JP2008128846A - Alkali aggregate reaction determination method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an alkali aggregate reaction determination method capable of easily and accurately determining the progression state of alkali aggregate reaction of a concrete structure. <P>SOLUTION: The alkali aggregate reaction determination method comprises a core sampling process of sampling a test core from the concrete structure, an excitation process of generating a longitudinal wave elastic wave in the test core, a receiving process of receiving the longitudinal wave elastic wave, an analysis process of analyzing a received signal and determining the propagation velocity of the longitudinal wave elastic wave in the test core, and a determination process of determining the progression state of the alkali aggregate reaction of the concrete structure based on the propagation velocity of the longitudinal wave elastic wave obtained in the analysis process. In the determination process, when the propagation velocity of the longitudinal wave elastic wave in a predetermined time obtained in the analysis process is a predetermined value or higher, it is determined as a sound concrete structure. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to an alkali aggregate reaction determination method.
The alkali aggregate reaction means that alkali components (Na and K) contained in cement concrete react with an aggregate containing a reactive mineral such as amorphous silica to produce alkali silica gel. .

Minerals that cause an alkali-aggregate reaction are unstable silica minerals (such as cristobalite, tridymite, opal, etc.) and crystalline quartz, which have fine crystal grains and a distorted crystal lattice. There are silicate minerals and amorphous volcanic glass. These minerals are contained in sedimentary rocks such as volcanic rocks (eg andesite) and chert.
When an aggregate containing a large amount of this kind of mineral is used in concrete, the pore water mainly composed of NaOH or KOH in the concrete reacts with the highly reactive silica mineral in the aggregate, and the aggregate. Alkaline silica gel is produced around Alkali silica gel absorbs water and swells, and causes abnormal expansion and cracking in concrete.
When this alkali-aggregate reaction occurs, mesh-like or tortoiseshell-like cracks develop in unreinforced concrete and concrete structures with a small amount of reinforcing steel, and in reinforced concrete and PC concrete structures, axial reinforcement and PC steel There is a directional crack along the direction.
In recent years, structures that have undergone excessive expansion due to alkali-aggregate reactions have been confirmed to have reduced concrete strength, reduced adhesion between the reinforcing bars and the cover, and breakage of the reinforcing bars at the bent and pressed parts. In the maintenance of the structure, it is predicted whether or not an alkali-aggregate reaction has occurred, and if so, how much damage has occurred and how much it will progress in the future. It is very important to do.

Deterioration of the concrete surface caused by the alkali-aggregate reaction (for example, cracks, discoloration, gel exudation) is unique to the alkali-aggregate reaction, and therefore the stage where deterioration has progressed to some extent (acceleration period or deterioration period) In some cases, the cause can be identified with relatively high accuracy even by visual inspection alone.
However, in the incubation period (when alkali-aggregate reaction occurs but no change in appearance) or in the early stage of development, structural cracks caused by changes in load and support conditions, concrete shrinkage, etc. In some cases, it is difficult to distinguish from cracks caused by materials or cracks caused by construction defects.

When visual judgment is difficult, generally, a core strength test taken from a structure or a core expansion rate test is performed.
In the core strength test, as shown in Non-Patent Document 4, it is determined from the results of the compressive strength and the static elastic modulus whether or not an alkali aggregate reaction has occurred. Judgment is possible because the static elastic modulus is remarkably reduced if the deterioration has progressed considerably, but even if there is a possibility that an alkali-aggregate reaction will occur in the future due to exogenous alkali, etc., this will become apparent. If it is before, it is difficult to judge only from the strength test.
On the other hand, in the residual expansion test of the core, a stainless steel band with a contact gauge measurement point attached to the sampled core was wrapped, the length change between the points was measured under various curing conditions, and the concrete expansion rate was measured over time. Measured automatically. This test method includes several methods (for example, the JCI-DD2 method, the Danish method, and the Canadian method) having different accelerated curing methods after core collection and different judgment criteria.

Patent Document 1 proposes a method for predicting deterioration due to an alkali-silica reaction using a correlation between a change in the amount of expansion of concrete obtained by an accelerated expansion test of concrete and an alkali hydroxide concentration.
Non-Patent Document 1 describes in detail a method for measuring an expansion amount of a core sample of a concrete structure that has caused an alkali-aggregate reaction.
Further, Non-Patent Document 2 describes Danish method, JIS A 1146 method, and ASTM C for glass sand composed of river sand and androgenic silica whose andesite particles are the main reactive aggregate, which is a feature of the Hokuriku region. An investigation by the 1260 method has been reported.
Non-Patent Document 3 reports a survey by Canadian law on river gravel used as concrete aggregate in the Hokuriku region.

JP-A-11-274291 Durability Diagnosis Research Committee Report (Japan Concrete Institute, June 1989) "Evaluation of alkali-silica reactivity of aggregates by accelerated curing test" (Kazuyuki Torii, Annual Report of Concrete Engineering Vol.26 No.1, 2004) "Judgment of Alkali-Silica Reaction of Concrete Structures by Core" (Nomura Masahiro, Annual Report of Concrete Engineering Vol.23 No.1, 2001) Kazusuke Kobayashi, Yahiro Mori, Kenji Nomura: Diagnosis method of alkali-aggregate reaction by compression loading test, Proceedings of Japan Society of Civil Engineers, No.460 / V ・ 18, pp.151-154, 1993.2

The method described in Non-Patent Document 1 is briefly introduced below.
FIG. 16 is a schematic diagram of expansion characteristics of the reactive core. When the core is standard-cured in a state close to 100% humidity immediately after collection, a certain amount of expansion occurs. Furthermore, when accelerated curing is performed in this state, expansion occurs due to reactive substances remaining in the concrete. The former is a measure of the alkali-aggregate reaction that has already occurred and is called free expansion. The latter is a measure of the risk of future expansion of the structure and is called residual expansion.
FIG. 17 is a diagram for explaining the principle of determining the progress of the alkali aggregate reaction from the expansion characteristics. Even if the expansion coefficient is the same, if the ratio of the expansion coefficient is large, it is judged that the alkali-aggregate reaction is close to the end stage. Conversely, if the ratio of the residual expansion coefficient is large, damage to the structure will occur in the future. Judge that there is room for expansion.

However, the interpretation of the results obtained has the following problems.
The rate of expansion is said to be a measure of the alkali-aggregate reaction that has already occurred, but there is little statistical data. For example, the expansion amount during the standard curing in FIG. 12 describing the test example of the present invention corresponds to the release expansion amount, but the numerical value is about 200 μm to 500 μm at most, depending on the storage situation after core collection. The value easily fluctuates due to the effect of drying, and the degree of damage in the past is often unknown.
On the other hand, the residual expansion rate is a useful index for predicting the progress of deterioration in the future, but if the reaction has already converged, the core will hardly expand and may not be distinguished from healthy concrete. There is.
The time required for the residual expansion test and determination of the core is about half a year in the JCI-DD2 method which is most commonly performed.

  In the above case, if the rock type determination by polarization microscope or powder X-ray diffraction, alkali content analysis, confirmation of silica gel, etc., it can be determined whether the cause of deterioration is alkali aggregate reaction, These methods require specialized knowledge and techniques, and the judgment criteria are not quantitative. In addition, when the number of samples is large, it is difficult to make a quick determination. Even if it is known that the cause of deterioration is an alkali aggregate reaction, it is not possible to know the past degree of damage or the possibility of future deterioration.

  The present invention has been made in view of the problems of the background art described above, and whether or not an alkali aggregate reaction has occurred in a concrete structure, and damage caused by an alkali aggregate reaction that has been received in the past. It is an object of the present invention to propose an alkali aggregate reaction determination method that can easily and quickly determine whether the deterioration due to an alkali aggregate reaction will progress in the future.

The above-described problems have been solved by the following alkali aggregate reaction determination methods according to the present invention [1] to [7]. That is,
[1] Core sampling process for sampling a test core from a concrete structure, excitation process for generating a longitudinal acoustic wave in the test core, a receiving process for receiving the longitudinal acoustic wave, and analysis of the received signal Then, the progress of the alkali-aggregate reaction of the concrete structure is determined from the analysis process for obtaining the propagation velocity of the longitudinal acoustic wave in the test core and the propagation velocity of the longitudinal acoustic wave obtained in the analysis process. A method for determining an alkali-aggregate reaction, including a determination process.
[2] The excitation process is a process in which an object having a predetermined weight and shape is dropped from the predetermined height onto the test core to excite a longitudinal elastic wave, and the reception process is the excited longitudinal wave This is a process of receiving an elastic wave with an acceleration sensor provided in the test core, and the analysis process performs a frequency analysis of the received longitudinal elastic wave and obtains a propagation velocity of the longitudinal elastic wave from a peak frequency. The method for determining an alkali-aggregate reaction according to [1], which is a process.
[3] The excitation process is a process of transmitting a pulse elastic wave from a transmitter provided in the test core, and the reception process is a process of receiving the pulse elastic wave by a receiver provided in the test core. The alkali aggregate according to [1], wherein the analysis step is a step of obtaining a propagation velocity of longitudinal elastic waves based on a difference in arrival time between the signal transmitted by the transmitter and the signal received by the receiver Reaction determination method.
[4] In the determination process, when the propagation velocity of the longitudinal acoustic wave at a predetermined time obtained in the analysis process is equal to or higher than a predetermined value, it is determined as a sound concrete structure. [1] Alkali-aggregate reaction determination method.
[5] In the determination process, when the propagation velocity of longitudinal acoustic waves for a predetermined period obtained in the analysis process is increased, the structure already damaged by a considerable alkali-aggregate reaction ( (1) Alkali-aggregate reaction determination method according to [1] above, which is determined as a concrete structure in a deterioration period
[6] In the case where the propagation speed of longitudinal acoustic waves in the predetermined period obtained in the analysis process is reduced in the determination process, a structure in which deterioration progress due to an alkali aggregate reaction is predicted in the future The alkali aggregate reaction determination method according to the above [1], which is determined as (concrete structure in the latent period).
[7] The method further includes an expansion amount measurement process for measuring the expansion amount of the test core to obtain a release expansion amount and / or a residual expansion amount, and in the determination process based on a result of the expansion amount measurement process. The method for determining an alkali aggregate reaction according to the above [1], wherein the progress of the alkali aggregate reaction is determined.

  According to the above-described alkali aggregate reaction determination method according to the present invention, whether or not the alkali aggregate reaction has occurred in the concrete structure, the degree of damage caused by the alkali aggregate reaction received in the past, and further in the future In particular, it can be determined easily and at an early stage whether or not the deterioration due to the alkali-aggregate reaction proceeds.

  Hereinafter, test examples showing the effectiveness of the above-described alkali aggregate reaction determination method according to the present invention will be described.

The test concrete was produced as follows.
Cement is ordinary Portland cement, fine aggregate is non-reactive land sand, coarse aggregate is reactive aggregate (aggregate determined to be non-hazardous as a result of chemical test) and non-reactive aggregate Used in a mixed ratio of 5: 5.
In order to promote the alkali aggregate reaction, NaOH was mixed and added to the water so that the equivalent alkali amount was 8.0 kg / m ³ .
A normal concrete to which no alkali was added was also prepared for the comparison test.

The specifications of the concrete specimens were as shown in Tables 1 and 2.

  FIG. 1 shows a side view (A) and a front view (B) of the concrete specimen used. The specimen was a PC (prestressed concrete) specimen prepared by a post-tension method, and the PC steel material used was a PC steel bar having a diameter of 11 mm.

The concrete specimen was subjected to poultice curing for 28 days after demolding, and then subjected to accelerated alkali-aggregate reaction curing in a constant temperature room at a humidity of 98% and a temperature of 40 ° C.
Then, a concrete specimen (sample No. 0: equivalent to the incubation period) before the accelerated curing, a concrete specimen (sample No. 1: equivalent to the development period) in which cracks were revealed by the alkali aggregate reaction, and the alkali aggregate Test cores were collected from concrete specimens (sample No. 2: equivalent to the degradation period) in which deterioration was considerably advanced by the reaction, and normal concrete specimens (sound).
The test core was collected at the position shown in FIG. Each test core had a diameter of 100 mm and a length of 300 mm.

  About the test core extract | collected as mentioned above, while performing the expansion amount test based on JCI-DD2 method, the propagation velocity of the elastic wave in a test core was measured with the following two methods.

FIG. 2 is a conceptual diagram of a first method for measuring the propagation velocity of elastic waves in the test core.
In this method, the electrical / acoustic transducers 2 and 2 are provided in close contact with both end faces of the test core 1. Then, a pulse signal is sent from the pulse signal generator 3 to one of the electric / acoustic transducers 2 to generate an elastic wave at one end of the test core 1 (excitation process). The acoustic signal that propagates through the test core 1 and reaches the other end is converted into an electrical signal by the other electrical / acoustic transducer 2 (a vibration receiving process). An input pulse signal S1 from the pulse signal generator 3 and a received signal S2 converted into an electric signal are sent to the analyzer 4. The signal is analyzed by the analyzer 4 and calculation of the propagation speed of the elastic wave transmitted through the test core and frequency analysis are performed (analysis process). The propagation speed of the elastic wave can be easily obtained using a known technique, for example, based on the delay at the rising edge of the signal pulse.

  FIG. 3 is an example of the received signal of the elastic wave propagated through the test core 1 taken from the concrete specimen (sample No. 0: equivalent to the incubation period) before the accelerated curing. FIG. 4 is an example of a received signal of an elastic wave propagated through the test core 1 collected from a concrete specimen (sample No. 1: equivalent to the development period) in which the alkali aggregate reaction proceeds and the expansion amount is 2860 μm. . 5 and 6 are frequency spectra of the signals of FIGS. 3 and 4, respectively.

Compared with the received signal in FIG. 3, the signal strength of the received signal in FIG. 4 is very small. Further, it can be seen from the frequency distribution of FIG. 6 that the high frequency component around 150 kHz seen in FIG. 5 has disappeared. This is presumably because the elastic waves were attenuated by being absorbed or scattered when passing through fine cracks generated by the progress of the alkali-aggregate reaction or alkali silica gel.
If the waveform of the output signal is broken in this way, it may be difficult to obtain the propagation speed of the elastic wave from the difference between the pulse input time and the rise time of the transmitted pulse. Although it is possible to make the rise time of the output waveform easier to see by increasing the pulse input intensity or shortening the test core length, it is not desirable because the test conditions change.

  From the above, in the method of transmitting the pulse of FIG. 2, the rising time of the transmitted pulse cannot be read accurately, and an error by the measurer may occur. Furthermore, the accuracy may not be expected depending on the time base resolution (sampling frequency) of the measuring device.

FIG. 7 is a conceptual diagram of a second method for measuring the propagation velocity of elastic waves in the test core.
In this method, the acceleration sensor 5 is provided in close contact with an arbitrary point of the test core 1, for example, one end face of the test core 1. Then, the test core 1 is supported so that one end face of the test core 1 faces upward and the vibration of the test core 1 is not damped, that is, free vibration is possible.
In this state, from a predetermined distance from the test core 1, for example, a height of 30 cm, a predetermined object 6, for example, a steel ball having a diameter of about 20 mm and a mass of about 30 g is dropped and applied to the end surface of the test core 1 to freely test the core 1 Vibrate (excitation process). The input elastic wave reciprocates on both end faces of the test core 1 and the entire test core vibrates freely. Then, the vibration is detected by the acceleration sensor 5 (a vibration receiving process).
In order to make free vibration, it is not always necessary to use the above steel balls, and a method of hitting with a hammer made of iron or plastic may be used. However, in order to standardize the conditions, a predetermined weight and shape are used. It is preferable to employ a method of dropping an object from a predetermined height.

When an impact is applied to the end face of a cylindrical object having a length L in the direction of the cylinder axis, the response frequency peak f of the free vibration of the elastic wave excited in the cylindrical body is a longitudinal elastic wave of the object. There is a relationship between the velocity V and the following equation.

V = 2fL

Accordingly, the longitudinal elastic wave velocity V can be obtained by detecting the response frequency peak f of free vibration (analysis process).
If the dimension of the test core is φ50 to 100 mm and the length is about 100 to 400 mm, the detected response frequency peak f is a value within a range of several kHz to several tens of kHz. The sampling interval is several tens of μs, and the number of data necessary for analysis is about 2000.

  FIG. 8 is an example of a signal received by the acceleration sensor 5 of the free vibration of the test core 1 taken from the concrete specimen (sample No. 0: equivalent to the incubation period) before the accelerated curing. FIG. 9 shows an example of a signal received by the acceleration sensor 5 from the free vibration of the test core 1 taken from a concrete specimen (sample No. 2: equivalent to the deterioration period) in which the alkali aggregate reaction proceeds and the expansion amount is 5000 μm. It is. 10 and 11 are frequency spectra of the signals of FIGS. 8 and 9, respectively.

  In the case of FIG. 11, the response frequency peak is lower than that of FIG. It is considered that when the alkali-aggregate reaction proceeds, the longitudinal acoustic wave velocity V of the test core 1 decreases due to the generation of alkali silica gel and fine cracks, and as a result, the response frequency peak decreases.

FIG. 0 (equivalent to incubation period) and sample no. 1 (equivalent to the development period) and sample no. It is the figure which performed the expansion | swelling amount test of the test core about 2 (deterioration period equivalent) and normal concrete (sound), respectively, and showed the open | release expansion amount and the residual expansion amount as a function of material age.
The expansion amount test was performed according to the JCI-DD2 method as described above.

Sample No. In the measurement of the expansion amount of the test core of 0 (latent period equivalent: black rhombus), the rise of the expansion amount after the accelerated curing is large. No. 1 (corresponding to the progressing period: white circle mark), the rise is small, and sample No. 2 (deterioration period equivalent: black triangle mark) hardly stands up, and it can be seen that it cannot be clearly distinguished from normal concrete (healthy: cross mark).
In other words, in the measurement of the amount of expansion, it is unclear how much it has already expanded by the time of the survey.For example, if the alkali aggregate reaction has converged, the test core will expand even if the cause of deterioration is the alkali aggregate reaction. It can be seen that the alkali aggregate reaction cannot be detected.

FIG. 0 (equivalent to incubation period) and sample no. 1 (equivalent to the development period) and sample no. 2 (corresponding to deterioration period) and normal concrete (healthy), in parallel with the above expansion test, the ultrasonic pulse propagation velocity was measured for each test core by the method shown in FIG. It is the figure which showed the measured value as a function.
14 shows the sample No. 0 (equivalent to incubation period) and sample no. 1 (equivalent to the development period) and sample no. 2 (corresponding to deterioration period) and normal concrete (healthy), in parallel with the above expansion test, the longitudinal elastic wave propagation velocity was measured for each test core by the method shown in FIG. It is the figure which showed the measured value as a function.

Generally, the propagation speed when the concrete structure is in a healthy state (for example, the propagation speed at the time of completion) is unknown, but if the concrete mixing conditions are known, the propagation speed can be estimated. is there.
For example, using the aggregate used for the test, the water cement ratio and the unit coarse aggregate amount were changed, a concrete specimen without addition of alkali was prepared, and the ultrasonic pulse propagation velocity was measured. I got the result.
As shown in Table 2, the composition of the concrete used in this test is W / C = 50% and the unit coarse aggregate amount is 380 L / m ³ , and the ultrasonic pulse propagation velocity in a healthy state is about 4500 m from FIG. / S. This estimation result almost coincides with the propagation speed of normal concrete (sound: cross) shown in FIG.
By a similar estimation method, the longitudinal elastic wave propagation velocity in a healthy state of the concrete blend used in the test can be estimated to be about 4200 m / s.

From FIG. 13 and FIG. 14, if the age is at least 90 days (standard curing 40 days + accelerated curing 50 days), the concrete in which the alkali-aggregate reaction has occurred and the normal concrete are clearly defined for all samples. It can be seen that they can be distinguished.
That is, only normal concrete (healthy: cross) is not lowered from the estimated propagation speed (about 4500 m / s, or about 4200 m / s), and is about 4500 m / s in FIG. 13 and 4100 m / s in FIG. Holds s strong. On the other hand, the concrete in which the alkali-aggregate reaction has occurred has a reduced propagation speed regardless of the deterioration state at the time of core collection, and is slightly over 4000 m / s in FIG. 13 and about 3400 m / s in FIG. .
In particular, it is possible to clearly distinguish between concrete corresponding to a deterioration period (No. 2: black triangle mark) and normal concrete (sound: cross mark) that could not be distinguished in the expansion rate test.
From the above, the propagation velocity measured at a predetermined time, for example, 50 days after the start of accelerated curing, is 95% or more of the propagation velocity estimated from the blending conditions (for example, 4200 m / in the case of measurement by inputting pulsed elastic waves) s or more and 4000 m / s or more in the case of measurement by input of impact elastic waves), it is possible to determine that the concrete structure is sound.

From FIGS. 13 and 14, it can be seen that the propagation speed increases during the release expansion test, that is, the age of about 40 days after release of the core immediately after the core is removed. It can be seen that only the sample No. 2 (corresponding to the deterioration period: black triangle mark) is observed, and no change in the propagation velocity is observed in the other samples.
From the above, for the test cores taken from the structure for a predetermined period, for example, the propagation speed immediately after removal of the core is compared with the propagation speed at the end of release expansion (about 40 days of age), and the propagation speed seems to increase. If there is, it is possible to determine that the structure has already been damaged by a considerable alkali aggregate reaction in the past (a concrete structure in a deterioration stage). Although the cause of the increase in the propagation speed is unknown in the sample with considerably advanced deterioration while showing expansion during the open expansion test period, for example, the core specimen itself under the wet conditions under test It is conceivable that fine cracks in the core specimen were filled due to water absorption or alkali silica gel swelling and absorbing water.

Furthermore, from FIG. 13 and FIG. 14, after the completion of the release expansion, the propagation speed suddenly decreases at the initial stage of accelerated curing (30 to 50 days after the start of accelerated curing). It can be seen that there is only a sample of 0 (latent period equivalent: black rhombus mark), and no significant change in propagation velocity is observed in other samples.
From the above, for the test core collected from the structure for a predetermined period, for example, the propagation speed immediately after the end of the open expansion is compared with the propagation speed 30 to 50 days after accelerated curing (age 70 to 80 days), and the propagation speed decreases. If so, it can be determined that the structure is expected to progress in the future due to the alkali aggregate reaction (concrete structure in the latent period). In addition, in the sample in the incubation period, the decrease in the propagation speed during this period is thought to be due to the generation of alkali silica gel, cracks, and cracks due to the rapid progress of the alkali aggregate reaction of the sample due to accelerated curing.

  In addition, the determination with the concrete structure in a deterioration period mentioned above, or the determination with a concrete structure in a latent period is performed with the increase or decrease of the propagation speed in a predetermined period, and it is not necessarily propagation from mixing conditions. Speed estimation is not necessary.

  Further, as in the above test example, when the propagation velocity is measured in parallel with the expansion amount test for the test core, information on the presence or absence of future expansion is obtained from the expansion amount test, and the propagation velocity is measured. From the value and its change, it is possible to obtain information on whether or not it has been damaged by the alkali-aggregate reaction up to the present time, and how much damage has occurred, and it is higher by comprehensively judging from both information It is possible to determine the progress of the alkali aggregate reaction of the concrete structure with accuracy.

  Compared with the pulse transmission method of FIG. 2, the impact elastic wave method by dropping the steel ball of FIG. 7 has a larger energy energy of the input elastic wave and causes the test core to vibrate freely. The average rigidity can be well understood, and the reproducibility of the results (for example, the response frequency peak measurement results) when the same measurement is performed multiple times with the same test core is high, and the reading error by the measurer is also low. Less.

両者の関係はポアソン比によって決まるが、アルカリ骨材反応を生じたコンクリートのポアソン比についてはこれまでに知見が得られていない。
試験コアではないが、同時に作製したテストピースの強度試験結果によれば、劣化前のコンクリートで０．２程度（この時、棒を伝わる縦波の速度は実体波Ｐ波速度の０．９５倍）、アルカリ骨材反応により５０００μｍ程度膨張したコンクリートで０．３程度（この時、棒を伝わる縦波の速度は実体波Ｐ波速度の０．８６倍）であった。このため、棒を伝播する縦波の速度として算出される衝撃弾性波法の方が、アルカリ骨材反応による伝播速度の低下が現れ易かったと考えられる。 From FIG. 13 and FIG. 14, it can be seen that the impact elastic wave method by dropping a steel ball tends to catch the decrease in propagation speed due to the alkali aggregate reaction, compared with the pulse transmission method. This is considered to be due to the following reason.
When a steel ball of φ10 to 20 mm is used, the wavelength of the elastic wave that can be input is several tens of cm, which is sufficiently longer than the size of the test core of φ100 mm. For this reason, in the shock elastic wave method, the velocity of the longitudinal wave traveling through the rod is required. On the other hand, in the pulse transmission method, the wavelength of the elastic wave used is several cm, and the body wave P wave velocity is calculated.
The following relationship is established between the body wave P wave velocity V _P and the longitudinal wave velocity V ₁ propagating through the rod.

The relationship between the two is determined by the Poisson's ratio, but no knowledge has been obtained about the Poisson's ratio of concrete that has caused an alkali-aggregate reaction.
Although it is not a test core, according to the strength test result of the test piece produced at the same time, it is about 0.2 in concrete before deterioration (at this time, the velocity of the longitudinal wave transmitted through the bar is 0.95 times the velocity of the body wave P wave) ), About 0.3 μm in concrete expanded by about 5000 μm due to the alkali aggregate reaction (at this time, the velocity of the longitudinal wave transmitted through the rod was 0.86 times the velocity of the body wave P wave). For this reason, it is considered that the impact elastic wave method calculated as the velocity of the longitudinal wave propagating through the rod is more likely to cause a decrease in the propagation velocity due to the alkali aggregate reaction.

As mentioned above, although the test example of the alkali-aggregate reaction determination method according to the present invention has been described, the present invention is not limited to the above test example, and is within the scope of the technical idea of the present invention described in the claims. Of course, various modifications and changes are possible.
For example, in carrying out the present invention, the method for detecting the propagation speed of elastic waves is not limited to the method described based on FIGS. For example, in the case of the method of FIG. 2, the input signal is not limited to a pulse, but a continuous wave is adopted and the propagation speed is obtained from the response function. In the case of the method of FIG. It is also possible to make a change such as detecting the vibration frequency in a mode in which the equation of V = 2fL is established.

It is a side view (A) and a front view (B) of a concrete specimen. It is the conceptual diagram which showed the 1st method of measuring the propagation velocity of the elastic wave in a test core. It is an example of the received signal of the elastic wave which propagated in the test core extract | collected from the concrete test body before carrying out accelerated curing. It is an example of the received signal of the elastic wave which propagated in the test core extract | collected from the concrete test body which alkali-aggregate reaction advanced. It is a frequency spectrum of the signal of FIG. 5 is a frequency spectrum of the signal of FIG. It is the conceptual diagram which showed the 2nd method of measuring the propagation velocity of the elastic wave in a test core. It is an example of the signal which received the free vibration of the test core extract | collected from the concrete test body before carrying out accelerated curing with the acceleration sensor. It is an example of the signal which received the free vibration of the test core extract | collected from the concrete test body which alkali-aggregate reaction advanced with the acceleration sensor. It is a frequency spectrum of the signal of FIG. 10 is a frequency spectrum of the signal of FIG. 9. This is an example in which the amount of expansion was measured as a function of age for samples corresponding to the incubation period, samples corresponding to the development period, samples corresponding to the deterioration period, and normal concrete. This is an example in which the ultrasonic pulse propagation velocity was measured as a function of material age for samples corresponding to the incubation period, samples corresponding to the development period, samples corresponding to the deterioration period, and normal concrete. This is an example in which the longitudinal elastic wave propagation velocity was measured as a function of age for a sample corresponding to the incubation period, a sample corresponding to the development period, a sample corresponding to the deterioration period, and normal concrete. It is the figure which showed the relationship between concrete mixing conditions and the ultrasonic pulse propagation velocity. FIG. 3 is a schematic diagram of expansion characteristics of a reactive core. It is a figure explaining the principle which determines progress of an alkali aggregate reaction from an expansion characteristic.

Explanation of symbols

1 Test Core 2 Electric / Acoustic Transducer 3 Pulse Signal Generator 4 Analyzer 5 Acceleration Sensor 6 Steel Ball S1 Input Pulse Signal S2 Received Signal

Claims (7)

  A core sampling process for sampling a test core from a concrete structure, an excitation process for generating a longitudinal acoustic wave in the test core, a receiving process for receiving the longitudinal acoustic wave, and analyzing a received signal to analyze the received signal An analysis process for determining the propagation velocity of longitudinal elastic waves in the test core, and a determination process for determining the progress of alkali-aggregate reaction of the concrete structure from the propagation velocity of longitudinal acoustic waves obtained in the analysis process A method for determining an alkali-aggregate reaction, comprising:   The excitation process is a process in which an object having a predetermined weight and shape is dropped from the predetermined height onto the test core to excite a longitudinal elastic wave, and the reception process includes the excited longitudinal wave elastic wave. It is a process of receiving with an acceleration sensor provided in the test core, and the analysis process is a process of performing a frequency analysis of the received longitudinal acoustic wave and obtaining a propagation velocity of the longitudinal acoustic wave from a peak frequency. The method for determining an alkali-aggregate reaction according to claim 1, wherein:   The excitation process is a process of sending a pulse elastic wave from a transmitter provided in the test core, and the reception process is a process of receiving the pulse elastic wave by a receiver provided in the test core; 2. The alkali according to claim 1, wherein the analyzing process is a process of obtaining a propagation velocity of a longitudinal elastic wave based on a difference in arrival time between a signal transmitted by the transmitter and a signal received by the receiver. Aggregate judgment method.   In the determination process, when the propagation velocity of the longitudinal elastic wave at a predetermined time obtained in the analysis process is equal to or higher than a predetermined value, it is determined as a sound concrete structure. The alkali-aggregate reaction determination method according to claim 1.   When the propagation speed of longitudinal acoustic waves in the predetermined period obtained in the analysis process is increased in the determination process, the structure already damaged by a considerable alkali-aggregate reaction (during the deterioration period) 2. The alkali aggregate reaction determination method according to claim 1, wherein the determination is made as a concrete structure.   When the propagation speed of the longitudinal acoustic wave in the predetermined period obtained in the analysis process is reduced in the determination process, a structure that is expected to progress in the future due to the alkali-aggregate reaction (in the latent period) 2. The alkali aggregate reaction determination method according to claim 1, wherein the determination is made as a concrete structure.   It further includes an expansion amount measurement process for measuring the expansion amount of the test core to obtain a release expansion amount and / or a residual expansion amount, and in the determination process based on the result of the expansion amount measurement process, the alkali aggregate of the concrete structure The method for determining an alkali-aggregate reaction according to claim 1, wherein the progress of the reaction is determined.

Images