JPH1081552A - Concrete capable of controlling heat of hydration and crack control of concrete - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress crack development in such concrete as mass concrete which is subject to crack development due to heat of hydration. SOLUTION: This method for suppressing crack development in concrete comprises incorporation of concrete essentially comprising cement, aggregate and water with an encapsulated retarder. The capsule is to melt due to heat of hydration in the concrete. The melting temperature (melting point) of the capsule is so designed as to fall within the temperature range between the higher-temperature portion and lower-temperature portion of the concrete with temperature raised due to hydration reaction therein. Therefore, the capsule does not melt in the lower-temperature portion, melting only in the higher- temperature portion, thus effecting release of the retarder. Since hydration reaction is retarded in the resultant higher-temperature portion, the temperature rise in the portion is suppressed. Therefore, the temperature difference between the higher-temperature and lower-temperature portions is diminished, effecting suppression of crack development.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a hydration heat-controllable concrete and a method for controlling concrete cracking, which can suppress the occurrence of cracks when the temperature may rise or fall due to the heat of hydration of cement. About.

[0002]

2. Description of the Related Art In recent years, as large-scale structures such as high-rise or high-rise buildings, large-scale foundation structures for supporting large spaces, and special structures such as nuclear power plants have become larger, they have been classified as mass concrete. There is an increasing need for the use of concrete. The above-mentioned mass concrete is concrete in which restraint stress acts as the temperature rises or falls due to heat of hydration of cement, and cracks may occur.

In construction, the use of high-strength concrete has been expanding in recent years. However, high-strength concrete with a low water cement ratio has a smaller cross section (unit) as compared with so-called mass concrete used for dams and the like. Even when the amount used is small), the calorific value due to hydration is high, and a problem due to heat of hydration may occur. Conventionally, as a basic concept of the crack control measures in the mass concrete as described above, there are a method of lowering the temperature of the concrete, a method of reducing the generated stress, and a method of increasing the resistance to the crack.

[0004] Concrete methods for lowering the temperature of concrete include pre-cooling for cooling the material with liquid nitrogen gas and mixing ice chips in the kneading, and burying a pipe in a frame to be constructed. Post-cooling, in which cooling water is cooled by passing cooling water, is known.

[0005]

However, the cooling method for cooling the concrete itself as described above requires the installation of a large-scale plant near the site and the need for uniform cooling of the entire system, which makes it difficult to control the temperature. If the temperature is difficult to control and the temperature cannot be controlled to cool the whole uniformly, the temperature difference inside the members and between the members will be rather increased by cooling, which may promote the occurrence of cracks, It is not always an effective technology.

There is also a method in which cracks are generated at planned locations and crack widths generated in other portions are controlled, or a crack-inducing joint is provided to control crack generation. This is not a fundamental measure, but it does not eliminate the cause of the occurrence.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and suppresses a rise in temperature due to heat of hydration only in a portion where the temperature is particularly high when the temperature of the poured concrete rises due to heat of hydration. The present invention provides a hydration heat control concrete and a concrete crack control method capable of reducing the maximum value of the temperature rise due to heat of hydration and reducing the temperature difference in the concrete. It is the purpose.

[0008]

The heat of hydration control concrete according to the present invention is characterized in that concrete containing at least cement, aggregate and water is melted or damaged by heat of hydration. The solution to the above-mentioned problem is that an admixture which is contained in a capsule capable of leaking out the contents and suppresses an increase in temperature due to a hydration reaction is added.

[0009] According to the above configuration, if the temperature of the concrete rises until the capsule melts or is damaged by the hydration reaction of the cement after casting the concrete, the admixture for suppressing the rise in the temperature due to the hydration reaction. Leaks out, and an increase in temperature due to heat of reaction in the hydration reaction is suppressed. Then, the temperature at which the admixture leaks from the capsule is set to a temperature between the temperature of a low-temperature portion such as the surface layer of concrete and the temperature of a high-temperature portion such as the center of the concrete whose temperature has increased due to the hydration heat reaction. By doing
In the low temperature part of the concrete, the admixture does not leak from the capsule, and the hydration reaction of the cement proceeds as it is. In the high temperature part of the concrete, the admixture leaks out of the capsule and the rise in temperature due to the hydration reaction is suppressed. You.

Accordingly, the temperature of the high-temperature portion of the concrete is lower than usual, the temperature difference between the high-temperature portion and the low-temperature portion is reduced, and the internal restraint stress caused by the internal temperature difference can be reduced, thereby suppressing the occurrence of cracks. can do. In addition, by suppressing the temperature rise in the high-temperature portion, the maximum temperature reached by the heat of hydration of the concrete is reduced, which can prevent adverse effects due to the high temperature, for example, the occurrence of residual stress in the reinforcing steel, and reduce the temperature during the temperature drop. The external restraint stress generated by the thermal shrinkage can be reduced.

When a retarder is used as the admixture, after the capsule is heated to a temperature at which the capsule melts or is damaged, the retarder is released from the capsule and the hydration reaction is delayed. Therefore, during the period from the start of the hydration reaction to the temperature at which the capsule is melted or damaged, the hydration reaction proceeds in the same manner as in the case where no retarder was used. Even if a retarder is used as an admixture, the hydration reaction is not significantly delayed, and the hardening and strength development of the concrete structure are not significantly delayed.

[0012] Even when the admixture is used as a retarder, if the temperature at which the capsule is melted or damaged falls within the above-mentioned temperature range, it does not act on the entire concrete on which the retarder is cast, but rather acts on the above-mentioned high-temperature portion. Therefore, the hydration reaction of the entire concrete is not delayed, and the hardening and strength development of the concrete structure are not significantly delayed. Also, if the encapsulated admixture is prepared in advance, it can be used simply by adding it to concrete, so that there is no need to provide a large plant near the site unlike the above-mentioned cooling method.

As described above, by setting the temperature at which the contents leak from the capsule to the above-mentioned temperature range, the hydration heat control concrete itself allows the reaction heat of the hydration reaction only in the high-temperature portion of the concrete. The rise in temperature due to heat is suppressed to reduce the temperature difference in the poured concrete, and the concrete material itself actively controls the heat of hydration.

As the above cement, a known cement can be used. For example, Portland cement (ordinary, early-strength, ultra-high-strength, moderate heat, sulfate resistant, low alkali type), mixed cement (fly ash cement, blast furnace cement, silica cement) and the like can be used. Further, as a special cement, a white cement, an oil well cement, a colloid cement, an alumina cement, a super-hard cement, or the like may be used.

As the above-mentioned aggregate, well-known natural aggregates and artificial aggregates can be used. For example, river sand,
Natural aggregate such as river gravel, mountain sand, mountain gravel, sea sand, sea gravel, natural lightweight fine (coarse) aggregate, crushed stone, crushed sand, artificial lightweight fine (coarse) aggregate, blast furnace slag fine (coarse) bone Artificial aggregates such as materials can be used. In addition, as the admixture, a well-known retarder that can basically suppress a rise in temperature due to the hydration reaction by delaying the hydration reaction can be used.

As the above-mentioned retarder, various well-known ones can be used. For example, an oxycarboxylate, a lignin sulfonate, a saccharide derivative, a fluorosilicic substance, or the like can be used as a reaction retarder or a super reaction retarder. In addition, other than the above-mentioned retarders, any compound capable of delaying the hydration reaction between cement and water can be used as the admixture of the present invention and can suppress an increase in temperature due to the hydration reaction. As long as it is a compound, it does not necessarily need to be a compound that delays the hydration reaction. For example, a compound that dissolves in water or reacts with water to absorb heat may be used as the admixture of the present invention.

Further, the capsule enclosing the admixture must be made of a substance that melts or is damaged by the heat of hydration generated in the poured concrete. Is preferably made of a substance that does not melt or damage in a portion where the temperature rise is relatively low, and melts or damages in a portion where the temperature rise is relatively high such as the center of cast concrete.

That is, the capsule must basically melt at a temperature higher than the air temperature (about 30 ° C.) and lower than the boiling point of water in the concrete (about 100 ° C.). Is preferably one that melts at a temperature between the peak temperature of the low-temperature portion and the peak temperature of the high-temperature portion of the concrete during curing. Further, the capsule does not necessarily need to be completely melted by the heat of hydration, and may be capable of being damaged and leaking out the contents in the above-mentioned temperature range.

Further, when dispersing the capsules in the concrete, if most of the capsules are broken, the admixture (retarder) is dispersed in the whole concrete. It is necessary to have such strength that many of them are not destroyed when dispersed therein. As a substance suitable for such a capsule material, wax (wax substance, fatty acid ester) can be preferably used. However, the substance used as the material of the capsule is not limited to wax, and any compound having the above-described conditions of temperature and strength can be suitably used as the material of the capsule.

As a method of encapsulation, a known method can be used. For example, well-known encapsulation methods include an interfacial polymerization method, an in-situ method, an insolubilization reaction method (curing method in liquid), a coacervation method, a drying method in liquid (interfacial precipitation method), and a spray drying method (spray). Drying method), fluidized bed method (powder bed method) and the like are known, but when the material of the capsule is wax, the spray drying method can be suitably used.

If the above conditions of temperature and strength can be satisfied by the above various encapsulation methods, the above methods other than the spray drying method and methods other than the above methods may be used. Further, at the time of encapsulation, it is possible to adopt a method of impregnating the retardant with a porous medium and then coating the surface of the medium. The porous medium at this time is not particularly limited, and for example, a porous sintered body or the like can be used.

In this case, a submerged drying method can be suitably used in addition to the spray drying method described above. Alternatively, the medium may be taken out after being immersed in the molten wax to form a wax film on the surface of the medium. Further, a wax powder containing a retarder obtained by solidifying the wax in a state in which the retarder or a porous medium in which the retarder has penetrated the molten wax is dispersed, and then pulverizing the solidified wax. The body may be used as the capsule of the present invention.

[0023] The concrete of the present invention may further comprise, in addition to the cement, aggregate, water, and the encapsulated admixture,
If necessary, various well-known admixtures (admixtures) may be added. For example, as an admixture, AE (Air En
training) agent, water reducing agent, AE water reducing agent, high strength water reducing agent,
Superplasticizer, rust inhibitor for reinforced concrete, accelerator, quick setting agent, foaming agent, foaming agent, admixture for pre-back concrete, admixture for underwater concrete, pumping aid, waterproofing agent, drying shrinkage reducing agent, Dust reducing agents, antifreezing agents, admixtures for blocks, heat of hydration inhibitors, water retention agents and the like can be used.

As the admixture, pozzolans such as fly ash and silica fume, blast furnace slag fine powder, expanding material for concrete, siliceous fine powder, admixture for high strength,
Coloring materials, polymers, extenders, reinforcing fibers such as carbon fibers, aramid fibers, and glass fibers can be used. Needless to say, concrete may be a steel material such as a reinforcing bar embedded therein.

According to a second aspect of the present invention, there is provided a method for controlling cracking of concrete, wherein the concrete is melted or damaged by heat of hydration before the concrete is poured, and is encapsulated in a capsule capable of leaking out the contents. The addition of an admixture that suppresses a rise in temperature due to the hydration reaction is a means for solving the above problem. According to the above configuration, it is possible to obtain the same operation and effects as those in the case where the hydration heat control concrete having the configuration described in claim 1 is cast.

The capsule containing the admixture may be added to the concrete at any time before the concrete is cast. The capsule may be added at a stage before kneading cement, aggregate and the like with water. Alternatively, after kneading, the capsules may be dispersed in concrete. Further, as the admixture, those similar to those used in the hydration heat control concrete according to claim 1 can be used.

As the capsule, the same capsule as that used in the hydration heat control concrete according to the first aspect can be used. As the concrete, a well-known concrete (including mortar) is used, except that an encapsulated admixture is added, similarly to the concrete used in the hydration heat control concrete according to claim 1. be able to.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a hydration heat control concrete and a concrete crack control method according to an embodiment of the present invention will be described based on the following experimental examples. In addition, the hydration heat control concrete and the concrete crack control method of the present invention are not limited to the following experimental examples. (Experimental example) The material shown in the following display 1 was used for the hydration heat control concrete of this experimental example.

[Table 1]

Palic K and Palic T are trade names of a water reducing agent and a retarder of FPC Co., Ltd. Palic T is a retarder mainly composed of oxycarboxylate. In addition, in the capsule containing PALIC T, which is an encapsulated retarder, the retarder contains 40% of the total weight of the capsule.

When the retarder was encapsulated, a solution of a retarder mainly composed of an oxycarboxylate was impregnated into a porous silica material, and the surface of the porous material was covered with wax. In this experimental example, a water reducing agent was used as the high-strength concrete to reduce the water-cement ratio.

Then, the mixing of the concrete material is as follows:
The tests were performed at the ratios shown in Table 2 below.

[Table 2] W / C indicates the water-cement ratio, Vagg indicates the volume of the aggregate, and Vpaste indicates the volume of the cement paste. The amount of the retarder was 0.5%.

When the concrete material is kneaded at the above mixing ratio, a cement mixer is used to knead the cement, water, and a water reducing agent for 3 minutes to form a cement paste, and then to the aggregate and the encapsulation. The added retarder was added, and the mixture was kneaded for another 3 minutes and then poured. In addition, a concrete structure to be a test body has a height of 50 cm and a width of 33 c.
m and a thickness of 15 cm.

The test piece was placed in a mold, and its periphery was covered with a heat insulating material on all six surfaces. This is similar to the condition for constructing a relatively large structure with concrete by surrounding the structure with a heat insulating material because the test body itself is small. With these conditions, there is no significant difference in temperature between the surface layer and the central part of the test specimen after the concrete has been poured. , To check whether the encapsulated retarder works.

As an experiment, the temperature of each of the test points T, 2, 3, 4, 5, and 6 of the test piece T shown in FIG. 1 was measured immediately after the concrete was poured. In addition, the temperature measurement was performed using a test piece # 1 containing no retarder as a comparative example,
Specimen # 2 with 0.5% unencapsulated retarder added, and two specimens # 3 and # 4 with about 0.4% encapsulated retarder as experimental example of the present invention And went in.

FIG. 2 shows test pieces # 1 and # 1 as described above.
The measurement results of the temperatures # 2, # 3, and # 4 are shown as graphs.
Note that, as described above, the experiment was performed under the condition that there was no large temperature difference between the surface layer portion and the center portion of the specimen, and FIG. 2 shows the measurement result of the measurement point 3 of the specimen T shown in FIG. It is shown as a representative value. As shown in FIG. 2, the specimens # 3 and # 4 to which the encapsulated retarder was added exhibited a temperature rise of approximately the same slope as the specimen # 1 to which no retarder was added until the temperature reached about 40 ° C. As can be seen, above 40 ° C., the slope of the temperature rise of test specimens # 3 and # 4 to which the encapsulated retarder was added was clearly lower than the slope of the temperature rise of test specimen # 1 to which no retarder was added. ing.

The peak temperatures of the specimens # 3 and # 4 to which the encapsulated retarder was added were lower by about 10 ° C. than those of the specimen # 1 without the retarder. It was confirmed that the temperature increase due to the heat of hydration was suppressed. Also, as described above, at 40 ° C. or higher, the slope of the temperature rise of the test specimens # 3 and # 4 to which the encapsulated retarder was added was clearly smaller than the slope of the temperature rise of the test specimen # 1 to which no delay agent was added. Since the temperature was lowered, it is considered that the wax which became the capsule material started to melt from about 40 ° C., and the retarder was leaking from the capsule.

In the test sample # 2 to which the unencapsulated delaying agent was added, the start of the temperature rise was delayed by more than 20 hours compared to the test sample # 1 in which no delaying agent was added. Shows that the hydration reaction of the cement is greatly delayed by the above method. However, the specimens # 3 and # 4 to which the encapsulated retarder was added had a temperature of 40 as described above.
Until the temperature rises to about ℃, it is not affected by the retarder,
This shows that the start of the hydration reaction is not significantly delayed by the retarder.

Further, as shown in the temperature measurement results of the test piece # 2 to which the unencapsulated retarding agent was added, the retarding agent did not simply delay the rate of temperature rise but increased the onset of the temperature rise. Although the effect of retarding is seen, in the test specimens # 3 and # 4 to which the encapsulated retarding agent is added, the hydration reaction proceeds without being affected by the retarding agent until the temperature rises to some extent. There is no delay in the temperature rise as compared with the test piece # 1 without a retarder.

That is, by encapsulating the retarding agent as described above, the hydration reaction is delayed by using the retarding agent, and the calorific value per time is reduced to give time allowance for heat to escape. Even if the temperature at the peak of the temperature rise is reduced, it is possible to minimize the delay in hardening of the concrete. As described above, in this experiment assuming the high temperature part of the poured concrete,
Because the temperature at the peak can be reduced, in actual concrete, by lowering the temperature of the part that becomes relatively hot due to the heat of hydration, such as the center, the water can be reduced as in the high-temperature part and the concrete surface layer. It is possible to reduce the temperature difference from the low temperature part where the temperature rise due to the sum heat is small.

Therefore, the occurrence of cracks can be suppressed by reducing the restraining stress due to the temperature difference during concrete casting. In addition, by reducing the temperature of the above-mentioned high-temperature portion of the concrete, the maximum value of the temperature rise of the concrete is reduced, so that the adverse effect of the high temperature can be prevented.

[0041]

According to the hydration heat control concrete according to the first aspect of the present invention, after the concrete is cast, when the temperature of the concrete increases due to the hydration reaction of the cement until the capsule melts or is damaged. In addition, the admixture that suppresses the temperature rise due to the hydration reaction leaks out, and the temperature rise due to the heat of the hydration reaction can be suppressed.

The temperature at which the admixture leaks out of the capsule is defined as the difference between the temperature of a low-temperature portion such as the surface layer of concrete and the temperature of a high-temperature portion such as the center of the concrete whose temperature has increased due to the hydration heat reaction. By setting the temperature, the admixture does not leak from the capsule in the low-temperature portion of the concrete, and the hydration reaction of the cement proceeds as it is. In the high-temperature portion of the concrete, the admixture leaks from the capsule and the hydration reaction proceeds. Since the rise in temperature due to is suppressed, the temperature of the high-temperature portion of the concrete becomes lower than usual, the temperature difference between the high-temperature portion and the low-temperature portion decreases, and the internal constraint stress caused by the internal temperature difference can be reduced, The occurrence of cracks can be suppressed.

Further, by suppressing the temperature rise in the high-temperature portion, the maximum temperature reached by the heat of hydration of the concrete is reduced, so that adverse effects due to the high temperature, for example, generation of residual stress in the reinforcing steel can be prevented. External restraint stress generated by heat shrinkage at the time of temperature drop can also be reduced. In addition, when a retarding agent is used as the admixture, the hydration reaction is suppressed by the retarding agent at a stage where the hydration reaction has progressed to some extent, so that the start of the hydration reaction itself is not significantly delayed. By using a retarder, the rise in temperature can be suppressed without greatly delaying the hardening of concrete.

Further, when the retarder is wrapped in a capsule that melts or is damaged in the above-mentioned temperature range, the retarder does not act on the entire cast concrete, but acts only on the above-mentioned high-temperature portion. Therefore, the hydration reaction of the entire concrete is not delayed, and the hardening and strength development of the concrete structure is not significantly delayed, so that the concrete structure can be used even when the construction period is limited. Therefore, even in the construction field where the construction period is short and the construction of the upper floor is performed continuously after the construction of the lower floor, the rise in temperature due to the retardant can be suppressed. Also,
If you prepare the above-mentioned admixture encapsulated in advance,
Since it can be used simply by adding it to concrete, there is no need to provide a large plant near the site unlike the cooling method described above.

According to the concrete crack control method of the second aspect of the present invention, the same effect as the configuration of the first aspect can be obtained.

[Brief description of the drawings]

FIG. 1 is a drawing showing a temperature measurement position of a specimen in an experimental example of a hydration heat control concrete and a concrete crack control method according to an embodiment of the present invention.

FIG. 2 is a graph showing experimental results of the experimental example.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Naohiro Nishiyama 2570-4 Shimotsuruma, Yamato-shi, Kanagawa Prefecture Nishimatsu Construction Co., Ltd.Technical Research Institute (72) Inventor Hanada Minami 1456, Hazama-cho, Hachioji-shi Tokyo

Claims (2)

[Claims] 1. A capsule containing at least cement, aggregate, and water, encapsulated in a capsule capable of melting or being damaged by heat of hydration and allowing the contents to leak out,
A hydration heat control concrete, characterized in that an admixture for suppressing an increase in temperature due to a hydration reaction is added. 2. Prior to casting concrete, the concrete is melted or damaged by the heat of hydration and encapsulated in a capsule capable of leaking out the contents, and is mixed to suppress a rise in temperature due to a hydration reaction. A method for controlling concrete cracking, characterized by adding an agent.