Контрольное задание 6 вариант 2

1. Прочтите и переведите текст Building Gypsum

Building gypsum is the name of an air binding agent produced by heat treatment of natural gypsum and subsequent grinding of the burned product. The basic process in the production of building gypsum is dehydration of natural gypsum. When heated to a temperature ranging from 140 to 170°C, natural gypsum rapidly decomposes into calcined gypsum and water. In manufacturing building gypsum careful attention should be paid to the burning temperature.

High-strength gypsum is produced by burning gypsum rock in special hermetic autoclaves at a steam t° of 125° C. As the moisture evaporates from the gypsum rock, the pressure in the autoclaves rises to 1.3 atm (gauge). The gypsum paste forming when gypsum is mixed with water gradually thickens and turns into a hard stone-like state. One must bear in mind that gypsum products must be dried at a temperature not exceeding 65-70° C, so as to prevent decomposition of the formed gypsum, for this may decrease its strength.

Strength and fineness of grinding are the most important properties of gypsum. When mixed with water, the gypsum paste rapidly sets, losing plasticity and binding ability in the process of setting, and these properties disappear at the end of setting altogether. The beginning of setting starts in 4-5 minutes and ends in 7-30 minutes after water is added.

Building gypsum is used in the manufacture of gypsum-concrete products and for casting moulds, patterns, architectural details and decorative products (cornices, rosettes, corners).

II. Ответьте на следующий вопрос:

How is high-strength gypsum produced?

22