Environmental Engineering Reference
In-Depth Information
10.1.2.4.
BET method
This laboratory test, proposed by Brunauer
et al.
[BRU 38], is based on
multimolecular adsorption theory. This method is complementary to mercury
porosimetry and gives the distribution of access diameters of pores in the range 1 nm
< diameter < 25 nm). It provides a more representative value of the specific surface
of the medium.
N
OTE
: Other methods enable us to determine the pore volume distribution
(suction). The RILEM, 1980, test n° I.4 [RIL 80] proposes three methods to take
into account the entire range of suction values from pF 0 to pF 7:
- suction plate (2,973 µm to 2.97 µm);
- method of the pressure membrane (2.97 µm to 0.19 µm);
- method of the dessicator under vacuum (0.09 µm to 0.0003 µm).
These three last methods are delicate and tedious to perform and mercury
porosimetry it generally preferred to measure these physical properties. The study
will be completed by a BET test if infraporosity has to be investigated or we need to
have a more realistic value for the specific surface.
10.1.3.
Mechanical tests
Mechanical tests in general require large sample volumes (around 1,000 cm
3
per
test), but remain the most relevant tests for qualifying the weakening of mechanical
strengths of stone due to a certain type of alteration, whether natural or produced
artificially in the lab. For these tests and in the case of sedimentary rocks, it will be
of great importance to know the bedding of the stone and indicate the orientation of
the sample regarding the bed for each experiment.
10.1.3.1.
Test of permeability under load
Stone degradation has a notable influence on permeability. Water transport in
stone may be disrupted by the state of stress the material is under. Stones in a
building are submitted to important loading; whereas permeability tests in the
laboratory are performed referring to norms without any load. Some authors have
studied the impact of stress on rock materials and their permeability. An
experimental device can be found, for example in [SKO 99], for measuring the
permeability of rocks under load.
