Environmental Engineering Reference
In-Depth Information
- If the medium that supplies capillary rises becomes drier, drainage of the
previously infiltrated water can occur. This can also be obtained by using suitable
architectural solutions ( capillary barriers ) that stop the supply of underground
water to the wall (see the example described in Chapter 10, section 10.2).
Nevertheless, wetting/drying cycles can also contribute to stone decay (see
Chapter 10).
9.1.3. Difficulties in assessing the global water cycle in a monument
The complexity of the various processes introduced above is increased by other
difficulties that occur when dealing with global water cycles at the monument scale:
- multiplicity and overlapping of time scales of interest (day, week, year, long-
range evolution, global change) and space scales: the stone, wall, overall
structure, etc.;
- heterogenities of the materials: different stone types, mortars, etc.;
- multiple coupling between thermal, hydric and mechanical phenomena in
relation to the dissolution/precipitation kinetics (see Chapter 8, section 8.2);
- exchanges at interfaces with the soil, the outer and inner atmospheres, etc.
Facing all of these difficulties, an “operational approach” based on observation
and empiricism and requiring only some normalized tests is often preferred.
Nevertheless, we think it is worth trying to connect the important know-how and
practices developed by curators and restorers in this field to the underlying physical
factors. This is the main objective of this chapter.
9.2. Water in stones: capillarity
9.2.1 . Water content
9.2.1.1. Definitions
The first parameter that characterizes water in stones is the water content :
volume of water per unit volume of a sample of volume V :
V water
θ
[9.1]
V
or mass of water, referred to the dry mass m dry of the same sample:
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