JP2002128551A - Method of manufacturing fine aggregate for concrete - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a fine aggregate for concrete capable of obtaining concrete excellent in durability by containing of a required amount of ultra fine sand having a sieved dimension of <=0.15 mm, suppressing of decrease in absolute volume percentage by removing of ultra fine sand having a large specific surface area and a sieved dimension of <=0.038 mm, improving of fluidity of concrete (slump value) and lowering of an unit amount of water, even when natural sea and river sands are used. SOLUTION: A frictional crushed aggregate is obtained with making round sea and river sands of raw material having sieved dimension of 0.15<=mm and pass rate of <=4% by frictional crushing and also with increasing amount of the fine sand so that the fine sand having sieved dimension of 0.15<=mm may have pass rate of <=3-10%. Subsequently this frictional crushed aggregate with a sieved dimension of <=0.038 mm is mainly removed by wet classification.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing fine aggregate for concrete (sand for concrete) using sea sand or river sand as a raw material.

[0002]

2. Description of the Related Art Natural sea sand and river sand are suitable as fine aggregate for concrete because their grain shape is round. However, this sea sand or river sand is fine sand having a sieve size of 0.15 mm or less. There are already few minutes. In other words, fine sand is washed away by waves and river flow, and fine sand is washed away by pumping and sampling,
In the case of sea sand, fine sand with a sieve size of 0.15 mm or less is often low, such as fine sand being washed away by washing with salt water. Often not).

As a result of research, the present applicant has come to the knowledge that the presence of fine sand having a sieve size of 0.15 mm or less gives good results on concrete fluidity (slump value) and concrete durability. Then, as fine aggregate for concrete, the sea sand itself having a sieve size of 0.15 mm or less and a passage rate of 4% or less is ground to form a sieve size of 0.15 mm or less.
A concrete aggregate having a passage rate of 15 mm or less having a pass rate of 5 to 15% was proposed (Japanese Patent Publication No. 7-74088). This concrete aggregate (hereinafter referred to as “processed sea sand”)
As a whole, sea sand is obtained by grinding sea sand to increase the content of fine sand having a sieve size of 0.15 mm or less to improve the actual loading rate. As a result of the test, It was possible to improve the durability of concrete by increasing the slump value (reducing the amount of water).

[0004]

However, the fine sand having a sieve size of 0.15 mm or less naturally includes an ultrafine sand having a sieve size of 0.038 mm or less. Since sand has a large specific surface area, there is a problem in that the water absorption becomes higher and the unit water volume is increased. Although it is not preferable to remove the ultrafine sand from the viewpoint of the actual loading rate, the particle size of the ultrafine sand (sieve size 0.038 mm or less) is the particle size of cement (general size). (The average particle size is assumed to be 0.014 mm), so that the superfine sand content can be said to be an extra component from the viewpoint of the particle size distribution of the entire concrete. In other words, even if the ultra-fine sand content is reduced, cement will compensate for this ultra-fine sand content, so it is possible to suppress the decrease in the performance rate,
It is preferable to remove ultrafine sand having a large specific surface area in order to reduce the unit water volume.

In the present invention, from such a viewpoint, a sieve size of 0.15 mm is used while using natural sea sand or river sand.
The required amount of the following fine sand is contained, and the ultra-fine sand having a large specific surface area and a sieve size of 0.038 mm or less is removed, thereby suppressing a decrease in the performance rate and a concrete fluidity (slump value). It is an object of the present invention to provide a method for manufacturing a fine aggregate for concrete, which can improve concrete quality and reduce unit water content to obtain concrete with excellent durability.

[0006]

In order to solve the above-mentioned problems, a method for producing fine aggregate for concrete according to the present invention (Claim 1) is characterized in that fine sand having a sieve size of 0.15 mm or less is passed through at a passing rate. By grinding the raw sea sand or raw river sand containing 4% or less, the grain shape of the sand particles is rounded, and the fine sand having a sieve size of 0.15 mm or less is passed at a rate of 3 to 10%. A milled fine aggregate having an increased fine sand content to be contained is obtained. Next, the milled fine aggregate was subjected to wet classification to mainly remove ultrafine sand having a sieve size of 0.038 mm or less.

In the present invention, the raw material sea sand includes both sea sand which has been washed with water and sea water which has not been washed to remove salt and impurities from the collected sea sand, and has a sieve size of 0.15 mm. It is assumed that the following fine sand content is contained at a passage rate of 4% or less. If the collected sea sand contains a large amount of impurities, it is preferable to remove the impurities by washing with water. If you do not wash sea sand sometimes,
Salt can be removed at the time of wet classification of the milled fine aggregate.
The raw material river sand includes both river sand that has been washed to remove impurities from the collected river sand and river sand that has not been washed. Fine sand having a sieve size of 0.15 mm or less has a passing rate of 4%. It shall be contained below. That is, the sea sand and the river sand before the grinding is performed, and the sieve size is 0.1 mm.
Raw material sand containing fine sand having a passage rate of 4% or less of 15 mm or less is called raw material sand, and it is optional to wash or not to wash it with water depending on the state of the collected sand.

In this method for producing fine aggregate for concrete, the raw material sand is ground to give a round shape to the sand particles, and the fine sand having a sieve size of 0.15 mm or less (sieve). A fine aggregate containing 3 to 10% of an ultrafine sand having a mesh size of 0.038 mm or less at a passage rate of 3 to 10% is obtained. That is, by grinding, the sand particles of the raw material sand, which originally have a rounded grain shape, are further provided with a rounded grain shape, and the fine sand content having a sieve size of 0.15 mm or less is increased. As a result, it is possible to obtain a milled fine aggregate having a high performance rate and to improve the fluidity of the concrete. As the grinding device, for example, a grinding device in which a rotor is eccentrically provided in a horizontal rotary drum (for example, Hurricane manufactured by Shinroku Seiki Co., Ltd.)
The raw material sand can be agitated while rotating the rotary drum and the rotor in the reverse direction, and the raw material sand can be rubbed or crushed so that the granules are rounded. May be used for grinding. That is, the grinding process in the present invention mainly means
This is a process that aims to increase the fine sand with a sieve size of 0.15 mm or less while making the grain round by rubbing or collision between the raw material sands. It is natural that cracking (crushing) occurs during processing, and it can be said that polishing is performed including such crushing. For this reason, devices mainly intended for crushing, such as ball mills and rod mills, are not suitable for the grinding process according to the present invention.

[0009] The fine aggregate obtained by grinding the raw material sand as described above has a sieve size of 0.05 mm or less in fine sand having a sieve size of 0.15 mm or less.
Naturally, ultrafine sand of 38 mm or less is contained. The ultrafine sand has a large specific surface area and a high water absorption, and thus causes an increase in the unit water volume. Therefore, the milled fine aggregate is subjected to wet classification to mainly remove ultrafine sand having a sieve size of 0.038 mm or less.

In this case, even if ultrafine sand having a sieve size of 0.038 mm or less is to be removed, fine sand having a sieve size of 0.038 mm or more (0.03 mm or more) is removed due to wet classification.
8 to 0.15 mm) can naturally flow out, and the present invention has a sieve size of 0.038 m
m is not a clear boundary, and is a production method aimed at mainly removing ultrafine sand having a sieve size of 0.038 mm or less, in other words, a sieve size of 0.038 mm by wet classification. What removes the following ultrafine sands regardless of the removal amount is included in the technical scope of the present invention.

Further, regarding the amount of ultrafine sand removed by wet classification, it is technically difficult to completely remove the ultrafine sand (100%), and the object of the present invention is to reduce the unit water amount. In light of the above, it is preferable to remove approximately 1/3 or more of the content, and more than approximately 1/2 of the content
More preferably, the above amount is removed.

When ultra-fine sand is removed in this way,
The effect of reducing the unit water amount (improving the slump value) by reducing the ultrafine sand having a large specific surface area, that is, improving the concrete quality can be obtained. It should be noted that removal of the ultrafine sand content leads to a decrease in the performance rate, but since the cement is replenished for the reduced ultrafine sand content, the reduction in the performance rate can be suppressed from the viewpoint of the entire concrete.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Conventional processed sea sand is obtained by grinding sea sand lacking the fine sand content itself to reduce the fine sand content having a sieve size of 0.15 mm or less within a range of 5 to 15%. It is increased. This sieve size 0.15mm
When the following fine sand is analyzed, the sieve size is 0.15m.
m to ultra-fine sand particles close to cement particles (generally average particle size is assumed to be 0.014 mm), and ultra-fine sand particles smaller than that. Conventional processed sea sand, as a result of grinding, increases fine sand with a sieve size of 0.15 mm or less, compared with sea sand before processing, and fine sand obtained from other sand It is known as a technique that can greatly reduce the unit water volume as compared with mixed sand obtained by adding water to sea sand. However, it has been found that the unit water volume can be further reduced by removing the ultrafine sand present in the fine sand having a sieve size of 0.15 mm or less in the processed sea sand. The following test kneading was carried out comparing sand and fine aggregate for concrete of the present invention (wet classification fine aggregate).

[0014] Table 1 shows the blending conditions for the test kneading. Table 2 shows the materials used. Table 3 shows the quality of the materials used (surface dry density, water absorption). Table 4 shows fine aggregate used (sand)
Shows the particle size and the fine sand content. Table 5 shows the test mix concrete mix. Table 6 shows the test results (slump value) of the test kneading. Table 7 shows the concrete composition when the concrete composition of Table 5 is modified so that the target slump value becomes substantially the same in order to confirm the unit water amount. Table 8 shows the results of the tests performed with the modified formulations of Table 7.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

[Table 3]

[0018]

[Table 4]

[0019]

[Table 5]

[0020]

[Table 6]

[0021]

[Table 7]

[0022]

[Table 8]

As shown in the above test results (Table 6), the fine aggregate for concrete (wet classification fine aggregate) of the present invention has a slump value improved by 3 cm. In addition, when the target slump values were set to the same level (Table 8), as shown in the modified mixture table (Table 7), the fine aggregate for the concrete of the present invention (wet classification fine aggregate) had a unit of almost 1 liter. The amount of water could be reduced.

[0024]

As described above, according to the method for producing fine aggregate for concrete of the present invention, the grinding process is performed while using natural sea sand or river sand having a rounded shape as a raw material. In addition to making the grain shape more rounded, the required amount of fine sand with a sieve size of 0.15 mm or less is contained, and ultrafine sand with a large specific surface area of 0.038 mm or less is removed by wet classification. can do. As a result, while suppressing the decrease in the performance rate, the fluidity (slump value) of concrete is improved,
It is possible to obtain concrete with excellent durability by reducing the unit water volume.

Claims (1)

[Claims] 1. A raw material sea sand or a raw river sand containing a fine sand having a sieve size of 0.15 mm or less at a passage rate of 4% or less by grinding, so that the grain shape of the sand particles is rounded. A ground fine aggregate in which the fine sand content is increased so that the fine sand content having a sieve size of 0.15 mm or less is contained at a passage rate of 3 to 10% is obtained. Next, a method for producing a fine aggregate for concrete, characterized in that this milled fine aggregate is subjected to wet classification to mainly remove ultrafine sand having a sieve size of 0.038 mm or less.