JPH08277154A - Concrete composition - Google Patents

Abstract

PURPOSE: To obtain a concrete composition excellent in workability, having small shrinkage after hardening and approximately the same strength as that of ordinary concrete, by using an aggregate not containing a fine aggregate at all or almost not containing it, controlling the blended amounts of a cement and fine powder of a mineral substance and the ratio of water/powder. CONSTITUTION: This concrete composition contains a cement, a coarse aggregate, fine powder of a mineral substance and water and comprises <=550 liter of the coarse aggregate based on a unit amount and <=250 liter unit water amount and has the ratio of water/powder (the amount of water to the total of the cement and the fine powder of a mineral substance) of >=60vol.%, preferably >=70vol.%. In the case of containing a fine aggregate, the sand ratio is <=10. Gravel, crushed stone, etc., are used as the coarse aggregate. Fly ash is used as the fine powder of a mineral substance. Ordinary Portland cement, etc., are used as the cement. A high-performance water reducing agent (e.g. polycarboxylic acid salt-based one) may be used and its added amount is preferably 0.1-10 wt.% based on 100 pts.wt. of Portland cement.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a concrete composition which does not contain fine aggregates such as sand, has good fluidity, and exhibits excellent strength.

[0002]

2. Description of the Related Art Concrete is manufactured by adding water to each material such as cement, aggregate and admixture and kneading. Of these, the aggregate is not a material that causes a hardening reaction, but the quality of it is that of the concrete after hardening. Since it has a great influence on the properties, the particle size and amount of the aggregate are variously adjusted during the production of concrete.

Aggregate is classified into fine aggregate and coarse aggregate based on the particle size. Fine aggregates are particles of 5 mm or less (85% by weight or more of particles that pass through 5 mm sieve mesh), and coarse aggregates are particles having a larger particle size. In general, when an aggregate containing a large amount of coarse aggregate and a small proportion of fine aggregate is used, the amount of unit water required to obtain a required slump value decreases, but the concrete itself becomes rough and the workability deteriorates. On the other hand, when the amount of fine aggregate is extremely large and the amount of coarse aggregate is small, the amount of unit water that can be kneaded is significantly increased, which adversely affects the development of strength. Therefore, in ordinary concrete, an aggregate having a grain size in which fine aggregate and coarse aggregate are appropriately mixed is used. Conventionally, river sand and mountain sand have been used as fine aggregates, but recently, sea sand and crushed sand are also used because it is difficult to obtain high quality sand.

Mineral fine powders such as fly ash, blast furnace slag fine powder, and siliceous fine powder are mainly used as admixtures for concrete, and workability is improved by adding fly ash. Can reduce the amount of unit water to obtain the consistency of
In addition, during a sufficient curing period, the pozzolanic reaction is promoted to make the concrete structure dense and improve the long-term strength. Further, effects such as alleviation of heat of hydration can be obtained.

[0005]

Aggregate in which coarse aggregate and fine aggregate are appropriately mixed is used for conventional concrete. Specifically, the concrete aggregate ratio (s / a: total Aggregates having a particle size distribution in which the volume s of fine aggregate to the volume a of aggregate is about 35 to 50% are mainly used. However, in recent years
It is difficult to obtain high-quality fine aggregate, and there is no choice but to use aggregate having a discontinuous particle size distribution. When aggregates with an unsuitable particle size distribution are used for concrete, the unit water amount for obtaining the required fluidity increases, which increases drying shrinkage and causes cracks, and also reduces concrete strength and material separation. It causes problems such as increasing tendency. In order to avoid such an inconvenience, conventionally, fine particles or coarse particles may be added to the aggregate having an inappropriate particle size distribution to adjust the particle size composition, but the adjustment requires a great deal of labor and cost.

[0006] The present invention provides a concrete composition that overcomes the above-mentioned problems of the prior art, and uses the aggregate that does not contain fine aggregates at all, and the unit required to obtain the required fluidity. The present invention provides a concrete composition having a small amount of water, good workability, and a small shrinkage after hardening.

[0007]

SUMMARY OF THE INVENTION The present invention uses aggregates that contain little or no fine aggregates, that is, only coarse aggregates. By adjusting the blending amount and the water / powder ratio, a concrete composition having excellent workability, small shrinkage after hardening, and strength comparable to general concrete was obtained.

That is, according to the present invention, there is provided a concrete composition having the following constitution. (1) Cement, coarse aggregate, fine mineral powder and water are included, the amount of coarse aggregate per unit amount is 550 liters or less, the unit water amount is 250 liters or less, water / powder ratio (cement and mineral fine powder The amount of water relative to the total amount of) is 60% by volume or more, preferably 70% by volume or more. (2) The concrete composition as described in (1) above, which contains a high-performance water reducing agent. (3) The concrete composition according to the above (1) or (2), wherein the cement is ordinary Portland cement or early-strength Portland cement. (4) The concrete composition as described in (1), (2) or (3) above, wherein the mineral fine powder is a natural mineral fine powder or an artificial mineral fine powder. (5) Above (4), in which the fine mineral powder is fly ash
The concrete composition according to.

[0009]

[Detailed Description] Although the aggregate used in the concrete composition of the present invention is a coarse aggregate composed of particles having a particle size of 5 mm or more, the coarse aggregate of the present invention does not include fine aggregate at all. And those containing a slight amount of fine aggregate having a fine aggregate ratio of 10 or less. The material and shape of the coarse aggregate are not limited, and gravel and crushed stone can be used. Further, the coarse particle ratio of the coarse aggregate is not particularly limited. As an example, it is possible to use the coarse aggregate having the actual volume ratio shown in Table 1 and the examples described later.

As the fine mineral powder, various rock powders having particle diameters approximately the same as those of cement particles, fine natural mineral powder such as diatomaceous earth and natural pozzolan, blast furnace slag fine powder, fly ash, silica fine powder, etc. Any of the artificial fine powders of artificial minerals can be used. Here, the fly ash is not limited to the range specified by JIS, but includes a wide range including fly ash and cinder ash that are usually called raw powder.

The cement used includes various portland cements such as normal, early strength, super early strength, moderate heat, sulfate resistant, white, etc., but exerts a great effect in improving initial and long-term strength development. For this purpose, normal Portland cement or early-strength Portland cement is preferably suitable.

A high performance water reducing agent can be added to the concrete composition of the present invention. As a high-performance water reducing agent,
Conventionally used as an admixture for concrete,
For example, any compound having a chemical composition of alkylylallyl type, naphthalene type, melamine type, and triazine type can be used, but a polycarboxylic acid salt type admixture is preferable. High performance AE with air entrainment performance
Water reducing agents or air entrainers can also be used. The addition amount of these high-performance water reducing agents is adjusted in consideration of the Portland cement, the aggregate, the fine powder of minerals, the required water reducing effect, etc., but in general, it is 0 for 100 parts by weight of Portland cement. 1 to 10% by weight is suitable. If it is less than 0.1% by weight, the water-reducing effect is substantially absent, and if it is added in excess of 10% by weight, the effect of improving the water-reducing property and the fluidity reaches a ceiling.

The concrete composition of the present invention contains
In addition to the above compounding ingredients, rapid-hardening / quick-setting materials usually used in concrete, high-strength admixtures, hydration accelerators,
Various concrete admixtures such as setting regulators, various fibers as reinforcing materials, steel and the like can also be used.

The mixing amount of each material per unit amount (m ³ ) in the concrete composition is such that the amount of the coarse aggregate is 550 liters or less and the unit water amount is 250 in the coarse aggregate having a real volume ratio of 55 to 65%. It is liter or less, and the water / powder ratio (the amount of water relative to the total amount of cement and fine mineral powder) is 60% by volume or more, preferably 70% by volume or more.

The unit water volume is 250 liters as the limit water volume,
If the amount of water is larger than this, the watertightness decreases, and cracks due to drying shrinkage are likely to occur, which causes a decrease in strength. If the amount of coarse aggregate compounded exceeds 550 liters (1452 kg / m ³ ) per unit amount, the aggregates tend to mesh with each other and the upper part of the slump will collapse even if a cement paste having a good viscosity is prepared. Since the unit water amount is 250 liters or less, the lower limit of the amount of coarse aggregate is about 400 liters.

The water / powder ratio is represented by the volume ratio (W / B) of the amount W of water to the total amount B of cement and fine powder of mineral matter, and when the water / powder ratio is less than 60% by volume. Due to an absolute water shortage, it is impossible to knead even if a high-performance water reducing agent is added, and a concrete composition cannot be obtained. water/
When the powder ratio is in the range of 60 to 70% by volume, the cement paste has high viscosity and adhesiveness, and the fine powder of minerals causes a gradual flow due to the bearing effect, but the workability is very poor. In this case, increasing the amount of the high-performance water reducing agent improves the fluidity of the paste, but causes material separation. On the other hand, when the water / powder ratio is 70% by volume or more, good workability can be obtained. Since the unit water amount is 250 liters or less, the upper limit of the water / powder ratio is about 120% by volume.
Is.

There is no limitation on the method of mixing and kneading the above components, as long as they can be uniformly kneaded, and the order of addition of the blending components is not particularly limited. Furthermore, various curing methods can be applied for curing after placing concrete, and any of room temperature curing, high temperature curing, normal pressure steam curing, and high temperature and high pressure curing can be adopted. May be.

[0018]

Examples of the present invention will be described below. It should be noted that this example is merely an example and does not limit the scope of the present invention.

Example Using the materials shown in Table 1, the blending amount of the materials was set to the amount of cement:
300 kg / m ^3, unit water: 150~250kg / m ^3, the addition amount of the high-performance AE water reducing agent: in a range of 3.0 wt% or less (by weight relative to the total weight of cement and mineral fine powder), coarse aggregate The bulk specific gravity of the material is 1.5 to 1.7.
Since the actual product rate is 61.5%, the maximum capacity is 550
Concrete compositions were prepared for Sample Nos. 1 to 23 in which the water / powder ratio and the volume of coarse aggregate were changed within the range shown in Table 1 in liters. The kneading method is the same as the conventional method,
High performance A in the range where slump can be obtained and there is no material separation
E Specimens were prepared when the addition amount of the water reducing agent was obtained.

For each sample, the slump of fresh concrete, the amount of air, the unit volume weight, and the kneading temperature were measured, and the compressive strength and the static elastic coefficient were measured 3 days, 7 days, and 28 days after curing. For the samples having a water / powder ratio in the range of 70 to 110, the compounding amounts of the materials are shown in Table 2, and the slump value, compressive strength and static elastic modulus of the fresh concrete are shown in Table 3. Furthermore, these results are shown in FIG. In the same figure, the range of the compounding amount in which a good slump was obtained without separation of the materials is shown. The 28-day age strength of each sample is shown in FIG.

As shown in FIG. 1, if the water / powder ratio was less than 60% by volume, it was impossible to knead even if the high-performance water reducing agent was added due to the absolute lack of water. Also, the water / powder ratio is 6
In the range of 0 to 70% by volume, the cement paste has high viscosity and adhesiveness, and the workability tends to be lowered although it slowly flows due to the bearing effect of the fine mineral powder. In this case, it was confirmed that increasing the amount of the high-performance water reducing agent improved the fluidity of the paste but caused material separation. On the other hand, the samples having a water / powder ratio of 70% by volume or more showed good workability.

According to the results of this example, if the unit water amount is about 225 liters (kg / m ³ ) or less by the age of 28 days, the water / cement ratio is constant, so the compressive strength is the unit. It tends to change according to the amount of water, and no significant increase in compressive strength is observed even if the amount of fine mineral powder mixed is increased. When the unit water volume is near the limit water volume (250 liters), the compressive strength tends to improve in proportion to the amount of fine mineral powder mixed. Moreover, the 28-day-old compressive strength of the sample (W / B = 80, G = 450 liter) from which good fresh concrete was obtained is 3
It was 95 kgf / m ³ , and it was confirmed that it exhibited strength equivalent to that of general concrete.

Next, the relationship between the 28-day-old compressive strength and the static elastic modulus of each sample is shown in FIGS. 3 and 4. FIG. 3 is a comparison of samples having different water / powder ratios, and FIG. 4 is a comparison of samples having different amounts of coarse aggregate. As is clear from the figure, in all cases, the static elastic modulus is lower than that of general concrete, and further, the elastic coefficient decreases as the water / powder ratio and the amount of coarse aggregate decrease. Further, as shown in Table 3, the static elastic modulus of this concrete decreases in proportion to the blending amount of the fine mineral powder (CA) with respect to the cement (C).

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

[Table 3]

[0027]

EFFECTS OF THE INVENTION The concrete composition of the present invention is an aggregate containing no or almost no fine aggregate, that is, using only coarse aggregate, while using the amount of coarse aggregate, cement and mineral fine powder. By adjusting the compounding amount and the water / powder ratio, the workability is excellent, the shrinkage after curing is small, and the strength is about the same as general concrete. Therefore, it is not necessary to use fine aggregate having a good particle size distribution, which is difficult to obtain, and it is not necessary to adjust the particle size of the aggregate, which has been indispensable in the past, and a good quality concrete product can be easily and inexpensively obtained . Also, the concrete composition of the present invention has a low elastic modulus and is therefore suitable for applications requiring such properties.

[Brief description of drawings]

FIG. 1 is a triangular diagram showing an appropriate range of a mixing ratio and a water / powder ratio of a concrete composition according to the present invention.

FIG. 2 is a triangular diagram showing the relationship between the mixing ratio of the concrete composition according to the present invention and the 28-day-old compressive strength.

FIG. 3 is a graph showing the relationship between the 28-day-old compressive strength and the static elastic modulus of the concrete composition according to the present invention.

FIG. 4 is a graph showing the relationship between the 28-day-old compressive strength and the static elastic modulus of the concrete composition according to the present invention.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location C04B 7/26 C04B 7/26 (72) Inventor Masahiro Kato 2-chome, Daisaku Sakura, Chiba Prefecture No. 2 Chichibu Onoda Central Research Institute (72) Inventor Koichiro Sato 2-4-2 Daisaku Sakura, Chiba Prefecture Chichibu Onoda Central Research Institute

Claims (5)

[Claims] 1. A cement, a coarse aggregate, a fine powder of a mineral substance and water, the amount of the coarse aggregate per unit amount being 550 liters or less,
Unit water amount is 250 liters or less, water / powder ratio (water amount relative to the total amount of cement and fine mineral powder) is 60 volume% or more,
The concrete composition is preferably 70% by volume or more. 2. The concrete composition according to claim 1, which contains a superplasticizer. 3. The cement according to claim 1, wherein the cement is ordinary Portland cement or early-strength Portland cement.
The concrete composition according to. 4. The concrete composition according to claim 1, 2 or 3, wherein the fine mineral powder is a fine natural mineral powder or a fine artificial mineral powder. 5. The concrete composition according to claim 4, wherein the fine mineral powder is fly ash.