A method for controlling cracks in construction of an ultra-long tunnel pavement layer concrete

Abstract

The application belongs to the technical field of tunnel construction, and particularly discloses a construction crack control method for super-long tunnel pavement layer concrete. The construction crack control method comprises the following steps: a tunnel bottom plate pretreatment step; a pavement layer concrete control step, including mix proportion design of pavement layer concrete and temperature control when entering a mold; a pavement layer concrete disturbance prevention step; and a pavement layer concrete temperature and moisture preservation and maintenance treatment step. The construction crack control method for super-long tunnel pavement layer concrete provided by the application can effectively solve the cracking problem of pavement layer concrete caused by shrinkage and disturbance by improving the pavement layer concrete material, construction and on-site management. Based on the construction crack control method, the pavement layer concrete can be free of cracks under the condition that the one-time pouring length exceeds 60 m.

Description

Technical Field

[0001] This invention belongs to the field of tunnel construction technology, specifically, it relates to a method for controlling cracks in the concrete construction of ultra-long tunnel pavement layers. Background Technology

[0002] Tunnels are an important component of highways and municipal roads. The pavement concrete layer, located between the tunnel floor slab and the asphalt surface layer, plays a leveling and connecting role. Typically, pavement concrete construction begins only after the main tunnel structure is completed and the floor slab is roughened, with the pouring length controlled by the length of the floor slab's expansion joints. Therefore, for tunnels with common expansion joint lengths of 60m to 80m, the pavement layer is considered an ultra-long structure. The pavement concrete strength grade is generally C30 or C35, and given its relatively small thickness (usually 10cm to 50cm), the concrete temperature rise and shrinkage are not significant. However, because the pavement concrete is poured directly onto the floor slab, it is strongly constrained by the floor slab concrete. Furthermore, due to the road drainage design, the pavement layer has a variable cross-section, making it prone to gradient stress within the structure. Therefore, cracking is a prominent issue in ultra-long pavement structures. Simultaneously, as a large-area plate-like structure, the pavement layer also faces plastic cracking and long-term drying shrinkage cracking due to moisture loss. Furthermore, the pavement layer construction is only one part of the overall tunnel construction process, and it inevitably overlaps with other surface construction operations. If the timing of commuter traffic is not accurately grasped, the pavement layer may also crack and suffer damage after being disturbed in the early stages. Cracks in the pavement layer concrete will inevitably affect the quality of the upper asphalt surface layer, impacting driving safety and reducing structural durability.

[0003] For crack control in cast-in-place concrete structures such as foundation slabs, sidewalls, and bridge pavement layers, relatively mature and comprehensive technical solutions have been developed in terms of design, materials, and construction. However, due to significant differences in the structural form and external constraints of tunnel pavement layers compared to foundation slabs and sidewalls, the factors influencing cracking in tunnel pavement concrete also differ. Therefore, crack control methods applied in the aforementioned scenarios are not suitable for this particular situation. Consequently, it is essential to propose targeted technical solutions to address the cracking challenges encountered during the construction of ultra-long tunnel pavement concrete. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of the prior art by providing a method for controlling construction cracks in the concrete pavement layer of ultra-long tunnels. This method integrates various influencing factors, can suppress cracks in the concrete structure of ultra-long tunnel pavement layers, and improve the quality of road construction.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for controlling cracks during the construction of concrete pavement layers in ultra-long tunnels includes the following steps:

[0007] Tunnel floor slab pretreatment steps;

[0008] Steps for controlling concrete paving layers;

[0009] Steps to prevent disturbance to the concrete paving layer;

[0010] Steps for thermal insulation and moisture retention curing of concrete paving layers.

[0011] In the tunnel floor slab pretreatment step, the following method is preferred for pretreatment of the tunnel floor slab: First, remove the floating dust on the surface of the tunnel floor slab and the loose laitance and aggregate remaining when the tunnel floor slab was roughened; then, continuously spray, sprinkle, or store water on the surface of the tunnel floor slab to ensure that the surface of the tunnel floor slab is kept moist for no less than 3 days.

[0012] In the concrete control process of the pavement layer, on the one hand, the mix proportion of the pavement layer concrete is designed, and on the other hand, the concrete pouring temperature of the pavement layer is controlled according to the difference between the average daily temperature of the surface and the average daily temperature of the project site.

[0013] Specifically, the mix design of the pavement concrete should ensure that its performance meets the following conditions:

[0014] The adiabatic temperature rise of the concrete should not exceed 25℃ in 1.5 days; the autogenous volumetric deformation should not be less than 150με in 14 days and not less than 100με in 28 days; and the concrete slump should be 170mm±30mm.

[0015] Each cubic meter of the above-mentioned pavement concrete also contains 28 kg to 35 kg of crack-resistant agent; the crack-resistant agent includes 97% to 98.5% calcium-magnesium composite expansion agent and 1.5% to 3% hydration temperature rise inhibitor, with the total mass of the crack-resistant agent being 100%.

[0016] The pouring temperature T of the pavement concrete r Based on the average daily temperature T on the surface of the paving layer concrete during construction c The adjustment is made according to the difference in the average daily temperature T at the project site; the specific control method is as follows:

[0017] 1) When -2℃≤T c When -T≤2℃, if T>10℃, then control T r ≤T+8℃ and T r ≤30℃; if T≤10℃, then control 5℃≤T r ≤18℃;

[0018] 2) When T c When -T < -2℃, if T > 10℃, then control T.r ≤T+5℃ and T r ≤28℃; if T≤10℃, then control 5℃≤T r ≤15℃;

[0019] 3) When T c When T > 2℃, if T > 10℃, then control T. r ≤T+10℃ and T r ≤32℃; if T≤10℃, then control 5℃≤T r ≤20℃.

[0020] The step of preventing disturbance to the concrete pavement layer is to control the concrete pavement layer from being disturbed by traffic for a certain period of time.

[0021] The preferred method for determining the above-mentioned undisturbed time period includes the following steps:

[0022] Test the first and last 1m sections of the pavement concrete to be poured. 3 The capillary negative pressure at the center point of the region was collected at intervals not exceeding 0.25 hours until the capillary negative pressure reached its peak.

[0023] The first to complete the pouring of 1m 3 The point at which the capillary negative pressure at the center of the region reaches 10 kPa is taken as T1.

[0024] The final drawing completes the 1m pouring. 3 The relationship between capillary negative pressure at the center point of the region and time is obtained by performing a differential process and recording the time corresponding to the maximum value of the differential curve as T2.

[0025] During the T1 to T2 time period, avoid driving within 10m of the edge of the concrete pavement layer.

[0026] Furthermore, the thermal insulation and moisture retention curing treatment of the pavement concrete includes the following steps:

[0027] From the start of concrete pouring to the T2 time period, one or more measures such as shading, spraying around the slab surface, and finishing should be taken to suppress plastic cracks. Finishing should be carried out at T2-1 h.

[0028] Within the T2 to 14d age range, cover with a layer of material with a specification of not less than 400g / m². 2 Use permeable geotextiles or similar materials, and take measures to keep the geotextiles continuously moist, ensuring that the temperature of the water used to moisten them is not lower than the average daily air temperature (T) of the storage area. c ;

[0029] For concrete paving layers that are exposed or located within 100m of the tunnel entrance and inside the tunnel, after 14 days of curing, an impermeable tarpaulin or equivalent material should be added over or replaced on top of the original permeable geotextile or cotton wadding, and the curing should continue until the upper surface layer construction is required at 28 days of curing.

[0030] The present invention has the following beneficial effects:

[0031] The present invention provides a method for controlling cracks in the concrete pavement layer of ultra-long tunnels, which improves upon aspects such as concrete materials, construction, and on-site management, effectively solving the cracking problem caused by shrinkage and disturbance in the pavement layer concrete. Based on this crack control method, even with a single pouring length exceeding 60m, crack-free pavement layer concrete can still be achieved. Attached Figure Description

[0032] Figure 1 This is the capillary negative pressure versus time curve during the period when the concrete of the pavement layer is undisturbed, as determined in Embodiment 1 of the present invention;

[0033] Figure 2 The capillary negative pressure versus time first differential curve is obtained when the period of time during which the concrete pavement layer is undisturbed is determined according to Embodiment 1 of the present invention.

[0034] Figure 3 This is the capillary negative pressure versus time curve during the period when the concrete of the pavement layer is undisturbed, as determined in Embodiment 2 of the present invention;

[0035] Figure 4 According to Embodiment 2 of the present invention, the capillary negative pressure versus time first differential curve is obtained when the period during which the paving layer concrete is undisturbed is determined. Detailed Implementation

[0036] This invention addresses the specific working conditions of ultra-long tunnel pavement layers, considering factors such as structure, materials, environment, and construction. Based on the multi-field coupling mechanism of concrete hydration, temperature, humidity, and constraints, a risk assessment model for concrete shrinkage cracking in pavement layers is established to quantitatively evaluate the impact of different factors on the risk of concrete shrinkage in tunnel pavement layers. The ratio of tensile stress caused by concrete shrinkage to its tensile strength is used as the cracking risk coefficient, and the final calculation results include control indicators such as concrete adiabatic temperature rise, deformation, placement temperature, and pouring length, with the cracking risk coefficient controlled to not exceed 0.7.

[0037] In order to achieve control indicators such as thermal insulation temperature rise and deformation of concrete, this invention adopts pavement concrete with specific properties and proposes key indicators and solutions from aspects such as tunnel bottom slab treatment, pavement concrete construction technology and on-site project management.

[0038] (I) Preparation of paving concrete and temperature control steps for pouring into the formwork.

[0039] First, the mix proportion of the pavement concrete needs to be determined. Due to the design requirements of the tunnel pavement, the pavement layer has a variable cross-section structure along the tunnel width. Since the road surface generally has a slope along the tunnel length, the pavement concrete must have good workability to meet the construction requirements. If the slump is too large, the concrete is prone to segregation and is not easy to stabilize and form on the slope. At the same time, the pavement layer of ultra-long tunnels is a large-area slab structure, and if the slump is too small, it will increase the construction difficulty.

[0040] Based on performance considerations and the specific working conditions of ultra-long tunnel pavement layers, control indicators for concrete crack resistance were derived, including 1.5-day adiabatic temperature rise, 14-day autogenous volumetric deformation, 28-day deformation, mold placement temperature control, and thermal insulation and moisture retention curing measures. These indicators were obtained through calculation and evaluation using a hydration-temperature-temperature-humidity multi-factor coupled model to establish a concrete shrinkage cracking model for the pavement layer.

[0041] In each embodiment, the pavement concrete was designed to meet the requirements of workability and crack resistance, as shown in Table 1.

[0042] Table 1. Mix proportions of pavement concrete (unit: kg / m²) 3

[0043]

[0044] As for the selection of raw materials, the performance of general-purpose Portland cement should meet the requirements of GB 175 "General-purpose Portland Cement" and CCES01 in "Guidelines for Durability Design and Construction of Concrete Structures"; the performance of fly ash should meet the requirements of Grade II or above as specified in GB / T 1596 "Fly Ash for Cement and Concrete"; the performance of blast furnace slag powder should meet the requirements of Grade S95 or above as specified in GB / T 18046 "Granulated Blast Furnace Slag Powder for Cement, Mortar and Concrete" and CCES01 in "Guidelines for Durability Design and Construction of Concrete Structures"; the fine aggregate should be natural Zone II medium sand with a mud content not exceeding 3.0% and a mud lump content not exceeding 1.0%; the performance of coarse aggregate should meet the requirements of 5mm to 20mm continuously graded crushed stone as specified in GB / T 14685 "Construction Gravel and Crushed Stone" with a loose packing porosity not exceeding 43%; the performance of water-reducing agent should meet the requirements of "Concrete Admixtures" (GB 8076) with a shrinkage ratio not exceeding 100%.

[0045] The crack-resistant agent consists of a calcium-magnesium composite expansive agent and a hydration temperature rise inhibitor. The performance of the calcium-magnesium composite expansive agent should meet the requirements of T / CECS 10082 "Calcium-magnesium Composite Expansive Agent for Concrete" and the performance of the concrete hydration temperature rise inhibitor should meet the requirements of JC / T 2608 "Concrete Hydration Temperature Rise Inhibitor".

[0046] It should be noted that the mixing water includes solid flake ice used to achieve the cooling effect, and is not limited to liquid water.

[0047] Therefore, the performance requirements for the pavement concrete are shown in Table 2.

[0048] Table 2 Performance Requirements for Pavement Concrete

[0049]

[0050] As understood by those skilled in the art, the thermal rise of concrete is tested according to the "Standard for Test Methods of Performance of Ordinary Concrete Mixtures" GB / T 50080, and the autogenous volume deformation is tested according to the non-contact method in the "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete" GB / T 50082. The selected zero point is the initial setting of concrete. 14-day autogenous volume deformation ≥150με means "14-day autogenous volume expansion deformation is not less than 150με". The 28-day deformation test method specifically involves sealing the specimen immediately after molding and placing it in a curing room at a temperature of (20±2)℃ for curing. After 14 days, the mold is removed, and the specimen is immediately moved into a curing room at a temperature of (20±2)℃ and a relative humidity of (60±5)% for continued curing until 28 days. During this period, readings are taken at least at 14 days, 21 days, and 28 days, referring to the "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete" GB / T 50082. In 50082, the contact method is used to calculate the deformation of the specimen from 14 days to 28 days and denoted as ε1. If the autogenous volume deformation of the specimen at 14 days is denoted as ε2, then the deformation at 28 days is the sum of ε1 and ε2. A deformation at 28 days ≥ 100 με means "the expansion deformation at 28 days is not less than 150 με".

[0051] Secondly, the required temperature of the concrete poured into the paving layer.

[0052] Specifically, there are three different scenarios:

[0053] When the concrete paving layer is being constructed, the average daily temperature of the work surface is T c When the temperature difference between the temperature at the project site and the average daily temperature T is -2℃ to +2℃, and the average daily temperature at the project site T is greater than 10℃, the temperature T for mold placement should be controlled. r ≤The average daily temperature at the project site is T+8℃ and T r ≤30℃; Under the condition that the average daily temperature T at the project site is ≤10℃, control the temperature T before placing the mold. rThe temperature ranges from 5℃ to 18℃.

[0054] When the concrete paving layer is being constructed, the average daily temperature of the work surface is T c When the daily average temperature difference T between the project site and the site is less than -2℃, and the daily average temperature T at the project site is greater than 10℃, the mold entry temperature T should be controlled. r ≤ Daily average temperature T+5℃ and T r ≤28℃; Under the condition that the average daily temperature T at the project site is ≤10℃, control the temperature T before pouring the mold. r The temperature ranges from 5℃ to 15℃.

[0055] When the concrete paving layer is being constructed, the average daily temperature of the work surface is T c When the difference between the average daily temperature T at the project site and the actual temperature T is greater than 2℃, and the average daily temperature T at the project site is greater than 10℃, the temperature T for mold placement should be controlled. r ≤ Daily average temperature T+10℃ and T r ≤32℃; Under the condition that the average daily temperature T at the project site is ≤10℃, control the temperature T before pouring the mold. r The temperature ranges from 5℃ to 20℃.

[0056] To control the temperature of concrete upon placement in the formwork, measures such as lowering the temperature of raw materials, using flake ice instead of mixing water, wrapping the concrete mixer truck, and constructing during low-temperature periods can be adopted.

[0057] (II) Crack control in concrete construction of ultra-long tunnel pavement layer involves three aspects of control in construction and on-site management.

[0058] (1) Pre-treatment of the tunnel floor slab.

[0059] First, remove the loose dust from the surface of the base slab, as well as any loose slurry and aggregate remaining from the roughening process, to ensure proper bonding between the pavement concrete and the tunnel base slab and reduce defects.

[0060] Then, continuously spray, sprinkle, or store water on the surface of the base plate to keep it moist for at least 3 days. This can reduce the constraint of the base plate on the concrete of the pavement layer and help reduce the risk of cracking.

[0061] (2) Control the concrete of the pavement layer to be free from traffic disturbance for a certain period of time.

[0062] During the plastic stage before initial setting, the concrete structure has not yet formed, and disturbances have little impact on its performance. After final setting and hardening, the concrete possesses a certain strength, increasing its resistance to disturbances. During the period from initial to final setting, defects left by disturbances can reduce the tensile strength of the concrete and may even directly lead to cracks. Tunnel pavement is an ultra-long, variable-section thin-plate structure; if the concrete is disturbed by commuter traffic during the initial to final setting period, damage to the pavement concrete is more likely, requiring precise control.

[0063] The setting time of mortar tested according to the "Test Method for Performance of Ordinary Concrete Mixture" (GB / T 50080-2016) is under (20±2)℃ or under the same conditions on the engineering site. This is significantly different from the setting time of solid structures under variable temperature conditions due to cement hydration and heat dissipation. Considering that the period of disturbance of the pavement concrete must be precisely controlled, this invention proposes to determine the setting time of solid structures by testing the capillary negative pressure of the actual poured pavement concrete, thereby accurately dividing the period of undisturbed pavement concrete.

[0064] The capillary negative pressure can be tested according to the apparatus and method provided in CN 102590483A or CN 105716745A.

[0065] Specifically, the methods for determining this undisturbed period include:

[0066] First, tests were conducted on the first and last 1m sections of the pavement concrete to be poured. 3 The capillary negative pressure at the center point of the region was collected at intervals not exceeding 0.25 hours until the capillary negative pressure had passed its peak value.

[0067] Secondly, the first 1m of pouring is completed 3 The point at which the capillary negative pressure at the center of the region reaches 10 kPa is taken as T1.

[0068] Next, draw the final pouring height of 1m. 3 The relationship curve between the capillary negative pressure at the center point of the region and time is obtained, and a differential curve is obtained by performing a differential process. The time corresponding to the maximum value of the differential curve is recorded as T2.

[0069] Finally, during the time period T1 to T2, avoid driving within 10m of the edge of the concrete pavement layer.

[0070] (3) Keep warm and moisturized.

[0071] From the start of concrete pouring to the T2 time period, one or more measures such as shading, spraying around the slab surface, and finishing should be taken to suppress plastic cracks. Finishing should be carried out at T2-1 h.

[0072] Within the T2 to 14d age range, cover with a layer of material with a specification of not less than 400g / m². 2 Use permeable geotextiles or cotton wadding and similar materials, and take measures to keep the geotextiles constantly moist, ensuring that the water temperature for wetting the geotextiles is not lower than the average daily air temperature of the storage area.

[0073] For concrete paving layers that are exposed or located within 100m of the tunnel entrance and inside the tunnel, after 14 days of curing, an impermeable tarpaulin or equivalent material should be added over or replaced on top of the original permeable geotextile or cotton wadding, and the curing should continue until the upper surface layer construction is required at 28 days of curing.

[0074] The following specific construction cases and experimental data illustrate the method for controlling concrete cracks in ultra-long tunnel pavement layers provided by this invention.

[0075] Example 1

[0076] The method for controlling cracks in the concrete pavement layer of ultra-long tunnels provided by this invention was applied to an underwater cast-in-place tunnel project. The concrete strength grade of the pavement layer is C30, the thickness is 14.9cm to 43.9cm, and it is poured on a C40 base slab concrete. The deformation joint of the main tunnel structure is 60m, and the length of the pavement layer concrete poured at one time is controlled at 60m.

[0077] (I) Pre-treatment work related to the tunnel floor slab.

[0078] First, remove the loose dust from the surface of the base plate, as well as any loose slurry and aggregate remaining from the roughening process.

[0079] Secondly, water was continuously sprayed onto the surface of the base slab to ensure that the surface of the base slab remained moist. In order to ensure that the base slab remained uniformly and continuously moist, permeable geotextile was covered on the surface of the base slab and water was sprayed regularly for 3 days.

[0080] (ii) Concrete mix design and temperature control for the paving layer.

[0081] This step includes limitations on two aspects: the mix design of the pavement concrete and the control of its pouring temperature.

[0082] Specifically, the first is the mix design of the paving layer concrete.

[0083] The selected concrete raw materials that meet the quality requirements include cement, fly ash, fine aggregate, coarse aggregate, crack-resistant agent, and water-reducing agent. The mass fraction ratio of calcium-magnesium composite expansion agent to hydration temperature rise inhibitor in the crack-resistant agent is 98:2. The paving layer concrete is prepared by mixing according to the dosage shown in Table 3 below.

[0084] Table 3. Mix proportions of pavement concrete (unit: kg / m²) 3

[0085]

[0086] The performance test results of the above-mentioned pavement concrete are shown in Table 4.

[0087] Table 4. Concrete properties of the pavement layer

[0088]

[0089]

[0090] Secondly, it involves controlling the temperature of the concrete poured into the paving layer.

[0091] In this embodiment, the average daily temperature T at the project site was less than 10℃ during the construction of the tunnel pavement layer. Statistical analysis revealed that the average daily temperature T on the surface of the tunnel during construction was... c The temperature T is 4℃ to 5℃ higher than the average daily temperature T at the project site; therefore, the concrete pouring temperature T should be controlled during the construction of the pavement layer inside the tunnel. r The temperature ranges from 5℃ to 20℃.

[0092] (iii) Determine the period during which the concrete of the pavement layer will not be disturbed.

[0093] Test the first and last 1m sections of the pavement concrete to be poured. 3 The capillary negative pressure at the center point of the region was collected every 0.05 hours until the capillary negative pressure reached its peak; the curve of capillary negative pressure versus time was plotted as follows. Figure 1 As shown, the first 1m of pouring was completed. 3 The time to reach 10 kPa at the center point of the area was 5.7 hours; finally, 1 meter of pouring was completed. 3 The first differential curve of capillary negative pressure versus time at the center point of the region is shown below. Figure 2 As shown, the maximum value corresponds to a time of 8.9 hours. Therefore, this means controlling the period from 5.7 hours to 8.9 hours after the start of concrete pouring for the pavement layer to avoid vehicle disturbance within 10 meters of the pavement layer edge.

[0094] (iv) Insulation and moisturizing maintenance.

[0095] After the concrete pavement layer is poured, the concrete surface is finished at 7.9 hours, and a 400g / m² layer is applied between 8.9 hours and 14 days. 2 The permeable geotextile is used and regularly watered for maintenance. The temperature of the maintenance water used should not be lower than the average daily air temperature inside the storage area. No maintenance is required after 14 days.

[0096] According to the aforementioned method for controlling cracks in the pavement concrete construction in this embodiment, the adjustment of various parameters, including the concrete pouring temperature T... rThe maximum temperature rise of the pavement concrete is 14.4℃, the maximum temperature difference between the inner and outer surfaces is only 2.9℃, and the maximum cooling rate is 1.9℃ / d. The unit temperature rise expansion deformation in the thickness direction at the center point of the pavement is 33.2με / ℃, which is much larger than the generally accepted linear expansion coefficient of concrete of 10με / ℃, and the unit temperature drop shrinkage deformation is 0.7με / ℃, which is much smaller than the generally accepted linear expansion coefficient of concrete of 10με / ℃. That is, after adopting the aforementioned technical solution in this embodiment, the temperature rise of the pavement concrete is small, and the deformation of the concrete during the temperature rise and temperature drop stages is effectively compensated, which greatly reduces the risk of shrinkage cracking of the pavement concrete. In addition, by precisely controlling the time when the pavement concrete is undisturbed in the early stage, damage or cracking of the concrete due to early disturbance is avoided.

[0097] The concrete of the pavement layer was continuously monitored at the construction site for more than 5 months, and no cracks were found in the concrete.

[0098] Example 2

[0099] The method for controlling cracks in the concrete pavement layer of ultra-long tunnels provided by this invention was applied to a municipal road rapid reconstruction tunnel project. The concrete strength grade of the pavement layer is C35, the thickness is 12.5cm to 45.3cm, and it is poured on a C40 base slab concrete. The deformation joint of the main tunnel structure is 80m, and the length of the pavement layer concrete poured at one time is controlled at 80m.

[0100] (I) Pre-treatment work related to the tunnel floor slab.

[0101] First, remove the loose dust from the surface of the base plate, as well as any loose slurry and aggregate remaining from the roughening process.

[0102] Secondly, water was continuously sprayed onto the surface of the base slab to ensure that the surface of the base slab remained moist. In order to ensure that the base slab remained uniformly and continuously moist, a permeable geotextile was covered on the surface of the base slab and water was sprayed regularly for 3.5 days.

[0103] (ii) Concrete mix design and temperature control for the paving layer.

[0104] This step includes limitations on two aspects: the mix design of the pavement concrete and the control of its pouring temperature.

[0105] Specifically, the first is the mix design of the paving layer concrete.

[0106] The selected concrete raw materials, meeting quality requirements, include cement, fly ash, fine aggregate, coarse aggregate, crack-resistant agent, and water-reducing agent. The mass fraction ratio of calcium-magnesium composite expansion agent to hydration temperature rise inhibitor in the crack-resistant agent is 97:3. The pavement concrete is prepared by mixing according to the dosages shown in Table 5 below.

[0107] Table 5. Mix proportions of pavement concrete (unit: kg / m²) 3

[0108]

[0109] The test results of the concrete performance of the above-mentioned pavement layer are shown in Table 6.

[0110] Table 6. Concrete properties of pavement layer

[0111]

[0112] Secondly, it involves controlling the temperature of the concrete poured into the paving layer.

[0113] In this embodiment, the average daily temperature T at the project site is greater than 25℃ during the construction of the tunnel pavement layer. Since it is located in the open section of the tunnel, the average daily temperature T on the surface of the pavement layer concrete during construction is also high. c The temperature is the same as the average daily temperature T at the project site. Therefore, during the construction of the open section pavement concrete, the temperature T upon placement of the formwork should be controlled. r ≤30℃.

[0114] To control the concrete pouring into the formwork r For temperatures ≤30℃, measures were taken to shade aggregates, pre-fill powder into storage, and replace mixing water with 70kg of ice flakes during concrete production.

[0115] (iii) Determine the period during which the concrete of the pavement layer will not be disturbed.

[0116] Test the first and last 1m sections of the pavement concrete to be poured. 3 The capillary negative pressure at the center point of the region was collected every 0.25 hours until the capillary negative pressure reached its peak; the relationship curve between capillary negative pressure and time was plotted as follows. Figure 3 As shown, the first 1m of pouring was completed. 3 The time for the capillary negative pressure at the center point of the area to reach 10 kPa was 6.25 hours; finally, a 1m section was poured. 3 The first differential curve of capillary negative pressure versus time at the center point of the region is shown below. Figure 4 As shown, the maximum value corresponds to a time of 11.0 hours. Therefore, traffic disturbance within 10 meters of the edge of the pavement concrete layer is avoided during the time period from 6.25 hours to 11.0 hours after the start of concrete pouring.

[0117] (iv) Insulation and Moisturizing Maintenance

[0118] After the concrete pavement layer is poured, the concrete surface is finished at 10.0h, and within 11.0h to 14d, a 600g / m² layer is applied. 2The permeable geotextile is used and regularly watered for curing, with the temperature of the curing water not lower than the average daily air temperature. Since the open section of the tunnel is exposed, after 14 days, an impermeable tarpaulin is added on top of the original permeable geotextile until 28 days.

[0119] According to the aforementioned method for controlling cracks in the concrete construction of the pavement layer of this invention, the adjustment of various parameters, including the concrete pouring temperature T... r The maximum temperature rise of the pavement concrete is 28.6℃, the maximum temperature difference between the inner and outer surfaces is only 2.4℃, and the maximum cooling rate is 1.8℃ / d. The expansion deformation per unit temperature rise in the thickness direction at the center point of the pavement is 30.2με / ℃, which is much larger than the generally accepted linear expansion coefficient of concrete of 10με / ℃. The shrinkage deformation per unit temperature drop is 1.2με / ℃, which is much smaller than the generally accepted linear expansion coefficient of concrete of 10με / ℃. That is, after adopting the aforementioned technical solution in this embodiment, the temperature rise of the pavement concrete is small, and the deformation of the concrete during the temperature rise and temperature drop stages is effectively compensated, which greatly reduces the risk of shrinkage cracking of the pavement concrete. In addition, by precisely controlling the time when the pavement concrete is undisturbed in the early stage, damage or cracking of the concrete due to early disturbance is avoided.

[0120] The concrete paving layer was continuously monitored at the construction site for more than 4 months, and no cracks were found in the concrete paving layer.

[0121] In summary, the method for controlling cracks in the concrete pavement layer of ultra-long tunnels provided by this invention improves and innovates in terms of concrete materials, construction, and on-site management. It can solve the cracking problem of concrete pavement layer caused by shrinkage and disturbance, and can achieve crack-free concrete pavement layer under the condition of a single pouring length exceeding 60m.

[0122] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for controlling cracks in the concrete construction of ultra-long tunnel pavement layers, characterized in that, Includes the following steps: S1. Pre-treatment of the tunnel floor slab; S2. Select the paving layer concrete and control the pouring temperature of the paving layer concrete; S3. The pavement concrete is laid on the tunnel floor to form a pavement layer; S4. Anti-disturbance treatment of the concrete within the pavement layer; S5. Perform heat preservation and moisture retention maintenance on the paving layer; The method of step S1 includes: Remove the loose dust from the surface of the tunnel floor slab, as well as any loose slurry and aggregate remaining after roughening the tunnel floor slab; The surface of the tunnel floor slab is continuously sprayed, sprinkled with water, or treated with water storage to keep the surface of the tunnel floor slab moist for no less than 3 days; In step S2, 28 kg to 35 kg of crack-resistant agent is added to each cubic meter of the pavement concrete; the crack-resistant agent includes 97% to 98.5% calcium-magnesium composite expansion agent and 1.5% to 3% hydration temperature rise inhibitor, with the total mass of the crack-resistant agent being 100%; The concrete of the pavement layer meets the following performance requirements: the adiabatic temperature rise of the concrete in 1.5 days does not exceed 25℃; the autogenous volume deformation in 14 days is not less than 150 με, and the deformation in 28 days is not less than 100 με; and the slump of the concrete is 170 mm ± 30 mm. The concrete pouring temperature T of the pavement layer r Based on the average daily temperature T on the surface of the paving layer concrete during construction c Adjustments are made based on the average daily temperature T at the project site to meet the following requirements: When -2℃≤T c When -T≤2℃, if T>10℃, then control T r ≤T+8℃ and T r ≤30℃; if T≤10℃, then control 5℃≤T r ≤18℃; When T c When -T < -2℃, if T > 10℃, then control T. r ≤T+5℃ and T r ≤28℃; if T≤10℃, then control 5℃≤T r ≤15℃; When T c When T > 2℃, if T > 10℃, then control T. r ≤T+10℃ and T r ≤32℃; if T≤10℃, then control 5℃≤T r ≤20℃; In step S4, the method for determining the time period during which the concrete in the pavement layer remains undisturbed is as follows: Test the concrete pouring of the pavement layer first and last, 1 m in length, respectively. 3 The capillary negative pressure at the center point of the region was collected at intervals not exceeding 0.25 h until the capillary negative pressure reached its peak. The first to complete the pouring of 1 m 3 The point at which the capillary negative pressure at the center of the region reaches 10 kPa is taken as T1. The final pouring was completed 1 m. 3 The relationship between capillary negative pressure at the center point of the region and time is obtained by performing a differential process and recording the time corresponding to the maximum value of the differential curve as T2. During the time period T1 to T2, avoid driving within 10 m of the edge of the concrete pavement layer; The specific method of step S5 includes: From the start of concrete pouring for the pavement layer to the T2 time period, the formed pavement layer is treated to suppress plastic cracks. Within the age range of T2 to 14 days, the paving layer is covered with a covering material, which is kept moist, and the water temperature of the covering material is not lower than the average daily air temperature T of the storage area. c ; For the pavement layer that is exposed or located within 100 m of the tunnel entrance, after 14 days of curing, a waterproof layer is added to the cover or the cover is replaced with a waterproof layer, and curing is completed when the upper surface layer construction is required at 28 days of curing.

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