Organic acid-activated solid waste-based geopolymer

Abstract

The present disclosure provides an organic acid-activated solid waste-based cementitious material, belonging to the technical field of solid waste utilization. The organic acid-activated solid waste-based cementitious material comprises 90-105 parts by mass of a silico-aluminous solid waste base material, 7-12 parts by mass of a sulfate, and 15.3-19.8 parts by mass of a composite organic acid activator; wherein the composite organic acid activator comprises a main acid and polyacrylic acid, the mass of the polyacrylic acid being 10%-40% of the mass of the main acid; and the main acid is one of citric acid and tartaric acid or a mixture of the two. The organic acid-activated solid waste-based cementitious material avoids using strong alkali as an activator, thereby avoiding the defects of a strong alkali activation system.

Description

Technical Field

[0001] This disclosure relates to the field of solid waste utilization technology, and more specifically, to an organic acid-activated solid waste-based cementitious material. Background Technology

[0002] With the advancement of the "dual-carbon" strategy, utilizing industrial solid waste to replace traditional cement in the preparation of green cementitious materials has become a research hotspot. Current research typically uses solid waste to prepare alkali-activated cementitious materials. These materials mainly utilize solid wastes such as fly ash, blast furnace slag, and carbide slag, which, under the action of strong alkaline activators (such as water glass, sodium hydroxide, and quicklime), generate cementitious products. However, strong alkaline activators suffer from problems such as high corrosivity, high energy consumption, large carbon emissions during preparation, and a tendency to cause alkali-aggregate reactions. In recent years, some studies have attempted to use sulfates (such as desulfurized gypsum) or other weakly alkaline substances as activators, but these methods suffer from drawbacks such as low activation efficiency and slow early strength development.

[0003] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0004] The purpose of this disclosure is to overcome the shortcomings of the prior art and provide an organic acid-activated solid waste-based cementitious material that avoids the use of strong alkali as an activator.

[0005] This invention provides an organic acid-activated solid waste-based cementitious material, comprising 90-105 parts by weight of a silica-alumina solid waste base, 7-12 parts by weight of sulfate, and 15.3-19.8 parts by weight of a composite organic acid activator;

[0006] The composite organic acid activator includes a primary acid and polyacrylic acid, wherein the mass of polyacrylic acid is 10% to 40% of the mass of the primary acid; the primary acid is one or a mixture of citric acid and tartaric acid.

[0007] According to one embodiment of this disclosure, the composite organic acid activator further includes a co-acid, which is one or a mixture of more than one of oxalic acid, malic acid, gluconic acid and ascorbic acid; the mass of the co-acid is 20% to 80% of the mass of the main acid.

[0008] According to one embodiment of this disclosure, the mass of polyacrylic acid is 20% to 35% of the mass of the main acid; and the mass of the auxiliary acid is 40% to 70% of the mass of the main acid.

[0009] According to one embodiment of this disclosure, the composite organic acid activator is a mixture of citric acid, oxalic acid and polyacrylic acid; wherein the mass ratio of citric acid to oxalic acid to polyacrylic acid is (3.8~4.2):(1.8~2.2):1.

[0010] According to one embodiment of this disclosure, the sulfate has an SO3 content of not less than 38% and a specific surface area of ​​not less than 500 m² / kg.

[0011] According to one embodiment of this disclosure, the sulfate is one or a mixture of desulfurized gypsum and phosphogypsum.

[0012] According to one embodiment of this disclosure, the silicon-aluminum solid waste base material includes high-calcium solid waste micro powder and low-calcium high-silicon-aluminum solid waste micro powder; the mass of the low-calcium high-silicon-aluminum solid waste micro powder is 0.4 to 2.5 times the mass of the high-calcium solid waste micro powder.

[0013] The CaO content of the high-calcium solid waste powder is not less than 15%; the CaO content of the low-calcium, high-silicon-aluminum solid waste powder is less than 15%.

[0014] According to one embodiment of this disclosure, the high-calcium solid waste powder includes one or more of blast furnace slag powder, steel slag powder, and carbide slag powder.

[0015] According to one embodiment of this disclosure, the low-calcium, high-silicon-aluminum solid waste powder includes one or more of fly ash, coal gangue powder, red mud powder, and metakaolin powder.

[0016] According to one embodiment of this disclosure, the D90 particle size of the silicon-aluminum solid waste base material is no greater than 20 micrometers.

[0017] This invention abandons the traditional strong base / strong acid activation pathway and adopts a composite organic acid system. Through a synergistic mechanism of "proton exchange-complexation control," it solves several long-standing technical challenges related to activity activation, reaction control, volume stability, and durability. Instead of using strong bases or strong inorganic acids to activate the solid waste substrate, a safer composite organic acid and sulfate are used together to activate the silicoaluminous solid waste substrate. Citric acid and tartaric acid, as the main acids, can effectively decompose the inert silicoaluminous glass layer on the surface of the silicoaluminous solid waste substrate, releasing active ions such as calcium, aluminum, and silicon, thereby achieving effective activation of the cementitious material. Traditional base activation systems mainly rely on strong OH-... - Hydroxide ions directly break covalent bonds such as Si-O (silicon-oxygen bonds) and Al-O (aluminum-oxygen bonds), causing the network to disintegrate. This requires the addition of a large amount of strong base, which poses risks such as efflorescence, rapid solidification, unstable strength, and shrinkage cracking. The composite organic acid activator of this invention differs from this, primarily utilizing the dissociated H+ ions... +(Protons) and the mesh modifiers in the aluminosilicate glass (e.g., calcium ions Ca) 2+ Ion exchange occurs; as the mesh modifier is exchanged, the glass framework of the aluminosilicate glass loosens, releasing H₄SiO₄ and [Al(OH)₄]. - Therefore, when using a composite organic acid activator to activate the silica-alumina solid waste substrate, this invention can reduce damage to the glass skeleton; this avoids the problem of severe damage to the glass skeleton caused by strong alkaline and strong acid systems.

[0018] The organic acids (especially the primary acid) in the complex organic acid activator can cause the vitreous body to release Ca through ion exchange. 2+ In addition, organic acid ions can effectively complex Ca. 2+ Effectively reduces free Ca 2+ The concentration of Ca, while avoiding 2+ Premature precipitation. Polyacrylic acid not only improves particle dispersibility and increases the reaction contact area, but its carboxyl groups can also react with Ca. 2+ Plasma chelation further modulates reaction kinetics. Sulfate can serve as an early sulfate excitation source, providing SO42-. 2- It combines with dissolved aluminate ions in Ca 2+ In its presence, ettringite is formed.

[0019] Therefore, the organic acid-activated solid waste-based cementitious material provided by the present invention can provide a stable low calcium-to-silicon ratio environment for the activation and hydration processes by utilizing the complexing ability of the composite organic acid activator. This effectively controls the reaction rate and product structure, guides the reaction towards the formation of more stable and durable products, and inhibits the formation of unstable and harmful products.

[0020] For example, during the hydration process, the cementitious material of this invention, thanks to the effective control of the free calcium ion concentration, mainly generates low-calcium-to-silica aluminosilicate gels (such as low-calcium CSH and / or NASH gels) and stable ettringite. Compared to the high-calcium-to-silica CSH gel in traditional cement, these low-calcium-to-silica gels are denser, closer to an amorphous polymer structure, and have better stability and durability. The composite organic acid system controls the Ca... 2+ The release rate of ettringtonite slows down and controls the formation process, allowing the generated ettringtonite to be evenly distributed within the gel matrix, providing reinforcement rather than causing destructive expansion in the hardened structure due to subsequent reactions. In contrast, in an alkaline-activated environment, a large amount of free Ca... 2+ Will react with OH - It combines to form Ca(OH)2, or forms C4AH with the aluminum phase. 13Ca(OH)₂ is readily soluble in water, especially in acidic or soft water environments. Its dissolution increases porosity and reduces strength. C₄AH 13 In a high sulfate environment, Ca(OH)2 reacts to form expansive ettringite or gypsum, generating huge internal stress, which leads to material cracking and spalling.

[0021] The organic acid-activated solid waste-based gelling material provided by this invention utilizes widely available and easily obtained organic acids, avoiding the risks associated with on-site storage of strong inorganic acids. Furthermore, its ease of on-site application stems from the absence of high-temperature equipment and its simple operation. This organic acid-activated solid waste-based gelling material can effectively dispose of siliceous aluminate solid waste and, compared to activation systems using strong alkalis or strong acids, exhibits lower energy consumption and lower cost. It effectively avoids the drawbacks of strong alkali and strong acid systems, and the prepared gelling material possesses better compressive strength, resulting in excellent overall product performance.

[0022] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0023] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0024] Figure 1 This is a gradation diagram of the aggregate for crushed stone that is yet to be stabilized. Detailed Implementation

[0025] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that this disclosure will be more complete and fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar structures, and therefore detailed descriptions of them will be omitted. Furthermore, the drawings are merely illustrative of this disclosure and are not necessarily drawn to scale.

[0026] This invention provides an organic acid-activated solid waste-based cementitious material, comprising 90-105 parts by weight of a silica-alumina solid waste base, 7-12 parts by weight of sulfate, and 15.3-19.8 parts by weight of a composite organic acid activator.

[0027] The composite organic acid activator includes a primary acid and polyacrylic acid, wherein the mass of polyacrylic acid is 10% to 40% of the mass of the primary acid; the primary acid is one or a mixture of citric acid and tartaric acid.

[0028] In this invention, the traditional strong base / strong acid activation pathway is abandoned. Instead, a composite organic acid system is adopted, and through the synergistic mechanism of "proton exchange-complexation control", several long-standing technical problems such as activity activation, reaction control, volume stability and durability are solved.

[0029] In one embodiment of this disclosure, the composite organic acid activator further includes a co-acid, which is one or a mixture of more than one of oxalic acid, malic acid, gluconic acid and ascorbic acid; the mass of the co-acid is 20% to 80% of the mass of the main acid.

[0030] Oxalic acid, with its strong acidity, can rapidly dissolve solid waste vitreous, promoting early dissolution efficiency and providing sufficient precursors for the entire hydration reaction. Simultaneously, the calcium oxalate formed by the combination of oxalic acid and calcium ions has low solubility, allowing for direct and efficient control of the free calcium ion concentration. This facilitates a low calcium-to-silicon ratio environment for the hydration reaction, inhibiting the formation of harmful phases. Furthermore, as a co-acid rather than the primary acid, the amount of oxalic acid used is limited, thus effectively removing excess free calcium ions while ensuring sufficient calcium ions participate in the hydration reaction and develop its intensity.

[0031] Among them, malic acid, gluconic acid and ascorbic acid can assist the main acid in dissolving the vitreous body. In addition, they have a strong ability to complex calcium ions, which can work synergistically with the main acid to provide a smoother and more lasting slowing effect, and improve the more precise control of the hydration process.

[0032] In one example, the co-acid in the composite organic acid activator is oxalic acid. In this example, the material temperature can be controlled during the activation and hydration processes, for example, by controlling the material temperature to not exceed 35°C, in order to reduce or avoid the formation of calcium oxalate precipitate. This utilizes the low cost and high solubility of oxalic acid, as well as the risk of excessively high free calcium ion concentration, while ensuring that there is a sufficient concentration of free calcium ions in the system for the hydration reaction.

[0033] In one example, the co-acid in the composite organic acid activator is gluconic acid. In this example, when curing the product formed from the gelling material, the curing humidity can be maintained at no less than 95% to prevent the gluconic acid from carbonizing and becoming ineffective.

[0034] In one embodiment of this disclosure, the mass of polyacrylic acid is 20% to 35% of the mass of the main acid; and the mass of the auxiliary acid is 40% to 70% of the mass of the main acid. Thus, by controlling the amount of main acid, the mass of auxiliary acid, and the mass of polyacrylic acid, better reaction kinetic control can be achieved in the activation and hydration processes.

[0035] In one embodiment of this disclosure, the mass ratio of the primary acid to the secondary acid to the polyacrylic acid is in the range of (3:2:1) to (5:2:1).

[0036] In one example, the composite organic acid activator is a mixture of citric acid, oxalic acid and polyacrylic acid; wherein the mass ratio of citric acid to oxalic acid to polyacrylic acid is (3.8~4.2):(1.8~2.2):1; for example, the mass ratio of citric acid to oxalic acid to polyacrylic acid is 4:2:1.

[0037] In one embodiment of this disclosure, the sulfate has an SO3 content of not less than 38% and a specific surface area of ​​not less than 500 m² / kg. This ensures that the sulfate has high activity to rapidly provide initial sulfate ions, guaranteeing the effective formation of ettringite.

[0038] In one embodiment of this disclosure, the sulfate is one of desulfurized gypsum and phosphogypsum, or a mixture of the two. Thus, the sulfate can simultaneously provide sulfate and calcium ions for the hydration process, promoting the formation of ettringite. It is understood that the calcium ions provided by desulfurized gypsum or phosphogypsum can be effectively complexed with organic acids to achieve a slow-release effect. This avoids both the problem of low calcium ion concentration in the early stages of activation and the problem of excessively high concentration of free calcium ions during activation.

[0039] In one example, the sulfate is desulfurized gypsum, especially dehydrated desulfurized gypsum.

[0040] In one embodiment of this disclosure, the silicon-aluminate solid waste base material is composed of one or more silicon-aluminate industrial solid wastes, such as micro powders of various silicon-aluminate industrial solid wastes.

[0041] Optionally, the silica-alumina solid waste base material is selected from two or more of the following: fly ash, blast furnace slag powder, steel slag powder, coal gangue powder, red mud powder, copper slag powder, nickel slag powder, calcium carbide slag powder, and metakaolin powder. When the silica-alumina solid waste base material includes two or more solid wastes, each solid waste can be ground separately and then mixed, or they can be mixed and then ground.

[0042] In one embodiment of this disclosure, the silica-alumina solid waste base material includes high-calcium solid waste micro powder and low-calcium high-silica-alumina solid waste micro powder; the mass of the low-calcium high-silica-alumina solid waste micro powder is 0.4 to 2.5 times the mass of the high-calcium solid waste micro powder. For example, the mass ratio of low-calcium high-silica-alumina solid waste micro powder to high-calcium solid waste micro powder is (3:7) to (7:3).

[0043] In this invention, the CaO content of the high-calcium solid waste powder is not less than 15%; the CaO content of the low-calcium, high-silicon-aluminum solid waste powder is less than 15%. In this invention, the ratio of high-calcium solid waste powder to low-calcium, high-silicon-aluminum solid waste powder can be adjusted, thereby regulating the calcium-silicon ratio, silicon-aluminum ratio, etc., in the system, thus controlling the hydration process and the formation process of ettringite, as well as adjusting the morphology and composition of the products.

[0044] In one embodiment of this disclosure, the high-calcium solid waste powder includes one or more of blast furnace slag powder, steel slag powder, and carbide slag powder.

[0045] In one embodiment of this disclosure, the low-calcium, high-silicon-aluminum solid waste powder includes one or more of fly ash, coal gangue powder, red mud powder, and metakaolin powder.

[0046] In one example, the silica-alumina solid waste base material includes blast furnace slag powder and fly ash, with the mass ratio of blast furnace slag powder to fly ash being (2:3) ~ (3:2).

[0047] In one embodiment of this disclosure, the D90 particle size of the aluminosilicate solid waste base material is no greater than 20 micrometers. This ensures that the aluminosilicate solid waste base material has a large specific surface area and is fully activated, thereby improving the performance of the cementitious material.

[0048] In one example, the dry material formed by combining silica-alumina solid waste and sulfate has a D90 particle size of no more than 20 micrometers, which ensures that the sulfate is fully activated.

[0049] In one example, the dry material formed by uniformly mixing silicon-aluminum solid waste base material and sulfate can be ground to a D90 particle size of no more than 20 micrometers.

[0050] In one example, the components of the composite organic acid activator other than polyacrylic acid can be uniformly mixed with the ground dry material (i.e., a mixture of silicoaluminous solid waste base material and sulfate). In this example, the silicoaluminous solid waste base material, sulfate, and the components of the composite organic acid activator other than polyacrylic acid can be premixed together. During use, polyacrylic acid can be added to water to form a polyacrylic acid aqueous solution; then, the premix of the silicoaluminous solid waste base material, sulfate, and the components of the composite organic acid activator other than polyacrylic acid is mixed and stirred with the polyacrylic acid aqueous solution to activate the solid waste-based cementitious material. Furthermore, when activating the solid waste-based cementitious material with water, the mass of water is 0.35 to 0.5 times the mass of the dry material, for example, 0.45 times.

[0051] Optionally, in this example, if the solid waste-based cementitious material needs to be used with aggregates, the premix (a mixture of components other than polyacrylic acid in the silica-alumina solid waste base, sulfate, and composite organic acid activator) can be mixed with the aggregates, and then polyacrylic acid aqueous solution can be added for mixing and stirring.

[0052] In another example, the ground dry material and the composite organic acid activator can be packaged separately. The components of the composite organic acid activator can be packaged separately, or the components other than polyacrylic acid can be packaged together while the polyacrylic acid is packaged separately. Before use, the silica-alumina solid waste base material and sulfates do not come into contact with the composite organic acid activator; therefore, even if they become damp due to storage conditions, they will not be prematurely activated, which effectively extends the shelf life of the organic acid-activated solid waste-based cementitious material. During use, the dry material can be mixed with the composite organic acid activator and then activated with water; alternatively, the composite organic acid activator can be pre-dissolved in water, and the aqueous solution of the composite organic acid activator can be mixed with the dry material to activate the cementitious material. It is understood that if aggregates are required, they can be added during activation (e.g., crushed stone, sand, clay, etc.).

[0053] In one embodiment of this disclosure, the organic acid-activated solid waste-based cementitious material can be prepared and used in a way that allows it to be used immediately after preparation.

[0054] Step S1: The silica-alumina solid waste base material and sulfate (e.g., desulfurized gypsum) are mixed evenly to obtain a dry material. Further, the silica-alumina solid waste base material and sulfate are ground evenly until the D90 particle size is no greater than 20 micrometers.

[0055] Step S2: Dissolve the components of the composite organic acid activator, except for polyacrylic acid, in water to form a weak acid solution; add polyacrylic acid to the weak acid solution to form a composite organic acid activator solution.

[0056] In this step, if the composite organic acid activator does not contain a secondary acid, the primary acid can be prepared into a weak acid solution, and then polyacrylic acid can be added to the weak acid solution. If the composite organic acid activator contains a secondary acid, the primary acid and the secondary acid can be prepared together into a weak acid solution, and then polyacrylic acid can be added to the weak acid solution to form a composite organic acid solution.

[0057] Optionally, when preparing a weak acid solution, the mass of water added is 0.35 to 0.5 times the mass of the dry material, for example, 0.45 times.

[0058] Optionally, the pH of the complex organic acid solution is 3.5–4.5. In this example, a dilute citric acid solution or sodium hydroxide solution can also be used to adjust the pH to 3.9–4.1. Of course, no adjustment is necessary.

[0059] Step S3: Mix the dry material and the composite organic acid solution, and stir thoroughly to obtain an activated gelling material slurry.

[0060] Optionally, if the organic acid-activated solid waste-based cementitious material needs to be used with aggregates, then in step S3, the dry material, aggregates and composite organic acid solution can be mixed and stirred thoroughly to obtain a slurry of aggregates and cementitious material.

[0061] In one example, the stirring reaction temperature was 30~40℃, the stirring speed was 1000~1800rpm, and the time was 20~40min.

[0062] Optionally, when the auxiliary acid contains oxalic acid, the stirring temperature is ≤35℃ to prevent the formation of calcium oxalate precipitate and inhibit the gelation reaction.

[0063] Step S4 involves applying and curing the slurry. For example, the slurry is poured into a mold and vibrated to form the shape. After curing for a certain period, it is demolded to obtain a component or structure made from the solid waste-based cementitious material activated by the organic acid.

[0064] Optionally, curing can be carried out at 20~35℃ with a film covering for 24~48 hours, followed by continued wet curing for 28 days.

[0065] Optionally, when the coagulant contains gluconic acid, the curing humidity should be ≥95% to prevent gluconic acid from carbonizing and becoming ineffective.

[0066] Thus, by taking several embodiments as examples, the composition and properties of the organic acid-activated solid waste-based cementitious material of the present invention will be further illustrated by way of example.

[0067] The fly ash used in the following embodiments and comparative examples of the present invention is Class F fly ash according to the ASTM C618 classification method, and its main components CaO, Al2O3 and SiO2 have mass percentages of 7.08%, 35.14% and 52.12%, respectively, as shown in Table 1.

[0068] The blast furnace slag used in the following embodiments and comparative examples of the present invention has the following mass percentages of main components: CaO, Al2O3, and SiO2, which are 33.12%, 19.06%, and 41.27%, respectively, as shown in Table 1.

[0069] The desulfurized gypsum used in the following embodiments and comparative examples of the present invention has undergone dehydration treatment, and the main components CaO and SO3 have mass percentages of 41.59% and 48.81%, respectively, as shown in Table 1.

[0070] Unless otherwise specified, the specific reagents, materials, methods, and equipment used in the embodiments and comparative examples are all conventional choices in this technical field.

[0071] Table 1: Main Components of Raw Materials

[0072]

[0073] Example 1

[0074] An organic acid-activated solid waste-based cementitious material, the raw materials by weight parts are: 45 parts by weight of fly ash, 45 parts by weight of blast furnace slag, 17.1 parts by weight of composite organic acid activator (citric acid, oxalic acid and polyacrylic acid in a mass ratio of 4:2:1), and 10 parts by weight of desulfurized gypsum.

[0075] The specific preparation and testing processes include the following steps:

[0076] (1) Mix fly ash, blast furnace slag and desulfurized gypsum evenly, and then ball mill until the material D90 particle size is ≤20μm;

[0077] (2) Dissolve citric acid and oxalic acid in deionized water (27.9 parts by mass), stir until completely dissolved, add polyacrylic acid, and continue stirring until completely dissolved to obtain a composite organic acid solution;

[0078] (3) Mix the dry material obtained in step (1) and the composite organic acid solution obtained in step (2), stir at 1500 rpm and 35°C for 30 min, and let stand for 30 min to form an organic acid-sulfate activated gelling material slurry.

[0079] (4) The activated cementitious material slurry obtained in step (3) is poured into a standard 40mm cube specimen. After molding, it is immediately covered with a film to keep it moist. It is cured for 36 hours at a temperature of 30℃ and a relative humidity of ≥95%. After demolding, the specimen continues to be wet-cured in the environment until the test age.

[0080] Example 2

[0081] An organic acid-activated solid waste-based cementitious material, the raw materials by weight parts are: 40 parts by weight of fly ash, 60 parts by weight of blast furnace slag, 18.5 parts by weight of composite organic acid activator (tartaric acid, oxalic acid and polyacrylic acid in a mass ratio of 5:2:1), and 8 parts by weight of desulfurized gypsum.

[0082] The preparation and testing processes are the same as in Example 1.

[0083] Example 3

[0084] An organic acid-activated solid waste-based cementitious material, the raw materials by weight parts are: 60 parts by weight of fly ash, 40 parts by weight of blast furnace slag, 18.8 parts by weight of composite organic acid activator (citric acid, malic acid and polyacrylic acid in a mass ratio of 4:2:1), and 10 parts by weight of desulfurized gypsum.

[0085] The preparation and testing processes are the same as in Example 1.

[0086] Example 4

[0087] An organic acid-activated solid waste-based cementitious material, the raw materials by weight parts are: 60 parts by weight of fly ash, 40 parts by weight of blast furnace slag, 18.5 parts by weight of composite organic acid activator (tartaric acid, ascorbic acid and polyacrylic acid in a mass ratio of 5:2:1), and 8 parts by weight of desulfurized gypsum.

[0088] The preparation and testing processes are the same as in Example 1.

[0089] Example 5

[0090] A method for stabilizing crushed stone using an organic acid-activated solid waste-based cementitious material. The organic acid-activated solid waste-based cementitious material is the cementitious material described in Example 1; the aggregate gradation of the crushed stone to be stabilized is as follows: Figure 1 As shown.

[0091] The method for stabilizing crushed stone includes:

[0092] 1) Through compaction tests, the maximum dry density of the solid waste cementitious material stabilized crushed stone was determined to be 2.514 g / cm³. 3 The optimal moisture content is 6.8%;

[0093] 2) The composite organic acid activator in the organic acid-activated solid waste-based cementitious material is dissolved in water to obtain a composite organic acid solution; wherein, the amount of water added is determined according to the optimum moisture content;

[0094] 3) Mix the dry materials of the crushed stone to be stabilized, the solid waste-based cementitious material, and the composite organic acid solution, and stir evenly to obtain a mixture.

[0095] 4) The mixture is compacted by vibration compaction and then cured according to standard to obtain the specimen of solid waste cementitious material stabilized crushed stone.

[0096] Comparative Example 1

[0097] The only difference from Example 1 is that the addition of oxalic acid and polyacrylic acid is omitted, that is, the composite organic acid activator contains only citric acid (9.8 parts by mass).

[0098] Comparative Example 2

[0099] The only difference from Example 1 is that the addition of polyacrylic acid is omitted, that is, the composite organic acid activator contains citric acid (9.8 parts by weight) and oxalic acid (4.9 parts by weight).

[0100] Comparative Example 3

[0101] The only difference from Example 1 is that the addition of citric acid is omitted, that is, the composite organic acid activator contains oxalic acid (4.9 parts by mass) and polyacrylic acid (2.4 parts by mass).

[0102] Comparative Example 4

[0103] The only difference from Example 1 is that the addition of desulfurized gypsum is omitted, that is, the cementitious material does not contain sulfate.

[0104] Comparative Example 5

[0105] The only difference from Example 5 is that oxalic acid was omitted.

[0106] The cubic specimens prepared in Examples 1-4 and Comparative Examples 1-4 were subjected to compressive strength and sulfate resistance tests. The compressive strength test was conducted according to GB / T 17671. The sulfate resistance test was conducted according to GB / T 749-2008, by measuring the compressive strength of the specimens after long-term immersion in 5% Na2SO4 solution and calculating its strength-corrosion resistance coefficient compared to specimens cured in clean water at the same age. The test results of the 3-day, 7-day, and 28-day compressive strength of the cubic specimens are shown in Table 2. The 90-day and 180-day strength-corrosion resistance coefficients of the cubic specimens are shown in Table 3.

[0107] Table 2: Compressive strength of Examples 1-4 and Comparative Examples 1-4 at different ages

[0108]

[0109] Table 3: Resistance to sulfate attack in Examples 1-4 and Comparative Examples 1-4

[0110]

[0111] As shown in Table 2, the 7-day compressive strength of the specimens prepared in Examples 1 to 4 all exceeded 15 MPa, and the 28-day compressive strength all exceeded 40 MPa. Among them, the specimen prepared in Example 1 had the best overall strength. Example 1 used an optimized ratio of citric acid, oxalic acid, and polyacrylic acid (4:2:1). Citric acid provided strong chelating and dissolving capabilities, oxalic acid effectively controlled the early calcium ion concentration, avoiding the formation of undesirable products, and polyacrylic acid ensured the uniformity and stability of the slurry through steric hindrance. The three components worked synergistically, thus exhibiting the best comprehensive performance.

[0112] Because citric acid has more polarized -COOH groups than tartaric acid, the compressive strength of the specimen in Example 2 is slightly lower than that of the specimen in Example 1. Furthermore, the strength of the specimens in Examples 3 and 4 is lower than that of Examples 1 and 2. This is mainly because malic acid and ascorbic acid are milder acids than oxalic acid, resulting in slightly weaker initial dissolving ability, while oxalic acid can rapidly dissolve solid waste vitreous, promoting early dissolution efficiency and providing sufficient precursors for the entire hydration reaction. Overall, the specimens of all examples exhibit excellent mechanical properties, demonstrating the superior performance of the organic acid-activated solid waste-based cementitious material of the present invention.

[0113] Comparative Examples 1 and 2 lacked the auxiliary acid and polyacrylic acid, respectively, and the workability and strength of their specimens were significantly lower than those of Example 1. This indicates that the combination of the main acid, auxiliary acid, and polyacrylic acid produced a synergistic effect, and none of them can be omitted. Although a single organic acid has a certain activating effect, it is difficult to effectively control the reaction rate and product structure, resulting in poor performance. Comparative Example 3 had the worst performance among the control groups lacking organic components, confirming that citric acid or tartaric acid, as the main acid, is the core driving force for dissolving the vitreous body of slag and fly ash. Lacking its strong chelating ability, Ca 2+ Si 4+ And Al 3+ The dissolution of ions was severely inhibited, hindering subsequent hydration reactions. Comparative Example 4 showed insufficient ettringite due to the lack of desulfurized gypsum, which prevented it from solidifying and resulting in a lack of strength. This indicates that sulfates are indispensable for forming a strong framework.

[0114] As shown in Table 3, all specimens from the various embodiments exhibited excellent resistance to sulfate attack. After 180 days of immersion, their strength and corrosion resistance coefficients remained above 94%, indicating that they not only possess resistance but also stability in sulfate environments. This is attributed to the system primarily generating CSH gel with a low calcium-to-silica ratio and stable ettringite, while avoiding the large-scale formation of C4AH, which is susceptible to sulfate attack, under highly alkaline conditions. 13 The system exhibits a stable chemical environment, effectively preventing the formation of vulnerable phases. In contrast, the comparative sample has a porous structure, providing pathways for ion invasion. Furthermore, the incomplete hydration reaction leaves behind a large amount of vulnerable active aluminum phase and unhydrated particles, which undergo a destructive expansion reaction in a sulfate environment.

[0115] In summary, the organic acid-activated solid waste-based cementitious material of the present invention has good mechanical properties and durability, while its cost and energy consumption are lower than those of traditional strong acid and strong alkali activated cementitious materials.

[0116] The specimens prepared in Example 5 and Comparative Example 5 were subjected to performance tests, and the test results are shown in Tables 4 and 5.

[0117] Table 4: Mechanical properties of Example 5 and Comparative Example 5

[0118]

[0119] Table 5: Durability performance of Example 5 and Comparative Example 5

[0120]

[0121] As can be seen from the test results in Tables 4 and 5, the solid waste-based cementitious material of this invention can still achieve a high stabilization effect when stabilizing crushed stone, even with a dosage of 5%. Meanwhile, the lack of oxalic acid in the composite organic acid activator adversely affects the strength development, toughness, and durability of the formed stable crushed stone body (the stable crushed stone body formed by the cementitious material).

[0122] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the appended claims.

Claims

1. An organic acid-activated solid waste-based cementitious material, characterized in that, It is composed of the following materials: 90-105 parts by weight of silicon-aluminum solid waste base material, 7-12 parts by weight of sulfate and 15.3-19.8 parts by weight of composite organic acid activator; The composite organic acid activator is composed of a primary acid, a secondary acid, and polyacrylic acid, wherein the mass of polyacrylic acid is 10% to 40% of the mass of the primary acid; the primary acid is one or a mixture of citric acid and tartaric acid; the secondary acid is one or a mixture of oxalic acid, malic acid, gluconic acid, and ascorbic acid; and the mass of the secondary acid is 20% to 80% of the mass of the primary acid.

2. The organic acid-activated solid waste-based cementitious material according to claim 1, characterized in that, The mass of polyacrylic acid is 20% to 35% of the mass of the main acid; the mass of the auxiliary acid is 40% to 70% of the mass of the main acid.

3. The organic acid-activated solid waste-based cementitious material according to claim 1, characterized in that, The composite organic acid activator is a mixture of citric acid, oxalic acid and polyacrylic acid; wherein, the mass ratio of citric acid to oxalic acid to polyacrylic acid is (3.8~4.2):(1.8~2.2):

1.

4. The organic acid-activated solid waste-based cementitious material according to claim 1, characterized in that, The sulfate has an SO3 content of not less than 38% and a specific surface area of ​​not less than 500 m² / kg.

5. The organic acid-activated solid waste-based cementitious material according to claim 1, characterized in that, The sulfate is one or a mixture of desulfurized gypsum and phosphogypsum.

6. The organic acid-activated solid waste-based cementitious material according to any one of claims 1 to 5, characterized in that, The silicon-aluminum solid waste base material includes high-calcium solid waste micro powder and low-calcium high-silicon-aluminum solid waste micro powder; the mass of the low-calcium high-silicon-aluminum solid waste micro powder is 0.4 to 2.5 times the mass of the high-calcium solid waste micro powder. The CaO content of the high-calcium solid waste powder is not less than 15%; the CaO content of the low-calcium high-silicon-aluminum solid waste powder is less than 15%.

7. The organic acid-activated solid waste-based cementitious material according to claim 6, characterized in that, The high-calcium solid waste powder includes one or more of blast furnace slag powder, steel slag powder, and carbide slag powder.

8. The organic acid-activated solid waste-based cementitious material according to claim 6, characterized in that, The low-calcium, high-silicon, aluminum solid waste powder includes one or more of the following: fly ash, coal gangue powder, red mud powder, and metakaolin powder.

9. The organic acid-activated solid waste-based cementitious material according to claim 6, characterized in that, The D90 particle size of the silicon-aluminum solid waste base material is no greater than 20 micrometers.

Images