JPH025217B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for constructing high-strength mass concrete, and more specifically, to properly arrange cooling water pipes within the mass concrete frame and to apply the unsteady transmission. Thermal cooling effect stops the temperature increase due to cement hydration reaction within the mass concrete structure to an appropriate temperature, prevents cracks from occurring in the mass concrete, allows mass concrete to be poured all at once, and eliminates defects. Concerning a method of constructing high-strength mass concrete.

[Conventional technology]

Conventionally, when constructing slab-like mass concrete several meters thick, it has been common to place the concrete in several layers of appropriate thickness. In this case, cracks often occur in the concrete of the top floor lift, and it is well known that cracks are caused by tensile strain caused by temperature distribution due to the heat of hydration reaction of cement after concrete is placed. The occurrence of such cracks is completely undesirable in, for example, load-bearing walls of large-scale vibrator for testing earthquake-resistant structures and their connecting parts.

As a measure to prevent concrete cracks,
For example, in dam concrete, measures such as installing cooling water pipes inside the mass concrete structure to cool the inside of the mass concrete, adjust the temperature of the concrete, and prevent the occurrence of defects in the concrete require a long-term maintenance period of several years. As a measure to cope with temperature changes,
This is done by pipe cooling. Pipe cooling in such dams accommodates long-term dam temperatures, such as several years.

However, there has not been an appropriate method for preventing the occurrence of cracks by appropriately adjusting the temperature rise during a short period of time (about 2 to 3 days), such as in high-strength prestressed mass concrete, for example.

[Problem that the invention seeks to solve]

The present invention aims to completely eliminate the occurrence of defects due to an increase in the hydration temperature of concrete during several days after placing mass concrete. In such cases: (1) The adiabatic temperature rise of concrete is approximately proportional to the unit amount of cement, and becomes a large value for high-strength concrete.

(2) For prestressed concrete slabs,
Arranging a large number of PC sheaths limits the arrangement of cooling water pipes. In particular, the conventional staggered arrangement of cooling water pipes has been difficult, making it difficult to properly predict the cooling effect.

As a result of various studies to overcome the above-mentioned situation, the present inventors have analyzed the short-term temperature rise of high-strength mass concrete and its cooling effect using unsteady heat transfer cooling theory. As a result of comparing the temperature measurement results in actual mass concrete, it was found that theory and reality match with extremely high accuracy.

The present invention aims to provide a novel method for constructing high-strength mass concrete using cooling conditions that allow such high-quality, high-strength mass concrete to be constructed properly, reliably, and with high reliability. It is.

[Means to solve problems]

Based on the above findings, for example, even when cooling water pipes are installed within a mass concrete structure in which a large number of PC sheaths are arranged without being restricted by the arrangement of PC sheaths,
It has become possible to accurately predict the temperature rise in various parts of concrete. In this case, the PC sheath can also be used as a cooling water pipe if necessary. In this way, defect-free mass concrete can be constructed by pouring thick prestressed mass concrete slabs at once while cooling the mass concrete so that the strain due to temperature rise is less than the tensile limit strain of the concrete. I have perfected the method.

This method consists of the following steps (a) to (d).

(a) Find the adiabatic temperature rise curve.

This adiabatic temperature rise curve is determined by the following equation (1) based on the type of cement used and the mix of concrete, and is determined according to the design based on the shape of the high-strength mass concrete to be constructed, the required strength, etc. It is.

T=K(1-e ^- 〓 ^t )...(1) Where, T: Adiabatic temperature rise (℃) K and α: Constants determined by the type of cement, amount of cement, and temperature at the time of concrete placement e : Base of natural logarithm t: Material age (days) (b) Next, give the concrete placement temperature and the adiabatic temperature rise curve as initial conditions, and the cooling water pipe arrangement, cooling water conditions, and concrete thermal properties as boundary conditions. give. That is, we assume the type of cement used, concrete mix, concrete thickness, pouring temperature, amount of cooling water, and the spacing, diameter, length, etc. of cooling water pipes that are not hindered by the PC sheath arrangement. Unsteady heat transfer equation due to cooling water, 1/a ∂T/∂t=∂ ² T/∂r ² +1/r ∂T/∂r…
(2) However, a: Thermal diffusivity (m ² /h) = λ/ρC λ: Thermal conductivity (Kcal/mh℃) ρ: Specific weight Kg/m ³ C: Specific heat Kcal/Kg・℃ r: Cooling The radius (m) from the center of the water pipe is solved under the above initial conditions and boundary conditions to determine the temperature at each age of each part in the concrete.

This will be explained more specifically. When considering one section perpendicular to the cooling water pipes in concrete, the temperature at the point farthest from each adjacent cooling water pipe in the center of the concrete is naturally the highest.

The area to be cooled by one cooling water pipe within this cross section is the area obtained by dividing the total cross section of the concrete by the number of cooling water pipes in that cross section. Now, replace this area with a circle and consider the radius r from the center of the cooling water pipe. At this time, the position of the maximum value of radius r can be treated as the point with the highest temperature within the concrete. The temperature inside the concrete is in an unsteady state and changes with the passage of time, so using the unsteady heat transfer equation (2) above, a computer successively calculates the temperature change at a position of an arbitrary radius r over time. do. Through this calculation, it is possible to calculate the temporal change in temperature at an arbitrary radial position from the center of the cooling water pipe within the cooling area to be shared by one cooling water pipe. Similar calculations are performed for each section in the concrete along the length of the cooling water pipe.

In this case, the maximum value of the radius r of the cooling area to be shared by one cooling water pipe is determined by the arrangement interval of the cooling water pipes, the minimum value of r is determined by the diameter of the cooling water pipe, and the inlet temperature of the cooling water, The temperature rise of the cooling water itself is determined by the amount of heat taken by the cooling water from the cooling water flow rate, and the heat transfer due to the temperature of the cooling water is calculated sequentially, making it possible to determine the temperature of each part of each material in the concrete.

In this way, temperature changes within concrete can be accurately predicted.

Figure 6 shows an example of the estimated value E of the temperature curve at each material age at the point farthest from the cooling pipe in the central section of mass concrete where the temperature rise is greatest, and its value when cooling is performed under different conditions according to the present invention. An example is shown for the estimated value D and the actual measured value F of the temperature at a point.

(c) The combination of strain ε ₁ due to internal restraint based on the difference between the concrete surface temperature and concrete internal temperature and ε ₂ due to external restraint determined from the average temperature Tm in the concrete cross section exceeds the tensile limit strain εcr of concrete. Determine the estimated value of the temperature change inside the concrete with an appropriate concrete temperature upper limit Tcr so that it does not occur.

(d) Determine the cooling water pipe spacing, diameter, and length that meet this condition.

(e) While adjusting the amount of cooling water to meet the above conditions, pour mass concrete all at once without dividing it into lifts. In this case, it goes without saying that fine adjustments may be made in response to changes in construction environmental conditions, such as outside air temperature and cooling water temperature.

[Effect]

In order to ensure high strength and prevent the occurrence of cracks, the composite of the strain ε ₁ due to internal restraint and the strain ε ₂ due to external restraint determined by the shape and dimensions of the high-strength concrete is the tensile strength of the concrete. It is necessary that the critical strain εcr not be exceeded. For this reason, it is necessary to appropriately determine the temperature rise within the concrete.

FIG. 1 illustrates the change in temperature within concrete over time after concrete is poured. Curve A shows the adiabatic temperature rise.

Figure 2 shows the temperature distribution at a certain point in the concrete between the cooling water pipe 7 and the adjacent cooling water pipe 8, and Figure 3a shows a partial cross section of the prestressed mass concrete slab 1. 2 indicates the upper surface, 3 indicates the lower surface, 4 indicates the cooling water pipe, and FIG.
The distribution of concrete internal temperature T up to T ₂ and T ₃ are the upper and lower surface temperatures, respectively, and Ti
is the maximum temperature within the concrete, and Tm is the average temperature within the concrete cross section.

When the difference between Ti and Tm is θ and the coefficient of thermal expansion is β, the tensile strain ε ₁ due to internal restraint is calculated as ε ₁ = β・θ, and the strain due to external restraint ε ₂ = βkTm (k
is a coefficient representing the degree of restraint). When the temperature drops, the maximum temperature in the concrete at which the composite tensile strain of ε ₁ and ε ₂ becomes equal to the tensile limit strain εcr of the concrete.
Let Ti be the upper temperature limit Tcr. The maximum temperature inside the concrete is determined so that the temperature inside the concrete does not exceed this Tcr.

For example, the amount of unsteady heat removed by the unsteady heat transfer calculation using equation (2) above becomes the temperature drop in the shaded area C in Figure 1, and the maximum temperature does not exceed Tcr, for example, the curve B is the estimated value curve that should suppress the temperature rise.

In this way, when the arrangement spacing of the cooling water pipes that limit the concrete temperature is obstructed by the PC sheath arrangement, the PC sheath can also be used as the cooling water pipe.

Further, the cooling water pipe circuit may be arranged in series or parallel as appropriate, the water flow direction of adjacent pipes may be reversed, or the arrangement pitch may be changed as desired.

The cooling water is preferably kept at a constant temperature using a cooling tower, but if ground water or the like is available, it may be used. In addition, the amount of cooling water, the cooling part,
It is also possible to increase or decrease the amount depending on the elapsed time, etc. For example, it is preferable to control the cooling water using a thermometer buried at a key point within the concrete structure for temperature measurement and monitoring.

By the method of the present invention, high-strength mass concrete can be constructed without producing defects such as cracks, and construction can be performed with high reliability.

In addition, although the above explanation took the slab as an example, it is of course applicable to the construction of large concrete containers and other high-strength prestressed mass concrete.

〔Example〕

Top slab 5 (l=
23 m, w = 10 m, h = 3.5 m) was constructed using the method of the present invention.

The strength of the concrete is 400Kg/cm ² , the unit cement amount is 300Kg/m ³ , the water-cement ratio is 47%, the aggregate used is S/A 42%, and the coarse aggregate is 25mm gravel from Kinugawa, and the fine aggregate is We used sand from Kashima. Under these conditions, k and α in the above equation (1) were determined by the least squares method from the adiabatic temperature rise curve determined in advance by a test, and k = 40 and α = 0.73.

Next, we used groundwater at 15°C 20/min as the cooling water, set the outside air temperature to 15°C, set the diameter of the cooling water pipes to 25 mm and the length of 10 m using the above conditions, and arranged the pipes.
Temperature changes between the cooling water pipes at the center of the upper slab cross section were calculated using the above-mentioned equation (2) through computer-based numerical calculations for the staggered and checkerboard shapes with pitches of 600 mm and 800 mm, respectively. An example of this temperature transition curve is shown in FIG. In the case of a grid pattern with a pitch of 600 mm, the curve D in Figure 6 is the curve E.
is for a grid array with a pitch of 800 mm. This temperature transition curve is the critical temperature Tcr of the concrete in question.
(Tcr-5 in this example)
A grid pattern arrangement with a pitch of 600 mm was determined as the appropriate cooling water pipe arrangement for the case of curve D where ℃ = 20 ℃). In other words, curve D was used as the estimated value.

FIG. 5 shows a partial view of the slab 5 of FIG. 4,
4 indicates a cooling water pipe, and 6 indicates a PC sheath.

Figure 6 shows the actual measured value F of the change in internal temperature of the concrete from concrete pouring to the 5th day of age. As is clear from Figure 6, the measured value F agrees well with the estimated value D, and the concrete temperature rise is 20°C.
It was possible to obtain concrete with the desired strength without defects such as cracks.

〔Effect of the invention〕

According to the present invention, it is possible to reliably control the temperature rise due to the hydration reaction in high-strength mass concrete under optimal conditions that do not cause defects in the concrete, and to obtain excellent high-strength mass concrete having desired strength. It became possible.

Therefore, it is completely possible to construct mass concrete, which requires high strength, defect-free, and high reliability, such as in earthquake-resistant structure testing equipment, and the present invention will greatly contribute to this field.

[Brief explanation of drawings]

Figure 1 is a graph illustrating the age and temperature rise of concrete. A is the adiabatic temperature curve, B is the temperature curve inside the concrete when water-cooled, and Figure 2 is the graph of the concrete temperature between two cooling water pipes in the concrete. Graph showing temperature distribution, Figure 3a is a partial cross-sectional view of mass concrete, Figure b is a graph showing its temperature distribution, Figure 4 is a perspective view of mass concrete of an example in which the present invention was implemented, Figure 5 is a partial cross-sectional view of mass concrete. FIG. 6 is a diagram showing the arrangement of the cooling water pipe and the PC sheath in the example, and is a graph showing the change in the temperature inside the concrete in the example of the present invention. 1...Mass concrete, 2...Top surface, 3...
...Bottom surface, 4...Cooling water pipe, 5...Slab, 6...
...PC sheath, 7, 8...Cooling pipe, w, l, h...
...Dimensions of concrete in the example.

Claims (1)

[Claims] 1. When constructing high-strength mass concrete, the adiabatic temperature rise curve of concrete is determined from the type of cement used, the mix of concrete, and the concrete temperature at the time of concrete placement using the following formula (1), Given the conditions of concrete thickness and length, casting temperature, cooling water amount, cooling water temperature, and outside air temperature, and assuming the cooling water pipe installation interval, diameter, and length, Calculate the amount of temperature drop from the adiabatic rise temperature in each material age of each part, and based on the calculation, determine the estimated value of temperature change in the concrete at which the tensile strain due to temperature of the mass concrete becomes less than the tensile limit strain. , install cooling water pipes in the mass concrete structure that match the installation spacing, diameter, and length assumed as the basis for calculation of the estimated value, and once cool the mass concrete while passing cooling water through the cooling pipes. A method for constructing high-strength mass concrete, which is characterized by pouring concrete into concrete. T=K(1−e ^- 〓 ^t ) …(1) 1/a ∂T/∂t=∂ ² T/∂r ² +1/r ∂T/∂r…
(2) Where, T: Adiabatic temperature rise (℃) K and α: Constants determined by the type of cement, amount of cement, and temperature at the time of concrete placement e: Base of natural logarithm t: Age of material (days) a : Thermal diffusivity (m ² /h) = λ/ρC λ: Thermal conductivity (Kcal/mh℃) r: Radius from the center of the cooling water pipe (m)