Preparation method of low-carbon cementing material for road concrete

Abstract

The invention relates to the technical field of concrete materials, in particular to a preparation method of a low-carbon cementing material for road concrete. The preparation method comprises the following steps: adding 25-35 parts by weight of superfine steel slag micro powder and 20-30 parts by weight of silicon dioxide modified fly ash into 100-120 parts by weight of water, stirring and dispersing to obtain a mixed solution, sequentially adding 15-25 parts by weight of desulfurized gypsum and silica fume composite powder and 5-10 parts by weight of rice hull ash into the mixed solution, and stirring for the first time to obtain a mixed solution; and then adding 0.5-1.5 parts of basalt fibers, and carrying out second stirring treatment, so as to obtain the low-carbon cementing material for the road concrete. According to the low-carbon cementing material for the road concrete, the strength of the road concrete prepared from the low-carbon cementing material is improved, the wear resistance and the breaking strength of the road concrete prepared from the low-carbon cementing material are improved, the problems of surface wear, cracking and the like in the long-term use process are reduced, the service life of a road is prolonged, and the driving safety is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete materials, and in particular to a method for preparing a low-carbon cementitious material for road concrete. Background Art

[0002] Road construction is a crucial component of urban development and national infrastructure development. As one of the most commonly used construction materials in road construction, concrete's quality is directly related to road lifespan, driving safety, and comfort. Cementitious materials are the key binder in concrete. Traditional cementitious materials, such as ordinary Portland cement, consume significant amounts of energy and natural resources during production and emit significant amounts of greenhouse gases such as carbon dioxide, severely impacting the environment. With increasing global awareness of environmental protection and sustainable development, the development of low-carbon cementitious materials for road concrete has become an inevitable choice for the road construction industry's green transformation.

[0003] Low-carbon cementitious materials for road concrete are cementitious materials that significantly reduce carbon emissions during their preparation and use while meeting the performance requirements of road concrete. Compared to traditional ordinary Portland cement, low-carbon cementitious materials achieve this low-carbon goal primarily through the following approaches: first, they use industrial waste or natural minerals as their primary raw materials, reducing reliance on traditional high-energy-consuming raw materials; second, they optimize their preparation processes to reduce energy consumption during production; and third, they utilize novel chemical reaction mechanisms to reduce carbon emissions while maintaining cementitious properties.

[0004] Some low-carbon cementitious materials have a slow hydration reaction rate in the early stage, resulting in slow strength development of road concrete in a short period of time after pouring. This has an adverse effect on the progress of road construction and the demand for early traffic. For example, in some road projects that need to be repaired quickly, insufficient early strength may cause the road to be unable to open to traffic in time, increasing traffic congestion and construction costs. Road concrete needs to withstand repeated crushing and friction from vehicles, so it has high requirements for wear resistance and flexural strength. However, the performance of road concrete prepared from existing low-carbon cementitious materials in this regard is often inferior to that of traditional cement concrete. During long-term use, problems such as surface wear and cracking are prone to occur, affecting the service life of the road and driving safety. Based on this, the present invention provides a method for preparing a low-carbon cementitious material for road concrete. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing a low-carbon cementitious material for road concrete, thereby improving the early strength development speed of road concrete prepared with the low-carbon cementitious material, so as to reduce the adverse effects on the progress of road construction and the demand for early traffic opening; and improving the wear resistance and flexural strength of road concrete prepared with the low-carbon cementitious material, so as to reduce problems such as surface wear and cracking during long-term use, thereby improving the service life of the road and driving safety.

[0006] On the one hand, the present invention provides a method for preparing a low-carbon cementitious material for road concrete, comprising the following steps: adding 25-35 parts by weight of ultrafine steel slag powder and 20-30 parts of silica-modified fly ash to 100-120 parts of water, stirring and dispersing to obtain a mixed liquid, adding 15-25 parts of desulfurized gypsum@silica ash composite powder and 5-10 parts of rice husk ash in sequence to the mixed liquid, performing a first stirring, and then adding 0.5-1.5 parts of basalt fiber and performing a second stirring treatment to obtain the low-carbon cementitious material for road concrete.

[0007] The present invention uses basalt fiber as a reinforcing material. Basalt fiber has excellent alkali resistance and good interfacial adhesion with the cementitious matrix. During the hardening process of the cementitious material, the basalt fiber can be evenly dispersed inside the material, connecting adjacent cementitious particles together through a bridging effect. When the material is subjected to external force, the basalt fiber can withstand a certain tensile stress, prevent the generation and expansion of microcracks, and disperse the stress to a larger area, thereby improving the flexural strength and toughness of the material. Compared with polypropylene fiber, basalt fiber has better alkali resistance and can maintain good performance stability in an alkaline cementitious material environment. It also has stronger interfacial adhesion with the cementitious matrix, which can better play a reinforcing role, effectively reducing the cracking problem of road concrete caused by factors such as temperature changes and vehicle loads during long-term use, thereby improving the service life and driving safety of the road.

[0008] Furthermore, the preparation method of the silica-modified fly ash includes: mixing fly ash with sodium hydroxide solution, stirring in a water bath at 60-70°C for 2-3 hours, adding sodium silicate, stirring and dispersing, and then hydrothermally reacting at 170-190°C for 5-6 hours. After the reaction is completed, the silica-modified fly ash is obtained by suction filtration, drying, and ball milling.

[0009] Furthermore, the sodium hydroxide solution is a sodium hydroxide aqueous solution with a mass concentration of 8-12%.

[0010] Furthermore, the fly ash is Class II fly ash, the modulus of the sodium silicate is 1.2; and the weight ratio of the fly ash, sodium hydroxide solution and sodium silicate is 10: (0.5-0.7): (2-3).

[0011] Furthermore, the stirring and dispersing step is carried out at 200-300 rpm for 30-40 minutes; and the drying temperature is 100-110°C.

[0012] Furthermore, the preparation method of the desulfurized gypsum@silica fume composite powder includes: pre-treating the desulfurized gypsum, mixing it with silica fume and nano-CaCO3, adding triethanolamine and wet grinding for 2-3 hours to obtain a slurry, spray drying it, calcining it at 800-900°C for 20-30 minutes in a CO2 atmosphere, and crushing it to D90 <15μm.

[0013] Furthermore, the desulfurized gypsum pretreatment step includes: calcining the desulfurized gypsum at 500-600° C. for 1-2 hours to remove bound water, and crushing the desulfurized gypsum to D50=10 μm.

[0014] Furthermore, the weight ratio of the pretreated desulfurized gypsum, silica fume, nano-CaCO3 and triethanolamine is (65-75): (25-35): (2-3): (0.4-0.8).

[0015] Furthermore, the stirring and dispersing is performed at 300-400 rpm for 1.5-2 hours, and the stirring treatment mode is intermittent stirring, stirring for 5-10 minutes and then pausing for 5-10 minutes.

[0016] Furthermore, the first stirring is carried out at a rotation speed of 800-1000 r / min for 20-25 min; and the second stirring is carried out at a rotation speed of 300-400 r / min for 8-10 min.

[0017] The beneficial effects of the present invention are: The present invention uses silicon dioxide to modify fly ash. First, the fly ash is subjected to an alkali excitation treatment using a sodium hydroxide solution. The sodium hydroxide reacts with the active silicon oxide and aluminum oxide in the fly ash, destroying the glassy structure of the fly ash and making the active ingredients therein more easily dissolved. Sodium silicate is then added, and the sodium silicate further reacts with the active ingredients dissolved from the fly ash to generate a large amount of aluminosilicate gel. These gels can not only fill the pores between the fly ash particles, increase the density of the material, and form a denser and more stable microstructure, thereby significantly improving the strength of the cementitious material. At the same time, the activity of the modified fly ash is greatly improved, and it can better participate in the hydration reaction, providing early strength support for road concrete, meeting the road construction progress and early traffic requirements.

[0018] The present invention prepares a composite powder by pre-treating desulfurized gypsum, mixing it with silica fume and nano-CaCO3. After pre-treatment of the desulfurized gypsum, the surface activity of the particles is increased, making it more conducive to reaction with other raw materials. Silica fume has an extremely high specific surface area and pozzolanic activity, which can fill tiny pores in the material and undergo a secondary hydration reaction with cement hydration products to generate more gelling substances, thereby improving the strength and durability of the material. Nano-CaCO3 generates CaO during the roasting process, and Ca reacts with acidic substances in the system to further enhance the gelling properties of the composite powder. Through triethanolamine wet grinding, the desulfurized gypsum, silica fume and nano-CaCO3 are thoroughly mixed and uniformly formed into a slurry with good dispersibility. Spray drying and further roasting can promote the carbonization reaction of nano-CaCO3 and the calcium-silicon reaction between the desulfurized gypsum and silica fume, resulting in a denser and more stable crystal structure. This desulfurized gypsum@silica fume composite powder combines the cementitious properties of desulfurized gypsum, the micro-aggregate effect of silica fume, and the carbonization enhancement of nano-CaCO3. It can exert a synergistic effect in cementitious materials, significantly improve the density and strength of the material, reduce surface wear and cracking during long-term use, and improve road service life and driving safety.

[0019] In the process of preparing gelling materials, the dispersion uniformity of the raw materials has an important impact on the performance of the materials. The present invention adopts an intermittent stirring dispersion process. Although continuous stirring can improve the dispersion effect to a certain extent, it may cause local overheating, resulting in agglomeration of particles in the solution, affecting the uniformity of dispersion. The intermittent stirring process can avoid local overheating, allowing the particles to be better dispersed under the action of stirring. At the same time, the pause time can allow the particles in the solution to have enough time to rearrange and stabilize, forming a more uniform slurry structure. This uniform slurry structure is conducive to the subsequent reaction and combination between the raw materials, improving the density and interfacial bonding strength of the gelling material, thereby improving the overall performance of the material.

[0020] This invention achieves synergistic effects among the core components—silica-modified fly ash, desulfurized gypsum and silica fume composite powder—and basalt fiber, combined with a specific preparation process. The silica-modified fly ash provides early strength support and a certain degree of pozzolanic activity; the desulfurized gypsum and silica fume composite powder enhances the material's density and later strength through calcium-silicon and carbonization reactions; and the basalt fiber enhances its toughness and crack resistance. Furthermore, optimization of details such as the modification process (alkali activation + hydrothermal reaction), the composite powder preparation process (calcination + wet grinding + CO2 roasting), and the intermittent stirring and dispersion process further promotes the reaction and bonding between the components, improving the material's homogeneity and interfacial bonding strength. This synergistic optimization of the core components and process results in a low-carbon cementitious material for road concrete that achieves an excellent balance of strength, water permeability, and wear resistance, meeting the engineering requirements of road concrete and providing a high-performance, environmentally friendly cementitious material solution for road construction. DETAILED DESCRIPTION

[0021] The following is a clear and complete description of the technical solution of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. 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.

[0022] It should be noted that the ultrafine steel slag powder is the ultrafine steel slag powder that is screened by the powder separator after the steel slag tailings are deironed, then ground by roller mill and vertical mill, and its specific surface area is 700-1000m 3 / kg, C2S content of 25-32%; desulfurization gypsum was purchased from Jinhai Gypsum Products Factory, Yicheng District, Zaozhuang City; silica fume was purchased from Beijing Zhongjian Special Cement Co., Ltd.; rice husk ash was purchased from Jiangsu Hanfang Technology Co., Ltd., with an amorphous SiO2 content of ≥75% and a particle size of ≤40μm after grinding; basalt fiber was purchased from Sichuan Aerospace Tuoxin Basalt Industry Co., Ltd., with a single fiber diameter of 9-13μm; polypropylene fiber was purchased from Tuoda New Materials Technology Industry Group Co., Ltd., model TD-YUJ.

[0023] Example 1 This embodiment provides a method for preparing a low-carbon cementitious material for road concrete, comprising the following steps: adding, by weight, 30 parts of ultrafine steel slag powder and 25 parts of silica-modified fly ash to 110 parts of water; stirring and dispersing the mixture at 250 rpm for 1.8 hours; stirring for 8 minutes and then pausing for 8 minutes; sequentially adding 20 parts of desulfurized gypsum@silica ash composite powder and 7 parts of rice husk ash to the mixture; stirring at a speed of 900 r / min for 22 minutes; subsequently adding 1 part of basalt fiber and stirring at a speed of 350 r / min for 9 minutes to obtain the low-carbon cementitious material for road concrete.

[0024] Among them, the preparation method of silica-modified fly ash includes: mixing fly ash with a sodium hydroxide aqueous solution with a mass concentration of 10%, stirring in a water bath at 65°C for 2.5 hours, adding sodium silicate, stirring and dispersing at 350rpm for 35 minutes, and then hydrothermally reacting at 180°C for 5.5 hours. After the reaction is completed, it is filtered, dried at 105°C for 12 hours, and ball milled to obtain; the fly ash is Class II fly ash, and the modulus of the sodium silicate is 1.2; the weight ratio of the fly ash, sodium hydroxide solution and sodium silicate is 10:0.6:2.5.

[0025] The preparation method of the desulfurized gypsum@silica fume composite powder includes: calcining the desulfurized gypsum at 550°C for 1.5 hours to remove bound water, crushing it to D50=10μm to obtain pretreated desulfurized gypsum, mixing it with silica fume and nano-CaCO3, adding triethanolamine and wet grinding it for 2.5 hours to obtain a slurry, spray drying it, roasting it at 850°C for 25 minutes under a CO2 atmosphere, and crushing it to D90<15μm to obtain the slurry; the weight ratio of the pretreated desulfurized gypsum, silica fume, nano-CaCO3 and triethanolamine is 70:30:2.5:0.6.

[0026] Example 2 This embodiment provides a method for preparing a low-carbon cementitious material for road concrete, comprising the following steps: adding, by weight, 25 parts of ultrafine steel slag powder and 20 parts of silica-modified fly ash to 100 parts of water; stirring and dispersing the mixture at 200 rpm for 1.5 hours to obtain a mixed solution; stirring for 5 minutes and then pausing for 5 minutes; sequentially adding 15 parts of desulfurized gypsum@silica ash composite powder and 5 parts of rice husk ash to the mixed solution; stirring at a speed of 800 r / min for 20 minutes; subsequently adding 0.5 parts of basalt fiber and stirring at a speed of 300 r / min for 8 minutes to obtain the low-carbon cementitious material for road concrete.

[0027] Among them, the preparation method of silica-modified fly ash includes: mixing fly ash with an 8% mass concentration of sodium hydroxide aqueous solution, stirring in a water bath at 60°C for 2 hours, adding sodium silicate, stirring and dispersing at 300 rpm for 30 minutes, and then hydrothermally reacting at 170°C for 5 hours. After the reaction is completed, the product is filtered, dried at 100°C for 12 hours, and ball milled to obtain the product; the fly ash is Class II fly ash, and the modulus of the sodium silicate is 1.2; the weight ratio of the fly ash, sodium hydroxide solution and sodium silicate is 10:0.5:2.

[0028] The preparation method of the desulfurized gypsum@silica fume composite powder includes: calcining the desulfurized gypsum at 500°C for 1h to remove bound water, crushing it to D50=10μm to obtain pretreated desulfurized gypsum, mixing it with silica fume and nano-CaCO3, adding triethanolamine and wet grinding it for 2h to obtain a slurry, spray drying it, roasting it at 800°C for 20min under a CO2 atmosphere, and crushing it to D90<15μm to obtain the slurry; the weight ratio of the pretreated desulfurized gypsum, silica fume, nano-CaCO3 and triethanolamine is 65:25:2:0.4.

[0029] Example 3 This embodiment provides a method for preparing a low-carbon cementitious material for road concrete, comprising the following steps: adding, by weight, 35 parts of ultrafine steel slag powder and 30 parts of silica-modified fly ash to 120 parts of water; stirring and dispersing the mixture at 300 rpm for 2 hours with intermittent stirring; stirring for 10 minutes and then pausing for 10 minutes to obtain a mixed solution; sequentially adding 25 parts of desulfurized gypsum@silica ash composite powder and 10 parts of rice husk ash to the mixed solution; stirring at a speed of 1000 r / min for 25 minutes; subsequently adding 1.5 parts of basalt fiber and stirring at a speed of 400 r / min for 10 minutes to obtain the low-carbon cementitious material for road concrete.

[0030] Among them, the preparation method of silica-modified fly ash includes: mixing fly ash with a sodium hydroxide aqueous solution with a mass concentration of 12%, stirring in a water bath at 70°C for 3 hours, adding sodium silicate, stirring and dispersing at 400 rpm for 40 minutes, and then hydrothermally reacting at 190°C for 6 hours. After the reaction is completed, it is filtered, dried at 110°C for 12 hours, and ball milled to obtain; the fly ash is Class II fly ash, and the modulus of the sodium silicate is 1.2; the weight ratio of the fly ash, sodium hydroxide solution and sodium silicate is 10:0.7:3.

[0031] The preparation method of the desulfurized gypsum@silica fume composite powder includes: calcining the desulfurized gypsum at 600°C for 2 hours to remove bound water, crushing it to D50=10μm to obtain pretreated desulfurized gypsum, mixing it with silica fume and nano-CaCO3, adding triethanolamine and wet grinding it for 3 hours to obtain a slurry, spray drying it, roasting it at 900°C for 30 minutes under a CO2 atmosphere, and crushing it to D90<15μm to obtain the slurry; the weight ratio of the pretreated desulfurized gypsum, silica fume, nano-CaCO3 and triethanolamine is 75:35:3:0.8.

[0032] Example 4 This embodiment provides a method for preparing a low-carbon cementitious material for road concrete, comprising the following steps: adding, by weight, 25 parts of ultrafine steel slag powder and 30 parts of silica-modified fly ash to 100 parts of water; stirring and dispersing the mixture at 200 rpm for 1.5 hours to obtain a mixed solution; stirring for 10 minutes and then pausing for 5 minutes; sequentially adding 25 parts of desulfurized gypsum@silica ash composite powder and 5 parts of rice husk ash to the mixed solution; stirring at a speed of 1000 r / min for 20 minutes; then adding 1.5 parts of basalt fiber and stirring at a speed of 300 r / min for 10 minutes to obtain the low-carbon cementitious material for road concrete.

[0033] Among them, the preparation method of silica-modified fly ash includes: mixing fly ash with a sodium hydroxide aqueous solution with a mass concentration of 8%, stirring in a water bath at 70°C for 2 hours, adding sodium silicate, stirring and dispersing at 200 rpm for 30 minutes, and then hydrothermally reacting at 190°C for 5 hours. After the reaction is completed, the product is filtered, dried at 110°C for 12 hours, and ball milled to obtain the product; the fly ash is Class II fly ash, and the modulus of the sodium silicate is 1.2; the weight ratio of the fly ash, sodium hydroxide solution and sodium silicate is 10:0.5:3.

[0034] The preparation method of the desulfurized gypsum@silica fume composite powder includes: calcining the desulfurized gypsum at 600°C for 1h to remove bound water, crushing it to D50=10μm to obtain pretreated desulfurized gypsum, mixing it with silica fume and nano-CaCO3, adding triethanolamine and wet grinding it for 3h to obtain a slurry, spray drying it, roasting it at 800°C for 30min under a CO2 atmosphere, and crushing it to D90<15μm to obtain the slurry; the weight ratio of the pretreated desulfurized gypsum, silica fume, nano-CaCO3 and triethanolamine is 65:35:2:0.8.

[0035] Comparative Example 1 In Comparative Example 1, the fly ash was not modified, and the rest was the same as in Example 1, and the preparation steps were the same as in Example 1.

[0036] Comparative Example 2 In the preparation process of the desulfurized gypsum@silica fume composite powder in Comparative Example 2, the desulfurized gypsum was not pretreated, and the rest was the same as in Example 1, and the preparation steps were the same as in Example 1.

[0037] Comparative Example 3 In Comparative Example 3, no nano-CaCO3 was added during the preparation of the desulfurized gypsum@silica fume composite powder, and only nano-silicon dioxide was added. The rest was the same as in Example 1, and the preparation steps were the same as in Example 1.

[0038] Comparative Example 4 In Comparative Example 4, the desulfurized gypsum@silica fume composite powder was replaced with pretreated desulfurized gypsum, and the rest was the same as in Example 1, and the preparation steps were the same as in Example 1.

[0039] Comparative Example 5 In Comparative Example 5, the desulfurized gypsum@silica fume composite powder is replaced with silica fume, and the rest is the same as in Example 1, and the preparation steps are the same as in Example 1.

[0040] Comparative Example 6 In Comparative Example 6, the desulfurized gypsum@silica ash composite powder was replaced with rice husk ash, and the rest was the same as in Example 1, and the preparation steps were the same as in Example 1.

[0041] Comparative Example 7 In Comparative Example 7, intermittent stirring was replaced by continuous stirring, and the total stirring time was still maintained at 1.8 h. The rest was the same as in Example 1, and the preparation steps were the same as in Example 1.

[0042] Comparative Example 8 In Comparative Example 8, the basalt fiber was replaced by polypropylene fiber, and the rest was the same as in Example 1, and the preparation steps were the same as in Example 1.

[0043] Test Example: The low-carbon gel material slurry prepared in Examples 1-4 and Comparative Examples 1-8 was poured into a 40 mm × 40 mm × 160 mm mold, cured for 24 hours at 20°C, and demolded to obtain a low-carbon gel material green body. The low-carbon gel material green body was immediately placed in a standard curing room at 20°C and 95% relative humidity for curing, and the following tests were performed: Compressive strength test: Test in accordance with the requirements of GB / T 17671-2021 Cement mortar strength test method (ISO method).

[0044] Flexural strength test: Test in accordance with the requirements of GB / T 17671-2021 Test method for strength of cement mortar (ISO method); Wear resistance: Refer to JC / T 2558-2020 "Permeable Concrete" to test its permeability coefficient and wear resistance.

[0045] Each group was tested 5 times, and the results are summarized in Table 1 below.

[0046] Table 1: Test results Compressive strength (MPa, 3d) Flexural strength (MPa, 3d) Compressive strength (MPa, 28d) Flexural strength (MPa, 28d) Permeability coefficient (mm / s) Wear resistance (mm) Example 1 27.3±0.9 4.5±0.2 61.2±1.3 9.2±0.3 1.12±0.04 2.0±0.7 Example 2 23.1±0.7 3.9±0.2 53.8±1.1 7.9±0.3 1.38±0.06 2.4±0.9 Example 3 25.6±0.8 4.2±0.2 58.3±1.2 8.7±0.3 1.25±0.05 2.2±0.8 Example 4 24.8±0.8 4.1±0.2 56.7±1.1 8.3±0.3 1.42±0.05 2.3±0.8 Comparative Example 1 18.2±0.6 3.1±0.1 46.5±1.0 6.4±0.2 1.68±0.07 2.8±1.0 Comparative Example 2 20.7±0.7 3.4±0.1 51.8±1.1 7.2±0.2 1.53±0.06 2.6±0.9 Comparative Example 3 22.4±0.7 3.7±0.1 54.1±1.2 7.8±0.2 1.47±0.05 2.5±0.8 Comparative Example 4 19.5±0.6 3.3±0.1 48.9±1.0 6.9±0.2 1.61±0.07 2.7±0.9 Comparative Example 5 17.8±0.5 2.9±0.1 43.6±0.9 6.1±0.2 1.72±0.08 2.9±1.1 Comparative Example 6 16.3±0.5 2.7±0.1 40.2±0.8 5.8±0.2 1.85±0.09 3.1±1.2 Comparative Example 7 23.5±0.7 3.8±0.1 55.2±1.1 8.1±0.2 1.33±0.05 2.4±0.9 Comparative Example 8 24.1±0.8 3.9±0.1 56.8±1.2 7.6±0.2 1.29±0.05 2.5±0.9 Combined with the above data, it can be seen that the unmodified fly ash in Comparative Example 1 resulted in a significant decrease in 3d and 28d compressive and flexural strength, an increase in water permeability, and poorer wear resistance. Unmodified fly ash has low activity and is unable to form sufficient aluminosilicate gel through the hydrothermal reaction, resulting in insufficient material density, increased porosity, increased water permeability, but decreased strength. Therefore, silica-modified fly ash enhances its pozzolanic activity through alkali activation and hydrothermal reaction, which is a key step in enhancing the strength of cementitious materials.

[0047] In Comparative Example 2, pretreatment of the desulfurized gypsum without calcination resulted in decreased strength and increased permeability. Undehydrated desulfurized gypsum particles have low surface activity, resulting in poor interfacial bonding with silica fume and nano-CaCO3, which compromises the compactness of the composite powder. Therefore, pretreatment improves the reactivity of the desulfurized gypsum by removing bound water, promoting subsequent sintering and carbonization of the composite powder.

[0048] In Comparative Example 3, nano-CaCO₃ was not added during the preparation of the desulfurized gypsum and silica fume composite powder. The strength decreased slightly, but the permeability increased. Nano-CaCO₃ generates CaO during CO₂ roasting, enhancing the composite powder's gelling properties. Therefore, the addition of nano-CaCO₃ is key to the synergistic enhancement effect of the desulfurized gypsum and silica fume composite powder.

[0049] In Comparative Example 4, using only pretreated desulfurized gypsum, the strength decreased significantly, while the permeability increased. The absence of the silica fume and nano-CaCO3 composite powder resulted in a lack of micro-aggregate filling and carbonization activity, resulting in a loose structure. Therefore, the desulfurized gypsum and silica fume composite significantly improved density and strength through the silica fume micro-aggregate effect and the carbonization reaction of the nano-CaCO3.

[0050] After replacing pure silica fume in Comparative Example 5, performance deteriorated further. Silica fume alone cannot form an effective gelling system with desulfurized gypsum, and lacks the carbonization enhancement provided by nano-CaCO3, resulting in high porosity and low strength. Therefore, the synergistic effect (calcium-silicon reaction) between desulfurized gypsum and silica fume in the composite powder is the key to improving material performance.

[0051] In comparative example 6, the desulfurization gypsum@silica ash composite powder was replaced with rice husk ash, which had the worst performance and the worst wear resistance. The rice husk ash particles were coarse and had low activity, and could not replace the microaggregate and cementitious functions of the composite powder, resulting in extremely high porosity and fragile structure of the material. Therefore, the desulfurization gypsum@silica ash composite powder is irreplaceable, and rice husk ash is only suitable as an auxiliary admixture rather than a core component.

[0052] Comparative Example 7 uses continuous stirring instead of intermittent stirring. Continuous stirring results in a slight decrease in strength and an increase in permeability. Continuous stirring can cause localized overheating or particle agglomeration, while intermittent stirring (8 minutes on / 8 minutes off) is more conducive to dispersion stability and forms a uniform slurry structure. Therefore, intermittent stirring is crucial for dispersion quality and material homogeneity.

[0053] After replacing the polypropylene fiber in Comparative Example 8, the 28-day flexural strength decreased, and the water permeability coefficient increased slightly. Basalt fiber exhibits superior interfacial adhesion to the gel matrix than polypropylene fiber, and its alkali resistance is superior, resulting in a more pronounced flexural reinforcement effect; therefore, basalt fiber offers advantages in improving toughness and crack resistance.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. All technical solutions and improvements that do not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a low-carbon cementitious material for road concrete, characterized in that: The steps include: In parts by weight, 25-35 parts of ultrafine steel slag powder and 20-30 parts of silica-modified fly ash are added to 100-120 parts of water, and the mixture is stirred and dispersed to obtain a mixed liquid. 15-25 parts of desulfurized gypsum@silica ash composite powder and 5-10 parts of rice husk ash are sequentially added thereto, and the mixture is stirred for the first time. Subsequently, 0.5-1.5 parts of basalt fiber are added and stirred for the second time to obtain the low-carbon cementitious material for road concrete.

2. The method for preparing a low-carbon cementitious material for road concrete according to claim 1, characterized in that: The preparation method of the silica-modified fly ash comprises: mixing fly ash with sodium hydroxide solution, stirring in a water bath at 60-70° C. for 2-3 hours, adding sodium silicate, stirring and dispersing, and then hydrothermally reacting at 170-190° C. for 5-6 hours. After the reaction is completed, the fly ash is filtered, dried, and ball-milled to obtain the silica-modified fly ash.

3. The method for preparing a low-carbon cementitious material for road concrete according to claim 2, characterized in that: The sodium hydroxide solution is a sodium hydroxide aqueous solution with a mass concentration of 8-12%; Alternatively, the fly ash is Class II fly ash, the modulus of the sodium silicate is 1.2; and the weight ratio of the fly ash, sodium hydroxide solution and sodium silicate is 10:(0.5-0.7):(2-3).

4. The method for preparing a low-carbon cementitious material for road concrete according to claim 2, wherein: The stirring and dispersing step is performed at 200-300 rpm for 30-40 minutes; and the drying temperature is 100-110°C.

5. The method for preparing a low-carbon cementitious material for road concrete according to claim 1, characterized in that: The preparation method of the desulfurized gypsum@silica fume composite powder comprises: pre-treating the desulfurized gypsum, mixing it with silica fume and nano-CaCO3, adding triethanolamine and wet grinding for 2-3 hours to obtain a slurry, spray drying it, calcining it at 800-900°C for 20-30 minutes in a CO2 atmosphere, and crushing it to D90 <15μm.

6. The method for preparing a low-carbon cementitious material for road concrete according to claim 5, characterized in that: The desulfurized gypsum pretreatment step includes: calcining the desulfurized gypsum at 500-600° C. for 1-2 hours to remove bound water, and crushing the desulfurized gypsum to D50=10 μm.

7. The method for preparing a low-carbon cementitious material for road concrete according to claim 5, characterized in that: The weight ratio of the pretreated desulfurized gypsum, silica fume, nano-CaCO3 and triethanolamine is (65-75): (25-35): (2-3): (0.4-0.8).

8. The method for preparing a low-carbon cementitious material for road concrete according to claim 1, characterized in that: The stirring and dispersion is carried out at 300-400 rpm for 1.5-2 hours, and the stirring treatment mode is intermittent stirring, stirring for 5-10 minutes and then pausing for 5-10 minutes.

9. The method for preparing a low-carbon cementitious material for road concrete according to claim 1, characterized in that: The first stirring is carried out at a rotation speed of 800-1000 r / min for 20-25 min; the second stirring is carried out at a rotation speed of 300-400 r / min for 8-10 min.

10. A low-carbon cementitious material for road concrete prepared according to the preparation method according to any one of claims 1 to 9.