JPS63117941A - Hydration exothermic speed reducer for mass concrete - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention consists of hydrolyzable tannins. This invention relates to additives for reducing the hydration exotherm rate of mass concrete.

With the increasing size of concrete structures and the increase in large-scale rapid construction due to advancements in construction methods, the temperature stress that occurs due to temperature changes in structures due to the heat of hydration generated during the hardening process of concrete is causing cracks in structures. Occurred,
Alternatively, residual temperature stress may not be negligible in the design.

A particularly important problem with mass concrete is that a large temperature rise occurs inside the concrete due to the heat generated by hydration of the cement, and deformation due to the temperature drop that follows this temperature rise may be restrained by the adjacent bedrock or existing concrete. In addition, extremely large and harmful cracks occur due to a type of internal restraint caused by the temperature difference between the inside and the surface. In order to analyze this temperature stress in concrete, various methods are currently being used to predict the temperature rise of concrete.
There are a wide variety of factors that determine the temperature rise of mass concrete, including the type and amount of cement admixtures and aggregates, outside temperature curing, and overall construction. However, the temperature rise in concrete is almost proportional to the amount of cement per unit due to the heat generated by hydration of the cement, but if the rate of heat generation due to hydration of the cement can be controlled, the temperature rise can also be controlled. Generally, it is desirable to use low heat generation cement such as moderate heat Portland cement, blast furnace cement, and fly ash cement.

However, the hydration heat generation rate of cement is strongly influenced by the temperature of the system. That is, the higher the temperature of the system, the more hydration is promoted and the rate of hydration heat generation becomes higher. It is known that the temperature inside mass concrete, where the generated heat is difficult to dissipate, can reach temperatures of 80°C or higher.

<Prior Art> Conventionally, in order to suppress the hydration heat generation of mass concrete, an additive called a super retardant that suppresses the hydration of cement has been added. For example, gluconates and silicofluorides. When added in a certain amount, these super-retarders can prolong the time it takes for cement to hydrate, but once hydration begins, it quickly generates heat, similar to concrete without additives. In addition, there are many problems such as no strength at all until hydration begins.

Therefore, by taking advantage of the fact that the solubility of dextrin varies greatly depending on temperature, at room temperature, the elution rate is slow, so there is little effective retardant in the solution, and therefore it has little effect on cement hydration, but at high temperatures, the A patent application has been filed for an additive in which a large amount of retardant is dissolved in the cement to strongly suppress heat generation due to hydration of cement (Japanese Patent Application Laid-Open No. 75956/1983).

In this case, since the elution rate differs depending on the temperature, a concentration distribution of the retarder is created in the concrete.
This becomes a defect. Furthermore, in order to effectively retard hydration, it is necessary to add about 1.5 g, which poses problems in terms of cost and the effect it has on the physical properties of hardened concrete.

<Problems to be Solved by the Invention> The present inventors have conducted extensive research in order to solve these drawbacks and develop a good additive for suppressing the hydration heat generation rate of mass concrete.

<Means for Solving the Problems> As a result, it was discovered that hydrolyzable tannin is an additive suitable for the above purpose, and the present invention was achieved based on this knowledge. That is, the present invention is a hydration exotherm rate reducing agent for mass concrete comprising hydrolyzable tannin.

Tannins are generally divided into two types: hydrolyzed tannins and condensed tannins. The condensed type closely matches a substance called proanthocyanidin, which is found in large amounts in natural resins. It is this tannin that causes the substances contained in the bark of coniferous trees to retard the hydration of cement. Japanese Patent Publication No. 59-13653
The "composition for retarding the setting of cement" in the publication utilizes the retarding effect of tannins. In the present invention, hydrolyzable tannin refers to substances whose main components are gallotanin, corilazine, keplagic acid, kepric acid, etc., in which phenolic carcinic acid and sugar are ester-bonded, and m-galloyl, which is known as tannic acid. Examples include gallic acid.

These substances are hydrolyzed into gallic acid, ellagic acid, and sugar. It is well known that these substances are susceptible to hydrolysis under acidic and alkaline conditions.

Furthermore, this additive can be used with other admixtures, such as water reducing agents such as lignin-based, naphthalene sulfonate formalin condensate7, and conventionally well-known retarders such as lignin-based, oxycarboxylate yarns, and silicofluorides. May be used together.

The cements that can be used are usually moderate heat, early strength, very early strength, sulfate resistant, mixed cements such as white Portland cement, silica cement, fly ash cement, blast furnace cement, or calcium aluminate as the main component. Alumina cement and C11A7CaF2
These include ultra-fast-hardening cement whose main ingredient is calcium sulfoaluminate (C4A, S), and special cement that uses calcium sulfoaluminate (C4A, S). Further, it is preferable that the additive according to the present invention is added to the cement in an amount of 0.05 to 3.0 g. The amount added varies greatly depending on the type of cement, but it is usually in the range of 0.1 to 1.0 g for Portland cement.

The additive according to the present invention may be mixed with cement in advance as a powder, or because it is water-soluble, it may be used by dissolving it in mixed water. When bubbles are generated, known silicone-based or alcohol-based antifoaming agents can be added.

Hydrolyzable tannins are mainly composed of ester bonds between phenolic carganic acids and sugars, and are gradually hydrolyzed in the presence of alkaline substances such as cement to produce phenolic carganic acids and sugars. do. These substances have significantly different effects on the aqueous phase of cement; hydrolyzable tannins have a relatively slow retarding effect, while the phenolic carcinic acid and sugar produced have a very strong retarding effect. For this purpose, it takes advantage of the fact that at high temperatures, where the rate of hydrolysis is fast, a large retardation effect occurs compared to hydration at room temperature. In other words, water-soluble and gradual hydrolysis produces low-molecular-weight phenolic carboxylic acids and sugars that are highly effective in delaying the hydration of cement by tannins and other substances, thereby slowing down the hydration of cement. The purpose of the present invention is to provide an additive that reduces the temperature rise rate of mass concrete while suppressing the temperature increase.

As shown in FIG. 1, generally, as the temperature of cement increases, the rate of heat generation due to hydration increases rapidly (a). However, the rate of hydration heat generation decreases by adding only 0.2 parts of tannic acid (b). The addition of 0.05% further decreases the amount (
c). Moreover, unlike conventional cement retarders, which retard at low temperatures, the higher the temperature, the greater the retardation.

As described above, the present invention is a cement hydration heat rate reducing agent consisting of hydrolyzable tannins, which gradually hydrolyzes in the presence of cement to produce a highly retarded substance. It has the effect of reducing the rate of temperature rise in concrete due to hydration.

<Examples> The present invention will be described in more detail below with reference to Examples.

As a method for estimating the internal temperature rise of mass concrete, there is an adiabatic temperature rise tester in which the concrete is packed in a container and the temperature of the surrounding tank is raised to match the temperature at the center.

Conventional testing machines do not allow heat to escape from the container, and with concrete that hydrates slowly, the temperature rise of the concrete is reduced due to heat escape. However, when mass concrete is actually poured, the heat generated is large and differs from the data from the testing machine. Therefore, we developed an improved adiabatic temperature rise tester manufactured by Jujum Cement Co., Ltd.
No. 257266) was used to conduct a comparison test with concrete to which a conventional super retardant was added. Since heat loss can be ignored, the final temperature reached will remain the same if the same cement is used.

Example 1 An adiabatic temperature rise test was conducted on concrete IJ-t using ordinary Portland cement. The formulation is shown in Table 1.

Table 1 Concrete pouring conditions The slump was 9.0cn1, the air content was 3.6%, and the actual pouring temperature was 19.4°C. The maximum dimension of the coarse aggregate was 50 m, and the specimen was φ60 x 60 m.

The results of the adiabatic temperature rise test (the effect of each heat of hydration inhibitor on concrete temperature rise) are shown in Figure 2.

Table 2 shows a comparison of physical properties when using the present invention and conventional additives.

Table 2 Compressive strength of concrete with various additives (2
0℃) Additives used (for cement Compressive strength Ckg/6
n2) against h) 3 days 7 days
28th (commercial reagent) 2, I/O, 5132170260
3. Gluconic acid 0.2 73
168 253 Sodium 4, Dextrin 1.6 63
169 2545, None -1
48172248 Table 2 and Figure 2 Additives 1
, 2 are the present invention, and 3 and 4 are conventional ones.

As mentioned above, the conventional adiabatic temperature rise tester caused heat to dissipate, but this tester has been improved and almost no heat escapes. However, when the same cement is used, the final temperature reached is not so hot, but there is a rapid rise in heat generation when no additive is used and when gluconate is added.

On the other hand, it can be seen that with the additive of the present invention, the temperature gradually increases10). Although almost the same effect can be obtained with dextrin, the amount added to obtain the same effect as the present invention is as large as 1.6 g, and the effect is also insufficient.

In addition, in the case of the additive of the present invention, the compressive strength was 0.3 days after 3 days.
With 5% additive, it was around 90 degrees without additives, and on the 28th it was higher than without additives, so there was no problem.

Example 2 Table 3 shows the driving conditions when medium heat Portland cement was used.

Table 3 Concrete pouring conditions The slump was 9.2 cm, the air content was 3.5%, and the actual measured temperature was 19.5°C. The maximum dimension of coarse aggregate is 50 mm. A specimen having the same dimensions as in Example 1 was used.

Figure 3 shows the results of the adiabatic temperature rise test for this concrete. Further, Table 4 shows the physical property test results of this concrete.

Table 4 Compressive strength of concrete with various additives (2
0℃) Additives used (for cement Compressive strength OCI!7
．． 2) 3 days 7 days 28 days 1, tannic acid 0.5 (commercial reagent) 65 13
5247 Gluconic Acid 0.15 Sodium 4, None -91142238 In Table 4 and FIG. 3, Additive 1 is an example according to the present invention, and is an example in which a conventional additive was used in combination. 2 and 3 are comparative examples using conventional additives.

The concrete strength at 3 days was slightly lower than that without additives, but the strength at 28 days was higher than that without additives.

<Effects of the Invention> The hydrolysable tannin of the present invention has a relatively weak effect of retarding the rate of hydration heat, but since the compounds produced by hydrolysis have a very strong retardant effect, the tannin of the present invention has a relatively weak effect of retarding the rate of hydration heat. Since hydration at high temperatures has a large retardation effect compared to hydration at room temperature, the water phase of cement can be gradually suppressed and the rate of temperature rise of mass concrete can be reduced.

[Brief explanation of the drawing]

FIG. 1 shows the relationship between temperature and hydration heat release rate during hydration of cement. (,) without additive, (b) and (C) with 0.2% and 0.0% tannic acid, respectively.
This is the case when 5. Figures 2 and 3 show the effect of the hydration heat generation inhibitor on the temperature rise of concrete for normal Portland cement and moderate heat Portland cement, respectively.

Claims (1)

[Claims] Hydration heat rate reducing agent for mass concrete consisting of hydrolyzable tannins.