JPH0545745B2 - - Google Patents

Description

[Detailed description of the invention]

<<Industrial Application Field>> This invention relates to a reverse pouring concrete method in which concrete is poured from the top to the bottom. <<Prior art>> In the reverse pour concrete method, it is difficult to make it adhere to the pre-cast concrete at the top because the lower post-cast concrete sinks. Therefore,
In most of the reverse casting methods to date, there are two methods: one is to inject grout into the gaps created at the joints after the concrete has hardened (injection method), and the other is to fill the gaps with non-shrinkage mortar (filling method). It was dealt with either way. Both the injection method and the filling method require post-treatment after concrete is placed, so there are issues with construction period, safety,
This is one of the technical issues that should be improved in terms of economic efficiency. In other words, there is a method (referred to as the direct method) that ensures the integration and watertightness of the joint by simply pouring post-cast concrete directly under the pre-cast concrete without any post-treatment as described above. Its development is strongly desired and has been actively researched. In the direct reverse concrete method, expansive concrete is used to compensate for settlement and shrinkage after concrete is poured. Expandable concrete, which is considered to be the most promising type based on research to date, is concrete with aluminum powder added as an expanding agent.
However, if aluminum powder is simply added to concrete, the expansion reaction will start immediately after mixing and almost end during pouring, resulting in the collapse of the concrete joint.
It can't be done quickly. For this reason, techniques have already been developed for expanding concrete for the reverse pouring method, such as applying surface treatment to aluminum powder so that an effective expansion reaction occurs after pouring.
Regarding this type of expansive concrete and the reverse concrete construction method using it, for example, JP-A-57-77065, JP-A-57-135757, JP-A-58
−60650 and other publications. <<Problems to be solved by the invention>> If expanded concrete to which aluminum powder is added (hereinafter treated to delay the expansion reaction unless otherwise specified) is used,
Compared to the reverse pouring method that uses ordinary concrete that does not use an expanding agent, the gap between pre-cast concrete and post-cast concrete can be much smaller, and they can be made to be in close contact with each other. However, even if expanded concrete made of aluminum powder is used, breathing cannot be completely suppressed, and even if pre-cast concrete and post-cast concrete come into close contact with each other due to expansion, a laitance layer is formed between them due to breathing. The adhesive strength was extremely low. Therefore, it has not become a method that can replace injection methods and filling methods. This invention was made in view of the above-mentioned conventional problems, and its purpose is to bring pre-cast concrete and post-cast concrete into close contact, prevent the formation of a laitance layer between them, and ensure sufficient adhesive strength. The object of the present invention is to provide a reverse concrete construction method using a direct method that enables the above-mentioned results. <Means for Solving the Problems> Therefore, in this invention, aluminum powder that has been surface-treated to delay the expansion start time is added as an expansion agent, and a breathing inhibitor such as water-soluble cellulose ether is added. The concrete is placed at least in the part that contacts the lower surface of the pre-cast concrete. 《Operation》 In addition to the aluminum powder expansion agent, a water-soluble cellulose ether breathing inhibitor is added, so that the concrete not only expands effectively after pouring, but also increases the viscosity of the concrete and prevents the separation of the constituent materials of the concrete. As a result, the post-cast concrete adheres well to the pre-cast concrete, and no laitance layer is formed. 《Example》 Concrete to which the above-mentioned expanding agent and breathing inhibitor have been added need only be poured in the part that contacts the lower surface of the pre-cast concrete, and these expanding agents and breathing inhibitors can be added to the lower part of the post-cast concrete. It is also possible to pour unconcrete concrete. Examples of the aluminum powder used as the above-mentioned expansion agent include those with an oxide film formed on the surface to delay the expansion start time (FC1550), and those with a coating material formed on the surface to delay the expansion start time. Use something like that (selmetsuku). The appropriate amount of aluminum powder to add differs depending on conditions such as the type of cement used and the construction scale, but in order to eliminate the gaps in the joints, an expansion rate of 0.6% or more is required, and for that purpose aluminum The amount of powder added is 0.01 to 0.08% by weight of cement.
That's about it. In addition, in order to uniformly disperse aluminum powder in concrete, a suspension of aluminum powder is made using a surfactant (e.g. Sunflow AD) or a cement dispersant for concrete (e.g. Sunflow PS). Mix this into mortar or concrete. The amount of water-soluble cellulose ether added as a breathing inhibitor should be adjusted to obtain a sufficient effect.
It should be 0.5% (weight ratio) or more of the unit water amount in concrete. If the amount is less than this, the viscosity of concrete will not increase much due to the addition of water-soluble cellulose ether, and the effect as a breathing inhibitor will not be obtained. Addition of water-soluble cellulose ether changes the expansion characteristics of concrete due to aluminum powder, so the amount to be added is determined by taking into consideration the synergistic effect with this. Various types of cement can be used, such as ordinary Portland cement, Mascon blast furnace class B cement, and Mascon blast furnace class B cement mixed with fly ash. Coarse aggregate and fine aggregate are added to this as appropriate, and AF water reducing agent and fluidizing agent are added as necessary to form base concrete. Next, more specific examples of the present invention and comparative test results of strength after construction will be described. Using the four types of concrete A, B, C, and D shown below, poured concrete specimens with the shapes shown were manufactured. In the figure, 1 is pre-cast concrete, 2 is post-cast concrete, and 3 is a joint. Concrete A...Base concrete in Table 1 only. Concrete B: Base concrete with 0.05% (weight ratio of cement) of aluminum powder (FC1550) added. Concrete C: Base concrete with 0.5% (weight ratio to unit water) of water-soluble cellulose ether added. Concrete D...Add 0.02% aluminum powder (FC1550) to the base concrete and add 0.5% water-soluble cellulose ether.
% added. However, the fluidizing agent in the base concrete shall be 0%. Bending strength tests were conducted on specimens using the above four types of concrete. The bending strength test was conducted 4 weeks after pouring concrete 2. Curing is done after pouring concrete.
It was left in a constant temperature, constant humidity room under air. Also, the exam is GISA
-1106, and was based on three-point loading. The test results are shown in Table 2 below.

【table】

[Table] As is clear from the above test results, compared to case A with only base concrete, case B with aluminum powder added as an expanding agent and case C with water-soluble cellulose ether added as a breathing inhibitor are both better. The strength has also been improved. However, in the case of the example of the present invention using concrete D containing both the above-mentioned expanding agent and the above-mentioned breathing inhibitor, the bending strength is about 4 times that of concretes B and C. The effect of using it in combination with a deterrent is clear. In addition, in the concrete A specimen, gaps due to settling of the post-cast concrete were observed, and only the paste was in line contact in the form of veins. Concrete B specimen had some parts in the innermost part where the pouring was insufficient, but other than that, the concrete was in close contact. The specimen made of Concrete D had good adhesion with no visible gaps at all. <<Effects of the Invention>> As explained in detail above, according to the present invention, aluminum powder subjected to a surface treatment to delay the expansion start time is used as an expansion agent, and water-soluble cellulose ether is used as a breathing inhibitor in concrete. Just add it to the concrete and pour it.
Since the joint between pre-cast concrete and post-cast concrete adheres well, and no laitance layer is formed at the joint due to breathing, the strength of the joint is extremely high and watertightness is also improved. In other words, the direct reverse concrete construction method can be satisfactorily implemented according to the present invention.

[Brief explanation of the drawing]

The figure is a perspective view of a specimen used in a bending strength test to demonstrate the effects of the present invention. 1... Pre-cast concrete, 2... Post-cast concrete, 3... Concrete joint.

Claims (1)

[Claims] 1. Concrete made by adding surface-treated aluminum powder to delay the expansion start time as an expansion agent and a breathing inhibitor such as water-soluble cellulose ether is applied to at least the part that contacts the lower surface of the pre-cast concrete. A reverse concrete construction method characterized by pouring concrete.