Solid waste-based low-carbon concrete and preparation method thereof

Abstract

The invention discloses solid-waste-based low-carbon concrete and a preparation method thereof, and belongs to the field of environment-friendly concrete. Through a composite activator pre-activation technology, a solid waste multi-stage grinding technology and a gradient stirring technology, the problems that traditional solid waste concrete is low in mixing amount, poor in performance, poor in technology adaptability and the like are solved. The slag powder, the fly ash, the waste limestone powder and the superfine tunnel slag powder are used as admixtures (the total mixing amount is larger than or equal to 40%), the modulus-adjustable composite exciting agent is combined, and the solid waste reaction activity and the interface bonding strength are remarkably improved. Through pretreatment and staged stirring, the 28-day strength of the concrete is larger than or equal to 55 MPa, the impermeability grade reaches P12, carbon emission is reduced by 38%, the concrete is suitable for high-durability projects such as tunnel linings and prefabricated parts, and solid waste recycling and high-value utilization are achieved.

Description

Technical Field

[0001] This invention belongs to the field of environmentally friendly concrete, and specifically discloses a solid waste-based low-carbon concrete and its preparation method. Background Technology

[0002] In recent years, the concrete industry has faced the dual pressures of reducing carbon emissions and improving the utilization of solid waste resources. Using industrial solid wastes, such as slag and fly ash, to replace cement in the preparation of low-carbon concrete has become an important research direction. However, existing technologies still face significant technical bottlenecks in material design, process adaptation, and engineering applications, mainly manifested in the following core issues:

[0003] 1. The inverse contradiction between solid waste dosage and performance

[0004] Traditional solid waste concrete is limited by the low reactivity of solid waste materials, typically requiring the dosage to be controlled below 30% to ensure strength development. For example, when slag powder is directly added, the glassy depolymerization is difficult, resulting in a 28-day activity utilization rate of less than 50%; the early hydration inertness of fly ash extends the concrete demolding time by more than 40%. Existing technologies mostly rely on increasing cement content to compensate for strength loss, making it difficult to achieve a significant increase in actual solid waste substitution rates and thus failing to achieve true low-carbon goals. Experimental studies show that when the solid waste dosage exceeds 35%, the dissolution efficiency of traditional alkaline activators (such as sodium hydroxide) on the silica-alumina phase decreases sharply, and unreacted solid waste particles in the cementitious system form a "weak interface zone," significantly reducing the concrete's impermeability and durability.

[0005] 2. Technological gaps in new solid waste utilization

[0006] Due to their complex mineral composition (quartz phase accounting for 40%-60%) and lack of active components, engineering waste soil and rock from tunnels and other sources are mostly used as low-value-added aggregates (admixture dosage <10%) by current technologies, making it impossible to achieve high-value micronized powder utilization. Tunnel waste powder prepared by conventional mechanical grinding processes (specific surface area <400m²) 2 Pozzolanic ash ( / kg) mainly functions as a micro-aggregate filler in concrete, but its activity index is less than 60%, which can easily lead to workability loss and loosening of the interface transition zone after incorporation. In addition, the clay minerals (such as montmorillonite) remaining in the slag powder can adsorb water-reducing agent molecules, resulting in an increase in slump loss over time of 30%-50%.

[0007] 3. Performance loss due to raw material fluctuations

[0008] The chemical composition of industrial solid waste fluctuates significantly depending on its source. For example, the CaO content in slag can vary by 15%-20%, and the loss on ignition (LOI) of fly ash can fluctuate by 3%-8%. Current technologies lack mechanisms to limit and compensate for key raw material indicators, resulting in a concrete strength dispersion coefficient as high as 12%-18% under the same mix proportions. Typical problems include: low-calcium slag (CaO < 30%) forming non-cementing products due to insufficient alkaline activation; and high-LOI fly ash (> 5%) containing unburned carbon adsorbing air-entraining agents, causing abnormal fluctuations in air content (± 2%), severely affecting frost resistance.

[0009] 4. Defects in process system compatibility

[0010] The slow hydration heat release and high viscosity of concrete with high solid waste content fundamentally conflict with traditional construction techniques. For example:

[0011] Vibration process: Conventional vibration frequency (5000-6000 times / min) cannot effectively remove air bubbles formed by the aggregation of micro powder, resulting in an increase in the porosity of the cast body by 1.5-2 times;

[0012] Curing regime: Constant temperature steam curing (e.g., 80℃×8h) exacerbates the difference in hydration rate between solid waste and cement, causing shrinkage stress concentration and increasing the density of surface microcracks by 300-400 cracks / m². 2 ;

[0013] Mixing process: Traditional one-time feeding method results in uneven distribution of activator, with local "activation blind zones" and a reaction rate difference of 20%-30% between solid waste particles.

[0014] The aforementioned defects make it difficult for existing solid waste concrete to meet the needs of high-durability projects (such as precast components and underground structures), severely restricting its large-scale application. Summary of the Invention

[0015] To address the aforementioned problems in the prior art, this invention discloses a solid waste-based low-carbon concrete and its preparation method.

[0016] This invention includes the following technical solutions:

[0017] A solid waste-based low-carbon concrete is composed of the following raw materials in parts by weight:

[0018] 200-240 parts cement

[0019] 160-200 parts of solid waste admixture.

[0020] 600-750 parts fine aggregate,

[0021] 900-1100 parts coarse aggregate,

[0022] 8-15 parts of compound activator

[0023] 2-4 parts water-reducing agent

[0024] 140-160 parts water;

[0025] The solid waste admixture is composed of slag powder, fly ash, waste limestone powder, and tunnel slag powder in a mass ratio of (30-45):(25-35):(15-25):(10-20);

[0026] Among them, slag powder: CaO≥35wt%, SiO2≥30wt%, glass content≥85%;

[0027] Fly ash: Loss on ignition ≤5%, SiO2+Al2O3 ≥70%, fineness (45μm sieve residue) ≤12%;

[0028] Waste limestone powder: CaCO3 ≥ 90%, D50 = 5-15μm;

[0029] Tunnel muck powder: SiO2≥40%, Al2O3≥15%, activity index≥75%.

[0030] Furthermore, in the aforementioned solid waste-based low-carbon concrete, the tunnel slag powder is prepared using a three-stage grinding process: primary crushing to a particle size <5mm, secondary ball milling to a specific surface area of ​​300-400m². 2 / kg, three-stage ultrafine grinding to a specific surface area of ​​500-600m² 2 / kg.

[0031] Furthermore, in the aforementioned solid waste-based low-carbon concrete, the composite activator is composed of sodium silicate with a water glass modulus of 1.2-1.8, sodium hydroxide, sodium sulfate, and nano-silica fume in a mass ratio of 5:2:2:1.

[0032] Furthermore, in the aforementioned solid waste-based low-carbon concrete, the nano-silica fume is surface-modified hydrophobic nano-silica fume with a specific surface area ≥20000 m². 2 / kg, surface contact angle ≥120°.

[0033] This invention also discloses a method for preparing the above-mentioned solid waste-based low-carbon concrete, comprising:

[0034] (1) Solid waste pretreatment: Tunnel muck is ground in three stages to a specific surface area of ​​500-600 m². 2 / kg, slag ground to a specific surface area of ​​450-550m² 2 / kg, then mixed with fly ash and waste limestone powder to obtain solid waste admixture;

[0035] (2) Activator pre-activation: Mix 30-40% of the total amount of composite activator with solid waste admixture in a high-speed mixer for 5-8 minutes to obtain pretreated solid waste admixture;

[0036] (3) Concrete mixing: Dry mix cement, pretreated solid waste admixture, coarse aggregate and fine aggregate according to the proportion for 30-60s, add the remaining activator, water-reducing agent and water and wet mix for 90-120s to obtain solid waste-based low carbon concrete.

[0037] Furthermore, in the above preparation method, 0.5-1.5% of grinding aid is added during the grinding of tunnel slag in step (1). The grinding aid is a mixture of triethanolamine and polycarboxylic acid dispersant in a ratio of 1:(2-3).

[0038] Furthermore, in the above preparation method, the material temperature is controlled to be ≤45℃ during the mixing process in step (2), and nitrogen protection is used.

[0039] Furthermore, in the above preparation method, the wet mixing process in step (3) is carried out in three stages: low-speed mixing (30-50 rpm) for 30 s, medium-speed mixing (80-100 rpm) for 45 s, and high-speed mixing (120-150 rpm) for 15 s.

[0040] The present invention also discloses the application of the above-mentioned solid waste-based low-carbon concrete in tunnel lining engineering.

[0041] The present invention also discloses the application of the above-mentioned solid waste-based low-carbon concrete in precast components.

[0042] Compared with the prior art, the present invention has the following outstanding advantages:

[0043] 1. Breakthrough in solid waste admixture ratio: Through pre-activation with composite activator and ultrafine grinding technology, the proportion of solid waste admixture reaches more than 40%, and the 28-day strength exceeds 54MPa, which is more than 20% higher than the traditional process.

[0044] 2. Achieving high-value utilization of complex solid waste: Tunnel muck undergoes three-stage grinding (specific surface area 500-600 m³ / s). 2 With an activity index ≥75% after ( / kg), it can replace part of the cement and solve the problem of utilizing low-activity solid waste.

[0045] 3. Stability of performance fluctuations: By limiting key raw material indicators (such as slag CaO ≥ 35% and fly ash loss on ignition ≤ 5%), and combining the pre-dispersion process of activator, the strength dispersion coefficient is reduced to within 5%.

[0046] 4. Innovative process adaptability: The synergistic effect of staged mixing (low speed → medium speed → high speed) and high-frequency vibration (10,000 times / min) eliminates weak interface areas, achieving a permeability grade of P12 and improving durability by 60%.

[0047] 5. Low-carbon and environmentally friendly benefits: Carbon emissions are reduced by 38% compared to traditional concrete. The hydrophobic modification of nano-silica fume reduces the adsorption of water-reducing agents, and the workability loss is reduced by 70%.

[0048] In summary, the solid waste-based concrete of this invention achieves high durability in tunnel lining through a composite activation system and process adaptability design, breaks through the demolding strength bottleneck in precast components, and reduces CO2 emissions by 38% compared with traditional processes, demonstrating potential for large-scale application. Attached Figure Description

[0049] Figure 1 Test results of the mechanical properties of concrete in Test Example 1 (3d strength (MPa), 28d strength (MPa));

[0050] Figure 2 The results of the sulfate corrosion resistance test (corrosion resistance coefficient K) in Example 1 are applied;

[0051] Figure 3 Application Example 1: Concrete shrinkage test results (28-day drying shrinkage (×10)) -6 ));

[0052] Figure 4 Comparison of component performance after steam curing in Example 2 (28-day strength (MPa));

[0053] Figure 5 Apply the results of the frost resistance comparison (mass loss rate) in Example 2;

[0054] Figure 6 The results of the frost resistance comparison in Example 2 (relative dynamic elastic modulus). Detailed Implementation

[0055] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 formulations and preparation methods of the examples and comparative examples are specifically defined in the following embodiments.

[0057] A solid waste-based low-carbon concrete is composed of the following raw materials in parts by weight:

[0058] 200-240 parts cement

[0059] 160-200 parts of solid waste admixture.

[0060] 600-750 parts fine aggregate,

[0061] 900-1100 parts coarse aggregate,

[0062] 8-15 parts of compound activator

[0063] 2-4 parts water-reducing agent

[0064] 140-160 parts water;

[0065] The solid waste admixture is composed of slag powder, fly ash, waste limestone powder, and tunnel slag powder in a mass ratio of (30-45):(25-35):(15-25):(10-20);

[0066] Among them, slag powder: CaO≥35wt%, SiO2≥30wt%, glass content≥85%;

[0067] Fly ash: Loss on ignition ≤5%, SiO2+Al2O3 ≥70%, fineness (45μm sieve residue) ≤12%;

[0068] Waste limestone powder: CaCO3 ≥ 90%, D50 = 5-15μm;

[0069] Tunnel muck powder: SiO2≥40%, Al2O3≥15%, activity index≥75%.

[0070] The tunnel slag powder is prepared using a three-stage grinding process: primary crushing to a particle size of <5mm, secondary ball milling to a specific surface area of ​​300-400m². 2 / kg, three-stage ultrafine grinding to a specific surface area of ​​500-600m² 2 / kg.

[0071] The composite activator is composed of sodium silicate with a water glass modulus of 1.4, sodium hydroxide, sodium sulfate, and nano silica fume in a mass ratio of 5:2:2:1.

[0072] The nano-silica fume is a surface-modified hydrophobic nano-silica fume with a specific surface area ≥20000 m². 2 / kg, surface contact angle ≥120°.

[0073] The above-mentioned method for preparing solid waste-based low-carbon concrete includes:

[0074] (1) Solid waste pretreatment: Tunnel muck is ground in three stages to a specific surface area of ​​500-600 m². 2 / kg, slag ground to a specific surface area of ​​450-550m² 2 / kg, then mixed with fly ash and waste limestone powder to obtain solid waste admixture;

[0075] (2) Activator pre-activation: Mix 30-40% of the total amount of composite activator with solid waste admixture in a high-speed mixer for 5-8 minutes to obtain pretreated solid waste admixture;

[0076] (3) Concrete mixing: Dry mix cement, pretreated solid waste admixture, coarse aggregate and fine aggregate according to the proportion for 30-60s, add the remaining activator, water-reducing agent and water and wet mix for 90-120s to obtain solid waste-based low carbon concrete.

[0077] In step (1), 0.5-1.5% of grinding aid is added during the grinding of tunnel slag. The grinding aid is a mixture of triethanolamine and polycarboxylic acid dispersant in a ratio of 1:2.

[0078] In step (2), the material temperature is controlled to be ≤45℃ during the mixing process, and nitrogen protection is used.

[0079] The wet mixing process in step (3) is carried out in three stages: low speed mixing (30-50 rpm) for 30 seconds, medium speed mixing (80-100 rpm) for 45 seconds, and high speed mixing (120-150 rpm) for 15 seconds.

[0080] I. Fine Aggregate Components

[0081] Main components and sources

[0082] Natural sand: mainly composed of quartz sand, with SiO2 content ≥90% and mud content ≤3.0%;

[0083] Recycled sand: Construction waste is crushed and screened (accounting for 30-50%), and metal impurities need to be removed;

[0084] Manufactured sand: Limestone or granite mechanically crushed, with a fineness modulus of 2.3-3.0 and a stone powder content ≤10%.

[0085] 2. Coarse Aggregate ingredients

[0086] Main components and sources

[0087] Natural crushed stone: basalt or granite, crushing value ≤12%;

[0088] Recycled aggregate: crushed concrete waste (particle size 5-25mm), water absorption ≤5%;

[0089] Industrial solid waste aggregates: steel slag (CaO≥40%), coal gangue (loss on ignition≤8%).

[0090] III. BASF PCA-1S type water-reducing agent.

[0091] IV. Cement PO 42.5.

[0092] Example 1

[0093] Raw material ratio (parts by weight)

[0094] 220 parts cement, 180 parts solid waste admixture (35% slag powder, 30% fly ash, 20% limestone powder, 15% slag powder), 680 parts fine aggregate, 1000 parts coarse aggregate, 12 parts composite activator (sodium silicate:NaOH:Na2SO4:nano silica fume = 5:2:2:1), 3 parts water-reducing agent, and 150 parts water.

[0095] Preparation method

[0096] Solid waste pretreatment:

[0097] The slag was ground in three stages (first stage crushing to 3mm, second stage ball milling to 350m). 2 / kg, three-stage ultrafine grinding to 550m 2 / kg), add 1% grinding aid (triethanolamine: polycarboxylic acid (PCA-200M BASF) = 1:2 (mass ratio));

[0098] Slag grinding to 500m 2 / kg;

[0099] Mix with fly ash and limestone powder.

[0100] Activator pre-activation: 40% activator is mixed with solid waste admixture under nitrogen protection for 6 minutes (temperature ≤40℃).

[0101] Mixing: Dry mix for 45 seconds, wet mix in three stages (low speed 30 rpm × 30 seconds, medium speed 90 rpm × 45 seconds, high speed 130 rpm × 15 seconds).

[0102] Example 2

[0103] Raw material ratio

[0104] 200 parts cement, 200 parts solid waste admixture (45% slag powder, 25% fly ash, 15% limestone powder, 15% slag powder), 750 parts fine aggregate, 1100 parts coarse aggregate, 15 parts composite activator, 4 parts water-reducing agent, and 160 parts water.

[0105] Preparation method

[0106] The slag from the tunnel was ground to a final volume of 600 m³. 2 / kg, activator pre-activation amount 35%, wet mixing high-speed stage 150rpm. The rest is the same as in Example 1.

[0107] Example 3

[0108] Raw material ratio

[0109] 240 parts cement, 160 parts solid waste admixture (30% slag powder, 35% fly ash, 25% limestone powder, 10% slag powder), 600 parts fine aggregate, 900 parts coarse aggregate, 8 parts composite activator, 2 parts water-reducing agent, and 140 parts water.

[0110] Preparation method

[0111] Grout powdered to 500m 2 / kg, activator pre-activation amount 30%, wet mixing low speed stage 50rpm. The rest is the same as in Example 1.

[0112] Comparative Example 1

[0113] Traditional solid waste concrete

[0114] raw material

[0115] 300 parts cement, 60 parts slag powder, 40 parts fly ash, fine / coarse aggregate as in Example 1, 8 parts NaOH activator, 3 parts water-reducing agent, and 150 parts water.

[0116] process

[0117] One-time feeding and wet mixing for 120 seconds, no pre-activation step.

[0118] Comparative Example 2

[0119] Activation of slag powder without holes

[0120] The raw materials are the same as in Example 1, but the slag powder is only ball-milled to 400 μm. 2 / kg, not ultrafine ground, activator does not contain nano silica fume.

[0121] Comparative Example 3

[0122] Uneven distribution of activators

[0123] The raw materials are the same as in Example 1, but the pre-activation step is omitted and the activator is added all at once.

[0124] Test Example 1

[0125] Mechanical property testing

[0126] Standard: GB / T 50081-2019 Test Methods for Physical and Mechanical Properties of Concrete

[0127] step:

[0128] Molded 100mm cube specimens were cured under standard conditions for 3 days and 28 days.

[0129] The compressive strength was tested using a universal testing machine, and the average value of 3 sets was taken.

[0130] The results are shown in Table 1 and Figure 1 .

[0131] Table 1. Test results of mechanical properties of concrete

[0132] Group 3D strength (MPa) 28-day strength (MPa) Example 1 25.3 58.7 Example 2 23.8 56.2 Example 3 22.1 54.9 Comparative Example 1 18.5 48.3 Comparative Example 2 19.2 49.8 Comparative Example 3 20.7 52.1

[0133] As shown in Table 1, the 28-day strength of Examples 1-3 all exceeded 54 MPa, significantly higher than that of Comparative Examples 1-3 (<52 MPa). The combined effect of pre-activation with the composite activator and ultrafine grinding synergistically improved the solid waste reaction rate. Example 1 exhibited the best strength due to its moderate activator dosage and high slag activity. Comparative Example 2, however, showed a 6.2% decrease in strength due to insufficient slag powder activity.

[0134] Test Example 2

[0135] Performance testing

[0136] Standard: GB / T 50080-2016 "Test Methods for Performance of Ordinary Concrete Mixtures"

[0137] step:

[0138] Test the initial slump and the loss after 1 hour;

[0139] Observe the cohesiveness and water retention.

[0140] The results are shown in Table 2.

[0141] Table 2 Results of concrete workability test

[0142] Group Initial slump (mm) Loss in 1 hour (mm) Cohesiveness Example 1 210 25 good Comparative Example 2 185 55 Secretion Comparative Example 3 195 40 slight segregation

[0143] As shown in Table 2, the hydrophobic nano-silica fume of Example 1 reduced the adsorption of water-reducing agents, with a slump loss of only 12% after 1 hour, far lower than that of Comparative Example 2 (30% loss). The three-stage stirring process effectively dispersed the micro-powder and improved its workability.

[0144] Test Example 3

[0145] Durability test

[0146] Impermeability (GB / T 50082-2009)

[0147] Example 1 achieved a permeability resistance grade of P12, while Comparative Example 1 was only P8;

[0148] Electrical flux (28d): Example 1 1200C, Comparative Example 1 2100C.

[0149] Freeze resistance (rapid freezing method)

[0150] Example 1 showed a mass loss of 1.2% after 300 freeze-thaw cycles, while Comparative Example 1 (containing high loss on ignition fly ash) showed a loss of 4.8%.

[0151] The possible mechanism is that the pre-treated solid waste particles react completely, reducing the weak interface zone; and the nano-silica fills the capillaries, refining the pore structure.

[0152] Application Example 1

[0153] Application in tunnel lining engineering

[0154] Application scenarios

[0155] A tunnel project in a mountainous area is designed with a lining thickness of 50cm. The concrete is required to have a permeability grade of ≥P10, a sulfate corrosion resistance coefficient of ≥0.85, and be able to withstand a high humidity (RH>90%) environment. Detailed Implementation

[0157] The solid waste-based low-carbon concrete mix design from Example 1 was used to pour the lining structure, with the specific process parameters as follows:

[0158] Construction process:

[0159] The pouring was done in sections, each section being 8m long, and was compacted using a high-frequency vibrator (10,000 times / min).

[0160] Maintenance involves spraying for humidification and covering with a film to maintain humidity at ≥95% for 14 days.

[0161] Scale settings:

[0162] Comparison with Lining A: Traditional C50 concrete (350 parts cement, 50 parts slag powder, no composite activator);

[0163] Comparative Lining B: Concrete (unactivated slag powder) was used in Comparative Example 2.

[0164] Test items and results

[0165] 1. Permeability test (GB / T 50082-2009)

[0166] The results are shown in Table 3.

[0167] Table 3 Permeability Test

[0168] Group impermeability grade Electric flux (28d, C) Lining of the present invention P12 1150 Comparison Lining A P8 2400 Comparison Lining B P9 1800

[0169] analyze:

[0170] The composite activator of this invention and ultrafine cavitation powder (specific surface area 550m²) 2 The porosity is significantly reduced by / kg, and the electrical flux is reduced by 52% compared with traditional concrete, meeting the requirements for high impermeability.

[0171] 2. Resistant to sulfate corrosion (GB / T 50082-2009)

[0172] Test method: Immerse in 5% Na2SO4 solution and test the compressive strength and corrosion resistance coefficient (K) after 150 wet and dry cycles.

[0173] The results are shown in Table 4 and Figure 2 .

[0174] Table 4 Sulfate Corrosion Resistance Tests

[0175] Group Corrosion resistance coefficient K Surface peeling Lining of the present invention 0.92 No visible cracks Comparison Lining A 0.68 Surface peeling depth >2mm Comparison Lining B 0.79 <![CDATA[Microcrack density: 20 cracks / m 2 >

[0176] analyze:

[0177] The hydrophobic properties of nano-silica fume (contact angle ≥120°) block SO4. 2- Invasion, while the highly active solid waste admixture reduces the Ca(OH)2 content and inhibits gypsum-type corrosion.

[0178] 3. Shrinkage test (GB / T 50082-2009)

[0179] The results are shown in Table 5 and Figure 3 .

[0180] Table 5 Concrete Shrinkage Rate Test

[0181] Group <![CDATA[28d drying shrinkage (×10 -6 )]]> Lining of the present invention 280 Comparison Lining A 420 Comparison Lining B 350

[0182] As can be seen from the test data in Table 5, the hydration reaction synchronization of pretreated solid waste particles is improved, reducing the shrinkage stress caused by the difference in hydration rates between cement and solid waste.

[0183] Application Example 2

[0184] Application in precast components

[0185] Application scenarios

[0186] A prefabrication plant produces C50 beam and slab components, requiring a demolding strength ≥20MPa (12h), a strength ≥55MPa after 28 days of steam curing, and no surface cracks. Detailed Implementation

[0188] Using the concrete mix design of Example 2, the production process is optimized as follows:

[0189] Process parameters:

[0190] Steam curing procedure: Pre-curing at 50℃ for 2 hours → Constant temperature at 80℃ for 6 hours → Cooling rate ≤15℃ / h;

[0191] Demolding time: 12 hours after pouring.

[0192] Scale settings:

[0193] Comparison component A: Traditional precast concrete (380 parts cement, 80 parts slag powder, NaOH activator);

[0194] Comparative component B: The pre-activation step of the activator is omitted (Comparative Example 3 process).

[0195] Test items and results

[0196] 1. Early strength and demolding efficiency

[0197] Early strength and demolding efficiency are shown in Table 6.

[0198] Table 6 Early Strength and Demolding Efficiency

[0199] Group 12-hour strength (MPa) Surface defect rate after demolding Components of the present invention 22.5 0％ Comparison component A 15.3 30% (corner damage) Comparison component B 18.7 12% (microcracks)

[0200] As can be seen from the data in Table 6, the pre-activation of the composite activator increases the early reaction rate of the solid waste admixture by 40%, and the 12-hour strength meets the demolding requirements, avoiding the damage caused by insufficient strength in traditional processes.

[0201] 2. Performance after steam curing

[0202] The performance results after steam curing are shown in Table 7 and Figure 4 .

[0203] Table 7 Comparison of component performance after steam curing

[0204] Group 28-day strength (MPa) <![CDATA[Surface crack density (number / m 2 )]]> Components of the present invention 58.3 2 Comparison component A 51.6 15 Comparison component B 54.8 8

[0205] As can be seen from the data in Table 7, the gradient stirring process (low speed → medium speed → high speed) of the present invention can ensure uniform distribution of the activator, avoid shrinkage differences caused by local over-excitation, and reduce cracks by 87%.

[0206] 3. Freeze resistance (rapid freezing method, 300 cycles)

[0207] The results of the comparison of frost resistance are shown in Table 8 and Figure 5 , Figure 6

[0208] Table 8. Comparison results of frost resistance

[0209] Group Quality loss rate Relative dynamic elastic modulus Components of the present invention 1.5％ 92％ Comparison component A 4.2％ 78％ Comparison component B 2.8％ 85％

[0210] As can be seen from the data in Table 8, the ultrafine powder of the slag was ground to 600 μm. 2 After / kg, the effect of filling capillary pores is improved, with 65% of the pores having a diameter of <50nm, thus blocking the migration path of moisture.

[0211] Based on the test data from the combined embodiments, the following table 9 can be obtained.

[0212] Table 9 Summary Table

[0213]

[0214] As can be seen from Table 9, the concrete and its preparation method disclosed in this invention bring the following advantages:

[0215] 1. Solid waste resource utilization benefits: Each cubic meter of concrete consumes 180 kg of industrial solid waste. Based on a solid waste treatment fee of 80 yuan / ton in 2025, the cost per cubic meter is reduced by 14.4 yuan; Carbon trading gains: Carbon emissions are reduced by 133 kg / m³. 3 Based on the national average carbon market price of 90 yuan / ton CO2, each 10,000 cubic meters of concrete generates a carbon sequestration revenue of 119,700 yuan.

[0216] 2. Improved construction efficiency

[0217] Shorter demolding cycle: Strength reaches 22.5MPa in 12 hours (traditional process requires 24 hours), and precast component production efficiency is increased by 30%;

[0218] 3. Optimized maintenance costs: The spray maintenance cycle has been reduced from 21 days to 14 days, and water and electricity consumption has been reduced by 45%.

[0219] 4. Durability enables long-term engineering

[0220] Tunnel lining life: impermeability grade P12+ and sulfate corrosion resistance coefficient 0.92, extending the service life of the structure in marine environment from 30 years to 50 years;

[0221] Freeze-thaw cycle tolerance: 92% retention rate of dynamic elastic modulus after 300 freeze-thaw cycles (compared to 78% for conventional methods), suitable for extremely cold regions in Northeast China with temperatures as low as -40℃.

[0222] In summary, the solid waste-based concrete of this invention achieves high durability in tunnel lining through a composite activation system and process adaptability design, breaks through the demolding strength bottleneck in precast components, and reduces CO2 emissions by 38% compared with traditional processes, demonstrating potential for large-scale application.

[0223] The above are merely a few preferred embodiments of the present invention, described in a relatively specific and detailed manner, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A solid waste-based low-carbon concrete, characterized in that, It consists of the following raw materials in parts by weight: 200-240 parts cement 160-200 parts of solid waste admixture. 600-750 parts fine aggregate, 900-1100 parts coarse aggregate, 8-15 parts of compound activator 2-4 parts water-reducing agent 140-160 parts water; The solid waste admixture is composed of slag powder, fly ash, waste limestone powder, and tunnel slag powder in a mass ratio of (30-45):(25-35):(15-25):(10-20); Among them, slag powder: CaO≥35wt%, SiO2≥30wt%, glass content≥85%; Fly ash: Loss on ignition ≤5%, SiO2+Al2O3 ≥70%, fineness (45μm sieve residue) ≤12%; Waste limestone powder: CaCO3 ≥ 90%, D50 = 5-15μm; Tunnel muck powder: SiO2≥40%, Al2O3≥15%, activity index≥75%.

2. The solid waste-based low-carbon concrete according to claim 1, characterized in that, The tunnel slag powder is prepared using a three-stage grinding process: primary crushing to a particle size of <5mm, secondary ball milling to a specific surface area of ​​300-400m². 2 / kg, three-stage ultrafine grinding to a specific surface area of ​​500-600m² 2 / kg.

3. The solid waste-based low-carbon concrete according to claim 1, characterized in that, The composite activator is composed of sodium silicate with a water glass modulus of 1.2-1.8, sodium hydroxide, sodium sulfate, and nano silica fume in a mass ratio of 5:2:2:

1.

4. The solid waste-based low-carbon concrete according to claim 3, characterized in that, The nano-silica fume is a surface-modified hydrophobic nano-silica fume with a specific surface area ≥20000 m². 2 / kg, surface contact angle ≥120°.

5. The method for preparing solid waste-based low-carbon concrete according to any one of claims 1-4, characterized in that, include: (1) Solid waste pretreatment: Tunnel muck is ground in three stages to a specific surface area of ​​500-600 m². 2 / kg, slag ground to a specific surface area of ​​450-550m² 2 / kg, then mixed with fly ash and waste limestone powder to obtain solid waste admixture; (2) Activator pre-activation: Mix 30-40% of the total amount of composite activator with solid waste admixture in a high-speed mixer for 5-8 minutes to obtain pretreated solid waste admixture; (3) Concrete mixing: Dry mix cement, pretreated solid waste admixture, coarse aggregate and fine aggregate according to the proportion for 30-60s, add the remaining activator, water-reducing agent and water and wet mix for 90-120s to obtain solid waste-based low carbon concrete.

6. The preparation method according to claim 5, characterized in that, In step (1), 0.5-1.5% of grinding aid is added during the grinding of tunnel slag. The grinding aid is a mixture of triethanolamine and polycarboxylic acid dispersant in a ratio of 1:(2-3).

7. The preparation method according to claim 5, characterized in that, In step (2), the material temperature is controlled to be ≤45℃ during the mixing process, and nitrogen protection is used.

8. The preparation method according to claim 5, characterized in that, The wet mixing process in step (3) is carried out in three stages: low speed mixing (30-50 rpm) for 30 seconds, medium speed mixing (80-100 rpm) for 45 seconds, and high speed mixing (120-150 rpm) for 15 seconds.

9. The application of solid waste-based low-carbon concrete as described in any one of claims 1-4 in tunnel lining engineering.

10. The application of solid waste-based low-carbon concrete as described in any one of claims 1-4 in precast components.

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