The paper takes the issue of susceptibility of rock materials used in historic and contemporary buildings to long-term salt crystallization. The influence of long-term action of salt crystallizing from water solutions on the rock material was studied by means of artificial accelerated aging tests. Out of the rock materials used in stone engineering objects two lithological types were chosen, which represent the sedimentary clastic rocks. The result of the performed tests were the structural changes, stress and strain changes as well as mass changes which occurred under influence of a temporary action of selected destructive factor. The quality assessment of deterioration was conducted through macro- and microscopic observations and the quantitative changes were determined on the basis of indicative assessment of geomechanical parameters that distinguishes the primary rock from the damaged one.

1 Introduction

One of the most common and extensive sources of deterioration of stone is the consequence of crystallization phenomena that take place in pores and cracks at near exposed surfaces.The greatest damage of stone monuments is caused by salts crystallizing at variable amounts of crystallization water when the temperature that determines the transformations is within the ambient temperatures. Some easily soluble sulfates, which often occur in the monuments also, have this ability. As a result of water evaporation, these salts deposit in the pores as hydrates: mirabilite – Na2SO4 ×10H2O, epsomite – MgSO4 × 7H2O, gypsum – CaSO4 × 2H2O. For the salts in anhydrous or hydrated state the transition from one state to another is dependent on the temperature and the relative humidity of the air. The commonly found in buildings sodium sulfate, which comes from rain and ground water as well as from cement binding the individual architectural details, is one of the most damaging salts. At temperatures above 32.4°C the sodium sulfate crystallizes in an anhydrous form (Na2S04 – thenardite). At lower temperatures it crystallizes first in the form with 7 molecules of water (Na2S04 ×7H2O) and below 24.3°Cthe amount of crystallization water increases to 10 molecules (Na2S04 × lOH2O – mirabilite). These transformations are accompanied by one of the biggest changes in volume, which in the case of the transition of sulfate from the anhydrous to the decahydrate form is about 400% (Domaslowski 1993, Jarmontowicz et al. 1994).

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