JPH11314977A - Lightweight concrete composition and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cured body having excellent pumpability, freezing damage resistance and refractoriness by constituting a concrete compsn. by using a coal ash-base artificial lightweight aggregate specified in an absolute dry sp. gr. and percentage of water absorption under pressurization as coarse aggregate. SOLUTION: The lightweight concrete compsn. is prepd. by adding water to a solid essential component consisting of cement, the coal ash-base artificial lightweight aggregate having the absolute dry sp. gr. of 0.9 to 2.3 and <=5 wt.% the percentage of water absorption under pressurization at a pressure of 4 N/mm<2> and fine aggregate. The artificial lightweight aggregate is mixed with the cement and the fine aggregate without prewetting. This artificial lightweight concrete compsn. is preferably such that the solid essential component per 100 pts.vol. compsn. consists of 5 to 25 pts. cement, 10 to 60 pts. coarse aggregate and 10 to 60 pts. fine aggregate. The aggregate, which is prepd. by compounding 30 to 120 pts.wt. active silicic acid powder with 100 pts. coal wash of 1 to 15 wt.% in unburned carbon content, then firing the mixture at 1150 to 1350 deg.C is usable as the above coal ash-base artificial lightweight aggregate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lightweight concrete composition which is excellent in pumping performance, has a small slump loss after pumping, and provides a hardened body having excellent durability and a method for producing the concrete composition. INDUSTRIAL APPLICABILITY The lightweight concrete composition of the present invention is suitably used in various fields in the fields of architecture and civil engineering due to its excellent properties.

[0002]

2. Description of the Related Art Conventionally, concrete has been used as a structural material having excellent durability and economy, but one disadvantage is that the weight is greater than the strength of other structural materials. . By using lightweight aggregates to reduce the weight of concrete, it is possible to increase the size of the structure.In addition, it is also possible to save steel for reinforcement to support the weight of structural members, simplify foundation work, etc. The cost of the entire structure can be reduced. On the construction side, most of the concrete placement work on site is performed by pumping in order to save labor and shorten the construction period. However, conventional artificial lightweight aggregates have high water absorption properties, so concrete prepared using completely dry artificial lightweight aggregates cannot be pumped. Used with sufficient water absorption. However, even with pre-etched aggregates, voids remain inside, causing water absorption due to pressurization by the pump, resulting in a large decrease in pumpability due to large slump loss and eventually leading to blockage. There is also. In addition, since the water content of the aggregate itself is extremely large, a cured product having inferior frost damage resistance and fire resistance can be obtained. Furthermore, it is difficult to control the moisture content of the pre-wetted aggregate, and it may be dried on site. As a solution to the problem derived based on the high water absorption of the aggregate, a method of coating the surface of the lightweight aggregate with an acrylic resin, a phenol resin, an epoxy resin or the like [for example, Tachibana et al. 469 / V-2
4, pp. 51-60 (1994)], and although water absorption has been improved, many problems to be solved such as cost and coating equipment remain.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lightweight concrete composition which solves the above-mentioned problems of the prior art. In other words, not only do not use aggregates that have been subjected to surface resin coating, but also do not include lightweight aggregates that have been subjected to troublesome pre-etching treatment, and have excellent pumping properties, frost damage resistance, and fire resistance. An object of the present invention is to provide a lightweight concrete composition that gives a cured product having excellent properties.

[0004]

SUMMARY OF THE INVENTION The present invention relates to a cement and a coal having an absolute dry specific gravity of 0.9 to 2.3 as coarse aggregate and a water absorption under pressure under a pressure of 4 N / mm ² of 5% by weight or less. The present invention relates to a lightweight concrete composition obtained by adding water to a solid main component composed of an ash-based artificial lightweight aggregate and a fine aggregate. In addition, the present invention provides a coal ash-based artificial lightweight aggregate having a pressed water absorption under a pressure of 0.9 to 2.3 and a pressure of 4 N / mm ² of 5% by weight or less as a coarse aggregate. The present invention relates to a method for producing a lightweight concrete composition to be mixed with cement and fine aggregate without wetting. Hereinafter, the present invention will be described.

BEST MODE FOR CARRYING OUT THE INVENTION

[0005] The concrete composition of the present invention comprises
Coal ash-based artificial light with extremely low water absorption compared to lightweight aggregate
It is characterized by using a large amount of aggregate as coarse aggregate. this
The artificial lightweight aggregate preferably has an unburned carbon content of 1 to 15 weight.
% Coal ash in 100 parts by weight
After adding and mixing 30 to 120 parts by weight of siliceous powder, granulation
・ Spherical particles with a rough surface, produced by firing
You. Because this artificial lightweight aggregate has few open pores,
It has the feature of extremely low water absorption compared to conventional artificial lightweight aggregates.
For example, 24 hours water absorption and 4 N / mm ^TwoAddition
The pressure absorption rate is 2% by weight or less and 5% by weight or less, respectively.
This low pressure absorption makes this lightweight aggregate a coarse aggregate.
The excellent pumping properties of the concrete composition
Is a factor that emerges. In addition, the aggregate itself has 200kg
f, high crushing strength and rough surface
Glass, such as balloons and perlite made from obsidian
Cement pace compared to those with a quality smooth surface
This artificial lightweight aggregate is used as coarse aggregate
By using conventional artificial lightweight aggregate as coarse aggregate
Lightweight and not available with the concrete composition used
A high-strength cured product can be obtained.

[0006] The concrete composition of the present invention is prepared by mixing the above-mentioned artificial lightweight aggregate as coarse aggregate with cement.
Various types of mixed cements such as Portland cement of high strength, ultra-high strength, moderate heat, sulfate resistance and low heat, blast furnace slag cement, fly ash cement and silica cement can be used. The amount of cement added is preferably the same as in the case of a general concrete composition, that is, 5 to 25 parts by volume per 100 parts by volume of the concrete composition.

[0007] The amount of artificial lightweight aggregate added as coarse aggregate is
As in the case of a general concrete composition, the content is 10 to 60 parts by volume, preferably 20 to 50 parts by volume, per 100 parts by volume of the concrete composition. If the amount of the artificial lightweight aggregate as the coarse aggregate is less than 10 parts by volume, the matrix portion increases, and a cured body having poor dimensional stability after curing may be obtained. If there is, the fluidity is reduced, and there is a possibility that molding becomes difficult.

[0008] Fine aggregate is further added to the concrete composition of the present invention. The amount of the fine aggregate to be added is 10 to 60, preferably 20 to 50 parts by volume, per 100 parts by volume of the concrete composition, as in the case of a general concrete composition. Outside this range, as in the case of coarse aggregate,
There is a possibility that a cured product having inferior dimensional stability after curing may be obtained, or that fluidity may be reduced and molding may be difficult. Fine aggregates include ordinary aggregates such as river sand, crushed sand, and slag aggregate, as well as shale,
Artificial lightweight aggregate made from clay, waste glass, and coal ash can be used.

The concrete composition of the present invention includes:
In addition to the above essential components consisting of cement, coarse aggregate and fine aggregate, various inorganic fine powder admixed materials such as blast furnace slag, fly ash, silica fume and the like, which are generally used in the manufacture of concrete products, and AE water reduction Agents, high-performance water reducing agents, water-reducing agents such as high-performance AE water reducing agents, and various admixtures such as AE agents, foaming agents, swelling agents, and setting speed regulators. Can be added. Especially,
The addition of the water reducing agent not only leads to an improvement in the fluidity of the slurry, but also makes it possible to reduce the water-cement ratio, and has a very favorable effect on improving the strength of the cured product.

The concrete composition of the present invention comprises a steel fiber,
It is also possible to further improve the bending strength of the cured product by adding various fibers such as glass fiber and carbon fiber as a reinforcing material, and it can be appropriately adopted according to the purpose of use.

The concrete composition of the present invention may be prepared by mixing all the components other than the liquid component in advance and adding the liquid component and water at the time of use to form a slurry. Ingredients and water may be added, and further, individual components and water may be added for use to form a slurry.

[0012]

The present invention will be described in more detail with reference to specific examples. (1) Materials used The following materials were used in the implementation. Cement: ordinary Portland cement Fine aggregate: sea sand (specific gravity: 2.57, water absorption: 1.28%) Coarse aggregate: coal ash (preparation method will be referred to as FAA later), expanded shale (commercially available) Products (trade name: Asanolite, manufactured by Nippon Cement Co., Ltd.) and ALA] were examined. The properties are shown in Table 1. Admixture: either naphthalene-based high-performance AE water reducing agent (SP) or ligninsulfonic acid-based high-performance AE water reducing agent (AE) was used.

[0013]

[Table 1]

Examples 1 to 4 and Comparative Examples 1 to 4 (2) Coal ash-based artificial lightweight aggregate as coarse aggregate 70 parts by weight of coal ash containing 3.4% by weight of unburned carbon and quartz as active siliceous material While adding 15 parts by weight of water to the raw material mixed powder to which 30 parts by weight of the roughened rock powder had been added, the mixture was granulated into a spherical molded body having a particle size of 5 to 20 mm using a bread granulator. The granulated material was obtained using a rotary kiln with a diameter of 0.45 m and a length of 12 m.
It was fired at a maximum temperature of 1200 ° C. to obtain an artificial lightweight aggregate FAA. Table 1 shows the characteristics of FAA.

(3) Preparation of concrete composition A mixture of cement and aggregate at the mixing ratio shown in Table 2 was kneaded with a forced mixer for 30 seconds, and then mixed with each other as shown in Table 2.
Add the amount of admixture and water shown in
After mixing, a concrete composition was obtained.

[0016]

[Table 2]

(4) Preparation of cured product The concrete composition after kneading and mixing has a diameter of 100 mm.
X: placed in a steel cylindrical mold having a height of 200 mm, cured for 24 hours, and then removed from the mold to obtain a cured product.

(5) Measurement of Water Absorption under Pressure of Aggregate As for the two types of coarse aggregates shown in Table 1, FAA was in a dry state and ALA was in a pre-wet state. The water absorption under pressure was measured by the method. A steel pressure vessel having a capacity of 5 liters is filled with 0.1 liter of aggregate and water, and while the water is supplied by a hydraulic pump, the pressure in the vessel is set to 4 N /.
After holding at 30 mm ² for 30 minutes, the water was released. The value obtained by dividing the amount of water flowing into and out of the hydraulic pump by the weight of the aggregate in a completely dry state was determined as the water absorption under pressure. The results are shown in FIG.

(6) Measurement of water absorption of aggregate in concrete by pressing A pressure bleeding test apparatus (12.5 cm inside diameter, 20.4 cm depth) is filled with 2.4 liters of kneaded concrete, and the pressure maximum 4.9 N / mm ² to pressurized with 2N / mm ² / min loading rate by, then after unloading at loading the same speed, the sample was taken out. The same operation was repeated seven times, and the total amount of the taken out sample was again kneaded in a kneaded plate form to obtain a concrete sample. The concrete 2k
g was washed with water to take out the coarse aggregate. The weight of the taken out coarse aggregate was measured in a surface-dry state, then dried and weighed again, and the water absorption was determined from the measured values. Regarding the concrete in the stationary state, the water absorption rate of the coarse aggregate was measured separately using the concrete which was left still for 45 minutes, which was the same time as the time required for the above-described pressure test. Water cement ratio 30
Table 3 shows the results for the cases of% and 50%.

(7) Measurement of change in slump and air amount due to pressurization The slump and air amount of concrete after pressurization and in the stationary state of the above (6) were measured. Slump is JIS A
1101 and the air amount were measured in accordance with JIS A 1116, respectively. 30% and 50% of water cement ratio
FIG. 2 shows the results for the case (1). In FIG. 2, the ratio of the difference between the measured value A in the stationary state and the measured value B after pressurization to A, that is, 100 × (A−B)
/ A shows the respective reduction rates.

(8) Evaluation of cured product: Compressive strength The cured product prepared by changing the water-cement ratio was determined according to JIS.
The compressive strength was measured by a method according to A1108.
FIG. 3 shows the relationship between the compressive strength and the water cement ratio.

(9) Evaluation of the cured product: freeze-thaw test The cured product prepared from the concrete composition shown in Examples 1 to 4 and Comparative Examples 1 and 3 was subjected to JIS A 620.
4 A freeze-thaw test was performed in accordance with Appendix 2 of “Chemical admixture for concrete” (freeze-thaw test method for concrete). FIG. 4 shows the results of the freeze-thaw test.

In the pressurized water absorption of FIG. 1, the FAA was 3 in spite of the fact that it was measured in a completely dry state.
%, Which is the value of A using the sample in the surface dry state.
The value is much lower than the pressure absorption rate indicated by LA. Also,
The depressurized water release rate is 2.0% for ALA and 1.5% for FAA, which are lower values for FAA.

Table 3 shows the measured water absorption of the aggregate in the concrete. The increase in aggregate water absorption by pressurization is 0.8 to 1.1% in ALA, but as small as 0.5% in FAA.

[0025]

[Table 3]

The pressurized water absorption characteristic of the FAA is exhibited as a slump characteristic of concrete using it as a coarse aggregate. FIG. 2 shows this. In FIG.
It has been shown that for both the 30% and 50% water cement ratios, the slump reduction due to pressurization is much smaller for concrete using FAA aggregates than for concrete using ALA aggregates. In addition, regarding the amount of air that affects the frost damage resistance and the fluidity of the concrete of the cured product, in the concrete using the FAA aggregate, even when the water cement ratio is 50%, the decrease due to the pressure is hardly recognized. That is, it is understood that the concrete of the present invention is much less affected by the pressure than the conventional concrete. Concrete using ALA in a surface-dry state has various problems, but is actually pumped and used. On the other hand, in the concrete of the present invention, which is much less affected by the pressurization, the problems associated with the pressurization have been solved, and it is clear that the concrete has properties more suitable for the pumping.

Table 4 shows the change over time in the water absorption of the FAA aggregate. It can be seen that the increase in the water absorption after 10 minutes is very slow. Therefore, aggregate FA
By using A in an absolutely dry state and adding a water amount corresponding to the water absorption amount for 10 minutes to the kneading water and kneading, the pre-wetting operation of the aggregate becomes unnecessary.

[0028]

[Table 4]

FIG. 3 is a plot of the compressive strength of the hardened material prepared using two types of aggregates against the water-cement ratio. FAA, an artificial lightweight aggregate using coal ash as a starting material, is shown. Concrete according to the present invention using as a coarse aggregate
It can be seen that the composition provides a hardened body having a higher compressive strength than ALA, a concrete composition containing a generally used expanded shale-based lightweight aggregate as a coarse aggregate at the same water cement ratio. Also, the difference in strength between the two, the lower the water-cement ratio, that is, the greater the strength, the greater the strength, the strength difference of the aggregate itself is considered to be remarkable in the high strength region. .

FIG. 4 shows the results of the freeze-thaw test. The cured product prepared from the concrete composition of the present invention using FAA as a coarse aggregate has a high water-cement ratio of 50%. While maintaining a high relative kinematic modulus after 300 freeze-thaw cycles, a conventional concrete composition using ALA as the coarse aggregate, even at a low water cement ratio of 30%. Immediately after the start of the test, the kinetic elasticity coefficient sharply decreased, and decreased to 20% or less at 60 cycles. In addition, the rate of change in weight of the cured product prepared from the concrete composition of the present invention due to repeated freezing and thawing is very small, and it is confirmed that mechanical deterioration of the surface of the cured product due to repeated freezing and thawing is unlikely to occur. That is, the concrete composition of the present invention,
It can be seen that compared with the concrete composition containing the expanded shale-based lightweight aggregate as a coarse aggregate, a hardened body excellent in freeze-thaw resistance performance is provided.

[0031]

Industrial Applicability The concrete composition of the present invention has a very small slump change due to pressurization even though a lightweight aggregate which is not subjected to pre-wetting treatment is used as a coarse aggregate, and has a pumping property. It has characteristics suitable for
Further, by adding an amount of water corresponding to the amount of water absorbed for 10 minutes to the kneading water and kneading the mixture, the pre-wetting operation of the aggregate becomes unnecessary. Furthermore, as compared with a conventionally used concrete composition, a cured product having a lighter weight and a higher compressive strength is provided at the same water cement ratio. Furthermore, it provides a hardened body that exhibits excellent freeze-thaw resistance performance and has significantly improved durability in cold regions, which has been a problem with concrete using lightweight aggregates. That is, since the concrete composition of the present invention is excellent in both construction characteristics and material characteristics, its use value in the field of construction or civil engineering is great.

[Brief description of the drawings]

FIG. 1 is a comparison of water absorption of two types of lightweight aggregates.

FIG. 2 shows concrete using two types of coarse aggregates.
It is a comparison of changes in slump and air volume due to pressurization.

FIG. 3 is a comparison of the relationship between the water-cement ratio of concrete using two types of coarse aggregate and the compressive strength of a hardened material.

FIG. 4 shows concrete using two types of coarse aggregates.
It is a comparison of the freeze-thaw test results of the cured product.

Claims (4)

[Claims] 1. A cement and artificial ash-based lightweight aggregate having a pressurized water absorption under a pressure of 0.9 to 2.3 and a pressure of 4 N / mm ² of 5% by weight or less as a coarse aggregate. And a lightweight concrete composition obtained by adding water to a solid main component comprising fine aggregate and water. 2. The solid main component per 100 parts by volume of the composition is 5 to 25 parts by volume of cement, 10 to 60 parts by volume of coarse aggregate and 10 to 60 parts by volume of fine aggregate. 2. The lightweight concrete composition according to item 1. 3. An artificial lightweight aggregate of coal ash, which is a coarse aggregate, comprising 30 to 120 parts by weight of activated siliceous powder per 100 parts by weight of coal ash having an unburned carbon content of 1 to 15% by weight. After that, 1
The lightweight concrete composition according to claim 1 or 2, which is fired at 150 to 1350 ° C. 4. An absolute dry specific gravity as coarse aggregate of 0.9 to 2.
A method for producing a lightweight concrete composition in which a coal ash-based artificial lightweight aggregate having a water absorption under pressure under a pressure of 3, 4 N / mm ² of 5% by weight or less is mixed with cement and fine aggregate without pre-wetting. .