Ultra-high strength sprayed concrete and spray method thereof

Abstract

To prevent ground loosening immediately after excavation without changing materials used, and to have sufficient strength to cope with long-term load increases and ground deformation.SOLUTION: In ultra-high strength sprayed concrete made by adding a liquid rapid-setting agent and a powder rapid-setting agent to concrete materials containing cement and water, a water-soluble aluminum salt-based liquid rapid-setting agent is used as the liquid rapid-setting agent, with an addition amount thereof being 4-6 wt.% relative to the cement weight, and a calcium aluminate-based powder rapid-setting agent is used as the powder rapid-setting agent, with an addition amount thereof being 6 wt.% relative to the cement weight. The water / cement ratio is set to 30-33%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to ultra-high-strength shotcrete, which is sprayed onto construction surfaces by high-speed jetting using compressed air without using forms in tunnel linings, slope protection works, etc., and which is designed to achieve strength higher than conventional design standard strength, and to a spraying method thereof. [Background technology]

[0002] The design standard strength of general shotcrete is 18N / mm for normal strength at 28 days. 2 However, when high strength quality is required due to the enlargement of the tunnel cross section, the strength is set to 36N / mm 2 In addition, for the initial strength, it is usually set to 5N / mm for 24 hours (1 day) of normal strength quality. 2 High strength quality at 24 hours, 10N / mm 2 , 2N / mm at 3 hours 2 was set to.

[0003] Examples of techniques for improving early quick-setting properties and obtaining high-strength shotcrete include Patent Documents 1 and 2 listed below. Patent Document 1 describes a technique in which, when adding a liquid quick-setting agent just before spraying concrete, a powder quick-setting agent that does not form a slurry is introduced into the concrete together with the liquid quick-setting agent and sprayed, thereby increasing the strength of the concrete at 28 days to 36 N / mm 2 Furthermore, Patent Document 2 below discloses a high-strength shotcrete that has an initial strength (at 3 hours) of up to 2.9 N / mm2 using a shotcrete containing cement concrete that does not contain an accelerator, a liquid accelerator, and an alkali-free powder accelerator. 2 A high-strength shotcrete is disclosed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-159239 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-226247 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when excavating a tunnel, for example, in geological conditions where the natural ground has low strength, higher early strength and support effectiveness are sometimes required. In other words, it has been desired to prevent loosening of the natural ground immediately after excavation, as well as to improve the resistance to long-term increases in load and deformation of the natural ground.

[0006] Furthermore, in order to increase the strength of shotcrete, the type of cement may be changed or admixtures may be added, but depending on the plant equipment, it may be difficult to change the materials used.

[0007] Therefore, the main object of the present invention is to provide an ultra-high-strength shotcrete and a method for spraying it that can prevent loosening of the ground immediately after excavation without changing the materials used and has the strength to cope with long-term increases in load and deformation of the ground. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention according to claim 1 provides an ultra-high strength shotcrete obtained by adding a liquid quick-setting admixture and a powder quick-setting admixture to a concrete material containing cement and water, The present invention provides an ultra-high strength shotcrete characterized in that a water-soluble aluminum salt-based liquid quick-setting agent is used as the liquid quick-setting agent, and the amount added is 4 to 6 weight % based on the cement weight, and a calcium aluminate-based powder quick-setting agent is used as the powder quick-setting agent, and the amount added is 6 weight % based on the cement weight, and the water / cement ratio is 30 to 33%.

[0009] In the invention described in claim 1 above, a water-soluble aluminum salt-based liquid quick-setting agent is used as the liquid quick-setting agent, and the amount added is C x 4 to 6 wt %, and a calcium aluminate-based powder quick-setting agent is used as the powder quick-setting agent, and the amount added is C x 6 wt %, under the conditions that the water / cement ratio is significantly reduced to 30 to 33% compared to normal, as is clear from the test results described in detail below, and the initial strength (at 3 hours and 24 hours) and strength at 28 days satisfy the design standard strength, and it is possible to prevent loosening of the ground immediately after excavation without changing the materials used, and it is also possible to cope with long-term increases in load and deformation of the ground.

[0010] In the present invention according to claim 2, the target compressive strength of the ultra-high strength shotcrete is a design standard strength of 4 N / mm at 3 hours of age. 2 The design standard strength at 24 hours is 18N / mm 2 The design strength at 28 days is 54N / mm 2 The ultra-high strength shotcrete according to claim 1 is provided.

[0011] In the invention described in claim 2, the strength at 3 hours is the strength at 3 hours of high-strength shotcrete (2N / mm 2 The strength at 24 hours is twice the design standard strength of normal strength shotcrete (18N / mm 2 The design strength at 28 days is set at 54N / mm, which is three times the normal strength and 1.5 times the high strength. 2 That's all.

[0012] According to a third aspect of the present invention, there is provided the ultra-high strength shotcrete according to the first aspect, wherein the amounts of the liquid quick-setting admixture and the powder quick-setting admixture added have a construction tolerance of ±10%.

[0013] In the invention described in claim 3 above, since it is difficult to always control the amount of liquid quick-setting admixture and powder quick-setting admixture added to a constant value and practically errors occur in the construction, the error range is set to ±10%.

[0014] The present invention according to claim 4 is a method for spraying ultra-high strength shotcrete, which is obtained by adding a liquid quick-setting admixture and a powder quick-setting admixture to a concrete material containing cement and water, as a ground reinforcement during tunnel excavation, and includes the steps of: a water-soluble aluminum salt-based liquid quick-setting agent and a calcium aluminate-based powder quick-setting agent are used as the liquid quick-setting agent, For natural ground where standard strength or high strength is required as the design standard strength, the amount of liquid quick-setting admixture added is 7 to 8% by weight relative to the cement weight, the amount of powder quick-setting admixture added is 5 to 4% by weight relative to the cement weight, and the water / cement ratio is 34 to 60% and sprayed. There is provided a method for spraying ultra-high strength shotcrete, characterized in that when encountering natural ground that requires ultra-high strength as a design standard strength, the ultra-high strength concrete according to any one of claims 1 to 3 is sprayed.

[0015] In the invention described in claim 4 above, since it may be difficult to change the type of cement or use admixtures depending on the plant equipment, in such cases, the types of liquid quick-setting admixture and powder quick-setting admixture used are not changed, but the addition rates of the liquid quick-setting admixture and powder quick-setting admixture and the water / cement ratio are appropriately adjusted to enable normal-strength, high-strength, and ultra-high-strength shotcrete to be used depending on the ground conditions. [Effects of the Invention]

[0016] As explained above in detail, according to the present invention, it is possible to provide an ultra-high strength shotcrete and a spraying method thereof that can prevent loosening of the ground immediately after excavation without changing the materials used and that has the strength to cope with long-term increases in load and deformation of the ground. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a construction system diagram of the ultra-high strength shotcrete according to the present invention. [Figure 2] 1 is a graph showing the results of a compressive strength test for a mortar test at a material age of 3 hours. [Figure 3] 1 is a graph showing the results of a compressive strength test in a mortar test at a material age of 24 hours. [Figure 4] 10 is a graph showing the results of a compressive strength test in a mortar test at 28 days old. [Figure 5] 1 is a graph showing the results of a compressive strength test of concrete at an age of 3 hours. [Figure 6] 1 is a graph showing the results of a compressive strength test for concrete at an age of 24 hours. [Figure 7] 1 is a graph showing the results of a compressive strength test on concrete at 28 days old. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0019] The ultra-high strength shotcrete 1 of the present invention is particularly suitable as a shotcrete for the primary lining of tunnels and shafts, or for the lining of large underground spaces, in geological conditions where the natural ground has low strength, and is a shotcrete that can produce high-strength structures in a short period of time and has the effect of acting as a support that directly supports the excavated ground.

[0020] In the present invention, the ultra-high strength shotcrete refers to both mortar and concrete.

[0021] As shown in Table 1, the ultra-high strength shotcrete 1 according to the present invention has a design standard compressive strength of 54 N / mm at 28 days. 2 This is set at the design standard strength of normal strength shotcrete, 18N / mm 2 This is three times the design strength of high-strength shotcrete, 36N / mm 2 The design standard strength for early strength is 4N / mm at 3 hours. 2 Above, 18N / mm at 24 hours 2This is because the strength at 3 hours is set to be equal to or greater than the strength at 3 hours of high-strength shotcrete (2N / mm 2 The strength at 24 hours is twice the design standard strength of normal strength shotcrete (18N / mm 2 As described above, the ultra-high strength shotcrete 1 according to the present invention is designed to have high strength at both 28 days and early age. [Table 1]

[0022] The ultra-high strength shotcrete 1 according to the present invention is made by adding a liquid quick-setting admixture and a powder quick-setting admixture to a concrete material containing at least cement and water. The concrete material can contain fine aggregate, coarse aggregate, admixtures, etc. in addition to the cement and water.

[0023] The liquid quick-setting agent is a water-soluble aluminum salt-based liquid quick-setting agent, and its amount is 4 to 6% by weight (C x 4 to 6% by weight) based on the cement weight.Also, the powder quick-setting agent is a calcium aluminate-based powder quick-setting agent, and its amount is 6% by weight (C x 6% by weight) based on the cement weight.

[0024] The amounts of these quick-setting admixtures added are standard amounts used in design, and naturally, errors will occur during application. In this invention, the application error range is estimated to be ±10% (C x 3.6 to 6.6% by weight for the liquid quick-setting admixture, and C x 5.4 to 6.6% by weight for the powder quick-setting admixture). If the application error is within this range, it will not have a significant effect on the strength of the shotcrete.

[0025] Furthermore, the ultra-high strength shotcrete 1 according to the present invention has a water / cement ratio of 30 to 33% (by weight) during mixing. If the water / cement ratio is less than 30%, pulsation occurs during pumping, which may impair stable fluidity and raise concerns about increased pressure inside the hose. On the other hand, if the ratio exceeds 33%, as shown in the results of concrete tests described later, the design standard strength of 4 N / mm at 3 hours of age is reached. 2 Not satisfied with the above.

[0026] In general, shotcrete is broadly divided into dry and wet types, depending on the method of supplying materials to the sprayer. In the dry type, cement and aggregate are mixed in the air, transported by air, and mixed with water just before the spray nozzle before being sprayed. In the wet type, mortar or concrete that has been mixed in a mixer in advance is supplied to the spray nozzle and sprayed with compressed air. In the following explanation, the wet type is used as an example, but the ultra-high-strength shotcrete 1 of the present invention can also be applied to the dry type.

[0027] As shown in Figure 1, the method for producing ultra-high-strength shotcrete 1 according to the present invention is similar to the conventional wet production method. Mortar or concrete, which has been mixed in advance at a concrete factory or the like, is transported to the construction site in an agitator truck 2 and supplied to a spray nozzle 4 by a concrete pump 3 or the like. Just before the spray nozzle 4, compressed air is passed through a compressor 5 and an air dryer 6 to dry the mixture, which is then supplied to a powder quick-setting agent adder 7, which pressurizes and delivers powder quick-setting agent 8. Additionally, auxiliary air from a pump 9 and the compressor 5 pressurizes and delivers liquid quick-setting agent 11 from a liquid quick-setting agent tank 10. The resulting mixture is then sprayed from the tip of the spray nozzle 4.

[0028] The ultra-high strength shotcrete 1 may be sprayed onto the surface of the excavated ground at all times, but it is preferable to spray a type of shotcrete selected from ultra-high strength, high strength, and normal strength shotcrete appropriately depending on the ground conditions such as the strength of the ground.

[0029] In this case, changes to ultra-high strength, high strength, and normal strength can be made by changing the materials used, such as the type of cement or additives, but since it may be difficult to change the materials used depending on the plant equipment, it is better to produce and spray shotcrete of the required strength by changing the addition rates of liquid and powder quick-setting admixtures and the water / cement ratio.Since shotcrete of each strength is obtained by changing the addition rates of liquid and powder quick-setting admixtures and the water / cement ratio, it can be applied to plant equipment where it is difficult to change the materials used.

[0030] To give a specific example, if a natural ground requiring ultra-high strength is encountered, the amount of liquid quick-setting admixture added is C×4-6% by weight, the amount of powder quick-setting admixture added is C×6% by weight, and the water / cement ratio is 30-33% as described above.Also, if a natural ground requiring normal or high strength is encountered, the amount of liquid quick-setting admixture added is C×7-8% by weight, the amount of powder quick-setting admixture added is C×5-4% by weight, and the water / cement ratio is 34-60%. [Example]

[0031] An overview of the compression test and its results are explained below. The compression test was carried out by determining the appropriate addition rate of the accelerator in a mortar test using mortar, and then by confirming performance in a concrete test using concrete. Because it takes a lot of time and effort to produce a large number of concrete specimens with different amounts of accelerator added, the test was carried out by using mortar to determine the appropriate addition rate of the accelerator, and then by confirming performance in a concrete spraying test based on this addition rate of the accelerator.

[0032] The materials used in the test are shown in Table 2. [Table 2]

[0033] (Mortar test) In the mortar test, mortar was produced using the materials shown in Table 2 except for coarse aggregate G.

[0034] The compressive strength test of the mortar was carried out in accordance with JIS R 5201 "Physical Test Method of Cement, Appendix C (Regulations) Strength Test." The test was carried out at a temperature of 20°C.

[0035] The test results of the compressive strength of the mortar are shown in Table 3. In Table 3, the test numbers marked with * indicate examples of the present invention. [Table 3]

[0036] Graphs showing the relationship between the water / cement ratio and compressive strength at ages of 3 hours, 24 hours, and 28 days for test numbers A-1 to A-3, B-1 to B-3, and C-1 to C-3 are shown in FIGS. 2 to 4, respectively.

[0037] At the age of 3 hours as shown in Figure 2, when the amount of powder quick-setting admixture added is C x 4% and C x 5%, the compressive strength is 4 N / mm 2 In addition, even if the amount of powdered accelerator added is C × 6%, if the water / cement ratio exceeds 34%, the compressive strength will be less than the design strength of 4 N / mm2 at 3 hours. 2 Therefore, in the case of mortar, when the amount of liquid quick-setting agent added is C x 4-6%, the amount of powder quick-setting agent added is C x 6%, and the water / cement ratio is 30-34%, the design standard strength of 4 N / mm2 at 3 hours is 2 can be satisfied.

[0038] The compressive strength at an age of 24 hours shown in FIG. 3 and at an age of 28 days shown in FIG. 4 both satisfy the design standard strength.

[0039] Furthermore, as shown in test numbers D and E, by increasing the water / cement ratio and adding a liquid quick-setting admixture in an amount of C x 7-8% and a powder quick-setting admixture in an amount of C x 5-4%, high-strength or normal-strength shotcrete can be obtained.

[0040] (Concrete testing) Next, a spraying test was conducted using the liquid quick-setting admixture at an amount C x 4% and the powder quick-setting admixture at an amount C x 6%, which satisfied the design standard strength obtained from the mortar test.

[0041] In the concrete tests, concrete was produced using all the materials shown in Table 2. The concrete mix is ​​shown in Table 4. [Table 4]

[0042] The compressive strength of specimens aged 3 and 24 hours was measured by a short-term strength test (pull-out test), and the compressive strength of specimens aged 7 and 28 days was measured by a core strength test.

[0043] The short-term strength test (pull-out test) was conducted in accordance with JSCE-F 561 "Procedure for preparing specimens for compressive strength tests of shotcrete (mortar) (draft)" in the Japan Society of Civil Engineers' Standard Specifications for Concrete [Criteria Edition], by spraying the specimens into a pull-out test dish. Tests were then conducted in accordance with JSCE-G 561 "Test method for initial strength of shotcrete by pull-out method," with three specimens per age and measured at ages of 3 and 24 hours. The curing conditions were in-situ curing for the 3-hour-old specimens, and a temperature of 20°C and humidity of 80% for the 24-hour-old specimens.

[0044] The core strength test was conducted in accordance with JSCE-F 561, "Proposal for Preparation of Test Specimens for Compressive Strength Tests of Shotcrete (Mortar)," as described in the Japan Society of Civil Engineers' Standard Specifications for Concrete [Standards Edition]. A rectangular panel formwork measuring 500 mm wide, 500 mm high, and 300 mm deep with open front and bottom surfaces was sprayed and cored from the front. Tests were conducted in accordance with JIS A 1107, "Methods for Core Extraction from Concrete and Compression Testing," with core dimensions of 50 mm diameter x 100 mm height (three cores per age) and measured ages of 7 and 28 days. The curing conditions were as follows: after spraying, the specimens were air-cured at room temperature for approximately three days, then cored. The cored specimens were then subjected to standard curing (underwater curing at 20°C). The cores were cut perpendicular to the sprayed surface, and both ends were cut and polished to obtain specimens of the specified dimensions.

[0045] The test results for the compressive strength of concrete are shown in Table 5. The compressive strengths at 3 and 24 hours are converted compressive strengths based on pullout, and were calculated by multiplying the measured shear strength by a factor of 4. The compressive strengths at 7 and 28 days are the compressive strengths of the shotcrete core. In Table 5, the test numbers marked with * indicate examples of the present invention. [Table 5] Graphs showing the relationship between the water / cement ratio and compressive strength at ages of 3 hours, 24 hours, and 28 days for test numbers A, B, and C are shown in FIGS. 5 to 7, respectively.

[0046] At the age of 3 hours as shown in Figure 5, when the water / cement ratio is 30-33%, the compressive strength is 4 N / mm 2 If the amount of liquid quick-setting admixture added is C x 4%, the amount of powder quick-setting admixture added is C x 6%, and the water / cement ratio is 30 to 33%, the compressive strength of the ultra-high-strength shotcrete according to the present invention satisfies the design standard strength. Furthermore, it is estimated that the compressive strength can be satisfied in accordance with the results of the above mortar test even when the amount of liquid quick-setting admixture added is C x 5% or 6%.

[0047] The compressive strength at the age of 24 hours shown in FIG. 6 and the compressive strength at the age of 28 days shown in FIG. 7 both satisfy the design standard strength.

[0048] Furthermore, as shown in test number E, by increasing the water / cement ratio and adding C x 8% of liquid quick-setting admixture and C x 4% of powder quick-setting admixture, shotcrete of normal strength can be obtained. [Explanation of symbols]

[0049] 1...Ultra-high strength shotcrete, 2...Agitator vehicle, 3...Concrete pump, 4...Spraying nozzle, 5...Compressor, 6...Air dryer, 7...Powdered set accelerator adder, 8...Powdered set accelerator, 9...Pump, 10...Liquid set accelerator tank, 11...Liquid set accelerator

Claims

1. An ultra-high strength shotcrete made by adding a liquid quick-setting admixture and a powder quick-setting admixture to a concrete material containing cement and water, The ultra-high strength shotcrete is characterized in that the liquid quick-setting agent is a water-soluble aluminum salt-based liquid quick-setting agent, and the amount added is 4 to 6 weight % based on the cement weight, and the powder quick-setting agent is a calcium aluminate-based powder quick-setting agent, and the amount added is 6 weight % based on the cement weight, and the water / cement ratio is 30 to 33%.

2. The target compressive strength of the ultra-high strength shotcrete is 4N / mm 2 The design standard strength at 24 hours is 18N / mm 2 The design standard strength at 28 days is 54N / mm 2 2. The ultra-high strength shotcrete according to claim 1, wherein the above-mentioned

3. 2. The ultra-high strength shotcrete according to claim 1, wherein the amounts of the liquid quick-setting admixture and the powder quick-setting admixture added have a construction tolerance of ±10%.

4. A method for spraying ultra-high strength shotcrete, which is made by adding a liquid quick-setting agent and a powder quick-setting agent to a concrete material containing cement and water, as a ground reinforcement method during tunnel excavation, a water-soluble aluminum salt-based liquid quick-setting agent and a calcium aluminate-based powder quick-setting agent are used as the liquid quick-setting agent, In the case of natural ground where normal strength or high strength is required as the design standard strength, the amount of the liquid quick-setting admixture added is set to 7 to 8% by weight relative to the cement weight, the amount of the powder quick-setting admixture added is set to 5 to 4% by weight relative to the cement weight, and the water / cement ratio is set to 34 to 60% and sprayed. A method for spraying ultra-high strength shotcrete, characterized in that when encountering natural ground that requires ultra-high strength as a design standard strength, the ultra-high strength concrete of any one of claims 1 to 3 is sprayed.

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