PORTLAND CEMENT - Materials for Civil and Construction Engineers - page 204

FIGURE 6.2 Blaine air permeability apparatus.

passes material smaller than 0.075 mm.) A kilogram of portland cement has
approximately 7 trillion particles with a total surface area of about
to ( to ). The total surface area per unit
weight is a function of the size of the particles and is more readily measured.
Thus, particle size specifications are defined in terms of the surface area per
unit weight.
Fineness of cement is usually measured indirectly by measuring the sur-
face area with the Blaine air permeability apparatus (ASTM C204) or the
Wagner turbidimeter apparatus (ASTM C115). In the Blaine test (Figure 6.2),
the surface area of the cement particles in is determined by measur-
ing the air permeability of a cement sample and relating it to the air perme-
ability of a standard material. The Wagner turbidimeter determines the
surface area by measuring the rate of sedimentation of cement suspended in
kerosene. The finer the cement particles, the slower the sedimentation. Both
the Blaine and Wagner tests are indirect measurements of surface area and
use somewhat different measurement principles. Therefore, tests on a single
sample of cement will produce different results. Fineness can also be mea-
sured by determining the percent passing the 0.045 mm sieve (No. 325)
(ASTM C430).

300 m 2

400 m 2 1500 ft 2 2000 ft 2 per pound

cm 2 /g

6.4 Specific Gravity of Portland Cement

The specific gravity of cement is needed for mixture proportioning calcula-
tions. The specific gravity of portland cement (without voids between parti-
cles) is about 3.15 and can be determined according to ASTM C188. The
density of the bulk cement (including voids between particles) varies con-
siderably, depending on how it is handled and stored. For example, vibration
during transportation of bulk cement consolidates the cement and increases
its bulk density. Thus, cement quantities are specified and measured by
weight rather than volume.