Dust reducing agent, cement composition, and method for spraying concrete

Abstract

Provided is a dust reducing agent containing a polymer having a glass transition temperature of -30°C or lower, wherein a first normal stress difference (N1) of a 5 mass% aqueous solution of the polymer at a temperature of 20°C and a shear rate of 100 s-1 is 1-2500 Pa.

Description

Dust reducing agent, cement composition, concrete spraying method

[0001] The present invention relates to a dust reducing agent, a cement composition containing the dust reducing agent, and a concrete spraying method using the cement composition.

[0002] Traditionally, concrete spraying has been used to reinforce exposed ground during tunnel excavation and to stabilize excavation surfaces. For example, a common wet spraying method involves preparing concrete by weighing and mixing materials at a weighing plant installed at the excavation site, then transporting the concrete pneumatically using a piston pump, while simultaneously supplying a quick-setting agent from the other branch pipe of a confluence pipe to mix the concrete and the quick-setting agent, and finally spraying the concrete from a nozzle.

[0003] Another proposed dry spraying method involves adding water to the dry-mix concrete during pneumatic transport, supplying a powdered quick-setting agent to a branch pipe of the confluence pipe, mixing the concrete with the quick-setting agent, and then spraying the concrete from a nozzle.

[0004] These spraying methods may generate a large amount of dust when spraying air-conveyed concrete. The Ministry of Health, Labour and Welfare's "Guidelines on Dust Control Measures in Tunnel and Other Construction Works" (Kihatsu 07200 No. 2, July 20, 2020) sets the target dust concentration level at 2 mg / m³. ３ The following requirements dictate that reducing dust levels is essential at concrete spraying construction sites. Furthermore, since large-scale spraying tests are necessary to experimentally measure dust levels, there is a need for dust reducing agents that can predict dust reduction effects in advance.

[0005] As a dust control measure, for example, a wet spraying method has been disclosed in which a hydraulic composition is produced by mixing solid polyethylene oxide with cement, water, aggregate, and an aqueous solution of polyethylene oxide under mixing conditions corresponding to the viscosity of the aqueous solution; a hydraulic composition for spraying is produced by mixing a solid fastener with the hydraulic composition; and the hydraulic composition for spraying is sprayed onto the target object, wherein the water / cement ratio of the hydraulic composition for spraying is 50% by mass or more and 70% by mass or less (see Patent Document 1). In addition, a dust reducing agent for wet sprayed concrete has been disclosed, which contains a water-soluble ether and polyethylene oxide, characterized in that the polyethylene oxide has a particle size of 150 μm or less and accounts for 70% by weight or more (see Patent Document 2).

[0006] Japanese Patent No. 7136972, Japanese Unexamined Patent Publication No. 2004-189529

[0007] Conventional dust control methods described above focus on the viscosity and particle size of polyethylene oxide aqueous solutions. However, our inventors' research revealed that not only are the viscosity and particle size of polyethylene oxide aqueous solutions insufficient to achieve a sufficient dust reduction effect, but dust can also be effectively reduced using dust reducing agents containing polymers other than polyethylene oxide.

[0008] Based on the above, the present invention aims to provide a dust reducing agent with excellent dust reduction effect by specifying the glass transition temperature and the first normal stress difference of the contained polymer.

[0009] Based on the above-mentioned problems, the inventors conducted diligent studies and found that a dust reducing agent containing a polymer with a predetermined glass transition temperature, wherein the first normal stress difference of the aqueous solution of the polymer is within a predetermined range, can solve the above problems, and thus completed the present invention. That is, the present invention is as follows.

[0010] [1] A dust reducing agent comprising a polymer having a glass transition temperature of -30°C or lower, wherein the temperature of a 5% by mass aqueous solution of the polymer is 20°C and the shear rate is 100 s. －１ The difference in stress on the first normal (N) １[1] A dust reducing agent having a first normal stress difference (N) of the polymer in the dust reducing agent. [2] The dust reducing agent according to [1], further containing 10% by mass or more of the polymer. [3] The dust reducing agent according to [1] or [2], further containing a water-reducing agent. [4] The dust reducing agent according to any one of [1] to [3], further containing talc. [5] A cement composition containing cement and the dust reducing agent according to any one of [1] to [4]. [6] The cement composition according to [5], wherein the content of the dust reducing agent is 0.01 to 10 parts by mass per 100 parts by mass of the cement. [7] The first normal stress difference (N) of the polymer in the dust reducing agent. １ ) and the ratio (N) of the viscosity (η) of a cement composition to which water was added at a water / cement ratio of 0.1% at a temperature of 20°C. １ / η) is 0.1 to 0.5 s －１ The cement composition described in [5] or [6] above. [8] A method for spraying concrete using the cement composition described in any one of [5] to [7] above.

[0011] According to the present invention, by specifying the glass transition temperature and the first normal stress difference of the contained polymer, a dust reducing agent with excellent dust reduction effect can be provided.

[0012] The embodiments of the present invention (this embodiment) will be described in detail below, but the present invention is not limited to this embodiment. In this specification, "%" refers to mass unless otherwise specified.

[0013] [Dust Reducing Agent] The dust reducing agent according to this embodiment is a dust reducing agent comprising a polymer having a glass transition temperature of -30°C or lower, wherein the temperature of a 5% by mass aqueous solution of the polymer is 20°C and the shear rate is 100 s. －１ The difference in stress between the first normals must be between 1 and 2500 Pa.

[0014] The polymer used in the present invention has a glass transition temperature of -30°C or lower, preferably -45°C or lower, and more preferably -50°C or lower. If the glass transition temperature of the polymer is higher than -30°C, there is a risk that dust cannot be reduced. In the present invention, the glass transition temperature of the polymer can be measured, for example, by a dynamic viscoelasticity measuring device DMA (manufactured by Mettler Toledo: DMA1). The measurement conditions are as follows: sample thickness 150 μm, width 4 mm, chuck-to-chuck distance 20 mm, temperature rising from -150°C at a rate of 3°C / min, measuring the dynamic viscoelasticity at a frequency of 1 Hz in the linear region within a measurement strain of 0.15%, and evaluating the temperature at the maximum value of tanδ as the glass transition temperature.

[0015] The polymer used in the present invention has a first normal stress difference of 1 to 2500 Pa at a temperature of 20°C and a shear rate of 100 s －１ in a 5% by mass aqueous solution, preferably 100 to 2000 Pa, and more preferably 500 to 1500 Pa. If the first normal stress difference is less than 1 Pa, there is a risk that dust cannot be reduced, and if it exceeds 2500 Pa, the pumpability of the concrete may decrease. In the present invention, the first normal stress difference can be measured, for example, using a commercially available rotational rheometer (manufactured by Anton Paar: MCR302), using a 50 mm parallel plate, a gap of 0.5 mm, a measurement temperature of 20°C, and a shear rate of 100 s －１ By setting it as such. However, when measurement is difficult due to the accuracy of the measuring device, twice the value of the storage modulus known as the Cox-Merz empirical rule can be used as a substitute physical property. The storage modulus can be measured by dynamic viscoelasticity measurement using a double-gap measurement jig in the same device as above, at a measurement temperature of 20°C and a measurement angular frequency of 100 rad / s.

[0016] The polymers used can be natural polymers, semi-synthetic polymers, or synthetic polymers, and their molecular structures can be linear or branched. Examples include polyethylene oxide, polyacrylamide, and polyvinyl alcohol. The first normal stress difference can be adjusted by controlling the molecular weight of the polymer. Since the first normal stress difference arises from the elastic properties within the system, increasing the molecular weight of the polymer, for example, increases the number of entanglement points, which tends to increase the first normal stress difference. However, this also increases viscosity. In the case of branched polymers, the first normal stress difference varies depending on the molecular weight of the branched chains. Branched chains long enough to entangle tend to increase the first normal stress, while branched chains not long enough to entangle tend to decrease viscosity. Therefore, in the case of branched polymers, not only the molecular weight of the branched chains but also the molecular weight distribution has an effect, and the first normal stress difference and viscosity can be adjusted by controlling these factors. The average particle size of the polymer measured using laser diffraction scattering is preferably 300 to 800 μm, and more preferably 400 to 700 μm.

[0017] The dust reducing agent according to this embodiment preferably contains 10% by mass or more of the polymer, more preferably 25% by mass or more, and even more preferably 30% by mass or more. It is also preferably 60% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less. When the polymer content in the dust reducing agent is within the above range, the dust reducing effect can be made even better.

[0018] The dust reducing agent according to this embodiment preferably further contains a water-reducing agent. Including a water-reducing agent in the dust reducing agent makes it easier to improve the dust reduction effect. As the water-reducing agent, high-performance water-reducing agents, high-performance AE water-reducing agents, AE water-reducing agents, and fluidizing agents can be used, and any of the polycarboxylate-based, naphthalene sulfonate-based, melamine sulfonate-based, and lignin sulfonate-based types can be used, and one or more of these may be used.

[0019] The water-reducing agent content is preferably 0.1 to 10% by mass, more preferably 1 to 10% by mass, and even more preferably 1 to 5% by mass, in the dust reducing agent. When the water-reducing agent content is within the above range, it is easier to achieve a better dust reduction effect.

[0020] The dust reducing agent according to this embodiment preferably further contains talc. Because talc is highly lubricated and has low hygroscopicity, the inclusion of talc in the dust reducing agent prevents the talc from covering the surface of the polymer and coming into contact with moisture to form lumps, making it easier to dissolve uniformly when added to concrete, and thus improving the dust reducing effect.

[0021] The talc content is preferably 10 to 300 parts by mass, more preferably 50 to 200 parts by mass, and even more preferably 75 to 150 parts by mass, per 100 parts by mass of polymer in the dust reducing agent. When the talc content is within the above range, it is easier to achieve a better dust reduction effect.

[0022] The dust reducing agent according to this embodiment may further contain known additives such as defoaming agents, if necessary.

[0023] [Cement Composition] The cement composition according to this embodiment contains cement and the dust reducing agent of the present invention. By containing the dust reducing agent, the cement composition can exhibit an excellent dust reduction effect when used in sprayed concrete, etc.

[0024] The cement according to the present invention is not particularly limited and includes various types of Portland cement such as ordinary, rapid-hardening, ultra-rapid-hardening, low-heat, and moderate-heat cements; various blended cements obtained by mixing these Portland cements with blast furnace slag, fly ash, silica fume, etc.; environmentally friendly cements (eco-cements) manufactured using municipal solid waste incineration ash and sewage sludge incineration ash as raw materials; commercially available fine-particle cements; and white cements. It is also possible to use various types of cement after they have been finely powdered. Furthermore, cements that have been adjusted by increasing or decreasing the amount of components commonly used in cement (e.g., gypsum) can also be used. In addition, combinations of two or more of these can also be used.

[0025] In this embodiment, the content of the dust reducing agent in the cement composition is preferably 0.01 to 10 parts by mass, preferably 0.05 to 8 parts by mass, and more preferably 0.1 to 5 parts by mass, per 100 parts by mass of cement. When the content of the dust reducing agent in the cement composition is within the above range, it can exhibit an excellent dust reduction effect when used in sprayed concrete or the like.

[0026] The cement composition according to this embodiment preferably contains aggregate. The aggregate is not particularly limited, but it is preferable to have a low water absorption rate and high aggregate strength. As for the type of aggregate, either fine aggregate or coarse aggregate can be used. As for fine aggregate, river sand, mountain sand, sea sand, lime sand, and silica sand can be used, and as for coarse aggregate, river gravel, mountain gravel, and lime gravel can be used, and crushed sand and crushed stone can also be used.

[0027] The fine aggregate ratio in the cement composition is preferably 50-80%, and more preferably 55-70%. When the fine aggregate ratio is within this range, the pumpability is good when used in sprayed concrete, etc., and excellent dust reduction effects can be achieved. The fine aggregate ratio can be calculated as the volume of total fine aggregate (s / a) relative to the total aggregate volume in the cement composition.

[0028] The cement composition according to this embodiment is the first normal stress difference (N) of the polymer in the dust reducing agent of the present invention. １ ) and the ratio (N) of the viscosity (η) of a cement composition to which water was added at a water / cement ratio of 0.1% at a temperature of 20°C. １ / η) is 0.1 to 0.5 s －１ Preferably, the duration is 0.2 to 0.45 s. －１ It is more preferable that the range be 0.25 to 0.4 s. －１ It is even more preferable that this is the case. １ When / η is within the above range, it can exhibit an excellent dust reduction effect when used for concrete spraying. Here, N １ / η tends to decrease when the content of the dust reducing agent in the cement composition is increased, and tends to increase when a water reducing agent is added to the cement composition. In the present invention, the above N １ / η can be calculated by mixing the cement composition and water with a mixer or the like so that they have a predetermined water / cement ratio, and measuring the viscosity at a temperature of 20°C using a rheometer with a 50 mm parallel plate and a gap of 1 mm.

[0029] The cement composition according to the present embodiment can be produced by mixing cement and a dust reducing agent with a mixer or the like. When the cement composition contains aggregate, it is preferable to add the dust reducing agent to the aggregate in advance. As an addition method, for example, the dust reducing agent can be added when weighing the aggregate, and then mixed with the cement using a mixer or the like to produce the cement composition.

[0030] [Concrete spraying method] The concrete spraying method according to the present embodiment uses the cement composition of the present invention. By using the cement composition of the present invention in the concrete spraying method, the amount of dust during concrete spraying can be reduced well.

[0031] The concrete spraying method according to the present embodiment can be applied to either a wet spraying method or a dry spraying method. When applying to the wet spraying method, the cement composition and water are kneaded in advance to prepare concrete for spraying. When applying to the dry spraying method, a cement composition not containing water is joined and mixed with water immediately before spraying to spray the concrete.

[0032] In the concrete spraying method according to the present embodiment, the water / cement ratio is preferably 40 to 60%, more preferably 45 to 55%, and even more preferably 50 to 55%. When the water / cement ratio is within the above range, the amount of dust during concrete spraying can be reduced well.

[0033] The concrete spraying method according to the present embodiment can use either a liquid accelerator or a powder accelerator as an accelerator, and it is also possible to use both in combination.

[0034] The concrete spraying method according to this embodiment can be carried out by pneumatically transporting the cement composition through a transport pipe using compressed air, pneumatically transporting the quick-setting agent through the transport pipe using compressed air from the other branch pipe of the confluence pipe, mixing the cement composition and the quick-setting agent together, and then spraying the concrete from a nozzle. For pumping the cement composition, for example, "MKW-25SMT" (manufactured by Syntec Co., Ltd.) can be used, and for pumping the quick-setting agent, for example, "Natomcrete" (manufactured by Chiyoda Seisakusho Co., Ltd.) can be used.

[0035] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to the following examples without departing from its essence.

[0036] <Measurement of Glass Transition Temperature> In this invention, the glass transition temperature of the polymer was measured using a dynamic viscoelasticity analyzer DMA (Mettler Toledo: DMA1). The measurement conditions were a sample thickness of 150 μm, a width of 4 mm, and a chuck distance of 20 mm. The temperature was increased from -150 °C at a heating rate of 3 °C / min, and the dynamic viscoelasticity was measured at a frequency of 1 Hz in the linear region with a measurement strain of 0.15% or less. The temperature at which the tanδ maximum value was obtained was evaluated as the glass transition temperature.

[0037] <Measurement of First Normal Stress Difference> In this invention, the first normal stress difference is measured using a rotary rheometer (Anton Paar: MCR302), with a 50 mm parallel plate, a gap of 0.5 mm, a measurement temperature of 20°C, and a shear rate of 100 s. －１ The measurement was performed in this manner. However, if measurement was difficult due to accuracy issues with the measuring device, twice the storage modulus, known as the Cox-Merz empirical rule, was used as a substitute property. The storage modulus was measured by dynamic viscoelasticity measurement using the same apparatus as above, with a double-gap measuring jig from the same manufacturer, at a measurement temperature of 20°C and a measurement angular frequency of 100 rad / s.

[0038] <Polymer> Polymer A: Polyethylene oxide, Density: 1.2 g / cm³ ３ Average particle size: 500 μm. Polymer B: polyethylene oxide, density: 1.2 g / cm³.３ Average particle size: 650 μm. Polymer C: polyethylene oxide, density: 1.3 g / cm³. ３ Average particle size: 610 μm. Polymer D: polyethylene oxide, density: 1.2 g / cm³. ３ Average particle size: 600 μm. Polymer E: polyethylene oxide, density: 1.3 g / cm³. ３ Average particle size: 580 μm. Polymer F: polyethylene oxide, density: 1.3 g / cm³. ３ Average particle size: 610 μm. Polymer G: Polyvinyl alcohol, Density: 1.3 g / cm³. ３ Average particle size: 550 μm. Polymer H: polyvinyl alcohol, density: 1.2 g / cm³. ３ , average particle size: 600 μm.

[0039] <Preparation of Dust Reducing Agent> Using the polymer described above and the materials shown below, a dust reducing agent was prepared so that the respective content amounts were as shown in Table 1.

[0040] <Materials Used> Water-reducing agent: Polyethylene glycol-based water-reducing agent. Talc: Density: 2.81 g / cm³ ３ , average particle size 10 μm.

[0041] <Preparation of Cement Composition> Using the materials listed below and the prepared dust reducing agent, 360 kg of cement, 1049 kg of fine aggregate, 716 kg of coarse aggregate, and 0.36 kg of dust reducing agent were mixed to prepare a cement composition.

[0042] <Materials Used> Cement: Ordinary Portland cement, specific gravity 3.15 g / cm³ ３ Fine aggregate: River sand from Himekawa, Niigata Prefecture, specific gravity 2.61 g / cm³ ３ Coarse aggregate: Gravel from Himekawa, Niigata Prefecture, specific gravity 2.67 g / cm³ ３ .

[0043] <N １Measurement of / η> Water is added to the prepared cement composition in a ratio of 0.1 parts by mass per 100 parts by mass of cement in the cement composition and mixed for 1 minute in a mixer (Sinky Co., Ltd.: ARE-310). The viscosity is measured at a temperature of 20°C using a rotary rheometer (Anton Paar Co., Ltd.: MCR302) with a 50 mm parallel plate and a gap of 1 mm, and the ratio (N) of the first normal stress difference of the polymer to the obtained viscosity is measured. １ The value of ( / η) was calculated. The results are shown in Table 1.

[0044] <Spraying of Concrete> Water was added to the prepared cement composition in an amount of 0.1 parts by mass per 100 parts by mass of cement in the cement composition and mixed. Concrete was then sprayed using a wet spraying method with a commercially available rapid setting agent ("Calcium Aluminate Rapid Setting Agent manufactured by Denka Co., Ltd.").

[0045] <Measurement of Dust Concentration> Ten minutes after spraying, the dust concentration was measured at a fixed position 5m from the spraying site using a digital dust meter (Shibata Scientific Co., Ltd.: LD-5R). The results are shown in Table 1.

[0046]

[0047] The dust reducing agent of the present invention can be suitably used, for example, in tunnels such as roads, railways, and water conduits, as well as in the spraying of concrete on exposed ground surfaces such as slopes.

Claims

1. A dust reducing agent comprising a polymer having a glass transition temperature of -30°C or lower, wherein the temperature of a 5% by mass aqueous solution of the polymer is 20°C and the shear rate is 100 s. －１ The difference in stress on the first normal (N) １ A dust reducing agent having a pressure of 1 to 2500 Pa.

2. The dust reducing agent according to claim 1, comprising 10% by mass or more of the polymer.

3. The dust reducing agent according to claim 1 or 2, further comprising a water-reducing agent.

4. The dust reducing agent according to claim 1 or 2, further comprising talc.

5. A cement composition comprising cement and the dust reducing agent described in claim 1 or 2.

6. The cement composition according to claim 5, wherein the content of the dust reducing agent is 0.01 to 10 parts by mass per 100 parts by mass of the cement.

7. The difference in the first normal stress of the polymer in the dust reducing agent (N １ ) and the ratio (N) of the viscosity (η) of the cement composition to which water was added at a water / cement ratio of 0.1% and measured at a temperature of 20°C. １ / η) is 0.1 to 0.5 s －１ The cement composition according to claim 5.

8. A method for spraying concrete using the cement composition described in claim 5.

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