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Accueil du site > 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 Ca(OH)2.

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.

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

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

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