The history of building binders and the emergence of high-strength gypsum
One of the first binders used by humans was unburned clay. This material is still used for the construction of the simplest structures, when products and structures do not require high strength. Due to its weak astringent properties, and most importantly, due to its low resistance in wet conditions, unburned clay eventually ceased to meet the increased requirements of construction equipment. In 2500— 3000 years BC, artificial methods were found for the production of binders, primarily gypsum and lime, obtained by firing the corresponding rocks.
Gypsum was already used in the construction of pyramids in Egypt. Over time, they learned to impart hydraulic properties to lime mortars using additives such as baked clay and rocks of volcanic origin (tuffs, ashes, pumice) in crushed form. Such solutions were used mainly in the construction of hydraulic structures.
Astringent substances in Russia were used already in ancient times. According to B. S. Shvetsov and V. N. Surovtsev, lime was used in the construction of the Tithe Church in Kiev in 990. The walls of St. Sophia Cathedral in Kiev, built in the XI century, are made of bricks on lime with the addition of such an amount of crushed bricks that the greatest durability of mortars is achieved. According to V. N. Jung, in the X-XV centuries. In Russia, both fatty calcium and lean magnesia lime were consumed.
In 1584, a Stone order was established in Moscow, which, along with the preparation of building stone and the production of bricks, was also responsible for the production of lime. The organization of Kamenny Prikaz served as a further impetus in the development of its production.
In the 18th century, the accumulated experience in the production and use of binders was systematized in Russia, and scientific and practical problems were fruitfully developed. Along with construction gypsum, high-strength gypsum is obtained in production conditions by sealing gypsum stone in hermetically sealed apparatuses (autoclave boilers). During heating of natural gypsum in autoclave boilers, at a pressure of water vapor entering them of 0.13 MN/m2 (1.3 at) and a temperature of 125° C, a modification of semi-aqueous gypsum is formed, consisting of large pronounced crystals and having a significantly lower water demand (40-46%) than the modification. As a result, high-strength gypsum obtained by heating natural gypsum under pressure has a strength 3-4 times higher than construction gypsum. In addition, high-strength gypsum is obtained by self-sealing.