Method for preparing concrete early strength nucleating agent by partially depolymerizing and modifying waste PET

Abstract

The application discloses a method for preparing a concrete early-strength nucleating agent by partially depolymerizing and modifying waste PET, and particularly relates to the technical field of concrete admixtures. The method comprises the following steps: preparing a high specific surface area active spherical structure by chemically reacting a partially degraded product of waste PET polyester treated in a dihydric alcohol with a multifunctional silane. The method for preparing the early-strength nucleating agent is simple in steps, green and mild, and low in cost, has an obvious early-strength enhancing effect, does not affect or even improves the late strength, and has a waste utilization rate close to 100%, thereby effectively reducing carbon emissions in the waste disposal process. The prepared early-strength nucleating agent is rich in active hydroxyl groups on the surface, can be easily combined with calcium ions in concrete to form hydrated calcium silicate cementation products, provides more nucleation sites, effectively improves the hydration rate and early strength, and has application prospects in the fields of road rescue and highland construction.

Description

Technical Field

[0001] This invention belongs to the field of concrete admixture preparation technology, and in particular relates to a method for preparing early-strength nucleating agents for concrete by partially depolymerizing and modifying waste PET and regenerating it. Background Technology

[0002] Concrete, as a primary building material, is widely used in roads, bridges, and national defense construction. However, in high-altitude climates, concrete products suffer from bottlenecks such as long laying cycles and severe cracking, seriously affecting the long-term safe and stable operation of important projects. Furthermore, under the dual-carbon context, its high emissions and high pollution levels also restrict the development of related industries and the achievement of carbon neutrality goals.

[0003] Concrete accelerators are concrete admixtures characterized by rapid cementation, strong adaptability, and high safety. They not only improve the strength development speed and early strength of concrete but also effectively improve pore structure and density. They are widely used in practical scenarios such as road emergency repairs and high-altitude construction, playing a crucial role in concrete performance. However, the accelerators currently mainly used in engineering are inorganic salts such as sulfates and chlorides, or organic compounds such as calcium formate and triethanolamine. These accelerators require large dosages and are costly in practical applications, and face bottlenecks such as decreased corrosion resistance, poor early strength effect, and even impact on later strength. Furthermore, some traditional accelerators have high carbon emissions during production and use, easily producing toxic and harmful substances, causing serious environmental pollution.

[0004] Therefore, developing new early-strength agents from waste materials to achieve rapid early hydration of concrete not only effectively solves the problem of slow early strength development under low-temperature conditions and accelerates the progress of concrete construction, but also has important significance for the green development of the concrete industry. Summary of the Invention

[0005] This invention addresses the above-mentioned problems by providing a method for preparing early-strength nucleating agents for concrete through partial depolymerization and modification of waste PET, aiming to solve at least some of the aforementioned technical issues. Its features are:

[0006] A high specific surface area active spherical structure was constructed by chemically reacting partially degraded products of waste PET polyester treated in diol with multifunctional silanes. The prepared early-strength nucleating agent is rich in active hydroxyl groups on its surface, which readily complex with calcium ions in concrete to form hydrated calcium silicate cementitious products, providing more nucleation sites, accelerating the hydration reaction of concrete, improving the early strength of concrete, and having little impact on the later strength, thus solving the problem of slow early strength development under low-temperature conditions.

[0007] This invention first discloses a method for preparing an early-strength nucleating agent for concrete by partially depolymerizing and modifying waste PET, comprising the following steps:

[0008] (1) After cleaning and drying the PET waste, crush it and put it into a flask. Add diol and catalyst, and stir at 190-200℃ for 2-4 hours until the waste is completely dissolved to obtain a slurry.

[0009] (2) After washing, filtering and drying the slurry, mix it with multifunctional silane and add it to a 250ml three-necked flask equipped with a stirrer, thermometer and reflux condenser. Heat and stir under nitrogen atmosphere for 1-2 hours to obtain the mixture.

[0010] (3) The cooled mixture is further purified by passing it through a dialysis bag to remove small molecules and obtain a purified liquid.

[0011] (4) After the purified liquid is heated to 60-80℃ in a vacuum oven until it is completely dried, a high specific surface area active spherical concrete early strength nucleating agent can be obtained.

[0012] Further, the diol in step (1) is selected from any one of ethylene glycol, propylene glycol or diethylene glycol; the catalyst is selected from one or two of tetrabutyl titanate, zinc acetate or manganese acetate.

[0013] Further, in step (1), the mass ratio of the diol to the PET waste is 1-3:1; the amount of catalyst added is 0.5-1.5% of the total mass of the PET waste and the diol solvent.

[0014] Further, the multifunctional silane in step (2) is selected from any one of n-butyltriethoxysilane, n-octyltriethoxysilane or isobutyltriethoxysilane.

[0015] Further, in step (2), the mass ratio of the multifunctional silane to the PET waste is 0.3-0.6:1; and the heating and stirring temperature is 120-130℃.

[0016] Furthermore, the molecular rejection capacity of the dialysis bag in step (3) is 3000, and the dialysis time is 48h.

[0017] This invention also discloses a concrete early strength nucleating agent prepared by any of the above methods. The surface of the early strength nucleating agent is rich in a large number of active hydroxyl groups, which can easily complex with calcium ions in concrete to form hydrated calcium silicate cementitious products, providing more nucleation sites and promoting the early hydration process of concrete. It can meet the requirements of different use environments, and has great application potential, especially in concrete construction scenarios in high-altitude and cold regions.

[0018] Compared with existing technologies, the method of preparing early-strength nucleating agent for concrete by partial depolymerization and modified recycling of waste PET described in this invention has the following characteristics:

[0019] (1) An early nucleating agent for concrete is prepared based on PET polyester material from waste sources. The surface of the product is rich in a large number of active hydroxyl groups, which can easily complex with calcium ions in concrete to form hydrated calcium silicate cement products. This avoids the problems of low early strength increase, decreased strength and corrosion resistance in the later stage of existing early strength agents, as well as high cost and excessive carbon emissions caused by complex synthesis.

[0020] (2) By controlling the type of diol, reaction time and reaction temperature during degradation, the molecular weight and surface active group density of the resulting partially degraded waste can be adjusted, making it suitable for different concrete application scenarios.

[0021] (3) The method described in this invention achieves a utilization rate of nearly 100% for waste plastics, does not generate pollutants, has a significant early strength effect, increases early strength by 200%, and does not affect or even improves later strength. Attached Figure Description

[0022] Figure 1 This refers to the material preparation method process described in the embodiments of the present invention.

[0023] Figure 2 This is a scanning electron microscope image of the early-strength nucleating agent synthesized according to Example 1 of the present invention.

[0024] Figure 3 The values ​​are the concrete compressive strengths at 1 day, 3 days, and 28 days after the addition of the early-strength nucleating agent as described in Example 1 of this invention. Detailed Implementation

[0025] The present invention will be specifically described below through embodiments. It should be noted that the following embodiments are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above content.

[0026] Example 1:

[0027] Take 50g of PET waste, wash and dry it, then crush it and put it into a flask. Add 100g of ethylene glycol and 0.225g of zinc acetate, and stir at 190℃ and 500r / min for 2h until the waste is completely dissolved to obtain a slurry. Wash, filter and dry the slurry, then add 10g and 3g of n-butyltriethoxysilane to a 250ml three-necked flask equipped with a stirrer, thermometer and reflux condenser. Heat and stir under nitrogen atmosphere for 2h. The cooled mixture is then treated through a dialysis bag with a molecular weight cutoff of 3000 for 48 hours for further purification to remove small molecules. The purified liquid is heated to 80℃ in a vacuum oven until completely dried to obtain a high specific surface area active spherical early strength nucleating agent. When the obtained early strength agent is mixed with concrete aggregate at a ratio of 1:200, the early strength of the concrete increases by 200% and the later strength also increases by about 11%.

[0028] according to Figure 2 The results show that the synthesized early strength nucleating agent forms a spherical structure by stacking flakes. Due to its high specific surface area, the surface of the early strength nucleating agent contains a large number of active hydroxyl sites, which are easy to complex with calcium ions in concrete to form hydrated calcium silicate, thus laying the foundation for accelerating the hydration process of concrete and improving early strength.

[0029] according to Figure 3 The results show that the concrete with 0.5wt% early strength nucleating agent added has a compressive strength increase of about 200% within 24 hours, with a significant early strength effect. The compressive strength also increases after 28 days when hydration is basically complete.

[0030] Example 2:

[0031] Take 50g of PET waste, wash and dry it, then crush it and put it into a flask. Add 80g of diethylene glycol and 0.2g of zinc acetate, and stir at 200℃ and 500r / min for 3h until the waste is completely dissolved to obtain a slurry. Wash, filter and dry the slurry, then add 10g and 5g of n-butyltriethoxysilane to a 250ml three-necked flask equipped with a stirrer, thermometer and reflux condenser. Heat and stir under nitrogen atmosphere for 2h. The cooled mixture is then treated through a dialysis bag with a molecular weight cutoff of 3000 for 48 hours for further purification to remove small molecules. The purified liquid is heated to 80℃ in a vacuum oven until completely dried to obtain a high specific surface area active spherical early strength nucleating agent. When the obtained early strength agent is mixed with concrete aggregate at a ratio of 1:100, the early strength of the concrete increases by 150% without affecting the later strength.

[0032] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A method for preparing an early-strength nucleating agent for concrete by partially depolymerizing and modifying waste PET, comprising: (1) After cleaning and drying the PET waste, crush it and put it into a flask. Add diol and catalyst, and stir at 190-200℃ for 2-4 hours until the waste is completely dissolved to obtain a slurry. (2) After washing, filtering and drying the slurry, mix it with multifunctional silane and add it to a 250ml three-necked flask equipped with a stirrer, thermometer and reflux condenser. Heat and stir under nitrogen atmosphere for 1-2 hours to obtain the mixture. (3) The cooled mixture is processed through a dialysis bag to obtain a purified liquid; (4) The purified liquid is heated to 60-80℃ in a vacuum oven until completely dried to obtain the concrete early strength nucleating agent; wherein: The multifunctional silane in step (2) is selected from any one of n-butyltriethoxysilane, n-octyltriethoxysilane or isobutyltriethoxysilane; the mass ratio of the multifunctional silane to PET waste is 0.3-0.6:

1.

2. The method of claim 1, wherein: The diol mentioned in step (1) is selected from any one of ethylene glycol, propylene glycol, or diethylene glycol; The catalyst is selected from one or two of tetrabutyl titanate, zinc acetate, and manganese acetate.

3. The method of claim 1, wherein: The mass ratio of the diol to PET waste in step (1) is 1-3:1; The catalyst addition amount is 0.5-1.5% of the total mass of PET waste and diol solvent.

4. The method of claim 1, wherein: The heating and stirring temperature in step (2) is 120-130℃.

5. The method of claim 1, wherein: The molecular rejection capacity of the dialysis bag in step (3) is 3000, and the dialysis time is 48h.

6. A concrete early-strength nucleating agent prepared by the method according to any one of claims 1 to 5.

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