Volumetric properties are important for mix design/
proportioning and production of PCC and HMA. However,
since mass measurements are usually much easier, they are
typically taken during testing and converted to volumes by
using specific gravities. According to ASTM C125: Standard
Terminology Relating to Concrete and Concrete Aggregates, specific
gravity is defined in Equation 2.1 as the ratio of mass of a
volume of material to the mass of an equal volume of distilled
water at a stated temperature.
G
M
V
M
V
M
V
s
W
W
W
= = (2.1)
where:
Gs = specific gravity
M = mass of material
V = volume of material
Mw = mass of water
Vw = volume of water = V
gw = unit weight of water = 1 g/cm3
In Equation 2.1, the mass is simply taken in air, and the volume
is measured using the water or gas displacement method.
Since coarse and fine aggregate particles generally have internal
and surface porosity as well as rough surfaces, measurements
of a particle’s volume must take into account the volume of
permeable pores. As a result, depending on the mass and volume
measurements used for the calculation in Equation 2.1,
the following three specific gravity values are defined for coarse
and fine aggregates (1, 2).
G
M
V
sa
s
s w
= (2.2)
G
M
V V
sb
s
s pp w
(2.3) ( ) =
+
G
M M
V V
ssd
s wpp
s pp w
(2.4) ( ) = +
+
where:
Gsa = apparent specific gravity
Gsb = bulk specific gravity
Gssd = bulk specific gravity (saturated-surface-dry basis)
Ms = mass of dry solids
Mwpp = mass of water filled in permeable pores
Vs = volume of solids
Vpp = volume of permeable pores
gw = unit weight of water
The mass and volume measurements also are used to
determine the water absorption capacity of aggregate. ASTM
C125 defines water absorption as the increase in the mass of
aggregate due to the water filled in the permeable pores of
the aggregate particles that may be dried out in an oven at a
temperature between 100° and 110°C. The water absorption
capacity is expressed as a percentage of the mass of ovendried
solids, as shown in Equation 2.5.
Absorption
M
M
wpp
s
= × 100 (2.5)
where:
Absorption = water absorption capacity of aggregate, percent