Concrete construction method

Abstract

To provide a concrete construction method capable of securing quality even under an environment where evaporated water quantity is large.SOLUTION: A concrete construction method comprises: a placing step of pouring concrete into a construction area and leveling the surface; a compacting step of applying vibration to the placed concrete after the placing step; a pressing step of leveling the surface by pressing an iron to the surface after the compacting step; and a water supply step of supplying water to the surface simultaneously with the pressing step. In the water supply step, water of 20% or more and 50% or less of water evaporating from the placed concrete is supplied to the surface from the placing step to the pressing step.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a concrete construction method, and more particularly to a concrete construction method in an environment where water evaporation is frequent. [Background technology]

[0002] Traditionally, floor slabs in buildings, such as logistics warehouses, are often exposed concrete with no surface finish. In exposed concrete floors, cracks and strength on the concrete surface have a direct impact on the user's operations. Also, in buildings such as logistics warehouses, beams are often made of steel, and unlike reinforced concrete structures in which the floor and beams are poured together, the concrete is poured for the floor alone. When pouring concrete for floor slabs, it is necessary to control the amount of water that evaporates from the concrete until it hardens.

[0003] In the wet curing of concrete disclosed in Patent Document 1, mist-like water is sprayed from a nozzle onto the concrete surface in order to achieve sufficient wet curing after demolding.

[0004] In the concrete floor finishing method disclosed in Patent Document 2, water is sprayed onto the floor surface when a rotary trowel is driven to finish the concrete floor surface. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2020-147989 A [Patent Document 2] Patent Publication No. 2022-76810 Summary of the Invention [Problem to be solved by the invention]

[0006] The wet curing method of concrete disclosed in Patent Document 1 involves wet curing of concrete after removing the formwork when concrete is poured using a formwork such as in a mountain tunnel. Wet curing is intended to promote the hydration reaction for a certain period of time after removal of the formwork. When concrete is poured using a formwork such as in a mountain tunnel, the concrete immediately after pouring hardens to a certain extent while being protected from drying by the formwork. However, the upper surface of the floor slab of a building does not have a formwork and is open to the outside air, so moisture evaporates during pouring. Furthermore, there are cases where concrete is poured outdoors under direct sunlight, and there is a problem that it is difficult to maintain the amount of moisture evaporated from the concrete under such an environment. In addition, in the "Guidelines and Commentary for Hot Weather Concrete Construction, Third Edition" (Architectural Institute of Japan, July 2019), in principle, watering is prohibited until the concrete hardens, but if moisture dissipates significantly during the hot season and the concrete dries significantly until the finishing is completed, it is permitted to supply a small amount of water. However, there is no specific knowledge regarding the amount of water to be supplied when pouring concrete, and there has been a problem in that it is difficult to ensure the quality of the concrete, particularly with regard to surface cracks and surface strength.

[0007] The present invention is made in response to the above demand, and has an object to provide a concrete construction method capable of ensuring quality even in an environment where a large amount of water evaporates. [Means for solving the problem]

[0008] The concrete construction method of the present invention comprises a pouring step of pouring concrete into a construction area and leveling the surface, a compaction step of vibrating the poured concrete after the pouring step, a pressing step of applying a trowel to the surface after the compaction step to level it, and a water supplying step of supplying water to the surface during the pressing step, wherein the water supplying step supplies water to the surface in an amount equal to or greater than 20% and equal to or less than 50% of the water that evaporates from the poured concrete between the pouring step and the pressing step. Effect of the Invention

[0009] According to the present invention, by adjusting the amount of water supplied before the concrete hardens during construction, it is possible to suppress cracks on the concrete surface and ensure strength. [Brief description of the drawings]

[0010] [Figure 1] 2 is a flowchart of a concrete construction method according to the first embodiment. [Diagram 2] FIG. 2 is an explanatory diagram of a concrete construction method according to the first embodiment and a construction experiment environment of a comparative example. [Diagram 3] 3 is a graph showing the transition of the cumulative amount of water evaporation from the open concrete surface in the experimental environment shown in FIG. 2. [Figure 4] This figure shows the scratch test results for each casting area in the construction experiment. [Diagram 5] This figure shows the results of air permeability tests for each casting area in the construction experiment. [Figure 6] This figure shows the results of compression tests on core concrete in each pouring area of ​​the construction experiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiment described below. Each figure is a schematic illustration, and the relative size and plate thickness of each member are not limited to the dimensions shown in the drawings. Also, the size relationship of each component member in the following drawings may differ from the actual one.

[0012] Embodiment 1 The concrete construction method according to the first embodiment is a concrete construction method for constructing a slab that constitutes, for example, the floor or roof of a building. For example, a floor slab may be constructed outdoors, in the heat of the day and under direct sunlight. In such an environment, a large amount of water evaporates from the poured concrete. The amount of water evaporation varies depending on the temperature, humidity, wind speed, and presence or absence of direct sunlight at the location where the concrete is poured. The concrete construction method according to the first embodiment is a concrete construction method particularly for use in the heat of the day.

[0013] (Concrete construction method) Fig. 1 is a flow chart of a concrete construction method according to embodiment 1. When constructing a floor slab or the like, first, surrounding formwork and reinforcing bars to be installed inside the concrete are laid. Then, concrete is poured into the casting area (step S1).

[0014] After pouring the concrete, the surface of the concrete is leveled using a drill or the like (step S2). Steps S1 and S2 are collectively referred to as the concrete pouring process.

[0015] Once the concrete pouring process is complete, a compaction process is carried out in which the concrete is vibrated (step S3). The compaction process can be carried out, for example, by inserting a vibrator into the concrete to apply vibration, by applying vibration from outside the formwork, or by applying vibration to the surface of the floor slab. By applying vibration to the poured concrete, the concrete spreads throughout the gaps in the formwork. The compaction process can be carried out using a ram or other tool as an auxiliary tool if necessary.

[0016] When the compaction process is completed and the concrete has developed a predetermined hardness (for example, when it has hardened enough that a worker wearing snowshoes can stand on it), the pressing process is carried out (step S4). In this process, the concrete surface is finished with a trowel. The concrete surface is pressed down with a manual or mechanical trowel to remove any unevenness that has occurred on the surface.

[0017] The time from the start of pouring concrete to the start of the pressing process is generally set to between 30 minutes and 120 minutes.

[0018] Concurrently with the compaction process, water is supplied to the concrete before it hardens. This process is called the water supplying process (step S5). In the water supplying process, water is sprayed onto the surface of the concrete depending on the cumulative amount of water that has evaporated since the start of pouring the concrete, and the amount of water supplied varies depending on weather conditions and the installation environment of the floor slab. In the concrete construction method according to the first embodiment, water that is 10% to 50% of the amount of water that evaporates from the poured concrete is supplied to the poured concrete. The water supplying process in step S5 involves spraying water onto the surface of the concrete before it hardens.

[0019] After the pressing and water supplying steps are completed, the poured concrete is left to harden for a specified time, and then the watering step is carried out (step S6). This watering is for curing the concrete in a moist state. Moist curing of concrete prevents the loss of moisture and promotes the hydration of the concrete.

[0020] Once the water sprinkling step is complete, a curing step (step S7) is carried out as necessary. Curing methods include flood curing, water sprinkling curing, film curing, moisture retention curing, heat retention curing, insulation curing, and steam curing. The curing step involves keeping the concrete that has been moistened by water sprinkling in that moist state, and involves pouring water on the surface of the concrete or covering the surface with a sheet as necessary. Note that steps S7 and S8 may be collectively referred to as the curing step.

[0021] (Details of the water supply process) The concrete application method according to the first embodiment is carried out in a time period before the concrete hardens. In the flow chart shown in FIG. 1, the water supply step (step S5) is shown to be carried out after the holding step (step S4), but water may be supplied to the surface of the cast concrete immediately before, immediately after, or simultaneously with the holding step. The amount of water supplied is determined according to the amount of water evaporated from the cast concrete during the time from pouring the concrete to the holding step. In the first embodiment, water of 10% to 50% of the amount of evaporated water is supplied to the cast concrete. In detail, the appropriate amount of water to be supplied varies depending on the W / C of the cast concrete. When the W / C of the cast concrete is 61% or less, it is desirable to supply water to the surface in an amount of 20% to 50% of the amount of water evaporated from the cast concrete.

[0022] In particular, when the W / C of the cast concrete is 38.5%, it is preferable to set the amount of water supplied to 20% to 50% of the amount of water that evaporates, and more preferably to 20%. On the other hand, when the W / C value of concrete is large, the amount of water contained in the concrete is large and cracks are less likely to occur, so when the W / C value is 38.5% to 61%, the amount of water supplied is effective in suppressing cracks as long as it is 20% to 50% of the amount of water that evaporates. Also, when the W / C of cast concrete is 48% or more, the amount of water supplied may be 10% to 50% of the amount of water that evaporates, and more preferably, it is 10% to 20%.

[0023] When the amount of water supplied is between 20% and 50% of the evaporation amount, the amount of water per unit area of ​​poured concrete is 0.28 L / m 2 More than 0.70L / m 2 This is the amount of water to be supplied when the water supply process is carried out between 60 and 120 minutes after the concrete is placed, when the outside temperature is about 38°C, and is set assuming work under direct sunlight in summer, for example. Thus, when the temperature of the environment in which the concrete is placed is 38°C or lower, the water supply amount is at least 0.70 L / m2 The following water should be supplied. Furthermore, if the W / C of the cast concrete is 48% or more, the water supply amount is 0.14L / m 2 More than 0.70L / m 2 It may be less than 0.14 L / m 2 More than 0.28L / m 2 It is recommended to keep the water supply at 0.14 L / m or less. This is because if the amount of water supplied is too much, the strength of the concrete surface may decrease, and the scratch test results tend to be poor. Also, if the amount of water supplied is too little, cracks are likely to occur on the concrete surface, so the amount of water supplied should be at least 0.14 L / m 2 It is desirable to have more than this.

[0024] When the outside temperature is lower than 38°C, the amount of water evaporated from the concrete is reduced, so it is desirable to reduce the amount of water supplied to less than the amount indicated above, but to a maximum of 0.70 L / m 2 In addition, when the W / C of the cast concrete is 48% or more, the amount of water supplied is preferably 0.28L / m 2 In order to prevent cracks from occurring due to an insufficient water supply, the water supply should be at least 0.14 L / m 2 In an environment where the outside temperature is below 38°C, if the W / C of the poured concrete is 48% or more, the water supply rate should be 0.14L / m 2 More than 0.28L / m 2 By setting the values ​​below, it is possible to prevent cracks in the concrete and ensure the strength of the concrete surface even if there are variations in the humidity, wind speed, and presence or absence of direct sunlight in the concrete pouring environment.

[0025] (About the effect of concrete construction methods) Fig. 2 is an explanatory diagram of the construction experiment environment of the concrete construction method according to the first embodiment and its comparative example. In the construction experiment environment, a 10m square concrete pouring area was constructed to evaluate the concrete construction method according to the first embodiment, and the pouring area was divided into eight areas. Of the eight areas, AE-0, AE-10, AE-20, and AE-50 were poured with concrete having a W / C of 48%, and SP-0, SP-10, SP-20, and SP-50 were poured with concrete having a W / C of 38.5%. Note that W / C is the average value of the concrete per 1m of concrete. 3 is the mass ratio of water to cement contained in the

[0026] Each of the eight pouring areas is 5m x 2.5m in size. Each area is partitioned and configured to allow concrete of different specifications to be poured.

[0027] [Table 1]

[0028] Table 1 above shows the specifications for the concrete poured in the AE and SP regions out of the eight regions. The concrete shown as "30-15-20N" is concrete poured in the AE region. The concrete shown as "42-15-20N" is concrete poured in the SP region. The two types of concrete have different W / C, but are otherwise adjusted to be roughly the same. The two types of concrete differ in compressive strength after hardening, with "30-15-20N" having a compressive strength of 30N / mm 2 The "42-15-20N" has a compressive strength of 42N / mm 2 The above-mentioned measures have been adjusted to achieve the above.

[0029] The "Slump" column in Table 1 above shows the results of the slump test for each type of concrete; the higher the value, the higher the fluidity of the fresh concrete. Fresh concrete was placed into a slump cone, which was then removed to measure how many centimeters the height of the top of the concrete had dropped. Slump tests can be measured using the method specified in JIS A 1101. Additionally, the "Air content" column in Table 1 above shows the amount of air contained in the fresh concrete. Air content tests can be measured using methods specified in JIS A 1116, 1118, 1128, etc.

[0030] The "receiving temperature" in Table 1 above is the temperature of the ready-mixed concrete itself when it was received at the site where the construction test was conducted. In this construction experiment, the receiving temperature was adjusted to be close to the allowable limit of 38°C. Additionally, the outside air temperature is the outside air temperature at the site where the construction test was conducted. These were set on the assumption that concrete construction would be conducted during the hot season.

[0031] In the upper half of the casting area shown in Figure 2, concrete indicated as "30-15-20N" in Table 1 was cast, and in the lower half, concrete indicated as "42-15-20N" in Table 1 was cast. These were cast simultaneously.

[0032] The concrete poured into the eight pouring areas shown in Figure 2 was constructed based on the flow shown in Figure 1. However, the amount of water supplied to each of the eight pouring areas differs during the water supply process. The amount of water supplied to the eight pouring areas is as follows:

[0033] [Table 2]

[0034] Water was sprayed in the casting areas AE-0, AE-10, AE-20, AE-50, SP-0, SP-10, SP-20 and SP-50 so that the ratio of the amount of water supplied to the amount of water evaporated from the concrete was the "target value" shown in Table 2. However, since the amount of water evaporated from the concrete and the amount of water supplied to the concrete vary, the amount of water actually supplied to the concrete was as shown in the "Actual amount of water sprayed relative to the amount of evaporation" column in Table 2. In this experiment, AE-0 and SP-0 are comparative examples in which no water was supplied, and the others are examples in which water was supplied.

[0035] Figure 3 is a graph showing the transition of the cumulative amount of water evaporation from the open surface of the concrete in the experimental environment shown in Figure 2. In this experiment, in order to estimate the amount of water evaporating from the pouring area shown in Figure 2, a 150 mm x 150 mm x 150 mm box was filled with concrete, the weight of the box was measured, and the amount of water evaporated from the open surface of the concrete was measured. The horizontal axis of Figure 3 is the time since the concrete was poured (material age), and the vertical axis is the amount of evaporated water [kg / m 2 The value shown in "Actual amount of water sprayed versus evaporation amount" in Table 2 above was calculated using the median amount of evaporation between the first and second water sprays and the third water spray shown in Figure 3. Specifically, the amount of water evaporated from the concrete was calculated by identifying the evaporation amount at 90 [min] in the graph in Figure 3. The relationship between this value and the amount of water sprayed (L / m 2 The values ​​in the column (above) were used to calculate the "actual amount of water sprayed relative to the amount of evaporation."

[0036] In other words, in this experiment, the ratio of the amount of water supplied in the water supply process to the amount of water evaporation, i.e., the value of "(amount of water supplied to concrete) / (amount of water evaporation from concrete)", is the value shown in "Actual amount of water sprayed relative to amount of evaporation."

[0037] (Evaluation Results) The rightmost column in Table 2 shows the evaluation results of the presence and size of cracks in the concrete poured in each area in this experiment. Cracks occurred in the concrete poured in the AE-0 and SP-0 areas, where no water was supplied during the water supply process. The concrete poured in AE-0 had a W / C of 48%, which means it contained a relatively large amount of water, but without water supply, small cracks measuring 0.06 mm in width occurred. Additionally, the concrete poured in SP-0 had a W / C of 38.5%, which means it contained a lower amount of water, resulting in even larger cracks.

[0038] In the casting area AE-0, cracks were present, although they were very small. In the casting area SP-0, cracks were present with a width of 0.45 mm, and in the casting area SP-10, cracks were present with a width of 0.35 mm. No cracks were present in the other casting areas.

[0039] In addition, the concrete poured into SP-10 cracked even after spraying water, but this concrete had a W / C of 38.5%, meaning that it contained a relatively small amount of water. As shown in Table 2, the amount of water sprayed onto SP-10 was actually 8.8% of the amount that evaporated, and the amount of water that could be supplied was less than 10%. From this, it can be said that for concrete that contains a small amount of water when poured, it is necessary to supply a relatively large amount of water during the water supply process. For concrete with a W / C of 38.5%, supplying at least 20% water can suppress surface cracks.

[0040] The concrete in the casting areas of AE-10, AE-20, and AE-50 did not crack and had a good surface.The concrete in the casting areas of SP-20 and SP-50 did not crack and had a good surface.

[0041] Generally, in summer, when the temperature is high and exposed to wind, water evaporates quickly and the surface shrinks, but since the matrix is ​​rapidly formed by cement hydration, the speed at which the water lost on the surface due to evaporation is supplied from the inside is delayed, and the surface shrinks and cracks occur. However, according to the concrete construction method of the first embodiment, it is possible to suppress cracks by supplying an appropriate amount of water from the direction of the concrete before hardening as described above. In addition, it can be said that cracks are less likely to occur when the W / C value of the concrete is large, that is, when the water content is large to begin with. Therefore, for example, when the W / C is even larger, such as 61%, cracks do not occur at least as in the concretes AE-10 to AE-50 in Table 2 above.

[0042] Figure 4 shows the results of the scratch test for each casting area in the construction experiment. The scratch test was carried out using an evaluation method used by the Architectural Finish Society of Japan, and measures the width of the scratch (seam width) created when the base concrete surface was scratched, thereby gauging the strength of the concrete surface. This makes it easy to determine whether there is a weak layer on the surface that could cause adhesion problems during construction. The results shown in Figure 4 were measured when the concrete was 91 days old.

[0043] The results of the scratch test showed that the surface strength tended to be relatively low in the casting area where a large amount of water was supplied in the water supply process. Specifically, the width of the scratches tended to be large in AE-50 and SP-50. However, the results showed that the concrete surfaces of AE-50 and SP-50 were also at a level that could be judged to be sufficiently strong.

[0044] Figure 5 shows the results of the air permeability test for each casting area in the construction experiment. The air permeability test was performed using the Trent method (RJ Trrent "A two-chamber vacuum cell for measuring the coefficient of permeability to air of the concrete cover on site" Materials and Structures, 1992, 25, 358-365). The air permeability test measures the degree of density of the concrete surface. Concrete with a high air permeability coefficient has a coarse structure near the surface and tends to have low durability. The results shown in Figure 5 were measured when the concrete was 91 days old.

[0045] The results of the air permeability test were generally good, but there was a large variation in the air permeability coefficient in the casting area where the water supply process was not performed. Specifically, only the casting area of ​​SP-0 had a high air permeability coefficient, which raised concerns about the durability of the concrete.

[0046] In addition, in the pouring area where the water supply process was performed, the air permeability coefficient was generally good. However, in the AE-50 and SP-50 areas, the air permeability coefficient tended to be slightly higher.

[0047] Figure 6 shows the results of the compression test of the core concrete in each casting area of ​​the construction experiment. The compression test was conducted according to the JIS A 1108:2018 concrete compressive strength test method. The results shown in Figure 6 were measured when the concrete was 91 days old.

[0048] In the construction experiment, the concrete strength in each casting area was 30 N / mm for the area with W / C=48% concrete. 2 , 42N / mm in the area of ​​concrete with W / C=38.5% 2 The results were satisfactory.

[0049] Conventionally, concrete has been constructed using a construction method that does not supply moisture before hardening, as with the concrete in the pouring regions of Comparative Examples AE-0 and SP-0, and there have been concerns that supplying moisture before hardening may have a negative effect on the quality of the concrete. However, according to the concrete construction method of embodiment 1, the concrete can ensure sufficient strength even if moisture is supplied before hardening, and surface cracks can be suppressed as shown in Table 2.

[0050] On the other hand, concrete that does not undergo a water supply process will develop cracks in the early stages of its life. In particular, the above construction experiment was carried out by simulating outdoor concrete construction in hot weather with an outside temperature of about 38°C, as shown in Table 1. In such an environment, cracks will develop if there is no water supply, but cracks on the concrete surface can be suppressed by carrying out an appropriate water supply process before the concrete hardens.

[0051] Although the present invention has been described above based on the embodiment, the present invention is not limited to the configuration of the above-mentioned embodiment. In short, it should be noted that the gist (technical scope) of the present invention includes various modifications, applications, and uses that a person skilled in the art may make as necessary.

[0052] The concrete construction method described above may include a combination of the features shown in the following Supplementary Notes 1 to 5. The combinations are described below.

[0053] [Appendix 1] The casting process involves pouring concrete into the construction area and leveling the surface. A compaction process in which vibration is applied to the concrete poured after the pouring process; a pressing step of pressing a trowel against the surface to level it after the compaction step; and a water supplying step of supplying water to the surface simultaneously with the pressing step, The water supplying step includes: A concrete construction method in which water is supplied to the surface in an amount of 20% to 50% of the water that evaporates from the poured concrete between the pouring step and the pressing step. [Appendix 2] The concrete construction method according to claim 1, wherein the W / C of the concrete is 38.5% or more. [Appendix 3] The pressing step includes: 3. The concrete construction method according to claim 1 or 2, wherein the concrete is poured while the age of the concrete is between 0.5 hours and 2 hours. [Appendix 4] The water supplying step includes: 0.28 L / m on said surface 2 More than 0.70L / m 2 4. The method for constructing concrete according to any one of claims 1 to 3, further comprising supplying the following amount of water: [Appendix 5] The water supplying step includes: 5. The concrete construction method according to any one of claims 1 to 4, wherein water is sprayed onto the concrete using a spray nozzle. [Explanation of symbols]

[0054] AE-0 pouring area, AE-10 pouring area, AE-20 pouring area, AE-50 pouring area, SP-0 pouring area, SP-10 pouring area, SP-20 pouring area, SP-50 pouring area.

Claims

1. The casting process involves pouring concrete into the construction area and leveling the surface. A compaction process in which vibration is applied to the concrete poured after the pouring process; a pressing step of pressing a trowel against the surface to level it after the compaction step; and a water supplying step of supplying water to the surface simultaneously with the pressing step, The water supplying step includes: A concrete construction method in which water is supplied to the surface in an amount of 20% to 50% of the water evaporated from the poured concrete between the pouring step and the pressing step.

2. 2. The concrete construction method according to claim 1, wherein the W / C of the concrete is 38.5% or more.

3. The pressing step includes:

3. The method for constructing concrete according to claim 1, wherein the concrete is poured while the age of the poured concrete is between 0.5 hours and 2 hours.

4. The water supplying step includes: 0.28 L / m on the surface ２ 0.70L / m or more ２ 3. The method for constructing concrete according to claim 1 or 2, wherein the following amount of water is supplied:

5. The water supplying step includes:

3. The method for constructing concrete according to claim 1 or 2, wherein water is sprayed onto the concrete using a spray nozzle.

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