Green low-carbon composite micro-powder concrete based on steel slag and slag and preparation method thereof

Abstract

The application discloses a kind of green low-carbon concrete based on steel slag and composite micro powder of slag and preparation method thereof, the concrete includes by mass fraction: 100 parts steel slag and blast furnace slag composite matrix;Controlled double-effect excitation system contains phosphate early strength precursor, sulfate excitation precursor and calcium ion chelation-buffer;And conventional accessories, when preparing, first water reducing agent and chelation buffer are dissolved in water to prepare bottom liquid, then add inorganic salt to prepare excitation solution, finally mixed with solid phase dry material and formed.The application introduces polyphosphate chelation buffer, uses the system alkalinity increase caused by free calcium oxide hydration as trigger condition, and constructs cascade reaction.The scheme guarantees the liquidity of construction at the same time, in-situ skeleton generation greatly improves early strength, and targets to consume free calcium oxide to eliminate late expansion hidden danger, generates in-situ gypsum to continuously excite slag, realizes the high unification of early strength and volume stability.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, specifically to a green low-carbon concrete based on steel slag and blast furnace slag composite micro powder and its preparation method. Background Technology

[0002] In the field of building materials, using industrial solid waste such as steel slag and blast furnace slag to replace silicate cement clinker in the preparation of concrete is an effective way to reduce carbon emissions. Steel slag contains tricalcium silicate and dicalcium silicate, which have certain potential hydration activity; blast furnace slag contains an amorphous aluminosilicate network, which can undergo pozzolanic reaction in alkaline or sulfate environments. The usual preparation process is to grind steel slag and blast furnace slag and then mix them with a small amount of cement and mixing water to form a mold. However, this conventional composite micro powder system faces serious performance bottlenecks in practical engineering applications.

[0003] Because steel slag leaves behind free calcium oxide during the smelting and cooling process, and this free calcium oxide formed at high temperatures has a dense structure and hydrates very slowly, it will only gradually hydrate into calcium hydroxide several months after the concrete has hardened and even during long-term service. The accompanying local volume expansion can cause microcracks or even structural damage inside the concrete, seriously affecting volume stability. At the same time, the early hydration activity of steel slag and blast furnace slag is much lower than that of conventional silicate cement, and using large amounts can lead to a serious deficiency in the early compressive strength of concrete.

[0004] Existing conventional treatment methods are insufficient to address the aforementioned conflicting engineering needs. To address the expansion hazard of free calcium oxide, engineering practices often employ natural aging lasting several months or high-temperature, high-pressure steam treatment to eliminate free calcium in advance. However, this significantly increases site requirements, production costs, and energy consumption. Regarding the issue of low early strength, current treatments typically involve the external addition of strong alkaline activators such as water glass or sodium hydroxide, or the introduction of large quantities of gypsum-based early-strength agents. However, the introduction of strong alkaline systems easily leads to rapid setting of the concrete mixture, causing it to quickly lose the fluidity and workability required for construction. Simultaneously, strong alkaline activation can cause a sharp increase in the later-stage shrinkage rate of hardened concrete and efflorescence. Therefore, how to simultaneously overcome the later-stage volume expansion caused by free calcium oxide and the early-stage low strength caused by large amounts of solid waste through a simple admixture synergistic system without incurring high-energy-consuming pretreatment, and without compromising construction fluidity, is a pressing technical challenge in this field. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the technical defects of existing composite systems with large amounts of steel slag and blast furnace slag, such as low early compressive strength, easy occurrence of free calcium oxide in steel slag causing volume expansion and cracking of concrete in the later stage, and easy occurrence of rapid setting and loss of workability of the mixture or aggravation of later shrinkage by conventional activation methods. The present invention provides a green low-carbon concrete based on composite micro powder of steel slag and blast furnace slag and its preparation method.

[0006] The first aspect of this invention provides a green low-carbon concrete based on steel slag and blast furnace slag composite micro powder, wherein, based on 100 parts of composite cementitious material matrix, each component comprises, by mass parts:

[0007] Composite cementitious material matrix: 100 parts, the composite cementitious material matrix includes 30-50 parts of steel slag powder and 50-70 parts of blast furnace slag powder;

[0008] Controlled dual-effect activation system: including 2.0-4.0 parts of phosphate early-strength precursor, 4.0-8.0 parts of sulfate activation precursor (by mass of heptahydrate), and 0.1-0.5 parts of calcium ion chelating buffer;

[0009] Conventional auxiliary materials include 105-135 parts fine aggregate, 165-195 parts coarse aggregate, 30-40 parts mixing water, and 0.1-0.2 parts polycarboxylate-based high-performance water-reducing agent with solid content.

[0010] Preferably, the phosphate early strength precursor is potassium dihydrogen phosphate with a purity ≥98%; the sulfate activation precursor is magnesium sulfate heptahydrate or anhydrous magnesium sulfate with a purity ≥98%; and the calcium ion chelating buffer is sodium tripolyphosphate or sodium hexametaphosphate with a purity ≥95%.

[0011] Preferably, the steel slag powder has a specific surface area of ​​400-500 m² / kg, an alkalinity coefficient ≥1.8, and a free calcium oxide mass fraction of 2.0%-5.0%; the blast furnace slag powder is S95 grade granulated blast furnace slag powder with a specific surface area of ​​450-550 m² / kg and an amorphous aluminosilicate glass content ≥85%.

[0012] Preferably, the fine aggregate is natural river sand with a fineness modulus between 2.3 and 3.0 and a mud content of ≤1.0%; the coarse aggregate is crushed stone with a continuous gradation of particle size in the range of 5-20 mm and a crushing value of ≤15%; and the polycarboxylate-based high-performance water-reducing agent is a comb-shaped polymer with a water reduction rate of ≥25%.

[0013] Preferably, the components, by weight, include the following proportions: 40 parts steel slag powder, 60 parts blast furnace slag powder, 3.0 parts phosphate early strength precursor, 6.0 parts sulfate activation precursor, 0.3 parts calcium ion chelating buffer, 120 parts fine aggregate, 180 parts coarse aggregate, 35 parts mixing water, and 0.15 parts polycarboxylate-based high-performance water-reducing agent with a solid content.

[0014] By adopting the above technical solution, the existing technology of high-volume solid waste systems suffers from low early strength, and the free calcium oxide contained in steel slag hydrates slowly, easily leading to volume expansion and cracking of concrete in the later stages. Conventional techniques usually use strong alkali activation or add a large amount of gypsum to improve strength, but this can easily cause the mixture to set too quickly, lose its workability, or exacerbate later shrinkage. This invention utilizes the physicochemical interactions between components to construct a controlled cascade reaction system, which does not require microstructural modification of the materials, and balances the control of setting time, improvement of early strength, and improvement of later volume stability. The specific reaction mechanism is divided into the following steps:

[0015] Step 1: Chelation Inhibition Reaction: In the initial stage of mixing, the free calcium oxide on the surface of the steel slag powder comes into contact with the mixing water and dissolves, releasing free calcium ions and hydroxide ions into the liquid phase. The polyphosphate calcium ion chelating buffer in the system coordinates and complexes with the released calcium ions to form soluble coordination complexes. This complexation process temporarily restricts the migration activity of calcium ions, preventing the disordered instantaneous precipitation reaction between calcium ions and free phosphate and sulfate ions in the system, thereby avoiding flash solidification and violent heat generation of the mixture and ensuring the basic fluidity of the fresh concrete paste during the construction stage.

[0016] Step 2, Alkalinity Triggering and In-situ Early Strength Reaction: As the free calcium oxide inside the steel slag continues to hydrate, the concentration of hydroxide ions in the pore solution increases, and the pH value gradually rises. When the system reaches a specific high-alkalinity environment, the structural stability of the aforementioned coordination complex decreases and it dissociates, slowly releasing calcium ions into the pore solution. At this time, the released calcium ions combine with the phosphate ions dissociated from potassium dihydrogen phosphate to generate calcium phosphate gel precursors with early strength. Simultaneously, the magnesium ions provided by the sulfate-activated precursor are converted into magnesium hydroxide precipitate under the local high-alkalinity environment. Calcium phosphate and magnesium hydroxide cross-grow in the gaps between slag and steel slag particles, constructing a micro-network skeleton, which significantly improves the early compressive strength of concrete.

[0017] Step 3: Targeted Consumption and In-situ Continuous Activation of Reactions: The precipitation reaction described above directionally consumes the calcium ions generated by the hydration of steel slag, further promoting the deep dissolution of dense free calcium oxide and eliminating the risk of volume expansion of steel slag in the later stages of hardening. Simultaneously, in the liquid phase environment of the precipitation reaction, excess calcium ions combine with sulfate ions provided by the sulfate precursor to generate micro-nano-scale gypsum dihydrate in situ within the system. This in-situ generated gypsum dihydrate has high surface activity and acts as a sulfate activator to continuously react with the amorphous aluminosilicate glass in the blast furnace slag powder, promoting its depolymerization and generating ettringite and hydrated calcium silicate gel. The hydration products continuously fill the early skeleton pores, making the matrix structure more compact and ensuring the growth of concrete strength in the later stages.

[0018] A second aspect of this invention provides a method for preparing green low-carbon concrete based on composite micronized steel slag and blast furnace slag powder, comprising the following steps:

[0019] Step S1, solid matrix pretreatment: Weighed steel slag powder and blast furnace slag powder are put into a planetary dry powder mixer for mechanical mixing to obtain a uniformly distributed matrix dry powder.

[0020] Step S2, Preparation of controlled dual-effect excitation solution: Place the mixing water in the reaction vessel, add the polycarboxylate-based high-performance water-reducing agent and calcium ion chelating buffer in sequence, and stir until completely dissolved to obtain a homogeneous buffer bottom liquid; then add the phosphate early strength precursor and sulfate excitation precursor to the buffer bottom liquid, and continue stirring until the inorganic salt crystals are fully dissolved to obtain a clear controlled dual-effect excitation solution;

[0021] Step S3, wet mixing: The dry powder of the matrix, fine aggregate and coarse aggregate are put into a forced concrete mixer for dry mixing. Then, while the mixer is running, the controlled double-effect activation solution is poured in, and after forced mixing, the material is discharged to obtain fresh concrete paste.

[0022] Step S4, Molding and Curing: Fill the fresh concrete slurry into the mold and vibrate to compact it. After standing in the mold for 24 hours, demold the specimen and transfer it to a standard constant temperature and humidity curing room for continuous curing.

[0023] Preferably, the rotation speed of the planetary dry powder mixer in the solid matrix pretreatment step is set to 30-60 rpm, and the mechanical mixing time is 2.0-3.0 minutes.

[0024] Preferably, in the controlled dual-effect activation solution preparation step, the stirring speed after adding the polycarboxylate-based high-performance water-reducing agent and calcium ion chelating buffer is set to 100-150 rpm, and stirring is continued for 1.0-2.0 minutes; after adding the inorganic salt precursor, the stirring speed is increased to 200-250 rpm, and stirring is continued for 3.0-5.0 minutes; after the inorganic salt is completely dissolved, stirring is stopped and the mixture is allowed to stand for 1.0 minute to defoam.

[0025] Preferably, in the wet mixing step, the dry mixing time is 60 seconds; the time for pouring the controlled dual-effect activation solution is controlled to be completed uniformly within 10-15 seconds; and the forced stirring time after pouring the solution is 120-180 seconds.

[0026] Preferably, in the molding and curing steps, the vibration compaction is carried out using a standard vibration table with a vibration frequency of 50Hz and a vibration duration of 15-20 seconds per layer until the surface slurry is produced and no large bubbles are overflowing; the ambient temperature for the molded static environment is controlled at 20±5℃; the temperature of the standard constant temperature and humidity curing room is set at 20±2℃ and the relative humidity is ≥95%.

[0027] By adopting the above technical solution, the preparation steps of the controlled dual-effect activation solution specify a mixing sequence in which the polycarboxylate-based high-performance water-reducing agent and calcium ion chelating-buffer are first dissolved to form a buffer solution before the inorganic salt precursor is added. This preparation sequence pre-establishes a coordination buffer environment in the liquid phase system, avoiding local ion concentration saturation and water-reducing agent salting-out caused by the direct dissolution of high-concentration inorganic salts, and ensuring the uniform dispersion of each chemically activated component in the liquid phase. In the wet mixing step, the controlled dual-effect activation solution is directly poured into a dry mixture composed of matrix dry powder and aggregate. Compared with the conventional process of directly dry mixing and adding water to solid inorganic salts, the feeding sequence of this invention ensures that the liquid phase containing calcium ion chelating-buffer can preferentially coat the surface of steel slag particles, so that the chelation inhibition reaction occurs before the salt precipitation reaction. With the clear stirring and molding parameters, the local coagulation defects caused by uneven contact between water and inorganic salts are eliminated, providing a process basis for the smooth progress of the reaction system according to the predetermined cascade path.

[0028] The present invention, by adopting the above technical solution, can bring the following beneficial effects:

[0029] 1. This invention solves the problem of rapid setting caused by direct mixing of inorganic salts by introducing a polyphosphate calcium ion chelating buffer into a controlled dual-effect activating solution. In the initial stage of mixing, the chelating buffer preferentially coordinates with the free calcium ions dissolved from the steel slag powder, temporarily limiting the chemical activity of the calcium ions and avoiding early precipitation reactions with phosphate and sulfate ions in the liquid phase, thereby ensuring the initial fluidity and workability of the fresh concrete paste during the pouring stage.

[0030] 2. This invention utilizes the increase in alkalinity caused by the hydration of free calcium oxide as a triggering condition for in-situ precipitation reaction, thereby improving the early mechanical properties of the composite gelling system. When the pH value of the pore solution increases to a specific alkaline condition as the hydration process progresses, the coordination complex dissociates and releases calcium ions, prompting the system to rapidly generate calcium phosphate gel and magnesium hydroxide precipitate, forming an early supporting skeleton in the gaps between solid waste particles, thus avoiding the risks of high shrinkage and efflorescence caused by using conventional strong alkali activation systems.

[0031] 3. This invention targets and consumes free calcium oxide and generates sulfate activators in situ through a cascade precipitation mechanism, which improves the volume stability of concrete and ensures its later strength. The precipitation reaction in the first stage forcibly consumes the expansion source of free calcium oxide in the steel slag, reducing the risk of cracking in the hardened specimens in the later stage. At the same time, the dihydrate gypsum byproduct generated in situ by this chemical process has high surface activity and can act as an activator to continuously react with the glass in the blast furnace slag powder, promoting the generation of hydration products and making the matrix structure more compact. Attached Figure Description

[0032] Figure 1 This is a flow chart of the process for preparing composite low-carbon concrete based on controlled cascade reaction according to the present invention.

[0033] Figure 2 The graphs show the evolution of hydration exothermic rate and pore solution pH value over time for the paste samples of Example 1 and Comparative Example 3 of this invention.

[0034] Figure 3 This is a bar chart comparing the compressive strength of specimens from different embodiments and comparative examples at different ages.

[0035] Figure 4 This is a comparison chart of the autoclaving expansion rates of the various embodiments and comparative examples of the present invention;

[0036] Figure 5 The X-ray diffraction (XRD) patterns of the specimen in Example 1 of this invention at 1 day and 28 days of age are shown. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0038] Please see the appendix Figure 1-5 This invention provides a green low-carbon concrete based on steel slag and slag composite micro powder and its preparation method.

[0039] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0040] The steel slag powder is obtained by mechanically grinding hot-quenched steel slag from a converter. It has a specific surface area of ​​400-500 m² / kg, an alkalinity coefficient R = (CaO + MgO) / (SiO₂ + P₂O₅) ≥ 1.8, and a free calcium oxide (f-CaO) mass fraction controlled between 2.0% and 5.0%.

[0041] The blast furnace slag powder uses S95 grade granulated blast furnace slag powder that meets the national standard GB / T18046, with a specific surface area of ​​450-550 m2 / kg and an amorphous aluminosilicate glass content of ≥85%.

[0042] Potassium dihydrogen phosphate, CAS number 7778-77-0, molecular formula KH2PO4, purity ≥98%;

[0043] Magnesium sulfate heptahydrate, CAS number 10034-99-8, molecular formula MgSO4·7H2O, purity ≥98%;

[0044] Anhydrous magnesium sulfate, CAS number 7487-88-9, molecular formula MgSO4, purity ≥98%;

[0045] Sodium tripolyphosphate, CAS number 7758-29-4, molecular formula Na5P3O 10 Purity ≥ 95%;

[0046] Sodium hexametaphosphate, CAS number 10124-56-8, molecular formula (NaPO3)6, purity ≥95%;

[0047] Polycarboxylate-based high-performance water-reducing agent is a comb-shaped polymer with a solid content of 40%-50% and a water reduction rate of ≥25%.

[0048] The fine aggregate is made of natural river sand with a fineness modulus of 2.3-3.0 and a mud content of ≤1.0%.

[0049] The coarse aggregate is crushed stone with a continuous gradation of 5-20mm particle size and a crushing value ≤15%.

[0050] The mixing water used is concrete mixing water that meets the industry standard JGJ63.

[0051] Preparation example:

[0052] Preparation Example 1:

[0053] This preparation example provides a baseline controlled dual-effect activation solution, formulated based on 100 parts by weight of a composite gelling material, and includes the following steps:

[0054] (1) Measure 35 parts by weight of the mixing water and place it in a reaction vessel equipped with a mechanical stirring device;

[0055] (2) Add 0.15 parts by weight of polycarboxylate-based high-performance water-reducing agent with solid content and 0.3 parts by weight of sodium tripolyphosphate to the container, set the mechanical stirring speed to 120 rpm, and continue stirring for 1.5 minutes until the solid is completely dissolved to obtain a homogeneous buffer solution;

[0056] (3) While maintaining stirring, add 3.0 parts by weight of potassium dihydrogen phosphate and 6.0 parts by weight of magnesium sulfate heptahydrate to the buffer solution at a uniform speed. Increase the mechanical stirring speed to 220 rpm and continue stirring for 4.0 minutes to ensure that the inorganic salt crystals are fully dissolved.

[0057] (4) Stop stirring and let stand for 1.0 minute to defoam, and a clear controlled double-effect excitation solution is obtained.

[0058] Preparation Example 2: This preparation example provides a controlled dual-effect activation solution with low concentration parameter limits. The formulation, based on 100 parts by weight of a composite cementitious material, includes the following steps:

[0059] (1) Measure 30 parts by weight of the mixing water and place it in a reaction vessel equipped with a mechanical stirring device;

[0060] (2) Add 0.1 parts by weight of polycarboxylate-based high-performance water-reducing agent with solid content and 0.1 parts by weight of sodium tripolyphosphate to the container, set the mechanical stirring speed to 100 rpm, and continue stirring for 2.0 minutes until the solid is completely dissolved to obtain a homogeneous buffer solution;

[0061] (3) While maintaining the stirring state, add 2.0 parts by weight of potassium dihydrogen phosphate and 4.0 parts by weight of magnesium sulfate heptahydrate to the buffer solution at a uniform speed, increase the mechanical stirring speed to 250 rpm, and continue stirring for 5.0 minutes to ensure that the inorganic salt crystals are fully dissolved.

[0062] (4) Stop stirring and let stand for 1.0 minute to defoam, and a clear controlled double-effect excitation solution is obtained.

[0063] Preparation Example 3:

[0064] This preparation example provides a controlled dual-effect activation solution with high concentration parameter limits. The formulation, based on 100 parts by weight of a composite cementitious material, includes the following steps:

[0065] (1) Measure 40 parts by weight of the mixing water and place it in a reaction vessel equipped with a mechanical stirring device;

[0066] (2) Add 0.2 parts by weight of polycarboxylate-based high-performance water-reducing agent with solid content and 0.5 parts by weight of sodium tripolyphosphate to the container, set the mechanical stirring speed to 150 rpm, and continue stirring for 1.0 minute until the solid is completely dissolved to obtain a homogeneous buffer solution;

[0067] (3) While maintaining stirring, add 4.0 parts by weight of potassium dihydrogen phosphate and 8.0 parts by weight of magnesium sulfate heptahydrate to the buffer solution at a uniform speed. Increase the mechanical stirring speed to 200 rpm and continue stirring for 3.0 minutes to ensure that the inorganic salt crystals are fully dissolved.

[0068] (4) Stop stirring and let stand for 1.0 minute to defoam, and a clear controlled double-effect excitation solution is obtained.

[0069] Preparation Example 4:

[0070] This preparation example provides a controlled dual-effect activation solution using a replaceable chelating agent and metasulfate ratio. The formulation, based on 100 parts by weight of a composite cementitious material, includes the following steps:

[0071] (1) Measure 38 parts by weight of the mixing water and place it in a reaction vessel equipped with a mechanical stirring device;

[0072] (2) Add 0.15 parts by weight of polycarboxylate-based high-performance water-reducing agent with solid content and 0.4 parts by weight of sodium hexametaphosphate to the container, set the mechanical stirring speed to 130 rpm, and continue stirring for 1.5 minutes until the solid is completely dissolved to obtain a homogeneous buffer solution;

[0073] (3) While maintaining stirring, add 2.5 parts by weight of potassium dihydrogen phosphate and 7.0 parts by weight of magnesium sulfate heptahydrate to the buffer solution at a uniform speed. Increase the mechanical stirring speed to 220 rpm and continue stirring for 4.0 minutes to ensure that the inorganic salt crystals are fully dissolved.

[0074] (4) Stop stirring and let stand for 1.0 minute to defoam, and a clear controlled double-effect excitation solution is obtained.

[0075] Example

[0076] Example 1:

[0077] This embodiment provides a green low-carbon concrete based on composite micro powder of steel slag and blast furnace slag, which is a central parameter optimization type, including the following steps:

[0078] Accurately weigh 40 parts by weight of steel slag powder and 60 parts by weight of blast furnace slag powder, put them into a planetary dry powder mixer, set the mixer speed to 45 rpm, and mechanically mix for 2.5 minutes to obtain a uniformly distributed matrix dry powder for later use.

[0079] The reference controlled dual-effect excitation solution was prepared according to the method of Preparation Example 1. The matrix dry powder prepared above was added together with 120 parts by weight of natural river sand and 180 parts by weight of crushed stone into a forced concrete mixer and dry-mixed for 60 seconds.

[0080] While the mixer is running, pour the entire amount of the controlled double-effect activation solution obtained in Preparation Example 1 evenly within 12 seconds, continue to forcibly stir for 150 seconds and then discharge the material. The fresh concrete slurry is then placed into a standard mold of 100mm×100mm×100mm in two layers and compacted using a standard vibration table at a vibration frequency of 50Hz. The vibration duration for each layer is 18 seconds until slurry appears on the surface and no large air bubbles overflow. The surface of the specimen is then smoothed.

[0081] After molding, the molded specimens were placed in an environment with a temperature of 20±5℃ and left to stand for 24 hours. After 24 hours, the specimens were demolded and immediately placed in a standard constant temperature and humidity curing room with a temperature of 20±2℃ and a relative humidity of ≥95% for continuous curing.

[0082] Example 2:

[0083] This embodiment provides a green low-carbon concrete based on composite micronized steel slag and blast furnace slag, which is a type that balances high steel slag content with high buffering parameters, and includes the following steps:

[0084] Accurately weigh 50 parts by weight of steel slag powder and 50 parts by weight of blast furnace slag powder. Due to the high content of steel slag, the free calcium dissolves very quickly and requires a large amount of water. Put them into a planetary dry powder mixer, set the mixer speed to 30 rpm, and mechanically mix for 2.0 minutes to obtain the matrix dry powder for later use.

[0085] In order to effectively suppress rapid coagulation caused by high amounts of free calcium, a controlled dual-effect activation solution with high concentration and high buffer parameters was prepared according to the method of Preparation Example 3.

[0086] The matrix dry powder prepared above was added together with 135 parts by weight of natural river sand and 165 parts by weight of crushed stone into a forced concrete mixer and dry-mixed for 60 seconds. While the mixer was running, the entire amount of the activation solution obtained in Preparation Example 3 was poured evenly within 15 seconds, and forced mixing was continued for 180 seconds before the material was discharged.

[0087] The freshly mixed concrete slurry was poured into a standard mold in two layers, vibrated to compact it, and then smoothed. The molded specimens were left to stand in an indoor environment for 24 hours before being demolded and moved into a standard constant temperature and humidity curing room for continuous curing.

[0088] Example 3:

[0089] This embodiment provides a green low-carbon concrete based on steel slag and slag composite micro powder, which is a type that limits the parameters of high slag content and low water-cement ratio, and includes the following steps:

[0090] Accurately weigh 30 parts by weight of steel slag powder and 70 parts by weight of blast furnace slag powder. Since the free calcium content in the system is low, put them into a planetary dry powder mixer. Set the mixer speed to 60 rpm and mechanically mix for 3.0 minutes to obtain the matrix dry powder for later use.

[0091] Due to the low buffering requirement, a controlled dual-effect activation solution with low concentration parameter limits was prepared according to the method of Preparation Example 2, but the solid content of the polycarboxylate-based high-performance water-reducing agent was slightly adjusted to 0.2 parts by weight to adapt to the low water-to-binder ratio.

[0092] The matrix dry powder prepared above was put into a forced concrete mixer along with 105 parts by weight of natural river sand and 195 parts by weight of crushed stone. The mixture was dry-mixed for 60 seconds. While the mixer was running, the full amount of fine-tuned solution was poured evenly within 10 seconds to prepare the activation solution of Example 2. The mixture was then forced-mixed for another 120 seconds before being discharged.

[0093] The freshly mixed slurry was poured into a standard mold, vibrated to compact it, and then smoothed. The molded specimens were left to stand in an indoor environment for 24 hours before being demolded and transferred to a standard constant temperature and humidity curing room for continuous curing.

[0094] Example 4:

[0095] This embodiment provides a green low-carbon concrete based on steel slag and blast furnace slag composite micro powder, which is a type with a replaceable chelating agent and metasulfate ratio, including the following steps:

[0096] Accurately weigh 35 parts by weight of steel slag powder and 65 parts by weight of blast furnace slag powder, put them into a planetary dry powder mixer, set the mixer speed to 50 rpm, and mechanically mix for 2.5 minutes to obtain a uniformly distributed matrix dry powder for later use.

[0097] A controlled dual-effect activation solution with a ratio of sodium hexametaphosphate to metasulfate was prepared according to the method of Preparation Example 4 to enhance the later-stage hydration activation of a large amount of slag.

[0098] The matrix dry powder prepared above was added together with 126 parts by weight of natural river sand and 174 parts by weight of crushed stone into a forced concrete mixer and dry-mixed for 60 seconds. While the mixer was running, the entire amount of the activation solution obtained in Preparation Example 4 was poured in evenly within 12 seconds, and forced mixing was continued for 160 seconds before the material was discharged.

[0099] The freshly mixed slurry was poured into a standard mold, vibrated to compact it, and smoothed. The molded specimens were left to stand in an indoor environment for 24 hours before being demolded and moved into a standard constant temperature and humidity curing room for continuous curing.

[0100] Comparative Example

[0101] Comparative Example 1:

[0102] Compared with Example 1, the difference is that no activating and controlling reagents were added (i.e., no potassium dihydrogen phosphate, magnesium sulfate heptahydrate and sodium tripolyphosphate were contained). In the preparation process, an equal amount of mixing water and water-reducing agent were directly mixed and added as the liquid phase. All other aspects were the same.

[0103] Comparative Example 2:

[0104] Compared with Example 1, the difference is that the controlled dual-effect excitation solution is replaced with a conventional strong base excitation solution in the art (using an equal mass of sodium silicate water glass and sodium hydroxide mixture instead of potassium dihydrogen phosphate and magnesium sulfate heptahydrate), and it does not contain sodium tripolyphosphate, all other aspects are the same.

[0105] Comparative Example 3:

[0106] Compared with Example 1, the difference is that no calcium ion chelating buffer (i.e., no sodium tripolyphosphate) was added during the preparation of the controlled dual-effect excitation solution; all other aspects are the same.

[0107] Comparative Example 4:

[0108] Compared with Example 1, the difference lies in the change of the preparation process sequence of the controlled cascade reaction. The conventional "one-pot" mixing method is adopted, that is, the solid powders of potassium dihydrogen phosphate, magnesium sulfate heptahydrate and sodium tripolyphosphate in the formula amount are directly put into the mixer along with the dry powder of the matrix and the aggregate for dry mixing, and then the mixing water and water-reducing agent are added uniformly for wet mixing. The proportions of the remaining components are the same.

[0109] Comparative Example 5:

[0110] Compared with Example 1, the difference is that the controlled dual-effect activation solution formulation does not contain sulfate activation precursor (i.e., does not contain magnesium sulfate heptahydrate), while the rest are the same.

[0111] Comparative Example 6:

[0112] Compared with Example 1, the difference is that the controlled dual-effect activation solution formulation does not contain phosphate early-strength precursor (i.e., does not contain potassium dihydrogen phosphate), while the rest are the same.

[0113] Test Example 1: Hydration Exothermic Test and Dynamic Evolution of Pore Solution Environment

[0114] This test example aims to verify the complexation retardation effect of sodium polyphosphate on calcium ions in the technical solution, and the triggering mechanism of the pH increase caused by the hydration of free calcium oxide in the system on the subsequent in-situ precipitation reaction. To eliminate the interference of aggregates on the testing instrument, this test example uses a paste sample with coarse and fine aggregates removed for testing. The ratio of each powder to the admixture in the paste corresponds to Example 1 and Comparative Example 3 (without sodium tripolyphosphate).

[0115] 1. Experimental steps:

[0116] Based on the formulations of Example 1 and Comparative Example 3, paste samples were prepared at a constant temperature of 20°C.

[0117] Weigh out an equal amount (5.00g) of freshly mixed slurry and put it into a glass ampoule. After sealing, immediately place it in the test channel of the isothermal microcalorimeter. Set the system baseline temperature to 20℃ and continuously collect the hydration heat release rate data for 72 hours.

[0118] Multiple sets of large-volume neat pulp samples were prepared simultaneously and sealed for curing. At specific time points (0.5h, 1.0h, 2.0h, 4.0h, 8.0h, and 24.0h), the corresponding samples were removed and transferred into a high-pressure pore hydraulic press. An axial pressure of 200MPa to 300MPa was applied to extrude the unbound pore solution inside the system.

[0119] The extruded liquid phase was filtered using a needle filter with a pore size of 0.22 μm, and the pH value of the filtrate was then measured using a high-precision composite electrode pH meter.

[0120] 2. Experimental data:

[0121] Table 1. Record of early hydration heat release rate and pore solution pH evolution of paste samples

[0122]

[0123] 2. Experimental data:

[0124] Test data shows that Comparative Example 3, lacking a calcium ion chelation mechanism, exhibited a dramatic exothermic peak of 28.43 mW / g within 0.2 hours of water addition. This corresponds to a transient, disordered precipitation reaction between free calcium and magnesium ions and phosphate ions in the system. In contrast, Example 1 showed an extremely low initial exothermic rate. Within 0 to 2 hours, the pH of the pore solution slowly increased from 10.62 to 11.75. During this stage, sodium tripolyphosphate formed a stable coordination structure with the calcium ions dissolved from the steel slag, inhibiting the dramatic exothermic reaction and ensuring the flow state of the slurry in the early stage. When the time progressed to 3.0 hours, as the free calcium oxide inside the steel slag continued to hydrate and accumulate, the pH of the pore solution exceeded the critical point of 12.1. At this time, the coordination system dissociated and released calcium ions due to high alkalinity, and subsequently, the system exhibited a main exothermic peak of 14.88 mW / g. This delayed exothermic phenomenon directly confirms that the controlled cascade mechanism using pH evolution as a reaction trigger condition is real and effective, effectively avoiding the flashover defects that are very easy to occur in conventional phosphate systems.

[0125] Test Example 2: Macroscopic working performance, mechanical properties and volumetric stability test

[0126] This test example uses the national and industry-standard methods for testing the physical and mechanical properties of concrete to evaluate the macroscopic performance of concrete specimens prepared in all the aforementioned examples and comparative examples.

[0127] 1. Experimental steps:

[0128] Workability test: The initial slump of freshly mixed concrete was measured according to GB / T 50080 "Standard for Test Method of Performance of Ordinary Concrete Mixture". The mixture was covered with plastic film and left to stand for 1 hour. The slump was measured again and the time loss was calculated.

[0129] Mechanical property determination: In accordance with GB / T 50081 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete", cubic specimens with a side length of 100 mm were cured in a standard curing room for 1 day and 28 days respectively, and their compressive strength was determined. Since the specimens in this scheme are non-standard sizes, the test results were corrected by multiplying by a size conversion factor of 0.95 according to the specification requirements.

[0130] Volume stability determination: Due to the hysteretic expansion of free calcium oxide in steel slag, conventional shrinkage tests are insufficient to reflect its harmful effects. Therefore, this test employs accelerated evolution testing based on the autoclaving expansion test method in GB / T 24111 "Steel Slag Silicate Cement". Mortar specimens measuring 25mm × 25mm × 280mm were prepared, demolded, and autoclaved in a 2.0MPa high-pressure steam autoclave for 3 hours. The length change rate before and after autoclaving was measured using a length comparator.

[0131] 2. Experimental data:

[0132] Table 2. Test results of workability, compressive strength and autoclave expansion rate of concrete mixture.

[0133]

[0134] Note: Comparative Example 3 solidified and hardened immediately after mixing (flash solidification), with an initial slump of 0, making it impossible to form specimens for subsequent strength and expansion rate tests.

[0135] 3. Results Analysis

[0136] From the perspective of working performance, Comparative Example 3, which did not add sodium tripolyphosphate, completely lost its engineering application value, which in turn verified the necessity of the chelation control component in the examples; the initial slump of Examples 1 to 4 was maintained above 195 mm, and the loss over 1 hour was controlled within 30 mm, indicating that the controlled dual-effect activating solution did not negatively interfere with the normal hydration process of the gelation system in the early stage; Comparative Example 4, due to the change in the order of feeding, caused local disordered reaction of solid salts, resulting in a significant decrease in the initial slump.

[0137] In terms of mechanical properties, Comparative Example 1, as the traditional blank group, had a 1-day compressive strength of only 3.8 MPa, exhibiting the typical characteristic of low early strength in a large-volume solid waste system. The 1-day strengths of Examples 1 to 4 all reached over 14.8 MPa, with Example 2 achieving an early strength of 22.4 MPa due to the large total amount of controlled precipitated substances. This confirms that the technical path of using a localized high-alkalinity environment induced by free calcium to promote the formation of an insoluble early-strength support network between the phosphate system and magnesium ions has achieved the expected engineering effect. Comparing the 28-day strengths of Example 1 and Comparative Example 5 (without magnesium sulfate), it can be found that the strength growth of Comparative Example 5 stagnated in the later stage, while the 28-day strength of Example 1 reached 46.2 MPa. This indicates that the in-situ calcium sulfate generated in the first stage reaction of this system does indeed play a role in continuously stimulating the activity of the slag.

[0138] Regarding volume stability, relevant national standards typically require that the autoclave expansion rate not exceed 0.50%. Comparative Examples 1 and 6, due to the presence of a large amount of uncontrolled dead-burned free calcium oxide within their systems, exhibited autoclave expansion rates as high as 0.86% and 0.58%, respectively, posing a serious risk of later-stage cracking. The autoclave expansion rates of the example groups were all suppressed to below 0.11%. This significant decrease in data is not due to the internal pore containment effect of conventional physical admixtures, but rather to the forced chemical consumption of free calcium oxide in the first stage using phosphate and sulfate ions in the technical solution. The above test data comprehensively demonstrate that the controlled cascade reaction model constructed in this scheme is fully feasible in practical engineering applications.

[0139] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A green, low-carbon concrete based on steel slag and blast furnace slag composite micro-powder, characterized in that, Based on 100 parts of composite cementitious material matrix, each component includes, by mass parts: Composite cementitious material matrix: 100 parts, wherein the composite cementitious material matrix comprises 30-50 parts of steel slag powder and 50-70 parts of blast furnace slag powder; Controlled dual-effect activation system: including 2.0-4.0 parts of phosphate early-strength precursor, 4.0-8.0 parts of sulfate activation precursor (by mass of heptahydrate), and 0.1-0.5 parts of calcium ion chelating buffer; Conventional auxiliary materials include 105-135 parts fine aggregate, 165-195 parts coarse aggregate, 30-40 parts mixing water, and 0.1-0.2 parts polycarboxylate-based high-performance water-reducing agent with solid content.

2. The green low-carbon concrete based on steel slag and blast furnace slag composite micro powder according to claim 1, characterized in that, The controlled dual-effect excitation system: The phosphate early strength precursor is potassium dihydrogen phosphate with a purity of ≥98%. The sulfate-activated precursor is magnesium sulfate heptahydrate or anhydrous magnesium sulfate with a purity ≥98%. The calcium ion chelating buffer is sodium tripolyphosphate or sodium hexametaphosphate with a purity of ≥95%.

3. The green low-carbon concrete based on steel slag and blast furnace slag composite micro powder according to claim 1, characterized in that, In the composite cementitious material matrix: The steel slag powder has a specific surface area of ​​400-500 m² / kg, an alkalinity coefficient ≥1.8, and a free calcium oxide mass fraction of 2.0%-5.0%. The blast furnace slag powder is S95 grade granulated blast furnace slag powder with a specific surface area of ​​450-550 m2 / kg and an amorphous aluminosilicate glass content of ≥85%.

4. The green low-carbon concrete based on steel slag and blast furnace slag composite micro powder according to claim 1, characterized in that, Among the conventional auxiliary materials: The fine aggregate is natural river sand with a fineness modulus between 2.3 and 3.0 and a mud content of ≤1.0%; The coarse aggregate is crushed stone with a continuous gradation of particle size ranging from 5 to 20 mm and a crushing value of ≤15%. The polycarboxylate-based high-performance water-reducing agent is a comb-shaped polymer with a water reduction rate of ≥25%.

5. The green low-carbon concrete based on steel slag and blast furnace slag composite micro powder according to claim 1, characterized in that, By mass, it comprises the following components in preferred proportions: 40 parts steel slag powder, 60 parts blast furnace slag powder, 3.0 parts phosphate early strength precursor, 6.0 parts sulfate activation precursor, 0.3 parts calcium ion chelating buffer, 120 parts fine aggregate, 180 parts coarse aggregate, 35 parts mixing water, and 0.15 parts polycarboxylate-based high-performance water-reducing agent with solid content.

6. A method for preparing green low-carbon concrete based on composite micro-powder of steel slag and blast furnace slag as described in any one of claims 1-5, characterized in that, Includes the following steps: Step S1, solid matrix pretreatment: The weighed steel slag powder and blast furnace slag powder are put into a planetary dry powder mixer for mechanical mixing to obtain a uniformly distributed matrix dry powder. Step S2, preparation of controlled dual-effect activation solution: Place the mixing water in a reaction vessel, add the polycarboxylate-based high-performance water-reducing agent and the calcium ion chelating buffer agent in sequence, and stir until completely dissolved to obtain a homogeneous buffer solution; Subsequently, the phosphate early-strength precursor and the sulfate activation precursor were added to the buffer solution, and the mixture was stirred continuously until the inorganic salt crystals were fully dissolved to obtain a clear controlled dual-effect activation solution. Step S3, wet mixing: The matrix dry powder, fine aggregate, and coarse aggregate are put into a forced concrete mixer for dry mixing. Then, while the mixer is running, the controlled double-effect activation solution is poured in, and after forced mixing, the material is discharged to obtain fresh concrete paste. Step S4, Molding and Curing: The freshly mixed concrete slurry is poured into the mold and vibrated to compact it. After standing in the mold for 24 hours, the specimen is demolded and then transferred to a standard constant temperature and humidity curing room for continuous curing.

7. The method for preparing green low-carbon concrete based on steel slag and blast furnace slag composite micro powder according to claim 6, characterized in that, In step S1: the rotation speed of the planetary dry powder mixer is set to 30-60 rpm, and the mechanical mixing time is 2.0-3.0 minutes.

8. The method for preparing green low-carbon concrete based on steel slag and blast furnace slag composite micro powder according to claim 6, characterized in that, In step S2: after adding the polycarboxylate-based high-performance water-reducing agent and calcium ion chelating buffer, the stirring speed is set to 100-150 rpm, and stirring is continued for 1.0-2.0 minutes; After adding the inorganic salt precursor, increase the stirring speed to 200-250 rpm and continue stirring for 3.0-5.0 minutes; after the inorganic salt is completely dissolved, stop stirring and let it stand for 1.0 minute to defoam.

9. The method for preparing green low-carbon concrete based on steel slag and blast furnace slag composite micro powder according to claim 6, characterized in that, In step S3: the dry mixing time is 60 seconds; The controlled dual-effect excitation solution was poured out uniformly within 10-15 seconds. The forced stirring time after pouring the solution is 120-180 seconds.

10. The method for preparing green low-carbon concrete based on steel slag and blast furnace slag composite micro powder according to claim 6, characterized in that, In step S4: vibration compaction is performed using a standard vibration table with a vibration frequency of 50Hz. The vibration duration for each layer is 15-20 seconds until slurry appears on the surface and no large bubbles are overflowing. The ambient temperature for the mold settling is controlled at 20±5℃. The temperature of the standard constant temperature and humidity curing room is set at 20±2℃, and the relative humidity is ≥95%.

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