Structural materials

a. Clay:

• Size : < 0.02mm

b. Bricks:

• Bricks are blocks of tempered clay moulded to suitable shape and size while it is still in plastic state. It is then dried in the sun and burnt to make it hard, strong and durable.
• Standard size of brick is 23x11x7 cm.
• Bricks are classified as first class, second class, third class and fourth class.

Composition of brick:

• Silica or sand (50-60 %) – it helps in hardening , strengthening and in durability of brick.
• Clay (20-30 % ) – it helps for plasticity which contains aluminium. Iron oxide (4-6 %) – it helps in fusion and binds the brick particles. Lime (2-5%) – it reduces shrinkage on drying.
• Manganese <1% – it provides yellowish black dark color to brick.

Selection of brick

For construction selection of brick can be done by considering following points:

• The brick should be well burnt.
• It should have regular shape, reddish color.
• It should provide metallic sound when struck to each other.
• It should not absorb the water more than 25 % of its weight when immersed in water for 24 hours.

c. Cement:

Composition of cement:

• Lime- 50-65% Silica: 20-25%
• Alumunium – 4-8 % Iron oxide : 2-4%
• Manganese – 1-3 % Sulphur – 0.5-1% Gypsum: 3-5 %

d. Sand:

Generally, known as the fine aggregate. It is always smaller than 2 mm size. On the basis of size it can be classified as :

1. Fine sand: 0.06-0.2mm
2. Medium sand : 0.2-0.6mm
3. Coarse sand : 0.6 – 2mm

• For construction, sand should be, pure, clean and free from impurities. Well graded.
• Moisture content should be such that there is no bulking of sand or else additional sand has to be added.

e. Water :

• When water is mixed with cement, the chemical process of hydrolysis and hydration occurs simultaneously during the reaction of cement and water.

I. Hydrolysis: it is the process of changing of compounds of cement into other as a result of chemical actions of water.

II. Hydration: it is the process of continuation cement with water. It helps in setting and hardening of cement.

f. Concrete :

• The mixture of sand, cement and coarse aggregate and the water in the correct proportion and thoroughly mixed so that setting it forms as the rock of mass is known as concrete.

Properties of concrete:

• High comprehensive strength.
• Free from corrosion and atmospheric weathering.
• Strength improves with age.

g. Steel reinforcement bars:

• Steel bars which have high tensile strength, are embedded in concrete to resist tensile forces.
• Should be free from from rusting.
• Should be uncracked and of uniform size throughout the length. Should not break while bending.
• In general minimum 4 nos. of minimum 12 mm diameter for rectangular beam and column should be used.

h. Timber:

• Woods suitable for building or any other engineering purposes are called timber. Timber is used as structural members like posts, beam, rafters etc.
• Timbers should be well seasoned, free from cracks and knots. Should have uniform surface and should not be twisted.
• Freshly cut trees have a lot of water in them. If this water content is not removed from them, timbers are likely to wrap, crack and shrink. So water has to be removed before they are used. The process of removing water gradually from the timber is called seasoning.

i. Mortar:

• Mortar is a mixture of cement, sand and water. For normal construction works mortar should be in the proportion of 1:4 or 1;5 but not less than 1:6 in any case.

Functions of mortar:

• To make strong bond between stones or/and bricks while constructing wall. To provide even bed to bricks and stones.
• To prevent from moisture penetration. To enhance outlook of the structure.