Precast concrete products

Abstract

This invention provides a precast concrete product in which the particle size of blast furnace slag fine powder contained in the precast concrete is adjusted to a specific range, thereby improving durability not only through salt resistance but also through the suppression of carbonation. [Solution] The precast concrete product of the present invention contains blast furnace slag fine powder with a particle size of 25 μm or less in the volume-based particle size distribution, at a rate of 25 kg / m³ in the concrete. 3 The above is the required amount. Precast concrete needs to contain a certain amount of fine particles of blast furnace slag powder. Furthermore, blast furnace slag powder with a particle size of 25 μm or larger in the volume-based particle size distribution must be present in the concrete at a concentration of 30 kg / m³. 3 The following is preferable: When there is little coarse blast furnace slag powder and the amount of fine blast furnace slag powder is included in precast concrete, the pore size in the hardened concrete becomes small and a dense structure is formed, which suppresses carbonation and inhibits the penetration of chloride ions.

Description

Technical Field

[0001] The present invention relates to a precast concrete product with improved durability by adjusting the particle size of blast furnace slag fine powder contained in precast concrete to a specific range.

Background Art

[0002] Conventionally, precast concrete is made through a manufacturing process that is sufficiently managed in a factory or the like, so concrete construction at the construction site is unnecessary and the construction period can be shortened.

[0003] However, since precast concrete is steam-cured for up to 24 hours after placing the concrete in the formwork and then cured in the air after demolding, there are problems with chloride shielding and carbonation due to the non-dense surface layer of the concrete.

[0004] On the other hand, mixing blast furnace slag fine powder into concrete improves chloride shielding not only in precast concrete but also in other types of concrete. However, carbonation tends to progress more easily when blast furnace slag fine powder is mixed.

[0005] Therefore, in precast concrete mixed with blast furnace slag fine powder, it is desired to achieve both chloride shielding and resistance to carbonation. Examples of inventions using blast furnace slag fine powder in concrete include the inventions described in Patent Documents 1 to 6.

[0006] Patent Document 1 discloses a mixed cement for concrete containing a binder, water, fine aggregate, coarse aggregate, and a high-performance water reducing agent, wherein the binder contains 45% by mass of ordinary Portland cement, 40 to 45% by mass of blast furnace slag fine powder, and 10 to 15% by mass of fly ash, the water-to-binder mass ratio is 40% or less, and the air content is 3.0 to 6.0%.

[0007] Patent Document 2 discloses a mixed cement for concrete comprising a binder, water, fine aggregate, coarse aggregate, and a high-performance water-reducing agent, wherein the binder comprises 45% to 65% by mass of ordinary Portland cement, 25% to 55% by mass of blast furnace slag fine powder, and 10% or less by mass of fly ash.

[0008] Patent Document 3 discloses a binder composition in which 35 to 65% by weight of blast furnace slag fine powder is added as an admixture to rapid-hardening Portland cement, and is mixed with water, fine aggregate, coarse aggregate, and a water-reducing agent so that the water-binder ratio is 45% by weight or less and the air content is 3.0 to 6.0%.

[0009] Patent Document 4 describes a concrete composition comprising a binder, water, fine aggregate, coarse aggregate, and admixtures, wherein the binder comprises 15-45% by mass of ordinary Portland cement and 55-85% by mass of blast furnace slag fine powder, with a water-to-powder volume ratio of 80-110% of the binder and an absolute volume of coarse aggregate of 320 L / m³. 3 The following disclosure states that the amount of air was kept below 2.0%.

[0010] Patent Document 5 discloses the preparation of a concrete material in which cement is replaced with blast furnace slag fine powder at a replacement rate of 71% to 95%, the supply of the concrete material to the molding space of a formwork while applying vibration, the press of the concrete material with a press plate that moves relative to the formwork while applying vibration to form a precast concrete product of the required shape, and the removal of the precast concrete product from the formwork immediately after molding.

[0011] Patent Document 6 discloses an expansive material for use in precast concrete, which contains hard-calcined quicklime with a total porosity of 5-10%, gypsum, and inorganic fine powder, wherein the particle size of the hard-calcined quicklime in the expansive material is such that 0.1% by mass or less is 150 μm or larger, 25-40% by mass is 50-150 μm, and 25-40% by mass is 10-50 μm, and the inorganic fine powder is one or more selected from the group consisting of fly ash, blast furnace slag fine powder, limestone fine powder, and Portland cement. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] Japanese Patent Publication No. 2014-144878 [Patent Document 2] Japanese Patent Publication No. 2015-202978 [Patent Document 3] Japanese Patent Publication No. 2010-006662 [Patent Document 4] Patent No. 7187090 [Patent Document 5] Japanese Patent Publication No. 2009-113296 [Patent Document 6] Japanese Patent Publication No. 2024-131926 [Overview of the Initiative] [Problems that the invention aims to solve]

[0013] The inventions described in Patent Documents 1 and 2 aim to reduce the amount of Portland cement used, and involve a high proportion of blast furnace slag powder and fly ash, with a Blaine specific surface area of ​​3000 to 6000 cm² for the blast furnace slag powder used. 2 The value is given as / g. Furthermore, this is not intended for precast concrete products.

[0014] The invention described in Patent Document 3 uses rapid-strength Portland cement, which exhibits excellent early strength development, and blast furnace slag fine powder, wherein the blast furnace slag fine powder has a Blaine specific surface area of ​​2500 to 6500 cm².2 It is / g.

[0015] The invention described in Patent Document 4 significantly reduces the amount of ordinary Portland cement used by increasing the proportion of blast furnace slag fine powder, and achieves high fluidity by limiting the admixtures used.

[0016] The invention described in Patent Document 5 has a high replacement rate of cement with blast furnace slag fine powder, ranging from 71% to 95%, and aims to significantly reduce the amount of cement used. Due to its low alkalinity and chloride-free properties, it is intended for use in general unreinforced precast concrete products such as road and sidewalk boundary blocks, as well as in river revetment blocks where ecosystem conservation should be a priority.

[0017] While the invention described in Patent Document 6 also mentions adding blast furnace slag fine powder as an expansive material for precast concrete, this invention focuses on using hard-fired quicklime with a total porosity of 5-10% in order to achieve good expansion performance and strength enhancement effects.

[0018] This invention provides a precast concrete product in which the particle size of blast furnace slag fine powder contained in the precast concrete is adjusted to a specific range, thereby improving durability not only through salt resistance but also through the suppression of carbonation. [Means for solving the problem]

[0019] The precast concrete product according to the present invention contains blast furnace slag fine powder with a particle size of 25 μm or less in the volume-based particle size distribution, at a rate of 25 kg / m³ in the concrete. 3 It is characterized by containing the above-mentioned amount.

[0020] The chemical composition of the blast furnace slag powder is not specified. For example, blast furnace slag powder specified in "JIS A 6206 Blast Furnace Slag Powder for Concrete" can be used. Blast furnace slag powder containing gypsum can also be used. Any type of gypsum can be used: dihydrate gypsum, hemihydrate gypsum, or anhydrous gypsum.

[0021] The Blaine value of the blast furnace slag fine powder can be used as long as it is within the range specified in "JIS A 6206 Blast Furnace Slag Fine Powder for Concrete". Preferably, it is 6000 cm 2 / g or more, more preferably 8000 cm 2 / g or more, and even more preferably 10000 cm 2 / g or more.

[0022] The particle size distribution of the blast furnace slag fine powder is not particularly limited. The particle diameter of the 50% cumulative volume ratio is preferably 15 μm or less, more preferably 10 μm or less, and even more preferably 5 μm or less. The particle diameter of the 95% cumulative volume ratio is preferably 45 μm or less, more preferably 30 μm or less, and even more preferably 15 μm or less.

[0023] In addition, in the precast concrete product of the present invention, the blast furnace slag fine powder with a particle diameter of 25 μm or less in the particle size distribution based on volume is 25 kg / m 3 to 90 kg / m 3 in the concrete.

[0024] The particle size of the blast furnace slag fine powder contained in the precast concrete is characterized in that the blast furnace slag fine powder with a particle diameter of 25 μm or less in the particle size distribution based on volume is 25 kg / m 3 or more to 90 kg / m 3 or less. If it is less than 25 kg / m 3 or exceeds 90 kg / m 3 , the suppression of the neutralization of the precast concrete may not be sufficient. The precast concrete needs to contain a certain amount of fine particles of the blast furnace slag fine powder. For example, when the blast furnace slag fine powder with a particle diameter of 5 μm or less at the 100% cumulative volume ratio is less than 25 kg / m 3 , the suppression of neutralization may not be sufficient.

[0025] The precast concrete product according to the present invention is characterized in that it contains 30 kg / m 3 or less of the blast furnace slag fine powder with a particle diameter of 25 μm or more in the particle size distribution based on volume in the concrete.

[0026] The particle size distribution of blast furnace slag fine powder contained in precast concrete is such that the particle size of 25 μm or larger in the volume-based particle size distribution is 30 kg / m³. 3 It has the following characteristics: 30 kg / m 3 If this value is exceeded, it may become impossible to suppress the decrease in strength and neutralization. A particle size of 45 μm or larger in the volume-based particle size distribution is 5 kg / m³. 3 The following is preferable: When there is less coarse blast furnace slag powder and more fine blast furnace slag powder is included in the precast concrete, the pore size in the hardened concrete becomes small and a dense structure is formed, which suppresses carbonation and the penetration of chloride ions. [Effects of the Invention]

[0027] The precast concrete product of the present invention can suppress not only salt resistance but also carbonation by adjusting the particle size of the blast furnace slag fine powder contained in the precast concrete to a specific range. [Modes for carrying out the invention]

[0028] The following describes the test conditions and results of the tests conducted to confirm the effects of the present invention.

[0029] The materials used are shown in Table 1. The type of cement is not limited; ordinary Portland cement, high-early-strength Portland cement, etc., can be used. The type of aggregate is not limited; aggregates commonly used in precast concrete plants can be used.

[0030] [Table 1]

[0031] The fresh properties of concrete can be adjusted using AE water-reducing agents, high-performance water-reducing agents, air-entraining agents, and defoaming agents. Materials such as expansive agents and fine limestone powder can be used. Admixtures such as fly ash and silica fume can also be used.

[0032] Table 2 shows the volume-based particle size distribution of blast furnace slag fine powder CR and blast furnace slag ultrafine powder B1S used in this test, measured by laser diffraction scattering.

[0033] [Table 2]

[0034] Table 3 shows the experimental concrete mix designs. Also, the unit amount (kg / m³) of blast furnace slag fine powder per particle is shown. 3 ) are shown in Table 4.

[0035] [Table 3]

[0036] The mixing procedure was carried out as follows, as an example. (1) Add all of the coarse aggregate, half of the fine aggregate, all of the cement and blast furnace slag fine powder, and the remaining half of the fine aggregate to the mixer in that order. (2) Knead the mixture in a dry state for 20 seconds. (3) Add water and admixtures (water-reducing agent, air-entraining agent). (4) Perform the main kneading for 90 seconds. (5) Let it stand for 5 minutes. (6) Let it stand for 5 minutes, then knead for 30 seconds before removing it from the mixer.

[0037] The concrete mix design is not limited to any type used in precast concrete. The concrete curing method is not limited to any type used in precast concrete.

[0038] Table 4 shows the unit amount (kg / m³) of blast furnace slag fine powder by particle size. 3 ) was shown. Comparative Example 1 is not shown in Table 4 because it does not contain blast furnace slag. Example 1 used 20 kg / m³ of fine-grained blast furnace slag ultrafine powder B1S. 3 The compounded product has a particle size of 25 μm or less and can be processed at a rate of 20 kg / m². 3It can be seen that... Example 2 uses blast furnace slag ultrafine powder B1S at a rate of 40 kg / m³ 3 The compound has a particle size of 25 μm or less and can be filled at 40 kg / m². 3 It can be seen that this is the case.

[0039] Example 3 involved using 40 kg / m³ of coarse-grained blast furnace slag fine powder CR. 3 The compound has a particle size of 25 μm or less and can be filled at 30 kg / m². 3 It can be seen that the particle size is 25 μm or larger, and the load capacity is 10 kg / m³. 3 And among those, those with a particle size of 45 μm or larger cost 2.4 kg / m³. 3 Comparative Example 2 uses blast furnace slag fine powder CR at a rate of 128 kg / m³. 3 The compounded product has a particle size of 25 μm or less and weighs 96 kg / m². 3 The particle size is 25 μm or larger and the load capacity is 32 kg / m³. 3 And among those, those with a particle size of 45 μm or larger are 8 kg / m 3 That's how it is.

[0040] [Table 4]

[0041] The curing method was steam curing until demolding, and was carried out according to the following procedure. (1) As a preliminary step, the plants were allowed to rest at 25°C for 3 hours. (2) Increase the temperature by 20°C per hour until it reaches 65°C. (3) Keep at 65°C for 3 hours. (4) Lower the temperature by 5°C per hour until it reaches 30°C. (5) Maintain a temperature of 30°C. (6) Demolded after 17 hours.

[0042] Compressive strength tests (JIS A 1107, JIS A 1108) were performed after demolding, followed by air curing for 24 hours (1 day) and up to 28 days. Furthermore, the "JIS A 1153 Accelerated Carbonation Test for Concrete" was initiated 56 days after the material was aged (20°C, 5% CO2, 60% relative humidity).

[0043] Table 5 shows the fresh properties and strength results for the concrete mix designs shown in Table 3.

[0044] [Table 5]

[0045] At 1 day of age, Example 2, which used fine-grained blast furnace slag ultrafine powder, showed greater strength. Except for Comparative Example 2, which contained a large amount of coarse-grained blast furnace slag fine powder, the formulations showed comparable strength at 28 days of age. In particular, Examples 1 and 2, which used blast furnace slag ultrafine powder, showed higher strength than Comparative Example 1, which did not use blast furnace slag fine powder.

[0046] The results of the accelerated carbonation test are shown in Table 6.

[0047] [Table 6]

[0048] The accelerated carbonation depth of Comparative Example 1 tends to be smaller than that of Example 1 and Comparative Example 2, which were given blast furnace slag ultrafine powder. Similarly, the carbonation rate index of Comparative Example 1, which does not contain blast furnace slag fine powder, tends to be smaller than that of Example 1 and Comparative Example 2, which were given blast furnace slag ultrafine powder.

[0049] Based on Table 4, the particle size of 25 μm or less is 20 kg / m³. 3 Example 1, particle size 25 μm or less, 96 kg / m 3 For particle size 25 μm or larger, the load capacity is 32 kg / m³. 3 Comparative Example 2, which did not contain blast furnace slag fine powder, showed a greater accelerated carbonation depth and a larger carbonation rate coefficient on the cast surface compared to Comparative Example 1, indicating that carbonation was not suppressed to a significant degree.

[0050] However, the accelerated carbonation depth and carbonation rate index for Example 2, in which blast furnace slag ultrafine powder was added, and Example 3, in which blast furnace slag fine powder was added, were both smaller than those of Comparative Example 1, which did not use blast furnace slag fine powder.

[0051] Furthermore, at all levels, the method of neutralizing from the concrete surface resulted in a smaller neutralization depth and neutralization rate index compared to the method of neutralizing from the bottom surface, indicating that neutralization was suppressed.

[0052] In Examples 1 and 2, which used blast furnace slag ultrafine powder B1S, the load was 20 kg / m³. 3 The amount added in Example 1 was 40 kg / m³. 3 In Example 2, the added material resulted in a smaller accelerated neutralization depth and neutralization rate index, thus suppressing neutralization. The cumulative volume fraction of blast furnace slag fine powder with a particle size of 5 μm or less was 20 kg / m³. 3 40 kg / m 3 When used, neutralization was suppressed. Neutralization was suppressed when a larger amount of fine blast furnace slag powder with a cumulative volume fraction of 100% and a particle size of 5 μm or less was used.

[0053] Furthermore, at all levels, the method of neutralizing from the pouring surface resulted in a smaller neutralization depth and neutralization rate index compared to the method of neutralizing from the bottom surface, indicating that neutralization was suppressed. In particular, no neutralization depth was observed when neutralization was performed from the bottom surface in Example 2.

[0054] Blast furnace slag ultrafine powder B1S 40 kg / m³ 3 The mixture used in Example 2 and blast furnace slag fine powder CR was 40 kg / m³ 3 In Example 3, which was used, Example 2, which used fine blast furnace slag ultrafine powder B1S, showed a smaller accelerated neutralization depth and neutralization rate index than Example 3, which used coarser blast furnace slag fine powder CR, indicating that neutralization was suppressed. Blast furnace slag fine powder with a particle size of 25 μm or less in the volume-based particle size distribution (hereinafter, volume-based particle size) was used at a rate of 40 kg / m³ 3 Example 2 contained 30 kg / m³ of blast furnace slag fine powder with a volume-based particle size of 25 μm or less. 3 Neutralization was suppressed compared to Example 3, which contained the same substance.

[0055] Blast furnace slag ultrafine powder B1S 20 kg / m³ 3 The mixture used in Example 1 and blast furnace slag fine powder CR was 40 kg / m³ 3In Example 3, the blast furnace slag fine powder with a volume-based particle size of 25 μm or less was used at a rate of 30 kg / m³. 3 The amount contained in Example 3 is 20 kg / m³ 3 Compared to Example 1, which contained the same material, the neutralization depth and neutralization rate index were smaller, and neutralization was suppressed. Also, as mentioned above, the particle size of 25 μm or less was 20 kg / m 3 Considering that Example 1 showed a greater accelerated neutralization depth than Comparative Example 1, which did not have blast furnace slag fine powder added, the particle size of 25 μm or less was 25 kg / m 3 It is presumed that a content of a certain degree or more is preferable. 25 kg / m³ of blast furnace slag fine powder with a cumulative volume of 100% and a particle size of 5 μm or less. 3 If the level is less than this, the suppression of carbonation may not be sufficient.

[0056] In Example 3 and Comparative Example 2, which used blast furnace slag fine powder CR, 40 kg / m³ of blast furnace slag fine powder CR was used. 3 The sample used in Example 3 was 128 kg / m³. 3 The accelerated carbonation depth and carbonation rate index were smaller than those of Comparative Example 2, indicating suppressed carbonation. 30 kg / m³ of blast furnace slag fine powder with a volume-based particle size of 25 μm or less was used. 3 Example 3 contained 96 kg / m³ of blast furnace slag fine powder with a volume-based particle size of 25 μm or less. 3 Neutralization was suppressed compared to Comparative Example 2, which contained the same substance.

[0057] Furthermore, as mentioned above, the particle size of 25 μm or less is 96 kg / m³. 3 Considering that Comparative Example 2, which does not contain blast furnace slag fine powder, has a greater or similar accelerated neutralization depth than Comparative Example 1, which does not contain blast furnace slag fine powder, the particle size of 25 μm or less is 90 kg / m 3 It is presumed that the content should preferably be below a certain level. Blast furnace slag fine powder: 90 kg / m³ 3 If the value exceeds this, the suppression of carbonation may not be sufficient.

[0058] Furthermore, for blast furnace slag fine powder with a volume-based particle size of 25 μm or larger, the amount is 32 kg / m³. 3 Including Comparative Example 2, 10 kg / m³ 3Example 3, which included the above, showed improved neutralization. Therefore, using precast concrete with a lower content of coarse blast furnace slag powder suppressed neutralization. Here again, the above-mentioned particle size of 25 μm or larger was 32 kg / m 3 Considering that Comparative Example 2, which does not contain blast furnace slag fine powder, has a greater or similar accelerated neutralization depth than Comparative Example 1, which does not contain blast furnace slag fine powder, the particle size of 25 μm or larger is 30 kg / m 3 It is presumed that it is preferable to contain it at or below a certain level.

[0059] When considering volume-based particle sizes of 45 μm or larger, Example 3 yields 2.4 kg / m³ 3 Comparative Example 2 is 8 kg / m 3 Therefore, for particle sizes of 45 μm or larger, the load capacity is 5 kg / m². 3 The following are considered preferable.

[0060] Table 7 shows the apparent diffusion coefficient of chloride ions. After immersing 28-day-old specimens in a 10% sodium chloride aqueous solution for one year, the apparent diffusion coefficient was calculated from the chloride ion concentration measured in the depth direction from the penetration surface according to "JIS A 1154 Test method for chloride ions contained in hardened concrete".

[0061] [Table 7]

[0062] Examples 1 and 2, which contain blast furnace slag ultrafine powder B1S, and Example 3 and Comparative Example 2, which contain blast furnace slag fine powder CR, showed lower apparent diffusion coefficients than Comparative Example 1, which does not contain blast furnace slag fine powder. This indicates a tendency for the apparent diffusion coefficient to decrease when blast furnace slag fine powder is included.

[0063] In Examples 1 and 2, which used blast furnace slag ultrafine powder B1S, the load was 20 kg / m³. 3 The amount added in Example 1 was 40 kg / m³. 3 In Example 2, the apparent diffusion coefficient decreased. The amount of blast furnace slag fine powder with a volume-based particle size of 25 μm or less was 20 kg / m³. 340 kg / m 3 When used, the salt-blocking properties were suppressed. The salt-blocking properties were suppressed when a large amount of fine blast furnace slag powder with a cumulative volume fraction of 100% and a particle size of 5 μm or less was used.

[0064] Blast furnace slag ultrafine powder B1S 40 kg / m³ 3 The mixture used in Example 2 and blast furnace slag fine powder CR was 40 kg / m³ 3 In Example 3, the apparent diffusion coefficient was lower in Example 2, which used fine blast furnace slag ultrafine powder B1S, than in Example 3, which used coarse blast furnace slag fine powder CR. 40 kg / m³ of blast furnace slag fine powder with a volume-based particle size of 25 μm or less. 3 Example 2 contained 30 kg / m³ of blast furnace slag fine powder with a volume-based particle size of 25 μm or less. 3 It contains blast furnace slag fine powder with a volume-based particle size of 25 μm or larger at a rate of 10 kg / m³ 3 The salt-blocking properties were suppressed compared to Example 3, which contained the same substance.

[0065] In Example 3 and Comparative Example 2, which used blast furnace slag fine powder CR, 40 kg / m³ of blast furnace slag fine powder CR was used. 3 Example 3, which used 128 kg / m³, 3 The apparent diffusion coefficient tended to be lower than that of Comparative Example 2. 30 kg / m³ of blast furnace slag fine powder with a volume-based particle size of 25 μm or less was used. 3 It contains blast furnace slag fine powder with a volume-based particle size of 25 μm or larger at a rate of 10 kg / m³ 3 Example 3 contains 96 kg / m³ of blast furnace slag fine powder with a volume-based particle size of 25 μm or less. 3 It contains 32 kg / m³ of blast furnace slag fine powder with a volume-based particle size of 25 μm or larger. 3 The salt-blocking properties were suppressed compared to Comparative Example 2, which contained the same substance.

[0066] Furthermore, the apparent diffusion coefficient was higher when chloride ions were introduced from the concrete surface than when they were introduced from the bottom.

[0067] Based on the above test results, in order to create a precast concrete product that improves durability not only through salt resistance but also through the suppression of carbonation, 25 kg / m³ of blast furnace slag fine powder with a particle size of 25 μm or less should be added to the concrete. 3 The above amount must be included (Examples 2 and 3), and blast furnace slag fine powder with a particle size of 25 μm or less must be added to the concrete at a rate of 25 kg / m³. 3 More than 90kg / m 3 The following must be included (Examples 2 and 3): 30 kg / m³ of blast furnace slag fine powder with a particle size of 25 μm or larger in the concrete. 3 The following must be included (Examples 2 and 3):

Claims

【Request Item 1】 25 kg / m³ of blast furnace slag fine powder with a particle size of 25 μm or less in the volume-based particle size distribution is added to the concrete. 3 A precast concrete product characterized by containing the above-mentioned amount. 【Request Item 2】 In the precast concrete product according to claim 1, blast furnace slag fine powder with a particle size of 25 μm or less in the volume-based particle size distribution is added to the concrete at a rate of 25 kg / m³. 3 More than 90kg / m 3 A precast concrete product characterized by containing the following: 【Request Item 3】 30 kg / m³ of blast furnace slag fine powder with a particle size of 25 μm or larger in the volume-based particle size distribution is added to the concrete. 3 A precast concrete product characterized by containing the following:

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