JPS62278151A - Degradation prevention of set concrete - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention ■ Mitsukuni Hadasato The present invention relates to a method for preventing deterioration of hardened concrete containing aggregate that causes an alkaline aggregate reaction.

Concrete is made by mixing cement, aggregate and water as basic ingredients. Gravel has traditionally been used as aggregate, but the production of high-quality gravel has gradually become insufficient, and in order to compensate for this, and also for the convenience of manpower, it has become necessary to crush minerals such as rocks. The so-called crushed stone obtained by this process is used as an aggregate in concrete instead of gravel. However, hardened concrete mixed with crushed stone as an aggregate often has the problem that, during long-term use, mesh-like or tortoise-shell-like cranks form on its surface, which grow and eventually lead to collapse. .

The above-mentioned mesh-like or tortoise-shell-like cranks are clearly different from linear or non-linear cracks that occur on the surface of hardened concrete containing high-quality gravel as aggregate. Alternatively, if you take a sample from the surface layer of hardened concrete where a tortoise-shell-shaped crank has formed and observe the aggregate inside using a microscope, you will find that the surface of the aggregate particles has turned black and has changed in quality. , or because whitened surface stones have appeared on the aggregate particles, the above-mentioned crank is already due to the expansion of the aggregate caused by the reaction between the alkali content in the cement and the aggregate, the so-called alkaline aggregate reaction. Are known.

Conventional technology As a method of preventing the above-mentioned alkaline aggregate reaction of hardened concrete mixed with crushed stone as aggregate, there is a method of adding a pozzolan substance when mixing concrete, and a method of adding synthetic resin etc. to the surface of concrete after hardening. Methods of forming waterproof coatings are known.

In addition, as a method for preventing the growth of cracks or the generation of new racks in deteriorated hardened concrete in which network or tortoise-like cracks have occurred on the surface due to the above-mentioned alkali aggregate reaction, or as a method for repairing the cracks, It is also known to cut out a V-shape or a U-shape, inject a filler such as mortar or epoxy resin into the resulting recess, and then coat it with waterproof paint.

As a method to prevent the deterioration of hardened concrete,
JP-A-20768 discloses a method of impregnating the surface of hardened concrete with a solution prepared by adding a small amount of sodium naphthalene sulfonate formaldehyde to an aqueous solution of lithium silicate. A method of impregnation in the same manner as above using a liquid to which a small amount of aliphatic alcohol is added is shown.

Depending on the method of adding the above-mentioned pozzolanic substance or forming a waterproof film on the hardened concrete surface, etc.
When hardened concrete is used for a long time, especially outdoors, cranking occurs on the concrete surface due to the alkaline aggregate reaction. Furthermore, the method of removing the crank portion from cracked concrete and filling it back with new filler is not only difficult to implement, but also causes the same cracks as described above after a long period of time has passed after this repair.

JP-A-58-20 which is easy to construct and relatively preferable
Even with the methods described in JP-A No. 768 and JP-A-60-36385, there is a limit to the depth at which the solution can penetrate from the surface of hardened concrete. Concrete tends to develop mesh or hexagonal cranks after a long period of time.

An object of the present invention is to provide a method for simply and completely preventing deterioration of hardened concrete containing aggregates that cause an alkali-aggregate reaction, due to the alkali-aggregate reaction.

. - The method for preventing the deterioration of hardened concrete containing aggregates that cause an alkaline aggregate reaction according to the present invention for improving the 0.0 as Li2O for cement
It is characterized by being contained in concrete in an amount of 1 to 5% by weight.

The concrete to which the method of the present invention is applied mainly contains ordinary cement that hardens through a hydration reaction and aggregate that causes an alkaline aggregate reaction with water. Examples of cements that can be used include ordinary Portland cement, early strength Portland cement, moderate heat Portland cement, and the like. These cements usually contain about 0.5 to 1.5% by weight of alkaline content in terms of oxides, such as Na, 0, K, 0, etc.

The aggregate contained in the concrete to which the method of the present invention is applied is obtained by crushing minerals such as rocks,
Examples of these minerals include proteinite, chalcedony, silicate magnesite, rhyolite, andesite, tuff, quartz andesite, trachyte, obsidian, abalite, tridymite, cristobalite,
Examples include various charts and flints. These minerals contain components that react with the alkaline content in the cement in the presence of water. Examples of such reactive components are:
Examples include silica, silicates, and the like. The reactivity of the mineral aggregate with the alkaline content in cement is not uniform, and the reactivity of crushed stone aggregate is generally tested before it is mixed into concrete.

The test methods include ASTM C289, a chemical method related to reactivity with alkaline components, and ASTM C22, which measures the expansion rate of aggregate using the mortar bar method.
A 7-way system is used.

The lithium-containing mineral used in the method of the present invention is a natural rock containing about 1 to 10 weight percent of lithium as Li2O, such as spodium mica containing 3 to 4 weight percent of Li2O, and 3.5 weight percent of Li2O. Examples include phyllodespar containing 5 to 4.5% by weight, spodumene containing 4 to 9.5% by weight of Li2O, and antase containing 7 to 9% by weight of Li2O. According to the present invention, the finer the particle size of these minerals to be mixed into concrete, the better, but they may be crushed to a size of about 300 microns or less. Therefore, these minerals are blended as powder, and the amount thereof is preferably 0.01 to 5% by weight as Li2O based on the cement.

The preparation and hardening of the concrete according to the present invention may be carried out by conventional methods, for example, a predetermined amount of the above cement as the main component,
When blending the aggregate and water, this can be easily done by adding the lithium-containing mineral powder so as to mix it into the cement. Further, concrete can be easily hardened by conventional methods such as at room temperature, heating, and water.

The concrete of the present invention may contain any other optional components, such as various commonly used admixtures, as long as the purpose of the present invention is achieved. In some cases, a more preferable hardened concrete can be obtained by adding lithium nitrite, lithium hydroxide, etc. in combination.

Furthermore, the hardened concrete according to the present invention can be provided with a conventional waterproof coating, and in this case as well, prevention of deterioration of the hardened concrete can be preferably achieved. The waterproof coating materials used for this purpose are those normally used for waterproofing concrete (for example, acrylic resin aqueous emulsion, epoxy resin aqueous emulsion,
Examples include styrene-butadiene rubber aqueous latex, acrylonitrile-butadiene rubber aqueous emulsion, paraffin aqueous emulsion, asphalt aqueous emulsion, cement paste, mortar, and cement paste and mortar containing the above emulsions.

According to the present invention, lithium-containing minerals added when preparing concrete prevent the alkaline aggregate reaction of hardened concrete and do not cause mesh or tortoise-like cracks in hardened concrete even after long-term outdoor use. .

This effect is thought to be due to the gradual release of lithium compounds from the lithium-containing minerals in concrete, which act to prevent alkaline aggregate reactions. Therefore, it is preferable that the lithium-containing mineral added has a fine particle size and is uniformly mixed into the concrete. Normally, in hardened concrete that undergoes an alkaline aggregate reaction, the reaction progresses gradually and causes the aggregate to expand, which is thought to lead to cracks in the hardened concrete. Therefore, it is necessary to prevent this alkaline aggregate reaction. A sufficient amount of lithium compounds must be released from the lithium-containing mineral into the concrete. The amount of lithium-containing minerals effective in preventing this alkaline aggregate reaction and preventing the occurrence of cracks in hardened concrete is the Li/Na molar ratio of the lithium content in the minerals and the sodium equivalent alkali content in the cement of 0.1. As mentioned above, it was found that preferably it is 0.3 or more. However, increasing the addition ratio of lithium-containing minerals will affect the amount of aggregate added separately, so it is preferable not to add lithium-containing minerals excessively. Therefore, the alkali content is 0.
Compared to normal cement, which is about 5 to 1.5% by weight,
It is preferable to mix lithium-containing minerals with a particle size of about 300 μm or less in an amount of about 0.01 to 5% by weight as Li2O.

Since the rate at which the above lithium-containing minerals release lithium compounds in concrete is slow, for concrete that undergoes an alkaline aggregate reaction relatively early after concrete placement, lithium nitrite, hydroxide, and the above lithium-containing minerals are recommended. By adding lithium or the like at the time of concrete preparation, early alkaline aggregate reactions can be prevented.

Furthermore, by providing a waterproof coating on the surface of the hardened concrete according to the present invention, it is possible to reduce the infiltration of water from the concrete surface into the interior while the waterproofing property is effective. As a result, the early progress of the alkaline aggregate reaction caused by the presence of water can be suppressed, albeit for a short period of time. In addition, this waterproof coating prevents alkaline aggregate reactions because lithium compounds, which are gradually released into the concrete from lithium-containing minerals, accumulate during this waterproofing period to a sufficient amount to prevent alkaline aggregate reactions in the concrete. It is also thought that this is due to the fact that

Example Work~4 and Comparative Example Cement containing 0.57% by weight of alkaline content calculated as Na2O, 40% fine aggregate that causes an alkali aggregate reaction, and Toyoura standard sand bone that does not cause an alkali aggregate reaction. Mixed aggregate with 60% of lithium-containing material, and spodumene (Li2O content 8.6% by weight) and feldspar (Li, 0 content 4.5% by weight) with a particle size of 50 to 180μ were prepared as lithium-containing minerals. In addition, the determination of whether or not the above aggregate causes an alkali aggregate reaction is based on ASTM
Determination was made using the chemical method specified in C289.

Next, Na0II was added to the mixing water so that the amount of Na2O to the cement was 1.2% by weight, and the cement, mixed aggregate, and water were mixed at a weight ratio of 1:2.25:0.5, Furthermore, the above-mentioned lithium-containing minerals were blended so as to have the Li2O mixing rate listed in Table 1, and L was cast by casting.
A cured mortar bar was obtained by molding into a mortar bar of QcmX 1 QcmX 40 cm, and removing the mold and curing according to the method specified in ASTM C227.

When the expansion rate of the mortar bar was measured for 90 days immediately after curing, the results shown in Table 1 were obtained.

As a comparative example, a mortar bar was formed in the same manner as above except that no lithium-containing mineral was added, and the expansion coefficient was measured.
The results listed in the table were obtained.

[Below, remainder white]

Comparing the results of Examples 1 to 4 above with Comparative Examples, it is found that the addition of lithium-containing mineral powder particularly reduces the amount of Li contained therein.
It is observed that as the zoffi increases relative to cement, the expansion rate decreases.

Examples 5 to 6 Instead of adding lithium mineral in Example 1, lithium mineral and nitrite, lithium, or lithium hydroxide were used together and added so that the Li2O content to the cement was as shown in Table 1. Except for this, a mortar bar was molded in the same manner as in Example 1, and the expansion coefficient was measured, and the results shown in Table 1 were obtained. However, in Example 5, lithium nitrite was
Further, in Example 6, lithium hydroxide was used. 1st
The results in the table show that by adding these lithium compounds in combination, the expansion rate can be further reduced even at the same Li2O mixing rate as in Example 1.

According to the present invention, by simply adding an effective amount of lithium-containing mineral powder consisting of finely crushed particles at the time of mixing concrete, it is possible to prevent the occurrence of cracks due to alkali aggregate reaction in concrete after hardening, and to improve hardened concrete. deterioration can be prevented for a long period of time. Conventionally, in order to completely prevent the deterioration of hardened concrete due to alkaline aggregate reactions, it was done by selecting aggregates that do not cause this reaction based on preliminary tests, and then using that aggregate. According to the invention, there is no need for a preliminary test, and it is possible to obtain hardened concrete that does not cause an alkali-aggregate reaction even when using aggregates that easily cause an alkali-aggregate reaction as described above.

Claims (1)

[Claims] When preparing concrete using aggregate that causes an alkaline aggregate reaction, lithium-containing mineral powder is added to cement.
A method for preventing deterioration of hardened concrete containing aggregate that causes an alkaline aggregate reaction, characterized in that i_2O is contained in the concrete in an amount of 0.01 to 5% by weight.