Sunday, August 12, 2012

Requirement of good building stones.

Hello there,

This post discusses the various requirements of a good building stone. The following are the qualities of the stones used in the building construction:

  • Compressive strength:  The compressive strength or the crushing strength of the stone is tested with the help of a crushing strength testing machine and for a good building stone the value should not be less than 100N/mm2. 

The various igneous rocks and the metamorphic rocks have the required amount of the strength that is why some of them makes it up to as a building stone.

  •  Appearance:  The stones should have a homogeneous color and should be resistant to the weathering agencies. The stone used in the face work should be of decent appearance. The color of the stone chosen should be according to the surrounding environment.

The light colored stones are preferred because they are weathering resistant. A good building stone is of uniform color and do not possess any clay spots or other color spots.

  •  Durability:  In general durability is defined as the ability to resist the weathering action of the surroundings. A good building stone should be durable. The various factors contributing to the durability of a stone  are its chemical composition, texture, resistance to atmospheric and other influences, location in the structure etc.

The various important environmental agents which affect the durability of a stone are alternate heating and cooling, alternate drying and wetting, chemical agencies such as dissolved gases in the environment, growth of the trees and creepers in the joints between the stone and wind and the high velocity; etc.
For making stone durable some people suggest that the natural bed of the stone should be noted and the stones should be so arranged in a structure such that the natural bed is perpendicular to the direction of the pressure.

  • Work-ability/ Facility of dressing: The stones should be such that they can be easily carved, molded, cut and dressed. It is important consideration from the economic point of view. However this property of stone is opposed to its strength, durability and hardness. Hence it is to be properly correlated with respect to the situation in which stone is to be used.

  • Fracture: For a good building stone its fracture should be sharp, even, bright and the grains well cemented together, or as suggested by the several books. A dull, chalky and earthly fracture will indicate an early future decay of the stone.
  •  Hardness: The stone to be used in the building should possess the good hardness. The co-efficient of hardness, as worked out in the hardness test, should be greater than 17 for a stone to be used in road work. If it is between 14 and 17 then the stone is said to be of medium hardness. If the hardness is less than the 14 then the stone is said to be of poor hardness.

  • Porosity/ Percentage water: 

 The porosity of stone is defined as the ratio of the volume of the air plus water voids present in the stone to the total volume of the stone. If we put the stone in the water for 24 hours it should not absorb the water more than 3% by weight.

The porosity may affect the durability of the stone. The rain water as it descends through atmosphere absorbs some acidic gases forming light acids. Such rain water if absorbed by stone reacts with the constituents of the stone causing them to crumble.

 Similarly, in cold regions the low temperature turns the water into ice which has more volume than the water. The absorbed water will further increase the cracks  as it needs more volume in the ice form.  So the porous stones should not be used in the places which are subjected to rain, frost or moisture.

  • Resistant to fire: 

The minerals composing the stone should be such that the shape of the stone is preserved when a fire occurs. The failure of stone in case of a fire is due to various reasons such as rapid rise in the temperature, sudden cooling, different co-efficient of linear expansion of minerals, etc.

 The limestone resists fire up to a temperature of 800 degrees C and then it is split in to CaO and Co2. The sandstone with silicates as binding material can resist a fire in a better way. The argillaceous stones are weak in strength but they can resist fire quite well.

  • Seasoning: 

 The stones should be well seasoned before putting into use. The stone obtained fresh from the quarry contain some moisture which is known as the quarry sap. The presence of this moisture makes the stone soft.

Hence the stones quarried freshly are easy to work. It is advised to dress them when the stone contain the quarry sap. The stones should be dried or seasoned before they are used in the structural use. A period of about 6 to 12 month is advised for the proper seasoning.

  • Specific Gravity:  For a good building stone its specific gravity should be greater than 2.7 or so. The heavy stones are compact and dense, thus less porous and they can be used for various civil engineering applications such as dams, weirs, retaining walls, docks, harbors etc. On the other hand if the stones are to be used for domes, roof coverings, etc. the lighter varieties of the stones are preferred. 
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Civil Engineering materials -Stone

Hello There,
How you doing?
Here is what you looked for:

The materials which are used in the building construction are known as the Civil Engineering materials or the building materials or the construction materials. It is important for a Civil Engineer to know about the various properties of the materials before they are used in the construction work.
The various civil engineering materials like the stone, brick, cement, ceremic, timber, iron, paints etc are divided into different categories according to their characteristics.

In general the civil engineering materials can be divided into three categories
1. Cementing materials  like cement, lime and mortar. 
2. Finishing materials like paint, plaster tiles etc.
3. Hard materials like stone, bricks, timber etc.

The building materials are not only used in the construction industry but they are used in every field of the engineering so there are the chances that our country may face the scarcity of the building materials in the near future. 

The demand of the building materials is always higher than the production. So it is advisable to encourage the industries which use the locally available raw material for the easy production of the building materials.

In the subsequent posts I will discuss about the stone as a building material used since a very long time ago. The stone is obtained from the rocks and has the same physical and chemical properties as that of the parent rock. The rocks are classified according to different properties taken at one time.
(1) Geological Classification
(2) Physical Classification
(3) Chemical or the Engineering Classification

(1) Geological Classification :  Geologically the rocks are classified in the three following categories:
(a) Igneous Rocks:  These are the rocks which are formed after the cooling of the magma. Magma is a molten mineral material present in the crust of the earth and has a tendency to come out if it finds any cracks or free path.  These rock are further classified in the three categories:

(i) Plutonic: These are the rocks which are formed at a considerable depth from the surface of the earth. The speed of the cooling of the magma is slow which results in the formation of the coarse grained crystalline structure. The general stones used for the building construction are obtained from the plutonic rocks. The example of the plutonic rock is granite.

(ii) Hypa-bysal Rocks: These are are the rocks which are formed at some shallow depth from the surface of the earth due to cooling of the magma. The rate of the cooling is slower than that in the plutonic rocks so the structure is finely grained crystalline. The dolerite is an example of such rocks.

(iii) Volcanic Rocks: These rocks are formed at the surface of the earth after the magma comes out on the surface. The rate of the cooling is very fast so the structure is extremely fine. They frequently contain glass which is a non crystalline material. The basalt is an example of the volcanic rock. 

(b) Sedimentary Rocks :  Sedimentary rocks are those rocks which are formed after the deposition of the products of the weathering on the pre-existing rocks.  The weathered material either remains at the place of the origin or is carried away the different agents like air, water, glaciers and frost etc.
Following four types of the deposits occur:

(i) Residual deposits:  Some product of the weathering remains at the place of their origin, such deposits are known as the residual deposits. 

(ii) Sedimentary deposits: When some insoluble weathering products are carried away in suspension and when such products are deposited , they give rise to the sedimentary deposits.

(iii) Chemical Deposits: Some materials which are carried away in solution may get deposited due to some phsio-chemical processes like the evaporation, precipitation etc. It give rise to chemical deposits. 
Some products may get deposited by some organisms/organic agency, such deposits are known as the organic deposits. Limestone, Gypsum, sandstone are the examples of the sedimentary rocks.

(c) Metamorphic Rock: These are the rocks which are formed after some physical or chemical transformation of the original rock, the resulting rock will have different properties from the parent rock.  These are formed by the change in the character of the pre-existing rocks.

The igneous and sedimentary rocks are changed in character when they are subjected to great heat and pressure, the process of the change is known as the metamorphism.

The original rock when attacked by the surrounding through some physical or chemical action, the state of the equilibrium of the present minerals and the texture of the rock gets disturbed and it attains a different state until it is again in equilibrium. The agents of the metamorphism are heat, pressure and the chemical fluids.

(2) Physical Classification :  The physical classification represents the general structure of the rocks:
(a) Stratified Rocks:  These rocks contains the planes of stratification and such rocks can easily be split up along these planes of stratification. Generally all the sedimentary rocks are stratified rocks. Example is sandstone, limestone and slate etc.

(b) Non-stratified Rocks:  These rocks may have a crystalline granular structure, and they are not stratified. The rocks of the volcanic agency and the sedimentary rocks which are disturbed by the movement of the earth are the non-stratified rocks. Granite and marble are the example of the non-stratified rocks.

(c) Foliated Rocks: These are the rocks which can be separated along a specific direction only. the foliated strcuture is common in the metamorphic rocks. The agents of the metamorphism may the pressure heat or the chemical liquids.

(3) Chemical Classification:  There are three categories of the rocks:
(i) Silicious rocks : Such rocks contains the silica as the major compound. These are hard in nature and is resistant to the weathering. The common example of the silicious rocks are granite and quartz.
(ii) Argilla
ceous rocks:  Such rocks contains the clay minerals. They can be dense and compact and can be soft.  The slates and laterite are the examples of the argillaceous rocks.

(iii) Calcareous Rocks: In these rocks the calcium carbonate predominates. The durability of such rocks will depend upon the chemicals present in the surrounding environment. The examples of the calcareous rock are limestone and marble etc.

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