A wet original soil base ultra-early strength backfill material and construction method for municipal pipe network repair in cold regions

Abstract

The application relates to the technical field of municipal underground pipeline engineering construction, and discloses a wet native soil base super-early-strength backfill material for municipal pipe network emergency repair in cold regions and a construction method, which comprises the following components: wet native soil 65-75 parts, sulphoaluminate cement 10-15 parts, aluminate cement 3-6 parts, calcium formate 1.0-2.0 parts, modified polycarboxylate water reducing agent 1.8-2.5 parts, phase change microspheres 4-8 parts, nano silicon dioxide sol with a solid content of 5-8% 3-5 parts, and water 5-9 parts. The wet native soil base super-early-strength self-compacting backfill material can be directly constructed under the condition that the ambient temperature is-12 DEG C to 5 DEG C, and the strength of the material formed within 4 hours can meet the temporary traffic requirement; and the trench construction method is especially suitable for emergency repair engineering of sewage pipes, heating pipes or power pipelines in northern and high-altitude cold regions.

Description

Technical Field

[0001] This invention relates to the field of municipal underground pipeline engineering construction technology, and in particular to an ultra-early strength backfill material and construction method for wetland soil foundations used in emergency repairs of municipal pipeline networks in cold regions. Background Technology

[0002] In cold regions during winter, after underground pipelines for municipal water supply, drainage, and heating are damaged, rapid backfilling of trenches is necessary to restore traffic and prevent secondary disasters. However, existing backfilling technologies face the following common challenges: (1) Wet original soil is difficult to use directly: The original soil excavated usually has a high water content, is easy to freeze at low temperature, and has poor fluidity. Traditional processes require it to be dried or baked to a lower water content before it can be used. However, in the scenario of emergency repair of urban roads, there is a lack of drying conditions, and rainy and snowy weather makes the process even more infeasible.

[0003] (2) Antifreeze measures have side effects: In order to maintain the working performance of materials at low temperatures, some solutions use chloride or nitrite additives. However, such substances may cause corrosion or environmental risks to nearby metal pipes, steel bars or manhole structures, which does not meet the requirements of green construction and long-term durability.

[0004] (3) External heating is not suitable for narrow trenches: Although electric heating is used in large-volume concrete projects, in urban pipe network trenches that are usually less than 1.2 meters wide and more than 2 meters deep, the space for laying heating equipment is limited, the operation is complicated, the energy consumption is high, and it is difficult to achieve uniform heat preservation, which is not suitable for the rapid operation requirements of emergency repair.

[0005] Therefore, the industry has long lacked a self-compacting backfill technology that can directly utilize wet soil that has not been dried in an environment of -12℃, without the addition of corrosive additives, and can form sufficient strength within a few hours to open temporary traffic. Summary of the Invention

[0006] This invention provides an ultra-early strength backfill material and construction method for wet original soil foundation used in emergency repair of municipal pipelines in cold regions. It overcomes the technical bias of existing technologies that "must use dry materials, rely on corrosive additives, and require continuous external heating", realizes the direct resource utilization of excavated original soil in a high water content state, and forms structural strength that meets the requirements for temporary traffic within 4 hours at an ambient temperature of -12℃ to 5℃.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: An ultra-early strength backfill material for wetland soil foundation used in emergency repairs of municipal pipelines in cold regions comprises the following components by weight: 65-75 parts wetland soil, 10-15 parts sulfoaluminate cement, 3-6 parts aluminate cement, 1.0-2.0 parts calcium formate, 1.8-2.5 parts modified polycarboxylate superplasticizer, 4-8 parts phase change microspheres, 3-5 parts nano-silica sol with a solid content of 5%-8%, and 5-9 parts water.

[0008] Preferably, the backfill material, under an ambient temperature of -12℃ to 5℃, has a slump expansion ≥ 500mm after mixing and a surface compressive strength ≥ 0.4MPa after 4 hours.

[0009] Preferably, the wet soil is the original soil that has been temporarily stockpiled and covered with insulation measures after trench excavation. After removing tree roots, weeds and hard objects with a particle size greater than 20mm and passing through a 20mm sieve, it is used directly without sun-drying or drying treatment, and its natural moisture content is 15%~25%.

[0010] Preferably, the wet soil is silty clay and / or clayey silt, with a liquid limit of 35% to 50% and a plastic limit of 15% to 28%.

[0011] Preferably, the modified polycarboxylate superplasticizer has C14-C18 alkyl hydrophobic groups grafted onto its molecular backbone.

[0012] Preferably, the core of the phase change microspheres is calcium chloride hexahydrate, which is wrapped with a nano-silica core-shell structure, with an average particle size of 50~200μm and a phase change temperature of -8℃~-2℃.

[0013] A method for emergency repair of municipal pipelines in cold regions involves using a wetland soil subgrade ultra-early strength backfill material described above for emergency repair of municipal pipelines in cold regions in low-temperature areas. The steps are as follows: Excavate trenches for municipal water supply and drainage pipe networks, temporarily stockpile the original soil and cover it with insulation cotton; The stockpiled undisturbed soil was crushed and passed through a 20mm sieve to obtain wet undisturbed soil; Wet soil, sulfoaluminate cement, aluminate cement, calcium formate, modified polycarboxylate superplasticizer, phase change microspheres, nano silica sol and water are added to a mixing device in a certain proportion to obtain a fluid slurry; After the equipment in the trench is installed, the slurry backfill material is pumped into the trench to achieve self-compacting filling; Two ± 0.3 minutes after pouring, a nano-silica sol with a solid content of 5%–8% is atomized and sprayed onto the surface of the slurry at a dosage of 180–220 g / m³. 2 ; After atomization, within 5±0.5 minutes, cover with a smart electrothermal film and energize for 10±1 minutes. The smart electrothermal film has a built-in carbon fiber heating mesh with a power density of 70–90 W / m². 2 ; After the power outage, the vehicle will undergo natural curing and will be temporarily allowed to pass through for light vehicles within 10 hours.

[0014] Preferably, the ambient temperature during construction in the low-temperature region is -12℃ to 5℃, and the wind speed is ≤4m / s.

[0015] Preferably, when mixing backfill materials in the mixing equipment, the outlet temperature is controlled to be ≥3℃, and the mixing time is 2~4 minutes.

[0016] Preferably, the backfill material after natural curing following a power outage has a compressive strength of ≥1.8MPa after 28 days and a strength retention rate of ≥90% after 300 freeze-thaw cycles.

[0017] The beneficial effects of this invention are: 1. Enables direct resource utilization of wet undisturbed soil. Natural excavated undisturbed soil with a moisture content of 15%–25% can be used directly without drying, baking, or adding water-absorbing materials for moisture adjustment, significantly shortening construction preparation time. It is suitable for emergency repair operations in cold regions where it is inconvenient to reduce the moisture content.

[0018] 2. Green and environmentally friendly, with no risk of corrosion. The material system does not contain corrosive antifreeze agents such as chlorides and nitrites, and has no corrosive effect on nearby metal pipes, reinforced concrete structures, and inspection wells, meeting the requirements of green construction and long-term durability.

[0019] 3. Ultra-early strength performance meets the timeliness requirements for emergency repairs in cold regions. Under ambient temperatures ranging from -12℃ to 5℃, the surface compressive strength is ≥0.4 MPa within 4 hours, and temporary passage for light vehicles can be opened within 10 hours, effectively solving the engineering problem of "same-day excavation, same-day backfilling, and same-day traffic opening".

[0020] 4. Low energy consumption and high-efficiency construction. Only 10 minutes of power is applied to the surface film about 5 minutes after pouring (energy consumption <0.1 kWh / m²) to form a dense hard shell to prevent frost damage. No continuous external heating is required, which significantly reduces energy consumption and labor costs.

[0021] 5. Reliable performance throughout the entire life cycle: 28-day compressive strength ≥1.8 MPa, strength retention rate ≥90% after 300 freeze-thaw cycles, combining short-term emergency repair strength with long-term service durability. Detailed Implementation

[0022] The embodiments are described in further detail below. It should be emphasized that all embodiments of the present invention are feasible.

[0023] As a preferred embodiment 1, a wetland soil-based ultra-early strength backfill material for emergency repair of municipal pipelines in cold regions comprises the following components by weight: 65-75 parts wetland soil, 10-15 parts sulfoaluminate cement, 3-6 parts aluminate cement, 1.0-2.0 parts calcium formate, 1.8-2.5 parts modified polycarboxylate superplasticizer, 4-8 parts phase change microspheres, 3-5 parts nano-silica sol with a solid content of 5%-8%, and 5-9 parts water.

[0024] Preferably, the backfill material, under an ambient temperature of -12℃ to 5℃, has a slump expansion ≥ 500mm after mixing and a surface compressive strength ≥ 0.4MPa after 4 hours.

[0025] Preferably, the wet soil is the original soil that has been temporarily stockpiled and covered with insulation measures after trench excavation. After removing tree roots, weeds and hard objects with a particle size greater than 20mm and passing through a 20mm sieve, it is used directly without sun-drying or drying treatment, and its natural moisture content is 15%~25%.

[0026] Preferably, the wet soil is silty clay and / or clayey silt, with a liquid limit of 35% to 50% and a plastic limit of 15% to 28%.

[0027] Preferably, the modified polycarboxylate superplasticizer has C14-C18 alkyl hydrophobic groups grafted onto its molecular backbone.

[0028] Preferably, the core of the phase change microspheres is calcium chloride hexahydrate, which is wrapped with a nano-silica core-shell structure, with an average particle size of 50~200μm and a phase change temperature of -8℃~-2℃.

[0029] A method for emergency repair of municipal pipelines in cold regions involves using a wetland soil subgrade ultra-early strength backfill material described above for emergency repair of municipal pipelines in cold regions in low-temperature areas. The steps are as follows: Excavate trenches for municipal water supply and drainage pipe networks, temporarily stockpile the original soil and cover it with insulation cotton; The stockpiled undisturbed soil was crushed and passed through a 20mm sieve to obtain wet undisturbed soil; Wet soil, sulfoaluminate cement, aluminate cement, calcium formate, modified polycarboxylate superplasticizer, phase change microspheres, nano silica sol and water are added to a mixing device in a certain proportion to obtain a fluid slurry; After the equipment in the trench is installed, the slurry backfill material is pumped into the trench to achieve self-compacting filling; Two ± 0.3 minutes after pouring, a nano-silica sol with a solid content of 5%–8% is atomized and sprayed onto the surface of the slurry at a dosage of 180–220 g / m³. 2 ; After atomization, within 5±0.5 minutes, cover with a smart electrothermal film and energize for 10±1 minutes. The smart electrothermal film has a built-in carbon fiber heating mesh with a power density of 70–90 W / m². 2 ; After the power outage, the vehicle will undergo natural curing and will be temporarily allowed to pass through for light vehicles within 10 hours.

[0030] Preferably, the ambient temperature during construction in the low-temperature region is -12℃ to 5℃, and the wind speed is ≤4m / s.

[0031] Preferably, when mixing backfill materials in the mixing equipment, the outlet temperature is controlled to be ≥3℃, and the mixing time is 2~4 minutes.

[0032] Preferably, the backfill material after natural curing following a power outage has a compressive strength of ≥1.8MPa after 28 days and a strength retention rate of ≥90% after 300 freeze-thaw cycles.

[0033] Using moist virgin soil with a moisture content of 15%–25% after simple pretreatment as the main aggregate, the pretreatment only includes removing tree roots, weeds, and hard objects with a particle size greater than 20mm. After crushing, the soil is sieved through a 20mm sieve and covered with insulating cotton to prevent freezing during temporary storage after excavation. It does not involve sun-drying, drying, or adding water-absorbing materials to adjust the moisture content. On this basis, CaCl2·6H2O@nano-SiO2 phase change microspheres are innovatively introduced as an embedded heat source to create a local liquid phase microenvironment inside the slurry. At the same time, a ternary early strength system of sulfoaluminate cement-aluminate cement-calcium formate is constructed to achieve controllable ultra-early strength. Furthermore, with a surface short-time electrothermal coating process with precise timing control, electricity is applied for 10 minutes 5±0.5 minutes after pouring, which only triggers the formation of a surface hard shell, while the internal strength development is completed by phase change self-insulation.

[0034] As a preferred embodiment 2, the preparation of phase change microspheres: Calcium chloride hexahydrate was melted at 30℃ and dropped into an ethanol dispersion containing 5% nano-SiO2 with a particle size of 20 nm. The mixture was emulsified by high-speed shearing at 10,000 rpm for 10 minutes and dried at 60℃ to obtain core-shell microspheres. The phase transition enthalpy was measured to be 182 J / g, the phase transition peak was at -4.6℃, and the average particle size was 120 μm.

[0035] As a preferred embodiment 3, the modified polycarboxylate superplasticizer is prepared by the following method: (1) Dissolve methacrylic acid, polyethylene glycol monomethyl ether methacrylate and chain transfer agent in deionized water and remove oxygen by passing nitrogen gas. (2) Heat to 70~80℃, add initiator solution dropwise, react for 3~4 hours to obtain polycarboxylic acid backbone; (3) Cool to 40~50℃, add C14~C18 alkylamine, and carry out amidation reaction for 2~3 hours under the action of catalyst; (4) Adjust the pH to 6-7 to obtain a modified polycarboxylate superplasticizer with a solid content of 35%-45%.

[0036] As a preferred embodiment 4, verification under typical cold-region conditions (ambient temperature -12℃, silty clay): Wet native soil: silty clay excavated from a sewage pipe trench in a cold region, with a liquid limit of 42%, a plastic limit of 20%, and a natural moisture content of 21%; Material proportions (calculated by weight components, unit: parts): wet soil 72, sulfoaluminate cement 13, aluminate cement 5, calcium formate 1.5, modified polycarboxylate superplasticizer 2.2, phase change microspheres 6, nano silica sol (solid content 6%) 4.2, water 8; Construction: Mixing temperature at the mixer outlet: 4℃; 2.1 min after pouring, atomize nano-SiO2; 5.2 min after coating with electric heating film and energize for 10 min (power density: 80W / m²). 2 ); Results: Slump spread 530 mm, 4-hour strength 0.48 MPa, 28-day strength 2.1 MPa, and strength retention rate after 300 freeze-thaw cycles 92%.

[0037] As a preferred embodiment 5, high-temperature boundary verification (ambient temperature 5°C, clayey silt). Moist soil: Clayey silt in a heating pipe trench in a cold region, with a liquid limit of 38%, a plastic limit of 18%, and a moisture content of 19%; Material ratio (lower limit combination, calculated by weight components, unit: parts): wet soil 65, sulfoaluminate cement 10, aluminate cement 3, calcium formate 1.0, water-reducing agent 1.8, phase change microspheres 4, nano SiO2 sol 3, water 5. Construction: The outlet temperature is 6℃, and the rest is the same as in Example 4; Results: Slump spread 510mm, 4h strength 0.42MPa, meeting the requirement of ≥0.4MPa.

[0038] As a preferred embodiment 6, high water content boundary verification (ambient temperature -8°C, water content 25%). Moist soil: Silty clay in a cold region after rain and snow, with a moisture content of 25%; Material ratio (upper limit combination, calculated by weight components, unit: parts): wet soil 75, sulfoaluminate cement 15, aluminate cement 6, calcium formate 2.0, water-reducing agent 2.5, phase change microspheres 8, nano SiO2 sol 5, water 9. Construction: Same as Example 4; Results: Slump spread 505 mm, 4-hour strength 0.41 MPa.

[0039] Comparative Example 1: Microspheres without phase change (other aspects are the same as in Example 4) The strength after 4 hours is approximately 0 MPa (the slurry is completely frozen), making it impossible to form a structure.

[0040] Comparative Example 2: Aluminate-free cement (replaced with an equal amount of sulfoaluminate, otherwise the same as in Example 4) The strength after 4 hours is 0.22 MPa, which does not meet the requirements for opening to traffic.

[0041] Comparative Example 3: Incorrect timing of energizing the electrothermal film (energized 10 minutes after pouring, otherwise the same as Example 4). The surface has been frozen and has developed a network of cracks. The strength after 4 hours is 0.28 MPa.

[0042] Comparative Example 4: Using ordinary PE film (no electricity, otherwise the same as Example 4) The surface bleeds water severely, and the early strength development is slow, with a strength of 0.31 MPa after 4 hours.

[0043] In summary, to achieve the desired effects on subsequent use and backfilling of the materials, it is essential to use moist soil with a moisture content of 15%–25% that has undergone simple pretreatment as the main aggregate, and to introduce CaCl2·6H2O@nano SiO2 phase change microspheres as an embedded heat source to create a local liquid phase microenvironment within the slurry. At the same time, a ternary early strength system of sulfoaluminate cement-aluminate cement-calcium formate is constructed to achieve controllable ultra-early strength. Furthermore, with the precise timing control of the surface short-time electrothermal coating process, power is applied for 10 minutes 5±0.5 minutes after pouring, which only triggers the formation of a hard shell on the surface, while the interior relies on phase change self-insulation to complete the strength development.

[0044] The above conditions must be met simultaneously. From materials to the precise timing of material construction, the whole process must be a system. Only by constructing according to the system can the required backfilling effect be achieved. It should also be noted that the optimal ambient temperature for the above system is -12℃ to 5℃, and the wind speed is ≤4m / s.

Claims

1. A wetland soil foundation ultra-early strength backfill material for emergency repair of municipal pipelines in cold regions, characterized in that, The composition by weight includes the following components: 65-75 parts wet soil, 10-15 parts sulfoaluminate cement, 3-6 parts aluminate cement, 1.0-2.0 parts calcium formate, 1.8-2.5 parts modified polycarboxylate superplasticizer, 4-8 parts phase change microspheres, 3-5 parts nano silica sol with a solid content of 5%-8%, and 5-9 parts water.

2. The wetland soil foundation ultra-early strength backfill material for emergency repair of municipal pipelines in cold regions according to claim 1, characterized in that, The backfill material, when mixed at an ambient temperature of -12℃ to 5℃, has a slump expansion ≥500mm and a surface compressive strength ≥0.4MPa after 4 hours.

3. The wetland soil foundation ultra-early strength backfill material for emergency repair of municipal pipelines in cold regions according to claim 2, characterized in that, The wet soil is the original soil that has been temporarily stockpiled and covered with insulation measures after trench excavation. After removing tree roots, weeds and hard objects with a particle size greater than 20mm and passing through a 20mm sieve, it is used directly without sun-drying or drying treatment, and its natural moisture content is 15%~25%.

4. A wetland soil foundation ultra-early strength backfill material for emergency repair of municipal pipelines in cold regions, as described in any one of claims 1 to 3, characterized in that, The wet soil is silty clay and / or clayey silt, with a liquid limit of 35% to 50% and a plastic limit of 15% to 28%.

5. The wetland soil foundation ultra-early strength backfill material for emergency repair of municipal pipelines in cold regions according to claim 2, characterized in that, The modified polycarboxylate superplasticizer has C14~C18 alkyl hydrophobic groups grafted onto its molecular backbone.

6. The ultra-early strength backfill material for wetland soil foundation used in emergency repair of municipal pipelines in cold regions, as described in claim 2, is characterized in that... The core of the phase change microspheres is calcium chloride hexahydrate, which is wrapped by a nano-silica core-shell structure. The average particle size is 50~200μm and the phase change temperature is -8℃~-2℃.

7. A method for emergency repair of municipal pipelines in cold regions, characterized in that, The following steps are taken when using the wetland soil foundation ultra-early strength backfill material for emergency repair of municipal pipelines in cold regions as described in any one of claims 1 to 6 in low-temperature areas: Excavate trenches for municipal water supply and drainage pipe networks, temporarily stockpile the original soil and cover it with insulation cotton; The stockpiled undisturbed soil was crushed and passed through a 20mm sieve to obtain wet undisturbed soil; Wet soil, sulfoaluminate cement, aluminate cement, calcium formate, modified polycarboxylate superplasticizer, phase change microspheres, nano silica sol and water are added to a mixing device in a certain proportion to obtain a fluid slurry; After the equipment in the trench is installed, the slurry backfill material is pumped into the trench to achieve self-compacting filling; Two ± 0.3 minutes after pouring, a nano-silica sol with a solid content of 5%–8% is atomized and sprayed onto the surface of the slurry at a dosage of 180–220 g / m³. 2 ; After atomization, within 5±0.5 minutes, cover with a smart electrothermal film and energize for 10±1 minutes. The smart electrothermal film has a built-in carbon fiber heating mesh with a power density of 70–90 W / m². 2 ; After the power outage, the vehicle will undergo natural curing and will be temporarily allowed to pass through for light vehicles within 10 hours.

8. A method for emergency repair of municipal pipelines in cold regions according to claim 7, characterized in that, The ambient temperature during construction in the low-temperature region is -12℃ to 5℃, and the wind speed is ≤4m / s.

9. A method for emergency repair of municipal pipelines in cold regions according to claim 7, characterized in that, When mixing backfill materials in the mixing equipment, control the outlet temperature to ≥3℃ and mix for 2~4 minutes.

10. A method for emergency repair of municipal pipelines in cold regions according to claim 7, characterized in that, After a power outage and natural curing, the backfill material has a compressive strength of ≥1.8MPa after 28 days, and a strength retention rate of ≥90% after 300 freeze-thaw cycles.