Concrete and Overview

Tips for Concrete Making:

CONCRETE is made by mixing: CEMENT WATER

COARSE AND FINE AGGREGATES. ADMIXTURES (if required).

Broad objectives to be kept in mind before making concrete

Concrete is to be made in such a way that It is workable Has the required compressive strength. It is Durable.

The constituents is to be mixed in such a way that it is easy to TRANSPORT PLACE COMPACT FINISH concrete

Right place for storing cement

Cement can absorb moisture and hence must be stored carefully

Cement should be stored off the ground in a well-aired, clean, dry place.

Aggregates

Aggregates are of two basic types COARSE: crushed rock, gravel or screenings.Size is more than 4.75 mm

FINE: fine and coarse sands and crusher fines.Size is generally less than 4.75 mm .

Properties of aggregates should be checked before use in concrete

• Aggregates should be: Strong and Hard: A stronger, harder aggregate will give a stronger final Concrete. Never use a crumble or flakey rock like sandstone. Durable: To stand up to wear and tear and weathering. Chemically inactive: So the aggregates don’t react with the cement. Clean: Dirt or clay sticking to the aggregates will weaken the bond between paste and aggregates.

Water for concrete

In large projects water is normally tested for its suitability.

• We must ensure that water of the right quality is used since water is mixed with cement powder to form a paste which holds the aggregates together like glue.
• Water must be clean, fresh and free from any dirt, unwanted chemicals or rubbish that may affect concrete.
• Check bore water before use.
• Don’t use sea water as it may rust the steel reinforcement in the concrete.

Purpose of chemical admixtures in concrete

Admixtures are mixed into the concrete to change or alter its properties, i.e.
the time concrete takes to set and harden, or its workability or to increase the rate of gain of compressive strength.

Process of mixing ingredients

• Measured amounts of the coarse and fine aggregates are mixed together.
• A measured amount of cement is added and mixed in. Enough water is added to make the mix workable. All the materials are then mixed together well. The cement powder and water form a paste which bonds the aggregates together like glue.

Four main properties of concrete

 

The four main properties of concrete are: WORKABILITY COHESIVENESS

STRENGTH DURABILITY

 

Different states of concrete

Concrete has three different states:

• PLASTIC
• SETTING
• HARDENING