JP6465432B2 - High strength shotcrete - Google Patents

Description

  The present invention relates to high-strength shotcrete that is sprayed onto a wall surface or the like.

For construction works such as tunnels, underground spaces, and slopes, slurry mortar and concrete (hereinafter collectively referred to as “concrete”) are used on the walls, ceilings, and slopes to reinforce natural ground and structures. Spraying is done. In general spraying construction, quick setting agent is added to the base concrete after pouring water to give quick setting, and cement setting is completed in a short time from water contact, thereby ensuring adhesion. It is an absolute condition that shotcrete is excellent in adhesion. However, for example, a construction object that requires reinforcement as soon as possible after excavation, such as an excavation site, requires a particularly high initial strength. Calcium aluminate is widely used as a powdery quick setting agent having excellent quick setting properties. The following are known as measures for enhancing the adhesion of shotcrete containing calcium aluminate as a quick-setting component. (1) Increase the vitrification rate of calcium aluminate. (2) Increasing the content molar ratio (CaO / Al ₂ O ₃ ) of CaO and Al ₂ O ₃ in calcium aluminate (see, for example, Patent Document 1). (3) Calcium aluminate contains MgO. (For example, refer to Patent Document 2.) (4) An alkali metal aluminate is used in combination. (For example, refer to Patent Document 3.) (5) An alkali metal carbonate is used in combination. (For example, refer to Patent Document 4.) In addition, as a measure for improving and improving the workability such as prevention of clogging of the spraying device, calcium aluminate containing 1-4% by mass of SiO ₂ is used as a quick setting component. It is known. (For example, refer to Patent Document 5.) Further, as a measure for increasing the initial strength of shotcrete containing calcium aluminate as a quick setting component, the following is known. (6) Increase the mass ratio (cement / water) of water and cement in shotcrete.

  However, a useful measure for improving both the adhesion and the initial strength of shotcrete containing calcium aluminate as a rapid setting component is not known. In particular, with regard to strength development, high initial or early strength development, which is known as a characteristic of conventional shotcrete, includes rapid setting components due to the rapid setting of cement due to the combination of rapid setting agents. As a result, the initial strength is inevitably higher than that of concrete, and the strength increase rate greatly exceeds the initial strength expression level of shotcrete containing conventional quick-setting components, and the initial strength value is greatly improved. A useful measure for this is not known at least as long as it does not impair the adhesion and workability.

JP 2005-247618 A JP 2014-88296 A JP-A-11-711145 Japanese Patent Laid-Open No. 10-1342 JP 2013-177279 A

  The present invention is sprayed concrete that can secure good workability by suppressing the instantaneous setting that hinders the work of spraying work, and has strong adhesion without rebounding or dripping of the sprayed material. It has excellent adhesion that can be held without deformation, and it has high strength that has all the characteristics that the strength increases significantly after spraying and can form sprays with much higher strength at short age. The issue is to provide shotcrete.

  As a result of studying to solve the above problems, the present inventor has obtained a mixture containing calcium aluminate clinker powder, sodium aluminate, anhydrous gypsum, etc., containing a specific amount of a specific component, cement, and anhydrous gypsum. The present invention was completed by obtaining knowledge that sprayed concrete blended in a composition containing a specific ratio solves the above problems as a whole.

That is, the present invention is a high-strength shotcrete represented by the following (1) to (4). (1) a cement composition containing 100 parts by mass of anhydrite 5-12 parts by weight cement, molar ratio of CaO and Al ₂ O ₃ in the glass content of at least 90% (CaO / Al ₂ O ₃₎ 1 .8 to 2.5 calcium aluminate clinker, silicon, magnesium and titanium in terms of oxides, SiO ₂ ; 4 to 6% by mass, MgO; 0.75 to 0.95% by mass, and TiO ₂ A powder admixture containing 0.8 to 1.3% by mass of clinker pulverized product, sodium aluminate and anhydrous gypsum is added in an amount of 5 to 100 parts by mass of cement in the cement composition; High-strength shotcrete added to 15 parts by weight. (2) A calcium aluminate clinker having a vitrification ratio of 90% or more and a molar ratio of CaO and Al ₂ O ₃ (CaO / Al ₂ O ₃ ) of 1.8 to 2.5. silicon, in terms of oxide of magnesium and titanium, SiO _2; 4 to 6 wt%, MgO; 0.75 to 0.95% by weight and TiO _2; grinding of 0.8 to 1.3 wt% content for clinker The high-strength shotcrete according to (1) above, comprising 100 parts by mass of a product, 2.4 to 12.8 parts by mass of sodium aluminate and 1.2 to 24.7 parts by mass of anhydrous gypsum. (3) The high-strength shotcrete according to (1) or (2), wherein the powder admixture further contains an alkali metal carbonate. (4) The high-strength shotcrete according to any one of (1) to (3), wherein the cement composition contains 40 to 55 parts by mass of water with respect to 100 parts by mass of cement.

  According to the present invention, it is possible to obtain sprayed concrete having good construction workability and strong adhesion, and capable of expressing very high strength in a short time after spraying.

  The cement composition constituting the high-strength shotcrete of the present invention contains cement and anhydrous gypsum in a specific quantitative ratio. This cement composition is commonly referred to as base concrete or base mortar in practice. The cement to be contained is not particularly limited as long as it is hydraulic, and examples thereof include normal, early strength, very early strength, moderate heat, low heat, and sulfate-resistant Portland cement. Moreover, the mixed cement which mixed fine powders, such as slag, such as Portland cement, blast furnace slag, and coal ash, can also be illustrated.

  Any anhydrous gypsum contained in the cement composition can be used and is not particularly limited. By containing anhydrous gypsum, curing is accelerated and high strength development is easily obtained. The content of anhydrous gypsum in the cement composition is 5 to 12 parts by mass with respect to 100 parts by mass of cement. If it is less than 5 parts by mass, it is not preferable because it is difficult to obtain a sustained high strength expression, and if it exceeds 12 parts by mass, the setting is delayed, and there is a possibility that adhesion and initial strength expression may be reduced. Absent.

  The water contained in the cement composition is used for hydration of the hydration-reactive substance, and the content thereof is not particularly limited, and may be appropriately determined according to construction conditions, other blending components, and the like. . Preferably, it is 40-55 mass parts with respect to 100 mass parts of cement. If it is this range, it will become easy to obtain high intensity | strength expression.

  The cement composition may contain components other than cement, anhydrous gypsum and water as long as the effects of the present invention are not impaired. Examples of such components include various water reducing agents, thickeners, pozzolanic reactive materials, admixtures and materials that can be used for concrete such as fine aggregates, but are limited to the description examples. It is not a thing.

Moreover, the powder admixture mix | blended with the said aqueous composition of the high strength shotcrete of this invention contains the clinker ground material of specific calcium aluminate, sodium aluminate, and anhydrous gypsum. The clinker pulverized product of specific calcium aluminate contained in the powder admixture is a substance containing CaO and Al ₂ O ₃ as main chemical components, and is a hydration active substance having a structure with advanced vitrification. Is obtained as a baked lump (clinker) obtained by firing a raw material mixture containing a raw material to be a CaO source and a raw material to be an Al ₂ O ₃ source until the mixture is melted and rapidly cooling it. In the present invention, the use of a calcium aluminate clinker having a vitrification rate of 90% or more contributes to the provision of high quick setting. If the vitrification rate is less than 90%, the reaction activity is low, and it may not be possible to impart quick setting suitable for spray construction, which is not preferable. The calcium aluminate contains CaO and Al ₂ O ₃ as chemical components in a molar ratio (CaO / Al ₂ O ₃ ) of 1.8 to 2.5. If the content molar ratio (CaO / Al ₂ O ₃ ) is less than 1.8, it is not preferable because the adhesiveness is lowered, and if it exceeds 2.5, the quick setting is strengthened and solidification occurs before reaching the spray target surface. Therefore, it is not preferable.

The calcium aluminate clinker contains at least a predetermined amount of silicon, magnesium and titanium. Specifically, SiO ₂ ; 4 to 6% by mass, MgO; 0.75 to 0.95% by mass, and TiO ₂ ; 0.8 to 1.3% by mass in terms of oxides, respectively. When the silicon content is out of the range of 4 to 6% by mass in terms of oxide (SiO ₂ ), there is a possibility that the instantaneous setting may increase or the adhesion may be lowered. In addition, it is not preferable that the magnesium content is out of the range of 0.75 to 0.95% by mass in terms of oxide (MgO) because adhesion may be lowered. Moreover, it is not preferable that the content of titanium is out of the range of 0.8 to 1.3% by mass in terms of oxide (TiO ₂ ), since there is a risk that rapid setting properties and initial strength development may be reduced. . Further, inclusion of other components other than these in the clinker powder is allowed as long as the effects of the present invention are not inhibited. The calcium aluminate clinker pulverized product is pulverized by pulverizing the calcium aluminate clinker with a crusher such as an all-steel ball mill or disk mill, and using a commercially available classifier or sieve as appropriate. It is a thing. The fineness is not particularly limited, but is preferably about 2500 to 9000 cm ² / g in terms of specific surface area of branes. If it is less than 2500 cm ² / g, the reaction activity becomes weak and it may be difficult to obtain high quick setting properties, and if it exceeds 9000 cm ² / g, it is not appropriate because the production cost related to grinding increases. .

  The sodium aluminate contained in the powder admixture has an action of rapidly accelerating the setting of mortar and concrete immediately after water contact, and contributes to obtaining high initial strength development. The sodium aluminate used is not particularly limited as long as it is in a powder form. Further, the content of sodium aluminate in the powder admixture is not limited. Preferably, 2.4 to 12.3 parts by mass of sodium aluminate is contained with respect to 100 parts by mass of the pulverized product of the calcium aluminate clinker. Examples of the alkali metal aluminate include one or more selected from the group consisting of sodium aluminate, potassium aluminate and lithium aluminate. By containing an alkali metal aluminate, it contributes to rapidly promoting the setting of mortar and concrete immediately after water contact.

  The anhydrous gypsum contained in the powder admixture contributes to improving the strength development and promotes the curing of the spray. Any anhydrous gypsum can be used. In addition, the content of anhydrous gypsum of the powder admixture is not limited, but as a preferable content, for the pulverized material content of 100 parts by mass of the calcium aluminate clinker, 1.2 ~ 24.7 parts by mass.

  In addition, the powder admixture may contain components other than the clinker pulverized product of the specific calcium aluminate, sodium aluminate, and anhydrous gypsum as long as the effect of the present invention is not inhibited. . A preferred example of such a component is sodium carbonate. Containing sodium carbonate promotes condensation and facilitates improvement of initial strength development. The content of sodium carbonate in the powder admixture is not limited, but is, for example, 1 to 10 parts by mass with respect to 100 parts by mass of the pulverized material content of the calcium aluminate clinker. Moreover, alkali metal carbonates other than sodium carbonate can also be used suitably.

  The high-strength shotcrete of the present invention is such that such a powder admixture is added to the cement composition in an amount of 5 to 15 parts by mass with respect to 100 parts by mass of the cement content in the cement composition. It is added.

  Moreover, the method of manufacturing the high strength shotcrete of the present invention is not limited. A recommended example is, for example, the above-mentioned calcium aluminate clinker pulverized product, sodium aluminate and anhydrous gypsum, etc., are put into a mixing device such as a Henschel mixer and dry mixed, and a powder admixture Is made. Separately, cement, anhydrous gypsum, water, and the like are kneaded with a mixing device such as a biaxial forced concrete mixer to produce a cement composition (base concrete) so that the predetermined composition is obtained. For example, a high-strength shotcrete can be manufactured by pumping and mixing the powder admixture produced in the spraying device with the cement composition.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to the described examples. The following examples were performed in a temperature environment of 20 ° C. (± 2 ° C.) unless otherwise specified.

[Preparation of calcium aluminate clinker]
Both use CaCO ₃ and Al ₂ O ₃ as commercially available powder reagents, SiO ₂ , MgCO ₃ , and TiO ₂ as commercially available express reagents, and the content molar ratio of CaO and Al ₂ O ₃ (CaO / Al ₂ O ₃ ) A critical amount of silicon, magnesium, and titanium was blended so that the clinker represented by the oxide-containing content shown in Table 1 was obtained, and a raw material formulation was prepared using a Henschel mixer. This raw material mixture was baked at about 1600 ° C. (± 50 ° C.) for 60 minutes using an electric furnace, and was immediately taken out of the furnace after the lapse of the baking time. Nitrogen for cooling was blown onto the surface of the baked lump (clinker) taken out at a flow rate of about 30 ml / second to quench it, and a clinker cooled product was obtained. In order to adjust the vitrification rate of the clinker, some clinker was sprayed with no cooling nitrogen gas sprayed or with a reduced gas flow rate. Next, the clinker was pulverized with a ball mill made of all steel, and applied to a classifier to obtain a calcium aluminate clinker powder having a brain specific surface area of about 5000 cm ² / g. In addition, the vitrification rate of this calcium aluminate is determined by using an X-ray powder diffractometer and the mass of each mineral contained in the calcium aluminate clinker having a mass of M1 is quantified by an internal standard method or the like. Total mass; M2 was calculated, the remainder was regarded as a pure glass phase, and the vitrification rate was calculated by the following formula.
Vitrification rate (%) = (1-M2 / M1) × 100

[Preparation of powder admixture]
Henschel mixer so that the materials selected from the clinker powder of calcium aluminate, sodium aluminate (commercial powder reagent), type II anhydrous gypsum (commercial product) and sodium carbonate (commercial powder reagent) prepared in the above manner have the composition shown in Table 2. And mixed for about 2 minutes to prepare a powder admixture.

[Evaluation of quick setting]
1000 g of ordinary Portland cement (commercial product) and 500 g of water were placed in a bottomed cylindrical container, mixed for 1 minute with a hand mixer, and then allowed to stand indoors for 30 minutes. After this standing, the mixture was remixed for 1 minute with a hand mixer, 70 g of the powder admixture prepared above was added, and further stirred for 5 seconds to prepare a cement paste. The quick setting property was evaluated by measuring the Procter penetration resistance value of the cement paste after 30 seconds, 60 seconds, 120 seconds and 5 minutes after addition of the powder admixture. Proctor penetration resistance value is measured in accordance with the Japan Society of Civil Engineers Concrete Standard Specification "Quality Standards for Sprayed Concrete" Annex "Method for Measuring Instantaneous Mortation Time of Mortar Using Penetration Resistance", with a cross-sectional area of 0.125 cm ² This was done using a Procter needle. The measurement results are shown in Table 3.

[Preparation of base concrete (cement composition)]
Ordinary Portland cement (commercial product), type II anhydrous gypsum (commercial product), fine aggregate and water are put into a concrete mixer so as to have the composition shown in Table 4, and mixed for 1 minute to obtain a cement composition (base concrete). Was made. Here, mountain sand produced in Kakegawa City (FM = 2.73) was used as the fine aggregate.

[Production of shotcrete]
The kneaded base concrete was pumped to a commercially available concrete spraying device, and the powder admixture was continuously added to the base concrete being fed in the spraying device. In the spraying device, the powder admixture is substantially mixed with the base concrete when added to form sprayed concrete. The addition amount of the powder admixture was set to the amount shown in Table 5 with respect to 100 parts by mass of ordinary Portland cement used for producing the base concrete.

[Evaluation of spraying properties of sprayed concrete]
A flow rate of 160 ml / min from the spray nozzle of the concrete spraying device toward the 3 m square concrete smooth wall surface installed vertically at a point about 100 cm away from the spray nozzle of the concrete spraying device. I sprayed it. As the evaluation of sprayability, in all cases, the rebound of the sprayed concrete from the wall surface was examined by visual observation. Judged “Yes”. Also, the concrete that was sprayed on the wall surface was judged to be “good” for adhesion that did not sag or flake off, and all other conditions were adherent. Judged as “bad”. Further, immediately after such spraying is continuously performed for 3 minutes, it is determined that the nozzle hole of the spraying device is partially clogged by the solidified matter, and the occurrence of the blockage is “present”. No occlusion was found, and it was judged that there was no occlusion. The above results are shown in Table 6.

[Evaluation of long-term strength development of shotcrete]
A core having a diameter of 5 × length of about 10 cm was punched out by using a core drill on the sprayed material after 28 days from the spraying of the sprayed concrete sprayed onto the concrete smooth wall. Next, the uniaxial compressive strength of this core was measured by the method specified in JIS A1107 “Method for collecting core from concrete and test method for compressive strength” to obtain the uniaxial compressive strength of sprayed concrete of 28 days of age. The results are shown in Table 6.

[Evaluation of initial strength development of shotcrete]
Further, the powder admixture prepared above is added to the base concrete in an amount shown in Table 6 with respect to 100 parts by mass of ordinary bolt land cement content in the base concrete, and further kneaded for 10 seconds to prepare a kneaded product. did. Immediately after preparation, the kneaded material is filled into a molding mold having an inner size of 40 × 40 × 160 mm, left standing indoors for a predetermined time, and then left to stand for demolding, and a specimen having a material age of 3 hours and 1 day. Got. The uniaxial compressive strength of this specimen was measured with an Amsler type compressive strength tester. This result is also shown in Table 6.

  From the results of Table 3, the shotcrete of the present invention has a low Proctor penetration resistance value until at least 30 seconds after the addition of the powder admixture, and increases rapidly after about 60 seconds. However, it can be seen that the instantaneous setting is suppressed. In addition, from the results of Table 5, it can be seen that the product of the present invention has a strong adhesion, hardly causes a spray loss such as rebound, and the adhesion word also shows a tendency of increasing strength over the medium to long term. Recognize. Furthermore, it can be seen from the results in Table 6 that the uniaxial compressive strength of the present invention product is much higher than that of the comparative product in the category of the prior art.

Claims (3)

A cement composition containing 100 parts by weight of cement and 5-12 parts by weight of anhydrous gypsum, molar ratio of CaO and _Al 2 _{O 3} in the glass content of at least 90% (CaO / _Al 2 _{O 3)} is 1.8 Clinker of 2.5 calcium aluminate, silicon, magnesium and titanium in terms of oxides, SiO ₂ ; 4 to 6% by mass, MgO; 0.75 to 0.95% by mass and TiO ₂ ; A powder admixture containing 100 parts by mass of clinker pulverized product containing 8 to 1.3% by mass , 2.4 to 12.3 parts by mass of sodium aluminate and 1.2 to 24.7 parts by mass of anhydrous gypsum, high strength Shotcrete amount added to cement content 100 parts by weight of the cement composition is formed by added pressure so as to be 5 to 15 parts by weight. Powder admixture further, high strength spray concrete according to claim 1 Symbol placement containing alkali metal carbonate. The high-strength shotcrete according to claim 1 or 2, wherein the cement composition contains 40 to 55 parts by mass of water with respect to 100 parts by mass of cement.