Alkali residue engineering soil curing agent for road and alkali residue engineering soil material cured by alkali residue engineering soil curing agent

Abstract

The invention provides a road alkali residue engineering soil curing agent and an alkali residue engineering soil material cured by the curing agent, and belongs to the technical field of comprehensive utilization of alkali residue engineering soil. The curing agent provided by the invention comprises a gelling component and an alkali excitation component, the curing agent is used for curing the alkaline residue engineering soil, the mechanical strength of the alkaline residue engineering soil is remarkably improved, and the leaching concentration of chloride ions and sulfate ions is reduced. The curing agent can effectively improve the pavement performance and environmental safety performance of the alkaline residue engineering soil, and solves the problem that the alkaline residue engineering soil is difficult to be used as a road filler.

Description

Technical Field

[0001] This invention relates to a road-use alkali slag engineering soil solidifier and the solidified alkali slag engineering soil material thereof, belonging to the field of comprehensive utilization technology of alkali slag engineering soil. Background Technology

[0002] my country is one of the world's largest producers of solid waste, generating over 10 billion tons of new solid waste annually, with a historical stockpile totaling 60-70 billion tons. The sheer volume of solid waste generation, inefficient recycling, illegal transfer and dumping, and difficulties in disposal are increasingly prominent problems, seriously impacting sustainable economic and social development. With the development of road construction in my country, the construction and maintenance of road projects consume over 10 billion tons of sand, gravel, and other materials annually, currently facing challenges such as raw material shortages, transportation difficulties, and high carbon emissions. As China's sustainable development strategy continues to advance, new requirements are being placed on achieving green and environmentally friendly goals in highway construction.

[0003] Alkali slag, a novel type of industrial solid waste, is characterized by high pH and high chloride content, making it difficult to utilize efficiently. While pretreatment with small amounts of fly ash, loess, and sulfuric acid to create alkali slag engineering soil can reduce its salt content to some extent, its modification effect is generally limited. The leaching concentrations of chloride and sulfate ions in the alkali slag engineering soil remain higher than the Class IV groundwater standard; furthermore, its mechanical strength is typically between 0.2 and 0.4 MPa, which is low and prevents its application in road construction.

[0004] In summary, the mechanical properties (strength, water stability) and environmental safety performance (sulfate ion and chloride ion leaching concentration) of alkali slag engineering soil cannot meet the requirements of road construction fillers. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a road-grade alkali slag engineering soil solidifier and the solidified alkali slag engineering soil material thereof. The selected solid waste-type solidifier comprises a cementing component and an alkali-activating component. The cementing component is one or more of granulated blast furnace slag powder, fly ash, or steel slag; the alkali-activating component is one or more of carbide slag, red mud, magnesium oxide, or sodium hydroxide. The silicon and calcium elements in the cementing component, after activation by the alkali-activating component, undergo a pozzolanic reaction with the metal ions in the alkali-activating component. The resulting cementitious product enhances the mechanical properties of the alkali slag engineering soil while reducing the leaching concentrations of chloride and sulfate ions. This solidifier effectively improves the road performance and environmental safety performance of alkali slag engineering soil, solving the problem that alkali slag engineering soil is difficult to use as road filler.

[0006] The present invention adopts the following technical solution: In one aspect, the present invention provides a road-use alkali slag engineering soil solidifier, comprising a cementing component and an alkali-activating component; the cementing component is one or more of granulated blast furnace slag powder, fly ash, or steel slag; the alkali-activating component is one or more of carbide slag, red mud, magnesium oxide, or sodium hydroxide; the mass ratio of the cementing component to the alkali-activating component is 14 / 1; the solidifier solidifies the alkali slag engineering soil, significantly improving the mechanical strength of the alkali slag engineering soil and reducing the leaching concentration of chloride ions and sulfate ions.

[0007] Fly ash, blast furnace slag, steel slag, and other bulk solid wastes, when used as solidifying agents, contain large amounts of amorphous SiO2 and Al2O3, making them excellent active mineral admixtures. The alkalinity of alkali-activated components in alkali-slag engineering soil and other solid wastes can, to a certain extent, activate the activity of cementitious components, promoting the rapid hydration of clinker minerals (such as tricalcium silicate and dicalcium silicate) in the solidifying agent, generating a large number of hydration products, such as CSH gel and Ca(OH)2. At the same time, CAH reacts with CaSO4 to generate AFt crystals. Alkali-activated cementitious materials have the characteristics of early strength, good mechanical properties, and dense structure, thus improving the strength of alkali-slag engineering soil.

[0008] Compared to traditional quicklime, alkali-activated solid waste-type solidifiers exhibit higher resistance to sulfate and chloride ion erosion, making them a promising candidate for preparing solidified alkali slag engineering soil. The addition of slag enhances the solidification capacity of alkali slag engineering soil for chloride and sulfate ions, which is related to the denser CASH gel produced by the slag reaction, forming a more tortuous pore structure. Furthermore, the reaction of alkali-activated granulated blast furnace slag powder and fly ash generates a layered double hydroxide (LDH) phase, which typically exhibits better chloride ion adsorption capacity than CASH and NASH. The addition of steel slag and red mud can increase the Al and Fe content to some extent, contributing to LDH formation. Sulfate ions are fixed by the solidifier through mineral phase transformation, changing from soluble sodium sulfate and potassium sulfate phases to insoluble AFt and calcium sulfate phases, thus reducing the sulfate ion leaching concentration in the system.

[0009] The density of granulated blast furnace slag powder is not less than 2.8 g / cm³. 3 Specific surface area not less than 400m² 2 / kg, after 28 days of standard curing, the activity index is not less than 95%, the fluidity ratio is not less than 95%, and the moisture content is less than 1%; the fly ash fineness is not higher than 30%, the water requirement is not higher than 105%, the loss on ignition is not higher than 8%, the calcium oxide content is not lower than 10%, and the density is not higher than 2.6g / cm³. 3 The strength activity index is not less than 70%, and the moisture content is less than 1%; the density of steel slag is not less than 3.2 g / cm³. 3 Specific surface area not less than 350m²2 per kg, the content of free calcium oxide is less than 4%, the chloride ion content is less than 0.06%, the activity index after standard curing for 28 days is not less than 80%, and the water content is less than 1%; the calcium hydroxide content in carbide slag is not less than 60%, the mesh number is not less than 200 meshes, and the water content is less than 1%; the red mud is Bayer red mud, the pH value is less than 12.5, and the average particle size is less than 15 μm; the magnesium oxide content is not less than 75%, the activity is not more than 100 s, and the water content is less than 1%; the sodium hydroxide content is not less than 70%, the sodium sulfate content is less than 0.5%, and the sodium chloride content is less than 0.05%.

[0010] In another aspect of the present invention, there is provided a solidified alkali residue engineering soil material. The above-mentioned curing agent is used to solidify the alkali residue engineering soil to form the solidified alkali residue engineering soil material; the alkali residue engineering soil material includes alkali residue engineering soil and the above-mentioned curing agent; the mass ratio of the alkali residue engineering soil to the curing agent is 1:0.1 to 0.2; the water content of the alkali residue engineering soil material is 45% to 55%.

[0011] Further, the alkali residue engineering soil includes 75% to 85% of alkali residue, 3% to 5% of fly ash, 4% to 8% of iron tailing sand, and 8% to 12% of loess; the pH value of the alkali residue engineering soil is 7.5 to 9.2, and it belongs to high liquid limit silt soil.

[0012] Further, the total amount of easily soluble salts in the alkali residue engineering soil is <5%, the total amount of chloride ions is 1.20 to 1.40%, the concentration of sulfate ions is 0.30 to 0.40%, and 1 < C(Cl - ) / 2C(SO4 2- ) < 2 belongs to chlorite saline soil, and 1% < C (content of easily soluble salts) < 5% belongs to medium saline soil.

[0013] Further, the leaching concentration of chloride ions in the alkali residue engineering soil is lower than 1400 mg / L; the leaching concentration of sulfate ions in the alkali residue engineering soil is lower than 800 mg / L.

[0014] In another aspect of the present invention, there is also provided a preparation method of the above-mentioned alkali residue engineering soil material, including the following steps: Step 1, mix the alkali residue engineering soil, the curing agent and water; Step 2, form by static compaction method; Step 3, carry out constant temperature and humidity curing to obtain the alkali residue engineering soil material.

[0015] Further, in the step 3, the curing temperature is 23 ± 1 °C; the relative humidity for curing is 98%; the curing age is set to 7 days or 28 days.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) The curing agent provided by the present invention uses bulk solid waste such as fly ash, blast furnace slag, and steel slag as raw materials. It not only realizes the recycling of resources and demonstrates excellent environmental friendliness, but also consumes a large amount of solid waste to a certain extent, improves the utilization rate of bulk industrial solid waste, and significantly reduces the production cost of curing agent. At the same time, the use of solid waste type curing agent can reduce the dependence on traditional road construction materials (such as quicklime) and further reduce engineering costs.

[0017] (2) The curing agent provided by the present invention uses bulk solid wastes such as fly ash, blast furnace slag, and steel slag as raw materials, which can replace a large amount of traditional road construction materials, thereby reducing the amount of greenhouse gas emissions such as carbon dioxide generated during the production, transportation and use of these materials, which is beneficial to ecological environmental protection.

[0018] (3) By optimizing the curing agent formula, this invention significantly improves the unconfined compressive strength of alkali slag engineering soil materials. Under the action of alkali-activated components, fly ash, steel slag and blast furnace slag generate cementitious products through pozzolanic reaction, enhance the release of active calcium, aluminum and silicon elements, and further promote hydration reaction, such as CSH gel, Ca(OH)2, etc. At the same time, CAH reacts with CaSO4 to generate AFt crystals, and alkali-activated cementitious materials improve the density and mechanical properties of materials.

[0019] (4) By optimizing the curing agent formula, the present invention significantly reduces the leaching concentration of chloride and sulfate ions in alkali slag engineering soil. The cementitious products such as CASH, NASH, and LDH generated by the reaction of volcanic ash can fix chloride and sulfate ions, reduce the leaching concentration of chloride and sulfate ions, and improve the environmental safety of road alkali slag engineering soil.

[0020] (5) By optimizing the curing agent formula, the components are varied and exhibit good synergistic effects, which improves the road performance and environmental safety performance of the alkali slag engineering soil, enabling it to meet the requirements of the road construction filler standard. This is of great significance for the large-scale disposal of alkali slag engineering soil. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0022] This invention provides a road-use alkali slag engineering soil solidifier comprising a cementing component and an alkali-activating component; the cementing component is one or more of granulated blast furnace slag powder, fly ash, or steel slag; the alkali-activating component is one or more of carbide slag, red mud, magnesium oxide, or sodium hydroxide; the mass ratio of the cementing component to the alkali-activating component is 14 / 1; the solidifier solidifies the alkali slag engineering soil, significantly improving its mechanical strength and reducing the leaching concentration of chloride and sulfate ions.

[0023] This invention provides a solidified alkali slag engineering soil material. The solidifying agent is used to solidify the alkali slag engineering soil to form the solidified alkali slag engineering soil material. The alkali slag engineering soil material includes alkali slag engineering soil and the solidifying agent. The mass ratio of alkali slag engineering soil to solidifying agent is 1:0.1~0.2. The moisture content of the alkali slag engineering soil material is 45~55%. The alkali slag engineering soil includes 75~85% alkali slag, 3~5% fly ash, 4~8% iron tailings sand, and 8~12% loess. The pH value of the alkali slag engineering soil is 7.5~9.2. The total amount of easily soluble salts in the alkali slag engineering soil is <5%, the total amount of chloride ions is 1.20~1.40%, and the concentration of sulfate ions is 0.30~0.40%. The chloride ion leaching concentration of the alkali slag engineering soil is less than 1400 mg / L. The sulfate ion leaching concentration of the alkali slag engineering soil is less than 800 mg / L.

[0024] This invention provides a method for preparing the above-mentioned alkali slag engineering soil material, comprising the following steps: Step 1: Mix the alkaline slag engineering soil, solidifying agent, and water; Step 2: Static compaction method for molding; Step 3: Curing under constant temperature and humidity to obtain alkaline slag engineering soil material.

[0025] In step 3, the curing temperature is 23±1℃; the relative humidity is 98%; and the curing period is set to 7 days or 28 days.

[0026] Examples 1-6 The specific material dosage of the alkali slag engineering soil material provided by the present invention is shown in Table 1.

[0027] Table 1. Specific implementation material admixture design schemes for alkali slag engineering soil materials in Examples 1-6

[0028] Comparative Examples 1-2 The material dosage of an alkaline slag engineering soil material is shown in Table 2.

[0029] Table 2. Material admixture design scheme for alkali slag engineering soil in Comparative Examples 1-2

[0030] The preparation process of the alkali slag engineering soil materials in Examples 1-6 and Comparative Examples 1-2 includes the following steps: The alkaline slag engineering soil, solidifying agent, and water are mixed and then molded and cured in sequence to obtain alkaline slag engineering soil material.

[0031] This invention refers to the provisions of GB / T 50123-2019 "Standard for Geotechnical Testing Methods", and the diameter and height of the solidified soil strength specimen are 5cm and 10cm respectively, and it is prepared by static compaction method.

[0032] Demolding and curing: After demolding, the specimen is quickly tested for size and mass using vernier calipers and electronic scale. If the deviation of the specimen diameter or height from the design value exceeds 1% or the deviation of the specimen mass from the design value exceeds 1%, the specimen is discarded and a new specimen is prepared. Then, the specimen that meets the requirements is put into a polyethylene sealed bag (to avoid moisture loss) and transferred to a standard curing room (relative humidity 98%, temperature 23±1℃) for curing until the design age.

[0033] Test measurements: Examples 1-6 and Comparative Examples 1-2 were subjected to unconfined compressive strength tests at curing ages of 7 days and 28 days, respectively, in accordance with GB / T50123-2019 "Standard for Geotechnical Testing Methods". After 27 days, they were immersed in distilled pure water for 1 day to conduct water stability tests and ion leaching concentration detection.

[0034] In practical engineering, unconfined compressive strength is one of the most important mechanical indicators for evaluation, and it is a key indicator for determining whether a material meets the requirements for effective service as a roadbed material. The roadbed base, surface cover, and bottom lining all require compaction during construction, necessitating indoor control of the compaction degree of the samples. In this embodiment of the invention, the solidified alkali slag engineering soil material is used in the roadbed base, with a compaction degree controlled at 96%.

[0035] Table 3. Test results of unconfined compressive strength of cured and compacted specimens

[0036] As shown in Table 3, the comparison results of the unconfined compressive strength of the cured and compacted samples of Examples 1-6 and Comparative Examples 1-2 show that the unconfined compressive strength of all samples significantly increased with the increase of curing time. The 28-day unconfined compressive strengths of Examples 1-6 were 5.29 MPa, 5.14 MPa, 6.21 MPa, 6.41 MPa, 5.66 MPa and 5.87 MPa, respectively, all higher than the 28-day unconfined compressive strengths of Comparative Examples 1-2. Compared with Examples 1-4, Comparative Example 1 showed that the alkali slag engineering soil itself had a weak alkali activation effect, while the addition of alkali activator could better activate the activity of fly ash, granulated blast furnace slag powder and steel slag, so that the alkali slag engineering soil could achieve better mechanical properties. The alkali slag engineering soil material prepared by this invention has significant advantages in mechanical properties, especially under longer curing time, exhibiting higher unconfined compressive strength.

[0037] The curing agent and activator exhibit a good synergistic effect. The alkali activator catalyzes the hydration process of raw materials such as granulated blast furnace slag powder, fly ash, and steel slag, promoting the dissolution of silicates and aluminates in these raw materials under alkaline conditions to form intermediate products such as sodium silicate and sodium aluminate. Subsequently, these intermediate products continue to react with other components in the alkali activator (such as calcium ions) to generate various gel substances such as hydrated calcium silicate and hydrated calcium aluminate. These gel products not only have excellent gelling properties, effectively filling the pores inside the raw materials and improving the density and strength of the materials, but also enhance the stability of the material's microstructure, thereby comprehensively improving the overall strength of the materials.

[0038] Water stability is a key indicator for determining whether a material meets the requirements for effective service in subgrade applications. In subgrade applications, the stability of materials in the presence of water is crucial, representing the material's ability to effectively maintain its performance under water erosion after curing. The ratio of the unconfined compressive strength of a water-soaked sample to that of a standard-cured sample is defined as the water stability coefficient (Kr). A higher water stability coefficient indicates better water stability. Simultaneously, the strength loss rate is defined as the percentage of the difference between the unconfined compressive strength of a standard-cured sample of the same age and that of a water-soaked sample, compared to the unconfined compressive strength of a standard-cured sample of the same age. This invention compares samples cured for 28 days with samples cured for 27 days and then soaked in water for 1 day. The water stability results of the cured alkaline slag engineering soil are shown in Table 4. The results indicate that, under the same alkaline slag engineering soil and curing age, the curing results using the curing agent proposed in this invention are superior to those using traditional quicklime curing.

[0039] Table 4. Water stability of solidified alkali slag engineering soil materials

[0040] The curing agent provided by this invention exhibits significant advantages over quicklime in terms of water stability. Granulated blast furnace slag powder and fly ash contain a large amount of potentially active silicon and calcium components. When these components come into contact with strongly alkaline activators (such as carbide slag, red mud, or magnesium oxide), a pozzolanic reaction is initiated. This reaction not only effectively fills the pores inside the material but also significantly improves the material's strength properties. The calcium ions in the system react chemically with the sulfate ions abundant in the alkaline slag engineering soil, promoting the early formation of high-strength ettringite (AFt), accelerating the hydration reaction rate, further refining the pore structure, and thus significantly enhancing the material's water stability.

[0041] Environmental safety is often overlooked during road construction. Alkali-slag engineering soil, a type of saline soil containing high levels of chloride and sulfate ions, can significantly impact the surrounding soil and groundwater if these ions are not fixed. Accumulation of chloride and sulfate ions in the soil leads to salinization, damaging soil structure. High-salt environments inhibit plant root absorption and growth, affecting ecosystem stability and biodiversity. Chloride ions have strong migration capabilities in water bodies and easily enter groundwater systems through infiltration, causing groundwater pollution. Polluted groundwater not only affects drinking water safety but may also adversely impact agricultural irrigation. Furthermore, the complexation of heavy metals by chloride ions increases the solubility of sparingly soluble heavy metals and reduces the adsorption capacity of soil colloids for heavy metals, thereby increasing the migration of heavy metals in the environment and causing secondary pollution. This invention controls the compaction degree to 96% and employs a batch leaching test method. Referring to the "Leaching Toxicity Method for Solid Waste - Horizontal Oscillation Method" (HJ / T 557-2010), the leaching concentration must be lower than the Class IV standard for groundwater, and referring to the "Groundwater Quality Standard" (GB / T14848-2017). Table 5 shows the comparison of chloride and sulfate ion leaching concentrations of the solidified and compacted samples from Examples 1-6 and Comparative Examples 1-2 after 27 days of standard curing followed by 1 day of immersion in water.

[0042] Table 5 Results of chloride and sulfate ion leaching tests on cured and compacted samples

[0043] As shown in Table 5, it can be seen that alkali-activated gelling and curing agents have a superior ability to fix chloride ions compared to traditional quicklime. This is related to the denser CASH gel produced by the reaction of granulated blast furnace slag powder, which forms a more tortuous pore structure. Fly ash, under the action of alkali activation, generates NASH and other gelling substances, which have a better ability to fix chloride ions than CASH. In addition, iron tailings sand in alkali slag engineering soil and Fe and Al in fly ash and steel slag in the curing agent will also generate another type of secondary reaction product, LDH, under the action of alkali activation. LDH usually has a better adsorption capacity for chloride ions than CASH and NASH. Using red mud as an activator can increase the content of Al and Fe to a certain extent, which is conducive to the formation of LDH. Using quicklime as a curing agent can only meet the mechanical performance requirements of road filler, while the chloride ion leaching concentration far exceeds the Class IV groundwater standard limit.

[0044] In summary, this invention provides a road-use alkali slag engineering soil solidifier that solidifies alkali slag engineering soil, significantly improving its mechanical strength and reducing the leaching concentration of chloride and sulfate ions. This solidifier effectively improves the road performance and environmental safety of alkali slag engineering soil, solving the problem that alkali slag engineering soil is difficult to use as road filler.

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any form or substance. It should be noted that those skilled in the art can make various improvements and additions without departing from the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention. Any modifications, alterations, and equivalent changes made by those skilled in the art based on the above-disclosed technical content without departing from the spirit and scope of the present invention are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and evolutions made to the above embodiments based on the essential technology of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A road-use alkaline slag engineering soil stabilizer, characterized in that, It includes a cementing component and an alkali-activating component; the cementing component is one or more of granulated blast furnace slag powder, fly ash, or steel slag; the alkali-activating component is one or more of carbide slag, red mud, magnesium oxide, or sodium hydroxide; the mass ratio of the cementing component to the alkali-activating component is 14 / 1; the curing agent solidifies the alkali slag engineering soil, significantly improving the mechanical strength of the alkali slag engineering soil and reducing the leaching concentration of chloride ions and sulfate ions.

2. A solidified alkali slag engineering soil material, characterized in that, The curing agent of claim 1 is used to cure alkali slag engineering soil to form a cured alkali slag engineering soil material; the alkali slag engineering soil material includes alkali slag engineering soil and the curing agent of claim 1; the mass ratio of the alkali slag engineering soil to the curing agent is 1:0.1~0.2; the moisture content of the alkali slag engineering soil material is 45~55%.

3. The alkali slag engineering soil material according to claim 2, characterized in that, The alkali slag engineering soil comprises 75-85% alkali slag, 3-5% fly ash, 4-8% iron tailings sand, and 8-12% loess; the pH value of the alkali slag engineering soil is 7.5-9.

2.

4. The alkali slag engineering soil material according to claim 2, characterized in that, The total amount of easily soluble salts in the alkali slag engineering soil is <5%, the total amount of chloride ions is 1.20~1.40%, and the concentration of sulfate ions is 0.30~0.40%.

5. The alkali slag engineering soil material according to claim 4, characterized in that, The chloride ion leaching concentration of the alkali slag engineering soil is less than 1400 mg / L; the sulfate ion leaching concentration of the alkali slag engineering soil is less than 800 mg / L.

6. A method for preparing alkali slag engineering soil material as described in any one of claims 2-5, characterized in that, Includes the following steps: Step 1: Mix the alkaline slag engineering soil, solidifying agent, and water; Step 2: Static compaction method for molding; Step 3: Curing under constant temperature and humidity to obtain alkaline slag engineering soil material.

7. The method for preparing alkali slag engineering soil material according to claim 6, characterized in that, In step 3, the curing temperature is 23±1℃; the relative humidity is 98%; and the curing period is set to 7 days or 28 days.

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