JP7574129B2 - Concrete Composition - Google Patents

Description

The present invention relates to a concrete composition.

Artificial lightweight fine aggregate is known to have features such as reducing the weight of concrete compositions and reducing autogenous shrinkage due to its internal curing effect. Patent Document 1 discloses a concrete composition containing artificial lightweight fine aggregate and containing water at 145 to 155 kg/ ^m3 .

Patent No. 6180946 specification

Artificial lightweight fine aggregate has many voids and is prone to moisture absorption. As a result, the moisture contained in the voids repeatedly freezes, expands, and melts, subjecting the concrete to repeated stress, which can reduce its frost resistance.

The present invention aims to provide a concrete composition that contains artificial lightweight fine aggregate and has high frost resistance.

A concrete composition in one embodiment of the present invention comprises a binder, water, and fine aggregate, the fine aggregate comprising lightweight fine aggregate, and when the amount of water per unit of water is W (kg/ ^m3 ) and the water-to-binder ratio is W/B (%), W is 110 or more and 140 or less, and W/B is 18 or more and (0.168 x (W-110) + 20) or less. A concrete composition in another embodiment of the present invention comprises a binder, water, and fine aggregate, the binder comprises cement, the fine aggregate comprises lightweight fine aggregate, and when the amount of water per unit of water is W (kg/ ^m3 ) and the volume ratio of fine aggregate to paste is vs/vp, W is 110 or more and 140 or less, and vs/vp is 0.67 or more and 1.00 or less. In yet another embodiment of the concrete composition of the present invention, the fine aggregate comprises a binder, water, and fine aggregate, the fine aggregate comprising lightweight fine aggregate, the unit water content W (kg/ ^m3 ) being 110 or more and 140 or less, and the unit fine aggregate content (kg/ ^m3 ) being 515 or more and 655 or less.

In the present invention, the unit water content is set to a low level of 110 to 150 kg/ ^m3 , so the amount of water that expands upon freezing is reduced. Therefore, according to the present invention, it is possible to provide a concrete composition that contains artificial lightweight fine aggregate and has high frost resistance.

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

The concrete composition of the present invention will be described below based on examples and comparative examples. Table 1 shows the mix proportions 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 specifications of the materials used in Examples 1 to 7 and Comparative Examples 1 to 3. In Table 3, BET means that the results are measured according to JIS R 1626 "Method for measuring the specific surface area of fine ceramic powders by the gas adsorption BET method."

Figure 1 (a) shows the relative dynamic modulus of elasticity for Examples 1 to 3 and Comparative Example 1, Figure 1 (b) shows the mass reduction rate for Examples 1 to 3 and Comparative Example 1, and Figure 1 (c) shows the mix ratio for Examples 1 to 3 and Comparative Example 1. The fine aggregate ratio (s/a) is set to 55.0. The relative dynamic modulus of elasticity and the mass reduction rate were determined based on the underwater freeze-thaw test method (Method A) specified in JIS A1148:2010 "Freeze-thaw test method for concrete". If the relative dynamic modulus of elasticity is 60% or more of the initial value after 300 cycles, it can be evaluated as having excellent frost resistance. In Comparative Example 1, the relative dynamic modulus of elasticity fell below 60% of the initial value after about 100 cycles, while in Examples 1 to 3, it remained at about 80 to 90% of the initial value even after 300 cycles. The mass reduction rate increased rapidly with the number of cycles in Comparative Example 1, but was almost constant in Examples 1 to 3. The concretes of Examples 1 to 3 contain silica fume as a binder, while 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.

Figure 2 (a) shows the shrinkage strain for Example 1 and Comparative Example 1, and Figure 2 (b) shows the mix proportions for Example 1 and Comparative Example 1. Both Example 1 and Comparative Example 1 use artificial lightweight fine aggregate, but the water content (unit water content) W and the water-binder ratio W/B are different. In Example 1, tests were conducted under two conditions: 18-W130-55.0 (20°C) and 18-W130-55.0 (7dry). For 18-W130-55.0 (20°C), the concrete was poured and then kept sealed (not dried) in a 20°C environment. For 18-W130-55.0 (7dry), the concrete was poured and then sealed in a 20°C environment until it was 7 days old, and then removed from the frame at 7 days old (point A in the figure) and allowed to cure in air (dry). In the comparative example, like 18-W130-55.0 (20°C), the concrete was poured and then kept sealed at 20°C. When few days have passed since pouring, shrinkage distortion is mainly caused by autogenous shrinkage (shrinkage in the early stage after concrete pouring, caused by the consumption of water in the concrete by cement hydration reaction). In 18-W130-55.0 (20°C) and the comparative example, sealing is continued, so drying shrinkage (shrinkage over a long period after concrete pouring, caused by water in the concrete escaping into the air) does not occur. From the above, it can be seen that the initial shrinkage distortion due to autogenous shrinkage is suppressed in all cases of 18-W130-55.0 (20°C), 18-W130-55.0 (7dry), and the comparative example. In 18-W130-55.0 (7dry), water evaporates after removal from the form, and as a result, shrinkage distortion due to drying shrinkage progresses.

Figure 3(a) shows the shrinkage strain for Examples 4-6 and Comparative Examples 2-3, and Figure 3(b) shows the mix proportions for Examples 4-6 and Comparative Examples 2-3. The fine aggregate ratio (s/a) is 47.5. In each Example and Comparative Example, the material was removed from the form after 7 days (point A in the figure) and cured in air. In Examples 4-6, artificial lightweight fine aggregate was used as the fine aggregate, and in Comparative Examples 2-3, crushed sand was used as the fine aggregate. The water content (unit water content) W is the same in all cases. In Examples 4-6, both autogenous shrinkage and drying shrinkage are suppressed. In Comparative Examples 2-3, autogenous shrinkage is large, but drying shrinkage is about the same as in Examples 4-6.

From the above, the following can be understood. First, comparing artificial lightweight fine aggregate with crushed sand, as shown in Figure 3 (a), autogenous shrinkage is suppressed when artificial lightweight fine aggregate is used. This is thought to be because the internal voids of artificial lightweight fine aggregate have a high ability to retain water, and the effect of suppressing autogenous shrinkage due to the internal curing effect is large. The effect of suppressing autogenous shrinkage due to the internal curing effect is a long-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 Figure 2 (a), even in 18-W130-55.0 (7dry), the shrinkage strain due to drying shrinkage does not increase significantly. This is thought to be because the water content (unit water content) W in Example 1 is low. In other words, water not used in the cement hydration reaction remains in the gaps in the artificial lightweight fine aggregate, which causes drying shrinkage, but because the unit water content W is small, the amount of residual water is reduced, and it is believed that drying shrinkage is suppressed. Furthermore, as a result of the reduction in the amount of residual water, frost resistance is improved. Frost damage occurs when the water contained in the voids in the concrete repeatedly freezes, expands, and melts, causing repeated stress on the concrete. The reduction in residual water suppresses stress, and it is believed that, as shown in Figure 1 (a), fluctuations in the relative dynamic modulus of elasticity and mass reduction rate are suppressed.

It is considered that the same results as those of each embodiment can be obtained when the unit water content W is in the range of 110 to 140 kg/ ^m3 , or in the range of about 125 to 140 kg/ ^m3 , and especially in the range of about ±5 kg/ ^m3 around 130 kg/ ^m3 (about 125 to about 135 kg/ ^m3 ). The only difference between the embodiments 1 and 3 is the water-binder ratio W/B, and the embodiment 1 (W/B=18) is slightly better in frost resistance than the embodiment 3 (W/B=20), but both have sufficient frost resistance. Therefore, it is preferable that the water-binder ratio W/B is at least in the range of 18 to 20%. In addition, by including PP (polypropylene fiber) (embodiment 6), the frost resistance is further improved. As the fiber, organic fibers other than 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 obtained even if only a part of the fine aggregates is artificial lightweight fine aggregate.

By using artificial lightweight fine aggregate as fine aggregate, the fluidity is greatly improved compared to 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 passing time is the time from the moment the cone is lifted until the diameter of the concrete expands to 50 cm, and is one of the indicators of concrete fluidity. Since the slump flow value of Comparative Example 2 did not reach 50 cm, there is no measurement value. The difference between Example 4 and Comparative Example 2 is the type of fine aggregate. Example 4 uses artificial lightweight fine aggregate as fine aggregate, and Comparative Example 2 uses crushed sand as fine aggregate. Comparative Example 2 uses a larger amount of high performance water reducing agent (SP) than the Examples, but the slump flow value is extremely smaller than the Examples. In other words, extremely high fluidity is obtained by using artificial lightweight fine aggregate as fine aggregate.

Figure 4 (a) shows the relationship between the accelerated age and the accelerated carbonation depth for Examples 1 and 3 and Comparative Example 1, and Figure 4 (b) shows the mix ratios for Examples 1 and 3 and Comparative Example 1. The accelerated carbonation depth was determined based on JIS A1153:2012 "Accelerated carbonation test method for concrete". Concrete is neutralized by the reaction of carbon dioxide in the atmosphere with calcium hydroxide in the concrete. Carbonation of concrete increases the possibility of corrosion of reinforcing bars. Therefore, the resistance of concrete to carbonation is one of the indicators of long-term durability of concrete, similar to frost resistance. If the accelerated carbonation depth is 25 mm or less 26 weeks after the start of the accelerated test, it is evaluated as having sufficient carbonation resistance. Although there is only data up to 13 weeks for Examples 1 and 3, it is considered that they have sufficient carbonation resistance in comparison with Comparative Example 1.

Figure 5(a) shows the relationship between material age and compressive strength for Examples 1-3, 7 and Comparative Example 1, while Figure 5(b) shows the mix proportions for Examples 1-3, 7 and Comparative Example 1. Figure 5(a) shows the relationship between material age and compressive strength for standard cured test specimens. Examples 1-3, 7 have greater compressive strength than Comparative Example 1. It is generally believed that the smaller the water-binder ratio W/B, the higher the compressive strength of concrete, and this general tendency is confirmed from Figure 5(a).

FIG. 6(a) shows the relationship between compressive strength and Young's modulus for Examples 1 to 3, 7 and Comparative Example 1, and FIG. 6(b) shows the mix ratios for Examples 1 to 3, 7 and Comparative Example 1. 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. 6(a) shows examples of γ=2.4 t/m ³ and 2.1 t/m ^3. Examples 1 to 3 and 7 show Young's modulus values that exceed the value obtained by multiplying the calculated value by 0.8 for γ=2.4 t/m ^3. Although artificial lightweight aggregate is softer than crushed sand and the Young's modulus tends to decrease accordingly, Examples 1 to 3 and 7 show satisfactory performance in terms of Young's modulus (rigidity).

Table 5 shows the mix proportions 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 uses a different lot from Example 1, but has the same mix proportions. The materials used in Examples 8 to 14 and Comparative Example 4 are basically the same as those used in Examples 1 to 7 and Comparative Examples 1 to 3.

Table 7 shows the fresh test results for Examples 8 to 14 and Comparative Example 4. The fresh tests were conducted in the same manner as the fresh test shown in Table 4. All showed better fluidity than Comparative Example 2 in Table 4, confirming that high fluidity can be obtained by using artificial lightweight fine aggregate as the fine aggregate. As will be described later, it is believed that the fluidity of Comparative Example 4 was reduced because there was more fine aggregate compared to the water and binder.

Figure 7 shows the compressive strength for Examples 8 to 14 and Comparative Example 4. In the figure, "90°C sealed σ7" refers to the compressive strength after concrete was poured and sealed in a 90°C environment for 7 days, "standard σ28" refers to the compressive strength after concrete was poured and cured in water for 28 days, and "20°C sealed σ7" refers to the compressive strength after concrete was poured and sealed in a 20°C environment for 7 days. Examples 8 to 14 and Comparative Example 4 achieved a level of compressive strength that was acceptable for practical use. Also, as in Figure 5, a tendency was confirmed for the compressive strength of concrete to increase as the water-binder ratio W/B decreased.

Figure 8(a) shows the relative dynamic modulus of elasticity up to 150 cycles for Examples 8 to 14 and Comparative Example 4. For Examples 8 to 11 and Comparative Example 4, the relative dynamic modulus of elasticity was measured up to 300 cycles, and is shown separately in Figure 8(b). Figure 9 shows the mass reduction rate for Examples 8 to 14 and Comparative Example 4. The relative dynamic modulus of elasticity 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 modulus of elasticity fell below 60% of the initial value at about 150 cycles, whereas in Examples 8 to 11, values equivalent to the initial value were obtained even after 300 cycles. For Examples 12 to 14, only measurement results up to 150 cycles were obtained, but judging from the tendency up to 150 cycles and Figure 8(b), it can be evaluated that the relative dynamic modulus of elasticity at 300 cycles is at least 60% or more. In Comparative Example 4, the mass reduction rate decreased around 150 cycles and then tended to recover. In contrast, in Examples 8 to 14, the mass reduction rate was less than 1% or negative (mass increased). Note that Figure 8(b) also shows the data for Example 1, and Examples 1 and 8, which have the same composition, showed almost the same results, confirming the reproducibility of the test results.

Fig. 10 shows the relationship between the unit amount of water W (kg/ ^m3 ) and the water-binder ratio W/B (%). In comparison with Fig. 8, the relative dynamic modulus of elasticity is 60% or more at 300 cycles in trapezoidal region A defined by W being 110 or more and 150 or less, and W/B being 18 or more and (0.168 x (W-110) + 20) or less, and preferably in trapezoidal region B defined by W being 110 or more and 140 or less, and W/B being 18 or more and (0.168 x (W-110) + 20) or less. In this region, the mass reduction rate is less than 1% or is negative (mass increases) in the range of 0 to 300 cycles. Therefore, in terms of the relationship between the unit amount of water W (kg/ ^m3 ) and the water-binder ratio W/B (%), region A is preferable, and region B is more preferable.

Figure 11 shows the relationship between air volume and durability index DF. Durability index DF is an index for evaluating the frost resistance of concrete, as defined in JIS A1148:2010 "Freeze-thaw test method for concrete," and generally, a value of 60 or higher is considered to be frost-resistant.

FIG. 12 shows the relationship between vs/vp and standard σ28. vs indicates the unit absolute volume of fine aggregate, and vp indicates the unit absolute volume of paste. FIG. 13 shows the relationship between unit fine aggregate amount (kg/m ³ ) and standard σ28. As can be seen from Table 5, Comparative Example 4 has a large amount of fine aggregate and small amounts of cement and water. For this reason, it is considered that sufficient compressive strength was not 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 modulus of elasticity is 60% or more at 300 cycles. 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 modulus of elasticity is 60% or more at 300 cycles. In these regions, the mass reduction rate is less than 1% or is negative (mass increases) in the range of 0 to 300 cycles.

Fig. 14 shows the shrinkage strain for Examples 8 to 11 and Comparative Example 4. Fig. 14(a) shows the shrinkage strain when sealed at 20°C, and Fig. 14(b) shows the shrinkage strain when sealed at 20°C until the material was 7 days old and then cured in air at 20°C and a relative humidity of 60%. No shrinkage was observed when sealed at 20°C for Examples 8 to 11 and Comparative Example 4. When sealed at 20°C until the material was 7 days old and then cured in air, the shrinkage strain progressed to about 200 x ^10-6 , but this is suppressed compared to the case shown in Fig. 3.

Figure 15 shows the relationship between unit water content and shrinkage strain, and Figure 16 shows the relationship between W/B and shrinkage strain. It can be seen that unit water content and W/B do not have a significant effect on shrinkage strain.

Claims (8)

The method includes the steps of: forming a concrete structure using a binder, water, and fine aggregate; and forming a concrete structure using the binder and water;
A concrete composition in which, when the unit water content of the water is W (kg/m ³ ) and the water-binder ratio is W/B (%), W is 110 or more and 140 or less, and W/B is 18 or more and (0.168×(W−110)+20) or less. The method includes the steps of: providing a binder, water, and fine aggregate, the binder including cement, and the fine aggregate including lightweight fine aggregate;
A concrete composition in which, 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 140 or less, and vs/vp is 0.67 or more and 1.00 or less. The method includes the steps of: forming a concrete structure using a binder, water, and fine aggregate; and forming a concrete structure using the binder and water;
The water content per unit weight W (kg/m ³ ) is 110 or more and 140 or less, and the fine aggregate content per unit weight W (kg/m ³ ) is 515 or more and 655 or less. 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. 6. The concrete composition according to claim 1, wherein the fine aggregate comprises an artificial lightweight fine aggregate. The concrete composition of claim 1 , further comprising organic fibers. 8. The concrete composition of claim 1, wherein the binder comprises silica fume.

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