Microstructural and mechanical parameters determining the susceptibility of porous building stones to salt decay
(EN)
Theoulakis, P
(EN)
Moropoulou, A
(EN)
In a previous work, the mechanism by which salt crystals grow in porous stone masonries has been studied. It has been shown that the pressure exerted by sodium chloride (NaCl) crystals on the pore walls, when the crystals have entirely filled the coarse pores (10 mu m), is the cause of disruption. In the present work, the microstructural parameters controlling the destructive effect of NaCl crystallization in porous stones, and specifically NaCl crystallization in the highly porous biocalcarenite of the historic masonries of the medieval city of Rhodes, which occurs favourable, are studied. Samples from both quarries and monuments have been examined. Porosimetric measurements were performed in order to calculate the NaCl crystallization pressures on the basis of the thermodynamics of crystal growth from a supersaturated solution in a porous material. Comparison of the calculated values of the crystallization pressure and the experimentally measured compressive strength permits one to assess the probability of rock destruction by salt crystallization. Energy balance analysis was performed in order to evaluate whether the successive crystallization of NaCl filling the smaller pores or the disruption of the pore walls is the most probable scenario for the given operating conditions. The release of free energy during the spontaneous crystallization from a supersaturated solution has been compared with the mechanical energy needed for the material's destruction, and the susceptibility of porous stone to salt decay is shown to be a function of the mechanical and structural parameters (compressive strength, modulus of compressibility and pore size distribution). (C) 1997 Elsevier Science Ltd.
(EN)
