JP2000335947A - Artificial lightweight aggregate, its production and cement hardened product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an artificial lightweight aggregate capable of sufficiently exhibiting mechanical strength without deteriorating the durability of a cement hardened product when utilized as an aggregate, to provide a method for producing the aggregate and to obtain the cement hardened product using the artificial lightweight aggregate. SOLUTION: This artificial lightweight aggregate is produced by coating all or a part of the surface of a pulverized material of a plastic which is, e.g. a polyvinyl chloride resin with a cement hardened product subjected to carbonating treatment. The method for producing the artificial lightweight aggregate comprises mixing the pulverized material of the plastic which is, e.g. the polyvinyl chloride resin with a cement and water, granulating the resultant mixture and then carrying out the carbonating treatment thereof with carbon dioxide in a supercritical state at preferably <=100 deg.C temperature. The cement hardened product is obtained by mixing the artificial lightweight aggregate with the cement and water and hardening the prepared mixture.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an artificial lightweight aggregate in which plastics can be mixed in a large amount as an aggregate into a cement material, waste plastics can be effectively used, a method for producing the same, and the artificial lightweight aggregate. It relates to a cement hardened body obtained by using the same.

[0002]

2. Description of the Related Art Conventionally, lightweight aggregates have been used for the purpose of reducing the weight of cement moldings and structures. However, natural lightweight aggregates have a high water absorption and require a large amount of water to be added during construction. As a result, the strength of the molded body is reduced. Therefore, an artificial aggregate in which the surface of a natural lightweight aggregate is coated with cement and further subjected to a carbonation treatment to improve the water absorption of the aggregate has been proposed (see JP-A-6-92700).

[0003] On the other hand, there are cases in which waste plastics are used as lightweight aggregates. However, when a plastic material is directly mixed into a cement slurry, a large amount of plastic is added due to a low affinity between the plastic and the cement. Durability and mechanical strength decrease. In addition, when a plastic material is mixed into a slurry having a high fluidity when used for casting or the like, a problem may occur that separation occurs due to an excessively large specific gravity difference between the two.

On the other hand, for the purpose of increasing the affinity between plastic and cement, the surface of the plastic material is chemically mineralized to increase the adhesion to the inorganic matrix, thereby suppressing the reduction in the strength of the molded article. (See Japanese Patent Application Laid-Open No. 10-265252).

However, in the former method, since the natural lightweight aggregate is expensive, the obtained lightweight aggregate cannot be inexpensive. Even in the latter method, the metal alkoxide is used to make the surface of the plastic material inorganic. After the plastic material is immersed in a solution in which is added to an organic solvent (and water), heat treatment must be performed, the operation is complicated, the composition used is limited, and again, it can be inexpensive. The problem that there was not was left.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and in producing an artificial lightweight aggregate by using plastic waste, a cement which is used as an aggregate when used as an aggregate. An object of the present invention is to provide an artificial lightweight aggregate in which the durability of the cured body is not impaired and the mechanical strength is sufficiently exhibited, a method for producing the same, and a cement hardened body obtained using the artificial lightweight aggregate.

[0007]

In order to achieve the above object, the present invention according to claim 1 is characterized in that the whole or a part of the surface of a crushed plastic is covered with a cement hardened material subjected to a carbonation treatment. To provide artificial lightweight aggregates.
Further, the present invention according to claim 2 provides a method for producing an artificial lightweight aggregate in which a pulverized plastic, cement and water are mixed and granulated, and then carbonation is performed. The present invention according to claim 3 provides a method for producing an artificial lightweight aggregate according to claim 2, wherein the carbonation treatment is performed using carbon dioxide in a supercritical state at a temperature of 100 ° C or lower. The present invention according to claim 4 provides a cement hardened body obtained by mixing and hardening the artificial lightweight aggregate according to claim 1 with cement and water.

According to a fifth aspect of the present invention, there is provided the artificial lightweight aggregate according to the first aspect, wherein the plastic is a vinyl chloride resin. The present invention according to claim 6 provides a method for producing an artificial lightweight aggregate according to claim 2 or 3, wherein the plastic is a vinyl chloride resin. Hereinafter, the present invention will be described in more detail. The plastic used in the present invention is not particularly limited, and general-purpose thermoplastic resins such as vinyl chloride resin, polypropylene, polyethylene, and polystyrene are preferably used. This is because these resins are used in various fields in a large amount and are therefore used at a high rate as waste. In addition, thermosetting resins can also be used.

Among the above-mentioned general-purpose thermoplastic resins, it is technically difficult to convert vinyl chloride resin waste to oil and the like, and at present, no effective disposal method other than landfill has been established. Very suitable. As the plastic pulverized product, a pulverized product of a product molded as various molded products is usually used, but a pulverized product of a waste product formed in the molding process may be used. The particle size of the pulverized plastic is not particularly limited as long as it meets the purpose of use, and ranges from about 200 μm used as fine aggregate to 5 mm or more used as coarse aggregate. It is said.

[0010] In the present invention, the term "carbonated hardened cement" refers to a cement unhydrated raw material or a cement hydrate adhering to the surface of the above-mentioned pulverized plastic, which is exposed to carbon dioxide gas or supercritical carbon dioxide. The carbonation treatment was carried out. The carbonized hardened cement body covers all or a part of the pulverized plastic, and the coating thickness is not limited. However, if it is too thick, the lightening effect as a lightweight aggregate is impaired. Therefore, it is not preferable. In addition, it is preferable to cover a range that does not easily fall off the pulverized plastic material, specifically, it is preferable to cover at least half of the surface area of the pulverized plastic product.

The cement used in the present invention is not particularly limited as long as calcium hydroxide is generated with hydration. For example, ordinary portland cement, special portland cement, alumina cement and the like can be used. Portland cement is preferred in that the effect of densification during the carbonation treatment is large.

Here, the Portland cement is a cement mainly composed of an unhydrated calcium silicate compound generally called alite (C3S: 3CaO.SiO2) or belite (C2S: 2CaO.SiO2). Portland cement, early strength Portland cement, ultra early strength Portland cement, moderate heat Portland cement, low heat Portland cement, sulfate resistant Portland cement,
Examples include portland cements such as various low alkali type portland cements, mixed cements such as blast furnace cements, silica cements, fly ash cements, and white cements.

According to the method for producing an artificial lightweight aggregate of the present invention, a pulverized plastic material, cement and water are mixed and granulated, followed by carbonation treatment.
The method of mixing water and cement is not particularly limited, and an appropriate method may be used depending on the type and particle size of the plastic. For example, there is a method in which water is added with stirring in a granulator or the like after mixing the plastic pulverized material and the cement, or a method in which a pre-prepared cement paste is added to the plastic pulverized material to granulate. The granulation method may be a general granulation method, and a rolling method, a compression molding method, or the like is employed.

The carbonation treatment of the present invention refers to a treatment in which an alkali component, in particular, a calcium component is carbonated in the hardening process of cement. As a method of carbonation treatment, carbon dioxide gas of any concentration or carbon dioxide in a supercritical state can be used. The carbonation treatment is performed after the stage where the final shape is obtained by the granulation process. Preferably, the hydration rate of the calcium silicate compound contained in the cement is 0% (substantially the initial stage of hydration of the cement). Immediately after granulation)
It is in the range of 30%, more preferably 20% or less.

In the present invention, the hydration rate of the calcium silicate compound means that the amount of the unhydrated calcium silicate compound contained in the cement raw material is A, and the amount of the remaining unhydrated calcium silicate compound when the hydration rate is measured is B. Then, ｛(AB) / A｝ × 10
Refers to the value indicated by 0. As a method for measuring the amount of the unhydrated calcium silicate compound (alite and belite) in the cement, a known method using an X-ray diffraction measurement device or each magnetic resonance device (29Si NMR using silicon) may be used. Yes (Reference for NMR-based method: G. Parr
y-Jones, Cementand Concrete Research, Vol.19, p228-
234, 1989).

When the carbonation treatment is carried out at the stage of hydration or hardening, a hydrated structure has already been formed to some extent. Therefore, although the strength of the cement coating film is improved to some extent by filling between the structures, the water The effect of performing the carbonation treatment in the early stage of summation cannot be obtained.

In the method for producing an artificial lightweight aggregate according to the present invention, preferably, the carbonation treatment is performed with carbon dioxide in a supercritical state at a temperature of 100 ° C. or less, so that the durability and mechanical properties are more effectively improved. Can be expressed. Here, the carbon dioxide in a supercritical state refers to carbon dioxide at a temperature of 31 ° C. or higher and a pressure of 7.4 MPa (75 kgf / cm ² ) or higher. When heating at more than 100 ° C. is performed even in a supercritical state, carbonation of the cement structure proceeds more quickly and reliably, but the coefficient of expansion between the resin and the cement structure is greatly different. The state may be impaired, and if the treatment is performed at a temperature of 100 ° C. or less using gaseous carbon dioxide, the carbonation reaction of the cement structure may be insufficient.

Therefore, it is preferable to carry out carbonation treatment using carbon dioxide in a supercritical state at 100 ° C. or lower. In particular, when the thickness of the cement film is large, the carbonation reaction may be insufficient in the treatment with carbon dioxide in a gaseous state. Therefore, the treatment with carbon dioxide in a supercritical state is preferable.

The hardened cement of the present invention is a hardened cement obtained by mixing the artificial lightweight aggregate according to the present invention, cement and water and hardening by a hydration reaction. The addition amount of the lightweight aggregate is not particularly limited as long as it is substantially equal to or less than a range (actual rate of the aggregate) that can be substantially added to the hardened cement body. Particularly, when the content of the plastic is 30% by volume or less, Even if the aggregate of the present invention is not used, a certain degree of strength can be achieved and the object of reducing the weight can be achieved by pulverizing and adding the plastic. Therefore, when the content of the plastic is 30% by volume or more, the cement hardened body according to the present invention using the lightweight aggregate of the present invention is very significant.

(Function) The artificial lightweight aggregate of the present invention has the surface of the pulverized plastic material coated with a very hard material which is a hardened cement material subjected to a carbonation treatment.
The coating surface is strong. In addition, the desired hard film can be easily and simply obtained by producing by granulation and carbonation. Furthermore, when carbonation is performed using carbon dioxide in a supercritical state at a temperature of 100 ° C. or lower, carbonation of the cement structure can be performed without impairing the adhesion between the resin and the cement.

Since the surface of such an artificial lightweight aggregate is formed of a cement-based material, the affinity for the cement material is improved when used as an aggregate, and the function as the aggregate is sufficiently exhibited. Thus, the obtained cement hardened body maintains its strength sufficiently. In addition, since waste can be used as a main material of the aggregate, it is very useful from the viewpoint of effective use of waste.

[0022]

EXAMPLES Example 1 A polyvinyl chloride resin molded product generated as waste was pulverized to a particle size of about 5 mm.
25 parts by weight of ordinary Portland cement was added to and mixed with parts by weight, and the mixture was placed in a pan-type tumbling granulator and granulated while adding 8 parts by weight of water. After the granulation, the granulated product was put in an autoclave, and subjected to carbon dioxide treatment for 15 minutes under supercritical conditions at a temperature of 40 ° C. and a pressure of 10 MPa to obtain a lightweight aggregate.

(Examples 2 to 4) A vinyl chloride resin molded product generated as waste was broken and cut, and finally a particle size of 20 was obtained.
50 parts by weight of ordinary Portland cement was added to and mixed with 100 parts by weight of the mixture classified to about 0 μm, and the mixture was placed in a fluidized bed tumbling granulator and granulated while adding 100 parts by weight of water. After granulation, the granulated product was cured in a carbon dioxide atmosphere at 60 ° C. for 3 hours to obtain a lightweight aggregate.

Table 1 shows the specific gravity and the water absorption of the lightweight aggregates produced in Examples 1 and 2. Next, using the lightweight aggregate produced in Examples 1 and 2, a mixture of cement and water having the composition shown in Table 2 was used to obtain 200 × 200 × 30.
A cured cement body having a thickness of 2 mm was molded (Examples 3 and 4). Curing was performed for 7 days for natural curing. The unit volume mass (t / m ³ ) of the mixture for producing a cured cement body was calculated.

[0025]

[Table 1]

[0026]

[Table 2]

Comparative Example 1 A cured cement was molded in the same manner as in Example 3 except that the pulverized vinyl chloride resin used in Example 1 was used in place of the lightweight aggregate of Example 1. However, at the time of casting, the pulverized vinyl chloride resin was separated from other components.

(Comparative Example 2) A cured cement was formed in the same manner as in Example 3 except that the lightweight aggregate of Example 1 was used without being subjected to the carbonation treatment. Examples 3 and 4 and Comparative Examples 1 and 2
The tensile strength was measured for the cement hardened body molded in the above. Table 2 shows the results.

[Measurement of Tensile Strength] The obtained cement hardened body was cut into a predetermined size to obtain a test piece, which was subjected to JIS A111
The tensile strength due to split fracture was measured according to 3. The results are shown in Table 2.

[Measurement of Dimensional Change] The square material of the cured cement body obtained in Examples 3 and 4 and Comparative Example 2 was dried at 60 ° C. for 24 hours, and the dimensional change when immersed in water at room temperature for 24 hours was measured. did. The result is shown in FIG. In addition, the dimensions at the time of drying were measured after taking out the hardened cement from the oven at 60 ° C., and then leaving it in a dry cabinet for 1 hour.
The wet dimensions were measured immediately after removal from the water.

As can be seen from Table 1, the lightweight aggregate manufactured in the examples is a lightweight aggregate having a low specific gravity and a low water absorption. In addition, the cured cement using these materials exhibited good tensile strength in Examples 3 and 4, whereas in Comparative Example 1, the use of only the pulverized plastic as an aggregate was attempted. It was impossible to produce a homogeneous hardened cement body by only separating the aggregate. Further, in Comparative Example 2, an aggregate obtained by temporarily covering the surface of the pulverized plastic material with the hardened cement was obtained and the hardened cement was molded without performing the carbonation treatment, but a decrease in tensile strength was observed.

FIG. 1 shows the dimensional change of the cured cement bodies produced in Example 3 and Comparative Example 2 during the dry and wet cycle test. In Comparative Example 2, significant accumulation of dimensional change was observed with repetition. Was done.

[0033]

The artificial lightweight aggregate of the present invention is specified as described above, and the surface of the crushed plastic is coated with a strong material such as a hardened carbonized cement.
Since it has a low specific gravity and a low water absorption, it is a lightweight aggregate suitable for mixing with a cement material and can be provided at low cost. In addition, the method for producing an artificial lightweight aggregate of the present invention can easily and easily produce the above-described artificial lightweight aggregate by performing a carbonation treatment after forming a granulated product of a crushed plastic and cement, As a result, artificial lightweight aggregate can be provided at low cost.

Further, in the hardened cement according to the present invention, the above-mentioned artificial lightweight aggregate has a high affinity for the cement material and can sufficiently exhibit the function as the aggregate.
Since it is possible to fill a large amount of the above-mentioned artificial lightweight aggregate, it has excellent mechanical strength while having a low specific gravity, and furthermore has a small accumulation of dimensional changes during repeated drying and wet tests, and has a good durability and is a hardened cement body. It is. In particular, in the present invention, when the plastic is a vinyl chloride resin, the above-mentioned artificial lightweight aggregate, or in the above-described method for producing the artificial lightweight aggregate, effectively uses a vinyl chloride resin, which is generally difficult to treat waste. Can be very meaningful.

[0035]

[Brief description of the drawings]

FIG. 1 is a view showing a dimensional change of a cured cement body produced in Example 3 and Comparative Example 2 during a dry / wet repeated test.

Claims (6)

[Claims] 1. An artificial lightweight aggregate characterized in that the whole or part of the surface of a crushed plastic is covered with a carbonized cement hardened material. 2. A method for producing an artificial lightweight aggregate, wherein a carbonized treatment is carried out after mixing and granulating a crushed plastic, cement and water. 3. The method for producing an artificial lightweight aggregate according to claim 2, wherein the carbonation treatment is performed using carbon dioxide in a supercritical state at a temperature of 100 ° C. or lower. 4. A hardened cement body comprising the artificial lightweight aggregate according to claim 1, cement and water mixed and hardened. 5. The artificial lightweight aggregate according to claim 1, wherein the plastic is a vinyl chloride resin. 6. The method for producing an artificial lightweight aggregate according to claim 2, wherein the plastic is a vinyl chloride resin.