Concrete structure construction method

Abstract

To solve a problem associated with conventional technology, that is, to provide a concrete structure construction method that can suppress thermal cracking due to external restraint without necessarily relying on low-heat cement.SOLUTION: A concrete structure construction method for constructing a concrete structure that is externally restrained comprises a planning step, a lower layer pouring step, and an upper layer pouring step. In the planning process, a lower layer to be poured and an upper layer to be poured are set for a pouring range of one lift, and a lower layer mix proportion of lower layer concrete and an upper layer mix proportion of upper layer concrete are set. In the planning process, the upper layer mix proportion and the lower layer mix proportion are set so that the upper layer concrete after pouring expands more than the lower layer concrete after pouring.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a concrete structure that is prone to thermal cracking due to external constraints, and more specifically, to a method for constructing a concrete structure in which a lower layer and an upper layer are set within a pouring range for one lift, and concrete is poured using different mix proportions and curing methods for the lower and upper layers. [Background technology]

[0002] Along with steel, concrete is one of the most important construction materials, and is used in a variety of structures, including civil engineering structures such as dams, tunnels, and bridges, as well as architectural structures such as apartment buildings and office buildings. These concrete structures may be prefabricated in a factory and transported to the designated location, but in the case of civil engineering and architectural structures, they are often constructed directly at the designated location (site). In either case, concrete structures are constructed by pouring concrete (fresh concrete), which is a mixture of cement, water, aggregate, etc., into a formwork, waiting for the concrete to harden, and then removing the formwork.

[0003] As mentioned above, concrete is a material that hardens over time, and as the internal temperature rises over time due to the hydration reaction of concrete, its strength also increases and its elastic modulus also improves. However, cracks can occur during the process of turning fresh concrete into hardened concrete, or while the concrete is being used as a structure after hardening. Some cracks in concrete are harmless and do not affect the use of the structure, but there are also harmful cracks that have a significant impact on the use of the structure. Therefore, much of the cause and mechanism of cracking has been elucidated, and various methods have been adopted to deal with them.

[0004] Cracks are classified according to the cause of their occurrence, and are further broadly divided into those caused before the concrete hardens and those caused after the concrete hardens. Causes before hardening include "initial cracks" caused by the movement of formwork or abnormal setting of cement, and "plastic shrinkage cracks" caused by rapid drying of the surface during curing. Meanwhile, causes after hardening include "drying shrinkage cracks" caused by shrinkage of the cement gel due to moisture loss, "physical and chemical cracks" caused by corrosion of rebar and alkali-aggregate reaction, and "structural cracks" caused by the action of excessive loads or settlement of structures.

[0005] Thermal cracks can also be a problem in concrete structures with relatively thick components (so-called mass concrete). Thermal cracks are broadly divided into those caused by internal restraints and those caused by external restraints, and the process (mechanism) by which cracks occur is different for each type.

[0006] As concrete hardens, a reaction between water and cement occurs, generating heat of hydration, causing the temperature of the concrete to rise over time. However, if the outside temperature is low, the surface temperature of the concrete does not rise significantly in the area close to the surface (periphery) due to heat dissipation (heat transfer) to the outside air. As a result, a significant temperature difference occurs between the inside and periphery of the concrete, and while the inside expands thermally, the periphery does not expand as much, so a tensile force acts on the periphery. This tensile force causes thermal cracks due to internal constraints.

[0007] On the other hand, once the concrete reaches a certain temperature, it begins to drop in temperature, and as the temperature drops, the concrete begins to thermally shrink overall. When it reaches this certain temperature (the peak of heat of hydration), the concrete changes from a plastic state to an elastic state. For this reason, where it is in contact with existing concrete, it is in a restrained state and cannot shrink freely. As a result, tensile forces act on the parts of the concrete that are restrained externally. This tensile force causes thermal cracks due to external restraint. Note that thermal cracks due to external restraint can sometimes penetrate the structure, in which case they can be harmful cracks that affect the durability of the structure.

[0008] Thus, although the mechanisms by which thermal cracks caused by internal restraints and thermal cracks caused by external restraints occur are different, they are both caused by the rise in concrete temperature due to the heat of hydration of cement. Therefore, the mainstream method of dealing with thermal cracks is to suppress the rise in concrete temperature. For example, design measures include using low-heat cement, reducing the amount of cement, and using admixtures that reduce heat of hydration in order to suppress the rise in heat of hydration. Alternatively, plans are sometimes made to install crack induction joints in order to induce cracks in places where they will not be affected even if they do occur.

[0009] Typical countermeasures against thermal cracks during construction include pre-cooling, post-cooling, and long-term adiabatic curing. Pre-cooling is a method of cooling fresh concrete when it is poured. Various cooling methods are used, such as using flake ice in the mixing water or spraying liquid nitrogen during mixing in a mixer or truck agitator.

[0010] Post-cooling includes a method of promoting natural cooling by providing a temperature diffusion surface inside the structure, such as a cooling slot, and a method of cooling the concrete by passing cooling water through cooling pipes, such as thin-walled steel pipes, that have been laid inside the structure beforehand. One method of pipe cooling involves sending low-temperature water or air into the cooling pipes after the concrete has been poured.

[0011] In addition to the above-mentioned conventional technologies, various new technologies have been proposed to combat thermal cracking. For example, Patent Document 1 discloses an invention in which a specific range including the restrained part is set for a concrete structure that is prone to thermal cracking due to external restraint, and only this set range is partially cooled. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Patent No. 6911260 Summary of the Invention [Problem to be solved by the invention]

[0013] As mentioned above, design measures include the use of low-heat cement, reducing the amount of cement, and using admixtures, but measures such as reducing the amount of cement and using admixtures are less effective than the use of low-heat cement. However, low-heat cement is more expensive than ordinary Portland cement and blast-furnace slag cement type B, and in some areas low-heat cement may not be available at all. That said, pre-cooling and post-cooling measures have problems such as the cost and effort required for materials and equipment, as well as the complexity of construction management.

[0014] The object of the present invention is to solve the problems associated with the conventional technology, that is, to provide a method for constructing a concrete structure that can suppress thermal cracking due to external constraints without necessarily relying on low-heat cement. [Means for solving the problem]

[0015] The present invention was made with a focus on dividing the pouring area for one lift into two, a lower layer and an upper layer, pouring concrete of different mixes into each layer and curing the concrete using different methods, thereby utilizing the "hoop effect" that occurs when the upper layer concrete contracts due to thermal expansion to suppress temperature cracks that are prone to occur in the lower layer, and is an invention based on an unprecedented idea.

[0016] The method for constructing a concrete structure of the present invention is a method for constructing an externally restrained concrete structure, and includes a planning step, a lower layer pouring step, and an upper layer pouring step. In the planning step, the pouring range for one lift is divided into two by a horizontal material boundary surface to set a "lower layer to be poured" and an "upper layer to be poured", and a "lower layer mix ratio" for the "lower layer concrete" to be poured into the lower layer and an "upper layer mix ratio" for the "upper layer concrete" to be poured into the upper layer are set. In the lower layer pouring step, the lower layer concrete is poured into the lower layer, and in the upper layer pouring step, the upper layer concrete is poured into the upper layer. In the planning step, the upper layer mix ratio and the lower layer mix ratio are set so that the upper layer concrete after pouring expands more than the lower layer concrete after pouring, or so that the lower layer concrete after pouring expands less than the upper layer concrete after pouring. Then, compressive force is applied to the lower layer concrete when the upper layer concrete shrinks after expansion (hoop tightening effect), thereby suppressing thermal cracking of the lower layer concrete.

[0017] The method for constructing a concrete structure according to the present invention may further include a concrete curing step. In this concrete curing step, the lower curing layer of one lift of poured concrete is cured by a lower curing method, and the upper curing layer is cured by an upper curing method. Therefore, in the planning step in this case, the pouring range for one lift is divided into two by a horizontal curing boundary surface to set a "lower curing layer" and an "upper curing layer," and a "lower curing method" for the lower curing layer and an "upper curing method" for the upper curing layer are set. In the planning step, the upper curing method and the lower curing method are set so that the upper layer concrete expands more than the lower layer concrete after pouring.

[0018] The method for constructing a concrete structure of the present invention may also be a method in which heat retention curing or heat supply curing is set as the upper curing method in the planning process.

[0019] The method for constructing a concrete structure of the present invention may also be a method in which cooling curing is set as the pre-curing method in the planning step.

[0020] The method for constructing a concrete structure of the present invention may also be a method for determining the mix proportion for an upper layer so that the cement content is greater than that of a lower layer in the planning process.

[0021] The method for constructing a concrete structure of the present invention can also be a method in which the upper layer mix is ​​set in the planning process so that it contains aggregate with a larger thermal expansion coefficient than the lower layer mix, or a method in which the lower layer mix is ​​set so that it contains aggregate with a smaller thermal expansion coefficient than the upper layer mix.

[0022] The method for constructing a concrete structure of the present invention may also be a method for setting the sub-layer mix so as to add limestone in the planning process.

[0023] The concrete structure construction method of the present invention can also be a method of setting the material interface and the lower layer mix and upper layer mix based on the analysis results. In this case, in the planning process, the crack index is calculated for multiple cases while changing the combination of the material interface, the lower layer mix and the upper layer mix, and the material interface, the lower layer mix and the upper layer mix for the case with the largest minimum crack index are set.

[0024] The method for constructing a concrete structure of the present invention can also be a method for setting the curing interface, the lower curing method, and the upper curing method based on the analysis results. In this case, in the planning step, the crack index is calculated for multiple cases while changing the combination of the curing interface, the lower curing method, and the upper curing method, and the curing interface, the lower curing method, and the upper curing method for the case with the largest minimum crack index are set. Effect of the Invention

[0025] The method for constructing a concrete structure according to the present invention has the following effects. (1) Since the upper layer of concrete expands and contracts more than the lower layer of concrete, the upper layer of concrete can apply compressive force to the lower layer of concrete, i.e., the "hoop effect," effectively suppressing thermal cracking in the lower layer of concrete. (2) Thermal cracking can be suppressed without necessarily relying on low-heat cement, i.e., even in areas where low-heat cement external restraint is not available. (3) This method involves simply pouring concrete of different mixes into the lower and upper layers. Compared with precooling and postcooling, this method reduces the costs and labor required for materials, etc., and allows for relatively easy construction management. [Brief description of the drawings]

[0026] [Figure 1] 1 is a cross-sectional view showing a schematic diagram of an inverted T-shaped retaining wall constructed by the concrete structure construction method of the present invention. [Diagram 2]FIG. 2( a ) is a model diagram showing a schematic diagram of the change in shape of concrete when no special measures are taken, and FIG. 2( b ) is a model diagram showing a schematic diagram of the change in shape of concrete constructed by the concrete structure construction method of the present invention. [Diagram 3] 1 is a flow chart showing the flow of main steps of the concrete structure construction method of the present invention. [Figure 4] A test result diagram showing the relationship between the thermal expansion coefficient of aggregate and the thermal expansion coefficient of concrete containing that aggregate. [Diagram 5] A model diagram showing an analytical model in which each node is colored according to the crack index. [Figure 6] An analysis summary diagram showing the results of the planned process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] An embodiment of the method for constructing a concrete structure according to the present invention will be described with reference to the drawings.

[0028] The concrete structure construction method of the present invention is an invention that suppresses thermal cracking of concrete caused by external restraint. Therefore, the concrete structure construction method can be particularly suitably used for various concrete structures that are easily subjected to external restraint, such as retaining walls and box culverts built on foundation rock, or tunnel lining concrete built on invert concrete.

[0029] Fig. 1 is a cross-sectional view showing a typical example of an inverted T-shaped retaining wall RW constructed by the concrete structure construction method of the present invention. The inverted T-shaped retaining wall RW shown in this figure is a concrete retaining wall directly based on the foundation rock BR, and concrete pouring is planned for the vertical wall on the footing in two separate steps, the "first lift" and the "second lift." Note that the "lift" here refers to the range (height) in which concrete is poured continuously. For example, in the case of Fig. 1, after pouring concrete for the first lift, concrete pouring for the second lift will be carried out a few days later (or the next day).

[0030] Since the inverted T-shaped retaining wall RW shown in Figure 1 is constructed on the foundation rock BR, there is a risk of thermal cracking due to external restraint occurring in the concrete of the footing or the first lift of the vertical wall if no measures are taken. In contrast, the concrete structure construction method can suppress such thermal cracking. Below, we will explain the outline of the concrete structure construction method and the mechanism for suppressing cracking.

[0031] One of the technical features of the concrete structure construction method is that one lift of concrete is divided into two layers for construction. More specifically, the pouring range for one lift is divided into two halves, top and bottom, by a horizontal plane (hereafter referred to as the "material boundary surface"), and a "lower pouring layer" and an "upper pouring layer" are set as shown in Figure 1. Alternatively, the pouring range for one lift is also divided into two halves, top and bottom, by a horizontal plane (hereafter referred to as the "curing boundary surface"), and a "lower curing layer" and an "upper curing layer" are set as shown in Figure 1. The material boundary surface and the curing boundary surface can be set as the same surface (i.e., the same height), or the material boundary surface and the curing boundary surface can be set as different surfaces (i.e., different heights).

[0032] The mix ratio for the concrete poured in the lower layer (hereinafter simply referred to as "lower layer concrete") and the mix ratio for the concrete poured in the upper layer (hereinafter simply referred to as "upper layer concrete") are planned to be different from each other. However, the upper layer mix ratio and the lower layer mix ratio are set so that the upper layer concrete will expand more than the lower layer concrete after pouring (especially during the expansion period).

[0033] Furthermore, the method for curing the lower layer concrete (hereinafter simply referred to as the "lower curing method") and the method for curing the upper layer concrete (hereinafter simply referred to as the "upper curing method") are planned as different methods. However, the lower curing method and the upper curing method are planned so that the upper layer concrete expands more than the lower layer concrete after pouring (especially during the expansion period). For example, it is a good idea to plan cooling curing as the lower curing method and heat retention curing or heat supply curing as the upper curing method.

[0034] Figure 2 is a model diagram showing the shape change during the expansion and contraction periods of concrete under external constraint, where (a) shows the case where no special measures against cracks are taken, and (b) shows the case where concrete is constructed using the concrete structure construction method of the present invention. As mentioned above, during the expansion period when the concrete temperature rises, the entire concrete thermally expands, and during the contraction period when the concrete temperature drops, the entire concrete thermally contracts. In the case of Figure 2(a), the concrete parts in contact with the foundation rock BR ​​etc. are in a restrained state and cannot freely contract, and as a result, tensile forces act on the restrained concrete parts, which means that thermal cracks due to external constraints occur.

[0035] On the other hand, in the case of Figure 2(b), if we focus on the upper layer concrete during shrinkage, we can see that the upper layer concrete shrinks by itself, which causes the lower layer concrete to shrink as well, i.e., the upper layer concrete deforms to introduce compressive force into the lower layer concrete. As a result, even if tensile force due to external restraint occurs in the lower layer concrete (i.e., the restrained part), the tensile force is reduced (alleviated) by the effect of the introduction of compressive force from the upper layer concrete, and the occurrence of thermal cracks due to external restraint is suppressed. This effect of reducing tensile force by compressive force from the upper layer concrete is the aforementioned "hooping effect." In order to maximize this hooping effect, the upper layer and lower layer mix proportions are set so that the upper layer concrete expands more than the lower layer concrete, and the lower curing method and upper curing method are planned so that the upper layer concrete expands more than the lower layer concrete.

[0036] Fig. 3 is a flow diagram showing the flow of the main steps of the concrete structure construction method of the present invention. As shown in this figure, the concrete structure construction method of the present invention can be roughly divided into a planning step (Step 100 in Fig. 3) and an actual work step (Step 200 in Fig. 3), and the actual work step is carried out based on various conditions set in this planning step.

[0037] In the planning process, first, multiple cases (hereafter referred to as "analysis cases") are set (Step 101 in Figure 3). When setting multiple analysis cases, the position (height) of the material boundary surface, the lower layer mix, and the upper layer mix are set as "construction conditions," and multiple analysis cases are set by changing the combination of these construction conditions. Furthermore, in addition to (or instead of) these construction conditions, multiple analysis cases can also be set by setting the position (height) of the curing boundary surface, the lower curing method, and the upper curing method as construction conditions.

[0038] As already explained, the upper layer and lower layer mix proportions are set so that the upper layer concrete expands more than the lower layer concrete. For example, the mix can be designed so that the amount of cement (unit cement amount) contained in the upper layer mix is ​​greater than the amount of cement (unit cement amount) contained in the lower layer mix. The greater the unit cement amount, the greater the concrete will thermally expand during the expansion period and thermally shrink during the contraction period, which will result in a greater hooping effect. Therefore, the mix is ​​designed so that the upper layer mix contains more cement than the lower layer mix.

[0039] The upper layer mix can be designed to include aggregates with a higher thermal expansion coefficient than the aggregates in the lower layer mix. Figure 4 shows the results of an actual test conducted by the inventors of the present invention to understand the relationship between the thermal expansion coefficient of aggregates and the thermal expansion coefficient of the concrete to which the aggregates are mixed. As shown in this figure, concrete containing aggregates with a higher thermal expansion coefficient has a higher thermal expansion coefficient. In other words, concrete containing aggregates with a higher thermal expansion coefficient has a larger thermal expansion during the expansion period and a larger thermal contraction during the contraction period, which results in a greater hooping effect. Therefore, the upper layer mix is ​​designed to include aggregates with a higher thermal expansion coefficient than the aggregates in the lower layer mix.

[0040] It is also possible to design the mix so that limestone is added only to the lower layer mix. It is known that concrete containing limestone has a small thermal expansion coefficient, so limestone is added to the lower layer mix but not to the upper layer mix. This causes the upper layer concrete to thermally expand and contract more than the lower layer concrete, and as a result, the hoop fastening effect is more pronounced. Therefore, the mix is ​​designed so that limestone is added only to the lower layer mix. In addition, it is also possible to design the mix so that expansive material is included in the lower layer mix, or to design the mix so that expansive material is included in both the lower and upper layer mixes, or to combine the contents explained so far (cement amount, aggregate, limestone, expansive material).

[0041] When setting up an analysis case, if the lower curing method and upper curing method are set as construction conditions, the upper layer concrete is planned to expand more than the lower layer concrete after pouring. For example, the lower curing method can be planned as cooling curing, the upper curing method can be planned as heat retention curing or heat supply curing and the lower curing method as natural curing, the upper curing method can be planned as natural curing and the lower curing method as cooling curing, or the upper curing method can be planned as heat retention curing or heat supply curing and the lower curing method as cooling curing.

[0042] Once multiple analysis cases have been set, a temperature stress analysis is performed for each of the set analysis cases (Step 102 in Figure 3). This temperature stress analysis can be performed using a three-dimensional FEM (Finite Element Method). In this temperature stress analysis, the temperature stress of a concrete structure (for example, the inverted T-shaped retaining wall RW in Figure 1) is calculated, and a crack index is obtained for each node as shown in Figure 5. Figure 5 is a model diagram showing an analysis model MD in which each node is colored according to the crack index. Note that this analysis model MD is a so-called 1 / 4 model in which the inverted T-shaped retaining wall RW is divided into four (two in the extension direction and two in the front and back directions).

[0043] Once the crack index for each node is obtained, the crack index showing the minimum value is extracted as the "minimum crack index" for that analysis case. At this time, a temperature stress analysis can be performed at a predetermined time (for example, two days after the concrete is poured) for each analysis case, and the minimum crack index can then be extracted. Alternatively, temperature stress analysis can be performed over multiple periods from the pouring of the concrete, the temperature stress history at each period can be calculated, the crack index for each node can be obtained, and the minimum crack index can then be extracted. In this case, the minimum crack index can be obtained for the number of periods for which the analysis was performed, and the one showing the smallest value among them can be extracted as the "minimum crack index" for that analysis case. When using a specified analysis software, if a long analysis period is set, all crack indexes experienced during that period can be recorded and saved, meaning that the minimum crack index can be obtained with a single calculation.

[0044] When performing a temperature stress analysis, parameters are set according to the construction conditions set for each analysis case. Specifically, various coefficients (parameters) of concrete are set, the thermal expansion coefficient of concrete is set, or the heat transfer coefficient (parameter) is set according to the curing method. For example, the thermal expansion coefficient of concrete is set according to the type of cement or aggregate, the expansion characteristics of concrete are set when an expansive material is used as an admixture, and the hydration heat characteristics (insulating temperature rise characteristics), strength, Young's modulus, Poisson's ratio, autogenous shrinkage, etc. are set as parameters of concrete that depend on the amount of cement. In addition, while the thermal expansion coefficient of concrete is set to 10 in a normal analysis, it is set to 11.8 (Figure 4) when it contains chert aggregate, and 7 to 8 when it contains limestone. Furthermore, while the thermal transfer coefficient of concrete that is exposed or that uses steel formwork is set to 14 in a normal analysis, it is set to 5 to 8 when it is cured to keep warm.

[0045] The material interface, lower layer mix, and upper layer mix are determined by repeatedly performing temperature stress analysis for the number of analysis cases set (Step 103 in Figure 3). When determining the material interface, lower layer mix, and upper layer mix, the largest value is selected from the multiple minimum crack indexes obtained by temperature stress analysis, and the material interface, lower layer mix, and upper layer mix of the analysis case associated with the largest minimum crack index are determined as the actual construction conditions.

[0046] Furthermore, if the lower curing method and upper curing method are set as construction conditions when setting up an analysis case, the curing boundary surface, the lower curing method, and the upper curing method are determined (Step 104 in Fig. 3). When determining the curing boundary surface, the lower curing method, and the upper curing method, the one showing the largest value is selected from the multiple minimum crack indexes obtained by the temperature stress analysis, and the curing boundary surface, the lower curing method, and the upper curing method of the analysis case associated with the largest minimum crack index are determined as the actual construction conditions.

[0047] Figure 6 is a diagram showing the results of an actual planned process. In this planned process, nine types of analysis cases are set for an inverted T-shaped retaining wall RW with a 1-lift height of 3.0 m. For example, in the analysis case "No01" in Figure 6, the material boundary surface is set at 1.5 m from the top (from the top end of 1 lift), and the single cement amount in the lower layer mix is ​​305 kg / m 3 (BB305), and the upper layer mix had a single cement content of 363 kg / m 3 (BB363), and the entire area is set as natural curing without setting a curing boundary surface. In the analysis case of "No05", the material boundary surface is set at 1.0 m from the top, and the single cement amount in the lower layer mix is ​​305 kg / m 3 The upper layer mix contains a single cement content of 305 kg / m 3 The entire area is set for natural curing without setting any curing boundary surfaces.

[0048] As a result of conducting temperature stress analysis for nine types of analysis cases, the minimum crack index was obtained as shown in Figure 6 (second column from the right). However, the result shown in the top row is the analysis result based on "no measures" in which the concrete structure construction method of the present invention was not implemented (minimum crack index = 0.78). As shown in Figure 6, a minimum crack index greater than the minimum crack index for no measures was obtained in each analysis case, which means that the effect of the concrete structure construction method of the present invention (hoop fastening effect) can be confirmed. Note that the "increase" shown in the rightmost column in Figure 6 indicates the difference between the minimum crack index for no measures and the minimum crack index for the analysis case in question.

[0049] In the example of Figure 6, the minimum crack index for the analysis case "No09" is the largest. Therefore, the contents of No09 are set as the actual construction conditions, that is, the material boundary surface is set at 1.0 m from the top, and the lower layer mix has a single cement amount of 305 kg / m 3 It contains an expansion agent and limestone, and the upper layer mix has a single cement content of 305 kg / m 3 It contains an expansion agent, the curing boundary surface is set at 0.7 m from the top, the bottom curing method is natural curing, and the top curing method is heat retention curing.

[0050] In the actual work process, the lower layer concrete is poured first (Step 201 in Figure 3). At this time, the lower layer concrete with the lower layer mix determined in the planning process is poured up to the material boundary surface determined in the planning process. After pouring the lower layer concrete, the upper layer concrete is poured next (Step 202 in Figure 3). At this time, the upper layer concrete with the upper layer mix determined in the planning process is poured up to the top of one lift.

[0051] After the lower layer concrete and the upper layer concrete are poured, concrete curing is performed (Step 203 in Figure 3). At this time, the lower layer is cured using the lower curing method determined in the planning process, and the upper layer is cured using the upper curing method determined in the planning process. When performing cooling curing as the lower curing method, various methods that have been used conventionally as post-cooling can be adopted, including pipe cooling, in which a refrigerant is passed through pipes inside the concrete structure. When performing heat retention curing as the upper curing method, various methods that have been used conventionally, such as placing an insulating mat on the concrete surface, can be adopted. When performing heat supply curing as the upper curing method, various methods that have been used conventionally, such as using electric heating wires, hot water, heaters, etc., can be adopted. [Industrial Applicability]

[0052] The method for constructing a concrete structure of the present invention can be used for various concrete structures that are at risk of thermal cracking due to external restraint, such as retaining walls and box culverts constructed on foundation rock, or tunnel lining concrete constructed on invert concrete. Considering that the present invention provides a high-quality concrete structure with little thermal cracking, it can be said to be an invention that can be expected to not only be used industrially, but also to make a great contribution to society. [Explanation of symbols]

[0053] BR Foundation rock MD analysis model RW Inverted T-shaped retaining wall

Claims

1. 1. A method for constructing an externally restrained concrete structure, comprising: A planning process for dividing the pouring range for one lift in half at a horizontal material boundary surface to set a lower layer and an upper layer, and for setting a lower layer mix of the lower layer concrete to be poured into the lower layer and an upper layer mix of the upper layer concrete to be poured into the upper layer; A lower layer pouring step of pouring the lower layer concrete into the pouring lower layer; and an upper layer pouring step of pouring the upper layer concrete into the pouring upper layer, In the planning step, the upper layer mix proportion and the lower layer mix proportion are set so that the upper layer concrete after pouring expands more than the lower layer concrete after pouring, By applying a compressive force to the lower layer concrete when the upper layer concrete shrinks after expansion, thermal cracking of the lower layer concrete can be suppressed. A method for constructing a concrete structure comprising the steps of:

2. In the planning step, a lower curing layer and an upper curing layer are set by dividing a pouring range for one lift in half with a horizontal curing boundary surface, and a lower curing method for the lower curing layer and an upper curing method for the upper curing layer are set, The method further includes a concrete curing step of curing the lower curing layer by the lower curing method and curing the upper curing layer by the upper curing method, out of the poured concrete for one lift, In the planning step, the upper curing method and the lower curing method are set so that the upper layer concrete after pouring expands more than the lower layer concrete after pouring.

2. The method for constructing a concrete structure according to claim 1.

3. In the planning step, heat retention curing or heat supply curing is set as the upper curing method.

3. The method for constructing a concrete structure according to claim 2.

4. In the planning step, cooling curing is set as the pre-curing method.

4. A method for constructing a concrete structure according to claim 2 or 3.

5. In the planning step, the upper layer mix is ​​set so that the cement content is greater than that of the lower layer mix.

2. The method for constructing a concrete structure according to claim 1.

6. In the planning step, the upper layer mix is ​​set so as to include aggregate having a thermal expansion coefficient larger than that of the lower layer mix.

2. The method for constructing a concrete structure according to claim 1.

7. In the planning step, the sub-layer mix is ​​set so as to add limestone.

2. The method for constructing a concrete structure according to claim 1.

8. In the planning step, the crack index is calculated for a plurality of cases while changing the combination of the material interface, the lower layer composition, and the upper layer composition, and the material interface, the lower layer composition, and the upper layer composition related to the case in which the minimum crack index is maximized are set.

2. The method for constructing a concrete structure according to claim 1.

9. In the planning step, a crack index is calculated for a plurality of cases while changing a combination of the curing boundary surface, the lower curing method, and the upper curing method, and the curing boundary surface, the lower curing method, and the upper curing method related to the case in which the minimum crack index is maximum are set.

3. The method for constructing a concrete structure according to claim 2.

Images