Evaluation methods for high-flow concrete for reinforced concrete structures.

Abstract

To provide an evaluation method for a high fluidity concrete which is assumed to be used for a reinforcement concrete structure, capable of more objectively evaluating use aptitude for an actual structure, using quantitative data.SOLUTION: A first test step is a test step for filling a concrete sample C in a sample putting chamber 14 of a two-chamber type concrete filling test machine 1, then, passing the concrete sample C through a flow obstacle part 13 and making the concrete sample C flow into a sample inflow chamber 15, then measuring a filling height of the concrete sample C in the sample inflow chamber 15 after flowing stop. A second test step is a test step for measuring an inflow mortar value into a cylindrical penetrometer type test machine 2 for each chamber of the sample putting chamber 14 and the sample inflow chamber 15, for calculating an absolute value of a difference between an inflow mortar value in the sample putting chamber 14 and an inflow mortar value in the sample inflow chamber 15, where quality of a high fluidity concrete is evaluated, on the basis of whether the absolute value calculated in the second test step, is a prescribed value or lower.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for evaluating high-fluidity concrete for reinforced concrete structures, and more particularly to a method for quantitatively evaluating the suitability of highly fluid concrete, such as "compaction-free concrete," which does not require a compaction step after pouring, for use in reinforced concrete structures. [Background technology]

[0002] In recent years, there has been progress in the development of "compaction-free concrete," which combines high levels of fluidity and resistance to segregation, allowing the concrete to self-fill without compaction after being poured into formwork (see Patent Document 1). When using high-fluidity concrete such as this "compaction-free concrete" in reinforced concrete structures (RC structures) with complex rebar arrangements, the high-fluidity concrete is required to have a high level of void permeability in addition to fluidity and resistance to segregation.

[0003] As a test device for evaluating the fluidity and material separation resistance of high-flow concrete as well as its gap passability, a test device (referred to in this specification as a "two-chamber concrete filling tester") has been proposed that consists of a sample loading section, a sample lifting section, and a flow obstacle installed in the flow path connecting these sections below (see Patent Document 2).

[0004] As methods for understanding the resistance of concrete to material segregation after passing through a flow obstacle using the above-mentioned test device ("two-chamber concrete filling tester"), in addition to a method of visually observing whether or not material segregation occurs after passing through the flow obstacle, other methods have been proposed, such as a method of washing out the coarse aggregate from samples taken from each of the above-mentioned parts, i.e., from each of the concretes before and after passing through the flow obstacle, and comparing the aggregate amount, or a method of measuring the density of each of the above-mentioned concretes using an RI device and comparing the density before and after passing through the flow obstacle (see Patent Document 3).

[0005] Of the above methods for understanding the segregation resistance of concrete after passing through a flow obstacle, the former, visual observation, is inexpensive and easy to implement, but is prone to individual differences depending on the evaluator, and the objectivity of the evaluation criteria is not fully guaranteed, which can be a problem.On the other hand, the latter two methods make it possible to obtain quantitative data that can be used as an objective evaluation standard, but the method comparing aggregate volume requires time-consuming identification and measurement of aggregate volume, and the method comparing density requires expensive measuring equipment, so they have not yet been widely adopted at construction sites.

[0006] On the other hand, a test method known as the "cylinder penetration test method" has been proposed as an example of a relatively simple technique for evaluating the material separation resistance of concrete (see Patent Document 4 and Non-Patent Document 1). This test method uses a test device (referred to as a "cylindrical penetrometer-type tester" in this specification) consisting of a hollow cylindrical pipe with a closed bottom and dimensions of approximately φ150 × 30 cm, with an opening for mortar flow arranged on the side, as shown in Figure 3. The test device is inserted into a concrete sample to be measured, and the material separation resistance of the concrete is evaluated based on the amount of mortar that flows through the opening for mortar flow within a specified time. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2019-99435 [Patent Document 2] Japanese Patent Application Publication No. 10-038787 [Patent Document 3] Japanese Patent Application Laid-Open No. 2000-121529 [Patent Document 4] Japanese Patent Application Publication No. 10-111287 [Non-patent literature]

[0008] [Non-Patent Document 1] "Guidelines for the Use of High-Fluidity Concrete: Aiming to Improve Building Quality and Workability by Promoting the Use of Concrete That Combines High Fluidity and Resistance to Material Separation" (September 2020, Study Group on the Promotion of High-Fluidity Concrete in the Building Industry, Materials and Construction Specialist Subcommittee, Building Technology Development Committee, Building Headquarters, Japan Federation of Construction Contractors) Summary of the Invention [Problem to be solved by the invention]

[0009] For example, by using a "cylindrical penetrometer type testing machine" to evaluate the material separation resistance of concrete after passing through a flow obstacle in the above-mentioned "two-chamber type concrete filling testing machine," it is thought that it will be possible to evaluate the material separation resistance of concrete after passing through a flow obstacle in a relatively simple manner.

[0010] However, even if the segregation resistance of concrete is evaluated using the above method, which simply combines a "two-chamber concrete filling tester" and a "cylindrical penetrometer tester," the evaluation results do not reflect the resistance to segregation that may occur before the concrete passes through the gaps between the rebars when used in actual RC structures, such as segregation caused by movement due to pressure transmitted from the pouring opening to the cover.Further improvements to the evaluation method were needed to obtain data for more objectively evaluating the suitability of highly fluid concrete for use in actual RC structures.

[0011] The present invention aims to provide an "evaluation method for high-flow concrete for reinforced concrete structures" that can objectively evaluate, based on quantitative data, the suitability of high-flow concrete that is expected to be used in reinforced concrete structures (RC structures) for use in actual RC structures, and that can reduce the effort and cost associated with evaluation tests compared to conventional methods. [Means for solving the problem]

[0012] The inventors have found that the above-mentioned problems can be solved by using a method for evaluating high-flow concrete that cleverly combines a "two-chamber concrete filling tester" and a "cylindrical penetrometer tester" and that evaluates the concrete according to unique evaluation criteria, and have thus completed the present invention. Specifically, the present invention provides the following methods, etc.

[0013] (1) A method for evaluating high-flow concrete for reinforced concrete structures, comprising a first test step performed using the following two-chamber concrete filling tester and a second test step performed using the following cylindrical penetrometer type tester, wherein the first test step is a test step of filling a concrete sample into a sample charging chamber of the two-chamber concrete filling tester, leaving it to stand for a predetermined time, and then passing the concrete sample through a flow obstacle portion into a sample inlet chamber, and measuring the filling height of the concrete sample in the sample inlet chamber after the flow has stopped, and the second test step is a test step of measuring the filling height of the concrete sample in the sample inlet chamber after the first test step has been performed. A method for evaluating high-fluidity concrete, comprising a test process in which the cylindrical penetrometer testing machine is inserted into and withdrawn from the concrete sample in the entrance and sample inflow chambers over a predetermined time period, measuring the mortar value flowing into the cylindrical penetrometer testing machine for each chamber, and calculating the absolute value of the difference between the flowing mortar value in the sample introduction chamber and the flowing mortar value in the sample inflow chamber; wherein, in the first test process, for concrete samples whose filling height is equal to or greater than a predetermined value, the quality of the high-fluidity concrete is evaluated based on whether the absolute value calculated in the second test process is equal to or less than a predetermined value. (Two-chamber concrete filling tester) A concrete testing machine comprising: a cylindrical sample charging chamber into which a concrete sample is charged from the top side and discharged from the lower side; a cylindrical sample inlet chamber into which the concrete sample discharged from the sample charging chamber flows from the lower side; and a connecting structure connecting the two chambers at the lower side, wherein the connecting structure is an openable and closable flow path that connects the two chambers so that the concrete sample discharged from the lower side of the sample charging chamber can flow into the sample inlet chamber from the lower side of the sample inlet chamber; and a flow obstruction section formed inside the connecting structure, comprising rod-shaped obstacles installed at predetermined intervals. (Cylindrical penetrometer type testing machine) A cylindrical concrete testing machine with multiple mortar inlet holes formed at approximately equal intervals on the side.

[0014] The evaluation method for high-flow concrete (1) can objectively grasp the change in material separation resistance before and after concrete passes through the gaps between rebars in reinforced concrete structures (RC structures). By using this change as the evaluation standard, the suitability of high-flow concrete for use in actual RC structures can be objectively evaluated based on quantitative data. Furthermore, the effort and cost required for evaluation testing can be reduced compared to conventional methods.

[0015] (2) A method for evaluating high-flow concrete according to (1), which evaluates the quality of concrete to be poured into a reinforced concrete structure at the pouring site of the reinforced concrete structure.

[0016] According to the evaluation method for high-flow concrete (2), the suitability of high-flow concrete that is expected to be used in reinforced concrete structures (RC structures) for use in RC structures can be evaluated with higher accuracy at the concrete pouring site just before pouring using an easy-to-implement evaluation method. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide an "evaluation method for high-flow concrete for reinforced concrete structures," which is an evaluation method that can objectively evaluate, based on quantitative data, the suitability of high-flow concrete that is expected to be used in reinforced concrete structures (RC structures) for use in actual RC structures, and which can reduce the effort and cost burden associated with evaluation tests compared to conventional methods. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a diagram schematically illustrating an embodiment of the "method for evaluating high-flow concrete for reinforced concrete structures" of the present invention, which is carried out using a "two-chamber concrete filling tester" and a "cylindrical penetrometer tester." [Figure 2] FIG. 2 is a partially enlarged view of the "two-chamber concrete filling test machine" shown in FIG. 1, and is a drawing for explaining the structure around the flow-impeded portion. [Figure 3] FIG. 2 is a side view of the "cylindrical penetrometer testing machine" shown in FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

[0020] <Evaluation method for high-fluidity concrete for reinforced concrete structures> The "method for evaluating high-flow concrete for reinforced concrete structures" of the present invention comprises a first testing step performed using a "two-chamber concrete filling tester" and a second testing step performed using a "cylindrical penetrometer testing machine." For concrete samples whose filling height is confirmed to be equal to or greater than a predetermined value in the first testing step using the "two-chamber concrete filling tester," the second testing step using the "cylindrical penetrometer testing machine" is performed, and the change (absolute value) in the material separation resistance of the concrete before and after passing through the gaps between the rebars of a reinforced concrete structure (RC structure) is calculated. In the second testing step, the quality of the high-flow concrete is further evaluated based on whether the calculated absolute value is equal to or less than a predetermined value.

[0021] [First test process] The first test process is a process in which the concrete sample C to be evaluated is filled into the sample feeding chamber 14 of the two-chamber concrete filling tester 1 shown in Figure 1, left to stand for a predetermined time, and then passed through the flow obstruction section 13 (see Figure 2) to flow into the sample inlet chamber 15, and the "filling height" of the concrete sample C in the sample inlet chamber 15 is measured after the flow stops.

[0022] (Two-chamber concrete filling tester) The "two-chamber concrete filling test machine" used to carry out the first test step can be, for example, a U-shaped filling test machine such as the two-chamber concrete filling test machine 1 shown in FIG.

[0023] As shown in Figure 1, this two-chamber concrete filling test machine 1 (U-shaped filling test machine) is a testing device that comprises a cylindrical sample charging chamber 14 into which a concrete sample C can be charged from the top side and allowed to flow out from the lower side, a cylindrical sample inlet chamber 15 into which the concrete sample C that has flowed out of the sample charging chamber 14 can flow in from the lower side, and a connecting structure that connects the sample charging chamber 14 and the sample inlet chamber 15 at their lower sides, forming an inlet and outlet flow path for the concrete sample C.

[0024] In the two-chamber concrete filling tester 1 (U-shaped filling tester), the connecting structure is a flow path that can be opened or closed to stop or start the flow of concrete as needed. In addition, a flow obstacle section 13 is formed in the middle of this flow path, consisting of rod-shaped obstacles installed at a predetermined interval w below the partition plate 12 (see Figure 2). In this two-chamber concrete filling tester 1, the concrete sample C filled in the sample charging chamber 14 passes through the flow obstacle section 13 and flows into the sample inlet chamber 15 when the flow path in the connecting structure is opened.

[0025] The spacing w between the obstacles in the flow obstruction section 13 can be optimized and adjusted as appropriate depending on the arrangement of rebars, etc., in the structure in which the concrete to be tested is expected to be used. As an example, when a typical RC structure is the target of use, the spacing w can be set arbitrarily within the range of approximately 60 mm to 200 mm.

[0026] The "two-chamber concrete filling tester" is a well-known device as a stand-alone test device, and various filling testers that have been conventionally used as stand-alone test devices can be used. For example, the "U-shaped test device" disclosed in Figure 1 of Patent Document 2 or the "box-shaped test device" disclosed in Figure 3 of Patent Document 4 can be used as the "two-chamber concrete filling tester" for carrying out the "first test step" in the "method for evaluating high-flow concrete" of the present invention.

[0027] (Test procedure) An example of the specific procedure of the first test step is as shown in steps 1) to 5) in Table 1 below.

[0028] [Table 1]

[0029] [Second test process] The second test step is a step performed after the first test step, in which a cylindrical penetrometer-type tester is inserted into the sample charging chamber 14 and the sample inflow chamber 15 of the two-chamber concrete filling tester 1 (U-shaped filling tester) to measure the inflow mortar value in each chamber and calculate the absolute value of the difference between the inflow mortar values ​​in each sample charging chamber in order to determine the material separation resistance of each of the concrete samples in the two-chamber concrete filling tester. In the first test step using the two-chamber concrete filling tester, a concrete sample whose filling height is confirmed to be equal to or greater than a predetermined value, i.e., a concrete sample confirmed to have minimum fluidity and void permeability, is the subject of the test in the second test step using the cylindrical penetrometer-type tester.

[0030] (Cylindrical penetrometer type testing machine) The "cylindrical penetrometer type testing machine" used to perform the second testing process is a concrete testing machine, such as the cylindrical penetrometer type testing machine 2 shown in Figure 3, in which multiple mortar inlet holes 22 are formed and distributed at approximately equal intervals on the side of a cylindrical testing machine body 21.

[0031] The "cylindrical penetrometer type testing machine" is a well-known device as a standalone testing device, and various filling test machines that have been conventionally used as standalone devices can be used. For example, the cylindrical penetrometer type testing machines disclosed in the above Patent Document 4 and Non-Patent Document 1 can be used as the "cylindrical penetrometer type testing machine, etc." for carrying out the "method for evaluating high-flow concrete" of the present invention.

[0032] An example of the specific operation procedure of the second test step is as shown in steps 6) to 8) of Table 1 above.

[0033] [Evaluation of high-flow concrete] In the "method for evaluating high-flow concrete for reinforced concrete structures" of the present invention, which consists of the above two steps, in the "first test step," concrete samples whose filling height is equal to or greater than a predetermined value are deemed to be concrete suitable for pouring into reinforced concrete structures. Then, for the concrete deemed to be the subject of evaluation, the absolute value of the difference between the two inflow mortar values ​​calculated in the "second test step" is used as an objective evaluation criterion, and the quality of the high-flow concrete is evaluated based on whether or not the absolute value is equal to or less than a predetermined value.

[0034] In the "first testing step," the standard value of the "filling height (the height from the chamber bottom to the top surface of the poured concrete sample in the sample inlet chamber)" for determining that the concrete to be tested is sufficient for pouring into reinforced concrete structures can be set arbitrarily depending on the expected construction conditions, etc. As an example, when the distance w between obstacles in the flow obstruction section 13 of the two-chamber concrete filling tester 1 (U-shaped filling tester) is 75 mm, the standard value can be set to 300 mm or more.

[0035] Furthermore, with regard to the absolute value of the difference between the inflow mortar value in the sample charging chamber and the inflow mortar value in the sample inflow chamber calculated in the "second testing step," the above-mentioned predetermined value, i.e., the specific numerical value used as the evaluation standard, can be set arbitrarily depending on the expected construction conditions, etc. As an example, this predetermined value can be 10 mm. In this case, concrete for which the "absolute value of the difference from the inflow mortar value" calculated in the "second testing step" is 10 mm or less is deemed to be "good" for use in reinforced concrete structures, thereby enabling an objective evaluation of high-flow concrete for reinforced concrete structures.

[0036] Furthermore, the "method for evaluating high-fluidity concrete" of the present invention can evaluate the suitability of high-fluidity concrete for use in RC structures immediately before pouring, at the concrete pouring site, using the easy-to-implement evaluation method described above. [Example]

[0037] As described below, the "method for evaluating high-flow concrete for reinforced concrete structures" of the present invention, which has been explained in detail above, was carried out according to steps 1) to 8) shown in "Table 1" above. The concrete samples to be evaluated were two types of fresh concrete (samples 1 and 2) prepared using the materials shown in "Table 2" below and with the mix ratios shown in "Table 3" below. A U-shaped filling tester was used as the two-chamber concrete filling tester in the first test step, and the distance between the obstacles in the flow-impeding section was set to 75 mm.

[0038] Furthermore, as described above, after carrying out the "method for evaluating high-flow concrete for reinforced concrete structures" of the present invention, in order to further verify the validity of the evaluation results, a "full-scale pouring experiment" was carried out for each sample for which the evaluation results were confirmed.

[0039] [Materials used] [Table 2]

[0040] [Mixing ratio] [Table 3]

[0041] [Evaluation results] The test results and evaluation results for the above samples 1 to 3 according to the "Method for evaluating high flowability concrete for reinforced concrete structures" are shown in Table 4 below.

[0042] [Table 4]

[0043] [Driving experiment] A full-scale pouring experiment was carried out, simulating a portion of the wall of a typical RC structure. The dimensions of the test specimen were 0.8m in width, 3m in length, and 0.9m in height. The main reinforcement bars, D25 deformed steel bars, were placed at 100mm intervals, and D16 distribution bars at 300mm intervals, so that the minimum gap between the rebars was 75mm. Fresh concrete for each sample was poured using a concrete pump truck at an average pouring speed of 30m / s. 3 The test specimen was fixed at the center (1.5 m from the edge) and the concrete was poured in at a depth of 0.9 m per layer. No compaction was performed.

[0044] For each test piece, core specimens were taken from the same three locations on each test piece, near the center, which is also the pouring position, and near both ends (centered at 50 mm from the bottom and 1500 mm from each side edge), and the static elastic modulus (kN / mm 2 ) was measured. The coarse aggregate area ratio was measured by sketching aggregates of 5 mm or more on a transparent sheet, painting them black, and binarizing the sketch. The static elastic modulus was measured using a method in accordance with JISA1149:2017. The results are shown in Table 5.

[0045] [Table 5]

[0046] As shown in Table 4, there is almost no difference between Sample 1 and Sample 2 in the "filling height" obtained in the first test step and the "inflow mortar value in the sample inflow chamber" obtained in the second test step. However, by focusing on the "absolute value of the difference between the two inflow mortar values," which is a unique evaluation criterion in the "method for evaluating high-flow concrete for reinforced concrete structures" of the present invention, Sample 1 can be evaluated higher than Sample 2 based on quantitative data. Furthermore, Table 5 shows that, based on this evaluation criterion, Sample 1 (Evaluation A), which received a relatively high evaluation, has significantly less variation in quality due to distance from the pouring position in the hardened reinforced concrete after pouring than Sample 2 (Evaluation B), which received a relatively low evaluation.

[0047] On the other hand, as shown in Table 4, the "inflow mortar value in the sample inflow chamber" obtained in the second test step for Sample 3 was less favorable than that for Sample 2. However, by focusing on the "absolute value of the difference between the two inflow mortar values," which is a unique evaluation criterion in the "evaluation method for high-flow concrete for reinforced concrete structures" of the present invention, Sample 3 can be evaluated higher than Sample 2 based on quantitative data. Table 5 shows that, based on this evaluation criterion, Sample 3 (evaluation A), which received a relatively high evaluation, had significantly less variation in quality due to distance from the pouring position in the hardened reinforced concrete after pouring than Sample 2 (evaluation B), which received a relatively low evaluation.

[0048] In addition, for Sample 4, the "filling height" obtained in the first test step was an unfavorable value compared to the other samples. This also resulted in a negative value for the difference ((A) - (B)) in the inflow mortar values ​​(mm). However, even in this case, by focusing on the "absolute value of the difference between the two inflow mortar values," a unique evaluation criterion in the "evaluation method for high-flow concrete for reinforced concrete structures" of the present invention, Sample 4, which was difficult to objectively evaluate solely based on the "filling height" and "inflow mortar value in the sample inflow chamber," was able to be objectively evaluated (Evaluation B) based on quantitative data, being inferior to Samples 1 and 3 (Evaluation A) but comparable to Sample 2. As shown in Table 5, Sample 4 (Evaluation B) actually exhibited greater variation in the quality of the reinforced concrete hardened body after pouring than Samples 1 and 3 (Evaluation A). However, compared to Sample 2, which received the same evaluation (Evaluation B), the variation was kept at a level equal to or greater than that of Sample 2.

[0049] From the above, it has been confirmed that the "method for evaluating high-flow concrete" of the present invention makes it possible to objectively evaluate the suitability of high-flow concrete that is expected to be used in reinforced concrete structures (RC structures) for use in actual RC structures based on quantitative data, including resistance to material separation that may occur at the scale of actual construction work, such as material separation caused by movement due to pressure transmitted from the pouring port to the cover, before the concrete passes through the gaps between the reinforcing bars. [Explanation of symbols]

[0050] 1. Two-chamber concrete filling test machine 11 Testing machine body 12 Partition 13 Flow Obstruction Section 14 Sample loading chamber 15 Sample inlet chamber 2. Cylindrical penetrometer type testing machine 21 Testing machine body 22 Mortar inlet C. Concrete sample

Claims

1. A method for evaluating high-fluidity concrete, A first test step performed using the following two-chamber concrete filling tester; A second test step is performed using the following cylindrical penetrometer type testing machine, The first test step is a test step of filling a concrete sample into a sample charging chamber of the two-chamber concrete filling tester, leaving the sample standing for a predetermined time, and then passing the sample through a flow obstruction section to flow into a sample inflow chamber, and measuring the filling height of the concrete sample in the sample inflow chamber after the flow has stopped; The second test step is a test step in which the cylindrical penetrometer type testing machine is inserted into the concrete sample in the sample charging chamber and the sample inflow chamber over a predetermined time period after the first test step is performed, and then pulled out, and the inflow mortar value into the cylindrical penetrometer type testing machine is measured for each chamber, and the absolute value of the difference between the inflow mortar value in the sample charging chamber and the inflow mortar value in the sample inflow chamber is calculated, In the first test step, for concrete samples whose filling height is equal to or greater than a predetermined value, the quality of the high-flow concrete is evaluated based on whether the absolute value calculated in the second test step is equal to or less than a predetermined value. Evaluation method for high flow concrete. Two-chamber concrete filling testing machine: A concrete testing machine comprising a cylindrical sample charging chamber into which a concrete sample is charged from the top side and flows out from the lower side, a cylindrical sample inlet chamber into which the concrete sample flowing out of the sample charging chamber flows in from the lower side, and a connecting structure that connects both chambers at the bottom, wherein the connecting structure is an openable and closable flow path that connects both chambers so that the concrete sample flowing out from the lower side of the sample charging chamber can flow into the sample inlet chamber from the lower side of the sample inlet chamber, and a flow obstruction section consisting of rod-shaped obstacles installed at predetermined intervals is formed inside the connecting structure. Cylindrical penetrometer testing machine: A cylindrical concrete testing machine with multiple mortar inlet holes formed at approximately equal intervals on the side.

2. Evaluating the quality of concrete to be poured into a reinforced concrete structure at the pouring site of the reinforced concrete structure; A method for evaluating the high-fluidity concrete according to claim 1.

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