Composite eco-cement, method for its production and use

Abstract

The application relates to the field of building materials, and discloses a composite ecological cement as well as a preparation method and application thereof. The cement contains Portland cement clinker, slag powder, fly ash, construction waste fine aggregate, a modifier, an activator and a grinding aid. The modifier contains nano silicon dioxide, polyvinyl alcohol fiber and lignosulfonate. The mass ratio of the nano silicon dioxide, the polyvinyl alcohol fiber and the lignosulfonate is 1:1-4:1.5-4. The cement provided by the application can realize a high solid waste content (the total content of the slag powder, the fly ash and the construction waste fine aggregate is 40-53%) while having good compressive strength, crack resistance, frost resistance and process adaptability, so that the 3d compressive strength of the cement product is greater than or equal to 32 MPa, the 28d compressive strength is greater than or equal to 55 MPa, and the frost resistance grade is greater than or equal to F250.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a composite eco-friendly cement, its preparation method, and its application. Background Technology

[0002] The cement industry currently faces the dual challenges of high resource consumption, high carbon emissions, and insufficient engineering durability. Traditional cement production consumes large amounts of limestone (accounting for more than 80% of raw materials) and coal (carbon emissions per unit of cement are approximately 0.8-1.0 t CO2 / t cement), accounting for 7-8% of global anthropogenic emissions, which is serious.

[0003] Traditional silicate cement production processes consume large amounts of resources such as limestone and coal, resulting in high carbon emissions. Ordinary cement undergoes significant drying shrinkage after hydration and hardening. In extreme cold and freeze-thaw environments, moisture easily penetrates the matrix pores and repeatedly freezes and expands, leading to cracking, surface peeling, and other problems, significantly shortening the service life of structures. Existing cements with added solid waste mostly only incorporate slag or fly ash, resulting in poor activation of solid waste and a comprehensive utilization rate generally below 35%. Various additives are also mostly simple blends, making it difficult to simultaneously achieve material strength, crack resistance, and freeze-thaw resistance. Furthermore, some modification processes require specialized equipment, leading to high modification costs; and commonly used chloride-based admixtures also pose risks such as steel corrosion and poor cement stability.

[0004] Therefore, how to achieve a synergistic improvement in cement's high strength, excellent crack and freeze resistance, and high solid waste utilization rate without significantly increasing production costs or relying on large-scale equipment upgrades is a technical challenge that the cement industry urgently needs to solve. Summary of the Invention

[0005] The purpose of this invention is to address the problems in existing technologies, such as low solid waste utilization rates, the potential for side effects from chemical admixtures, and the high dependence on specialized equipment for improved processes. This invention provides a composite eco-cement, its preparation method, and its applications. The composite eco-cement provided by this invention can achieve a high solid waste content while also possessing good compressive strength, crack resistance, freeze-thaw resistance, and process adaptability.

[0006] To achieve the above objectives, the present invention provides a composite ecological cement, wherein the cement contains silicate cement clinker, slag powder, fly ash, fine aggregate from construction waste, modifier, activator, and grinding aid; wherein the modifier contains nano-silica, polyvinyl alcohol fiber, and lignin sulfonate; the mass ratio of the nano-silica, the polyvinyl alcohol fiber, and the lignin sulfonate is 1:1-4:1.5-4.

[0007] A second aspect of the present invention provides a method for preparing composite ecological cement, the method comprising the following steps: grinding silicate cement clinker, slag powder, fly ash, construction waste fine aggregate, activator and grinding aid to obtain a grinding mixture (I); then grinding a modifier with the grinding mixture (II); wherein the modifier contains nano-silica, polyvinyl alcohol fiber and lignin sulfonate; the mass ratio of the nano-silica, the polyvinyl alcohol fiber and the lignin sulfonate is 1:1-4:1.5-4.

[0008] A third aspect of the present invention provides the application of the composite ecological cement as described above and / or the composite ecological cement prepared by the method as described above in the preparation of cement-based materials.

[0009] Through the above technical solution, the present invention uses a specific ratio of nano-silica, polyvinyl alcohol fiber and lignin sulfonate to obtain a modifier. Through the synergistic effect between the modifier and silicate cement clinker, slag powder, fly ash, construction waste fine aggregate, activator and grinding aid, the resulting composite ecological cement can achieve a high solid waste content (total content of slag powder, fly ash and construction waste fine aggregate reaches 40-53%) while also having good compressive strength, crack resistance, frost resistance and process adaptability. Detailed Implementation

[0010] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0011] The first aspect of this invention provides a composite ecological cement, wherein the cement contains silicate cement clinker, slag powder, fly ash, fine aggregate from construction waste, modifier, activator, and grinding aid; wherein the modifier contains nano-silica, polyvinyl alcohol fiber, and lignin sulfonate; the mass ratio of the nano-silica, the polyvinyl alcohol fiber, and the lignin sulfonate is 1:1-4:1.5-4.

[0012] During the research process, the inventors of this invention unexpectedly discovered that a modifier is obtained by combining nano-silica, polyvinyl alcohol fiber and lignosulfonate in a specific ratio. Through the synergistic effect between the modifier and silicate cement clinker, slag powder, fly ash, fine aggregate of construction waste, activator and grinding aid, the resulting composite ecological cement can achieve a high solid waste content while also possessing good compressive strength, crack resistance, frost resistance and process adaptability.

[0013] In this invention, nano-silica strengthens the aggregate-slurry interface bond by filling the micropores of cement stone, optimizing the structure of the interface transition zone; polyvinyl alcohol fibers, 3-6 mm in length, can bridge microcracks, dissipate deformation energy, and improve the material's crack resistance and toughening effect; lignin sulfonate disperses particles through electrostatic repulsion and steric hindrance effects, optimizing the uniform distribution of components and forming a multi-scale reinforcement mechanism of "nano-reinforcement-fiber crack resistance-dispersion homogenization". Therefore, this invention, while achieving high solid waste content, endows cement with excellent compressive strength, freeze-thaw resistance, and crack resistance, and significantly reduces carbon emissions and production costs.

[0014] According to the present invention, preferably, based on the total weight of the cement, the content of slag powder is 21-24% by weight, the content of fly ash is 16-19% by weight, the content of fine aggregate from construction waste is 5-7% by weight, the content of modifier is 3-5% by weight, the content of activator is 3-4% by weight, the content of grinding aid is 0.08-0.12% by weight, and the remainder is silicate cement clinker. The inventors discovered in their research that, through the synergistic effect between the components of the raw materials within the above-mentioned specific dosage range, composite ecological cement can achieve a high solid waste content (40-53% by weight) while simultaneously possessing excellent compressive strength, frost resistance, and crack resistance, and significantly reducing carbon emissions and overall costs, thus achieving a synergistic improvement in green environmental protection and high performance.

[0015] According to the present invention, more preferably, based on the total weight of the cement, the content of the nano-silica is 0.5-1% by weight, the content of the polyvinyl alcohol fiber is 1-2% by weight, and the content of the lignin sulfonate is 1.5-2% by weight. The inventors discovered in their research that through the synergistic effect between the raw material components of the modifier within the above-mentioned specific dosage range, a multi-scale reinforcement mechanism of "nano-reinforcement-fiber crack resistance-dispersion homogenization" is formed, thereby significantly improving the compressive strength, frost resistance, and crack resistance of the composite ecological cement.

[0016] According to the present invention, preferably, the activator is a sulfate activator, which may be selected from at least one of anhydrous sodium sulfate, anhydrous potassium sulfate, and anhydrous aluminum sulfate. The inventors have discovered that sulfate ions can effectively activate the activity of slag powder and fly ash by disrupting the surface glassy structure of slag powder and fly ash, steadily optimizing later-stage strength and durability, and further improving the early-stage strength and durability of cement.

[0017] According to the present invention, preferably, the activator contains anhydrous sodium sulfate and calcium sulfate dihydrate; the mass ratio of the anhydrous sodium sulfate to the calcium sulfate dihydrate is 1.5-1.78:1, specifically 1.5:1, 1.6:1, 1.7:1, 1.78:1, or any intermediate value between the above two values. In the present invention, the purity of anhydrous sodium sulfate is ≥98%, and the purity of calcium sulfate dihydrate is ≥95%. Anhydrous sodium sulfate accelerates the early hydration reaction (promotes the reaction of tricalcium aluminate and gypsum to form ettringite), while calcium sulfate dihydrate precisely controls the setting time (avoids rapid setting) and promotes the formation of gypsum dihydrate (calcium sulfate dihydrate)-ettringite composite crystals, enhancing later-stage strength. The inventors discovered in their research that through the synergistic effect of anhydrous sodium sulfate and calcium sulfate dihydrate within the above-mentioned specific dosage range, early hydration can be accelerated and setting time can be controlled, enabling cement to achieve both early-stage and later-stage strength and durability.

[0018] According to the present invention, preferably, the grinding aid contains an alkanolamine and / or a polyol. The inventors have discovered that this preferred embodiment, through the use of a specific grinding aid, can improve material flowability and grindability, increase grinding efficiency, reduce energy consumption, and help to uniformly disperse the components, thereby ensuring the strength, crack resistance, and frost resistance of the cement.

[0019] According to the present invention, preferably, the grinding aid contains an alkanolamine and a polyol. The inventors have discovered that this preferred embodiment, through the synergistic effect between the alkanolamine and the polyol, can further improve grinding efficiency, reduce energy consumption, and promote uniform dispersion of the components, thereby stabilizing the mechanical and durability properties of cement.

[0020] According to the present invention, preferably, the amine is triethanolamine and the polyol is ethylene glycol. This preferred embodiment, through the synergistic effect between triethanolamine and ethylene glycol, can further improve grinding efficiency and dispersion uniformity, and helps to fully exert the synergistic effect of each component.

[0021] More preferably, the mass ratio of the alkanolamine to the polyol is 1:0.8-1.2. This preferred embodiment, through the synergistic effect between the alkanolamine and polyol in the above-mentioned specific ratio, can more precisely control the material flowability and particle surface activity during the grinding process, thereby achieving a balance between the mechanical properties and durability of cement.

[0022] A second aspect of the present invention provides a method for preparing composite ecological cement, the method comprising the following steps: grinding silicate cement clinker, slag powder, fly ash, construction waste fine aggregate, activator and grinding aid to obtain a grinding mixture (I); then grinding a modifier with the grinding mixture (II); wherein the modifier contains nano-silica, polyvinyl alcohol fiber and lignin sulfonate; the mass ratio of the nano-silica, the polyvinyl alcohol fiber and the lignin sulfonate is 1:1-4:1.5-4.

[0023] The method provided by this invention can significantly improve the mechanical and durability properties of cement, giving it excellent compressive strength, frost resistance, and crack resistance. Simultaneously, this method achieves efficient utilization of industrial solid waste and construction waste, significantly reducing carbon dioxide emissions and overall costs per ton of cement, and is easily scalable for industrial application.

[0024] The preferred embodiments of the method for preparing composite ecological cement provided in the second aspect of the present invention refer to the preferred embodiments provided in the first aspect of the present invention, and the applicant will not repeat them here.

[0025] According to the present invention, preferably, the conditions for milling I include: such that the specific surface area of ​​the milled mixture is ≥350 m². 2 / kg. The inventors discovered in their research that this preferred embodiment achieves a specific surface area of ​​≥350 m² for the powder mixture. 2 / kg, which can effectively activate the potential activity of slag powder and fly ash, providing a good particle size distribution basis for the uniform dispersion and hydration reaction of subsequent modifiers.

[0026] Further preferably, the conditions for grinding II include: a time of 30-50 min, specifically 30 min, 35 min, 40 min, 45 min, 50 min, or any intermediate value between two of these values; a rotation speed of 20-60 rpm, specifically 20 rpm, 30 rpm, 40 rpm, 50 rpm, 60 rpm, or any intermediate value between two of these values; and a temperature of 60-120℃. The inventors discovered in their research that this preferred embodiment, by adjusting the temperature, time, and rotation speed, can achieve thorough homogenization and fine grinding of cement materials without damaging the structure of the modifier fibers and nanoparticles, ensuring the full realization of the synergistic effect of each component.

[0027] According to the present invention, preferably, the method further includes: mixing the anhydrous sodium sulfate and the calcium sulfate dihydrate before grinding I. The inventors have found that this preferred embodiment, by mixing the anhydrous sodium sulfate and calcium sulfate dihydrate in advance, allows the two activator components to be fully contacted and homogenized beforehand, thereby enabling them to exert a more synergistic effect in early strength and setting regulation during subsequent grinding and cement hydration processes.

[0028] More preferably, the mixing conditions include: a temperature of 80-120℃, specifically 80℃, 90℃, 100℃, 110℃, 120℃, or any intermediate value between two of these values; a time of 3-5 min, specifically 3 min, 3.5 min, 4 min, 4.5 min, 5 min, or any intermediate value between two of these values; and a rotation speed of 100-150 rpm, specifically 100 rpm, 110 rpm, 120 rpm, 130 rpm, 150 rpm, or any intermediate value between two of these values. This preferred embodiment, by adjusting the temperature, time, and rotation speed, can accelerate the interfacial reaction and diffusion of anhydrous sodium sulfate and calcium sulfate dihydrate, enabling them to form a uniform composite activator masterbatch, thereby more stably improving the early strength and later durability of cement.

[0029] The modification agent addition process of this invention includes: first, ultrasonically dispersing nano-silica (frequency 35-45kHz, power 180-220 W, time 6-10 min), then mechanically stirring (speed 800-1000 rpm, time 10-14 min) to prevent agglomeration, and then precisely adding it to the powdered mixture. Polyvinyl alcohol fiber is treated with ion wind static electricity removal (voltage 4.5-5.5 kV, wind speed 8-12 m / s), then uniformly dispersed by a high-speed forced premixer before being added. Lignosulfonate is added in liquid atomization form using a metering pump (flow accuracy ±0.5 wt%) combined with an atomizing spray system (pressure 0.3-0.5 MPa, atomized particle size ≤50 μm). The modification agent contains nano-silica, polyvinyl alcohol fiber, and lignin sulfonate; the mass ratio of nano-silica, polyvinyl alcohol fiber, and lignin sulfonate is 1:1-4:1.5-4. The inventors discovered in their research that the modifier obtained by the above-mentioned precise addition method of grouping can effectively avoid the problems of nano-silica agglomeration, polyvinyl alcohol fiber entanglement and clumping, and uneven dispersion of lignin sulfonate, ensuring that the three-component modifier is evenly distributed in the cement matrix, thereby giving full play to the multi-scale synergistic effect of "nano-reinforcement-fiber crack resistance-dispersion homogenization".

[0030] A third aspect of the present invention provides the application of the composite ecological cement as described above and / or the composite ecological cement prepared by the method as described above in the preparation of cement-based materials.

[0031] The application provided by this invention utilizes the composite eco-cement to prepare cement-based materials. It can be directly produced using existing conventional cement production lines consisting of roller presses and ball mills. The resulting cement products significantly improve the compressive strength, freeze-thaw cycle resistance, and crack resistance of cement-based materials, meeting the stringent requirements of high-durability scenarios in infrastructure and water conservancy projects in frigid regions. It demonstrates excellent performance in high-durability cement-based engineering applications such as municipal roads, bridge structures, and dam panels in frigid regions, which are subjected to long-term freeze-thaw cycles. Simultaneously, this application extensively utilizes industrial solid waste and construction waste, effectively reducing carbon emissions and raw material costs, significantly reducing limestone consumption, lowering CO2 emissions per ton of cement by 25-35%, and reducing overall production costs by 15-20%, aligning with the industrial direction of green environmental protection and sustainable development. Furthermore, it only requires optimizing existing roller press-ball mill process parameters, eliminating the need for specialized equipment, resulting in a short production line modification cycle and convenient mass production. As a particularly preferred embodiment of the present invention, a method for preparing composite ecological cement is provided, comprising the following steps: S1. Construction waste pretreatment: Waste concrete and bricks are mixed in a ratio of 7:1-3. Metal, plastic, and wood chips are manually removed. Large pieces >30mm are screened out. The mixture is crushed to the specified particle size, naturally dried until the moisture content meets the standard, and then homogenized to obtain fine aggregate from construction waste. The crushed particle size of the fine aggregate is ≤5mm, of which ≤3mm particles account for ≥70% by weight, and the moisture content is ≤15% by weight. The aggregate is naturally dried until the moisture content is ≤15% and then homogenized for later use.

[0032] S2. Preparation of composite activator masterbatch: Anhydrous sodium sulfate and calcium sulfate dihydrate are mixed at a mass ratio of 1.5-1.78:1 and mixed at 80-120℃ and 100-150 rpm for 3-5 minutes to obtain a uniform masterbatch.

[0033] S3. Grinding I (Pre-grinding): Silicate cement clinker, slag powder, fly ash, fine aggregate from construction waste, composite activator masterbatch and grinding aid are put into a roller press for pre-grinding until the specific surface area is ≥350 m² / kg.

[0034] S4. Modifiers are added in groups and separately: Nano-silica is ultrasonically treated at 35-45 kHz for 6-10 min, and then stirred at 800-1000 rpm for 10-15 min to eliminate agglomeration; Polyvinyl alcohol fibers are electrostatically eliminated by high voltage of 4.5-5.5kV, and then premixed at 1000-2000 rpm for 45-60 s; Sodium lignosulfonate is added by atomization spray under 0.3-0.5 MPa conditions; The metering accuracy of the modified components is controlled within ±0.1%.

[0035] S5. Grinding II (Final Grinding): The above mixture is fed into a ball mill and ground for 30-50 minutes at a speed of 20-60 rpm and a temperature of 60-120℃. The entire production process is subject to three-level metering control: main material metering error ±0.5%, functional component metering error ±0.1%, and additive metering error ±0.05%. The output material is finished cement.

[0036] Based on the total weight of the cement, the content of slag powder is 21-24% by weight, the content of fly ash is 16-19% by weight, the content of fine aggregate from construction waste is 5-7% by weight, the content of modifier is 3-5% by weight, the content of activator is 3-4% by weight, the content of grinding aid is 0.08-0.12% by weight, and the remainder is silicate cement clinker. The content of nano-silica is 0.5-1% by weight, the content of polyvinyl alcohol fiber is 1-2% by weight, and the content of lignin sulfonate is 1.5-2% by weight. The grinding aid contains alkanolamine and polyol, and the mass ratio of alkanolamine to polyol is 1:0.8-1.2.

[0037] The composite ecological cement prepared through the above-mentioned preferred embodiments can achieve a high solid waste content while also possessing good compressive strength, crack resistance, frost resistance, and process adaptability.

[0038] The cement prepared by this invention can be used to formulate concrete for roads, bridges, hydraulic engineering and prefabricated projects. It is especially suitable for projects such as highway surface layers in high-altitude and cold regions, small and medium-sized water conservancy seepage prevention dams, and prefabricated foundations in frigid areas. It can maintain excellent durability performance in harsh service environments with alternating wet and dry conditions and frequent freeze-thaw cycles.

[0039] The present invention will be described in detail below through examples. In the following examples, the silicate cement clinker, nano-silica, polyvinyl alcohol fiber, sodium lignosulfonate, anhydrous sodium sulfate, and calcium sulfate dihydrate are all commercially available qualified industrial products; all raw materials have been tested and qualified in accordance with the corresponding national standards and technical indicators before being put into use.

[0040] Testing standards: compressive strength refers to GB / T 17671-2021; frost resistance and crack resistance refer to GB / T 50082-2009. The freeze-thaw index is determined by the rapid freezing method, and the crack area ratio is determined by the plate constraint method.

[0041] The raw material specifications and testing methods are shown in Table 1. Table 1

[0042] Example 1 I. Raw material ratio The grinding aid is added externally based on the total mass of cement. The content of slag powder is 22% by weight, fly ash is 18% by weight, and fine aggregate from construction waste is 6% by weight (moisture content 12% by weight). The content of modifier is 4% by weight, comprising 0.8% by weight nano-silica, 1.5% by weight polyvinyl alcohol fiber, and 1.7% by weight sodium lignosulfonate, with a mass ratio of 1:1.875:2.125. The content of composite activator is 4% by weight, comprising 2.5% by weight anhydrous sodium sulfate and 1.5% by weight dihydrate gypsum (calcium sulfate dihydrate), with a mass ratio of 1.67:1. The content of cement grinding aid is 0.1% by weight, composed of triethanolamine and ethylene glycol in a 1:1 mass ratio. The remainder is silicate cement clinker.

[0043] II. Preparation Process 1. Construction waste pretreatment: Mix waste concrete and bricks at a mass ratio of 7:3, manually remove impurities such as metal and wood, screen out particles >30mm using a vibrating screen, crush to ≤5mm using a jaw crusher (of which ≤3mm particles account for 72% by weight), air dry naturally until the moisture content is 12% by weight, and mix evenly in a homogenization shed.

[0044] 2. Pre-production of composite activator masterbatch: Weigh anhydrous sodium sulfate (2.5% by weight of total cement mass) and gypsum dihydrate (calcium sulfate dihydrate) (1.5% by weight of total cement mass), and put them into a twin-shaft mixer (5 m³ / h). 3 The mixture was stirred at 100℃ and 120 rpm for 4 min to obtain a uniform masterbatch.

[0045] 3. Pre-grinding (Grinding I): Silicate cement clinker, slag powder, fly ash, fine aggregate from construction waste, composite activator masterbatch, and cement grinding aid are fed into a roller press (model CLF180-120). The working pressure is set to 10 MPa, the roller gap to 24 mm, and the pressure response time to ≤2 s. Pre-grind until the material specific surface area is ≥350 m². 2 / kg.

[0046] 4. Modifiers are added in groups and in stages: Nano-silica is first dispersed ultrasonically (frequency 40 kHz, power 200 W, time 8 min), then mechanically stirred (speed 900 rpm, time 12 min) to prevent agglomeration, and then precisely added to the pre-ground material. Polyvinyl alcohol fiber is treated with ion wind to remove static electricity (voltage 5 kV, wind speed 10 m / s), and then evenly dispersed by a high-speed forced premixer (speed 1500 rpm, time 50 s) before being added. Sodium lignosulfonate is added in liquid atomization form using a metering pump (flow accuracy ±0.5%) in conjunction with an atomizing spray system (pressure 0.4 MPa, atomized particle size ≤50 μm).

[0047] 5. Final Grinding (Grinding II): The above mixture is fed into a ball mill (3.2 m × 13 m) and ground for 40 min at 30 rpm. A three-level metering network is used to control the addition accuracy throughout the process: main material ±0.5%, functional components ±0.1%, additives ±0.05%. The process temperature is ≤120℃. The discharged material is composite ecological cement.

[0048] III. Performance test results are shown in Table 2 Table 2

[0049] Example 2 I. Raw material ratio The method was carried out according to Example 1, except that: the content of slag powder was 24% by weight, the content of fly ash was 19% by weight, and the content of fine aggregate from construction waste was 7% by weight (moisture content 12% by weight). The content of modifier was 3% by weight, of which nano-silica accounted for 0.5% by weight, polyvinyl alcohol fiber accounted for 1.2% by weight, and sodium lignosulfonate accounted for 1.6% by weight, with a mass ratio of 1:2:2. The content of composite activator was 4% by weight, of which anhydrous sodium sulfate accounted for 2.56% by weight and gypsum dihydrate (calcium sulfate dihydrate) accounted for 1.44% by weight, with a mass ratio of 1.78:1. The content of cement grinding aid was 0.08% by weight, which was compounded from triethanolamine and ethylene glycol in a mass ratio of 1:1.2, with the remainder being silicate cement clinker.

[0050] II. Preparation Process The method was carried out according to Example 1, except that: the mixing temperature of the composite activator masterbatch was 80°C, the time was 5 min, and the rotation speed was 100 rpm; the working pressure of the roller press was 9 MPa, and the roller gap was 25 mm; the ultrasonic frequency of the nano-silica was 35 kHz, and the time was 10 min; the rotation speed of the ball mill was 25 rpm, and the grinding time was 45 min.

[0051] III. Performance test results are shown in Table 3 Table 3

[0052] Example 3 I. Raw material ratio The method was carried out according to Example 1, except that: the content of slag powder was 21% by weight, the content of fly ash was 16% by weight, and the content of fine aggregate from construction waste was 5% by weight (moisture content 12% by weight). The content of modifier was 5% by weight, of which nano-silica accounted for 1% by weight, polyvinyl alcohol fiber accounted for 2% by weight, and sodium lignosulfonate accounted for 2% by weight, with a mass ratio of 1:2:2. The content of composite activator was 4% by weight, of which anhydrous sodium sulfate accounted for 2.5% by weight and gypsum dihydrate (calcium sulfate dihydrate) accounted for 1.6% by weight, with a mass ratio of 1.5:1. The content of cement grinding aid was 0.12% by weight, which was composed of triethanolamine and ethylene glycol in a mass ratio of 1:0.8, with the remainder being silicate cement clinker.

[0053] II. Preparation Process The method was carried out according to Example 1, except that: the mixing temperature of the composite activator masterbatch was 120°C, the time was 3 min, and the rotation speed was 150 rpm; the working pressure of the roller press was 11 MPa, and the roller gap was 23 mm; the ultrasonic dispersion frequency of nano-silica was 40 kHz, and the time was 8 min, which remained unchanged; the rotation speed of the ball mill was 60 rpm, and the grinding time was 35 min.

[0054] III. Performance test results are shown in Table 4 Table 4

[0055] Example 4 The method described in Example 2 was followed, except that the content of slag powder was 21% by weight, the content of fly ash was 16% by weight, and the content of fine aggregate from construction waste was 5% by weight. The content of modifier was 1% by weight, the content of activator was 1% by weight, the content of cement grinding aid was 0.04% by weight, and the remainder was silicate cement clinker. The performance test results are shown in Table 5.

[0056] Table 5

[0057] Example 5 The method provided in Example 2 was followed, except that the mass ratio of the anhydrous sodium sulfate to the calcium sulfate dihydrate was 1:1. The performance test results are shown in Table 6.

[0058] Table 6

[0059] Example 6 The method provided in Example 2 was followed, except that the content of the nano-silica was adjusted to 0.2% by weight, the content of the polyvinyl alcohol fiber was adjusted to 5% by weight, and the content of the sodium lignosulfonate was adjusted to 0.5% by weight. The performance test results are shown in Table 7.

[0060] Table 7

[0061] Example 7 The method provided in Example 2 was followed, except that the grinding aid contained only triethanolamine, and the performance test results are shown in Table 8.

[0062] Table 8

[0063] Example 8 The method provided in Example 2 was followed, except that the activator contained only anhydrous sodium sulfate. The performance test results are shown in Table 9.

[0064] Table 9

[0065] Comparative Example 1 The method was carried out according to Example 1, except that the mass ratio of the lignosulfonate to sodium lignosulfonate was changed to 1:0.5:1 (i.e., nano-silica accounts for 1.6% by weight, polyvinyl alcohol fiber accounts for 0.8% by weight, and sodium lignosulfonate accounts for 1.6% by weight). The performance test results are shown in Table 10.

[0066] Table 10

[0067] Comparative Example 2 The method of Example 1 was followed, except that the content of the modifier was maintained at 4% by weight, but the mass ratio of the nano-silica, the polyvinyl alcohol fiber, and the sodium lignosulfonate was changed to 1:5:2 (i.e., nano-silica accounts for 0.5% by weight, polyvinyl alcohol fiber accounts for 2.5% by weight, and sodium lignosulfonate accounts for 1.0% by weight). The performance test results are shown in Table 11.

[0068] Table 11

[0069] Comparative Example 3 The method was carried out according to Example 1, except that no modifier was added, and everything else remained the same. Performance test results: 3-day compressive strength was 24.2 MPa, 28-day compressive strength was 42.5 MPa, freeze-thaw resistance grade was F150, mass loss rate after 50 freeze-thaw cycles was 2.8%, relative dynamic elastic modulus was 70.2%, and crack area ratio was 0.92%.

[0070] Comparative Example 4 The method of Example 1 was followed, except that the modifier contained only polyvinyl alcohol fiber, while other properties remained unchanged. Performance test results: 3-day compressive strength was 26.8 MPa, 28-day compressive strength was 46.1 MPa, freeze-thaw resistance grade was F200, mass loss rate after 50 freeze-thaw cycles was 1.6%, relative dynamic modulus of elasticity was 79.5%, and crack area ratio was 0.41%.

[0071] Comparative Example 5 The method of Example 1 was followed, except that the modifier contained only nano-silica, while other properties remained unchanged. Performance test results: 3-day compressive strength was 27.5 MPa, 28-day compressive strength was 47.3 MPa, freeze-thaw resistance grade was F200, mass loss rate after 50 freeze-thaw cycles was 1.5%, relative dynamic elastic modulus was 80.3%, and crack area ratio was 0.65%.

[0072] Comparative Example 6 The method of Example 1 was followed, except that the modifier contained only sodium lignosulfonate, while other properties remained unchanged. Performance test results: 3-day compressive strength was 25.9 MPa, 28-day compressive strength was 44.8 MPa, freeze-thaw resistance grade was F150, mass loss rate after 50 freeze-thaw cycles was 2.2%, relative dynamic modulus of elasticity was 74.6%, and crack area ratio was 0.78%.

[0073] Comparative Example 7 The method was followed as in Example 1, except that the modifier contained only polyvinyl alcohol fiber and nano-silica, with polyvinyl alcohol fiber accounting for 1.5% by weight and nano-silica accounting for 0.8% by weight. Performance test results: 3-day compressive strength was 28.6 MPa, 28-day compressive strength was 48.9 MPa, freeze-thaw resistance grade was F220, mass loss rate after 50 freeze-thaw cycles was 1.3%, relative dynamic modulus of elasticity was 82.1%, and crack area ratio was 0.32%.

[0074] Comparative Example 8 The method was followed as in Example 1, except that the modifier contained only polyvinyl alcohol fiber and sodium lignosulfonate, with polyvinyl alcohol fiber accounting for 1.5% by weight and sodium lignosulfonate accounting for 1.7% by weight. Performance test results: 3-day compressive strength was 27.9 MPa, 28-day compressive strength was 47.7 MPa, freeze-thaw resistance grade was F200, mass loss rate after 50 freeze-thaw cycles was 1.4%, relative dynamic modulus of elasticity was 80.8%, and crack area ratio was 0.27%.

[0075] Comparative Example 9 The method was followed as in Example 1, except that the modifier contained only nano-silica and sodium lignosulfonate, with nano-silica accounting for 0.8% by weight and sodium lignosulfonate accounting for 1.7% by weight. Performance test results: 3-day compressive strength was 28.2 MPa, 28-day compressive strength was 48.3 MPa, freeze-thaw resistance grade was F210, mass loss rate after 50 freeze-thaw cycles was 1.3%, relative dynamic modulus of elasticity was 81.5%, and crack area ratio was 0.53%.

[0076] Comparative Example 10 The method was followed as in Example 1, except that no activator was added. Performance test results: 3-day compressive strength was 29.3 MPa, 28-day compressive strength was 49.5 MPa, freeze-thaw resistance grade was F230, mass loss rate after 50 freeze-thaw cycles was 1.1%, relative dynamic elastic modulus was 83.7%, and crack area ratio was 0.21%.

[0077] The above results show that the samples using a single modified component or any combination of two modified components without any modifier exhibited significantly inferior compressive strength, freeze resistance, and crack resistance compared to the three-component composite activator of this invention. This demonstrates a significant synergistic effect between nano-silica, polyvinyl alcohol fiber, and sodium lignosulfonate. Furthermore, with the complete addition of the three-component modifier, the removal of the composite activator system resulted in a simultaneous decrease in all product properties, confirming a synergistic effect between the composite activator composed of anhydrous sodium sulfate and gypsum dihydrate (calcium sulfate dihydrate) and the modified components.

[0078] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A composite eco-friendly cement, characterized in that, The cement contains silicate cement clinker, slag powder, fly ash, fine aggregate from construction waste, modifier, activator, and grinding aid; wherein the modifier contains nano-silica, polyvinyl alcohol fiber, and lignin sulfonate; the mass ratio of the nano-silica, the polyvinyl alcohol fiber, and the lignin sulfonate is 1:1-4:1.5-4.

2. The composite eco-friendly cement according to claim 1, characterized in that, Based on the total weight of the cement, the content of slag powder is 21-24% by weight, the content of fly ash is 16-19% by weight, the content of fine aggregate from construction waste is 5-7% by weight, the content of modifier is 3-5% by weight, the content of activator is 3-4% by weight, the content of grinding aid is 0.08-0.12% by weight, and the remainder is silicate cement clinker.

3. The composite eco-friendly cement according to claim 1, characterized in that, Based on the total weight of the cement, the content of nano-silica is 0.5-1% by weight, the content of polyvinyl alcohol fiber is 1-2% by weight, and the content of lignin sulfonate is 1.5-2% by weight.

4. The composite eco-friendly cement according to any one of claims 1 to 3, characterized in that, The activator is a sulfate activator, and more preferably at least one selected from anhydrous sodium sulfate, anhydrous potassium sulfate and anhydrous aluminum sulfate; Preferably, the activator contains anhydrous sodium sulfate and calcium sulfate dihydrate; Preferably, the mass ratio of the anhydrous sodium sulfate to the calcium sulfate dihydrate is 1.5-1.78:

1.

5. The composite eco-friendly cement according to any one of claims 1 to 3, characterized in that, The grinding aid contains alkanolamines and / or polyols; Preferably, the grinding aid contains an alkanolamine and a polyol; Preferably, the alkanolamine is triethanolamine, and the polyol is ethylene glycol; Preferably, the mass ratio of the alkanolamine to the polyol is 1:0.8-1.

2.

6. A method for preparing composite eco-friendly cement, characterized in that, The method includes the following steps: Silicate cement clinker, slag powder, fly ash, fine aggregate from construction waste, activator, and grinding aid are ground to obtain a grinding mixture (I), and then the modifier is ground with the grinding mixture (II). The modifier contains nano-silica, polyvinyl alcohol fiber, and lignin sulfonate; the mass ratio of the nano-silica, the polyvinyl alcohol fiber, and the lignin sulfonate is 1:1-4:1.5-4.

7. The method according to claim 6, characterized in that, Based on the total weight of the cement, the content of slag powder is 21-24% by weight, the content of fly ash is 16-19% by weight, the content of fine aggregate from construction waste is 5-7% by weight, the content of modifier is 3-5% by weight, the content of activator is 3-4% by weight, the content of grinding aid is 0.08-0.12% by weight, and the remainder is silicate cement clinker; Preferably, based on the total weight of the cement, the content of nano-silica is 0.5-1% by weight, the content of polyvinyl alcohol fiber is 1-2% by weight, and the content of lignin sulfonate is 1.5-2% by weight. Preferably, the activator is a sulfate activator, and more preferably at least one selected from anhydrous sodium sulfate, anhydrous potassium sulfate, and anhydrous aluminum sulfate; Preferably, the activator contains anhydrous sodium sulfate and calcium sulfate dihydrate; Preferably, the mass ratio of the anhydrous sodium sulfate to the calcium sulfate dihydrate is 1.5-1.78:1; Preferably, the grinding aid contains alkanolamines and / or polyols; Preferably, the grinding aid contains an alkanolamine and a polyol; Preferably, the alkanolamine is triethanolamine, and the polyol is ethylene glycol; Preferably, the mass ratio of the alkanolamine to the polyol is 1:0.8-1.

2.

8. The method according to claim 6 or 7, characterized in that, The conditions for milling I include: ensuring that the specific surface area of ​​the milled mixture is ≥350 m². 2 / kg; Preferably, the conditions for grinding II include: time of 30-50 min, rotation speed of 20-60 rpm, and temperature of 60-120℃.

9. The method according to claim 7, characterized in that, The method further includes: mixing the anhydrous sodium sulfate and the calcium sulfate dihydrate before grinding I; Preferably, the mixing conditions include: a temperature of 80-120°C, a time of 3-5 min, and a rotation speed of 100-150 rpm.

10. The application of the composite ecological cement prepared by the method according to any one of claims 1-5 and / or any one of claims 6-9 in the preparation of cement-based materials.

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