Environmental Engineering Reference
In-Depth Information
this way is a maximum that is very difficult to reach when the material is in its
natural environment.
A test at atmospheric pressure is closer to real conditions. It measures the
porosity accessible to water at atmospheric pressure
(
N
48
). The definition of the
degree of saturation (
S
48
) is the ratio
N
48
/
N
t
(see section 8.2.4). This coefficient is
used to evaluate the gelivity of rocks (see section 8.3.1). The French standard
describes the procedure by which to determine this value [AFN 73a]. The test
procedure, made on at least five probes, underlines the importance of having sample
probes on the same bench to avoid getting highly dispersed results.
RILEM also suggests a very close test, n°II.1 “saturation coefficient”. It should
be carried out on dried probes that are immersed in water for 48 hours. The
saturation rate is therefore calculated by subtracting the dried sample mass from the
mass of the sample following immersion.
Other physical properties may be deduced from these tests, in particular apparent
and absolute volumetric masses. Corresponding standards are the following: NF B
10-512, n, April 1975 “Pierres calcaires - mesure de la teneur en eau critique”
[AFN 75a]; NF EN 1936, July 1999b, “Méthodes d'essai pour pierres naturelles -
détermination des masses volumiques des masses volumiques réelles et apparentes
et des porosités ouverte et totale” [AFN 99a]. Information is also available in the
RILEM recommendations “absolute and apparent volumetric masses”. These
different properties should be determined by running many tests on several samples
to take into account the eventual heterogeneity of the the material.
10.1.2.2
. Helium pycnometry
This device enables us to measure the density of the skeleton of the sample and
thus, by knowing its apparent volume, determine its total porosity. The intrusive gas
is helium, which has a molecule size less than 1 nm (diameter of 0.265 mm). The
use of molecules below this size makes it possible to fill the smallest pores in the
materials under study.
10.1.2.3
. Mercury porosimetry
Mercury porosimetry typically gives the intrusive curve volume of penetrating
mercury
versus
imposed pressure. Then the application of the Laplace principle
leads to the distribution of access diameters of pores (360 µm to 3.6 µm), total
porosity and an evaluation of the specific surface [MET 92, RIL 80]. Access radii of
pores are determined from macropores (around 100 µm) to mesopores (around
10 nm) according to International Union of Pure and Applied Chemistry
terminology [IUP 84].
