Ferroaluminate cement with low hydration heat and preparation method thereof

Abstract

The invention discloses low-hydration-heat iron aluminate cement and a preparation method thereof, and belongs to the technical field of maritime work cement, and the low-hydration-heat iron aluminate cement comprises 70-85 parts of iron aluminate cement clinker, 5-7 parts of a bio-based retarder, 4-8 parts of a nano friction regulator, 3-4.5 parts of a microcapsule dual repair agent, 5-10 parts of gypsum and 15-25 parts of a mixed material. The fucoidan polysaccharide sulfate and calcium ions in a cement hydration product form a complex through sulfate groups in molecules of the fucoidan polysaccharide sulfate, and further hydration of cement particles is prevented, so that the early heat release rate is effectively reduced, temperature cracks are prevented from being generated in a concrete structure, and the stability and durability of the structure are improved. According to the microcapsule dual-repairing agent, the problem of delayed volume expansion of the steel slag powder caused by fluctuation of the content of free calcium oxide is effectively solved through the matching effect of the inner-layer repairing agent and the outer-layer carrier. According to the gradient clinker sintering process, mineral distribution and chemical reaction paths in clinker are optimized, so that the generation amount of cement hydration heat is remarkably reduced, and meanwhile, the thermal stability of slurry is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of marine engineering cement, and particularly relates to a low heat of hydration ferroaluminate cement and a preparation method thereof. Background Art

[0002] Ferroaluminate cement has attracted much attention in marine engineering and low-temperature environments due to its high early strength, strong corrosion resistance and other characteristics.

[0003] In the prior art, although ferroaluminate cement has advantages such as rapid hardening and corrosion resistance, the heat of hydration release is concentrated in the acceleration period within 1 day, and the heat release in 24 hours accounts for a high proportion. Although the total heat of hydration is lower than that of Portland cement, the concentrated heat release may still cause too fast early temperature rise of large-volume structures, and complex temperature control measures are required.

[0004] When steel slag powder is used as a blending material, the content of free calcium oxide is affected by the fluctuations in the steel plant production process. It is easy to react with water to form calcium hydroxide in the later stage of cement hardening, causing delayed volume expansion and resulting in cracking risks.

[0005] In addition, in order to regulate the cement hydration heat release curve, the prior art attempts to introduce water-absorbing resin as an internal humidity regulator. However, a small deviation in the reaction conditions during the resin synthesis process will cause the water absorption rate to drop suddenly by 30%, directly affecting the shrinkage effect of the cement paste. Summary of the Invention

[0006] In view of the above-mentioned drawbacks of the prior art, the present invention provides a low heat of hydration ferroaluminate cement and a preparation method thereof.

[0007] To achieve the above object, the present invention is realized through the following technical solutions: A low heat of hydration ferroaluminate cement, by mass, comprises the following components:

[0008] 70 - 85 parts of ferroaluminate cement clinker, prepared by high-temperature firing from calcareous raw materials, aluminous raw materials, ferrous raw materials, phosphogypsum - red mud composite sulfur source, rare earth oxides and nano-strontium titanate;

[0009] 5 - 7 parts of bio-based retarder; the bio-based retarder is fucoidan, with a molecular weight of 50 - 80 kDa and a sulfate group content ≥ 30%;

[0010] 4 - 8 parts of nano friction regulator; the nano friction regulator is polyelectrolyte-functionalized carbon dots, with a particle size of 3 - 7 nm and containing sulfonic acid groups (-SO3H) and carboxyl groups (-COOH) on the surface;

[0011] 3 - 4.5 parts of microcapsule double repair agent; the microcapsule double repair agent includes polydopamine-coated epoxy resin microcapsules as the inner layer repair agent and basophilic bacteria loaded on nano-metakaolin as the outer layer carrier;

[0012] 5 - 10 parts of gypsum;

[0013] 15 - 25 parts of admixture.

[0014] Furthermore, the raw material ratio of the ferrite cement clinker is as follows:

[0015] Calcareous raw material: 45 - 60 wt%;

[0016] Aluminous raw material: 15 - 25 wt%;

[0017] Ferrous raw material: 9 - 20 wt%;

[0018] Phosphogypsum - red mud composite sulfur source: 8 - 20 wt%;

[0019] Rare earth oxide (mass ratio of La2O3 / Nd2O3 is 1:1): 0.3 - 0.8 wt%;

[0020] Nano - strontium titanate (SrTiO3): 0.2 - 0.7 wt%.

[0021] In the phosphogypsum - red mud composite sulfur source, the mass ratio of phosphogypsum to red mud is 3:1, and the CaSO4·2H2O content of the phosphogypsum ≥ 85%, and the Fe2O3 content of the red mud ≥ 25%.

[0022] A preparation method of the low - heat - of - hydration ferrite cement described above includes the following steps:

[0023] S1. Prepare the microcapsule double repair agent:

[0024] Inner - layer microcapsule synthesis: Mix epoxy resin and polydopamine in deionized water, add emulsifier sodium dodecyl benzene sulfonate, and disperse at high speed to form an oil - phase emulsion;

[0025] Under acidic conditions, drop - add melamine - formaldehyde prepolymer, react to form inner - layer microcapsules, filter and dry for later use;

[0026] Outer - layer carrier compounding: Mix nano - metakaolin and alkaliphilic bacteria, add silane coupling agent, and stir to form a nano - composite carrier loaded with bacteria;

[0027] Mix the inner - layer microcapsules with the carrier, and use the fluidized - bed coating process with polyvinyl alcohol as the binder to form a double - layer structure to obtain the microcapsule double repair agent;

[0028] S2. Prepare the bio - based retarder:

[0029] Raw material treatment: Crush brown algae, degrease it with ethanol, and remove impurities;

[0030] Polysaccharide extraction: The hot water extraction method was used, magnesium chloride hexahydrate was added, and the alginate precipitate was removed by centrifugation to obtain a crude brown algae polysaccharide solution;

[0031] Sulfation: The crude brown algae polysaccharide solution was reacted with a chlorosulfonic acid-pyridine complex, the pH was adjusted with sulfuric acid, and after dialysis purification and freeze-drying, fucoidan sulfate was obtained. The fucoidan sulfate was diluted with water to obtain a bio-based retarder;

[0032] S3. Preparation of nano friction modifier:

[0033] Carbon dot synthesis: Using citric acid as a carbon source and polyelectrolyte as a surface modifier, polyelectrolyte-functionalized carbon dots were generated by heating in a microwave reactor;

[0034] Dispersion treatment: The polyelectrolyte-functionalized carbon dots were diluted with water and ultrasonicated to form a stable suspension;

[0035] S4. Clinker preparation: The calcareous raw material, aluminous raw material, ferrous raw material, phosphogypsum-red mud composite sulfur source, rare earth oxide and nano strontium titanate were mixed and ball-milled to obtain raw meal powder;

[0036] Gradient temperature firing was carried out in a rotary kiln to obtain ferroaluminate cement clinker;

[0037] S5. The admixture was activated by Ar / O2 mixed gas plasma and pulverized by supersonic airflow;

[0038] The ferroaluminate cement clinker, bio-based retarder, nano friction modifier and microcapsule double repair agent were mixed according to the ratio of claim 1 to obtain a mixed clinker;

[0039] The mixed clinker, activated admixture and gypsum were mixed to obtain low heat of hydration ferroaluminate cement.

[0040] Furthermore, S1 is specifically: Epoxy resin and polydopamine were mixed in deionized water, and sodium dodecylbenzenesulfonate as an emulsifier was added, and high-speed dispersion was carried out to form an oil-phase emulsion;

[0041] Under acidic conditions, melamine-formaldehyde prepolymer was added dropwise to react to form an inner microcapsule with a particle size controlled at 50-100 μm, and after filtration and drying, it was reserved for use;

[0042] Nano metakaolin and alkaliphilic bacteria were mixed at a mass ratio of 1:1, and silane coupling agent KH-550 was added, and stirring was carried out to form a nano composite carrier loaded with bacteria;

[0043] The inner microcapsule and the carrier were mixed at a mass ratio of 1:1-2, and the fluidized bed coating process was used, with polyvinyl alcohol as an adhesive, and the total admixture of the adhesive was 1.5-2.0 wt% of the total amount of the inner microcapsule and the carrier, to form a double-layer structure to obtain a microcapsule double repair agent.

[0044] Furthermore, S2 is specifically as follows: The brown algae are crushed to a particle size of ≤2 mm, degreased with ethanol to remove impurities;

[0045] The hot water extraction method is adopted, magnesium chloride hexahydrate is added, and the alginate precipitate is removed by centrifugation to obtain a crude brown algae polysaccharide solution;

[0046] The crude brown algae polysaccharide solution is reacted with a chlorosulfonic acid-pyridine complex at 50-60 °C for 3-4 h, the pH is adjusted to neutral with sulfuric acid, purified by dialysis and then freeze-dried to obtain a fucoidan sulfate with a molecular weight of 50-80 kDa and a sulfate group content of ≥30%. The fucoidan sulfate is diluted with water to obtain a bio-based retarder.

[0047] Furthermore, S3 is specifically as follows: Using citric acid as a carbon source and a polyelectrolyte as a surface modifier, after heating in a microwave reactor, polyelectrolyte-functionalized carbon dots with a particle size of 3-7 nm and -SO3H and -COOH groups on the surface are generated; <F

[0048] The polyelectrolyte-functionalized carbon dots are diluted with water and ultrasonicated to form a stable suspension.

[0049] Furthermore, S4 is specifically as follows: The calcareous raw material, aluminous raw material, ferrous raw material, phosphogypsum-red mud composite sulfur source, rare earth oxide and nano-strontium titanate are mixed and ball-milled to D90≤4μm to obtain raw meal powder; gradient temperature firing is carried out in a rotary kiln:

[0050] Preheating section: 900-950 °C, irradiated with 5-8 kW microwave for 10-15 min;

[0051] Decomposition section: 1250-1280 °C, calcined for 30-40 min with a hydrogen-oxygen burner at a hydrogen ratio of 25-30%;

[0052] Firing section: 1300-1350 °C, calcined with pure oxygen for 30-60 min;

[0053] Cool to room temperature to obtain ferrite cement clinker.

[0054] Furthermore, S5 is specifically as follows: An Ar / O2 mixed gas is used to plasma-activate the admixture at a power of 5-6 kW and super-sonic airflow pulverize it to D50≤3μm.

[0055] The beneficial effects of the present invention compared with the prior art are as follows:

[0056] 1. The present invention uses fucoidan sulfate to form a complex with calcium ions in the hydration products of cement through the sulfate groups in its molecules, preventing the further hydration of cement particles, thereby effectively reducing the early heat release rate, avoiding the generation of temperature cracks inside the concrete structure, improving the stability and durability of the structure. This regulatory effect can not only avoid the structural problems caused by concentrated heat release but also optimize the hydration kinetics of cement, making its hydration reaction more uniform and continuous. At the same time, as a bio-based retarder, fucoidan sulfate realizes the precise control of the autogenous shrinkage rate of the paste by regulating the hydration kinetics process of the ferroaluminate cement paste. Compared with traditional water-absorbing resins, this retarder is not restricted by the synthetic process conditions, can stably delay the early hydration reaction rate, and avoid the shrinkage fluctuation caused by excessive hydration in the later stage, thus ensuring the volume stability of the paste at different construction stages.

[0057] 2. The microcapsule dual repair agent developed by the present invention effectively solves the problem of delayed volume expansion caused by the fluctuation of free calcium oxide content in steel slag powder through the combined action of the inner repair agent (polydopamine-coated epoxy resin microcapsules) and the outer carrier (alkaliphilic bacteria loaded on nano-metakaolin). The inner microcapsules provide a rapid repair effect in the early stage, quickly responding to the generation of microcracks, while the alkaliphilic bacteria in the outer carrier continuously consume calcium hydroxide in the later stage, delaying the occurrence of volume expansion. This hierarchical repair mechanism not only significantly reduces the cracking risk but also improves the long-term durability of the hardened body.

[0058] 3. The gradient sintering clinker process introduced by the present invention significantly reduces the generation amount of cement hydration heat by optimizing the mineral distribution and chemical reaction path inside the clinker. This process makes the hydration reaction rates of silicate minerals and aluminate minerals inside the clinker tend to be balanced, reducing the violent release of hydration heat and improving the thermal stability of the paste at the same time.

[0059] 4. When the gradient sintering clinker process and the microcapsule dual repair agent are compounded, a significant synergistic effect can be produced. The gradient sintering process optimizes the release path of hydration heat, and the microcapsule dual repair agent further inhibits volume expansion through chemical repair. The synergistic effect of the two not only makes the reduction amplitude of hydration heat exceed the sum of single technologies but also significantly improves the anti-expansion performance of the hardened body and the stability of the autogenous shrinkage rate.

[0060] 5. The gradient sintering clinker process controls the temperature and energy input in stages, making the heat released by the clinker more uniform during the initial hydration stage. This process optimizes the crystal structure of the clinker, reduces local overheating, and provides a more stable chemical environment for the subsequent action of the repair agent. At the same time, the microcapsule dual repair agent can slowly release the repair substances during the cement hydration process, filling the microcracks in the cement matrix and further reducing the concentrated release of hydration heat. The synergistic effect of the two makes the hydration reaction of the cement matrix more uniform and continuous, not only significantly reducing the hydration heat of early calcium aluminate cement, but also improving the overall performance and durability of the cement matrix. Detailed implementation mode

[0061] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following clearly and completely describes the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0062] Example 1: This example provides a calcium aluminate cement with low hydration heat, which includes the following components by mass parts:

[0063] 85 parts of calcium aluminate cement clinker, which is prepared by high-temperature firing of calcareous raw materials, aluminous raw materials, ferrous raw materials, phosphogypsum-red mud composite sulfur source, rare earth oxides, and nano-strontium titanate;

[0064] 7 parts of bio-based retarder; the bio-based retarder is fucoidan sulfate with a molecular weight of 80 kDa and a sulfate group content ≥ 30%;

[0065] 8 parts of nano friction modifier; the nano friction modifier is polyelectrolyte-functionalized carbon dots with a particle size of 7 nm and containing sulfonic acid groups (-SO3H) and carboxyl groups (-COOH) on the surface;

[0066] 4.5 parts of microcapsule dual repair agent; the microcapsule dual repair agent includes polydopamine-coated epoxy resin microcapsules as the inner layer repair agent and basophilic bacteria loaded on nano-metakaolin as the outer layer carrier;

[0067] 10 parts of gypsum;

[0068] 25 parts of admixture.

[0069] The raw material ratio of the calcium aluminate cement clinker is:

[0070] Calcareous raw material (CaO ≥ 52%): 45 wt%

[0071] Aluminous raw material (Al2O3 ≥ 65%): 25 wt%;

[0072] Iron raw material (Fe2O3≥75%): 20 wt%;

[0073] Phosphogypsum - red mud composite sulfur source: 9 wt%;

[0074] Rare earth oxide (mass ratio of La2O3 / Nd2O3 is 1:1): 0.3 wt%;

[0075] Nano - strontium titanate (SrTiO3): 0.7 wt%.

[0076] In the phosphogypsum - red mud composite sulfur source, the mass ratio of phosphogypsum to red mud is 3:1, and the CaSO4·2H2O content of the phosphogypsum ≥ 85%, and the Fe2O3 content of the red mud ≥ 25%.

[0077] The preparation method of the low - heat - of - hydration ferroaluminate cement includes the following steps:

[0078] S1. Prepare the microcapsule double repair agent:

[0079] Inner - layer microcapsule synthesis:

[0080] Mix epoxy resin (mass ratio of epoxy resin E51 to epoxy resin 127 is 6:4) and polydopamine (mass ratio is 10:1) in deionized water, add emulsifier sodium dodecylbenzenesulfonate (dosage 0.8 wt%), and disperse at a high speed of 3000 r / min to form an oil - phase emulsion;

[0081] Under the acidic condition of pH = 3.5, drop - add melamine - formaldehyde prepolymer, react at 70 °C for 3 h to form inner - layer microcapsules with a particle size of 100 μm, filter and dry for later use;

[0082] Outer - layer carrier compounding:

[0083] Mix nano - metakaolin (specific surface area 600 m 2 / g) and alkaliphilic bacteria (cell density 5×10 8 CFU / g) in a mass ratio of 1:1, add silane coupling agent KH - 550 (dosage 2 wt%), and stir at 40 °C for 2 h to form a nano - composite carrier loaded with bacteria;

[0084] Mix the inner - layer microcapsules and the carrier in a mass ratio of 1:2, and adopt the fluidized - bed coating process with polyvinyl alcohol (molecular weight 67000) as the binder (total dosage 2.0 wt%) to form a double - layer structure and obtain the microcapsule double repair agent;

[0085] S2. Prepare the bio - based retarder:

[0086] Raw material treatment: The brown algae is crushed to a particle size of ≤2 mm, degreased with ethanol (concentration 70%) for 2 h to remove impurities;

[0087] Polysaccharide extraction: The hot water extraction method (90 °C, 10 h) is used, magnesium chloride hexahydrate (concentration 0.05 mol / L) is added, and the alginate precipitate is removed by centrifugation to obtain a crude brown algae polysaccharide solution;

[0088] Sulfation: The crude brown algae polysaccharide solution is reacted with a chlorosulfonic acid - pyridine complex (mass ratio 1:3) at 60 °C for 4 h, the pH is adjusted to neutral with sulfuric acid, purified by dialysis and then freeze - dried to obtain brown algae polysaccharide sulfate (molecular weight 80 kDa, sulfate group content ≥30%). The brown algae polysaccharide sulfate is mixed with water at a ratio of 1:5 to obtain a bio - based retarder;

[0089] S3. Preparation of nano - friction modifier:

[0090] Carbon dot synthesis: Using citric acid as the carbon source and polyelectrolyte (sodium polystyrene sulfonate - acrylic acid copolymer) as the surface modifier, mixed at a mass ratio of 2:1, heated to 200 °C in a microwave reactor (power 800 W, frequency 2.45 GHz) and maintained for 30 min to generate polyelectrolyte - functionalized carbon dots with a particle size of 7 nm (the surface contains - SO3H and - COOH groups);

[0091] Dispersion treatment: The polyelectrolyte - functionalized carbon dots are mixed with deionized water at a ratio of 1:10 and ultrasonically treated (power 500 W, frequency 40 kHz) for 30 min to form a stable suspension;

[0092] S4. Clinker preparation: The calcareous raw material, aluminous raw material, ferrous raw material, phosphogypsum - red mud composite sulfur source, rare earth oxide and nano - strontium titanate are mixed and ball - milled to D90 ≤ 45 μm to obtain raw meal powder; Gradient temperature firing is carried out in a rotary kiln:

[0093] Pre - heating section: 950 °C, microwave irradiation (2.45 GHz, 8 kW) treatment for 10 min;

[0094] Decomposition section: 1280 °C, calcined with a hydrogen - oxygen burner (hydrogen ratio 30%) for 40 min;

[0095] Firing section: 1350 °C, calcined with pure oxygen combustion for 60 min;

[0096] Cooled to room temperature to obtain ferrite aluminate cement clinker;

[0097] S5. Mixing: The admixtures (steel slag powder and fly ash with a mass ratio of 1.8:2) are treated by plasma activation with an Ar / O2 mixed gas (volume ratio 4:1, power 6 kW) and pulverized by supersonic airflow to D50 ≤ 3 μm;

[0098] Mix the calcium aluminate cement clinker, bio-based retarder, nano friction regulator and microcapsule double repair agent according to the above ratios to obtain the mixed clinker;

[0099] Mix the mixed clinker, activated mixed materials and gypsum to obtain the low heat of hydration calcium aluminate cement.

[0100] Example 2: This example provides a low heat of hydration calcium aluminate cement, which includes the following components by mass:

[0101] 70 parts of calcium aluminate cement clinker, which is prepared by high-temperature firing of calcareous raw materials, aluminous raw materials, ferrous raw materials, phosphogypsum-red mud composite sulfur source, rare earth oxides and nano strontium titanate;

[0102] 5 parts of bio-based retarder; the bio-based retarder is fucoidan, its molecular weight is 50 kDa, and the sulfuric acid group content ≥ 30%;

[0103] 4 parts of nano friction regulator; the nano friction regulator is polyelectrolyte-functionalized carbon dots, its particle size is 3 nm, and the surface contains sulfonic acid groups (-SO3H) and carboxyl groups (-COOH);

[0104] 3 parts of microcapsule double repair agent; the microcapsule double repair agent includes polydopamine-coated epoxy resin microcapsules as the inner layer repair agent and alkaliphilic bacteria loaded on nano metakaolin as the outer layer carrier;

[0105] 5 parts of gypsum;

[0106] 15 parts of mixed materials.

[0107] The raw material ratio of the calcium aluminate cement clinker is:

[0108] Calcareous raw materials (CaO ≥ 52%): 60 wt%;

[0109] Aluminous raw materials (Al2O3 ≥ 65%): 15 wt%;

[0110] Ferrous raw materials (Fe2O3 ≥ 75%): 16 wt%;

[0111] Phosphogypsum-red mud composite sulfur source: 8 wt%;

[0112] Rare earth oxides (mass ratio of La2O3 / Nd2O3 1:1): 0.8 wt%;

[0113] Nano strontium titanate (SrTiO3): 0.2 wt%.

[0114] The mass ratio of phosphogypsum to red mud in the phosphogypsum-red mud composite sulfur source is 3:1, and the CaSO4·2H2O content of the phosphogypsum ≥ 85%, and the Fe2O3 content of the red mud ≥ 25%.

[0115] The preparation method of the low heat of hydration ferroaluminate cement includes the following steps:

[0116] S1. Prepare a microcapsule double repair agent:

[0117] Inner layer microcapsule synthesis:

[0118] Mix epoxy resin (mass ratio of epoxy resin E51 to epoxy resin 127 is 6:4) and polydopamine (mass ratio is 10:1) in deionized water, add sodium dodecylbenzenesulfonate as an emulsifier (dosage 0.8 wt%), and disperse at a high speed of 3000 r / min to form an oil-phase emulsion;

[0119] Under acidic conditions with pH = 3.5, dropwise add melamine-formaldehyde prepolymer, react at 70 °C for 3 h to form inner layer microcapsules with a particle size of 50 μm, filter and dry for later use;

[0120] Outer layer carrier compounding:

[0121] Mix nano-metakaolin (specific surface area 500 m 2 / g) and alkaliphilic bacteria (cell density 1×10 8 CFU / g) in a mass ratio of 1:1, add silane coupling agent KH-550 (dosage 1 wt%), and stir at 40 °C for 2 h to form a nano-composite carrier loaded with bacteria;

[0122] Mix the inner layer microcapsules and the carrier in a mass ratio of 1:1 - 2, adopt the fluidized bed coating process, and use polyvinyl alcohol (molecular weight 67000) as an adhesive (total dosage 1.5 wt%) to form a double-layer structure to obtain the microcapsule double repair agent;

[0123] S2. Prepare a bio-based retarder:

[0124] Raw material treatment: Crush brown algae to a particle size ≤ 2 mm, degrease with ethanol (concentration 70%) for 2 h to remove impurities;

[0125] Polysaccharide extraction: Adopt the hot water extraction method (90 °C, 10 h), add magnesium chloride hexahydrate (concentration 0.05 mol / L), and centrifuge to remove alginate precipitate to obtain a crude brown algae polysaccharide solution;

[0126] Sulfation: React the crude brown algae polysaccharide solution with a chlorosulfonic acid-pyridine complex (mass ratio 1:3) at 50 °C for 3 h, adjust the pH to neutral with sulfuric acid, dialyze and purify, and then freeze-dry to obtain brown algae polysaccharide sulfate (molecular weight 50 kDa, sulfate group content ≥ 30%). Mix brown algae polysaccharide sulfate and water in a ratio of 1:5 to obtain a bio-based retarder;

[0127] S3. Prepare a nano friction modifier:

[0128] Carbon dot synthesis: Using citric acid as the carbon source and polyelectrolyte (sodium polystyrene sulfonate-acrylic acid copolymer) as the surface modifier, they are mixed in a mass ratio of 2:1 and heated to 200 °C in a microwave reactor (power 800 W, frequency 2.45 GHz) and maintained for 30 min to generate polyelectrolyte-functionalized carbon dots with a particle size of 3 nm (the surface contains -SO3H and -COOH groups);

[0129] Dispersion treatment: Mix the polyelectrolyte-functionalized carbon dots and deionized water in a ratio of 1:10 and ultrasonically treat (power 500 W, frequency 40 kHz) for 30 min to form a stable suspension;

[0130] S4. Clinker preparation: Mix calcareous raw materials, aluminous raw materials, ferrous raw materials, phosphogypsum-red mud composite sulfur source, rare earth oxides and nano-strontium titanate, and ball mill to D90 ≤ 45 μm to obtain raw meal powder; conduct gradient temperature firing in a rotary kiln:

[0131] Preheating section: 900 °C, microwave irradiation (2.45 GHz, 5 kW) treatment for 15 min;

[0132] Decomposition section: 1250 °C, calcination with a hydrogen-oxygen burner (hydrogen ratio 25%) for 30 min;

[0133] Firing section: 1300 °C, pure oxygen combustion calcination for 30 min;

[0134] Cool to room temperature to obtain ferrite aluminate cement clinker;

[0135] S5. Mixing: Use an Ar / O2 mixed gas (volume ratio 4:1, power 5 kW) for plasma activation treatment of admixtures (slag powder and fly ash with a mass ratio of 1.8:2), and ultrafine pulverize with a supersonic air flow to D50 ≤ 3 μm;

[0136] Mix the ferrite aluminate cement clinker, bio-based retarder, nano friction modifier and microcapsule double repair agent according to the above ratio to obtain a mixed clinker;

[0137] Mix the mixed clinker, activated treatment admixtures and gypsum to obtain low heat of hydration ferrite aluminate cement.

[0138] Example 3: This example provides a low heat of hydration ferrite aluminate cement, which includes the following components by mass parts:

[0139] 82 parts of ferrite aluminate cement clinker, prepared by high-temperature firing of calcareous raw materials, aluminous raw materials, ferrous raw materials, phosphogypsum-red mud composite sulfur source, rare earth oxides and nano-strontium titanate;

[0140] 6 parts of bio-based retarder; the bio-based retarder is fucoidan sulfate with a molecular weight of 70 kDa and a sulfate group content of ≥ 30%;

[0141] 7 parts of nano friction modifier; the nano friction modifier is polyelectrolyte-functionalized carbon dots with a particle size of 5 nm and containing sulfonic acid groups (-SO3H) and carboxyl groups (-COOH) on the surface;

[0142] 4 parts of microcapsule double repair agent; the microcapsule double repair agent includes polydopamine-coated epoxy resin microcapsules as the inner layer repair agent and basophilic bacteria loaded on nano-metakaolin as the outer layer carrier;

[0143] 6 parts of gypsum;

[0144] 21 parts of admixture.

[0145] The raw material ratio of the ferroaluminate cement clinker is as follows:

[0146] Calcareous raw material (CaO ≥ 52%): 50 wt%;

[0147] Aluminous raw material (Al2O3 ≥ 65%): 20 wt%;

[0148] Ferrous raw material (Fe2O3 ≥ 75%): 9 wt%;

[0149] Phosphogypsum - red mud composite sulfur source: 20 wt%;

[0150] Rare earth oxide (mass ratio of La2O3 / Nd2O3 is 1:1): 0.5 wt%;

[0151] Nano strontium titanate (SrTiO3) · 0.5 wt%.

[0152] In the phosphogypsum - red mud composite sulfur source, the mass ratio of phosphogypsum to red mud is 3:1, and the content of CaSO4·2H2O in the phosphogypsum is ≥ 85%, and the content of Fe2O3 in the red mud is ≥ 25%.

[0153] The preparation method of the low heat of hydration ferroaluminate cement includes the following steps:

[0154] S1. Prepare the microcapsule double repair agent:

[0155] Synthesis of inner layer microcapsules:

[0156] Mix epoxy resin (mass ratio of epoxy resin E51 to epoxy resin 127 is 6:4) and polydopamine (mass ratio is 10:1) in deionized water, add emulsifier sodium dodecylbenzenesulfonate (dosage 0.8 wt%), and disperse at a high speed of 3000 r / min to form an oil phase emulsion;

[0157] Under acidic conditions with pH = 3.5, the melamine-formaldehyde prepolymer was added dropwise, and the reaction was carried out at 70 °C for 3 h to form the inner microcapsules with a particle size of 80 μm. After filtration and drying, they were reserved for use;

[0158] Composite of the outer carrier:

[0159] Nano-metakaolin (specific surface area 560 m 2 / g) and alkaliphilic bacteria (cell density 3×10 8 CFU / g) were mixed at a mass ratio of 1:1, and silane coupling agent KH-550 (dosage 1.5 wt%) was added. The mixture was stirred at 40 °C for 2 h to form a nano-composite carrier loaded with bacteria;

[0160] The inner microcapsules and the carrier were mixed at a mass ratio of 1:1.8, and the fluidized bed coating process was adopted. Polyvinyl alcohol (molecular weight 67000) was used as the binder (total dosage 1.8 wt%) to form a double-layer structure, and a microcapsule double repair agent was obtained;

[0161] S2. Preparation of a bio-based retarder:

[0162] Raw material treatment: The brown algae were crushed to a particle size of ≤2 mm and degreased with ethanol (concentration 70%) for 2 h to remove impurities;

[0163] Polysaccharide extraction: The hot water extraction method (90 °C, 10 h) was adopted, and magnesium chloride hexahydrate (concentration 0.05 mol / L) was added. The alginate precipitate was removed by centrifugation to obtain a crude brown algae polysaccharide solution;

[0164] Sulfation: The crude brown algae polysaccharide solution and the chlorosulfonic acid-pyridine complex (mass ratio 1:3) were reacted at 58 °C for 3 h. The pH was adjusted to neutral with sulfuric acid, and after dialysis purification and freeze-drying, brown algae polysaccharide sulfate (molecular weight 60 kDa, sulfuric acid group content ≥30%) was obtained. The brown algae polysaccharide sulfate was mixed with water at a ratio of 1:5 to obtain a bio-based retarder;

[0165] S3. Preparation of a nano-friction modifier:

[0166] Synthesis of carbon dots: Using citric acid as the carbon source and polyelectrolyte (sodium polystyrene sulfonate-acrylic acid copolymer) as the surface modifier, they were mixed at a mass ratio of 2:1 and heated to 200 °C in a microwave reactor (power 800 W, frequency 2.45 GHz) and maintained for 30 min to generate polyelectrolyte-functionalized carbon dots with a particle size of 5 nm (the surface contains -SO3H and -COOH groups);

[0167] Dispersion treatment: The polyelectrolyte-functionalized carbon dots and deionized water were mixed at a ratio of 1:10 and ultrasonically treated (power 500 W, frequency 40 kHz) for 30 min to form a stable suspension;

[0168] S4, Clinker Preparation: Mix calcareous raw materials, aluminous raw materials, ferrous raw materials, phosphogypsum - red mud composite sulfur source, rare earth oxides, and nano - strontium titanate, and ball - mill them until D90 ≤ 45 μm to obtain raw meal powder; conduct gradient - temperature firing in a rotary kiln:

[0169] Pre - heating section: At 930 °C, treat with microwave irradiation (2.45 GHz, 5 kW) for 15 min;

[0170] Decomposition section: At 1260 °C, calcine with a hydrogen - oxygen burner (hydrogen ratio 28%) for 36 min;

[0171] Firing section: At 1320 °C, calcine with pure - oxygen combustion for 50 min;

[0172] Cool to room temperature to obtain ferrites cement clinker;

[0173] S5, Mixing: Activate admixtures (slag powder and fly ash with a mass ratio of 1.8:2) using an Ar / O2 mixed - gas (volume ratio 4:1, power 5 kW) plasma, and crush them with a supersonic gas flow until D50 ≤ 3 μm;

[0174] Mix the ferrites cement clinker, bio - based retarder, nano - friction regulator, and micro - capsule double - repair agent according to the above ratio to obtain mixed clinker;

[0175] Mix the mixed clinker, activated admixtures, and gypsum to obtain low - heat - of - hydration ferrites cement.

[0176] Comparative Example 1: The difference between this comparative example and Example 3 is that no bio - based retarder is added.

[0177] Comparative Example 2: The difference between this comparative example and Example 3 is that no micro - capsule double - repair agent is added.

[0178] Comparative Example 3: The difference between this comparative example and Example 3 is that the raw meal powder is not pre - heated and decomposed, but directly calcined with pure - oxygen combustion at 1320 °C for 20 min to obtain cement clinker.

[0179] Comparative Example 4: The difference between this comparative example and Example 3 is that neither the micro - capsule double - repair agent is added, nor the raw meal powder is pre - heated and decomposed, but directly calcined with pure - oxygen combustion at 1320 °C for 20 min to obtain cement clinker.

[0180] Experimental Example:

[0181] 1. Self - shrinkage rate detection;

[0182] 1.1 Specimen preparation: The test mold specification is a PVC pipe with φ100 mm × 420 mm. Coat the inner side with lubricating oil, seal the base, and wrap it with plastic wrap to prevent leakage;

[0183] Molding requirements: The fresh concrete mixture is prepared according to the T0551 specification, with the maximum aggregate size ≤ 31.5 mm. After molding, the surface is leveled and sealed (only when measuring autogenous shrinkage).

[0184] 1.2 Test environment: Constant temperature and humidity, temperature 20°C ± 2°C, humidity 60% ± 5%, equipped with an automatic temperature and humidity recorder;

[0185] 1.3 Measurement steps

[0186] Initial measurement: Immediately install a dial gauge after molding, record once every 30 minutes for the first 8 hours, and gradually extend the interval until the end of 3 days;

[0187] Data collection: Accurate to 0.001 mm, take the arithmetic mean of 3 specimens in each group, and the calculation formula is:

[0188]

[0189] In the formula, ε auto is the autogenous shrinkage rate (unit: ×10 -6 ); L ao is the initial reading, L at is the reading at time t, and 400 is the original length of the specimen (mm).

[0190] 2. Expansion rate test;

[0191] 2.1 Test materials and instruments

[0192] Materials: The cement sample needs to pass through a 0.9 mm square-hole sieve and be mixed evenly;

[0193] The mixing water is distilled water of grade three or above;

[0194] Instruments and equipment: Planetary mortar mixer (meeting the requirements of JC / T 681);

[0195] Length comparator, with a scale value of 0.01 mm, a measuring range ≥ 10 mm, and a base length ≥ 300 mm;

[0196] Triplet mold, with dimensions of 25 mm × 25 mm × 280 mm, and the end plates are equipped with nail heads (made of stainless steel or copper).

[0197] Balance, with a measuring range ≥ 2000 g and a scale value ≤ 1 g;

[0198] 2.2 Test steps

[0199] Specimen preparation: Add water according to the standard consistency water consumption, weigh 1200 g of cement sample, and load it into the triplet mold after stirring;

[0200] After vibration molding, place the mold in a curing box at 20 ± 1°C and humidity ≥ 90% for 24 hours and then demold.

[0201] 2.3 Initial length measurement: measure the initial length (L0) of the specimen immediately after demoulding, with an accuracy of 0.001mm;

[0202] Curing and measurement: The specimens were immersed in water at 20±1℃ for curing, and the length (L1) at the ages of 1d, 3d, 7d, and 28d was measured regularly.

[0203] Before measurement, the surface of the specimen must be wiped dry and the readings must be taken at a fixed position on the comparator.

[0204] 2.4 Result calculation:

[0205]

[0206] For result processing, take the average value of the expansion rate of the three specimens; if the range is greater than 0.010%, take the average value of the two closest ones, where the constant 250 is the initial effective measurement length of the specimen (unit: mm).

[0207] 3. Hydration heat measurement;

[0208] 3.1 Calorimeter calibration: Use zinc oxide to calibrate the heat capacity of the calorimeter and ensure that the temperature of the acid solution (2.00 mol / L nitric acid) is controlled at 20 ± 0.1 °C;

[0209] Record the initial temperature of the acid solution and the temperature change after dissolving zinc oxide, and calculate the heat capacity error ≤ 5J / ℃;

[0210] 3.2 Sample testing

[0211] For unhydrated cement, add 7g of cement to the acid solution and record the change in dissolution temperature. Repeat twice and take the average value.

[0212] Hydrated cement: Grind the cement cured to the specified age and pass it through a 0.6 mm sieve. Repeat the dissolution steps and calculate the difference in heat of dissolution.

[0213] 3.3 Result calculation;

[0214] Heat of hydration formula:

[0215] q=q1-q2+0.4(T″-T′)

[0216] Where q1 is the heat of dissolution before hydration (kJ / kg), and q2 is the heat of dissolution after hydration (kJ / kg);

[0217] T″ is the temperature change when hydrated cement dissolves in acid solution;

[0218] T′ is the temperature change when unhydrated cement is dissolved in acid solution;

[0219] The unit of hydration heat q is kJ / kg;

[0220] The constant 0.4 is the heat dissipation correction factor of the calorimeter (unit: J / (g·°C)), which is used to compensate for the heat loss during the dissolution process.

[0221]

[0222] As shown in the table above, fucoidan sulfate, as a bio-based retarder, can maintain the stability of autogenous shrinkage by regulating the hydration dynamics of ferroaluminate cement paste. Its mechanism of action is to slow the early hydration reaction rate of cement while preventing shrinkage fluctuations caused by excessive hydration in the later stages, thereby ensuring the volume stability of the paste at different construction stages.

[0223] Fucoidan sulfate forms a complex with calcium ions in cement hydration products through the sulfate groups in its molecules, preventing further hydration of cement particles, thereby effectively reducing the early heat release rate, thereby avoiding the generation of temperature cracks inside the concrete structure and improving the stability and durability of the structure.

[0224] The microcapsule dual repair agent synthesized from an inner layer repair agent (polydopamine-coated epoxy resin microcapsules) and an outer layer carrier (alkaliphilic bacteria loaded on nano-metakaolin) can effectively control the problem of steel slag powder reacting with water to produce calcium hydroxide in the later stage of cement hardening. The repair agent is designed with a layered structure, so that the inner layer microcapsules provide rapid repair effects in the early stage, while the alkaliphilic bacteria in the outer layer carrier continue to consume calcium hydroxide in the later stage, delaying the occurrence of volume expansion, significantly reducing the risk of cracking, and improving the long-term durability of the hardened body.

[0225] The gradient clinker firing process significantly reduces the amount of cement hydration heat generated by optimizing the mineral distribution and chemical reaction pathways within the clinker. This process balances the hydration reaction rates of silicate and aluminate minerals within the clinker, reducing the dramatic release of hydration heat. It also improves the thermal stability of the slurry and avoids structural damage caused by temperature differences.

[0226] When the gradient-fired clinker process is combined with the microcapsule dual-healing agent, a significant synergistic effect can be achieved. The gradient firing process optimizes the release path of hydration heat, while the microcapsule dual-healing agent further suppresses volume expansion through chemical repair. The synergistic effect of the two technologies reduces hydration heat by a magnitude greater than that achieved by either technique alone. Simultaneously, the expansion rate of the hardened body is effectively controlled, and the stability of the autogenous shrinkage rate is significantly improved, demonstrating a synergistic benefit of "functional complementarity" and "performance superposition."

[0227] In addition, the gradient burning clinker process enables the clinker to release heat more uniformly during the initial stage of hydration through staged temperature control and energy input. This process optimizes the crystal structure of the clinker, reduces local overheating, and provides a more stable chemical environment for the subsequent action of the repair agent. At the same time, the microcapsule dual repair agent can slowly release repair substances during the cement hydration process, filling the microcracks in the cement matrix and further reducing the concentrated release of hydration heat. The synergistic effect of the two makes the hydration reaction of the cement matrix more uniform and continuous, not only significantly reducing the hydration heat of the ferroaluminate cement, but also improving the overall performance and durability of the cement matrix.

[0228] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low heat of hydration ferroaluminate cement, characterized in that, By mass parts, it includes the following components: 70 - 85 parts of ferrite cement clinker, which is prepared by high-temperature firing of calcareous raw materials, aluminous raw materials, ferrous raw materials, phosphogypsum - red mud composite sulfur source, rare earth oxides and nano-strontium titanate; 5 - 7 parts of bio-based retarder; the bio-based retarder is fucoidan, with a molecular weight of 50 - 80 kDa and a sulfate group content of ≥30%; 4 - 8 parts of nano friction modifier; the nano friction modifier is polyelectrolyte-functionalized carbon dots, with a particle size of 3 - 7 nm and sulfonic acid groups and carboxyl groups on the surface; 3 - 4.5 parts of microcapsule double repair agent; the microcapsule double repair agent includes polydopamine-coated epoxy resin microcapsules as the inner layer repair agent and basophilic bacteria loaded on nano-metakaolin as the outer layer carrier; 5 - 10 parts of gypsum; 15 - 25 parts of admixture.

2. The low heat of hydration ferroaluminate cement according to claim 1, wherein The raw material ratio of the ferrite cement clinker is as follows: Calcareous raw materials: 45 - 60 wt%; Aluminous raw materials: 15 - 25 wt%; Ferrous raw materials: 9 - 20 wt%; Phosphogypsum - red mud composite sulfur source: 8 - 20 wt%; Rare earth oxides: 0.3 - 0.8 wt%; Nano-strontium titanate: 0.2 - 0.7 wt%. In the phosphogypsum - red mud composite sulfur source, the mass ratio of phosphogypsum to red mud is 3:1, and the CaSO4·2H2O content of the phosphogypsum is ≥85%, and the Fe2O3 content of the red mud is ≥25%.

3. A preparation method of the low heat of hydration ferroaluminate cement as described in claim 2, characterized in that, It includes the following steps: S1. Prepare the microcapsule double repair agent: Synthesis of the inner layer microcapsule: Mix epoxy resin and polydopamine in deionized water, add the emulsifier sodium dodecylbenzenesulfonate, and disperse at high speed to form an oil-phase emulsion; Under acidic conditions, dropwise add melamine - formaldehyde prepolymer, react to form the inner layer microcapsule, filter and dry for later use; Compound the outer layer carrier: Mix nano-metakaolin and basophilic bacteria, add a silane coupling agent, and stir to form a nano-composite carrier loaded with bacteria; Mix the inner layer microcapsule and the carrier, and use the fluidized bed coating process with polyvinyl alcohol as the binder to form a double-layer structure to obtain the microcapsule double repair agent; S2. Prepare the bio-based retarder: Raw material treatment: Crush brown algae, perform degreasing treatment with ethanol, and remove impurities; Polysaccharide extraction: Use the hot water extraction method, add magnesium chloride hexahydrate, and centrifuge to remove alginate precipitate to obtain a crude brown algae polysaccharide solution; Sulfation: React the crude brown algae polysaccharide solution with a chlorosulfonic acid - pyridine complex, adjust the pH with sulfuric acid, dialyze and purify, and then freeze-dry to obtain fucoidan. Dilute fucoidan with water to obtain the bio-based retarder; S3. Prepare the nano friction modifier: Synthesis of carbon dots: Use citric acid as the carbon source and polyelectrolyte as the surface modifier, and heat in a microwave reactor to generate polyelectrolyte-functionalized carbon dots; Dispersion treatment: Dilute the polyelectrolyte-functionalized carbon dots with water and perform ultrasonic treatment to form a stable suspension; S4. Prepare the clinker: Mix calcareous raw materials, aluminous raw materials, ferrous raw materials, phosphogypsum - red mud composite sulfur source, rare earth oxides and nano-strontium titanate, and ball mill to obtain raw meal powder; Perform gradient temperature firing in a rotary kiln to obtain ferrite cement clinker; S5. Activate and treat the admixture with Ar / O2 mixed gas plasma, and pulverize it by supersonic airflow; Mix the ferrite cement clinker, bio-based retarder, nano friction regulator and microcapsule double repair agent according to the ratio of Claim 1 to obtain the mixed clinker; Mix the mixed clinker, activated treated admixture and gypsum to obtain the low heat of hydration ferrite cement.

4. The preparation method of the low heat of hydration ferroaluminate cement according to claim 3, characterized in that, Specifically, S1 is: mix epoxy resin and polydopamine in deionized water, add emulsifier sodium dodecylbenzenesulfonate, and disperse at high speed to form an oil-phase emulsion; Under acidic conditions, dropwise add melamine-formaldehyde prepolymer, react to form the inner microcapsules, control the particle size at 50-100 μm, filter and dry for later use; Mix nano-metakaolin and alkaliphilic bacteria in a mass ratio of 1:1, add silane coupling agent KH-550, and stir to form a nano-composite carrier loaded with bacteria; Mix the inner microcapsules and the carrier in a mass ratio of 1:1-2, adopt the fluidized bed coating process, use polyvinyl alcohol as the binder, and the total dosage of the binder is 1.5-2.0 wt% of the total amount of the inner microcapsules and the carrier to form a double-layer structure to obtain the microcapsule double repair agent.

5. The preparation method of the low heat of hydration ferroaluminate cement according to claim 3, characterized in that Specifically, S2 is: crush brown algae to a particle size ≤ 2 mm, degrease it with ethanol to remove impurities; Adopt the hot water extraction method, add magnesium chloride hexahydrate, centrifuge to remove the alginate precipitate to obtain the crude brown algae polysaccharide solution; React the crude brown algae polysaccharide solution with chlorosulfonic acid-pyridine complex at 50-60 °C for 3-4 h, adjust the pH to neutral with sulfuric acid, dialyze and purify, and then freeze-dry to obtain brown algae polysaccharide sulfate with a molecular weight of 50-80 kDa and a sulfate group content ≥ 30%, and dilute the brown algae polysaccharide sulfate with water to obtain the bio-based retarder.

6. The preparation method of the low heat of hydration ferrites cement according to claim 3, characterized in that, Specifically, S3 is: use citric acid as the carbon source and polyelectrolyte as the surface modifier, heat in a microwave reactor to generate polyelectrolyte-functionalized carbon dots with a particle size of 3-7 nm and -SO3H and -COOH groups on the surface; Dilute the polyelectrolyte-functionalized carbon dots with water and perform ultrasonic treatment to form a stable suspension.

7. The preparation method of the low heat of hydration ferroaluminate cement according to claim 3, characterized in that, Specifically, S4 is: mix calcareous raw materials, aluminous raw materials, ferrous raw materials, phosphogypsum-red mud composite sulfur source, rare earth oxides and nano-strontium titanate, and ball mill to D90 ≤ 45 μm to obtain the raw meal powder; carry out gradient temperature firing in a rotary kiln: Preheating section: 900-950 °C, irradiate with 5-8 kW microwave for 10-15 min; Decomposition section: 1250-1280 °C, the hydrogen-oxygen burner burns according to the hydrogen ratio of 25-30%, and calcines for 30-40 min; Firing section: 1300-1350 °C, calcine with pure oxygen for 30-60 min; Cool to room temperature to obtain the ferrite cement clinker.

8. The preparation method of the low heat of hydration ferroaluminate cement according to claim 3, wherein Specifically, S5 is: adopt Ar / O2 mixed gas, activate and treat the admixture with plasma at a power of 5-6 kW, and pulverize it by supersonic airflow to D50 ≤ 3 μm.

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