Gradient excitation type gypsum slag hydraulic cement as well as preparation method and application thereof

Abstract

The invention provides gradient excitation type gypsum slag hydraulic cement as well as a preparation method and application thereof. The gradient excitation type gypsum slag hydraulic cement is prepared from the following components in parts by weight: 1 to 4 parts of clinker, 65 to 75 parts of water-quenched blast furnace slag, 10 to 20 parts of fly ash, 8 to 15 parts of composite gypsum, 2 to 4 parts of gradient alkaline excitant and 1 to 3 parts of function regulator, wherein the function regulator is prepared by compounding nano SiO2 and metakaolin according to a mass ratio of 1: (1-5); the 45-micron screen residue of the fly ash is less than or equal to 25%, and the ignition loss is less than or equal to 8% The composite gypsum is formed by compounding dihydrate gypsum and anhydrous gypsum according to the mass ratio of (2-5): 1; the gradient alkaline activator is prepared by compounding slaked lime, silica fume and sodium carbonate according to the mass ratio of 5: (2-5): (1-4). The hydraulic material which is high in compressive strength and flexural strength, excellent in early crack resistance, low in hydration heat and excellent in chloride ion resistance and sulfate corrosion resistance is prepared through design of compounding of the gradient excitant, dynamic regulation and control of the composite gypsum, synergism of the functional regulator and the like, and the hydraulic material has important practical significance and wide application prospects.

Description

Technical Field

[0001] This invention belongs to the field of hydraulic cement technology, specifically relating to a gradient-activated gypsum slag hydraulic cement, its preparation method, and its application. Background Technology

[0002] In water conservancy engineering construction, cement, as a key cementing material, directly affects the quality and durability of the project. Currently, silicate cement (mainly PO ordinary silicate cement) is widely used in water conservancy projects. PO silicate cement possesses certain strength and stability, playing a vital role in numerous projects.

[0003] However, PO silicate cement has some obvious limitations in the application of water conservancy projects. In water conservancy projects, the core shortcomings of PO silicate cement stem from its high clinker content, which leads to high heat of hydration, high shrinkage, low impermeability, low corrosion resistance, and high cost. It is difficult to fully meet the requirements of water conservancy projects for large-volume temperature control, crack resistance and seepage prevention, resistance to complex water environments, and economy.

[0004] Therefore, the development of a hydraulic cementitious material with high compressive and flexural strength, excellent early crack resistance, low heat of hydration, resistance to chloride ion and sulfate corrosion, and excellent impermeability is of great practical significance and application prospect for improving the durability of underground and hydraulic engineering structures. Summary of the Invention

[0005] The purpose of this invention is to provide a gradient-activated gypsum slag hydraulic cement, which, by weight, is composed of the following components:

[0006] 1-4 parts clinker, 65-75 parts water-quenched blast furnace slag, 10-20 parts fly ash, 8-15 parts composite gypsum, 2-4 parts gradient alkaline activator, and 1-3 parts functional regulator.

[0007] The functional regulator is composed of nano-SiO2 and metakaolin in a mass ratio of 1:(1-5).

[0008] In a preferred embodiment, the total weight of clinker, water-quenched blast furnace slag, fly ash, composite gypsum and gradient alkaline activator in the gradient-activated gypsum-slag hydraulic cement is 100 parts, and the dosage of functional regulator is 1-3 parts.

[0009] In a preferred embodiment, the clinker is ordinary silicate cement clinker, and the magnesium oxide content in the clinker is limited to ≤5.0%, and the free calcium oxide content is limited to ≤1.2%.

[0010] In this invention, a small amount of clinker is ordinary silicate clinker, and the product complies with the national standard GB / T21372—2024. At the same time, by limiting the specific magnesium oxide and free calcium oxide content in the clinker, the risk of poor volume stability is controlled. The Ca(OH)2 generated by hydration helps to construct a highly alkaline environment, which also promotes the destruction of the slag and fly ash glass and increases the dissolution of SiO2 and Al2O3. In addition, the significant reduction in the amount of clinker used solves the high carbon emission problem of traditional high clinker cement, and has the beneficial effect of green energy saving.

[0011] In a preferred embodiment, the water-quenched blast furnace slag has a glass content of ≥90% and an Al2O3 content of 15-18%.

[0012] In a preferred embodiment, the fly ash has a 45μm sieve residue of ≤25% and a loss on ignition of ≤8%.

[0013] In this invention, the fly ash is limited to 10-20 parts by weight with a 45μm sieve residue of ≤25% and a loss on ignition of ≤8%. This range can give full play to the micro-aggregate effect of fly ash and improve the later strength through the secondary hydration of SiO2, increase the density of cement, and improve the 28-day strength by 12-18% compared with traditional silicate cement.

[0014] In this invention, the content of vitreous slag in water-quenched blast furnace slag is limited to generate higher activity. Additionally, a suitable Al2O3 content ensures the formation of ettringite, thereby improving flexural strength. Simultaneously, the aforementioned limited fly ash, as a substitute for slag, reduces the total heat of hydration per unit volume of cement, resulting in a more gradual hydration exothermic rate. By compounding water-quenched blast furnace slag and fly ash in a specific ratio, a gradient excitation mechanism can be used to achieve a 3-day compressive strength ≥32MPa and a 28-day compressive strength ≥55MPa, while also leveraging the micro-aggregate effect to reduce porosity, resulting in a chloride ion diffusion coefficient ≤0.7×10⁻⁶. -1 2m 2 / s, while the high solid waste content (85-90%) significantly reduces carbon emissions, and the 0.03-0.04% limiting expansion rate reduces cracks, thus fully realizing the invention's purpose of high strength, low carbonization, high durability and volume stability of cement.

[0015] In a preferred embodiment, the composite gypsum is prepared by mixing dihydrate gypsum and anhydrous gypsum in a mass ratio of (2-5):1; more preferably, the composite gypsum is prepared by mixing dihydrate gypsum and anhydrous gypsum in a mass ratio of 3:1; more preferably, the dihydrate gypsum contains ≥95% CaSO4·2H2O and has a specific surface area of ​​200-300 m². 2 / kg; the anhydrous gypsum contains ≥98% CaSO4 and has a specific surface area of ​​300-400 m² / kg. 2 / kg.

[0016] In this invention, a specific ratio of dihydrate gypsum to anhydrous gypsum is designed to provide a basis for achieving a three-stage gradient excitation. Specifically, the dihydrate gypsum rapidly releases SO4 within 0-3 days. 2- With Ca in slag 2+ Al 3+ The reaction produces ettringite, which shortens the setting time and improves early flexural strength (≥5.5 MPa after 3 days); anhydrous gypsum slowly dissolves over 3-28 days, continuously providing SO4. 2- It synergistically generates C-(A)-SH gel with Al2O3 released from quicklime, silica fume, slag and fly ash, enhancing the later compressive strength (≥55MPa after 28 days).

[0017] In a preferred embodiment, the gradient alkaline activator is prepared by compounding quicklime, silica fume, and sodium carbonate in a mass ratio of 5:(2-5):(1-4); preferably, the gradient alkaline activator is prepared by compounding quicklime, silica fume, and sodium carbonate in a mass ratio of 5:3:2; more preferably, the quicklime contains ≥90% Ca(OH)2, has a fineness (45μm sieve residue) ≤10%, and free water ≤2%; the silica fume contains ≥90% SiO2 and has a specific surface area ≥15000 m². 2 / kg, and loss on ignition ≤6%; the sodium carbonate contains Na2CO3 with a purity ≥98%, a particle size ≤150μm, and a moisture content ≤1%.

[0018] In this invention, based on the three-level gradient activation requirement, sodium carbonate is used for rapid dissolution, providing initial high alkalinity (pH≥12.5), which promotes rapid depolymerization and release of active ions in the slag glass within 0-3 days; quicklime is used to continuously replenish Ca(OH)2, and reacts with gypsum to form ettringite to fill the pores within 3-7 days; silica fume, with its high specific surface area, participates in the reaction to generate additional CSH gel within 7-28 days. After compounding quicklime, silica fume, and sodium carbonate in a mass ratio of 5:(2-5):(1-4), the compressive strength at 3 days can be ≥32MPa and at 28 days ≥55MPa through the synergistic effect of alkali activation and sulfate activation. The dense, high-strength hydrate makes the corrosion resistance coefficient of 5% Na2SO4 solution ≥0.90. At the same time, by controlling the hydration rate, the heat of hydration at 7 days can be controlled at 170-190kJ / kg. Combined with a 0.03-0.04% limiting expansion rate to reduce cracks, the invention fully realizes the invention's objective of high strength, low heat of hydration, and high durability of cement.

[0019] In a preferred embodiment, the nano-SiO2 has an average particle size of 15-25 nm and a SiO2 content greater than 99%.

[0020] In a preferred embodiment, the metakaolin has a 45μm square-hole sieve residue of ≤5.0%, SiO2 content of ≤55%, and Al2O3 content of ≥35%; more preferably, the metakaolin has an activity index of ≥90% at 3d, ≥95% at 7d, and ≥105% at 28d.

[0021] In this invention, nano-SiO2 and metakaolin are compounded at a mass ratio of 1:(1-5) as a functional modifier. The small particle size and high activity of nano-SiO2 can fill cement pores and participate in the hydration reaction to generate more (CSH) gel, while the high activity and specific chemical composition of metakaolin can promote cement hydration and improve the density of cement paste. The synergistic effect of these two materials effectively improves the compressive and flexural strength of cement, enhances its resistance to freeze-thaw cycles, water, and sulfate attack, reduces the heat of hydration, and utilizes its expansion properties to compensate for shrinkage, reducing cracks. This achieves the invention's objectives of high strength, low heat of hydration, high durability, and good volume stability in cement.

[0022] In a preferred embodiment, the gradient-activated gypsum slag hydraulic cement has a 3-day compressive strength ≥32 MPa, a flexural strength ≥5.5 MPa, a 28-day compressive strength ≥55 MPa, a flexural strength ≥8.5 MPa, an initial setting time of 160-190 minutes, and a restricted expansion rate of 0.03-0.04%.

[0023] In a preferred embodiment, the gradient-activated gypsum slag hydraulic cement has a 7-day hydration heat of 170-190 kJ / kg, a corrosion resistance coefficient ≥0.90 after immersion in 5% Na₂SO₄ solution for 180 days, and a chloride ion diffusion coefficient ≤0.7 × 10⁻⁶ in 5% NaCl solution. -12 m 2 / s.

[0024] Another object of the present invention is to provide a method for preparing gradient-activated gypsum slag hydraulic cement as described in any one of the above claims, comprising the following steps:

[0025] (1) After mixing water-quenched blast furnace slag and fly ash, grind them to a specific surface area of ​​480-520 m². 2 / kg, to obtain mixed slag powder; after mixing the obtained mixed slag powder with clinker and gradient alkaline activator, control the grinding temperature at 60-70℃, and grind to a specific surface area of ​​450-500m². 2 / kg;

[0026] (2) Control the grinding temperature of the composite gypsum below 60℃ and grind it to a specific surface area of ​​500-550m². 2 / kg;

[0027] (3) Mix the products obtained in steps (1) and (2) with the functional regulator and stir until homogeneous to obtain the final product.

[0028] In a preferred embodiment, the mixing time in step (3) is 15-20 minutes.

[0029] In this invention, in step (1), after mixing the mixed slag powder, clinker, and gradient alkaline activator, grinding them in a temperature range of 60-70℃ can promote the dispersion of silica fume and avoid the decomposition of sodium carbonate; in step (2), controlling the grinding temperature of composite gypsum to ≤60℃ can avoid the dehydration of dihydrate gypsum.

[0030] Another object of the present invention is to provide the application of the gradient-activated gypsum slag hydraulic cement described in any of the above-mentioned claims in hydraulic engineering.

[0031] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0032] 1. In this invention, a composite activator of sodium carbonate, quicklime, and silica fume is designed to achieve a three-stage gradient activation mechanism, enabling synergistic activation of slag and fly ash. This solves the problem of delayed strength development under high fly ash content. Specifically, within 0-3 days, the rapid dissolution of sodium carbonate provides initial alkalinity, promoting rapid depolymerization of the slag glass and releasing Ca. 2+ Al 3+ Ions are used to achieve primary excitation; within 3-7 days, Ca(OH)2 is continuously replenished by quicklime, which reacts with the SO4 released by the composite gypsum. 2- The reaction generates ettringite, which fills the capillary pores and achieves secondary excitation. Within 7-28 days, additional CSH gel is generated through the synergistic reaction of fly ash, silica fume and metakaolin, which optimizes the structure of the interfacial transition zone and thus achieves deep excitation.

[0033] 2. In this invention, by limiting the fly ash content to 10-20 parts with a 45μm sieve residue ≥25% and a loss on ignition ≤8%, the micro-aggregate effect is utilized while avoiding the problems caused by high carbon content, such as reduced pozzolanic activity of fly ash, increased water demand in concrete, and even impact on durability. This results in a 12-18% increase in 28-day strength compared to traditional high-fly ash cement. Simultaneously, by adjusting the gradient alkaline activator ratio, the problem of prolonged setting time due to increased fly ash content is effectively solved. Furthermore, this invention uses a mixture of dihydrate gypsum and anhydrous gypsum at a ratio of (2-5):1, ensuring both rapid early sulfate release and sustained later activation, thus resolving the balance between early strength and later stability.

[0034] 3. This invention is the first to use nano-SiO2 and metakaolin in a ratio of 1:(1-5) as a functional regulator, which promotes CSH gel formation through the seed effect and supplements Al2O3 to strengthen the ettringite structure, thereby achieving a dual improvement in strength and durability.

[0035] 4. Through the specific raw material and dosage ratio design described above, the gradient-activated gypsum-slag hydraulic cement provided by this invention exhibits a 3-day compressive strength ≥32MPa, a 28-day compressive strength ≥55MPa, an initial setting time of 160-190 minutes, and a later-stage limited expansion rate of 0.03-0.04%, far exceeding that of traditional ordinary and slag silicate cements. Simultaneously, the gradient-activated gypsum-slag hydraulic cement has a 7-day hydration heat of 170-190kJ / kg, a corrosion resistance coefficient ≥0.90 after 180 days in 5% Na2SO4 solution, and a chloride ion diffusion coefficient ≤0.7×10⁻⁶. -12 m 2 / s, with excellent durability, is particularly suitable for large-volume hydraulic concrete projects. Detailed Implementation

[0036] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to specific embodiments. However, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0037] Unless otherwise specified, the technical means used in this invention are conventional means well known to those skilled in the art. All raw materials, reagents, instruments, and equipment used in this invention can be purchased commercially or prepared using existing methods. Unless otherwise specified, all reagents used in this invention are of analytical grade.

[0038] In this invention, the weight parts can be weight units known in the art such as μg, mg, g, kg, or multiples thereof, such as 1 / 10, 1 / 100, 10 times, 100 times, etc.

[0039] In this embodiment of the invention, the clinker is ordinary silicate cement clinker, with a magnesium oxide content ≤5.0% and a free calcium oxide content ≤1.2%. The water-quenched blast furnace slag has a glass content ≥90% and an Al2O3 content of 15-18%. The fly ash used has a 45μm sieve residue ≤25%, a loss on ignition ≤8%, and a moisture content ≤1%. The dihydrate gypsum used has a CaSO4·2H2O content ≥95% and a specific surface area of ​​200-300 m². 2 / kg; the anhydrous gypsum used contains ≥98% CaSO4 and has a specific surface area of ​​300-400 m² / kg. 2 / kg. The slaked lime used must have a Ca(OH)₂ content ≥90%, a fineness (45μm sieve residue) ≤10%, and free water ≤2%; the silica fume used must have a SiO₂ content ≥90% and a specific surface area ≥15000m². 2 / kg, and loss on ignition ≤6%; the sodium carbonate used has a Na2CO3 purity ≥98%, particle size ≤150μm, and moisture ≤1%. The nano-SiO2 used has an average particle size of 15-25nm and a SiO2 content greater than 99%. The metakaolin used has a 45μm square-hole sieve residue ≤5.0%, an activity index of ≥90% at 3d, ≥95% at 7d, ≥105% at 28d, a SiO2 content ≤55%, and an Al2O3 content ≥35%.

[0040] In this embodiment of the invention, the testing method and execution standard for material properties are as follows:

[0041] Compressive strength and flexural strength: GB / T17671-1999 "Test Method for Strength of Cement Mortar (ISO Method)" was adopted. After curing 40mm×40mm×160mm prism specimens in water at 20℃ to the specified age (3 days and 28 days), the flexural failure load and compressive failure load were measured respectively.

[0042] Heat of hydration: According to GB / T12959-2024 "Determination of heat of hydration of cement", the heat of hydration after 7 days is determined by the heat of solution method (substitution method) and calculated by the difference in heat of solution between unhydrated cement and hydrated cement in standard acid solution.

[0043] Limiting expansion rate: Refer to GB / T23439-2017 "Concrete Expansion Agent" and use a dial gauge to measure the initial length of the specimen within 1 hour after demolding. After curing in water to the specified age (7 days), measure the length again and calculate according to the formula. The process requires strict control of the calibration of the measuring instrument, the consistency of the specimen position and the accuracy of the reading to 0.001 mm. The average value of two similar specimens is taken as the result.

[0044] Corrosion resistance coefficient: According to GB / T749-2008 "Test method for resistance of cement to sulfate attack", the specimens were immersed in 5% Na2SO4 solution for 180 days, and the compressive strength before and after immersion was compared to calculate the corrosion resistance coefficient.

[0045] Chloride ion diffusion coefficient: The diffusion coefficient of chloride ions in the specimen was determined according to the RCM method (rapid chloride ion migration coefficient method) in GB / T50082-2009 "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete".

[0046] Example 1

[0047] A gradient-activated gypsum slag hydraulic cement, the formula of which is as follows:

[0048] 2 parts clinker, 70 parts water-quenched blast furnace slag, 15 parts fly ash, 10 parts composite gypsum, 3 parts gradient alkaline activator, and 2 parts functional regulator;

[0049] The clinker is a common silicate clinker (MgO 4.5%, free CaO 0.8%).

[0050] The glass content of water-quenched blast furnace slag is 93%, and the Al2O3 content is 17%.

[0051] The residue on a 45μm sieve in fly ash was 22%, and the loss on ignition was 7%.

[0052] Composite gypsum consists of dihydrate gypsum (CaSO4·2H2O content 96%, specific surface area 260m²) 2 / kg) and anhydrous gypsum (CaSO4 content 98%, specific surface area 360m²) 2 ( / kg) is compounded at a mass ratio of 3:1;

[0053] The gradient alkaline activator consists of quicklime (Ca(OH)₂ content 92%, 45μm sieve residue 7%, free water content 1.5%) and silica fume (SiO₂ content 92%, specific surface area 17000 m²). 2 It is a compound of sodium carbonate (Na2CO3 content 99%, particle size 100μm, moisture 0.8%) and sodium carbonate (Na2CO3 content 99%, particle size 100μm, moisture 0.8%) in a mass ratio of 5:3:2;

[0054] The functional regulator is a compound of nano-SiO2 (particle size 20nm, SiO2 content 99.6%) and metakaolin (Al2O3 content 37%, SiO2 content 52%, 45μm sieve residue 3%, 28d activity index 110%) in a mass ratio of 1:2.

[0055] The preparation method includes the following steps:

[0056] 1. Mix water-quenched blast furnace slag and fly ash, then grind them to a specific surface area of ​​500 m². 2 / kg, to obtain mixed slag powder;

[0057] 2. Grind the composite gypsum at a temperature below 60℃ to a specific surface area of ​​520m². 2 / kg;

[0058] 3. Mix the mixed slag powder obtained in step 1 with clinker and gradient alkaline activator, and grind at below 65℃ until the specific surface area is 460m². 2 / kg;

[0059] 4. Add the composite gypsum powder obtained in step 2 and the functional regulator to the product obtained in step 3, stir and mix for 18 minutes to obtain the finished product.

[0060] The performance of the material obtained in this embodiment was tested, and the results are as follows:

[0061] 3-day compressive strength: 35 MPa / flexural strength: 5.9 MPa; 28-day compressive strength: 63 MPa / flexural strength: 9.0 MPa; initial setting time: 180 minutes; 7-day heat of hydration: 180 kJ / kg; restricted expansion rate: 0.036%; corrosion resistance coefficient after 180 days of immersion in 5% Na₂SO₄: 0.93; diffusion coefficient of 5% NaCl: 0.64 × 10⁻⁶. -12 m 2 / s; Strength loss of 7.2% after 300 freeze-thaw cycles.

[0062] In this embodiment, the synergistic effect of the three-level gradient excitation is significant. Sodium carbonate rapidly increases alkalinity and promotes early hydration, quicklime continuously replenishes Ca(OH)2 to generate ettringite, silica fume and functional regulators refine the pores, and composite gypsum dynamically releases SO4. 2- Balance the intensity of early and late stages.

[0063] Example 2 (High Dosage of Functional Regulator)

[0064] A gradient-activated gypsum slag hydraulic cement, the formula of which is as follows:

[0065] 2 parts clinker, 70 parts water-quenched blast furnace slag, 15 parts fly ash, 10 parts composite gypsum, 3 parts gradient alkaline activator, and 3 parts functional regulator;

[0066] The functional regulator is composed of nano-SiO2 and metakaolin in a mass ratio of 1:4. The specifications of the other raw materials are the same as in Example 1, and the preparation method is the same as in Example 1.

[0067] The performance of the material obtained in this embodiment was tested, and the results are as follows:

[0068] 3-day compressive strength 37 MPa / flexural strength 6.2 MPa, 28-day compressive strength 69 MPa / flexural strength 9.3 MPa; 7-day heat of hydration 176 kJ / kg; restricted expansion rate 0.039%; corrosion resistance coefficient 0.94; diffusivity 0.61 × 10⁻⁶ -12 m 2 / s.

[0069] In this embodiment, the higher dosage of functional regulators further enhances the filling and seeding effects, increases the amount of C-(A)-SH gel generated, further reduces porosity, and simultaneously improves strength and durability.

[0070] Example 3 (Upper Limit Ratio of Fly Ash)

[0071] A gradient-activated gypsum slag hydraulic cement, the formula of which is as follows:

[0072] 2 parts clinker, 65 parts water-quenched blast furnace slag, 20 parts fly ash, 10 parts composite gypsum, 3 parts gradient alkaline activator, and 3 parts functional regulator;

[0073] The fly ash had a 45μm sieve residue of 24% and a loss on ignition of 8%. The specifications of the other raw materials were the same as in Example 1, and the preparation method was the same as in Example 1.

[0074] The performance of the material obtained in this embodiment was tested, and the results are as follows:

[0075] 3-day compressive strength 33 MPa / flexural strength 5.6 MPa, 28-day compressive strength 59 MPa / flexural strength 8.6 MPa; 7-day heat of hydration 178 kJ / kg; restricted expansion rate 0.033%; corrosion resistance coefficient 0.91; diffusivity 0.67 × 10⁻⁶. -12 m 2 / s.

[0076] In this embodiment, fly ash accounts for 20 parts and has a loss on ignition of 8%. The quicklime in the gradient activator can effectively activate the fly ash while maintaining its basic performance.

[0077] Example 4 (Adjustment of Composite Plaster Ratio)

[0078] A gradient-activated gypsum slag hydraulic cement, the formula of which is as follows:

[0079] 2 parts clinker, 70 parts water-quenched blast furnace slag, 15 parts fly ash, 12 parts composite gypsum, 3 parts gradient alkaline activator, and 2 parts functional regulator;

[0080] The composite gypsum is composed of dihydrate gypsum and anhydrous gypsum in a mass ratio of 5:1. The specifications of the other raw materials are the same as in Example 1, and the preparation method is the same as in Example 1.

[0081] The performance of the material obtained in this embodiment was tested, and the results are as follows:

[0082] 3-day compressive strength 34MPa / flexural strength 5.8MPa, 28-day compressive strength 61MPa / flexural strength 8.8MPa; restricted expansion rate 0.037%; corrosion resistance coefficient 0.92.

[0083] In this embodiment, the amount of composite gypsum is increased to 12 parts and the proportion of dihydrate gypsum is increased to 5:1, resulting in a gradient release of SO4. 2- It is better matched with the hydration process, and ettringite continues to be generated, limiting the expansion rate to 0.037%, while the strength and corrosion resistance remain stable and meet the standards.

[0084] Example 5 (Adjustment of Gradient Exciter Ratio)

[0085] A gradient-activated gypsum slag hydraulic cement, the formula of which is as follows:

[0086] 2 parts clinker, 70 parts water-quenched blast furnace slag, 15 parts fly ash, 10 parts composite gypsum, 4 parts gradient alkaline activator, and 2 parts functional regulator;

[0087] The gradient alkaline activator is composed of quicklime, silica fume and sodium carbonate in a mass ratio of 5:4:1. The specifications of the other raw materials are the same as in Example 1, and the preparation method is the same as in Example 1.

[0088] The performance of the material obtained in this embodiment was tested, and the results are as follows:

[0089] 3-day compressive strength 36 MPa / flexural strength 6.0 MPa, 28-day compressive strength 65 MPa / flexural strength 9.1 MPa; 7-day heat of hydration 179 kJ / kg; diffusivity 0.62 × 10⁻⁶ -12 m 2 / s.

[0090] In this embodiment, the activator dosage is increased to 4 parts and the silica fume ratio is increased, which enhances the synergistic effect of alkali activation and volcanic ash, making the C-(A)-SH gel denser, reducing porosity, significantly improving strength, and optimizing hydration heat and diffusion coefficient.

[0091] Comparative Example 1 (without gradient alkaline activator)

[0092] Compared with Example 1, the only difference is the removal of the gradient alkaline activator; the specifications of the other raw materials are the same as in Example 1, and the preparation method is the same as in Example 1.

[0093] That is, the specific formula is: 2 parts clinker, 70 parts water-quenched blast furnace slag, 15 parts fly ash, 10 parts composite gypsum, and 2 parts functional regulator.

[0094] The performance of the material obtained in this comparative example was tested, and the results are as follows:

[0095] 3-day compressive strength 16 MPa / flexural strength 3.1 MPa, 28-day compressive strength 27 MPa / flexural strength 5.1 MPa; restricted expansion rate 0.007%; corrosion resistance coefficient 0.67; diffusion coefficient 2.9 × 10⁻⁶. -12 m 2 / s.

[0096] In this comparative example, due to the lack of an activator, the Si-O bonds in the slag / fly ash glass were not broken by the alkali, and active ions could not be released. The composite gypsum and Al... 3+ The reaction is missing, the functional regulator does not participate in the hydration of alkaline media, and the system has no effective gel structure.

[0097] Comparative Example 2 (Single activator)

[0098] Compared with Example 1, the only difference is that the alkaline activator is only quicklime, while the specifications of the other raw materials are the same as in Example 1, and the preparation method is the same as in Example 1.

[0099] That is, the specific formula is: 2 parts clinker, 70 parts water-quenched blast furnace slag, 15 parts fly ash, 10 parts composite gypsum, 3 parts quicklime, and 2 parts functional regulator.

[0100] The performance of the material obtained in this comparative example was tested, and the results are as follows:

[0101] 3-day compressive strength 23 MPa / flexural strength 4.3 MPa, 28-day compressive strength 43 MPa / flexural strength 6.8 MPa; 7-day heat of hydration 160 kJ / kg; restricted expansion rate 0.018%; diffusion coefficient 1.3 × 10⁻⁶ -12 m 2 / s.

[0102] In this comparative example, the basicity of quicklime alone was insufficient and there was no gradient release, which prevented efficient depolymerization of slag. The lack of silica fume filling and volcanic ash reaction, the early strong activation of sodium carbonate, and the insufficient C-(A)-SH gel in the later stage led to synergistic failure and performance degradation.

[0103] Comparative Example 3 (deviation of gradient alkaline activator ratio)

[0104] Compared with Example 1, the only difference is that the gradient alkaline activator is composed of quicklime, silica fume and sodium carbonate in a mass ratio of 5:1:4, while the specifications of the other raw materials are the same as in Example 1, and the preparation method is the same as in Example 1.

[0105] The performance of the material obtained in this comparative example was tested, and the results are as follows:

[0106] 3-day compressive strength 26 MPa / flexural strength 4.6 MPa, 28-day compressive strength 50 MPa / flexural strength 7.8 MPa; 7-day heat of hydration 208 kJ / kg; limiting expansion rate 0.024%.

[0107] In this comparative example, the low proportion of silica fume resulted in insufficient filling and reaction with pozzolanic ash, while the excessive sodium carbonate caused an overly rapid early reaction, disrupting the gradient balance and leading to a decrease in product performance. This demonstrates that the specific range of activator proportions defined in this invention is one of the key factors in generating a synergistic effect.

[0108] Comparative Example 4 (without functional regulator)

[0109] Compared with Example 1, the only difference is the removal of the functional regulator; the specifications of the other raw materials are the same as in Example 1, and the preparation method is the same as in Example 1.

[0110] That is, the specific formula is: 2 parts clinker, 70 parts water-quenched blast furnace slag, 15 parts fly ash, 10 parts composite gypsum, and 3 parts gradient alkaline activator.

[0111] The performance of the material obtained in this comparative example was tested, and the results are as follows:

[0112] 3-day compressive strength 27 MPa / flexural strength 4.7 MPa, 28-day compressive strength 50 MPa / flexural strength 7.9 MPa; porosity 19%; confined expansion rate 0.025%; 5% NaCl diffusion coefficient 0.92 × 10⁻⁶ -12m 2 / s; 14% strength loss after 300 freeze-thaw cycles.

[0113] In this comparative example, due to the lack of functional modifiers, the filling effect of nano-SiO2 on the 20-50nm pores and the Al2O3 supplemented by metakaolin are lost, resulting in a loose C-(A)-SH gel structure in the hydration products and an increase in defects in the interfacial transition zone. The gel generated by the gradient activator is prone to forming coarse crystals due to the lack of nano-seed guidance, leading to a significant decrease in strength, density, and freeze resistance. It can be seen that the specific functional modifiers and activators defined in this invention form a synergistic effect of physical filling and chemical gel strengthening, which is one of the key factors in improving product performance.

[0114] Comparative Example 5 (Single-function regulator)

[0115] Compared with Example 1, the only difference is that the functional regulator is only nano-SiO2 (without metakaolin), while the specifications of the other raw materials are the same as in Example 1, and the preparation method is the same as in Example 1.

[0116] The performance of the material obtained in this comparative example was tested, and the results are as follows:

[0117] 3-day compressive strength 30 MPa / flexural strength 5.2 MPa, 28-day compressive strength 55 MPa / flexural strength 8.2 MPa; restricted expansion rate 0.028%; corrosion resistance coefficient of 5% Na2SO4 0.86; diffusion coefficient 0.80×10 -12 m 2 / s.

[0118] In this comparative example, although single nano-SiO2 can play a filling role, it cannot react with the SiO2 and Ca released by the activator due to the lack of Al2O3 supplementation from metakaolinite. 2+ To form a stable CASH gel, Al in the ettringite structure 3+ Insufficient strength leads to decreased stability, slower strength growth in later stages, and reduced corrosion resistance. Comparing Example 1 and Comparative Example 3, it can be seen that only by using a combination of nano-SiO2 and metakaolin as a functional modifier can the dual synergy of physical filling and chemical gel reinforcement be achieved; no single component can replace it.

[0119] Comparative Example 6 (Single Plaster Substitute)

[0120] Compared with Example 1, the only difference is that the gypsum is anhydrous gypsum, while the specifications of the other raw materials are the same as in Example 1, and the preparation method is the same as in Example 1.

[0121] That is, the specific formula is: 2 parts clinker, 70 parts water-quenched blast furnace slag, 15 parts fly ash, 10 parts anhydrous gypsum, 3 parts gradient alkaline activator, and 2 parts functional regulator.

[0122] The performance of the material obtained in this comparative example was tested, and the results are as follows:

[0123] 3-day compressive strength 24MPa / flexural strength 4.4MPa, 28-day compressive strength 52MPa / flexural strength 8.0MPa; 3-day expansion rate 0.01%; corrosion resistance coefficient 0.83.

[0124] In this comparative example, the early SO4 content of single anhydrous gypsum was... 2- The slow release and insufficient formation of ettringite lead to low early strength. Although it is supplemented later, it cannot make up for the early defects. It can be seen that the composite gypsum "gradient sulfur release" and gradient alkaline activator defined in this invention have a synergistic effect.

[0125] Comparative Example 7 (Clinker admixture exceeding the standard)

[0126] Compared with Example 1, the only difference is that the amount of clinker used is 6 parts, while the specifications of the other raw materials are the same as in Example 1, and the preparation method is the same as in Example 1.

[0127] That is, the specific formula is: 6 parts clinker, 70 parts water-quenched blast furnace slag, 15 parts fly ash, 10 parts composite gypsum, 3 parts gradient alkaline activator, and 2 parts functional regulator.

[0128] The performance of the material obtained in this comparative example was tested, and the results are as follows:

[0129] 3-day compressive strength 38MPa / flexural strength 6.3MPa, 28-day compressive strength 60MPa / flexural strength 8.5MPa; 7-day heat of hydration 235kJ / kg; restricted expansion rate 0.022%; corrosion resistance coefficient of 5% Na2SO4 0.85; porosity 17%.

[0130] In this comparative example, after the clinker content exceeded the standard, the strength increased in the early stage due to the rapid hydration of the clinker. However, the heat of hydration brought by the high clinker content was significantly higher than that in Example 1, which easily led to early temperature cracks in the hydraulic structure. At the same time, the excessive clinker consumed SO4 in the system. 2- The reduced formation of ettringite decreases the expansion rate, and the enrichment of Ca(OH)2 in the clinker hydration products reduces corrosion resistance. Therefore, the 1-4 parts of clinker specified in this invention are key factors in balancing strength, heat of hydration, and durability. Excessive dosage will disrupt the synergistic effect and is detrimental to the low-carbon and environmentally friendly concept.

[0131] Comparative Example 8 (Clinker specifications not up to standard)

[0132] Compared with Example 1, the only difference is that the clinker contains 6.5% MgO and 2.0% free CaO, while the specifications of the other raw materials are the same as in Example 1, and the preparation method is the same as in Example 1.

[0133] The performance of the material obtained in this comparative example was tested, and the results are as follows:

[0134] 3-day compressive strength 32MPa / flexural strength 5.5MPa, 28-day compressive strength 56MPa / flexural strength 8.1MPa; 28-day expansion rate abnormally increased to 0.05% (local micro-cracks); 7-day heat of hydration 205kJ / kg; corrosion resistance coefficient 0.82.

[0135] In this comparative example, due to the high levels of free CaO and MgO in the clinker, the continuous reaction during the later stages of hydration generates Ca(OH)₂ and Mg(OH)₂, resulting in excessive volume expansion and internal microcracks. Although the early strength was close to that of Example 1, the later strength growth was weak and the structural integrity was compromised, leading to a decrease in corrosion resistance due to crack penetration. It is evident that the specific low free CaO and low MgO content specified in the clinker of this invention is one of the foundations for ensuring volume stability and durability; failure to meet these specifications directly undermines the synergistic effect of the system.

[0136] Comparative Example 9 (Fly ash specifications exceeded standards)

[0137] Compared with Example 1, the only difference is that the fly ash residue on the 45μm sieve is 30% and the loss on ignition is 10%, while the other raw material specifications and preparation methods are the same as in Example 1.

[0138] The performance of the material obtained in this comparative example was tested, and the results are as follows:

[0139] 3-day compressive strength 25MPa / flexural strength 4.7MPa, 28-day compressive strength 49MPa / flexural strength 7.7MPa; porosity 21%; corrosion resistance coefficient 0.84.

[0140] In this comparative example, the accumulation of coarse fly ash leads to uneven slurry, and high loss on ignition carbon particles adsorb activators and moisture, both of which reduce reaction efficiency. Therefore, the fly ash residue of ≤25% on a 45μm sieve and loss on ignition of ≤8% as defined in this invention are of great significance.

[0141] Comparative Example 10 (Functional Regulator Specifications Not up to Standard)

[0142] Compared with Example 1, the only difference is that the nano-SiO2 particle size is 40nm and the metakaolin Al2O3 content is 32%, while the other raw material specifications and preparation methods are the same as in Example 1.

[0143] The performance of the material obtained in this comparative example was tested, and the results are as follows:

[0144] 3-day compressive strength 28 MPa / flexural strength 4.9 MPa, 28-day compressive strength 51 MPa / flexural strength 7.9 MPa; 15% strength loss after 300 freeze-thaw cycles; diffusion coefficient 0.86 × 10⁻⁶. -12 m 2 / s.

[0145] In this comparative example, the filling effect of large-particle-size nano-SiO2 is weak, and the low-Al2O3 kaolinite cannot supplement sufficient Al. 3+ This leads to a decrease in the synergistic effect of the activator on the dense structure, highlighting the significant importance of the functional regulator specifications defined in this invention.

[0146] Comparative Example 11 (Slag specifications not up to standard)

[0147] Compared with Example 1, the only difference is that the slag is 80% glass and 14% Al2O3, while the specifications of the other raw materials are the same as in Example 1, and the preparation method is the same as in Example 1.

[0148] The performance of the material obtained in this comparative example was tested, and the results are as follows:

[0149] 3-day compressive strength 21 MPa / flexural strength 3.9 MPa, 28-day compressive strength 39 MPa / flexural strength 6.4 MPa; corrosion resistance coefficient 0.74; diffusion coefficient 1.7 × 10⁻⁶. -12 m 2 / s.

[0150] In this comparative example, due to the stable structure of the low-glass slag, the activator is difficult to depolymerize, and the insufficient Al2O3 results in a low amount of ettringite formation. This proves that the slag glass content of ≥90% and Al2O3 content of 15-18% as defined in this invention are one of the foundations for achieving high product performance.

[0151] In summary, it can be seen that Examples 1-7 of the present invention, through the design of gradient activator compounding, dynamic control of composite gypsum, and synergistic effect of functional regulators, are superior to Comparative Examples 1-11 in terms of strength (3-day compressive strength ≥32MPa) and durability (corrosion resistance coefficient ≥0.90). Comparative Examples 1-11, due to problems such as lack of gradient alkaline activator, single activator, deviation of gradient alkaline activator ratio, lack of functional regulator, single functional regulator, single gypsum, excessive clinker content, substandard clinker specifications, excessive fly ash specifications, substandard functional regulator specifications, and substandard slag specifications, have resulted in a significant decline in product performance. This fully demonstrates that the present invention achieves a significant improvement in the performance of hydraulic cement through multi-component synergistic design.

[0152] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A gradient-activated gypsum slag hydraulic cement, characterized in that, The gradient-activated gypsum slag hydraulic cement, by weight, comprises the following components: 1-4 parts clinker, 65-75 parts water-quenched blast furnace slag, 10-20 parts fly ash, 8-15 parts composite gypsum, 2-4 parts gradient alkaline activator, and 1-3 parts functional regulator. The functional regulator is composed of nano-SiO2 and metakaolin in a mass ratio of 1:(1-5).

2. The gradient-activated gypsum slag hydraulic cement as described in claim 1, characterized in that, The clinker is ordinary silicate cement clinker, with the magnesium oxide content limited to ≤5.0% and the free calcium oxide content limited to ≤1.2%.

3. The gradient-activated gypsum slag hydraulic cement as described in claim 1, characterized in that, The water-quenched blast furnace slag has a glass content of ≥90% and an Al2O3 content of 15-18%. The fly ash has a 45μm sieve residue of ≤25% and a loss on ignition of ≤8%.

4. The gradient-activated gypsum slag hydraulic cement as described in claim 1, characterized in that, The composite gypsum is made by mixing dihydrate gypsum and anhydrous gypsum in a mass ratio of (2-5):

1.

5. The gradient-activated gypsum slag hydraulic cement as described in claim 1, characterized in that, The gradient alkaline activator is composed of quicklime, silica fume and sodium carbonate in a mass ratio of 5:(2-5):(1-4).

6. The gradient-activated gypsum slag hydraulic cement as described in claim 1, characterized in that, The nano-SiO2 has an average particle size of 15-25 nm and a SiO2 content greater than 99%. The metakaolin clay has a sieve residue of ≤5.0% on a 45μm square mesh sieve, a SiO2 content of ≤55%, and an Al2O3 content of ≥35%.

7. The gradient-activated gypsum slag hydraulic cement as described in claim 1, characterized in that, The gradient-activated gypsum slag hydraulic cement has a 3-day compressive strength ≥32 MPa, a flexural strength ≥5.5 MPa, a 28-day compressive strength ≥55 MPa, a flexural strength ≥8.5 MPa, an initial setting time of 160-190 minutes, and a restricted expansion rate of 0.03-0.04%.

8. The gradient-activated gypsum slag hydraulic cement as described in claim 1, characterized in that, The gradient-activated gypsum slag hydraulic cement has a 7-day hydration heat of 170-190 kJ / kg, a corrosion resistance coefficient ≥0.90 after immersion in 5% Na2SO4 solution for 180 days, and a chloride ion diffusion coefficient ≤0.7×10-12 in 5% NaCl solution. m 2 / s.

9. The method for preparing gradient-activated gypsum slag hydraulic cement as described in any one of claims 1-8, characterized in that, Includes the following steps: (1) After mixing water-quenched blast furnace slag and fly ash, grind them to a specific surface area of ​​480-520 m². 2 / kg, to obtain mixed slag powder; after mixing the obtained mixed slag powder with clinker and gradient alkaline activator, control the grinding temperature at 60-70℃, and grind to a specific surface area of ​​450-500m². 2 / kg; (2) Control the grinding temperature of the composite gypsum below 60℃ and grind it to a specific surface area of ​​500-550m². 2 / kg; (3) Mix the products obtained in steps (1) and (2) with the functional regulator and stir until homogeneous to obtain the final product.

10. The application of gradient-activated gypsum slag hydraulic cement as described in any one of claims 1-8 in hydraulic engineering.