JP2000109378A - Lightweight concrete - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide concrete which is capable of reducing internal defects in its initial age, regard less of whether or not the aggregate contains water absorbed before the use, and irrespective of content of the absorbed water, when super-lightweight coarse aggregate is used, and has sufficient placing workability and long-term durability. SOLUTION: This concrete contains 0.3 to 0.4 m3/m3 of super-lightweight coarse aggregate having <=5.0 wt.% in 24-hour water absorption ratio, <=10 wt.% in boiling water absorption ratio and a specific gravity in absolute dry condition of 0.7 to 1.3, and also has a unit cement content of >=400 kg/m3 and a water/cement ratio of <=40 wt.%. In the concrete, preferably, this super- lightweight coarse aggregate has >=800 N crushing strength and contains a composition consisting essentially of an alkylene oxide polymer.

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 high-rise building materials such as columns and beams of high-rise RC buildings, non-structural members such as curtain walls, and civil structures such as railway bridges and road bridges. The present invention relates to a concrete using ultra-lightweight coarse aggregate applied to an upper structure, a lower structure, and the like, which has a low water / cement ratio so as to have high strength.

[0002]

2. Description of the Related Art Existing light-weight coarse aggregates, such as ultra-light-weight coarse aggregates, have a high water absorption, and in a state where the pre-absorption of the aggregates is insufficient, the aggregates immediately remove water in concrete immediately after mixing. Water is absorbed and workability at the time of driving is significantly reduced. Therefore, in order to secure workability, it is common to use the existing lightweight concrete in a state where sufficient water absorption has been performed in order to secure workability.

[0003] However, this causes a defect to be formed inside the concrete at an early age.
That is, the pre-absorbed aggregate supplies the cement paste portion with water contained in the aggregate during the hardening process of the concrete, so that the structure of the cement paste portion swells to generate coarse voids.

In particular, such internal defects are likely to occur at the interface where the aggregate and the cement paste are in contact with each other, causing a decrease in the adhesive strength between the cement paste and the aggregate and an increase in the water permeability and air permeability of the concrete. , Making the production of durable concrete difficult.

[0005] In addition, when the pre-absorbed aggregate is used, the drying shrinkage of the hardened concrete in the long-term age increases, which is one of the causes of the occurrence of cracks in the structure. Concrete defects tend to increase.

[0006]

As described above, the water absorption state of the lightweight coarse aggregate has a great effect on the properties of the lightweight concrete. For this reason, it is extremely important to control the moisture content of the lightweight coarse aggregate during the production of lightweight concrete, but the operation is complicated. Therefore,
There is a demand for lightweight concrete that can maintain workability and durability without strictly controlling the water content of the lightweight coarse aggregate.

Accordingly, the present invention has been made in view of the above-mentioned problems in the prior art, and has been developed in consideration of the internal defect at the initial age regardless of the presence or absence and the degree of prior water absorption at the time of using the ultralight coarse aggregate. It is an object of the present invention to provide a lightweight concrete which can reduce the amount of work, and has workability at the time of driving and long-term durability.

[0008]

Means for Solving the Problems The present inventors have found that the above object can be achieved by using a specific ultralight coarse aggregate in a specific mixing amount as a coarse aggregate. Also,
Rather than ordinary pre-absorption, the inventor has found that the above object can be achieved more effectively by including a composition mainly containing an alkylene oxide polymer in advance in the ultralight coarse aggregate, and completed the present invention. It was made.

The invention according to claim 1 is a lightweight concrete having a 24-hour water absorption of 5.0% by weight or less, a boiling water absorption of 10% by weight or less, and an absolute dry specific gravity of 0.7 to 1.
The ultra-light coarse aggregate is 3 comprises 0.3~0.4m ³ / m ^3,
It is characterized in that the unit cement amount is 400 kg / m ³ or more and the water / cement ratio is 40% by weight or less.

The invention according to claim 2 is characterized in that the crushing strength of the ultralight coarse aggregate is 800 N or more.

The invention according to claim 3 is characterized in that the ultra-lightweight coarse aggregate contains a composition containing an alkylene oxide polymer as a main component.

According to the first aspect of the present invention,
4 hours water absorption of 5.0% by weight or less and boiling water absorption of 10%
Wt% or less, and the ultra-light coarse aggregate absolute dry specific gravity is 0.7 to 1.3 include 0.3~0.4m ³ / m ^3, the amount of the unit cement 400 kg / m ³ or more, a water / cement Since the concrete is a lightweight concrete having a ratio of 40% by weight or less, the workability of the lightweight concrete using the aggregate is improved due to the synergistic effect of the specific aggregate and the specific concrete composition, and the inner weight of the lightweight concrete at the initial age is reduced. The number of defects is reduced and the durability is improved.

According to the second aspect of the present invention, among the ultralight coarse aggregates, those having a crushing strength of 800 N or more are used, but the elastic modulus increases as the crushing strength of the ultralight coarse aggregate increases. Lightweight concrete with higher strength and higher elastic modulus can be obtained.

According to the third aspect of the present invention, since the ultralight coarse aggregate contains a composition containing an alkylene oxide polymer as a main component, the effect of reducing internal defects and the workability are reduced. Dry shrinkage of lightweight concrete can be effectively reduced, and long-term durability can be improved.

[0015]

Next, a concrete example of an embodiment of the lightweight concrete according to the present invention will be described.

In the present invention, as the coarse aggregate, an ultralight having a 24-hour water absorption of 5.0% by weight or less, a boiling water absorption of 10% by weight or less, and a bone-dry specific gravity of 0.7 to 1.3 is used. Use coarse aggregate.

Here, the term "24-hour water absorption" refers to the rate of water absorption when soaked coarse aggregate is immersed in water for 24 hours. Shows the water absorption when boiled for 2 hours at room temperature.
SA 1134 (Test method for specific gravity and water absorption of lightweight structural coarse aggregate) ". Incidentally, 24
Time water absorption is an index that is naturally affected by natural water absorption under normal pressure and is mainly affected by the pore properties of the aggregate surface,
The boiling water absorption is considered to be an index reflecting the porosity inside the aggregate because the water absorption is forcibly absorbed into the aggregate by the vapor pressure.

The ultralight coarse aggregate is granulated by adding a foaming agent such as SiC and an adhesive such as bentonite to a vitreous raw material such as obsidian, perlite, etc.
It is obtained by firing and foaming at 1300 ° C. In addition, limestone is granulated by adding an adhesive such as bentonite,
The granules can also be obtained by firing and foaming at 1150 to 1350 ° C.

As an ultra-lightweight coarse aggregate having such properties, Asano Superlight (trade name, manufactured by Taiheiyo Cement Co., Ltd.) is a commercially available product.

The ultralight coarse aggregate has few pores communicating with the outside, and fine closed pores having a size of about several μm to 20 μm are uniformly distributed inside. The water absorption becomes 10% by weight or less, indicating low water absorption. As a result, good workability can be provided without substantially absorbing the moisture in the concrete.

In the curing process up to one day of age,
Since the water content in the aggregate is not supplied to the cement paste portion and the concrete does not expand, no internal defects such as a coarse paste structure and an interface structure between the aggregate and the paste are formed. Further, even if the hardened concrete is exposed to drying for a long time, the amount of water escaping from the concrete is small, the drying shrinkage is small, and the durable concrete can be manufactured.

Furthermore, even if the pre-absorbing time of the aggregate is sufficient, the amount of water absorbed into the aggregate during the pre-absorbing process is small and the number of pores communicating with the surface of the aggregate is small, so that the initial setting During the process, the supply of moisture from the aggregate to the paste portion is unlikely to occur. Thus, the use of the pre-absorbed ultralight coarse aggregate does not cause the formation of internal defects and increase in drying shrinkage.

[0023] Ultra-light coarse aggregate other than the above properties,
Those having a 24-hour water absorption of more than 5.0% by weight or a boiling water absorption of more than 10% by weight have coarse pores and communicating pores inside, and thus exhibit high water absorption. Therefore, sufficient pre-absorption is necessary to ensure workability, and the large amount of water content generated by this pre-absorption expands the concrete during the hardening process and roughens the structure, that is, causes internal defects. Further, the drying shrinkage of the hardened concrete also increases, which is not preferable.

In the ultra-lightweight coarse aggregate used in the present invention, when the absolute dry specific gravity is 0.7 or more, fine closed pores are formed inside the aggregate, and the workability of the lightweight concrete is improved. It is suitable for improving, preventing internal defects and reducing drying shrinkage.
On the other hand, it is not preferable to use an ultralight coarse aggregate having a specific gravity of more than 1.3 because the effect of reducing the weight of concrete is reduced.

Further, as the crushing strength of the ultralight coarse aggregate increases, the elastic modulus of the aggregate increases, and the effect of restraining the shrinkage of the cement paste portion due to drying of the aggregate also increases. It is preferable to use a crushing strength of 800 N or more.

Further, by using an ultra-lightweight coarse aggregate having the above-mentioned properties impregnated with a composition containing an alkylene oxide polymer as a main component, the effect of reducing internal defects and the workability can be reduced. Drying shrinkage can be reduced more effectively. Examples of the impregnation method of the composition include immersion in the composition under normal pressure, and immersion in the composition after deaeration under vacuum.

[0027] The ultra-lightweight coarse aggregate impregnated with the composition hardly absorbs moisture in concrete from immediately after kneading until the end of pouring, so that slump loss does not increase. Further, the composition impregnated in the aggregate,
Since the capillary is held in the open pores of the aggregate with a larger capillary tension than in the case of water, it is not supplied to the paste portion in a short time, in other words, during the hardening process, and the structural tissue does not swell. Thereafter, as the hardened concrete is dried for a long period of time, the composition is gradually supplied to the paste portion, and the drying shrinkage of the concrete in the long-term age can be more effectively reduced.

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.

Examples of the water reducing agent include melamine-based, naphthalene-sulfonic acid-based, and polycarboxylic acid-based water reducing agents (including high-performance water reducing agents and high-performance AE water reducing agents).

Examples of the mixing water include commonly used tap water and the like. The mixing conditions of the lightweight concrete according to the present invention are as follows: the unit cement amount is 400 kg / m ³ or more, the water / cement ratio is 40% by weight or less, and the ultralight coarse aggregate amount is 0.3 to 0.
4 m ³ / m ³ .

When the unit cement amount is less than 400 kg / m ^3, when the water / cement ratio is more than 40% by weight, and when the ultralight coarse aggregate amount is more than 0.4 m ³ / m ³ ,
This is not preferable because the effect of reducing internal defects is reduced due to expansion during the curing process. In particular, when the amount of the ultra-light coarse aggregate is more than 0.4 m ³ / m ³ , the floating of the ultra-light coarse aggregate is apt to occur, which makes it difficult to finish the iron on the concrete surface.

When the amount of the ultralight coarse aggregate is less than 0.3 m ³ / m ³ , the effect of the aggregate to restrain the shrinkage of the paste is reduced. In other words, the paste volume occupying the concrete increases. It is not preferable because shrinkage is likely to occur and the drying shrinkage of the hardened concrete increases, and the effect of reducing the weight of the concrete is small.

In the present invention, the concrete is mixed by an omni-type mixer, a pan-type mixer, a twin-shaft type mixer or the like which has been conventionally used. Also, the kneading method and the kneading time are not particularly limited, and, for example, a predetermined concrete constituent material may be collectively charged into the mixer and kneaded.

Next, an embodiment of the lightweight concrete according to the present invention will be described. (1) Materials used Cement: ordinary Portland cement: manufactured by Taiheiyo Cement Co., Ltd. Water: tap water Admixture: water reducing agent (Reobuild SP-8S: AE agent manufactured by NMB Corporation (Micro Air 775S: coarse manufactured by NMB Corporation) Aggregate impregnated material: A1; Tetraguard AS ₂₁ (main component: lower alcohol alkylene oxide adduct): manufactured by Sanyo Chemical Industries, Ltd. A2: Hibidan (main component: polyether): fine aggregate manufactured by Takemoto Yushi Co., Ltd. : Ome-produced crushed sand coarse aggregate: G1; Asano Super Light, manufactured by Taiheiyo Cement Co., Ltd., crushing strength 1652N, absolute dry specific gravity 1.25, 24-hour water absorption 2.86% by weight (3.58% by volume), boiling Water absorption 6.25% by weight (7.81% by volume) G2: Prototype of Taiheiyo Cement Corp., crushing strength 1169N, absolute specific gravity 0.98, water absorption for 24 hours 4. 8% by weight (4.68% by volume), boiling water absorption 9.05% by weight (8.87% by volume) G3; manufactured by Asano Superlight Taiheiyo Cement Co., Ltd., crushing strength 821N, absolute dry specific gravity 0.82, Water absorption rate for 24 hours 4.93% by weight (4.04% by volume), boiling water absorption rate 9.89% by weight (8.11% by volume) G4; Mesalite, manufactured by Mesalite Industry Co., Ltd., crush strength 539N, absolutely dry Specific gravity 1.27, 24-hour water absorption 15.8% by weight (20.1% by volume), boiling water absorption 27.9% by weight (35.4% by volume)

The results of examining the surface of each coarse aggregate and the fractured fracture surface using an electron microscope are shown below. G1: pores of about 5 to 10 μm are uniformly distributed inside. G2: pores of about 5 to 15 μm are uniformly distributed inside. G3: pores of about 5 to 20 μm are uniformly distributed inside. G4: Many pores communicated with the surface, and coarse pores of 30 μm or more were also observed.

The absolute specific gravity and the water absorption of the coarse aggregate are as described in "J.
According to IS A1134 (Test method for specific gravity and water absorption of lightweight coarse aggregate for structure), the crushing strength is defined by JIS Z884.
1 (granulated material-strength test method) "
One mm was measured.

(2) Mixing conditions and kneading Each material was mixed in the ratio shown in Table 1 in a pan-type mixer (0.1 m ³ ).
And mixed for 2 minutes to prepare lightweight concrete. The coarse aggregate was used in an absolutely dry state and in a state in which water was previously absorbed. The pre-absorption was performed by immersing the absolutely dry aggregate in water for 24 hours or boiling the absolutely dry aggregate in water for 2 hours.

The impregnation of the alkylene oxide polymer can be carried out by immersing the bone-dried aggregate in the composition for 24 hours or by evacuating the bone-dry aggregate in a vacuum and immersing it in the composition for 30 minutes. went. In addition, the concrete of the composition shown in the same table, the slump and air volume at the time of kneading, each 18 ± 1.5c
m, a range of 5.0 ± 1.0%.

In the same table, Examples Nos. 1 to 15 are lightweight concretes according to the present invention. In addition, Comparative Example No. 1
No. 3 to No. 3 using the existing lightweight aggregate, Comparative Example No. 4
And No. 5 were those with less and more coarse bone material, respectively.
Comparative Examples No. 6 and No. 7 all have a high water / cement ratio, and Comparative Examples No. 8 and No. 9 all have a low cement amount.

[0040]

[Table 1]

(3) Evaluation Initial Internal Defects ・ Volume Change of Initial Age The volume change of the lightweight concrete immediately after the completion of the injection of the concrete is referred to as the self-shrinkage of cement paste, mortar and concrete by the Japan Concrete Institute Association of Self-Shrinkage Research Committee. And self-expansion test method (draft) ". In addition, the specimen immediately after the injection was used as the base length, and the measurement was performed up to 24 hours after the material age. From this measurement, it can be determined that an internal defect is not formed when a contraction strain or a very slight expansion strain is generated, and that an internal defect is formed when a large expansion strain is generated.

Interfacial Properties between Coarse Aggregate and Paste A sample piece was taken out of the concrete specimen after the above volume change measurement was completed, and an SEM image of the interface between the coarse aggregate and the paste was observed. And ◎: Almost no internal defects were observed on the surface of the aggregate, ×: A thick phase of internal defects was present over a wide range of the surface of the aggregate.

Workability and durability Slump loss The slump of lightweight concrete is measured according to "JIS A1101 (Slump test method for concrete)" immediately after kneading and one hour after the end of kneading, to reduce workability. Slump loss was calculated as an index.

Surface finishability The workability in ironing the concrete surface was evaluated as ◎: extremely good, ：: good, ×: poor.

Dry Shrinkage The specimen used in the test for determining the effect of reducing the internal defects was demolded at a material age of 24 hours, and cured in water (20 days) until the material age was 14 days.
° C), and then dried in a constant temperature and humidity chamber (20 ° C, 60%). The measurement of the length change during drying is described in “JIS A1
129 (Method of testing length change of mortar and concrete) ".

[0046]

[Table 2]

As is clear from the table, Example No. 1
Lightweight concretes according to the present invention of Nos. 1 to 15 do not cause significant expansion at the initial age, have good interfacial properties between the coarse aggregate and the paste, and can be judged as having no initial internal defects. Also, as in Examples No. 6 and Nos. 13 to 15, when an ultralight coarse aggregate containing a composition containing an alkylene oxide polymer as a main component is used, an initial internal defect may occur. It is also possible to reduce drying shrinkage more effectively.

On the other hand, in Comparative Examples Nos. 1-3 and Nos. 5-9,
Large expansion at early age, coarse aggregate-pace
Internal defects were observed at the interface between the substrates. Comparative Examples No. 2 to 4
In this case, the water content of the coarse aggregate is high or the amount of coarse aggregate is low.
800 × 10 ^-6Bigger drying shrinkage
Sudden occurrence has occurred. In the case of Comparative Example No. 5, coarse aggregate
The surface finish of ironing on the surface was reduced due to the rise of.

[0049]

As described above, according to the first aspect of the present invention, the workability is good regardless of the presence or absence and the degree of prior water absorption at the time of using the ultra-lightweight coarse aggregate, and the inner part at the initial age is improved. Defects can be reduced and lightweight concrete with high durability can be provided.

According to the second aspect of the invention, in addition to the above effects, it is possible to provide a lightweight concrete having a higher strength and a higher elastic modulus.

According to the third aspect of the present invention, in addition to the above-described effects, it is possible to more effectively reduce the drying shrinkage of the lightweight concrete, and to provide a lightweight concrete excellent in durability for a long term. it can.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 4G012 LA15 PA07 PB33 PC14 4G019 LA02 LB02

Claims (3)

[Claims] 1. A 24-hour water absorption rate of 5.0% by weight or less, a boiling water absorption rate of 10% by weight or less, and an absolute dry specific gravity of 0.7 to less.
The ultra-light coarse aggregate is 1.3 includes 0.3~0.4m ³ / m ^3, the amount of the unit cement 400 kg / m ³ or more, the water / cement ratio is equal to or more than 40% by weight Lightweight concrete. 2. The crushing strength of the ultralight coarse aggregate is 800N.
The lightweight concrete according to claim 1, characterized in that: 3. The lightweight concrete according to claim 1, wherein the ultralight coarse aggregate contains a composition containing an alkylene oxide polymer as a main component.