Sprayed concrete and method for manufacturing the same

Abstract

To provide a method for manufacturing sprayed concrete that achieves a reduction in the complexity of the construction system and a reduction in dust by using only a liquid set accelerator without using a powder set accelerator and without requiring a complicated supply system.SOLUTION: A powder setting regulator, which is a mixture of gypsum and slaked lime with a mass ratio of gypsum / slaked lime from 0.1 to 0.3 inclusive, is mixed into base concrete, and the resulting concrete composition is mixed with a liquid set accelerator immediately before spraying and is then applied by spraying.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a shotcrete and a method for producing the same. [Background technology]

[0002] In recent years, in order to ensure the safety of the construction environment, the Ministry of Health, Labor and Welfare has revised its "Guidelines for dust control in tunnel and other construction works," and the target level of dust concentration at work sites has been increased from the previous 3 mg / m 3 to 2 mg / m 3 In addition, reducing the amount of concrete that bounces back without adhering to the wall surface (rebound concrete) is also important in terms of material costs and the working environment. It is difficult to achieve low dust (low rebound) using powdered accelerators, so liquid accelerators are preferable. Liquid quick-setting admixtures are advantageous for reducing dust, but their quick-setting effect is weaker than that of powder quick-setting admixtures, and there is a risk that the adhesion and compressive strength of the sprayed concrete will decrease.

[0003] Therefore, techniques that use both powder and liquid quick-setting admixtures in combination have been reported (Patent Documents 1 and 2). These techniques require complex piping for supplying concrete, powder and liquid quick-setting admixtures, and compressed air, making management at the construction site difficult and requiring various devices (material tanks, delivery pipes, liquid pumps, compressors, etc.), which require storage space and power sources. Furthermore, if any one of the piping breaks down or becomes clogged, the entire system shuts down, resulting in frequent problems. Supplying powder quick-setting admixture with compressed air also increases the amount of dust produced during spraying, affecting the working environment.

[0004] In addition to using liquid or powdered quick-setting admixtures, methods for applying shotcrete have also been reported in which various components are added to the base concrete composition. For example, known methods include a method for applying shotcrete in which cement concrete containing hydrated lime, organic acids, and gypsum but no quick-setting admixture is mixed with an inorganic salt such as sodium aluminate or an quick-setting admixture such as calcium aluminate (Patent Documents 3 to 5), a method for applying shotcrete in which inorganic powder such as silica fume is mixed into the base concrete in advance and a liquid quick-setting admixture is added when the concrete is used (Patent Document 6), and a method for applying shotcrete in which powdered aluminum sulfate is mixed into the base concrete and a liquid quick-setting admixture is added when the concrete is used (Patent Document 7). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-03160 [Patent Document 2] Japanese Patent Application Publication No. 10-317671 [Patent Document 3] Japanese Patent Application Laid-Open No. 2001-172062 [Patent Document 4] Japanese Patent Application Laid-Open No. 2001-172063 [Patent Document 5] Japanese Patent Application Laid-Open No. 2001-172065 [Patent Document 6] Japanese Patent Application Laid-Open No. 2001-294470 [Patent Document 7] Japanese Patent Application Laid-Open No. 2007-55831 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the methods of Patent Documents 3 to 5 use powdered quick-setting admixtures as quick-setting agents, so low dust reduction cannot be expected and sufficient early strength cannot be obtained. The method of Patent Document 6 cannot be expected to have the effect of improving early strength due to inorganic powder. Furthermore, the method of Patent Document 7 has the problem of low fluidity retention. Therefore, an object of the present invention is to provide a method for producing shotcrete that does not use a powder quick-setting admixture but uses only a liquid quick-setting admixture, does not require the complex supply system, and achieves a streamlined construction system and low dust production. [Means for solving the problem]

[0007] Therefore, the inventors have conducted various studies on additives that can be mixed into base concrete in advance and then mixed with a liquid quick-setting admixture at the time of construction and sprayed to provide the base concrete with sufficient fluidity while also achieving excellent quick-setting properties, adhesion properties, and compressive strength. They have found that these problems can be solved by mixing into the base concrete a powder setting adjuster that is a mixture of gypsum and slaked lime, with a gypsum / slaked lime mass ratio of 0.1 to 0.3, and have completed the present invention.

[0008] That is, the present invention provides the following [1] to [7]. [1] A powder setting adjuster for a concrete composition for spray application, which is a mixture of gypsums and slaked limes, and is characterized in that the mass ratio of gypsums / slaked limes is 0.1 or more and 0.3 or less. [2] The powder setting modifier according to [1], which does not contain organic acids. [3] A concrete composition for spray application containing cement, aggregate, admixtures, and the powder set adjuster described in [1] or [2], wherein the content of the powder set adjuster is 7 parts by mass or more and 18 parts by mass or less per 100 parts by mass of cement, and the composition does not contain a quick-setting admixture. [4] A method for producing shotcrete, comprising mixing the concrete composition for shotcrete according to [3] with a liquid quick-setting admixture immediately before spraying. [5] The method according to [4], wherein the liquid quick-setting admixture is a liquid quick-setting admixture containing aluminum sulfate as a main component. [6] The method according to [4] or [5], wherein the concrete composition for spray application according to [3] is prepared in advance before spray application. [7] [3] A sprayed concrete comprising the sprayed concrete composition according to the present invention and a liquid quick-setting admixture. [Effects of the Invention]

[0009] By using a base concrete (concrete composition for spraying) that has been mixed with the powder set adjuster of the present invention in advance, it is possible to produce a shotcrete that has excellent quick-setting properties, adhesion properties, and compressive strength while imparting sufficient fluidity to the base concrete by simply mixing in a liquid quick-setting admixture immediately before spraying. Therefore, according to the present invention, a complex supply system is not required, and a streamlined construction system with low dust generation can be achieved. DETAILED DESCRIPTION OF THE INVENTION

[0010] The method for producing shotcrete of the present invention is basically a method for producing shotcrete by mixing base concrete and liquid quick-setting admixture just before spraying. The shotcrete produced in this way is sprayed onto the required area. In the present invention, this base concrete is referred to as a "concrete composition for spray application." The concrete composition for spray application used in the present invention contains, in addition to the ordinary base concrete, a specific powder set modifier, and the powder set modifier is mixed into the base concrete before spray application. The concrete in the present invention is a concrete containing cement, aggregate, and chemical admixtures, and is a concept that includes mortar. The base concrete contains cement, aggregate, and chemical admixtures. The shotcrete of the present invention is a concrete produced by mixing a liquid quick-setting admixture into the above-mentioned concrete composition for shotcrete application.

[0011] One aspect of the present invention is a powder set adjuster for a concrete composition for spray application, which is a mixture of gypsums and slaked limes, and is characterized in that the mass ratio of gypsums / slaked limes is 0.1 or more and 0.3 or less. The powder set adjuster of the sprayed concrete composition of the present invention is a mixture of gypsum and slaked lime. When the organic acids described in Patent Documents 3 to 5 are contained, the penetration resistance value decreases and the quick-setting performance is impaired, so it is preferable not to contain them.

[0012] Examples of gypsum include anhydrous gypsum, dihydrate gypsum, and hemihydrate gypsum, and anhydrous gypsum is preferred from the viewpoint of strength development. The Blaine specific surface area of ​​the gypsum is 3500 to 11000 cm from the viewpoint of ensuring fluidity and reactivity. 2 / g is preferred, and 6000 to 8500 cm 2 / g is more preferred. Examples of slaked lime include slaked lime and carbide slag produced as a by-product when acetylene is generated from calcium carbide. The Blaine specific surface area of ​​slaked lime is 9000 to 15000 cm from the viewpoint of ensuring fluidity and reactivity. 2 / g is preferred, and 11000 to 13000 cm 2 / g is more preferred.

[0013] The mass ratio of gypsums to slaked limes in the powder setting modifier is preferably 0.1 or more and 0.3 or less from the viewpoint of obtaining high initial strength and adhesion and maintaining fluidity during spray application.

[0014] Another aspect of the present invention is a concrete composition for spray application, which contains cement, aggregate, admixtures, and the powder set adjuster, in which the content of the powder set adjuster is 7 parts by mass or more and 18 parts by mass or less per 100 parts by mass of cement, and which does not contain a quick-setting admixture. Here, the composition before the powder setting modifier is added is concrete (base concrete) used in ordinary spraying applications, and contains cement, aggregate, and admixtures. The cement is not particularly limited, and examples thereof include various Portland cements such as ordinary, early strength, extra early strength, low heat, and medium heat, as well as various blended cements obtained by mixing these Portland cements with blast furnace slag, fly ash, and limestone powder. Furthermore, the cement may be one of the above cements, or two or more of them. The aggregate is not particularly limited, and any of fine and coarse aggregates used in the production of ordinary concrete or mortar can be used. In the case of concrete, fine and coarse aggregates are used, and in the case of mortar, fine aggregate is used. Examples of admixtures include water-reducing agents. Commercially available water-reducing agents can be used. Examples include polycarboxylic acid-based water-reducing agents, naphthalene sulfonic acid-based water-reducing agents, and melamine-based water-reducing agents. To ensure fluidity and improve quick-setting properties, the amount of water-reducing agent used is preferably 1.0 to 5.0 parts by mass, and more preferably 1.2 to 3.0 parts by mass, per 100 parts by mass of cement.

[0015] The content of the powder set adjuster in the concrete composition for spray application (total content of gypsums and hydrated limes) is preferably 7 to 18 parts by mass per 100 parts by mass of cement, more preferably 7 to 17 parts by mass, and even more preferably 7 to 16 parts by mass, from the viewpoint of enhancing initial strength and adhesion and maintaining fluidity during spray application.

[0016] The amount of gypsum in the sprayed concrete composition is preferably 0.1 to 4.0 parts by mass, more preferably 1.0 to 3.0 parts by mass, and even more preferably 1.5 to 2.5 parts by mass, per 100 parts by mass of cement. The amount of slaked lime in the sprayed concrete composition is preferably 5.0 to 15.0 parts by mass, more preferably 7.0 to 13.0 parts by mass, and even more preferably 9.0 to 11.0 parts by mass, per 100 parts by mass of cement. The composition ratio of anhydrous gypsum to slaked lime in the shotcrete composition is preferably 0.10 to 0.30, more preferably 0.15 to 0.25. If the composition ratio of anhydrous gypsum to slaked lime is less than 0.1, the initial strength development is poor, and if it exceeds 0.3, fluidity cannot be maintained.

[0017] It is preferable that a concrete composition for spraying not contain an accelerator, from the viewpoint of maintaining fluidity during transportation to the work site and during spraying.

[0018] It is preferable that the concrete composition for spraying be prepared in advance before spraying, from the viewpoint of not requiring a complicated supply system and streamlining the construction system. For example, the powder set modifier may be mixed with the base concrete in a base concrete production plant or in an agitator truck immediately before unloading. Addition in the plant is preferable from the viewpoint of uniformly mixing the powder set modifier into the concrete.

[0019] Another aspect of the present invention is a method for producing shotcrete, characterized in that the above-mentioned concrete composition for shotcrete application and a liquid quick-setting admixture are mixed immediately before spraying. Another aspect of the present invention is a shotcrete containing the above-mentioned concrete composition for shotcrete application and a liquid quick-setting admixture. The quick-setting admixture used here is preferably a liquid quick-setting admixture from the viewpoint of reducing dust during spraying. The liquid quick-setting admixture is not particularly limited, but from the viewpoints of quick-setting property, adhesion, and early strength, a liquid quick-setting admixture containing aluminum sulfate as a main component is preferred. From the viewpoint of reactivity with the powder setting modifier, the content of aluminum sulfate in the liquid quick-setting admixture is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more. Other components that may be contained in the liquid quick-setting admixture include various alums, aluminum hydroxide, precipitated silica, alkanolamines, and the like.

[0020] In order to ensure adhesion performance and compressive strength, the amount of liquid quick-setting admixture added is preferably 5 to 15 parts by mass per 100 parts by mass of cement, more preferably 6 to 14 parts by mass, and even more preferably 8 to 12 parts by mass.

[0021] In an example of mixing the sprayed concrete composition and the liquid quick-setting admixture immediately before spraying, the sprayed concrete composition is preferably pumped through a hose, and the liquid quick-setting admixture and compressed air are supplied through an externally connected hose, so that the two join together at the nozzle and are sprayed. According to the present invention, such a simple configuration can be achieved, and the construction system can be made slimmer and less dusty.

[0022] A preferred example of the resulting shotcrete is a shotcrete containing cement, fine aggregate, coarse aggregate, the powder set modifier, admixtures and liquid quick-setting admixture, in which the water-cement ratio is 35 to 55% and the unit amount of cement is 350 to 600 kg / m 3 , the unit amount of water is 175 to 220 kg / m 3 , the unit weight of fine aggregate is 600 to 1300 kg / m 3 , the unit amount of coarse aggregate is 400 to 1000 kg / m 3 It is a type of sprayed concrete. [Example]

[0023] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to these examples. % in the examples is by mass unless otherwise specified.

[0024] (1) Materials used [Concrete material] Tap water, ordinary Portland cement, mountain sand, crushed stone [Chemical admixture (SP)] Pozzolith Solutions, Mastergranium NT-1000 V2 X2 [Powder setting modifier] Anhydrite (density 2.92g / cm3 , Blaine specific surface area 8,000cm 2 / g) Slaked lime (density 2.22 g / cm 3 , Blaine specific surface area 11,500cm 2 / g) [Calcium aluminate] CaO / Al2O3 molar ratio is 2.1, Blaine specific surface area is 5000 cm 2 / g was used. [Liquid quick-setting agent] Pozzolith Solutions, MasterLoc SA 167 [Powder Accelerator] Calcium aluminate powder accelerator (commercially available)

[0025] (2) Test contents (mortar) The flow (measured twice, immediately after mixing and 90 minutes later) and SP amount of the S / C 2.5 mortar were measured before adding the accelerator, and the Proctor penetration resistance was measured 120 seconds after adding the accelerator. The Proctor test is used to understand the rapid setting characteristics of the accelerator, and the higher the penetration resistance, the better the bond performance when made into concrete. The compressive strength of the mortar was also measured at 1 and 28 days of age.

[0026] (3) Test content (concrete spraying test) W / C 45%, unit water content 203kg / m 3 , unit cement amount 450kg / m 3 , unit fine aggregate amount 997 kg / m 3 , unit fine aggregate amount 685kg / m 3 A concrete spraying test was conducted using concrete with an s / a ratio of 60%, and the dust amount, rebound rate, pullout strength (3h, 1d), and core strength (7d) were measured. Dust amount was measured using a digital dust meter (LD-5R, manufactured by Shibata Chemical Co., Ltd.) in accordance with JSCE-F 564-2005. The rebound rate was calculated by laying a blue tarp under the sprayed area and calculating the ratio of the mass of the concrete supplied to the mass of the concrete that fell onto the blue tarp in accordance with JSCE-F 563-2005.

[0027] (4) Examples and Comparative Examples Mortar or concrete was prepared with the mix proportions shown in Table 1, using the powder setting adjuster and the amount of liquid quick-setting admixture as parameters. Examples 1 and 2 use a mix that combines a powder setting adjuster and a liquid quick-setting admixture, with a W / C of 45%. Examples 3 and 4 vary the water-cement ratio, to 55% and 35%, respectively. Examples 5 and 6 vary the composition ratio of the setting adjuster, with an anhydrous gypsum / slaked lime ratio of 0.1 or 0.3. Comparative Example 1 is a blend that uses only liquid quick-setting admixture without using a powder setting modifier. Comparative Examples 2 and 3 change the composition ratio of the powder setting modifier, with the anhydrous gypsum / slaked lime ratio being 0.05 or 0.4. Comparative Example 4 is a blend that uses a small total amount of powder setting modifier. Comparative Example 5 uses calcium aluminate as the powder setting modifier. Comparative Example 6 uses citric acid as the retarder. The reference example is shotcrete that uses a powder setting modifier.

[0028] [Table 1]

[0029] (5) Mortar test results The results of the mortar test are shown in Table 2.

[0030] [Table 2]

[0031] [Liquidity evaluation] In Comparative Example 5, which used calcium aluminate, the flow value decreased over time after mixing, and fluidity was lost. If premixed with base concrete in actual construction, it is thought to solidify during transportation. When powder setting modifiers of slaked lime and anhydrous gypsum were used, fluidity was maintained even 90 minutes after mixing. In Comparative Example 3, the proportion of gypsum was high and the total amount of powder setting modifier was large, so the amount of SP required was large.

[0032] [Adhesion evaluation] The penetration resistance was low in Comparative Example 1, which used only a liquid quick-setting admixture. It was also low in Comparative Example 4, which used a total amount of powder setting modifier C x 6%, which is thought to be due to an insufficient amount of powder setting modifier. In Comparative Example 6, which used a retarder, the penetration resistance value decreased, impairing quick-setting performance.

[0033] [Compressive strength evaluation] In Comparative Example 2, where the ratio of anhydrous gypsum was small, the 1d strength was low, so it is thought that a certain amount of anhydrous gypsum or more was necessary to ensure initial strength. In Example 2, where C×15% of liquid quick-setting admixture was added, the 28d strength decreased slightly, but strength was still ensured. It is expected that adding too much liquid quick-setting admixture would result in insufficient strength.

[0034] (6) Results of concrete spraying test The results of the concrete tests are shown in Table 3.

[0035] [Table 3]

[0036] [Liquidity evaluation] In Example 1, in which a powder setting modifier was added, the amount of SP was increased compared to Comparative Example 1, in which no powder setting modifier was added, and the base concrete had the required fluidity at the time of unloading.

[0037] [Compressive strength evaluation] In Example 1, in which a powder setting modifier was added, the strength was higher than in Comparative Example 1 at all ages. The improvement in 1d strength is thought to be due to the reaction of the powder setting modifier. As for the improvement in 7d strength, since this was an evaluation of core specimens, it is thought that this is because the improved adhesion in Example 1 reduced voids and the like in the sprayed concrete. In Comparative Example 1, voids formed inside the core specimen during spraying, which became structural defects and reduced the core strength.

[0038] [Dust and rebound evaluation] In the Comparative Example and Reference Example, not only was the dust concentration high, but the rebound amount was also high, resulting in poor adhesion performance. In contrast, in Example 1, both dust and rebound were reduced.

Claims

1. A powder set adjuster for a concrete composition for spray application, which is a mixture of gypsum and slaked lime, and has a mass ratio of gypsum / slaked lime of 0.1 or more and 0.3 or less.

2. 2. The powder setting modifier according to claim 1, which does not contain organic acids.

3. 3. A concrete composition for spray application, comprising cement, aggregate, admixtures, and the powder set adjuster according to claim 1 or 2, wherein the content of the powder set adjuster is 7 parts by mass or more and 18 parts by mass or less per 100 parts by mass of cement, and wherein no quick-setting admixture is blended.

4. 4. A method for producing shotcrete, comprising mixing the concrete composition for shotcrete according to claim 3 with a liquid quick-setting admixture immediately before shotcrete application.

5. 5. The method according to claim 4, wherein the liquid quick-setting admixture is a liquid quick-setting admixture containing aluminum sulfate as a main component.

6. 5. The method according to claim 4, wherein the concrete composition for spray application according to claim 3 is prepared in advance before spray application.

7. A sprayed concrete comprising the sprayed concrete composition according to claim 3 and a liquid quick-setting admixture.

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