Modified activated steel slag-based admixture, preparation method and application thereof, cementing material and application thereof

Abstract

The invention relates to the technical field of solid waste resource utilization, in particular to a modified activated steel slag-based admixture, a preparation method and application thereof, a cementing material and application thereof. The modified activated steel slag-based admixture provided by the invention comprises modified steel slag powder and an auxiliary material, the auxiliary materials comprise fly ash microspheres, silica fume, calcium carbonate whiskers and a nano crystal nucleus material; the modified steel slag powder is obtained by calcining, cooling and crushing steel slag and a hardening and tempering modifier. The prepared modified steel slag powder is low in free calcium oxide content and high in volume stability and gelling activity. The modified steel slag powder, the nanocrystal nucleus material, the fly ash microbeads, the silica fume and the calcium carbonate whisker compounded high-activity auxiliary material are matched for use, so that the gelling activity of the modified activated steel slag-based admixture is further improved, and the modified activated steel slag-based admixture can be used as a high-quality mineral admixture to be applied to preparation of high-strength and ultrahigh-strength concrete; the method has a wide application space, and the high value-added resource utilization rate of the solid waste is high.

Description

A modified and activated steel slag-based admixture, its preparation method and application; cementitious materials and their applications. Technical Field

[0001] This invention relates to the technical field of solid waste resource utilization, specifically to a modified and activated steel slag-based admixture, its preparation method and application, and a cementing material and its application. Background Technology

[0002] Steel slag is a waste residue discharged during the steelmaking process and belongs to the category of large-volume industrial solid waste. The discharge of steel slag is generally about 15% to 20% of steel production. The large-scale dumping and accumulation of steel slag not only pollutes the environment and occupies a large amount of land, but also wastes resources. The main mineral composition of steel slag is: tricalcium silicate, dicalcium silicate, calcium magnesium olivine, calcium magnesium rhodochrosite, calcium aluminoferrite, and solid solutions formed by oxides of silicon, magnesium, iron, manganese, and phosphorus, as well as a small amount of free calcium oxide. Among these, silicate minerals have certain potential cementitious activity, providing a potential basis for development as cement admixtures or concrete additives. However, compared to cement clinker, the total amount of cementitious active minerals in steel slag is insufficient, and the high formation temperature, dense crystallization, and slow hydration rate of silicate minerals result in overall low cementitious activity. Furthermore, the free CaO (f-CaO) and RO in steel slag pose a potential hazard to the volume stability of cement concrete. Currently, steel slag activation methods mainly include: mechanical activation, thermal activation, surface modification, and the addition of chemical activators. The aforementioned steel slag activation methods have failed to address the harmful effects of the RO phase in steel slag, and the fluctuations in steel slag composition and cementitious activity have not been fundamentally eliminated or improved. Therefore, there is an urgent need for a new steel slag activation method to improve the cementitious activity of steel slag and increase the utilization rate of high-value-added resources from steel slag. Summary of the Invention

[0003] Therefore, the purpose of this invention is to provide a modified and activated steel slag-based admixture, its preparation method and application, and a cementing material and its application. The modified steel slag powder provided by this invention has a low free calcium oxide content, high volume stability and cementing activity, significantly improving the high-value-added resource utilization rate of steel slag.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: The present invention provides a modified activated steel slag-based admixture, comprising modified steel slag powder and auxiliary materials; the preparation method of the modified steel slag powder includes the following steps: mixing steel slag and a conditioning modifier, and sequentially calcining, cooling and crushing to obtain modified steel slag powder; the conditioning modifier is a mineral rich in silica-alumina components; the auxiliary materials include fly ash microspheres, silica fume, calcium carbonate whiskers and nanocrystalline nuclei.

[0005] Preferably, by mass percentage, the auxiliary materials include 50-70% fly ash microspheres, 20-40% silica fume, 5-10% calcium carbonate whiskers, and 0.1-1% nanocrystalline nuclei.

[0006] Preferably, the mass ratio of the modified steel slag powder to the auxiliary materials is 8~9:1~2.

[0007] Preferably, the preparation method of the nanocrystalline nucleus material includes the following steps: mixing steel slag powder with nitric acid solution, carrying out a hydrothermal reaction, separating the solid and liquid to obtain a steel slag leachate; mixing the steel slag leachate with a dispersant, adjusting the pH value to 11-13, carrying out a complexation reaction, and then drying to obtain the nanocrystalline nucleus material.

[0008] Preferably, the effective components in the nanocrystalline nucleus material include CaO, Fe2O3 and SiO2, wherein the molar ratio of CaO to Fe2O3 is 1:0.2~0.3 and the molar ratio of CaO to SiO2 is 1:0.5~1.

[0009] Preferably, the specific surface area of ​​the steel slag powder is 200~400m². 2 / kg; the concentration of the nitric acid solution is 4~6 mol / L; the solid-liquid ratio of the steel slag powder to the nitric acid solution is 1kg:8~12L; the hydrothermal reaction temperature is 40~60℃, and the time is 5~9h; the dispersant includes polycarboxylate superplasticizer, and the dispersant is used in the form of an alkaline dispersant aqueous solution; the mass ratio of the steel slag powder to the dispersant is 1:4~6; the temperature of the complexation reaction is 40~60℃, and the time is 10~40h.

[0010] Preferably, the conditioning modifier includes one or more of coal gangue, refining slag, and fly ash; the mass ratio of steel slag to conditioning modifier is 75-90:10-25; the pulverization includes: primary crushing of the cooled material obtained from cooling, ball milling and sieving the resulting modified coarse powder, and grinding the undersize material to obtain modified steel slag powder; the particle size of the modified coarse powder is ≤4.75mm; the sieve size is 0.6-1.18mm; the ball milling time is 25-35min; the grinding time is 15-25min; the calcination temperature is 1200-1500℃, and the holding time is ≥0.5h; the specific surface area of ​​the modified steel slag powder is 350-700m². 2 / kg.

[0011] The present invention also provides a method for preparing the modified activated steel slag-based admixture described in the above technical solution, comprising the following steps: mixing modified steel slag powder and auxiliary materials to obtain the modified activated steel slag-based admixture.

[0012] The present invention also provides a cementitious material, comprising an admixture and cement; the admixture comprising the modified activated steel slag-based admixture described in the above technical solution or the modified activated steel slag-based admixture prepared by the preparation method described in the above technical solution.

[0013] The present invention also provides the application of the modified and activated steel slag-based admixture described in the above technical solutions, the modified and activated steel slag-based admixture prepared by the preparation method described in the above technical solutions, or the cementitious material described in the above technical solutions in building materials.

[0014] This invention uses minerals rich in silica and aluminum components as conditioning modifiers. During calcination, the iron-aluminum-calcium mineral phase and RO phase components in the steel slag decompose, releasing components such as calcium oxide and aluminum oxide. The calcium oxide and aluminum oxide react chemically with the silicon and aluminum components in the conditioning modifier at high temperature, regenerating new, more active hydraulic minerals such as silicates and aluminates. This fundamentally optimizes the mineral composition of the steel slag, significantly reduces the free calcium oxide (f-CaO) in the steel slag, improves the volume stability and cementing activity of the steel slag, and thus improves the high-value-added resource utilization rate of the steel slag.

[0015] The modified steel slag powder prepared by this invention has low f-CaO content and high volume stability and cementitious activity. This invention combines modified steel slag powder with highly active auxiliary materials such as nanocrystalline nuclei, fly ash microspheres, silica fume, and calcium carbonate whiskers, further enhancing the cementitious activity of the modified and activated steel slag-based admixture. This allows it to be used as a high-quality mineral admixture in the preparation of high-strength and ultra-high-strength concrete, with broad application prospects. The modified and activated steel slag-based admixture provided by this invention exhibits high cementitious activity, realizing the large-scale resource utilization of steel slag solid waste, while simultaneously addressing the current shortage of high-quality mineral admixture resources.

[0016] Using nano-SiO2 (Ca-free) as the nanocrystal nucleus material requires reacting with Ca(OH)2 generated during cement hydration to form CSH, resulting in more nucleation steps and lower efficiency. Using nano-Al2O3 as the nanocrystal nucleus material requires first forming an aluminate phase, also resulting in more nucleation steps and lower efficiency. This invention uses aluminum-containing hydrated calcium silicate nanocrystal nuclei as the nanocrystal nucleus material, exhibiting better compatibility with the cement system and higher hydration promotion efficiency. The nanocrystal nucleus material of this invention is CFSH (containing iron-containing hydrated calcium silicate), which perfectly matches the composition and crystal structure of the core product of cement hydration (CSH, which actually contains a small amount of Al), significantly reducing the nucleation energy barrier and resulting in high nucleation efficiency.

[0017] The cementitious material provided by this invention includes the modified and activated steel slag-based admixture and cement described in the above-mentioned technical solution. The modified and activated steel slag-based admixture used in this invention has high cementitious activity, and when used in combination with cement, it can significantly improve the early strength of the cementitious material, with continuous growth in later strength.

[0018] Furthermore, this invention uses steel slag as raw material, first dissolving calcium ions, iron ions, and silicate ions with acid. Under alkaline conditions, these ions complex in the solution to form iron-rich nanocrystalline nuclei (CFSH). The nanocrystalline nuclei prepared by the above chemical method has high gelling activity and can significantly improve early strength.

[0019] As shown in the test results of the examples, the modified steel slag powder prepared by this invention has an f-CaO mass content of <2%, which improves the volume stability and cementitious activity of the steel slag. The modified and activated steel slag-based admixture prepared by this invention has an activity index of over 95% at 7 days and over 105% at 28 days, respectively, realizing the large-scale, high-value-added utilization of steel slag solid waste and also making up for the current shortage of high-quality mineral admixture resources. Detailed Implementation

[0020] This invention provides a modified activated steel slag-based admixture, comprising modified steel slag powder and auxiliary materials; the preparation method of the modified steel slag powder includes the following steps: mixing steel slag and a conditioning modifier, and sequentially calcining, cooling and crushing to obtain modified steel slag powder; the conditioning modifier is a mineral rich in silica and aluminum components; the auxiliary materials include fly ash microspheres, silica fume, calcium carbonate whiskers and nanocrystalline nuclei.

[0021] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0022] In this invention, the preparation method of the modified steel slag powder includes the following steps: mixing steel slag and a conditioning modifier, and sequentially calcining, cooling and crushing to obtain modified steel slag powder; the conditioning modifier is a mineral rich in silica-alumina components.

[0023] In this invention, the steel slag can be crushed before use to obtain slag powder; the specific surface area of ​​the slag powder can be 200~400 m². 2 / kg, and can also be 250~350m 2 / kg, which can be specifically 400m 2 / kg. All specific surface areas in this invention refer to Blaine specific surface area. This invention does not have a specific limitation on the pulverization process; any slag powder capable of obtaining the above-mentioned specific surface area is acceptable. This invention does not have a specific limitation on the slag; any slag well-known to those skilled in the art can be used. In this invention, the conditioning and modifying agent is a mineral rich in silica and alumina components, and the conditioning and modifying agent may include one or more of coal gangue, refining slag, and fly ash. In this invention, the conditioning and modifying agent can be pulverized before use to obtain conditioning and modifying agent powder; the specific surface area of ​​the conditioning and modifying agent powder can be 200~400m². 2 / kg, and can also be 250~350m 2 / kg, which can be specifically 300m 2 / kg. This invention does not have a specific limitation on the pulverization process; any conditioned modifier powder capable of achieving the aforementioned specific surface area is acceptable. In this invention, the conditioned modifier is mixed with steel slag and then modified at high temperature, which can adjust the mineral composition of the steel slag, thereby improving its volume stability and cementitious activity.

[0024] In this invention, the mass ratio of steel slag to quenching and tempering modifier is 75~90:10~25, and can also be 85~90:10~15, specifically 75:10, 80:10, 85:10, 90:10, 75:11, 80:11, 85:11, 90:11, 75:12, 80:12, 85:12, 90:12, 75:13, 80:13, 85:13, 90:13, 75:14, 80:14, 85:14, 90:14, 75:15, 80:15, 85:15, or 90:15.

[0025] The mixed raw materials also include water, the mass of which is 3 to 10% of the total mass of steel slag and conditioning modifier, or 4 to 8%, specifically 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0026] In this invention, the mixed raw materials also include water, and the mixing process involves mixing steel slag, a conditioning modifier, and water. In this invention, the mass of the water can be 3-10% of the total mass of the steel slag and the conditioning modifier (referred to as solid raw materials), or it can be 5-8%, specifically 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%. In this invention, the addition of water facilitates a more uniform mixing of the solid raw materials, steel slag and the conditioning modifier.

[0027] In this invention, the step before calcination may further include: pressing the mixture obtained from the mixing process, and then subjecting the resulting cake to subsequent calcination. In this invention, the pressing pressure can be ≤100kN, or it can be 30~100kN, or 50~80kN, specifically 30kN, 40kN, 50kN, 60kN, 70kN, 80kN, 90kN, or 100kN; the pressing time can be 10~60s, or it can be 20~50s, specifically 10s, 20s, 30s, 40s, 50s, or 60s. This invention does not have a specific limitation on the size of the cake; it can be determined according to actual needs. In a specific embodiment of this invention, the size of the cake can be Φ12cm×2cm. In this invention, the main function of the pressing is to facilitate the solid-phase reaction and firing at high temperatures (calcination) through powder interface contact.

[0028] In this invention, the calcination temperature can be 1200~1500℃, or 1250~1450℃, or even 1300~1400℃, specifically 1350℃; the heating rate from room temperature to the calcination temperature can be 5~15℃ / min, or 8~12℃ / min, specifically 10℃ / min; the holding time for calcination can be ≥0.5h, or 0.5~2h, or even 1~1.5h; the calcination atmosphere can be air; the calcination can be carried out in a high-temperature electric furnace, specifically by stacking the material cake in layers in a high-purity ceramic crucible, and then placing it in a high-temperature electric furnace for calcination.

[0029] In this invention, the cooling can be rapid cooling, which can be cooling the calcined material to below 150°C within 1-2 hours, or cooling the calcined material to 80-100°C within 1-1.5 hours. The cooling method can include one or more of water quenching, air quenching, and spraying. This invention uses the above-mentioned rapid cooling method to quickly cool the highly active, high-temperature product, avoiding the crystal growth of active minerals such as C2S and C3S, maintaining fine grains and a glassy phase structure (the glassy phase has higher hydration activity), while inhibiting the regeneration of free CaO and free MgO, further eliminating the risk of volume instability. If the cooling rate is too slow, the active minerals are prone to activity decay due to coarse crystal formation, significantly improving the gelling activity and stability of the modified mineral admixture.

[0030] In this invention, the pulverization may include: primary crushing of the cooled material obtained from the cooling process, ball milling and sieving the resulting modified coarse powder, and grinding the undersize material to obtain modified steel slag powder. In this invention, the particle size of the modified coarse powder can be ≤4.75mm, or it can be 0.6~4.75mm. This invention does not have a specific limitation on the primary crushing; any crushing method well-known to those skilled in the art that can obtain modified coarse powder with a particle size ≤4.75mm is acceptable. In this invention, the sieve size can be 0.6mm. In this invention, the ball milling time can be 25~35min, or it can be 30min. In this invention, the grinding time can be 15~25min, or it can be 20min; the grinding media used in the ball milling may include chromium alloyed wear-resistant cast steel balls and / or chromium alloyed wear-resistant cast steel segments; the ball-to-material ratio in the ball milling can be 6~8:1, or it can be 7:1. This invention, employing the above-mentioned stepped grinding method, can improve grinding efficiency.

[0031] In this invention, the specific surface area of ​​the modified steel slag powder can be 350~700 m². 2 / kg, and can also be 400~650m 2 / kg, which can be further increased to 450~600m 2 / kg, which can be specifically 455m 2 / kg, 460m 2 / kg, 472m 2 / kg, 500m 2 / kg or 550m 2 / kg.

[0032] In this invention, the mass ratio of the modified steel slag powder to the auxiliary materials is 8~9:1~2, which can be specifically 8:1, 8:1.5, 8:2, 8.5:1, 8.5:1.5, 8.5:2, 9:1, 9:1.5 or 9:2.

[0033] In this invention, the auxiliary materials include fly ash microspheres, silica fume, calcium carbonate whiskers, and nanocrystalline nuclei. In this invention, the auxiliary materials, by mass percentage, may include: fly ash microspheres 50-70%, or 55-65%, specifically 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, or 70%; silica fume 20-40%, or 25-35%, specifically 20%, 21%, 22%, 23%, 24%, 24.7%, 25%, 26%, 27%, 28%, 2... 9%, 30%, 31%, 32%, 33%, 34%, 34.2%, 34.5%, 35%, 36%, 37%, 38%, 39%, or 40%; calcium carbonate whiskers 5-10%, or 7-8%, specifically 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, or 10%; nanocrystalline nuclei material 0.1-1%, or 0.5-0.8%, specifically 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%.

[0034] In this invention, the particle size of the fly ash microspheres can be 10-100 μm, 20-80 μm, or even 40-60 μm. By adding fly ash microspheres, this invention optimizes the particle size distribution of the cementitious material system, leveraging the "ball effect" to improve the workability and fluidity of the freshly mixed mortar. Its spherical hollow structure can fill the capillary pores of cement hydration products, reducing the porosity of the hardened body. Simultaneously, the active SiO2 and Al2O3 on the surface of the microspheres can participate in secondary hydration reactions, generating CSH gel and ettringite, significantly improving the mechanical strength and durability of concrete.

[0035] In this invention, the particle size of the silica fume can be 0.1~1μm, or 0.2~0.8μm, or even 0.4~0.6μm. By adding silica fume microspheres, this invention, with its ultrafine particle size and high pozzolanic activity, can fill the gaps between cement particles and fly ash microspheres, achieving dense packing of the cementitious material system. The amorphous SiO2 in the silica fume can rapidly react with Ca(OH)2 produced during cement hydration to generate a large amount of low-calcium-ratio CSH gel, refining the microporous structure of the hardened body, significantly improving the early strength, compressive strength, and chloride ion penetration resistance of concrete, while also improving the volume stability of the concrete.

[0036] In this invention, the diameter of the calcium carbonate whiskers can be 0.5~5μm, or 1~4μm, or even 2~3μm; the length of the calcium carbonate whiskers can be 10~50μm, or 20~40μm, or even 30μm. By adding calcium carbonate whiskers, this invention can leverage the "bridging" effect of the fibrous reinforcing phase, significantly improving the flexural strength, bending strength, and toughness of concrete, and inhibiting the initiation and propagation of microcracks. Simultaneously, the calcium carbonate whiskers can act as nuclei for cement hydration, accelerating the formation and growth of CSH gel and optimizing the structure of the interfacial transition zone.

[0037] In this invention, the particle size of the nanocrystalline nucleus material can be 10-100 nm, 20-80 nm, or even 40-60 nm. By adding the nanocrystalline nucleus material, this invention can leverage the high specific surface area and surface activity of nanoparticles to provide a large number of nucleation sites for cement hydration, significantly accelerating the hydration reaction rate and improving the early strength development of concrete. The nanoparticles can fill the nanoscale pores of hydration products, forming a dense microstructure and improving the interfacial transition zone performance between cement paste and aggregate.

[0038] In this invention, the effective components in the nanocrystalline nucleus material may include CaO, Fe2O3, and SiO2. The molar ratio of CaO to Fe2O3 is 1:0.2~0.3, specifically 1:0.2, 1:0.21, 1:0.22, 1:0.23, 1:0.21, 1:0.25, 1:0.26, 1:0.27, 1:0.28, 1:0.29, or 1:0.3. The molar ratio of CaO to SiO2 may be 1:0.5~1, or 1:0.6~0.8, specifically 1:0.5, 1:0.55, 1:0.6, 1:0.65, 1:0.7, 1:0.75, 1:0.8, 1:0.85, 1:0.9, 1:0.95, or 1:1. In this invention, the effective component of the nanocrystalline nucleus material may further include H2O, and the molar ratio of CaO to H2O may be 1:1~4, or 1:1.5~3.5, or even 1:2~3. The nanocrystalline nucleus material added in this invention, by utilizing the high specific surface area and surface activity of nanoparticles, provides a large number of heterogeneous nucleation sites for cement hydration, significantly accelerating the hydration reaction rate and improving the early strength development of concrete.

[0039] In this invention, the preparation method of the nanocrystalline nucleus material may include the following steps: mixing steel slag powder with nitric acid solution, carrying out a hydrothermal reaction, separating the solid and liquid to obtain a steel slag leachate; mixing the steel slag leachate with a dispersant, adjusting the pH value to 11-13, carrying out a complexation reaction, and then drying to obtain the nanocrystalline nucleus material.

[0040] This invention involves mixing steel slag powder with nitric acid solution, carrying out a hydrothermal reaction, and separating the solid and liquid phases to obtain a steel slag leachate.

[0041] In this invention, the specific surface area of ​​the steel slag powder can be 200~400 m². 2 / kg, and can also be 250~350m 2 / kg, which can be specifically 300m 2 / kg. In this invention, the concentration of the nitric acid solution can be 4~6 mol / L, or 4.5~5.5 mol / L, specifically 5 mol / L. In this invention, the solid-liquid ratio of the steel slag powder to the nitric acid solution can be 1 kg: 8~12 L, or 1 kg: 9~11 L, specifically 1 kg: 10 L.

[0042] In this invention, the hydrothermal reaction temperature can be 40~60℃, or 45~55℃, or specifically 50℃; the hydrothermal reaction time can be 5~9h, or 6~8h, or specifically 7h.

[0043] The present invention does not have any special limitations on the solid-liquid separation, and any solid-liquid separation method known to those skilled in the art can be used.

[0044] In this invention, the addition of nitric acid solution causes the silicate phase, ferrate phase and glass phase in the steel slag to dissolve during the hydrothermal reaction, thereby obtaining calcium ions, iron ions and silicate ions.

[0045] After obtaining the steel slag leachate, the present invention mixes the steel slag leachate with a dispersant, adjusts the pH value to 11-13, performs a complexation reaction, and then dries it to obtain nanocrystalline nuclei material.

[0046] In this invention, the dispersant includes a polycarboxylate superplasticizer, specifically a highly dispersed, high-slump-retention polycarboxylate superplasticizer. In this invention, the dispersant can be used in the form of an aqueous dispersant solution, where the mass concentration of the dispersant in the aqueous solution can be 5-10%, or 7-8%, specifically 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, or 10%. In this invention, the mass ratio of the electric furnace slag powder to the dispersant (anhydrous dispersant) can be 1:0.2-0.6, or 1:0.3-0.5, specifically 1:0.4. By adding the above-mentioned dispersant, this invention can fully disperse the components in the steel slag leaching solution, solving the problem of agglomeration of nanoparticles caused by high surface energy. Moreover, if the particles agglomerate and settle after the complexation reaction to obtain a nanocrystalline nucleus liquid suspension, subsequent filtration, drying, and grinding processes will be difficult, and product performance will easily fluctuate. The addition of dispersants can significantly increase the absolute value of the zeta potential of the suspension, keeping the suspension in a thermodynamically stable state and preventing particle sedimentation and stratification.

[0047] In this invention, the alkali used to adjust the pH value may include alkali metal hydroxides, specifically sodium hydroxide and / or potassium hydroxide; the alkali may be used in the form of an alkaline aqueous solution, the concentration of which may be 3-10%, 4-9%, or even 5-8%. In this invention, the pH value may also be 11.5-12.5, specifically 12.

[0048] In this invention, the temperature of the complexation reaction can be room temperature (18~30℃); the time of the complexation reaction can be 10~40h, or 15~30h, specifically 10h, 15h, 20h, 24h, 30h, 35h, or 40h. Under strongly alkaline conditions, calcium ions, iron ions, and silicate ions undergo a complexation reaction to form a suspension rich in CFSH. Iron ions are doped into the crystal lattice to form an iron-stable nanocrystalline nucleus suspension. By utilizing the high specific surface area and surface activity of nanoparticles, a large number of heterogeneous nucleation sites are provided for cement hydration, significantly accelerating the hydration reaction rate and improving the early strength development of concrete.

[0049] In this invention, the drying process may include vacuum drying, and the vacuum drying temperature may be 50-60°C, or 52-58°C, specifically 55°C. This invention does not have a specific limitation on the drying time; drying to a constant weight is sufficient. In this invention, the storage method for the nanocrystalline nucleus material may include sealed storage.

[0050] This invention uses steel slag as raw material. First, calcium ions, iron ions, and silicate ions are dissolved by acid. Under alkaline conditions, the above ions complex in the solution to form iron-rich nanocrystalline nuclei (CFSH). The nanocrystalline nuclei prepared by the above chemical method have high gelling activity and can significantly improve early strength.

[0051] This invention, by adding nanocrystalline nuclei, can significantly stimulate the cementitious activity of steel slag, accelerate the hydration process, and improve mechanical properties. Specifically, the gel particles in the CFSH suspension serve as highly efficient nuclei templates for cement hydration, and their surface hydroxyl groups (-OH) and coordinated water can adsorb Ca from the surface of the steel slag particles. 2+ SiO3 2- Plasma induces the dissolution of inert mineral phases in steel slag, while simultaneously accelerating the hydration reaction of active minerals (C2S, C3S) in the slag, promoting the formation of more hydration products such as CSH and ettringite (AFt). Compared to the undoped system, iron-stabilized CFSH has a stronger inducing effect, significantly improving the 7-day hydration degree of steel slag-based admixtures and significantly mitigating the defects of slow hydration rate and low early strength in steel slag. Moreover, the Fe in the CFSH gel... 3+ Al can be produced by the hydration of steel slag 3+ SO4 2- Plasma bonding forms aluminoferrite hydration products, which can fill the pores of CSH gel, enhancing the crosslinking density of the hydration product network. Ultimately, this significantly improves the 7-day and 28-day compressive strength of steel slag-based cementitious materials, and the strength development is more stable.

[0052] This invention uses steel slag as the raw material for preparing nanocrystal nuclei. Steel slag itself is rich in CaO, SiO2, and Al2O3, which is similar to the composition of cement raw materials. There is no need to add pure calcium / silicon / aluminum sources (such as Ca(NO3)2, Na2SiO3), which reduces raw material costs and reduces the environmental pressure of solid waste storage.

[0053] This invention employs a mild process to prepare nanocrystalline nuclei. The synergistic effect of acid dissolution and hydrothermal action allows nitric acid to efficiently destroy the silicate and aluminate mineral structures in steel slag, thereby enabling Ca... 2+ Si 4+ Al 3+ It can be fully dissolved under mild hydrothermal conditions of 40~60℃; subsequent adjustment of the pH to a strongly alkaline level (pH=11~13) can promote the formation of CFSH through ion complexation, without the need for high-temperature reaction.

[0054] This invention addresses the "homogeneity" between the CFSH nanocrystalline nucleus material and the cement hydration product. The strength of cement hydration originates from CSH gel (CFSH is formed when a small amount of Al is present), while the nanocrystalline nucleus of this invention is CFSH. The Ca-O, Si-O, and Al-O bonds in its crystal structure are completely matched with the hydration product. The hydration product can be directly epitaxially grown on the surface of the nucleus, resulting in a nucleation efficiency far higher than that of nanocrystalline nucleus materials that are "non-homogeneous" and require multiple steps to be converted into CSH (such as nano-SiO2 and nano-Al2O3).

[0055] The nanocrystalline nucleus material prepared by this invention has better compatibility with cement systems and higher hydration promotion efficiency. The nanocrystalline nucleus material of this invention is CFSH (calcium silicate containing aluminum hydration), which is completely matched with the composition and crystal structure of the core product of cement hydration (CSH, which actually contains a small amount of Al), and can significantly reduce the nucleation energy barrier.

[0056] This invention also provides a method for preparing the modified activated steel slag-based admixture described in the above technical solution, comprising the following steps: mixing modified steel slag powder and auxiliary materials to obtain the modified activated steel slag-based admixture. This invention does not impose any special limitations on the mixing process; any mixing method well-known to those skilled in the art can be used to ensure uniform mixing of the raw materials.

[0057] This invention also provides a cementitious material, comprising an admixture and cement, wherein the admixture comprises the modified activated steel slag-based admixture described in the above-described technical solution or the modified activated steel slag-based admixture prepared by the preparation method described in the above-described technical solution. In this invention, the mass content of the modified activated steel slag-based admixture in the cementitious material can be 20-50%, or 25-45%, or even 30-40%.

[0058] The present invention also provides the application of the modified activated steel slag-based admixture described in the above technical solution, the modified activated steel slag-based admixture prepared by the preparation method described in the above technical solution, or the cementitious material described in the above technical solution in building materials.

[0059] The modified steel slag powder used in this invention has a low f-CaO content and high volume stability and cementitious activity. Furthermore, it is combined with highly active auxiliary materials, including nanocrystalline nuclei, fly ash microspheres, silica fume, and calcium carbonate whiskers, to further enhance the cementitious activity of the modified and activated steel slag-based admixture. This allows it to be used as a high-quality mineral admixture in the preparation of high-strength and ultra-high-strength concrete, with broad application prospects. The modified and activated steel slag-based admixture provided by this invention exhibits high cementitious activity, realizing the large-scale resource utilization of steel slag solid waste, and has excellent application prospects in building materials, while simultaneously addressing the current shortage of high-quality mineral admixture resources.

[0060] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, provides a modified activated steel slag-based admixture, its preparation method, its application, and a cementing material and its application. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0061] The main chemical composition of the converter steel slag raw materials used in the following examples is shown in Table 1; the particle size of fly ash microspheres is 10~30μm; the particle size of silica fume is 0.1~0.5μm; the diameter of calcium carbonate whiskers is 2~3μm and the length is 10~50μm; the particle size of the prepared nanocrystalline nuclei material is 50~80nm.

[0062] Example 1 (1) Preparation of modified steel slag powder: Converter steel slag was crushed to a specific surface area of ​​280 m². 2 / kg, to obtain converter steel slag powder. The coal gangue was crushed to a specific surface area of ​​310 m². 2 / kg, to obtain coal gangue powder. Solid raw materials (converter slag powder and coal gangue powder in a mass ratio of 9:1) and water were mixed evenly at a mass ratio of 1:0.08, and then pressurized (maximum pressure 100kN, held for 30s) to form Φ12cm×2cm cakes. The cakes were layered and stacked in a high-purity ceramic crucible, placed in a high-temperature electric furnace, heated to 1400℃, and calcined for 90min under an air atmosphere. Rapid cooling (air quenching, reducing the calcined material to 100℃ within 1.5h) yielded modified steel slag coarse powder. The chemical composition of the modified steel slag coarse powder was determined using YB / T 140-2009 "Chemical Analysis Methods for Steel Slag," and the results are shown in Table 1.

[0063] The modified steel slag coarse powder was crushed to a particle size ≤4.75mm using a crusher, and 5kg was weighed. The material was ground in a 500×500mm ball mill for 30 minutes, then passed through a 0.6mm sieve. The sieved material was then ground for another 20 minutes to obtain modified steel slag powder with a specific surface area of ​​455 m². 2 / kg.

[0064] (2) Preparation of nanocrystalline nuclei (obtained by extraction from steel slag) 100g of nanocrystalline nuclei with a specific surface area of ​​200~400m² 2 / kg of converter steel slag powder was added to 1L of 5mol / L nitric acid solution and stirred at 40℃ for 6h. The solution was then filtered through a vacuum pump to obtain the steel slag leaching liquid.

[0065] Add sodium hydroxide solution of a concentration of ... to 500 mL of a 5% (w / w) aqueous solution of polycarboxylate superplasticizer until the pH of the system reaches 11.0. Stir for 30 min to obtain an alkaline polycarboxylate superplasticizer dispersion.

[0066] The steel slag leaching solution was slowly added dropwise to the alkaline polycarboxylate superplasticizer dispersion at a rate of 1 mL / min, and the pH value of the mixture was stabilized at 11.0 in real time with a 5 wt% sodium hydroxide solution. The mixture was stirred at 40°C for 16 h to obtain a nanocrystalline nucleus (CFSH) suspension.

[0067] The CFSH suspension was dried in a vacuum drying oven at 55°C to obtain nanocrystalline nuclei.

[0068] (3) Preparation of modified and activated steel slag-based admixtures: The auxiliary materials are composed of: fly ash microspheres 70%, silica fume 24.7%, calcium carbonate whiskers 5%, and nanocrystalline nuclei 0.3% by mass percentage.

[0069] Modified steel slag powder and auxiliary materials are mixed evenly at a mass ratio of 9:1 to obtain modified activated steel slag-based admixture.

[0070] (4) Preparation of cementitious material: 42.5 standard cement and modified activated steel slag-based admixture were mixed evenly at a mass ratio of 7:3 to obtain cementitious material. The cementitious material was tested for mortar fluidity and mortar strength according to GB / T 2419-2021 "Test Method for Flowability of Cement Mortar" and (GB / T 17671-2021) "Test Method for Strength of Cement Mortar (ISO Method)". The cementitious activity index was calculated after 7 days and 28 days of curing, based on the compressive strength of the standard cement. The test results are shown in Table 2.

[0071] Example 2: Modified steel slag powder, nanocrystalline nuclei, modified activated steel slag-based admixtures, and cementitious materials were prepared according to the method of Example 1. The only difference from Example 1 was that: (1) In the preparation process of modified steel slag powder, the mass ratio of converter steel slag powder and refining furnace slag powder of the solid raw materials was 85:15, the calcination temperature was 1450℃, and the specific surface area of ​​the modified steel slag powder was 472m². 2 / kg.

[0072] (2) During the preparation of nanocrystalline nuclei, the concentration of nitric acid solution was 6 mol / L and the pH value was 12.

[0073] (3) In the preparation of modified and activated steel slag-based admixture, the auxiliary materials consist of: 60% fly ash microspheres, 34.5% silica fume, 5% calcium carbonate whiskers, and 0.5% nanocrystalline nuclei; the mass ratio of modified steel slag powder to auxiliary materials is 85:15.

[0074] Example 3: Modified steel slag powder, nanocrystalline nuclei, modified activated steel slag-based admixtures, and cementitious materials were prepared according to the method of Example 1. The only difference from Example 1 was that: (1) In the preparation process of modified steel slag powder, the solid raw materials were converter steel slag powder: coal gangue powder: refined furnace slag powder in a mass ratio of 80:10:10, and the specific surface area of ​​modified steel slag powder was 460 m². 2 / kg.

[0075] (2) In the preparation of nanocrystalline core materials, the mass concentration of polycarboxylate superplasticizer aqueous solution is 10%.

[0076] (3) In the preparation of modified and activated steel slag-based admixture, the auxiliary materials consist of: 60% fly ash microspheres, 34.2% silica fume, 5% calcium carbonate whiskers, and 0.8% nanocrystalline nuclei; the mass ratio of modified steel slag powder to auxiliary materials is 80:20.

[0077] The only difference between Comparative Example 1 and Example 2 is that no auxiliary materials are added.

[0078] The only difference between Comparative Example 2 and Example 2 is that the auxiliary material does not contain nanocrystalline nuclei, and is supplemented with fly ash microspheres to make up 100%.

[0079] The only difference between Comparative Example 3 and Example 2 is that the auxiliary material does not contain calcium carbonate whiskers, and is supplemented with fly ash microspheres to make up 100%.

[0080] Comparative Example 4 prepared modified steel slag powder, nanocrystalline nuclei, modified activated steel slag-based admixtures, and cementitious materials according to the method of Example 2. The only difference from Example 2 was that: (1) in the preparation of modified steel slag powder, the conditioning modifier was bituminous coal, the atmosphere for calcination and cooling was nitrogen, the high-temperature electric furnace was first evacuated and then filled with nitrogen before calcination, and the calcination time was 120 min; the modified steel slag coarse powder was crushed by a jaw crusher, Grinding with a 500×500mm ball mill yielded a specific surface area of ​​400m². 2 / kg of modified steel slag powder, modified steel slag powder.

[0081] Table 1. Chemical composition of converter steel slag and modified steel slag prepared in Examples 1-3 and Comparative Example 4.

[0082] Table 2. Performance Test Results of Cementitious Materials (Mortar)

[0083] As shown in Table 3, the modified activated steel slag-based admixture provided by this invention has excellent cementitious activity. When the modified activated steel slag-based admixture and cement are mixed in a mass ratio of 3:7 to form a cementitious material, the cementitious activity index is 96-103% after 7 days of curing and 107-114% after 28 days of curing. Compared with Comparative Example 1, the addition of auxiliary materials in Example 2 increased the activity index by about 30% at 7 days and 28 days. Compared with Comparative Example 2, the addition of nanocrystalline nuclei or calcium carbonate whiskers to the auxiliary materials in Example 2 can increase the activity index of the admixture by more than 10% at 7 days and 28 days. Compared with Comparative Example 4, the addition of bituminous coal to activate the steel slag at high temperature can improve its activity index, but the experimental conditions of Comparative Example 4 are demanding (vacuuming first, then nitrogen filling), which is not conducive to industrial production, and the activity index at 7 days and 28 days is about 6% lower than that of Example 2. Compared with the comparative example, the modified and activated steel slag-based admixture provided by the present invention has significantly improved cementitious activity, realizing the large-scale resource utilization of steel slag solid waste, while making up for the current shortage of high-quality mineral admixture resources.

[0084] In summary, this invention utilizes the uniform mixing and calcination of steel slag with a silica-alumina modifier to induce a chemical reaction between the components. This decomposes the iron-aluminum-calcium mineral phase in the steel slag, releasing calcium oxide and promoting the formation of silicate and aluminate minerals. This fundamentally optimizes the mineral composition of the steel slag, reduces the f-CaO content, and improves its volume stability and cementitious activity. Furthermore, by extracting CFSH nuclei from the silicate minerals in the steel slag and combining them with microspheres, silica fume, and calcium carbonate whiskers to prepare a highly active auxiliary material, the cementitious activity of the modified and activated steel slag-based admixture is further enhanced. This material can be used as a high-quality mineral admixture in the preparation of high-strength and ultra-high-strength concrete, demonstrating broad application potential.

[0085] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A modified and activated steel slag-based admixture, characterized in that, The mixture includes modified steel slag powder and auxiliary materials; the preparation method of the modified steel slag powder includes the following steps: mixing steel slag and a conditioning modifier, and then calcining, cooling and crushing in sequence to obtain modified steel slag powder; the conditioning modifier is a mineral rich in silica and aluminum components; the auxiliary materials include fly ash microspheres, silica fume, calcium carbonate whiskers and nanocrystalline nuclei.

2. The modified activated steel slag-based admixture according to claim 1, characterized in that, The auxiliary materials, by mass percentage, include 50-70% fly ash microspheres, 20-40% silica fume, 5-10% calcium carbonate whiskers, and 0.1-1% nanocrystalline nuclei.

3. The modified activated steel slag-based admixture according to claim 1 or 2, characterized in that, The mass ratio of the modified steel slag powder to the auxiliary materials is 8~9:1~2.

4. The modified activated steel slag-based admixture according to claim 1 or 2, characterized in that, The preparation method of the nanocrystalline nucleus material includes the following steps: mixing steel slag powder with nitric acid solution, carrying out a hydrothermal reaction, separating the solid and liquid to obtain a steel slag leachate; mixing the steel slag leachate with a dispersant, adjusting the pH value to 11-13, carrying out a complexation reaction, and then drying to obtain the nanocrystalline nucleus material.

5. The modified activated steel slag-based admixture according to claim 4, characterized in that, The effective components in the nanocrystalline nucleus material include CaO, Fe2O3 and SiO2, wherein the molar ratio of CaO to Fe2O3 is 1:0.2~0.3 and the molar ratio of CaO to SiO2 is 1:0.5~1.

6. The modified activated steel slag-based admixture according to claim 4, characterized in that, The specific surface area of ​​the steel slag powder is 200~400 m². 2 / kg; the concentration of the nitric acid solution is 4~6 mol / L; the solid-liquid ratio of the steel slag powder to the nitric acid solution is 1kg:8~12L; the hydrothermal reaction temperature is 40~60℃, and the time is 5~9h; the dispersant includes polycarboxylate superplasticizer, and the dispersant is used in the form of an alkaline dispersant aqueous solution; the mass ratio of the steel slag powder to the dispersant is 1:4~6; the temperature of the complexation reaction is 40~60℃, and the time is 10~40h.

7. The modified activated steel slag-based admixture according to claim 1, characterized in that, The conditioning and modifying agent includes one or more of coal gangue, refining slag, and fly ash; the mass ratio of steel slag to conditioning and modifying agent is 75~90:10~25; the pulverization includes: primary crushing of the cooled material obtained from the cooling process, ball milling and sieving the resulting modified coarse powder, and grinding the undersize material to obtain modified steel slag powder; the particle size of the modified coarse powder is ≤4.75mm; the sieve size is 0.6~1.18mm; the ball milling time is 25~35min; the grinding time is 15~25min; the calcination temperature is 1200~1500℃, and the holding time is ≥0.5h; the specific surface area of ​​the modified steel slag powder is 350~700m². 2 / kg.

8. The method for preparing the modified activated steel slag-based admixture according to any one of claims 1 to 7, characterized in that, Includes the following steps: Modified steel slag powder and auxiliary materials are mixed to obtain modified activated steel slag-based admixture.

9. A cementitious material, characterized in that, It includes admixtures and cement, wherein the admixtures include the modified activated steel slag-based admixtures according to any one of claims 1 to 7 or the modified activated steel slag-based admixtures prepared by the preparation method according to claim 8.

10. The application of the modified activated steel slag-based admixture according to any one of claims 1 to 7, the modified activated steel slag-based admixture prepared by the preparation method according to claim 8, or the cementitious material according to claim 9 in building materials.

Images