JP6075933B2 - Seawater-mixed concrete and concrete structures - Google Patents

Description

  The present invention relates to seawater-mixed concrete in which sea sand is used as an aggregate and seawater is used as mixing water, and a concrete structure made from the seawater-mixed concrete.

  When manufacturing concrete, concrete using seawater as mixing water is known. For example, Patent Document 1 describes seawater-mixed concrete obtained by mixing alumina cement, fine aggregate, and coarse aggregate with seawater.

However, in general, when seawater or sea sand is used in the production of concrete, various restrictions are imposed. For example, regarding the use of seawater, it is stipulated in the construction edition (established in 2007) of the Concrete Standard Specification of the Japan Society of Civil Engineers that "generally it should not be used as mixing water". In addition, it is defined that “in the case of unreinforced concrete that does not use a precautionary rebar, it may be used after confirming that there is no effect on quality”. On the other hand, for the sea sand, the above-mentioned specification also specifies that the amount of chloride ions should be “0.04% or less with respect to the absolute dry weight of fine sand in terms of NaCl” after salt removal. Furthermore, since chloride ions are also supplied from cement and admixture in addition to these seawater and sea sand, “The total amount of chloride ions supplied during mixing is, in principle, 0.3 kg / m ³ or less. ”.

Here, when seawater is used as mixing water, the amount of chlorine ions in the concrete is about 3.5 kg / m ³ . Moreover, since the chlorine ion concentration of sea sand is 0.3% in terms of NaCl, the amount of chlorine ions derived from sea sand in concrete is about 1.5 kg / m ³ . In consideration of the above provisions, seawater and sea sand cannot be used as they are for concrete except for unreinforced concrete.

JP 2005-281112 A

On the other hand, in both remote islands and coastal areas, it is necessary to use seawater for mixing water and sea sand for fine aggregates, and ensure the same durability as RC structures. It may not be possible. Here, as long as the above-mentioned regulations are observed, when only seawater can be procured as mixed water, seawater must be desalinated. The degree of desalination shall be such that the contained components conform to waterworks, Japan Society of Civil Engineers water quality standard (JSCE-B101), or JIS standard (JIS A 5308 Annex 3), but desalination equipment is required. Procurement of equipment costs and transportation costs is indispensable, and power is required for the operation of the desalination equipment, which causes a large amount of CO ₂ generation. Therefore, it is difficult to use fresh water abundantly.

  Even in a situation where fresh water can be transported, transport costs are incurred, and transport of fresh water is the source of carbon dioxide generation regardless of land transport or sea transport. For this reason, in areas where environmental conservation is a requirement in remote islands and coastal areas, there will be a considerable impact on the environment. Therefore, even in such a case, it is difficult to use fresh water abundantly.

  Salt removal is required when using sea sand. Here, when fresh water is used for salt removal, the above-described problems occur. The use of rainwater is also conceivable, but it is not necessary to dare to use seawater because it is easy to procure freshwater in an area where rainwater can be used. In the case of a dry region, it takes a considerable amount of time to store the amount of rainwater necessary for salt removal. Therefore, the use of rainwater is not realistic.

  As described above, in areas where fresh water cannot be used abundantly, particularly in remote islands and coastal areas, it is required to construct concrete structures using seawater and sea sand. The standard of the above specifications is considered to have been formulated from the durability of the concrete structure, and if the required durability can be guaranteed, it is not necessarily required to follow this standard.

  This invention is made | formed in view of such a situation, The objective is to enable it to obtain required durability in the seawater kneaded concrete using seawater and sea sand.

  The inventors of the present invention have a problem when RC structures are constructed from seawater-mixed concrete using sea sand as fine aggregate and seawater as mixed water, and originate from sodium chloride contained in seawater and sea sand. Thought to be in sodium and chloride ions. And when blast furnace system cement was used as a cement component, it came to complete this invention based on the knowledge that the alkali aggregate reaction by a sodium ion can be suppressed.

That is, the seawater kneading concrete of the present invention, a mixture of blast furnace cement and sea sand a seawater kneading concrete kneading in seawater, and the diffusion coefficient of water ^{1.60 × 10 -3 cm 2 / se} c Thus, it contains 1.3% by volume of a nitrite-based admixture and 10% by weight of silica fume with respect to a binder obtained by combining the blast furnace cement and silica fume .

  According to the seawater-mixed concrete of the present invention, since sea sand is used for the fine aggregate and seawater is used for the mixed water, the compressive strength of the concrete after hardening can be increased as compared with that using tap water. . And since a blast furnace system cement suppresses an alkali aggregate reaction, even if sodium ion originating in the sodium chloride contained in seawater or sea sand exists abundantly, expansion of concrete can be suppressed. From the above, even if seawater and sea sand are used, concrete having the required durability can be obtained.

Moreover, in addition to a blast furnace cement, the compressive strength in the concrete after hardening can be made high by using a 1.3 volume% nitrite admixture.

Furthermore, by using 10% by weight of silica fume with respect to the combined material of the blast furnace cement and silica fume, the diffusion coefficient of water in the concrete after hardening can be reduced, and harmful factors enter from the outside. Can be suppressed. For example, it is possible to suppress the intrusion of salinity caused by seawater or sea breeze or carbon dioxide into the concrete.

  In addition, when a concrete structure is produced by placing the above-mentioned seawater-mixed concrete in a mold and demolding after hardening, sand without salt is used as fine aggregate and water supply as mixing water It is possible to remove the mold at an early stage as compared with general concrete using water. As a result, the construction period can be shortened.

  According to the present invention, concrete having required durability can be obtained even when seawater and sea sand are used.

It is a figure explaining the material used by each test in a tabular form. It is a figure which shows each sample and compressive strength in a compressive strength test in a tabular form. It is a bar graph which shows the compressive strength of each sample. It is a figure which shows the compressive strength of seawater kneaded concrete. It is a figure which shows the comparison of seawater kneaded concrete and general concrete. It is a figure which shows the result of a water permeability test, and is a figure which shows the pressurized water penetration | invasion condition after the test body splitting in the sample which kneaded blast furnace cement with tap water. It is a figure which shows the result of a water permeability test, and is a figure which shows the pressurized water penetration | invasion condition after the test body splitting in the sample which kneaded the blast furnace cement with seawater. It is a figure which shows the result of a water permeability test, and is a figure which shows the pressurized water penetration | invasion condition after a test body splitting in the sample which kneaded the blast furnace cement which added the nitrite type admixture with seawater. It is a figure which shows the result of a water permeability test, and is a figure which shows the pressurized water penetration | invasion condition after a test body splitting in the sample which kneaded the blast furnace cement which added the nitrite type admixture and the silica fume with seawater. It is a figure which shows the result of a water permeability test, and is a figure which shows the pressurized water penetration | invasion condition after a test body splitting in the sample which kneaded normal Portland cement with tap water. It is a figure which shows the result of a water permeability test, and is a figure which shows the pressurized water penetration | invasion condition after a test body splitting in the sample which kneaded normal Portland cement with seawater. It is a figure which shows the water permeability coefficient in each sample.

  Hereinafter, embodiments of the present invention will be described. In this embodiment, a compressive strength test and a water permeability test were performed as tests for grasping the properties of seawater-kneaded concrete.

  First, the materials used in this test will be described. The materials used are shown in FIG.

Blast furnace cement type B manufactured by Taiheiyo Cement Co., Ltd. was used as the cement. In this blast furnace cement type B, the density is 3.04 cm ³ and the specific surface area is 3750 cm ² / g. In some tests, ordinary Portland cement was used as the comparative cement.

As the silica fume which is a kind of pozzolana, trade name “ELCHEM 940-U” manufactured by ELCHEM Co., Ltd. was used. In this silica fume, the density is 2.20 cm ³ and the specific surface area is about 19 cm ² / g. This silica fume also acts as a pore occluding agent.

The fine aggregate was land sand from Kisarazu, Chiba Prefecture. The reason for using land sand is to manage the salinity. That is, by using land sand not containing salt (sodium chloride) and adding salt water (described later) at a predetermined concentration during kneading, a seawater-kneaded concrete having a controlled salt concentration is artificially produced. In the above-mentioned land sand, the density is 2.62 cm ³ , the water absorption is 1.76%, and the coarse particle ratio is 2.94. As the coarse aggregate, sandstone produced in Ome, Tokyo was used. In this sandstone, the density is 2.66 cm ³ , the water absorption is 0.71%, the coarse particle ratio is 6.63, and the actual volume ratio is 60.3%.

As the steel fiber, a trade name “Dramix” manufactured by Shinko Construction Materials Co., Ltd. was used. In this steel fiber, the density is 7.85 cm ³ , the fiber diameter φ is 0.6 mm, and the length L is 30 mm. This steel fiber also functions as a sacrificial anode. The iron powder was produced using the above dramix.

As the nitrite-based admixture, trade name “Lassine” manufactured by Taiheiyo Material Co., Ltd. was used. This admixture is mainly composed of a polyhydric alcohol nitroester and is liquid. Then, 3.7 kg / m ³ of chloride ions can be treated (immobilized) per 10 L of the admixture.

  The AE water reducing agent, the high performance AE water reducing agent, and the air amount adjusting agent are all admixtures for concrete. As the AE water reducing agent, trade name “Pozoris No. 70” manufactured by BASF Pozzolith was used. This AE water reducing agent has a lignin sulfonic acid compound as a main component and is in a liquid state. As a high-performance AE water reducing agent, a trade name “Reobuild SP-8SV” manufactured by BASF Pozzolith was used. This high-performance AE water reducing agent has a polycarboxylic acid compound as a main component and is in a liquid state. As the air amount adjusting agent, trade name “Micro Air 404” manufactured by BASF Pozzolith Co., Ltd. was used. This air amount adjusting agent has a polyalkylene glycol derivative as a main component and is in a liquid state.

  Next, mixing water is demonstrated. The mixing water in this test is artificial seawater prepared by adding salt to tap water. The salt concentration in the artificial seawater is adjusted to a concentration corresponding to the total amount of chloride ions derived from both seawater and sea sand.

The standard amount of chloride ions contained in the collected seawater is 19 g / L (Cl ⁻ concentration 1.9%). If the molecular weight of sodium chloride is 58, the atomic weight of sodium is 23, and the atomic weight of chlorine is 35, the amount of sodium chloride derived from seawater is 31 g per liter.

Regarding sea sand, the unit amount of sea sand is 800 kg / m ³ , the unit amount of mixing water is 175 kg / m ^3, and the sodium chloride content in the sea sand is 0.3%. In this case, the amount of sodium chloride contained in the unit amount of sea sand is 800 kg / m ³ × 0.3% = 2.4 kg / m ³ . Therefore, if 2.4 kg of sodium chloride is added to 175 kg of mixed water, even if land sand that does not contain sodium chloride is used, the salt content is the same as when sea sand is used. And the amount of sodium chloride contained in 1 L of this kneaded water is 14 g.

From the above, the addition of sodium chloride Mixing water 1L per 45g (= 31g + 14g), even using tap water and land sand on that does not contain salt, equivalent to that using sea water or sea sand concrete Can be obtained. The amount of sodium chloride in 1 m ³ of concrete is 7.8 kg (= 0.045 kg / m ³ × 175 m ³ ). Further, the chloride ion concentration is 4.7 kg / m ³ .

  Hereinafter, each test will be described. First, the compressive strength test will be described. The compressive strength test was conducted on the case using the above-described artificial seawater and the case using seawater collected in Sagami Bay (also called actual seawater).

  In the test using artificial seawater, seven types of samples shown in FIG. 2 were produced. Sample 1 is a comparative example in which blast furnace cement is kneaded with tap water. Sample 2 is a mixture of blast furnace cement mixed with artificial seawater. Sample 3 is obtained by adding a nitrite admixture to blast furnace cement and kneading with artificial seawater. Sample 4 is obtained by adding silica fume to blast furnace cement and kneading with artificial seawater. Sample 5 is obtained by adding a nitrite admixture and silica fume to blast furnace cement and kneading with artificial seawater. Sample 6 is obtained by adding steel fibers to blast furnace cement and kneading with artificial seawater. Sample 7 is obtained by adding iron powder to blast furnace cement and kneading with artificial seawater.

The water binder ratio (W / B) was 50% for all samples. The fine aggregate rate was 45% in samples 1 to 3 and 6 and 44.7% in other samples. Artificial seawater was 170 kg / m ³ for all samples. Binder, a blast furnace cement and 340 kg / m ³ in samples 1 to 3, 6, blast furnace cement 306 kg / m ³ for the other sample was silica fume and 34 kg / m ^3. Fine aggregate is a 794kg / m ³ in the sample 1 to 3, 6, was 782kg / m ³ in other samples. The coarse aggregate was 985 kg / m ³ for all samples.

As for the nitrite admixture, 13 L / m ^{3 was} added in Samples 3 and 5. Regarding the steel fiber, 78 kg / m ^{3 was} mixed in Sample 6. Regarding the iron powder, 78 kg / m ^{3 was} mixed in Sample 7. Regarding the admixture, AE water-reducing agent was added in 0.25% of the binder amount in samples 1 to 3 and 6, and 1.00% of binder amount was added in the other sample in the high-performance AE water reducing agent. Further, the air amount adjusting agent was added in an amount of 0.0035% of the amount of binder in all samples.

  The kneading was carried out batchwise using a biaxial forced kneading mixer. The amount of kneading was 30 L per batch. For kneading, coarse aggregate, fine aggregate, and blast furnace cement were put into a mixer and kneaded for 10 seconds, and then artificial seawater and an admixture were added and kneaded for 60 seconds. Other materials were added to the mixer together with blast furnace cement and artificial seawater.

  After kneading, specimens were prepared for each sample. The specimen was manufactured according to JIS A1132. That is, each sample after completion of kneading was driven into a predetermined mold and cured. Curing was carried out in three types: standard water curing immersed in water, high-temperature air-dried curing exposed to a high-temperature (50 ° C.) atmosphere, and sealed curing. There were three types of curing periods: 7th, 28th, and 91st. And the compressive strength test was done with respect to the test piece immediately after hardening. The compressive strength test was conducted according to JIS A 1108. The test results are shown in the right column of FIG. 2 and FIG.

  In a test using seawater (actual seawater) in Sagami Bay, six types of samples shown in FIG. Sample 1 ′ is a comparative example in which ordinary Portland cement is kneaded with tap water. Sample 2 'is a blast furnace cement kneaded with tap water and is also a comparative example. Sample 1 is a mixture of ordinary Portland cement mixed with real seawater. Sample 2 is a mixture of blast furnace cement mixed with real seawater. Sample 3 is obtained by adding a nitrite admixture to blast furnace cement and kneading with real seawater. Sample 4 is obtained by adding a nitrite admixture and silica fume to blast furnace cement and kneading with actual seawater.

Regarding actual seawater, the chloride ion concentration was 1.83%. Then, sodium chloride was added so that the chloride ion concentration was 4.7 kg / m ^3, and mixed water was obtained. Thereby, although land sand is used as a fine aggregate, it is adjusted to salt content equivalent to the case where sea sand is used. In addition, about other conditions, it is the same as that of the sample using artificial seawater. Therefore, the description is omitted. In addition, since the mixing conditions are the same as those of the sample using artificial seawater, description thereof is omitted.

  After kneading, specimens were prepared for each sample. The specimen was manufactured according to JIS A1132. Regarding the curing conditions, only the sealed curing was used in this test, and the curing period was two types of 7 days and 28 days. And the compressive strength test based on JISA1108 was done with respect to the specimen immediately after hardening. The test results are shown in the right column of FIG. 4 (a) and FIG. 4 (b).

  The results of the compressive strength test will be described. First, we will consider the differences in the types of mixing water and fine aggregates. It was confirmed that the sample using artificial seawater or actual seawater as mixing water had a tendency to have higher compressive strength than the sample using tap water as mixing water.

Specifically, in sample 2 (blast furnace cement, artificial seawater) in the artificial seawater test, the compressive strength at 7 days of age is 31.9 N / mm ² (standard water), 26.1 N / mm ² (high temperature). Air-dried), 29.8 N / mm ² (sealed), and the compressive strength at 28 days of age is 39.2 N / mm ² (standard water), 27.6 N / mm ² (high-temperature air-dried), 36. The compressive strength at the age of 91 days is 73.6 N / mm ² (sealed), 43.6 N / mm ² (standard water), 26.1 N / mm ² (high temperature air drying), 41.4 N / mm ² (sealed). )Met. Further, in sample 2 (blast furnace cement, actual seawater) in the actual seawater test, the compressive strength at age 7 is 37.0 N / mm ² (sealed), and the compressive strength at age 28 is 47.4 N. / mm is ² (sealing), the compressive strength at the age of 91 days was 53.1N / mm ² (sealing).

On the other hand, in sample 1 (blast furnace cement, tap water) in the artificial seawater test, the compressive strength at 7 days of age is 21.9 N / mm ² (standard water), 19.6 N / mm ² (high temperature air (Dry) 20.9 N / mm ² (sealed), and the compressive strength at the age of 28 days is 34.2 N / mm ² (standard water), 19.2 N / mm ² (high temperature air dry), 30.6 N / mm ² a (sealing), the compressive strength at the age of 91 days, 48.7N / mm ² (standard water), 19.1N / mm ² (high temperature air-dried), 39.8N / mm ² (sealing) Met. Moreover, in sample 2 '(blast furnace cement, tap water) in the actual seawater test, the compressive strength at age 7 is 23.1 N / mm ² (sealed), and the compressive strength at age 28 is 35. The compressive strength was 91 N / mm ² (sealing) and the age of 91 days was 51.6 N / mm ² (sealing).

  The test results up to the age of 28 days will be examined. It can be easily understood by comparing the leftmost column and the second column from the left in FIGS. 3A to 3C and the second column and the fourth column from the left in FIG. In the period up to 28 days of age, the concrete kneaded with seawater and sea sand shows a higher value than the concrete kneaded with tap water and land sand. This means that seawater-mixed concrete using seawater and sea sand hardens earlier than general concrete. And the value of the compressive strength at the age of 7 days in each sample using seawater is equal to or higher than the compressive strength at the age of 28 days in the sample using tap water.

For demolding the formwork, the compressive strength of the concrete is required to be a specified value (5 N / mm ² ) or more. According to the results of this test, the curing period until the compressive strength of the seawater-mixed concrete reaches the specified value or more is considered to be sufficiently shorter than the curing period of general concrete. Therefore, when seawater-mixed concrete produced using seawater and sea sand is placed in a mold, it can be said that the curing period until demolding can be sufficiently shorter than that of general concrete.

The test results on the age of 91 days will be examined. Regarding sample 1 of the artificial seawater test as a comparative example, the compressive strength of the standard water curing showed a high value of 48.7 N / mm ² . Moreover, the compressive strength of the sealing curing was 39.8 N / mm ² . On the other hand, in sample 2 of the artificial seawater test, the compressive strength of the standard water curing was 43.6 N / mm ² and the compressive strength of the sealing curing was 41.4 N / mm ² . Although the compressive strength of the sample 2 was lower than the compressive strength in the standard water curing of the sample 1, it showed a higher value than the compressive strength in the sealing curing of the sample. This means that even a seawater-kneaded concrete produced using seawater and sea sand exhibits a compressive strength comparable to that of general concrete over a long period of time. That is, from the viewpoint of compressive strength, it can be said that general concrete can be replaced with seawater-mixed concrete.

  Next, various materials added to the blast furnace cement, specifically, nitrite admixture, silica fume (pozzolana), steel fiber, and iron powder will be considered.

  From the viewpoint of compressive strength, the compressive strength of Samples 3 to 7 in the artificial seawater test is higher than the compressive strength of Sample 2. Similarly, the compressive strength of Samples 3 and 4 in the actual seawater test shows a higher value than the compressive strength of Sample 4. From this, it can be said that the compressive strength of the seawater kneaded concrete can be increased by adding the above materials such as nitrite-based admixture and kneading. Here, referring to FIG. 3 (a), when comparing the compressive strength of samples 3 to 7 at the age of 91 days in the artificial seawater test, there is no significant difference in the compressive strength of each sample.

  From the above, it can be said that any seawater-kneaded concrete prepared by adding the above materials exhibits higher compressive strength than seawater-kneaded concrete prepared without adding the above materials. And even if it changes the kind of material to add, it can be said that equivalent compressive strength is obtained.

  As shown in FIG. 4 (b), in the actual seawater test, the compressive strength of sample 3 to which nitrite-based admixture was added was nitrite-based admixture at both 7 days and 28 days of age. The value was higher than the compressive strength of Sample 2 which was not added. From this, it can be said that the effect of increasing the compressive strength can be obtained early by adding a nitrite-based admixture. Moreover, the compressive strength of the sample 4 which added the nitrite type admixture and the silica fume showed the value higher than the compressive strength of the sample 3 in any of the material age 7th day and 28th day. From this, it can be said that the effect of further increasing the compressive strength of seawater kneaded concrete can be obtained by adding silica fume to the nitrite-based admixture, compared to the case of adding only the nitrite-based admixture.

  Next, the difference between blast furnace cement and ordinary Portland cement will be considered. Here, samples 1 ′, 2 ′, 1 and 2 in FIGS. 4A and 4B are compared. When kneaded with tap water, up to 28 days of age, sample 1 ′ using normal Portland cement has a higher compressive strength value than sample 2 ′ using blast furnace cement. On the day, sample 2 'using blast furnace cement had higher compressive strength than sample 1' using ordinary Portland cement. On the other hand, when kneaded using seawater, Sample 2 using blast furnace cement had higher compressive strength values at all ages than Sample 1 using ordinary Portland cement.

  Blast furnace cements such as blast furnace cement are known to be effective in suppressing alkali-aggregate reaction. In this reaction, alkali ions such as sodium ions react with a certain type of aggregate and exhibit expansibility. When blast furnace cement is used, blast furnace cement suppresses alkali-aggregate reaction, so even if there is a large amount of sodium ions originating from sodium chloride contained in seawater or sea sand, concrete expansion can be suppressed. it is conceivable that. Therefore, when seawater and sea sand are used, the use of blast furnace cement is effective in making concrete durable.

  Next, with reference to FIGS. 5A to 5C, a reduction in the amount of cement by using seawater and sea sand will be considered.

  Sample a in FIG. 5A is Sample 1 (comparative example using tap water) in the artificial seawater test, and Sample b is Sample 2 (containing salt equivalent to seawater and sea sand). In both samples a and b, the curing method is underwater standard curing, and the age is 28 days. Sample c is a virtual sample in the case where a compressive strength comparable to that of sample b is obtained with a sample using tap water. This sample c is calculated using the relational expression of fc28 (fc28 = 24.769 × C / W-12.924) shown in FIG.

  Similarly, samples d and e in FIG. 5A are samples 1 and 2 in the artificial seawater test, and the age is 28 days. Samples d and e differ from samples a and b in that the curing method is sealing curing. And the sample f is a virtual sample when obtaining compressive strength comparable to the sample e with the sample using tap water. This sample f is calculated using a relational expression of fc28 (fc28 = 22.262 × C / W-11.564) shown in FIG.

Samples a and b are both 340 kg / m ³ cement kneaded with 170 kg / m ³ water (tap water or artificial seawater). While the compressive strength of sample a was 34.2 N / mm ² , the compressive strength of sample b was 39.2 N / mm ² , which was higher than the compressive strength of sample a.

The corresponding cement water ratio (C / W) was determined by substituting 39.2 N / mm ² for fc28 in the relational expression of fc28 shown in FIG. Furthermore, in the obtained cement water ratio, W = 170 kg / m ³ was substituted, and the cement amount of sample c was obtained. The amount of cement in sample c was 358 kg / m ³ . For this reason, when a concrete structure with a compressive strength of 39.2 N / mm ² is constructed by standard curing at an age of 28 days, concrete 1 m ^{3 is} obtained by using seawater and sea sand instead of the combination of tap water and land sand. It was found that 18 kg of cement could be saved.

The same procedure was used for samples df. As a result, when a concrete structure with a compressive strength of 36.7 N / mm ² is constructed with a sealing curing at a material age of 28 days, seawater and sea sand are used in place of the combination of tap water and land sand, and concrete 1 m ³ It was found that 30 kg of cement could be saved.

Next, the water permeability test will be described. In the water permeability test, six types of samples shown in FIG. 12 were prepared. Each sample is the same formulation as the sample described in FIG. 4 (a). That is, sample 1 ′ is a comparative example in which ordinary Portland cement is kneaded with tap water. Sample 1 is a mixture of ordinary Portland cement mixed with real seawater. Sample 2 is a mixture of blast furnace cement mixed with real seawater. Sample 3 is obtained by adding a nitrite admixture to blast furnace cement and kneading with real seawater. Sample 7 is obtained by adding a nitrite admixture and silica fume to blast furnace cement and kneading with actual seawater. Sample 2 'is a comparative example in which blast furnace cement is kneaded with tap water. And the salt content which sea sand holds was adjusted by adding the required amount of sodium chloride.

  Each sample was poured into a mold having a diameter φ of 100 mm and a height of 200 mm, and sealed up to 28 days of age to prepare a specimen. The prepared specimen was set in a pressurized container and pressurized water was supplied. The specimen supplied with pressurized water was divided in half (divided into two) along the axial direction, and the penetration depth of the pressurized water into the specimen was measured. A diffusion coefficient was obtained based on the measured penetration depth, and an estimated permeability coefficient was obtained based on the obtained diffusion coefficient. Note that three specimens were prepared for one type of sample, and the average value of the diffusion coefficients of the three specimens was taken as the diffusion coefficient of the sample (see FIGS. 12A and 12B).

  Cross-sectional photographs showing the penetration of pressurized water are shown in FIGS. In each figure, cross-sectional photographs of three specimens are shown in each of the upper, middle, and lower stages.

  FIG. 6 is a cross-sectional photograph of sample 2 ′ (blast furnace cement, tap water), and FIG. 7 is a cross-sectional photograph of sample 2 (blast furnace cement, actual seawater). In the upper part of FIG. 7, the penetration direction and penetration depth of the pressurized water are shown. FIG. 8 is a cross-sectional photograph of sample 3 (blast furnace cement, actual seawater, nitrite-based admixture), and FIG. 9 is a cross-sectional photograph of sample 7 (blast furnace cement, actual seawater, nitrite-based admixture, silica fume). FIG. 10 is a cross-sectional photograph of Sample 1 ′ (ordinary Portland cement, tap water), and FIG. 11 is a cross-sectional photograph of Sample 1 (ordinary Portland cement, actual seawater).

As shown in FIG. 12 (a), the average value of the diffusion coefficient is 8.16 × 10 ⁻² cm ² / sec for sample 2 ′ (blast furnace cement, tap water), and for sample 2 (blast furnace cement, actual seawater). 4.82 × 10 ⁻² cm ² / sec and Sample 3 (blast furnace cement, actual seawater, nitrite admixture) were 2.11 × 10 ⁻² cm ² / sec. Sample 7 (blast furnace cement, sea water, nitrite admixture, silica fume) is 1.60 × 10 ⁻³ cm ² / sec, and sample 1 ′ (ordinary Portland cement, tap water) is 3.51 × 10 ^{−. 2} cm ² / sec and Sample 1 (ordinary Portland cement, actual seawater) were 3.96 × 10 ⁻² cm ² / sec.

  This water permeability test confirmed the following points. First, on the premise of using blast furnace cement, when seawater is used as the mixing water, the diffusion coefficient (permeability coefficient) can be reduced compared to the case where tap water is used. Secondly, even when seawater is used as the mixing water, no significant difference is observed in the diffusion coefficient (permeability coefficient) when normal portland cement is used compared to when tap water is used. Third, on the premise of using blast furnace cement, mixing a nitrite admixture or silica fume is extremely effective in reducing the diffusion coefficient (water permeability coefficient) even when seawater is used as mixing water. It is understood that the diffusion coefficient can be reduced by using fly ash instead of silica fume. In short, it is understood that the same effect can be obtained if pozzolana is mixed.

In general, when the blast furnace cement was kneaded above tap water, become dense at the effect of the blast furnace slag in long-term ages (91 days), it has been said that the diffusion coefficient can be reduced. From this water permeability test, it was confirmed that the diffusion coefficient could be reduced even when the material was 28 days old by using seawater as mixing water and sea sand as fine aggregate.

  Based on the results of the compressive strength test, the durability test, and the water permeability test described above, the following was found.

  In seawater-mixed concrete using seawater as the mixing water and sea sand as the fine aggregate, it can be said that using blast furnace cement type B as the cement component is effective because it can be densified. In particular, in the period up to 28 days of age, the compressive strength can be made higher than that of concrete produced using tap water. Thereby, early demolding becomes possible. And since a blast furnace cement suppresses an alkali-aggregate reaction, even if sodium ion originating in the sodium chloride contained in seawater or sea sand exists abundantly, expansion of concrete can be suppressed.

As mentioned above, even if it uses seawater and sea sand, the concrete structure provided with required durability can be constructed. Then, sea water and sea sand, in order to ensure the above tap water can be easily procured locally even in difficult remote islands and coastal areas, is particularly useful in the case of building a concrete structure in such a region. For example, when secured transport and on tap water materials, energy saving can be realized, cost can be reduced.

  In addition, it was found that when nitrite-based admixtures such as rasnaine are included in seawater-mixed concrete, defects such as corrosion due to chloride ions can be suppressed and the diffusion coefficient in the concrete after curing can be reduced. . Thereby, the penetration | invasion of harmful factors from the outside, such as the salt content resulting from seawater or a sea breeze, or the penetration | invasion of the inside of concrete, such as a carbon dioxide gas, can be suppressed.

  In addition, it was found that the diffusion coefficient in the concrete after curing can be reduced even in the case where pozzolan such as silica fume is contained in the seawater kneaded concrete. Therefore, similarly to the case where the nitrite admixture is included, it is possible to suppress the entry of harmful factors from the outside, such as the salt content caused by seawater or sea breeze or the intrusion of carbon dioxide into the concrete.

  By the way, the description regarding the above embodiment is for making an understanding of this invention easy, and does not limit this invention. The present invention can be changed and improved without departing from the spirit and purpose of the present invention, and the present invention naturally includes equivalents thereof.

  For example, with regard to nitrite-based admixtures, those having polyhydric alcohol nitroester as the main component have been exemplified. However, as long as nitrite ions can be supplied, other types of nitrite-based admixtures have the same effects. Play. For example, a material mainly composed of calcium nitrite or a material mainly composed of lithium nitrite may be used.

  Moreover, regarding blast furnace cement, other than blast furnace cement B type may be used. In short, if blast furnace slag is included as a cement component, the same effects can be obtained even with other types of cement.

Claims (2)

A seawater-mixed concrete made by mixing a mixture of blast furnace cement and sea sand with seawater,
As the diffusion coefficient of water is ^{1.60 × 10 -3 cm 2 / se} c, 1.3 % by volume of nitrites admixture, and, with respect to binding material combined with said blast furnace based cement and silica fume And 10% by weight silica fume. A concrete structure characterized in that the seawater-kneaded concrete according to claim 1 is placed in a mold and demolded after curing.