Strong Builders

 

                                            ROCKS AND STONES

Rocks and stones

Stone used in construction are obtained from the rock forming the crust of the earth's surface. A natural material of construction which is obtained from rocks by any suitable method is called a stone.

Rock

Rock is defined as the portion of the earth's its having no shape and structure.

Different types of classification of stones

The building stones are obtained from the rocks which are classified as follows. 

1. Geological classification

2. Physical classification

3. Chemical classification

1.    Geological classification

This classification is depending upon the process of formation, it can be divided into three main types, namely.

(i)              Igneous rocks

(ii)            (ii) Sedimentary rocks and

(iii)          (iii) Metamorphic rocks

 

Igneous rocks

These are formed by cooling and solidifying of molten mass lying below or above the earth surface. This type has a crystalline, glassy or fused texture. If is generally strong and durable. Principal stones obtained from igneous rocks are.

 

1. Granite 2. Basalt

 

2.      Sedimentary rocks

            These are formed by deposition of materials like sand, clay, dis integrated rocks, dead sea                          organism etc., by the action of air or water. The sediments get consolidated in horizontal                          beds due to the pressure by overlying material. The rock may be either granular or                                   fragmental, close grained, compact or open textured.Their strength and durability depends                       upon the quality of grains and cementing materials.Principal stones obtained from sedimentary               rocks are

 

          1.     Sand stone 2. Lime stone 3. Laterite

 

 

 

Metamorphic rocks

These are formed from igneous or sedimentary rocks. These are formed by the metamorphic action of pressure or internal heat or by both. These rocks represent either bedded, foliated or crystalline structure. They are generally hard and durable. Principal stones obtained from metamorphic rocks are

 

1: Slate 2. Marble 3. Quartzite

 

2.     Physical classification

 

This classification is based on general structure of stone. It is the manner in which the mass is arranged. There are three main divisions.

(i)              Stratified

(ii)            Un stratified

(iii)          Foliated

 

Stratifiedrock

These rocks which shows clear signs of layers and can be easily splittedup. into layers are called stratified Stratified rocks rocks.

 

Example : Sand stone, lime stone, slate etc

 

Un stratified rocks

These rocks which do not have strata and cannot be easily split into thin slabs are called un stratified rocks

 

Example: Granite, basalt, trap etc.,

 

Foliated rocks

These rocks which can be splitted up into this sheets are known as foliated rocks. These rocks have tendency to split-ups in definite direction only

 

Example : Slate

 

3.Chemical classification

It is based on the chemical composition of rocks. Chemically, rocks are classified as following.

(i)              Siliceous rocks

(ii)             (ii) Argillaceous

(iii)          (iii) Calcareous rocks (or) calcarious rock

 

Siliceous rocks

These rock consist of silica, as its maincomponent. These rocks are very hard and durable and are not easily affected by any weathering agencies.

 

Example : Granite, quartzite,trap, basalt and sand stone.

 

Argillaceous rocks

The rock having alumina or clay as their major component are known as argillaceous rocks, they may be hard like slate or soft like mud stone.

Example :Laterite, Slate etc.,

 

Calcareous rocks

These rocks have calcium carbonate as their main content. The durability of these rocks depends upon the atmospheric action.

Example : Marble, limestone etc.,

 

Uses of stones

·       Stones are used in the construction of buildings mainly in foundation, walls,

columns, lintels, arches etc.,

·       Stones are used as the basic material for making concrete.

·       Stones are used in mass construction works like dams, bridges, piers &

retaining walls etc.,

·       Stones as thin slabs are used for roofing and for pavements.

·       Lime stones are used in the manufacturing of cement.

·       Crushing stone is used as a substitute for sand.

·       Broken stones are used in the formation of railway track as ballast, and also in road work.

·       Granite, marble stones are used for ornamental works.

 

Requirements of a good building stone

 

1.     Crushing strength

The crushing strength should be greater than 100N/mm

2.     Appearance

Appearance is very important for stones used for decorative works and the facing work for buildings.

3.     Density

It should be dense. Its specific gravity should be greater than 2.7.

4.     Durability

This property depends on its usage stones used for facing worksfor building should have easiness to get dressed to the required texture.

5.     Resistance to fire

A good stone should be able to resist high temperature. Its mineral contends should have equal co-efficient of expansion.

6.     Fracture

The grains should be well cemented and sharp if we check a fractured surface.

7.     Impact

resistance It is a measure of toughness of the stone. An impact test value of 19 is good and a value below 13 shows bed quality of stone.

 

 

8.     Hardness

This test given resistance against wear as in road works. Hardness greater than 17% is good and less than 14% is considered as poor.

9.     Resistance to wear

Resistance to wear is indicated by attrition test. It is  also an important quality for use as course aggregate in concrete for a good facing stone,its value can be as low as 3, however, for use as course aggregate a much higher value is needed.

10.  Seasoning

 Good stone must be free from quarry sap. To ensure this, the stones after quarrying and dressing should be left for a period of 6 to 12 months for proper seasoning, before using in construction work.

11.  Texture

It should have a pleasing texture and should be free from cracks and cavities.

12.  Water absorption

For durability the percentage of absorption should be less than 0.6 percent otherwise, in exposed situations, water can seep into the stone and leach out the salts.

13.  Weathering

It should weather well as shown by its use in similar types of old buildings in which they have weathered well.

14.  Percentage of water

If wear is more than 3% the stone is not satisfactory. If it isequal to 3% the stone is just tolerable. For a good building stone, wear should beless than 3%.

15.  Dressing

The art of surface shaping a stone is known as dressing. Stones should possess uniform texture and softness so that they may be easily dressed it is too hard finish will be poor and dressing uneconomical.

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