Building Materials about stone

 Building Materials 

Introduction 

The building materials include stones , bricks , lime , cement , concrete , mortar and timber . These materials are discussed , in brief , as follows :  

Stones 

The stones are derived from rocks which form the earth's crust and have no definite shape or chemical composition but are mixtures of two or more minerals . The rocks from which stones are obtained may be classified in the following three groups : 

1. Geological classification Geologically , the rocks are classified into three types as follows : 

( a ) Igneous rocks The igneous rocks are formed due to the solidification of molten mass laying below or above the earth surface . It has a crystalline glossy or fused texture . 

( b ) Sedimentary rocks The sedimentary rocks are formed due to gradual deposition of materials like sand , clay etc .. generally by setting water . These are also called stratified because these rocks are formed in layers . Limestone and sandstone belong to this category of rocks 

( c ) Metamorphic rocks The metamorphic rocks are formed due to alteration of original structure under heat and excessive pressure . Marble is an example of metamorphic rock . 

2. Physical classification Physically , the rocks are classified as follows : 

( a ) Stratified rocks The stratified rocks are those which exhibit distinct layers which can be separated . The limestone , slate and sandstone are examples of stratified rocks . 

( b ) Unstratified rocks The unstratified rocks are those which do not show any sign of strata and cannot be easily split into slabs . The granite and marble are examples of unstratified rocks . 

3. Chemical classification Chemically , the rocks are classified as follows : 

( a ) Silicious rocks The silicious rocks are those which contain silica as the main constituent . The granite , quartzite , gneiss are examples of silicious rocks . 

( b ) Argillaceous rocks . The argillaceous rocks are those which contain clay or alumina as the main constituent . The slate , laterite . Kaoline are the examples of argillaceous rocks . 

( c ) Calcarious rocks . The calcarious rocks are those which contain lime or calcium carbonate as the main constituent . The limestone and marble are the examples of calcarious rocks .  

Important Building Stones 

The following are important building stones , their composition , properties and uses : 

1. Granite . It is an igneous rock It is mainly composed of quartz . * felspar and mica . Its specific gravity is 2.64 and compressive strength varies from 70 to 130 MN / m . Its colour depends upon that of felspar which may be brown , grey , green and pink . A fine grained granite offers high resistance to weathering . It can be easily polished and worked . It is used for exterior facing of buildings . .

 Felspar is a silicate of aluminium with varying amounts of potash , soda or lime . 

 2. Slate . It is an argillaceous rock . It is mainly composed of alumina mixed with sand or carbonate of lime . Its specific gravity is 2.8 and compressive strength varies from 60 to 70 MN / m² It has grey or dark blue colour . A good slate is hard , tough and fine grained . It is suitable for use in cisterns . The slate in the form of tiles is used as an excellent roof covering material . 

3. Gneiss . It is a silicious rock . It is mainly composed of quartz and felspar . It is more easily worked than granite . It is a good material for street paving 

4. Sandstone It is a sedimentary rock of silicious variety . It is mainly composed of quartz , lime and silica . Its specific gravity is 2.65 to 2.95 and compressive strength varies from 35 to 40 MN / m Its usual colours are white , grey , brown , pink etc. The fine grained stones are strong and durable . It is suitable for ashlar work , mouldings , carvings etc. 

5. Limestone It is a sedimentary rock of calcarious variety . Its specific gravity is 2.6 It is available in brown , yellow and dark grey colours . It is used in large quantities in blast furnaces . It may be used as stone masonry for walls . 

6 Marble . It is a metamorphic rock of calcarious variety . available in many colours . It is very hard and takes a fine polish . It work . Its specific gravity is 2.7 and is used for carving and decoration . 

7. Kankar . It is an impure limestone containing 30 % of alumina and silica . The hard kankar is used for foundations of buildings . 

8. Laterite . It is a sandy claystone containing high percentage of iron oxide . It has a porous and cellular structure . Its specific gravity , varies from 2 to 2.2 . The laterite blocks are suitable as building stones whereas nodular laterite proves a very good road metal .

9. Moorum . It is a decomposed laterite and has deep brown or red colour . It is used in surfacing fancy paths and garden walks . 

10. Quartzite . It is a silicious sandstone which has been subjected to metamorphic action . It is strong and durable . It is used as a road metal or railway ballast or in concrete . 

 Bricks 

The brick is the most commonly used building material and used for constructing walls , columns , roofs , paving floors etc. A good brick clay contains 20 to 30 percent of alumina , 50 to 60 percent of silica and the remaining constituents are lime , magnesia , sodium , potassium , manganese and iron oxide . It may be noted that 

1. The excess of alumina in the clay makes the brick crack and warp on drying .  

2 .The excess of silica in the clay makes the brick brittle and weak .

 3 .The excess of lime in the clay causes the bricks to melt and distort during burning . 

 4 The alkaline salt present in the bricks , absorb moisture from air which on drying leaves powder deposit on the brick . This effect is known as efflorescence . It is also caused if the clay used for making bricks contain pyrite and the water used for pugging the clay contain gypsum . 

 Manufacture of Bricks 

The manufacture of bricks consist of the following four major operations :

1. Preparation of brick clay . First of all , the earth is dug out in clear weather and cleaned off stones , pebbles , grits , vegetable matter etc. The earth after digging out is left to atmospheric action for few weeks . This process is known as weathering . It is found that 1.5 to 2.5 cum of earth is required for moulding 1000 bricks . The clay is then tempered in pug - mills . Note : The process of mixing clay , water and other ingredients to make bricks is known as kneading 

2 Moulding bricks After preparing the clay , the moulding of bricks is carried out either by hand or by machine . In hand moulding , the bricks are moulded by hand i.e. manually . It is preferred where manpower is cheap and readily available . The hand moulding may be done either on ground or