Nscp 2001 Pdf Free 146

Admixtures are classified by the following chemical and functional physical=
 characteristics (Mamlouk, 2006)7:Air entrainers (ASTM C 260): produce tiny=
 air bubbles in the hardened concrete to provide space for water to expand =
upon freezing.Water reducers: increase the mobility of the cement particles=
 in the plastic mix, allowing workability to be achieved at lower water con=
tents.Retarders: used to delay the initial set of concrete.Hydration contro=
ller admixtures: stops and reactivates the hydration process of concrete al=
lowing for extended use of ready-mixed concrete.Accelerators (ASTM D 98): u=
sed to develop early strength of concrete at a faster rate than that develo=
ped in normal concrete.Supplementary cementitious admixtures: byproducts of=
 other industries that are used to improve some properties of concrete and =
to reduce the problem of discarding them. Fly Ash (ASTM C 618), Ground Gran=
ulated Blast Furnace Slag (ASTM 989, AASHTO M 302), Silica Fume (ASTM C 124=
0, AASHTO M 307), and Natural Pozzolans (ASTM C595) are common admixtures.S=
pecialty admixtures: several admixtures are available to improve concrete q=
uality in different ways. These admixtures include but are not limited to w=
orkability agents, corrosion inhibitors, pumping aids, and bonding agents.

According to ASTM C33 coarse aggregate consists of gravel, crushed gravel, =
crushed stone, air-cooled blast furnace slag, crushed hydraulic-cement conc=
rete, or a combination. The use of crushed hydraulic-cement concrete may re=
quire some additional precautions. Although it regularly produces satisfact=
ory results; additional mixing water and the affects of freeze-thaw resista=
nce and air void properties may need to be further tested.3

Nscp 2001 Pdf Free 146
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