Building Material : Stone Types, Physical Classification, and Requirements on Stones

Stone is a ‘naturally available building material’ which has been used from the early age of civilization. It is available in the form of rocks, which is cut to required size and shape and used as building block.

Type of Stones

Stones used for civil engineering works may be classified in the following three ways:

Geological

Physical

Chemical

Physical Classification

Based on the structure, the rocks may be classified as:

Stratified rocks

Uncertified rocks

(1)Stratified Rocks: These rocks are having layered structure. They possess planes of Stratification or cleavage. They can be easily split along these planes. Sand stones, lime stones, slate etc. are the examples of this class of stones.

(2 ) Uncertified Rocks: These rocks are not stratified. They possess crystalline and compact grains. They cannot be split in to thin slab. Granite, trap, marble etc. are the examples of this type of rocks.

Requirements of Good Building Stones

The following are the requirements of good building stones:

(1) Strength: The stone should be able to resist the load coming on it. Ordinarily this is not of primary concern since all stones are having good strength. However in case of large structure, it may be  necessary to check the strength.

(2) Durability: Stones selected should be capable of resisting adverse effects of natural forces like wind, rain and heat.

(3) Hardness: The stone used in floors and pavements should be able to resist abrasive forces caused by movement of men and materials over them.

(4) Toughness: Building stones should be tough enough to sustain stresses developed due to vibrations. The vibrations may be due to the machinery mounted over them or due to the loads moving over them. The stone aggregates used in the road constructions should be tough.

(5) Specific Gravity: Heavier variety of stones should be used for the construction of dams, retaining walls, docks and harbors. The specific gravity of good building stone is between 2.4 and 2.8.

(6) Porosity and Absorption: Building stone should not be porous. If it is porous rain water enters into the pour and reacts with stone and crumbles it. In higher altitudes, the freezing of water in pores takes place and it results into the disintegration of the stone.

(7) Dressing: Giving required shape to the stone is called dressing. It should be easy to dress so that the cost of dressing is reduced. However the care should be taken so that, this is not be at the cost of the required strength and the durability.

(8) Appearance: In case of the stones to be used for face works, where appearance is a primary requirement, its color and ability to receive polish is an important factor.

(9) Seasoning: Good stones should be free from the quarry sap. Literate stones should not be used for 6 to 12 months after quarrying. They are allowed to get rid of quarry sap by the action of nature. This process of removing quarry sap is called seasoning.

(10) Cost: Cost is an important consideration in selecting a building material. Proximity of the quarry to building site brings down the cost of transportation and hence the cost of stones comes down. However it may be noted that not a single stone can satisfy all the requirements of a good building stones, since one requirement may contradict another. For example, strength and durability requirement contradicts ease of dressing requirement. Hence it is necessary that site engineer looks into the properties required for the intended work and selects the stone.