JP2002338322A - Coal ash concrete and compounding method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coal ash concrete and a compounding method thereof which enables a large quantity and effective use of coal ash as concrete raw material. SOLUTION: The unit cement quantity and water/cement ratio is determined on the basis of target strength of the concrete and, thereafter, the quantity of coal ash and aggregate to be compounded for cement and water of unit cement quantity and unit water quantity is determined. Coal ash is compounded for the unit cement quantity with outer percentage and the compounding quantity of fine aggregate of the weight corresponding to the coal ash quantity is decreased. Freshness property, strength and neutralizing speed of the concrete is regulated by the compounding quantity of the coal ash.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to coal ash concrete and a method for preparing the same, and more particularly, to coal ash concrete and a method for preparing the same, which enable large-scale and effective utilization of coal ash as a raw material for concrete. It is about the method.

[0002]

2. Description of the Related Art A large amount of coal ash generated as a by-product from pulverized coal combustion boilers of coal-fired power plants, etc., is used as a substitute for clay during cement production and as a cement-related raw material such as fly ash cement. However, most of the rest is landfilled and its use as a concrete admixture is low at about 3%. The amount of coal ash generated from thermal power plants nationwide is currently about 5.4 million tons, but is expected to exceed 10 million tons in FY2010.

[0003] In the future, it is difficult to expect a dramatic increase in the consumption of cement, and in the current situation in which landfill disposal is becoming more difficult year by year, the amount of generation will continue to increase from the viewpoint of environmental conservation and effective use of resources. There is a need to establish a method for effectively and efficiently using coal ash in concrete.

[0004]

In the case of mixing coal ash with concrete, the blending design has been carried out in accordance with a blending method of a blending method in which coal ash is blended in a proportion of a unit cement amount. As shown in Table 1 below, the inner proportioning is a blending design in which the amount of cement and the amount of coal ash are constant, that is, the amount of unit binder is set to a constant amount. Not only does the amount of cement used decrease,
The use of high-quality coal ash can improve the fluidity of concrete, and can also provide advantages such as reduction of heat of hydration in high-powder concrete.
However, in this blending method, problems such as a decrease in strength and a decrease in durability (particularly, a decrease in durability due to neutralization) tend to occur with an increase in the cement replacement ratio by coal ash. The upper limit of the amount of coal ash tends to be inevitably determined by concrete strength and durability.

[0005]

[Table 1] In the case of such an internal proportioning, since the unit cement amount decreases with an increase in the coal ash replacement rate, the strength at the initial age is reduced as compared with ordinary Portland cement alone. In addition, the strength and durability at the long-term age may be higher than those of plain Portland cement plain concrete and may be lower, depending on the replacement ratio and the mixing and curing conditions.

With respect to durability, in particular, calcium hydroxide produced by the hydration reaction of cement is consumed by the pozzolanic reaction of coal ash. The rate of incorporation increases.

[0007] Accordingly, in the case of the inner split preparation, since the strength and durability are reduced due to the decrease in the unit cement amount with the increase in the replacement rate, the upper limit of the coal ash replacement rate is basically limited. It is determined by the limit that can reduce the strength and durability in comparison with ordinary Portland cement plain concrete. For this reason, the Architectural Institute of Japan has specified an upper limit of the internal replacement rate of 30%, and the amount of coal ash used is subject to restrictions. In addition, it is recognized that the strength and durability of concrete are greatly affected by the quality of the coal ash used in the inner split ratio.

[0008] The present invention has been made in view of the above problems, and an object of the present invention is to provide coal ash concrete and a method of preparing coal ash concrete which enable large-scale and effective utilization of coal ash as a raw material for concrete. Is to provide.

[0009]

The present inventors have conducted intensive studies to achieve the above object, and as a result, in the case of an outer mix in which coal ash is mixed with cement and water in an outer split,
The amount of coal ash used will be changed after setting the unit cement amount and the water cement ratio constant, but in this case, at least the target compressive strength and durability of concrete can be ensured, and The present inventors have found that by increasing the structure by mixing of coal ash, it is possible to expect an increase in strength and an improvement in durability from a young material age, and have achieved the present invention based on such findings.

That is, the present invention relates to a method for preparing coal ash concrete in which cement, water, aggregate and coal ash are mixed, wherein a unit cement amount is determined, and coal ash is compounded with respect to the unit cement amount. And reducing the amount of fine aggregate having a mass corresponding to the amount of coal ash.

[0011] The present invention also provides a method for preparing coal ash concrete in which cement, water, aggregate and coal ash are mixed,
Determine the unit cement amount and water cement ratio based on the target strength of concrete, determine the amount of coal ash and aggregate to be mixed with the unit cement amount and unit water amount of cement and water, and determine the amount of coal ash The present invention provides a method for preparing coal ash concrete, which comprises adjusting the fresh properties, strength and neutralization rate of concrete.

In another aspect, the present invention provides a coal ash concrete prepared by the above method. When coal ash is mixed with a constant amount of cement, the compressive strength and durability of concrete are improved from the initial age due to densification of the concrete structure by a mechanism unrelated to the pozzolanic reaction. Mixing coal ash with cement always results in an increase in compressive strength and a decrease in the rate of neutralization, so that it is possible to mix a large amount of coal ash, which is a large amount of coal ash as a raw material for concrete. Make use possible. In addition, the effect of densifying the concrete structure by a mechanism unrelated to the pozzolanic reaction can be obtained in the same manner even with low-fineness coal ash, and the effect of the quality of coal ash is small. Of coal ash can be used as a raw material for concrete.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to a preferred embodiment of the present invention,
The composition that optimizes the fluidity of the concrete is determined from the gap ratio of the prepared material. Preferably, the theoretical closest gap ratio and the theoretical closest composition are determined from the inherent gap ratio of the material to be prepared, and the composition for which the fluidity is optimal is determined based on the theoretical closest gap ratio and the theoretical closest composition. You.

In the proportioning method, since the proportion of the coal ash in the constituent material of the concrete is large, the difference in the fineness of the constituent material and the type of the coal ash has a relatively large effect on the fluidity of the concrete. According to the above configuration, the fluidity (flow rate) of concrete is determined based on the theoretical or measured gap ratio, or based on the theoretical closest gap ratio and the theoretical closest composition, which are theoretically obtained from the gap ratio specific to each constituent material. Value)
Can be determined theoretically and quantitatively, or a formulation that minimizes the amount of chemical admixture added can be determined. According to such a blending method, coal ash having a different particle size distribution can be blended relatively easily.
Conventionally, it is possible to effectively utilize coal ash coarse powder, which has been recognized as having relatively low availability. Preferably, the fluidity of the concrete is controlled by setting the mixing ratio of coarse and fine coal ash. There is a composition in which the flow value becomes a maximum value by changing the mixing ratio of the fine powder and the coarse powder,
From the relationship between the void ratio (the maximum void ratio that can be filled with water) and the void ratio of the mixed powder in each formulation, the surplus water amount corresponding to the unit water amount is predicted, and the fluidity of concrete is estimated. Can be adjusted. Also high performance
It is also possible to set the limit at which the addition of an AE water reducing agent or the like is indispensable based on the void ratio and the unit water volume.

In another preferred embodiment of the present invention, the compressive strength of concrete is obtained by adding a strength increase value due to coal ash mixing to a compressive strength obtained in the case of plain cement. The increase value is defined as a function of unit coal ash content and concrete age. Preferably, the amount of voids in the concrete after mixing is obtained, and the amount of voids is used as a factor for setting the compressive strength of the concrete. More preferably, a void amount having a void diameter of 50 nm or more is required, and the compressive strength of concrete is reduced in accordance with the increase in the void amount.

According to still another embodiment of the present invention, the carbonation rate coefficient of concrete is reduced in accordance with an increase in the unit coal ash amount. In the outer split formulation, the neutralization rate factor is
It can be shown as a function of unit coal ash. According to the outer split ratio, as the amount of coal ash used increases, the carbonation rate coefficient always decreases.Therefore, the use of large amounts of coal ash prevents the neutralization of concrete regardless of the water-cement ratio. Is effective in

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the coal ash concrete mixing method according to the present invention will be described in detail. As shown in Table 2 below, after setting the cement amount to a constant value,
This is a blending method for changing the amount of coal ash and the amount of aggregate. Since the unit cement amount is constant, the minimum strength and durability can be secured, but the fluctuation of coal ash usage greatly changes the water binder ratio and the amount of aggregate,
Formulation needs to be established.

[0018]

[Table 2] FIG. 1 shows the difference between the inner and outer split proportions of coal ash. In the figure, the horizontal axis is the unit cement amount C, and the vertical axis is the unit coal ash amount
F. The dotted line passing through the origin in the figure represents a constant line for the replacement rate Afin = F / (C + F) in the case of the inner split, and the solid line passing through the origin is the replacement rate Afout = F / in the case of the outer split. C represents a constant line. Further, the solid line on the lower right is a line where the sum of the unit cement amount and the unit coal ash amount is constant, and when the unit water amount is constant, the water powder ratio is also constant on this line.

The unit coal ash amount in the case of the inner ratio is as follows: the upper limit value of the inner ratio replacement rate is 30%, the lower limit value of the unit cement amount is 270 kg / m ³ ,
The lower limit of the water powder ratio that can be kneaded is determined within a region (region within a square with dots) surrounded by each straight line with a lower limit of about 20%. To simply increase the unit coal ash amount in this region, it is inevitable to increase the unit cement amount, but even in this case, the maximum value of the unit coal ash amount is about 300 kg / m ³ .

On the other hand, the unit coal ash amount in the case of the outer split is 20% (see FIG. 3 described later) of the lower limit of the water powder ratio that can be kneaded.
And the area surrounded by the lower limit of the unit cement amount, that is,
Defined in the triangle in the figure including the inner divided area, it is possible to mix the coal ash exceeds 600kg per concrete 1 m ^3. That is, the outer split preparation has a feature that the unit coal ash amount can be increased when the unit cement amount is small.

With respect to the performance such as the strength and durability of concrete mixed with coal ash, that is, the potential, FIG. 1 shows an equipotential line (as an image) as a line which can be regarded as constant. In addition, as shown in a specific example by experimental data described later, the potential increases as the position moves to the upper right side in the diagram of FIG.

In the inner split blending, when the replacement rate is increased, the blending is performed on an oblique arrow along a (C + F) fixed line in FIG. In this case, the replacement ratio increases in the direction of the arrow, and the unit cement amount decreases. For this reason, depending on the conditions, there are cases where the performance of the concrete decreases and cases where the performance improves on the contrary. In other words, when the oblique arrow is above the line of constant potential with respect to the line with a constant potential (for example, 900 kg / unit cement amount in the figure)
arrow from m ³ starts), improved performance, if at the bottom (for example starting from the drawing unit amount of cement 500 kg / m ³ arrows),
Performance decreases.

[0023] On the other hand, in the outer compounding, the compounding is performed along the vertical arrow having a constant unit cement amount. Therefore, as the replacement ratio increases, the arrow always goes to the higher potential side.
This means that performance such as strength and durability is improved by increasing the replacement ratio.

Next, a method of the outer split mixing will be described.
In the outer split preparation, the water-powder ratio fluctuates greatly depending on the amount of coal ash used, and a wide range of concrete, from ordinary concrete to high-strength concrete and high-flowable concrete, can be prepared. In addition, as the amount of coal ash used increases, the amount of fine aggregate having the same volume decreases, and as a result, the fine aggregate volume also fluctuates greatly, and this greatly affects the fresh properties of concrete. At the same time, the strength and durability change greatly according to the value of the unit coal ash amount.

A method for setting the amount of each material used according to the amount of coal ash used and a method for estimating the properties of concrete obtained by this method will be described below.

(1) Mixing method for obtaining desired properties of fresh concrete The relationship between the volumes of water W, cement C, coal ash F, fine aggregate S and coarse aggregate G, which are the constituent elements of concrete, is as follows. Lower formula
Indicated by (1). Where air is 1 m ^{3 of} concrete
Shows the air content (l / m ³ ).

(Equation 1)

Using equation (1) as a basic equation, the unit coal ash volume V _F and the replacement rate V _s / (V _F + V _s ) when the coal ash is considered to be replaced with the fine aggregate. The following equation representing the relationship
(2) is obtained.

(Equation 2)

[0028] In _{addition, V F / (V F +} V S) = 1-V S / (V
_F + V _S ), the relationship between the unit coal ash volume V _F and the unit fine aggregate volume V _S is given by the following equation (3).

(Equation 3)

Similarly, from the following equation (4) indicating that the water powder ratio becomes minimum when the unit coal ash amount becomes maximum, the maximum value of the unit coal ash amount, the minimum value of the water powder ratio, and The following equation (5) representing the relationship between the water cement ratio is derived.

(Equation 4)

(Equation 5)

In the splitting, the water-cement ratio and the unit cement amount are determined first, and then the unit coal ash amount and the amount of aggregate and other materials used are determined. As an example, water-cement ratio W / C = 65%, the unit water amount W = 185kg / m ^3, the unit amount of cement
FIG. 2 shows the relationship between the amount of each of the constituent materials including coal ash when C = 285 kg / m ³ and the amount of air is 4.5%. The values shown in the figure are obtained using Expressions (2) and (3).

Using the figure, a unit coal ash volume V _F (vertical axis in the figure), a unit coarse aggregate volume V _G (a straight line passing through the origin in the figure),
Any two values out of the unit fine aggregate volume V _S (hyperbolic in the figure) and the replacement rate V _F / (V _F + V _S ) (horizontal axis in the figure) when coal ash is regarded as a substitute for fine aggregate Gives the other two values. The range of the theoretically possible preparation is limited to the hatched portion in the figure due to restrictions such as the actual volume ratio of the coarse aggregate and the ratio of water powder that can be mixed. A formulation solution that satisfies conditions such as slump or slump flow, fresh properties such as separation resistance and pumping property, strength development properties, and durability exists in this region. FIG. 3 shows the relationship between the lower limit value of the water powder ratio and the upper limit value of the unit coal ash amount obtained from the equation (4). If the water cement ratio and the unit water amount are the same, the upper limit Fmax of the unit coal ash amount sharply increases as the water powder ratio decreases. The higher the value of the water cement ratio and the unit water amount, the larger the Fmax, but the effect is not as remarkable as the case of the water powder ratio.

The following is a description of an optimal blending method in such a kneadable region. The fluidity of coal ash concrete is determined by whether the unit water volume is insufficient or surplus to the void volume formed by other constituent materials. FIG. 4 is a diagram conceptually showing the relationship between the theoretical closest composition and the theoretical closest gap ratio that gives the minimum value of the theoretical gap ratio in the closest packing theory. In the figure, the composition X (= Vg / (Vs + Vg) (Vs and Vg are the volumes of the particle groups s and g, respectively)) on the horizontal axis indicates the absolute volume ratio of the particle group g to the total particle group. When X is 0 or 1, the particle group is plain s and the particle group g is plain.
Further, the gap ratio P on the vertical axis is a value obtained by dividing the amount of voids when the particle group is filled in the container by the volume of all the particle groups, and is an index indicating the magnitude of the void amount. The theoretical close-packed composition X ₀ that gives the theoretical minimum value of the gap ratio and the theoretical close-packed gap ratio P ₀ are [X = 0, P
= Ps (specific gap ratio of particle group s)] and [X = 1, P = 0]
And a straight line P2 connecting [X = 1, P = Pg (specific gap ratio of the particle group g)] and [X = 0, P = -1]. . The void ratio curve of the actual mixed material always appears above the theoretical value because the particles actually have an asymmetric shape, and the void ratio at the time of closest packing, that is, the minimum value of the curve is also the theoretical value. It becomes larger than the closest gap ratio P ₀ .

Here, the gap ratio corresponding to the unit water amount, that is, the maximum void amount that can be filled with water is shown in FIG. When the gap ratio of the constituent materials (mixed particle group) is lower than this (Case 1 in the figure), water surpluses the constituent materials, and the fluidity is improved. On the other hand, when the gap ratio is on the upper side (Case 2), water is insufficient for the constituent materials, and it is considered that dispersion of the constituent materials is difficult with water alone. Therefore, this area is
This is an area where it is necessary to add a dispersant such as a water reducing agent.

Tables 3 and 4 below show the materials used and the quality of the coal ash.

[Table 3]

[Table 4]

In this example, ordinary Portland cement is used as cement, and sea sand from Genkai is used as fine aggregate.
5mm sieve was used. As the coal ash, a classified fine powder (F40) and a coarse powder (F10) not subjected to particle size adjustment were used. The two types of coal ash are hereinafter simply referred to as fine powder and coarse powder, respectively.

The following Tables 5 (a) and 5 (b) show the mixing conditions. In this preparation condition, Formulation relates paste portion and mortar part of concrete, the unit water amount W to 185 kg / m ^3, has a unit cement content C to a constant value of 285 kg / m ^3. Each table shows the values when converted to concrete. Of these, Table 5 (a) shows that the coarse powder was replaced with 0, 20, 40, 60, 80, and 100% by volume ratio of fine powder while keeping the coal ash volume constant. Table 5 (b) shows the mixing ratio of the fine powder to the fine aggregate in the outer mixing.

[Table 5]

The porosity was measured to calculate the gap ratio of the constituent materials. The porosity was measured by first mixing the sample by hand kneading, and then, as shown in FIG.
m (196.2 ml) was placed in a stainless steel container, and the sample was filled in the container by giving a falling motion with a flow table. The sample was filled until the height of the sample upper surface read on the scale did not change. Incidentally, the number of drops is about 500 per sample. Thereafter, the sample was ground so that the upper surface of the sample was aligned with the upper surface of the stainless steel container, and the mass was measured to determine the actual product rate. The porosity and the void ratio were calculated by the following equations (6) and (7), respectively, based on the actual moments obtained from the measurement results. The density of the mixed sample required for calculating the actual product ratio was a value calculated from the mixture.

(Equation 6)

(Equation 7)

Here, the respective symbols are as follows. p: void ratio P: void ratio a: actual ratio

FIGS. 6 (a) and 6 (b) show the relationship between the composition and the flow value and the relationship between the composition and the void ratio when the mixing ratio of the fine powder and the coarse powder of the coal ash is changed. Have been. 6 (a) and 6 (b) show the results when the volume ratio of water to powder is 93%, 78% and 63% from the left. Powder ratio is about 35 by mass
%, 30%, and 25%.

As can be seen from the figure, there is a composition in which the flow value has a maximum value when the mixing ratio of the fine powder and the coarse powder changes, and the composition at this time is a composition in which the gap ratio curve shows a minimum value. Matches. Also, when focusing on the gap ratio corresponding to the unit water amount in each preparation, that is, the relationship between the maximum gap ratio that can be filled with water and the gap ratio of the mixed powder,
At a water powder ratio of 35%, in most compositions, the void ratio is lower than the broken line corresponding to the unit water amount, so that water is in a surplus state. As the void ratio falls below this line, the fluidity improves.
Therefore, in this case, the degree of freedom of mixing for obtaining the target liquidity is relatively large. On the other hand, as the water powder ratio becomes smaller, the gap ratio of the constituent materials often exceeds the broken line corresponding to the amount of water, and water is in short supply. In particular, at a water powder ratio of 25%, the gap ratio of most of the compositions with respect to the broken line corresponding to the unit water amount comes to the upper side. In addition, the region of the composition that cannot be kneaded is also widened. In addition, even when the water powder ratio is 25%, when the composition [F10 / (C + F40 + F10)] is about 55%, the water ratio is low because the gap ratio and the amount of water are almost the same. Nevertheless, kneading was possible without the addition of a high-performance AE water reducing agent.

Next, when a mixed system of powder and fine aggregate, which is an expanded powder, that is, a mortar portion of concrete is assumed, the composition and flow of the fine powder of coal ash and the fine aggregate change. The relationship between the values and the relationship between the composition and the gap ratio are shown in FIGS. 7 (a) and 7 (b). As in the case of the fine powder and the coarse powder, the composition in which the flow value has the maximum value and the composition in which the gap ratio has the minimum value match very well. Further, when the gap ratio of the constituent materials is lower than the gap ratio corresponding to the unit water amount, kneading can be performed without a dispersant. Therefore, in the area where a small amount of coal ash is used, the fluidity is improved by mixing the coal ash, but if the mixing amount is increased to a certain amount, it cannot be dispersed only with water,
Addition of a high-performance AE water reducing agent is indispensable. This boundary is represented by the intersection of the gap ratio curve and the amount of water.

From the above, when coal ash is mixed by the splitting method, when a mixed system of coarse particles and fine particles is targeted, if the specific gap ratio of each is known, the above method is used based on the specific gap ratio. It is possible to obtain an optimum composition in which the fluidity is optimized, and to design an optimal mixture in which the amount of the chemical admixture added can be minimized in relation to the gap ratio corresponding to the unit water amount. In this blending method, what needs to be actually measured is only the specific gap ratio of the constituent material alone, and a blending method that can be easily applied to actual work regardless of the particle size distribution characteristics is provided. Further, according to the present method, it is possible to effectively use coarse powder having a relatively low utilization rate.

[0043] Then as example in which the formulation for concrete, in each of the preparation of unit water ^{185kg / m 3, 165kg / m} 3, relates concrete subjected to kneading slump 18cm as a target, a unit of coal ash content and high FIG. 8 shows the relationship with the performance AE water reducing agent addition amount. Table 6 below shows the formulation, Table 7 below shows the quality of the coal ash, and Table 8 shows the specifications of other materials used. Coal ash is JIS A 62
EP compatible with 01 (fly ash for concrete) class II
Classified coarse powder (FA1,000) that does not conform to any of ash (FA4,000) and any of I-IV types. On the other hand, it was used by substituting 40% for the mass ratio.

[Table 6]

[Table 7]

[Table 8]

Regarding the effect of the fineness, when the unit coal ash amount is small, the effect of the use of the coarse powder is small, but when the unit coal ash amount is large, the effect tends to become more apparent. In other words, the required amount of the high-performance AE water reducing agent was smaller when using approximately 40% of a mixture of 1,000-brane coarse powder than by using 4,000-blane fine powder alone (see FIG. 9). ). This supports the relationship between the gap ratio curves and the amount of water shown in FIGS.

FIGS. 10 (a) and 10 (b) show the amounts of the constituent materials used and the properties of the fresh concrete in the formulations of the unit water amounts of 185 kg / m ³ and 165 kg / m ^3, respectively. Using this figure, it is possible to predict the type of concrete (normal, medium-flow, high-fluidity concrete) obtained from the set mix, or to know the range of mix to achieve the desired type of concrete. (2) Mixing method to obtain target compressive strength

FIG. 11 shows the relationship between the compressive strength and the unit coal ash amount of the test specimens which were kneaded using the coal ash shown in Table 7 and the mixture shown in Table 9 below.

[Table 9]

FIG. 11 illustrates the relationship between the unitary coal ash amount and the compressive strength at the age of 28 days. The strength when coal ash is externally mixed is generally larger than that of cement alone, and at the same time, increases as the unit coal ash amount increases. There is a clear correlation between unit coal ash content and compressive strength,
The relationship between the two can be expressed as the following equation (8).

(Equation 8)

The first term α _s in the equation (8) is the compressive strength (N / mm ² ) in the case of plain cement, and the compressive strength is a function of the water-cement ratio and is a measured value shown in FIG. Is expressed by the following equation (9).

(Equation 9)

In the equation (8), β _s (N / mm ² ) of the second term is
Indicates the size of the contribution of coal ash to compressive strength. FIG.
The alignment between the actual measurement values shown ^{_{in, β s (N / mm 2}} ) as a function of only the age, ^{_{also, γ s (kg / m 3}} ) independently of one such material age or unit coal ash amount, The following formulas (10) and (11) respectively
Can be defined by

(Equation 10)

[Equation 11]

Summarizing these results, the above equation (8) is
It can be represented by the following equation (12).

(Equation 12) From these, a relational expression between the unit coal ash amount and the unit cement amount is obtained as a function representing the equipotential line with respect to the compressive strength, and is expressed by the following expression (13).

(Equation 13)

FIGS. 13 to 15 show the results for the ages of 7 days, 28 days, and 91 days.
The iso-poncial lines for compressive strength at day are shown respectively. As described above, the equipotential line is given by equation (12)
Alternatively, it is calculated as the relationship between the unit cement amount C and the unit coal ash amount F when fc in the equation (13) is fixed. The black circles in each figure are the measured values of the compressive strength. For example, in FIG. 13 showing the 28-year-old material, paying attention to the oblique arrow indicating the inner split ratio, in the case of the arrow starting from the unit cement amount of 740 kg / m ³ , the inner split replacement rate is about 20%. Has an improved compressive strength and decreases at higher substitution rates. On the other hand, in the case of the preparation starting from the unit cement amount of 463 kg / m ^{3, the} strength always decreases as the replacement ratio increases. It can be seen that, even at other ages, the compressive strength may be reduced or improved as compared with ordinary Portland cement alone depending on the unit cement amount and the age in the case of the inner split preparation. On the other hand, the vertical arrow indicating the split ratio always increases toward the higher potential as the unit coal ash increases,
The advantage of the outer split is confirmed. In addition, it is clear that in the case of the split ratio, the strength is higher than in the case of the cement alone from the early stage of the material age (FIG. 13). Furthermore, it can be formulated also in the amount of area units cement is small, even in the formulation of the unit cement content 200 kg / m ^3, in a region where the amount unit coal ash exceeds ^{100 kg / m 3, 30N /} mm 2 The above compressive strength is obtained.

As described above, the concrete strength of the set mix can be obtained by the above method. Conversely, the formulation for obtaining the target strength is determined from the above method. Regarding the strength development mechanism of coal ash split concrete, FIG. 16 shows a pore structure model of portland cement plain concrete and concrete of coal ash split mixed. This model is composed of fine particles in a space corresponding to one fine aggregate particle in the mortar, such as cement or coal ash, which fills the fine aggregate and the surrounding space, and their voids. Here, it is assumed that the constituent particles are spherical and have a single size corresponding to the average diameter for each particle.

FIG. 16 (a) shows the case of Portland cement alone (W / C = 65%), and the only particles that fill the space other than the fine aggregate are cement. In addition, the voids are occupied by water, and the voids will be filled with products generated by the hydration reaction of the cement. When cement particles are arranged in conformity with the volume of each constituent particle calculated from the formulation and the number of particles obtained from each particle size, the gap in this case becomes 4 as shown in the enlarged view on the right side of FIG. It becomes a model surrounded by individual cement particles. Radius of the inscribed circle, i.e. the void diameter, and the radius of the cement particles and r _C, the 0.414r _C. Next, when the coal ash was mixed 244kg / m ³ in outer percentage (water powder ratio W / P = 35%), since the fine aggregate amount by the volume fraction is decreased, corresponding to one fine aggregate The space is relatively large. Filling this space is cement and coal ash particles. When the total volume of the powder increased, the particle arrangement became denser, and when the particle diameters of cement and coal ash were approximately the same, the void was surrounded by three powder particles as shown in the enlarged view of Fig. 16 (b). Must be done. Therefore, the gap radius is 0.15
5 r _C The characteristic of this model is that the total amount of voids is equal to the unit water amount, and the unit water amount is constant in the coal ash extra-split mix, so that the total pore volume of both mixes is equal. In other words, in concrete in which coal ash is externally mixed, the total void volume in the same volume is the same, but the number of particles constituting the voids per volume is different. The larger the body size, the smaller it becomes. This difference is established immediately after mixing. This means that regarding the strength development, the size of the void filled with the hydration product of the cement is small immediately after kneading, and therefore, it is easy to form a dense hardened body structure from the initial age. As a result, the strength of coal ash split mixed concrete increases from the initial age compared to the strength of Portland cement alone concrete.

Table 10 below shows the materials used in the demonstration experiment. Cement is JIS R 5210 (Portland cement)
The normal portland cement specified in, and the fine aggregate used sea sand from Iki. Coal ash (FA) has a specific surface area of 100
Four types of 0, 2700, 4000, and 7000 cm ² / g were used. Also,
For comparison, a stone powder (GP) having a specific surface area of 1200 cm ² / g was used.

[Table 10]

The formulations in the demonstration experiments are shown in Table 11 below.

[Table 11] In the demonstration experiment, the unit water volume was 185 kg / m ³ and the water cement ratio was 65%
(Unit cement content = 285 kg / m3) and a constant, a unit of coal ash amount, 0, is changed from 85,126 and 332kg / m ^3, water powder ratio
W / P was changed. Coarse aggregate is excluded from the mix of concrete. The volume ratio of each powder was constant. No high-performance AE water reducing agent was used in any of the formulations.

According to JIS R 5201 (physical test method for cement), the test piece was molded into a mold having dimensions of 40 × 40 × 160 mm,
The specimens were subjected to wet-air curing in an environment of 90 ° C. and 90% RH for 1 day, removed from the mold, and cured in water until a predetermined age (1, 3, 7, 28 days). A sample is taken from the inside of the specimen at each age, and the sample is
Grind into ~ 3mm granules, stop hydration with acetone,
After vacuum drying for one day, the pore volume distribution was measured using a mercury intrusion porosimeter with a pore radius ranging from 6.0 to 90432 nm to determine the pore volume. The strength test is JIS R5201
(Cement physical test method).

FIG. 17 shows the results of the measurement of the total pore volume measured by the mercury intrusion porosimeter for the various formulations that were set.
The case of 1,3,7 days of age is shown. Regardless of the age, the total pore volume is almost the same regardless of the unit coal ash content. This means that in the coal ash splitting, the unit cement and unit water are constant, and a part of the fine aggregate is replaced with coal ash. It shows that it is constant, which is consistent with the results of the study using the model shown earlier. In FIG. 17,
The results for the case where the specific surface area of coal ash is different and the case where stone powder is used as the powder are also described.In all cases, the total pore volume is almost the same if the water powder ratio is constant. I understand.

FIG. 18 shows, as an example, the pore size distribution in each formulation for the case of a material age of 3 days. As is clear from the figure, it can be seen that as the unit powder amount increases, the pore size distribution shifts to a smaller side. This tendency was the same at other ages. Considering that the pozzolanic reaction of coal ash hardly progresses at this time, the densification of the voids is, as described above, because the number of particles filling the space increases due to the increase in the amount of powder. It can be determined that the pore diameter inside the concrete is small immediately after mixing. Therefore, even if the amount of cement hydrate that fills the voids is the same, it is clear that as the unit powder amount increases, the microstructure at the same age becomes more dense. FIG. 19 shows the relationship between the unit powder amount and the void amount of 50 nm or more. As is clear from the figure, there is a tendency that the amount of voids having a diameter of 50 nm or more decreases as the unit powder amount increases.

FIG. 20 shows the relationship between the compressive strength and the amount of unit powder for each formulation and each material age. As in the previous Figure 11,
As the unit powder amount increases, the compressive strength increases from the initial age. FIG. 21 shows the relationship between the amount of pores and the compressive strength. As a result of examining the correlation with the strength at various pore diameters, the compressive strength showed the highest correlation with the void amount of 50 nm or more, and the reduction of the void amount of 50 nm or more resulted in an increase in the compressive strength. As shown in FIG. 19, by mixing the coal ash (FA) by the outside ratio, the void volume of 50 nm or more is reduced from the early age of the portland cement compared to the case of Portland cement alone, so the coal ash outside concrete Was found to develop high strength from the initial age when the pozzolanic reaction hardly progressed. This is also true when using non-reactive crushed stone powder (GP) as shown in FIGS. Obviously, it depends on the void-forming properties of these powders and is independent of the reactivity of the powders. In addition, it is clear that the strength expression mechanism shown in this method can be applied to powders other than coal ash for which effective use is desired.

(3) Formulation Method for Obtaining Targeted Neutralization Resistance Properties The neutralization rate coefficient can be expressed by the following formula (14) from the amount of calcium hydroxide and the air permeability coefficient of the cured product. it can.

[Equation 14]

The calcium hydroxide amount Q and the air permeability coefficient K can be expressed by the following equations (15) and (16), respectively.

(Equation 15)

(Equation 16)

Next, when these are substituted into the above equation (14), the neutralization rate equation is expressed as the following equation (17) as a function of the unit coal ash amount.

[Equation 17]

Specimens of the same material and composition as the compressive strength were prepared and subjected to an accelerated neutralization test in an environment at a temperature of 20 ° C., a relative humidity of 60% and a carbon dioxide gas concentration of 5%. The specimens were removed from the mold at 91 days of age, and then dried for one week in a constant temperature and humidity room at 20 ° C and a relative humidity of 60%. Measurement of neutralization depth is phenolphthalein
After spraying a 1% solution on the split surface, the portion that did not develop color was measured with a vernier caliper, and the average was taken as the neutralization depth.

FIG. 22 shows the relationship between the neutralization rate coefficient and the unit coal ash amount. The neutralization rate coefficient was obtained by approximating the experimental result at each test material age by the Δt law. 90% water cement ratio, other water cement ratio (65, 50, 40%)
The rate of neutralization is significantly higher than that of. However, at all water-cement ratios, the neutralization rate coefficient decreases as the amount of coal ash used increases. It is clear that it is effective in suppressing hydration. Further, the solid line in the figure is a result obtained by approximating the equation (17) to the actually measured value, and in any case, the tendency of the actually measured value is well shown. Where equation (17)
The values of the experimental constants α _c , γ _c1, and γ _c2 can be expressed as the following equations (18) to (20), respectively, as a function of the unit cement amount, by matching with the actually measured values shown in FIG. 23. it can.

(Equation 18)

[Equation 19]

(Equation 20)

To summarize these results, equation (17) is represented by the following equation (21).

(Equation 21) From the above, a relational expression of the unit coal ash amount and the unit cement amount representing the equipotential line regarding the neutralization rate is obtained,
It is represented by equation (22).

(Equation 22)

FIG. 24 shows an equipotential line for the neutralization rate calculated from equation (22). Similarly to the compressive strength, the equipotential line is calculated as the relationship between the unit cement amount C and the unit coal ash amount F when the neutralization rate coefficient A in the equation (22) is fixed. Similarly to the compressive strength, the diagonal arrows indicating the internal proportions show that the neutralization rate is lower than that of ordinary Portland cement as the replacement rate increases, and that it increases in the opposite direction. Can be However, since the potential line becomes perpendicular to the horizontal axis when the substitution rate exceeds a certain substitution rate, it can be seen that the neutralization resistance is sharply reduced in the internal proportioning as compared with plain Portland cement alone. On the other hand, the vertical arrow indicating the outer ratio is always higher toward the higher potential with the increase of the unit coal ash amount regardless of the unit cement amount, so that the advantage of the outer ratio is confirmed. In addition, even when the unit cement amount is as small as 200 kg / m ³ , it can be seen that the performance is improved by using coal ash.

From the above results, the concrete in which coal ash is externally mixed is always improved in compressive strength and neutralization resistance at any age and mix, as compared to the base Portland cement plain concrete. In addition, these properties, as well as fresh properties, became predictable at the planning and formulation stage.

[0068]

As described above, according to the above-described structure of the present invention, it is possible to provide coal ash concrete and a compounding method thereof, which enable large-scale and effective utilization of coal ash as a raw material for concrete.

[Brief description of the drawings]

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram showing a relationship and a difference between an inner split proportion and an outer split proportion of coal ash.

FIG. 2 is a diagram showing a relationship between usage amounts of respective constituent materials in coal ash outer concrete.

FIG. 3 is a diagram showing a relationship between a lower limit value of a water powder ratio and an upper limit value of a unit coal ash amount.

FIG. 4 is a diagram conceptually showing a relationship between a theoretical close-packed composition and a theoretical close-packed ratio that gives a minimum value of a theoretical gap ratio.

FIG. 5 is a schematic front view of a measuring instrument showing a test method of a porosity measurement test.

FIG. 6 shows the relationship between the composition and the flow value observed when the mixing ratio of fine powder and coarse powder of coal ash is changed,
FIG. 3 is a diagram illustrating a relationship between a composition and a gap ratio.

FIG. 7 is a diagram showing the correspondence between the maximum value of the gap ratio and the maximum value of the flow value.

FIG. 8 is a diagram showing a relationship between a unit coal ash amount and a high-performance AE water reducing agent addition amount in concrete kneaded with a slump of 18 cm as a target.

FIG. 9 is a graph showing the effect of fineness on the amount of a high-performance AE water reducing agent added.

FIG. 10 is a diagram showing the relationship between the amount of each constituent material used and the properties of fresh concrete.

FIG. 11 is a diagram showing the relationship between compressive strength and unit coal ash amount.

FIG. 12 is a diagram showing a relationship among an experimental constant, a unit cement amount, and a water cement ratio.

FIG. 13 is a diagram showing an isoponcial line relating to compressive strength of 7-year-old material.

FIG. 14 is a diagram showing an isoponical line relating to compressive strength of a 28-year-old material.

FIG. 15 is a diagram showing an isoponical line relating to compressive strength of a 91-year-old material.

FIG. 16 is a conceptual diagram showing a void structure model for portland cement-only concrete and concrete obtained by mixing coal ash in an outer portion.

FIG. 17 is a diagram showing the effect of coal ash outer mixing on the total pore volume.

FIG. 18 is a graph showing the effect of coal ash outer mixing on the pore size distribution.

FIG. 19 is a diagram showing a relationship between a unit powder amount and a void amount of 50 nm or more.

FIG. 20 is a diagram showing the effect of coal ash outer mixing on the compressive strength of concrete.

FIG. 21 is a graph showing the relationship between the amount of pores of 50 nm or more and the compressive strength of concrete.

FIG. 22 is a diagram showing a relationship between a neutralization rate coefficient and a unit coal ash amount.

FIG. 23 is a diagram showing a relationship between an experimental constant and a unit cement amount.

FIG. 24 is a diagram showing equipotential lines relating to a neutralization rate.

Continuation of the front page (72) Inventor Tomoyuki Koyama 1-40-809 Mishimazaki, Higashi-ku, Fukuoka, Fukuoka F-term (reference) 4G012 PA26 PA27 PC11

Claims (10)

[Claims] Claims: 1. A method for preparing coal ash concrete in which cement, water, aggregate and coal ash are mixed, a unit cement amount is determined, and coal ash is blended with the unit cement amount by an external mixing, A method for preparing coal ash concrete, comprising reducing the amount of fine aggregate having a mass corresponding to the amount of coal ash. 2. A method for preparing coal ash concrete in which cement, water, aggregate and coal ash are mixed, wherein a unit cement amount and a water cement ratio are determined based on a target strength of concrete, and the unit cement amount and the unit water amount are determined. Determine the amount of coal ash and aggregate to be mixed with cement and water,
A method for preparing coal ash concrete, comprising adjusting the fresh properties, strength, and neutralization rate of concrete according to the blending amount of coal ash. 3. The method for preparing coal ash concrete according to claim 1, wherein a composition at which the fluidity of the concrete is optimized is determined from a gap ratio of the prepared material. 4. A theoretical closest gap ratio and a theoretical closest composition are determined from a specific gap ratio of a material to be prepared, and a composition at which fluidity is optimal is determined based on the theoretical closest gap ratio and the theoretical closest composition. The method for blending coal ash concrete according to claim 1 or 2, wherein the coal ash concrete is blended. 5. The method for blending coal ash concrete according to claim 3, wherein the fluidity of the concrete is adjusted by setting the mixing ratio of coarse powder and fine powder of coal ash. 6. The compressive strength of concrete is determined by adding a strength increase value due to coal ash mixing to a compressive strength obtained in the case of plain cement, and the strength increase value is calculated based on a unit coal ash amount. 7. A method for preparing coal ash concrete according to claim 1, wherein the method is defined as a function of the concrete age. 7. The amount of voids in the mixed concrete is determined,
The method according to claim 1, 2 or 6, wherein the void amount is used as a factor for setting the compressive strength of the concrete. 8. The method for preparing coal ash concrete according to claim 6, wherein a void amount having a void diameter of 50 nm or more is determined, and the compressive strength of the concrete is reduced in accordance with the increase in the void amount. . 9. The method for preparing coal ash concrete according to claim 1, wherein the carbonation rate coefficient of the concrete is reduced in accordance with an increase in the unit coal ash amount. 10. A coal ash concrete prepared by the preparation method according to any one of claims 1 to 9.