JPH0231182B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides concrete pouring joints (especially reverse pouring) that can achieve extremely good strength and water-stopping properties in concrete pouring joints without sacrificing consistency or using filler joints, while maintaining normal concrete construction. ) Regarding construction methods. Particularly in the case of reverse pour concrete construction, in which concrete is poured from below onto already constructed concrete, sufficient adhesion strength is not developed at the pour joints, so various countermeasures have been taken in the past. In other words, as is well known, during the setting process of concrete, water is generated on the top of the concrete due to breathing, causing volumetric contraction, and especially in the case of reverse pouring, the top surface of the concrete becomes a pouring seam, resulting in a decrease in adhesive strength. Conventional countermeasures for this problem include (a) adding an expanding agent to give the concrete volumetric expansion, and (b) leaving the joints in place and filling them with special mortar. , (c) using so-called hard-mixed concrete in which the mixed water content is lowered to minimize breathing, etc., are being implemented singly or in combination. However, in method (a), an expanding agent such as aluminum powder is added to compensate for volumetric shrinkage, but with this alone, it is difficult to completely remove water channels and weak layers of laitance at pour seams. However, the problem remains that sufficient adhesion at the seams and sufficient water-stopping properties cannot be expected. In addition, method (b), in which the joints are filled with a special expandable mortar, requires a lot of work and impairs workability, and requires complete removal of laitance from the poured concrete, leaving the joints. Otherwise, it will not be effective and there will be difficulties in the construction of large concrete. Furthermore, when hardened concrete is used in (c), it becomes difficult to fill and compact the concrete, and as a result, the constructed structure is likely to have areas where the concrete is not filled, leading to water leakage. Furthermore, in recent years, it has become increasingly difficult to obtain good quality aggregates and to ensure good workability with a small amount of water, and this hardening method is also not suitable for actual construction. The purpose of the present invention is to solve such problems in conventional concrete pouring (reverse pouring) construction, and it does not require expansion as in (a) (however,
In addition, even if you do not reduce the amount of mixed water as in (c), the strength of this joint will be Workability and strength comparable to the base material,
This provides a concrete pour joint construction method with good water-stop properties. In other words, in the concrete pouring method of the present invention, when directly pouring concrete that is not yet hardened to concrete that is in the middle of hardening or has already hardened, mortar prepared in accordance with the physical test method for cement according to JIS R5201 is used as pouring mortar for prepackaged concrete. A thickening agent that reduces the breathing rate to 0.1% or less by adhering the cement particles and sand particles in this mortar when subjected to the breathing rate and expansion rate test method (Japan Society of Civil Engineers) of It is characterized by adding 0.2 to 2% by weight of water into unhardened concrete to increase the strength of the pour joint without reducing the amount of water mixed. In other words, the present invention is completely different from the approach of trying to prevent breathing as much as possible by reducing the unit water volume that lowers the consistency, and the consistency is still adjustable to the extent necessary for construction. Even when the seam is on the top surface, such as in reverse casting, the distribution of cement and water in this area is completely different from that inside. The particles are made to adhere to each other, and even when placed under gravity while still unhardened, the distribution density of cement and sand in the upper and lower kneaded materials remains unchanged until hardening. . Based on this idea, the inventors of the present invention have conducted various tests and studies, and have found that the degree of adhesion between cement and sand is
When mortar prepared in accordance with the cement physical test method according to JIS R5201 is subjected to the testing method for breathing rate and expansion rate of poured mortar for prepacked concrete (Japan Society of Civil Engineers), the breathing rate shall be 0.1% or less. Select a thickening agent and add this thickening agent to the weight ratio of water in concrete from 0.2 to
It was found that it was necessary to add 2%.
Here, mortar prepared according to the physical test method for cement according to JIS R5201 is defined as "cement mixed at once with a weight ratio of 1 part cement, 2 parts standard sand, and a water-cement ratio of 0.65. The specified amount of standard sand and water to be collected is 520 g of cement, 1040 g of standard sand, and 338 g of water.
Mortar made by a method defined as ``If machine mixing is not possible, hand mixing may be used.'' In addition, as is well known, the breathing rate is determined in accordance with the ``Test Method for Breathing Rate and Expansion Rate of Prepacked Concrete Pouring Mortar'' (JSCE-1986) stipulated by the Japan Society of Civil Engineers by performing the following operations. 1) Fill a polyethylene bag with a length of 50 cm or more, with a diameter of about 5 cm when filled with mortar, to a height of about 20 cm, taking care not to trap air. 2) 400ml of water in a measuring cylinder with a capacity of 1000c.c.
cc and gently place the bag containing the mortar into the water. 3) Lower the bag until the water level in the graduated cylinder matches the mortar level, and calculate the volume of mortar Vc.c. by subtracting 400 c.c. from the water level reading at this time. 4) Tie the top of the bag and hang it up. 5) After 3 hours have elapsed from the start of the measurement, use a pipette to suck up the water from the breathing on the top of the mortar, put it into a 20 c.c. graduated cylinder, and measure it, and use this as Bc.c. Gently pour this water back onto the top of the mortar. 6) If 20 hours or more have passed after the start of measurement, repeat step 5 above.
Measure the water due to breathing in the same way as
Let it be B′cc. 7) The test shall be conducted on three or more specimens. Based on the above test, the breathing rate is determined by the following formula. Breathing rate after 3 hours = (B/V) x 100 (%) Final breathing rate = (B'/V) x 100 (%) In the present invention, the breathing rate after 3 hours and the final Both breathing rates are measured. Then, it is checked whether the measured values of both are 0.1% or less, and if both are 0.1% or less, it is determined that the requirements of the present invention are satisfied. Thickening agents that can reduce the breathing rate to 0.1% or less according to the above test include polyvinyl alcohol, polyacrylamide, polyethylene oxide, sodium polyacrylate, carboxymethyl cellulose, methyl cellulose, and cellulose ethers represented by these. Sodium alginate, guar gum, Korean ginkgo herb, or similar thickening agents may be mentioned. These thickeners are often in powder form, and can be added uniformly to dry mix when mixing concrete, but they can also be made into an aqueous solution and added in a ready-mixed concrete truck. Further, some of these thickening agents entrain fine air bubbles, and in such cases, it is preferable to use antifoaming agents such as dibutyl phthalate and water-insoluble alcohols. Furthermore, at construction sites where it is desired to obtain a particularly high consistency without increasing the amount of water, a water reducing agent such as a polymeric aromatic sulfonate, melamine sulfonate, etc. may be used in combination. In any case, regardless of the presence or absence of such composite additives, a thickening agent that satisfies the above test conditions has a weight ratio of 0.2 to the amount of water in the concrete being constructed.
It is necessary to mix 2%. If it is less than 0.2%, it is difficult to obtain sufficient seam strength under the normal consistency according to the construction conditions. The effect is saturated and meaningless. By mixing the thickener according to these conditions, even in the case of reverse pouring construction, the strength of the pour joint with the upper concrete can be increased to the same level as that of the base material, and the water can be completely stopped. Since this concrete maintains good fluidity not only at the top joint but also at the side, slope, and bottom joints, the same effect as the top joint can be obtained. In particular, depending on the construction location, the formwork and retaining material may sink or shift in position unexpectedly, resulting in gaps at the joints, but even in such cases, the present invention can solve the problem due to its flow characteristics. It is possible to eliminate gaps between joints and obtain sufficient joint strength. However, if such gaps are large, or if it is thought that adding some expansion to the concrete will result in more reliable construction, it is recommended to add an expansion agent such as aluminum powder in addition to this thickening agent. The expansion effect can further strengthen the integrity and water-stopping properties at the seams. In this way, the method of the present invention can be used while satisfying the necessary consistency determined by the scale of the structure and construction conditions, that is, without special reduction of unit water volume. By pouring it in the same way as concrete construction, it is possible to ensure the strength and water-tightness of the pour joints, and in particular, as a reverse pouring construction method, it exhibits effects that cannot be achieved with conventional methods. The effects of the present invention will be specifically explained below with reference to typical examples. Example: With a water-cement ratio of 55% and a slump of 15 to 18 cm, the following four types of concrete mixes were made using the same cement and aggregate materials, and these were placed in the formwork shown in Figure 1. We carried out the typing. No.1... Ordinary concrete. No. 2: Concrete with aluminum powder added to No. 1 at a weight ratio of 0.012% to the amount of cement. No. 3: Concrete with 0.6% methylcellulose-based thickener added to No. 1 based on the weight ratio of water. No. 4...Methylcellulose-based thickening agent is added to No. 1 at a weight ratio of 0.6% to the amount of water, and aluminum powder is added at a weight ratio of 0.012 to the amount of cement.
% added concrete. In addition, in FIG. 1, 1 indicates pre-cast concrete (fully hardened concrete), 2 indicates poured concrete, 3 indicates formwork, and 4 indicates edge cutting tape. A bending test was conducted on each specimen at 2 days old using the loading method shown in FIG. In FIG. 2, 5 indicates a loading position and 6 indicates a reaction force position. The results are shown in Table 1.

[Table] From the results in Table 1, even if aluminum powder is simply added and expanded (in the case of No. 2), a slight improvement in seam strength can be obtained compared to No. 1, but according to the present invention By using the thickening agent, the bending strength was approximately three times higher than that in the case of adding this aluminum powder (No. 2), regardless of the presence or absence of this aluminum powder (No. 3 and No. 4). ). The strength of the seam produced by this invention is comparable to the strength of the base material. Furthermore, concrete with mix No. 4 was poured into concrete having the dimensions and shape shown in Figure 3.
In FIG. 3, 7 is hardened pre-cast concrete, 8 is poured concrete, and 9 is a poured joint. One week after the construction of this joint, a water permeability test was conducted by applying a water pressure of 3 kg/cm ² to the joint. As a result, it was found that no water permeation occurred at all, and that the seams were completely integrated.

[Brief explanation of drawings]

Figure 1 is a diagram for explaining the shape and dimensions of the reverse concrete specimen used in the embodiment of the method of the present invention, Figure 2 is a diagram showing the loading method for the bending test of the specimen in Figure 1, FIG. 3 is a perspective view for explaining the shape and dimensions of an example of a reverse concrete construction body. 1, 7... Pre-cast concrete, 2, 8... Pour concrete.

Claims (1)

[Claims] 1. When directly pouring concrete that is not yet hardened to concrete that is in the middle of hardening or has already hardened,
When mortar prepared in accordance with the cement physical test method according to JIS R5201 was subjected to the "Test method for breathing rate and expansion rate of poured mortar for prepackaged concrete" (JSCE-1986) specified by the Japan Society of Civil Engineers, this mortar The breathing rate is reduced to 0.1 by making the cement particles and sand particles stick together.
Add a thickening agent to the above-mentioned unhardened concrete for pour joints at a water weight ratio of 0.2 to 0.2% or less.
A concrete pouring joint construction method characterized by adding 2% of water to increase the strength of the pouring joint without reducing the amount of mixed water. 2. The concrete pour joint construction method according to claim 1, wherein the pour joint portion is located above the concrete that has not yet hardened. 3. When directly pouring concrete that is not yet hardened to concrete that is in the middle of hardening or has already hardened,
When mortar prepared in accordance with the cement physical test method according to JIS R5201 was subjected to the "Test method for breathing rate and expansion rate of poured mortar for prepackaged concrete" (JSCE-1986) specified by the Japan Society of Civil Engineers, this mortar The breathing rate is reduced to 0.1 by making the cement particles and sand particles stick together.
Add a thickening agent to the above-mentioned unhardened concrete for pour joints at a water weight ratio of 0.2 to 0.2% or less.
A concrete pouring joint construction method characterized by adding 2% of concrete and adding an appropriate amount of an expanding agent to expand the concrete, thereby increasing the strength of the pouring joint without reducing the amount of mixed water. 4. The concrete pour joint construction method according to claim 3, wherein the pour joint portion is located above the concrete that has not yet hardened.