Until a certain time, air lime was used in construction only in slaked form. IV Smirnov in the thirties suggested using the substance in a different way. He, and later Osip B. V., showed that under certain conditions, hydrated hardening of the material can occur. This process is similar to the hardening of Portland cement or gypsum.
General information
Lime is a concept generally accepted throughout the world, conditionally combining the products of roasting (and subsequently processing) of chalk, limestone and other carbonate rocks. Classification is carried out in accordance with the chemical composition. As a rule, the word "lime" refers to quicklime and the product of its interaction with water. This material may be in powdered, ground or dough form. The formula for quicklime is CaO. This compound is a product of roasting rocks, in which calcium oxide acts as the main chemical component. It actively interacts with water. As a result of hydration, slaked lime is formed - Ca (OH) 2.
Classification
According to the chemical composition, they are dividedan air mixture (consisting mainly of magnesium and calcium oxides) and a hydrate mixture (containing a large amount of iron, aluminum and silicon oxides). In industry, quicklime construction lump and powder is used. The latter is also divided into two types. The first is ground quicklime. The second type is obtained by using a special technology. Slaked lime (fluff) is obtained by slaking magnesian, calcium and dolomite lime using a limited amount of water. There are other types. These include, in particular, bleach and soda lime.
Production
Building quicklime is produced using natural calcium-magnesium rocks. They mainly include calcium and magnesium carbonate. They also include impurities of clay and sand. During heat treatment (when heated) in a furnace to a temperature of 800 to 1200 degrees, calcium-magnesium rocks begin to decompose. As a result of this process, oxides of magnesium (MgO) and calcium (CaO) are formed, as well as carbon dioxide.
Technology for obtaining a mixture of fine grinding
Quicklime ground is obtained by grinding the mixture in conventional ball mills. Their work is carried out in a closed cycle with a separator separating particles of the required size. In some cases, two separators are placed in series in the unit. This greatly increases productivity. To date, questions on fine grinding of limeinsufficiently developed. In the process of selecting mills and grinding schemes, it is necessary to take into account, first of all, the degree of firing of the material (heavy, medium or soft fired product). Be sure to take into account the presence of overburning, underburning, the presence of solid inclusions. It is more expedient to crush strongly and medium burnt lime, acting on its particles by abrasion and impact. This is what happens in ball mills. It should be noted that the tendency of solid particles to aggregate requires short mills and rapid removal of fine fractions from the total mass of the milled mixture, as well as the use of methods that reduce aggregation.
Use of quicklime and its products
This substance is widely used in various fields of human activity. The largest consumers include: ferrous metallurgy, agriculture, sugar, chemical, pulp and paper industries. CaO is also used in the construction industry. The connection is of particular importance in the field of ecology. Lime is used to remove sulfur oxide from flue gases. The compound is also able to soften water and precipitate organic products and substances present in it. In addition, the use of quicklime ensures the neutralization of natural acidic and waste water. In agriculture, when in contact with soils, the compound eliminates acidity that is harmful to cultivated plants. Quicklime enriches the soil with calcium. Due to this, the workability of the land increases, and the decay of humus accelerates. Together with thatthe need for high doses of nitrogen fertilizers is reduced.
Hydrate mixture is used in poultry and livestock for feeding. This eliminates the lack of calcium in the diet. In addition, the compound is used to improve general sanitary conditions in the maintenance and breeding of livestock. In the chemical industry, hydrated lime and sorbents are used to produce calcium fluoride and calcium hydrochloride. In the petrochemical industry, the compound neutralizes acid tars, and also acts as a reagent in the main inorganic and organic synthesis. Lime is widely used in construction. This is due to the high environmental friendliness of the material. The mixture is used in the preparation of binders, concretes and mortars, the production of products for construction.
Quickly ground lime. Benefits
Quicklime, as mentioned above, is used in the manufacture of concrete and mortar. This connection has a number of advantages. In particular, in comparison with hydrated lime in the form of dough or powder, the finely ground mixture does not leave any waste. At the same time, all its components are used most rationally during hardening. Ground quicklime is characterized by lower water demand. In addition, its specific surface area is also much smaller. In this regard, the "workability" of concrete or solution based on CaO is obtained with a reduced volume of water. Reducing the water demand of concreteand mortar mixtures helps to increase their strength during hardening. When hydrated in already prepared mixtures, lime binds more water (up to 32% upon transition to hydrate). This contributes to the production of products, concretes and solutions of increased density and strength. In the process of hydrated hardening of quicklime, a significant amount of heat is released. In this regard, products based on this compound at low (below zero) temperatures harden more calmly and have better strength indicators, since the surrounding conditions provide for rapid heat removal and a decrease in thermal stresses. It is these advantages that determine the widespread use of CaO in the construction industry.
How do you get quality concrete and mortar mixes?
In hydrated hardening of quicklime, good results are possible under a number of conditions. First, the mixture must be finely ground. It is also necessary to maintain a certain ratio of lime and water. During the hardening process, optimal heat removal is necessary or other methods should be used that do not allow heating of hardening concretes or solutions to temperatures that can cause intense evaporation of moisture (especially during boiling). It is also important to stop mixing the mixture at a certain stage of the lime hydration process.
Storage and cost
The price of quicklime depends on the grade, type and quantity in which you needmaterial. So, for example, the cost of a bag is from 300-400 rubles, and a ton - from 8-10 thousand rubles. The product is stored in warehouses with mechanized unloading and loading. The duration of the content of the compound should not be more than five to ten days (to avoid carbonization and hydration of calcium oxide). Quicklime lump or ground lime is sent to the consumer in containers, bituminized bags or in wagons equipped for its transportation, or in cement trucks. Packaging in bags is carried out using modern units with shaking devices. In bags, the product should be stored no longer than fifteen days.
