Stability of ancient masonry towers: Moisture diffusion, carbonation and size effect

Moisture diffusion and carbonation influence the behavior of multiple-leaf ancient masonry walls, producing during centuries a redistribution of stresses from the core of lime mortar concrete to the external cladding of stiff masonry. This is likely one of the causes of long-time damage of some ancient masonry towers. With these motivations, coupled processes of moisture diffusion, carbon dioxide diffusion and carbonation reaction are analyzed numerically. Due to the absence of models and data for lime mortar, one of the simplest models proposed for Portland cement concrete is adapted for this purpose. The results reveal the time scales of the processes involved and their dependence on wall thickness (size). It is found that the temporal scale is set mainly by diffusion of moisture trough the massive concrete wall and is only slightly modified by carbonation. Moisture evolution in time is needed for stress analysis that is relegated to a subsequent paper.