JP2000344563A - Lightweight aggregate concrete excellent in pump forced feedability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To resolve the problem that lightweight aggregate concrete is inferior in a pump force feedability and freezing-melting resistance and to obtain lightweight aggregate concrete having an excellent executing property and quality applicable to even a civil construction. SOLUTION: This lightweight aggregate concrete are manufactured by utilizing a lightweight coarse aggregate having absolute dry specific gravity of 0.8-1.5. and 2-8% water absorption and an usual fine aggregate and slump flow at the time of kneading is adjusted to >=50 cm and <=60 cm. This concrete preferably has 185 kg/m3 unit quantity of water, high performance AE water reducing agent mixed as a mixing agent and 300-450 kg/m3 mixed quantity of fine powder including cement.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lightweight aggregate concrete excellent in pumpability.

[0002]

2. Description of the Related Art The manufacture and construction of lightweight concrete structures is common in construction work, but is hardly practical in civil engineering work. However, civil engineering structures such as bridges and tunnels have recently become larger and larger in cross-section, and it has become necessary to reduce dead loads and reduce member cross-sections. Is noted. However, from the viewpoint of workability and durability, it cannot be easily applied to conventional structures.

[0003] The lighter the weight of the conventional lightweight aggregate, the higher the water absorption, and there are usually those having a water absorption of 20% or more. Here, the lightweight aggregate means one having an absolute dry specific gravity of about 0.8 to 1.5. Concrete using such a lightweight aggregate cannot usually be pumped. In addition, when using lightweight aggregates pre-wetted to improve pumpability, the freeze-thaw resistance of concrete deteriorates because the lightweight aggregates have a high water content, making them suitable for application to civil engineering structures. Is a problem. For these reasons, lightweight aggregate concrete has hardly been applied to civil engineering work.

Recently, special lightweight aggregates having a small water absorption have been developed (for example, Concrete Engineering, VOL. 36, N
o.1, 1998.1, pp. 48-52) and Japanese Patent Application No. 10-300184 filed by the same applicant proposed a lightweight aggregate whose surface was coated with an iron compound to thereby significantly reduce the water absorption. The application of such lightweight aggregates with low water absorption to civil engineering is expected, but there are many unknowns.

[0005]

A lightweight aggregate having a small specific gravity and a small water absorption rate is expected to improve pumpability and freeze-thaw resistance. In the case of porous lightweight aggregates, even if the water absorption rate is reduced, it cannot be denied that the water absorption rate is higher than that of ordinary solid aggregates.
% Of water absorption. For this reason, the pumping performance of a general formulation is inferior to that of a case using ordinary aggregate.

[0006] Further, in the case of a lightweight aggregate having a small water absorption, even if pre-wetting, it does not absorb water sufficiently, and the internal voids are not completely filled with water (saturated state). It is difficult to obtain a state (called a surface-dry state), and if anything, it is close to an absolutely dry state (called a completely dry state). Therefore, when pressure is applied, water easily permeates into the internal voids. That is, a large amount of water is absorbed into the lightweight aggregate by the pressure of the pumping, and as a result, the fluidity of the concrete is reduced, which causes a closing trouble at the time of pumping.

The present invention has been made to solve the above problems and to provide a lightweight aggregate concrete capable of obtaining a structure having good pumping performance and excellent freeze-thaw resistance applicable to civil engineering works. Is the subject.

[0008]

According to the present invention, a light-weight aggregate concrete using a light-weight coarse aggregate having a bone-dry specific gravity of 0.8 to 1.5 and a water absorption of 2 to 8% and ordinary fine aggregate is provided. In addition, the present invention provides a lightweight aggregate concrete excellent in pumpability by adjusting a slump flow value during kneading to 50 cm or more and 60 cm or less. This lightweight aggregate concrete preferably has a unit water content of 185 kg / m ³ or less, contains a high-performance AE water reducing agent as an admixture, and has a compounding amount of fine powder containing cement of 300 to 450 kg / m ³ . Yes, air volume is 5-9%. Then, the unit volume mass in the cured state is 1.6 to 1.9 t / m ³ and the 28-day compressive strength is 40 to
60 N / mm ² .

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted various tests and researches in order to solve the above-mentioned problems, but have used ordinary fine aggregates such as natural sand and crushed sand as fine aggregates. As the coarse aggregate, a lightweight coarse aggregate having a specific gravity of 0.8 to 1.5 and a water absorption of 2 to 8% is used, and the slump flow value at the time of kneading is 50 cm.
When adjusted to be at least 60 cm or less, the pump can be sufficiently pumped, the flowability before and after the pumping is small, good workability can be secured, and the coarse aggregate can be used without pre-etching. It has been found that concrete with good durability can be obtained.

First, in the present invention, the absolute dry gravity is 0.8.
A lightweight coarse aggregate having a water absorption of 2 to 8%, preferably 2 to 5%, and more preferably 2 to 3% is used. Such lightweight coarse aggregates fall into a special category because of their light but low water absorption. It is not to say that there is no such thing that is light and has a low water absorption in nature, but it is preferable that the water absorption is artificially adjusted. As a typical example, there is one proposed in Japanese Patent Application No. 10-300184 of the same applicant. In this method, the surface of the lightweight aggregate is coated with one or more iron compounds of iron oxide, iron hydroxide, or iron oxyhydroxide. After contact with a colloidal solution of iron oxide, iron hydroxide or iron oxyhydroxide; or a suspension of iron oxide, iron hydroxide or iron oxyhydroxide particles in water; This method is a simple method using a wet method, in which a light-weight coarse aggregate having a specific gravity of about 0.8 to 1.5 is dried, and a water absorption of 2 to 8%, preferably 2 to 5%, more preferably about 2 to 3%. This is an excellent method for lowering the water absorption of lightweight coarse aggregate, because it can be modified into lightweight coarse aggregate and the coating does not change the strength of concrete.

A lightweight coarse aggregate having such absolute dry specific gravity and water absorption is preferably used without pre-etching, and a fine powder containing cement and ordinary fine aggregate such as natural sand or crushed sand is used. , Slump flow value during kneading is 5
The concrete is blended so as to be 0 to 60 cm.
At that time, if the slump flow value is increased by increasing the unit water amount (when the fluidity is increased), the durability of the concrete is reduced. Therefore, the unit water amount is not increased as much as possible. For example, the unit water amount is 185 kg / m ³ or less, preferably 180 kg.
/ M ³ or less, more preferably about 175 Kg / m ³ ± 5 to ensure a slump flow value of 50 to 60 cm. For this purpose, it is preferable to use a high-performance AE water reducing agent as an admixture. As the high-performance AE water reducing agent, it is preferable to use a polycarboxylic acid type or a polyether type, but a naphthalene type or an aminosulfonic acid type may also be used.

Further, in order to secure material separation resistance even when the fluidity is increased in this way, the amount of fine powder (cement and, if necessary, stone powder, fly ash,
It is preferable to slightly increase the total amount of silica fume and the like.
^A good value is about ³ . Also, the amount of air is preferably higher than that of ordinary concrete, for example, about 5 to 9%. In general, the strength decreases when the air volume is increased, but in the concrete of the present invention, the unit fine powder volume is increased,
This is not a problem because the unit water volume (actually, the ratio of fine water powder) is reduced. And the air volume is 5
By setting the content to ９9%, preferably 6 to 8%, it is possible to alleviate a decrease in fluidity before and after pumping, and to secure freeze-thaw resistance.

According to such a material composition, when the lightweight coarse aggregate is blended in an absolutely dry state without pre-etching and the slump flow value is adjusted to 50 to 60 cm, and pumped by pumping, the conventional water absorption rate is high. The decrease in the slump flow value is smaller than in the case where a lightweight coarse aggregate (for example, one having a water absorption of 27%) is pre-etched and used, and as shown in an example described later, a pipe having a total length of 122.8 m (125
Pumping in the A transport pipe) can be carried out without any trouble, good workability can be maintained even after the transportation, and a concrete structure that is more excellent in strength than concrete before the transportation can be constructed.

Hereinafter, preferred embodiments of the present invention will be further described based on tests performed by the present inventors.

Table 1 shows the materials used for concrete.
Table 2 shows the composition (No. 1 and No. 2) of the concrete used in the test.

[0016]

[Table 1]

[0017]

[Table 2]

As shown in Table 1, as the coarse aggregate, an artificial lightweight coarse aggregate having an absolute dry specific gravity of 1.10 and a water absorption of 2.90% for 24 hours was used. At that time, the lightweight coarse aggregate was mixed with the concrete material in an absolutely dry state.

In the composition of Table 2, the composition of No. 1 is such that the target slump is 21 ± 1.5 cm.
Is such that the target slump flow is 55 ± 5.0 cm. SP means a high-performance AE water reducing agent, and a polycanrubonic acid-based high-performance AE water reducing agent was used.

The mixing of the concrete is carried out using a twin-screw forced kneading mixer (capacity: 2.5 m ³ ,
The mixture was kneaded for 60 seconds after the introduction of all the materials using a rotation speed of 60 rpm (the lightweight coarse aggregate used was in a completely dry state). In each case in one batch 1.5 m ³ kneading the 3 batches 4.5 m ^3, were charged into the agitator wheel (10t). A fresh property test shown in Table 3 was conducted for the concrete.
After confirming that the specified properties were satisfied, they were transported to the experimental site in about 120 minutes, and immediately after the agitator truck arrived at the experimental site, a pumping test was performed. The pump used was a hydraulically driven piston type with the specifications shown in Table 4, the transport pipe was 125 A, and the pipe was 122.8 m in total length shown in FIG.
And two courses of 44.8m. For the test, the tests shown in Table 3 were performed on the concrete before and after the pumping as appropriate. The moisture content of the lightweight coarse aggregate shown in Table 3 was measured by washing the collected concrete on a 5 mm sieve and making the remaining coarse aggregate dry.

[0021]

[Table 3]

[0022]

[Table 4]

[Test Results] FIG. 2 shows the time-dependent changes in the slump value of the formulation No. 1 and the slump flow value of the formulation No. 2. It can be seen that each of the concretes has sufficiently maintained fluidity for a long time. In addition, the amount of air was constant at approximately 7% over the same time. From this, it can be seen that even when transported and agitated by the agitator truck, no water was absorbed into the lightweight aggregate.

FIG. 3 shows the change over time of the front pressure of the piston during the pressure feeding test. This figure illustrates the following events: First, in the concrete with the composition No. 2, when the pumping is started, the front pressure of the piston gradually increases and eventually becomes constant at a pressure of 3 N / mm ² , and while maintaining this pressure, the total amount of 4.5 m ³ of concrete reaches the piping distance 122. .8m could be pumped smoothly.

Subsequently, 12 parts of concrete of the composition No. 1
Although it was subjected to 2.8 m of pumping, the pressure at the front of the piston became 7 N / mm ² or more and about 7 minutes after the start of pumping, and was closed.
Then, when the pipe was cut and the state of the concrete was observed, it was found that the concrete was hardest near the piston, and the fluidity increased as the distance from the piston increased. For this reason, the piping distance must be 44.
When the concrete with the composition No. 1 was pumped again with the length shortened to 8 m, also in this case, the piston front pressure became 7 N / mm ² or more in about 7 minutes from the start of the pumping, so that the piston was closed.
From this, it can be seen that the concrete of No. 1 is not suitable for pumping, but the concrete of No. 2 can be pumped.

Next, in order to know the change in the physical properties of the concrete of No. 2 after pumping, the change in the slump flow was examined first. FIG. 4 shows the result. As can be seen in FIG. 4, No. 15 minutes, 20 minutes, and 30 minutes after pumping.
2 Slump flow value of concrete is 43.3-46.7
cm (57.3-57.8 cm before pumping). The slump was about 22 cm. Therefore, it is clear that the concrete has good workability and maintains sufficient fluidity even after pumping.

According to the Proceedings of the Annual Conference of Concrete Engineering, Vol.10-2, 1988, PP225-230, the water absorption rate was 27%.
% In a pumping test of concrete pre-etched using a lightweight aggregate of about%, the slump flow before pumping was 46.8 cm, but after pumping it was reduced to 38.4. The concrete of No. 2 maintains high fluidity after pumping even if it is blended in a completely dry state (no pre-etching). The ability to perform pumping without pre-etching and maintain high fluidity after pumping is advantageous for improving workability and quality (particularly freeze-thaw resistance) of concrete after pumping.

FIG. 5 shows the change in the water content of the lightweight coarse aggregate before and after the No. 2 mixed concrete is pumped. Before the pumping, the water content is constant at about 2%, while the water content becomes 3 to 15 minutes, 20 minutes, and 30 minutes after the pumping.
It showed a tendency to increase slightly to about 4.4%, but the absolute value of the water content was small. In addition, when the moisture content of the sample near the piston when the blockage was caused by the blending of No. 1 was measured, it was 7% or more, which was compared with 4.58% of the sample 75 m away from the pump. And was higher. For this reason, in a composition such as No. 1, even if a lightweight coarse aggregate having a low water absorption rate is used, the water absorption into the lightweight coarse aggregate becomes large near the piston and the fluidity is reduced. It can be seen that the deterioration of the performance further increases the pressure on the front face of the piston and further promotes water absorption, thereby causing a vicious cycle and eventually leading to a closed state. On the other hand, when the slump flow value was adjusted to 50-60 cm, even if water was absorbed by the lightweight coarse aggregate, the decrease in the fluidity of the concrete was small, and as a result, the pressure at the front of the piston was stable without increasing. It is considered that pumping has become possible.

FIG. 6 shows the results of compressive strength of concrete before and after pumping. As can be seen from the results in FIG. 6, no change in the compressive strength was observed before and after the pressure feeding in the No. 1 blend, and it can be judged that they were almost the same.
However, in the case of No. 2 compound, the compressive strength after pumping is higher than that before pumping. This is presumably because No. 2 having a larger unit water content has a relatively larger amount of water absorbed in the mortar after being pumped into the lightweight coarse aggregate than No. 1. According to the above-mentioned Journal of Concrete Engineering Annual Conference, Vol. 10-2, 1988, PP225-230, when a lightweight aggregate with a water absorption of 27% was used by pre-etching, The compression strength is slightly higher. Therefore, in this Example N using a light-weight coarse aggregate in a dry state,
It can be seen that the formulation of o.2 provided an effect of improving the compressive strength after pumping, which was not expected from the conventional one.

As can be seen from the above test, the concrete containing No. 2 according to the present invention can be pump-pumped while using a light-weight coarse aggregate in a dry state without pre-etching, and has good workability after pump-pumping. In light of maintaining the (fluidity) and improving the compressive strength after pumping, it has properties not found in conventional lightweight aggregate concrete for pumping.

According to the method of the present invention, workability is good in that a lightweight coarse aggregate can be compounded into concrete without pre-wetting and pumped. Since the pre-wetting of the lightweight coarse aggregate can be omitted, the freeze-thaw resistance of the concrete is improved. In a freeze-thaw test performed by the present inventors on concrete equivalent to the above-mentioned blend 2, the durability index (relative kinetic modulus%) after 300 cycles was about 90%, indicating excellent freeze-thaw resistance.

Further, the lightweight aggregate concrete according to the present invention has a relationship between unit mass and compressive strength as shown in FIG. In other words, FIG.
The composition of No. 2 in Table 2 was used except that the light-weight coarse aggregate with a water absorption of 2-3% at 8-1.5 was used in an absolutely dry state, and the relative ratio of fine aggregate and light-weight coarse aggregate was changed. 3 shows the relationship between the mass per unit volume and the compressive strength when a number of tests were conducted with substantially the same formulation. As can be seen from FIG. 7, the lightweight aggregate concrete according to the present invention has a higher compressive strength per unit mass than the conventional lightweight aggregate concrete, and has a compressive strength of 1.6 to 1.9 per unit volume. Is 40-60N /
mm ² of high-strength concrete is obtained.

Therefore, by using such lightweight and high-strength concrete for civil engineering structures, the weight of the members can be reduced, and the dead load, the inertial force during an earthquake, and the burden on the substructure can be reduced. , Streamlining design,
The shoring and construction machines can be simplified.

That is, according to the present invention, the absolute specific gravity is 0.8.
A lightweight aggregate concrete using a lightweight coarse aggregate having a water absorption rate of 8% or less as a coarse aggregate having a unit volume mass of 1.6 to 1.9 t / m ³ and a compressive strength of 28 days. 40-60
It is possible to provide N / mm ² lightweight aggregate concrete for civil engineering structures.

[0035]

As described above, according to the present invention,
The problem of poor pumpability when using a lightweight aggregate is solved, and a lightweight aggregate concrete with good pumpability is obtained. The method of the present invention maintains good fluidity even after pumping and has good pumping properties even when lightweight aggregate is blended without pre-wetting. Concrete with excellent melting resistance can be provided. It is also advantageous in that the compressive strength is improved after pumping. From the above, according to the present invention, a lightweight aggregate concrete that can be applied particularly to civil engineering structures is provided, and as a result, the weight of the civil engineering structure members can be reduced, and dead loads and inertial forces during earthquakes can be reduced. In addition, it is possible to reduce the burden on the lower structure, etc., and to omit the shoring and the construction machinery, thereby achieving the rationalization of the design and the reduction of the construction cost which could not be achieved by the conventional civil engineering work.

[Brief description of the drawings]

FIG. 1 is a diagram showing a pipe state in a pumping test.

FIG. 2 is a diagram showing slump and slump flow of concrete subjected to a test over time.

FIG. 3 is a diagram showing a change with time of a piston front pressure of concrete subjected to a pumping test.

FIG. 4 is a diagram showing a slump flow value after pumping of No. 2 concrete subjected to a pumping test in comparison with that before pumping.

FIG. 5 is a view showing the water content of lightweight aggregate after pumping of No. 2 concrete subjected to a pumping test in comparison with that before pumping.

FIG. 6 is a diagram showing the compressive strength of concrete subjected to a pumping test after pumping in comparison with that before pumping.

FIG. 7 is a view showing a preferable range of a unit volume mass and a compressive strength of the lightweight aggregate concrete according to the present invention.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Noboru Sakata 2-9-1-1, Tobita-Ki, Chofu-shi, Tokyo Kashima Construction Co., Ltd. (72) Inventor Shuji Yanai 2-9-1-1, Tobita-Shiita, Chofu-shi, Tokyo Kashima Construction Co., Ltd.Technical Research Institute (72) Inventor Yoshihisa Okamoto 1-2-23 Kiyosumi, Koto-ku, Tokyo Pacific Cement Co., Ltd. (72) Inventor Takashi Togigi 1-2-23 Kiyosumi, Koto-ku, Tokyo No. Taiheiyo Cement Co., Ltd. Research Headquarters (72) Inventor Yuyasu Ishikawa 1-2-3 Kiyosumi, Koto-ku, Tokyo F-term in Taiheiyo Cement Co., Ltd. Research Headquarters 4G012 PA02 PA04 PC04 PC03

Claims (7)

[Claims] 1. Absolute dry specific gravity of 0.8 to 1.5 and water absorption of 2 to 8%
Lightweight aggregate concrete using light coarse coarse aggregate and ordinary fine aggregate, and the slump flow value during kneading is 50c.
Lightweight aggregate concrete with excellent pumping performance adjusted to m or more and 60 cm or less. 2. The lightweight aggregate concrete according to claim 1, wherein the unit water content is 185 kg / m ³ or less and a high-performance AE water reducing agent is blended as an admixture. 3. The compounding amount of the fine powder containing cement is 300.
~450Kg / m ³ a lightweight aggregate concrete of claim 1 or 2. 4. The light-weight coarse aggregate whose surface is coated with one or more iron compounds of iron oxide, iron hydroxide or iron oxyhydroxide. Lightweight aggregate concrete. 5. The lightweight aggregate concrete according to claim 1, wherein the lightweight coarse aggregate is blended into the concrete without pre-etching. 6. The lightweight aggregate concrete according to claim 1, wherein the amount of air at the time of kneading is 5 to 9%. 7. A unit volume mass in a cured state is 1.6.
~1.9t / m ³ at 28 days compressive strength 40~60N / mm
The lightweight aggregate concrete according to any one of claims 1 to 6, which is ² .