A cured sulphate-salt sodic soil base prepared using a constraint process

Abstract

The application discloses a kind of solidified sulphate saline soil base prepared by using constraint process, belong to traffic engineering field.Its characteristics are: the preparation material of solidified sulphate saline soil base includes soil body, solidifying agent, water, soil body is sulphate saline soil with salt content 1-50%, use slow type material as cementing component of solidifying agent, use the material that quick hydration and with sulphate ion in soil to generate swelling hydrate as swelling component of solidifying agent;Swelling component includes not limited to by aluminium slag, alkaline waste residue, gypsum waste residue or sulphate waste residue etc.composition mixture;According to the strength design value of sulphate saline soil itself property and solidified sulphate saline soil base, select specific rolling mechanical, rolling rate, rolling frequency and constraint load value, solidifying agent is mixed with sulphate saline soil near optimum moisture content with fixed water-cement ratio uniformly, using rolling mechanical compaction and under constraint load maintenance 7 days after constraint removal, obtain solidified sulphate saline soil base.

Description

Technical Field

[0001] This invention relates to a solidified sulfate soil base course prepared using a constraint process, belonging to the field of transportation engineering. Background Technology

[0002] Sulfate ions, especially high-content sulfates, often cause severe corrosion to silicate-based cement base courses, posing a significant challenge to road and airport construction. Currently, base course materials mainly use silicate-based cement, crushed stone, and gravel. The production of silicate-based cement results in massive carbon emissions, and the over-exploitation of crushed stone and gravel causes serious damage to natural resources. Therefore, developing a new type of base course that is low-carbon, environmentally friendly, economical, and exhibits good durability in sulfate environments is of great significance.

[0003] The constrained solidification technology utilizes a solidifying agent containing an expansive component, organically combining it with the constrained structure to achieve soil resource utilization. Under constrained conditions, the compaction effect of the expansive component significantly improves the strength of the solidified soil, as detailed in patents "Construction Method for Solidified Soil Piles" (ZL201610183422.6) and "Treatment Method for Contaminated Soil" (201610184702.9). This technology primarily uses ordinary Portland cement as the main binding material. However, the corrosive effect of sulfate ions on Portland cement products limits its application in sulfate-saline soil areas, and the production of Portland cement generates significant carbon emissions. Furthermore, under the premise of constant expansive and binding component content in the solidifying agent, combinations of expansive and binding components with different hydration rates result in significantly different solidified soil strengths, hindering further improvements in solidified soil strength.

[0004] Based on this, the present invention proposes a solidified sulfate soil base course prepared using a constraint process. Summary of the Invention

[0005] This invention proposes a solidified sulfate soil base course prepared using a constrained process, aiming to provide a new type of base course that is low-carbon, environmentally friendly, economical, and durable for sulfate soil areas. The resulting solidified sulfate soil base course has good load-bearing capacity, water stability, and durability. It realizes the complete replacement of silicate cement as a cementing component with industrial waste residue and the use of locally sourced sulfate soil as the base course preparation material, which can significantly save carbon emissions, building material consumption, and engineering costs of the base course.

[0006] This invention proposes a method for preparing a solidified sulfate-alkali soil base course using a constrained process. Specifically, the preparation materials for the solidified sulfate-alkali soil base course include soil, a solidifying agent, and water. The soil is sulfate-alkali soil with a salt content of 1-50%. The solidifying agent consists of a cementing component and an expansion component. A material with a slow hydration rate is used as the cementing component of the solidifying agent, while a material that hydrates rapidly and forms expanding hydrates with sulfate ions in the soil is used as the expansion component. The mass ratio of the cementing component to the expansion component in the solidifying agent is 35-85:15-65, respectively. Based on sulfate... The specific compaction machinery, compaction rate, number of compaction passes, and constraint load value are selected based on the properties of the soil itself and the design value of the solidified sulfate soil base course. The water-cement ratio of the curing agent and the moisture content of the sulfate soil are controlled. The curing agent is mixed evenly with the sulfate soil at a fixed water-cement ratio and near the optimum moisture content, compacted by compaction machinery, and cured under constraint load for 7 days before the constraint is removed to obtain the solidified sulfate soil base course. This invention can realize the resource utilization of sulfate and the reduction of carbon in the base course, and significantly reduce the cost of base course engineering. The solidified sulfate soil base course has good bearing capacity, water stability, and durability.

[0007] The compaction rate range of the present invention is 1-8 km / h; the curing under constrained load refers to setting a constrained load on the surface of the solidified sulfate soil after compaction. The method of setting the constrained load includes, but is not limited to, laying a flexible geotextile on the surface of the compacted solidified sulfate soil and covering it with a soil load of equal thickness, or laying a sheet sandbag load of equal thickness on the surface of the compacted solidified sulfate soil.

[0008] The cementing component of this invention is a material with a slow hydration rate, and the cementitious hydrates produced by its hydration include, but are not limited to, hydrated calcium silicate. The cementing component is composed of cementing materials and activators, with the mass ratio of cementing materials and activators in the cementing component being 70~100:0~30, respectively. The cementing materials include, but are not limited to, one or more combinations of slag, copper slag, phosphorus slag, coal gangue, bottom ash, rice husk ash, kiln ash, etc. The activator is an alkaline activator, including, but not limited to, one or more combinations of quicklime, hydrated lime, active magnesium oxide, sodium hydroxide, hydrated sodium silicate, etc.

[0009] The expansion component of this invention is a rapidly hydrating material. The expansion component rapidly hydrates with sulfate ions in the soil to generate an expansion hydrate. The expansion hydrate generated by the hydration of the expansion component includes, but is not limited to, hydrated calcium sulfoaluminate. The expansion component includes, but is not limited to, a mixture composed of aluminum-containing waste residue, alkaline waste residue, gypsum-based waste residue, or sulfate waste residue.

[0010] The cementing component described in this invention requires the selection of an activator based on the hydration rate of the cementing component design, and the specific ratio of cementing material and activator in the cementing component is determined through preliminary experiments.

[0011] The expansion component described in this invention needs to be determined according to the sulfate ion content in the sulfate-saline soil and the chemical equation for the formation of expansion hydrates by hydration, and the specific proportion of each component material in the expansion component needs to be determined by a known calculation method.

[0012] The curing agent described in this invention comprises industrial-grade materials, all of which have a specific surface area greater than 150 m². 2 / kg of powder; the dosage of the curing agent is 10~100% of the total dry weight of the curing agent and the sulfated soil.

[0013] The water referred to in this invention refers to drinking water that meets the "Standards for Drinking Water Quality" (GB 5749-2022). When non-drinking water is used, a comparative test should be conducted with drinking water.

[0014] The water-cement ratio control of the curing agent described in this invention refers to controlling the water-cement ratio according to the composition of the curing agent to meet the minimum water consumption required for all curing agent materials to be fully hydrated.

[0015] The optimal moisture content mentioned in this invention refers to the moisture content of sulfate-saline soil. w The optimum moisture content obtained from the compaction test according to the "Standard for Geotechnical Testing Methods" (GB / T 50123-2019) is compared with that obtained from the compaction test. satisfy .

[0016] The application scope of the solidified sulfate soil base course described in this invention includes, but is not limited to, road engineering, airport engineering, and parking lot engineering.

[0017] The specific construction process of the solidified sulfate-saline soil base layer described in this invention is as follows: First, laboratory tests were conducted on the sulfate-saline soil to understand its salt content, ion types, and physical properties. Second, based on the sulfate ion content and the design value of the 7-day unconfined compressive strength of the solidified sulfate-saline soil base course, the material composition of the cementing and expansion components in the curing agent, the curing agent dosage, and the water-cement ratio were determined. The compaction machinery, compaction rate, number of compaction passes, and constraint load were also determined. Finally, the moisture content of the sulfate-saline soil was controlled. w Make it satisfy The curing agent was mixed evenly with sulfate soil at a fixed water-cement ratio and near the optimum moisture content. The soil was then compacted using a rolling machine at a set rolling rate and number of passes. A constraint load was set on the surface of the compacted sulfate soil. After curing the solidified sulfate soil under constraint conditions for 7 days, the constraint load was removed to obtain the solidified sulfate soil base course. The performance of the solidified sulfate soil base course was then tested.

[0018] The advantages of this invention are: 1. This invention utilizes locally sourced sulfate-contaminated soil as a material for preparing solidified sulfate-contaminated soil base courses, significantly reducing the consumption and transportation of traditional building materials, thereby significantly reducing the cost of base course engineering. At the same time, it transforms sulfate from "harmful" to "beneficial," enabling the solidified sulfate-contaminated soil base course to have good durability in sulfate environments.

[0019] 2. The solidified sulfate soil base layer obtained by the present invention has high density and high strength characteristics, as well as good bearing capacity and water stability.

[0020] 3. This invention uses industrial waste residue to completely replace silicate cement as a binding component, realizing the low-carbon preparation of solidified sulfate soil base course while further reducing engineering costs.

[0021] It should be noted that this invention is mainly for sulfated soils with a salt content of 1-50%, but it is also applicable to sulfated soils with a salt content of less than 1%. Detailed Implementation

[0022] The following detailed description of a solidified sulfate-alkali soil base course prepared using a constraint process according to the present invention is provided with specific embodiments. However, the application forms and scope of the solidified sulfate-alkali soil base course provided by the present invention are not limited to this.

[0023] Example 1 A highway in a sulfate-rich area is planned to utilize a solidified sulfate-rich soil base course prepared using the constrained process described in this invention. Indoor testing of the sulfate-rich soil in the highway construction section revealed a salt content of 1.33%, with the main ionic component and content being Ca. 2+ 0.11%, Mg 2+ 0.12%, K + and Na + 0.13%, 0.95%, 0.01%, The moisture content of the sulfate-saline soil is 0.01% and 24%. The solidified sulfate-saline soil base course prepared using the constrained process described in this invention has a design value of 9 MPa for unconfined compressive strength after 7 days.

[0024] The composition of the curing agent, calculated by weight, is as follows: cementing component: 4.0 parts slag, 4.0 parts bottom ash, 2.0 parts hydrated sodium silicate; expansion component: 3.5 parts aluminum-containing waste residue, 2.6 parts alkaline waste residue, and 3.2 parts gypsum-based waste residue. The curing agent dosage is 25% of the total dry weight of the curing agent and the sulfate-saline soil, with a water-cement ratio of 0.42. The compaction machinery selected is a 25-ton vibratory roller, a compaction speed of 3 km / h, 4 compaction passes, and a constraint load of 18 kPa. The moisture content w of the sulfate-saline soil is controlled to meet the following requirements. The curing agent was mixed evenly with sulfate soil at a fixed water-cement ratio near its optimum moisture content. The mixture was then compacted using a rolling mill at a set speed and number of passes. A constraint load was applied to the compacted sulfate soil surface. The solidified sulfate soil was cured under constraint conditions for 7 days, after which the constraint load was removed, resulting in the solidified sulfate soil base course. Testing showed that the performance of the solidified sulfate soil base course met the requirements.

[0025] Example 2 A first-class highway in a sulfate-rich area is planned to use a solidified sulfate-rich soil base course prepared using the constrained process described in this invention. Indoor testing of the sulfate-rich soil in the construction section revealed a salt content of 18.36%, with the main ionic component and content being Ca. 2+ 2.52%, Mg 2+ 1.23%, K + and Na + 1.33%, 13.26%, 0.01%, The water content of the sulfated soil is 33%, with a moisture content of 0.01%. The solidified sulfated soil base course prepared using the constrained process described in this invention has a design value of 5 MPa for its 7-day unconfined compressive strength.

[0026] The composition of the curing agent, calculated by weight, is as follows: the cementing component consists of 4.0 parts phosphorus slag, 5.0 parts copper slag, and 1.0 part quicklime; the expanding component consists of 5.2 parts aluminum-containing waste residue, 3.6 parts alkaline waste residue, and 3.2 parts gypsum-based waste residue. The curing agent dosage is 15% of the total dry weight of the curing agent and the sulfate-saline soil, and the water-cement ratio of the curing agent is 0.45. The compaction machinery selected is an 18-ton vibratory roller, a compaction rate of 5 km / h, 2 compaction passes, and a constraint load of 13 kPa. The moisture content w of the sulfate-saline soil is controlled to meet the following requirements. The curing agent was mixed evenly with sulfate soil at a fixed water-cement ratio near its optimum moisture content. The mixture was then compacted using a rolling mill at a set speed and number of passes. A constraint load was applied to the compacted sulfate soil surface. The solidified sulfate soil was cured under constraint conditions for 7 days, after which the constraint load was removed to obtain the solidified sulfate soil base course. Testing showed that the performance of the solidified sulfate soil base course met the requirements.

[0027] Example 3 A highway service area parking lot in a sulfate-rich soil region plans to use a solidified sulfate-rich soil base course prepared using the constrained process described in this invention. Indoor testing of the sulfate-rich soil in the construction section revealed a salt content of 49.97%, with the main ionic component and content being Ca. 2+ 1.26%, Mg 2+ 3.18%, K + and Na + 11.66%, 33.85%, 0.01%, The moisture content of the sulfated soil is 0.01%, and the water content is 29%. The solidified sulfated soil base course prepared using the constrained process described in this invention has a design value of 4 MPa for its 7-day unconfined compressive strength.

[0028] The composition of the curing agent, calculated by weight, is as follows: the cementing component consists of 4.5 parts rice husk ash, 4.5 parts kiln ash, and 1.0 part hydrated lime; the expansion component consists of 6.8 parts aluminum-containing waste residue and 6.0 parts alkaline waste residue. The curing agent dosage is 20% of the total dry weight of the curing agent and the sulfated soil, and the water-cement ratio of the curing agent is 0.46. The compaction machinery selected is a 15-ton vibratory roller, with a compaction speed of 8 km / h, 2 compaction passes, and a constraint load of 12 kPa. The moisture content w of the sulfated soil is controlled to meet the following requirements. The curing agent was mixed evenly with sulfate soil at a fixed water-cement ratio near its optimum moisture content. The mixture was then compacted using a rolling mill at a set speed and number of passes. A constraint load was applied to the compacted sulfate soil surface. The solidified sulfate soil was cured under constraint conditions for 7 days, after which the constraint load was removed to obtain the solidified sulfate soil base course. Testing showed that the performance of the solidified sulfate soil base course met the requirements.

[0029] Example 4 An airport project in a sulfate-rich area plans to use a solidified sulfate-rich soil base course prepared using the constrained process described in this invention. Indoor testing of the sulfate-rich soil in the construction section revealed a salt content of 32.58%, with the main ionic component and content being Ca. 2+ 3.32%, Mg2+ 3.41%, K + and Na + 1.38%, 24.45%, 0.01%, The moisture content of the sulfated soil is 0.01% and 25%. The solidified sulfated soil base course prepared using the constrained process described in this invention has a 7-day unconfined compressive strength design value of 13 MPa.

[0030] The composition of the curing agent, calculated by weight, is as follows: the cementing component consists of 4.0 parts slag, 4.0 parts rice husk ash, and 2.0 parts active magnesium oxide; the expansion component consists of 4.8 parts aluminum-containing waste residue and 5.5 parts alkaline waste residue. The curing agent dosage is 37% of the total dry weight of the curing agent and the sulfate-saline soil, and the water-cement ratio of the curing agent is 0.41. The compaction machinery selected is a 40-ton vibratory roller, a compaction rate of 1.2 km / h, 4 compaction passes, and a constraint load of 32 kPa. The moisture content w of the sulfate-saline soil is controlled to meet the following requirements. The curing agent was mixed evenly with sulfate soil at a fixed water-cement ratio near its optimum moisture content. The mixture was then compacted using a rolling mill at a set speed and number of passes. A constraint load was applied to the compacted sulfate soil surface. The solidified sulfate soil was cured under constraint conditions for 7 days, after which the constraint load was removed to obtain the solidified sulfate soil base course. Testing showed that the performance of the solidified sulfate soil base course met the requirements.

Claims

1. A solidified sulfate-alkali soil base course prepared using a constrained process, characterized in that: The materials for preparing a solidified sulfate-saline soil base course include soil, a solidifying agent, and water. The soil is sulfate-saline soil with a salt content of 1-50%. The solidifying agent consists of a cementing component and an expansive component. A material with a slow hydration rate is used as the cementing component of the solidifying agent, while a material that hydrates rapidly and forms expansive hydrates with sulfate ions in the soil is used as the expansive component. The mass ratio of the cementing component to the expansive component in the solidifying agent is 35-85:15-65, respectively. The preparation process is based on the properties of the sulfate-saline soil itself and the solidification of the sulfate-saline soil base course. The design value of the layer strength is determined by selecting specific compaction machinery, compaction rate, number of compaction passes, and constraint load value. The water-cement ratio of the curing agent and the moisture content of the sulfate soil are controlled. The curing agent is mixed evenly with the sulfate soil at a fixed water-cement ratio and near the optimum moisture content. The mixture is compacted using compaction machinery and cured under constraint load for 7 days before the constraint is removed to obtain the cured sulfate soil base course. This invention can realize the resource utilization of sulfate and reduce carbon emissions in the base course, and significantly reduce the cost of base course engineering. The cured sulfate soil base course has good bearing capacity, water stability, and durability. The rolling rate ranges from 1 to 8 km / h; the curing under constrained load refers to setting a constrained load on the surface of the solidified sulfate soil after rolling. The method of setting the constrained load includes, but is not limited to, laying a flexible geotextile on the surface of the rolled solidified sulfate soil and covering it with a soil load of equal thickness, or laying a sheet sandbag load of equal thickness on the surface of the rolled solidified sulfate soil. The cementing component is a material with a slow hydration rate, and the cementing hydrates produced by its hydration include, but are not limited to, hydrated calcium silicate. The cementing component is composed of cementing materials and activators, with the mass ratio of cementing materials and activators in the cementing component being 70~100:0~30. The cementing materials include, but are not limited to, one or more combinations of slag, copper slag, phosphorus slag, coal gangue, bottom ash, rice husk ash, kiln ash, etc. The activator is an alkaline activator, including, but not limited to, one or more combinations of quicklime, hydrated lime, active magnesium oxide, sodium hydroxide, hydrated sodium silicate, etc. The expansion component is a material with a rapid hydration rate, and the expansion component rapidly hydrates with sulfate ions in the soil to generate expansion hydrates, and the expansion hydrates produced by the hydration of the expansion component include, but are not limited to, hydrated calcium sulfoaluminate. The expansion component includes, but is not limited to, a mixture composed of aluminum-containing waste residue, alkaline waste residue, gypsum waste residue, or sulfate waste residue.

2. The solidified sulfate-alkali soil base course prepared using a constraint process according to claim 1, characterized in that: The cementing component requires the selection of an activator based on the designed hydration rate, and the specific ratio of cementing material and activator in the cementing component must be determined through preliminary experiments. The expansion component requires the specific ratio of each component material in the expansion component to be determined according to the sulfate ion content in the sulfate-saline soil and the chemical equation for the formation of expanding hydrates, using known calculation methods. The curing agent consists of industrial-grade materials, all with a specific surface area greater than 150 m². 2 / kg of powder; the dosage of the curing agent is 10~100% of the total dry weight of the curing agent and the sulfated soil.

3. The solidified sulfate-alkali soil base course prepared using a constraint process according to claim 1, characterized in that: The water referred to is drinking water that meets the "Standards for Drinking Water Quality" (GB 5749-2022). When using non-drinking water, a comparative test with drinking water should be conducted. The control of the water-cement ratio of the curing agent refers to controlling the water-cement ratio according to the composition of the curing agent to meet the minimum water consumption required for all curing agent materials to complete hydration. The near-optimal moisture content refers to the moisture content of the sulfate-saline soil. w The optimum moisture content obtained from the compaction test according to the "Standard for Geotechnical Testing Methods" (GB / T 50123-2019) is compared with that obtained from the compaction test. satisfy .

4. A solidified sulfate-alkali soil base course prepared using a constraint process according to claim 1, characterized in that: The application scope of the solidified sulfate soil base course includes, but is not limited to, road engineering, airport engineering, and parking lot engineering.

5. A solidified sulfate-alkali soil base course prepared using a constraint process according to claim 1, characterized in that: The specific construction process for the solidified sulfate-alkali soil base course is as follows: ① Conduct indoor tests on the sulfate-alkali soil to understand its salt content, ion types, and physical properties; ② Based on the sulfate ion content and the design value of the 7-day unconfined compressive strength of the solidified sulfate-alkali soil base course, determine the material composition of the cementing and expansion components in the curing agent, the curing agent dosage, the water-cement ratio, and determine the compaction machinery, compaction rate, number of compaction passes, and constraint load; ③ Control the moisture content of the sulfate-alkali soil. w Make it satisfy The curing agent was mixed evenly with sulfate soil at a fixed water-cement ratio and near the optimum moisture content. The soil was then compacted using a rolling machine at a set rolling rate and number of passes. A constraint load was set on the surface of the compacted sulfate soil. After curing the solidified sulfate soil under constraint conditions for 7 days, the constraint load was removed to obtain the solidified sulfate soil base course. The performance of the solidified sulfate soil base course was then tested.