In the construction of buildings and structures, a large number of materials and components are used. One of these substances is air lime. What is it, what are the material properties and applications?
Description
Building air lime is a product that is obtained by firing lime and lime-magnesium carbonate rocks at a temperature of 900-1250 degrees. As a result, carbon dioxide is completely removed from them, mainly calcium and magnesium oxide remain in the composition.
A small amount of clay, quartz sand is also allowed. However, their amount should not exceed 6-8%, otherwise the product may partially lose its properties and turn into hydraulic lime.
Varieties
There are several main types of material:
Air quicklime lump is a product of roasting lime rocks and has the appearance of formed pieces of different sizes. It consists of calcium and magnesium oxide, and may contain impurities of calcium carbonate, silicate, aluminate, calcium and magnesium ferrite, which did not decompose during heat treatment
Ground quicklime is lump lime crushed to powder. Their chemical composition is identical
- Air hydrated lime is a highly dispersed powder, which is obtained by slaking lump or ground quicklime. The procedure is performed by spraying liquid or vaporous water. The aim of the technique is to convert calcium and magnesium oxides into their hydrates. The moisture content of the finished product should not exceed 5%.
- Lime dough is the product of quenching lump or ground lime with a large amount of water. The result is a plastic mass that contains up to 50% liquid.
Depending on the concentration of magnesium oxide, the following types of lime are distinguished:
- magnesian;
- calcium;
- dolomitic.
The activity of lime is determined by the amount of content in it of active oxides of calcium and magnesium. Accordingly, the higher their number, the better the material is.
Also, according to the norms, lime varies in slaking speed:
- fast-extinguishing has a extinguishing speed of about 8 minutes;
- medium extinguishing - no more than 25 minutes;
- slow fading - over 25 minutes.
The quench rate is determined from the moment the liquid is added until the temperature of the mass begins to decrease.
Raw materials
In order to get building air lime,the following raw materials need to be heat treated:
- fine-grained crystalline limestone-marble;
- dense limestones;
- calcareous tuff;
- dolomitic limestone;
pure limestones
Among all the presented varieties of raw materials for air lime, fine-grained crystalline limestone-marble is used the least, as it has increased decorative properties that negatively affect practical application.
Properties
Different types of building material have different characteristics. The properties of air lime can be as follows:
- The true density of the quicklime material varies from 3.1 to 3.3 g/cm3 and depends on the temperature at which the firing was carried out.
- The average density of lump lime can be from 1.6 to 2.9 g/cm3. Such significant differences are also explained by the temperature and duration of heat treatment.
- Bulk density for ground quicklime is 900-1100 kg/m3 in a loose state, for hydrated lime - 400-500 kg/m3 , for lime paste - 1300-1400 kg/m3.
- Air lime has the property of plasticity. It is necessary for the viscosity of the building material. Lime mortars are easy to apply and spread over the surface, provide good adhesion to brick or concrete and are water-retaining.
- Water demand andwater-retaining capacity depends on the type of product. The highest characteristics are slaked powdered or paste-like lime, the lowest - ground quicklime.
- The hardening time of air lime also depends on the type of material. So, for example, slaked hardens very slowly, while quicksand sets already 15-20 minutes after application. Also, this figure may vary depending on the layer of material and conditions.
- Design changes. Mortars based on air lime may be subject to changes such as drying shrinkage, swelling, uneven volume change.
- Strength directly depends on the conditions of solidification of solutions. For example, slow-setting mortars have low strength, unlike fast-setting ones.
The durability of materials depends both on their initial quality characteristics and on the conditions of hardening and operation. Thus, dry conditions are most favorable for long-term operation of buildings.
Material advantages
Air lime has the following advantages:
- hygroscopicity - the material is resistant to conditions of high humidity, while its quality characteristics do not change;
- disinfection of surfaces on which the solution is applied, while destroying all harmful bacteria and molds;
- material has a neutral smell;
- versatility - equal efficiency when used as onthe old coating, and on the cleaned one.
In addition, the production of air lime is not too expensive, so the cost of the final material is very affordable for consumers.
Flaws
Like all building materials, air lime can have downsides:
- the possibility of bubbles or cracks appearing when the mixture hardens if the mortar was made with errors;
- when working with lime, you must adhere to some safety precautions - use gloves, a protective mask and a respirator, as the material is too caustic.
In order to get the perfect mixture, it is important to follow the instructions that are indicated on the individual packaging with the material.
Uses
This material is quite multifaceted. The most widely used methods of using air lime are:
- Disinfection of premises. To do this, lime is diluted to a liquid state and used to treat rooms. After these procedures, mold fungi do not form on the walls.
- As a heater. When lime is mixed with sawdust and gypsum, an inexpensive and environmentally friendly insulation is obtained, which is in demand in private construction.
- When laying bricks, lime is needed to increase the adhesion of surfaces.
- Lime is a component of many compositions of plaster, slag concrete, paint and varnish coatings.
Slaked and quicklime varieties of material havedifferent properties, so they are used for different purposes. For example, quicklime should not be used on fireplaces and other heated surfaces, as it can release carbon dioxide, which is toxic to humans.
Slaked lime is used for the following purposes:
whitewashing houses, borders, trees;
- in the industry for the processing of genuine leather, as it has softening properties;
- disinfection of the mouth and dental canals in dentistry;
- to increase the adhesion of sand-cement compounds in construction;
- is a food additive E526 that helps to mix non-combinable components;
- as a feed additive for farm animals.
In addition, the material is used to neutralize sewage and waste water during their treatment at treatment plants.
How to slake lime?
Today, you can purchase many varieties of material, including ready-to-use slaked. However, there are situations that may require you to do it yourself.
In order to get airy slaked lime, you need to add water to it. The liquid reacts with calcium oxide, releasing large amounts of heat and carbon dioxide. This process occurs due to the transformation of water into steam, which loosens lime lumps to a fine fraction.
To obtain a hydrated composition - fluff, you needadd liquid in an amount of 70-100% of the total weight of lime. To get building lime paste, you need to add water in a ratio of 3: 1, where 3 is the amount of limestone.
Helpful tips
Depending on the purpose of use, lime is diluted in different proportions:
- for whitewashing walls and ceilings, you need to take 1 kg of powder and 2 liters of water;
- for processing tree trunks, 1 kg of material is taken per 4 liters of liquid.
When performing construction work, experts recommend adhering to the following points:
- When used as a plaster mix, add a small amount of wallpaper paste. It will make the mixture stronger.
- In decorative whitewash, you can add natural drying oil (1/3 tsp per 1 liter of composition) to make the coating resistant to adverse external conditions.
In addition, lime compounds can be painted if necessary. For these purposes, blue or latex-based paint is used.
Safety
Lime is a rather caustic material, so when in contact with it, you need to follow some rules:
- mixing of compounds or quenching must be carried out exclusively in metal containers;
- should not neglect the use of protective equipment - gloves, mask, respirator;
- when slaking lime, a large amount of heat and gas is released, so it is undesirable to lean over the vessel during the active phase;
- it is important to carry out extinguishing in the fresh air, as inthe process releases a gas that is toxic to humans.
Also, you can not knead the compositions with your hands, even if they are wearing protective gloves.
Storage rules
There is a small set of guidelines for storing limestone:
- storage of the quicklime product should take place in a dry room in a waterproof bag or container, as even slight moisture can start the extinguishing process;
- when storing the material in a paper bag, its shelf life when opened is reduced to a month, as lime quickly loses its properties;
- The storage room must be equipped with wooden floors that are raised 30 cm above ground level.
Violation of storage recommendations is fraught not only with a deterioration in the quality of the material, but also with the possibility of fire if the lime is close to electrical appliances. It is also forbidden to use water to extinguish limestone, only powder fire extinguishers are allowed.
Burns
If safety precautions are not followed, chemical damage to the skin, mucous membranes or respiratory tract can occur. The alkali, of which the solution consists, penetrates into the deeper layers of the skin. In this case, the lesion is much larger than the zone of skin contact with lime. Affected tissues partially lose their ability to regenerate, wound healing takes a long period. Contact with the mucous membrane of the eye may result in inflammation or partial loss of vision with a large amount of damage.
It is important to call the medical team immediately after receiving a burn tofirst aid. It is recommended to wash the skin after contact with slaked lime with cool water. But in case of a burn with quicklime, it is strictly forbidden to use water for washing. You can try to remove the remains with a soft cloth, and apply oil or any other fat to the lesion itself, and then cover it with a soft cloth. Pain medication may be used to reduce pain.
