Types of natural stone products

NATURAL STONE MATERIALS

Natural stone materials are the materials which are obtained both directly during output, and at the subsequent mechanical treatment of rocks.

Natural stone materials due to high mechanical strength, durability, decoratively are widely used since the ancient times as walling and facing materials in construction for paving, hydraulic and other buildings, for strengthening and cladding of slopes, embankments, etc. At present they are about 50% of all of the materials mass applied in the construction. Especially requirement in such construction materials as crushed stone, gravel and sand is large.

Natural stone materials are divided into two groups - regular and irregular shape. Sawn, sledged, rubbed, polished products belong to the first group, and mainly quarry, crushed and graded materials belong to the second one.

Basic ways of application in construction of different products from natural stone are shown in Table 5.1.

Table 5.1

Application different kinds of stone in construction

Raw materials for the production of natural stone materials are rocks - mineral aggregations of certain composition and structure, which are the products of geological processes in the earth's crust.

The problem of the careful use of natural raw material, utilization of by-products of its processing such as screenings, stone powder, oversize and others is gained the greater value.

Rocks

Types, composition and structure of rocks. About thousand types of rocks are known for today. By formation conditions (by genesis) they are divided into three classes:

- Magmatic, or igneous rocks, formed as a result of magma cooling in the bowels of the earth or on its surface, e.g. silicate melts;

- Sedimentary rocks, formed on the Earth surface are as a result of accumulation and transformation of destruction products of rocks formed before, remains of vegetable and animal organisms and products of their vital activity;

- Metamorphic rocks, formed on high deepness as a result of sedimentary and igneous rocks change under the action of high temperature and large pressure, caused by the influence of gaseous substances, escaped from magma, and hot solutions.

Slowly cooled hypogene (intrusive) rocks (granites, syenites, diorites, gabbro, etc.) and formed in overhead horizons of earth’s crust, (effusive) rocks (basalts, andesites, porphyrites, pumice stones, etc.) are outpoured rocks.

Chemical composition of igneous rocks can be expressed by content of oxides of silicon, aluminum, iron, magnesium, calcium, sodium, potassium, hydrogen. The major components of igneous rocks, called minerals, are quartz and silicates. It is calculated, that average minerals content in igneous rocks is following %: feldspars - 60, quartz - 12, amphiboles and pyroxenes - 17, mica - 4, other silicates - 6.

Sedimentary rocks by the way of their formation are divided into three groups:

Fragmental - the sediments mechanical by origin (boulders, pebble, sand, clay);

Chemical – the sediments chemical by origin (sulfates, carbonates, halogen compound);

Organogenic - the sediments biochemical by origin (carbonate, siliceous, carbonic rocks, etc.).

Fragmental rocks are appeared as a result of destruction (weathering) of igneous rocks influenced by temperature, water, glaciers and other external agents, chemical ones are appeared at sedimentation mineral substances from water solutions and organogenic ones are the products of sedimentation of weeds wastes and animal organisms at the bottoms of reservoirs.

Chemical and mineralogical composition of sedimentary rocks is more diverse, than igneous rocks. Along with minerals of initial mother rocks they can include also a series of other ones, formed in consequence of sedimentation (carbonates, mineral salts, etc.).

Among metamorphic rocks two groups are selected: modified changed igneous (gneiss) and modified sedimentary (for example: quartzite, clay shale). In the process of transformation, or metamorphism of rocks chemical and mineralogical composition undergoes certain changes depending on the actual values of temperature and pressure. Thus, at temperature up to 500°С and at pressure 40-90 MPa the various stratified silicates containing hydroxyl groups are appeared. If a temperature is higher, and pressure is lower, the crystals of amphibole, different micas and other similar minerals are appeared.

Rocks differ by the mode of occurrence, structural and textural features (Fig. 5.1-5.3).

The peculiarities of their internal structure, predefined by the crystallinity degree, sizes and form of crystals are meant by a structure of rock, and the complex of signs determined by relative location of rock components in the space they occupy is meant by a texture.

By crystalllinity degree there are differed шт holocrystalline, semi crystalline and glassy structures. Holocrystalline structures are representative for the hypogene rocks, formed as a result of slow magma cooling, and also for the most of the metamorphic rocks. Semi crystalline and glassy structures are representative for outpours rocks.

Depending on the grains sizes the structures are divided onto coarse-grained (sizes of grains over 5 mm), medium-grained (2-5 mm) and fine-grained ones (less than 2 mm). If minerals grains which compose a rock are close by sizes, the structure is evenly grained, in opposite case — unevenly grained. The typical varieties of unevenly grained structures are porphyritic structures, which are characterized by a presence of glassy or fine-grained great bulk in the rock, where large crystals - inclusions are dissipated.

Basic types of textures are uniform, or massive, ordinary texture in igneous rocks, nonuniform (taxite) and gneissoid (foliated structure).

Granites are the most important in the natural stone materials manufacturing among the igneous rocks, carbonate rocks among sedimentary ones (limestones and dolomite), metamorphic ones - gneisses, quartzites and marble.

Granites are acidic (SiO₂>65%) hypogene rocks which are easy to distinguish (Fig.5.1), typical minerals: quartz (20-40%), feldspar (40-70%) and mica - muscovite or biotite (5-20%). Among other minerals amphiboles and pyroxenes occur. Grainy-crystalline structure is typical for granite. The color of granite is determined the colors of feldspars entering into composition, and more often grey, bluish-grey, dark red.

Syenites, diorites, gabbro are close to the granites. Unlike granites they practically do not contain quartz and consist mainly of feldspars and dark colored minerals - hornblende, augite, etc. These rocks are mostly grey or dark-green in colour.

The rocks of granite group belong to the strongest and most resistant rocks, they are well polished. They are applied in construction for cladding of constructions and structures, in particular structures subjected to impact and wearing loads (floors, starlings, etc.). The rocks of granite group are processed also on crushed stone, used as concrete aggregate.

Basalts are the most common outpoured rocks. Feldspar and large amount of dark-colored minerals are included in their composition. The structure of basalts is glassy or cryptocrystalline. High hardness and brittleness complicates their processing. The color of basalts is darkly grey or black. Basalts as well as granites are widely used as a building stone. They are applied in the industry of stone casting, as electrical insulation and acid-resistant materials. In those industries, that basalt, other outpoured rock diabase is applied.

Andesites and porphyrites are the widespread outpoured igneous rocks. Basalts and diabases belong to the high basic rocks (40-50% SiО₂); andesites and porphyrites to the low basic rocks (52-65% SiО₂). Porphyrites and andesites are applied for pavestone making, acid-proof elements, etc.

Carbonate rocks - are mainly limestones and dolomite. Limestones are formed mainly of calcite CaCO₃, dolomite CaMg(CO₃)₂, clay and other minerals are as admixtures in them. Structure and properties of limestones are predefined by terms of their formation. As a result of CaCO₃ precipitation calcareous tuff is formed from the sources of carbonate waters; it is a soft easily-sawn porous rock. A type of calcareous tuff is a travertine which is the result of CaCO₃ precipitation from thermal springs. Travertine has dense, fine-grained structure and is applied as cladding stone.

Some types of limestones are organogenic by origin. They are formed as a result of compression and cementation of skeletal residuals of elementary animals (shells, shellfishes, etc.). Shelly limestone and chalk are the limestones organogenic by origin.

Dense limestones are applied for obtaining cladding details, crushed stone for heavy-weight concretes, and porous ones for wall stone and blocks. Limestones widely are applied as raw materials for obtaining lime, Portland cement and other artificial construction materials.

Along with limestones there are also used conglomerate rocks - sandstones which consist of quartz sand grains, consolidated by clayey, siliceous, calcareous and other substances. Siliceous and calcareous sandstones are the most strongest and resistant.

Marbles, which are applied mostly as cladding materials, are formed as a result of limestones and dolomites recrystallization.

Typical metamorphic rocks - gneisses by mineral composition correspond to igneous rocks of granite type. For them, as well as for other metamorphic rocks, crystalline-grainy structure and foliated (gneissic) texture are typical. Gneisses are applied mainly as crushed stone for highways and for ballasting of railway bed.

Quartzites are formed as a result of metamorphization of quartz sandstones. Depending on the admixtures they can be white, yellowish and reddish colors. Quartzites are used as cladding, acid-proof material, for refractory materials production.

Rocks properties. Application area of rocks is determined by their physical-mechanical properties, predefined by peculiarities of formation, chemical and mineralogical composition, structure and texture. The values of basic properties of a series of construction rocks are shown in Table 5.2.

Table 5.2

Basic properties of rocks

Compressive strength is the most important property of natural stone. This parameter is highest for rocks which have a homogeneous crystalline structure. If glass prevails in rocks, their strength decreases, they are more affected by temperature changes. Fine-grained rocks, composed of grains of the irregular, ragged form, have higher strength. Porosity makes significant influence on compressive strength of rocks as it diminishes contact area between. If, for instance, porosity of limestones diminishes from 40 to 2%, their compressive strength grows from 5 to 180 MPa. Flexural strength of rocks is in 10-20 times lower, than compressive strength.

In rocks, especially sedimentary rocks, weak forms can be found, contained as separate layers. Homogeneity of rock properties is the most important indicator of their quality.

While selecting the type of the stone its average density is in great importance; for the rocks of certain mineral composition and structure it can describe their strength and durability. As far as chemical basicity of rocks increases (ratio of basic oxides content to acidic ones) the density of rocks grows.

Frost resistance of the most rocks can be defined approximately by water absorption. Water absorption of dense igneous rocks not subjected to the weathering does not exceed 0.7%, water absorption of sedimentary rocks is 10% and more.

Weathering resistance of minerals containing in the rock has substantial value for durability of natural stone. Quartz is resistant to weathering; orthoclase and microcline are low-resistant; plagioclases, amphiboles, olivine, calcite, dolomite, gypsum and others are nonresistant. Chemically active minerals like sulfides, sulfates and others can negatively influence on the stone preservation. For example, sulfides oxidization on the polished surface of cladding stone causes foxing and results in destruction, oxidization of sulfides in crushed stone - volume increasing and reducing in concrete strength.

In the case of application of natural stone as walling material thermal and sound conductivity, air permeability are very important properties along to porosity, frost-resistance, weathering resistance. All of these properties are correlated and predefined mainly by porosity of rock. Effective wall materials are elements from such high-porous rocks, as tuff, shell limestone.

For cladding natural stone their decoratively and processability are of important value.

The color of the rock is determined by the color of minerals, that it is consisted of. Igneous rocks have the most stable coloring, sedimentary and metamorphic rocks are less proof.

Workability of rocks (abilities to smoothing, polishing) reduces as far as their strength growths, at a coarse-crystalline structure, also at the presence of clots.

Soils as natural materials. Rocks which are the objects of structural engineering activity are called soils. Soils are natural basis, environment and construction material for various constructions. Soils are divided onto:

- Rocky - consolidated rocks, which are practically uncompressed and have compressive strength in the water-saturated state more than 5 MPa (granites, basalts, some types of sandstones, etc.);

- Semirocky or loose rockswith compressive strength in dry or water saturated state less than 5 MPa (gypsum conglomerates, etc.);

- Earth – coarse fragmental (uncemented rocks which contain more than 50% of particles more than 2 mm by mass ), sandy (friable in the dry state rocks which contain less than 50% of particles larger than 2 mm by mass) and clayey (for which certain plasticity is typical).

Soils are divided also by softening coefficient, weathering degree, by solubility in water. Humidity has large influence on strength properties and especially on the soils cohesion. Dry clayey soils at considerable moistening become fluid. At the soil compression the most its density at minimal work is reached at ring optimal humidity.

In construction process of earthworks soil consolidates due to approaching of particles between each other under load action. Compressibility of soils is characterized by reduction of porosity coefficient at increasing in compressive stress. Determination of dependence between the porosity coefficient and compressive stresses is defined by compression equipment.

Strength of soils is characterized their ability to resist to sliding stress. Cohesion c (MPa) and angle of internal friction j (degree), applied for the calculations of load-carrying capacity and resistance of soils are rated to a number of parameters of soil strength. Density and humidity of soil, loading rate influence significantly on the values с and j .

Important parameter of soil at its irrigation estimation is filterability. Depending on the type of soil, volume of its pores and structure of pore space soils have different filtration coefficient (Table 5.3).

Table 5.3

Filtration characteristics of soils

For earthworks construction all the types of soils are accepted, with the exception of pulverescent sands, soils which contain the water soluble inclusions, and also soils which contain the decayed organic substances, etc. Clays are used for construction of waterproof elements of buildings, where they are at permanent humidity. Hydraulic earth-fill dams are built of gravel sandy, loamy sand soils. At the construction of earth-to-rockfill and rock-fill dams rocks are used with softening coefficient equal 0.9 (for igneous and metamorphic rocks) and 0.8 (for sedimentary). Stones should have sufficient strength and frost resistance.

Types of natural stone products

Natural stone materials are produced by industry of construction materials. The basic types of products are crushed stone, gravel, sand, rubble stone, cladding elements, wall sawn stone, paving and other elements of the special assignment (Fig.5.4).

Rubble stoneis a construction material which consists of pieces of rock irregular in shape 70-1000 mm in size. It is used for laying of foundations, underground parts of buildings, walls of nondomestic, subsidiary and production buildings, for strengthening of earthen slopes, in road construction, and also as an aggregate for rubble concrete. In hydrotechnical construction fill dams are also erected of rubble stones. Stone composition by coarseness is assigned from getting minimum porosity taking into account the peculiarities of dams.

Strength of rubble stone is estimated by compressive strength of initial rock in the water saturated state. Ultimate strength of rubble stone is in the range of 10-140 MPa. Stone made of metamorphic rocks should have strength not less, than 40 MPa, but the stone made of igneous rocks - not less, than 60 MPa. Frost resistance of rubble stone is approximately equal 15-300 cycles of freezing and thawing. There are accepted not more than 15% fragments with dimensions, different from limit ones in rubble stone batch. Clay content in stone should not exceed 2% by mass, softening coefficient should be not less, than 0.7.

Facing and walling stone. Facing slabs and stones are produced by sawing of natural stone blocks. In the case of application of off-quality blocks there are obtained sledged slabs and stones.

For obtaining facings elements rocks of granite group and metamorphic rocks like marble and colored variations of quartzites are commonly used. Sedimentary rocks - limestones, sandstones, dolomites, travertines and gypsums are applied mainly for internal facing. Quartzites and granites have the highest durability; marbles have considerably lower durability, and can quickly to collapse at outdoor conditions.

Rocks which are used for the application of facings elements should have compressive strength not less than 5 MPa, frost resistance - not less than 15 cycles. Depending on blocks dimensions they are divided into some groups. There is accepted in a block no more than one crack, which is visible at two adjacent surfaces, less than one third of measuring long. Cracks on slabs less than one third of width length are allowed in that case, when slabs are made from the colored marble. Facings elements have abrasive (polished, rubbed, honed) or impact (tooled, boasted, pointed) finishes. The most common are sawn slabs 6-80 mm thick, 200-400 mm width.

Decorative slabs with mosaic and ornamented surfaces are produced utilizing separate pieces of natural stone, crushed stone and sand, and also inorganic or synthetic binders. Slabs are marked by grades, type, kind of face and overall dimensions are specified in which.

Due to high durability of natural stone facing their maintenance costs are considerably less than, at finishing of buildings by paints, coloured mortars and concretes.

As walling materials sawn work stones and large-size blocks are used. For walls light-weight porous rocks are used which have average density 900-2100 kg/m³, compressive strength 0.4-50 MPa and frost-resistance not less than 15 cycles. Minimal value of softening coefficient of walling materials and blocks is 0.6, water absorption for tuffs is 50%, for limestones and other rocks it is 30%.

Walling stone and blocks often have following basic dimensions, mm:

Stones – length 390, 490, width 190, 240, height 188, 288;

Blocks - length 400, 500, width 820, 1000, height 2360, 2520, 2860, 3020.

By assignment wall stones are divided into facial and ordinary ones. Ordinary stones are used for walls erection with subsequent plastering.

Ultimate compressive strength of wall stones is 0.4-40 MPa, blocks - 2.5-40 MPa.

At symbolic notation of walling stone they specify type of stone by dimensions, its kind by assignment and compressive strength grade.

Walling elements made of natural stone have beautiful surface finish (rose, blue, yellow tuffs; white, yellow light grey limestones), they are processed easily.

From separate blocks, sawn from light-weight rocks, it is possible to make on mortar-based large composite blocks and panels the application of which enables to promote productivity of building.

It is effective to utilize composite blocks "floor" in high, which are made of 6-8 ordinary blocks, gaps between them are filled with cement mortar. Large panels, glued from separate elements by polymers are perspective products made of natural stone.

Border stone, pavestone, sledged stone and cobblestone are used for road construction as a workstone. These elements are served for detaching the traffic ways and highways from pedestrian ways (sidewalks), for paving roadways, tram-car ways, strengthening the slopes of earthen coatings and subbases. Raw materials for them are high-strength rocks with strength not less than 60 MPa, frost resistance not less than 25 cycles, with softening coefficient 0.6-0.9, water absorption 1-4%, impact resistance 15 kPа.

Piece natural stones are transported on pallets or separately, by purpose, by types and grades.

Stone materials and elements are widely used in water industry construction. At construction stone irregular in shape: rubble stone, cobblestone, sometimes boulders, gravel and crushed stone are utilized for laying of foundations of hydraulic structures, erecting the earth-and-rock-fill and rock-fill dams, preparation of rubble concrete for the erecting of interior zone of concrete and reinforced-concrete dams, foundations of the hydro systems of the pumping stations and hydroplanes, consolidation of hay-crops of canals and ponds, arranging of stoning round concrete hydraulic structures to protect concrete from corrosion. The stone of regular shape from igneous dense rocks and sandstones are used for dams stonework by the method of dry rubble (without mortar) by regular rows with bonding; arranging of finishing stonework of underwater and above-water parts of structures (embankments, pumping stations, hydroplanes buildings); masonry work of footings of aqueducts, bridges and retaining wall; architectural elements production (columns, semi-columns, basement parts of buildings). A cobblestone made of dense rocks is used for arrangement of fortifications from wave and speed influence of water, hay-crops of earthen dams, canals, water storages, at roadway pavings.

Hewn and sawn slabs made of dense water resistant rocks are used during the external cladding of underwater part of hydro systems, embankments, sometimes facing of hay-crops of the hydrosystems, floors arranging in buildings of hydroplanes and pumping stations. As facing material inside the pumping stations and hydroplanes buildings different types of marble, conglomerates and breccia are used. To improve architectural expressiveness of hydraulic structures there are applied different architectural compositions, produced of water resistant rocks (granite, gabbro, sandstone).

Especially wide application in water construction has clastic rocks such as sand, crushed stone and gravel, gravel-pebble and gravel-sand mixtures. These materials are used for concrete mixtures production for hydraulic and normal concrete; arranging the underlayers under monolithic and precast reinforced-concrete canal linings, roads, constructions; preparation of the drainage filings ups; at consolidation of hay-crops of canals and hydro systems, water storages.

Taking into account that stone materials used in hydraulic construction practically have permanent or periodical contact with water, which often is aggressive one, they have to meet raised requirements not only at density, strength but also in frost-resistance, resistance to aggressive environment.

Date: 2015-12-18; view: 1817