Method for estimating start time of expansive concrete and method for placing the same

Abstract

To precisely estimate a start time to determine by a JIS A1147 method from the result of measuring change of the expansion strain of expansive concrete by a simple measurement device.SOLUTION: The method for estimating a start time of expansive concrete uses an expansive concrete including an expansive material as a sample. The time from water injection is started to when the expansive strain of the sample starts increasing and the expansive strain becomes larger than a predetermined level is determined as a predetermined amount strain time by using an expansive concrete strain expansion test technique employing a cylindrical frame 2 described later. Further, the start time in the expansive concrete condensation process is determined from the predetermined amount strain time.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for estimating the initial setting time of expansive concrete and a method for placing expansive concrete.

Background Art

[0002] As a prior art document regarding a method for estimating the initial setting time of expansive concrete, Patent Document 1 can be cited. Patent Document 1 discloses a measuring method and a measuring instrument that can simply measure the workable time of concrete without using a Proctor penetration test device (JIS A1147 cited in JIS A6204). The measuring instrument is composed of a restraint bar installed inside the concrete and a strain gauge (academically strain, hereinafter the notation when citing Document 1 is changed to strain) attached to the restraint bar. As Example 2, for concrete obtained by blending an expansive agent with ordinary Portland cement, the change in expansive strain after water contact is continuously measured, and it is described that the point in time when the change in expansive strain turns from no change to an increase is the initial setting point, that is, the workable time of the cockcrete. Here, the "workable time" of concrete used herein is a term also referred to as the "initial setting time" of concrete.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, Patent Document 1 does not describe an explanation that enables understanding that the available time determined as the point at which the expansion strain starts to increase when measured with the said measuring instrument is the same as the available time measured with the said Proctor penetration test apparatus (JIS A1147 cited in JIS A6204). Therefore, there remained an unclear point as to whether the available time obtained with the said measuring instrument could be directly used as the available time measured with the said Proctor penetration test apparatus (JIS A1147 cited in A6204). Also, there was room for improvement in effectively exerting the ability of the expansion material in expansive concrete.

[0005] The inventors of the present invention conducted independent studies on the said unclear points. As a result, it was found that the change in the expansion strain of expansive concrete was measured by a simple device using a strain gauge, and the elapsed time from water injection until the change in the expansion strain began to increase and the expansion strain exceeded a predetermined amount had a good correlation with the initial time obtained by JIS A1147 "Test Method for Setting Time of Concrete" (hereinafter referred to as the "JIS A1147 method"). That is, from the results of measuring the change in expansion strain with a simple device, it was found that by utilizing the said good correlation, it was possible to accurately estimate the initial time obtained by the JIS A1147 method. Thus, the present invention was completed.

[0006] An object of the present invention is to enable accurate estimation of the initial time obtained by the JIS A1147 method without using the JIS A1147 method, based on the results of measuring the change in the expansion strain of expansive concrete with a simple device. Also, it is to easily realize a state in which the ability of the expansion material in expansive concrete can be effectively exerted.

Means for Solving the Problems

[0007] In order to achieve the above object, the method for estimating the initial setting time of expansive concrete according to the first aspect of the present invention uses expansive concrete containing an expansive agent as a sample, and uses a restrained expansion test method for expansive concrete using a cylindrical formwork (hereinafter also referred to as the "cylindrical formwork method"). The elapsed time from water injection until the expansion strain of the sample begins to increase and exceeds a predetermined amount is obtained as the predetermined strain time, and the initial setting time in the setting process of the expansive concrete is estimated from the predetermined strain time. Here, the "restrained expansion test method for expansive concrete using a cylindrical formwork" refers to the restrained expansion test method for expansive concrete specified in "JCI-S-009-2012" of the Japan Concrete Institute's JCI standard.

[0008] According to this aspect, the operation of measuring the restrained expansion amount of expansive concrete using the cylindrical formwork method is simpler than the JIS A1147 method, so the initial setting time of expansive concrete can be easily obtained. Then, by measuring the change in the expansion strain of the expansive concrete by the cylindrical formwork method, and using the fact that the elapsed time from water injection until the change in the expansion strain begins to increase and exceeds a predetermined amount has a good correlation with the initial setting time obtained by the JIS A1147 method, the initial setting time obtained by the JIS A1147 method can be accurately estimated and used. Moreover, without using the JIS A1147 method, the initial setting time can be easily and accurately estimated and used by the simple cylindrical formwork method. Therefore, in the adjustment of expansive concrete, a state in which the ability of the expansive agent is effectively exerted can be easily realized.

[0009] The method for estimating the initial setting time of expansive concrete according to the second aspect of the present invention is characterized in that the predetermined amount is 5×10 -6

[0010] According to this aspect, the predetermined amount is 5×10 -6 ​This numerical value is determined from the results of a large number of measurements made by the inventors when finding the above-mentioned good correlation, because it tended to show the best correlation. It does not mean that the predetermined amount exactly coincides with this numerical value. Thus, by setting the predetermined amount to 5×10 -6 the initial setting time obtained by the JIS A1147 method can be easily estimated and used.

[0011] The method for estimating the initial setting time of the expansive concrete according to the third aspect of the present invention is characterized in that an approximate formula showing the correlation between the initial setting time obtained by the JIS A1147 method and the predetermined amount of strain time is obtained in advance, and the initial setting time in the setting process of the expansive concrete is obtained based on the approximate formula from the predetermined amount of strain time.

[0012] According to this aspect, since the approximate formula between the initial setting time obtained by the JIS A1147 method and the predetermined amount of strain time obtained by the cylindrical mold method is obtained in advance, by measuring the change in the expansive strain by the simple cylindrical mold method to obtain the predetermined amount of strain time, the initial setting time obtained by the JIS A1147 method can be easily estimated and used.

[0013] The placing method of the expansive concrete according to the fourth aspect of the present invention is characterized in that a specific amount of an expansive agent is added, the concrete is prepared at the assumed initial setting time, a sample is taken from the expansive concrete transported to the placing site by a mixer truck, the estimation method of any one of the first to third aspects is carried out on the sample to obtain the estimated initial setting time, and based on the estimated initial setting time, the suitability of the assumed initial setting time is determined.

[0014] The expansive concrete is produced by adjusting the proportions of cement, expansive agent, fine aggregate, coarse aggregate, water, and admixtures, etc. so that it reaches its assumed start time. Then, the adjusted expansive concrete is transported to the placement site by a mixer truck and placed. Usually, there is no problem because the start time of the expansive concrete placed at the placement site is within the allowable range of displacement from the assumed start time. However, in a severe heat environment such as in summer, it is thought that a large change in the concrete temperature, etc. may cause the start time to deviate from the allowable range of displacement from the assumed start time. In that case, drying shrinkage cracks may easily occur in the concrete. According to this aspect, a sample is taken from the expansive concrete transported to the placement site by a mixer truck, and the start time determined by the JIS A1147 method can be accurately estimated simply by any of the methods of the first to third aspects. Thereby, it is possible to easily determine whether or not it deviates from the allowable range of displacement from the assumed start time, and by feeding back the determination result to the manufacturing site of the expansive concrete, it is possible to easily take measures against the occurrence of cracks in the concrete.

Brief Description of Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0016] Hereinafter, Embodiment 1 of the method for estimating the initial setting time of expansive concrete according to the present invention will be described in detail with reference to FIGS. 1 to 3. [Embodiment 1] In the method for estimating the initial setting time of the expansive concrete of Embodiment 1, the expansive concrete containing an expansive agent is used as a sample. Then, using the method for the restrained expansion test of expansive concrete using a cylindrical formwork 2 (FIG. 1) described later, the elapsed time from water injection until the expansion strain of the sample begins to increase and the expansion strain exceeds a predetermined amount is obtained as a predetermined strain time. Further, the initial setting time in the setting process of the expansive concrete is estimated from the predetermined strain time. Hereinafter, it will be described in detail.

[0017] <Expansive concrete> In this embodiment, the expansive concrete has a general composition including cement, an expansive agent, fine aggregate, coarse aggregate, and water, and further includes an admixture as required. This expansive concrete is adjusted so as to expand in the setting process by the effect of the expansive agent. Specifically, as the cement, commonly used cements such as Portland cement, blast furnace cement, and fly ash cement can be used. Specifically, examples of the expansive agent include ordinary ones such as lime-based expansive agents, ettringite-based expansive agents, and ettringite-lime composite expansive agents. The fine aggregate and the coarse aggregate are also those generally used in concrete. As the admixture, general ones such as water reducing agents, high-performance water reducing agents, AE agents, AE water reducing agents, and high-performance AE water reducing agents can be used.

[0018] <Method for the restrained expansion test of expansive concrete using a cylindrical formwork (cylindrical formwork method)> The method for the restrained expansion test of expansive concrete using a cylindrical formwork used in this embodiment, that is, the cylindrical formwork method, is a method (JCI-S-009-2012) adopted in the JCI standard of the Japan Concrete Institute. As shown in Fig. 1, the measuring device 1 used in the cylindrical formwork method (JCI-S-009-2012) includes a cylindrical formwork 2 and a strain gauge 3. The cylindrical formwork 2 is a bottomed cylindrical body made of tin with a diameter of 100 mm and a length of 200 mm. As shown in Fig. 1, the strain gauge 4 of the strain gauge 3 is attached to the central part in the length direction of the cylindrical formwork 2 with an epoxy resin adhesive. The gauge length of the strain gauge 4 is 10 mm. The strain gauge 4 is coated with a waterproof and protective sheet 5.

[0019] An expanded concrete containing an expansive agent is used as a sample to be measured and filled into the cylindrical formwork 2. The filling is carried out so as to be in the state specified by the cylindrical formwork method (JCI-S-009-2012). When the sample in the cylindrical formwork 2 expands, an expansion strain occurs in the cylindrical formwork 2. By sensing the expansion strain with the strain gauge 4, the strain gauge 3 can measure the expansion amount of the sample. Specifically, this measuring device 1 continuously measures the change in the expansion strain of the cylindrical formwork 2 based on the passage of time starting from the time when the expanded concrete is watered. This continuous change in the expansion strain of the cylindrical formwork 2 corresponds to the continuous change in the expansion strain of the sample filled inside the cylindrical formwork 2.

[0020] Fig. 2 is a graph showing the results of measuring each sample 11, 12, and 13 of the expanded concrete with the measuring device 1 for three specimens of expanded concrete containing an expansive agent. Samples 11, 12, and 13 are those with the largest addition amount of the expansive agent, which is 30 kg / m 3 In Fig. 2, the horizontal axis is the elapsed time (h:m) with the time of watering set as 0 hours and 0 minutes. The vertical axis is the expansion strain amount (×10 -6 ). Here, since the expansion strain amount (×10 -6 ) is a ratio of strain, it is dimensionless.

[0021] As shown in Fig. 2, for each of the samples 11, 12, and 13, no significant change in the expansion strain is observed during the elapsed time from 0:00 to about 5:00. There are irregular increases and decreases in the expansion strain within this elapsed time of about 5:00, but these increases and decreases are due to noise rather than the expansion effect of the expansion material of each of the samples 11, 12, and 13. When the elapsed time exceeds 5:00, the expansion strain of each of the samples 11, 12, and 13 begins to increase. After the start of the increase, the change in the expansion strain follows a gentle increasing curve. For sample 11, the expansion strain reaches 5×10 -6 at around 6:00. For sample 12, the expansion strain reaches 5×10 -6 at around 6:20. For sample 13, the expansion strain reaches 5×10 -6 at around 6:30. And the change in the expansion strain of each of the samples 11, 12, and 13 becomes a steep increasing curve when it reaches 5×10 -6 .

[0022] The inventors further increased the number of samples and measured and examined the change in the expansion strain shown in Fig. 2 in the same way. As a result, as shown in Fig. 3, the change in the expansion strain of the expansive concrete was measured by the measuring device 1 used in the cylindrical mold method (JCI-S-009-2012), and it was found that there is a good correlation between the elapsed time from the addition of water until the change in the expansion strain begins to increase and the expansion strain exceeds a predetermined amount and the initial time obtained by the JIS A1147 method. Here, the predetermined amount is 5×10 -6 . In Fig. 3, the horizontal axis represents the initial time (h:m) obtained by the penetration resistance test according to the JIS A1147 method. The vertical axis represents the amount of strain time (h:m) of the predetermined amount of the expansion strain measured by the measuring device 1 used in the cylindrical mold method (JCI-S-009-2012). Here, the amount of strain time (h:m) is the elapsed time until the change in the expansion strain begins to increase and the amount of the expansion strain exceeds 5×10 -6 . Therefore, in Fig. 3, it is marked on the vertical axis as "time exceeding 5×10 -6 (h:m)".

[0023] Figure 3 shows that 23 types of expansive concrete were made by changing the addition amount of the expansion material, the type of admixture, etc., and samples of each of the 23 types of expansive concrete were collected. For one type of expansive concrete, JIS The results obtained by both the A1147 method and the cylindrical mold method (JCI-S-009-2012) were plotted for all 23 types. Here, the addition amount of the expansion material was adjusted to either 30 kg / m 3 or 25 kg / m 3 . The round marks "〇" in Figure 3 are the positions of each plot. These 23 types were measured at a temperature of 30°C. From each plot position in Figure 3, it can be understood that there is a strong positive correlation, that is, a good correlation, between the results obtained by the JIS A1147 method and the cylindrical mold method (JCI-S-009-2012) for the expansive concrete. Taking the horizontal axis as the X-axis and the vertical axis as the Y-axis, when the correlation was obtained by the least squares method, an approximate line 21 with the following correlation of formula (A) was obtained. Y = 1.0776X + 0.0054 ……(A)

[0024] This formula (A) shows that for the adjusted samples of expansive concrete, if the time (h:m) exceeding 5×10 -6 is obtained by the measuring device 1 used in the cylindrical mold method (JCI-S-009-2012), X can be calculated and obtained by introducing the obtained value into Y of formula (A). That is, it can be said that for the adjusted samples of expansive concrete, it is possible to accurately estimate the initial time obtained by the JIS A1147 method by formula (A) without performing the time-consuming measurement by the JIS A1147 method.

[0025] Also, in FIG. 3, the five square marks “□” are the results obtained by making five types of expansive concrete and plotting the same measurements as those for the 23 types of expansive concrete at a temperature of 20°C. It can be seen that the results measured at a temperature of 20°C follow the approximate line 21 with the correlation of the formula (A). This indicates that the difference in ambient temperature is not a problem. From the above, regardless of the types and contents of cement, expansive agent, fine aggregate, coarse aggregate, water, and admixture that make up the components of expansive concrete, and further regardless of temperature, it is possible to accurately estimate the initial setting time obtained by the JIS A1147 method by applying the formula (A).

[0026] <Description of the effects of Embodiment 1> (1) In this embodiment, the operation of measuring the restrained expansion amount of expansive concrete using the cylindrical mold method (JCI-S-009-2012) is simpler than the JIS A1147 method, so the initial setting time of the expansive concrete can be easily obtained. Then, by measuring the change in the expansion strain of the expansive concrete by the cylindrical mold method (JCI-S-009-2012) and using the fact that the elapsed time from water injection until the change starts to increase and the expansion strain exceeds a predetermined amount has a good correlation with the initial setting time obtained by the JIS A1147 method, the initial setting time obtained by the JIS A1147 method can be accurately estimated and used. Also, without using the JIS A1147 method, the initial setting time can be easily and accurately estimated and used by the simple cylindrical mold method (JCI-S-009-2012). Therefore, in the adjustment of expansive concrete, a state where the ability of the expansive agent is effectively exerted can be easily realized.

[0027] (2) Also, in this embodiment, the predetermined amount is 5×10 -6 This makes it possible to more accurately estimate and use the initial setting time obtained by the JIS A1147 method. (3) Also, in this embodiment, as shown in FIG. 3, an approximate line 21 having a correlation between the starting time obtained by the JIS A1147 method and the predetermined strain time obtained by the cylindrical formwork method (JCI-S-009-2012) is obtained in advance. Therefore, by measuring the change in the expansion strain by the simple cylindrical formwork method (JCI-S-009-2012) to obtain the predetermined strain time, the starting time obtained by the JIS A1147 method can be easily and accurately estimated.

[0028] [Embodiment 2] Next, the placing method of the expansive concrete according to Embodiment 2 will be described. The same parts as those in Embodiment 1 are denoted by the same reference numerals, and the description of the configuration and the corresponding effects thereof will be omitted. The placing method of ordinary expansive concrete is generally performed as follows. (1) The expansive concrete is prepared by adjusting the proportions of cement, expansive agent, fine aggregate, coarse aggregate, water, and further admixtures so as to reach the assumed starting time. (2) The expansive concrete adjusted in (1) is transported to the placing site by a mixer truck and placed. Normally, the expansive concrete placed at the placing site has no problem because the starting time is within the allowable range of displacement from the assumed starting time. However, in an environment with severe heat such as in summer, it is considered that a large change in the concrete temperature or the like causes the starting time to be out of the allowable range of displacement from the assumed starting time. In that case, drying shrinkage cracks may easily occur in the concrete.

[0029] In this embodiment, the placing method of the expansive concrete is performed as follows. (1) The expansive concrete is prepared by adjusting the proportions of cement, expansive agent, fine aggregate, coarse aggregate, water, and further admixtures so as to reach the "assumed starting time". The time when water is added to this expansive concrete, that is, the time when water is injected, is recorded. (2) The expansive concrete adjusted in (1) is transported to the placing site by a mixer truck and placed. (3) Collect samples from the expansive concrete placed on site, measure the change in expansion strain for the samples using the measuring device 1 of Embodiment 1, and obtain the "predetermined strain time". This measurement measures the elapsed time with the "time of water injection" recorded in (1) as 0 hours 00 minutes. (4) Using the formula (A) of the approximate line 21 that has a correlation with the "predetermined amount of strain time", that is, the "time exceeding 5×10 -6 obtained from the measurement in (3), obtain the "estimated starting time". (5) Based on the estimated starting time, determine the suitability of the assumed starting time.

[0030] In this embodiment, as described above, samples are collected from the expansive concrete transported to the placement site by the mixer truck, and the estimated starting time in (4) is obtained. This estimated starting time accurately estimates the starting time obtained by the JIS A1147 method. Thereby, it is possible to easily determine whether it is outside the allowable range of displacement from the assumed starting time, and by feeding back the determination result to the manufacturing site of the expansive concrete, it is possible to easily take measures against the occurrence of cracks in the concrete.

[0031] Next, based on FIGS. 4 to 6, using adjusted various types of expansive concrete as samples, the relationship between the estimated starting time obtained from the "predetermined amount of strain time" measured by the measuring device 1 used in the cylindrical form method (JCI-S-009-2012) and the maximum expansion amount of the expansion strain of the same sample will be described. In each figure, the horizontal axis is the estimated starting time obtained from the "predetermined amount of strain time". Here, since the "predetermined amount of strain time" is the "time exceeding 5×10 -6 the horizontal axis of each figure is described as the "starting time (h:m) obtained from the initial expansion time exceeding 5×10 -6 ". Also, in each figure, the vertical axis is the maximum expansion amount (×10 -6 ). This maximum expansion amount is obtained by measuring with the measuring device 1 until the increase in expansion strain stops.

[0032] Figure 4 shows the results plotted for 14 types of expansive concrete samples with an expansion material added at 30 kg / m 3 measured at a temperature of 30°C. It can be seen that there is a negative correlation between the "initial start time (h:m) obtained from the time exceeding 5×10 -6 " and the maximum expansion amount (×10 -6 ). When an approximate line 31 with a correlation is obtained by the least squares method, it becomes the following formula (B). Y = -795.22X + 495.8......(B)

[0033] Figure 5 shows the results plotted for 6 types of expansive concrete samples with an expansion material added at 25 kg / m 3 measured at a temperature of 30°C. When an approximate line 41 with a correlation is obtained by the least squares method, it becomes the following formula (C). Y = -366.32X + 303.24......(C)

[0034] Figure 6 shows the results plotted for 3 types of expansive concrete samples with an expansion material added at 20 kg / m 3 measured at a temperature of 30°C. When an approximate line 51 with a correlation is obtained by the least squares method, it becomes the following formula (D). Y = -101.62X + 157.6......(D)

[0035] Figures 4 to 6 show that as the initial start time increases, the maximum expansion amount of the expansive concrete decreases. When similar measurements are made at 20°C with different temperatures, it was confirmed that there is also a negative correlation. From this, in the adjustment of expansive concrete, by adjusting the formulation so as to shorten the estimated initial start time, it is possible to easily realize a state in which the ability of the expansion material is effectively exerted.

[0036] [Other Embodiments] The method for determining the initial setting time of expansive concrete and the placing method of expansive concrete according to the present invention are based on having the configuration as described above. However, it is of course possible to make partial configuration changes, omissions, etc. within the scope not departing from the gist of the present invention. In the above embodiment, it was described that X is calculated and obtained from Y measured using the formula (A) of the approximate line 21 having a correlation. However, X corresponding to Y may be obtained from the graph of FIG. 3 without using the formula (A).

Explanation of Signs

[0037] 1... Measuring device, 2... Cylindrical formwork, 3... Strain measuring device, 4... Strain gauge, 5... Waterproof and protective sheet, 11... Specimen, 12... Specimen, 13... Specimen, 21... Approximate line, 31... Approximate line, 41... Approximate line, 51... Approximate line

Claims

1. Using expansive concrete containing an expansive agent as a sample, using the restrained expansion test method for expansive concrete using a cylindrical formwork, determining the elapsed time from water injection until the expansion strain of the sample begins to increase and until the expansion strain exceeds a predetermined amount as a predetermined strain time, estimating the initial time in the setting process of the expansive concrete from the predetermined strain time, A method for determining the initial time of expansive concrete, characterized in that.

2. In the method for estimating the initial time of expansive concrete according to Claim 1, The predetermined amount is 5 × 10 －６ and is A method for estimating the initial time of expansive concrete, characterized in that.

3. In the method for estimating the initial time of expansive concrete according to Claim 1 or Claim 2, previously obtaining an approximate formula having a correlation between the initial time obtained by the concrete setting time test method of JIS A1147 and the predetermined strain time, estimating the initial time in the setting process of the expansive concrete from the predetermined strain time based on the approximate formula, A method for estimating the initial time of expansive concrete, characterized in that.

4. Adding a specific amount of expansive agent, preparing at the assumed initial time, collecting a sample from the expansive concrete transported to the placement site by a mixer truck, performing the estimation method described in any one of Claims 1 to 3 on the sample to obtain an estimated initial time, judging the suitability of the assumed initial time based on the estimated initial time, A method for placing expansive concrete, characterized in that.

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