JPH08337454A - Concrete composition having low strength and high packing property - Google Patents

Abstract

PURPOSE: To obtain a concrete composition excellent in fluidity and packing property, having low strength and excellent in workability by controlling and compounding a starting material composition in a specified range of water to cement ratio and slump flow value. CONSTITUTION: In the concrete composition containing cement, aggregate, water and bentonite, the water to cement ratio (W/C) is set in >=100% and unit water content and bentonite content are set in a slump flow value of 40-50. 70-83wt.% usually used aggregate is compounded per total composition and 5.0-10.0 pts.wt. bentonite is compounded per 100 pts.wt. cement so as to obtain the slump flow value of 40-50. The prepared concrete has a preferably a compression strength after 28day aging of 70-130kgf/cm<2> .

Description

Detailed Description of the Invention

[0001]

The present invention relates to a concrete composition having a low strength and a high filling property, which has a low strength, is excellent in fluidity and filling property and can be used as a concrete material for an underground continuous wall, a retaining wall, etc. Regarding things.

[0002]

2. Description of the Related Art Conventionally, when constructing a concrete continuous wall, it was common to install a form such as a rocking pipe or a partition plate in the joint, but due to the recent progress of excavating machines, the form is installed. The cutting joint construction method etc. which construct a continuous wall without it are implemented. In this construction method, since it does not take time to install the formwork, the construction period is shortened accordingly. That is, it is a method of constructing a leading element at a constant interval without providing a formwork, and then constructing a trailing element in the gap between the leading elements, wherein when the trailing element is constructed, It is a method of constructing while cutting a part. The time required for this cutting depends on the concrete strength of the preceding element and the like, and the concrete strength is an important factor for shortening the construction time.

[0003]

However, in the conventional art, the fact that the strength of concrete is made to be low has not been studied so far. The reason why this concrete strength is not studied so much is that, generally, when the water-cement ratio is increased to reduce the strength of concrete, bleeding increases, material separation is large, and poor concrete with reduced workability results. It is also considered that the higher the strength, the better. Therefore, it has been conventionally considered difficult to develop concrete having low strength and little variation in quality. Moreover, in the conventional concrete structure,
Not only those that are required to have the same strength as the present, but, for example, those that only require sufficient waterproofness such as earth retaining walls and rigidity to suppress earth retaining deformation, On the contrary, the concrete strength is a cause of a decrease in construction capacity and an increase in cost.

Therefore, the object of the present invention is to provide excellent fluidity and filling properties and low strength, and to exhibit excellent workability for construction of underground continuous walls, retaining walls, etc.
It is to provide a highly-fillable concrete composition.

[0005]

According to the present invention, in a concrete composition containing cement, aggregate, water and bentonite, the water-cement ratio (W / C) is 100% or more, the unit water content and the bentonite content. To provide a slump flow value of 40 to 50 cm, which provides a low-strength, high-filling concrete composition.

The present invention will be described in more detail below. The composition of the present invention contains cement, aggregate, water, and bentonite as active ingredients, and in particular, by setting the water-cement ratio and the unit water amount and the bentonite content ratio to specific amounts, for example, the obtained concrete is 100 kgf / cm. Even if the strength is as low as ² , it exhibits excellent filling and fluidity. This composition can be used as concrete in the construction of underground continuous walls, retaining walls, and the like.

As the cement, ordinary Portland cement, early-strength Portland cement, blast furnace cement or the like can be used.

The aggregate is not particularly limited as long as it is usually used for concrete, and any of natural aggregate, artificial aggregate and by-product aggregate can be used. The maximum particle size is preferably about 20 mm. The blending ratio of the aggregate is not particularly limited and is 70 to 83% by weight, especially 75% by weight based on the total amount of the composition.
~ 82 wt% is preferred.

The water has a water-cement ratio of 100% or more,
It is preferable that the content is 100 to 150% so that the concrete has a compressive strength of 70 to 130.
It is preferably about kgf / cm ² . When the water-cement ratio is less than 100%, the obtained concrete strength is high, and when it is used in, for example, a cutting joint construction method, cutting becomes difficult and the construction time is extended.

The bentonite is used to separate each material of the composition obtained even when the water-cement ratio is increased,
It is a component that prevents the deterioration of workability and reduces variations in concrete quality. The composition ratio of bentonite is such that the slump flow value of the composition is 40 to 50 cm,
It can be appropriately blended so as to preferably be 45 to 50 cm. When this slump flow value is less than 40 cm, the fluidity is insufficient, and when it exceeds 50 cm, the fluidity is sufficient, but separation of other components such as aggregate occurs,
The composition cannot be uniform. The blending ratio of this bentonite may be such that it has the above-mentioned slump flow value, and can be appropriately selected according to other compositions. For example, 5.0 to 10.0 with respect to 100 parts by weight of cement.
It can be blended in the range of parts by weight. The slump flow value is a value measured in accordance with the standards of the Japan Society of Civil Engineers (concrete slump flow test method).

In addition to the above-mentioned essential components, the composition of the present invention contains various types of AE agents, high-performance AE water reducing agents, AE water reducing agents, etc. within the range where the water cement ratio, slump flow value and the like are secured. It is also possible to add an admixture or the like. Particularly, as a high-performance AE water reducing agent, polyglycol ester, naphthalenesulfonic acid formalin high condensate, sulfonated melamine formalin condensate, polystyrene sulfonate,
Hydroxy polyacrylate, copolymer of unsaturated dicarboxylic acid and olefin, isobutylene-styrene maleic acid copolymer, isobutylene-acrylic acid ester-
Examples thereof include maleic acid-based copolymers, isobutylene-styrene-acrylic acid ester-maleic acid-based copolymers, aromatic aminosulfonic acid-based polymer compounds, and the like.

To prepare the composition of the present invention, cement, aggregate, water, for example, in a raw plant or on-site,
It can be prepared by a method such as adding bentonite and uniformly stirring and mixing. The prepared composition can be used in a manner similar to the usual use in applications where the concrete strength meets the low strength of the present invention. Use as concrete for cutting joint construction method such as underground continuous wall, earth retaining wall, etc. whose compressive strength after curing for 28 days is preferably 70 to 130 kgf / cm ² , particularly preferably about 100 kgf / cm ^2. By doing so, the construction time can be shortened.

[0013]

EFFECTS OF THE INVENTION The low-strength, high-filling concrete composition of the present invention has a slump flow value adjusted by a unit amount of water and a blending amount of bentonite, and a water-cement ratio of 10.
Since the content is 0% or more, low-strength concrete exhibiting excellent fluidity and filling property and having a compressive strength after curing for 28 days of about 70 to 130 kgf / cm ² is obtained without requiring compaction. Therefore, in the construction of the underground continuous wall, the earth retaining wall, etc., it is possible to shorten the construction time and surely fill every corner.

[0014]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples below, but the present invention is not limited thereto.

[0015]

Example 1 273 parts by weight of ordinary Portland cement,
164 parts by weight of water, 753 parts by weight of fine aggregate, 776 parts by weight of coarse aggregate and 1.09 parts by weight of AE water reducing agent are mixed together, and water 1 is further added.
A mixture of 36 parts by weight and 13.7 parts by weight of bentonite was added and uniformly mixed with stirring to prepare a concrete composition. The water-cement ratio (W / C) of the obtained composition is 1
The slump flow value was 10%, the amount of air was 0.7%, and the slump flow value was 50.0 cm, which was measured according to the JSCE standard (concrete slump flow test method).

Next, the following tests were carried out on the obtained composition. The results are shown in Table 1. Breathing rate: Measured by the JIS A 1123 concrete breathing test method. Fillability; using the L-type box fillability test apparatus shown in FIG. 1, after filling the box (A) with the concrete composition through the opening 1, the slide plate 2 is slid upward to fill the box (A). The amount of the concrete composition moved to the box (B) through the obstacles 3 having a diameter of 13 mm (obstacle distance 50 mm) was measured. Compressive strength: Measured by the JIS A 1108 concrete compressive strength test method.

[0017]

Comparative Example 1 A composition was prepared in the same manner as in Example 1 except that the amount of bentonite was changed to 10 parts by weight based on 100 parts by weight of cement (27.3 parts by weight based on 273 parts by weight of cement). did. Water-cement ratio (W
/ C) was 110%, the amount of air was 0.9%, and the slump flow value was 30.5 cm. Next, the same test as in Example 1 was performed on the obtained composition. The results are shown in Table 1.

[0018]

Comparative Example 2 333 parts by weight of ordinary Portland cement,
133 parts by weight of water, 728 parts by weight of fine aggregate, 751 parts by weight of coarse aggregate and 1.33 parts by weight of AE water reducing agent are mixed, and further 1 part of water is mixed.
A mixture of 67 parts by weight of bentonite and 16.55 parts by weight of bentonite was added and uniformly mixed with stirring to prepare a concrete composition. The water-cement ratio (W / C) of the obtained composition is
90%, the amount of air was 0.6%, and the slump flow value measured by Japan Society of Civil Engineers standard (concrete slump flow test method) was 34.5 cm. Next, the same test as in Example 1 was performed on the obtained composition. The results are shown in Table 1. From Table 1, it can be seen that in Comparative Example 2, the concrete compressive strength after curing for 28 days becomes too high.

[0019]

[Table 1]

[Brief description of drawings]

FIG. 1 is a schematic view of a filling property test apparatus used in Examples and Comparative Examples.

Claims (1)

[Claims] 1. A concrete composition containing cement, aggregate, water and bentonite, wherein a water-cement ratio (W /
A low-strength and highly-fillable concrete composition, wherein C) is 100% or more, and the unit water content and the bentonite content are slump flow values of 40 to 50 cm.