Method for estimating the state of hardened cement paste

Abstract

To provide a method for estimating the state of a cement hardening body that allows the determination of the degree of progress of hydration of a cement hardening body.SOLUTION: The present invention relates to a method for estimating the state of a cement hardening body for determining the degree of progress of hydration of a cement hardening body. The method includes: the step S1 of setting a sensor capable of a dielectric measurement, in contact with the inside of the cement hardening body; the step S3 of performing a dielectric measurement on the inside of the cement hardening body by the sensor after a predetermined time has passed; and the step S4 of estimating the degree of progress of hydration of the cement hardening body on the basis of the result of the dielectric measurement.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for estimating the state of a hardened cement body and a dielectric measuring device for determining the degree of hydration progress of the hardened cement body. [Background technology]

[0002] Hardened cement products such as concrete and ground improvement bodies, which increase in strength through hydration reactions, will develop the desired strength after undergoing a curing period in an appropriate environment to promote the hydration reaction.

[0003] For example, the Japan Society of Civil Engineers' Standard Specifications for Concrete specifies the curing method by indicating specific means of water supply, and also clearly indicates the number of curing days that should be ensured for typical average daily temperatures (above 15°C, above 10°C, above 5°C) and for each common type of cement.

[0004] The curing period indicated in this Standard Specifications for Concrete is based on the assumption that curing is carried out in an appropriate environment, and only indicates the number of curing days that should be ensured for safety reasons, and does not take into account the actual condition of the concrete, which varies from site to site.

[0005] On the other hand, it is known that compressive strength can be estimated from the accumulated temperature after concrete is poured, as disclosed in Patent Document 1. Therefore, in Patent Document 1, a temperature sensor is placed in the formwork for the tunnel lining concrete to directly measure the temperature of the concrete poured on site, thereby calculating the actual accumulated temperature. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-26734 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the actual strength of concrete is not determined solely by the accumulated temperature during the curing period; whether the concrete was kept in an appropriate moist state, such as whether it had dried out, is also an important factor (see Figure 10). Also, temperature sensors attached to the inside of the formwork can only measure the temperature of the concrete surface, and cannot accurately grasp the internal condition.

[0008] Therefore, an object of the present invention is to provide a method for estimating the state of a hardened cement body that makes it possible to determine the degree of progress of hydration of the hardened cement body, and a dielectric measuring device that can be used for the method. [Means for solving the problem]

[0009] In order to achieve the above object, the method for estimating the state of a hardened cement body of the present invention is a method for estimating the state of a hardened cement body for determining the degree of hydration of the hardened cement body, and is characterized by comprising the steps of: installing a sensor capable of dielectric measurement so as to be in contact with the inside of the hardened cement body; performing dielectric measurement of the inside of the hardened cement body using the sensor after a given period of time has elapsed; and estimating the degree of hydration of the hardened cement body based on the results of the dielectric measurement.

[0010] Here, the method may further include a step of determining a time to end curing of the hardened cement body based on the estimated degree of hydration progress. The hardened cement body may be concrete, and the sensor may be placed in advance at a position where the concrete will be filled, and then the concrete may be filled.

[0011] Furthermore, the invention of a dielectric measuring device is a dielectric measuring device for performing dielectric measurements on hardened cement bodies, characterized in that it comprises a rod-shaped sensor with a sensing part at the tip, a measuring instrument connected to the sensor, and a protective part that allows the sensing part to come into contact with the hardened cement body and prevents contact between the sensing part and an object of a predetermined size or larger. [Effects of the Invention]

[0012] The method for estimating the state of a hardened cement body of the present invention configured as described above involves installing a sensor capable of dielectric measurement so as to be in contact with the inside of the hardened cement body, performing dielectric measurement over time using the sensor, and estimating the degree of hydration of the hardened cement body based on the results of the dielectric measurement.

[0013] By conducting dielectric measurements on hardened cement paste, it becomes possible to distinguish the dynamic state of the water inside, i.e., between free water and bound water such as bound water, and to determine the degree of hydration progress inside the hardened cement paste.

[0014] The strength of the hardened cement body can also be estimated from the estimated degree of hydration progress, making it possible to determine the end time for curing of the hardened cement body.If the hardened cement body is concrete, the sensor can be easily installed inside the concrete by placing it in advance at the position where the concrete will be filled.

[0015] In addition, in the dielectric measuring device of the present invention, the sensing part at the tip of the rod-shaped sensor is protected by a protective part that prevents contact between the sensing part and an object of a certain size or larger, thereby preventing the sensing part from coming into contact with concrete aggregate, which would prevent accurate dielectric measurement from being performed. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a flowchart illustrating a processing flow of a method for estimating the state of a hardened cement body according to the present embodiment. [Figure 2] FIG. 2 is an explanatory diagram schematically showing a state of dielectric measurement by a dielectric measurement device. [Figure 3] 10A and 10B are explanatory diagrams illustrating measurement results and analysis results of dielectric measurements. [Figure 4] FIG. 1 is an explanatory diagram illustrating the relationship between the relaxation time of dielectric relaxation and the material age. [Figure 5]FIG. 10 is an explanatory diagram illustrating the relationship between the rate of change of relaxation time with time and the age of a material. [Figure 6] FIG. 2 is an explanatory diagram illustrating a schematic example of the relationship between the degree of hydration and the age of a material. [Figure 7] FIG. 1 is an explanatory diagram illustrating a schematic example of the relationship between the dielectric index and the degree of hydration. [Figure 8] These are diagrams explaining the protective part of a sensor that measures the dielectric properties of concrete, where (a) is an explanatory diagram showing the sensing part without the protective part attached, (b) is an explanatory diagram when a cylindrical guard is attached, and (c) is an explanatory diagram when a mesh guard is attached. [Figure 9] FIG. 1 is an explanatory diagram illustrating a method for estimating the degree of hydration from a dielectric index. [Figure 10] FIG. 1 is an explanatory diagram showing the relationship between the curing state, age, and degree of hydration of concrete. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a flowchart illustrating the process flow of a method for estimating the state of a hardened cement body according to this embodiment. Fig. 2 is an explanatory diagram schematically illustrating the state of dielectric measurement by a dielectric measurement device 1.

[0018] The method for estimating the state of a hardened cement body of this embodiment is applied to determining the state of a hardened cement body such as concrete or ground improvement body whose strength increases as the hydration reaction progresses. In other words, it is applied to determining the degree of hydration progress of a solidifying material such as cement or a cement-based solidifying material contained in the hardened cement body.

[0019] To accelerate the hydration reaction of cement and other solidifying materials, they must be cured for a specified period of time (age) under an environment with appropriate temperature and humidity. If curing is carried out properly, the desired strength will be achieved.

[0020] In the method for estimating the state of a hardened cement paste according to this embodiment, whether or not the curing has been carried out appropriately is determined based on the results of the dielectric measurement. First, the dielectric measurement will be described.

[0021] Dielectric measurements are a technique for determining the dielectric spectrum, which reflects the movement of the electric dipole moment, by observing the frequency dependence of the complex dielectric constant (ε*(ω) = ε′-j ε′′). The intensity of the dielectric spectrum is proportional to the number of dipoles in a unit volume, and the peak frequency of the imaginary part of the dielectric spectrum reflects the time scale of the rotational movement of the dipoles. Because water molecules have a large electric dipole moment, dielectric measurements are thought to be able to appropriately evaluate the state of water molecules.

[0022] 2, a dielectric measurement device 1 that performs dielectric measurement is mainly composed of a sensor 2 that is capable of dielectric measurement and a measuring instrument 3 that is connected to the sensor 2. In this figure, the sensor 2 and the measuring instrument 3 are connected by a cable 11.

[0023] An impedance analyzer can be used as the measuring device 3. A rod-shaped probe (electrode) is used as the sensor 2. The tip of the sensor 2 is a flat sensing part 21, which measures the state of an object in contact with the sensing part 21. For example, a coaxial electrode with a diameter of about 6 mm can be used as the sensor 2.

[0024] For example, to measure the internal condition of the concrete structure M, the sensing unit 21 is installed at a desired position (depth) of the concrete structure M. For example, before filling the concrete, the sensor 2 is attached to the formwork so that the sensing unit 21 is installed at a desired position, and then the concrete is poured into the formwork.

[0025] The measuring device 3 measures impedance, for example, in the frequency range of 40 Hz to 110 MHz at an applied voltage of 500 mV. That is, measurements and processing of the results are performed in multiple frequency bands in the range of 40 Hz to 110 MHz.

[0026] Such dielectric measurements are performed to separate and understand the free water and bound water (such as bound water) in an object such as a concrete structure M. In other words, if the amount of bound water (bound water) in the cement paste can be determined, it becomes possible to determine the degree of hydration. The degree of hydration can be indicated by the degree of hydration or the hydration rate.

[0027] If the degree of hydration and other progress of hydration can be estimated, it becomes possible to determine the time to end curing based on the desired concrete performance (concrete potential). Figure 3 is an explanatory diagram illustrating the measurement and analysis results of the dielectric measurement.

[0028] Figure 3 shows the dielectric spectrum in the MHz frequency range obtained when dielectric measurements were performed on a mortar specimen made using ordinary Portland cement with a water-cement ratio (W / C) of 0.55.

[0029] Here, the dielectric loss (ε'') peak reflects the rotational motion of bound water (restricted water) observed in the measurement frequency range. As shown in the lower panel of Figure 3, the frequency of this dielectric loss peak shifted to lower frequencies with increasing curing time (8 h, 26 h, 74 h, 121 h, 169 h). Furthermore, the shift in peak frequency after 74 h was smaller than that at the early stage of the material age, and the plots for 121 h and 169 h overlapped around the peak frequency.

[0030] These results suggest that once hydration has progressed to a certain extent, the state of bound water (restricted water) becomes less likely to change, which is reflected in the overlap around the loss peak frequency.

[0031] 4 is an explanatory diagram illustrating the relationship between the relaxation time τ (s: seconds) of dielectric relaxation and the material age (days), i.e., the relationship between the relaxation time τ obtained from the loss peak frequency and the material age.

[0032] This relaxation time increases as the hydration reaction progresses and strength is developed. Therefore, the rate of change of the relaxation time (δ(logτ) / δt) was calculated and its relationship with the material age is shown in Figure 5. For reference, the material age at which 50% of the 28-day strength is developed is plotted on each corresponding curve with an "x" mark.

[0033] As a result, the time change rate (δ(logτ) / δt) of the relaxation time corresponding to the age at which 50% of the 28-day strength was achieved was approximately 10 -1 The range is as follows, and it was found that the strength development state can be estimated from the results of the dielectric measurement.

[0034] Strength development varies depending on the type of cement (normal Portland cement, blended cement type B, high-early-strength Portland cement, etc.) and the mix proportions, such as the water-cement ratio (W / C). Therefore, it is necessary to understand the relationship between the degree of hydration and age (days) for each cement type and mix proportion, as shown in Figure 6. This relationship between the degree of hydration and age can be obtained by conducting experiments using actual test specimens, but it can also be obtained from existing literature.

[0035] Once this relationship between the degree of hydration and material age is obtained, it is possible to derive the relationship between the degree of hydration and relaxation time τ by combining it with the relationship between relaxation time τ and material age shown in Figure 4. Here, instead of using the relaxation time τ itself as an index, a value obtained by processing the measurement results of dielectric measurement (such as the rate of change over time (δ(logτ) / δt)) can also be used, and therefore this is referred to as the "dielectric index" in a broader sense. Figure 7 is an explanatory diagram that schematically illustrates the relationship between the dielectric index and the degree of hydration.

[0036] Next, the process flow of the method for estimating the state of a hardened cement body according to this embodiment will be described with reference to FIG. First, in step S1, the sensor 2 is attached to a formwork assembled to construct the concrete structure M so that the sensing unit 21 of the sensor 2 is positioned inside the concrete structure M (see FIG. 2). For example, the sensing unit 21 is placed at an arbitrary position that is about 10 mm to 30 mm away from the surface of the concrete structure M.

[0037] 8(a), aggregate K contained in the concrete being filled may come into contact with and cover the sensing unit 21. For example, if aggregate K having a size of 3 mm or more comes into contact with the sensing unit 21 having a diameter of about 6 mm, the influence of aggregate K may prevent accurate dielectric measurement.

[0038] Therefore, for example, protective parts (4A, 4B) of the sensing unit 21 as shown in Figures 8(b) and (c) are attached to the sensor 2. The protective parts (4A, 4B) are configured to allow contact between the sensing unit 21 and a hardened cement product such as cement paste, and to prevent contact between the sensing unit 21 and an object of a predetermined size or larger.

[0039] For example, the cylindrical guard 4A serving as the protective part shown in Figure 8(b) is formed in a cylindrical shape with approximately the same diameter as the sensor 2 and has an open front. The cement paste component of the concrete can flow in from this front and come into contact with the sensing part 21.

[0040] On the other hand, aggregate K that is too large to pass through a circle with a diameter of 6 mm will not come into contact with the sensing unit 21. Although not shown, by attaching a cross-shaped or other lattice to the front surface of the cylindrical guard 4A, it is possible to prevent the intrusion of aggregate K that is 3 mm or larger.

[0041] On the other hand, the mesh guard 4B, which serves as the protective part shown in Fig. 8(c), is formed in a dome shape using wires. The cement paste component of the concrete can flow through the gaps between the wires and come into contact with the sensing part 21, while the mesh guard 4B can prevent the intrusion of aggregate K that is larger than the gaps between the wires.

[0042] Next, in step S2, concrete is poured inside the formwork to which the sensor 2 is attached. The concrete filled in the formwork flows around the sensing part 21 of the sensor 2, allowing the sensor 2 to measure the internal condition of the concrete structure M.

[0043] By connecting a measuring device 3 to this sensor 2 via a cable 11, it becomes a dielectric measuring device 1. Once the dielectric measuring device 1 is set up, it becomes possible to perform dielectric measurement inside the concrete structure M at any time after concrete is poured (step S3).

[0044] After concrete is poured, it is cured by keeping it moist by flooding, sprinkling water, applying wet compresses, using curing mats, etc. Dielectric measurements are then taken when the general curing period specified in the Standard Specifications for Concrete, or the curing period specified in the design, has been reached or has passed.

[0045] That is, an AC voltage of 500 mV is applied by the measuring device 3, and the impedance in the frequency range of 40 Hz to 110 MHz is measured using an impedance analyzer. Then, by analyzing the measurement results, the complex dielectric constant around the sensing part 21 of the sensor 2 at the time of measurement is calculated.

[0046] Then, a dielectric index such as the dielectric relaxation time is calculated from the calculated complex dielectric constant. Fig. 9 is a diagram for explaining a method for estimating the degree of hydration from the dielectric index. This relationship diagram or a conversion formula for calculating the degree of hydration from the dielectric index as explained in this diagram is prepared in advance.

[0047] Relationship diagrams and conversion formulas such as those shown in Figure 9 are prepared for each type of cement and mix. Figure 9 is a conversion diagram that can be used when the cement type is ordinary Portland cement (OPC) and the water-cement ratio (W / C), which indicates the mix, is around 50% to 60%.

[0048] For example, if cured for 7 days in water at 20°C, the degree of hydration will be about 0.7. If cured for 28 days in water at 20°C, the degree of hydration will be about 0.85. However, in reality, the temperature does not remain constant throughout the curing period, and the number of curing days may vary. There are also cases where you want to quantitatively indicate the potential of concrete obtained as a result of sufficient curing beyond the standard curing period.

[0049] Therefore, with the method for estimating the state of a hardened cement paste according to this embodiment, the degree of hydration can be quantitatively determined from the quantitative value of the dielectric index obtained by dielectric measurement (Step S4). In other words, it is possible to prove (guarantee) that the paste has been sufficiently cured under an appropriate environment using the actual measured value.

[0050] If the estimated degree of hydration does not reach the planned value, it can be decided to continue the curing (step S5).The results obtained by the extended curing can then be confirmed by performing dielectric measurements again.

[0051] Figure 10 is an explanatory diagram showing the relationship between the curing state, age, and degree of hydration of concrete. The degree of hydration (degree of hydration, hydration rate) of concrete corresponds to strength such as compressive strength, and increases as the material ages.

[0052] However, the rate (speed) of this increase is affected by the curing conditions. For example, even if curing is done at the same temperature of 20°C, the rate at which the degree of hydration increases will be different if curing is done in air than if curing is done in water. In other words, it is not possible to determine whether or not curing can be completed based on the accumulated temperature alone.

[0053] Furthermore, even when underwater curing is performed, the increase in the degree of hydration varies depending on the conditions under which the concrete is placed during the curing process. In contrast, the method for estimating the state of a hardened cement paste according to this embodiment can quantitatively indicate the state of the concrete at the time of dielectric measurement, regardless of the environment under which the concrete was cured. In other words, it is possible to take into account the effects of both temperature and moisture conditions during curing. Furthermore, it is possible to know the internal state of the concrete structure M.

[0054] Next, the method for estimating the state of a hardened cement body according to this embodiment and the operation of the dielectric measuring device 1 suitable for use in this method will be described. The method for estimating the state of a hardened cement body according to this embodiment, configured as described above, involves installing a sensor 2 capable of dielectric measurement so as to be in contact with the inside of a hardened cement body such as a concrete structure M, performing dielectric measurement over time using the sensor 2, and estimating the degree of hydration progress (degree of hydration) of the hardened cement body based on the results of the dielectric measurement.

[0055] By conducting dielectric measurements on hardened cement paste, it becomes possible to distinguish the dynamic state of the water inside, i.e., between free water and bound water such as bound water, and to determine the degree of hydration progress inside the hardened cement paste.

[0056] The strength of the hardened cement body such as the concrete structure M can then be estimated from the estimated degree of hydration, making it possible to determine the end time for curing of the hardened cement body. If the hardened cement body is concrete, the sensor 2 can be easily installed inside the concrete structure M by placing it in advance at the position where the concrete will be filled.

[0057] Furthermore, in the dielectric measuring device 1 of this embodiment, the sensing part 21 at the tip of the rod-shaped sensor 2 is protected by protective parts (4A, 4B) that prevent contact between the sensing part 21 and an object such as aggregate K of a predetermined size or larger. This makes it possible to prevent a situation in which correct dielectric measurement cannot be performed due to contact between the concrete aggregate K and the sensing part 21.

[0058] The embodiments of the present invention have been described above in detail with reference to the drawings, but the specific configuration is not limited to this embodiment, and design changes that do not deviate from the gist of the present invention are included in the present invention.

[0059] For example, in the above embodiment, concrete was used as an example of a cement hardened body, but this is not limited to this, and the present invention can also be applied to estimating the condition of an improved body in ground improvement work in which cement-based solidification material is mixed with ground or soil and sand. [Explanation of symbols]

[0060] 1: Dielectric measurement device 2: Sensor 21: Sensing part 3: Measuring equipment 4A: Cylindrical guard (protective part) 4B: Mesh guard (protective part) M: Concrete structure (hardened cement) K: Aggregate (objects larger than a specified size)

Claims

1. A method for estimating the state of a hardened cement body for determining the degree of hydration progress of the hardened cement body and whether an appropriate wet state has been maintained, comprising: a step of placing a sensor capable of dielectric measurement so as to be in contact with the inside of the hardened cement body; a step of measuring the dielectric constant of the hardened cement body using the sensor after a given time has elapsed; and estimating a degree of hydration or a hydration rate indicating a degree of progress of hydration of the hardened cement body based on the result of the dielectric measurement, a dielectric index based on a relaxation time of the dielectric relaxation of the bound water, which is determined by observing the frequency dependence of the complex dielectric constant obtained by the dielectric measurement;

2. 2. The method for estimating the state of a hardened cement body according to claim 1, further comprising a step of determining an end time for curing the hardened cement body based on the estimated degree of hydration or hydration rate.

3. 3. The method for estimating the state of a hardened cement body according to claim 1, wherein the hardened cement body is concrete, and the sensor is placed in advance at a position where the concrete will be filled, and then the concrete is filled.

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