JPH11108815A - Estimation method for strength of concrete - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an estimation method, for the compressive strength of concrete, which is practical, whose reliability is high, whose operation is simplest, which does not take time and which uses an anchor pull-out test. SOLUTION: An undercut 3 whose bottom is expanded to be a taper shape is formed on the hole bottom of a lower hole 2 which is bored and formed in concrete 1 to be tested. An anchor 6 which is composed in such a way that an anchor bolt 7 comprising a taper head part 9 at its tip part is fitted to a sleeve 8 comprising a plurality of expanding and opening tongue pieces 10 at its tip part is inserted into the lower hole 2 is formed. The sleeve 8 is driven in. Thereby, the respective expanding and opening tongue pieces 10 are expanded and opened by the taper head part 9. At the same time, they are made to intervene into a gap between the taper head part 9 and the undercut 3. Then, the anchor 6 is pulled out without being given a rotation by a tension testing apparatus 13. A pull-out-proof stress is measured. The compressive strength of the concrete 1 to be tested is computed on the basis of the pull-out proof stress by using a pull-out proof stress-compressive strength relational expression which is found in advance by an experiment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for estimating concrete strength. Since the Great Hanshin-Awaji Earthquake, there has been a demand for a method for easily estimating the compressive strength of concrete in reinforced concrete structures, mainly for repair and reinforcement work. Structures that require such a guess are usually used in many cases, and it is actually difficult to collect cores.
Therefore, a non-destructive test method or a local destructive test method is indispensable. The present invention relates to a method for estimating concrete strength by an anchor pull-out test belonging to a local fracture test among these test methods.

[0002]

2. Description of the Related Art There are many conventional non-destructive testing methods such as a rebound hardness method and an ultrasonic wave propagation velocity method. In each case, a quantity whose compressive strength and physical relationship are ambiguous is measured. Since the estimation is performed using the correlation, there is a problem in accuracy. Also, in the anchor pull-out test of the local destruction test method, it is known that the accuracy of the presetting method of embedding an anchor in advance at the time of concrete is high is high. Since there are many that have not been installed, it is a key point in the post-setting method for post-installing anchor embedding how to secure the same accuracy as the preset method. Various post-set local destructive test methods have been tried so far, but at present, a highly accurate test method has not yet been established.

[0003]

The method of estimating the compressive strength by the post-set type anchor pull-out test has been reported in Japan, for example, by Tanikawa and Kosaka, etc. (The 3rd Annual Conference on Concrete Engineering) Lecture Paper Collection
1981 "[35] Composite non-destructive test method for strength distribution of concrete in the height direction of driving"), compiled by the Japan Concrete Institute, "Non-destructive test method for concrete research committee report", Both are based on the fact that there is a correlation between the strength at the time of tensile failure by the anchor (pull-out strength) and the compressive strength of concrete. However, these have the following disadvantages. The extent of the floor expansion by the anchor is weak, the wedge slips, and the cone breaking properties vary. The construction error of the embedding depth greatly affects the pull-out strength (skill in setting work). When a torque test device (DPG100, manufactured by Hilti) by Morita et al. Is used as a pull-out test device, the occurrence of slippage is promoted by rotation. In general, the estimation accuracy of the compression strength is low and the correlation coefficient is small (in the above report, the estimation accuracy is about ± 25%, and the correlation coefficient is about 0.841). Therefore, it is generally recognized that the anchor extraction method is not practical. Also, in the Japan Highway Public Corporation Standard “Test method for compressive strength of concrete by pull-out method (JHS309-1992)”, when estimating the compressive strength from pull-out strength, it is stated that the embedding depth is corrected due to the construction error. Have been. The present invention has been made in consideration of the above, and has a practical, reliable, and
An object of the present invention is to provide a method for estimating the compressive strength of concrete by an anchor pull-out test, which is the simplest operation and does not require time.

[0004]

Means for Solving the Problems In order to achieve this object,
According to the present invention, a pilot hole 2 for anchor embedding is formed in a test concrete 1 and an undercut 3 is formed in the bottom of the concrete hole 1 in a tapered shape at the bottom of the hole. An anchor bolt 7 having a tapered head 9 at a distal end thereof and a sleeve 8 fitted into an intermediate portion of the anchor bolt so as to be able to be driven into the anchor bolt 7. An anchor 6 having a plurality of expanding tongues 10 which are expanded following the tapered head 9 is provided. Then, the anchor is deeply inserted into the pilot hole 2 to remove the sleeve 8. After the tapered head 9 is positioned in the undercut 3 and the sleeve 8 is driven into the lower hole 2, each of the expanding tongue pieces 10 at the distal end is inserted into the tapered head 2. At the same time as being expanded by the part 9 The anchor 6 is immovably embedded in the pilot hole 2 by intervening in the gap between the tapered head 9 and the undercut 3.
Is pulled out by the tensile tester 13 without rotation, the pull-out strength is measured, and the compressive strength of the test concrete 1 is calculated from the pull-out strength obtained by the pull-out strength-compressive strength relational expression obtained from the experiment in advance. It is characterized by the following.

According to a second aspect of the present invention, there is provided a method for estimating concrete strength according to the first aspect, wherein the following regression equation previously extracted by an experiment is used as the drawing strength-compression strength relational equation.

[0006]

(Equation 1)

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an anchor pull-out test method according to the concrete strength estimating method of the present invention. In the drawing, reference numeral 1 denotes a specimen concrete, and 2 denotes a specimen drilled in the specimen concrete. A pilot hole, 3 is an undercut formed at the bottom of the pilot hole, 6 is an anchor set in the pilot hole, and 13 is an intervening member between the anchor and the specimen concrete to pull out the anchor. This is a tensile test apparatus with a peak hold. This test method is shown in FIG.
To (4).
This will be described in order.

(1) A pilot hole 2 is drilled in the test concrete 1 and an undercut 3 is formed at the bottom of the hole. For this drilling, an FZUB (trade name) drill bit 4 manufactured by Fischer, Germany may be used. The drill bit 4 has a stopper 5 for regulating the depth of the pilot hole in the middle part. In drilling, first, the pilot hole 2 is drilled vertically until the stopper 5 reaches the concrete surface, and then The drill bit 4 is tilted and turned once or twice while pressing the stopper 5 against the concrete surface to form the undercut 3 in which the hole bottom is tapered. The expansion width due to the widening of the bottom is +4 to 6 mm with respect to the anchor diameter. By using the drill bit 4, the drilling depth and the hole diameter can be controlled. In particular, the error in the depth direction is ± 1 mm.
It is possible to eliminate the necessity of correcting for the construction error when estimating the compressive strength (Table 3,
(See FIGS. 5 and 6 and the following description of these.) Pilot hole 2
The drilling diameter and drilling depth (embedding depth) of each anchor 6
(See (2)). The following Table 1 shows an example of the relationship between the drilling diameter and the embedding depth depending on the type of anchor as a reference value.

[0009]

[Table 1] In general buildings, "FZA 14 × 4
0 M10 "can be used as standard, but a suitable anchor type is selected depending on the size and type of the structural member.

(2) As the anchor 6, a ZYKON (trademark) anchor manufactured by Fischer, Germany shown in Table 1 above is used, and the anchor is deeply inserted into the prepared bore 2. This Z
The YKON anchor 6 is composed of an anchor bolt 7 and a cylindrical sleeve 8 fitted to the outer periphery of an intermediate portion of the anchor bolt so as to be able to be driven in the distal direction, and the outer diameter of the anchor shown in Table 1 above that is adapted to the prepared hole 2. (Outer diameter of the sleeve 8) and the embedding depth. The anchor bolt 7 has a tapered head 9 at the distal end, and the sleeve 8 has a tapered head at the distal end.
A plurality of expanding tongue pieces 10 formed by an appropriate number of interruptions 11 in the cylindrical direction and circumferential folding grooves 12 and expanded along the tapered head 9 of the anchor bolt 7 when driven in the distal direction. Have.

(3) The sleeve 8 of the ZYKON anchor 6 inserted into the pilot hole 2 is sufficiently driven until the end is flush with the concrete surface, and each of the expanding tongue pieces at the tip of the sleeve is inserted.
10 is expanded by the tapered head 9 of the anchor bolt 7, and is interposed in the gap between the tapered head 9 and the undercut 3 of the pilot hole 2. Note that ZYK
The use of the ON anchor 6 can reduce wedge slippage.

(4) The ZYKON anchor 6 thus embedded in the test concrete 1 is pulled out without rotation by a tensile test device 13 comprising a hydraulic jack with a peak hold or the like, and the maximum load at this time, that is, the pulling strength is measured. (FIG. 1). The two-dot chain line in the figure indicates a broken part. Then, from the relational expression (regression equation) between the pull-out strength and the compressive strength determined in advance, the test concrete 1
Is calculated. Note that an initial force may be applied with a torque wrench or the like to suppress slippage (this step can be omitted). As the tensile test device 13, a device sold by Fuji Bussan Co., Ltd. (manufacturer: Yamamoto Hoikiki Co., Ltd.) is effective. This type of hydraulic jack with a peak hold can eliminate the occurrence of slippage due to rotation and the promotion of slippage during pull-out.

The relational expression (regression equation) between the pull-out strength and the compressive strength in the above-mentioned concrete specimen was obtained from the results of experiments shown in Table 2 below. Table 2 shows the following contents.
W / C indicates the water cement ratio (%) of the test concrete. Each of the two wall specimens at seven levels was tested. The core strength was determined by extracting three cores from each of the wall specimens, measuring the compressive strength of each core, and indicating the average value. The zykon method is based on the above (1) to (5) according to the present invention.
This is the same as the anchor pull-out test method performed in the procedure of (4), and six anchor pull-out tests were performed for each wall specimen. Anchor is FZA14 × 40M1 mentioned above.
0 was used. The pilot hole for inserting this anchor is a FZUB14 × 40 drill bit for the anchor FZA14 × 40M10 (the distance from the stopper to the cutting edge is 47.9).
0 mm). Table 3 shows the drill hole depth in this case. The average value of each level in Table 3 is shown in the graph of FIG. The graph of FIG. 6 shows the actually measured power of the drill hole depth measured with a vernier caliper. That is, the error of one drill hole that is significant to the drill hole depth error in the range of water cement ratio of 40 to 75% is ± 9.
It is ± 0.94 mm (1.645σ) or less at 0% probability. Therefore, there is no need for correction as in the Japan Highway Public Corporation Standard (JHS309-1992). Konishi E200 refers to a conventional pin post-set pin pull-out test using synthetic resin filling, which was performed as a comparative test with the anchor pull-out test according to the present invention. However, Konishi E200 itself is the name of a synthetic resin-based adhesive filled after pin embedding, but this was used for convenience. In this case, five pin pull-out tests were performed for each wall specimen. For the pin set of this pin pull-out test, the hole diameter and depth of the prepared hole were made equivalent to the zykon method, a pin having a force plate was inserted into the prepared hole, and Konishi E200 was filled and fixed. did. For the pulling, a tensile testing device including a hydraulic jack with a peak hold and the like, which was released by Fuji Bussan Co., Ltd. (manufacturer: Yamamoto Houkiki Co., Ltd.) was used.

[0014]

[Table 2]

[0015]

[Table 3]

When the average values in Table 2 are represented in a graph, a regression line shown in FIG. 3 is obtained. In FIG. 3, the thick line is a regression line of the average value of the results of the anchor pull-out test (zykon method) according to the present invention, and the regression equation obtained from this line is

[0017]

(Equation 2) Becomes The dotted line is the regression line of the average value of the results of the pin post set pin pull-out test (Konishi E200). The regression equation obtained from this line is

[0018]

(Equation 3) Becomes By the way, it is already known that a regression line by the conventional Morita's preset method becomes like a thin line in FIG. The thin line regression line by the Morita's preset method and the anchor pull-out test (zyk
On method), the regression line of the dotted line is significantly different from the regression line of the thin line when compared with the regression line of the bold line by the on-line method) and the regression line of the dotted line by the pin post-set type pin pullout test (Konishi E200). On the other hand, it can be seen that the thick regression line is similar to the thin regression line. That is, the anchor pull-out test (zykon method) according to the present invention.
The regression line of approximation is similar to the regression line of the preset method of Morita formula, and its accuracy can be greatly improved to ± 20% and the correlation coefficient is 0.9547. It is much better. Therefore, thereafter, if only the pull-out strength is measured by the anchor pull-out test, a highly accurate compressive strength can be immediately calculated from the measurement result by the regression equation of Expression 2, and it can be sufficiently put to practical use.

FIG. 4 is a graph showing the difference in the correlation depending on the number of data according to Table 2, and Table 4 shown in FIG.
3 shows a regression equation obtained from each regression line and a correlation coefficient thereof. It can be seen that none of them is significantly different from the average value plot of FIG.

[0020]

[Table 4]

The accuracy, cost, and required days were compared between the anchor pullout test according to the present invention and the conventional core compression test, and the results shown in Table 5 below were obtained.

[0022]

[Table 5] The experimental results show that the anchor pull-out test according to the present invention is significantly superior to the conventional core compression test.

[0023]

According to the present invention, the following effects can be obtained. A. Accuracy can be significantly improved. FZU with stopper made by German company Fischer for drilling pilot holes
The use of B drill bits allows accurate and easy drilling of hole diameters, hole depths, and the size of the undercut of the expanded bottom with little error and variation, eliminating the need to correct for construction errors when estimating compressive strength. In addition, by using ZYKON anchor manufactured by Fischer, Germany as the anchor, it can be embedded properly in the prepared hole, can be fixed without slipping, and the variation of the cone breaking property can be reduced. Can be reduced, and
By using a tensile testing device including a hydraulic jack with a peak hold and the like released by Fuji Bussan Co., Ltd., the embedded anchor can be pulled out without slip. Therefore, even if the embedding of the anchor is post-construction,
The measured value of the anchor pull-out test has a good accuracy of ± 20% and a correlation coefficient of 0.9547, and can be approximated to the Morita-type preset method with high measurement accuracy. Then, an appropriate regression equation can be obtained from the experiment, and thereafter, a highly accurate and highly reliable compressive strength can be immediately calculated and estimated from the measured value of the anchor pull-out test. Practical application with a problem can be realized without hindrance. B. The number of working days can be reduced. The work is simplest and does not take much time. Therefore, as is clear from Table 5, the number of working days can be remarkably reduced as compared with the core compression test. C. Cost can be reduced. Overall, the cost can be significantly reduced and, as evident in Table 5, can be significantly reduced compared to the core compression test.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a test method according to a concrete strength estimation method of the present invention.

FIG. 2 is an explanatory sectional view showing an operation procedure of the test method.

FIG. 3 is a graph showing an average value plot in Table 2.

FIG. 4 is a graph showing a difference in correlation depending on the number of data according to Table 2.

5 is a graph showing an average value plot of each level in Table 3. FIG.

FIG. 6 is a graph showing the actually measured power for the drill hole depth.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Test concrete 2 ... Prepared hole 3 ... Undercut 4 ... Drill bit 5 ... Stopper 6 ... Anchor 7 ... Anchor bolt 8 ... Sleeve 9 ... Taper head 10 ... Expanding tongue piece 11 ... Interruption 12 ... Fold groove 13 ... Tensile test equipment

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masanobu Tokuhisa 1-5-1, Otsuka, Inzai City, Chiba Prefecture Inside the Research Institute of Takenaka Corporation (72) Inventor Masaaki Kojima 4-chome, Tenjin, Chuo-ku, Fukuoka City, Fukuoka Prefecture No. 20 Inside the Kyushu branch of Takenaka Corporation

Claims (2)

[Claims] A preparatory hole 2 for embedding anchors is drilled in a concrete specimen 1, and an undercut 3 is formed in the prepared hole in a tapered shape at the bottom of the hole. Correspondingly, it is composed of an anchor bolt 7 having a tapered head 9 at the tip and a sleeve 8 fitted so as to be able to be driven into an intermediate part of the anchor bolt. Along with the tapered head 9, there is provided an anchor 6 having a plurality of expanding tongues 10 which are expanded, and the anchor is deeply inserted into the pilot hole 2 to form a sleeve 8. After the tapered head 9 is positioned in the undercut 3 and the sleeve 8 is driven in, the expanding tongue pieces 10 at the distal end are tapered. Same as when expanded by head 9 In the meantime, the anchor 6 is immovably embedded in the pilot hole 2 by intervening in the gap between the tapered head 9 and the undercut 3, and then the anchor 6 is rotated by the tensile test device 13. The concrete strength is measured by extracting the specimen without giving it, and measuring the pull-out strength, and calculating the compressive strength of the specimen concrete 1 from the pull-out strength-compression strength relational expression obtained in advance from an experiment. Estimation method. 2. The concrete strength estimating method according to claim 1, wherein the following regression equation extracted in advance by an experiment is used as the pull-out strength-compression strength relational equation. x = 121.95y−50.390 x: Compressive strength of test specimen concrete 1 (kgf / cm ² ) y: Pull-out strength of anchor 6 (ton)