JP2020106377A - Concrete heating characteristic testing method - Google Patents

Abstract

To more quickly and simply acquire a plurality of concrete heating characteristics having different implantation temperatures.SOLUTION: First and second containers 11, 12 are filled with concrete of the same composition, at least one of the first container 11 and the second container 12 filled with the concrete is heated or cooled, and the concrete with which the first and second containers 11, 12 are filled is adjusted to temperatures different from each other. After adjusting the concrete temperatures, the first container 11 is housed in a first heat insulating container 31 having a lower heat transfer coefficient than the first container 11, and the second container 12 is housed in a second heat insulating container 32 having a lower heat transfer rate than the second container 12. A heating characteristic due to a hydration reaction of the concrete 1 with which the first container 11 is filled is measured with the first container 11 housed in the first heat insulating container 31, and a heating characteristic due to a hydration reaction of the concrete 2 with which the second container 12 is filled is measured with the second container 12 housed in the second heat insulating container 32.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for testing heat generation characteristics of concrete.

In the construction of mass concrete structures, temperature crack analysis is performed in advance for temperature cracks caused by the heat of hydration of cement. In the thermal stress analysis, the heat generation rate of concrete is used as input data. According to the Japan Society of Civil Engineers Concrete Standard Specification (established in 2012), "In principle, the heat generation rate of concrete used for temperature analysis of concrete should be modeled in consideration of age and concrete temperature that varies from place to place. It will be done." Therefore, the heat generation rate is obtained as a function of temperature, and this function is also called a temperature-dependent hydration heat generation rate equation. In order to calculate the temperature-dependent hydration heat generation rate equation, it is necessary to perform an adiabatic temperature rise test on at least two types of concrete having different temperature histories and obtain the heat generation characteristics of the concrete. For this reason, generally, an adiabatic temperature rise test is conducted on concretes having the same composition but different driving temperatures, and the heat generation characteristics of the concrete are obtained from the results.

Patent Document 1 discloses a test method for obtaining heat generation characteristics of concrete. A test tank filled with concrete is housed inside a storage container equipped with a heater. The temperature of the concrete filled in the test tank and the containment vessel is measured with a thermometer. When the temperature of the concrete rises as the hydration reaction of the concrete progresses, the heater operates so that the temperature of the containment vessel follows the temperature of the concrete. As a result, the concrete is kept in an adiabatic state, and the adiabatic temperature rise amount is obtained.

JP 62-116244A

When the adiabatic temperature rise test is performed by the method described in Patent Document 1, only one type of test body can obtain the adiabatic temperature rise amount in one test. This is because concrete having different driving temperatures has different heat generation characteristics and different temperature rise patterns, and thus it is not possible to simultaneously maintain a heat insulating state for a plurality of test bodies. Therefore, when performing an adiabatic temperature rise test for a plurality of concretes having different driving temperatures, it is necessary to perform the test as many as the number of test bodies, which is a constraint for prompt data acquisition.

It is an object of the present invention to provide a heat generation characteristic test method for concrete that can more rapidly obtain heat generation characteristics of concretes having different driving temperatures.

The exothermic property test method for concrete of the present invention is to fill the first and second containers with concrete of the same composition, and heat at least one of the first container and the second container filled with concrete. Alternatively, the concrete filled in the first and second containers is cooled and adjusted to different temperatures, and after the temperature of the concrete is adjusted, the heat transfer coefficient of the first container is lower than that of the first container. A state in which the first container is accommodated in the first heat retaining container, the second container is accommodated in the second heat retaining container having a lower heat transfer coefficient than the second container, and the first container is accommodated in the first heat retaining container. Then, the exothermic characteristic of the concrete filled in the first container due to the hydration reaction is measured, and the water of the concrete filled in the second container is stored in the state where the second container is accommodated in the second heat insulating container. Measuring exothermic properties due to the sum reaction.

According to the present invention, the concrete filled in the first and second containers is heated by heating or cooling at least one of the first container and the second container before measuring the heat generation characteristics of the concrete. The temperature is adjusted to be different from each other. This simulates multiple concretes with different driving temperatures. Since the first and second containers are housed in the first and second heat insulating containers, respectively, it is possible to measure the heat generation characteristics of the concrete filled in the first and second containers in parallel. Therefore, according to the heat generation characteristic test method for concrete of the present invention, heat generation characteristics of a plurality of concretes having different driving temperatures can be obtained more quickly.

It is a schematic flow diagram of a heat generation characteristic test method for concrete and a method for estimating a temperature-dependent hydration heat generation rate equation of the present invention. It is a perspective view and a sectional view of a 1st container. It is a side view and a sectional view of the 1st heat retention container. It is an explanatory view showing how to obtain a temperature-dependent hydration exothermic rate formula. log H _∞ and (Q) is a graph showing an example of measurement of -E (Q) / R.

An embodiment of a method for testing heat generation characteristics of concrete according to the present invention and a method for estimating a temperature-dependent hydration heat generation rate equation using the results will be described below with reference to the drawings. FIG. 1 shows a schematic flow of a heat generation characteristic test method for concrete and a temperature-dependent hydration heat generation rate estimation method according to an embodiment of the present invention. INDUSTRIAL APPLICABILITY The present invention can be applied to any concrete, but can be suitably applied to a concrete used for a mass concrete structure, in particular, a mass concrete structure for which a temperature stress analysis with respect to a temperature crack is required by the concrete standard specification.

(1) Step 1 (S1)
First, concrete is prepared with a predetermined composition. It is desirable that the concrete has the same composition as the concrete used for the concrete structure to be constructed, that is, the same cement, aggregate, admixture, water-cement ratio, fine aggregate ratio, slump, air amount, etc.

(2) Step 2 (S2)
Next, the created concrete is filled in the first to third containers 11 to 13. The reason will be described later. Concrete is filled into the first to third containers 11 to 13 in substantially the same amount. Since the first to third containers 11 to 13 have the same shape and size and are made of the same material, the following description will be made on the first container 11. 2A is a perspective view of the first container 11, and FIG. 2B is a cross-sectional view taken along the line AA of FIG. 2A. The first container 11 is a tin-made cylindrical container having an open top, and has a function not only as a container for housing a concrete test body but also as a concrete formwork. The dimensions of the first container 11 are, for example, about 150 mm in diameter and about 300 mm in height. The concretes 1 to 3 with which the first to third containers 11 to 13 are filled are preferably concretes having the same composition, and more preferably concretes of the same batch. The shape of the first to third containers 11 to 13 is not limited to a cylindrical shape, and may be a shape in which a cross section perpendicular to the vertical centerline is a polygon such as a square.

Heat flow sensors HS1 to HS3 are installed on the outer surface of the first container 11. The heat flow sensors HS1 to HS3 measure a heat quantity density of heat radiated in a direction orthogonal to the heat radiation surface, that is, the outer surface of the first container 11. The heat flow sensors HS1 to HS3 are attached to the outer surface of the first container 11 by a heat conductive double-sided tape. The heat flow sensor may be provided at only one place, but it is preferable to provide it at a plurality of places. In the present embodiment, the three heat flow sensors HS1 to HS3 are provided at a height where the center position of the heat-sensitive portion coincides with the center position of the first container 11 in the height direction and at 120° intervals in the circumferential direction. By providing the three heat flow sensors HS1 to HS3, when one heat flow sensor shows an abnormal value, it is considered that the heat flow sensor is abnormal, and only the measured values of the remaining two heat flow sensors excluding the heat flow sensor are measured. Can be adopted. The installation position and the number of installed heat flow sensors are not limited to this, and they can be installed on the bottom surface of the first container 11, for example. Alternatively, the upper opening of the first container 11 may be covered with a heat flow sensor. Inside the first container 11, a thermometer T that measures the temperature of concrete is installed. A T-type thermocouple is used as the thermometer T. The thermometer T is fixed to the first container 11 using an aramid rod. The thermometer T is preferably installed at the center of the first container 11 in the radial direction and the center of the height direction. The temperatures of the concretes 1 to 3 are measured immediately after being filled in the first to third containers 11 to 13. At this time, the elapsed time after filling is also measured. Therefore, the temperatures T of the concretes 1 to 3 are obtained as a function of the elapsed time t after filling.

(3) Step 3 (S3)
Next, by heating the first container 11 and cooling the third container 13, the concretes 1 to 3 filled in the first to third containers 11 to 13 are adjusted to temperatures different from each other. The second container 12 is neither heated nor cooled, and is stored at ambient temperature until the heating of the first container 11 and the cooling of the third container 13 are completed. The heating and cooling temperatures are not particularly limited, but it is not preferable to make a too large temperature difference because the heating and cooling to the inside of the concrete is completed before the hydration reaction is started. Further, if the temperature difference is small, the measurement accuracy of the heat generation characteristics of the concrete decreases, so it is preferable that the temperature difference between them is about 5 to 15°C. For example, when the temperature difference is 10° C. and the environmental temperature is 20° C., the temperature of the concrete 1 filled in the first container 11 is 30° C. and the temperature of the concrete 2 filled in the second container 12 is 20° C. The temperature of the concrete 3 filled in the third container 13 can be 10°C. The concrete 1 filled in the first container 11 and the concrete 3 filled in the third container 13 are adjusted so as to have a constant temperature in the respective regions. Usually, the temperature changes in the central portions of the first and third containers 11 and 13 are the slowest. Therefore, the fact that the entire areas of the concrete 1 and 3 are adjusted to a predetermined temperature means that the first and third containers 11 and 13 are adjusted. , 13 can be confirmed from the measurement value of the thermometer T which measures the temperature of the central part. Note that, once the temperature is adjusted to a predetermined temperature, the concrete temperature in the first container 11 is almost uniform. The combination of cooling and heating is not particularly limited as long as the concretes 1 to 3 filled in the first to third containers 11 to 13 are adjusted to have different temperatures. For example, the first container 11 and the second container 12 may be heated and the third container 13 may be cooled, or the first container 11 and the second container 12 may be heated and the third container 13 may be heated. The container 13 may be stored at ambient temperature without being heated or cooled. That is, at least any two of the first to third containers 11 to 13 filled with concrete may be heated or cooled.

The heating of the first container 11 is performed by immersing the first container 11 in hot water having a temperature higher than the ambient temperature, specifically, hot water having the same temperature as the target temperature. For example, when adjusting the temperature of the concrete 1 filled in the first container 11 to 30° C., the temperature of hot water is set to 30° C. The heating method is not limited, but a method of filling water in the water tank 21 and heating the water in the water tank 21 to a predetermined temperature with a throw-in heater (not shown) can be mentioned. At this time, it is preferable to use a throw-in heater having an automatic temperature adjusting function. The cooling of the third container 13 is performed by immersing the third container 13 in cold water whose temperature is lower than the ambient temperature. Although the cooling method is not limited, a method of filling water in the water tank 23 and cooling the water in the water tank 23 to a predetermined temperature by a throw-in cooler (not shown) can be mentioned. For example, when adjusting the temperature of the concrete 3 filled in the third container 13 to 10° C., the temperature of cold water is set to 10° C. A pump (not shown) for circulating water may be provided inside the water tank 23 to prevent freezing of cold water due to local supercooling. Thus, the heating of the first container 11 and the cooling of the third container 13 are performed by immersing each container in water having a temperature different from the environmental temperature. Although heating and cooling with water is the most convenient and suitable for work at the site, it is also possible to put the container in a constant temperature bath for heating and cooling.

(4) Step 4 (S4)
The first to third containers 11 to 13 whose concrete temperatures have been adjusted as described above are housed in the first to third heat retaining containers 31 to 33, respectively. Since the first to third heat insulation containers 31 to 33 have the same shape and size and are made of the same material, the following description will be made on the first heat insulation container 31. 3A is a side view of the first heat insulation container 31, and FIG. 3B is a cross-sectional view taken along the line AA of FIG. 3A. The first heat insulation container 31 is a hollow container made of expanded polystyrene. Specifically, a cylindrical hole 315 penetrating the radial center region 314 is drilled in the styrofoam block having a cylindrical shape. Next, the styrofoam block having the holes 315 is inverted, the hollowed cylindrical portion is divided into three in the length direction, and the lower portion 312B of the divided three cylindrical portions is returned to the original position. Next, the styrofoam block is inverted again, and the first container 11 is inserted into the hole 315 through the opening opposite to the portion 312B of the hole 315. Next, the upper portion 312A of the three-divided cylindrical portion is returned to its original position. Therefore, the first heat insulating container 31 has a body portion 311 provided with a hole 315 penetrating the central region 314 and a hole 315 such that the center portion in the longitudinal direction of the hole 315 serves as the accommodation space 313 of the first container 11. It is composed of a pair of lids 312A and 312B for closing both ends of the. It is preferable that the diameter of the accommodation space 313 is larger than the diameter of the first container 11 by about 10 to 20 mm, and the vertical height of the accommodation space 313 is larger than the vertical height of the first container 11 by about 20 to 30 mm. .. The vertical centerline of the storage space 313 coincides with the vertical centerline of the first heat retaining container 31, and the vertical centerline of the storage space 313 is the first centerline so that the heat retention performance can be obtained as uniformly as possible in all directions. It is preferable that the position is aligned with the vertical center position of the heat insulating container 31. The material of the first heat insulating container 31 is not limited as long as it has a lower heat transfer coefficient than that of the first container 11, and a material having a certain heat insulating performance such as glass wool, rock wool or urethane can be used.

The first to third containers 11 to 13 are housed in the first to third heat retaining containers 31 to 33 before the hydration reaction is started. When the diameter of the first container 11 is about 150 mm and the height is about 300 mm, the time required for heating and cooling with a temperature difference of 10° C. under the condition of the outside air temperature of 20° C. is generally 1 to 2 hours. Met. Moreover, the accommodation of the first to third containers 11 to 13 in the first to third heat retaining containers 31 to 33 is completed in a very short time. On the other hand, the temperature of the concrete hardly rises 3 hours after the mixing of the concrete is completed, and it is considered that the hydration reaction of the concrete has not yet started at this point. Therefore, before the hydration reaction is started, the first to third containers 11 to 13 are filled with concrete, adjusted to a predetermined temperature, and the first to third containers 11 to 13 are set to the first to third. A sufficient time margin for accommodating the heat insulation containers 31 to 33 is secured.

(5) Step 5 (S5)
The 1st-3rd containers 11-13 are maintained in the state accommodated in the 1st-3rd heat retention containers 31-33, respectively. During this time, the hydration reaction of the concretes 1 to 3 is started, and the concretes 1 to 3 generate heat. The temperature of the concrete 1 to 3 filled in the first to third containers 11 to 13 is measured by the thermometer T installed in the center of the first to third heat insulating containers 31 to 33. Since the hydration reaction occurs almost uniformly, the temperatures of the concretes 1 to 3 are almost constant over the entire area. Further, the heat flow sensors HS1 to HS3 measure the amount of heat radiation Qd from the first to third containers 11 to 13. The heat radiation amount Qd can be obtained, for example, as an average value of heat flow densities (heat amounts that cross a unit area in a unit time) measured by the heat flow sensors HS1 to HS3×surface area of the containers 11 to 13×time. If necessary, the outside temperature is also measured.

(6) Step 6 (S6)
Next, the temperature-dependent hydration exothermic rate equation is estimated using the measured values obtained in the above steps.

The temperature-dependent hydration exothermic rate equation can be expressed as follows.

here,
H : Heat rate of hydration of cement per unit weight Q: Cumulative heat value of cement per unit weight
H _∞ (Q): Critical hydration heat generation rate (Q)
-E(Q)/R: Temperature activity of cement log H _∞ (Q) and -E(Q)/R are obtained from measured values. The specific procedure is as follows.

First, from the test results, the elapsed time t from filling the first to third concrete 1 to 3 into the first to third containers 11 to 13 and the first to third concrete 1 to 3 respectively. The relationship with the temperature rise value ΔT is obtained (FIG. 4(a)). The temperature rise value ΔT is a difference from the concrete temperature adjusted in step 3. For example, when the temperature of the first concrete 1 is adjusted to 30° C., the temperature increase value ΔT of the first concrete 1 is obtained as an increment with respect to 30° C. The three graphs in the figure show the relationship between the elapsed time t and the temperature rise value ΔT for the first to third concretes 1-3.

Next, the relationship between the elapsed time t and the integrated heat generation amount Q is obtained from the temperature increase value ΔT and the heat radiation amount Qd (FIG. 4(b)). The cumulative calorific value Q is obtained from the following equation.
Q=cρΔT/C ^* +Qd/C ^* /V (Equation 2)
here,
c: Specific heat of concrete ρ: Density of concrete C ^* : Unit amount of cement V: Volume of containers 11 to 13 Since the first to third heat insulating containers 31 to 33 are not completely heat insulating containers, some heat is radiated. Therefore, the actual integrated heat generation amount Q can be estimated by correcting cρΔT/C ^* with Qd (by adding Qd to cρΔT/C ^* ).

Next, the relationship between the elapsed time t and the heat generation rate H is obtained from the temperature increase value ΔT and the heat radiation amount Qd (FIG. 4(c)). The heat generation rate H is obtained from the following equation.

Next, the relationship between the integrated heat generation amount Q and the heat generation rate H is obtained from FIGS. 4(b) and 4(c) (FIG. 4(d)). At this time, temperatures T1 to T3 of the first to third concretes 1 to 3 with respect to the respective cumulative heat generation amounts Q1, Q2,... Are calculated from FIGS. 4(a) and 4(b).

Next, the relationship between the temperatures T1 to T3 obtained in FIG. 4D and the heat generation rate H is obtained (FIG. 4E). The temperatures T1 to T3 are treated as absolute temperatures. In FIG. 4E, the horizontal axis represents the reciprocal of absolute temperature (1/T), and the vertical axis represents the logarithm log( H ) of the heat generation rate H. Log( H ) at 1/T1, 1/T2, 1/T3 is plotted against a plurality of integrated heat generation amounts Q1, Q2,... And log( H ) for each integrated heat generation amount Q1, Q2,. Find the regression line of. The slope of the regression line thus obtained is −E/R, and the intersection with the vertical axis is log H _∞ .

This shows that it is necessary to use at least two concretes having different driving temperatures in order to calculate log H _∞ (Q) and −E(Q)/R. This is the reason for filling concrete into a plurality of containers in step 2 (S2). As the number of concretes with different driving temperatures increases, the number of plots in FIG. 4(e) increases, so that the accuracy of calculating the regression line increases. In this embodiment, in order to ensure the accuracy of calculation of the regression line, three concretes 1 to 3 having different driving temperatures are used.

Next, the effect of this embodiment will be described. As described above, in order to obtain log H _∞ (Q) and −E(Q)/R, it is necessary to perform an adiabatic temperature rise test using at least two types of concrete having different driving temperatures. Further, as the number of concretes having different driving temperatures increases, the calculation accuracy of log H _∞ (Q) and −E(Q)/R improves. As a conventional method of obtaining the cumulative heat generation amount Q, as described in the background art, for example, a method of operating a heater so that the temperature of the storage container follows the temperature of the concrete and keeping the concrete in a heat insulating state is known. There is. However, as described above, this method can test only one test body at a time, and in order to obtain the cumulative heat generation amount of a plurality of test bodies having different driving temperatures, it is necessary to perform the test by the number of types of test bodies. is there. In addition, since this method can perform measurement while keeping the heat insulation state, the measurement accuracy is high, but the apparatus is large and expensive. Therefore, it is suitable for use in testing institutions and research laboratories, but not suitable for use in ready-mixed concrete plants and fields. On the other hand, according to the present embodiment, the concrete of the same composition is divided and filled in a plurality of containers, and then the temperature is adjusted by cooling or heating, whereby the concrete prepared at different driving temperatures is prepared. It is a simple simulation. Cooling and heating can be performed at the same time by using different water tanks, and the temperature can be measured at the same time for a plurality of test bodies, so that the measurement can be performed more quickly than before. Moreover, even if the number of test bodies increases, it can be dealt with by increasing the number of containers, so that it is easy to improve the measurement accuracy. The equipment used is a container, a polystyrene foam insulation container, a water tank for heating and cooling, which can be procured inexpensively and easily, and does not require a large installation space. Furthermore, in the conventional method, it is necessary to create concrete each time when testing a plurality of test bodies having different driving temperatures, but in the present embodiment, the same batch of concrete can be used. It is also advantageous in terms of identity.

Further, in this embodiment, since the heat flow sensors HS1 to HS3 are used to measure the heat radiation amount Qd, the heat radiation amount Qd can be easily measured. For example, in order to obtain the heat radiation amount Qd, it is possible to measure the heat transfer coefficient of the heat insulation container after putting the test body in the heat insulation container of styrofoam and conducting the test. Specifically, after the test of the test body is finished, the test body is once taken out from the heat-retaining container, heated to a high temperature (for example, 80° C.), returned to the heat-retaining container, and then placed in a constant temperature bath (for example, 20° C.), The heat radiation amount Qd can be obtained by measuring the temperature drop amount of the test body. However, this method is not only time-consuming and requires a constant temperature bath, and is not suitable for on-site work. Furthermore, in this method, the calculation accuracy of log H _∞ (Q) and −E(Q)/R tends to vary depending on the type of concrete. FIG. 5 shows the relationship between Q and −E/R and the relationship between Q and log H _∞ . Fig. 5(a) shows -E/R when using early strength Portland cement, Fig. 5(b) shows -E/R when using normal Portland cement, and Fig. 5(c) shows blast furnace cement B. -E/R when using seeds, FIG. 5(d) shows log H _∞ when using early-strength Portland cement, and FIG. 5 (e) shows log H _∞ when using ordinary Portland cement. FIG. 5( f) shows an example of log H _∞ when blast furnace cement type B is used. The "heat flow density" in the figure is the case where the heat radiation amount Qd is calculated by the heat flow density measured by the heat flow sensor of the present embodiment, and the "heat conductivity" is the heat transfer coefficient of the heat insulation container obtained by the above-mentioned method. The case where the heat radiation amount Qd is calculated is shown. -E/R and log H _∞ in the case of using early strength Portland cement (Figs. 5(a) and 5(d)) are relatively in agreement with each other, but in the case of using normal Portland cement (Fig. 5). Differences occur in (b) and (e), and the difference further expands when blast furnace cement type B is used (FIGS. 5(c) and (f)). Since the method using the heat flow sensors HS1 to HS3 uses the heat flow density, the measurement accuracy of the heat radiation amount Qd is high.

1-3 Concrete 11-13 First-third container 21,23 Water tank 31-33 First-third heat insulation container HS1-HS3 Heat flow sensor T Thermometer

Claims (8)

Filling the first and second containers with concrete of the same mix;
Heating or cooling at least one of the first container and the second container filled with the concrete to adjust the concrete filled in the first and second containers to different temperatures; ,
After the temperature of the concrete is adjusted, the first container is housed in a first heat-retaining container having a lower heat transfer coefficient than the first container, and the second container is transferred from the second container by heat transfer. Housing in a second insulation container with a low rate;
In the state where the first container is accommodated in the first heat-retaining container, the exothermic property due to the hydration reaction of the concrete filled in the first container is measured, and the second container is the second container. A method for testing the exothermic characteristic of concrete, comprising: measuring the exothermic characteristic due to a hydration reaction of the concrete filled in the second container in a state of being housed in a heat retaining container. The heat generation characteristic test method for concrete according to claim 1, wherein the heating or cooling is performed by immersing at least one of the first container and the second container in water having a temperature different from an environmental temperature. .. The exothermic characteristic test method for concrete according to claim 1 or 2, wherein the first and second containers are respectively housed in the first and second heat retaining containers before the hydration reaction is started. The heat generation characteristic test method for concrete according to claim 1, wherein the first and second heat insulation containers are made of expanded polystyrene. The first and second heat-retaining containers have a main body part having a hole penetrating a central region, and the hole is formed so that the center part in the longitudinal direction of the hole serves as a storage space for the first and second containers. The heat generation characteristic test method for concrete according to claim 4, comprising a pair of lids that close both ends of the. The heat generation characteristic test method for concrete according to any one of claims 1 to 5, wherein the concrete of the same mixture is the same batch of concrete. A heat flow sensor is installed on the outer surfaces of the first and second containers, the heat flow sensor determines the heat radiation amount from the first and second containers, and the integrated heat generation amount of concrete calculated from the measured heat generation characteristics. The heat generation characteristic test method for concrete according to any one of claims 1 to 6, wherein is corrected by the heat radiation amount. The first and second containers have a cylindrical shape, and three heat flow sensors are provided in each of the first and second containers, and in the three heat flow sensors, the center position of the heat-sensitive portion is the first The heat generation characteristic test method for concrete according to claim 7, wherein the heat generation characteristic test method is provided at 120° intervals in the circumferential direction at a height that coincides with the center position in the height direction of the second container.

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