JPS6128669A - Wet concrete spraying method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an improvement in a wet concrete spraying method.

(Conventional technology J) Shotcrete has the advantage of being able to cast concrete on slopes and ceilings without the need for formwork, so it is widely used for applications such as concrete lining of tunnels and protection of slopes. has been done.

Concrete sprayed onto sloped surfaces or ceiling surfaces tends to flake off due to its own weight or impact during spraying, so it is common practice to add a fast-setting agent to give concrete the strength to resist flaking in a short period of time. ing.

Shotcrete construction methods can be roughly divided into dry spraying and wet spraying.In the past, dry spraying was the mainstream, but recently it has become easier to control the water-cement ratio of concrete and is less likely to generate dust. The wet spraying method is being reconsidered due to its advantages such as less use.

In the wet spraying method, concrete is mixed according to a predetermined composition, conveyed by air current through a long transport hose, and sprayed onto the construction surface from a nozzle. (In some cases, the material is pumped halfway through the transport hose and then transported by airflow.In this case, the quick setting agent is added into the transport hose near the nozzle and mixed with the concrete by the airflow.

There are powder and liquid types of quick-setting agents, and liquid types are easier to add into the transport hose near the nozzle. Powder products generally have poor powder fluidity and tend to cause problems such as clogging of the air pressure system to the concrete transport hose, making it difficult to add quantitatively and stably. Some powder products are water soluble and can be dissolved in water and used in liquid form on site, but this poses some problems.

One of them is that the water-cement ratio of concrete increases. In other words, the water-cement ratio is an important factor that controls the strength of concrete, and in shotcrete, it is also a factor that controls the slowness of the rapid setting effect. This has the disadvantage of being added to the concrete together with the quick setting agent and increasing its water-cement ratio. (As the water-cement ratio increases, the quick-setting effect decreases rapidly.) Furthermore, the amount of quick-setting agent used (
Since the level (addition amount based on cement weight) is large, this increase in the water-cement ratio is also large.

Another problem is the formation of precipitates. That is, some quick-setting agents may precipitate in an aqueous solution, and this precipitation may cause an accident in which the piping system for the quick-setting agent solution is clogged. If an attempt is made to make the concentration as high as possible in order to reduce the increase in the water-cement ratio due to the addition of the quick setting agent solution as described above, the tendency for precipitation to form will rapidly increase, making it impossible to increase the concentration beyond a certain level. . Further, some quick-setting agents are insoluble in water, and some harden when they come into contact with water, and it is impossible to add these in liquid form from the beginning.

(Problem to be Solved by the Invention λ) The present invention first aims to solve the above-mentioned problem of adding a powdered quick setting agent in wet shotcrete.

Shotcrete, whether dry or wet, has the following problems. One of them is the amount of accelerating agent used. Quick-setting agents are more expensive than cement, sand, and gravel, which are the main materials used in concrete, but several units are required to achieve the desired quick-setting effect, and the cost of quick-setting agents accounts for a small portion of the cost of concrete. is by no means small. Therefore, it is desirable to reduce the amount of quick-setting agent required to obtain the desired quick-setting effect. Next, when spraying concrete onto a construction surface, the percentage of material that bounces off and does not stick to the construction surface (
It has a particular drawback of having a high bounce rate.

This causes loss of concrete and increases costs, so it is desirable to increase the adhesion of concrete and reduce the rebound rate. Furthermore, concrete to which an accelerating agent has been added has the disadvantage that although the initial strength is greater than that without the addition, the long-term strength is lower, and improvement of this defect is desired.

The present invention also aims to solve these problems of shotcrete in general.

(Means for Solving the Problems) The present invention provides a method for spraying concrete with a mixed fine powder prepared by mixing 0.5 to 5 parts by weight of fine mineral powder with 1 part by weight of a powdered quick-setting agent at a position close to a spray nozzle. This is a wet concrete spraying method characterized by adding it into a transportation hose.

The powdered quick-setting agent in the present invention refers to a powdered quick-setting agent used as a quick-setting agent for shotcrete.
Examples include alkali aluminate salts, alkali carbonate salts,
It is a single or a mixture of two or more calcium aluminate-based rapidly hardening materials. The above calcium aluminate-based rapidly hardening materials include CA, Cl2A7, CA2, C,, A, (J
Calmium aluminates such as P2, C3A3, CaF2, their amorphous substances, and these (and gypsum such as anhydrite) are blended together and are called cementitious quick-setting agents.This material is easy to set. There are drawbacks. (
Here C is Cab.

A is a symbol representing A, t20g. ) Recently, sulfocalcium aluminate-based products have also been provided.

The fine mineral powder in the present invention is a fine mineral powder with a fineness comparable to or higher than that of cement, and examples thereof include fly assemblies, amorphous silica powder, blast furnace slag powder, etc., which have latent hydraulic properties. These include powder, crushed holmite minerals, talc, clay, and limestone powder.

Among these, latent hydraulic powder is preferred because it has the effect of increasing the long-term strength of sprayed concrete.

Among these, it is preferable to use ultrafine powdered amorphous silica called silica heat. This material is obtained as a by-product during the production of ferrosilicon, and its particle size is less than 1 micron.

Further, among the fine mineral powders, crushed holmite minerals are preferably used because they have a large effect of increasing zero adhesion to the sprayed surface of shotcrete and reducing the bounce rate. Holmite minerals are minerals that consist mainly of aggregates of magnesium monoate-based acicular crystals such as attapulgite, sepiolite, and palygorskite, and their crushed products are produced using methods that do not damage these acicular crystals as much as possible. It is separated and crushed appropriately.

In the present invention, the mixing ratio of the powdered quick-setting agent and the fine mineral powder is 0.5 to 0.5 parts by weight of the fine mineral powder to 1 part by weight of the powdery quick-setting agent.
5 parts by weight (preferably 0.7 to 3 parts by weight) is suitable. If the mixing ratio of fine mineral powder is smaller than the above range, the effects described below (improvement of powder fluidity, improvement of adhesion, etc.) will be too small and impractical, and if the mixing ratio exceeds the above range, it will not be practical. However, the improvements in these effects reach a plateau and become uneconomical.

In the present invention, the mixed powder of powdered quick-setting agent and fine mineral powder is added into the concrete transport hose in front of the mouth of the spray nozzle from which concrete is spouted, but when the distance from the mouth of the nozzle is short, The mixing of the concrete and quick-setting agent will be insufficient, and if this distance is long, the concrete will harden in the transportation hose circle, so the selection of the addition position should be determined as appropriate with these considerations in mind. Generally (second), the appropriate position is 3 to 10m from the nozzle mouth.

The mixed powder is continuously measured and added at a desired addition ratio according to the amount of mixed concrete transported per unit time, and is fed into a concrete transport hose using air pressure.

In general, the amount of quick-setting agent added to concrete is based on the weight of cement in the concrete.In the case of cementitious quick-setting agents, a mixture of about 5 to 10% alkali aluminate and alkali carbonate is used for quick setting. The agent is about 2-5%
The amount of the mixed powder to be added is selected so that the amount of the quick-setting agent contained in C1 is about the standard amount of the quick-setting agent.

(Effects of the invention: By using a mixed powder of this and fine mineral powder as a powder quick-setting agent added to wet shotcrete,
Compared to the conventional case of adding a powdered quick-setting agent, the following advantages are brought about.

(1 liter) Easy to measure and add.

Powdered quick-setting agents have poor powder flowability, leading to large measurement errors during continuous measurement, and tend to cause problems such as clogging of the air pressure system to concrete transportation hoses, but the combination of fine mineral powder has improved powder flowability. These problems will be greatly improved.

The improvement effect is particularly great for cementitious quick-setting agents that harden easily.

(2) Rapid setting effect increases.

The rapid setting effect when using a mixed powder is greater than when using only the amount of quick setting agent in the mixed powder. Since the fine mineral powder itself does not have a rapid setting effect, this increase in the rapid setting effect is a synergistic effect brought about by blending the fine mineral powder.

(3) Improved adhesion of shotcrete and reduced bounce rate.

(4J Shotcrete strength increases.

(5) Shot concrete using latent hydraulic powder
The long-term strength of the grip increases.

Thus, the present invention makes it possible to reliably measure the quick-setting agent during the construction of wet shotcrete, making the construction easier and also improving its economic efficiency, which is of great industrial significance.

Example 1 In this example, the effectiveness of the present invention was tested in a mortar test.

(The composition of 12 mortar is as follows: W/ = 50%, 8/c = 3.2, the amount of powdered binder used is 8%, the amount of unused mixed powder is 12% (the powdered The amount used in terms of quick-setting agent is 8 Chino (2)
Powdered quick-setting agent, etc. (a) Powdered quick-setting agent, alkali aluminate and alkaline earth metal carbonate (b) Mineral fine powder, silica hume and fly ash (/1 Mixed powder of powdered quick-setting agent and fine mineral powder) 1=3 weight ratio mixture (3) The test results are shown in Table 1.

As is clear from Table 1 above, it can be seen that by using mineral fine powder in combination, the setting time is shortened and the quick setting effect is increased with the same amount of quick setting agent used. It can also be seen that the strength also increases. Furthermore, it can be seen that these effects are greater for silica hume.

Example 2 This example is a test conducted using a wet shotcrete machine.

A shotcrete machine was used as the wet spraying machine, and the transportation hose had a diameter of 3 inches and a length of 30 m, and the target of spraying was a vertical wall. The mix of concrete was as follows.

(The unit of C-S is Ky/m") (υ Accelerating agent, etc.) A mixture of alkali aluminate and alkali carbonate (symbol Q) (B) A substance mainly composed of cementitious accelerating agent (symbol N ] 7~) 33 weight ratio mixture B/N to mixed powder A+'Q Nijirikahium-
Table 2 shows comparative values of the repulsion rate (relative values when 100 is the case where no fine mineral powder is used) when spraying silica hume-1:1.5 weight ratio mixture (2).

From the upper table of Table 2, it can be seen that the repulsion rate is significantly reduced by the combination of fine mineral powder. In addition, the measurement and addition conditions of the mixed powder containing all of the fine mineral powders were better than those using only the quick-setting agent.

Claims (1)

[Claims] 0.5 to 1 part by weight of fine mineral powder to 1 part by weight of powdered quick setting agent
A wet concrete spraying method characterized by adding 5 parts by weight of mixed fine powder into a concrete transport hose at a position close to a spray nozzle.