Research activity

Frost behaviour of cementitious media

Frost action is an important cause of damage of concrete structures in North America, Europe, Asia and also in some France regions. It is admitted that there is two way of deterioration. The former is take place within the media and acts as microscale damage. As a consequence, a decrease of the mechanical proprieties is seen.
The latter, which is called scaling, affect any exposed saturated surfaces of the structure. Locally pieces of surface are stick out until a depth of some millimetres. This phenomenon is particularly harmful. Indeed, on the one hand, it aesthetically shades off the visible part of the structure. And on the other hand, it reduces the coating of steel reinforcement. Thus, it enhances the penetration of noxious substances as CO2 and sulphates and raises the risk of diseases like corrosion.
Actually, when a porous media is submitted to frost action, all the water he contains does not freeze at the same temperature. This is manly in case of the interaction between water and pore's surfaces, which is a function of the pore's diameter. As a consequence, an initially water saturated frozen porous media is refilled with ice and liquid water. And the latter would be able to move onto the porous network.
Nowadays, damages were mainly attributed to the combination of the volume expansion due to the phase transition and transport of liquid water towards ice crystals. The raison of this transfer is attributed to chemical potential difference between ice and water which temperature is below the bulk solidification one. This phenomenon is well known in non-consolidated porous media mechanic as "cryosuccion mechanism".
Yet, despite the main mechanisms were already understood and put in equation, the mechanical analysis of their coupling, so as to determinate the state of damage is not made. To do so we choose to use a standard poromechanics (see Poromecanics from O. Coussy published at Wiley & Sons (2004)) approach coupled with an experimental study. As it is an important parameter in frost durability of porous medium, an experimental device leading to the amount of unfrozen water measurement is also built up.

My PhD dissertation (in french)

Dissertation: Physics and mechanics of cementitious materials submitted to frost-thaw actions

Determination of liquid water content in a partially frozen porous medium

Publications (preprint)

A. Fabbri, T. Fen-chong (2013), Indirect measurement of the ice content curve of partially frozen porous media Cold Regions Science and Technology, Accepted

A. Fabbri, T. Fen-Cong, A. Azouni, J-F. Thimus. (2009) “Investigation of water to ice phase change in porous media by ultrasonic and dielectric measurements”, Journal of Cold Regions Engineering 23 pp 69-90.

T. Fen-Chong, A. Fabbri, A. Azouni. (2006) Transient freezing–thawing phenomena in water-filled cohesive porous materials, Cold Regions Science and Technology 46 pp 12-26

A. Fabbri, T. Fen-Chong, O. Coussy. (2006) Dielectric capacity, liquid water content, and pore structure of thawing-freezing materials, Cold Regions Science and Technology 44 pp 52-66

T. Fen-Chong, A. Fabbri. (2005) Freezing and thawing porous media: Experimental study with a dielectric capacitive method, Comptes Rendus Mecanique 333 pp 425-430.

T. Fen-Chong, A. Fabbri, JP. Guilbaud, O. Coussy. (2004) “Determination of liquid water content and dielectric constant in porous media by the capacitive method”, Comptes Rendus Mecanique 332 pp 639-645

Figure 1 : Sl(T) curve (left) and comparison between the capacitive device and sorption/desorption pore size distribution curves (right) for W/C=0,5 cement pastes. more pictures

A capacitive sensor-based experimental approach is worked out to study the ice to water phase change in cohesive porous media subject to freezing and thawing. This technique relies upon the dielectric properties of liquid water, ice, air, and mineral substrate in the radio-frequency range. A semi-empirical method based upon the Lichtenecker model and combining drying and freezing tests, provides an accurate estimation of the liquid water content versus the temperature in freezing cement pastes (cf. figure 1-left). This estimation is further analysed with the help of thermoporometry concepts in order to characterize the pore size distribution and the specific surface area. The results range in the same order of magnitude as those assessed from gravimetric sorption/desorption isotherms (cf. figure 1-right).

Poromechanics of freezing materials

Publications (preprint)

T. Fen-chong, A. Fabbri, M. Thiery, P. Dangla (2013) Poroelastic analysis of partial freezing in cohesive porous materials, Journal of Applied Mechanics, 80, 021038.

A. Fabbri, O. Coussy, T. Fen-Chong, P.J.M Monteiro (2008) Are de-icer salt necessary to promote scaling in concrete ?, Journal of Engineering Mechanics 134 pp 589-598.

A. Fabbri, O. Coussy, T. Fen-Chong (2007) Influence of the permeability on the frost-thaw behaviour of concrete, Revue Européenne de Génie Civil 11 pp751-761.

Figure 2 : Results from a scaling test without salts for two kind of hardened cement pastes. more pictures

The main purpose of the present study is to investigate the mechanisms that produce surface deterioration (surface scaling) of cementitious materials submitted to frost action. An experimental device, in which a cement paste specimen is exposed to freezing-thawing cycles under a thermal gradient, has been developed. The experimental results show that under high thermal gradient (20°C between the two faces of a 20mm-thick specimen), skin damage can occur without a saline layer in contact with the frozen surface. Most existing models cannot predict this observation, therefore a poroelastic model for surface scaling is developed. The model is based on the coupling between liquid - ice crystal thermodynamic equilibrium, Darcean water transport, thermal conduction and elastic properties of the different phases that form the porous material. The pore overpressure can be calculated once the dependence of ice content as a function of temperature is determined experimentally. The model predicts that the maximum pore overpressure is reached near the surface, explaining the observed experimental results.

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