JPH06117098A - Kneading method of cement - Google Patents

Abstract

PURPOSE:To prevent pollution of the natural world such as soil or ocean by performing kneading of cement under the condition of existence of a reducing agent, at building a concrete structure. CONSTITUTION:A reducing agent such as ferrous iron or stannous tin of powder or solution is previously kneaded with cement, aggregate, sand, and the like before kneading, and then a concrete structure is built. By building the concrete structure in this method, hexavalent chromium in the cement is transformed to trivalent chromium by the reducing agent, and it is enclosed and solidified in the structure. Consequently, outflow of trivalent chromium into bleeding water or drain water can be prevented.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for kneading cement.

[0002]

2. Description of the Related Art Conventionally, there has been a problem of soil pollution by hexavalent chromium or pollution of rivers and the like. Hexavalent chromium in cement, which has not been a problem until recently, has recently come to the fore as a pollution source.

Incidentally, in concrete products, 0.5 to
0.8 ppm of hexavalent chromium is present, and 0.12 to 0.2 ppm of hexavalent chromium is also present in the concrete product surface. In the past, when making concrete structures, breathing water was collected to convert hexavalent chromium into harmless trivalent chromium, but even if it exists in the natural state in the state of trivalent chromium, it may be converted into hexavalent chromium again depending on the conditions of the natural world. There was a fear of converting into.

[0004]

Therefore, the present inventor has conducted various studies to solve these conventional drawbacks and has completed a method of not releasing the hexavalent chromium in the cement or the treated trivalent chromium into the natural world.

[0005]

The present invention is carried out in the presence of a reducing agent at the time of kneading a cement to form a concrete structure, thereby converting hexavalent chromium present in the cement into trivalent chromium to obtain a concrete structure. It is a method of encapsulating the product. Conventionally, it has been considered effective to convert hexavalent chromium to trivalent chromium on the acidic side (for example, pH 3), and therefore, it was considered to be ineffective when used for alkaline substances such as cement.

However, surprisingly, it has been found that even in the alkaline region, reduction can suitably act to convert hexavalent chromium into trivalent chromium.

Generally 4 to 18 mg / kg in cement
Hexavalent chromium is contained, but the amount of reducing agent to be used may be equivalent in terms of chemical theory, but if safety is taken into consideration, 15 to 30 times the reducing agent is added to the amount of hexavalent chromium. Preference is given to using.

As a means for allowing the reducing agent to be present at the time of kneading the cement, a method of premixing the cement, aggregate, sand, etc. before the kneading in a powder or solution state, or preliminarily dissolving it in water used for the kneading of the cement is used. A method of preserving the reducing agent is preferably used in consideration of workability and the like.

The concentration of the reducing agent in the aqueous solution containing the reducing agent may be appropriately selected depending on the content of hexavalent chromium in the cement, but it is generally desirable to set the concentration to 10 to 30%.

Examples of the reducing agent used in the method of the present invention include ferrous iron, stannous, stannous vanadium, cuprous, etc. Among them, ferrous sulfate is preferable.

Next, the present invention will be described with reference to examples in order to more specifically show the present invention, but the present invention is not limited to the following examples.

EXAMPLE Cement containing 10 mg / kg of hexavalent chromium was used, and 12 parts by weight of cement, 47 parts by weight of aggregate and 34 parts of sand were used.
When mixing 3 parts by weight and 7 parts by weight of water, 0.3 part by weight of a 25% ferrous sulfate aqueous solution is added and sufficiently kneaded, and then filled into a pier formwork to be constructed in a river, and then a concrete structure. made. According to this method, the hexavalent chromium in the cement is converted into the trivalent chromium by the reducing agent during the kneading, and in that state, the hexavalent chromium is encapsulated and solidified in the concrete structure, so that it does not flow out to a river or the like.

[0013]

As described above, according to the method of the present invention, hexavalent chromium in cement can be converted into trivalent chromium during cement kneading, and in that state it can be encapsulated and solidified in a concrete structure. Since trivalent chromium does not flow out into breathing water or drainage, it does not pollute the natural world such as soil, rivers, and oceans.

Claims (1)

[Claims] 1. A method for kneading cement, which is characterized in that a reducing agent is allowed to exist during kneading of cement when a concrete structure is produced.