2

BUILDING STONES

2.1 INTRODUCTION

The earth’s crust is composed of rocks. Rock is a mineral mass of a more or less uniform composition. It may consist of a single mineral (monomineralic) or of several minerals (polymineralic). A mineral is a natural body, homogeneous in chemical composition and physical properties. Further minerals are the products of physical and chemical processes occurring in the earth’s crust.

Monomineralic rocks are quartz sand, pure gypsum and magnesite, and the polymineralic ones are granite, basalt and porphyries.

Natural rock materials are widely used for building purposes owing to their universal occurrence and physical and mechanical properties. They are used as mined materials, e.g., gravel, sand, or mechanically processed materials, e.g., crushed stone, sawn, dressed and polished stones, and for various architectural and decorative purposes.

Rocks are the main source of material for the manufacture of mineral binding materials, such as gypsum, lime, cement and of artificial rock materials, e.g., brick, glass, items for concrete and mortar.

2.2 CLASSIFICATION OF ROCKS

The origin and conditions of rock formation predetermine their chemical and mineralogical composition, crystalline structure and texture. These characteristics, underlying the strength and decorative properties of rocks, are the starting point for the engineering and economic evaluation of rocks for various structures of buildings and installations.

The three major classifications are based on the following aspects:

1. Geological or genetic classification
2. Physical classification and
3. Chemical classification

2.2.1 Geological or Genetic Classification

According to the geological classification, rocks are subdivided into three large groups, viz., igneous rocks, sedimentary rocks and metamorphic rocks.

1. Igneous rocks: Cooling and hardening of molten magma result in the formation of igneous rocks. Depending on the rate of cooling the sizes of crystals are formed. Granites, syenites, diorites and gabbros have large crystals, while basalts, rhyolites and andesites have small crystals. Igneous rocks are generally very hard.
2. Sedimentary rocks: Transportation agents like wind, water and ice may move the loose weathered rock materials and deposit them in the form of layers called sediments. Such sediments when subjected to heavy pressure undergo compaction and cementation, resulting in sedimentary rocks. Limestone, dolomite, shale, sandstone, etc., are sedimentary rocks.
3. Metamorphic rocks: Sedimentary rocks and to some extent igneous rocks when subjected to changes brought about by the combination of heat, pressure and plastic flow (called metamorphism) undergo changes in the structure, texture and mineral composition, and this results in the formation of metamorphic rocks. Gneiss, schist, slate, marble, etc., are metamorphic rocks.

2.2.2 Physical Classification

The basis for such a classification is the physical properties of rocks, the manner and arrangement of different particles and mass forming a stone. They are classified as follows:

1. Stratified rocks
2. Unstratified rocks
3. Foliated rocks

(i) Stratified Rocks

Stratified structure is formed due to the splitting of a series of parallel layers of sedimentary rocks. They exhibit distinct layers which can be separated. The plane of separation is called a cleavage plane. Limestone, slate and sandstone are examples of stratified rocks.

(ii) Unstratified Rocks

They are of granular or crystalline structure and become solid on cooling. They do not show any sign of strata, e.g., igneous rocks like granite, basalt, etc.

(iii) Foliated Rocks

These rocks show definite parallel arrangement of minerals showing a tendency to split in a specific direction, e.g., metamorphic rocks like gneiss, schist, etc.

2.2.3 Chemical Classification

The presence of chemical constituents in the rocks is the basis for their type of classification. They are as follows:

1. Siliceous rocks
2. Argillaceous rocks
3. Calcareous rocks

(i) Siliceous Rocks

In these rocks silica is the main constituent. The presence of silica in the free state is called sand, and in the combined state is a silicate. Rocks containing silica in the free state are harder, and those found in the combined form are likely to be disintegrated. Examples of silicate rocks are sandstone, quartzite, etc.

(ii) Argillaceous Rocks

In these rocks, clay or alumina is the main constituent. Examples of argillaceous rocks are slate, laterite, etc.

(iii) Calcareous Rocks

Calcium carbonate or lime is the main constituent in these rocks. They are readily acted upon by dilute hydrochloric acid. Examples are limestone, marble, etc.

2.3 PROPERTIES OF GOOD BUILDING STONES

Different civil engineering constructions use stone. It is necessary to find their suitability under different conditions. The following properties need to be examined before their use:

2.3.1 Appearance and Colour

Stones must look good in appearance and be of uniform colour. Such a quality is essential for stones to be used for decoration work. Light-coloured stones are preferred as they resist weathering action in a better way. Stones with iron oxide should not be used as the presence of iron oxide disfigures the stones and brings about disintegration.

2.3.2 Strength

Stones are used as a compression member and should have sufficient compressive strength. In general, all stones possess a reasonable degree of strength. The crushing strength of stone should be greater than 100 N/mm². Igneous rocks have a strength of around 100 N/mm² and some of the metamorphic rocks also possess these strengths. But sedimentary rocks have a lower strength.

2.3.3 Weight

In general, good building stones should have a high weight to resist higher compressive forces. Good building stones must have a specific gravity greater than 2.70. A heavy stone possesses more compactness and less porosity.

2.3.4 Hardness and Toughness

Stones must be hard and tough so that they can resist wear and tear. Hardness is assessed by scratching and toughness by hammering. A good building stone should have a wearing resistance less than 3%, and if it is more than 3% it is not satisfactory. Stones used for road work should be hard to resist wear and tear.

2.3.5 Porosity and Absorption

All stones possess porosity. Stones that have a porosity over a certain percentage are unsuitable for building purposes. The presence of a higher percentage of pores may absorb rain, which may deteriorate the stone. A good stone should not absorb water more than 0.6% by weight. It must be capable of withstanding effects of atmosphere. If stones in a cold climate absorb water, they may freeze and even split.

2.3.6 Compactness

A good stone must have a compact, fine, crystalline structure and must be strong. A compact stone is capable of withstanding the effects of external agencies effectively.

2.3.7 Fineness of Grain

Stones that are fine grained are suitable for moulding purposes. Such stones are easily carved and dressed. Non-crystalline structured stones are likely to disintegrate under the action of natural agencies.

2.3.8 Resistance to Fire

Stones must be fire resistant, i.e., they must retain their shape when subjected to fire. Limestone resists fire up to about 800°C. Sandstone can resist fire in a better way. Although argillaceous stones are poor in strength, they are highly fire resistant.

2.3.9 Durability

Stones must be durable. Basically, stones that have their natural bed perpendicular to the direction of pressure are durable. Durable stones are those which are compact, homogeneous, acid resistant and have negligible water absorption.

2.3.10 Dressing

Dressing is the act of shaping a stone for a decorative purpose or for other purposes. For this, the stone should possess uniform texture and softness so that they may be easily dressed. Hard stones can not be dressed.

2.4 TYPES OF BUILDING STONES

Stones of geological origins have been identified and classified as building stones which are used for different purposes. They are discussed subsequently.

2.4.1 Granite

It is a deep-seated igneous rock, hard, durable and available in different colours. It has high crushing strength and is capable of sustaining high weathering.

2.4.2 Basalt and Trap

Basalt and trap are also of igneous origin. These are effective solid rocks which have been formed on the earth’s surface in the absence of pressure by rapid cooling of the magma which also carries crystals of various minerals. These are hard, tough and durable and are available in different colours.

2.4.3 Limestone and Chalk

These are sedimentary rocks which have been formed of remnants of seaweeds and living organisms consolidated and cemented together. They are easy to work with and contain a high percentage of calcium carbonate.

2.4.4 Sandstone

This is another form of sedimentary rock formed by the action of mechanical sediments. It shows a sandy structure which is low in strength and easy to work with and dress. This is available in different colours.

2.4.5 Laterite

This is a metamorphic rock and is a sandy clayey stone. It is porous and soft. It can be cut easily into blocks and contains a high percentage of iron oxide.

2.4.6 Gneiss

It is a metamorphic rock which can be easily split into thin slabs and is easy to work on.

2.4.7 Marble

It is a metamorphic rock which can be easily cut with a saw and can be carved.

2.4.8 Slate

It is also a metamorphic rock which is black in colour and can be split easily.

2.4.9 Gravel

It is available in river beds in the form of pebbles and is of different shapes.

2.4.10 Quartzite

It is a metamorphic rock which is hard, brittle and crystalline. It is difficult to work with and is very durable.

2.5 USES OF COMMON BUILDING STONES

Common building stones are used for the following purposes:

1. For foundations, walls, columns, arches, lintels, roofs, floors, etc.
2. For facing work of masonry
3. For concrete and road construction as coarse aggregate
4. For railways as ballast
5. For bridges as floors, piers, abutments, retaining walls, etc.
6. For lighthouses and dams

2.6 USEFUL BUILDING STONES OF INDIA

2.6.1 Granite

Granite is used for stone columns, road metal, ballast for railways, bridge components, etc. It is found in Karnataka, Maharashtra, Rajasthan, Uttar Pradesh, Madhya Pradesh, Punjab, Assam, Tamil Nadu and Kerala.

2.6.2 Sandstone

Sandstone is used for building and ornamental purposes and also as road metal. It is available in Uttar Pradesh, Madhya Pradesh, Rajasthan, Himachal Pradesh and Tamil Nadu.

2.6.3 Limestone

Limestone is used for flooring, roofing, pavements and in general building construction. Also used for manufacturing cement and lime, it is found in Maharashtra, Andhra Pradesh, Punjab, Himachal Pradesh and Tamil Nadu.

2.6.4 Gneiss

Gneiss is used for flooring and pavement and not for major purposes because of its weakness. It is found in Andhra Pradesh, Karnataka, Gujarat and Tamil Nadu.

2.6.5 Marble

Marble is used for ornamental purposes, flooring, facing works, etc. It is found in Rajasthan, Gujarat and Andhra Pradesh.

2.7 QUARRYING OF BUILDING STONES

Quarrying is the process by which stones are obtained from rock beds. Quarry is the place from where the stone is obtained. Quarrying differs from mining in which various operations are carried out for exploring minerals such as coal, quartzite, etc. from a mine under the ground.

2.7.1 Quarry Location

Before starting to quarry, the quarry location has to be decided based on the following factors:

1. On the Earth’s surface, a large quantity of stones of good quality should be available.
2. The location should be as close to highways and railways as possible.
3. Adequate space should be available for the installation of machinery, storing of stones and other materials.
4. If the blasting technique is to be used, the location should be away from any permanent structure and inhabitants.
5. Sufficient provision should be made for the drainage of rain water.

2.7.2 Methods of Quarrying

The following methods of quarrying are listed based on the outcrop of the rock and the purpose for which stones are intended to be used.

1. Digging

In soft rocks, stones are obtained merely by digging with the help of hand tools, viz., pick-axes, hammers, chisels, etc. Only those stones that occur in the form of detached nodules buried in the Earth can be easily quarried by this method.

2. Heating

This method is adopted by burning certain kinds of fuel (usually wood is used) and the exposed surface of the portion of the rock to be separated. On burning for several hours continuously, due to unequal expansion of the rock, the rock gets separated from the cold mass with a dull noise. The detached portion is then removed and made to the required sizes by using quarrying tools. This method is employed for obtaining road metals, ballast for railways and aggregates for concrete.

3. Wedging

Soft stratified rocks can be removed by wedging as these rocks are in the form of layers and are easy to split. Soft rocks are removed with the help of pick axes and crow bars. Limestone, marble, slate and laterite are removed by this simple method.

In hard rocks, holes are made and grooves are cut at shorter intervals. Blunt wedges are inserted into the grooves and are forced to get separated. Alternatively, conical pairs of steel are driven into the holes with a hammer and further force to get separated. In the case of very hard stones, the holes are originated by a pneumatic drill.

4. Blasting

This technique is employed for quarrying hard and compact rocks. Blasting is done in stages as discussed below.

Holes may be made with a steel bar with knife-edged ends called jumpers. In case large quantities of stones are required, holes may be drilled by a drilling machine. In order to facilitate the operation, water is used. The slurry produced as a result of drilling is removed by a scraper or a spoon or by a compressed air blast.

The drilled holes are charged with an explosive of suitable capacity. It is necessary for the holes to be made a day before charging with explosive.

Tamping of the explosives is done before firing in order to prevent the blasting within the hole itself. Tamping consists of filling the hole with stiff sandy clay and tamping with a brass rod. A fuse is inserted to fire the explosive. While tamping, a small quantity of gun powder is sprinkled to link the explosive to the bottom of the fuse.

The fuse is fired carefully. During the explosion, masses of stones around the hole are removed. A properly packed explosive shall produce a dull sound followed by displacing of the mass of rock around it.

2.7.3 Precautions in Handling Explosives

The explosives generally used are blasting-powder, dynamite, gun-cotton, blasting-gelatine, cordite and gelignite. From the time of getting an explosive for use, it has to be properly stored, cautiously handled and effectively utilised. The following precautious are to be meticulously adhered to:

1. Storing

Explosives are stored in a specially built buildings called magazines. A magazine should adhere to the following norms:

1. It should be 100% leak proof and must be provided with an efficient lightening conductor.
2. It should be located away from petrol bunks, diesel storages, public places, residential and industrial areas.
3. Electrical wiring of magazines should be concealed.
4. It should be located at least 500 m away from any working establishment.
5. Smoking/firing should be strictly prohibited within a radius of 50 m from the magazine.
6. The magazine should be properly protected by a high barbed wire fencing.
7. Outsiders should not be permitted to enter the magazines without prior permission.

2. Handling

1. Explosive packages must be handled carefully.
2. Detonators should be kept entirely away from other explosives.
3. In case of power failure no open fire should be used, but only torches should be used for lightings.
4. During the time of charging and tamping, extraordinary precaution should be taken to prevent any fire hazard.
5. It is necessary to give adequate time for the person to retire to a safe place before the explosions.

2.8 DRESSING OF STONES

Generally the stones obtained after quarrying have a rough surface and are irregular in shape. The process of bringing the stones to a regular shape and required finish is known as dressing. The purposes of dressing are as follows:

1. To set the stones in a regular shape and appearance.
2. To prepare the stones for a suitable site for easy handling and transport.
3. To make hammer-dressed surface, tooled surface, polished surface, rubbed surface or cut-stone surface to suit a particular stone masonry.
4. To secure proper bedding in stone masonry.

Two types of dressing are in use, viz., quarry dressing and site dressing. Quarry dressing is one where the stones are dressed at the quarry and sent to the work site. Site dressing comprises of dressing the stones at the site to the specific size and type. Proper choice depends on the quality of labour at the quarry, distance of the quarry and work site, etc.

2.9 DURABILITY OF STONES

Durability of stones depends on the environment at which they are constructed. For proper durability assurance, it is necessary to know the agencies which deteriorate stones and to take adequate steps to preserve the quality of stone during its lifespan.

2.9.1 Deteriorating Agencies of Stones

Various agencies which are responsible for the deterioration of stones are discussed below.

1. Rain

Rain is one among the main causes for wetness on stones. This wetness is dried by the sun. The process of wetting and drying go a long way in deteriorating the stone. Gases and acids contained in rain water may have damaging effect on stones.

2. Climate

Climate is another factor which causes deterioration. In hot climates there are frequent changes in temperature which result in deterioration. Similarly, stones exposed to cold climate causes freezing of water in the pores resulting in expansion, which causes splitting of the stone. Hence, porous stones should be avoided in cold regions.

3. Wind

Wind laden with grit and dust strikes the stones and causes wear of the stones. Also the impurities in the atmosphere along with moisture penetrate into the pores due to the wind and causes dampness resulting in deterioration.

4. Vegetation Growth

Vegetation growth along the cleavages of joints of stones secretes certain acids by the roots, and thereby cause deterioration. The presence of moisture in roots causes further decay.

5. Chemicals

Chemicals of different kinds move and react due to the usage of different stones such as limestone and sandstone. Such movements of chemicals from one to the other cause deterioration.

6. Living Organisms

Living organisms sometimes cause holes to form in the joints of stones and cause instability to the structure. Further, these holes provide room for the accumulation of moisture and thereby deteriorate the stones.

2.9.2 Preservation of Stones

Preservation of stones is intended to protect the structure against the action of weathering agents and also to protect the good appearance of the face work. The durability of stones increases remarkably if the stones are properly preserved. Preservation is effected in the following ways:

1. Voids existing in the pores are filled properly.
2. Preservation of stones by coating with suitable oils like coal tar, linseed oil, etc.
3. Entry of moisture into the surface of the stones is to be avoided.
4. Stones with carbonate of lime should be discouraged from use in industrial towns.
5. Brick masonry with a combination of limestone and sandstone or magnesium limestone and granular limestone should not be laid close to each other.
6. Building materials which are inactive with stones should be used.
7. Growth of plants on the joints of stones should be prevented.

2.10 SELECTION OF STONES FOR VARIOUS WORKS

Stones have to be selected for a specific work based on the strength and other properties including durability. Stones needed for building exposed to different environments and stones needed for other civil engineering works are discussed below.

2.10.1 General Building Works

Stones are used for foundations, walls and superstructure. Stones with a high mechanical strength and pleasant colours are widely used which are also highly durable. Sandstone is in general used for the above purpose.

2.10.2 Buildings Exposed to High Wind

Such buildings are those constructed near the sea or locations where more wind prevails. Here, apart from the general requirements the stones will be subjected to high weathering action. Hence, stones with a high crushing strength and the presence of silica in addition to hardness should be preferred. Granite and basalt may be used.

2.10.3 Buildings in Industrial Areas

Here the buildings may be subjected to polluted atmosphere which may contain harmful gases, acids and moisture. These elements adversely affect the stones leading to deterioration. Stones that could sustain the effect of acidity and smoke on them are preferred. Granite and compact sandstone may be used.

2.10.4 Buildings Exposed to Heat and Fire

Buildings constructed in regions where hot weather conditions are prevalent throughout the year and chemical factories which may have hot air which are susceptible for frequent fires. For such cases, the stones should have high fire-resisting properties. In general, stones are free from calcium carbonate can resist fire.

2.10.5 Heavy Engineering Works

Heavy engineering works include docks, harbours, bridges, etc. These are constructed in general in an open area and on the seashore. Structures constructed for the above purposes should be able to resist thrust, salt environment, must be strong and highly durable. Granite and quartzite are generally preferred for such purposes, and gneiss is also used for the inside purposes of such structures.

2.10.6 Road Metals and Railway Ballasts

Road metals and railway ballasts are subjected to high compression and abrasion. Further, railway ballasts are exposed to atmosphere throughout their lifespan. Stones selected for such purposes should be hard, tough and highly abrasive resistant. Generally, igneous rocks are preferred for this purpose, viz., granite and basalt.

2.10.7 Facing and Architectural Items

Facing slabs and stones, parts of stairs and landings, parapets and guard rails are made of slabs sawn or split from natural stone and worked on by mechanical means. Sandstone, slate and marble are used for these purposes.

2.11 TESTS ON BUILDING STONES

Building stones must be tested to assess their properties to use for various purposes. Some tests are simple which can be conducted in the field, and some can be tested only in a laboratory. Accordingly, they may be grouped as field tests and laboratory tests (IS: 1121, 1974 and IS: 1124, 1998).

2.11.1 Field Tests

Simple field tests are the absorption test, Smith’s test, the toughness test, the hardness test, the acid test and the crystallization test.

1. The Absorption Test

This is usually called the water absorption test. This is a simple test conducted on all stones. It consists of keeping a cubical specimen of the stone of about 50 g weight immersed in water for 24 hours and finding the volume of the absorbed water. This is represented as a percentage of absorption by weight. This percentage should not be more than 0.6%. This test is also called the electrical resistance test.

2. Smith’s Test

This test is conducted to find the presence of earthly matter or the deterioration of stones when immersed in water. A specimen of the stone is placed in a glass container with water and stirred vigorously. It is placed in water for at least 24 hours. If the water shows turbidity, then the stone is assumed to contain earthly substances. This test is to be conducted for all stones.

3. The Toughness Test

It is a rough test without any rigid specification or procedure. A stone is struck by a hammer to gauge the toughness of the stone. The force required to break the stone reflects the toughness of the stone.

4. The Field Hardness Test

This test is also called Mohs’ scale of hardness test. This is a simple test in which the hardness of the test is based on the hardness of the surface. The surface of the stone is scratched with the help of a pen knife, and the hardness is gauged based on the relative abrasiveness of minerals (the soft being talc and the hardest being diamond). Such a classification is given by Mohs and the scale is divided into the ten following scales:

1. Talc
2. Gypsum
3. Calcite
4. Fluorspar
5. Apatite
6. Orthoclase feldspar
7. Quartz
8. Topaz
9. Corundum (saphire)
10. Diamond

Thus, if a mark is made by the pen knife on the surface of the stone, the hardness may be equated to that of a calcite and hence the hardness, H = 3. A siliceous rock surface can not be scratched which may be equated to that of quartz and in this instance, H = 7.

5. The Acid Test

This test is performed to determine the presence of alkaline or lime content. This test consists of placing a cube of 50 to 100 gm weight in 1% hydrochloric acid for 1 week. If the corners of the cube show roundish and loose particles deposited on the surface, the stone has some alkaline content. If the stones exhibit florescence when subjected to the action of acids, then it reflects the presence of lime content. Stones that do not react to sulphuric acid are highly fire resistant.

6. The Crystallization Test

Because of crystallization on reaction with some chemicals, the stones may show a loss of weight and some defects. This test consists of immersing a cubical specimen of 40 mm side in a sodium sulphate solution for 2 hours and then drying it in an oven at 100°C. This procedure is repeated for five times. The loss of weight and the presence of cracking on the surface are noted. The presence of visible defects and loss in weight should be minimal indicating high durability and good resistance to weathering.

2.11.2 Laboratory Tests

Laboratory tests on stones comprise of the attrition test, the crushing test, the freezing and thawing test, the hardness test, the impact test and the microscopic test.

1. The Attrition Test

This is also called the abrasion test. This test is performed to determine the percentage of the wear of stones that are used for road construction. This test is carried out in Deval’s Attrition Testing Machine.

In this test, a certain quantity of stone is placed on Deval’s Attrition cylinder. The cylinder is rotated about its horizontal axis at the rate of 30 rpm for 5 hours. After the end of rotation, the contents of the cylinder are sieved, and the quantity of material retained on the stone is weighed. The percentage weight is the ratio of loss in weight to the initial weight which is expressed as a percentage.

2. The Crushing Test

This test is performed on the stones which are to be subjected to compressive stress. In this test a cubical specimen of 40 mm side is tested in a compression testing machine. The maximum load at which the stone specimen fails by crushing is noted. Then the crushing strength of the stone is the ratio of maximum load at failure and area of bearing face.

3. The Impact Test

The toughness of a stone is determined by the impact test using an impact testing machine. Here, a stone specimen of 25 mm diameter and 25 mm height is placed on the machine. A steel hammer of 2 kg weight is allowed to fall down axially on the cylinder from 1 cm height for the first blow, 2 cm height for the second blow, 3 cm height for the third blow and so on. The blow at which the specimen breaks is noted, which is the Toughness Index of the stone.

4. The Laboratory Hardness Test

This test is different from the field hardness test and the attrition test. This test is carried out in Dorry’s testing machine. A cylinder of 25 mm of the stone is rubbed against a steel disc spindled with coarse sand. The specimen is subjected to a pressure of 1.25 kg/mm². After 1000 revolutions in the machine, the loss in weight is found, and the coefficient of hardness is determined as

Coefficient of hardness =

5. The Microscopic Test

This is a geologist’s test. In this test, a thin section of a stone is taken and placed on a microscope to study the following properties:

1. Mineral constituents
2. Texture of stone
3. Average grain size
4. Nature of cementing material
5. Presence of pores, fissures and veins

6. The Freezing and Thawing Test

This test is conducted for the use of stones in regions where the temperature goes below the freezing point. The test consists of keeping a specimen of stone in water for 24 hours and then placing it in a freezing mixture at –12°C for 24 hours. The specimen is taken out and thawed (warmed) to atmospheric temperature. The procedure is repeated at least seven times after which the specimen is examined for any damage.

2.12 ARTIFICIAL STONES

Artificial stones are known as cast stones or reconstructed stones. In many localities natural stones are not available at a reasonable cost. In such cases, these stones are useful. However, because of their high cost, they can not be treated as a substitute for natural stones.

2.12.1 Types of Artificial Stones

Different types of materials are combined, and a variety of stones are manufactured. Some of the types of artificial stones are discussed below.

1. Cement Concrete Blocks

These are made using cement, fine aggregate, coarse aggregate and water similar to that of concrete. They may be cast-in-situ or cast-in-moulds in the required shapes. Sometimes they are precast with steel and are therefore called reinforced cement concrete blocks.

2. Artificial Marble

It is made using sand with Portland cement or one of the gypsum or magnesite cements. It is either precast or cast-in-situ and is used for external work.

Another form of artificial marble is made by fusing and moulding constituent mixture, which is composed of 60 parts of plaster in powder, 20 parts of pulverised marble, 15 parts of sulphate of potash with 5% solution of glue mixed with water. Such marble stones are mostly used in France.

3. Terrazo

It is prepared using mixtures of marble chips with white cement and some pigment. It is also either precast or cast-in-site. It is generally used in bathrooms, residential buildings, etc.

4. Mosaic Tiles

These are precast tiles where the upper surface is made of marble chips. They are available in different sizes and colours.

5. Reconstructed Stone

This is made from the debris of limestone quarries by crushing them into grit. This is mixed with lime made from dolomite and heated in a closed retort up to 980°C to drive out CO₂. This is slaked, mixed with water and consolidated into blocks under pressure. It is then dried, and CO₂ is admitted until the carbonization of the hydrate of lime blocks is complete.

6. Bituminous Stone

Diorite and other granite stones are impregnated with prepared or refined tar to form bituminous stones. These are preferred where noise-, wear- and dust-resistant stone surfaces are needed.

2.12.2 Advantages of Artificial Stones

The advantages of artificial stones are as follows:

1. In areas where natural stones are costly and are unavailable, artificial stones are used.
2. Any desired size and shape can be attained easily.
3. Can be made in-site, and thereby the cost of dressing the stone and transport can be saved.
4. They are practically defect free when compared with natural stones.
5. Cavities in artificial stones can be made for wiring or plumbing work easily.
6. Good in resisting deterioration and disintegration caused by various atmospheric agencies.
7. The strength of artificial stones can be assured as it is design based.
8. It is comparatively more durable than natural stones.

1. Rock is a mineral mass of a more or less uniform composition. It may consist of a single mineral (monomineralic) or of several minerals (polymineralic).
2. Monomineralic rocks are in quartz sand, pure gypsum and magnesite.
3. Polymineralic rocks are granite, basalt and porphyries.
4. According to geological classification, rocks are subdivided into three large groups, viz., igneous rocks, sedimentary rocks and metamorphic rocks.
5. The cooling and hardening of molten magma resulted in the formation of igneous rocks. Depending on the rate of cooling, various sizes of crystals are formed.
6. Transportation agencies like wind, water and ice may move the loose weathered rock materials and deposit them in the form of a layer called sediments. Such sediments when subjected to heavy pressure undergo compaction and concentration resulting in sedimentary rocks.
7. Sedimentary rocks and to some extent igneous rocks when subjected to changes brought about by the combination of heat, pressure and plastic flow (called metamorphism) undergo changes in structure, texture and mineral composition, and this results in the formation of metamorphic rocks.
8. Physical classification is based on the physical properties of rocks, the manner and arrangement of different particles and mass forming a stone.
9. The presence of chemical constituents in the rocks are the basis for chemical classification.
10. Granite is a deep-seated igneous rock, hard, durable and available in different colours.
11. Basalt and trap are of igneous origin, which are effective solid rocks.
12. Limestone and chalk are sedimentary rocks which have been formed by remnants of seaweeds and living organisms consolidated and cemented together.
13. Sandstone is another form of sedimentary rock formed by the action of mechanical sediments.
14. Laterite is a metaphoric rock and is a sandy clayey stone.
15. Gneiss is a metamorphic rock which can be easily split into thin slabs.
16. Marble is a metamorphic rock which can be easily cut with a saw and then be carved.
17. Slate is a metamorphic rock which is black in colour and can be split easily.
18. Gravel is available on river beds in the form of pebbles of different shapes.
19. Quartzite is a metamorphic rock which is hard, brittle and crystalline.
20. Quarrying is the process by which stones are obtained from rock beds.
21. Methods of quarrying are: digging, heating, wedging and blasting.
22. Explosives generally used for blasting are blasting-powder, dynamite, gun-cotton, blasting-gelatine, cordite and gelignite.
23. Dressing is the process of bringing the stones to a regular shape with the required finish.
24. Quarry dressing is one where the stones are dressed to the required size and type at the quarry and sent to the work site.
25. Site dressing comprises of dressing the stones at the site to the specific size and type.
26. Deteriorating agencies of stones are rain, climate, wind, vegetation growth, chemicals and living organisms.
27. Preservation of stones is intended to protect the structure against the action of weathering agents and also to protect the good appearance of the face work.
28. Field tests conducted on stone are: the absorption test, Smith’s test, the toughness test, the hardness test, the acid test and the crystallization test.
29. Laboratory tests on stones comprise the attrition test, the crushing test, the freezing and thawing test, the hardness test, the impact test and the microscopic test.

1. Name the geological, physical and chemical classifications of rocks.
2. Distinguish between sedimentary and metamorphic rocks.
3. Explain the physical classification of rocks.
4. How are igneous rocks formed?
5. Give examples of igneous, sedimentary and metamorphic rocks.
6. Enumerate the properties of building stones.
7. Explain the properties of good building stones.
8. Briefly describe some important varieties of building stones.
9. Classify and give the properties of the following stones:

   (i) Basalt

   (ii) Sandstone

   (iii) Laterite

10. What are the requirements of good building stones?
11. Briefly describe the building stones of India, and name the places where they are available.
12. Discuss the methods of quarrying.
13. What are the precautions to be adopted in handling explosives?
14. What are the purposes of dressing?
15. Discuss the factors that affect the durability of stones.
16. What is the necessity of preserving stones? How is it done effectively?
17. Explain the factors to be considered for the selection of stones for various civil engineering works.
18. What are the simple field tests you would suggest to determine the suitability of stones for various purposes?
19. Explain the various laboratory tests that determine the crushing strength and freezing and thawing qualities of stones.
20. Discuss the factors which are responsible for the deterioration of stones.
21. What are artificial stones? Give their advantages.