The igneous rocks were formed from magma, and sedimentary rocks were formed as a result of physical, chemical and organic destruction, weathering of igneous rocks, as well as from the products of vital activity of plant and animal organisms inhabiting huge water basins. Transformed or metamorphic rocks are formed as a result of the influence of high temperature, pressure and chemical processes on igneous and sedimentary rocks. They have a beautiful color, pattern, perceive processing, which gives them a decorative appearance, and in their physico-mechanical properties are suitable for use in facing buildings and structures.
Depending on the geological origin and mineralogical composition of rocks, physical and mechanical parameters, the method of manufacturing, processing, designation and decorative features, materials and articles made of natural stone are used in various construction sectors. Thus, for facing buildings and structures, granites, diorites, syenites, gabbros, porphyries, lar- drites, and volcanic tuffs are most often used. These rocks belong to the igneous. In addition, sedimentary rocks are used - dolomites, limestones, gypsum stones, travertines, sandstones, and metamorphic rocks - marbles, marble limestones, gneisses, quartzites.
In a natural stone, which is used for finishing buildings, such parameters as strength, bulk density, frost resistance, water absorption, porosity, softening, abrasion, hardness, solubility, acid and alkali resistance, impact resistance are important.
For rocks, the following brands are installed:
in terms of compressive strength (MPa) - 0.47; 1.0; 1.5; 2.5; 3.5; 5.0; 7.5; 10; 12.5; 15; 20; thirty; 40; 50; 60; 80; 100;
frost resistance (Мрз) - 10,15, 25, 35,50,100,150, 200, 300, 400, 500, (Кмрз should be not less than 0, 75);
on water resistance (Krazm) - 0,60, 0,70; 0.90, 1.00;
by volumetric mass (kg / m3) - heavy (more than 1800) and light (1800 or less).
The main indicators of decorative stone are the texture of the face of the stone, the pattern, color, structure of the rock. Stone, used as a material for the decoration of buildings and structures, is called facing. It is intended to provide not only the durability of buildings and structures, but also their architectural expressiveness, therefore it must possess not only high strength characteristics and a long service life, but also its decorative qualities, such as, for example, drawing and coloring. Facing stone is classified into four main features: origin, workability, service life in the outer lining of a building or structure and decorativeness.
The hardness of the minerals that make up the stone is the basis of the technological classification. Technological classification makes it possible to reasonably determine the methods and laboriousness of processing various rocks of the facing stone. The laboriousness of stone processing, in addition to hardness, is affected by the uniformity of the stone and its structure. The less resistance of the stone to abrasion, the easier it is to process it. Corrosion resistance of products made from natural stone is evaluated qualitatively by changes in physical and mechanical properties, such as strength, permeability, etc. So, to the stones that are used in the facing of buildings and structures, they make demands on durability, degree of decorative, mineralogical composition, structure and texture.
Longevity of a facing stone means its ability to maintain its original qualities during the operation of a building or structure. Natural stones for durability are divided into four groups: high-durable, durable, relatively durable and short-lived.
According to the degree of decorativeness, the facing stone is subdivided into highly decorative, decorative, poorly decorative and non-decorative.
The term "stone structure" implies the structure of the stone, due to the shape, size and quantitative ratio of the minerals composing the rock. Structural features include: the degree of crystallization, the shape and size of grains of minerals, uniformly-granularity. The structures are subdivided into full-crystal, cryptocrystalline and glassy. Depending on the size of the grains, the structures are coarse-grained, medium-grained and fine-grained.
So, granites, quartzites, diorites, syenites, gabbros, labradorites, basalts and others, refer to hard stones. Their structure can be coarse-grained, medium-grained and fine-grained with a grain size of more than 10 mm, from 10 to 2 mm and less than 2 mm.
Marbles, marbled limestones, dense sandstones, dolomites, dense tuffs, etc. belong to the stones of medium hardness and soft. Their structure can be coarse, medium-grained and fine-grained with a grain size of more than 1 mm, from 1 mm to 0.25 and less than 0.25 mm.
The structure affects the properties of the stone quite significantly. A stone with a fine-grained structure is stronger and more durable than a stone with a coarse-grained structure. The non-uniformly-grained structure is less resistant to atmospheric influences, because different in the size of the mineral grains, respectively, different coefficients of linear expansion, and with the change of temperatures this leads to the formation of cracks in the stone. Ice, frozen in cracks, contributes to their expansion and destruction of the stone. The term "stone texture" implies the spatial arrangement of the constituent parts of the rock in its volumes. Textural features include the uniformity of the arrangement of grains of minerals and the presence of voids. There are massive textures with a uniform dense arrangement of grains: banded - with alternating in the stone areas of different mineral composition or different structures and slag - with visible voids. The durability of the stone and the quality of the lining materials made from it depends on the physical and mechanical properties of the rocks.
The physical properties of the stone determine the possibility of its use for facing buildings, structures and other surfaces. These include bulk density, porosity, fracturing, frost resistance and water absorption. Porosity is the degree of filling of the stone with pores. It is defined as the percentage of pore volume to the entire volume of the stone.
Fracture is an indicator of the presence of cracks in the stone.
Water absorption is the ability of a material to absorb and retain water in the pores. It is defined as the percentage of the mass of a sample of a stone saturated with water, to its mass in an absolutely dry state. Strength - the ability of a stone to resist destruction under the influence of external loads. For the ultimate strength of the material, a stress corresponding to the load at which the material is destroyed is taken. The stone well resists compression and is much worse than stretching.
Friability - the property of the material under the action of external forces to break down immediately, without detecting significant deformations. Plates of marble, granite and other rocks do not resist the shock.
Limits of strength of natural stones used for finishing surfaces are as follows: granite 100-280 MPa at compression and 3 MPa at stretching; dense limestone - 50-150 MPa at compression and 0 at stretching; sandstone - 40-150 MPa under compression and 2 MPa under tension.
Hardness is the ability of a stone to resist the penetration of more rigid bodies into it. The hardness of the stone is usually assessed on the Mohs hardness scale. For more accurate determinations use a special device - a sclerometer.
Among the igneous rocks, the hardness of natural stones is as follows: granites - Mohs hardness - 7; syenites - 6, diorites - 6, gabbro - 6, labradorites - 6, volcanic tuffs - 2,5-3.
Among the sedimentary rocks in sandstones, Mohs hardness is 4-5; limestone - 3; in the dolomites - 4; travertines - 3; anhydrite - 1.5-2.5; gypsum stones - 1,5-2.
In minerals of metamorphic rocks, hardness values on the Mohs scale in marble are 3-4, and for quartzites - 7.
Abrasion is the ability of a stone to decrease in mass and volume as a result of abrasion. It is characterized by the loss of the mass of the stone (g), referred to the square centimeter of the abradable surface. Physicochemical properties characterize the influence of the physical state of the material on the course of certain chemical processes (for example, the degree of dispersion of crushed rock, which affects the rate of chemical reaction).
Chemical properties indicate the ability of the material to chemical transformations or its resistance to the effects of substances with which it comes into contact, for example, resistance to aggressive media. These properties are used in determining the longevity of the rock by testing in a solution of sodium sulphate.
Technological properties in their totality characterize the ability to be processed by various methods. The main technological properties of the stone include: machinability, production output, abrasivity, anisotropy.
Workability is the property of a stone to be processed by taking a given shape and texture as a result of the impact of a stone-working tool on it. This indicator is estimated by the relative parameter (the coefficient of machinability), which is the ratio of the productivity of the machine when processing the stone taken as the standard, to the productivity when processing this type of stone.
The output is the ability of the stone to ensure the safety of the product or workpiece during processing, estimated by the quantity of products obtained from the source material unit (square meter from a square meter of blanks or square meter from a cubic meter of blocks). This property is dependent on fracturing. Thus, from blocks of monolithic stone with insignificant fracturing, the yield of finished products (plates 20 mm thick) is 25-30 m2 / m3, and from a stone with a high specific density of cracks (over 2 m / m2) does not exceed 8-10 m2 / m3.
The abrasivity of the stone is characterized by the wear of the stone-working tool in the process of work. This property depends on the content in the stone of abrasive minerals (quartz, corundum, etc.).
Anisotropy (from the Greek words "anisos" - unequal and "tropos" - property) - the ability of a stone to split in some directions is easier than in others. Anisotropy is caused by the unequal physical properties of the rock in different directions, which in turn is caused by the peculiarities of the spatial orientation of the minerals in it. Most of this property is characteristic of granites. Anisotropy should be considered when impacting stone.
The building properties characterize the degree of suitability of the material for the operating conditions. In this sense, such properties considered as strength, water absorption, abrasion, etc., directly affecting the efficiency of the use of facing materials, can also be attributed to the group of building properties. In addition, this group includes such important operational properties as durability, frost resistance, fire resistance, etc.
The frost resistance of a stone is its ability to retain the basic physical and mechanical properties within the given boundaries under repeated action of variable temperatures in a water-saturated state. Quantitatively this property is characterized by the number of cycles of alternate freezing and thawing, which can withstand a water-saturated sample. It is allowed to reduce the compressive strength by no more than 20% and the mass loss is not more than 5%.
For the stone, which is used in external cladding, the following minimum frost resistance is established: granites and anlogic igneous rocks of 5Q cycles; marbles, limestones, dolomites, travertines, sandstones, tuffs, volcanic and porous basalts-25 cycles; limestone shells and tuffs felsitovyh - 15 cycles.
Frost resistance of a stone, as a rule, is due to its properties such as water absorption, porosity, fracturing. In turn, frost resistance in large part predetermines another important building property of stone - durability.
Durability of the stone - is determined by the preservation of its original construction and aesthetic properties depending on the service life.
On the durability of stones are divided into four groups: very durable (quartzite and fine-grained granite) with the onset of destruction in 650 years; long-lived (coarse-grained granites, gabbro, labradorites) - after 200 years; relatively durable (white marbles, dense limestones, dolomites) - in 100 years; short-lived (colored marbles, gypsum stones, porous limestones) - in 25 years.
The aesthetic properties of building materials are a complex of architectural and artistic qualities that characterize the level of their artistic expressiveness. The most general aesthetic property of the facing stone is its decorativeness, which serves as an important criterion in the selection and evaluation of the material. The level of decorative stone can be estimated expertly on a point scale. The determining factors for this are color, pattern and texture. Depending on this index, the facing stone is divided into four classes: highly decorative, decorative, low-decorative and non-decorative.
An important role in the design is played by the texture of the face of the facing slabs. She may be:
Polished - with a mirror shine, a clear reflection of objects, without any traces of processing the previous operation. Polishing is especially bright in the color and pattern of the stone. It is not recommended to use such boards on floors in wet rooms and for external staircases and platforms (without applying an anti-slip buchard strip) - when a water hits it, the polished surface becomes slippery.
Smooth matte (polished) - velvety matt surface without any traces of processing the previous operation and with full identification of the stone pattern.
Grinded - uniformly rough, with reliefs that are obtained only when grinding with a height of up to 0.5 mm. Grinding makes the surface evenly rough, the stone pattern is smoothed. On dark and patterned stones is completely unplayable, as almost completely conceals the color. It is recommended for floors where it is necessary to reduce sliding, and for external steps and platforms.
Sawed - unevenly rough - with roughness of relief up to 2 mm in height, coarser than polished surface, with revealed color and pattern of stone.
The heat-treated - rough surface with traces of peeling, looks slightly "melted", which allows more brightly than when grinding, to show the color and texture of the stone. It is recommended for external cladding (step, platform).
Spot (bucardirovannaya) - uniformly rough with irregularities of a relief with a height of up to 5 mm. The granite treated in this way is especially effective where it is undesirable or impossible to use polished stones, namely, with external works (blind area, landing area, external steps, etc.).
The face of plates made of natural stone can also be artificially aged (this has already been written above). Recommended for "textured", porous, soft marbles. The aged marble not only revet the surface, it is made of various curbs, rosettes, mosaic rotundas and carpets.
There are also plates with sandblasting, such scratches are hardly noticeable. The use of sandblasted panels for finishing the floor in wet areas significantly increases the comfort and safety of the coating.
According to the processing method, the marble surface can be: polished, ground and aged; and granite; polished, polished, polished, sawn, bucarded and burnt.
The decision on the method of processing a stone is taken, first of all, depending on its color and granularity.
It should be noted that until recently, the floor was most often decorated with stone tiles with a polished or polished surface. Recently, other types of processing have become more common. Buckled facing elements prevent the shoes from slipping and can be successfully used, as already mentioned above, for finishing external entrance groups, ramps, staircases, etc. Facing the floor with tiles with the specified relief in the areas with the greatest patency allows you to hide the defects that inevitably arise during the long operation of the coating. Such elements of the cladding in combination with polished tiles allow organizing the necessary functional accents.