Until a certain time, air lime in construction was used only in slaked form. I.V.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 generally accepted concept around the world that conditionally combines the products of firing (and subsequently processing) 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 powder form, milled or in the form of dough. The quicklime formula is CaO. This compound is a product of firing rocks in which calcium oxide acts as the main chemical component. It actively interacts with water. As a result of hydration, hydrated lime is formed - Ca (OH) 2 .
Classification
In accordance with the chemical composition, the air mixture (consisting mainly of magnesium and calcium oxides) and hydrated (containing a large amount of iron, aluminum and silicon oxides) are separated. The industry uses quicklime lump and powdery lime. The latter is also subdivided into two types. The first is quicklime powder. The second type is obtained by applying special technology. Slaked lime (fluff) is obtained by the method of quenching magnesia, calcium and dolomite lime using a limited amount of water. There are other types. These include, in particular, bleach and soda lime.
Production
Quicklime is made using natural calcium-magnesium rocks. They mainly include calcium and magnesium carbonate . They also include clay and sand impurities. During heat treatment (when heated) in a furnace to a temperature of from 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.
The technology of obtaining a mixture of fine grinding
Quicklime powder is obtained by grinding the mixture in conventional ball mills. Their work is carried out in a closed cycle with a separator emitting particles of the required size. In some cases, two separators are placed in series in the unit. This significantly increases productivity. To date, questions on fine grinding of lime are not sufficiently 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 (strongly, medium, or soft-burned product). Be sure to take into account the presence of burnout, underburning, the presence of solid inclusions. It is more expedient to grind highly and medium calcined lime by 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 aggregation requires short mills and the rapid removal of fine fractions from the total mass of the crushed mixture, as well as the use of methods that reduce aggregation.
The 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 industry. CaO is also used in the construction industry. The compound is of particular importance in the field of ecology. Lime is used to clean flue gas from sulfur oxide. The compound is also able to soften water and precipitate the organic products and substances present in it. In addition, the use of quicklime neutralizes natural acidic and wastewater. In agriculture, when in contact with soils, the compound eliminates acidity harmful to cultivated plants. Quicklime enriches the soil with calcium. Due to this, the cultivability of the earth increases, the rotting of humus is accelerated. At the same time, the need for large doses of nitrogen fertilizers is reduced.
The hydrated 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 for the maintenance and raising of livestock. In the chemical industry, hydrated lime and sorbents are used to produce calcium fluoride and 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 cementitious materials, concrete and mortar, the manufacture of products for construction.
Quicklime, finely ground. Benefits
Quicklime, as mentioned above, is used in the manufacture of concrete and mortar. This compound has several advantages. In particular, in comparison with hydrated lime in the form of dough or powder, the finely ground mixture leaves no waste. Moreover, all its components are used most rationally during hardening. Quicklime, ground lime has a lower water demand. In addition, its specific surface area is also significantly smaller. In this regard, the "workability" of concrete or CaO-based mortar is obtained with a reduced volume of water. Reducing the water demand of concrete and mortar mixtures helps to increase their strength during hardening. During hydration in already prepared mixtures, lime binds more water (up to 32% upon transition to hydrate). This contributes to the production of products, concrete and mortars of increased density and strength. During hydrated hardening with quicklime, a significant amount of heat is released. In this regard, products based on this compound at lower (below zero) temperatures harden more calmly and have better strength indicators, since the surrounding conditions provide rapid heat removal and a reduction in thermal stresses. It is these advantages that determine the widespread use of CaO in the construction industry.
How to get high-quality concrete and mortar mixes?
With hydrated hardening with quicklime, good results are possible under a number of conditions. First, the mixture should be finely ground. It is also necessary to observe a certain ratio of lime and water. In the hardening process, optimal heat removal is necessary or other methods should be applied that do not allow the hardening of concrete or mortars to temperatures that can cause intense evaporation of moisture (especially when 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 variety, type and quantity in which the material is needed. So, for example, the cost of a bag is from 300-400 rubles, and tons - from 8-10 thousand rubles. Product storage is carried out 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 carbonation and hydration of calcium oxide). Bulk or ground quicklime is sent to the consumer in containers, tar 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.