JPH06179209A - Method for kneading cold ready-mixed concrete - Google Patents

Abstract

PURPOSE:To lower a temperature of a kneaded ready-mixed concrete and to knead a low-temperature ready-mixed concrete in a short time by a method wherein after cement, sand, and ice are stirred, a cooled aggregate is added thereto and stirred. CONSTITUTION:In a kneading method for a ready-mixed concrete, before the addition of a cooled aggregate from an aggregate containing tank 1, ice is added to cement and sand and stirred in an aggregate cooling tank 3. In this state, the surfaces of the ice particles stirred with the cement is covered with fine cement particles. The cement particles having a high temperature come into contact with the local areas of the ice and melt it into water under heat. The resultant water penetrates into gaps between the cement particles and the ice. Thus, the ice comes into contact with the water and the cement at a larger area and melts immediately. In this manner, the cooled aggregate from the aggregate containing tank 1 is added to the stirred and cooled cement and sand and stirred, whereby the temperature of the kneaded ready-mixed concrete can be lowered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for kneading forcibly cooled green concrete, and more particularly to a method for cooling aggregate and kneading green concrete.

[0002]

2. Description of the Related Art Fresh concrete is required to have a low kneading temperature. In particular, the concrete in the hot weather where the daytime temperature exceeds 25 ° C. can improve the properties after hardening by cooling.

Hot summer concrete, which has a high temperature, has a drawback that the slump becomes low, cracks occur, and the strength is lowered.

Fresh concrete slumps degrade as water evaporates. For example, when the kneading temperature is 30 ° C. and the fresh concrete having a slump of 18 cm is transported by a truck agitator for about 1 hour, the slump is lowered by about 6 cm. In addition, in the case of green concrete, even if the amount of water added is adjusted to be the same, the slump decreases as the kneading temperature increases. Ready-mixed concrete with reduced slump becomes difficult to drive. Fresh concrete with reduced slump needs to be remixed by adding cement paste.

Internal heat generation during setting of green concrete causes cracking. Unfortunately, the hydration reaction in which concrete hardens is an exothermic reaction. The hydration reaction causes the cement to generate 80 kcal of heat per kg. 1 m ³ of concrete contains 180-300 kg of cement. Thus, the heat of hydration of the cement raises the concrete to 50-60 ° C. when it hardens. The concrete that generates heat inside has a temperature difference between the inside and the outside surface, the heated inside expands thermally, and the cooled outside surface shrinks and cracks occur.

Cracking of concrete causes significant adverse effects in all applications. In particular, dams, bridge piers installed in the sea, bulkheads of nuclear reactors, etc. are fatal defects. In addition, hot concrete has reduced strength upon hardening.

By cooling the ready-mixed concrete,
These adverse effects can be eliminated. Methods have been developed to use liquid nitrogen to cool ready-mixed concrete. For example, JP-A-1-26407 describes a method of blowing liquid nitrogen into an aggregate tank to forcibly cool the aggregate. Further, JP-A-1-26408 describes a method of immersing aggregate in liquid nitrogen and cooling it. further,
JP-A-63-804 and JP-A-1-2640
No. 6 discloses a method in which liquid nitrogen is blown into a mixer for kneading aggregate, cement, sand and water to directly cool fresh concrete.

[0008]

As described in these publications, the method of cooling ready-mixed concrete using liquid nitrogen has a feature that it can be cooled at a low temperature in an ideal state. This is because the raw concrete can be cooled to a low temperature by the large amount of heat of vaporization of liquid nitrogen at ultra-low temperature, and the cooled liquid nitrogen completely disappears as gas. However, this method can only be used in very limited applications. This is because the running cost is extremely high because the liquid nitrogen that is consumed in large quantities is expensive.

The present inventor has developed a method of cooling the aggregate with cold water in order to reduce the running cost. This method is advantageous in that running cost can be reduced because the aggregate is immersed in cold water without using liquid nitrogen, or is cooled by sprinkling cold water during the transportation of the aggregate. In this method, by cooling the aggregate to 3 to 5 ° C, it is possible to cool the green concrete having a kneading temperature of more than 30 ° C to 15 ° C to 18 ° C in the summer. However, although it is required to cool to a lower temperature depending on the application, it is difficult to cool to an ultralow temperature of 15 ° C. or lower by this method, and there is a drawback that the cooling temperature is limited.

By the way, it is also possible to cool the added water to lower the kneading temperature of green concrete. However, since the amount of water added is only 3 wt% of the whole fresh concrete, even if it is cooled, the kneading temperature can hardly be lowered. When ice is used instead of water, the melting heat of ice is 79 cal, so that the kneading temperature of green concrete can be lowered. However, with this method, the kneading temperature of the fresh concrete cannot be cooled to 20 ° C. or lower in the summer, and the fresh concrete cannot be sufficiently cooled to a low temperature.

If ice can be added to the cooled aggregate, the kneading of fresh concrete can be significantly reduced. However, in reality, it is actually impossible to mix ice, sand, and cement with the cooled aggregate and stir it to obtain ready-mixed concrete. This is because the ice aggregate takes a very long time to melt due to the low temperature of the aggregate. In particular, when kneading is carried out without adding water or adding a small amount of water, the melting time of ice becomes remarkably long. This is because water does not contact the surface of ice. It is possible to melt the ice with the heat of hydration that hardens the concrete. However, green concrete that does not completely melt ice has a significantly reduced strength after hardening. This is because the melting of ice creates voids in the concrete.

In order to shorten the melting time of ice, the amount of ice added may be reduced and the amount of water added may be increased. However, when the mixing amount of ice is reduced, the kneading temperature of green concrete becomes high. In order to lower the kneading temperature, it is necessary to reduce the amount of water added and increase the amount of ice added. Mixing ice, cement, sand, and cooled aggregate with a mixer without adding any water produces the coldest raw concrete.
However, in this state, since there is no water at all, it takes a very long time to melt the ice due to the dry mixing state.
In particular, since the aggregate is cooled to a low temperature, the action of melting the ice is very weak, and the dry-mixed ice only comes into contact with the cooled aggregate at a local portion of the surface. For this reason, the method of adding ice instead of water can be used when the aggregate is not cooled, but when using the aggregate cooled to a low temperature, use it in a state where the kneading temperature of fresh concrete can be lowered. That is actually quite difficult.

The present invention was developed with the object of further solving this drawback. An important object of the present invention is to add ice to lower the kneading temperature of fresh concrete and to melt the ice. It is an object of the present invention to provide a kneading method for cooled ready-mixed concrete which can shorten the time and mix low-temperature ready-mixed concrete in a short time.

[0014]

In order to achieve the above-mentioned object, the method for kneading cooled ready-mixed concrete according to the present invention comprises adding ice to cement to which cooled aggregate has not been added and stirring the mixture to heat the cement. Is effectively used for thawing ice, and then cooled aggregate is added. Cement without the addition of cooling aggregate effectively melts the mixed ice in a short time. It has a high temperature because the cement is not cooled by the aggregate,
In addition, extremely fine cement particles adhere to cover the entire surface of the ice, and the amount of cement added is approximately 8w.
The reason is that there are about 3 times as much as t% and water. The ice particles, whose surface is covered with fine cement particles, are melted at a part of the surface heated by the high temperature cement particles. The melted water penetrates into the minute gaps between the ice and the cement particles. The ice with the gap filled with water melts the ice more effectively with the front surface covered with water.

The heat of melting of ice added in place of water is about 8
It is 0 cal / g. The heat of hydration of cement is about 60-80
It is cal / g. Therefore, the heat of melting of ice is almost equal to the heat of hydration of cement. Therefore, the heat of hydration of the cement can be effectively absorbed by the heat of melting of ice.
However, in fresh concrete, the amount of cement added is about twice the amount of water added. By adding all the water in the ice state without adding water, about half of the heat of hydration of cement can be absorbed as the heat of melting of ice. However, the heat of hydration of cement does not occur immediately after kneading the cement with a mixer. It occurs over time as the cement hardens. The heat of hydration generated over time is radiated from the surface when the ready-mixed concrete hardens. Therefore, if the kneading temperature of green concrete is forcibly cooled with ice to a low temperature, the temperature rise due to the heat of hydration generated during hardening can be reduced.

[0016]

EXAMPLES Examples of the present invention will be described below. However,
The examples shown below are examples of a kneading method of cooled ready-mixed concrete embodying the technical idea of the present invention, and the method of the present invention specifies the conditions of the treatment step, the equipment used, etc. as follows. Not something to do. The method of the present invention is subject to various modifications within the scope of the claims.

[Example 1] 200 kg of cement and 5
20 kg of sand, 50 kg of ice and 30 liters of water are charged into a mixer and stirred. Use cement and sand that do not cool. For ice, flake ice is used. Flake ice is produced by, for example, supplying water to the surface of a cylindrical drum that has been forcibly cooled to -20 ° C to freeze it and scraping it with a scraper. The flake ice is a thickness for scraping frozen ice, and the thickness can be adjusted. The flake ice has a thickness of, for example, 0.1 to 3 mm, preferably 0.3 to 1 mm. The kneading time of the mixer is adjusted to, for example, 2 to 5 minutes so that the ice is completely melted and water, cement and sand can be uniformly dispersed.

Cement, sand, and water were kneaded to form a mortar, and 1600 kg of aggregate cooled to 3 ° C. was added to the mixer and further stirred. The temperature of the green concrete thus kneaded is 9 ° C. However, the cement temperature is 60 ° C, the sand temperature is 30 ° C, the ice temperature is 0 ° C,
The water temperature is 20 ° C and the aggregate temperature is 3 ° C.

[Example 2] 200 kg of cement and 5
Fill the mixer with 20 kg of sand and 80 kg of ice and stir. Use cement and sand that do not cool. For ice, flake ice is used. The kneading time of the mixer is adjusted to, for example, 3 to 5 minutes so that the ice is completely melted and water, cement and sand can be uniformly dispersed. Cement, sand and water are kneaded to form a mortar, and 1600 kg of aggregate cooled to 3 ° C. is added to the mixer and further stirred. The temperature of the fresh concrete thus kneaded is 5 ° C. However, the cement temperature is 60 ° C., the sand temperature is 30 ° C., the ice temperature is 0 ° C., and the aggregate temperature is 3 ° C.

[Example 3] 200 kg of cement and 5
Charge 0 kg of ice and 30 liters of water into a mixer and stir. Use cement that is not cooled. For ice, flake ice is used. The kneading time of the mixer is adjusted to, for example, 2 to 5 minutes so that the ice is completely melted and water, cement and sand can be uniformly dispersed. Cement, ice and water were kneaded and then cooled to 3 ° C. 50
Add 0 kg of sand to the mixer and stir to make mortar. Thereafter, 1600 kg of aggregate cooled to 3 ° C. is added to the mixer and further stirred. The temperature of the green concrete kneaded in this way is extremely low at 4 ° C. However, cement temperature is 60 ℃, sand temperature is 30
℃, ice temperature 0 ℃, water temperature 20 ℃, sand temperature 3
C, and the aggregate temperature is 3C.

In the method of kneading cooled ready-mixed concrete of the present invention, aggregates that have been cooled are used. The cooling temperature of the aggregate is usually adjusted to 1 to 15 ° C, preferably 2 to 10 ° C. The aggregate can be cooled efficiently using cold water. An example of an apparatus for cooling aggregate is shown in FIG. The apparatus shown in this figure includes an aggregate storage tank 1 for storing aggregates, an aggregate cooling tank 3 for immersing and cooling the aggregates in cold water, and an aggregate for immersing the aggregates in the cold water of the aggregate cooling tank 3 for transfer. And a cooling chiller 4 that chills the cold water in the aggregate cooling tank 3 with a circulation pump 15 to cool it to a predetermined temperature.

The aggregate storage tank 1 is for pre-cooling the aggregate stored therein, and is designed to have a volume for storing the aggregate more than the daily usage amount, and an aggregate discharge port 7 is provided at the bottom. ing.
The discharge port 7 is provided with a gate (not shown) through which cold water can pass but aggregate cannot pass. The gate opens when the aggregate is discharged, and is closed in a state where the aggregate is stored.

Immediately below the discharge port 7 of the aggregate storage tank 1,
A cold water receiving hopper 9 is arranged. Cold water receiving hopper 9
Receives cold water flowing out from the outlet 7. A pipe is connected to the bottom of the cold water receiving hopper 9, and the pipe is the reflux pump 1
It is connected to the aggregate cooling tank 3 via 0.

The aggregate cooling tank 3 is in the shape of an elongated gutter having an opening at the top. The aggregate cooling tank 3 immerses and cools the aggregate. The size of the aggregate cooling tank 3 is determined by the cooling amount of the aggregate per unit time. The aggregate cooling tank 3 shown in FIG. 1 allows cold water to flow from left to right and transfers aggregate from right to left. That is,
The aggregate is cooled by the supplied cold water having a low temperature and then discharged.

The transport conveyor 25 is for immersing the aggregate in cold water and transferring it, and is provided in the aggregate cooling tank 3. The transport conveyor 25 continuously cools the aggregate while transferring it. The conveyor 25 is a porous conveyor belt 2
6 is provided. The porous conveyor belt 26 carries the aggregate, dips it into the cold water of the aggregate cooling tank 3, and transfers it. In FIG. 1, the porous conveyor belt 26 transfers the aggregate from right to left of the aggregate cooling tank 3.

The cold water in the aggregate cooling tank 3 is cooled by the cooling chiller 4. The apparatus shown in FIG. 1 has a cooling chiller 4,
While cooling the cold water in the aggregate cooling tank 3, the cold water is also supplied to the aggregate storage tank 1. That is, the cooling chiller 4
Supplies cold water by switching to either the aggregate storage tank 1 or the aggregate cooling tank 3. Therefore, the outflow side of the cooling chiller 4 is bifurcated.

The branch passages on the outflow side of the cooling chiller 4 are connected to the switching valves 5A and 5B. That is, the cooling chiller 4
To the aggregate storage tank 1 via the switching valve 5A, and the switching valve 5
It is connected to the aggregate cooling tank 3 via B. The suction side of the cooling chiller 4 is connected to the aggregate cooling tank 3 via the circulation pump 15. By operating the switching valves 5A and 5B, the cold water cooled by the cooling chiller 4 is supplied to either the aggregate storage tank 1 or the aggregate cooling tank 3.

The circulation pump 15 circulates cold water from the cooling heat exchanger to the aggregate cooling tank 3 and the aggregate storage tank 1 to cool the aggregate. The ready-mixed concrete aggregate cooling device shown in FIG. 1 is used by opening one of the switching valves 5A and 5B and closing the other. When cooling the aggregate of the aggregate storage tank 1, the switching valve 5A is opened and the switching valve 5B is closed. In this state, the cold water is cooled by the chiller 4 → the switching valve 5A →
The aggregate storage tank 1 → reflux pump 10 → aggregate cooling tank 3 → circulation pump 15 → circulation in the circulation loop of the chiller 4 cools the aggregate stored in the aggregate storage tank 1.

When the aggregate is taken out of the aggregate storage tank 1 to prepare ready-mixed concrete, the switching valve 5A is closed and the switching valve 5B is closed.
To open. At this time, the cold water circulates through a circulation loop of the cooling chiller 4, the switching valve 5B, the aggregate cooling tank 3, the fine particle separation tank, the circulation pump 15, and the cooling chiller 4, and the aggregate cooling tank 3 cools the aggregate. To do.

The fresh concrete aggregate cooling device shown in FIG. 1 is used as follows. [Step of Cooling Aggregate in Aggregate Storage Tank at Night] The aggregate storage tank 1 is supplied with more than the daily amount of aggregate. Water is added to the aggregate cooling tank 3 to a predetermined level. The circulation pump 15, the cooling chiller 4, and the reflux pump are operated to cool the water filled in the aggregate cooling tank 3 and store it in the aggregate cooling tank 3. At night, cold water in the aggregate cooling tank 3 is circulated to the aggregate storage tank 1 to cool the aggregate stored in the aggregate storage tank 1. In this state, the cold water supplied to the aggregate storage tank 1 flows down between the aggregates to cool it, flows down from the drain port at the lower end, and flows into the aggregate cooling tank 3. In this state,
At night, the aggregate in the aggregate storage tank 1 is cooled to a predetermined temperature. In this step, the aggregate does not need to be cooled to the kneading temperature of the green concrete. This is because the aggregate is further cooled in the aggregate cooling tank 3 and kneaded with the fresh concrete immediately before use.

[Step of cooling aggregate mixed with ready-mixed concrete during the day] The switching valve 5A is closed, the switching valve 5B is opened, and the operation of the reflux pump 10 is stopped. In this state, the circulation of cold water to the aggregate storage tank 1 is stopped. Therefore, the cold water in the aggregate cooling tank 3 is not circulated in the aggregate storage tank 1. The aggregate pre-cooled in the aggregate storage tank 1 is supplied to the aggregate cooling tank 3. The cooling chiller 4 and the circulation pump 15 are operated to cool the cold water in the aggregate cooling tank 3. The aggregate is cooled by the transport conveyor 25.
Immersed in cold water and transported while being cooled.

[0032]

EFFECT OF THE INVENTION According to the method for kneading cooled ready-mixed concrete of the present invention, ice is added to cement and stirred before addition of cooled aggregate. Ice mixed with cement in this state is
The surface of the particles is covered with fine cement particles. The cement particles have a high temperature and are heated by melting the local parts in contact with ice. The melted water penetrates into the gap between the cement particles and ice. When water enters the gaps between the cement particles, the surface of the ice is covered with water and the cement particles in a surface contact state, and the water and the cement are contacted with each other over a wider area to be rapidly melted.

On the other hand, when the cement, the cooling aggregate and the ice are agitated as in the conventional case, the cement adheres to the surface of the aggregate to which 8 times the weight ratio of the cement is added, and the surface of the ice is added. Cannot be coated efficiently. Also, the aggregate is
Since the particles are so large as to be incomparable with the cement particles, even if a small amount of water is melted, the gap between the aggregates cannot be filled with water. Therefore, the melted water cannot cover the surface of the ice, and the ice locally contacts the cooling aggregate and a small amount of the cement particles and cannot be efficiently melted.

As described above, the kneading method for cooled ready-mixed concrete of the present invention is capable of efficiently melting ice with cement having a high temperature and in a short time, increasing the addition amount of ice, and mixing the ready-mixed concrete. An excellent feature that can lower the rise is realized. In addition, the method of the present invention can cool running green concrete by using water as ice, and can cool running aggregates, thereby reducing running cost and significantly reducing kneading of fresh concrete.

By the way, according to the method for kneading cooled ready-mixed concrete of the present invention, it becomes possible to cool the cement to a super low temperature of 10 ° C. or lower at a cement temperature of 60 ° C. in summer.
The kneading can be freely adjusted within the range of 4 ° C to 20 ° C by adjusting the amount of ice added and adjusting the cooling temperature of the aggregate and sand.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of an aggregate cooling device used in the method of the present invention.

[Explanation of symbols]

 1 ... Aggregate storage tank 3 ... Aggregate cooling tank 4 ... Cooling chiller 5A, 5B ... Switching valve 7 ... Discharge port 9 ... Cold water receiving hopper 10 ... Reflux pump 15 ... Circulation pump 25 ... Conveyor conveyor 26 ... Porous conveyor belt

Front Page Continuation (72) Inventor Ryuzo Yamada 2840, Ueno, Ikeda-cho, Miyoshi-gun, Tokushima Prefecture (72) Inventor Masayuki Takeuchi 457, Chufu-cho, Tokushima City, Tokushima Prefecture

Claims (2)

[Claims] 1. A method for kneading cement, sand, and cooled raw concrete in which ice is mixed with cooled aggregate to knead the cement, sand, and ice, and then the cooled aggregate is mixed. A kneading method for cooled ready-mixed concrete, which is characterized by additionally stirring. 2. A method for kneading cement, sand, and cooled raw concrete in which ice is mixed and kneaded in a cooled aggregate, and in the method, ice is added to the cement and stirred, and then sand and the bone are cooled. A method for kneading chilled concrete, which comprises adding and mixing a material.