JP2022019528A - Concrete composition - Google Patents

Abstract

To improve frost damage resistance in a concrete composition containing an artificial lightweight fine aggregate.SOLUTION: A concrete composition of the present invention contains a binder, water, and a fine aggregate, and when assuming a water-binder ratio as W/B (%), W is 110 or more and 150 or less, and W/B is 18 or more and (0.168×(W-110)+20) or less. A concrete composition of other aspects of the present invention contains a binder, water, and a fine aggregate, and the binder contains cement and the fine aggregate contains a lightweight fine aggregate, and when assuming a unit water content of water as W (kg/m3) and a volume ratio of a fine aggregate to a paste as vs/vp, W is 110 or more and 150 or less, and vs/vp is 0.67 or more and 1.00 or less. A concrete composition of yet other aspect of the present invention contains a binder, water, and a fine aggregate, and the fine aggregate contains a lightweight fine aggregate, and when assuming a unit water content of water as W(kg/m3), W is 110 or more and 150 or less, and a unit fine aggregate amount (kg/m3) is 515 or more and 655 or less.SELECTED DRAWING: Figure 9

Description

The present invention relates to a concrete composition.

The artificial lightweight fine aggregate is known to have features such as weight reduction of the concrete composition and reduction of self-shrinkage due to the internal curing effect. Patent Document 1 discloses a concrete composition containing an artificial lightweight fine aggregate and to which water is added at a rate of 145 to 155 kg / m ³ .

Japanese Patent No. 6180946

Artificial lightweight fine aggregate has many voids and tends to contain water. For this reason, the moisture contained in the voids repeatedly freezes and expands and thawes, so that stress is repeatedly applied to the concrete, which may reduce the frost damage resistance.

It is an object of the present invention to provide a concrete composition containing an artificial lightweight fine aggregate and having high frost damage resistance.

The concrete composition of one aspect of the present invention contains a binder, water and a fine aggregate, the fine aggregate contains a lightweight fine aggregate, the unit water amount of water is W (kg / m ³ ), and the water binder. When the ratio is W / B (%), W is 110 or more and 150 or less, and W / B is 18 or more and (0.168 × (W-110) +20) or less. The concrete composition of another aspect of the present invention comprises a binder, water and a fine aggregate, the binder contains cement, the fine aggregate comprises a lightweight fine aggregate, and the unit water volume of water is W (kg). / M ³ ), where the volume ratio of the fine aggregate to the paste is vs / vp, W is 110 or more and 150 or less, and vs / vp is 0.67 or more and 1.00 or less. The concrete composition of still another aspect of the present invention comprises a binder, water and a fine aggregate, the fine aggregate comprises a lightweight fine aggregate, and the unit water content of water is W (kg / m ³ ) of 110. As mentioned above, 150 or less, and the unit fine aggregate amount (kg / m ³ ) is 515 or more and 655 or less.

In the present invention, since the unit water amount of water is as low as 110 to 150 kg / m ³ , the water content that freezes and expands is reduced. Therefore, according to the present invention, it is possible to provide a concrete composition containing an artificial lightweight fine aggregate and having high frost damage resistance.

It is a graph which shows the freeze-thaw test result of Examples 1 to 3 and Comparative Example 1. It is a graph which shows the shrinkage strain of Example 1 and Comparative Example 1. 3 is a graph showing shrinkage strains of Examples 4 to 6 and Comparative Examples 2 to 3. It is a graph which shows the neutralization promotion test result of Examples 1 and 3 and Comparative Example 1. It is a graph which shows the relationship between the age and the compressive strength in Examples 1 to 3 and 7 and Comparative Example 1. It is a graph which shows the relationship between the compressive strength and the Young's modulus of Examples 1 to 3 and 7 and Comparative Example 1. It is a graph which shows the compressive strength of Examples 8 to 14 and Comparative Example 4. It is a graph which shows the freeze-thaw test result (relative dynamic elastic modulus) of Examples 8 to 14 and Comparative Example 4. It is a graph which shows the freeze-thaw test result (mass reduction rate) of Examples 8 to 14 and Comparative Example 4. It is a graph which shows the relationship between the unit water amount and W / B in Examples 8 to 14 and Comparative Example 4. 3 is a graph showing the relationship between the amount of air and the durability index in Examples 8 to 14 and Comparative Example 4. 6 is a graph showing the relationship between vs / vp and compressive strength in Examples 8 to 14 and Comparative Example 4. It is a graph which shows the relationship between the unit fine aggregate amount and compressive strength in Examples 8 to 14 and Comparative Example 4. It is a graph which shows the shrinkage strain of Examples 8 to 11 and Comparative Example 4. It is a graph which shows the relationship between the unit water amount and shrinkage strain in Examples 8 to 11 and Comparative Example 4. It is a graph which shows the relationship between W / B and shrinkage strain in Examples 8 to 11 and Comparative Example 4.

Hereinafter, the concrete composition of the present invention will be described based on Examples and Comparative Examples. Table 1 shows the composition of the concrete compositions of Examples 1 to 7 and Comparative Examples 1 to 3, Table 2 shows the unit mass and unit volume of the concrete compositions of Examples 1 and 3 and Comparative Example 1, and Table 3 shows the unit mass and volume. The specifications of the materials used in Examples 1 to 7 and Comparative Examples 1 to 3 are shown. In Table 3, BET means that it is a measurement result by JIS R 1626 "Measurement method of specific surface area by gas adsorption BET method of fine ceramic powder".

1 (a) shows the relative dynamic elastic modulus of Examples 1 to 3 and Comparative Example 1, and FIG. 1 (b) shows the mass reduction rate of Examples 1 to 3 and Comparative Example 1 (FIG. 1). c) shows the combination of Examples 1 to 3 and Comparative Example 1. The fine aggregate ratio (s / a) is 55.0. The relative dynamic elastic modulus and the mass reduction rate were determined based on the underwater freeze-thaw test method (method A) specified in JIS A1148: 2010 “Concrete freeze-thaw test method”. If the relative dynamic elastic modulus is 60% or more of the initial value after 300 cycles, it can be evaluated as having excellent frost damage resistance. In Comparative Example 1, the relative dynamic elastic modulus was less than 60% of the initial value in about 100 cycles, whereas in Examples 1 to 3, it remained at about 80 to 90% of the initial value even after 300 cycles had elapsed. .. The mass reduction rate increases sharply with the number of cycles in Comparative Example 1, but is almost constant in Examples 1 to 3. The concrete of Examples 1 to 3 contains silica fume as a binder, and the concrete of Comparative Example 1 does not contain silica fume as a binder. Silica fume has the effect of increasing the fluidity of concrete.

FIG. 2A shows the shrinkage strains of Example 1 and Comparative Example 1, and FIG. 2B shows the combination of Example 1 and Comparative Example 1. Both Example 1 and Comparative Example 1 use artificial lightweight fine aggregates, but the water content (unit water amount) W and the water binder ratio W / B are different. In Example 1, the test is conducted under two conditions, 18-W130-55.0 (20 ° C.) and 18-W130-55.0 (7dry). At 18-W130-55.0 (20 ° C), the concrete was placed and then maintained in a sealed state (not dried) in a 20 ° C environment. In 18-W130-55.0 (7dry), after concrete was placed, it was sealed in an environment of 20 ° C until the age of 7 days, unframed at the age of 7 days (point A in the figure), and cured in the air (dried). ). In the comparative example, as in 18-W130-55.0 (20 ° C), after the concrete was poured, the sealed state was maintained in a 20 ° C environment. In the stage where the number of days elapsed from the completion of pouring is short, the shrinkage strain is mainly caused by self-shrinkage (shrinkage in the initial stage after concrete pouring, which is caused by the consumption of water in the concrete by the cement hydration reaction). Since sealing is continued in the comparative example with 18-W130-55.0 (20 ° C), drying shrinkage (shrinkage over a long period of time after concrete placement caused by the dissipation of water in the concrete into the air) is basically performed. Not happening. From the above, it can be seen that the initial shrinkage strain due to self-shrinkage is suppressed in both cases of 18-W130-55.0 (20 ° C) and 18-W130-55.0 (7dry) in the comparative example. In 18-W130-55.0 (7dry), after deframement, water evaporation progresses, and along with this, shrinkage strain due to drying shrinkage progresses.

FIG. 3A shows the shrinkage strains of Examples 4 to 6 and Comparative Examples 2 to 3, and FIG. 3B shows the combination of Examples 4 to 6 and Comparative Examples 2 to 3. The fine aggregate ratio (s / a) is 47.5. In each Example and Comparative Example, the material was removed from the frame at the age of 7 days (point A in the figure) and cured in the air. In Examples 4 to 6, an artificial lightweight fine aggregate is used as the fine aggregate, and in Comparative Examples 2 and 3, crushed sand is used as the fine aggregate. The water content (unit water amount) W is the same in all cases. In Examples 4 to 6, both self-shrinkage and dry shrinkage are suppressed. In Comparative Examples 2 and 3, self-shrinkage is large, but dry shrinkage is about the same as in Examples 4 and 6.

From the above, the following can be understood. First, comparing the artificial lightweight fine aggregate and the crushed sand, as shown in FIG. 3A, the self-shrinkage is suppressed by using the artificial lightweight fine aggregate. It is considered that this is because the artificial lightweight fine aggregate has a high ability to retain water in the internal voids and has a large effect of suppressing self-shrinkage due to the internal curing effect. The self-shrinkage suppressing effect due to the internal curing effect is a conventionally known feature of artificial lightweight fine aggregate. On the other hand, 18-W130-55.0 (20 ° C) and 18-W130-55.0 (7dry) differ only in the presence or absence of sealing after 7 days of age, but as shown in Fig. 2 (a), 18-W130-55.0. Even in (7dry), the shrinkage strain associated with the drying shrinkage did not increase significantly. It is considered that this is because the water content (unit water amount) W in Example 1 is small. That is, the water not used in the hydration reaction of cement remains in the gaps of the artificial lightweight fine aggregate, which causes drying shrinkage. However, since the unit water amount W is small, the residual water amount decreases. It is considered that the drying shrinkage was suppressed. Further, as a result of reducing the residual water content, the frost damage resistance is improved. Freezing damage occurs when the water contained in the voids of concrete repeats freezing expansion and thawing, and the concrete is repeatedly stressed. It is considered that the stress is suppressed by reducing the residual water content, and the fluctuations in the relative dynamic elastic modulus and the mass reduction rate are suppressed as shown in FIG. 1 (a).

The unit water volume W is in the range of 110 to 140 kg / m ³ , or in the range of about 125 to 140 kg / m ³ , especially in the range of about ± 5 kg / m ³ centered on 130 kg / m ³ (about 125 to about 135 kg / m ³ ). In the range of), it is considered that the same result as in each example can be obtained. Examples 1 and 3 differ only in the water binder ratio W / B, and Example 1 (W / B = 18) is slightly superior to Example 3 (W / B = 20) in frost damage resistance, but both are Has sufficient frost damage resistance. Therefore, the water binder ratio W / B is preferably in the range of at least 18 to 20%. Further, by including PP (polypropylene fiber) (Example 6), the frost damage resistance is further improved. As the fiber, an organic fiber other than the polypropylene fiber can also be used. It is preferable that all the fine aggregates are artificial lightweight fine aggregates, but the effect of the present invention can be exhibited even if some of the fine aggregates are artificial lightweight fine aggregates.

By using an artificial lightweight fine aggregate for the fine aggregate, the fluidity is greatly improved as compared with the case where crushed sand is used. Table 4 shows the fresh test results of Example 4 and Comparative Example 2. The slump flow value was measured according to JIS A1150: 2014 “Concrete slump flow test method”. The 50 cm slump flow passage time is the time when the diameter of the concrete expands to 50 cm from the moment when the cone is pulled up, and is one of the indexes of the fluidity of the concrete. In Comparative Example 2, since the slump flow value did not reach 50 cm, there was no measured value. The difference between Example 4 and Comparative Example 2 is the type of fine aggregate. In Example 4, an artificial lightweight fine aggregate is used as the fine aggregate, and in Comparative Example 2, crushed sand is used as the fine aggregate. In Comparative Example 2, although the amount of the high-performance water reducing agent (SP) used is larger than that of the example, the slump flow value is much smaller than that of the example. That is, by using an artificial lightweight fine aggregate for the fine aggregate, extremely high fluidity can be obtained.

FIG. 4A shows the relationship between the accelerated material age and the accelerated neutralization depth for Examples 1 and 3 and Comparative Example 1, and FIG. 4B shows the combination of Examples 1 and 3 and Comparative Example 1. ing. The accelerated neutralization depth was determined based on JIS A1153: 2012 "Promoted Neutralization Test Method for Concrete". Concrete is neutralized by the reaction of carbon dioxide present in the atmosphere with calcium hydroxide in concrete. Neutralization of concrete increases the possibility of corrosion of reinforcing bars. Therefore, the difficulty of neutralizing concrete is one of the indicators of long-term durability of concrete as well as frost damage resistance. If the accelerated neutralization depth is 25 mm or less at the time when 26 weeks have passed since the start of the accelerated test, it is evaluated to have sufficient neutralization resistance. Although Examples 1 and 3 have only data up to 13 weeks, it is considered that they have sufficient neutralization resistance performance from the comparison with Comparative Example 1.

5 (a) shows the relationship between the age and the compressive strength of Examples 1 to 3 and 7 and Comparative Example 1, and FIG. 5 (b) shows the combination of Examples 1 to 3 and 7 and Comparative Example 1. ing. FIG. 5A shows the relationship between the age of the standard cured test piece and the compressive strength. Examples 1 to 3 and 7 have a large compressive strength as compared with Comparative Example 1. Generally, it is said that the smaller the water binder ratio W / B, the higher the compressive strength of concrete, but this general tendency was confirmed from FIG. 5 (a).

FIG. 6A shows the relationship between the compressive strength and the Young's modulus for Examples 1 to 3 and 7 and Comparative Example 1, and FIG. 6B shows the combination of Examples 1 to 3 and 7 and Comparative Example 1. ing. As the Young's modulus, a value obtained by multiplying the calculated value by 0.8 is often used in consideration of the design margin. The specific gravity γ of concrete using artificial lightweight fine aggregate is considered to be about 2.3 t / m ³ . FIG. 6A shows an example of γ = 2.4 t / m ³ and 2.1 t / m ³ . Examples 1 to 3 and 7 show a Young's modulus that exceeds the value obtained by multiplying the calculated value in the case of γ = 2.4 t / m ³ by 0.8. The artificial lightweight aggregate is softer than the crushed sand, and the Young's modulus tends to decrease by that amount. However, in Examples 1 to 3 and 7, no problem was obtained from the viewpoint of the Young's modulus (rigidity).

Table 5 shows the formulations of the concrete compositions of Examples 8 to 14 and Comparative Example 4, and Table 6 shows the specifications of the materials used in Examples 8 to 14 and Comparative Example 4. Example 8 has a different lot from Example 1, but has the same composition. The materials used in Examples 8 to 14 and Comparative Example 4 are basically the same as the materials used in Examples 1 to 7 and Comparative Examples 1 to 3.

Table 7 shows the fresh test results of Examples 8 to 14 and Comparative Example 4. The fresh test was carried out in the same manner as the fresh test shown in Table 4. All of them showed better fluidity than Comparative Example 2 in Table 4, and it was confirmed that high fluidity can be obtained by using an artificial lightweight fine aggregate as the fine aggregate. As will be described later, it is considered that the fluidity of Comparative Example 4 is lowered because the amount of fine aggregate is larger than that of water or the binder.

FIG. 7 shows the compressive strengths of Examples 8 to 14 and Comparative Example 4. In the figure, "90 ° C sealing σ7" is the compressive strength after concrete is placed and sealed in a 90 ° C environment for 7 days, and "standard σ28" is the compressive strength after concrete is placed and cured in water for 28 days. As for the strength, "20 ° C. sealing σ7" means the compressive strength after concrete is placed and sealed in a 20 ° C. environment for 7 days. In Examples 8 to 14 and Comparative Example 4, a level of compressive strength that does not cause a problem in practical use was obtained. Further, as in FIG. 5, it was confirmed that the compressive strength of concrete tends to increase as the water-bonding material ratio W / B becomes smaller.

FIG. 8A shows the relative dynamic elastic modulus up to 150 cycles for Examples 8 to 14 and Comparative Example 4. Since the relative dynamic elastic modulus was measured up to 300 cycles in Examples 8 to 11 and Comparative Example 4, they are shown separately in FIG. 8 (b). FIG. 9 shows the mass reduction rates of Examples 8 to 14 and Comparative Example 4. The relative dynamic elastic modulus and the mass reduction rate were determined based on the underwater freeze-thaw test method (method A) specified in JIS A1148: 2010 “Concrete freeze-thaw test method”. In Comparative Example 4, the relative dynamic elastic modulus was less than 60% of the initial value in about 150 cycles, whereas in Examples 8 to 11, the same value as the initial value was obtained even after 300 cycles. In Examples 12 to 14, only the measurement results up to 150 cycles were obtained, but judging from the tendency up to 150 cycles and FIG. 8 (b), the relative dynamic elastic modulus at the time of reaching 300 cycles was at least 60% or more. It can be evaluated as being. In Comparative Example 4, the mass reduction rate tended to decrease around 150 cycles and then recover. On the other hand, in Examples 8 to 14, the mass reduction rate is less than 1% or minus (mass increase). Although the data of Example 1 are also shown in FIG. 8 (b), the results of Examples 1 and 8 having the same composition were almost the same, and the reproducibility of the test results was confirmed.

FIG. 10 shows the relationship between the unit amount W (kg / m ³ ) of water and the water binder ratio W / B (%). From the comparison with FIG. 8, the trapezoidal region A defined by the region where W is 110 or more and 150 or less, W / B is 18 or more and (0.168 × (W-110) +20) or less, preferably W. In the trapezoidal region B defined by the region of 110 or more, 140 or less, W / B of 18 or more, and (0.168 × (W-110) +20) or less, the relative dynamic elastic modulus is 60% or more in 300 cycles. It has become. Further, in this region, the mass reduction rate is less than 1% or minus (mass increase) in the range of 0 to 300 cycles. Therefore, the region A is preferable and the region B is more preferable as the relationship between the unit amount W (kg / m ³ ) of water and the water binder ratio W / B (%).

FIG. 11 shows the relationship between the amount of air and the durability index DF. The durability index DF is an index for evaluating the frost damage resistance of concrete specified in JIS A1148: 2010 “Concrete freeze-thaw test method”, and generally, if this value is 60 or more, it has frost damage resistance. Is determined.

FIG. 12 shows the relationship between vs / vp and the standard σ28. vs indicates the unit absolute volume of the fine aggregate, and vp indicates the unit absolute volume of the paste. FIG. 13 shows the relationship between the unit amount of fine aggregate (kg / m ³ ) and the standard σ28. As can be seen from Table 5, Comparative Example 4 has a large amount of fine aggregate and a small amount of cement and water. Therefore, it is probable that sufficient compressive strength could not be obtained. From FIG. 11, when W is 110 or more and 150 or less, preferably 110 or more and 140 or less, and vs / vp is 0.67 or more and 1.00 or less, the relative dynamic elastic modulus is 60% or more in 300 cycles. It has become. From FIG. 12, when W is 110 or more and 150 or less, preferably 110 or more and 140 or less, and the unit fine aggregate amount (kg / m ³ ) is 515 or more and 655 or less, the relative dynamic elastic modulus is 300 cycles. It is 60% or more. Further, in these regions, the mass reduction rate is less than 1% or minus (mass increase) in the range of 0 to 300 cycles.

FIG. 14 shows the shrinkage strains of Examples 8 to 11 and Comparative Example 4. FIG. 14 (a) shows the shrinkage strain under the condition of sealing at 20 ° C., and FIG. 14 (b) shows the shrinkage strain under the condition of sealing at 20 ° C. until the age of 7 days and then curing at 20 ° C. and 60% relative humidity. ing. No shrinkage was observed in Examples 8 to 11 and Comparative Example 4 under the condition of sealing at 20 ° C. When the material was sealed at 20 ° C. until the age of 7 days and then cured in the air, the shrinkage strain progressed to about 200 × 10 ^-6 , but the shrinkage strain was suppressed as compared with the case shown in FIG.

FIG. 15 shows the relationship between the unit water amount and the shrinkage strain, and FIG. 16 shows the relationship between W / B and the shrinkage strain. It can be seen that the unit water volume and W / B do not have a large effect on the shrinkage strain.

Claims (9)

It contains a binder, water and fine aggregate, said fine aggregate including lightweight fine aggregate.
When the unit water amount of the water is W (kg / m ³ ) and the water binder ratio is W / B (%), W is 110 or more and 150 or less, W / B is 18 or more, (0.168 × (0.168 ×). A concrete composition of W-110) +20) or less. The binder contains water and fine aggregate, the binder contains cement, and the fine aggregate contains lightweight fine aggregate.
When the unit amount of water is W (kg / m ³ ) and the volume ratio of the fine aggregate to the paste is vs / vp, W is 110 or more and 150 or less, vs / vp is 0.67 or more and 1 A concrete composition of .00 or less. It contains a binder, water and fine aggregate, said fine aggregate including lightweight fine aggregate.
A concrete composition having a unit water amount of W (kg / m ³ ) of 110 or more and 150 or less, and a unit fine aggregate amount (kg / m ³ ) of 515 or more and 655 or less. The concrete composition according to any one of claims 1 to 3, wherein W = 110 to 140. The concrete composition according to any one of claims 1 to 3, wherein W = 125 to 140. The concrete composition according to any one of claims 1 to 3, wherein W = 125 to 135. The concrete composition according to any one of claims 1 to 6, wherein the fine aggregate comprises an artificial lightweight fine aggregate. The concrete composition according to any one of claims 1 to 7, further comprising organic fibers. The concrete composition according to any one of claims 1 to 8, wherein the binder contains silica fume.

Images