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3. Results
3.1. Thermo-hydraulic properties
The distribution of water content along the bentonite column occurs soon after the beginning of the
experiment. As observed in figure 2, Relative Humidity increases in the coldest end of the block,
where hydration is applied. Close to the Fe/bentonite interface, however, where temperature is
about 100ºC, bentonite loses its absorbed water. Water content of samples collected near the interface
(section I) remains below the initial value (13.7%) in both tests.
Apart from the hydraulic gradient, there is also a dry density gradient caused by the different swelling
of bentonite, since the more hydrated sections swelled more. In the zones affected by hydration,
the densities decreased below the initial value (nominal 1.65 g/cm 3 ) due to the expansion caused by
saturation. On the contrary, near the heater, the dry density increased, due to the shrinkage caused
by desiccation.
% Relative Humidity
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RH% - Hydration
Temperature - Heater
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Relative Humidity %
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Figure 2. Evolution of Relative Humidity and Temperature along the bentonite block in the cells
dismantled after a) 6 months; b) 15 months.
3.2. Geochemical evolution
The hydration of bentonite produces the dissolution of the soluble accessory minerals in the bentonite
(sulphates, carbonates and chlorides). These anions can have a certain influence on corrosion
processes. Carbonates can precipitate at the interface as siderite (FeCO3), once the barrier is fully
saturated. Chlorides and sulphates are hygroscopic and its precipitation can favour the starting of
corrosion processes or enhance it, even at low relative humidity. As expected, soluble carbonates
were only detected in saturated areas (934 and 980 mg of CO3 2- per kilogram of dry bentonite, for
the cell dismantled after 6 and 15 months, respectively). Figure 3 shows the advance of the chloride
and sulphate fronts towards the heater. In the cell dismantled after 15 months, it is observed that
most of soluble chloride is concentrated at the interface. So, it seems that after the initial precipitation
of chlorides when heating started, there is a later precipitation that results from the advective
transport of chloride towards the heater[1]. Sulphate concentration is controlled by gypsum solubility.
So, in both tests, the sulphate concentration at the interface is much smaller than that of chloride.
3.3. Corrosion processes
Different corrosion processes were observed in iron powder depending on the distance from the interface.
In both tests, iron oxide accumulations were found at the interface (Fig.4). In the case of the
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Temperature (ºC)