Handbook for Bridge Inspections - TSP2

* The density of the concrete in relationship to the transfer of oxy
gen (quality of the concrete, thickness of the cover).
* The electrochemical properties of the concrete (variation in its
qual ity, high mo isture content, possible presence of macro
cells).
Chl oride can penetrate concrete via three different sources:
* Embedded chloride
* Defrosting sa lt
* Mari ne climate
Embedded Chloride
This can be found in older bridges due to the lise of sea water
during construction, or aggregate or setting agent containing chloride.
The use of sea water and aggregate dredged from the sea
were previously acceptable and can still be found in several older
coastal bridges.
Calcium chloride (CaCI) is used as a setting agent especially by
the concrete casting industry to allow casts to be speedily released
for reuse. Elements so cast can be found, for example, on the
underside of bridge decks supported on steel plates where the brid·
ge deck is partially prefabricated.
Embedded chloride produces a flat chloride profile deep within
concrete. The chloride profile can be overlaid by chloride which
has penetrated from outside the concrete. A further effect of carbo·
ni sation wi ll be a reduction in the concrete's ability to bind the
chlorides. Consequently the chloride profi le achieves a low value
in carbonised concrete or in crushed stone with a hi gher concentra·
tion at the leading edge of the carbonisation process before the
concentration flattens out to the embedded level. (Refer to Figure
7.3-4)