JPH0215499B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for constructing prepackaged concrete. Construction methods used to construct concrete structures underwater can be roughly divided into the following three types. (1) A method in which a temporary enclosure is set up underwater, the water inside the temporary enclosure is drained, and then concrete is poured in dry conditions in the same way as on land. (2) A method in which a steel or concrete well is lowered into the water, and concrete is poured directly into the water using a tremie pipe or special concrete bucket, without removing the water inside the well. (3) Lower wells and forms into the water, fill these frames with coarse aggregate without draining the water inside, and inject the aggregate downward into the voids of the coarse aggregate through a pre-installed injection pipe. The so-called pre-packed construction method involves injecting mortar and combining it with coarse aggregate to form concrete. These methods are used in various ways depending on the location conditions, the shape of the structure, etc., but when the water gets deeper than a certain level, method (1) becomes difficult to implement from both a technical and cost standpoint. . Furthermore, when the base area of a structure becomes large, method (2) becomes technically difficult, and in these cases, prepacked construction method (3) is often used. However, when using the prepackaged construction method,
Mortar is injected from below the coarse aggregate that has been submerged in water, and is pushed up through the voids in the coarse aggregate. As the mortar moves, it traps water and causes a separation phenomenon, causing it to spread around the coarse aggregate. Leaving a void or
It is difficult to construct a fairly homogeneous concrete by forming an area of only aggregate separated from the cement paste. For this reason, foaming expanding agents and air entraining agents are often added to improve the fluidity of mortar, but although these methods improve mortar separation to some extent, the foaming causes concrete to deteriorate. strength decreases. The present invention has been made based on these points, and will be explained below with reference to Examples. In the present invention, a part of the water in the designed amount of mortar or concrete is added to cement in advance and stirred to form a lump of cement, and then the cement is mixed with a high-frequency vibrator. By applying forced vibrations, a liquefaction phenomenon is caused, and by adding the remaining amount of water in the designed mixture and stirring again, the resulting cement paste has a higher fluidity than cement paste made by conventional conventional methods. A method for producing high-strength mortar and concrete by mixing this cement paste with sand or sand and gravel. It is related to. Generally, Portland cement has a cement weight of
When water equivalent to 55% is added, stirred well, and left to stand in a glass cylinder, it can be observed that the cement paste settles out to some extent and separated water accumulates at the top. If the cylinder is left as it is for 5 to 6 hours, the settled cement paste will solidify, and the cylinder can be tilted to easily take out only the separated water. Such separated water also occurs in mortar or concrete made by mixing cement paste with sand or sand and gravel, and has a great effect on the quality of the mortar or concrete. When we prepare a cement paste with a water/cement ratio of 55% without adding an injection admixture to ordinary Portland cement and measure the rate of formation of separated water, that is, the breathing rate, we find that breathing reaches 7 to 8% of the paste volume. reach however,
According to the method of the present invention, water equivalent to 25% of the cement weight is first added to the cement, stirred, and then subjected to high frequency vibration using a vibrator or the like to cause liquefaction, and then the remaining water is removed. When a cement paste with a water/cement ratio of 55% was made by adding and stirring again, and the breathing was measured in the same way,
Breathing rate decreased to 1-2%. Furthermore, by adding a certain amount of sand to the cement paste produced by the method of the present invention and kneading it, it is possible to produce a mortar with far less bleeding and better fluidity than mortar produced by a conventional method. Ta. In the case of the pre-packed construction method, the mortar must be pushed up and filled through the voids in the coarse aggregate, so it is not possible to form dense concrete unless the mortar has good fluidity. Furthermore, since the mortar is transferred while displacing water in the voids of the coarse aggregate, it is not possible to construct homogeneous prepacked concrete without separation unless the mortar has a low rate of breathing. Example 1 The launch speed of the present invention was calculated when water was filled in a cylinder with an inner diameter of 15 cm and ordinary mortar with a cement:sand ratio of 1:1 and a water/cement ratio of 0.55 was injected through a pipe with an inner diameter of 12.5 mm. The method was compared with that of mortar with the same composition. The figure shows the results. Therefore, as can be seen from the figure, the method of the present invention can be applied at three times the speed of the conventional method, and it can be seen that the fluidity is extremely improved. Example 2 Mortar with cement: sand = 1:1, water-cement ratio 0.55 and cement: sand = 1:2, water-cement ratio 0.69, using the conventional method and the method of the present invention. Prepackaged concrete was constructed and the density and compressive strength of each type of concrete were compared. The following table shows the results.

[Table] As is clear from the table, the method according to the present invention is far superior in both density and compressive strength. Therefore, when performing pre-packed construction, it is common to add a foaming injection admixture to improve the fluidity of the injection mortar. There is a drawback that the compressive strength of concrete decreases when these admixtures are used, and even though the fluidity of poured mortar is improved by the addition of these admixtures, the effect of inhibiting separation is small, but the method according to the present invention has a much greater It is effective, and according to examples in which these admixtures are added to the method of the present invention, the synergistic effect of both shows very excellent workability.

[Brief explanation of drawings]

The drawing is a graph diagram showing a comparison between the present invention and a conventional method.

Claims (1)

[Claims] 1. High-frequency vibration is applied to Portland cement mixed with water of 25% or more of the weight of the cement within a predetermined water-cement ratio range of a pre-packaged concrete pouring mortar. After adding the remaining amount of water to the mixture and stirring it again, the resulting mortar is mixed with the designed amount of fine aggregate. A prepacked concrete construction method characterized by injecting coarse aggregate into an air source that has been filled in the formwork in advance. 2. Within the specified water-cement ratio of prepackaged concrete pouring mortar, high-frequency vibration is applied to Portland cement mixed with water of 25% or more of the weight of the cement to induce liquefaction. After this, the remaining amount of water in the design mix with the specified injection admixture added is added to this, stirred again, and the resulting mortar is mixed with the designed amount of fine aggregate. A method of constructing prepackaged concrete, which is characterized by injecting coarse aggregate into the voids of coarse aggregate that has been filled in advance in formwork.