JP2004098549A - Method for producing ready-mixed concrete - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the strength of crushed concrete and stably and economically produce ready-mixed concrete having good workability, in a method for producing the ready-mixed concrete by using a crushed matter of concrete lumps as an amount corresponding to aggregate. <P>SOLUTION: Water is applied to the entire surface of the crushed matter A of concrete to mix cement in a layered state through this water. By this method, a cement cured film, wherein the cement inner layer part on the surface side of the crushed matter A of concrete is reacted with water, is formed not only to increase the strength of the crushed matter A of concrete but also to prevent the penetration of water at the time of production of redy-mixed concrete to enhance the workability. Further, the outer layer part of cement is formed into a thin cement layer C3 unreacted with water to increase the bonding force of water and cement at time of production of ready-mixed concrete to economically and stably obtain concrete having excellent strength. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a method for producing ready-mixed concrete with good workability using a crushed concrete mass generated by demolition of a concrete structure or the like as an aggregate.
[0002]
[Prior art]
In recent years, from the viewpoint of effective use of resources, concrete blocks generated when demolishing concrete structures are crushed, and it is possible to use all fine and coarse particles obtained by crushing as aggregate for ready-mixed concrete. It has been proposed and is being put into practical use. Concretely, concrete mass accumulated from the demolition site of the concrete structure is crushed by a crusher, and the crushed material, water and cement are put into a mixer at a fixed mixing ratio and kneaded to mix fresh concrete. Manufacturing is performed (for example, see Patent Document 1).
[0003]
In addition, a method is known in which an inorganic crystalline waterproofing agent is infiltrated into a crushed concrete mass to reduce the water absorption of the crushed material and increase the strength, and then cement and water are added to the crushed material to produce ready-mixed concrete. (For example, see Patent Document 2).
[0004]
[Patent Document 1]
JP-A-2001-130944 (pages 2-3, FIG. 4).
[Patent Document 2]
JP-A-10-316460 (pages 2 to 4, FIG. 1).
[0005]
[Problems to be solved by the invention]
However, the crushed material A obtained by crushing the concrete mass is, as shown in FIG. 4, a hard mortar layer A2 adhered to the surface of the original coarse aggregate A1 such as crushed stone. On the surface of the cured mortar layer A2, a large number of sharply protruding corners a1 and concave portions a2 are formed, and the degree of irregularity of the surface is increased, and further, cracks a3 are partially generated. .
[0006]
Therefore, as shown in FIG. 5, when the crushed material is directly poured into cement milk composed of cement and water and kneaded to produce ready-mixed concrete, as shown in FIG. 5, cracks a3 and recesses a1 are formed. It is said that the air present inside is in a sealed state, the cement milk c is not evenly distributed, and the cracks a3 and the recesses a2 become weak parts in strength, so that it is impossible to obtain a homogeneous ready-mixed concrete. There is a problem, and furthermore, since the water absorption of the hardened mortar in the crushed material is high, the workability related to concrete casting, that is, the workability is reduced quickly and the time available for casting is limited to a short time. In addition, there is a problem that shrinkage during curing is large and cracks are easily generated.
[0007]
On the other hand, according to the latter method, that is, according to Patent Literature 2, the water absorption of the crushed material can be reduced by infiltration of the inorganic crystalline waterproofing agent. Concrete is expensive and uneconomical, and it is difficult to increase the strength of a weak part such as a crack a or a concave portion as in the method of Patent Document 1, and there is a possibility that the strength of the concrete may be impaired. .
[0008]
The present invention has been made in view of such problems, and it is an object of the present invention to provide a method of producing ready-mixed concrete using crushed concrete as an aggregate equivalent, with excellent strength and good workability. It is an object of the present invention to provide a method for stably and economically producing ready-mixed concrete.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a method for producing ready-mixed concrete according to claim 1 of the present invention is a method for producing ready-mixed concrete comprising a crushed concrete mass, water and cement, wherein the entire surface of the crushed material is A step of adhering water to the crushed material; a step of dusting the crushed material with the water; and a step of spraying the cement powder onto the surface of the crushed material by the reaction between the cement powder dusted on the surface of the crushed material and the water. A step of allowing the crushed concrete to stand for a certain period of time until a cement-hardened film is obtained, and a step of adding water and cement to the crushed material forming the unreacted cement thin layer and kneading it. Features.
[0010]
In such a method for producing a ready-mixed concrete, the invention according to claim 2 is characterized in that a cement accelerator is added to the cement powder when the cement powder is sprayed on the surface of the crushed material to which water is adhered. Features.
[0011]
Furthermore, the invention according to claim 3 obtains, in advance, a relationship between a standing time of a crushed material whose surface is covered with cement and a change in workability of ready-mixed concrete using the crushed material, and from this relationship, the workability is determined. It is characterized in that a good standing time is set.
[0012]
[Action]
After a predetermined amount of crushed concrete is prepared in advance, for example, an amount of crushed concrete necessary for producing one batch of ready-mixed concrete, water is added to the crushed concrete and the mixture is stirred and mixed. When water is sprayed on the surface of the crushed material, the mortar layer at the surface layer of the crushed material has good water absorption, so that the mortar layer penetrates the entire surface layer including the cracked portion of the crushed material and adheres to the entire surface. . At this time, if the concrete crushed material is impregnated with a large amount of water, the subsequent treatment time becomes longer. Therefore, a small amount of water is added to the entire amount of the concrete crushed material and stirred, or the concrete is immersed in a large amount of water. By immersing the crushed material only for a short time, water is allowed to adhere shallowly to only the surface layer of the concrete crushed material and evenly over the entire surface, so that the surface becomes wet.
[0013]
Next, an appropriate amount of cement powder is added to the crushed concrete and stirred to adhere to the surface of the crushed concrete. In this case, since water is adhered to the entire surface of the crushed concrete, the cement powder is adsorbed by this water and adheres in a state where it is evenly layered on the entire surface of the crushed concrete, A cement coating layer that fills the cracks and recesses by being adsorbed by the water held in the cracks and recesses.
[0014]
In this state, the crushed concrete is converted into a cement-hardened film by the reaction of water with the inner layer of the cement coating layer adhering to the surface and the cement layer in the cracks and depressions, and the outer layer is unreacted. Let it stand for a certain period of time until a cement thin layer is obtained. Thereafter, a fixed ratio of water and cement is added to the crushed concrete and the mixture is kneaded to produce ready-mixed concrete.
[0015]
During the production of this ready-mixed concrete, the entire surface of the crushed concrete is covered with the cement hardening film, so that the strength of the crushed concrete increases and water penetrates into the crushed material. It is possible to easily and efficiently produce ready-mixed concrete with good workability, which is prevented by the above, and furthermore, since the cement hardened film is the inner layer and the outer layer is the unreacted thin cement layer, it is added to this crushed concrete. As a result, the bonding strength between the water and the cement increases and concrete with excellent strength can be stably supplied. In addition, shrinkage during hardening after casting concrete can be reduced, and cracks are less likely to occur.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, a specific embodiment of the present invention will be described with reference to the flowchart of FIG. 1. First, a concrete mass of a predetermined amount of ready-mixed concrete, for example, an amount of concrete mass required for manufacturing one batch (one batch) of ready-mixed concrete. Is taken out of the stock yard and put into a crusher (crusher), and the entire concrete block is crushed to obtain a crushed concrete A. As the crusher, any of a jaw crusher 1A as shown in FIG. 2A, a cone crusher 1B as shown in FIG. 2B, and a roll crusher 1C as shown in FIG. Good.
[0017]
As shown in FIG. 4, the concrete crushed material A crushed by the crusher has a cross-sectional shape in which the hardened mortar layer A2 is attached to the surface of the original coarse aggregate A1 such as crushed stone. The hardened mortar layer A2 is formed with sharply protruding corners a1 and recesses a2. Further, when cracks are partially generated and the crushed concrete A is directly used as aggregate of ready-mixed concrete, Corners a1, cracks a3, and the like become weakened portions, thereby reducing the strength of concrete.
[0018]
For this reason, the hardened mortar layer A2 of the crushed concrete A, the corners a, the cracks a3, and the like are subjected to reinforcing treatment so that ready-mixed concrete that can sufficiently secure concrete strength can be easily and economically manufactured. That is, first, the entire amount of the crushed concrete A is put into a mixer, a small amount of water is added to the mixer, and then the crushed concrete A and the water are stirred and mixed by starting and rotating the mixer, and the concrete is stirred. Water is evenly attached to the entire surface of the crushed material A, and the state is such that water is also penetrated into the recesses a2 and the cracks a3. At this time, since the hardened mortar layer A2 is excellent in water absorption, water is uniformly attached to the entire surface of the crushed concrete A in a short time, and at the same time, it fills the recesses a2 and the cracks a3.
[0019]
Incidentally, such a treatment for adhering water to the surface of the crushed concrete A may be performed by immersing the crushed concrete A in a large amount of water such as a water tank for a certain period of time and then taking out the crushed concrete A without performing the treatment in a mixer. Alternatively, it may be performed by spraying water on the crushed concrete A. However, in any case, it is not necessary to infiltrate water to the deep part of the hardened mortar layer A2 in the crushed concrete A, and if it is made to penetrate deep, the hardening time of the cement in the subsequent processing step becomes longer. Therefore, it is sufficient to make the surface slightly wet only in the surface layer portion of the hardened mortar layer A2 so that the surface is entirely wet.
[0020]
After uniformly adhering water to the entire surface of the concrete crushed material A in this manner, a small amount of cement powder is put into the mixer and the mixer is rotated to separate the concrete crushed material A and the cement powder in the mixer. When the mixture is stirred and mixed, the water adheres in a layer on the surface of the crushed concrete A, so that the cement powder is adsorbed by the water and adheres uniformly and in a layer on the entire surface of the crushed concrete A. The cement coating layer C covers the entire surface of the crushed material A. In addition, the inside of the recesses a2 and the cracks a3 formed in the hardened mortar layer A2 of the crushed concrete A is also adsorbed by the water held in the recesses a2 and the cracks a3, and the cement powder is removed. And the inside of the crack part a3 are filled without gaps.
[0021]
The amount of cement powder added to the crushed concrete A is such that the cement coating layer C can be provided on the entire surface of the crushed concrete A, that is, the sum of the surface areas of all the crushed concrete A The amount is obtained by multiplying the thickness of the coating layer C.
[0022]
When a certain processing time elapses until the cement powder is evenly sprinkled on the surface of the crushed concrete A by stirring and mixing the crushed concrete A and the cement powder, the rotation of the mixer is stopped and Let stand still for a certain period of time. In the cement coating layer C adhering to the surface of the crushed concrete A during the standing time, water is applied from the surface side of the crushed concrete A to which a large amount of water adheres, that is, from the inner cement layer portion. The hardening of the cement portion in the concave portion a2 and the crack portion a3 is started simultaneously with the reaction with the reaction with, and as shown in FIG. 3, the cement hardened portion C1 is formed in the concave portion a2 and the crack portion a3 and the inner layer is formed. When the cement layer part of the part becomes the cement hardened film C2, while the outer layer part remains as the unreacted thin cement layer C3 without being hardened yet, the ready-mixed concrete is manufactured in the mixer. A required constant amount of water and cement are charged, and the crushed concrete A, water and cement are kneaded by rotating a mixer to produce ready-mixed concrete. That.
[0023]
In addition, in the cement coating layer C on the surface of the crushed concrete A, in order to increase the setting speed by the reaction between the cement and the water and shorten the above-mentioned standing time, a small amount of cement powder was introduced into the mixer. Alternatively, a fixed amount of a cement hardening accelerator may be charged and added at the same time as the charging.
[0024]
In the method for producing a ready-mixed concrete, the concrete crushed material A provided with the cement coating layer C on its surface is allowed to stand in a mixer to form a cement hardened portion C1 in the concave portion a2 or the crack portion a3 and to crush the concrete crushed material. Setting of the time until the inner layer portion of the cement coating layer C on the surface side of A is formed on the cement hardened film C2 and the outer layer portion is formed on the unreacted thin cement layer C3, that is, it is possible to obtain ready-mixed concrete with good workability. The setting of the time until it is completed is set in advance to the standing time of a fixed amount of crushed concrete having a surface coated with cement, and the change in the workability of the ready-mixed concrete when the ready-mixed concrete is manufactured using the crushed concrete. This is done by asking for the relationship.
[0025]
That is, after adhering water to the entire surface of the crushed concrete material A in a certain amount, when the cement powder is applied to the crushed concrete material A to form the cement coating layer C on the surface, the static after crushing the cement is applied. The workability of each of the ready-mixed concrete obtained by preparing a certain amount of concrete crushed materials with different placement times, stirring and mixing a fixed amount of water and cement in these concrete crushed materials in a tank The stationary time at which the workability becomes the best is determined by detecting the rate of decrease in the above.
[0026]
As means for detecting the workability of ready-mixed concrete, means for detecting the rotating torque of the stirring blades in the tank by a torque meter, means for measuring the sound pressure in the tank, or kneading of crushed concrete, water and cement Means for detecting the degree of irregularities on the surface of the object can be employed.
[0027]
In order to determine the workability of the kneaded material based on the rotation torque of the stirring blade, a correlation between the slump value, which is an index indicating the degree of softness (fluidity) of the ready-mixed concrete, and the rotation torque of the stirring blade, And, a predetermined slump value when the workability becomes good is determined, the torque of the stirring blade for kneading the kneaded material is continuously detected, and the workability is determined from the slump value of the kneaded material corresponding to the torque value. Good or bad may be determined. The rotational torque value of the stirring blade increases as the flowability of the kneaded material decreases, and the rotational torque value of the stirring blade decreases as the flowability increases.
[0028]
Further, in order to determine the quality of the workability of the kneaded material based on the sound pressure, a relationship between the magnitude of the sound pressure and the degree of the workability of the kneaded material (mixed concrete) is determined in advance, as in the case of the torque. The workability is determined by continuously detecting the sound pressure of the kneaded material.
[0029]
On the other hand, in order to determine the workability based on the unevenness of the surface of the kneaded material, the degree of unevenness of the surface increases when the kneaded material has poor fluidity, and the degree of unevenness of the surface decreases when the flowability is good. Since the flatness increases like a water surface, the surface state of the kneaded material, that is, the degree of unevenness is detected by an optical distance meter or an ultrasonic distance meter, and the quality of workability is determined from the degree of unevenness. For example, a range finder is scanned in a radial direction above a kneading unit (mixer) to obtain a coefficient of variation of the surface height of the kneaded material, and the degree of surface unevenness is detected from the magnitude of this value. In this case, a correlation between the slump value indicating the fluidity of the kneaded material and the coefficient of variation is determined in advance.
[0030]
【The invention's effect】
As described above, according to the method for producing ready-mixed concrete of the present invention, as described in claim 1, a step of attaching water to the entire surface of the crushed concrete, And a step of allowing the concrete crushed material to stand for a certain time until the cement inner layer in contact with the surface of the crushed material by the reaction of the cement powder and the water sprayed on the surface of the crushed material becomes a cement hardened film, A process of adding water and cement to the crushed material forming the unreacted cement thin layer and kneading the crushed material, so that the mortar layer at the surface layer portion of the crushed material has a water absorption property. Because of the goodness, water can be uniformly and quickly attached to the entire surface layer including the recesses and cracks of the crushed material, and therefore, cement can be applied to the entire surface of the crushed concrete material through the attached water. It can be a state of being filled with cement in the recess and cracking unit it is possible to form easily and reliably cement coating layer comprising sprinkled to evenly layered.
[0031]
Furthermore, since the inner layer portion of the cement coating layer deposited on the surface of the crushed concrete is formed into a cement hardened film by reaction with water, and the cement in the concave portions and cracks generated in the crushed concrete is hardened, so that the concrete is hardened. The strength of the crushed material is increased, and at the time of producing ready-mixed concrete using this crushed concrete as an aggregate, the cement hardened film can reliably prevent water from penetrating into the crushed concrete. Therefore, ready-mixed concrete with good workability can be easily produced.
[0032]
In addition, since the outer layer of the cement coating layer is a thin layer of unreacted cement, the bonding strength between water and cement added to the crushed concrete increases and concrete of excellent strength can be economically and stably manufactured. In addition, it is possible to reduce the shrinkage at the time of hardening after placing the concrete, and to obtain ready-mixed concrete in which cracks are less likely to occur.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a production process of ready-mixed concrete,
FIG. 2 is a simplified front view of several types of crushers that can be used;
FIG. 3 is a cross-sectional view of a crushed concrete product provided with a cement coating layer on the surface.
FIG. 4 is a cross-sectional view of a concrete crushed material having a concave portion or a crack portion on a surface,
FIG. 5 is a cross-sectional view of a crushed concrete for explaining a conventional example.
[Explanation of symbols]
A Crushed concrete a1 Corner a2 Concave a3 Crack C Cement coating layer C1 Cement hardened part C2 Cement hardened film C3 Cement thin layer

Claims (3)

A method for producing ready-mixed concrete comprising a crushed material of concrete mass, water and cement, wherein a step of attaching water to the entire surface of the crushed material, and a step of dusting the crushed material with water with cement powder. A step of allowing the concrete crushed material to stand for a certain period of time until the cement inner layer in contact with the surface of the crushed material becomes a hardened cement film by the reaction between the cement powder dusted on the surface of the crushed material and the water, and this unreacted Adding water and cement to the crushed material forming the thin cement layer and kneading the mixture. The method for producing a ready-mixed concrete according to claim 1, wherein a hardening accelerator is added to the cement powder when the surface of the crushed material to which water is adhered is coated with the cement powder. In advance, the relationship between the standing time of the crushed material coated with cement on the surface and the change in the workability of ready-mixed concrete using this crushed material is determined, and from this relationship, the standing time at which the workability becomes good is set. The method for producing ready-mixed concrete according to claim 1, wherein:

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