MASS TRANSFER DURING THE DRYING OF BUILDING MATERIALS

The study of the durability of cementitious materials like mortar which are the object of massive use in building and engineering
works implies a perfect understanding of their mass transfer properties.
This work reports the results of experimental study concerning the influence of water-to cement ratios used for the preparation
of the material on its convective drying kinetics. Three tips of mortar were realized and studied with three different water to
cement (W/C) ratios; W/C =0.4, W/C = 0.5 and Mortar with ratio W/C = 0.6.
The first experimental campaign was done in a convective dryer, using cubic samples of mortar of size (15 X 15 X 10) mm3. The
sample was continuously weighed during the drying test and its mass was recorded every 2 minutes in order to obtain the drying
curves. These tests present the advantage of reproducing the natural conditions met in the problems of atmosphere-material
interactions.
A second experimental campaign aimed to characterize from both a textural and hydric point of views, the materials, by mean of
DVS (dynamic vapour sorption). The mass diffusivity coefficient and the pore size distribution of mortar were obtained from
adsorption-desorption cycles.
On the other hand the influence of the air drying humidity during the convective drying in the conditions of velocity,
temperature and debit of air checked by the convective dryer was studied.
From these campaigns, it was observed that the increase of the ratio W/C engenders an increase of the drying kinetics due to
the increase of the initial porosity