Environmental Engineering Reference
In-Depth Information
concentrations are provided in terms of damage classes or classes of intervention
emergency.
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0 (minimal)
1 (low)
2 (average)
3 (high)
Damage class
Sulfates
Nitrates
Chlorides
Fluorides
Oxalates
Figure 8.17.
Maximum salt loads, expressed in terms of damage
classes [SNE 05], reported by [BOU 09]
8.3.2.3
. Degradation patterns due to salts
The salt-related deterioration patterns of stones are linked to their water and
water vapor transfer properties, to the environmental conditions and also to the
properties of the salts themselves. Indeed, experiments performed on Monks Park
oolithic limestone in the UK have shown that mirabilite and thenardite tend to form
subflorescences under conditions of constant relative humidity and temperature, thus
inducing more damage than halite, which tends to grow as efflorescence or to fill the
smallest pores of the stone in a homogenous way [ROD 99].
If salts precipitate within the material (subflorescences), they participate in the
formation of scales (see Figure 8.18). If they crystallize at the stone's surface, they
form efflorescence and crusts. If they crystallize between the grains very close to the
surface, they induce granular disintegration. In such a case, two types of patterns
may develop: if the stone is homogenous, the granular disintegration will develop
evenly and the stone will show an eroded and smooth surface. If the stone is not
homogenous, its surface will deteriorate unevenly and alveolization will develop
(see Figures 8.8 and 8.19).
