JP3087848B1 - Method for improving pumpability of lightweight aggregate concrete - Google Patents

Abstract

A lightweight aggregate concrete solves the problem of poor pumpability and poor freeze-thaw resistance, and enables use of lightweight aggregate concrete in civil engineering structures. SOLUTION: In pumping concrete using lightweight aggregate as coarse aggregate, a lightweight aggregate having a bone-dry specific gravity of 0.8 to 1.5 and a water absorption of 8% or less is used as the lightweight aggregate. And a method for improving pumpability of lightweight aggregate concrete, wherein a biogum-based thickener is incorporated into the concrete.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for improving pumpability of lightweight aggregate concrete, and to provide a high-performance lightweight concrete having high workability and excellent durability, particularly for civil engineering structures. It is.

[0002]

2. Description of the Related Art The manufacture and construction of lightweight concrete structures has been generalized in construction work, but has not been practically used in civil engineering work. However, civil engineering structures such as bridges and tunnels have recently become longer and larger in section, and it has become necessary to reduce dead loads and reduce the section of members. Is done. However, from the viewpoint of workability and durability, it cannot be easily applied to conventional structures.

[0003] That is, the lighter the conventional lightweight aggregate, the higher the water absorption rate, and the water absorption rate is usually 20% or more. Light-weight aggregate concrete using such a lightweight aggregate has poor pumpability. In addition, when pre-wetting lightweight aggregate to improve pumping performance, the freeze-thaw resistance becomes poor due to the high water content of the lightweight aggregate, which is a problem for application to civil engineering structures. Become. For these reasons, lightweight 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 reduced water absorption is expected to improve pumpability and resistance to freezing and thawing, but the weight is reduced by the presence of minute closed cells. Even if the porous lightweight aggregate has a reduced water absorption rate, it cannot be denied that the water absorption rate is higher than that of solid ordinary aggregate, and usually shows a water absorption rate of about 2 to 8%. 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 blockage trouble at the time of pumping.

An object of the present invention is to solve such a problem and to obtain a lightweight aggregate concrete having good pumping performance and freeze-thaw resistance applicable to civil engineering works.

[0008]

According to the present invention, when pumping concrete using lightweight aggregates as coarse aggregates, the water-absorptivity at a bone-dry specific gravity of 0.8 to 1.5 is used as the lightweight aggregates. A method for improving pumpability of lightweight aggregate concrete, characterized by using a lightweight aggregate of 8% or less and incorporating a bio-gum thickener into the concrete.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have concluded that, in concrete containing a lightweight aggregate, even if the lightweight aggregate itself is improved to have a low water absorption, the state of water in the concrete is reduced. A variety of tests were performed, noting that it would affect the penetration of water into the interior. As a result, in order to suppress water absorption into the lightweight aggregate due to the pressure during pumping, use a lightweight aggregate with a low water absorption rate, whose surface is appropriately coated, and reduce the water condition in the concrete. Control has been found to be extremely effective.

If the surface of the lightweight aggregate is coated properly, the water absorption can be reduced, but the quality of the concrete may be adversely affected depending on the coating material and the coating method, and the cost becomes so high that it cannot be put to practical use. I don't have to. Japanese Patent Application No. Hei 10-3001 proposed earlier
In the method of No. 84, the surface of the lightweight aggregate is coated with one or more iron compounds of iron oxide, iron hydroxide, or iron oxyhydroxide. Aqueous solution containing iron oxide, iron hydroxide or iron oxyhydroxide; or a suspension of iron oxide, iron hydroxide or iron oxyhydroxide particles in water; It is a simple method by wet method of separating liquid, and it is possible to modify a lightweight aggregate with a water absorption of 20% or more into a lightweight aggregate with a water absorption of about 2 to 8% and to apply this coating. Since it does not change the strength of concrete, it is an excellent method for reducing the water absorption of lightweight aggregate.

However, even in the case of a lightweight aggregate coated with such an iron compound, a phenomenon occurs in which moisture in the concrete is forced into internal voids due to the pressure in the pumped concrete. This phenomenon is
It is difficult to avoid by the pre-wetting treatment because it is coated so that the water absorption is low. In the case of untreated high-absorbent lightweight aggregate, the voids are filled with water by pre-wetting, whereas the voids (bubbles) remain in the coated one even after pre-wetting. It is.

Therefore, it can be said that this phenomenon is peculiar to the lightweight aggregate whose water absorption is reduced by the coating treatment. The present inventors have examined in detail how the water retention state in concrete affects the pumping performance of lightweight aggregate concrete using such coated lightweight aggregate in relation to pressurization. Examined. As a result, it was found that it was very effective to add a suitable amount of biogum to concrete. Hereinafter, the contents will be specifically described with reference to representative test results.

Table 1 shows the materials used for concrete.
Table 2 shows the composition of the concrete subjected to the test and the test levels.

[0014]

[Table 1]

[0015]

[Table 2]

As shown in Table 1, two types of rhyolite (G09 and G10) having a specific gravity of 0.94 and 1.06 are used as coarse aggregates as lightweight aggregates. Hard sandstone crushed stone (GN) was used for comparison. These coarse aggregates were dry and pre-wet for 24 hours (surface dry)
In Table 2, the former is referred to as "absolutely dry" and the latter as "observable". In Table 2, what is described as coating is
The surface of the aggregate is coated with an iron compound.

In the coating treatment of the lightweight aggregate, caustic soda is added to an aqueous solution of ferric chloride to form a colloidal solution of iron hydroxide or a suspension of iron hydroxide, and this liquid is brought into contact with the lightweight aggregate. At the same time, air is introduced into the colloidal solution or suspension of iron hydroxide to oxidize to obtain a colloidal solution or suspension in which iron oxyhydroxide is precipitated, and this liquid is brought into contact with a lightweight aggregate, It is formed by coating iron hydroxide and iron oxyhydroxide on the surface of lightweight aggregate.
By the coating treatment with the iron compound, the water absorption is reduced without substantially changing the absolute specific gravity. For example, the results obtained by measuring the absolute dry specific gravity before and after the coating treatment on the G09 aggregate shown in Table 1 before and after the treatment and the water absorption after prewetting for 24 hours or 48 hours are as follows.

Before coating treatment After coating treatment Absolute dry specific gravity 0.94 0.92 24 hours water absorption (%) 7.77 3.02 48 hours water absorption (%) 7.95 3.22

Therefore, the 24-hour water absorption and the 48-hour water absorption are greatly reduced by the coating treatment of the iron compound.

In the composition shown in Table 2, the target slump of the concrete was set to 21 cm, and a high-performance AE water reducing agent (polycarboxylic acid type) was used for the concrete in order to minimize the unit water amount. Welan gum (0.05% based on unit water content), which is a kind of biogum, is No.
5, No. 8 and No. 9 were used in the examples.

For mixing the concrete, a forced pan type mixer (capacity: 50 liters) was used, and the mixing amount was 30 liters. The mixing time was 120 seconds after the introduction of all the materials, and the pressurized bleeding test apparatus (φ200 × h250m
m) was used to perform a pressure test. Pressing force is 1.5N /
mm ² , the pressurizing time was 1 minute, and the measurement items were slump, air volume, unit mass per unit volume and water content of aggregate before and after pressurization. That is, the amounts of change in these items due to the pressurization were measured.

FIG. 1 is a table showing the proportions of concrete (No.
1 to 9) show the measured values of slump, air volume, and aggregate moisture content before (□) and after (■) pressurization. The test numbers are arranged in this order. The following can be seen from the results of FIG.

(1) Nos. 1 and 2 using hard sandstone have smaller slumps, smaller slump loss before and after pressurization than Aggregates No. 3 to 9 using lightweight aggregates, and the water content of the aggregates is small. Are almost equivalent. This may be attributed to the very low pressure absorption into the aggregate. (2) In the case of G10 aggregate (No. 3 to 5), the slump loss is No. 4 (absolutely dry, no welan gum added, No. 3 (surface dry, no welan gum added), No. 5 (absolutely dry, welan gum) In particular, the fact that the slump loss of No. 5 is smaller than that of No. 3 in the surface-dry state indicates that welan gum has an improved slump loss effect. (3) G10 aggregate G09 aggregate (No.
Cases 6 to 9) are as follows.

A) No. 6 (absolutely dry, no welan gum added)
In this case, the slump 21 cm decreased to 8 cm after the pressurization (slump loss = 13 cm), and the decrease in the slump due to the pressurization was remarkable. B) In No. 7 (with coating treatment and no welan gum added), the decrease in slump due to pressure was 20.5 → 11.
0 cm = 9.5 cm, which is smaller than No. 6 and an effect of coating is seen, but the slump is greatly reduced by pressurization. C) In No. 8 (no coating treatment / welan gum added), the decrease in slump due to pressure was 23.0 → 17.
0 cm = 6.0 cm, which is smaller than No. 7. In other words, the effect of suppressing the water absorption of the lightweight aggregate by pressurization is greater with the addition of welan gum than with the coating treatment. D) In No. 9 (with coating treatment and welan gum added), the decrease in slump due to pressurization was 22.5 → 22.
0 cm = 0.5 cm, and it can be said that it hardly occurs. In other words, by the synergistic effect of the coating treatment and the addition of welan gum, the suppression of water absorption into the lightweight aggregate by pressurization is almost completely achieved.

As described above, in the case of the lightweight aggregate concrete in which the surface of the lightweight aggregate is coated with the iron compound and the welan gum is blended, the slump value does not decrease even when pressed (water is not absorbed by the lightweight aggregate even when pressed). ). This phenomenon is due to the fact that the water absorption properties of the aggregate itself are improved by the coating process, and the viscosity (water retention) of the water in the coating changes due to the addition of welan gum, a water-soluble thickener. It may be considered that pressure absorption into the aggregate is less likely to occur even after receiving. For this reason, the fluidity is prevented from lowering even when the pressure is applied during pumping, so that pumping can be performed well over a relatively long distance.

FIG. 2 shows the relationship between the ratio of the moisture content of the aggregate after pressurization to the ratio of the slump before pressurization in the test. From FIG. 2, it can be seen that there is a high correlation between the two using the absolutely dry lightweight aggregate, and the slump loss tends to increase as the water content of the aggregate increases by pressing. As shown in FIG. 1, the coating method and the addition of welan gum have the effect of suppressing the increase in the water content of the aggregate due to pressurization. Therefore, this method is very effective as a method for improving the pumpability of lightweight aggregate concrete. You can see that. In the above tests, the air volume tended to decrease by about 2 to 3% and the mass per unit volume tended to increase by 3 to 6% before and after the pumping.

In the above test, it was found that welan gum had the effect of appropriately increasing the viscosity of water in concrete and suppressing water absorption into lightweight aggregates without impairing the fluidity of concrete. However, similar effects are seen to a greater or lesser extent with biogum such as ramzan gum and succinoglucan. The amount of biogum added to concrete is 0.01 to 0.1 for unit water in welan gum.
10%, preferably about 0.01 to 0.05% may be added.

In the above test, the required effect was obtained by adding welan gum even if the amount of the high-performance AE water reducing agent was the same. This has a great cost advantage. It is normal to think that the addition of a thickener will increase the viscosity and consequently the amount of the high-performance AE water reducing agent to be added will increase in order to ensure fluidity, but this is not the case with welan gum. The same amount of the high-performance AE water reducing agent may be used irrespective of the presence or absence of the addition of lanthanum. On the other hand, when MC (methylcellulose) or HEC (hydroxyethylcellulose), which is generally used as a thickener, is used, the fluidity of concrete is greatly impaired with an increase in viscosity. It is not preferable because the amount of other admixtures for securing such as a high-performance AE water reducing agent or an AE water reducing agent is greatly increased. In addition,
In the test, a polycarboxylic acid type high-performance AE water reducing agent was used, but other naphthalene type, melamine type,
Aminosulfonic acid type and the like can also be used.

The lightweight aggregate used in the present invention is an artificial lightweight aggregate mainly composed of expanded shale, expanded clay, expanded slate, fired fly ash, etc., a natural lightweight aggregate such as volcanic debris, and an auxiliary lightweight aggregate. Although there are light-weight aggregates, the pumping ability when blending recycled aggregates or blast furnace slag coarse aggregates with high water absorption can be similarly improved.

According to the method of the present invention, the workability is good because the lightweight aggregate can be mixed with concrete without pre-wetting and pumped. In other words, as shown in the above test, even if prewetting is omitted, water absorption into the aggregate due to the pressure during pumping is suppressed, as shown in the above test. In other words, it means that the hardened concrete has good freeze-thaw resistance. In a freeze-thaw test performed by the present inventors on concrete having a composition equivalent to that of No. 9 in the above test, the durability index (relative kinetic elasticity%) after 300 cycles was about 90%, and excellent freeze-thaw resistance was obtained. showed that.

The lightweight aggregate concrete according to the present invention has a relationship between the unit volume mass and the compressive strength as shown in FIG. That is, as the lightweight aggregate, the absolute dry specific gravity is 0.8 to
A lightweight aggregate with a water absorption rate of 8% or less at 1.5 is used. For example, in a compounding design (water-cement ratio of 40% level and air amount of 6% level) (compounding of high-performance AE water reducing agent), the unit volume mass is 1. A high-strength concrete having a compressive strength of 40 to 60 N / mm ² with a compressive strength of 6 to 1.9 is obtained. By using such lightweight, high-strength concrete for civil engineering structures, the weight of members can be reduced, and dead loads, inertial forces during earthquakes, and loads on substructures can be reduced. The shoring and construction machines can be simplified.

That is, according to the present invention, the absolute dry gravity is 0.8.
A lightweight aggregate concrete with excellent pumpability, containing a bio-gum and using a lightweight aggregate having a water absorption of 8% or less as a coarse aggregate having a unit volume mass of 1.6 to 1.5.
Provided is a lightweight aggregate concrete for civil engineering having a compressive strength of 40 to 60 N / mm ² at 9 t / m ³ for 28 days.

[0033]

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. Further, according to the method of the present invention, even if the lightweight aggregate is blended without pre-wetting, it has a good pumping property, so that a concrete excellent in freeze-thaw resistance even when the lightweight aggregate is used can be obtained. Therefore, according to the present invention, there is provided a lightweight aggregate concrete which can be applied particularly to civil engineering structures. As a result, it is possible to reduce the weight of civil engineering structural members, reduce dead load, inertia during earthquakes, burden on substructures, etc., and omit supports and construction machinery. Unnecessary design rationalization and construction cost reduction can be achieved.

[Brief description of the drawings]

FIG. 1 is a diagram showing changes in physical properties of concrete before and after pressurization when assuming a pressure applied to concrete during pumping.

FIG. 2 is a diagram showing the correlation between the ratio of the water content before and after the pressure applied to concrete and the slump ratio.

FIG. 3 is a view showing a preferred range of a unit volume mass and a compressive strength of the lightweight aggregate concrete according to the present invention.

────────────────────────────────────────────────── (5) References JP-A-5-213650 (JP, A) Patent 3012615 (JP, B2) Patent 3031916 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , (DB name) C04B 28/02 C04B 24/38

Claims (5)

(57) [Claims] In pumping concrete using lightweight aggregate as coarse aggregate, a lightweight aggregate having a bone-dry specific gravity of 0.8 to 1.5 and a water absorption of 8% or less is used as the lightweight aggregate. And a method of improving the pumpability of lightweight aggregate concrete, wherein a biogum-based thickener is incorporated into the concrete. 2. The pumpability improvement according to claim 1, wherein the lightweight aggregate has a surface coated with one or more iron compounds of iron oxide, iron hydroxide or iron oxyhydroxide. Law. 3. The concrete according to claim 1, further comprising a high-performance AE water reducing agent in addition to the biogum-based thickener.
4. The method for improving pumping ability according to 2 or 3. 4. The method for improving pumpability according to claim 1, wherein the biogum-based thickener is welan gum. 5. A lightweight aggregate concrete which is excellent in pumping property and contains a bio-gum, wherein a lightweight aggregate having a bone-dry specific gravity of 0.8 to 1.5 and a water absorption of 8% or less is used as a coarse aggregate. The unit volume mass in a cured state is 1.6 to 1.9 t /
m ³ at 28 days compressive strength lightweight aggregate concrete civil engineering structures 40~60N / mm ^2.