Basics in Building Construction

Basics in Building Construction 4(2+2)

Lesson 12 and 13: Basic Building Construction Materials

Water

Water is an important and essential ingredient in a concrete mortar mix. It is intended to take part in the process of chemical reaction due to which the mix become hard finally. Besides taking part in the process of hydration, water makes the concrete fluid enough to fill all cavities. In fact a water cement ratio of 0.3 is enough for the process of hydration but such mix will be too stiff and is not workable. Hence depending upon the requirement of workability the water content is increased. It must be kept in mind that water enough to make the concrete workable only should be added and any extra water added will decrease the strength or concrete and makes it porous, less durable and less dense. Excessive water also causes bleeding by capillary action and this will lead to formation of liatance on the concrete surface, which does not allow proper bond with successive layers of concrete.

Being an important ingredient of concrete water must have definite qualities. Any impurities and salts present in water will affect the process of hydration, setting time gain of strength and causes corrosion of reinforcement. In general water that is fit for drinking can be safely used for making concrete:

Required Qualities Of Water For Making Concrete

1. It should be free from impurities.
2. It should be free from silt. Water containing silt can be used after allowing the particles of silt to settle in a storage tank.
3. Use of brackish and saline water should be avoided to the extent possible.
4. It should be free from harmful salts. Salty water causes efflorescence on the concrete surface. It also increases corrosion of reinforcement. Presence of sugar in water increases the setting time.
5. Water with a pH value of not less than 6 should be used. Pure water is not good for making concrete. Natural water which is slightly acidic is harmless.
6. It should be free from organic matter and vegetation like algae.
7. Use of sea water for making concrete should be avoided as far as possible. Sea water causes efflorescence and corrosion of reinforce­ment. In tropical regions this reaction is more rapid. However in case of structures permanently under water no corrosion or deterioration of concrete is observed. Sea water should never be used for making prestressed concrete.