JP4384902B2 - Manufacturing method of mortar and concrete - Google Patents

Description

The present invention relates to a method for producing mortar / concrete used as a building material having high strength and high workability, in which a powder mainly composed of zirconium dioxide-containing silicon dioxide (SiO ₂ ) is prepared.

  Mortar is mainly composed of a hardener such as cement, fine aggregate such as sand, water and the like, and concrete is mainly composed of the composition of this mortar and coarse aggregate such as gravel. When these mortar-concrete compositions are kneaded, the cement composition reacts with water and gradually hardens and solidifies, including the aggregate.

Conventionally, as a means for producing high-strength mortar / concrete, there is a technique for increasing the strength by pozzolanic reaction by reducing the water binder ratio and using silica fume as an admixture (for example, patents). Reference 1). Here, the silica fume is fine particles having an amorphous silicon dioxide as a main component and an average particle size of the order of 0.1 μm. In addition to using silica fume directly as an admixture, slurry silica fume in which silica fume is suspended in water has also been used as an admixture (see, for example, Patent Document 2).
JP-A-5-58701 JP-A-8-333144

  However, when conventional silica fume is used as an admixture, silica fume has a small average particle size, so that secondary agglomeration is likely to occur and dispersibility in mortar / concrete is poor. Furthermore, when the water binder ratio of the mortar / concrete is less than 15%, the fluidity is lowered, and there is a problem that mixing with a conventional mixer is difficult. Moreover, since it was in the form of ultrafine powder, it was easily scattered during work. Therefore, silica fume has a problem that it is difficult to handle and accurate metering is difficult.

  Furthermore, if the addition rate of the high-performance AE water reducing agent is increased in order to improve the fluidity, there is a problem that the cost is increased and the setting is delayed.

  Further, in the conventional silica fume, the self-shrinkage strain of the mortar / concrete is increased, and is restrained by the reinforcing bars, and there is a possibility that cracking or the like occurs. For this reason, it is necessary to newly use an expansion material or a shrinkage reduction material as an admixture. In this case, the types of admixtures increase, making the production of mortar / concrete complicated and incurring costs. There was also a problem. In addition, if an expanding material is mixed, there is a concern about strength reduction, and it is difficult to appropriately control shrinkage reduction and securing strength.

  On the other hand, when the slurry silica fume is used for the production of mortar and concrete, the water that is the solvent of the slurry silica fume plays the role of mixing water at the same time. Here, it is not easy to adjust the concentration of the silica fume in the slurry silica fume while maintaining the water binder ratio at a predetermined value, and a special measuring facility is required to finely adjust the concentration of the slurry silica fume. . And it is expensive to maintain such weighing equipment.

  This invention is made | formed in view of this subject, The place made into the objective provides the cement used for the manufacturing method of the mortar concrete which can perform high strength simply, and such a manufacturing method. There is.

Therefore, the present invention is a mortar-concrete manufacturing method for preparing a powder composed of fine particles containing silicon dioxide (SiO ₂ ) as a main component and zirconium oxide as a component,
The average value of the specific surface area of the fine particles measured by the BET method is 8 to 11 m ² / g,
The average value of the content of zirconium oxide in the fine particles is 3 to 5% by weight,
The powder is produced by the following steps 1 and 2,
Step 1: Zircon sand is electrofused by increasing the temperature stepwise up to 2,200 ° C. in an electric furnace ,
Step 2: Next, a plurality of predetermined cyclones are connected in series to remove coarse particles, and after collecting the particles, the mixture is re-stirred in the silo to reduce the variation in particle size.

The present invention also relates to mortar / concrete prepared by mixing a cement, a fine aggregate, and a powder composed of fine particles containing silicon dioxide (SiO ₂ ) as a main component and zirconium oxide as a component. A manufacturing method of
The average value of the specific surface area of the fine particles measured by the BET method is 8 to 11 m ² / g,
The average value of the content of zirconium oxide in the fine particles is 3 to 5% by weight,
The powder is produced by the following steps 1 and 2,
Step 1: Zircon sand is electrofused by increasing the temperature stepwise up to 2,200 ° C. in an electric furnace ,
Step 2: Next, a plurality of predetermined cyclones are connected in series to remove coarse particles, and after collecting the particles, the mixture is re-stirred in the silo to reduce the variation in particle size.

  According to the mortar / concrete manufacturing method and the cement used in the manufacturing method of the present invention, the mortar / concrete has high strength and high workability by using a small amount of water reducing agent, which is easy to handle during manufacturing operations. Can be manufactured.

  That is, the average particle size of the fine particles used in such a production method is the average particle size of fine particles mainly composed of silicon dioxide used in the conventional production method and having a negligible zirconium oxide content. It is about 2 to 10 times larger than that.

  Therefore, the fine particles used in the production method of the present invention are less dispersed due to the difficulty of secondary agglomeration in mortar / concrete, and are less likely to be scattered during mortar / concrete manufacturing operations. Accurate blending makes manufacturing work easier.

  On the other hand, since the main component of the fine particles used in the production method of the present invention is silicon dioxide, a pozzolanic reaction occurs in the same manner as in the case of mortar concrete formed by mixing fine particles used in the conventional production method. This increases the strength of mortar and concrete.

  In addition, when mixing mortar and concrete by mixing powder with cement, fine aggregate, water, high-performance AE water reducing agent, coarse aggregate, etc., less high-performance AE than conventional preparation. Despite the use of water reducing agents, higher workability of mortar concrete is obtained.

  Moreover, according to this invention, since it can be used as a grout used for the filling of a high-rise RC building joint part, and a bulk density becomes large, storage and conveyance become easy. Moreover, dust and rebound in shotcrete can be improved.

  Furthermore, according to the present invention, it is possible to suppress the cost increase and the setting delay of the mortar / concrete, and it is possible to shorten the production time of the secondary product such as the precast plate.

  Further, according to the present invention, it is possible to reduce the self-shrinkage strain of mortar / concrete, so that the occurrence of cracks and the like can be suppressed.

=== First Embodiment ===
The materials constituting the concrete manufactured in the present embodiment are high belite cement, Kisarazu land sand (fine aggregate), Ome hard sandstone crushed stone (coarse aggregate), high-performance AE water reducing agent, and book It comprises the inventive special siliceous fine powder (admixture).

Here, the special siliceous fine powder in the present embodiment is a powder composed of fine particles containing silicon dioxide (SiO ₂ ) as a main component and zirconia (zirconium oxide, ZrO ₂ ) as one component. The average content of silicon dioxide per particle of special siliceous fine powder is approximately 91 to 95% by weight, and the average content of zirconia is approximately 3 to 5% by weight. Further, the specific surface area of the special siliceous fine powder measured by the BET method is 8 to 11 m ² / g, which corresponds to an average particle diameter on the order of 1 μm.

Such special siliceous fine powder is produced by the process described below. First, the zircon sand is electrofused by raising the temperature stepwise to 2,200 ° C. in an electric furnace to uniformize the average particle size of the fine particles of the zircon sand to about 1 μm, thereby preventing secondary aggregation. Next, a plurality of predetermined cyclones are connected in series to remove coarse particles, and after the particles are collected, they are stirred again in the silo to reduce the variation in particle size. The special siliceous fine powder produced in this manner has a particle size approximately 2 to 10 times larger than that of silica fume conventionally used as an admixture.

An example of the main components, pH, and specific surface area of the special siliceous fine powder produced by the process as described above is as follows.
SiO _{2: 92.74%} by weight, ZrO 2: 4.76 _{wt%, Fe} 2 O 3: 0.35 _{wt%, Al} 2 O 3: less than 0.01 _wt%, TiO 2: 0.05 wt%, H ₂ O: 0.18 wt%, Na ₂ O: 0.02 wt%, pH: 4.2, and specific surface area measured by BET method: 9.22 m ² / g.

Concrete using the special siliceous fine powder in this embodiment as an admixture (first example) and concrete using conventional silica fume as an admixture (conventional example 1, conventional example 2, except for admixtures) Table 1 shows the water binder ratio (W / B) and the unit amount of each component in the same example).

The concrete in the present embodiment and the concrete in Conventional Example 1 and Conventional Example 2 are prepared by kneading fine aggregate, cement, and admixture for about 15 seconds, and adding a high-performance AE water reducing agent and water to this. The mixture was kneaded for 1 second, and then coarse aggregate was added and kneaded for 60 seconds. In this embodiment, a pan mixer (100L) is used. Table 2 shows data representing the performance of the concrete thus obtained.

  The data shown in Table 2 was obtained when the concrete temperature was 19 to 21 ° C and the outside air temperature was 20 to 22 ° C. As is clear from Table 2, in the concrete according to the present embodiment, the slump flow is approximately 11 to 16 compared with the conventional example even if the addition rate of the high-performance AE water reducing agent is lower than that in the conventional example. % Higher. Moreover, as shown in Table 2, the compressive strength of the concrete of the present embodiment is comparable to that of the conventional case. Therefore, it can be said that the concrete according to the present embodiment has less water reducing agent, higher workability, and has the same strength as the conventional case, compared with the conventional concrete.

=== Second Embodiment ===
The material constituting the concrete manufactured in the present embodiment includes a binder, Kisarazu land sand (fine aggregate), Ome hard sandstone crushed stone (coarse aggregate), high-performance AE water reducing agent, and antifoaming agent. Comprising. Here, the binder of the present embodiment is a cement (binder 1) obtained by previously kneading high belite cement and special siliceous fine powder in a mixing ratio of about 9: 1 at first. It consists of two types: high belite cement and special siliceous fine powder (binding material 2) that are mixed when kneaded to produce concrete.

Table 3 shows the water binder ratio (W / B) and the unit amounts of the respective components in the concrete in the present embodiment and the concrete in the conventional example described later.

  The concrete in Conventional Example 3 shown in Table 3 is manufactured using cement (silica fume premix cement) obtained by kneading cement and silica fume in advance at a predetermined mixing ratio. This silica fume premix cement is disclosed in JP-A-6-345507.

  As shown in Table 3, the concrete in the present embodiment using the binding material 1 and the concrete in the conventional example 3 are kneaded for about 15 seconds with fine aggregate and cement previously mixed with the admixture, A high performance AE water reducing agent and water were added to this and kneaded for 240 seconds, and then coarse aggregate was added and kneaded for 120 seconds. Moreover, the concrete in the present embodiment using the binder 2 is prepared by kneading fine aggregate, cement, and special siliceous fine powder as an admixture for about 15 seconds, and then adding a high-performance AE water reducing agent and water. Was added and kneaded for 240 seconds, and then coarse aggregate was added and kneaded for 120 seconds. In this embodiment, a pan mixer (100L) is used.

  The admixture data in Table 3 is the data for the special siliceous fine powder or silica fume to be prepared at the time of concrete production. The special siliceous fine powder or silica fume that is kneaded in advance as cement is described as the admixture data in Table 3. Absent.

Table 4 shows data representing the performance of the concrete thus obtained.

  The data shown in Table 4 was obtained when the concrete temperature was 27.3 to 30.5 ° C and the outside air temperature was 22 to 24 ° C. As is apparent from Table 4, in the concrete of the present embodiment, even if the addition rate of the high-performance AE water reducing agent is lower than that in the conventional example, the slump flow is about twice as high as that in the conventional example. It has become. Moreover, as shown in Table 4, the compressive strength of the concrete of the present embodiment is higher than that of the conventional example, which satisfies the required strength. Furthermore, the data corresponding to the binders 1 and 2 show the same value for both the slump flow and the compressive strength for the same addition rate of the high-performance AE water reducing agent.

  Therefore, it can be said that the concrete of this embodiment has higher workability and strength with less water reducing agent than conventional concrete. In addition, when cement and special siliceous fine powder are kneaded in advance and used as cement, concrete is produced from this (binding material 1), and when special siliceous fine powder is prepared at the time of concrete production (binding material 2). ), It can be said that high workability and strength can be obtained.

  In addition, since the required slump flow could not be obtained in Conventional Example 3 and a good specimen could not be prepared, the compressive strength was lowered.

  In the concrete production method of the present embodiment, the particle size of the special siliceous fine powder as the admixture is large, so that the admixture is less scattered than in the conventional case using silica fume having a small particle size. In addition, an accurate blending ratio is obtained and the operation is simplified. Moreover, if the cement in which such a special siliceous fine powder was kneaded beforehand is used, the said workability will become easier.

  In the above embodiment, the aggregate used is that used for ordinary concrete. However, aggregate suitable for high strength, such as crushed sand of hard sandstone, crushed sand of quartz schist, or crushed stone, is used. This makes the concrete even stronger.

=== Third embodiment ===
In the present embodiment, when the water binder ratio was changed, concrete was produced for each binder using the special siliceous fine powder of the present invention.

Here, the material composing the concrete produced in the present embodiment is a binder, land sand produced from Mandano (fine aggregate), crushed stone produced from both deities (coarse aggregate), and the special silica of the present invention as an admixture. Fine powder (density: 2.4 g / cm ³ ), and further, a high-performance AE water reducing agent (seeker 1200N: Nippon Seeka Co., Ltd.) as an admixture.

The special siliceous fine powder in the present embodiment has a specific surface area of 8 to 11 m ² / g smaller than that of conventional silica fume, and its average particle size is 2 to 10 times larger. In addition, it contains silicon dioxide as a main component and has the same pozzolanic activity as conventional silica fume.

  Furthermore, in the present embodiment, the special siliceous fine powder of the present invention was replaced at a ratio of 10 to 20% with respect to the cement weight. However, this substitution rate was changed according to the water binder ratio (W / B). That is, the replacement ratio of the binder 1 (water binder ratio 17%) is 10%, while the replacement ratio of the binder 2 (water binder ratio 14%) is 15% and the binder 3 (water binder ratio 12). %) Was 20%.

  In the present embodiment, various Portland cements are used. Of these, those with moderate heat and low heat are desirable, and normal and early may be used when obtaining strength early.

  Moreover, the special siliceous fine powder in the present embodiment may be premixed with other materials such as cement in advance, not as an admixture.

Hereinafter, regarding the blending of each concrete in the present embodiment, the water binder ratio (W / B), the fine aggregate ratio (S / a), the unit amount (kg / m ³ ), the addition rate of the high-performance AE water reducing agent Each data of (P ×%) is shown in Table 5.

The manufacturing conditions of each concrete in this Embodiment based on the mixing | blending of Table 5 are as follows.
First, when the binding material 1 and the binding material 2 were used, the cement and fine aggregate were kneaded for 15 seconds, and then a high-performance AE water reducing agent and water were added thereto and kneaded for 120 seconds. Next, coarse aggregate was added, kneaded for 90 seconds, allowed to stand for 5 minutes, and then kneaded for another 30 seconds.
On the other hand, when the binder 3 was used, the cement and fine aggregate were kneaded for 15 seconds, and then a high-performance AE water reducing agent and water were added thereto and kneaded for 150 seconds. Next, coarse aggregate was added and kneaded for 120 seconds and allowed to stand for 5 minutes, and then kneaded for 30 seconds.
In the present embodiment, medium-heated Portland cement was used, and concrete 30L was mixed using a double forced kneading type mixer (60L).

  As shown in Table 5, in the present embodiment, not only the case where the binder 1 having a water binder ratio of 17% is used, but also the water binder ratio that is conventionally difficult to knead is 15% or less. When the binder 2 was used (14%) and the binder 3 was used (12%), the increase in the addition rate of the high-performance AE water reducing agent could be suppressed to a low level.

Tables 6 and 7 show data representing the performance of concrete obtained by such blending.

Table 6 is data which shows the test result of the fresh concrete in this Embodiment. This test was performed under the conditions of a concrete temperature of 26 to 27 ° C. and an outside air temperature of 24 ° C.
In addition, even when the water binder ratio is as low as 14% and 12%, the above data can be obtained with values that ensure fluidity to such an extent that mixing is possible with each binder. Indicated. This shows that it is possible to produce concrete having a water binder ratio of 15% or less, which has been difficult to knead in the past.
Such a result is because the special siliceous fine powder in the present embodiment has a large particle size, so there is little secondary agglomeration and good dispersion in the mortar / concrete, thus ensuring the fluidity of the fresh concrete. It is thought that.

Hereinafter, Table 7 shows the measurement results of the compressive strength of the hardened concrete manufactured using the various binders in the present embodiment.

As is clear from Table 7, the lower the water binder ratio, the higher the compressive strength of the hardened concrete. In particular, the water binder ratio is 14% (Binder 2) and 12% (Binder 3). In some cases, at a stage of 28 days of age, the compressive strength showed a high value exceeding 140 N / mm ² .
In this embodiment, since the aggregate of ordinary articles that are usually used in ready-mixed concrete factories is used, the compressive strength shows a low value compared to the case of using andesite from Koshu, It still satisfied the required strength.
According to the above embodiment, by selecting an appropriate aggregate and curing method, high workability is ensured even when the water binder ratio is 12% or less, and the compressive strength is 200 N / mm ² or more. It is considered possible to produce ultra high strength concrete.

=== Fourth embodiment ===
In the present embodiment, when the water binder ratio was constant (17%), concrete was manufactured for each binder using the special siliceous fine powder of the present invention.

  Here, the materials constituting the concrete manufactured in the present embodiment are a binder, an andesite crushed sand (fine aggregate) from Koshu, an andesite crushed stone (coarse aggregate) from Koshu, and a special siliceous fine powder (admixture). And a high-performance AE water-reducing agent (Nihon Seika Seika 1200N: polycarboxylic acid type) and an antifoaming agent (Nihon Seika Antifoam) as admixtures.

In addition, in the binder 1, the comparative example 2, and the prior art example 3 in this embodiment, as a cement, a high belite cement (density: 3.20 g / cm ³ , specific surface area: 4,250 cm ² / g Pacific cement High flow cement).
Further, in the binder 1 in the present embodiment, the special siliceous fine powder of the present invention having a substitution rate of 10% (density: 2.45 g / cm ³ , SiO ₂ : 94.5 wt%, ZrO ₂ as an admixture. : 4.0 wt%, pH: 3 to 4, average particle size: 1 μm, and specific surface area measured by BET method: 8.7 m ² / g).

Further, in Comparative Example 2 in the present embodiment, silica fume (SiO ₂ : 92.59 wt%, ZrO ₂ : 6.18 wt%) consisting of substantially the same chemical components as in the present invention and having a specific surface area larger than that of the present invention. , PH: 3 to 4, average particle size: 0.5 μm, specific surface area: 15 to 17 m ² / g).
Further, in Conventional Example 3 in the present embodiment, conventional silica fume (density: 2.2 g / cm ³ , specific surface area: 20 m ² / g) was used as an admixture.
Furthermore, two types of silica fume mixed cement mixed with conventional silica fume were also compared (Conventional Example 4 and Conventional Example 5). However, Conventional Example 4 used a low fume cement-based silica fume mixed cement made by Mitsubishi Ube, while Conventional Example 5 used a first cement-made ordinary cement-based mixed slab gypsum and silica fume cement.

Hereinafter, Table 8 shows the data of the water binder ratio (W / B), the fine aggregate ratio (S / a), and the unit amount (kg / m ³ ) for the blending of each concrete in the present embodiment.

  Each concrete shown in Table 8 using the binder 1, the comparative example 2, and the conventional example 3 in this embodiment is made of fine aggregate, cement, and a special siliceous fine powder as an admixture for about 15 seconds. A high-performance AE water reducing agent, an antifoaming agent, and water were added to this and kneaded for 120 seconds, and then coarse aggregate was added and kneaded for 60 seconds.

  Moreover, each concrete using the conventional example 4 and the conventional example 5 shown in Table 8 is kneaded for about 15 seconds with fine aggregate and cement previously kneaded with the mixed material. A high-performance AE water reducing agent, an antifoaming agent and water were added to and kneaded for 120 seconds, and then coarse aggregate was added and kneaded for 60 seconds. In the present embodiment, a pan mixer (50L) is used.

  Moreover, the data of the admixture in Table 8 is the data of the special siliceous fine powder or silica fume prepared at the time of concrete production, and the silica fume mixed with the cement in advance is not described as the data of the admixture in Table 8 (conventionally) See Example 4 and Conventional Example 5).

Table 9 shows the test results of the fresh concrete thus obtained.

As is apparent from Table 9, in the case of the binder 1 using the special siliceous fine powder of the present invention as an admixture, the addition rate of the high-performance AE water reducing agent is as low as 0.8%, The slump flow representing the fluidity showed a relatively large value (67.5 cm). Also, the stop time showed a relatively long value, while the 50 cm flow time and the O funnel flow time showed relatively short values.
From this, it can be seen that when the special siliceous fine powder of the present invention is used as an admixture, the flowability of fresh concrete is ensured even though the addition rate of the high-performance AE water reducing agent is small.

Furthermore, in this embodiment, the setting time until the fresh concrete sets and becomes hardened concrete was measured. The measurement results are shown in Table 10.

  As is clear from Table 10, in this embodiment, the addition rate of the high-performance AE water reducing agent was low, so that in each case, the initial setting time was shortened. In particular, when the special siliceous fine powder of the present invention is used as an admixture (binding material 1), the addition rate of the high-performance AE water reducing agent is lower than other binding materials, so that the initial setting time becomes faster. You can see that In the case of Conventional Example 5, it is considered that the setting time was shortened because the cement that is easily set was originally used.

Next, the measurement results of the compressive strength of the hardened concrete are shown in Table 11 and FIG.

  As is clear from Table 11, when the special siliceous fine powder of the present invention is used (binding material 1), the conventional silica fume is used despite the low addition rate of the high-performance AE water reducing agent. Similar compressive strength was obtained. The specimen curing method in the present embodiment is standard water curing (20 ° C.).

  FIG. 1 is a graph showing the data in Table 11, showing the expression properties of the compressive strength of the hardened concrete produced using various binders in the present embodiment, along with the lapse of age days from the beginning. Yes.

As can be seen from FIG. 1, when the age of the material passed 28 days, the compressive strength showed a large value exceeding 140 N / mm ² . In addition, when the special siliceous fine powder of the present invention is used (binding material 1), the expression property of the compressive strength of the hardened concrete changes in the same manner as when conventional silica fume is used together with the age of the material age. showed that.

Furthermore, in this Embodiment, the self-shrinkage distortion was measured about the hardened concrete manufactured using various binding materials.
At this time, the self-shrinkage strain was measured according to the self-shrinkage test method for high-fluidity concrete (Japan Concrete Institute: Superfluid Concrete Research Committee Report (II), May 1994).

Specifically, an embedded strain gauge (manufactured by Tokyo Sokki Kenkyujo Co., Ltd .: KM-100BT, apparent elastic modulus: 40 N / mm ² ) is set in advance in a mold of 100 mm × 100 mm × 400 mm, and concrete. After 24 hours, the mold was removed and sealed. Curing was performed at 20 ° C. ± 3 ° C. and 60%. In addition, the number of specimens was two, and thermal expansion due to temperature change was removed from the measured actual strain. The starting point of the measurement of the self-shrinkage strain was set at the time of the initial setting in consideration of the volume reduction after the initial setting caused by hydration. The measurement results are shown in FIG.

As is clear from FIG. 2, when the special siliceous fine powder of the present invention was used (binding material 1), the self-shrinkage strain was reduced by 20 to 40% compared to the case where the conventional silica fume was used. I understand.
This is because the special siliceous fine powder of the present invention has a specific surface area smaller than that of conventional silica fume (specific surface area: 20 m ² / g) (specific surface area: 8.7 m ² / g). Is considered to be reduced.

It is a graph which shows the expression property of the compressive strength in one Embodiment of this invention. It is a graph which shows the self contraction distortion effect in one Embodiment of this invention.

Claims (2)

A method for producing mortar / concrete comprising preparing a powder comprising fine particles containing silicon dioxide (SiO ₂ ) as a main component and zirconium oxide as a component,
The average value of the specific surface area of the fine particles measured by the BET method is 8 to 11 m ² / g,
The average value of the content of zirconium oxide in the fine particles is 3 to 5% by weight,
The powder is produced by the following steps 1 and 2,
Step 1: Zircon sand is electrofused by increasing the temperature stepwise up to 2,200 ° C. in an electric furnace ,
Step 2: Next, a plurality of predetermined cyclones are connected in series to remove coarse particles, and after collecting the particles, the mixture is re-stirred in the silo to reduce the variation in particle size. A method for producing mortar / concrete using a mixture of cement, fine aggregate, and powder composed of fine particles containing silicon dioxide (SiO ₂ ) as a main component and zirconium oxide as a component. ,
The average value of the specific surface area of the fine particles measured by the BET method is 8 to 11 m ² / g,
The average value of the content of zirconium oxide in the fine particles is 3 to 5% by weight,
The powder is produced by the following steps 1 and 2,
Step 1: Zircon sand is electrofused by increasing the temperature stepwise up to 2,200 ° C. in an electric furnace ,
Step 2: Next, a plurality of predetermined cyclones are connected in series to remove coarse particles, and after collecting the particles, the mixture is re-stirred in the silo to reduce the variation in particle size.

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