ConcRetE MateRiaL~~continue

STORAGE Cement should be stored off the ground in a

well-aired, clean, dry place.

Wrapping the cement bags in plastic sheets gives extra

protection,Bulk cement will normally be stored in silos.

AGGREGATES Aggregates are of two basic types:

COARSE: crushed rock, gravel or screenings.

FINE: fine and coarse sands and crusher fines.

Sand should be concreting sand and not brickies sand or plasterers sand.

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.

GRADED Aggregates should range in size so that they fit together well.

This gives a stronger and denser concrete.

Rounded aggregates give a more

workable mix. Angular aggregates

make concrete harder to place, work and compact,

but can make concrete stronger.

STORAGE Aggregates should be stored where they will stay clean, separated from other

materials and dry. If the aggregates are very wet use less water in the mix.

WATER Water is mixed with the 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.

Many concrete plants now use recycled water.

Always check bore water before use.

Don’t use sea water as it may rust the steel

reinforcement in the concrete.

ADMIXTURES Admixtures are mixed into the concrete to change or alter its properties, ie

the time concrete takes to set and harden, or its workability.

HOW THE PROCESS WORKS 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.