Stone properties|Selection|Quarrying|Dressing|Test of stones

Selection of stones for construction

i. The type of building and the situation

(e.g. a residential building, commercial building or monumental building)

ii. The precise location in the building where the stone shall give a preferential benefit in terms of cost, appearance and durability such as in foundation superstructures, arches, columns, beams flooring, roofing or cantilevers etc.

iii. Availability of stone and its cost.

Quarrying of stone:- The process of extraction of suitable stones from their natural place of occurrence for use in construction is called quarrying of stone.

Selection of quarry site :-

I. Availability of sound rock.

ii. Distance of area of construction.

iii. Availability of water and dumping space.

Dressing of stone - The process of giving a proper size, shape and finish to the roughly broken stone as obtained from the quarry is known as dressing of stone.

Properties/Characteristics of Good Building Stones

1.Structure

Structure of the stone may be stratified (layered) or unstratified.A broken stone should not be dull in appearance and should have uniform texture free from cavities, cracks, and patches of loose or 

soft material.Stratification should not be visible to naked eye.

2. Texture

Fine grained stones with homogeneous distribution look attractive and hence they are used for carving. Such stones are usually strong and durable.

3.Appearance

For face work it should have fine, compact texture; light-colored stone is preferred as dark colors are likely to fade out in due course of time. A stone with uniform and attractive color is durable. Marble and granite get a very good appearance, when polished. Hence they are used for face works in buildings.

4.Weight

It is an indication of the porosity and density. For stability of structures such as dams, retaining walls, docks and harbors, heavier stones are required, whereas for arches, vaults, domes, etc.  light stones may be the choice.

5.Density

Denser stones are stronger and Light weight stones are weak. The specific gravity of a good building stone is between 2.4 and 2.8.

6.Strength

Strength is an important property to be looked into before selecting stone as a building block. The stone should be able to resist the load coming on it. As per IS code, a minimum crushing strength of

3.5 N/mm² for any building block is required.

7.Hardness

It is an important property to be considered when stone is used for flooring and pavement. The stone used in floors and pavements should be able to resist abrasive forces caused by movement of men and materials over them.

8.Toughness

The resistance to impact is called toughness. It should be tough enough to resist sudden impact due to moving vehicle

9.Durability

Stones selected should be capable of resisting adverse effects of natural forces like wind, rain and heat.

10. Percentage wear

It is measured by an attrition test. It is an important property to be considered in selecting aggregate for road works and railway ballast.

11. Porosity and Absorption

All stones have pores and hence absorb water. The reaction of water with material of stone causes disintegration. For a good stone it should be as small as possible and in no case more than 5% when

is immersed under water for 24 hours.

12.Weathering

Rain and wind cause loss of good appearance of stones. Hence stones with good weather resistance should be used for face works.

13.Resistance to Fire

Sand stones resist fire better. Argillaceous materials, though poor in strength, are good in resisting fire.

14.Seasoning

The stones obtained from quarries contain moisture in the pores. The strength of the stone improves if this moisture is removed before using the stone. A stone should be well seasoned before using it in

construction.

15. Cost

Cost is an important consideration in selecting a building material. Proximity of the quarry to the building site brings down the cost of transportation and hence the cost of stones comes down.

Following are different tests on building stones:

i)Acid test

ii)Smith's Test

iii)Crystalline test

iv)Water absorption test

v)Hardness Test

vi)Freezing and thawing test

vii) Crushing test

viii) Attrition test

ix) Impact test