JP4112049B2 - Low shrinkage concrete composition - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a concrete composition, and more particularly to a high strength, high density, low shrinkage concrete composition.
[0002]
[Prior art]
Conventionally, in high-strength concrete, high-fluidity concrete, etc., for the purpose of obtaining high density, strength, etc., a coarse aggregate having an absolute dry specific gravity of 2.5 or more is usually used as the aggregate, The powder ratio is a low value of about 25 to 50%. However, when concrete is cured at such a low water / powder ratio, there is a problem that cracks due to self-shrinkage occur and the strength development is hindered.
[0003]
Self-shrinkage is significantly affected by the water-powder ratio, regardless of whether or not it is dried from the surface. In order to prevent the occurrence of cracks due to self-shrinkage, it is necessary to allow sufficient moisture in the vicinity of the cement particles in the initial stage of curing (within 1 week of age), but it is difficult to supply water from the outside. is there. Further, even if the curing water is supplied from the outside and the wet curing is performed, the process becomes complicated and the construction period is extended. In addition, in the case of mass concrete, or concrete that has a lot of formwork, plastering surface, surface directly in contact with the ground, etc., it is difficult to supply curing water, so internal cracks cannot be supplied. Will occur and cause cracks.
[0004]
Alternatively, the same can be said for preventing the occurrence of cracks due to drying shrinkage.
[0005]
Accordingly, there is a need for a concrete that has little self-shrinkage and drying shrinkage even at high strength and high density and does not generate cracks.
[0006]
It should be noted that, in light-weight concrete intended to obtain a low density, including only light-weight coarse aggregate having an absolute dry specific gravity of less than 1.4 as the coarse aggregate, an absolute dry specific gravity of 1 is intended as a fine aggregate. Although it is known to use a lightweight fine aggregate of less than .8, it is intended to reduce shrinkage in ordinary concrete containing coarse aggregate having an absolute dry specific gravity of 2.5 or more. It has not been conventionally known to contain.
[0007]
[Problems to be solved by the invention]
The object of the present invention is to reduce self-shrinkage and drying shrinkage without supplying curing water in concrete requiring high density and strength, such as high-strength concrete and high-fluidity concrete, with less cracking and fewer steps. The object is to provide concrete capable of developing high strength.
[0008]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventor surprisingly added a small amount of lightweight fine aggregate, which has been conventionally used for further weight reduction of lightweight concrete, to high-strength concrete and the like. As a result, it was found that a lightweight fine aggregate that easily contains moisture can supply moisture to the concrete inside the concrete during the curing process, and can prevent cracking without supplying curing water, thereby completing the present invention. .
[0009]
That is, according to the present invention, a coarse aggregate having a specific gravity of 2.5 or more, a lightweight fine aggregate having a porosity of 15% or more, or containing 10% or more of moisture , cement, and water. A low shrinkage concrete composition is provided.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The low shrinkage concrete composition of the present invention contains coarse aggregate, lightweight fine aggregate, cement and water.
[0011]
The coarse aggregate is not particularly limited as long as it has an absolute dry specific gravity of 2.5 or more, and ordinary coarse aggregates such as crushed stone, blast furnace slag, river gravel and the like can be used.
[0012]
The blending ratio of the coarse aggregate in the low shrinkage concrete composition of the present invention is preferably 800 to 1200 kg / m ³ , particularly 900 to 1100 kg / m ³ .
[0013]
The lightweight fine aggregate is a fine aggregate having an absolute dry specific gravity of 1.8 or less. The lightweight fine aggregate is preferably a fine aggregate having a porosity of 15% or more or containing 10% or more of moisture. The porosity indicates the amount of voids in the aggregate particles and is expressed as a volume ratio. Further, the phrase “can contain 10% or more moisture” means that the amount of water that penetrates into the voids and replaces the air in the internal bubbles and penetrates into the interior can be 10% or more of the aggregate weight.
[0014]
The material of the lightweight fine aggregate is not particularly limited. Artificial lightweight fine aggregates such as expansive clay and shale fired products, natural lightweight fine aggregates such as volcanic gravel and pumice, and by-product lightweight fine aggregates such as expanded slag. Aggregates can be used.
[0015]
The blending ratio of the lightweight fine aggregate in the low shrinkage concrete composition of the present invention is preferably 300 to 900 kg / m ³ , particularly preferably 300 to 600 kg / m ³ . By setting it to 300 kg / m ³ or more, it is possible to sufficiently supply water and obtain the effects of the present invention, and by setting it to 600 kg / m ³ or less, it is possible to prevent the strength, density, etc. from being lowered, which is preferable. .
[0016]
The optimum content ratio of the lightweight fine aggregate in the low shrinkage concrete composition of the present invention varies depending on how much the lightweight fine aggregate can contain water. Specifically, in order to obtain the effects of the present invention, it is sufficient that the lightweight fine aggregate contains an amount of water corresponding to about 50 kg per 1 m ^{3 of} the concrete composition. Therefore, for example, if it is a lightweight fine aggregate that can contain about 15% by weight of water, sufficient effects of the present invention can be obtained by containing about 300 to 400 kg / m ³ , optimally about 333 kg / m ^3. be able to.
[0017]
As the cement contained in the low shrinkage concrete composition of the present invention, Portland cement, mixed cement or the like can be used.
[0018]
The blending ratio of the cement in the low-shrinkage concrete composition of the present invention is preferably 450 to 700 kg / m ³ if no other powder component is blended. Is preferably in the range of 450 to 700 kg / m ³ as the total of the powder components.
[0019]
The mixing ratio of water contained in the low shrinkage concrete composition of the present invention can be 140 to 185 kg / m ³ .
[0020]
The low-shrinkage concrete composition of the present invention contains the specific coarse aggregate, the specific lightweight fine aggregate, cement and water, but in addition to these, fly ash, blast furnace slag fine powder, silica fume, stone powder and the like Other components such as admixtures, water reducing agents, high-performance AE water reducing agents, thickeners and the like may be contained. The blending ratio of these other components is preferably ^{30 to} 300 kg / m ^{3 for} the admixture and 0.1 to 20 l / m ³ for the admixture.
[0021]
The low shrinkage concrete of the present invention preferably has a water / powder ratio of 40% or less. Here, the water / powder ratio refers to the mixing ratio of water to powder components such as cement and stone powder.
[0022]
Usually, the self-shrinkage ratio of concrete having a low water powder ratio (W / C = 30 to 20%) is about 400 to 800 × 10 ⁻⁶ after about 2 weeks after the start of curing. On the other hand, the low shrinkage concrete of the present invention can have a self-shrinkage rate of about 100 × 10 ⁻⁶ or less, or can shrink the shrinkage to the expansion side.
[0023]
【The invention's effect】
The low-shrinkage concrete composition of the present invention includes a specific lightweight fine aggregate in addition to a specific high specific gravity coarse aggregate, and thus reduces self-shrinkage and dry shrinkage without supplying curing water. It is hardened, has few cracks, and can produce high strength with few steps. Therefore, the amount of powder was increased and the water-to-powder ratio was reduced in order to eliminate the need for compaction work to meet high-strength concrete used for RC high-rise buildings, PC structures, and other construction conditions that are difficult to compact. Useful as high fluid concrete.
[0024]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.
[0025]
[Example 1]
(High-strength concrete)
Table dry specific gravity 2.6, coarse aggregate particle size 25 mm (crushed stone) 1092kg / m ^3, fine aggregates-dry specific gravity 2.6 (crushed sand) 100 kg / m ^3, porosity of 30% weight fine aggregate ( Product name “Mesalite” (manufactured by Nippon Mesalite Industrial Co., Ltd.) 330 kg / m ³ , cement (ordinary cement) 550 kg / m ³ , water 165 kg / m ³ (water / powder ratio 30%) and high-performance water reducing agent 5.5 kg / M ³ was blended to obtain a concrete composition. The composition was cured according to normal casting procedures. However, no curing water was supplied.
[0026]
About the obtained hardened | cured material, it was 750 kg / cm < ² > when the compressive strength in material age 28th was measured. Further, no cracks were observed in the obtained cured product.
[0027]
[Example 2]
(High-strength concrete)
Coarse aggregate (crushed stone) of 996 kg / m ^{3 with} a surface dry specific gravity of 2.65, particle size of 20 mm, lightweight fine aggregate with a porosity of 30% (trade name “Mesalite”, manufactured by Nippon Mesalite Industrial Co., Ltd.) 440 kg / m ³ , Cement (medium heat Portland cement) 660 kg / m ³ , water 165 kg / m ³ (water / powder ratio 25%) and high performance water reducing agent 11.22 kg / m ³ were blended to obtain a concrete composition. The composition was cured according to normal casting procedures. However, no curing water was supplied.
[0028]
About the obtained hardened | cured material, it was 900 kg / cm < ² > when the compressive strength in material age 28th was measured. Further, no cracks were observed in the obtained cured product.
[0029]
[Example 3]
(High fluidity concrete)
Coarse aggregate (crushed stone) 800 kg / m ^{3 with} a surface dry specific gravity of 2.60, a particle size of 20 mm, fine aggregate (sea sand) with a surface dry specific gravity of 2.56, 360 kg / m ³ , and a lightweight fine aggregate with a porosity of 30% (Product name “Mesalite”, manufactured by Nippon Mesalite Industry Co., Ltd.) 300 kg / m ³ , Cement (Blast Furnace Cement B Type) 200 kg / m ³ , Limestone Powder 331 kg / m ³ , Water 159 kg / m ³ (Water / Powder Ratio 29 .9%), blended high AE water reducing agent 14.34kg / m ³ and a thickening agent 0.1 kg / m ^3, to obtain a concrete composition. The composition was cured according to normal casting procedures. However, no curing water was supplied.
[0030]
About the obtained hardened | cured material, it was 300 kg / cm < ² > when the compressive strength in material age 28th was measured. Further, no cracks were observed in the obtained cured product.

Claims (1)

Coarse aggregate having an absolute dry specific gravity of 2.5 or more, lightweight fine aggregate having a porosity of 15% or more, or containing 10% or more of moisture , cement and water Concrete composition.