JP2002211966A - Secondary product of concrete and method of manufacturing for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain secondary products of concrete which are small in a shrinkage rate and are highly strong without degrading their workability. SOLUTION: The secondary products of concrete formed by compounding fly ash of <=20 μm in grain size to prepare the concrete and molding the concrete and the method of manufacturing for the same. If the fly ash of <=20 μm in grain size is added to the concrete, the workability of the concrete is greatly improved and consequently, the reduction of a unit water volume is made possible. The obtaining of the secondary products of the concrete having high strength is thus made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a concrete secondary product manufactured in a factory for manufacturing concrete members and a method for manufacturing the same.

[0002]

2. Description of the Related Art A secondary concrete product is a concrete molded product used for civil engineering structures, architectural structures, or other general uses, and is a general summary of what is produced in advance in a manufacturing plant or the like. It is something. Generally, in the production of such concrete secondary products, ordinary concrete, one type of lightweight concrete and two types of concrete are used.
Seeds are used. The design standard strength of the secondary concrete product and the range of the air-drying unit volume mass of the concrete secondary product when such concrete is used are shown in JASS 5, and the design standard strength is 18 to 36 N / m for ordinary concrete.
m ² , air drying unit volume mass is 2.2 to 2.4 t / m ³ , and similarly, one kind of lightweight concrete is 18 to 27 N / mm ² and 1.7 to 2.
0t / m ^3, the lightweight concrete two 18~27N / m
m ² , 1.4 to 1.7 t / m ³ .

Accordingly, the maximum design standard strength per unit mass of air-drying of 1 t / m ³ is 16.4 N / mm ² when ordinary concrete is used, and 15.9 N when one kind of lightweight concrete is used. / Mm ² , lightweight concrete 2
When a seed is used, it is 19.3 N / mm ² . That is, in general, the design standard strength per unit mass of air-drying of 1 t / m ³ is at most 20 N / mm ² .

If the design reference strength per unit mass of air-drying 1 t / m ³ can be increased, the thickness of the members used in the structure can be reduced, the weight of the members can be reduced, and heavy machinery such as cranes can be used. Can be reduced in size.

Conventionally, in order to meet such demands, methods for improving the strength of secondary concrete products by reducing the water binder ratio have been studied.

[0006] However, reducing the water binder ratio leads to an increase in the amount of binder, and as a result, the amount of self-shrinkage and drying shrinkage of the manufactured concrete member increases, and the periphery and corner of the opening of the member become large. There is a problem that cracks easily occur around the corners. Therefore, the amount of cement that can be used per unit volume is limited, and the strength is also limited.

[0007] Further, a method of improving the strength by adding fly ash has been studied. However, when ordinary fly ash specified by JIS or the like is used, a desired strength improving effect cannot be obtained. .

[0008]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to obtain a high-strength concrete secondary product having a small amount of shrinkage without deteriorating workability.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in view of the above problems, and have completed the following invention.

[0010] That is, the means of the present invention is a method for producing a concrete secondary product, which comprises mixing concrete with fly ash having a particle size of 20 µm or less to prepare and mold concrete. The proportion of the fly ash is preferably 5 to 20% by weight of the binder composed of fly ash and cement, and the water binder ratio is preferably 15 to 30%. In this specification, the ratio of fly ash in the binder is also referred to as a replacement ratio.

[0011] The means of the present invention is a secondary concrete product comprising fly ash having a particle size of 20 µm or less.

In the production of secondary concrete products, when fly ash having a particle size of 20 μm or less is added, the ball bearing effect of the fly ash is increased as compared with conventional fly ash, and the workability of concrete is significantly improved. Therefore, it is possible to produce concrete by reducing the unit water volume, and it is possible to obtain a high-strength concrete secondary product. In addition, since the amount of cement can be reduced by replacing with fly ash, the amount of self-shrinkage and the amount of dry shrinkage can be reduced, and cracks and the like are less likely to occur.
Note that the amount of self-shrinkage and the amount of dry shrinkage are determined by the measurement method described later.

Furthermore, since the fly ash particles are filled in the gaps between the cement particles, the so-called microfiller effect in which the voids in the concrete are reduced and the strength is increased is also remarkable. Therefore, the amount of the binder for obtaining the same strength can be reduced, whereby the amount of self-shrinkage and the amount of dry shrinkage can be reduced.

Furthermore, the pozzolanic reaction by fly ash is slower in reaction rate than the hydration reaction of cement, so that the amount of water consumed for hydration is reduced, and the self-shrinkage is reduced.

In particular, when fly ash having a particle size of 20 μm or less is used, the microfiller effect and the pozzolan reaction as described above act as more remarkable,
Since the structure of the concrete hardened body is extremely dense, the concrete strength can be effectively improved, and the amount of water lost during drying can be reduced, and drying shrinkage can be suppressed. Further, since the structure of the concrete hardened body is extremely dense, the neutralization rate of the concrete secondary product is extremely low, and the thickness from the reinforcing bar to the outer surface (so-called “cover”) can be reduced. Become.

Further, in the concrete secondary product and the method for producing the same according to the present invention, 0.3 to 0.3%
Preferably, 3% by weight of a high performance AE water reducing agent is added to the concrete.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION One embodiment of a method for producing a secondary concrete product according to the present invention comprises cement and a particle size of 20 μm.
A binder, water, fine aggregate, coarse aggregate and a high-performance AE water reducing agent composed of the following fly ash are prepared.

As the cement, any portland cement specified in JIS can be used without being limited to the type of cement. However, the following mixed cements, ie, blast furnace cement, fly ash cement, and silica cement, can be used. Can not be used.

The use of blast-furnace cement has the disadvantage that the amount of autogenous shrinkage of concrete is large.
It becomes 00 μm or more.

Further, fly ash cement and silica cement cannot be used. Because the ratio of Portland cement in the binder is small, the strength per unit mass of air-dried 1 t / m ³ is reduced. Conversely, if the desired strength is to be secured, the water binder ratio is extremely small. This is because good workability cannot be obtained.

On the other hand, as fly ash, JIS
It is possible to use fly ash for concrete or any other fly ash specified in A6201 and classify it to 20 μm or less by means such as air classification. If the particle size is at least 20 μm, the reactivity of pozzolans due to fly ash will be undesirably reduced.

The amount of the fly ash is preferably 5 to 20% by weight of the binder. If the content is 5% by weight or less, workability is reduced and workability is deteriorated. On the other hand, if the content is 20% by weight or more, the ratio of cement in the binder is reduced, and the same problem as in the case of using the mixed cement occurs. Absent.

The fine aggregate can be used without any particular limitation as long as it is used as an ordinary concrete aggregate. The type is not particularly limited, and river sand, sea sand, land sand, artificial lightweight aggregate, and the like can be used.

Similarly, the coarse aggregate is not particularly limited. There is no restriction on the type, and general coarse aggregate such as river gravel, crushed stone, and artificial lightweight aggregate can be used. Particularly, when natural aggregate such as river gravel or crushed stone is used, a solid material is preferable.

The artificial lightweight aggregate used as the fine aggregate or the coarse aggregate is of an extent that satisfies the quality standard of JIS A5002 (light structural concrete aggregate).

The high-performance AE water reducing agent has an effect of securing a good workability while reducing the unit water amount and, consequently, the unit binder amount at a low water binder ratio, and is therefore preferably added as necessary. The addition amount is preferably from 0.3 to 3.0% by weight based on the cement. If the amount is less than 0.3% by weight, the effect is hardly obtained.

The high-performance AE water reducing agent is a naphthalene type,
They are roughly classified into four types: polycarboxylic acids, melamines, and aminosulfonic acids, and are further subdivided by components. In the present invention, JIS
Any material can be used as long as it satisfies the quality standard specified in A6204 (chemical admixture for concrete). However, from the viewpoint of reduction in self-shrinkage and drying shrinkage, polycarboxylic acid-based maleic anhydride is used. It is preferable to use those having an acid and an allyl ether copolymer as main components.

In addition, the procedure for producing the secondary concrete product of the present invention can be carried out in the same manner as the known procedure for producing a secondary concrete product.

[0029]

The present invention will be described below in detail with reference to examples.

(Examples 1 to 6) Water, cement, admixture,
A mixture of fine aggregate, coarse aggregate and admixture at a predetermined ratio is mixed in a biaxial forced kneading mixer for 2 minutes, and then filled in a mold and cured to produce a concrete secondary product of 10φ × 20 cm. Specimens were prepared. The following materials were used.

Cement: ordinary Portland cement (density 3.15 g / c
m ³ ) Admixture: fly ash with a particle size of 20 μm or less (density 2.
36 g / cm ³ ) Fine aggregate: sand from Ibigawa, Gifu prefecture (surface dry density 2.65 g / cm ³ ) Coarse aggregate: crushed stone from Takatsuki, Osaka prefecture (surface dry density 2.69 g / cm ³ )
³ ) Admixture: High-performance AE water reducing agent (Neologic Corp., "Leobuild 8000H")

(Comparative Examples 1 to 5) Of the above compositions, test pieces were prepared in the same manner as in the examples except that no admixture was added.
Comparative Example 1 was used. Further, Comparative Example 2 was the same as the above-mentioned Example except that the water-binding material ratio was 35%. Hereinafter, in the same manner, ordinary fly ash (JIS
Comparative Example 3 using two kinds of A6201 and a density of 2.28 g / cm ³ , and silica fume (a density of 2.24 g) as an admixture
/ cm ³ ) in Comparative Example 4, 20% by weight of admixture
The one added above was designated as Comparative Example 5.

Table 1 shows the amounts of the components of the examples and comparative examples. In addition, at the time of compounding the materials, the compounding amounts of the respective components were determined with the aim of satisfying a slump of 21 cm and an air amount of 2%, based on a certain workability.

(Test Method) The concrete secondary product specimens of Examples and Comparative Examples prepared as described above were measured for air-dry volume mass, compressive strength and autogenous shrinkage at 28 days of age, and dry material age of 91 days. The amount of drying shrinkage per day was measured. Here, the air-dry volume mass is a value obtained by dividing the mass of a specimen stored in the atmosphere by its volume. The amount was measured in accordance with JIS A1129 "Method for changing the length of mortar and concrete", and the compressive strength was measured in accordance with JIS A1108 "Test method for compressive strength of concrete". Regarding the test results,
Also shown in Table 1.

[0035]

[Table 1]

As shown in Table 1 above, in Examples 1 to 6 according to the present invention, compressive strength at 28 days of age per unit mass of air-dried 1 t / m ³ (shown as “B / A” in the table) )
However, it can be seen that each of them is 30 N / mm ² or more.
Furthermore, in Examples 1 to 6 according to the present invention,
It can be seen that the amount of self-shrinkage on the 8th day is 400 μm or less and the amount of dry shrinkage on the 91st day is 500 μm or less. That is, it is understood that the concrete secondary product according to the present invention has a high strength and a reduced amount of shrinkage at the same time.

Subsequently, a load test in the case of molding as an actual box culvert product was performed as follows.

(Example 7, Comparative Examples 6 to 9) Concrete (Example 7 and Comparative Examples 6 to 9) having the composition shown in Table 2 below was prepared using the same materials as in the above-mentioned Example.
A box culvert according to the standards of the Japan Box Culvert Association as shown in FIG. 1 was formed from such concrete. The dimensions in the figure are B = 1.50 (unit m, the same applies hereinafter), H = 1.60, L1 = 0.10, L2 = 0.16, L3 = 0.14, C = 0.1
5, BO = 1.76, HO = 1.82, BL = 1.84, HL = 1.66, and the product length was 1.00.

[0039]

[Table 2]

(Test 1) Using the box culvert prepared as described above, a test regarding the external pressure strength was performed by a test method according to the standards of the Japan Box Culvert Association. Specifically, as shown in FIG. 2, the box culvert is placed on a solid base that is set horizontally and in parallel, and a steel girder is placed via a rubber plate at the center of the top plate. The load was evenly distributed from above. Table 3 shows the results.

[0041]

[Table 3]

(Test 2) Comparative Example 1 having the same design standard strength as the box culvert of Example 7
Box culverts 0 and 11 were made by conventional methods and examined for cracking. Specifically, concrete was prepared with the composition shown in Table 4 below, a box culvert having the same shape as that of FIG. 1 was produced, and the surface properties after curing for 4 weeks were observed. FIG. 3 shows the occurrence of cracks in Example 7 and Comparative Examples 10 and 11.

[0043]

[Table 4]

According to Test 1, 1 corresponding to 8 m of high embankment
At a load of 02 kN, cracks occurred in all of Comparative Examples 6 to 9, whereas in Example 7, cracks did not occur and it was found that they had sufficient strength. According to Test 2, as shown in FIG. 3, the box culvert of Example 7 did not crack, while the boxes of Comparative Examples 10 and 11 prepared by the conventional method so that the design standard strength was 80 kN. The culvert was cracked due to shrinkage as shown in FIGS. 3B and 3C, respectively, and the product value was reduced.

Subsequently, the following tests were performed as curtain wall products.

First, as the design specifications required for a high-rise building of about 60 m, the following conditions are applied, and the curtain wall required according to the design standard strength of the concrete of Example 7 and Comparative Examples 6 to 9 is used. Was calculated. 2 hours fire resistance: Reinforced concrete structure and plate thickness of 10 cm or more. (Building Standards Act) Deflection δ: When fulcrum L = 4000 mm, δ <δ ₀ = L / 1
To be 50. (JASS14 “Curtain wall construction”) Allowable stress: Tensile stress σ _t becomes allowable tensile stress Ft =
0.07 × Fc or less. (Architectural Institute of Japan "PRC
Design and construction standards ”) Wind resistance: q = 120 × H ^1/4 × 1.5 ≒ 500 (kgf /
cm ² ) ≒ 5000 (N / m ² ) Table 5 shows the calculation results.

[0047]

[Table 5]

As shown in Table 5, the plate thicknesses at which the tensile stress .sigma.t and the deflection .delta. Satisfy predetermined standards were 170 to 110 mm, respectively.

(Test 3) Then, based on the obtained calculation results, a curtain wall lithographic plate was actually produced, and a placement test was performed with a concentrated load (10 kN / m ² ) corresponding to the uniform distribution load ω. . Table 6 shows the results.

[0050]

[Table 6]

(Test 4) Further, in the same manner as in Test 2 described above, a curtain wall lithographic plate was prepared using concrete prepared by mixing the composition of Example 7 and Comparative Examples 10 and 11, and the surface properties after curing for 4 weeks were observed. did. FIG. 4 shows the state of occurrence of cracks.

According to Test 3, the curtain wall of Example 7 according to the present invention showed no abnormality even when the plate thickness was as thin as 110 mm, and had the strength calculated by the above calculation. Verified. According to Test 4, no cracking occurred in the curtain wall according to Example 7 (FIG. 4A), while in the curtain wall according to Comparative Examples 10 and 11, FIGS. 4B and 4C respectively.
As shown in Fig. 5, cracks occurred due to shrinkage.

[0053]

As described above, according to the method for producing a secondary concrete product according to the present invention, a secondary concrete product having high strength and low shrinkage can be produced while maintaining the workability of concrete. .

Therefore, according to the secondary product for a civil engineering structure according to the present invention, a normal formwork is changed even when higher strength is required in order to be buried deeper than usual. Without this, a secondary product having the same thickness as usual can be formed and used.

In such a place, it is usually necessary to increase the thickness of the concrete in order to prevent corrosion of the reinforcing steel due to leachate such as groundwater, but according to the secondary concrete product of the present invention, cracks are generated. Since the concrete is small and the concrete is dense, it is extremely low in water penetration and there is little need to increase the concrete thickness.

On the other hand, according to the secondary product for a building structure according to the present invention, the same strength can be expressed with a smaller thickness than before, and therefore the weight of the secondary product is significantly reduced. be able to. Therefore, it is possible to provide a concrete secondary product which is extremely suitable for a high-rise building.

[Brief description of the drawings]

FIG. 1 is a front view showing the shape of a box culvert manufactured as an example.

FIG. 2 is an explanatory diagram showing a state of a loading test of a box culvert.

FIG. 3 is a front view showing a crack generated in a box culvert by a test, wherein (a) is Example 7 and (b).
Shows the results of Comparative Example 10, and (c) shows the results of Comparative Example 11.

FIG. 4 is a front view showing cracks generated in a curtain wall lithographic plate by a test.
(B) shows the result of Comparative Example 10, and (c) shows the result of Comparative Example 11.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Kikuo Tachibana 7-55 Minamienkajima, Taisho-ku, Osaka City Sumitomo Osaka Cement Co., Ltd. Cement Concrete Research Laboratory (72) Inventor Nobuo Kayama Kumamoto, Kumamoto 3-9-5, Suizenji, Ichiyama Yamaguchi Co., Ltd. (72) Inventor: Manabu Matsuda 3-9-5, Suizenji, Kumamoto, Kumamoto F-term (reference) 4G012 PA27 PB25

Claims (8)

[Claims] 1. A method for producing a concrete secondary product, comprising preparing concrete by mixing fly ash having a particle size of 20 μm or less and molding the concrete. 2. The method for producing a secondary concrete product according to claim 1, wherein the proportion of the fly ash in the binder comprising the fly ash and the cement is 5 to 20% by weight. 3. The method for producing a secondary concrete product according to claim 1, wherein the water binder ratio is 15 to 30%. 4. The concrete secondary product according to claim 1, wherein 0.3 to 3% by weight of a high-performance AE water reducing agent based on cement is added to the concrete. Production method. 5. A secondary concrete product comprising fly ash having a particle size of 20 μm or less. 6. The secondary concrete product according to claim 5, wherein the compounding amount of the fly ash is 5 to 20% by weight of a binder composed of cement and fly ash. 7. The concrete secondary product according to claim 5, wherein the water binder ratio is adjusted to 15 to 30%. 8. The concrete secondary product according to claim 5, wherein 0.3 to 3% by weight of a high-performance AE water reducing agent is added to the cement.