Civil Engineering Reference
In-Depth Information
Fig. 3-5. Ground granulated blast-furnace slag. (69800)
Fig. 3-7. Silica fume powder. (69801)
carbon contents usually less than 5%, but some may be as
high as 10%. Class C materials are often high-calcium (10%
to 30% CaO) fly ashes with carbon contents less than 2%.
Many Class C ashes when exposed to water will hydrate
and harden in less than 45 minutes. Some fly ashes meet
both Class F and Class C classifications.
Fly ash is used in about 50% of ready mixed concrete
(
PCA 2000
). Class F fly ash is often used at dosages of 15%
to 25% by mass of cementitious material and Class C fly
ash is used at dosages of 15% to 40% by mass of cementi-
tious material. Dosage varies with the reactivity of the ash
and the desired effects on the concrete (
Helmuth 1987
and
ACI 232 1996
).
glassy sandlike granulated material. The granulated mate-
rial, which is ground to less than 45 microns, has a surface
area fineness of about 400 to 600 m
2
/kg Blaine. The relative
density (specific gravity) for ground granulated blast-
furnace slag is in the range of 2.85 to 2.95. The bulk density
varies from 1050 to 1375 kg/m
3
(66 to 86 lb/ft
3
).
The rough and angular-shaped ground slag (Fig. 3-6)
in the presence of water and an activator, NaOH or CaOH,
both supplied by portland cement, hydrates and sets in a
manner similar to portland cement. However, air-cooled
slag does not have the hydraulic properties of water-
cooled slag.
Granulated blast furnace slag was first developed in
Germany in 1853 (
Malhotra 1996
). Ground slag has been
used as a cementitious material in concrete since the begin-
ning of the 1900s (
Abrams 1925
). Ground granulated blast-
furnace slag, when used in general purpose concrete in
North America, commonly constitutes between 30% and
45% of the cementing material in the mix (Fig. 3-4) (
PCA
2000
). Some slag concretes have a slag component of 70%
or more of the cementitious material. ASTM C 989
(AASHTO M 302) classifies slag by its increasing level of
reactivity as Grade 80, 100, or 120 (Table 3-1). ASTM C 1073
covers a rapid determination of hydraulic activity of
SLAG
Ground granulated blast-furnace slag (Fig. 3-5), also called
slag cement, is made from iron blast-furnace slag; it is a
nonmetallic hydraulic cement consisting essentially of sili-
cates and aluminosilicates of calcium developed in a
molten condition simultaneously with iron in a blast
furnace. The molten slag at a temperature of about 1500°C
(2730°F) is rapidly chilled by quenching in water to form a
Fig. 3-6. Scanning electron microscope micrograph of slag
particles at 2100X. (69541)
Fig. 3-8. Scanning electron microscope micrograph of silica-
fume particles at 20,000X. (54095)
