A porous lightweight geopolymer cement and a method of making the same

Abstract

This invention relates to the field of green building materials technology, and discloses a porous lightweight geopolymer cement and its preparation method, comprising the following raw materials in parts by weight: 55.0-70.0 parts metakaolin, 30.0-45.0 parts granulated blast furnace slag powder, 70.0-90.0 parts composite alkali-activated liquid, 6.0-12.0 parts waste cooking oil, 0.6-2.0 parts photovoltaic cutting silicon waste slag, and 1.5-4.0 parts waste polyester plastic powder. This invention aligns with the concept of a circular economy, achieving complete solid waste treatment of raw materials through the synergistic utilization of industrial and domestic wastes such as metakaolin, granulated blast furnace slag powder, waste cooking oil, photovoltaic cutting silicon waste slag, and waste polyester plastic powder. This promotes the resource utilization of solid waste and reduces production costs. Simultaneously, by using a geopolymer room-temperature or self-heating curing process to replace the high-temperature calcination process of traditional Portland cement, energy consumption and CO₂ emissions are significantly reduced, resulting in a novel green cementitious material with both high performance and low-carbon environmental protection characteristics.

Description

Technical Field

[0001] This invention relates to the field of green building materials technology, specifically to a porous lightweight geopolymer cement and its preparation method. Background Technology

[0002] Cement, as a fundamental hydraulic cementitious material, is an indispensable building material in modern civil engineering construction. However, ordinary cement-based materials suffer from low thermal insulation efficiency due to their high density and thermal conductivity, limiting their application in building energy conservation. To meet the demands of building energy conservation, various thermal insulation materials have emerged on the market, but they generally suffer from the inability to achieve all performance goals simultaneously: organic foam materials, while lightweight, are prone to aging, difficult to recycle, and have poor environmental performance; mineral wool materials, while durable, are heavy, complex to install, and contain harmful substances. Therefore, developing a porous lightweight geopolymer cement that combines lightweight, high strength, and excellent thermal insulation properties to overcome the common defects of existing insulation materials has become an important issue urgently needing to be addressed in the field of green building materials.

[0003] In current technologies, the preparation of porous cement-based materials still primarily relies on traditional Portland cement clinker as the cementitious matrix. The production process of Portland cement involves the high-temperature calcination of raw materials such as limestone in a rotary kiln. This process not only consumes large amounts of fossil fuels but also results in massive carbon dioxide emissions, placing a heavy burden on the environment. Although technologies for preparing geopolymers using slag and fly ash have emerged, most existing processes still struggle to achieve efficient and synergistic utilization of various industrial and domestic wastes, and often rely on external heat sources for heating and solidification, failing to fully utilize the potential of chemical reactions. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a porous lightweight geopolymer cement and its preparation method, which solves the problems of traditional porous cement material production relying on high-energy-consuming and high-emission high-temperature calcination processes, as well as the difficulty in achieving complete solid waste treatment of raw materials and low-carbon energy-saving preparation.

[0005] In a first aspect, the present invention provides a porous lightweight geopolymer cement, comprising the following raw materials in parts by weight:

[0006] Metakaolin 55.0~70.0 parts, granulated blast furnace slag powder 30.0~45.0 parts, composite alkali activation solution 70.0~90.0 parts, waste cooking oil 6.0~12.0 parts, photovoltaic cutting silicon waste slag 0.6~2.0 parts, waste polyester plastic powder 1.5~4.0 parts.

[0007] By adopting the above technical solution, metakaolin and granulated blast furnace slag powder are used as the cementitious matrix of the geopolymer, and activated by a composite alkaline activating solution, replacing traditional Portland cement. This method utilizes industrial and domestic waste and reduces carbon emissions. In the system, photovoltaic cutting silicon waste reacts in an alkaline environment to generate gas for foaming, simultaneously releasing chemical reaction heat as an internal heat source. This heat promotes the alkaline hydrolysis reaction of waste polyester plastic powder, generating terephthalate and ethylene glycol. The generated terephthalate reacts with the granulated blast furnace slag powder... Calcium ions dissolved from slag powder combine to form calcium terephthalate whiskers in situ, which are distributed in the pore walls of the matrix, enhancing the compressive strength of the material. At the same time, waste cooking oil undergoes saponification under alkaline conditions to generate glycerol. This glycerol, together with ethylene glycol produced by the hydrolysis of waste polyester plastic powder, forms a diol water-retaining network in the pore liquid phase, reducing the surface tension of the pore solution and delaying water evaporation, thus inhibiting the drying shrinkage of the matrix. This process produces a porous lightweight geopolymer cement with good lightness, high strength, fire resistance, and volume stability.

[0008] Preferably, the metakaolin has an average particle size D50 of 3.0~5.0μm and a SiO2 content ≥52%;

[0009] The granulated blast furnace slag powder has a specific surface area of ​​400~450m² / kg and an alkalinity coefficient of 0.9~1.1.

[0010] By adopting the above technical solution, the average particle size and SiO2 content of metakaolin are limited to provide the active silica-alumina components required to participate in the geopolymerization reaction to construct the cementitious skeleton. By limiting the specific surface area and alkalinity coefficient of granulated blast furnace slag powder, the dissolution concentration of calcium ions in the system is controlled, so that the dissolved calcium ions can react with the terephthalate ions generated by the alkaline hydrolysis of waste polyester plastic powder, and generate calcium terephthalate whiskers in situ in the pore walls of the porous matrix, thus constructing a three-dimensional reinforced and toughened network and improving the compressive strength of porous lightweight geopolymer cement.

[0011] Preferably, the composite alkali activating solution is prepared from industrial water glass, sodium hydroxide and water, wherein the mass ratio of industrial water glass, sodium hydroxide and water is 6~10:1:2~5.

[0012] By adopting the above technical solution, and using a composite alkaline activating solution prepared from industrial water glass, sodium hydroxide, and water, the alkalinity and silicon-aluminum ratio of the system are adjusted. The alkaline environment provided stimulates the reaction of photovoltaic cutting silicon waste slag, releasing chemical reaction heat, which provides a heat source and reaction conditions for the alkaline hydrolysis of waste polyester plastic powder, generating terephthalate and ethylene glycol. At the same time, it triggers the saponification reaction of waste catering oil to generate glycerol. The generated terephthalate combines with calcium ions to form whiskers to strengthen the matrix, and the generated ethylene glycol and glycerol form a diol water-retaining network to reduce the drying shrinkage value. Meanwhile, the active silicon component provided by industrial water glass participates in the geological polymerization reaction to construct the gel skeleton, giving the porous lightweight geological polymer cement mechanical strength.

[0013] Preferably, the particle size range of the waste polyester plastic powder is 45~75μm;

[0014] The elemental Si content in the photovoltaic cutting silicon waste residue is ≥90%.

[0015] By adopting the above technical solution, and by limiting the elemental Si content in the photovoltaic cutting silicon waste slag, sufficient high chemical reaction heat is released during the reaction with alkali as an internal heat source, driving the alkaline hydrolysis of waste polyester plastic powder in situ. By limiting the particle size range of the waste polyester plastic powder, the reaction specific surface area is increased to match the release cycle of the above chemical reaction heat, promoting its full hydrolysis to generate terephthalate and ethylene glycol. The generated terephthalate and calcium ions in the slag self-assemble in situ to generate calcium terephthalate whiskers with high aspect ratio, constructing a three-dimensional reinforcing and toughening network in the pore walls of the porous matrix, improving the compressive strength of the material. At the same time, the generated ethylene glycol participates in the formation of a diol water-retaining network in the pore liquid phase, effectively reducing the surface tension of the pore solution and delaying water evaporation, reducing the drying shrinkage value of the geopolymer, and improving the crack resistance and volume stability of the material.

[0016] Secondly, the present invention provides a method for preparing porous lightweight geopolymer cement, comprising the following steps:

[0017] S1. After the photovoltaic cutting silicon waste residue and the waste polyester plastic micro powder are mixed evenly, they are added to the waste catering oil and a uniform oil-in-solid structure suspension is formed under shearing action.

[0018] S2. The metakaolin and the granulated blast furnace slag powder are dry-mixed, and then the composite alkali activation liquid is added and stirred to obtain the initial slurry of the geopolymer matrix.

[0019] S3. Add the oil-encapsulated solid structure suspension obtained in S1 to the geopolymer matrix slurry obtained in S2, stir and disperse, and then pour it into a mold.

[0020] S4. Place the mold after casting in an insulated or semi-insulated environment, and use the heat generated by the chemical reaction between the photovoltaic cutting silicon waste residue inside the slurry and the alkali to perform self-heating curing. After demolding and curing, the product is obtained.

[0021] By adopting the above technical solution, a suspension with an oil-encapsulated solid structure is constructed in S1, which encapsulates photovoltaic cutting silicon waste slag and waste polyester plastic micro powder in waste catering oil. This achieves pre-dispersion and delayed release of foaming components and reinforcing precursors. Combined with stirring and dispersion in S3, it ensures the formation of a microporous structure with uniform pore size. In the adiabatic or semi-adiabatic environment of S4, the chemical reaction heat released by the reaction between photovoltaic cutting silicon waste slag and alkali inside the slurry achieves self-heating solidification, replacing the external heat source and reducing energy consumption. This internal heat source simultaneously drives the waste polyester plastic micro powder to undergo alkaline hydrolysis and the waste catering oil to undergo saponification. The generated terephthalate ions and calcium ions in the slag self-assemble in situ to form calcium terephthalate whiskers to construct a three-dimensional reinforcing and toughening network. At the same time, the generated ethylene glycol and glycerol form a diol water-retaining network in the porous liquid phase to reduce the drying shrinkage value. Thus, a porous lightweight geopolymer cement with good lightness, high strength, good volume stability, and low carbon and environmental protection is prepared.

[0022] Preferably, in step S1, the rotation speed during shearing is 2500~3500 rpm, and the shearing dispersion lasts for 10~15 minutes until a hydrophobic suspension is formed.

[0023] By adopting the above technical solution, and by setting the rotation speed and time of the shearing action, mechanical shearing force is provided to uniformly disperse and suspend the photovoltaic cutting silicon waste residue and waste polyester plastic micro powder in the continuous phase of catering waste oil, forming a uniform oil-encapsulated solid structure hydrophobic suspension. This structure utilizes the hydrophobic properties of the oil layer to physically isolate the solid particles inside, preventing the foaming component from contacting the alkaline solution too early in the initial stage of subsequent mixing, thus achieving delayed release and uniform dispersion of the foaming agent, thereby obtaining a microporous structure with uniform pore size after curing.

[0024] Preferably, in step S2, the compound alkali activating solution is allowed to stand and age for 24 hours before being added. The stirring is divided into two stages: low-speed stirring and high-speed stirring. The low-speed stirring speed is 100~150 rpm and the time is 1~2 minutes. The high-speed stirring speed is 250~350 rpm and the time is 3~4 minutes.

[0025] By adopting the above technical solution, the composite alkali activating liquid is allowed to stand and age, so that the components inside the solution reach chemical equilibrium and the heat of dissolution is eliminated, ensuring the stability of the activator performance. Low-speed stirring is used to initially wet the metakaolin and granulated blast furnace slag powder with the composite alkali activating liquid. Then, the strong shear force generated by high-speed stirring breaks up the powder agglomeration, promotes the depolymerization of solid raw materials and the dissolution of active silicon, aluminum and calcium ions. The fully dissolved calcium ions provide a calcium source for the subsequent in-situ self-assembly with terephthalate to form calcium terephthalate whiskers. At the same time, the depolymerized silicon and aluminum components condense to form a geopolymer gel skeleton, thereby obtaining a uniform and highly reactive geopolymer matrix slurry, which is beneficial to improving the compressive strength of porous lightweight geopolymer cement.

[0026] Preferably, in step S3, the stirring speed is 250~300 rpm and the stirring time is 45~90 seconds.

[0027] By adopting the above technical solution, the oil-encapsulated solid structure suspension obtained in S1 is uniformly dispersed in the geopolymer matrix slurry obtained in S2 through stirring, and the oil film is maintained to encapsulate the internal solid to avoid premature demulsification reaction of the foaming component before casting. This uniform dispersion ensures the delayed release and uniform foaming of the subsequent foaming agent, and obtains a microporous structure with uniform pore size. At the same time, it also ensures that the waste polyester plastic powder is uniformly distributed in the matrix.

[0028] Preferably, in step S3, the filling volume poured into the mold is 40% to 60% of the mold volume.

[0029] By adopting the above technical solution, by limiting the filling volume poured into the mold, space is reserved for the foaming and expansion of the slurry. This adapts to the volume increase caused by the reaction of photovoltaic cutting silicon waste with alkali during the subsequent self-heating curing process, so that the slurry can fill the mold cavity after expansion, thereby producing porous lightweight geopolymer cement with the target density. This realizes the lightweight characteristics of the material, making it suitable for building exterior wall insulation, roof insulation and lightweight filling and other fields.

[0030] Preferably, in step S4, the ambient temperature of the adiabatic or semi-adiabatic environment is 20~30℃, the relative humidity is ≥90%, no external heat source is applied during the curing process, and the peak temperature inside the slurry during the self-heating curing process is controlled at 65℃~95℃.

[0031] By adopting the above technical solution, by setting the ambient temperature and relative humidity of the adiabatic or semi-adiabatic environment, and without applying an external heat source during the curing process, the self-heating curing is achieved by utilizing and accumulating the chemical reaction heat released by the reaction between photovoltaic cutting silicon waste slag and alkali inside the slurry. This replaces the traditional high-temperature external heat source curing, significantly reducing energy consumption. By controlling the peak temperature inside the slurry during the self-heating curing process, the thermodynamic conditions required for the alkaline hydrolysis of waste polyester plastic powder and the saponification reaction of waste catering oil are provided. This drives the generated terephthalate ions to self-assemble in situ with calcium ions in the slag to form calcium terephthalate whiskers, constructing a three-dimensional reinforcing and toughening network in the porous matrix pore walls to improve compressive strength. At the same time, the generated ethylene glycol and glycerol form a diol water-retaining network, reducing the drying shrinkage value of the geopolymer and improving the volume stability of the material.

[0032] This invention provides a porous lightweight geopolymer cement and its preparation method. It has the following beneficial effects:

[0033] 1. This invention aligns with my country's circular economy development philosophy. By utilizing industrial and domestic waste such as metakaolin, granulated blast furnace slag powder, waste cooking oil, photovoltaic silicon waste slag, and waste polyester plastic powder, it achieves complete solid waste treatment of raw materials. This reduces production costs and promotes the resource utilization of solid waste, turning waste into treasure, which is in line with the waste recycling encouragement direction of the "Industrial Structure Adjustment Guidance Catalogue (2024 Edition)". Simultaneously, the use of geopolymer room-temperature or self-heating curing technology replaces the high-temperature calcination process of traditional Portland cement, significantly reducing energy consumption and CO2 emissions, achieving energy conservation and carbon reduction in the preparation process. The geopolymer cement produced by this invention is a new type of green cementitious material, a preferred alternative for emission reduction and carbon reduction in the cement industry. It combines high performance with low-carbon and environmentally friendly characteristics, effectively promoting the green and low-carbon transformation of the cement industry, promoting the high-quality development of the green building materials industry, and helping to achieve the "dual carbon" goal.

[0034] 2. The porous lightweight geopolymer cement prepared by this invention has comprehensive properties such as lightweight, high strength, heat insulation, fire resistance, and water repellency. Its overall performance is superior to flammable organic foam materials, low-strength and easily pulverized mineral wool, and ordinary concrete insulation boards with high thermal conductivity. It can be widely used in building exterior wall insulation, roof insulation, lightweight filling, industrial insulation and other fields, effectively solving the industry problem that traditional building insulation materials cannot simultaneously take into account fire safety, heat insulation efficiency and durability.

[0035] 3. This invention utilizes the high chemical reaction heat released by the reaction of photovoltaic cutting silicon waste slag with alkali as an internal heat source to drive the alkaline hydrolysis of waste polyester plastic powder in situ. The generated terephthalate ions and calcium ions in the slag self-assemble in situ to form calcium terephthalate whiskers with high aspect ratio. A three-dimensional reinforced and toughened network is constructed in the pore walls of the porous matrix, which improves the compressive strength of the material and overcomes the defects of low strength and easy cracking of traditional porous materials.

[0036] 4. This invention utilizes waste cooking oil to construct an oil-encapsulated solid pre-dispersion structure, achieving delayed release and uniform dispersion of the foaming agent, and obtaining a microporous structure with uniform pore size. At the same time, the glycerol produced by oil saponification and the ethylene glycol produced by PET hydrolysis form a diol water-retaining network in the pore liquid phase, effectively reducing the surface tension of the pore solution and delaying water evaporation, reducing the drying shrinkage value of the geopolymer, and improving the crack resistance and volume stability of the material.

[0037] 5. This invention offers significant cost reduction and efficiency improvement economic benefits. On the raw material side, it fully utilizes solid waste to replace natural limestone and other mineral resources, resulting in extremely low raw material acquisition costs and even generating revenue from waste disposal. On the production side, it completely abandons the traditional high-temperature calcination process for cement, relying instead on a chemical reaction within the system to achieve self-heating curing. This not only saves substantial fuel costs and investment in high-temperature heavy equipment but also significantly reduces potential compliance costs due to carbon emissions. On the application side, the material produced by this invention combines structural load-bearing capacity with excellent thermal insulation performance, enabling integrated insulation structure in building construction. This eliminates the cumbersome process of additionally laying flammable insulation boards on the exterior walls of traditional buildings, significantly reducing the overall cost and labor costs of construction projects. Attached Figure Description

[0038] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0039] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Example 1

[0041] This invention provides a porous lightweight geopolymer cement, comprising the following raw material components in parts by weight:

[0042] Metakaolin 55.0 parts, granulated blast furnace slag powder 30.0 parts, composite alkali activation solution 70.0 parts, waste cooking oil 6.0 parts, photovoltaic cutting silicon waste slag 0.6 parts, waste polyester plastic powder 1.5 parts.

[0043] Among them, the average particle size D50 of metakaolin is 3.0μm, and the SiO2 content is ≥52%; the specific surface area of ​​granulated blast furnace slag powder is 400m² / kg, and the alkalinity coefficient Kb is 0.9; the particle size range of waste polyester plastic powder is 45μm; and the elemental Si content in photovoltaic cutting silicon waste slag is ≥90%.

[0044] The composite alkali activating solution is prepared from industrial water glass, sodium hydroxide and water, wherein the mass ratio of industrial water glass, sodium hydroxide and water is 6:1:2.

[0045] The above-mentioned method for preparing polymer cement includes the following steps:

[0046] S1. After uniformly mixing photovoltaic cutting silicon waste residue and waste polyester plastic micro powder, add it to waste catering oil and form a uniform oil-in-solid structure suspension under shearing action.

[0047] The rotation speed during shearing is 2500 rpm, and the shearing dispersion lasts for 10 minutes until a hydrophobic suspension is formed.

[0048] S2. Mix metakaolin with granulated blast furnace slag powder dry, then add composite alkali activation liquid and stir to obtain the initial slurry of geopolymer matrix;

[0049] The compound alkali activating solution was allowed to stand and age for 24 hours before being added. The stirring was divided into two stages: low-speed stirring and high-speed stirring. The low-speed stirring speed was 100 rpm for 1 minute, and the high-speed stirring speed was 250 rpm for 3 minutes.

[0050] S3. Add the oil-encapsulated solid structure suspension obtained in S1 to the geopolymer matrix slurry obtained in S2, stir and disperse, and then pour it into a mold.

[0051] The stirring speed is 250 rpm and the stirring time is 45 seconds; the filling volume poured into the mold is 40% of the mold volume.

[0052] S4. Place the mold after casting in an insulated or semi-insulated environment, and use the heat of chemical reaction generated by the reaction between photovoltaic cutting silicon waste residue and alkali inside the slurry to perform self-heating curing. After demolding and curing, the mold is obtained.

[0053] The ambient temperature of the thermal or semi-thermal environment is 20℃, the relative humidity is ≥90%, no external heat source is applied during the curing process, and the peak temperature inside the slurry during the self-heating curing process is controlled at 65℃.

[0054] Example 2

[0055] This invention provides a porous lightweight geopolymer cement, comprising the following raw material components in parts by weight:

[0056] Metakaolin 62.5 parts, granulated blast furnace slag powder 37.5 parts, composite alkali activation solution 80.0 parts, waste cooking oil 9.0 parts, photovoltaic cutting silicon waste slag 1.3 parts, waste polyester plastic powder 2.8 parts.

[0057] Among them, the average particle size D50 of metakaolin is 4.0μm, and the SiO2 content is ≥52%; the specific surface area of ​​granulated blast furnace slag powder is 425m² / kg, and the alkalinity coefficient Kb is 1.0; the particle size range of waste polyester plastic powder is 60μm; and the elemental Si content in photovoltaic cutting silicon waste slag is ≥90%.

[0058] The composite alkali activating solution is prepared from industrial water glass, sodium hydroxide and water, wherein the mass ratio of industrial water glass, sodium hydroxide and water is 8:1:3.5.

[0059] The above-mentioned method for preparing polymer cement includes the following steps:

[0060] S1. After uniformly mixing photovoltaic cutting silicon waste residue and waste polyester plastic micro powder, add it to waste catering oil and form a uniform oil-in-solid structure suspension under shearing action.

[0061] The rotation speed during shearing was 3000 rpm, and the shearing dispersion lasted for 12.5 minutes until a hydrophobic suspension was formed.

[0062] S2. Mix metakaolin with granulated blast furnace slag powder dry, then add composite alkali activation liquid and stir to obtain the initial slurry of geopolymer matrix;

[0063] The compound alkali activating solution was allowed to stand and age for 24 hours before being added. The stirring was divided into two stages: low-speed stirring and high-speed stirring. The low-speed stirring speed was 125 rpm for 1.5 minutes, and the high-speed stirring speed was 300 rpm for 3.5 minutes.

[0064] S3. Add the oil-encapsulated solid structure suspension obtained in S1 to the geopolymer matrix slurry obtained in S2, stir and disperse, and then pour it into a mold.

[0065] The stirring speed is 275 rpm and the stirring time is 68 seconds; the filling volume poured into the mold is 50% of the mold volume.

[0066] S4. Place the mold after casting in an insulated or semi-insulated environment, and use the heat of chemical reaction generated by the reaction between photovoltaic cutting silicon waste residue and alkali inside the slurry to perform self-heating curing. After demolding and curing, the mold is obtained.

[0067] The ambient temperature of the thermal or semi-thermal environment is 25℃, the relative humidity is ≥90%, no external heat source is applied during the curing process, and the peak temperature inside the slurry during the self-heating curing process is controlled at 80℃.

[0068] Example 3

[0069] This invention provides a porous lightweight geopolymer cement, comprising the following raw material components in parts by weight:

[0070] Metakaolin 70.0 parts, granulated blast furnace slag powder 45.0 parts, composite alkali activation solution 90.0 parts, waste cooking oil 12.0 parts, photovoltaic cutting silicon waste slag 2.0 parts, waste polyester plastic powder 4.0 parts.

[0071] Among them, the average particle size D50 of metakaolin is 5.0μm, and the SiO2 content is ≥52%; the specific surface area of ​​granulated blast furnace slag powder is 450m² / kg, and the alkalinity coefficient Kb is 1.1; the particle size range of waste polyester plastic powder is 75μm; and the elemental Si content in photovoltaic cutting silicon waste slag is ≥90%.

[0072] The composite alkali activating solution is prepared from industrial water glass, sodium hydroxide and water, wherein the mass ratio of industrial water glass, sodium hydroxide and water is 10:1:5.

[0073] The above-mentioned method for preparing polymer cement includes the following steps:

[0074] S1. After uniformly mixing photovoltaic cutting silicon waste residue and waste polyester plastic micro powder, add it to waste catering oil and form a uniform oil-in-solid structure suspension under shearing action.

[0075] The rotation speed during shearing is 3500 rpm, and the shearing dispersion lasts for 15 minutes until a hydrophobic suspension is formed.

[0076] S2. Mix metakaolin with granulated blast furnace slag powder dry, then add composite alkali activation liquid and stir to obtain the initial slurry of geopolymer matrix;

[0077] The compound alkali activating solution was allowed to stand and age for 24 hours before being added. The stirring was divided into two stages: low-speed stirring and high-speed stirring. The low-speed stirring speed was 150 rpm for 2 minutes, and the high-speed stirring speed was 350 rpm for 4 minutes.

[0078] S3. Add the oil-encapsulated solid structure suspension obtained in S1 to the geopolymer matrix slurry obtained in S2, stir and disperse, and then pour it into a mold.

[0079] The stirring speed is 300 rpm and the stirring time is 90 seconds; the filling volume poured into the mold is 60% of the mold volume.

[0080] S4. Place the mold after casting in an insulated or semi-insulated environment, and use the heat of chemical reaction generated by the reaction between photovoltaic cutting silicon waste residue and alkali inside the slurry to perform self-heating curing. After demolding and curing, the mold is obtained.

[0081] The ambient temperature of the thermal or semi-thermal environment is 30℃, the relative humidity is ≥90%, no external heat source is applied during the curing process, and the peak temperature inside the slurry during the self-heating curing process is controlled at 95℃.

[0082] To verify the necessity and synergistic effects of the core components and unique process parameters of this invention, Example 2, which exhibits the best overall performance, was selected as a benchmark. The following eight comparative experiments were rigorously conducted using the controlled variable method. By comparing the performance changes after removing or replacing a certain core technical feature, the inventiveness and irreplaceability of this invention's technical solution are fully demonstrated:

[0083] Comparative Example 1

[0084] The only difference from Example 2 is that in steps S1 and S3, photovoltaic cutting silicon waste residue, waste polyester plastic powder, and waste catering oil are directly added to the initial slurry of the geopolymer matrix prepared in S2 for mixing and stirring.

[0085] Comparative Example 2

[0086] The only difference from Example 2 is that the photovoltaic cutting silicon waste in the raw materials is replaced with aluminum powder with an equimolar gas production rate.

[0087] Comparative Example 3

[0088] The only difference from Example 2 is that the waste polyester plastic powder in the raw materials is replaced with an equal part by weight of waste polypropylene (PP) plastic powder.

[0089] Comparative Example 4

[0090] The only difference from Example 2 is that the waste cooking oil in the raw materials is replaced with an equal part by weight of waste mineral oil (engine oil).

[0091] Comparative Example 5

[0092] The only difference from Example 2 is that the raw materials do not contain granulated blast furnace slag powder, but are replaced by an equal part by weight of metakaolin.

[0093] Comparative Example 6

[0094] The only difference from Example 2 is that in step S4, the mold is placed in an ice-water bath jacket for forced cooling, and the peak temperature inside the slurry is strictly controlled below 40°C.

[0095] Comparative Example 7

[0096] The only difference from Example 2 is that step S1 is changed to first adding waste cooking oil to the initial slurry of the geopolymer matrix obtained in S2 for mixing and emulsification, and then adding a mixture of photovoltaic cutting silicon waste residue and waste polyester plastic micro powder.

[0097] Comparative Example 8

[0098] The only difference from Example 2 is that the particle size range of the waste polyester plastic powder used is 1mm to 2mm.

[0099] Experiment 1: Testing of Physical and Mechanical Properties and Lightweight High-Strength Characteristics

[0100] The tests were conducted according to the national standard GB / T11969-2020, "Test Methods for Performance of Autoclaved Aerated Concrete". First, fresh slurry prepared in Examples 1-3 and Comparative Examples 1-8 was cast into cubic specimens of 100mm × 100mm × 100mm, with three specimens prepared for each group as parallel samples. These specimens were cured for 28 days under standard curing conditions of 20±2℃ and ≥95% humidity. Subsequently, the specimens were dried to constant weight in an oven, and their oven-dry density (kg / m³) was measured. Their compressive strength (MPa) was then tested using a universal testing machine at a loading rate of 2.0±0.5kN / s.

[0101] Experiment 2 Thermal Insulation Performance Test

[0102] This experiment was conducted according to GB / T10294-2008 "Determination of Steady-State Thermal Resistance and Related Properties of Thermal Insulation Materials - Protective Hot Plate Method". The samples prepared in Examples 1-3 and Comparative Examples 1-8 and cured for 28 days were cut into 300mm×300mm×30mm flat plate specimens. After drying, they were placed in a flat plate thermal conductivity meter, and their thermal conductivity [W / (m·K)] was measured under the condition that the temperature difference between the hot and cold plates was 15℃.

[0103] Experiment 3: Volume stability (drying shrinkage) and water absorption rate test

[0104] The drying shrinkage value and water absorption rate were determined according to GB / T11969-2020. The slurries prepared in Examples 1-3 and Comparative Examples 1-8 were cast into prism specimens of 40mm×40mm×160mm, and their drying shrinkage value (mm / m) was measured after being placed in an environment of 20±2℃ and 43±2% relative humidity for 28 days; at the same time, the mass water absorption rate (%) of the specimens after being immersed in water for 24 hours was measured.

[0105] Table 1 Test data of physical and mechanical properties and lightweight high strength characteristics Group Oven-dry density (kg / m³) 28-day compressive strength (MPa) Example 1 285 2.1 Example 2 320 2.8 Example 3 375 3.5 Comparative Example 1 335 1.6 Comparative Example 2 310 1.2 Comparative Example 3 315 1.3 Comparative Example 4 550 4.2 Comparative Example 5 305 1.1 Comparative Example 6 322 1.2 Comparative Example 7 340 1.7 Comparative Example 8 318 1.4

[0106] Table 2 Test data of physical and mechanical properties and lightweight high strength characteristics Group Thermal conductivity [W / (m·K)] Example 1 0.056 Example 2 0.060 Example 3 0.064 Comparative Example 1 0.082 Comparative Example 2 0.075 Comparative Example 3 0.076 Comparative Example 4 0.145 Comparative Example 5 0.068 Comparative Example 6 0.074 Comparative Example 7 0.085 Comparative Example 8 0.072

[0107] Table 3. Volume stability (drying shrinkage) and water absorption test data Group Drying shrinkage value (mm / m) 24-hour water absorption rate (%) Example 1 0.38 8.5 Example 2 0.35 7.8 Example 3 0.32 7.2 Comparative Example 1 0.55 15.6 Comparative Example 2 0.92 12.3 Comparative Example 3 0.65 11.5 Comparative Example 4 0.88 9.2 Comparative Example 5 0.52 18.5 Comparative Example 6 0.95 12.0 Comparative Example 7 0.58 16.2 Comparative Example 8 0.62 10.5

[0108] Based on the experimental data from the above embodiments and comparative examples, the following conclusions are drawn:

[0109] As can be seen from Examples 1-3 and Comparative Examples 1-8, and Table 1, the porous lightweight geopolymer cement prepared in Examples 1-3 of this invention achieves extremely low density while maintaining a compressive strength above 2.1 MPa, achieving a perfect balance between lightweight and high strength. In contrast, Comparative Example 1, due to the lack of an oil-encapsulated pre-dispersion process, resulted in uneven bubble distribution, increased macropore defects, and a strength decrease to 1.6 MPa. Comparative Examples 2 and 6, respectively, failed to drive alkaline hydrolysis of PET due to insufficient chemical reaction heat and insufficient ambient temperature. Comparative Examples 3 and 5, respectively, failed to grow reinforcing whiskers in situ in the matrix due to the replacement of PET with inert PP and the lack of an active calcium source in the system, resulting in a significant drop in strength to the 1.1-1.3 MPa range. This indicates that this invention, through a specific oil-encapsulated pre-dispersion structure combined with a thermo-chemical coupling mechanism, successfully utilizes the reaction heat of silicon waste to drive the conversion of PET into calcium terephthalate whiskers, effectively solving the technical problem of insufficient strength in traditional lightweight geopolymers due to weak pore walls.

[0110] As can be seen from Examples 1-3 and Comparative Examples 1-8, and Table 2, this invention demonstrates significant advantages in constructing highly efficient thermal insulation microstructures. The thermal conductivity of Examples 1-3 is consistently controlled at an extremely low level of 0.056~0.064 W / (m·K), superior to conventional insulation materials. However, Comparative Example 4, due to the use of non-saponifiable mineral oil, lost its in-situ foam-stabilizing function, leading to severe mold collapse and solid heat transfer, with the thermal conductivity soaring to 0.145 W / (m·K). Comparative Examples 1 and 7, due to the disruption of the oil film's encapsulation structure of the solid waste or changes in the feeding sequence, resulted in premature foaming and microemulsion demulsification, forming interconnected macroporous structures, and the thermal conductivity deteriorated to above 0.082 W / (m·K). This indicates that this invention utilizes the dual effects of emulsification and in-situ saponification of waste oil to achieve delayed control of the foaming process and fine shaping of the pore structure, fundamentally ensuring the material's excellent thermal insulation performance.

[0111] Combining Examples 1-3 and Comparative Examples 1-8 with Tables 1-3, it can be seen that the present invention exhibits excellent overall performance in terms of volume stability and crack resistance and seepage prevention. Comparative Examples 2 and 6, due to the lack of a thermal environment, failed to generate ethylene glycol; Comparative Example 4, due to the lack of saponification of oils, resulted in the absence of glycerol. The drying shrinkage values ​​of all three surged to over 0.88 mm / m, far exceeding the 0.32~0.38 mm / m level of the examples, and their water absorption rates were also high. In summary, the present invention, through the synergistic effect of photovoltaic silicon waste, waste PET, waste oils, and slag matrix, not only utilizes the heat of reaction to achieve a self-heating curing energy-saving process, but also constructs a unique dual-ol water-retaining network through in-situ generated ethylene glycol and glycerol. This effectively solves the common technical bottleneck of geopolymers being prone to cracking and water seepage due to rapid water loss, achieving a breakthrough in the preparation of high-performance green energy-saving building materials from all solid waste raw materials.

[0112] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A porous lightweight geopolymer cement, characterized in that, The raw materials consist of the following parts by weight: Metakaolin 55.0~70.0 parts, granulated blast furnace slag powder 30.0~45.0 parts, composite alkali activation solution 70.0~90.0 parts, waste cooking oil 6.0~12.0 parts, photovoltaic cutting silicon waste slag 0.6~2.0 parts, waste polyester plastic powder 1.5~4.0 parts.

2. The porous lightweight geopolymer cement according to claim 1, characterized in that, The metakaolin has an average particle size D50 of 3.0~5.0μm and a SiO2 content ≥52%; The granulated blast furnace slag powder has a specific surface area of ​​400~450m² / kg and an alkalinity coefficient of 0.9~1.

1.

3. The porous lightweight geopolymer cement according to claim 1, characterized in that, The composite alkali activating solution is prepared from industrial water glass, sodium hydroxide and water, wherein the mass ratio of industrial water glass, sodium hydroxide and water is 6~10:1:2~5.

4. The porous lightweight geopolymer cement according to claim 1, characterized in that, The particle size range of the waste polyester plastic micro powder is 45~75μm; The elemental Si content in the photovoltaic cutting silicon waste residue is ≥90%.

5. A method for preparing porous lightweight geopolymer cement, characterized in that, The method for preparing a porous lightweight geopolymer cement according to any one of claims 1-4 comprises the following steps: S1. After the photovoltaic cutting silicon waste residue and the waste polyester plastic micro powder are mixed evenly, they are added to the waste catering oil and a uniform oil-in-solid structure suspension is formed under shearing action. S2. The metakaolin and the granulated blast furnace slag powder are dry-mixed, and then the composite alkali activation liquid is added and stirred to obtain the initial slurry of the geopolymer matrix. S3. Add the oil-encapsulated solid structure suspension obtained in S1 to the geopolymer matrix slurry obtained in S2, stir and disperse, and then pour it into a mold. S4. Place the mold after casting in an insulated or semi-insulated environment, and use the heat generated by the chemical reaction between the photovoltaic cutting silicon waste residue inside the slurry and the alkali to perform self-heating curing. After demolding and curing, the product is obtained.

6. The method for preparing porous lightweight geopolymer cement according to claim 5, characterized in that, In step S1, the rotation speed is 2500~3500 rpm during shearing, and the shearing dispersion lasts for 10~15 minutes until a hydrophobic suspension is formed.

7. The method for preparing porous lightweight geopolymer cement according to claim 5, characterized in that, In step S2, the compound alkali activating solution is allowed to stand and age for 24 hours before being added. The stirring is divided into two stages: low-speed stirring and high-speed stirring. The low-speed stirring speed is 100~150 rpm and the time is 1~2 minutes; the high-speed stirring speed is 250~350 rpm and the time is 3~4 minutes.

8. The method for preparing porous lightweight geopolymer cement according to claim 5, characterized in that, In step S3, the stirring speed is 250~300 rpm and the stirring time is 45~90 seconds.

9. The method for preparing porous lightweight geopolymer cement according to claim 5, characterized in that, In step S3, the filling volume poured into the mold is 40% to 60% of the mold volume.

10. The method for preparing porous lightweight geopolymer cement according to claim 5, characterized in that, In step S4, the ambient temperature of the adiabatic or semi-adiabatic environment is 20~30℃, the relative humidity is ≥90%, no external heat source is applied during the curing process, and the peak temperature inside the slurry during the self-heating curing process is controlled at 65℃~95℃.

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