1. General Introduction:The engineering structures are composedof materials. These materials are knownas the engineering materials or buildingmaterials. It is necessary for an engineer to become conversant with the propertiesof such materials. A building demand wide range of materials with various properties such as water-resistance, strength, durability, temp-resistance,

appearance, permeability etc. So these are to be properly studied before making final selection for any building material for a particular use. As many materials are used for a single infrastructure to come up. So the grouping of

building materials for construction is done by considering these before mentioned specific properties of the materials such as stones, ceramics, cement concrete, timber, metals and bricks etc. So out of all these materials we will further study in this chapter in detail about the building stones and bricks.

Following are the some characteristics of a good building stone:

Durability (They are durable enough to dress and fit it in structure easily)

Hardness (Stones are harder than other materials) Resistance to fire

Resists Weathering (capable of withstanding the adverse effects of rain, frost, wind etc.) Appearance and Textures (Provides different styles to

the structure)

Possessing such characteristics still stones with exposed faces when are acted upon by atmospheric and external agencies gets deteriorated. Following are the causes of decay of stones:Alternate wetness and drying by rain and sunshine wear out stones quickly.Frost in cold places makes the moisture present in the atmosphere deposited in pores of stones. At freezing temperature it expands and causes splitting of stones.

Living Organisms like worms and bacteria act upon stones and deteriorate them. These organisms makes holes in them and thus weaken them.

Impurities in Atmosphere have adverse effects on stones for instance, the acids and fumes are predominant in

atmosphere in industrial areas in cities which deteriorates the stones.

Rain Water has chemical action also on stones as when it descends through atmosphere it absorbs CO2 and H2S gases. These gases acts adversely on stones and deteriorate them.

Temperature Variations such as rise and fall of temperature causes expansion and contraction in stones respectively and frequent changes like this may result in deterioration of stones.

Vegetable Growth occurs in stones such as creepers and certain trees develop with there roots in joints between them. They absorb moisture and make the stone surface dump and expand to break it resulting in deterioration.

Wind contains fine particles of dust. If it is blowing with high velocity such particles will strike against the stone surfaces and thus the stones will get decayed with the high pressure.

The decay of building stones are to some extent prevented, if they are properly preserved. For this purposes, the preservatives are applied on the stone surfaces. An ideal preservative has the following properties:

It does not allow moisture to penetrate the stone surface. It does not develop objectionable colour. It is easily penetrated in stone surface. It is economical. It is non-corrosive and harmless. It remains effective for a long time after drying. Its application on stone is easy.

Following are the preservatives which are commonly used to preserve the stones:

Coal Tar: If coal tar is applied on stone surface it preserves stone but the colour of coal tar produces objectionable

appearance and surface coated with coal tar absorbs heat of the sun So it is not generally used. Paint: An application of paint on stone surface serves as a preservative. The paint changes the original colour of stones. It is applied under pressure if deep penetration is

required.

Paraffin: This preservative may be used alone or it may be dissolved in neptha and then applied on stone surface. It changes the original colour of stone.

Artificial stone is a name for various kinds of synthetic stone products used from the 18th century onward. They have been

used in building construction and civil engineering work and industrial uses such as grindstones.

1. A good cast stone should resemble a natural stone fully to achieve it white cement with aggregate of the crushed stone and sand selected to have matching colour are used.

2. Aggregate must be clean and durable.

3. Pigments used for colouring the cast stone should be judiciously chosen, so that they do not interfere with the setting of cement.

4. They should not be used in a proportion greater that 15% by volume of the cement used.

5. Cement and aggregates are usually mixed in 1:3 proportion.

6. BRICK EARTH: A. Composition: A good brick

earth should be such that when prepared with water it can be easily moulded, dried and burnt without cracking or warping. It should contain a small quantity divided lime to help in binding the particles of brick together by melting the particles of sand. A little oxide of iron should also be present which would give the brick its peculiar red colour.Alumina - 20-30%Silica - 50-60%Magnesia - Small quantityLime - Small quantityOxide of Iron - Small quantity

The bricks should be table-moulded, well burnt in kilns, copper coloured, free from cracks and with sharp and square edges. The colour should be uniform and bright.

The bricks should be uniform in shape and should be of standard size.

The bricks should give a clear metallic ringing sound when struck with each other.

The brick should not absorb water more than 20 percent by weight for first class bricks and 22 percent by weight for second class bricks, when soaked in cold water for a period of 24 hours.

The bricks should have low thermal conductivity and they should be sound proof.

The brick earth is classified into following three categories:

1. Loamy, mild or sandy clay: This type of earth consists of considerable amount of free silica in addition to alumina. The addition of lime in such clay helps to fuse sand and thereby to increase hardness of bricks. Also the presence of sand helps in preventing cracking, shrinking and warping of bricks.

2. Plastic, strong or pure clay: This clay consists of alumina and silica and it is referred to as strong clay or fat clay. The raw bricks will crack, shrink and warp during drying if pure clay alone is used in making bricks

Hence such clay is corrected by the addition of sand and ash. The sand prevents shrinkage and the ash provides lime to act as flux.

3. Marls, chalky or calcareous clay: This clay consists of considerable amount of chalk in addition to alumina and silica. Such clay generally makes good bricks. But to avoid undesirable effects of excess lime, the sand is sometimes added to such clay.

A brick is generally subjected to the following tests to find out its suitability for construction work:

Absorption: A brick is taken and it is weighed dry. It is then immersed in water for a period of 16 hours. It is weighed again and the differences in weight indicates the amount of water absorbed by the brick. It should not in any case exceed 20 percent of weight of dry brick.

Crushing Strength: The crushing strength of a brick is found out by placing it in a compression testing machine. It is pressed till it breaks. As per BIS: 1077-1957, the minimum crushing strength of bricks is 3.50 N/mm square. The bricks with crushing strength of 7 to 14

N/m

m square are graded as A and those having above 14 N/mm square are graded as AA.

Hardness: In this test, a scratch is made on brick surface with the help of a finger nail. If no impression is left on the surface, the brick is treated to be sufficiently hard.

Soundness: In this test, the two bricks are taken and they are struck with each other. The bricks should not break and a clear ringing sound should be produced.

Structure: A brick is broken and its structure is examined. It should be homogeneous, compact and free from any defects such as holes, lumps etc.

These bricks are made from fire-clay. These bricks are usually white or yellowish white in colour. The weight is about 30 to 35 N. They can resist high temperature without softening and melting. Hence they are used for linings of interior surfaces of furnaces, chimneys, kilns etc. The compressive strength for these is between 200 to 220 N/mm square. Following are three varieties of fire bricks:

1. Acidic Bricks: These bricks are used for acidic lining. Following are the types of acidic bricks:

Ordinary fire-bricks

Silica bricks

2. Basic Bricks: These bricks are used for basic lining and basic refractory materials are used in the manufacture of such bricks. The magnesia bricks are prepared from lime and magnesia rocks. The dolomite may also be adopted for the manufacture of these bricks.

3. Neutral Bricks: These bricks are used for neutral lining. They offer resistance to the corrosive action of slag's and acid fumes. As compared to the basic bricks, the neutral bricks are more inert to the slag's. Following are the types of neutral bricks:

Chromic bricks High alumina bricks