JPS635345B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for constructing concrete in cold weather, and by using an admixture with a specific composition, it can be applied during the initial curing period even under environmental conditions below -5°C, the temperature at which concrete freezes. A particular advantage is provided that the concrete can be constructed without the need for warm or warm curing. When performing so-called cold concrete construction, in which concrete is poured during the cold season, the compressive strength of the poured concrete is sufficient to ensure resistance to frost damage (generally considered to be 30 to 50 kg/cm ² ).
During the initial curing period until reaching the desired temperature, heat curing or heat retention curing is required to prevent frost damage. However, it is not easy to carry out such thermal curing or heating curing at the site where concrete is poured due to the labor and equipment involved, and the energy consumed when carrying out is extremely large. For this reason, with current technology, it is normal to be forced to suspend concrete pouring work during the cold season. This has hindered year-round construction, which has long been desired by the construction industry, and has become a major problem in terms of the overall economic efficiency and construction period. It has been reported that in foreign countries, such as the Soviet Union, attempts are being made to solve the above problems by adding large amounts of chemicals such as calcium chloride to lower the freezing temperature of concrete and promote strength development at low temperatures. However, the use of such so-called antifreeze agents significantly lowers the basic performance of concrete, creating new problems regarding the performance of concrete as a structural material. For this reason, in our country, the use of so-called antifreeze agents has not been adopted when constructing concrete during cold weather. The freezing temperature of concrete is said to be approximately -1 to -2 degrees Celsius, but even with the use of so-called antifreeze agents, the freezing temperature of concrete can be lowered to -1 within a reasonable amount that does not significantly reduce the physical properties of concrete. It cannot be lowered below 5°C. Therefore, even if an antifreeze is used, heat retention or heating cannot be omitted at temperatures below -5°C. The basic performance of concrete here refers to the performance that concrete should have and is the standard for concrete performance evaluation and design. Specifically, it is represented by the compressive strength of the standard curing material ordinance 28 days. It refers to the performance achieved. Some of the above-mentioned antifreeze agents, when used in large quantities, induce abnormal setting of concrete and significantly impair workability, so there are also problems in use in this respect. The purpose of the present invention is to provide an admixture for cold concrete that has a remarkable effect of improving strength at low temperatures without impairing the above-mentioned basic performance of concrete, and does not cause abnormal setting of concrete even when used in large quantities. It was completed as a result of various studies. By using the admixture used in the construction method of the present invention, heating curing can be omitted even at low temperatures of -10°C (-15°C in some cases),
Shows excellent effectiveness even under harsh conditions of repeated freezing and thawing. The present invention comprises: (a) 1 part by weight of a formalin condensate water-soluble salt of an aromatic hydrocarbon sulfonic acid; and (b) a mixture of one or more compounds selected from the group consisting of nitrates, nitrites, and urea.
Using concrete mixed with an admixture of 1 to 20 parts by weight and 2 to 10% by weight based on the weight of cement, the concrete is essentially heat-cured under environmental conditions with an initial curing temperature of -5℃ to -15℃. Another object of the present invention is to provide a cold concrete construction method characterized by curing concrete without heating it. Here, the formalin condensate water-soluble salt of aromatic hydrocarbon sulfonic acid (ARF) refers to naphthalene,
It is a water-soluble salt of a formalin condensate of a polycyclic aromatic hydrocarbon sulfonic acid such as anthracene, and the aromatic hydrocarbon may be one in which an alkyl group has been substituted. It may also be a technical product that is a mixture (eg creosote oil). Furthermore, the above-mentioned nitrates and nitrites refer to water-soluble salts such as ammonium salts, sodium salts, potassium salts, and calcium salts of nitric acid or nitrous acid. The above ARF is known as a cement dispersant or concrete water reducer.
Its practical usage amount (wt% based on cement weight)
In the range of 0.1 to 1%, which is the addition amount shown in , the effect of improving concrete strength at low temperatures is not particularly excellent. Further, although the above-mentioned combined components exhibit a certain strength-enhancing effect at low temperatures, they greatly impair the basic performance of concrete. However, when ARF and the above-mentioned combined components are used in combination within the above-mentioned composition ratio range, the strength-enhancing effect at low temperatures is much greater than the effect expected from the effects of each individual component, indicating a synergistic effect. Moreover, in this case, there is an effect of improving the basic performance of concrete without impairing it. Such effects can be obtained when the composition ratio of ARF and the above-mentioned combined ingredients is 1:1 to 20 (preferably 1:1) by weight.
This is particularly noticeable in the range of 3 to 10). The admixture for cold concrete used in the construction method of the present invention is used in the same manner as general admixtures when mixing concrete.
The appropriate amount to use is in the range of about 2 to 10%, and it is preferable to increase the amount as the daily minimum temperature is lower. %, about 5 to 6% at about -10°C, and about 7 to 10% at about -15°C. Generally, when a large amount is used, it is preferable to select a composition with a large proportion of the above-mentioned combined components. The construction method of the present invention does not prevent concrete from freezing itself. According to the construction method of the present invention, regardless of whether concrete freezes or not, it can be used without heat curing or heat curing. This provides the advantage that concrete of desired strength can be obtained. Concrete to which the construction method of the present invention is applied exhibits good strength when cured at a low temperature for a period of time and then at a curing temperature of 20°C. By applying the construction method of the present invention, the daily maximum temperature is +
5℃, the lowest temperature is -10℃ (-15℃ in some cases)
Even under harsh freeze-thaw conditions,
It is possible to perform concrete construction in the cold without heat curing or heating curing. This makes it possible to save a huge amount of energy that would otherwise be consumed during heating and curing. Furthermore, the present invention has made possible year-round construction, which has traditionally been a desire of the construction industry. The economic benefits brought about by making these things possible, which were previously considered impossible, are enormous. Examples of the present invention are shown below, but the present invention is not limited to these Examples. Example 1 This example shows the effect of the construction method of the present invention at low temperatures. W/c = 50% and S/a = 43% are each constant, slump target value = 15 cm, air amount target value = 4.5
The formulation was determined to be ±0.5%, and kneaded and mixed in a room at about 5°C using a 4-cut tilting mixer. 10cm
A specimen of φ×20cm was molded and heated to -5℃, -10℃, and 20℃.
The samples were cured at each temperature for a specified period of time. After curing, the specimens were placed in a room at 20°C for about 30 minutes before performing the compressive strength test.
I let it sit for a while to thaw. The concrete materials used are as follows. Cement: Onoda ordinary Portland cement Fine aggregate: Kinugawa river sand, specific gravity = 2.62 FM = 2.78 Coarse aggregate: crushed sandstone, MS = 20mm ARF: Naphthalene sulfonic acid formalin condensate sodium salt (abbreviated as NSF) Kao Soap Co., Ltd. Product "Mighty" The results of a test were conducted to compare the case where NSF, combined ingredients, and conventional antifreeze agents (calcium chloride and ethylene glycol) were used separately with the case where the construction method of the present invention was applied. It is shown in Table 1. The test results when the construction method of the present invention was applied are shown in Table 2. (However, the results for -10℃ have been omitted)

[Table] * Abnormal condensation has occurred and the slump has become much smaller than the expected value.
This slump further decreased after 5 minutes and reached almost 0 cm.

[Table] As is clear from the test results, when the construction method of the present invention is used, compared to when the constituent components of the admixture used in the construction method of the present invention are used alone and when conventional antifreeze agents are used. It has a remarkable effect of increasing the initial strength at low temperatures, and also shows an excellent effect that can be called epoch-making in that it does not impair the basic performance of concrete. Example 2 This example shows the effectiveness of the construction method of the present invention under severe conditions in which concrete is repeatedly frozen and thawed. (1) The materials and mixture of concrete are the same as in Example 1. (2) Freeze-thaw repeated test Mixed concrete was placed in 10cmφ x 20
The specimen was molded by filling it into a cm specimen frame. The concrete pouring temperature was 10-12℃. This was immediately stored in a test chamber adjusted to the temperature cycle shown below, and after a predetermined age, the compressive strength of the specimen was measured. The temperature cycle of the test chamber was 15 hours per cycle, which consisted of -10°C and +5°C holding periods of 5 hours each, and heating and cooling periods of 2.5 hours each. For comparison, the compressive strength of specimens subjected to standard curing at 20°C was also measured. (3) The test results are shown in Table 3.

[Table] Note that the results for sodium nitrate, sodium nitrite, and urea alone have been omitted, but all of them had +5
The results at −10°C were significantly inferior to EFG. As is clear from the above table, concrete construction by the construction method of the present invention exhibits excellent effects under severe conditions of repeated freezing and thawing.

Claims (1)

[Scope of Claims] 1 (a) 1 part by weight of a water-soluble salt of a formalin condensate of an aromatic hydrocarbon sulfonic acid, and (b) one or more compounds selected from the group consisting of nitrates, nitrites, and urea. mixture of
Using concrete mixed with an admixture of 1 to 20 parts by weight and 2 to 10% by weight based on the weight of cement, the concrete is essentially heat-cured under environmental conditions with an initial curing temperature of -5℃ to -15℃. Or a cold concrete construction method characterized by curing concrete without heating it.