JPH0336313A - Crushing method for excessive concrete in cast-in-place concrete pile - Google Patents

Abstract

PURPOSE:To improve the workability by mixing an expansibility substance in crushing-expected unhardened excessive concrete, and generating a crack in the excessive concrete total unit to crush it, for execution of cast-in-place concrete piles. CONSTITUTION:For execution of cast-in-place concrete piles 1, a granular hydration expansibility substance is forcedly stirred by an electrically driven stirring machine, mixed, cast and hardened in unhardened excessive concrete 2 in the interior of reinforcement cage main bars 4, 4' in excessive concrete after ready- mixed concrete is cast. The excessive concrete 2, by generating a crack in its total unit, is crushed and removed from a pile main unit. Here a crushing- expected surface A is set in the upper about 100mm from an upper surface B of the pile main unit so as to prevent expansion action and the crack from being propagated to the pile main unit. In this way, the excessive concrete 2, in which the crack is totally generated, can be easily removed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for constructing cast-in-place concrete piles.
This invention relates to a method in which when pouring fresh concrete, an expandable substance is mixed into so-called unhardened concrete at the head of the counter, the mixture is hardened, and a crank is generated to crush the hardened concrete.

[Conventional technology]

Cast-in-place concrete piles are constructed by inserting a reinforcing bar cage into a hole excavated in the ground where construction is planned, and then pouring fresh concrete from the bottom through a transport pipe that contains large particles and allowing it to harden.

However, after construction, the ready-mixed concrete at the head of the pile is mixed with muddy water and earth and sand from the hole, so it does not achieve the specified strength.
Pour a large amount of material so that it is about m high, or add extra material.)
A commonly used method is to crush and remove hardened excess concrete.

Hardened excess concrete has conventionally been crushed mechanically using a breaker or the like, but recently a method using a static crushing agent has also been adopted.

For example, a water-permeable tube filled with a static crushing agent is fixed to a suitable location of a reinforcing bar cage in extra-heavy concrete, absorbs the mixing water of the poured fresh concrete, causes a hydration reaction, and generates an expansion force. In addition, a slurry of static crushing agent is applied near the planned crushing plane between the pile body and the pile and at appropriate locations in the pile. There is a known method in which a sheathed pipe enclosing concrete is installed, poured, hardened, cracks are generated partially in the excess concrete, the concrete is divided, and the concrete is divided into smaller pieces for removal.

Therefore, in order to improve crushing efficiency in conventional methods,
Developments have focused on how to arrange and fix the tubes and sheath pipes (Special Publication Publication No. 63-2).
7488, JP-A-62-59686, JP-A-61-14
6912, JP-A-61-122322, JP-A-6O-2
6719).

[Problem that the invention seeks to solve]

In the conventional method, before pouring fresh concrete, water-permeable tubes and sheathed pipes were manually attached to the reinforcing bars of the reinforcing bar basket in the extra heap area scheduled for crushing. Because the work was surprisingly complicated and troublesome, the water-permeable tube and sheath tube were often damaged, and the attachments had to be replaced each time. In addition, when we placed water-permeable tubes, etc. into the reinforcing bar cage in advance and inserted them into the large cage, the six members were too large, so the reinforcing bar cage went deeper than planned, and the crank was also placed in the concrete that was supposed to be left as a pile. Occasionally, I was forced to do unexpected work. Furthermore, since muddy water and earth and sand mixed in unhardened concrete are unevenly distributed, the properties of hardened concrete are not uniform, with some parts being weak and others porous. Because of this, cracks did not always occur as designed, or at most, micro-cranks were often generated.

In such cases, the work to remove the hardened excess concrete was not simple and required the use of conventional mechanical removal methods, making the work difficult. This problem has been a concern since the development of the method for removing excess concrete using static crushing agents, and has remained unresolved to this day.

[Means for solving problems]

Therefore, the present inventors conducted research on a method of generating numerous cracks in the entire excess concrete to be removed in order to make the work simple, without loss of static crushing agent, and to facilitate the work of dividing into small pieces. As a result, they discovered that the intended purpose could be achieved by a surprisingly simple method of mixing an expansive substance into the cast extra concrete before it hardened, and based on this, the present invention was completed. .

That is, when constructing a cast-in-place concrete shaft, the present invention includes adding an expandable substance to at least the uncured excess concrete inside the reinforcing bar cage in the excess concrete after pouring fresh concrete, and forcibly mixing it. Let it harden.
This causes cracks to occur in the entire excess concrete,
This method involves crushing and removing it from the pile body.

The present invention will be explained in detail below.

The expandable material used in the present invention is a powdery granular material that, when mixed with fresh concrete, hydrates and expands somewhat later than the start of hydration hardening of the cement in the fresh concrete. In particular, it is desirable to use a substance that hydrates and expands about 12 hours after mixing. Specifically, it may be appropriately selected from commercially available static crushing agents, calcined dolomite, calcined magnesia, hard calcined lime, and the like.

The method of adding and mixing the expandable substance into the uncured extra concrete after pouring is not particularly limited in the present invention; the expandable substance may be mixed so as to be dispersed throughout the extra concrete. However, at least, the reinforcing bar cage (the main reinforcement of the reinforcing bar cage is
Generally, the piles are installed about 20% inward and along the outer periphery in the pile height direction. The purpose can also be achieved by mixing it with the excess concrete existing inside the concrete and sufficiently dispersing it, and this is more practical in terms of working time and simplifying the work.

The method of introducing the expandable substance may be, for example, by stirring the uncured excess concrete in powder form or in the form of a slurry, or by press-fitting it into the excess concrete through a vibrator. Mixing can be done by hand if there is a small amount of uncured concrete, but it is usually done forcibly using an electric mixer (e.g. a powerful hand mixer). It is preferable to stir and mix.

The amount of expansive material to be mixed cannot be determined unconditionally as it is related to the properties and amount of muddy water and earth and sand that get mixed in during pouring, but it is recommended to mix 5 to 30 kg of the remaining concrete to be mixed. desirable. If the weight is 5 kg or less, the width of the crank produced may not become large, and if the weight is 30 kg or more, the crushing effect tends to increase to a certain extent, but it is economically disadvantageous considering the effect.

Next, the planned fracture surface with the pile body will be described.

As with the conventional method, the design height,
In other words, 100n from the position of the top surface of the pile body (Fig. 1, B)
It is preferable to use the front and upper sides as the planned crushing plane (FIG. 1, A), and to mix an expandable substance into the uncured excess concrete above the plane. The reason for this is that the pile body and the reinforcement are formed continuously, and because the expansion fracture is based on a chemical reaction, it is necessary to prevent the expansion action and cracks from propagating to the pile body, so the above-mentioned It is desirable to provide a crushing surface at the location.

It should be noted that crack prevention bars and concrete adhesion prevention tubes used in conventional methods may be used in the present invention.

〔Example〕

Fresh concrete was poured and three cast-in-place concrete shafts with a diameter of 1000n+ were constructed with a design trench height of 600n.

The planned fracture plane was set at 100 fl above the design shaft height. As shown in Figure 1, a commercially available lime-silicate static crushing agent (Nippon Cement Co., Ltd. 6 kg, 11 kg, and 16 kg of Calamite, Bulk Type SJ, manufactured by Caramite, Inc., trade name, were mixed into the unhardened concrete of each pile.The mixing of each pile was carried out by stirring the concrete of the pile with a powerful hand mixer. The above-mentioned static crushing agent was added in four portions and thoroughly stirred and mixed.

When the hardened concrete was observed after 72 hours, it was found that many cracks of 1 to 3 fi had occurred on the outer periphery and upper surface of all three concrete. The excess concrete up to the planned crushing surface could be easily broken into small pieces with a hand breaker, and the removal work was completed in a short time. In either case, there was no effect of the crank on the pile body.

〔Effect of the invention〕

When constructing a cast-in-place concrete shaft, the present invention provides the following:
This is a method that facilitates the removal of so-called excess concrete, in which an expandable substance is mixed with unhardened excess concrete to be crushed, and its expansion action causes cracks to occur throughout the cured excess concrete, causing it to fracture. Compared to conventional methods, there is no loss of expandable substances such as static crushing agents, there is no deviation of the planned crushing plane, and the workability is good. Furthermore, regardless of the amount of soil and sand, they are sufficiently mixed, so that they are not unevenly distributed. Therefore, since many relatively small and large cracks are generated in the entire hardened concrete reinforcement, there is less noise associated with the subdivision work, and it has the advantage of being easy to perform.

[Brief explanation of drawings]

FIG. 1 is an application example of the present invention, and is a longitudinal cross-sectional view of a cross-section head showing a state in which an expansible substance is mixed with extra concrete to be crushed. 1... Pile body 2... Remaining concrete to be crushed 3... Remaining concrete 4 mixed with an expansive substance,
4゛... Rebar cage main bar A... Planned fracture surface B... Design pile height

Claims (1)

[Claims] When constructing cast-in-place concrete piles, a method for crushing extra concrete for cast-in-place concrete piles, which is characterized by mixing an expandable substance into unhardened extra concrete after pouring fresh concrete and hardening it.