Actions during service 143
a risk of injuries for the technicians operating the bridge. The concrete
contains limestone aggregates from Tournai in Belgium and is made with
ordinary Portland cement. In spite of the good concrete quality, severe
ASR expansion rapidly occurred in the columns in open air, which were
exposed to rain. Identical columns positioned in the construction hall protected from rain also show damage caused by ASR, although it is much less
pronounced. This illustrates the important role of moisture on the ASR
expansion rate.
5.3.2 sulfate attack and delayed ettringite formation
According to Skalny et al. (2002), sulfate attack is the term used to describe
a series of chemical reactions between sulfate ions and the components of
hardened concrete, principally the cement paste, which is caused by the
exposure of concrete to sulfates and moisture. This definition includes a
complex set of overlapping chemical reactions, which are duly influenced
by environmental and physical conditions.
Figure 5.27 ASR in concrete columns.