Civil Engineering Reference
In-Depth Information
Internal cracking
100%
Ref
Pz
Freeze-thaw cycles
Scaling test
Pz
Ref
Freeze-thaw cycles
8.9
Schematic representation of frost resistance of SCMs concrete
(
Pz
) compared to reference (
Ref
).
1972), and combinations of these processes. Most of these theories agree on
the significant parameters responsible for frost damage in concrete:
∑
Degree of saturation -
Concretes with or without pozzolan that have
internal relative humidity below approximately 75 to 80% are normally
not subject to internal damage from freezing, whatever the concrete
composition (ACI Committee 201, 2008).
∑
Air-void -
Frost damage is practically eliminated when a proper air-void
system is achieved. Since air bubbles are practically never completely
filled with water, ice can be formed without creating excessive internal
pressure. In order to resist freeze-thaw cycles, it is generally recognized
that concretes should contain more than 4% of air, with a bubble spacing
factor of less than 200-250 mm. This is usually achieved by the use of
air-entraining admixture.
It has been shown that the use of very active pozzolans such as
silica fume in very high strength concretes (> 90 MPa) generally gives
satisfactory behaviour in freeze-thaw cycles, without the need for a
particular air void structure (Gagné et al., 1990; Pigeon et al., 1991).
For other concretes with or without pozzolan, a correct air void structure
is almost always necessary (Gagné and Linger, 2008).
