Concrete construction methods

Abstract

This invention provides a concrete construction method that can prevent initial frost damage to concrete constructed during cold periods. [Solution] The method includes the following steps: Step S1: Before pouring the concrete, set the start time for pouring the concrete, the planned end time for pouring the concrete, the expected temperature after pouring, and the expected bleeding duration after pouring; Step S2: Calculate the bleeding end time by adding the bleeding duration to the planned end time; Step S3: If the expected temperature between the planned end time and the bleeding end time is below a predetermined value, set the amount of setting-promoting admixture to be added to shorten the bleeding duration; and Step S4: After adding the set amount of setting-promoting admixture to the concrete, pour the concrete at the start time.

Description

[Technical Field]

[0001] This invention relates to a method for constructing concrete, for example, during cold seasons. [Background technology]

[0002] Traditionally, in cold weather, concrete setting is significantly slower, leading to a large amount of bleeding (separated water) depending on conditions such as mix design, temperature, and placement height. If bleeding occurs and is not adequately treated, and the outside temperature gradually drops to near freezing, the moisture on the surface exposed to the outside air freezes, resulting in initial frost damage.

[0003] Generally, after placement, concrete must be kept at a temperature of 5°C or higher until it achieves sufficient strength to prevent initial frost damage, and then at 0°C or higher for two more days. Therefore, initial curing must be performed using methods such as thermal insulation or heat curing to achieve the required strength (generally, a compressive strength of 5.0 N / mm²). 2 It is required to prevent freezing until the desired result is obtained.

[0004] To mitigate setting delays and bleeding and maintain the subsequent curing temperature, temporary enclosures such as blue tarpaulins are used around the pouring site in outdoor locations, and warming is performed using jet heaters. While warming with jet heaters is effective in mitigating cold, the heat may not be distributed evenly, and it cannot be expected to accelerate setting, so it cannot significantly reduce bleeding. When finishing work is required on the concrete surface, the work itself extends for a long time after the pouring is completed, making it difficult to warm the area as the finishing area increases.

[0005] In addition, in cases where the temperature raises concerns about initial strength development, methods such as using cold-hardening accelerators and rapid-strengthening agents can be employed (see, for example, Patent Document 1). These are not admixtures designed to improve bleeding issues; most are liquids added during production at ready-mix concrete plants, and since they require a redesign of the concrete mix as part of the concrete material, they are not widely used. The use of accelerators such as AE water-reducing agents and rapid-strength Portland cement also does not have a sufficient effect to solve the bleeding problem. In other words, the effectiveness of current countermeasures is limited. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. WO2019 / 244601 [Overview of the project] [Problems that the invention aims to solve]

[0007] The presence of floating water on the concrete surface due to bleeding suggests that there are water pathways (channels) from within the concrete, and that some water remains in areas closer to the surface that are not completely discharged as bleeding. This surface layer is susceptible to the effects of ambient temperature, and a large amount of residual water increases the risk of initial frost damage. Compressive strength: 5.0 N / mm² 2 Even when curing is allowed to occur, the very surface layer, which is susceptible to the effects of outside temperature, may not develop strength in the same way as the inside of the concrete, and the possibility of weakening cannot be ruled out. When surface finishing work is carried out, work is done to meticulously reinforce this surface layer with a large amount of residual water, but if the setting is prolonged and the work itself is carried out at night or late at night, there is a risk that the water will freeze during the work.

[0008] The present invention has been made in view of the above, and aims to provide a concrete construction method that can prevent initial frost damage to concrete when it is constructed during cold seasons. [Means for solving the problem]

[0009] To solve the above-mentioned problems and achieve the objective, the concrete construction method according to the present invention is characterized by comprising the steps of: setting a start time for starting concrete placement, a planned end time for ending placement, a predicted temperature after placement, and a predicted bleeding duration after placement, before placing the concrete; calculating a bleeding end time by adding the bleeding duration to the planned end time; setting an amount of setting-promoting admixture to shorten the bleeding duration if the predicted temperature between the planned end time and the bleeding end time is below a predetermined value; and adding the set amount of setting-promoting admixture to the concrete, and then placing the concrete at the start time for placement.

[0010] Furthermore, another concrete construction method according to the present invention is characterized in that, when performing finishing work on the top surface of the concrete in the above invention, it includes the steps of: calculating the finishing work completion time by adding the finishing work time to the calculated bleeding completion time; and setting the amount of setting-promoting admixture to be added to shorten the bleeding duration when the temperature expected between the bleeding completion time and the finishing work completion time is below a predetermined value.

[0011] Furthermore, another concrete construction method according to the present invention is characterized in that, in the above-described invention, the amount of the setting-accelerating admixture to be added is set by applying the difference in the starting time, which is set based on the type of cement, the temperature at the time of placement, and the expected bleeding duration, to the relationship between the amount of the setting-accelerating admixture to be added, which has been obtained in advance for each type of cement used in the concrete and the temperature at the time of placement, and the difference between the starting time of setting of concrete without the setting-accelerating admixture and the starting time of setting of concrete with the setting-accelerating admixture added. Note that the starting time of setting refers to the time until the concrete begins to harden, that is, the time until it begins to lose its fluidity. [Effects of the Invention]

[0012] The concrete construction method according to the present invention includes the steps of setting a start time for concrete placement, a planned end time for placement, a predicted temperature after placement, and a predicted bleeding duration after placement, before placing the concrete; calculating a bleeding end time by adding the bleeding duration to the planned end time; setting an amount of setting-promoting admixture to shorten the bleeding duration if the predicted temperature between the planned end time and the bleeding end time is below a predetermined value; and adding the set amount of setting-promoting admixture to the concrete and then placing the concrete at the start time. Therefore, if the temperature during the bleeding duration is expected to be below freezing, for example, by adding a setting-promoting admixture to the concrete, the bleeding duration can be shortened to avoid the period of sub-zero temperatures. Consequently, it has the effect of preventing initial frost damage to concrete constructed during cold seasons.

[0013] Furthermore, according to another concrete construction method of the present invention, when performing finishing work on the top surface of concrete, the method includes the steps of calculating the finishing work completion time by adding the finishing work time to the calculated bleeding completion time, and setting the amount of setting-promoting admixture to be added to shorten the bleeding duration when the temperature expected between the bleeding completion time and the finishing work completion time is below a predetermined value. Therefore, when the temperature during the finishing work time is expected to be below freezing, for example, the bleeding duration can be shortened to avoid the period of sub-zero temperatures by adding the setting-promoting admixture to the concrete. Consequently, it has the effect of preventing initial frost damage to concrete constructed during cold seasons.

[0014] Furthermore, according to another concrete construction method of the present invention, the amount of the setting-accelerating admixture to be added is set by applying the difference in the starting time, which is set based on the type of cement, the temperature at the time of placement, and the expected bleeding duration, to the relationship between the amount of the setting-accelerating admixture to be added, which has been obtained in advance for each type of cement used in the concrete and the temperature at the time of placement, and the difference in the starting time of setting of concrete without the setting-accelerating admixture and the starting time of setting of concrete with the setting-accelerating admixture added. This has the effect of making it easy to set the amount of the setting-accelerating admixture to be added. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 is a schematic procedure diagram showing an embodiment of the concrete construction method according to the present invention. [Figure 2] Figure 2 shows the time progression of concrete pouring during the winter. [Figure 3] Figure 3 shows the state of bleeding in concrete. [Figure 4] Figure 4 shows the approximate amount of setting-promoting admixture to add and the time required for setting to begin. [Figure 5]Figure 5 is a diagram showing the bleeding occurrence state of concrete to which a setting accelerating admixture is added. [Figure 6] Figure 6 is a diagram showing the time lapse state of concrete placement to which a setting accelerating admixture is added. [Mode for Carrying Out the Invention]

[0016] Hereinafter, an embodiment of the concrete construction method according to the present invention will be described in detail based on the drawings. Note that the present invention is not limited by this embodiment.

[0017] As shown in Figure 1, the concrete construction method according to the embodiment of the present invention consists of steps S1 to S4. First, in step S1, before placing concrete, a placement start time at which concrete placement is started, a scheduled end time at which placement is ended, an air temperature expected after placement, and an expected bleeding duration after placement are respectively set. The placement start time and the scheduled end time can be set based on the construction plan. For the air temperature, the value of the local weather forecast for the placement time period can be used. The bleeding duration may be estimated from past actual values, or may be estimated by performing trial mixing of concrete at a similar outside air temperature and conducting a bleeding test (JIS A 1123).

[0018] In the next step S2, a bleeding end time obtained by adding the bleeding duration to the scheduled end time is calculated. When finishing work is performed on the top surface of concrete, a finishing work end time obtained by adding the finishing work time to the calculated bleeding end time may be calculated.

[0019] In the next step S3, when the air temperature expected during the period from the scheduled end time to the bleeding end time (or the finishing work end time) is equal to or lower than a predetermined value (for example, below freezing), the addition amount of the setting accelerating admixture for shortening the bleeding duration is set.

[0020] The amount of setting-accelerating admixture to be added may be determined using the relationship between the initial setting time and the amount added, which has been obtained in advance. Specifically, the amount of setting-accelerating admixture to be added may be determined by applying the difference in initial setting time, which has been set based on the type of cement used, the temperature at the time of placement, and the expected bleeding duration, to the relationship between the amount of setting-accelerating admixture to be added, which has been obtained in advance for each type of cement used in the concrete and the temperature at the time of placement, and the difference between the initial setting time of concrete without the setting-accelerating admixture and the initial setting time of concrete with the setting-accelerating admixture added.

[0021] For the setting-promoting admixture, it is desirable to use Denka ACF material (hereinafter simply referred to as "ACF") manufactured by Denka Co., Ltd., which promotes the initial hydration reaction. ACF is a powder mainly composed of sulfo-based salts or calcium sulfoaluminate.

[0022] In the next step, S4, the set amount of setting-promoting admixture is added to the concrete, and then this concrete is poured at the scheduled start time.

[0023] According to this embodiment, if the temperature during the bleeding period (or during the finishing work period) is expected to fall below a predetermined value (e.g., below freezing) where there is a risk of initial frost damage, the bleeding period can be shortened by adding a setting-promoting admixture to the concrete, thereby avoiding the period when the temperature is below the predetermined value. Therefore, initial frost damage to concrete constructed during cold seasons can be prevented.

[0024] <Examples> Next, embodiments of the present invention will be described. Figure 2 shows the temperature and the time elapsed during concrete pouring work for two days in winter (February) at a construction site in northern Kanto. Pouring began around 8:30 a.m. and continued until around 14:00, with the outside temperature maintained above 5°C until this point. Bleeding occurred on the concrete surface during or after pouring, and treatment was carried out, during which time the temperature gradually decreased.

[0025] Figure 3 shows the experimental results of the time-dependent change in bleeding water content of poured concrete at an ambient temperature of 5°C. According to these results, bleeding continues for 6 hours, meaning that bleeding from the portion poured at 2 PM will finally converge at 8 PM. As shown in Figure 2, the ambient temperature begins to fall below 0°C around this point, but the concrete is still setting, and the penetration resistance is still 0.3-0.5 N / mm². 2 The degree of frost settling slows down. If initial curing by insulation or heat curing is not carried out properly, the risk of initial frost damage increases significantly. If finishing work is required, it will be carried out in temperatures below 0°C, which could lead to freezing during the work. Therefore, the present invention will be applied to this site, and initial frost damage will be prevented by the following procedure.

[0026] (Step 1) First, information on the expected temperature after concrete placement is prepared, including the change in ambient temperature from the scheduled concrete placement date to the following morning (numerical values ​​or a graph). In this example, the temperature change shown in Figure 2 corresponds to this.

[0027] (Step 2) Determine the start and end times for concrete pouring on the scheduled pouring day. In this example, 8:30 on the first day in Figure 2 corresponds to the start time of concrete pouring, and 14:00 on the same day corresponds to the scheduled end time.

[0028] (Step 3) For the concrete to be used at the placement site, the duration of bleeding at the average ambient temperature during placement is estimated. If actual bleeding duration data is available, it is used for estimation. If actual data is not available, a trial mix of concrete is performed at similar ambient temperatures, and a bleeding test (JIS A 1123) is conducted to estimate the duration. In this example, from Figure 3, the bleeding duration is estimated to be 6 hours.

[0029] (Step 4) The estimated bleeding duration is added to the scheduled completion time of concrete placement to calculate the bleeding end time. If there is finishing work on the top surface of the concrete, the time from the end of this work to the completion of the finishing work is added to calculate the finishing work completion time. If the temperature falls below freezing during the bleeding duration or the concrete finishing work time, it can be determined that there is a high risk of initial frost damage. In this example, 20:00, which is 6 hours added to 14:00, corresponds to the bleeding end time, and 23:00, which is 3 hours added to 20:00, corresponds to the finishing work completion time.

[0030] (Step 5) It is known that the setting-accelerating effect of adding ACF (Accelerated Coolant) reduces working time by measuring the difference in the initial setting time between concrete without ACF and concrete with ACF. Therefore, the amount of ACF to be added is set, and the difference in initial setting time is calculated.

[0031] Figure 4 shows an example of the relationship between the amount of ACF added to concrete using ordinary Portland cement and the initial setting time, for different average temperatures at the time of placement (5°C and 10°C). As shown in this figure, the difference in initial setting time is represented by the difference between the initial setting time when no ACF is added and the initial setting time when an arbitrary amount of ACF is added. In other words, the difference in initial setting time can be determined from the type of cement used in the concrete, the average temperature at the time of placement, and the amount of ACF added.

[0032] In this example, ordinary Portland cement is used for the concrete. For ordinary Portland cement, the difference in start time is calculated using either formula (1) or formula (2) below. When the average temperature at placement is 5°C, the ACF addition amount is 3 kg / m³. 3 When set to this value, equation (1) calculates that the difference in the first departure time compared to the case without additive is 247 minutes. In other words, the addition of ACF creates a difference of about 4 hours.

[0033] • When the average temperature at the time of concrete pouring is 5°C Difference in first departure time (minutes) = 82.5 × ACF addition amount (kg / m³) 3 )...Equation (1) • When the average temperature at the time of concrete placement is 10℃ Difference in initial setting time (minutes) = 60 × ACF addition amount (kg / m 3 ) ··· Equation (2)

[0034] Herein, when the cement used for concrete is early-strength Portland cement, the difference in initial setting time can be determined using the following Equation (3) or (4).

[0035] · When the average temperature during placing is 5°C Difference in initial setting time (minutes) = 75 × ACF addition amount (kg / m 3 ) ··· Equation (3) · When the average temperature during placing is 10°C Difference in initial setting time (minutes) = 57.5 × ACF addition amount (kg / m 3 ) ··· Equation (4)

[0036] Further, when the cement used for concrete is blast furnace cement Type B, the difference in initial setting time can be determined using the following Equation (5) or (6).

[0037] · When the average temperature during placing is 5°C Difference in initial setting time (minutes) = 147.5 × ACF addition amount (kg / m 3 ) ··· Equation (5) · When the average temperature during placing is 10°C Difference in initial setting time (minutes) = 87.5 × ACF addition amount (kg / m 3 ) ··· Equation (6)

[0038] In the above example, the description has been given taking the cases where the average temperature during placing is 5°C and 10°C as examples, but the present invention is not limited thereto. For example, for cases where the average temperature during placing is other than 5°C and 10°C, a relational expression between the difference in initial setting time and the ACF addition amount may be determined in advance, and the ACF addition amount may be determined based on the determined relational expression. Further, the description has been given taking the cases where the cement type is ordinary Portland cement, early-strength Portland cement, and blast furnace cement Type B as examples, but the present invention is not limited thereto. That is, for other cement types, a relational expression between the difference in initial setting time and the ACF addition amount may be determined in advance for each average temperature during placing, and the ACF addition amount may be determined based on the determined relational expression.

[0039] (Step 6) Next, the concrete is poured according to the ACF construction procedure. Assuming an average temperature of 5°C during pouring, the ACF addition amount is 3 kg / m³. 3 If this is decided, the ACF added to the concrete is added, and the concrete is poured. Except for the addition of ACF, the pouring and compaction methods are the same as for ordinary concrete. Figure 5 shows the bleeding test results (example) of concrete with ACF added according to the above example. This figure also shows the test results (comparative example) of concrete without ACF, as shown in Figure 3. As shown in Figure 5, assuming a predicted setting-promoting effect of 4 hours, the bleeding time was also reduced by 4 hours. The amount of bleeding can also be significantly reduced.

[0040] Figure 6 shows the temperature and the time elapsed for concrete placement work over two days in winter (February) at a site in northern Kanto when the present invention is applied. As shown in this figure, similar to Figure 3, placement starts around 8:30 a.m. and continues until around 14:00, with the outside temperature maintained above 5°C until this point. Bleeding occurs on the concrete surface during or after placement, but the action of ACF promotes concrete setting, reducing waiting time and significantly decreasing bleeding, with the bleeding subsiding by 16:00. Therefore, the work required for bleeding treatment is greatly reduced.

[0041] According to this embodiment, concrete curing can be started at a time when the temperature does not fall below 0°C, ensuring that setting proceeds reliably and significantly reducing the risk of initial frost damage.

[0042] Furthermore, since the amount of ACF to be added can be arbitrarily determined from formula (1) or formula (2) according to the outside temperature and the planned completion time, the optimal construction method can be used for each construction condition.

[0043] As described above, the concrete construction method according to the present invention includes the steps of setting a start time for starting concrete placement, a planned end time for ending placement, an expected temperature after placement, and an expected bleeding duration after placement, before placing the concrete; calculating a bleeding end time by adding the bleeding duration to the planned end time; setting an amount of setting-promoting admixture to shorten the bleeding duration if the expected temperature between the planned end time and the bleeding end time is below a predetermined value; and adding the set amount of setting-promoting admixture to the concrete and then placing the concrete at the start time. Therefore, if the temperature during the bleeding duration is expected to be below freezing, for example, the bleeding duration can be shortened by adding the setting-promoting admixture to the concrete to avoid the period of sub-freezing temperatures. Consequently, initial frost damage to concrete constructed during cold seasons can be prevented.

[0044] Furthermore, according to another concrete construction method of the present invention, when performing finishing work on the top surface of concrete, the method includes the steps of calculating the finishing work completion time by adding the finishing work time to the calculated bleeding completion time, and setting the amount of setting-promoting admixture to be added to shorten the bleeding duration when the temperature expected between the bleeding completion time and the finishing work completion time is below a predetermined value. Therefore, when the temperature during the finishing work time is expected to be below freezing, for example, the bleeding duration can be shortened to avoid the period of sub-zero temperatures by adding the setting-promoting admixture to the concrete. Consequently, initial frost damage to concrete constructed during cold seasons can be prevented.

[0045] Furthermore, according to another concrete construction method of the present invention, the amount of the setting-accelerating admixture to be added is set by applying the difference in the starting time, which is set based on the type of cement, the temperature at the time of placement, and the expected bleeding duration, to the relationship between the amount of the setting-accelerating admixture to be added, which has been obtained in advance for each type of cement used in the concrete and the temperature at the time of placement, and the difference between the starting time of setting of concrete without the setting-accelerating admixture and the starting time of setting of concrete with the setting-accelerating admixture added. This makes it easy to set the amount of the setting-accelerating admixture to be added.

[0046] Furthermore, the "Sustainable Development Goals (SDGs)" are among the 17 international goals adopted at the UN Summit in September 2015. The concrete construction method according to this embodiment can contribute to achieving some of the 17 SDGs, such as Goal 8, "Decent Work and Economic Growth." [Industrial applicability]

[0047] As described above, the concrete construction method according to the present invention is useful for construction of concrete structures, and is particularly suitable for preventing initial frost damage to concrete constructed during cold seasons.

Claims

1. Before pouring the concrete, the process involves setting the start time for pouring, the planned end time for pouring, the expected temperature after pouring, and the expected bleeding duration after pouring. The steps include: calculating the breeding end time by adding the breeding duration to the scheduled end time; The steps include setting the amount of a coagulation-promoting admixture to be added to shorten the bleeding duration when the temperature expected between the scheduled end time and the end time of bleeding is below a predetermined value, A concrete construction method characterized by comprising the steps of adding a set amount of the setting-promoting admixture to the concrete, and then pouring the concrete at the start time of pouring.

2. When performing finishing work on the top surface of concrete, the steps include: calculating the finishing work completion time by adding the finishing work time to the calculated bleeding completion time; The concrete construction method according to claim 1, further comprising the step of setting the amount of setting-promoting admixture to shorten the bleeding duration when the temperature expected between the end of the bleeding time and the end of the finishing work is below a predetermined value.

3. The concrete construction method according to claim 1 or 2, characterized in that the amount of setting-accelerating admixture to be added is determined by applying the difference in the starting time, which is set based on the type of cement, the temperature at the time of placement, and the expected bleeding duration, to the relationship between the amount of setting-accelerating admixture to be added, which has been obtained in advance for each type of cement used in the concrete and the temperature at the time of placement, and the difference between the starting time of setting of concrete without the setting-accelerating admixture and the starting time of setting of concrete with the setting-accelerating admixture added.

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