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Accueil > Productions scientifiques > Séminaires à PHENIX > 2010 > Séminaire 04.06.2010 - 14h

Séminaire 04.06.2010 - 14h

par Guillaume Mériguet - 25 mai 2010

Heloisa N. Bordallo présentera un séminaire le 4 juin 2010 à 14h dans la bibliothèque du laboratoire PECSA (Bat F 7e étage, porte 754) intitulé :

Hindered water motions in hardened cement pastes investigated over broad time and length scales
Heloisa N. Bordallo & Laurence P. Aldridge
Helmholtz-Zentrum Berlin GmbH, Glienicker-Str. 100, D-14109 Berlin, Germany &
Institute of Materials Engineering, ANSTO, PMB 1 Menai NSW 2234, Australia

Résumé :

Concrete, the most abundant of the man-made materials, also predates both
pottery and metal as the first industrially produced material. Over 8000
years ago it was produced in half ton from fired limestone giving a
concrete with compressive strength similar to that of conventional
construction concrete produced in ready mix plants today. About 5000 years
ago the Egyptians heated gypsum to use as a cementitious material, and
later the Greeks developed a calcium silicate system, which was used by
the Romans to produce concrete that has proven to be durable for over 2000
years. Today, Portland cement, is normally used for concrete production,
following a hydration reaction :
Ca3SiO5 + 5.3 H2O = Ca1.7SiO3.7 4H2O + 1.3

In a time where the effects of climate change on weather patterns is
accepted as real and serious, and where the cement industry produces 5-7%
of the world’s carbon dioxide emission, decreasing the production of
carbon dioxide is perceived crucial. Thus, improvements in the production
of concrete are critical ; more durable concrete that requires less carbon
dioxide per unit of manufacture has to be made. To reach such a goal the
knowledge of the physical chemistry of the water-cement paste
interactions, that are fundamental in understanding and predicting the
service life of concrete infrastructure, must be expanded. The durability
of concrete is related to its ability to limit fluid transmission and
knowledge of how to reduce the rate at which water will be transmitted
through cement paste is critical to achieve durability.

Our motivation is to use incoherent inelastic neutron scattering to
differentiate between the capillary pore water and gel water, focusing is
on the mobility of water in hydrated cement paste [1] [2] . While the onset
of the water dynamics, which is modified by the local environment, could
be investigated with elastic temperature scans using high-resolution
neutron backscattering, neutron spin echo spectroscopy was used to measure
the water diffusion over the pore network.

In summary, different motions of water in capillary or gel pores were
monitored ; by using a combination of cement pastes ; cured at different
times and RH, and examined by neutron scattering spectroscopy at different
time (space) scales allowing for the understanding of the water-cement
paste interaction at the molecular level. Such interactions control some
of the most important macro properties of concrete. Moreover to extend our
understanding the mobility of interlayer water in clays will be
considered [3].

To conclude neutron scattering may eventually prove to be as valuable as
the nitrogen adsorption techniques to understand this amorphous, complex
and extremely valuable material.

[1H.N. Bordallo, L.P. Aldridge et al, J. Phys. Chem B 110 (2006) 17996.

[2H.N. Bordallo, L.P. Aldridge et al, ACS Applied Materials & Interfaces
1 (2009) 2154.

[3H.N. Bordallo, L.P. Aldridge et al, J. Phys. Chem C 112 (2008) 19982.