Civil Engineering Reference
In-Depth Information
that the surface of the reinforcement is alternatively damp and dry. In cases
where both mechanisms occur simultaneously, then chloride penetration is
normative; it is of primary importance that the concrete is adequately pro-
tected against this.
Fig. 6.7
Causes of corrosion of
the reinforcement
Chloride penetration (CI
)
Solid (Chloride contaminated)
x
c
(Joints)
x
c
(Outside)
x
c
(Joints)
x
c
(Inside)
Leakage possible
Inside (ventilated),
Exposed to CO
2
and chloride contaminated
Salt fog and splash zone environment
Carbonatation (CO
2
)
Chloride penetration (Cl
)
Fig. 6.8
Production of the
reinforcement
Chloride from ground water can penetrate into the concrete on the outside
of the tunnel. In cases of leakage it could also reach the inner side of the lining.
The access ramps and the closed section of the tunnel are also affected by
thawing salts. These thawing salts, in any case, are scattered near the
entrance and exit of the tunnel. Besides, the traffic carries the thawing salts
into the tunnel.
In the vertical direction, four zones exist in the tunnel:
- an atmospheric zone which is incidentally sprayed with water containing
thawing salt (minor amounts, rapid absorption);
- a splash zone which is frequently splashed with water that is spattered
by the traffic, but can also dry out (large amounts, transported through
diffusion and absorption);
- a seasonal zone under the road embankment (
wet sand), which is mois-
tened quite frequently but can also dry out (large amounts, transported
through diffusion and absorption) dependent on the degree of drainage
and the pumping regimen;
- an underwater zone (below the drainpipes in the bottom of the tunnel),
which is in permanent contact with salt water; there is very little refreshment
because hardly any fresh water comes in (large amounts of salt water,
minor amounts of fresh water, transported through diffusion).
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