A method for preparing ternary solid waste alkali-activated cementitious materials based on particle size control

Abstract

This invention discloses a method for preparing a ternary solid waste alkali-activated cementitious material based on particle size control, relating to the fields of building materials and solid waste resource utilization technology. The method includes: obtaining three solid waste raw materials—blast furnace slag, red brick powder, and waste glass powder—and setting differentiated target particle size grinding parameters based on their differences in mineral crystal structure and chemical activity; mechanically grinding the three solid waste raw materials separately and detecting the particle size of the three powders after mechanical grinding; dry-mixing the three powders according to a preset mass ratio to prepare a ternary composite precursor; adding an alkali activator solution to the ternary composite precursor and mixing to activate the hydration reaction of the system; and curing under standard curing conditions to obtain the finished cementitious material. This invention employs the above-mentioned method for preparing a ternary solid waste alkali-activated cementitious material based on particle size control, which has the advantages of being low-carbon and environmentally friendly, and while improving early strength, ensures the volume stability of the material in later stages.

Description

Technical Field

[0001] This invention relates to the field of building materials and solid waste resource utilization technology, and in particular to a method for preparing ternary solid waste alkali-activated cementitious materials based on particle size control. Background Technology

[0002] Blast furnace slag (GGBS), waste glass powder (WGP), and red brick powder (RP), as typical aluminosilicate or calcareous solid wastes, possess excellent potential for alkali-activated reactions due to their rich content of active SiO2, Al2O3, and CaO. Utilizing these solid wastes to prepare alkali-activated cementitious materials can not only significantly reduce carbon emissions from cement production but also address the environmental burden caused by solid waste storage, representing an important pathway to achieving low-carbon building materials.

[0003] However, in practical applications, the physicochemical properties and hydration kinetics of the three types of solid waste exhibit significant differences, hindering their efficient synergy in ternary composite systems. Specifically, blast furnace slag is a "fast-reaction" precursor with an extremely rapid early reaction rate, releasing hydration heat within 24 hours, which easily leads to excessive temperature rise in the matrix and chemical shrinkage cracks; waste glass powder, limited by its dense Si-O network structure, has extremely low early activity and a significant reaction delay period, making it difficult to provide early strength; red brick powder contains a large amount of stable crystalline minerals (such as quartz and mullite), with limited solubility in alkaline environments, and is usually only used as an inert physical filler. Existing technologies often employ simple "mixing and grinding" or "equal-volume substitution" processes, neglecting the temporal matching of the reactivity of different components, resulting in an imbalance in the gel formation rate and uneven microstructure within the system, thereby limiting the mechanical properties and volume stability of the material.

[0004] To address the aforementioned issues, there is an urgent need to develop a preparation method based on particle size effect and reaction kinetics control. By differentially physical grinding and particle size distribution design of each component, its specific surface area and reaction activity window can be precisely controlled. The aim is to utilize the rapid exothermic reaction of slag to induce deagglomeration of glass powder, while simultaneously leveraging the micro-aggregate effect of red brick powder to mitigate shrinkage. This constructs a relay-style hydration model of "early rapid reaction – mid-term transition – late-stage densification," thereby achieving complementary advantages and synergistic performance of the ternary solid waste system in terms of hydration heat release, gel growth, and microstructure densification. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing ternary solid waste alkali-activated cementitious materials based on particle size control, which solves the problems of unbalanced reaction rates of single solid waste components in alkali-activated systems in the prior art (such as shrinkage caused by excessively fast reaction of slag and low early strength caused by delayed reaction of glass powder) and insufficient strength and density in the later stage.

[0006] To achieve the above objectives, this invention provides a method for preparing a ternary solid waste alkali-activated cementitious material based on particle size control, comprising the following steps:

[0007] S1. Obtain three solid waste raw materials: blast furnace slag, red brick powder, and waste glass powder, and set differentiated target particle size grinding parameters based on their differences in mineral crystal structure and chemical activity.

[0008] The target particle size grinding parameters in S1 include:

[0009] Control the particle size of blast furnace slag to ensure that the median particle size D50 ≤ 22 μm;

[0010] Control the particle size of red brick powder to make the median particle size D50 27.0-27.9μm;

[0011] Control the particle size of waste glass powder to make the median particle size D50 26.0-26.9μm.

[0012] S2. Mechanically grind the three solid waste raw materials respectively, and test the particle size of the three powders after mechanical grinding. If they meet the target particle size grinding parameters, proceed to S3; otherwise, repeat S2.

[0013] S3. According to the preset mass ratio, the three powders obtained by mechanical grinding in S2 are dry-mixed to prepare a ternary composite precursor.

[0014] S4. Add an alkaline activator solution to the ternary composite precursor and mix to activate the hydration reaction of the system.

[0015] S5. After the hydration reaction is completed, the material is cured under standard curing conditions to obtain the finished cementitious material.

[0016] Preferably, in step S2, a mechanical ball mill is used to grade and grind the three solid waste materials, including:

[0017] For blast furnace slag, the ball milling time should be controlled at 8 minutes;

[0018] For waste glass powder, the ball milling time should be controlled at 5 minutes;

[0019] For red brick powder, control the ball milling time to 3 minutes.

[0020] Preferably, the mass ratio of S3 is: 50% blast furnace slag, 30% waste glass powder, and 20% red brick powder.

[0021] Preferably, in step S3, the three powders—blast furnace slag, waste glass powder, and red brick powder—are mixed in a dry mixer for 2 minutes until homogeneous.

[0022] Preferably, the alkali activator in S4 is prepared from solid sodium hydroxide and water glass, with the modulus adjusted to 1.4, the alkali equivalent to 5%, and the water-to-binder ratio fixed at 0.4.

[0023] Preferably, the hydration reaction in S4 includes:

[0024] S41, 0-24 hours, is dominated by slag, resulting in a rapid reaction and releasing a large amount of heat;

[0025] S42, gel continues to form for 1-3 days;

[0026] S43, 3-7 days of red brick powder for bridging and micro-filling;

[0027] S44. After 7 days, the continuous depolymerization reaction of the glass powder fills the pores, forming a dual gel network of CASH and NASH.

[0028] Preferably, S41 includes:

[0029] Within 0-5 hours, blast furnace slag rapidly dissolves and undergoes condensation, exhibiting the characteristics of dot-like gel formation;

[0030] Over 5-24 hours, the gel products gradually coalesce into sheets.

[0031] Therefore, the present invention employs the above-mentioned method for preparing ternary solid waste alkali-activated cementitious materials based on particle size control, which has the following beneficial effects:

[0032] (1) This method takes into account the differences in reactivity of three solid wastes: blast furnace slag, red brick powder and waste glass powder, and adopts differentiated particle size grinding technology to achieve time matching of hydration reaction.

[0033] (2) This method precisely adjusts the particle size of each component by controlling the grinding time, retains the porous honeycomb structure of red brick powder, enhances the early reaction activity of slag, and strengthens the later deagglomeration ability of glass powder.

[0034] (3) This method constructs a hydration model of “early rapid reaction - mid-term transition - late compaction”, which solves the problem of single solid waste reacting too fast or having insufficient strength, and finally realizes the efficient synergistic utilization of multi-source solid waste. It has significant low-carbon and environmental protection advantages, and while improving early strength, it ensures the volume stability of the material in the later stage.

[0035] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0036] Figure 1 This is a flowchart illustrating an embodiment of a method for preparing a ternary solid waste alkali-activated cementitious material based on particle size control according to the present invention;

[0037] Figure 2 The images are SEM images of the microstructure of three solid waste raw materials of the present invention, wherein (a) is a SEM image of the microstructure of blast furnace slag, (b) is a SEM image of the microstructure of red brick powder, and (c) is a SEM image of the microstructure of waste glass powder.

[0038] Figure 3 The graphs are hydration heat release rate and cumulative heat release curves of the ternary system of the present invention, wherein (a) is the hydration heat release rate curve and (b) is the cumulative heat release curve.

[0039] Figure 4 The FTIR infrared spectrum of the material of this invention;

[0040] Figure 5 The following are SEM images showing the microstructure evolution of hydration products in embodiments of the present invention, wherein (a) is the hydration product of blast furnace slag, (b) is the hydration product of red brick powder, and (c) is the hydration product of glass powder.

[0041] Figure 6 The XRD pattern of blast furnace slag in this invention embodiment;

[0042] Figure 7 The XRD pattern of red brick powder used in this invention;

[0043] Figure 8 The image shows the XRD pattern of the glass powder used in this invention. Detailed Implementation

[0044] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0045] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0046] Example

[0047] Please see Figures 1-8This invention provides a method for preparing a ternary solid waste alkali-activated cementitious material based on particle size control, comprising the following steps:

[0048] S1. Obtain three solid waste raw materials: blast furnace slag (GGBS), red brick powder (RP), and waste glass powder (WGP), and analyze their mineral composition and microstructure characteristics. Based on the differences in their mineral crystal structure and chemical activity, set differentiated target particle size grinding parameters. The target particle size grinding parameters include:

[0049] To activate early-stage reactivity, the particle size of blast furnace slag is controlled to ensure a median particle size (D50) ≤ 22 μm. As the primary calcium source and exothermic phase, particle size control of blast furnace slag aims to ensure the release of the main heat of hydration within 24 hours. Similarly, the particle size of red brick powder is controlled to maintain a median particle size (D50) of 27.0-27.9 μm to preserve its porous honeycomb structure. Finally, the particle size of waste glass powder is controlled to maintain a median particle size (D50) of 26.0-26.9 μm to regulate the dissolution rate. Waste glass powder serves as a later-stage silicon source, primarily depolymerizing in the later stages of the reaction to increase density.

[0050] In this embodiment, S95 grade granulated blast furnace slag powder was selected for blast furnace slag (GGBS). SEM scanning showed that its particles exhibited an irregular blocky glassy structure with a dense, non-porous surface and sharp edges. Figure 2 As shown in (a) above, XRD shows that it has typical glassy dispersion peaks (20-35° 2θ), indicating that it has extremely high potential hydration activity.

[0051] Red brick powder (RP) is obtained from waste red bricks in construction through crushing and screening. SEM analysis shows that its particles have a rough surface, exhibiting a significantly loose, porous, honeycomb structure with a large specific surface area. Figure 2 As shown in (b) in the figure. XRD shows that it contains a large amount of quartz and mullite crystals, indicating that it has low chemical activity and is suitable as a physical framework.

[0052] Waste glass powder (WGP) is made from waste flat glass. SEM images show that its particles have a smooth and dense surface, exhibiting a typical conchoidal fracture, such as... Figure 2 As shown in (c) in the figure. XRD shows that it is a completely amorphous structure, but it is difficult to dissolve in the early stages due to the high Si-O bond energy.

[0053] S2. Mechanically grind the three solid waste materials separately, and then test the particle size of the three powders after mechanical grinding. If they meet the target particle size grinding parameters, proceed to S3; otherwise, repeat S2. Based on the "fast-response-transition-delay" mechanism, graded grinding is used to match the reaction time windows of the three materials. A mechanical ball mill is used to perform differentiated "graded grinding" treatment on the three solid waste materials. Specifically, the graded grinding treatment of the three solid waste materials using a mechanical ball mill includes:

[0054] For blast furnace slag (fast reverse phase), the ball milling time is controlled at 8 minutes. By extending the grinding time, the particle size is refined to the target particle size grinding parameter of D50≤22μm, so as to significantly increase its specific surface area and ensure its rapid hydration in the early stage of reaction.

[0055] For waste glass powder (delayed phase), the ball milling time is controlled to be 5 minutes to meet the target particle size grinding parameters of medium particle size D50≈27μm, so as to preserve its porous structure and adjust the pore structure and moisture adsorption.

[0056] For red brick powder (transition / skeletal phase), the ball milling time is controlled at 3 minutes. By moderately grinding, it meets the target particle size grinding parameters of medium particle size D50≈26μm, maintaining the reaction delay and providing time for subsequent deagglomeration.

[0057] In this embodiment, the median particle size (D50) of blast furnace slag is made to reach 21.4 μm; the median particle size (D50) of waste glass powder is made to reach 26.2 μm; and the median particle size (D50) of red brick powder is made to reach 27.8 μm.

[0058] S3. According to the preset mass ratio, mix the three powders obtained from mechanical grinding in S2 in a dry mixer for 2 minutes until homogeneous, ensuring uniform mixing, to prepare a ternary composite precursor. The ternary composite precursor has efficient hydration heat release capability and structural stability, and can achieve a balance between early strength and later volume stability.

[0059] The mass ratio used in this embodiment is as follows: 50% blast furnace slag, providing early strength framework and main Ca source; 30% waste glass powder, providing active Si source required for later densification; and 20% red brick powder, providing physical support and trace Al source.

[0060] S4. Add an alkaline activator solution to the ternary composite precursor and mix to activate the hydration reaction. The alkaline activator is prepared from solid sodium hydroxide and water glass, with the modulus adjusted to 1.4, the alkaline equivalent (Na2O as a percentage of powder mass) to 5%, and the water-cement ratio fixed at 0.4. The hydration reaction includes:

[0061] S41, 0-24 hours, is a rapid reaction dominated by slag, releasing a large amount of heat. This includes:

[0062] Within 0-5 hours, blast furnace slag rapidly dissolves and undergoes condensation, exhibiting the characteristics of dot-like gel formation.

[0063] Over 5-24 hours, the gel products gradually connect into sheets, achieving a smooth transition between continuous gelation and exothermic peaks.

[0064] S42, gel formation continues for 1-3 days.

[0065] S43, 3-7 days of red brick powder for bridging and micro-filling.

[0066] S44. After 7 days, the continuous depolymerization reaction of the glass powder fills the pores. The active silicon components released by the depolymerization of waste glass powder promote the further densification and cross-linking of the gel network, forming a dual gel network of CASH and NASH.

[0067] This embodiment verifies the system's evolution along a predetermined path through SEM microscopic morphology monitoring. Induction and nucleation period (1 hour): Blast furnace slag reacts first. SEM observation shows that the slag particles are affected by OH groups on their surface. - Erosion begins, and dot-like and sheet-like CSH gels begin to precipitate. At this point, the glass powder and red brick powder are basically inert and only play a dispersing role.

[0068] Acceleration and connection period (5 hours): Slag releases a large amount of heat (first exothermic peak), Ca 2+ With SiO4 4- Rapid polymerization. SEM showed that the gel products began to intercalate and overlap, the pores were initially filled, and an early strength framework was formed.

[0069] Network densification period (18-24 hours): As the system temperature rises (caused by the exothermic reaction of the slag) and alkalinity persists, the Si-O bonds on the surface of the glass powder begin to break. SEM shows that the gel structure has been connected into a continuous network, the number of unreacted particles has significantly decreased, and the system has entered a stable hardening stage.

[0070] S5. After the hydration reaction is complete, the mixed slurry is poured into a mold and cured under standard curing conditions to obtain the finished cementitious material. Through the above reaction process, the material forms a dense structure mainly composed of amorphous CASH and NASH gels at 28 days of age, significantly reducing unreacted particles and pores, thereby achieving excellent mechanical properties and volume stability, and realizing the efficient synergistic utilization of multi-source solid waste. The finished cementitious material has a dense microstructure, which gradually evolves from a dot-like gel to a network structure, showing excellent mechanical properties and volume stability. The micromorphology of the finished cementitious material evolves with age, from the precipitation of flocculent products on the particle surface to the interpenetration of various hydrations, and finally the formation of a dense cross-linked network.

[0071] In this embodiment, the XRD pattern shows the phase composition as follows: Figure 6 , Figure 7 and Figure 8As shown, no obvious Ca(OH)2 crystals were formed in the system, and the main products were amorphous CASH and NASH gels, proving that the active Si / Al components of the red brick powder and glass powder had successfully participated in the geopolymerization reaction. In terms of microstructure, compared to the control group without particle size control, the 28-day sample in this embodiment had an extremely dense microstructure. The porous structure of the red brick powder was completely filled by the gel generated later, achieving a "pore self-repair" effect. In terms of macroscopic performance, due to the "peak-shaving" effect of the red brick powder alleviating thermal stress and the "valley-filling" effect of the glass powder increasing the later density, no visible shrinkage cracks appeared in the material, and the 28-day compressive strength showed better strength retention and volume stability than the single-blended slag system.

[0072] like Figure 3 The figure shown is a graph of the hydration heat release rate and cumulative heat release curve of the ternary system in this embodiment, reflecting the reaction contribution of each component in different time windows.

[0073] like Figure 4 The image shown is the FTIR infrared spectrum of the material, reflecting the degree of polymerization of the aluminum-silicon framework and the process of chemical bond reconstruction.

[0074] like Figure 5 The image shown is a SEM image depicting the microstructure evolution of the hydration products. Figure 5 This method utilizes a ternary system at different ages to demonstrate the evolution of its microstructure, aiming to reveal the physical characteristics of the "relay-style" hydration of each component at the microscopic level and to verify the formation mechanism of the dense structure of the final hardened body. This includes:

[0075] In the early stages: From a microscopic perspective, blast furnace slag is the first to undergo a dissolution-condensation reaction. SEM images show that after the slag particles are eroded by alkaline solution, a large number of dot-like and short fibrous CSH gels precipitate. At this time, red brick powder and waste glass powder particles mainly act as inert fillers and nucleation sites, providing a supporting framework for gel growth.

[0076] Mid-term: From a microscopic perspective, the gel product gradually connects from initially isolated dots into a continuous sheet-like structure. Due to its unique porous honeycomb structure, red brick powder acts as a "micro-pump" and "anchor" at the microscopic level. The gel embeds into the micropores of the red brick powder, achieving a physical bridging and micro-filling effect.

[0077] Later stage: From a microscopic perspective, the system exhibits a clear "porosity self-repair" characteristic. Under the induction of alkaline environment and residual heat from slag reaction, the silica-oxygen network in the waste glass powder undergoes deep depolymerization, and the resulting secondary gel further fills the microcracks and capillary pores formed in the early stage. Ultimately, an extremely dense microstructure with interwoven CASH and NASH dual gel networks is formed, and unreacted particles and pores are significantly reduced.

[0078] SEM images confirm that this method achieves spatial and temporal synergy of the reactivity of each component through particle size control. The microstructure evolution exhibits characteristics of transitioning from a discrete particle state to a gel intercalation state, and finally developing into a highly dense cross-linked network. This physically explains the fundamental reason why the material possesses high early strength and long-term volume stability.

[0079] Therefore, this invention employs the aforementioned method for preparing ternary solid waste alkali-activated cementitious materials based on particle size control. Addressing the differences in reactivity among three solid wastes—blast furnace slag, red brick powder, and waste glass powder—differentiated particle size grinding technology is used to achieve temporal matching of the hydration reaction. By precisely adjusting the particle size of each component through controlled grinding time, the porous honeycomb structure of the red brick powder is preserved, enhancing the early reactivity of the slag and strengthening the later deagglomeration ability of the glass powder. This method constructs a hydration model of "early rapid reaction - mid-term transition - later compaction," solving the problem of excessively rapid reaction or insufficient strength of a single solid waste. Ultimately, it achieves efficient synergistic utilization of multiple solid waste sources, exhibiting significant low-carbon and environmentally friendly advantages. Furthermore, while improving early strength, it ensures the volume stability of the material in the later stages.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a ternary solid waste alkali-activated cementitious material based on particle size control, characterized in that, Includes the following steps: S1. Obtain three solid waste raw materials: blast furnace slag, red brick powder, and waste glass powder, and set differentiated target particle size grinding parameters based on their differences in mineral crystal structure and chemical activity. The target particle size grinding parameters in S1 include: Control the particle size of blast furnace slag to ensure that the median particle size D50 ≤ 22 μm; Control the particle size of red brick powder to make the median particle size D50 27.0-27.9μm; Control the particle size of waste glass powder to make the median particle size D50 26.0-26.9μm; S2. Mechanically grind the three solid waste raw materials respectively, and test the particle size of the three powders after mechanical grinding. If they meet the target particle size grinding parameters, proceed to S3; otherwise, repeat S2. S3. According to the preset mass ratio, the three powders obtained by mechanical grinding in S2 are dry-mixed to prepare a ternary composite precursor. S4. Add an alkaline activator solution to the ternary composite precursor and mix to activate the hydration reaction of the system. S5. After the hydration reaction is completed, the material is cured under standard curing conditions to obtain the finished cementitious material. In S2, a mechanical ball mill is used to grade and grind the three solid waste raw materials. The mass ratio of S3 is: 50% blast furnace slag, 30% waste glass powder, and 20% red brick powder; The alkali activator in S4 is prepared from solid sodium hydroxide and water glass, with the modulus adjusted to 1.4, the alkali equivalent to 5%, and the water-cement ratio fixed at 0.

4. The hydration reaction in S4 includes: S41, 0-24 hours, is dominated by slag, resulting in a rapid reaction and releasing a large amount of heat; S42, gel continues to form for 1-3 days; S43, 3-7 days of red brick powder for bridging and micro-filling; S44. After 7 days, the continuous depolymerization reaction of the glass powder fills the pores, forming a dual gel network of CASH and NASH.

2. The preparation method of a ternary solid waste alkali-activated cementitious material based on particle size control according to claim 1, characterized in that, In step S3, blast furnace slag, waste glass powder, and red brick powder are mixed in a dry mixer for 2 minutes until homogeneous.

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