatment = (mass of sample before drying - mass of sample after drying) / mass of sample before drying; S2: Solid phase component moisture content test: The actual moisture content of fine waste residue and coarse waste residue was determined by drying method, with the moisture content of fine waste residue being 100%~200% and the moisture content of coarse waste residue being 0%~15%; S3: Production mix ratio correction: Based on the dry basis raw material mix ratio of claim 1, calculate the actual amount of each component according to the following formula: ① Amount of wet fine waste residue = Amount of dry fine waste residue × (1 + Measured moisture content of fine waste residue); ② Amount of wet coarse waste residue = Amount of dry coarse waste residue × (1 + Measured moisture content of coarse waste residue); ③ Moisture content of pretreated concrete residual cementitious material = Amount of pretreated concrete residual cementitious material × Measured moisture content of pretreated concrete residual cementitious material; ④ Actual amount of recycled water added = Total water consumption in dry mix proportion - Moisture content of pretreated concrete residual cementitious material - Moisture content of wet fine waste residue - Moisture content of wet coarse waste residue; S4: Preparation of mixture: The pretreated concrete residue binder, wet fine waste residue, wet coarse waste residue and actual added recycled water are sequentially put into a forced mixer and stirred at 60~80r / min for 5~10min until the mixture is uniform and free of lumps. The discharge temperature is controlled at 5~35℃. S5: Transportation, pouring and curing: Controlled low-strength material mixtures are transported by concrete mixer trucks, with a transportation time of ≤3 hours. They are poured using methods such as chutes and pumps, and after setting and hardening, they form controlled low-strength materials.

5. The method for preparing low-carbon, controllable, low-strength materials based on concrete residue and slag according to claim 4, characterized in that, In step S1, the molasses has a solids content of 40%~60% and a pH value of 5.0~7.

0. Its function is to slow down the cement hydration rate in the residual concrete slurry and extend the fluidity retention time and usable time of the residual concrete slurry.

6. The method for preparing low-carbon, controllable, low-strength materials based on concrete slurry and waste residue according to claim 4, characterized in that, Before discharging the mixture in step S4, a quality test must be performed. If the fluidity is less than 200 mm, add recycled water, with each addition amount ≤ 5% of the total water consumption. If the fluidity is greater than 350 mm, add coarse waste residue, with each addition amount ≤ 10% of the dry basis coarse waste residue consumption. After adjustment, stir for 1~2 minutes before discharging.

7. The low-carbon, controllable low-strength material based on concrete residue and slag according to claim 1 or 4, characterized in that, The recycled water is recycled water from a concrete mixing plant, and its specifications meet the following requirements: pH value: 9~14; Insoluble matter content: ≤30000 mg / L; Soluble content: ≤10000 mg / L; Content: ≤3500mg / L; Alkali content: ≤1500 mg / L; SO4 2－ Content: ≤2700mg / L.

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