Bulk solid waste-based road cementing material and preparation method thereof

Abstract

The invention discloses a road cementing material based on bulk solid wastes and a preparation method thereof, and belongs to the field of geopolymer cementing materials. The material is prepared from 35-38 parts of fly ash, 15-18 parts of acid-washed red mud, 22-25 parts of carbide slag, 20-23 parts of phosphogypsum, 5-8 parts of rice hull ash, 6-9 parts of a water reducing agent and water, and the water-binder ratio is (0.4-0.5): 1. Wherein the pickling red mud is treated by 5-6% dilute sulphuric acid (pH is 8-9, and heavy metal is reduced by 30%), and the rice hull ash (SiO2 is greater than or equal to 85%) and the nano silicon dioxide (10-30nm) synergistically optimize the microstructure. The 28-day compressive strength of the material is larger than or equal to 35 MPa, the load cycle strength loss rate is smaller than or equal to 5%, the CO2 emission amount is 62 kg / t, the heavy metal leaching concentration is lower than the national standard by 50%, and the cost is only 31.6% of that of traditional cement. According to the invention, efficient synergistic utilization of four solid wastes of fly ash, red mud, carbide slag and ardealite is realized, and the concrete has the characteristics of high strength, low pollution, salt corrosion resistance and the like, is suitable for heavy-duty road base and severe cold area engineering, and has remarkable environmental protection and economic values.

Description

Technical Field

[0001] The present invention belongs to the field of geopolymers as new cementitious materials, and specifically discloses a road cementitious material based on bulk solid wastes and a preparation method thereof. Background Art

[0002] With the further development of the domestic and international ecological and environmental protection industries, and the proposal of the goals of carbon neutrality and carbon peak, the treatment of solid wastes and its derivative industries have received increasing attention from the state and provinces and cities. Bulk solid wastes are the core field of comprehensive resource utilization. Their efficient comprehensive utilization is an important part of deeply implementing the sustainable development strategy, and also an important means to improve the local environmental quality and promote the overall green transformation of economic and social development.

[0003] Fly ash (FA) is a solid waste generated by the high-temperature combustion of pulverized coal during the industrial coal combustion and cooling process. At present, thermal power generation in China accounts for about 72% of the total power generation. As one of the main solid wastes in thermal power generation, the ecological environmental pollution caused by FA is an important environmental problem faced by today's society.

[0004] Red mud (RM) is an industrial solid waste generated during the extraction of alumina from bauxite. The increasing global demand for aluminum has led to an increase in the production of RM. RM contains a large amount of harmful heavy metal elements and has a high alkalinity. Storing RM occupies land, and at the same time, it will cause the alkaline solution to seep into the ground, resulting in soil salinization and groundwater pollution. Due to the continuous increase in the storage volume of RM and its significant environmental hazards, innovative methods for its safe disposal are needed.

[0005] Calcium carbide slag (CS) is a coal-based industrial by-product generated during the production of acetylene. Due to technical defects and immature reprocessing and utilization methods, a large amount of CS that has not been effectively utilized is directly disposed of in landfills. Its high alkalinity will pollute groundwater and soil, further endangering human health.

[0006] Phosphogypsum (PG) is a by-product of phosphoric acid production and is a typical industrial solid waste. It is mainly composed of calcium sulfate dihydrate, and also contains impurities such as soluble phosphorus, fluorine, and heavy metals. During the production of one ton of phosphoric acid, about five tons of PG are generated. The global P production is about 300 million tons per year.

[0007] Currently, cement and concrete are still important materials in highway construction and maintenance. As a commonly used inorganic binder in the highway industry, the demand and consumption of cement are also increasing continuously. Among them, the usage of Portland cement is the largest. The calcination temperature of cement clinker is about 1400 °C. This process not only consumes a large amount of energy but also generates a large amount of CO2 gas, which has a greater impact on the environment. Reducing CO2 gas emissions is a very urgent task globally. Therefore, if a solid waste binder that can replace the commonly used cement in highway construction can be prepared using the above-mentioned several industrial solid wastes, it will provide a green and sustainable innovative way to solve problems such as high energy consumption in cement production and low utilization rate of common industrial solid wastes.

[0008] The existing research on solid waste binders mainly uses slag, steel slag, coal gangue, etc. as the main materials, and fly ash, red mud, etc. are commonly used as admixtures, and often an external alkaline activator needs to be added. Moreover, the co-utilization of four common industrial solid wastes, namely fly ash, red mud, carbide slag, and phosphogypsum, is less at present. Adding a large amount of admixtures will also cause a large amount of CO2 gas emissions. Therefore, it is urgent to develop and utilize a road-use binder without any admixtures based on the synergistic effect of these four common industrial solid wastes, namely fly ash, red mud, carbide slag, and phosphogypsum.

[0009] Some existing patents on solid waste binders have been developed and published. However, there is still no published patent regarding the road-use binder formed by mixing four common industrial solid waste materials, namely fly ash, red mud, carbide slag, and phosphogypsum, in a specific ratio without adding any alkaline admixtures and synergistically playing a role. And existing patents all have certain deficiencies to some extent.

[0010] (1) A lithium slag-containing all-solid waste binder and its preparation method (Application No. 202410440546.2). This patent focuses on the research of a lithium slag-containing all-solid waste binder and its preparation method, and does not involve the research of the road-use binder prepared by synergistically using multiple bulk solid wastes involved in the present invention.

[0011] (2) A steel slag-based solid waste binder containing fluidized bed fly ash, its preparation method and application (Application No. 202311431024.8). This patent focuses on the research of a steel slag-based solid waste binder containing fluidized bed fly ash, its preparation method and application. However, a liquid alkaline activator is added therein, which is not conducive to carbon reduction, energy conservation and environmental protection, and the cost is relatively high.

[0012] (3)A fully solid waste cementitious material, its preparation method and application (Application No. 202310659811.1), provides a fully solid waste cementitious material, its preparation method and application. The main raw materials are solid wastes such as coal gangue, and it does not involve several major solid wastes with less co-utilization in the present invention. The material is mainly used for filling and does not involve the use of the solid waste cementitious material of the present invention for road base construction. Summary of the Invention

[0013] In view of the deficiencies of the prior art, the present invention proposes a road-use cementitious material based on major solid wastes and its preparation method, providing a green and sustainable way for the reuse of major solid waste materials, environmental protection, and energy conservation and emission reduction in engineering construction.

[0014] The present invention includes the following technical solutions:

[0015] A road-use cementitious material based on major solid wastes, which is composed of the following components in parts by mass:

[0016] 35 - 38 parts of fly ash, 15 - 18 parts of pickled red mud, 22 - 25 parts of carbide slag, 20 - 23 parts of phosphogypsum, 5 - 8 parts of rice husk ash, 6 - 9 parts of water reducer, and the balance is water. The mass ratio of water to the above solids is the water-cement ratio, and the ratio is 0.4 - 0.5:1;

[0017] Among them, the pickled red mud is the product after the Bayer red mud is soaked in 5 - 6% dilute sulfuric acid, its pH value drops to 8 - 9, and the soluble heavy metal content is reduced by more than 30%;

[0018] The silicon dioxide content of the rice husk ash ≥ 85%, and the particle size ≤ 10μm.

[0019] Further, for the above road-use cementitious material based on major solid wastes, the fly ash is high-calcium fly ash, the calcium oxide content ≥ 18%, and it has been mechanically activated, and the specific surface area after activation ≥ 450m 2 / kg; the free calcium oxide content in the phosphogypsum ≤ 1.5%, and the purity of calcium sulfate dihydrate ≥ 90%.

[0020] Further, for the above road-use cementitious material based on major solid wastes, it also includes 0.5 - 1.5 parts of nano-silica, and the particle size of the nano-silica is 10 - 30nm.

[0021] The present invention discloses a preparation method of the above road-use cementitious material based on major solid wastes, including the following steps:

[0022] S1. Crush the pickled red mud, carbide slag, and phosphogypsum to a particle size less than 10mm;

[0023] S2. After drying the crushed materials, put them into a ball mill and grind for 30 - 60 minutes;

[0024] S3. Screen and select the powder with a particle size ≤ 50 μm for standby;

[0025] S4. Mechanically activate the fly ash to make its specific surface area ≥ 450 m 2 / kg;

[0026] S5. Weigh the pickled red mud, carbide slag, phosphogypsum in S3 and the activated fly ash in S4 in proportion, and add rice husk ash, water reducer and optional nano-silica. The mixing sequence is: first add the activated fly ash, then add the carbide slag and pickled red mud, and finally add the phosphogypsum, rice husk ash and other additives, and stir until uniform;

[0027] S6. Add water according to the water-binder ratio, stir evenly, then pour it into the mold, vibrate it to compact and level it;

[0028] S7. Leave it standing at room temperature for 24 hours to demold, and cure it for 3 - 28 days at 25 °C and a humidity ≥ 95%.

[0029] Further, in the above preparation method, the mechanical activation treatment in step S4 uses a high-energy ball mill with a rotation speed ≥ 300 rpm, a ball-to-material ratio of 5:1, and an activation time of 30 minutes.

[0030] Further, for the cementitious material prepared by the above preparation method, its 3-day compressive strength ≥ 25 MPa, 28-day compressive strength ≥ 35 MPa, and the heavy metal leaching concentration is lower than 50% of the limit value in "GB 5085.3 - 2007".

[0031] The present invention discloses the application of the above road cementitious material in the base course of heavy-duty traffic roads.

[0032] Further, in the above application, the strength loss rate of the cementitious material after 10^6 times of load cycle tests ≤ 5%.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] Through innovative designs such as pickled red mud pretreatment, mechanical activation of fly ash, multi-solid waste collaborative proportioning and nano-material enhancement, the present invention realizes an overall improvement in environmental benefits and engineering performance. Specifically, it is reflected in:

[0035] ① Environmental protection breakthrough: The pickled red mud (pH 8 - 9) reduces the leaching concentration of Pb and Cd to 0.08 - 0.10 mg / L, a decrease of more than 70% compared with untreated red mud, solving the problem of strong alkaline pollution of traditional red mud; at the same time, the all-solid waste formula does not require the calcination of cement clinker, and the CO2 emission is only 62 kg / t, a reduction of 82% compared with traditional cement.

[0036] ② High strength and durability: Through the pore filling effect of mechanically activated fly ash (specific surface area ≥ 450 m 2 / kg) and nano-silica (10 - 30 nm), the 28-day compressive strength of the material reaches 35 - 43.5 MPa, the 3-day strength ≥ 25 MPa, and the strength loss rate is ≤ 5% after 10^6 load cycles; the salt erosion loss rate is only 7.2% - 8.3%, far lower than 22.7% of ordinary cement, attributed to the synergistic dense structure of ettringite (AFt) and C-S-H gel.

[0037] ③ Multi-scenario applicability: The fluidity with a slump of 85 - 95 mm is suitable for mechanized construction, and the 7-day strength reaches 30 MPa, which can meet the rapid opening requirement of the heavy-duty road base, and the cost is only 31.6% of that of traditional cement.

[0038] ④ Efficient resource utilization: Every 10,000 tons of the material can consume 3,500 tons of fly ash, 1,500 tons of red mud and other bulk solid wastes, reducing the storage land by 10 mu, which meets the construction goal of "waste-free city". In summary, the present invention takes "solid waste resource utilization - low-carbon preparation - high-performance output" as the core, and provides a green, economical and durable cementitious material solution for road engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is the preparation industrial flow chart of a road cementitious material based on bulk solid wastes of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0040] A road cementitious material based on bulk solid wastes is composed of the following components in parts by mass:

[0041] 35 - 38 parts of fly ash, 15 - 18 parts of pickled red mud, 22 - 25 parts of carbide slag, 20 - 23 parts of phosphogypsum, 5 - 8 parts of rice husk ash, 6 - 9 parts of water reducing agent, and the balance is water. The mass ratio of water to the above solids is the water-binder ratio, and the ratio is 0.4 - 0.5:1;

[0042] Among them, the pickled red mud is the product after the Bayer red mud is soaked in 5% dilute sulfuric acid, its pH value drops to 8 - 9, and the soluble heavy metal content is reduced by more than 30%;

[0043] The silicon dioxide content of the rice husk ash ≥ 85%, and the particle size ≤ 10 μm;

[0044] Optionally, the fly ash is high-calcium fly ash, the calcium oxide content ≥ 18%, and it has been mechanically activated, and the specific surface area after activation ≥ 450 m 2 / kg; the free calcium oxide content in the phosphogypsum ≤ 1.5%, and the purity of dihydrate calcium sulfate ≥ 90%;

[0045] Optionally, it further includes 0.5 - 1.5 parts of nano-silica, and the particle size of the nano-silica is 10 - 30 nm.

[0046] The preparation method of the above road-use cementitious material refers to Figure 1 shown, and includes the following steps:

[0047] S1. Crush the pickled red mud, carbide slag, and phosphogypsum to a particle size less than 10 mm;

[0048] S2. After drying the crushed materials, put them into a ball mill respectively and grind for 30 - 60 minutes;

[0049] S3. Select and reserve the powder with a particle size ≤ 50 μm by sieving;

[0050] S4. Mechanically activate the fly ash to make its specific surface area ≥ 450 m 2 / kg;

[0051] S5. Weigh the pickled red mud, carbide slag, phosphogypsum in S3 and the activated fly ash in S4 in proportion, and add rice husk ash, water reducer and optional nano-silica. The mixing order is: first add the activated fly ash, then add the carbide slag and pickled red mud, and finally add the phosphogypsum, rice husk ash and other additives, and stir until uniform;

[0052] S6. Add water according to the water-cement ratio, stir evenly and then pour it into the mold, vibrate it to make it dense and scrape it flat;

[0053] S7. Leave it standing at room temperature for 24 hours to demold, and cure it for 3 - 28 days at 25 °C and a humidity ≥ 95%.

[0054] Optionally, in step S4, the mechanical activation treatment uses a high-energy ball mill with a rotation speed ≥ 300 rpm, a ball-to-material ratio of 5:1, and an activation time of 30 minutes.

[0055] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0056] The raw material sources are shown in Table 1.

[0057] Table 1 Experimental raw materials

[0058]

[0059] Table 2 Experimental instruments

[0060] Instrument Name Model / Parameters Crusher Jaw Crusher, Discharge Granularity ≤ 10mm Ball Mill Planetary Ball Mill, Rotation Speed 0 - 500rpm, Volume 50L High - energy Ball Mill Vibrating High - energy Ball Mill, Rotation Speed ≥ 300rpm, Ball - to - Material Ratio 5:1 Sieving Machine Vibrating Screen, Screen Mesh Aperture 50μm Universal Testing Machine Hydraulic Servo Universal Testing Machine, Measuring Range 1000kN, Accuracy ±0.5% Fatigue Testing Machine Electro - hydraulic Servo Fatigue Testing Machine, Frequency 0 - 50Hz, Load Range 0 - 500kN Mercury Intrusion Porosimeter Full - automatic Mercury Intrusion Porosimeter, Pore Size Testing Range 3nm - 360μm Curing Box Constant Temperature and Humidity Chamber, Temperature Control Range 0 - 50℃, Humidity Control Range 50 - 100% Slump Tester Standard Slump Cone (Height 300mm, Bottom Diameter 200mm, Top Diameter 100mm)

[0061] Example 1

[0062] Formulation and Preparation

[0063] Solid components (parts by mass): 35 parts of fly ash, 15 parts of pickled red mud, 22 parts of carbide slag, 20 parts of phosphogypsum, 5 parts of rice husk ash, 6 parts of water reducing agent;

[0064] Total mass of solids: 35 + 15 + 22 + 20 + 5 + 6 = 103 parts;

[0065] Water - binder ratio: 0.4:1 → Water consumption: 0.4×103 = 41.2 parts;

[0066] Nano - silica: Not added.

[0067] Nano - silica: Not added.

[0068] Preparation method:

[0069] S1. Crush the pickled red mud, carbide slag, and phosphogypsum to a particle size less than 10 mm;

[0070] S2. After drying the crushed materials, put them into a ball mill respectively and grind for 40 minutes;

[0071] S3. Screen and select the powder with a particle size ≤ 50 μm for standby;

[0072] S4. Activate the fly ash in a high - energy ball mill (rotation speed 300 rpm, ball - to - material ratio 5:1) for 30 minutes, and the specific surface area reaches 480 m 2 / kg;

[0073] S5. Weigh the pickled red mud, carbide slag, and phosphogypsum in S3 and the activated fly ash in S4 proportionally, and add rice husk ash, water reducing agent, and optional nano - silica. The mixing sequence is: first add the activated fly ash, then add carbide slag and pickled red mud, and finally add phosphogypsum, rice husk ash, and other additives, and stir until uniform;

[0074] S6. Add water according to the water - binder ratio, stir evenly, then pour it into a mold, vibrate it to compact, and scrape it flat;

[0075] S7. Leave it standing at room temperature for 24 hours to demold, and cure it for 28 days at 25℃ and humidity ≥ 95%.

[0076] Example 2

[0077] Solid components: 38 parts of fly ash, 18 parts of pickled red mud, 25 parts of carbide slag, 23 parts of phosphogypsum, 8 parts of rice husk ash, 9 parts of water reducing agent;

[0078] Total mass of solids: 38 + 18 + 25 + 23 + 8 + 9 = 121 parts;

[0079] Water-cement ratio: 0.45:1 → Water consumption: 0.45 × 121 = 54.45 parts;

[0080] Nano-silica: Add 1.0 part.

[0081] Preparation method:

[0082] Crushing and ball milling are the same as in Example 1, and the ball milling time is extended to 50 minutes;

[0083] Activation treatment of fly ash is the same as in Example 1;

[0084] Add nano-silica (particle size 20 nm) during mixing;

[0085] Curing conditions are the same as in Example 1.

[0086] Example 3

[0087] Solid components: 36 parts of fly ash, 16 parts of pickled red mud, 22 parts of carbide slag, 20 parts of phosphogypsum, 5 parts of rice husk ash, 7 parts of water reducer;

[0088] Total solid mass: 36 + 16 + 22 + 20 + 5 + 7 = 106 parts;

[0089] Water-cement ratio: 0.5:1 → Water consumption: 0.5 × 106 = 53 parts;

[0090] Nano-silica: Not added.

[0091] Preparation method:

[0092] Ball mill for 30 minutes after crushing, and sieve to obtain powder with ≤50 μm;

[0093] Activation treatment of fly ash is the same as in Example 1.

[0094] Example 4

[0095] Solid components: 37 parts of fly ash, 17 parts of pickled red mud, 24 parts of carbide slag, 22 parts of phosphogypsum, 7 parts of rice husk ash, 8 parts of water reducer;

[0096] Total solid mass: 37 + 17 + 24 + 22 + 7 + 8 = 115 parts;

[0097] Water-cement ratio: 0.42:1 → Water consumption: 0.42 × 115 = 48.3 parts;

[0098] Nano-silica: Add 1.5 parts.

[0099] Preparation method:

[0100] Extend the ball milling time to 60 minutes to improve fineness;

[0101] Increase the rotation speed to 350 rpm during the activation treatment of fly ash;

[0102] Let it stand for 10 minutes to defoam before injecting into the mold after mixing.

[0103] Others are the same as in Example 1

[0104] Example 5

[0105] Solid components: 36 parts of fly ash, 16 parts of pickled red mud, 22 parts of carbide slag, 20 parts of phosphogypsum, 6 parts of rice husk ash, 7 parts of water reducer;

[0106] Total solid mass: 36 + 16 + 22 + 20 + 6 + 7 = 107 parts;

[0107] Water-binder ratio: 0.38:1 → Water consumption: 0.38 × 107 = 40.66 parts;

[0108] Nano-silica: Add 0.5 part.

[0109] Preparation method:

[0110] Use 6% dilute sulfuric acid (pH drops to 8.5) during the pretreatment of pickled red mud;

[0111] Adjust the curing conditions to humidity 90% and temperature 20°C.

[0112] Others are the same as in Example 1

[0113] Comparative Example 1

[0114] Does not contain rice husk ash, and the fly ash is increased to 40 parts

[0115] Formula and preparation

[0116] Solid components (parts by mass): 40 parts of fly ash, 15 parts of pickled red mud, 22 parts of carbide slag, 20 parts of phosphogypsum, 6 parts of water reducer;

[0117] Total solid mass: 40 + 15 + 22 + 20 + 6 = 103 parts

[0118] Water-binder ratio: 0.4:1 → Water consumption: 0.4 × 103 = 41.2 parts

[0119] Nano-silica: Not added.

[0120] Others are the same as in Example 1

[0121] Comparative Example 2

[0122] Does not contain red mud, and the fly ash is increased to 50 parts.

[0123] Formula and preparation

[0124] Solid components (parts by mass): 50 parts of fly ash, 22 parts of carbide slag, 20 parts of phosphogypsum, 5 parts of rice husk ash, 6 parts of water reducer;

[0125] Total mass of solids: 50 + 22 + 20 + 5 + 6 = 103 parts

[0126] Water-binder ratio: 0.4:1 → Water consumption: 0.4 × 103 = 41.2 parts

[0127] Nano-silica: Not added.

[0128] Others are the same as in Example 1.

[0129] Comparative Example 3

[0130] Does not contain rice husk ash and red mud, and the fly ash is increased to 55 parts

[0131] Formulation and preparation

[0132] Solid components (parts by mass): 55 parts of fly ash, 22 parts of carbide slag, 20 parts of phosphogypsum, 6 parts of water reducer;

[0133] Total mass of solids: 55 + 22 + 20 + 6 = 103 parts

[0134] Water-binder ratio: 0.4:1 → Water consumption: 0.4 × 103 = 41.2 parts

[0135] Nano-silica: Not added.

[0136] Others are the same as in Example 1.

[0137] Comparative Example 4

[0138] Unpickled red mud

[0139] Formulation and preparation:

[0140] Solid components: 35 parts of fly ash, 15 parts of untreated red mud (pH 12), 22 parts of carbide slag, 20 parts of phosphogypsum, 5 parts of rice husk ash, 6 parts of water reducer;

[0141] Total mass of solids: 35 + 15 + 22 + 20 + 5 + 6 = 103 parts

[0142] Water-binder ratio: 0.4:1 → Water consumption: 0.4 × 103 = 41.2 parts.

[0143] Others are the same as in Example 1.

[0144] Comparative Example 5

[0145] Rice husk ash is not added

[0146] Formulation and preparation:

[0147] Solid components: 41 parts of fly ash, 15 parts of pickled red mud, 22 parts of carbide slag, 20 parts of phosphogypsum, 6 parts of water reducer;

[0148] Total mass of solids: 41 + 15 + 22 + 20 + 6 = 104 parts

[0149] Water-binder ratio: 0.4:1 → Water consumption: 0.4 × 104 = 41.6 parts

[0150] Others are the same as in Example 1.

[0151] Comparative Example 6

[0152] Unmechanically activated fly ash

[0153] Solid components: 35 parts of unactivated fly ash (specific surface area 300 m 2 / kg), 15 parts of pickled red mud, 22 parts of carbide slag, 20 parts of phosphogypsum, 5 parts of rice husk ash, 6 parts of water reducer;

[0154] Total mass of solids: 35 + 15 + 22 + 20 + 5 + 6 = 103 parts

[0155] Water-binder ratio: 0.4:1 → Water consumption: 0.4 × 103 = 41.2 parts

[0156] Others are the same as in Example 1.

[0157] Test Example 1

[0158] Verification test on compressive strength and material synergy effect

[0159] Test method:

[0160] Compressive strength: According to "Test Method for Strength of Cement Mortar (GB / T 17671-2021)", specimens of 40 × 40 × 160 mm are prepared, cured under standard conditions for 3 days and 28 days, and the compressive strength is tested using a universal testing machine.

[0161] Load cycle test: Using a hydraulic servo fatigue testing machine, simulating heavy traffic loads (10^6 cycles, frequency 5 Hz, stress level 70% of the ultimate strength), the loss rate is calculated based on the ratio of the remaining strength after testing to the initial strength.

[0162] The results are shown in Table 3

[0163] Table 3 Verification test on compressive strength and material synergy effect

[0164]

[0165] It can be seen from the data in Table 3 that the solution of the present invention has the following beneficial effects:

[0166] Synergistic effect: The 28-day compressive strength of Example 1 (synergistic utilization of four solid wastes) reached 38.2 MPa, significantly higher than that of Comparative Example 1 (without rice husk ash, 26.8 MPa) and Comparative Example 3 (without red mud + without rice husk ash, 20.5 MPa), proving that fly ash, red mud, carbide slag, and phosphogypsum are all indispensable.

[0167] Nano-enhancement: The early strength of Example 2 (adding nano-SiO2) increased by 12.6%. The nano-particles optimized the microstructure by filling pores and accelerating the hydration reaction.

[0168] Necessity of mechanical activation: In Comparative Example 6 (unactivated fly ash), the 28-day strength decreased by 36.9% due to insufficient activity, highlighting the key role of mechanical activation in the activity of fly ash.

[0169] Test Example 2

[0170] Test on environmental protection performance and heavy metal solidification effect

[0171] Heavy metal leaching: According to the "Solid Waste Leaching Toxicity Leaching Method Sulfuric Acid-Nitric Acid Method (HJ / T 299-2007)", the concentrations of Pb and Cd in the leachate were detected and compared with the limits of the "Identification Standard for Hazardous Wastes (GB 5085.3-2007)".

[0172] CO2 emission calculation: Based on the energy consumption of raw material production and the process carbon emission factors (fly ash: 0.01 t CO2 / t, red mud: 0.02 t CO2 / t, traditional cement clinker: 0.85 t CO2 / t), the life-cycle emissions were calculated.

[0173] The results are shown in Table 4.

[0174] Table 4 Test on environmental protection performance and heavy metal solidification effect

[0175]

[0176] It can be seen from Table 4 that the solution of the present invention has the following beneficial effects.

[0177] Acid washing to reduce toxicity: The Pb leaching concentration of Example 1 was only 0.08 mg / L (0.35 mg / L for Comparative Example 4 without acid-washed red mud), and the acid washing process effectively reduced the heavy metal migration risk.

[0178] Low-carbon advantage: The CO2 emission of the all-solid-waste formula was 62 kg / t, only 17.7% of that of traditional cement (350 kg / t), meeting the carbon neutrality goal.

[0179] Energy consumption optimization: The energy consumption of mechanical activation (0.5 kWh / t) was much lower than that of cement clinker calcination (1500 kWh / t), with significant energy-saving effect.

[0180] Test Example 3

[0181] Durability and Porosity Tests

[0182] Test Methods

[0183] Salt Erosion Test: The specimens were immersed in 5% Na2SO4 solution for 90 days, and the loss rate of compressive strength was measured.

[0184] Porosity Test: The porosity of the material was determined by mercury intrusion porosimetry (MIP), and the microstructure was observed by scanning electron microscopy (SEM).

[0185] Analysis of Hydration Products: The composition of hydration products was characterized by X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS).

[0186] The results are shown in Table 5

[0187] Table 5 Durability and Porosity Tests

[0188]

[0189] Salt Erosion Resistance: The salt erosion strength loss rate of Example 2 was only 7.2%, far lower than that of ordinary cement (22.7%). This is attributed to the ettringite (AFt) and monosulfate calcium sulfoaluminate (AFm) generated in the solid waste system filling the pores and inhibiting sulfate erosion.

[0190] Microscopic Optimization: The combination of rice husk ash and nano-SiO2 synergistically reduced the porosity (12.1% in Example 2 vs. 21.8% in Comparative Example 5 without rice husk ash). SEM showed that the proportion of C-S-H gel reached 70% and the structure was dense.

[0191] Test Example 4

[0192] Economic Benefits and Engineering Applicability

[0193] Cost Accounting: Based on the market prices in 2024 (fly ash: 50 yuan / ton, red mud: 30 yuan / ton, traditional cement: 380 yuan / ton), the raw material costs were calculated.

[0194] Construction Fluidity: The fluidity of the fresh cementitious material was tested using a slump cone.

[0195] Curing Period: The strength development at different curing days was tested, and the standard strength was referred to the "Technical Specification for Construction of Highway Pavement Base (JTG / T F20-2015)".

[0196] The results are shown in Table 6.

[0197] Table 6 Economic Benefits and Engineering Applicability

[0198]

[0199]

[0200] From the data in Table 6, it can be seen that the present invention has the following advantages:

[0201] Cost advantage: The raw material cost of Example 1 is 120 yuan / ton, which is only 31.6% of that of traditional cement (380 yuan / ton), and the use of solid waste resources reduces the local environmental protection governance cost.

[0202] Fast construction: The 7-day strength of Example 1 reaches 30 MPa, meeting the requirement of rapid opening to traffic for road subgrades, and the maintenance period is shortened to 1 / 4 of that of traditional cement.

[0203] Wide applicability: The slump of 85 ± 5 mm indicates that the material has moderate fluidity, is suitable for mechanical paving, and covers various scenarios from rural roads to heavy-duty highways.

[0204] The above are several limited preferred embodiments of the present invention, and their descriptions are relatively specific and detailed. However, it should not be construed as a limitation of the scope of the present invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A road-use cementitious material based on bulk solid waste, characterized in that, It consists of the following components by mass parts: 35 - 38 parts of fly ash, 15 - 18 parts of pickled red mud, 22 - 25 parts of carbide slag, 20 - 23 parts of phosphogypsum, 5 - 8 parts of rice husk ash, 6 - 9 parts of water reducing agent, and the balance is water. The mass ratio of water to the above solids is the water - binder ratio, and the ratio is 0.4 - 0.5:1; Among them, the pickled red mud is the product after the Bayer red mud is soaked in 5 - 6% dilute sulfuric acid, its pH value drops to 8 - 9, and the soluble heavy metal content is reduced by more than 30%; The rice husk ash has a silica content of ≥85% and a particle size of ≤10μm.

2. The road cementitious material according to claim 1, characterized in that The fly ash is high-calcium fly ash with a calcium oxide content of ≥18% and has been mechanically activated, with a specific surface area of ≥450 m 2 / kg after activation; the free calcium oxide content in the phosphogypsum is ≤1.5%, and the purity of calcium sulfate dihydrate is ≥90%.

3. The road-use cementitious material according to claim 1, wherein It also includes 0.5 - 1.5 parts of nano - silica, and the particle size of the nano - silica is 10 - 30nm.

4. The preparation method of the road cementitious material according to any one of claims 1-3, characterized in that, It includes the following steps: S1. Crush the pickled red mud, carbide slag, and phosphogypsum to a particle size less than 10mm; S2. After drying the crushed materials, put them into a ball mill respectively and grind for 30 - 60 minutes; S3. Screen and select the powder with a particle size of ≤50μm for standby; S4. Mechanically activate the fly ash to make its specific surface area ≥ 450 m 2 / kg; S5. Weigh the pickled red mud, carbide slag, and phosphogypsum in S3 and the activated fly ash in S4 according to the proportion, and add rice husk ash, water reducing agent and optional nano - silica. The mixing order is: first add the activated fly ash, then add the carbide slag and pickled red mud, and finally add phosphogypsum, rice husk ash and other additives, and stir until uniform; S6. Add water according to the water - binder ratio, stir evenly and then pour it into the mold, vibrate it to make it dense and scrape it flat; S7. Let it stand at room temperature for 24 hours and then demold, and cure it for 3 - 28 days at 25℃ and a humidity of ≥95%; 5. The preparation method according to claim 4, characterized in that, In step S4, the mechanical activation treatment uses a high - energy ball mill with a rotation speed of ≥300rpm, a ball - to - material ratio of 5:1, and an activation time of 30 minutes.

6. The road cementitious material according to claim 1, characterized in that, The 3 - day compressive strength is ≥25MPa, the 28 - day compressive strength is ≥35MPa, and the heavy metal leaching concentration is lower than 50% of the limit value in 《GB 5085.3 - 2007》.

7. Application of the road - use cementitious material as described in claim 1 in the base layer of heavy - duty traffic roads.

8. The application according to claim 7, wherein After 10^6 times of load - cycle tests, the strength loss rate of the cementitious material is ≤5%.

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