Environmental Engineering Reference
In-Depth Information
10-619 [AFN 99d] and makes it possible to study the crystallization strength of
stone blocks.
RILEM suggests three tests to evaluate rocks resistance to salt crystallization:
n°V.1a and V.1b “Crystallization by total immersion” and n°IV.2 “Crystallization
by partial immersion”. Results may be spectacular after only few cycles. An
example of the test applied on sandstones is reported by Chéné [CHE 96].
10.1.3.10
Ultrasonic velocity (P waves)
Ultrasonic velocity may be representative of the state of damage of a stone. The
correlation between sound velocity and compressive strength has been highlighted
by various authors [CHI 95]. The measure of this velocity will be influenced by the
hygrometric state of the stone [ESB 89]. The procedure to get this measure is given
in NF B 106505 [AFN 73e].
The principle of the test consists in measuring the time while an impulse travels
through the sample. The sound velocity is given by the ratio:
Vp + L/t
[10.2]
where Vp is sound velocity [m/s], L distance transmitter
- receiver [m] and t time
[s].
10.2. Hydric and thermal transfers: specific techniques
10.2.1.
Problems
It has been seen in Chapter 8, section 8.2, the essential role water can play in the
alteration of stones by itself - freezing effect for example − or as a vector of
chemical species. It has been seen in Chapter 9, section 9.2, how using the basic
physical principles - Darcy's law and the mass conservation law - we can describe
water migration due to liquid water. Chapter 9 also gave some metrology elements
of these hydric transfers: measure of water content, suction and mass diffusivity. In
section 9.3.5 it indicated that a more complete theory on transfers had to take into
account those of water vapor, described in particular by Fick's law, thermal transfers
described by Fourier's law, and coupling between these various transfers
(see e.g. [CRA 96]). This study will not be re-started here. It is enough to formulate,
for our current purpose, the system of coupled equations that is reached by making
the restrictive hypothesis of the absence of any hysteresis phenomena. This system
can be written:
