A kind of low hydration heat ferroaluminate cement and preparation method thereof

Abstract

The present invention discloses a low hydration heat ferroaluminate cement and a preparation method thereof, belonging to the field of marine cement technology, comprising 70-85 parts of ferroaluminate cement clinker, 5-7 parts of bio-based retarder, 4-8 parts of nano friction modifier, 3-4.5 parts of microcapsule dual repair agent, 5-10 parts of gypsum and 15-25 parts of admixture. Fucoidan sulfate forms a complex with calcium ions in cement hydration products through the sulfate groups in its molecules, thereby preventing further hydration of cement particles, thereby effectively reducing the early heat release rate, avoiding the generation of temperature cracks inside the concrete structure, and improving the stability and durability of the structure. The microcapsule dual repair agent, through the coordinated action of the inner layer repair agent and the outer layer carrier, effectively solves the problem of delayed volume expansion of steel slag powder caused by fluctuations in the free calcium oxide content. The gradient clinker firing process significantly reduces the generation of cement hydration heat by optimizing the mineral distribution and chemical reaction path inside the clinker, while improving the thermal stability of the slurry.

Description

Technical Field

[0001] The present invention relates to the technical field of marine engineering cement, and in particular to a low-hydration heat 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 and strong corrosion resistance.

[0003] In the existing technology, although ferroaluminate cement has advantages such as fast hardening and corrosion resistance, its hydration heat release is concentrated in the acceleration period within 1 day, and the 24-hour heat release accounts for a high proportion. Although the total hydration heat is lower than that of silicate cement, the concentrated heat release may still cause large-volume structures to rise too quickly in the early stage, requiring reliance on complex temperature control measures.

[0004] When steel slag powder is used as an admixture, its free calcium oxide content is affected by fluctuations in the steel plant's production process. In the later stage of cement hardening, it is easy to react with water to form calcium hydroxide, causing delayed volume expansion and leading to the risk of cracking.

[0005] Furthermore, to control the cement hydration exotherm, existing technologies have attempted to incorporate water-absorbing resins as internal humidity regulators. However, even slight deviations in reaction conditions during resin synthesis can lead to a 30% drop in water absorption, directly impacting the shrinkage of the cement paste. Summary of the Invention

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

[0007] To achieve the above object, the present invention is implemented by the following technical solution: a low hydration heat of ferroaluminate cement, which comprises the following components in parts by mass:

[0008] 70-85 parts of ferroaluminate cement clinker, which is prepared by high-temperature calcination of calcium raw materials, aluminum raw materials, iron raw materials, phosphogypsum-red mud composite sulfur source, rare earth oxides and nano-strontium titanate;

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

[0010] 4-8 parts of a nano-friction modifier; the nano-friction modifier is a polyelectrolyte functionalized carbon dot having 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 a microcapsule dual repair agent; the microcapsule dual repair agent comprises polydopamine-coated epoxy resin microcapsules as an inner layer repair agent and alkaliphilic bacteria loaded on nano-metakaolin as an outer layer carrier;

[0012] 5-10 parts gypsum;

[0013] 15-25 parts mixed material.

[0014] Furthermore, the raw material ratio of the ferroaluminate cement clinker is:

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

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

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

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

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

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

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

[0022] A method for preparing low-hydration thermal ferroaluminate cement comprises the following steps:

[0023] S1. Preparation of microcapsule dual repair agent:

[0024] Inner microcapsule synthesis: epoxy resin and polydopamine are mixed in deionized water, and sodium dodecylbenzene sulfonate as an emulsifier is added, and the mixture is dispersed at high speed to form an oil phase emulsion;

[0025] Under acidic conditions, melamine-formaldehyde prepolymer is added dropwise to react and form inner layer microcapsules, which are then filtered and dried for later use;

[0026] The outer layer carrier is composited by mixing nano-metakaolin with alkaliphilic bacteria, adding a silane coupling agent, and stirring to form a nano-composite carrier loaded with bacteria;

[0027] The inner layer microcapsules are mixed with the carrier, and a fluidized bed coating process is adopted with polyvinyl alcohol as a binder to form a double-layer structure to obtain a microcapsule dual repair agent;

[0028] S2. Preparation of bio-based retarder:

[0029] Raw material processing: crush the brown algae and defatting with ethanol to remove impurities;

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

[0031] Sulfate esterification, reacting a crude brown algae polysaccharide solution with a chlorosulfonic acid-pyridine complex, adjusting the pH with sulfuric acid, dialysis purification, and freeze-drying to obtain brown algae polysaccharide sulfate, which is then diluted with water to obtain a bio-based retarder;

[0032] S3. Preparation of nano friction modifier:

[0033] Carbon dots were synthesized by using citric acid as carbon source and polyelectrolyte as surface modifier, and heating in a microwave reactor to generate polyelectrolyte functionalized carbon dots;

[0034] Dispersion treatment: dilute the polyelectrolyte-functionalized carbon dots with water and perform ultrasonic treatment to form a stable suspension;

[0035] S4. Clinker preparation: mixing calcium raw materials, aluminum raw materials, iron raw materials, phosphogypsum-red mud composite sulfur source, rare earth oxides and nano-strontium titanate, and ball milling to obtain raw material powder;

[0036] Carry out gradient temperature firing in a rotary kiln to obtain ferroaluminate cement clinker;

[0037] S5, using Ar / O2 mixed gas plasma activation treatment of the mixed material, and supersonic air flow pulverization;

[0038] Mixing ferroaluminate cement clinker, bio-based retarder, nano friction modifier and microcapsule dual repair agent according to the proportion of claim 1 to obtain mixed clinker;

[0039] The low hydration heat ferroaluminate cement is obtained by mixing mixed clinker, activated mixed material and gypsum.

[0040] Furthermore, S1 specifically comprises: mixing epoxy resin and polydopamine in deionized water, adding an emulsifier, sodium dodecylbenzenesulfonate, and dispersing at high speed to form an oil phase emulsion;

[0041] Under acidic conditions, melamine-formaldehyde prepolymer is added dropwise to react and form inner layer microcapsules with a particle size of 50-100 μm, which are then filtered and dried for later use;

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

[0043] The inner layer microcapsules and the carrier are mixed in a mass ratio of 1:1-2, and a fluidized bed coating process is adopted. Polyvinyl alcohol is used as an adhesive, and the total amount of the adhesive is 1.5-2.0wt% of the total amount of the inner layer microcapsules and the carrier to form a double-layer structure to obtain a microcapsule dual repair agent.

[0044] Furthermore, S2 specifically comprises: crushing the brown algae to a particle size of ≤2 mm, defatting with ethanol to remove impurities;

[0045] The brown algae crude polysaccharide solution was obtained by hot water extraction, adding magnesium chloride hexahydrate, and centrifuging to remove the alginate precipitate.

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

[0047] Furthermore, S3 specifically uses citric acid as a carbon source and a polyelectrolyte as a surface modifier, and after heating in a microwave reactor, generates polyelectrolyte functionalized carbon dots with a particle size of 3-7 nm and containing -SO3H and -COOH groups on the surface;

[0048] The polyelectrolyte-functionalized carbon dots were diluted with water and ultrasonically treated to form a stable suspension.

[0049] Furthermore, S4 specifically comprises: mixing calcium raw materials, aluminum raw materials, iron raw materials, phosphogypsum-red mud composite sulfur source, rare earth oxides and nano-strontium titanate, ball milling to D90≤45μm to obtain raw material powder; and performing gradient temperature sintering in a rotary kiln:

[0050] Preheating stage: 900-950℃, 5-8kW microwave irradiation for 10-15min;

[0051] Decomposition stage: 1250-1280℃, calcination for 30-40min in an oxyhydrogen burner with a hydrogen ratio of 25-30%;

[0052] Firing stage: 1300-1350℃, pure oxygen combustion calcination for 30-60min;

[0053] The mixture was cooled to room temperature to obtain ferroaluminate cement clinker.

[0054] Furthermore, S5 is specifically as follows: using Ar / O2 mixed gas, plasma activation treatment of the mixed material at a power of 5-6kW, and supersonic air flow pulverization to D50≤3μm.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] 1. The present invention uses fucoidan sulfate to form a complex with calcium ions in cement hydration products through the sulfate groups in its molecules, thereby 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. 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, fucoidan sulfate, as a bio-based retarder, achieves precise control of the slurry's autogenous shrinkage rate by regulating the hydration kinetics of ferroaluminate cement slurry. Compared with traditional water-absorbing resins, this retarder is not limited by the conditions of the synthesis process, can stably delay the early hydration reaction rate, and avoid shrinkage fluctuations caused by excessive hydration in the later stage, thereby ensuring the volume stability of the slurry at different construction stages.

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

[0058] 3. The gradient clinker burning process introduced in the present invention significantly reduces the amount of cement hydration heat generated by optimizing the mineral distribution and chemical reaction path within the clinker. This process balances the hydration reaction rates of silicate minerals and aluminate minerals within the clinker, reduces the dramatic release of hydration heat, and improves the thermal stability of the slurry.

[0059] 4. When the gradient firing process and the microcapsule dual repair agent are compounded, a significant synergistic effect can be produced. The gradient firing 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 reduces the hydration heat by more than the sum of any single technology, but also significantly improves the anti-expansion performance of the hardened body and the stability of the autogenous shrinkage rate.

[0060] 5. The gradient clinker firing process uses staged temperature control and energy input to make the clinker release heat more evenly in the early stage of hydration. 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 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, which not only significantly reduces the hydration heat of early ferroaluminate cement, but also improves the overall performance and durability of the cement matrix. DETAILED DESCRIPTION

[0061] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0062] Example 1: This example provides a low-hydration heat of ferroaluminate cement, which comprises the following components in parts by mass:

[0063] 85 parts of ferroaluminate cement clinker, prepared by high-temperature calcination of calcium raw materials, aluminum raw materials, iron raw materials, phosphogypsum-red mud composite sulfur source, rare earth oxides and nano-strontium titanate;

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

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

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

[0067] 10 parts gypsum;

[0068] 25 parts mixed material.

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

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

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

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

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

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

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

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

[0077] The method for preparing the low-hydration thermal ferroaluminate cement comprises the following steps:

[0078] S1. Preparation of microcapsule dual repair agent:

[0079] Inner microcapsule synthesis:

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

[0081] Under acidic conditions of pH=3.5, melamine-formaldehyde prepolymer was added dropwise and reacted at 70°C for 3 hours to form inner layer microcapsules with a particle size of 100 μm. The inner layer microcapsules were filtered and dried for later use.

[0082] Outer carrier composite:

[0083] Nano-metakaolin (specific surface area 600m 2 / g) and alkaliphilic bacteria (cell density 5×10 8 CFU / g) were mixed at a mass ratio of 1:1, and a silane coupling agent KH-550 (2 wt % was added) was stirred at 40°C for 2 h to form a nanocomposite carrier loaded with bacteria;

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

[0085] S2. Preparation of bio-based retarder:

[0086] Raw material processing: The brown algae were crushed to a particle size of ≤2 mm and defatted with ethanol (70%) for 2 h to remove impurities;

[0087] Polysaccharide extraction: hot water extraction (90°C, 10 h), adding magnesium chloride hexahydrate (concentration 0.05 mol / L), centrifuging to remove the alginate precipitate, to obtain a crude brown algae polysaccharide solution;

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

[0089] S3. Preparation of nano friction modifier:

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

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

[0092] S4. Clinker preparation: Calcium raw materials, aluminum raw materials, iron raw materials, phosphogypsum-red mud composite sulfur source, rare earth oxides and nano-strontium titanate are mixed and ball-milled to D90≤45μm to obtain raw material powder; and gradient temperature sintering is carried out in a rotary kiln:

[0093] Preheating stage: 950°C, microwave irradiation (2.45 GHz, 8 kW) for 10 min;

[0094] Decomposition stage: 1280℃, calcination in hydrogen-oxygen burner (hydrogen ratio 30%) for 40min;

[0095] Firing stage: 1350℃, pure oxygen combustion calcination for 60min;

[0096] Cooling to room temperature to obtain ferroaluminate cement clinker;

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

[0098] The ferroaluminate cement clinker, the bio-based retarder, the nano friction modifier and the microcapsule dual repair agent are mixed in the above proportions to obtain a mixed clinker;

[0099] The low hydration heat ferroaluminate cement is obtained by mixing mixed clinker, activated mixed material and gypsum.

[0100] Example 2: This example provides a low-hydration thermal ferroaluminate cement, which comprises the following components in parts by mass:

[0101] 70 parts of ferroaluminate cement clinker, which is prepared by high-temperature calcination of calcium raw materials, aluminum raw materials, iron raw materials, phosphogypsum-red mud composite sulfur source, rare earth oxides and nano-strontium titanate;

[0102] 5 parts of a bio-based retarder; the bio-based retarder is fucoidan sulfate, having a molecular weight of 50 kDa and a sulfate content of ≥30%;

[0103] 4 parts of a nano-friction modifier; the nano-friction modifier is a polyelectrolyte functionalized carbon dot having a particle size of 3 nm and containing sulfonic acid groups (-SO3H) and carboxyl groups (-COOH) on the surface;

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

[0105] 5 parts gypsum;

[0106] 15 parts mixed material.

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

[0108] Calcium raw material (CaO ≥ 52%): 60wt%;

[0109] Aluminum raw material (Al2O3≥65%): 15wt%;

[0110] Iron raw material (Fe2O3≥75%): 16wt%;

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

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

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

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

[0115] The method for preparing the low-hydration thermal ferroaluminate cement comprises the following steps:

[0116] S1. Preparation of microcapsule dual repair agent:

[0117] Inner microcapsule synthesis:

[0118] Epoxy resin (Epoxy resin E51 and epoxy resin 127, mass ratio 6:4) and polydopamine (mass ratio 10:1) were mixed in deionized water, and an emulsifier, sodium dodecylbenzenesulfonate (dosage 0.8 wt%), was added and dispersed at a high speed of 3000 r / min to form an oil phase emulsion;

[0119] Under acidic conditions of pH=3.5, melamine-formaldehyde prepolymer was added dropwise and reacted at 70°C for 3 hours to form inner layer microcapsules with a particle size of 50 μm. The inner layer microcapsules were filtered and dried for later use.

[0120] Outer carrier composite:

[0121] Nano-metakaolin (specific surface area 500m 2 / g) and alkaliphilic bacteria (cell density 1×10 8 CFU / g) were mixed at a mass ratio of 1:1, and a silane coupling agent KH-550 (1 wt%) was added, and stirred at 40°C for 2 h to form a nanocomposite carrier loaded with bacteria;

[0122] The inner layer microcapsules and the carrier were mixed in a mass ratio of 1:1-2, and a fluidized bed coating process was used with polyvinyl alcohol (molecular weight 67000) as a binder (total dosage 1.5wt%) to form a double-layer structure to obtain a microcapsule dual repair agent;

[0123] S2. Preparation of bio-based retarder:

[0124] Raw material processing: The brown algae were crushed to a particle size of ≤2 mm and defatted with ethanol (70%) for 2 h to remove impurities;

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

[0126] Sulfation: The crude brown algae polysaccharide solution was reacted with a chlorosulfonic acid-pyridine complex (mass ratio 1:3) at 50°C for 3 hours, the pH was adjusted to neutral with sulfuric acid, the product was dialyzed and purified, and then freeze-dried to obtain brown algae polysaccharide sulfate (molecular weight 50 kDa, sulfate content ≥30%). The brown algae polysaccharide sulfate was mixed with water in a ratio of 1:5 to obtain a bio-based retarder.

[0127] S3. Preparation of nano friction modifier:

[0128] Carbon dot synthesis: Citric acid was used as the carbon source and polyelectrolyte (sodium polystyrene sulfonate-acrylic acid copolymer) was used as the surface modifier. The mixture was mixed at a mass ratio of 2:1 and heated to 200°C in a microwave reactor (power 800 W, frequency 2.45 GHz) for 30 min to generate polyelectrolyte-functionalized carbon dots (containing -SO3H and -COOH groups on the surface) with a particle size of 3 nm.

[0129] Dispersion treatment: polyelectrolyte-functionalized carbon dots were mixed with deionized water at a ratio of 1:10 and ultrasonicated (power 500 W, frequency 40 kHz) for 30 min to form a stable suspension;

[0130] S4. Clinker preparation: Calcium raw materials, aluminum raw materials, iron raw materials, phosphogypsum-red mud composite sulfur source, rare earth oxides and nano-strontium titanate are mixed and ball-milled to D90≤45μm to obtain raw material powder; and gradient temperature sintering is carried out in a rotary kiln:

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

[0132] Decomposition stage: 1250°C, calcination in an oxyhydrogen burner (hydrogen ratio 25%) for 30 minutes;

[0133] Firing stage: 1300℃, pure oxygen combustion calcination for 30min;

[0134] Cooling to room temperature to obtain ferroaluminate cement clinker;

[0135] S5. Mixing: The mixed material (steel slag powder and fly ash with a mass ratio of 1.8:2) is treated by plasma activation using Ar / O2 mixed gas (volume ratio 4:1, power 5kW), and then pulverized by supersonic air flow to D50 ≤ 3μm;

[0136] The ferroaluminate cement clinker, the bio-based retarder, the nano friction modifier and the microcapsule dual repair agent are mixed in the above proportions to obtain a mixed clinker;

[0137] The low hydration heat ferroaluminate cement is obtained by mixing mixed clinker, activated mixed material and gypsum.

[0138] Example 3: This example provides a low-hydration thermal ferroaluminate cement, which comprises the following components in parts by mass:

[0139] 82 parts of ferroaluminate cement clinker, prepared by high-temperature calcination of calcium raw materials, aluminum raw materials, iron raw materials, phosphogypsum-red mud composite sulfur source, rare earth oxides and nano-strontium titanate;

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

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

[0142] 4 parts of a microcapsule dual repair agent; the microcapsule dual repair agent comprises polydopamine-coated epoxy resin microcapsules as an inner layer repair agent and alkaliphilic bacteria loaded on nano-metakaolin as an outer layer carrier;

[0143] 6 parts gypsum;

[0144] 21 parts mixed material.

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

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

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

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

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

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

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

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

[0153] The method for preparing the low-hydration thermal ferroaluminate cement comprises the following steps:

[0154] S1. Preparation of microcapsule dual repair agent:

[0155] Inner microcapsule synthesis:

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

[0157] Under acidic conditions of pH=3.5, melamine-formaldehyde prepolymer was added dropwise and reacted at 70°C for 3 hours to form inner layer microcapsules with a particle size of 80 μm, which were filtered and dried for later use;

[0158] Outer carrier composite:

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

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

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

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

[0163] Polysaccharide extraction: hot water extraction (90°C, 10 h), adding magnesium chloride hexahydrate (concentration 0.05 mol / L), centrifuging to remove the alginate precipitate, to obtain a crude brown algae polysaccharide solution;

[0164] Sulfation: The crude brown algae polysaccharide solution was reacted with a chlorosulfonic acid-pyridine complex (mass ratio 1:3) at 58°C for 3 hours, the pH was adjusted to neutral with sulfuric acid, the product was dialyzed and purified, and then freeze-dried to obtain brown algae polysaccharide sulfate (molecular weight 60 kDa, sulfate content ≥30%). The brown algae polysaccharide sulfate was mixed with water in a ratio of 1:5 to obtain a bio-based retarder.

[0165] S3. Preparation of nano friction modifier:

[0166] Carbon dot synthesis: Citric acid was used as the carbon source and polyelectrolyte (sodium polystyrene sulfonate-acrylic acid copolymer) was used as the surface modifier. The mixture was mixed at a mass ratio of 2:1 and heated to 200°C in a microwave reactor (power 800 W, frequency 2.45 GHz) for 30 min to produce polyelectrolyte-functionalized carbon dots (containing -SO3H and -COOH groups on the surface) with a particle size of 5 nm.

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

[0168] S4. Clinker preparation: Calcium raw materials, aluminum raw materials, iron raw materials, phosphogypsum-red mud composite sulfur source, rare earth oxides and nano-strontium titanate are mixed and ball-milled to D90≤45μm to obtain raw material powder; and gradient temperature sintering is carried out in a rotary kiln:

[0169] Preheating stage: 930°C, microwave irradiation (2.45 GHz, 5 kW) for 15 min;

[0170] Decomposition stage: 1260°C, calcination in an oxyhydrogen burner (hydrogen ratio 28%) for 36 minutes;

[0171] Firing stage: 1320℃, pure oxygen combustion calcination for 50min;

[0172] Cooling to room temperature to obtain ferroaluminate cement clinker;

[0173] S5. Mixing: The mixed material (steel slag powder and fly ash with a mass ratio of 1.8:2) is treated by plasma activation using Ar / O2 mixed gas (volume ratio 4:1, power 5kW), and then pulverized by supersonic air flow to D50 ≤ 3μm;

[0174] The ferroaluminate cement clinker, the bio-based retarder, the nano friction modifier and the microcapsule dual repair agent are mixed in the above proportions to obtain a mixed clinker;

[0175] The low hydration heat ferroaluminate cement is obtained by mixing mixed clinker, activated mixed material and gypsum.

[0176] Comparative Example 1: This comparative example differs from Example 3 in that no bio-based retarder is added.

[0177] Comparative Example 2: This comparative example differs from Example 3 in that no microcapsule dual repair agent is added.

[0178] Comparative Example 3: This comparative example differs from Example 3 in that the raw meal powder is not preheated or decomposed, but is directly calcined in pure oxygen at 1320° C. for 20 min to obtain cement clinker.

[0179] Comparative Example 4: This comparative example differs from Example 3 in that neither microcapsule dual repair agent is added nor the raw meal powder is preheated or decomposed. Instead, the raw meal powder is directly calcined in pure oxygen at 1320°C for 20 minutes to obtain cement clinker.

[0180] Experimental example:

[0181] 1. Autogenous shrinkage rate test;

[0182] 1.1 Test piece preparation: Test mold specifications: PVC pipe with a diameter of 100mm × 420mm, lubricating oil applied to the inside, sealing the base and wrapping it with plastic wrap to prevent leakage;

[0183] Molding requirements: Concrete mixture is made according to T0551 specification, the maximum aggregate size is ≤31.5mm, and the surface is smoothed and sealed after molding (only when autogenous shrinkage is measured)

[0184] 1.2 Test environment: constant temperature and humidity, temperature 20℃±2℃, humidity 60%±5%, equipped with automatic temperature and humidity recorder;

[0185] 1.3 Measurement steps

[0186] For initial measurement, install the dial indicator immediately after forming and record every 30 minutes for the first 8 hours, and then gradually extend the interval to 3 days;

[0187] Data collection, accurate to 0.001mm, takes the arithmetic mean value of 3 specimens in each group, calculation formula:

[0188]

[0189] Where 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: Cement samples must pass through a 0.9mm square hole sieve and be mixed evenly;

[0193] Mixing water should be grade 3 or above distilled water;

[0194] Instruments and equipment, planetary mortar mixer (in compliance with JC / T 681 requirements);

[0195] Comparator, graduation value 0.01mm, range ≥10mm, base length ≥300mm;

[0196] Triple test mold, size 25mm×25mm×280mm, end plates with nail heads (stainless steel or copper).

[0197] Balance, range ≥ 2000g, graduation value ≤ 1g;

[0198] 2.2 Experimental steps

[0199] To prepare the test specimen, add water according to the standard consistency, weigh 1200g of cement sample, stir it and put it into the triple test mold;

[0200] After vibration molding, the test mold is placed in a curing box at 20±1℃ and humidity ≥90% for 24 hours before demoulding;

[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 Calculation of results;

[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 clinker firing process allows for more uniform heat release in the early stages 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 cement hydration, filling 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, which not only significantly reduces the hydration heat of ferroaluminate cement, but also improves 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 the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A low hydration heat ferroaluminate cement, characterized in that: Calculated by mass, it includes the following ingredients: 70-85 parts of ferroaluminate cement clinker, which is prepared by high-temperature calcination of calcium raw materials, aluminum raw materials, iron raw materials, phosphogypsum-red mud composite sulfur source, rare earth oxides and nano-strontium titanate; 5-7 parts of a bio-based retarder; the bio-based retarder is fucoidan sulfate, having a molecular weight of 50-80 kDa and a sulfate content of ≥30%; 4-8 parts of a nano-friction modifier; the nano-friction modifier is a polyelectrolyte functionalized carbon dot having a particle size of 3-7 nm and containing sulfonic acid and carboxyl groups on the surface; 3-4.5 parts of a microcapsule dual repair agent; the microcapsule dual repair agent comprises polydopamine-coated epoxy resin microcapsules as an inner layer repair agent and alkaliphilic bacteria loaded on nano-metakaolin as an outer layer carrier; 5-10 parts gypsum; 15-25 parts mixed material.

2. The low hydration thermal ferroaluminate cement according to claim 1, characterized in that The raw material ratio of the ferroaluminate cement clinker is: Calcium raw material: 45-60wt%; Aluminum raw material: 15-25wt%; Iron raw material: 9-20wt%; Phosphogypsum-red mud composite sulfur source: 8-20wt%; Rare earth oxides: 0.3-0.8wt%; Nano-strontium titanate: 0.2-0.7wt%; The mass ratio of phosphogypsum to red mud in the phosphogypsum-red mud composite sulfur source is 3:1, the CaSO4·2H2O content of the phosphogypsum is ≥85%, and the Fe2O3 content of the red mud is ≥25%.

3. A method for preparing low hydration thermal ferroaluminate cement according to claim 2, characterized in that: The following steps are involved: S1. Preparation of microcapsule dual repair agent: Inner microcapsule synthesis: epoxy resin and polydopamine are mixed in deionized water, and sodium dodecylbenzene sulfonate as an emulsifier is added, and the mixture is dispersed at high speed to form an oil phase emulsion; Under acidic conditions, melamine-formaldehyde prepolymer is added dropwise to react and form inner layer microcapsules, which are then filtered and dried for later use; The outer layer carrier is composited by mixing nano-metakaolin with alkaliphilic bacteria, adding a silane coupling agent, and stirring to form a nano-composite carrier loaded with bacteria; The inner layer microcapsules are mixed with the carrier, and a fluidized bed coating process is adopted with polyvinyl alcohol as a binder to form a double-layer structure to obtain a microcapsule dual repair agent; S2. Preparation of bio-based retarder: Raw material processing: crush the brown algae and defatting with ethanol to remove impurities; Polysaccharide extraction: hot water extraction method was used, magnesium chloride hexahydrate was added, and the alginate precipitate was removed by centrifugation to obtain the crude polysaccharide solution of brown algae; Sulfate esterification, reacting a crude brown algae polysaccharide solution with a chlorosulfonic acid-pyridine complex, adjusting the pH with sulfuric acid, dialysis purification, and freeze-drying to obtain brown algae polysaccharide sulfate, which is then diluted with water to obtain a bio-based retarder; S3. Preparation of nano friction modifier: Carbon dots were synthesized by using citric acid as carbon source and polyelectrolyte as surface modifier, and heating 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. Clinker preparation: mixing calcium raw materials, aluminum raw materials, iron raw materials, phosphogypsum-red mud composite sulfur source, rare earth oxides and nano-strontium titanate, and ball milling to obtain raw material powder; Carry out gradient temperature firing in a rotary kiln to obtain ferroaluminate cement clinker; S5, using Ar / O2 mixed gas plasma activation treatment of the mixed material, and supersonic air flow pulverization; Mixing ferroaluminate cement clinker, bio-based retarder, nano friction modifier and microcapsule dual repair agent according to the proportion of claim 1 to obtain mixed clinker; The low hydration heat ferroaluminate cement is obtained by mixing mixed clinker, activated mixed material and gypsum.

4. The method for preparing low hydration thermal ferroaluminate cement according to claim 3, characterized in that: S1 specifically comprises: mixing epoxy resin and polydopamine in deionized water, adding an emulsifier, sodium dodecylbenzenesulfonate, and dispersing at high speed to form an oil phase emulsion; Under acidic conditions, melamine-formaldehyde prepolymer is added dropwise to react and form inner layer microcapsules with a particle size of 50-100 μm, which are then filtered and dried for later use; Nano-metakaolin and alkaliphilic bacteria were mixed in a mass ratio of 1:1, silane coupling agent KH-550 was added, and stirred to form a nano-composite carrier loaded with bacteria; The inner layer microcapsules and the carrier are mixed in a mass ratio of 1:1-2, and a fluidized bed coating process is adopted. Polyvinyl alcohol is used as an adhesive, and the total amount of the adhesive is 1.5-2.0wt% of the total amount of the inner layer microcapsules and the carrier to form a double-layer structure to obtain a microcapsule dual repair agent.

5. The method for preparing low hydration thermal ferroaluminate cement according to claim 3, characterized in that: S2 specifically comprises: crushing the brown algae to a particle size of ≤2 mm, defatting with ethanol, and removing impurities; The brown algae crude polysaccharide solution was obtained by hot water extraction, adding magnesium chloride hexahydrate, and centrifuging to remove the alginate precipitate. The crude brown algae polysaccharide solution is reacted with a chlorosulfonic acid-pyridine complex at 50-60°C for 3-4 hours, the pH is adjusted to neutral with sulfuric acid, the solution is dialyzed and purified, and then freeze-dried to obtain brown algae polysaccharide sulfate with a molecular weight of 50-80 kDa and a sulfate content of ≥30%. The brown algae polysaccharide sulfate is diluted with water to obtain a bio-based retarder.

6. The method for preparing low hydration thermal ferroaluminate cement according to claim 3, characterized in that: S3 specifically uses citric acid as a carbon source and a polyelectrolyte as a surface modifier, and after heating in a microwave reactor, generates polyelectrolyte-functionalized carbon dots with a particle size of 3-7 nm and containing -SO3H and -COOH groups on the surface; The polyelectrolyte-functionalized carbon dots were diluted with water and ultrasonically treated to form a stable suspension.

7. The method for preparing low hydration thermal ferroaluminate cement according to claim 3, characterized in that: S4 specifically comprises: mixing calcium raw materials, aluminum raw materials, iron raw materials, phosphogypsum-red mud composite sulfur source, rare earth oxides and nano-strontium titanate, ball milling until D90 ≤ 45 μm to obtain raw material powder; and sintering in a rotary kiln at a gradient temperature: Preheating stage: 900-950℃, 5-8kW microwave irradiation for 10-15min; Decomposition stage: 1250-1280℃, calcination for 30-40min in an oxyhydrogen burner with a hydrogen ratio of 25-30%; Firing stage: 1300-1350℃, pure oxygen combustion calcination for 30-60min; The mixture was cooled to room temperature to obtain ferroaluminate cement clinker.

8. The method for preparing low hydration thermal ferroaluminate cement according to claim 3, characterized in that: S5 specifically includes: using Ar / O2 mixed gas, plasma activation treatment of the mixed material at a power of 5-6kW, and supersonic air flow pulverization to D50≤3μm.

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