Weight or Weigh Batching ~ this is a more accurate method of
measuring materials for concrete than volume batching since it
reduces considerably the risk of variation between different
batches. The weight of sand is affected very little by its dampness
which in turn leads to greater accuracy in proportioning materials.
When loading a weighing hopper the materials should be loaded in a
specific order †
Coarse aggregates † tends to push other materials out and
leaves the hopper clean.
Cement † this is sandwiched between the other materials
since some of the fine cement particles could be blown away
if cement is put in last.
Sand or fine Aggregates † put in last to stabilise the fine
lightweight particles of cement powder.
Typical Densities ~ cement † 1440 kg/m^3 sand † 1600 kg/m^3 coarse
aggregate † 1440 kg/m^3
Water/Cement Ratio ~ water in concrete has two functions †
Start the chemical reaction which causes the mixture to set
into a solid mass.
Give the mix workability so that it can be placed, tamped or
vibrated into the required position.
Very little water is required to set concrete (approximately 0„2 w/c
ratio) the surplus evaporates leaving minute voids therefore the
more water added to the mix to increase its workability the weaker
is the resultant concrete. Generally w/c ratios of 0„4 to 0„5 are
adequate for most purposes.
Concrete Production---Weight (Weigh) Batching