JPS59102852A - Dust reducing agent for spray concrete - 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 The present invention relates to a dust reducing agent used in the shotcrete construction method, in which concrete is layered on tunnel excavation surfaces by spraying. This relates to a dust reducing agent that eliminates dust.

In tunnel construction and the like, in recent years, sprayed conocrete has been used instead of or in combination with the conventional steel arch shoring to prevent the surrounding ground from collapsing.

The role of this sprayed concrete is to prevent stress concentration by applying it immediately after excavation to smooth out unevenness on the bottom of the surrounding rock, and to prevent the rock surface from being exposed to the outside air and weathering. Furthermore, as part of the shoring member, it can be used to prevent the collapse of the ground and to have resistance against earth pressure.

In addition, the desirable conditions for spraying concrete in tunnels are that the dust caused by spraying does not affect the health or motivation of the workers, and that the construction machinery must be controlled so that the work inside the tunnel is not overcrowded. The concrete must be as small as possible, the material must be transported smoothly and the material can be fed to the spraying machine smoothly, and the quality of the concrete after spraying must be ensured.

The Conocrete method is a construction method in which a material consisting of cement, aggregate, water, additives, etc. is kneaded and compressed, and the material is forced through a hose with air and sprayed onto the wall surface. However, there are many factors that influence construction, and various construction methods are being developed.

That is, as a concrete method for spraying, the dry method 1 is mainly used, and the wet method 1 is also sometimes used.

Dry method 1 is the method most commonly used in tunnel construction, in which fine aggregate, coarse aggregate and cement are dry mixed in a mixer, and this is supplied to the spray machine via an agitator car. At this time, an accelerating agent is added, and then compressed air from a compressor is introduced into the spraying machine, and the dry mink material is forced into the material hose connected to the nozzle, and water is sprayed at the end of the hose along the way. The spray is applied to the rock surface by the operation of the nozzle man who holds and operates the nozzle.

However, in this construction method, the aggregate and cement are mixed in a dry mix state, so the aggregate and cement do not adhere well, and the cement may be pumped in a powdered state. Since the material and cement are mixed only in the vicinity of the nozzle, the mixing time is short (or when the spray collides with the rock wall due to insufficient mixing, there is a lot of rebound and dust generation). There are problems such as loss of material and poor working environment.On the other hand, since the material cart is in a lime mix state,
If it is easy to pump with compressed air and can be pumped over long distances (・
It has the advantage of

On the other hand, in the wet type 1 method, all materials such as fine aggregate, coarse aggregate, cement, and water are kneaded in a mixer, and then the spray is supplied to the machine using an agitator force, and the spray is applied to the compressed air from the compressor. The spraying method is to spray from a nozzle while supplying the quick-setting agent.

According to this method, since the material is thoroughly kneaded before being pumped, quality control is easy and there is almost no separation of the material (therefore, spraying does not cause the generation of dust during the process). Although it has the advantage of less material rebound,
The distance for pumping the material is short, the hose may become blocked by the material during spraying, and all materials such as aggregate, water, and cement are mixed in advance, so the time between mixing and spraying is It has drawbacks such as being subject to restrictions and causing a lot of material loss when spraying a small area in multiple passes.

For this reason, recently, construction methods have been developed that incorporate the advantages of both the dry method and the wet method. , Add the required amount of water at the outlet and immediately pump it with compressed air from a compressor, or add the required amount of water to the compressed air and mix it with the dry mix material in a hose and pump it. There is a way to do it.

According to this method, the water and dry mix material are sufficiently mixed while being pumped in the hose, reducing the generation of dust, and the pumping distance is also somewhat longer (although the spraying does not collide with the rock surface). There is no improvement in the bounce when the ball is used.

In addition, when spraying concrete inside a tunnel, it prevents the concrete adhering to the wall surface from peeling off due to its own weight during upward construction, and in addition, in soft ground, spraying can resist ground pressure in a short time after the concrete is constructed. The use of quick-setting agents is essential because it is necessary to develop strength in a short time to prevent the rock from collapsing when blasting is performed for the next excavation even in hard rock. is common to all of the above construction methods.

The inventors of the present invention have conducted extensive studies on preventing the splashing of materials such as cement, etc., which is generated when using materials that cannot be solved by the above-mentioned construction methods alone. completed.

That is, the present invention relates to a sprayed concrete dust reducing agent made of polyacrylamide.

Cellulose-based compounds have traditionally been used as dust reducing agents, but they either cannot reduce splashing or dust concentration, or they must be used in large quantities to reduce them, which reduces operability or reduces dust. Since it was used as a spray agent, it had the disadvantage of reducing the strength of sprayed concrete.

The dust reducing agent of the present invention can reduce the dust concentration and repulsion rate when used in a small amount, and solves all the drawbacks of conventional reducing agents without reducing the strength of concrete.

The reasons why the dust reducing agent of the present invention causes a decrease in dust concentration and a decrease in bounce rate in the concrete spraying method are thought to be as follows, although there are no specific details.

Spraying generates a lot of dust and splashes during construction (the things that occur are
This is because once mixed, the materials move through the hose at high speed, and are often separated into individual materials between the time they are discharged from the nozzle and the time they collide with a surface. On the other hand, if the viscous water bath solution of the dust reducing agent of the present invention is added, the adhesion between the particles will be strengthened, and the separation will be reduced, reducing the amount of dust. It is thought that the cement powder attached to the surrounding area acts as a cushion and reduces the bounce. ' The reduced penalty of the present invention can be used in any of the above-mentioned dry method 1 method, wet method 1 method, and their improved construction methods, but there is a problem with wet method 1, namely that the spraying method is not blocked by the hose or the material. Even if it doesn't get blocked (even if it sticks to the inner wall of the hose, there is a risk that spraying will cause problems such as increased pulsation of the nozzle. Also, this wet method 1 method does not generate dust, reduce splashing, etc.) Since a particularly strong reduction agent is not required, the dry method 1 or an improved method thereof is preferable as a construction method using the reducing agent of the present invention, and it is particularly preferable to employ the following method.

That is, the construction method using the reducing agent of the present invention involves forming a dry mix-like aggregate in which cement powder is adhered to the surface of the coarse aggregate and fine aggregate through the aqueous solution, which will become the concrete material, Next, raw concrete IJ-
A particularly preferred method is to add an appropriate amount of water and a quick-setting agent to harden the concrete, and then spray the concrete onto the wall with compressed air through a hose.

To further explain this method, first, fine aggregate and coarse aggregate are put into a mixer and both aggregates are sufficiently stirred and mixed. Next, an appropriate amount of the reduced aqueous solution of the present invention is added to the mixer together with the primary water, and mixed together with both aggregates.

This water bath liquid has the following properties: the sum of the surface water of both aggregates and the amount of water in which the reducing agent of the present invention is dissolved is the unit water amount required for the desired concrete (the amount of water required to form the desired unit concrete) The amount of water was made to be equal to 172 to 3/4 of the weight of the container.

When both aggregates and the water bath liquid are stirred and kneaded, the aqueous solution adheres to the surface of the fine aggregate and coarse aggregate, and due to the stickiness of the water bath liquid, both aggregates adhere through the aqueous solution and harden. The aggregates as a whole are in a state of adhesion to each other, such as by forming , or by forming a mass of fine aggregates.

Next, when cement powder is added all at once or gradually to the aggregate in this state, the amount required for the desired conocrete is added to the aggregate being stirred by a mixer. The cement is gradually mixed into the bathing liquid adhering to the surface of the aggregate, and finally the cement comes to adhere to the outer surface of the bathing liquid layer adhering to the aggregate surface, causing the aggregate particles to adhere to each other. There is no aqueous solution in between, and each aggregate has an aqueous solution coating layer containing cement on its surface, and is separated through the cement attached to the surface of the aqueous solution coating layer to become independent aggregates in a dry mix state. or a state in which fine aggregate is attached to the periphery of coarse aggregate, or a state in which fine aggregate and coarse aggregate are attached to each other, and each has a bathing liquid coating layer containing cement on its surface, and the coating layer It becomes an independent aggregate state with cement attached to the surface.

Such a state is caused by the ratio of the amount of aqueous solution to the amount of cement and the stirring ability of the mixer. Desirably, each aggregate has a cement-containing aqueous solution coating layer on its surface, and the surface of the coating layer is It is best to use a dry mix with a cement layer attached to the aggregate, but it can be used as long as the size of the agglomerated aggregate does not interfere with pressure feeding to the nozzle.

In this way, after obtaining aggregate in a dry mix state with aqueous solution and cement attached to the surface using the dry method, next 6, this aggregate is transported from the mixer to the spraying machine using a conveyor such as a belt conveyor. , the spraying is fed into the machine.

During transportation by this transportation means, a fixed amount of quick-setting agent is added evenly to the amount of aggregate.

In the spraying machine, an air hose that delivers compressed air from a separately installed compressor is connected to the aggregate outlet, and a material hose that transports the aggregate to the tunnel wall is connected to the machine. The sprayer is designed to continuously discharge a predetermined amount of aggregate fed into the machine from the outlet. Furthermore, a spray nozzle is attached to the tip of the material hose, the tip of which is open to the atmosphere.

The aggregate that has entered the blowing machine is discharged quantitatively from the outlet of the blowing machine, and the compressed air from the compressor flows at high speed through the material hose toward the open end of the nozzle. Aggregate is introduced and is carried by the air flow from the material hose to the nozzle. During the flow, that is, during spraying, the unit amount of water required to form concrete (172 to 1/4, which is the remaining amount of water mentioned above) is applied to the appropriate part of the material hose between the machine and the nozzle. Supply water by appropriate means.

This secondary water plays the role of turning the cement attached to the surface of the aggregate into a cement paste.

In this state, it is sprayed onto the tunnel wall from the nozzle tip opening.

The fine aggregate sprayed onto the wall has a sticky aqueous solution on its surface and a layer of cement attached to the inside and surface of the solution, and the cement is turned into a cement paste by water. Therefore, due to the tackiness of the aqueous solution and cement paste, and the water bath liquid film layer acting as a cushion, the adhesive can be reliably attached to the wall surface without rebounding.

In addition, coarse aggregate loses repulsive energy in the same way as fine aggregate, and due to the viscosity of the solution on the surface of the fine aggregate that adheres to the wall, the rate of adhesion to each other and repulsion from the wall is extremely low.

In addition, in the explanation of the method above, fine aggregate and coarse aggregate were put into a mixer and mixed together, but these aggregates were put into separate mixers and appropriate amounts of aqueous solution and cement were mixed respectively. These may be added to the mixer and stirred and mixed, and then further stirred and mixed together. In addition, when spraying onto a wall surface using only mortar, it is sufficient to form only fine aggregate.

The dust reducing agent of the present invention is capable of reducing dust concentration and repelling rate regardless of the construction method, but when used in the construction method described above, the following excellent effects can be obtained.

In other words, a sticky water bath liquid coating layer containing cement is formed on the surface of the aggregate, and aggregates with a layer of cement powder attached to the surface of the coating layer are formed. It is in the same state as the mixed aggregate and can be smoothly flowed through the pressure hose without clogging it, and the distance for pumping the aggregate can be increased by using a long hose. It is. Furthermore, since the cement is attached in a layered manner to the water bath liquid film layer on the surface of the aggregate, fine and coarse aggregates will not separate or adhere to the inner wall surface of the aggregate car hose. It is possible to form shotcrete of uniform quality with no waste.

In addition, as mentioned above, a sticky aqueous solution film layer is formed on the surface of the aggregate, and when the surface cement layer is turned into fresh concrete, an appropriate amount of water is added to form a cement paste. Therefore, if it adheres to the walls of tunnels etc., it will significantly reduce the bounce rate.Furthermore, cement and fine aggregate from Kyoku/JX cannot be sprayed on their own, so there is no dust. It is possible to effectively eliminate the occurrence of

Furthermore, the sum of the surface water of the aggregate, the water in the bathing liquid, and the amount of water for making ready-mixed concrete is the amount of water required for the aggregate to be sprayed, and the amount of water required for spraying the aggregate is The amount of water required to make ready-mixed concrete is automatically determined by adjusting the variation in unit water amount with the water content of the aqueous solution.This results in better quality concrete than the conventional method of spraying while adjusting the amount of water with a nozzleman. can be obtained.

In addition, when fine aggregate and coarse aggregate are mixed with viscous liquid and cement separately to form dry mix fine aggregate and coarse aggregate, and then the fine aggregate is mixed, Since dedicated mixers with different capacities can be used when mixing cement, efficient mixing can be achieved.

The reducing agent of the present invention can be added as a powder in cases such as wet method 1, but due to the poor solubility of polyacrylamide in water, it is better to use it as a water bath liquid in dry method 1 and the above methods. This is a preferred method because it is easy to operate and the effects described above can be obtained, and in that case, it is preferable to use it as an aqueous solution of 1 liter or less.

The dust preventive agent of the present invention is used together with cement, aggregate, water, additives, etc., and the amount used takes into consideration the type and amount of cement used, water-cement weight ratio (W/C), etc. Generally speaking, it is preferably 0.05 to 0.4 inches, particularly preferably 0.1 to 0.2 inches, based on the amount of water used.

The effects of the present invention will be explained below using Examples and Comparative Examples.

Examples 1 to 2 and Comparative Examples 1 to 14 The amount of concrete per batch was 0.2 m' according to the standard mix shown in Table 1, and cement, fine aggregate, and coarse aggregate were weighed and dry mixed using a mixer. For spraying, the material is supplied to the machine along with the quick-setting agent, and is forced through the material hose using compressed air from a conobresser.For spraying, water or water in which various compounds shown in Table 2 are dispersed or dissolved is added to the material hose in front of the nozzle and mixed. It was sprayed onto the steel panel from a post-spray nozzle. When the amount of dust generated, the rebound rate, and the strength of the sprayed concrete were measured, the results shown in Table 2 were obtained. Those using the dust reducing agent of the present invention (Examples 1 and 2 have a small amount and a steep slope compared to those using other compounds (comparative examples),
It can be seen that the strength is also excellent.

Table 1 Standard formulation characteristics measurement method is as follows, and the test was repeated five times or more.

a Rebound rate After completing one batch of spraying, the spraying rate is determined by the weight of the conocrete that adheres to the panel (hereinafter referred to as adhered concrete) and the material that has rebounded onto the sheet spread around the panel (hereinafter referred to as bounced concrete). The weight of each sample (referred to as "1") is measured using a load cell, and the rebound rate is determined from the following formula.

Rebound rate - Rebound weight / (Rebound weight attached weight) x 10' [1 (- b Dust concentration / Dust mass concentration and number concentration were measured at a point 3.5 m behind the tip of the slurry.The measurement of mass concentration was Using a gravimetric dust meter, we weighed the dust collected on the filter paper from the start to the end of spraying, and measured the amount of air sucked in with the dust meter during the same period of time.Also, Digital dust meter CLIMET-M-CL-2 is used to measure the number concentration.
50 was used.

C strength test In accordance with JIS-AI+07, Al 108, specimens with a diameter of 5 cR and a height of 10 cIIL were prepared, and compressive strength tests and compressed tensile strength tests were conducted at 1 week and 4 week ages.

The specimens were prepared and cured as follows.

For spraying, the concrete was sprayed onto a formwork set up in a part of the panel and cured on-site for one day in a simulated tunnel.Then, a core with a diameter of 5cm was cut out and cured in water until the specified material age.
On the day of the test, the end face was shaped and used for the test.

Claims (1)

[Claims] 1. Spraying made of polyacrylamide is a dust reducing agent for concrete.