Binders are powders that, after mixing with water, can form a plastic mass that subsequently hardens into hard stone. There are several types of such substances. For example, hydraulic binders can harden not only in air but also under water. At the same time, they can maintain their strength under such conditions for a long time. Hydraulic lime also belongs to the group of such binders .
Varieties
Construction lime of this type is produced in the form of finely ground powder. Currently, two main varieties of this material can be used:
A special formula is used to characterize the active part of this material. For hydraulic lime, it is as follows:
m = (% CaO total -% CaO free ) / ((% SiO 2 (total) -% SiO 2 (free) ) +% Al 2 O 3 +% Fe 2 O 3 ).
The properties
Hardening of hydraulic lime occurs as a result of hydration of aluminates, Ca ferrites and silicates. That is, the processes in this case in the substance occur exactly the same as in Portland cement. The calcium oxide hydrate in such lime during solidification gradually crystallizes upon evaporation of moisture. Further, under the influence of water, it undergoes carbonization.
The color of this material may be yellowish, light gray or brownish, depending on the percentage of CaO content (lime formula). Its specific gravity may be 2.8-2.9.
To increase the strength and prevent cracking of the material, a small amount of sand is sometimes mixed in it, among other things.
The hardening of hydraulic lime, as you know, starting in air, can continue in water. This material is checked for rupture and compression as follows:
After a week of being in water, the index of resistance of a solid body from a weakly hydraulic lime to rupture should not be less than 2, and after 5 weeks - 3 kg / cm 2 . The compressive strength of hardened lime for these periods should be 6 and 15 kg / cm 2, respectively.
In approximately the same way, the strongly hydrovidic variety of this material is also checked. A solution of such lime 1: 3 is usually kept in air for 1 week. Next, the stone is immersed in water for a month. After this time, its tensile strength should be 2, compression - 12 kg / cm 2 . After two months of exposure, the properties of hydraulic lime should be such that these indicators are equal to 8 and 20 kg / cm 2, respectively.
What raw materials are used for manufacturing
This building material is made of marls and marl limestones. Rocks of this type contain:
The percentage of these components is determined by treating the material with hydrochloric acid. The entire sediment is attributed to clay. In addition to the two main components, marls can contain the following substances:
Only marls can be used to produce hydraulic lime in which the ratio of silica content to Fe₂O₂ and alumina reaches at least 2.5.
Where is the raw material mined?
Large deposits of marl in our country are, for example, near Novorossiysk. Also, industrial deposits of this material are in the Bryansk region. The rocks of this particular deposit are very well suited for the production of hydraulic lime. Also, a large number of marl in our country is extracted at the Bakhchisaray and Vygonich deposits.
How to produce
Hydraulic limes are made exclusively from natural marls. One of the features of this rock is that its components are very finely ground and mixed as uniformly as possible. All attempts to make lime of this variety from an artificial substance have so far failed. It is currently not possible to create suitable raw materials for the production of such material under industrial conditions.
Hydraulic lime is obtained by firing marls at moderate temperatures of 900-1100 ° C. The raw materials coming from the quarries are broken into pieces, the size of which ultimately should be 60-150 mm. Then the marl is immersed in a shaft furnace equipped with a complete combustion chamber or gas.
The finished hydraulic lime is subjected to even finer crushing. This subsequently improves the quenching conditions.
Application features
Unlike cement, hydraulic lime is not extinguished directly at a construction site, but in factories. This is due primarily to the complexity of such a procedure. When extinguishing, lime is first loaded into the moistening augers. Then it is sprayed with water. Then the lime is sent to extinguishing silos.
Scope of hydraulic lime
Annealed crushed marl is usually used as a raw material in the preparation of various kinds of mortars. Most often, such lime is added to plaster or masonry mixtures. Sometimes low-grade concrete is also made using this powder. The use of this material allows you to make mortars more ductile.
Unlike air lime, hydraulic can be used to prepare mixtures intended for masonry or plastering those parts of buildings and structures that will subsequently be operated at high humidity. Also, this material is sometimes added to concrete mortars designed to fill part of the foundations below the groundwater level.
Benefits of using
The advantages of using hydraulic lime, among other things, include:
Ecological cleanliness. This material is produced, as already mentioned, exclusively from natural raw materials.
Vapor permeability. Due to this property of hydraulic lime, the likelihood of condensation forming in the walls of those buildings that were built using solutions prepared on its basis is reduced.
Increase in labor productivity. It is not necessary to spend time extinguishing such lime directly at the construction site.
The lack of efflorescence. White spots on the walls erected using plastic solutions containing such lime never appear. That is, buildings and structures built on masonry mixtures with hydraulic lime always look attractive and aesthetically pleasing.
The solutions prepared on the basis of building hydraulic lime are resistant to heat, frost, precipitation. At the same time, they are able to well resist microflora and chemicals.