Preparation method of concrete

Abstract

To provide a preparation method of concrete with suppressed dry shrinkage at a low cost.SOLUTION: The preparation method of concrete, includes: treating an aggregate with an aqueous solution or an aqueous suspension of a metal carbonate or a metal bicarbonate; preparing ready mixed concrete by mixing cement, the treated aggregate and water; and curing the ready mixed concrete. The preparation method may further include adding carbon dioxide-containing gas to the aqueous solution or to the aqueous suspension.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] One embodiment of the present invention relates to a method for producing concrete.

Background Art

[0002] Concrete is mainly composed of cement hydrates, aggregates, water, and additives, and due to its excellent mechanical properties, weather resistance, ease of handling, and economy, it is widely used in various fields as one of the important structural materials for creating social production infrastructure and economic infrastructure. Patent Document 1 discloses that by using limestone as an aggregate during the production of concrete, it is possible to suppress the drying shrinkage of concrete and the occurrence of cracks caused thereby. For example, by utilizing limestone aggregates with a low drying shrinkage rate or by using a shrinkage reducing agent, the drying shrinkage of concrete can be suppressed. However, in the former method, in areas where limestone aggregates cannot be procured, the cost of transporting limestone aggregates increases, and the carbon dioxide emissions associated with transportation also become a problem. In the latter method, it is necessary to use a large amount of expensive shrinkage reducing agent.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] One embodiment of the present invention aims to provide a novel method for producing concrete. Alternatively, one embodiment of the present invention aims to provide a method for producing concrete with suppressed drying shrinkage at low cost. Alternatively, one embodiment of the present invention aims to provide a method for suppressing the drying shrinkage of aggregates.

Means for Solving the Problems

[0005] One embodiment of the present invention is a method for producing concrete. This production method includes treating aggregates with an aqueous solution or water suspension of a metal carbonate or bicarbonate, mixing cement, the aggregates after the above treatment, and water to prepare ready-mixed concrete, and curing the ready-mixed concrete.

[0006] One embodiment of the present invention is a method for producing concrete. This production method includes treating aggregates with a carbon dioxide-containing gas in a pressure-resistant container, mixing cement, the aggregates after the above treatment, and water to prepare ready-mixed concrete, and curing the ready-mixed concrete.

[0007] One embodiment of the present invention is a method for treating aggregates used in the production of concrete. This treatment method includes treating aggregates with an aqueous solution or water suspension of a metal carbonate or bicarbonate.

[0008] One embodiment of the present invention is a method for treating aggregates used in the production of concrete. This treatment method includes treating aggregates with a carbon dioxide-containing gas in a pressure-resistant container.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0010] Hereinafter, each embodiment of the present invention will be described with reference to the drawings and the like. However, the present invention can be implemented in various forms without departing from the gist thereof, and is not to be construed as being limited to the description of the embodiments exemplified below.

[0011] For the sake of clearer explanation, the drawings may schematically represent the width, thickness, shape, etc. of each part compared to the actual aspect, but this is merely an example and does not limit the interpretation of the present invention. In this specification and each figure, elements having the same functions as those already described with respect to the previously shown figures may be denoted by the same reference numerals, and duplicate explanations may be omitted.

[0012] In this specification, concrete refers to a cured product that does not exhibit fluidity, obtained by the hardening of a cement hydrate generated by the reaction of cement, which is one of the raw materials, with water. Therefore, mortar that does not contain aggregate or contains a small amount of aggregate is also included in the category of concrete. On the other hand, concrete before hardening, that is, a mixture containing cement and water and having fluidity without being completely hardened, is called ready-mixed concrete (also referred to as fresh concrete). Ready-mixed concrete may contain additives such as AE agents (air-entraining agents), fluidizing agents, and thickeners in addition to cement, water, and aggregate.

[0013] Hereinafter, a method for producing concrete according to one embodiment of the present invention will be described. FIG. 1 is a flowchart showing this production method. In this production method, aggregates are pretreated, ready-mixed concrete is prepared using cement and the pretreated aggregates, and this ready-mixed concrete is placed and cured. Thereby, concrete with a small drying shrinkage rate can be produced. The produced concrete can be used for various applications. For example, the concrete produced by this production method can be used for columns, walls, beams of buildings and houses, bridge piers and abutments of bridges, dam embankments, dikes and breakwaters provided in rivers and harbors, wave-dissipating blocks, and covering concrete used for roads and tunnels. Alternatively, this concrete may be used for the production of movable property (concrete products) including concrete such as concrete blocks and paving stones having various shapes. Hereinafter, this production method will be described in detail.

[0014] 1. Pretreatment of Aggregates There are no particular restrictions on the aggregates used in this production method. Examples of aggregates include sand, gravel, and rock with a density of 2.5 to 3.0 g / cm 3 and a water absorption rate of 1 to 3%. Examples of the rock type of the aggregates include hard sandstone, limestone, granite, phyllite, sericite, and porphyry. However, the aggregates contain clay minerals mainly composed of metal silicate minerals such as aluminum and magnesium. There are no restrictions on the structure of the clay minerals, and in addition to layered clay minerals, fibrous clay minerals or amorphous clay minerals may also be used. Specific examples of clay minerals include kaolinite, smectite, montmorillonite, sericite, illite, glauconite, chlorite, talc, and zeolite. There are also no restrictions on the composition of the clay minerals in the aggregates, and for example, the aggregates may contain clay minerals in the range of 3% by weight or more and 20% by weight or less, or 5% by weight or more and 10% by weight or less.

[0015] There are no restrictions on the size of the aggregates. Therefore, the aggregates may include fine aggregates with a diameter of 5 mm or less and / or coarse aggregates with a diameter exceeding 5 mm (for example, larger than 5 mm and 20 mm or less, or 10 mm or more and 20 mm or less). Each particle of sand, gravel, rock, etc. that constitutes the aggregates contains the above-mentioned clay minerals.

[0016] The pretreatment of the aggregate is classified into the wet method and the dry method described below, and either one may be selected, or both may be selected. In the latter case, there is no restriction on the order of the wet method and the dry method, and the pretreatment by the wet method may be performed after the pretreatment by the dry method, or vice versa.

[0017] (1) Wet method In the wet method, the aggregate is treated with an aqueous solution or water suspension of a metal carbonate and / or bicarbonate (hereinafter referred to as the treatment liquid). Examples of the metal include alkali metals such as lithium, sodium, and potassium, and alkaline earth metals such as calcium and magnesium. The treatment liquid may contain both a metal carbonate and a bicarbonate, or may contain carbonates or bicarbonates of different metals. The concentration of the metal carbonate and / or metal bicarbonate in the treatment liquid may be its saturation concentration, or may be 10% or more and less than 100% of the saturation concentration. When the treatment liquid is a suspension, part of the metal carbonate and / or metal bicarbonate precipitates. In this pretreatment, the aggregate is put into the treatment liquid, and if necessary, the treatment liquid is appropriately stirred. The pretreatment temperature may be room temperature (for example, 20°C to 25°C), or may be a temperature higher than room temperature (for example, exceeding 25°C and 35°C or lower). The treatment time may be 1 day or more and 1 month or less, or 1 day or more and 3 months or less.

[0018] At this time, a carbon dioxide-containing gas may be added to the treatment liquid. The addition of the carbon dioxide-containing gas may be performed, for example, by bubbling the carbon dioxide-containing gas into the treatment liquid. Alternatively, the treatment liquid and the aggregate may be placed in a pressure-resistant container, and a carbon dioxide-containing gas at a pressure higher than atmospheric pressure may be supplied. The carbon dioxide-containing gas may be carbon dioxide (for example, with a purity of 99.9% or more), or may contain nitrogen, oxygen, air, or a noble gas such as argon together with carbon dioxide. When a mixed gas is used as the carbon dioxide-containing gas, the concentration of the carbon dioxide is higher than the carbon dioxide concentration in the atmosphere, for example, 1% or more and 99% or less.

[0019] As a source of carbon dioxide-containing gas, a cylinder or tank filled with carbon dioxide may be used, or dry ice may also be used. Alternatively, if a facility that emits a large amount of carbon dioxide (such as a chemical plant, a waste incineration facility, a thermal power plant, or various other factories) is already established near the facility where the pretreatment is performed, the gas emitted from these facilities, or the purified gas obtained by performing dust removal, desulfurization, denitrification, etc. on the exhaust gas may be used as the carbon dioxide-containing gas. In this case, these facilities function as a source of carbon dioxide-containing gas, the cost for transporting carbon dioxide is reduced, and the emission of carbon dioxide associated with transportation is prevented.

[0020] Thereafter, the aggregate is taken out from the treatment liquid and dried. The drying may be performed at room temperature, or at a higher temperature (for example, 30°C or higher and 100°C or lower). The drying time can also be arbitrarily determined, and for example, it may be appropriately selected from the range of 1 hour or more and 1 week or less, or 6 hours or more and 3 days or less. The humidity during drying is also arbitrary, and for example, a humidity of 30% or more and 80% or less may be used. Alternatively, the aggregate may be dried under reduced pressure. In this case, the pressure may be appropriately selected from the range of, for example, 5×10 -5 MPa or more and 5×10 -3 MPa or less. After drying, the aggregate is used for the preparation of ready-mixed concrete.

[0021] (2) Dry method In the dry method, the aggregate is brought into contact with a carbon dioxide-containing gas at a pressure equal to or higher than atmospheric pressure. A schematic diagram of a pretreatment system suitable for the dry method is shown in Figure 2. As shown in Figure 2, the pretreatment system 100 has a pressure-resistant container 102 and a cylinder (or tank) 106 containing compressed (or liquefied) carbon dioxide. The pressure-resistant container 102 and the cylinder 106 are connected, and the pretreatment system 100 is configured such that the carbon dioxide contained in the cylinder 106 is supplied to the pressure-resistant container 102. For this reason, for example, a regulator 108 is attached to the cylinder 106, and the pretreatment system 100 is configured such that carbon dioxide whose pressure is adjusted by the regulator 108 is supplied to the pressure-resistant container 102. A gauge 104 is provided on the pressure-resistant container 102, and the internal pressure can be monitored using the gauge 104.

[0022] The pretreatment system 100 may further include a cylinder (or tank) 110 that functions as a source of nitrogen, oxygen, air, or a noble gas. In this case, a regulator 112 is also attached to these cylinders 110, and the pressure-regulated nitrogen, oxygen, air, or noble gas is supplied to the pressure-resistant container 102. Note that a plurality of cylinders 110 may be provided. In this case, a plurality of cylinders 110 filled with different gases may be used.

[0023] The pretreatment system 100 may further include a pump 114 for exhausting the inside of the pressure-resistant container 102. The pump 114 is connected to the pressure-resistant container 102 and is configured to decompress the inside thereof. An example of the pump 114 is an oil-type rotary pump or a dry pump, whereby the inside of the pressure-resistant container can be appropriately decompressed within the range of 1×10 -5 MPa or more and 5×10 -4 MPa or less.

[0024] The pretreatment system 100 may further include a steam generator 116. The steam generator 116 is also connected to the pressure-resistant container 102 and is configured to supply nitrogen, oxygen, air, or a noble gas containing steam (i.e., gaseous water). By using the steam generator 116, the humidity of the carbon dioxide-containing gas introduced into the pressure-resistant container 102 can be adjusted. In this case, although not shown, a hygrometer may be provided in the pressure-resistant container 102. Also, although not shown, the pretreatment system 100 may include a heating device or a cooling device for heating or cooling the gas inside the pressure-resistant container 102.

[0025] In the dry method, first, the aggregate 120 is put into the pressure-resistant container 102. Then, carbon dioxide is introduced from the cylinder 106 into the pressure-resistant container 102. The introduction of carbon dioxide may start when the pressure inside the pressure-resistant container 102 is at atmospheric pressure, or may start after decompressing the inside of the pressure-resistant container 102 using the pump 114. At this time, one or more cylinders 110 may be further used to introduce nitrogen, oxygen, noble gas, etc. into the pressure-resistant container 102.

[0026] The pressure of the carbon dioxide-containing gas in the pressure-resistant container 102 may be set, for example, higher than atmospheric pressure (0.1 MPa) and not more than 2.0 MPa. The partial pressure of carbon dioxide in the pressure-resistant container 102 may be adjusted within the range of 1% or more and 100% or less with respect to the total pressure in the pressure-resistant container 102. In other words, the carbon dioxide concentration in the carbon dioxide-containing gas in contact with the aggregate 120 may be 1% or more and 100% or less. Further, using the heating device or the cooling device described above, the temperature of the carbon dioxide-containing gas in the pressure-resistant container 102 may be adjusted, for example, within the range of -50°C to 200°C. Further, a gas containing water vapor may be introduced into the pressure-resistant container 102 using the water vapor generator 116. In this case, the humidity of the carbon dioxide-containing gas in the pressure-resistant container 102 may be adjusted, for example, to 40% or more and 80% or less.

[0027] The treatment time of the aggregate may be arbitrarily set, for example, 1 hour or more and 1 week or less, 12 hours or more and 3 days or less, 1 day or more and 3 days or less, or 5 days or more and 10 days or less, 20 days or more and 30 days or less. During this treatment time, carbon dioxide or other gas may be introduced to keep the pressure in the pressure-resistant container 102 constant, or the valve 118 may be closed after the start of the treatment to keep the pressure-resistant container 102 in a sealed state.

[0028] Thereafter, the aggregate 120 is taken out from the pressure-resistant container 102 and used for the preparation of ready-mixed concrete.

[0029] 2. Preparation of ready-mixed concrete The preparation of ready-mixed concrete is performed by mixing the pretreated aggregate, cement, and water. At this time, various additives and admixtures may be added.

[0030] There is no restriction on the type of cement used in the manufacturing method of this product. For example, a cement containing at least one of minerals mainly containing tricalcium silicate (3CaO·SiO2), also known as alite, minerals mainly containing dicalcium silicate (2CaO·SiO2), also known as belite, minerals mainly containing tricalcium aluminate (3CaO·Al2O3) that forms an aluminate phase, and minerals mainly containing tetracalcium aluminoferrite (4CaO·Al2O3·Fe2O3) that forms a ferrite phase may be used. Alternatively, a cement containing all of these minerals may also be used. Typically, ordinary Portland cement, white Portland cement containing iron oxide, alumina cement containing alumina, blast furnace cement added with blast furnace slag by-produced in the manufacturing process of steel, fly ash cement added with fly ash cement by-produced during the combustion of lime ash, eco-cement containing waste such as incineration ash and sludge, etc. can be used.

[0031] The weight ratio of cement to aggregate may also be appropriately set considering the properties required for the resulting concrete. For example, an aggregate with a weight 3 times or more and 10 times or less that of the cement may be used. There is no restriction on the water / cement ratio either, but it may be selected from the range of 10% to 100%.

[0032] There is also no restriction on the admixture. Ash such as fly ash, slag, biomass ash, and incineration ash, silica fume, etc. may be used as admixtures. The amount of the admixture may also be determined as appropriate, but it may be adjusted so that the water-binder ratio (W / B) is 10% or more and 100% or less. Here, the binder refers to cement and the admixture, and the water-binder ratio is the mass of water relative to the total mass of cement and the admixture.

[0033] There are no restrictions on the type and concentration of the additives. For example, an AE agent (air-entraining agent) that prevents the freezing of ready-mixed concrete or a fluidizing agent that increases the fluidity of ready-mixed concrete can be used. Examples of AE agents and fluidizing agents include surfactants that generate air bubbles in concrete, such as oxycarboxylic acid (hydroxycarboxylic acid) salts, lignin sulfonate salts, naphthalene sulfonic acid formaldehyde high condensate salts, melamine sulfonic acid formaldehyde high condensate salts, and styrene sulfonic acid copolymer salts. Alternatively, a thickening agent for enabling the construction of concrete underwater may be used as an additive. Examples of thickening agents include cellulose derivatives such as methylated cellulose and polyacrylamide. The thickening agent can be selected from the range of 0.1% or more and 20% or less, or 1% or more and 10% or less based on the weight of the cement used.

[0034] Alternatively, when using ready-mixed concrete for placing cast-in-place concrete, an accelerating agent for promoting the hardening of the mixture of cement and water may be used as an additive. Examples of accelerating agents include chlorides, nitrates, sulfates, carbonates, and silicates of sodium, calcium, and magnesium, such as calcium chloride, sodium nitrate, calcium nitrate, sodium sulfate, calcium sulfate, magnesium sulfate, sodium carbonate, calcium carbonate, sodium silicate, magnesium silicate, and calcium silicate. Alternatively, organic compounds such as sodium salts and calcium salts of acrylic acid and amine compounds may be used as accelerating agents.

[0035] 3. Placement and hardening of ready-mixed concrete Thereafter, the ready-mixed concrete is placed and hardened. Since this process may be appropriately applied using known methods, a detailed description is omitted. Briefly, the ready-mixed concrete may be poured into a formwork that gives the shape required for the concrete and cured as appropriate. At this time, steel bars may be arranged in the formwork. Alternatively, the ready-mixed concrete may be mixed with high-pressure air and sprayed onto slopes, rock masses in tunnels, etc.

[0036] The main causes of the drying shrinkage of concrete are considered to be the evaporation of water from ready-mixed concrete or concrete, and the shrinkage of aggregates. As described above, in the method for producing concrete according to one embodiment of the present invention, the aggregates are pretreated according to the wet method and / or the dry method. Although the mechanism needs to be elucidated, it is presumably that metal salts precipitate between the layers of the aggregates, particularly clay minerals, or carbon dioxide is adsorbed by this pretreatment, and as a result, the voids of the aggregates decrease and the water content of the clay minerals decreases. It is considered that this decrease in the water content contributes to the reduction of the drying shrinkage rate of the aggregates. In fact, as demonstrated in the examples, the drying shrinkage of the aggregates can be suppressed by performing this pretreatment. Therefore, it becomes possible to suppress the drying shrinkage rate of concrete, and effectively suppress the occurrence of cracks in concrete caused by drying shrinkage. In addition, compared with the conventional method using limestone as an aggregate, it becomes possible to provide concrete with suppressed drying shrinkage at low cost.

[0037] In addition, in this production method, carbon dioxide can be used in the pretreatment. For this reason, it is considered that carbon dioxide is adsorbed by the aggregates, particularly the clay minerals in the aggregates, and / or a part of the aggregates, typically the clay minerals contained in the aggregates, reacts (carbonates) with carbon dioxide and is fixed. Since the immobilized carbon dioxide is finally fixed in the concrete, it can be said that this production method also contributes to the reduction of greenhouse gas emissions by fixing carbon dioxide, which is a greenhouse gas, in the concrete.

Examples

[0038] In this example, an example in which the aggregates are pretreated by the wet method described above will be described.

[0039] An aggregate with an average particle size of 20 mm, to which a strain gauge with a gauge length of 5 mm (manufactured by Tokyo Sokki Kenkyujo Co., Ltd.) was attached, was immersed in an aqueous sodium hydrogen carbonate solution (3 L) at 8 - 10 wt% in a container. As the aggregates, 20 pieces each of sandstone produced in Tokushima Prefecture (Sample 1) and sandstone produced in Fukushima Prefecture (Sample 2) were used. Twenty days after the start of immersion, Samples 1 and 2 were taken out from the aqueous sodium hydrogen carbonate solution and dried in a thermostatic chamber at a temperature of 20°C and a humidity of 60°C for 20 days. During the period from the start of immersion to the completion of drying, the strain rate was measured every 30 minutes. As a comparative example, using Samples 1 and 2, the same measurement was carried out using water instead of the aqueous sodium hydrogen carbonate solution. In the examples and the comparative example, the difference between the maximum value of the strain rate obtained during immersion (i.e., from the start to the end of immersion) and the minimum value of the strain rate obtained during drying (i.e., from the start to the end of drying) was calculated as the drying shrinkage rate.

[0040] The measurement results of Samples 1 and 2 are shown in Figures 3 and 4 respectively. As can be understood from Figures 3 and 4, in any of the samples, the change in the strain rate during immersion is significantly smaller in the examples compared to the comparative example. For this reason, the drying shrinkage rate is also larger in the comparative example compared to the examples. Specifically, in the case of Sample 1, the drying shrinkage rates of the example and the comparative example were 186 and 235 respectively, and in the case of Sample 2, the drying shrinkage rates of the example and the comparative example were 57 and 130 respectively. From these results, it was found that by performing the pretreatment, the drying shrinkage strain of the aggregate is reduced by about 20%. This suggests that it is possible to produce concrete with suppressed drying shrinkage by applying one of the embodiments of the present invention.

[0041] As described above, the embodiments described as the embodiments of the present invention can be implemented in appropriate combinations as long as they do not contradict each other. Based on each embodiment, those in which those skilled in the art have appropriately added, deleted, or changed the design of the components are also included in the scope of the present invention as long as they have the gist of the present invention.

[0042] Even other effects different from the effects brought about by each of the above-described embodiments, those that are obvious from the description in this specification or can be easily predicted by those skilled in the art are naturally understood to be brought about by the present invention.

Explanation of Signs

[0043] 100: Pretreatment system, 102: Pressure-resistant container, 104: Gauge, 106: Cylinder, 108: Regulator, 110: Cylinder, 112: Regulator, 114: Pump, 116: Steam generator, 118: Valve after start of treatment, 120: Aggregate

Claims

1. Treating the aggregate with an aqueous solution or water suspension of a metal carbonate or bicarbonate, mixing cement, the treated aggregate, and water to prepare ready-mixed concrete, and hardening the ready-mixed concrete, a method for producing concrete.

2. The method according to claim 1, wherein the aggregate contains clay minerals.

3. The method according to claim 1, further comprising adding a carbon dioxide-containing gas to the aqueous solution or the water suspension in the treatment.

4. The method according to claim 1, wherein the metal is selected from alkali metals and alkaline earth metals.

5. The method according to claim 1, further comprising drying the treated aggregate before the mixing.

6. Treating the aggregate with a carbon dioxide-containing gas in a pressure vessel, mixing cement, the treated aggregate, and water to prepare ready-mixed concrete, and hardening the ready-mixed concrete, a method for producing concrete.

7. The method according to claim 6, wherein the aggregate contains clay minerals.

8. The method according to claim 6, wherein in the treatment, the pressure of the carbon dioxide-containing gas in the pressure vessel is 0.1 MPa or more and 2.0 MPa or less.

9. The method according to claim 6, wherein the carbon dioxide-containing gas is introduced into the pressure vessel after evacuating the inside of the pressure vessel.

10. The method according to claim 6, wherein the humidity of the carbon dioxide-containing gas is 40% or more and 80% or less.

11. A method for treating an aggregate used in the production of concrete, the method comprising treating the aggregate with an aqueous solution or water suspension of a metal carbonate or bicarbonate.

12. The method according to claim 11, wherein the aggregate contains clay minerals.

13. The method according to claim 11, further comprising adding a carbon dioxide-containing gas to the aqueous solution or the water suspension in the treatment.

14. The method according to claim 11, wherein the metal is selected from alkali metals and alkaline earth metals.

15. The method according to claim 11, further comprising drying the treated aggregate.

16. A method for treating an aggregate used in the production of concrete, A treatment method including treating the aggregate with a carbon dioxide-containing gas inside a pressure vessel.

17. The treatment method according to claim 16, wherein the aggregate contains a clay mineral.

18. The treatment method according to claim 16, wherein the pressure of the carbon dioxide-containing gas inside the pressure vessel is 0.1 MPa or more and 2.0 MPa or less.

19. The treatment method according to claim 16, wherein the carbon dioxide-containing gas is introduced into the pressure vessel after evacuating the inside of the pressure vessel.

20. The treatment method according to claim 16, wherein the humidity of the carbon dioxide-containing gas is 40% or more and 80% or less.

Images