JPH0217504B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for constructing underwater concrete. Prior art and its problems Concrete is basically constructed in the air, and even when concrete is to be constructed in areas that come into contact with water, it is desirable to drain the water before pouring.
However, in some cases, it is not uncommon to be forced to perform concrete construction underwater. Especially in our country, which is surrounded by the sea on all sides,
In construction work on the ocean, ports, rivers, etc., underwater concrete construction is rather routinely performed. Currently, the construction methods for underwater concrete are as follows:
The tremie method, concrete pump method, prepack concrete method, bagged concrete method, open-bottom box method, etc. are used. However, the properties of underwater concrete placed by these methods that use ordinary cement are greatly influenced by the environmental conditions at the time of placement, the mix of concrete, etc. In addition, if the construction method is not appropriate, the concrete will be washed away by surrounding water, resulting in an uneven and defective construction, resulting in a low-strength, unreliable structure. Furthermore,
Water leaks due to concrete flowing into water.
There is also the risk of water pollution due to changes in pH and increases in turbidity. In recent years, a so-called special underwater concrete construction method has been developed that uses concrete with increased viscosity by adding a special polymer compound composition to concrete that uses ordinary cement. In this special underwater concrete, due to its high viscosity, the cement, fine aggregate and coarse aggregate adhere well to each other, so that it exhibits high resistance to the action of water from the outside. Therefore, it is said that it is possible to directly cast underwater concrete, that it has excellent self-leveling properties, that there is little separation of materials, and that it is possible to obtain highly reliable underwater concrete with stable strength and high construction efficiency. However, since this special underwater concrete does not yet have sufficient self-leveling properties, further improvement in construction efficiency is desired when constructing large or complex structures. Means for Solving the Problems As a result of repeated experiments and research in view of the current state of the technology as described above, the present inventor has found that when using a cement composition having a specific composition and generating a low amount of heat of hydration, discovered that underwater concrete with excellent self-leveling properties could be obtained. That is, the present invention provides the following method: ``When constructing concrete in water, 100 parts by weight of blast furnace slag, early strength Portland cement, etc.
The present invention provides a method for constructing underwater concrete, which comprises using a cement composition containing 15 to 40 parts by weight of gypsum fluoride and 3 to 10 parts by weight of gypsum fluoride. In the low heat type cement composition used in the present invention, which generates a small amount of heat of hydration, 15 to 40 parts by weight of early strength Portland cement and 3 to 10 parts by weight of hydrofluoric gypsum are blended with 100 parts by weight of blast furnace slag. There is.
When the amount of early-strength Portland cement is less than 15 parts by weight, the amount of blast furnace slag increases relatively, so the strength of the concrete decreases, and the degree of decrease in strength becomes large, especially in the case of long-term aging. on the other hand,
If the amount of early strength Portland cement exceeds 40 parts by weight, the heat of hydration will increase. In addition, if the amount of hydrofluoric acid gypsum is less than 3 parts by weight, the setting will be rapid and the workability will deteriorate, whereas if it exceeds 10 parts by weight, the cost will increase and the amount of ettringite will increase. There is a possibility that expansion cracks may occur due to formation. The particle size of blast furnace slag and hydrofluoric gypsum is not particularly limited, but the former usually has a specific surface area of 5000 to 7500.
cm ² /g, in the latter case the specific surface area is 3500 to 4500
It is about cm ² /g. When placing underwater concrete using the cement composition of the present invention, the proportions of fine aggregate, coarse aggregate, water, etc., mixing method, etc. differ from those when placing known underwater concrete. do not have. Effects of the Invention The cement composition used in the present invention has a lower amount of heat generated during the hydration reaction than known low-heat cements such as moderate-heat Portland cement, blast furnace cement, and moderate-heat fly ash cement. Concrete with excellent self-leveling properties can be obtained in a short pouring time, making it possible to construct highly reliable large-scale concrete structures with high construction efficiency. Further, the strength of the obtained underwater concrete at the early stage of its life is approximately the same as that of concrete using ordinary cement. Examples Examples will be shown below to further clarify the features of the present invention. Example 1 and Comparative Example 1 ¹⁰⁰ parts by weight of blast furnace slag (approx.
Cement composition consisting of 5.2 parts by weight (4000cm ² /g)
Add 196 parts by weight of fine aggregate, 266 parts by weight of coarse aggregate, and 54 parts by weight of water to 100 parts by weight, mix uniformly, and then pour concrete in water to determine self-leveling properties, compressive strength, and heat of hydration. We investigated the situation. still,
In the above formulation, an underwater separation inhibitor and a water reducing agent were used together as usual. On the other hand, as Comparative Example 1, concrete was prepared in the same manner as above except that blast furnace cement type B was used instead of the cement composition, and the same test was conducted. Self-levelling property is achieved by installing a partition plate 3 in the center of a container 1 with a width of 500 mm as shown in Figures 1 and 2.
After pouring concrete to a height of 250 mm in one space, remove the partition plate 3 and measure the heights H ₁ and H ₂ of the concrete at both ends after 5 minutes.
H=H ₁ −H ₂ (cm) was determined. The results are shown in Table 1. In Table 1, A indicates the amount (%) of the anti-separation agent in water.

[Table] It is clear that the concrete according to the invention has excellent self-leveling properties. In addition, Figures 3 and 4 show test pieces prepared in water and air (per cubic meter of cement).
370Kg) at the early stage of the material age. In Figures 3 and 4, a straight line (contains 1.00% of anti-separation agent in water), a straight line (contains 1.15% of anti-separation agent in water), and a straight line (contains 1.30% of anti-separation agent in water).
% content) shows the results for the present invention, and the straight line (contains 1.00% of anti-segregation agent in water), straight line (contains 1.15% of anti-segregation agent in water), and straight line (contains 1.30% of anti-segregation agent in water) shows the results for blast furnace cement B. Results are shown for a comparative example using seeds. The concrete according to the present invention is blast furnace cement B
It is clear that compared to concrete using seeds, it exhibits significantly improved early strength both in water and in air. Furthermore, Figure 5 shows the results of an adiabatic temperature rise test on concrete containing 1.30% of an underwater anti-separation agent. Curve (per cubic meter of cement)
370 Kg) and the curve (517 Kg per cubic meter of cement) shows the results for the present invention,
Curve (370Kg per cubic meter of cement)
and curve (per cubic meter of cement
517Kg) shows the results for a comparative example using B blast furnace cement. In either case, in the present invention, less heat of hydration is generated and the temperature is lowered by about 10°C.

[Brief explanation of drawings]

Figures 1 and 2 are drawings showing an outline of the device for measuring the leveling properties of concrete, Figures 3 and 4 are graphs showing the compressive strength of concrete, and Figure 5 is a diagram showing the concrete's insulation. The results of the temperature rise test are shown. 1... Container, 3... Partition plate.

Claims (1)

[Claims] 1 When constructing concrete underwater, 100 parts by weight of blast furnace slag, 15 parts by weight of early-strength Portland cement
A method for constructing underwater concrete, characterized by using a cement composition containing ~40 parts by weight and 3 to 10 parts by weight of hydrofluoric gypsum.