Binders are called powders that, after mixing with water, form a plastic mass, which subsequently solidifies into a hard stone. There are several types of such substances. For example, hydraulic binder powders can harden not only in air, but also under water. At the same time, they can maintain their strength in such conditions for a long time. Belongs to the group of such binders and hydraulic lime.
Varieties
Building lime of this type is produced in the form of fine powder. Two main varieties of this material can currently be used:
- low hydraulic lime with module 4, 5..9;
- high hydraulic with module 1, 7…4, 5.
A special formula is used to characterize the active part of this material. For hydraulic lime it looks like this:
m=(% CaOtotal - % CaOfree) / ((% SiO2(total) - % SiO2(free)) + % Al2O 3 + % Fe2O3).
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. Calcium oxide hydrate in such lime during hardening gradually crystallizes when moisture evaporates. 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 (lime formula). Its specific gravity in this case can be 2, 8-2, 9.
To increase the strength and prevent cracking of the material, a small amount of sand is sometimes mixed into it, among other things.
Hardening of hydraulic lime, as you know, starting in air, can continue in water. This material is tested for tensile and compression as follows:
- prepare lime mortar;
- keep it in the air for 3 weeks;
- dip the finished solid into water.
After a week of being in water, the tear resistance of a solid made of weakly hydraulic lime should not be less than 2, and after 5 weeks - 3 kg/cm2. The resistance of hardened lime to compression for these periods should be respectively 6 and 15 kg/cm2.
The highly hydraulic variety of this material is checked in much the same way. The solution islime 1:3 is usually kept in the air for 1 week. Next, the stone is immersed in water for a month. After this time, its resistance to rupture should be 2, to compression - 12 kg/cm2. After a two-month exposure, the properties of hydraulic lime should be such that these indicators are equal to 8 and 20 kg/cm2 respectively.
Which raw materials are used for manufacturing
This building material is made from marl and marl limestone. Rocks of this type contain:
- carbonic lime;
- clay.
The percentage of these components is determined by treating the material with hydrochloric acid. The entire sediment is classified as clay. In addition to the two main components, marls may contain the following substances:
- carbonic s alts of iron and magnesium;
- oxides of iron and manganese.
Only those marls can be used for the production of hydraulic lime, in which the ratio of silica content to the amount of Fe₂O₃ and alumina reaches at least 2.5.
Where raw materials are mined
There are large deposits of marl in our country, for example, near Novorossiysk. There are also industrial deposits of this material in the Bryansk region. The rocks of this particular deposit are very well suited for the production of hydraulic lime. Also, a large amount of marl in our country is mined in the Bakhchisarai and Vygonichskydeposits.
How it is produced
Hydraulic limes are made exclusively from natural marls. One of the features of this rock is that its components are very much crushed and mixed with each other as homogeneously as possible. All attempts to prepare lime of this variety from an artificial substance have so far ended in failure. It is currently not possible to create suitable raw materials for the production of such a material under industrial conditions.
Hydraulic lime is obtained by firing marls at moderate temperatures of 900-1100 °C. The raw material preliminarily coming from the quarries is broken into pieces, the size of which should eventually be 60-150 mm. Then the marl is immersed in a shaft furnace equipped with a complete combustion or gas furnace.
Ready hydraulic lime is subjected to even finer crushing. This further improves the extinguishing conditions.
Application features
Unlike cement, hydraulic lime is slaked not directly at the construction site, but at factories. This is primarily due to the complexity of such a procedure. When slaking, lime is first loaded into dampening augers. Then it is sprayed with water. The lime is then sent to slaking silos.
Application scope of hydraulic lime
Burnt crushed marl is usually used as a raw material in the preparation of various types of mortars. Most often, such lime is added to plaster or masonry mixtures. Sometimes low-grade concretes are also made using this powder. The use of this material makes mortars more plastic.
Unlike air lime, hydraulic lime can be used to prepare mixtures intended for masonry or plastering of those parts of buildings and structures that will subsequently be operated at high humidity. Also, this material is sometimes added to concrete solutions intended for pouring the part of foundations located below the groundwater level.
Benefits of using
The advantages of using hydraulic lime, among other things, include:
- Environmental 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 in the walls of those buildings that were erected using mortars 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.
- No efflorescence. White spots on walls erected using plastic mortars containing such lime never appear. That is, buildings and structures built on masonry mixtures with hydraulic lime always look attractive and aesthetically pleasing.
Solutions prepared on the basis of building hydraulic lime are resistant to heat, frost, precipitation. At the same time, they are able to resist microflora and chemicals well.
