Concrete evaluation method

Abstract

To provide a concrete evaluation method capable of evaluating the likelihood of formation of a lump that lead to blockage of a pipe.SOLUTION: A concrete evaluation method involves: setting an outside temperature, a pressurization time and a pressurization force for concrete of a given composition; mixing a concrete test; performing a pressurization test under the condition of the outside temperature, pressurization time and pressurization force; performing a vane shear test; allowing the concrete to flow from a container to observe the presence or absence of lumps; and setting a threshold for a vane shear test as an increase rate of a vane shear test value after pressurization being less than 100%, based on a test value before pressurization.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for evaluating concrete. [Background technology]

[0002] Conventionally, pump trucks have been used for pumping at high altitudes (see Patent Document 1 below). When pumping is interrupted, the concrete in the pipes near the pump truck is subjected to its own weight equivalent to the height. The higher the pumping height and the longer the interruption, the more consolidation progresses, and not only does the fluidity decrease uniformly, but the concrete is also more likely to form localized lumps near shutter valves, etc. If the fluidity only decreases and the pumping pressure increases, measures can be taken such as calculating pumpability on the safe side, but localized lumps require separate measures.

[0003] In particular, during the hot season, not only does the concrete dehydrate and become lumpy, but the setting rate also increases, causing the lumpy parts to harden quickly, and after pumping is resumed, they are prone to becoming clogged in curved pipes, tapered pipes, etc. on the pouring floor.

[0004] Once a blockage occurs, it takes time to clear it, which can easily hinder subsequent pumping and return work. If the return work takes too long, the pipe itself may have to be discarded.

[0005] To prevent this from happening, it is important to minimize interruptions and to select a concrete mix that will not compact and form lumps. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2008-267051 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, there is no test method to evaluate whether the concrete being pumped is easy to clump or not. Although the pumpability can be judged by conducting slump tests, slump flow tests, 50 cm flow time tests, tests of their changes over time, and pressure bleeding tests, it is very difficult to evaluate whether the concrete is easy to clump. For this reason, it is certain to conduct actual pumping tests, but this is extremely expensive and it is difficult to pump various mixes. It is also difficult to conduct high-altitude pumping tests before the structure is constructed.

[0008] Given this background, there is a demand for a method of evaluating concrete used for pumping at high altitudes that evaluates the likelihood of lump formation that could lead to blockages, separate from the calculation of the pumping pressure.

[0009] Therefore, the present invention has been made in consideration of the above circumstances, and provides a method for evaluating concrete for evaluating the likelihood of formation of lumps that lead to clogging of pipes. [Means for solving the problem]

[0010] In order to achieve the above object, the present invention employs the following means. In other words, the concrete evaluation method of the present invention involves setting the outside air temperature, pressurization time and pressure for concrete of a predetermined composition, conducting a concrete test mix, conducting a pressurization test under the conditions of the outside air temperature, pressurization time and pressure, conducting a vane shear test and allowing the concrete to flow from a container to observe the presence or absence of lumps.

[0011] The concrete evaluation method configured in this manner makes it possible to determine the concrete mix, pressure application time, and pressure force that are less likely to cause lumps in pipes, and to evaluate the likelihood of lumps forming that could lead to pipe blockages.

[0012] Furthermore, in the method for evaluating concrete according to the present invention, in the vane shear test, the threshold value may be set to a value when the rate of increase in the vane shear test value after pressurization is less than 100% with the test value before pressurization being taken as a reference value.

[0013] In the concrete evaluation method configured in this manner, if the rate of increase in the vane shear test value after pressurization is less than 100%, the formation of lumps in the pipe can be suppressed.

[0014] Furthermore, the method for evaluating concrete according to the present invention may be based on the absence of the lumps.

[0015] In the concrete evaluation method configured in this manner, if no lumps are found when the concrete is allowed to flow after the pressure test, the formation of lumps in the pipes can be suppressed.

[0016] Furthermore, the method for evaluating concrete according to the present invention may involve changing at least one of the mix proportions of the concrete, the pressurizing time, and the pressurizing force so that, in the vane shear test, the increase rate of the vane shear test value after pressurization is less than 100% with the test value before pressurization as a reference, and so that no lumps are present.

[0017] In the concrete evaluation method configured in this manner, if the increase rate of the vane shear test value after pressurization is less than 100% and if no lumps are found when the concrete is allowed to flow after the pressurization test, the formation of lumps in the pipes can be further suppressed. Effect of the Invention

[0018] According to the method for evaluating concrete of the present invention, it is possible to evaluate the likelihood of formation of lumps that may lead to clogging of pipes. [Brief description of the drawings]

[0019] [Figure 1] 1 is a flowchart showing the steps of a concrete evaluation method according to one embodiment of the present invention. [Diagram 2](a) and (b) are photographs showing an example of concrete that was discharged with lumps. [Diagram 3] (a) and (b) are photographs showing an example of concrete being discharged without any lumps. [Figure 4] 1 is a graph showing the change in vane shear test value. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] A concrete evaluation method according to one embodiment of the present invention will be described with reference to the drawings. The concrete evaluation method according to this embodiment is a method for evaluating the tendency of lumps to form, which can lead to blockages in concrete used for pumping to high altitudes, where the concrete is subjected to its own weight and other high pressures when pumping is interrupted. This is a test method that can be performed indoors to evaluate the tendency of lumps to form in various concrete mixes, without the need for pumping tests. This is an evaluation method that uses visual inspection to evaluate without quantifying the results.

[0021] It is possible to carry out both a relative evaluation to judge the quality of concrete with different mixes and materials under a fixed pressure and for a fixed time, and an evaluation under a simulated construction environment taking into account the pressure and interruption time expected during actual pumping. The concrete evaluation method is a test carried out at the same time as the concrete test mix is ​​carried out.

[0022] (Concrete pumping plan) FIG. 1 is a flowchart showing the steps of a method for evaluating concrete according to one embodiment of the present invention. A concrete pumping plan is made as shown in Figure 1. The concrete pumping plan is made taking into consideration the pumping height of the piping plan, the actual pumping distance, the type and mix of concrete, and the transportation time from the ready-mix concrete plant.

[0023] The concrete evaluation method is to be performed in either (A) or (B) below. (A) When construction conditions have already been determined: When construction conditions have already been determined, the pumping height has already been set, and a vane shear test (described later) is performed under those pressure conditions to check what will happen to the concrete (presence or absence of lumps, etc.) It is a relative evaluation to judge the quality of different concretes under a certain pressure and time. (B) To find out the pumping height of the selected mixture: When the pumping height is not set and you want to evaluate the maximum height that the selected mixture can be pumped without problems An assessment of the acceptable degree of pressure and interruption time.

[0024] (Outside temperature setting) It is preferable to conduct test mixes and actual tests of concrete at 20°C. However, if the hot season is anticipated, the conditions should be adjusted to match the on-site conditions of an outside temperature of 30°C or higher.

[0025] This test should not be conducted immediately after mixing the concrete, but should be conducted 30 minutes after discharging the concrete from the mixer and leaving it to stand. If it is expected that the time elapsed from mixing will be longer than 30 minutes, such as if the transportation time is longer, the test time may be set according to the site conditions.

[0026] Use a large pressure bleeding test vessel as specified in the Japan Society of Civil Engineers standard JSCE-F-502. Fill the vessel with concrete in accordance with the Japan Society of Civil Engineers standard JSCE-F-502.

[0027] A vane shear test is carried out using the concrete in the vessel before pressurization. The vane shear test method involves inserting cross-shaped vanes into the concrete and manually rotating the shaft to measure the maximum torque value.

[0028] After the vane shear test, the piston is installed and set in the pressurizing device.

[0029] (Setting the pressure time t) The setting of the pressurization time t is considered based on the maximum possible interruption time of the pump pumping work during construction (for changeover, breaks, etc.). For a site with a short intermediate stage time, the pressurization duration should be set to 10 minutes, and for a site with a longer interruption time, it should be set to 15 minutes.

[0030] (Setting of pressure P) The pressure P is determined from the unit volume mass of the concrete mix and the pumping height to the concrete weight at the pumping height. The pressure P is set to the safe side based on the calculation result using the formula below (for example, if the calculation result is 4.1 MPa, set it to 5.0 MPa). To be on the safe side, for example, round up the decimal point. P (MPa) = unit volume weight W (t / m 3 ) x Height H(m) x 10 -3

[0031] The pressurized bleeding vessel is pressurized with the determined pressurization time t and pressure P. According to the Japan Society of Civil Engineers standard JSCE-F-502, the pressure is set at 3.5 N / mm 2 In this test, the pressure time t and pressure P are determined based on the construction conditions, and all the taps for dehydration are closed to prevent dehydration.

[0032] After applying a constant pressure for a specified time, the load is removed. The piston is removed, and the upper piston of the pressure bleeding vessel is removed. The vane shear test is carried out in this state without disturbing the concrete in the vessel. After the vane shear test, the concrete is removed.

[0033] When removing the concrete, let it flow naturally and do not scoop it out with a hand shovel, etc. The bottom of the container is covered with an iron plate (wire mesh protective plate), so the concrete often falls due to its weight. If it has solidified sufficiently and will not fall, simply let it flow naturally (fall).

[0034] Figures 2(a) and (b) are photographs showing an example of concrete discharged with lumps, and Figures 3(a) and (b) are photographs showing an example of concrete discharged without lumps. Observe the condition of the concrete that has been allowed to flow naturally. Do not mix it with a shovel or other tool to make it uniform. Figure 2 shows the condition of lightweight type 1 27-21-15N concrete that has been consolidated after testing. Figure 3 shows the condition of lightweight type 1 27-21-15N concrete with an admixture that provides separation resistance added after testing.

[0035] When observed, there are mixes where the concrete is consolidated and some of it forms clumps even under conditions where water is not discharged from the container, as shown in the photograph in Figure 2. On the other hand, in the mix in Figure 3, where an admixture with high separation resistance has been added, even when consolidated in the same way, no clumps form in the container and it can be observed that the concrete flows down in an almost uniform state.

[0036] If the two conditions are not observed or compared and a slump test is then carried out after uniform kneading, the difference in slump can be evaluated, but if the slump only decreases, it will be evaluated as being pumpable. For this reason, uniform kneading makes it impossible to evaluate the tendency for localized lumps to form and the fact that this is a factor in causing blockages.

[0037] If the concrete is consolidated and hardens significantly without falling off, it can be determined that the concrete is more likely to be consolidated and form lumps than that shown in Figure 2.

[0038] Figure 4 is a graph showing the change in vane shear test value. It shows the rate of increase in vane shear test value after pressurization, with the test value before pressurization as the base value. When lumps form, the increase in the vane shear test value before and after pressure application is 100% or more, and the change is large. Mixtures with an increase rate of 186% to 286% as shown in Figure 4 are mixes where there is concern about blockages due to lumps. A vane test value increase rate of 100% or more is evaluated as a failure.

[0039] Mixtures that are less likely to form lumps will have an increase rate of less than 100%, and there will be little change even when pressure is applied. However, depending on the length of the interruption, the change may progress and the risk of blockage may increase, so caution is required for mixtures with an increase rate of 50% or more and less than 100%. The mixture with an increase rate of 58% shown in Figure 4 has few lumps, but there is a concern that blockage may occur if the mixture is interrupted for a long period of time. An increase rate of 50% or more and less than 100% in the vane test value is acceptable.

[0040] A mix with an increase rate of 41% to 48% is a mix that does not have lumps, but there is concern about blockages if it is interrupted for a long period of time. A vane test value increase rate of less than 50% is rated as good.

[0041] The vane shear test value before pressurization at this time may be the standard blend value before adding pumping aids to prevent clogging, and in the case of blend changes, the values ​​before and after pressurization of the changed blend may be used. A reliable evaluation is possible by evaluating both the presence or absence of lumps and the change in the vane shear test value.

[0042] In addition, since lumps can form not only in the bottom of the container but also in the top and middle, it is necessary to observe the natural flow. Selecting a mix like that shown in Figure 3, which is less likely to form lumps, is important for preventing blockages during high-altitude pumping and for safely pumping the material to create high-quality structures.

[0043] If the increase rate of the vane shear test value is less than 100% and there are no lumps, the process ends. On the other hand, if the increase rate of the vane shear test value is 100% or more or if there are lumps, (A) is the case, change the materials used or the composition and conduct the process again. If the increase rate of the vane shear test value is 100% or more or if there are lumps, (B) is the case, change the pressurization time t or the pressurization force P and conduct the process again (either one of the pressurization time t or the pressurization force P may be changed, or both may be changed). If the increase rate of the vane shear test value is less than 100% and there are no lumps under the changed conditions, the process ends.

[0044] A blend that is less likely to form lumps can be selected by comparing different blends while keeping the determined pressurization time t and pressure P constant. On the other hand, for one blend, it is also possible to observe the extent to which the pressure and interruption time expected in actual pumping can be tolerated by changing the pressurization time t and pressure P.

[0045] The concrete evaluation method configured in this way makes it possible to grasp the concrete mix, pressure time, and pressure force that are less likely to cause lumps in pipes, and evaluate the likelihood of lumps forming that can lead to pipe blockages. This makes it possible to prevent blockages during pumping to high altitudes, and to perform safe pumping to create high-quality structures.

[0046] Furthermore, if the increase rate of the vane shear test value after pressurization is less than 100%, the formation of lumps in the piping can be suppressed.

[0047] In addition, if no lumps are found when the concrete is poured after the pressure test, the formation of lumps in the pipes can be suppressed.

[0048] Furthermore, if the increase rate of the vane shear test value after pressurization is less than 100% and if no lumps are found when the concrete is poured after the pressurization test, the formation of lumps in the pipes can be further suppressed.

[0049] Although one embodiment of the present invention has been described above, the technical scope of the present invention is not limited to the above embodiment, and it is possible to change the combination of components, add various modifications to each component, or delete components without departing from the spirit of the present invention. Some modifications are illustrated below, but these are not all inclusive, and other modifications are also possible. In addition, two or more of these modifications may be appropriately combined.

[0050] The "Sustainable Development Goals (SDGs)" are 17 international goals that were adopted at the United Nations Summit in September 2015. The concrete evaluation method according to this embodiment can contribute to the achievement of one of the 17 SDGs, for example goal 9 "Build resilient infrastructure, promote industry, innovation and infrastructure."

Claims

1. For a given concrete mix, set the outside temperature, pressure time and pressure, Conduct concrete test mixes, A pressurization test is carried out under the conditions of the outside temperature, the pressurization time, and the pressurization force. A method for evaluating concrete in which a vane shear test is conducted and the concrete is allowed to flow from a container to observe whether or not there are lumps.

2. The method for evaluating concrete according to claim 1 , wherein the threshold value in the vane shear test is a value when the increase rate of the vane shear test value after pressurization is less than 100% with respect to the test value before pressurization.

3. The method for evaluating concrete according to claim 1 or 2, wherein the absence of said lumps is used as a criterion.

4. 2. The method for evaluating concrete according to claim 1, wherein at least one of the concrete mix, the pressurizing time, and the pressurizing force is changed so that in the vane shear test, the increase rate of the vane shear test value after pressurization is less than 100% based on the test value before pressurization and no lumps are present.

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