Thermal-insulation-maintenance-free tunnel molded lining concrete construction method

Abstract

The invention discloses a heat-preservation-maintenance-free tunnel molded lining concrete construction method which comprises the following steps that S1, before concrete pouring, a hollow pipe is pre-buried in the middle of a lining structure in the length direction; s2, low-temperature-rise lining concrete is prepared, a hydration temperature rise inhibitor is doped in the concrete mixing proportion, the early heat release rate of the concrete is reduced, and the temperature peak value of the concrete is reduced by 5-8 DEG C; and S3, when the lining concrete is poured, circulating cooling water is synchronously introduced into the hollow pipe, the internal temperature of the concrete is further reduced through the cooling circulating water, the strength reaches 75% or above, and then formwork removal can be conducted without heat preservation and maintenance, the temperature difference between the inner surface and the outer surface of the tunnel lining concrete in the whole process is controlled within 15 DEG C all the time, and the construction period is shortened. And after the requirement for the formwork removal strength is met, formwork removal can be conducted, heat preservation and maintenance measures are not needed, and the problems that lining formwork removal is early and maintenance is difficult are effectively solved.

Description

Technical Field

[0001] The invention belongs to the technical field of concrete, and more specifically, relates to a method for constructing tunnel formwork lining concrete without thermal insulation maintenance. Background Art

[0002] During the construction process, the main structure of the tunnel generally adopts a composite lining structure, and the secondary lining concrete structure is the main structure that bears the bottom pressure, prevents the deformation of the surrounding rock, and ensures the long-term durability of the tunnel. Therefore, ensuring the safe and durable service of the secondary lining concrete of the tunnel is an important guarantee for achieving long-life service of the tunnel. However, during the construction process, it was found that there were large differences between the demolding time and maintenance methods of the tunnel lining and other concrete projects. From the survey of the construction period, the lining concrete is usually demolded within one day after pouring, and at this time the internal and external temperatures of the concrete are still very high, which is very easy to produce temperature cracks. In addition, since the lining structure is usually arched and has a large span, it is often difficult to maintain after demolding or even directly abandons maintenance, which further increases the risk of concrete cracking. In recent years, there are more and more underground space structures, and a large number of structures have a large number of leakage problems due to concrete cracking, causing immeasurable economic losses.

[0003] The maintenance of tunnel lining concrete is currently mainly based on spray wet maintenance. This measure can reduce the occurrence of surface drying microcracks to a certain extent, but it cannot solve the temperature cracks caused by the temperature difference between the inside and outside. On the contrary, if the spray water temperature is too low in the early stage, it may further aggravate the occurrence of temperature cracks. In addition, there are also methods of maintenance by covering the entire arch surface with insulation materials after demolding. Although the insulation maintenance effect is obvious, its construction operation is extremely complicated. The core problem is that it is necessary to solve the problem of the close fitting laying and hanging fixation of the insulation material on the surface of the arch lining, and it often requires a large economic cost. Although the method of insulation maintenance by covering the entire arch surface with insulation materials can solve the problem of tunnel temperature cracks, in actual projects, due to the complexity of the process and on-site management, higher requirements are required for construction operations, but it is often difficult to achieve on the construction site, and the problem still cannot be solved. Summary of the invention

[0004] The invention provides a tunnel formwork lining concrete construction method free of thermal insulation maintenance in order to solve the problem of early demoulding and difficult maintenance of the lining.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for constructing tunnel cast lining concrete without thermal insulation maintenance, comprising the following steps:

[0007] S1. Before pouring concrete, pre-embed hollow pipes in the middle of the lining structure along the length direction;

[0008] S2. Prepare low-temperature rise lining concrete, add hydration temperature rise inhibitor into the concrete mix ratio, reduce the early heat release rate of concrete, and reduce the peak temperature of concrete by 5-8°C;

[0009] S3. When pouring lining concrete, circulating cooling water is simultaneously introduced into the hollow pipe to further reduce the internal temperature of the concrete by cooling the circulating water. When the strength reaches 75% or above, the formwork can be removed without the need for thermal insulation maintenance.

[0010] Furthermore, the hollow tube in step S1 is a cast iron tube, a steel tube or a copper tube.

[0011] Further, in step S1, 1 to 2 layers of inner diameter are embedded in the middle of the lining structure along the length direction. For hollow pipes, the horizontal spacing between hollow pipes in the same layer is 20cm~30cm, the vertical spacing is 20~50cm, and the distance between the first layer of pre-buried hollow pipes and the construction joint is 20~50cm.

[0012] Furthermore, in step S1, for a structure with a lining thickness of less than 70 cm, a layer of hollow tubes is buried in the middle of the structure along the length direction.

[0013] Furthermore, in step S1, for a structure with a lining thickness exceeding 70 cm, two layers of hollow tubes are buried in the middle of the structure along the length direction.

[0014] Furthermore, in step S2, the low temperature rise lining concrete is a concrete in which 1-2% by mass of a hydration temperature rise inhibitor is added to the cementitious material.

[0015] Furthermore, in step S3, the pouring temperature of the low-temperature rise lining concrete should be controlled below the daily average temperature of the tunnel environment.

[0016] Furthermore, in step S3, the temperature difference between the inner surface of the concrete and the maximum temperature difference between the surface and the environment are controlled to be no more than 15° C. by controlling the temperature and circulation rate of the circulating water inside the concrete.

[0017] Furthermore, the temperature field variation of the lining concrete is determined based on finite element simulation or on-site temperature monitoring results of similar components.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) The method for constructing tunnel formwork lining concrete without thermal insulation and maintenance provided by the present invention can solve the technical problems of early formwork removal and difficult maintenance of the lining after formwork removal without affecting the construction period by optimizing and adjusting the concrete performance and construction process.

[0020] (2) The problem of temperature cracks in the tunnel lining concrete is fundamentally solved through prior process adjustment, so that there will be no leakage caused by temperature shrinkage cracking after the lining concrete is poured. Compared with most existing post-repair measures, this method is safer, has no repair and maintenance costs, and is more feasible and implementable, ensuring the safe and long-term operation of the tunnel.

[0021] (3) The addition of a hydration temperature rise inhibitor during concrete pouring can reduce the cement hydration temperature rise rate. Combined with the cooling circulating water for continuous temperature control, combined with the previous simulation calculation conditions, concrete performance and construction technology, it is possible to achieve the goal of eliminating the need for insulation maintenance for the tunnel lining concrete after demolding, thus simplifying the concrete maintenance conditions after demolding, which has great reference significance for similar projects.

[0022] The present invention will be described in more detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The following is a brief description of the contents and symbols in the drawings of this specification:

[0024] Figure 1 This is a schematic diagram of the buried section of the cooling pipe when the lining thickness is greater than 70cm;

[0025] Figure 2 It is a schematic diagram of the buried surface of the cooling pipe of the lining;

[0026] Marked in the figure: 1. Lining structure; 2. Hollow tube; 3. Casting interface; 4. Invert structure. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiment is only one embodiment of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] Comparative Example 1

[0029] like Figures 1-2 As shown, according to experimental components or similar components that have been constructed, the lining is prone to temperature cracks due to early demoulding and difficult maintenance. Before pouring the lining concrete, a hollow tube 2 is buried.

[0030] The lining thickness is 80cm, the concrete strength grade is C40, and two layers of inner diameter are embedded in the middle of the lining structure along the length direction. For hollow pipes, the horizontal spacing between hollow pipes in the same layer is 30cm, the vertical spacing is 50cm, and the distance between the first layer of pre-buried hollow pipes and the construction joint is 30cm.

[0031] Before construction and pouring, the temperature of the concrete entering the mold should be controlled not to exceed the daily average temperature of the tunnel environment, so as to reduce the peak temperature inside the concrete.

[0032] According to the insulation data of lining concrete and combined with the actual size of the lining, a finite element model is established using software such as Midas to simulate the temperature conditions inside the lining concrete when cooling water is flowing. Alternatively, temperature sensors are buried in the component model of the same size to monitor the internal temperature field and determine the cooling water flow conditions.

[0033] Before pouring the lining concrete, circulating cooling water is introduced into the embedded pipe. The maximum temperature difference between cooling water and concrete shall not exceed 25°C. After testing, the cooling water pipe working condition is taken alone. The internal temperature of the concrete is shown in Table 1. The maximum temperature difference between the inner and outer surfaces of the concrete will exceed 25°C, and the maximum temperature difference between the surface and the environment will exceed 20°C. In order to avoid temperature cracks caused by excessive temperature drop, thermal insulation maintenance is still required after the lining is demolded.

[0034] Table 1 The internal temperature of the cooling water pipe lined with concrete

[0035]

[0036] Comparative Example 2

[0037] like Figures 1-2 As shown, according to the experimental components or similar components that have been constructed, which are prone to temperature cracks due to early demoulding and difficult maintenance, low-temperature rising lining concrete is used to cast the tunnel lining before pouring the lining concrete.

[0038] The lining thickness is 80cm, and the concrete strength grade is C40. In a certain engineering case, the low temperature rise lining concrete is a concrete in which 2.0% of the total amount of cementitious materials is added to the base mix ratio. The amount of hydration temperature rise inhibitor should not exceed 2.0%. Exceeding the amount is likely to affect the early concrete strength and is not conducive to early demolding. In this embodiment, the method for determining the amount of concrete hydration temperature rise inhibitor is as follows:

[0039] Table 2 Concrete hydration temperature rise inhibitor dosage

[0040]

[0041]

[0042] The hydration heat reduction rate of concrete hydration temperature rise inhibitor is expressed as the ratio of the difference between the hydration heat of cement in the reference mortar and the hydration heat of cement in the tested mortar within the specified age to the hydration heat of cement in the reference mortar. Based on the cement dosage, 300% standard sand, 40% water and a certain proportion of concrete hydration temperature rise inhibitor are mixed according to Table 2. The temperature change inside the mortar is directly measured in a constant temperature environment using a calorimeter for the evenly mixed mortar, and the hydration heat at different ages is calculated. In addition, each group reserves a compression test block to ensure that the influence of the hydration temperature rise inhibitor on the concrete strength is within the control range.

[0043] Table 3 shows the data summary of hydration heat release and reduction rate at different ages and 28d compressive strength ratio of 7 groups of mortars formed according to the dosage in Table 2 in Comparative Example 2.

[0044] Table 3 Mortar hydration heat release and reduction rate

[0045]

[0046]

[0047] Table 3 shows the effect of different dosages of hydration temperature rise inhibitor on cement hydration efficiency and strength. It can be seen that with the increase of the dosage of hydration temperature rise inhibitor, the hydration heat release of cement at 3d / 7d decreases successively, and the 28d mortar compressive strength also decreases accordingly. According to the "Concrete Hydration Temperature Rise Inhibitor" (JC / T2608-2021), the 24h hydration heat reduction rate is ≥30%, and the 7d hydration heat reduction rate is ≤15%. In the present invention, when the hydration heat temperature rise is suppressed to 1.0-2.0%, the specification requirements are met, and the 28d compressive strength ratio is greater than 90%, and the influence on strength is also within the control range.

[0048] Comprehensively consider the hydration control and strength guarantee of hydration temperature rise inhibitors, that is, excessive hydration temperature rise inhibitors can greatly reduce the early hydration heat release rate and heat release, but it is very likely to cause slow strength development of concrete in the later stage due to over-addition, so the amount of hydration temperature rise inhibitor should not be too high. Therefore, with temperature control as the goal, reduce the risk of shrinkage cracking of concrete structure, and suppress hydration heat temperature rise at 1.0-2.0%, and the optimal dosage is 2.0%.

[0049] After full-scale model tests, when the hydration temperature rise inhibitor is added alone, the time to reach the temperature peak is prolonged, and the internal temperature of the concrete is shown in Table 4. However, the maximum temperature difference between the inner and outer surfaces and the temperature difference between the surface and the environment are both over 20°C. In order to avoid temperature cracks caused by excessive temperature drop, thermal insulation maintenance is still required after the lining is demolded.

[0050] Table 3 Mortar hydration heat release and reduction rate

[0051] Table 4 Internal temperature of lining concrete when adding hydration temperature rise inhibitor

[0052]

[0053]

[0054] Example 1

[0055] like Figures 1-2 As shown, according to experimental components or similar components that have been constructed, the lining is prone to temperature cracks due to early demoulding and difficult maintenance. Before pouring the lining concrete, a hollow tube 2 is buried.

[0056] The lining thickness is 80cm, the concrete strength grade is C40, and two layers of concrete with an inner diameter of For hollow pipes, the horizontal spacing between hollow pipes in the same layer is 30cm, the vertical spacing is 50cm, and the distance between the first layer of pre-buried hollow pipes and the construction joint is 30cm.

[0057] At the same time, low-temperature rise lining concrete is used to cast the tunnel lining. The low-temperature rise lining concrete is a concrete with a hydration temperature rise inhibitor accounting for about 2% of the total amount of cementitious materials added to the base mix ratio.

[0058] Before construction and pouring, the temperature of the concrete entering the mold should be controlled not to exceed the daily average temperature of the tunnel environment, so as to reduce the peak temperature inside the concrete.

[0059] According to the insulation data of lining concrete and combined with the actual size of the lining, a finite element model is established using software such as Midas to simulate the temperature conditions inside the lining concrete when cooling water is flowing. Alternatively, in the component model of the same size, temperature sensors are buried to monitor the internal temperature field and determine the cooling water flow conditions.

[0060] Before pouring the lining concrete, circulating cooling water is introduced into the embedded pipe, and the maximum temperature difference between the cooling water and the concrete shall not exceed 25°C. After testing, it is found that the temperature control index requirements cannot be met when cooling water pipes or hydration temperature rise inhibitors are used alone. Cooling water pipes and hydration temperature rise inhibitors must be used together to achieve the effect of free insulation maintenance. The internal temperature of the concrete is shown in Table 5. Since the maximum temperature difference between the inner surface temperature of the concrete and the temperature difference between the surface and the environment do not exceed 15°C, the formwork can be removed after meeting the demolding strength requirements without insulation maintenance, which solves the problem of early demolding and difficult maintenance of the arch lining.

[0061] Table 5 Internal temperature of lining concrete when using cooling water pipes and hydrated temperature rise inhibitor at the same time

[0062]

[0063] Working principle and method

[0064] The present invention is described above by way of example in conjunction with the accompanying drawings. It is obvious that the specific implementation of the present invention is not limited to the above-mentioned method. As long as various non-substantial improvements are made using the method concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A method for constructing tunnel lining concrete without thermal insulation maintenance, characterized in that: The steps include: S1. Before pouring concrete, pre-embed hollow pipes in the middle of the lining structure along the length direction; S2. Prepare low-temperature rise lining concrete, add hydration temperature rise inhibitor into the concrete mix ratio, reduce the early heat release rate of concrete, and reduce the peak temperature of concrete by 5-8°C; S3. When pouring lining concrete, circulating cooling water is simultaneously introduced into the hollow pipe to further reduce the internal temperature of the concrete by cooling the circulating water. When the strength reaches 75% or above, the formwork can be removed without the need for thermal insulation maintenance.

2. A method for constructing tunnel lining concrete without thermal insulation maintenance according to claim 1, characterized in that: The hollow tube in step S1 is a cast iron tube, a steel tube or a copper tube.

3. The method for constructing a tunnel lining concrete without thermal insulation maintenance according to claim 1, characterized in that: In step S1, 1 to 2 layers of concrete with an inner diameter of 1.5 mm are pre-buried in the middle of the lining structure along the length direction. For hollow pipes, the horizontal spacing between hollow pipes in the same layer is 20cm~30cm, the vertical spacing is 20~50cm, and the distance between the first layer of pre-buried hollow pipes and the construction joint is 20~50cm.

4. The method for constructing a tunnel lining concrete without thermal insulation maintenance according to claim 1, characterized in that: In the step S1, for a structure with a lining thickness of less than 70 cm, a layer of hollow tubes is buried in the middle of the structure along the length direction.

5. The method for constructing a tunnel lining concrete without thermal insulation maintenance according to claim 1, characterized in that: In the step S1, for a structure with a lining thickness exceeding 70 cm, two layers of hollow tubes are buried in the middle of the structure along the length direction.

6. The method for constructing a tunnel lining concrete without thermal insulation maintenance according to claim 1, characterized in that: In step S2, the low temperature rise lining concrete is a concrete in which 1-2% by mass of a hydration temperature rise inhibitor is added to the cementitious material.

7. The method for constructing a tunnel lining concrete without thermal insulation maintenance according to claim 1, characterized in that: In step S3, the pouring temperature of the low-temperature rise lining concrete should be controlled below the average daily temperature of the tunnel environment.

8. The method for constructing tunnel cast lining concrete without thermal insulation maintenance according to claim 1, characterized in that: In step S3, the temperature difference between the inner surface of the concrete and the temperature difference between the surface and the environment are controlled to be no more than 15° C. by controlling the temperature and circulation rate of the circulating water inside the concrete.

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