JPH0369542A - Inhibitor for heat of hydration of cement and method for inhibiting temperature rise due to heat of hydration of cement - Google Patents

Abstract

PURPOSE:To prevent the lowering of the strength of concrete and the occurrence of cracks by adding a thermo-accumulating material having a prescribed m.p. or transition point to fresh concrete, etc., and by absorbing heat of hydration at the time of hardening cement. CONSTITUTION:A thermo-accumulating material having 5-60 deg.C m.p. or transition point, e.g., polyethylene, paraffin or inorg. salts are added to fresh concrete, mortar, a cement slurry, etc., so as to inhibit the rise of temp. due to heat of hydration at the time of hardening cement.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a technology for suppressing temperature rise due to heat of hydration of cement, and is particularly applicable to mass concrete casting work in architecture and civil engineering work (for example, in deep underground spaces). Suppresses temperature rise due to heat of hydration of cement in structures, foundations of large buildings, bridge piers, dams, foundations of water and sewage treatment plants, foundations of long bridges, etc.), thereby preventing concrete from cracking and decreasing strength. Regarding things.

(Prior Art and Problems to be Solved by the Invention) When concrete is placed, hardening begins due to a hydration reaction between cement and water, and heat of hydration is generated at this time. This heat of hydration generally reaches its maximum within 2 to 3 days after pouring, and in large cast members (mass concrete), a temperature rise of 30 to 60°C, sometimes up to about 80°C, is observed.

As a result, there is a considerable temperature difference between the outside (the part that comes into contact with the outside air) and the inside of the poured concrete, causing local distortion, which can lead to cracks in the hardened concrete 1. Ta.

Therefore, in order to prevent temperature cracks during mass concrete construction, as a method to suppress the rise in cement hydration heat,
The following are being considered:

■ Pre-cooling method This method uses liquid nitrogen to directly cool concrete during or after mixing, cools fine aggregate in concrete, or adds flake ice.

However, this method has problems such as not being able to maintain a low temperature for a long time, limiting the construction time, and requiring a special cooling plant for each construction site.

■ Method of mixing blast furnace slag powder, etc. This is a method of substituting part of the ordinary Portland cement with blast furnace cement, and it has been reported that the heat of hydration is reduced.

However, at low temperatures, the development of initial strength is small, which delays the demolding of the formwork, and conversely, at high temperatures, the temperature of concrete tends to rise significantly compared to ordinary Pol 1-land cement. be.

■ Heat of hydration reducing admixture The expansion agent C3A (calcium sulfoaluminate) is mixed with glucose, a setting retarder, which suppresses the heat of hydration, but delays the setting of concrete. Moreover, if the expanding agent acts unevenly, it may conversely promote the occurrence of cracks.

In addition, there are also examples in which urea is added for the purpose of reducing the heat of hydration. This utilizes an endothermic reaction based on the hydrolysis of urea (NH2)Co2+2H20→H2C○3→2NH3 reaction.

However, it requires a very large amount of addition, and the generated H2CO3 may accelerate the carbonation of concrete, which may reduce the durability of concrete.

(Means for Solving the Problems) In view of the problems of the above-mentioned conventional techniques, the present inventors have developed a new and effective technology for suppressing the heat of hydration of cement as a result of intensive research.

The present invention utilizes a latent heat storage material that has the property of absorbing heat at a predetermined temperature, that is, (1) 5 to 60°
A hydration heat suppressing material for cement, which is made of a heat storage material having a melting point or transition point at (2)5
Hydration of cement, characterized in that a heat storage substance having a melting point or transition point of ~60°C is added to fresh concrete, mortar, or cement slurry to suppress a temperature rise due to heat of hydration during hardening into cement 1. This is a method of suppressing temperature rise due to heat.

In the present invention, the cement hydration heat suppressing material may be formed by impregnating a porous substance with a heat storage substance, or may be formed by coating the heat storage substance with another substance and encapsulating it. Good too. Furthermore, a composite material may be formed by mixing the heat storage material and another material.

The heat storage material in the present invention is a material that has a melting point or transition point between 5 and 60°C and absorbs and releases heat at this temperature, and preferably has a large amount of latent heat such as heat of fusion or heat of transition. Specific examples include polyethylene, paraffin, and inorganic salts (eg, magnesium chloride, storum acetate, etc.).

If the melting point is too low, the poured concrete will be kept at an unnecessarily low temperature, which may inhibit the hydration reaction of the cement.

Furthermore, if the melting point is below room temperature, it is inconvenient during storage and construction.

For these reasons, a material with a melting point of 5 to 60°C is appropriate (a lower limit of about 5°C can also be used during winter construction).

The transition point or melting point of the heat storage material used in the present invention is preferably 45 to 60°C.

The reason is that the strength of concrete decreases when the temperature rises above 60°C during the hydration reaction. On the other hand, the hydration reaction of cement is difficult to proceed unless the temperature exceeds a certain level.
A heat generation of about 5°C will not cause a decrease in strength. For this reason, it is necessary to absorb heat at 45 to 60°C, and the melting point or transition point of the heat storage material is preferably 45 to 60°C.

This heat storage material can be made into fine powder beads or spherical beads and can be added in an appropriate amount to mixed concrete with cement, aggregate, and water, or into fresh concrete during construction.

Alternatively, a material obtained by impregnating a heat storage material into strips of a porous inorganic material or a porous material such as a nylon sponge may be added to the ready-mixed concrete.

Furthermore, a heat storage material coated with another material and encapsulated may be added to the ready-mixed concrete.

Alternatively, a composite obtained by mixing the heat storage material and another substance may be added.

As described above, it is possible to absorb the heat of hydration of cement, prevent a decrease in the strength of concrete, and prevent the occurrence of cracks due to uneven temperature distribution.

(Function) Cement generates heat due to a hydration reaction, and heat accumulates particularly inside mass concrete members, reaching temperatures close to 80'C. On the other hand, heat is dissipated from the surface of the poured concrete, which creates a temperature difference between the surface and the inside, disrupting the balance of shrinkage forces and causing cracks in the poured concrete.

Therefore, if a heat storage material (for example, one with a melting point of 55°C) is added to concrete 1- during kneading, when the temperature inside the concrete reaches around 55°C due to the heat of hydration of cement 1, the heat storage material will melt and tighten. absorbs heat. As a result, an increase in the internal temperature of the concrete 1 is suppressed, and the temperature difference between the surface and the inside becomes small, making it possible to suppress the occurrence of cracks.

Furthermore, the concrete temperature during curing can be maintained at 60° C. or lower, and a decrease in product strength can also be prevented.

(Example) Next, examples of the present invention will be described.

A: Preparation of [spherical paraffin heat storage material] The heat storage material is
It is a spherical paraffin with a particle size of 1 μm to 1000 μn'l, and is a suitable material because of its good mixability and dispersibility with other materials.

An example of the production of this spherical paraffin is given below.

First, various paraffins shown in Table 1 below are heated to a temperature higher than their melting point and melted.

Table 1 Next, the above various paraffins are dispersed in water together with a suitable emulsifier to prepare an O/W emulsion.

Thereafter, the emulsion is solidified by cooling to below the melting point to obtain spherical paraffin.

The particle size of spherical paraffin varies from 1 to 100 depending on the type and amount of emulsifier, the stirring speed during emulsification, and the volume ratio of paraffin to water.
It can be controlled within a range of 0 μm.

B: Preparation of [thermal storage material impregnated with porous carrier] The various paraffins described above are heated above their melting point to become liquid, and this is impregnated into heated porous inorganic substance spherules (particle size 1 to 11,000 u). By cooling, a heat storage material is prepared in which a porous alumina ceramic carrier is impregnated with a paraffin heat storage material.

Since the heat storage material itself is a small ball with high strength and has excellent adhesion to cement, the concrete product obtained by adding the heat storage material to fresh concrete has low mechanical strength. I can maintain it.

C: Preparation of [Microencapsulated ripening material] On the surface of the spherical paraffin (paraffin beads) prepared in A above,
For example, ultrafine stainless steel powder is adsorbed and fixed using a commercially available surface modification device to prepare "stainless steel wall paraffin microcapsules."

The mechanical strength of the microcapsules thus obtained can be improved and the specific gravity can be adjusted.

Furthermore, if the surface is coated with silica fume and encapsulated, the affinity for cement will be improved due to the pozzolanic reaction on the surface, and a decrease in the strength of concrete can be suppressed.

D = Preparation of [Composite Heat Storage Material] Using a mixture of the above-mentioned various paraffins and admixtures such as a fluidizing agent, a water reducing agent, and a setting retarder under heat, 1. Granules are produced by an appropriate granulation means.

Since the heat storage material is combined with the admixture, there is no need to add the admixture and add the heat storage material separately when preparing ready-mixed concrete, which saves time and effort.

Hereinafter, we have described various types of stored materials A to D, and their structural diagrams are shown in FIG. 3 as (a) to (d). That is, FIG. 3(a) is an external view of a spherical body made entirely of paraffin 1, FIG. 3(b) is a partial cross-sectional view of a porous inorganic spherule 2 whose communicating pores are impregnated with paraffin 1; c) is a cross-sectional view of a microencapsulated heat storage material whose entire surface is covered with a coating layer (stainless steel ultrafine powder) 3; (d)
) mixes 4 admixtures (plasticizers, etc.) with 1 paraffin,
An external view of the granulated product is shown.

However, the present invention is not limited to these, and various other forms of heat storage materials may be used.

Next, 1.6 kg of spherical paraffin (n docozan, particle size 20 urn) described in A above was added to cement base T-40k.
The mixture was poured into a mold with an inner diameter of 240 cm x 40 cm x 40 cm, and allowed to cure naturally.

Prior to pouring, a large number of temperature sensors are installed at various locations within the fresh concrete (as if crossing the poured concrete, from one outside (point A) to the center, and then to the other outside (point A').
) and connected to an external temperature indicator.

The displayed temperature obtained over time from the temperature sensor placed at the center of the poured concrete is shown by curve (3) (sample-3) in Figure 1, and reaches its maximum temperature at 0.5 days old. The temperature reached approximately 55°C.

Furthermore, as a comparative example, ordinary ready-mixed concrete was placed in the same formwork as above and the temperature at the center was measured over time.The results are shown in the curve (↑) in Figure 1 (Sample-1). As shown, the temperature reached a high temperature of about 97°C at 14 hours of age.

The temperature distribution from the outside to the center to the outside (A-A') on the second day of age of the poured concrete in this example is as shown by curve (1) in Fig. 2, and the temperature distribution between the center and outside. The temperature difference was about 25°C.

Furthermore, no cracks were observed in the hardened concrete.

On the other hand, in the case of ordinary concrete prepared and cured by the conventional method (sample-1), the temperature difference between the center and the outside temperature reached 60℃, as shown by curve (2) in Figure 2. was. As a result, it was inferred that in the comparative example, heat was dissipated from the surface, resulting in a temperature difference between the surface and the inside, causing an imbalance in the shrinkage force.

As other examples, a sample of Chinoku-2) in which 8 kg of the spherical paraffin was mixed with 40 kg of cement, and a cement 1
~40 kg of the spherical paraffin weighing 32 kg was prepared (sample-4) and subjected to a hydration heat temperature measurement test, and the results were as shown in Table 2.

Table 2 (Cement heat of hydration measurement experiment results) The amount of the heat storage material of the present invention added needs to be adjusted depending on the outside temperature at the time of pouring in order to reduce the temperature difference between the surface and the inside of concrete 1. However, it can generally be used in a range of 0.15% to 50% based on cement.

For example, Portland cement has a calorific value of 60 kcal/g, so depending on the amount of cement in the poured concrete, for example, flake paraffin (manufactured by Mitsubishi Yuka Co., Ltd.),
By adding 0.15 to 50% of 0.15 to 50% of the heat absorption amount (40 kca 17' kg), it is possible to suppress the abnormal temperature rise of the poured concrete and eliminate the occurrence of cracks.

5 (Effects of the Invention) According to the present invention, the heat storage material absorbs the heat of hydration during hardening of cement, prevents a decrease in the strength of concrete, suppresses the generation of temperature difference between the surface and the inside of concrete, and prevents cracks. Occurrence can be prevented.

In addition, ■The heat of hydration suppressing material according to the present invention can be added in the same way as a normal admixture at the ready-mixed concrete plant or at the construction site. No need for a plant. ■
Hydrophobic heat storage materials such as paraffin must not inhibit the hydration reaction of cement.

■The heat storage material that melts, lowers its viscosity, and penetrates between the cement particles solidifies again, making it possible to improve the density of concrete (polymer concrete,
High durability (when using paraffin, etc.). Many excellent effects such as these can be obtained.

6 FIG. 1 is a graph diagram showing temperature changes over time at the center of poured concrete in various examples and comparative examples of the present invention;
Figure 2 is a temperature distribution diagram from the outside to the center to the outside (A to A') of the poured concrete of this example and comparative example, and Figure 3 (
a) to (d) respectively show schematic structural explanatory diagrams (some of which are cross-sectional views) of various heat storage materials of Examples.

Claims (11)

[Claims] (1) Cement water is made of a heat storage material with a melting point or transition point of 5 to 60°C, and is added to fresh concrete, mortar, or cement slurry to suppress the temperature rise due to heat of hydration during hardening of cement. Japanese heat suppressant. (2) The cement hydration heat suppressing material according to claim 1, wherein the cement hydration heat suppressing material is formed by impregnating a porous material with a heat storage substance. (3) The cement hydration heat suppressing material according to claim 1, wherein the cement hydration heat suppressing material is a heat storage substance encapsulated by surface coating with another substance. (4) The cement hydration heat suppressing material according to claim 1, wherein the cement hydration heat suppressing material is encapsulated by coating the surface of a heat storage substance with silica fume. (5) The cement hydration heat suppressing material according to claim 1, wherein the cement hydration heat suppressing material is a composite obtained by mixing a heat storage substance and another substance. (6) The heat of hydration suppressing material for cement according to any one of claims 1 to 5, wherein the heat storage substance has a melting point or transition point of 45 to 60°C. (7) Cement water characterized by adding a heat storage substance having a melting point or transition point of 5 to 60°C to fresh concrete, mortar, or cement slurry to suppress the temperature rise due to heat of hydration during hardening of cement. A method to suppress the temperature rise caused by Japanese heat. (8) A cement hydration heat suppressing material made by impregnating a porous material with a heat storage substance is added to fresh concrete, mortar, or cement slurry to suppress the temperature rise due to hydration heat during hardening of cement. Claim 7
A method for suppressing the temperature rise due to heat of hydration of the described cement. (9) Adding a cement hydration heat suppressing agent, which is made by encapsulating a heat storage material by coating the surface with silica fume, to fresh concrete, mortar, or cement slurry, suppresses the temperature rise due to hydration heat during hardening of cement. A method for suppressing a temperature rise due to heat of hydration of cement according to claim 7. (10) A heat storage material is mixed with other substances to form a composite, and a heat of hydration suppressant for cement is added to ready-mixed concrete, mortar, or cement slurry to suppress the temperature rise due to heat of hydration during hardening of cement. A method for suppressing a temperature rise due to heat of hydration of cement according to claim 7. (11) The method for suppressing temperature rise due to heat of hydration of cement according to any one of claims 7 to 10, wherein the heat storage material has a melting point or transition point of 45 to 60°C.