JPH0625011B2 - Suppression method of concrete expansion by alkali-aggregate reaction - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for suppressing an alkaline aggregate reaction using a water-soluble cellulose ether.

Recently, the reaction between alkali and aggregate in mortar and concrete structures has become a problem. Mortar and concrete structures often expand, crack and deteriorate due to this alkaline-aggregate reaction. As a countermeasure, the Ministry of Construction recently (2 June 1986)
Month) a. Use of aggregate recognized as safe (by chemical method or mortar bar method) b. Use of low-alkali type (Na ₂ O equivalent of 0.6% or less) c. Use of mixed cement (Blast furnace cement type B or C) that has a suppressing effect d. It has issued a notice that it is desirable to take measures to suppress the total amount of alkali in concrete (Na ₂ O content should be 3.0 kg / m ³ or less).

The cements mentioned in (b) and (c) are special cements, each of which has special characteristics, but so far, the amount of them used is small, and in ordinary civil construction and other concrete construction, ordinary portland cement is used. However, it is used in 80% or more of the total cement usage. This ordinary Portland cement has a Na ₂ O equivalent of 0.6-1.0%.
It may be about 1.2% in some cases.

An object of the present invention is to provide a simple method capable of effectively suppressing an undesired alkaline-aggregate reaction even when using a normal Portland cement that does not satisfy the requirements b and c of the Ministry of Construction notification. Is.

In addition, the alkaline aggregate reaction in question largely depends on the type of aggregate used. For this reason, the above-mentioned Ministry of Construction Notification states that it is desirable to test the reactivity of aggregates with alkalis in advance and use aggregates that are safe as a result of the test.

Another object of the present invention is to provide a method capable of effectively suppressing an undesired alkaline-aggregate reaction even when an aggregate having a high reactivity with alkali is used.

The method of the present invention for achieving the above-mentioned object is characterized in that a sufficient amount of water-soluble cellulose ether is added to the mortar or concrete mixture to suppress the alkali-aggregate reaction between the alkali and the aggregate in the system. And

That is, the present inventors have found that the water-soluble cellulose ether is significantly effective in suppressing the alkaline aggregate reaction.
Cellulose ethers are known to have the effect of suppressing material separation and bleeding due to their thickening and water-retaining effects until they harden, but they do not allow alkaline-aggregate reactions to proceed gradually after hardening. It was not known at all to have a suppressing effect. The field of materials and breathing, which are so-called separable phenomena, and the long-term chemical phenomenon of alkali-aggregate reaction (also referred to as vitrification of the aggregate surface) are completely different from each other. According to the report, the alkaline aggregate reaction, which may lead to concrete collapse, could be largely contributed to this field in that it could be prevented by cellulose ether which does not adversely affect other properties. .

Therefore, in the present invention, unlike the case where cellulose ether is blended for the purpose of preventing material separation and breathing, the cement and the aggregate which cause an excessive expansion due to a gradual reaction between the alkaline component in the cement and the aggregate after curing. It is intended for the concrete of the material mixture system using the above, and it is necessary to mix water-soluble cellulose ether in an amount sufficient to suppress the reaction when mixing the concrete with the material mixture. It is a feature.

Hereinafter, the method of the present invention and its effects will be specifically described by describing the experiments and the results that form the basis of the present invention.

[Materials used]

 The following materials were used in the experiment.

(1). Cement Ordinary boltland cement (“Asano Cement” manufactured by Nippon Cement Co., Ltd., Na ₂ O equivalent: 0.6%) (2). Aggregate A Toyoshima andesite Grain size distribution Grain weight% 0.15 to 0.6 mm 20% 0.6 to 2.5 mm 50% 2.5 to 5.0 mm 30% (3). Aggregate B Toyoura standard sand (4). Water Distilled water (5) from tap water in Chofu, Tokyo. Sodium hydroxide special grade reagent (6). Additives Methylcellulose [Mortar blend] The amounts of cement, aggregate and water mixed at one time are as follows.

Cement 600 g Aggregate A 600 g Aggregate B 600 g Sodium hydroxide aqueous solution 300 ml However, the amount of sodium hydroxide aqueous solution is adjusted so that the amount of alkali in mortar is 1.2% by weight based on cement, calculated as Na ₂ O. I adjusted.

[Kneading]

Kneading of mortar was performed using the kneading machine specified in JIS R 5201 9.1.1 in the following manner. That is, the dough and paddle are fixed in the mixing position, and the amount of cement,
Aggregates (A and B) and 0, 2.5 or 5.0% by weight of an additive (methylcellulose) based on cement were added to start the kneader and kneaded for 30 seconds while rotating the paddle. Then, after stopping the kneader and adding the above amount of the aqueous sodium hydroxide solution, the kneader was driven for 30 seconds and rested for 20 seconds. During this pause, the mortar adhering to the spoon, the dough and the paddle was scraped off. In addition, the kneading machine
A cycle of driving for 30 seconds and resting for 20 seconds was repeated 3 times. After the final pause, knead for 120 seconds. The obtained mortar was immediately subjected to molding.

[Formwork]

A 40 x 40 x 160 mm triple mold frame specified by JIS R 5021 9.1.2, with holes for fixing gauge plugs at both ends was used so that gauge plugs for measuring length change could be embedded.

[Molding of specimen]

The mortar was filled up to about half the height of the mold, and the whole surface was struck by using a stick. Next, the mortar was filled up to the upper end of the form, and was similarly pierced with a stick rod, and finally the remaining mortar was raised by about 5 mm.

[Initial curing and demolding] After placing the mortar, the mold was demolded after curing for 24 hours in an atmosphere of 20 ° C and 100% relative humidity.

〔storage〕

The specimen taken out from the water was stood with the end in the longitudinal direction facing downward and steam-cured at a temperature of 40 ° C.

[Measurement age]

The age of the measurement (the period of steam curing mentioned above) was 0 month, 0.5 month, 1 month, 2 months, 3 months, 4 months, 5 months and 6 months.

[Measurement] Specimens that reached each measurement age were kept in an atmosphere of 20 ° C and 100% relative humidity for 16 hours, and then their length (distance between the inner end faces of the gauge plug) was measured, and the measured value was measured. Then, the rate of change (expansion amount) of the length in the relevant age was calculated from the initial measured value of the length (in 0 month of age).

The results obtained are shown in Table 1. The expansion amount shown is an average value of the values obtained for three specimens of the same age, which were simultaneously prepared from the same mortar using a triple mold and aged under the same conditions.

FIG. 1 is a graph showing the results of Table 1. In Fig. 1, each curve shows the change with time of the expansion amount of the mortar bar, curve C is the case where methylcellulose is not added, and curves A and B are the cases where methylcellulose is added at 2.5% by weight and 5% by weight per cement, respectively. Regarding the case.

According to the experimental results shown in Table 1 and FIG. 1, the expansion amount of the mortar tested was 0.095% in 3 months and 0.128% in 6 months without addition of methylcellulose.
On the other hand, when 2.5% by weight and 5% by weight of methylcellulose were added to the cement, the expansion amount was 0.044% and 0.026% respectively in 3 months and 0.062% and 0.034% in 6 months respectively, and the addition amount of methylcellulose was It can be seen that the amount of expansion decreases as it increases. This means that the addition of methylcellulose can substantially suppress the alkaline aggregate reaction in mortar or concrete.

In the above experiment, methyl cellulose was used as the alkaline aggregate reaction inhibitor, but a water-soluble cellulose ether other than methyl cellulose, for example, ethyl cellulose,
Propyl cellulose, cyanoethyl cellulose, carboxymethyl cellulose and hydroxyethyl cells can also be used in the practice of the present invention.

As described above, the alkali-aggregate reaction largely depends on the amount of alkali in the cement used and the type of aggregate used. Therefore, in carrying out the method of the present invention, the water-soluble alkali to be added to the mortar or concrete mixture should be treated. A suitable amount of cellulose ether may be determined in advance by a test. That is, the mortar bar method was tested with various amounts of water-soluble cellulose ether added, and as a result, the expansion amount was less than the specified amount (0.05% or less in 3 months and 0.1% in 6 months).
In the case of the following), the addition amount in that case is an appropriate amount of the water-soluble cellulose ether.

The addition and mixing of the cellulose ether can be performed in the same manner as the mixing of mortar or concrete which is usually performed.
That is, it can be mixed with a water-soluble cellulose ent and aggregate by kneading in a concrete mixer.

According to the present invention, if an appropriate amount of cellulose ether is added to the mortar or concrete mixture, the alkali-aggregate reaction in the mortar or concrete structure can be effectively suppressed, and the requirements (i), (ii), (ii), (ii), and (ii) of the above Ministry of Construction notification are required. Even if is not satisfied, expansion and deterioration of the structure can be avoided or at least substantially reduced, and safe mortar or concrete construction is possible.

The mechanism by which cellulose ethers suppress the alkaline-aggregate reaction has not yet been fully elucidated, but cellulose ether reacts preferentially with the alkali in the system, and as a result, the alkaline-aggregate reaction is suppressed. It seems to be.

[Brief description of drawings]

FIG. 1 is a graph showing the change over time in the expansion amount of the mortar bar.

Claims (1)

[Claims] 1. A concrete containing a material in which an alkali component in the cement and the aggregate gradually react to cause excessive expansion after the concrete hardens, and a water-soluble cellulose ether suppresses the reaction when the concrete is mixed. A method for suppressing expansion of concrete by an alkali-aggregate reaction, which is characterized by being mixed in a sufficient amount.