JPS633109B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the invention of a concrete spraying method,
Creates appropriate conveyance conditions through pipes for spraying concrete or refractory materials, enables smooth spraying of concrete with less dust generation and splashing, and has excellent strength. The purpose is to obtain a method capable of forming concrete. The spraying method is already known as one of the concrete construction methods. In other words, while concrete construction like this generally requires forming a formwork and then filling and forming, this spraying method does not require such a formwork and can be applied to walls, slopes, etc. It has the great advantage of completely eliminating the process of installing formwork and removing the formwork after it hardens, allowing concrete work to be completed within a short time, and is suitable for civil engineering works such as tunnel walls and created slopes. It is being put into practical use to some extent. However, there are three general concrete spraying methods conventionally adopted: dry, wet, and semi-wet, but although each of these methods has its merits, it also has disadvantages and drawbacks. ing. The inventors of the present invention filed a patent application in 1983 to eliminate the disadvantages of the conventional method.
-50060 (Japanese Unexamined Patent Publication No. 55-142823) proposed a method. That is, according to this method, the slurry-like raw kneaded material and the powder-like mixture are separately pumped and fed with high-pressure gas, and then they are combined near the nozzle and sprayed, so that both pumping systems can smoothly pump the mixture. Moreover, in the spraying method in which these methods are combined, the water-to-cement ratio is small, making it possible to achieve construction that is strong and favorable in terms of strength. The present invention was devised after further practical studies regarding such technology, and is intended to enable construction that effectively reduces the dust generation rate and rebound rate during such spraying construction. be. That is, as a result of many practical studies in accordance with the above-mentioned new method, the present inventors have developed a method in which a slurry-like mixture and fine aggregate or coarse aggregate is added thereto are appropriately moistened. It has been discovered that by using a material to which hydraulic material powder is added, it is possible to achieve preferable construction with less dust and splashing, improved strength, and a small coefficient of variation. The details of the present invention will be explained below using examples. Example 1 Sand, water, and a water reducing agent were weighed and blended into Portland cement in weight proportions as shown in Table 1, and the surface water content of the sand was adjusted in advance as shown in Table 1. First, cement and sand are kneaded to form a shell, and then the remaining water and water reducing agent are added to make mortar _.
λ, ΔF ₀ ) and compressive strength are shown in the table.

【table】

【table】

[Table] These mortars are used as primary mortar and are pumped to the mixing pipe near the nozzle, while
Add and mix cement to river sand with a maximum grain size of 5 mm and adjust the water adhesion to the surface to 4%, and sprinkle it on the surface of the sand grains.
Prepare the aggregates so that they have the values shown in the air-fed aggregate column of another Table 2, change this in various ways and air-fed it, and mix the mortar and various air-fed aggregates in the mixing pipe. The mixture was mixed and sprayed onto the ceiling of a tunnel with an arched top surface. The composition of the obtained shotcrete, the performance of the ready-mixed shotcrete during spraying, the strength and other properties of the obtained shotcrete are shown in Table 3 below.

[Table] However, if these results are organized and shown in a chart, as shown in Figure 1, the amount of dust generated and the rebound rate are greatly influenced by the sand-cement ratio (S/C) of the sprayed mortar. In general, by setting the S/C to 1 to 4, especially 1.5 to 3.0, it is possible to achieve a preferable construction with fewer such problems.In other words, when the S/C is 1 or less, the shear stress can be reduced to 20 g/cm ² or less. It was confirmed that sagging occurred significantly, and when the S/C was 4 or more, the rebound rate was 15% or more and the number of flakes increased rapidly, making it impossible to perform a desirable construction in any case. As a comparative example for the present invention as described above, an air-fed aggregate that does not form a shell was prepared using primary mortar and sand that had the same composition as No. 1 in Tables 2 and 3, and When this material was similarly sprayed using the same spraying mechanism (two systems force-fed and combined near the nozzle), the rebound rate was extremely high at 36%, and the dust generation rate was 19.5mg/m ³ . It was also inferior. In other words, in the No. 1 formulation in Tables 2 and 3, the amount of water for spraying is 255
Kg/m ³ is quite high and sagging is large, so the spraying thickness at the top surface is around 10mm, and the separation is remarkable, and the compressive strength after 28 days of spraying is 525kg on average. /cm ² , but the coefficient of variation was as large as 28.2 (the coefficient of variation of No. 1 according to the present invention was 7.5), and desirable spraying could not be achieved. Also, as a comparative example, the primary mortar with the same composition as No. 6 in Tables 2 and 3 and air-fed aggregate without shelling were adjusted to sand, and the results of spraying in the same manner were as follows: is 31.5%, the dust generation rate is 13.5 mg/m ³ , the sprayable thickness is 20 mm, and the average compressive strength after 28 days is 435 Kg/cm ² , but the coefficient of variation is as high as 27.2 (the present invention No. 6 was 6.3), and there was a lot of variation. Furthermore, with respect to No. 12 in Tables 2 and 3, with the same composition, but with air-fed aggregate that did not form shells in the sand, the rebound rate was 27.3%, and the dust generation rate was 27.3%. 11.5mg/ ^m3
The sprayable thickness is 10mm, the average compressive strength after 28 days is 314Kg/ ^cm2 , and the coefficient of variation is
19.9 (No. 12 according to the present invention had a coefficient of variation of 5.6). In other words, from the results of the comparative examples mentioned above, it is not possible to perform smooth spraying when the sprayable thickness is 1 to 2 cm, and originally, with such a composition, spraying cannot be performed without an quick-setting agent regardless of the amount of cement. However, it has been confirmed that the present invention enables spraying without the use of quick-setting agents, provides high strength, and is excellent in workability. Example 2 The same materials as in Table 1 above were used, and 15 to 20 mm of coarse aggregate was added to the shelling sand in various ways as shown in Table 4 below, and air-fed bones were added. The results of pressure-feeding the material and constructing it in the same manner are shown separately in Table 5.

【table】

[Table] In other words, all of the products in Table 5 had a small amount of dust and a low rebound rate, and could be constructed under favorable conditions. On the other hand, as a comparative example, No. 4 in Tables 4 and 5.
With the same composition as in 1, the result of spraying the air-fed aggregate with sand without shelling resulted in a rebound rate of 24.5% and dust generation of 9.2mg/m ³ , which was the average after 28 days. The compressive strength was 426 Kg/cm ² and the coefficient of variation was 11.3 (the coefficient of variation of No. 1 according to the present invention was 4.5). As shown in Tables 4 and 5, the same composition as No. 9 in Tables 4 and 5 was used by spraying sand without shelling, and the rebound rate was 33%, resulting in no dust generation. is 12.7 mg/m ³ , and the average compressive strength after 28 days is 295 Kg/cm ² , and its coefficient of variation is
The coefficient of variation was 15.2 (the coefficient of variation of Invention No. 9 was 4.8). That is, the rebound rate of the product according to the present invention is 1/3 to 1/3.5 of those of the comparative examples, the dust generation is 1/4 to 1/10, and the average compressive strength is around 200 Kg/cm ² It was confirmed that even the coefficient of variation can be reduced to less than half. Example 3 In addition to the above-mentioned series, various formulations of shell mortar as shown in Table 6 below were prepared.

[Table] In addition to pumping this mortar, prepare air-fed aggregate that has been adjusted to have a W/C of 15% in the sand shell-forming paste, and combine these at the nozzle in the same manner as above and spray. Constructed.
That is, the combination relationship between the primary mortar pumped by the pump and the air pumped aggregate is as shown in Table 7.
The composition, properties during spraying, and strength of the obtained shotcrete are shown separately in Table 8.

【table】

【table】

[Table] The results shown in Table 8 are summarized in the form of a diagram as shown in Figure 2.Due to the difference in W/C in the shell layer of air-fed aggregate, there are significant differences in specific numerical values. Even if there are variations, it has been confirmed that advantageous construction can be achieved by setting the S/C value in shotcrete to 1 to 4, particularly 1.5 to 3.5. On the other hand, as a comparative example, No. in Tables 7 and 8.
Using the conventional dry method to spray the air-fed aggregate with the composition No. 1, which does not form shells on the sand, the rebound rate was 23.2% and the dust generation rate was 10.6 mg/ ^m3 . The average compressive strength after 28 days was 374 Kg/cm ² and its coefficient of variation was 32.5 (the coefficient of variation was 6.9 for No. 1 of the present invention). Similarly, regarding No. 9 in Tables 7 and 8, when the air-fed aggregate was sprayed without forming a shell on the sand, the rebound rate was 25%.
The dust generation rate was 17.3 mg/m ³ and the average compressive strength after 28 days was 323 Kg/cm ² with a coefficient of variation of 17.6.
(The coefficient of variation of the sample according to No. 9 of the present invention was 4.8). That is, Examples 1 and 2 show that the product according to the present invention is excellent in rebound rate, dust generation, average compressive strength, and coefficient of variation thereof.
The same is true for . Example 4 Spraying containing steel fibers was also carried out. That is, the primary mortar to be pumped has a W/C of 38%, an S/C of 1.7, a water reducing agent of 1%, and a relative flow characteristic value of F ₀ of 1 g/cm ² and λ of 1.2.
g·sec/cm ⁴ and ΔF ₀ of 0.0015 g/cm ⁴ were used. In addition, as the air-fed aggregate for this, sand with a W/C of 18% for the cement shell layer was used at 640Kg/ ^m3.
and gravel 670Kg/m ³ with 30mm length and 0.3mm diameter steel fiber
These were mixed and combined at a ratio of 98.4 kg/m ³ and sprayed. The composition of the obtained shotgun is S/C: 2.68, W/C=
31%, cement 393Kg/m ³ and sand 1055
Kg/m ³ , gravel 637Kg/m ³ , steel fiber 98.4Kg/m ³ , water
120Kg/m ³ , the amount of dust generated during spraying is 2.5mg/m ³ , the rebound rate is 9.2%,
The shear stress was 173 g/cm ² . The thickness of the sprayed workpiece formed was 19cm, and the average compressive strength after 7 days was
495Kg/cm ² , the average compressive strength after 28 days is 588Kg/cm ² ,
Its coefficient of variation was 6.3. On the other hand, as a comparative example, when air-fed aggregate with the same composition as above was used without cement shelling, the rebound rate was 32%, and the dust generation was 11.6%. mg/
^m3 , and the average compressive strength after 28 days is 314Kg/
The coefficient of variation in cm ² was 23.6. In other words, even with the same materials and composition, the rebound rate is 3.5 times higher, the amount of dust generated is 4.5 times higher, the average compressive strength is about 1/2, and the coefficient of variation is 4.
It was nearly twice that, confirming the advantage of the method according to the present invention. Example 5 The same primary mortar as in Example 4 was used to be pumped. In addition, as an air-fed aggregate for this purpose, only ultra-early-strength jet cement (manufactured by Onoda Co., Ltd.), a mixture of equal amounts of this ultra-early-strength jet cement and ordinary cement, and a mixture made by adding half of ordinary cement are available. Five types were prepared: one in which ultra-early strength jet cement was added after shelling, one in which only ordinary cement was added, and one in which 4% sodium aluminate quick-setting agent was added to ordinary cement to form a shell. For the five types, the ratio of sand was 250Kg/m ³ (W/C of shell = 18%) and gravel was 426Kg/m ³ . That is, the composition, properties during spraying, and strength of these materials were mixed and combined at the nozzle and sprayed as shown in Table 9 below.

[Table] Note: The amount in parentheses in the table is for ultra-early strength jet cement.
According to the present invention as explained above, when the slurry-like raw kneaded material and the powdery mixture, which have been separately pumped by pump feeding and high-pressure air feeding, are combined and sprayed, it is possible to By properly moistening fine aggregate and then adding and adhering hydraulic substance powder, both of these materials are in a state suitable for transportation, and the hydraulic substance powder such as cement is It is transferred and sprayed in a state where it is difficult to disperse even on the side, and therefore, preferred construction can be carried out under conditions where dust generation and amount of rebound are small, and moreover, it is possible to precisely obtain spraying that is advantageous in terms of strength. This invention is highly effective for this type of concrete spraying construction.

[Brief explanation of the drawing]

The drawings show the technical content of the present invention, and Figure 1 is a chart showing the relationship between the amount of dust generated in shotcrete mortar and the rebound rate and its sand-cement ratio, and Figure 2 is the amount of dust generated in shotcrete. and a chart showing the relationship between the rebound rate and its sand-cement ratio.

Claims (1)

[Scope of Claims] 1. A slurry-like raw kneaded material that is a mortar consisting mainly of powdered hydraulic substances such as cement or gypsum, water and sand, or a similar fine granular material, and mixed with other additives. Then, fine-grained material such as sand is properly moistened, mixed with hydraulic material powder, and added and attached to the peripheral surface of the fine-grained material, or coarse aggregate such as gravel and other additives are added to this. Concrete characterized in that a powdery mixture of either one or both of the materials is pumped through separate pipes, and these separately pumped materials are combined near the nozzle part and sprayed. Spraying construction method. 2. The concrete spraying method according to claim 1, wherein the sand-to-cement ratio in the spraying method is 1 to 4 in which the different pumped materials are combined. 3. The concrete spraying construction method according to claim 1, wherein the slurry-like raw kneaded material is pumped and the granular mixture is sent under high-pressure air pressure. 4. The concrete spraying method according to claim 1, wherein an accelerating agent is added as an additive to the powdery mixture and the mixture is pumped. 5. The concrete spraying method according to claim 1, in which steel fibers or other fibrous materials are added as additives to the powdery mixture and then pumped. 6. The concrete spraying method according to claim 1, which uses early-strengthening cement as the hydraulic substance powder.