Method for managing integrated temperature during lining concrete heat curing

Abstract

To provide a lining concrete heat curing method capable of ensuring that the required compressive strength is achieved in the lining concrete within a target formwork removal time so that construction can be accelerated.SOLUTION: A target integrated temperature M0 at which lining concrete is expected to achieve the required compressive strength is calculated in advance; the transition of the temperature of the lining concrete heated by a heater is measured at not less than two measurement points on the side of a center formwork and on the side of a tunnel natural ground, the former being the point of finishing installation of the lining concrete in the center formwork and the top end position of the center formwork avoiding a planar heater; the lining concrete is heated by the heater so that an integrated temperature M of the lining concrete estimated from the transition of the temperature measured at each measurement point may reach the target integrated temperature M0 within a setting target form-removal time t0 for removing the center formwork; and the center formwork is removed when the integrated temperature M of the lining concrete reaches the target integrated temperature M0 at all the measurement points.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a heating and curing method for lining concrete that can reliably cause the lining concrete to develop the required compressive strength within a targeted demolding time so as to realize faster construction. [Background technology]

[0002] Patent Document 1 is known as a technology for heating and curing lining concrete poured on the inner surface of a tunnel using a heater installed in a center formwork.

[0003] The "Lining Concrete Temperature Control Method" of Patent Document 1 has the objective of providing an effective and appropriate temperature control method for appropriately controlling the temperature of lining concrete when it is young in tunnel construction, and involves attaching a heat-generating sheet in advance to a formwork for pouring and molding the lining concrete. When the lining concrete is poured into the formwork, the surface temperature of the lining concrete is measured, and once the surface temperature reaches its peak temperature, the heat-generating sheet heats the surface layer of the lining concrete through the formwork, preventing a sudden drop in temperature of the surface layer and ensuring a heating and curing time to reduce the temperature difference between the internal temperature and the surface temperature, and then the formwork is removed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2014-88743 A Summary of the Invention [Problem to be solved by the invention]

[0005] When curing young lining concrete immediately after pouring, it is necessary for the lining concrete to develop a compressive strength that is sufficient to withstand its own weight and loads, and that does not cause damage such as surface peeling when the center formwork is removed.

[0006] In order to ensure this level of compressive strength, a curing time of about one day and one night is required. However, in order to speed up construction, it is necessary to shorten this curing time, i.e., to be able to remove the formwork in a short time.

[0007] Lining concrete develops compressive strength through hydration reactions, but the hydration reaction proceeds faster the higher the temperature of the concrete and slower the lower the temperature, so the environmental temperature of the location where the lining concrete is being constructed has a significant impact on the hydration reaction in the early stages of concrete pouring.

[0008] Specifically, inside the tunnel where the lining concrete is being constructed, there is a difference in temperature between the ground side and the center formwork side.

[0009] While the temperature on the natural ground side is almost constant, the temperature on the center formwork side is higher in summer and lower in winter due to the temperature of the outside air flowing into the tunnel. Also, the temperature of fresh concrete produced outside the tunnel is almost the same as the outside air temperature.

[0010] Therefore, the hydration reaction in the lining concrete proceeds relatively faster in the thickness direction of the lining concrete on the center formwork side in summer and on the natural ground side in winter.

[0011] For these reasons, as disclosed in Patent Document 1, the lining concrete is heated and cured using a heat-generating sheet to promote the hydration reaction evenly, thereby generating the necessary compressive strength for the early-age lining concrete.

[0012] However, in Patent Document 1, the temperature of the lining concrete is heated after it has reached its peak due to the heat of hydration reaction, and it does not promote the hydration reaction at the early stage of concrete pouring when the temperature of the center formwork is low due to the influence of the environmental temperature described above. Regarding the heating of early-age lining concrete, there was a need to develop a heating control method that could reliably achieve the required compressive strength within the target demolding time, so as to speed up construction.

[0013] The present invention has been devised in consideration of the above-mentioned conventional problems, and has an object to provide a heating and curing method for lining concrete that can reliably cause the lining concrete to develop the required compressive strength within the targeted stripping time, thereby enabling faster construction. [Means for solving the problem]

[0014] The method for heating and curing lining concrete according to the present invention is a method for heating and curing the lining concrete to be poured on the inner surface of a tunnel ground by a temperature-controllable heater provided in a center formwork, characterized in that a target integrated temperature at which the lining concrete is estimated to develop the required compressive strength is determined in advance, and a temperature transition of the lining concrete heated by the heater is measured at at least two measurement points, one on the side of the center formwork and one on the side of the tunnel ground, at the position where the lining concrete has been poured into the center formwork and at the top position of the center formwork avoiding the heater, the lining concrete is heated by the heater so that the integrated temperature of the lining concrete estimated from the temperature transitions measured at each of the measurement points reaches the target integrated temperature within a set target demolding time for demolding the center formwork, and the center formwork is demolded when the integrated temperature of the lining concrete at all of the measurement points has reached the target integrated temperature. Effect of the Invention

[0015] The heating and curing method for lining concrete according to the present invention can reliably cause the lining concrete to develop the required compressive strength within the targeted demolding time, thereby enabling faster construction. [Brief description of the drawings]

[0016] [Figure 1] FIG. 2 is an explanatory diagram for explaining the construction state of lining concrete to which the heating and curing method for lining concrete according to the present invention is applied. [Diagram 2]FIG. 2 is an explanatory diagram illustrating the procedure for pouring the lining concrete shown in FIG. 1. [Diagram 3] 2 is a cross-sectional view taken along line AA in FIG. [Figure 4] 1 is a graph illustrating the relationship between compressive strength and accumulated temperature obtained in an experiment on a concrete specimen. [Diagram 5] FIG. 2 is an explanatory diagram of the change in the accumulated temperature of the lining concrete over time, explaining a preferred embodiment of the heating and curing method for the lining concrete according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, a preferred embodiment of the heating and curing method for lining concrete according to the present invention will be described in detail with reference to the accompanying drawings.

[0018] As shown in FIG. 1, a center form 2 used for pouring lining concrete 1 in mountain tunnel construction is conventionally well known.

[0019] The center formwork 2 is formed in an approximately hollow semi-cylinder shape so that it has a predetermined length in the direction in which the center formwork 2 advances within the excavated tunnel and presents a semicircular arc shape that follows the inner surface of the excavated tunnel ground 3.

[0020] An arch-shaped casting space is formed between the center formwork 2 and the tunnel ground 3, and lining concrete 1 is poured into this casting space. The inner surface of the tunnel is formed as the lining concrete 1 hardens.

[0021] A temperature-controllable surface heater 4 is disposed in an appropriate position on the inner surface of the center formwork 2 (the space opposite the tunnel ground 3) in order to heat and cure the lining concrete 1 poured in the pouring space.

[0022] The planar heater 4 is disposed so as to be able to heat the entire surface of the center formwork 2 (not the entire lining concrete 1) almost uniformly.

[0023] In the illustrated example, the planar heater 4 is formed in a band shape along the longitudinal direction of the center formwork 2, and multiple such planar heaters 4 are arranged at intervals from each other in the circumferential direction of the center formwork 2, and are provided in a striped configuration on the center formwork 2.

[0024] The planar heater 4 may be formed in a band shape along the circumferential direction of the center form 2, and a plurality of such planar heaters 4 may be arranged at intervals from each other in the longitudinal direction of the center form 2.

[0025] Alternatively, the sheet heaters 4 may be disposed in a dot pattern over the entire surface of the center form 2 .

[0026] In this embodiment, the surface heater 4 is installed to avoid the top end position on the gable formwork 2a side (the side not in contact with the lining concrete 1 that has been poured) of the center formwork 2, which is the position where the pouring of the lining concrete 1 is completed, for reasons that will be described later.

[0027] Generally, concrete hardens through a hydration reaction, and its compressive strength increases.

[0028] The hydration reaction of concrete is affected by the surrounding environmental temperature, and whether the environmental temperature is high or low affects the time it takes to obtain the required compressive strength.

[0029] On the other hand, by heating and curing the concrete, the hydration reaction can be accelerated, shortening the time it takes to develop the required compressive strength.

[0030] As for the environmental temperature inside the tunnel where the lining concrete 1 is laid, as described above, there is a difference in temperature between the tunnel natural ground 3 side and the center formwork 2 side.

[0031] When considering the environmental temperature during construction of the lining concrete 1 throughout the year, particularly in winter, the temperature is lower on the side of the center formwork 2 in the thickness direction of the lining concrete 1, and the temperature is lower on the side of the gable formwork 2a in the longitudinal direction of the center formwork 2.

[0032] For the entire poured lining concrete 1, and particularly for the lining concrete 1 in these locations, it will take a long time to develop the required compressive strength during the low temperatures of winter.

[0033] Heat curing of the lining concrete 1 using a heating means such as a surface heater 4 is effective in shortening the time from pouring the lining concrete 1 to stripping the center formwork 2, but it is not possible to know whether or not this heat curing has reliably ensured the necessary compressive strength for the lining concrete 1, in other words, whether the lining concrete 1 has developed a compressive strength that can withstand its own weight and load at the time the center formwork 2 is stripped, and that will not cause defects such as surface peeling in the lining concrete 1 when the formwork is stripped.

[0034] In addition, the time required from pouring the lining concrete 1 to stripping the center formwork 2 is extremely important in realizing high-speed construction of the lining concrete 1, and it is necessary to shorten this time, that is, to make it fall within the short target stripping time required for high-speed construction. However, simply performing heating and curing does not make it possible to know whether the center formwork 2 can be stripped within such target stripping time.

[0035] The method for heating and curing the lining concrete in this embodiment involves heating and curing the poured lining concrete 1 with a surface heater 4 so that the lining concrete 1 develops the required compressive strength σ0 at the target demolding time t0, which contributes to high-speed construction of the lining concrete 1 (see Figures 4 and 5).

[0036] In controlling the temperature-controllable surface heater 4, in this embodiment, the temperature change of the poured lining concrete 1 is measured at the top end of the center formwork 2, on the gable formwork 2a side of the center formwork 2, where the temperature of the poured lining concrete 1 is thought to be lowest due to the influence of the ambient temperature, and where the lining concrete 1 is poured latest (filled last) into the pouring space.

[0037] Figure 2 shows how the lining concrete 1 is poured into the center formwork 2. Pouring of the lining concrete 1 starts from the lowest layer on the left and right sides of the center formwork 2 when viewed from the front, over the entire length in the longitudinal direction, and this is repeated in the upper layers until the concrete is spread throughout the entire center formwork 2 except for the top end, and then the top end is poured. At this time, an air bleed is ensured in the gable formwork 2a, and pouring is completed by pouring concrete sequentially from the side in contact with the lining concrete 1' that has been poured toward the gable formwork 2a, and a lining concrete 1 without air pockets is constructed.

[0038] Because of this pouring procedure, the lining concrete 1 is poured latest near the top end of the gable formwork 2a of the center formwork 2, whereas in other areas where pouring has been completed earlier, the hardening of the lining concrete 1 has progressed considerably.

[0039] In other words, if the required compressive strength is achieved near the top end of the gable formwork 2a of the center formwork 2, which will be the last to be poured, it can be said that the required compressive strength has of course been achieved in the preceding pouring area.

[0040] As described above, for the reason that temperature measurements are performed at points exposed to the outside air where the temperature tends to be low and where the development of compressive strength is relatively slow, the surface heater 4 is arranged to avoid the top end position on the gable formwork 2a side of the center formwork 2.

[0041] As a means for measuring the temperature transition, a temperature measuring means such as a thermocouple 5 is used as shown in Fig. 3. Fig. 3 is a cross-sectional view taken along line AA in Fig. 1.

[0042] The thermocouples 5 are installed at two locations, one on the side of the center formwork 2 and the other on the side of the tunnel natural ground 3, on the side of the end formwork 2a of the center formwork 2, which is the position where the pouring of the lining concrete 1 is completed, and at the top end of the center formwork 2 and its surroundings, avoiding the planar heaters 4. Therefore, the temperature transition of the lining concrete 1 is measured at these two locations.

[0043] Of course, measurements may be made not only on the side of the center formwork 2 and the side of the tunnel ground 3, but also between them.

[0044] Specifically, on the side of the center formwork 2, the thermocouple 5 is installed on the inner space side of the center formwork 2, where the measured temperature is approximately the same as that of the surface (inner surface) of the lining concrete 1 due to thermal conduction, and is covered with insulation material 6.

[0045] On the tunnel natural ground 3 side, the thermocouple 5 is provided near the inside of a waterproof sheet (not shown) stretched on the tunnel natural ground 3 side.

[0046] These two thermocouples 5 measure the temperature transition of the lining concrete 1 heated by the sheet heater 4 .

[0047] In the heating and curing method for the lining concrete according to this embodiment, first, a heating and curing experiment is carried out on a concrete specimen prepared with the same mix as the lining concrete 1 to be actually constructed.

[0048] From this experiment, the relationship between compressive strength σ and accumulated temperature M of the concrete specimen is obtained.

[0049] From the experimental results, the accumulated temperature at which the lining concrete 1 used in actual construction develops the above-mentioned required compressive strength σ0 is determined in advance, and this accumulated temperature is set as the target accumulated temperature M0 at which the lining concrete 1 is estimated to develop the required compressive strength σ0.

[0050] In heating and curing experiments on concrete specimens, the temperature of the concrete is measured at equal time intervals, for example every minute, and the temperatures measured every hour are accumulated, for example with an accumulating thermometer, to obtain the accumulated temperature M. The compressive strength σ developed in the concrete specimen at each temperature measurement is also measured.

[0051] During the experiment, the concrete specimen may or may not be subjected to heating and curing.

[0052] Figure 4 shows a graph plotting the experimental values ​​of accumulated temperature M and compressive strength σ of concrete specimens obtained in the heating curing experiment, with the vertical axis representing compressive strength σ and the horizontal axis representing accumulated temperature M.

[0053] For the plots on the graph, the regression line equation of the following formula (1) is obtained. This regression line equation is a "calculation formula for estimated compressive strength" that can be applied to the concrete specimen, i.e., the lining concrete 1 that will actually be used. σ = α × M(T t) + β … (1) σ(N / mm2): Compressive strength M (℃ / hour): Accumulated temperature α, β: For concrete specimen (lining concrete), Coefficients determined from the regression line equation

[0054] From the first-order linear graph of the "calculation formula for estimated compressive strength," the accumulated temperature at which the lining concrete 1 to be used is estimated to exhibit the required compressive strength σ0 described above is calculated, and this is set as the "target accumulated temperature M0."

[0055] In other words, if the accumulated temperature based on the temperature trend of the lining concrete 1 measured by the thermocouple 5 shown in Figure 3 reaches the "target accumulated temperature M0", it can be estimated that the lining concrete 1 has developed the required compressive strength σ0.

[0056] Next, the temperature change of the lining concrete 1, which is actually poured into the center formwork 2 and heated by the surface heater 4, is measured using a thermocouple 5 at the top end of the gable formwork 2a side of the center formwork 2, and the rate of increase in the accumulated temperature of the lining concrete 1 at that measurement point is determined.

[0057] Figure 5 is a graph showing the relationship between the accumulated temperature M, calculated by an integrating thermometer to measure the temperature change of the lining concrete 1, and the passage of time t, in which the vertical axis is the accumulated temperature M of the lining concrete 1 and the horizontal axis is time t, and lines MA and MB show the rate of increase in the accumulated temperature per hour on the side of the center formwork 2 and the side of the tunnel ground 3.

[0058] 5, the state of heating and curing the lining concrete 1 by the sheet heater 4 over time can be understood. In FIG. 5, t0 is the set target form stripping time.

[0059] The illustrated example shows that the rates of increase in the accumulated temperature of the lining concrete 1 from immediately after pouring to the specified measurement time ts are MA and MB, and that the accumulated temperature M of the lining concrete 1 at the set target demolding time t0 estimated from the rates of increase MA and MB does not reach the target accumulated temperature M0.

[0060] In such a case, the temperature of the temperature-controllable plane heater 4 is increased to heat the lining concrete 1, and the rate of increase in the integrated temperature M at each measurement point is increased (MA→MA1, MB→MB1).

[0061] By increasing the rate of increase of the accumulated temperature M, the lining concrete 1 can reach the target accumulated temperature M0 at times t1 and t2 within the set target demolding time T0 for demolding the center formwork 2, whether on the side of the center formwork 2 or the side of the tunnel ground 3.

[0062] Then, when the accumulated temperature M of the lining concrete 1 reaches the target accumulated temperature M0 at all measurement points as measured by the thermocouples 5, the center formwork 2 is removed.

[0063] When the pouring of the lining concrete 1 into the center formwork 2 is completed (the position on the gable formwork 2a side), the accumulated temperature M at the top position of the center formwork 2 has reached the target accumulated temperature M0, and the required compressive strength σ0 has been achieved, then of course the lining concrete 1 in the preliminary pouring area will have achieved the required compressive strength σ0.

[0064] In Figure 5, the set temperature of the planar heater 4 is controlled to be changed to a higher temperature halfway through, but the present invention is not limited to this. For example, MA and MB in the figure can be regarded as estimated values ​​at a certain set temperature of the planar heater 4, and based on a simulation result that the estimated values ​​of MA and MB when a temperature (Tx) of the planar heater 4 higher than the set temperature is set satisfies the target accumulated temperature M0 within the target demolding time t0, the temperature of the planar heater 4 can be set to temperature Tx from the beginning of heating.

[0065] In the heating and curing method of the lining concrete according to the present embodiment described above, a target integrated temperature M0 at which the lining concrete 1 is estimated to develop the required compressive strength σ0 is obtained in advance, and the temperature transition of the lining concrete 1 heated by the planar heater 4 is measured at at least two measurement points on the side of the center formwork 2 and the side of the tunnel ground 3 at the position where the pouring of the lining concrete 1 into the center formwork 2 is completed and at the top end position of the center formwork 2 avoiding the planar heater 4. The lining concrete 1 is heated by a surface heater 4 so that the accumulated temperature M of the lining concrete 1 estimated from the temperature progression reaches the target accumulated temperature M0 within the set target demolding time t0 for demolding the center formwork 2, and the center formwork 2 is demolded when the accumulated temperature M of the lining concrete 1 at all measurement points reaches the target accumulated temperature M0. This makes it possible to reliably make the early-age lining concrete 1 develop the required compressive strength σ0 within the target demolding time t0, thereby enabling construction to be carried out at higher speeds. [Explanation of symbols]

[0066] 1 Lining concrete 2 Center formwork 2a Gable formwork 3 Tunnel ground 4 Planar heater σ0 Required compressive strength M0 Target accumulated temperature M Accumulative temperature of lining concrete t0 Set target demolding time

Claims

[Claim 1] A method for curing a lining concrete poured on the inner surface of a tunnel ground by heating it with a temperature-controllable heater installed in a center form, comprising the steps of: A target accumulated temperature at which the lining concrete is estimated to exhibit the required compressive strength is obtained in advance, Measure the temperature transition of the lining concrete heated by the heater at at least two measurement points on the side of the center form and the side of the tunnel ground at the position where the lining concrete has been poured into the center form and at the top end position of the center form avoiding the heater, The lining concrete is heated by the heater so that the accumulated temperature of the lining concrete estimated from the temperature transition measured at each of the measurement points reaches the target accumulated temperature within a set target demolding time for demolding the center formwork, A heating and curing method for lining concrete, characterized in that the center formwork is removed when the accumulated temperature of the lining concrete at all of the measurement points reaches the target accumulated temperature.

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