Stone

 

  Stones form one of the most important building materials in civil engineering. Stones are derived from rocks, which form the earth's crust and have no definite shape or chemical combination but are mixtures of two or more minerals. The mineral is a substance which is formed by the natural inorganic process and possesses a definite chemical combination and molecular structure. They are strong, durable and descent in appearance

Application and uses of Stones

 Uses of stones:

  • Face work

·         Stones are adopted to give Massive appearance to the structure, walls are of the bricks and facing is done in stones of desired shades. This is known as composite masonry

  • Paving
    • Stones are used to cover floor of building of various types such as residential, commercial industrial etc.
    • They are also adopted to form paving of roads, footpath etc.
  • Basic materials
    • Stones are disintegrated and converted which are called as aggregates to form a basic material for cement, concrete, Murom of roads, artificial stones, and hollow bricks.
  • Sandstone is a popular stone with sculptors.
  • Good and durable construction material
  • Thresholds and steps in manor houses
  • Limestone for burning lime and also for manufacture of cement
  • Insulators in electrical appliances
  • Miscellaneous material
    • Ballast for railway
    • Limestone as a flux in blast furnaces
    • Blocks in the construction of Bridge, piers, abutment, retaining walls, dams etc.

Building Stones:

·         Millions of tones of crushed rock are needed annually for road base, paving, ready-mixed concrete and asphalt.

·         Sandstone which is not so hard-wearing or beautifully patterned is used for garden walls and paths in landscaping.

·         Basalt: It is quarried and crushed as "Blue Metal" which is used as a road-base, and in reinforced concrete as aggregate.

·         Although wood, straw and mud is used for houses in some parts of the world, most buildings are preferred to be built of stones.

·         Building wells.

·         Material for foundation and walling of buildings, dams, bridges, etc.

·         Aggregate

·         Stone walls

·         Roof tile in the form of slates

·         Murom for covering and flooring of road surface

·         Limestone for burning lime and for the manufacture of Portland cement

·         Shale is a component of bricks and may also be used in manufacturing of cement.

·         Nite, another stone type is used for architectural construction, ornamental stones and monuments.

·         Marble is widely used in construction industry, for aesthetic purposes, beautification and strength

Stone being so important in the light of the above uses still is not widely used in construction. The reasons are:

Stones are replaced by the increased use of RCC. Dressing of stones is time consuming Stones are not cheaply and conveniently available in plain areas.

Characteristics of Good Building Stones

Every building stone which is used for construction cannot satisfy all the ideal requirements. For example, when the stone satisfies the requirement of strength and durability, it may not do the same with other necessities such as ease of dressing. Hence it is the job of the site engineer to look into the properties which are required for the specific work and select the stone accordingly.

Construction Aggregate Properties

A good building stone should have the following qualities:

Appearance: 

Building Stones used for the face work of the building should have fine, compact texture. Light colour stone is usually preferred as dark colours are prone to fade out with time. They should be free from clay holes, bands or spots of colour.

Durability:

A good building stone should be durable. Various factors contributing to durability of a stone are its chemical composition, texture, resistance to atmosphere and other influences, location in structure

Structure: 

A stone when broken should not be dull in appearance and should show uniformity of texture. It should be free from cavities, cracks, and patches of loose or soft material. Stratifications, which are usually found in sedimentary rocks, should not be visible to naked eye.

 

Strength: 

Stones used in construction should be strong and durable to withstand the disintegrating action of weather. Generally the stones can withstand the forces they encounter in usual constructions but in case of constructions where the forces encountered are unusual, they should be tested for its strength. Stones with compact fine crystalline texture are stronger. Compressive strength of building stones in practice, range between 60 to 200 N/mm2.

 

Specific gravity: 

The specific gravity of Building stone is directly proportional to its weight and strength. Hence the stones having higher specific gravity should not be used for dams, retaining walls, docks and harbours. Specific gravity of a good building stone lies between 2.4 to 2.8.

 

Hardness: 

When stones are utilized for floors, pavements, aprons of bridges and weirs of rivers, the stones are subjected to abrasive forces which are caused by the wear and friction. Hence the stones which are to be used in such places should be tested for hardness.

Coefficient of hardness, as worked out in hardness test should be greater than 17  for a stone to be used in road work. If it is between 14 to 17 , ston is said to be of medium hardness. If less than 14, stones is said to be of poor hardness and such stone not to be used in road work

 

 

Toughness: 

It is the measure of impact that a stone can withstand. When the stones are supposed to undergo vibrations of machinery and moving loads, they should be tough.

 

Porosity and Absorption: 

The porous building stones are not suitable in construction especially for exposed surfaces of structures. The rain water which comes down carries some acidic gases forming light acids which get soaked on the surface. Acids react with the constituents of stones causing them to crumble. In cold regions water freezes in the pores of stones. This water causes the disintegration of stones because of its increase in volume on freezing.

Stones should be tested for porosity and porous stones should be used only at places where they don’t encounter frost, rain or moisture in any form. Water absorption is directly proportional to the porosity of the rock. The more porous the rock is, the more water it will absorb and leads to the damaging of stone.

The types of some of the stones and their maximum limit of water absorption (%) is as follows:

  • Sandstone   : 10
  • Limestone   : 10
  • Granite         : 1
  • Trap              : 6
  • Shale            : 10
  • Gneiss          : 1
  • Slate             : 1
  • Quartzite     : 3

 

Seasoning: 

All freshly quarried stones contain a certain amount of moisture known as quarry sap, which makes them soft and easier to work upon .Good stones should be free from quarry sap. They are allowed to get rid of quarry sap by the action of nature. This process of removing quarry sap is called seasoning. A period of 6-12 months is generally enough for proper seasoning.

 

Weathering:  

It is the extent to which the face of a stone resists the action of weather. Stones with good weathering properties only should be used in the construction of important buildings.

Workability:

Stones are said to be workable if the wok which is involved in their cutting, dressing and shaping is considered as economical and easy to conduct. Know the Current House construction cost

 

Fire Resistance: 

Mineral composing stone should be such that shape of stones preserved when a fire occurs. Failure of stones in case of fire is due to various reasons such as rapid rise in temperature sudden cooling , different coefficient of thermal linear  expansion of minerals etc.

Building Stones should be free from calcium carbonate, oxides of iron, and minerals having different coefficients of thermal expansion. Igneous rocks undergo major disintegration because of quartz which disintegrates into small particles at a temperature of about 575 oC. Limestone, however, can withstand a little higher temperature; i.e. up to 800 oC after which they disintegrate.

 

 

 

 

 

 

 

 


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