JP2002128574A - Lightweight concrete - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide lightweight concrete having mass of unit volume of 1,800-2,000 kg/m3 with high performance at a low cost, which is especially suitable for structural constructions such as railway bridges, road bridges, etc. SOLUTION: For lightweight concrete manufactured by mixing at least cement, fine and coarse aggregates, and water and hardening, artificial lightweight aggregate with specific gravity in absolute dry condition of 0.7-1.0 and water absorption of <=5.0%, which is determined by JIS A1135 'Methods of test for particle density and water absorption of lightweight coarse aggregates for structural concrete', and crushed stone which meets JIS A5005 'Crushed stone and manufactured sand for concrete' are mixed at volume ratio of artificial lightweight aggregate to crushed stone of 9:1 to 6:4 and used as coarse aggregate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to lightweight concrete, and more particularly, to a concrete unit having a unit volume mass of 1,800 to 2,000 kg / m applicable to general civil engineering structures such as railway bridges and road bridges.
³ relates to lightweight concrete for civil engineering.

[0002]

2. Description of the Related Art Generally, concrete is classified into three types based on its weight: lightweight, ordinary, and heavy concrete. Lightweight concrete is manufactured by using aggregates with a low specific gravity.Since it is lightweight, it can be used to increase the size of structures, and it is also necessary to use steel for reinforcement to support the weight of structural members. The entire structure can be economically designed, such as saving on construction and simplifying the foundation work.

[0003] Here, general lightweight aggregates used for the production of lightweight concrete have high water absorption due to the existence of countless continuous air holes on the surface thereof, and the prior water absorption of the aggregates is insufficient. In the state, the aggregate absorbs the water in the concrete immediately after mixing, and the workability at the time of driving is significantly reduced. Therefore, in the related art, when manufacturing concrete using lightweight aggregate, it is general to use the aggregate in a state where sufficient water absorption has been performed.

[0004] However, the use of the pre-absorbed aggregate causes the water in the aggregate to move to the cement paste portion during the hardening process of the concrete, swelling the structure of the cement paste portion, and causing coarse voids. In the early age of the concrete, it caused a defect inside the concrete. In addition, when using the aggregate that has absorbed water in advance, the amount of drying shrinkage of the hardened concrete in the long-term aging is large, which has caused a crack in the structure.

[0005] The inventors of the present invention have previously conducted a method based on JIS A 1135 "Testing method for density and water absorption of lightweight coarse aggregate for structure" having an absolute dry specific gravity of 0.7 to 1.3. Artificial light aggregate having a water absorption of 5.0% or less [trade name: Asano Superlite (manufactured by Taiheiyo Cement Corporation)
L "), and especially, a product having an absolute dry specific gravity of 0.7 to 1.0 with ASL0.
85, ASL1.2G with absolute dry specific gravity of 1.1 to 1.3]
Developed and offered to the market.

This artificial lightweight aggregate is an artificial lightweight aggregate obtained by firing granulated pellets containing a rhyolitic vitreous powder as a main raw material and an inorganic binder and a foaming agent. ,
Since the surface of the artificial lightweight aggregate is denser than the inside, the pores communicated with the outside are small and the artificial lightweight aggregate exhibits low water absorption. As a result, even if the aggregate is used without prior water absorption, it hardly absorbs the water in the concrete, so that concrete having good driving workability can be obtained, and the hardening process up to 1 day of age. In, the moisture contained in the aggregate is supplied to the cement paste portion and the cement paste portion does not swell, the internal defect is hardly formed, and the hardened concrete is exposed to drying for a long time. Also, the amount of water that escapes from concrete is small, and the amount of drying shrinkage is small,
This made it possible to produce high-performance lightweight concrete.

At present, using the above-mentioned artificial lightweight aggregate exhibiting low water absorption, for example, a unit volume mass of 1,800 to
When producing high-performance lightweight concrete of 2,000 kg / m ³ , the absolute specific gravity as coarse aggregate is 1.1 to
The use of 1.3 lightweight artificial aggregates (eg, ASL1.2G) has been achieved. However, the artificial lightweight aggregate exhibiting such low water absorption has a high manufacturing cost. In particular, the artificial lightweight aggregate having an absolute dry specific gravity of 1.1 to 1.3 is an artificial lightweight aggregate having a lower specific gravity. (For example, ASL 0.85)
However, the production cost is high because the amount of raw materials used is larger than that of conventional concrete, and the resulting lightweight concrete has a large difference between ordinary concrete and the required price in the market.

The present invention has been made in view of the present situation of lightweight concrete using the above-mentioned artificial lightweight aggregate,
Its purpose is, high-performance lightweight concrete, unit volume mass that is particularly applicable to civil engineering structures general railway bridges and road bridges or the like for civil engineering lightweight concrete 1,800~2,000kg / m ^3, inexpensively provide Is to do.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above-mentioned object, and as a result, as a coarse aggregate, an artificial lightweight aggregate having a low specific gravity is used among the artificial lightweight aggregates having low water absorption. The present inventors have found that the desired high-performance lightweight concrete can be obtained at a low cost by using the aggregate and the crushed stone that is a common aggregate in a specific mixing ratio, and completed the present invention. That is, the present invention provides a lightweight concrete obtained by hardening a composition obtained by kneading at least cement, fine aggregate, coarse aggregate and water, wherein the absolute aggregate has an absolute dry specific gravity of 0.7 to 1. 0, an artificial lightweight aggregate having a water absorption of 5.0% or less, which is made in accordance with JIS A 1135 "Test method for density and water absorption of lightweight coarse aggregate for structure", and JIS 50
Crushed stones conforming to “Crushed stone for concrete” 05 were mixed and used, and a lightweight concrete in which the volume mixing ratio of the artificial lightweight aggregate and the crushed stone was 9: 1 to 6: 4.

According to the lightweight concrete according to the present invention, since a part of the artificial lightweight aggregate is replaced by crushed stone which is a common aggregate as coarse aggregate, it is used for the expensive artificial lightweight aggregate. The amount of water used can be reduced and inexpensive lightweight concrete can be provided, and the artificial lightweight aggregate used has a low water absorption rate of 5.0% or less. There is no need to provide a high-performance lightweight concrete that is less likely to cause internal defects or cracks.

Here, as the artificial lightweight aggregate used in the present invention, rhyolitic glassy powder is used as a main raw material, and granulated pellets containing an inorganic binder and a foaming agent are fired. It is preferable to use an artificial lightweight aggregate having a surface portion that is denser than the inside thereof. This is because the artificial lightweight aggregate is 5.0%
In addition to exhibiting the following low water absorption, it has a crushing strength of 1,000 N or more, and is preferable because the obtained lightweight concrete has high strength.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the lightweight concrete according to the present invention will be described below in detail.

In the present invention, as the coarse aggregate, the absolute dry weight is 0.7 to 1.0, and the water absorption is determined in accordance with JIS A1135 "Test method for density and water absorption of lightweight structural coarse aggregate". An artificial lightweight aggregate having a percentage (hereinafter simply referred to as “24-hour water absorption”) of 5.0% or less, and JIS A 5005
Crushed stones (hereinafter simply referred to as "crushed stones") compatible with "crushed stones for concrete" are used in combination.

Here, as the artificial lightweight aggregate to be used, one having an absolute dry specific gravity of 0.7 to 1.0 is used.
When the absolute dry gravity is 0.7 or more, fine closed pores are formed inside the aggregate, which is suitable for improving workability of lightweight concrete, preventing internal defects, and reducing drying shrinkage. On the other hand, when an artificial lightweight aggregate having a bone-dry specific gravity exceeding 1.0 is used, the amount of crushed stone that can be replaced becomes small in order to obtain lightweight concrete, and the amount of the artificial lightweight aggregate cannot be reduced. Not preferred.

[0015] The use of artificial lightweight aggregate having a water absorption rate of not more than 5.0% for 24 hours is the reason why concrete having a water absorption rate of more than 5.0% for 24 hours ensures the workability of concrete pouring. In order to do so, prior water absorption is necessary, and the large amount of aggregate-containing water generated by this pre-water absorption leads to the formation of internal defects in concrete and increases drying shrinkage, so that high-performance lightweight concrete cannot be obtained. Not preferred.

Further, in the present invention, the volume mixing ratio between the artificial lightweight aggregate having low specific gravity and low water absorption and crushed stone is as follows:
Used as 9: 1 to 6: 4. This is because, when the volume ratio of the artificial lightweight aggregate to the crushed stone is less than 9: 1, the effect of reducing the use of the artificial lightweight aggregate by the crushed stone is small, and an inexpensive lightweight concrete can be obtained. Conversely, the use of crushed stone having a volume mixing ratio exceeding 6: 4 is not preferable because the desired lightweight concrete is lost.

The artificial lightweight aggregate is mainly composed of rhyolite-based vitreous powder such as perlite and obsidian, and in addition to the raw material, an inorganic binder such as bentonite or silica sol;
And granulated pellets containing a foaming agent such as SiC, Si ₃ N ₄ , AlN and the like are primarily fired to shrink the pellets so that the relative density of the fired material becomes 90% or more, and at the same time, the surface layer portion of the fired material After the foaming agent present in the above is subjected to an oxidation reaction, the fired product can be manufactured by secondary firing and heating and foaming. The thus manufactured artificial lightweight aggregate has a surface portion that is smaller than that of the inside. And an artificial lightweight aggregate having a low water absorption of 5.0% or less and a crushing strength of 1,000 N or more. As such an artificial lightweight aggregate, Asano Superlight manufactured by Taiheiyo Cement Co., Ltd. is commercially available.

The crushed stone is JIS A 5005
Crushed stone suitable for "crushed stone for concrete", that is, specific gravity of 2.5 or more, water absorption of 3% or less, stability of 12% or less,
Satisfies the quality of less than 40% of abrasion loss when using a Los Angeles test machine. It was done.

Examples of the cement used in the present invention include Portland cement such as ordinary Portland cement and early-strength Portland cement, and mixed cement such as blast furnace cement and silica cement, and are usually used as mixing water. Tap water, groundwater, river water, and the like. Also, if necessary, an AE agent, high performance A
Admixture materials such as E water reducers can be used.

The mixing conditions of the lightweight concrete according to the present invention are as follows: the water cement ratio is 45% or less, and the absolute volume of the coarse aggregate obtained by mixing the artificial lightweight aggregate and the crushed stone is 300 to 40.
0 L / m ³ , a slump value of 8 to 21 cm, and an air volume of 4 to 9%, more preferably 5 to 7%.

This is because when the water cement ratio exceeds 45% and when the absolute volume of the coarse aggregate exceeds 400 L / m ³ , the water content becomes excessive, and the cement paste portion swells during the hardening process. This is not preferable because internal defects increase. In particular, when the absolute volume of the coarse aggregate exceeds 400 L / m ³ , the concrete strength is remarkably reduced, which is not preferable. When the absolute volume of the coarse aggregate obtained by mixing the artificial lightweight aggregate and the crushed stone is less than 300 L / m ³ , the effect of the aggregate to restrain the shrinkage of the paste is reduced,
It is not preferable because the amount of drying shrinkage of the hardened concrete increases and the effect of reducing the weight of the concrete also decreases. On the other hand, if the slump value is less than 8 cm, it is difficult to cast into a mold or the like and the filling property is deteriorated, which is not preferable. Conversely, if the slump value exceeds 21 cm, the mixed artificial lightweight aggregate and crushed stone And the aggregates and the paste are likely to be separated from each other, which is unfavorable because it adversely affects the construction. Further, when the air content is less than 4%, the freeze-thaw resistance is poor. Conversely, when the air content exceeds 9%, the strength is lowered, which is not preferable.

The lightweight concrete according to the present invention can be produced by the usual mixing method under the above-mentioned mixing conditions. For example, cement, fine aggregate, and coarse aggregate consisting of the artificial lightweight aggregate and crushed stone are put into a pan mixer or the like, and after kneading, water and, if necessary, an AE agent, a high-performance AE water reducing agent, and the like. It can be produced by adding an admixture and kneading. Since the artificial lightweight aggregate used in the present invention has low water absorption, it is not necessary to absorb water before kneading and can be used as it is in a completely dry state.

The cured lightweight concrete according to the present invention has a compressive strength of at least 40 N / mm ² , a ratio of tensile strength to compressive strength of at least 1/15, and a unit volume mass of from 1,800 to 2,000 kg / m 2. ³ light-weight concrete. Such light-weight concrete is a light-weight concrete for civil engineering that can be suitably used particularly for general civil engineering structures such as railway bridges and road bridges.

[0024]

Test Examples Hereinafter, test examples in which the above-described lightweight concrete according to the present invention was found will be described.

Materials used Cement (C): Portland cement of early strength (manufactured by Taiheiyo Cement Co., Ltd.) Fine aggregate (S): Land sand from Ogasawara [surface dry specific gravity 2.62;
Water absorption 1.56%] Coarse aggregate (G1): ASL 0.85 [manufactured by Taiheiyo Cement Co., Ltd., absolute dry specific gravity 0.86, water absorption 2.82%] (G2): Ome crushed stone [surface dry specific gravity 2] (G3): ASL1.2G (manufactured by Taiheiyo Cement Co., Ltd., absolute dry specific gravity: 1.25, water absorption: 1.83%) (G4): Mesalite (manufactured by Mesalite Industry Co., Ltd.) Absolute dry specific gravity 1.27 Water absorption 10.0%] High performance AE water reducing agent (WR): Rheobuild SP8S-X2
[Manufactured by NMB Corporation] AE agent (AE): Micro Air 775S [Manufactured by NMB Corporation] Water (W): Tap water The absolute dry specific gravity and the water absorption of the above coarse aggregate are JIS A
1135 "Measured in accordance with" Density and Water Absorption Test Method of Lightweight Structural Coarse Aggregate ".

Mixing The above-mentioned materials were mixed at various mixing ratios shown in Table 1 to prepare lightweight concrete. In the mixing, cement, fine aggregate and coarse aggregate were mixed in a constant temperature room at 20 ° C. by a forced mixer (pan type, volume 5).
5L) and kneaded for 15 seconds, then water and admixtures (SP, AE) were added and kneaded for 105 seconds. Various coarse aggregates were used in an absolutely dry state, and the amount of water absorbed during mixing (water absorption for 10 minutes) was added to the mixing water as a corrected water amount.

[0027]

[Table 1]

In Table 1, in Test Example 1, an artificial lightweight aggregate (mesalite) having a water absorption exceeding 5.0% as a coarse aggregate was used.
In Test Examples 2 to 7, the artificial light-weight aggregate (ASL1.2G) having a water absorption of 5.0% or less as a coarse aggregate but an absolute dry specific gravity exceeding 1.0 was used alone. In Test Examples 8 to 10, the water absorption was 5.0 as coarse aggregate.
% And an artificial lightweight aggregate having an absolute dry specific gravity of 0.7 to 1.0 (A
SL0.85) alone, and Test Example 11
Thereafter, as a coarse aggregate, an artificial lightweight aggregate (ASL 0.85) having a water absorption of 5.0% or less and an absolute dry specific gravity of 0.7 to 1.0 is used.
And crushed stone (crushed stone from Ome), which is a common aggregate, is used.

Evaluation: Fresh properties Slump and air volume were measured according to JIS A 1101 "Concrete slump test method" and JIS A 112, respectively.
8 Measured in accordance with “Test method for pressure of air volume of concrete that has not yet solidified by pressure”. In addition, the unit volume mass was measured in accordance with JIS A1116 “Method for testing unit volume mass of concrete and test method by weight of air amount”. -Hardened body properties Compressive strength and tensile strength were measured according to JIS A 1108, respectively.
"Test method for compressive strength of concrete", JIS A1
The measurement was carried out in accordance with 113 "Test Method for Tensile Strength of Concrete". Further, the ratio of the tensile strength to the measured compressive strength was determined. Table 2 shows the measurement results. In addition, the unit volume mass of the cured body property was within a value obtained by adding ³⁰ to 50 kg / m ³ to the unit volume mass of the fresh property.

[0030]

[Table 2]

From the above test examples, as a coarse aggregate, an artificial lightweight aggregate having a low specific gravity among artificial lightweight aggregates exhibiting low water absorption,
It was found that high-performance lightweight concrete can be obtained by mixing and using crushed stone, which is ordinary aggregate. In order to increase the strength, it was effective to decrease the water cement ratio and increase the crushed stone mixing ratio, and it was found that the smaller the absolute volume of the coarse aggregate, the higher the strength. Furthermore, it was found that the unit volume mass of the concrete immediately after kneading increased with the increase of the crushed stone mixing ratio, and high linear regression was observed.

Further, from the above test examples, as the coarse aggregate, A
SL0.85 and crushed stone were used at a volume mixing ratio of 9: 1 to 6: 4, and the absolute volume of the coarse aggregate was 300 to 400 L /
When m ³ and the water cement ratio are 45% or less, the compressive strength is 40 N / mm ² or more, the ratio of the tensile strength to the compressive strength is 1/15 or more, and the unit volume mass is 1,800 to
It was found that a lightweight concrete of 2,000 kg / m ³ could be obtained. .

[0033]

As described above, according to the lightweight concrete according to the present invention, since a part of the artificial lightweight aggregate is replaced with the crushed stone, which is ordinary aggregate, as the coarse aggregate, it is expensive. The amount of lightweight aggregate used is reduced, and inexpensive lightweight concrete can be provided. The artificial lightweight aggregate used has a low water absorption rate of 5.0% or less. There is no need to absorb water in advance, and it is possible to provide high-performance lightweight concrete in which internal defects or cracks hardly occur.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C04B 111: 40 C04B 111: 40 (72) Inventor Akihiko Kodama 2-4-2 Daisaku, Sakura City, Chiba Pref. Central Research Institute, Inc. (72) Inventor Hiroaki Mori 2-4-2 Daisaku, Sakura City, Chiba Pref. Central Research Institute (72) Inventor Hiroyuki Obata 2-4-2 Daisaku, Sakura City, Chiba Pref. 4G012 PA04 PA17 PC02 PC11 4G019 JA02 JA03 LA02 LB02 LD02

Claims (5)

[Claims] 1. A lightweight concrete obtained by hardening a composition obtained by kneading at least cement, fine aggregate, coarse aggregate and water, wherein the coarse aggregate has an absolute dry specific gravity of 0.7 to 0.7.
1.0, an artificial lightweight aggregate having a water absorption of 5.0% or less made in accordance with JIS A 1135 "Testing method for density and water absorption of lightweight coarse aggregate for structure", and JISA 5005
A lightweight concrete characterized by using a mixture of crushed stones conforming to "crushed stone for concrete" and a volume mixing ratio of the artificial lightweight aggregate and the crushed stone of 9: 1 to 6: 4. 2. The artificial lightweight aggregate is an artificial lightweight aggregate obtained by firing granulated pellets containing a rhyolite-based vitreous powder as a main raw material and an inorganic binder and a foaming agent. 2. The lightweight concrete according to claim 1, wherein the surface portion of the artificial lightweight aggregate is denser than the inside thereof. 3. The composition has a water cement ratio of 45% or less, an absolute volume of coarse aggregate of 300 to 400 L / m ³ , a slump value of 8 to 21 cm, and an air amount of 4 to 9%. The lightweight concrete according to claim 1 or 2, characterized in that: 4. The lightweight concrete has a compressive strength of 4
0 N / mm ² or more, the ratio of the tensile strength to the compressive strength is 1/15 or more, and the unit volume mass is 1,800 to 2,0
3. The method according to claim 1, wherein the weight is 00 kg / m ^3.
Or the lightweight concrete according to 3. 5. The lightweight concrete according to claim 1, wherein the lightweight concrete is used for construction of a civil engineering structure.