Frequently Asked Questions
Q: What are the unit weights (densities) of cement and concrete?
Cement (finely ground gray or white powder used to bind
concrete mixtures) weighs between 830 kg/m3 and 1650
kg/m3 (52 lbs/ft3 and 103 lbs/ft3)
depending on its handling. The weight of cement that has been pneumatically
loaded into a cement silo may be as low as 830 kg/m3
(52 lbs/ft3), while cement that
has been stored for a period of time exposed to vibration may be
as heavy as 1650 kg/m3 (103 lbs/ft3). It is
standard practice to consider a 94 lb bag of cement to be one cubic
foot when freshly packed.
||Both 500-mL beakers contain 500 grams of dry powdered cement.
On the left, cement was simply poured into the beaker. On the
right, cement was slightly vibrated—imitating consolidation
during transport or packing while stored in a silo. The 20%
difference in bulk volume demonstrates the need to measure cement
by mass instead of volume
for batching concrete.
Concrete: Concrete is a mixture of cement, coarse
and fine aggregates, water, and sometimes supplementary cementing
materials and/or chemical admixtures. A normal weight concrete weighs
approximately 2300 kg/m3 (145 lbs/ft3). The
unit weight (density) of concrete varies, depending on the amount
and density of the aggregate, the amount of air that is entrapped
or purposely entrained, and the water and cement contents, which
in turn are influenced by the maximum size of the aggregate.
||Fresh concrete is measured in a container of known
volume to determine density (unit weight). Scale must be sensitive
to 0.3% of anticipated mass of sample and container. Size of
container varies according to the size of the aggregate, the
7-L (0.25-ft3) air meter container for up to
(1-in.) nominal max. size aggregate:
14-L (0.5 ft3) container for aggregates up to 50-mm
Container should be calibrated at least annually (ASTM C1077).