JP7799565B2 - High-Strength Concrete - Google Patents

Description

The present invention relates to high-strength concrete.

High-strength concrete has a low weight ratio of water to binder (water-binder ratio) and has a denser concrete structure after hardening, thereby increasing its compressive strength.
Furthermore, the use of high-strength concrete in concrete structures makes it possible to build taller buildings and use smaller cross-section components, and so various technologies for increasing the strength of concrete are currently being proposed.

For example, Patent Document 1 proposes a concrete composition for the purpose of increasing the strength of concrete, which contains a binder containing at least cement and silica fume, 145 to 155 kg/ ^m3 of water added so that the weight ratio to the binder is 10 to 20%, coarse aggregate with an absolute volume of 270 to 330 L/ ^m3 , and artificial lightweight fine aggregate with an absolute volume of 88 to 168 L/ ^m3 .
Furthermore, Patent Document 2 proposes high-strength concrete that contains water, a binder made of cement and admixtures, fine aggregate, and coarse aggregate, the water-to-binder ratio being 30% or less, the cement being high-early-strength Portland cement, and the admixtures including silica fume, ground granulated blast furnace slag, and a gypsum-based component.
Furthermore, Non-Patent Document 1 proposes ultra-high strength concrete with a design strength (Fc) of 150 N/mm ² .

Patent No. 6180946 Japanese Patent Application Laid-Open No. 2019-48742

Shuichi Matsumoto, Kazumasa Goto, Shusuke Kuroiwa, Yoichi Takase, "Otemachi Tower: Application of CFT Columns with Fc150N/mm2 Concrete and 780N/mm2 Steel to a High-Rise Building," Taisei Corporation Technology Center Report No. 46 (2013)

The level of demand for various properties of concrete is constantly increasing, and strength is no exception. Therefore, it is necessary to achieve even higher strength than the high-strength concrete proposed in Patent Documents 1 and 2.
However, increasing the strength of concrete increases the viscosity of the concrete, and this tendency is particularly pronounced in the case of ultra-high strength concrete such as that described in Non-Patent Document 1. As a result, ultra-high strength concrete can have workability problems, such as being difficult to handle during construction and increasing the load on the pump when pumping. Thus, although the technology described in Non-Patent Document 1 can provide ultra-high strength concrete, there is still room for improvement in terms of workability.

The present invention aims to provide high-strength concrete that exhibits high compressive strength and excellent workability by reducing viscosity.

The high-strength concrete according to the present invention for solving the above-mentioned problems is a high-strength concrete having a compressive strength of 80 N/ ^mm2 or more at 28 days old, containing a binder including low-heat cement, silica fume, and a slag gypsum admixture, and 140 to 180 kg/ ^m3 of water added so that the weight ratio of the binder to the water is 15 to 30%, where the weight of the low-heat cement is 70 to 82, the weight of the silica fume is 13 to 20, and the weight of the slag gypsum admixture is 5 to 10 , where the slag gypsum admixture contains granulated blast furnace slag and gypsum dihydrate as raw materials and is a non-combustible material that is reactively hardened at atmospheric pressure, and conforms to the standards set forth in Appendix 3 of JASS5 M-701:2018.
The low-heat cement of the high-strength concrete according to the present invention is preferably low-heat Portland cement or moderate-heat Portland cement.
According to the present invention, the binders used are low-heat cement, silica fume, and a slag gypsum-based admixture, and the weight ranges of these three materials are precisely specified. This not only provides high compressive strength, but also reduces viscosity, making it possible to realize high-strength concrete with excellent workability.
Furthermore, since the present invention does not require special curing (steam curing at about 50°C) as is done in Patent Document 2, it can also be applied to cast-in-place concrete produced, for example, at ready-mix concrete factories in the city.

The high-strength concrete of the present invention exhibits high compressive strength and excellent workability due to its reduced viscosity.

1 is a graph showing the results of slump flow values in Example 1. 1 is a graph showing the results of 50 cm flow arrival time in Example 1. 10 is a graph showing the results of the 50 cm flow time and the compressive strength when the composition ratio of silica fume in Example 2 is changed. 10 is a graph showing the results of the 50 cm flow time and compressive strength when the composition ratio of the slag gypsum-based admixture in Example 2 is changed.

Hereinafter, an embodiment for carrying out the high-strength concrete according to the present invention (high-strength concrete according to the present embodiment) will be described.
[High-strength concrete]
The high-strength concrete of this embodiment contains low-heat cement, silica fume, a binder containing a slag gypsum-based admixture, and water, and when the total weight of the binder is taken as 100, the weight of the low-heat cement, the weight of the silica fume, and the weight of the slag gypsum-based admixture each fall within a specified range.
Each of the constituent elements will be described in detail below.

(Binding material)
The binder contains low-heat cement, silica fume, and a slag gypsum admixture. The binder may be a premixed product that has been mixed in advance to a predetermined ratio, or may be mixed during concrete production.
The binder may contain three types of materials: low-heat cement, silica fume, and slag gypsum-based admixture. As long as the materials do not adversely affect the compressive strength or viscosity, they may also contain, for example, fly ash, blast furnace slag powder, limestone powder, expansive materials, etc.

(Binder: low-heat cement)
Low-heat cement is a cement that has been adjusted to reduce the heat generation rate and amount of heat generated during the hydration reaction, making it possible to control the temperature cracking of concrete using concrete materials.
The low-heat cement is preferably low-heat Portland cement or moderate-heat Portland cement. The low-heat Portland cement and moderate-heat Portland cement conform to the specifications set forth in JIS R 5210:2009.
(Binder: Low-heat cement composition ratio)
When the total weight of the binder is 100, if the weight of the low-heat cement is less than 70, the desired compressive strength cannot be obtained. On the other hand, if the weight of the low-heat cement exceeds 82, the viscosity becomes too high and it becomes difficult to ensure excellent workability.
Therefore, the weight of the low-heat cement is 70 to 82 parts by weight when the total weight of the binder is 100 parts by weight.
The weight of low-heat cement per 1 m ³ of high-strength concrete is not particularly limited, but is, for example, 500 to 1000 kg/m ³ (preferably 600 to 900 kg/m ³ ).

(Binder: Silica fume)
Silica fume is an amorphous, spherical, ultrafine particle composed primarily of silicon dioxide that is collected from exhaust gas generated when producing metallic silicon or ferrosilicon in an arc-type electric furnace, and is defined in JIS A 6207: 2016. As the silica fume, powdered silica fume for concrete can be used.
(Binder: Silica fume composition ratio)
When the total weight of the binder is 100, if the weight of silica fume is less than 13, the desired compressive strength cannot be obtained and the viscosity becomes high. On the other hand, if the weight of silica fume exceeds 20, the compressive strength improvement effect saturates.
Therefore, the weight of silica fume is 13 to 20 parts by weight when the total weight of the binder is 100 parts by weight.
The weight of silica fume per 1 m ³ of high-strength concrete is not particularly limited, but is, for example, 70 to 200 kg/m ³ (preferably 98 to 130 kg/m ³ ).

(Binder: slag gypsum-based admixture)
Slag gypsum-based admixture is a non-combustible material that is reacted and hardened at atmospheric pressure using granulated blast furnace slag produced at steelworks and dihydrate gypsum, a by-product of flue gas desulfurization equipment at thermal power plants, as its main raw materials, and complies with the standards set forth in Annex 3 of JASS5 M-701:2018.
(Binder: Composition ratio of slag gypsum admixture)
When the total weight of the binder is 100, if the weight of the slag gypsum admixture is less than 5, the viscosity becomes high and excellent workability cannot be ensured. On the other hand, if the weight of the slag gypsum admixture exceeds 10, the compressive strength decreases.
Therefore, the weight of the slag gypsum-based admixture is 5 to 10 parts by weight when the total weight of the binder is 100 parts by weight.
The weight of the slag gypsum admixture per 1 m ³ of high-strength concrete is not particularly limited, but is, for example, 30 to 150 kg/m ³ (preferably 53 to 100 kg/m ³ ).

(water)
If the weight ratio of water to binder is less than 15%, mixing may be difficult, and if the weight ratio of water to binder is more than 30%, the desired compressive strength may not be obtained.
Therefore, water is added so that the weight ratio of water to the binder is 15 to 30%.
Furthermore, if the weight of water per ^{cubic meter} of high-strength concrete (unit water content) is less than 140 kg/ ^m3 , the fluidity of the fresh concrete will deteriorate, resulting in poor workability. If the unit water content exceeds 180 kg/ ^m3 , the desired compressive strength may not be achieved.
Therefore, the unit water content is 140 to 180 kg/ ^m3 .

(Compressive strength)
Because the high-strength concrete according to this embodiment has the above-described configuration (particularly the configuration of the binder), the compressive strength at 28 days (cured in hot water at 40°C) is 80 N/ ^mm2 or more, preferably 150 N/ ^mm2 or more, and more preferably 175 N/ ^mm2 or more. Also, the compressive strength at 28 days (cured in water at 20°C) is 80 N/ ^mm2 or more, preferably 130 N/ ^mm2 or more, and more preferably 150 N/ ^mm2 or more.
The compressive strength at 28 days is, more specifically, the compressive strength at 28 days of a cylindrical specimen 10 cm in diameter and 20 cm in height cured in hot water at 40°C or cured in water at 20°C, and is a value obtained using the test method specified in JIS A1108:2018, "Testing method for compressive strength of concrete."
As described above, as shown in Table 6 (described later), the high-strength concrete according to this practical embodiment can ensure a compressive strength of 80 N/ ^mm2 or more at 28 days for test specimens with a water-bonding ratio of 15 to 20%, whether cured underwater at 20°C or cured in hot water at 40°C. Specifically, the compressive strength at 28 days was 120 N/ ^mm2 to 159 N/ ^mm2 for 20°C underwater curing, and 145 N/ ^mm2 to 176 N/ ^mm2 for 40°C hot water curing. Therefore, it was confirmed that if a compressive strength of 160 N/ ^mm2 or more at 28 days is desired, 40°C hot water curing is preferable to 20°C underwater curing.

(others)
The high-strength concrete according to this embodiment contains fine aggregate, coarse aggregate, admixtures, and the like in addition to binder and water.
The fine aggregate is not particularly limited, and can be one or more selected from mountain sand, river sand, sea sand, crushed sand, silica sand, lime sand, etc. The weight of the fine aggregate per 1 ^m3 of high-strength concrete is not particularly limited, but is, for example, 350 to 800 kg/ ^m3 (preferably 410 to 660 kg/ ^m3 ).
The coarse aggregate is not particularly limited, and natural gravel or crushed stone can be used. The weight of the coarse aggregate per 1 ^m3 of high-strength concrete is not particularly limited, but is, for example, 730 to 950 kg/ ^m3 (preferably 790 to 860 kg/ ^m3 ).
The admixture may be a conventionally known material, such as a separation reducing agent, a water reducing agent, an antifoaming agent, a setting retarder, a setting accelerator, an air entrainer agent, or an air entrainer water reducing agent.
The high-strength concrete according to this embodiment may also contain other commonly used substances.

[Example 1]
In Example 1, the change in fresh properties over time was confirmed.
(Test Contents of Example 1)
The concrete materials used in Example 1 are shown in Table 1.
For the concrete materials shown in Table 1, the amounts of admixtures used and the mixing time were adjusted so that the slump flow immediately after mixing would be about 70 cm. An air content test was then conducted immediately after mixing, and slump flow tests were also conducted 15, 60, 120, and 180 minutes after mixing to check changes in the fresh properties over time. A high-performance water-reducing agent was used as the admixture.
The slump flow test was carried out in accordance with JIS A 1150:2020 "Concrete slump flow test method," and the "slump flow value" and "50 cm flow time" were measured at each time.
The air content test was performed in accordance with JIS A 1128:2019 "Pressure test method for air content of fresh concrete - Air chamber pressure method."
The tests were carried out in an environment of about 20° C., as in Examples 2 and 3 described below.

The abbreviations shown in each table (Table 1 above and Tables 2 to 6 below) are as shown at the bottom of each table.
Furthermore, the "composition ratio of binder" shown in each table and described below is the weight of each binder when the total weight of the binders is 100. For example, if the total weight of the binders is 1000 kg and the weight of silica fume is 130 kg, the ratio is 13 (= 130/1000 x 100;%).
Furthermore, V (high-strength three-component cement) in each table is specifically a three-component cement containing ordinary Portland cement, slag gypsum-based admixture, and silica fume, and when expressed as a mass ratio, the composition ratio is, for example, 7:2:1.

(Results of Example 1)
The results of the change in slump flow value over time in Example 1 are shown in FIG. 1, and the results of the time to reach 50 cm flow are shown in FIG.
Case 1-1 shows the results when a conventionally mixed concrete material was used, and cases 1-2 and 1-3 show the results when concrete materials that meet the specifications of the present invention were used.
Compared to Case 1-1, Cases 1-2 and 1-3 had higher slump flow values at all elapsed times (specifically, an increase of approximately 3 to 10%), and it was confirmed that the difference in slump flow values increased over time.
Furthermore, compared to Case 1-1, Cases 1-2 and 1-3 showed shorter times to reach 50 cm flow at all elapsed times, with the time being reduced by approximately 40% at 15 minutes and 60 minutes, and by approximately 25% at 120 minutes.
From these results, it was confirmed that the viscosity of the concrete material according to the present invention was reduced compared to the concrete material of the conventional mix.

[Example 2]
In Example 2, the influence of the binder composition ratio on the fresh properties and compressive strength was confirmed.
(Test details of Example 2)
The concrete materials used in Example 2 are shown in Table 2.
For the concrete materials shown in Table 2, the amount of admixture used and the mixing time were adjusted so that the slump flow immediately after mixing was approximately 80 cm. Then, immediately after mixing, a slump flow test and an air content test were conducted, and specimens (cylinders 10 cm in diameter x 20 cm in height) for compressive strength tests were collected. The collected specimens were left to stand in a constant temperature and humidity chamber at 20°C and 70% RH, and the next day (after approximately 24 hours), they were demolded and 40°C hot water curing was initiated. Then, a compressive strength test was conducted at an age of 28 days.
The slump flow test and the air content test were carried out in the same manner as in Example 1.
The compressive strength test was performed in accordance with JIS A1108:2018 "Method for testing compressive strength of concrete."
The compressive strength values shown in Example 2 are the average values obtained from three test specimens for each case.

(Results of Example 2)
The results of Example 2 are shown in Table 3. The results of Cases 2-3 and 2-6 in Table 3 (cases where the composition ratio of the slag gypsum-based admixture was constant at 7%) are shown in Figure 3, and the results of Cases 2-1 to 2-5 in Table 3 (cases where the composition ratio of silica fume was constant at 13%) are shown in Figure 4.
In addition, the dotted line extending from the compressive strength plot (▲) in Figure 3 and the dotted line extending from the 50 cm flow time plot (●) were estimated by the inventors based on previous literature (Shinichi Koizumi and Yoshihiro Masuda, "Effect of high temperature curing on the hydration reaction and strength development of low water-binder ratio silica fume-mixed cement paste," Journal of Structural Engineering, Architectural Institute of Japan, Vol. 78, No. 685, pp. 427-433, March 2013).
Approximation curve 1 in Fig. 4 is an approximation curve of the plot (●) of the 50 cm flow arrival time, specifically "Y = 0.0048X ² - 0.2439X + 13.666 (R ² = 0.7716)". Approximation curve 2 in Fig. 4 is an approximation curve of the plot (▲) of the compressive strength, specifically "Y = -0.0067X ² - 0.2633X + 180.18 (R ² = 0.7812)".
From the results in Figure 3, it was confirmed that when the composition ratio of silica fume is 13% or more, the compressive strength becomes 175 N/ ^mm2 or more (i.e., high compressive strength is exhibited), and the 50 cm flow time becomes ¹³ seconds or less (i.e., low viscosity). Furthermore, estimating from the above-mentioned existing literature, it can be inferred that if the composition ratio of silica fume is in the range of 13 to 20%, the compressive strength will become 175 N/mm2 or more, and the 50 cm flow time will become 13 seconds or less.
From the results shown in Figure 4, it was confirmed that if the composition ratio of the slag gypsum-based admixture is in the range of 5 to 10%, the compressive strength will be 175 N/ ^mm2 or more and the 50 cm flow time will be 13 seconds or less.

[Example 3]
In Example 3, the influence of the water-binder ratio on the compressive strength was confirmed.
(Test details of Example 3)
The concrete materials used in Example 3 are shown in Tables 4 and 5.
For the concrete materials shown in Tables 4 and 5, the amount of admixture used and the mixing time were adjusted so that the slump flow immediately after mixing was approximately 70 cm. Then, an air content test was conducted immediately after mixing (Cases 3-1 to 3-3 only), and specimens (10 cm diameter x 20 cm height cylinders) for compressive strength tests were collected. The collected specimens were placed in a constant temperature and humidity chamber at 20°C and 70% RH. The following day (approximately 24 hours later), they were demolded and then subjected to 20°C water curing and 40°C hot water curing. Compressive strength tests were then conducted at 28 days. To confirm the compressive strength of the cores at 91 days, cores were taken from a 1 m square mock column and subjected to compressive strength tests.
The compressive strength values shown in Example 3 are the average values obtained from three test specimens for each case. For example, the compressive strengths of the 20°C water curing and 40°C hot water curing cases 3-1 to 3-3 shown in Table 6 are the results of two tests (average values obtained from three test specimens × 2 times).
The air content test was carried out in the same manner as in Example 1.
The compressive strength test was carried out in the same manner as in Example 2. The core collection method was in accordance with JIS A1107:2012 "Method for collecting cores from concrete and compressive strength test method."

(Results of Example 3)
The results of Example 3 are shown in Table 6.
Cases 3-1 to 3-3 are the results of using concrete materials that meet the specifications of the present invention, and cases 3-4 to 3-9 are the results of using conventionally mixed concrete materials.
When comparing Case 3-1, which has a water-binder ratio of 15%, with Cases 3-4, 3-6, and 3-8, it was confirmed that Case 3-1, which satisfies the provisions of the present invention, exhibits the highest compressive strength value under any of the conditions (20°C water curing, 40°C hot water curing, core).
In addition, when comparing Case 3-2, which has a water-binder ratio of 20%, with Cases 3-5, 3-7, and 3-9, it was confirmed that Case 3-2, which satisfies the provisions of the present invention, exhibits the highest compressive strength value under any of the conditions (20°C water curing, 40°C hot water curing, core).
In other words, it was confirmed that the present invention can provide the desired effect (high compressive strength) even if the water binding ratio varies.
Furthermore, the results of Cases 3-1 to 3-3 confirmed that if the water-bonding ratio is within a predetermined range, a sufficiently high compressive strength can be exhibited.

(Action and effect)
As described above, the high-strength concrete of this embodiment is a high-strength concrete having a compressive strength of 80 N/ ^mm2 or more at 28 days, and contains a binder containing low-heat cement, silica fume, and a slag gypsum admixture, and 140 to 180 kg/ ^m3 of water added so that the weight ratio to the binder is 15 to 30%, and is realized by the weight of the low-heat cement being 70 to 82, the weight of the silica fume being 13 to 20, and the weight of the slag gypsum admixture being 5 to 10, where the total weight of the binder is taken as 100. It is preferable to use low-heat Portland cement or moderate-heat Portland cement as the low-heat cement.
According to this embodiment, the binders include low-heat cement, silica fume, and a slag gypsum-based admixture, and the weight ranges of these three types are precisely specified, so that not only does it exhibit high compressive strength, but by reducing viscosity, it is possible to realize high-strength concrete with excellent workability.

Claims (2)

A high-strength concrete having a compressive strength of 80 N/mm ² or more at 28 days old,
a binder including low-heat cement, silica fume, and a slag gypsum-based admixture;
and 140 to 180 kg/ ^m3 of water added so that the weight ratio to the binder is 15 to 30%,
When the total weight of the binders is 100, the weight of the low-heat cement is 70 to 82, the weight of the silica fume is 13 to 20, and the weight of the slag gypsum-based admixture is 5 to 10,
The slag gypsum-based admixture is a non-combustible material containing granulated blast furnace slag and dihydrate gypsum as raw materials and reacted and hardened at normal pressure, and is characterized in that it complies with the standards described in Annex 3 of JASS5 M-701:2018. High-strength concrete. 2. The high-strength concrete according to claim 1, wherein the low-heat cement is low-heat Portland cement or moderate-heat Portland cement.