6 research outputs found
Time-dependent behaviour of hardened cement paste under isotropic loading
International audienceThe experimental results of isotropic compression tests performed at 20°C and 90°C on a class G hardened cement paste hydrated at 90°C (Ghabezloo et al., 2008, Cem. Conc. Res. 38, 1424-1437) have been revisited considering time-dependent response. Within the frame of a viscoplastic model, the non-linear responses of the volumetric strains as observed in drained and undrained tests and of the pore pressure in undrained tests are analysed. The calibration of model parameters based on experimental data allows to study the effect of the test temperature on the viscous response of hardened cement paste showing that the creep is more pronounced for a higher test temperature. The effect of the hydration temperature on the time dependent behaviour is also studied by evaluating the model parameters for a cement paste hydrated at 60°C. The time-dependent deformations are more pronounced for hydration at a higher temperature
Effective stress law for the permeability of a limestone
The effective stress law for the permeability of a limestone is studied
experimentally by performing constant head permeability tests in a triaxial
cell with different conditions of confining pressure and pore pressure. Test
results have shown that a pore pressure increase and a confining pressure
decrease both result in an increase of the permeability, and that the effect of
the pore pressure change on the variation of the permeability is more important
than the effect of a change of the confining pressure. A power law is proposed
for the variation of the permeability with the effective stress. The
permeability effective stress coefficient increases linearly with the
differential pressure and is greater than one as soon the differential pressure
exceeds few bars. The test results are well reproduced using the proposed
permeability-effective stress law. A conceptual pore-shell model based on a
detailed observation of the microstructure of the studied limestone is
proposed. This model is able to explain the experimental observations on the
effect of the total stress and of the pore pressure on the permeability of the
limestone. Effective stress coefficients for the stress-dependent permeability
which are greater than one are obtained. It is shown that the controlling
factor is the ratio of the different bulk moduli of the various constituents of
the rock. This ratio is studied experimentally by performing microhardness
tests.Comment: International Journal of Rock Mechanics and Mining Sciences (2008) In
pres
Poromechanical behaviour of hardened cement paste under isotropic loading
The poromechanical behaviour of hardened cement paste under isotropic loading
is studied on the basis of an experimental testing program of drained,
undrained and unjacketed compression tests. The macroscopic behaviour of the
material is described in the framework of the mechanics of porous media. The
poroelastic parameters of the material are determined and the effect of stress
and pore pressure on them is evaluated. Appropriate effective stress laws which
control the evolution of total volume, pore volume, solid volume, porosity and
drained bulk modulus are discussed. A phenomenon of degradation of elastic
properties is observed in the test results. The microscopic observations showed
that this degradation is caused by the microcracking of the material under
isotropic loading. The good compatibility and the consistency of the obtained
poromechanical parameters demonstrate that the behaviour of the hardened cement
paste can be indeed described within the framework of the theory of porous
media.Comment: Cement and Concrete Research (2008) In pres
L’analyse pétrographique : un outil de la géologie de l’ingénieur
L’examen pétrographique des matériaux rocheux utilisés en génie civil (pierres en œuvre, granulats pour béton) permet de mettre en évidence des éléments nuisibles ou des caractéristiques défavorables et, plus généralement, d’évaluer l’aptitude à une utilisation donnée, en complément d’essais pétrophysiques et mécaniques. L’accent est mis sur l’analyse pétrographique de lames minces au microscope optique polarisant, éventuellement complétée par l’examen au microscope électronique à balayage. Cette analyse peut être utilisée a priori, lors d’une recherche de matériaux, ou pour le diagnostic de désordres observés sur ouvrages. Plusieurs exemples sont donnés : dissolution ou gélifraction de calcaires, altération par lessivage des argiles dans un grès poreux, fissuration d’un marbre en œuvre sous l’effet des variations de température, aide au diagnostic de roches siliceuses vis-à -vis de l’alcali-réaction. Quelques normes ou recommandations relatives à l’examen pétrographique sont commentées. On insiste en conclusion sur les compétences, spécifiques aux questions de géologie de l’ingénieur, que doit posséder le pétrographe