Low-carbon composite cementitious material for deep foundation engineering and preparation method thereof

Abstract

The application discloses a kind of low-carbon composite cementitious material for deep foundation pit engineering and preparation method thereof, belong to building material technical field.The low-carbon composite cementitious material for deep foundation pit engineering, including following weight parts raw materials: 70-90 parts of slag, 5-10 parts of cement, 10-30 parts of phosphogypsum, 5-20 parts of modified secondary aluminum ash, 2-10 parts of modified 5A zeolite, 5-10 parts of organic curing agent, 1-5 parts of carbide slag, 0.03-0.2 parts of alcohol amine early strength agent, 0.5-8 parts of potassium dihydrogen phosphate, 2-8 parts of magnesium oxide, 2-3.5 parts of acid activator, 20-50 parts of water, by making full use of industrial waste slag, secondary aluminum ash, carbide slag, phosphogypsum, reduce resource waste and environmental pollution, convert industrial solid waste into environmental protection building material, realize the diversification of product, functionalization, green, can replace traditional reinforced concrete material, significantly reduce the carbon emission in deep foundation pit engineering, help building industry low-carbon transformation.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a low-carbon composite cementitious material for deep foundation pit engineering and its preparation method. Background Technology

[0002] Large aluminum plants generate a large amount of secondary aluminum ash annually. The accumulation of this waste not only occupies land resources but also causes serious environmental pollution. The proper treatment and utilization of this waste has become an urgent problem to be solved. On the other hand, phosphate composite supersulfate cement is a new type of green and environmentally friendly material, and its low-carbon characteristics align with the direction of future sustainable development. Researching how to use this new low-carbon cementitious material in deep foundation pit engineering to replace traditional reinforced concrete materials has significant practical implications. This can not only reduce the carbon emissions of reinforced concrete in deep foundation pit engineering but also bring significant economic and social benefits.

[0003] Deep foundation pit engineering, as a crucial link in the development of underground space in buildings, is an important area for energy conservation and emission reduction throughout the building's life cycle. However, most deep foundation pit projects currently still rely on traditional support systems that primarily use reinforced concrete with steel as a secondary material. While this system possesses good mechanical properties, its drawbacks are becoming increasingly apparent due to its short service life, high carbon emissions, and lack of recyclability. Therefore, developing a new all-steel, low-carbon foundation pit support system has become an important direction for the low-carbon transformation of deep foundation pit engineering.

[0004] Furthermore, with the acceleration of urbanization, the demand for multi-level underground space development is constantly increasing, leading to a corresponding increase in the depth of deep foundation pit engineering. However, the excavation of deep underground spaces often faces more complex geological conditions, such as the uneven distribution of soil mechanical properties and the potential presence of unsuitable soil types and interlayers. These complex conditions pose significant challenges to the stability and safety of the foundation pit excavation process. Therefore, developing a low-carbon cementitious material suitable for deep foundation pit engineering can not only effectively improve the mechanical properties of solidified soil but also enhance the stability of the construction environment, which is of great significance for promoting the green development of deep foundation pit engineering. Summary of the Invention

[0005] The main objective of this invention is to propose a low-carbon composite cementitious material for deep foundation pit engineering, which makes full use of secondary aluminum ash waste, alleviates the environmental pollution problem caused by waste accumulation, and prepares a low-carbon cementitious material suitable for deep foundation pits, and promotes it as a green low-carbon composite cementitious material.

[0006] To achieve the above objectives, this invention proposes a low-carbon composite cementitious material for deep foundation pit engineering, comprising the following raw materials by weight: 70-90 parts slag, 5-10 parts cement, 10-30 parts phosphogypsum, 5-20 parts modified secondary alumina ash, 2-10 parts modified 5A zeolite, 5-10 parts organic curing agent, 1-5 parts carbide slag, 0.03-0.2 parts alkanolamine early strength agent, 0.5-8 parts potassium dihydrogen phosphate, 2-8 parts magnesium oxide, 2-3.5 parts acidic activator, and 20-50 parts water.

[0007] Preferably, the modified secondary aluminum ash is prepared by subjecting the secondary aluminum ash to ultrasonic-enhanced denitrification and hydrolysis treatment.

[0008] More preferably, the ultrasonic-enhanced denitrification hydrolysis treatment conditions are: ultrasonic power 200-300, liquid-solid ratio 5-10:1, reaction temperature 60-80℃, reaction time 3-5h, and pH value 10-14. Since the secondary aluminum ash contains a large amount of aluminum nitride, it will react with water to generate a large amount of ammonia. By performing ultrasonic-enhanced denitrification hydrolysis treatment on the secondary aluminum ash, the active aluminum content of the system can be enhanced.

[0009] Preferably, the modified 5A zeolite is prepared by: spreading 5A zeolite powder evenly in a ceramic boat, then placing it in a muffle furnace for thermal activation, cooling, drying, and sealing for preservation to obtain modified 5A zeolite; thermal activation of 5A zeolite is beneficial to promoting the reaction of cementitious materials, forming more gel pores to reduce the average pore size, playing the roles of microparticle filling, internal curing and cation exchange in the matrix, and is beneficial to enhancing the compressive strength of cementitious materials in the later stage.

[0010] More preferably, the thermal ignition temperature is 250-350℃ and the activation time is 1.5-3h.

[0011] More preferably, the drying temperature is 40-60℃ and the drying time is 48-72h.

[0012] Preferably, the organic curing agent is polyacrylamide; polyacrylamide (PAM) is a linear polymer with good water absorption and water retention properties. Through the polymerization, adsorption and encapsulation of polymer chains, it binds soil particles into a whole, thereby forming a spatial elastic network structure, improving the overall strength of soil particles, improving the water stability and durability of soil, and achieving the effect of soil solidification when mixed with soil in the later application stage.

[0013] Preferably, the early strength agent is an alcohol amine early strength agent, which is at least one of triethanolamine, diethanol monoisopropanolamine, and triisopropanolamine. The addition of the alcohol amine early strength agent can further reduce the total porosity and pore size distribution of the low carbon composite material, improve the resistance to drying shrinkage, significantly promote the hydration of Si and Al in the slag, generate more hydration products, and improve the compressive strength.

[0014] The potassium dihydrogen phosphate added in this invention can reduce the average pore size and porosity of low-carbon composite cementitious materials used in deep foundation pit engineering, significantly improving the early strength of the material and reducing the "frost" phenomenon on the material surface. The addition of magnesium oxide also generates magnesium hydroxide through hydration, which fills the pores of the specimen, leading to increased early strength and slowing down the time it takes for magnesium ions in the corrosion solution to enter the specimen, thus improving the resistance of low-carbon composite cementitious materials used in deep foundation pit engineering to magnesium ion corrosion.

[0015] Preferably, the acid activator is phosphoric acid; PO in phosphoric acid 4- The tetrahedral units react with amorphous SiO2 in slag, cement, and gypsum to form an amorphous (-Si-O-PO-) structure. On the other hand, they react with AlO2 in secondary aluminum ash to obtain crystalline AlPO4, which eventually condenses in the amorphous phase. In addition, secondary aluminum ash can enhance the extra magnesium aluminum spinel and gibbsite phases in the composite material, increase the amount of hydration products generated at various ages, and thus improve the strength of low-carbon composite cementitious materials used in deep foundation pit engineering.

[0016] This invention also discloses a method for preparing the low-carbon composite cementitious material for deep foundation pit engineering, comprising the following steps:

[0017] S1. Weigh each component according to the formula, mix the carbide slag and phosphogypsum, seal and place to obtain modified phosphogypsum.

[0018] S2. Mix slag, cement, modified phosphogypsum, secondary aluminum ash, modified 5A zeolite, organic curing agent, early strength agent, potassium dihydrogen phosphate, and magnesium oxide evenly to obtain a dry mixture.

[0019] S3: Phosphoric acid is added to water and mixed thoroughly to obtain an aqueous solution of phosphoric acid;

[0020] S4: Add the dry mixture to the phosphoric acid aqueous solution, mix and stir evenly to obtain a slurry;

[0021] S5: The slurry is poured into a mold, compacted on a vibrating table, and then cured under standard curing conditions to obtain the low-carbon composite cementitious material for deep foundation pit engineering.

[0022] Preferably, the sealing and placement time in step S1 is 1-2 days; the phosphogypsum is modified by sealing with industrial waste carbide slag. Since water-soluble fluorine is easily leached out and adheres to the surface of the phosphogypsum, it prevents the hydration process, resulting in a prolonged setting and hardening time, which affects the early strength of the low-carbon composite material. The carbide slag reacts with acidic residues such as fluoride ions in the phosphogypsum, converting the water-soluble fluoride ions into inert water-insoluble salts.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] 1) The low-carbon composite cementitious material for deep foundation pit engineering of the present invention makes full use of industrial waste slag, secondary aluminum ash, carbide slag and phosphogypsum, reducing resource waste and environmental pollution, transforming industrial solid waste into environmentally friendly building materials, realizing product diversification, functionalization and greening, can replace traditional reinforced concrete materials, significantly reduce carbon emissions in deep foundation pit engineering, help the low-carbon transformation of the construction industry, and meet the requirements of the "dual carbon" target;

[0025] 2) The low-carbon composite cementitious material of the present invention for deep foundation pit engineering has good mechanical strength. Its 28-day compressive strength reaches 42.2-52.3 MPa, which is significantly higher than that of traditional solidified soil (30 MPa of EP30). The strength improvement rate can reach 40.67-74.33%, which meets the requirements of deep foundation pit engineering for high strength and stability. Detailed Implementation

[0026] To avoid unnecessary details, unless otherwise specified, all items used in the following examples are commercially available products, and all methods used are conventional methods unless otherwise specified.

[0027] Example 1

[0028] A method for preparing a low-carbon composite cementitious material for deep foundation pit engineering includes the following steps:

[0029] S1. Mix 20g of carbide slag with 150g of phosphogypsum and seal the mixture to obtain modified phosphogypsum.

[0030] S2. Add 200g of secondary aluminum ash to 1600g of water, adjust the pH value to 13, and sonicate at an ultrasonic power of 250W and a reaction temperature of 75℃ for 4 hours. After the treatment is completed, filter, collect the solids, wash and dry to obtain modified secondary aluminum ash.

[0031] S3. Spread 100g of 5A zeolite powder evenly in a porcelain boat, then place it in a muffle furnace at 300℃ for thermal activation for 2 hours. After activation, cool it and dry it in a 50℃ constant temperature electric heating drying oven for 72 hours. Seal and store to obtain modified 5A zeolite.

[0032] S4. Mix 900g slag, 80g cement, modified phosphogypsum, 125g modified secondary aluminum ash, 20g modified 5A zeolite, 75g polyacrylamide, 2g triethanolamine, 42.5g potassium dihydrogen phosphate, and 60g magnesium oxide evenly to obtain a dry mixture.

[0033] S5. Add 20g of 85wt% phosphoric acid to 200g of water and mix thoroughly to obtain an aqueous solution of phosphoric acid;

[0034] S6. Add the dry mixture to the phosphoric acid aqueous solution, mix and stir evenly to obtain a slurry;

[0035] S7. The slurry is poured into a mold, compacted on a vibrating table, and then cured under standard curing conditions (temperature 20±2℃, relative humidity 95%) to obtain the low-carbon composite cementitious material for deep foundation pit engineering.

[0036] Example 2

[0037] A method for preparing a low-carbon composite cementitious material for deep foundation pit engineering includes the following steps:

[0038] S1. Mix 10g of carbide slag with 100g of phosphogypsum and seal the mixture to obtain modified phosphogypsum.

[0039] S2. Add 200g of secondary aluminum ash to 1000g of water, adjust the pH value to 10, and sonicate at an ultrasonic power of 200W and a reaction temperature of 80℃ for 5 hours. After the treatment is completed, filter, collect the solids, wash and dry to obtain modified secondary aluminum ash.

[0040] S3. Spread 100g of 5A zeolite powder evenly in a porcelain boat, then place it in a muffle furnace for thermal activation at 250℃ for 3 hours. After activation, cool it and dry it in a 40℃ constant temperature electric heating drying oven for 72 hours. Seal and store to obtain modified 5A zeolite.

[0041] S4. Mix 700g slag, 50g cement, modified phosphogypsum, 50g secondary aluminum ash, 20g modified 5A zeolite, 50g polyacrylamide, 0.3g triisopropanolamine, 5g potassium dihydrogen phosphate, and 20g magnesium oxide evenly to obtain a dry mixture.

[0042] S5. Add 20g of 85wt% phosphoric acid to 200g of water and mix thoroughly to obtain an aqueous solution of phosphoric acid;

[0043] S6. Add the dry mixture to the phosphoric acid aqueous solution, mix and stir evenly to obtain a slurry;

[0044] S7. The slurry is poured into a mold, compacted on a vibrating table, and then cured under standard curing conditions to obtain the low-carbon composite cementitious material for deep foundation pit engineering.

[0045] Example 3

[0046] A method for preparing a low-carbon composite cementitious material for deep foundation pit engineering includes the following steps:

[0047] S1. Mix 30g of carbide slag with 200g of phosphogypsum and seal the mixture to obtain modified phosphogypsum.

[0048] S2. Add 200g of secondary aluminum ash to 1600g of water, adjust the pH value to 13, and sonicate at an ultrasonic power of 250W and a reaction temperature of 75℃ for 4 hours. After the treatment is completed, filter, collect the solids, wash and dry to obtain modified secondary aluminum ash.

[0049] S3. Spread 100g of 5A zeolite powder evenly in a porcelain boat, then place it in a muffle furnace at 300℃ for thermal activation for 2 hours. After activation, cool it and dry it in a 50℃ constant temperature electric heating drying oven for 72 hours. Seal and store to obtain modified 5A zeolite.

[0050] S4. Mix 800g slag, 70g cement, modified phosphogypsum, 100g modified secondary aluminum ash, 80g modified 5A zeolite, 80g polyacrylamide, 1g triethanolamine, 40g potassium dihydrogen phosphate, and 50g magnesium oxide evenly to obtain a dry mixture.

[0051] S5. Add 30g of 85wt% phosphoric acid to 350g of water and mix thoroughly to obtain an aqueous solution of phosphoric acid;

[0052] S6. Add the dry mixture to the phosphoric acid aqueous solution, mix and stir evenly to obtain a slurry;

[0053] S7. The slurry is poured into a mold, compacted on a vibrating table, and then cured under standard curing conditions (temperature 20±2℃, relative humidity 95%) to obtain the low-carbon composite cementitious material for deep foundation pit engineering.

[0054] Comparative Example 1

[0055] A method for preparing a low-carbon composite cementitious material for deep foundation pit engineering is similar to that in Example 1, except that the phosphogypsum is not modified, and includes the following steps:

[0056] S1. Add 200g of secondary aluminum ash to 1600g of water, adjust the pH value to 13, and sonicate at an ultrasonic power of 250W and a reaction temperature of 75℃ for 4 hours. After the treatment is completed, filter, collect the solids, wash and dry to obtain modified secondary aluminum ash.

[0057] S2. Spread 100g of 5A zeolite powder evenly in a porcelain boat, then place it in a muffle furnace at 300℃ for thermal activation for 2 hours. After activation, cool it and dry it in a 50℃ constant temperature electric heating drying oven for 72 hours. Seal and store to obtain modified 5A zeolite.

[0058] S3. Mix 900g slag, 80g cement, 20g carbide slag, 150g phosphogypsum, 125g modified secondary alumina ash, 20g modified 5A zeolite, 75g polyacrylamide, 2g triethanolamine, 42.5g potassium dihydrogen phosphate, and 60g magnesium oxide evenly to obtain a dry mixture.

[0059] S4. Add 20g of 85wt% phosphoric acid to 200g of water and mix thoroughly to obtain an aqueous solution of phosphoric acid;

[0060] S5. Add the dry mixture to the phosphoric acid aqueous solution, mix and stir evenly to obtain a slurry;

[0061] S6. The slurry is poured into a mold, compacted on a vibrating table, and then cured under standard curing conditions (temperature 20±2℃, relative humidity 95%) to obtain the low-carbon composite cementitious material for deep foundation pit engineering.

[0062] Comparative Example 2

[0063] A method for preparing a low-carbon composite cementitious material for deep foundation pit engineering is similar to that in Example 1, except that the secondary aluminum ash is not modified, and includes the following steps:

[0064] S1. Mix 20g of carbide slag with 150g of phosphogypsum and seal the mixture to obtain modified phosphogypsum.

[0065] S2. Spread 100g of 5A zeolite powder evenly in a porcelain boat, then place it in a muffle furnace at 300℃ for thermal activation for 2 hours. After activation, cool it and dry it in a 50℃ constant temperature electric heating drying oven for 72 hours. Seal and store to obtain modified 5A zeolite.

[0066] S3. Mix 900g slag, 80g cement, modified phosphogypsum, 125g secondary aluminum ash, 20g modified 5A zeolite, 75g polyacrylamide, 2g triethanolamine, 42.5g potassium dihydrogen phosphate, and 60g magnesium oxide evenly to obtain a dry mixture.

[0067] S4. Add 20g of 85wt% phosphoric acid to 200g of water and mix thoroughly to obtain an aqueous solution of phosphoric acid;

[0068] S5. Add the dry mixture to the phosphoric acid aqueous solution, mix and stir evenly to obtain a slurry;

[0069] S6. The slurry is poured into a mold, compacted on a vibrating table, and then cured under standard curing conditions (temperature 20±2℃, relative humidity 95%) to obtain the low-carbon composite cementitious material for deep foundation pit engineering.

[0070] Comparative Example 3

[0071] A method for preparing a low-carbon composite cementitious material for deep foundation pit engineering is similar to that in Example 1, except that the 5A zeolite is not modified, and includes the following steps:

[0072] S1. Mix 20g of carbide slag with 150g of phosphogypsum and seal the mixture to obtain modified phosphogypsum.

[0073] S2. Add 200g of secondary aluminum ash to 1600g of water, adjust the pH value to 13, and sonicate at an ultrasonic power of 250W and a reaction temperature of 75℃ for 4 hours. After the treatment is completed, filter, collect the solids, wash and dry to obtain modified secondary aluminum ash.

[0074] S3. Mix 900g slag, 80g cement, modified phosphogypsum, 125g modified secondary aluminum ash, 20g 5A zeolite, 75g polyacrylamide, 2g triethanolamine, 42.5g potassium dihydrogen phosphate, and 60g magnesium oxide evenly to obtain a dry mixture.

[0075] S4. Add 20g of 85wt% phosphoric acid to 200g of water and mix thoroughly to obtain an aqueous solution of phosphoric acid;

[0076] S5. Add the dry mixture to the phosphoric acid aqueous solution, mix and stir evenly to obtain a slurry;

[0077] S6. The slurry is poured into a mold, compacted on a vibrating table, and then cured under standard curing conditions (temperature 20±2℃, relative humidity 95%) to obtain the low-carbon composite cementitious material for deep foundation pit engineering.

[0078] Performance testing

[0079] The low-carbon composite cementitious materials obtained in Examples 1-3 and Comparative Examples 1-3 for deep foundation pit engineering were cured for 3 days, 7 days, and 28 days, respectively. Their compressive strength was then tested according to GB / T-50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete". The 28-day compressive strength was compared with that of commercially available EP30 type solidified soil (EP30: liquid solidified soil, which is liquid during mixing and has the appearance of concrete after solidification; the solidified soil strength reaches 30 MPa, the minimum solidification time is 24 hours, and the dosage is 35 kg / m³). 3(Approximately 1000-1000 mm in diameter, suitable for bridge piers, tunnel supports, and highway subgrade solidification; a classic model of EP-type liquid solidified soil) The solidification effect was compared based on compressive strength, and the strength improvement rate was calculated using the formula: Strength Improvement Rate (%) = (28-day Compressive Strength - 30) / 30 × 100. The test results are shown in Table 1.

[0080] Table 1. Performance test results of low-carbon composite cementitious materials used in deep foundation pit engineering.

[0081]

[0082] As can be seen from the experimental results in Table 1, the low-carbon composite cementitious material for deep foundation pit engineering prepared by this invention has good mechanical properties. Compared with commercially available EP30 type solidified soil, the mechanical properties of the low-carbon composite cementitious material for deep foundation pit engineering prepared by this invention are significantly improved.

[0083] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the patent protection scope of the present invention.

Claims

1. A low-carbon composite cementitious material for deep foundation pit engineering, characterized in that, The raw materials include the following parts by weight: 70-90 parts slag, 5-10 parts cement, 10-30 parts phosphogypsum, 5-20 parts modified secondary alumina ash, 2-10 parts modified 5A zeolite, 5-10 parts organic curing agent, 1-5 parts carbide slag, 0.03-0.2 parts alkanolamine early strength agent, 0.5-8 parts potassium dihydrogen phosphate, 2-8 parts magnesium oxide, 2-3.5 parts acidic activator, and 20-50 parts water; The modified secondary aluminum ash is prepared by subjecting the secondary aluminum ash to ultrasonic-enhanced denitrification and hydrolysis treatment. The modified 5A zeolite is prepared by: spreading 5A zeolite powder evenly in a porcelain boat, then placing it in a muffle furnace for thermal activation, cooling, drying, and sealing for preservation to obtain modified 5A zeolite; The ultrasonic-enhanced denitrification and hydrolysis treatment conditions are: ultrasonic power 200-300W, liquid-solid ratio 5-10:1, reaction temperature 60-80℃, reaction time 3-5h, and pH value 10-14. The thermal activation temperature is 250-350℃, and the activation time is 1.5-3h; The acidic activator is phosphoric acid.

2. The low-carbon composite cementitious material according to claim 1, characterized in that: The drying temperature is 40-60℃, and the drying time is 48-72h.

3. The low-carbon composite cementitious material according to claim 1, characterized in that: The organic curing agent is polyacrylamide.

4. The low-carbon composite cementitious material according to claim 1, characterized in that: The alkanolamine early strength agent is at least one of triethanolamine, diethanol monoisopropanolamine, and triisopropanolamine.

5. A method for preparing the low-carbon composite cementitious material according to any one of claims 1-4, characterized in that, The process includes the following steps: S1. Weigh each component according to the formula, mix the carbide slag and phosphogypsum, seal and place to obtain modified phosphogypsum. S2. Mix slag, cement, modified phosphogypsum, modified secondary aluminum ash, modified 5A zeolite, organic curing agent, alkanolamine early strength agent, potassium dihydrogen phosphate, and magnesium oxide evenly to obtain a dry mixture. S3: Phosphoric acid is added to water and mixed thoroughly to obtain an aqueous solution of phosphoric acid; S4: Add the dry mixture to the phosphoric acid aqueous solution, mix and stir evenly to obtain a slurry; S5: The slurry is poured into a mold, compacted on a vibrating table, and then cured under standard curing conditions to obtain the low-carbon composite cementitious material for deep foundation pit engineering.

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