JP3164546B2 - Method for manufacturing PC member by heat insulating curing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for manufacturing a PC member.

[0002]

2. Description of the Related Art In the manufacturing process of PC members, tension is introduced on the next day of concrete casting (age 1) to increase productivity.
(About 5 to 18 hours). In order to secure the strength (compression strength of 35 MPa or more) necessary for introducing tension at this age, steam curing or addition of an accelerator is performed as a means for promoting the development of strength. Here, the accelerator is a kind of admixture for concrete and is used for adjusting the setting and hardening time of cement.

[0003]

However, steam curing requires boiler equipment, a specialized manager and a large amount of energy, increases the production cost, and reduces the long-term performance of concrete for PC members. There was a problem of adverse effects. In addition, the accelerator itself is expensive, and requires special equipment for the addition work. On the other hand, when the temperature of the inside of the PC member manufacturing plant becomes 10 ° C. or less, the compressive strength is 35 MPa or more at the age of 15 to 18 hours. It will be difficult to achieve the goal.

[0004] The present invention has been made to solve the above-mentioned problems of the prior art, and its object is to provide a compressive strength necessary for introducing tension without adding an accelerator and without carrying out steam curing. Is to provide a method for manufacturing a PC member that can secure the PC member within a material age of 15 hours or less.

[0005] Another object of the present invention is to provide an optimum mix of concrete, particularly an optimum unit cement amount, for securing a compressive strength required for introducing tension to PC members within 15 hours of age. It is another object of the present invention to provide a method for manufacturing a PC member that can be obtained from a PC.

[0006]

According to the present invention, concrete containing early-strength Portland cement is poured into a form for a prestressed concrete member (hereinafter referred to as PC member), and the water of the early-strength Portland cement is poured into the mold. In order to prevent the heat loss of Japanese heat, the mold is sealed with a heat insulating member, and the heat of hydration is used for curing to promote the hardening of the concrete, so that the compressive strength required for introducing tension can be reduced. A method for producing a PC member, characterized in that the PC member is obtained within 15 hours, and a compounding strength of concrete capable of obtaining a compressive strength necessary for introducing tension within 15 hours of the age of the material by adiabatic curing, A relationship diagram between the initial temperature of fresh concrete and the unit cement amount of concrete is created in advance, and the flesh mixed experimentally at the concrete manufacturing site for mix design Actually measuring the initial temperature of the shoe concrete, using the relationship diagram between the measured value, to provide a method of manufacturing a PC member characterized by determining a unit cement content of the concrete for the PC member manufacturing.

In the method for manufacturing a PC member of the present invention, a foamed resin member such as styrene foam or urethane foam is employed as the heat insulating member, or a film such as an aluminum vapor-deposited polyester film is formed on both sides of a fiber layer such as glass wool or cotton. A member provided with a layer may be employed.

Further, in the present invention, the early-strength Portland cement is used, the content of the early-strength Portland cement in the concrete is preferably 350 to 650 kg / m ³ , and the content of water is 135 to 175 kg / m ^3.
m ³ is preferred. Further, the concrete temperature at the time of casting is preferably 5 to 40C, particularly preferably 15 to 30C. Furthermore, the mixing strength of concrete (28 days old, standard underwater curing) is 50MPa or more, especially 70M
It is preferably Pa or more.

[0009] Further, the relationship diagram may be any diagram as long as the lower limit value of the unit cement amount of concrete can be determined from the mixing strength of concrete and the initial temperature of fresh concrete. Any two parameters of the lower limit value and the initial temperature of fresh concrete are separately taken on the XY axes, and the remaining 1
A plurality of measured values having the same one parameter are plotted on the XY axis, and a curve or a straight line is drawn, and the relationship diagram may be created so that the number of the curved lines or the straight lines becomes an appropriate number.

[0010]

The present invention will be described in more detail with reference to the following examples.
The present invention is not limited to these.

Early strength Portland cement (specific gravity 3.1
4) 400 kg / m ³ , a polycarboxylic acid-based high-performance AE water reducing agent (trade name “Leobuild SP-8N”, manufactured by NMB Corporation) 6.0 kg / m ³ , fine aggregate (crushed sand, coarse particle ratio 2. 67, surface dry specific gravity 2.64) 871 kg / m ³ , coarse aggregate (crushed stone 2005, coarse particle ratio 6.76, surface dry specific gravity 2.67)
The actual rate of 60.6%) 1074kg / m ^3, water 140kg / m ³
Was mixed to obtain concrete for manufacturing PC members. The mixing strength of the concrete (28 days old, standard water curing) is 70 MPa, the air volume is 2.8%, and the slump is 1
9 cm, and the concrete temperature was 22 ° C.

[0012] In order to examine the rise in temperature due to the heat of hydration of the early-strength Portland cement in the concrete, five test pieces (diameter 100) formed of the concrete were used.
mm, height 200 mm) is formed by a 180 mm thick styrofoam so that the inside is sealed so that the inner dimensions (length x width x height) = 250 mm x 250 mm x 230 mm hexahedral insulation box (insulation for testing) Box). Then, the temperature of the atmosphere inside the heat insulation box, the temperature of the inside and surface of the test piece inside the heat insulation box, the outside air temperature, and the inside temperature of the test piece left in the outside air are measured, and the change over time of these temperatures is plotted. 1 is shown.

In FIG. 1, the temperature of the insulated concrete starts to rise from 5 hours and a half after casting, and 15 hours after casting.
After an hour, the internal temperature of the concrete rose to 60 ° C. or higher. On the other hand, in the test piece which was left in the open air without performing the adiabatic curing, the internal temperature did not reach 30 ° C. or more. From FIG. 1, it was found that an excellent heat insulating effect on the heat of hydration of concrete was obtained inside the closed box formed by the heat insulating material. The rapid rise in the temperature inside the test piece after 5 hours of casting is due to the fact that the hydration reaction of the cement enters an accelerated period and a large amount of heat is released.

In order to manufacture an RC track girder having a length of 7200 mm, a width of 400 mm and a height of 700 mm from the concrete having the above composition, concrete was poured into a formwork.
This mold was covered with a heat insulation box (heat insulation box for a girder) and sealed to form. Here, as the heat insulating box, the inner dimension (length × width × height) = 9100 mm × so that the top surface and the four side surfaces of the formwork can be covered with styrene foam having a thickness of 180 mm.
A pentahedral box having a size of 920 mm × 1000 mm was formed, placed on a mold placed on the floor, and hermetically sealed. Then, a thermocouple is buried in the center and the end of the RC track girder to measure the internal temperature, and a test piece having the same dimensions as above is placed on the side of the RC track girder in the heat insulation box. Then, the internal temperature of the test piece was measured, and the outside air temperature was also measured. Concrete placement 15 at each of these measurement positions
The temperature after the time (during demolding) is shown in FIG.

FIG. 3 shows the compressive strength of the test piece 15 hours after placing concrete. Here, as the test pieces, those left in the open air, those cured in the above-mentioned heat insulation box for test, and those cured in the heat insulation box for girders were used.

In FIG. 3, the test pieces cured in the heat insulation box for the girder show lower compressive strength than the test pieces cured in the heat insulation box for the test, but in all cases, the test pieces are 40MP.
a, and sufficiently satisfied the strength (compression strength of 35 MPa or more) necessary for introducing tension. As shown in FIG. 2, the temperature at the center of the RC track girder rose to 70 ° C., and the end of the RC track girder reached 56 ° C., whereas the internal temperature of the test piece was 49 ° C. was.
Therefore, it can be presumed that the compressive strength at the center and the end of the RC track girder reaches a higher level than the compressive strength of the test piece.

As described above, when manufacturing a PC member,
The heat loss of heat of hydration of cement is prevented by adiabatic curing, and if the heat of hydration can be used as energy for thermal curing, PC members of 15 hours of age can be used without adding a curing accelerator or steam curing. Thus, it is possible to obtain the compressive strength necessary for introducing tension.

Here, the heat value of the hydration reaction of cement is greatly affected by the amount of unit cement, and the heat value of hydration necessary for adiabatic curing is determined by the initial temperature of fresh concrete and the mixing of the concrete (including the mixing strength). Therefore, as a new problem, it is required to determine an optimum unit cement amount. In other words, if the amount of unit cement is small, the amount of heat of hydration necessary for promoting the hardening of concrete becomes insufficient, or a disadvantage that the workability of fresh concrete is reduced occurs.On the other hand, when the amount of unit cement is excessive, In addition to the uneconomical effects, the shrinkage of concrete increases.

Therefore, the present invention proposes a method for simply obtaining the optimum unit cement amount at the concrete manufacturing site in the following. As shown in FIG. 4, when manufacturing the PC member, the design standard strength of the concrete is determined in advance according to the type of the structure, and the strength of the concrete at the age of 15 hours is increased.
It has been found that the compressive strength required for the C member is also approximately 35 MPa or more. Furthermore, the mixing strength of concrete is
The design reference strength is determined by multiplying it by an extra coefficient, and the temporary mixing of the concrete (including the unit cement amount) is determined so as to satisfy the mixing strength. Then, a small batch of concrete is experimentally made based on the temporary mixing of the concrete, comparatively examined while changing the mixing. In the process of studying and modifying this formulation, the unit cement amount is
For example, it can be obtained using a relational diagram as shown in FIG. 5 obtained by an experiment in advance.

Here, the relationship diagram of FIG. 5 shows that the mixing strength of concrete capable of obtaining a compressive strength of 35 MPa or more within 15 hours of age is taken on the X-axis, the lower limit of the unit cement amount is taken on the Y-axis, Each initial temperature of concrete (temperature immediately before concrete is poured) 10 ° C, 20
It is the graph calculated | required about several samples of 30 degreeC and 30 degreeC.

When determining the unit cement amount with reference to FIG. 5, first, the initial temperature of the trial-mixed fresh concrete is actually measured, and the measured value is plotted with the concrete mixing strength. Can be determined. For example, when the concrete mixing strength is 60 MPa and the actual measured value of the initial temperature of the trial-mixed fresh concrete is 25 ° C., it is necessary to determine the concrete mixing so that the unit cement amount is 300 kg / m ³ or more. If the concrete of this composition is cast into a PC member form and heat-insulated, the PC member can be compressed to a concrete strength of 35 MPa within 15 hours without adding an accelerator and without steam curing.
It can be cured up to the above.

FIG. 5 shows a relationship diagram for three types of samples in which the initial temperature of fresh concrete is 10 ° C., 20 ° C., and 30 ° C. The initial temperature of the sample and the number of measurements are appropriately determined. A relation diagram can be obtained. In addition, in the formulation exemplified at the beginning of the present example, a larger amount of cement is used than the lower limit of the unit cement amount obtained from FIG. 5, but this is increased in order to improve workability. Of course, sufficient compressive strength for 15 hours can be obtained with the lower limit of the cement amount in FIG.

[Brief description of the drawings]

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a graph showing a change over time in temperature and the like inside and on a surface of a test piece cured in a test heat insulating box.

FIG. 2 shows the internal temperature of the RC track girder in the heat insulation box at the center and at the end 15 hours after placing concrete.

FIG. 3 shows the compressive strength of a test piece 15 hours after placing concrete.

FIG. 4 is a flowchart schematically showing a procedure for determining a unit cement amount.

FIG. 5 is a graph showing in advance a relationship between concrete mixing strength, a lower limit value of a unit cement amount, and an initial temperature of fresh concrete, which can obtain a compressive strength of 35 MPa or more within 15 hours of material age. .

Claims (1)

(57) [Claims] 1. A concrete containing an early-strength Portland cement is pre-stressed concrete member (hereinafter referred to as P
C), and in order to prevent heat loss due to heat of hydration of the early-strength Portland cement, the form is sealed with a heat insulating member, and the heat of hydration is hardened in concrete. A method for producing a PC member, wherein a compressive strength required for introducing tension is obtained in a PC member within 15 hours of age by using the material for accelerating curing. Create a diagram of the relationship between the concrete mix strength, the initial temperature of fresh concrete, and the unit cement amount of concrete that can obtain the compressive strength necessary to introduce tension within the concrete production site. The initial temperature of the fresh concrete kneaded experimentally in the above is actually measured, and the unit cement amount of the concrete for manufacturing the PC member is determined using the measured value and the relational diagram. P characterized the door
Manufacturing method of C member.