JP2014080367A - Fly ash concrete - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a reduction in early strength and improve workability of concrete using fly ash as an admixture to promote the practical use thereof.SOLUTION: In using fly ash as an admixture for concrete, 10 to 40% (preferably 20 to 30%) of the total volume of coarse aggregate or fine aggregate is substituted with artificial aggregate of clay fired at high temperature such as waste roof tiles. The early strength equivalent to that of ordinary concrete can be obtained with a low water-to-cement ratio (15 to 30%) using less amount of mixing water. In contrast, good workability is obtained with a high water-to-cement ratio (30 to 55%), which results in extremely high fluidity.

Description

  The present invention relates to concrete using fly ash as an admixture.

Conventionally, it has been widely known to use pozzolanes such as fly ash as concrete admixtures. Pozzolana reacts with calcium hydroxide released during the hydration reaction of cement to produce calcium silicate hydrate (CSH) (so-called pozzolanic reaction), and the skeletal structure of concrete formed by the hydration reaction. It has the effect of reinforcing the body and increasing the strength of the concrete in the long run.

  In particular, fly ash is a kind of ash (coal ash) generated when combusting finely pulverized coal in a coal-fired power plant, and since it is a spherical fine particle, There is also an advantage that fluidity is improved (ball bearing effect).

  However, since concrete containing fly ash has lower strength (early strength) at a young age than ordinary concrete and requires a relatively long wet curing period, it is mostly used for structural members. The fact is not.

The early strength of concrete decreases due to the mixing of fly ash because the amount of cement is reduced by the amount of fly ash mixed in the inner part, and the water-cement ratio (W / C) is relatively low.
On the other hand, it is considered that the progress of the pozzolanic reaction takes longer than the hydration reaction of the cement, etc., whereas in Patent Document 1, fly ash is 4000 cm ² in terms of the specific surface area of brain. The technology of accelerating the development of the strength of concrete by ultra-fine pulverization so as to be over / g, kneading with an alkaline reaction accelerator solution of 7% or less, heating and pressurizing at a high temperature below the boiling point of water. Proposed.

JP-A-9-118556

  However, it is not easy to finely pulverize fly ash as in the above proposal, and there is a difficulty in increasing the cost, and further, concrete is kneaded with an alkaline reaction accelerator solution, heated and pressurized. Naturally, however, it is costly and causes great problems in workability.

  On the other hand, in the high-strength concrete having a low water-cement ratio, the inventors of the present application replace water with a crushed waste tile in advance and replace a part of the aggregate, so that moisture for cement hydration reaction is obtained. A patent application has already been filed (for example, Japanese Patent Application No. 2008-81739), with the knowledge that the strength development is accelerated by the promotion of the hydration reaction (so-called internal curing). Etc.).

  Using the effect of promoting the hydration reaction due to such internal curing, the present inventor conducted intensive and experimental studies to improve the early strength of fly ash concrete. Thus, the synergistic effect of further promoting the hydration reaction was found, and the present invention was completed.

  That is, the present invention focuses on internal curing by waste tiles and the like, and is based on a completely new finding that the hydration reaction of cement and the pozzolanic reaction of fly ash are synergistically promoted. The purpose of this invention is to suppress the early drop in strength of fly ash and concrete and to promote its practical use without causing an increase in cost.

  In addition, it is known that fly ash and waste tiles are mixed in concrete, but these are only for recycling waste materials, and the above-mentioned effects by using both simultaneously are not reported. In addition, there is no example of mixing fly ash and waste tile, which are waste materials, into concrete at the same time for recycling.

  The invention according to claim 1 of the present application is an artificial aggregate obtained by kneading at least water, cement, and aggregate, and by crushing waste tile into the aggregate in fly ash concrete containing fly ash as an admixture. Is included.

  In such an artificial aggregate, water is consumed by the hydration reaction of the cement during the hardening process of the concrete as disclosed in the prior application of the present inventors (Japanese Patent Application No. 2008-81739). In response, water is supplied into the pores of the concrete (internal curing). In this way, the uniform water supply in the concrete promotes the hydration reaction of the cement and also promotes the pozzolanic reaction of fly ash, which consumes the hydration product and thereby the hydration reaction. Will be further promoted.

  The reason why the pozzolanic reaction is promoted by internal curing is not clear, but the pozzolanic reaction is originally triggered by hydroxide ions released by the hydration reaction of the cement, and the state of low water In this case, calcium hydroxide does not dissolve, but if there is too much water, the concentration of hydroxide ions does not increase and the pozzolanic reaction cannot be induced. In this respect, it is considered that the supply of water from the artificial aggregate as the water is consumed by the cement hydration reaction as described above favors the progress of the pozzolanic reaction.

  In this way, the internal hydration synergistically promotes the cement hydration reaction and the fly ash pozzolanic reaction, strengthening the skeleton structure of the concrete relatively early. The decrease can be suppressed. In addition, the product of the pozzolanic reaction fills the pores of the hydrated product of cement, densifying the concrete and improving its durability.

  In addition, the fluidity of fresh concrete is increased by the ball bearing effect of fly ash, so it is excellent in workability, and accordingly, the water binder ratio (volume ratio of water to cement and fly ash) during mixing is lowered. Can do. Even in such a case, as with the high-strength concrete according to the previous application, the hydration reaction of the cement will be sufficiently accelerated by the internal curing effect, so there is a possibility that early strength exceeding that of ordinary concrete may be obtained depending on the curing conditions. There is.

  In order to sufficiently obtain such an effect, it is preferable to replace 10 to 40% of the total volume of the aggregate with an artificial aggregate for internal curing. If the replacement rate is less than 10%, the internal curing effect may not be sufficiently obtained. On the other hand, the strength of the artificial aggregate is lower than that of natural aggregate. If the replacement rate is too high, the strength of the concrete is adversely affected. This is because there is a risk of effect.

  More specifically, since the degree of the above-mentioned effect varies depending on the amount of water in the concrete, the appropriate value of the aggregate replacement rate that determines the amount of water supplied by internal curing is a balance with the amount of water mixed. There seems to be an appropriate range. According to the experiments by the present inventors, it is considered more preferable in terms of increasing the strength that the replacement rate with the artificial aggregate is 20 to 30% and the water binder ratio at the time of kneading is 20 to 35%. It is done.

  In this way, the mixing water is not so much and the pores of the concrete are made small, while the sufficient curing effect by water supply from the artificial aggregate is obtained, and the effect of promoting the strength expression of fly ash concrete is very effective To be high. In the above-mentioned range, basically, the lower the aggregate replacement rate, the higher the water binder ratio is preferable. However, it is considered that the influence of curing conditions should be considered.

  At that time, the proportion of fly ash mixed internally should be 30% or less in terms of the mass ratio when expressed as the replacement rate of cement, and the amount of cement contained in fly ash is considered to be small. For example, 20% or less is considered preferable in order to sufficiently obtain the above effect. According to the experiments by the present inventors, it was found that when the fly ash mixing ratio was suppressed to about 10%, the strength development was promoted even when the water binder ratio during mixing was 35 to 55%.

  Artificial aggregates having a water absorption rate of at least 5%, preferably 8% or more, are immersed in water for 3 days or more in advance, so that the moisture content is a surface dry state or a wet state with a water absorption rate or more. It is good to do.

  If waste tiles crushed as artificial aggregates as described above are used, waste materials can be recycled and the cost merit is great, but this is not restrictive.For example, for high-temperature firing such as clay for clay and clay for ceramics. Artificial aggregates can also be produced by kneading durable clay with a vacuum kneader or the like, granulating to a predetermined size, and firing at a temperature of about 950 to 1150 ° C.

  The artificial aggregate produced in this way, like waste tiles, is higher in density and strength than conventional artificial lightweight aggregate, so even if the aggregate is replaced up to about 40%, the strength of the concrete will be adversely affected. There is no worry about In addition, the artificial aggregate produced in this way is unlikely to receive minute damage during crushing like a waste tile, and the variation in strength and water absorption characteristics is reduced, so that the operational effects of the invention described above are more stable. It is expected to be obtained.

  As described above, according to the fly ash concrete according to the present invention, by synthesizing the cement hydration reaction and the fly ash pozzolanic reaction by internally curing using artificial aggregate made of waste tiles and the like. This can be promoted, thereby suppressing an early decrease in strength due to the mixing of fly ash. This significantly improves the workability in combination with excellent workability.

  In addition, the effect of shrinkage of concrete and suppression of cracks can be obtained by internal curing, and further, the concrete is densified by promoting the pozzolanic reaction, thereby increasing resistance to salt damage and neutralization and improving durability. To do.

It is a graph which shows an example of the compressive strength ratio in the age of 7 days of the fly ash concrete which concerns on embodiment of this invention. It is a graph which shows a time-dependent change of the moisture content of the waste tile which substitutes aggregate. It is a figure of the test result which investigated the compressive strength in the material age 7 days of the test body of Example 1. FIG. FIG. 3 is a view corresponding to FIG. 3 for the same material age 28 days. It is a figure which shows the test result of the split tensile strength about the same material age 7th and 28th. It is a figure of the test result which investigated the cumulative pore volume about the test piece of the sealing curing. It is a figure of the test result which investigated pore size distribution when a water binder ratio is 50%. FIG. 8 is a diagram corresponding to FIG. 7 for a water binder ratio of 30%. FIG. 8 is a diagram corresponding to FIG. 7 for a water binder ratio of 20%. It is a figure of the test result which investigated the mode of self contraction about the specimen of an example. It is the FIG. 3 equivalent view which added the test result about Example 2 (G20FA20). FIG. 5 is a view corresponding to FIG. 4 with the same test result added. It is a graph which shows the mode of intensity | strength expression in the case of B / W = 5. It is FIG. 13 equivalent figure which shows the change of the intensity | strength expression by the difference in curing conditions. FIG. 8 is a view corresponding to FIG. 7 with the same test result added. FIG. 9 is a view corresponding to FIG. 8 with the same test result added. FIG. 10 is a diagram corresponding to FIG. 9 to which the test results have been added. FIG. 11 is a view corresponding to FIG. 10 with the same test result added.

  Hereinafter, embodiments of the present invention will be described in detail. It should be noted that the following description of the preferred embodiment is merely illustrative in nature, and is not intended to limit the present invention, its application, or its use.

(Concrete mix)
The concrete according to the present invention is obtained by kneading water, cement, aggregate, admixture and the like, and in particular, fly ash is used as the admixture. Specifically, various ordinary cements such as ordinary Portland cement, low heat Portland cement, medium heat Portland cement, early strong Portland cement, blast furnace cement, silica cement and the like can be used. As will be described later, fly ash cement can be used as long as it does not exceed a predetermined ratio together with fly ash mixed as an admixture.

  Among the admixtures, examples of the admixture include water reducing agents, AE agents, antifoaming agents, and shrinkage reducing agents. In particular, when reducing the water binder ratio at the time of kneading to increase the strength, it is preferable to add a high-performance water reducing agent from the viewpoint of satisfactorily dispersing cement particles. A shrinkage reducing agent may be added to reduce the self-shrinkage of concrete.

  In addition to fly ash, admixtures include silica fame, fine powder of blast furnace slag, expansion material, etc. Generally, when fly ash is mixed, self-shrinkage is reduced, and it consists of waste tile as described below. Since the shrinkage of concrete is reduced by the use of artificial aggregates, the need for further expansion material is low.

  Aggregates are generally classified into fine aggregates having a particle size of less than 5 mm and coarse aggregates having a particle size of 5 mm or more. The fine aggregate includes natural aggregate such as sand, and the coarse aggregate includes natural aggregate such as gravel and crushed stone. In this embodiment, as a main characteristic part of the present invention, an artificial bone formed by crushing waste tiles. Contains wood. Since waste tiles are considerably stronger than conventional general artificial lightweight aggregates, there is no fear of adversely affecting the strength of concrete even if 40% of aggregates are replaced.

  The artificial aggregate preferably has a water absorption rate of 5% or more, and more preferably 8% or more for internal curing described below. The water absorption is the absolute dry state by completely wiping away the surface water of the so-called wet aggregate to make the surface dry and saturated (surface dry state), and further drying to a constant mass at 100 to 110 ° C. As described above, using the mass A in the absolute dry state and the mass B in the surface-saturated saturated water state, the water absorption rate is expressed as (BA) / A × 100 (%).

  If such an artificial aggregate is immersed in water for about 3 days or more in advance and sufficient water is contained in the voids (pores), water is appropriately contained in the concrete pores during the concrete hardening process. Can be supplied (internal curing effect). That is, if the water-absorbed artificial aggregate is widely dispersed in the concrete, water is consumed by the hydration reaction of the cement in the concrete pores in the hardening process, and the water pressure in the pores decreases. Accordingly, water is quickly supplied from the nearby artificial aggregate, and the hydration reaction of cement is always promoted in the presence of sufficient reaction water.

  In addition, since the required amount of water is always present in the pores of the concrete, the calcium hydroxide produced during the hydration reaction of the cement quickly dissolves in the water, and the hydroxide ions It is thought that fly ash's pozzolanic reaction is triggered. That is, the hydroxide ion concentration of water contained in the pores of the concrete becomes a state suitable for promoting the pozzolanic reaction.

  Thus, when the pozzolanic reaction of fly ash is accelerated, the hydration reaction of the cement is further accelerated by the consumption of calcium hydroxide (hydroxide ions). By synergistically promoting the hydration reaction and the pozzolanic reaction of fly ash, the strength development of the concrete is accelerated and the early decrease in strength due to the mixing of fly ash is suppressed.

  Specifically, in the fly ash concrete of this embodiment, as shown in FIG. 1, the improvement in strength is already seen at the age of 7 days. That is, as will be described in detail later, (a) to (c) in the figure are fly ash concrete (based on normal concrete strength (□)) for air curing, sealing curing, and water curing, respectively. The strength ratio of (○) and those replaced with waste tiles (●) are shown for each binder water ratio (B / W).

It can be seen from the figure that the strength reduction is suppressed by the replacement of the waste tile in the case of (a) air curing and (b) sealing curing. In other words, in the case of (a) air curing, all the B / W shown in the figure, and in the case of (b) sealed curing, when B / W ≧ 3.3, The strength of concrete (●) exceeds about 90% of ordinary concrete (□), and the effect is higher when the water is relatively low (when B / W is large).

In particular, the strength (●) of fly ash concrete replaced with waste tile when B / W = 5 is
Both sealed and in the air are equivalent to ordinary concrete (□), and high early strength is obtained by compensating for the weight loss of cement by mixing fly ash. The result of air curing is that fly ash concrete, which is deframed in one day after construction and dried in the air, has the same early strength as ordinary concrete, despite severe conditions. It can be said that it contributes to a drastic improvement in workability and shortening the construction period.

In the case of (b) sealed curing, the strength is rather reduced when there is relatively much mixing water (B / W ≦ 2.8 in the example in the figure), and (c) in the case of underwater curing In addition to the fact that no improvement in strength is observed regardless of the amount of water, the strength decreases rather as the amount of water increases (B / W ≦ 3.3). This is because the effect of internal curing is almost lost when there is a lot of mixing water, and it is considered that the pores of the concrete are enlarged due to the excess water, leading to a decrease in strength.

  From the above, according to the fly ash concrete according to this embodiment, first, by using an artificial aggregate made of waste tiles and internally curing, the early decrease in strength due to the mixing of fly ash is effectively suppressed. If the amount of water at the time of kneading is reduced, depending on the curing conditions, it is possible to ensure an early strength comparable to that of ordinary concrete. Even if there is little mixing water, the fall of workability is complemented by the high fluidity of fly ash.

On the other hand, from the graph in Fig. 1 (a), which shows the case of air curing, there is an early drop in strength due to the mixing of fly ash even when the amount of mixing water is relatively high (B / W ≤ 3.3). It turns out that it is suppressed. Therefore, if it is cured in the air, by adding a relatively large amount of mixing water, combined with the ball bearing effect of fly ash, the fluidity of the fresh concrete becomes extremely high and workability is particularly excellent.

  In other words, in fly ash concrete, which generally has excellent workability but is required to have a long-term wet curing, it is possible to remove the frame early after placing, compared to the past. Combined with excellent workability, the workability is greatly improved and the construction period can be shortened.

  In addition, the original characteristics of fly ash and concrete are that long-term strength is enhanced by pozzolanic reaction and concrete is densified, and it is durable in combination with reduction of concrete shrinkage and suppression of cracking due to internal curing. It becomes a very high thing.

  In addition, in this embodiment, it is assumed that about 10 to 40% of the total volume of the aggregate is replaced by the crushed waste tile that is an artificial aggregate. From the viewpoint of enhancing the internal curing effect, the replacement rate is A higher value is preferable, but it is considered that the aggregate replacement rate has a particularly preferable range in view of the mixing water amount and curing conditions from the viewpoint of developing the early strength of concrete. The artificial aggregate may be replaced with either coarse aggregate or fine aggregate. However, if the fine aggregate has the same volume, the number of particles is larger than that of the coarse aggregate. If the replacement ratio with the material is increased, the dispersibility is increased, the contact area with the cement is increased, and the internal curing function is further enhanced.

Example 1
Next, the actual test results will be described. First, Table 1 shows the materials used for the test specimens. In this example, artificial aggregates (waste coarse aggregate: CG) obtained by crushing waste tiles are immersed in water, and the water content becomes the water absorption rate. After almost reaching, it is replaced with coarse aggregate. In addition, as shown in FIG. 2, when the waste tile coarse aggregate CG used for the test is immersed in water for 3 days or more from the storage state, the water content becomes stable and becomes approximately 8% or more. Even if it is completely dried, if it absorbs water for 3 days, the water content becomes 8% or more, and it stabilizes in about 10 days.

  In Table 2, (a) to (c) are water binder ratios (W / B) of 0.5, 0.3, 0.2 (B / W = 2, 3.3, 5 respectively). The composition of the test specimen is shown. NC: Neither waste tile nor fly ash is replaced, G40NC: 40% of the total volume of coarse aggregate is replaced with waste tile, FA20: 20% of cement is replaced with fly ash by volume And G40FA20: replacement of both waste tiles and fly ash as described above. In FIGS. 3 to 10 described later, NC is a □ graph, and G40NC is a ■ graph. , FA20 is indicated by a circle, and G40FA20 is indicated by a ●.

Thus, 12 types of specimens with different compositions were each cured in air (exposed to room temperature 20 ° C. and humidity 60% after being cured for one day in the mold), sealed curing (room temperature 20 ° C., humidity 60 % Curing in the mold until the age of the strength test material) and underwater curing (water temperature 20 ° C.) for the strength test, pore size distribution test and self-shrinkage test described below. Provided. The binder amount B in the binder water ratio (B / W) is the sum of cement C and fly ash FA, and the water amount W is the amount of kneaded water that is absorbed by the waste tile. The amount of water is not considered.

1) Strength test The compressive strength was in accordance with the concrete compression test method (JIS A1108), and the splitting tensile strength was in accordance with the concrete splitting tensile strength test method (JIS A1113). First, FIGS. 3 and 4 show the compressive strength at the age of 7 days and 28 days, respectively. In each figure, graphs (a) and (d) are air curing, (b) and (e) are sealed curing, and (c) and (f) are underwater curing. a) to (c) show the measured values of compressive strength, and the three graphs (d) to (f) arranged on the right side thereof show the compressive strength ratio based on NC.

  In the graph of the compressive strength ratio, the difference in compressive strength for each specimen is slightly exaggerated. For example, in the graph of Fig. 3 showing the compressive strength at 7 days of age, in the case of (d) air curing and (e) sealing curing, both have a relatively low water binder ratio (when B / W is large) G40NC has a higher intensity ratio than NC, and G40FA20 has a higher intensity ratio than FA20. That is, the strength improvement effect by the water supply (internal curing) from a waste tile becomes high, so that there is little mixing water.

  Therefore, as the B / W value increases, the compressive strength ratio of G40FA20 to NC increases, and in the example shown in the figure, when B / W = 5, (d) air curing and (e) sealing curing In both cases, the strength ratio of G40FA20 is equivalent to NC. In other words, because fly ash is mixed in, the amount of cement is small, but early strength comparable to that of ordinary concrete is obtained, and fly ash concrete generally requires long-term wet curing, In particular, the test results in the case of air curing are remarkable.

On the other hand, when the water binder ratio is relatively high (when B / W is small), the strength ratio of G40NC is lower than that of NC. Rather it seems to have a bad influence. However, in the case of air curing, G40FA20 even when the water binder ratio is high
The strength ratio is higher than FA20, exceeding 90% of NC. In other words, it can be said that fly ash concrete has an early strength improvement effect due to internal curing even in a relatively mixed water state.

  In the case of air curing, this is considered to be due to the fact that water is rapidly dissipated from the specimen exposed to the room after the frame is removed, so that it is likely to be relatively water-deficient. In fly ash concrete, the calcium hydroxide produced by the cement hydration reaction dissolves in water and triggers the pozzolanic reaction. It is thought that the effect of internal curing can be obtained even in many states.

The same tendency as described above also appears in the graph of FIG. 4 showing the compressive strength at the age of 28 days. Particularly, in the case of (d) air curing, the effect of improving the strength of fly ash concrete by internal curing is high. I understand that. In addition, in the case of underwater curing shown in FIGS. 3 and 4 (f), even when the water binder ratio is the lowest (B / W = 5), strength improvement by internal curing is hardly seen. This is considered to be due to the fact that there is sufficient reaction water in the case of underwater curing.

  Although detailed explanation of the split tensile strength is omitted, as shown in the graph of the strength ratio of the 7th and 28th ages in FIG. 5, there is an effect of improving the early strength generally similar to the compressive strength, and the crack resistance. (Figs. 5 (a) to (c) show the age of 7 days, and (d) to (f) show the age of 28 days).

2) Pore size distribution test The pore size distribution was determined by collecting only the central mortar part from the specimen for sealing curing immediately after the strength test described above, stopping the hydration, and then using a mercury intrusion method porosimeter. The pore volume was measured.

FIG. 6 shows the cumulative pore volume for each binder water ratio (B / W) at a material age of 7 days and 28 days. At the age of 7 days ((a) in the same figure), G40NC had the smallest void in any binder water ratio. In the other three formulations (NC, FA20, G40FA20), no significant difference can be confirmed. In addition, at 28 days of age ((b) in the same figure), a decrease in voids was observed in FA20 and G40FA20 with a decrease in the water binder ratio. At B / W = 5, G40FA20 has less air gap than NC. In any of the blends, the voids decreased on the material age 28 compared with the material age 7 days.

FIG. 7 shows the pore size distribution of B / W = 2 at the age of 7 and 28 days, and FIGS. 8 and 9 show the pore size distribution of B / W = 3.3 and 5 respectively. For example, in the cumulative pore volume at the age of 7 days shown in (a) of each figure, there is no significant difference for each formulation. On the other hand, looking at the pore size distribution (B / W = 2) shown in FIG. 7 (b), relatively large (0.4 to 4.0 μm) pores are reduced by the replacement of the waste tile, and the concrete becomes denser. A trend can be confirmed.

In addition, comparing (b) and (d) in the figure, the 0.1 to 0.4 μm pores of fly ash concrete (G40FA20, FA20) decreased from 7 to 28 days of age. It can be seen that the pores are filled by the progress of the pozzolanic reaction, and the concrete is densified. In particular, G40FA20 has fewer fine pores than G40NC at the age of 28 days, indicating that the pozzolanic reaction is promoted by internal curing.

When the water binder ratio is relatively low (B / W is large), the results are as shown in FIGS. 8 and 9, respectively. As in the case of B / W = 3.3, the effects of fly ash mixing and internal curing Although the effect of this is not clear, as in the case of B / W = 5, densification due to the effect of mixing fly ash and the effect of internal curing is observed in the pore diameter range of 0.1 to 0.3 μm. In general, it can be said that there is an effect of both.

3) Self-shrinkage test The self-shrinkage amount is measured with a laser displacement meter (accuracy 1 / 1000mm) for 24 hours from the start of concrete setting, with steel bolts fixed on both sides in the long axis direction of the specimen. The length change was measured by the contact gauge method. The specimen is a concrete specimen of 100 × 100 × 400 mm. Measures to prevent free deformation of concrete from being constrained by the formwork conformed to the “Concrete Self-Shrinkage Stress Test Method” (Japan Concrete Institute, JCI Standards Collection).

  FIG. 10 shows the self-shrinkage strain and the drying shrinkage strain at a water binder ratio of 20% (B / W = 5) and 30% (B / W = 3.3). The downward branching after the age of 7 days indicates the drying shrinkage strain when the frame is unframed and dried in the air at the age of 7 days.

It can be seen from FIGS. 4A and 4B that self-shrinkage is suppressed by internal curing (G40NC, G40FA20). The self-shrinkage strain at the age of 28 days is reduced by about 80% regardless of the presence or absence of fly ash, but with the mixture containing fly ash (G40FA20), the strain until the age of 7 days is also very small, 0-50 μm. It can be said that it is preferable. In addition, the tendency of drying shrinkage shows the same grade regardless of the presence or absence of internal curing.

Based on the above test results, the fly ash concrete (G40FA20) of Example 1 effectively suppresses the early decrease in strength due to the mixing of fly ash by internal curing, and lowers the water binder ratio during kneading. As a result, it was found that early strength equivalent to that of normal concrete (NC) was obtained, concrete was densified and durability was improved, and further, effects such as shrinkage reduction and crack suppression were obtained.

(Example 2)
Next, Example 2 in which the influence of the replacement rate of waste tiles and fly ash was examined will be described. The specimen was a waste tile with a volume replacement rate changed to 20% (G20FA20), and the water binder ratio (W / B) was 0.5, 0.3, and 0.2. For W / B = 0.5, a test was also conducted for one in which 10% of the cement was replaced with fly ash (G20FA10) and for which no waste tile replacement was performed (FA10). Table 3 shows the composition of the specimen.

1) Strength test FIGS. 11 and 12 show the compressive strength at the age of 7 days and 28 days, respectively. In each figure, graphs (a) and (c) are the results of sealing curing, (b) and (d) are the results of underwater curing, and the graphs (a) and (b) on the left as in FIGS. Graphs (c) and (d) on the right show the compression strength ratio. In addition, □ indicates NC, ○ indicates FA20, ● indicates G40FA20, and G20FA20, which was retested this time, is indicated by a ▲ graph. NC (□) is not shown in the graph because the intensity ratio = 1.

In particular, as apparent from FIGS. 12 (c) and 12 (d), at the age of 28 days, the strength ratio of G20FA20 is significantly higher than that of G40FA20 in both sealing and underwater curing. (c) In case of sealed curing, higher strength than NC is obtained regardless of water binder ratio. (d) Even in case of underwater curing, strength higher than NC is obtained if B / W ≧ 3. ing. It is unprecedented that the early strength of fly ash concrete is increased like this, and it can be said that it has a wonderful effect.

If you look closely, the strength ratio of G20FA20 as a whole is B / W ≧ 3, that is, it is high when the amount of mixing water is small, but when B / W = 3-5, it decreases slightly as the amount of water decreases. The intensity ratio is decreasing, and it seems to be particularly high at around B / W = 3. On the other hand, the strength ratio of G40FA20 is B / W
= 3-5 also increases as the amount of water decreases. This suggests that the substitution rate for determining the amount of water absorbed from the waste tiles has an appropriate range for the water binder ratio in consideration of the amount of mixing water.

  That is, as described above, the effect of the present invention that promotes the strength expression of fly ash concrete by internal curing varies depending on the amount of water in the concrete, and the replacement rate of waste tile includes the amount of mixed water and It is considered that there is a preferable range in consideration of curing conditions. Comparing Examples 1 and 2, the substitution rate is particularly preferably about 20 to 30% even within the range of 10 to 40%. The water binder ratio at the time of kneading corresponding to this substitution rate is B / W = About 3 to 5 is considered preferable.

A similar tendency also appears in the graph of age 7 days in FIG. 11 and, of course, the strength is lower than that of the age of 28 days as a whole, but (c) G20FA20 (▲) of the sealing curing B NC at / W ≧ 3
(D) Even underwater curing is comparable to NC. That is, even at 7 days of age, G20FA20 has a higher strength ratio than G40FA20. Moreover, in G20FA20 of the age of 7 days, the tendency for a strength ratio to increase with a decrease in the amount of water is seen at B / W = 3-5.

FIG. 13 shows the fly ash replacement ratio of 10 for the least effective case of B / W = 2.
It is the result of improving the strength by reducing the content to 50%. In this figure, the horizontal axis of the graph indicates the age of the fly ash concrete with the passage of time. As shown in the figure, the compressive strength of the sealed G20FA10 (△) exceeded that of G20FA20 (▲) for 7 to 28 days. This is because the amount of cement contained in the fly ash is reduced. It is thought that it depends on the increase.

  In the example shown in the figure, the compressive strength of G20FA10 is reduced to NC (□) at 7 days of age, despite the large amount of mixing water (B / W = 2). Is over. Considering this together with the data of FIGS. 11 and 12, for example, the strength of G20FA10 when B / W = 3 to 5 is extremely high, and is expected to greatly exceed NC.

FIG. 14 shows the change in strength expression due to the difference in curing conditions. FIG.
In addition to the above-mentioned sealed curing (●: equivalent to Δ in FIG. 13), the three-day in-air (△) and the seven-day in-air (▲) were used for the test specimen (G20FA10, B / W = 2) The appearance of strength under conditions is shown. In addition, 3 days air and 7 days air are those exposed to the room after sealing and curing in the mold for 3 days and 7 days, respectively. The figure also shows the NC seal curing for comparison (□).

According to the figure, G20FA10 can obtain almost the same strength regardless of the curing conditions until the age of 7 days, and after that, the strength of the air curing for 3 days is slightly decreased until the age of 28 days. It turns out that it is above. In addition, higher strength is obtained in the air for 7 days or in the sealed curing. Furthermore, when the material age is 91 days, the strength of NC or higher is obtained in the air and sealed curing for 7 days.

The same tendency can be seen for G20FA20, B / W = 3.3, 5 in Figs. (B) and (c), but especially when B / W = 5 in Fig. (C), it depends on the curing conditions. The strength development of G20FA20 is fast and has already greatly exceeded NC at the age of 7 days. Further, only this graph shows the results up to the age of 28 days, but it can also be seen that the difference due to the curing conditions is small when B / W = 5. This is considered to be due to the fact that when there is relatively little mixing water, the water is scarce regardless of the curing conditions, and the internal curing effect due to the waste tile is high, so that the difference due to the curing conditions is difficult to appear.

2) Pore size distribution test FIGS. 15 to 17 show the results of the pore size distribution test corresponding to FIGS. 7 to 9 of Example 1, and the graph (■) of G40NC is deleted from those graphs, and instead of G20FA20 A graph (▲) is added. In both B / W = 3.3 (FIG. 16) and B / W = 5 (FIG. 17), it can be seen that relatively large pores are reduced and the concrete is densified in G20FA20. In particular, when B / W = 5, a tendency toward densification has already been seen from the age of 7 days, and this is considered to contribute to the above-described early strength development.

3) Self-Shrinkage Test FIG. 18 is a graph in which the G40NC graph (■) is deleted from FIG. 10 of Example 1 showing the state of shrinkage strain, and a G20FA20 graph (（) is added instead. The horizontal axis is not a logarithmic scale but a regular scale. In the case of B / W = 3.3 in FIG. (B), G20FA20 also shows the effect of suppressing self-contraction due to internal curing, similar to G40FA20. G20FA20 has almost no initial expansion. On the other hand, when B / W = 5 in FIG.

From the above test results, according to the fly ash concrete (G20FA20) of Example 2,
Compared to that of Example 1 (G40FA20), a higher compressive strength is expressed earlier,
Although the effect of promoting the strength development of concrete by internal curing varies depending on the water binder ratio and curing conditions during kneading, it is considered to be preferably about 20 to 30%.

  In addition, the pore size distribution and self-shrinkage data show that despite the fact that G20FA20 has a lower replacement rate of waste tile than G40FA20, the concrete is sufficiently densified and self-shrinkage is sufficiently suppressed. .

(Other embodiments)
In addition, the mixing | blending of the fly ash concrete which concerns on this invention is not limited to the thing of embodiment mentioned above. For example, the replacement rate of aggregate with waste tiles should be at least 10% or more of the total volume, and it is considered that 15 to 35% is preferable although it depends on the curing conditions and the amount of mixing water. Moreover, the substitution rate of fly ash should just be 30% or less, and about 10 to 20% is preferable. When fly ash cement is used, the substitution rate may be set in combination with those contained therein.

  The artificial aggregate is not limited to the waste tile as in the above-described embodiment, and a dedicated artificial aggregate obtained by granulating and firing tile clay or ceramic clay (ceramic clay) can also be used. The clay should just be what can endure high temperature baking to 1000-1200 degreeC.

  The fired artificial aggregate is not an irregular shape like crushed waste tiles, but contributes to improving the fluidity of fresh concrete, and allows multiple sizes of artificial aggregate to be distributed in the concrete by adjusting the particle size. By doing so, the internal curing effect can be obtained more uniformly, which is advantageous for both improving the strength of concrete and reducing its shrinkage.

  The present invention can increase the strength of so-called fly ash concrete and improve its workability, and since it can use waste tiles, it is low cost and has high industrial applicability.

Claims (4)

A concrete obtained by kneading at least water, cement, fine aggregate and coarse aggregate,
Contains fly ash as an admixture,
For the coarse aggregate, artificial aggregate obtained by crushing waste tiles, or clay for clay or ceramics is kneaded and granulated to a predetermined size and fired at a temperature of about 950 to 1150 ° C. The fly ash concrete is characterized in that 10 to 20% of the total volume of the coarse aggregate is contained. In the coarse aggregate, the artificial aggregate contains 20% of the total volume of the coarse aggregate,
The fly ash concrete according to claim 1, wherein a water binder ratio at the time of kneading is 20 to 35%. In the coarse aggregate, the artificial aggregate contains 20% of the total volume of the coarse aggregate,
The fly ash concrete according to claim 1, wherein a water binder ratio at the time of kneading is 45 to 55%, and 10% of cement is replaced with fly ash by internal splitting.   The fly ash concrete according to any one of claims 1 to 3, wherein the artificial aggregate has a water absorption rate of 8% or more.

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