Building Stone(2)

Hardness

Hardness of rock entirely depend upon that of its individual mineral components . If constituent mineral have higher hardness the rock will also be harder . This requirement is of importance when stone is subjected to great wear and tear by abrasion.

Ease of Dressing

To receive dressing easily a rock must not be hard. This is exactly opposite to what is required for strength. A  good building stone has therefore to strike golden mean. It must be so hard as to make dressing difficult and at the same time must be hard enough to have adequate strength .As very high crushing strength brings no advantages in preference to very strong rocks which are difficult to dress because of their hardness . Softer rocks with comparatively lower but adequate strength should be choosen as they will be easier to dress.

Eg. Softer amygdaloidal basalt are better than hard compact basalt . Rocks with crushing strength between 500 to 800 kg/cm2 are most suitable . Fine grained compact homogenous rocks are suitable for dressing.

Blocks from quarry

The size of blocks available from the quarry will depend on the spacing of divisional planes in rocks such as bedding planes ,joints, slaty cleavage etc .Closely spaced joints would make a rock unsuitable by breaking it up into small blocks and chips only. Dolerite  compact basalt columnar basalt being good examples of this type. The suitability of a rock for any particular purpose will therefore depend on spacing of divisional planes in it.

Good appearance

Light coloured rock have in general a more pleasing appearance . Therefore granite , syenite, trachyte and sandstone and limestone having light colours are better looking than basalt and highly ferruginous sandstone.

All the light coloured rocks can not maintain their light shade as the colour will  darken on exposure to sun and rain if harmful minerals are present.

Eg. If pyrite is present it will quickly decomposed liberating iron oxides and hydroxides the deposition of which will produce dark patches and streaks.

Cost

It is considered as important factor . cost of building stone depends on it availability, accessibility, workability.

Important building stones locally available in Maharashtra

Archean granite ,Chandrapur quartzite, Kamtee sandstone, Dharwar schist,

Peninsula gneiss , Deccan trap basalt.

Important building stones available in India

1)    Archean of south india

       Granite, gneisses, porphyritic granite, synites charnockites, marbles,

2)    Upper    vindhyan sandstone

            It is best architectural stone or dimension stone

3)    Cuddapha vindhyan, porbunder limestone

4)    Deccan trap basalt.

o � a � P� rgin-left:.5in'>Such misleading results from testing can be avoided if simple precaution are observed.

Maximum force expressed per unit area which stone can with stand is called compressive strength. Any force beyond the compressive strength will cause failure of the stone.

Co=    p/A        Co=  compressive strength     P=   load of failure 

 A =area of cross section.

The crushing strength of rock depend upon no. of factors such as

a)     Its mode of formation

b)    Its composition

c)     Texture

d)    Structure

e)      Its moisture content

f)      Extent of weathering.