Concrete composition and molded articles obtained by molding therefrom

Abstract

To provide: a composition for concrete having low carbon durability which expresses freeze-thaw resistance even in a small amount of cement; and a molded product formed by molding the composition.SOLUTION: A composition for concrete contains: a fine aggregate including a blast-furnace slag fine aggregate; a coarse aggregate; a binding material including cement; water; and an air-entraining agent. A unit cement content is 192 kg / m3. A mass ratio of water to the binding material is 25%. A mass ratio of the cement to the binding material is 30-40%. A mass ratio of the blast-furnace slag fine aggregate to the fine aggregate is 100%.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] This invention relates to a concrete composition with excellent freeze-thaw resistance and a molded article obtained by molding the same. [Background technology]

[0002] Conventionally, concrete using blast furnace slag fine aggregate has been known to have excellent freeze-thaw resistance (see, for example, Patent Documents 1 and 2). Patent Document 1 describes a mortar or concrete composition containing fine aggregate including blast furnace slag fine aggregate, a binder, and water, wherein the unit binder amount (unit cement amount) is 219 to 700 kg / m³. 3 The water-binder ratio is 25% to 80%, and the mass ratio of blast furnace slag fine aggregate to fine aggregate is 100%.

[0003] Patent Document 2 describes a mortar or concrete composition containing fine aggregate including blast furnace slag fine aggregate, a binder containing cement and blast furnace slag fine powder, and water, and not containing an agent having the ability to entrain air, wherein the mass ratio of water to the binder is 25 to 40%, the mass ratio of blast furnace slag fine powder to the binder is 20 to 60%, and the mass ratio of blast furnace slag fine aggregate to the fine aggregate is 33% or more.

[0004] On the other hand, concrete with excellent salt damage resistance is known, for example, the one described in Patent Document 3. This Patent Document 3 contains blast furnace slag fine aggregate, a binder containing blast furnace slag fine powder and Portland cement, and water, with a mass ratio of blast furnace slag fine aggregate to fine aggregate of 66.7% or more, a mass ratio of water to binder of 25%, a mass ratio of Portland cement to binder of 40%, a mass ratio of blast furnace slag fine powder to binder of 60%, and a unit binder amount (unit cement amount) of 256 kg / m³. 3 It belongs to them. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6130767 [Patent Document 2] Patent No. 5953247 [Patent Document 3] Patent No. 6131459 [Overview of the project] [Problems that the invention aims to solve]

[0006] The conventional concrete described in Patent Documents 1 and 2 above can exhibit a certain degree of freeze-thaw resistance without the use of air-enhancing agents by using blast furnace slag fine aggregate, but the unit cement content is 219 to 700 kg / m³. 3 This required a relatively large amount of cement. On the other hand, in recent years, in order to realize a decarbonized society, there has been a demand for the development of low-carbon concrete that minimizes the use of cement, which has a large CO2 emission in its manufacturing process.

[0007] The present invention has been made in view of the above, and aims to provide a low-carbon, durable concrete composition that exhibits freeze-thaw resistance even with a small amount of cement, and a molded product made therefrom. [Means for solving the problem]

[0008] To solve the above-mentioned problems and achieve the objective, the concrete composition according to the present invention is a concrete composition containing fine aggregate including blast furnace slag fine aggregate, coarse aggregate, a binder including cement, water, and an air-entraining agent, wherein the unit cement content is 192 kg / m³. 3 The composition is characterized by having a water-to-binder mass ratio of 25%, a cement-to-binder mass ratio of 30-40%, a blast furnace slag-to-fine aggregate mass ratio of 100%, and a relative dynamic modulus of elasticity of 60% or more after 300 freeze-thaw cycles in a freeze-thaw test based on Method A described in JIS A 1148 for concrete specimens made with the concrete composition, thus exhibiting excellent freeze-thaw resistance.

[0009] Furthermore, another concrete composition according to the present invention is characterized in that, in the above-described invention, the fine aggregate ratio is 45%.

[0010] Furthermore, the molded article according to the present invention is a molded article obtained by molding the above-mentioned concrete composition. [Effects of the Invention]

[0011] The concrete composition according to the present invention contains fine aggregate including blast furnace slag fine aggregate, coarse aggregate, a binder including cement, water, and an air-entraining agent, wherein the unit cement content is 192 kg / m³. 3 The composition has a water-to-binder mass ratio of 25%, a cement-to-binder mass ratio of 30-40%, and a blast furnace slag-to-fine aggregate mass ratio of 100%. The relative dynamic modulus of elasticity after 300 freeze-thaw cycles in a freeze-thaw test based on Method A described in JIS A 1148 for concrete specimens made from the concrete composition is 60% or more, indicating excellent freeze-thaw resistance. Therefore, it provides a low-carbon, durable concrete composition that exhibits freeze-thaw resistance even with a small amount of cement, and molded products made from it. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a list of materials used in the embodiments of the present invention. [Figure 2] Figure 2 shows the formulation table of an embodiment of the present invention. [Figure 3] Figure 3 shows the results of the freshness test of an embodiment of the present invention. [Figure 4] Figure 4 shows the temperature history curve of steam curing in an embodiment of the present invention. [Figure 5] Figure 5 shows the relationship between the number of freeze-thaw cycles and the relative dynamic elastic modulus in an embodiment of the present invention. [Figure 6]FIG. 6 is a diagram showing the relationship between the number of freeze-thaw cycles and the mass loss rate in an embodiment of the present invention. [Figure 7] FIG. 7 shows the relationship between the mixing ratio of blast furnace slag fine aggregate and the chloride ion diffusion coefficient. [Figure 8] FIG. 8 is a comparison diagram of the formulation and performance evaluation in an embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments of the concrete composition according to the present invention and a molded article formed therefrom will be described in detail based on the drawings. Note that the present invention is not limited by this embodiment.

[0014] The concrete composition according to the present invention is a concrete composition containing fine aggregate including blast furnace slag fine aggregate, coarse aggregate, a binder containing cement, water, and an AE agent (air-entraining agent), and the relative dynamic elastic modulus at 300 freeze-thaw cycles in a freeze-thaw test based on Method A described in JIS A 1148 for a concrete specimen produced from this concrete composition is 60% or more, and it has excellent freeze-thaw resistance. Further, the molded article according to the present invention is a concrete (molded article) formed by molding and curing this concrete composition.

[0015] The blast furnace slag that is the raw material of the blast furnace slag fine aggregate is a by-product produced when pig iron is manufactured in a blast furnace, and its main components are CaO, SiO2, Al2O3, and MgO. This blast furnace slag can be used in the form of blast furnace slag fine powder or blast furnace slag fine aggregate. The blast furnace slag fine powder is used as a binder, and the blast furnace slag fine aggregate is used as a fine aggregate.

[0016] Blast furnace slag fine aggregate is amorphous blast furnace slag fine aggregate. As amorphous blast furnace slag fine aggregate, for example, granulated blast furnace slag, which is obtained by rapidly cooling blast furnace slag with water, is lightly crushed and an anti-caking agent is added. In the production of granulated blast furnace slag, the temperature of the molten blast furnace slag just before rapid cooling is 1400°C to 1500°C, and rapid cooling causes it to solidify into a glassy (amorphous) state without the atomic arrangement into crystals occurring. The quality of blast furnace slag fine aggregate is specified in JIS A 5011-1.

[0017] The mass ratio of blast furnace slag fine aggregate (BFS) to fine aggregate (S) (blast furnace slag fine aggregate ratio: BFS / S) should preferably be 100%. In addition, as long as it does not hinder the effects of the present invention, a small amount of general fine aggregate, such as crushed sandstone, may be included in addition to blast furnace slag fine aggregate.

[0018] For example, ordinary Portland cement, rapid-hardening Portland cement, ultra-rapid-hardening Portland cement, moderate-heat Portland cement, low-heat Portland cement, etc., can be used. The mass ratio of cement (C) to binder (B) (cement-to-binder ratio: C / B) is preferably 30-40%. The unit cement content (C) is, for example, 192 kg / m³. 3 It can be set to a certain degree. In this way, even with a smaller unit cement amount compared to conventional methods, excellent freeze-thaw resistance can be achieved. Note that the unit cement amount (C) may be less than or equal to the above cement amount, as long as it does not hinder the effects of the present invention.

[0019] The mass ratio of water (W) to binder (B) (water-binder ratio: W / B) is preferably 25%. In addition to cement, other components may be included as the binder, as long as they do not hinder the effects of the present invention. For example, blast furnace slag powder (BF) may be included as the binder.

[0020] For the coarse aggregate, a general type of coarse aggregate such as crushed sandstone can be used. Preferably, the mass ratio of coarse aggregate (G) to binder (B) is set to approximately 130%. However, the amount of coarse aggregate used may be set to a mass ratio other than the above, as long as it does not hinder the effects of the present invention.

[0021] Furthermore, it is preferable for the concrete composition of the present invention to contain an admixture having air-entraining properties, such as an AE agent (air-entraining agent), in order to effectively exhibit the effect of improving freeze-thaw resistance. If such an admixture is not included, the freeze-thaw resistance may be reduced compared to when it is included.

[0022] Concrete using the concrete composition of the present invention exhibits excellent freeze-thaw resistance, i.e., resistance to frost damage. Therefore, it is effective as a material for concrete structures in cold regions where resistance to frost damage is required.

[0023] Furthermore, concrete using the concrete composition of the present invention exhibits excellent resistance to salt damage (salt damage resistance). Therefore, it is particularly effective in the construction of buildings and other structures where salt damage resistance is required, and in locations where frost damage, salt damage, and fatigue may occur in combination, such as highways in mountainous areas where de-icing agents are spread in winter. In addition to these applications, it is also suitably used in locations where frost damage resistance, fatigue resistance, and salt damage resistance are required, such as coastal structures, marine structures, waterway structures, road structures, and retaining wall structures in cold regions. In this case, the concrete composition of the present invention may be molded in advance and constructed as a molded product (precast concrete product). When applied to structures in environments where frost damage and salt damage are possible, such as coastal and marine structures in cold regions, excellent frost damage resistance and salt damage resistance are exhibited, thus extending the service life of the structure compared to structures constructed with ordinary mortar or concrete.

[0024] In particular, concrete using the concrete composition of the present invention exhibits excellent resistance to frost damage and salt damage despite having a small amount of cement. Therefore, it is suitable as a material for low-carbon concrete structures that are resistant to frost damage and salt damage, contributing to the realization of a decarbonized society.

[0025] <Examples> Next, embodiments of the present invention will be described. The concrete in this embodiment has a unit cement content (C) of 192 kg / m³. 3 The mixture consisted of a W / B ratio of 25%, a C / B ratio of 30%, and a BFS / S ratio of 100%, and an AE agent was used.

[0026] Figure 1 shows the materials used in the concrete of this example. Figure 2 shows the concrete mix of this example. As shown in these figures, the fine aggregate ratio (s / a) was 45%, and the air content (Air) was 2.5%. In addition, among the admixtures, the high-performance water-reducing agent (Ad) was used at a mass ratio of 0.60% of the binder (B), the air-entraining agent (AE) at a mass ratio of 0.002% of the binder (B), and the defoaming agent (DF) at a mass ratio of 0.006% of the binder (B).

[0027] (Verification of frost resistance) Next, we will explain the verification results regarding the freeze-thaw resistance of the concrete in this embodiment. To verify freeze-thaw resistance, a freeze-thaw test was conducted in accordance with Method A described in JIS A 1148:2010. The concrete specimens were cured under steam curing followed by air curing, with a test start age of 14 days. Figure 3 shows the results of the fresh properties test of the concrete specimens. Figure 4 shows the temperature history curve during steam curing of the concrete specimens.

[0028] Figures 5 and 6 show the freeze-thaw test results. As shown in Figure 5, all concrete specimens (specimen numbers 1-3) had a relative dynamic modulus of 90-100% after 300 freeze-thaw cycles in the freeze-thaw test, indicating excellent freeze-thaw resistance (frost damage resistance).

[0029] (Verification of salt damage resistance) Next, we will explain the verification results of the salt damage resistance of the concrete in this embodiment. Figure 7 shows the relationship between the blast furnace slag fine aggregate content and the apparent diffusion coefficient of chloride ions (Source: Figure 5 of Patent Document 3). This figure was obtained by testing a mortar with W / D (W / B) = 25% and C / D (C / B) = 40% in accordance with the method described in Reference 1 below. This test involves immersing the mortar in a 10% sodium chloride aqueous solution for a predetermined period, and then measuring the chloride ions to determine the apparent diffusion coefficient, which represents the permeability of chloride ions.

[0030] [Reference 1] A proposed method for testing the apparent diffusion coefficient of chloride ions in concrete by immersion (JSCE-G 572-2010)

[0031] As shown in Figure 7, the apparent diffusion coefficient of chloride ions decreases as the proportion of blast furnace slag fine aggregate increases. This indicates that using a large amount of blast furnace slag fine aggregate suppresses the penetration of salt (chloride ions). Therefore, mortar using a large amount of blast furnace slag fine aggregate is excellent at suppressing salt penetration, and resistance to salt damage improves as the mass ratio of blast furnace slag fine aggregate increases. This trend is thought to be similar in concrete to which coarse aggregate is added to mortar. Figure 7 shows the case where C / B = 40%, but the same trend is thought to be observed even when C / B = 30%, as in this example. For this reason, it is presumed that the concrete in this example also has excellent resistance to salt damage.

[0032] (Performance evaluation results) Next, we will explain the performance evaluation results of the concrete in this embodiment. Figure 8 compares the concrete mix and performance evaluation results of this embodiment. In this figure, the superiority and inferiority in the evaluation items of frost resistance and salt damage resistance are evaluated as ○ (superior) and × (inferior). In the evaluation item of low carbon, the CO2 emissions corresponding to cement are evaluated in the order of ◎, ○, and × from the lowest. As shown in this figure, considering only frost resistance, the suitable mixing ratio is greatly affected by the AE agent. Using blast furnace slag fine aggregate and AE agent, frost resistance can be achieved even when the cement usage is suppressed. When C / B = 30% and BFS / S = 100%, it has salt damage resistance and is further a concrete with frost resistance and low carbon performance. Therefore, it can be seen that the mix of concrete with lower carbon and excellent durability is the mix No. 1 (W / B = 25%, C / B = 30%, BFS / S = 100%, with AE agent). Thus, according to this embodiment, even with a small amount of cement (C) of 192 kg / m 3 it is possible to provide a low-carbon type durable concrete that exhibits frost resistance and salt damage resistance with such a small amount of cement.

[0033] As described above, according to the concrete composition according to the present invention, it is a concrete composition containing fine aggregate including blast furnace slag fine aggregate, coarse aggregate, binder containing cement, water, and air-entraining agent, and the unit cement amount is 192 kg / m 3 and the mass ratio of water to the binder is 25%, the mass ratio of the cement to the binder is 30 - 40%, the mass ratio of the blast furnace slag fine aggregate to the fine aggregate is 100%, and the relative dynamic elastic modulus at 300 freeze-thaw cycles in the freeze-thaw test based on Method A described in JIS A 1148 for the concrete specimen prepared from the concrete composition is 60% or more, and it has excellent freeze-thaw resistance. Therefore, it is possible to provide a low-carbon type durable concrete composition that exhibits freeze-thaw resistance even with a small amount of cement and a molded product formed therefrom.

Industrial Applicability

[0034] As described above, the concrete composition according to the present invention and the molded articles obtained by molding them are useful for mortar and concrete products, and are particularly suitable for exhibiting freeze-thaw resistance with a small amount of cement.

Claims

1. A concrete composition containing fine aggregate including blast furnace slag fine aggregate, coarse aggregate, a binder containing cement and blast furnace slag fine powder, water, and an air-entraining agent, The unit cement content is 192 kg / m³. ３ And, The mass ratio of water to the binder is 25%. The mass ratio of the cement to the binder is 30%. The mass ratio of the blast furnace slag fine aggregate to the fine aggregate is 100%. The fine aggregate ratio is 45%. A concrete composition characterized by having a relative dynamic elastic modulus of 60% or more after 300 freeze-thaw cycles in a freeze-thaw test based on Method A described in JIS A 1148 for concrete specimens prepared using the aforementioned concrete composition, and exhibiting excellent freeze-thaw resistance.

2. A molded article obtained by molding the concrete composition described in claim 1.

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