JPH03137046A - Material for underwater concrete - Google Patents

Abstract

PURPOSE:To lower the amt. of the expensive specific admixture to be used while maintaining the strength of concrete by adding fly ash to the material for underwater concrete formed by kneading cement, aggregate, specific admixture, and high-performance water-reducing agent with water. CONSTITUTION:The material for the underwater concrete is formed by compounding E) the classified fly ash (grain size: >=90% is <=10 mu) with the cement compsn. consisting of A) cement (ordinary Portland cement, grain size: 40 to 60 mu), B) the aggregate (e.g.: sea sand, bulk density.: 0.54, coefft. of water absorption: 1.33), C) the specific admixture (e.g.: 'Acrys 12S, D(R)' produced by Nisso Master Builders), and D) the high-performance water-reducing agent (e.g.: 'Mighty 150(R)' produced by Kao). The amt. of the specific admixture to be added is lowered to 75% of the reference amt. of addition by the addition of the fly ash.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Applications) The present invention relates to concrete materials used underwater in marine construction such as ports and river construction, so-called underwater concrete materials.

(Prior art) In the past, special admixtures for underwater concrete (hereinafter simply referred to as special admixtures) have been added to such materials for underwater concrete in addition to ordinary concrete materials, so that concrete can be made underwater. The separation resistance is increased to ensure performance such as predetermined strength.

(Problems to be Solved by the Invention) By the way, this type of special admixture is expensive, so the cost of materials for construction work has increased significantly, and at present, it has not been possible to use it in large quantities.

This invention was made based on this background, and aims to reduce the amount of expensive special admixtures used while maintaining performance such as strength of underwater concrete.

(Means for Solving the Problem) In order to achieve this object, the present invention provides an underwater concrete material in which cement, aggregate, special admixture, high performance water reducing agent, and water are kneaded. This is added with fly ash that has been selected to have a particle size smaller than the diameter of the fly ash.

(Function) According to this invention, since fly ash selected to have a particle size smaller than that of cement particles is added, after this underwater concrete material is constructed underwater, it is ensured that the particle size is small between the cement particles. By interposing a small amount of fly ash, breathing can be effectively suppressed.

As a result, by reducing the loss of cement particles from the concrete underwater, the underwater separation resistance of the underwater concrete increases, and it is possible to prevent the structure of the concrete from becoming uneven, thereby maintaining performance such as strength. The amount of special admixture added can be reduced compared to conventional methods.

(Example) An embodiment shown in the drawings will be described below.

FIG. 1 is an enlarged cross-sectional view of the underwater concrete material of the example in a state where it is constructed underwater.

In the figure, 1 indicates underwater concrete and 2 indicates water.

Underwater concrete 1 is similar to normal concrete,
In addition to cement, aggregate, superplasticizer, and water, special admixtures for underwater concrete are added.

Then, to this underwater concrete 1, fly ash (hereinafter referred to as classified fly ash) that has been sorted to a particle size of 10 μm or less, which is smaller than the particle size of cement particles, is added, mixed, and then applied underwater. It is something that

The cement of this underwater concrete 1 is ordinary Portland cement (manufactured by Osaka Cement Co., Ltd.), and the cement particles 3 have a particle size of about 40 to 60 μm.

Sea sand, which is a fine aggregate, is used as the aggregate. The specific gravity of this sea sand is 2. 54, the water absorption rate is 1°33, and 4 in the figure indicates sea sand grains.

As the high performance water reducer, for example, the high performance water reducer Mighty 150 (trade name) manufactured by Kao Corporation is used.

Acrys 12S (trade name) manufactured by Nisso Master Builders Co., Ltd. is used as a special admixture for underwater concrete, but as described later, the amount added is 75% of the standard sensitized amount. There is.

Furthermore, this underwater concrete is produced by burning coal. Fly ash is added, and the fly ash particles 5 of the classified fly ash added to this underwater concrete 1 are selected to have a particle size of approximately 10 μm or less.

As shown in FIG. 2, the particle size distribution of this classified fly ash is such that 90% or more of the fly ash particles 5 have a particle size of 10 μm or less.

In this example, the particle size of the classified fly ash was set to 10μ because the particle size of the cement grains 3 was 40 to 60μ.
This is because, as will be described later, the purpose of adding fly ash is to appropriately suppress breathing.

Therefore, depending on the degree to which breathing should be suppressed,
For example, even if the particle size of the classified fly ash is adjusted within the range of 20μ to 5μ, it is possible to carry out the process in exactly the same manner as in this embodiment.

If such materials are mixed with water and then applied underwater,
The composition of the underwater concrete 1 is that cement grains 3 and fly ash grains 5 are distributed around sea sand grains 4 which are aggregates.

At this time, since the grain size of the cement grains 3 is large as described above and the grain size of the fly ash grains 5 is small, the fly ash grains 5 are distributed so as to fill the gaps between the sea sand grains 4 and the cement grains 3. Become.

Therefore, these fly ash particles 5 make it difficult for breathing to occur after construction of the underwater concrete 1.

Breathing in underwater concrete 1 causes aggregates such as sea sand to sink and unevenly distribute the composition of the concrete, and also causes the surface of the concrete that comes into contact with water to be in a state of excessive cement, causing cement particles to be washed away by water. be.

According to this embodiment, by adding the fly ash particles 5, breathing can be prevented as described above, and this problem of underwater concrete can be solved.

Based on this viewpoint, the inventor of the present application conducted the following experiments and confirmed that the above-mentioned effects were achieved.

The materials used in this experiment, such as cement, aggregate, special admixture, high performance water reducer, and classified fly ash, were as follows:
Using the same materials as mentioned above, specimens of the same shape were prepared with the formulations shown in Table A-G below. ).

Surface water Cement F/A Aggregate Water reducer Admixture A
250 450 50 1250 5 7
5%B 250 425 75 1250
5 75%C2504001001250575χ
D 250 350 150 1250 5
75χg 275 500 g2.511
87.5 5 75%F 275 500
125 1125 5 75%G 275
500 0 1250 5 100% In this table, F/A is fly ash, aggregate is sea sand, water reducer is high performance water reducer, and admixture is special admixture. , the addition ratio to the standard addition amount is shown, and in other columns, the unit is shown in durams.

The standard amount of special admixture added in this experiment was 7k
g/m3, and what is indicated as 75% in the table is added at a rate of 5.25 kg/m''.

In this table, mix examples A-D are cases where classified fly ash is added as part of the cement, and mix examples E
and F are cases where classified fly ash was added as part of the fine aggregate. In addition, Formulation Example G shows a comparative example in which a standard amount of a special admixture was added.

After thoroughly kneading each of the concrete materials having the above-mentioned mixing ratios, specimens were prepared as follows.

The method for preparing the specimen is described in the "Special Underwater Concrete Manual" (published by the Coastal Development Technology Research Center).
The method for preparing the specimen in 1-2 of Appendix-1 Special Underwater Concrete Test was applied mutatis mutandis.

That is, length 70an, width 50ro, depth 30an
At the bottom of the container, three mortar frames were lined up, and water was poured so that the depth from the water surface to the top of the mold was 15 an.

Then, the grooved material was placed on a mortar mixing spoon, the tip of the mixing spoon was placed on the water surface, and the material was allowed to fall freely into the water to produce a rectangular parallelepiped (4anX 4C!OX 1 BG!l) specimen.

At this time, compaction was not performed as in the normal case.

Using each specimen prepared in this way,
B. Material Regulation 14 F3. The compressive strength at 28 days of age was measured, and the elongation of the strength was obtained with the strength at 7 days of age as 100.

The reason why we decided to evaluate each specimen based on the strength increase obtained in this way is that in construction using underwater concrete, we place emphasis on the final strength, and
This is because many construction projects take a long time, and experience shows that the greater the increase in strength, the greater the final strength.

Note that this compressive strength test was conducted according to JIS R5201, and the increase in strength is as shown in FIG. 2.

According to Figure 3, in the case of specimens A to D, in which classified ply ash was added as part of the cement, specimen G and specimen G were all mixed, even though the amount of special admixture added was 75% of the standard amount. It is possible to confirm that the strength has increased to the same level or higher.

In addition, in the case of specimens E and F, in which classified fly ash is added as part of the fine aggregate, although the amount of special admixture added was reduced, specimen G, which is a comparative example, This shows that the addition of classified fly ash contributes to reducing the amount of special admixtures that need to be added to concrete.

In addition to this experiment, the inventor also observed the turbidity of underwater concrete using the uncured concrete material according to the formulation example.

The method for observing this turbidity is to use a glass measuring cylinder with a capacity of 2 Yz (inner diameter 7.7 an, height 45.6 (!11)
The mortar was filled with water, the kneaded materials were placed on a mortar mixing spoon, the tip of the mixing spoon was placed on the water surface, and the material was allowed to fall freely into the water, and the appearance of turbidity and separation was visually observed.

The results are shown in Figure 4, and the criteria for determining turbidity were determined as follows.

Maximum: When the scale on the other side of the graduated cylinder cannot be seen at all.

If the scale on the other side of the female cylinder cannot be seen completely, but the upper part is less cloudy than the lower part.

If the scale on the other side of the middle cylinder is slightly visible.

Small: When the scale on the other side of the graduated cylinder is clearly visible.

Poles/1 yam When the scale on the other side of the graduated cylinder is clearly visible.

According to Fig. 4, which shows the observation results of this turbidity, when classified ply ash is added as a part of cement, the mixing ratios A and B are the same as Comparative Example G, but the mixing ratio is In the case of C and D, the turbidity becomes large.

In view of this turbidity, when adding classified fly ash as part of cement, there is a limit between the amount of classified fly ash added in specimen B and the amount of classified fly ash added in specimen C. It is expected that

On the other hand, when classified fly ash is added as part of the fine aggregate, Comparative Example G
is equivalent to

From these experimental results, it is clear that by adding classified fly ash to underwater concrete, it is possible to reduce the amount of special admixtures added, and because the amount of expensive special admixtures used is reduced, it is possible to reduce the amount of special admixtures used. Costs can be reduced.

In the embodiments described above, the amount of the special admixture added was set to 75% of the standard amount, but the present invention also allows the amount of the special admixture to be reduced by setting the amount other than this. Needless to say, it can be implemented.

(Effects of the Invention) As explained above, according to the present invention, since fly ash selected to have a particle size smaller than that of cement particles is added, the cement particles are By reliably interposing fly ash with a small particle size between the particles, breathing can be effectively suppressed.

As a result, by reducing the loss of cement particles from the concrete underwater, the underwater separation resistance of the underwater concrete increases, and it is possible to prevent the structure of the concrete from becoming uneven, thereby maintaining performance such as strength. The amount of special admixture added can be reduced compared to conventional methods.

[Brief explanation of the drawing]

The drawings relate to embodiments of the present invention; Fig. 1 shows a cross-section of underwater concrete, Fig. 2 shows a particle size distribution diagram of classified fly ash, Fig. 3 shows a graph showing the strength growth of each specimen, and Fig. 4 shows a graph showing the strength growth of each specimen. is a graph showing the observation results of turbidity of each specimen. No. 27 1; Underwater concrete, 2; Water, 3; Cement grains, 4; Sea sand grains (aggregate), 5; Fly ash private body #I: (Dom)

Claims (1)

[Claims] An underwater concrete material made by kneading cement, aggregate, a special admixture, a high-performance water reducing agent, and water, which is characterized by adding fly ash selected to have a particle size smaller than that of cement grains. Materials for use.