Environmental Engineering Reference
In-Depth Information
Figure 8.7.
Spalling of a Tuffeau wall on Henry IV bridge
in Chatellerault, France
If liquid water transfer towards the surface is possible during most of the drying
phase, for instance in stones with a very low critical moisture content, alteration will
occur very close to the stone's surface. Granular disintegration develops in such
cases if salts are present (see Figure 8.8). Migné limestone, for instance, has a
critical moisture content equal to 10%, and develops granular disintegration rather
than scaling. Some stones develop scaling in certain environments (strong
ventilation inducing a high air exchange rate at their surface), and granular
disintegration in places where they are allowed to dry very slowly.
Figure 8.8.
Granular disintegration developing on the limestone wall of a salt storage
building in Honfleur, France. Granular disintegration occurs evenly on the restoration stone.
The original stone (a partially hardened chalk) is heterogenous, however, and develops
differential granular disintegration, resulting in the formation of alveoli
